{"history":[],"article":{"id":"cd2c2e8d-2057-4baf-973b-3574f8429110","title":"Hybrid Synergy Drive","slug":"hybrid-synergy-drive","content":":::summary\n:::\n\n# \n**Hybrid Synergy Drive** (**HSD**), also known as **[Toyota](https://bliptext.com/articles/toyota) Hybrid System II**, is the brand name of [Toyota Motor Corporation](https://bliptext.com/articles/toyota-motor-corporation) for the [hybrid car](https://bliptext.com/articles/hybrid-car) drive train technology used in vehicles with the [Toyota](https://bliptext.com/articles/toyota) and [Lexus](https://bliptext.com/articles/lexus) marques.\nFirst introduced on the [Prius](https://bliptext.com/articles/toyota-prius), the technology is an option on several other Toyota and Lexus vehicles and has been adapted for the electric drive system of the [hydrogen](https://bliptext.com/articles/hydrogen-vehicle)-powered [Mirai](https://bliptext.com/articles/toyota-mirai), and for a [plug-in hybrid](https://bliptext.com/articles/plug-in-hybrid) version of the [Prius](https://bliptext.com/articles/toyota-prius).\nPreviously, Toyota also licensed its HSD technology to [Nissan](https://bliptext.com/articles/nissan) for use in its [Nissan](https://bliptext.com/articles/nissan) Altima Hybrid.\nIts parts supplier [Aisin](https://bliptext.com/articles/aisin) offers similar hybrid transmissions to other car companies.\nHSD technology produces a [full hybrid](https://bliptext.com/articles/full-hybrid) vehicle which allows the car to run on the electric motor only, as opposed to most other brand hybrids which cannot and are considered [mild hybrids](https://bliptext.com/articles/mild-hybrid).\nThe HSD also combines an [electric drive](https://bliptext.com/articles/electric-vehicle) and a [planetary gearset](https://bliptext.com/articles/planetary-gearset) which performs similarly to a [continuously variable transmission](https://bliptext.com/articles/continuously-variable-transmission).\nThe Synergy Drive is a [drive-by-wire](https://bliptext.com/articles/drive-by-wire) system with no direct mechanical connection between the engine and the engine controls: both the [gas pedal/accelerator](https://bliptext.com/articles/accelerator-car) and the [gearshift lever](https://bliptext.com/articles/gear-stick) in an HSD car merely send electrical signals to a control [computer](https://bliptext.com/articles/computer).\nHSD is a refinement of the original **Toyota Hybrid System** (**THS**) used in the 1997 to 2003 Toyota Prius.\nThe second generation system first appeared on the redesigned Prius in 2004.\nThe name was changed in anticipation of its use in vehicles outside the Toyota brand ([Lexus](https://bliptext.com/articles/lexus); the HSD-derived systems used in [Lexus](https://bliptext.com/articles/lexus) vehicles have been termed **[Lexus](https://bliptext.com/articles/lexus) Hybrid Drive**), was implemented in the 2006 [Camry](https://bliptext.com/articles/camry) and Highlander, and would eventually be implemented in the 2010 [\"third generation\" Prius](https://bliptext.com/articles/toyota-prius-xw30), and the 2012 [Prius c](https://bliptext.com/articles/prius-c).\nThe Toyota Hybrid System is designed for increased power and efficiency, and also improved \"scalability\" (adaptability to larger as well as smaller vehicles), wherein the ICE/MG1 and the MG2 have separate reduction paths, and are combined in a \"compound\" gear which is connected to the final reduction gear train and differential; it was introduced on [all-wheel drive](https://bliptext.com/articles/all-wheel-drive) and [rear-wheel drive](https://bliptext.com/articles/rear-wheel-drive) Lexus models.\nBy May 2007 Toyota had sold one million hybrids worldwide; two million by the end of August 2009; and passed the 5 million mark in March 2013.\n, more than 7 million Lexus and Toyota hybrids had been sold worldwide.\nThe United States accounted for 38% of TMC global hybrid sales.\n# [Hybrid Synergy Drive logo | upload.wikimedia.org/wikipedia/commons/e/ed/Jb///hsd.png]\n# [Lexus Hybrid Drive logo | upload.wikimedia.org/wikipedia/commons/9/9e/Lexus///hybrid///logo.png]\n\n# Principle\nToyota's HSD system replaces a normal geared [transmission](https://bliptext.com/articles/transmission-mechanics) with an [electromechanical](https://bliptext.com/articles/electromechanical) system.\nAn [internal combustion engine](https://bliptext.com/articles/internal-combustion-engine) (ICE) delivers power most efficiently over a small [speed](https://bliptext.com/articles/speed) range, but the wheels need to be driven over the vehicle's full [speed](https://bliptext.com/articles/speed) range.\nIn a conventional automobile the geared [transmission](https://bliptext.com/articles/transmission-mechanics) delivers different discrete engine speed-torque power requirements to the wheels.\nGeared transmissions may be manual, with a [clutch](https://bliptext.com/articles/clutch), or automatic, with a [torque converter](https://bliptext.com/articles/torque-converter), but both allow the engine and the wheels to rotate at different speeds.\nThe driver can adjust the speed and torque delivered by the engine with the [accelerator](https://bliptext.com/articles/accelerator-car) and the transmission mechanically transmits nearly all of the available power to the wheels which rotate at a different rate than the engine, by a factor equal to the gear ratio for the currently selected gear.\nHowever, there are a limited number of \"gears\" or [gear ratios](https://bliptext.com/articles/gear-ratios) that the driver can choose from, typically four to six.\nThis limited gear-ratio set forces the engine [crankshaft](https://bliptext.com/articles/crankshaft) to rotate at speeds where the ICE is less efficient, i.e., where a liter of fuel produces fewer joules.\nOptimal engine speed-torque requirements for different vehicle driving and acceleration conditions can be gauged by limiting either [tachometer](https://bliptext.com/articles/tachometer) RPM rate or engine noise in comparison with actual speed.\nWhen an engine is required to operate efficiently across a broad RPM range, due to its coupling to a geared transmission, manufacturers are limited in their options for improving [engine efficiency](https://bliptext.com/articles/engine-efficiency), reliability, or lifespan, as well as reducing the size or weight of the engine.\nThis is why the engine for an [engine-generator](https://bliptext.com/articles/engine-generator) is often much smaller, more efficient, more reliable, and longer life than one designed for an automobile or other variable speed application.\nHowever, a continuously variable transmission allows the driver (or the automobile computer) to effectively select the optimal gear ratio required for any desired speed or power.\nThe transmission is not limited to a fixed set of gears.\nThis lack of constraint frees the engine to operate at its optimal [brake-specific fuel consumption](https://bliptext.com/articles/brake-specific-fuel-consumption).\nAn HSD vehicle will typically run the engine at its optimal efficiency whenever power is needed to charge batteries or accelerate the car, shutting down the engine entirely when less power is required.\nLike a [CVT](https://bliptext.com/articles/continuously-variable-transmission), an HSD transmission continuously adjusts the effective [gear ratio](https://bliptext.com/articles/gear-ratio) between the engine and the wheels to maintain the engine speed while the wheels increase their rotational speed during acceleration.\nThis is why Toyota describes HSD-equipped vehicles as having an **e-CVT** (**electronic continuously variable transmission**) when required to classify the transmission type for standards specification lists or regulatory purposes.\n# [Toyota 1NZ-FXE engine (left) with early HSD, sectioned and highlighted (right). Generation 1/Generation 2, chained, ICE-MG1-MG2 Power Split Device HSD is shown. | upload.wikimedia.org/wikipedia/commons/7/79/Toyota///1NZ-FXE///Engine///01.JPG]\n\n## Power flows\nIn a conventional car design the [separately-excited alternator with integral rectifier](https://bliptext.com/articles/alternator-auto) (DC generator) and [starter](https://bliptext.com/articles/starter-motor) (DC motor) are considered accessories that are attached to the internal combustion engine (ICE) which normally drives a transmission to power the wheels propelling the vehicle.\nA battery is used only to start the car's internal combustion engine and run accessories when the engine is not running.\nThe alternator is used to recharge the battery and run the accessories when the engine is running.\nThe HSD system replaces the geared transmission, alternator, and starter motor with:\nThrough the power splitter, a series-parallel full hybrid's HSD system thus allows for the following intelligent power flows:\n# [Power electronics from Prius NHW11 \"Classic\" | upload.wikimedia.org/wikipedia/commons/7/73/ToyotaOpenHSD.jpg]\n\n### MG1 and MG2\n\n## Transmission\nThe mechanical gearing design of the system allows the mechanical power from the ICE to be split three ways: extra torque at the wheels (under constant rotation speed), extra rotation speed at the wheels (under constant torque), and power for an electric generator.\nA computer running appropriate programs controls the systems and directs the power flow from the different engine + motor sources.\nThis power split achieves the benefits of a [continuously variable transmission](https://bliptext.com/articles/continuously-variable-transmission) (CVT), except that the torque/speed conversion uses an electric motor rather than a direct mechanical gear train connection.\nAn HSD car cannot operate without the computer, power electronics, battery pack, and motor-generators, though in principle it could operate while missing the internal combustion engine.\n(See: [Plug-in hybrid](https://bliptext.com/articles/plug-in-hybrid)) In practice, HSD equipped cars can be driven a mile or two without gasoline, as an emergency measure to reach a [gas station](https://bliptext.com/articles/filling-station).\nAn HSD [transaxle](https://bliptext.com/articles/transaxle) contains a [planetary gear](https://bliptext.com/articles/planetary-gear) set that adjusts and blends the amount of torque from the engine and motor(s) as it's needed by the front wheels.\nIt is a sophisticated and complicated combination of gearing, electrical motor-generators, and computer-controlled electronic controls.\nOne of the motor-generators, MG2, is connected to the output shaft, and thus couples torque into or out of the drive shafts; feeding electricity into MG2 adds torque at the wheels.\nThe engine end of the drive shaft has a second [differential](https://bliptext.com/articles/differential-mechanics); one leg of this [differential](https://bliptext.com/articles/differential-mechanics) is attached to the internal combustion engine and the other leg is attached to a second motor-generator, MG1.\nThe differential relates the rotation speed of the wheels to the rotation speeds of the engine and MG1, with MG1 used to absorb the difference between wheel and engine speed.\nThe differential is an [epicyclic gear set](https://bliptext.com/articles/epicyclic-gearing) (also called a \"power split device\"); that and the two motor-generators are all contained in a single transaxle housing that is bolted to the [engine](https://bliptext.com/articles/engine).\nSpecial couplings and sensors monitor rotation speed of each shaft and the total torque on the drive shafts, for feedback to the control computer.\nIn Generation 1 and Generation 2 HSDs, MG2 is directly connected to the ring gear, that is, a 1:1 ratio, and which offers no torque multiplication, whereas in Generation 3 HSDs, MG2 is connected to the ring gear through a 2.5:1 planetary gear set, and which, consequently, offers a 2.5:1 torque multiplication, this being a primary benefit of the Generation 3 HSD as it provides for a smaller, yet more powerful MG2.\nHowever, a secondary benefit is the MG1 will not be driven into overspeed as frequently, and which would otherwise mandate employing the ICE to mitigate this overspeed; this strategy improves HSD performance as well as saving fuel and wear-and-tear on the ICE.\n# [Late Toyota HSD, sectioned and highlighted. Generation 3, chainless, ICE-MG1 Power Split Device/MG2 Motor Speed Reduction Device HSD is shown. This is a P510 transaxle, from a 2012– Prius c; a P410 transaxle, from a 2010–2015 Prius, is similar, but is physically larger; a Generation 4 P610 transaxle from a 2016– Prius is 47mm narrower than a P410 by implementing side-by-side motors rather than end-to-end motors. | upload.wikimedia.org/wikipedia/commons/6/67/Toyota///electronic///continuously///variable///transmission///%282010-10-16%29///03.jpg]\n\n## High voltage battery\nThe HSD system has two principal battery packs, the High Voltage (HV) battery, also known as the traction battery, and a 12 volt [lead-acid battery](https://bliptext.com/articles/lead-acid-battery) known as the Low Voltage (LV) battery, which functions as an auxiliary battery.\nThe LV battery supplies power to the electronics and accessories when the hybrid system is turned off and the high-voltage battery main relay is off.\nThe traction [battery](https://bliptext.com/articles/rechargeable-battery) is a [sealed](https://bliptext.com/articles/seal-mechanical) [nickel-metal hydride](https://bliptext.com/articles/nickel-metal-hydride) (NiMH) [battery](https://bliptext.com/articles/rechargeable-battery) pack.\nThe battery pack of the first generation Toyota Prius consisted of 228 cells packaged in 38 modules, while the second generation Prius consisted of 28 Panasonic prismatic nickel metal hydride modules, each containing six 1.2 volt cells, connected in series to produce a nominal voltage of 201.6 volts.\nThe discharge power capability of the second gen Prius pack is about 20 [kW](https://bliptext.com/articles/kw) at 50% [state of charge](https://bliptext.com/articles/state-of-charge) (SoC).\nThe power capability increases with higher temperatures and decreases at lower temperatures.\nThe Prius has a computer that's solely dedicated to keeping the battery at the optimum temperature and optimum charge level.\nLike the second generation Prius, the third generation Prius battery pack is made up of the same type of 1.2 volt cells.\nIt has 28 modules of 6 cells for a total nominal voltage of only 201.6 volts.\nA boost converter is used\nto produce 500 volt DC supply voltage for the inverters for MG1 and MG2.\nThe car's electronics only allow 40% of total rated capacity of the battery pack (6.5 ampere-hour) to be used in order to prolong the battery life.\nAs a result, the SoC is allowed to vary only between 40% and 80% of the rated full charge.\nThe battery used in the [Highlander Hybrid](https://bliptext.com/articles/toyota-highlander-hybrid) and the [Lexus RX 400h](https://bliptext.com/articles/lexus-rx-400h) was packaged in a different metal battery casing with 240 cells that deliver high voltage of 288 volts.\nA button labelled \"EV\" maintains [electric vehicle](https://bliptext.com/articles/electric-vehicle) mode after being powered on and under most low-load conditions at less than 25 mph if the traction battery has enough charge.\nThis permits [all-electric driving](https://bliptext.com/articles/all-electric-mode) with no fuel consumption for up to 1 mi. However, the HSD software switches to EV mode automatically whenever it can.\nOnly the [Toyota Prius Plug-in Hybrid](https://bliptext.com/articles/toyota-prius-plug-in-hybrid) has a longer driving [all-electric range](https://bliptext.com/articles/all-electric-range) in [blended operation](https://bliptext.com/articles/blended-mode) electric-gasoline of 11 mi ([EPA](https://bliptext.com/articles/epa) rating) until the battery is depleted.\nThe Prius PHEV is outfitted with 4.4 [kWh](https://bliptext.com/articles/kwh) [lithium-ion batteries](https://bliptext.com/articles/lithium-ion-battery) co-developed with [Panasonic](https://bliptext.com/articles/panasonic) that weighs 80 kg compared with the [nickel-metal hydride battery](https://bliptext.com/articles/nickel-metal-hydride-battery) of the [third generation Prius](https://bliptext.com/articles/toyota-prius-xw30), which has a capacity of only 1.3 [kWh](https://bliptext.com/articles/kwh), and weighs 42 kg. The larger battery pack enables all-electric operation at higher speeds and longer distances than the conventional Prius hybrid.\nThe following table details the HV battery capacity for several Lexus and Toyota vehicles.\n# [High voltage nickel-metal hydride (NiMH) battery of second generation Toyota Prius. | upload.wikimedia.org/wikipedia/commons/3/37/Ni-MH///Battery///02.JPG]\n# [EV mode button in the 2012 Toyota Camry hybrid. | upload.wikimedia.org/wikipedia/commons/6/67/Camry///Hybrid///2012///07///VA///4177.JPG]\n\n# Operation\nThe HSD drive works by shunting electrical power between the two motor generators, running off the battery pack, to even out the load on the internal combustion engine.\nSince a power boost from the electrical motors is available for periods of rapid acceleration, the ICE can be downsized to match only the average load on the car, rather than sized by peak power demands for rapid acceleration.\nThe smaller internal combustion engine can be designed to run more efficiently.\nFurthermore, during normal operation the engine can be operated at or near its ideal speed and torque level for power, economy, or emissions, with the battery pack absorbing or supplying power as appropriate to balance the demand placed by the [driver](https://bliptext.com/articles/driving).\nDuring traffic stops the internal combustion engine can even be turned off for even more economy.\nThe combination of efficient car design, regenerative braking, turning the engine off for traffic stops, significant electrical energy storage and efficient internal combustion engine design give the HSD powered car significant efficiency advantages—particularly in city driving.\n\n## Phases of operation\nThe HSD operates in distinct phases depending on speed and demanded torque.\nHere are a few of them:\n# [A typical Hybrid Synergy Drive configuration | upload.wikimedia.org/wikipedia/commons/a/ad/Prius2004HSD.JPG]\n# [Lexus Hybrid Drive | upload.wikimedia.org/wikipedia/commons/9/9e/Lexus///GS450h///03.JPG]\n\n## Performance\nThe [Toyota Prius](https://bliptext.com/articles/toyota-prius) has modest acceleration but has extremely high efficiency for a midsized four-door sedan: usually significantly better than 40 mpg (US) (5.9 L/100 km) is typical of brief city jaunts; 55 mpg (4.3 L/100 km) is not uncommon, especially for extended drives at modest speeds (a longer drive allows the engine to warm up fully).\nThis is approximately twice the fuel efficiency of a similarly equipped four-door sedan with a conventional power train.\nNot all of the extra efficiency of the Prius is due to the HSD system: the [Atkinson cycle](https://bliptext.com/articles/atkinson-cycle) engine itself was also designed specifically to minimize engine drag via an offset [crankshaft](https://bliptext.com/articles/crankshaft) to minimize piston drag during the [power stroke](https://bliptext.com/articles/power-stroke-engine), and a unique intake system to prevent drag caused by [manifold vacuum](https://bliptext.com/articles/manifold-vacuum) (\"pumping losses\") versus the normal [Otto cycle](https://bliptext.com/articles/otto-cycle) in most engines.\nFurthermore, the Atkinson cycle recovers more energy per cycle than the Otto because of its longer power stroke.\nThe downside of the Atkinson cycle is much reduced torque, particularly at low speed; but the HSD has enormous low-speed torque available from MG2.\nThe [Highlander Hybrid](https://bliptext.com/articles/toyota-highlander-hybrid) (also sold as the Kluger in some countries) offers better acceleration performance compared to its non-hybrid version.\nThe hybrid version goes from 0–60 mph in 7.2 seconds, trimming almost a second off the conventional version's time.\nNet power is 268 hp compared to the conventional 215 hp.\nTop speed for all Highlanders is limited to 112 mi/h.\nTypical fuel economy for the Highlander Hybrid rates between 27 and 31 mpg (8.7–7.6 L/100 km).\nA conventional Highlander is rated by the EPA with 19 city, 25 highway mpg (12.4 and 9.4 L/100 km respectively).\nThe HSD mileage boost depends on using the gasoline engine as efficiently as possible, which requires:\nMost HSD systems have batteries that are sized for maximal boost during a single acceleration from zero to the top speed of the vehicle; if there is more demand, the battery can be completely exhausted, so that this extra torque boost is not available.\nThen the system reverts to just the power available from the engine.\nThis results in a large decline in performance under certain conditions: an early-model Prius can achieve over 90 mi/h on a 6 degree upward slope, but after about 2000 ft of altitude climb the battery is exhausted and the car can achieve only 55–60 mph on the same slope.\n(until the battery is recharged by driving under less demanding circumstances)\n# [Cutaway display of the HSD Note: Generation 1/Generation 2, chained, ICE-MG1-MG2 Power Split Device HSD is shown | upload.wikimedia.org/wikipedia/commons/5/5e/Toyota///Paris///9.JPG]\n\n# Prius Platform Generations\nThe design of the Toyota Hybrid System / Hybrid Synergy Drive has now had five generations since the original 1997 Japanese-market Toyota Prius.\nThe power train has the same basic features, but there have been a number of significant refinements.\n\n## Generation 1 (Toyota Hybrid System)\nThe system was called the Toyota Hybrid System (THS) when it was introduced with the Prius in 1997.\nThe hybrid [transaxle](https://bliptext.com/articles/transaxle), designated P110, includes two electric motors (MG1 and MG2) and a [planetary gearset](https://bliptext.com/articles/planetary-gearset), which Toyota calls the \"Power Split Device\" (PSD); mechanical power from the internal combustion engine (E) can be directed either to the wheels or to MG1, acting as a generator.\nElectrical power flows between MG1, MG2, and a storage battery through an inverter.\nAlthough MG1 typically operates as a generator (alternator), it also serves as the starter motor for the internal combustion engine.\nMG2 usually acts as a motor, either by itself at low speeds or to assist the internal combustion engine, but MG2 also can act as a generator, for instance, during deceleration for [regenerative braking](https://bliptext.com/articles/regenerative-braking).\nSchematically, MG1 is connected to the central sun gear (S), the internal combustion engine is connected to the planetary gear carrier (P) and not to any individual gear, and MG2 is connected to the ring gear (R).\nThe wheels are connected to the ring gear through appropriate [reduction gearing](https://bliptext.com/articles/reduction-gear) and a differential, not illustrated in the diagram.\nThe Toyota Hybrid System uses a high-voltage battery pack, ranging between 276 and 288 V. There has been a continuous, gradual improvement in the specific capacity of the traction battery.\nThe original Prius used shrink-wrapped 1.2 volt D cells, and all subsequent THS/HSD vehicles have used custom 7.2 V battery modules mounted in a carrier.\n# [Schematic diagram of the First- and Second-Generation Toyota Hybrid System transaxle (P110/ P111/ P112):\n

S: Central \"'sun\" gear
P: Planetary gear carrier
R: Outer ring gear
1: Motor-Generator 1
2: Motor-Generator 2
E: Internal Combustion Engine

| upload.wikimedia.org/wikipedia/commons/8/8c/G01///%26///G02///Toyota///Hybrid///System.svg]\n\n### G1 single-motor\nIn 2001, a modified version of the Generation 1 THS transaxle was released in the Japanese domestic market as the P210 transaxle, fitted to the [Estima](https://bliptext.com/articles/toyota-previa) minivan.\nThe P210 couples the internal combustion engine with the sun gear and couples the starter/generator (MG1) with the planetary gear carrier, which is the opposite of the G1 THS scheme.\nIn addition, the single-motor G1 THS omits the traction motor (MG2) and uses a belt-drive [continuously variable transmission](https://bliptext.com/articles/continuously-variable-transmission) which can be selectively coupled via rotating clutches to either the planetary gear carrier or the ring gear.\nAn all-wheel drive option for the Estima was released at the same time; the Q410 rear drive unit uses an electric traction motor with no mechanical coupling to the front transaxle.\n# [Schematic diagram of single-motor THS transaxle (P210) with v-belt CVT | upload.wikimedia.org/wikipedia/commons/a/a4/G01///Toyota///Hybrid///System///%28CVT%29.svg]\n\n## Generation 2 (Toyota Hybrid System-II)\nTHS was followed by THS-II in the 2004 Prius.\nStarting with THS-II, Toyota also began referring to the system as Hybrid Synergy Drive (HSD).\nCompared to THS, THS-II offered reduced consumption and better performance with increased power and torque.\nTHS-II uses the same design as THS, combining traction power from an internal combustion engine and an electric motor via a planetary gearset (power split device) which can divert some power to an electrical generator.\nElectrically, HSD/THS-II adds a [DC to DC converter](https://bliptext.com/articles/dc-to-dc-converter) boosting the potential of the battery to 500 V or more.\nThis allows smaller battery packs to be used, and more powerful motors.\nCompared to THS, the physical size of the traction motor (MG2) in THS-II remains approximately the same, but the maximum output has increased from 33 to 50 kW and the maximum torque has increased from 350 to 400 Nm.\nThe stator windings are connected in series, which requires a higher potential.\nAlthough not part of the THS/HSD as such, starting with the 2004 Prius, all THS/HSD vehicles have been fitted with an electric air-conditioning compressor, instead of the conventional engine-driven type.\nThis removes the need to continuously run the engine when cabin cooling is required.\nTwo [positive temperature coefficient](https://bliptext.com/articles/positive-temperature-coefficient) heaters are fitted in the heater core to supplement the heat provided by the engine.\n\n## Generation 3 (Hybrid Synergy Drive)\nThe updated version of HSD first delivered in the model year 2006 RX 400h is similar to THS/THS-II, with the addition of a second planetary gearset, which Toyota calls the Motor Speed Reduction Device (MSRD); it is compounded with the first planetary gearset (PSD) by coupling the two ring gears together.\nThe coupled ring gears are still used to drive the front wheels of the vehicle.\nThe traction motor (MG2) uses the MSRD as a reduction gear, making it possible to increase the power density of the motor.\n[Ford](https://bliptext.com/articles/ford-motor-company) has also developed a similar hybrid system, introduced in the [Ford](https://bliptext.com/articles/ford-motor-company) Escape Hybrid.\nToyota CEO [Katsuaki Watanabe](https://bliptext.com/articles/katsuaki-watanabe) said in a February 16, 2007 interview that Toyota was \"aiming at reducing, by half, both the size and cost of the third-generation HSD system\".\nThe new system will feature [lithium-ion](https://bliptext.com/articles/lithium-ion) batteries in later years.\nLithium-ion batteries have a higher energy capacity-to-weight ratio compared to [NiMH](https://bliptext.com/articles/nimh), but operate at higher temperatures, and are subject to thermal instability if not properly manufactured and controlled, raising safety concerns.\n# [Schematic diagram of the Third-Generation Hybrid Synergy Drive transaxle (P31x/ P410/ P510); a second planetary gearset has been added | upload.wikimedia.org/wikipedia/commons/1/1c/G03///Toyota///Hybrid///System.svg]\n\n### G3 all-wheel drive with hybrid transaxle\nIn 2005, vehicles such as the Lexus RX 400h and Toyota Highlander Hybrid added four-wheel drive operation by adding a third electric motor (\"MGR\") on the rear axle.\nIn this system, the rear axle is purely electrically powered, and there is no mechanical link between the engine and the rear wheels.\nThis also permits regenerative braking on the rear wheels.\n\n### G3 rear-wheel drive (Lexus Hybrid Drive)\nIn 2006 and 2007, a further development of the HSD drivetrain, under the Lexus Hybrid Drive name, was fitted to the Lexus GS 450h / LS 600h sedans as the L110 transmission.\nPrevious versions of HSD/THS were fitted to [transaxles](https://bliptext.com/articles/transaxle) used with front-wheel drive platforms; Lexus Hybrid Drive applied the two-motor HSD concept to a longitudinal transmission for rear-wheel drive vehicles.\nThis system uses two clutches (or brakes) to switch the second motor's gear ratio to the wheels between a ratio of 3.9 and 1.9, for low and high speed driving regimes respectively.\nThis decreases the power flowing from MG1 to MG2 (or vice versa) during higher speeds.\nThe electrical path is only about 70% efficient, thus decreasing its power flow while increasing the overall performance of the transmission.\nThe second planetary gearset is extended with a second carrier and sun gear to a [ravigneaux-type gear](https://bliptext.com/articles/ravigneaux-planetary-gearset) with four shafts, two of which can be held still alternatively by a brake/clutch.\nThe GS 450h and LS 600h systems utilized [rear-wheel drive](https://bliptext.com/articles/rear-wheel-drive) and [all-wheel drive](https://bliptext.com/articles/all-wheel-drive) drivetrains, respectively, and were designed to be more powerful than non-hybrid versions of the same model lines, while providing comparable engine class efficiency.\nA simplified version was released in 2012 with the [fourteenth generation Crown (S210)](https://bliptext.com/articles/toyota-crown); the L210 transmission omits the two clutches but retains the second planetary gearset (MSRD) applied to the output of MG2, in common with other Generation 3 transaxles.\nHowever, compared to the G3 transaxles, instead of coupling the two ring gears, the L210 couples the PSD ring gear to the MSRD planetary gear carrier, and grounds the ring gear of the MSRD instead of the planetary gear carrier.\n# [Schematic diagram of rear-wheel Lexus Hybrid Drive transmission (L110/ L110F) | upload.wikimedia.org/wikipedia/commons/e/e8/G03///Toyota///Hybrid///System///%28RWD%29.svg]\n# [Schematic diagram of updated rear-wheel Hybrid Synergy Drive transmission (L210/ L210F) | upload.wikimedia.org/wikipedia/commons/9/95/G03///Toyota///Hybrid///System///%28RWD///alt%29.svg]\n\n## Generation 4\nOn October 13, 2015, Toyota announced details of the Fourth Generation Hybrid Synergy Drive which was introduced for the 2016 model year.\nThe overall design returns to a single planetary gearset similar to THS/THS-II; parallel reduction gears on the Fourth Generation transaxles replace the Motor Speed Reduction Device, which is a second planetary gear set found in the Third Generation transaxles.\nThe transaxle and traction motor have been redesigned, delivering a reduction in size and combined weight.\nThe traction motor itself is considerably more compact and gains a better [power-to-weight ratio](https://bliptext.com/articles/power-to-weight-ratio).\nNotably there is a 20 percent reduction in mechanical losses due to friction compared to the previous model.\nThe 2012– Prius c retains the P510 transaxle.\nThe P610 transaxle employs helical gears rather than the straight-cut spur gears employed in the earlier transaxles, and which run more smoothly and quietly, while also accommodating higher mechanical loads.\n# [Schematic diagram of Fourth-Generation Hybrid Synergy Drive transaxle (P610/ P71x/ P810/ P910) | upload.wikimedia.org/wikipedia/commons/6/63/G04///Toyota///Hybrid///System.svg]\n\n### G4 all-wheel drive with hybrid transaxle\nWith the Fourth Generation HSD, Toyota is also offering a four-wheel drive option, dubbed \"E-Four\", similar to the 2005 RX400h and Highlander Hybrid, in which an electric traction motor is added to the rear, but is not mechanically coupled to the internal combustion engine or front inverter.\nIn fact, the \"E-Four\" system has its own rear inverter, although this inverter draws power from the same hybrid battery as the front inverter.\n\"E-Four\" began being offered in Prius models in the United States in the 2019 model year.\n\"E-Four\" is an integral part of the [RAV4](https://bliptext.com/articles/toyota-rav4) Hybrid models offered in the United States, and all such [RAV4](https://bliptext.com/articles/toyota-rav4) Hybrids are \"E-Four\" only.\n\n### G4 rear-wheel drive (Multistage THS-II)\nThe L310 transmission for rear-wheel drive applications succeeded the prior L110 transmission in premium vehicles.\nCompared to the L110 and L210, the L310 couples MG2 to the ring gear of the PSD.\nIn addition L310 adds a third planetary gearset, compounded with the second (MSRD) by coupling the planetary gear carrier of the second planetary gearset with the ring gear of the third planetary gearset, and by coupling the ring gear of the second with the planetary gear carrier of the third.\nIn addition, several rotating clutches and brakes have been added, including a [one-way clutch](https://bliptext.com/articles/sprag-clutch) on the planetary gear carrier of the second planetary gearset.\nBy selectively engaging these, the transmission can simulate ten different gear ratios.\n# [Fourth Generation L310 / L310F Hybrid Synergy Drive transmission for rear-wheel drive vehicles | upload.wikimedia.org/wikipedia/commons/f/f2/G04///Toyota///Hybrid///System///%28RWD///alt%29.svg]\n\n## Generation 5\nThe fifth generation Hybrid Synergy Drive transaxle is similar to the prior generation, with detail improvements making the electric motors lighter, more compact, and more powerful.\n\n# List of vehicles with HSD technology\nThe following is a list of vehicles with Hybrid Synergy Drive and related technologies (Toyota Hybrid System):\n\n# Patent issues\n\n## Antonov\nAs of autumn 2005, the Antonov Automotive Technology BV Plc company has sued [Toyota](https://bliptext.com/articles/toyota), the Lexus brand mother company, over alleged patent infringement relating to key components in the RX 400h's drivetrain and the [Toyota](https://bliptext.com/articles/toyota) Prius hybrid compact car.\nThe case has been pending in secret since April 2005, but settlement negotiations did not bring a mutually acceptable result.\nAntonov eventually took legal recourse in the German court system, where decisions are usually made relatively swiftly.\nThe patent holder seeks to impose a levy on each vehicle sold, which could make the hybrid SUV less competitive.\nToyota fought back by seeking to officially invalidate Antonov's relevant patents.\nThe court motion in Microsoft Word document format can be read here.\nOn 1 September 2006 Antonov announced that the Federal Patent Court in Munich has not upheld the validity of the German part of Antonov's patent (EP0414782) against Toyota.\nA few days later, a court in Düsseldorf had ruled that the Toyota Prius driveline and the Lexus RX 400h driveline do not breach the Antonov hybrid CVT patent.\n\n## Ford\n[Ford Motor Company](https://bliptext.com/articles/ford-motor-company) independently developed a system with key technologies similar to Toyota's HSD technology in 2004.\nAs a result, Ford licensed 21 patents from Toyota in exchange for patents relating to emissions technology.\n\n## Paice\n[Paice LLC](https://bliptext.com/articles/undefined) received a patent for an improved hybrid vehicle with a controllable torque transfer unit and has additional patents related to hybrid vehicles.\nIn 2010 Toyota agreed to license Paice's patents; terms of the settlement were not disclosed.\nIn the settlement \"The parties agree that, although certain Toyota vehicles have been found to be equivalent to a Paice patent, Toyota invented, designed and developed the Prius and Toyota’s hybrid technology independent of any inventions of Dr. Severinsky and Paice as part of Toyota’s long history of innovation\".\nPaice earlier entered into an agreement with Ford for the license of Paice's patent.\n\n# Comparison with other hybrids\n[Aisin Seiki Co.](https://bliptext.com/articles/aisin-seiki-co), minority-owned by Toyota, supplies its versions of the HSD transmission system to Ford for use as the \"Powersplit\" e-CVT in the [Ford Escape](https://bliptext.com/articles/ford-escape) hybrid and [Ford Fusion Hybrid](https://bliptext.com/articles/ford-fusion-hybrid).\n[Nissan](https://bliptext.com/articles/nissan) licensed Toyota's HSD for use in the [Nissan](https://bliptext.com/articles/nissan) Altima hybrid, using the same Aisin Seiki T110 transaxle as in the [Toyota Camry](https://bliptext.com/articles/toyota-camry) Hybrid.\nThe 2011 [Infiniti M35h](https://bliptext.com/articles/infiniti-m35h) uses a different system of one electric motor and two clutches.\nIn 2010, [Toyota](https://bliptext.com/articles/toyota) and Mazda announced a supply agreement for the hybrid technology used in [Toyota](https://bliptext.com/articles/toyota)'s [Prius](https://bliptext.com/articles/toyota-prius) model.\n[General Motors](https://bliptext.com/articles/general-motors-corporation), [DaimlerChrysler](https://bliptext.com/articles/daimlerchrysler)'s and [BMW](https://bliptext.com/articles/bmw)'s [Global Hybrid Cooperation](https://bliptext.com/articles/global-hybrid-cooperation) is similar in that it combines the power from a single engine and two motors.\nIn 2009, the [Presidential Task Force on the Auto Industry](https://bliptext.com/articles/presidential-task-force-on-the-auto-industry) said that \"GM is at least one generation behind Toyota on advanced, 'green' powertrain development\".\nIn contrast, [Honda](https://bliptext.com/articles/honda)'s [Integrated Motor Assist](https://bliptext.com/articles/integrated-motor-assist) uses a more traditional [ICE](https://bliptext.com/articles/internal-combustion-engine) and transmission where the flywheel is replaced with an electric motor, thereby retaining the complexity of a traditional transmission.\n\n# Aftermarket\nSome early non-production [plug-in hybrid electric vehicle](https://bliptext.com/articles/plug-in-hybrid-electric-vehicle) [conversions](https://bliptext.com/articles/electric-vehicle-conversion) have been based on the version of HSD found in the 2004 and 2005 model year Prius.\nEarly [lead-acid battery](https://bliptext.com/articles/lead-acid-battery) conversions by [CalCars](https://bliptext.com/articles/undefined) have demonstrated 10 mi of ev-only and 20 mi of double mileage [mixed-mode](https://bliptext.com/articles/blended-mode) range.\nA company planning to offer conversions to consumers named [EDrive systems](https://bliptext.com/articles/undefined) will be using [Valence](https://bliptext.com/articles/undefined) [Li-ion](https://bliptext.com/articles/li-ion) batteries and have 35 mi of electric range.\nBoth of these systems leave the existing HSD system mostly unchanged and could be similarly applied to other hybrid powertrain flavors by simply replacing the stock [NiMH](https://bliptext.com/articles/nickel-metal-hydride) batteries with a higher capacity [battery pack](https://bliptext.com/articles/battery-pack) and a charger to refill them for about $0.03 per mile from standard household outlets.","current_revision":null,"created_by":"kACnuQmH5k9Nr5VNVEpVeg7XpvUmMctD","created_at":"2025-01-25T21:16:04.569Z","updated_at":"2025-01-25T21:16:04.569Z","search_vector":"'drive':3 'hybrid':1 'synergi':2","search_content":" \n \n\n# \n**Hybrid Synergy Drive** (**HSD**), also known as **[Toyota](https://bliptext.com/articles/toyota) Hybrid System II**, is the brand name of [[Toyota](https://bliptext.com/articles/toyota) Motor Corporation](https://bliptext.com/articles/toyota-motor-corporation) for the [hybrid car](https://bliptext.com/articles/hybrid-car) drive train technology used in vehicles with the [Toyota](https://bliptext.com/articles/toyota) and [Lexus](https://bliptext.com/articles/lexus) marques.\nFirst introduced on the [[Prius](https://bliptext.com/articles/toyota-prius-plug-in-hybrid)](https://bliptext.com/articles/toyota-prius), the technology is an option on several other Toyota and Lexus vehicles and has been adapted for the electric drive system of the [hydrogen](https://bliptext.com/articles/hydrogen-vehicle)-powered [Mirai](https://bliptext.com/articles/toyota-mirai), and for a [plug-in hybrid](https://bliptext.com/articles/plug-in-hybrid) version of the [[Prius](https://bliptext.com/articles/toyota-prius-plug-in-hybrid)](https://bliptext.com/articles/toyota-prius).\nPreviously, Toyota also licensed its HSD technology to [Nissan](https://bliptext.com/articles/nissan) for use in its [Nissan](https://bliptext.com/articles/nissan) Altima Hybrid.\nIts parts supplier [Aisin](https://bliptext.com/articles/aisin) offers similar hybrid transmissions to other car companies.\nHSD technology produces a [full hybrid](https://bliptext.com/articles/full-hybrid) vehicle which allows the car to run on the electric motor only, as opposed to most other brand hybrids which cannot and are considered [mild hybrids](https://bliptext.com/articles/mild-hybrid).\nThe HSD also combines an [electric drive](https://bliptext.com/articles/electric-vehicle) and a [planetary gearset](https://bliptext.com/articles/planetary-gearset) which performs similarly to a [continuously variable transmission](https://bliptext.com/articles/continuously-variable-transmission).\nThe Synergy Drive is a [drive-by-wire](https://bliptext.com/articles/drive-by-wire) system with no direct mechanical connection between the engine and the engine controls: both the [gas pedal/accelerator](https://bliptext.com/articles/accelerator-car) and the [gearshift lever](https://bliptext.com/articles/gear-stick) in an HSD car merely send electrical signals to a control [computer](https://bliptext.com/articles/computer).\nHSD is a refinement of the original **Toyota Hybrid System** (**THS**) used in the 1997 to 2003 Toyota Prius.\nThe second generation system first appeared on the redesigned Prius in 2004.\nThe name was changed in anticipation of its use in vehicles outside the Toyota brand ([Lexus](https://bliptext.com/articles/lexus); the HSD-derived systems used in [Lexus](https://bliptext.com/articles/lexus) vehicles have been termed **[Lexus](https://bliptext.com/articles/lexus) Hybrid Drive**), was implemented in the 2006 [Camry](https://bliptext.com/articles/camry) and Highlander, and would eventually be implemented in the 2010 [\"third generation\" Prius](https://bliptext.com/articles/toyota-prius-xw30), and the 2012 [Prius c](https://bliptext.com/articles/prius-c).\nThe Toyota Hybrid System is designed for increased power and efficiency, and also improved \"scalability\" (adaptability to larger as well as smaller vehicles), wherein the ICE/MG1 and the MG2 have separate reduction paths, and are combined in a \"compound\" gear which is connected to the final reduction gear train and differential; it was introduced on [all-wheel drive](https://bliptext.com/articles/all-wheel-drive) and [rear-wheel drive](https://bliptext.com/articles/rear-wheel-drive) Lexus models.\nBy May 2007 Toyota had sold one million hybrids worldwide; two million by the end of August 2009; and passed the 5 million mark in March 2013.\n, more than 7 million Lexus and Toyota hybrids had been sold worldwide.\nThe United States accounted for 38% of TMC global hybrid sales.\n# [Hybrid Synergy Drive logo | upload.wikimedia.org/wikipedia/commons/e/ed/Jb///hsd.png]\n# [Lexus Hybrid Drive logo | upload.wikimedia.org/wikipedia/commons/9/9e/Lexus///hybrid///logo.png]\n\n# Principle\nToyota's HSD system replaces a normal geared [transmission](https://bliptext.com/articles/transmission-mechanics) with an [electromechanical](https://bliptext.com/articles/electromechanical) system.\nAn [internal combustion engine](https://bliptext.com/articles/internal-combustion-engine) (ICE) delivers power most efficiently over a small [speed](https://bliptext.com/articles/speed) range, but the wheels need to be driven over the vehicle's full [speed](https://bliptext.com/articles/speed) range.\nIn a conventional automobile the geared [transmission](https://bliptext.com/articles/transmission-mechanics) delivers different discrete engine speed-torque power requirements to the wheels.\nGeared transmissions may be manual, with a [clutch](https://bliptext.com/articles/clutch), or automatic, with a [torque converter](https://bliptext.com/articles/torque-converter), but both allow the engine and the wheels to rotate at different speeds.\nThe driver can adjust the speed and torque delivered by the engine with the [accelerator](https://bliptext.com/articles/accelerator-car) and the transmission mechanically transmits nearly all of the available power to the wheels which rotate at a different rate than the engine, by a factor equal to the gear ratio for the currently selected gear.\nHowever, there are a limited number of \"gears\" or [gear ratios](https://bliptext.com/articles/gear-ratios) that the driver can choose from, typically four to six.\nThis limited gear-ratio set forces the engine [crankshaft](https://bliptext.com/articles/crankshaft) to rotate at speeds where the ICE is less efficient, i.e., where a liter of fuel produces fewer joules.\nOptimal engine speed-torque requirements for different vehicle driving and acceleration conditions can be gauged by limiting either [tachometer](https://bliptext.com/articles/tachometer) RPM rate or engine noise in comparison with actual speed.\nWhen an engine is required to operate efficiently across a broad RPM range, due to its coupling to a geared transmission, manufacturers are limited in their options for improving [engine efficiency](https://bliptext.com/articles/engine-efficiency), reliability, or lifespan, as well as reducing the size or weight of the engine.\nThis is why the engine for an [engine-generator](https://bliptext.com/articles/engine-generator) is often much smaller, more efficient, more reliable, and longer life than one designed for an automobile or other variable speed application.\nHowever, a continuously variable transmission allows the driver (or the automobile computer) to effectively select the optimal gear ratio required for any desired speed or power.\nThe transmission is not limited to a fixed set of gears.\nThis lack of constraint frees the engine to operate at its optimal [brake-specific fuel consumption](https://bliptext.com/articles/brake-specific-fuel-consumption).\nAn HSD vehicle will typically run the engine at its optimal efficiency whenever power is needed to charge batteries or accelerate the car, shutting down the engine entirely when less power is required.\nLike a [CVT](https://bliptext.com/articles/continuously-variable-transmission), an HSD transmission continuously adjusts the effective [gear ratio](https://bliptext.com/articles/gear-ratio) between the engine and the wheels to maintain the engine speed while the wheels increase their rotational speed during acceleration.\nThis is why Toyota describes HSD-equipped vehicles as having an **e-CVT** (**electronic continuously variable transmission**) when required to classify the transmission type for standards specification lists or regulatory purposes.\n# [Toyota 1NZ-FXE engine (left) with early HSD, sectioned and highlighted (right). Generation 1/Generation 2, chained, ICE-MG1-MG2 Power Split Device HSD is shown. | upload.wikimedia.org/wikipedia/commons/7/79/Toyota///1NZ-FXE///Engine///01.JPG]\n\n## Power flows\nIn a conventional car design the [separately-excited alternator with integral rectifier](https://bliptext.com/articles/alternator-auto) (DC generator) and [starter](https://bliptext.com/articles/starter-motor) (DC motor) are considered accessories that are attached to the internal combustion engine (ICE) which normally drives a transmission to power the wheels propelling the vehicle.\nA battery is used only to start the car's internal combustion engine and run accessories when the engine is not running.\nThe alternator is used to recharge the battery and run the accessories when the engine is running.\nThe HSD system replaces the geared transmission, alternator, and starter motor with:\nThrough the power splitter, a series-parallel full hybrid's HSD system thus allows for the following intelligent power flows:\n# [Power electronics from Prius NHW11 \"Classic\" | upload.wikimedia.org/wikipedia/commons/7/73/ToyotaOpenHSD.jpg]\n\n### MG1 and MG2\n\n## Transmission\nThe mechanical gearing design of the system allows the mechanical power from the ICE to be split three ways: extra torque at the wheels (under constant rotation speed), extra rotation speed at the wheels (under constant torque), and power for an electric generator.\nA computer running appropriate programs controls the systems and directs the power flow from the different engine + motor sources.\nThis power split achieves the benefits of a [continuously variable transmission](https://bliptext.com/articles/continuously-variable-transmission) (CVT), except that the torque/speed conversion uses an electric motor rather than a direct mechanical gear train connection.\nAn HSD car cannot operate without the computer, power electronics, battery pack, and motor-generators, though in principle it could operate while missing the internal combustion engine.\n(See: [Plug-in hybrid](https://bliptext.com/articles/plug-in-hybrid)) In practice, HSD equipped cars can be driven a mile or two without gasoline, as an emergency measure to reach a [gas station](https://bliptext.com/articles/filling-station).\nAn HSD [transaxle](https://bliptext.com/articles/transaxle) contains a [planetary gear](https://bliptext.com/articles/planetary-gear) set that adjusts and blends the amount of torque from the engine and motor(s) as it's needed by the front wheels.\nIt is a sophisticated and complicated combination of gearing, electrical motor-generators, and computer-controlled electronic controls.\nOne of the motor-generators, MG2, is connected to the output shaft, and thus couples torque into or out of the drive shafts; feeding electricity into MG2 adds torque at the wheels.\nThe engine end of the drive shaft has a second [differential](https://bliptext.com/articles/differential-mechanics); one leg of this [differential](https://bliptext.com/articles/differential-mechanics) is attached to the internal combustion engine and the other leg is attached to a second motor-generator, MG1.\nThe differential relates the rotation speed of the wheels to the rotation speeds of the engine and MG1, with MG1 used to absorb the difference between wheel and engine speed.\nThe differential is an [epicyclic gear set](https://bliptext.com/articles/epicyclic-gearing) (also called a \"power split device\"); that and the two motor-generators are all contained in a single transaxle housing that is bolted to the [engine](https://bliptext.com/articles/engine).\nSpecial couplings and sensors monitor rotation speed of each shaft and the total torque on the drive shafts, for feedback to the control computer.\nIn Generation 1 and Generation 2 HSDs, MG2 is directly connected to the ring gear, that is, a 1:1 ratio, and which offers no torque multiplication, whereas in Generation 3 HSDs, MG2 is connected to the ring gear through a 2.5:1 planetary gear set, and which, consequently, offers a 2.5:1 torque multiplication, this being a primary benefit of the Generation 3 HSD as it provides for a smaller, yet more powerful MG2.\nHowever, a secondary benefit is the MG1 will not be driven into overspeed as frequently, and which would otherwise mandate employing the ICE to mitigate this overspeed; this strategy improves HSD performance as well as saving fuel and wear-and-tear on the ICE.\n# [Late Toyota HSD, sectioned and highlighted. Generation 3, chainless, ICE-MG1 Power Split Device/MG2 Motor Speed Reduction Device HSD is shown. This is a P510 transaxle, from a 2012– Prius c; a P410 transaxle, from a 2010–2015 Prius, is similar, but is physically larger; a Generation 4 P610 transaxle from a 2016– Prius is 47mm narrower than a P410 by implementing side-by-side motors rather than end-to-end motors. | upload.wikimedia.org/wikipedia/commons/6/67/Toyota///electronic///continuously///variable///transmission///%282010-10-16%29///03.jpg]\n\n## High voltage battery\nThe HSD system has two principal battery packs, the High Voltage (HV) battery, also known as the traction battery, and a 12 volt [lead-acid battery](https://bliptext.com/articles/lead-acid-battery) known as the Low Voltage (LV) battery, which functions as an auxiliary battery.\nThe LV battery supplies power to the electronics and accessories when the hybrid system is turned off and the high-voltage battery main relay is off.\nThe traction [battery](https://bliptext.com/articles/rechargeable-battery) is a [sealed](https://bliptext.com/articles/seal-mechanical) [nickel-metal hydride](https://bliptext.com/articles/nickel-metal-hydride) (NiMH) [battery](https://bliptext.com/articles/rechargeable-battery) pack.\nThe battery pack of the first generation Toyota Prius consisted of 228 cells packaged in 38 modules, while the second generation Prius consisted of 28 Panasonic prismatic nickel metal hydride modules, each containing six 1.2 volt cells, connected in series to produce a nominal voltage of 201.6 volts.\nThe discharge power capability of the second gen Prius pack is about 20 [kW](https://bliptext.com/articles/kw) at 50% [state of charge](https://bliptext.com/articles/state-of-charge) (SoC).\nThe power capability increases with higher temperatures and decreases at lower temperatures.\nThe Prius has a computer that's solely dedicated to keeping the battery at the optimum temperature and optimum charge level.\nLike the second generation Prius, the third generation Prius battery pack is made up of the same type of 1.2 volt cells.\nIt has 28 modules of 6 cells for a total nominal voltage of only 201.6 volts.\nA boost converter is used\nto produce 500 volt DC supply voltage for the inverters for MG1 and MG2.\nThe car's electronics only allow 40% of total rated capacity of the battery pack (6.5 ampere-hour) to be used in order to prolong the battery life.\nAs a result, the SoC is allowed to vary only between 40% and 80% of the rated full charge.\nThe battery used in the [Highlander Hybrid](https://bliptext.com/articles/toyota-highlander-hybrid) and the [Lexus RX 400h](https://bliptext.com/articles/lexus-rx-400h) was packaged in a different metal battery casing with 240 cells that deliver high voltage of 288 volts.\nA button labelled \"EV\" maintains [electric vehicle](https://bliptext.com/articles/electric-vehicle) mode after being powered on and under most low-load conditions at less than 25 mph if the traction battery has enough charge.\nThis permits [all-electric driving](https://bliptext.com/articles/all-electric-mode) with no fuel consumption for up to 1 mi. However, the HSD software switches to EV mode automatically whenever it can.\nOnly the [Toyota Prius Plug-in Hybrid](https://bliptext.com/articles/toyota-prius-plug-in-hybrid) has a longer driving [all-electric range](https://bliptext.com/articles/all-electric-range) in [blended operation](https://bliptext.com/articles/blended-mode) electric-gasoline of 11 mi ([EPA](https://bliptext.com/articles/epa) rating) until the battery is depleted.\nThe Prius PHEV is outfitted with 4.4 [kWh](https://bliptext.com/articles/kwh) [lithium-ion batteries](https://bliptext.com/articles/lithium-ion-battery) co-developed with [Panasonic](https://bliptext.com/articles/panasonic) that weighs 80 kg compared with the [nickel-metal hydride battery](https://bliptext.com/articles/nickel-metal-hydride-battery) of the [third generation Prius](https://bliptext.com/articles/toyota-prius-xw30), which has a capacity of only 1.3 [kWh](https://bliptext.com/articles/kwh), and weighs 42 kg. The larger battery pack enables all-electric operation at higher speeds and longer distances than the conventional Prius hybrid.\nThe following table details the HV battery capacity for several Lexus and Toyota vehicles.\n# [High voltage nickel-metal hydride (NiMH) battery of second generation Toyota Prius. | upload.wikimedia.org/wikipedia/commons/3/37/Ni-MH///Battery///02.JPG]\n# [EV mode button in the 2012 Toyota Camry hybrid. | upload.wikimedia.org/wikipedia/commons/6/67/Camry///Hybrid///2012///07///VA///4177.JPG]\n\n# Operation\nThe HSD drive works by shunting electrical power between the two motor generators, running off the battery pack, to even out the load on the internal combustion engine.\nSince a power boost from the electrical motors is available for periods of rapid acceleration, the ICE can be downsized to match only the average load on the car, rather than sized by peak power demands for rapid acceleration.\nThe smaller internal combustion engine can be designed to run more efficiently.\nFurthermore, during normal operation the engine can be operated at or near its ideal speed and torque level for power, economy, or emissions, with the battery pack absorbing or supplying power as appropriate to balance the demand placed by the [driver](https://bliptext.com/articles/driving).\nDuring traffic stops the internal combustion engine can even be turned off for even more economy.\nThe combination of efficient car design, regenerative braking, turning the engine off for traffic stops, significant electrical energy storage and efficient internal combustion engine design give the HSD powered car significant efficiency advantages—particularly in city driving.\n\n## Phases of operation\nThe HSD operates in distinct phases depending on speed and demanded torque.\nHere are a few of them:\n# [A typical Hybrid Synergy Drive configuration | upload.wikimedia.org/wikipedia/commons/a/ad/Prius2004HSD.JPG]\n# [Lexus Hybrid Drive | upload.wikimedia.org/wikipedia/commons/9/9e/Lexus///GS450h///03.JPG]\n\n## Performance\nThe [Toyota Prius](https://bliptext.com/articles/toyota-prius) has modest acceleration but has extremely high efficiency for a midsized four-door sedan: usually significantly better than 40 mpg (US) (5.9 L/100 km) is typical of brief city jaunts; 55 mpg (4.3 L/100 km) is not uncommon, especially for extended drives at modest speeds (a longer drive allows the engine to warm up fully).\nThis is approximately twice the fuel efficiency of a similarly equipped four-door sedan with a conventional power train.\nNot all of the extra efficiency of the Prius is due to the HSD system: the [Atkinson cycle](https://bliptext.com/articles/atkinson-cycle) engine itself was also designed specifically to minimize engine drag via an offset [crankshaft](https://bliptext.com/articles/crankshaft) to minimize piston drag during the [power stroke](https://bliptext.com/articles/power-stroke-engine), and a unique intake system to prevent drag caused by [manifold vacuum](https://bliptext.com/articles/manifold-vacuum) (\"pumping losses\") versus the normal [Otto cycle](https://bliptext.com/articles/otto-cycle) in most engines.\nFurthermore, the Atkinson cycle recovers more energy per cycle than the Otto because of its longer power stroke.\nThe downside of the Atkinson cycle is much reduced torque, particularly at low speed; but the HSD has enormous low-speed torque available from MG2.\nThe [Highlander Hybrid](https://bliptext.com/articles/toyota-highlander-hybrid) (also sold as the Kluger in some countries) offers better acceleration performance compared to its non-hybrid version.\nThe hybrid version goes from 0–60 mph in 7.2 seconds, trimming almost a second off the conventional version's time.\nNet power is 268 hp compared to the conventional 215 hp.\nTop speed for all Highlanders is limited to 112 mi/h.\nTypical fuel economy for the Highlander Hybrid rates between 27 and 31 mpg (8.7–7.6 L/100 km).\nA conventional Highlander is rated by the EPA with 19 city, 25 highway mpg (12.4 and 9.4 L/100 km respectively).\nThe HSD mileage boost depends on using the gasoline engine as efficiently as possible, which requires:\nMost HSD systems have batteries that are sized for maximal boost during a single acceleration from zero to the top speed of the vehicle; if there is more demand, the battery can be completely exhausted, so that this extra torque boost is not available.\nThen the system reverts to just the power available from the engine.\nThis results in a large decline in performance under certain conditions: an early-model Prius can achieve over 90 mi/h on a 6 degree upward slope, but after about 2000 ft of altitude climb the battery is exhausted and the car can achieve only 55–60 mph on the same slope.\n(until the battery is recharged by driving under less demanding circumstances)\n# [Cutaway display of the HSD Note: Generation 1/Generation 2, chained, ICE-MG1-MG2 Power Split Device HSD is shown | upload.wikimedia.org/wikipedia/commons/5/5e/Toyota///Paris///9.JPG]\n\n# Prius Platform Generations\nThe design of the Toyota Hybrid System / Hybrid Synergy Drive has now had five generations since the original 1997 Japanese-market Toyota Prius.\nThe power train has the same basic features, but there have been a number of significant refinements.\n\n## Generation 1 (Toyota Hybrid System)\nThe system was called the Toyota Hybrid System (THS) when it was introduced with the Prius in 1997.\nThe hybrid [transaxle](https://bliptext.com/articles/transaxle), designated P110, includes two electric motors (MG1 and MG2) and a [planetary gearset](https://bliptext.com/articles/planetary-gearset), which Toyota calls the \"Power Split Device\" (PSD); mechanical power from the internal combustion engine (E) can be directed either to the wheels or to MG1, acting as a generator.\nElectrical power flows between MG1, MG2, and a storage battery through an inverter.\nAlthough MG1 typically operates as a generator (alternator), it also serves as the starter motor for the internal combustion engine.\nMG2 usually acts as a motor, either by itself at low speeds or to assist the internal combustion engine, but MG2 also can act as a generator, for instance, during deceleration for [regenerative braking](https://bliptext.com/articles/regenerative-braking).\nSchematically, MG1 is connected to the central sun gear (S), the internal combustion engine is connected to the planetary gear carrier (P) and not to any individual gear, and MG2 is connected to the ring gear (R).\nThe wheels are connected to the ring gear through appropriate [reduction gearing](https://bliptext.com/articles/reduction-gear) and a differential, not illustrated in the diagram.\nThe Toyota Hybrid System uses a high-voltage battery pack, ranging between 276 and 288 V. There has been a continuous, gradual improvement in the specific capacity of the traction battery.\nThe original Prius used shrink-wrapped 1.2 volt D cells, and all subsequent THS/HSD vehicles have used custom 7.2 V battery modules mounted in a carrier.\n# [Schematic diagram of the First- and Second-Generation Toyota Hybrid System transaxle (P110/ P111/ P112):\n \n S: Central \"'sun\" gear \n P: Planetary gear carrier \n R: Outer ring gear \n 1: Motor-Generator 1 \n 2: Motor-Generator 2 \n E: Internal Combustion Engine \n | upload.wikimedia.org/wikipedia/commons/8/8c/G01///%26///G02///Toyota///Hybrid///System.svg]\n\n### G1 single-motor\nIn 2001, a modified version of the Generation 1 THS transaxle was released in the Japanese domestic market as the P210 transaxle, fitted to the [Estima](https://bliptext.com/articles/toyota-previa) minivan.\nThe P210 couples the internal combustion engine with the sun gear and couples the starter/generator (MG1) with the planetary gear carrier, which is the opposite of the G1 THS scheme.\nIn addition, the single-motor G1 THS omits the traction motor (MG2) and uses a belt-drive [continuously variable transmission](https://bliptext.com/articles/continuously-variable-transmission) which can be selectively coupled via rotating clutches to either the planetary gear carrier or the ring gear.\nAn all-wheel drive option for the Estima was released at the same time; the Q410 rear drive unit uses an electric traction motor with no mechanical coupling to the front transaxle.\n# [Schematic diagram of single-motor THS transaxle (P210) with v-belt CVT | upload.wikimedia.org/wikipedia/commons/a/a4/G01///Toyota///Hybrid///System///%28CVT%29.svg]\n\n## Generation 2 (Toyota Hybrid System-II)\nTHS was followed by THS-II in the 2004 Prius.\nStarting with THS-II, Toyota also began referring to the system as Hybrid Synergy Drive (HSD).\nCompared to THS, THS-II offered reduced consumption and better performance with increased power and torque.\nTHS-II uses the same design as THS, combining traction power from an internal combustion engine and an electric motor via a planetary gearset (power split device) which can divert some power to an electrical generator.\nElectrically, HSD/THS-II adds a [DC to DC converter](https://bliptext.com/articles/dc-to-dc-converter) boosting the potential of the battery to 500 V or more.\nThis allows smaller battery packs to be used, and more powerful motors.\nCompared to THS, the physical size of the traction motor (MG2) in THS-II remains approximately the same, but the maximum output has increased from 33 to 50 kW and the maximum torque has increased from 350 to 400 Nm.\nThe stator windings are connected in series, which requires a higher potential.\nAlthough not part of the THS/HSD as such, starting with the 2004 Prius, all THS/HSD vehicles have been fitted with an electric air-conditioning compressor, instead of the conventional engine-driven type.\nThis removes the need to continuously run the engine when cabin cooling is required.\nTwo [positive temperature coefficient](https://bliptext.com/articles/positive-temperature-coefficient) heaters are fitted in the heater core to supplement the heat provided by the engine.\n\n## Generation 3 (Hybrid Synergy Drive)\nThe updated version of HSD first delivered in the model year 2006 RX 400h is similar to THS/THS-II, with the addition of a second planetary gearset, which Toyota calls the Motor Speed Reduction Device (MSRD); it is compounded with the first planetary gearset (PSD) by coupling the two ring gears together.\nThe coupled ring gears are still used to drive the front wheels of the vehicle.\nThe traction motor (MG2) uses the MSRD as a reduction gear, making it possible to increase the power density of the motor.\n[Ford](https://bliptext.com/articles/ford-motor-company) has also developed a similar hybrid system, introduced in the [Ford](https://bliptext.com/articles/ford-motor-company) Escape Hybrid.\nToyota CEO [Katsuaki Watanabe](https://bliptext.com/articles/katsuaki-watanabe) said in a February 16, 2007 interview that Toyota was \"aiming at reducing, by half, both the size and cost of the third-generation HSD system\".\nThe new system will feature [lithium-ion](https://bliptext.com/articles/lithium-ion) batteries in later years.\nLithium-ion batteries have a higher energy capacity-to-weight ratio compared to [NiMH](https://bliptext.com/articles/nimh), but operate at higher temperatures, and are subject to thermal instability if not properly manufactured and controlled, raising safety concerns.\n# [Schematic diagram of the Third-Generation Hybrid Synergy Drive transaxle (P31x/ P410/ P510); a second planetary gearset has been added | upload.wikimedia.org/wikipedia/commons/1/1c/G03///Toyota///Hybrid///System.svg]\n\n### G3 all-wheel drive with hybrid transaxle\nIn 2005, vehicles such as the Lexus RX 400h and Toyota Highlander Hybrid added four-wheel drive operation by adding a third electric motor (\"MGR\") on the rear axle.\nIn this system, the rear axle is purely electrically powered, and there is no mechanical link between the engine and the rear wheels.\nThis also permits regenerative braking on the rear wheels.\n\n### G3 rear-wheel drive (Lexus Hybrid Drive)\nIn 2006 and 2007, a further development of the HSD drivetrain, under the Lexus Hybrid Drive name, was fitted to the Lexus GS 450h / LS 600h sedans as the L110 transmission.\nPrevious versions of HSD/THS were fitted to [transaxles](https://bliptext.com/articles/transaxle) used with front-wheel drive platforms; Lexus Hybrid Drive applied the two-motor HSD concept to a longitudinal transmission for rear-wheel drive vehicles.\nThis system uses two clutches (or brakes) to switch the second motor's gear ratio to the wheels between a ratio of 3.9 and 1.9, for low and high speed driving regimes respectively.\nThis decreases the power flowing from MG1 to MG2 (or vice versa) during higher speeds.\nThe electrical path is only about 70% efficient, thus decreasing its power flow while increasing the overall performance of the transmission.\nThe second planetary gearset is extended with a second carrier and sun gear to a [ravigneaux-type gear](https://bliptext.com/articles/ravigneaux-planetary-gearset) with four shafts, two of which can be held still alternatively by a brake/clutch.\nThe GS 450h and LS 600h systems utilized [rear-wheel drive](https://bliptext.com/articles/rear-wheel-drive) and [all-wheel drive](https://bliptext.com/articles/all-wheel-drive) drivetrains, respectively, and were designed to be more powerful than non-hybrid versions of the same model lines, while providing comparable engine class efficiency.\nA simplified version was released in 2012 with the [fourteenth generation Crown (S210)](https://bliptext.com/articles/toyota-crown); the L210 transmission omits the two clutches but retains the second planetary gearset (MSRD) applied to the output of MG2, in common with other Generation 3 transaxles.\nHowever, compared to the G3 transaxles, instead of coupling the two ring gears, the L210 couples the PSD ring gear to the MSRD planetary gear carrier, and grounds the ring gear of the MSRD instead of the planetary gear carrier.\n# [Schematic diagram of rear-wheel Lexus Hybrid Drive transmission (L110/ L110F) | upload.wikimedia.org/wikipedia/commons/e/e8/G03///Toyota///Hybrid///System///%28RWD%29.svg]\n# [Schematic diagram of updated rear-wheel Hybrid Synergy Drive transmission (L210/ L210F) | upload.wikimedia.org/wikipedia/commons/9/95/G03///Toyota///Hybrid///System///%28RWD///alt%29.svg]\n\n## Generation 4\nOn October 13, 2015, Toyota announced details of the Fourth Generation Hybrid Synergy Drive which was introduced for the 2016 model year.\nThe overall design returns to a single planetary gearset similar to THS/THS-II; parallel reduction gears on the Fourth Generation transaxles replace the Motor Speed Reduction Device, which is a second planetary gear set found in the Third Generation transaxles.\nThe transaxle and traction motor have been redesigned, delivering a reduction in size and combined weight.\nThe traction motor itself is considerably more compact and gains a better [power-to-weight ratio](https://bliptext.com/articles/power-to-weight-ratio).\nNotably there is a 20 percent reduction in mechanical losses due to friction compared to the previous model.\nThe 2012– Prius c retains the P510 transaxle.\nThe P610 transaxle employs helical gears rather than the straight-cut spur gears employed in the earlier transaxles, and which run more smoothly and quietly, while also accommodating higher mechanical loads.\n# [Schematic diagram of Fourth-Generation Hybrid Synergy Drive transaxle (P610/ P71x/ P810/ P910) | upload.wikimedia.org/wikipedia/commons/6/63/G04///Toyota///Hybrid///System.svg]\n\n### G4 all-wheel drive with hybrid transaxle\nWith the Fourth Generation HSD, Toyota is also offering a four-wheel drive option, dubbed \"E-Four\", similar to the 2005 RX400h and Highlander Hybrid, in which an electric traction motor is added to the rear, but is not mechanically coupled to the internal combustion engine or front inverter.\nIn fact, the \"E-Four\" system has its own rear inverter, although this inverter draws power from the same hybrid battery as the front inverter.\n\"E-Four\" began being offered in Prius models in the United States in the 2019 model year.\n\"E-Four\" is an integral part of the [RAV4](https://bliptext.com/articles/toyota-rav4) Hybrid models offered in the United States, and all such [RAV4](https://bliptext.com/articles/toyota-rav4) Hybrids are \"E-Four\" only.\n\n### G4 rear-wheel drive (Multistage THS-II)\nThe L310 transmission for rear-wheel drive applications succeeded the prior L110 transmission in premium vehicles.\nCompared to the L110 and L210, the L310 couples MG2 to the ring gear of the PSD.\nIn addition L310 adds a third planetary gearset, compounded with the second (MSRD) by coupling the planetary gear carrier of the second planetary gearset with the ring gear of the third planetary gearset, and by coupling the ring gear of the second with the planetary gear carrier of the third.\nIn addition, several rotating clutches and brakes have been added, including a [one-way clutch](https://bliptext.com/articles/sprag-clutch) on the planetary gear carrier of the second planetary gearset.\nBy selectively engaging these, the transmission can simulate ten different gear ratios.\n# [Fourth Generation L310 / L310F Hybrid Synergy Drive transmission for rear-wheel drive vehicles | upload.wikimedia.org/wikipedia/commons/f/f2/G04///Toyota///Hybrid///System///%28RWD///alt%29.svg]\n\n## Generation 5\nThe fifth generation Hybrid Synergy Drive transaxle is similar to the prior generation, with detail improvements making the electric motors lighter, more compact, and more powerful.\n\n# List of vehicles with HSD technology\nThe following is a list of vehicles with Hybrid Synergy Drive and related technologies (Toyota Hybrid System):\n\n# Patent issues\n\n## Antonov\nAs of autumn 2005, the Antonov Automotive Technology BV Plc company has sued [Toyota](https://bliptext.com/articles/toyota), the Lexus brand mother company, over alleged patent infringement relating to key components in the RX 400h's drivetrain and the [Toyota](https://bliptext.com/articles/toyota) Prius hybrid compact car.\nThe case has been pending in secret since April 2005, but settlement negotiations did not bring a mutually acceptable result.\nAntonov eventually took legal recourse in the German court system, where decisions are usually made relatively swiftly.\nThe patent holder seeks to impose a levy on each vehicle sold, which could make the hybrid SUV less competitive.\nToyota fought back by seeking to officially invalidate Antonov's relevant patents.\nThe court motion in Microsoft Word document format can be read here.\nOn 1 September 2006 Antonov announced that the Federal Patent Court in Munich has not upheld the validity of the German part of Antonov's patent (EP0414782) against Toyota.\nA few days later, a court in Düsseldorf had ruled that the Toyota Prius driveline and the Lexus RX 400h driveline do not breach the Antonov hybrid CVT patent.\n\n## Ford\n[Ford Motor Company](https://bliptext.com/articles/ford-motor-company) independently developed a system with key technologies similar to Toyota's HSD technology in 2004.\nAs a result, Ford licensed 21 patents from Toyota in exchange for patents relating to emissions technology.\n\n## Paice\n[Paice LLC](https://bliptext.com/articles/undefined) received a patent for an improved hybrid vehicle with a controllable torque transfer unit and has additional patents related to hybrid vehicles.\nIn 2010 Toyota agreed to license Paice's patents; terms of the settlement were not disclosed.\nIn the settlement \"The parties agree that, although certain Toyota vehicles have been found to be equivalent to a Paice patent, Toyota invented, designed and developed the Prius and Toyota’s hybrid technology independent of any inventions of Dr. Severinsky and Paice as part of Toyota’s long history of innovation\".\nPaice earlier entered into an agreement with Ford for the license of Paice's patent.\n\n# Comparison with other hybrids\n[Aisin Seiki Co.](https://bliptext.com/articles/aisin-seiki-co), minority-owned by Toyota, supplies its versions of the HSD transmission system to Ford for use as the \"Powersplit\" e-CVT in the [Ford Escape](https://bliptext.com/articles/ford-escape) hybrid and [Ford Fusion Hybrid](https://bliptext.com/articles/ford-fusion-hybrid).\n[Nissan](https://bliptext.com/articles/nissan) licensed Toyota's HSD for use in the [Nissan](https://bliptext.com/articles/nissan) Altima hybrid, using the same Aisin Seiki T110 transaxle as in the [Toyota Camry](https://bliptext.com/articles/toyota-camry) Hybrid.\nThe 2011 [Infiniti M35h](https://bliptext.com/articles/infiniti-m35h) uses a different system of one electric motor and two clutches.\nIn 2010, [Toyota](https://bliptext.com/articles/toyota) and Mazda announced a supply agreement for the hybrid technology used in [Toyota](https://bliptext.com/articles/toyota)'s [Prius](https://bliptext.com/articles/toyota-prius) model.\n[General Motors](https://bliptext.com/articles/general-motors-corporation), [DaimlerChrysler](https://bliptext.com/articles/daimlerchrysler)'s and [BMW](https://bliptext.com/articles/bmw)'s [Global Hybrid Cooperation](https://bliptext.com/articles/global-hybrid-cooperation) is similar in that it combines the power from a single engine and two motors.\nIn 2009, the [Presidential Task Force on the Auto Industry](https://bliptext.com/articles/presidential-task-force-on-the-auto-industry) said that \"GM is at least one generation behind Toyota on advanced, 'green' powertrain development\".\nIn contrast, [Honda](https://bliptext.com/articles/honda)'s [Integrated Motor Assist](https://bliptext.com/articles/integrated-motor-assist) uses a more traditional [ICE](https://bliptext.com/articles/internal-combustion-engine) and transmission where the flywheel is replaced with an electric motor, thereby retaining the complexity of a traditional transmission.\n\n# Aftermarket\nSome early non-production [plug-in hybrid electric vehicle](https://bliptext.com/articles/plug-in-hybrid-electric-vehicle) [conversions](https://bliptext.com/articles/electric-vehicle-conversion) have been based on the version of HSD found in the 2004 and 2005 model year Prius.\nEarly [lead-acid battery](https://bliptext.com/articles/lead-acid-battery) conversions by [CalCars](https://bliptext.com/articles/undefined) have demonstrated 10 mi of ev-only and 20 mi of double mileage [mixed-mode](https://bliptext.com/articles/blended-mode) range.\nA company planning to offer conversions to consumers named [EDrive systems](https://bliptext.com/articles/undefined) will be using [Valence](https://bliptext.com/articles/undefined) [Li-ion](https://bliptext.com/articles/li-ion) batteries and have 35 mi of electric range.\nBoth of these systems leave the existing HSD system mostly unchanged and could be similarly applied to other hybrid powertrain flavors by simply replacing the stock [NiMH](https://bliptext.com/articles/nickel-metal-hydride) batteries with a higher capacity [battery pack](https://bliptext.com/articles/battery-pack) and a charger to refill them for about $0.03 per mile from standard household outlets.","revisionCount":0},"hasMore":false,"nextCursor":null}

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