Hybrid Synergy Drive (HSD) is a set of hybrid car technologies developed by Toyota and used in the company's Yaris, Auris, Prius, Highlander Hybrid, Camry Hybrid, Estima, Alphard, Lexus RX 400h/RX 450h, Lexus GS 450h, Lexus LS 600h/LS 600hL, Lexus CT 200h, and Lexus HS 250h automobiles. Toyota also licenses its HSD technology to Nissan for use in that company's Nissan Altima Hybrid. Its parts supplier Aisin Seiki Co. sells similar hybrid transmissions to other car companies.
HSD technology produces a 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. The HSD also combines an electric drive and a planetary gearset which performs similarly to a continuously variable transmission. The Synergy Drive is a drive-by-wire system with no direct mechanical connection between the engine and the engine controls: both the gas pedal/accelerator and the gearshift lever in an HSD car merely send electrical signals to a control computer.
HSD is a refinement of the original Toyota Hybrid System (THS) used in the 1997 to 2003 Toyota Prius. The second generation system THS II first appeared on the redesigned Prius in 2004. The name was changed in anticipation of its use in vehicles outside the Toyota brand (Lexus; the HSD-derived systems used in Lexus vehicles have been termed Lexus Hybrid Drive since 2006). The Lexus Hybrid Drive system is tuned for increased power and performance along with efficiency concerns; it was introduced on all-wheel drive and rear-wheel drive Lexus models. By May 2007 Toyota had sold one million hybrids worldwide and by the end of August 2009 had sold a total of two million. By April 2012 Toyota had sold four million hybrids worldwide. Toyota-produced hybrids make up approximately 75% of United States hybrid sales.
The Toyota HSD replaces a normal geared transmission with an electromechanical system. An internal combustion engine (ICE) delivers power most efficiently over a small range of speeds (RPMs), but the wheels need to be driven at the speed required for the vehicle. In a conventional automobile a geared transmission and drivetrain transmits the power from the engine to the wheels. Geared transmissions may be manual, with a clutch, or automatic, with a torque converter, but both allow the engine and the wheels to rotate at different speeds. The driver can adjust the speed and torque delivered by the engine with the accelerator and the transmission mechanically transmits nearly all of the available power to the wheels which rotate at lower rate than the engine, by a factor equal to the gear ratio for the currently selected gear. However, there are a limited amount of "gears" or gear ratios that the driver can chose from, typically 3 to 5. This limited gear-ratio set, forces the engine crankshaft to rotate at speeds where the ICE is less efficient, where a gallon of gas produces less power for less time. The range of RPMs required to operate a particular vehicle and transmission can be seen by monitoring the tach ("revs" or RPM gauge) while driving and accelerating at a variety of speeds. When an engine is required to operate efficiently across a broad range of RPMs, due to its coupling to a geared transmission, manufacturers are limited in their options for improving engine efficiency, reliability, or lifespan, as well as reducing the size or weight of the engine. This is why the engine for a genset is often much smaller, more efficient, more reliable, and longer life than one designed for an automobile or other variable speed application.
However, 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. The transmission is not limited to a set of gears. This lack of constraint frees the engine to operate at its optimal (most efficient) speed (RPM). The most efficient speed (RPM) for an ICE is often around 1500-2000 rpm for the typical power required to propel an automobile. An HSD vehicle will typically rev the engine its optimal efficiency speed whenever power is needed to charge batteries or accelerate the car, shutting down the engine entirely when less power is required.
Like a CVT, an HSD transmission continuously adjusts the effective gear ratio between the engine and the wheels to maintain the engine speed while the wheels increase their rotational speed during acceleration. This is why Toyota describes HSD-equipped vehicles as having an e-CVT (electronically controlled variable transmission) when required to classify the transmission type for standards specification lists or regulatory purposes.
Power sources Edit
In the "standard" car design the alternator (AC generator) and starter (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. A battery is used only to start the car's internal combustion engine and run accessories when the engine is not running. The alternator is used to recharge the battery and run the accessories when the engine is running. HSD replaces the gear box (transmission), alternator and starter motor with a pair of powerful motor-generators (designated MG1 and MG2, ~60 Hp total) with a computerized shunt system to control them, a mechanical power splitter that acts as a second differential, and a battery pack that serves as an energy reservoir. The motor-generator uses power from the battery pack to propel the vehicle at startup and at low speeds or under acceleration. The ICE may or may not be running at startup. When higher speeds, faster acceleration or more power for charging the batteries is needed the ICE is started by the motor-generator (acting as a starter). These features allow the ICE to normally be turned off for traffic stops—accessory power (including air conditioning if needed) is normally provided by the battery pack.
When a moving vehicle operator wants the vehicle to slow down, the initial travel of the brake pedal engages the motor-generator(s) into generator mode converting much of the forward motion into electrical current flow which is used to recharge the batteries while slowing down the vehicle. In this way the forward momentum regenerates (or converts) much of the energy used to accelerate the vehicle back into stored electrical energy. (See regenerative braking) Harder braking action engages standard front disk and rear drum (rear disk for 2010 and later models) brakes which are also provided for faster stops and emergency use.
MG1 and MG2 Edit
- MG1 (motor generator 1): generates electrical power. MG1 recharges the EV battery and supplies electrical power to drive MG2. In addition, by regulating the amount of electrical power generated (thus varying MG1's internal resistance and rpm), MG1 effectively controls the transaxle's continuously variable transmission. MG1 also serves as the engine starter motor, hence the use of the term "motor generator" for MG1 rather than simply "generator".
- MG2 (motor generator 2): drives the vehicle. MG2 drives the wheels with electrical power generated by the engine and MG1. This is the motor portion of its "motor generator" capabilities. Like any electrical motor, MG2 provides a smooth (nearly imperceptible) acceleration from standstill to forward (or reverse) motion. During regenerative braking, MG2 acts as a generator, converting kinetic energy into electrical energy, storing this electrical energy in the battery, driving the engine (when an engine braking mode is enabled), or dissipating the electrical energy as heat (when the batteries are fully charged).
The 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. A computer program running appropriate actuators controls the systems and directs the power flow from the different engine + motor sources. This power split achieves the benefits of a continuously variable transmission (CVT), except that the torque/speed conversion uses an electric motor rather than a direct mechanical gear train connection. An 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. (See: 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.
An HSD transaxle contains a 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. It is a sophisticated and complicated combination of gearing, electrical motor-generators and computer controlled electronic controls. One of the motor-generators (MG2 in Toyota manuals; sometimes called "MG-T" for "Torque") is mounted on the drive shaft, and thus couples torque into or out of the drive shafts: feeding electricity into MG2 adds torque at the wheels. The engine end of the drive shaft has a second differential; one leg of this differential is attached to the internal combustion engine and the other leg is attached to a second motor-generator (MG1 in Toyota manuals; sometimes "MG-S" for "Speed"). The 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. The differential is an epicyclic gear set (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. Special couplings and sensors monitor rotation speed of each shaft and the total torque on the drive shafts, for feedback to the control computer.
The 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. Since 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. The smaller internal combustion engine can be designed to run more efficiently. Furthermore, 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. During traffic stops the internal combustion engine can even be turned off for even more economy.
The 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.
Phases of operation Edit
The HSD operates in distinct phases depending on speed and demanded torque. Here are a few of them:
- Battery charging: The HSD can charge its battery without moving the car, by running the engine and extracting electrical power from MG1. The power gets shunted into the battery, and no torque is supplied to the wheels. The shifter must be in the "Park" position.
- Engine start: To start the engine, power is applied to MG1 to act as a starter. Because of the size of the motor generators, starting the engine requires relatively little power from MG1 and the conventional starter motor sound is not heard. Engine start can occur while stopped or moving.
- Reverse gear: There is no reverse gear as in a conventional gearbox: the computer feeds negative voltage to MG2, applying negative torque to the wheels. Early models did not supply enough torque for some situations: there have been reports of early Prius owners not being able to back the car up steep hills in San Francisco. The problem has been fixed in recent models. If the battery is low, the system can simultaneously run the engine and draw power from MG1, although this will reduce available reverse torque at the wheels.
- Neutral gear: Most jurisdictions require automotive transmissions to have a neutral gear that decouples the engine and transmission. The HSD "neutral gear" is achieved by turning the electric motors off. Under this condition, the planetary gear is stationary (if the vehicle wheels are not turning); if the vehicle wheels are turning, the ring gear will rotate, causing the sun gear to rotate as well (the engine inertia will keep the carrier gear stationary unless the speed is high), while MG1 is free to rotate while the battries do not charge. The owners manual  warns that Neutral gear will eventually drain the battery, resulting in "unnecessary" engine power to recharge batteries; a discharged battery will render the vehicle inoperable.
- EV operation: At slow speeds and moderate torques the HSD can drive without running the internal combustion engine at all: electricity is supplied only to MG2, allowing MG1 to rotate freely (and thus decoupling the engine from the wheels). This is popularly known as "Stealth Mode". Provided that there is enough battery power, the car can be driven in this silent mode for some miles even without gasoline.
- Low gear (equivalent): When accelerating at low speeds in normal operation, the engine turns more rapidly than the wheels but does not develop sufficient torque. The extra engine speed is fed to MG1 acting as a generator. The output of MG1 is fed to MG2, acting as a motor and adding torque at the driveshaft.
- High gear (equivalent): When cruising at high speed, the engine turns more slowly than the wheels but develops more torque than needed. MG2 then runs as a generator to remove the excess engine torque, producing power that is fed to MG1 acting as a motor to increase the wheel speed. In steady state, the engine provides all of the power to propel the car unless the engine is unable to supply it (as during heavy acceleration, or driving up a steep incline at high speed). In this case, the battery supplies the difference. Whenever the required propulsion power changes, the battery quickly balances the power budget, allowing the engine to change power relatively slowly.
- Regenerative braking: By drawing power from MG2 and depositing it into the battery pack, the HSD can simulate the deceleration of normal engine braking while saving the power for future boost. The regenerative brakes in an HSD system absorb a significant amount of the normal braking load, so the conventional brakes on HSD vehicles are undersized compared to brakes on a conventional car of similar mass.
- Engine braking: The HSD system has a special transmission setting labelled 'B' (for Brake), that takes the place of a conventional automatic transmission's 'L' setting, providing engine braking on hills. This can be manually selected in place of regenerative braking. During braking when the battery is approaching potentially damaging high charge levels, the electronic control system automatically switches to conventional engine braking, drawing power from MG2 and shunting it to MG1, speeding the engine with throttle closed to absorb energy and decelerate the vehicle.
- Electric boost: The battery pack provides a reservoir of energy that allows the computer to match the demand on the engine to a predetermined optimal load curve, rather than operating at the torque and speed demanded by the driver and road. The computer manages the energy level stored in the battery, so as to have capacity to absorb extra energy where needed or supply extra energy to boost engine power.
The Toyota Prius has modest acceleration but has extremely high efficiency for a mid sized four-door sedan: usually significantly better than 40 mpg (US) (5.9 l/100km) is typical of brief city jaunts; 55 mpg (4.3 l/100km) is not uncommon, especially for extended drives at modest speeds (a longer drive allows the engine to warm up fully). This is approximately twice the fuel efficiency of a similarly equipped four-door sedan with a conventional power train (except, of course, ULEV's such as the Chevrolet Cruze Eco which averages 40 mpg, but lacks a spare tire and 5th lugnut to reduce weight and to cut costs). Not all of the extra efficiency of the Prius is due to the HSD system: the Atkinson cycle engine itself was also designed specifically to minimize engine drag via an offset crankshaft to minimize piston drag during the power stroke, and a unique intake system to prevent drag caused by manifold vacuum versus the normal Otto cycle in most engines. Furthermore, the Atkinson cycle recovers more energy per cycle than the Otto because of its longer power stroke. The downside of the Atkinson cycle is much reduced torque, particularly at low speed; but the HSD has enormous low-speed torque available from MG2.
The Highlander Hybrid (also sold as the Kluger in some countries) offers better acceleration performance compared to its non-hybrid version. The hybrid version goes from 0–60 mph in 7.2 seconds, trimming almost a second off the conventional version's time. Net hp is 268 hp (200 kW) compared to the conventional 215 hp (160 kW). Top speed for all Highlanders is limited to 112 mph (180 km/h). Typical fuel economy for the Highlander Hybrid rates between 27 and 31 mpg (8.7-7.6 l/100km). A conventional Highlander is rated by the EPA with 19 city, 25 highway mpg (12.4 and 9.4 l/100km respectively).
The HSD mileage boost depends on using the gasoline engine as efficiently as possible, which requires:
- extended drives, especially in winter: Heating the internal cabin for the passengers runs counter to the design of the HSD. The HSD is designed to generate as little waste heat as possible. In a conventional car, this waste heat in winter is usually used to heat the internal cabin. In the Prius, running the heater will then require the engine to continue running to generate cabin-usable heat. This effect is most pronounced by turning the climate control (heater) off when at a stop when the engine is running. Normally the HSD control system will shut the engine off as it is not needed, and will not start it again until the generator reaches a maximum speed.
- moderate acceleration: Because hybrid cars can throttle back or completely shut off the engine during moderate, but not rapid, acceleration, they are more sensitive than conventional cars to driving style. Hard acceleration forces the engine into a high-power state while moderate acceleration keeps the engine in a lower power, high efficiency state (augmented by battery boost).
- gradual braking: Regenerative brakes re-use the energy of braking, but cannot absorb energy as fast as conventional brakes. Gradual braking recovers energy for re-use, boosting mileage; hard braking wastes the energy as heat, just as for a conventional car. Use of the "B" (braking) selector on the transmission control is useful on long downhill runs to reduce heat and wear on the conventional brakes, but it does not recover additional energy. Use of "B" constantly is discouraged by Toyota as it may promote excessive wear on certain gears.
Most 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. Then the system reverts to just the power available from the engine. This results in a large decline in performance under certain conditions: an early-model Prius can achieve over 90 mph (140 km/h) on a 6 degree upward slope, but after about 2,000 feet (610 m) of altitude climb the battery is exhausted and the car can only achieve 55–60 mph on the same slope (until the battery is recharged by driving under less demanding circumstances).
Subsequent developments Edit
The basic design of the Toyota Hybrid System / Hybrid Synergy Drive has not changed since its introduction in the 1997 Japanese-market Toyota Prius, but there have been a number of significant refinements.
The schematic diagrams illustrate the paths of power flow between electric motor-generator 1 (MG1), gasoline internal combustion engine (ICE), planetary gearset "power split device" elements (S:central "sun", C:planetary carrier, R:outer ring) and motor-generator 2 (MG2).
There has been a continuous, gradual improvement in the specific capacity of the traction battery. The 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.
Called Toyota Hybrid System for initial Prius generations, THS was followed by THS II in the 2004 Prius, with subsequent versions termed Hybrid Synergy Drive. The THS relied on the voltage of the battery pack: between 276 and 288 V. The Hybrid Synergy Drive adds a DC to DC converter boosting the potential of the battery to 500 V or more. This allows smaller battery packs to be used, and more powerful motors.
Hybrid Synergy Drive (HSD)Edit
Although not part of the HSD as such, all HSD vehicles from the 2004 Prius onwards have been fitted with an electric air-conditioning compressor, instead of the conventional engine-driven type. This removes the need to continuously run the engine when cabin cooling is required. Two positive temperature coefficient heaters are fitted in the heater core to supplement the heat provided by the engine.
In 2005, vehicles such as the Lexus RX 400h and Toyota Highlander Hybrid added four-wheel drive operation by the addition of a third electric motor ("MGR") on the rear axle. In this system, the rear axle is purely electrically powered, and there is no mechanical link between the engine and the rear wheels. This also permits regenerative braking on the rear wheels. In addition, the motor (MG2) is linked to the front wheel transaxle by means of a second planetary gearset, thereby making it possible to increase the power density of the motor. Ford has also developed a similar hybrid system, introduced in the Ford Escape Hybrid.
In 2006 and 2007, a further development of the HSD drivetrain, under the Lexus Hybrid Drive name, was applied on the Lexus GS 450h / LS 600h sedans. This 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. This decreases the power flowing from MG1 to MG2 (or vice versa) during higher speeds. The electrical path is only about 70% efficient, thus decreasing its power flow while increasing the overall performance of the transmission. The second planetary gearset is extended with a second carrier and sun gear to a ravigneaux-type gear with four shafts, two of which can be held still alternatively by a brake/clutch. The GS 450h and LS 600h systems utilized rear-wheel drive and 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.
Toyota CEO 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". The new system will feature lithium-ion batteries in later years. Lithium-ion batteries have a higher energy capacity-to-weight ratio, but cost more, don't last as long as NiMH, and operate at higher temperatures, and are subject to thermal instability if not properly manufactured and controlled, raising safety concerns.
List of vehicles with HSD technologyEdit
The following is a list of vehicles with Hybrid Synergy Drive and related technologies (Toyota Hybrid System I/II; Lexus Hybrid Drive)
- Toyota Prius
- with THS: December 1997–October 2003
- with THSII: October 2003–present
- Lexus RX 400h / Toyota Harrier Hybrid (March 2005–)
- Toyota Highlander/Kluger Hybrid
- with THSI: July 2005–September 2008
- with THSII: October 2008–present
- Lexus GS 450h (March 2006–present)
- Toyota Camry Hybrid (May 2006–present)
- Lexus LS 600h/LS 600hL (April 2007–present)
- Toyota A-BAT (concept truck)
- Nissan Altima Hybrid (2007–present)
- Lexus RX 450h (2009–present)
- Lexus HS 250h (2009–present)
- Lexus CT 200h (late 2010–)
- Toyota Auris (July 2010–)
- Toyota Yaris (March 2012–)
As of autumn 2005, the Antonov Automotive Technology BV Plc company has sued Toyota, the Lexus brand mother company, over alleged patent infringement relating to key components in the RX 400h's drivetrain and the Toyota Prius hybrid compact car. The case has been pending in secret since April 2005, but settlement negotiations did not bring a mutually acceptable result. Antonov eventually took legal recourse in the German court system, where decisions are usually made relatively swiftly. The patent holder seeks to impose a levy on each vehicle sold, which could make the hybrid SUV less competitive. Toyota fought back by seeking to officially invalidate Antonov's relevant patents. The court motion in Microsoft Word document format can be read here.
On 1 September 2006 Antonov announced: The Board of Antonov plc announces that the Federal Patent Court in Munich has not upheld the validity of the German part of Antonov's patent (EP0414782) against Toyota. A few days earlier, a court in Düsseldorf had ruled that the Toyota Prius driveline breached the Antonov hybrid CVT patent. Equivalent patents are still in force in various countries worldwide. The position is therefore at an impasse, with the Toyota Prius probably breaching the Antonov hybrid CVT patents outside Europe, Antonov PLC lacking the financial muscle to enforce their patents, and Toyota prepared to try to get the Antonov patents cancelled elsewhere if Antonov tries to enforce them. 
Ford Motor Company independently developed a system with key technologies similar to Toyota's HSD technology in 2004. As a result, Ford licensed 21 patents from Toyota in exchange for patents relating to emissions technology.
Paice LLC received a patent for an improved hybrid vehicle with a controllable torque transfer unit (US patent 5343970, Severinsky; Alex J., "Hybrid electric vehicle", issued 1994-09-06 ) and has additional patents related to hybrid vehicles. In 2010 Toyota agreed to license Paice's patents; terms of the settlement were not disclosed. In 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". Paice earlier entered into an agreement with Ford for the license of Paice's patent.
Comparison with other hybrids Edit
Nissan licensed Toyota's HSD for use in the Nissan Altima hybrid, using the same Aisin Seiki T110 transaxle as in the Toyota Camry Hybrid. The 2011 Infiniti M35h uses a different system of one electric motor and two clutches.
General Motors, DaimlerChrysler's and BMW's Global Hybrid Cooperation is similar in that it combines the power from a single engine and two motors. In 2009, the Presidential Task Force on the Auto Industry said that "GM is at least one generation behind Toyota on advanced, 'green' powertrain development".
In contrast, Honda's Integrated Motor Assist uses a more traditional ICE and transmission where the flywheel is replaced with an electric motor, thereby reducing complexity and increasing serviceability due to the familiar layout.
Some early non-production plug-in hybrid electric vehicle conversions have been based on the version of HSD found in the 2004 and 2005 model year Prius. Early lead-acid battery conversions by CalCars have demonstrated 10 miles (16 km) of ev-only and 20 miles (32 km) of double mileage mixed-mode range. A company planning to offer conversions to consumers named EDrive systems will be using Valence Li-ion batteries and have 35 miles (56 km) of electric range. Both 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 batteries with a higher capacity battery pack and a charger to refill them for about $0.03 per mile from standard household outlets. Another provider of a plug-in module for the Toyota Prius is Hymotion.
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- Comparison of Toyota hybrids
- Hybrid car
- Inverter (electrical)
- IGBT transistor
- Variable-frequency drive
- Global Hybrid Cooperation
- Integrated Motor Assist
- List of hybrid vehicles
- ↑ 1.0 1.1 Vasilash, Gary (2005-02). A Lexus Like No Other But Like The Rest:Introducing The RX 400h. Automotive Design and Production. Retrieved on 2010-07-12.
- ↑ 2.0 2.1 Lexus GS450h - Road Tests. www.carmag.co.za. Retrieved on 2010-07-13.
- ↑ 3.0 3.1 Vasilash, Gary (2006-07). The Lexus LS 600H L: Not Just Another Production Car. Automotive Design and Production. Retrieved on 2010-04-12.
- ↑ News Releases > Worldwide Sales of TMC Hybrids Top 2 Million Units. TOYOTA (2009-09-04). Retrieved on 2009-12-03.
- ↑ News Releases > Worldwide sales of Toyota and Lexus full hybrid vehicles top 4 million. TOYOTA (2012-05-22). Retrieved on 2012-05-22.
- ↑ Toyota Captures 75% of US Hybrid Share. MixedPower.com. Retrieved on 2009-12-03.
- ↑ All electric motors can be used as generators (and vice-versa) so the term motor-generator is normally used only when the same device is being used for both purposes.
- ↑ 8.0 8.1 Document:
- ↑ Bill Siuru. Synergy Drive: Why Toyota’s Hybrids Rock. Green Car Journal. Yahoo. Retrieved on 2008-03-12.
- ↑ Camry Hybrid 2012 owner's manual]
- ↑ http://www.techno-fandom.org/~hobbit/cars/b-mode.html
- ↑ 2007 Prius Owners Manual
- ↑ "6 - Body Electrical" (PDF). Toyota Hybrid System - Course 071. Toyota Technical Training. p. 1. http://www.autoshop101.com/forms/Hybrid06.pdf. Retrieved 2008-10-15.
- ↑ 2008 Lexus LS 600h L Overview. Vehix.com. Retrieved on 2010-07-13.
- ↑ Toyota's Bid for a Better Battery.
- ↑ Halvorson, Bengt. Li-ion Not Ready for Prius. BusinessWeek, June 18, 2007. Retrieved on 2007-08-07.
- ↑ DailyTech - Toyota Shuns Lithium-ion Batteries for Next Gen Prius
- ↑ http://hugin.info/132838/R/1012362/157707.doc
- ↑ Toyota gets Antonov hybrid CVT patent cancelled in Europe.
- ↑ Bruce Nussbaum (2005-11-01). Is Ford Innovative? Part Two.. Bloomberg Businessweek. Retrieved on 2011-03-09.
- ↑ Joann Muller (2010-07-19). Toyota Settles Hybrid Patent Case. Forbes.com. Retrieved on 2011-03-09.
- ↑ "Toyota and Paice reach settlement of patent disputes" (Press release). Paice LLC. 2010-07-09. http://www.paice.net/toyota-and-paice-reach-settlement-of-patent-disputes. Retrieved 2011-03-09.
- ↑ "Paice and Ford Reach Settlement in Hybrid Vehicle Patent Infringement Disputes" (Press release). Paice LLC via PR Newswire. 2010-07-16. http://www.prnewswire.com/news-releases/paice-and-ford-reach-settlement-in-hybrid-vehicle-patent-infringement-disputes-98646969.html. Retrieved 2011-03-09.
- ↑ AISIN at a Glance. Aisin Seiki Co. (2005-09-21). Archived from the original on 2007-11-17. Retrieved on 2011-03-09. “Developed the HD-10 proprietary hybrid drive “dual system” for use in the Ford Escape Hybrid”
- ↑ Ford Fleet - Showroom - Cars - 2010 Fusion Hybrid. Ford Motor Company. Retrieved on 2011-03-09.
- ↑ "TMC and Mazda Agree to Hybrid System Technology License" (PDF) (Press release). Toyota & Mazda. 2010-03-29. http://www.mazda.com/publicity/release/2010/201003/100329b.html. Retrieved 2010-03-29.
- ↑ GM Viability Assessment Determination of Viability Summary: General Motors Corporation (2009-03-30). Retrieved on 2009-12-03.
- HSD explanation at HowStuffWorks
- Planetary Gear explanation at HowStuffWorks
- Hybrid Synergy Drive movie from Toyota
- Animation showing how HSD works
- Power Split Device Animation showing
- MG1 and the MG2