Hybrid Transaxles

The transmission is the most complex component in the vehicles drive train, and is responsible for finding the balance between torque and speed during all phases of vehicle operation.

WHY A TRANSMISSION IS NECESSARYIn order to move a vehicle, torque must be applied to its wheels. Torque is twisting force. Applying more torque to the wheels will make the vehicle accelerate more quickly, but once a vehicle is up to speed, less torque is required to maintain that speed. The vehicle transmission is responsible for increasing engine torque in the lower speed ranges when acceleration is required, then reducing torque in favor of speed when the vehicle is cruising.

TorqueICE produces zero torque at zero RPM, because the engine is not running. Zero RPM is when an electric motor produces the most torque.

It is difficult to keep the engine in this range during all phases of vehicle operation. Automotive engineers overcome this difficulty in two ways: 1. By increasing the RPM range where the engine produces torque (flattening the torque curve). 2. By increasing the number of speeds in the transmission. With more transmission speeds, it is easier to match the vehicle speed with the engines most efficient RPM.

Speed versus Torque When torque is increased in a transmission, output speed is decreased.

What Is the Difference between Horsepower and Torque?Torque is twisting force. Horsepower is the rate at which work is done, and is a function of torque and engine RPM. Horsepower can be calculated using the following formula: Horsepower = Torque RPM 5,252

MANUAL TRANSAXLESThe manual transaxles currently being used in production hybrid electric vehicles (HEVs) are 5-speed designs except the new CRZ. This means that these transaxles have five forward gear ratios and one reverse gear ratio.

Manual Trans ModelsFirst generation Honda Insight (2000 06) First generation Honda Civic (2003 05) New Honda CRZ (2011 model - ?)

Insight & Civic ServiceThe most important service procedure with any manual transaxle is fluid inspection and replacement.

Civic & Insight ServiceB = fill plugD = drain plug

Civic & Insight serviceHonda genuine MTFHolds 1.6 quartsCan use motor oil but may cause stiffer shifting120k mile service interval30k service interval for Honda CVT

Be absolutely sure to use fluids that have been approved for use by the vehicle manufacturer.

GM Silverado/Sierra Hybrid Automatic TransmissionDescription and Operation. The transmission in the Chevrolet Silverado/GMC Sierra hybrid pickup is based on the 4L60E electronically controlled automatic transmission design with minor modification to adjust for its new role in a hybrid power train. It has four forward speeds and one reverse, with the fourth speed being an overdrive.

GM Silverado/Sierra Hybrid Automatic TransmissionThis transmission was originally designed with mechanical/hydraulic controls only, but was later modified to incorporate electronic shift control.

GM Silverado/Sierra Hybrid Automatic TransmissionConstruction. However, changes were made to accommodate the addition of the integrated starter generator (ISG) inside the bell-housing assembly. The transmission was modified only to the extent where it was absolutely necessary, and otherwise used as much of the original design as possible.

GM Silverado/Sierra Hybrid Automatic TransmissionThe primary change was a decrease in the diameter of the torque converter in order for it to fit inside the rotor assembly of the ISG.

GM Silverado/Sierra Hybrid Automatic TransmissionWhenever the engine goes into idle stop, the electric fluid pump is turned on to maintain oil pressure on the transmissions forward clutch and keep the drive train connected to the engine.

GM Silverado/Sierra Hybrid Automatic TransmissionPump has its own serviceable filter; two filters in all

GM Silverado/Sierra Hybrid Automatic Transmission

GM Silverado/Sierra Hybrid Automatic TransmissionDexron III2 filtersReplacement interval 50k miles

GM Silverado/Sierra Hybrid Automatic TransmissionService. Transmission service for the 4L60E model M33 is limited to fluid and filter changes.

GM Silverado/Sierra Hybrid Automatic TransmissionA scan tool can be used to access DTCs (diagnostic trouble codes) and also to perform bi-directional testing of the transmission solenoids. A scan tool can also be utilized for clearing the transmission adaptive pressure (TAP) values if any of the following has occurred: 1. If the transmission has been overhauled or replaced 2. Repair or replacement of an apply or release component (band, clutch, servo, piston, etc.) 3. Repair or replacement of a component that directly affects line pressure

Honda Accord Hybrid Five-Speed Automatic TransmissionDescription and Operation. Honda uses an automatic transmission (transaxle) in the Accord Hybrid that is similar to the ones used in its vehicles with conventional power trains.

The various speeds are selected through application of six multiple-disc clutches and a single one-way clutch.Honda Accord Hybrid Five-Speed Automatic Transmission

The integrated motor assist (IMA) assembly is located between the ICE and the transmission. The torque converter drive plate (flexplate) is attached to the IMA rotor, which in turn is driven by the ICE crankshaft.Honda Accord Hybrid Five-Speed Automatic Transmission

Honda Accord Hybrid Five-Speed Automatic TransmissionHonda ATF-Z1 Automatic Transmission FluidHas a fill bolt even though theres a dipstickNo specified replacement interval

Honda Accord Hybrid Five-Speed Automatic TransmissionIn order to accommodate the hybrid power train, an electric auxiliary pump is used to maintain fluid pressure in the transmission during ICE idle stop. Once the ICE restarts, the auxiliary pump is turned off and hydraulic pressure is again supplied by the mechanically driven transmission fluid pump.

Honda Accord Hybrid Five-Speed Automatic TransmissionThe auxiliary transmission fluid pump is operated using three-phase AC from a special motor control unit. The pump is mounted on the outside of the transmission case. Three wires connect the pump motor to the controller.

Honda Accord Hybrid Five-Speed Automatic TransmissionATF pump control module

Honda Accord Hybrid Five-Speed Automatic TransmissionThe torque converter clutch (TCC) is applied and released by reversing the flow of fluid through the torque converter housing.

Honda Accord Hybrid Five-Speed Automatic TransmissionIn order to release the TCC, the flow of fluid in the torque converter housing is reversed. This causes the clutch piston to move away from the torque converter cover and the turbine is thus released.

Honda Accord Hybrid Five-Speed Automatic TransmissionThe power train control module is responsible for the automatic transmission functions, and it receives input data from many different sensors in order to make the transmission operate smoothly and efficiently.

Honda Accord Hybrid Five-Speed Automatic TransmissionService. When a problem has been detected, the PCM will generate a DTC (diagnostic trouble code) and may also place the transmission in limp-home mode, depending on what sort of problem has been detected.

Honda Accord Hybrid Five-Speed Automatic TransmissionThere are some situations where the PCM has detected a transmission malfunction that is not noticeable by the driver, and some means must be employed to alert the driver that service is necessary. Honda does this by flashing the D indicator on the transmission range display on the instrument panel.

Honda Accord Hybrid Five-Speed Automatic TransmissionIf a scan tool is not available, Honda also makes it possible to identify the transmission DTCs by interpreting the blinking of the D light on the instrument panel. This can be enabled by connecting a jumper wire from the SCS (brown) wire of the DLC to a body ground with the key in the RUN position.

CONTINUOUSLY VARIABLE TRANSMISSIONS (CVTs)Internal combustion engines run most efficiently in a relatively narrow RPM range. Eliminate transmission speed ranges completely using a continuously variable transmission (CVT). There are two primary designs of continuously variable transmissions being used in production HEVs: the power-split CVT being used by Toyota/Lexus and Ford, and the belt- and-pulley system being used by Honda.

Toyota/Lexus Power-Split SystemDescription and Operation. During most phases of vehicle operation, the system is operating as both series and parallel at the same time. The basic transaxle is very simple in design as it is built around a single planetary gearset (power-split device) and two electric motor/generators.

Toyota/Lexus Power-Split SystemA planetary gearset is comprised of three main components: the ring gear, the planet carrier, and the sun gear. In the power-split transaxle, a large electric motor/generator (MG2) is directly attached to the transaxle final drive and to the planetary ring gear. The ICE is connected to the planet carrier, and the small electric motor/generator (MG1) is connected to the sun gear.

Toyota/Lexus Power-Split SystemThe torque split percentages remain the same regardless of what mode the transaxle is operating in because they are determined by the number of teeth on the planetary ring gear and the sun gear.

Operating ModesWARNING-When towing a Prius, do not let the front wheels rotate. They are directly connected to MG2 and it may generate high voltage, creating a shock hazard or damage the inverter or HV battery

Operating ModesSee http://eahart.com/prius/psd/ for a visual representation

STARTINGWhen the Prius starts to move under light acceleration, MG2 supplies all power to the front wheels (stealth mode)

Operating ModesLOW SPEEDICE and MG2 move the car

Operating ModesFULL THROTTLE & HIGH SPEED MG2 and ICE drive the car

Operating ModesDECELERATION & BRAKINGMG2 recharges the HV battery through regenerative braking

Operating ModesREVERSEAccomplished by MG2 running in reverse

Vehicle StoppedThe ICE is shut off, and both electric motors/generators are shut off as well.

Light Acceleration

When the vehicle is driven at low speeds and light acceleration, it is driven by MG2 alone.

Toyota/Lexus Power-Split SystemCurrent from the HV battery is sent through the inverter and on to MG2 to move the vehicle. When the engine is stopped (zero RPM), MG2 is turning forward (+), and this causes MG1 to turn backward (-).

Normal DrivingWhen higher vehicle speeds are required, the ICE must be started so that its output can be combined with that of MG2. Current from the HV battery is directed through the inverter and operates MG1 as a motor, turning clockwise and spinning the ICE up to 1000 RPM for starting.

Once the ICE is started, MG1 operates as a generator, but turns in the counterclockwise direction. ICE output is now divided or split between the drive wheels (ring gear) and MG1 (sun gear). Power generated by MG1 is either directed to MG2 to help move the vehicle, or is used to recharge the HV battery if necessary.

Full-Throttle Acceleration and High-Speed CruiseWhen greater acceleration is required, both MG2 and the ICE continue sending torque to the vehicle drive wheels, but MG2 can also receive power from the HV battery to increase its output.

Deceleration and BrakingAs the vehicle is decelerating, MG2 is configured as a generator. The ICE and MG1 are shut off, and current from MG2 is sent through the inverter and is then used to recharge the HV battery.

What Is Recirculated Energy?In the Toyota Hybrid System, MG2 is the main traction motor. When the vehicle is running on battery power only, MG2 is the motor that is driving it. In many situations, it is MG2 that is generating torque in conjunction with the ICE to move the vehicle.

Toyota/Lexus Power-Split SystemHowever, there are situations aside from regenerative braking where MG2 operates as a generator and MG1 is a traction motor.

ReverseIf reverse is selected, power is sent from the HV battery to the inverter and then on to MG2. MG2 operates in the reverse direction to back up the vehicle, but the other components in the drive system are turned off at this time.

Toyota/Lexus Power-Split SystemConstruction. The Toyota power-split transaxle is built with an aluminum case composed of two major assemblies. These are known as the MG1 assembly and the MG2 assembly, and each houses its respective motor/generator.

Toyota/Lexus Power-Split SystemEach of these major assemblies has its own water jacket for cooling the motor/generator windings in the housing.

Toyota/Lexus Power-Split SystemThe ICE, MG1, the power-split device, MG2, and the oil pump are all assembled on a common axis. The final drive is housed between the two major assemblies and utilizes a conventional open differential for sending torque to the front drive wheels. A chain drive attaches the ring gear of the power-split device to the counter drive gear, which drives the counter driven gear that is meshed with the ring gear of the differential assembly.

Toyota/Lexus Power-Split SystemThe ICE is connected directly to the transaxle input shaft using a damper disc mechanism.

ServiceService procedures to be performed at specified intervals include changing the transaxle oil and the coolant for the inverter (high-voltage) system. There are drain plugs for both at the bottom of the transaxle assembly.

ServiceThe transaxle is refilled through a hole in the front of the case, with the level being brought up to a specified distance from the bottom of the hole.

ServiceThe coolant is refilled at the reservoir that is located on the inverter assembly, and must be bled properly before placing the vehicle back into service.

Ford Escape Hybrid eCVTThe Ford Escape Hybrid uses an electronically controlled continuously variable transmission (eCVT) that is very similar in operation to the Toyota power-split transaxle.

The transmission control module (TCM) is an integral part of the eCVT. Coolant is sent through the water channel and absorbs heat from the ATF channel below and the heat sink for the electronic control unit above.

A small oil pump inside the eCVT circulates ATF for lubricating the gear train and for cooling the two electric motors. This oil pump is driven directly by the ICE through the planet carrier of the planetary gear set. Like the Toyota system, the oil pump will not circulate ATF unless the engine is running. This means that the gear train is splash-lubricated when the vehicle is in electric-only operation.

The eCVT is considered lubricated-for-life with a special Mercon fluid. There is a fill plug and a drain plug located on the left side of the case, but these are used only in special service situations.

Honda Belt-and-Pulley CVTDescription and operation. Are no distinct speed ranges (or shifts) in this design, as variable drive and driven pulleys are used with a special steel belt to provide nonstaged speeds forward.

If a low hydraulic pressure is applied to the drive pulley and a high hydraulic pressure is applied to the driven pulley, a low speed ratio is achieved. As the vehicle speed increases, the drive pulley will have progressively higher pressure applied to it, while the driven pulley application pressure is lowered.

The Honda CVT Belt Pushes the Driven PulleyOne unique aspect of the Honda belt-and-pulley CVT is that the belt pushes the driven pulley instead of pulling it. This is in contrast to conventional automotive belt drive systems where the belt normally pulls the driven pulley. The drive belt is made up of two steel loops of 12 layers each, which are held together by approximately 280 steel belt links, also known as elements. These elements are compressed when placed under a load as the drive pulley pushes the driven pulley.

There is no clutch or torque converter utilized in this design. Instead, the transmission input shaft is splined directly to the ICE through the drive plate and flywheel.

There are three multiple-disc clutches used in the internal gear train: one for the forward clutch, one for the reverse brake, and the third for the start clutch.

The forward clutch and the start clutch are in operation whenever the transmission is placed in a forward gear position (D or L).

Start ClutchThe start clutch has multiple responsibilities. The start clutch is engaged whenever the vehicle is moving, either in forward or reverse. When the driver releases the brake pedal, the brakes are held on briefly until the ICE restarts and the start clutch begins its engagement.

Start ClutchThe start clutch engages/disengages the secondary drive gear, and is located at the end of the driven pulley shaft.

Forward ClutchThe forward clutch engages/disengages the sun gear, and is located at the end of the drive pulley shaft. The forward clutch is supplied hydraulic pressure by its ATF feed pipe within the drive pulley shaft.

Reverse BrakeWhen the reverse brake is applied, the planet carrier is held and the sun gear (splined to the input shaft) causes the ring gear to turn backward. The ring gear is attached to the drive pulley through the forward clutch drum, so the drive pulley also turns backward. This torque is sent through the start clutch and the vehicle moves in reverse.

Reverse BrakeThe reverse brake locks the planetary carrier in the R position, and is located inside the intermediate housing around the planetary carrier. The reverse brake discs are mounted to the planetary carrier and the reverse brake plates are mounted on the intermediate housing. The reverse brake is supplied hydraulic pressure by a circuit connected to the internal hydraulic circuit.

Planetary GearsetThe planetary gear train is only used for switch the rotational direction of the pulley shafts in the R position. The planetary gear train consists of the sun gear, planetary pinion gears, and ring gear. The sun gear is connected to the input shaft with splines. The pinion gears are mounted on the planetary carrier. The planetary carrier is located on the end of the input shaft, over the sun gear. The ring gear is located in the planetary carrier, and connected to the forward clutch drum. The sun gear inputs the engine power via the input shaft to the planetary gears, and the carrier outputs the engine power. In the D, S, and L positions (forward range), the pinion gears do not rotate and revolve around the sun gear, so the carrier rotates. In the R position (reverse range), the reverse brake locks the planetary carrier, and the sun gear drives the pinion gears to rotate. The pinion gears rotate, but do not revolve around the sun gear. The pinion gears drive the ring gear in the opposite direction from the rotational direction of the sun gear.

PulleysBoth pulleys consist of a movable face and a fixed face, and the effective pulley ratio changes with engine speed. The drive pulley and the driven pulley are linked by the steel belt. To achieve a low pulley ratio, high hydraulic pressure works on the movable face of the driven pulley and reduces the effective diameter of the drive pulley, and a lower hydraulic pressure works on the movable face of the driven pulley to eliminate the steel belt slippage. To achieve a high pulley ratio, high hydraulic pressure works on the movable face of the drive pulley and reduces the effective diameter of the driven pulley, and low hydraulic pressure works on the movable face of the driven pulley to eliminate the steel belt slippage.

PumpThe belt drive, the multiple-disc clutches, and the control system would all cease to function without hydraulic pressure. This pressure is supplied by a chain-driven pump that is driven by the transmission input shaft. Since the input shaft is driven directly by the ICE, hydraulic pressure is only present when the ICE is running.

ConstructionThe transmission has a total of four parallel shafts: the input shaft, drive pulley shaft, driven pulley shaft, and the secondary gear shaft. The secondary gear shaft is comprised of the secondary driven gear and the final drive gear. The final drive gear is meshed with the final driven gear, which is attached to a conventional open differential assembly.

A transmission control module (TCM), sensors, switches, and solenoid valves are utilized to make the transmission operate smoothly and efficiently.

P positionHydraulic pressure is not applied to the start clutch, forward clutch, and reverse brake. Power is not transmitted to the secondary drive gear. The secondary drive gear is locked by the park pawl, interlocking the park gear.

N position Engine power transmitted from the flywheel drives the input shaft, but hydraulic pressure is not applied to the forward clutch and reverse brake. Power is not transmitted to the drive pulley shaft. Also hydraulic pressure is not applied to the start clutch.

D, S, and L positionsForward clutch: engaged Reverse brake: released Start clutch: engaged Hydraulic pressure is applied to the forward clutch and start clutch, and the sun gear drives the forward clutch. The forward clutch drives the drive pulley shaft, which drives the drive pulley shaft linked by the steel belt. The driven pulley shaft drives the secondary drive gear via the start clutch. Power is transmitted to the secondary driven gear and final drive gear, which in turn drives the final driven gear.

D, S, and L positions

R positionForward clutch: released Reverse brake: engaged Start clutch: engaged Hydraulic pressure is applied to the reverse brake and the start clutch, and the planetary carrier locks with the reverse brake. The sun gear drives the pinion gears to rotate, and the pinion gears drive the ring gear in the opposite direction from the rotational direction of the sun gear. The ring gear drives the drive pulley shaft via the forward clutch drum, and drive pulley shaft drives the driven pulley shaft linked by the steel belt. The driven pulley shaft drives the secondary drive gear via the start clutch. Power is transmitted to the secondary driven gear and final drive gear, which in turn drives the final driven gear.

R position

ServiceOne service item that is unique and very important is the start clutch calibration. This procedure must be performed whenever any of the following vehicle components is replaced or removed: 1. Battery 2. Backup fuse 3. TCM 4. Transmission assembly 5. Lower valve body assembly 6. Engine assembly replacement or overhaul

Honda CVTFluid level checks are performed with the vehicle level, transmission up to the operating temperature, but with the engine turned off. A dipstick is used to check the level, and fluid may be poured into the dipstick pipe to bring the level up if it is low.

Honda CVTYou must use genuine Honda CVT fluid (P/N 08200-9006)

Adaptive StrategiesOne advantage of using electronic controls on an automatic transmission is that adaptive strategies can be utilized to make shifting smooth and consistent throughout the life of the transmission. As the clutches wear, it takes progressively more time for them to apply as more fluid is required to move the piston to the point of clutch application.

***********The 4L60-E is a series of automatic transmissions from GM. Designed RWD vehicles, the series includes 4 forward gears. It is an evolution of the Turbo-Hydramatic 700R4, originally produced in 1982.**********************MG2 runs as an electric motor and gets its power from the HV battery. The engine may not run while in this mode. However, the engine starts and runs automatically if the HV battery needs charging.*As speed increases, the hybrid system starts the engine using MG1, which acts as the starter. To do this MG1 gets power from the HV battery and runs as an electric motor in reverse.The car is driven by the ICE and MG2 which runs as an electric motor to add torque to the wheels.MG2 gets power from MG1 which is rotated by the engine as a generator. MG1 may also charge the HV battery

*Power from MG1 drives MG2 as an electric motor. Engine power is split to drive the wheels and MG1 as a generator. Power from MG2 can also be increased by the HV battery*As soon as the accelerator pedal is released, the hybrid system causes MG2 to function as a generator and recharge the HV battery. In a conventional car, when you let off the accelerator and close the throttle, engine compression slows the car (engine braking). In the Prius the magnetic resistance of MG2 acting as a generator slows the car and is programmed to feel like engine braking. As the car slows, the ICE may stop running and MG1 will turn backwards.*During reverse, MG1 rotates forward and just idles. It does not generate electricity or charge the HV battery.*********************************************