Continuously Variable Transmission/Transaxle: Description and Operation
Transaxle Description
Transaxle Components
The Electronically Controlled Continuously Variable Transmission (eCVT) has the following internal components:
- Traction motor
- Generator
- Transmission Control Module (TCM)
- Planetary gearset
Range Selection
Park
With the range selector in PARK:
- the parking pawl locks the output shaft to the case.
- the engine may be started.
- the ignition key can be removed.
- the ignition switch can be cycled from OFF to START or RUN.
Reverse
With the range selector in REVERSE:
- the vehicle may be operated in a rearward direction.
- reversing lamps are illuminated.
- if the vehicle is not started, there is no reverse gear engagement.
Neutral
With the range selector in NEUTRAL:
- no power flows through the transmission.
- the output shaft is disengaged from the drive wheels.
Drive
The range selector DRIVE position provides:
- low speed driving.
- acceleration.
- cruise conditions.
- deceleration.
- maximum fuel economy during normal operation.
If the vehicle is not started, there is no forward gear engagement.
Low
The range selector LOW position provides:
- engine braking.
- improved traction on slippery roads.
If the vehicle is not started, there is no forward gear engagement.
Silent Key Start (SKS)
The Silent Key Start (SKS) is essentially the ability for the customer to get in the vehicle, turn the key to crank, and start the vehicle (it would enter run mode) with the engine OFF.
The transaxle is required to permit the vehicle to operate in a silent start mode. If both the engine coolant and the transmission fluid temperatures are between 4°C-43°C (40°F-110°F) when the driver requests the vehicle to start, the vehicle will enter run mode with the engine off.
The engine will remain off until the driver shifts out of PARK and one or more of the following conditions are met:
- the vehicle speed is greater than 16 km/h (10 mph).
- the distance traveled is greater than 3 m (10 ft).
- the accelerator pedal position is greater than 5 counts about 1%.
The engine may pull up at any time to facilitate the climate control function or to charge the high voltage battery.
Silent Drive Away (SDA)
Silent Drive Away (SDA) is the ability for the customer to get in, silently start the vehicle and drive away with the engine OFF.
The transaxle is required to permit the vehicle to operate in a silent drive away mode. If both the engine coolant and the transaxle fluid temperatures are greater than 43°C (110°F) when the driver requests the vehicle to start, the vehicle will enter run mode and can be driven with the engine off.
The engine will remain off until the driver shifts out of PARK and one or more of the following conditions are met:
- the vehicle speed is greater than 32 km/h (20 mph).
- the distance traveled is greater than 50 m (150 ft).
- the driver demanded power is greater than the lesser of either 8 kWh or the battery discharge limit existing during the silent driving event.
The engine may pull up at any time to facilitate the climate control function or to charge the high voltage battery.
Brake Shift Interlock System
The brake shift interlock system prevents a shift out of PARK unless the brake pedal is depressed. The brake shift interlock system has a Brake Shift Interlock Actuator (BSIA) mounted on the floor selector lever assembly. If the ignition switch is in the RUN position, the BSIA is continually on unless the brake pedal is depressed.
External Controls
The external control of the eCVT is mechanically controlled by a selector lever cable connected to the floor selector lever. The floor shifter position determines PARK, REVERSE, NEUTRAL, DRIVE and low modes.
Motor Electronics Cooling System (MECS)
The vehicle uses a pump driven cooling system (referred to as the Motor Electronics Cooling System (MECS)) to transfer heat generated by the eCVT and the Hybrid Electric Vehicle (HEV) battery pack to the atmosphere. The system uses a coolant-to-air radiator design.
The MECS pump is an electric pump that runs any time the ignition is in the ON position. Unlike traditional cooling systems, there is no thermostat in the MECS, so coolant flow should be continuous and considerably less than traditional powertrain cooling systems.
The flow direction is from the degas bottle and DC/DC converter to the MECS pump through the eCVT, then through the MECS radiator from the LH to RH side of the vehicle back to the degas bottle.
The MECS cooling pump will make an audible noise if it is running and a slight vibration may be felt. Flow can be verified by visually inspecting for coolant flow into the degas bottle. Only a portion of the coolant flow is diverted to the degas bottle via the "T" in the coolant outlet hose.
