Hybrid Drive Systems: Description and Operation

HYBRID DRIVE SYSTEM
The hybrid drive system switches between pure electric power, pure gasoline engine power, or a combination of electric battery and gasline engine working together.

The major components of the hybrid drive system include:
- Atkinson 2.3L gas engine
- Synchronous AC electric motor
- 330-volt drive battery in addition to the conventional 12-volt vehicle battery
- DC-to-DC converter
- Regenerative braking system
- eCVT: electronic continuously variable transmission



COOLING
The hybrid powertrain has three cooling systems:
- Conventional engine cooling system
- Hybrid battery pack cooling system
- Motor electronics cooling system

The conventional cooling system utilizes the radiator and reservoir to cool the engine and provide cabin heat. When the engine is warmed up but not running, an electric circulation pump provides cabin heat.

The hybrid battery pack cooling system uses cooling provided by the A/C system. This is similar to a rear A/C system except that the rear-cooling function is used for the hybrid battery module. A/C lines are routed under the vehicle, along the frame rail.






The Tribute uses a pump driven cooling system - the motor electronics cooling system (MECS). This system transfers heat generated by the electronically controlled continuously variable transmission (eCVT) and the hybrid electric vehicle DC/DC converter to the atmosphere. The system uses a coolant-to-air radiator design.

CHARGING
The charging system includes a conventional 12-volt battery and a new 330-volt battery.

The 12-volt battery:
- is charge by the DC/DC converter.
- is not the source to spin the engine during cranking.
- provides for the low voltage needs of the Tribute, such as the electric power assisted steering, headlights, climate control and audio.

There is no belt-driven generator on the Tribute Hybrid. This function is performed by the generator inside the eCVT.

The 330-volt battery, known as the traction battery, is designed to provide electrical power to the traction motor, generator motor and DC/DC converter.






TRANSAXLE
The hybrid combines an electronic transmission - electronically controlled continuously variable transmission, eCVT - with the 2.3L Atkinson engine to effectively meet peak demands for power and to capture energy that is wasted during braking. Captured energy is converted to electricity and stored in the high voltage battery.

The eCVT consists of:
- traction motor
- generator
- planetary gear set
- a transmission control module (TCM) located on top of the eCVT case






The planetary gear set connects the engine, traction motor, and generator with the drive wheels. Based on commands from the PCM for optimum fuel efficiency, the TCM continuously adjusts the contribution of the engine, traction motor and generator.

BRAKES
A new electro-hydraulic brake (EHB) system is used that replaces a portion of the conventional hydraulic brake system.

The EHB system includes:
- A new actuation control unit (ACU) which is similar to a modified master cylinder.
- A modified brake system control module (BSCM) assembly (including the hydraulic control unit (HCU))

The EHB system has no conventional brake booster. The booster was deleted because the gasoline engine does not run constantly and cannot provide a sufficient vacuum to the braking system.