Exhaust Gas Heat Recovery System
The exhaust gas heat recovery system utilizes an exhaust mounted air-to-liquid heat exchanger (2) to transfer wasted energy (heat) from the exhaust to help warm the engine coolant faster. An exhaust-mounted dual-butterfly valve (1) allows engine exhaust to either flow across the exchanger or to bypass the exchanger.
Exhaust gas heat recovery increases fuel economy by allowing the engine to enter Autostop sooner and reducing cold engine friction losses. A small fuel economy benefit also occurs when warmer passenger cabin air heats up a cold Hybrid/EV battery pack.
The Exhaust Heat Exchanger assembly contains an internal coolant heat exchanger, a dual butterfly valve and a Local Interconnect Network (LIN) controlled valve actuator. The engine control module provides a serial data Inhibit status as well as engine coolant temperature to the hybrid/EV powertrain control module 2. The hybrid/EV powertrain control module 2 will then transmit a LIN message to the valve actuator to position the dual butterfly valve position to either Heat or Bypass based upon engine coolant temperature (ECT) and outside air temperature (OAT).
Heat recovery occurs until the desired ECT temperature, +/- 5°C (9°F) is attained:
| OAT Range | Heat mode until ECT Reaches |
|---|---|
| -40°C (-40°F) to -20°C (-4°F) | 95°C (203°F) |
| -20°C (-4°F) to 0°C (32°F) | 90°C (194°F) |
| 0°C (32°F) to 20°C (68°F) | 85°C (185°F) |
| 20°C (68°F) or greater | 80°C (176°F) |
Additional requirements for Heat recovery mode:
- Engine speed is 700 RPM or greater.
- Transmission gear range selector is not in Park.
- At least 2 seconds have occurred since a warm engine start of 50°C (122°F) or greater.
OR
At least 5 seconds have occurred since a cold engine start of less than 50°C (122°F).
OR
At least 1 second has occurred after a transition from Autostop to engine running.
A valve position learning process is performed once at the beginning of every ignition-ON key cycle. The hybrid/EV powertrain control module 2 commands the dual-butterfly valve actuator between fully closed and fully open, if the valve command is not close to the valve position a DTC is set.
After an Autostop, the status transitions to Unlearned for the remainder of the ignition key cycle.
The engine/passenger compartment heater cooling system circulates a 50/50 mixture of DEX-COOL® and clean, drinkable water.