Method for controlling exhaust gas heat recovery systems in vehicles

1. A method of operating a vehicle including an engine, a transmission, an exhaust gas heat recovery (EGHR) heat exchanger, an oil-to-water heat exchanger providing selective heat-exchange communication between the engine and transmission, and a transmission radiator, the method comprising:

controlling a two-way valve, wherein the two-way valve is configured to be set to one of an engine position and a transmission position, wherein the engine position allows heat-exchange communication between the EGHR heat exchanger and the engine and does not allow heat-exchange communication between the EGHR heat exchanger and the oil-to-water heat exchanger, and the transmission position allows heat-exchange communication between the EGHR heat exchanger, the oil-to-water heat exchanger, and the engine;

monitoring an ambient air temperature;

comparing the monitored ambient air temperature to a predetermined cold ambient temperature;

if the monitored ambient air temperature is greater than the predetermined cold ambient temperature, setting the two-way valve to the transmission position;

controlling a transmission thermostat, wherein the transmission thermostat is configured to be set to one of an EGHR position and a radiator position, wherein the EGHR position allows heat-exchange communication between the transmission and the oil-to-water heat exchanger, and the radiator position allows heat-exchange communication between the transmission and the transmission radiator and blocks heat-exchange communication between the transmission and the oil-to-water heat exchanger, and wherein the transmission thermostat has three ports:

an inlet port in fluid-flow communication with an oil outlet of the transmission,

a first outlet port in fluid-flow communication with the oil-to-water heat exchanger, and

a second outlet port in fluid-flow communication with the transmission radiator, wherein the EGHR position allows fluid-flow communication between the inlet port and the first outlet port and the radiator position allows fluid-flow communication between the inlet port and the second outlet port;

monitoring a transmission oil temperature;

comparing the monitored transmission oil temperature to a transmission thermostat temperature;

if the monitored transmission oil temperature is above the transmission thermostat temperature, setting the transmission thermostat to the radiator position;

controlling an engine thermostat, wherein the engine thermostat is configured to be set to one of an open position and a closed position, wherein the open position allows heat-exchange communication between the engine and the engine radiator and the closed position blocks heat-exchange communication between the engine and the engine radiator;

monitoring an engine water temperature;

comparing the monitored engine water temperature to an engine thermostat temperature;

if the monitored engine water temperature is above the engine thermostat temperature, setting the engine thermostat to the open position;

wherein controlling the two-way valve includes providing an engine signal configured to place the two-way valve into the engine position;

wherein the transmission thermostat temperature is within five degrees Celsius of the engine thermostat temperature;

if the monitored ambient air temperature is below the predetermined cold ambient temperature, comparing the monitored engine water temperature to an engine target temperature;

if the monitored engine water temperature is below the engine target temperature, setting the two-way valve to the engine position;

if the monitored engine water temperature is above the engine target temperature, monitoring for an auto-stop mode, wherein the auto-stop mode occurs when the engine is not producing positive torque; and

if the engine is not in the auto-stop mode, setting the two-way valve to the transmission position.

2. The method of claim 1 , further comprising:

if the engine is in the auto-stop mode, comparing the monitored transmission oil temperature to a transmission target temperature;

if the monitored transmission oil temperature is above the transmission target temperature, setting the two-way valve to the engine position; and

if the monitored transmission oil temperature is below the transmission target temperature, setting the two-way valve to the transmission position.

3. The method of claim 2 , wherein the two-way valve is set to the transmission position whenever the engine signal is not provided, such that the two-way valve is configured to default to the transmission position when unpowered.

4. A method of operating a vehicle including an engine, a transmission, an exhaust gas heat recovery (EGHR) heat exchanger, and an oil-to-water heat exchanger providing selective heat-exchange communication between the engine and transmission, the method comprising:

controlling a two-way valve, wherein the two-way valve is configured to be set to one of an engine position and a transmission position in response to an engine signal which is configured to place the two-way valve into the engine position, wherein the engine position allows heat-exchange communication between the EGHR heat exchanger and the engine and does not allow heat-exchange communication between the EGHR heat exchanger and the oil-to-water heat exchanger, and the transmission position allows heat-exchange communication between the EGHR heat exchanger, the oil-to-water heat exchanger, and the engine;

monitoring an ambient air temperature;

comparing the monitored ambient air temperature to a predetermined cold ambient temperature; and

if the monitored ambient air temperature is greater than the predetermined cold ambient temperature, setting the two-way valve to the transmission position, wherein the two-way valve is set to the transmission position whenever the engine signal is not provided, such that the two-way valve is configured to default to the transmission position when unpowered; and

if the monitored ambient air temperature is below the predetermined cold ambient temperature, comparing the monitored engine water temperature to an engine target temperature:

if the monitored engine water temperature is below the engine target temperature, setting the two-way valve to the engine position, and

if the monitored engine water temperature is above the engine target temperature, monitoring for an auto-stop mode, wherein the auto-stop mode occurs when the engine is not producing positive torque:

if the engine is not in the auto-stop mode, setting the two-way valve to the transmission position, and

if the engine is in the auto-stop mode, comparing the monitored transmission oil temperature to a transmission target temperature:

if the monitored transmission oil temperature is above the transmission target temperature, setting the two-way valve to the engine position, and

if the monitored transmission oil temperature is below the transmission target temperature, setting the two-way valve to the transmission position.

5. The method of claim 4 , wherein the vehicle further includes a transmission radiator, and further comprising:

controlling a transmission thermostat, wherein the transmission thermostat is configured to be set to one of an EGHR position and a radiator position, wherein the EGHR position allows heat-exchange communication between the transmission and the oil-to-water heat exchanger, and the radiator position allows heat-exchange communication between the transmission and the transmission radiator and blocks heat-exchange communication between the transmission and the oil-to-water heat exchanger;

monitoring a transmission oil temperature;

comparing the monitored transmission oil temperature to a transmission thermostat temperature; and

if the monitored transmission oil temperature is above the transmission thermostat temperature, setting the transmission thermostat to the radiator position.

6. The method of claim 5 ,

wherein the transmission thermostat has three ports:

an inlet port in fluid-flow communication with an oil outlet of the transmission,

a first outlet port in fluid-flow communication with the oil-to-water heat exchanger, and

a second outlet port in fluid-flow communication with the transmission radiator; and

wherein the EGHR position allows fluid-flow communication between the inlet port and the first outlet port and the radiator position allows fluid-flow communication between the inlet port and the second outlet port.

7. The method of claim 6 ,

wherein the transmission thermostat has three ports:

an inlet port in fluid-flow communication with the oil-to-water heat exchanger and an oil outlet of the transmission,

a first outlet port in fluid-flow communication with the transmission, and

a second outlet port in fluid-flow communication with the transmission radiator; and

wherein the EGHR position allows fluid-flow communication between the inlet port and the first outlet port and the radiator position allows fluid-flow communication between the inlet port and the second outlet port.

8. The method of claim 7 , wherein the transmission thermostat temperature is within five degrees Celsius of the engine thermostat temperature.