Method and system for exhaust gas recirculation and heat recovery

Patent metadata

Field	Value
Publication number	US-10323587-B2
Application number	US-201615341973-A
Country	US
Kind code	B2
Filing date	Nov 2, 2016
Priority date	Nov 2, 2016
Publication date	Jun 18, 2019
Grant date	Jun 18, 2019

Abstract

Methods and systems are provided for exhaust heat recovery and EGR cooling via a single heat exchanger. In one example, a method may include selecting a specific mode of operation of an engine exhaust system with the heat exchanger based on engine operating conditions and an estimated fuel efficacy factor. The fuel efficiency factor may take into account fuel efficacy benefits from EGR and exhaust heat recovery.

First claim

The invention claimed is:

1. An engine method, comprising:
operating an exhaust system in a first mode with exhaust flowing to a tailpipe via a heat exchanger,
operating the exhaust system in a second mode with a first portion of exhaust recirculating to an intake manifold, and a second portion of exhaust flowing to the tailpipe, via the heat exchanger,
estimating a level of condensate accumulated at the heat exchanger, and, in response to a higher than threshold condensate level, operating the exhaust system in the first mode.

2. The method of claim 1 , wherein operating in each of the first mode and the second mode includes flowing an engine coolant through the heat exchanger, transferring heat from the exhaust to the engine coolant, then flowing the engine coolant through one or more of an engine, a heater core, and a radiator, then transferring heat from the engine coolant to one or more of the engine, the heater core, and the radiator, the method further comprising heating the engine by drawing heat from the engine coolant based on an engine heating demand and heating a passenger cabin by drawing heat from the heater core based on a cabin heating demand.

3. The method of claim 1 , further comprising:
operating the exhaust system in a third mode with a third portion of exhaust recirculating to the intake manifold via the heat exchanger, and a fourth portion of exhaust concurrently flowing directly to the tailpipe; and
operating the exhaust system in a fourth mode with exhaust flowing directly to the tailpipe, bypassing the heat exchanger.

4. The method of claim 3 , further comprising selecting between the first, second, third, and fourth modes based on each of an engine temperature and an engine load, wherein the first mode is selected in response to a lower than threshold engine temperature, the fourth mode is selected in response to each of a higher than threshold engine temperature and a higher than threshold engine load, and wherein one of the second mode and the third mode is selected in response to each of the higher than threshold engine temperature and a lower than threshold engine load.

5. The method of claim 4 , wherein the selecting further includes selecting between the second and third modes by estimating a first fuel efficiency factor based on a fuel efficiency benefit achieved by operating the exhaust system in the second mode, estimating a second fuel efficiency factor based on the fuel efficiency benefit achieved by operating the exhaust system in the third mode, comparing the first fuel efficiency factor to the second fuel efficiency factor, and selecting one of the second and third modes having a higher of the first and second fuel efficiency factors.

6. The method of claim 5 , wherein the fuel efficiency benefit in each of the second mode and the third mode is calculated based on the third portion of exhaust recirculated to the intake manifold, a temperature of the recirculated exhaust, and a change in coolant temperature, the fuel efficiency benefit increasing with each of an increase in the third portion of exhaust recirculated, a decrease in the temperature of the recirculated exhaust, and an increase in the change in coolant temperature.

7. The method of claim 3 , wherein the heat exchanger is coupled to a bypass passage, downstream of one or more exhaust catalysts and the third portion of exhaust is recirculated to the intake manifold via an exhaust gas recirculation (EGR) passage coupled downstream of the heat exchanger.

8. The method of claim 7 , wherein, during the first mode, a diverter valve coupled to a junction of the bypass passage and a main exhaust passage downstream of the heat exchanger is in a first, fully open position and an EGR valve is closed; during the second mode, the diverter valve is in the first position and the EGR valve is open; during the third mode, the diverter valve is in a second, fully closed position and the EGR valve is open; during the fourth mode, the diverter valve is in the second position and the EGR valve is closed; and, in each of the second mode and the third mode, an opening of the EGR valve is adjusted based on an amount of EGR requested, the opening increasing as the amount of EGR requested increases.

9. The method of claim 8 , wherein the first, fully open position of the diverter valve enables exhaust to be routed to the tailpipe via the bypass passage, and the second, fully closed position of the diverter valve disables exhaust flow to the tailpipe via the bypass passage.

10. The method of claim 1 , wherein, during the second mode, a ratio of the first portion of exhaust to the second portion of exhaust is based on an EGR demand, the first portion of exhaust increased as the EGR demand increases.

11. A method for an engine coupled in a vehicle, comprising:
during an engine cold-start,
operating an engine exhaust system in a first mode by closing an exhaust gas recirculation (EGR) valve, and actuating a diverter valve to a first position to enable exhaust flow to a tailpipe via a heat exchanger in a bypass passage;
transferring heat from exhaust to a coolant circulating through the heat exchanger; and
circulating the coolant through the engine and a heater core to increase one or more of engine temperature and vehicle cabin temperature; and

when conditions for the engine cold-start are not prevalent,
operating the engine exhaust system in a third mode with the EGR valve open and the diverter valve in a second position, where the third mode includes cooling the exhaust via the heat exchanger, and then flowing the cooled exhaust from the heat exchanger to an intake manifold of the engine without flowing the cooled exhaust through any additional heat exchangers between the heat exchanger and the intake manifold; and
when a level of condensate accumulated at the heat exchanger or a delivery passage EGR is above a threshold level,
operating the engine exhaust system in the first mode.

12. The method of claim 11 , wherein the engine exhaust system is further operated in the third mode responsive to an EGR demand being received at a higher engine temperature.

13. The method of claim 12 , wherein an opening of the EGR valve is adjusted based on the EGR demand.

14. The method of claim 13 , further comprising,
during the third mode, circulating the coolant at the heat exchanger, and transferring heat from the exhaust to the coolant to cool the exhaust via the heat exchanger.

15. The method of claim 14 , wherein operating in the third mode includes selecting the third mode in response to the conditions for the engine cold-start not being prevalent and based on a fuel efficiency of the third mode being higher than a fuel efficiency of a second mode, wherein in the second mode the EGR valve is open and the diverter valve is in the first position.

16. An engine system coupled to a vehicle, comprising:
an engine intake manifold;
an engine exhaust system with an exhaust passage and a bypass passage, the exhaust passage including an exhaust humidity sensor, an exhaust temperature sensor, an exhaust pressure sensor, an exhaust catalyst, and a muffler, the bypass passage coupled to the exhaust passage from downstream of the catalyst to upstream of the muffler, the bypass passage including a heat exchanger;
a coolant system fluidly coupled to the heat exchanger, an engine block, and a heater core, the coolant system including an engine coolant temperature sensor;
a diverter valve coupled to the exhaust passage regulating exhaust flow via the bypass passage;
an EGR passage with an EGR valve for recirculating exhaust from the bypass

Assignees

• Ford Global Tech Llc

Inventors

• Schwartz William Samuel
• Mcconville Gregory Patrick
• Baker Chad Allan
• Blatchley Timothy Noah
• Uhrich Michael James

Classifications

• F02D41/1446

  the characteristics being exhaust temperatures · CPC title

• F02D41/064

  at cold start (F02D41/067 takes precedence) · CPC title

• F02M26/14

  in relation to the exhaust system · CPC title

• F02N19/10

  by heating of engine coolants · CPC title

• F02M26/33

  controlling the temperature of the recirculated gases · CPC title