Systems and method for exhaust gas recirculation

1. An exhaust gas recirculation (EGR) system, comprising:

an EGR passage coupling an engine exhaust system to an engine intake system;

an EGR cooler positioned in the EGR passage;

a recirculation passage, coupling an outlet of the EGR cooler to an inlet of the EGR cooler;

an EGR cooler recirculation valve positioned in the recirculation passage and controllable to change a flow of exhaust gas though the recirculation passage; and

a controller configured to adjust a position of the EGR cooler recirculation valve based on a temperature at the inlet of the EGR cooler.

2. The EGR system of claim 1 , wherein the controller is configured to receive, from a temperature sensor, a signal indicative of the temperature of the inlet of the EGR cooler and to open the EGR cooler recirculation valve responsive to the temperature exceeding a threshold temperature.

3. The EGR system of claim 1 , wherein the controller is configured to estimate the temperature at the inlet of the EGR cooler as a function of engine output and to open the EGR cooler recirculation valve responsive to the temperature exceeding a threshold temperature.

4. The EGR system of claim 1 , further comprising an EGR valve positioned to control the flow of exhaust gas through the EGR passage.

5. The EGR system of claim 4 , wherein the controller is configured to adjust a position of the EGR valve based on a target intake oxygen fraction.

6. The EGR system of claim 5 , wherein the controller is configured to further adjust the position of the EGR valve based on one or more of the temperature at the inlet of the EGR cooler and the position of the EGR cooler recirculation valve.

7. The EGR system of claim 1 , further comprising a turbocharger including a turbine positioned in the engine exhaust system and a compressor positioned in the engine intake system, an amount of boost pressure created by the turbocharger controlled by a turbine bypass valve coupled across the turbine, and wherein the controller is configured to adjust a position of the turbine bypass valve based on one or more of the temperature at the inlet of the EGR cooler or the position of the EGR cooler recirculation valve.

8. The EGR system of claim 1 , further comprising a venturi fluidically coupling the EGR passage and the recirculation passage to the inlet of the EGR cooler.

9. The EGR system of claim 1 , wherein the EGR cooler is an air-to-liquid EGR cooler comprising one or more coolant passages configured to flow coolant and one or more air passages configured to flow the exhaust gas.

10. A system, comprising:

an engine having a first subset of cylinders and a second subset of cylinders;

a first exhaust manifold coupled to the first subset of cylinders and a second exhaust manifold coupled to the second subset of cylinders;

an EGR passage coupling the first exhaust manifold to an intake manifold of the engine;

an EGR cooler positioned in the EGR passage;

a recirculation passage coupling the EGR passage downstream of the EGR cooler to the EGR passage upstream of the EGR cooler via a venturi;

an EGR cooler recirculation valve positioned in the recirculation passage; and

a controller configured to adjust a position of the EGR cooler recirculation valve based on a temperature at an inlet of the EGR cooler.

11. The system of claim 10 , further comprising an exhaust passage coupling the first exhaust manifold and the second exhaust manifold to a turbocharger turbine.

12. The system of claim 11 , further comprising an EGR metering valve controlling a flow of exhaust from the first exhaust manifold to the EGR passage and an EGR bypass valve controlling the flow of exhaust from the first exhaust manifold to the exhaust passage.

13. The system of claim 10 , wherein the controller is configured to adjust the position of the EGR cooler recirculation valve to be more open as the temperature at the inlet of the EGR cooler increases.

14. The system of claim 10 , wherein the controller is configured to adjust the position of the EGR cooler recirculation valve based on an amount of condensate in the EGR cooler.

15. A method, comprising:

with an exhaust gas recirculation (EGR) cooler recirculation valve positioned in a recirculation passage, changing a flow of exhaust gas though the recirculation passage, wherein the recirculation passage couples an outlet of an EGR cooler to an inlet of the EGR cooler, the EGR cooler is positioned in an EGR passage, and the EGR passage couples an engine exhaust system to an engine intake system; and

with a controller, adjusting a position of the EGR cooler recirculation valve based on a temperature at the inlet of the EGR cooler.

16. The method of claim 15 , further comprising, with the controller, receiving from a temperature sensor a signal indicative of the temperature of the inlet of the EGR cooler, wherein adjusting the position comprises opening the EGR cooler recirculation valve responsive to the temperature exceeding a threshold temperature.

17. The method of claim 15 , further comprising, with the controller, estimating the temperature at the inlet of the EGR cooler as a function of engine output, wherein adjusting the position comprises opening the EGR cooler recirculation valve responsive to the estimated temperature exceeding a threshold temperature.

18. The method of claim 15 , further comprising, with the controller, adjusting a position of an EGR valve, which controls the flow of exhaust gas through the EGR passage, based on a target intake oxygen fraction.

19. The method of claim 18 , further comprising, with the controller, further adjusting the position of the EGR valve based on one or more of the temperature at the inlet of the EGR cooler or the position of the EGR cooler recirculation valve.

20. The method of claim 15 , further comprising, with the controller, adjusting a position of a turbine bypass valve based on one or more of the temperature at the inlet of the EGR cooler or the position of the EGR cooler recirculation valve, wherein an amount of boost pressure created by a turbocharger is controlled by the turbine bypass valve coupled across a turbine of the turbocharger, the turbocharger including the turbine positioned in the engine exhaust system and a compressor positioned in the engine intake system.