Methods and system for operating an engine

Abstract

Systems and methods for operating an engine of a vehicle that may be automatically stopped and started are disclosed. In one example, a speed at which a vehicle system induced automatic engine stop inhibit request is cleared may be adjusted to permit automatic engine stopping during a wide variety of driving conditions so that fuel may be conserved and the possibility of disturbing vehicle occupants may be reduced.

The invention claimed is: 
     
       1. A system, comprising:
 an engine; and 
 a controller including executable instructions stored in non-transitory memory to automatically stop the engine, monitor vehicle speed while the engine is automatically stopped, automatically restart the engine in response to a vehicle system induced automatic engine stop inhibit request, and clear the vehicle system induced automatic engine stop inhibit request in response to a lowest vehicle speed achieved while the engine was automatically stopped. 
 
     
     
       2. The system of  claim 1 , where the lowest vehicle speed is a speed of a vehicle that the engine propels. 
     
     
       3. The system of  claim 1 , further comprising additional instructions to assert the vehicle system induced automatic engine stop inhibit request in response to a battery state of charge. 
     
     
       4. The system of  claim 1 , further comprising additional instructions to assert the vehicle system induced automatic engine stop inhibit request in response to a vacuum level. 
     
     
       5. The system of  claim 1 , further comprising additional instructions to assert the vehicle system induced automatic engine stop inhibit request in response to a vehicle climate control system. 
     
     
       6. The system of  claim 1 , where clearing the vehicle system induced automatic engine stop inhibit request allows the engine to automatically stop. 
     
     
       7. An engine operating method, comprising:
 automatically stopping an engine; 
 automatically starting the engine after automatically stopping the engine in response to a vehicle system induced automatic engine stop inhibit request; and 
 adjusting a vehicle speed at which the vehicle system induced automatic engine stop inhibit request is cancelled responsive to a lowest vehicle speed achieved while the engine was automatically stopped. 
 
     
     
       8. The method of  claim 7 , further comprising adjusting the vehicle speed at which the vehicle system induced automatic engine stop inhibit request is cancelled responsive to a predetermined offset vehicle speed. 
     
     
       9. The method of  claim 7 , where the vehicle system induced automatic engine stop inhibit request is asserted to automatically start the engine. 
     
     
       10. The method of  claim 9 , where the vehicle system induced automatic engine stop inhibit is asserted in response to a battery state of charge. 
     
     
       11. The method of  claim 9 , where the vehicle system induced automatic engine stop inhibit is asserted in response to a low vacuum level. 
     
     
       12. The method of  claim 9 , where the vehicle system induced automatic engine stop inhibit is asserted in response to a vehicle passenger cabin climate control device request. 
     
     
       13. The method of  claim 9 , where the vehicle system induced automatic engine stop inhibit is asserted in response to a steering angle that is greater than a threshold. 
     
     
       14. The method of  claim 7 , further comprising cancelling the vehicle system induced automatic engine stop inhibit request in response to a speed of a vehicle exceeding the lowest vehicle speed achieved while the engine was automatically stopped plus an offset speed. 
     
     
       15. An engine operating method, comprising:
 automatically stopping an engine a first time; 
 restarting the engine at a first vehicle speed after stopping the engine the first time in response to a vehicle system induced automatic engine stop inhibit request, and cancelling the vehicle system induced automatic engine stop inhibit request when a vehicle reaches first vehicle speed plus an offset speed; 
 automatically stopping the engine a second time; and 
 restarting the engine at a second vehicle speed after stopping the engine the second time in response to a vehicle system induced automatic engine stop inhibit request, and cancelling the vehicle system induced automatic engine stop inhibit request when a vehicle reaches second vehicle speed plus an offset speed. 
 
     
     
       16. The method of  claim 15 , where cancelling the vehicle system induced automatic engine stop inhibit request permits the engine to be automatically stopped. 
     
     
       17. The method of  claim 15 , where the vehicle system induced automatic engine stop inhibit request prevents the engine from being automatically stopped. 
     
     
       18. The method of  claim 15 , where the engine is coupled to an automatic transmission. 
     
     
       19. The method of  claim 15 , where the engine is coupled to a manual transmission. 
     
     
       20. The method of  claim 15 , where the first speed is different from the second speed, and where the first speed is a lowest vehicle speed achieved while the engine was automatically stopped the first time.