System and method for determining engine knock

Abstract

Systems and methods for detecting and controlling knock in an engine are presented. In one example, engine knock sensors are selected based on whether or not certain cylinders are activated and combusting air and fuel or deactivated and not combusting air and fuel. Output of selected knock sensors is the basis for adjusting engine spark timing.

The invention claimed is: 
     
       1. A vehicle system, comprising:
 an engine including one or more cylinder poppet valve deactivating mechanisms and a knock sensor; and 
 a controller including non-transitory executable instructions, which, when executed by the controller, cause the controller to select a knock reference value from a first knock reference value and a second knock reference value, divide an integrated output of the knock sensor by the first knock reference value to provide an engine knock indication during a first condition, divide the integrated output of the knock sensor by the second knock reference value to provide the engine knock indication during a second condition, and adjust engine spark timing in response to the engine knock indication. 
 
     
     
       2. The vehicle system of  claim 1 , where the second condition is the first knock reference value greater than a threshold value. 
     
     
       3. The vehicle system of  claim 1 , further comprising additional instructions to divide the integrated output of the knock sensor by the second knock reference value in response to deactivating one or more valves of a cylinder. 
     
     
       4. The vehicle system of  claim 1 , further comprising additional instructions to divide the integrated output of the knock sensor by a third knock reference value in response to deactivating fuel flow to a cylinder and flowing air through the cylinder. 
     
     
       5. The vehicle system of  claim 1 , further comprising instructions to filter output of the knock sensor to provide the first knock reference value. 
     
     
       6. The vehicle system of  claim 1 , further comprising additional instructions to save the first knock reference value to memory in response to deactivating one or more cylinders of the engine.