Fail-safe engine cooling control algorithm for hybrid electric vehicle

Abstract

This invention is a fail-safe algorithm for a hybrid electric vehicle (HEV). The method and system allow an HEV to continue to operate without damage after the engine cooling system is compromised, such as when there has been a total loss of engine coolant. Goals include a fail-safe vehicle strategy to maintain acceptable engine temperatures and minimal noise, vibration and harshness (NVH), while greatly extending the vehicle's operating range. First is a determination if the vehicle can rely on an electric traction motor's torque output to operate the vehicle. If engine operation is needed, engine fueling and firing of the cylinders is alternated to allow those cylinders to cool when no combustion is occurring. Engine speed is also optimized. NVH must remain within acceptable levels under most operating conditions. Further, the HEV parallel mode of operation (i.e., with a generator motor brake applied) is prohibited. And finally, the speed of at least one engine compartment cooling fan is optimized to minimize electrical load while maximizing airflow.

I claim:  
     
         1 . A fail-safe engine cooling control system for a hybrid electric vehicle (HEV) when the engine temperature exceeds a predetermined calibratable level comprising: 
 An electric traction motor;    An engine;    An Engine temperature sensor;    A system to cool the engine, whereby safe and efficient engine operating temperatures are maintained;    A Vehicle System Controller;    A fail-safe system to assure that in the event the system to cool the engine fails, acceptable engine temperatures are maintained while vehicle operating range is extended, adequate power is provided to the vehicle, and noise, vibration and harshness (NVH) is kept to a minimum.    
     
     
         2 . The fail-safe cooling system of  claim 1 , wherein adequate power to the vehicle is limited to half its normal operating power.  
     
     
         3 . The fail-safe cooling system of  claim 1 , further comprising a determination of whether to halt engine operation and rely on the power output of the electric traction motor.  
     
     
         4 . The fail-safe cooling system of  claim 1 , wherein NVH is kept to a minimum by not allowing the HEV to operate in a parallel mode, whereby the generator used to reduce torque pulses from the engine.  
     
     
         5 . The fail-safe cooling system of  claim 1 , further comprising at least one engine compartment cooling fan controlled to an optimal speed to minimize electrical load while maximizing air circulation based on vehicle speed and engine temperature.  
     
     
         6 . The fail-safe cooling system of  claim 2 , whereby engine power is reduced to half its normal operating power by a fuel cut method to one or more cylinders in an alternating fashion.  
     
     
         7 . The fail-safe cooling system of  claim 3 , wherein the determination to halt engine operation is based on driver demand, vehicle speed, battery state of charge, or air conditioning requests.  
     
     
         8 . A fail-safe engine cooling control method for a hybrid electric vehicle (HEV) when engine temperature exceeds a predetermined calibratable level comprising the steps of: 
 Sensing Engine temperature;    Cooling the engine, whereby safe and efficient engine operating temperatures are maintained;    Controlling Vehicle systems; and    Assuring through a fail-safe system that in the event the system to cool the engine fails, comprising the steps of maintaining acceptable engine temperatures, extending vehicle operating range, powering the vehicle adequately, and minimizing noise, vibration and harshness (NVH).    
     
     
         9 . The fail-safe cooling method of  claim 8 , wherein powering the vehicle adequately comprises limiting the engine to half its normal operating power.  
     
     
         10 . The fail-safe cooling method of  claim 8 , further comprising the step of determining whether to halt engine operation and rely on the power output of the electric traction motor.  
     
     
         11 . The fail-safe cooling method of  claim 8 , wherein the step of minimizing NVH is achieved by prohibiting the HEV to operate in a parallel mode, whereby fixing a generator speed to a zero is prohibited.  
     
     
         12 . The fail-safe cooling method of  claim 8 , further comprising the step of controlling at least one engine compartment cooling fan to an optimal speed minimizing electrical load while maximizing air circulation based on vehicle speed and engine temperature.  
     
     
         13 . The fail-safe cooling method of  claim 9 , whereby powering the vehicle adequately is limited to reducing the engine to half its normal operating power by a cutting fuel to half the cylinders in an alternating fashion.  
     
     
         14 . The fail-safe cooling method of  claim 10 , wherein determining whether to halt engine operation is based on driver demand, vehicle speed, battery state of charge, or air conditioning requests.