Method and Apparatus for Starting an Engine in a Hybrid Vehicle

Abstract

A method and apparatus for starting an engine in a hybrid vehicle being driven by an electric motor is disclosed. The motor is operably configured to deliver mechanical power through an automatic transmission to at least one vehicle drive wheel to cause an acceleration of the vehicle. The method involves coupling the engine to the motor to cause an inertial load on the motor thus causing the motor to decelerate to a reduced rotational speed to provide a starting torque to the engine for starting the engine, and causing the automatic transmission to change gear ratio to a target gear ratio associated with the reduced rotational speed while causing the motor to decelerate, the motor being operable to deliver increased torque at the reduced rotational speed, thereby generally maintaining the acceleration of the vehicle.

What is claimed is: 
     
         1 . A method for generally maintaining or reducing a speed of a vehicle, comprising:
 stopping an engine;   decoupling the engine from a motor and an automatic transmission to eliminate engine load on the motor; and   causing the automatic transmission to change a gear ratio resulting in an increased rotational speed of the motor, the motor being operable to deliver increased power at the increased rotational speed.   
     
     
         2 . The method of  claim 1 , wherein decoupling the engine from the motor occurs when an operating condition of the hybrid vehicle meets a criterion for stopping the engine. 
     
     
         3 . The method of  claim 2 , wherein the criterion for stopping the engine comprises at least one of:
 the rotational speed of the motor reaches a reference speed;   the hybrid vehicle reaches a reference velocity;   the energy storage element reaches a reference state of charge; and/or   a voltage at which electrical energy is supplied to the motor reaches a reference level.   
     
     
         4 . The method of  claim 1 , wherein causing the automatic transmission to change the gear ratio further comprises producing a shift signal at a controller. 
     
     
         5 . The method of  claim 1 , wherein decoupling the engine from the motor comprises causing a clutch to change state from an engaged state to a disengaged state. 
     
     
         6 . The method of  claim 5 , wherein causing a clutch to change state further comprises producing a clutch control signal at a controller. 
     
     
         7 . The method of  claim 1 , further comprising producing an engine off signal at a controller. 
     
     
         8 . An apparatus for generally maintaining or reducing a speed of a vehicle comprising:
 a controller configured to communicate with an engine, a clutch, and an automatic transmission of the vehicle, the controller operable to:
 turn off the engine; 
 cause the clutch to decouple the engine from an electric motor of the vehicle to eliminate engine load on the motor; and 
 cause the automatic transmission to change a gear ratio resulting in an increased power supplied by the electric motor at an increased rotational speed. 
   
     
     
         9 . The apparatus of  claim 8 , wherein causing the clutch to decouple the engine from the motor occurs when an operating condition of the vehicle meets a criterion for turning off the engine. 
     
     
         10 . The apparatus of  claim 9 , wherein the criterion for turning off the engine comprises at least one of:
 the rotational speed of the motor reaches a reference speed;   the vehicle reaches a reference velocity;   a storage element for supplying electrical energy to the motor reaches a reference state of charge; and/or   a voltage at which electrical energy is supplied to the motor reaches a reference level.   
     
     
         11 . The apparatus of  claim 8 , wherein the controller is further operable to cause the clutch to change from an engaged state to a disengaged state. 
     
     
         12 . The apparatus of  claim 8 , wherein the controller is further operable to generate an engine off signal. 
     
     
         13 . A vehicle, comprising:
 an engine;   an electric motor coupleable to the engine through a clutch;   an automatic transmission coupled to the motor; and   a controller configured to communicate with the engine, clutch, and automatic transmission, the controller operable to:
 turn off the engine; 
 cause the clutch to decouple the engine from an electric motor of the vehicle to eliminate engine load on the motor; and 
 cause the automatic transmission to change a gear ratio resulting in an increased power supplied by the electric motor at an increased rotational speed to generally maintain or reduce a speed of the vehicle. 
   
     
     
         14 . The vehicle of  claim 13 , wherein causing the clutch to decouple the engine from the motor occurs when an operating condition of the vehicle meets a criterion for turning off the engine. 
     
     
         15 . The vehicle of  claim 14 , wherein the criterion for stopping the engine comprises at least one of:
 the rotational speed of the motor reaches a reference speed;   the hybrid vehicle reaches a reference velocity;   a storage element for supplying electrical energy to the motor reaches a reference state of charge; and/or   a voltage at which electrical energy is supplied to the motor reaches a reference level.   
     
     
         16 . The vehicle of  claim 13 , wherein the controller is further operable to cause the clutch to change from an engaged state to a disengaged state. 
     
     
         17 . The vehicle of  claim 13 , wherein the controller is further operable to generate an engine off signal.