Hill holding brake system for hybrid electric vehicles

Abstract

A hill holding function of a hybrid electric vehicle is initiated when the powertrain control module determines that a hill holding condition exists. In the hill holding condition, the electro-hydraulic brakes will provide brake torque to each wheel and the powertrain control module will turn off the internal combustion engine. The system can also detect a two footer condition where the vehicle operator requests both acceleration torque and brake torque simultaneously. The hill holding function of the hybrid electric vehicle in a two footer situation will apply the electro-hydraulic brakes and turn off the internal combustion engine. When the operator requests acceleration in either the hill holding or the two footer condition, the electric brake controller will transition the release of the electro-hydraulic brakes and the powertrain control module will turn on the internal combustion engine.

1 . A hybrid electric vehicle comprising: 
 an internal combustion engine configured to rotate in a single direction to selectively drive a drive wheel and provide engine compression braking torque to the drive wheel;    an integrated starter generator motor connected to the internal combustion engine that rotates in a same direction as the internal combustion engine, the integrated starter generator motor adapted to selectively start the internal combustion engine;    a powertrain control module that controls the operating parameters of the internal combustion engine and the integrated starter generator motor, the powertrain control module being selectively actuated by a vehicle operator by actuating an accelerator pedal to request an accelerator torque;    an electro-hydraulic brake system for vehicle braking, the electro-hydraulic brake system being selectively actuated by the vehicle operator by actuating a vehicle brake pedal to request a brake torque;    an electronic brake controller for controlling the brake torque applied to the drive wheel by the electro-hydraulic brake system; and    a vehicle rollback sensor for determining a vehicle rollback state;    wherein the electronic brake controller actuates the electro-hydraulic, brake system in a hill holding condition, when vehicle rollback is detected, the requested brake torque is less than a first predetermined level, the requested accelerator torque is less than a second predetermined level, and the internal combustion engine is running.    
   
   
       2 . The hybrid electric vehicle of  claim 1  wherein the powertrain control module turns off the internal combustion engine in the hill holding condition.  
   
   
       3 . The hybrid electric vehicle of  claim 1  wherein, the internal combustion engine is started to provide torque to the drive wheel and an adaptive filter is applied to decrease the brake torque exerted by the electro-hydraulic braking system when the accelerator pedal is actuated and the hybrid electric vehicle is in a hill holding condition in which the hybrid electric vehicle is stationary on an inclined surface.  
   
   
       4 . The hybrid electric vehicle of  claim 1  further comprising a transmission having a plurality of gear ratios and wherein the electronic brake controller does not actuate the electro-hydraulic brake system during a vehicle creep condition, in which the accelerator and brake pedals are not actuated, a gear ratio of the transmission is engaged and the powertrain control module determines whether vehicle creep will be powered by the internal combustion engine, the integrated starter generator motor or both;  
   
   
       5 . The hybrid electric vehicle as set forth in  claim 1  further comprising a transmission having a plurality of gear ratios and wherein the electronic brake controller actuates the electro-hydraulic brake system during a predetermined two footer condition in which, the hybrid electric vehicle is on a grade, the transmission is in gear, the accelerator pedal and the brake pedal are actuated, and the brake torque requested is greater than the accelerator torque requested.  
   
   
       6 . The hybrid electric vehicle as set forth in  claim 5 , wherein the powertrain control module turns off the internal combustion engine in the predetermined two footer condition.  
   
   
       7 . A method of hill holding a hybrid electric vehicle comprising: 
 measuring a vehicle rollback state based on a first signal from a vehicle rollback sensor;    measuring a brake torque request based on a second signal from a brake pedal sensor;    measuring an accelerator torque request based on a third signal from an accelerator pedal sensor    determining a running state of an internal combustion engine based on a fourth signal from an engine sensor    determining a vehicle creep output by comparing a fifth signal from a vehicle speed sensor to a predetermined vehicle creep speed:    determining whether hill holding condition exists based on the first, second, third, and fourth signals and the vehicle creep output;    actuating a set of electro-hydraulic brakes in the hill holding condition.    
   
   
       8 . The method as set forth in  claim 7  further comprising turning off the internal combustion engine while in the hill holding condition.  
   
   
       9 . The method as set forth in  claim 8  further comprising, de-actuating the electro-hydraulic brakes turning on the internal combustion engine and accelerating the hybrid electric vehicle using the internal combustion engine when the vehicle operator actuates the accelerator pedal  
   
   
       10 . The method as set forth in  claim 7  further comprising detecting a vehicle gear selection using a gear selection sensor calculating presence of a two footer condition when second signal is greater than the third signal, and actuating the electro-hydraulic brakes while in the two footer condition.  
   
   
       11 . The method as set forth in  claim 10  further comprising turning off the internal combustion engine in the two footer condition.  
   
   
       12 . The method as set forth in  claim 10  further comprising sensing a vehicle acceleration request using the accelerator pedal sensor, de-actuating the electro-hydraulic brakes turning on the internal combustion engine and accelerating the hybrid electric vehicle using the internal combustion engine.