System and method for regulating pressure in an automatic transmission

Abstract

An apparatus and a method for controlling the pressure in an automatic transmission with an electric pump. The electric pump supplies and removes hydraulic fluid from the automatic transmission in response to various conditions. The addition of an electric pump to control pressure within the transmission allows the mechanical pump driven by the engine to be reduced in size and improve fuel economy.

What is claimed is:  
     
         1 . A hydraulic system for supplying fluid to a transmission clutch actuator comprising: 
 an outlet having a fluid pressure;    a first pump having a supply conduit and a discharge conduit;    a second pump having a supply conduit and a discharge conduit, said discharge conduits of said first and second pumps hydraulically communicating with said outlet, said second pump being operable in a first operating state wherein said second pump increases the fluid pressure in said outlet and a second operating state wherein said second pump decreases the fluid pressure in said outlet;    a pressure regulating system operably coupled to said second pump to control the operating state of said second pump.    
     
     
         2 . The hydraulic system of  claim 1  wherein said pressure regulating system includes a torque source operably coupled to said second pump, said torque source communicating a unidirectional torque to said second pump during said first and second operating states.  
     
     
         3 . The hydraulic system of  claim 2  wherein said torque source is an electric motor and wherein said pressure regulating system further includes a control system communicating a command current to control said torque said electric motor communicates to said second pump.  
     
     
         4 . The hydraulic system of  claim 3  wherein said pressure regulating system further includes a servo amplifier receiving said command current and an input current, said servo amplifier communicating a control output to said electric motor.  
     
     
         5 . The hydraulic system of  claim 2  wherein said electric motor generates electricity when said second pump is in said second operating state.  
     
     
         6 . The hydraulic system of  claim 2  wherein said torque communicated by said electric motor to said second pump is less than a fluid torque exerted on said second pump when said second pump is in said second operating state, said torque difference causing said second pump to rotate backward in said second operating state.  
     
     
         7 . The hydraulic system of  claim 1:   wherein a fluid pressure in a second pump discharge conduit exerts a first torque on said second pump,    wherein said pressure regulating system includes an electric motor communicating a unidirectional second torque to said second pump, said second torque having a magnitude controlled by said pressure regulating system, and    wherein said electric motor is operably coupled to said second pump such that said second pump operates in said first operating state when said first torque is less than said second torque and in said second operating state when said first torque is greater than said second torque.    
     
     
         8 . The hydraulic system of  claim 1  wherein said supply conduits and said discharge conduits form a hydraulic circuit and wherein said first pump and said second pump operate in parallel in said first operating state and in series in said second operating state.  
     
     
         9 . A hydraulic system for an automatic transmission of a vehicle having an engine, said hydraulic system comprising: 
 an actuating assembly having a fluid pressure;    a first pump having a first fluid supply;    a second pump having a second fluid supply, said first and second fluid supplies combining to form said fluid pressure;    a pressure regulation system including an electric motor communicating a unidirectional torque to said second pump to control said second fluid supply.    
     
     
         10 . The hydraulic system of  claim 9  wherein said first fluid supply is a positive fluid supply to said actuating assembly and said second fluid supply is a positive fluid supply rate in a first operating state and a negative fluid supply in a second operating state.  
     
     
         11 . The hydraulic system of  claim 10  further including a control system, said control system communicating a command current to vary said unidirectional torque, said unidirectional torque creating a second pump pressure, said second pump pressure being greater than said fluid pressure in said first operating state, and said second pump pressure being less than said fluid pressure in said second operating state.  
     
     
         12 . A method of controlling a fluid pressure in an actuator assembly of an automatic transmission of a vehicle having an engine, comprising: 
 supplying a hydraulic fluid to the actuator assembly with a first pump to create a fluid pressure;    determining a desired pressure; and    controlling said fluid pressure with a second pump.    
     
     
         13 . The method of  claim 12  further including the step of determining a hydraulic fluid supply rate of said first pump.  
     
     
         14 . The method of  claim 13  further including the step of determining a drag torque of said second pump.  
     
     
         15 . The method of  claim 14  further including the step of determining a current compensation associated with each of said desired pressure, said drag torque, and said first pump hydraulic fluid supply rate.  
     
     
         16 . The method of  claim 15  comprising the step of determining a command current associated with said current compensation, said command current being the sum of said current compensations.  
     
     
         17 . The method of  claim 16  comprising the step of supplying said command current to a servo amplifier, said servo amplifier providing a control output to a torque source coupled to said second pump.  
     
     
         18 . The method of  claim 17  further including the step of providing said control output to an electric motor coupled to said second pump.  
     
     
         19 . The method of  claim 18  further including the step of applying a forward torque to said second pump with said electric motor.