Patent ID: 7147078

Claim:
In a powertrain for a motor vehicle having an engine driveably connected to the wheels, a pump/motor driveably connected to the wheels and engine, and a accumulator for storing and releasing fluid, a method for replenishing a charge of pressurized fluid in the accumulator, the method comprising the steps of: determining a current fluid volume and pressure in the accumulator; determining a fluid volume that would be pumped to the accumulator if a brake regeneration event were to occur at a current speed of the vehicle; determining a prospeptive accumulator pressure that would result due to said brake regeneration event and the current fluid volume and pressure in the accumulator; determining a maximum allowable accumulator preasure; setting a current cruise charge messure limit equal to a difference between the maximum allowable accumulator pressure and said prospective accumulator pressure; determining a desired magnitude of pump/motor torque with which to pump fluid to the accumulator; determining a desired magnitude of engine torque with which to drive the pump/motor at the desired magnitude of pump/motor torque; and using the engine to produce the desired magnitude of engine torque, to drive the pump/motor in a pumping mode at the desired magnitude of pump/motor torque, and to pump fluid to the accumulator.