Charging a fluid accumulator while operating a hybrid vehicle powertrain including an engine and a pump/motor

A system for replenishing a source of pressurized fluid for use in driving the wheels of a motor vehicle comprising:

• an accumulator containing fluid at relatively high pressure;
• a reservoir containing fluid at lower pressure;
• an engine driveably connected to the wheels and having a variable torque output;
• a pump/motor driveably connected to the wheels, including an inlet and an outlet, and having a variable volumetric displacement for pumping fluid between the accumulator and the reservoir;
• a controller for determining a current cruise charge pressure limit for the accumulator, 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 controlling the eugine 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, to pump fluid to the accumulator from the reservoir;
• determining a current fluid volume and pressure in the accumulator;
• determining a fluid volume that would be pumped to the accumulator if a brake regenention event were to occur at a current speed of the vehicle;
• determining a prospective accumulator pressure that would result due said brake regeneration event and the current fluid volume and pressure in the accumulator;
• determining a maximum allowable accumulator pressure;
• and
• setting the current cruise charge pressure limit equal to a differene between the maximum allowable accumulator pressure and said prospective accumulator pressure.