Abstract: A hydraulic accumulator system alternately stores energy in the form of gas pressure and converts the stored energy into work by gas expansion. The hydraulic accumulator system, by connection to drive wheels of a vehicle, can serve as a hydropneumatic powertrain for the vehicle. High-pressure and low-pressure fluid drive units are operable either in a motor mode or in a pump mode. A plurality of high-pressure liquid vessels and a plurality of low-pressure liquid vessels are connected in parallel between the fluid drive units and a gas reservoir, with the high-pressure fluid drive unit connecting with the high-pressure liquid vessels and the low-pressure fluid drive unit connecting with the low-pressure liquid vessels. A liquid reservoir supplies liquid to the fluid drive units when operating in the pump mode and receives liquid from the fluid drive units operating in a motor mode. A method of operating the system is also disclosed herein.

Abstract: Engine output speed is controlled for optimum efficiency by adjustment of input speed of a continuously variable transmission (CVT). Where power in excess of that provided by the engine is required, additional power is input to the drivetrain from a fluidic motor driven by fluid pressure stored in an accumulator. In driving conditions where the engine, operating at optimum efficiency, produces power in excess of that demanded by of the vehicle, the fluidic motor is reversed for operation as a pump and excess engine power is utilized to drive the pump and store energy in the accumulator in the form of fluid pressure. A CPU determines power output required of the engine as a sum of that indicated by a sensor which senses power demanded of the vehicle by a driver and an increment of power required to maintain the pressure of the accumulator above a threshold amount.