Energy storage device

Abstract

An energy storage device comprising a high pressure liquid accumulator, a low pressure liquid accumulator and at least one pump and motor unit, i.e. a device able to be used as a pump and a motor which is connected to a means, such as the drive train of a vehicle, supplying or absorbing energy as the case may demand and during charging of the high pressure liquid accumulator from the low pressure accumulator functions as a pump and on discharge thereof functions as a motor, at least that pressure line connecting the high pressure accumulator and the pump and motor unit having a shut off valve therein. A piston delimiting the storage space of the low pressure liquid accumulator is connected to a telescoping cylinder bearing against the end plate of the accumulator and the cylinder is connected via an operating pressure line with the high pressure accumulator for pressurization. On charging of the high pressure accumulator with an accompanying discharge of the low pressure accumulator it is thus possible to avoid a fall in the pressure in the latter to an overly low level; in fact the pressure fluctuates about an average value between a relatively high minimum value and a maximum value. The latter feature is due to the changing size of the active pressure faces as the telescoping pressure cylinder is extended one part after another.