Power operator for vehicle liftgate

Abstract

A power operator raises and lowers a vehicle liftgate to open and close a vehicle rear hatch. A pair of double-acting hydraulic cylinders pivotally interconnect the vehicle and the liftgate to move the liftgate through a raise cycle and a lower cycle. First and second branches of hydraulic circuitry connect an electrohydraulic pump assembly and a hydraulic accumulator to the cylinders. A controller isolates the accumulator and causes the pump assembly to power the initial portion of the liftgate raise cycle through the first circuit branch. When the liftgate reaches a predetermined position, the controller deactuates the pump assembly and connects the accumulator to the first branch to power the remainder of the liftgate raise cycle. Fluid exhausts through the second branch to the pump assembly. The pump powers the liftgate lower cycle through the second branch, while cylinder exhaust fluid flowing through the first branch recharges the accumulator. The pump assembly can include a single direction motor-driven pump and a directional valve, or a bi-directional motor-driven pump. If power fails, the accumulator connects to the cylinders to assist manual raising of the liftgate and to be recharged during manual lowering of the liftgate. The reservoir is sized to contain all system hydraulic fluid and configured to conform to available vehicle space.