A hydraulic module designed to be mounted on a hydraulic hybrid vehicle, characterised in that it forms a rigid and compact assembly comprising a body (32) receiving the high- and low-pressure accumulators intended to supply traction motors of the vehicle, comprising a generally parallelepipedal shape, and having attachment means designed to be fixed under a floor at the rear of the vehicle.

There is set forth herein an actuator having a housing and a piston assembly. The piston assembly can have a piston and a piston rod extending from the piston. In one embodiment, the housing can receive the piston and a portion of the piston rod. The piston assembly can define a piston assembly interior and a fluid reservoir can be located within the piston assembly interior. A chamber region within the interior of the housing can be separated by the piston assembly to define a piston side chamber and rod side chamber. The piston assembly can be moveable so that respective volumes of each of the piston side chamber and the rod side chamber are variable. For operation of the actuator by movement of the piston assembly within the interior of the housing, fluid can be moved between the reservoir and the chamber region.

An accumulator includes: an exterior body including a bottom, a shell and a port; and a bellows provided inside the exterior body and having an S-shape being capable of expansion and contraction. In a case where the bellows has expanded maximally in the accumulator, the bellows has expanded from a free state where no load other than gravitational force is being applied to the bellows.