Pump for an engine

A pump for an engine includes a suction chamber, a discharge chamber, and a piston at least partly received within a relief chamber. The piston has first and second passageways provided therein. The second passageway is located closer to a face of the piston than the first passageway. The piston is movable within the relief chamber, so that the volume of the fluid transfer from the suction chamberto the discharge chamber is varied according to a pressure in the relief chamber. The first and second passageways form fluid paths between the suction chamber and the discharge chamber at a first and second pressure in the relief chamber, respectively, the first pressure being less than the second pressure. 种用于发动机的泵，其包括抽吸腔室、排放腔室以及活塞，该活塞至少部分地接纳在减压腔室内。活塞具有设置在其中的第和第二通道。第二通道定位成比第通道更靠近活塞的表面。该活塞能在减压腔室内移动，以使得流体从抽吸腔室转移至排放腔室的容积根据减压腔室中的压力改变。第和第二通道分别以减压腔室中的第和第二压力在抽吸腔室和排放腔室之间形成流体通路，该第压力小于第二压力。