The present invention relates to a pump unit applied to a high-pressure cleaning machine, including: a water inlet chamber, a water outlet chamber, and a central chamber connected to the water inlet chamber and the water outlet chamber. The pump unit further includes a plunger disposed in the central chamber and an eccentric mechanism connected to the plunger. The eccentric mechanism drives the plunger to perform reciprocating motion in the central chamber.

An oil pump is provided. The oil pump comprises: a shell; a rotor mounting part on the shell and having a rotor supporting structure; and a rotor mechanism disposed on the rotor mounting part. The shell has an inlet and an outlet and defines a low-pressure oil chamber and a high-pressure oil chamber. A partition wall is disposed between the low-pressure oil chamber and the high-pressure oil chamber for separating the low-pressure oil chamber and the high-pressure oil chamber. An engine cover comprising the oil pump and an engine comprising the engine cover are also provided.

Provided is a hollow rotor and method for making a hollow rotor for a gerotor system, the gerotor system including inner and outer rotors having interengaging lobed profiles. At least one of the inner or outer rotors comprises the hollow rotor, the hollow rotor including radially inner and outer walls radially spaced-apart in relation to a rotational axis of the rotor and walls extending between the radially inner and outer walls for closing axial ends of the hollow rotor. The radially inner and outer walls define therebetween a cavity, thus providing for a hollow or empty interior of the hollow rotor. At least one of the radially inner or outer walls forms a plurality of lobes circumferentially spaced-apart around the cavity.