22 the slide 22 is rotatably connected to the housing wall 6 through a rotary axis 24 and is rotatable in order to vary the displacement of the pump chambers 23 the displacement of the pump 1 is proportional to the eccentricity of the slide 22 relative to the axis 21 of the rotor 19 when the pump 1 is in a state of rest the slide 22 is forced into a position of maximum eccentricity relative to the rotor 19 when the pump operates and the slide 22 is in that position the displacement of the pump is at its maximum value when the slide 22 turns away from a position of maximum eccentricity the displacement of the pump is reduced and the output flow of the pump generally decreases when the middle of the slide 22 is turned into a position in which it is aligned with the axis of the rotor 19 the slide 22 is located at an eccentricity of approximately 0 i e approximately 100 of its maximum eccentricity and the pump 1 operates at a displacement of approximately zero the pump 1 also has an oil inlet channel which is not shown in the figures which provides a first.