The invention relates to hydraulic or pneumatic pumps and motors.

There are known pumps and motors comprising a housing accommodating rotors forming chambers with said housing, the size of said chambers varying as a result of the rotation of the rotors, the chambers thus producing a displacement effect.

Examples of such pumps and motors are gear pumps, vanes motors and so on. However, pumps and motors of this type have the disadvantage that the relation¬ ship between an angle variation of the rotors and the volume variation of the displacer chambers resulting therefrom is interrupted onece or several times during each revolution and exhibits discontinuities. These interruptions or discontinuities are attributable to the fact that the shape of the rotors exhibits irregularities such as lugs, recesses, partitions, teeth and so forth.

The invention has for its object to provide a pump or motor in which a linear or substantially linear relationship exists between the magnitude of the angle of rotation of the pump or motor shaft and the displaced volume of the medium concerned. A further object of the invention is to provide a pump or motor of the kind set forth in which seals are formed by gaps of very small dimensions, which are maintained at any instant between the rotors and the housing and between the rotors themselves as a result of the shape and the relative positions of the rotors.-

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The pump or motor comprises a housing accomodating a set of rotors formed by at least two disc-like rotors adapted to rotate by means of parallel shafts journalled in said housing and having the rotors fastened to them in cylindrical, partly coinciding chambers, whilst the shape and the relative positions of the rotors ar ^' such that the outer surface of each of these rotors is invariably at least at one place tangential to the cylindrical wall of the chamber concerned along a line parallel to the rotor shafts, whilst, in addition, at an instant the outer surfaces of the rotors are tangential to one another along a line parallel to the rotor shafts and located in the plane going through the centre lines of the rotor shafts so that enclosed between the walls of the housing and the outer surfaces of the rotors there are ^' formed at least one inlet chamber and one outlet chamber, whose volume varies substantially linear as a result of the rotation,of the rotors with the mag¬ nitude of the said rotation. The invention will be described with reference to th accompanying drawing, which shows a cross-sectional view of a pump or motor in accordance with the invention. The pump or motor comprises a housing 1, in which the rotor shafts 2 and 3 are arranged. On these shafts are arrange rotors 4 and 5 and a gear wheel transmission ensures a fixed relationship between the angles of rotation of the rotor shafts. This relationship is such that the mean values of the circumferential speeds of the rotors in th common tangential point are equal to one another. The volume variation of the chambers A and B per unit time is determined by the product of the width of the rotors, the difference between the maximum rotor radius Ro and the value R at the place of the common tangential point and the circumferential speed at said tangential point. Since the sum of the rotor radii at the tangential poin is constant, the volume variation of the chambers will also be constant in the case of constant rotor speeds

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with the exception of a minute variation due to the fact that the variation in circumferential speed is not completely the same for the two rotors.

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