GB1565641A - Hydrostatic rotary piston pump or motor - Google Patents

Description

(54) HYDROSTATIC ROTARY PISTON PUMP OR MOTOR We, VEB INDUSTRIEWERKE KARL-MARX STADT, a body corporate organised and existing under the laws of the German Democratic Republic, of 221 Zwickauer Strasse, 9030 Karl-Marx-Stadt, German Democratic Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particu larly described in and by the following statement: - This invention relates to hydrostatic rotary piston pumps and motors having a rotor or rotors securely mounted on a drive shaft, and radially movable members ar ranged in the stator which lie in contact with or closely adjacent to the curved per ipheral surface of said rotor or rotors and separate a low pressure working-fluid area from a high pressure working-fluid area.

A hydrostatic rotary piston pump having a plurality of coaxial annular stator cham bers in which rotors phase-displaced by 90" are rotatably arranged, is known (German Patent Specification No. 822652). The rotors have curved peripheral surfaces with differing circular arcs, hollow plungers lying adjacent to the said curved surfaces. These hollow plungers formed as "abutment" plungers are guided in radial recesses in the stators and are urged by the operating pres sure of the rotary piston pump and by springs against the peripheral surfaces of the rotors. The rotors are securely ar ranged on a drive shaft mounted at both ends in the housing, the torque in each case being transmitted between the shaft and rotors by a drive key. In this connection, the length of the drive key corresponds to the width of the rotor.

Furthermore, a rotary piston pump hav ing a plurality of rotors which receive the radially movable working plungers is also known (German Auslegeschrift 1,203,611).

By means of the eccentric arrangement of the rotors with respect to the surrounding stators, the output of the rotary piston pump can be varied. The rotors are securely arranged on a drive shaft which is itself securely mounted at both ends of the housing. The torque is transmitted between the drive shaft and rotors by a drive key in each case.

A rotary piston pump is also known ("Control Revue" Journal, Vol. 3/74, pages 17/24), whose rotors are carried by a drive shaft having a multi-sided and multi-edged profile. The cross-section is square and transmits the torque between the drive shaft and the rotors. The drive shaft is provided with longitudinal and transverse bores in order to drain off the leakage.

These known multi-sided connections secure a satisfactory centering of the paired parts. Also, the surface pressure on the contact surfaces between the shaft and rotor counteracting the torque transmission is substantially reduced by means of feather keys. When such multi-sided connections are used for hydrostatic rotary piston pumps and engines, the said connections are subjected to high alternating frequency impacts. Undesirable shaft wear cannot be avoided even by using optimum materials.

According to the present invention there is provided a hydrostatic rotary piston pump or motor having a rotor or rotors securely mounted on a drive shaft, the outer peripheral surface of the or each rotor having a convexly curved profile when viewed along the axis of the rotor, and radially movable members arranged in the stator in contact with or closely adjacent to the said peripheral surface of the or each rotor so as to separate a low pressure working-fluid area from a high pressure working-fluid area, the portion of said drive shaft engaging with the or each rotor having a four or more sided cross-sectional profile for transmitting torque to the or each rotor, the said profile of said portion of the drive shaft being recessed at least at two of the corners.

Preferably the drive shaft has a profile with four corners.

The recesses at the corners of the drive shaft extend over the whole length of the polygonal profile. It is possible for only two oppositely located corners of the drive shaft to be machined to provide recesses.

The said recesses preferably have a semicircular cross-section. The present invention obviates the need for edges since the recesses in the corners of the profile mean that the places subjected to the highest surface pressure are resiliently relieved of the latter. This elastic and resilient compensation enlarges the contact surface between the drive surface and rotor, and provides a reduced surface pressure with considerably improved operating life of the structural parts effecting the torque transmission.

These recesses at the corners of the drive shaft simultaneously form oil-conveying channels and obviate the need to provide such channels in the drive shaft.

An embodiment of the present invention will now be described, by way of an example, with reference to the accompanying drawings, in which: - Figure 1 is a longitudinal section through the hydrostatic rotary piston pump, Figure 2 is a cross-section through the pump taken along the line 2-2 of Figure 1, and Figure 3 is an enlarged sectional view of the drive shaft.

The housing of the rotary piston pump is of plate type construction and consists of two annular stators 10, an intermediate plate 12, and two end starting discs 13 and 14. A flanged end plate 15 and connection housing 16 are mounted adjacent to the outside faces of the starting discs 13, 14, and receive rolling-contact bearings 17 and 18 for mounting a drive shaft 19. All parts of the housing are secured together by a plurality of longitudinally extending screws 20 distributed on a common circle.

The stators 10 are provided with cylindrical recesses 21 in each of which is arranged a rotor 22 with a convexly curved profile when viewed along the axis of the rotor.

These rotors 22 are mounted securely, and displaced relatively to each other by 90 , on the drive shaft 19, the latter having a four or more sided cross-sectional profile in this region.

In the embodiment illustrated the shaft 19 and the bore of the rotors 22 has a substantially square profile with each side being slightly convex. The shaft 19 is provided with recesses 24 at the corners which lie opposite curved sections 23 of the bore of the rotors 22. These recesses 24 have a semi-circular cross-section, though other cross-sections (e.g. angular) are also possible.

Each recess 24 occupies approximately the whole width of the associated circularcylindrical curved section 23 of the bore of the rotor 22 and extends over the length of the drive shaft 19 between the discs 13 and 14. A longitudinal channel corresponding to each recess 24 and section 23 is thus formed between the rotors 22 and the drive shaft 19.

Two diametrically arranged hollow plungers 25 lie in contact with or closely adjacent to the curved periphery of each rotor 22, and are radially movably arranged in radial slits 26 in the stators 10. The medium/hydraulic oil is supplied and removed via low pressure and high pressure channels 27, 28 in the end housing 16.

It is not necessary to provide details of the mode of operation of this rotary piston pump since this is generally known to a person skilled in the art of rotary piston machines.

It is possible to use such a device as a hydraulic motor.

In a modified embodiment of the invention only two opposite corners of the drive shaft 19 are provided with recesses 24.

WHAT WE CLAIM IS: - 1. A hydrostatic rotary piston pump or motor having a rotor or rotors securely mounted on a drive shaft, the outer peripheral surface of the or each rotor having a convexly curved profile when viewed along the axis of the rotor, and radially movable members arranged in the stator in contact with or closely adjacent to the said peripheral surface of the or each rotor so as to separate a low pressure working-fluid area from a high pressure working-fluid area, the portion of said drive shaft engaging with the or each rotor having a four or more sided cross-sectional profile for transmitting torque to the or each rotor, the said profile of said portion of the drive shaft being recessed at least at two of the corners.

2. A hydrostatic rotary piston pump or motor as claimed in Claim 1, in which said portion of the drive shaft has a profile with four corners.

3. A hydrostatic rotary piston pump or motor as claimed in Claim 1 or Claim 2, in which the recesses at the corners of the drive shaft extend over the whole length of the said portion.

4. A hydrostatic rotary piston pump or motor as claimed in any preceding claim, in which only two opposite corners of the drive shaft are provided with recesses.

5. A hydrostatic rotary piston pump or motor as claimed in any preceding claim, in which the recesses have a semi-circular cross-section.

6. A hydrostatic rotary piston pump or motor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. shaft to be machined to provide recesses. The said recesses preferably have a semicircular cross-section. The present invention obviates the need for edges since the recesses in the corners of the profile mean that the places subjected to the highest surface pressure are resiliently relieved of the latter. This elastic and resilient compensation enlarges the contact surface between the drive surface and rotor, and provides a reduced surface pressure with considerably improved operating life of the structural parts effecting the torque transmission. These recesses at the corners of the drive shaft simultaneously form oil-conveying channels and obviate the need to provide such channels in the drive shaft. An embodiment of the present invention will now be described, by way of an example, with reference to the accompanying drawings, in which: - Figure 1 is a longitudinal section through the hydrostatic rotary piston pump, Figure 2 is a cross-section through the pump taken along the line 2-2 of Figure 1, and Figure 3 is an enlarged sectional view of the drive shaft. The housing of the rotary piston pump is of plate type construction and consists of two annular stators 10, an intermediate plate 12, and two end starting discs 13 and 14. A flanged end plate 15 and connection housing 16 are mounted adjacent to the outside faces of the starting discs 13, 14, and receive rolling-contact bearings 17 and 18 for mounting a drive shaft 19. All parts of the housing are secured together by a plurality of longitudinally extending screws 20 distributed on a common circle. The stators 10 are provided with cylindrical recesses 21 in each of which is arranged a rotor 22 with a convexly curved profile when viewed along the axis of the rotor. These rotors 22 are mounted securely, and displaced relatively to each other by 90 , on the drive shaft 19, the latter having a four or more sided cross-sectional profile in this region. In the embodiment illustrated the shaft 19 and the bore of the rotors 22 has a substantially square profile with each side being slightly convex. The shaft 19 is provided with recesses 24 at the corners which lie opposite curved sections 23 of the bore of the rotors 22. These recesses 24 have a semi-circular cross-section, though other cross-sections (e.g. angular) are also possible. Each recess 24 occupies approximately the whole width of the associated circularcylindrical curved section 23 of the bore of the rotor 22 and extends over the length of the drive shaft 19 between the discs 13 and 14. A longitudinal channel corresponding to each recess 24 and section 23 is thus formed between the rotors 22 and the drive shaft 19. Two diametrically arranged hollow plungers 25 lie in contact with or closely adjacent to the curved periphery of each rotor 22, and are radially movably arranged in radial slits 26 in the stators 10. The medium/hydraulic oil is supplied and removed via low pressure and high pressure channels 27, 28 in the end housing 16. It is not necessary to provide details of the mode of operation of this rotary piston pump since this is generally known to a person skilled in the art of rotary piston machines. It is possible to use such a device as a hydraulic motor. In a modified embodiment of the invention only two opposite corners of the drive shaft 19 are provided with recesses 24. WHAT WE CLAIM IS: -

1. A hydrostatic rotary piston pump or motor having a rotor or rotors securely mounted on a drive shaft, the outer peripheral surface of the or each rotor having a convexly curved profile when viewed along the axis of the rotor, and radially movable members arranged in the stator in contact with or closely adjacent to the said peripheral surface of the or each rotor so as to separate a low pressure working-fluid area from a high pressure working-fluid area, the portion of said drive shaft engaging with the or each rotor having a four or more sided cross-sectional profile for transmitting torque to the or each rotor, the said profile of said portion of the drive shaft being recessed at least at two of the corners.

2. A hydrostatic rotary piston pump or motor as claimed in Claim 1, in which said portion of the drive shaft has a profile with four corners.

3. A hydrostatic rotary piston pump or motor as claimed in Claim 1 or Claim 2, in which the recesses at the corners of the drive shaft extend over the whole length of the said portion.

4. A hydrostatic rotary piston pump or motor as claimed in any preceding claim, in which only two opposite corners of the drive shaft are provided with recesses.

5. A hydrostatic rotary piston pump or motor as claimed in any preceding claim, in which the recesses have a semi-circular cross-section.

6. A hydrostatic rotary piston pump or motor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.