GB2126284A

GB2126284A - Radial piston pump

Info

Publication number: GB2126284A
Application number: GB08315283A
Authority: GB
Inventors: Ludwig Budecker; Georg Obersteiner
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1982-08-28
Filing date: 1983-06-03
Publication date: 1984-03-21
Also published as: FR2532366B1; FR2532366A1; GB2126284B; IT1163843B; GB8315283D0; DE3232083C2; IT8322210A0; DE3232083A1; IT8322210A1

Abstract

A radial piston pump for the delivery of fusible media, in particular hydraulic fluids, is of the kind wherein at least one piston element is supported on a cam curve, the latter being located eccentrically relative to the axis of a drive shaft, and being adapted to perform reciprocating movements in a cylinder bore, check valves being arranged in the pump inlet and in the pump outlet which are adapted to open in the direction of the fluid flow. To improve the mechanical and the volumetric efficiency of the pump, the drive shaft (10, 11) is provided with a continuous groove (15) having a circular cross-section, the centre of the circumferential groove (15) being spaced from the axis of the drive shaft (10, 11). A ball (16) is used as a piston element, the ball's radius being at most equal to the radius of the groove's cross-section. <IMAGE>

Description

SPECIFICATION Radial piston pump This invention relatestoa radial piston pumpforthe delivery of fusible media, in particular hydraulic fluids, ofthe kind wherein at least one piston element is supported by a cam curve, the latter being located eccentrically relative to the axis of a drive shaft, the piston being adapted to perform stroke movements in a cylinder bore, and wherein check valves are arranged in the pump inlet and in the pump outlet which are adaptedto open in the direction ofthefluid flow.

A radial piston pump having the preceding features is known for example from German printed patent application 1653632. The known arrangement includesadriveshaftwhich is provided with a radial circumferential groove with a rectangularly-shaped cross-section, the centre of the circumferential groove being at a distance from the axis of the drive shaft. The bottom ofthe radial groove ofthe drive shaft receives a sliding sleeve against which bear cylinder pistons which are movable to and fro in cylinder bores. When the pistons perform a stroke movement, a control edge will be overridden at a specific stroke so that now the end face ofthe cylinder piston which is remote from the drive shaft confines a chamber in the cylinder bore, which chamber is closed in itself and is now isolated from the suction side of the pump.Upon continuation ofthe stroke of the cylinder piston, the fluid volume disposed in this closed chamber will be delivered to the pump outletwhile its pressure is increased.

It has to be regarded as a disadvantage in this known radial piston pump that the pump is portcontrolled which results in a relatively poorvolumetric efficiency. Furthermore, relatively high friction forces occur between the piston and the sliding sleeve and the bottom of the drive shaft so that there ensues also a relatively poor mechanical efficiency, whereby the necessary driving forces at the drive shaft become relatively high.

It is therefore an object of the present invention to provide a radial piston pump ofthe kind initially referred to which is of straightforward design, while it affords high mechanical and volumetric efficiency.

According to the invention in its broadestaspect, a radial piston pump of the kind referred to is characterised in that the drive shaft is provided with a continuous circumferential groove of circular crosssection, in that the centre of the circumferential groove is spaced from the axis of the drive shaft, and in that a ball is used as piston element whose radius is at most equal to the radius ofthe groove's crosssection. It hasty be considered a particular advantage in such a design that the ball rolls in the circumferential groove so that the corresponding friction forces or the necessary driving torque atthe drive shaft are low.

Astandardised ball of a ball bearing may be used as the ball,forexample. Moreover, the pump is exclusivelyvalve-controlled so that the volumetric efficiencywill be improved in comparison with the known arrangement. If the radius of the ball and that of the groove are identical, the ball will come into line contact with the groove contour so that the ball will most probably roll in the groove. This entails relatively little slip whereby there will be avoided flattened portions on the ball which occur when there is sliding engagement between the ball and the groove. If the radius of the ball is less than the radius of the groove's cross-section, there will be caused virtually a point contact between the ball and the drive shaft which is characterised by extremely high friction forces and which ensuresthatthe ball rolls reliably.

The ball is retained in the circumferential groove by a compression spring. This is necessary in particular in the event of a suction stroke with a view to keeping the ball in contact with the drive shaft. Owing to its size being conformed to the cylinder bore, the ball acts as if it were a cylinder piston. However, the volumetric efficiency can be further improved in a favourable manner in thatthe cylinder bore accommodates a substantially cylindrical piston between the ball and the compression spring. By this means, the sealing effect in relation to the wall ofthe cylinder bore will be decisively improved, since the cylinder piston is, with its entire peripheral surface, in contact with the wall of the cylinder bore. Preferably, the end faces ofthe cylindrical piston are hydraulically interconnected.

Any elastomeric plastic having good sliding properties can be expediently utilised as the material for the piston. The sealing effect of the piston can be augmented further by an elastic circumferential sealing lip at the piston surface that is remote from the ball.

The invention can be developed further in a favourable manner if the drive shaft is made axially slidable and the axial position of the drive shaft is brought about by the positive engagement between the ball and the circumferential groove. It is not necessary in this case to meettighttolerancesas regards the drive shaft, since the drive shaft will centre itself during operation of the pump. It will furthermore be advantageous in this respect if the drive shaft has two portions, a first portion thereof carrying the circumferential groove and engaging, in a torsionallysecured manner, a second shaft portion at which the driving torque becomes directly effective. Greater tolerances can be admitted in a like design in the connection between the pump housing and the drive assembly. Likewise, heat-conditioned expansions of the shaft parts will nottake effect.This will be furthermore accomplished in a favourable manner if the first shaft portion is axially movable in relation to the second shaft portion, while theirtorsionallysecured engagement is maintained.

It will also be expedientforthe pump housing accommodating the cylinder bore to be supported via sealing rings in a hollow cylinder body. In this way, noises produced by the pump will be reduced drastically. Besides, as experience has shown, the reduced vibration ensures a longer life.

The pressure chamber of the pump is sealed by another sealing ring, whereby there is produced a constructively simple design on the one hand, and which has as a result, on the other hand, that pressure pulsations in the pressure chamber will be damped.

Pressure peaks in the pressure chamber will be lessened the more, the higherthe elasticity ofthe sealing ring is. Therefore, particularly good results can be obtained if the sealing ring is hollow.

An embodiment ofthe invention will now be described by way of example with reference to the accompanying drawing.

In the drawing, reference numeral 1 designates a suction portthrough which pressure fluid is sucked in from a supply reservoir, not shown. The sucked-in pressure fluid propagates through a suction channel 2 into an annular chamber 3 which informed by the pump housing 4 and a master cylinder body 5 accommodating the pump housing 4 in combination with sealing rings 6,7. The pump housing4 is further provided with a pressure port8atwhich pressurised hydraulic fluid is available during operation of the pump.

In addition, the pump housing contains an axial blind-end bore 9 in which afirst portion 10 of a drive shaft is rotatably supported. Formed at the end ofthe first shaft portion 10, which end is remote from the bottom ofthe blind-end bore 9, is a pivot 11 which engages a recess 12 in a second shaft portion 13 and thus establishes a torsionally-secured connection betweentheshaftportions 10,13.Theshaftportion 13 is typically the axle of an electric motor 14.

The shaft portion 10 has a circumferential groove 15 having a circular cross-section, with the centre of the circumferential groove 15 being offset in relation to the axis of the first shaft portion 10. In this way, there is formed an eccentric cam curve of circular crosssection in which a ball 16 is disposed. The radius of the ball is at most equal to the radius ofthe cross-section ofthegroove 15.

As shown in the drawing, above the ball 16, a substantially cylindrical piston 17 is arranged which is retained in abutment on the ball 16 by means of a compression spring 18. Above the cylindrical piston 17, a check valve 19,20 is inserted which is responsible forsucking-in the pressure fluid. A channel 23 extends from a chamber 21 in the cylinder bore 22 via another check valve 24,25 to a pressure chamber 26 which latter is sealed by an elastic sealing ring 28.

In operation of the radial piston pump, the ball 16 together with the piston 17 performs axial movements in the cylinder bore 22. In the phase of movement between the upper and the bottom dead centre, the check valve 19,20 is opened so that pressure fluid is allowed to flow from the suction port 1 through the annularchamber3 into the chamber21 which is increasing during this phase. Afterthe bottom dead centre has been overcome, the check valve 19,20 will close due to the force ofthe compression spring 18, the closing force being assisted by the pressure which now develops in the chamber 21. The pressure fluid in the now decreasing chamber 21 moves via the channel 23 to the check valve 24,25, which will then open and constitute a connection between the channel 23 and the pressure chamber 26 ofthe pump. Via another channel 27, the fluid delivered is fed to the pressure port 8 ofthe pump.

Claims

1. A radial piston pumpforthe delivery offusible media, in particular hydraulic fluids, ofthe kind wherein at least one piston element is supported by a cam curve, the latter being located eccentrically relative to the axis of a drive shaft, the piston being adapted to perform stroke movements in a cylinder bore, and wherein check valves are arranged in the pump inlet and in the pump outlet which are adapted to open in the direction ofthe fluid flow, characterised in that the drive shaft (10, 13) is provided with a continuous circumferential groove (15) of circular cross-section, in that the centre ofthe circumferential groove (15) is spaced from the axis of the drive shaft (10), and in that a ball (16) is used as piston element whose radiusis at most equal to the radius of the groove's cross-section.

2. Aradial piston pump as claimed in claim 1, characterised in that the ball (16) is retained in the circumferential groove (15) by means of a compression spring (18).

3. A radial piston pump as claimed in claim 2, characterised in that asubstantially cylindrical piston (17) is arranged in the cylinder bore (22) between the ball (16) and the compression spring (18).

4. A radial piston pump as claimed in claim 3, characterised in thatthe end faces ofthe piston (17) are hydraulically interconnected.

5. A radial piston pump as claimed in any one of the preceding claims, characterised in thatthe drive shaft (10, 13) is axially slidable and in thatthe axial position ofthe drive shaft (10) is brought about by the positive engagement between the ball (16) and the circumferential groove (15).

6. A radial piston pump as claimed in claim 5, characterised in that the drive shaft (10,13) is in two portions, with a first portion (10) carrying the circumferential groove (15) and engaging in a torsionally secured manner a second shaft portion (13) at which latter the driving torque becomes directly effective.

7. A radial piston pump as claimed in claim 6, characterisied in thatthe first shaft portion (10) is axially movable in relation to the second shaft portion (13), while theirtorsionally-secured engagement is maintained.

8. A radial piston pump as claimed in any one of the preceding claims, characterised in thatthe pump housing (4) accommodating the cylinder bore (22) is supported via sealing rings (6,7) in a hollow cylinder body (5).

9. A radial piston pump as claimed in any one of the preceding claims, characterised in that the pressure chamber (26) is closed by an elastic sealing ring (28).

10. A radial piston pump as claimed in claim 9, characterised in thatthe sealing ring (28) is a hollow O-ring.

11. A radial piston pump substantially as described with reference to the accompanying drawings.