GB2163493A

GB2163493A - Radial piston device

Info

Publication number: GB2163493A
Application number: GB08519797A
Authority: GB
Inventors: Ludwig Budecker; Georg Obersteiner
Original assignee: Alfred Teves GmbH
Current assignee: Continental Teves AG and Co oHG
Priority date: 1984-08-24
Filing date: 1985-08-07
Publication date: 1986-02-26
Also published as: GB8519797D0; GB2163493B; DE3431158A1; DE3431158C2; JPH081168B2; FR2569447B1; FR2569447A1; JPS6161985A

Abstract

A radial piston device (especially a pump) has pistons (25) slidably guided directly in respective cylinder bores (14) of a rotary cylinder body (7), the pistons carrying balls (15) for co-operating with the inner surface of an eccentrically mounted cam ring (8). The cylinder body (7) is rotatable around a pintle (20) provided with inflow and outflow passages (21, 22). The cam ring (8) is rotatably mounted on the casing (1) via roll bodies (30). If due to high friction in the cylinder bore (14) the balls (15) tend to slide on the cam ring (8) instead of rolling, the cam ring (8) can rotate. Thus sliding of the balls (15) on the running surface of the cam ring (8), which is unfavourable with regard to efficiency, is prevented by the rotation of the cam ring (8). <IMAGE>

Description

SPECIFICATION Radial piston device This invention relates to a radial piston device, in particular a ball piston pump, comprising at least one ball piston of which the ball, which is in rolling contact with a lifting ring, with its surface is slidably guided in a cylinder bore of a cylinder body which is rotatable around a pintle provided with inflow and outflow passages.

A radial piston device of the above-mentioned type is known from the patent application DE-PS 873 207. Rotatably carried on a pintle which is fixed at the casing is the cylinder body with the ball pistons which are guided in cylinder bores arranged radially to the axis. A lifting ring is positioned eccentrically to the pintle axis inside the casing. With the cylinder body rotating, the ball pistons are displaced outwardly in their guide cylinders due to the action of centrifugal force, contact the lifting ring and normally roll along the running surface of the lifting ring, while performing oscillating movements within the cylinder bores.The ball slides at the wall of the cylinder bore and at the same time rotates around its centre as a result of the rolling movement along the lifting ring, which in turn causes a further sliding movement of its outer surface at the wall of the cylinder bore. The sliding of the ball at the inner wall of the cylinder bore is influenced by the type of working medium and its lubricity. In unfavourable working conditions, e.g. in case of high operating temperatures and/or working media of poor lubricity, there is the danger that the sliding movements of the ball, which result from its rotation within the cylinder bore, are rendered difficult or prevented entirely, which may cause a sliding movement of the ball along the running surface of the lifting ring. The resulting friction will lead to low efficiency of the machine and excessive wear.

An object of the present invention is to create a radial piston device of simple construction and high efficiency.

According to the present invention there is provided a radial piston device, in particular ball piston pump, comprising at least one ball piston of which the ball, which is in. rolling contact with a lifting ring, with its surface is slidably guided in a cylinder bore of a cylinder body which is rotatable around a pintle provided with inflow and outflow passages, characterised in that the lifting ring is supported on the casing via roll bodies or via a slide bearing.

The result of the design as proposed by the invention is that instead of the unfavourable sliding friction (ball/lifting ring) occurring in unfavourable operating conditions, the frictional conditions are considerably more advantageous with regard to efficiency. Instead of direct support against the casing, it may be advantageous to provide for support via a stator or the pintle.

Particularly advantageous is an improvement of the invention wherein the ball piston comprises a further piston element sliding in the cylinder bore and co-operating with the ball. If under certain operating conditions (high temperature, low viscosity of the working medium) the ball and the further piston element are in contact with each other, the ball will slide due to its rotation at surfaces of the piston element. A considerably improved volumetric efficiency is reached due to the additional sealing effect of the piston element; whereas the mechanical efficiency decreases due to the additional friction between ball and piston element.Due to the rolling or sliding method of bearing the lifting ring in the casing, there is rolling or sliding friction of a low coefficient between the lifting ring and the support part fixed at the casing, while at the same time the ball does not perform any sliding movement at surfaces of the further piston element resulting from its rotation nor any sliding movement along the lifting ring. Due to the low-friction method of bearing the lifting ring, this improvement of the invention further improves both the mechanical and the volumetric efficiency and thus the overall efficiency.If under certain operating conditions (low temperature, h(gh viscosity of the working medium) the ball and the further piston element are not in contact with each other, because due to the high viscosity of the working medium the piston element does not perform a lifting movement synchronous to the ball movement, the ball slides only at the wall of the cylinder bore and not at the further piston element and essentially rolls along the lifting ring, the rotation of which is retarded or completely eliminated due to the high viscosity of the hydraulic medium. Apart from a high volumetric efficiency, a high mechanical efficiency is reached. Irrespective of the momentarily prevailing operating conditions, this improvement of the invention provides an improvement of the overall efficiency.

As regards the choice of material, fabrication, and assembly, it is advantageous that a bearing ring is disposed between the roll bodies and the abutment part fixed at the casing. Fine machining of the running surface for the roll bodies at the casing or the stator or at the pintle is not required.

Advantageous improvements of the invention requiring little space provide that ball piston(s) and roll bodies are arranged in a common cross-sectional plane or that ball pistons and roll bodies are arranged in different crosssectional planes which are axially spaced from each other. Depending on the embodiment chosen, saving in space in the radial or in the axial direction is achieved.

Embodiments which are particularly favour able due to the use of standard components provide that the roll bodies are designed as balls or as rollers or that a complete roller bearing or particularly low-friction slide bearing (for example with teflon-coated surfaces) is used.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through one embodiment of a ball piston pump; Figure 2 is a cross-section of the pump according to Figure 1; Figure 3 is a longitudinal section of a further embodiment of a ball piston pump, and Figure 4 is a longitudinal section of another embodiment of a ball piston pump.

The ball piston pump illustrated in Figures 1 and 2 comprises a pot-like casing 1 which is closed at one end and is flanged to a drive mechanism which is not illustrated in detail.

The casing 1 includes a suction port 2 and a discharge port, not illustrated in detail, leading into a collecting chamber 3.

Inside the casing 1 there is a rotor-stator unit which is supported, via elastically sealing supporting elements 4 in the form of o-rings, at the casing 1. The rotor-stator unit substantially comprises an outer stator 5 and an inner rotor 7 disposed in a pot-like cavity 12 of the stator 5 and forming the cylinder body. The stator 5 is prevented from rotating in the casing 1 by means of a pin 6 which is arranged in bores in adjoining end surfaces of the stator 5 and the casing 1.

The rotor 7 is arranged rotatably on an end of a central pintle 20 protruding into the cavity 12, the other end of said pintle being disposed in an internal bore of the stator 5. Inside the pintle 20 there are an inflow passage 21 and an outflow passage 22.

Inside the rotor 7 there is a through-going radial cylinder bore 14, of which the diametrically opposed sections each confine a radially slidable ball piston 10.

The ball piston 10 consists of two parts, namely a ball 15 disposed radially outward in the cylinder bore and a piston element 25 in the form of a sleeve. Ball 15 and sleeve 25 slide within the cylinder bore 14 and are movable in both directions. Inflow passage 21 and outflow passage 22 can be connected with the inner chambers of the cylinder bore 14 by rotation of the rotor 7.

Positioned eccentrically to the pintle 20 in the cavity 12 of the stator 5 is a lifting ring 8 with a running surface 9 for the bail pistons 10. The lifting ring 8 is arranged rotatably in the stator 5 and the casing 1 via roll bodies in the form of rollers and a bearing ring 31.

As the rotor 7 rotates, the balls 15 of the ball pistons 10 are in rolling contact with the running surface 9 of the eccentrically arranged lifting ring 8. In case of the sliding movement of the ball 15 of the ball piston 10 within the cylinder bore 14 being too tight due to its rolling movement at the lifting ring 8, the rolling kind of bearing allows the lifting ring 8 to rotate substantially synchronous with the rotor 7, with the balls 15 no longer rolling along the lifting ring 8.

Between the running surface 9 of the lifting ring 8 and the opposite part of the rotor's circumferential surface an annular working chamber 17 is formed, the radial dimensions of the cross-section of said chamber varying along the circumference. A closing plate 11 encircles the section of the rotor 7 protruding from the cavity 12 and closes the pot-like cavity 12 of the stator 5 in the axial direction except for an inlet port 13.

Between the bottom of the pot-like cavity 12 and the front surface of the rotor 7 facing said cavity, there is an annular chamber 16 which is radially confined by circumferential surfaces of the rotor 7 and the stator 5. The annular chamber 16 communicates with the working chamber 17 located between the running surface 9 and the rotor 7 via a recess 18. Protruding into the annular chamber 16 parallel to its axis is a pin 19 serving as retaining element, of which the diameter corresponds approximately to the radial cross-sectional dimensions of the annular chamber 16.

Before the retaining element as viewed in the direction of rotation,, there is a connecting port 28 which is connected with the inflow passage 21.

Via an axially and torsionally elastic spring coupling 23 the rotor 7 is connected with one end of the connecting shaft 24 of the drive mechanism.

The ball piston pump as illustrated in Figures 1 and 2 has a total of three pump stages. First the hydraulic medium entering at the suction port 2 is boosted in two steps to reach the boost pressure at which it is then supplied to the high pressure stage. The ball pistons 10 sliding within the rotor's cylinder bores 14 cause the pressure to be boosted in the high pressure stage.

The working chamber 17 of the first boosting stage is located between the running surface 9 and the rotor's circumferential surface and is divided by the balls 15 protruding over the rotor's circumference.

The working chamber of the following second boosting stage is the annular chamber 16, into which the pin 19 protrudes axially.

In operation of the ball piston pump, the working medium is supplied from the suction port 2 via the inlet port 13 into the working chamber 17 between the rotor's circumference and the running surface 9 and, as the rotor rotates, is fed in the direction of rotation indicated by an arrow via recess 18 into the annular chamber 16 while the pressure increases due to the changing volume. Rotation of the rotor 7 causes a circular flow in the annular chamber 16. By the pin 19 approximately covering the cross-section of the annular chamber 16 at the place where it is mounted, the working medium is retained at that place and a further pressure increase is caused by the retaining pressure in the working medium.

The working medium has now reached the boost pressure and is fed via the connecting port 28 into the inflow passage 21 in the pintle 20 and, within a certain speed range, via inflow passage 21 in the pintle 20 into the high pressure working chamber inside the rotor's cylinder bore 14. Upon further rotation of the rotor 7 by a certain amount, the high pressure working chamber is connected with the outflow passage 22 in the pintle 20, which via a connecting passage 27 provided in the stator 5 is connected with a collecting chamber 3 between the stator 5 and the casing 1, where finally the discharge port leads in.

In operation of the pump, the rotor 7 is pressed by the pressure prevailing in the annular chamber 16 in axial direction against the spring coupling 23, which is elastic in this direction and exerts a prestressing force on the rotor, and thus does not abut to the stator 5.

Due to the rolling method of bearing by means of roller or needle bearing or needle cage or otherwise due to a sliding method of bearing not shown, the pump requires little space in radial direction. The extension in radial direction can be further reduced by the radially outer bearing ring of the roller bearing abutting directly to the casing instead of an intermediate stator as is the case in the above described embodiment; this type of embodiment is illustrated in Figure 4.

Figure 3 shows a ball piston pump similar to the initially described embodiment; like parts have been assigned like references. The essential difference, apart from differences in the manner of guiding the working medium and the fact of there being no boosting to a boost pressure, is that the ball pistons and the roll bodies are no ionger arranged in a common cross-sectional plane, but in two cross-sectional planes which are at an axial distance from each other.

The rotor-stator unit is elastically supported within the casing 1 of the ball piston pump.

The rotor-stator unit comprises a pot-like stator 5, in the bottom part whereof a bushing 40 protruding into the cavity 12 of the stator 5 is inserted to receive the pintle 20 and serve as abutment for the roll bodies 30, which in turn support the lifting ring 8. The pintle 20 carries the rotor 7 of which an extension serving for coupling with a drivev mechanism protrudes from the cavity 12 of the stator 5 which is closed by a closing plate 11.

Inside the pintle 20 an inflow passage 21 leads to the cylinder bore 14 in the rotor 7, which at the front side of the pintle 20 facing away from the drive mechanism leads into a chamber 45 communicating with the suction port 2 of the pump. The outflow passage 22 in the pintle 20 which can be connected with the cylinder bore 14 is continued through the stator 5 and leads into a collecting chamber 3, which is in communication with a discharge port.

The lifting ring 8 has a stepped inner bore.

The portion of the lifting ring 8 having the bigger internal diameter encircles the outer circumferential surface of the rotor 7 and extends in axial direction beyond the centre of the cylinder bore 14. The portion having the smaller internal diameter serves as running surface for the spherical roll bodies 30. The smaller internal diameter has been chosen to ensure that the roll bodies 30 roll on a smaller diameter and thus the moment of friction is reduced. The portion having the smaller diameter extends essentially from the front surface of the rotor 7 facing the bottom of the stator 5 to the bottom of the stator 5. The roll bodies 30 abut on a bushing 40 disposed in the stator 5 via a bearing ring 31; the bushing 40 and the stator 5 can also be a single unit.The width of the bearing ring 31 essentially corresponds to the axial extension of the lifting ring portion having the smaller internal diameter. The cross-sectional planes in which there is provision for abutment of the balls of the ball pistons, on the one hand, and for abutment of the spherical roll bodies, on the other hand, are at an axial distance from each other.

The ball piston pump shown in Figure 3 is very small in radial extension, since between the casing 1 and the stator 5 there is merely a lifting ring portion; the lifting ring 8 is positioned axially next to the rotor 7.

The mode of operation of the ball piston pump as shown in Figure 3 corresponds to that of the pump as shown in Figure 1 except for the boosting of the pressure medium.

The ball piston pump as shown in Figure 4 in principle corresponds to the pump illustrated in Figure 1; corresponding parts have been assigned like references. The essential difference is that there is no stator and that the bearing ring 31, against which the lifting ring 8 abuts via the roll bodies 30, is fastened directly in the casing 1. The bearing ring 31 is designed as a sheet metal part partially encircling the needle-type roll bodies 30.

The ball piston pump as illustrated in Figure 4 has essentially the same manner of guiding the working medium as the pump as shown in Figure 1, and like the latter has a total of three pump stages.

The working chamber 17 of the first boosting stage is positioned between the running surface 9 and the rotor's circumference and is divided by the balls 15 protruding over the rotor's circumference.

The working chamber of the following sec ond boosting stage is the annular chamber 16, into which the pin 19 protrudes axially.

The ball pistons 10 sliding in the rotor's cylinder bores 14 cause the pressure to be boosted in the high pressure stage.

Claims

1. A radial piston device, in particular ball piston pump, comprising at least one ball piston of which the ball, which is in rolling contact with a lifting ring, with its surface is slidably guided in a cylinder bore of a cylinder body which is rotatable around a pintle provided with inflow and outflow passages, characterised in that the lifting ring (8) is supported on the casing (1) via roll bodies (30) or via a slide bearing.

2. A radial piston device according to claim 1, characterised in that the lifting ring (8) is supported on a stator (5) elastically supported in the casing (1).

3. A radial piston device according to claim 1, characterised in that the lifting ring (8) is supported on the pintle (20).

4. A radial piston device according to any one of the preceding claims, characterised in that the ball piston (10) comprises a further piston element (25) sliding in the cylinder bore (14) and co-operating with the ball (15).

5. A radial piston device according to any one of the preceding claims, characterised in that a bearing ring (31) is disposed between the roll bodies (30) and a supporing part arranged in fixed position at the casing.

6. A radial piston device according to any one of the preceding claims, characterised in that the ball piston (10) or the ball pistons and the roll bodies (30) are arranged in a common cross-sectional plane.

7. A radial piston device according to any one of the preceding claims, characterised in that the ball piston (10) or the ball pistons and the roll bodies (30) are arranged in different cross-sectional planes which are axially spaced from each other.

8. A radial piston device according to any one of the preceding claims, characterised in that the roll bodies (30) are designed as balls.

9. A radial piston device according to any one of claims 1 to 7, characterised in that the roll bodies (30) are designed as rollers.

10. A radial piston device according to any one of claims 1 to 7, characterised in that for the support of the lifting ring (8) commercial roller bearings or slide bearings are used.

11. A radial ball piston pump substantially as herein described with reference to Figures 1 and 2, Figure 3 or Figure 4 of the accompanying drawings.