GB2102082A

GB2102082A - Radial piston pump

Info

Publication number: GB2102082A
Application number: GB08218856A
Authority: GB
Inventors: Georg Liska
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1981-07-08
Filing date: 1982-06-30
Publication date: 1983-01-26
Also published as: FR2509386A1; DE3126917C2; FR2509386B1; GB2102082B; JPS5815770A; IT8246840A1; BR8203941A; JPH0257232B2; IT1159206B; IT8246840A0; DE3126917A1; ZA823963B

Abstract

A radial piston pump has in each cylinder 6, a pin 10, which is urged by a spring 5 against a screwthreaded cap 7 which closes the cylinder. The pin effectively makes a point contact with the cap, thus reducing the frictional force, required for rotation of the piston. The pistons are reciprocated by the cam 3. The pin 10 has the effect of a reducing the dead space 8, thus improving the intake characteristic of the pump, and b aiding running in of the piston, by reducing the resistance to rotation of the piston in the cylinder. <IMAGE>

Description

SPECIFICATION Radial piston pump This invention relates to a radial piston pump.

A radial piston pump having a pin which extends into the pressure chamber of the delivery piston and is rigidly attached to a screwed cap is known, for example, from German Offenlegungsschrift 22 48 518. On the one hand a pin of this kind reduces the clearance volume for pressurised oil in the pressure chamber above the delivery piston, and on the other hand it acts as a guide for a spring which forces the delivery piston against an eccentric. A reduction in the clearance volume can improve the intake behaviour of the pump, since at the start of the delivery operation the enclosed amount of air in the delivery piston pressure chamber is substantially smaller.

Consequently the associated outlet valve opens early.

German Patent Specification 27 44 006 discloses a concave construction of the end of the delivery piston which engages an eccentric. As a result of this feature, there is point pressure contact of the piston end against the eccentric.

Moreover, due to slight angular errors of the piston axis in relation to the shaft axis, due to manufacture or loading, a component of force is operative around the piston longitudinal axis, which enables the piston to rotate and therefore makes possible uniform running-in of the piston end, thus substantially reducing the risk of scoring.

The invention, which starts from a piston pump of the construction mentioned at the beginning (German Offenlegungsschrift 22 48 518), has the object of further improving the running-in behaviour at low constructional expense.

Accordingly, the present invention consists in a radial piston pump for hydraulic installations, comprising at least one eccentric-actuated, spring-loaded delivery piston, a cylinder bore receiving the delivery piston and being closed by a screwthreaded cap, and a pin extending into a pressure chamber disposed between the screwthreaded cap and the delivery piston in order to reduce the clearance volume of said chamber, wherein the pin is retained in bearing engagement against the screwthreaded cap by means of the spring loading the delivery piston, and there is effectively point contact between the screwthreaded cap and the pin, the point of contact lying substantially on the axis of the pin.

Thus, the contact pressure spring for the delivery piston bears via a separate pin with, for example, a crowned end face, against the screwthreaded cap. The small, effectively pointform bearing surface substantially reduces the frictional force on the screwthreaded cap, so that rotary motion of the delivery piston about its longitudinal axis is facilitated and consequently the loading of the piston end is further reduced. It is essential for reducing the frictional force that the effective point of contact of the pin with the screw-threaded cap lies substantially on the axis of the pin.

The invention can be used with a flat piston end or particularly advantageously with a concave piston end, as disclosed in German Patent Specification 27 44 006.

The easier rotation of the delivery piston about its axis, resulting from the reduced torque, affords the following advantages: a) improved running of the piston end; b) reduced wear during its whole life; c) reduced variation in delivery flow during the whole life, due to the reduced wear on the piston end; d) reduced variation in pressure pulsation during life, due to the reduced wear; e) no additional components are needed. The improvement is achieved by small alterations of existing constructional members, so that there is no appreciable extra expense in manufacture.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate example embodiments diagrammatically and in which: Figure 1 is a partial longitudinal section through a radial piston pump in accordance with the invention, and Figures 2 to 6 show further modifications.

Figure 1 shows a driving shaft 2 mounted in a casing 1 and having an eccentric 3. A delivery piston 4 is retained in bearing engagement against the eccentric 3 by a spring 5. A cylinder bore 6 in the casing 1 accommodating the delivery piston 4 is closed by a screwthreaded cap 7. A pin 10 is provided to limit the clearance volume in a pressure chamber 8. According to this embodiment of the invention, the pin 10 has a convex end face 11 bearing by means of the force of the spring 5 against a flat or concave internal surface of the screwthreaded cap 7. The internal surface of the screwthreaded cap 7 can also be convex provided its radius is clearly greater than that of the end face of the pin 10.

Figure 2 shows a modification in which the end face of the pin is formed with a small axial projection 21.

The modified pin illustrated in Figure 3 has a conical end face 31.

In the modification shown in Figure 4, the pin has a flat end face, but the screwthreaded cap has a small, internal, axial projection 40.

A conical recess 50 is machined on the inside of the screwthreaded cap illustrated in Figure 5, a ball 51 being inserted between the recess 50 and a flat end face of the pin.

Lasity, the modification illustrated in Figure 6 employs a screwthreaded cap formed internally with a recess having a convex base 60, again engaging with a flat end face on the pin.

1. A radial piston pump for hydraulic installations, comprising at least one eccentricactuated, spring-loaded delivery piston, a cylinder bore receiving the delivery piston and being closed by a screwthreaded cap, and a pin extending into a pressure chamber disposed between the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Radial piston pump This invention relates to a radial piston pump. A radial piston pump having a pin which extends into the pressure chamber of the delivery piston and is rigidly attached to a screwed cap is known, for example, from German Offenlegungsschrift 22 48 518. On the one hand a pin of this kind reduces the clearance volume for pressurised oil in the pressure chamber above the delivery piston, and on the other hand it acts as a guide for a spring which forces the delivery piston against an eccentric. A reduction in the clearance volume can improve the intake behaviour of the pump, since at the start of the delivery operation the enclosed amount of air in the delivery piston pressure chamber is substantially smaller. Consequently the associated outlet valve opens early. German Patent Specification 27 44 006 discloses a concave construction of the end of the delivery piston which engages an eccentric. As a result of this feature, there is point pressure contact of the piston end against the eccentric. Moreover, due to slight angular errors of the piston axis in relation to the shaft axis, due to manufacture or loading, a component of force is operative around the piston longitudinal axis, which enables the piston to rotate and therefore makes possible uniform running-in of the piston end, thus substantially reducing the risk of scoring. The invention, which starts from a piston pump of the construction mentioned at the beginning (German Offenlegungsschrift 22 48 518), has the object of further improving the running-in behaviour at low constructional expense. Accordingly, the present invention consists in a radial piston pump for hydraulic installations, comprising at least one eccentric-actuated, spring-loaded delivery piston, a cylinder bore receiving the delivery piston and being closed by a screwthreaded cap, and a pin extending into a pressure chamber disposed between the screwthreaded cap and the delivery piston in order to reduce the clearance volume of said chamber, wherein the pin is retained in bearing engagement against the screwthreaded cap by means of the spring loading the delivery piston, and there is effectively point contact between the screwthreaded cap and the pin, the point of contact lying substantially on the axis of the pin. Thus, the contact pressure spring for the delivery piston bears via a separate pin with, for example, a crowned end face, against the screwthreaded cap. The small, effectively pointform bearing surface substantially reduces the frictional force on the screwthreaded cap, so that rotary motion of the delivery piston about its longitudinal axis is facilitated and consequently the loading of the piston end is further reduced. It is essential for reducing the frictional force that the effective point of contact of the pin with the screw-threaded cap lies substantially on the axis of the pin. The invention can be used with a flat piston end or particularly advantageously with a concave piston end, as disclosed in German Patent Specification 27 44 006. The easier rotation of the delivery piston about its axis, resulting from the reduced torque, affords the following advantages: a) improved running of the piston end; b) reduced wear during its whole life; c) reduced variation in delivery flow during the whole life, due to the reduced wear on the piston end; d) reduced variation in pressure pulsation during life, due to the reduced wear; e) no additional components are needed. The improvement is achieved by small alterations of existing constructional members, so that there is no appreciable extra expense in manufacture. In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate example embodiments diagrammatically and in which: Figure 1 is a partial longitudinal section through a radial piston pump in accordance with the invention, and Figures 2 to 6 show further modifications. Figure 1 shows a driving shaft 2 mounted in a casing 1 and having an eccentric 3. A delivery piston 4 is retained in bearing engagement against the eccentric 3 by a spring 5. A cylinder bore 6 in the casing 1 accommodating the delivery piston 4 is closed by a screwthreaded cap 7. A pin 10 is provided to limit the clearance volume in a pressure chamber 8. According to this embodiment of the invention, the pin 10 has a convex end face 11 bearing by means of the force of the spring 5 against a flat or concave internal surface of the screwthreaded cap 7. The internal surface of the screwthreaded cap 7 can also be convex provided its radius is clearly greater than that of the end face of the pin 10. Figure 2 shows a modification in which the end face of the pin is formed with a small axial projection 21. The modified pin illustrated in Figure 3 has a conical end face 31. In the modification shown in Figure 4, the pin has a flat end face, but the screwthreaded cap has a small, internal, axial projection 40. A conical recess 50 is machined on the inside of the screwthreaded cap illustrated in Figure 5, a ball 51 being inserted between the recess 50 and a flat end face of the pin. Lasity, the modification illustrated in Figure 6 employs a screwthreaded cap formed internally with a recess having a convex base 60, again engaging with a flat end face on the pin. CLAIMS

1. A radial piston pump for hydraulic installations, comprising at least one eccentricactuated, spring-loaded delivery piston, a cylinder bore receiving the delivery piston and being closed by a screwthreaded cap, and a pin extending into a pressure chamber disposed between the screwthreaded cap and the delivery piston in order to reduce the clearance volume of the chamber, wherein the pin is retained in bearing engagement with the screwthreaded cap by means of the spring loading the delivery piston, and there is effectively point contact between the screwthreaded cap and the pin, the point of contact lying substantially on the axis of the pin.

2. A radial piston pump as claimed in claim 1, wherein the end face of the pin engaging the screwthreaded cap is convex.

3. A radial piston pump as claimed in claim 1, wherein the end face of the pin engaging the screwthreaded cap has a small axial projection.

4. A radial piston pump as claimed in claim 1, wherein the end face of the pin engaging the screwthreaded cap is conically pointed.

5. A radial piston pump as claimed in claim 1, wherein the screwthreaded cap has a small axial projection which cooperates with the end face of the pin.

6. A radial piston pump as claimed in claim 1, wherein the screwthreaded cap has an internal conical recess, and a ball is inserted between the end face of the pin and the base of the recess in the cap.

7. A radial piston pump as claimed in claim 1, wherein the screwthreaded cap has an internal recess with a crowned base.

8. A radial piston pump for hydraulic installations, substantially as herein described with reference to and as shown in the accompanying drawings.