GB1585788A - Valve-controlled radial piston pump - Google Patents

Description

(54) VALVE-CONTROLLED RADIAL PISTON PUMP (71) We, BARMAG BARMER MAS CHINENFABRIK AKTIENGESELLSCHAFT, a body corporate organised under the laws of Federal Republic of Germany, of Remscheid-Lennep, Federal Republic of Germany, 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 particularly described in and by the following statement: This invention relates to a valvecontrolled radial piston pump with radially arranged outlet openings.

A radial piston pump is known from French Patent No. 1,247,443 in which a thin flexible steel ring lies above the outlet openings. This steel ring acts as a valve which is raised by the pressure of compressed oil in a respective cylinder and is stretched elastically thereby, thus clearing the outlet.

Steel has the disadvantage that its elasticity decreases or it becomes fatigued relatively quickly by its being raised successively at different points. The rate at which this takes place depends on the number of pistons, the tension in the steel and the material parameters of the steel. Plastic deformation and cold flow are produced, causing losses by leakage and thus a drop in the maximum pump pressure available.

It is not possible to use a material containing rubber since rubber loses its elastic properties and becomes brittle after a prolonged period of use and, in addition, the operating temperature may be too high for rubber to be used.

The object of the invention is to provide a radial piston pump with a valve-controlled outlet whose outlet valve has a constant sealing effect when in use without requiring greater expense than hitherto.

According to the invention there is provided a valve-controlled radial piston pump, comprising radially arranged cylinder outlets, continuous elastic ring covering all of the outlets the said ring being of a plastics material which is capable of stretching elastically by an amount greater than 5%, and a respective thin plate arranged beneath the plastics ring above each outlet.

The invention ensures that fatigue does not occur during the entire operation period so that the seal effect is always at an optimum. Furthermore, plastics materials can be used which retain the desired characteristics over a relatively wide temperature range and are insensitive to oil, thus ensuring a long life-span.

The invention is illustrated in more detail below with reference to the accompanying drawing which is a longitudinal section through an embodiment of radial piston pump formed in accordance with the invention.

The drawing shows a drive shaft 1 which has a control cam 2 and is mounted in bearings 4 in a housing 3. The housing 3 has an inlet opening 6 which communicates with the inner chambers of a plurality of hollow pistons 5 via bore holes 15 therein.

In this embodiment, the inlet opening 6 is arranged in such a way that it no longer communicates with the bore hole 15 of each piston after that piston exceeds a predetermined stroke. The pistons 5 are kept in contact with the control cam 2 by means of a spring 8.

A respective outlet opening 7 is arranged above each piston in the housing 3 and opens into an annular channel 9 which is in the form of a rectangular cross-section groove machined in the housing. The annular channel 9 communicates with a pressure pipe via a suitable bore-hole 10. Each outlet opening 7 is sealed by a thin, rectangular, steel plate 14 which is held in a pocket by a dog formed on the plate and extending at an angle thereto. A continuous plastics nng 13 capable of stretching elastically by an amount greater than 5% is stretched over all of the thin steel plates 14. The dogs mentioned above prevent the steel plates from becoming off-centered during operation.

The annular channel 9 is limited in the radial direction by a sealing ring 11 of constant diameter. Two gaskets 12 are arranged beneath the sealing ring 11 in the housing 3 at a distance from the annular channel 9 in order to provide greater protection against leakage.

When the pump is in operation, the bore-hole 15 in the pistons 5 communicate with the inlet opening 6 during a downward movement so that oil may flow into the interior of the piston. The pistons 5 are raised again by rotation of the control cam 2 so that the bore-holes 15 are cut off from the inlet opening 6. During further movement, the oil enclosed in the pistons is compressed. The pressure of the oil is so high just before the top dead centre of the piston that it raises the thin steel plate 14 and the plastics ring 13 which it supports. The compressed oil can now enter the annular channel 9, from which it can flow out via the bore-hole 10.

As soon as the piston 5 moves downwards, the thin steel plate 14 is again pressed against the outlet opening 7 by the plastics ring 13 and it seals the outlet opening tightly.

If desired the outlet opening 7 may be divided into a plurality of small bore-holes.

Alternatively a filter of constant porosity may be used instead of one or more outlet holes per piston and the compressed oil is forced through this filter. The filter also has the advantage that the compressed oil is fed to the pressure pipe without any impurities.

WHAT WE CLAIM IS: 1. A valve-controlled radial piston pump, comprising radially arranged cylinder outlets, a continuous elastic ring covering all of the outlets the said ring being of a plastics material which is capable of stretching elastically by an amount greater than 5%, and a respective thin plate arranged beneath the plastics ring above each outlet.

2. A pump according to Claim 1, wherein each plate is of steel.

3. A pump according to Claim 2 or 3, wherein the thin plates are rectangular and one edge thereof has a dog extending at an angle thereto.

4. A pump according to any preceding claim wherein each cylinder outlet opening beneath the plastics ring comprises a plurality of individual bore-holes.

5. A pump according to any one of Claims 1 to 3 wherein each cylinder outlet opening is provided by a material of constant porosity.

6. A pump according to any preceding claim, wherein the thin plates and the plastics ring are with an annular chamber rectangular cross-section which is closed on the radially outer side by a circular sealing ring.

7. A valve-controlled radial piston pump, substantially as herein described with reference to the accompanying drawing.

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

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. When the pump is in operation, the bore-hole 15 in the pistons 5 communicate with the inlet opening 6 during a downward movement so that oil may flow into the interior of the piston. The pistons 5 are raised again by rotation of the control cam 2 so that the bore-holes 15 are cut off from the inlet opening 6. During further movement, the oil enclosed in the pistons is compressed. The pressure of the oil is so high just before the top dead centre of the piston that it raises the thin steel plate 14 and the plastics ring 13 which it supports. The compressed oil can now enter the annular channel 9, from which it can flow out via the bore-hole 10. As soon as the piston 5 moves downwards, the thin steel plate 14 is again pressed against the outlet opening 7 by the plastics ring 13 and it seals the outlet opening tightly. If desired the outlet opening 7 may be divided into a plurality of small bore-holes. Alternatively a filter of constant porosity may be used instead of one or more outlet holes per piston and the compressed oil is forced through this filter. The filter also has the advantage that the compressed oil is fed to the pressure pipe without any impurities. WHAT WE CLAIM IS:

1. A valve-controlled radial piston pump, comprising radially arranged cylinder outlets, a continuous elastic ring covering all of the outlets the said ring being of a plastics material which is capable of stretching elastically by an amount greater than 5%, and a respective thin plate arranged beneath the plastics ring above each outlet.

2. A pump according to Claim 1, wherein each plate is of steel.

3. A pump according to Claim 2 or 3, wherein the thin plates are rectangular and one edge thereof has a dog extending at an angle thereto.

4. A pump according to any preceding claim wherein each cylinder outlet opening beneath the plastics ring comprises a plurality of individual bore-holes.

5. A pump according to any one of Claims 1 to 3 wherein each cylinder outlet opening is provided by a material of constant porosity.

6. A pump according to any preceding claim, wherein the thin plates and the plastics ring are with an annular chamber rectangular cross-section which is closed on the radially outer side by a circular sealing ring.

7. A valve-controlled radial piston pump, substantially as herein described with reference to the accompanying drawing.