Swashplate Axial Piston Pump

The invention relates to a swashplate axial piston pump according to the preamble of claim 1.

A swashplate axial piston pump having several pistons, as specified in the preamble of claim 1, is disclosed in German Offenlegungsschrift No. 19 39 242. The piston heads are held in contact with the swash plate by means of a retraction plate. A pressure spring acts indirectly on the retraction plate and is supported on a structural member of the axial piston pump which member is fixed in relation to the housing. In the known construction a regulating valve upon which the pressure in the pressure chamber is able to act against a spring force and which establishes a connection between the pressure chamber and the suction chamber above a certain pressure, is arranged centrally between the pistons. The spring force of the regulating valve is generated by a pressure spring which acts upon the valve spool and which is indirectly supported on the retraction plate. Thus, in the known construction, there are two pressure springs whose effects can overlap although mutual influence is not intended and is not even effective, as the spring force of the valve spring is low compared with the force of the pressure spring which holds the retraction plate on the swash plate. The latter is to be adjusted so that it is greater than the force which tends to lift the retraction plate from the swash plate whilst the axial piston pump is in operation.

A swash plate axial piston pump of this type is described and represented in German Auslegeschrift No. 10 01 593. In the case of this known axial piston pump, the retraction plate is supported on a spherical head and is fixed in the direction of the feed movement of the pistons by means of an arrangement which is specifically provided for that purpose, namely, a flange on the swash plate. A construction of this kind is not only expensive to produce and install but it also gives rise to a great deal of running noise because of the rattling of the retraction disc, particularly after a prolonged running period (wear).

The underlying object of the invention is to find a way of fixing the retraction plate to the swash plate which is simple and cheap to construct and which is also easy to install.

This object is achieved by means of an arrangement according to claim 1. In an arrangement according to the invention, the spring force of the spring which acts upon the valve body in the pressure-regulating valve, is used to fix the retraction plate on the swash plate. This fixing is elastic so that play cannot develop in the bearing, for example because of wear, and the running noise can, therefore, be kept at a low level. The fixing does not require a special, specifically provided arrangement but uses one which is already present and which is constructed according to the invention. According to claim 2 a spring piston is inserted between the valve spring and the retraction plate. This is advantageous for production and installation. The spherical sliding surface necessary for the support of the retraction plate may be formed on the spring piston.

Moreover, supporting surfaces according to claim 4 for the valve spring can be formed on the spring piston in a simple manner.

In an arrangement according to claim 5 the hydraulic fluid is conducted from the pressure chamber back into the suction chamber when the pressure-regulating valve opens.

The construction according to claim 6 results in a back-up for the force which acts upon the retraction plate towards the swash plate when the pressure-regulating valve opens. This reinforcement is based upon dynamic pressure which is built up when the hydraulic fluid flows off through the channel in the hollow cylinder.

The arrangement according to claim 7 is advantageous because a channel can be produced simply and cheaply in the spring piston as a small separate structural part.

If a sphere is inserted between the retraction plate and the spring piston it is recommended that the spring piston and the channel be constructed as in claim 8.

An embodiment which is likewise advantageous both to produce and to install is included in claim 9. In this case the working surfaces which are to be produced with a comparatively high level of precision are concentrated in a pump block in which they can expediently be incorporated. Moreover, the pump block comprises the delicate wearing parts of the swash plate axial piston pump so that when these portions become worn, they can be exchanged easily and simply. In addition, after the pump block has been installed, it automatically provides the separation between the suction and pressure chambers.

The arrangement described above also renders possible in a simple manner the coordination of a diaphragm valve plate if the pressure channels are constructed according to claim 10.

According to claim 11, the valve body has, in a manner known per se, a well tested cone head or spherical head.

The form of suction chamber described in claim 12 is advantageous because provision can be made for it from the start when a cast part is used and no special processing is therefore required. Thus, for the purpose of connecting the working areas with the suction chamber all that is needed are short radial bore holes which can be incorporated easily and quickly on the pump block.

According to claim 13 the pressure-regulating valve is a pressure relief valve which is closed up to a given working pressure and only opens when this pressure is exceeded, for example, for reasons of safety so that hydraulic fluid can flow back out of the pressure chamber to the suction chamber and higher pressure cannot, therefore, build up in the pressure chamber. The force of the valve spring and the opening surface on the cone or spherical head are, therefore, coordinated with each other in a predetermined manner.

An exemplary embodiment of the invention is described in greater detail in the following with the aid of a simplified drawing. The swash plate axial piston pump is represented in this drawing in a longitudinal section.

The swash plate axial piston pump comprises a housing indicated generally as 1, a drive shaft 2, a pumping mechanism indicated generally as 3, a suction chamber 4 to which a suction line 5 which is represented as an arrow, may be connected and a pressure chamber 6 to which a pressure line 7, which is also represented as an arrow, may be connected.

The pumping mechanism 3 consists of a swash plate 8 which is arranged at the end of the drive shaft 2 and which is to be set in rotation by the latter, several pistons 9 which are arranged in a circle and are guided along the axis 11 of the pump in hollow cylinders 12 and which form working areas 13 in front of their free front sides, a retraction plate 14 (described hereinafter), a pressure relief valve indicated generally as 15, a diaphragm valve plate 16, and a pump block 17 in or on which the movable parts of the pumping mechanism 3 are received.

The pressure relief valve 15 is arranged centrally along the axis of the pump 11 and consists of a valve body 18, the cone head 19 of which cooperates with a valve seat (bore hole) 21, and a valve spring 22 which, on the one hand, acts on the cone head 19 and, on the other hand, is received in a coaxial bore hole 23 of a spring piston 24.

The spring piston 24 can be moved along the pump axis 11 in a hollow cylinder 25, the base of which forms the valve seat 21. The retraction plate 14 and the spring piston 24 have opposed concave sliding surfaces 26, 27 which are formed as spherical segments and between which a sphere 28 is housed. In operation, the rotating swash plate 8 gives rise to a reciprocating movement of the pistons 9. The retracting movement 29 of the pistons 9 takes place in each case through the retraction plate 14, which grips from behind the flanges 31 of sliding shoes 32 which embrace spherically-shaped heads 33 of the pistons 9. As the valve spring 22 is supported on the spring piston 24, the spring force which it generates is transferred by the sphere 28 to the retraction plate 14, whereby the latter is pressed against the swash plate 8 and is thus fixed. The spring force of the pressure relief valve 15 is thus used at the same time for the purpose of fixing the retraction plate 14.

When the pistons 9 execute the feed movement 34, the hydraulic fluid in the working areas 13 is forced through pressure channels 35 into the pressure chamber 6 lifting the diaphragm valve plate 16 which immediately closes again after the feed movement 34 is completed. When the pistons 9 free radial suction channels 36 in the course of their return movement 29, hydraulic fluid is sucked out of the suction chamber 4 which extends into an annulus 37 which surrounds the pump block 17, into the working areas 13 where the hydraulic fluid is available to be forced into the pressure chamber 6 by the next feed movement 34 of the pistons 9.

When the pressure in the pressure chamber 6 exceeds a predetermined value, the valve body 18 of the pressure relief valve 15 opens so that hydraulic fluid can flow back into the suction chamber 4 through the hollow cylinder 25 and through an axial channel 39 and radial channels 41 in the spring piston 24.

The pump block 17 has a flange 42 which forms shoulders 43,44. The pump block 17 is clamped by these shoulders 43,44 between a first part 45 and a second part 46 of the housing so that the said block is simultaneously embraced on its periphery in a form-locking manner and is thus fixed both axially and radially. This clamping also serves, at the same time, to secure the diaphragm valve plate 16 which the shoulder 44 overlaps.

For repair or inspection, all that is necessary is to unscrew the screws 47 and to remove the second part 46 of the housing which encloses and covers the pressure chamber 6. The pressure side of the pump block 17 is then exposed. If a close inspection of the pumping mechanism 3 is necessary, the pump block 17 can be simply drawn out axially. Installation is similarly simple and easy by inserting the whole pumping mechanism 3 with the exception of the swash plate 8 in the exposed pump block 17.