GB2302569A - Hydraulic axial piston machine - Google Patents

Description

- 1 Hydraulic axial piston machine.

2302569 The invention relates to a hydraulic axial piston machine having a cylinder drum, in which at least one cylinder is arranged, and a shaft which is connected to the cylinder drum so that they rotate together.

The construction of such machines in known in principle. Pistons are arranged in the cylinders to move back and forth. At the end at which they project from the cylinder, the pistons bear, by means of a slide shoe, against a swash plate. When the machine is operated as a motor, the other end of the piston, more precisely, the pressure chamber formed there, is periodically supplied with fluid under pressure, so that the cylinder drum rotates on the swash plate on account of the forces resulting from the inclination of the swash plate. This rotation is conveyed to the shaft and taken to the outside as the driving power. In pump operation, the power progression is reversed. Here, the shaft is rotated and with the assistance of the piston, which moves up and down on account of the inclination of the swash plate, hydraulic fluid is sucked into the working chamber and pressurized.

In order to have a reliable and durable connection between shaft and cylinder drum, the shaft and cylinder drum have in many cases been manufactured as one piece. Since the shaft has a substantially smaller diameter than the cylinder drum, this represents considerable expense in manufacture. A comparatively large amount of surplus material has to be removed, in general by turning off on a lathe or by similar materialremoving machining operations.

As an alternative to this, the shaft and cylinder drum can be constructed as separate parts and joined together subsequently. A weakness in this case, however, is the transfer of torque. Normally, multiple-spline profiled members are used for that purpose, so that a number of working faces are available for the transfer of torque. The problem of that, however, is that when all working faces of the multiple-spline profiled member are to be acted upon with the same forces, high-precision manufacture is required, which again makes manufacture more expensive. If the profiled member is not manufactured with the desired accuracy, individual subfaces are acted upon more forcefully than others and wear out correspondingly more quickly. In particular in the case of loads on the connection which change violently, this leads sooner or later to rattling of the machine, which is the first sign of wear. A machine that rattles cannot be expected to have a long service life.

The invention is based on the problem of providing an axial piston machine that is simple to manufacture, and has a long service life for the connection between shaft and cylinder drum.

That problem is solved in an axial piston machine of the kind mentioned in the introduction in that the shaft has a first thread and the cylinder drum has a second thread, and the shaft and the cylinder drum are screwed to one another by means of the two threads, the shaft and the cylinder drum each having a respective axial stop member, which stop members lie adjacent to one another.

Threads can be produced relatively easily. Their accuracy need not be especially high. For assembly, shaft and cylinder drum are simply screwed to one another. During the screwing-together operation, although the shaft and the cylinder drum are rotated with respect to one another, the opportunity for rotation exists in practice only for as long as both axial stop members of shaft and cylinder drum still do not lie against each other. As soon as they lie adjacent, further turning with respect to one another, at least in the screwing-in direction, is not possible, because the inward movement of the shaft into the cylinder drum necessary for that purpose is prevented by the axial stop members. A small further rotation of the shaft with respect to the cylinder drum then leads, if it is effected with the necessary torque, to jamming of the cylinder drum and the shaft against each other, so that releasing the two parts from one another is possible only with considerable effort, that is, by applying the same or a greater torque. The tightening torque must therefore be chosen to be greater than the greatest torque occurring in operation. This is easily possible, however, because both in the case of the shaft and in the case of the cylinder drum there is a relatively large diameter available, so that the two threads can be made large enough to absorb the corresponding torques. With this kind of connection, rattling is virtually excluded. The connection is accordingly durable, which leads to an increased service life of the machine in this region.

Preferably, the first thread is in the form of an external thread and the second thread is in the form of an internal thread. The first thread is located on the shaft, which normally has a smaller diameter than the cylinder drum. The thread can here be arranged in the region of the circumference, which allows a very economic use of material. Similarly, it is advantageous to form the bore for the internal thread in the cylinder drum, because here the necessary wall thickness is available in order to be able to absorb greater forces as well.

The axial stop members are preferably formed by an increase in diameter of the bore receiving the internal thread and/or by a reduction in diameter of the part having the external thread. The two axial stop members are then located in the immediate vicinity of the threads. When the two parts shaft and cylinder drum are tightened up against each other, the fixing is restricted to a relatively small region. The risk that larger - material regions will become deformed and thereby contribute to a loosening of the connection, is relatively small.

The thread direction preferably corresponds to the running direction of the machine. In the case of pumps, a right-hand thread is chosen in the case of a pump running clockwise and a left-hand thread is chosen in the case of a pump running anti-clockwise. In the case of a motor, this is reversed. A motor running clockwise is accordingly provided with a lefthand screw and a motor running anticlockwise is provided with a righthand screw. Upon any stress, the thread is then loaded so that it only draws the two axial stop members even closer together. In that case, final tightening of the two parts shaft and cylinder on assembly is unnecessary.

As an addition or an alternative thereto, the threaded connection can be self-locking. Self-locking threads are known per se. For example, a locking ring can be used, which prevents unscrewing, that is, rotating of the two threads with respect to one another in the loosening direction. The axial stop members may also be provided with faces having teeth with lock into one another during screwing together. This is possible in particular when the teeth have flanks of different inclination.

Finally, in a further preferred construction, the threads are adhesively secured to one another. For reliable adhesive securing, many adhesives require a certain pressure. This pressure can be produced relatively easily within the thread. The two threads (or even just one of them) can therefore be provided with the adhesive, and the two threads can then be screwed together. The pressure which then arises during tightening up imparts the necessary strength to this adhesive connection.

A further advantage of such a connection is provided when the shaft is arranged in a through-opening in the cylinder drum and has a channel which connects the opening with a shaft region outside the cylinder drum. Such a construction is important principally only for initial operation. For example, pumps have to have air removed from them before being put into use. The opening in which the internal thread is arranged can be used for this removal of air. The air rising up in that opening can be brought through the channel within the shaft to the outside. If desired, the channel can be closed again after removal of air has finished.

With the two-part construction it is advantageously possible for shaft and cylinder drum to consist of different materials. For example. a somewhat more stable material can be used for the shaft because with a smaller diameter it has to absorb the same torque as the cylinder drum does. For the cylinder drum on the other hand, a somewhat less expensive material can be used.

Sliding-contact faces of the cylinder drum are preferably covered with a material that has a higher wear-resistance than the material from which the cylinder drum is formed. The wear-resistance comprises in particular an increased abrasion resistance. This increased wear-resistance or abrasion-resistance is necessary only at those places where friction actually occurs. This is the case only, however, at the slidingcontact faces, with which the cylinder drum is guided in the housing. If a less expensive, and thus in many cases also less resistant, material is used for the cylinder drum, the added fact that the sliding-contact faces are covered with the material that has a higher wearresistance means that the operating properties are nevertheless virtually the same as they always are.

A ring of the wear-resistant material is preferably tightly fitted to the circumference of the cylinder drum, at least over a part of its axial extent. This ring can also be arranged in a groove from which it stands proud only slightly. The tight-fitting application can be effected, for example, by a shrinkdown process.

The term "ring" is not intended here to be restricted to a separate machine element. The ring can also be produced in situ, for example, by a coating on the circumferential face of the cylinder drum, in particular a plasma coating or a ceramic coating; in 8 - that case no particular demands are made of the quality of the surface which forms the substrate for the coating.

The wear-resistant material is preferably high-grade steel. High-grade steel presents at the same time satisfactory resistance to corrosion by the hydraulic fluid, which is especially important when water is being used as the hydraulic fluid.

A shaft end projecting into the cylinder drum advantageously serves as abutment for a slide shoepressure-applying arrangement which includes a spring. Through the choice of shaft, or more precisely, through the choice of the length of the shaft end projecting into the cylinder, the biassing characteristic of the slide shoe-pressure-applying arrangement can be modified. Further measures for providing an abutment for the spring are unnecessary.

A hydraulic axial piston machine will now be described, by way of example only, with reference to the single figure of the accompanying drawing, which showsa diagrammatic cross-section of part of the axial piston machine.

Referring to the drawing, the Figure illustrates a cylinder drum 2 and a shaft 3 of an axial piston machine 1. The cylinder drum 2 has at least one cylinder 4 in which a piston 5 is arranged to move back and forth in the direction of a double arrow 6. The piston 5 has one end projecting from the cylinder drum 2. At this end a slide shoe 8 is secured to the piston 5 by way of a joint arrangement 7. The slide shoe 8 bears on a swash plate 9 and is held in contact with the swash plate by means of a pressure plate 10.

At the opposite end, a control plate 11 is provided, which has a supply opening 12 for each cylinder 4. The control plate 11 is connected to the cylinder drum 2 by way of a plug-in bushing 13 for each cylinder 4.

At its end adjacent to the cylinder drum 2 the shaft 3 has an external thread 14 provided on a portion of reduced diameter. This external thread 14 is screwed into an internal thread 15 which is arranged in a throughbore 16 in the cylinder drum 2. The depth to which the shaft 3 is screwed into the cylinder drum 2 is limited by two axial stop members 17, 18. The stop member 17 belonging to the shaft 3 is formed by enlarging the diameter of the shaft with respect to the portion having the external thread 14. The stop member 18 associated with the cylinder drum 2 is formed by the end face of the cylinder drum 2. It could, however, instead of being formed by the end face of the cylinder drum 2, also be formed by an internal stop face spaced from the end face of the drum and cooperating with the stop member 17, such an internal stop face being produced by an enlargement (relative to the diameter of the internal thread) of the diameter of the bore 16 receiving the external thread 14. If necessary, the diameter of the shaft 3 may be reduced in the region adjacent the end of the external thread 14 to allow it to enter the enlarged portion of the bore 16.

The shaft 3 can therefore be screwed up to a certain depth into the cylinder drum 2. After that, the two stop members 17, 18 lie adjacent to one another. Further rotation is virtually impossible. Additional torque acting upon the shaft 3 and the cylinder drum 2 to move them towards one another leads, at any rate, to jamming of the two threads 14, 15 against each other, so that shaft 3 and cylinder drum 2 can be released from one another again only by applying an increased torque. This torque can be chosen to be larger than the torque normally occurring in operation. The torque required for release can be additionally increased by constructing the pair of threads 14, 15 to be self-locking. For example, teeth or similar configurations can be provided here. In an alternative construction, the two threads 14, 15 can be adhesively secured to one another. As the two threads 14, 15 are tightened, the jamming force required for adhesion is produced.

To avoid shearing, a hollow groove or circumferential recess 19 is provided at the end of the thread adjacent to the shaft 3.

At the end adjacent to the pressure plate 10, the cylinder drum 2 has a high-grade steel ring 20, which is shrunk onto the circumference of the cylinder drum 2.

11 - High-grade steel has a higher wear-resistance or abrasion-resistance than the material of which the cylinder drum 2 is made, and is more resistant to corrosion, which is especially advantageous when using water as the hydraulic fluid.

At its end facing the cylinder drum 2, the pressure plate 10 has a universal ball joint 21 which lies against a bearing piston 22. The bearing piston is arranged in an enlargement 23 of the bore 16 and is likewise movable back and forth slightly in the direction of the double arrow 6. The bearing piston 22 bears by way of a spring 24 against the end of the shaft 3 which has been screwed into the cylinder drum 2. By means of different shafts, more precisely, by different lengths of the portion screwed into the cylinder drum 2, the bias of the spring 24 can be changed and adapted to different requirements.

If the machine 1 is to be used as a pump, it is necessary to remove air from it before it is put into use. Such commissioning must always be effected whenever the fluid to be pumped has left the machine 1. A critical region in this case is a chamber 25 in which the slide shoes 8 move. A channel 26 which joins the bore 16 to a region outside the cylinder drum 2 is therefore provided in the shaft 3 for removal of air. An outlet opening 27 is provided there. Air passes into the bore through gaps found as a consequence of bearing 10, slackness between the universal ball joint 21 and the bearing piston 22 or between the bearing piston 22 and the enlargement 23.

Claims (13)

C L A I M S:

1. A hydraulic axial piston machine having a cylinder drum, in which at least one cylinder is arranged, and a shaft which is connected to the cylinder drum so that they rotate together, wherein the shaft has a first thread and the cylinder drum has a second thread and the shaft and the cylinder drum are screwed to one another by means of the two threads, the shaft and the cylinder drum each having a respective axial stop member, which stop members lie adjacent to one another.

2. A machine according to claim 1, wherein the first thread is in the form of an external thread and the second thread is in the form of an internal thread.

3. A machine according to claim 1, wherein the axial stop members are formed by a first face defined by an increase in diameter of the bore receiving the external thread and by a second face defined by a change in diameter of the part having the external thread.

4. A machine according to one of claims 1 to 3, wherein the thread direction corresponds to the running direction of the machine.

5. A machine according to claim 1, wherein the threaded connection is self-locking.

6. A machine according to one of claims 1 to 5, wherein the threads are adhesively secured to one another.

- 14

7. A machine according to one of claims 1 to 6, wherein the shaft is arranged in a through-opening in the cylinder drum and has a channel which connects the opening with a shaft region outside the cylinder drum.

8. A machine according to one of claims 1 to 7, wherein the shaft and cylinder drum consist of different materials.

9. A machine according to one of claims 1 to 8, wherein sliding-contact f aces of the cylinder drum are covered with a material that has a higher wear-resistance than the material from which the cylinder drum is formed.

10. A machine according to claim 9, wherein a ring of the wear-resistant material is tightly fitted over the circumference of the cylinder drum, at least over a part of its axial extent.

11. A machine according to claim 9 or 10, wherein the wear-resistant material is high-grade steel.

12. A machine according to one of -.laims 1 to 11, wherein a shaft end projecting into the cylinder drum serves as abutment for a slide shoepressure-applying arrangement which includes a spring.

13. A hydraulic axial-piston machine substantially as herein described with reference to, and as illustrated by, the single figure of the accompanying drawings.