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Title:
HYDRAULIC PLANETARY PISTON MOTOR
Document Type and Number:
WIPO Patent Application WO/1996/041950
Kind Code:
A1
Abstract:
A hydraulic planetary piston motor (1) is disclosed having a set of gearwheels (4) comprising an internally toothed annular gear (2) and an externally toothed gearwheel (3) which mesh with one another and form working chambers (5), which chambers are connectable by way of a commutation valve to a suction port and a delivery port (15) respectively, the commutation valve comprising a rotary slide valve (21) and a valve plate (19), the motor also having a driven shaft (7) which is in rotary connection with the rotating part of the set of gearwheels (4). It is desirable for such a motor to be of simple and robust construction. For that purpose, the driven shaft (7) passes through the rotary slide valve (21).

Inventors:
CHRISTENSEN ROLF (DK)
SOERENSEN OLE FALCK (DK)
Application Number:
PCT/DK1996/000241
Publication Date:
December 27, 1996
Filing Date:
June 06, 1996
Export Citation:
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Assignee:
DANFOSS AS (DK)
CHRISTENSEN ROLF (DK)
SOERENSEN OLE FALCK (DK)
International Classes:
F03C2/08; F04C2/10; (IPC1-7): F03C2/22
Foreign References:
US3841801A1974-10-15
US3771905A1973-11-13
SE385393B1976-06-28
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Claims:
Patent Claims
1. Hydraulic planetary piston motor having a set of gearwheels comprising an internally annular gear and an externally toothed gearwheel which mesh with one another and form working chambers, which chambers are arranged to be connected by way of a commutation valve to a suction port and a delivery port respectively, the commutation valve comprising a rotary slide valve and a valve plate, the motor also having a driven shaft which is in rotary connection with the rotating part of the set of gearwheels, characterized in that the driven shaft (7) passes through the rotary slide valve (21) .
2. A motor according to claim 1, characterized in that the rotary slide valve (21) is mounted non rotatably on the driven shaft (7) .
3. A motor according to claim 1 or 2, characterized in that the driven shaft (7) has a radial bearing (35, 36) on each side of the rotary slide valve (21) .
4. A motor according to one of claims 1 to 3, characterized in that, between the rotary slide valve (21) and the driven shaft (7) there is a gap (26) which forms part of a fluid path between the working chambers (5) and one of the two ports (15, 16) .
5. A motor according to claim 4, characterized in that the rotary slide valve (21) has inner valve pockets (25) which merge radially inwards into the gap (26) and depending on the rotated position produce a connection between the working chambers (5) and the gap (26) .
6. A motor according to claim 5, characterized in that the rotary slide valve (21) has outer valve pockets (23) which are arranged offset circumferentially in relation to the inner valve pockets (25) and are in fluid connection with the other of the two ports (15, 16).
7. A motor according to one of claims 4 to 6, characterized in that the rotary slide valve (21) has radially inwardly directed projections (28) with which it lies on the driven shaft (7) .
8. A motor according to claim 7, characterized in that the projections (28) are arranged circum ferentially at positions where there is also an outer valve pocket (23) .
9. A motor according to one of claims 1 to 8, characterized in that the rotary slide valve (21) has recesses (23, 25) only, which extend from one axial end face.
10. A motor according to one of claims 1 to 9, characterized in that the rotary slide valve (21) is sintered.
11. A motor according to one of claims 1 to 10, characterized in that a pressureapplying plate (20) is provided, which supports the rotary slide valve (21) from the side remote from the valve plate (19) , the pressureapplying plate (20) being centred in the housing (8) and forming a gap (47) jointly with the driven shaft (7) .
12. A motor according to claim 1, characterized in that the housing (8) and the pressureapplying plate (20) define a sealing chamber (42) , in which a sealing ring (38) is arranged, the housing (8) and the pressureapplying plate (20) each forming just one axial and one radial defining wall (40, 41) of the sealing chamber (42) .
13. A motor according to claim 11 or 12, characterized in that a spring (37) acting in the axial direction is arranged between the pressureapplying plate (20) and the housing (8) .
14. A motor according to one of claims 1 to 13, characterized in that an annular channel (18) that is connected to one of the two ports (15, 16) and which has clamping bolts (34) passing axially through it is provided.
15. A motor according to claim 14, characterized in that at least one clamping bolt (34) is introduced into a recess of the pressureapplying plate (20) .
Description:
Hydraulic planetary piston motor.

The invention relates to a hydraulic planetary piston motor having a set of gearwheels comprising an internally toothed annular gear and an externally toothed gearwheel which mesh with one another and form working chambers, which chambers are arranged to be connected by way of a commutation valve to a suction port and a delivery port respectively, the commutation valve comprising a rotary slide valve and a valve plate, the motor also having a driven shaft which is in rotary connection with the rotating part of the set of gearwheels.

Such machines are well known, see, for example, DE 30 29 997 C2. In that publication, the gearwheel orbits and rotates within the annular gear. For that purpose the annular gear has more teeth than the gearwheel. In many cases the difference in the number of teeth is 1. The gearwheel is connected to the driven shaft by way of an articulating shaft.

A similar motor is known from EP 0 399 277 Bl.

To be able to connect the working chambers in the correct position with the pressure port, the commutation valve is provided; its rotary slide valve rotates with respect to the valve plate synchronously with the gearwheel. The elements provided for control of the pressure admission to the working chambers take up a considerable amount of space. If it is wished to make such a motor small and compact, there is only relatively little space available for mounting the

driven shaft. The bearings with which the driven shaft is supported relative to the housing therefore have to be of relatively large dimensions in order to be able to withstand the stresses.

The invention is based on the problem of providing a simple and robust motor.

That problem is solved in the case of a hydraulic planetary piston motor of the kind mentioned at the outset in that the driven shaft passes through the rotary slide valve.

In this manner the limited space that is available in the case of small sizes can be utilised more profitably. The driven shaft can be guided over a longer length which makes it more stable and more robust. This extension is not associated with an additional space requirement, however, because the rotary slide valve is arranged around the driven shaft. Such a motor can be used, for example as the driving motor for a lawn-mower.

In a preferred construction, the rotary slide valve is mounted non-rotatably on the driven shaft. The driven shaft rotates synchronously with the gearwheel. In this construction the rotary slide valve accordingly rotates likewise synchronously with the gearwheel. In this manner a direct and synchronous control of the rotary slide valve in relation to the gearwheel is achieved with very simple means.

The driven shaft advantageously has a radial bearing on each side of the rotary slide valve. The two radial bearings can then be spaced axially a greater distance apart. The radial forces acting on the radial bearings

then become smaller. The bearings can be of correspondingly smaller dimensions, which despite a more simple construction results in a more robust motor.

Between the rotary slide valve and the driven shaft there is preferably a gap which forms part of a fluid path between the working chambers and one of the two ports. In this manner it is possible for fluid to get past the rotary slide valve without colliding with fluid from the other port. Altogether, with this feature a relatively compact construction can be achieved.

The rotary slide valve preferably has in this case inner valve pockets which merge radially inwards into the gap and depending on the rotated position produce a connection between the working chambers and the gap. In combination with the inner valve pockets, the gap therefore serves as a control instrument for the flow of fluid from or into the working chambers of the set of gearwheels. The rotary slide valve can in this case be of very simple and compact construction. The valve pockets therefore have to be open towards one face so that they can be brought into register with corresponding counter-openings in the valve plate. They should by definition also be open towards the gap. These valve pockets can thus be constructed as recesses opening from two edges, namely from the circumference and from one end face of the rotary slide valve, which simplifies the manufacture of the rotary slide valve quite considerably. There is no need for any control bores.

The rotary slide valve preferably has outer valve pockets which are arranged offset circumferentially in

relation to the inner valve pockets and are in fluid connection with the other of the two ports. These outer valve pockets can be constructed in exactly the same manner as the inner valve pockets, namely, as recesses which are open towards two edges. There is no need for any control bores or other through-openings in the rotary slide valve. Manufacture is relatively simple. In that construction, between the inner and the outer valve pockets the rotary slide valve has merely a wall running in a serpentine fashion which is supported on the side remote from the valve plate by a continuous wall. In this manner, great stability combined with a compact construction is achieved.

The rotary slide valve preferably has radially inwardly directed projections with which it lies on the driven shaft. The projections admittedly interrupt the gap between the rotary slide plate and the driven shaft for small circumferential sections. This can be accommodated without difficulty, however, since the remaining cross-section of the gap between the rotary slide valve and the driven shaft is sufficiently large to allow the required fluid to pass through. Centring of the rotary slide valve on the driven shaft, however, is achieved in a relatively simple manner by means of the projections.

It is especially preferred for the projections to be arranged circumferentially in positions where there is also an outer valve pocket. Where there is an outer valve pocket, radial pressure is able to act inwardly from the outside. If the projections are arranged there, they are able to absorb this pressure. Deformation of the rotary slide plate, which will admittedly occur only in extreme cases, can be counteracted by that measure.

The rotary slide valve advantageously has recesses only, which extend from one axial end. Such a construction facilitates manufacture.

The rotary slide valve is preferably sintered. By virtue of its simple yet robust construction, the rotary slide valve can be shaped by relatively inexpensive manufacturing methods. It can be sintered as an unmachined part. After that, only a few machining steps are required, for example, a grinding of the end face co-operating with the valve plate. More comprehensive machining operations, such as the construction of through-bores, are unnecessary. The opening receiving the driven shaft can be formed during the sintering process. There are no great demands on the accuracy of the gap.

A pressure-applying plate is advantageously provided, which supports the rotary slide valve from the side remote from the. valve plate, the pressure-applying plate being centred in the housing and forming a gap jointly with the driven shaft. This gap continues the gap between the rotary slide valve and the driven shaft. The fluid path between the working chambers and the one in question of the two ports is therefore also not impeded by the pressure-applying plate. Moreover, no friction occurs between the rotating driven shaft and the stationary pressure-applying plate. The pressure-applying plate ensures that the rotary slide valve is always pressed with the necessary pressure against the valve plate in order to keep the internal leakages of the motor as small as possible.

In this case it is preferred for the housing and the pressure-applying plate to define a sealing chamber, in which a sealing ring is arranged, the housing and the

pressure-applying plate each forming just one axial and one radial defining wall of the sealing chamber. This on the one hand enables the pressure-applying plate and the housing to be displaced axially with respect to one another. During such a displacement, the axial defining walls approach one another or move away from one another. The sealing ring can move axially within this sealing chamber. It can therefore take up a position either against the one or against the other axial defining wall and there form a seal. This construction has the advantage that the area which is available for receiving pressure can be altered in dependence on the pressure direction. The pressure in fact pushes the sealing ring closer and closer to the furthest removed axial end wall of the sealing chamber, so that the pressure is able to spread as far as that point. The motor can therefore operate in both directions of rotation with the desired pressure application force between rotary slide valve and valve plate being maintained.

A spring acting in the axial direction is preferably arranged between the pressure-applying plate and the housing. During start up of the motor, this spring applies the necessary pressure to hold the rotary slide valve against the valve plate. During operation, it acts as an additional force.

An annular channel that is connected to one of the two ports and which has clamping bolts passing axially through it is advantageously provided. The annular channel therefore represents the connection between one of the two ports and the rotary slide valve, or more accurately, the outer valve pockets. Because the clamping bolts pass right through the annular channel, a relatively small circle, on which the clamping bolts

can be arranged, is achieved. This measure produces a very compact motor. With a larger circle, parts of the motor of correspondingly larger dimensions would be required to prevent deformation at the pressures in question. The clamping bolts cannot be arranged further in, because the clamping bolts would otherwise come into conflict with the rotating parts. Although the clamping bolts take up part of the cross-section of the annular channel, there is still a sufficiently large free cross-section left to allow the individual working chambers to be supplied with the required pressure.

Preferably at least one clamping bolt is introduced into a recess of the pressure-applying plate. The clamping bolt thus serves at the same time to secure the pressure-applying plate against twisting. In another construction, the pressure-applying plate can be manufactured with an integral peg which fits into a corresponding recess, for example, a countersinking, in the housing. Such a construction is more stable than the anti-rotation safeguard employing just a relatively thin pin, which is additionally more difficult to mount.

The invention is described hereinafter with reference to a preferred embodiment in conjunction with the drawings, in which:

Fig. 1 is a diagrammatic cross-section through a motor, Fig. 2 is a section A-A according to Fig. 1, Fig. 3 is a section B-B according to Fig. 1, Fig. 4 is an enlarged fragmentary view from Fig. 1 and

Fig 5 is the fragmentary view according to Fig. 4 in another operational state.

A motor 1 has a set 4 of gearwheels comprising an internally toothed annular gear 2 and an externally toothed gearwheel 3. Gearwheel 3 and annular gear 2 mesh with one another and form working chambers 5, of which some are supplied with hydraulic fluid under pressure in order to expand them. During this expansion, working chambers 5 in other regions are reduced in size. Hydraulic fluid is expelled from those chambers. Because of this periodic enlargement and reduction in the size of the working chambers 5, the gearwheel 3 orbits in the annular gear 2 and in so doing rotates. This rotary movement is translated by way of an articulating shaft 6 to a driven shaft 7 which is rotatably mounted in a housing 8.

For that purpose, the housing 8 has a bore 9. At the end where the driven shaft 7 emerges from the housing 8, the driven shaft is sealed with respect to the housing by means of a dust seal 10 and an axle seal 11, which is in the form of a high-pressure seal. In that region there is also arranged an axial bearing 12 which supports the driven shaft 7 axially with respect to the housing. The axial bearing has two bearing washers 13, 14, of which the bearing washer 13 facing the housing 8 is stationary, whilst the bearing washer 14 facing the driven shaft 7 is able to rotate jointly therewith.

To feed the hydraulic fluid in and out, two ports 15, 16 are provided. Depending on the desired rotated position of the driven shaft 7, one of the two ports 15, 16 is acted upon by pump pressure P (or the pressure from a different pressure source) , whilst the other port is acted upon by tank pressure T (or the

pressure of a different pressure sink) . From port 15 the fluid passes through a channel 17 to an annular channel 18 which is defined by the housing 8 on the one side and by a valve plate 19 on the other side. Finally, the annular channel 18 is defined radially inwardly by a rotary slide valve 21. The rotary slide valve 21 is pressed by a pressure-applying plate 20 towards the valve plate 19. In the valve plate 19 there are channels 22 which are connected to the working chambers 5. By means of the rotary slide valve 21, when this is in the appropriate position, these channels 22 are either supplied with hydraulic fluid under pressure or connected to tank pressure.

The construction of the rotary slide valve 21 is apparent from Figs 1 and 3. The rotary slide valve is a substantially flat plate which is arranged between the pressure-applying plate 20 and the valve plate 19. On the side facing the valve plate 19, the rotary slide valve 21 has outer valve pockets 23 through which hydraulic fluid is able to flow from the annular channel 18 into the channel 22, as illustrated in Fig. 3 by the arrow 24. The outer valve pockets 23 are here matched to the channels 22, and thus to the working chambers 5, so that only the working chambers 5 that are in the process of expanding are supplied with hydraulic fluid under pressure.

Fluid that is displaced from working chambers that are in the process of becoming smaller is passed through inner valve pockets 25. These inner valve pockets open towards an annular gap 26 which is formed between the rotary slide valve 21 and the driven shaft 7, which for that purpose passes through the rotary slide valve with an extension 27. The rotary slide valve 21 is in this case supported on the extension 27 of the shaft by

means of projections 28. These projections are arranged radially beneath outer valve pockets 23.

The rotary slide valve 21 further has a driver 29 which is arranged in a corresponding recess 30 on the extension 27 of the driven shaft 7. In this manner a synchronous movement of the rotary slide valve 21 and driven shaft 7 with respect to one another is ensured.

On the side lying opposite the valve plate 19, the pressure-applying plate 20 is held stationary in the housing. For that purpose it is provided with a projection 31 which engages in a corresponding recess 32 in the housing 8.

The housing 8, the valve plate 19, the set of gearwheels 4 and a cover 33 are held together by clamping bolts 34 which run substantially axially and are arranged in a circle around the driven shaft 7. It is desirable that this circle should have as small a radius as possible. For that reason the clamping bolts 34 pass through the annular channel 18, which does constrict the free flow cross-section somewhat yet still allows sufficient room for the hydraulic fluid to be able to get into and out of the working chambers. The pressure-applying plate 20 can then be made large enough to reach as far as the region of the clamping bolts 34. If the pressure-applying plate 20 is provided with a suitable recess for the clamping bolts 34 to pass through, it can be secured in this manner against twisting.

Because the driven shaft 7 is taken with its extension 27 right through the rotary slide valve 21, the driven shaft can be mounted at two points spaced apart from one another. Two radial bearings 35, 36, which are

located on opposite sides of the rotary slide valve 21, are provided for that purpose. Because of the large spacing, the two radial bearings 35, 36 have to absorb only relatively small moments and can accordingly be of smaller dimensions.

The pressure-applying plate 20 is pressed by means of a spring 37, which is provided between the pressure- applying plate 20 and the housing 8, towards the valve plate 19 and thus presses the rotary slide valve 21 onto the valve plate 19. This produces a certain tightness of seal, in particular at the instant of starting up, where the necessary hydraulic pressures are not necessarily available.

Further, as best seen in Figs 4 and 5, the pressure- applying plate 20 is secured in the housing 8 in a predetermined manner and sealed by means of a sealing ring 38.

The pressure-applying plate 20 in fact has an axial extension 39 which points away from the rotary slide valve 21. This axial extension 39 is inserted in the bore 9 of the housing 8. The extension 39 has inside the bore 9 a step 40, that is to say, a reduction in its diameter. Similarly, the bore 9 has a step 41, that is, an increase in diameter, in a region which surrounds the axial extension 39. A sealing chamber 42 in which the sealing ring 38 is arranged is formed between the two steps 40, 41. The sealing chamber 42 is here illustrated with an exaggeratedly large length. A comparison between Figs 4 and 5 shows that the sealing ring 38 is able to move axially in this sealing chamber 42. It can therefore (Fig. 4) lie against an axial defining wall which is formed by the step 41 in the housing. But it can also (Fig. 5) lie against the

other axial end wall of the sealing chamber 42 which is formed by the step 40 on the extension 39 of the pressure-applying plate 20.

The sealing ring 38 forms a pressure block in each case. Whereas fluid is able to get between the housing 8 and the pressure-applying plate 20 through gaps which are inevitable on account of limited accuracy during manufacture, the sealing ring 38 prevents further onward flow of fluid. If the annular channel 18 is now at pump pressure P, the fluid applies the sealing ring 38 to the axial defining wall of the sealing chamber 42 which is formed by the step 41. In this case the pump pressure is able to act on the area of the pressure- applying plate 20 which lies radially beyond a line 43. The force generated thereby is sufficient to overcome the counter-forces formed between valve plate 19 and rotary slide valve 21 and thus to lead to a tightly sealed engagement of the rotary slide valve 21 on the valve plate 19.

If, on the other hand, the direction of rotation of the machine is reversed, as illustrated in Fig. 5, the bore 9 is under pump pressure P. The pressure in the annular channel 19 on the other hand is the tank pressure. In that case, the pump pressure P pushes the sealing ring 38 to the other axial defining wall formed by the step 40. The pump pressure P can then act on an area which lies radially inside a line 44. The annular region between the two lines 43 and 44 is therefore always acted upon by pump pressure. The corresponding surfaces of the pressure-applying plate 20 which are exposed to pressure can then be dimensioned relatively easily so that, taking into account the area between the lines 43 and 44 constantly under pump pressure P, there is always sufficient force available to press the

rotary slide valve 21 against the valve plate 19. This improves the sealing of the machine in a simple manner. The sealing ring 38 forms as it were an automatic change-over means which, irrespective of the pressure direction between the two ports, acts upon a specific pressure area with the higher of the two pressures at the ports. The sealing ring 38 is moved by the pressure difference.

The driven shaft 7 additionally has a channel 46 which is able to conduct fluid for lubrication purposes to the axial bearings 12, 13, 14. At the same time, it can drain off fluid that has escaped into the inside of the driven shaft 7 on account of the internal leakage of the set of gearwheels 4. At least within the extension 27 there is a cavity 147 for receiving the articulating shaft 6.

As apparent from Fig. 1, starting from the pressure- applying plate 20, the diameter of the bore 9 of the housing 8 becomes increasingly smaller. The motor 1 can accordingly also be assembled from one side only. For example, the driven shaft 7 can be inserted in the housing with the necessary seals and bearings. The pressure-applying plate 20 is then mounted. Further, the rotary slide valve 21 and the valve plate 19 can be put in position (still from the right-hand side in Fig. 1) . Finally, together with the universal shaft 6 the set of gearwheels 4 is mounted and everything is closed off by the cover 33. Finally, the clamping bolts 34 are secured. It is not necessary to do anything from the other side (from the left in Fig. 1) .