WO1996041951A1

WO1996041951A1 - Hydraulic planetary piston motor

Info

Publication number: WO1996041951A1
Application number: PCT/DK1996/000242
Authority: WO
Inventors: Rolf Christensen; Ole Falck SØRENSEN
Original assignee: Danfoss A/S
Priority date: 1995-06-08
Filing date: 1996-06-06
Publication date: 1996-12-27
Also published as: DE19520405C2; AU5997496A; DE19520405A1

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 in a housing (8), the commutation valve comprising a rotary slide valve (21) which is pressed against a valve plate (19) by a pressure-applying plate (20) that is mounted with an axial extension (39) in a bore (9) in the housing (8). It is desirable for such a motor to be constructed so that it can be operated in two directions of rotation with negligible leakages in the region of the commutation valve. For that purpose, the extension (39) has a pressure face pointing perpendicular to the axial direction. Furthermore, a change-over device (38) is provided, which acts upon this pressure face with the higher of the two pressures at the ports, irrespective of the pressure direction between the two ports (15).

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 in a housing, the commutation valve comprising a rotary slide valve which is pressed against a valve plate by a pressure-applying plate that is mounted with an axial extension in a bore in the housing.

Such a motor is known from DE 30 29 997 C2. In the known motor the pressure-applying plate is acted upon over a very large part of its area by pump pressure. Only a relatively small region in the middle of the plate, namely, that region with which its extension is introduced into the housing, is not directly subjected to pump pressure. Under the effect of the pump pressure the pressure-applying plate presses the rotary slide valve against the valve plate. In this manner leakages between the rotary slide valve and the valve plate are kept small. In the known construction provision is furthermore made for a feed channel to pass through the pressure-applying plate. Leakages at this point are also kept small or even avoided because the pressure-applying plate is pressed with the necessary force against the rotary slide valve. Further, a pressure-applying spring is provided, which presses the rotary slide valve against the valve plate. If the direction of rotation of the motor is now reversed, the pressures at the two ports have to be exchanged. It is possible to effect this without difficulty, but as a consequence the pressure relationships at the pressure-applying plate change. The construction of the pressure-applying plate is therefore complicated if it is wished to maintain the equilibrium of hydraulic forces in both directions of rotation.

The invention is based on the problem of constructing a motor in such a manner that it combines a simple construction of the pressure-applying plate with the ability to be driven in two directions of rotation with negligible leakage in the region of the commutation valve.

In a planetary piston motor of the kind mentioned at the outset this problem is solved in that the extension has a pressure face and in that a change-over device is provided which acts upon this pressure face with the higher of the two pressures at the ports, irrespective of the pressure direction between the two ports.

One therefore ensures that this pressure face, which should run perpendicular to the axial direction or at least have such a component, is always used to press the pressure-applying plate in the direction of the rotary slide valve and consequently the rotary slide valve in the direction of the valve plate. For example, it is possible selectively to allow a specific surface region of the pressure-applying plate to be acted upon by the pressure in one port and another surface portion of the pressure-applying plate to be acted upon by the pressure in the other port. Such a construction normally requires considerable structural complexity because it is extremely difficult to counterbalance the surface regions sufficiently accurately for there to be hydraulic equilibrium in both directions of rotation, that is, for the hydraulic forces that press the pressure-applying plate in one direction to be exactly the same as the hydraulic forces that press the rotary slide valve away from the valve plate. Using the subject matter of the invention, such an accurate definition of the corresponding surfaces is no longer necessary. The pressure face is in fact always acted upon by the absolute value of the pressure difference between the two ports, regardless of the direction in which the pressure difference is acting. In this manner, in both directions of rotation it is possible to achieve equilibrium or even excess of those hydraulic forces that move the pressure-applying plate to press the rotary slide valve so firmly against the valve plate that leakages in this region remain low. Nevertheless, such a motor can be of relatively small and compact construction, so that it can be used, for example, as wheel-driving motor, for small special vehicles, for example, in a lawn mower.

The change-over device preferably acts automatically on the basis of a pressure difference direction. No additional measures therefore have to be taken on a change in the direction of rotation of the motor.

It is also especially preferred, however, for the change-over device to be arranged on the extension. It is thus located in the immediate vicinity of the pressure face, so that virtually no pressure losses which could again reduce the pressure gain, occur. In an especially preferred construction, provision is made for the extension inside the bore to have a step which forms the pressure face, for the bore to have a step, for the housing and extension to define a sealing chamber which is formed by the steps, and for a sealing ring to be arranged in the sealing chamber. This construction enables the desired change-over function to be achieved in a simple manner. Although the hydraulic fluid is able to escape through gaps between the housing and the extension, which are inevitable on account of an only finite accuracy during manufacture, it is accordingly also able to spread pressure and build it up. Onward flow of the hydraulic fluid is limited by the sealing ring, however. The sealing ring forms a pressure block for the hydraulic fluid so that the hydraulic pressures on both sides of the sealing ring are different. If the pressure of the hydraulic fluid now acts only on one side of the sealing ring, forces occur likewise only on that one side.

In that case it is especially preferred for the sealing ring to be brought in dependence on the pressure direction to bear against one of the two axial defining faces of the sealing chamber formed by the steps. The sealing ring is therefore, at least to a limited extent, movable in the axial direction in the sealing chamber. If the pressure now acts on one side of the sealing ring, the sealing ring is caused to bear against the correspondingly opposing axial defining face of the sealing chamber. The hydraulic forces can then act by way of the sealing ring on this defining face. The hydraulic forces then try to enlarge the sealing chamber, that is, to enlarge the axial distance between the sealing ring and the other axial defining face of the sealing chamber, so that in each case the desired pressure is applied to the pressure-applying plate. The axial movement need not necessarily be realized by a displacement of the sealing ring. In many cases a small rolling movement is sufficient.

It is also an advantage for movement of fluid between the housing and the extension to be possible. This allows a relatively quick pressure build-up so that on a change in direction the corresponding tight seal is reproduced relatively soon after re-start.

The pressure-applying plate is preferably sintered. On the basis of the above described construction, the pressure-applying plate has a relatively simple form. There is no need for a groove for the sealing ring to be machined. For that reason it is also possible to use relatively simple shaping methods, for example, sintering. The advantage of sintering is that one is relatively free in one's choice of material.

In a direction away from the rotary slide valve, the diameter of the bore preferably changes only to smaller diameters. This has the advantage that the motor can be assembled from one side. This simplifies manufacture quite considerably. For example, the driven shaft can be provided with the necessary accessory parts and then the resulting unit can be inserted complete into the housing. Advantages are to be gained here in particular in the case of automated manufacture.

A pressure-applying spring is advantageously arranged between the housing and the pressure-applying plate, which spring presses the pressure-applying plate towards the rotary slide valve. During start up of the motor, this pressure-applying spring serves to produce an initial pressure force so that the leaks during start-up can be kept small. During start-up the smaller force is generally sufficient because here the hydraulic forces are not as yet too great. Later on in operation, when the hydraulic forces have grown, the pressure-applying spring still serves to assist in pressing the rotary slide valve against the valve plate.

In the bore there is preferably arranged a driven shaft which projects from the housing, the driven shaft being sealed with respect to the housing by a high-pressure seal. The region of the other side of the pressure- applying plate can now also be acted upon by pump pressure or high pressure, without risk of the machine losing appreciable amounts of hydraulic fluid. The construction and the control during a change in direction of rotation are thereby simplified.

The driven shaft preferably passes through the pressure-applying plate and the rotary slide valve and has a radial bearing on the side of the rotary slide valve remote from the pressure-applying plate. The driven shaft is therefore radially mounted on both sides of the pressure-applying plate and the rotary slide valve. The spacing between the two radial bearings can consequently be increased. A more precise guidance of the driven shaft and the parts connected thereto, for example, the set of gearwheels, can therefore be achieved, which likewise improves the sealing of the machine.

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 or 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 specific 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 surface 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 face 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 take any measures from the other side (from the left in Fig. 1) .

Claims

Patent Claims

1. 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 in a housing, the commutation valve comprising a rotary slide valve which is pressed against a valve plate by a pressure-applying plate that is mounted with an axial extension in a bore in the housing, characterized in that the extension (39) has a pressure face (40) and in that a change-over device (38) is provided which acts upon this pressure face with the higher (P) of the two pressures (P, T) at the ports (15, 16), irrespective of the pressure direction between the two ports (15, 16).

2. A motor according to claim 1, characterized in that the change-over device (38) acts automatically on the basis of a pressure difference direction.

3. A motor according to claim 1 or 2 , characterized in that the change-over device (38) is arranged on the extension (39) .

4. A motor according to one of claims 1 to 3, characterized in that the extension (39) inside the bore (9) has a step (40) which forms the pressure face, in that the bore (9) has a step (41) , in that the housing (8) and extension (39) define a sealing chamber

(42) which is formed by the steps (40, 41), and in that a sealing ring (38) is arranged in the sealing chamber

(42).

5. A motor according to claim 4, characterized in that the sealing ring (38) is arranged to be brought in dependence on the pressure direction to bear against one of the two axial defining faces of the sealing chamber (42) formed by the steps (40, 41) .

6. A motor according to claim 4 or 5, characterized in that movement of fluid between the housing (8) and the extension (39) is possible.

7. A motor according to one of claims 1 to 6, characterized in that the pressure-applying plate (20) is sintered.

8. A motor according to one of claims 1 to 7, characterized in that, in a direction away from the rotary slide valve, the diameter of the bore (9) changes only to smaller diameters.

9. A motor according to one of claims 1 to 8, characterized in that a pressure-applying spring (37) is arranged between the housing (8) and the pressure- applying plate (20) , which spring presses the pressure- applying plate towards the rotary slide valve (21).

10. A motor according to one of claims 1 to 9, characterized in that in the bore (9) there is arranged a driven shaft (7) which projects from the housing (8) , the driven shaft (7) being sealed with respect to the housing (8) by a high-pressure seal (11) .

11. A motor according to claim 10, characterized in that the driven shaft (7) passes through the pressure- applying plate (20) and the rotary slide valve (21) and has a radial bearing (36) on the side of the rotary slide valve ⁽²¹⁾ remote from the pressure-applyin_g plate (20). ^y