GB1564854A

GB1564854A - Gerotor-type rotary fluid-pressure machine

Info

Publication number: GB1564854A
Application number: GB4687/77A
Authority: GB
Original assignee: Danfoss AS
Current assignee: Danfoss AS
Priority date: 1976-02-17
Filing date: 1977-02-04
Publication date: 1980-04-16
Also published as: DK62077A; JPS52100604A; DE2606172A1; SE7701700L; SE433375B; JPS5547237B2; FR2341758B1; BR7700925A; DK147950B; FR2341758A1; ES455914A1; IT1072900B; DD128197A5; DE2606172C2; BE850931A

Description

(54) IMPROVEMENTS IN AND RELATING TO A GEROTOR TYPE ROTARY FLUID-PRESSURE MACHINE (71) We, DANFOSS A/S, a Danish Company, of DK 6430 Nordborg, Denmark, 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 gerotor-type rotary fluid-pressure machine comprising two toothed elements, namely an externally toothed gear wheel and an internally toothed gear ring, the elements meshing with each other and having parallel axes, one of the elements being rotatable about its axis, and the axis of the gear wheel being orbitally movable about the axis of the gear ring, the ring and wheel being mounted between two end walls which define working chambers with the gear ring and the gear wheel, and a coupling shaft extending through an aperture in one of the end walls and being in driving engagement with a central aperture in the gear wheel.

Such machines may be used as motors, pumps or fluid metering devices. They are used as a drive for vehicle and machines, in hydrostatic steering units and for many other applications.

In such machines, the spacing between the two end walls must be so selected that the gear wheel can turn without considerable friction losses. This leads to the formation of gaps causing leakage losses between the gear wheel and the adjoining end walls. In addition, the aperture in the said one end wall has to be comparatively large because, to transmit the desired power, the shank of the coupling shaft must have a certain cross-section and the aperture must be appropriately larger to take into account the gyratory motion of the shaft. However, this means that, if a permissible amount of leakage loss is not to be exceeded, the diameter of the gear wheel has to be chosen to be so large that the facing areas of the gear wheel and the said one end wall do not become too small.

This necessitates a corresponding large gear ring and is in conflict with basic engineering requirements of building machines that are as small as possible. On the other hand, excessively large leakage losses lead to a higher slip. This is particularly detrimental in machines for controlling steering units because the displacement prescribed by the steering wheel is not proportionally transmitted to the steered wheels and there must be continuous further control even during rectilinear travel with a lateral load on the steered wheels. With given radial dimensions for the machine, the narrower the width of the gear wheel, the more disruptive are these leakage losses because the leakage losses amount to a higher percentage of the total quantity of fluid in the working chambers.

The invention is based on the problem of providing a rotary machine of the aforementioned kind in which the radial dimensions can be kept small without exceeding the permissible leakage losses.

The present invention provides a gerotortype rotary fluid-pressure machine comprising two toothed elements, namely an externally toothed gear wheel and an internally toothed gear ring, the elements meshing with each other and having parallel axes, one of the elements being rotatable about its axis, and the axis of the gear wheel being orbitally movable about the axis of the gear ring, the ring and wheel being mounted between two end walls which define working chambers with the gear ring and the gear wheel, and a coupling shaft extending through an aperture in one of the end walls and being in driving engagement with a central aperture in the gear wheel, wherein a sealing ring is provided between the other end wall and the gear wheel to provide a barrier against fluid leaking from the working chambers and passing between the gear wheel and the said other end wall towards the aperture in the gear wheel.

This machine construction takes into account the fact that leakage losses predominate along the end wall having the aperture and a reduction in the gear wheel diameter necessarily leads to an increase in those leakage losses. However, this is compensated by the fact that along the other (continuous) end wall there is, because of the use of the sealing ring, practically complete sealing of the gap between it and the gear wheel. In this way, there- fore, it is possible to reduce the total leakage losses and to keep the dimensions of the gear wheel and thus of the entire machine very small in relation to the aperture in the end wall for the shaft, without exceeding a predetermined leakage loss.

For example, in a hydraulic machine with pressures of about 100 bar, a respective minimum spacing between the aperture and the root of a tooth of the gear wheel of about 1.5mm will be sufficient, With particular advantage, the sealing ring is disposed in an annular groove provided in the gear wheel. Even when the space between the root of a tooth of the gear wheel and the aperture in the wheel (for receiving the head of the coupling shaft) is relatively small, it can be large enough to accommodate the annular groove. The area of the said other (continuous) end wall swept by the annular groove, during the gyratory and, if, as is preferred, the gear ring is fluxed, rotary motion of the gear wheel, may be considerably larger.

Whereas it is generally conventional for such machines to provide sealing rings between two components that are fixed to each other, the gear wheel moves relative to the continuous end wall. Such relative motion does not, however, damage the sealing ring because it is comparatively small. In any case, special provisions may be made to take the relative motion into account.

In particular, the sealing ring may be made of a material comprising polytetrafluoroethylene. This material has two concurrent advantageous properties. It is easily deformable in the cold state and therefore has good sealing properties. In addition, it has a good slidability in relation to metal.

It is also possible to cover one face of the sealing ring by an annular ring of metal which is fixed relative to the sealing ring and which can reduce friction with the continuous end wall.

Since there is no leakage flow along the continuous end wall owing to the presence of the sealing ring, there is also no pressure drop between the pressurised working chambers and the unpressurised interior of the gear wheel. However, pressure can build up on the gear wheel radially outwards of the sealing ring. This could possibly lead to the gear wheel being pressed against the apertured end wall with such a large force that frictional losses are created. This can be counteracted in a simple manner if that face of the wheel adjacent the said one wall is provided with regions which are in fluid communication with the working chambers. These pressure compensating regions can readily be selected so that the pressure variations arising as a result of using the sealing ring are substantially compensated.

It is of particular advantage if the said regions are in the form of depressions or recesses in the said face of the gear wheel and which, preferably, open into the outer peripheral surface of the wheel. This is particularly so if the annular groove is also provided in the gear wheel because in that case the respective areas can be accurately adapted to one another.

Preferably, a depression is provided in each of the two flanks of, and adjacent to the crest of each tooth of the toothed wheel, the depressions being arranged so that a sealing face is left on the crest of the tooth. The provision of the depressions at the tooth crest permits comparatively large pressure compensating areas to be achieved without thereby shortening the sealing gap between the root of the tooth and the aperture in the said one end wall.

The sealing face ensures that non-adjacent working chambers are short-circuited.

Advantageously, each depression is arranged to provide fluid communication between two adjacent working chambers when those two chambers are both coil- nected to the high or to the low pressure sides of the machine, and a commutator valve is provided, the valve having two parts, one part of which is fixed relative to the element which is rotatable about its axis and has control openings and the other part of which is fixed and has control openings, the said openings in the two parts being registrable to control fluid flow to and from the working chambers. In this way the depressions act as a valve which compensates for timing inaccuracies of the commutator valve.

A gerotor type rotary fluid pressure machine constructed in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawing, wherein: Fig. 1 is a longitudinal section through the machine, Fig. 2 is an elevation of the gear wheel and gear ring of the machine as seen from the right-hand side of Fig. 1, Fig. 3 is a plan view of the gear wheel from the opposite side, and Fig. 4 is a sectional view of a modified form of the seal.

Referring to the accompanying drawing, the machine of Fig. 1 comprises an externally toothed gear wheel 1 and an internally toothed gear ring 2 co-operating with the wheel. The ring 2 is fixed, the wheel 1 is rotatable about its own axis and the axis of the wheel is orbitally movable about the axis of the ring. The ring and wheel are covered on the one side by a first end wall 3 formed by a cover and on the other side by a second end wall 4 formed by an intermediate plate. The end wall 3, gear ring 2 and end wall 4 are connected to each other and to a housing 6 by screws 5. Working chambers 7 are formed between the gear wheel 1 and gear ring 2 and the end walls 3 and 4.In the housing there are connecting passages 8 which connect respective control apertures 9 at the inner periphery 10 of the housing 6, which forms part of a commutating valve, to passages 11 in the end wall 4, which passages in turn communicate with the working chambers 7. In addition, connections 12 are provided in the housing that likewise lead to the inner peripheral wall 10 by way of passages 13 or 14 but are axially offset with respect to the control apertures 9. A closureplate 16 is secured to the free end of the housing by means of screws 15.

A main shaft 17 is radially mounted within a sleeve bearing 18 and between a thrust bearing disc 19 and a roller thrust bearing 20 held by the plate 16. A coupling shaft 21 has, at one end, a splined head 22 engaging with a splined opening 23 of the main shaft and, at the other end a splined head 24 engaging with a splined opening 25 provided in a central aperture 26 of the gear wheel 1. The shank of the coupling shaft 21 extends through an aperture 27 in the end wall 4.

Part of the main shaft 17 is designed to act as a rotary valve element 28 having two annular grooves 29 and 30 communicating with the connecting passages 13 and 14. From these circumferential grooves there alternately extend control apertures 31 and 32 which are formed by axial grooves and the number of which is twice the number of teeth on the gear wheel 1, whereas the number of control apertures 9 is equal to the number of teeth on the gear ring 2. Consequently the working chambers 7 formed between the gear wheel 1 and the gear ring 2, which has one more tooth than the wheel, are filled with and emptied of liquid in the correct sequence.

The rotary valve element 28 and the inner periphery 10 of the housing therefore operate as a commutatory valve in conventional manner. An O-ring 34 of rubber is disposed in an annular groove 33 between two parts that are fixed with respect to the housing, e.g. the gear wheel 2 and the end wall 3.

In one face of the gear ring 1, an annular groove 36 is provided between the aperture 26 and the teeth 35 of the gear wheel 1, a sealing ring 37 of polytetraflyoroethylene being disposed in the annular groove. This sealing ring substantially completely seals the gap between the gear wheel 1 and the end wall 3. Any leakage loss is therefore restricted to the gap defined between the other face of the gear wheel 1 and the second end wall 4, the gap having a radial extent depending on the relative disposition of the wheel to the aperture 27 in the wall 4. In Fig. 2, the aperture 27 is shown in broken lines.

The shortest radial dimension of the gap is, in the illustrated position of the gear wheel 1, between the outer peripheral surface of the wheel at each of the roots of the lowermost tooth 35 and the marginal edge of the aperture 27.

Because the leakage path is eliminated between the gear wheel 1 and the end wall 3, the gear wheel 1 can have a small circumference so that the shortest radius of the gap between the gear wheel 1 and intermediate wall 4 only amounts to, for example, 1.5mm without having an excessive leakage loss.

Since the sealing ring 37 prevents leakage flow, a pressure can build up radially outwards of the sealing ring in the region 38 of the wheel 1 (which is cross-hatched in Fig. 2), which pressure is equal to the pressure in the adjacent working chambers 7. This pressure may cause the gear wheel 1 to be forced too hard against the end wall 4, resulting in high friction losses.

To overcome this each tooth 35 has two depressions 39, 40 on the face of the wheel remote from the sealing ring 37, the depressions being separated from one another by a radial web 41. This results in pressure compensating areas 42 in which the pressure of the adjacent working chambers 7 likewise obtains. These depressions can, in addition, be dimensioned so that, together with the gear wheel 2, they form a secondary or auxiliary commutating valve downstream of the primary commutating valve 10, 28. Thus each of these depressions can be arranged to provide fluid communication between adjacent working chambers 7.Connection between adjacent chambers is maintained unless one of those chambers has its maximum or minimum size or un less one of the chambers is connected (by commutating valve 10, 28) to the high and the other to the low pressure side of the machine when the connection is broken by engagement between ports of the inner peripheral surface of the ring 2 and the other peripheral surface of the wheel 1.

Thus, when a tooth crest of the gear ring 2 makes contact either with a tooth root or with a tooth crest in the region of the web 41 of the gear wheel 1 connection between adjacent working chambers 7 is broken. This permits substantial compensation of inaccuracies in the operation of the commutating valve 10, 28 since all the working chambers 7 which are connected to the high (or low) pressure side of the machine are connected by the depressions 39, 40.

Fig. 4 illustrates a modification in which the sealing ring 37 in the annular groove 36 is covered by an annular plate 42 of metal. This annular plate 43 remains stationary relatively to the sealing ring 37 but results in little friction in relation to the end wall 3.

The machine described and illustrated above can be modified in a number of ways. For example, the rotary valve spool 28 may be replaced by a rotary disc-like valve plate arranged coaxially with the ring 2 and provided with a plurality of axially disposed circumferentially spaced valve openings. In this case the end wall 4 may also serve directly as a valve plate, it being provided with axially disposed, circumferentially spaced, valve openings cooperating with the openings in the said valve plate to act as a commutator valve connecting the high and low pressurue sides of the machine to the working chambers 7.

In the machine (which may be a pump or motor, for example) described and illustrated above, the ring 2 is stationary and the wheel 1 rotates about its own axis while the axis of the wheel orbits about the axis of the ring. In a modification of this arrangement the ring and not the wheel could be arranged to rotate about its own axis and the axis of the wheel arranged to orbit about the axis of the ring.

WHAT WE CLAIM IS:- 1. A gerotor-type rotary fluid-pressure machine comprising two toothed elements, namely an externally toothed gear wheel -and an internally toothed gear ring, the elements meshing with each other and having parallel axes, one of the elements being rotatable about its axis, and the axis of the gear wheel being orbitally movable about the axis of the gear ring, the ring and wheel being mounted between two end walls which define working chambers with the gear ring and the gear wheel, and a coupling shaft extending through an aperture in one of the end walls and being in driving engagement with a central aperture in the gear wheel, wherein a sealing ring is provided between the other end wall and the gear wheel to provide a barrier against fluid leaking from the working chambers and passing between the gear wheel and the said other end wall towards the aperture in the gear wheel.

2. A machine as claimed in claim 1, in which the ring is fixed.

3. A machine as claimed in claim 1 or claim 2, in which the sealing ring is disposed in an annular groove provided in the wheel.

4. A machine as claimed in any one of claims 1 to 3, in which the sealing ring is made of a material comprising polytetrafluorethylene.

5. A machine as claimed in any one of claims 1 to 4, in which one face of the sealing ring is covered by an annular ring of metal which is fixed relative to the sealing ring.

6. A machine as claimed in any one of claims 1 to 5, in which that face of the wheel adjacent the said one wall is provided with regions which are in fluid communication with the working chambers.

7. A machine as claimed in claim 6, in which the said regions are in the form of depressions or recesses in the said face of the wheel.

8. A machine as claimed in claim 7, in which the depressions open into the outer peripheral surface of the wheel.

9. A machine as claimed in claim 7 or claim 8, in which a depression is provided in each of the two flanks of, and adjacent to the crest of each tooth of the toothed wheel, the depressions being arranged so that a sealing face is left on the crest of the tooth.

10. A machine as claimed in any one of claims 7 to 9, in which each depression is arranged to provide fluid communication between two adjacent working chambers when those two chambers are both connected to the high or to the low pressure sides of the machine, and in which a commutator valve is provided, the valve having two parts, one part of which is fixed relative to the element which is rotat

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. less one of the chambers is connected (by commutating valve 10, 28) to the high and the other to the low pressure side of the machine when the connection is broken by engagement between ports of the inner peripheral surface of the ring 2 and the other peripheral surface of the wheel 1. Thus, when a tooth crest of the gear ring 2 makes contact either with a tooth root or with a tooth crest in the region of the web 41 of the gear wheel 1 connection between adjacent working chambers 7 is broken. This permits substantial compensation of inaccuracies in the operation of the commutating valve 10, 28 since all the working chambers 7 which are connected to the high (or low) pressure side of the machine are connected by the depressions 39, 40. Fig. 4 illustrates a modification in which the sealing ring 37 in the annular groove 36 is covered by an annular plate 42 of metal. This annular plate 43 remains stationary relatively to the sealing ring 37 but results in little friction in relation to the end wall 3. The machine described and illustrated above can be modified in a number of ways. For example, the rotary valve spool 28 may be replaced by a rotary disc-like valve plate arranged coaxially with the ring 2 and provided with a plurality of axially disposed circumferentially spaced valve openings. In this case the end wall 4 may also serve directly as a valve plate, it being provided with axially disposed, circumferentially spaced, valve openings cooperating with the openings in the said valve plate to act as a commutator valve connecting the high and low pressurue sides of the machine to the working chambers 7. In the machine (which may be a pump or motor, for example) described and illustrated above, the ring 2 is stationary and the wheel 1 rotates about its own axis while the axis of the wheel orbits about the axis of the ring. In a modification of this arrangement the ring and not the wheel could be arranged to rotate about its own axis and the axis of the wheel arranged to orbit about the axis of the ring. WHAT WE CLAIM IS:-

1. A gerotor-type rotary fluid-pressure machine comprising two toothed elements, namely an externally toothed gear wheel -and an internally toothed gear ring, the elements meshing with each other and having parallel axes, one of the elements being rotatable about its axis, and the axis of the gear wheel being orbitally movable about the axis of the gear ring, the ring and wheel being mounted between two end walls which define working chambers with the gear ring and the gear wheel, and a coupling shaft extending through an aperture in one of the end walls and being in driving engagement with a central aperture in the gear wheel, wherein a sealing ring is provided between the other end wall and the gear wheel to provide a barrier against fluid leaking from the working chambers and passing between the gear wheel and the said other end wall towards the aperture in the gear wheel.

2. A machine as claimed in claim 1, in which the ring is fixed.

able about its axis and has control openings and the other part of which is fixed and has control openings, the said openings in the two parts being registrable to control fluid flow to and from the working chambers.

11. A gerotor-type rotary fluid-pressure machine substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.