GB2048385A - A rotary fluid pump or motor - Google Patents

Abstract

The pump or motor is of the externally-meshing gear type and has bearing bushes 6, 6' held against the gears 4, 4' by fluid pressure transmitted from the high- pressure side of the gears to recesses 10, 10'. Initial loading of the bushes is provided by resilient seals 8, 8'; 9, 9'. To reduce the output to substantially zero the recesses are connected to a fluid container 21. Alternatively, the recesses are connected permanently to the high-pressure side by way of a variable throttle (26), Fig. 5 (not shown), connection of the recesses to the container to reduce the output then allowing a proportion of the fluid to circulate for cooling and lubricating purposes. <IMAGE>

Description

SPECIFICATION A rotary pump or motor provided with apparatus for controlling the fluid flow This invention relates to a rotary pump or motor of the kind wherein it is necessary to switch the fluid flow on and off given a constant driving speed, provided with apparatus for controlling the fluid flow.

Gear pumps are known wherein different effective gear widths and thus a variable conveying flow can be obtained with a constant driving speed, by axial displacement of one of the gears. The components of these pumps are relatively expensive to manufacture and assemble, particularly the complicated adjusting pieces required for sealing. Another disadvantage is that the displacement of the gears and meshing between gears of different widths lead to increased and uneven wear on the teeth of the gears. This shortens the life of the gears and increases the cost of repair.

The same applies to apparatus for varying the conveying flow in pumps operating as zero stroke pumps, where one of the gears is displaced against a spring force in dependence on the pumping pressure.

The two above mentioned known arrangements have not yet proved successful in practice because of the deficiencies mentioned.

In another known gear pump, displacement of a control piston produces a change in the gap between the ends of the rotating gears and the control piston itself, which is arranged displaceably at the level where the gears engage. By displacing the control piston a varying degree of leakage is deliberately obtained between the compression and suction side of the gear pump, bringing a change in the effective conveying flow. This apparatus is also relatively expensive because of the complicated components and their assembly. It further has the disadvantage that the throttling of the partial stream flowing from the compression to the suction side causes part of the usable energy to be lost through conversion to thermal energy. The heat leads to increased wear or may even damage the pump.

As means of reducing the high costs incurred in connection with adjustable pumps, it is generally known to change the rotary speed of hydraulic motors in an infinitely variable manner by using constant conveying pumps in conjunction with flow control valves, whereby the conveying flow and thus the velocity or rotary speed of the motors can be varied. To obtain a constant flow, only the set portion of the conveying flow is carried to the motor by the flow control valve, while the remaining stream is returned to the vessel via a pressure limiting valve. Because of the energy lost in the process this solution is only suitable for low or medium outputs.

As a means of reducing energy losses, particularly with high outputs, a plurality of constant conveying pumps have already been arranged in parallel and switched on and off by a switching device in accordance with the conveying stream requirement. Separately controlled pressure-limiting valves, also known as switch off valves, are frequently employed as the switching device. The total flow through the optionally switched on constant conveying pumps meets the conveying stream requirement in stepped form. A constant conveying pump with a pressure limiting valve is required for each step in the flow.

In order to obtain a larger number of steps in the flow with a smaller number of constant conveying pumps, pumps with a conveying flow of different magnitudes have been used, each pump being associated with a short circuiting multi-way valve. In this arrangement, for example, three steps in the flow can be obtained even with two constant conveying pumps with different conveying flows, and seven steps with three pumps. This solution may reduce capital costs as compared with the solution previously described, but the cost of the switching device is increased, since a short circuiting multi-way valve of appropriate nominal width, adapted to the magnitude of the conveying stream, and also a multi-way valve of small nominal width, which can be controlled as described, are needed for each constant conveying pump.

According to the present invention there is provided a rotary pump or motor of the kind wherein the fluid flow has to be switched on and off given a constant drive speed, provided with apparatus for controlling the fluid flow of the pump or motor, in which bearing bushes or piston-like elements provided in the rotary pump or motor and movable to compensate for play can be impinged on by the fluid pressure of the rotary pump or motor to obtain minimum clearance at the sealing surface of the pump or motor, and lie against a resilient seal at the side of the surfaces to be impinged on, said surfaces being optionally impinged on by the working fluid pressure or relieved of fluid pressure by means of a discharge conduit connected to a fluid container, such that when the surfaces are thus relieved the bearing bushes or piston-like elements can be displaced to adjust a gap, formed for switching off the effective fluid flow, between the suction side and the compression side of the rotary pump or motor, in the direction of the resilient seal, the amount of displacement and thus the size of the gap being such that when the effective fluid flow in the rotary pump or motor is switched off there is still just sufficient residual pressure for lubricating the pump or motor and switching it over to full fluid flow.

An embodiment of the invention provides apparatus for controlling fluid flow which, with the use of only a few simple components, will allow the effective fluid flow to be switched optionally to the values "full fluid flow" or "zero fluid flow", given a constant speed of the rotary pump or motor. Throttling effects which develop a large amount of heat must be avoided. The apparatus must be applicable without disadvantage both to rotary pumps or motors with small or large output. It must also be suitable for interconnecting a plurality of rotary pumps or motors with identical or different fluid flow, using substantially simpler means than the known solutions.

The bearing bushes or piston-like elements provided in the rotary piston machine can be impinged on by the pressure fluid of the rotary pump or motor to obtain minimum clearance at the sealing surfaces of the pump or motor, and lie against a resilient seal at the side of the surfaces to be impinged on. The said surfaces can optionally be impinged on by the working pressure of the pump or motor or relieved by means of a discharge line to the fluid vessel. When the surfaces are thus relieved the bearing pushes or piston-like elements can be displaced through the necessary portion of a gap, formed for switching off the effective fluid flow, between the suction side and the compression side of the rotary piston machine, in the direction of the resilient seal.

The amount of displacement and thus the size of the gap between the suction and compression side are chosen so that, when the effective fluid flow in the rotary pump or motor is switched off, there is still just sufficient residual pressure for lubricating the machine and switching it over to full fluid flow.

The pressure chamber provided in the rotary pump or motor behind the surface of the bearing bushes or piston-like elements facing towards the resilient seal may communicate, via a connecting conduit and an interpolated multi-way valve, optionally either with the pressure conduit of the pump or motor or with a discharge line leading to the fluid container.

In large rotary pumps or motors it is desirable for the said chamber to be permanently connected to the pressure conduit of the pump or motor, and for the pressure chamber and at the same time, via an adjustable throttle, the pressure conduit to be optionally connected by a valve to a discharge line leading to the fluid container.

The impingement of pressure from the pressure conduit onto the surfaces of the bearing bushes or the piston-like elements facing towards the resilient seal causes the bushes or the piston-like elements to be moved axially, thereby largely eliminating the clearance at the sealing surfaces. If the pressure chamber is connected, behind the surfaces facing towards the resilient seal, to the discharge conduit leading to the fluid container, these surfaces will be relieved of the working pressure.

The residual pressure still present in the pump or motor will therefore shift the bearing bushes or the piston-like elements a predetermined distance onto a stop. The clearance at the sealing surfaces will thereby be enlarged to the predetermined extent. The enlarged gap causes the fluid still being conveyed to flow back from the compression to the suction side. The size of the gap and the viscosity of the liquid flowing through determine the residual pressure against which the pump has to convey fluid when the effective stream of fluid is switched off. The size of the gap is chosen so that the residual pressure is as low as possible yet still provides for the necessary lubrication and ensures that, when the pump is switched over to full fluid flow, the bearing bushes or the piston-like elements will be shifted axially to reduce the gap.The fact that the bearing bushes or the piston-like elements are constantly supported against the resilient seal provides a tight sealing action in both switching states. It is an advantage for the residual pressure to remain almost identical when switching over to zero fluid flow", even if the viscosity of the fluid flowing through changes. This effect is obtained because, with higher viscosity, the residual pressure initially rises, resulting in a stronger force to keep open the gap for the return flow of fluid. However, resistance to through-flow drops and the residual pressure is reduced.

The pressure is of course slightly higher than the residual pressure with low viscosity. The supporting force against the resilient seal increases simultaneously.

The two switching positions may be controlled with the aid of a valve of small nominal width, since only the volume of fluid displaced by the switching movement of the bearing bushes or the piston-like elements and any leaking oil need be guided through the valve the fluid container. If the "zero fluid flow" position is maintained for a long time, the temperature of the fluid will rise to a saturation value, which in a pump or motor of a given overall size will depend on the level of the residual pressure, the size of the stream of leaking oil through the gap in the guide, and the provision for heat transfer in the pump or motor. With larger rotary pumps or motors, therefore, the second modified form of control described is desirable, since here when the full fluid flow is switched off by the valve, there is a possibility of influencing saturation temperature by allowing a limited return flow of fluid from the pressure conduit through the valve to the fluid container, the amount being selected with the aid of a throttle.

The apparatus proposed may be used wherever a fluid flow has to be started and stopped. A plurality of constant conveying pumps, possibly with different conveying streams, may particularly advantageously be provided with the control apparatus and used for delivering a flow in stages to circuits controlled by a flow valve, for infinitely varying the velocities or rotary speeds of hydraulic motors. In this way a considerable amount of energy can be saved at low cost, compared to the use of a single large constant conveying pump. The invention may also be used widely for supplying hydro-accumulators.

When the invention is applied to hydraulic motors, the torque transmitted by the motor can be influenced by the invention, either so that the motor transmits the appropriate full load torque, or so that it generates a moment which is approximately zero and which fluctuates in the vicinity of the idling moment depending on the difference in residual pressure.

The special advantage of the invention resides in the conscious reversal of the principle of known apparatus for compensating for play, where a specific play is deliberately created, its size being adapted to the existing conditions for switching off the fluid flow, lubricating and switching on the effective "full fluid flow" again. Particularly with rotary piston machines already equipped with known means for compensating for play, the invention may be realised with the simplest means, without interfering greatly with the existing construction of the rotary piston machine in maintaining the function of compensating for play, for switching the effective fluid flow on and off.

Two embodiments of the invention will now be described, by way of examples, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a gear pump with external teeth and with means to compensate for play, with the apparatus according to the invention fitted on it at a later stage, Figure 2 is a section taken along the line A-A indicated in Fig. 1, Figure 3 is a section taken along the line B-B indicated in Fig. 1, Figure 4 is a diagrammatic representation of the control means when the apparatus according to the invention is used for small gear pumps, and Figure 5 is a diagrammatic representation of the control means when the apparatus according to the invention is used for large gear pumps.

The gear pump shown in Fig. 1 substantially comprises a housing 1 which is closed at one end by an end cover 2 and closed at its other end by a flanged cover 3. The housing 1 contains gear shafts 4 and 4' mounted in axially displaceable bearing bushes 5; 6 and 5'; 6' respectively. Two thrust rings 7 and 7', each associated with two respective flexible, circular seals 8; 9 and 8'; 9' of large volume, are located in corresponding recesses 10 and 10' provided in the end cover 2 and together act as a resilient seal 11. The bearing bushes 5 and 5' lie against the sealing surface of the flanged cover 3 and the bushes 6 and 6' lie against the resilient seal 11. The resilient seal 11 may be constructed differently, if it ensures that with limited axial movement of the bearing bushes 6 and 6' the sealing function will always be provided.The recesses 10 and 10', the resilient seal 11 and the surface of the bearing bushes 6 and 6' facing towards the resilient seal together form a pressure chamber 1 2. The chamber 1 2 communicates with a control means 1 5 via a connection 1 3 and a connecting conduit 14.

It will be seen from Fig. 2 that the gear pump further has a connection 1 6 for the suction conduit 1 7 and a connection 1 8 for the pressure conduit 19. As shown in Figs. 1, 4 and 5, a connecting conduit 19' leads from the pressure conduit 1 9 to the control means 1 5. The control means 1 5 further has a discharge conduit 20 leading to the fluid container 21.

Referring now to Fig. 4, the control means 1 5 is provided with a two-way valve 22. The valve 22 can be moved from a position a as shown to a position b against a spring 23, by an adjustment means which will not be described in detail but which may be operated e.g. mechanically, hydraulically or electromagnetically. In position a of the two-way valve 22 the pressure conduit 1 9 communicates via the connecting conduit 19' with the connecting conduit 1 4 and thus via the pressure chamber 1 2 (Fig. 1) with the end surfaces of the bearing bushes 6; 6' facing towards the resilient seal 11.

In position b of the two-way valve 22 a connection is established between the pressure chamber 1 2 and the discharge conduit 20 leading to the fluid container 21, via the connecting conduit 1 4. This arrangement is sufficient for small gear pumps.

As shown in Fig. 5, a different arrangement may be provided in the control means 1 5 for large gear pumps, in order to avoid excessive development of heat. A two position valve 25 is provided, with positions a and b which can be obtained with the aid of the adjusting means 24 and compression spring 23 as in the previous example. In position a the pressure chamber 1 2 communicates via the connecting conduits 1 4 and 19' with the pressure conduit 19. In position bthe discharge conduit 20, leading to the fluid container 21, communicates firstly with the pressure chamber 1 2 via the connecting conduit 14, and secondly with the pressure conduit 1 9 via the connecting conduit 19' and an adjustable throttle 26 fitted in the conduit 19'.

The mode of operation will now be explained in greater detail with reference to the examples described.

When the gear shaft 4 is driven in the rotary direction indicated by the arrow in Fig.

2, the fluid is conveyed from the suction conduit 1 7 to the pressure conduit 1 9 is known manner. In the Fig. 4 example and with the two-way valve 22 in position a, the pressure chamber 1 2 is simultaneously connected to the pressure conduit 1 9. The working pressure in the conduit 1 9 acts on the end surfaces of the bearing bushes 6 and 6' producing an axial force. The displac ment of the bushes 6 and 6' establishes the axial compensation for play of the gear pump, and clearance losses at the seals between the ends of the rotating gears of the shafts 4; 4' and the bearing bushes 5; 5' and 6; 6' are minimized. The gear pump conveys the full, effective stream of fluid.In order to stop the effective stream of fluid the two-way valve 22 is moved by the adjusting means 24 into position b. The pressure chamber 1 2 is thereby connected to the discharge conduit 20, making the axial compensation for play of the gear pump ineffective. The working pressure which is initially still present moves the bearing bushes 6 and 6' to the left as viewed in Fig. 1. A return flow gap, leading from the compression to the suction side, is thereby formed between the end faces of the bearing bushes 6 and 6' and the gears of the shafts 4 and 4'. As a result of the low resistance of the return flow gap the working pressure drops to a low residual pressure. An effective fluid flow in the gear pump when loaded is thus no longer possible. If there is no load the pump does convey fluid, but its stream of fluid drops to zero even under a small load.The residual pressure is necessary to provide for lubrication and to ensure that the bearing bushes 6 and 6' make an initial movement towards reducing the clearance when switching over to the full fluid flow. The residual pressure is determined by the size of the return flow gap, the returning force of the resilient seal 11 with the gap and the viscosity of the fluid to be conveyed. The pressure must be selected as low as possible, since a rise in temperature is produced by the constant return flow of the same fluid, which is only partially renewed by leakage through the gaps between the bearing bushes 5; 5' and 6; 6' and the housing 1, and the maximum temperature at saturation must be kept below the admissible level for the pump. The resilient action of the sealing almost precludes any effect of viscosity on residual pressure.

In the Fig. 5 example there is permanent communication between the pressure conduit 1 9 and the pressure chamber 1 2 through the connecting conduits 19'; 14, and when the gear pump is driven the "full fluid flow" is in action. The effective fluid flow of the pump is switched off when the valve 25 is moved into position b. The discharge conduit 20 is connected by the conduit 14 to the pressure chamber 1 2 and also by the conduit 19' and adjustable throttle 26 to the pressure conduit 1 9. Thus the pressure chamber 12 is depressurized and the displacement of the bearing bushes 6 and 6' to the left produces a return flow gap between the compression and suction side of the pump.In addition there is a return flow from the pressure conduit 1 9 through the connecting conduit 19' and throttle 26 to the discharge conduit 20. Particularly in the case of large gear pumps this provides for more favourable temperature limitation, through constant exchange of part of the fluid circulated in the gear pump with the cooled fluid in the container 21. The throttle 26 restricts this exchange and ensures that no pressure head can form in the connecting conduit 14 and thus the pressure chamber 12, as a result of too large a return flow in the discharge conduit 20.

In both examples the effective fluid flow of the gear pump can be switched on and off at little cost, with a constant driving speed, by switching the two-way valve 22 or the valve 25 into position a or b as desired. When there is a means to compensate for play all that is required is the two-way valve 22 or valve 25, each with a small nominal width, a connection 1 3 to the gear pump, connecting conduits 14; 19' and the discharge conduit 20.

The invention is not restricted in its application to gear pumps with external teeth, and may be applied to gear pumps with internal teeth, cell pumps and rotary piston machines.

Here again, provided that there is a means for compensating for play, only a small outlay is required for subsequent fitting of the apparatus according to the invention. The invention can be applied in a similar way to hydraulic motors. By appropriate shifting of the twoway valve 22 or valve 25 the transmissible torque can be switched on or off while the supply of the stream of fluid is maintained.

Similarly to the residual pressure on switching off the effective fluid flow in constant conveying pumps, in the case of the hydraulic motor in the "off" state a residual moment is created, which is generally of the same order as the idling moment and which consequently causes the motor to stop in the absence of any external loading moment. In this state the motor can be turned through the so-called floating position by hand. The residual moment is present only so long as the stream of fluid is supplied to the motor. The magnitude of the residual moment depends on the stream of fluid.

Claims (4)

1. A rotary pump or motor of the kind wherein the fluid flow has to be switched on and off given a constant drive speed, provided with apparatus for controlling the fluid flow of the pump or motor, in which bearing bushes or piston-like elements provided in the rotary pump or motor and movable to compensate for play can be impinged on by the fluid pressure of the rotary pump or motor to obtain minimum clearance at the sealing surfaces of the pump or motor, and lie against a resilient seal at the side of the surfaces to be impinged on, said surfaces being optionally impinged on by the working fluid pressure or relieved of fluid pressure by means of a discharge conduit connected to a fluid container, such that when the surfaces are thus relieved the bearing bushes or piston-like elements can be displaced to adjust a gap, formed for switching off the effective fluid flow, between the suction side and the compression side of the rotary pump or motor, in the direction of the resilient seal, the amount of displacement and thus the size of the gap being such that when the effective fluid flow in the rotary pump or motor is switched off there is still just sufficient residual pressure for lubricating the pump or motor and switching it over to full fluid flow.

2. A rotary pump or motor as claimed in claim 1, in which a pressure chamber 12 is provided in the pump or motor behind the surfaces of the bearing bushes or piston-like elements facing towards the resilient seal and said pressure chamber 1 2 communicating, via a connecting conduit and a multi-way valve, optionally either with the pressure conduit 1 9 of the pump or motor or with a discharge conduit leading to the fluid container.

3. A rotary pump or motor as claimed in claim 1, in which a pressure chamber is provided behind the surfaces of the bearing bushes or piston-like elements facing towards the resilient seal, the pressure chamber communicating permanently with the pressure conduit of the pump or motor, and said discharge conduit leading to the fluid container being connected by a valve optionally to the pressure chamber and simultaneously, via an adjustable throttle, to the pressure conduit.

4. A rotary pump or motor substantially as hereinbefore described with reference to and as illustrated in Figs. 1 to 4 or Figs. 1 to 3 and 5 of the accompanying drawings.