GB2160595A - Reciprocating pump - Google Patents

Abstract

A multi-cylinder pump comprises plungers (1) reciprocable in chambers (3) to cause fluid from an inlet tank (9) to pass through inlet check valves (6) to the chambers (3) and thence through outlet check valves (7) to an outlet (19A). The capacities of the chambers (3) are adjustable by slidable control bodies (5) in order to adjust the delivery rate of the pump. The control bodies may be displaceable by a control pressure supplied through a duct 13. Alternatively a differential pressure across a throttle (21) in the outlet (19A) can be used to move the bodies (4) by application thereto to opposite sides of a piston area (11). The pump may be of the axial swash plate piston or eccentric radial piston kind. <IMAGE>

Description

SPECIFICATION Improved pump The invention relates to a pump for example an axial swash plate piston pump or an eccentric radial piston pump. In an axial swash plate or an accentric radial piston pump, a plurality of plungers are receiprocated in respective clyinders utilising a common swash plate or cam, so as to pump fluid from an inlet to an inlet. If the swash plate angle or cam position is constant in these pumps, the travel of the plungers and hence the delivery volume of the cylinders remains unaltered and it is not possible to regulate the delivery flow.

A known method of regulating the delivery flow is to adjust the angle of the swash plate or cam accordingly. However a disadvantage of this method lies in the fact that a relatively expensive adjusting device is required. Furthermore, the known swash plate pumps become less efficient as the angle of traverse decreases owing to higher frictional forces.

An object of the present invention is therefore to provide delivery flow regulation which will enable the power and operation to be adapted to the respective requirement, which, if necessary, can be stepless and which does not entail undue construction costs or a noticeable reduction in efficiency upon changes in volume.

According to the invention there is provided a pump including an inlet, an outlet, a plurality of fluid delivery assemblies each including a relatively reciprocal plunger and chamber and each having a delivery volume for delivering fluid from the inlet to the outlet, common eccentric means operative to produce relative reciprocation of the plungers and chambers, and control bodies in said assemblies, said control bodies being operative in response to a control pressure applied thereto to move and thereby vary the delivery volumes of the assemblies as a function of the control pressure.

The arrangement of the pump with the control body enables the respective delivery volume swept through by a plunger to be easily adjusted using little power. Furthermore, the adjustment times are very rapid and it is possible to achieve stepless regulation of the delivery flow.

Since the delivery volume can be adjusted by an applied pressure on the low-loaded intake side, only very low adjustment forces need be required.

The delivery flow can be regulated in many different ways. For example, the control pressure acting on the control body can be constituted by an applied fluid operating pressure.

In this case, a bias spring acts against the control body to counteract the force produced by the operating pressure. As long as the spring force is greater than that produced by the operating pressure on the control body it remains in its starting position i.e. a position for producing a maximum swept delivery volume for the associated plunger. However, should the force deriving from the operating pressure exceed the spring force the control body is moved accordingly so as to reduce the delivery volume.

This movement of the control body occurs as a function of the operating pressure. The displacement of the control body continues until a state of equilibrium is reached with respect to the associated spring force. As the eccentric means produces a compression stroke of a plunger it compresses the volume of fluid sucked in and also moves the control body until the forces are balanced. It is thus possible to obtain a regulating range from a theoretical volumetric delivery of zero up to maximum delivery.

A further advantage with respect to the known delivery flow regulation by appropriate angle adjustments lies in the fact that a pump according to the invention can be operated in both directions of rotation without the necessity of undertaking any structural alterations.

It is advantageous if the springs are at the same time the return springs for the plungers and the movable control bodies are arranged coaxially with the plungers. This arrangement permits additional construction costs to be kept very low, as the return springs assume a dual function and are supported on the control bodies. The dead volumes are also reduced to a minimum.

Fluid inlets to the fluid delivery assemblies may lead through the control bodies, and inlet-side check valves may also be arranged in the control bodies.

If necessary, a plurality of springs with different characteristics may also be used, thus providing further regulating possibilities.

The above description relates to pressuredependent regulation. However, regulation with the movable control bodies can be achieved by applying a pressure difference derived from the outlet of the pump. Regulation of this kind is particularly suitable for hydraulic operating pumps in construction machines, stackers, for multi-circuit supply systems, e.g. with steering and brakes,etc.

A throttle in the pump outlet flow can be used to control the movement of the control bodies. An increased differential pressure across the throttle indicates an increasing fluid delivery rate from the pump outlet. This pressure difference is applied across opposed faces on the movable control bodies in such a way that they are maintained at a position providing a relatively high volumetric flow.

However, if a lower differential pressure is developed across the throttle the control bodies are moved accordingly so as to reduce the delivery volume.

If the pressure rises above a permissible limit, the volumetric delivery can be reduced to zero. All that is required is to co-ordinate the characteristics of the relevant springs and of the areas of pressure accordingly. It is thus possible to regulate the pressure and quantity delivered with a high degree of accuracy and a short adjustment time.

To avoid the dissipation of considerable amounts of energy when adjusting the control bodies, it is advantageous to connect the fluid delivery assemblies together. In this case compression need not take place. Instead, when the plungers are displaced the fluid is simply moved to-and-fro in the chambers. In order that the invention may be more fully understood embodiments thereof will now be described by way of example with reference to the drawings, in which: Figs 1-3 are functional diagrams showing regulation of the control bodies by means of an applied operating pressure to achieve different fluid delivery rates.

Fig 4 is a longitudinal section througha swash plate pump in accordance with the invention, with regulation of the control bodies according Figures 1-3, Figs 5-7 are functional diagrams showing regulation of the control bodies by means a differential pressure, Fig 8 is a longitudinal section through a swash plate pump with differential pressure regulation according to Figures 5-7, Fig 9 is a longitudinal section through a further embodiment of a swash plate pump with regulation by means of a differential pressure derived from fluid delivery rate.

Figures 1 to 3 are functional diagrams showing the regulation according to the invention with the movable bodies for different volumetric flows. Figure 1 is a functional diagram for the maximum volumetric flow during one revolution. These diagrams relate to swash plate pumps. Plungers 1 are pressed by return springs 2 against a swash plate, which is not shown in Figures 1 to 3. but can be seen in Figure 4. The plungers 1 are provided in the conventional manner with hollow spaces, which accomodate return springs 2. The plungers 1 are slidably mounted for reciprocation in cylindrical chambers 3. Movable control bodies 4 are disposed coaxially with the plungers 1 in the rear area of the chambers 3, one control body being provided for each plunger.Each control body 4 includes a central through hole 5, in which an intake-side check valve 6 of conventional construction is in each case incorporated. Delivery-side check valves 7 are provided in delivery-side outlets of the chambers 3. The through holes 5 are connected via a common connection conduit 8 to an inlet fluid supply tank 9.

The control bodies 4 each comprise a generally cylindrical body provided with collar 10, which is provided on its side distant from the plungers 1 with a pressure receiving area 11 with an associated hollow space 1 2 (not shown in Figure 1). The hollow spaces 1 2 and thus also the areas of pressure 11 are connected via a common pressure conduit 1 3 to a conduit under operating pressure.

The control bodies 4 act as differential pistons. As long as the force of the return springs and the force from pressure on the movable control bodies from the chamber 3 is greater than the force produced by the operating pressure on the pressure receiving area 11, the replacement body 4 remains in its rear end position and the maximum delivery volume is swept by the plungers 1 in the chambers 3. However, should the operating pressure rise accordingly until the force produced by pressure acting on the area 11 predominates, the control bodies move so as to reduce the delivery volume of the chambers 3. This movement continues until, on account of the compression of the return springs 2, a state of equilibrium is again reached, whereupon, as the swash plate rotates, the control bodies 3 lag behind the plungers 1.Figure 2 is a functional diagram showing how the delivery volumes of the chambers 3 are reduced in size through a corresponding displacement of the control bodies 4, thus resulting in a reduction in the volumetric flow rate.

Figure 3 is a functional diagram in which the operating pressure is so high that the control bodies 4 are moved such that they always rest against the plungers, thus preventing any delivery. This means, for example, that when a fluid consuming device (not shown) is disconnected (blocked pressure pipe), delivery ceases. However in practice it is possible to provide a minimum gap between the plungers 1 and the control bodies 4 in order to maintain a pilot flow. As the connection conduit 1 3 and the compensating chambers 14 are connected together and to the intake pipe (not shown) by an appropriate annular conduit, compression need not take place in order to move the replacement bodies 4, as the fluid is merely moved to-and-fro between the individual chambers.

Figure 4 shows a swash plate pump which operates basically in the same way as that described in Figures 1 to 3. As swash plate pumps are generally known, per se, only the parts essential to the invention are discussed in the following.

A plurality of plungers 1 are symmetrically distributed around the circumference of a cylindrical housing 1 6. The plungers 1 are provided internally with hollow spaces 1A, in which the return springs 2 are supported. The control bodies 4 are arranged in the longitudinal direction, i.e. coaxial with the plungers 1, and are connected to the tank 9 as shown in Figures 1 to 3. The two check valves 6 and 7 are also shown.

The front ends of the plungers 1 are pressed against a swash plate 17, which is secured to a rotary shaft 18. During the rotation of the shaft 1 8 the plungers 1 are thus reciprocated in the chambers 3. A pressure exhaust pipe 1 9 is connection in each case to the chambers 3 by way of the delivery-side check valves 7. The check valves 7 are mounted in a resilient buffer 20 and, after the corresponding chamber has been compressed, open the connection to the pressure exhaust pipe 1 9A.

The housing 16, in which the plungers 1 are mounted, can be lengthened accordingly in order to accomodate the control bodies 4.

Alternatively, a further appropriate housing part can be flange-connected.

Instead of the illustrated suction of the fluid out of the tank 9 through the connection conduit 8 and the through holes 5, it is of course also possible to arrange the intake pipe and the pressure exhaust pipe in opposite directions. This means that the fluid is drawn in through a central hole in the housing, before passing laterally through slits into the chambers 3 and subsequently through the through holes in the control bodies 4. It is also possible for the fluid to be drawn in by way of suction pockets in the swash plate.

When starting up, all control bodies 4 are in the bottom dead centre position, so that there will be no pressure control for a brief period during one revolution. However the control bodies 4 will then also adjust in accordance with the adjusting operating pressure.

In a modification of the above description, it is possible to use a separate control pressure instead of the operating pressure.

Figures 5 to 7 are functional diagrams of regulation by means of movable control bodies responsive to a pressure. The arrangement of these Figures is essentially the same as that of Figures 1 to 3, which is why the same reference numbers are used. The only differences lie in the fact that a throttle 21 is arranged in the pressure exhaust pipe 1 9 and that the control bodies 4 are in each case provided at their rear end, i.e. the end distant from the plunger 1, with a control spring 22.

A differential pressure occurs across the throttle 21 when the fluid flows between the measuring points x1/x2. Each collar 10 of the bodies 4 is provided with a second pressure receiving area 23, which is opposite the pressure receiving area 11. Compensating chambers 14 no longer serve simply to compensate for the fluid to be moved, but become hollow piston spaces, which are connected via a common pressure conduit 24 to the pressure exhaust pipe 1 9 upstream of the throttle 21. The hollow piston spaces 12 and thus the pressure receiving areas 11 are connected by the pressure pipe 1 3 to receive the fluid pressure pertaining in the pressure exhaust pipe 1 9 downstream of the measuring throttle 21.As a result, the movable control bodies 4 are displaced as a function of the pressure difference at the points "x2" and "xl", the force of the control spring 22, the pressure in the chambers 3 and the force of the return spring 2.

Like Figure 1, Figure 5 is a functional diagram in which the maximum delivery volume of the chambers 3 is available to the pump, as the control bodies 4 remain in their rear starting position. Like Figure 2, Figure 6 shows an intermediate position with smaller delivery volumes for the chambers 3, while Figure 7, like Figure 3, shows the no delivery position for the control bodies 4.

Figure 8 is a sectional view of a swash plate pump, the delivery flow of which is regulated by the throttle 21. The components shown in this figure have the same reference numbers as those in Figure 4. The plungers 1 slide in the conventional manner in bores in the housing 16.

The fluid passes from the tank 9 into the common connection conduit or annular space 8 and from there into the through holes 5 in the control bodies 4. Each chamber 3 thus receives fluid.

A spring 27 represents the spring for the intake-side check valve 6 and is supported in the control body 4.

The control body 4 is provided with two annular pressure receiving piston areas 11 and 23, which act against one another, are arranged on the collar 10 and are separated by a discharge duct 31.

The effective piston area 11 of the control body 4 is acted upon by the pressure xl and the effective piston area 23 by the pressure x2. The pressures xl and x2 are developed across the throttle. The throttle 21 is disposed between the check valves 7 and an outlet connection 1 9a. The check valves 7 operate in the conventional manner as discharge valves.

The fluid flow rate requirement of a hydraulic circuit load (not shown) connected to the outlet 1 9A is measured by the throttle 21. If there is no fluid flow, the pressure drop between "x2" and "xl" is nil, i.e. there is no pressure difference. The control bodies will therefore rest at top dead centre, i.e. against the plungers 1. There is no delivery due to the fact that all the delivery chambers are connected together by means of annular conduits. Although circulation losses are to be expected, these can be reduced to a minimum by appropriate design.

If a fluid outlet flow is required, a flow passes through the throttle 21, the pressure drops at xl, the bodies 4 are moved to the left due to the pressure differential, so as to increase the delivery volume of the chambers 3. Thus, the delivery rate is increased accordingly until a maximum is reached, when the control bodies come to rest in their top dead centre position. It is thus possible to regulate the flow rate as a function of the pressure difference across the throttle 21.

Figure 9 shows how the operation can be extended to regulate pressure and delivery flow. Here again the same reference numbers are used for the same parts. However, in contrast to Figure 8, a further piston 37 is provided for each control body 4. The piston area 41 of the piston 37 moves in a hollow piston space 40 and is acted upon by the pressure x2 upsteam of the measuring diaphragm 21, this pressure being applied to each hollow piston space 40 of the pistons 37 via a connection 38 and an annular conduit 39. The return spring 2 is designed such that it additionally assumes the characteristic of pressure regulation. An additional spring (not shown) may be necessary or advantageous.

If the pressure rises above a permissible limit the pressure and delivery rate can be regulated with a high degree of accuracy and a short adjustment time.

Claims (18)

1. A pump including an inlet, an outlet, a plurality of fluid delivery assemblies each including a relatively reciprocal plunger and chamber and each having a delivery volume for delivering fluid from the inlet to the outlet, common eccentric means operative to prodUce relative reciprocation of the plungers and chambers, and control bodies in said assemblies, said control bodies being operative in response to a control pressure applied thereto to move and thereby vary the delivery volumes of the assemblies as a function of the control pressure.

2. A pump according to claim 1 wherein each said control body comprises a generally cylindrical member slidably mounted in a cylindrical portion of said chamber, the member having a peripheral pressure receiving surface arranged to receive said control pressure.

3. A pump according to claim 1 or 2 wherein for each said assembly said plunger and control body are slidably mounted on a common axis for movement into and out of said chamber.

4. A pump according to claim 3 including return spring means in the chamber for biassing the control body and plunger outwardly of the chamber.

5. A pump according to any preceding claim wherein said inlet includes paths for fluid extending through the control bodies to the chambers.

6. A pump according to claim 5 wherein said paths include undirectional check-valves.

7. A pump according to any preceding claim including outlet check-valves to permit fluid to pass from the chambers to the outlet.

8. A pump according to any preceding claim wherein said control bodies each in dude first and second pressure receiving areas arranged to receive respective different control pressures defining a pressure difference such that the control bodies are operative to move and thereby vary said delivery volumes as a function of the pressure difference.

9. A pump according to claim 8 including a throttle in a path of fluid passing through the outlet, and means for deriving said pressure difference from the pressure difference established across the throttle.

10. A pump according to claim 8 or 9 wherein each said control body comprises a generally cylindrical member with an annular collar defining on opposed faces thereof said pressure receiving areas.

11. A pump according to claim 10 wherein said collar includes an annular discharge duct between said areas.

1 2. A pump according to claim 8, 9 or 10, including spring means urging said control bodies inwardly of said chamber.

1 3. A pump according to claim 9, 10 11 or 1 2 wherein each said control body includes a further pressure receiving surface so arranged that when the pressure in the outlet exceeds a predetermined value, the body is urged to move to reduce the delivery volume of its associated delivery assembly.

14. A pump according to any preceding claim wherein said common eccentric means comprises a rotary swash plate.

1 5. A pump according to any one of claims 1 to 1 3 wherein said common eccentric meanas comprises a rotary cam.

16. A pump substantially as herein described with reference to Figure 1 to 4 of the accompanying drawings.

1 7. A pump substantially as herein described with reference to Figures 5 to 8 of the accompanying drawings.

18. A pump substantially as herein described with reference to Figure 9 of the accompanying drawings.