GB2167811A - Oil pump - Google Patents

Abstract

An oil pump has a rotor 24 with sliding vanes which rotates off-centre inside a cylindrical cavity 32 in a stator 26. As the rotor rotates, the vanes slide in and out altering the volume of chambers enclosed in the stator and pumping oil from an inlet 14 to an outlet 16. The displacement of the pump depends on the degree of eccentricity of the rotor in the stator. This can be varied during operation by relative movement of the rotor and stator to vary the pump throughput in accordance with the lubrication requirements of the engine. Control of the relative movement can be effected by feedback from the pump output, and in the embodiment described the oil pressure at the pump outlet is used to move the stator relative to the rotor (Fig. 5). <IMAGE>

Description

SPECIFICATION Oil pump This invention relates to an oil pump for use with an internal combustion engine.

Conventionally the drive for the oil pump of an internal combustion engine is taken from the camshaft or crankshaft. A disadvantage of a direct drive from the camshaft is that, as the engine speed increase, the oil flow rate and the pump power consumption increase linearly. Such increases are not however needed for lubrication of the engine during op eration,,and to avoid adversely affecting engine operation, it is known to dump excess oil through a relief valve. This is however only a palliative and is not directed to the root of the problem.

According to the present invention, there is provided an oil pump comprising a rotor having an axis of rotation and radial vanes slidable in grooves in a cylindrical rotor body, a stator enclosing a cylindrical chamber in which the rotor is mounted for rotation, with the cylinder axis of the chamber and the rotor axis parallel, an inlet to and an outlet from the chamber, and means for altering the relative positions of the rotor axis and the chamber axis to change the degree of offset between the two axes and vary the displacement of the pump.

The rotor and stator are preferably mounted in a common housing, arUd in a preferred embodiment, the rotor axis is fixed relative to the housing and the stator is slidable in the housing in a direction perpendicular to the axes of rotation.

The stator may be biassed in one direction by a spring, and in the opposite direction by a hydraulic control piston. Preferably the spring acts in the direction of increasing the pump displacement and the piston acts in the direction of reducing pump displacement. Pump displacement is zero (no pumping action) when the axes coincide, this position will correspond to one end position of the stator movement in the housing.

In order to control the pump displacement in accordance with the engine's operating requirements for lubrication, it is proposed that the control piston be acted upon by the outlet oil pressure of the pump. A passage can connect the rear of the piston to the pump outlet, so that the pump displacement is controlled by feedback from the pump operation.

In this way, the pump displacement need never rise substantially above the engine oil requirement, whatever the actual engine speed. When the pump displacement is reduced, the flow rate and the power required to drive the pump are also reduced.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a pump in accordance with the invention; Figure 2 is a side elevation of the pump shown in Fig. 1; Figure 3 is a front elevation of the pump shown in Fig. 1; Figure 4 is a section through the pump housing showing some details; Figure 5 is also a section through the pump housing showing other details of the pump; Figure 6 is a vertical section through the pump; and Figures 7 and 8 are graphs illustrating operating characteristics of the pump.

The pump shown in Figs. 1 to 3 has a conventional pump body 10 with a pump housing 12. The housing 12 has a rectangular shape and houses a rotor and a stator. The positions of an inlet port 14 and an outlet port 16 (the ports are actually in the opposite, hidden housing face) are indicated in dotted lines in Fig. 1. The position of the rotor axis 18 is also shown.

The pump body 10 will have the conventional connections to the engine lubrication system. In addition, a feedback passage 20 will connect a point on the outlet side of the pump with a control port 22 in the housing.

Looking now at Figs. 4, 5 and 6, the rotor is indicated by numeral 24 and the stator by numeral 26. The rotor is driven in rotation by a drive taken from the engine in a conventional way, and has radial grooves 28 with vanes 30 sliding in the grooves and pressed outwards against the wall of a cylindrical chamber 32 in the stator. The axis of rotation of the rotor is indicated at 34 in Fig. 5, and the axis of the cylindrical chamber at 36.

The chamber 32 is closed at one end by an integral wall 37 of the housing 12 and at its other end by a cover plate 39 (see Fig. 6).

So long as the axes are offset from one another, the rotation of the rotor will be eccentric in the chamber. Within the chamber the four spaces, each of which is bounded between a pair of vanes 30 and the stator wall 32, which vary in size as the rotor rotates. The inlet and outlet ports 14 and 16 are positioned so that oil is drawn into each of these spaces as the volume of the space is increasing. As each space is rotated its volume will decrease, thus forcing oil, under pressure, out of the outlet port 16.

The variation in the volume enclosed in each space as it moves between the inlet and the outlet determines the volume of oil pumped per revolution. Thus the. pumping capacity can be varied by varying the distance between the rotor and chamber axes.

To vary this distance, the stator 26 is made slidable in the housing 12. As the stator slides, so the chamber axis is moved relative to the rotor axis which is fixed relative to the housing. In one end position of the stator, the axes of the rotor and of the chamber will coincide. In this position, there will be no change in chamber volume during rotation and the pump will cease to pump. In the opposite end position of the stator, there will be a maximum change in chamber volume and therefore a maximum pumping rate.

To control the sliding movement of the stator, a coil spring 38 is mounted in the housing 12 on one side of the stator. A piston 40 working in a cylinder 42 is provided at the opposite side of the stator. The cylinder 42 is connected by a passage 20 to the oil in the pump outlet. When the engine is not running, or is running at low speeds, the outlet oil pressure reaching the cylinder 42 is not sufficient to overcome the biasing force of the spring 38. The stator will be in its extreme left-hand position, as seen in Fig. 5. As the engine runs faster, and the outlet pressure from the pump imcreases, the pressure in the cylinder 42 will increase and will act on the piston 40 which slides the stator to the right against the spring 38.

The result of this is shown in Fig. 7 (where oil flow rate is plotted against pump rpm) and in Fig. 8 (where power consumption is plotted against pump rpm). The line 44 represents the engine oil requirement, and the line 46 the pump delivery of a conventional oil pump. It will be seen that the conventional pump output continues to rise far beyond the engine requirement as the speed of the engine increases. On the other hand, the flow rate achieved by a pump in accordance with the invention is indicated by the line 48 and it will be seen that this follows closely the engine oil requirement.

A similar picture emerges from Fig. 8, where the line 50 represents the power consumption of a conventional pump. This rises continuously and linearly as the engine speed (and thus the pump speed) increases. On the other hand, a pump in accordance with the invention has a power consumption which levels off once the engine oil requirement has been achieved.

Claims (10)

1. An oil pump comprising a rotor having an axis of rotation and radial vanes slidable in grooves in a cylindrical rotor body, a stator enclosing a cylindrical chamber in which the rotor is mounted for rotation, with the cylinder axis of the chamber and the rotor axis parallel, an inlet to and an outlet from the chamber, and means for altering the relative positions of the rotor axis and the chamber axis to change the degree of offset between the two axes and vary the displacement of the pump.

2. A pump as claimed in Claim 1, wherein the rotor and stator are mounted in a common housing.

3. A pump as claimed in Claim 2, wherein the rotor axis is fixed relative to the housing and the stator is slidable in the housing in a direction perpendicular to the axes of rotation.

4. A pump as claimed in any preceding claim, wherein the stator is biassed in one direction by a spring, and in the opposite direction by a hydraulic control piston.

5. A pump as claimed in Claim 4, wherein the spring acts in the direction of increasing the pump displacement and the piston acts in the direction of reducing pump displacement.

6. A pump as claimed in any preceding claim, wherein the stator has one end position in which the rotor axis and the chamber axis coincide and in which the pump displacement is zero.

7. A pump as claimed in any preceding claim, wherein the means for altering the relative positions of the rotor and stator axes is controlled by a signal from the output of the pump.

8. A pump as claimed in Claim 7, when dependent on Claim 4 or Claim 5, wherein the control piston is acted upon by the outlet oil pressure of the pump.

9. A pump as claimed in Claim 8, wherein a passage connects the rear of the piston to the pump outlet, so that the pump displacement is controlled by feedback from the pump operation.

10. An oil pump substantially as herein described with reference to the accompanying drawings.