GB2085969A

GB2085969A - Rotary positive-displacement pumps

Info

Publication number: GB2085969A
Application number: GB8130252A
Authority: GB
Original assignee: Hobourn Eaton Ltd
Current assignee: Hobourn Eaton Ltd
Priority date: 1980-10-17
Filing date: 1981-10-07
Publication date: 1982-05-06
Also published as: GB2085969B

Abstract

In a pump of the gerotor type comprising an outer rotor 3 with internal teeth or lobes 6 and an inner rotor 4 mounted eccentrically within the outer rotor and having external teeth or lobes 7, to prevent installation of either of the rotors the wrong way about in a pocket 1 in an internal-combustion engine 2 the teeth or lobes on both of the rotors are made asymmetric about radial planes containing the rotor axes and extending through the tips of the respective teeth or lobes, Fig. 2 (not shown). Additionally, the inner rotor may have an axial projection 8 which engages with an aperture in a stationary plate 9 and thus renders it impracticable to fit the inner rotor into the pocket the wrong way about. <IMAGE>

Description

SPECIFICATION Improvements relating to pumps The invention relates to pumps of the type comprising an externally toothed or lobed inner rotor mounted eccentrically within the meshing with an internally toothed or lobed outer rotor. One pump of this type comprises a lobed inner rotor which rotates eccentrically within an outer rotor having one more lobe than the inner rotor, the inner and outer rotors making permanent sliding contact at points spaced around their periphery and defining a gap which decreases in volume between fixed inlet and outlet ports.

Pumps of the said type are used extensively as oil pumps in internal combustion engines.

In such an application it is customary to mount the pump rotors in a pocket in the cylinder block of the engine and to assemble the pump in the pocket. The driving shaft for the pump projects axially into the pocket and drives the inner rotor, and the pocket is dimensioned to the size of the outer rotor, but has at its remote end a radiussed corner which would foul a sharp edge on the outer rotor. For this reason one edge of the outer rotor is chamfered. It is not convenient to chamfer both edges of the outer rotor since the outer rotor is generally made by a sintering process. Accordingly, it is necessary to fit the outer rotor in the pocket a particular way round, although it is possible to fit it the wrong way round, this resulting in incorrect operation. It is therefore desirable to provide an arrangement which prevents wrong assembly.

According to the invention there is provided a pump of the type comprising an externally toothed or lobed inner rotor mouted eccentrically within and meshing with an internally toothed or lobed outer rotor, wherein the teeth or lobes on both of said rotors are asymmetrical about radial planes extending through the tips of the teeth or lobes in such a manner as to prevent one of the rotors being fitted the wrong way round. Preferably the inner rotor has an axial projection which extends through an aperture in a fixed end plate which holds the rotors in the pocket, the two rotors each having an end face in rotational sliding engagement with the inner side face of the end plate. With this arrangement the inner rotor fits only one way round in the outer rotor and if the outer rotor has been placed in the pocket the wrong way round, the inner rotor cannot be fitted in place.

Lobe shapes for rotor type fluid pumps can be designed in different ways. For example, the outer rotor lobes may be determined first by striking circular arcs about predetermined centres, the shape of the inner rotor lobes being subsequently determined by reference to the shape of the outer rotor lobes. Alternatively, the shape of the inner rotor lobes may be determined first by striking arcs about predetermined centres, the shape of the outer rotor lobes being subsequently determined by reference to the shape of the inner rotor lobes.

With either of the above methods, the asymmetrical arrangement of the invention may be achieved at the stage of striking the circular arcs by composing each lobe of two arcs of different radius, the arc for one side of the lobe being struck about a first centre and the arc for the other side of the lobe being struck about a second centre radially spaced from the first centre of the centre line of the lobe.

Where the rotors are toothed, the tooth shape is not based on circular arcs but is of gear-tooth shape. In this form of rotor pump the shape of the lobes can be made asymmetrical by adopting different gear forms on the leading and trailing flanks of the lobes.

The invention will now further be described with reference to the accompanying drawings, in which: Figure 1 is a cross sectional view of a pump in accordance with the invention, and Figure 2 is an elevation of the rotors of the pump of Fig. 1.

Referring to Fig. 1 the pump is mounted in a pocket 1 in the wall of the cylinder block 2 of an internal combustion engine. The pump serves to pump lubricating oil from an inlet port to an outlet port (not shown). The pump comprises an outer rotor 3 and an inner rotor 4 which is driven to rotate about an axis offset from the axis of the outer rotor. The inner rotor has internal splines 5 and is driven by being engaged on a correspondingly splined shaft 20 of the engine, which shaft projects into the pocket. The outer rotor has lobes 6 and the inner rotor has lobes 7, one fewer in number than lobes 6. Lobes 6 and 7 make sliding contact and pumping action is effected by decreasing volume of the gap between the rotors from inlet to outlet port.

The inner rotor has an axial extension 8 which is in spigoted engagement in an aperture in a stationary end plate 9. The adjoining end faces of the two rotors are in rotary sealing engagement with the end plate.

Pocket 1 has a radiussed corner 10 at its remote end and to ensure that the outer rotor clears the corner 10 the inner edge 11 of the outer rotor is chamfered. Therefore, if the outer rotor is inserted in the pocket the other way around the sharp edge 1 2 which is normally outermost will foul corner 10 and cause the outer rotor to sit slightly proud of the pocket. If the pump were run like this, there would be undue friction and wear. In order to prevent assembly in this way, the lobes 6 and 7 are made asymmetrical, so that the inner rotors cannot be inserted if the outer rotor is the wrong way round.

Fig. 2 shows one suitable shape for the lobes. In this particular instance, the lobes of the outer rotor are first determined by striking circular arcs about predetermined radii. The shape of the inner rotor lobes are consequential on the outer rotor lobe shapes and are developed therefrom. instead of using a single circular arc for each lobe, the outer rotor lobe profile is composed of two arcs. In the illustrated form, one flank of each lobe is determined by an arc of radius R1 centred at 13 on the intersection of the centre plane 14 of the lobe with a circle 15, and the other flank is determined by an arc of radius R2 centred at 1 6 on the intersection of plane 14 with a circle 1 7. Other lobe shapes are however possible.

Thus, both the outer rotor and inner rotor lobes are asymmetrical about radial planes extending through the tips of the lobes and the inner rotor will fit the outer rotor only one way round.

It will be appreciated that a similar design technique can be employed if the shape of the inner rotor lobes is first determined by circular arcs and the outer rotor lobe shape is developed therefrom.

Other forms of asymmetry are possible. For example, the profile of each flank of each lobe may be defined by one or more circular or involute arcs or by combination of circular and involute arcs, the two flanks of each lobe differing in such a way as to prevent one of the rotors being fitted to the other the wrong way round.

It will be understood that the invention is equally applicable to crescent pumps and any other form of pump which employs an externally toothed or lobed rotor mounted eccentrically within and meshing with an internally toothed outer rotor.

Claims

1. A pump of the type comprising an externally toothed or lobed inner rotor mounted eccentrically within and meshing with an internally toothed or lobed outer rotor, wherein the teeth or lobes on both of said rotors are asymmetrical about radial planes extending through the tips of the teeth or lobes in such a manner as to prevent one of the rotors being fitted to the other the wrong way round.

2. A pump as claimed in claim 1, further comprising a fixed end plate, said inner and outer rotors each having an axial end face thereof in abutment with one side face of said end plate, said end plate further having an aperture therein and said inner rotor having an axial projection extending into said aperture.

3. A pump of the type comprising an externally toothed or lobed inner rotor mounted eccentrically within and meshing with an internally toothed outer rotor, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.