GB2389967A

GB2389967A - Wet-running commutator with grooved surface for fuel pump

Info

Publication number: GB2389967A
Application number: GB0213879A
Authority: GB
Inventors: Joachim Friebe
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2002-06-18
Filing date: 2002-06-18
Publication date: 2003-12-24
Also published as: GB0213879D0

Abstract

A commutator for a flow-through fuel pump motor has a spiral groove in its brush contact surface which, as the commutator rotates in use, provides a continuous wiping action on the contact surface of the brush to prevent skating or aquaplaning of the brush on the commutator. The invention may be applied to cylindrical and planar commutators.

Description

1. Commutator 2389967 This invention relates to commutators and in

particular but not exclusively, to commutators for use in fuel pump motors in which the fuel flows through the motor.

s Fuel pump motors, as used for example in vehicles, may be of the type where the fuel passes through the motor. This removes the problem of sealing the pump chamber about the motor shag. This also provides an effective cooling medium for the motor.

Another advantage is that the fuel acts as a lubricant between the motor brushes and 10 the commutator reducing friction and mechanical wear. Unfortunately, this lubrication is also a problem.

The fuel adheres to the surface of the commutator and forms a thin lubricating film which actually separates the brush from the commutator. Normally, the film is so thin 15 that this separation does not affect the operation of the motor and has the positive effect of lubricating the brush/commutator interface. However, under certain conditions, this thin film layer can become thick enough to cause a significant increase in the resistance of the brush/commutator interface to adversely affect the performance of the motor. This large separation between the brush and the 20 commutator is known as aquaplaning. Aquaplaning may be a steady state condition or an intermittent condition but in either case, the adverse effect on the performance of the fuel pump motor can affect the operation of the engine being supplied with the fuel. Aquaplaning becomes more likely as the brush beds in creating a large surface in contact with the commutator surface and is known to occur in both cylindrical or 25 barrel type commutators as well as planar or flat type commutators.

Accordingly, the present invention provides a commutator for an electric motor comprising: a base; a plurality of commutator segments supported by the base, wherein the segments have a terminal portion and a brush contact portion, the brush 30 contact portions forming a brush contact surface; characterized in that channels formed in the brush contact portions of the segments form a continuous groove which spirals across the brush contact surface.

Preferred and/or optional features are set out in the dependent claims.

Four preferred embodiments will now be described, by way of example only, in which:

Figure 1 is a side view of a cylindrical commutator according to a first embodiment, Figure 2 is a side view of a cylindrical commutator according to a second embodiment, Figure 3 is an end view of a planar commutator according to a third embodiment, and Figure 4 is an end view of a planar commutator according to a fourth embodiment.

10 As shown in Figure 1, a cylindrical commutator 10 according to the first embodiment of the present invention has a number of commutator segments 12 fixed to a base 14 for mounting on a motor shaft. The segments 12 have a terminal portion 16 and a brush contact portion 18.

15 The terminal portions 16 may connect directly to lead wires of an armature winding or may be joined to a separate connector for making connections to windings.

The brush contact portions 18 for a cylindrical surface on which the brushes slide, in use, to transfer electrical power Bom the motor terminals to the armature windings.

20 Evident in Figure 1 is a single helical groove 20 formed in the cylindrical surface of the commutator. The groove 20 cuts into the brush contact portion 18 of each of the segments 12. The groove 20 extends helically around the outer surface of the commutator extending from one axial end ofthe brush contact region to the other, in a single turn or spiral (approximately). The depth of the groove is less than the 25 thickness of the segment so as not to divide the segment into two (or more) separate pieces. Figure 2 shows a similar commutator to that of Figure 1. Here, though, the groove 20 makes two turns or spirals around the brush contact surface of the commutator.

Figure 3 shows the invention being applied to a planar or flat commutator 10. The commutator 10 has similarly a plurality of commutator segments 12 fixed to a supporting base 14 which is adapted to be fitted to the shah of a motor. The segments 12 have terminal portions extending rearwardly of the base 14 and thus not visible in 35 Figure 3. The segments also have a brush contact portion 18 which, in this case, forms a flat or planar brush contact surface.

( A groove 20 is formed in the brush contact surface and cuts into the brush contact portion 18 of each segment 12 and spirals from the center or radially inner edge 22 to radially outer edge 24 ofthe brush contact surface.

5 The groove 20 of Figure 3 makes a single turn or spiral (approximately) across the brush contact surface.

Figure 4 shows a similar planar commutator 10 to that of Figure 3. However, in this embodiment, the groove 20 makes a multiple revolution spiral across the brush 10 contact surface, in this case, approximately 3 - 4 revolutions from the inner edge 22 to the outer edge 24.

The commutator segments in all four embodiments may be substantially copper, but it is preferred that the segments have substantially carbon bodies moulded to or 15 otherwise affixed to copper or other conductive metal members at least in the brush contact region. This construction has certain advantages when used with modern fuels which aggressively attack copper. In such segments, the spiral groove is formed in the carbon layer only and does not expose the copper member.

20 In use, the groove 20 will wipe the contact face of each brush being pressed onto the brush contact surface of the commutator. This wiping action helps to remove any debris or dust forming between the brush and the commutator to ensure good electrical contact. This wiping action is also very important when the commutator is being used in a submerged state as occurs, for example, id a flow-through final pump 25 motor. This wiping action not only removes dust and debris but also provides a pressure relief path for fuel (liquid) trapped under the blush. This trapped liquid may cause aquaplaning of the brush on the commutator surface resulting in lost of electrical contact between the brush and commutator, thus having devastating effect on the performance ofthe motor.

The helix or spiral direction of the groove is best chosen to aid the flow of dust or fuel depending on the direction of rotation of the armature to move dust and/or fuel to the axially outer end (away from the terminal portions) for cylindrical commutators and radially outwardly for the planar type commutators.

The embodiments described above are given by way of example only and venous modifications -rill be apparent to persons skilled in the art without departing from the scope of the invention as defined in the appended claims. In particular, while only a

( single groove with one or more revolutions has been shown, suitable embodiments using multiple grooves with one or more revolutions may be possible.

Also, while a groove with a part circular cross-section is shown in the embodiment, 5 the shape of the cross-section of the groove is not significant and square, rectangular, triangular, semi-circular, etc. cross-sections may be used and depends in most part on the method of forming the groove.

Claims

( Claims

1. A commutator for an electric motor comprising: a base; 5 a plurality of commutator segments supported by the base, wherein the segments have a terminal portion and a brush contact portion, the brush contact portions forming a brush contact surface; characterized in that channels formed in the brush contact portions of the segments form a continuous groove which spirals across the brush contact surface.

2. A commutator according to Claim 1, wherein the commutator segments have conductive metal terminal portions in electrical contact with contact portions of a predominantly graphite material and the groove is formed in the graphite material of the contact portions of the segments.

3. A commutator according to Claim I or 2, wherein the groove makes a single spiral from start to finish.

4. A commutator according Claim I or 2, wherein the groove makes more than 20 one spiral from start to finish.

5. A commutator according to any one of the preceding claims wherein the commutator is a planar type commutator and the groove extends radially in a spiral from a radially inner location to a radially outer location.

6. A commutator according to Claim S. wherein the groove is arranged so that, in use, matter in the groove would be urged radially outward.

7. A commutator according to any one of Claims 1 to 4, wherein the commutator 30 is a cylindrical type commutator and the groove spirals axially along the commutator.

8. A commutator according to Claim 7, wherein the groove is arranged to urge matter in the groove to move axially away from the terminals of the commutator segments.

9. A commutator according any one of the preceding claims, wherein the y,roove is only interrupted by gaps between adjacent segments.

10. A commutator for an electric motor substantially as hereinbefore described with reference to the accompanying drawings.

11. An electric motor incorporating a commutator as defined in any one of the 5 preceding claims.