GB2092390A - Detecting component wear - Google Patents

Abstract

Wear of a component slidable in a holder, particularly an electrical machine brush in a brush box, is detected by means of one or more permanent magnets in cooperation with one or more reed switches positioned to be closed by the magnet(s) when a predetermined wear limit is reached, and held closed until the components completely worn. Assemblies described include double brushes, relatively sliding split brushes and a rocker ring type assembly. In the latter, (Figure 8 not shown), a boss containing the reed switch also locates the brush box.

Description

SPECIFICATION Detecting component wear This invention relates to the detection of wear of a component, particularly but not exclusively a brush in a dynamoelectric machine.

It is known to provide dynamoelectric machines having brushes with means for wear detection.

Typically, microswitches and other small forms of mechanically-actuated contacts have been used to provide means of detecting brushes worn down to their usual working limits. These systems have generally been expensive and difficult to seal against the ingress of carbonaceous dust in the difficult environment close to a sliding contact area. To achieve mechanical switch actuation it is often necessary to carry out additional machining operations to brushes in order to provide recesses or bosses giving the necessary axial assymetry to actuate a switch. Efforts to properly seal the switches against the ingress of carbon dust by means of elastomeric gaiters tend to be frustrated by packing with carbon dust, and consequent malfunction of lightweight moving parts.It is not possible to use heavy contacts or springs as these would tend to frictionally impede the brush and render proper contact surface following difficult or impossible.

The invention seeks to eliminate or mitigate the above disadvantages by providing a contact-less method of brush wear detection capable of operating hermetically sealed contacts which therefore impose no frictional loads on the normal function of the brush, which must include axial brush movemenu to follow an imperfectly round commutator for example.

The invention also seeks to provide means for contact operation which are simple and low cost to apply both the brush and to the brush box. It also seeks to provide such means in a form suitable for use with a number of brush variants in common usage in dynamoelectric machines, such as split brushes and brushes with carbon fibre fringe on one or more faces.

Accordingly, the present invention provides an arrangement for detecting wear of a consumable part slidably mounted in a holder, such as a dynamoelectric machine brush in a brush box, in which at least one magnet is mounted in the part and a reed switch is mounted on the holder, the positioning of the magnet(s) and reed switch being such that the switch is closed by the magnet(s) when a predetermined degree of wear has occurred and is held closed until the part is completely worn.

Preferably, two rod-type magnets are fitted into the head of a brush in side-by-side transverse locations.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a brush in accordance with the invention; Figure 2 is a perspective view of a brush box for use with the brush of Figure 1; Finllrn .? A-C m sr.hf?matic side views illustrating the operation of Figures 1 and 2; Figure 4 is a perspective view of a double brush box; Figure 5 is a section on A-A' of Figure 4; Figures 6 and 7 illustrate alternative forms of brush; and Figure 8 illustrates an alternative brush box and rocker ring assembly.

As seen in Figure 1, a brush 10 is bored to receive two rod magnets 12,14 which are arranged with opposite polarity. The magnets may be bonded in position, e.g. by epoxy resin. The brush box 16 (Figure 2) mounts a reed switch assembly 18. The reed switch assembly 18 is connected to to a warning circuit (not shown) by flying leads 20. The positioning of the magnets 12 and 14 in the brush 10 and the positioning of the reed switch assembly 18 in the brush box 16 are chosen such that the magnets close the switch at a chosen wear limit (Figure 3B) and maintain the switch closed even if the brush is allowed to completely wear out (Figure 3C). As seen in Figure 3, the reed switch assembly comprises a reed switch 17 encapsulated in epoxy material 19.

Suitable circuitry using closure of the reed switch to produce an audible and/or visual warning will be apparent and is therefore not described.

Figures 4 and 5 illustrate a similar arrangement for two brushes (not shown) in a double brush box 16'.

Two reed switches 17, 17' are connected in parallel to the leads 20.

Figure 6 illustrates in cross-section the invention applied to a split brush 20. The brush 20 is in two parts 20a and 20b which may slide relative to one another. A spring counter plate 22 covers the tops of the brush parts 20a and 20b, being secured to the master part 20a. A rubber spacer 23 is provided between the other brush part 20b and the counter plate 22. These details are well known per se. A pair of rod magnets, one of which is seen at 24, is provided as in the previous embodiment. Each magnet 24 is fitted in a bore in the master part 20a. A larger bore 26 is provided in the other part 20b to provide a clearance, thereby allowing the brush parts to slide relative to one another.

The brush illustrated in Figure 7 is provided with a shaped recess 28 for attachment of a ligament by a rivet (not shown). It will be seen that the magnets 12, 14 can readily be accommodated in a rivetted brush.

In the arrangement of Figure 8, an insulating rocker ring 30 has an integral, axially projecting brush arm 32 on which a brush box 34 is mounted. A boss 36 projecting from the brush arm 32 contains the reed switch, and also serves to locate the brush box 34 by interfitting with a slot 38 in the latter. The box 34 is then secured by a bolt (not shown) in bolt holes 40. The brushes used are as previously described.

The invention allows the warning to persist from a chosen degree of wear until the brush is completely worn out. Preferably, the warning is given from 10% life remaining to 0% life remaining, by suitable positioning of magnets and switch.

It would also be possible, within the scope of the invention, to use a single magnet in conjunction with a reed switch. However the double magnet arrangement is preferred because of the following advantages: 1) it permits the brush to be put in the box either way round 2) it causes the reed switch blades to be polarised, and thus makes the angular position of the switch mounting unimportant.

CLAIMS (Filed 11Jan 1982) 1. An arrangement for detecting wear of a consumable part slidably mounted in a holder, in which at least one magnet is mounted in the part and a reed switch is mounted on the holder, the positioning of the magnet(s) and reed switch being such that the switch is closed by the magnet(s) when a predetermined degree of wear has occurred and is held closed until the part is completely worn.

2. The arrangement of claim 1, in which two rod-type magnets are mounted in the part adjacent one end thereof in side-by-side transverse locations.

3. The arrangement of claim 2, in which the magnets are oppositely poled.

4. The arrangement of any preceding claim, in which the part is a brush for a dynamoelectric machine, and the holder is a brush box.

5. The combination of claim 4, in which the reed switch or switches is/are encapsulated to form a unit removably mounted on the brush box.

6. The combination of claim 4, in which the reed switch or switches is/are carried by a brush arm of a rocker ring, and the brush box is removably mounted on the brush arm.

7. The combination of any of claims 4 to 6, in which the brush is formed of first and second longitudinally abutting brush parts, the first brush part having rigidly secured thereto a counter plate which bears on the second brush part via a resilient block, the or each magnet being secured in an aperture in the first brush part and passing with clearance through a larger aperture in the second brush part.

8. An arrangement for detecting wear of a consumable part slidably mounted in a holder, substantially as herein described with reference to and as shown in the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. a reed switch. However the double magnet arrangement is preferred because of the following advantages:

1) it permits the brush to be put in the box either way round

2) it causes the reed switch blades to be polarised, and thus makes the angular position of the switch mounting unimportant.

CLAIMS (Filed 11Jan 1982) 1. An arrangement for detecting wear of a consumable part slidably mounted in a holder, in which at least one magnet is mounted in the part and a reed switch is mounted on the holder, the positioning of the magnet(s) and reed switch being such that the switch is closed by the magnet(s) when a predetermined degree of wear has occurred and is held closed until the part is completely worn.

2. The arrangement of claim 1, in which two rod-type magnets are mounted in the part adjacent one end thereof in side-by-side transverse locations.

3. The arrangement of claim 2, in which the magnets are oppositely poled.

4. The arrangement of any preceding claim, in which the part is a brush for a dynamoelectric machine, and the holder is a brush box.

5. The combination of claim 4, in which the reed switch or switches is/are encapsulated to form a unit removably mounted on the brush box.

6. The combination of claim 4, in which the reed switch or switches is/are carried by a brush arm of a rocker ring, and the brush box is removably mounted on the brush arm.

7. The combination of any of claims 4 to 6, in which the brush is formed of first and second longitudinally abutting brush parts, the first brush part having rigidly secured thereto a counter plate which bears on the second brush part via a resilient block, the or each magnet being secured in an aperture in the first brush part and passing with clearance through a larger aperture in the second brush part.

8. An arrangement for detecting wear of a consumable part slidably mounted in a holder, substantially as herein described with reference to and as shown in the drawings.