GB2197431A

GB2197431A - Electric motor with belt pulley

Info

Publication number: GB2197431A
Application number: GB08726494A
Authority: GB
Inventors: Siegfried Tillner; Dieter Hadeler
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1986-11-15
Filing date: 1987-11-12
Publication date: 1988-05-18
Anticipated expiration: 2007-11-12
Also published as: IT8722603A0; DE3639132A1; FR2606950A1; GB8726494D0; GB2197431B

Abstract

An electric motor for the drive of a washing machine can be constructed as a commutator motor, preferably operated by direct current, and carries a belt pulley (6) on its rotor shaft (1). The pulley is pressed onto the shaft with the interposition of a high strength, electrically insulating layer (4, 5), which consists of a non-flowing synthetic material. The belt pulley (6) is held on the shaft without further fastening means. <IMAGE>

Description

SPECIFICATION Electric motor with belt pulley The present invention relates to an electric motor with belt pulley.

In the case of electric motors operated by direct current, in particular for household appliances, particular protective measures are required, for example the application of fault current protective switches for protection of the user. However, arising fault currents, such as between the motor winding and the lamination packets, usually have a direct current component which can prevent or at least impair reliable switching-off of the motor by the fault current test switch. For this reason, all metallic transitions between the motor and the appliance must be electrically insulated. This necessary insulation represents a problem for the belt pulley arranged on the rotor shaft of the motor, since for constructional reasons the pulley should have the smallest possible diameter.In addition, the V-belt engaging the pulley is not permitted as insulating means by, for example, the VDE (Association of German Engineers) because of the possibility of deposition of abraded metal thereon during operation.

There is thus a need for insulation between motor shaft and belt pulley, which insulation should not impair rotationally secure seating of the belt pulley.

According to the present invention there is provided an electric motor provided with a belt pulley which is press-fitted on an output shaft of the motor with the interposition of a high-strength, electrically insulating layer of flow-resistant synthetic material and which is retained on the shaft exclusively by the pressfitting.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional view of part of a rotor shaft of a motor embodying the invention, with a belt pulley mounted on the shaft; and Figure 2 is an end view of the shaft and pulley.

Referring now to the drawings, there is shown in Fig. 1 an electric motor rotor shaft 1 provided at the output side of the motor with an inwardly-stepped portion 2 which has splines 3 or a knurling over a part of its axial length. A bush 4, which is made of an electrical insulating material and includes a collar 5 lying against the step shoulder of the shaft 1, is pressed or pushed onto the portion 2. A belt pulley 6 is pushed onto the bush 4 in press fit up to the collar 5.

Preferably, the bush 4 consists of a polyphenylene oxide (PPO) with 20 to 30% glass fibre reinforcement, known as "NORYL GFN 2 or 3" (Trade Mark). This synthetic material entails the advantage that on the one hand it does not flow under pressure and that on the other hand it maintains this property on heating-up (for example 100 C). The expansion factor of this synthetic material on heating is greater than that of steel, so that the connection between the rotor shaft, the bush and the belt pulley becomes ever firmer with increasing heating-up when the other components are of steel. The roughening of the rotor shaft surface as well as, as is evident from Fig. 2, the grooves 7 arranged in the axial bore of the belt pulley, contribute to the rotational security of the connection; the sharp edges of the grooves dig into the surface of the bush 4.One or more such grooves 7 can be arranged.

An arrangement of the described kind possesses a torque greater than 30 Newtons per metre in the temperature range 100 to 100 C.

The above-described construction of the individual components and, in particular, the use of a synthetic material of the PPO group, entails appreciable advantages for a commutator motor operated by direct current insofar as a higher output performance is achievable, a longer on-duration is possible and altogether a better motor utilisation may be attainable compared with an asynchronous motor of the same power consumption. It is of particular importance that a belt pulley with the same small external diameter can be used as for an asynchronous motor, since the insulating bush can be kept very thin but still possesses the required strength or torsional resistance. Stepdown ratios of 15:1 to 20:1 are possible within the small installation space of a household washing machine. The simplicity of the components permits automated production.

Either the rotor shaft or the bush can be made of polyphenylene oxide.

1. An electric motor provided with a belt pulley which is press-fitted on an output shaft of the motor with the interposition of a highstrength, electrically insulating layer of flowresistant synthetic material and which is retained on the shaft exclusively by the pressfitting.

2. A motor as claimed in claim 1, wherein the layer is in the form of a bush with a collar.

3. A motor as claimed in claim 2, wherein the shaft is provided with splines in a portion thereof carrying the bush.

4. A motor as claimed in any one of the preceding claims, wherein shaft extends in a bore of the pulley and the pulley is provided in the wall of the bore with at least one axially extending groove.

5. A motor as claimed in any one of the preceding claims, wherein one of the shaft and the layer comprises polyphenylene oxide

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electric motor with belt pulley The present invention relates to an electric motor with belt pulley. In the case of electric motors operated by direct current, in particular for household appliances, particular protective measures are required, for example the application of fault current protective switches for protection of the user. However, arising fault currents, such as between the motor winding and the lamination packets, usually have a direct current component which can prevent or at least impair reliable switching-off of the motor by the fault current test switch. For this reason, all metallic transitions between the motor and the appliance must be electrically insulated. This necessary insulation represents a problem for the belt pulley arranged on the rotor shaft of the motor, since for constructional reasons the pulley should have the smallest possible diameter.In addition, the V-belt engaging the pulley is not permitted as insulating means by, for example, the VDE (Association of German Engineers) because of the possibility of deposition of abraded metal thereon during operation. There is thus a need for insulation between motor shaft and belt pulley, which insulation should not impair rotationally secure seating of the belt pulley. According to the present invention there is provided an electric motor provided with a belt pulley which is press-fitted on an output shaft of the motor with the interposition of a high-strength, electrically insulating layer of flow-resistant synthetic material and which is retained on the shaft exclusively by the pressfitting. An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional view of part of a rotor shaft of a motor embodying the invention, with a belt pulley mounted on the shaft; and Figure 2 is an end view of the shaft and pulley. Referring now to the drawings, there is shown in Fig. 1 an electric motor rotor shaft 1 provided at the output side of the motor with an inwardly-stepped portion 2 which has splines 3 or a knurling over a part of its axial length. A bush 4, which is made of an electrical insulating material and includes a collar 5 lying against the step shoulder of the shaft 1, is pressed or pushed onto the portion 2. A belt pulley 6 is pushed onto the bush 4 in press fit up to the collar 5. Preferably, the bush 4 consists of a polyphenylene oxide (PPO) with 20 to 30% glass fibre reinforcement, known as "NORYL GFN 2 or 3" (Trade Mark). This synthetic material entails the advantage that on the one hand it does not flow under pressure and that on the other hand it maintains this property on heating-up (for example 100 C). The expansion factor of this synthetic material on heating is greater than that of steel, so that the connection between the rotor shaft, the bush and the belt pulley becomes ever firmer with increasing heating-up when the other components are of steel. The roughening of the rotor shaft surface as well as, as is evident from Fig. 2, the grooves 7 arranged in the axial bore of the belt pulley, contribute to the rotational security of the connection; the sharp edges of the grooves dig into the surface of the bush 4.One or more such grooves 7 can be arranged. An arrangement of the described kind possesses a torque greater than 30 Newtons per metre in the temperature range 100 to 100 C. The above-described construction of the individual components and, in particular, the use of a synthetic material of the PPO group, entails appreciable advantages for a commutator motor operated by direct current insofar as a higher output performance is achievable, a longer on-duration is possible and altogether a better motor utilisation may be attainable compared with an asynchronous motor of the same power consumption. It is of particular importance that a belt pulley with the same small external diameter can be used as for an asynchronous motor, since the insulating bush can be kept very thin but still possesses the required strength or torsional resistance. Stepdown ratios of 15:1 to 20:1 are possible within the small installation space of a household washing machine. The simplicity of the components permits automated production. Either the rotor shaft or the bush can be made of polyphenylene oxide. CLAIMS

5. A motor as claimed in any one of the preceding claims, wherein one of the shaft and the layer comprises polyphenylene oxide with 20 to 30 percent glass fibre reinforcement.

6. A motor as claimed in any one of the preceding claims, the motor being a direct current commutator motor for driving a washing machine.

7. A motor substantially as hereinbefore described with reference to the accompanying drawings.