GB2226090A

GB2226090A - Bearing assembly for electric motor

Info

Publication number: GB2226090A
Application number: GB8826614A
Authority: GB
Inventors: Georg Strobl
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1988-11-14
Filing date: 1988-11-14
Publication date: 1990-06-20
Also published as: DE8913404U1; JPH02104758U; GB8826614D0; CN2062128U; JPH083158Y2

Abstract

In a fractional horsepower DC motor, a self aligning bearing 4 is canted at an angle to the motor shaft by a resilient finger 16a to reduce the clearance between the shaft 2 and bearing surface 8. The finger 16a is part of a spring steel clip 15. <IMAGE>

Description

BEARING ARRANGEMENT IN AN ELECTRIC MOTOR The present invention provides a bearing arrangement in an electric motor, particularly in a fractional horsepower permanent magnet direct current motor.

Fractional horsepower PMDC motors are used more and more in low noise environments, for example inside the passenger compartment of luxury automobiles. It is thus becoming more and more important to reduce the mechanical noise of such motors. Typically, the motor shaft runs in a pair of wintered, self-aligning bearings. The tolerance required in the gap between the shaft and bearing means that the shaft can "rattle" laterally in the bearings, creating significant mechanical noise. One arrangement which has been proposed to overcome this is to bias the stator magnetic field to one side of the motor shaft axis so that the shaft is pulled against one side of the inner bearing surfaces. This requires alteration of the motor geometry and may present other drawbacks.

The present invention provides an electric motor comprising a frame or housing carrying a stator and having self-aligning bearings at opposite ends thereof, the bearings each having an inner cylindrical bearing surface, and a rotor comprising a shaft and a commutator and armature mounted on the shaft, the shaft being rotatably mounted in the bearings to run on the inner cylindrical bearing surfaces, wherein means is provided to apply a twisting force to at least one of the bearings to bias the bearing into a position in which the axial direction of the inner cylindrical bearing surface is at an angle to the axial direction of the shaft.

By twisting the axis of the bearing surface relative to the shaft the clearance between the bearing surface and shaft can be reduced.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional part view through an end of a PMDC motor housing showing a rotor shaft mounted in a bearing arrangement in accordance with the invention; Figure 2 is a plan view on arrow A of Figure 1; and Figure 3 is a schematic view of a motor shaft and two bearings.

Referring to the drawings, a motor shaft 2 carries a commutator and armature (not shown). The shaft 2 is supported at its ends in two self aligning bearings 4. The bearings are carried respectively in an end cap 6 of the motor and a closed end of a deep drawn steel can-like casing (not shown). The end cap 6 and casing forming the motor housing. The end cap 6 also carries brushgear (not shown).

Each bearing 4 has a cylindrical inner bearing surface 8 which is chamferred at its outer ends 10. The outer surface 12 of the bearing 4 is part spherical or spheroidal, being circular in plan view and also arcuate in axial cross-section (Figure 1). The bearing 4 sits in a correspondingly shaped cup 14 in the end cap (or casing end wall). The bearing 4 is held in place by a spring steel clip 15 which surrounds the bearing and has resilient fingers 16 which bear on the outer surface 12 pressing the bearing into the cup 14. One 16a of the fingers bears on a step 18 formed in the surface 12 of the bearing.

The finger 16a is arranged to apply a twisting force or torque to the bearing to swivel it in the cup 14 so that the axis B-B of the bearing is at an angle to (i.e. not parallel or coincident with) the axis S-S of the shaft 2.

The clip 15 has an upturned peripheral lip 20 which grips a surrounding wall 22 in the end cap 6 to hold the clip 15 in place.

The finger 16a is resilient and applies only a small force so that the bearing 4 retains its self-aligning property and is able to twist along its axial direction with the shaft but will be subject to a preload applied by the finger 16a and tending to align the bearing at an angle to the shaft. Typically the bearing axis will be at an angle of about 0.5 degrees to the shaft axis.

Different preloads or torques can be applied to the bearing by altering the unstrained configuration of the finger 16a. A range of clips 15 may be provided to allow selection of the preload or a single clip may have several fingers 16a of different configuration, one of which is selected to bear on the step 18.

Referring to Figure 3, when both bearings have a biassing force applied to them they are preferably canted in opposite directions relative to the shaft.

Various modifications may be made to the described embodiment and it is desired to include all such modifications as fall within the scope of the accompanying claims.

Claims

1. An electric motor comprising a housing carrying a frame or housing carrying a stator and having self aligning bearings at opposite ends thereof, the bearings each having an inner cylindrical bearing surface, and a rotor comprising a shaft and a commutator and armature mounted on the shaft, the shaft being rotatably mounted in the bearings to run on the inner cylindrical bearing surfaces, wherein biassing means is provided to apply a twisting force to at least one of the bearings to bias the bearing into a position in which the axial direction of the inner cylindrical surface is at an angle to the axial direction of the shaft.

2. A motor as claimed in claim 1, wherein the biassing means applies a force to one side of the bearing and acts generally parallel to the axial direction of the bearing.

3. A motor as claimed in claim 2, wherein the biassing means is a resilient finger which bears on the bearing.

4. A motor as claimed in claim 3, wherein the bearing sits in a cup and is held in position by a clip having a plurality of resilient fingers bearing on the bearing to hold it in the cup, at least one of said fingers being arranged to apply the biassing force.

5. A motor as claimed in any one of claims 1 to 4, wherein a twisting force is applied to both bearings.

6. A motor as claimed in claim 5, wherein the bearings are twisted in opposite directions relative to the shaft.

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