GB2189556A

GB2189556A - Bearing system for an electric motor shaft

Info

Publication number: GB2189556A
Application number: GB08608419A
Authority: GB
Inventors: Shiu-Kee Fung
Original assignee: Johnson Electric Industrial Manufactory Ltd
Current assignee: Johnson Electric Industrial Manufactory Ltd
Priority date: 1986-04-07
Filing date: 1986-04-07
Publication date: 1987-10-28
Also published as: GB8608419D0

Abstract

A bearing system for an electric motor shaft 15 comprises a self-aligning sintered bearing 22 supported in a spherical cup 21 in an end cap 18. The shaft 15 bears on a steel ball 24. Changes in the pressure in the space enclosed by the end cap 18, shaft 15 and bearing 22, may result in increased load on the ball 24 as the shaft is drawn into the enclosed space. This is relieved by a bleed aperture formed by a channel 26 in the bearing seat 22. <IMAGE>

Description

SPECIFICATION Bearing system for an electric motor shaft The present invention relates to a bearing system for an electric motor shaft. The invention is particularly useful in vertically mounted motors, in particular motors for use in food processors.

One form of bearing system for an end of an electric motor shaft comprises a selfaligning sintered bearing which is seated in an end cap. The end cap is closed to retain oil in the vicinity of the sintered bearing and a ball is located between the end of the motor shaft and the end cap to take any axial loading of the shaft in the direction of the end cap. Such an end thrust system have been found to create noise and heat if the axial load is excessive and continuous. The present applicants have realised that excess axial load could be created by the development of a vacuum in the ball enclosure, thus drawing the shaft down on to the ball.

The present invention provides a bearing system for a shaft in an electric motor, comprising a sintered bearing housed in an end cap, an end of the shaft bearing on a support surface in a space enclosed by the end cap, bearing and shaft, wherein a bleed aperture is provided to relieve pressure changes in the enclosed space.

The bleed aperture may be provided in the end cap, and is preferably formed by providing a channel in the seat of the sintered bearing, the bleed aperture equalising the pressure on either side of the bearing.

It is anticipated that the invention is also applicable to other bearings, such as plain sleeve bearings, where the space to one side of the bearing is fully enclosed.

The invention has been found to result in a substantial reduction in the running temperature of the motor. Without limiting the scope of the invention in any way, it is thought that a pressure differential is created across the bearing and housing wall due to the expansion and contraction of air in the enclosed space, the space being effectively sealed by an oil film between the bearing and shaft and the bearing and end caps. This may create a reduced pressure or partial vacuum in the enclosed space, which causes the shaft to be drawn into the space by causing the shaft to bear down on its a bearing surface at the end of the shaft, creating excessive noise and heat. By providing a bleed aperture the change in pressure is avoided or at least reduced.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side view of an electric motor embodying a bearing assembly according to the invention; Figure 2 is a cross section through an end cap of the motor of Fig. 1, showing also the self aligning sintered bearing and motor shaft; and Figure 3 is a cross-section along the line Ill-Ill of Fig. 2.

Referring to Fig. 1, an electric motor 10 which may be used in a food processor in the orientation shown in the drawing, comprises a laminated rotor 11 and laminated stator 12 each with their respective windings. The motor has an upper frame part 14 and lower frame part 13. The lower frame part 13 is of cast aluminium and defines a bearing support 18 which forms the subject of this invention.

A gear box 20 is mounted above the motor in the frame part 14 and a fan 23 is mounted on the motor shaft 15. The motor shaft 15 is connected to an output shaft 16 via the gear box 20.

Brush gear is designated generally by the reference numeral 17 and is mounted in the lower frame 13 to contact a commutator 19 on the motor shaft 15.

Fig. 2 shows in schematic detail on enlarged cross-section through the bearing assembly and support 18.

Support 18 is an integral part of the lower frame member 13 and has a generally hemispherical support surface or cup 21 which supports a self-aligning sintered bearing 22 which is generally spherical but flat at its top and bottom. The bearing may tilt slightly in the seat 22 and remain fully supported. Shaft 15 extends through the bearing and bears on a steel ball 24 which forms a bearing between the shaft 15 and the bottom wall 25 of the support 18. In the prior art device the space between the bearing 22, shaft 15 and support 18 is enclosed, giving rise to the aforementioned disadvantages. The invention provides a channel 26 in the support surface 21, which forms a bleed aperture to and from the enclosed spaced to the ambient, or at least to the internal space of the motor 10.

The channel subtends an arc of a few degrees, peferably 5 to 10 at the centre of the support cup 21. A plurality of channels may be provided, and particularly two channels positioned diametrically opposite one another.

Fig. 3 illustrates the channel cross-section.

It is envisaged that a bleed aperture may be provided through the casing wall, preferably horizontally from the outside, or through the bearing 22. However the former may result in loss of oil from the bearing assembly and the latter may be difficult to achieve with a sintered bearing.

Other modifications may be made within the scope of the invention and it is desired to include all such modifications as fall within the scope of the patent warranted hereon.

1. A bearing system for a shaft in an electric motor, comprising a sintered bearing

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Bearing system for an electric motor shaft The present invention relates to a bearing system for an electric motor shaft. The invention is particularly useful in vertically mounted motors, in particular motors for use in food processors. One form of bearing system for an end of an electric motor shaft comprises a selfaligning sintered bearing which is seated in an end cap. The end cap is closed to retain oil in the vicinity of the sintered bearing and a ball is located between the end of the motor shaft and the end cap to take any axial loading of the shaft in the direction of the end cap. Such an end thrust system have been found to create noise and heat if the axial load is excessive and continuous. The present applicants have realised that excess axial load could be created by the development of a vacuum in the ball enclosure, thus drawing the shaft down on to the ball. The present invention provides a bearing system for a shaft in an electric motor, comprising a sintered bearing housed in an end cap, an end of the shaft bearing on a support surface in a space enclosed by the end cap, bearing and shaft, wherein a bleed aperture is provided to relieve pressure changes in the enclosed space. The bleed aperture may be provided in the end cap, and is preferably formed by providing a channel in the seat of the sintered bearing, the bleed aperture equalising the pressure on either side of the bearing. It is anticipated that the invention is also applicable to other bearings, such as plain sleeve bearings, where the space to one side of the bearing is fully enclosed. The invention has been found to result in a substantial reduction in the running temperature of the motor. Without limiting the scope of the invention in any way, it is thought that a pressure differential is created across the bearing and housing wall due to the expansion and contraction of air in the enclosed space, the space being effectively sealed by an oil film between the bearing and shaft and the bearing and end caps. This may create a reduced pressure or partial vacuum in the enclosed space, which causes the shaft to be drawn into the space by causing the shaft to bear down on its a bearing surface at the end of the shaft, creating excessive noise and heat. By providing a bleed aperture the change in pressure is avoided or at least reduced. The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side view of an electric motor embodying a bearing assembly according to the invention; Figure 2 is a cross section through an end cap of the motor of Fig. 1, showing also the self aligning sintered bearing and motor shaft; and Figure 3 is a cross-section along the line Ill-Ill of Fig. 2. Referring to Fig. 1, an electric motor 10 which may be used in a food processor in the orientation shown in the drawing, comprises a laminated rotor 11 and laminated stator 12 each with their respective windings. The motor has an upper frame part 14 and lower frame part 13. The lower frame part 13 is of cast aluminium and defines a bearing support 18 which forms the subject of this invention. A gear box 20 is mounted above the motor in the frame part 14 and a fan 23 is mounted on the motor shaft 15. The motor shaft 15 is connected to an output shaft 16 via the gear box 20. Brush gear is designated generally by the reference numeral 17 and is mounted in the lower frame 13 to contact a commutator 19 on the motor shaft 15. Fig. 2 shows in schematic detail on enlarged cross-section through the bearing assembly and support 18. Support 18 is an integral part of the lower frame member 13 and has a generally hemispherical support surface or cup 21 which supports a self-aligning sintered bearing 22 which is generally spherical but flat at its top and bottom. The bearing may tilt slightly in the seat 22 and remain fully supported. Shaft 15 extends through the bearing and bears on a steel ball 24 which forms a bearing between the shaft 15 and the bottom wall 25 of the support 18. In the prior art device the space between the bearing 22, shaft 15 and support 18 is enclosed, giving rise to the aforementioned disadvantages. The invention provides a channel 26 in the support surface 21, which forms a bleed aperture to and from the enclosed spaced to the ambient, or at least to the internal space of the motor 10. The channel subtends an arc of a few degrees, peferably 5 to 10 at the centre of the support cup 21. A plurality of channels may be provided, and particularly two channels positioned diametrically opposite one another. Fig. 3 illustrates the channel cross-section. It is envisaged that a bleed aperture may be provided through the casing wall, preferably horizontally from the outside, or through the bearing 22. However the former may result in loss of oil from the bearing assembly and the latter may be difficult to achieve with a sintered bearing. Other modifications may be made within the scope of the invention and it is desired to include all such modifications as fall within the scope of the patent warranted hereon. CLAIMS

1. A bearing system for a shaft in an electric motor, comprising a sintered bearing housed in an end cap, an end of the shaft bearing on a support surface in a space enclosed by the end cap, bearing and shaft, wherein a bleed aperture is provided to relieve pressure changes in the enclosed space.

2. A bearing system as claimed in claim 1, wherein a ball is positioned between the end of the shaft and the end cap.

3. A bearing system as claimed in claim 2, wherein the sintered bearing is supported on a support surface of the end cap and the bleed aperture comprises a channel in the support surface.