WO1997009769A1

WO1997009769A1 - Brake in an electric motor

Info

Publication number: WO1997009769A1
Application number: PCT/SE1996/001080
Authority: WO
Inventors: Robert Axelsson; Jan Svenson
Original assignee: Robert Axelsson; Jan Svenson
Priority date: 1995-09-06
Filing date: 1996-09-02
Publication date: 1997-03-13
Also published as: SE9503065D0; AU6948796A

Abstract

Brake in an electric motor having a stator (10) and a rotor rotatably mounted in the stator, comprising a brake disc (12) on the rotor and at least one brake shoe which can be engaged with the brake disc (19). The stator is provided with a mounting element (14) for mounting the motor, which allows limited relative pivotal movement between the mounting element and the stator about the rotor shaft (11). Electromagnetic forces or frictional forces acting between the stator and the rotor when the rotor continues to rotate by inertia after the current to the electric motor has been switched off, then causes the stator to pivot in relation to the mounting element, said movement being transmitted to the brake shoe for engaging the brake shoe with the brake disc.

Description

Brake in an electric motor

The invention relates to a brake in an electric motor having a stator and a rotor rotatably mounted in the sta¬ tor, comprising a brake disc on the rotor and at least one brake shoe which can be engaged with the brake disc.

In many applications wherein electric motors are used it is desired that the motor stops rather abruptly after the current having been switched off, and that the rotor shaft then is prevented from rotating under the influence of external forces transmitted to the rotor shaft from the apparatus driven by the motor. For this purpose it is known to provide the motor with a conventional brake of some type usually a strap brake acting on the rotor shaft, which is engaged manually, hydraulically, pneumatically or electro¬ magnetically at the same time as the current to the elec¬ tric motor is being switched off. The purpose of the invention is to provide a brake of the kind referred to above which is engaged automatically when the current to the electric motor is being switched off, by the course of forces which then arises in the motor itself. For this purpose the brake has obtained the charac- terising features of claim 1.

In order to explain the invention in more detail embodiments thereof will be described below reference being made to the accompanying drawings wherein

FIG. 1 is a fragmentary axial cross-sectional view of an electric motor with the brake according to the invention in one embodiment thereof,

FIG. 2 is a diagrammatic end view of the brake in disengaged position,

FIG. 3 is a diagrammatic end view of the brake in engaged position, FIG. 4 is a diagrammatic end view of the brake in another embodiment and discloses the brake with the elec¬ tric motor in operation, and

FIG. 5 is a diagrammatic end view similar to that in FIG. 4 with the brake engaged.

In FIG. 1 there is disclosed fragmentarily a stator housing 10 of an electric motor. The rotor shaft 11 of the electric motor which is provided with a brake disc 12 attached to the shaft, is rotatably mounted in housing 10 by means of ball bearings 13 and also in a disc-shaped mounting element 14 by means of ball bearings 15. Mounting element 14 shall be used for mounting the motor for example to a gear box or to the apparatus to be driven by the motor said mounting taking place at studs 14A. Thus, it is not the stator housing 10 itself that is fixedly mounted but instead the mounting element 14. In the mounting element there are provided a number of slots 16, and studs 17 on the stator housing 10 are displaceably received in these slots the stator housing being connected to the mounting element by means of bolts 18 screwed into the studs and allowing pivotal movement between the mounting element 14 and the stator housing 10 as far as such movement is allowed by the slots 16. The relative pivotal movement between the mounting element and the stator housing takes place about the rotor shaft 11 in the ball bearings 13. Two brake shoes 19 which can be engaged with the brake disc 12 are pivotally mounted on the stator housing 10 by means of pins 20, and a projecting resilient tongue 21 is provided on each brake shoe and engages a pin or pro- jection 22 on the stator housing to maintain the associated brake shoe lifted from the brake disc. Each brake shoe engages a guide 23 provided on the mounting element 14.

If it is assumed that the electric motor is operating and that the rotor shaft 11 and thus the brake disc 12 is rotating clockwise as indicated in FIG. 2 the stator hous- ing 10 mounted for pivotal movement in relation to the mounting element 14 is held in the position shown the studs 17 by the course of electromagnetic forces acting between rotor and stator in the motor being maintained in the position shown at one end of the slots because a force is acting counter-clockwise on the housing 10 by the stator. The brake shoes 19 then exert no braking forces on the brake disc 12.

When the current to the electric motor is being switched off the rotor will continue to rotate clockwise but the course of electromagnetic forces in the motor will now be reversed so that a force is acting on the stator housing 10 clockwise or, alternatively, in motors wherein said course of electromagnetic forces does not exist when the current to the motor is being switched off, said force is produced due to friction in the rotor bearings. By this force the stator housing 10 will be pivoted clockwise about the rotor shaft 11 in relation to the mounting element 14 the studs 17 being displaced in the slots 16. By the pivotal movement of the stator housing the brake shoes 19 will be displaced in relation to the guides provided on the fixed mounting element 14, said guides being shaped such that the brake shoes are swung towards the brake disc 12 and are engaged therewith to exert a braking frictional force as is disclosed in FIG. 3. Brake shoes and guides are, however, so shaped that the brake shoes will be wedged between the brake disc and the guide so that the rotation of the rotor shaft 11 will be stopped practically momentarily when the current to the electric motor is being switched off.

It is not necessary to bias the brake shoes 19 towards the guides 23 by means of a spring 21; the brake shoes can be without such spring and can be allowed to slide against the brake disc when the motor is operating without braking the rotor. Moreover it should be mentioned that the brake disc 12 can be replaced by a brake drum and, therefore, the term "brake disc" is used herein to include also a brake drum on the rotor shaft 11.

The embodiment described is intended for an electric motor which can run in one direction only. In FIGS. 4 and 5 there is shown an embodiment of the invention which is intended for an electric motor which can run in both direc¬ tions. In this embodiment the stator housing 10 is pivoted about the rotor shaft 11 in the same manner as in the embodiment previously described studs 17 on the stator housing being displaceable in slots 16 in the mounting ele¬ ment 1 . The brake shoes in this case indicated at 19A and 19B are substantially semicircular and are mounted at one end thereof on pins 20 which in this case are supported by the mounting element 14, while the other end of the shoes can be engaged with the brake disc 12. Between the brake shoes there is provided at said latter end a weak helical tension spring 24, and between the ends of the brake shoes, interconnected by the tension spring, a pin 25 is provided on the stator housing, which can be engaged with said ends. When the current to the motor is being switched on in order that the motor shall rotate clockwise as indicated by an arrow in FIG. 4 the course of electromagnetic forces in the motor as previously described provides a force on the stator housing 10 which acts in the opposite direction so that the studs 17 will take the position in the slots which is disclosed in FIG. 4. By the pivotal movement of the stator housing thus produced the pin 25 will be engaged with the brake shoe 19B which is lifted from the brake disc against the bias of the spring 24 while the brake shoe 19A on the contrary will be maintained in engagement with the brake disc but at such light pressure that the frictional force produced will be substantially neglectable because the spring 24 is not very strong. When the current to the electric motor is being switched off the condition shown in FIG. 5 will be obtained i.e. in the manner previously described the stator housing 10 by the course of electromagnetic forces in the motor or due to friction in the rotor bearings will be displaced clockwise so that the studs 17 will take the position in the slots 16 as shown in FIG. 6. By the movement of the stator housing the pin 25 will engage the brake shoe 19A and the brake shoe 19B will engage the brake disc 12 the shaft 11 rotating clockwise due to the inertia of the rotor. By the way in which the brake shoes are mounted and shaped wedging will be produced between the brake shoe 19B and the brake disc 12 so that the rotation of the shaft 11 will be stopped momentarily when the brake shoe 19B engages the brake disc.

When the shaft 11 is rotating in the opposite direc¬ tion, counter clockwise, the same course of events will take place but then the condition of FIG. 5 will exist when the motor is operating, and the condition in FIG. 4 will then exist when the current to the motor is being switched off the brake shoe 19A being active for braking the rotor shaft 11.

The two embodiments of the invention shown diagram¬ matically herein are illustrative only for the realisation of the inventive concept . It is within the knowledge of the skilled man to propose other mechanical means than those disclosed herein in order to operatively connect the brake shoes with the stator housing 10 pivoted in relation to the mounting element 14, in order to provide the necessary adjustment of the brake shoes by the movement of the stator housing when the current to the motor is being switched off.

Claims

CLAIMS 1. Brake in an electric motor having a housing (10) and a rotor rotatably mounted in a stator (10) , comprising a brake disc (12) on the rotor and at least one brake shoe (19; 19A, 19B) which can be engaged with the brake disc, c h a r a c t e r i z e d in that the stator (10) is pro¬ vided with a mounting element (14) for mounting the motor, which allows limited relative pivotal movement between the mounting element (14) and the stator (10) about the rotor shaft (11) in order to engage the brake shoe by the pivotal movement of the stator in relation to the mounting element, effected by electromagnetic forces or frictional forces between the stator and the rotor rotating by inertia after the current to the electric motor having been switched off. 2. Brake as in claim 1, c h a r a c t e r i z e d in that the brake shoe (19; 19A, 19B) can be engaged with the brake disc (12) under wedging.