GB2243421A

GB2243421A - An electromagnetic brake for a motor

Info

Publication number: GB2243421A
Application number: GB9106449A
Authority: GB
Inventors: Jean Alexi Melinand; Jacques Henri Ernest Royer
Original assignee: Moulinex SA
Current assignee: Moulinex SA
Priority date: 1990-03-30
Filing date: 1991-03-26
Publication date: 1991-10-30
Anticipated expiration: 2011-03-26
Also published as: FR2660381A1; DE4109786A1; GB9106449D0; GB2243421B; FR2660381B1

Abstract

An electromagnetic brake for an electric motor (1) having a shaft (2) projecting from the motor casing (3), comprises a coil (4) coaxial with the shaft, and friction pads (5) mounted on a support (6) which is fixed on the shaft. The brake is mounted on the outside of the casing (3), and includes a cap (10) having bayonet-type or other fixing means (11 or 11') removably attachable on the casing. The cap encloses the coil and the support (6), together with a braking member (17) which is slidably mounted in the cap and biassed by a spring (18) which, through the braking member (17), when the coil is de-energised, forces the friction pads to be clamped between a braking surface on the base (16) of the cap and another braking surface formed on the braking member itself to arrest rotation of the shaft. Energisation of the electrical coil (4) moves the braking member against bias of spring (18) to release the brake. The invention is particularly applicable to lawn mower motors. <IMAGE>

Description

1 AN ELECTROMAGNETIC BRAKE FOR A MOTOR This invention relates to an

electromagnetic brake for a motor having a casing from which one end of the rotor shaft of the motor projects, the brake comprising an electrical coil mounted concentrically with the shaft, together with friction pads mounted on a support which is fixed to the shaft for rotation with the latter, whereby the brake can arrest the rotation of the shaft by frictional engagement of the pads on at least one braking surface when the coil is de-energised.

Such electromagnetic brakes are known. They are arranged either inside or outside the motor casing. The motor is specially designed to have such a brake, and it is in fact difficult to fit a brake on an existing motor without considerable modification. In the case in which the motor is not adapted for a brake to be fitted, and in particular if it is intended for use with dangerous apparatus (for example lawnmowers, circular saws or chain saws etc.), the adaptation of the motor for an effective and fastacting brake involves considerable manufacturing costs.

An object of the invention is to overcome this drawback and to provide a brake which is easily adaptable to any kind of motor, while ensuring particularly good braking in the event cf the power supply being interrupted.

According to the invention, in an electromagnetic brake for a motor having a casing from which one end of the rotor shaft of the motor projects, the brake comprising an electrical coil mounted concentrically with the shaft, together with friction pads mounted on a support which is fixed to the shaft for rotation with the latter, whereby the brake can arrest the rotation of the shaft by 2 frictional engagement of the pads on at least one braking surface when the coil is de-energised, the brake includes a cap having fixing means for removable attachment of the cap to the outside of the motor casing, the cap enclosing the coil and friction pad support with the friction pads being arranged between a first braking surface, formed on the base of the cap, and a second braking surface formed on braking member which is mounted around the shaft, the braking member being arranged for sliding movement, against the action of resilient means and in proximity to the coil, between a rest position in which it is drawn against action of the the resilient means by the coil when, the motor being in rotation, the coil is energised, whereby the friction pads and shaft are freely rotatable in the rest position, and a working position in which the braking member is pushed by the resilient means, as soon as the coil is de-energised, so that it in turn urges the friction pads against the cap so as to arrest the rotation of the shaft.

The brake is thus able to be adapted for any type of motor, since it is fitted removably on the outside of the motor casing. It is thus easily fitted to the motor on a massproduction basis, and can readily be removed for ease of maintenance. In addition, at the instant when the power supply is out, the brake pads come into simultaneous frictional engagement against two friction surfaces, i.e. the base of the cap and the braking member. Braking force is thus doubled, so that rotation is arrested practically simultaneously with the interruption of the power supply to the motor.

The invention thus offers a high degree of safety to the user under working conditions.

3 1 An embodiment of the invention will now be described by way of example only, illustrating features and advantages of the invention with reference to the accompanying drawings, in which:- Figure 1 is a view in cross section of part of a brake in accordance with the invention, showing the braking member in its rest position; 2 is a view similar to Figure 1 showing the braking Figure member in its working position; and Figure 3 is an isometric view showing the brake before being secured on the casing of a motor.

The electromagnetic brake shown in Figures 1 to 3 is applied to a motor indicated diagrammatically at 1. end of the rotor shaft 2 of the motor projects from a casing 3 of the motor. The brake comprises an annular electric coil 4, which is mounted concentrically with the shaft 2 and connected electrically in series with the motor 1, together with brake pads 5, of friction material, which are mounted on a support 6 which is fixed on the shaft 2 for rotation with the latter. The support 6 includes a driving bush 7 which is force-fitted on to the end of the shaft 2, together with a support portion 8 in the form of a diaphragm which is flexible in the axial direction. The friction pads 5 are mounted on the diaphragm 8. The flexible support portion 8 comprises a atisc, the central part of which is firmly secured to the driving bush 7, with the friction pads 5 being mounted in holes 9 formed close to the periphery of the support portion 8, with part of each friction pad 5 lying on each side of the latter. There are preferably three friction pads 5.

The brake is mounted on the outside of --ne mo-,-r cas-Ing 3, 4 for which purpose it includes a cap 10 which is provided with fixing means 11 or 11' that are removably attachable to the casing 3.

Each of the fixing means 11 consists of a bayonet arrangement comprising hook elements 12, carried by the cap 10, for passing through apertures 13 formed in the end wall of the motor casing 3. Any kind of motor can be adapted for attachment of the brake. simply by forming these apertures 13 in its casing. The hook elements 12 may also include resilient retaining means (not shown) to enable the hook element 12 to be retained by friction on the edge of the apertures 13, by gripping part of the lower carrier flange 14 of the coil 4 between the motor casing 3 and the lower edge 15 of the cap 10, thus preventing the cap 10 from becoming dislodged of its own accord.

In another embodiment of the invention the removable fixing means consist of a resilient clasp 11', which is indicated in phantom lines in Figure 2. The clasp 11' is arranged so that one of its ends can be hooked into a lateral aperture.22 formed in the skirt of the cap 10, with its other terminal end being hooked into a lateral aperture 23 formed in the side wall of the motor casing 3.

The cap 10 encloses the coil 4 and the support 6 for the ion pads are operative between friction pads 5. The frict.,. two brakJn,-= surfaces, namely a first surface formed on the base 16 of the cap 10, and a second surface which is formed on a braking member 17. The braking member 17 is mounted for sliding movement about the shaft 2, close to the coil 4 and against the action of resilient means 18, which may for example (and as shown) consist of a coil spring which is concentric with the shaft 2, and which is mounted in the braking member 17 comprises a dished portion 19 having a central aperture 19', through which the shaft 2 extends. The braking member 17 is retained in position by at least one tab 20 which is carried by it and which extends through a lateral slot 21 formed in the cap 10, parallel to the shaft 2, so that the braking member 17 is able to slide axially around the shaft 2.

The braking member 17 is able to occupy two positions, namely a rest position shown in Figure 1, in which it is drawn down, against the action ofthe spring 18, by thecoil 4 when the latter is energised. It is energised by being under a voltage when the motor 1 is rotating. In this rest position, the friction pads 5 and the shaft 2 are freely rotatable. The other position of the braking member is the working position shown in Figure 2, in which it is urged by the spring 18, once the coil 4 is deenergised, outwardly so as to force the friction pads 5 against the base 16 of the cap 10, thus applying a braking torque to the shaft 2.

it can thus be seen that the operation of the brake is extremely simple. When the motor is rotating (Figure 1), the coil is energised and draws the braking member 17 towards it, against the action of the spring 18. The support 6 of the friction pads 5 is thus freely driven in.otation with the shaft 2. As soon as the supply to the mcter 1 is interrupted (Figure 2), the supply to the coil 4 is also interrupted and the braking member 17 is no longer attracted by the coil 4: thus the spring 18 forces the member 17 towards the base 16 of the cap 10, so that the pads 5 come into frictional engagement against the two opposed braking surfaces formed on the inside of the cap base 16 and on the outer side of the braking member 17, thus arresting the roratLon of the shaft 2 virzually 6 instantaneously.

_z 7

Claims

CLAIMS 1. An electromagnetic brake for a motor having a casing from which one end of the rotor shaft of the motor projects, the brake comprising an electrical coil mounted concentrically with the shaft, together with friction pads mounted on a support which is fixed to the shaft for rotation with the latter, whereby the brake can arrest the rotation of the shaft by frictional engagement of the pads on at least one braking surface when the coil is deenergised, wherein the brake includes a cap having fixing means for removable attachment of the cap to the outside of the motor casing, the cap enclosing the coil and friction pad support with the friction pads being arranged between a first braking surface, formed on the base of the cap, and a second braking surface formed on a braking member, which is mounted around the shaft, the braking member being arranged for sliding movement, against the action of resilient means and in proximity to the coil, between a rest position in which it is drawn against the action of the resilient means by the coil when, the motor being in rotation, the coil is energised, whereby the friction pads and shaft are freely rotatable in the rest position, and a working position in which the braking member is pushed by the resilient means, as soon as the coil is de-energised, so that it in turn urges the friction pads against the cap so as to arrest the rotation of the shaft.

1

2. An electromagnetic brake according to Claim 1, wherein the removable fixing means for securing the cap on the motor casing comprise a bayonet device consisting of hook elements carried by the cap and adapted to pass through apertures formed in the casing.

5. - - An br2ke according to Claim 1, wherein 8 the removable fixing means for securing he cap on the casing comprise a resilient clasp means, the free ends of which are adapted to hook into respective apertures formed in the cap and in the casing.

4. An electromagnetic brake according to any one of Claims 1 to 3, wherein the friction pad support includes a driving element which is force-fitted on the shaft, together with an axially flexible portion on which the friction pads are mounted.

5. An electromagnetic brake according to Claim 4, wherein the flexible portion of the support comprises a disc having peripheral holes in which the friction pads are mounted, with part of each friction pad lying on either side of the flexible portion.

6. An electromagnetic brake according to any one of the preceding Claims, wherein the braking member comprises a dished port-Lon having a centralaperture through, which 4-1heshaft- extends, the braking member having at least one tab cooperating with a slot formed in the cap parallel to the shaft, whereby to prevent rotation of the braking member while enabling it to slide axially around the shaft.

7. An electromagnetic brake substantially as described herein with reference to the accompanying drawings.

Published 1991 at The Patent Office, Concept House, Cardiff Road. Newport, Gwent NP9 1RH. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. CwnifelWach. Cross Keys. Newport, NP I 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.