Braking system with safe torque take-up

The present invention relates to a braking system for an electric motor, the braking system comprising:

This non provisional application claims the benefit of French Application No. 03 08362 filed on Jul. 8, 2003.

The present invention relates to braking systems for electric motors, and particular to those for use with motors driving elevators or other hoist systems.

BACKGROUND OF THE INVENTION

Braking systems are known which comprise electromagnetic brakes each comprising a brake disk secured to the motor shaft and provided with friction linings, together with an armature that is movable under drive from an electromagnet. If the electromagnet is not excited, then the armature is pressed against the friction linings by springs, so braking torque is exerted on the disk, and by reaction also on the brake and the chassis supporting it.

Brakes are conventionally assembled by being bolted onto the chassis, with braking torque being taken up by the chassis by the friction due to the bolts being tightened.

Screw-tightened assemblies suffer from a large amount of dispersion in characteristics, which makes it necessary to overdimension the braking system by using more screws and/or stronger materials, and this has repercussions on costs.

There exists a need for a braking system that presents the required level of safety, while enabling it to be manufactured at lower cost.

BRIEF SUMMARY OF THE INVENTION

In a first aspect, the invention thus provides a braking system for an electric motor, in particular for driving an elevator, the braking system comprising:a chassis; andat least one brake supported by the chassis, the brake comprising:at least one brake disk connected via a fluted connection to a shaft driven by the motor;an armature that is movable in translation along the axis of rotation of the shaft;armature-guiding spacers, at least one of the spacers being engaged at one end in a corresponding housing in the chassis, so as to enable the chassis to take up the torque that is exerted on the brake during braking;springs for urging the armature against the disk; andan electromagnet which, when powered, serves to attract the armature and move it away from the disk against the action of the springs.

The brake may include, in particular, three spacers each having one end engaged in a corresponding housing of the chassis so as to enable the chassis to take up the torque that is exerted on the brake during braking.

Such a braking system enables the braking torque to be taken up reliably and safely without it being necessary to overdimension the brake, by making the spacers perform an additional function, namely that of transmitting the braking torque.

In a particular embodiment, the armature includes at least one oblong opening that is elongate in the radial direction and through which a corresponding spacer passes. This oblong opening may, in particular, open out into the circumference of the armature. The presence of the oblong opening makes it easier to position the armature on the spacer and makes it possible to make the braking system with looser manufacturing tolerances, and thus at lower cost.

Each spacer may be screwed into a yoke of the brake, thus enabling the axial travel of the armature to be adjusted, with the armature, in the absence of power being supplied to the electromagnet, being pressed by the springs against a head of the spacer, which head may be hexagonal in shape so as to make the spacer easier to tighten or loosen.

Advantageously, the braking system includes a second brake juxtaposed with the first brake, and comprising like the first brake, a brake disk connected via a fluted connection to the shaft that is driven by the motor, an armature that is movable in translation along the axis of rotation of the shaft, armature-guiding spacers, springs for urging the armature against the disk, and an electromagnet which, when powered, serves to attract the armature and move it away from the disk against the action of the springs.

Where appropriate, each of the spacers of the second brake may be engaged at one end in a corresponding housing in the yoke of the first brake, so as to enable said yoke to take up the torque that is exerted on the second brake during braking.

The braking system may include threaded rods passing through the spacers and holding the two brakes pressed one against the other. These threaded rods may be screwed at one end into the chassis and may serve at their opposite ends to receive nuts that are screwed on to bear against the yoke of the second brake.

The yoke may include a housing for receiving one end of the shaft driven by the motor, which housing may be closed at one end by a plug serving to reduce the operating noise of the braking system.

MORE DETAILED DESCRIPTION

The braking system1shown inFIG. 1comprises a chassis2that is shown in part, and that is secured to a main structure (not shown). Inside the chassis2, there rotates a shaft3of axis X carrying a pulley for driving an elevator cable. The shaft3has two fluted portions4and5at one end.

In the example described, the braking system also comprises two brakes8and9each comprising respective brake disks11and12provided with hubs that are capable of sliding over the respective fluted portions3and4along the axis X of the shaft, while rotating therewith.

The brakes11and12are provided at their peripheries and on both faces with friction linings13.

The brakes8and9also comprise respective moving armatures15and16which are guided in their movement in translation along the axis X by spacers17for the first brake and18for the second brake, these spacers17and18being screwed into the respective yokes19and20of the brakes8and9.

Electromagnets22and23housed respectively in the yokes19and20of the brakes8and9enable the corresponding armatures15and16to be attracted thereto when they are powered electrically, in with case the brake disks associated with said armatures can rotate without significantly braking rotation of the shaft2.

Springs29are located in housings in the yokes19and20to press the armatures15and16against the corresponding brake disks11and12when the electromagnets22and23are not powered, so that the friction linings13then rub against the armature15and the chassis2for the first brake8and against the armature16and the yoke19for the second brake, thereby exerting braking torque on the shaft3.

An O-ring33is disposed on each yoke19or20so as to be elastically interposed relative to the corresponding armature when the associated electromagnet is powered, for the purpose of reducing vibration and noise due to brake operation.

As can be seen inFIG. 3in particular, the spacers17are hollow as are the spacers18, thus enabling rods34to pass for fixing the brakes8and9to the chassis2. These rods34extend parallel to the axis X and are screwed at one end35into the chassis2and each of them receives at its opposite end36a nut that bears against the rear face37of the yoke20of the second brake9. Fixing systems other than rods34could also be used.

The spacers17present respective threaded portions17afor screwing into the yoke19and respective hexagonal heads17bwhich define respective shoulders17c. By tightening the spacers17to a greater or lesser extent, it is possible to vary the air gap of the brake8.

The spacers17present respective intermediate portions17dthat are circularly cylindrical and smooth, extending between the corresponding head17band threaded portion17a, and serving to guide the armature15.

In accordance with an aspect of the invention, each of the spacers17has an annular lip17eprojecting beyond the hexagonal head17band arranged to be received in a corresponding housing40in the chassis2, so as to enable the braking torque exerted on the brakes8and9to be transmitted to the chassis2.

In the example ofFIG. 1, the spacers18differ from the spacers17solely by the absence of the lips17e.

In another aspect of the invention, each armature15or16includes at its periphery and as can be seen inFIG. 5, three forks41disposed at 120° from one another, each presenting an oblong opening42for passing the corresponding spacer17or18, the width of each opening42corresponding substantially to the outside diameter of the intermediate cylindrical portion17d.

In the example shown, the oblong openings42open out radially to the outside of the corresponding armature15or16, thus making it possible to accommodate a certain amount of radial movement of the spacers17and18, thereby facilitating fabrication and assembly of the brakes8and9.

The yokes19and20include respective housings46and47for passing the shaft3. A plug50closes the housing47in the yoke20, thus making it possible to reduce noise in operation.

It would not go beyond the ambit of the present invention for the spacers18of the second brake to be identical to those of the first brake, and consequently for each of them to include an extension formed by an annular lip18e(as shown in part and diagrammatically inFIG. 6) for engaging in a corresponding setback52in the yokes19of the first brake8, so as to enable torque to be taken up between the two brakes8and9other than by friction, and thus further improve the safety of the assembly.

Naturally, the invention is not limited to the examples described above.

In particular, the spacers can be given different shapes, and where appropriate it is possible to provide a braking system having a different number of brakes.

Throughout the description, including in the claims, the term “comprising a” should be understood as being synonymous with “comprising at least one”, unless specified to the contrary.