GB1586180A

GB1586180A - Electro-magnetically operated friction clutch or brake

Info

Publication number: GB1586180A
Application number: GB3453277A
Authority: GB
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1976-08-28
Filing date: 1977-08-17
Publication date: 1981-03-18
Also published as: DE2638944A1; SE7709624L; ES460851A1; IT1080083B; CH618243A5; FR2363027B1; SE431781B; FR2363027A1

Abstract

A fixed part of a clutch (1) comprises a magnet body (2), a permanent magnet (3), a coil of an electromagnet (5) and a nonmagnetic insert (4). An armature (19) comprises an armature disc (12) which is made up of two concentric rings and is connected firmly in terms of rotation to a driver (18) via an annular spring (11). Between the fixed clutch part (2, 3, 4, 5) and the armature (19) there is an axially fixed but rotatable clutch disc (15) which has a deflector (8), a nonmagnetic intermediate layer (9) with an insert (10) and a hub (17). A nonmagnetic intermediate layer (16) is arranged in the hub (17), concentrically to the axis of the hub. In the deenergised condition of the coil of the electromagnet (5), the magnetic flux lines of the permanent magnet (3) follow a path (26). In the excited condition of the coil, the magnetic flux lines follow a path (22) while the flux lines of the electromagnet (5) follow a path (21). The nonmagnetic intermediate layer (16) and the nonmagnetic insert (4) reduce the magnetic leakage flux to a minimum. A fail-safe clutch or brake with a high torque and a short response time and with small dimensions is thus created. <IMAGE>

Description

(54) ELECTRO-MAGNETICALLY OPERATED FRICTION CLUTCH OR BRAKE (71) We, ZAHNRADFABRIK FRIED RICHSHAFEN AKTIENGESELLSCHAFT, of Friedrichshafen-on-the-Bodensee, Federal Republic of Germany, a Joint-Stock Company organised under the laws of the Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an electromagnetically operated friction clutch or brake which is frictionally engaged in the currentless state and is disengaged electromagnetically.

Electromagnetically disengageable spring force brakes are known for use in conjunction with electric motors, particularly for hoisting equipment. In such brakes the electromagnet serves only to disengage the brakes, for which purpose one half of the brake is lifted off the second half by axial displacement of said one half against the force of a spring. Since the electromagnet here acts by way of an air gap which increases with the wear of the brake lining, the force of the brakes spring must be so selected that the pulling power of the electromagnet is sufficient to effect disengagement even with the maximum air gap, which may amount to a multiple of the initial value. In known electromagnetically disengageable spring force brakes the electromagnetic system is thus utilised in a disadvantageous manner. Furthermore, when the brake lining wears, the resulting variation of the displacement path results in not only a lengthening of the reaction time but also a variation of the braking torque, while finally there is a danger of brake failure if re-adjustment is not effected in good time.

Electro-magnetically operated friction clutches or brakes have therefore been produced in which a permanent magnet was provided in the armature and served to engage the clutch or brake, while an electromagnet was provided in the stationary part of the clutch or brake and used to disengage the clutch or brake. The installation of the permanent magnet in the armature gives rise to heavy armature masses, which in turn results in long response times.

It has also been proposed (German Patent Specification 1,067,267) to dispose the electromagnet and the permanent magnet together in the stationary half of a brake, a relatively soft spring being used to repel the two friction halves. However, negative properties were ascribed to this arrangement, such as the reduction of the attraction of the permanent magnet by force of the spring, whereby it was intended to lengthen the reaction time.

Electromagnetically operated friction clutches or brakes are also known (German Published Specification 1,964,311) which consists of a stationary magnet body provided with a magnet coil, an armature disc consisting of two concentric rings separated from one another, a ring spring, and a driven component or one which is to be driven, and of a rotably mounted guide disc which is magnetically insulated for the purpose of double flux. These known clutches or brakes have the advantage of relatively high transmissible torque, with a short make time and a small, compact construction. In the event of a current failure, however, the clutch or brake is disengaged, which constitutes a relatively great risk of accident.

The invention aims at providing an electro-magnetically operated friction clutch or brake which while of simple, compact construction has a high attractive force, that is to say a high transmissible torque, very short response times, and also great operational reliability.

Accordingly, the present invention consists in an electro-magnetically operated friction clutch or brake having a stationary magnet body provided with an electromagnet coil for disengaging the clutch or brake and with a permanent magnet for engaging the clutch or brake, characterised in that between an armature, which consists of an armature disc comprising two separate concentric rings, a ring spring and a drivable member, and the stationary magnet body there is provided a clutch or brake disc comprising a hub carrying a magnetically conducting disc in which there are a nonmagnetic insert and a magnetic insert. The Friction clutch or brake consists substantially of a clutch or brake body in which a permanent magnet is provided for engaging the clutch or brake and an electromagnet for disengaging the clutch or brake, of a clutch or brake disc which for the purpose of double flux is provided in known manner with a magnetically insulated insert and for the purpose of reducing stray magnetic flux is provided with a non-magnetic insert in its hub, and of an armature which is known per se and whose armature disc is composed of two separated concentric rings and is fastened on the driver of the armature by means of a ring spring which serves to pull back the armature disc. The permanent magnet is advantageously an oxide permanent magnet whose lines of force are guided by way of the magnet body into the armature and into the clutch or brake disc. The armature and clutch or brake disc have four poles which are adjusted to the two-part armature disc and whose cross-section is kept so small that saturation induction is approximately achieved, while the induction in the permanent magnet amounts to only about 15 to 20% of the saturation of the iron. The clutch or brake works with pure pole face friction, that is to say without a working air gap. When the magnet coil is energised so that it builds up a counter-field, the field lines of the permanent magnet are displaced to such an extent that induction equal to zero is achieved in all four pole faces. The return forces of the ring spring then disengages the clutch or brake. The permanent magnet is not de-magnetised thereby, so that this operation can be repeated as often as desired without weakening the magnet.

A great advantage of the clutch or brake of the invention is its construction as a closed-circuit coupling that is to say its transmission of torque without the application of a voltage, so that it complies with very important operational safety regulations.

By virtue of the double flux, that to say the avoidance of stray magnetic fluxes with the aid of additional magnetic insulations, a very high attractive force and consequently a relatively high transmission torque are achieved.

A very short response time is obtained because of the small armature masses.

All these advantages are achieved in the clutch or brake of the invention with a very compact construction of surprisingly small dimensions. In addition, these devices can be built without play incurring expence.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammically and by way of example one embodiment thereof, and in which: Fig. 1 is a half view of an electro-magnetic clutch according to the invention in the currentless state (engaged), and Fig. 2 is a half view of the clutch with the electromagnet coil energised (disengaged).

A magnet body 2, a permanent magnet 3, the coil of an electromagnet 5, and a nonmagnetic insert 4 together form the stationary part of a clutch 1. An armature disc 12, composed of two separate concentric rings, is rotationally fixed in known manner on a driver 18 with the aid of a ring spring 11, so as to form armature 19.

Between the stationary part of the clutch and the rotating armature 19 is provided an axially immovable but rotatable clutch disc 15. For the purpose of a double flux the clutch disc 15 comprises in known manner a magnetically conducting disc 8, a first nonmagnetic insert 9, a magnetically conducting insert 10, and a hub 17. A second nonmagnetic insert 16 is provided in the hub, and is disposed substantially concentrically to the axis of the hub. With the coil of the electromagnet 5 in the de-energised state 25 the magnetic lines of force of the permanent magnet 3 have the pattern 26. When the coil is in the energised state 24 the magnet lines of force of the permanent magnet 3 have the pattern 22, while the lines of force of the electromagnet 5 have the pattern 21.

The clutch of the invention operates in the following manner: When the clutch 1 is in the currentless state, as shown in Fig. 1, the permanent magnet 3 has a magnetic field whose lines of force have the pattern 26 by virtue of the shape of the magnet body 2 together with its non-magnetic insert 4, and by virtue of the shape of the clutch disc 15 and the construction of the armature plate 12. The armature plate 12 is attracted, so that it frictionally connects the armature 19 to the clutch disc 15. The clutch 1 is engaged and torque can be transmitted.

When the electric current is switched on, the state 24 shown in Fig. 2 is obtained, in which the coil is energised. The electromagnet 5 generates a magnetic field whose lines of force, which have the pattern 21, displace the lines of force of the magnetic field of the permanent magnet 3 to such an extent that they assume the pattern 22, while at the same time producing induction equal to zero in all the pole faces of the clutch disc 15.

Since no further magnetic attraction force exists, the armature disc 12 is detached from the clutch disc 15 and pulled back towards the driver 18 by the ring spring 11. The clutch is disengaged.

The non-magnetic insert 16 in the hub 17 can be produced by providing a gap of the size and shape of the insert between two parts lying concentrically one within the other, the desired non-magnetic material being cast therein.

Because of the non-magnetic insert 16 provided in the hub 17 of the clutch disc 15 and because of the non-magnetic insert 4 in the magnet body 2 the stray magnetic fluxes are reduced to the greatest possible extent, so that optimum utilisation of the permanent magnet field is permitted.

The importance of the invention consists in that a new closed-circuit clutch or brake of high torque and short response time is provided, which is of small dirnensions.

WHAT WE CLAIM IS:- 1. An electro-magnetically operated friction clutch or brake having a stationary magnet body provided with an electromagnet coil for disengaging the clutch or brake and with a permanent magnet for engaging the clutch or brake, characterised in that between an armature, which consists of an armature disc comprising two separate concentric rings, a ring spring and a drivable member, and the stationary magnet body there is provided a clutch or brake disc comprising a hub carrying a magnetically conducting disc in which there are a nonmagnetic insert and a magnetic insert.

2. A friction clutch or brake according to claim 1, wherein a further non-magnetic insert is provided in the hub and is arranged substantially concentrically to the axis of the hub.

3. An electro-magnetically operated friction clutch, substantially as herein described with reference to and as shown in the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. size and shape of the insert between two parts lying concentrically one within the other, the desired non-magnetic material being cast therein. Because of the non-magnetic insert 16 provided in the hub 17 of the clutch disc 15 and because of the non-magnetic insert 4 in the magnet body 2 the stray magnetic fluxes are reduced to the greatest possible extent, so that optimum utilisation of the permanent magnet field is permitted. The importance of the invention consists in that a new closed-circuit clutch or brake of high torque and short response time is provided, which is of small dirnensions. WHAT WE CLAIM IS:-

1. An electro-magnetically operated friction clutch or brake having a stationary magnet body provided with an electromagnet coil for disengaging the clutch or brake and with a permanent magnet for engaging the clutch or brake, characterised in that between an armature, which consists of an armature disc comprising two separate concentric rings, a ring spring and a drivable member, and the stationary magnet body there is provided a clutch or brake disc comprising a hub carrying a magnetically conducting disc in which there are a nonmagnetic insert and a magnetic insert.