GB1602627A

GB1602627A - Magnetic clutch

Info

Publication number: GB1602627A
Application number: GB2088278A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1978-02-04
Filing date: 1978-05-19
Publication date: 1981-11-11
Also published as: DE2804884A1

Description

(54) MAGNETIC CLUTCH (71) We, ROBERT BOSCH GmbH, a Germany company of 50, Postfach, Stuttgart, 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:- The present invention relates to a magnetic clutch.

Magnetic clutches area already known, for example for small servo-motor drives, which comprise two clutch plates which are provided with pins and bores respectively.

The magnet coil necessary for the actuation of the magnetic clutch is rigidly connected to one clutch plate, however, that is to say it rotates with this. This means that the current supply means to the magnet coil must be constructed in the form of slip rings which, in many cases, can lead to disturbances, for example in the event of soiling.

Furthermore, in the case of magnetic clutches for servo-drives, it is necessary for these clutches to be able to be released rapidly. This is difficult in clutches with a rotating magnetic coil, however, because on a sudden release of the magnetic clutch, the mass of the magnet coil has to be braked.

Furthermore, magnetic clutches are known wherein the connection between one clutch plate and the other is established by balls which engage in appropriately dimensioned bores. This has the disadvantage, however, that as a result of the use of balls, many parts are necessary in the construction of the clutch, which is undesirable with a compact form of construction of the magnetic clutch and that finally, because of the inevitable manufacturing tolerances, it is impossible to ensure that all the balls are always in engagement, and the carrying of only two balls can be counted on at the most.

The present invention provides a magnetic clutch having a first axially movable clutch plate, a second clutch plate arranged to resist axial movement, the plates being arranged to rotate about a common axis, and an armature including a stationary magnet coil for axially moving the first clutch plate, the first clutch plate being provided with a dome like portion on its side remote from the second clutch plate and on its axis of rotation so that in use the armature acts on the dome like portion.

In use, axial and central actuation of the clutch is achieved with a stationary magnet coil. As a result, the current supply of the magnet coil is facilitated and the clutch can be made particularly compact.

In a preferred form of the magnetic clutch, the frictional connection between the armature and clutch plate is established through a metallic and a plastics part, as a result of which the wear is reduced. The deflection of the clutch plate is preferably achieved by a pressure plate disposed resiliently in the armature. This transmission of force through a resilient element compensates for manufacturing tolerances, compensates the abrasion occurring in operation, ensures a firm seating of the engaged clutch by initial tension and finally limits the clutch torque which can be transmitted because, on the appearance of too high a torque, the clutch can then slip like an overload clutch.

As a result of the division of the air gap between armature and magnet coil into a main and a subsidiary air gap, a steady increase in the magnetic force is achieved: A particularly satisfactory effect is achieved if the resiliently mounted pressure plate comprises a contact stud which, when the clutch is engaged, closes an electric contact which can be used as a holding contact for the clutch.

In another particularly preferred form of embodiment of the invention, the clutch plates are provided with bores and crowned pins respectively, the pins being so formed that as the clutch is being released, and the pins are being withdrawn from the bores, relative rotational movement between the clutch plates causes an additional axial force in a direction to assist release of the clutch. The number of pins and bores, may advantageously amount to three or five, in order to render possible a "floating" engagement of the clutch.

The magnetic clutch according to the invention can be constructed not only with a concentric magnet coil, instead the magnet coil may be offset laterally in relation to the clutch in which case the transmission of force to the clutch plates is effected through a lever mechanism.

One form of embodiment of a magnetic clutch according to rthe invention is illustrated in the drawing and explained in more detail in the following description.

Figure I shows a section through a magnetic clutch; and Figure 2 shows a detail from Figure I for the operational state of the engaged clutch.

In Figure 1, a magnetic clutch is indicated at 10 which comprises a first clutch plate 11 and a second clutch plate 12. The first clutch plate 11 carries a toothed rim 13 in which there engages a worm wheel 14 of a drive not illustrated here. The second clutch plate 12 is mounted on a driven shaft 15.

The connection between the first clutch plate 11 and the second clutch plate 12 is established by crowned pins 16 and bores 17 respectively, as illustrated on a larger scale in Figure 2 in a detail showing the engaged state of the magnetic clutch 10. The bores 17 may advantageously be formed by a hardened perforated dise 18 which is inserted in the first clutch plate 11, otherwise consisting of plastics material. If the magnetic clutch 10 is not being energised, a corrugated dise 19 ensures separation of the clutch plates 11, 12. The magnetic clutch 10 is accommodated in a housing 20 in which is disposed a stationary magnet coil 21 formed by an annular former with a winding 22. For the engagement of the first clutch plate 11, an armature 23 is provided which comprises a round armature plate 24 having a hollow cylindrical cup-shaped depression 25 received in the bore of the former of the magnet coil 21. The hollow cylindrical cupshaped depression 25 is bent over at its edge and surrounds a round pressure plate 26 which is held in the depression 25 by a spring 27, which in turn is held by staking the periphery of the hollow cylindrical formed-out portion 25. The bore of the former of the magnet coil 21 is preferably lined with a sleeve 28 of non-magnetic material which projects from the bore on to the side of the former adjacent the armature plate 24.

When the magnetic clutch 10 is disengaged, that is to say when the magnet coil is de-energized, there is an air gap 29 between the magnet coil 21 and the armature plate 24. When the magnet coil 21 is energized, the armature plate 24 moves towards the magnet coil 21. In this case, in addition to the "main air gap" 29, there is a "subsidiary air gap" due to the presence of the sleeve 28. The effect of this is that the clutch already has an adequate attractive force at the beginning. In addition, the portion of the sleeve 28 on the side of the former adjacent the armature plate 24 has the effect that the armature plate 24 cannot rest completely on the magnet coil 21, but a residual air gap remains. By this means the armature 23 is prevented from sticking to the magnet coil 21. When the armature 23 moves in the axial direction towards the first clutch plate 11, force is exerted by the pressure plate 26 on the first clutch plate 11, which is provided with a domed portion at the contact point between these two parts.

The transmission of force is therefore effected only at one point. Apart from the hardened perforated disc 18, the first clutch plate 11 consists of a plastics material, preferably polyamide, and the pressure plate 26 consists of sheet steel. As a result of the use of a metallic part and a plastics part "scuffing" of the frictional-contact members is avoided and the abrasion is reduced as far as possible. As a result of the force which is now exerted by the pressure plate 26 on the first clutch plate 11, the spring 27 is compressed. The effect of this is that the slight but inevitable abrasion on the first clutch plate 11 is compensated and that the first clutch plate 11 has a firm seating in the engaged state. In addition, the clutch plates are now held together by the action of the spring 27 which has the effect that the torque which can be transmitted by the clutch is limited. The pins 16 in the second clutch plate 12 are actually so constructed that when the clutch is released an axial component of force develops which rises with the disengagement of the clutch. If too high a torque were to act on the clutch, the crowned pins 16 would slip out of the bores 17 and, on exceeding a limiting torque, the axial force would overcome the spring force of the spring 27 and the clutch would begin to slip. If it is desired to release the magnetic clutch 10 rapidly, as is frequently the case in servo-drives, the release operation is reinforced by the axial forces appearing at the crowned pins 16.

Moreover, since the magnet coil 21 is stationary, the magnetic clutch 10 can be released very quickly.

Finally, the pressure plate 26 carries an insulating contact stud 30 which permits an electrical contact between two contact tongues 31 when the clutch is engaged and the armature has moved away from the contact tongues 31. This closing contact can be used in an advantageous manner as a holding contact for the magnetic clutch 10.

As an alternative to the above arrangement, the magnet coil 21 may be disposed laterally of the clutch plates Il, 12 in which case the armature 23 includes a prestressed lever for acting on the domelike portion of the first clutch plate 11.

WHAT WE CLAIM IS: 1. A magnetic clutch having a first axially movable clutch plate, a second clutch plate arranged to resist axial movement, the plates being arranged to rotate about a common axis, and an armature including a stationary magnet coil for axially moving the first clutch plate, the first clutch plate being provided with a dome-like portion on its side remote from the second clutch plate and in its axis of rotation so that in use the armature acts on the dome-like portion.

2. A magnetic clutch as claimed in claim 1, characterised in that the dome-like shaped portion of the first clutch plate consists of plastics material and the part of the armature which acts thereon consists of metal.

3. A magnetic clutch as claimed in claim 1 or 2, characterised in that the magnet coil is disposed stationary and coaxially;ound the axis of rotation of the clutch plates and that the armature comprises a circular armature plate with a central hollow cylindrical cupshaped portion recieved in the bore of the magnet coil, which cup-shaped portion surrounds a pressure plate which is held by a spring and which rests on the dome-like portion of the first clutch plate.

4. A magnetic clutch as claimed in claim 3, characterised in that the bore of the magnet coil is lined with a sleeve of nonmagnetic material.

5. A magnetic clutch as claimed in claim 3 or 4, characterised in that the pressure plate is provided with a contact stud which permits an electrical contact between two contact tongues in the engaged state of the magnetic clutch.

6. A magnetic clutch as claimed in claim 1 or 2, characterised in that the magnet coil is disposed laterally of the clutch plates and that the armature acts on the dome-like portion of the first clutch plate through a prestressed lever.

7. A magnetic clutch as claimed in one of the preceding claims, characterised in that the second clutch plate comprises shaped pins and the first clutch plate comprises bores.

8. A magnetic clutch as claimed in claim 7, characterised in that there are three pins and three bores.

9. A magnetic clutch as claimed in claim 7, characterised in that there are five pins and five bores.

10. A magnetic clutch as claimed in claims 7, 8 or 9, characterised in that the ends of the pins are crowned so that an axial component of force is transmitted to the axially movable clutch plate as the magnetic clutch is being released.

11. A magnetic clutch as claimed in one of the claims 7 to 10, characterised in that the first clutch plate consists of plastics material and the bores are provided with portions of a hardened perforated disc, which portions are arranged to receive the pins.

12. A magnetic clutch substantially as hereinbefore described with reference to the accompanying drawing.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. contact tongues 31. This closing contact can be used in an advantageous manner as a holding contact for the magnetic clutch 10. As an alternative to the above arrangement, the magnet coil 21 may be disposed laterally of the clutch plates Il, 12 in which case the armature 23 includes a prestressed lever for acting on the domelike portion of the first clutch plate 11. WHAT WE CLAIM IS:

1. A magnetic clutch having a first axially movable clutch plate, a second clutch plate arranged to resist axial movement, the plates being arranged to rotate about a common axis, and an armature including a stationary magnet coil for axially moving the first clutch plate, the first clutch plate being provided with a dome-like portion on its side remote from the second clutch plate and in its axis of rotation so that in use the armature acts on the dome-like portion.