GB2054279A

GB2054279A - Hysteresis clutch

Info

Publication number: GB2054279A
Application number: GB8023290A
Authority: GB
Original assignee: ZF Friedrichshafen AG
Current assignee: ZF Friedrichshafen AG
Priority date: 1979-07-18
Filing date: 1980-07-16
Publication date: 1981-02-11
Also published as: IT1128128B; FR2462049A1; JPS5622570A; SE8005202L; DE2929095A1; IT8049222A0

Abstract

A hysteresis clutch, more particularly for cooling fans 5 of motor vehicles, has an energising part 7, 8 carried by a rotor 9, and a hysteresis part 3 connected to the fan 5. The energising part comprises two concentric rings 7, 8 which are rotationally fast with one another and axially nondisplaceable. The soft magnetic rings 7, 8 are polarised by a coil 13 and have impressed poles of the same number which are peripherally offset in relation to one another. The hysteresis part 3 is constructed as a ring of permanent magnetic material and is rotatably guided between the energising rings 7, 8. <IMAGE>

Description

SPECIFICATION Hysteresis clutch This invention relates to a hysteresis (slipping) clutch, more particularly for cooling fans of motor vehicle engines, having an energising part and a hysteresis part (input and output elements) which are arranged close to one another, but without contact, the energising part having a multiple polarity and the hysteresis part consisting of a permanently magnetic material which enables the magnetism of the hysteresis part to be multiply reversed.

More particularly in motor vehicle engines, cooling fans are only rarely required in unusual operational conditions, in which case they are switched on and off via clutches. It is known to use simple electromagnetically operated clutches for switching the cooling fans on and off. When required to do so, the clutches switch on the fans even at very high speeds, and this causes very loud noises and reduces output. Nor can the torque of these clutches be regulated.

Torque-limited (hysteresis) slipping clutches are also known (cf. the article "Permanent Magnet Clutches" in TEW-Technische Berichte 2, 1962, pages 153-159), which have an energising part and a hysteresis part, the energising part having a permanent magnet and the hysteresis part consisting of a hysteresis disc disposed parallel with the energising part. The axial-parallel arrangement of the parts produces axial forces which load the bearing. With that prior art hysteresis clutch there is a constant loss of output, combined with considerable heating. Moreover, its torque cannot be regulated and it cannot be switched off.

It is an object of the invention to provide a clutch, more particularly for a cooling fan, which operates quietly and has minimum loss of power, and whose torque can be regulated and which can be completely switched off, produces no axial forces and generates minimum heat.

Accordingly, the present invention consists in a hysteresis clutch having an energising part and a hysteresis part (input and output elements) which are arranged close to one another, but without contact, the energising part having a multiple polarity and the hysteresis part consisting of a permanently magnetic material which enables the magnetism of the hysteresis part to be multiply reversed, characterised in that the energising part has two rings which are rotationally fast with one another and axially non-displaceable and which have impressed poles of the same number which are offset in relation to one another and between which the hysteresis part is rotatably guided.

The clutch of the invention is a slipping clutch which is constructed on the principle of the hysteresis clutch, i.e. has an energising part and a hysteresis part (input and output elements). These parts are disposed close to one another but without contact, the energising part having two rows of impressed poles of the same number which are connected rotatably and displaceably fast to one another and are disposed offset by one half pitch in relation to one another. The hysteresis part is disposed rotatably between these two rows of poles. The offsetting of the poles by half the pitch forces the magnetic flux to adopt a direction which is substantially tangential, but which varies from pole to pole in the hysteresis part disposed between the rows of poles, the flux magnetising certain zones oppositely.

When one part of the clutch rotates, those zones are constrainedly reversed in magnetism, and this produces a torque.

Advantageously, the energising part is an electromagnet which consists of a soft magnetic yoke having an energising coil. The high field strength of an electromagnet enables hysteresis material with high magnetism-reversing energy to be used, and this ensures a high torque. The current absorption of the energising coil may be variable, for example due to a temperature-dependent series resistance, the result being stepless torque regulation.

Conveniently, the number of poles of the energising part can be very considerable, due to fine division of the soft iron poles, and this affords the advantage of a relatively high torque.

Preferably, the pole width is approximately twice the thickness of the ring, and the pole division approximately four to five times the thickness of the ring.

According to a further development of the invention, the two rows of poles of the energising part and the hysteresis part are constructed substantially disc-shaped, so that the arrangement is like two interconnected pole discs with an interposed hysteresis disc.

According to another optional feature of the invention, the two rows of poles of the energising part and the hysteresis part are substantially annular and arranged concentrically in relation to one another, so that they form two pole rings, which are connected rotatably and displaceably fast to one another, and a hysteresis ring which is disposed between the two pole rings and is rotatable in relation thereto. This annular arrangement affords the advantage that the hysteresis ring is guided through radially, so that no axial forces are produced and the radial forces cancel one another out. The offset poles of the pole rings constrainedly produce a tangential direction of flux which pre-magnetises parts of the hysteresis ring in opposite directions. A reaction force against a magnetic reversal is produced when the hysteresis ring rotates in relation to the poled rotor.This force is independent of the speed and is uniformly operative at every place. The magnetic reversal of the whole volume of the hysteresis ring takes place during one rotation as often as there are poles provided at a sweep of the hysteresis loop of the permanent magnetic material used.

Apart from being used as a clutch for motor vehicle cooling fans, the hysteresis clutch of the invention when suitably altered can also be used as a brake with slip regulation.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example an embodiment thereof, and in which: Figure 1 is a partial, axial section through an annular clutch according to the invention, Figure 2 is a cross-section on the line ll-ll of Fig. 1, showing the arrangement of the rows of poles according to the invention, and Figure 3 shows a flat development of part of the rows of poles illustrated in Fig. 2.

The hysteresis clutch illustrated comprises an electromagnet coil 13, which is arranged on a coil member 14 and is attached to a casing part 1 6. A shaft 1 7 is mounted rotationally but axially non-displaceably, via a bearing 1 5 in the casing part 16. Attached to the shaft 1 7 is a rotor 9 having on its outer periphery a conducting plate 11 which partially encloses the periphery of the coil member 1 4 and on which a belt pulley 1 0 is provided. The rotor 9, representing the soft magnetic yoke of the energising coil 13, has two rows of poles, an inner row 7 and an outer row 8, which are disposed concentrically in relation to one another and have the same pitch 20. The poles of the two rows are displaced in the peripheral direction in relation to one another by half the pole pitch 20.To ensure that the magnetic flux 2 flows exclusively through the pole parts, a magnetic insulation 1 2 is provided on that part of the rotor 9 axially adjacent to the coil 1 3. Arranged between the two rows of poles is a hysteresis ring 3 whose inner and outer surfaces are very close to the pole surfaces but do not contact the latter. The hysteresis ring 3 is arranged rotatably and displaceably fast in a flange 4 mounted rotatably but axially nondisplaceably via a bearing 1 8 on the shaft 1 7.

A fan 5 is attached by a screw 1 to the flange 4. When the coil 1 3 is energised, the magnetic flux 2 in the rotor 9 will follow a substantially radially inward course; due to the offsetting of the rows of poles, when the magnetic flux passes through the poles in the hysteresis ring 3 the flux will follow a substantially tangential course. It can be assumed that at each pole of the top row of poles about one half of the magnetic flux (cf. Fig. 3) takes a leftward, tangential direction, while the other half of the magnetic flux takes a rightward, tangential direction, the result being a reversal of magnetism 1 9 in zones of the hysteresis ring 3.

The example of a clutch explained can of course also be advantageously used in slipping clutches for other purposes than for driving a fan, preferably in cases in which a drive must be operated silently over a wide speed range and a speed-independent reaction force is required to transmit the drive force to the output.

Claims

1. A hysteresis clutch having an energising part and a hysteresis part (input and output elements) which are arranged close to one another, but without contact, the energising part having a multiple polarity and the hysteresis part consisting of a permanently magnetic material which enables the magnetism of the hysteresis part to be multiply reversed, characterised in that the energising part has two rings which are rotationally fast with one another and axially non-displaceable and which have impressed poles of the same number which are offset in relation to one another and between which the hysteresis part is rotatably guided.

2. A hysteresis clutch according to claim 1, wherein the energising part is an electromagnet having a soft magnetic yoke with an energising coil.

3. A hysteresis clutch according to any of claims 1 or 2, wherein a close sequence of soft iron poles is provided, so that a large number of poles is disposed on each ring.

4. A hysteresis clutch according to claim 1, wherein the hysteresis part is made from hysteresis material with magnetism-reversing energy.

5. A hysteresis clutch according to any of claims 1 to 3, wherein the current absorption of the energising coil is variable.

6. A hysteresis clutch according to claim 1, wherein the pole width is approximately twice the thickness of the hysteresis ring.

7. A hysteresis clutch according to claims 1 and 6, wherein the pole pitch is approximately four to five times the thickness of the hysteresis ring.

8. A hysteresis clutch according to any of claims 1 to 7, wherein the two rows of poles of the energising part and the hysteresis part are substantially disc-shaped and disposed axially offset in relation to one another.

9. A hysteresis clutch according to any of claims 1 to 7, wherein the two rows of poles of the energising part and the hysteresis part are substantially annular in construction and are disposed concentrically in relation to one another.

10. A hysteresis clutch according to any of the preceding claims, wherein the energising part represents the input side, while the hysteresis part is the output side of the clutch.

11. A hysteresis clutch, substantially as herein described with reference to and as shown in the accompanying drawings.