The present invention relates to a clutch mechanism and more particularly a clutch mechanism for use within a motor vehicle to provide power to an air conditioning compressor of an air conditioning system of such a vehicle.

It is known to provide power for various auxiliary systems on a motor vehicle by appropriate take off from the main shaft of the vehicle engine.

However, it will be appreciated that some of these auxiliary systems do not require power continuously and therefore have an intermittent operational profile in order to avoid unnecessary power loss from the main shaft. In order to achieve such intermittent operation, it is necessary that appropriate engage\disengage arrangements, ie. a clutch, are in place to take power drive from the main shaft only when necessary. It will also be appreciated that a clutch is required to protect the engine if the auxiliary system, ie. compressor, seizes.

Typically, a clutch arrangement will be used to take power from the main shaft. This clutch will engage an actuation mechanism from the main drive shaft for the auxiliary system as required. Unfortunately, traditional clutches are quite bulky and therefore can present packaging problems

within an engine compartment of a motor vehicle. Furthermore, if the engage\disengage arrangement requires ongoing power consumption in order to maintain engagement, or, for that matter, disengagement, this too could be a significant power drain on the overall engine system of the motor vehicle.

A typical clutch mechanism based upon utilisation of magnetism is described with regard to Figure 55.7, page 350 to 351 of the text book "Fundamentals of Vehicle Technology (4th Edition) by V A W Hillier, published by Stanley Thorns (Publishers) Ltd, 1991. This teaching is incorporated into the present description by way of reference. It will be appreciated that maintenance of the electromagnetic field is necessary whilst the clutch remains engaged. This necessitates a consumption of approximately 3 to 5 amps of electrical power continuously when engaged.

Furthermore, the clutch tends to have a large diameter in order to accommodate the windings necessary to achieve the appropriate electromagnetic field to achieve and maintain engagement under load.

It is an object of the present invention to provide a clutch mechanism suitable for powered auxiliary systems (PAS) of a motor vehicle in which the clutch has a reduced diameter and electrical power requirements.

In accordance with the present invention there is provided a clutch mechanism for a motor vehicle and in particular an air conditioning compressor of that vehicle, the mechanism comprising a clutch plate arranged to be coupled to a drive shaft for an auxiliary device and including angled engagement means associated with a permanent magnet, an electromagnetic device being arranged to stimulate engagement of said angled engagement means with actuation means from an engine, said angled engagement means and said actuation means being clamped in abutting engagement by said permanent magnet alone thereafter in order to power the auxiliary device from the engine until stimulated to disengage by said electromagnetic device opposing the permanent magnet clamping force.

Preferably, the actuation means is configured between the angled engagement means and said electromagnetic device. The actuation means is most typically a hub pulley type wheel from which a drive belt from the engine may be coupled in order to actuate the device/powered auxiliary system. Typically, the actuation means will also be angled relative to the drive shaft similarly to the engagement means in order to reduce clutch diameter.

Generally, the electromagnetic generator device will be solenoid activated by an electrical current precipitated by a requirement for power to the powered auxiliary system as determined by a controller.

Preferably, the angled engagement means comprises a plurality of clutch fingers each with a respective permanent magnet in order to reduce the necessary magnetic force required from the electromagnetic device in order to distort said angled engagement means into and out of contact with the actuation means. Alternatively, the angled engagement means could slide fore and aft on the drive shaft as a result of attraction/repulsion from the electromagnetic device.

Preferably the engagement means is at a relatively inclined angle relative to the actuation means such that the angled engagement means essentially pivots into engagement with the actuation means with an arc pivoted about the junction between the clutch plate and the angled engagement means such that a more flat or laminar contact is made between the angled engagement means and the actuation means.

Preferably, the angled engagement means is at an angle of 5 to 10° to the clutch plate.

The electromagnetic device is used to stimulate engagement and disengagement between the engagement means and the actuation means by appropriate creation of attractive and repulsive magnetic forces which act upon the permanent magnet associated with the engagement means, the electromagnetic device providing sufficient activation to overcome the

relaxed relative position of the engagement means with a gap, generally of a wedge shape, to the actuation means. The electromagnetic means acting to bias the engagement means towards the actuation means and maintenance of the engagement means in such a bias state being achieved by the permanent magnet whilst the repulsive electromagnetic device condition acting against the permanent magnet bias to release the engagement means from contact with the actuation means of the powered auxiliary system under such bias.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a schematic cross-section of a clutch mechanism; and Figure 2 is a schematic isometric view of the compressor mechanism depicted in Figure 1.

Referring to Figure 1 illustrating a schematic cross-section of a clutch mechanism in accordance with the present invention. A drive shaft 1 for an auxiliary device is coupled through a bearing arrangement 2 with a clutch plate 3. This shaft 1 provides power to an auxiliary device (not shown) The clutch plate 3 includes a plane surface 4 and angled engagement surface 5.

The plane surface 4 and engagement surface 5-are respectively hinged about

a pivot elbow 6. Associated with the engagement surface 5 is a permanent magnet 7.

The bearing arrangement 2 is located within a housing or casing 8 which also accommodates an actuator assembly.

The actuator assembly illustrated in Figure 1 comprises a pulley actuator 10 in the form of a hook about the bearing assembly 9. The actuator 10 has teeth in order to accommodate a pulley belt which powers an auxiliary system through the shaft 1. The teeth prevent lateral slippage for the pulley belt (not shown). Essentially, the actuator 10 is allowed to rotate through the bearing assembly 9 relatively freely, although in use being coupled to a tensioned pulley belt 2 said rotation is inhibited by the inertia of the auxiliary system and, when not operational, the engine thereby coupled to the actuator 10. Thus, power for the actuator 10 in the form of rotation is provided by an engine coupled to the actuator through the pulley belt 2.

In order to power the shaft 1 the engagement surface 5 must come into contact with the corresponding surface of the actuator 10. It will be appreciated by those skilled in the art, that the contact surfaces of the actuator 10 and the clutch 3 will generally be of the type which can

withstand operational wear and temperatures but have sufficient friction to achieve good power transfer therebetween In order to bring the engagement surface 5 into contact with the actuator 10, it must be rotated about the pivotal elbow 6. It will be appreciated by those skilled in the art, that pivotal rotation is preferable to displacement, but is not an essential requirement, and is the only mechanism available without a complicated radial expansion facility being incorporated into the clutch 3. In such circumstances, it is important that upon pivotal rotation about the elbow 6 that the surface 5 becomes substantially parallel and flat, ie. laminar, with the underside, ie. contact area of the actuator 10. Such parallel engagement achieves the most efficient combination for power transfer and wear control between the components. It will be understood that if the tip of the surface 5 was the only point of contact then a significantly greater force of engagement would be required and that the engagement surface 5 would differentially and rapidly wear in use.

In the present invention, a combination of the permanent magnet 7 and the electromagnetic device 11 is used to achieve necessary engagement retention and disengagement between the engagement surface 5 and the actuator 10. Essentially, the electromagnetic device 11 provides the control stimulation for such engagement and disengagement. In order to facilitate

the engagement, the electromagnetic device 11 provides an attractive magnetic force in the direction A. This attractive force A, in addition to the attraction induced into the surface 5 by the permanent magnet 7, acts to bring the surface 5 into engagement with the actuator 10. Once physical contact is made between the surface 5 and the actuator 10 then the permanent magnet 7 has sufficient strength to hold these elements in abutting engagement. Thus, the electromagnetic device 11 is no longer required to facilitate abutting engagement between the surface 5 and the actuator 10 and so can be switched off reducing electrical power consumption. Once engaged, the surface 5 and actuator 10 will be held together by the clamping effect of the permanent magnet 7. This clamping effect will be durable and may only be substantially relieved with excessive force or by appropriate stimulation for reversal by the electromagnetic device 11.

As will be appreciated, such disengagement through the electromagnetic device 11 will be achieved by passing an electrical current in an opposite direction to that used to create attractive force A in order to achieve a repulsive force B in the direction of the broken arrow head. This electrical current my be greater than or less than or equal to the value of the current used to provide the attractive force A but in the opposite direction. Thus, the clamping force created by the permanent magnet 7 is opposed by the force B and is substantially overcome in order to reverse the

attractive bias created by the permanent magnet 7. In such circumstances, the surface 5 and the actuator 10 will disengage with the result that power to the shaft 1 is no longer provided by the actuator 10, and subsequently the auxiliary system attached thereto. It will also be understood that the surface 5 may be additional biased towards disengagement by shape memory of the material etc, of the surfaces 4,5 about the pivot 6.

In order to achieve the most efficient performance for the clutch mechanism it will be appreciated that various factors must be relatively determined. First, the relative strengths of the permanent magnet 7 and electromagnetic device 11 must be accurately controlled with reference to the angle of the inclined surface 5 relative to the plane surface 4 of the clutch 3 along with the strength in terms of thickness and material type of the clutch 3. The strength of the clutch 3 will determine the necessary attractive force required of the electromagnetic device 11 in order to bring the surface 5 into engagement with the actuator 10 and the necessary strengths of the permanent magnet 7 to retain such engagement. Finally, the arc 12 subtended by the engagement surface 5 in order to achieve abutting engagement with the actuator 10 must be determined as indicated above in order to achieve the necessary flat engagement and so maximise contact surface whilst being within the appropriate deformation range for the clutch 3 without creating cyclical or stress-induced material failure, etc.

As an example, it has been found that the actuator 10 and so the

engagement surface 5 may be at an angle between 30 to 90 degrees° to the axis of the drive shaft 1 whilst an angle of 5 to 10 degrees° between the actuator 10 and the surface 5 is acceptable.

As indicated above, generally the surface 5 will pivot about elbow 6 but it is possible to provide for radial expansion in the flat area 4 of the clutch 3 and so the elements and actuator 10 could come into engagement as a result of such radial action. But, the increased complexity of such a radial expansion mechanism makes the pivotal approach illustrated more appropriate. However, it will be appreciated by those skilled in the art that if the clutch assembly had a continuous or solid surface 5 around the complete radius of the clutch 3 deformation would be difficult. Thus, typically, the contact surface 5 of the clutch 3 will be formed as fingers or petals around the radius of the clutch 3 and normally the plane section 4.

Each individual petal or finger being deformable into contact with a corresponding segment of the actuator 10. Deformation about the elbow 6 to create the arcuate movement 12 for each petal being far easier and necessitating a weaker attractive force A to achieve this deformation effect.

Alternatively, the shaft 1, bearing 2 and clutch 3 could be held in spline engagement such that a longitudinal slide movement is achieved under the control of the electromagnetic device 11 to bring the clutch mechanism into and out of engagement operation.

Figure 2 is an isometric view of the mechanism illustrated in Figure 1 where fingers or petals are provided. The solenoid 11 is presented upon a carrier plate 14 generally secured to the housing 8. The actuator 10 is located beneath the solenoid 11 and above the engagement surface 5 constituted as a finger or petal around the circumference of the clutch plate 3. The permanent magnet 7 is located below the surface 5 in each respective finger or petal.

In order to engage the clutch 3 through surfaces 5 it will be appreciated that only one solenoid 11 may be required as engagement between each petal surface 5 and the actuator 10 can be progressive as the clutch 3 is rotated. However, it will be understood that the initial engagement between the surface 5 and the actuator 10 must translate sufficient rotative force to turn the actuator 10 to bring further areas or zones of the actuator 10 into engagement with further petal engagement surfaces 5. In such circumstances, there may be a degree of slippage between the surface 5 and actuator 10 but such an effect may be advantageous to avoid"clutch shudder"inherent with abrupt clutch engagement.

Operation of a petalled clutch surface 5 configuration is similar to that described with regard to Figure 1. Thus, once all the petals of the surface 5 are in engagement with the actuator 10, the solenoid 11 can be switched off but again activated, with reverse force B for repulsion, in order to disengage

the actuator 10 from the clutch plate 3 by disengaging each petal in turn.

In such circumstances, the electric current flows in the opposite direction to that for attraction upon engagement to give a reversed magnetic field.

The dimensions of each finger or petal which constitute the surface 5 is determined by operational conditions. Thus, each petal will generally be spaced by a gap 15 from its neighbour petal and may include a keyhole 16 in order to reduce the width of the pivot elbow 6 and so the force necessary to deflect that petal. Similarly, in order to introduce more flexibility into each petal this elbow 6 may be weakened by grooving, treatment or other means.

To summarise in accordance with the present invention, the clamping force between the clutch 3 and the actuator pulley 10 generated through the engagement surface 5 is provided by the permanent magnet 7 whilst the electromagnetic device 11 produces an attractive or repulsive magnetic force in order to overcome the gap between the actuator pulley 10 and the surface 5 in a relaxed state along with any material resistance to deflection from such a state. Furthermore, by angling the engagement surface 5, actuator 10 contact surface and the electromagnetic device 11, ie. solenoid, it will be appreciated that the radial diameter of the clutch is reduced at the possible expense of an increase in lateral length for the clutch mechanism. Finally, as the present clutch mechanism does not depend upon electromagnetic force to retain clutch engagement, it will be appreciated that power is only

consumed upon engagement and disengagement but not continuously.

Thus, a more powerful electromagnetic solenoid 11 may be used for short term operation to achieve the necessary pivotal deflection of the engagement surface 5 than previously acceptable due to long term continuous operation presenting a drain upon available power.

It will be appreciated by those skilled in the art that a particular problem with regard to air conditioning in prior art embodiments is that diesel engines generally run at a lower rate of revolutions per minute (rpm) compared to petrol engines and so the use of large diameter actuator pulleys can result in the air conditioning compressor operating too slowly for efficient use. By use of inclined clutch surfaces in accordance with the present invention, the lower diameter actuator pulley 10 generally means that greater compressor speed can be generated and so improve auxiliary air conditioning performance.

It will be appreciated that generally the components of the present clutch mechanism will be made from magnetic metals. However, it will be understood that some plastics materials with appropriate loading with magnetic fillers may be used provided other mechanical properties can be maintained. Furthermore, it may be that the surface 5 of the clutch 3 is loaded with magnetic fillers or plated with a magnetic element to achieve the appropriate clamping in association with the permanent magnet 7.

The permanent magnet 7 could be incorporated into the surface 5 as an integral component rather than as illustrated as two discrete elements secured together.

The pivot elbow 6 could be a discrete robust hinge arrangement between separate members forming the surfaces 4,5. However, it will be appreciated that this would significantly increase component number and assembly complications.