This invention relates to a pulley of variable effective diameter for a transmission comprising two pulleys connected by a drive belt, the variable effective diameter providing for a change in the transmission ratio between the pulleys.

The type of pulley to which the invention relates comprises two pairs of pulley discs, namely a first pair (herein termed the outer pair) of discs axially spaced from one another and a second pair (herein termed the inner pair) of discs axially spaced from one another by a distance less than the axial spacing of the outer pair, the inner pair of discs lying between the discs of the outer pair. The spacing between the discs of the inner pair is sufficient to receive the drive belt therebetween, the belt being a flat belt. The inner discs are connected rigidly together and so are the outer discs, but the assembly of the inner discs is able to move angularly about the axis of rotation of the pulley relative to the assembly of outer discs. The discs of one of the pairs thereof are provided with a number of circumferentially spaced guideways generally of spiral form, and the discs of the other pair are provided with guideways which are so configured that as the pulley is viewed axially the guideways of the inner discs appear to intersect the guideways of the outer discs and, when the inner discs are moved angularly relative to the outer discs, the distance of the intersections from the axis of the pulley varies. Belt drive elements are disposed circumferentially about the pulley, having end portions engaged in the spiral guideways of the inner and

outer pairs of discs at the intersections thereof, the belt drive elements further comprising body portions which extend between the inner discs and upon which the drive belt is supported. Thus, by virtue of the above-described arrangement of spiral guideways, the belt drive elements are moved radially inwardly or outwardly as the inner and outer discs are moved angularly relative to one another, thereby to change the effective diameter of the pulley. Such a pulley will hereafter be referred to as a pulley of the kind specified.

In a pulley of the kind specified, the guideways in both the inner pair of pulley discs and the outer pair of pulley discs are preferably of the same spiral configuration as one another but extending in the opposite sense, clockwise or anticlockwise, circumferentially as they extend radially, in the axial view of the pulley. Transmissions incorporating such pulleys are disclosed in US patents 4,295,836 and 4,591,351; in such transmissions both pulleys are pulleys of the kind specified, and the correct tension in the belt connecting the pulleys is maintained by causing the effective diameter of one pulley to decrease as that of the other pulley is increased. However, it will be appreciated that a transmission of variable transmission ratio may be provided utilising only one pulley of the kind specified, if some other means is provided for maintaining the required tension in the drive belt.

The present invention is concerned particularly with the configuration of the pulley discs for a pulley of the kind specified, in respect of the form of the spiral guideways therein. One problem which stress analysis has predicted may arise with pulley discs of the form disclosed in the US patents aforesaid is that of

potential failure where the spiral guideways approach the outer circumference of the discs, and it is the object of the present invention to overcome or reduce this problem.

According to one aspect of the present invention, we provide a pulley disc for a pulley of the kind specified, wherein each spiral guideway has an outer end portion extending generally parallel to the outer circumference of the disc.

It has been found that providing each spiral guideway with such an outer end portion has the effect of relieving stresses which arise in the material of the discs at the outer ends of the guideways due to centrifugal force. Thereby the above described potential problem is reduced.

The invention also provides a pulley of the kind specified, wherein each of the spiral guideways in the pulley discs thereof has an outer end portion extending substantially parallel to the outer circumference of the disc wherein it is provided.

A further detail of a pulley according to the invention is concerned with the configuration of the belt drive elements thereof. In the pulleys of the transmissions disclosed in the US patents afc .:asa id, the belt drive elements have shoulders at the ends ox their body portions, adjacent their end portions, which shoulders abut the inner discs to prevent the belt drive elements from moving in the direction parallel to the axis of rotation of the pulley. It has been found that such shoulders act as stress raisers in the belt drive elements, and failures have occurred there.

In the pulley according to the present invention, the end portions of the belt drive elements may terminate in abutment sur aces which engage abutment means provided axially beyond the guideways of the outer discs, to prevent movement of the belt drive element axially relative to the pulley discs.

By arranging the belt drive elements with their abutment surfaces at the free ends of their end portions to engage the abutment means, there is no necessity for the above referred to shoulders at the transition between the central body portions and end portions of the belt drive elements. Therefore the above described problem is eliminated.

In the embodiment described hereafter, the abutment means comprises plates disposed beyond the outer pulley discs. Such plates form part of the means by which torque is transmitted to the pulley and by which relative angular movement between the inner and outer discs is effected. The guideways in both the inner and outer discs comprise slots which extend axially right through the discs. However, it would be within the scope of the invention if the guideways in the outer discs did not extend right through such discs but instead took the form of grooves whose bases constituted the abutment means engaged by the abutment surfaces of the belt drive elements.

The invention will now be described by way of example with reference to the accompanying drawings, of which:-

Figure 1 is a plan view of a transmission of the kind specified, partly sectioned along the axis of one of the pulleys thereof;

Figure 2 is a section on the line Y-Y of Figure 1;

Figure 3 is an axial view of one of the pulley discs of the transmission;

Figure 4 is an elevation of a belt drive element of the transmission;

Figure 5 is an enlarged view of part of Figure 1.

The illustrated transmission comprises a casing with an end plate 10 and a cover 11 secured to the end plate by bolts 12. Within the casing is supported a first shaft 13 which is intended to be the input shaft of the transmission, having an end part 14 adapted for connection to a driving member, e.g. a clutch arrangement providing a releasable driving connection in a motor vehicle. The shaft 13 is supported in bearings 15, 16 which are carried in a bearing holder member 17 secured to the end plate 10, and a cap 18 secured to the housing cover 11 at the opposite end of the shaft 13, respectively. The transmission comprises two pulleys which are of variable effective diameter, drivingly connected by a drive belt entrained around the pulleys.

One of the pulleys will hereafter be described in detail, and the other pulley and its associated parts are shown in outline only within the non-sectioned part of Figure 1. The other pulley would be associated with an output shaft, not shown.

The pulley of the transmission which is sectioned comprises an outer pair of discs 20, 21 spaced from one another along the shaft 13. The discs 20, 21 are rotationally fast on a sleeve 22 which is movable angularly around the shaft 13. The pulley further

comprises a pair of inner discs 23, 24 whose axial spacing is less than that of the outer discs 20, 21, the discs 23, 24 being received between the discs 20, 21. The discs 23, 24 are rotationally fast with a sleeve 25 which is movable angularly on the outside of the sleeve 22.

The general form of each of the discs 20, 21, 23, 24 is as shown in Figure 3. It is of annular form, with a central aperture 26 dimensioned to receive the appropriate sleeve 22 or 25. Radially inwardly extending tongues 27 are engagable with appropriate slots in the sleeve 22 or 25 so that the disc is rotationally fast with the sleeve. At its outer circumference, the outer disc 21 and the inner disc 23 have radially outwardly extending tongues 28 for the purpose described hereafter, but the other outer disc 20 and the other inner disc 24 are not provided with such tongues. The disc further comprises a number of circumferentially spaced guideways in the form of slots 29 which are of generally spiral, logarithmic or exponential, form, extending from positions adjacent the aperture 26 to positions adjacent the outer circumference of the disc. Each slot 29 terminates at its outermost end in a circumferentially extending portion 30. As viewed along the axis of the shaft 13, the slots in the outer discs 20, 21 extend in one helical sense, clockwise or anti-clockwise, and are in alignment with one another. The slots in the inner discs 23, 24 are also in alignment with one another but extend in the opposite helical sense, so that as viewed axially the slots appear to intersect one another and provide square, axially extending, through-apertures at their points of intersection. It will further be appreciated that as the outer discs together move angularly about the axis of the shaft 13 relative to the

inner discs, the through-apertures provided by the intersections of the slots in the discs move radially inwardly or outwardly.

The pulley further comprises a number of circumferentially spaced belt drive elements 31 of which two are visible in Figure 1 and one is shown in greater detail in Figure 4. Each belt drive element comprises a central portion 32 which bridges between the inner discs 23, 24 and end portions 33 which are of square cross-section and are received in the axially extending through-apertures provided by the intersections of the slots in the inner and outer discs as they are viewed axially. Thus, as the above described relative angular movement between the pairs of discs is carried out, the belt drive elements are moved radially inwardly or outwardly to change the effective diameter of the pulley. The central portion 32 of each belt drive element has a recess 34 to accommodate a flat drive belt 35.

There will now be described the means by which the discs comprising the pulley are connected to the shaft 13, and by which the above described variation in the effective diameter of the pulley is carried out.

A drive plate 36 of annular form is spl_ ,o the shaft 13, the drive plate 36 being provided at - _.- outermost circumference with an axially extending flange 37 which extends axially to engage with the outer tongues 28 on the inner disc 23. At the opposite end of the pulley, there is a further plate 38 which forms the cover of a hydraulic actuator to be described hereafter. The plate 38 has an axially extending flange 39 which engages the outwardly extending tongues 28 provided at the outerside circumference of the outer disc 21. The plates

36, 38 are abutted by axially presented end faces of the end portions 33 of the belt drive elements, so that the belt drive elements are held in the correct position in engagement with the discs 20, 21, 23, 24.

The hydraulic actuator will now be described with reference to Figure 2 in addition to Figure 1. It comprises a body 40 to which the cover plate 38 is secured by bolts 41, defining a generally annular space surrounding the shaft 13. A vane assembly most clearly seen in Figure 2 is disposed within the body 40, comprising a central annular part 43 with a central bore which has splined engagement on the shaft 13 so as to be rotationally fast thereon, and two outwardly extending vanes 44 which reach to the internal circumference of the body 40 to seal therewith and divide the space within the body into two halves. Connected to the body and cover plate 38 of the actuator, by bolts 42, are two diametrically opposed abutments 45 which seal two respective part-cylindrical outer surface parts of the annular part 43 of the vane assembly. The arrangement of the actuator is such that, whilst the vane assembly remains angularly fixed on the shaft 13, the body 40, cover plate 38 and abutments 45 can move angularly thereabout between limits determined by engagement of the abutments 45 with the vanes 44. In Figure 2, one limiting position of such angular movement is depicted.

The above described angular movement in the actuator is caused to take place by admitting or releasing oil to the variable-volume spaces defined between the abutments 45 and vanes 44. This is effected through passageways in the shaft 13. There is a central passageway 47 leading into a cross-drilling 48 communicating with the respective one sides of the vanes 44, and two other

passageways 49 which are parallel to the central passageway 47 but radially spaced therefrom, and lead into radial bores 50 communicating with the respective other sides of the vanes 44.

The central passageway 47 extends to the end of the shaft 13, communicating with a space leading to a passage 51 in the cap 18, for connection at 52 to a hydraulic line. The passageways 49 are plugged at the end of the shaft and communicate via radial bores with an annular groove 53 adjacent the end of the shaft 13. This annular groove 53 communicates with a further passage 54 in the cap 18, for connection at 55 to a hydraulic line. Piston ring seals 56, 57 provide for sealing between the shaft 13 and the cap 18, and prevent communication between the central passageway 47 and the passageways connected thereto, and the passageways 49 and the other passages with which it communicates. Other seals, in conventional arrangements not described in detail, retain lubricant in the bearings of the transmission, and prevent access of lubricant and hydraulic fluid to the drive belt.

Figure 5 shows on an enlarged scale and in greater detail the arrangement of the passages 51, 54 in the cap 18, the annular groove 53 provided in the shaft 18, and the piston ring seals 56, 57 associated therewith. Figure 5 does not, however, show the passageways 47, 49 in the shaft 13. Each of the piston ring seals 56, 57 comprises, as is generally known, a resilient metallic ring which fits in an annular groove provided around the shaft 13 and engages an internal cylindrical surface provided in the cap 18. The ring has a radial gap therein to enable it to be expanded to fit over the shaft 13 until it can enter its groove. The resilience of the ring causes it to engage the internal surface of the cap

18 with a predetermined pressure so that leakage of fluid is resisted.

In use, appropriate supply and release of fluid from the respective variable volume spaces provided in the hydraulic actuator will effect relative angular movement between the body of the actuator and the vane assembly thereof to a required angular position. Because the vane assembly of the actuator is angularly fixed on the shaft 13 as are the inner pulley discs 23, 24, whilst the actuator body and cover plate assembly are together angularly fixed to the outer pulley discs 20, 21, the movement in the actuator will effect relative angular movement between the inner and outer pulley discs. Thus, the belt drive elements will be moved radially inwardly or outwardly, to change the effective pulley diameter.

It will be appreciated that the other pulley shown in outline only in the casing of the transmission similarly has a variable effective diameter, and an associated actuator for pulley adjustment. A control system would be provided to co-ordinate the adjustment of the effective diameter of the two pulleys so that the belt remains correctly tensioned therebetween.

In the above described embodiment, the hydraulic actuator effects the relative angular movement between the inner and outer pulley discs, to change the effective pulley diameter. It will be appreciated that the invention is also applicable to pulleys wherein other means are used to change the effective diameter thereof.