GB2033031A

GB2033031A - Improvements in vee pulleys

Info

Publication number: GB2033031A
Application number: GB7842736A
Authority: GB
Original assignee: Delta Materials Research Ltd
Current assignee: Delta Materials Research Ltd
Priority date: 1978-11-01
Filing date: 1978-11-01
Publication date: 1980-05-14
Also published as: GB2033031B

Abstract

A vee pulley comprises two members on a rotatable shaft 1 and each provides one inclined face of the vee groove of the pulley. One member 3 is fixed to the shaft and the other 11 is slidable along the shaft to vary the separation of the inclined faces. The position of the movable member relative to the other member is determined by an SME element 17, i.e. of a material whose elastic modulus varies significantly and reversibly with temperature over a transition temperature range. The element 17 may be in the form of a coil spring opposed by a spring 19 and formed of a heat treated alloy of composition Cu 70%, Al 4%, Zn 26%. <IMAGE>

Description

SPECIFICATION Improvements in vee pulleys This invention relates to vee pulleys and in particular to vee pulleys having thermallyresponsive means by which the effective diameter of the pulley can be altered.

A conventional vee pulley has two members each of which defines an inclined face, the faces being opposed so that together they define the vee groove. In use, a belt of substantially vee cross-section is wrapped around part of the pulley so that the belt engages with the inclined faces of the vee groove and the distance from the axis of the pulley to the contacting areas of the belt with the pulley determines the effective diameter of the pulley. In a conventional pulley the two members are fixed relative to each other so that, for a given belt, the effective diameter of the pulley is constant.

It is an object of the present invention to provide a vee pulley the effective diameter of which is adjustable.

According to the present invention, a vee pulley comprises a shaft, a first member secured to the shaft and providing one inclined face of the vee groove of the pulley, a second member providing the other inclined face of then vee groove of the pulley and being slidable along the shaft to vary the separation of said inclined faces, the position of the second member on the shaft relative to the first member being determined by an SME element (as herein defined) interposed between a stop and the second member and means biasing the second member towards the element, the element being such that, in the transition range of temperature, the force applied to the second member by the element overcomes that provided by the biasing means causing the second member to slide relative to the first member to vary the separation of said inclined faces.

By a "shape memory effect element" (SME) as used herein is meant an element of a material, usually an alloy, having an elastic modulus which varies significantly with temperature in a reversible manner over a transition temperature range dependent on the material employed. There are a number of known alloys which display shape memory effect when subject to a pre-conditioning heat treatment. A suitable alloy is one having a composition by weight of the order of copper 70%, aluminium 4% and zinc 26%. Above and below the transition temperature range, change of temperature have no appreciable effect on the thermal properties of the material. In the transition range however, increase in temperature results in progressive increase in the elastic modulus, and hence in decrease in the strain of the stress element.

In the vee pulley of the present invention, the two members are positioned such that a vee belt wrapped around the pulley takes up a position in the groove at a particular effective distance from the centre of the shaft. When the temperature is in the transition range of the SME element, the second member is slid along the shaft against the action of the biasing means to a position which allows the belt to take up a different position in the vee of the pulley, thereby changing the effective diameter of the pulley.

In one embldiment of the invention, the second member is caused to move towards the first member, thereby reducing the width of the vee groove and a belt positioned in the groove moves outwardly from the centre of the shaft, thereby increasing the effective diameter of the pulley. In an alternative embodiment however, the second member can be caused to move away from the first member when the temperature is in the transition range so that a vee belt positioned in the groove moves radially towards the centre of the shaft, thus reducing the effective diameter of the pulley.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawing, in which: Figure 1 is a sectional side elevation of part of a pulley in accordance with one embodiment of the invention, Figure 2 shows diagrammatically the effect on a transmission system of the use of a pulley in accordance with the present invention, and conventional pulley, and Figure 3 is a sectional side elevation of part of a pulley in accordance with an alternative embodiment of the invention.

Referring to Fig. 1, a vee pulley comprises rotatable shaft 1 having a first member 3 firmly attached to it by means of a key 5. The member 3 provides an inclined face 7 which defines one face of the vee groove 9 of the pulley. A second member 11 is mounted on the shaft so as to be slidable along the shaft towards and away from the member 3. This second member also provides an inclined face 1 3 which provides one of the inclined faces of the vee groove 9. A stop member 1 5 is mounted on the shaft and an SME element in the form of a coil spring 1 7 is positioned between the stop 1 5 and the second member 11.A biasing spring 1 9 is positioned around the shaft and acts between the fixed member 3 and the second movable member 11 and it serves to bias the second member towards the element 1 7. The member 11 has a plurality of fingers 21 which project through openings 23 formed in the member 3. A vee belt 25 is shown in the vee groove 9 and the dimensions of the belt are such that it takes up a position towards the bottom of the vee groove. In use, the belt 25 is driven by means not shown and it causes the pulley and shaft to rotate about the longitudinal axis of the shaft. The effective diameter of the pulley is relatively small, since the belt 25 takes up its position towards the bottom of the vee groove.

The element 1 7 is made from a heat treated alloy which exhibits a variable elastic modulus over a transition temperature range which is determined by the alloy composition. In the transition range, increase in temperature results in progressive increase in the elastic modulus of the material and hence in decrease in the strain of the element. In this temperature range therefore the force applied to the second member 11 by the SME element is such as to overcome the biasing force of the spring 9 and the member 11 moves towards the fixed member 3. This causes the vee belt 25 to move outwardly along the groove to take up the position shown by broken lines in Fig. 1. The effective diameter of the pulley is thus increased.The action of the SME element is reversible: on fall of temperature from the transition range, the biasing means 1 9 overcomes the force applied by the element 1 7 and the member 11 is forced away from the member 3 allowing the belt to take up its original position towards the bottom of the vee. To enable the vee belt to take up these different positions in the groove, some form of tensioner is required to act on the belt.

Referring to Fig. 2, the pulley 25 is a variable diameter pulley, as shown in Fig. 1 the pulley 27 is a conventional fixed diameter pulley and a spring biased jockey pulley 29 is used to keep the tension in the vee belt 31 constant. In Fig. 2, the vee belt 31 is shown in full lines for the initial position of the belt towards the bottom of the vee groove 9 in pulley 25 and, during the transition range temperatures, the vee belt takes the position shown in broken lines towards the outer end of the groove 9 and the jockey pulley 29 keeps the tension in the belt substantially constant. It can be seen therefore from Fig. 2 that the transmission ratio between the pulleys 25 and 27 varies dependent upon the position of the belt in the groove 9 of pulley 25.

Referring now to Fig. 3, a shaft 41 carries a fixed member 43 and movable member 51.

Fingers 61 on the movable member project through openings in the fixed member and the SME element 57 acts between a stop 55 and the fingers 61. A biasing spring 59 acts between a stop on the shaft and the slidable member 51.

Below the transition temperature of the SME element, the biasing spring 59 forces the slidable member 51 towards the fixed member 43 so that the vee belt 65 takes up a position towards the outer end of the vee groove 49. During the transition temperature range, the element 57 overcomes the forces on the member 51 due to the biasing spring 59 and forces the member 51 away from the member 43, thereby increasing the width of the vee groove. This allows the belt 65 to move down the groove 49 to take up the position shown in broken lines.

A fan may be rotatably mounted on the shaft of the pulley so that the fan is not normally rotated during rotation of the pulley.

However, during the transition temperature of the SME element, the second member of the pulley is displaced along the shaft into engagement with the fan so that the rotation of the second member is transmitted to the fan causing the fan to rotate with the pulley. In this way the second member and the fan act as a clutch so that the movement of the second member into engagement with the fan causes it to rotate with the pulley. An application of such a pulley and fan combination is in heat exchangers for refrigerating equipment employing fans in which the fans are caused to rotate with an increase in temperature.

In an alternative arrangement, the fan could be mounted on the pulley 27 shown in Fig. 2, the arrangement being such that, when the pulley 25 changes it effective diameter, the fan on pulley 27 rotates at a faster speed.

Furthermore, if the pulley 27 is of the form of the pulley shown in Fig. 1 or Fig. 3, but with the spring 17, 57 being of steel rather than SME material, the tension in the belt would be self-correcting by varying the effective diameter of the pulley 27 and there is no need for a jockey pulley.

The SME element may be in the form of a coil spring as shown in Figs. 1 and 3 but alternatively it may be a diaphragm or disc spring.

Claims

1. A vee pulley comprising a rotatable shaft and two members on the shaft, each member providing one inclined face of the vee groove of the pulley, one of said members is fixed to the shaft and the other is slidable along the shaft to vary the separation of the inclined faces, and the position of the movable member on the shaft relative to the other member is determined by an SME element (as herein defined).

2. A vee pulley comprising a rotatable shaft, a first member secured to the shaft and providing one inclined face of the vee groove of the pulley, a second member drivable with the shaft and providing the other inclined face of the vee groove of the pulley, said second member being slidable along the shaft to vary the separation of said inclined faces, the position of the second member on the shaft relative to the first member being determined by an SME element (as herein defined) interposed between a stop and the second member, the element being such that, in the transition range of temperature, a force applied to the second member by the element is such as to cause the second member to slide relative to the first member to vary the separation of said inclined faces.

3. A vee pulley as claimed in claim 2, in which in the transition range of temperature the second member is caused to move towards the first member to thereby reduce the separation of said inclined faces.

4. A vee pulley as claimed in claim 2, in which in the transition range of temperature the second member is caused to move away from the first member to thereby increase the separation of said inclined faces.

5. A vee pulley as claimed in claim 3 or 4, in which means are provided for biasing the second member towards said element and in the transition range of temperature the force applied to the second member by the element overcomes the bias on the second member.

6. A vee pulley as claimed in claim 3 in which the second member comprises a first part slidably mounted on the shaft and a second part projecting outwardly of the first part and providing said inclined face, and said element acts between the second member and said stop which is positioned on the shaft on the side of the second member which is away from the first member.

7. A vee pulley as claimed in claim 6 in which the SME element is in the form of a coil spring.

8. A vee pulley as claimed in claim 4 in which the second member comprises a first part slidably mounted on the shaft and a second part projecting outwardly of the first part and providing said inclined face, and said element acts between said stop which is positioned on the shaft on the side of the first member which is away from the second member and a portion of the second member which projects through the first member to a position on the side of the first member which is away from the second member.

9. A vee pulley as claimed in claim 8 in which the SME element is in the form of a coil spring.

10. A vee pulley as claimed in any preceding claim including a fan freely rotatably mounted on the shaft, the second member of the pulley -being displaced into driving relation with the fan in the transition range of temperature.

11. A vee pulley substantially as hereinbefore described with reference to the accompanying drawings.