GB2264153A

GB2264153A - Continuously variable transmission

Info

Publication number: GB2264153A
Application number: GB9306346A
Authority: GB
Inventors: John Pierce Martin Parry
Original assignee: JPM Parry and Associates Ltd
Current assignee: JPM Parry and Associates Ltd
Priority date: 1989-04-04
Filing date: 1993-03-26
Publication date: 1993-08-18
Anticipated expiration: 2013-03-26
Also published as: GB9306346D0; GB8907553D0; GB2264153B

Abstract

The transmission comprises an input shaft 51 and an output shaft 52 providing axially extending, mutually adjacent frusto-conical drive members 52, 54 with the narrow end of each drive member adjacent to the broad end of the other. Disposed between the drive members is a transmission element, eg a rubber ball 55, which in operation is drawn into the nip to transmit torque from the input shaft 51 to the output shaft 52. Actuation mechanism is provided to move the transmission element longitudinally to vary the gear ratio. Optionally a third frusto-conical drive member is provided, torque being transmitted from the third drive member to the input shaft similarly by a transmission element afforded by a rubber ball. In this manner in an acceleration mode torque is transmitted from the drive member 53 to the drive member 54, and in a decelerating mode torque is transmitted from the drive member 82 to the drive member 53. <IMAGE>

Description

Title: "Continuously variable transmission" Description of Invention This invention relates to a continuously variable drive transmission suitable for continuously varying the gearing ratio between input and output shafts of a machine or apparatus such as a motor vehicle, particularly but not exclusively a transport vehicle described in the specification of our copending application No. 9120946.0 (Serial No. 2248046).

Continuously variable transmission arrangements are known which comprise input and output shafts each bearing a frusto-conical drive member, which may be rectilinear or curvi-linear, the drive members lying mutually adjacent and tapering in opposite directions to one another. The frusto-conical members are frictionally engaged by a transmission element afforded by a belt which is movable longitudinally of them to effect a change in the gearing ratio between the two shafts. The torque transmitted between the input and output shafts depends upon the degree of constant pressure between the driving belt and each of the frusto-conical members and the coefficient of friction of the surfaces of the frusto-conical members and the drive belt. A certain degree of slippage of the belt invariably occurs leading to loss of efficiency.This is partly because the belt has to constantly change shape as it moves relative to the frusto-conical members because of the difference in the shapes of the surfaces of the frusto-conical at each point along their length. A problem therefore arises in providing a belt of high flexibility and strength so as to meet the criterion of good frictional contact between the belt and the frusto-conical members.

The present invention provides a continuously variable drive transmission including a transmission element which overcomes or reduces some of the disadvantages described above.

According to the invention there is provided a continuously variable drive transmission comprising two drive members each drive member providing a generally conical transmission surface, the end of narrower diameter of one transmission surface lying adjacent the end of larger diameter of the other transmission surface, and a transmission element adapted to drivingly inter-engage the two drive members, transmission of drive between the drive members being afforded by a surface having a high coefficient of friction.

Preferably the surface comprises rubber or plastic, and conveniently it is the transmission element which comprises a material having a high coefficient of friction. Most conveniently the transmission element is in the form of a rubber ball.

Actuating means may be provided to permit moving the transmission element longitudinally relative to the drive members so as to vary the gearing ratio between the two shafts. The actuating means may manually operable means, or may be automatically operable.

The actuating means may be operatively connected to a support which supports the transmission element such that actuation of the actuating means brings about movement of the support and hence of the transmission element longitudinally of each of the drive members, free movement of the transmission element longitudinally of said drive members being prevented by the support.

Preferably the support comprises an inverted "U" shaped frame, depending arms of which provide idlers which engage the surface of the transmission element and a cross member extending between the arms which provides a further idler, the idlers permitting rotation of the transmission element about any axis passing through a centre thereof.

The arms of the frame may include respective aligned apertures through which extends a guide rail for the support, the support being movable longitudinally of the guide rail.

The apertures may be elongate such that the support may be raised and lowered relative to the guide rail to disengage the transmission element from the drive members and to re-engage the transmission element therewith.

The support may provide further member which provides an idler such that the transmission element is held captive by the support when raised so as to be disengaged from the drive members.

The two drive members may comprise a first drive member which is connected to a source of motive power, and a second drive member which is connected to an output system, such as the drive wheels of a vehicle.

Under normal operation, the first drive member will thus provide a driving means, and the second drive member will provide a driven means.

Preferably however the construction and operation is such that the transmission means may be operated to return power from the second drive member to the first drive member, in the event that the ratio selected is one in relation to which the speed of the output system is greater than the speed of the power source, as seen by the transmission mechanism.

The continuously variable drive transmission according to the invention may further include a third frusto-conical drive member and a second transmission element operable between the third drive member and one of the other drive members, e.g. the drive member provided on the input shaft.

The third rotatable shaft may provide a frusto-conical drive member which tapers in the opposite direction to the drive member provided on the input shaft (i.e. that connected to the power source), and coupling means may be provided to couple the output shaft and the third rotatable shaft.

The second transmission element may comprise a sphere which is supported in a support in like manner to the aforementioned transmission element, and may be movable by a further actuating means which permits of disengagement of the second transmission element from the drive members provided on the input shaft, and the third rotatable shaft.

The second transmission element may be movable longitudinally of the input shaft and the third rotatable shaft, and may be engageable with the drive members provided by the input shaft and the third rotatable shaft when the transmission element is engaged between the drive members provided by the input and the output shafts.

Further coupling means may be provided to couple together the actuating means and the further actuating means such that operation of the actuating means causes operation of the further actuating means.

The further coupling means is preferably a mechanical coupling and operation of the actuating means to move the driving element relative to the input and output shafts brings about a corresponding movement of the second driving element relative to the input and output shafts.

There will now be given detailed description, to be read with reference to the accompanying drawings, of a continuously variable transmission mechanism which is a preferred embodiment of this invention.

In the accompanying drawings: FIGURE 1 is a schematic elevational view of the vehicle comprising the transmission mechanism which is the preferred embodiment of the invention; FIGURE 2a is a schematic view of the vehicle drive train: FIGURE 2b, 2c and 2d are are graphs illustrating power transfer during the use of the vehicle; FIGURE 3 is a schematic view of part of a continuously variable transmission system of the invention; FIGURES 4 and 5 are views of alternative forms of the transmission system: FIGURE 6 is a schematic view illustrating a means for controlling the position of drive transmission means of the system; FIGURE 7 is a schematic view of an alternative continuously variable transmission system; FIGURE 8 is a view of a trackway system utilising the invention:: FIGURES 9 and 10 are schematic views illustrating the transfer of torque between the various drive elements of Figure 7; FIGURE 11 is an underneath plan view of an actuating mechanism of the preferred embodiment; FIGURE 12 is an end elevation of the actuating mechanism; and FIGURE 13 is a plan view of the actuating mechanism.

The vehicle shown in Figure 1 of the drawings is conveniently in the form of a tram, comprising wheels running on a trackway T. The vehicle comprises a vehicle body 4 supporting wheels, including drive wheels D.

Mounted in the body 4 is a power source mechanism 5 including a fly-wheel 6 designed to provide up to 50 MJ (Mega Joules) of energy when rotating at 6000 rpm, the fly-wheel rotating in a low-pressure housing 8, and incorporating safety features which ensure containment and safe energy release in the event of bearing failure, loss of vacuum, or other malfuction.

Advantageously the fly-wheel is rotatable with drive shaft 7 in bearings 10, 12 about a vertical axis A, and may be mounted on gimbels to accomodate relative tilting movement between the vehicle body and axis of rotation.

The shaft 7 is connected by a drive element 15 to a continuouslyvariable transmission mechanism 14, hereinafter abreviated for "CVT", illustrative of this invention and which is adapted in a driving mode to cause output shaft 16 to rotate, said output shaft 16 being connected, optionally through a clutch, to the driving wheels D of the vehicle.

The continuously-variable transmission mechanism is also operative, in a braking mode, to apply torque transmitted from the driving wheels D by way of the output shaft 16, to the drive shaft 7 of the fly-wheel 6.

On braking of the vehicle, e.g. reducing speed to zero, the energy of momentum of the vehicle may thus be returned to the fly-wheel.

As is shown schematically in Figure 2a, the transmission train of the vehicle comprises fly-wheel, CVT, optionally a clutch, and the vehicle drive wheels. In this manner, energy is imparted progressively from the fly-wheel to the vehicle drive wheels on acceleration of the vehicle and maintenance by the vehicle of a constant speed, and is returned to the fly-wheel from the vehicle directly through the CVT, in the event of decerlation of the vehicle.

Desirably the vehicle drive train comprises a DC motor which is connected to the fly-wheel drive shaft, enabling the fly-wheel to be energised conveniently by the application of an electric power supply to a pick-up 22 of the vehicle, on return of the vehicle to a terminus, or at one or more way stations provided along the vehicle route.

In addition if desired, the vehicle may carry one or more batteries for an emergency application of power to the fly-wheel, in the event that this becomes run down whilst the vehicle is some distance from a convenient supply fo electricity.

Alternatively of course, the fly-wheel may be re-powered at the vehicle terminus by mechanical means applied directly to the drive shaft 7, if desired.

Figure 2b illustates acceleration of the vehicle from a stop condition to a speed of 40 kph, and returning to a stop condition, whilst Figure 2e illustates the transfer of energy from the fly-wheel to the vehicle, and return to the fly-wheel on the vehicle being brought to a halt. From this it will be seen that approximately 10 kW are utilised in maintaining the vehicle at its cruising speed.

As will be seen from Figure 2d, initially 1MJ of fly-wheel energy is utilised in accelerating the vehicle from rest, and thereafter approximately 1MJ is utilised in maintaining the vehicle at it cruising speed. On deceleration to rest, approximately 1MJ is returned to the fly-wheel.

It has been found that the vehicle, when fully charged, will be able to cover a route of up to 30 km with up to 30 stops before a further charge is required. This is normally sufficient in urban areas to permit the vehicle to return to a terminus L for recharging (Figure 2c), although if necessary recharging stations may be provided on the route.

The continuously variable drive transmission comprises an input shaft 51 and a output shaft 52 providing respective axially extending, mutually adjacent frusto-conical drive members 53, 54. The drive members 53, 54 are fixed rigidly to their respective shafts and are positioned relative to one another so that the narrow end of the drive member 53 on the input shaft 51 lies adjacent the broad end of the drive member 44 on the output shaft 52.

Whilst the input shaft 3 and output shaft 52 shown in the drive transmission arrangement of Figure 1 lie parallel to one another, in an alternative arrangement, such as is shown in Figure 4 the input and output shafts run at an angle to one another. Moreover, whilst in the arrangement shown in Figure 3 the transmission members are each of the same angle of taper, in an alternative arrangement, such as is shown in Figure 4, the drive members may each have a different angle of taper. Still further, whilst the drive members 53, 54 shown in the arrangement in Figure 3 each have the same diameters at their respective narrow and broad ends, in an alternative arrangement, the broad and the narrow ends of one of the drive members may be broader than the respective ends of the other drive member whilst both drive members still retain the same angle of taper.

Further, whilst the arrangement shown in Figures 3 and 4 are those of drive members in the form of rectilinear frusto-cones, it will be appreciated that curvi-linear frusto-cones may be utilised, as is shown in Figure 5, which may be desirable in the event that a non-linear gear ratio is desired.

In Figure 3 a sphere 55 is shown disposed between the drive members 53 and 54 and the sphere 55 constitutes a transmission element which drivingly inter-engages the two shafts 51, 52 so as to transmit drive from the input shaft 51 to the output shaft 52.

As the output shaft 51 turns, the conical member 53 also turns and by frictional engagement with the sphere 55 the sphere is made to rotate in an opposite direction to the direction of rotation of the input shaft 51. By frictional engagement of the sphere 55 with the curved surface of the drive member 44 on the output shaft 52 the drive member 54 and the output shaft 52 are caused to rotate in the same direction as the input shaft 51.

For the purposes of efficient transmission between the input shaft 1 and output shaft 52 the sphere is made of rubber or some other such material which has a high coefficient of friction. Alternatively or additionally the curved surface of the drive members 53, 54 comprises rubber also or some other suitable material having a high coefficient of friction.

As the input shaft 51 is turned the sphere 55 is drawn into the nip between the drive members 53, 54 but its diameter is too large to permit its be drawn completely through the nip between the drive members.

Desirably the sphere 55 is supported by a support 56 (see Figure 6) which limits movement of the sphere 55 in a direction parallel to the adjacent curved surfaces of the drive members 53, 54. The support 56 comprises an invert "U" shaped frame depending arms 57, 58 of which provide aligned idlers 59 such as ball bearings which may be captive in the depending arms 57, 58 of the frame but which can rotate in all directions. The depending arms 57, 58 also provide a cross bar 60 which extends between them, the cross bar 60 also providing an idler 61.

Because the sphere 55 is supported in the frame of the support 56 in this way it is free to rotate about any axis passing through its centre.

Because this is so, when it is desired to move the sphere relative to the longitudinal axes of the input and output shafts 51, 52 such movement is made easy.

The depending arms 57, 58 also provide aligned apertures 62, 63 through which passes a guide rail 64 which serves to guide the support and to permit of movement of the support longitudinally of the guide rail. The support 66 provides a handle 55 which may be operated by a user of the drive transmission to move the ball relative to the input and output shafts 51, 52 so as to effect a change in the gearing ratio, the output being lowest from when the ball is positioned adjacent the broad end of the drive member 54 on the output shaft 52 and adjacent the narrow end of drive member 53 on the input shaft 51.

It will be understood that the sphere 55 may be supported in the frame of the support 6 by alternative means to that shown in Figure 6 and that disengagement of the sphere 55 could be achieved using the support 56 and guide rail 64 shown in Figure 6 provided that the guide rail 64 itself may be moved perpendicularly to the longitudinal direction of the guide rail.

It can be seen from the arrangement described and shown in Figures 4 and 6 that, by actuation of the handle 65, gear changes can be effected and, moreover, by lifting the handle 65 a suitable clutch mechanism is obtained for disengaging the drive sphere 55 from the transmission arrangement.

Preferably however the drive transmission mechanism comprises a third rotatable shaft 80 (shown schematically in Figure 7) and drive from output shaft 52 is transmitted via a suitable coupling to the third rotatable shaft 80 which is provided with a frusto-conical drive member 82 which tapers in the opposite direction to the drive member on the input shaft 51.

The output from the third rotatable shaft 80 may then be used, for example, to drive the input shaft 51 thus effecting some conservation of energy by engaging a further transmission element 81 between the drive members 53 and 82. The transmission element 81 is spherical and is similar to the transmission element 55.

The operation of the CVT, will now be described with reference to Figures 9 and 10. As has been mentioned, the drive member 53 is connected to the drive shaft 7 of the fly-wheel means, whilst the drive members 54 and 82 are connected via an output shaft to the vehicle driving wheels D.

When the vehicle is cruising at a steady state, there will be frictional retardation of the vehicle, and the drive members 54 and 82 will lag, rotationally speaking, somewhat behind the drive member 53. Thus the surface velocity A/B will be slightly greater than the surface velocity C1/B, resulting in the transmission element 55 being drawing into the nip between the drive members 53 and 54, in consequence providing a positive transmission of energy from the fly-wheel to the vehicle driving wheels.

Conversely, the surface velocity A/D will be greater than the surface velocity D/C2, resulting in a tendency for the spherical transmission element 81 to be lifted from the nip between the drive members 53 and 82. Thus in general, where the position of the control means of the CVT results in a gear ratio of which the drive member connected to the fly-wheel is rotating at a greater rate than the drive member connected to the driving wheels, torque will be transmitted to the transmission member 54 by the transmission element 55.

Conversely, in the event that the drive member 53 is rotating at a speed lower than the drive member 54, 82 (as far as the transmission elements 55 and 81 are concerned), the transmission element 81 will be drawn into the nip between the drive members 82 and 53, whilst the transmission element 55 will be lifted from the nip between the drive members 53 and 54.

Thus simply by adjusting the position of the control mechanism in the directional longitudinally of the drive members, the CVT may be moved between a condition in which power is applied from the fly-wheel to the driving wheels of the vehicle, or applied from the driving wheels to the flywheel. In both cases, the distance of the transmission elements from a medium centreline (corresponding to equal velocity positions) will determine the rate at which power is so applied, and hence the rate of acceleration or deceleration of the vehicle.

The continuously variable transmission mechanism which is the preferred embodiment of this invention comprises actuating mechanism shown in Figures 11 to 13, by which gear change may be effected smoothly, reversibly, and automatically. The actuating mechanism comprises a crosshead 70 mounted on a worm 72 extending beneath, and generally parallel to, the axis of the drive member 53. By rotation of the worm 72, the cross-head 70 may be driven lengthwise of the drive member 53 in either direction.

Mounted on the cross-head, for movement in the widthwise direction, are twin carriages 74, being guided for widthwise movement by wheels 76.

Mounted on each carriage 74 is a pivoted bracket 75 which carries, spaced in the longitudinal direction, twin guide cones 76, the guide cones being rotatable on the bracket 75 by an eccentric pivot axis 77.

The two transmission members (rubber balls 55 and 81) are mounted each between a pair of guide cones 76, and as the balls rotate in the transmission of torque from one drive member to the other, they rotate the guide cones about their eccentric axis 77, causing a backwards and forwards rocking movement of the bracket 75 about the axis 73. Such reciprocating movement produces unbalanced forces against the transmitting element, preventing the transmitting element from adopting a "set" which may result in undue wear being produced along a circumferential line of the ball.

It will be appreciated that by rotation of the worm 72 the cross-head 70 may be moved longitudinally (i.e. in the axial direction) of the transmission mechanism, to vary the gear ratio between the input and output shafts, widthwise movement of the balls 55 and 81 being accommodated by movement of the carriages 74 on the cross-head 70.

If desired the carriages 74 may be guided on tie rods 78, said tie rods being spaced equidistantly from each adjacent pair of axes, i.e. dividing the space between the two adjacent conical surfaces.

As has been stated, on movement of the actuating mechanism longitudinally of the transmission mechanism, first one torque transmitting ball, and then the other, will be called into play, the ball which is not transmitting torque being lifted slightly from between the nip of the two adjacent cones, being retained against falling out of position by the guide cones 76.

Of course if desired a cage system somewhat similar to that illustrated in Figure 6 may be utilised, physically to prevent the torque transmitting balls from becoming detached from their operative positions.

Claims

1. A continuously variable drive transmission comprising two drive members each providing a generally conical transmission surface, the end of narrow diameter of one transmission surface lying adjacent to the end of larger diameter of the other transmission surface, and a transmission element adapted drivingly to interengage the two drive members, transmission of drive between the drive members by the transmission elements being afforded by a surface having a high co-efficient of friction.

2. A transmission according to Claim 1 wherein the surface comprises rubber or plastic.

3. A transmission according to one of Claims 1 and 2 wherein the transmission element comprises a material having a high coefficient of friction.

4. A transmission according to any one of the preceding claims wherein the transmission element is in the form of a rubber ball.

5. A transmission according to any one of the preceding claims wherein actuating means is provided to permit moving the transmission element relative to the drive members so as to vary the gearing ratio between the two drive members.

6. A transmission according to Claim 5 wherein the actuating means is manually operable.

7. A transmission according to one of Claims 5 and 6 wherein the actuating means is operative to move the transmission element in a direction longitudinally of the two drive members.

8. A transmission according to any one of Claims 5, 6 and 7 wherein the actuating means is operatively connected to a support which supports the transmission element such that actuation of the actuating means brings about movement of the support and hence of the transmission element longitudinally of each of the drive members, free movement of the transmission element longitudinally of said drive members being prevented by the support.

9. A transmission according to Claim 8 wherein the support comprises and inverted "U" shaped frame, depending arms of which provide idlers which engage the surface of the transmission element and a cross member extending between the arms which provides a further idler, the idlers permitting rotation of the transmission element about any axis passing through a centre thereof.

10. A transmission according to Claim 9 wherein the arms of the frame include respective aligned apertures through which extend a guide rail for the support, the support being movable longitudinally of the guide rail.

11. A transmission according to Claim 10 wherein the apertures are elongate such that the support may be raised and lowered relative to the guide rail to disengage the transmission element from the drive members and to reengage the transmission element therewith.

12. A transmission according to any one of Claims 9, 10 and 11 wherein the support provides an idler such that the transmission element is heid captive by the support when raised so as to be disengaged from the drive members.

13. A transmission according to any one of the preceding claims wherein the two drive members comprise a first drive member which is connected to a source of motive power, and a second drive member which is connected to an output system.

14. A transmission according to Claim 13 wherein the construction and operation is such that the transmission means may be operated to return power from the second drive member to the first drive member, in the event that the ratio selected is one in relation to which the speed of the output system is greater than the speed of the power source, as seen by the transmission mechanism.

15. A transmission according to any one of the preceding claims comprising a third frusto-conical drive member and a second transmission element operable between the third drive member and one of the other drive members.

16. A transmission system according to Claim 15 wherein the second transmission element is in accordance with any one of claims 2, 3 and 4.

17. A transmission according to one of Claims 15 and 16 wherein the transmission element is moved in a direction longitudinally of the two said drive members by a further actuating means in accordance with any one of Claims 5 to 12.

18. A transmission according to any one of Claims 15, 16 and 17 comprising coupling means to couple together the actuating means and the further actuating means such that operation of the actuating means causes operation of the further actuating means.

19. A transmission according to any one of Claims 15 to 18 wherein said coupling means is a mechanical coupling.

20. A transmission according to any one of the preceding claims, the construction and arrangement being such that, when the surface of that drive member at the point where it engages the transmission element, which is travelling faster than the other drive member at the point where it engages the transmission element is travelling from the transmission element towards the nip, the transmission element is drawn into the nip, whilst when the surface of that drive member, at the point where it engages the transmission element, which is travelling faster than the other drive member at the point where it engages the transmission element, is travelling from the nip towards the transmission element, the transmission element is lifted from the nip between said drive members.

21. A continuously variable transmission, constructed and arranged substantially as hereinbefore described with reference to any one of the accompanying drawings.