GB2537151A

GB2537151A - Auxiliary drive arrangement

Info

Publication number: GB2537151A
Application number: GB1506049.4A
Authority: GB
Inventors: John Burtt David; William Edward Fuller John; Shawe James; Kendrick Robinson Leslie
Original assignee: Torotrak Development Ltd
Current assignee: Torotrak Development Ltd
Priority date: 2015-04-09
Filing date: 2015-04-09
Publication date: 2016-10-12
Anticipated expiration: 2035-04-09
Also published as: GB201506049D0; WO2016162702A1; GB2537151B

Abstract

Disclosed is an auxiliary drive arrangement having a variable speed transmission 18, the transmission input being coupled via a drive coupling 1 to an output drive of a prime mover and the transmission output being coupled to an auxiliary device 30, wherein the drive coupling permits rotation of the prime mover output drive relative to the transmission input. Preferably the transmission is a traction drive continuously-variable transmission, the prime mover is an internal combustion engine and the auxiliary device is a supercharger or centrifugal compressor. The drive coupling may comprise a one-way and/or torsional coupling. The transmission may be a full toroidal variator comprising tilting rolling elements as torque transfer elements and races as drive elements, and means for applying an end load to at least one race in order to generate a contact force between the rolling elements and races, for example a cam. The drive coupling alleviates the effects of uneven power delivery to the crankshaft as a result of firing events of the engine.

Description

AUXILIARY DRIVE ARRANGEMENT

The present invention relates to a drive arrangement for a variable speed auxiliary drive for an internal combustion engine. It is particularly concerned with a variable speed auxiliary drive such as a supercharger that includes a variable drive transmission, for example a continuously-variable transmission (CVT).

The invention has particular application to vehicles including passenger cars, light road vehicles and commercial vehicles such as buses, trucks and construction vehicles. It also has particular application to variable speed superchargers. While this is not the only application of the invention, this application will be used as a basis for description of how the invention might be implemented.

Forced induction is seen as making an important contribution to improving the efficiency of internal combustion engines, resulting in reduced carbon dioxide emissions. In particular, superchargers driven from the engine (as contrasted with exhaust-driven turbochargers) can offer a considerable degree of control over the amount of air and hence fuel entering the engine at any given time, which in turn can offer improved control of engine power and driving response in combination with reduced exhaust emissions.

In general, the rotational speed at which the supercharger must be driven is greater than the rotational speed of the crankshaft of the engine by a large factor. For example, a typical petrol engine for a passenger car will operate at speeds between 750 and 6000 rpm, while a centrifugal supercharger might be required to operate at between 40 000 and 250 000 rpm.

Hitherto, this has typically been achieved by providing a step-up gear train of fixed ratio between the crankshaft and the supercharger.

It is apparent that causing the supercharger to be driven at a fixed multiple of the crankshaft speed is not optimal. If the supercharger system is configured to deliver the maximum possible engine torque at low engine speed then the power is wasted at high engine speed.

If the supercharger system is geared such that it supplies the required engine torque at high engine speed then engine torque at low engine speed may be insufficient. It is clear that providing a variable ratio drive between the crankshaft and the supercharger could be used to reduce the amount of wasted energy that is delivered to the supercharger whilst maximising engine torque output at low engine speeds, and that a continuously-variable ratio drive has clear advantages over a step-change ratio drive.

The present invention may be applied to a variety of variable drive technologies. Traction drive CVTs have certain advantages in that they offer high power density, durability and efficiency, and in certain cases, low cost. They comprise torque transfer elements in the form of ball bearings, rollers or other rolling elements that tilt in order to effect a change in CVT speed ratio. The rolling elements typically roll against input and output races and are clamped between them. The rolling elements contact the input and output races at input and output traction contacts respectively. An axial (end loading) means applied to one or both input and output races urges the rolling elements against the races creating contact normal forces that enable power to be transferred between them. Drive is transmitted from the input race via the rolling elements to the output race via shear forces in a traction fluid which is entrained into the traction contacts. This type of fluid becomes highly viscous when subjected to high contact stress, thus enabling efficient transfer of shear force (resulting in transmission of torque) with minimal slip. "Over-clamping", however, can result in increased power losses and reduced CVT durability. The normal contact load should ideally therefore be controlled generally in proportion to the contact shear forces, the ratio of the shear force to contact normal force being known as the "traction coefficient'. With some provisos, a CVT that operates at a constant or near constant traction coefficient may generally be efficient and durable.

One particular type of traction drive CVT is the full toroidal CVT. In this CVT the input and output races are mounted for coaxial rotation about a variator axis, the races having working surfaces that face each other, each being of concave arcuate section. Rollers are disposed between the races in what is known as the toroidal cavity, so termed because the working surfaces describe a toroidal space between the races. The rollers are arranged to tilt, thus causing a change in radius of the respective input and output traction contacts with respect to the variator axis. The tilt angle of the rollers determines the ratio of input to output traction contact radii, this generally corresponding with the ratio of speeds of the CVT input and output races.

Variable drive superchargers used in passenger car engine systems may benefit from being small in size, compact and low cost. They typically comprise a compressor (either positive displacement or a dynamic compressing device) driven from the crank of an internal combustion engine (ICE) via a CVT. The crank exhibits speed fluctuations because the firing events of an ICE cause uneven delivery of power to the crank. An ICE typically comprises a main drive transmission input coupling (also typically comprising a flywheel) to smooth this unevenness, but since the supercharger is connected on the engine side of the input coupling, it does not benefit from its smoothing effect. The CVT is therefore forced to accelerate the compressor cyclically, bearing cyclic torques that arise from the firing pulses of the engine. These torques may require the CVT to be increased in size in order to bear the additional cyclic stresses, or to exhibit the required durability. Some CVTs, for example traction drive CVTs, can offer some torsional compliance by virtue of an end load clamping mechanism that converts rotational wind-up of its input or output into an end load of the CVT. However, the torsional compliance of such mechanisms is typically limited. Further, as the clamping mechanism winds up, the axial clamp of the variator is increased cyclically which can reduce efficiency and durability of the CVT in any case.

A further challenge exists in some CVTs which offer possibilities of low power actuation and therefore reduced cost. An example is a traction drive CVT that is controlled by displacing the rolling elements in a sense other than that required to change the CVT ratio, and then allowing the discs to tilt the rolling elements to provide the desired ratio. The control input to the rolling element or elements is typically orthogonal to the direction in which the rolling element moves to change the CVT ratio. The control input to the rolling elements is cancelled out' as the rolling element approaches a new equilibrium tilt angle, and there as the CVT approaches a corresponding new speed ratio. The 'cancelling' of the control input as the rollers tilt results in a stable negative feedback loop, but one that is only effective if the CVT races are rotated in a particular direction, as this ensures that the rolling elements steer in the correct sense in response to the control input. In some situations, such as turning off an ICE that is coupled to a CVT, reverse rotation of a CVT input race can occur, and this may result in damage to the CVT.

This invention aims to provide a solution for, or at least ameliorate, some or all of the above problems.

This invention provides an auxiliary drive arrangement comprising: a variable speed transmission comprising a variable drive, preferably a continuously-variable transmission (CVT) having a transmission input and a transmission output and arranged to transmit drive therebetween, the transmission input being coupled via a transfer drive arrangement to an output drive of a prime mover, for example an internal combustion engine (ICE), and the transmission output being coupled to an auxiliary device, wherein the transfer drive arrangement comprises a drive coupling that permits rotational displacement of the prime mover output drive relative to the transmission input.

The auxiliary device may be an oil pump, a water pump, a fan, alternator, a generator or an energy storage high speed flywheel. In a preferred embodiment, the auxiliary device is a compressor and the prime mover is an ICE and the compressor is arranged for the delivery of air to the inlet of the internal combustion engine (ICE).

The compressor may be a positive displacement compressor but is preferably a dynamic compressor such as a centrifugal compressor. The compressor suitably can pressurise the air at the inlet of ICE to a pressure in excess of atmospheric pressure (that is, 1 bar absolute), and preferably in excess of 0.5 or 1.0 bar above atmospheric pressure.

The CVT may be a type selected from a variable ratio belt-and-sheave type, a hydrostatic pump-motor or a motor-generator, but is preferably a traction drive CVT. Preferably the CVT includes torque transfer elements such as a belt, or in the case of a traction drive CVT, rolling elements, clamped between input and output drive elements. The torque transfer elements are preferably formed at least in part from a steel, preferably a hardened steel. In the case of a traction drive CVT, the input and output drive elements are races on which at least one rolling element runs. The races are mounted coaxially with one another for rotation about a variator axis, and preferably there are a plurality of rolling elements disposed between the input and output races. The rolling elements (which may be rollers) spin about a rolling axis, and contact working surfaces of the races at traction contacts. In the type of variator known as a 'full toroidal variator' the working surfaces are arcuate and concave, and define a toroidal-like space between the races in which the rolling elements are disposed, this space being known as the 'toroidal cavity'. The rolling elements are arranged to tilt within the cavity in order to change or accommodate changes in speed ratio of the races.

The CVT is preferably arranged for unidirectional rotation of its torque transfer elements and may preferably be arranged for unidirectional rotation of a given CVT drive element. In the case of a traction drive CVT, the CVT is preferably arranged for unidirectional rotation of its rolling elements about their rolling axes. Such a CVT may also be preferably arranged for unidirectional rotation of a given race about the variator axis. When a change in CVT ratio is required, the rolling elements may be caused to be displaced by a control member that is coupled to an actuator. When a ratio change is required, the rolling elements are typically rotated in a direction generally orthogonal to that required to directly cause the ratio to change. Preferably the rolling elements are made to tilt to cause a ratio change. The input to the rolling element may be via a control member that displaces a part on which the rolling element is rotatably mounted in a direction substantially perpendicular to the rolling element force reaction that arises due to the transmission of torque. This ensures that substantially no work is done on the rolling element by the control member, thus helping to minimise the actuator power requirement of the ratio change mechanism. Accordingly, at least one rolling element may be caused to pitch, such pitching causing pivotal movement about an axis passing through the contact regions between the said rolling element and the races. The rolling element may be configured to tilt about a tilt axis. The tilt axis is preferably inclined to the plane that is perpendicular to the variator axis. The angle between the tilt axis and the plane of the races defines a castor angle. Thus tilting of the rolling element results in both a change in the contact radii, and also a change in pitch angle of the rolling element. In this configuration, the control input displacement to the rolling elements results in a first mode of rotation of the rolling element, this in turn causing the rolling element to be steered by the races such that its tilt angle changes. As the tilt angle changes the CVT ratio changes. If a special steering geometry exists in the variator, for example if the tilt axis is inclined to the plane of the races, then as rolling element tilts the rolling element also experiences a secondary mode of rotation, this being a similar mode of movement to the control input displacement but in the opposite direction. Thus the tilting of the rollers causes the control input to be progressively 'cancelled out' as the rolling element approaches a new equilibrium tilt angle corresponding to the control input. This mechanism is only effective if the CVT input race, or the CVT output race, is rotated in a required direction. This mechanism allows the rolling elements to be actuated by power means with an output power of less than 20W.

Preferably the CVT includes an end loading arrangement comprising at least one clamping arrangement. Preferably the clamping arrangement is arranged to provide an end load that is dependent upon the torque transmitted to a race. Preferably, the clamping arrangement has a torsional stiffness that is dependent upon the axial stiffness of the CVT. Preferably, the clamping arrangement has a torsional stiffness that is also dependent upon the relationship between the end load that it generates and that the torque that it transmits.

Advantageously the torsional compliance afforded by the CVT mechanical clamping arrangement attenuates the firing pulses of the ICE.

The clamping arrangement is preferably comprises a cam. The cam preferably comprises balls or rollers disposed between one of the races and a drive disc. The balls or rollers may reside and run within mutually facing helical grooves that sweep around in a circumferential direction of the non-working surface of the race and a facing surface of the drive disc. The balls or rollers are trapped between the mutually facing helical grooves that extend simultaneously in the circumferential direction and in the direction of the axis of the races, and transmit torque between the drive disc and race whilst simultaneously generating an end load. The end load is a function of the torque transmitted. This function is dependent upon the helix angle of the helical grooves and the radial distance between these grooves and the variator axis. The end load may be dependent upon, and preferably proportional to, the torque transmitted.

The torsional compliance of the clamping mechanism may have a maximum travel indicated by a rotational end stop, or it may have a practical limit such as a maximum operating torque that corresponds with a maximum torsional wind-up of the mechanism. In order to achieve a statically determinate structure in the clamping mechanism, and to maximise wind-up capability, it is beneficial that the clamping mechanism comprises three rolling elements, and preferably only three rolling elements, disposed 120 degrees apart from one another about the variator axis. In such arrangements the angular wind-up of the clamp mechanism is limited to less than 60 degrees, and more typically less than 50 degrees, for devices requiring a drive torque in both directions (for example, where the auxiliary device is a positive displacement compressor) because the clamping mechanism must be able to wind up in both rotational directions. If the CVT is arranged to drive a unidirectional torque device, such as a centrifugal or an axial compressor, then a wind-up of less than 120 degrees, and more typically less than 110 degrees is available since the clamping arrangement needs only to wind up in a single direction. In both cases the angular wind-up capability, and therefore the torsional compliance afforded by the clamp mechanism, is limited.

The torsional compliance afforded by the drive coupling of the transfer drive arrangement may therefore be used to supplement the limited torsional compliance of the CVT clamping arrangement. The torsional compliance of the two devices act as 'springs in series' such that overall compliance is increased.

The CVT end loading arrangement preferably comprises two clamping arrangements, one on the CVT input and the other on the CVT output, such that at any one time the maximum of the two end loads tending to be generated by the respective clamping arrangements (in response to the respective transmitted torques) dominates over the other. Advantageously this provides a clamp load that is approximately in proportion to the shear forces (torque bearing forces) at the rolling element-race contacts, thus providing a near-uniform traction coefficient at all CVT ratios. Such an arrangement may be lower cost than other clamping arrangements such as a hydraulic system comprising a piston that acts on one of the races.

The transfer drive arrangement suitably comprises an engine (ICE) crank pulley and a drive coupling, and a belt that couples one to the other. The drive coupling receives drive from the ICE at a drive coupling pulley. There is a drive ratio of preferably between 1.5 and 4.5 (in magnitude) between the engine crank pulley and the drive coupling pulley. The pulley may drive a torsionally compliant member termed a torsional coupling. The pulley may also or alternatively be coupled directly or indirectly to a one-way device adapted for transmission of torque in a single direction only, such as a one-way clutch, one-way roller clutch, mechanical diode or sprag clutch. The pulley may drive both of these devices, in which case the two devices may be arranged in series, the output of one of the devices being coupled to the input of the CVT.

Advantageously, a unidirectional torque transfer device may attenuate firing pulses. When the application requires torque transfer in one direction only, such as for supercharging arrangement that includes a centrifugal or an axial compressor, inclusion of the one-way device is may be used to reduce the severity of the firing pulses experienced by the CVT. As previously described, the torsional travel (wind-up) capability of the clamping device for such a unidirectional torque device may be greater than 60 degrees, greater than 75 degrees or greater than 90 degrees or even greater than 100 degrees.

Where a torsional coupling is included, this may take the form of resiliently deformable means such as an elastomeric coupling, damper or a spring. Preferably it is a spring so that the transmission of firing pulses to the CVT is reduced, but without the associated energy loss of a damping device. The spring is preferably a torsion spring.

Advantageously the torsional coupling and/or one-way device provides attenuation of the engine firing pulses that is in addition to the torsional compliance of the CVT end loading arrangement.

The CVT may drive the compressor via a step-up gear ratio, preferably an epicyclic gear set.

Preferably the epicyclic is a traction epicyclic as this operates near-silently. A traction drive CVT also operates near silently, thus offering a solution with low overall noise output. The epicyclic preferably shares fluid with the CVT. Preferably the epicyclic is a traction epicyclic, the CVT is a traction drive and the fluid is a traction fluid.

Where the driven device is an air compressor, it may deliver air to the air inlet of an internal combustion engine (ICE), which is preferably adapted to burn a hydro-carbon fuel. The ICE is preferably either a diesel or a gasoline engine. The ICE preferably is preferably adapted to run at a rotational speed of above 1000rpm.

The CVT preferably has an operating 'ratio spread' with magnitude in excess of 3, but preferably in excess of 6. 'Ratio spread' is defined as the magnitude of the maximum operating ratio divided by the minimum operating ratio. This is especially advantageous for operation with a centrifugal compressor, whose speed is generally regulated to provide the required air boost pressure to the air inlet of an ICE, even as the speed of the ICE crank changes. The CVT preferably has an actuator arranged to control its ratio or torque. Preferably the CVT controls ratio as this generally offers a low power, low cost actuator solution. A control signal is indicative of a target CVT ratio, and typically causes the actuator to receive an electrical power input signal indicative of a target ratio. The actuator typically causes one or more rolling elements to be displaced such that the CVT ratio is caused to change to the new target ratio.

The CVT preferably comprises two and only two rollers in a toroidal cavity. The belt imparts a force radial to the variator axis to the CVT, tending to bend the CVT structure such that contact normal loads tend to be increased at one pair of traction contacts and decreased at the other pair of traction contacts. Preferably the belt is arranged to impart a radial load that is substantially normal to a plane that substantially passes through the traction contacts of all rolling elements within the toroidal cavity at least at one operating ratio of the variator. In this way, the normal contact loads are not altered significantly by the tension in the belt. This configuration may be effective when the auxiliary device is arranged to receive unidirectional torque, or bidirectional torque from the CVT.

Embodiments of the invention are illustrated in the accompanying drawings: Figure 1 shows a variable speed supercharger driven by, and delivering air to the inlet of an ICE; Figure 2 shows a variable speed supercharger with drive pulley according to an embodiment of this invention; Figure 3 shows a section view through a drive coupling assembly according to an embodiment of this invention; Figure 4 shows an exploded view of the drive coupling assembly of Figure 3; Figure 5 shows a drive disc of a CVT according to an embodiment of this invention; Figure 6 shows a race of a CVT according to an embodiment of this invention; With reference to Figures 1 to 4, an Internal Combustion Engine (ICE) 33 has a crank 35 on which a crank pulley 32 drives a supercharger drive pulley 14 via a belt 31. The engine 33 also outputs drive on the crank 35 to the driven wheels of a vehicle via a main drive vehicle transmission 34. Drive coupling assembly 1 comprises the pulley 14 which is coupled via a one-way drive coupling 4 and/or a torsional coupling 3 (and this is understood to offer energy absorption, torsional stiffness, or both). The one-way drive coupling 4 and torsional coupling 3 may be arranged in series, and either the torsional coupling 3 or the one-way drive coupling 4 may be driven directly by the pulley 14. The output of the drive pulley assembly 1 is coupled to the input clamping arrangement of the CVT 18, which comprises an input race 21a driven by a drive disc 20a via ball bearings 23a. The ball bearings 23a are disposed in mutually facing helical grooves 24a formed in a face of the drive disc 20a and a surface (that is not in contact with the rolling elements) of the input race 21a respectively. As torque is applied to the drive disc 20a, the ball bearings 23a move circumferentially around the helical grooves 24a. As they do so they move to a shallower region of the grooves, thus tending to apply a clamp load (end load) to the CVT 18 rolling elements 22, which in this example are rollers. In this way the clamp load on the rolling elements 22 is increased which allows torque transmission between races 21a,b and rolling elements 22. As is understood in the art, the tangent of the helix angle of the grooves 24a and the radius of the grooves 24a with respect to the variator axis (that is, the axis about which the races 21a, 21b rotate) defines the end load generated per unit torque (transmitted by the input race of CVT 18). The helical groove 24a helix angle, its radial distance from the variator axis, and the axial stiffness of the CVT 18 together define the torsional compliance of the input clamping arrangement. As described earlier, this torsional stiffness is limited because the input clamping arrangement may only wind up by a limited angle if the preferred number of balls (that is, three) is to be used in the clamping arrangement.

Additional attenuation of disturbances from the engine 33 crankshaft 35 may advantageously be provided by the drive coupling arrangement 1 which comprises one or both of the torsional coupling 3 and a one-way drive coupling 4. The couplings may be arranged functionally in series with one another. The one-way drive coupling 4 includes a ratchet wheel 5 and pawl wheel 7, the pawl wheel 7 comprising pawls 6 may pivot about a pin. The pawls 6 may be biased to point radially inwards. The pawls 6 engage with the ratchet wheel 5, allowing drive torque to be transmitted in one, but not the other direction. In this example, drive from the one-way drive coupling 4 is transferred by the ratchet wheel 5 to an output shaft. Drive may be transferred from the ratchet wheel 5 via an interference fit, a key, or by any other suitable means. This output shaft is coupled to the input of the CVT 18, which, together with the traction epicyclic 25 and compressor 30, form the principal elements of the supercharger arrangement 2. Of this, the traction epicyclic 25 and compressor 30 make up the principle elements of the auxiliary device.

The detailed construction of the drive coupling arrangement 1 will now be described in the context of a centrifugal supercharger auxiliary device, by way of example. The torsional coupling 3, in this case a resilient member (and specifically a spring), is driven by pulley 14. At the end of the spring 3 that is farthest from the compressor 30, a tang of the spring 14 is engaged and driven by a radial slot in the pulley 14. At the axially opposite end of the torsion spring 3, a second tang engages with the pawl wheel 7. Pawls 6 mounted for pivotal rotation about pins on the pawl wheel 7 engage with the ratchet wheel 5. The pawls 6 may be biased to point radially inwards, for example, using torsional springs. The pawls 6 are arranged so that they may pivot about pins, but the profile of the teeth on the ratchet wheel 5 mean that they are unable to engage with and transmit torque to the ratchet wheel 5 when torque transmission in a freewheeling direction of the drive coupling arrangement 1 is attempted. The pawls 6 are unable to engage with the teeth of the ratchet wheel 7 and transmit drive in this freewheel direction. When transmission of torque at the drive coupling pulley 14 is attempted in the opposite direction (that is, in the drive direction of the machine) the pawls 6 tend to positively engage with the teeth of the ratchet wheel 5. The drive direction may also be in the direction in which the CVT 18 input race 21a is arranged to rotate, particularly if the CVT 18 has self-steering rolling elements 22. In this case, the drive direction also corresponds with a working direction of rotation of the rolling elements 22. Thus the pawls 6 may become locked in engagement with the teeth of the ratchet wheel 5, so long as the transmitted torque is in the same sense as the working direction of the machine. This direction also corresponds with the working direction of the ICE 33, which tends to be arranged for unidirectional rotation, except when it is turned off. The one-way drive coupling 4 may assist in the attenuation of firing pulses from the engine. This is because the supercharger arrangement 2 can freewheel when the speed of the engine crank 35 is falling or when the speed of crank 35 is such in relation to the speed of the supercharger arrangement 2 that there is no drive torque transmitted to the drive coupling pulley 14, but it may be driven again when the speed of the crank 35 rises sufficiently so that drive torque is reinstated. In this way, the one way drive coupling 4 acts like a half-cycle rectifier. A benefit of this one-way drive coupling 14 arrangement is that it does not dissipate power as it attenuates engine 33 firing pulses. A further advantage is that, when used with a CVT 18 that is arranged to operate in one direction only (for example, a traction drive CVT 18 comprising self-steering rolling elements, as described earlier), the one-way drive coupling 4 may also prevent reverse rotation of the CVT 18 if the engine 33 tends to rotate momentarily in a reverse sense when it is turned off (due to rebound from the compression stroke of its pistons).

If the auxiliary device requires a drive torque in both rotary directions, then the one-way drive coupling 4 may be omitted. Such a device may be a positive displacement compressor which is used to both compress and throttle air (as required) at an ICE inlet.

The spring 3 may optionally be used to perform the combined functions of the torsional coupling and one-way drive coupling. For example, rather than engaging in a slot in the drive coupling pulley 14, one of the tangs of the spring 3 may bear axially against a series of teeth arranged circumferentially on an axial face of the drive coupling pulley 14. Each of the teeth may have a shallow rising face and a steep falling face, the tooth profile resembling a saw-tooth. In this way the spring 3 can only transmit torque in one direction because one of its tangs would ride over the shallow faces of the teeth in a freewheel direction, but would engage with the steep side of a tooth in the drive direction.

The drive coupling pulley 14 may be mounted for free rotation on bearings 8, 9. The bearings 8, 9 may radially locate and support the pulley 14. The radially inner part of the assembly may comprise the ratchet wheel 5, bearing 8, separator sleeve 10 and second bearing 9, which may be arranged axially on a central drive shaft 15 of the drive coupling arrangement 1. A race of bearing 8 may be retained by a shoulder of the pulley 14 and by a retainer 12 bolted to the front face of the drive coupling pulley 14. Bearing 9 may be retained by the ratchet wheel 5 on one side, and the separator sleeve 10 on the other side. The bearings 8, 9 may be mounted and constrained in any suitable manner. The spring 3 may be mounted concentrically and radially outwardly of the bearings 8, 9, and transmits drive from the pulley 14 to the pawl wheel 7. Drive may be transmitted, but in the drive direction only, to the ratchet wheel 5 via the pawls 6, to the output shaft which may be coupled to the CVT 18 input. It should be noted that the radial positions of the pawl wheel 7 and the ratchet wheel 5 may be reversed, so that the pawl wheel 7 is instead radially inwardly of the ratchet wheel 5.

Within the CVT 18, drive may be transmitted through rolling elements 22 disposed between input race 21a and output race 21b. Preferably there are two and only two rolling elements 22 disposed between the races 21a,b. The rolling elements 22 are preferably arranged to tilt such the angle between their rolling axes and the variator axis may be allowed to change. The tilt angle corresponds generally with the variator ratio (that is, the speed ratio of the races 21a, 21b).

It should be noted that there may be an output clamping arrangement only, an input clamping arrangement only, but preferably there is an input and an output clamping arrangement, as shown in Figure 2. Similarly to the input clamping arrangement, the output clamping arrangement may comprise an output race 21b coupled to an output drive disc 20b via ball bearings 23. The output clamping arrangement may be similarly configured to the input clamping arrangement. The relationship between the transmitted torque and resulting end load generated by the respective clamping arrangements may or may not be different. In other words, if the relationship between the transmitted torque and resulting end load by a clamping arrangement is described by a gain, then the gain of one of the clamping arrangements may be more than 10% greater, more than 25% greater, more than 50% greater, or more than 100% greater than the gain of the other clamping arrangement. Where the auxiliary device is a centrifugal supercharger, preferably the gain of the output clamping arrangement is greater than the input clamping arrangement, and preferably it is more than 25% greater.

The output drive disc may be coupled via a step-up epicyclic 25 to a compressor 30, preferably a centrifugal compressor. The large step-ratio allows the centrifugal compressor to operate at speeds in excess of 50,000rpm, greater than 100,000rpm or even at speeds greater than 150,000rpm.

The epicyclic 25 is preferably a traction epicyclic, and may conventiently be mounted coaxially with the CVT 18 within a common housing 16. The epicyclic comprises annulus, carrier and sun elements. The CVT 18 output drives the annulus, the carrier may be grounded to housing 16 and the sun may drive the compressor 30. The CVT 18 and traction epicyclic 25 are preferably served by a common traction fluid.

Claims

CLAIMS1. An auxiliary drive arrangement comprising: a variable speed transmission comprising a variable drive having a transmission input and a transmission output and arranged to transmit drive therebetween, the transmission input being coupled via a transfer drive arrangement to an output drive of a prime mover, and the transmission output being coupled to an auxiliary device, wherein the transfer drive arrangement comprises a drive coupling that permits rotational displacement of the prime mover output drive relative to the transmission input.
2. An auxiliary drive arrangement according to claim 1 wherein the variable drive is a continuously-variable transmission.
3. An auxiliary drive arrangement according to claim 2 wherein the continuously-variable transmission is a traction drive continuously-variable transmission.
4. An auxiliary drive arrangement according to any one of the preceding claims wherein the prime mover is an internal combustion engine.
5. An auxiliary drive arrangement according to any one of the preceding claims wherein the auxiliary device is a supercharger.
6. An auxiliary drive arrangement according claim 5 wherein the supercharger is a centrifugal supercharger.
7. An auxiliary drive arrangement according to any one of the preceding claims wherein the drive coupling comprises a one-way drive coupling.
8. An auxiliary drive arrangement according to any one of the preceding claims wherein the transfer drive arrangement comprises a torsional coupling.
9. An auxiliary drive arrangement according to claim 8 wherein the torsional coupling comprises resiliently deformable means.
10. An auxiliary drive arrangement according to any one of the preceding claims wherein the continuously-variable transmission comprises first and second drive elements and at least one torque transfer element arranged for torque transmission between the first and second drive elements, wherein the continuously-variable transmission further comprises means for generating a contact force between the torque transfer element and each drive elements, the contact force enabling said torque transmission.
11. An auxiliary drive arrangement according to claim 10 where in the continuously-variable transmission is a traction drive continuously-variable transmission, the torque transfer elements are rolling elements arranged to tilt about a tilt axis, the tilt angle corresponding generally to a speed ratio of the continuously-variable transmission, the drive elements are races, the races rotate about a common continuously-variable transmission axis, wherein the continuously-variable transmission further comprises means for applying an end load to at least one race in order to generate the said contact force.
12. An auxiliary drive arrangement according to claim 11 wherein means for applying an end load is configured to transmit torque whilst simultaneously applying an end load that is dependent upon the torque transmitted.
13. An auxiliary drive arrangement according to claim 12 wherein means for applying an end load is a cam.
14. An auxiliary drive arrangement according to claim 12 or claim 13 wherein the means for applying an end load has a maximum torsional wind-up that is less than 120 degrees.
15. An auxiliary drive arrangement according to claim 14 wherein the means for applying an end load arrangement has a maximum torsional wind-up that is less than 100 degrees.
16. An auxiliary drive arrangement according to any one of claims 12 to 15 wherein the auxiliary device is configured for substantially unidirectional drive torque.
17. An auxiliary drive arrangement according to any one of claims 12 to 16 wherein the auxiliary device is a centrifugal compressor.
18. An auxiliary drive arrangement according to either of claims 12 or 13 wherein the means for applying an end load arrangement has a torsional wind-up that is less than 80 degrees.
19. An auxiliary drive arrangement according to claim 18 wherein the means for applying an end load arrangement has a torsional wind-up that is less than 60 degrees.
20. An auxiliary drive arrangement according to any one of claims 12, 13, 18 or 19 wherein the auxiliary device is configured for bidirectional torque transfer.
21. An auxiliary drive arrangement according to any one of claims 12, 13, 18, 19 or 20 wherein the auxiliary device is a positive displacement compressor.
22. An auxiliary drive arrangement according to any one of claims 11 to 21 wherein the continuously-variable transmission is arranged for unidirectional rotation of its rolling elements.
23. An auxiliary drive arrangement according to any one of claims 11 to 22 wherein the continuously-variable transmission is arranged for unidirectional rotation of any of a given race.
24. An auxiliary drive arrangement according to any one of claims 9 to 21 wherein the continuously-variable transmission is arranged such that the races steer the rolling elements to change the tilt angle of the rolling elements.
25. An auxiliary drive arrangement according to claim 24 wherein the continuously-variable transmission is a full toroidal variator and the rolling elements are configured to be pitched about an axis passing through the rolling element contact regions, said pitching causing the rolling elements to be steered by the races such that their tilt angle is caused to change.
26. An auxiliary drive arrangement according to any one of claims 11 to 25 wherein the tilt axis is inclined to a plane that is perpendicular to the continuously-variable transmission axis.
27. An auxiliary drive arrangement according to any one of the preceding claims wherein the rolling elements are actuated by power means with an output power of less than 20W.
28. An auxiliary drive arrangement substantially as herein described with reference to the accompanying figures.