BACKGROUND ART Known manual transmission systems typically rely on synchronising cones causing friction between the drive shaft and a particular gear to enable synchronisation of their rotational speed to allow transition between gear ratios.

This approach adds a level of complexity to a transmission system, bringing with it cost and maintenance issues. Alternatively, a programmable logic controller, microprocessor, computer, or engine management system may achieve a similar result by increasing engine speed on up-changes and decreasing engine speed on down changes by way of throttle control whilst the engine is disconnected from the load by way of a clutch arrangement. However, the interruption in the transmission of power from the engine to the load is often undesirable, particularly during acceleration.

In conventional automatic transmissions the engagement of a particular gear is mediated by a clutch system, and synchronisation of shaft and engine speeds may be achieved thereby. A considerable disadvantage of such an arrangement is that it requires constant hydraulic pressure.

In other systems which avoid the need to interrupt the transmission of power, such as the constant mesh gearbox described in International Patent Application PCT/AU98/00181 (WO 98/41779), the change in engine speed associated with a change in gear ratio may produce an undesirable impact on a driver's perception of ride smoothness.

The present invention has as one object thereof to substantially overcome the abovementioned problems associated with the changing of gear ratios associated with the prior art.

Throughout the specification, unless the context requires otherwise, the word "comprise"or variations such as"comprises"or"comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Further, throughout this specification, unless the context requires otherwise, the term'launch clutch'or variations thereof will be understood to describe a clutch mediating the passage of power from the engine to the transmission system.

DISCLOSURE OF THE INVENTION In accordance with the present invention there is provided a transmission system, the transmission system comprising a drive shaft about which are provided at least three drive gear wheels, and a driven shaft adapted to receive rotational power from the drive shaft by way corresponding driven gear wheels provided thereabout, the engagement of at least one such gear wheel on either the drive shaft or the driven shaft, with the drive shaft or driven shaft being mediated by a clutch system.

Preferably, the drive and driven gear wheels on each of the drive or driven shafts respectively are of differing diameter. Typically, several drive or driven gear wheels of intermediate diameter are provided between the drive or driven gear wheels of greatest diameter and the drive or driven gear wheels of least diameter on each shaft.

Preferably, the engagement of at least the drive gear wheel of greatest diameter with the drive shaft, or the driven gear wheel of smallest diameter with the driven shaft, is mediated by a clutch system.

In a highly preferred form of the present invention, the engagement with the drive shaft or the driven shaft of both the drive or driven gear wheel of greatest diameter and the drive or driven gear wheel of least diameter are mediated by one or more clutch systems.

In one form of the invention, the engagement with the drive shaft or the driven shaft of both the drive or driven gear wheel of greatest diameter and the drive or driven gear wheel of least diameter are each mediated by a separate clutch system.

Preferably, the or each clutch system is releasably engageable with both the drive or driven gear wheel and the drive or driven shaft about which it is provided.

In an alternate form of the invention, the engagement with the drive shaft or the driven shaft of both the drive or driven gear wheel of greatest diameter and the drive or driven gear wheel of least diameter are both mediated by a single clutch system.

Preferably, the drive and driven gear wheels of greatest and least diameter are provided about a clutch pack to form a clutch and gear wheel assembly wherein the clutch pack is independently releasably engageable with each of the gear wheels, such that engagement of the clutch housing with either of the gear wheels allows the clutch pack to mediate the engagement of that gear wheel with the drive or driven shaft.

In one form of the invention, the clutch pack comprises at least one clutch plate rotationally fixed to the shaft but axially slidable therealong, and at least one clutch plate fixed to a clutch housing, the clutch housing being independently rotatable about the drive or driven shaft.

The transmission of power to the drive shaft may be mediated by a launch clutch.

Preferably, the means by which the drive or driven gear wheels are selectively engaged with the drive or driven shafts is such that the engagement of a higher

gear ratio causes or allows the spontaneous disengagement of the lower gear ratio, when changing up a gear. Preferably still, the means by which the drive or driven gear wheels are selectively engaged with the drive or driven shafts is such that the engagement of a lower gear ratio causes or allows the spontaneous disengagement the higher gear ratio, when changing down a gear.

Thus, the gear wheels may be selectively engaged with the shaft by a pawl system, such as that disclosed in PCT/AU98/00181 (WO 98/41779), or a bi- directional roller type clutch system or similar.

In accordance with the present invention there is further provided a clutch and gear wheel assembly comprising a clutch pack and two gear wheels provided about a shaft, wherein the clutch pack is interposed between the gear wheels and independently releasably engageable with each of the gear wheels, such that engagement of the clutch housing with either of the gear wheels allows the clutch pack to mediate the engagement of that gear wheel with the shaft.

In one form of the invention, the clutch pack comprises at least one clutch plate rotation fixed to the shaft but axially slidable therealong, and at least one clutch plate fixed to a clutch housing, the clutch housing being independently rotatable about the shaft.

Preferably, a plurality of clutch plates are provided rotationally fixed to the shaft and axially slidable therealong, and an equal number provided fixed to the clutch housing such that clutch plates fixed to the shaft are interleaved with those fixed to the clutch housing.

The means by which the clutch housing is releasably engaged with either of the gear wheels may be analogous to means disclosed in our earlier International Patent Applications PCT/AU97/00024 (W097/26468) (A Gear System with Gears Selectively Locked with Shaft) or PCT/AU98/00181 (W098/41770) (Preload Constant Mesh Gearbox), or Australian Provisional Applications PP5034 (Method and Apparatus for Controlling the Engagement and Disengagement of Gear

Wheels) or PP5035 (Method and Apparatus for Engaging and Disengaging Gear Wheels), the contents of which are hereby incorporated by reference.

Alternately, the means by which the clutch housing is releasably engaged with either of the gear wheels may be analogous to the means by which gear wheels are engaged in a standard manual gearbox, wherein a synchronisation cone and dog ring assembly controlled by a selector fork mediates the engagement of each of the gear wheels with the clutch assembly.

The transmission system of the present invention may be applied to constant mesh gearboxes of the type described in International Patent Application PCT/AU98/00181 (W098/41779), the content of which is incorporated herein by reference, as well as conventional transmissions including automatic transmissions and standard synchromesh manual transmissions.

In accordance with the present invention there is further provided a method for control of the transmission system of the present invention, wherein at least three drive gear wheels are provided about the drive shaft, said gear wheels being in constant meshed engagement with corresponding driven gear wheels provided about the driven shaft to form at least low, intermediate and high gear wheel pairs of ascending gear ratios, and in which at least the drive or driven gear wheel of each gear wheel pair is selectively engageable with the drive or driven shaft about which it is provided, and in which the engagement of at least the drive or driven gear wheel of the high gear wheel pair with the drive or driven shaft is mediated by a clutch system, the method comprising, when changing from the low gear wheel pair to the intermediate gear wheel pair, the steps of: calling for a change in gear ratio from that provided by the low gear wheel pair to that provided by the intermediate gear wheel pair; partially engaging the high gear wheel pair by partially applying the clutch system to provide torque from the high gear ratio in addition to torque from the engine inertia from the reduction in engine speed to suit the intermediate gear ratio;

simultaneously disengaging the low gear wheel pair or allowing the low gear wheel pair to be disengaged by disengaging or allowing the disengagement of at least the drive or driven gear wheel thereof from the drive or driven shaft; controlling the degree of application of the clutch system to ensure a gradual decrease from the level of torque provided by the low gear wheel pair to the level that will be provided by the intermediate gear wheel pair; ensuring that the speed of the driven shaft is synchronised with the intermediate gear; disengaging the clutch system; and engaging the intermediate gear wheel pair by engaging at least the drive or driven gear wheel thereof from the drive or driven shaft.

Preferably, the clutch system is engaged to a higher degree initially, then allowed to slip to an increasing degree.

The call for a change may be initiated by a user or an engine/transmission management system.

Preferably, whilst the clutch system is engaged, an increase in engine power is applied to enable the high gear wheel pair to generate the levels of torque required.

Where the or each clutch system of the transmission system of the present invention is releasably engageable with both the drive or driven gear wheel and the drive or driven shaft about which it is provided, before partially engaging the high gear wheel pair by partially applying the clutch system to provide torque from the high gear ratio, the method may comprise the additional steps of, whilst the clutch system is disengaged from the gear wheel, applying the appropriate pressure to the clutch system then engaging the clutch system with the gear wheel.

Where the engagement of at least the drive or driven gear wheels of the low gear wheel pair is with the drive or driven shaft respectively is also mediated by a clutch system, the method of the present invention further comprises, when changing from the high gear wheel pair to the intermediate gear wheel pair, the steps of: calling for a change in gear ratios from that provided by the high gear wheel pair to that provided by the intermediate gear wheel pair; partially engaging the low gear wheel pair by partially applying the clutch system to provide braking torque from the low gear ratio in addition to braking torque to the engine inertia from the increase in engine speed to suit the intermediate gear ratio; simultaneously disengaging the high gear wheel pair or allowing the high gear wheel pair to be disengaged by disengaging or allowing the disengagement of at least the drive or driven gear wheel thereof from the drive or driven shaft; controlling the degree of application of the clutch system to ensure a gradual increase from the level of braking torque provided by the high gear wheel pair to the level that will be provided by the intermediate gear wheel pair; ensuring that the speed of the driven shaft is synchronised with the intermediate gear; disengaging the clutch system; and engaging the intermediate gear wheel pair by engaging at least the drive or driven gear wheel thereof from the drive or driven shaft.

Preferably, the clutch system is engaged to a higher degree initially, then allowed to slip to an increasing degree.

Where the or each clutch system of the transmission system of the present invention is releasably engageable with both the drive or driven gear wheel and the drive or driven shaft about which it is provided, before partially engaging the high gear wheel pair by partially applying the clutch system to provide torque from

the high gear ratio, the method may comprise the additional steps of, whilst the clutch system is disengaged from the gear wheel, applying the appropriate pressure to the clutch system then engaging the clutch system with the gear wheel.

The degree of application of the clutch system may be controlled with reference to engine data, a signal from a torque sensor, a signal from an acceleration sensor, or a combination thereof.

In accordance with the present invention there is further provided a method for control of the transmission system of the present invention, where the gear wheels provided on each shaft are of differing diameter and where the present invention is applied to a constant mesh style gearbox incorporating gear wheels provided with means for actuable engagement therebetween in both rotational and counter-rotational directions, such that engagement of the means for actuable engagement of the or each gear wheel in both the rotational and counter- rotational directions causes the or each gear-wheel to rotate in conjunction with the shaft and prevents such from counter-rotating relative to the shaft, disengagement of the means for actuable engagement of the or each gear-wheel in both the rotational and counter-rotational directions allows the or each gear- wheel to rotate independently of the shaft and counter-rotate relative to the shaft, engagement of the means for actual engagement in the rotational direction and disengagement of the means for actual engagement in the counter-rotational direction of the or each gear wheel causes such to rotate in conjunction with the shaft and allows such to counter rotate relative to the shaft, and engagement of the means for actual engagement in the counter-rotational direction and disengagement of the means for actual engagement in the rotational direction of the or each gear wheel allows such to rotate relative to the shaft, but prevents such from counter rotating relative to the shaft, the method for control of the present invention comprising, when changing up a gear, the steps of: disengaging the means for actuable engagement in the counter-rotational direction of the presently selected gear wheels;

momentarily partially engaging a gear wheel of larger diameter provided about the drive shaft with the drive shaft, or the gear wheel of smallest diameter provided about the driven shaft with the driven shaft, by way of partial engagement of a clutch ; whilst that gear wheel is momentarily partially engaged, disengaging. the means for actuable engagement in the rotational direction of the presently selected gear wheels, or allowing such to be disengaged; and when the engine speed has decreased to match the shaft speed of the desired higher gear, engaging the means for actuable engagement in the rotational and counter-rotational directions of the desired higher gear wheels whilst simultaneously disengaging the gear wheel of larger diameter from the drive shaft by way of the clutch.

Preferably, the gear wheel of larger diameter is the gear wheel of largest diameter.

Where the present invention is applied to a constant mesh style gearbox incorporating gear wheels provided with means for actuable engagement therebetween in both rotational and counter-rotational directions, such that engagement of the means for actuable engagement of the or each gear wheel in both the rotational and counter-rotational directions causes the or each gear- wheel to rotate in conjunction with the shaft and prevents such from counter- rotating relative to the shaft, disengagement of the means for actuable engagement of the or each gear-wheel in both the rotational and counter- rotational directions allows the or each gear-wheel to rotate independently of the shaft and counter-rotate relative to the shaft, engagement of the means for actual engagement in the rotational direction and disengagement of the means for actual engagement in the counter-rotational direction of the or each gear wheel causes such to rotate in conjunction with the shaft and allows such to counter rotate relative to the shaft, and engagement of the means for actual engagement in the counter-rotational direction and disengagement of the means for actual engagement in the rotational direction of the or each gear wheel allows such to rotate relative to the shaft, but prevents such from counter rotating relative to the

shaft, where the gear wheels provided on each shaft are of differing diameter and where a clutch system mediates the engagement of both the gear wheels of smallest and largest diameter with the drive shaft or the driven shaft, the method for control of the present invention comprises, when changing down a gear with the means for actuable engagement in the counter-rotational direction under load, such as when engine braking, the steps of: calling for a change; disengaging means for actuable engagement in the rotational direction of presently selected gear wheels ; momentarily partially engaging a gear wheel of smaller diameter provided about the drive shaft with the drive shaft, or the gear wheel of largest diameter provided about the driven shaft with the driven shaft, by way of the clutch; whilst that gear wheel is momentarily partially engaged, disengaging means for actuable engagement in the counter-rotational direction of the selected gear or allowing such to be disengaged; and once the engine speed has increased to match the shaft speed of the desired lower gear, engaging means for actuable engagement in the counter-rotational and rotational directions of the selected lower gear whilst simultaneously disengaging the gear wheel of smaller diameter from the drive shaft by way of the clutch.

Preferably, the gear wheel of smaller diameter is the gear wheel of smallest diameter.

Where the present invention is applied to a constant mesh style gearbox incorporating gear wheels provided with means for actuable engagement therebetween in both rotational and counter-rotational directions, such that engagement of the means for actuable engagement of the or each gear wheel in both the rotational and counter-rotational directions causes the or each gear- wheel to rotate in conjunction with the shaft and prevents such from counter- rotating relative to the shaft, disengagement of the means for actuable

engagement of the or each gear-wheel in both the rotational and counter- rotational directions allows the or each gear-wheel to rotate independently of the shaft and counter-rotate relative to the shaft, engagement of the means for actual engagement in the rotational direction and disengagement of the means for actual engagement in the counter-rotational direction of the or each gear wheel causes such to rotate in conjunction with the shaft and allows such to counter rotate relative to the shaft, and engagement of the means for actual engagement in the counter-rotational direction and disengagement of the means for actual engagement in the rotational direction of the or each gear wheel allows such to rotate relative to the shaft, but prevents such from counter rotating relative to the shaft, where the gear wheels provided on each shaft are of differing diameter and where the supply of power to the input shaft from the power source is mediated by a launch clutch, the method for control of the present invention may comprise, when changing down a gear with the means for actuable engagement in the rotational direction under load, such as when overtaking or accelerating, by the steps of: calling for a change; disengaging the means for actuable engagement in the counter-rotational direction of the presently selected gear; momentarily allowing the launch clutch, mediating the transmission of power to the driven shaft, to slip ; temporarily cutting power to the transmission system; disengaging the means for actuable engagement in the rotational direction of the presently selected gear; and engaging the means for actuable engagement in the rotational direction and then means for actuable engagement in the counter-rotational direction of the desired lower gear, and locking the launch clutch.

Preferably, power is cut to the transmission system for a period of about 10 ms.

Preferably still, the method of the present invention is put into effect by way of a form of programmable logic controller, microprocessor, computer, or

engine/transmission management system. The step of calling for a change in gear may be initiated automatically by the programmable logic controller, microprocessor, computer, or engine/transmission management system or may be initiated manually.

Where the present invention is applied to a constant mesh style gearbox incorporating gear wheels provided with means for actuable engagement therebetween in both rotational and counter-rotational directions, such that engagement of the means for actuable engagement of the or each gear wheel in both the rotational and counter-rotational directions causes the or each gear- wheel to rotate in conjunction with the shaft and prevents such from counter- rotating relative to the shaft, disengagement of the means for actuable engagement of the or each gear-wheel in both the rotational and counter- rotational directions allows the or each gear-wheel to rotate independently of the shaft and counter-rotate relative to the shaft, engagement of the means for actual engagement in the rotational direction and disengagement of the means for actual engagement in the counter-rotational direction of the or each gear wheel causes such to rotate in conjunction with the shaft and allows such to counter rotate relative to the shaft, and engagement of the means for actual engagement in the counter-rotational direction and disengagement of the means for actual engagement in the rotational direction of the or each gear wheel allows such to rotate relative to the shaft, but prevents such from counter rotating relative to the shaft, and where the gear wheels provided on each shaft are of differing diameter, the method for control of the present invention comprises, when changing down a gear with the means for actuable engagement in the rotational direction under load, such as when overtaking or accelerating, by the steps of: calling for a change; disengaging the means for actuable engagement in the counter-rotational direction of the presently selected gear; reducing engine power; disengaging the means for actuable engagement in the rotational direction of the presently selected gear;

restoring engine power; and engaging the means for actuable engagement in the rotational direction and then means for actuable engagement in the counter-rotational direction of the desired lower gear.

Where the means for actuable engagement is provided in the form of at least one pair of pawl members comprising forward and reverse pawl members provided in the shaft or in the or each gear-wheel, wherein the forward pawl member is adapted to engage a leading surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member, and the reverse pawl member is adapted to engage a trailing surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member, the method of control of the present invention comprises, when changing up a gear, the steps of: disengaging the reverse pawls of the presently selected gear wheels ; momentarily partially engaging a gear wheel of larger diameter provided about the drive shaft with the drive shaft, or the gear wheel of smallest diameter provided about the driven shaft with the driven shaft, by way of partial engagement of a clutch ; whilst that gear wheel is momentarily partially engaged, disengaging the forward pawls of the presently selected gear wheels, or allowing such to be disengaged; and when the engine speed has decreased to match the shaft speed of the desired higher gear, engaging the forward and reverse pawls of the desired higher gear wheels whilst simultaneously disengaging the gear wheel of larger diameter from the drive shaft by way of the clutch.

Where the means for actuable engagement is provided in the form of at least one pair of pawl members comprising forward and reverse pawl members provided in the shaft or in the or each gear-wheel, wherein the forward pawl member is adapted to engage a leading surface of a substantially complimentary recess in

an opposed surface positively during rotation of that opposed surface with respect to the pawl member, and the reverse pawl member is adapted to engage a trailing surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member, and where a clutch system mediates the engagement of both the gear wheels of smallest and largest diameter with the drive shaft or the driven shaft, the method for control of the present invention comprises, when changing down a gear with the reverse pawls under load, such as when engine braking, the steps of: calling for a change; disengaging forward pawls of presently selected gear wheels ; momentarily partially engaging a gear wheel of smaller diameter provided about the drive shaft with the drive shaft, or the gear wheel of largest diameter provided about the driven shaft with the driven shaft, by way of the clutch; whilst that gear wheel is momentarily partially engaged, disengaging reverse pawls of the selected gear or allowing such to be disengaged; and once the engine speed has increased to match the shaft speed of the desired lower gear, engaging forward and reverse pawls of the selected lower gear whilst simultaneously disengaging the gear wheel of smaller diameter from the drive shaft by way of the clutch.

Where the means for actuable engagement is provided in the form of at least one pair of pawl members comprising forward and reverse pawl members provided in the shaft or in the or each gear-wheel, wherein the forward pawl member is adapted to engage a leading surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member, and the reverse pawl member is adapted to engage a trailing surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member and where the supply of power to the input shaft from the power source is mediated by a launch clutch, the method for control of the present invention may more

particularly comprise, when changing down a gear with the forward pawls under load, such as when overtaking or accelerating, by the steps of: calling for a change; disengaging the reverse pawls of the presently selected gear; momentarily allowing the launch clutch, mediating the transmission of power to the driven shaft, to slip; temporarily cutting power to the transmission system; disengaging the forward pawls of the presently selected gear; engaging the forward and then reverse pawls of the desired lower gear, and locking the launch clutch.

Where the means for actuable engagement is provided in the form of at least one pair of pawl members comprising forward and reverse pawl members provided in the shaft or in the or each gear-wheel, wherein the forward pawl member is adapted to engage a leading surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member, and the reverse pawl member is adapted to engage a trailing surface of a substantially complimentary recess in an opposed surface positively during rotation of that opposed surface with respect to the pawl member, the method for control of the present invention more particularly comprises, when changing down a gear with the forward pawls under load, such as when overtaking or accelerating, by the steps of: calling for a change; disengaging the reverse pawls of the presently selected gear; reducing engine power; disengaging the forward pawls of the presently selected gear; restoring engine power; and engaging the forward and then reverse pawls of the desired lower gear.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example only, with reference to three embodiments thereof and the accompanying drawings, in which:- Figure 1 is a schematic representation of a cross section through a first embodiment of the transmission system of the present invention, showing in particular high end and low end clutch packs located on a drive shaft, interposed between which are a series of pawl gear wheels engaging complimentary pawl gear wheels on a driven shaft; Figure 2 is a schematic representation of a cross section through a third embodiment of the transmission system of the present invention, showing on particular a single clutch pack located on a drive shaft and interposed between gear wheels of largest and smallest diameter provided thereabout; Figure 3 is a schematic representation of the clutch pack of Figure 2; Figure 4 is schematic representation of a cross section through a clutch pack for a transmission system in accordance with a fourth embodiment of the present invention; Figure 5 is a graphical representation of a change in acceleration as a function of time, associated with a transition from a low gear wheel pair to an intermediate gear wheel pair of higher ratio in a transmission system to which the method of the present invention is applied ; Figure 6 is a graphical representation of the degree of application of a support clutch mediating the engagement of the drive or driven gear wheel of a high gear wheel pair with a drive or driven shaft respectively, during the transition of Figure 1; and

Figure 7 is a graphical representation of car speed versus time, comparing a conventional six speed manual transmission to a six speed automatic transmission and a six speed constant mesh stepped ratio transmission to which the method of the present invention has been applied.

BEST MODE (S) FOR CARRYING OUT THE INVENTION In Figure 1 there is shown a transmission system 10, in accordance with one embodiment of the present invention, the transmission system 10 comprising a drive shaft 12, provided about which are a series of six pawl gear wheels 14,16, 18,20,22 and 24, such that the pawl gear wheels 14,16,18,20,22 and 24 may rotate freely and independently about the drive shaft 12. The pawl gear wheels are of known type, each being provided with forward and reverse pawls (not shown), as disclosed in International Patent Application PCT/AU98/00181. When required, the pawl gear wheels 14,16,18,20,22 and 24 may be engaged with and disengaged from the drive shaft 12 by known means (not shown), for example means disclosed in International Patent Applications PCT/AU98/00181 or PCT/AU97/00024, or Australian Provisional Patent Applications PP 5054 or PP 5035. The means for engaging and disengaging the pawl gear wheels is provided in a hollow bore 26 provided through at least a portion of the drive shaft 12.

The transmission system 10 further comprises a driven shaft 28, provided about which are a further series of six gear wheels 30,32,34,36,38 and 40, such that the gear wheels 30,32,34,36,38 and 40 rotate in conjunction with the driven shaft 28.

Each of the pawl gear wheels 14,16,18,20,22 and 24 provided on the drive shaft 12 engages a complimentary gear wheel 30,32,34,36,38 and 40 on the driven shaft 28, thereby providing a series of six gear wheel pairs 44,46,48,50, 52 and 54. The gear wheel pairs 44,46,48,50,52 and 54 enable the transmission of power from the drive shaft 12 to the driven shaft 28, and the relative diameters of the pawl gear wheels 14,16,18,20,22 and 24 and the gear

wheels 30,32,34,36,38 and 40 on the drive and driven shafts 12 and 28 of a gear wheel pair determine the gear ratio provided by that gear wheel pair.

The transmission of rotational energy from the drive shaft 12 to the gear wheel 14 is mediated by way of a hydraulic clutch pack of known type 56. Hydraulic pressure is applied to the clutch pack 56 by way of tubing 58 situated in the ho'slow bore 26 of the drive shaft 12. Similarly, the transmission of rotational energy from the drive shaft 12 to the gear wheel 24 is mediated by way of a hydraulic clutch pack 60. The hydraulic clutch pack 60 is provided with hydraulic pressure by way of tubing 62 in the hollow bore 26 of the drive shaft. The transmission of power from the power source (not shown) to the drive shaft is mediated by a launch clutch pack 63.

The engagement and disengagement of pawl gear wheels 14,16,18,20,22 to and from the drive shaft 12 is controlled by way of a programmable logic controller (not shown), as is the supply of hydraulic pressure to the clutch packs 56 and 60.

The method for control of the transmission system 10 will now be described in the context of use within a motor vehicle (not shown).

When accelerating from rest, first gear wheel pair 44 is typically selected, either by a user (not shown) or an engine/transmission management system (not shown). The gear wheel 14 is engaged with the drive shaft 12 by the known means for engaging and disengaging pawl gear wheels. Rotational energy provided to the drive shaft 12 is thereby transmitted to the gear wheel 14, in turn to the gear wheel 30 and on to the driven shaft 28. Control of the transmission of power from the source (not shown) to the drive shaft 12 is achieved by conventional means (not shown), for example a clutch or torque converter interposed therebetween.

When a higher gear ratio is called for, either by the user or the engine/transmission management system, the reverse pawls of the gear wheel of the first gear wheel pair 44 are disengaged from the drive shaft 12. The gear wheel 24 is partially engaged with the drive shaft 12 by way of the partial

engagement of the clutch pack 60. Rotational energy is now being transmitted to the driven shaft 28 from the drive shaft 12 by way of the sixth gear wheel pair 54.

This results in a drop in engine speed, and allows the retraction of the forward pawls of the gear wheel 14.

When the engine speed has decreased such that the engine speed almost matches the shaft speed of the desired gear ratio, as determined by the engine /transmission management system, the gear wheel corresponding to the gear wheel pair of the desired ratio, for example gear wheel 16 of the second gear wheel pair 46, is engaged with the drive shaft 12, and the gear wheel 24 simultaneously disengaged by way of the clutch pack 60, resulting in a substantially smooth transition between gear ratios.

Transition to the sixth gear wheel pair 54 cannot be assisted by way of the momentary engagement of a higher gear ratio as none is provided. Instead, the transition is smoothed by way of the clutch pack 60. The clutch pack 60 is engaged until the shaft speed almost matches then engine speed, then the pawls of the gear wheel 24 engage the drive shaft 12 and allow the clutch pack 60 to disengage, thus reducing the need for hydraulic power.

The transition from a higher gear ratio to a lower gear ratio when reverse pawls are under load, for example from that corresponding to the fourth gear wheel pair 50 to that corresponding to the third gear wheel pair 48 whilst engine braking, occurs by an analogous procedure. After a call for change, either by the user the engine/transmission management system, the forward pawls of the gear wheel 20 of the fourth gear wheel pair 50 are disengaged from the drive shaft 12.

Momentarily, the gear wheel 14 is partially engaged with the drive shaft 12 by way of the partial engagement of the clutch pack 56. Rotational energy is being transmitted to the driven shaft 28 from the drive shaft 12 by way of the first gear wheel pair 44. This results in an increase in engine speed, and allows the retraction of the reverse pawls of the gear wheel 20.

When the engine speed has increased to a suitable level, as determined by the engine/transmission management system, the gear wheel 18 of the third gear wheel pair 48 is engaged with the drive shaft 12, and the gear wheel 14 disengaged by way of the clutch pack 60, resulting in a substantially smooth transition between gear ratios.

Transition to the first gear wheel pair 44 cannot be assisted by way of the momentary engagement of a lower gear ratio as none is provided. Instead, the transition is smoothed by way of the clutch pack 56. The clutch pack 56 is engaged until the shaft speed almost matches the engine speed, then the pawls of the gear wheel 14 engage the drive shaft 12 and allow the clutch pack 56 to disengage.

The transition from a higher gear ratio to a lower gear ratio when forward pawls are under load, for example from that corresponding to the fourth gear wheel pair 50 to that corresponding to the third gear wheel pair 48 whilst overtaking or travelling uphill, utilises the launch clutch pack 63.

After a call for change, either by the user the engine/transmission management system, the reverse pawls of the gear wheel 20 of the fourth gear wheel pair 50 are disengaged from the drive shaft 12. The launch clutch pack 63 is allowed to slip, causing the engine speed to rise. Power is cut to the transmission system 10 for a period of about 10 ms, and the forward pawls of the gear wheel 20 of the fourth gear wheel pair 50 disengaged from the drive shaft, before the forward and reverse pawls of the gear wheel 18 engaged with the drive shaft 12, and the clutch plate 63 locked.

A second embodiment of the present invention is substantially identical to the transmission system 10, save for the exception that the clutch pack 56 is absent therefrom, and like numerals will be used to denote like parts. The methods for changing up and changing down under load are identical to those described above. However, the absence of the clutch pack 56 necessitates a different approach to down changing whilst reverse pawls are under load, for example whilst decelerating or engine braking.

Using a change from the gear ratio corresponding to the fourth gear wheel pair 50 to that corresponding to the third gear wheel pair 48 as an example, the procedure is as follows. After a call for change, either by the user the engine/transmission management system, the gear wheel 20 of the fourth gear wheel pair 50 is disengaged from the drive shaft 12, leaving the transmission momentarily without a gear engaged.

An increase in engine speed is then applied by way of a momentary opening of the throttle under the control of the engine/transmission management system.

When the engine speed is matched to the appropriate shaft speed for the lower gear ratio as determined by the engine/transmission management system, the gear wheels 18 and 34 are engaged with the drive and driven shafts 12 and 28 respectively.

In Figures 2 and 3 there is shown a transmission system 64, in accordance with a third embodiment of the present invention. The transmission system 64 is substantially identical to the transmission system 10 and like numerals denote like parts. However, the pawl gear wheels 14,16,18,20,22 and 24 are provided about the driven shaft 28, whilst the gear wheels 30,32,34,36,38 and 40 are fixed about the drive shaft 12. Further, clutch packs 56 and 60 have been replace by a single clutch pack 66, and the sequence of the gear wheel pairs 44, 46,48,50,52 and 54 altered such that the clutch pack 66 is interposed between the gear wheels 14 and 24 on the driven shaft 28 to form a clutch assembly 68, as can best be seen in Figure 2. Additionally, the clutch pack 63 is absent.

The clutch pack 66 comprises several clutch plates 70, fixed to the driven shaft 28 and several clutch plates 72 fixed to clutch housing 74, such that the clutch plates 72 are interleaved with the clutch plates 74, as can best be seen in Figure 3. The clutch housing 74 is independently rotatable about the driven shaft 28, and independently releasably engageable with each of the gear wheels 14 and 24, by way of engagement means in the form of pawl arrangements 76 and 78 respectively analogous to that disclosed in our International Application PCT/AU98/00181. Engagement of the clutch housing 74 with either of the gear

wheels 14 or 24 allows the clutch pack 66 to mediate the engagement of the gear wheel 14 or 24 with the driven shaft 28.

The method for control of the transmission system 64 is substantially identical to the transmission system 10, save for the exception that the clutch pack 66 fulfils the role of both the clutch packs 56 and 60. When the clutch pack 66 is required to mediate the transmission of power from the driven shaft 28 to the gear wheel 14, the clutch housing 74 is releasably engaged with the gear wheel 14 by way of the pawl arrangement 76, and disengaged from the gear wheel 24, before hydraulic pressure is applied. Similarly, when the clutch pack 66 is required to mediate the transmission of power from the driven shaft 28 to the gear wheel 24, the clutch housing 74 is releasably engaged with the gear wheel 24 by way of the pawl arrangement 78, and disengaged from the gear wheel 14 before hydraulic pressure is applied.

Additionally, when accelerating from rest, first gear wheel pair 44 is typically selected, either by a user (not shown) or an engine/transmission management system (not shown). The gear wheel 14 is engaged with the clutch housing 74 by way of the pawl arrangement 76. Rotational energy provided to the drive shaft 12 is thereby transmitted to the gear wheel 14, in turn to the gear wheel 30 and on to the driven shaft 28, as mediated by the clutch pack 66.

Further, the transition from a higher gear ratio to a lower gear ratio when forward pawls are under load, for example from that corresponding to the fourth gear wheel pair 50 to that corresponding to the third gear wheel pair 48 whilst overtaking or travelling uphill, necessarily differs due to the absence of the launch clutch pack 63.

After a call for change, either by the user the engine/transmission management system, the reverse pawls of the gear wheel 20 of the fourth gear wheel pair 50 are disengaged from the drive shaft 12. Engine power is reduced, and the forward pawls of the gear wheel 20 of the fourth gear wheel pair 50 disengaged from the drive shaft. Engine power is restored before the forward and reverse pawls of the gear wheel 18 engaged with the drive shaft 12.

In Figure 4 there is shown a clutch assembly 80, in accordance with a fourth embodiment of the present invention. The clutch assembly 80 is substantially identical to the clutch assembly 68 of the transmission system 64, and like numerals denote like parts.

However, the pawl arrangements 76 and 78 mediating the engagement of the gear wheels 14 and 24 with the clutch housing 74 are absent. In their place are provided conventional manual synchronisation assemblies 82 and 84, each comprising a synchronisation cone 86 and a dog ring 88 provided about the shaft 28. The clutch assembly 80 further comprises a fork actuator 90.

The operation of the clutch assembly 80 is similar to that of the clutch assembly 68 of the transmission system 64. When the clutch pack 66 is required to mediate the transmission of power from the driven shaft 28 to the gear wheel 14, the clutch housing 74 is moved toward the gear wheel 14 by the fork actuator 90. The synchronisation cone 86 interposed between the clutch housing 74 and the gear wheel 14 adjusts the rotational speed of the clutch housing 74. As the fork actuator 90 moves the clutch housing 74 toward the gear wheel 14, the dog ring 88 engages and the clutch plates 70 are brought into contact with the clutch plates 72, thereby engaging the clutch pack 66. The clutch is applied until synchronisation of the new gear ratio is correct for engagement. As the new gear engages, the clutch pack 66 is rapidly disengaged by way of a hydraulic relief valve (not shown). This arrangement has the advantage of not needing automatic transmission fluid.

Although the present invention is described in the context of a constant mesh style gearbox, it is to be understood that the present invention is applicable with considerable advantage to other types of gearbox, including a standard synchromesh manual gearbox or conventional automatic transmissions.

The method of the present invention will be further described by way of example only with reference to a constant mesh, stepped ratio transmission system (not shown) comprising a drive shaft and a driven shaft about each of which are provided six gear drive or driven gear wheels respectively forming first, second,

third, fourth, fifth and sixth gear wheel pairs in constant meshed engagement.

The drive gear wheels are releasably engageable with the drive shaft by a pawl type mechanism such as that described in PCT/AU98/00181 (W098/41779), and the engagement of the driven gear wheel of the sixth gear wheel pair with the driven shaft is mediated by a support clutch.

The change in gear ratio discussed in this example corresponds to a change from the first gear wheel pair to the second gear wheel pair, by way of the sixth gear wheel pair. Thus, for the purposes of the present example, the first gear wheel pair corresponds to the low gear wheel pair discussed in the Summary of the Invention, the second gear wheel pair to the intermediate gear wheel pair, and the sixth gear wheel pair to the high gear wheel pair.

Figure 5 shows the acceleration, which is proportional to the torque, generated by the system when the first gear wheel pair is engaged, the acceleration corresponding to approximately 0.6g. At about 0.10 seconds, a call for a change in gear ratio is initiated, either by a user, or an engine/transmission management system.

The sixth gear wheel pair is engaged by way of the support clutch, causing the spontaneous disengagement of the first gear wheel pair. In a conventional system, disengagement of the first gear wheel pair would result in a marked decrease in available torque and a noticeable and undesirable momentary deceleration. However, the engagement of the sixth gear wheel pair, accompanied by an increase in power from the engine combines with the inertia of the engine to ease the transition to second gear. Initially, the support clutch is applied at a high level to provide the necessary torque, but is applied to a decreasing degree until the second gear wheel pair is engaged at about 0.56 seconds, once synchronisation of shaft speed is attained.

This decrease in the degree to which the support clutch is applied is most readily apparent from Figure 6. Initially, the clutch is applied such that the sixth gear wheel pair provides approximately 1250 Nm of torque. However, by the time the

second gear wheel pair is engaged, at about 0.56 seconds, the torque provided through the support clutch has dropped to approximately 700 Nm.

Figure 7 shows that the maintenance of torque during transitions between gear wheel pairs achieves a markedly more efficient use of power than both the manual and automatic transmissions, as reflected in the greater car speeds, and a ride of comparable or superior smoothness to the automatic transmission.

Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.