BACKGROUND ART In existing manual transmission systems, reverse gear typically occupies as much space on the shaft as any other gear. In many applications, such as in motor racing, considerable advantage can be obtained by minimising the length of the transmission system. Indeed, in some applications, a reverse gear is sacrificed in favour of such advantage.

The improved transmission system of the present invention has as one object thereof the provision of a reverse gear without increasing the length of the transmission system.

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.

DISCLOSURE OF THE INVENTION In accordance with the present invention there is provided an improved transmission system comprising a drive shaft, provided about which are at least two drive gear wheels, a driven shaft, provided about which are provided at least two driven gear wheels, and an idler shaft, provided about which are at least two idler gear wheels, wherein the drive gear wheels are in constant meshed engagement with the driven gear wheels to form at least two gear wheel pairs, and at least one of said idler gear wheels is in constant meshed engagement with one

of said drive gear wheels and at least another of said idler gear wheels is in constant meshed engagement with one of said driven gear wheels comprising, with the idler shaft, at least one reverse gear train, and wherein at least the drive gear wheel of the gear wheel pair in which the driven gear wheel is engaged with one of said idler gear wheels is releasably engageable with the drive shaft, and wherein at least one of said drive gear wheels in constant meshed engagement with one of said idler gear wheels, said driven gear wheels in constant meshed engagement with one of said idler gear wheels, said at least two idler gear wheels and said idler shaft of the reverse gear train is releasably engageable with another of said drive gear wheels in constant meshed engagement with one of said idler gear wheels, said driven gear wheels in constant meshed engagement with one of said idler gear wheels, said at least two idler gear wheels and said idler shaft of the reverse gear train, or the drive or driven shafts, such that the releasable engagement of such governs whether power is transmitted directly from the drive shaft to the driven shaft, or indirectly by way of the idler shaft, and thereby determines the direction of rotation of the driven shaft.

Preferably, the driven gear wheel of the gear wheel pair in which the drive gear wheel is engaged with one of said idler gear wheels is releasably engageable with the driven shaft.

In one form of the invention, the drive and driven gear wheels of the reverse gear train are releasably engageable with the drive and driven shafts respectively, whilst the idler gear wheels are fixed to the idler shaft.

In a further form of the invention, at least one of said idler gear wheels of the reverse gear train is releasably engageable with the idler shaft wheels of the reverse gear train, and the drive and driven gear wheels of the reverse gear train are fixed to the drive and driven shafts respectively.

In a still further form of the invention, the idler shaft comprises first and second releasably engageable idler shaft elements, fixed about each of which is provided at least one idler gear wheel. In a preferred form of the invention, the engagement of the first and second idler shaft elements is effected by way of deployable

projections in an annular receiving portion in either the first or second drive shaft elements being received by complimentary recesses in the corresponding portion.

Preferably, the drive and driven gear wheels are of differing diameters so as to form gear wheel pairs corresponding to different gear ratios.

Preferably, several gear wheel pairs which are not engaged with the idler gear wheels are provided about the drive and driven shafts providing a range of gear ratios. For each gear wheel pair not engaged with the idler gear wheels, either the drive or driven gear wheel is releasably engageable with the drive or driven shaft.

For each pair of gear wheel pairs engaged with the idler gear wheels, the improved transmission system is preferably further provided with at least one gear wheel pair which is not engaged with the idler gear wheels and which corresponds to a gear ratio intermediate the gear ratios of the pair of gear wheel pairs so engaged.

Preferably, the improved transmission system further comprises means to control the releasable engagement of gear wheels with shafts, the means being adapted to control the releasable engagement of the drive, driven or idler gear wheels with the drive, driven or idler shafts respectively.

The or each means to control the releasable engagement gear wheels with shafts may be analogous to that disclosed in our earlier International Patent Applications PCT/AU97/00024 (W097/26468) (A Gear System with Gears Selectively Locked with Shaft), PCT/AU98/00181 (W098/41779) (Preload Constant Mesh Gearbox), PCT/AU99/00630 (Method and Apparatus for Controlling the Engagement and Disengagement of Gear Wheels) or PCT/AU99/00629 (Method and Apparatus for Engaging and Disengaging Gear Wheels), the contents of which are hereby incorporated by reference.

In accordance with the present invention there is further provided a method for use of the improved transmission system of the present invention, where the drive and driven gear wheels of the reverse gear train are releasably engageable with the

drive and driven shafts respectively, the method comprising, when engaging a reverse gear, the steps of: Engaging the drive shaft with a drive gear wheel engaged with an idler gear wheel; Engaging the driven shaft with a driven gear wheel engaged with an idler gear wheel other than that to which the drive gear wheel is engaged; and Disengaging all other releasably engageable drive and driven gear wheels from the drive and driven shafts respectively.

In accordance with the present invention there is further provided a method for use of the improved transmission system of the present invention, where at least one of said idler gear wheels of the reverse gear assembly is releasably engageable with the idler shaft, and the drive and driven gear wheels of the reverse gear train are fixed to the drive and driven shafts respectively, the method comprising, when engaging a reverse gear, the steps of: Engaging the idler shaft with the or each idler gear wheel of the reverse gear train; and Disengaging all other drive and driven gear wheels from the drive and driven shafts respectively.

When disengaging a forward gear corresponding to a gear wheel pair engaged with an idler gear wheel, where the drive and driven gear wheels of the reverse gear train are releasably engageable with the drive and driven shafts respectively, the method comprises the step of: Completely disengaging both the drive gear wheel from the drive shaft and the driven gear wheel from the driven shaft.

When engaging a forward gear corresponding to a gear wheel pair engaged with an idler gear wheel, where at least one of said idler gear wheels of the reverse

gear train is releasably engageable with the idler shaft, and the drive and driven gear wheels of the reverse gear train are fixed to the drive and driven shafts respectively, the method comprises the steps of: Ensuring that the or each idler gear wheel is completely disengaged from the idler shaft; and Engaging the drive or driven gear wheels of the desired gear wheel pair with the drive or driven shafts respectively.

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 partial axial cross section through an improved transmission system in accordance a first embodiment of the present invention, showing in particular a drive shaft and a driven shaft about which are provided drive and driven gear wheels respectively forming gear wheel pairs, and an idler shaft about which are provided idler gear wheels in constant mesh engagement with drive or driven gear wheels; Figure 2 is a simplified end view of the improved transmission system of Figure 1, showing only the idler shaft and gear wheel pairs in which a drive or driven gear wheel is engaged with an idler gear wheel; Figure 3 is a schematic partial axial cross section through an improved transmission system in accordance a second embodiment of the present invention; and Figure 4 is a schematic partial axial cross section through an improved transmission system in accordance a third embodiment of the present invention, showing in particular first and second releasably engageable idler shaft elements.

BEST MODE (S) FOR CARRYING OUT THE INVENTION In Figures 1 and 2 there is shown an improved transmission system 10, in accordance with a first embodiment of the present invention, comprising a driven shaft 12, a drive shaft 14, and idler shaft 16. Provided about the driven shaft 12 are a series of six driven gear wheels 18,20,22,24,26 and 28, such that the driven gear wheels 18,20,22,24,26 and 28 are releasably engageable with the driven shaft 12, and may rotate freely and independently thereabout.

Similarly, provided about the drive shaft 14 are a series of six drive gear wheels 30,32,34,36,38 and 40, in constant meshed in constant meshed engagement with complimentary driven gear wheels 18,20,22,24,26 and 28 thereby providing a series of six gear wheel pairs 42,44,46,48,50 and 52, as can best be seen in Figure 1. Drive gear wheels 30,32,34 and 38 are fixed to the drive shaft 14, whilst drive gear wheels 36 and 40 are releasably engageable therewith and may rotate freely and independently thereabout.

The gear wheel pairs 42,44,46,48,50 and 52 enable the transmission of power from the drive shaft 14 to the driven shaft 12, and the relative diameters of the drive gear wheels 30,32,34,36,38 or 40 and the driven gear wheels 18,20,22, 24,26 or 28 of a gear wheel pair 42,44,46,48,50 or 52 determine the gear ratio provided by that gear wheel pair 42,44,46,48,50 or 52.

Provided about the idler shaft 16 are idler gear wheels 54 and 56. The idler gear wheels 54 and 56 are fixed about the idler shaft 16. The idler gear wheel 54 is in constant meshed engagement with the driven gear wheel 24, whilst the idler gear wheel 56 is in constant meshed engagement with the drive gear wheel 40, to form a reverse gear train comprising drive gear wheel 40, idler gear wheel 56, idler shaft 16, idler gear wheel 54 and driven gear wheel 24, as can be seen in Figure 2. The gear wheel pair 50 is of intermediate gear ratio relative to the gear wheel pairs 48 and 52, engaged to the idler gear wheels 54 and 56.

The driven gear wheels 18,20,22,24,26 and 28 and the drive gear wheels 36 and 40 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 driven gear wheels 18,20,22,24,26 and 28 and the drive gear wheels 36 and 40 may be engaged with, and disengaged from, the driven and drive shafts 12 and 14 respectively, by known engagement means 58 to control the releasable engagement of gear wheels with shafts 12 and 14, such as those disclosed in International Patent Applications PCT/AU98/00181, PCT/AU97/00024, PCT/AU99/00629 or PCT/AU99/00630. The means 58 are provided in hollow bores 60 and 62 provided through at least a portion of the driven and drive shafts, 12 and 14 respectively.

The engagement and disengagement of driven gear wheels 18,20,22,24,26 and 28 to and from the driven shaft 12, and the drive gear wheels 36 and 40 from the drive shaft 14 is controlled by way of a programmable logic controller (not shown).

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

When engaging reverse gear, a user (not shown) or more typically an engine management system (not shown) instigates the engagement of the drive shaft 14 with the gear wheel 40, and the driven shaft 12 with the gear wheel 24, by way of the engagement means 58. The user or engine management system then ensures that all other driven gear wheels 18,20,22,26 and 28 are disengaged from the driven shaft 12, and the drive gear wheel 36 from the drive shaft 14, also by way of the engagement means 58. The application of power to the drive shaft 14 causes rotation thereof, and rotation of drive gear wheels 30,32,34 and 38 which are fixed to the drive shaft 14 in addition to drive gear wheel 40 which is releasably engaged with the drive shaft 14.

Rotation is imparted to the idler gear wheel 56, although in a direction counter to that of the drive shaft 14, by way of its meshed engagement with the drive gear wheel 40, and accordingly, to the idler shaft 16 to which the idler gear wheel 56 is

fixed. Whilst rotation is imparted to the driven gear wheel 28 by way of its meshed engagement with the drive gear wheel 40, disengagement of the driven gear wheel 40 from the driven shaft 12 prevents rotational force being imparted to the driven shaft 12 by this arrangement.

The rotation of the idler shaft 16 induces rotation of the idler gear wheel 54, which by way of its meshed engagement therewith, induces rotation of the driven gear wheel 24, although in the opposite direction. The driven gear wheel 24, being engaged with the driven shaft 12, causes such to rotate. Whilst rotation is imparted to the drive gear wheel 36 by way its meshed engagement with the driven gear wheel 24, disengagement of the drive gear wheel 36 from the drive shaft 14 prevents rotation being imparted to the drive shaft 14 by this means.

Accordingly, rotational motion may be imparted to the driven shaft 12 in the opposite direction to that which would be imparted by direct transfer from the drive shaft 12 to the driven shaft 14, thereby creating a reverse gear.

When using the forward gears of the improved transmission system 10, where rotation is imparted directly from the drive shaft 14 to the driven shaft 12, and disengaging a forward gear corresponding to the a gear wheel pairs 48 and 52 engaged with the idler gear wheels 54 and 56, the user or engine management system must disengage both the drive and driven gear wheels 24 and 36, or 28 and 40 of the gear wheel pair 48 or 52. Failure to do so will result in two forward gears being engaged simultaneously, or conflicting rotational forces being imposed on the drive shaft 14.

Further, when changing from the forward gear corresponding to gear wheel pair 48 to the forward gear corresponding to gear wheel pair 52, the user or engine managements system must engage the gear corresponding to gear wheel pair 50, being of intermediate gear ratio and not engaged with an idler gear wheel 54 or 56.

In Figure 3 there is shown an improved transmission system 59, in accordance with a second embodiment of the present invention. The improved transmission system is substantially identical to the improved transmission 10, and like numbers

denote like parts. However, the drive gear wheel 40 is fixed to the drive shaft 14 and the driven gear wheel 24 fixed to the driven shaft, whilst the idler gear wheel 54 is releasably engaged with the idler shaft 16 by way of the engagement means 58.

When engaging reverse gear, a user (not shown) or more typically an engine management system (not shown) engages the idler gear wheel 54 with the idler shaft 16, by way of said engagement means 58, before disengaging all other drive and driven gear wheels, including the drive wheel 36 and the driven gear wheel 28 from the drive and driven shafts 14 and 12 respectively, also by way of said engagement means 58.

The application of power to the drive shaft 14 causes rotation thereof, and rotation of drive gear wheels 30,32,34,38 and 40 fixed thereto. The drive gear wheel 36, being disengaged from the drive shaft 14, does not rotate. Rotation is imparted to the idler gear wheel 56, although in a direction counter to that of the drive shaft 14, by way of its meshed engagement with the drive gear wheel 40, and accordingly, to the idler shaft 16.

Engagement of the idler gear wheel 56 with the idler shaft 16 causes the idler gear wheel 56 to rotate, and by way of its meshed engagement with the driven gear wheel 24, causes such to rotate, although in the opposite direction to the idler shaft 16. Whilst rotation is imparted to the drive gear wheel 36 by way its meshed engagement with the driven gear wheel 24, disengagement of the drive gear wheel 36 from the drive shaft 14 prevents rotation being imparted to the drive shaft 14 by this means. Accordingly, rotational motion may be imparted to the driven shaft 12 in the opposite direction to that which would be imparted by direct transfer from the drive shaft 12 to the driven shaft 14, thereby creating a reverse gear.

When the user or engine management system wishes to engage a forward gear corresponding to a gear wheel pair 48 or 52 engaged with an idler gear wheel 54 or 56, the user or engine management system first ensures that the idler gear wheel 56 is completely disengaged from the idler shaft 16, before engaging the

drive or driven gear wheels 36 or 28 of the desired gear wheel pair 48 or 52 with the drive or driven shafts 14 or 12 respectively.

In Figure 4 there is shown an improved transmission 60, in accordance with a third embodiment of the present invention. The improved transmission system 60 is substantially identical to the improved transmission 10, and like numbers denote like parts. However, the idler shaft 16 comprises first and second releasably engageable idler shaft elements 62 and 64, the drive gear wheel 40 is fixed to the drive shaft 14, and the driven gear wheel 24 is fixed to the driven shaft.

The engagement of the first and second idler shaft elements 62 and 64 is effected by way of deployable projections 66, in an annular receiving portion 68 of the second drive shaft element, releasably engaging a portion 70 of the first drive shaft element received therein.

In use, the improved transmission system 60 is substantially identical to the improved transmission system in accordance with a second embodiment of the present invention. However, the step of engaging the idler gear wheel 54 with the idler shaft 16 is replaced by the step of engaging the first idler shaft element 62 with the second idler shaft element 64.

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