The present invention relates to a gear mechanism for power transmission. In particular, the present invention relates to a multiple speed power transmission gear mechanism.

Standard power transmission mechanisms typically comprise fixed gears mounted on a transmission output shaft and a cluster gear assembly mounted on, or formed as part of, a counter shaft wherein the fixed gears engage with the cluster gears of the counter shaft. An example of a simple transmission gear mechanism 2 is shown in Figure 1. Wherein power is supplied from an engine (not shown) which drives shaft 10 which is provided with fixed connector gear 12 which is in direct engagement with gear 14 on transmission output shaft 18. Transmission output shaft 18 is also provided with fixed gears 15 and 16. Fixed gears 15 and 16 are engaged with gears 20 and 21 respectively of cluster gear assembly 22 which is located on counter shaft 24. The counter shaft 24 is a sp lined shaft which can be in direct connection with, for example, the differential (not shown) of a car. Gears 20 and 21 are mounted on bearings (not shown) and thus can spin on shaft 24. Sliding gear 26, which in this case is provided on a gear selector fork 28 can, at any time, selectively engage any one of gears 20, 21 in the cluster gear assembly 22. Use of the gear selector 18 can determine which of gears 20, 21 the sliding gear 26 will engage with and thus effect the desired transmission of power from the

transmission output shaft 18 to the counter shaft 24. This power can then, in this example, effect forward motion at a desired speed by transmission through the differential (not shown) to the wheels of a car.

It will be appreciated that a transmission mechanism such as mechanism 2 will be built with suitable tolerances to enable ease of manoeuvre between gears. As can also be seen, gear mechanisms such as mechanism 2, require the provision of gears, such as gears 20 and 21 which will be in permanent rotation which transmission output shaft 18 is rotating but at any given time, at least one of gears 20 and 21 will be rotating freely. When one or both of gears 20, 21 is not engaged and transmitting power, the tolerances which ensure ease of manoeuvre will unfortunately allow a degree of movement, and due to this, wear and tear, as well as energy loss, is experienced in the gear mechanism 2. Furthermore, the arrangement of mechanism 2 requires a volume of space, to enable disengagement and engagement of the desired gears as and when required.

It is an object of the present invention to obviate or mitigate at least one of the aforementioned problems.

According to a first aspect of the invention there is provided a gear mechanism comprising a first rotatable shaft having a first axis; a first plurality of gears mounted coaxially on the first shaft, and rotatable therewith, each gear of the first plurality of gears being moveable axially with respect to the other gears of the first plurality, a second rotatable shaft having a second axis; and a second plurality of gears mounted coaxially on the second shaft, and rotatable therewith, each gear of the second plurality of gears being movable axially with respect to the other gears of the second plurality, wherein the gear mechanism has a plurality of engagement positions in which a gear of the first plurality is engaged with a gear of the second plurality.

The provision of a first and second plurality of gears which can be moved axially such that a gear of the first plurality can engage with a gear of the second plurality provides a compact gear mechanism with a range of selectable gear engagement options.

Preferably, the second plurality of gears is biased towards first plurality of gears which enables a gear of the second plurality of gears to be selectably engaged by a gear from the first plurality of gears. The first plurality of gears may comprise a series of gears having an innermost gear adjacent the first rotatable shaft and subsequent gears increasing in outer diameter and engagable with the previous gear of the series. The circumferential organisation of gears outwards from the first rotatable shaft provides a compact first gear set arrangement.

Preferably the innermost gear of the first plurality of gears is connected with the first rotatable shaft which enables the rotation of the first rotatable shaft to drive the first plurality of gears.

The second plurality of gears may comprise a series of gears having an innermost gear adjacent the second rotatable shaft and subsequent gears increasing in outer diameter and engagable with the previous gear of the series. The circumferential organisation of gears outwards from the second rotatable shaft provides a compact second gear set arrangement.

Preferably, the innermost gear of the second plurality of gears is connected with the second rotatable shaft which enables the rotation of the second plurality of gears to drive the second rotatable shaft.

An outer gear of the first plurality of gears may engage with an inner gear of the second plurality of gears. Similarly, an outer gear of the second plurality of gears engages with an inner gear of the first plurality of gears. The selection of an outer gear to engage with an inner gear is facilitated by the biasing of the second plurality of gears towards the first plurality of gears and enables power input to the mechanism through the first rotatable shaft to be transmitted at a desired gear ratio to the second rotatable shaft. The gear mechanism may be provided with a synchroniser mechanism. Each gear of the first plurality of gears may be formed of two gear parts such that the synchroniser mechanism is selectably engagable with each of the two gear parts of a selected gear.

Preferably the synchroniser mechanism is formed of an inner unit and an outer unit. The inner unit may be operable to engage frictionally with a selected gear and the outer unit may be provided with gear parts which are operable to engage with the selected gear.

An embodiment of the invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 illustrates a known gear mechanism;

Figure 2 illustrates a cross section view of a gear mechanism according to the first embodiment of the present invention in a neutral state;

Figure 3 illustrates a plan view of a gear set of the gear mechanism of Figure 2;

Figure 4 illustrates a cross section view of the gear mechanism of Figure 2 in an engaged state; Figure 5A illustrates a detail of a plan view and corresponding cross section of a detail of a gear mechanism provided with a synchronisation mechanism according to a second embodiment of the present invention;

Figure 5B illustrates a perspective view of a detail of the gear mechanism of Figure 5 A; Figure 6A illustrates a cross section of the synchronisation mechanism of Figure 5 A in an unengaged state; Figure 6B illustrates a cross section of the synchronisation mechanism of

Figure 5 A in an engaged state;

Figure 7 illustrates a cross section view of the gear mechanism of Figure 5A in an un-engaged state;

Figure 8 illustrates a cross section view of the gear mechanism of Figure 5A in a partially engaged state; and

Figure 9 illustrates a cross section view of the gear mechanism of Figure 5 A in a fully engaged state.

In Figure 2 there is shown a cross section of a gear mechanism 30, in a neutral, unengaged, state, comprising a first plurality of gears 32 mounted on a first rotatable shaft 34, which in this case is the input shaft, and a second plurality of gears 36 mounted on a second rotatable shaft 38 which in this case is the output shaft, wherein the first rotatable shaft 34 is arranged in parallel to but spaced apart from second rotatable shaft 38.

The first plurality of gears 32 comprises three gears 40, 42, 44 arranged co-axially with inner surface 40a of innermost gear 40 connected directly to first rotatable shaft 34, outer gear teeth 40b of gear 40 are enmeshed with inner gear teeth 42a of gear 42. Gear 44 is of greater diameter than gear 42 with outer gear teeth 42b of gear 42 enmeshed with inner gear teeth 44a of gear 44. Gears 40, 42 and 44 are arranged such that in the neutral position they lie together forming first planar surface 46 and second planar surface 48. The second plurality of gears 36 comprises three gears 50, 52, 54 arranged coaxially with inner surface 50a of innermost gear 50 connected directly to first rotatable shaft 36, outer gear teeth 50b of gear 50 are enmeshed with inner gear teeth 52a of gear 52. Gear 54 is of greater diameter than gear 52 with outer gear teeth 52b of gear 52 enmeshed with inner gear teeth 54a of gear 54. Gears 50, 52 and 54 are arranged such that in the neutral position they lie together forming a third planar surface 56 and a fourth planar surface 58. The first plurality of gears 32 and second plurality of gears 36 are arranged such that between the first rotatable shaft 34 and the second rotatable shaft 38 the second planar surface 46 is adjacent third planar surface 56 whereby the second plurality of gears 36 is biased towards the first plurality of gears 32. In Figure 3 is shown a schematic representation of a cross section through first plurality of gears 32 which clearly illustrates the co-axial arrangement of gears 40, 42 and 44 arranged around rotatable shaft 34. Between gear teeth 40b and 42a can be seen a tolerance gap 41 , and between gear teeth 42b and 44a can be seen a tolerance gap 43. It will be clearly understood that a cross section through the second plurality of gears would be similarly represented.

In Figure 4 is shown a schematic representation of a cross section of the gear mechanism 30 in use, such that it is in an engaged state, whereby an actuator 31 , which in this case is a strut, has been applied to the first plurality of gears 32 in the direction indicated by arrows A such that gear 42 has been selected and thus the actuator pushes shaft 34, gear 40 and gear 42 forwards such that they act against gears 52 and 54 of the second plurality of gears 36 which are biased against the first plurality of gears 32. Thus gears 40 and 42 push gears 52 and 54 out of alignment with gear shaft 38 and gear 50 such that gear teeth 42b engage with gear teeth 50b thus enabling power to be transmitted from shaft 34 to shaft 38. It will be appreciated that for an efficient performance of the gear mechanism, there is provided, between the planar surfaces 48 and 56, a mechanism (not shown) to alleviate effect of friction which in this case is an oil based lubricant fluid.

Figures 5 A and 5B show a plan view detail and corresponding cross section and perspective view of gear 142 of a first plurality of gears (not shown). Gear 142 is provided with has inner gear teeth 142a, outer gear teeth 142b and first planar surface 146 and second planar surfacel48. As can be seen, gear 142 is formed of two sections 142c and 142d respectively between which is formed a "V" shaped channel 149, the opposing upper edges of which are provided with inner gear teeth 149a and outer gear teeth 149b respectively. Gear 142 is further provided with a synchronisation mechanism 160 formed of an outer ring 162 and an inner ring 164. The outer ring 162 is provided with inner gear teeth 162a and outer gear teeth 162b which are arranged at opposing edges of outer planar surface 162d so that they project beyond inner planar surface 162. Inner ring 164 projects from outer ring 162 and is provided with a "V" shaped profile from by profile sides 164a and 164b such that the profile correspond to the profile of channel 149. In Figures 6A and 6B the cross section of the synchronisation mechanism 160 is shown in more detail. As can be seen, the inner gear teeth 162a and outer gear teeth 162b of outer ring 162 extend beyond inner planar surface 162c creating a recess 163. Inner ring 164 is arranged such that lower profile surfaces 164a and 164b are provided with an upper profile surfaces 164e and 164f respectively which are of a size that upper profile surfaces 154e, 164f and upper surface 164c of inner ring 164 can be received into the recess 163 formed by outer ring 162. The lower profile surfaces 164a and 164b and upper surface 164c of the inner ring are provided with a serrated texture. The inner planar surface 162c of outer ring 162 is connected to the upper surface 164c of inner ring 164 by resilient members 166 which in this case are coiled springs which are set into recesses 165 in the upper surface 164c of inner ring 164. When the synchronisation mechanism 160 is in an un-engaged position such as is shown in Figure 6A, the springs 166 are not compressed and project beyond the upper surface 164c of inner ring 164 such that the inner planar surface 162c of outer ring 162 and the upper surface 164c of inner ring 164 are spaced apart. When the synchronisation mechanism 160 is in an engaged position such as is shown in Figure 6B, the springs 166 are fully compressed and are fully contained within recesses 165 such that the inner planar surface 162c of outer ring 162 and the upper surface 164c of inner ring 164 are in direct frictional contact by way of the serrated texture of upper surface 164c.

With reference to Figures 7, 8 and 9, the synchronization mechanism 160 can be seen to act on gear 142 when in use with second plurality of gears 150. In Figure 7, is shown the arrangement as a gear, in this case gear 142, is selected and an actuator (not shown) begins to act on gear 142 in the direction shown by arrow A. At this point in time, the selected gear 142 and the gear 152 which will be displaced are not in contact with one another. The two parts 142c and 142c are still in direct contact with one another and act as a single unit, and synchronization mechanism 160 is not acting upon gear 142. As the actuator moves gear 142 towards gear 152, the upper surface 162d or the outer ring 162 of synchronization mechanism 160 is first to come into contact with surface 156 of gear 152. As the force exerted by the actuator pushes gear 142 further towards gear 152, more force is exerted on the outer ring 162 of the synchronization mechanism 160. The force acting on the outer ring 162 is transferred through springs 166 to inner ring 164 causing the upper profiles surfaces 164e and 164f and upper surface 164c to be received into the recess 163 whilst also pushing lower profile surfaces 164a and 164b of inner ring 164 into contact with channel surfaces 149c and 149d. The contact between lower profile surfaces 164a and 164b of inner ring 164 and channel surfaces 149c and 149d causes the gear parts 142c and 142d to separate at split 142f . The serrated texture provided on lower profile surfaces 164a and 164b break down any lubricant oil film provided on the channel surfaces 149c and 149d and friction causes the inner ring 164 and gear 142 to rotate at the same speed without at this stage engaging the inner gear teeth 149a and outer gear teeth 149b of gear parts 142c and 142d respectively with inner gear teeth 162a and outer gear teeth 162b of the outer ring 162.

As is shown in Figure 8, only once sufficient force has been applied by the actuator to gear 142 such that the displaced gear 162 cannot be moved any further and inner ring 164 is fully inserted into recess 163, does the inner gear teeth 149a and outer gear teeth 149b of gear parts 142c and 142d engage respectively with inner gear teeth 162a and outer gear teeth 162b of the outer ring 162 causing the gear 142 to become locked into a single unit and engaged with the appropriate gear 150 of the second plurality of gears 136.

It will be clearly understood that the process of disengaging selected gears will follow the above process, described with reference to Figures 7, 8 and 9, in reverse order.

Although aspects of the invention have been described with reference to the embodiment shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort, for example the mechanism to alleviated the effects of friction is detailed as being an oil based lubricant fluid, however alternative mechanisms could be used including, but not limited to, bearings.