GB2472838A

GB2472838A - Dog drive

Info

Publication number: GB2472838A
Application number: GB0914604A
Authority: GB
Inventors: William Hewland
Original assignee: HEWLAND ENGINEERING Ltd
Current assignee: HEWLAND ENGINEERING Ltd
Priority date: 2009-08-21
Filing date: 2009-08-21
Publication date: 2011-02-23
Also published as: GB0914604D0

Abstract

A dog drive assembly 100 for an automotive gearbox that includes a hub 102 for coupling to a gear shaft and a clutch ring 103 slidably coupled to the hub 102 for rotation with the hub 102. The clutch ring 103 includes a plurality of dogs (132, fig 4) and is slideable along the hub 102 to engage or disengage the dogs (132, fig 4) with cooperating dogs 42 on a gear 4 that is rotatably mounted coaxially with respect to the hub 102 in order to selectively couple or uncouple the hub 102 to the gear 4. The slideable coupling between the clutch ring 103 and the hub 102 is provided by a plurality of splines (134, fig 4) projecting inwardly from the clutch ring 103 which cooperate with slots 120 in the circumferential surface of the hub 102.

Description

DRIVE ASSEMBLY

This invention relates generally to drive assemblies for a non-synchromesh automotive gearbox and more specifically, although not exclusively, dog drive assemblies incorporated in an automotive gearbox.

Drive dogs are used extensively in the transmission of drive power from rotating shafts to the gears in gearboxes for high performance race car applications. Drive dogs enable fast changes between gears, which is necessary to minimise the interruption of drive power from the engine to the road wheels. The dog drive assembly must be monitored and maintained on a regular basis since the aggressive nature of the transition into drive often results in damaged components. Drive dogs are generally not adopted in road car gearbox applications because of their need for continual maintenance and replacement of expensive components.

Known dog drive assemblies generally include a hub secured to a gearbox main shaft or lay shaft, a clutch ring slidably coupled to the hub for rotation therewith and a gear rotatably mounted coaxially with respect to the hub. The clutch ring includes a plurality of dogs and is slidable along the hub to engage or disengage corresponding dogs on the gear to selectively couple or uncouple the gearbox main shaft or lay shaft to the gear.

The slideable coupling between the clutch ring and the hub is provided by a plurality of splines projecting from the hub which cooperate with correspondingly shaped slots in a facing surface of the dog ring. It is known to align the slots with the dogs such that the slots are formed in part in the dogs themselves in order to maximise the length of the splined engagement.

However, whilst this arrangement improves the strength and reliability of the splined engagement, the applicants have observed that this has a detrimental effect on the robustness of the dogs.

It is therefore a specific non-exclusive object of this invention to provide a dog drive assembly which mitigates the aforementioned issues. It is a more general non-exclusive object of the invention to provide an improved and more robust dog drive assembly.

One aspect of the invention provides a drive assembly, e.g. a dog drive assembly, for an automotive gearbox, the assembly comprising a hub for coupling to a gear shaft and a clutch ring slidably coupled to the hub for rotation therewith, the clutch ring having a plurality of protrusions or dogs and being slideable along the hub to engage or disengage the protrusions or dogs with cooperating protrusions or dogs on a gear rotatably mounted, in use, coaxially with respect to the hub to selectively couple or uncouple the hub to the gear, wherein the slideable coupling between the clutch ring and the hub is provided by a plurality of splines projecting inwardly from the clutch ring which cooperate with slots in the outer, e.g. circumferential, surface of the hub.

This arrangement provides additional robustness to the clutch ring and, more specifically, makes the dogs more robust and less susceptible to damage and/or wear. Thus, the dogs may be smaller, thereby reducing the time required to effect the shift and reducing the interruption of drive power from the engine to the road wheels.

At least one of the splines is preferably aligned with one of the protrusions or dogs, e.g. such that the at least one spline projects in part from the protrusion or dog. This is arrangement further increases the robustness of the protrusions or dogs and permits their size to be reduced even further. More preferably, the clutch ring comprises the same number of splines to the number of protrusions or dogs, or a number of splines which is divisible by the number of protrusions or dogs, for example such that one spline projects in part from each protrusion or dog. The clutch ring may further comprise a plurality of protrusions or dogs extending from each side thereof, wherein each protrusion or dog on one side may be aligned with a protrusion or dog on the other side.

The or at least one of the splines may comprise an involute shape or profile, a full radius root shape or profile or a straight sided shape or profile. The or at least one of the slots of the hub preferably comprises substantially the same or a corresponding or a cooperating shape or profile. The or at least one of the slots preferably comprises a slightly larger cross-section, e.g. to allow sliding movement between the clutch ring and the hub.

The clutch ring may be machined, for example the protrusions or dogs may be machined into or onto the clutch ring, e.g. one or both of its end faces. The clutch ring may advantageously have protrusions or dogs on both of its end faces and/or may be configured to cooperate, in use, with two gears, e.g. which are rotatably mounted, in use, coaxially with respect to the hub. For example, the clutch ring may be slideable along the hub between the two gears, e.g. for engagement or disengagement with corresponding protrusions or dogs on facing portions of each gear, e.g. to selectively couple or uncouple the hub to one of the two gears. The clutch ring is preferably formed of metal, e.g. steel.

The assembly may include the gear, for example rotatably mounted coaxially with respect to the hub, which may include protrusions or dogs on one of its end faces, e.g. machined into or onto one of the end faces of the gear. The protrusions or dogs of the clutch ring preferably cooperate, e.g. are matched, in use, with the protrusions or dogs of the gear to selectively couple the hub to the gear.

A second aspect of the invention provides an automotive gearbox comprising the protrusion or dog drive assembly described above.

A third aspect of the invention provides an automobile comprising the gearbox or protrusion or dog drive assembly described above.

A fourth aspect of the invention provides a kit of parts for assembly into the protrusion or dog drive assembly described above. The kit may comprise the hub and/or the clutch ring is and/or the or at least one of the, for example both of the, gears.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is an exploded perspective view of a known dog drive assembly; Figure 2 is a perspective view of the clutch ring of the assembly of Figure 1; Figure 3 is an exploded perspective view of a dog drive assembly according to one embodiment of the invention; Figure 4 is a perspective view of the clutch ring of the assembly of Figure 3; Figure 5 is a schematic view of the interaction between the clutch ring and hub of the dog drive assembly of Figure 3; Figure 6 is a schematic view of the interaction between the clutch ring and hub of a dog drive assembly according to a second embodiment of the invention; and Figure 7 is a schematic view of the interaction between the clutch ring and hub of a dog drive assembly according to a third embodiment of the invention.

Referring to Figures 1 and 2, there is shown a dog drive assembly 1 which includes a hub 2 secured to a gearbox main shaft or lay shaft (not shown), a clutch ring 3 and a gear 4 rotatably mounted, in use, coaxially with respect to the hub 2. The dog drive assembly 1 illustrates one known arrangement for coupling the clutch ring 3 to the hub 2.

The hub 2 is in the form of a hollow cylinder with eight male drive splines 20 equally spaced about its outer circumferential surface 21. The splines 20 have an involute cross-sectional profile and extend along the axis of the hub 2.

The clutch ring 3 is in the form of a thin hollow cylinder or ring with a thickened outer peripheral portion 30 and an inner portion 31 with eight equally spaced protrusions or dogs 32 extending from each of its side faces 33 and eight axially extending female drive splines or slots 34, about its inner circumferential surface 35. The dogs 32 are in the form of a substantially truncated triangle in plan with the base of the triangle aligned with the is inner circumferential surface 35 of the clutch ring 3.

The dogs 32 have rounded corners and each dog 32 of one side face 33 is aligned with one of the dogs 32 of the other side face 33. The slots 34 have an involute cross-sectional profile which is shaped to correspond to those of the splines 20 and each slot 34 is aligned with one of dogs 32 on each of the side faces 33 such that each slot 34 is formed in part in the inner portion 31 and in part in each of the aligned dogs 32.

The gear 4 is ring-shaped with gear teeth 40 about its periphery in the normal way and includes a central portion 41 with eight protrusions or dogs 42 extending from one of its side faces 43. The dogs 42 of the gear 4 are also in the form of a substantially truncated triangle in plan with the truncated apex of the triangle facing inwardly, i.e. in the opposite orientation to the dogs 32 of the clutch ring 3. The dogs 42 of the gear 4 also have rounded corners and are equally spaced about the gear 4.

In an assembled condition, the splines 20 of the hub 2 engage the slots 34 of the clutch ring 3 to provide a slidable coupling between the clutch ring 3 and the hub 2. This coupling 20, 34 ensures that the clutch ring 3 and the hub 2 rotate with one another but allows the clutch ring 3 to slide along the axis of the hub 2.

When this gear 4 is not selected, it is free to spin about its own axis located by axial and radial bearings (not shown). Meanwhile the hub 2, and therefore the clutch ring 3 are rotating at the speed of the gearbox shaft (not shown).

In use and when the gear 4 in question is required, a selector fork (not shown) operated by the driver of an automobile (not shown) to which the dog drive assembly 1 is fitted forces the clutch ring 3 toward the gear 4. This movement causes the dogs 32 of the clutch ring 3 to engage corresponding dogs 42 on the gear 4 to couple the gearbox shaft (not shown) to the gear 4, thereby driving the gear 4 at the same rotational speed as the hub 2 and gearbox shaft (not shown). To disengage the gear 4 from the hub 2, the reverse operation is carried out.

As discussed above, the applicants have observed that this arrangement requires the size of the dogs 32 to be increased in order to prevent premature damage thereto. Increasing the size of the dogs 32 results in slower shifting which increases the interruption of drive power from the engine to the road wheels.

is Figures 3 to 5 illustrate the principle differences of the invention, more particularly a dog drive assembly 100 according to a first embodiment of the invention is shown which is similar to the prior art dog drive assembly 1, wherein like references depict like features and consequently these will not be described herein. The main distinguishing features of the dog drive assembly 100 according to this embodiment relate to the coupling between the clutch ring 103 and the hub 102 and its impact on the configuration of the dogs 132.

The clutch ring 103 includes eight male drive splines 134 projecting inwardly from the inner surface 35 each of which cooperates with a respective correspondingly shaped female drive spline or slot 120 in the outer circumferential surface of the hub 102. Each spline 134 is aligned with one of the dogs 132 on each of the side faces 33 such that each spline 134 extends in part from in the inner portion 31 and in part from each of the aligned dogs 132 on either side 33 of the clutch ring 103.

As shown in Figure 5 each spline 134 has an involute shape or profile, more specifically it comprises a truncated triangular cross-section with rounded corners. Similarly, each slot has a cross-section which corresponds to that of the splines 134 and is configured to cooperate with a respective spline 134. The outer diameter of the hub 102 is slightly smaller than the diameter of the inner surface 35 of the clutch ring 103 in order to prevent interference therebetween whilst maximising the engagement surfaces between the splines 134 and the slots 120.

It will be appreciated by those skilled in the art that the provisions of splines 134 projecting from the dogs 132 and inner portion 31 of the clutch ring 103 in place of the slots 34 provides a structure with increased robustness. In particular, the effective cross-sectional area of each dog 132 in an arrangement according to the invention is greater than that of the dogs 32 in arrangements which employ the coupling arrangement 32, 20 according to the prior art firstly by virtue of the absence of the slots 34 therethrough and secondly by the addition of the male driving splines 134.

Thus, this arrangement permits the size of the dogs 132 to be reduced without io compromising their performance, which in turn allows for faster shifting time thereby decreasing the interruption of drive power from the engine to the road wheels.

Figure 6 shows a dog drive assembly 200 according to a second embodiment of the invention with male driving splines 234 and female driving splines or slots 220 having a is different shape to those of the dog drive assembly 100 of the first embodiment. The dog drive assembly 200 of this embodiment includes splines 234 which have a profile with a full radius root shaped cross-section extending from the inner surface 35 and the dogs 232 of the clutch ring 203. Each slot 220 of the hub 202 has a cross-section which corresponds to that of the splines 234 and is configured to cooperate with a respective spline 234.

Figure 7 shows a dog drive assembly 300 according to a third embodiment of the invention with male driving splines 334 and female driving splines or slots 320 having a different shape to those of the dog drive assemblies 100, 200 of the first and second embodiments. The splines 234 according to this embodiment have a profile with a straight sided or rectangular cross-section and extend from the inner surface 35 and the dogs 332 of the clutch ring 303. Each slot 320 of the hub 302 has a cross-section which corresponds to that of the splines 334 and is configured to cooperate with a respective spline 334.

Several variations to the embodiments described herein are envisaged without departing from the scope of the invention. For example, although it is preferred that the splines 134 are aligned with the dogs 132, 232, 332 they need not be. The number of splines 134, 234, 334 may be more or less than the number of dogs 132, 232, 332, but is preferably divisible by the number of dogs 132, 232, 332 such that one spline 134, 234, 334 projects in part from each dog 132, 232, 332 or the number of dogs 132, 232, 332 may be divisible by the number of splines 134, 234, 334.

The splines 134, 234, 334 may comprise a different profile than one of those shown and/or the splines 134, 234, 334 may have different shapes than one another. The clutch ring 103, 203, 303 may be movable between two gears 4, wherein a further gear 4 is provided at the other end of the hub 102, 202, 302 and the clutch ring 103, 203, 303 is movable therealong to selectively engage the first gear 4, the second gear (not shown) or neither of the gears 4. The male and female drive splines 134, 234, 334 and 120, 220, 320 may comprise any suitable shape for achieving an effective engagement between clutch ring 103, 203, 303 and the hub 102, 202, 302.

For the avoidance of doubt, the term "slot" as used herein refers to female drive splines.

It will be appreciated by those skilled in the art that any number of combinations of the aforementioned features and/or those shown in the appended drawings provide clear is advantages over the prior art and are therefore within the scope of the invention described herein.

Claims

CLAIMS1. A dog drive assembly for an automotive gearbox, the assembly comprising a hub for coupling to a gear shaft and a clutch ring slidably coupled to the hub for rotation therewith, the clutch ring having a plurality of dogs and being slideable along the hub to engage or disengage the dogs with cooperating dogs on a gear rotatably mounted, in use, coaxially with respect to the hub to selectively couple or uncouple the hub to the gear, wherein the slideable coupling between the clutch ring and the hub is provided by a plurality of splines projecting inwardly from the clutch ring which cooperate with slots in the outer surface of the hub.
2. Assembly according to claim 1, wherein at least one of the splines is aligned with one of the dogs such that the at least one spline projects in part from the dog.
3. Assembly according to claim 2, wherein one spline is aligned with and projects in part from each dog.
4. Assembly according to claim 2 or claim 3, wherein the clutch ring comprises a plurality of dogs extending from each side thereof, each dog on one side being aligned with a dog on the other side.
5. Assembly according to any preceding claim, wherein the or at least one of the splines comprises an involute shape or profile.
6. Assembly according to any one of claims 1 to 4, wherein the or at least one of the splines comprises a full radius root shape or profile.
7. Assembly according to any one of claims 1 to 4, wherein the or at least one of the splines comprises a straight sided shape or profile.
8. Assembly according to any preceding claim, wherein the or at least one of the slots of the hub comprises a cooperating shape or profile to that of the or at least one of the splines.
9. Assembly according to any preceding claim, wherein the or at least one of the slots of the hub comprises a corresponding shape or profile to that of the or at least one of the splines.
10. Assembly according to any preceding claim, wherein the or at least one of the slots of the hub comprises substantially the same shape or profile to that of the or at least one of the splines.
11. Assembly according to any preceding claim further comprising a first gear mounted coaxially with respect to the hub, the first gear including a plurality of dogs on one of its end faces.
12. Assembly according to claim 11 when dependent on claim 4 further comprising a second gear mounted coaxially with respect to the hub in an axially spaced relationship with respect to the first gear, the second gear including a plurality of dogs on one of its end faces, wherein the clutch ring is mounted between the first and second gears and slideable along the hub therebetween to engage or disengage the dogs of the clutch ring with corresponding dogs on facing portions of is each gear to selectively couple or uncouple the hub to one of the two gears.
13. A dog drive assembly for an automotive gearbox substantially as described herein and/or as shown in the accompanying drawings.
14. An automotive gearbox comprising a dog drive assembly according to any preceding claim.
15. An automobile comprising a dog drive assembly as claimed in any one of claims 1 to 13 or a gearbox according to claim 14.
16. A clutch ring for use in a dog drive assembly according to any one of claims ito 12, the clutch ring comprising a plurality of dogs extending laterally therefrom and a plurality of splines projecting inwardly therefrom.
17. A clutch ring substantially as described herein and/or as shown in the accompanying drawings.
18. A hub for use in a dog drive assembly according to any one of claims 1 to 12, the hub comprising female drive splines or slots extending along the length of is outer surface.
19. A hub substantially as described herein and/or as shown in the accompanying drawings.
20. A kit of parts comprising a clutch ring according to claim 16 or claim 17 and a hub according to claim 18 or claim 19.