GB2409014A

GB2409014A - Anti-backlash gear assembly

Info

Publication number: GB2409014A
Application number: GB0329931A
Authority: GB
Inventors: Daniel Charmbury Ward
Original assignee: CNH UK Ltd
Current assignee: CNH UK Ltd
Priority date: 2003-12-08
Filing date: 2003-12-24
Publication date: 2005-06-15
Also published as: GB0329931D0; GB0328265D0

Abstract

An anti-backlash gear assembly is formed of two axially adjacent concentric gearwheels 10, 12 coupled to one another by means of at least one elastomeric element 28 which is resiliently deformable to permit a limited degree of circumferential movement of the gearwheels 10, 12 relative to one another. One of the gearwheels (10) is provided with pins (26) that project axially into holes (24) formed in the other gearwheel (12). The holes (24) have a larger cross-sectional area than the pins (26). A plurality of annular elastomeric elements (28) is deposed within the gaps between the holes (24) and the pins (26). The elastomeric elements (28) are moulded in situ in the gaps surrounding the pins (26) while the gearwheels are held in a predetermined angular position due to the alignment holes (30, 32).

Description

ANTI-BACKLASH GEAR ASSEMBLY

Field of the invention

The present invention relates to a gear assembly for eliminating backlash in a drive train in order to reduce noise and vibration.

Background of the invention

When the teeth of two gears in a drive train mesh with one another, there is usually a degree of free play or backlash between the teeth. As a result, as the direction of torque transmission changes, the teeth move relative to one another causing noise, vibration and timing errors.

GB-A-2,330,188 and GB-A-2,364,362 disclose anti- backlash gear assemblies comprising two coaxial gearwheels with a spring bias for rotating the gearwheels relative to one another about a common centre. The combined axial thickness of the two gearwheels is the same as that of a further gear with which they both mesh at the same time. The teeth of one gearwheel contact one flank of the teeth of the further gear while the teeth of the second gearwheel are urged by the spring bias into contact with the opposite flank of the teeth of the further gear. Thus, the spring bias ensures that the backlash is taken up so as to avoid noise and vibration.

It is, however, a disadvantage of known gear assemblies that they are formed of a large number of parts with the result that they are expensive to manufacture and assemble.

Summary of the invention

With a view to mitigating the foregoing disadvantages, the present invention provides an anti-backlash gear assembly formed of two axially adjacent concentric gearwheels coupled to one another by means of at least one elastomeric element which is resiliently deformable to permit a limited degree of circumferential movement of the gearwheels relative to one another.

Preferably, one of the gearwheels is provided with pins that project axially into holes formed in the other gearwheel, the pins having a greater cross-sectional area than the pins and a plurality of annular elastomeric elements being disposed within the gaps between the pins and the holes.

Conveniently, the elastomeric elements are moulded in situ in the gaps surrounding the pins while the gearwheels are held in a predetermined angular position with the teeth of the two gearwheels sufficiently out of alignment with one another to take up backlash.

It is preferred for the hubs of the two gearwheels to have mating formations to ensure that they remain concentric with one another at all times.

It is further preferred to provide alignment holes in the hubs of the gearwheels which are coaxial with one another when the teeth of the two gearwheels are aligned with one another. Such holes may receive a pin to maintain the teeth of the gearwheels in alignment while the gear assembly is being mounted in a drive train. Once both the gearwheels of the antibacklash gear assembly are in mesh with a common further gear, the pin in the alignment holes can be removed to allow the teeth of the two gearwheels to be resiliently urgent apart circumferentially by the elastomeric element(s) in order to take up any free play.

It will be seen that the anti-backlash gear assembly invention need only have two metal parts coupled to one another by elastomeric elements and the latter may be conveniently be moulded in situ. Hence, the gear assembly uses fewer parts and can be manufactured with less expense.

According to a second aspect of the invention, there is provided a method of manufacturing an anti-backlash gear assembly which comprises providing two concentric and axially adjacent gearwheels one of which has a projection received with clearance in a hole in the other, holding the two gearwheels in a position in which the flanks of their teeth are not all in alignment with one another and moulding an elastomeric element into the gap between the projection and the hole.

Preferably, the projection comprises a plurality of circular pins. The holes in the other gearwheel into which the pins project may either also be circular or they may be circumferentially elongated.

Brief description of the drawings

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded view showing all the components of a gear assembly of the present invention, Figure 2 is a front view of the gear assembly, Figure 3 is a rear view of the gear assembly, Figure 4 is a perspective view of the gear assembly when serving as an idler gear meshing with three further gears, and Figure 5 is a section through the gear assembly.

Detailed description of the preferred embodiment

Referring to Figure 1, a gear assembly of the invention is formed of two gearwheels 10 and 12 having identical teeth - 4 in so far as concerns their number, size and pitch. However, the teeth of the gearwheel 10 have a significantly greater axial length than those of the gearwheel 12, the latter serving primarily to eliminate backlash. The gearwheel 10 is formed in a conventional manner by casting or by machining a solid blank but the gearwheel 12 may be formed by stamping.

As most clearly seen from the section of Figure 5, the gearwheel 10 has a hub 14 that receives a bearing shell 16.

The hub 14 also has an axially projecting collar 18 which fits within the hub 20 of the gearwheel 12 to align the two gearwheels 10 and 12 and to maintain them concentric with one another. As shown to the left in Figure 5, the hubs 20 and 14 are formed with aligned holes 22 and 24, the holes 24 in the hub 14 of the gearwheel 10 having the larger diameter. Furthermore, as shown to the right in Figure 5, the two gearwheels 10 and 12 are coupled for rotation in unison with one another by means of pins 26 that project from the gearwheel 10 into the holes 24 in the gearwheel 10 and are surrounded by elastomeric elements 28. The pins 26 may either be an interference fit in the holes 22 of the gearwheel 12, or they may be secured within the holes 22 by in any suitable manner, such as by welding or heat shrinking.

The elastomeric elements 28 may be preformed and held in place, for example by the use of an adhesive, as shown in Figure 1. However, it is preferred in a preferred aspect of the present invention for them to be moulded in situ from a suitable material, such as HNBR rubber, which is injected into the gaps between the pins 26 and the holes 24 from the rear side of the gear assembly.

The two gearwheels 10 and 12 are formed with two further sets of holes 30 and 32 that are used for alignment, the holes in each set having the same diameter as one another. When a pin is inserted into the holes 30 to align - 5 them with one another, the teeth are moved into a slightly misaligned position and it is while they are being held by a pin in this position that the elastomeric elements 30 are moulded about the pins 26. On the other hand, when a pin is inserted into the holes 32, the elastomeric elements 28 are compressed and the teeth of the two gearwheels 10 and 12 are brought into exact alignment with one another.

A pin is inserted into the holes 32 while the gear assembly is being mounted within a drive train, such as the drive train shown in Figure 4. In this drive train, the gear assembly of the invention acts as an idler supplying drive from one drive gear 40 to two driven gears 42 and 44. All the gears 40, 42 and 44, have an axial length equal to, or greater than, the combined axial length of the teeth of the two gearwheels 10 and 12 so that they mesh with both sets of teeth simultaneously. Because the teeth of the gearwheels 10 and 12 are held in alignment by the pin inserted into the holes 32, all the gears of the gear train can be mounted to mesh with one another without difficulty.

Once all the gears of the drive train have been mounted in this manner, the pin in the holes 32 is removed and the resilience of the elastomeric elements 26 will force the two gearwheels 10 and 12 apart circumferentially. Thus, the teeth of the gearwheel 12 will resiliently engage the opposite flanks of the teeth of the gears 40, 42 and 44 so that the drive gear 40 can transmit torque to both driven gears 42 and 44 in opposite directions without backlash, thereby reducing noise and vibration.

Though the holes 24 are shown as having a circular cross section, it would be alternatively possible for them to be circumferentially elongated to increase the permissible degree of angular movement between the gearwheels. - 6 -

Claims

1. An anti-backlash gear assembly formed of two axially adjacent concentric gearwheels coupled to one another by means of at least one elastomeric element which is resiliently deformable to permit a limited degree of circumferential movement of the gearwheels relative to one another.

2. An anti-backlash gear assembly as claimed in Claim 1, wherein one of the gearwheels is provided with pins that project axially into holes formed in the other gearwheel and having a larger cross-sectional area than the pins, a plurality of annular elastomeric elements being disposed within the gaps between the pins and the holes.

3. An anti-backlash gear assembly as claimed in Claim 2, wherein the holes in said other gearwheel are circumferentially elongated.

4. An anti-backlash gear assembly as claimed in Claim 2 or 3, wherein the elastomeric elements are moulded in situ in the gaps surrounding the pins while the gearwheels are held in a predetermined angular position with the teeth of the two gearwheels sufficiently out of alignment with one another to take up backlash.

5. An anti-backlash gear assembly as claimed in any preceding claim, wherein the hubs of the two gearwheels have mating formations to ensure that they remain concentric with one another.

6. An anti-backlash gear assembly as claimed in any preceding claim, wherein alignment holes are provided in the hubs of the gearwheels, the alignment holes being coaxial with one another when the teeth of the two gearwheels are aligned with one another. - 7

7. A method of manufacturing an anti-backlash gear assembly which comprises providing two concentric and axially adjacent gearwheels one of which has a projection received with clearance in a hole in the other, holding the two gearwheels in a position in which the flanks of their teeth are not all in alignment with one another and moulding an elastomeric element into the gap between the projection and the hole.

8. An anti-backlash gear assembly constructed, arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.