GB2037394A

GB2037394A - Gearing

Info

Publication number: GB2037394A
Application number: GB7924081A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-04-28
Filing date: 1979-07-11
Publication date: 1980-07-09
Also published as: GB2037394B

Abstract

A gear drive comprises a gear wheel unit in mesh with another toothed component or gear unit 6, the gear wheel unit comprising two coaxial gear wheel members 8, 10 and a coupling between the two members, the coupling including a shaft 2 or tube 12, 24 acting as a torsion spring about the axis of the members, the spring being prestressed so that, within a range of torque transmitted by the gear drive, there is no backlash between the units. The coupling also includes two cooperating splined rings 14, 16; 20, 22 coaxial with the gear wheel members 8, 10, the rings having equal numbers of splines, that number being different from the number of teeth on each member. <IMAGE>

Description

SPECIFICATION Gearing This invention relates to toothed gear wheel units intended to mesh with another toothed component in order to transmit motion, and to gear drives comprising a gear wheel unit in mesh with another toothed component or gear unit.

Toothed gear wheels are usually substantially rigid. During operation, one flank of each tooth makes sliding engagement with a flank of a cooperating tooth on the other component, and driving forces are transmitted from one engaging flank to the other. In order to avoid high frictional losses, it is usual to design gear wheels and their mountings so that the other flank of each tooth has slight clearance from the adjacent flank of the next cooperating tooth. In consequence, "backlash" is present. That is to say, if the direction of drive is reversed, these clearances close, while clearances open between the flanks which were previously in engagement.

Undesirable consequences are noise, and lack of precision in the position of the other toothed component corresponding to any particular angular position of the gear wheel.

A gear drive according to this invention comprises a gear wheel unit in mesh with another toothed component or gear unit, the gear wheel unit comprising two coaxial gear wheel members and a coupling between the two members, the coupling including a shaft or tube acting as a torsion spring about the axis of the members, the spring being pre-stressed so that, within a range of torque transmitted by the gear drive, there is no backlash between the units.

A gear wheel unit according to the present invention preferably comprises two coaxial gear wheel members having equal numbers of teeth, and a coupling between the two members, the coupling including a shaft or tube acting as a torsion spring about the axis of the members, and also including two cooperating splined rings coaxial with the members, the rings have equal numbers of splines, that number being different from the number of teeth on each member.

The unit is intended to cooperate with a toothed component arranged to mesh with both the gear wheel members simultaneously, the splined rings being meshed in such a relationship as to cause the torsion spring to be stressed and the members to engage the cooperating component with clearances in opposite senses between tooth flanks, so that there is no backlash between the unit and the cooperating component.

This will be explained more fully with reference to an example, shown in the accompanying drawing.

Following the example is description of modifications and variants, some involving a second gear unit. The single Figure of the drawing is a diagram of a gear wheel unit according to the invention, in mesh with a rigid gear wheel.

The drawing shows a transmission between a shaft 2 and a shaft 4. The shaft 4 carries a rigid gear wheel 6 of ordinary construction. The shaft 2 carries a gear wheel unit embodying the present invention. This unit comprises two coaxial gear wheel members 8 and 10 having equal numbers of teeth, and a coupling between the two members 8, 10. In this example, the coupling incorporates parts of the shaft 2, and comprises a tube 12, a splined ring 14, a splined ring 16, which is part of the shaft 2, a length 18 of the shaft 2, a splined ring 20, which is part of the shaft 2, a splined ring 22, and a-tube 24. The tube 12 is rigidly connected at its two ends to the gear wheel member 8 and to the splined ring 14, while the tube 24 is rigidly connected at its two ends to the gear wheel member 10 and to the splined ring 22.

Each of the gear wheel members 8, 10 has forty straight teeth of ordinary involute form. The gear wheel 6 has thirty similar teeth. The shafts 4 and 2 are mounted, (by bearings not shown) at a centre distance such that either of the members 8, 10, considered individually, would mesh with the gear wheel 6 with some backlash, e.g. 1 of rotation of the member 8.

The rings 14, 16, 20, 22 each have 36 splines.

The alignment of the splines angularly in relation to the teeth of the gear wheel members 8 and 10 in such that it is possible to assemble the gear wheel unit with the teeth of the members 8 and 10 exactly in alignment. If, now, for example, the components 10, 24, 22 are shifted to the right in the Figure, so as to disengage the rings 20, 22, and the components 10, 24, 22 are rotated through 100, then the rings 20,22 can be reengaged by moving the components to the left again. Because the interval between teeth on the members 8, 10 is 90, it will be found that the teeth on the member 8, 10 are now 1 out of relative alignment.By repetition of this sequence of operations, the teeth of the members 8, 10 may be taken further out of alignment by successive steps of 1 . The teeth may then be brought back into alignment by applying torques to the members 8, 10 in opposite directions. When this is done, the tubes 12 and 24 become twisted, and act as torsion springs.

If, now, the members 8, 10 are brought into mesh with the gear wheel 6, and the opposite torques are released, then the members 8, 10 will tend to rotate in opposite directions, and the teeth on the members 8, 10, will engage opposite flanks of the teeth on the gear wheel 6, so that there is no backlash between the gear wheel 6 and the gear wheel unit including the members 8, 10.

Drive can now be transmitted through the gear wheel 6 and the members 8, 10 from the shaft 4 to the shaft 2, or vice versa. No backlash will occur, unless the torque transmitted becomes greater than the torque which remained as a prestress in the tubes 1 2, 24, after the members 8, 10 were brought into mesh with the gear wheel 6 and released.

In the operation of the transmission, there is friction not only between the toothed flank which transmit drive, as is usual in gearing, but also between the opposite toothed flanks. If the conditions of use are such that friction is desirably kept to a minimum, then the pre-stressing of the tubes 12, 24 should be no greater than is necessary to ensure that backlash does not start to occur at maximum driving torque. If, on the other hand, circumstances of use are such that friction is positively advantageous, for example in some form of adjusting mechanism, which is desired to remain stationary in any position to which it has been moved, then the pre-stressing can be selected to provide the friction desired (within the elastic limits of the components of the transmission).

The introduction of pre-stress into the tubes 12 and 24, by relative rotation of the splined rings 22 and 20, has been described starting from a position in which the teeth on the gear wheel members 8, 1 0 are in exact alignment. However, in fact it is not essential for such a position of exact alignment to exist.

The adjustment of prestress by disengaging and reengaging the components as described above depends on there being a small difference, but only a small one, between the angular spacing of the teeth on the gear wheel members and the angular spacing of the splines on the splined rings.

In design for a particular purpose, once the number of teeth required is known, a number of splines appropriate to the torsional stiffness of the components can be selected.

The pre-stressing has been described in terms of torsional deformation of the tubes 12 and 24.

However, the portion 18 of the shaft 2 is likewise pre-stressed, and may also undergo significant torsional deformation, while it is also possible for all significant torsional deformation to be in the shaft. Which situation occurs depends upon the proportions and material of the shaft portion 18, in relation to the proportions and material of the tubes 12 and 24.

It may be desirable to incorporate some form of bearing at the points indicated as 26 and 28, to ensure that the gear wheel members 8, 10 remain sufficiently nearly coaxial with the shaft 2 in operation, bearing in mind that the forces exerted on the flanks of the teeth of the members 8, 10 by the teeth of the gear wheel 6 have not only circumferential components, but also radial components, in the upward direction in the Figure.

The numbers of teeth mentioned for the gear wheel members, and for the splined rings, are purely one example. So also is the angular backlash initially present, and the magnitude of the steps of relative angular movement of the gear wheel members, 8, 10 prior to pre-stressing of the tubes 12, 24.

In a more compact arrangement, the tube 24 is of larger diameter, and the tube 12 extends to the right from the gear wheel member 8, and lies within the tube 24. The splined rings 1 4, 1 6 are then close to the splined rings 20, 22, and indeed the two pairs of rings cooperating with the shaft 2 may be replaced by a pair of splined rings directly coupling the tube 12, 24 together and a second pair of splined rings coupling the tube 1 2 to the shaft 2. Then the shaft 2 is not part of the coupling between the gear wheel members 8, 10.

In another layout, the tube 12 is omitted, and the gear wheel member 8 is coupled to the shaft 2 by means at the point 26. In one version of this layout, the torsional deformation is wholly in the shaft while the tube 24 is rigid and may perform the functions of a roller in a machine in which it is installed.

Although splines at 14, 16 and also at 20, 22 provide a convenient means of coupling the components, in fact only one pair of splines is necessary for purposes of adjustment, and the other pair may be replaced by some other form of nonslipping coupling.

In the example so far described, the teeth are straight. As an alternative, they could be helical.

They could have a form other than involute, e.g.

elliptical, or cycloidal.

In the example shown, the gearing is between parallel shafts. A similar construction can be used in bevel gearing between shafts with axes which intersect.

In the example shown, the cooperating toothed component is the gear wheel 6. This could be replaced by a rack. It is even possible that the cooperating component could be a worm, while the gear wheel members 8, 10 take the form of two halves of a worm wheel.

As a modification of the construction shown in the drawing, the splined coupling, instead of being between the outer ends of the tubes 12, 24 and the shaft 2, could be between the inner ends of the tubes 12, 24 and the gear members 8, 10, respectively.

A gear wheel unit is defined in the fourth paragraph of this specification is intended to cooperate with a rigid unitary component, such as the gear wheel 6. However, the invention includes certain alternatives. For example, if the gear wheel 6 were divided into two gear wheels side by side on the shaft 4, meshing with respective members 8, 10 becoming in effect a second gear wheel unit, then at least two variations become possible: A. The adjustable splined coupling could be between the shaft 4 and the two parts of the gear wheel 6, instead of being in the unit on the shaft 2.

B. It ceases to be essential for the two gear members 8, 10 to have the same number of teeth, provided that the gear ratio between each member 8, 10 and its cooperating part of the gear wheel 6 is the same.

For most uses it is convenient for the two gear wheel members of a gear wheel unit to be closely side by side, but it is possible to space them apart, especially if there are two meshing gear wheel units.

In all the constructions described so far, at least one pair of splined rings is present, and provides for adjustment of the torsional prestress in the gearing. However, in mass production for one particular use, it may be possible to dispense with adjustment. Then the splined rings may be replaced by any form of non-slipping interconnection which will ensure that a designed prestress is established in the gearing as a consequence of asssembly.

Claims

1. A gear drive comprising a gear wheel unit in mesh with another toothed component or gear unit, the gear wheel unit comprising two coaxial gear wheel members and a coupling between the two members, the coupling including a shaft or tube acting as a torsion spring about the axis of the members, the spring being pre-stressed so that, within a range of torque transmitted by the gear drive, there is no backlash between the units.

2. A gear drive according to claim 1, in which the gear wheel unit comprises two coaxial gear wheel members having equal numbers of teeth, and a coupling between the two member, the coupling including a shaft or tube acting as a torsion spring about the axis of the members, and also including two cooperating splined rings coaxial with the members, the rings having equal numbers of splines, that number being different from the number of teeth on each member.

3. A gear wheel unit comprising two coaxial gear wheel members having equal numbers of teeth, and a coupling between the two members, the coupling including a shaft or tube acting as a torsion spring about the axis of the members, and also including two cooperating splined rings coaxial with the members, the rings having equal numbers of splines, that number being different from the number of teeth on each member.

4. A drive according to claim 2, or a unit according to claim 3, in which the two gear wheel members are closely side by side, and the coupling lies partly to one side of the gear wheel members and partly to the other side of the gear wheel members.