GB2130314A - Variable-ratio friction planetary gear - Google Patents

Abstract

A variable-ratio friction planetary gear comprises rotary input and output members 9, 15, and two sets of races 17-20, 23-26 defining passages receiving balls 21, 27 which are in rolling contact with the races. The input races 17, 23 and 18, 24 as well as the output races 20, 26 being so arranged and interconnected that the axial thrusts exerted thereon by the balls are oppositely directed and balance each other out whereby thrust bearings for the input and output members are obviated. In the embodiment shown in Fig. 1 the axial thrusts are rendered torque-responsive by rollers 30 and 32 between ramp surfaces of races 17 and 23 and 24 and 18 respectively. Axial movement of non-rotating race 19 varies the ratio. <IMAGE>

Description

SPECIFICATION Variable ratio drive This invention relates to an improved variable ratio traction drive for transmitting power from an input shaft to an output member and of the kind disclosed in British patent specification No. 2103313.

In the aforesaid specification there is described a variable ratio traction drive comprising a series of freely rotating balls confined in an annular passage defined by four coaxial races having concave raceways with which each of the balls makes point contact. One race remains stationary, a second race is displaceable axially, and the remaining two races constitute input and output races and are acted upon by springs or torque dependent devices for maintaining the balls in firm rolling contact with the races. The second race is rotationally fast with the input race as a result of which, by relative axial adjustment of the races, the gear ratio may be varied and there is permitted a forward, geared neutral and reverse ratio range. In operation of the drive there are two relative motions of the balls at any given instant.Firstly, the balls roll around the stationary race and thereby tend to rotate the output race in the same direction as the input race, and secondly the balls spin about an axis determined by the relative positions of the races and this spinning motion tends to drive the output race in the opposite direction to the input race. If the rolling motion is greater than the spinning motion the drive is in the forward range; if the spinning motion is greater the drive is in the reverse range; and, if the motions are equal they cancel each other out to give a geared neutrai and the output shaft remains stationary.

Although the variable ratio traction drive as described above has a number of advantages it has one drawback in that thrust bearings are required to support the substantial axial loads on the input and output races. The need to provide the thrust bearings significantly increases manufacturing costs.

The present invention seeks to provide a solution to this drawback and according to the invention there is provided a variable ratio traction drive comprising a first series of balls confined in an annular passage defined by a first set of races comprising two axially opposed pairs of inner and outer races, and a second series of balls confined in an annular passage defined by a second set of races comprising two axially opposed pairs of inner and outer races, all the races being coaxial and the races of each set including a stationary race, an input race, an output race and a further race rotatable with the race paired therewith, the output races and the input races respectively of the two sets being so arranged that the axial thrusts thereon are directed oppositely and substantially cancel each other.

A full understanding of the invention will be had from the following detailed description which is given by way of example with reference to the accompanying drawings, in which Figure 1 is a side elevation of a drive embodying the invention with the upper half shown in cross-section and the lower half shown partly broken away; and Figure 2 illustrates a modification to the drive of Fig. 1.

The variable ratio traction drive shown in Fig. 1 has a casing comprising a cylindrical body 1 and end covers 2, 3 fastened together on the body by bolts 4. Mounted axially in the casing is a stationary shaft 5 having a splined connection with the end cover 3. An end of the shaft protruding through the cover 3 is screw threaded and receives a nut 6 to which an adjusting handle 7 is fixed. The inner end of the shaft carries a flange 8 and defines an axial recess in which the end of an input shaft 9 is journalled by bearings 10.

Keyed for rotation with the input shaft 9 is a drive plate 11 whose outer periphery has a splined connection with a drive sleeve 1 2 so as to permit axial movement of the sleeve.

Motor M drives the shaft 9. Rotatably mounted on the shaft 5 by a bearing 1 3 is a sleeve 1 4. The outer end of sleeve 14 is splined and receives a toothed pulley 1 5 retained by a circlip and around which a tooth belt 1 6 is trained, the belt 1 6 constituting the output member of the drive.

Accommodated in the casing are two sets of four races. The first set 17-20 confines an annular passage receiving a first series of balls 21 held by a cage 22, and the second set 23-36 defines an annular passage receiving a second series of bails 27 held in a cage 28.

All the races are coaxial and define concave raceways with which the balls 21, 27 make point contact. The first set of races includes two pairs of axially opposed races 17, 1 8 and 19, 20. The race 1 7 is fixedly mounted on the drive sleeve 12; the race 1 8 rotates with race 1 7 (as described below); race 1 9 is fixedly mounted on the flange 8 of the stationary shaft 5; and, race 20 is fast with the sleeve 1 4. The second set of races similarly comprises two sets of axially opposed races 23, 24 and 25, 26.The race 23 is the input race; the race 24 has a splined connection with the race 23; race 25 is fixedly mounted on the casing end cover 3; and output race 26 is fast with the sleeve 1 4. The axially confronting faces of the races 1 7 and 23 have complementary ramp cam surfaces 29 and receive between them rollers 30, and the confronting axial faces of races 18, 24 are provided with complementary ramp cam surfaces 31 and receive between them larger diameter rollers 32. A spring 33 is located between the races 18, 24 to provide an initial preload.

The input shaft 9 rotates the plate 11 and hence the sleeve 12 and the input race 1 7.

Due to the ramp cams 29, 31 and rollers 30, 32 as well as the splined connection between races 23 and 24, the four races 17, 1 8, 23 and 24 are all driven at the same speed. The balls 21, 27 are thereby driven at the same speeds and hence the respective output races 20, 26 are also driven at the same speed for driving the output pulley 15 through the sleeve 14. The necessary axial thrust on the races needed to maintain them in firm rolling contact by the balls is provided by the torque dependent pressure devices defined by the ramp cams 29, 31 and rollers 30, 32. As the torque increases so does the axial thrust.To adjust the relative axial positions of the races in each set for altering the gear ratio, the handle 7 is turned to displace axially the stationary race 1 9. The relative positions of the remaining races are adjusted automatically under the axial forces produced by the springs 33 and, in operation by the ramp cams 29, 31 and rollers 30, 32.

The axial thrusts on the two putput races 20, 26 are equal and oppositely directed so that they can be taken up by tension in the sleeve 1 4. Similarly, the axially directed thrusts on the input races 17, 1 8 and 23, 24 are supported by each other through the rollers 30, 32. Since there is substantially no resultant axial thrust on either the input shaft 9 or the output sleeve 14 the need for thrust bearing is obviated. With the back-to-back arrangement of the drive transmitting mechanisms twice the power can be transmitted for a drive of given diameter.

As described above the drive is adjustable to provide forward, reverse or geared neutral drive. For a unidirectional drive a balanced adjusting device can be achieved by a ramp cam adjuster and dispensing with the splines on the shaft 5. Such an arrangement allows the torque on one stationary race to counteract the axial thrust.

In Fig. 2 there is shown a modified drive in which the torque responsive pressure devices 29-32 are replaced by springs for applying the necessary axial loads on the races. In the two Figures the same reference numerals have been used to denote corresponding parts and only the differences in construction will be described in detail.

The two input races 17, 23 are integral with each other and the input races 18 and 24 have splined connections with the integral race 17, 23. A Belleville spring 46 is interposed between the races 1 8 and 24 and acts to push these races away from each other and into contact with the balls 21 and 27, respectively. A second Bellville spring 41 is located between the pulley 1 5 and its retaining circlip and acts to press towards each other the two output races 20, 26. The nut 6 has a ball screw connection 42 with the end of the stationary shaft 5. The forces of the springs 40, 41 act on the stationary shaft 5 through the races and balls, thereby pressing the nut 6 towards the end cover 3.To take up this thrust and facilitate rotation of the nut 6 to adjust the gear ratio a thrust bearing 43 is located between the nut and cover 3 of the casing. The axial thrust on the ball screw 42 tends to rotate the nut 6 and handle 7 and a locking eccentric 44 is provided on the handle to retain it in the adjusted position.

The operation of the drive shown in Fig. 2 is essentially the same as described above for the embodiment of Fig. 1. The integral input race 17, 23 is rotated by the shaft 9 of the motor M, and rotates with it the races 18 and 24. The axial thrusts on the output races 20, 26 are directed oppositely and are taken up by tension in the sleeve 14, although in this case relative axial movement of the races 20, t6 is permitted by the spring 41, this being necessary due to the input races 17, 23 being integral. The output races drive the belt or chain 1 6 through the sleeve 14 and pulley 1 5. The axial thrusts on the input races 17, 23 and 18, 24 are oppositely directed and balance each other out.

To change the gear ratio the handle 7 is turned to adjust the axial position of the stationary race 1 9. The axial positions of the remaining races are changed automatically as a result under the influence of springs 40, 41.

In place of the spring 41, separate input races 17, 23 could be provided and have a spring located between them. A splined or other connection between the races would be needed to ensure that they are rotated together.

Claims (16)

1. A variable ratio traction drive, comprising rotatable input and output members, and two co-axial sets of races each defining an annular passage accommodating a series of balls in rolling contact with the races, each set of races comprising axially opposed pairs of inner and outer races and including a stationary race, an input race coupled for rotation with the input member, an output race coupled for rotation with the output member, and a further race coupled to be rotationally fast with the race paired therewith, the races of each set being adjustable axially relative to each other for changing the speed ratio of the drive, and the input races and the output races respectively of the two sets of races being so arranged and interconnected that the axial thrusts thereon are directed oppositely and substantially cancel each other.

2. A drive according to claim 1, wherein the races have concave surfaces contacting the balls, and said further races are coupled to rotate with said input races.

3. A drive according to claim 2, wherein the input races and said further races respectively are located axially adjacent each other and are connected for axial thrusts to be transmitted directly therebetween.

4. A drive according to claim 3, wherein the input race of one set is connected to the input member, and the input race of the other set is coupled to the input race of said one set through a torque dependent pressure device.

5. A drive according to claim 4, wherein said further races are connected by a torque dependent pressure device, and one of said further races has a direct rotational coupling to the input race paired therewith.

6. A drive according to claim 4 or 5, wherein the (or each) torque dependent device between the races comprises a series of rolling elements received between the ramp surfaces provided on the confronting faces of the races.

7. A drive according to claim 1, 2 or 3, wherein the input races are fixed together for axial thrusts thereon to be transmitted directly therebetween.

8. A drive according to claim 7, wherein said further races are directly coupled for rotation with the respective input races paired therewith and are urged apart by spring means acting therebetween.

9. A drive according to any one of claims 1 to 8, wherein the output races are fast with a common rotary member, said rotary member supporting the axial thrusts on the output races.

10. A drive according to claim 9, wherein the axial thrusts act on the output races to force them away from each other and said axial thrusts are supported by axial tension in said rotary member.

11. A drive according to claim 9 or 10, wherein said output races are fixed axially on said rotary member.

12. A drive according to claim 9 or 10, wherein the output races are axially movable relative to each other and spring means acts between the rotary member and the output races to urge said races towards each other.

1 3. A drive according to claim 8 or 12, wherein the spring means is a Belleville spring.

1 4. A drive according to any one of the preceding claims, wherein the stationary race of one set of races is fixed and the stationary race of the other set is adjustable axially for changing the speed ratio of the drive.

1 5. A drive according to claim 14, wherein the adjustable stationary race is supported by an axial shaft, and the output member is rotatably supported about said shaft.

16. A variable ratio traction drive substantially as herein described with reference to the accompanying drawings.