GB2342130A

GB2342130A - Planetary-ball continuous variable transmission

Info

Publication number: GB2342130A
Application number: GB9818557A
Authority: GB
Inventors: Peter James Milner
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-08-27
Filing date: 1998-08-27
Publication date: 2000-04-05
Anticipated expiration: 2018-08-27
Also published as: GB2342130B; GB9818557D0

Abstract

A planetary-ball continuous variable transmission comprises planetary members, eg planetary balls 15, in rolling contact with radially inner and outer races 14, 13 each having axially spaced parts 14a, 14b, 13a, 13b. Control means comprising a screw 29 operated by a Bowden cable (30, fig 5) determines axial displacement of the outer races 13a, 13b and thereby a radial position of the balls 15. Axial displacement of the outer races 13a, 13b causes, via balls 15, axial displacement of the inner races 14a, 14b and the forces exerted on the balls 15 is regulated by a bi-directional torque-sensitive coupling comprising a screw thread on shaft 11 engaging in screw thread in inner races 14a, 14b. The planetary balls 15 may have peripheral grooves (25, fig 2) which receive planet followers (16) and contact surfaces of the planetary balls 15 may have a plurality of conical surfaces (26, fig 6) to form annular facets which define a given gear ratio.

Description

2342130 A BI-DIRECTIONAL CONTINUOUSLY VARIABLE TRANSMISSION DEVICE The

present invention relates generally to a continuously variable transmission device, and particularly to such a device in which the forces are transmitted by rolling traction.

The present invention is an improvement in and development of the continuously variable transmission device described in the Applicant's earlier application number 9815952.8. That earlier application describes a continuously variable transmission device of the type having planet members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planet members in rolling contact therewith.

In that device there are provided means sensitive to the torque applied to a drive-transmitting member of the transmission, which is operable both to determine the compensating variation in the separation of the two parts of the other race and thus the transmission ratip., Of V device, and also to vary the forces exchanged between the j, planets and the races normal to the interface between them.

2 In that earlier application the drive transmission from an input shaft to an output shaft could only take place in one direction of rotation since the torque-sensing mechanism described, which in the specific embodiment described involved a helical interengagement between one of the two race parts in the "other" race and a cooperating component allowed the two race parts to be urged towards one another by the forces exerted on them in operation only when the direction of rotation of the input shaft corresponded to that of the helical interengagement. Relative rotation between the input shaft and the output shaft in the opposite direction would result in a relative separation of the "other" race parts which would effectively result in a reduction in the contact forces and, ultimately, to a decoupling of the input and output members. This, of course, has certain advantages in some circumstances, particularly where an over-run free-wheel effect is desirable.

However, for use as a motor vehicle transmission, 20 especially one in which engine over-run is used for braking, the free-wheel effect is unwanted and, indeed, decidedly undesirable.

The present invention seeks to provide a continuously 25 variable transmission device of the type described in the Applicant's earlier patent application number 9815952.8 (the contents of which are incorporated herein by reference) in which the transmission of torque from an 3 input to an output shaft can take place in either direction of rotation.

According to one aspect of the present invention, 5 therefore, there is provided a continuously variable transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which there are provided means sensitive to the torque applied to a drive-transmitting member of the transmission device, operable both to determine the compensating variation in the separation of the two parts of the other race and thus the transmission ratio of the device and to vary the forces exchanged between the planets and the races normal to the interface between them, and in which the said torque-sensitive means include the two axially spaced, relatively moveable parts of the said other race, each said part being itself axially movable in two directional senses from a central position and engagable by limit stop means whereby to allow the transmission of rotary drive from a rotary drive input member to a rotary drive output member of the transmission device in each of two opposite senses of rotation.

In a preferred embodiment of the invention the said 4 relatively movable race parts of the torque-sensitive means are interconnected with the input drive member by a screw-thread engagement of the same hand by which rotary drive is transmitted when axial displacement of a 5 race part is restrained.

The thread flights of the screw thread engagement are preferably interengaged by rolling elements such as balls although this is not essential. The provision of interengaging balls helps significantly to reduce frictional resistance in the device.

The said two relatively movable race parts of the torquesensitive means may be oppositely axially resiliently biased. This resilient bias act to "prime" the torquesensing reaction of the device and in a preferred embodiment of the invention the resilient biasing of the said two relatively movable race parts is achieved by a compression spring located between them.

of course, in order to ensure that bi-directional rotation can take place each of the two race parts must ultimately be restrained from axial movement such that the other race part can, effectively "screw up" against it by the helical action exerted on it by the input member. Such limit stop means may comprise respective abutments on or carried by or associated with the said input drive member.

In one embodiment of the invention the two race parts of the said one race of the transmission device, the axial separation of which is selectively variable, are each carried on a casing of the transmission device in such a way as to have a limited rotational displacement in each of two opposite rotational senses. The relative axial separation of the two race parts of the said one race may be achieved by a helical interengagement of at least one of the two race parts with a fixed member of the transmission device, the two race parts both being relatively turnable with respect to the said fixed member. Such relative turning movement of the two race parts of the said one race may be achieved by any means which act directly between them rather than between one member and a fixed part. one means by which this can be achieved comprises a Bowden cable acting between the two race parts.

The present invention also comprehends, independently of the structure allowing bi-directional rotation tobe achieved, a continuously variable transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which the planetary members each have a circumferential annular groove the axis of 6 which substantially coincides with the respective rolling axis about which each planetary member turns as it rolls in contact with the races, the said annular grooves being engaged by roller follower members acting to guide the planetary members to maintain their orientation in their planetary motion.

This latter feature enables a greater load-carrying capacity to be achieved because a greater number of planetary members can be arranged in a given annular space because the circumferential space occupied by a planetary member can overlap that occupied by a planet follower.

The planet followers are preferably carried by a common carrier member through which drive transmission is conveyed to an output drive member of the device.

According to a further aspect of the present invention a continuously variable transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, has planetary members each with arcuately curved surface portions in rolling contact with correspondingly curved portions of the respective races, 7 the radius of curvature of the said surface portions of the planetary members being greater than the effective radius of the planetary member itself.

This can be visualised by imagining the planetary members as spheres of a given diameter notionally split to remove a central portion and reassembled with the remaining quadrants in contact with one another. The radius of curvature of the surface portions will thus match that of the "original" sphere whilst the diameter of the newly assembled sphere will be less than the diameter of the original sphere. Such planets may also be formed with circumferential grooves for receiving roller follower guide members as discussed above. There may further be provided means for guiding the planetary members to maintain the orientation of their rolling axes as they roll over the contacting surfaces of the races. Such guide members may be the above-mentioned rollers engaged in the circumferential grooves.

The purpose of enlarging the radius of curvature of the surface portions in relation to the diameter of the planetary member itself, is to extend the range of ratios which can be transmitted by the transmission device. In a specific embodiment, which will be described in more detail hereinbelow, the ratio range can be extended to 4.3:1.

In a further aspect of the present invention, which may 8 be considered independently of the other aspects described hereinabove, there is provided a continuously variable transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which each planetary member has a plurality of elementary annular contact surface portions having a substantially constant inclination to the rolling axis of the planetary member itself.

This allows the continuously variable transmission to be provided with preferred adjustment positions effectively representing specific gear ratios of a conventional gear box. Increased load-bearing capacity is also achieved by providing what amounts to a line rather than a point contact between the planets and the races over the surface portions having substantially constant inclinations.

This can be viewed as a planetary member having a generatrix which includes a section comprising a plurality of substantially rectilinear elementary portions. The races may have substantially continuously curved contact surfaces or may have respective contact surfaces for rolling contact with the planetary members, 9 each having correspondingly inclined elementary annular contact surface portions substantially matching those of the planetary members.

Various embodiments of the present invention will be more particularly described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an axial sectional view through a first embodiment of the present invention; 10 Figure 2 is a cross-sectional view taken on the line II-II of Figure 1; Figures 3 and 4 are schematic detail views showing components of the embodiment of Figures 1 and 2 in two different operating configurations; 15 Figure 5 is a schematic cross-sectional view of the embodiment of Figure 1 showing the relative positions of an adjustment mechanism; Figure 6 is an axial sectional view of an alternative embodiment of the invention; and 20 Figures 7 - 12 are schematic views of a detail of the embodiment of Figure 6 showing the components in different configurations for achieving different gear ratios.

Referring first to Figures 1 - 5 the device shown comprises a bidirection continuously variable transmission device for transmitting rotary drive from an input shaft 11 to an output drive member 12 illustrated as a tubular component to which, of course, an output drive shaft may be coupled by any known means.

The drive transmission device comprises inner and outer races 13, 14 each comprising axially spaced parts 13a, 13b; 14a, 14b between which roll planet members 15 circumferentially intercalated with roller follower members 16 carried on a common carrier 17 from which the output shaft 12 projects and which is borne on the input shaft 11 by a rolling element bearing 18 and on an outer casing 19 by a rolling element bearing 20.

The common carrier 17 has respective spindles 21 extending through and supporting the roller followers 16.

Each spindle 21 is carried at its other end by a carrier plate 22 born on the input shaft 11 by a rolling element bearing 23. At this end the drive shaft 11 is born on the casing 19 by a rolling element bearing 24.

As can be seen in Figures 3 and 4, the planetary members 15 are generally spherical bodies divided into two axially separated parts by a circumferential annular groove or channel 25 into which the adjacent roller followers 16 engage in order to guide the planetary bodies 15 to turn about a rolling axis parallel to the axis of the drive shaft 11. Other than their engagement with the roller followers 16 and the races 13, 14 the planetary members 15 are unrestrained.

11 Contact between the planetary members 15 and the races 13, 14 takes place at two curved surface portions 26, 27 of the planetary body which, as will be appreciated from Figures 3 and 4 have a radius of curvature which is greater than the overall radius of the generally spherical body 15.

The radial position of the planetary body 15 is determined by the axial separation of the radially outer race parts 13a, 13b which axial separation is controlled by a screw threaded interengagement between the two race parts themselves, for which purpose the race part 13a is secured to a cylindrical sleeve 28 for rotation therewith. The screw threaded inter engagement of the two race parts is represented in Figure 1 of the drawings by the balls 29. A Bowden cable 30 (see Figure 5) is connected with its outer sheath engaging one of the two race members 13a, 13b and its inner cable engaged with the other such that axial forces applied between the sheath and the inner cable can cause relative turning motion of the race parts 13a, 13b. Depending on the direction of rotation of the shaft 11, this will result in axial displacement of the two race parts the rotation of which is limited by a stop 31 which engages in a recess 32 defined between end shoulders 33, 34 and a projecting head.

As will be appreciated from a consideration of Figures 3 12 and 4, relative approach of the two race parts 13a, 13b, as shown in Figure 3, will cause the planet member 15 to be urged radially inwardly towards the axis of the shaft 11, and this causes a corresponding separation of the parts 14a, 14b of the inner race 14. The forces exerted on the planet member 15 by the inner race 14 is generated by a torque-sensitive coupling comprising a screw threaded portion of the shaft 11 engaged in correspondingly threaded portions of the parts 14a, 14b, each of the same hand and represented in the drawing by the interconnection balls 35, 36.

Axial displacement of the inner race parts 14a, 14b is limited by abutment stops 37, 38 and a priming spring 39 urges the two race parts 14a, 14b apart. Thus, depending on the direction of rotation of the shaft 11, one or other of the race parts 14a, 14b will be limited in its axial displacement by the respective axial abutment shoulder 37, 38 such that the screw-turning motion imparted to the other by the rotation of the shaft 11 will compensate the forces exerted by the choice of axial separation of the two outer race parts 13a, 13b. As illustrated in Figure 3, with the two parts 13a, 13b closely together, the planet member 15 is urged radially inwardly such that the inner race parts 14a, 14b are urged apart so that the rolling contact of the planet member between the inner and outer races results in a low ratio in the region of 0.14:1. When the outer race parts 13 13a, 13b are allowed to separate by action of the cable 30 reducing the tension between the inner cable and outer sheath, the torque exerted by the shaft 11 will cause the inner race parts 14a, 14b to move towards one another 5 increasing the transmission ratio up to a maximum of 0.62:1 as illustrated in Figure 4. This ratio range is increased by the enlargement of the radius of curvature of the contacting surfaces, 26, 27 of the planet 15 in relation to the overall general diameter of the planet itself. The load-bearing capacity of the transmission is also increased by the presence of the channels 25 in the planets which allows a greater number of planets to be arranged within a transmission casing of given size. As illustrated in Figure 2 it will be seen that there are five planet members in the array, intercalated with five roller followers each carried on a respective spindle 21. The effective diameter is determined by the need for the presence of the spindles 21 to transmit forces from the roller followers to the carrier. Moreover, by mounting the inner race parts 14a, 14b on a common thread axially compressive forces can be generated regardless of the direction of rotation of the drive shaft 11 as, in each case, the "trailing" race part will be urged towards the other when this contacts its respective abutment.

Turning now to Figure 6 there is shown a transmission device in which, although still notionally continuously variable, will act to provide a number of preferential 14 gear ratios at which the device will stop in the absence of overriding forces. The general configuration of the device illustrated in Figure 6 is similar to that of Figure 1 and, therefore, the same or corresponding components will not be described again. In this embodiment the planet members 15 have contact surfaces 26, 27 composed of a plurality of annular conical surfaces having a linear generatrix to form effectively annular "facets" which therefore effectively define a given gear ratio when in contact with the corresponding contact surfaces of the race parts. Figures 7 to 12 illustrate the relative positions of the inner and outer race parts for the six gear ratios determined by the six annular facets of the planet members in this embodiment.

Claims

1. A continuously variable drive transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which there are provided means sensitive to the torque applied to a drivetransmitting member of the transmission operable both to determine the compensating variation in the separation of the two parts of the other race and thus the transmission ratio of the device and to vary the forces exchanged between the planets and the races normal to the interface between them, in which the said torque-sensitive means include the two axially spaced, relatively movable parts of the said "other" race, each said part being itself axially movable in two directional senses from a central position and engagable by limit stop means whereby to allow the transmission of rotary drive from rotary drive input member to a rotary output member of the transmission device in each of two opposite senses of rotation.

2. A continuously variable drive transmission device as claimed in Claim 1, in which the said relatively movable race parts of the torquesensitive means are 16 interconnected with the input drive member by a screwthread engagement of the same hand by which rotary drive is transmitted when axial displacement of a race part if restrained.

3. A continuously variable drive transmission device as claimed in Claim 2, in which the thread f lights of the screw-thread engagement are interengaged by rolling elements such as balls.

4. A continuously variable drive transmission device as claimed in any of Claims 1 to 3, in which the said two relatively variable race parts of the torque-sensitive means are oppositely axially resiliently biased.

5. A continuously variable drive transmission device as claimed in Claim 4, in which the resilient biasing of the said two relatively movable race parts is achieved by a compression spring located between them.

6. A continuously variable drive transmission device as claimed in any preceding claim, in which the said limit stop means comprise respective abutments on or carried by or associated with the said input drive member.

7. A continuously variable drive transmission device as claimed in any preceding claim, in which the two race parts of the said one race of the transmission device the 17 axial separation of which is selectively variable, each carried on a casing of the transmission device in such a way as to have a limited rotational displacement in each of two opposite rotational senses.

8. A continuously variable drive transmission device as claimed in Claim 7, in which the relative axial separation of the two race parts of the said one race are achieved by a helical interengagement of at least one part of the two race parts with a f ixed member of the transmission device, the two race parts both being relatively turnable with respect to the said fixed member.

9. A continuously variable drive transmission device as claimed in claim 8, in which the relative turning of the two race parts of the said one race is achieved by means of a Bowden cable acting between them.

10. A continuously variable drive transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which the planetary members each have a circumferential annular groove the axia of which substantially coincides with the respective rolling 18 axis about which each planetary member turns as it rolls in contact with the races, the said annular grooves being engaged by a roller follower members acting to guide the planetary members to maintain their orientation in their 5 planetary motion.

11. A continuously variable drive transmission device as claimed in Claim 10, in which the planet follower members are carried by a common carrier member through which drive transmission is conveyed to an output drive member of the device.

12. A continuously variable drive transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which the planetary members each arcuately curved surface portions in rolling contact with the corresponding curved portions of the respective races, and the radium of curvature of the said surface portions of the planetary members is greater than the effective radius of the planetary member itself.

13. A continuously variable drive transmission device s claimed in Claim 12, in which there are further provided means for guiding the planetary members to maintain the 19 orientation of their rolling axis as they roll over the contacting surfaces of the races.

14. A continuously variable drive transmission device of the type having planetary members in rolling contact with radially inner and outer races each comprising two axially spaced parts, with control means for selectively varying the axial separation of the two parts of one race and thus the radial position of the planetary members in rolling contact therewith, in which each planetary member has a plurality of elementary annular contact surface portions having a substantially constant inclinations to the rolling axis of the planetary member itself.

15. A continuously variable drive transmission device as claimed in Claim 14, in which the generatrix of 'each planetary member includes a section comprising a plurality of substantially rectilinear elementary portions.

16. A continuously variable drive transmission device as claimed in Claim 14 or Claim 15, in which the races have respective substantially continuously curved contact surfaces.

17. A continuously variable drive transmission device as claimed in Claim 14 or Claim 15, in which the races have respective contact surfaces for rolling contact with the planetary members, having correspondingly inclined elementary annular contact surface portions substantially matching those of the planetary members.