GB2389156A

GB2389156A - Rolling traction epicyclic

Info

Publication number: GB2389156A
Application number: GB0306347A
Authority: GB
Inventors: Forbes George De Brie Perry
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-04-10
Filing date: 2003-03-20
Publication date: 2003-12-03
Anticipated expiration: 2023-03-20
Also published as: GB0306347D0; GB0208246D0; GB2389156B

Abstract

A rolling traction epicyclic stage 16 is combined with a toroidal race variable ratio rolling traction unit 6. The epicyclic stage 16 comprises a planet carrier 23 having planet rollers 28 with a bevelled roller surface that converges at an intersection on axis A and engage matching contact surfaces 21a, 22. Contact surface 21a is on an annular member 21 carded by a piston 19 and the contact surface 22 is on a rear side of an outer member 8 of the variable ratio traction unit 6. An end load device comprises the piston 19 which is disposed within a hub 18 to form a space that contains a preload spring 40 and which receives pressurized fluid to axially compress the planet rollers 28. In other embodiments the end load device may comprise a face cam (60, fig 6) and the planet rollers 28 may have a convex roller surface which is obliquely inclined to the axis A.

Description

( 2389 1 56

ROLLER DRIVE SYSTEMS

This invention relates to roller drive systems and particularly such drive systems including a roller epicyclic stage.

s Roller drive systems and particularly continuously variable transmissions which include an epicyclic roller stage are known in the art. Such systems may include a set of variable speed ratio rollers, for example in the form of a toroidal race rolling traction unit, as well as a set of constant speed-ratio rollers constituting an 10 epicyclic system. Roller transmissions of this kind are exemplified by patent numbers US5074830 and US-5319466. The former describes an epicyclic stage wherein the planet rollers engage a roller, fixed to an input shad, and a raceway on the rear of an output member of the set of variable speed rollers The output from the epicyclic is taken from the planet carrier. The axes of the planet rollers are 15 inclined with respect to a perpendicular to the common axis of the aforesaid roller and output member. The general purpose of the transmission described in US 5074830 is to provide at least one fixed transmission ratio of low loss within the range of continuously variable transmission ratios that the rolling race unit can provide and the principal mechanism for this purpose is a means operable to inhibit 20 at least partially the epicyclic action of an epicyclic gear stage driven from the epicyclic roller stage. The latter document, US-5139466, includes an epicyclic roller stage disposed between an output member of the variable speed rolling traction unit and a disc fixed to an input shaft. The planet carrier is coupled to an output by way of a simple drive train including a clutch In this general kind of drive system, if the disc-to-roller contacts for the epicyclic roller stage are left similar to those for a variable set wherein the rotational plane of a roller is always normal to a disc contact surface, then the radial 'pip' load due to rolling with true bevel angles would be largely eliminated and merely 30 centrifi3al forces would remain. However, there will be a penalty in that the spin motion inherent in variable set roller contacts would cause torque and speed losses which are detrimental to the overall efficiency of the transmission. It is therefore

( 1 - 2 - advantageous to keep as closely as possible to true rolling in the epicyclic set with due regard to the life expectancy of the stressed elements.

The present invention concerns the shaping of the rolling contacting surfaces to 5 minimise rolling losses, and the construction required to support the loads involved. In order to make the contact losses as low as possible, the present invention employs a construction in which the rolling contacts in the epicyclic stage are 10 always substantially on a true bevel line, that is to say the contact lines when projected converge towards and preferably substantially intersect on the rotational axis of the epicyclic assembly In practical embodiments of the invention, owing to axial loading of the whole 15 transmission rolling assembly, the bevel contact angles will produce an outward thrust component on the planet rollers; this load may be taken by a thrust bearing.

In addition, the output torque forces need to be transferred to the body of the output member of the epicyclic; the assembly requires a careful balancing of geometry and stresses if adequate life expectancy is to be achieved.

Specific embodiments of the invention will now be described with reference to the accompanying drawings In the drawings: Figure 1 illustrates an embodiment of the invention in the context of a variable ratio rolling traction unit; and Figures 2 to 7 illustrate modifications of the embodiment shown in Figure I. The embodiment shown in Figure I is contained within a housing 1, through which extends a main shaft 2 which may be driven in rotation by a motor or engine (not shown). The shaft 2 is supported at one end of the housing by a bearing 3 and is

- 3 supported at the other end of the housing by a bearing 4 supported in a circular flange 5 provided on the inner side of the respective end wall of the housing 1. In this embodiment of the invention there is a variable speed-ratio rolling traction stage 6 The input and output members of this rolling traction stage 6 are a disc 7 5 which includes a toroidal race and is keyed to the input shaft 2, and an output disc 8 which is supported by a bearing 9 on a bracket 10 fixed by bolts 11 to a flange 12 on the side wall of the housing 1. The disc 8 also includes a toroidal race on its face confronting the respective face of the input disc 7 En' aging the toroidal races of the discs 7 and 8 are a set of at least two rollers, of which only one roller 10 14 is shown. The velocity ratio between the input and output members 7 and 8 is variable by altering the attitude of the rollers 14 (e.g. to the position indicated by 14a), as is well known in itself and is described in the aforementioned publications and in a variety of earlier documents.

15 The rolling traction unit shown in Figure I includes an epicyclic roller stage generally indicated by the reference number 16 and directly connected to the toroidal race rolling traction stage. A first member of the epicyclic stage is the output' member 8 of the variable ratio unit 6. A second member of the epicyclic stage is generally indicated by the reference 17. This comprises a hub 18 keyed to 20 the shaft 2 and a disc 19 which is keyed at its periphery to a disc spring preload member 40. The disc 19 carries an annular member 21 which has an oblique, convexly cambered contact surface 21a On the 'rear' side of the output member 8 is another annular contact surface 22 which is also suitably cambered 25 The preload member 40 is keyed to the hub 18 at its inner periphery. The disc 19 acts as a torsionally locked but axially moveable piston to compress axially the whole assembly. Hydraulic seals 41 and 42 are disposed at the outer and inner rims of the disc 19 The torsional rigidity of the spring transmits the torques between planet rollers 28 (to be described) and the hub 18. Fluid from a pump 43 30 pressurises assembly 17 by way of passageway 44, axial bore 45 and radial bore 46 in shaR 2 into the cavity where member 40 is located

( - 4 The other principal element of the epicyclic stage is a planet assembly which includes a planet carrier in the form of a disc 23. The outer periphery of the disc 23 may be formed as an annular gear 24 in order, in this embodiment, to provide an output drive. It will be understood that in a different configuration disc 23 could be 5 a reaction member and the member 17 could be the output member, though then the member 17 would need to be able to rotate freely relative to the shaft 2.

The disc 23 is supported by a bearing 25 relative to the main shaft 2 Disc 23 also has a flanged hub 26 which is supported by a bearing 27 relative to the bracket 10 10 In an alternative construction the bearing 27 could run the main shaft instead of on the hub 10a of bracket 10.

Disc 23 and its flanged hub 26 constitute a planet carrier for a multiplicity of planet rollers 28 each of which is rotatable relative to a respective spindle 29 15 supported in the planet carrier and disposed in this embodiment so that the axis of the spindle is perpendicular to the main rotational axis A of the planet carrier and the input shaft 2.

It will be observed that the contact lines between the rolling surface 30 of each 20 planet roller 28 and the (cambered) contact surfaces 21a and 22 are on true bevel angles, converging towards an intersection (as shown by the chain lines) substantially on the axis A where the spindle axis also intersects the axis A. Each planet roller can be contacted at any point on its peripheral surface and give true rolling contact without the spin which occurs if the contact lines do not meet on the 25 rotational axis A of the assembly The contact surfaces 21a and 22 could be radially straight but are preferably cambered In order to support the axial thrust produced by this arrangement, each planet is supported by a thrust bearing relative to the carrier. More particularly, the outer 30 end of the spindle 29 is supported in an axial flange 31 near the periphery of disc 23. Within the flange is a washer support 32 which transmits the thrust from roller 28 via thrust bearing 33 to the head of spindle 29. The flange 31 takes only

circumferential torque forces from the spindle 29; the radial planet loads are taken by the hub 26 of the disc 23 Between each spindle 29 and its planet roller are an inner needle bearings and an 5 outer needle bearing 35 The inner end of spindle 29 is screwed or otherwise locked radially into the flanged hub 26 of the disc 23. All radial forces from the roller 28 via thrust bearing 33 are taken by tension in the spindle 29 The spindle end 36 has an oil passage 37 connected to a supply of lubricating oil (not shown).

The inner needle bearing 34 is lubricated by way of the passage 37 and the outer 10 needle bearing 35 is lubricated by oil which passes from the needle bearing 34 up the annular passageway 38 between the spindle and a bore of the planet roller.

Figures 2 to 6 illustrate various modifications of the assembly shown in Figure 1.

Each of them is only a partial view, showing principally the epicyclic roller stage 15 and the immediately adjacent components Figure 2 illustrates a first modification in which the planet rollers 28 engage the raceways 21 and 22 in zones which are radially spaced, being at different radially distances from the (common) axis of rotation of the planet assembly and the main 20 shaR 2 Accordingly, different portions of the bevelled engagement surface of the planet rollers engage the raceways 21 and 22. In this manner the fatigue life of the whole roller assembly is increased by the distribution of the contact stress cycles over more than one path.

25 Figure 3 illustrates another modification showing an extension of the principle embodied by Figure 2. In this modification the member 21 has two inclined, cambered, annular contact surfaces 21a and 21b contacted by the planet rollers 28 in zones radially spaced from each other and from the zone of contact on the raceway 22 on the output member 8 of the toroidal stage 6 Figure 4 illustrates a yet further embodiment in which there is a four-track engagement of the planet rollers 28 with the raceways. Member 21 has two convexly cambered surfaces 21 and 21b, similar to those shown in Figure 3, and

- 6 the output disc 8 has two convexly cambered radially spaced surfaces 22a and 22b.

The various surfaces 21a, 21b, 22a and 22b all engage the planet rollers in different, radially spaced engagement zones. Provided that the planet rollers have a true straight-sided bevel there can be in principle any reasonable number of 5 contacting paths. It will be appreciated that the convex surfaces need in this embodiment to be on the members 21 and 28 rather than on the planet rollers.

The axes of the planet rollers need not, as shown in the previous Figures, be normal to the axis A of the main assembly. When the planet axes are normal to that 10 main axis, there is an effective epicyclic ratio of unity. However, in single regime systems, that is to say where there is a single transmission path from the toroidal rolling traction stage to the final output, a maximum required reverse speed ratio is generally less in magnitude than a maximum forward speed ratio. Figures 5 and 6 illustrate a modification in which the epicyclic axis is obliquely inclined to the 15 principal axis, though in both these embodiments the roller contacts are concentric with the main axis A When the epicyclic ratio corresponds to the speed ratio in the drive stage 6 the output speed is zero. Thus one may provide a speed ration ranging from the 20 equivalent to a clutch to a desired maximum forward ratio, such a range is suitable for use in, for example, motorcycles and scooters Figure 6 illustrates a yet further embodiment as well as illustrating the oblique inclination of the epicyclic planet axis. In Figure 6, the hydraulic piston and 25 cylinder arrangement, embodied in the earlier embodiments by disc 19 and the associated components, is replaced by an end load device comprising, a tapered roller 60 in a face cam 61. In this embodiment the cam 61 has a convexly cambered surface 62 which is engaged by the straight bevelled surface of each planet roller; the contact lines intersect on the principal axis.

The end load device provides an end load which is preferably proportional to the output torque. In contrast, in the earlier embodiments having the hydraulically

- 7 actuated piston, the pressure is preferably made proportional to the variable roller reaction by way of the roller control system.

In the embodiment shown in Figure 7 the cam 61 has a bevelled surface 62a 5 which is engaged by a convex annular surface 28a of each planet roller. The output disc 8 has likewise a straight bevel 8a engaged by the convex surface 28a of each planet roller 28. It is difficult in practice, where the periphery of the planet roller is a continuous curve to ensure that the contact lines meet exectly on the principal axis. In Figure 7 the true bevel line is shown by the chain line B. which will 10 intersect the true bevel line C of the face cam 61 at a location slightly removed from the principal axis A, though within the main shah 2 The embodiments shown in Figures 6 and 7 include a needle bearing 34 at the inner end of the epicyclic roller 28 and an annular contact bearing 33a at the outer 15 end. The contact bearing 33a can support both radial and side loads It is important' to achieve low loss, to maintain the roller contacts truly concentric with the main axis A because there is no mechanism for equalising torques as there is in the toroidal race section Various expedients can be adopted to avoid reliance on very narrow manufacturing tolerances. Both involve locating relative to a concentric surface, one being external and the other internal.

25 As is shown in Figures I to 5, the spindles 29 are screwed into a concentric hub (26) up to their shoulders. Only two dimensions need to be tightly maintained, namely the distance from the threaded shoulder to the head shoulder and the thickness of the washer which supports the thrust bearing 33. The spindle may be screwed home and locked against rotation by staking into a slot in the head.

In Figures and 7, the epicyclic roller spindle protrudes through the epicyclic carrier and contacts the inner circumference of the collar 23a which is integral with the output member. This is also a fundamentally concentric surface and the

- 8 outward load, which is a proportion of the main end load, on the epicyclic roller will maintain the spindle against the collar at two points, thereby preventing rotation of the spindle. The 'tight' dimension is only the distance of the bearing locating shoulder from the top of the spindle.

Claims

- 9 - CLAIMS

1. A roller epicyclic comprising first and second members (8, 17) which are mutually rotatable about a principal axis (A) and which each provides a respective 5 contact surface (21a, 22); and a planet carrier (23) carrying a multiplicity of planet rollers (28) each of which has a roller surface engaging the said contact surfaces; wherein the lines of contact between the planet rollers and the contact surfaces converge towards the principal axis 10

2. A roller epicyclic according to claim I wherein said lines intersect substantially on said principal axis

3. A roller epicyclic according to claim I or 2 wherein the said contact surfaces are convexly cambered

4 A roller epicyclic according to any foregoing claim wherein the planet rollers have radially spaced engagement zones with the said contact surfaces.

5. A roller epicyclic according to any foregoing claim wherein at least one of 20 the first and second members provides at least two distinct radially spaced contact surfaces (21a, 21b) for simultaneous engagement by the planet rollers

6 A roller epicyclic according to claim 1 wherein the planet roller surface has a convexly cambered engagement zone.

7. A roller epicyclic according to any foregoing claim wherein the second member (17) comprises a torsionally locked but axially moveable piston (19) disposed to respond to fluid pressure to compress axially the assembly including the contact surfaces and the planet rollers.

8. A roller epicyclic according to claim 7 wherein the piston (19) is disposed within a hub (18) and means are provided to supply fluid pressure to a space between the piston and the hub

( - 10

9. A roller epicyclic according to claim 8 and including a preload spring (40) between the hub and the piston 5 10 A roller epicyclic according to any of claims 1 to 6 wherein the second member is a face cam (60) urged by an end load device (61) against the planet rollers. 11. A roller epicyclic according to any foregoing claim wherein the first 10 member is an input drive member for the epicyclic, the second member is a reaction member and the planet carrier is an output drive member 12 A roller epicyclic according to any foregoing claim wherein each planet roller is mounted for rotation by means of at least one needle bearing (34. 35) on a 15 respective spindle (29) 13 A roller epicyclic according to any foregoing claim wherein the planet carrier includes a thrust bearing (33) for resisting outward movement of each respective planet roller.

14 A roller epicyclic according to any foregoing claim wherein the axes of rotation of the planet rollers (28) are perpendicular to the principal axis (A).

15 A roller epicyclic according to any foregoing claim wherein the axes of 25 rotation of the planet rollers (28) are obliquely inclined to the principal axis (A).

16 A drive system comprising a toriodal race rolling traction unit (6) having an output member (8) which constitutes or is connected to the said input member of a roller epicyclic according to any foregoing claim