TO VARIABLE GEARS AND DRIVES

This invention relates to a variable gear or drive. Applications are,

for example, continuously variable transmissions, or variable camshafts.

There is a demand for variable gear sets, particularly in automotive applications and many well known methods have been used. However, none use a truly variable gear set in which the centreline of two gears

may be varied whilst exerting full power and remaining at constant

velocity.

This invention makes use of the type of centreline displacement made possible by a constant velocity joint of the type described in PCT/GB 92/02219. This invention uses the circumference of one or both of the flanges to transmit drive in either direction. The flanges may be of different sizes and shapes, including eccentric or camshaft profile.

According to the present invention there is provided a variable drive comprising a driving flange, a driven flange facing the driving flange, guides disposed in each flange and extending radially with respect to the centre of the flange, members retained for movement in the guides, means for operatively connecting the members in the two flanges together whereby torque may be transmitted through the members between the flanges and the rotational axes of the flanges moved laterally

relative to one another and a transmission member disposed to be driven through the periphery of one of the flanges or through the periphery of a member operative to rotate with the said one flange.

Three example implementations of the invention are outlined in the

following sections. These are; use in a continuously variable transmission using friction drives or a sequential gearbox using direct gear drive in a series of distinct steps; use in the special case of an epicyclic gear set; and use in the generation of variable controlled eccentric drive such as

those generated by camshafts.

The invention may be used in continuously variable transmissions (cvt's). It may relate to those which use the adhesion between smooth, rotating surfaces to transmit power, though application of the invention to types using sliding gears, in discrete speed steps, is also possible. As distinct from previous cvt's and gearboxes with fixed speed steps, these cvt's exploit the facility of the invention to continuously vary the centreline of driving, or driven shafts, whilst exerting full power, at constant velocity and over a wide range of centres.

The cvt described by way of example transmits power through the adhesion between two cones, hard surfaces, under hydrostatic, or other pressure. Such surfaces, though apparently touching one another, are not in direct contact and their adhesion is due to the action of a suitable

"sticky" lubricant under pressure, i.e. one with a high shearing resistance.

An alternative is also available, consisting of a number of parallel steps with a coned surface joining each successive one, operated by a profiled

driving, or driven, member, with a parallel portion and matching coned end, so as to continue to drive during progression between steps. In this way, by variation of pressure between steps, whilst traversing the cone, drive can be maintained to give a near simulation to the smooth

transmission of power between the two cones of the preferred method

for a cvt. Ether the main cone, or the driving, or driven, but lesser cone,

are moved sideways and endwise to bring about speed variation of whichever of them is the output shaft, whilst the power unit speed and torque remain substantially constant and under external, e.g. driver, control.

To achieve this longitudinal movement alongside the main cone, the lesser driving, or driven, cone, must translate inwards, or outwards, as well, whilst maintaining drive, which is readily arranged by use of the invention. This drive will operate on either side of the centreline bisecting the extreme positions, or at any other location dictated by the power unit design and proportions viewed as a whole.

Pressure between the two cones is maintained by means of a telescopic hydrostatic jack and a roller assisted yoke, positioning the smaller cone to suit the rate of working required by the central system, as

well as by two pistons thrusting, the inner housing carrying the driving, or driven shaft sideways. In conjunction with the telescopic jack, rollers act

on a pair of surfaces on either side of the centreline of the jack and

angled to be parallel to the major cone profile.

If the major cone is not intended to translate sideways on tall splines, then the lesser cone does so and to do this has telescopic

driving, or driven tubes, each with ball spline, one inside another.

The system may be controlled in a number of ways and complexity from simple mechanical positioning with manual selection, through to microprocessor control using various inputs and high speed positioning devices.

A variation of the drive is to use a step cone with parallel sections for steady operation between coned portions. A further variation is to use a sliding gear arrangement in which a pinion is substituted for the lesser cone, and the major cone has a series of mating gears with successively differing numbers of teeth but to a common module. The matching cones on the pinion and between the gears on the major cone, in conjunction with a control system, act to synchronise gear wheel and pinion peripheral speeds, together with a clutch or fluid flywheel.

Figure IA depicts, in semi diagrammatic form a plan view of the

cvt. (Some features are shown in plan view for clarity, whereas they would in reality lie in another plane). An inversion of Rgure IA is also available though it is not illustrated. In this inversion the adhesive surfaces operate on the inside of the major cone whilst the telescopic

assembly operates inside its open end. Again the major cone can be

arranged to slide on ball splines to replace the telescopic arrangement of shafts contained in the inner housing with a long fixed and supported spindle.

In order that the invention may be more clearly understood, several

embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which:-

Rgure IA diagrammatically shows in section one form of continuously variable transmission incorporating a variable gear according

to the invention,

Rgure IB is a partial view of a modified profile for use in the embodiment of Rgure IA,

Rgure IC is a partial view of a modified cone and gear profile for a sliding gear for use in the embodiment of Rgure IA,

Rgures 2A and 2B respectively diagrammatically show another

form of gear according to the invention in side and end elevationai sectional views.

Rgures 3A and 3B are views corresponding to Rgures 2A and 2B but of a modification of the embodiment shown in those latter figures,

Rgures 4A and 4B are views corresponding to Rgures 3A and 3B

but of a modification of the embodiment shown in the latter figures,

Rgure 5 diagrammatically illustrates a further embodiment of the invention relating to a cam shaft,

Rgure 6 shows a diagrammatic split section illustrating the coupling between two adjacent flanges,

Rgures 7 and 8 illustrate members of the coupling shown in Rgure 6 and

Rgures 9 and 10 diagrammatically illustrate different operational positions of parts of the coupling.

For clarity of exposition the control circuits are not included.

Referring to Figure IA, a major cone I, in this case driven, is

journalled in a continuously variable transmission (cvt) housing 2 with a hollow output shaft, so as to accept a through shaft 3 and mating with the smaller driving cone 4. Any input gear and flange 5 is situated midway between the extreme sideways positions of the centreline of the smaller driving cone 4.

In order that the driving cone 4 can traverse along the major cone I, internal housing 7, not only journals the driven flange of the flexible drive

6, but also houses telescopic driving tubes 8 and 9, each equipped with

ball bearing spline and which extend outwards as the driving cone 4 reaches the outer larger end of the major driven cone I. The ball spline ensures a friction free longitudinal extension of the complete driving assembly, containing cone 4 and its spindle, whilst the flexible drive 6 operates on either side of the centreline of input gear and flange 5, ensuring a constant velocity drive at full power.

The smaller driving or driven cone 4 is shown in the fully extended position by the chain dotted line with edge marked.

Housing 7 moves inwards or outwards under the control of two hydraulic cylinders 10, situated above and below, that is on either side of, inner housing 7, but shown herein diagrammatically as a single piston and cylinder 10 for clarity of exposition. The piston and cylinders 10, also control the adhesion loading between cones I and 4.

Longitudinal motion and exact locating of cone 4 is under the control of a telescopic positioning jack II. A roller yoke 12, to which the

positioning jack II is pinned, together with the machined ribs 13 on either

side of the yoke 12, on which the rollers 14 operate, relieve the bearings of

housing 7 of the side thrust due to the adhesion loading of piston and

cylinder 10.

As mentioned earlier in the text, the reverse gear is not shown. It would be situated in the open end of the large cone, ahead of the

differential.

For drive of the two wheels of a vehicle, for example, the drive from the major cone I is taken through a casing 15 of a well known type of parallel differential. Output drive is taken from a short output shaft 16 and a long through shaft 3. Alternatively, if only one drive is required it may be taken direct from the output shaft of the cone I, which need not be hollow.

Rgure IB illustrates a profile needed for a stepped version of the major cone I.

Rgure IC illustrates the cone and gear profile for a sliding gear, multiple stepped version of the major cone I.

For clarity, a reversing gear, which in the case illustrated in Figure I would be fitted in the open end of the major cone and ahead of the differential is not illustrated.

In another example the invention may be used to replace the sun and planet gear of a conventional epicyclic gear set. The input side replaces the sun gear and the output side replaces the planet gear which

meshes with the ring gear (annulus gear). This opens up a form of epicyclic gear set in which a different range of gear ratios is possible than

would be the case in a conventional epicyclic gear. Furthermore this

arrangement results in the ring gear rotating in the same direction as the sun gear. The input and output sides may be reversed in this application. An example in which the ring gear is fixed is shown in Rgure 2A and 2B in which an input shaft 21 is connected to one side of the invention. A driven planet gear 22 is connected on the output side of the invention meshing with a fixed ring gear 23. An output shaft 24 is connected to the driven gear 22 by means of a flange 25. In this arrangement the output shaft rotates in the opposite direction to the input shaft.

In order to derive a greater range of gear ratios the output or driven shaft may be reduced in size and used to drive either a ring gear or a sun gear. An arrangement using a fixed sun gear is shown in Rgures 3A and 3B and using a fixed ring gear in Rgure 4A and 4B.

Referring to Rgure 3A and 3B, the input shaft 31 drives the output side planet gear 32 which meshes with the fixed sun gear 33. The plant

gear 32 is retained in place by two follower gears 34 connected by a

flange 35. As the planet gear 32 rotates the sun gear 33 the flange 35 rotates about the sun gear and drives output shaft 36 in the same direction as the input shaft 31.

Referring to Rgure 4A and 4B, in a similar arrangement an input shaft 41 drives a planet gear 42 which meshes with a ring gear 43. The

planet gear 42 is retained in place by two follower gears 44 connected by a flange 45. As the planet gear 42 rotates and drives the flange 45 around the ring gear, the output shaft 46 rotates in the opposite direction to the input shaft 41. By using an additional pinion between the planet gear 42 and ring gear 43, the output shaft 46 may rotate in the same direction as the input shaft 41.

In another example the invention may be used to provide a means of incorporating non-circular motion into adjacent components such as in commonly provided for by camshafts. However, in this application, and unlike conventional camshafts, the motion may be variable and controlled by means of suitable positioning devices.

It is not proposed to detail these positioning devices which may be hydrostatic, electrohydrauiic, pneumatic or mechanical and may vary from

a simple lever to a high speed positioning device.

Similarly control of the positioning devices can vary from manual operation of a simple lever, to a microprocessor controlled and high complex system for imparting various inputs under differing conditions.

For example, in an engine, the control signal might well consist of a combination of variables including engine speed, throttle opening, load

and so on.

An example of such a system is shown in Rgure 5 for use as a camshaft capable of variable valve opening. Camshaft follower 51 (valve stem) is to be controlled. This is operated by the output side 52 of the invention. This output side may either be circular or have an eccentric or lobe shape, as a normal camshaft. It is connected to a positioning device 53 through a bearing 54 such that it may be moved either side to side, up or down, or in any combination. The input side 55 of the invention is a gear driven by a corresponding gear 56 on a shaft 57 having one or more such gears. The input side gear is located by a conventional bearing 58 mounted to the cylinder head. In the case of a typical engine, the gear 56 could drive two sets of input gears, to provide inlet and exhaust valve sets. Similarly, the output ear may be used to operate more than one valve.

By moving the positioning device 53, the effective camshaft profile

may be modified as the shaft rotates. For example if the positioning device moves the camshaft downwards toward the valve stem, then it

causes the valve to open, or increases its degree of opening. In the

extreme case the camshaft profile on item 52 may be completely circular.

The opening rate, profile, amount and duration of the valve 51 may be determined by the movement of the positioning device during a revolution of the camshaft. More usually, the camshaft profile on item 52 would provide the basic shape of the required valve characteristics, and the

control system and positioning device would be used to modify that

profile as required in different circumstances.

Referring to Rgures 6 to 10 briefly the joint described in PCT/GB 92/02219 comprises three concentrically journalled members spaced at 120° intervals between driven and driving flanges. Two members 61 and 62 are shown respectively in Rgures 7 and 8, member 62 being journalled around member 61. A further member similar to member 62 would be journalled around that member. Each member has two oppositely directed extensions 63 and 64 which form rollers which run in radially extending guides formed in the facing faces of the two flanges. Three guides in one face are respectively referenced 65, 66 and 67 in Rgure 6. There are three similar guides in the other face.

The rotating faces may move in any direction within the limits of

the members and whilst maintaining their faces parallel to each other.

Thus one rotating face may follow an orbital or eccentric path around the other whilst both are spinning. The direction of movement of the orbital or

eccentric path may either be in the same direction as the direction of rotation of the faces, or in the counter direction. Rgure 9 shows the

position of the rollers in the slots of adjacent flange faces when those flanges are in line. Rgure 9 shows a similar view but when the flanges are displaced laterally with respect to one another. In both figures 9 and 10

the rollers in one face are shown blacked in and those in the other face in

outline.

It will be appreciated that the above embodiments have been described by way of example only and that many variations are possible without departing from the scope of the invention.