GB2028441A

GB2028441A - Continuously Variable Ratio Transmission

Info

Publication number: GB2028441A
Application number: GB7834185A
Authority: GB
Original assignee: COLES D N
Current assignee: COLES D N
Priority date: 1978-08-22
Filing date: 1978-08-22
Publication date: 1980-03-05

Abstract

Two frictionally engaging rotors are connected respectively to an input and an output shaft. The first rotor comprises a hollow part spherical member A rotating about an axis Y through its centre and the second rotor comprises a body B holding a plurality of wheels C which are mounted to rotate freely on axes tangential to a circle with its centre at the centre O of the spherical member, the rotor being rotable about the axis of this circle. Reaction between the two rotors is transmitted by axial forces on the wheels which engage with the first rotor either only frictionally or also by other means, such as a depressable pinned surface on the interior of the first rotor. By varying the inclination of the axes of the two rotors the ratio of the angular velocities of the two rotors can be varied continuously and infinitely. <IMAGE>

Description

SPECIFICATION Continuously and Infinitely Variable Ratio Gearbox Using Frictionally Engaging Elements Introduction The following describes the principle and underlying theory of an infinitely and continuously variable ratio gearing device using frictionally engaging elements.

All frictionally engaging elements are rolling, even during the process of changing ratio, thereby always transmitting force under static friction. Thus the device is perfectly efficient mechanically i.e. no energy is lost under than that lost in ball race bearings.

Because of this statically frictional arrangement of the engaging elements the power and torque transmission through the device may be increased without iimit by increasing the reaction loading between the frictionally engaging elements.

The device would be particularly suitable for automatic transmission of power in motor vehicles.

The principle and underlying theory are particularly simple and elegant not having been previously implemented in this arrangement to my knowledge, and because of the simple and symmetrical mechanical arrangement implementations of the device would be simple and cheap to manufacture, small in size and robust and reliable mechanically.

Description of Principle and Underlying Theory The functional working parts are shown in Fig. 1. A system of orthogonal axes X, Y, Z origin 0 are shown to aid description.

There are two fundamental engaging components.

1. A body (A) having spherical cavity with an aperture which rotates symmetrically about the Y axis with the centre of the spherical cavity at the origin 0. The radius of the circular aperture whose centre lies on the Y axis is less than that of the spherical cavity. For future reference this body will be named the 'cavity'.

2. A circuit disc (B) with small wheels (C) arranged round its perimeter. The wheels (C) are identical and each has its centre P lying on the perimeter of the disc (B) and is free to rotate in the plane perpendicular to the disc and passing through P and the centre of the disc. It is supposed that the wheels (C) are arranged symmetrically around the perimeter of the disc but this is not a necessary requirement to the principle. The combined disc and wheels will in future be referred to as the 'rotor' and has an overall diameter equal to that of the cavity i.e. the diameter of the disc plus the diameter of a wheel equals the diameter of the cavity.

These two components are arranged so that the disc has its centre at 0 and is free to rotate about an axis (D) normal to the disc and passing through 0. The axis (D) can move in the XY plane from lying along the X axis to lying along the Y axis i.e. the disc changes its inclination from lying in the YZ plane to lying in the XZ plane. The points of contact of the wheels (C), for any given inclination of the disc, all lie on a great circle of the spherical cavity.

If the cavity is driven at W (revolutions per minute) the disc will rotate at WSin H (revolutions per minute) and the ratio of the device will thus change smoothly from one to zero as the angle of inclination 0, between the axis of the rotor and the X-axis, changes from 900 to 00.

The angle of inclination can always be changed effortlessly irrespective of the normal loading force applied between the wheels (C) and the cavity because the wheels are always rolling along generators of the cavity.

In an implementation of this device the wheels (C) would be loaded by springs to exert a normal force on the surface of the cavity and the magnitude of these normal forces could be increased indefinitely to obviate slipping. Each frictional velocity reaction between the rotor wheels and the surface of the cavity is of course tangential to the rotor and the component of that velocity perpendicular to the plane of the rotor is lost (by rotating the wheel) whilst the component lying in the plane of the rotor rotates the rotor about its axis.

Variations in diameter of the wheels (C) such as might be incurred by wear in an implementation of the device, will have no effect on the principle providing the points of contact with the cavity are copianar with the disc.

The rotor may be regarded effectively as a disc of diameter equal to that of the cavity, with an edge which is frictionally perfectly smooth perpendicular to its plane and perfectly rough in its plane.

A theoretical proof of the fact that all wheels (C) act in unison i.e. all rotate the disc at the same angular velocity for any value of 0, is now given, (see Fig. 2).

Let the radius of the cavity and that of the rotor be denoted by r.

Consider the disc in the horizontal position (YZ plane, 0=0) and let Q be a point of contact (o, -r, o). A unit vectors tangential to the rotor at this point i.e. tangential to the circle of radius r concentric with the rotor and lying in its plane is (o, o, 1).

If the axis of the rotor is now moved in the XY plane towards the Y-axis through an angle o 90 ) and the rotor is then rotated through an angle a about its axis in the direction shown (Fig. 2) the co-ordinates of any point X on the rotor will transform to it

cos cos8 -cosasinO sinasinO where X'= sin 6 cos a cos 0 -sin a cos 0 X 0 sin a cos cu a Thus the unit vectors becomes

sin α cos V' = -sin α cos # cos α and the point Q becomes

r cos α sin # Q'= -r cos α cos # -r sin a Thus the generator on the cavity through the point Q' is the circle P with centre (0, -r cos a cos 0,0).

Thus the radius vector from the centre of the circle P to the point Q' is

r cos α sin # sin sin ) Thus the unit tangent to the circle P at the point Q' is

( sin a 2+2 sin26112 0cos asin 6 sinacosa cos sin 0 / The radius R of circle P is r(sinα+cosαsin#) Thus the velocity vector S of the cavity at the point 0' is

sin sin O cos α sin # where w is the angular velocity of the cavity (R.P.M.) and the component of this vector in the direction V' isV' . S=2 nr rw (Sin2a Sin 6+cos2a sin 0)=2 or row sin 0 Thus the angular velocity of the rotor is w sin 0 (R.P.M.) and is independent of .

Implementation (see Figs. 3 and 4).

In theory the cavity could be extended to a completely spherical chamber but this would not allow a drive to be extracted from the rotor. In a practical implementation the cavity has an aperture large enough to accommodate the carrier for the rotor, the drive shaft and the mechanism to control the inclination of the rotor.

The arrangement could be rather similar in principle to that normally deployed on front wheel drive vehicles. A constant velocity joint would be used, the input drive shaft lying at an angle of 450 to the rotor plane when at either extreme of its inclination so that the required 900 swing of the rotor plane could be achieved with the constant velocity joint only swinging about the input drive shaft through an angle of 450 in either direction.

A 450 constant mesh gearbox could be mounted on the carrier so that the drive shaft emerging from the cavity would lie paraliel and close to the carrier body thereby enabling the cavity to have an opening only sufficiently large to accommodate the carrier body support, the drive shaft and the mechanism for controlling the inclination of the rotor.

This later could be a simple mechanical rod and lever arrangement or deploy a Bowden Cable etc.

The wheels (C) are constantly accelerating and decelerating, whilst the cavity is rotating. In order to reduce the associated inertial forces the wheels would be implemented as small rings i.e. the outer ring of a ball race.

The acceleration of the wheels is greatest when the angle of inclination of the rotor is 450 in which position the total torque on the rotor is low for a given power transmission compared to that which it is designed to accommodate for small values of the angle of inclination.

Detailed investigation (not presented here) shows that the inertial forces on the wheels present no obstacle to the successful implementation of the device. Also the number of wheels is immaterial to the principle. However, in a practical implementation of the device it could be desirable (depending on the application) to have as many wheels as practically possible to reduce the frictional load transmitted by each wheel for a given total torque on the rotor.

For applications involving low power and torque transmission the number of wheels could be appropriately few thereby reducing energy lost in bearings.

In the arrangement shown in Fig. 5 a 12" diameter rotor could accommodate 100 wheel bearing assemblies of 1/2" diameter having a thickness of .1875" whilst retaining a .125" 'pillar' and a clearance of approximately .017" either side of each wheel assembly.

In the 'description of the principle' given earlier the wheels were stated to have their axes situated on the perimeter of the disc. Clearly in an implementation of the device the disc would be extended between the wheels as in Fig. 5 to provide additional strength.

Thus the 'disc' in Fig. 5 would be of radius 5.75" in the context of the 'description of the principle'.

Claims

1. A variable ratio gearbox assembly having one drive member as a hollow part spherical member engaging frictionally with three or more wheels which are each mounted to rotate on axes tangential to a circle which has its centre at the centre of the spherical member while axial forces on the wheels are transmitted to the second drive member being rotatable about the axis of the circle.

2. An assembly according to claim 1 where the axis of the second drive member passes through the centre of the hollow part spherical member at an adjustable inclination.

3. An assembly according to claim 1 or claim 2, wherein the one drive member is connected so as to transmit power to or from a shaft.

4. An assembly according to any one of claims 1 to 3, wherein the second drive member is connected so as to transmit power to or from a shaft.

5. An assembly according to any one of claims 1 to 4, wherein the second drive member is carried in bearings in a housing where the housing can be fixed or controllably tilted about an axis through the centre of the second drive member.

6. An assembly according to any one of claims 1 to 5, wherein the hollow part spherical member is carried in bearings in a housing where the housing can be fixed or controllably tilted about an axis through the centre of the hollow part spherical member.

7. An assembly according to any one of claims 1 to 6, wherein the geometry of the elements is better than 90% perfect.

8. An assembly according to any one of claims 1 to 7, wherein the aforesaid wheels engage with the hollow part spherical member not only frictionally but also by other means which allow said wheels to roll but not slip at right angles to the direction of roll (as in a depressable pinned surface to the interior of the hollow part spherical member).