GB2182736A

GB2182736A - A variable drive assembly

Info

Publication number: GB2182736A
Application number: GB08626536A
Authority: GB
Inventors: Frederick Michael Stidworthy
Original assignee: Individual
Current assignee: Individual
Priority date: 1985-11-07
Filing date: 1986-11-06
Publication date: 1987-05-20
Also published as: GB8626536D0; CN86107529A; AU6593186A; GB8527525D0; EP0245344A1; WO1987003055A1

Abstract

A variable drive assembly comprises a first rotatable member (1) carrying a first coupling element (b) which is rotatable with the first member and engages a second coupling element (a) rotatably mounted on a carrier (5, 6, 7) which is rotatable with a second member (2). Rotation of the second coupling element (a) by the first coupling element (b) is precluded so that rotation of the first coupling element (a) causes rotation of the carrier (5, 6, 7) and the second member (2) rotatable therewith. Adjusting drive means (9) are mounted on the carrier (5, 6, 7) for rotating the second coupling element (a) via gears (c and d) to vary the coupling between the first and second rotatable members.

Description

SPECIFICATION A variable drive assembly This invention relates to a variable drive assembly in which first and second rotatable members, such as shafts and/or components, are coupled together in order to transmit torque and/or rotary motion in an adjustable manner.

It is envisaged that an assembly embodying the present invention will find its primary application in the motor vehicle industry, but it will be appreciated that the assembly could be employed in any other suitable situation, such as aircraft production and machine tool manufacture.

According to the present invention, there is provided a variable drive assembly in which a first rotatable member carries a first coupling element which is rotatable with the first member and engages a second coupling element rotatably mounted on a carrier which is rotatable with the second member, rotation of the second coupling element by the first coupling element is precluded so that rotation of the first coupling element causes rotation of the carrier and the second member rotatable therewith, and adjusting drive means are mounted on the carrier for rotating the second coupling element to vary the coupling between the first and second rotatable members.

In order that the invention may be readily understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a view from one side of a variable drive assembly embodying the invention; Figure 2 is a partly sectioned view taken from the left in Fig. 1; Figure 3 is a view of the assembly from the other side; and Figure 4 is a partly cross-sectional plan view of the assembly.

Throughout the drawings bearing surfaces are indicated by thick lines.

The Figures of the drawings illustrate a variable drive assembly comprising a first shaft 1 coupled to a second shaft 2, the shafts being freely rotatably supported by respective bearings, indicated schematically by the arrows B in Fig. 3, for rotation about a common axis xx.

The shaft 1 carries at its end nearest the shaft 2 a worm-wheel b which is fixed to, or part of, shaft 1.

The shaft 2 carries at its end nearest the shaft 1 a carrier-hub 8 which is fixed to, or part of, shaft 2.

A carrier structure is mounted on the carrier-hub 8 and comprises a back-plate 7 from which extend two parallel arms 5 and 6 which are integral with or fixed to the backplate 7 which itself is integral with, or fixed to, the carrier-hub 8.

A worm a is mounted at the ends of the arms 5 and 6 on a lay-shaft 3 extending transversely of the axis x-x, the worm a being engaged with the worm-wheel b carried by the shaft 1. In the present example, the combination of worm and worm-wheel has a ratio of 10:1, that is 10 revolutions of the worm will produce one revolution of the wormwheel.

The carrier arms 5 and 6 also support an electric motor 9 having a drive shaft 4 extending through the carrier arm 6 and carrying a spur-gear which is engaged with a spur-gear c on the lay shaft 3. The worm a and the spur-gear d are integral with or fixed to the lay shaft 3 which is freely rotatable about axis Y-Y in bearings provided in the carrier arms 5 and 6. The spur-gear c is integral with, or fixed to, the motor drive shaft 4 which in rotatable about axis Z-Z. The spur-gear d has 16 teeth, whilst spur-gear c has 80 teeth, so that one revolution of gear c will cause gear d to rotate 5.5625 revolutions.

Any rotational movement of the motor shaft 4 will cause gear c to rotate, thereby rotating gear d and causing shaft 3 to rotate to drive the worm a.

The lead angle between the worm a and worm-wheel b is selected to be a "locking angle", that is an angle between about 5 degrees and 1 5 degrees. With such a lead angle, it is possible to drive the worm-wheel b by rotating the worm a, but impossible to drive the worm a by rotating the worm wheel b. Consequently, upon rotation of the first shaft 1 in the direction R in Fig. 1 the wormwheel b will lock with the worm a and cause the carrier structure together with the second shaft 2 to rotate en masse with the shaft 1 in the direction R.

If power is supplied to the electric motor 9, for example by means of a slip-ring arrangement (not shown), then the motor shaft 4 will rotate the spur-gear c in the direction SR (Figs. 1 and 3), for example, thereby rotating the lay shaft and worm a in the direction WR (Figs. 2 and 4). The rotation of the spur-gear c and worm a could, of course, be in either direction depending upon the direction of rotation of the motor shaft 4.

The driving of the worm a by the electric motor 9 varies the transmission ratio between the shafts 1 and 2 depending upon the speed at which the electric motor 9 is rotated. Thus, if the electric motor 9 were driven at a speed to drive the worm a at 10 revolutions per revolution of the worm wheel b in the directions indicated, then the rotation of the shaft 1 would not be transmitted to the carrier and the shaft 2 which would remain stationary.

This enables the described assembly to function as a clutch. Thus, if the motor 9 is given sufficient power to rotate at, for example, 2000 rpm, the ratios employed in the assembly would allow shaft 1 to rotate at 1112.5 rpm without causing shaft 2 to move.

Consequently, if shaft 2 is loaded, i.e. subject to some resistance to rotation, it will be possible to rotate shaft 1 at 1112.5 rpm without any rotation being transmitted to shaft 2, assuming that the motor 9 is running at 2000 rpm. From this zero coupling condition, power can gradually be applied to shaft 2 by gradually reducing the power to motor 9 and thus effecting a gradual engagement of the shafts 1 and 2, culminating in a fully coupled condition when the motor is fully de-energised and the shaft 2 rotates at the same speed as the shaft 1.

If the worm wheel b and shaft 1 are stationary and power is provided to the motor 9, the worm a would orbit or "walk" around the worm-wheel b at a 5:1 rate of advantage. If this is done with the motor providing an initial 5000 rpm, then by reducing the power to the motor in direct proportion to an increase (up to 1000 rpm) in the speed of shaft 1 from its initial stationary condition, a low-gear to 1:1 coupling can be realised. This approach would include, in this example, a mixed power drive, that is electric drive to motor 9 and whatever other power supply is provided for shaft 1.

As supplying power to the motor 9 can cause the worm a to shift its angular position realtive to the worm-wheel b in either direction, the phase of the rotation of the shaft 2 can be advanced or retarded relative to the rotation of the shaft 1 by any required amount. Furthermore, although the above description assumes that shaft 1 acts as an in put shaft and shaft 2 as an output shaft, either shaft can, in fact, assume the role of input or output.

The above described assembly finds particu lar application in internal combustion engines, where the valve timing can be varied by incor porating an assembly embodying the present invention in the usual drive from the crank shaft to the camshaft. The phase of the rotation of the camshaft relative to the crankshaft can then readily be varied in a continuously variable manner throughout a full 360 .

The invention also finds application in transmissions, where the assembly can pro vide a clutching action which can also provide advance/r,etard characteristics once the basic clutching action has been completed or par tially completed. For example, if full engage ment with a 1:1 ratio has been achieved, power may be fed to the motor 9 in order to rotate the worm a in a direction so as to drive the shaft 2 faster than shaft 1, provide an overdrive capability. In the case of an all electric source powering the transmission, for example, the supply could be split between a main motor driving the shaft 1 and the secon dary motor 9.In such circumstances, assum ing shaft 1 is provided with a fixed (say 4:1) coupling between worm-wheel b and a power source driving the shaft 1, once the power source has been driven up to its maximum revolutions (say 8000 rpm), thereby providing 2000 rpm rotation of shaft 1, then the shaft 1 could be slowed down by energising the moytor 9.

The electric motor 9 of the described embodiments could, 6f course, be replaced by a hydraulic motor or pump, with a pressure regulated hydraulic supply being the prime mover for the worm a.

In applying the present invention to a camshaft, the drive sprocket of the camshaft could be attached to one of shafts 1 and 2 and the camshaft could be constituted by or attached to the other of the shafts. Alternatively, a drive assembly embodying the invention could be connected between the crankshaft and its output pulley or gear, thereby leaving the camshaft totally standard, if desired.

In the described embodiment of the invention, gearing is included between the motor 9 and the worm a. However, it is envisaged that this may not be necessary in all circumstances and that the assembly may employ a direct drive from the electric motor to the lay-shaft 3, with the motor and lay-shaft being in-line.

Alternatively, the motor 9 could be disposed paralle to the output shaft 2 with a flexible or angled coupling to the worm a by means of cables or gears. It is further envisaged that the motor 9 could be mounted concentrically within the worm with a stationary rotor and a driven outer case integral with, or attached to, the worm a.

Claims

1. A variable drive assembly in which a first rotatable member carries a first coupling element which is rotatable with the first member and engages a second coupling element rotatably mounted on a carrier which is rotatable with the second member, rotation of the second coupling element by the first coupling element is precluded so that rotation of the first coupling element causes rotation of the carrier and the second member rotatable therewith, and adjusting drive means are mounted on the carrier for rotating the second coupling element to vary the coupling between the first and second rotatable members.

2. A variable drive assembly according to claim 1, in which the second coupling element is mounted on the carrier for rotation about an axis transverse to the axis of rotation of the second member.

3. A variable drive assembly according to claim 2, in which the adjusting drive means has a drive shaft extending transversely of the axis of rotation of the second member.

4. A variable drive assembly according to claim 3, in which the drive shaft of the adjust ing drive means drives a lay-shaft rotatable carried by the carrier and carrying the second coupling element by means of gearing.

5. A variable drive assembly according to any preceding claim, in which the first and second members are rotatable about a common axis.

6. A variable drive assembly according to any preceding claim, in which the first coupling element comprises a worm-wheel and the second coupling element comprises a worm engaged with the worm-wheel, the lead angle of the worm and worm-wheel being a locking angle.

7. A variable drive assembly according to any preceding claim, in which the adjusting drive means comprise an electric motor.

8. A variable drive assembly according to any one of claims 1 to 6, in which the adjusting drive means comprise a hydraulic motor.

9. A variable drive assembly substantially as hereinbefore described with reference to the accompanying drawings.

10. A camshaft drive arrangement incorporating a variable drive assembly according to any preceding claim.

11. Any novel feature or combination of features described herein.