GB2076081A

GB2076081A - Power transmission system

Info

Publication number: GB2076081A
Application number: GB8015835A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-05-13
Filing date: 1980-05-13
Publication date: 1981-11-25
Also published as: GB2076081B

Abstract

A power transmission system for a motorised vehicle or the like comprises two aligned drive shafts (18, 18') the remote ends of which are adapted to be universely jointed to respective output shafts (20) and the adjacent ends of which are guided for movement along respective predetermined paths in slots (24, 24') extending generally radially of the axis of rotation of the drive shafts in an intermediate driven flywheel (14). Each shaft extends through a conical bore in a member (27) secured to a housing of the system, the conical bore tapering towards the outer end of the shaft (18). A respective disc- shaped member (28) is coaxially mounted on each drive shaft for engagement with the surface of the conical bore and is axially displaceable along the drive shaft in response to relative rotation between the disc- shaped member and the drive shaft. <IMAGE>

Description

SPECIFICATION Power transmission system The present invention relates to power transmission systems.

According to the present invention there is provided a power transmission system for a motorised vehicle or the like, the system comprising a drive shaft one end of which is adapted to be universely jointed to an output shaft and the other end of which is guided for movement along a predetermined path extending generally radially of the axis of rotation of the drive shaft; a member secured relative to a housing of the system and having a throughbore coaxial with the axis of rotation of the drive shaft, said throughbore tapering inwardly towards said one end of the drive shaft; and a substantially discshaped member coaxially mounted on said drive shaft for engagement with the surface of said throughbore, said disc-shaped member being axially displaceable along said drive shaft responsively to relative rotation between said disc-shaped member and said drive shaft.

In a preferred embodiment of the invention the disc-shaped member is engaged in a helical groove in the drive shaft so that relative rotation of the two screws the disc-shaped member along the drive shaft. Alternatively, one or more tether cables may be arranged substantially parallel to the drive shaft with one end secured to a fixed member on the shaft and the other end secured to the disc-shaped member. Relative rotation of the disc-shaped member and the drive shaft twists the tether cables to shorten the distance between the two members and move the disc-shaped member axially along the drive shaft.

The present invention is further described hereinafter, by way of example, with reference to the accompanying drawing which shows one embodiment of a power transmission system according to the present invention for a motorised vehicle.

In the drawing the transmission system 10 has a housing 12 which contains a flywheel 14 of substantially H-shaped cross section rotatably mounted centrally of the housing 12. The wheel 14 is driven by an engine 1 6 by suitable drive means such as a chain drive or crown wheel and pinion drive. The engine 1 6 is preferably a twodirectional internal combustion engine but may be for example an electric motor. The system 10 is divided into two halves which operate in the same manner and are substantially identical in construction. Only the left half as seen in the drawing will be described for convenience.

One end of a drive shaft 18 is universally coupled to an output shaft 20 which mounts a road wheel 22. The other end of the drive shaft 1 8 engages in a slot 24 in the flywheel 14, the slot 24 extending radially of the flywheel 14 from a location spaced a small distance from the centre thereof. The corresponding slot 24' on the opposing side of the flywheel 14 extends in the opposite direction to that of the slot 24 to provide a balance operation of the system.

The drive shaft 1 8 passes through a throughbore 26 in a member 28 which is rigidly secured in the housing 12. The through bore 26 is arranged coaxial with the drive shaft 1 8 when the latter is centred in the flywheel 14 and is frusto-conical in shape tapering towards the outer end of the drive shaft 18. The latter mounts a disc-shaped member 28 which is preferably in the form of a finely studded wheel which is arranged to contact the surface of the bore 26 when rotation of the flywheel 1 4 urges the associated end of the drive shaft 1 8 radially outwardly. The narrow end of the bore 26 is of smaller diameter than the wheel 28.

The drive shaft 1 8 is, of course, free to rotate in the slot 24.

The wheel 28 is keyed into a helical groove in the drive shaft 1 8 so that relative rotation of the wheel 28 and the drive shaft 1 8 screws the wheel 28 along the drive shaft. A stop may be provided on the drive shaft 1 8 to limit axial movement of the wheel 28 towards the flywheel 14. The groove preferably has a very course pitch so that when the wheel 28 is rotated the major component of force developed acts to rotate the drive shaft 1 8 with only a small component of force acting to move the wheel 28 axially along the drive shaft.

The wheel 28 is adapted to engage at all times the surface of the bore 26 and the radially outer edge of the wheel 28 is contoured to ensure substantially full engagement with the surface of the bore 26. The edge of the disc is conveniently finely studded with points to reduce the possibility of slip. In addition, the surface of the bore 26, may comprise tightly packed nylon or steel wire bristles with the surface, although generally being frustoconical, being in longitudinal cross-section convexly curved with the exact contour of the surface being chosen in dependence upon various factors such as the power output of the engine, its economic range of rpm, the pitch of the helical groove and the resilience and length of the aforementioned bristles.

The operation of the system will now be described.

If the system is considered initially at rest, as the flywheel 14 begins to rotate, driven by the engine 16, the drive shaft 18 will tend to move along the slot 24 towards its outer end thus bringing the wheel 28 into engagement with the surface 26 of the member 27. When the wheel 28 comes into contact with the surface 26 it will begin to run along the surface 26 and will therefore rotate. This rotation of the wheel 28 will act on the initially stationary drive shaft 18 to cause the latter to begin to rotate and drive the road wheel 22. However, the wheel 28 will also tend to move along the drive shaft 18 because of its engagement in the helical groove on the drive shaft.Depending on the relative diameters of the wheel 28 and the surface of the bore 26 at its point of contact with the wheel 28 the drive shaft 1 8 may make considerably more or fewer revolutions than the engine, or none, in the opposite direction to that of rotation of the flywheel 14 and thus by suitable choice of these diameters any desired gear ratio may be obtained.

As the wheel 28 winds itself towards the outer end of the member 27 the gear ratio is reduced, that is the road wheel 22 makes fewer are no revolutions for a given rpm of the engine.

When the vehicle is driving the engine, that is the road wheels are being turned faster than they are being driven by the engine then the drive shaft 1 8 is rotated relative to the wheel 28 to cause the latter to move towards the wider end of the member 27 and the gear ratio will increase. In addition, if the speed of the vehicle increases rotation of the drive shaft 1 8 will increase causing the wheel 28 to move towards the wider end of the member 27 again increasing the gear ratio and the engine rpm will therefore remain substantially constant.

In a modified system according to the present invention only one drive shaft is provided and its associated flywheel is conveniently coupled coaxially with the crank shaft of the engine. The drive shaft is conveniently coupled to the drive wheels of the vehicle by way of a differential gear as is well known.

In front wheel drive vehicles the illustrated system may be divided into two halves each mounted on a respective side of the engine in line with the crank shaft. This embodiment would not require either a clutch or differential gear.

In a further modified system according to the present invention, instead of the helical groove in the half shaft 18 the wheel 28 is coupled to a disc 30 by way of a number of tether cables 32. The disc 30 is axially and rotatably secured on the half shaft 18 between the member 27 and the drive shaft 20 and may be mounted by way of a universal joint to allow some small degree of pivoting of the disc 30. The tether cables 32 are arranged generally parallel to the axis of the shaft 1 8 as substantially equal angular intervals about the disc 30 and the wheel 28 to ensure balanced operation. When the wheel 28 rotates relative to the half shaft 1 8 the tether cables 32 twist about the shaft 1 8 thus drawing the wheel 28 along the shaft 18 towards the narrower end of the bore 26 hence reducing the drive ratio from the engine to the shaft 1 8. To reverse the drive the engine drive is reversed. This is relatively simple with a two stroke engine: the concept lends itself to twostroke diesel engines because of the use of a constant rpm. Finally, the positions of the member 22 and the relative positions of the wheel 28 and disc 30 may be reversed on the drive shaft 1 8.

Claims

1. A power transmission system for a motonsed vehicle or the like, comprises a drive shaft one end of which is adapted to be universely jointed to an output shaft and the other end of which is guided for movement along a predetermined path extending generally radially of the axis of rotation of the drive shaft; a member secured relative to a housing of the system and having a throughbore coaxial with the axis of rotation of the drive shaft, said throughbore tapering inwardly towards said one end of the drive shaft; and a substantially disc-shaped member coaxially mounted on said drive shaft for engagement with the surface of said throughbore, said disc-shaped member being axially displaceable along said drive shaft responsively to relative rotation between said disc-shaped member and said drive shaft.

2. A system as claimed in claim 1 wherein the disc-shaped member is engaged in a helical groove in the drive shaft so that relative rotation of the two screws the disc-shaped member along the drive shaft.

3. A system as claimed in claim 1 further comprising at least one tether cable arranged substantially parallel to and spaced from the drive shaft and wherein the or each cable is secured at one end to a fixed member on the shaft and at the other end to the disc-shaped member such that relative rotation of the disc-shaped member and the drive shaft twists the tether cables to shorten the distance between the two members and move the disc-shaped member axially along the drive shaft.

4. A system as claimed in claim 1,2 or 3 comprising two said drive shafts whose axes are generally aligned with one another and wherein said one ends of said shafts are guided for movement along said paths by means of a flywheeled intermediate said one ends, said paths being formed by respective radial slots in said Hywheel which slots extend in radially opposing directions.

5. A power transmission system for a motorised vehicle or the like, substantially as hereinbefore described with reference to the accompanying drawing.