GB2371606A

GB2371606A - A CVT having brakes which vary output speed

Info

Publication number: GB2371606A
Application number: GB0102184A
Authority: GB
Inventors: Charles David Wilkins
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-01-27
Filing date: 2001-01-27
Publication date: 2002-07-31
Also published as: GB0102184D0

Description

CONTINUOUSLY VARIABLE TRANSMISSION MEANS This invention relates to a continuously variable transmission means. More particularly, this invention relates to a means by which the torque exerted by a first rotating shaft can be transmitted to a second shaft in such manner that the second shaft rotates at an angular speed that may be the same as, or different from, the angular speed at which the first shaft rotates.

The invention finds one application in transmission systems by which the power exerted by an internal combustion engine is transmitted to means for making use of that power, for instance, the propulsion of a vehicle. Among such means that have been proposed, and used in practice, there are purely mechanical systems, such as one which comprises a belt or chain running over two parallel and oppositely directed conical members; fluid couplings; and systems making use of a hydraulic torque converter. The latter type is that most commonly used. While the first type can be regarded as being continuously variable, it no longer is widely used. The third type is not, properly speaking, continuously variable, since it usually involves complex sun-and-planet gearing with three or more forward gears, the actual forward gear used being determined by engine speed, unless that engine speed is overridden manually.

Running an internal combustion engine at varying speeds is not necessarily the most fuel-efficient way. There is therefore a need for a transmission system by means of which the torque exerted by a first rotating shaft may be transmitted to a second rotating shaft in a manner which can be continuously varied, so that the rate of rotation of the first shaft may be kept as near constant as possible, while

that of the second shaft may be varied over a wide range.

The present invention provides such a system.

According to one embodiment, the present invention provides an apparatus for transmitting torque exerted on a first rotatable shaft to a second rotatable shaft in such manner that the second shaft rotates at an angular speed that may be the same as, or different from, the angular speed at which the first shaft rotates, which comprises providing a first gear means attached to, and coaxial with, one of said first and second shafts, and at least one second gear means meshing with said first gear means and operatively linked to braking means, whereby torque exerted on one of said first and second shafts is transmitted to the other of said first and second shafts in response to braking force exerted by said braking means.

According to one embodiment of the invention, the apparatus comprises a first gear wheel attached to, and coaxial with, one of said first and second shafts, and at least one second gear wheel meshing with said first gear wheel, each of said second gear wheel or wheels being mounted on a respective gear shaft, parallel to said first and second shafts, and rigidly mounted on and orthogonal to, a cross member rigidly fixed to that one of said first and second shafts to which the first gear wheel is not attached, each of said gear shafts being operatively linked to braking means, whereby torque exerted on one of said first and second shafts is transmitted to the other of said first and second shafts in response to braking force exerted by said braking means.

According to another embodiment, the apparatus comprises a first bevel gear attached to, and coaxial with, one of said first and second shafts, and at least one third bevel gear meshing with said first bevel gear, and a second bevel gear

meshing with said third bevel gears or gears and attached to and coaxial with the other of said first and second shafts, each of said third bevel gear or gears being mounted on a respective gear shaft, orthogonal to said first and second shafts, and mounted on a rotatable mounting ring orthogonal to said first and second shafts, said gear shafts being operatively linked to braking means, whereby torque exerted on one of said first and second shafts is transmitted to the other of said first and second shafts in response to braking force exerted by said braking means.

A further embodiment of the invention provides ring-braking means operatively linked to said mounting ring to control the rate of rotation of said mounting ring.

It will be apparent that, whichever of the gearing means is provided between the first and second shafts, it does not matter which of the first and second shafts is driven by the primary power source. For the sake of clarity, the first shaft will be referred to as the drive shaft.

The invention will be further described with reference to the accompanying schematic drawings, in which: Fig. 1 is an elevation of a first embodiment of the invention; Fig. 2 is an elevation of a second embodiment of the invention; Fig. 3 is a diagrammatic representation of the gear engagement in Fig. 1; and Fig. 4 shows a variation of the gear engagement shown in Fig. 3.

Referring to Fig. 1 of the drawings, a drive shaft (1) is connected to a motor (M). The particular type of motor is

not critical to the invention. It may be a petrol or diesel engine, a steam engine, an electrical motor, or any other means of imparting torque to a rotatable shaft. A second shaft (2) is capable, when caused to rotate, of transmitting power for application elsewhere, e. g. for propulsion of a road or other vehicle. At the end of shaft (1) and coaxial therewith, there is provided a first gear wheel (3) which is appropriately toothed to mesh with further gear wheels (4,5), each of which is mounted at the end of, and coaxial with, a respective gear shaft (6,7). Each of said gear shafts is associated with its respective braking means (8,9), to be more fully described below. The gear shafts and braking means are mounted on a cross member (10) which is mounted at the end of, and orthogonal to, the second shaft. It will be apparent that the shafts (1) and (2), and the first gear wheel (3), are not in contact with one another, being separated by a distance that depends upon the length of gear shafts (6,7). The shafts (1,2) may therefore project towards one another for a short distance beyond the first gear wheel (3) and cross member (1) respectively.

Braking means (8,9) may be of any suitable means capable of producing a controllable braking force. Each may, for example, be: 1. A frictional brake, e. g. a disc or drum brake ; 2. An electromagnetic brake, e. g. an electric motor operating in reverse whereby an electric current retards rotation of the respective gear shaft, or the introduction of a fixed or adjustable resistance into a conductor connecting the positive and negative leads of an alternator, providing an increased resistance to rotation of the gear shaft; 3. A fluid brake, typically a pneumatic brake or a hydraulic brake, e. g. a positive displacement pump that provides a retarding force to the gear shafts as a

result of partial or complete operation of a valve controlling the outflow of fluid from the pump.

A combination of such systems may be employed, if desired, e. g. an electromagnetic brake to slow down rotation of the drive shaft, with a friction brake to bring rotation of the drive shaft to a halt and to keep it locked.

The manner in which the system operates is as follows. The gear wheel (3) rotates with the shaft (1) and correspondingly produces rotation of the meshing second gear wheels (4, 5) and their respective gear shafts (6,7). When the braking means (8,9) are set to be inoperative, the above-mentioned rotation has no effect upon the cross member (10) and the second shaft (2). Operation of the braking means, however, provides a mechanical resistance to rotation of the second gears (4,5) which in turn produces rotation of the cross member (10) and hence of the second shaft (2). The speed of rotation of the second shaft will be dependant upon the braking force applied by braking means (8,9) and by making the braking force continuously variable, the speed of rotation of the second shaft (2) may be continuously variable up to a speed determined by the rate of rotation of the first shaft (1).

In the foregoing description, shaft (1) has been termed the drive shaft, but it will be apparent that the system will also operate in the reverse sense, with shaft (2) being the drive shaft and shaft (1) the driven shaft.

Moreover, although the embodiment of the invention described above has two second gear wheels (4,5), a different number of such gear wheels may be employed, if desired. Preferably, when a plurality of the second gear wheels is employed, they should be symmetrically located around the circumference of the first gear wheel (3). When more than two second gear wheels are employed, the cross member (10) will be

appropriately shaped, being for instance a star wheel with an appropriate number of limbs, or a disc, optionally with cut outs. A cross member (10) in the form of a disc may be utilised for any number of second gear wheels. The rotating assembly comprising the cross member, the second gear wheel or wheels and the associated braking means should be rotationally balanced on the shaft (2).

Fig. 3 of the accompanying drawings is a plan view of the first gear wheel (3) and the second gear wheels (4,5) of the above-described embodiment, the first wheel being a serrated disc, although shown in the figure as a circle. It is also possible, however, for the first gear (3) to be provided with internal rather than external serrations. This embodiment (3A) is shown in Fig. 4 of the accompanying drawings.

Another embodiment of the invention is shown in Fig. 2 of the accompanying drawings in which a first rotatable shaft (1A) has a first bevel gear (11) at its end, and a second rotatable shaft (2A) has a second bevel gear (12) at its end.

The first and second bevel gears have their narrower ends adjacent but not in contact with one another. A pair of third bevel gears (13,14) meshes with said first and second bevel gears, and each of said third gears is mounted on a respective gear shaft (15,16) journalled within a respective braking means (17,18) mounted on a freely rotatable mounting ring. As in the previously-described embodiment, applying a braking force on the gear shafts (15,16) controls the amount of rotation transmitted from the shaft (1A) to the shaft (2A).

This embodiment of the invention is capable of providing a means of reversing the rotation transmitted from the first to the second shaft. This is achieved by providing ring-braking means (20,21), operation of which slows down rotation of the

mounting ring (19) and, when sufficient braking force is applied, preventing the ring from rotating. A further increase in the braking force will result in an increase in the torque transferred from shaft (lA) to shaft (2A), but shaft (2A) will then be rotated in the reverse direction to

shaft (lA). Operation of the braking means (17, 18) is not required in order to effect the reversal of the direction of the output. The various braking means (17,18 ; 20,21) may be friction brakes or any other type of brake mentioned above.

Claims

CLAIMS 1. An apparatus for transmitting torque exerted on a first rotatable shaft to a second rotatable shaft in such manner that the second shaft rotates at an angular speed that may be the same as, or different from, the angular speed at which the first shaft rotates, which comprises a first gear means attached to, and coaxial with, one of said first and second shafts, and at least one second gear means meshing with said first gear means and operatively linked to braking means, whereby torque exerted on one of said first and second shafts is transmitted to the other of said first and second shafts in response to braking force exerted by said braking means.
2. An apparatus according to claim 1 which comprises a first gear wheel attached to, and coaxial with, one of said first and second shafts, and at least one second gear wheel meshing with said first gear wheel, each of said second gear wheel or wheels being mounted on a respective gear shaft, parallel to said first and second shafts, and rigidly mounted on and orthogonal to, a cross member rigidly fixed to that one of said first and second shafts to which the first gear wheel is not attached, each of said gear shafts being operatively linked to braking means, whereby torque exerted on one of said first and second shafts is transmitted to the other of said first and second shafts in response to braking force exerted by said braking means.
3. An apparatus according to claim 1 which comprises a first bevel gear attached to, and coaxial with, one of said first and second shafts, and at least one third bevel gear meshing with said first bevel gear, and a

second bevel gear meshing with said third bevel gears or gears and attached to and coaxial with the other of said first and second shafts, each of said third bevel gear or gears being mounted on a respective gear shaft, orthogonal to said first and second shafts, and mounted on a rotatable mounting ring orthogonal to said first and second shafts, each of said gear shafts being mounted on said mounting ring with shaft-braking means, whereby torque exerted on one of said first and second shafts is transmitted to the other of said first and second shafts in response to braking force exerted by said shaft-braking means.
4. An apparatus according to claim 3 which comprises ring braking means operatively linked to said mounting ring to control the rate of rotation of said mounting ring.
5. An apparatus according to any one of claims 1 to 4 wherein the braking means operates by frictional, electromagnetic, or fluid means, or by a combination of such means.
6. An apparatus according to claim 5 wherein the braking means comprises a positive displacement fluid pump that provides a retarding force to the gear shafts as a result of partial or complete operation of a valve controlling the outflow of fluid from the pump.
7. An apparatus for transmitting torque exerted on a first rotatable shaft to a second rotatable shaft in such manner that the second shaft rotates at an angular speed that may be the same as, or different from, the angular speed at which the first shaft rotates substantially as herein described with reference to and as illustrated in any of the accompanying drawings.