GB1603853A

GB1603853A - Variableratio transmissions

Info

Publication number: GB1603853A
Application number: GB1903077A
Authority: GB
Original assignee: Rover Co Ltd
Current assignee: Rover Co Ltd
Priority date: 1978-05-08
Filing date: 1978-05-08
Publication date: 1981-12-02

Description

(54) VARIABLERAO TRANSMISSIONS (71) We, BL CARS LhlITED, formerly known as BRITISH LEYLAND UK L MITED, a British Company of 35-38 Portman Square, IJondon, fomlerly of Leyland House, 174 Marylebone Road, London NWl 5AA, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Etatement:-- This invention relates to socalled continuously variable-ratio transmissions, and more particularly to the control of such a transmission which comprises a pair of pulleys of variable effective diameter interconnected by an endless drive band and each connected to drive a respective one of two of the elements of an epicyclic gearset. Such a transmission will hereinafter be referred to as being "of the kind described".

Viewed from one aspect the present invention provides a transmission of the kind described, including means for monitoring the torque in an output shaft of said transmission, means for controlling the ratio provided by the pulleys, and feedback means operable in accordance with the torque in said output shaft to bias said control means in such manner as to oppose the generation of said torque.

The invention can therefore prevent the output torque from becoming undesirably high because of variation of the input torque, pulley drive ratio, or some other factor.

A feature of some transmissions of the kind described is that it is possible, at a suitable pulley drive ratio, to achieve a geared neutral condition, in which the output shaft of the transmission is not subject to torque whatever the speed of the input shaft. Naturally initial variation of the pulley drive ratio from that required for a geared neutral condition when the output shaft is stationary, will result in an extremely high overall gear ratio capable of producing a correspondingly large torque multiplication across the transmission, and thus very high torque in the output shaft.

Viewed from a second aspect the present invention provides a transmission of the kind described having means for monitoring the torque in an output shaft of the transmission and means operable in accordance with said torque for so controlling the ratio provided by the pulleys as to maintain said torque at substantially zero.

Thus the pulley drive is maintained at the correct ratio for the achievement of a geared neutral condition by means of a feedback based on the transmission output.

When, in accordance with the foregoing aspects of the invention, it is necessary to determine the output torque of the transmission, it is of course possible to use many of the known methods of sensing and measuring torque in a shaft. There are, however, problems associated with use of such methods when applied to the transmission output shaft.

Preferably, therefore, the means for monitoring output torque includes a torque transmitting sensing element that is indirectly connected to the output shaft of the transmission and that in use has a torque loading proportional to the torque loading on said output shaft, and includes means for monitoring the torque loading on said element.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Figure 1 is a schematic view of a transmission in accordance with the invention, suitable for use in a motor vehicle; Figure 2 is a schematic detailed view in cross-section of the mounting of a gear wheel in the transmission of Figure 1, and shows its connection to a valve means; and Figure 3 shows in schematic cross-section a valve for controlling the ratio of the chain drive shown in Figure 1.

Figure 1 shows one of the many ways in which a variable-ratio belt or chain drive can be connected to an epicyclic gearset. The transmission comprises a chain drive 11, a three element epicyclic gearset 12 and a set of helical spur gears 13, 14 and 15.

Chain drive 11 consists of an input pulley 16, an output pulley 17 and a chain 18, the input pulley 16 being mounted for rotation with input shaft 19 of the transmission along with spur gear 13, while output pulley 17 is mounted for rotation with intermediate shaft 20 and the planet carrier 21 of epicyclic gearset 12.

Carrier 21 caries planet gears which mesh with a sun gear 22 and an annulus 23. Annulus 23 is coaxial and rotates with an output shaft 24 of the transmission. Sun gear 22 is coaxial and rotates with spur gear 15 and is thereby connected, through spur gears 14 and 13, with input shaft 19.

Compound spur gear 14 acts as an idler gear and consists of two oppositely handed helical portions, one of which engages with spur gear 13, the other with gear 15. By means of this arrangement, when gear 14 is transmitting load between gears 13 and 15 it is subject to summing end thrusts from the two points of mesh, the direction in which the end thrust acts depending upon which of gears 13 and 15 is driving. The torque transmitted by, and hence the end thrust upon gear 14 is related in direction and proportional in magnitude to the torque in the output shaft 24. Alternatively, spur gear 14 could of course comprise one gear ring of helical teeth and one straight cut ring, gear 13 or 15 being suitably adapted.

Chain drive 11 has a continuously variable ratio, and utilises the known principle of varying the effective diameter of each of the pulleys by altering the axial spacing of the pulley sheaves by means of hydraulic pressure in piston-cylinder units connected to the sheaves.

The piston-cylinder units are not illustrated since they are of conventional construction.

Hydraulic fluid is fed to the pulley pistoncylinder units from a pump source (not shown) via a control valve 25 (Figure 3). Hydraulic fluid is fed from a source to port 26 of valve 25, from where it may be communicated to either port 27 or port 28 which connect respectively with the piston cylinder units of pulleys 16 and 17. Communication between the ports is controlled by a spool 29, which is so shaped that when one of ports 27 and 28 is in communication with port 26, the other communicates with port 31 or port 30 respectively both of which communicate with a tank at a base pressure. Spool 29 can be moved by means of a torque demand level 32 which may be actuated manually or by an automatic control; alternatively electical means, for example, could be used to actuate spool 29 directly.

Thus the ratio of the chain drive may be varied according to the addition or removal of fluid from the piston-cylinder units of pulleys 16 and 17, by use of spool 29.

Naturally, variation of the chain drive ratio when the transmission is under load will also alter the output torque. Changes in output torque are reflected by a corresponding change in the end thrust on spur gear 14. As shown in Figure 2, spur gear 14 is journalled in plain bearings 33 having no axial load bearing ability.

As a result, a change in end thrust results in axial movement of the gear which is transmitted through thrust bearings 34 to spools 37 and 38 of a pair of valves 35 and 36 for monitoring output torque. Valves 35 and 36 are of known type and have, respectively, inlet ports 39 and 40 which communicate with the source of pressurised hydraulic fluid, and ports 41 and 42 which lead to the tank at base pressure, while ports 43 and 44 communicate with ports 43a and 44a, respectively, of valve 25.

The arrangement is such that when gear 14 is displaced axially an equilibrium position will be reached when the difference in pressures acting on the faces 45 and 46 of the spools 37 and 38 becomes sufficient to balance the end thrust on the gear. At the same time a corresponding pressure difference acts across the spool 29 of valve 25, and thus a force related to the output torque acts on the lever 32.

Thus when lever 32 is moved there begins a resulting ratio change and corresponding change in torque in the output shaft, which causes a change in pressures in the parts of the valve 25 communicating with ports 43a and 44a whereby a resultant force in opposition to the direction of movement of the valve spool 29 is produced.

The force on lever 32 is then equal and opposite to the sum of the forces which result from the pressure difference between ports 27 and 28 (which causes the output torque) and the pressure difference between ports 43a and 44a (which results from the torque). The output torque is therefore related to the force on lever 32; thus to limit the torque in output shaft 24 it is merely necessary to impose an upper limit on the force actuating lever 32.

A geared neutral condition is obtained by applying zero load to lever 32 which means that the system can support no output torque.

Again, when moving from a geared neutral condition excessive output torque can be avoided by limiting the force applied to lever 32.

It will be seen that the gear 14 and valves 35 and 36 constitute means for monitoring the output torque of the transmission while the incorporation of ports 43a and 44a and their associated chambers in valve 25 constitute feedback means making the ratio control means of the chain drive responsive to output torque.

There are many alternative ways in which the output torque could be monitored. As an alternative, for example, it would be possible to monitor output torque direct in the output shaft, although this presents practical difficulties.

Further alternatives would be to monitor torque in input shaft 19 and the reaction torque in a casing containing the transmission 11, or to monitor input torque and overall speed ratio of the transmission, either of which methods would enable output torque to be computed. Essentially, however, the output torque value would be fed back to the chain drive ratio control means which is responsive thereto.

From another aspect difficulties inherent in monitoring output torque direct, for example, by measurement of strain in the output shaft, have been avoided by monitoring instead the torque in an element of the transmission which, although indirectly connected to the output shaft, is subject to a torque proportional to that in the output shaft. It will be appreciated that although hydraulic feedback means have been illustrated, other systems are possible, for example, electrical or even mechanical means.

WHAT WE CLAIM IS: 1. A transmission of the kind described, including means for monitoring the torque in an output shaft of said transmission, means for controlling the ratio provided by the pulleys, and feedback means operable in accordance with the torque in said output shaft to bias said control means in such manner as to oppose the generation of said torque.

2. A transmission of the kind described having means for monitoring the torque in an output shaft of the transmission and means operable in accordance with said torque for so controlling the ratio provided by the pulleys as to maintain said torque at substantially zero.

3. A transmission as claimed in claim 1 or 2, wherein said means for controlling the ratio provided by the pulleys comprises a hydraulic circuit having means for varying the effective diameter of at least one of said pulleys.

4. A transmission as claimed in claim 3, including valve means controlling the flow of fluid from a source to said diameter varying means.

5. A transmission as claimed in claim 4 including means for biasing said valve means in response to the output of said monitoring means.

6. A transmission as claimed in claim 1,2, 3, 4 or 5 wherein said monitoring means provides an output of pressurised fluid.

7. A transmission as claimed in claim 1, 2, 3,4 or 5 wherein the output of said monitoring means is electrical.

8. A transmission as claimed in claim 1, 2, 3, 4 or 5 wherein the output of said monitoring means is transmitted through a mechanical linkage.

9. A transmission as claimed in any preceding claim, wherein said monitoring means monitors the torque on a torque transmitting element directly connected to said output shaft.

10. A transmission as claimed in any one of claims 1 to 8, wherein said monitoring means monitors torque on a torque transmitting element which is indirectly connected to said output shaft and has a torque loading directly proportional to that of the output shaft.

11. A transmission as claimed in claim 9 or 10, wherein said torque transmitting element comprises compound spur gear acting as an idler gear in the transmission, at least one of the gear rings of which has non straight-cut teeth.

12. A transmission as claimed in claim 11 wherein said compound gear has two oppositely handed helical gears.

13. A transmission as claimed in claim 11 or 12 when dependent on Claim 10 wherein said idler gear is interposed between one of said pulleys and an element of said epicyclic gearset.

14. A transmission as claimed in claim 1 or 2, arranged substantially as shown in Figure 1 of the accompanying drawings.

15. A transmission as claimed in claim 1 or 2, wherein said torque monitoring means is substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

16. A transmission as claimed in claim 4, wherein said valve means is substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

17. A transmission substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. although indirectly connected to the output shaft, is subject to a torque proportional to that in the output shaft. It will be appreciated that although hydraulic feedback means have been illustrated, other systems are possible, for example, electrical or even mechanical means. WHAT WE CLAIM IS:

1. A transmission of the kind described, including means for monitoring the torque in an output shaft of said transmission, means for controlling the ratio provided by the pulleys, and feedback means operable in accordance with the torque in said output shaft to bias said control means in such manner as to oppose the generation of said torque.