POWER TRANSMISSION

Abstract: A power transmission comprising a discrete step ratio gear system (36) having at least two discrete step output ratios and which is shiftable therebetween, a continuously variable output gear system (15) arranged to transmit power to, or to receive power from, the discrete step ratio gear system (36) and having an input shaft and an output shaft, and means (31) for varying in use the continuously variable output gear system (15) to vary the output shaft speed and/or torque by not greater than +/- 30 %.

Description: TITLE: POWER TRANSMISSION FIELD OF THE INVENTION: 5 This invention relates to power transmission. In a particular aspect this invention relates to the use of a continuously variable output gear system in a power transmission. 10 BACKGROUND TO THE INVENTION: When a front end loader comprising a tractor and an hydraulically operated bucket is used to dig soil, 15 substantial power is required at the commencement of lifting of the bucket, commonly called breakout, while at the same time it would be usual for the tractor to be advancing forwardly at a very slow speed. To achieve the power necessary for breakout, it is usual to drive the 20 engine of the tractor at high output to generate the necessary power for breakout but this is likely to also cause substantial power to be transmitted to the wheels of the tractor with resultant wheel spin and damage to the tyres. 25 Similar problems occur with respect to ditch diggers, graders, bulldozers, track vehicles in general and harvesters. 30 Many of the above problems can be overcome by the use of a full hydraulic transmission in which an engine drives an » hydraulic pump which in turn drives a motor for the wheels or tracks of a vehicle and further the hydraulic power « * generated can also be used for front end buckets and other 35 things. However, such hydraulic transmissions are expensive, have substantial losses and require the storage and cooling of large volumes of hydraulic fluid. Applicant has considered the use of continuously variable transmission as a means of controlling speed and/or torque but investigations have shown that continuously variable transmissions have substantial problems as is generally indicated by the following papers:- 1. Puttre, Michael (Assoc Ed) (1991) 'Continuously Variable Transmissions' . Mechanical Engineering March P64 - 67. 2. White, G. (1967) 'Properties of Differential Transmissions'. The Engineer. July P105 - 111. 3. White, G. (1977) 'A Two-Path Variable Ratio Transmission with Extended Range of Ratios' . Journal of Mechanisms, Transmissions and Automation in Design. August P656 - 661. 4. White, G. (1976) 'Compounded Two-Path Variable Ratio Transmissions with Coaxial Gear Trains' . Mechanism and Machine Theory. Pergamon Press, U.K. Vol. 11, P227 - 240. 5. Hsieh, Long-Chang & Yan, Hong-Sen (1990) "On the Mechanical Efficiency of Continuously Variable Transmissions with Planetary Gear Trains' . International Journal of Vehicle Design. Inderscience Enterprises Ltd, U.K. Vol. 11, Nos. 2, P176 - 187. 6. Yu, D. & Beachley, N. (1985) 'On the Mechanical Efficiency of Differential Gearing'. Journal of Mechanisms, Transmissions and Automation in Design. March, Vol. 107, P61 - 67. 7. Macmillan, R. H. S. Davies, P. B. (1965) 'Analytical Study of Systems for Bifurcated Power Transmission'. Journal Mechanical Engineering Science. Vol. 7, No. 1, P40 - 47. 8. Lloyd, R. A. (1991) 'Power Flow and Ratio Sensitivity in Differential Systems' . Proc. Institution of Mechanical Engineers. Vol. 205, P59 - 67. SUMMARY OF THE INVENTION The present invention provides a power transmission comprising a discrete step ratio gear system having at least two discrete step output ratios and which is shiftable therebetween, a continuously variable output gear system arranged to transmit power to, or to receive power from, the discrete step ratio gear system and having an input shaft and an output shaft, and means for varying in use the continuously variable output gear system to vary the output shaft speed and/or torque by not greater than +/- 30%. The present invention also provides a method of transmitting power comprising utilising a discrete step ratio gear system having at least two discrete step output ratios, and a continuous variable output gear system arranged to transmit power to, or receive power from, the discrete step ratio gear system and operating the continuously variable output gear system to produce an output shaft speed and/or torque varying by not greater than +/- 30%. PREFERRED ASPECTS OF THE INVENTION It is preferred that when in use with an engine and the engine is at or approaching idle speed the speed of rotation of the output shaft of the continuously variable output gear system can be varied to be about zero. This is a feature additional to varying by +/- 30% which is considered the desirable maximum variation under load conditions. However, under some load conditions when no output from the gearbox is required the output shaft speed may also be reduced to about zero. It is preferred that the means for varying should vary the output shaft speed and/or torque by not greater than +/- 20%. In this last respect, means may be provided for sensing the idle condition of an invention. Thus, a mimicking of a torque converter coupling and decoupling may be obtained and this is particularly desirable in a first or reverse gear or other low speed gear. The means for varying may be manually operated or may be operated in response to a parameter associated with output or load. Preferably the continuously variable output gear system comprises a sun gear, a first shaft drive connected to the sun gear, planetary gears in drive engagement with the sun gear, a second shaft drive connected to the planetary gears, an annulus in drive engagement with the planetary gears, and means for controlling in use the speed and direction of rotation of the annulus to vary the drive ratio of the continuously variable output gear system. The discrete step ratio gear system may be a manual transmission, a power shift transmission or an automatic transmission. In general, gearboxes as are commonly used in motor vehicles, front end loaders, ditch diggers, earth moving equipment, tractors, crawler tractors, harvesters and other agricultural equipment and in trucks and heavy haulage equipment have been found to be suitable. Said means for controlling preferably comprises a gear for controlling in drive engagement with a gear carried by the annulus and drive means for selectively controlling the speed and direction of rotation of said gear for controlling. Said drive means may be mechanically, electrically or hydraulically driven or may be driven via a torque converter. The annulus may be a crown wheel and the planetary gears may be pinions or the various gears may take any desired form. The gear system in accordance with this invention may also be applied to regenerative braking. An exemplary transmission in accordance with this invention will now be described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS Figure 1 is a schematic representation of a continuously variable gear system, Figure 2 is a side view of a continuously variable gear system, Figure 3 is an exploded view of part of the gear system of Figure 2, Figure 4 is a schematic representation of a vehicle including a transmission in accordance with this invention. Figure 5 is a schematic representation of another vehicle including a transmission in accordance with this invention, Figure 6 is a schematic representation of another vehicle including a transmission in accordance with this invention, and Figure 7 is a schematic representation of another vehicle including a transmission in accordance with this invention. 51. Controller DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS The gear system shown schematically in Figure 1 is a continuously variable transmission 15 (CVT) and comprises a shaft 1 which may be an input or an output shaft, a sun gear 2 on the shaft 1 which is in drive engagement with planet gears 3, an annulus 4 which on the inside 5 is in drive engagement with the planet gears 3 and a control gear 6 which is in drive engagement with the outside 7 or the inside of the annulus. A shaft, not shown, which may be an output or an input shaft is connected to the planet gears 6. In use, controlling the speed and direction of rotation of the annulus 4 by means of control gear 6 will vary the drive ratio. Reference is made to Figure 2 and where like numerals denote like parts but additionally there is shown a drive transmitter 20 connected to the planet gears 3, a shaft 21 which may be an output or an input shaft connected to the drive transmitter 20 and bearing parts 22, 23 and 24 for supporting shafts 1 and 21 and a drive means 25 for driving the control gear 6. The drive means 25 may be mechanically, electrically or hydraulically driven or may be driven by a torque converter. In the description that follows, the shaft 1 will be considered to be an input shaft 1 and the shaft 21 will be considered to be an output shaft 21. Input at the input shaft 1 will drive the sun gear 2 which will drive the planet gears 3 which will drive the annulus 4 via the inside 5 and the planet gears 3 will drive the output shaft 21. The drive ratio and direction of rotation at the output shaft 21 can be varied. The output shaft 21 can be varied from direct drive, to stop or in a reverse direction with respect to the input shaft 1. This can be achieved by driving or holding the control gear 6 to vary the rotational speed and direction of the annulus 4. A direct drive can be had by incorporating a lock up device between the input shaft 1 and the output shaft 21 and locating a clutch 26 or other freewheel or disengagement system between the drive means 25 and the control gear 6. In this instance, the control gear 6 will freely rotate and there will be direct drive from the input shaft 1 to the output shaft 21. If the control gear 6 is prevented from rotating, the annulus 4 will not rotate and the output shaft 21 will be driven by the planet gears 3 from the sun gear 2 at a ratio being the number of teeth on the inside 5 of the annulus divided by the number of teeth on the sun gear 2. That ratio is called the normal ratio. This will inevitably be a reduction ratio. If the drive means 25 drives the control gear 6 at the same speed as, and in the same direction as, the input shaft 1, the planetary gears 3 will not rotate with respect to the annulus but will revolve with the annulus and there will be direct drive from the input shaft 1 to the output shaf't 21 and if desired a lock up can be effected. If the control gear 6 is driven at a selected lesser rotational speed then a selected ratio intermediate said normal ratio and direct drive can be obtained. If the control gear 5 is rotated in the opposite direction to the input shaft 6 a ratio of output to input can vary from the normal ratio to, in theory an infinite ratio and when the rotation of the control gear is in drive terms equal to the inverse of the normal ratio there will be no output shaft rotation, this being equivalent to a neutral drive. Increasing the speed of the control gear further in said opposite direction will enable a reverse drive to be had. Thus, continuous variation of output can be had for constant input. The above described gear systems should find many applications. If desired, a clutch may be located on the input shaft and may be coupled to a locking device on the planetary gears such that when the clutch is engaged, it will engage the locking device to be locked up and when the clutch is released to a drive condition, the locking device will be released. In some instances two or more such gear systems use coupled together so that the output of one drives the input of another. By this method velocity or torque may be increased. Reference is now made to Figure 4 which shows the continuously variable transmission 15 in an application. In Figure 4, the drive means 25 is an hydraulic motor 31 and an hydraulic pump 32 is provided for driving the motor 31. Also shown in Figure 4 is an engine 33, a clutch 34, a gearbox 36, a final drive 37 and wheels 38. The gearbox 36 is discrete step ratio gearbox which has multiple gears. The gearbox 36 is used in a conventional way but the motor 31 may be driven by the pump 32 to cause the continuously variable transmission 15 to vary the rotational speed or torque being delivered to the final drive. Reference is now made to Figure 5 which is the same as Figure 4 except that a clutch 35 is shown which is differently positioned to clutch 34 and that the pump 32 rakes drive via gears 41 and 42. Reference is now made to Figure 6 which is the same as Figure 4 excepting that the clutch is omitted and a gearbox 43 is used. The gearbox 43 is a power shift transmission. Reference is made to Figure 7 which is the same as Figure 5 except that the alternative clutch 34 is shown. In practice, only one of clutch 34 and 35 would be used. also shown in Figure 7 is a clutch actuator 46. Also shown in Figure 7 are hydraulic lines 47 and 48, a pressure gauge 49 and a controller 51. The controller 51 is connected to the pump 32 to vary its output and the gauge 49 will show hydraulic pressure. a user may use the gauge 49 to give a measure of pressure and may adjust the controller 51 appropriately to drive the motor 31 to obtain the desired speed and/or torque. This may be done with respect to all or some of the gear ratios which the gearbox 36 or gearbox 43 can provide. The particular combination of the continuously variable transmission and multi step gearbox provides many advantages. One particular advantage is that the output shaft speed of the continuously variable transmission might be controlled to provide a braking effect on the engine during deceleration. Another particular advantage is that the output shaft speed of the continuously variable transmission might be controlled so that the output shaft speed approaches zero as the engine approaches idle. Varies from zero at engine idle to a maximum speed differential with respect to the input shaft, as a vehicle accelerates through a gear of the gearbox 36 or 46. Further, when shifting to another gear for higher vehicle speed the same may be repeated. On shifting to another gear for lower vehicle speed a reverse variation may be effected. Another particular advantage is that the output shaft speed of the continuously variable transmission might be controlled so that the output shaft speed approaches zero under conditions in which high engine power is required to drive ancillary equipment such as an hydraulic pump for operation of non-tractive equipment such as a front end loader bucket or ditch digging equipment but little power is required for traction of the vehicle or where vehicle speed should be slowed or at least not substantially increase. A foot pedal, or means or hand operated means may be provided to control the continuously variable output transmission. In particular, the present invention will find application in front end loaders, ditch diggers, earthmoving equipment, tractors, crawler tractors, harvesters and other agricultural equipment and in trucks and heavy haulage equipment. Finally, it is to be understood that the inventive concept in any of its aspects can be incorporated in many different constructions so that the generality of the preceding description is not to be superseded by the particularity of the attached drawings. Finally it is to be understood that various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit and ambit of the invention. The claims and drawings form part of the disclosure of this specification.

Claims: CLAIMS 1. A power transmission comprising a discrete step ratio gear system having at least two discrete step output ratios and which is shiftable therebetween, a continuously variable output gear system arranged to transmit power to, or to receive power from, the discrete step ratio gear system and having an input shaft and an output shaft, and means for varying in use the continuously variable output gear system to vary the output shaft speed and/or torque from about zero to not greater than +/- 30%. 2. A power transmission comprising a discrete step ratio gear system having at least two discrete step output ratios and which is shiftable therebetween, a continuously variable output gear system arranged to transmit power to, or to receive power from, the discrete step ratio gear system and having an input shaft and an output shaft, and means for varying in use the continuously variable output gear system to vary the output shaft speed and/or torque by not greater than +/- 30%. 3. A power transmission as claimed in Claim 1 or Claim 2, wherein the continuously variable output gear system comprises a sun gear, a first shaft drive connected to the sun gear, planetary gears in drive engagement with the sun gear, a second shaft drive connected to the planetary gears, an annulus in drive engagement with the planetary gears; and means for controlling in use the speed and direction of rotation of the annulus to vary the drive ratio of the continuously variable output gear system. 4. A power transmission as claimed in Claim 3, wherein said means for controlling comprises a gear for controlling in drive engagement with a gear carried by the annulus and drive means for selectively controlling the speed and direction of rotation of said gear for controlling. 5. A power transmission as claimed in Claim 4, wherein said drive means is mechanically, electrically or hydraulically driven or may be driven via a torque converter. 6. A method of transmitting power comprising utilising a discrete step ratio gear system having at least two discrete step output ratios and a continuously variable output gear system arranged to transmit power to, or receive power from, the discrete step ratio gear system and operating the continuously variable output gear system to produce an output shaft speed and/or torque varying from about zero to not greater than +/- 30%. 7. A method of transmitting power comprising utilising a discrete step ratio gear system having at least two discrete step output ratios and a continuously variable output gear system arranged to transmit power to, or receive power from, the discrete step ratio gear system and operating the continuously variable output gear system to produce an output shaft speed and/or torque varying by not greater than +/- 30%. 8. A power transmission substantially as hereinbefore described with reference to any one of the accompanying drawings. 9. A method of transmitting power substantially as hereinbefore described with reference to any one of the accompanying drawings. 10. The steps, features, compositions and compounds referred to or indicated in the specification and/or claims of this application, individually or collectively, and any and all combinations or any two or more of said steps or features.

Inventors: ATKINSON GRAHAM EDWARD, ATKINSON, GRAHAM, EDWARD
Applicants: ATKINSON GRAHAM EDWARD, ATKINSON, GRAHAM, EDWARD
Application year: 1993
Main classification: F16H3
IPC codes: F16H3, F16H47