Continuously variable transmission capable of torque control

Details Continuously variable transmission capable of torque control Continuously variable transmission capable of torque control

1996-06-13

1998-06-16

Graysay, Tamara L.

Endless belt power transmission systems or components

Pulley with belt-receiving groove formed by drive faces on...

Load responsive

474 17, 474 28, 474 29, 474 32, 474 35, F16H 5900, F16H 6100, F16H 6300

Patent

active

057661057

DESCRIPTION:

BRIEF SUMMARY
This invention relates generally to continuously-variable-ratio transmissions ("CVT's"), and particularly to the ratio-varying components ("variators") of CVT's of the band-and-sheave type. In this type of CVT a continuous, flexible and substantially inelastic band, usually in the general form of a belt or chain, passes over two pulley units running on parallel but separated axes, and in a common radial plane relative to those two axes. The width of the band does not vary, and the two sheaves of each pulley unit are coaxial, but the axial clearance between them can be varied, so varying the radius at which the band runs in contact with the pulley unit. If the sheaves of a first of the two units move axially apart, whereby reducing the radius of contact of the band, the sheaves of the second unit must approach in order to increase the radius and so maintain tension in the band. At the same time. if the first and second units are regarded respectively as the input and output members of the variator, the transmitted ratio falls. Conversely, if the sheaves of the first unit had moved axially together and those of the second apart, the ratio would have risen. At all times during operation the sheaves of both units must of course be urged axially together with a force sufficient to generate enough pulley/belt friction to transmit the required traction between them. Typically, one sheave of each pulley unit has been fixed to its shaft Awhile the other has been slidably connected to the shaft by axial splines. and the face of that sheave remote from the belt has formed the face of a piston moving within a cylinder connected to a source of fluid under hydraulic pressure which has generated the required axial load. It will be apparent that if one sheave of each pulley unit is fixed and the other axially movable, as just described, any ratio change must be accompanied by a slight axial shift of the belt relative of each pulley unit. Means for avoiding any adverse effects of this are well known to one skilled in the art, including axially-reversing the arrangement of the two sheaves--fixed and movable--between the two pulley units, so that the direction of the axial shift of the belt at the unit where the sheaves approach is matched by the corresponding belt shift at the other unit where the sheaves move apart.
In known variators of this kind it has been customary for the operator to change the transmitted ratio by what has become known in the art as "ratio control", that is to say a direct command on the hydraulic controls of the two movable sheaves to cause those of one unit to execute a predetermined movement apart and those of the other to execute a related predetermined movement together, while maintaining sufficient axial loading at both pulley units to maintain the necessary belt/sheave friction. In contrast, recent developments in the related technical field of CVT's of the toroidal-race rolling-traction type have demonstrated the advantages of so-called "torque control", where what the operator demands, by movement of the accelerator pedal or other control member, is a particular driving torque applied to the variator either by way of the driving shaft (i.e. torque load on the engine), or by way of a particular output torque on the driven shaft. Examples of a CVT control system of this type, and of a toroidal-race CVT well-suited to such control, are to be found in patent publications WO 93/21031 and EP-B-0444086 respectively.
Occasional proposals have been made to include some element of torque control in a CVT where the variator is of band-and-sheave type. One such proposal appears in Paper 730003, entitled "Design Equations for a Speed and Torque Controlled Variable Ratio V-Belt Transmission", presented at the International Automotive Engineering Congress and Exposition in Detroit, Mich. in Jan. 1973. In the variator described in that proposal one of the two pulley units exhibits some torque-sensitive capacity due to the capacity of one of the sheaves to move spirally relative to the shaft on which it is m

REFERENCES:
patent: 5173084 (1992-12-01), Lemieux
patent: 5184981 (1993-02-01), Wittke
patent: 5217412 (1993-06-01), Indlekoer et al.
Patent Abstracts of Japan vol. 13 No. 340 (M-857), 31 Jul. 1989 & JP,A, 01 116365 (Daihatsu Motor Co Ltd).
Paper 73003, Entitled Design Equations for a Speed and Torque Controlled Variable Ratio V-Belt Transmission.

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