Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Nonplanetary transmission is friction gearing
Patent
1993-07-14
1995-09-26
Marmor, Charles A.
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Nonplanetary transmission is friction gearing
475216, F16H 1538, F16H 372
Patent
active
054530610
DESCRIPTION:
BRIEF SUMMARY
This invention relates to continuously-variable-ratio transmissions (CVT's) of the toroidal-race rolling-traction type. It relates in particular to CVT's of this type in which a ratio-varying component (variator) and a gearing combination are arranged in that sequence, between an engine and the output of the CVT, in which the gearing combination is driven by the outputs both of the engine and of the variator, and in which the gearing combination is capable of two different settings so that the CVT is capable of working in two different "regimes", thus extending the effective ratio range of the CVT. Typically in one regime and assuming constant engine speed, a full sweep of the ratio range of the variator from one extreme to the other will result in the CVT output speed beginning at a maximum reverse value, reducing to zero speed (a condition known in the art as "geared neutral" or "geared idle") and then rotating in the forward sense and with increasing speed, reaching a low value of forward speed when the opposite extreme of the variator range is reached. If ratios are appropriately chosen it will then be possible to change the setting of the gearing combination, so that the CVT changes from one regime to the other, in a so-called synchronous manner, that is to say without instantaneous change of the speed of rotation of the CVT output. The CVT is now said to be in high regime, and if the variator is progressed back to the original end of its ratio range the forward speed of the CVT output increases steadily to maximum value.
BACKGROUND OF THE INVENTION
Examples of such two-regime CVT's of the toroidal-race rolling-traction type are to be found described in Patent Specification GB-A-1078791, GB-B-2150240 and many other prior publications. It has been a common feature of most such known CVT's that in the first or low regime, the gearing combination typically --of epicyclic type--has been used in conjunction with the variator as an output side or downstream shunt: in this regime power has recirculated, and the variator output has subtracted speed from its engine-driven input. In contrast in the second or high regime, there has in effect been a direct driving connection between the engine and the CVT output: the variator has taken full engine power, and the output range of the transmission has been the same as that of the variator.
In a variator which reverses the direction of rotation between input and output, the torque reaction (on the casing) will be the sum of the input and output torques. The tractive forces between the discs and rollers are proportional to the torque reaction. The ratio between tractive force and normal force between each disc and roller, commonly known in the art as the "design traction coefficient", is usually fixed by the layout of the variator. The normal force determines the contact stresses and therefore the size of the variator for a specified fatigue life. For any given operating condition size is approximately proportional to the cube root of the normal force, i.e. the cube root of the torque reaction. It is therefore advantageous to reduce torque reactions as far as possible.
If, for example, a variator with a ratio range from 0.5:1 to 2.0:1 is connected in high ratio to an input producing 100 Nm of torque, the torque reactions would range from 300 Nm at the low output speed end of the range to 150 Nm at the high end. The size of a variator will be influenced by its duty cycle, i.e. the time spent at full and part load and the time spent at each ratio. In most road vehicles little time is spent in low regime. Hard acceleration or hill climbing in high regime will tend to utilize low variator ratios at large engine torques. Benefits in size and weight (size cubed) can therefore be achieved by reducing the maximum torque reaction which occurs in high regime at the low end of the variator ratio range.
SUMMARY OF THE INVENTION
The present invention arises from appreciating the possibility of reducing the maximum torque reaction in high regime within the variator of a two-r
REFERENCES:
patent: 3106855 (1963-10-01), Reichenbaecher
patent: 4768398 (1988-09-01), Greenwood
patent: 4885955 (1989-12-01), Kraus
Estremsky Sherry Lynn
Marmor Charles A.
Torotrak (Development) Limited
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