Friction gear transmission systems or components – Friction gear includes idler engaging facing concave surfaces – Toroidal
Patent
1995-01-19
1997-09-16
Marmor, Charles A.
Friction gear transmission systems or components
Friction gear includes idler engaging facing concave surfaces
Toroidal
476 10, 476 2, 476 15, 475214, F16H 3702
Patent
active
056674562
DESCRIPTION:
BRIEF SUMMARY
This invention relates to CVT's, that is to say to continuously-variable-ratio transmissions, for transmitting power at a variable speed ratio between the rotary output of a prime mover and a rotary point of use. While it relates to such transmissions generally, it relates in particular to automotive vehicles.
The steplessly-variable ratio varying units (variators) of many known types of CVT are incapable of achieving zero ratio, that is to say zero output speed in response to finite input speed. This has led many designers to include within the CVT, in addition to the variator, a starting device typically in the form of a torque converter or other hydrokinetic coupling. When the prime mover is started from rest, it is connected to the driven wheels by way of the device and a gearing unit, and the variator is disconnected from the drive train. The characteristics of the coupling are such that when the impeller rotates at idling speed, insufficient torque is transmitted to the turbine to rotate the downstream gearing and the wheels or other driven members. In such transmissions it is then customary to maintain the variator disconnected when the throttle is first opened so that the prime mover accelerates the coupling impeller to apply enough torque to the turbine to move the wheels away from rest, either forwards or in reverse. As the throttle then continues to open, it is well known in the art that the speed of rotation of the turbine rises towards equality with that of the impeller. As that equality is approached, it has been customary in transmissions of this type to connect the variator, which is directly coupled to the prime mover, to the output and, by raising the variator ratio, to transfer power from the gearing unit to the variator.
Patent specification GB-B-2025545 describes a transmission of this kind. However, because there are two concentric input shafts to the transmission--one directly from the prime mover to the variator and the other from a hydrokinetic coupling (or its equivalent) to the fixed ratio gearing--the location of the principal components is constrained. This can present a problem, particularly when a variator of the toroidal-race rolling-traction type is used in place of a belt because of its greater axial length.
A key feature of a CVT according to the present invention is that the variator should, whenever the control force applied to it falls to zero, seek a ratio equal to that of the fixed ratio gearing. CVTs according to the present invention are thus to be contrasted with those described in patent specification U.S. Pat. No. 5,088,352 in which, in the absence of control forces applied hydraulically to the pulley sheaves of the V-belt variator by their loading cylinders, the variator automatically tends to remain at whatever ratio it is already at, rather than seek the ratio of the associated fixed-ratio gearing. The variators of the present invention and U.S. Pat. No. 5,088,352 therefore behave quite differently, when control pressure is relaxed. One consequence of this, for variators according to the present invention, is that it becomes possible to arrange for the CVT to transmit drive in a forward sense--which it will do for the majority of the time, in a typical automotive application for example--by including just a single one-way clutch and a single hydraulic or other engageable clutch between the variator and the CVT output. Operation in forward drive of the mechanism described in U.S. Pat. No. 5,088,352 is not possible without a one-way clutch and two hydraulic clutches in the corresponding part of the CVT.
In addition it is not easy to adjust the ratio of a ratio-controlled variator so that the variator can take over the drive from the fixed ratio gearing without shock. A torque-controlled variator, on the other hand, will move automatically to a ratio which is synchronous with that of the gearing and the two can thus be used in parallel, i.e. with a single input shaft, and without a separate clutch for the variator. Flexibility of installation is thus improved: f
REFERENCES:
patent: Re26917 (1970-06-01), Dickenbrock
patent: 3823613 (1974-07-01), Abbott
patent: 5060769 (1991-10-01), Yoshimura et al.
patent: 5088352 (1992-02-01), Ishimaru
patent: 5248285 (1993-09-01), Nakano
patent: 5401221 (1995-03-01), Fellows et al.
Patent Abstracts of Japan, vol. 10, No. 301 (M-525)(2357) 14 Oct. 1986 & JP,A,61 112 857 (Daihatsu Motor Co Ltd) 30 may 1986 see abstract.
Patent Abstracts of Japan, vol. 10, No. 286 (M-521)(2342) 27 Sep. 1986 & JP,A,61 103 055 (Daihatsu Motor Co Ltd) 21 May 1986 see abstract.
Fenstermacher David M.
Marmor Charles A.
Torotrak (Development) Limited
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