Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Nonplanetary transmission is friction gearing
Patent
1995-05-17
1996-10-15
Wright, Dirk
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Nonplanetary transmission is friction gearing
F16H 3708
Patent
active
055649980
DESCRIPTION:
BRIEF SUMMARY
This invention relates to continuously-variable-ratio transmissions ("CVT's"). The invention is broadly applicable to such CVT's in which the variator--that is to say, the ratio-varying component--is incapable of achieving zero ratio. That is to say, although the speed of rotation of the output member can be varied steplessly over a predetermined range, while the input member rotates at constant speed, the output speed range does not include zero. To enable the transmission to deliver zero output speed, it is customary to drive the CVT output from one component of an epicyclic gear unit, the other two components of which are connected, through gearing as necessary to match the epicyclic ratio to the output and input of the variator. When such a variator and an epicyclic are so combined it becomes possible, if the variator input speed is held steady and the variator is then traversed from one end of its ratio range to the other, to cause the CVT output speed to change continuously, first falling from a maximum speed in one direction to zero. In some cases it may then continue by rising to a maximum in the other direction. Throughout this process, and particularly at the moment (known in the art as "geared neutral") when the output speed is zero, the epicyclic will be recirculating power through the variator and other components of the CVT. Such an epicyclic is therefore known in the art as a "recirculating epicyclic". It is also well known for the CVT to include a second or "input" epicyclic, with one component connected to the prime mover.
It is also well-known in the art, and especially where the variator is of the toroidal-race rolling-traction type, to extend the ratio range of the CVT by introducing gearing and clutches whereby the variator is enabled to work in more than one "regime". That is to say, once the rollers of a variator of that type have swept from one end of their ratio angle range to the other, so progressing the CVT output speed from one value to another and perhaps with change of direction as just described, by operation of clutches so as to engage different gearing it is then possible to sweep the rollers back over their range of movement in the opposite direction and in so doing to progress the CVT output speed still further. By correct choice of gear ratios it is possible to change thus from one regime to another without instantaneous change of any speeds. Such a regime change is known in the art as a synchronous change.
An example of a CVT including the known features so far described, and also the provision of two separate driven members to which the final drive of the CVT may alternatively be connected, is to be found in Patent Specification GB-A-1454702. A CVT with the characterising features of the present invention differs in that it causes power to be recirculated within the recirculating epicyclic only in the regime including geared neutral, and in that in the other regimes the CVT output is simply connected to one of two shafts, these two shafts being located to opposite sides both of the variator and of the input epicyclic. This avoids the power losses that would be inevitable if power recirculation also took place in some or all of those other regimes and thus offers the prospect of substantial advantages, including reduced variator size, particularly in vehicles such as excavator trucks which are often required to deliver high torque when moving at low or zero road speed.
The invention is defined by the claims and includes the CVTs as shown in the accompanying, simplified and schematic drawings. The invention will now be described, by way of example, with reference to these drawings in which:
FIG. 1 is a system diagram;
FIG. 2 compares shaft speeds graphically;
FIG. 3 shows one embodiment of a CVT, and
FIG. 4 shows one alternative to the system diagram of FIG. 1.
In FIG. 1 a CVT having an output shaft 1 and input shaft 2 (for connection to a prime mover at 3) comprises a toroidal-race variator 4, a recirculating epicyclic E (reference 5) and an input epicyclic e (referenc
REFERENCES:
patent: 3091132 (1963-05-01), Mayfield et al.
patent: 4768398 (1988-09-01), Greenwood
patent: 5098350 (1992-03-01), Sackschewsky
patent: 5232414 (1993-08-01), Fellows et al.
patent: 5401221 (1995-03-01), Fellows et al.
Torotrak (Development) Limited
Wright Dirk
LandOfFree
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