Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Nonplanetary transmission is friction gearing
Patent
1996-05-15
1998-02-24
Ta, Khoi Q.
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Nonplanetary transmission is friction gearing
475216, F16H 3708
Patent
active
057206872
DESCRIPTION:
BRIEF SUMMARY
The invention relates to transmissions and in particular to continuously-variable-transmissions (CVT's) of the kind which include a differential with two outputs and a ratio-varying unit or variator connecting the two outputs together. The differential is driven by an engine and for a constant engine speed, as the variator is cycled through its ratio range, one output speed increases whilst the other output speed simultaneously decreases. A final output shaft is driven from either of the outputs via selectable gear pairs. The selectable gear pair ratios are chosen such that, at the extreme of the variator ratio cycle, the output speed from one gear pair from one differential output shaft is the same as the output speed from the next gear pair from the other differential output shaft. Thus the drive to the final output shaft may be shifted from one differential output shaft to the other without breaking the drive.
It is the object of the present invention to provide an improved CVT, in particular one suitable for use in agricultural tractors.
Thus according to the present invention there is provided a continuously-variable-transmission (CVT) operable in a plurality of regimes comprising a ratio-varying unit ("variator"), an epicyclic unit, a plurality of ratio combinations, a plurality of regime engaging couplers, a clutch and a drive output shaft, the epicyclic unit including a splitting epicyclic gear and the CVT being arranged such that: ends of the variator; plurality of different ways to the drive output shaft by way of the plurality of ratio combinations and the plurality of regime engaging couplers in order to provide the plurality of regimes, and zero upwards.
The CVT provides the advantage that when starting from rest, particularly under light load, the clutch may be engaged gradually to provide the speed range of the lowest ratio regime(s) whilst a higher ratio regime is operative. This avoids rapid changing of of low ratio regimes when high acceleration is achieved under light load conditions.
The epicyclic unit may also include a recirculating epicyclic gear with the CVT being further arranged such that: with two components of the recirculating epicyclic gear;
(ii) the epicyclic unit and variator ratios are chosen so that at a predetermined variator ratio the epicyclic unit rotates as one whereby alternate regime changes occur at the predetermined variator ratio;
(iii) the recirculating epicyclic gear provides an additional output from the epicyclic unit which is connectable to the output shaft to provide one or more creep regimes with speed ranges including zero, and
(iv) the clutch may be (a) locked when starting from rest with one of the creep regimes operative or (b) gradually engaged when starting from rest with a non-creep regime operative in order to by-pass the creep regime(s).
This embodiment provides the advantage that a clutch is provided which may be used to start from rest by-passing one or more of the lowest speed regimes or the clutch may be locked and the transmission used as a full CVT. Alternatively the clutch may be provided in place of one or more of the lowest speed regimes thus making the construction of the transmission simpler and cheaper.
The CVT may also comprise a power-take-off (PTO) output shaft the drive from the input shaft to which by-passes the variator, the epicyclic unit, the ratio combinations and the couplers. The inclusion of a PTO output shaft is important if a CVT is to be suitable for use in an agricultural tractor.
The variator may be of any suitable form, for instance toroidal-race rolling-traction type, belt-and-sheave or hydrostatic. The variator may be enclosed in a variator casing within a main transmission casing in order that the oil in which the variator operates is kept separate from that in which the remaining portions of the CVT operate.
Embodiments of the invention will now be described, by way of example only, with reference to the drawings in which:
FIG. 1 is a schemmatic view of a novel form of CVT;
FIG. 2 is a graphical representation of
REFERENCES:
patent: 4402237 (1983-09-01), Tomlinson
patent: 5147254 (1992-09-01), Baier et al.
patent: 5337848 (1994-08-01), Bader
patent: 5403241 (1995-04-01), Jarchow et al.
Massey Ferguson Manufacturing Limited
Ta Khoi Q.
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