Planetary gear transmission systems or components – Nonplanetary variable speed or direction transmission... – Nonplanetary transmission is friction gearing
Patent
1991-02-13
1992-02-25
Look, Edward K.
Planetary gear transmission systems or components
Nonplanetary variable speed or direction transmission...
Nonplanetary transmission is friction gearing
74200, 91409, F16H 3706
Patent
active
050909517
DESCRIPTION:
BRIEF SUMMARY
This invention relates to hydraulic control circuits for CVT's, that is to say for continuously-variable-ratio transmissions. It relates especially to automotive CVT's, and in particular to such CVT's of the known toroidal-race rolling-traction type. Hydraulically controlled transmissions of the latter type, of which examples are to be found in patent specifications GB-C-2023753, EP-B-0078125 and U.S. Pat. No. 4,662,248, are now well known in the art.
The control mechanisms of all efficient automotive CVT's have to include features to protect the transmission against the consequences of abuse and/or overload. For a CVT of the toroidal race type, one likely consequence of certain types of abuse or overload is that the rollers may tend to exceed the normal span of angular movement through which they move in order to change the transmitted ratio, and in so exceeding to run off the edges of the part-toroidal races on the input and output discs of the variator, that is to say the ratio-varying unit. In a CVT where the primary function of the drive train is the transmission of power from engine to wheels, abuse or overload interrupts that function. An overriding demand at the wheels is a typical example of such an overload, and may be created at the vehicle brakes, as in an emergency stop, or at the interface between the wheels and the ground as when traction is lost or regained during wheel spin.
It is well known in the art to incorporate in such CVT's a hydraulic end-stop mechanism which operates so as to resist further angular movement of the roller mountings, whenever they approach the extremes of their permitted range of angular movement. Such mechanisms are incorporated in all three of the prior patent specifications quoted by number in the first paragraph. However in the prior art generally, and particularly in the three specifications referred to, it has been customary to create the end-stop effect by a series of steps that may be summarised as follows. First the hydraulic ram piston, to which the roller carriage is connected and by which it is angularly moved, overshoots one extreme of its range of normal movement. Second, that overshoot gives rise to a variation of hydraulic pressure somewhere within the operating circuit of the CVT. Third, that pressure variation causes movement of a valve-type component within the CVT--in embodiments shown in EP-B-0078125, U.S. Pat. No. 4,662,248 and GB-C-2023753 these components are the spools of valves 22 and 23 and spool 161 respectively. Fourth, that moving part either bears directly against the piston (as with spool 161) or causes a pressure rise in a chamber of the ram cylinder (as with valves 22, 23) to oppose further movement of the piston. This process, although it has proved reasonably effective in practice, is necessarily more indirect and less immediate in operation than may be desirable to respond to the sudden changes in roller angle and/or circuit pressures that may result from overload or abuse.
One aim of the present invention is to provide a potentially quicker and more direct change in hydraulic pressure within a ram cylinder, to oppose the overshoot of the piston in such abuse or overload conditions. Another general aim of the invention, in a CVT including a clutch or other mechanism capable of acting as a safety link in the mechanical linkage between the variator and the final output of the transmission, is to provide the facility for using the increased ram chamber pressure to modulate the degree of engagement of such a clutch. In a hydraulically-operated CVT of the toroidal-race, rolling traction type, another aim of the invention is to reflect any increase in ram cylinder pressure in a higher pressure in the hydraulic mechanism which exerts an end load upon the variator so as to maintain continuous traction between the input disc and the rollers, and between the rollers and the output disc.
The invention is defined by the claims, the contents of which are to be read as part of the disclosure of this specification, and the invention will now be
REFERENCES:
patent: 4355547 (1982-10-01), Poole et al.
Look Edward K.
Lopez F. Daniel
Torotrak (Development) Limited
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