Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Load responsive
Patent
1997-03-18
1999-10-05
Jeffery, John A.
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
Load responsive
474 28, 474 29, F16H 5900, F16H 918
Patent
active
059614080
DESCRIPTION:
BRIEF SUMMARY
According to the preamble of claim 1, the invention concerns a device for controlling a continuously variable transmission (CVT) driven by a drive unit.
BACKGROUND OF THE INVENTION
Continuously variable transmissions, hereinafter called CVT, have a first pair of cone pulleys upon an input shaft and a second pair of cone pulleys upon an output shaft. Each pair of cone pulleys comprises a first pulley stationary in axial direction and a second pulley movable in axial direction, hereinafter called respectively primary pulleys and secondary pulleys. Between the pairs of cone pulleys extends a belt-drive organ such as a sliding band. The primary pulley and secondary pulley are each adjusted by a pressure medium. For that purpose an electronic control device controls the pressure level of the adjustment spaces of primary pulley and secondary pulley via the electromagnetic actuators and hydraulic valves.
DE-OS 42 34 103 has disclosed an apparatus for control of the pressure of the primary pulley. The device comprises an electromagnetically controlled primary valve and a hydraulic secondary valve. The primary valve is controlled by an electronic control device. In case of line disconnection of the electronic control device to the primary valve, the device passes to emergency running. The pressure level of the primary pulley is determined here by the secondary valve. The position of the secondary valve is, in turn, adjusted by a mechanical coupling of the primary pulley. The device has the disadvantage of not coping with the complete breakdown of the electronic control device.
SUMMARY OF THE INVENTION
The problem to be solved by the invention is to provide a device for emergency running of a CVT. According to the invention the problem is solved by the fact that in case of breakdown of the electronic control device, an emergency running unit is activated by an adjusting means with a constant compression ratio or power ratio of the primary pulley to the secondary pulley. The pressure level in the adjustment space of the secondary pulley remains constant. It is possible to establish the magnitude of the change of ratio of the CVT from normal operation to emergency running by the amount of said power ratio. The solution proposed by the invention thus offers the advantage of a safe transition from normal operation to emergency running. Overspeed or too sharp a reduction of the speed of the drive unit is prevented. In the invention, emergency running, is to be understood as the condition of the CVT in which no speed regulation and no regulation of applied pressure take place.
This development proposes that the adjusting means be a primary valve and a secondary valve. This solution according to the invention offers the advantage that in emergency running the CVT is not operated only with a single fixed ratio. In the solution according to the invention the ratio of the CVT varies depending on the generated torque of a drive unit such as an internal combustion engine. During emergency running the variable ratio change makes possible, for example, a safe starting on a mountain and an improved drive-ability with a high final speed. Another advantage of the solution according to the invention is that in said emergency running device no additional sensors or mechanical levers have to be used.
In another development of the invention it is proposed that the primary and secondary valves be pre-controlled by a first and second emergency valves and in development of this that a single electromagnetic pressure-regulating valve act as pre-control upon the first and second emergency valves. The advantage offered by this solution is that the first and second emergency valves are simultaneously engaged so that tolerances and signal running periods of the pressure-regulating valve have no effect .
BRIEF DESCRIPTION OF THE DRAWING(S)
One embodiment is shown in the drawings where:
FIG. 1 is a block diagram of an electronically controlled continuously variable transmission;
FIG. 2 is a hydraulic diagram of emergency running device;
REFERENCES:
patent: 4584909 (1986-04-01), Abo et al.
patent: 4714451 (1987-12-01), Yoshiida et al.
patent: 5201687 (1993-04-01), Friedmann
patent: 5203233 (1993-04-01), Hattori et al.
patent: 5222417 (1993-06-01), Sato
patent: 5232406 (1993-08-01), Sato
patent: 5263387 (1993-11-01), Reniers
patent: 5295915 (1994-03-01), Friedmann
patent: 5334102 (1994-08-01), Sato
Konig Hubert
Stoll Hans Peter
Vorndran Ralf
Jeffery John A.
Kaness Matthew A.
ZF Friedrichshafen AG
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