Endless belt power transmission systems or components – Pulley with belt-receiving groove formed by drive faces on... – Fluid pressure actuator for adjustment of member
Patent
1998-07-29
1999-10-19
Graysay, Tamara L.
Endless belt power transmission systems or components
Pulley with belt-receiving groove formed by drive faces on...
Fluid pressure actuator for adjustment of member
474 70, 477 45, 318491, F16H 5900, F16H 6100, B60K 4104, H02P 100
Patent
active
059679182
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a regulating system for a CVT of the cone-disc continuously variable type in which the variator corresponds to the control path and the ratio is regulated.
BACKGROUND OF THE INVENTION
Continuously variable automatic transmissions (hereinafter called "CVT") are comprised of the following units: a start unit, a forward/reverse gear unit, a variator, an intermediate shaft, a differential, and hydraulic and electronic control devices. The variator, in turn, is comprised of a first cone disc pair disposed on the input side and having a hydraulic adjustment unit, a second cone disc pair disposed on the output side and having a hydraulic adjustment unit and a continuously variable part which moves between the cone disc pairs. The first cone disc pair comprises one cone disc, stationary in an axial direction, and one movable cone disc. The movable cone disc placed on the input side is hereinafter designated as the primary disc. The second cone disc pair likewise comprises a cone disc, stationary in an axial direction, and one movable cone disc. The cone disc situated on the output side is hereinafter designated as the secondary disc. The axial position of the primary disc here determines the moving radius of the continuously variable part and thus the ratio of the CVT. The axial position of the secondary disc determines the contact pressure of secondary disc/continuously variable part and thus the capacity for torque transmission. The primary and secondary discs are adjusted by the pressure level in the respective hydraulic adjustment units. These pressure levels are determined by the electronic control device with the aid of an electromagnetic pressure regulator, which is in the hydraulic control device. In such a CVT, the ratio is usually regulated. The engine performance desired by a driver, or the ratio or pressure level, for example, are selected as set point variables. In connection with this a control loop was disclosed in EP-A-0 565 144. In the control loop shown therein, a desired pressure level is a set point variable. The value to be controlled, in turn, corresponds to an actual pressure level. An electromagnetic pressure regulator or the variator represents the control path. The error results from the comparison between the value to be controlled and the set point variable. The error is the input variable for a regulator. Different disturbances act upon the control path, here, the variator. Disturbances are, for example, the speed of the primary and secondary discs, the pressure level in the adjustment space of the secondary disc, and the power ratio of the primary disc to the secondary disc. The later, in turn, is a function of the torque to be transmitted, of the ratio, and of the power of the secondary disc. The disturbances and the existing non-linearities must be compensated for in the regulator. The prior art thus has the disadvantage that a disturbance modulation and a non-linear regulator must be used. These regulator structures are known to be very complex and difficult to tune.
SUMMARY OF THE INVENTION
The problem to be solved by the invention is to provide an easy to tune regulating system for a CVT.
According to the invention, the problem is solved by locating a corrector upstream of the control path. With the corrector, by means of a mathematical model, the non-linearities and disturbances of the control path are compensated for. The regulator is designed herein as a PID regulator.
The solution according to the invention offers the advantage that the regulator resembles an almost linear alternative control path.
In an embodiment of the invention, the pressure level in the adjustment unit of the primary disc is calculated according to the following formula:
______________________________________ p2: pressure level of the second adjustment
unit;
A2: active surface of the second adjustment
unit;
A1: active surface of the first adjustment unit
.mu.: power ratio of primary disc to secondary
disc (kp/ks)
d(i): ratio-dependent parameter;
di_ref/dt: r
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Danz Wolfgang
Knapp Thomas
Graysay Tamara L.
Kaness Matthew A.
ZF Friedrichshafen AG
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