192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
2001-10-26
2003-12-09
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S003310, C192S003290, C192S10900B, C477S176000, C477S180000
Reexamination Certificate
active
06659253
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for operating a clutch, whose clutch slip is adjusted to a setpoint value, using a manipulated variable. The present invention also relates to a control device for a slip-controlled clutch, in order to implement the method.
BACKGROUND INFORMATION
A slip-controlled clutch can be used in the power train of a motor vehicle. Such a clutch usually transmits a torque applied to an input shaft, to an output shaft, via a number of frictionally interconnected coupling elements. In this context, the slip occurring between the coupling elements can result in the output shaft having a speed lower than that of the input shaft, an exact definition of the slip being the difference of the speeds of the input and output shafts.
SUMMARY OF THE INVENTION
The response characteristic and the general characteristic curve of such a clutch can be dependent on the current slip condition. This can be used in a clutch control system, in order to set a desired clutch performance. To this end, the clutch slip in a slip-controlled clutch is adjusted to a preselected, e.g. operating-point-dependent setpoint, by defining a manipulated parameter.
The object of the present invention is to specify a method for operating a clutch of the type mentioned above, which allows particularly reliable and stable control. In addition, the intention is to specify a control device that is particularly suitable for implementing the method.
The object of the present invention is achieved with regard to the method, in that a slip value is only selected as a reliable setpoint value, when the derivative of the friction coefficient/slip characteristic at this slip value exceeds a specifiable limiting value.
Advantageous refinements of the present invention are the subject matter of the dependent claims.
The present invention starts out from the consideration that, for particularly reliable and stable operation, the slip-controlled clutch should be operated, using a setpoint slip value, at which the clutch has self-stabilizing characteristics. In this context, self-stabilization of the clutch can be achieved using an operating point, at which the coefficient of friction of the coupling elements increases with increasing clutch slip. Using the increase in the friction coefficient, the clutch namely allows a comparatively large torque to be transmitted as a result of increasing slip. But if the transmitted torque remains constant with increasing slip, then the slip decreases automatically as a result of the increase in the coefficient of friction. In order to attain the self-stabilizing characteristics of the clutch, the operating point or setpoint value for the slip should therefore be selected in a range, in which the coefficient of friction continuously increases as a function of the slip.
In particular, the characteristic curve of the friction coefficient as a function of the slip can have a maximum as a result of the material properties of the coupling elements. In this case, it is intended that the setpoint value for the slip always be selected in an advantageous manner, to be less than the maximum point on the friction coefficient/slip characteristic. In other words, the setpoint value is advantageously selected as a function of a number of operating parameters, inside a range of permissible setpoint values; the slip value, at which the derivative of the friction coefficient/slip characteristic falls below a specifiable limiting value, being selected as an upper limit of the range of permissible setpoint values.
In order to detect a possible maximum in the friction coefficient/slip characteristic, it is provided that the relationship be monitored between a manipulated variable, by means of which the coefficient of friction is directly controlled and the slip is therefore indirectly controlled, and the slip. In this context, it is deduced that the coefficient of friction is continuously increasing as a function of the slip, and that the clutch therefore has the desired, self-stabilizing characteristic, when the magnitude of the derivative of the manipulated variable/slip characteristic does not yet fall below an additional, specifiable limiting value. In other words, the manipulated variable/slip characteristic is determined in order to evaluate the friction coefficient/slip characteristic. All of the slip values, for which the magnitude of the derivative of the manipulated variable/slip characteristic is greater than the additional limiting value, are considered to be permissible setpoint slip values in the sense of self-stabilizing performance.
The clutch is advantageously used in the power train of a motor vehicle. In an advantageous further refinement, the clutch is used on the output end of a continuously variable transmission. For such a continuously variable transmission is comparatively sensitive to torque surges, which may be introduced into the transmission, via the output shaft, due to changing road characteristics or driving situations. Therefore, the continuously variable transmission is advantageously protected against such torque surges, by inserting the clutch into the output shaft. In this context, the operation of the clutch in the self-stabilizing range is particularly advantageous for especially stable and reliable vehicle performance.
The method can be used in a control method for the clutch, in a particularly favorable and simple manner, by utilizing a parameter as a manipulated variable, which is simple to measure and physically available. To this end, a clutch pressure or a clamping force is advantageously used as a manipulated variable. In this context, the clutch pressure is particularly suitable for a method to operate a wet multi-plate clutch or a torque-converter lockup clutch, where the slip is set by the clutch pressure in each instance, the coefficient of friction being a function of the clutch pressure. In this case, the clutch pressure is therefore an available parameter already, and can be used in a particularly simple manner as an input variable for controlling the clutch. On the other hand, the clamping force is particularly suitable for a method to operate a dry clutch. In the case of such a clutch, the coupling elements are brought into frictional contact by an externally applied clamping force, the coefficient of friction between the coupling elements being a function of the clamping force. In this case, the clamping force is therefore an available parameter already.
For a wet multi-plate clutch, transmittable torque M is given as a function of coefficient of friction &mgr; and clutch pressure P as follows:
M=&mgr;·r·z·
(
A·P−F
),
where r is the effective friction radius, z is the number of friction surfaces, A is the piston area of the friction-clutch actuating device, and F is a minimum force for power transmission. In the case of a constant transmitted torque M, this function yields the following relationship between clutch pressure P and coefficient of friction u:
P
=1
/A·
(
M
/(&mgr;·
r·z
)+
F
).
Therefore, clutch pressure P decreases with increasing coefficient of friction u; thus, a maximum in the functional relationship between coefficient of friction &mgr; and the slip corresponds to a minimum in the relationship between clutch pressure and slip. Therefore, a setpoint slip value less than the minimum point on the clutch pressure/slip characteristic is selected when using the clutch pressure as a manipulated variable. Even when the derivative of the clutch pressure/slip characteristic has a negative value in this range, one can infer that a setpoint slip value is permissible in this sense, when the derivative of the clutch pressure/slip characteristic does not yet exceed the specifiable limiting value.
For a dry clutch in which the clamping force is used as a manipulated variable, the same relationship regarding the functional dependence of slip is obtained from a qualitative standpoint: the clamping force also decreases with increasing coefficient of friction &mgr;.
In order to con
Baeuerle Peter
Dominke Peter
Senger Karl-Heinz
Kenyon & Kenyon
Robert & Bosch GmbH
Williams Eric M.
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