Abstract:
The control method comprises the stages of: generating a reference torque signal, the instantaneous value of which indicates the desired value of the torque transmitted through the clutch; generating a reaction signal correlated to the position of an actuating member of the clutch, the position of the actuating member being comprised between a first end-of-travel position in which the clutch is completely open and a second end-of-travel position in which the clutch is completely closed; generating an estimated torque signal, the instantaneous value of which indicates the estimated value of the torque transmitted through the clutch, on the basis of the reaction signal and a transmissibility function of the clutch; and generating a control signal for adjusting the position of the clutch as a function of the reference torque signal and the estimated torque signal. The method comprises, moreover, the stage of updating the transmissibility function of the clutch during operation of the clutch (for example at acceleration of the vehicle) so as to adapt it to the variations, over time, in the mechanical characteristics of the clutch itself.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method and a device for controlling the clutch of a vehicle. 
     As is known, during the operation of opening and closing of the clutch, for example during gear-changing or acceleration manoeuvres of the vehicle, the torque value transmitted by the engine to the drive wheels via the clutch itself depends mainly on the load acting on the clutch disc, the value of which depends on the position of the actuating lever of the clutch itself. 
     The clutch actuating operations are normally performed manually by the driver of the vehicle, who adjusts the approach position of the clutch so as to obtain a substantially gradual transfer of the torque through the clutch itself and therefore a comfortable travel progression of the vehicle. 
     It is also known to perform the clutch actuating operations in an entirely automatic manner by means of electronic control devices which have the purpose of adjusting, during operation of the clutch, the position of the actuating lever of the clutch itself depending on a plurality of input signals. 
     An example of embodiment of a control device of the electronic type is shown in FIG. 1. 
     According to that shown in this figure, the control device, denoted in its entirety by 1, operates, by means of an actuator 2 driven by a solenoid valve 3, an actuating lever 4 (of the known type and shown schematically) of a clutch 5 arranged between the output shaft 6a of an engine 6 (shown schematically) and an input shaft 7a of a gearbox 7 (shown schematically). 
     In particular, by means of the actuating lever 4 it is possible to vary in a known manner the load acting on a disc (not shown) of the clutch 5 and therefore the torque transmitted through the clutch 5 itself. 
     The control device 1 comprises a signal generator circuit 8 receiving at its input a plurality of information signals S INF  and generating at its output, on the basis of the input signals, a reference torque signal C RIF , the instantaneous value of which indicates the desired value of the torque transmitted via the clutch 5. 
     In particular, the information signals S INF  on the basis of which the reference torque signal C RIF  is generated, are signals correlated to parameters of an operational nature and relating to the status of the vehicle, namely parameters such as, for example, the position of the accelerator pedal, the angular velocity of the engine 6, the angular velocity of the clutch 5, the position of the brake pedal, etc. 
     The control device 1 comprises, moreover, an adder circuit 9 receiving at its input the reference torque signal C RIF  and an estimated torque signal C ST , the instantaneous value of which indicates the estimated value of the torque transmitted through the clutch 5, and generating at its output an error signal C E  resulting from the difference between the reference torque signal C RIF  and the estimated torque signal C ST . 
     The control device 1 comprises, moreover, a control circuit 10 of the known type, for example of the proportional-integral type PI, receiving at its input the error signal C E  and generating at its output a control signal C M  used for operating the solenoid valve 3 and therefore for controlling the actuator 2 and adjusting the position of the actuating lever 4. 
     The control device 1 comprises, moreover, a position sensor 11 coupled to the actuator 2 and generating at its output a reaction signal X correlated to the operational position of the actuator 2 (and hence to the position of the actuating lever 4 of the clutch 5) and a memory 12 receiving at its input the reaction signal X and generating at its output the aforementioned estimated torque signal C ST . 
     In particular, the memory 12 has stored in it a table containing a plurality of numerical values defining a transmissibility function F(X) of the clutch 5, which enables a corresponding value of the torque transmitted through the clutch 5 itself to be estimated for each of the positions assumed by the actuating lever 4 of the clutch 5. 
     In detail, the transmissibility function F(X) of the clutch 5 defines a one-to-one association between each of the instantaneous values x i  of the incoming reaction signal X and a corresponding instantaneous value, indicated by C FRIZ .sbsb.-- OLD , of the outgoing estimated torque signal C ST  ; therefore a plurality of pairs of values are stored in the memory 12, each pair relates to a respective position assumed by the actuating lever 4 and comprises an instantaneous value x i  of the reaction signal X and a corresponding instantaneous value C FRIZ .sbsb.-- OLD  of the estimated torque signal C ST . 
     During use, the control device 1 operates in the form of a closed loop following the reference torque signal C RIF  generated by the signal generator circuit 8 and operating, via the solenoid valve 3, the actuator 2 of the actuating lever 4 of the clutch 5. In particular, on the basis of the position of the actuator 2, the memory 12 generates at its output the estimated torque signal C ST  supplied to the adder circuit 9 so that the torque transmitted to the drive wheels of the vehicle is as far as possible equal to the desired torque, in order to obtain a substantially gradual transfer of the torque through the clutch 5 and therefore a comfortable travel progression of the vehicle. 
     The progression, over time, of the torque transmitted through the clutch 5 during operation of the clutch 5 itself depends substantially on the progression of the aforementioned transmissibility function F(X), which is in turn dependent upon the mechanical characteristics of the clutch 5. 
     The mechanical characteristics of the clutch 5, however, are subject to changes during the life of the clutch 5 itself on account of inevitable phenomena of wear and variations in the operating temperature of the clutch 5. 
     Therefore, when the transmissibility function F(X) no longer reflects the actual mechanical characteristics of the clutch 5, electronic control of the torque transmitted through the clutch 5 becomes unreliable and therefore results in a worsening in the performance of the vehicle during the gear-changing and acceleration manoeuvres. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is that of providing a method and a device for controlling the clutch of a vehicle, which enable the problems of electronic control devices of the known type to be resolved in a simple and economical manner. 
     According to the present invention, a method for controlling the clutch of a vehicle is provided, comprising the stages of: 
     generating a reference torque signal representing at least one desired value of the torque transmitted through the said clutch; 
     generating a reaction signal correlated to the position of an actuating member of the said clutch; the said position of the actuating member being comprised between a first end-of-travel position in which said clutch is completely open and a second end-of-travel position in which said clutch is completely closed; 
     generating an estimated torque signal representing at least one estimated value of the torque transmitted through the said clutch, on the basis of the said reaction signal and a transmissibility function of the said clutch; 
     generating a control signal for adjusting the position of the said actuating member of the clutch as a function of the said reference torque signal and the said estimated torque signal; 
     characterized in that it comprises an additional stage of periodically updating the said transmissibility function of the clutch so as to adapt it to the variations, over time, of the mechanical characteristics of the clutch itself. 
     According to the present invention a device for controlling the clutch of a vehicle is also provided, comprising: 
     signal generating means receiving at their input a plurality of information signals and generating at their output a reference torque signal representing at least one desired value of the torque transmitted through the said clutch; 
     position detecting means coupled to the said clutch and generating at their output a reaction signal correlated to the position of an actuating member of the said clutch, the said position of the actuating member being comprised between a first end-of-travel position in which said clutch is completely open and a second end-of-travel position in which said clutch is completely closed; 
     means for memorising a transmissibility function of the said clutch, receiving at their input said reaction signal and generating at their output, on the basis of the said reaction signal and the said memorized transmissibility function, an estimated torque signal representing at least one estimated value of the torque transmitted through the said clutch; 
     control means receiving at their input said reference torque signal and said estimated torque signal and generating at their output a control signal for adjusting the position of the said actuating member of the clutch; 
     characterized in that it comprises moreover: 
     updating means designed to update periodically the said transmissibility function of the clutch so as to adapt it to the variations, over time, of the mechanical characteristics of the clutch itself. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be more fully understood, a preferred embodiment is now described, purely by way of a non-limiting example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a device for controlling a clutch of the known type; and 
     FIG. 2 is a flow diagram relating to the method according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is based on the principle of periodically updating the transmissibility function F(X) of the clutch 5 stored in the memory 12 (FIG. 1) and in particular updating it at each acceleration manoeuvre of the vehicle, by performing a series of operations illustrated in detail in the flow diagram according to FIG. 2 and implemented by a gearbox control unit (not shown). 
     In particular, in order to detect that the vehicle is performing an acceleration manoeuvre, namely a manoeuvre involving gradual closing, with the vehicle at a standstill, of the clutch 5 in order to raise the number of revolutions of the input shaft 7a of the gearbox 7 so as to be substantially equal to the number of revolutions of the output shaft 6a of the engine 6, the logic status (0 or 1) of a logic flag stored in the gearbox control unit is read and updated by the control unit itself during normal operation of the vehicle. 
     During the acceleration manoeuvre of the vehicle, the actuating lever 4 of the clutch 5 assumes a plurality of adjacent positions comprised between a first end-of-travel position in which the clutch 5 is completely open, and a second end-of-travel position in which the clutch 5 is completely closed. For each of the intermediate positions comprised between the first and the second end-of-travel position, the operations illustrated in the flow diagram of FIG. 2 are repeated so as to update the transmissibility function F(X) at that particular position of the actuating lever 4 of the clutch 5. 
     The operations according to FIG. 2 start when the actuating lever 4 of the clutch 5 is arranged, during the vehicle acceleration manoeuvre, in the first end-of-travel position where the clutch 5 is completely open. 
     In this position, two series of operations represented by the steps 20, 21 and 22, 23 are performed in parallel. 
     In step 20 an effective value C MOT  of the torque produced by the engine 6 and an effective value ω MOT  of the angular velocity of the engine 6 itself are acquired; in particular, the effective values C MOT  and ω MOT  of the torque produced by the engine 6 and its angular velocity are generally provided by the engine control unit (not shown) which, for each particular instant, detects the instantaneous value thereof. 
     From step 20 one passes to step 21 where, on the basis of the effective value ω MOT , a value dω MOT  /dt of the angular acceleration of the engine 6 and, on the basis of the effective value C MOT  and the value dω MOT  /dt, an estimated value C FRIZ .sbsb.-- NEW  of the torque transmitted through the clutch 5 are calculated. 
     In particular, the calculation of the estimated value C FRIZ .sbsb.-- NEW  of the torque transmitted through the clutch 5 is performed using the following equation of dynamic equilibrium: ##EQU1## where J MOT  is the moment of inertia of the engine 6. 
     At the same time as the operations described in steps 20, 21, the operations illustrated in steps 22, 23 are performed. 
     In particular, in step 22 the instantaneous value x i  of the reaction signal X generated by the position sensor 11 and the relating to the position assumed by the actuating lever 4 of the clutch 5 is acquired. 
     From step 22 one passes to step 23 where the instantaneous value C FRIZ .sbsb.-- OLD  of the estimated torque signal C ST  generated at the output of the memory 12 on the basis of the instantaneous value x i  of the incoming signal X is detected. 
     From steps 21, 23 one passes to step 24 where the absolute value of the difference between the estimated value C FRIZ .sbsb.-- NEW  of the torque transmitted through the clutch 5 and the instantaneous value C FRIZ--   OLD  detected, is calculated; the absolute value of this difference is moreover compared with a predetermined threshold value Soglia1. 
     In step 24 the value dω MOT  /dt of the angular acceleration of the engine 6 calculated previously is also detected and this value is compared with a predetermined threshold value Soglia2. 
     In particular, in step 24 the following comparisons are performed: ##EQU2## The comparisons performed with the in equations 2) enable the reliability of the estimated value C FRIZ .sbsb.-- NEW  calculated by means of the equation 1) to be verified. In particular, the unreliability of the estimated value C FRIZ .sbsb.-- NEW  is detected, if the latter differs excessively from the instantaneous value C FRIZ .sbsb.-- OLD  determined on the basis of the transmissibility function F(X) or if the value dω MOT  /dt is greater than the associated threshold value since, in this case, the term J MOT .dω MOT  /dt in the equation 1) prevails over the term C MOT  and the estimate provided by 1) is no longer reliable. 
     If the difference between the values C FRIZ .sbsb.-- NEW  and C FRIZ .sbsb.-- OLD  is less, in terms of absolute value, than the associated threshold value and the acceleration of the engine 6 is less than the associated threshold value (option YES of step 24), the reliability of the estimated value C FRIZ .sbsb.-- NEW  is detected and one passes to step 25, otherwise (option NO of step 24) the unreliability of the estimated value C FRIZ .sbsb.-- NEW  is detected and therefore no updating of the transmissibility function F(X) is performed; in this case, the step 24 is followed by a step 29 described below. 
     In step 25, the value T FRIZ  of the temperature of the clutch 5 is acquired, said value being generally estimated on the basis of a known temperature model of the clutch 5. 
     Step 25 is followed by step 26 where it is verified whether the value T FRIZ  of the temperature of the clutch 5 is comprised within a predetermined range of values, the lower and upper limits of which are defined by respective predetermined threshold temperature values Soglia3 and Soglia4; in step 25 it is therefore verified whether: 
     
         Soglia3&lt;T.sub.FRIZ &lt;Soglia4                                3) 
    
     The comparison performed in the inequation 3) enables a condition of excessive overheating or excessive cooling of the clutch 5 to be detected in the case where the value T FRIZ  of the temperature of the clutch 5 should not satisfy the inequation 3. 
     In fact, if the clutch 5 is excessively overheated (for example owing to excessive use) or excessively cooled (for example when the temperature of the gearbox 7 is very low), the estimated value C FRIZ .sbsb.-- NEW  calculated in step 21 is valid solely for these operational conditions, but is unreliable during operation of the clutch 5 at the normal operating temperatures. 
     Therefore, in the case where the clutch 5 is excessively overheated or excessively cooled (option NO of step 26), step 26 is followed by a step 28 where no updating of the transmissibility function F(X) is performed, otherwise (option YES of step 26) the step 26 is followed by a step 27 which performs updating of the transmissibility function F(X). 
     In step 27 the transmissibility function F(X) of the clutch 5 is updated with the estimated value C FRIZ .sbsb.-- NEW  of transmitted torque, calculated with the equation 1). 
     In particular, updating of the transmissibility function F(X) involves modifying the one-to-one relation defined by the transmissibility function F(X) at a point corresponding to the instantaneous value x i  assumed by the reaction signal X in the considered position of the actuating lever 4 of the clutch 5. 
     In detail, modification of the one-to-one relation is performed by replacing, in the table memorised in the memory 12, the instantaneous value C FRIZ .sbsb.-- OLD  associated with the instantaneous value x i  assumed in that moment by the reaction signal X, with the estimated value C FRIZ .sbsb.-- NEW  of transmitted torque calculated with the equation 1) by step 21. 
     Moreover, the estimated value C FRIZ .sbsb.-- NEW  is used by the control device 1 of FIG. 1 to perform adjustment of the position of the actuating lever 4 of the clutch 5. 
     In step 28, on the other hand, the transmissibility function F(X) of the clutch 5 memorised in the memory 12 is not updated with the estimated value C FRIZ .sbsb.-- NEW  calculated with the equation 1), but this value is used nevertheless by the control device of FIG. 1 to perform adjustment of the position of the actuating lever 4 of the clutch 5. 
     From steps 27, 28 one passes to step 29 where it is verified whether the actuating lever 4 of the clutch 5 has reached the second end-of-travel position, namely whether the clutch 5 is completely closed. 
     When the clutch 5 is completely closed (option YES of block 29), the acceleration manoeuvre of the vehicle is terminated and the operations of updating of the transmissibility function F(X) of the clutch 5 are terminated and will recommence with those described in connection with steps 20, 21 at the next acceleration manoeuvre performed by the vehicle; if, on the other hand, the clutch 5 is not completely closed (option NO of step 29), then the acceleration manoeuvres of the vehicle are not yet terminated and the operations of updating of the transmissibility function F(X) of the clutch 5 recommence with those described in connection with steps 20, 21. 
     From the description above it is clear how the method described allows periodic updating of the transmissibility function F(X) of the clutch 5 so as to take account of variations, over time, in the mechanical characteristics of the clutch 5 itself, which inevitably occur during the life of the clutch 5 on account of variations in the operating temperature and inevitable wear-related phenomena. 
     Owing to this updating feature, therefore, even when the mechanical characteristics of the clutch 5 change, it is possible to optimise the performance of the vehicle during the gear-changing and acceleration manoeuvres and obtain a comfortable travel progression of the vehicle. 
     Moreover, the present method is simple, easy to implement and does not require modifications to the control device 1 of the clutch 5 or the availability of dedicated devices, since the operations required may be performed directly by the control unit controlling the gearbox. 
     Finally, it is obvious that modifications and variations may be made to the method described and illustrated herein without thereby departing from the protective scope of the present invention. 
     For example, the operations of updating of the transmissibility function F(X) of the clutch 5 memorised in the memory 12 could be performed not necessarily at each acceleration manoeuvre of the vehicle, but also, for example, periodically during general operation of the clutch 5. 
     Moreover, step 25, where the value T FRIZ  of the temperature of the clutch 5 is acquired, could be arrived at after performing checks different from those described in step 24. In particular, step 24 could perform solely the comparison of the difference between the estimated and memorised values C FRIZ .sbsb.-- NEW  and C FRIZ .sbsb.-- OLD  and the respective threshold value, without any additional and/or simultaneous verification. 
     Moreover, in the case where the clutch 5 is excessively overheated or excessively cooled, namely the temperature T FRIZ  of the clutch 5 does not satisfy the inequation 3), operations different from those described in step 28 could be performed. 
     For example, the control device 1 of FIG. 1, in order to perform adjustment of the position of the actuating lever 4 of the clutch 5, could use, instead of the estimated value C FRIZ .sbsb.-- NEW  calculated with the equation 1), the corresponding instantaneous value C FRIZ .sbsb.-- OLD  memorised in the memory 12 and corrected in accordance with a predetermined law which correlates the torque transmitted to the drive wheels with the value T FRIZ  of the operating temperature of the clutch 5, and in particular corrected on the basis of a parameter K which is also memorised in the memory 12 and the dependency of which on the temperature T FRIZ  is determined experimentally during laboratory tests. 
     Finally, step 27, where the transmissibility function F(X) of the clutch 5 is updated, could be arrived at directly from step 24 (option YES) without performing the operations described in steps 25 and 26, i.e. without performing detection of the value T FRIZ  of the operating temperature of the clutch 5 and consequent comparison with the associated threshold values Soglia3 and Soglia4 for determining whether the clutch 5 is excessively overheated or excessively cooled.