Abstract:
Actuation devices are disclosed for a pressure-closed clutch where the position of an actuation member is acquired by an incremental sensor. In an embodiment of the actuation device, the signal of the incremental sensor is acquired in case of a sudden change in the power consumption of an actuator and is used as a new reference signal. In another embodiment, the actuation member, while the spindle is rotating, is moved by a recovery spring during the closing of the clutch against a stop and the signal of the incremental sensor upon the attainment of said stop is used as a reference signal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This patent application claims priority of German Patent Application No. 10 2004 031 481.0 filed Jun. 30, 2004, which application is incorporated herein by reference. 
   FIELD OF THE INVENTION 
   This invention relates to a method for adjusting an incremental path measurement unit in an actuation device of a pressure-closed clutch as well as an actuation device for a pressure-closed clutch. 
   BACKGROUND OF THE INVENTION 
   Automated clutches are increasingly used in motor vehicles, just as automated gears, not only for improvement in comfort, but also due to the resultant possible reduction of consumption. Conventional clutches contain a plate spring that keeps the clutch in the engaged state. The clutch must be disengaged with an actuation device against the force of the plate spring. It is especially due to the use of precisely controllable electric motors that it has recently become possible to eliminate the powerful plate spring that closes the clutch by pressure and to close the clutch by pressure with the help of the external actuation device. In that way, the clutch can be made in a lightweight fashion. Weak opening springs can be contained in it so that the clutch will reliably open completely. 
   Electric motor actuation devices for automated clutches frequently contain a spindle drive in which the rotation of a spindle, driven by the electric motor, is converted into a movement of an actuation member for the clutch. The rotation of the spindle is acquired by an incremental sensor, which, depending on a predetermined angle of rotation, produces a pulse that is counted in a control unit. The position of the actuation member must be known absolutely for the sake of the precise control of the clutch; therefore, the actuation device must be adjusted as required, that is to say, the counting status of the incremental sensor must be associated with a predetermined position of the actuation member. This is done in an actuation device according to DE 443 38 25 C2 in the following manner: As a result of the drive provided by the electric motor, stops are approached where one corresponds to the fully opened position of the clutch, while the other one corresponds to the fully closed position. The fact that the stop has been reached is sensed on each occasion so that the currently existing counting status of the pulses of the incremental sensor can be taken as a standard or reference status. 
   BRIEF SUMMARY OF THE INVENTION 
   The object of the invention is to provide a simply executed method for the adjustment of an incremental path measurement unit in an actuation device of a pressure-closed clutch. The invention furthermore is intended to provide an actuation, device for a pressure-closed clutch by means of which one can implement such a method. 
   A first solution of the task underlying the invention is achieved with a method for the adjustment of an incremental path measurement unit in an actuation device of a pressure-closed clutch, where the actuation device contains an actuator whose position is acquired by an incremental sensor and that is connected with a transmitter piston, which, via a hydraulic segment with a snifting borehole on the side of the transmitter piston, is connected with a receiver piston that actuates the clutch, which method includes the following steps:
         acquisition of the force that the actuator needs to move the transmitter piston;   acquisition of the output signal of the incremental sensor at the precise moment at which the force chances abruptly as the transmitter piston runs over the snifting borehole; and,   fixing the output signal of the incremental sensor at the precise moment of the abrupt change as a new reference signal.       

   Preferably, the actuation device contains an electric motor that is connected with the transmitter piston via a self-inhibiting spindle drive and the movement of the transmitter piston in the direction of the closing of the clutch is supported by a compensation spring in the course of which method the abrupt change in the force will be acquired only in case of a change of the transmitter piston in the direction of the opening of the clutch. 
   An actuation device for a pressure-closed clutch by means of which the above-mentioned method can be implemented includes:
         an electric motor for the purpose of moving a transmitter piston that via a hydraulic segment with snifting borehole on the transmitter piston side is connected with a receiver piston that actuates the clutch;   a self-inhibiting spindle drive for the conversion of a rotation of the spindle driven by the electric motor into a linear motion of the transmitter piston;   an incremental sensor for the acquisition of the rotation of the spindle;   a compensation spring that supports a movement of the transmitter piston in the direction of the closing of the clutch; and,   a control device that acquires the power consumption of the electric motor during the movement of the transmitter piston with which the incremental sensor is connected and that has a storage unit, which stores the signal of the incremental sensors in case of an abrupt change in the power consumption as a reference signal.       

   Advantageously, the pressure-closed clutch is pre-stressed in the opening direction and the opening stroke of the clutch is limited by a stop. 
   Let us look at another method for the adjustment of an incremental path measurement unit in an actuation device in a pressure-closed clutch by means of which the problem involved in the invention can be solved: Here, the actuation device contains an actuator that can be impacted with power output and whose position is acquired by an incremental sensor and that is connected with an actuation member for the clutch, where the actuation member is so pre-stressed in the clutch opening direction by one of the pre-stressing units that, when the actuator is without power, is pushed so that it will come to rest against a fixed stop, which method includes the following steps:
         switching the actuator so that it will have no power;   acquiring the fact that the actuation member has come to a stop; and,   fixing the output signal of the incremental sensor at the moment the actuation member comes to a stop as a new reference signal.       

   Preferably, the actuator is an electric motor that drives a spindle that is in non-inhibiting thread engagement with the actuation member and the incremental sensor acquires the rotation of the spindle. 
   The actuation device for a pressure-closed clutch by means of which the two above-mentioned methods can be implemented includes:
         an electric motor for the rotary drive of a spindle, an actuation member for the actuation of the clutch that is in non-inhibiting thread engagement with the spindle and an incremental sensor for the acquisition of the rotation of the spindle;   a pre-stressing device that pre-stresses the actuation member in the clutch opening direction in such a manner that, when the motor has no current, it will move while the spindle is rotating against a fixed stop; and,   a control device that controls the electric motor with which the incremental sensor is connected and that has a storage unit that stores the signal of the incremental sensor when the electric motor has no power and stores a standstill of the incremental sensor that acquires the spindle as a reference signal.       

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described below with reference to the diagrams and by way of examples along with further details. 
     The figures show the following: 
       FIG. 1  shows a first embodiment of an actuation device for a pressure-closed clutch in a basic illustration; 
       FIG. 2  shows force-path curves to explain the way the actuation device shown in  FIG. 1  works; 
       FIG. 3  shows a basic diagram of another embodiment of an actuation device; and, 
       FIG. 4  shows force-path curves to explain the function of the actuation unit according to  FIG. 3 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   According to  FIG. 1 , an electric motor  10  is connected with a gear  12  whose output shaft ends in a spindle  14 , which is in threaded engagement with a transmitter piston  16  of a transmitter piston/cylinder unit  18 . The transmitter cylinder  20  is connected via a hydraulic line  22  with a receiver piston/cylinder unit  24  whose receiver piston  26  actuates a clutch  28 , whose structure is known as such, where the clutch is pressure closed by the receiver piston  26 , that is to say, it is pressed into engagement. Weak recovery springs (not shown) are possibly arranged in the clutch and these recovery springs force the clutch  28  into disengagement where the opening stroke of the clutch is limited by a stop  32  that is made on cylinder  30  of the transmitter piston/cylinder unit  18 . 
   Transmitter cylinder  20  is made with a snifting borehole  34  that leads to a hydraulic medium tank  36 . The movement of transmitter piston  16  according to  FIG. 1  to the right is supported by a compensation spring  38  that is supported between a fixed stop  40  and the transmitter piston  16 . 
   The rotation of spindle  14  is acquired by an incremental sensor  42  that is connected with an input of electronic control unit  44 . The operation of electric motor  10  is controlled via outputs of the control unit  44 . Another input of control unit  44  acquires the power consumption of electric motor  10 . 
   Control unit  44  contains a microcomputer and a storage unit in which, for example, the momentary characteristic of the clutch  24  is stored, which indicates the transmissible clutch moment as a function of the position of the receiver piston  26 . Other inputs of control unit  44  are connected with the sensors or other control units according to which the operation of the clutch is controlled. 
   The structure and the operating mode of the described components are known as such and will therefore not be explained here in any further detail. 
   Looking at  FIG. 2 , the operation of the arrangement according to  FIG. 1  is explained below in greater detail with a view to an adjustment of the incremental sensor  42 . 
   The three graphic illustrations of  FIG. 2  on the abscissa side in each case indicate the position x of transmitter piston  16  where a movement to the right will correspond to an opening of clutch  28  and a movement to the left will correspond to the closing or engagement of clutch  28 . The topmost diagram shows the coupling moment MK on the ordinate. The diagram in the middle on the ordinate shows the force KGK that acts on the transmitter piston and the bottom diagram on the ordinate shows the load moment NL of electric motor  10 . 
   Referring now to the top diagram, clutch  28 , when transmitter piston  16  after running over the snifting borehole  34  according to  FIG. 1  is moved to the right, is then increasingly closed by the receiver piston  26 , which then correspondingly moves to the left, as a result of which a rising clutch moment MK can be transmitted. The curve, given in the top diagram, is run through in both directions without any essential hysteresis. 
   When the transmitter piston  16  according to  FIG. 1  is moved to the right (in the middle diagram in  FIG. 2 , that corresponds to a movement to the left), then this movement essentially takes place without any force so long as transmitter piston  16  is to the left of the snifting borehole  34  and, the moment the transmitter piston  16  runs over the snifting borehole  34  (position xS) against the force of clutch  28 , receiver piston  26  first of all is moved against the opening springs of the clutch and then places the friction linings of the clutch into friction engagement. The solid line in the middle diagram thus represents the force that works from the hydraulic segment upon the transmitter piston  18 , which force essentially is independent of the direction of movement of transmitter piston  16 . Superimposed upon this force that acts from the hydraulic segment is the force of compensation spring  38  that supports the movement of transmitter piston  16  in the clutch closing direction so that one gets the dot-dash line III as the resultant total force acting upon transmitter piston  16 . To move transmitter piston  16  against resultant force III, electric motor  10  must provide a load moment NL that depends on the translation of the spindle drive. When the spindle is without friction and is designed without self-inhibition, the load moment that must be supplied by electric motor  10  independently of the direction of movement will have the outline of curve III. The spindle drive, however, is advantageously designed in a self-inhibiting manner so that clutch  28  will remain in its closed state even when the electric motor  10  is switched in a currentless manner. 
   When spindle  14  is so rotated that piston  16  is moved into the opening direction, piston  16  works in the area in which it runs over the snifting opening  34  according to  FIG. 1  to the left against the force of the compensation spring  38  so that the force jump at xS will be noticed in case of a jump of the load moment NL. The development of the load moment of the motor during the opening of the clutch is given in the bottom diagram by the curve A. 
   As the clutch is closed (curve B), the movement of transmitter piston  16  is supported by the force of compensation spring  38  so that the moment to be supplied by the spindle or electric motor  10  in the area where the snifting opening  34  is run over will be very small and so that the force jump of curve III is essentially smoothed out. 
   When the spindle gear is designed in a self-inhibiting manner, the force jump of curve III in terms of a jump of load moment NL of electric motor  10  is noticed only when the clutch is opened. This moment jump can be acquired by control unit  44  by means of a sudden change in the power consumption of electric motor  10 . The counting level, present at the time of the load jump of the pulses of the incremental sensor  42  analyzed in control unit  44 , can be set at zero at the moment of the load jump so that this counter status, which corresponds to the position of piston  18  as the snifting borehole  34  is run over, can be used as a reference value for the further control of electric motor  10  or for the purpose of clutch actuation. 
   Referring to  FIG. 3 , another embodiment of an actuation device for a pressure-closed clutch is explained below; here, corresponding parts according to the embodiment in  FIG. 1  are labeled with the same reference numbers. 
   According to  FIG. 3 , an electric motor  10  drives a spindle  14  that is in thread engagement with an actuation member  50 , which is received in a fixed housing  52  in a nonrotary but axially movable manner. Actuation member  50  here directly actuates the pressure-closed clutch  28 . 
   As one can furthermore see in  FIG. 3 , a recovery spring  54  works between a basic body of the actuation member  50  and the housing  52  and that recovery spring prestresses the actuation member  50  in the direction of the opening of a clutch  28 . The thread engagement between spindle  14  and actuation member  50  is not self-inhibitory in contrast to the preferred embodiment in  FIG. 1 . Furthermore, electric motor  10  is so designed that, when it is in the currentless state, it will be overpressed by the recovery spring  54  so that actuation member  50  is moved by the force of spring  54  with rotation of spindle  14  to the left according to  FIG. 3  until actuation member  50  rests against a stop  56  on the inside of housing  52 . The rotation of the spindle is acquired by incremental sensor  42 . 
   The way the arrangement according to  FIG. 3  works will be explained below in greater detail with reference to the force-path curves according to  FIG. 4 . 
   In  FIG. 4 , the abscissa represents the position x of actuation member  50 . The ordinate in each case indicates a force K. Curve I indicates the engagement force of clutch  28  where the illustration is schematic and curve I actually runs in the form of a curved line. Position xo is the position that is assumed by the actuation member  50  when it rests against stop  56 . 
   The broken straight line II indicates the force by means of which actuation member  50  presses upon the recovery spring  54 . The dot-dash curve III indicates the resultant total force by means of which actuation member  50  is moved as clutch  28  is either closed or opened. 
   When, during the opening of the clutch, electric motor  10  is switched currentless, then the recovery spring  54 , as a result of its prestress, is in a position to move the actuation member  50  with rotation of spindle  14  to the left up to stop  56 . The rotation of spindle  14  is acquired by the incremental sensor  42  and can be analyzed in control unit  44 . The rotation of spindle  14  ends the moment actuation member  50  comes to rest against stop  56 . Incremental sensor  42  thus no longer produces a pulse, something that is recognized in the control unit. The counting status of the pulses at the moment spindle  14  comes to a standstill can be used as a reference counting status so that every time stop  56  is reached, the incremental sensor can be adjusted and the absolute position of actuation member  50  or of clutch  28  will be known. 
   The above-mentioned adjustment strategy is basically also possible when clutch  28  itself provides a sufficiently high recovery force in order to move actuation member  50  against stop  56 . But there is a disadvantage to that. The clutch itself must be made in a more demanding fashion and the entire actuation segment is impacted with a high resetting force. Besides, the resetting device, integrated into the clutch, would have to be made very strong so that, considering the action, straight lines and frictions that change with the temperature, oscillations, service life, etc., one could in every situation make sure that the spindle will be pressed against the stop when the electric motor is currentless. 
   By shifting the recovery spring  54 , which can be formed by any kind of force storage unit into the actuator consisting of electric motor  10 , spindle  14 , housing  52  and actuation member  50 , only the electric motor and the translation mechanics will be loaded with the recovery spring force. 
   The embodiment of the actuation device, shown in the diagram in  FIG. 3 , can be employed advantageously especially in double-clutch systems where one must make sure that the clutches will open in case of a failure of the onboard supply unit or control unit, in other words, when they are in the currentless state. 
   The exemplary embodiments, described by way of example, can be modified in many different ways. Other toothed gear drives can be used as desired in place of a spindle drive. The actuator need not necessarily contain an electric motor; instead, for example, it can be formed by a hydraulic or other kind of setting cylinder. 
   LIST OF REFERENCES 
   
       
         10  Electric motor 
         12  Gear 
         14  Spindle 
         16  Transmitter piston 
         18  Transmitter piston/cylinder unit 
         20  Transmitter cylinder 
         22  Hydraulic line 
         24  Receiver piston/cylinder unit 
         26  Receiver piston 
         28  Clutch 
         30  Cylinder 
         32  Stop 
         34  Snifting borehole 
         36  Hydraulic medium tank 
         38  Compensation spring 
         40  Stop 
         42  Incremental sensor 
         44  Control unit 
         50  Actuation member 
         52  Housing 
         54  Recovery spring 
         56  Stop