Abstract:
The invention relates to a control device and to a method for controlling an automated clutch, which includes a hydraulic clutch actuating system, which has a hydrostatic actuator, which is driven by and electric-motor actuating drive having an incremental displacement sensor in such a way that the actuator moves in a translatable manner. The invention includes an absolute displacement sensor, which detects the actuator position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is filed under 35 U.S.C. §120 and §365(c) as a continuation of International Patent Application No. PCT/DE2011/000317, filed Mar. 24, 2011, which application claims priority from German Patent Application No. 10 2010 014 199.2, filed Apr. 8, 2010, which applications are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a control device and a method for controlling an automated clutch that includes a hydraulic clutch actuating system with a hydrostatic actuator that is driven by an actuating drive in the form of an electric motor including an incremental displacement sensor in a way to cause the actuator to carry out a translatory movement. 
     BACKGROUND OF THE INVENTION 
     The published German Patent Application No. 10 2008 044 823 A1 discloses a method for controlling a friction clutch where the clutch travel distance is detected during actuation by incremental displacement sensors that count distance increments and can thus detect relative clutch travel and are calibrated for the detection of absolute clutch travel. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the invention is to determine an accurate position signal of the actuator in a simple way using a control device and/or a method. 
     In a control device for controlling an automated clutch that includes a hydraulic clutch actuating system with a hydrostatic actuator driven by an actuating drive in the form of an electric motor including an incremental displacement sensor in a way to cause the actuator to carry out a translatory movement, this object is attained by an absolute displacement sensor that detects the position of the actuator. The actuator is used to adjust a master cylinder piston in a master cylinder of the hydraulic clutch actuating system. Hydraulic clutch actuating systems, including an actuator, a master cylinder, a slave cylinder and a clutch are known, for example, from the published German Patent Application No. 10 2008 057 656 A1. The actuating drive in the form of an electric motor includes incremental displacement sensors for measuring the incremental displacement. However, the incremental displacement measurement does not allow the determination of sufficiently accurate conclusions on the position of the actuator. In fact, during operation, unnoticed positional changes may occur within a short period of time and may cause an intolerable displacement of the clutch and thus of the transmittable clutch torque, which may even result in safety-critical situations. Thus, in accordance with an essential aspect of the invention, in addition to an incremental distance measurement, which is also used for commutating the electric-motor actuating drive, an absolute displacement sensor is provided for detecting the position of the actuator. 
     In one embodiment of the control device, the electric-motor actuating drive is embodied as an electronically commutated DC motor and/or is coupled to the actuator via a threaded spindle with which the absolute displacement sensor may be associated. The threaded spindle is preferably a planetary roller spindle that is used to convert a rotary driving movement of the electric-motor actuating drive into a longitudinal movement of the actuator. An advantage of the planetary roller spindle is that it has a very high transmission ratio. However, the transmission behavior of the planetary roller spindle may be subject to slip, i.e., in some circumstances there may not be a constant transmission ratio between the rotary movement created by the electric-motor actuating drive on the drive side and the longitudinal movement on the power take-off side, i.e., the side of the master cylinder. Due to the arrangement of the absolute displacement sensor on the power take-off side, the master cylinder position may be reliably detected independently of any operational slip of the threaded spindle. The absolute displacement sensor is associated with the power take-off end of the threaded spindle/planetary roller spindle that carries out the longitudinal movement. The absolute displacement sensor may likewise be associated with a piston rod of a master cylinder piston or with the master cylinder piston itself. 
     In another embodiment, using the control device described above, in a method for controlling an automated clutch having a hydraulic clutch actuating system with a hydrostatic actuator that is driven by an actuating drive in the form of an electric motor including an incremental displacement sensor in a way to cause the actuator to carry out a translator movement, the object indicated above is attained by detecting the position of the actuator both in a relative way using the incremental displacement sensor and in an absolute way using the absolute displacement sensor. In a further aspect of the invention, the absolute displacement sensor may be a simple sensor that has a significantly lower degree of position resolution and accuracy than the incremental position measurement on the motor side. This may reduce costs. 
     In one embodiment of the method, at least one position signal of the incremental displacement sensor and at least one position signal of the absolute displacement sensor are superimposed. Due to its rather limited accuracy and resolution, the absolute displacement sensor on the power take-off side alone may not be sufficient to set the clutch torque with sufficient accuracy. Thus, in accordance with a further aspect of the invention, both position signals may be combined in order to determine a position signal that is suitable for the control of the clutch. 
     In another embodiment of the method, the two position signals are superimposed in a position model in such a way that a small-signal behavior, and if applicable, displacing movements within a short period of time is/are dominated by a high-resolution incremental displacement measurement of the incremental displacement sensor. Small modulatory movements as they may be necessary for the control of the clutch in certain situations can be implemented by the high-resolution incremental displacement measurement even though they are beyond the position resolution of the absolute displacement sensor on the power take-off side. 
     In yet another embodiment of the method, a lower-resolution absolute displacement measurement of the absolute displacement sensor is used as a reference measure for a large-signal behavior. A positional drifting of the threaded spindle that cannot be detected by the motor-side incremental displacement measurement may be avoided by including the absolute displacement sensor on the power take-off side. An avoidance of positional deviations also serves to protect the actuating system because the danger of undesired collisions with stops on the ends of the actuator displacement range is avoided. In addition, an absolute comparison or referencing of the incremental displacement measurement may be dispensed with. 
     In another embodiment of the method, with the aid of a scaling factor, a position increment of the incremental displacement sensor is converted into a displacement difference that is added to a current actuator position. The scaling factor preferably corresponds to a medium transmission of the threaded spindle. 
     In yet another embodiment of the method, a position signal of the absolute displacement sensor is coupled in. The position signal of the absolute displacement sensor is preferably coupled in via a separate path of the position model. 
     In another embodiment of the method, a dead zone is used as a non-linear transmission element for the position signal of the absolute displacement sensor. As a consequence, in case of small differences between the measured and calculated absolute positions, the determined displacement signal may be updated simply by adding up the motor-side position increments. This allows a fine-tuned adjustment of the actuator position and of the clutch torque in the small-signal behavior. 
     In yet another embodiment of the method, in case of a significant difference between the determined or current actuator position and the position signal of the absolute displacement sensor, a fault signal is fed back, for example, via a parametrizable feedback amplification. The value of the feedback amplification preferably specifies a time constant indicating how fast the positional deviation is to be reduced. 
     The automated clutch is preferably an automated double clutch associated with an automated manual transmission. The clutch, for example, a double clutch, is preferably directly actuated by the hydrostatic actuator, i.e., without any interconnected lever mechanisms. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
         FIG. 1  is a simplified representation of a clutch actuating system for actuating an automated friction clutch; and, 
         FIG. 2  is a block diagram indicating a position model for controlling the clutch. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements of the invention. While the present invention is described with respect to what is presently considered to be the preferred aspects, it is to be understood that the invention as claimed is not limited to the disclosed aspects. 
     Furthermore, it is understood that this invention is not limited to the particular methodology, materials and modifications described and, as such, may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the preferred methods, devices, and materials are now described. 
       FIG. 1  is a simplified representation of clutch actuating system  1  for friction clutch  10 , for example, an automated double clutch. Clutch actuating system  1  is associated with friction clutch  10 , embodied as a double clutch, in a drive train of a motor vehicle. Clutch actuating system  1  includes master cylinder  4  connected to slave cylinder  6  by hydraulic line  5 , also referred to as a pressure line. Slave piston  7  is movable to and fro in slave cylinder  6 . Slave piston  7  actuates friction clutch  10 , embodied as a double clutch, via an actuating member, and preferably, an interposed bearing. 
     Master cylinder  4  is connectable to a compensation container via a connecting opening. Master piston  14  is movable to and fro in master cylinder  4 . Piston rod  15 , extending from master piston  14 , is translatorily movable in the longitudinal direction together with master piston  14 . 
     Piston rod  15  of master piston  14  is connected to actuating drive  20  in the form of an electric motor via threaded spindle  18  embodied as a planetary roller spindle. Actuating drive  20  in the form of an electric motor includes commutated DC motor  22  and control or control device  24 . Incremental displacement measurement device  26  having at least one incremental displacement sensor is integrated in actuating drive  20  in the form of an electric motor. 
     Planetary roller spindle  18  is used to convert the rotary driving movement of DC motor  22  into a longitudinal movement of actuator  19 , which includes a longitudinally movable part of planetary roller spindle  18  and/or piston rod  15 , and as the case may be, master cylinder piston  14 . The clutch is actuated in an automated way by DC motor  22  via threaded spindle  18 , the actuator  19 , master cylinder  4 , and slave cylinder  6 . In the actuation of the clutch, DC motor  22 , which generates the rotary driving movement, represents the drive side and actuator  19 , which carries out the longitudinal movement, represents the power take-off side. 
     In the context of the present invention it has been found that the transmission behavior of the clutch actuation is subject to slip, i.e., that there is no constant transmission ratio between the rotary movement on the drive side and the longitudinal movement on the power take-off side. Although it is possible to determine the approximate transmission ratio when planetary roller spindle  18  is constructed, the actual transmission ratio is variable and depends on complex influencing factors and is difficult to calculate using a model. 
     In terms of controlling actuator  19 , this means that incremental displacement measurement  26  is not sufficient to draw sufficiently accurate conclusions on the position of actuator  19 . Instead, undesired positional fluctuations within a short period of time during operation need to be reckoned with. 
     In one aspect of the invention, in addition to incremental displacement measurement  26 , which is also used for the commutation of DC motor  22 , absolute displacement sensor  30  is arranged on the power take-off side of planetary roller spindle  18 . For cost-efficiency reasons, a simple sensor is used as absolute displacement sensor  30 , which may have a significantly lower degree of position resolution and accuracy than drive-side incremental displacement measurement  26 . 
     Due to its limited accuracy and resolution, absolute displacement sensor  30  provided on the power take-off side is not sufficient to be able to set the clutch torque with a sufficient degree of accuracy. Consequently, the position information of incremental displacement measurement  26  and of absolute displacement sensor  30  are superimposed in a way to ensure that a small-signal behavior and adjustment movements within a short period of time are dominated by high-resolution incremental displacement measurement  26 , whereas the less accurate absolute displacement sensor  30  is used as a reference measure for the large-signal behavior. 
       FIG. 2  represents a block diagram of a position model with two paths. The input signal of the lower path of  FIG. 2  is position increment  41  of incremental displacement measurement  26  shown in  FIG. 1 . The input signal of the upper path of  FIG. 2  is a position signal  42  of power take-off side absolute displacement sensor  30  of  FIG. 1 . 
     At first, we will examine the lower path of the block diagram. With the aid of scaling factor  44  corresponding to a medium transmission of planetary roller spindle  18  of  FIG. 1 , position increments  41  of the electric motor are converted into displacement differences that are added to current actuator position  51  at summation point  45 . Arrows  49  and  51  indicate that actuator position  48  is passed over delaying block  50 . This means that summand  51  corresponds to detected actuator position  48  of the previous calculation step. 
     To avoid positional drifting caused by planetary roller spindle  18 , position signal  42  of the power take-off side is coupled in via the upper path in  FIG. 2 . Globally, power take-off side signal  42  acts as a command variable in a control loop from which the controlled or actual variable  48  is subtracted and is then fed back via a non-linear approach as correcting variable. Dead zone  52  is particularly suitable as a non-linear transmission element. In case of small deviations between position signal  42  and model position  48 , no corrections are made due to dead zone  52 . Determined displacement signal  48  is then updated exclusively by adding motor-side position increments  41 . This enables a fine-tuned adjustment of the actuator position and of the clutch torque in the small-signal behavior. 
     However, if there are greater significant differences between position signal  42  and the model position or previous actuator position  48 , a fault signal is fed back from dead zone  52  via feedback point  58  and parameterizable feedback amplification  54  to model position  48 . The value of feedback amplification  54  specifies a time constant indicating how fast the positional deviation is to be reduced. In practice, this time constant is specified as a function of the slip of planetary roller spindle  18  and the resultant drifting speed. Moreover, the correction behavior is defined by the width of dead zone  52 , which must be geared to the resolution and accuracy of power take-off side absolute displacement sensor  30  and to the requirements for the absolute accuracy of the clutch torque. 
     Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  clutch actuating system 
           4  master cylinder 
           5  hydraulic line 
           6  slave cylinder 
           7  slave piston 
           8  actuating member 
           9  bearing 
           10  friction clutch 
           12  compensation container 
           14  master piston 
           15  piston rod 
           18  planetary roller spindle 
           19  actuator 
           20  electric-motor actuating drive 
           22  DC motor 
           24  control 
           26  incremental displacement sensor 
           30  absolute displacement sensor 
           41  position increment 
           42  position signal 
           44  scaling factor 
           45  summation point 
           48  currently detected actuator position 
           49  currently detected actuator position 
           50  delaying block 
           51  last detected actuator position 
           52  dead zone 
           54  feedback amplification 
           58  feedback point