Abstract:
A device and a method for determining the position of a gear shift element  1  in a claw clutch operated automated gear box of a vehicle. The gear shift element  1  has gear teeth that correspond to at least two gear wheels  5, 8  which have a different axial extension on both sides of a groove  9 . The position of the gear shift element  1  can be determined by way of the method according to the invention.

Description:
This application claims priority from German Application Ser. No. 10 2004 010 271.6 filed Mar. 3, 2004. 
   FIELD OF THE INVENTION 
   The invention concerns a device as well as a method for detecting the position of a gear shift element in a transmission, in particular in a claw clutch operated automatic gearbox of a vehicle. 
   BACKGROUND OF THE INVENTION 
   Electric motors which drive mechanical shifting devices are generally used in known adjusting devices of gear shift elements in claw clutch operated automated gear boxes of vehicles. The mechanical shifting devices usually convert the rotary motion of the electric motor into a translatory motion. The gear shift elements, such as gear shift sleeves, are moved by the mechanical shifting devices. A spindle, for example, can serve as a mechanical shifting device. 
   A control device is responsible for controlling shifting of the gear shift element. 
   It is necessary for the control device to know the exact position of the shifting device and, consequently the position of the gear shift element, before shifting the gear shift element. 
   There are several possibilities for detecting the position of the shifting device. One possibility is to measure the translation of the shifting device absolutely via a travel sensor. However, these sensors are expensive and require a relatively large installation space. A further possibility is to equip the electric motors with known sensors to measure the direction of rotation and the engine speed. In order to enable an exact determination of the position of the shifting device, these are customarily combined with reference sensors. A reference point is selected therein in a first step and the position of the shifting device is calculated based on a movement starting from this reference point. Selection of the reference point is necessary therein, since the memory, in which the position is stored, is usually non-permanent and, in addition, the position of the gear shift element can change due to the vibration of the vehicle. 
   For this reason, it is the object of the invention to enable a more economical method and device for detecting the position of gear shift elements in claw clutch operated automated gear boxes. 
   SUMMARY OF THE INVENTION 
   According to the invention, the device consists of at least one control device, a drive, a mechanical shifting device, a shift fork, a gear shift element, at least two gear wheels, and a sensor, which measures the motion of the mechanical shifting device. The position of the gear shift element is determined without using a reference sensor. The drive, which moves the mechanical shifting device of the gear shift element, is controlled for this purpose in such a way by the control device that the position of the gear shift element can be determined from the resulting motion of the shifting device. 
   The drive is advantageously an electric motor, which is connected via at least one line to the control device. The amount of current flowing through the motor can be measured via this line. The specification of the direction of rotation of the motor by the control device is additionally possible via this line. 
   The mechanical shifting device is advantageously a device that converts a rotary motion of the electric motor into a translatory motion of the gear shift element. This is possible, for example, by way of a spindle, a worm gear, a gear rod, a crank gear, an eccentric or also a Bowden cable. The gear shift element is mechanically connected via a shift fork to the mechanical shifting device on which a transmitter wheel, having discontinuities distributed over the periphery, is arranged fixed against rotation. An incremental sensor can be used in order to be able to determine the movement of the spindle. A signal based on the motion of the transmitter wheel is generated in this sensor. This signal is forwarded to the control device. A number of impulses can be allocated; a number of rotations of the mechanical shifting device according to the spacing of the discontinuities of the transmitter wheel distributed over the periphery. The control device can calculate therefrom, for example, the axial adjusting travel of the gear shift element while taking into consideration the spindle pitch and using the sum of the impulses. 
   The gear shift element is advantageously a gear shift sleeve. It is mounted between two gear wheels and has gear teeth that correspond to the gear wheels. The gear shift sleeve has a radial groove for accommodating a shift fork, which is mechanically connected to the mechanical shifting device. The gear teeth have a different axial extension on both sides of the groove according to the invention, as do the corresponding teeth of the gear wheels. The maximum adjusting travel for engaging the gear shift sleeve is thus different in the two different gear wheels. 
   The position of the gear shift sleeve can be precisely determined by way of a method, according to the invention based on this embodiment, without having to select a reference point. 
   The electric motor is selected for this purpose by the control device in such a way that the gear shift element moves in the direction of the first gear wheel. The gear teeth of the gear shift element can come into contact with the teeth of the corresponding gear wheel in such a way that it can or cannot engage the gear wheel. This is referred to below with the terms “shifting through” for a possible engagement or “tooth on tooth” for a prevented engagement. If the gear shift element has arrived at one of the described end positions, the current in the drive increases depending on the design. If then a limit value of the current has been reached at an end position, a counter is set to the value “zero” in the control device. Thereafter, the control device controls the motor in such a way that the shifting device moves the gear shift element in the direction of the second gear wheel until the gear shift element arrives again at an end position and the current has increased up to a limit value. The axial adjusting travel is now dependent upon whether the case “shifting through” or “tooth on tooth” applies when the first or second final position is reached. A precise position at the end of the adjusting process can be determined because the gear teeth of the gear shift element have a different axial extension on both sides. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
       FIG. 1  shows a schematic representation of an device for determining the position of a gear shift element according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The sole Figure shows a gear shift element  1 , which is axially displaceably mounted on an axle  2 . The gear shift element  1  has gear teeth on a surface  3  that correspond to a surface  4  of a first gear wheel  5 . In addition, the gear shift element  1  has gear teeth on a surface  6  that correspond to a surface  7  of a second gear wheel  8 . The gear shift element  1  has a cavity  9  that can accommodate a shift fork  10 . The shift fork  10  is mounted advantageously on a spindle  11 , which is driven by an electric motor  12 . A transmitter wheel  13  is also mounted against rotation on the spindle  11 , which generates signals in a sensor  14 . The sensor  14  has a signal line  15  to a control device  16 . The electric motor  12  has a line  17  to the control device  16 . The control device  16  has at least one incremental counter  24 , which counts the impulses originating from the sensor  14 . The gear shift element  1  has a surface  19  on the side facing the first gear wheel  5 , and a surface  20  on the side facing the second gear wheel  8 . The first gear wheel  5  has a surface  18  at the inner end of the gear teeth and a surface  23  at the outer end of the gear teeth. The second gear wheel  8  has a surface  21  at the inner end of the gear teeth and a surface  22  at the outer end of the gear teeth. 
   On a bar  25 , the points are marked corresponding to the characteristic positions of the gear wheels  5 ,  8  or the gear shift element  1 . With the aid of the points, the axial adjusting path of the gear shift element can be calculated. Therein, the following describe: 
   a: end of the gear teeth of the gear wheel  5 , 
   b: start of the gear teeth of the gear wheel  5 , 
   c: start of the gear teeth of the gear shift element in the direction of the gear wheel  5 , 
   d: start of the gear teeth of the gear shift element in the direction toward the gear wheel  8 , 
   e: start of the gear teeth of the gear wheel  8 , and 
   f: end of the gear teeth of the gear wheel  8 . The method for determining the position of the gear shift element  1 , according to the invention, progresses according to the following steps. The start of the position determination can be triggered either by starting the drive of the motor vehicle or by a detection of the disengagement of the separating clutch of the gear box of the vehicle corresponding to the gear shift element  1 . Basically, the power flow between the gear shift element  1  and the gear wheels  5 ,  8  must be interrupted. Thereupon a first engagement attempt of the gear shift element  1  into the first gear wheel  5  is made until the current of the electric motor  12  increases due to locking. In a possible shifting through operation, the motor  12  locks as soon as the surface  19  of the gear shift element  1  meets with the surface  18  of the gear wheel  5 . In the case of “tooth on tooth,” the motor  12  locks if the teeth of the corresponding gear tooth systems of the gear shift element  1  and the gear wheel  5  meet each other and further engagement is not possible. In this case, the surfaces  19  and  23  rest against each other. 
   As soon as the current of the motor  12  increases to a limit value, the control device  16  detects this via the line  17 . The counter  24 , preferably an incremental counter in the control device  16 , is set to the value zero. In the further movement of the shifting device  11 , the impulses received from the sensor  14  are transmitted to the control device  16  and added in the incremental counter  24 . The drive  12  is then selected by the control device  16  in such a way that it moves the gear shift element  1  via the mechanical shifting device  11  in the direction of the second gear wheel  8  until the current in the motor  12  increases again to a limit value way a locking of the motor  12 . Here either the “shifting through” or the “tooth on tooth” cases are possible as well. The counted increments are now compared to fixed stored values and the position of the gear shift element  1  in the control device  16  is determined therewith. The impulses received via the sensor  14  can be converted into the rotary motion of the motor  12 . Eighteen impulses, for example, can correspond to one rotation. The linear movement and the position of the gear shift element can be determined via the spindle pitch from the number of impulses. 
   The possible results are shown in the following table. In the first case, the gear shift element  1  moves first by the distance (c-a) toward the left. The motor  12  is prevented from moving further and the incremental counter  24  is set to the value zero. The gear shift element  1  moves by the distances (c-a) and (f-d) toward the right. The cases  2 - 4  can be interpreted accordingly. 
   
     
       
             
             
             
             
           
             
             
             
             
           
         
             
                 
                 
             
             
                 
                 
               Measured 
               Position of Gear shift 
             
             
                 
               Completed Shifting Operation 
               Distance 
               element 
             
             
                 
                 
             
           
           
             
                 
             
           
        
         
             
               1 st   
               Shifting through in gear wheel 5 and 8 
               (c − a) + (f − d) 
               Surface 20 on surface 21 
             
             
               2 nd   
               Tooth on tooth in gear wheel 5, 
               (c − b) + (f − d) 
               Surface 20 on surface 21 
             
             
                 
               shifting through in gear wheel 8 
             
             
               3 rd   
               shifting through in gear wheel 5, tooth on 
               (c − a) + (e − d) 
               Surface 20 on surface 22 
             
             
                 
               tooth in gear wheel 8 
             
             
               4 th   
               Tooth on tooth in gear wheel 5 and 8 
               (c − b) + (e − d) 
               Surface 20 on surface 22 
             
             
                 
             
           
        
       
     
   
   
     
       
             
           
             
             
           
         
             
                 
             
             
               Reference Numerals 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               gear shift element 
             
             
               2 
               axle 
             
             
               3 
               surface 
             
             
               4 
               surface 
             
             
               5 
               gear wheel 
             
             
               6 
               surface 
             
             
               7 
               surface 
             
             
               8 
               gear wheel 
             
             
               9 
               cavity 
             
             
               10 
               shift fork 
             
             
               11 
               shifting device 
             
             
               12 
               drive 
             
             
               13 
               transmitter wheel 
             
             
               14 
               sensor 
             
             
               15 
               signal line 
             
             
               16 
               control device 
             
             
               17 
               line 
             
             
               18 
               surface 
             
             
               19 
               surface 
             
             
               20 
               surface 
             
             
               21 
               surface 
             
             
               22 
               surface 
             
             
               23 
               surface 
             
             
               24 
               incremental counter 
             
             
               25 
               bar