Abstract:
A full-bridge circuit includes a first, second, third and fourth switch element. According to the method the checking includes at least one measuring process. For the at least one measuring process either only the second or only the third switch element or only the first and the second switch element or only the third and the fourth switch element is/are switched on. At least one recording time in each measuring process, a parameter is recorded which is representative of an electrical current flowing through a measuring resistance Rm. Depending on the recorded parameter and the switched-on switch element(s), a fault or lack of fault is recognized in an inductive load L of an electromechanical converter in the full-bridge circuit. A duration for the checking is set such that during said duration an idle condition for the electromechanical converter is maintained.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. national stage of application No. PCT/EP2006/064616, filed on 25 Jul. 2006. Priority is claimed on German Application No. 10 2005 036 769.0, filed 4 Aug. 2005, the content of which is incorporated here by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method for checking an inductive load on an electromechanical transducer, in particular a valve with an electromagnetic actuator, in a full-bridge circuit or in a half-bridge circuit. 
     2. Description of the Prior Art 
     Valves with an electromagnetic actuator, which are used by way of example in motor vehicles, are subject to stringent safety and reliability requirements. In order to allow reliable and safe operation of the motor vehicle to be ensured, it must be possible to electrically check the valves so that faults, for example shorting or an interruption in a supply line, can be identified. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a simple and reliable method for checking an inductive load on an electromechanical transducer in a full-bridge circuit or in a half-bridge circuit. 
     According to one embodiment, the invention is distinguished by a method for checking an inductive load on an electromechanical transducer in a full-bridge circuit. The full-bridge circuit comprises a first, second, third and fourth switching element. The third and the second switching element form a first series circuit, and the first and the fourth switching element form a second series circuit. The first and the second series circuit are arranged electrically in parallel with one another between a supply potential and a reference ground potential. The first and the third switching element are coupled to the supply potential, and the second and the fourth switching element are coupled to the reference ground potential. The inductive load is electrically coupled at a first connection via a measurement resistor to a center tap of the first series circuit, and is electrically coupled at a second connection to a center tap of the second series circuit. In the method, the check comprises at least one measurement process. Within the at least one measurement process, in each case either only the second or only the third switching element is switched on or only the first and the second switching element are switched on, or only the third and the fourth switching element are switched on. At least one detection time within the respective measurement process, a variable is detected which is representative of an electric current which is flowing through the measurement resistor. A fault or soundness of the inductive load in the full-bridge circuit is identified depending on the detected variable and the respectively switched-on switching element or the respectively switched-on switching elements. A time period for the check is predetermined such that the electromechanical transducer remains in a rest position within this time period. 
     The invention is based on the discovery that the rest position of the electromechanical transducer, for example a valve with an electromagnetic actuator or an electric motor, is departed from when a minimum current level flows through the inductive load for a minimum time period. However, the check of the inductive load should not lead to the electromechanical transducer being changed from its rest position in order to ensure that the check of the inductive load has no undesirable effects resulting from the electromechanical transducer being moved away from its rest position, for example the production of noise. The time period for the check of the inductive load is therefore predetermined such that it is less than the minimum time period. A further advantage is that this allows the check of the inductive load to be carried out very quickly, for example within a few milliseconds. 
     The invention is also based on the discovery that the current rise when a current flows between the supply potential and the reference ground potential, with this current being limited only by the measurement resistor, is greater than the current rise in the case of a current flow which is additionally restricted by the inductive load. Furthermore, the aim is for a current to flow through the inductive load and the measurement resistor in the full-bridge circuit only when the first and the second switching element or the third and the fourth switching element are switched on. 
     A further advantage is that the circuitry of the full-bridge circuit need not be modified in order to allow the method for checking the inductive load to be carried out. Faults in the inductive load or a coupling state of the inductive load in the full-bridge circuit can therefore be identified easily and reliably. 
     In a further embodiment of the method, shorting of the first connection to the supply potential is identified when only the second switching element is switched on and the magnitude of the detected variable is greater than a predetermined upper threshold value. The predetermined upper threshold value may be dependent on the respective detection time or the inductive load. The advantage is that the method is very simple and, if the predetermined upper threshold value is preset appropriately, allows reliable identification of shorting of the first connection to the supply potential. 
     In yet a further embodiment the method, shorting of the second connection to the supply potential is identified when only the second switching element is switched on and the magnitude of the detected variable is greater than a predetermined lower threshold value and less than the predetermined upper threshold value. The predetermined lower threshold value may be predetermined as a function of the respective detection time or of the inductive load, in the same way as the predetermined upper threshold value. The advantage is that the method is very simple and that shorting of the second connection to the supply potential can be identified reliably if the predetermined upper and lower threshold values are preset appropriately. 
     In another embodiment of the method, shorting of the first connection to the reference ground potential is identified when only the third switching element is switched on and the magnitude of the detected variable is greater than the predetermined upper threshold value. The advantage is that the method is very simple and that the shorting of the first connection to the reference ground potential can be identified reliably if the predetermined upper threshold value is preset appropriately. 
     In yet another embodiment of the method, shorting of the second connection to the reference ground potential is identified when only the third switching element is switched on and the magnitude of the detected variable is greater than the predetermined lower threshold value and less than the predetermined upper threshold value. The advantage is that the method is very simple and that shorting of the second connection to the reference ground potential can be identified reliably if the predetermined upper and lower threshold values are preset appropriately. 
     In a further embodiment of the method, shorting between the first and the second connection is identified when only the first and the second switching element or only the third and the fourth switching element are switched on, and the magnitude of the detected variable is greater than the predetermined upper threshold value. The advantage is that the method is very simple and that shorting between the first and the second connection can be identified reliably if the predetermined upper threshold value is preset appropriately. 
     In a further embodiment of the method, an interruption between the first and the second connection is identified when only the first and the second switching element or only the third and the fourth switching element are switched on, and the magnitude of the detected variable is less than the predetermined lower threshold value. This has the advantage that the method is very simple and that the interruption between the first and the second connection can be identified reliably if the predetermined lower threshold value is preset appropriately. 
     According to a further embodiment, the invention is distinguished by a method for checking an inductive load on an electromechanical transducer in a half-bridge circuit. The half-bridge circuit comprises a first and a second switching element. The first switching element is coupled to the supply potential, and the second switching element is coupled to the reference ground potential. The inductive load is electrically coupled at a first connection by a measurement resistor to the second switching element, and is electrically coupled at a second connection to the first switching element. In the method, the check comprises at least one measurement process. Within the at least one measurement process, in each case only the second switching element is switched on or the first and the second switching element are switched on. At least one detection time within the respective measurement process, a variable is detected which is representative of an electric current which is flowing through the measurement resistor. A fault or soundness of the inductive load in the half-bridge circuit is identified depending on the detected variable and the respectively switched-on switching element or the respectively switched-on switching elements. A time period for the check is predetermined such that the electromechanical transducer remains in a rest position within this time period. 
     The advantages of the method correspond to those of the method for checking the inductive load on the electromechanical transducer in the full-bridge circuit. 
     In one advantageous embodiment of the method, shorting of the first connection to the supply potential is identified when only the second switching element is switched on and the magnitude of the detected variable is greater than a predetermined upper threshold value. The advantage is that the method is very simple and that shorting of the first connection to the supply potential can be identified reliably if the predetermined upper threshold value is preset appropriately. 
     In a further embodiment of the method, shorting of the second connection to the supply potential is identified when only the second switching element is switched on and the magnitude of the detected variable is greater than a predetermined lower threshold value and less than the predetermined upper threshold value. The advantage is that the method is very simple and that shorting of the second connection to the supply potential can be identified reliably if the predetermined upper and lower threshold values are preset appropriately. 
     In yet a further embodiment of the method, shorting between the first and the second connection is identified when the first and the second switching element are switched on and the magnitude of the detected variable is greater than the predetermined upper threshold value. The advantage is that the method is very simple and that shorting between the first and the second connection can be identified reliably if the predetermined upper threshold value is preset appropriately. 
     In another embodiment of the method, an interruption between the first and the second connection is identified when the first and the second switching element are switched on and the magnitude of the detected variable is less than the predetermined lower threshold value. The advantage is that the method is very simple and that the interruption between the first and the second connection can be identified reliably if the lower threshold value is preset appropriately. 
     In yet another embodiment of the method, the half-bridge circuit has a parallel resistor which is arranged electrically in parallel with the inductive load. The signal level at the first connection is detected at the at least one detection time. Shorting of the first or of the second connection to the reference ground potential is identified when only the first switching element is switched on and the detected signal level corresponds to the reference ground potential. The advantage is that the method is very simple and that shorting of the first or of the second connection to the reference ground potential can be reliably identified simply by adding the parallel resistor to the half-bridge circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will be explained in the following text with reference to the schematic drawings, in which: 
         FIG. 1  is a schematic diagram of a full-bridge circuit in which an embodiment of the invention is implemented; 
         FIG. 2  is a current/time diagram; 
         FIG. 3  is a half-bridge circuit in which a further embodiment of the invention is implemented; 
         FIGS. 4   a, b, c  is a flowchart of a program for checking the inductive load on an electromechanical transducer in a full-bridge circuit, and 
         FIGS. 5   a, b  is a flowchart of a program for checking the inductive load on the electromechanical transducer in a half-bridge circuit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Elements with the same design or function are provided with the same reference symbols throughout all the figures. 
     A full-bridge circuit comprises a first, second, third and fourth switching element T 1 , T 2 , T 3 , T 4  which, for example, are in the form of transistors and can be operated by a control unit, which is not illustrated ( FIG. 1 ). The third and the second switching element T 3 , T 2  form a first series circuit and the first and the fourth switching element T 1 , T 4  form a second series circuit, which are electrically arranged between a supply potential Ubat and reference ground potential GND. The first and the third switching element T 1 , T 3  are for this purpose coupled to the supply potential Ubat, and the second and the fourth switching element T 2 , T 4  are coupled to the reference ground potential GND. 
     A center tap K 1  is provided on the first series circuit electrically between the third and the second switching element T 3 , T 2 , and a center tap K 2  is provided on the second series circuit, electrically between the first and the fourth switching element. An inductive load L is coupled at a first connection A 1  via a measurement resistor Rm to the center tap K 1  on the first series circuit. The inductive load L is also coupled via a second connection A 2  to the center tap K 2  of the second series circuit. 
     A measurement voltage is tapped off across the measurement resistor Rm, and is amplified by a measurement amplifier MV. The amplified measurement voltage may be smoothed by an RC element, which is formed by a first resistor R 1  and a first capacitor C 1 , and, for example, can be supplied to the control unit. By way of example, the control unit is designed to appropriately operate the first, second, third or fourth switching element T 1 , T 2 , T 3 , T 4  as a function of the measurement voltage Um, in order to operate the inductive load. By way of example, the measurement voltage Um is a variable which is representative of an electric current I flowing through the measurement resistor Rm. 
     The inductive load L is, for example, formed by an electromechanical transducer, for example by a valve with an electromagnetic actuator or an electric motor. An electromechanical transducer such as this has, for example, an armature which can be deflected from a rest position when a suitable current flows through the inductive layer L, for example in order to open or close the valve or in order to rotate the rotor of the electric motor. In order to deflect the armature from the rest position, a minimum current level must flow through the inductive load for a minimum time period in order to produce a magnetic field of adequate strength. For example, the minimum time period is about 30 milliseconds. 
     However, when checking the inductive load L in the full-bridge circuit, the armature should remain in its rest position in order to prevent undesirable effects, which may be caused by deflection of the electromechanical transducer from the rest position. For this purpose, the first, the second, the third or the fourth switching element T 1 , T 2 , T 3 , T 4  is switched on only briefly, for example for a few milliseconds, in order to allow measurements. The check of the inductive load L in the full-bridge circuit must be completed before the electric current I through the inductive load L has become sufficiently great that the electromechanical transducer is deflected from its rest position. 
     By way of example, the check of the inductive load L in the full-bridge circuit may be subdivided into one or more measurement processes, which are carried out successively in a rapid sequence, or at a relatively long time interval from one another. The time period for the check is in this case predetermined such that the electromechanical transducer remains in its rest position throughout this time period. For example, the time period for the check is a maximum of ten to twenty milliseconds. 
     Within the respective measurement process, the measurement voltage Um is detected at least one detection time. The inductive load in the full-bridge circuit is identified as being faulty or sound on the basis of the measurement voltage Um in the switching element which is switched on in the respective measurement process. Faults include, for example, shorting of the first or of the second connection A 1 , A 2  to the supply potential Ubat or to the reference ground potential GND, or shorting or an interruption between the first and the second connection A 1 , A 2 . 
     Shorting of the first connection A 1  to the supply potential Ubat can be identified by only the second switching element T 2  being switched on and by detection of the measurement voltage Um at the at least one detection time which, for example, occurs one millisecond after the second switching element T 2  has been switched on. This short causes a large current to flow through the measurement resistor Rm, and therefore a measurement voltage Um with a large magnitude. In particular, the electric current I through the measurement resistor Rm is not restricted by the inductive load L. This short can therefore be identified very easily if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is greater than a predetermined upper threshold value THR_H ( FIG. 2 ). The predetermined upper threshold value THR_H is preferably predetermined to be dependent on the respective detection time. This ensures that the predetermined upper threshold value THR_H is exceeded only when the electric current I is not being restricted by the inductive load L. In consequence, the predetermined upper threshold value THR_H preferably in each case rises as well after the second switching element T 2  has been switched on, corresponding to the electric current I which is restricted by the inductive load L, even if the electric current I is not actually restricted by the inductive load L. 
     Shorting of the second connection A 2  to the supply potential Ubat can be identified by only the second switching element T 2  being switched on and by detection of the measurement voltage Um at the at least one detection time. The electric current I flowing through the measurement resistor Rm is then restricted by the inductive load L, so that any rise in the magnitude of the electric current I as a function of the inductive load L takes place more slowly than if the first connection A 1  were to be shorted to the supply potential Ubat. Shorting of the second connection A 2  to the supply potential Ubat can be identified very easily if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is less than the predetermined upper threshold value THR_H and is greater than a predetermined lower threshold value THR_L. The predetermined lower threshold value THR_L may also be predetermined as function of the respective detection time. 
     However, if neither the first connection A 1  nor the second connection A 2  is shorted to the supply potential Ubat, then the magnitude of the electric current I remains less than the predetermined lower threshold value THR_L. 
     A check can be carried out in the corresponding manner to determine whether the first connection A 1  or the second connection A 2  is shorted to the reference ground potential GND. For this purpose, only the third switching element T 3  is switched on, and the measurement voltage Um is detected at the at least one detection time. Shorting of the first connection A 1  to the reference ground potential GND is identified if the magnitude of the electric current I, or of the measurement voltage Um which represents it, exceeds the predetermined upper threshold value THR_H. Shorting of the second connection A 2  to the reference ground potential GND is identified if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is less than the predetermined upper threshold value THR_H and is greater than the predetermined lower threshold value THR_L. Shorting of the first connection A 1  or of the second connection A 2  to the reference ground potential GND does not take place, however, if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is less than the predetermined lower threshold value THR_L. 
     In order to identify shorting between the first and the second connection A 1 , A 2  or an interruption between the first and the second connection A 1 , A 2 , either only the first and the second switching element T 1 , T 2  or only the third and the fourth switching element T 3 , T 4  are switched on. If there is a short between the first and second connection A 1 , A 2 , the electric current I through the measurement resistor Rm is not restricted by the inductive load L. This short is identified in a corresponding manner if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is greater than the predetermined upper threshold value THR_H. An interruption between the first and the second connection A 1 , A 2  is identified if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is less than the predetermined lower threshold value THR_L. However, there is no short or interruption between the first and the second connection A 1 , A 2  if the magnitude of the electric current I, or of the measurement voltage Um which represents it, is less than the predetermined upper threshold value THR_H and greater than the predetermined lower threshold value THR_L. 
     Soundness of the inductive load L in the full-bridge circuit is identified when the first connection A 1  is not shorted to the supply potential Ubat or to the reference ground potential GND, the second connection A 2  is not shorted to the supply potential Ubat or to the reference ground potential GND, and no short or interruption is identified between the first and the second connection A 1 , A 2 . 
       FIGS. 4   a ,  4   b  and  4   c  show a flowchart of a first program which, for example, is run by the control unit. The first program comprises steps of a method for checking the inductive load on the electromechanical transducer in the full-bridge circuit. The first program starts with a step S 1 . The first, the second, the third and the fourth switching element T 1 , T 2 , T 3 , T 4  are switched off in a step S 3 . A first waiting time period TW 1  is allowed to pass in a step S 5 . The waiting time period TW 1  is preferably chosen such that any magnetic field of the inductive load which may be present has been essentially completely dissipated. The first waiting time period TW 1  is dependent on the inductive load L and is, for example, about 50 milliseconds. 
     The second switching element T 2  is switched on in a step S 7 . A second waiting time period TW 2  is allowed to pass in a step S 9 . A first current I 1  flowing through the measurement resistor Rm is detected in a step S 11 . The first current I 1  may also be represented by the corresponding measurement voltage Um or by some other variable which is representative of the electric current I flowing through the measurement resistor Rm. 
     A check is carried out in a step S 13  to determine whether the first current I 1  is greater than the predetermined upper threshold value THR_H. If this condition is satisfied, then shorting of the first connection A 1  to the supply potential Ubat is identified as a fault in the step S 15 , and the first program continues in a step S 16 . The first, the second, the third and the fourth switching element T 1 , T 2 , T 3 , T 4  are switched off in the step S 16 . The first program ends at a step S 17 . 
     However, if the condition in Step S 13  is not satisfied, then a third waiting time period TW 3  is allowed to pass in a step S 19 . A second current I 2  is detected in a step S 21 . A check is carried out in a step S 23  to determine whether the second current I 2  is greater than the predetermined lower threshold value THR_L and less than the predetermined upper threshold value THR_H. If the condition is satisfied, then the shorting of the second connection A 2  to the supply potential Ubat is identified as a fault in a step S 25 , and the first program is continued in the step S 16 , and ends at the step S 17 . 
     If the condition in the step S 23  is not satisfied, then the first, the second, the third and the fourth switching element T 1 , T 2 , T 3 , T 4  are switched off in a step S 27 , and a fourth waiting time period TW 4  is allowed to pass in the step S 29 . The third switching element T 3  is switched on in a step S 31 . A fifth waiting time period TW 5  is allowed to pass in a step S 33 , and a third current I 3  is detected in a step S 35 . A check is carried out in a step S 37  to determine whether the third current I 3  is greater than the predetermined upper threshold value THR_H. If the condition is satisfied, then shorting of the first connection A 1  to the reference ground potential GND is identified as a fault in a step S 39 , and the first program is continued in the step S 16 , and ends at the step S 17 . 
     However, if the condition in the step S 37  is not satisfied, then a sixth waiting time period TW 6  is allowed to pass in a step S 41 , and a fourth current I 4  is detected in a step S 43 . A check is carried out in a step S 45  to determine whether the fourth current I 4  is greater than the predetermined lower threshold value THR_L and less than the predetermined upper threshold value THR_H. If the condition is satisfied then shorting of the second connection A 2  to the reference ground potential GND is identified as a fault in a step S 47 , and the first program is continued in the step S 16 , and ends at the step S 17 . 
     However, if the condition in the step S 45  is not satisfied, then a seventh waiting time period TW 7  is allowed to pass in a step S 49 . The third and the fourth switching element T 3 , T 4  are switched on in a step S 51 . As an alternative to the step S 51 , the first and the second switching element T 1 , T 2  can be switched on in a step S 53 . An eighth waiting time period TW 8  is allowed to pass in a step S 55 . A fifth current I 5  is detected in a step S 57 . A check is carried out in a step  59  to determine whether the fifth current I 5  is greater than the predetermined upper threshold value THR_H. If the condition is satisfied, then shorting between the first and the second connection A 1 , A 2  is identified as a fault in a step  61 , and the first program is continued in the step S 16 , and ends at the step S 17 . 
     However, if the condition in step S 59  is not satisfied, then a ninth waiting time period TW 9  is allowed to pass in a step S 63  and a sixth current I 6  is detected in a step S 65 . A check is carried out in a step S 67  to determine whether the sixth current I 6  is less than the predetermined lower threshold value THR_L. If the condition is satisfied, then the interruption between the first and the second connection A 1 , A 2  is identified as a fault in a step S 69 , and the first program is continued in the step S 16 , and ends at the step S 17 . However, if the condition in the step S 67  is not satisfied, soundness is identified and the first program ends at the step S 17 , after carrying out the step S 16 . If soundness is identified, the electromechanical transducer can also be operated as desired, without the step S 16  having previously been carried out. 
     A corresponding check of the inductive load L of the electromechanical transducer can also be carried out by operating the inductive load L in a half-bridge circuit ( FIG. 3 ). A series circuit comprising the first switching element T 1 , the inductive load L, the measurement resistor Rm and the second switching element T 2  is electrically arranged between the supply potential Ubat and the reference ground potential GND. Furthermore, the half-bridge circuit has a parallel resistor Rp, which is arranged electrically in parallel with the inductive load. The signal level at the first connection A 1  may be supplied to the control unit as a status voltage Ustat via a further RC element, which comprises a second resistor R 2  and a second capacitor C 2 . The status voltage Ustat is kept at the reference ground potential GND by an input resistor Re which, for example, is arranged in the control unit, until no other potential is assigned to the first connection A 1 . 
       FIGS. 5   a  and  5   b  show a flowchart of a second program which, for example, is run by the control unit. The second program comprises steps of a method for checking the inductive load on the electromechanical transducer in the half-bridge circuit. The second program starts with a step S 100 . The first and the second switching element T 1 , T 2  are switched off in a step S 102 . The first waiting time period TW 1  is allowed to pass in a step S 104 . 
     The status voltage Ustat is detected in a step S 106 . A check is carried out in a step S 108  to determine whether the status voltage is at a high level, that is to say it corresponds approximately to the supply potential Ubat. If the condition is satisfied, then the second switching element T 2  is switched on in a step S 110 . A tenth waiting time period TW 10  is allowed to pass in a step S 112 . The first current I 1  is detected in a step S 114 . A check is carried out in a step S 116  to determine whether the first current I 1  is greater than the predetermined upper threshold value THR_H. If the condition is satisfied, then shorting of the first connection A 1  to the supply potential Ubat is identified as a fault in the step S 118 , and the second program is continued in a step S 119 . The first and the second switching element T 1 , T 2  are switched off in the step S 119 . The second program ends at a step S 120 . However, if the condition in the step S 116  is not satisfied, then shorting of the second connection A 2  to the supply potential Ubat is identified as a fault in a step S 122 , and the second program is continued in the step S 119 , and ends at the step S 120 . 
     However, if the condition in the step S 108  is not satisfied, that is to say the status voltage Ustat is at a low level, that is to say it corresponds approximately to the reference ground potential GND, then an eleventh waiting time period TW 11  is allowed to pass in a step S 124 . The first switching element T 1  is switched on in a step S 126 . A twelfth waiting time period TW 12  is allowed to pass in a step S 128 , and the status voltage Ustat is detected in a step S 130 . A check is carried out in a step S 132  to determine whether the status voltage is at the low level. If this condition is satisfied, then shorting of the first or of the second connection A 1 , A 2  to the reference ground potential GND is identified as a fault in the step S 134 , and the second program is continued in the step S 119 , and ends at the step S 120 . 
     However, if the condition in the step S 132  is not satisfied, then the first and the second switching element T 1 , T 2  are switched on in a step S 136  and a thirteenth waiting time period TW 13  is allowed to pass in a step S 138 . The fifth current I 5  is detected in a step S 140 . A check is carried out in a step S 142  to determine whether the fifth current I 5  is greater than the predetermined upper threshold value THR_H. If this condition is satisfied, then shorting between the first and the second connection A 1 , A 2  is identified as a fault in a step S 144  and the second program is continued in the step S 119 , and ends at the step S 120 . 
     However, if the condition in the step S 142  is not satisfied, then a fourteenth waiting time period TW 14  is allowed to pass in a step S 146 , and the sixth current I 6  is detected in a step S 148 . A check is carried out in a step S 150  to determine whether the sixth current I 6  is less than the predetermined lower threshold value THR_L. If this condition is satisfied, then an interruption between the first and the second connection A 1 , A 2  is identified as a fault in a step S 152 , and the second program is continued in the step S 119 , and ends at the step S 120 . However, if the condition in the step S 150  is not satisfied, then soundness is identified and the second program is ended at the step S 120  after carrying out the step S 119 . If soundness is identified, the electromechanical transducer can also be operated as desired without the step S 119  having previously been carried out. 
     The parallel resistor Rp makes it possible to distinguish between shorting of the first or of the second connection A 1 , A 2  to the reference ground potential and an interruption between the first and the second connection A 1 , A 2 . The parallel resistor Rp allows the status voltage Ustat to be at a high level even when there is an interruption between the first and second connection A 1 , A 2 . In the step S 130 , the status voltage Ustat is therefore at a low level only when the first or the second connection A 1 , A 2  is shorted to the reference ground potential. As an alternative to the parallel resistor Rp and tapping off the status voltage Ustat at the first connection A 1 , a further measurement resistor can also be arranged electrically between the second connection A 2  and the first switching element T 1 , and a further measurement voltage can be detected which is representative of the electric current I flowing through the further measurement resistor. In this case, shorting of the first or of the second connection A 1 , A 2  to the reference ground potential GND can also be identified by switching on only the first switching element T 1  and by detection of the further measurement voltage, corresponding to the method for checking the inductive load on the electromechanical transducer in the full-bridge circuit. 
     The second to fourteenth waiting time period TW 2 -TW 14  are each, for example, about one millisecond. These waiting time periods may, however, also be chosen to be shorter or longer, or to be different. In particular, the second to the fourteenth waiting time periods TW 2 -TW 14  may be chosen as a function of the inductive load L or as a function of the resistance of the first resistor R 1  and of the first capacitor C 1 , or of the second resistor R 2  and of the second capacitor C 2 , in order to allow the first to sixth currents I 1 -I 6  or the status voltage Ustat to be reliably detected. Furthermore, the sum of the second to ninth waiting time periods TW 2 -TW 9  and the sum of the tenth to fourteenth waiting time periods TW 10 -TW 14  are limited because the electromechanical transducer must remain in its rest position during the check.