Abstract:
A system for driving an electric actuator unit with a polarity-dependent actuation direction contains a driving unit with a voltage input, at least one polarity control input and two voltage outputs whose polarity depends on the polarity control signal at the polarity control input, and a control input. The actuator unit is operated in at least one of the drive directions only if a corresponding polarity control signal is present and the control input is additionally supplied with a predefined control signal.

Description:
FIELD OF THE INVENTION 
     The invention generally relates to a method for driving an electric actuator unit and more particularly relates to a device for driving an electric actuator unit by means of a driving unit. 
     BACKGROUND OF THE INVENTION 
     In modern motor vehicles, use is increasingly being made of electric actuator devices which must fulfill stringent safety requirements. For example in the case of an electric steering lock, the device must never lock while the vehicle is traveling. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An object of the invention is to drive an electric actuator device in such a way that a maximum degree of safety against inadvertent or incorrect driving of the actuator is achieved. 
     A method for achieving the object of the invention includes supplying an actuator unit having a voltage with a polarity which is dependent on the actuation direction with the result that the actuation direction can be reliably predefined. Furthermore, the actuator unit whose actuation direction is predefined by the polarity of the voltage which is supplied, at least in one of the actuation directions, is activated only if a further condition is fulfilled. This further condition can be, for example, in the case of an actuator unit designed for a steering mechanism lock, the fact that a stationary state of the vehicle is detected. 
     When the actuator unit is used for a steering lock, it is then actuated in such a way that it is effective in the direction of locking the steering only if it is supplied with voltage with a polarity which brings about actuation in the direction of locking the steering, and if, in addition, a signal indicating a stationary state of the vehicle is present. 
     The present invention can be applied wherever electric actuator units are to be actuated with a particularly high level of reliability. In particular, it can be used for motor vehicles where it should be possible to actuate numerous electric actuator devices only if specific travel state conditions are fulfilled and/or specific operating states are present. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained below in more detail, by way of example, with reference to schematic drawings, in which: 
     FIG. 1 is a simplified circuit diagram of a system having a driving unit and an actuator unit; and 
     FIGS. 2 and 3 are circuit diagrams illustrating the method of operation of the circuit according to FIG. 1 in two different switched states. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a system for driving an electric actuator unit B contains a control unit S and a driving unit A. The design of the driving unit A will be described first. 
     The driving unit A contains a voltage input  2  to which a voltage supply is connected. The voltage input  2  appears several times in the figure and it is possible to connect the voltage inputs  2  together and feed them, for example, from a battery. Furthermore, the driving unit A contains ground terminals  4 , which can also be connected together to a common terminal. A line leads from the voltage input  2  via a relay coil  6  to an electronic switch  8  which is embodied, for example, as a transistor. A control electrode (base) of electronic switch  8  is connected to a first control terminal  10  of the control unit S. 
     The relay coil  6  actuates a change-over switch  12  which in one position connects the voltage input  2  to a first voltage output  14  and in a second position connects the voltage output  14  to the ground terminal  4  via a line  16  and a measuring resistor  18 . The terminal of the measuring resistor  18  which is remote from the ground is connected to a ground terminal  34  of control unit S and to ground  4  via a line. 
     A further relay coil  20  connects the voltage terminal  2  to an electronic switch  22  which control electrode is connected to a further control input  24  of control unit S. A change-over switch  26  which is actuated by the relay coil  20  connects, in one position, the voltage input  2  to a further voltage output  28 , and in the position illustrated, connects the voltage output  28  to ground  4 . 
     A line leads from the voltage output  14  to a diagnostic terminal  30  of control unit S. A line leads from the voltage output  28  to a further diagnostic terminal  32  of control unit S. Furthermore, a control input  36  which is connected to a control output  38  is provided. 
     As illustrated, the voltage outputs  14  and  28  of the driving unit A form corresponding voltage inputs of the actuator unit B and are connected thereto. Likewise, the control output  38  of the driving unit A forms a control input of the actuator unit B. The actuator unit B has an electric motor  40  the operating direction of which depends on the polarity of the voltage applied to the inputs  14  and  28 . The electric motor  40  displaces, for example, a locking bolt  42  in one direction or the other depending on its direction of rotation. The end positions of the locking bolt  42  are sensed by position sensors  44 , such as Hall-effect sensors. 
     An electronic unit  46  is connected to the voltage outputs  14  and  28  via a rectifier bridge  48 , with the result that the voltage supply of the electronic unit  46  is ensured irrespective of the polarity of the voltage present at the voltage outputs. A relay coil  50  is connected downstream of the electronic unit  46  and actuates a switch  52  which lies in the power supply path of the electric motor  40 . 
     A control line  54 , which is advantageously embodied or connected as a bidirectional data line, leads from the control output  38  to the electronic unit  46 . 
     The control unit S has connections for the described terminals  30 ,  10 ,  32 ,  34 ,  24  and  36  and inputs  56 ,  58  and  60 . A signal is present at the input  56  when the vehicle is in a stationary state. In the “ignition on” state a signal is present at the input  58  and a diagnostic signal can be applied to the input  60 . 
     The control unit S may be embodied as a control unit containing, if appropriate, a microprocessor with associated memories. The control unit operates under the control of logic on software in such a way that signals which depend on the signals applied to the inputs are present in particular at the outputs of said control unit S which correspond to the control input  10 , the control input  24  and the control input  36 . 
     It will be assumed in the first instance that an “ignition on” signal is present at the input  58 . This “ignition on” signal causes the control input  10  to remain deactivated, i.e. the relay coil  6  does not attract the change-over switch  12 , with the result that the change-over switch  12  remains in the position illustrated in FIG. 1 and a signal is generated at the control output  24  which switches the electronic switch  22  to a conductive position so that the relay coil  20  moves the change-over switch  26  into the position shown in FIG.  2 . As is clear from FIG. 2, the polarity of this voltage present at the electric motor  40  is such that the pole located at the bottom according to FIG. 2 is the positive pole. This arrangement of the poles of the electric motor  40  corresponds to a direction of rotation in which the locking bolt  42  (FIG. 1) is moved in a direction which releases the steering mechanism (column). 
     When the signal “ignition on” is present at the input  58 , a signal or a serial pulse sequence is additionally generated at the control output  36 . This signal or serial pulse sequence causes the relay coil  50  in the electronic unit  46  to be activated, with the result that the switch  52  is closed and the electric motor  40  moves the locking bolt into the position which releases the steering column. An end position of the release bolt is detected by the associated position sensor  44  which is connected to the electronic unit  46  (lines not illustrated) and triggers a signal in the electronic unit  46 . This signal is transmitted to the control unit S via the bidirectional control line  54  and displays the release of the steering column. The release of the bolt or of the line is the “nonhazardous” state with respect to the lock so that in the present case only the “ignition on” signal is used. 
     FIG. 3 shows the circuit state in a situation where a signal which indicates a stationary state of the vehicle is present at the input  56  of the control unit, and a signal which signifies “ignition off” is applied to the input  58 . The “ignition off” signal at the input  58  causes the change-over switch  12  to connect the voltage input  2  to the voltage output  14 , as in FIG.  3 . The change-over switch  26  remains in the position as in FIG. 1 in which it connects the voltage output  28  to ground  4 . The arrangement of the poles of the electric motor  40  is then such that the positive pole is located at the top according to FIG. 3, i.e., the electric motor operates in the direction to lock the steering column. The “vehicle stationary state” signal at the input  56  causes the control unit S to transmit a signal to the electronic unit  46  via the control input  36 . In response to this signal, the electronic unit  46  closes the switch  52 , with the result that the electric motor  40  moves the locking element into the position which locks the steering column. In a way similar to the release position, the lock position can be detected by activating the respective position sensor  44  and generating a locking signal in the electronic unit  46 . 
     For diagnostic purposes, when the input  60  is supplied with a diagnostic signal, the change-over switches can be switched as illustrated in FIG. 2 at all times, i.e., the steering column is released. The power drain of the electric motor  40  can be measured by measuring the voltage across resistor  18  and terminal  34 , and comparing this voltage with a setpoint value. Furthermore, the voltages at the diagnostic terminals can be used to determine whether a change-over switch or a relay is sticking or otherwise not functioning satisfactorily. 
     In summary, the invention uses only three interfaces connections ( 14 ,  28  and  38 ) between the driving unit A and the actuator unit B. The actuator unit may be spatially remote from the driving unit A and still achieve reliable and largely failsafe actuation of the actuator unit B. This arrangement also permits diagnostics to be performed. 
     The system described can be modified in various ways. For example, the driving unit A may be a component of the control unit S. The relay switches can be replaced by other types of electronic switches. The interfaces  14 ,  28  and  38  may be galvanically isolated. The electric motor  40  may be a solenoid or a hydraulic unit driven by a magnet. The relay coil  50  may be combined with the switch  52  to form an electronic switch, for example a transistor. Further information relating to the actuator unit B can be transmitted to the control unit S via the bidirectional line  54 . 
     One of the control inputs  10  or  24  may be dispensed with if the switches  12 ,  26  arranged downstream are switched in such a way that when signals are supplied to the single control input the switches go, for example, into the positions according to FIG. 2, and into the positions in FIG. 3 when there is no signal. 
     The control unit S can have a plurality of inputs which input signals are converted into the respective supply configuration of the outputs according to requirements. 
     An alternative to the procedure described with reference to FIGS. 2 and 3, the procedure is when the ignition key is inserted into the ignition lock or when the operator begins to turn it, the polarity is switched to the “release” actuation direction. The edge of an “ignition on” signal then causes a release or activation signal to be transmitted via the control line  54 . In this way the line is released more quickly. 
     The polarity for the “lock” actuation direction can, like the activation signal, be switched only if both conditions “ignition off” and vehicle stationary state are fulfilled. For the activation signal it is possible for additional conditions to be required, such as ignition key removed from lock etc.