Abstract:
An engine control unit for driving an electric circuit, e.g., a starter in a vehicle, includes at least a first element for making a first signal, particularly an ignition signal, available, a second element for making a voltage available for the electric circuit, a third element for connecting the electric circuit, a first switch which is disposed between the second and third elements to control the electric, circuit, and a fourth elements for generating a second signal, the first signal cooperating with the second signal to form a virtual second switch for turning the electric circuit on or off with the aid of the first switch.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an engine control unit for driving an electric circuit, particularly a starter in a vehicle. 
         [0003]    2. Description of the Related Art 
         [0004]    Engine control units are employed in automotive engineering and are used there for controlling engine components, e.g., a starter of the engine or a fuel pump. Via inputs and outputs, corresponding engine components are able to be connected to the engine control unit in order to control them. For example, the battery voltage is applied via a first input of the engine control unit, and via a second input, a signal may be made available, e.g., an ignition signal, which then actuates corresponding switches within the engine control unit, so that ultimately the starter or the fuel pump is able to be energized, and the engine is then started by the switching-on of the starter and the fuel pump. 
         [0005]    The switches are usually either connected on one side to the positive pole of the battery voltage, and after a suitable signal of the microcontroller, switch a starter relay, etc., to ground. Such switches are known as high-side switches. However, there is also the opposite case, in which what is termed a low-side switch connects the starter relay or the fuel-pump relay to the negative pole of the battery voltage. 
         [0006]    To allow detection of faults in the electric circuits during operation of a vehicle, e.g., short circuits of the starter to negative or ground, published German patent document DE 196 165 43 C1 or published German patent application document DE 44 02 115 A1 have described suitable devices having special circuitry or engine control units that permit fault detection of short circuits. 
         [0007]    Moreover, in order to increase safety with respect to faults, especially with respect to short circuits when starting vehicles, it has become known to provide both a high-side and a low-side switch. The operating principle is as follows: In the engine control unit, a high-side switch is provided that is connected on one side to the battery voltage, and on the other side, to a first output of the engine control unit. The high-side switch is driven via a microcontroller of the engine control unit. Also provided in the engine control unit is a low-side switch which is connected to an output of the engine control unit—the output being connected to ground—and to a second input. Connected between the first output and the second input of the engine control unit is a relay for the starter, which energizes the electric circuit of the starter only when both the high-side and the low-side switch are switched on, that is, are conductive. Therefore, in response to a short circuit of an individual switch, the electric circuit of the starter is not supplied with current, thereby increasing safety, since it is undesirable for a starter or a fuel pump to start up in uncontrolled manner. 
         [0008]    However, there is a trend to minimize the weight of cables, etc., in order to keep the overall weight of the vehicle as low as possible. Therefore, in practice, either the high-side switch or the low-side switch is often short-circuited. This saves on weight, since it is possible to dispense with additional cable for the connection of the relay to the second input of the engine control unit. In the case of the short circuit of the high-side switch, the relay of the starter is thus connected directly to the battery voltage; in the case of the short circuit of the low-side switch, the relay of the starter is connected directly to ground. It may be that there are thus savings in cable and weight; however, the likelihood that the starter will switch on in uncontrolled fashion is consequently increased, since in each case, a relay only opens or closes the electric circuit of the starter with one switch. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The engine control unit for driving an electric circuit, e.g., a starter in a vehicle, as well as the corresponding method have the advantage that safety against an unintentional closing of the electric circuit due to a short circuit is increased, and at the same time, the number of connections necessary for this purpose is further reduced, which substantially decreases the costs over all, while maintaining safety. In the same way, the likelihood of a false connection of the electric circuit is reduced, since only one output is available for the respective electric circuit. 
         [0010]    According to one preferred further development of the invention, the first and second means include an input of the engine control unit, and the third means includes an output of the engine control unit. The advantage in this connection is that the engine control unit is able to be integrated into electric circuits of vehicles in an inexpensive and uncomplicated manner, and the signals are then able to be made available. 
         [0011]    According to a further preferred development, at least one third switch is disposed between the first switch and an output of the engine control unit in order to control a second electric circuit, especially for a fuel pump. The advantage in this context is that not just one electric circuit, particularly the electric circuit for the starter, is able to be switched via the engine control unit, but also, independently of that, further electric circuits, e.g., for a fuel pump, sensors for monitoring, ignition coils, etc., as well. The number of engine control units needed is thus reduced to a minimum. The same holds true for the number of cables, etc., for driving the electric circuits. Likewise, the maintenance and the replacement of the engine control unit is simplified, since in the event of damage or malfunction, the entire engine control unit may simply be replaced. 
         [0012]    According to a further preferred refinement, the engine control unit includes a device, particularly a microcontroller, for controlling at least the third switch. This offers the advantage that the device may be used not only for controlling the third switch, but rather, the device may likewise be used to monitor electric circuits which are connected to the engine control unit. 
         [0013]    According to another preferred development, the engine control unit includes at least one device for detecting faults. The advantage here is that both faults within the engine control unit as well as faults in the electric circuits connected to the outputs of the engine control unit, e.g., in the case of the starter, sensors, etc, are able to be detected. The device for detecting faults first of all detects these faults and, in so far as a differentiation of the various faults is not possible, checks, based on further tests, e.g., by opening and closing different electric circuits and/or by applying different voltages within a small time window, which faults are present in detail. The faults are then stored in a fault memory, so that they are then able to be read out, for example, by connecting an external diagnostic tool. Likewise, it is possible for the documented fault to be signaled on a display device for a driver of a vehicle, so that the driver can go to an auto repair shop and have the fault rectified. 
         [0014]    According to another preferred refinement, the at least one device for detecting faults includes at least one analog-to-digital converter. The advantage in this case is that the prevailing status of the switch or electric circuit to be monitored is able to be picked off in an easy manner. By setting suitable tolerance threshold values, the device, with the aid of the analog-to-digital converter, e.g., with the help of a software running on it, is then able to analyze different analog levels and to detect and document the prevailing status of the electric circuit to be monitored. 
         [0015]    According to a further preferred development, the fourth means includes a low-side output stage, in particular, a starter output-stage component, e.g., an R2S2. The advantage in this context is that the use in particular of a specially developed low-side output stage is possible even at low voltages, particularly less than 5V during the starting procedure of an engine, during which the voltage drops very sharply for a brief period. In this manner, the reliability of the engine control unit is increased overall. 
         [0016]    According to another preferred refinement, the device for controlling at least the third switch includes detection of faults of the fourth means. This offers the advantage that costs may thereby be reduced, since the device both controls the third switch and detects faults of the fourth means. Consequently, the highest possible integration of the control components and monitoring components of the engine control unit is achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows, in simplified manner, an engine control unit for driving an electric circuit according to a first specific embodiment of the present invention, in symbolic logic representation. 
           [0018]      FIG. 2  shows an engine control unit for driving an electric circuit according to a first specific embodiment of the present invention, in a circuit diagram. 
           [0019]      FIG. 3   a  shows an engine control unit for driving an electric circuit in a simplified circuit diagram. 
           [0020]      FIG. 3   b  shows an engine control unit for driving an electric circuit in a simplified circuit diagram for the case of a short circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    In the figures, identical reference numerals denote the same or functionally-equivalent elements. 
         [0022]      FIG. 1  shows, in simplified manner, an engine control unit for driving an electric circuit according to a first specific embodiment of the present invention, in symbolic logic representation. In  FIG. 1 , reference numeral  1  denotes a first signal which is applied to a first input of engine control unit V (see  FIG. 2 ) according to the first specific embodiment. A module  67 , including a low-side output-stage component  6   a  in the form of a starter output-stage component, for example, particularly an R2S2 output-stage component, and an inverter  7  downstream of output-stage component  6   a,  provides a second signal  1   a.    
         [0023]    First signal  1  and second signal  1   a  cooperate in such a way that a virtual second switch  5   b  is formed. Virtual second switch  5   b  is in the form of an AND gate. The output of this virtual second switch  5   b  is connected to a first switch  5   a  in order to control this first switch  5   a.  A further signal  2 , here in the form of battery voltage  2 , is applied to first switch  5   a.  If second switch  5   b  is closed, i.e., a corresponding signal is present at the output of second switch  5   b,  first switch  5   a  is switched in such a way that battery voltage  2  is then also applied to a line  2   a  that is connected to the output of switch  5   a.    
         [0024]    Starting from first switch  5   a,  further switches  4   a,    4   b  are connected to line  2   a  and make battery voltage  2  available for external loads or electric circuits  3   a,    3   b,  e.g., a starter or a fuel pump, via corresponding connections, so that they are energized. Switches  4   a,    4   b  are likewise in the form of logic AND gates. Switch  4   a  is additionally connected to a line  8   a,  and switch  4   b  is connected to a line  8   b.  Via lines  8   a,    8   b,  in each case a signal, e.g., from a microcontroller  10  (see  FIG. 2 ), is made available, that actuates switches  4   a,    4   b  and controls electric circuits  3   a,    3   b.    
         [0025]      FIG. 2 . shows an engine control unit for driving an electric circuit according to the first specific embodiment of the present invention in a circuit diagram. 
         [0026]    An engine control unit V according to the first specific embodiment is shown in a circuit diagram in  FIG. 2 . A first signal  1  is applied to a first input  20  of engine control unit V when a switch  20 ′ is closed, e.g., by turning an ignition key of a vehicle, in order to start the vehicle. A primary relay  12  is thereby actuated, so that in a line  2 , a battery voltage is then applied to a first switch  5   a  on the input side. At the same time, a microcontroller  10  receives a signal from a voltage regulator chip  11 , connected to it via a line  40 , which in turn detects that first signal  1  is being applied to engine control unit V. Microcontroller  10  then switches on a module  13 ,  14  via a line  41 , reference numeral  13  (in  FIG. 1 :  6   a ) denoting an output-stage component (low-side output stage, particularly starter output-stage component R2S2) and reference numeral  14  (in  FIG. 1 :  7 ) denoting an inverter in the form of a transistor. Module  13 ,  14  (in  FIG. 1 :  67 ) generates an outgoing signal  1   a.  Signals  1  and  1   a  then cooperate in such a way that a virtual second switch  5   b  is formed, which is used to control first switch  5   a.  Second switch  5   b  controls first switch  5   a  in such a way that first switch  5   a  is only switched on in response to the application of a signal  1  and simultaneously upon the application of corresponding signal  1   a  of module  13 ,  14 , so that the battery voltage is then made available in an electric circuit or line  2   a  that is connected to the output of switch  5   a.    
         [0027]    Lines  4   a′  and  4   b′,  respectively, in turn branch off from this electric circuit  2   a  or line  2   a  to switches  4   a,    4   b,  which supply voltage to electric circuits  3   a,    3   b,  connected to engine control unit V at outputs  20   a,    20   b,  for a starter relay of the engine of a vehicle, for example, or a fuel pump, when corresponding switch  4   a,    4   b  is closed. In order to control switches  4   a,    4   b,  in each case a control line  8   a,    8   b  is provided between microcontroller  10  and respective switch  4   a,    4   b.  For example, in order to start the engine, microcontroller  10  then controls both the starter by closing switch  4   a,  as well as the fuel pump with the aid of switch  4   b,  if they are connected to engine control unit V via corresponding lines  3   a,    3   b.    
         [0028]    Between the outputs of switches  4   a,    4   b  and outputs  20   a,    20   b  of engine control unit V for the connection of electric circuits  3   a,    3   b,  diagnostic lines  11   a,    11   b  are disposed, which are connected to corresponding inputs of microcontroller  10 . Finally, also connected to electric circuit  2   a  is a diagnostic line  11   c,  which is likewise connected to an input of microcontroller  10 . These diagnostic lines  11   a,    11   b,    11   c  are used to detect, differentiate and document faults in engine control unit V, as well as faults in electric circuits  3   a,    3   b  connected via corresponding lines. For example, these faults are documented in a fault memory of microcontroller  10 , which is provided with an external connection for a diagnostic tool. 
         [0029]    The faults are diagnosed with the aid of analog-to-digital converters in microcontroller  10 . A software which runs on microcontroller  10  then ascertains the specific faults on the basis of various tolerance threshold values for the voltage which is made available via lines  11   a,    11   b,    11   c.    
         [0030]    Using an engine control unit V according to a first specific embodiment as an example, in the following, the detection by engine control unit V of an internal fault of engine control unit V ( FIG. 3   a ) as well as a fault in an external electric circuit ( FIG. 3   b ) is described exemplarily. 
         [0031]      FIG. 3   a  shows a simplified representation according to  FIG. 2 , having a first switch  5   a  and a second switch  4   a  that controls a starter relay  30  of a vehicle via a line  3   a.  A diagnostic line  11   a  for second switch  4   a  as well as a diagnostic line  11   c  for first switch  5   a  are also shown. Diagnostic lines  11   a,    11   c  are connected to a microcontroller (not shown here) in a manner corresponding to the setup in  FIG. 2 , and tap off a voltage at the output of respective switch  4   a,    5   a  in order to detect faults of engine control unit V or of the electric circuit for starter relay  30 . 
         [0032]    First of all, a fault-free state, that is, without the bridging of starter relay  30  by short circuit K, is described. 
         [0033]    During normal operation of a vehicle, switch  5   a  is closed, that is, the battery voltage is applied to downstream line  4   a ′. However, switch  4   a  which controls a starter relay  30  is out of circuit, i.e., the battery voltage is not applied to line  3   a.  Accordingly, in diagnostic line  11   c,  an analog-to-digital converter measures a voltage which lies above a specific tolerance threshold value A, since switch  5   a  is closed. If switch  5   a  were out of circuit, a voltage below tolerance threshold value A would be measured. 
         [0034]    With switch  4   a  out of circuit, it cannot be ascertained with the aid of diagnostic line  11   a —to which a 5V diagnostic voltage is applied in order to diagnose faults—whether a short circuit K of starter relay  30  is present. In order to now ascertain whether a short circuit K exists, switch  4   a  is closed for a very brief time, and at least the voltage in diagnostic line  11   a  is measured by an analog-to-digital converter in microcontroller  10 . A fault-free operation is determined if an impedance of electric circuit  3   a,  connected via diagnostic line  11   a,  lies above a certain tolerance threshold value B for specific DC and AC voltages. In the event of a short circuit K, a smaller voltage value or an impedance less than tolerance threshold value B for the specific DC and AC voltages is determined in diagnostic line  11   a,  so that a short circuit K to ground M is then ascertained correspondingly. In this case, microcontroller  10  then controls switch  4   a  and switch  5   a  accordingly, so that they are closed and/or opened correspondingly in order to permit an analysis or repair of short circuit K. In the case of starter relay  30 , both switch  4   a  and switch  5   a  may then be switched off, in order to prevent starter relay  30  from spinning. 
         [0035]      FIG. 3   b , with the aid of a simplified diagram according to  FIG. 2 , now shows schematically a case of a short circuit K in switch  4   a.  Without a short circuit K, given switch  4   a  in the OFF state and switch  5   a  in the ON state, a voltage above corresponding tolerance threshold value A is measured in diagnostic line  11   c,  while only the usual voltage is measured in diagnostic line  11   a  in the case of switch  4   a  in the OFF state. 
         [0036]    If switch  4   a  is now bridged by a short circuit K, a direct connection then exists between the output of switch  5   a  and electric circuit  3   a  of starter relay  30 . 
         [0037]    If the engine is started, at first no fault is diagnosed, since for its starting, both switch  5   a  and switch  4   a  must be closed in order to actuate the starter. However, if, because of a successful starting procedure of the engine, switch  4   a  is then turned off so that the starter does not spin, or if the engine is already in the running operating state, but the same voltage as in the closed state is nevertheless still measured in corresponding diagnostic line  11   a,  microcontroller  10  then determines an internal fault of engine control unit V and, if indicated, then turns switch  5   a  off in order to avoid further damage to engine control unit V or connected electric circuit  3   a.    
         [0038]    Ascertainment and differentiation of further internal and external faults, e.g., a short circuit of the starter motor with the battery voltage, an interruption of line  3   a  outside of engine control unit V or perhaps a short circuit of switch  5   a  are also possible with the aid of diagnostic lines  11   a,    11   c  or microcontroller  10 . In order to differentiate the individual faults from each other, in addition, switch  4   a  and switch  5   a  may then be turned on and off reciprocally by the engine control unit, in order to detect and differentiate the various types of faults. 
         [0039]    A separate line to the starter or a short circuit to the battery are measured, for example, via diagnostic lines  11   a,    11   c  in the OFF state of switch  4   a,  whereas a short circuit to ground M is measured during the ON state of switch  4   a.  In the case of an interruption of a line in connected electric circuit  3   a,  for instance, the impedance of the connected electric circuit is ascertained with the aid of diagnostic line  11   a.  If the impedance is above a specific tolerance threshold value C, e.g., several hundred kiloohm, an interruption is detected as fault. If the impedance lies below a specific tolerance threshold value D, e.g., a few kiloohm, no fault is detected by microcontroller  10 . Tolerance threshold value D is specified commensurate with typical resistance values of the connected electric circuit. 
         [0040]    Moreover, certain faults must be checked continuously by engine control unit V. For example, a fuel pump connected to engine control unit V should be prevented from delivering fuel unchecked by bridging a switch  4   a —via which a fuel pump is connected—by a short circuit. In this case, switch  4   a  and switch  5   a  are then turned off within 500 ms, if a corresponding fault is detected. 
         [0041]    Furthermore, after a first determination of a fault, it is necessary to verify the fault again within a fixed time span in order, for example, to likewise detect a short circuit K on the basis of a cable that is loose and flapping around, and then to turn off switch  4   a  and switch  5   a  in order to avoid damage to the device and to the external electric circuits. 
         [0042]    Although the present invention was described above on the basis of preferred exemplary embodiments, it is not limited to them, but rather is modifiable and alterable in many ways.