DE19826685A1 - Circuit arrangement for adjustment element e.g. electrically controllable brake force amplifier of motor vehicle - Google Patents

Abstract

The circuit arrangement has two electronically activated switches (105,106) in conductors between a first and a second potential (101,102) and corresponding connections (100a,100b) of the adjustment element (100). A control arrangement (112) controls the first switch (106) with a first, preferably pulse-width modulated control signal (S1), and the second switch (105) through a second control signal (S2). The circuit arrangement also includes a first and a second conductor (103, 104) which supply the two potentials to the two connections of the adjustment element. The first switch is provided in the conductor (104) between the first potential (102) and the first connection (100b) of the adjustment element. The control arrangement controls the first switch with a first, preferably pulse-width modulated control signal. The second switch (105) is provided in the conductor (103) between the second potential (101) and the second connection (100a) of the adjustment element, and the control arrangement controls it through the second control signal.

Description

The invention relates to a circuit for an actuator and a method for checking the wiring of a Actuator according to the generic terms of the independent Expectations. The actuator considered is in particular a electrically actuated actuator with two connections, preferably an electromechanically actuated Device that is an electromagnet, a coil or has similar. In particular, actuators for considered security-critical applications. Such one Actuator is an electronically controlled Brake booster. There are like conventional ones Brake boosters the actual, pneumatic operated reinforcement part. However, he will not mechanically directly by operating the brake pedal controlled, but by an electrically operated Valve that the vacuum side according to electrical Signals vented or not. The function of the electrically actuated ventilation valve thus intervenes directly into the braking behavior of the vehicle, so that on the one hand, the perfect functioning of such a device Ventilation valve or actuator is desired, on the other hand but it is also necessary to ensure that through a review such an actuator no unwanted interference in the braking system of a vehicle.  

In DE-OS 44 25 578 a braking system is shown schematically an electrically controllable brake booster shown. However, it is not specified here how one on the one hand reliable and on the other hand for the braking behavior of the Vehicle uncritical inspection of the components of the electrical control of the valve can take place.

The object of the invention is a circuit for a Actuator or a procedure for checking the Specify circuitry of an actuator, the simple, reliable and for the braking behavior of the vehicle uncritical checking of the electrical or electronic Enable components. This task is accomplished with the Features of the independent claims solved. dependent Claims are on preferred embodiments of the Invention directed.

Before individual embodiments of the invention are described, possible errors are described with reference to FIG. 1. Fig. 1 shows with reference numeral 100, the actuator or its regarded electrical component, in particular, for example, an electromagnet, a coil, an electric motor or the like. The actuator has two connections 100 a and 100 b. This actuator can be connected between two potentials 101 , 102 by means of its connections 100 a, 100 b. 102 may be ground, for example, 101 the battery supply voltage (usually 12 V) or another suitable voltage. In conventional systems, the operation of actuator 100 is controlled by means of a switch: the actuator operates when the switch is closed and it is at rest when the switch is open. Various errors can occur:
The switch can be short-circuited or no longer closable. One of the connections 100 a, 100 b of the actuator 100 can be short-circuited to one of the potentials 101 , 102 . Actuator 100 may internally have an open or short circuit. Finally, leakage currents to the potentials mentioned can occur via high-resistance shunts. Most of the above-mentioned errors represent an error that directly affects the function of the actuator and must be recognized as early as possible in order to be able to largely avoid unsafe operating states.

It is therefore desirable to have a circuit that is used frequently Checking the actuator allowed. In particular, a Checking may also be possible if the actuator can potentially be used, for example during driving a motor vehicle. On the other hand make sure the check is not too leads to undesired interventions, for example undesired Brake interventions.

According to the invention, a circuit is therefore specified that two electronically operated switches on each of the Has connections of the actuator. With the conventional Actuation of the actuator can be one of the switches closed and another one of the switches as specified other control criteria can be controlled. in the Verification operation, a switch can remain open and on others are closed, so that due to Potential relationships errors can be detected.

Referring now to the drawings, individual Embodiments of the invention described, show  

Fig. 1 shows schematically a first embodiment of the invention,

Fig. 2 schematically shows a further embodiment of the invention,

Fig. 3 different error states and the type of their detection in tabular form, and

Fig. 4 shows an embodiment of a checking device.

Fig. 1 shows a first embodiment of the invention. 100 is the actuator or the electrical component therefor, for example an electromagnet, a coil, an electric motor or the like. It has connections 100 a and 100 b. A switch 105 , 106 is provided on each side of the actuator 100 . Switch 105 is in line 103 between terminal 100 a and potential 101 , while switch 106 is in line 104 between terminal 100 b and potential 102 . The switches 105 , 106 are preferably electronically actuated switches, for example FETs, power FETs, thyristors, GTOs or the like. The switches 105 , 106 are switched in accordance with control signals S1, S2, which are fed to the switches via lines 111 , 110 . In conventional operation of the actuator (for example light braking), the procedure can be such that switch 105 receives a control signal S2 via line 110 , so that it closes permanently. In contrast, switch 106 receives a signal S1 via line 111 , so that actuator 100 is actuated in the desired manner. For example, the signal S1 can be a pulse-width-modulated signal generated in accordance with the desired braking force. As a result, the electronically actuatable switch 106 is opened and closed at a comparatively high frequency, so that a desired average current is set by the actuator 100 . Instead of a pulse-width-modulated signal, other signals can also be provided, for example an analog signal that switches the switch 106 in an analog manner, that is to say opens more or less, for example in order to set a desired current.

Furthermore, one or more of the test signal feedback circuits described below are provided for checking electrical values or time relationships:
Test signal P1 on line 108 , which is tapped in the vicinity of the connection 100 b of the actuator 100 , test signal P2 on line 107 , which is tapped in the vicinity of the connection 100 a of the actuator 100 , and test signal 109 , which corresponds to the first control signal.

If the actuator 100 or its wiring is to be checked, the switches 105 , 106 can then first be actuated in a suitable manner and the test signals P1 to P3 on the signal lines 107 to 109 can then be checked.

Different test modes can be set to check the aforementioned error possibilities, for example mode 0, in which both switches 105 , 106 are open, mode 1, in which one switch is closed and another is open (so that the actuator is still not actuated electrically ), and mode 2, in which one switch is closed and the other is closed so briefly that there is no significant actuation of the actuator.

Referring to FIG. 3, these modes will be explained later exactly.

By providing two switches, it is possible to disconnect both connections 100 a, 100 b of actuator 100 from the respective potentials 101 , 102 (see mode 0 above), so that different error conditions can be recognized which would be difficult or impossible without this disconnection would be recognizable. By providing two switches, one can also be closed and another can be kept open, so that further errors can be identified (mode 1) without brake intervention.

Referring to FIG. 2, a more detailed From will be described guide die, wherein the same reference numerals as in Fig. 1 denote the same components. 205 is a switch designed as an FET and corresponds to switch 105 in FIG. 1, the same applies analogously to switch 206. Driver circuits 231 , 233 are provided for control.

The signals S1, S2, after which provided the switches 205, 206 are controlled to be, by a control circuit 112, 235 - 237 generated in a suitable manner. The components 235-237 in FIG. 2 essentially correspond to the control circuit 112 in FIG. 1. The first control signal S1 is fed back through line 109 as a test signal P3 into a signal monitoring circuit 236 . Likewise, the potentials in the vicinity of the connections 100 a, 100 b of the actuator are tapped and fed back into the signal monitoring circuit 236 as test signals P1, P2 via feedback circuits 221 , 222 and 224 , 225 , respectively. The resistors 221 a and 221 b act as voltage dividers, which are used to adjust the value of the signal level P2. The resistors 223 and 226 are comparatively high-resistance and pull the terminals 100 a, 100 b of the actuator 100 to defined values when the switches 205 , 206 are open. Together, the resistors 223 , 226 with the ohmic resistance of the coil 100 also act as a voltage divider.

235 is a processing device that receives higher-ranking signals 239 and generates a first output signal S1 ′ in accordance with these signals, which serves as the input signal of a generating device 237 . The generating device 237 generates the actual first control signal S1, which is preferably pulse width modulated and digital. But it can also be an analog signal that opens a transistor more or less wide.

The processing device 235 communicates with the signal monitoring device 236 via data lines 238.

The monitoring device 236 , the more detailed structure of which will be explained later with reference to FIG. 4, can on the one hand monitor the signal levels on the lines 21 and P2. On the other hand, it can check the control signal S1 for correctness. If the control signal S1 is, for example, a pulse-width-modulated signal, the processing device 235 can keep switch 205 open and generate a pulse-width-modulated signal S1 for switch 206 with a known pulse duty factor. The monitoring device 236 then checks whether the signal S1 is generated in the expected manner, for example in which (in the case of pulse-width-modulated signals) the timing of edges is checked or (for example in the case of an analog control signal) the level of the signal is checked.

Referring to Fig. 3 different error conditions and the manner of its determination will be described. The specified threshold values are to be understood as examples, they result from the dimensioning of the individual resistors in the circuit of FIG. 2. The errors considered in FIG. 3 relate to errors in the wiring of the actuator or in the actuator itself, which are based on the test signals P1, P2 can be recognized. The modes mentioned above can be set during the check. In mode 0, both switches 105 , 106 and 205 , 206 are open if they work properly. Via the resistors 223 and 226 , the connections 100 a and 100 b of the actuator 100 are drawn to defined potentials which are different from the potentials 101 , 102. If one of the switches is short-circuited, this can be recognized from the fact that the Terminals 100 a, 100 b, despite the theoretically open switch 205 , 206, the potential 101 or 102 is present. In a similar way, short circuits of the connection 100 a to ground 102 or of the connection 100 b to the supply voltage can be detected. A ground short circuit of the connection 100 a can be recognized by a very low potential at this connection. Conversely, the short circuit of the connection 100 b to the supply voltage can be recognized by a very high potential both at the connection 100 b and at the connection 100 a. In this context it is pointed out that it is not absolutely necessary to distinguish between individual errors. It is important that suitable measures are triggered as soon as any error occurs, whereby the exact nature of the error is then irrelevant.

Leakage currents can be determined in a manner similar to short-circuits of a connection 100 a, 100 b to one of the potentials if both switches are open. Such leakage currents also have an effect on the potentials at the terminals, so that they can be determined by suitable threshold value settings and checking the potential s on the lines 222 , 225 .

In mode 1 , for example, switches 105 , 205 can be closed and switches 106 , 206 can be open. In this way it can be recognized whether switch 105 , 205 closes. If not, the potential at terminal 100 a will not assume the required value, so that this is communicated to signal monitoring device 236 via voltage divider 221 a, b and line 222 in the form of test signal P2. The ground short circuit of the connection 100 b of the actuator 100 (which can already be seen in mode 0) can be recognized by a very low level of the test signal P1. The same applies to an interruption of the coil itself. The high potential 101 , which is communicated to the connection 100 a via the closed switch 205 , is not visible at the connection 100 b, so that the test signal P1 remains below a threshold value.

As in mode 0, a short circuit of switch 206 is finally recognizable because terminal 100 b is then pulled to the low ground potential 102 , although switch 206 should be open.

Finally, in mode 2, both switches 105 , 106 and 205 , 206 are closed. This mode is critical in that it energizes the actuator and actually operates it. It is therefore advantageous to set this mode only very briefly, for example by switching switches 106 , 206 only very briefly in addition to the already closed switch 105 , 205 . In this mode 2, the non-switching of the switch 106 , 206 can be seen , because then the potential at the connection 100 b is not drawn from ground, but remains above a threshold value. A short circuit of the actuator 100 can be recognized according to the same criterion. Because of the short circuit, the expected voltage will not drop at the actuator 100 , so that the connection 100 b again will not assume a potential close to the earth, but will remain above a threshold value.

The modes described with reference to FIG. 3 allow the detection of error conditions in each case with reference to only one of the test signals P1 or P2. Thus, the test signal is, for example, P1 (b corresponds to the potential at the terminal 100) with a first, relatively low threshold value as compared in the mode. 2 In mode 0, the test signal P2 is (which will be produced in accordance with the potential at the connection 100a) are each checked to see if it is lower than a second threshold value which is slightly higher than the first threshold value, or if it is higher than a third Threshold that is higher than the second threshold. In mode 1, the test signal P1 is essentially considered and then checked whether it is above the second threshold value. Here, the test signal P2 can also be checked for exceeding a comparatively high fourth threshold value in order to be able to determine the correct switching of the switches 105 , 205 .

The modes 0-2 described so far serve to check the wiring of the actuator or the actuator itself. In a further mode 3 (not shown in FIG. 3), the comparatively complex first control signal S1 can be checked. For this purpose, a specific first control signal S1 is generated and checked for correct generation. In order to avoid the actual actuation of the actuator 100 , switches 105 , 205 are opened. The control device 112 , 235-237 then generates a specific first control signal S1, for example a pulse-width-modulated signal, and checks the generated signal. For example, a pulse width modulated signal with a certain duty cycle can be generated and then checked whether the edges of this signal appear in the desired manner.

In order to be able to carry out the check according to the invention, the control device 112 , 235-237 and in particular the processing device 235 has a test device which on the one hand generates the necessary control signals S1, S1 ', S2 for setting one or more of the above-mentioned modes and on the other hand notifies the signal monitoring device 236 of the control signals required (for example the start and end of the check, signal values to be expected or threshold values to be checked).

In addition, an interruption device can be provided which interrupts or terminates the check described (in particular the setting of modes 0-3) when a request for an actual use of the actuator becomes recognizable, for example in accordance with the input signals 239 .

Fig. 4 shows an embodiment of the signal monitoring device 236. In the upper part are shown (on the wiring of the actuator or the actuator itself) means for checking the test signals P1, P2, the lower part shows systems for verifying the first control signal S1, P3. These two circuit parts (as shown) can be combined with one another. A separate embodiment and the omission of one of the two parts are also possible.

As already described with reference to FIG. 3, the test signals P1, P2 are to be compared with threshold values in order to check the wiring and the actuator itself. For this purpose, the signal monitoring device 236 has two comparators 407 , 408 , each of which monitors one or the other signal. However, since only one error signal is to be monitored in each case, as shown in FIG. 3, in order to be able to recognize the respective errors, an embodiment can also be provided in which the two error signals P1, P2 are passed through a changeover switch to a single comparison device. Threshold values can be communicated via signal lines 413 and the question of whether to be checked for overshoot or undershoot. In a gate 409 , the individual error signals that arise as the output of the comparison devices 407 , 408 can be combined to form an error signal F, which can be output separately as a signal 411 , or which can be communicated to the processing device 235 via the line 238 .

The lower part of FIG. 4 shows a device for checking a pulse width modulated signal (which is input as test signal P3). First, edge detectors 401 , 402 are provided, one responding to rising and one falling edge. There is also a time measuring device 403 . Whenever an edge is detected, the point in time just determined is written serially into a memory 404 with several memory locations. This is indicated schematically by arrow 406 . Accordingly, there is a serial entry in the memory device 404 of times which alternately characterize the time of rising and falling edges. The storage device 404 can be designed, for example, in the manner of a shift register, into which data is continuously written, shifted in accordance with data subsequently written, and finally falls out. Finally, an evaluation device 405 checks the correctness of the times entered.

Theoretically, correct pulse width modulation can be identified based on the correct position of three successive edges. Accordingly, the evaluation device 405 can, for example, be designed in such a way that it evaluates the three most recent entries in the memory device 404 for correctness and then, if it detects errors, outputs an error signal which, if necessary, is combined with the error signals from the comparison device 407 , 408 Error signal F, 411 can be combined.

In order to avoid false alarms, it can be useful to examine further groups of edges for their temporal position upon the detection of a first irregularity and only to issue an error signal if multiple errors are found. The evaluation device 405 can also receive data via line 412 , which provide it with the information it requires, for example the expected duty cycle, etc.

Carrying out the described check in the signal monitoring device 236 can be made dependent on the supply voltage being in a defined range. Only then is it ensured that checking the level of signals P1, P2 leads to correct results if the threshold values are set comparatively short or narrow.

Processing device 235 , generating device 237 and signal checking device 236 can be digital circuits which are formed on different chips. The processing device 235 and the signal checking device 236 can preferably be identical chips, some of which work redundantly, but carry out the measures described above independently of one another.

Mode 2 (both switches closed) preferably lasts less than 1 ms, more preferably less than 500 µs.

The check described is preferably periodic initiated. The check of the first control signal S1 can for example once a second or more, preferably three times a second or more. The same goes for for checking the wiring and the actuator based on the test signals P1, P2.

One possibility is that as a pulse width modulated signal trained first control signal S1 to check is a pulse width modulated signal with a predetermined Duty cycle (ratio between on times and off times), including the total cycle time is predetermined. For example, a test control signal with a  Duty cycle of 33% can be set at which the on-time 18 µs and the off time is 36 µs. If these times are predetermined, the signal checking device are not told what values are to be expected. However, it can also be desirable to be flexible Generate test signals. The test control generated is preferably First signal S1 unbalanced, so it has a duty cycle of not equal to 50%. A device is also preferred to ensure that the polarity of the signal is correctly recognized. This ensures that not an incorrectly generated test signal with a complementary one Duty cycle (e.g. 67% instead of 33%) based on the Edge times are recognized as correct.

Provided on the one hand the verification of the wiring and the Actuator based on the signals P1, P2 and the other Checking the control signal S1 using the signal P3 are generally provided together, they can alternate. For example consecutively modes 0, 1, 2 and 3 as described above can be set and within these modes the respective Checks are made. Are here too Repetition frequencies greater than 1 Hz, preferably greater than 3 Hz desirable. If not all of the above Reviews can be considered necessary single or multiple modes or within these modes different test steps are omitted.

If an error is found in one of the modes, indicates this is due to a fault in the wiring, in the actuator or in the generation of the first control signal. Accordingly  appropriate countermeasures are to be initiated, for example output of an alarm signal or the like.

The sequence of the checking process can be controlled by a processor (not shown). Instead of the discrete structure of the circuitry shown in FIG. 2, an integrated structure as indicated by FIG. 1 can also be provided.

Claims (20)

1. Wiring for an actuator ( 100 ) of an electrically controllable brake booster that can be switched between two potentials ( 101 , 102 ) and has two connections ( 100 a, b)

• a first and a second line ( 103 , 104 ), which feed the two potentials to the connections,
• - An electronically actuated first switch ( 106 , 206 ) provided in the first line ( 104 ) between the first potential ( 102 ) and the first connection ( 100 b) of the actuator, and
• a control device ( 112 , 235-237 ) which switches the first switch with a first, preferably pulse-width-modulated control signal (S1),

characterized by an electronically actuatable second switch ( 105 , 205 ) provided in the second line ( 103 ) between the second potential ( 101 ) and the second terminal ( 100 a) of the actuator, the control device providing the second switch with a second control signal (S2 ) switches. 2. Circuit according to claim 1, characterized in that a first signal guide ( 109 ) to a signal monitoring device ( 236 ) is provided for the first control signal (S1). 3. Circuit according to claim 1 or 2, characterized in that between the first switch and the first connection and / or between the second switch and the second connection a second signal routing ( 107 , 108 , 221 , 222 , 224 , 225 ) to one Signal monitoring device ( 236 ) is provided. 4. Circuitry according to one of the preceding claims, characterized in that the control device generates a pulse-width-modulated first control signal and has a processing device ( 235 ) which generates a first output signal (S1 ') indicating the pulse duty factor of the pulse-width modulation, and a generating device ( 237 ) which receives the first output signal and outputs the first control signal (S1). 5. Circuit according to claim 2 or 3, characterized characterized in that the signal monitoring device one identical to the processing device and with of this data-exchanging electronic circuit. 6. Circuit according to one of the preceding claims, characterized characterized in that the processing device Test device for generating a suitable first Output signal (S1 ') and a suitable second Control signal (S2) to check the wiring and the actuator and / or the pulse width modulated has first control signal (S1).   7. Circuit according to one of the preceding claims, characterized in that the signal monitoring device has a first test device ( 401-406 ) for monitoring and / or assessing the level changes of the pulse-width-modulated first control signal. 8. Circuitry according to one of the preceding claims, characterized in that the signal monitoring device has a second test device ( 407 , 408 ) for monitoring and / or assessing the electrical values on the second signal feedback. 9. Circuit according to claim 7, characterized in that the first test device each has an edge detector ( 401 , 402 ) for rising and falling edges of a digital signal and a time measuring device ( 403 ). 10. Circuitry according to claim 9, characterized in that the first test device has a memory device ( 404 ) into which the times of the detected edges are written serially, and an evaluation device ( 405 ) which has at least three successive entries in the memory device ( 404 ) evaluates. 11. Procedure for checking the wiring of an between two potentials switchable, with two connections provided actuator of an electronically controlled Brake booster and the actuator itself, wherein the wiring has lines that the two Potentials of a first and a second Provide a reference point, a first switch between the first reference point and the first connection of the  Actuator, a second switch between the second Reference point and the second connection of the actuator and a control device that the first and the second switch with a preferably pulse width modulated first control signal and one second control signal switches, characterized by the step Checking at least one potential s on at least one Connect the actuator when both switches are open are. 12. The method according to claim 11, characterized by the further steps

• - keeping the first switch open and closing the second switch, and
• - Checking at least one potential at at least one connection of the actuator

13. The method according to claim 11 or 12, characterized by the further steps

• - Closing the second switch and briefly closing the first switch and
• - Checking at least one potential at at least one connection of the actuator while the first switch is closed.

14. The method according to claim 13, characterized in that the first switch less than 1 ms, preferably is kept closed for less than 500 µs.   15. The method according to any one of the preceding claims, characterized characterized in that the potentials at both connections of the actuator can be checked. 16. The method according to any one of the preceding claims, characterized characterized in that when checking a potential this is compared to a threshold. 17. Procedure for checking a pulse width modulated first control signal for one between two potentials switchable actuator with two connections an electronically controlled brake booster, where the wiring of the actuator lines having the two potentials of a first and provide a second reference point, a first switch between the first reference point and the first connection of the actuator, a second switch between the second reference point and the second connection of the Actuator and a control device that the first and second switches with the pulse width modulated first control signal and one second control signal switches, characterized by the Steps Keep the second switch open, initiate the generation of the pulse width modulated first Control signal with a certain duty cycle, and Check the temporal relationships between several Edge of the generated first control signal and output an error signal if there are no target conditions available.   18. The method according to claim 17, characterized in that the temporal relationships between at least three successive edges of the generated first Control signal to be checked. 19. The method according to claim 18, characterized in that the time intervals between successive Edges are determined and then checked whether they a setpoint or range corresponding to correspond to certain duty cycle. 20. The method according to any one of claims 17 to 19, characterized characterized that first the temporal relationships between edges of a first group of edges generated first control signal are checked and if there are no target ratios here temporal relationships between flanks at least one second group of edges of the generated first Control signal to be checked and then, if here too there are no target conditions, the error signal is issued.