DE10246107B4 - Method and circuit arrangement for fault monitoring of at least one electrical load - Google Patents

Abstract

A method in which the DC voltage at the load is measured by means of a measuring resistor in at least one voltage measurement high and / or low impedance and b) the DC voltage at the load additionally in at least one voltage measurement medium impedance by means of a in one area is measured between high and low resistance compared to the consumer measuring resistor, characterized in that the variable measuring resistor is formed by a controllable switch in series hinzuschaltbaren high-resistance and per consumer a medium-resistance in comparison to the consumer, the measurement with a measuring resistor repeated several times in succession and the measuring resistance value is changed in at least one subsequent measurement.

Description

The invention relates to a method and a circuit arrangement for fault monitoring of electrical consumers in a motor vehicle.

Such methods and circuit arrangements are used, for example, in vehicle technology in order to be able to detect faulty electrical consumers.

The errors that occur in a vehicle electrical system of a motor vehicle are usually short circuits or a line interruption in a consumer or in a load including their connections.

For example, in the EP 0 581 993 B1 proposed a circuit arrangement which allows the monitoring and detecting a line break. In this case, a measuring resistor is arranged in series with a consumer whose resistance value is adjusted in dependence on the load current in the amount so that the power loss is kept low. If the voltage drop caused by the load current falls below a certain threshold value via the measuring resistor, a diagnostic signal is generated by means of a diagnostic device. In the DE 2227964 is proposed as a diagnostic device a monostable multivibrator with a corresponding threshold voltage to detect a line break.

Furthermore, from the generic DE 4112996 A1 a device and a method for monitoring the function of an electrical load is known, in which or in which an actual power consumption of a consumer is compared with an expected power consumption, so that the faults short circuit and line interruption are distinguishable.

In practice, however, often occur on errors that are difficult or impossible to detect by these known methods and circuitry. For example, consumers may experience increased or decreased internal resistances due to a fault without the need for a short circuit or open circuit.

Thus, individual windings of an engine (ventilation, actuator for a variety of vehicle functions, etc.), individual tracks of a window heating, etc. may be shorted, and in this way undesirably reduce the internal resistance of the (thus already defective) consumer and increase the power consumption accordingly.

Likewise, for example, the internal resistance of a consumer including its supply, for example, be increased by corrosion undesirable, so that the operability of the consumer is impaired.

In addition, especially in multiple voltage on-board networks, for example, in a combined 42 volt / 12 volt electrical system, faulty loads can lead to overvoltages or short circuits between the two networks, which do not pose to the outside either as a short circuit or a line break.

The DE 2227964 A describes an error monitoring circuit that checks the functionality of a lamp. Between the positive pole of the battery and the lamp, a high-impedance resistor is arranged. Between this resistor and the lamp the potential is measured. Since the second terminal of the lamp is connected directly to the negative pole of the battery and the resistance of the lamp is much lower than the high-resistance, the potential at the measuring point is at the potential of the negative pole. Parallel to the high-impedance resistor, a medium-resistance resistor is arranged, which can be switched on or off by a switch. When the switch is closed, the medium resistance with the lamp forms a voltage divider. Should the lamp be inoperative, the potential of the positive pole would be present at the measuring point. A functional lamp has a potential that is substantially equal to the ratio between the medium resistance and the resistance of the lamp.

The DE 3439875 C2 describes a circuit arrangement for the remote supply of electrical consumers by means of alternating voltage parallel supply, which allows a low power reserve.

The present invention has for its object to provide a method and a circuit arrangement, which also allow the monitoring of other errors than short circuit or line interruption, as described above.

This object is achieved by a method having the features of claim 1, and by a circuit arrangement with the features of claim 5.

By measuring with a medium impedance in comparison to the internal resistance measuring resistor in addition to a measurement with a high and / or low impedance measuring resistor changes in the internal resistance of a consumer can be monitored and detected in a simple manner.

In this case, the respective measurement can take place both in the case of a consumer activated by a user and in the case of a consumer that is not activated.

In particular, in the case of a circuit arrangement with a measuring resistor connected in series with the load, it becomes clear that, according to the invention, even smaller changes in the resistance value of a load can be detected.

In a circuit arrangement for carrying out the method according to the invention, a voltage divider is formed for example by the measuring resistor and the consumer and the voltage drop across the measuring resistor or the potential at the center tap by means of a measuring device, such as an A / D converter o. Ä., Measured.

In the case of a measurement with a high-impedance measuring resistor, for example a resistance value in the kQ range, the center tap is in the region of a potential X (low potential for a high-side circuit or high potential for a lowside circuit), since the voltage drop across the measuring resistor is essential , for example by a factor of 100 to 1000, is greater than at the consumer. Consequently, with a high-impedance measuring resistor only a short circuit of the consumer (against the respective other potential) can be reliably detected.

On the other hand, if a medium-impedance (ie for example a smaller measuring resistor 10 times larger by a factor of 10) is measured with respect to the consumer, the center tap is at a potential between low and high potential and is very much affected by a change in the voltage drop across the load dependent. Accordingly, due to a direct proportionality can be concluded in a simple manner on a voltage change causing change in the (internal) resistance of the consumer.

On the other hand, if a medium-impedance (ie for example a smaller measuring resistor 10 times larger by a factor of 10) is measured with respect to the consumer, the center tap is at a potential between low and high potential and is very much affected by a change in the voltage drop across the load dependent. Accordingly, due to a direct proportionality can be concluded in a simple manner on a voltage change causing change in the (internal) resistance of the consumer.

According to the invention, a measurement with a measuring resistor is repeated several times in succession, so that a possible scattering of the measurement results can be averaged and measurement errors can be avoided.

Here, the measurement resistance value is changed in at least one of the successive measurements, for example, from high or low impedance to medium impedance, so that other errors can be monitored and detected.

These sequential measurements or measurement sequences can be performed permanently or intermittently in a further embodiment of the invention, wherein advantageously the power consumption can be minimized by appropriate choice of the interval and pause times, taking into account a sufficient for the necessary availability of the consumer sampling rate.

In an advantageous embodiment of the invention, the measuring resistor is designed as a variable measuring resistor. In this case, it comprises a resistance which is medium-impedance in comparison to a respective consumer and has a high-impedance resistor which can be connected in series via a controllable switch. This series circuit is connected in total parallel to a controllable switch for the consumer. The controllable switches are in this case, for example, designed as a relay or MOSFET transistor and have a very low in the mΩ range "switch resistance" on.

By means of such a circuit, all three types of measurement (low, medium and high impedance) can be realized in a simple manner, advantageously an already existing controllable switch, namely the existing, for example in the form of a control unit switch for closing and opening the load circuit when required (as an input signal on the control unit) by an operator-operated switch or button in the vehicle interior for realizing at least one measurement can be used.

Further advantageous embodiment of the invention will become apparent from the dependent claims.

The invention will be explained in more detail with reference to embodiments illustrated in the drawings.

In the drawing show:

1 a circuit diagram of a first embodiment of a circuit arrangement according to the invention and

2 a circuit diagram of a second embodiment of a circuit arrangement according to the invention.

1 shows a part of a schematically illustrated vehicle electrical system of a motor vehicle. This necessary for carrying out the method according to the invention partial or detail of a vehicle electrical system includes a voltage source, such as a 36 volt battery to power the 42 volt electrical system and multiple electrical loads or loads 3 to 11 , whose respective circuit via controllable switches 19 to 27 , for example in the form of relays or MOSFET transistors, can be closed and opened.

These controllable switches are usually in addition to other components part of a motor vehicle usually multiple existing control unit 29 , According to the invention is at the respective center tap 3a to 11a between switches 19 to 27 and loads 3 to 11 each one to the load medium impedance measuring resistor 31 to 39 connected, which by means of a controllable switch 45 either in series with a high-impedance resistor 41 or via supply line directly to the respective switches 19 to 27 can be switched in parallel.

Furthermore, this will be at the respective medium potential 3a to 11a applied potential via a measuring device 47 , For example, in the form of an A / D converter, a measuring bridge, etc., measured or monitored permanently or intermittently. These other components, namely measuring resistors 31 to 41 , Supply line 43 , controllable switch 45 as well as measuring equipment 47 can - as shown - also part of the control unit 29 be or be structurally separate from it.

How out 1 can be seen, there is the respective switch 19 to 27 for the loads 3 to 11 between the positive pole of the battery and the load, so that the respective second terminal of the load 3 to 11 with the mass of the vehicle and therefore connected to the negative terminal of the battery. in this type of circuit according to the first embodiment, consequently, the connection of the loads 3 to 11 by means of switch 19 to 29 switched, which is at high potential, here, for example, plus 36 volts. Such a circuit is usually referred to as highside circuit accordingly.

In the 1 shown loads 3 to 11 describe by way of example those in such a network, apart from the normal case according to load 3 , possibly occurring different errors in loads 5 to 11 ,

This is how Last shows 3 a normal case of a functional load with an exemplary internal resistance of 30. With load 5 On the other hand, an error case of an increased internal resistance, for example 300, which can be caused by corrosion of leads or terminals of a load or by corrosion of contacts, bad conduction in windings of motors, poor conduction or interruption of at least one path of a rear window heater and the like. Based on the example of the load 7 on the other hand, the case of a reduced internal resistance, for example, due to the conclusion of individual windings, connections of individual or multiple tracks of a heated rear window or the like, without a complete short circuit in the 0 Ω or mΩ range is present.

Based on the load 9 a peculiarity of a fault is presented, which can occur in a dual voltage on-board network, such as a combined 42 volt / 12 volt electrical system. Here are the 42 volt load 9 and a 12 volt load 17 which has a 12 volt battery 13 supplied, a common ground point, which due to corrosion (in the form of a resistor 15 represented by, for example, 300) is no longer grounded but at an increased potential. Accordingly, in this case, both the load 9 , as well as the load 17 no longer supplied with the desired voltage.

Based on the load 11 is a second error, which can occur in a dual-voltage on-board network, shown, namely a short circuit to the 12 volt electrical system or its voltage source in the form of a 12 volt battery 13 , so that adjusts itself to this consumer, a mixed voltage, such as between 20 and 28 volts, in particular 23 volts. All illustrated error cases consequently relate to situations in which the voltage due to a total short circuit or a line break does not change in the two extremes, namely high potential (in the embodiment 36 volts) or low potential (in the embodiment 0 volts), but changes in the voltage at the load 3 to 11 , which fail to a lesser extent and lead to malfunction, these changes are difficult or impossible to detect with conventional methods or circuitry.

The following describes how the errors shown can be monitored and detected by means of this circuit arrangement. Each of the illustrated loads 3 to 11 can through an interaction of controllable load switch 19 to 27 and the parallel-connected measuring resistors 31 to 39 with or without additional measuring resistor 41 be subjected to a low-impedance, high-impedance or medium-impedance measurement.

For a low-impedance measurement, the respective load switch 19 to 27 (For example, a processor-controlled control of the gate of a MOSFET or the control line of a relay) is closed, resulting, for example, in a MOSFET transistor, a switching resistance occurs at best in the mΩ range. The parallel circuit of a medium-impedance resistor 31 to 39 via supply line 43 with appropriate switch position of the controllable switch 45 influenced due to the parallel connection of this branch to the very low resistance or zero resistance, such as relay contact the total resistance only slightly, so that it would also be conceivable to leave the controllable switch in its other position for a low-impedance measurement, in which the high-impedance resistance 41 , For example, 3 kΩ is switched on.

In the case of such a low-impedance measurement, no or only a very low voltage drops in the 0 or mO range in such a way on the low-resistance measuring resistor formed in this way, so that the center tap 3a to 11a the respective consumer 3 to 11 at high potential, such as 36 volts and at the consumer 3 to 11 the entire voltage drops to ground. This potential at the tap changes with the errors shown 5 (eg by 30 mV) and 7 (eg by 300 mV), which can occur both in a single-voltage network and in a multiple-voltage network, not or only insignificantly, so that these errors do not or not over such a measurement are reliably detectable.

For the errors described above 9 and 11 , which can occur in a double voltage network or multiple voltage network, cause these errors in the case (apart from open switches 19 to 27 ) to a similar small change in the mV range, so that such errors would not be reliably detected via such a low-impedance measurement.

For a high-impedance measurement, the switches are located 19 to 27 in contrast, in its open position, the controllable switch 45 in its position in which the branch with the high-impedance measuring resistor 41 is connected, so that the measuring resistor of the high-impedance and the series-connected low-impedance measuring resistor 31 to 39 is active.

Correspondingly, a voltage which is higher by a factor of 3040: 3 drops at this high-impedance measuring resistor of, for example, 3040 Ω than at a functional load, with an internal resistance of 30. At the center tap 3a to 11a Accordingly, the low potential of approximately or equal to 0 volts or a few mV is applied to the circuit to be recorded in each case as a load divider consisting of load and measuring resistor.

Accordingly, by this measurement, a change in the normal internal resistance of a consumer 3 to 11 up to 0 Ω, ie a complete short-circuit can not be detected, since the voltage drop across the measuring resistor is thereby influenced at most in the mV range. Accordingly, only such a change in a very high-impedance region, such as line interruption detectable by such a measurement, since only this is a significant change in the potential at the center tap 3 to 11a entails.

In the case of the medium-impedance measurement according to the invention, by contrast, when the load switch is open 19 to 27 the measuring resistor in each case from one of the medium-impedance measuring resistors 31 to 39 formed, which via supply line 43 over the switch 45 in the appropriate position with the other terminal of the opened switch 19 to 27 and corresponding high potential of the battery 1 connected is. Now falls in such a medium-impedance measuring resistor from a voltage which is not 100 or even 1000 times higher or lower than the voltage drop across a functioning load 3 to 11 is but in the range of a factor 10 until, for example, 30 is smaller or larger than the normal internal resistance of the corresponding load.

Advantageously, as shown, the medium-impedance measuring resistor is larger, that is, for example 40O, than an error-free load of 3 Ω, so that the power consumption during this measurement is low compared to a user-activated normal power consumption, ie, for example, by a factor of 40: 3 lower remains.

Despite this factor of about 10 can now be at the center tap 3a to 11a also a lower voltage change at the loads 3 to 11 , which is caused due to errors detected, since this is not insignificant, but essential, namely, for example, only by the factor 10 reduced, on the measuring resistor affects, Accordingly, the reduced by means of the measuring device 47 measurable potential at the crossover 3a to 11a , so that for each line branch with one or more consumers such errors can be monitored and detected.

As with the circuit according to 1 not only a medium-impedance but also a low-impedance and high-impedance measurement can be carried out, with this circuit advantageously measurement series can be carried out in which measurements can also be taken with different measuring resistances.

So it is conceivable, for example, in the case of an operator-operated switch, the signal via the control unit activates the corresponding load switch and turns on the corresponding load, this load several times, for example, nine times low impedance and only a few times, for example, once to measure medium impedance or to testing. This is advantageously necessary for a low-impedance measurement closed load switch 19 to 27 already closed due to operator activity, leaving only the switch 45 in the appropriate position, ie position to close the supply line 43 , must be brought or in its position at measuring resistance 41 remains because because of the parallel connection, as explained above, this has only an insignificant effect on the low-impedance measuring resistor.

For measuring with a medium-impedance measuring resistor, however, the corresponding load switch must be at least temporarily switched on even if the load is switched on by an operator 19 to 27 be opened and in this time the above-described medium-impedance measurement (with switch 45 in position for supply 43 and consequently effective medium-impedance measuring resistor 31 to 39 ) be performed. As soon as possible after completion of the medium-impedance measurement, the corresponding load switch must 27 again in its closed position, so as not to affect the operability of the load switched on by an operator noticeably (as in the case of motors, lamps and heating elements, for example).

In the off state, ie in a device not switched on by an operator, the respective load switch is located 19 to 27 in contrast, in the open position, so that in this case can be measured in a simple manner high impedance and medium impedance, since this does not or only imperceptibly affects the (non-active) consumer. So it is possible to measure the consumer several times, for example, nine times high impedance and also several times or even once medium impedance.

This in 2 illustrated second embodiment differs from the first embodiment by the position of the load switch 19 to 27 which, in contrast to the first embodiment now on the low potential side, ie ground or 0 volts, so that the other terminal of the loads 3 ' to 11 ' instead of on ground now at high potential, so for example plus 36 volts of the battery 1' are located. Such a circuit, which does not differ except for the reversal of the potentials of the first embodiment, is commonly called lowside circuit or controller with lowside switches.

Because of the reversal of the potentials, what has been said above for the first embodiment with regard to the low-resistance and high-resistance measurement applies, however, taking into account the reversal of the potentials - ie high potential and low potential or respectively 36 volts and 0 volts.

Even in the case of the medium-impedance measurement, the only difference to the first embodiment is that the voltage excursion occurs correspondingly in the direction of the other potential, but in the same order of magnitude with a corresponding error, as in the first embodiment. The mistakes 9 ' and 11 ' (However, due to the lowside circuit in another representation) concern as well as in the first embodiment on the basis of the loads 9 and 11 described, the corresponding possibly occurring in a double or multiple voltage network, namely short circuit to the other voltage network (short circuit before the load or after the load), each with a mixed voltage at the center taps 3a ' to 11a ' will adjust.

As explained above, turns on the tap 3a to 11a respectively. 3a ' to 11a ' in a medium-ohmic measurement, a voltage between supply voltage and ground, which is strongly influenced by the internal resistance of the load 3 to 11 respectively. 3 ' to 11 ' is determined, so that this load can be monitored very well in this state.

In a particularly advantageous embodiment of the invention, in a medium-impedance measurement in a high-side circuit, or the controller with high-side switches, the medium-impedance measuring resistor can be selected so that at the load 3 to 11 Sets a voltage and a current below corresponding limits, which even allows a deletion of arcing that may have occurred.

In a 42 volt electrical system with a 36 volt battery 1 As shown in the exemplary embodiment, the medium-impedance measuring resistor or its resistance value could be selected such that, for example, a voltage of just over 15 volts or a current of less than about 500 mA sets. A possibly connected to the load electronics can remain at this voltage with a corresponding design advantageously still functional. For example, for a 42 V / 12 V vehicle electrical system, the medium-impedance resistor would have to be about twice as large as the load resistor. In this case, the measuring resistor may advantageously also be an already existing heating resistor.

Of course, the errors detectable according to the above statements can be buffered or stored for a longer time, subjected to an evaluation and read as data during a repair or maintenance, in order to be able to evaluate the functionality of consumers or lines with consumers with regard to errors that have occurred.

For example, it is conceivable that arcing occurred, which are torn off or deleted at a corresponding medium-impedance measurement and are therefore eliminated as errors, the resulting voltage increase as an event "arc, which was deleted" (or only the corresponding values) stored in a memory in order to be able to be read out at a later time. In the event of an increase in the occurrence of errors, which however are only of a temporary nature, it is possible to prematurely react to a permanent occurrence of the errors during maintenance or repair and to replace the corresponding consumer or even the entire wiring harness.

Claims (6)

A method in which the DC voltage at the load is measured by means of a measuring resistor in at least one voltage measurement high and / or low impedance and b) the DC voltage at the load additionally in at least one voltage measurement medium impedance by means of a in one area is measured between high and low resistance compared to the consumer measuring resistor, characterized in that the variable measuring resistor is formed by a controllable switch in series hinzuschaltbaren high-resistance and per consumer a medium-resistance in comparison to the consumer, the measurement with a measuring resistor repeated several times in succession and the measuring resistance value is changed in at least one subsequent measurement. A method according to claim 1, characterized in that the measurements are made permanently or intermittently. Method according to one of the preceding claims, characterized in that the measurements are performed with an activated consumer several times with a low-impedance measuring resistor and at least once with a medium-impedance measuring resistor. A method according to claim 1 or 2, characterized in that the measurements are performed in a non-activated consumer several times with a high-impedance measuring resistor and at least once with a medium-impedance measuring resistor. Circuit arrangement in a motor vehicle, a) with at least one electrical load and b) arranged in series with the consumer variable measuring resistor, c) and a measuring device for DC voltage measurement of the voltage drop across the consumer, d) wherein the measuring resistor both a high and a low impedance value and in addition can assume a lying between these two values of medium value, characterized in that e) the variable measuring resistor comprises a controllable switch in series hinzuschaltbaren high-resistance and per consumer a medium-resistance in comparison to the consumer resistance and f) the switching arrangement is arranged to perform a method according to any one of the preceding claims. Circuit arrangement according to claim 5, characterized in that the medium value in the range of a 10 times the internal resistance value of the consumer, the low value in the range of a 0 times the internal resistance value of the consumer and the high value in the range of a 100-fold to 1000-fold the internal resistance value of the consumer is.

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