DE19813964A1 - Ring bus system with a central unit and a number or control modules, in particular for motor vehicle passenger protection systems - Google Patents

Abstract

The control modules (M1..Mx) supplied from the input/output ports of the central unit (1) are connected in series to the bus conductors (L1,L2). Each module is provided with test units (4) which test ifr there is a short circuit on the output to the next control module. According to whether a fault is present or not switches (5a,5b) connect or disconnect the output to the next module.

Description

The invention relates to a according to the preamble of claim 1 Bus system in which a plurality of Control modules in a row in at least one supply line are arranged, in particular for occupant protection systems in force vehicles.

Bus systems for electrical energy supply, especially in Motor vehicles are known in the way that a line with a Voltage of z. B. +12 volts to numerous consumers (e.g. electrical motors, other devices), which are each single-pole on the line and are also connected to earth (negative pole of the power supply). If there is a low resistance leakage resistance or a short circuit of the 12 volt Line to ground, so all consumers are no longer operational, and there is a possibility that the vehicle battery is too large current drain discharges.

DE 35 20 904 C2 describes an electronic switching device for a circuit breaker of a network branch of a change to be switched voltage power network, in which the individual network branches in parallel are arranged with respect to each other with respect to the busbar. The electro African switching device checks the electrical resistance of the assigned network and switches the power only depending of them to or clamps the relevant network branch from the busbar from. It is for a bus system with one behind the other Control modules or consumers connected to them, for example occupants protective devices not applicable.

From US 5,063,471 a battery protection circuit is also to remove from a battery source when a short circuit occurs is separated from it in the load circuit. The disadvantage is ins  special, for this a short-circuit current must already flow. Is the amount the short-circuit current unexpectedly high, the battery or other important electronic assemblies are already disturbed by it. Burning of the measuring resistor may also be feared.

In addition, from the unpublished patent application DE 196 43 014 to take a bus system with a one-wire line, at of the central unit and / or the control modules a voltage have supply device, which by means of a test device checks each output section for a short circuit and via a switch device, the input Ver supply voltage to the output only when the Test did not result in a short circuit on the output side. You can According to this application, several supply lines are also provided be, however, these are a star structure with a corresponding number of inputs / outputs on the central unit. For 2-wire Cables in which the modules are in series between each other these are arranged, is obvious at first, also here for a line to provide the switching devices. However, occurs Short circuit on the other line, this can not on the short-circuited line section can be limited. In addition, the electrical circuit of the test device a certain operating voltage ahead, which is not on both lines. Checking both lines it is essential, however, if in particular data in Form of voltage pulses are to be transmitted.

The object of the invention is therefore the bus system of the beginning described type in such a way that it is suitable for a 2-wire Line is suitable.

This object is achieved through the characteristic features of the patent claim 1 solved. Advantageous further training and possible uses can be found in the subordinate claims.

First, a bus system with an appropriate two-wire line provided, between the control modules in series are ordered. At least one test device is provided, which the Checks outputs for an effective short circuit there. This can be done for everyone Output a separate test facility or for the outputs via Multiplex a test facility to be used together. For every  Line is provided a switching device with which the line between the input and output can be connected or disconnected. By doing this is provided for both lines, there can be in both lines occurring short circuit detected and the affected line section be electrically disconnected while the other line continues can be used for energy and data transmission. By the Voltage offset is achieved even against a short circuit Ground potential of the line, which is just a low voltage potential leads, can be recognized as defective and isolated.

By activating the subsequent line section, too depending on reaching one necessary for operation Supply voltage will be a gradual one and therefore by the Power consumption significantly gentler commissioning of the modules causes, since the power consumption drops significantly and is slower. This is crucial for bus systems, especially in motor vehicles, if the Supply voltage is initially provided by a battery. In addition, errors in signal detection due to too few Avoided supply voltage.

Such a bus system can be used particularly advantageously if Generation of the digital voltage signal with a signaling output stage three switching means is used according to claim 3. Through the three Switching means it becomes possible to switch the two voltage potentials on each to switch both lines and so both lines together as well as over the remaining undisturbed line alone, if the other line is disconnected due to a short circuit. Until then disconnected line section, the signaling can be undisturbed be continued. If a ring structure is provided, then also those from the previously considered direction after the short circuit Modules are supplied from the other direction.

The invention is described below using exemplary embodiments and Figures explained in more detail.

Brief description of the figures:

Fig. 1 ring bus system with short to ground in the lower line;

Fig. 2 bus system with a central unit with a switching means between the two lines and a short circuit to a third voltage potential ϕ3;

Fig. 3 embodiment of a test device with switch device.

Fig. 1 shows a first embodiment of a bus system, wherein the modules M via two lines L1, L2 of the supply line are connected to both ends in a ring structure with a central unit 1. The central unit 1 can switch to each of the I / O ports A, B, C, D one of the two voltage potentials ϕ1 and ϕ2 used for the voltage supply and signaling.

The modules are M1 via the two lines L1 and L2. . . Mx. . . connected to the central unit 1 , in which they are arranged in parallel between the two lines L1 and L2, one behind the other. The individual modules M1. . . Mx each receive the emerging potential difference between the first and second lines L1, L2. A high potential difference between L1 and L2 is regarded as a high voltage level, and a low potential difference, in particular the voltage zero, is regarded as a low voltage level. The assignment of a digital logical value (logical 0 or 1) is independent of this. A high voltage level can thus be used in particular as the idle state in order to supply the voltage to the individual modules M1. . . Mx. . . to ensure, even if no signals are transmitted.

In this exemplary embodiment, all modules M have a short-circuit test device 4 for each line L1, L2, which checks the output of the respective line for an effective short circuit, namely a resistance that is too low there. For each of the two lines L1, L2, a switch device ( 5 a = close, 5 b open) is provided between the input and output of a line in a module (Mx, Mx-1), which is conductive ( 5 a) or non-conductive can be ( 5 b) and is controlled by the respective test device 4 .

Thus, for example, if the central unit 1 first controls the voltage potential ϕ1 via the I / O port A to the line L1, then after passing through the previous (not shown) modules M1. . . Mx-2 reaches the Mx module. Initially, all switch devices 5 in Mx-1 and in all subsequent modules Mx were still open ( 5 b). However, the test device 4 did not detect a short circuit in the subsequent line section of the line L1 and therefore closed the switch device ( 5 a). The voltage potential ϕ1 will thus reach the module Mx on line L1 and also check there for a short circuit on the output side. Since no short circuit occurred in this case either, this switch device ( 5 ) was also closed.

If the central unit 1 receives the voltage potential ϕ1 connected to the line L1 in A at the I / O port C, it can recognize the line L1 as released. For safety reasons, the second voltage potential ϕ2 can be used for testing. Decisive for the detection of a short circuit by the test devices 4 is a potential difference between the voltage potential of the line section on the output side. Therefore, if the voltage potential released up to the module Mx coincides with the short-circuit potential, detection is not readily possible. This can be checked by testing with a different voltage potential. For this reason, it is also essential that both voltage potentials ϕ1, ϕ2 have a voltage offset compared to a ground potential ϕ0. In order to explain this clearly, a short circuit to the ground potential Mass0 is indicated in Fig. 1 between the modules Mx-1 and Mx. The short circuit to ground is generally particularly frequent, since the electrical ground is often routed to the uninsulated metallic housing, particularly in motor vehicles. Even slight insulation faults in the line section can therefore cause such a short circuit. If the second line L2 were now operated with the same voltage potential, that is to say the ground potential ϕ0, a short-circuit test would not be easily possible. However, since the line L2 is preferably operated with the voltage potential ,2, which has a voltage offset of, for example, 2 volts compared to the ground potential die0, the test device 4 detects in Mx-1 the short circuit at the output, for example via a potential difference adjusting test current. The switch device 5 is therefore kept open ( 5 b).

The following modules Mx. . . therefore no longer receive the voltage potential ϕ1 from the I / O port B. Consequently, the switch devices 5 of these modules initially remain open. Signaling is nevertheless possible by applying the respective voltage potential only to I / O port A, for example ϕ1 for "High" and ϕ2 for "Low" if ϕ1 <ϕ2. The potential reference takes place via the ground connection of the modules to the ground potential ϕ0.

In addition, 1, the advantage of two longitudinal switch 5 by the I / O is based on Fig. Per module M clear in a ring structure, as so, the central unit 1 can also continue the conventional signaling as a potential difference of φ1 and φ2 via the lines L1 and L2 - Send ports in parallel, in the event of a short circuit in line L2, I / O ports B and D of central unit 1 . A ground short in line L1 compared to ϕ1 would also be recognized by the test devices 4 of the adjacent modules Mx-1, Mx in the manner described above.

First, the case will be discussed of a short circuit to another third voltage potential φ3 with reference to FIG. 2. This form of a short circuit can occur in a poorly insulated line, for example to the operating voltage potential of a battery electrical system in motor vehicles.

If the potential difference between the first and third voltage potentials is too weak for the detection by the test devices 4 , they can also test against the separate ground connection of the modules M for the ground potential ϕ0.

In addition, both voltage potentials ϕ1 and ϕ2 on line L1 such a short circuit to a third voltage potential ϕ3 can be recognized, since generally at least one of these voltage potentials ϕ1 or ϕ2 the potential difference to ϕ3 for the Short circuit detection is sufficient.

For this reason, it proves to be particularly advantageous if a signaling output stage is used in the central unit 1 , which has three switching means S1, S2 and S3, each between the first voltage potential ϕ1, the line L1, the line L2 and the second voltage potential ϕ2 are arranged. The switching means S1 to S3 are outlined in FIG. 2 as switches, but in reality, of course, in the form of transistor switches known per se. This makes it particularly easy to test both lines for all possible short circuits and to continue signaling even in the event of a line (L1) short circuit (to ϕ3) via the intact line (L1), since both lines can assume both voltage potentials. Thus, with the switching means S2 closed, opening S1 and closing S3 ϕ2 can be applied to line L2, ϕ1 by closing S1 and opening S3. This is particularly advantageous when the supply line is only an open branch line and no signaling can take place via the other section of the bus system as in the ring according to FIG. 1. The lines L1 and L2 are floating and floating when the switching devices S1, S2, S3 are open in the normal operating state.

A short circuit can thus always be limited to a line section between two modules (Mx, Mx-1) and the signaling can be continued by means of the switch devices 5 , the so-called longitudinal switches, with short-circuit test device 4 .

So the consumers Vx connected to the Mx modules can continue supplied with a voltage and the control of these are continued. This is of particular importance if such a bus system for an occupant protection system of motor vehicles is used because in this If at least some of the modules M as consumer V are safety-relevant Have occupant protection devices, for example airbags, belt tensioners, etc. These must also with a simple defect of the supply and Data line can continue to be operated. Especially in the case of accidents the risk of injury or destruction of the cables is particularly high. Through the 2-wire supply line with the two series switches per module it becomes possible with only one completely intact line Maintain energy and data transmission and a duration avoid stress on the power supply via the short circuit, which would make signaling mostly impossible or at least the limited energy reserves, especially of a car battery, are strong charged.

Fig. 3 now a possible embodiment shows such a testing device 4 with switch means 5.

The test device 4 has a connection 2 directed to the central unit 1 , which is supplied with a DC voltage of, for example, +12 or +20 volts (voltage potential ϕ1) when the preceding modules have enabled the relaying through the series switches.

The test device 4 is designed such that after the voltage potential ϕ1 has been switched on, the test device 4 initially assumes a stable state and does not directly switch the voltage of 12 volts through to the output 3 , but first checks whether the output 3 has such a low terminating resistance compared to the voltage potential ϕ1 or ground that this is regarded as a short circuit. In the presence of such a condition interpreted as a short circuit, the voltage of, for example, 12 volts from terminal 2 is not switched through to terminal 3 . This prevents too much power from being unnecessarily drawn from the vehicle battery. In addition, possible dangers from overheating can be avoided.

In the example, test device 4 has a capacitor 23 connected between terminal 2 and ground potential ϕ0, which in the example has a value of 47.0 μF. Connected to terminal 2 is the non-inverting terminal of a comparator 25 , at the inverting input of which a voltage of +8 volts is present. The output signal of the comparator 25 therefore assumes a high value when the voltage at terminal 2 exceeds a value of +8 volts. The output of the comparator 25 is connected to a control input of a current source 27 . This is symbolized by an arrow symbol inserted between two parabolic lines. The current input of the current source 27 is connected to the connection 2 , the current output of the current source 27 is connected to the connection 3 . The inverting input of a further comparator 29 is also connected to the terminal 3 , the non-inverting input of which is connected to a positive voltage of +4 volts. The output of the further comparator 29 is connected to the control input of the electrically controlled switch device, the series switch 5 , which is connected on the one hand to the connection 2 and on the other hand to the connection 3 and, depending on the value of the voltage supplied to the control input, the connection between produces or separates the two connections mentioned, insofar as there is a current flow from connection 2 to connection 3 .

In the example, the switch device 5 is realized by a low-resistance semi-conductor switch, specifically a transistor, in the example a field effect transistor (FET) 32 , in the example of FIG. 3 by a p-channel FET. The gate connection G of the FET 32 is, as mentioned, connected to the output of the comparator 29 , the source connection S is connected to the positive connection of the capacitor 23 and thus to the connection 2 , the drain connection D is connected to the Connection 3 connected. In the FET 32 , as is generally customary, a diode 33 is integrated as a protective diode which, when the FET 32 is blocked, enables a current to flow from the terminal D to the terminal S.

The mode of action is as follows:
After switching on the voltage potential, for example .phi.1 (12 volts), the capacitor 23 is charged with a certain time constant. The switch device 5 is blocked for the current flow from the capacitor 23 to the output 3 .

As soon as the voltage across the capacitor 23 exceeds the value of 8 volts, the current source 27 is switched on via the comparator 25 . This feeds a constant current, which in the example has a value of 30 mA, into the lines connected to connection 3 . If the connection 3 is not terminated with a too low resistance to ground, ie if there is no short circuit, the voltage at the output 3 reaches a value of +4 volts after a certain time. As a result, the voltage at the gate G of the FET 32 changes from a positive value to a negative value, and the FET 32 is thereby turned on and thus a current flow from the capacitor 23 to the output 3 is possible. On the other hand, if output 3 were short-circuited, the mentioned voltage of 4 volts would not be reached and the FET 32 would not be turned on. The comparators form threshold devices, and the comparator 29 forms, together with the current source 27, a device for checking the output 3 for a short circuit present there. The current of the current source is significantly smaller than the current that would flow when switching the switching device 5 in the event of a short to terminal 3 .

Instead of a p-channel FET for the switch device 5 , an n-channel FET could also be provided, in which case only its connections S and D and the gate control voltage would be interchanged with respect to FIG. 3. The diode present in the n-channel FET to protect the FET is polarized with respect to the current to be supplied to the terminal 3 in the same way as in FIG. 3.

In order to test all connections of a module Mx, this test device 4 must be switched over either by means of a multiplexer. On the other hand, it is advantageous to provide such a test device 4 for each connection of a module, despite the higher component expenditure. In the case of ring structures, it must also be noted that the voltage potential can be propagated in two directions and consequently a bidirectional test device 4 can also be provided, as can be seen, for example, from the unpublished patent application DE 196 43 014. Preferably, only one common capacitor 23 is used for all test devices 4 of a module Mx, as a result of which space is saved for relatively large components and it can be made larger for energy storage.

Claims (4)

1. Bus system, in particular for occupant protection systems in motor vehicles, in which a plurality of control modules are arranged in series in a row in a ring and / or linearly in at least one supply line with a central unit, characterized in that

• a) the supply line (s) is (are) and
• b) each control module has an input and an output for each of the two lines (L1, L2),
• c) that at least one test device ( 4 ) is provided, which is designed to test an output for a short circuit effective at this output, namely a resistance that is too low effective there,
• d) for each of the two lines (L1, L2) a switch device ( 5 a, 5 b) is provided between the input and output of a line and
• e) the switch devices ( 5 a, 5 b) only connect a connection ( 5 a) between the input and output of each of the two lines (L1, L2) when a test is carried out at the respective output using the test device ( 4 ) was carried out and this resulted in the absence of a short circuit, whereby
• f) on the input side, both lines have the same or different voltage potential / e (ϕ1, ϕ2), which, however, has or have a voltage offset that is sufficient for short-circuit testing with respect to the ground potential (ϕ0).

2. Bus system according to claim 1, characterized in that the switch devices ( 5 a, 5 b) only then switched through at least one of the outputs to the respective input of the lines (L1, L2) when a voltage supply device ( 23 ) is one for the operation of the Control module (M) and preferably has sufficient voltage for the operation of a consumer (V) connected to it. 3. Use of a bus system according to one of the preceding claims for

• a) bus systems with a signaling output stage ( 1 ) for generating digital high and low voltage level signals, the signaling output stage,
• b) a first switching means (S1) between a first voltage potential (ϕ1) and the first line (L1),
• c) a second switching means (S2) between the first (L1) and the second line (L2)
• d) and a third switching means (S3) between a second lower than the first voltage potential (ϕ2) and the second line (L2) are provided, and
• e) depending on a short circuit on one of the lines, the signaling as a potential difference between the two lines or as a potential difference of the one, not short-circuited line to a fixed third voltage potential, in particular the ground potential.

4. Use of a control module according to one of the preceding Claims for a bus system of an occupant protection system, in particular in motor vehicles, in which the control modules via the bus system able to communicate with each other and with a central unit are connected and in the at least part of the control modules Occupant protection devices are assigned by the tax modules are triggered upon a trigger command.