JP2009175092A - Disconnection detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a disconnection detector which can perform discrimination with a status of expressing off in a signal or a disconnection of a signal line, when the signal line is disconnected from a signal generator outputting one status on or off to a control part processing this signal. <P>SOLUTION: The detector comprises a switch which carries out outputting by switching on-status and off-status selectively, the switch which is connected on one edge, a signal line which is connected to a signal input circuit inputting the status of the signal line on the other edge, a pulse signal output circuit which outputs a pulse signal with a predetermined timing into the signal line, an impedance adjusting circuit which is connected with parallel to the switch near the switch, and a disconnection determination circuit which determines the disconnection of the signal line, when a reflected wave of the pulse signal is input into the signal input circuit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a disconnection detection device, and in particular, a signal line from a signal generation source that outputs an on / off state to a control unit such as an ECU (Electronic Control Unit) that processes this signal. The present invention relates to a disconnection detection device capable of discriminating between a state in which a signal indicates OFF and a disconnection of a signal line when the signal is disconnected.

  In recent years, for example, in an engine control device of a vehicle, it is necessary to input an electric signal from a sensor that detects an operating state of the engine to the engine control device. In such an engine, a wire harness (signal line) is used between the sensor and the control device, and electric signals are input and output.

  By the way, in a control device that transmits and receives an electrical signal using such a wire harness, if the input electrical signal is 0 (off state), it is due to the output of the sensor or due to the disconnection of the signal line. If it is not judged correctly, the engine will be controlled in the wrong direction. Therefore, in an electronic control engine, it is very important to determine when a signal line to the control device is broken. Conventionally, a signal line break detection device has been devised.

  For example, an abnormality detection method and circuit for a forward / reverse sensor for detecting an abnormality such as a decrease in the level of an output waveform of a sensor that detects forward / reverse rotation of a rotating body, and disconnection or short-circuit in the sensor have been devised (Patent Document) 1).

  In addition, when a signal line from a pulse signal generation source, for example, a speed sensor that generates a pulse signal corresponding to the speed of the vehicle to a control unit that processes the pulse signal is disconnected, a state in which the pulse signal indicates 0 and a signal line A disconnection detection device has been devised that can be discriminated from the disconnection (see Patent Document 2).

Japanese Patent Laid-Open No. 10-267951 Japanese Patent Laid-Open No. 07-141583

  In the configuration of Patent Document 1, the object of the invention is limited to the forward / reverse sensor, and the application to other sensors is not disclosed.

  In the configuration of Patent Document 2, when a signal line from a “pulse signal generation source” to a control unit that processes this pulse signal, such as a speed sensor that generates a pulse signal corresponding to the speed of the vehicle, is disconnected, There is a problem that it is only possible to discriminate between a state in which the signal represents 0 and a disconnection of the signal line, and it cannot be applied to a signal generation source that outputs either an on / off state.

  For example, there are many on / off switches that are switched to an on / off state in a vehicle, but when a signal line connected to the on / off switch is disconnected, the user “does not move even if operated”. It is often found for the first time after a complaint such as This is because it is difficult to determine the OFF state (OPEN state of the switch) and the disconnection state of the signal line.

  Conventionally, a specialist engineer at a dealer or factory uses a tool to check the continuity of a signal line for user complaints. In this case, in order to check whether or not the signal line is broken while estimating from information (vehicle phenomenon) heard from the user, the signal line that is not broken is used to find the broken signal line. It was also necessary to check the continuity. In order to infer from the phenomenon, it took a considerable amount of time and effort to determine whether the cause was a signal line.

  In addition, since the user knows that the disconnection has occurred as a phenomenon, the user may experience some inconvenience.

  With the above problem as a background, the problem of the present invention is that a signal is turned off when a signal line from a signal generation source that outputs either on / off state to a control unit that processes this signal is disconnected. It is an object of the present invention to provide a disconnection detection device capable of discriminating between a signal line disconnection and a signal line disconnection.

Means for Solving the Problems and Effects of the Invention

  A disconnection detection apparatus for solving the above-described problem is provided with a switch that selectively switches on and output between an on state and an off state, and a signal input circuit that has a switch connected to one end and inputs the state of the signal line to the other end. A connected signal line, a pulse signal output circuit that outputs a pulse signal to the signal line at a predetermined timing, an impedance adjustment circuit connected in parallel to the switch, and a signal input circuit in the vicinity of the switch And a disconnection determination circuit that determines that the signal line is disconnected when a reflected wave of the pulse signal is input.

  It is well known that transmission signal reflection occurs at a connection point between two signal lines having different impedances. With the above configuration, when a break occurs in the signal line between the connection point of the impedance adjustment circuit (that is, the switch) on the signal line and the signal input circuit, the break can be detected. Even when a signal generation source that outputs one of the on / off states is connected, it is possible to determine the switch off state and the signal line disconnection state. It is possible to identify the signal line.

  In addition, the circuit impedance of the impedance adjustment circuit in the disconnection detection device of the present invention is configured to be determined such that no reflection of the pulse signal occurs when the signal line is not disconnected.

  With the above configuration, when the signal line is not disconnected, no reflection of the pulse signal occurs, so that erroneous determination can be prevented.

  In addition, the impedance matching circuit in the disconnection detection device of the present invention includes a resistance element.

  Usually, a resistor is mainly used for impedance matching because of easy matching. With the above configuration, the disconnection determination device of the present invention can be configured with a low cost and simple configuration.

  Further, the signal input circuit in the disconnection detecting device of the present invention is configured to input the state of the signal line based on the timing at which the pulse signal is output.

  As a method for detecting a signal input, sampling for detecting a signal input at a predetermined timing is known. If the sampling timing is synchronized with the output timing of the pulse signal by the above configuration, detection of signal input and determination of disconnection can be performed simultaneously. Further, the duty and cycle of the pulse signal may be set so that signal input can be detected (for example, the ON duty ratio is made as small as possible), and the power consumption for outputting the pulse signal is reduced. Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the whole structure of a disconnection detection apparatus is shown. The disconnection detecting device 1 is configured to include an ECU 30 and a display unit 40 connected to the ECU 30 and switches SW1, SW2 connected to the ECU 30 via signal lines L1, L2.

The switches SW1 and SW2 are capable of selectively switching and outputting an on state and an off state. Also, termination resistors R1 and R2 are connected in parallel near the switches SW1 and SW2. The resistance values of the termination resistors R1 and R2 are determined so as to satisfy the following two conditions.
Considering the inductance and capacitance of the signal lines L1 and L2 from the ECU 30 (input terminals In1 and In2) that outputs a pulse signal (described later) to the terminating resistors R1 and R2, the resistance value is a value that does not cause reflection. To do. That is, the impedances of the signal lines L1 and L2 and the impedances of the termination resistors R1 and R2 are made the same to achieve impedance matching.
The resistance value is set as large as possible so as not to hinder the input of the on / off signals from the switches SW1 and SW2 to the ECU 30. This is a measure for erroneously determining that the ECU 30 side is in an ON state even if the switches SW1 and SW2 are in an OFF state if the resistance value is small.
The termination resistors R1 and R2 correspond to the impedance adjustment circuit and the resistance element of the present invention.

  The ECU 30 includes a voltage comparison circuit 32, a pulse generation circuit 36, a communication device 37, and a control circuit 31 to which these are connected.

  The control circuit 31 includes a well-known CPU 31a, ROM 31b, RAM 31c, a memory 31d as a nonvolatile storage medium, and an A / D 31e as a well-known A / D conversion circuit, and the CPU 31a stores a control program (not shown) in the ROM 31b. ) Is performed, the operation as the ECU 30 is performed. The control circuit 31 corresponds to the signal input circuit and the disconnection determination circuit of the present invention.

  The voltage comparison circuit 32 is configured by, for example, a known operational amplifier, and includes two comparison circuits, CMP1 and CMP2. The voltage comparison circuit 32 corresponds to the signal input circuit and the disconnection determination circuit of the present invention.

  The pulse generation circuit 36 is for outputting a pulse signal to the signal lines L1 and L2, and includes a switching element such as a transistor TR, for example, and switches the output level based on an on / off control signal from the control circuit, Outputs a pulse waveform. Note that a single pulse generation circuit can output a pulse signal to a plurality of signal lines.

  The communication device 37 is configured as a well-known wireless communication device or a wired communication device such as a LAN interface circuit, and communicates with an external device.

  The display unit 40 includes a well-known LCD and LED and their drive circuits, and displays various types of information based on display commands from the control circuit 31.

  Details of signals input to the ECU 30 (control circuit 31) will be described using the switch SW1 as an example with reference to FIG. The switch SW2 is the same as the switch SW1 except that the logic of the signal output in the on / off state is different.

  From the pulse generation circuit 36, a pulse signal having a cycle T (ms) and an H level time t (ms) is always output to the signal line L1 (also L2). The H level time t is set shorter on condition that a reflected wave when the signal line L1 is disconnected can be detected. In this way, power consumption in the pulse generation circuit 36 can be reduced. The pulse signal is continuously transmitted until at least the influence of the reflected wave reaches the ECU 30 to be monitored.

  The switch SW1 outputs an L level in the on state and an H level in the off state. Then, the pulse signal from the pulse generation circuit 36 and the output signal from the switch SW1 are combined and input to the control circuit 31 (corresponding to the input signal in FIG. 2).

  When the switch SW1 is in the OFF state, the input signal has a pulse shape synchronized with the pulse signal output from the pulse generation circuit 36. Therefore, the trigger is when the output of the pulse generation circuit 36 changes from the L level to the H level. If sampling is performed, the state of the switch SW1 can be acquired. The trigger may be when an H level output command signal is output from the control circuit 31 to the pulse generation circuit 36.

  Details of the reflected wave will be described with reference to FIG. In FIG. 3, only one pulse is shown for ease of explanation. When a disconnection occurs at X1 on the signal line L1, the pulse signal output from the pulse generation circuit 36 is reflected at X1. The pulse signal coming from the ECU 30 side (left side in the figure) is reflected through the processes (1) to (10) at X1. The incident wave is indicated by a solid line, and the reflected wave is indicated by a broken line. In addition, the reflected pulse signal is indicated by a broken line in the right region with X1 as a boundary in (4) to (7). That is, the original pulse signal waveform is a combination of the solid line part on the left side of the boundary and the broken line part on the right side.

  While the pulse signal corresponding to (4) to (7) in FIG. 3 is being reflected, a composite waveform of the incident wave and the reflected wave is generated, so that normal reflection occurs at the H level. It is about twice as much as a non-pulse signal. Therefore, by measuring the level of the pulse signal input to the ECU 30, the occurrence of reflection, that is, the disconnection of the signal line (L1) can be detected.

  Further, if there is only one pulse signal, the influence of reflection can be confirmed only near the reflection point, but the influence of reflection can be confirmed at any location on the signal line by outputting a continuous pulse signal.

With reference to FIG. 4, a signal line disconnection determination process included in the above-described control program and repeatedly executed by the CPU 31 a will be described. First, it is determined whether or not the timing for taking in the input of the switches (SW1, SW2) has come (S11). One or both of the following are used as the determination method.
When the pulse signal output control in the pulse generation circuit 36 is executed by a control program, the timing for changing the pulse signal output from the L level to the H level is determined as the timing for taking in the switch input. To do.
A signal (only a pulse signal) at the connection point between the transistor TR and the resistor R11 of the pulse generation circuit 36 is input to the control circuit 31, and the input of the switch is captured when the rising edge of the pulse signal is detected. It is determined that the timing has arrived.

  When it is determined that the timing for capturing the inputs of the switches (SW1, SW2) has arrived (S11: Yes), the inputs of these switches are captured (S12). Next, it is determined whether or not the signal lines (L1, L2) are disconnected (S13).

  As shown in FIG. 5, when the signal lines (L1, L2) are disconnected, reflection occurs at the disconnection point, and the H level voltage V1 at that time is higher than the H level voltage V when no reflection occurs. It is large and V1 = 2 × V at maximum. Therefore, determination is made using either or both of the following.

When the voltage comparison circuit 32 is used, first, the voltage threshold Vth1 in the comparison circuit CMP1 is set so that 0 (reference potential) <Vth1 <V, for example, V / 2, and the voltage in the comparison circuit CMP2 is set. The threshold value Vth2 is set such that V <Vth2 <V1, such as V + (V1−V) / 2. Then, when a voltage (pulse signal) exceeding the respective voltage thresholds is input, the comparators CMP1 and CMP2 are set to output an H level signal.

  When reflection does not occur, the H level voltage of the pulse signal exceeds the voltage threshold Vth1, but does not exceed the voltage threshold Vth2. On the other hand, when reflection occurs, both the voltage threshold Vth1 and the voltage threshold Vth2 are exceeded. Therefore, it is determined that a disconnection has occurred when the comparison circuits CMP1 and CMP2 output that the H level voltage of the pulse signal exceeds both the voltage threshold value Vth1 and the voltage threshold value Vth2.

When using the A / D 31e which is an A / D conversion circuit, if the value after the A / D conversion of the input pulse signal exceeds the value corresponding to the voltage threshold Vth2, a disconnection has occurred. judge.

  In FIG. 1, in the ECU 30, the input from the signal line L1 is connected so that both voltage comparison and A / D conversion are possible, and the input from the signal line L2 can only be A / D conversion. However, only one or both of the configurations may be possible.

Returning to FIG. 4, when it is determined that the signal line (L1, L2) is disconnected (S14: Yes), a predetermined process corresponding to the disconnection is executed (S15). Examples of the disconnection handling process include the following.
The memory 31d stores data specifying the signal line where the disconnection has occurred. When the ECU 30 includes a clock function, the disconnection occurrence date and time may also be stored. In addition, the data on the RAM 31c used in the process of performing control using the switch connected to the signal line where the disconnection has occurred may be stored.
The display unit 40 displays that the disconnection has occurred and details thereof (disconnection occurrence location, disconnection date and time, etc.).
The communication device 37 outputs to the external device that the disconnection has occurred and details thereof. It may be a form that does not output in real time. For example, a method of reading a content stored in the external device memory 31d by connecting a known diagnostic diagnosis tool may be used.

  In the above example, the CPU (microcomputer) is used. However, the CPU may not be used. For example, the output from the comparison circuits CMP1 and CMP2 of the voltage comparison circuit 32 is connected to the input of a known AND circuit that outputs the logical product of the input values, and when the output of the AND circuit becomes H level, the LED or the like is connected. It is to light up.

  Although the embodiments of the present invention have been described above, these are merely examples, and the present invention is not limited to these embodiments, and the knowledge of those skilled in the art can be used without departing from the spirit of the claims. Various modifications based on this are possible.

The block diagram which shows the whole structure of a disconnection detection apparatus. The figure shown about the detail of the signal input into ECU. The figure shown about the detail of reflection. The flowchart explaining a signal line disconnection determination process. The figure which shows the detail of the waveform of a reflected wave.

Explanation of symbols

1 Disconnection detection device 30 ECU
31 Control circuit (signal input circuit, disconnection judgment circuit)
31a CPU
32 Voltage comparison circuit (signal input circuit, disconnection judgment circuit)
36 Pulse generation circuit 40 Display unit L1, L2 Signal line R1, R2 Termination resistor (impedance adjustment circuit, resistance element)
SW1, SW2 switch X1, X2 Disconnection position

Claims (4)

A switch that selectively switches between an on state and an off state and outputs;
A signal line having one end connected to the switch and the other end connected to a signal input circuit for inputting the state of the signal line;
A pulse signal output circuit that outputs a pulse signal to the signal line at a predetermined timing;
In the vicinity of the switch, an impedance adjustment circuit connected in parallel to the switch;
A disconnection determination circuit that determines that the signal line is disconnected when a reflected wave of the pulse signal is input to the signal input circuit;
A disconnection detecting device comprising:   2. The disconnection detection device according to claim 1, wherein a circuit impedance of the impedance adjustment circuit is determined so that a reflected wave of the pulse signal is not generated when the signal line is not disconnected.   The disconnection detection apparatus according to claim 1, wherein the impedance adjustment circuit includes a resistance element.   The disconnection detecting device according to any one of claims 1 to 3, wherein the signal input circuit inputs a state of the signal line based on a timing at which the pulse signal is output.

Images