JP2013093655A - In-vehicle communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate a plurality of lamps disposed at the rear end of a vehicle, by performing DC current supply and signal transmission/reception between a meter ECU and a communication ECU disposed at the vehicle rear end, using a single circuit.SOLUTION: An in-vehicle communication system includes: a meter ECU (master unit) 1 disposed on an instrument panel for supplying DC current, a communication ECU (sub-unit) 2 disposed on the vehicle rear end section and a single transmission line L for connecting between the meter ECU (master unit) 1 and the communication ECU (sub-unit) 2. The meter ECU (master unit) 1 includes means for converting a DC power supply (battery 3) voltage into a pulse-shaped sequence voltage according to a switch signal. The communication ECU (sub-unit) 2 includes means for monitoring the pulse-shaped sequence voltage.

Description

  The present invention relates to an in-vehicle communication system, and more particularly, to an in-vehicle communication system that can achieve space saving, light weight, and cost reduction by wire saving of a wire harness.

  Conventionally, such an in-vehicle communication system as shown in FIG. 4 is known.

  In the figure, a conventional in-vehicle communication system includes a switch group 100, a meter 200, a relay group 300, and a battery 400 that are arranged around an engine room or an instrument panel, and a lamp group 500 that is arranged at the rear end of the vehicle. The battery 400 is connected to first to fourth relays 300a to 300d constituting the relay group 300, and the first relay 300a includes a pedal switch 100a constituting the switch group 100 and a first communication line. A stop lamp 500a constituting the lamp group 500 is connected via La. The second relay 300b has a back lamp 500b via a shift lever switch 100b, a meter 200, and a second communication line Lb, and the third relay 300c has a light switch 100c, the meter 200, and a third communication line. A clear lamp 500c is connected via Lc, and a turn lamp 500d is connected to the fourth flash relay 300d via a light switch 100c, a meter 200 and a fourth communication line Ld.

  In the in-vehicle communication system having such a configuration, the first relay 300a is driven by the signal of the pedal switch 100a operated by the driver, for example, and the stop lamp 500a is turned on when the DC power is supplied from the battery 400. It is configured as follows.

  However, the in-vehicle communication system having such a configuration has the following difficulties.

  First, since relays and communication lines are assigned to each lamp, the diameter of the bundle of electric wires routed before and after the vehicle becomes thicker, which in turn increases the weight of the vehicle, increasing the weight of the vehicle and compressing the indoor space. Is done.

  Secondly, the battery of a general passenger car has a direct current of 12V, but an LED or an electronic control unit, that is, an in-vehicle ECU (Electronic Control Unit) does not necessarily require a 12V power supply.・ It is necessary to use it down to the current value.

  Third, the communication line from the relay to the lamp is long, and a plurality of long wires connected to other devices are bundled and run side by side, so that when the other devices operate, the wires act like an antenna. As a result, a weak current flows through the signal line, and as a result, an LED that consumes less power than a normal bulb (lamp) may malfunction.

  For this reason, (b) abolishing the communication line connecting each on-board electrical equipment, superimposing the signal on the power line connected from the DC power supply (battery), and performing power supply and communication with a single circuit A device that operates a device (for example, Patent Document 1), or (b) a device that operates a sensor by performing power supply and communication with a single circuit that connects an airbag control ECU and an airbag sensor (for example, a patent) Document 2 etc.) has been developed.

  Here, in the in-vehicle communication system of (a), each ECU has a communication transmission circuit and a reception circuit connected to the power supply line, respectively, and each ECU superimposes a signal to be transmitted on the carrier wave. The receiving side extracts the frequency component of the carrier wave from the power line and receives it as a signal. Note that the ECU is constantly supplied with power.

  However, in the in-vehicle communication system (a), space efficiency can be improved by reducing the wire harness, the weight can be reduced, and the cost can be reduced, but the signal is superimposed on the carrier wave and placed on the power line. When the power supply line becomes longer, the signal is deteriorated, noise is superposed, and it is difficult to discriminate noise having a frequency close to the carrier wave.

  On the other hand, in the in-vehicle communication system of (b), the air bag can be reduced in space, weight and cost by reducing the wire harness as in the in-vehicle communication system of (b). Since the current consumption of the sensor needs to be small and stable, a large load cannot be driven, and the rated consumption of the device that receives power supply (hereinafter referred to as “slave unit”) There is a problem that it is necessary to adjust a threshold value of a device (hereinafter referred to as “master unit”) that supplies power by current, and it is difficult to connect slave units having different rated currents.

JP 2011-156953 A Japanese Patent Laid-Open No. 11-53677 JP 2001-144659 A

  The present invention has been made to solve the above-described problems, and a vehicle is provided by supplying DC power and transmitting / receiving signals on a single circuit between a meter ECU and a communication ECU disposed at the rear end of the vehicle. An object of the present invention is to provide an in-vehicle communication system capable of operating a plurality of lamps arranged at the rear end.

  An in-vehicle communication system according to a first aspect of the present invention includes a meter ECU that is disposed on an instrument panel and supplies DC power, a communication ECU that is disposed at a rear end of the vehicle, and between the meter ECU and the communication ECU. The meter ECU includes means for converting the voltage of the DC power source into a voltage in a pulse train in response to a switch signal, and the communication ECU monitors the voltage in the pulse train. Means are provided.

  According to the in-vehicle communication system according to the first aspect, firstly, it is possible to reduce the weight and space by wire-saving of the wire harness, and to reduce the cost of the wire harness member. By applying a signal converted into a pulse train voltage to the signal, the signal does not deteriorate even when the transmission line (power supply line) is long, and erroneous communication due to noise superposition can be reduced.

  Third, by adjusting the threshold value, it is possible to improve erroneous communication due to power supply fluctuations caused by deterioration of the DC power supply (battery), alternator (generator) on / off, or the like.

  Fourth, by configuring with a general DC digital circuit, it can be easily added to an existing system.

  According to a second aspect of the present invention, in the in-vehicle communication system according to the first aspect, the communication ECU electrically disconnects the transmission line when the voltage of the pulse train is a Lo (low potential) voltage. Means, means for driving each circuit of the communication ECU, and means for sending a signal to the meter ECU.

  According to the in-vehicle communication system according to the second aspect, in addition to the operation and effect of the in-vehicle communication system according to the first aspect, a signal can be sent from the communication ECU to the meter ECU.

  According to a third aspect of the present invention, in the in-vehicle communication system according to the first aspect or the second aspect, another communication ECU having the same configuration as the communication ECU is arranged in parallel with the communication ECU on the communication ECU side of the transmission path. Is connected to.

  According to the in-vehicle communication system according to the third aspect, in addition to the operation and effect of the in-vehicle communication system according to the first aspect or the second aspect, a signal can be sent from another communication ECU to the meter ECU. It is possible to transmit and receive signals between one communication ECU and another communication ECU.

  The in-vehicle communication system according to the first to fourth aspects of the present invention has the following effects.

  First, it is possible to reduce the weight and space by reducing the wire harness and to reduce the cost of the wire harness member.

  Second, by applying a signal converted into a pulse train voltage to the transmission line, even if the transmission line (power supply line) is longer than communication using a carrier wave, the signal does not deteriorate, and noise is superimposed. Miscommunication can be reduced.

  Third, by adjusting the threshold value, it is possible to improve erroneous communication due to power supply fluctuations caused by deterioration of the DC power supply (battery), alternator (generator) on / off, or the like.

  Fourth, by configuring with a general DC digital circuit, it can be easily added to an existing system.

  Fifth, by enabling transmission / reception between the meter ECU and the communication ECU or between the communication ECUs, for example, vehicle information such as bulb (lamp) burnout can be acquired based on information from the communication ECU.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows an example of the communication system in a vehicle of this invention typically. The block diagram which shows an example of meter ECU (parent machine) shown in FIG. The block diagram which shows an example of communication ECU (slave machine) shown in FIG. Explanatory drawing which shows an example of the conventional communication system in a vehicle typically.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments to which an in-vehicle communication system of the invention is applied will be described with reference to the drawings.

  FIG. 1 is an explanatory view schematically showing an embodiment of the in-vehicle communication system according to the present invention, FIG. 2 is a block diagram showing an embodiment of the meter ECU in the in-vehicle communication system of the present invention, and FIG. It is a block diagram which shows one Example of communication ECU in the communication system in a vehicle of this invention.

  In FIG. 1, the in-vehicle communication system according to the present invention is arranged on an instrument panel (not shown) and supplies a meter ECU (master unit) 1 for supplying DC power, and a communication ECU (child unit) arranged at the rear end of the vehicle. Machine) 2 and a single transmission line L that electrically connects the meter ECU (master unit) 1 and the communication ECU (slave unit) 2 to the meter ECU 1 and a battery 3 as a DC power source. A switch group 4 including a pedal switch 4a, a shift lever switch 4b, a light switch 4c, and the like is connected, and a lamp group including a stop lamp 5a, a back lamp 5b, a clear lamp 5c, a turn lamp 5d, and the like is connected to the communication ECU 2. 5 is connected.

  As shown in FIG. 2, the meter ECU (base unit) 1 includes a transmission circuit (hereinafter referred to as “base unit transmission circuit”) 11, a reception circuit (hereinafter referred to as “base unit reception circuit”) 12, and a transmission path. A regulator (hereinafter referred to as “parent device regulator”) 13 for adjusting the voltage of L and a microcomputer (hereinafter referred to as “parent device microcomputer”) 14 for controlling each part (circuit) are provided, and the transmission line L A battery 3 serving as a DC power source is connected to one end of the power supply, and further, on the downstream side (communication ECU (slave unit) 2 side), the base unit regulator 13, the base unit transmission circuit 11, and the base unit are sequentially arranged toward the downstream side. A receiving circuit 12 is connected.

  A switch group 4 such as a pedal switch 4a, a shift lever switch 4b, and a light switch 4c is connected to a parent microcomputer 14, and the parent microcomputer 14 includes a parent regulator 13, a parent transmission circuit 11, and a parent machine. A receiving circuit 12 is connected.

  Base device transmission circuit 11 converts first to fourth electric resistances 11a to 11d, first to third transistors 11e to 11g, and a voltage of battery 3 as a DC power source into a voltage in a pulse train. The drain of the field effect transistor 11h is on the battery 3 side of the transmission line L, the source is on the communication ECU 2 side of the transmission line L, and the gate is the fourth electric resistance 11d. To the second and third transistors 11f and 11g.

  The base unit receiving circuit 12 includes first and second electric resistors 12a and 12b, a comparator (hereinafter referred to as “base unit comparator”) 12c, and a threshold voltage (hereinafter referred to as “base unit threshold voltage”) V1. The input side of the main unit comparator 12c is connected to the connecting portion P1 of the first and second electric resistors 12a and 12b as a voltage dividing resistor and the positive side of the main unit threshold voltage V1, and A master microcomputer 14 is connected to the output side.

  On the other hand, as shown in FIG. 3, the communication ECU (slave unit) has a reception circuit (hereinafter referred to as “slave unit reception circuit”) 21, a transmission circuit (hereinafter referred to as “slave unit transmission circuit”) 22, and transmission. A diode as a commutator 23 having a function of electrically disconnecting the path L, a capacitor 24 as means for driving each circuit of the communication ECU (slave unit) at a predetermined time, and a regulator for adjusting the voltage of the transmission path L (Hereinafter referred to as “slave unit regulator”) 27, a microcomputer (hereinafter referred to as “slave unit microcomputer”) 25 for controlling each part (circuit), first to fourth transistors 26a to 26d, To fourth electric resistances Ra to Rd, the switch group 5 is connected to the other end of the transmission line L, and further to the upstream side (meter ECU (master unit) 1 side) on the upstream side. Child sequentially Regulator 27, a capacitor 24, diode as commutator 23, handset transmitter circuit 22 and the handset receiver circuit 21 is connected. Here, the capacitor 24 is connected between the transmission line L and the ground, the anode of the diode as the commutator 23 is connected to the meter ECU (master unit) 1 side of the transmission line L, and the cathode is connected to the capacitor 24 side of the transmission line L. Has been.

  The slave unit receiving circuit 21 includes first and second electric resistors 21a and 21b, a comparator (hereinafter referred to as “slave unit comparator”) 21c, and a threshold voltage (referred to as “slave unit threshold voltage”) V2. The input side of the slave unit comparator 21c is connected to the connection portion P2 of the first and second electric resistors 21a and 21b as a voltage dividing resistor and the plus side of the slave unit threshold voltage V2, and the slave unit comparator 21c A slave microcomputer 25 is connected to the output side.

  The handset transmission circuit 22 includes first to third electric resistors 22a to 22c and first and second transistors 22d and 22e. The emitter side of the second transistor 22e is connected to a capacitor 24, and a collector. The side is connected to the anode side of the diode as the commutator 23. The base side of the first transistor 22d is connected to the slave microcomputer 25 via the first electric resistor 22a, and the collector side is connected to the base side of the second transistor 22e via the second electric resistor 22b. It is connected.

  The handset microcomputer 25 is connected to the handset regulator 27 and the first to fourth electric resistances Ra to Rd. The first electric resistance Ra is connected to the stop lamp 5a via the first transistor 26a. The back lamp 5b is connected to the second electric resistance Rb via the second transistor 26b, and the clear lamp 5c is connected to the third electric resistance Rc via the third transistor 26c. A turn lamp 5d is connected to Rd via a fourth transistor 26d.

  Next, the operation of the in-vehicle communication system of the present invention configured as described above will be described.

  For example, when the pedal switch 4a is turned on, the master microcomputer 14 recognizes that the pedal switch 4a has been pressed, and the master microcomputer 14 sends an ON signal of the pedal switch 4a to the first transistor 11e. As a result, the first transistor 11e is operated, and the second and third transistors 11f and 11g are operated, so that an ON signal of the pedal switch 4a is sent to the field effect transistor 11h.

  As a result, a signal obtained by intermittently connecting the voltage of the DC power supply on the transmission line L from the base unit transmission circuit 11, that is, a signal obtained by converting the voltage of the DC power supply into a voltage in a pulse train as follows. Is superimposed on.

  First, the meter ECU (master unit) 1 of the present invention is configured to send signals preferentially from the meter ECU (master unit) 1 and to facilitate transmission / reception of signals on the transmission line L. Is set.

  Specifically, between the meter ECU (master unit) 1 and the communication ECU (slave unit) 2 in the present invention, the voltage on the transmission line L is Hi (high potential “12 V”) or Lo (low potential “0 V”). The signal is transmitted and received. For this reason, if a signal is sent simultaneously from a plurality of ECUs, it is impossible to determine the signal, and it becomes impossible to transmit and receive the signal. For example, even if one ECU tries to set the signal to Lo (low potential “0 V”), if the signal from another ECU is in the Hi state (high potential “12 V”), the voltage on the transmission line L becomes Hi ( This is because the high potential becomes “12 V”.

  In this way, the Hi (high potential “12 V”) signal is given priority over the Lo (low potential “0 V”) signal, so that only one ECU is transmitted at a time. It is necessary to wait in the state (low potential “0 V”).

  From such a viewpoint, in the present invention, in order to prevent a plurality of signals from being transmitted at the same time, the meter ECU (master unit) 1 manages the timing of signal transmission.

  Specifically, by changing the signal (voltage) on the transmission line L as follows, it is set not to send the signal at the same time.

  For example, when two communication ECUs (slave units) 2 are connected in parallel to the meter ECU (master unit) 1 via the transmission line L, the meter ECU (master unit) 1 sets “1100” to the right Assuming that one communication ECU (slave unit) 2 as a lamp transmits “1100” and the other communication ECU (slave unit) 2 as a left lamp transmits “1011”, the meter ECU (master unit) 1 adds “0” to the head of the signal, and the voltage on the transmission line L is changed to “0 (0 V: 0.1 ms)” → “1 (12 V: 0.1 ms)” → “1 ( 12V: 0.1 ms) ”→“ 0 (0 V: 0.1 ms) ”→“ 0 (0 V: 0.1 ms) ”. Thereafter, the meter ECU (master unit) 1 waits for 0.1 ms × 8 bits = 0.8 ms at Lo (low potential “0 V”) so that the two communication ECUs (slave units) 2 can transmit.

  One communication ECU (child device) 2 waits for 0.1 ms × 5 bits = 0.5 ms after receiving the first signal 0 (Lo “low potential”) from the meter ECU (parent device) 1 and then waits for the child. The transmission line L is set to “1 (12 V: 0.1 ms)” → “1 (12 V: 0.1 ms)” → “0 (0 V: 0.1 ms)” → “0 (0 V: 0.1 ms) from the transmission circuit 22. ) ”. The other communication ECU (child device) 2 waits 0.1 ms × 9 bits = 0.9 ms after receiving the first signal 0 (Lo “low potential”) from the meter ECU (parent device) 1 and then waits for the child. The transmission line L is set to “1 (12 V: 0.1 ms)” → “0 (0 V: 0.1 ms)” → “1 (12 V: 0.1 ms)” → “1 (12 V: 0.1 ms) from the transmitter circuit 22. ) ”.

  On the other hand, the power source of each part (circuit) of the communication ECU (slave unit) 2 depends on the Hi (high potential “12V”) signal of the meter ECU (master unit) 2, so that the communication ECU (slave unit) 2 In order to supply power to the meter, it is necessary to keep the meter ECU (master unit) 1 in the Hi state (high potential “12V”) as much as possible. Since there are only one ECU, it is necessary to give priority to the meter ECU (master unit) 1.

  As described above, a signal (for example, an ON signal of the pedal switch 4a) desired to be transmitted from the parent device transmission circuit 11 to the communication ECU (child device) 2 is converted into a pulse train voltage and superimposed on the transmission line L.

  Accordingly, the voltage (signal) of the pulse train superimposed on the transmission line L is monitored in the slave unit reception circuit 21 of the communication ECU (slave unit) 2 as follows.

  That is, when the voltage (signal) of the pulse train superimposed on the transmission line L is input to the slave unit comparator 21c via the first electric resistance 21a, the voltage of the pulse train and the slave unit threshold voltage V2 are compared. The comparison data is sent to the slave microcomputer 25. In the slave microcomputer 25, the voltage of the transmission line L is monitored, that is, whether the voltage of the pulse train on the transmission line L is higher than the slave unit threshold voltage V2. It is judged whether it is low.

  Here, the threshold value of the child device threshold voltage V2 and the adjustment thereof will be described.

  First, the normal voltage of the battery 3 as the DC power source is 12V. When the battery 3 deteriorates, the voltage of the battery 3 decreases, for example, from 11V → 10V → 9V. Further, when the battery is charged by the alternator (generator), a voltage of about 14V is generated, and the voltage of 14V is also supplied to the electrical components connected to the battery.

  In addition, when the voltage of the battery 3 is 12V under normal conditions, when the electrical component is actually mounted on the vehicle, the transmission line L connecting the meter ECU (master unit) 1 and the communication ECU (slave unit) 2 is Since power supply and signal transmission / reception are shared, when the voltage of the battery 3 increases or decreases, the voltage of the transmitted / received signal also increases or decreases, resulting in noise, and there is a possibility that signals cannot be transmitted or received in a good state. In addition, there is a phenomenon in which a signal can be transmitted and received satisfactorily in a certain vehicle but a signal cannot be transmitted and received satisfactorily in a vehicle of another different shape.

  In this case, the conventional technique using a carrier wave requires a complicated measure such as attenuating noise of a specific frequency from the transmission line L and amplifying a signal of another frequency to be transmitted. Can be adjusted by changing the threshold of the threshold voltage V2 applied to the slave comparator 21c.

  Specifically, when the transmission side transmits a 1 (Hi “high potential”) signal but the reception side recognizes 0 (Lo “low potential”), the threshold value of the slave unit threshold voltage V2 is lowered. On the other hand, when the transmitting side transmits 0 (Lo “low potential”) signal but the receiving side recognizes 1 (Hi “high potential”), the threshold value of the slave unit threshold voltage V2 is increased. For example, when the initial value of the threshold value of the slave unit threshold voltage V2 is 11V, if the battery 3 as the DC power supply deteriorates and decreases to 10V, the 1 (Hi “high potential”) signal on the transmission side becomes only 10V. And 0 (Lo “low potential”) at the receiving side. Therefore, in the case of such a vehicle (vehicle type), if the threshold value of the child device threshold voltage V2 is set to 8 V, for example, it may take a long time until the battery 3 deteriorates and drops to 8 V in some cases. Communication performance can be maintained.

  As described above, in the communication ECU (child device) 2, the stop lamp 5a is turned on / off by reading the signal (the ON signal of the pedal switch 4a).

  In this case, since the stop lamp 5a is driven by using the signal as a direct power source, the stop lamp 5a is momentarily interrupted (about 2 ms at the maximum), but the communication ECU (child device) 2 is temporarily stored in the capacitor 24 as described later. Since the electric charges are discharged and the instantaneous interruption of various lamps is extremely short, communication is completed earlier than the lamps are extinguished, so that there is no problem in performance. Further, when a problem occurs, power is supplied from the capacitor 24 (FIG. 3 is a diagram in the case where power is supplied from the capacitor 24).

  As described above, the in-vehicle communication system of the present invention has the following effects.

  1stly, the weight reduction and space saving by wire-saving of a wire harness, and the cost reduction of a wire harness member can be aimed at.

  Second, by applying a signal converted into a pulse-like train voltage to the transmission line L, the signal does not deteriorate even when the transmission line (power supply line) L is long, and erroneous communication due to noise superposition can be reduced. .

  Third, by adjusting the threshold value of the threshold voltage V2 of the slave receiver circuit 21, erroneous communication due to power supply fluctuations due to deterioration of the battery 3 or on / off of an alternator (generator) can be improved.

  Fourth, by configuring with a general DC digital circuit, it can be easily added to an existing system.

  Next, an operation when a signal is sent from the communication ECU (child device) 2 to the meter ECU (parent device) 1 will be described.

  First, as described above, when a Hi (high potential “12 V”) signal and a Lo (low potential “0 V”) signal are simultaneously sent on the transmission line L, the signal on the transmission line L is Hi (high potential). Therefore, the communication ECU (slave unit) 2 can send data only when the meter ECU (master unit) 1 is in the Lo (low potential “0 V”) state.

  Therefore, in the present invention, when the voltage of the pulse train on the transmission line L becomes Lo (low potential) voltage, the transmission line L is electrically disconnected by the diode as the commutator 23. Thus, when the transmission line L is electrically disconnected, the electric charge stored in the capacitor 24 is discharged, whereby power is supplied to each circuit of the communication ECU (slave unit) 2 and the communication ECU (slave unit) ) Each part circuit of 2 becomes active. Here, by superimposing a predetermined signal from the slave unit transmission circuit 20 on the transmission line L, the master unit receiving circuit 12 of the meter ECU (master unit) 1 can receive the signal.

  As described above, in this embodiment, the communication ECU (slave unit) includes means for electrically disconnecting the transmission line L, means for driving each circuit of the communication ECU, and means for sending a signal to the meter ECU. ) 2 can send a signal to the meter ECU (master unit) 1.

  The present invention has been described with respect to the present invention with specific embodiments shown in the drawings. However, the present invention is not limited to these embodiments, and as long as the effects of the present invention are exhibited. Any configuration known so far can be employed.

  For example, in the above-described embodiment, one communication ECU (slave unit) 2 is connected to one meter ECU (master unit) 1, but a plurality of meters are connected to one meter ECU (master unit) 2. You may connect the communication ECU (slave machine) of the same structure. In this case, by enabling transmission / reception between the meter ECU (master unit) 1 and the communication ECU (slave unit) 2 or one communication ECU (slave unit) 2 and another communication ECU (slave unit) 2, For example, vehicle information such as a bulb (lamp) burnout can be acquired from information from the communication ECU (2).

  In addition, the communication rule in the above-described embodiment is an example for preventing the transmission from occurring at the same time, and the data length, the transmission order, the transmission time, etc., use arbitrary values of the designer. Also good. In this case, it can be realized by changing the program of the microcomputer.

1 ... Meter ECU (master unit)
11 ... Transmission circuit (base unit transmission circuit)
11h ... Field effect transistor 2 ... Communication ECU (child device)
21 ... Receiving circuit (slave unit receiving circuit)
23 ... Commutator (diode)
24 ... Capacitor V2 ... Threshold voltage 3 ... DC power supply (battery)

Claims (3)

A meter ECU that is arranged on the instrument panel and supplies DC power, a communication ECU that is arranged at the rear end of the vehicle, and a single transmission path that connects between the meter ECU and the communication ECU,
The meter ECU includes means for converting the voltage of the DC power source into a pulse-like voltage in accordance with a switch signal,
The in-vehicle communication system, wherein the communication ECU includes means for monitoring the voltage of the pulse train.   The communication ECU has means for electrically disconnecting the transmission path, means for driving each circuit of the communication ECU, and a signal to the meter ECU when the voltage of the pulse train is a Lo (low potential) voltage. The in-vehicle communication system according to claim 1, further comprising means for sending   The in-vehicle communication according to claim 1 or 2, wherein another communication ECU having the same configuration as the communication ECU is connected in parallel with the communication ECU on the communication ECU side of the transmission path. system.

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