JP2014083932A - CAN communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CAN communication device which provides a good result in both an electrostatic discharge trial and a BCI trial.SOLUTION: An ECU 1 for a vehicle is one example of a CAN communication device. The ECU 1 has a CAN transceiver element 3 and a bi-direction Zener diode 6. The bi-direction Zener diode 6 is connected to a bus line 7 of a CAN which is connected to the CAN transceiver element 3 and a reference potential point. A Zener voltage of the bi-direction Zener diode 6 is larger than 58 V and smaller than 66 V.

Description

  The present invention relates to a CAN communication apparatus that performs communication in accordance with a CAN (Controller Area Network) protocol.

  As shown in Patent Documents 1 and 2, it is known that a Zener diode is used for a surge countermeasure in a vehicle represented by an automobile.

  On the other hand, in vehicles, CAN is widely spread as a communication network between a plurality of ECUs (Electric Control Units). The CAN protocol is an international standard defined by ISO11898. An ECU in a vehicle is an element in which an IC (Integrated Circuit) of a CAN transceiver is integrated into one chip in order to perform communication according to the CAN protocol.

  Further, in a vehicle, a bidirectional Zener diode is provided in a state of being connected to a CAN bus line connected to a CAN transceiver element and a reference potential point as a countermeasure against surge. Usually, a bidirectional Zener diode having a Zener voltage of 16V is employed in a CAN bus line of a vehicle. In this case, good results can be obtained in the electrostatic discharge test.

  In the electrostatic discharge test of the vehicle ECU, an immunity test is performed by injecting an electrostatic discharge from a range of −5 kV to +5 kV to a range of −25 kV to +25 kV, for example, on the signal line to be tested through a probe.

JP 10-136564 A JP 10-311241 A

  By the way, in recent years, a communication device mounted on a vehicle must pass an EMC (Electromagnetic Compatibility) test for confirming the effect of electromagnetic wave countermeasures in addition to passing an electrostatic discharge test for confirming the effect of surge countermeasures. Is also required. A well-known BCI (Bulk current injection) test is usually employed as an EMC test in electrical equipment for vehicles. The BCI test is an immunity test in which a high-frequency interference current in a frequency range of, for example, about 1 MHz to 400 MHz is injected into a signal line to be tested through a probe.

  In a CAN communication device that forms a backbone network in a vehicle, acceptance criteria for electrostatic tests and BCI tests (EMC tests) are becoming increasingly strict. However, when the Zener voltage of the bidirectional Zener diode provided on the CAN bus line is 16V, it has been found that a good result is obtained in the electrostatic discharge test, but a communication error is likely to occur in the BCI test.

  An object of the present invention is to provide a CAN communication apparatus that can obtain good results in both the electrostatic discharge test and the BCI test.

  The CAN communication apparatus which concerns on the 1st aspect of this invention is provided with each component shown below. The first component is connected to a CAN transceiver element, a CAN bus line connected to the CAN transceiver element, and a reference potential point, and a bidirectional Zener diode having a Zener voltage higher than 58V and lower than 66V. .

  The CAN communication apparatus according to the second aspect of the present invention is an aspect of the CAN communication apparatus according to the first aspect. In the CAN communication apparatus according to the second aspect, the withstand voltage of the CAN transceiver element is in a range from −40V to + 40V.

  The CAN communication apparatus according to the third aspect of the present invention is one aspect of the CAN communication apparatus according to the first aspect or the second aspect. The CAN communication apparatus which concerns on a 3rd aspect is further provided with the choke coil which is connected to the bus line of the said CAN, and the impedance is the range of 200-1000 (ohm).

  If the CAN communication apparatus according to the present invention is employed, good results can be obtained in both the electrostatic discharge test and the BCI test, as will be described later.

It is a schematic block diagram of ECU1 for vehicles which is an example of the CAN communication apparatus which concerns on embodiment of this invention. It is a figure showing the result of the BCI test and electrostatic discharge test of vehicle ECU in each case where bidirectional Zener diodes having different Zener voltages are employed.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiment is an example embodying the present invention, and is not an example of limiting the technical scope of the present invention.

  First, a schematic configuration of a vehicle ECU 1 that is an example of a CAN communication apparatus according to an embodiment of the present invention will be described with reference to FIG. The ECU 1 is an example of a CAN communication device for a vehicle, and is a gateway ECU having a function of relaying data communication between a plurality of CAN bus lines 7.

  As shown in FIG. 1, the ECU 1 includes one MCU (Micro Computer Unit) 2 and a plurality of CAN communication units 30. Each CAN communication unit 30 includes a CAN transceiver element 3, a choke coil 5, a bidirectional Zener diode 6, and a connector 8. Some of the CAN communication units 30 further have a current limiting termination resistor 4. Each element constituting the MCU 2 and the CAN communication unit 30 is mounted on the circuit board 10. Note that “CC” and “TR” in FIG. 1 are abbreviations of “Choke Coil” and “Terminating Resistor”, respectively.

  In the following description, the CAN communication unit 30 that does not include the termination resistor 4 is referred to as a first CAN communication unit 30A, and the CAN communication unit 30 that includes the termination resistor 4 is referred to as a second CAN communication unit 30B.

  In the example shown in FIG. 1, the ECU 1 includes one first CAN communication unit 30A and one second CAN communication unit 30B, and is connected to each of the two CAN bus lines 7. The CAN bus line 7 is a pair of bus lines including a CAN bus line 71 for Low level and a CAN bus line 72 for High level.

  The MCU 2 is a microcomputer that relays data communication between a plurality of CAN communication units 30. The MCU 2 has a plurality of communication ports 21 connected to each of the plurality of CAN communication units 30. Each communication port 21 includes a signal transmission port and a signal reception port.

  On the other hand, the CAN transceiver element 3 has a data input / output terminal 31 connected to the communication port 21 of the MCU 2 and a CAN bus connection terminal 32. The data input / output terminal 31 includes a data input terminal and a data output terminal at each of the signal transmission port and the signal reception port in the communication port 21 of the MCU 2. The CAN transceiver element 3 conforms to an international standard defined by ISO11898.

  The CAN bus connection terminal 32 of the CAN transceiver element 3 is composed of a pair of terminals connected to the CAN bus line 71 for Low level and the CAN bus line 72 for High level.

  In each CAN communication unit 30, the choke coil 5 is connected to a portion of the CAN bus line 7 near the CAN transceiver element 3. Similarly, in the second CAN communication unit 30 </ b> B, the termination resistor 4 is connected to the CAN bus line 7 in a state of being arranged in series with the choke coil 5. Since the choke coil 5 and the termination resistor 4 are well known, detailed description thereof will be omitted.

  In each CAN communication unit 30, each of the two bidirectional Zener diodes 6 is connected to each of the low level CAN bus line 71 and the high level CAN bus line 72 and a reference potential point. That is, one of the two terminals of the bidirectional Zener diode 6 is connected to the CAN bus line 7 and the other is connected to the reference potential point. The reference potential point is a portion that serves as a potential reference in grounding the housing, and the reference potential point in the vehicle is, for example, a metal member that constitutes the body of the vehicle or a conductor connected to the member.

  The connector 8 is a connector that relays between the CAN bus line 7 on the circuit board 10 of the ECU 1 and the CAN bus line 7 outside the ECU 1.

  In the present embodiment, the withstand voltage of the CAN transceiver element 3 is in the range from −40V to + 40V. The impedance of the choke coil 5 connected to the CAN bus line 7 together with the bidirectional Zener diode 6 is in the range of 200 to 1000Ω.

  In the vehicle ECU 1, the withstand voltage of the CAN transceiver element 3 and the impedance of the choke coil 5 described above are often employed. For example, it is conceivable that the impedance of the choke coil 5 is 600Ω.

  Furthermore, in the conventional vehicle ECU 1, the configuration of the second CAN communication unit 30 </ b> B is often employed from the viewpoint of protecting the CAN transceiver element 3. Conventionally, a bidirectional Zener diode 6 having a Zener voltage of 16V is employed in the second CAN communication unit 30B including the termination resistor 4. In the second CAN communication unit 30B, the termination resistor 4 has an impedance of 60.4Ω.

  On the other hand, as shown in FIG. 1, when it is necessary to employ the first CAN communication unit 30A that does not include the termination resistor 4, if the Zener voltage of the bidirectional Zener diode 6 is 16V, the BCI test is satisfactory. It turned out that the result is not obtained.

  In the first CAN communication unit 30A of the present embodiment, the Zener voltage of the bidirectional Zener diode 6 is 62V. The bidirectional Zener diode 6 having such a specification is not employed in a CAN bus line in a conventional vehicle ECU. As described above, conventionally, a bidirectional Zener diode having a Zener voltage of 16V has been adopted in a CAN bus line of a vehicle.

  Next, the results of the BCI test and the electrostatic discharge test of the vehicle ECU in each case where the bidirectional Zener diodes 6 having different Zener voltages are employed will be described with reference to FIG. FIG. 2 shows the ECU BCI test and ESD (ESD) when the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A is 16V, 36V, 51V, 58V, 62V, 66V, 70V, 80V and 90V, respectively. Represents the result of the ElectroStatic Discharge test. The conditions of the withstand voltage of the CAN transceiver element 3 and the impedance of the choke coil 5 are as described above, for example, 600Ω. Further, the Zener voltage of the bidirectional Zener diode 6 in the second CAN communication unit 30B is 16V.

  The BCI test is a test by an immunity test method in which a disturbing current is injected into the CAN bus line 7 in the first CAN communication unit 30A via the BCI probe. More specifically, high-frequency interference current in the frequency range of 1 MHz to 400 MHz was injected at a level of 160 mA. The injected high-frequency interference current is an unmodulated current and an AM modulated current. The standard for passing the test is that the CAN communication is normally performed in all the frequency bands of the injected disturbing current.

  The ESD test is a test in which electrostatic discharge in a range of 5 kV to +25 kV is applied to a predetermined location on the CAN bus line 7. Moreover, electrostatic discharge was implemented by both contact discharge and air discharge. The standard for passing the test is that the device does not malfunction or break due to electrostatic discharge.

  In the result of the BCI test in FIG. 2, “OK” indicates that no CAN communication error occurred during the test, and “NG” indicates that a CAN communication error occurred during the test. In the result of the ESD test in FIG. 2, “OK” indicates that no CAN communication error occurred during the test, and “NG” indicates that a CAN communication error occurred during the test. Further, “Break Down” indicates that the CAN transceiver element 3 has failed due to the test.

  The following can be understood from the test results shown in FIG. First, when the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A without the termination resistor 4 is 66 V or more, the result of the ESD test (electrostatic discharge test) is “NG”. Therefore, from the viewpoint of surge countermeasures, the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A needs to be less than 66V. From this, it can be said that the conventional ECU employing the bidirectional Zener diode having a Zener voltage of 16V in the first CAN communication unit 30A has a slightly excessive specification as a countermeasure against surge.

  Further, the test result shown in FIG. 2 indicates that the result of the BCI test is “NG” when the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A is 58V or less. Therefore, from the viewpoint of electromagnetic wave noise countermeasures, the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A needs to be a voltage higher than 58V.

  As described above, in the ECU 1, when the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A is larger than 58V and smaller than 66V, good results are obtained in both the ESD test and the BCI test. It is thought that it is obtained. For example, it is conceivable that the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A is 62V. As shown in FIG. 2, if the Zener voltage of the bidirectional Zener diode 6 in the first CAN communication unit 30A is 62V, good results can be obtained in both the ESD test and the BCI test.

  Note that the bidirectional Zener diode 6 in the first CAN communication unit 30A may be configured by two Zener diodes that are opposed and connected in series.

1 ECU
2 MCU
3 CAN transceiver element 4 resistance element 5 choke coil 6 bidirectional Zener diode 7 CAN bus line 8 connector 10 circuit board 21 communication port 30 CAN communication unit 30A first CAN communication unit 30B second CAN communication unit 31 data input / output terminal 32 CAN bus connection terminal 71 CAN bus line for low level 72 CAN bus line for high level

Claims (3)

A CAN (Controller Area Network) transceiver element;
A CAN communication device, comprising: a CAN Zener diode connected to the CAN transceiver element; and a bidirectional Zener diode having a Zener voltage greater than 58V and less than 66V. The CAN communication device according to claim 1,
A CAN communication device, wherein a withstand voltage of the CAN transceiver element is in a range from -40V to + 40V. The CAN communication device according to claim 1 or 2,
A CAN communication apparatus further comprising a choke coil connected to the CAN bus line and having an impedance in a range of 200 to 1000Ω.

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