Automobile multiplex communication system

Abstract: An automobile multiplex communication system has a plurality of control units (1) mounted on an automobile body and having respective circuits (3) which are connected to communication signal lines (4) through respective connectors (5) for multiplex communications between the control units. Shield wires (7) which cover the communication signal lines between the control units are electrically separate from the connectors and connected to ground. The shield wires have respective ends grounded to a conductor (6) of the automobile body outside of the control units or grounded to conductive housings (2) of the control units.

Description: The present invention relates to an automobile multiplex communication system and in particular to a wiring structure therefor. In recent years, there have been developed automobile multiplex communication systems in which a plurality of control units each comprising a microcomputer or the like are installed on an automobile body for multiplex communications between those control units. As shown in FIG. 3 of the accompanying drawings, a conventional automobile multiplex communication system includes a plurality of control units (ECUs) "a" interconnected by communication signal lines "b" in the form of twisted pairs which are connected to circuits "d" including microcomputers in the ECUs "a" through connectors "c" such as multiterminal connectors or the like. Since automobiles are subject to external noise, the communication signal lines "b" are covered with shield wires "e" between the ECUs "a" for preventing the communication signal lines "b" from being affected by such external noise. The shield wires "e" are required to be grounded to a location which is not susceptible to external noise, e.g., a conductor of the automobile body. Heretofore, the shield wires "e" have been grounded as follows: As with the communication signal lines "b", the ends of the shield wires "e" which cover the communication signal lines "b" between the ECUs "a" are introduced into the ECUs "a" through the connectors "c". In the ECU "a" in which plural communication signal lines "b" and shield wires "e" are introduced, i.e., in the central ECU "a" shown in FIG. 3, the communication signal lines "b" are connected to each other, and the shield wires "e" are connected to each other. With respect to one of the ECUs "a", i.e., with respect to the central ECU "a" shown in FIG. 3, the shield wires "e" introduced through the connector "c" into the ECU "a" are led out of the ECU "a" and grounded to a conductor "f" of the automobile body. The above wiring structure for the automobile multiplex communication system suffers the following drawbacks: The portions of the communication signal lines "b" which are covered by the shield wires "e" between the ECUs "a" are protected against entry of external noise into the communication signal lines "b". However, since the connector terminals of the connectors "c" which are connected to the communication signal lines "b" tend to be not fully shielded, external noise applied to the shield wires "e" is likely to be picked up by the shield wires "e" serving as an antenna and applied through the connector terminals to the communication signal lines "b". Consequently, it has been impossible to sufficiently protect the automobile multiplex communication system against entry of external noise into the communication signal lines "b". EP 0491 179 (BMW) discloses a linear databus for an automobile according to the preamble of claim 1 and US 3697896 (Westinghouse) discloses a signal transmission system. It is therefore an object of the present invention to provide an automobile multiplex communication system having a wiring structure which sufficiently shields communication signal lines that interconnect a plurality of control units through connectors against external noise, for thereby making the automobile multiplex communication system highly resistant to external noise. To achieve the above object, there is provided in accordance with the present invention an automobile multiplex communication system, comprising: a plurality of control units mounted on an automobile body, said control units having respective circuits and respective connectors connected thereto; communication signal lines connected to said circuits through said respective connectors for multiplex communications between said control units; shield wires covering said communication signal lines between said control units and being electrically separate from said connectors and connected to ground; characterised in that said shield wires have respective ends grounded directly to a conductor of the automobile body outside said control units. Since the shield wires are grounded in electric isolation from the connectors by which the communication signal lines are connected to the circuits of the control units, external noise applied to the shield wires is prevented from being introduced into the communication signal lines through the connectors. Because external noise applied to the shield wires is prevented from being introduced into the communication signal lines through the connectors, the communication signal lines are sufficiently shielded against external noise, and hence the automobile multiplex communication system is highly resistant to external noise. Inasmuch as the shield wires are grounded closely to the connectors of the control units, external noise is prevented from being radiated through the shield wires in the vicinity of the connectors. Therefore, external noise is effectively prevented from being introduced into the communication signal lines through the connectors and nearby locations. The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example. FIG. 1 is a schematic view of a wiring structure for an automobile multiplex communication system according to a first embodiment of the present invention; FIG. 2 is a schematic view of a conventional wiring structure for an automobile multiplex communication system. As shown in FIG. 1, an automobile multiplex communication system according to a first embodiment of the present invention has a plurality of, e.g., three, control units (ECUs) 1 mounted on an automobile body (not shown). Each of the ECUs 1 has a housing 2 which accommodates a circuit 3 including a microcomputer or the like. Communication signal lines 4 comprising twisted pairs are connected to the ECUs 1 through connectors 5 mounted on the respective housings 2 for multiplex communications between the ECUs 1. The circuits 3 of the ECUs 1 have respective ground terminals G that are grounded to a conductor 6 of the automobile body. The communication signal lines 4 are covered with shield lines 7 which surround the communication signal lines 4 between the ECUs 1. The shield lines 7 are mounted on the communication signal lines 4 substantially the full length of the portions of the communication signal lines 4 which extend between the ECUs 1. The shield lines 7 have respective ends positioned closely to the connectors 5 of the ECUS 1, but electrically separate from the connectors 5 and grounded to the conductor 6 of the automobile body. In the automobile multiplex communication system with the above wiring structure, multiplex communications are carried out between the ECUs 1 through the communication signal lines 4. The shield lines 7 which cover most of the communication signal lines 4 are electrically separate from the connectors 5 by which the communication signal lines 4 are connected to the circuits 3 of the ECUs 1. The ends of the shield lines 7 which are positioned closely to the connectors 5 are directly grounded to the conductor 6 of the automobile body which is not susceptible to external noise. Therefore, even when external noise is applied to the shield lines 7, the external noise picked up by the shield lines 7 is reliably prevented from being introduced into the communication signal lines 4 through the connectors 5 that are positioned near the ends of the shield lines 7. Consequently, the automobile multiplex communication system is highly resistant to noise with respect to multiplex communications between the ECUs 1. Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the invention, which is defined by the appended claims.

Claims: An automobile multiplex communication system, comprising: a plurality of control units (1) mounted on an automobile body, said control units having respective circuits (3) and respective connectors (5) connected thereto; communication signal lines (4) connected to said circuits through said respective connectors for multiplex communications between said control units; shield wires (7) covering said communication signal lines between said control units and being electrically separate from said connectors (5) and connected to ground; characterised in that said shield wires (7) have respective ends grounded directly to a conductor (6) of the automobile body outside said control units.

Inventors: HASHIMOTO HIROSHI, NAGATANI YUJI, HASHIMOTO, HIROSHI, NAGATANI, YUJI
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1996
Main classification: B60R16
IPC codes: B60R16, B60R11, H04B3