Patent Publication Number: US-2006013267-A1

Title: Integrated branching network system

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention in general relates to an integrated branching network system and in particular relates to an art for reduction of distortions of a waveform at branching points existing on the network system.  
      2. Description of the Related Art  
      Vehicles are these days equipped with network systems for communication of signals for controlling various electronic equipments. Such a network system is typically provided with a main line and a plurality of nodes and branching points linking the nodes with the main line. Japanese Patent Application Laid-open No. 2000-151153 discloses an art of the network system. In these network systems, distortions of waveforms of data signals are investigated in certain cases and often cause occurrence of data errors.  
     SUMMARY OF THE INVENTION  
      The inventors had found out that particular branching points to which plural branch nodes are centralized and connected cause considerable impedance mismatches, which lead to the distortions of the waveforms. The present invention was accomplished in view of the finding and is intended for providing an integrated branching network system, which reduces distortions of a waveform at branching points existing on the network system.  
      According to a first aspect of the present invention, a network system is provided with: plural branch lines for respectively linking with nodes, each of the branch lines including a transmission line and a reception line; a branching point linked with the reception lines, the branching point including and being linked with a switching device for selectively establishing contact with one selected from the transmission lines and separating the others of the transmission lines, wherein the transmission lines are so regulated as to have characteristic impedances respectively matching with a total of characteristic impedances of the reception lines and a trunk line for linking the branching point with an external branching point.  
      According to the above constitution, a characteristic impedance of the transmission line matches the total of characteristic impedances of the plural reception lines and a main line. Thereby distortion of the waveform transmitted from the transmission node comes to be minimum. This leads to improvement in reliability of a data communication.  
      The transmission lines and the reception lines may be so configured as to satisfy an equation of Z 0 r=n·Z 0 , where Z 0  represents the characteristic impedances of the transmission lines, Z 0 r represents the characteristic impedances of the reception lines and n represents a number of the branch lines linked with the branching point.  
      According to the above constitution, quality of the impedance match at the particular branching point is further improved. This leads to improvement in reliability of a data communication.  
      The network system may be further provided with: plural second branch lines for respectively linking with second nodes, each of the second branch lines including a second transmission line and a second reception line; a second branching point linked with the second reception lines, the second branching point including and being linked with a second switching device for selectively switching on one selected from the second transmission lines and switching off the others of the second transmission lines, the second branching point linked with the branching point via the trunk line, wherein the transmission lines, the reception lines, the second transmission lines, the second reception lines and the trunk line are so configured as to satisfy equations of Z 0 r=2·x·Z 0  and Z 0 r=2·y·Z 0 , where Z 0 r represents the characteristic impedances of the reception lines and the second reception lines, Z 0  represents the characteristic impedances of the transmission lines, Z 0 r represents the characteristic impedances of the reception lines and the second reception lines, x represents a number of the branch lines linked with the branching point and y represents a number of the second branch lines linked with the second branching point.  
      According to the above constitution, quality of the impedance match is further improved particularly in a case where the first branching point and the second branching point are interconnected.  
      The nodes may be ECUs equipped on a vehicle.  
      According to the above constitution, reliability of a data communication between ECUs equipped on a vehicle can be improved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of an integrated branching network system in accordance with a first embodiment of the present invention;  
       FIG. 2  is a graph illustrating a waveform transmitted from a node;  
       FIG. 3  is a flow chart with respect to an operation of the network system; and  
       FIG. 4  is a block diagram of an integrated branching network system in accordance with a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A first embodiment of the present invention will be described hereinafter with reference to FIGS.  1  to  3 . A network system  1  in accordance with the first embodiment is provided with a branching part  4 , plural nodes  3  ( FIG. 1  exemplarily illustrates a case including n nodes  3 - 1  to  3 -n), branch lines  2  for respectively linking the nodes  3  ( 3 - 1  to  3 -n) with the branching part  4  and a switching device  5  included in the branching part  4 .  
      These nodes are for example respective ECUs (Electronic Control Unit) equipped in a vehicle.  
      Each of the branch lines  2  is composed of a transmission line  2   a  linking with a transmission part Tx of the node  3  and a reception line  2   b  linking with a reception part Rx of the node  3 . The plural reception lines  2   b  are interlinked at a point P 1  of the branching part  4 .  
      The plural transmission lines  2   a  are interlinked at a point P 2  via switching device  5 . More specifically, the transmission line  2   a  linking with the transmission part Tx of the node  3 - 1  links with the point P 2  via a switch SW 1  and the-transmission line  2   a  linking with the node  3 - 2  links with the point P 2  via a switch SW 2 . The same applies to the other nodes  3 - 3  to  3 -n. Moreover the point P 1  and the point P 2  are interlinked.  
      The branching part  4  uses the switching device  5  to control ON and OFF of the respective switches SW 1  to SWn by later described operation procedures.  
      Each of the transmission lines  2   a  has a characteristic impedance Z 0  and each of the reception lines  2   b  has a characteristic impedance Z 0 r. The characteristic impedance Z 0 r is regulated to be n times as great as the impedance Z 0 . More specifically, Z 0 r=n·Z 0 .  
      An operation of the network system of the present embodiment will be described hereinafter with reference to  FIG. 3 .  
      In a state that communications are established through the network system  1 , when the transmission node is established, switching of the switches SW 1  to SWn are accomplished correspondently to the transmission node.  
      In a case where the node  3 - 1  is established as the transmission node (a conditional branch step ST 2 : YES), the switch SW 1  is switched ON and the other switches SW 2  to SWn are switched OFF (Step ST 3 ).  
      Meanwhile, in a case where the step ST 2  is NO, the step moves to a step ST 4 . In case where the node  3 - 2  is established as the transmission node (a conditional branch step ST 4 : YES), the switch SW 2  is switched ON and the other switches SW 1  and SW 3  to SWn are switched OFF (Step ST 5 ).  
      In a case where the step ST 4  is NO, the step moves to a step ST 6 . If NO, the same steps are subsequently accomplished. If any of subsequent conditional branch steps is decided to be YES, a correspondent switch selected from the switches SW 3  to SWn is switched ON and the other switches are switched OFF.  
      Finally, if all the conditional branch steps are decided to be NO, namely all the nodes  3  are not in a transmission state, all the switches SW 1  to SWn are switched OFF (Step ST 10 ).  
       FIG. 2  illustrates a waveform of a transmission signal transmitted from the node  3 - 1  accompanied with an equivalent circuit of the network system  1  when the node  3 - 1  is established as the transmission node.  
      As described above, since each of the reception lines  2   b  has a characteristic impedance Z 0 r which is n times as great as the characteristic impedance Z 0  of the transmission lines  2   a,  a characteristic impedance of the transmission line  2   a  from the node  3 - 1  to the branching part  4  comes to be Z 0  and a total of characteristic impedances of the reception lines  2   b  beyond the branching part  4  similarly comes to be Z 0 . Thereby the impedances match with each other at the branching part  4 .  
      Because of the impedance match, as shown in  FIG. 2 , the waveform of the signal transmitted from the node  3 - 1  is transmitted to the respective nodes  3 - 2  to  3 -n as receivers without distortion.  
      As constituted in accordance with the above description, the network system  1  is provided with the plural branch lines  2  for respectively linking with the nodes  3 , which respectively have the transmission lines  2   a  and the reception lines  2   b,  so that any of the transmission lines  2   a  has a characteristic impedance matching with a total of characteristic impedances of the reception lines  2   b.  Therefore, a relatively great change in characteristic impedance at the branching part  4  can be prevented and distortion of the waveform passing through the branching part  4  can be prevented. This leads to improvement of reliability of data transmission.  
      A second embodiment of the present invention will be described herein after with reference to  FIG. 4 . A network system  11  is provided with a trunk line  12  and branching parts  14   a  and  14   b  respectively linked with both ends of the trunk line  12 . The branching part  14   a  is provided with plural (three in this example) nodes  13  ( 13 - 1  to  13 - 3 ) and branch lines  2  for respectively linking the nodes  13  with the branching part  14   a.  Similarly, the branching part  14   b  is provided with plural (three in this example) nodes  13  ( 13 - 4  to  13 - 6 ) and branch lines  2  for respectively linking the nodes  13  with the branching part  14   b.    
      Each of the branch lines  2  of the branching parts  14   a  and  14   b  is composed of a transmission line  2   a  linking with a transmission part Tx of the node  3  and a reception line  2   b  linking with a reception part Rx of the node  3 . The reception lines  2   b  linked with the nodes  13 - 1  to  13 - 3  are interlinked at a point P 11  and the reception lines  2   b  linked with the nodes  13 - 4  to  13 - 6  are interlinked at a point P 12 . The points P 11  and P 12  are interlinked via the trunk line  12 .  
      The branching parts  14   a  and  14   b  are respectively provided with switches SW 11  and SW 12 . The switch SW 11  is linked with the point P 11  and configured to selectively establish contact with any of the transmission lines  2   a  linked with the nodes  13 - 1  to  13 - 3 . Similarly the switch SW 12  is linked with the points P 12  and configured to selectively establish contact with any of the transmission lines  2   a  linked with the nodes  13 - 4  to  13 - 6 . The network system  11  is capable of establishing data communication between any transmitting node and the other receiving node by switching the switches SW 11  and SW 12  so as to switch link among the transmission lines  2   a  and the reception lines  2   b.    
      Each of the transmission lines  2   a  linked with the nodes  13 - 1  to  13 - 3  has a characteristic impedance Z 0  and each of the reception lines  2   b.  linked with the nodes  13 - 1  to  13 - 3  has a characterisitic impedance Z 0 r. The characteristic impedance Z 0 r is regulated to be 2-x times (three times in this example) as great as the impedance Z 0 . More specifically, Z 0 r=2·x·Z 0 .  
      Similarly, each of the transmission lines  2   a  linked with the nodes  13 - 4  to  13 - 6  has a characteristic impedance Z 0  and each of the reception lines  2   b  linked with the nodes  13 - 4  to  13 - 6  has a characterisitic impedance Z 0 r. The characteristic impedance Z 0 r is regulated to be 2·y times (three times in this example) as great as the impedance Z 0 . More specifically, Z 0 r=2·y·Z 0 .  
      Moreover, a characteristic impedance Z 0 _trunk of the trunk line  12  is regulated to be 2 times as great as the impedance Z 0 , more specifically, Z 0 _trunk=2·Z 0 .  
      An operation of the network system of the present embodiment will be described hereinafter. A case where the node  13 - 1  transmits a data is supposed. In this case, the switch SW 11  of the branching part  14   a  is switched to establish contact with the transmission line  2   a  linked with the node  13 - 1 . The characteristic impedance of the transmission line  2   a  is Z 0 .  
      Since the characteristic impedances Z 0 r of the respective reception lines  2   b  are 2·x·Z 0  (provided x=3) and the characteristic impedance Z 0 _trunk of the trunk line  12  is 2·Z 0  as mentioned above, a characteristic impedance beyond the point P 11  from the view of the transmitting node comes to be Z 0 . Therefore the impedances match with each other at the branching part  14   a  and hence a waveform of the signal transmitted from the node  13 - 1  is prevented from distortion. The same applies to any case where any of the nodes  13 - 2  and  13 - 3  transmits a data.  
      Moreover, in any case where any of the nodes  13 - 4  to  13 - 6  branched from the branching part  14   b  transmits a data, a characteristic impedance beyond the point P 12  from the view of the transmitting node comes to be Z 0  and hence distortion of a waveform can be prevented. Thereby, reliability of data transmission between any transmitting node and the other receiving node can be ensured.  
      As constituted in accordance with the above description, the network system  11  is provided with the branching points  14   a  and  14   b  so that distortion of the wave format the branching points  14   a  and  14   b  is effectively prevented even though the branching points  14   a  and  14   b  are interlinked via the trunk line  12 . This leads to improvement of reliability of data transmission.  
      Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings.  
      For example, the number of the branching points is not limited to be one as the first embodiment or two as the second embodiment. Three or more branching points may be included in the network system under a condition that characteristic impedances of transmission lines, reception lines and trunk lines are so regulated as to match with each other at the respective branching points.  
      Moreover, the above description are given with an example that the nodes are ECUs equipped on a vehicle, however, the above embodiments can be applied to any other communication device.