JP2008227741A - On-vehicle communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make speed in relay processing of a relay connection unit in an on-vehicle communication system faster than that of a cut-through system. <P>SOLUTION: The on-vehicle communication system is provided with an ECU 30 connected to a CAN communication line 11 and a relay connection unit 20 for relaying a message frame 40 transmitted and received among ECUs 30 belonging to a different CAN communication line 11. The message frame 40 to be transmitted from the ECU 30 grants to a higher order bit of an arbitration field 42 a bus identifier 42a for indicating a CAN communication line 11 of transmission destination, and to a lower order bit following the bus identifier 42a a message identifier 42b for identifying the message. The relay connection unit 20 starts to perform transmission to the CAN communication line of the transmission destination when it has read the bus identifier 42a of the arbitration field 42 of the message frame 40 to be received. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an in-vehicle communication system, and more particularly, in an in-vehicle communication system that transmits and receives a message frame between electronic control units (ECUs) connected to different multiple communication lines via a relay connection unit. The unit relays message frames transmitted from the ECU at high speed.

In recent years, the number of electrical components and electrical devices mounted on a vehicle has increased rapidly as the functions and performance of the vehicle have increased, and the wiring in the vehicle has become more complex and larger.
Therefore, in order to suppress the increase in the number of wires in the vehicle, ECUs that control in-vehicle electrical components are divided into groups such as body systems for seats and doors, power train systems such as engines and throttles, and the like. ECUs belonging to the above are connected by multiple communication lines, and a relay connection unit (gateway unit) is interposed between multiple communication lines connected to different ECUs, and the relay connection unit relays communication between ECUs in the group. An in-vehicle communication system is employed.
In this way, a large number of ECUs mounted on the vehicle are classified into groups, and within each group, a multiplex communication line connected to the ECU is connected to the relay connection unit, thereby reducing the number of wires. The communication speed between the ECUs via the relay connection unit is increased.
In the above-described in-vehicle communication system, in each group, for example, when a message frame is transmitted from an ECU connected to the first multiplex communication line, the relay connection unit receives the message frame and relays the message frame. The message frame is relayed to the second multiplex communication line which is the transmission destination.

  CAN is becoming a standard communication protocol for in-vehicle communication systems. In the CAN protocol, specifications of message frames to be transmitted and received are defined in advance, and each message frame has an arbitration field in which a message identifier for identifying a message is described.

The relay connection unit that receives the message frame having the message identifier includes a routing map that describes the correspondence between the message identifier of the received message frame and the multiple communication line to which the transmission destination ECU for relay transmission is connected. .
Specifically, the relay connection unit receives the message frame and reads the message identifier in the arbitration field. Next, the destination communication multiplex communication line corresponding to the message identifier is determined with reference to the routing map, and the message frame is transmitted to the specified transmission destination multiplex communication line.

  As the number of electrical components mounted on the vehicle increases, the number of ECUs that control these electrical components also increases, and the number of message frames transmitted and received between the ECUs increases. This increases the burden of the relay processing in the relay connection unit. There is a problem of slow speed. Therefore, in order to speed up communication, it is desired that the relay connection unit relays message frames as fast as possible.

  As a relay processing method of the relay connection unit, for example, a store-and-forward method and a cut-through method are known as described in JP-A-9-162917 (Patent Document 1).

In the store-and-forward method, after the relay connection unit has received the message frame to the end, the message identifier is read from the arbitration field, the routing communication map is referenced to determine the multiplex communication line of the relay destination corresponding to the message identifier, This is a method for starting transmission on a multiplex communication line.
Since the relay connection unit has received all the message frames, if an error has occurred in the received message frame, the transmission of the message frame can be stopped by detecting the error. However, since the transmission to the other multiplex communication line has been started after the message frame is received to the end, the time from the start of the reception of the message frame to the start of transmission compared to the cut-through method described later Becomes longer.

On the other hand, in the cut-through method, when the relay connection unit receives up to the arbitration field in which the message identifier is written in the message frame, the relay communication unit refers to the routing map and determines the multiplex communication line of the relay destination corresponding to the message identifier. This is a method for determining and starting transmission to the multiplex communication line.
Even if an error exists in the message frame, the relay connection unit has already started transmission to another multiplex communication line when it receives the arbitration field, and therefore stops transmitting the message frame having the error. I can't.
However, since the transmission to the multiplex communication line is started without receiving the message frame to the end, the time from the start of the reception of the message frame to the transmission is shortened compared to the store & forward method, Relay processing can be speeded up.

Japanese Patent Laid-Open No. 9-162917

  However, even in the cut-through method that can increase the speed of relay compared with the store and forward method, in order to read out the message identifier, all the arbitration fields of the message frame must be received, and further, refer to the routing map. However, since it is necessary to determine the relay destination multiplex communication line corresponding to the read message identifier, there is room for improvement in order to shorten the relay processing time and increase the speed of the relay.

  The present invention has been made in view of the above problems, and an in-vehicle system that transmits and receives a message frame between ECUs connected to different multiplex communication lines by providing a relay connection unit in the multiplex communication line to which the ECU is connected. In the communication system for communication, it is an object to further increase the speed of the relay processing performed by the relay connection unit as compared with the conventional cut-through method.

In order to solve the above-mentioned problems, the present invention provides an in-vehicle device that includes an electronic control unit connected to a CAN communication line and a relay connection unit that relays message frames transmitted and received between the electronic control units belonging to different CAN communication lines. A communication system,
In the message frame transmitted from the electronic control unit, a bus identifier indicating the transmission destination CAN communication line is given to the upper bits of the arbitration field, and a message identifier for identifying the message is given to the lower bits following the bus identifier. ,
The relay connection unit provides an in-vehicle communication system characterized by starting transmission to a destination CAN communication line at the time of reading a bus identifier in an arbitration field of the received message frame.

  As described above, in the present invention, the message frame transmitted from the electronic control unit (ECU) uses the upper bits of the arbitration field as the destination bus identifier and the remaining lower bits as the message identifier. As a result, when the relay connection unit receives the message frame from the ECU, it first reads the bus identifier of the upper bits of the arbitration field, and at the time of reading, it can start transmission to the CAN communication line (bus) identified by the bus identifier. Thus, the relay processing time in the relay connection unit is shortened, and the relay is speeded up.

That is, when each message frame is transmitted, each ECU assigns a bus identifier indicating the destination CAN communication line to which the message frame is relayed to the arbitration field.
When the relay connection unit receives a message frame from each ECU, when it receives the bus identifier of the upper bit of the arbitration field in the message frame, it determines the CAN communication line of the transmission destination that relays the message frame from the bus identifier, Transmission to the destination CAN communication line is started.

As described above, since the relay connection unit can start transmitting the message frame to another CAN communication line at the time of receiving up to the upper bus identifier in the arbitration field, the relay connection unit starts transmitting the message frame after receiving all the arbitration fields. Relay processing can be performed faster than the conventional cut-through method.
In the cut-through method, the destination CAN communication line is determined by referring to the routing map based on the read message identifier. However, in the present invention, the destination CAN communication line is described in the bus identifier. The relay process can be performed at a higher speed without the process of referring to the routing map.
Furthermore, since it is not necessary to record the routing map in the memory of the relay connection unit, the memory capacity can be reduced.

In both the conventional store-and-forward method and the cut-through method, the relay connection unit is provided with a routing map to determine the CAN communication line to be relayed. When a message frame is transmitted while connected, or when a message identifier is changed even in a message frame transmitted by an existing ECU, the routing map of the relay connection unit must be changed each time. Therefore, it is difficult to change the design of the in-vehicle communication system.
Furthermore, since the ECU connected to the in-vehicle communication system is different for each vehicle type, a different routing map for each vehicle type must be set in the relay connection unit, and the part number of the relay connection unit increases.

  However, according to the present invention, since the message frame transmitted from each ECU is attached with the bus identifier describing the CAN communication line of the transmission destination, the relay connection unit does not need to have a routing map. The communication system design can be easily changed. Even if the ECU connected to the in-vehicle communication system is different for each vehicle type, it is not necessary to set a routing map for each vehicle type, so the relay connection unit can be shared.

The number of bits to which the bus identifier in the arbitration field of the message frame is preferably set according to the number of CAN communication lines connected to the relay connection unit.
That is, if the number of CAN communication lines is small, the number of bits can be reduced. If the number of CAN communication lines increases, the number of bits increases, but the number of bits to which a bus identifier is assigned is preferably 4 bits or less.
This is because if the number of bits of the bus identifier is 5 bits or more, it takes time for the relay connection unit to receive the bus identifier in the arbitration field, and therefore the relay processing cannot be performed at high speed.
If the bus identifier is 5 bits or more, since the arbitration field is 11 bits in the CAN standard format, the message identifier for message identification can take only 6 bits or less. This is because the message identifier must have a different value for each message transmitted on the CAN communication line, and the number of messages that can be handled on the CAN communication line is reduced.

Specifically, the bus identifier specifies a CAN communication line in advance for each bit, and represents “0” when relaying is necessary for the specified CAN communication line, and “1” when relaying is not necessary. .
With the above configuration, the relay connection unit determines “0 (dominant)” or “1 (recessive)” for each bit of the bus identifier, and transmits a message frame to the CAN communication line corresponding to the “0” bit. be able to. Therefore, the relay connection unit does not need to determine the transmission destination with reference to the routing map, and can perform relay processing at high speed.

  The bit specifying the CAN communication line that is the message frame transmission source is also set to “0”. However, the relay connection unit does not transmit the message frame to the CAN communication line that is the transmission source of the message frame.

  As described above, the CAN communication line is specified in advance for each bit of the bus identifier, and the message frame transmission destination and the transmission source CAN communication line are represented by “0” and “1”. Which other CAN communication line the message frame received from each connected CAN communication line is transmitted to can be determined by a combination of “0” and “1” of each bit of the bus identifier.

When performing a relay processing operation check test of a relay connection unit, in the conventional technology, the destination of the received message frame is described in the routing map, and the relay processing operation is performed for all message frames described in the routing map. Confirmation must be done. Since the message frame is transmitted from each ECU, the number of relay processes is enormous, and it takes time to perform an operation check test.
On the other hand, in the case of the present invention, it is only necessary to confirm the operation of relay processing for all combinations of “0” and “1” of each bit of the bus identifier, and the number of combinations is the number of relay processing described in the routing map. Since the number is significantly smaller than the number, the number of man-hours for the operation check test can be reduced.

  When a message that needs to be relayed to another CAN communication line and a message that does not need to be relayed to another CAN communication line are transmitted from a plurality of electronic control units connected to one CAN communication line, Each electronic control unit that transmitted the message performs arbitration by comparing the bus identifier of the arbitration field of the message frame transmitted by the electronic control unit with the signal level of the CAN communication line bit by bit, A message frame that needs to be relayed to the CAN communication line is preferentially transmitted.

  In addition, the electronic control unit connected to one CAN communication line transmits a message frame that does not need to be relayed to another CAN communication line, and at the same time, the relay connection unit receives from another CAN communication line. When the transmitted message frame is transmitted to the CAN communication line to which the electronic control unit is connected, each electronic control unit and the relay connection unit can arbitrate the message frame transmitted by the own electronic control unit or the own relay connection unit. The bus identifier in the field and the signal level of the CAN communication line are compared bit by bit to perform arbitration, and the relay connection unit preferentially transmits a message frame.

As described above, the bus identifier specifies a CAN communication line for each bit in advance, and is represented by “0” when relaying is required for the specified CAN communication line, and “1” when relaying is not necessary. The bit specifying the CAN communication line as the transmission source is also set to “0”.
By setting in this way, message frames that need to be relayed to other CAN communication lines from a plurality of electronic control units connected to one CAN communication line, and relays to other CAN communication lines are unnecessary. When message frames are transmitted at the same time, when each electronic control unit performs arbitration, the electronic control unit that always transmits a message frame that needs to be relayed to another CAN communication line transmits the message frame preferentially. be able to.

  Similarly, the electronic control unit connected to one CAN communication line transmits a message frame that does not need to be relayed to another CAN communication line, and at the same time, the relay connection unit is connected from another CAN communication line. When the received message frame is transmitted to the CAN communication line to which the electronic control unit is connected, if the relay connection unit and the electronic control unit perform arbitration, the relay connection unit always transmits the message frame preferentially. it can.

  As described above, according to the in-vehicle communication system of the present invention, a relay connection unit is interposed in a CAN communication line (multiplex communication line) to which an ECU is connected, and between ECUs connected to different CAN communication lines. In an in-vehicle communication system that transmits and receives a message frame, the message frame transmitted from the ECU has a bus identifier attached to the upper bits of the arbitration field, so the relay connection unit receives the bus identifier of the message frame received from the ECU. The message frame transmission can be started to the CAN communication line designated as the transmission destination at the time of reading. As described above, the relay process can be speeded up compared to the conventional cut-through method in which the transmission of the message frame is started after receiving all the arbitration fields.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 6 show a first embodiment of the present invention.
In the in-vehicle communication system 10 of the present invention, a bus composed of a plurality of CAN communication lines 11 conforming to the CAN protocol is connected to the relay connection unit 20, and each of the CAN communication lines 11 includes one or a plurality of electronic control units. (ECU) 30 is connected.
In the present embodiment, as shown in FIG. 1, four CAN communication lines 11A to 11D are connected to the relay connection unit 20, and the ECU 30A-1 and ECU 30A-2 are connected to the CAN communication line 11A and the CAN communication line 11B. , 11C, 11D are connected to one ECU 30B, 30C, 30D, respectively.

  The message frame 40 transmitted from the ECU 30 to another CAN communication line via the relay connection unit 20 includes a bus identifier 42a indicating the CAN communication line 11 of the transmission destination in its arbitration field 42. When the relay connection unit 20 receives the message frame 40 from the ECU 30, the relay connection unit 20 reads the bus identifier 42a described in the high-order bits of the arbitration field 42 of the message frame 40, and determines the destination CAN communication line 11 from the bus identifier 42a. Then, transmission of the message frame 40 received from the ECU 30 to the specified CAN communication line 11 is started.

The message frame 40 provided with the bus identifier 42a transmitted from the ECU 30 will be described with reference to FIG.
The message frame 40 has a 1-bit start-of-frame (SOF) field 41 indicating the start of the message frame, an arbitration field 42 including a bus identifier 42a and a message identifier 42b, and information related to control of the message length, etc. And a data field 44 indicating message contents to be transmitted and received.
The lower bits after the data field 44 include a CRC field (not shown), an end-of-frame (EOF) field of the frame, and the like.

  The identifier of the arbitration field 42 is composed of 11 bits. A bus identifier 42a indicating the transmission destination CAN communication line 11 is given to the upper bits, and a message identifier 42b for identifying the message is assigned to the lower bits following the bus identifier 42a. Has been granted. The least significant bit of the arbitration field 42 includes an RTR bit 42c.

The number of bits to which the bus identifier 42 a is assigned is set according to the number of CAN communication lines 11 connected to the relay connection unit 20. In the present embodiment, since four CAN communication lines 11 are connected to the relay connection unit 20, the bus identifier 42a is 4 bits, and the remaining lower bits are message identifiers 42b.
Further, the CAN communication line 11 is preset for each bit in the 4-bit bus identifier 42a. For example, the highest bit is specified as the CAN communication line 11D, the second bit is specified as the CAN communication line 11C, the third bit is specified as the CAN communication line 11B, and the fourth bit is specified as the CAN communication line 11A. Yes.

Next, a method for setting the bus identifier 42a will be described using the present embodiment in which the four CAN communication lines 11 are connected to the relay connection unit 20 as an example.
First, the bus ID of each CAN communication line 11 is set with 4 bits as shown in FIG. In the CAN communication line 11A, the least significant bit is “0”, and the other bits are “1”.
In the CAN communication line 11B, the third bit from the top is “0” and the other bits are “1”. The CAN communication line 11C is in the second bit from the top “0” and the other bits are “1”. In the line 11D, the most significant bit is “0” and the other bits are “1”.

Next, the bus identifier 42a is set as a logical product (and) of the bus ID of the transmission source CAN communication line 11 and the bus ID of the transmission destination CAN communication line 11.
Here, the CAN communication line 11 of the transmission source is the CAN communication line 11 to which the ECU 30 that transmits the message frame 40 is connected. The relay connection unit 20 receives the message frame 40 from the CAN communication line 11. The transmission destination CAN communication line 11 is the CAN communication line 11 through which the relay connection unit 20 transmits the message frame 40, and the ECU 30 that receives the message frame 40 is connected thereto.

An example of setting the bus identifier 42a is shown in FIGS.
The vertical column in the figure indicates the CAN communication line 11 of the transmission source, and the horizontal column indicates the CAN communication line 11 of the transmission destination.
FIG. 3B is a diagram showing the bus identifier 42 a when the relay connection unit 20 transmits to one CAN communication line 11. For example, when the transmission source is the CAN communication line 11A and the transmission destination is the CAN communication line 11B, the bus identifier 42a is “1100” which is a logical product (and) of the bus IDs of the CAN communication line 11A and the CAN communication line 11B. Become.
FIG. 3B also shows a case where the transmission destination and the transmission source are the same CAN communication line 11. In this case, the bus identifier 42 a is the same as the bus ID of the CAN communication line 11. When the transmission destination and the transmission source are the same CAN communication line 11, the relay connection unit 20 does not perform the relay process.

FIG. 3C is a diagram showing the bus identifier 42a when the transmission destination is two CAN communication lines 11.
For example, when the transmission source is the CAN communication line 11A and the transmission destinations are the CAN communication line 11B and the CAN communication line 11C, the bus identifier 42a is the bus ID of the CAN communication line 11A, the CAN communication line 11B, and the CAN communication line 11C. The logical product (and) is “1000”.
Note that FIG. 3C shows not only the case where the transmission destination and the transmission source are different, but also the case where there are two transmission destinations including the CAN communication line 11 of the transmission source.
In FIG. 3C, when the transmission source is the CAN communication line 11A and the transmission destination is the CAN communication line 11A and the CAN communication line 11B, the bus identifier 42a “1100” is the transmission source of FIG. 11A, which is the same as the bus identifier 42a “1100” when the transmission destination is the CAN communication line 11B.
When the transmission destination CAN communication line 11 includes the transmission source CAN communication line 11 in this way, the relay connection unit 20 has a CAN communication line 11 different from the transmission source among the two transmission destination CAN communication lines 11. However, the same CAN communication line 11 is not relayed.

FIG. 3D is a diagram showing the bus identifier 42a when the transmission destination is the three CAN communication lines 11.
For example, when the transmission source is the CAN communication line 11A and the transmission destinations are the CAN communication line 11B, the CAN communication line 11C, and the CAN communication line 11D, the bus identifier 42a is the CAN communication line 11A, the CAN communication line 11B, and the CAN communication line 11C. And “0000”, which is the logical product (and) of the bus IDs of the CAN communication line 11D.
3D shows not only the case where the transmission destination and the transmission source are different, but also the case where there are three transmission destinations including the CAN communication line 11 of the transmission source. Of the CAN communication lines 11 of the book transmission destination, relay processing is performed on the CAN communication line 11 different from the transmission source, but relay processing is not performed on the same CAN communication line 11.

Further, when the message frame 40 received by the relay connection unit 20 does not need to be transmitted to another CAN communication line 11, that is, not relayed to another CAN communication line, the CAN to which the ECU 30 that transmitted the message frame 40 is connected is connected. In the case of a message frame (referred to as a local frame) 40 used only on the communication line 11, the bus identifier 42a is the same as the transmission source bus ID shown in FIG.
A message frame that needs to be relayed to another CAN communication line with respect to the local frame is referred to as a CAN frame.

The bus identifier 42a to be set in the setting method is (1) the CAN communication line 11 to which the ECU 30 to which the ECU 30 transmits the message frame 40 is connected, that is, the relay destination of the relay connection unit 20. A bit for which a certain CAN communication line 11 is specified is “0 (dominant)”, (2) other bits, that is, a bit for which the CAN communication line 11 for which the relay connection unit 20 does not require relay is specified is “1 (recessive)”. (3) The bit specifying the CAN communication line 11 to which the own ECU 30 is connected is set as “0”.
The combinations of “0” and “1” that can be taken by the bus identifier 42a are any of the combinations shown in FIGS.

A configuration of the ECU 30 connected to each CAN communication line 11 will be described.
1, the ECU 30 includes a processing unit 31 and a transmission / reception unit 32. The processing unit 31 writes a transmission destination in the bus identifier 42a of the arbitration field 42 of the message frame 40 based on the setting method described above, and transmits / receives the transmission / reception unit. The message frame 40 is transmitted via the terminal 32.
Further, the message frame 40 transmitted from the other ECU 30 is received via the transmission / reception unit 32.
Further, when a plurality of ECUs 30 connected to the same CAN communication line 11 transmit the message frame 40 at the same time, arbitration of collision of the message frame 40 described later is performed.

The processing unit 31 is composed of, for example, a CPU and a memory such as a ROM and a RAM. The memory stores in advance which ECU 30 or the CAN communication line 11 the ECU 30 transmits the message frame 40 to. The CPU refers to the memory. Thus, the transmission destination is written in the upper bits assigned to the bus identifier 42a. In addition, the CPU reads and transmits the message frame 40 by reading the program stored in the memory.
The ECUs 30A-1, 30A-2, 30B, 30C, and 30D all have the same configuration.

  The relay connection unit 20 connected to the plurality of CAN communication lines 11 includes a relay processing unit 21 and transmission / reception units 22A to 22D respectively connected to the CAN communication lines 11 as shown in FIG. When the relay processing unit 21 receives the message frame 40 transmitted by the ECU 30 up to the bus identifier 42a of the arbitration field 42, the relay processing unit 21 reads the transmission destination of the message frame 40 from the bus identifier 42a, The message frame 40 is transmitted. The relay processing unit 21 includes, for example, a CPU and a memory such as a ROM and a RAM.

The operation of the in-vehicle communication system 10 will be described using the flowchart of FIG.
As an example, an operation in which the ECU 30A-1 connected to the CAN communication line 11A transmits the message frame 40 to the ECU 30B connected to the CAN communication line 11B and the ECU 30C connected to the CAN communication line 11C will be described.
In step S1, the processing unit 31 of the ECU 30A-1 reads the CAN communication line 11B and the CAN communication line 11C, which are transmission destinations of the message frame 40 to be transmitted, from the memory of the own ECU 30, and assigns them to the bus identifier 42a of the arbitration field 42. Write to 4 bits. As shown in FIG. 3C, the bus identifier 42a is “1000”.

In step S2, ECU 30A-1 transmits message frame 40 to CAN communication line 11A.
In step S3, the relay connection unit 20 receives the message frame 40 from the CAN communication line 11A.
In step S4, when the transmission / reception unit 32 of the relay connection unit 20 reads up to the bus identifier 42a “1000” in the arbitration field 42 of the message frame 40, the relay processing unit 21 is specified as a bit indicating “0”. The CAN communication lines 11A, 11B, and 11C are discriminated. Since the message frame 40 is transmitted from the CAN communication line 11A, it is determined that the message frame 40 is transmitted to the CAN communication lines 11B and 11C excluding the CAN communication line 11A.

In step S5, the relay processing unit 21 of the relay connection unit 20 starts transmitting the message frame 40 to the destination CAN communication lines 11B and 11C. Even if the reception of the message frame 40 is not completed to the end, transmission is started from the head SOF field 41. That is, the message frame 40 is received and transmitted.
In step S6, the ECUs 30B and 30C connected to the destination CAN communication lines 11B and 11C receive the message frame 40.

Next, with reference to FIG. 5, the time required for relaying the message frame 40 in the relay connection unit 20 will be described.
FIG. 5A is an explanatory diagram of the relay of the relay connection unit 20 according to the present invention. The time A is the time when the relay connection unit 20 starts to receive the message frame 40, and the time B is to the destination CAN communication line 11. This is the time when transmission of the message frame 40 is started.
The shorter the time T from time A to time B, the faster the message frame 40 is relayed.

In FIG. 5A, after receiving the message frame 40 at the time A, the message frame is received at the time B when the 1-bit SOF field 41 and the bus identifier 42a of the arbitration field 42 of the message frame 40 are received. 40 transmissions have started. In this embodiment, since the bus identifier 42a is 4 bits, the time for receiving a total of 5 bits is the time T1 from point A to point B.
The time T1 at which the relay connection unit 20 receives 5 bits is expressed by Equation (1) when the transmission speed of the CAN communication line 11 is 500 kbps.
T1 = 5 bits × (1/500 kbps) = 10 μsec (1)

FIG. 5B is an explanatory diagram of the relay of the relay connection unit 20 according to the conventional store-and-forward method, and transmission of the message frame 40 is started at time B when all the message frames 40 are received.
For this reason, the time for receiving the total number of bits of the message frame 40 is the time T2 from point A to point B. Assuming that the total number of bits of the message frame 40 is 111 bits, the time T2 is expressed by Equation (2).
T2 = 111 bits × (1/500 kbps) = 222 μsec (2)

FIG. 5C is an explanatory diagram of the relay of the relay connection unit 20 according to the conventional cut-through method. When the 11 bits of the arbitration field 42 of the message frame 40 are received, the transmission of the message frame 40 is started. Yes.
For this reason, the time for receiving a total of 12 bits including 1 bit in the SOF field 41 is a time T3 from the point A to the point B, and the time T3 is expressed by equation (2).
T3 = 12 bits × (1/500 kbps) = 24 μsec (3)

  As described above, in the store and forward method of FIG. 5B, the time T2 from time A to time B is 222 μsec, and in the cut-through method of FIG. 5C, time T3 from time A to time B is 24 μsec. In contrast, in FIG. 5A of the present invention, the time T1 from the time A to the time B is 10 μsec, and the message frame 40 can be relayed at high speed.

Next, the operation when the message frame 40 is simultaneously transmitted from the ECU 30 connected to one CAN communication line 11 will be described with reference to FIG.
When transmission of message frames to the same CAN communication line collides, arbitration is performed in which each ECU determines which message frame 40 of the collision message frames 40 is preferentially transmitted to the CAN communication line 11. . The message frame 40 for which priority is recognized by the arbitration is preferentially transmitted to the CAN communication line 11, and the message frame 40 with inferior superiority is transmitted again after transmission of the priority message frame 40 is completed.

  A message frame (CAN frame) 40 that needs to be relayed to another CAN communication line 11 and a message frame (local frame) 40 that does not need to be relayed to another CAN communication line 11 are simultaneously transmitted to the same CAN communication line 11 In this case, the message frame 40 that needs to be relayed is preferentially transmitted to the CAN communication line 11 by setting the bus identifier 42a of the arbitration field 42 as shown in FIG.

Arbitration of which message frame is preferentially transmitted when the message frame 40 is simultaneously transmitted to the one CAN communication line 11 will be described.
The ECU 30A-1 connected to the CAN communication line 11A transmits the CAN frame 40A-1 that needs to be relayed to the CAN communication line 11B, and the ECU 30A-2 connected to the same CAN communication line 11A receives another CAN communication line. A local frame 40A-2 that does not need to be relayed to 11 is transmitted as an explanatory example.

The bus identifier 42a of the CAN frame 40A-1 that needs to be relayed to the CAN communication line 11B is “1100” as shown in FIG.
As described above, the bus identifier 42a of the local frame 40A-2 that does not need to be relayed is “1110”, which is the same as the bus ID of FIG.
The processing units 31 of the ECU 30A-1 and the ECU 30A-2 detect the bus level (“0” or “1”) of the CAN communication line via the transmission / reception unit 32, respectively. The value of the bus identifier 42a is compared for each bit, and if the level is different, transmission of the message frame 40 is stopped.
The bus level of the CAN communication line 11A is “0” for each bit when one of the ECUs 30A connected to the CAN communication line 11A transmits the message frame 40 of “0”. That is, the bus level is the same as the logical product of each message frame 40 for each bit.

As shown in FIG. 6, the bus level of the first bit of the bus identifier 42a is “1”, and both the CAN frame 40A-1 and the local frame 40A-2 are “1”. Therefore, the ECU 30A-1 and the ECU 30A-2 Continues sending frames. The same applies to the second bit.
Next, in the third bit, the bus level is “0”, and the local frame 40A-2 is “1”. For this reason, ECU30A-2 stops transmission of local frame 40A-2. On the other hand, since the level of the CAN frame 40A-1 is “0”, the CAN frame 40A-1 is recognized as superior in arbitration, and the ECU 30A-1 continues to transmit.

Similarly, the CAN frame 40A-1 relayed to the other CAN communication line 11 is relayed to the other CAN communication line 11 regardless of the value of any bus identifier 42a shown in FIGS. The superiority is recognized in the arbitration with the unnecessary local frame 40A-2, and it is transmitted preferentially.
As described above, when the message frame 40 that needs to be relayed to another CAN communication line 11 and the message frame 40 that does not need to be relayed to another CAN communication line 11 are simultaneously transmitted to the same CAN communication line 11, the relay is performed. The message frame 40 that requires is always transmitted with priority.
When CAN frames 40 that need to be relayed to other CAN communication lines 11 are simultaneously transmitted from both ECUs 30A-1 and 30A-2 connected to one CAN communication line 11, the respective buses are transmitted. Arbitration is performed based on the setting value of the identifier 42a, and it is determined which one has priority.

In addition, a local frame 40 that does not require relaying from one ECU 30 connected to the CAN communication line 11 to another CAN communication line 11 is transmitted to one CAN communication line 11, and at the same time, another CAN communication line 11. Even when the message frame (CAN relay frame) 40 transmitted from the ECU 30 connected to the relay communication unit 11 is transmitted from the relay connection unit 20 to the CAN communication line 11, it is transmitted from the other CAN communication line 11 and the relay connection unit 20 The transmitted message frame 40 is preferentially transmitted.
For example, the ECU 30A-2 connected to the CAN communication line 11A transmits the local frame 40A-2 that does not need to be relayed to the other CAN communication line 11, and simultaneously transmits the CAN relay frame 40B transmitted by the ECU 30B to the relay connection unit 20 Is transmitted to the CAN communication line 11 communication line A, the following arbitration is performed.

The bus identifier 42a of the local frame 40A-2 is “1110” from FIG.
Considering the possibility that the CAN relay frame 40B is transmitted to the CAN communication lines 11C and 11D, the bus identifier 42a of the CAN relay frame 40B is any one of “1100”, “1000”, “0100”, and “0000”.
At this time, the local frame 40A-2 and the CAN relay frame 40B are simultaneously transmitted to the CAN communication line 11A, and the arbitration shown in FIG. 6 is performed. Even if the CAN relay frame 40B is any of the bus identifiers 42a, the arbitration is superior. Therefore, the data is preferentially transmitted to the CAN communication line 11A.

  Similarly, the message frame 40 transmitted from the other CAN communication line 11C or the CAN communication line 11D to the CAN communication line 11A is also superior in arbitration with the CAN frame 40A-1 that does not require relaying to the other CAN communication line 11. The message frame 40 relayed from the other CAN communication line 11 is transmitted to the CAN communication line 11 with higher priority than the message frame 40 that does not need to be relayed to the other CAN communication line 11.

  With the above configuration, a CAN frame that needs to be relayed to another CAN communication line 11 and a CAN relay frame that is relayed by a relay connection unit are relayed preferentially over a local frame that does not need to be relayed to another CAN communication line 11. It can be carried out.

It is a block diagram which shows the structure of the vehicle-mounted communication system which shows 1st Embodiment of this invention. It is a block diagram of a message frame. (A) shows the bus ID of the CAN communication line, (B) shows the bus identifier when the transmission destination is one CAN communication line, and (C) shows the case where the transmission destination is two CAN communication lines. (D) indicates a bus identifier when the transmission destination is three CAN communication lines, It is a figure which shows the flowchart of operation | movement of a vehicle-mounted communication system. (A) is explanatory drawing of the relay time of the relay connection unit of the vehicle-mounted communication system of this invention, (B) is explanatory drawing of the relay time in the store & forward system which is a prior art, (C) is a prior art. It is explanatory drawing of the relay time in a cut-through system. It is explanatory drawing of arbitration of a message frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 In-vehicle communication system 11 (11A-11D) CAN communication line 20 Relay connection unit 30 (30A-30D) Electronic control unit (ECU)
40 Message frame 42 Arbitration field 42a Bus identifier 42b Message identifier 43 Control field 44 Data field

Claims (6)

An in-vehicle communication system comprising an electronic control unit connected to a CAN communication line and a relay connection unit that relays message frames transmitted and received between the electronic control units belonging to different CAN communication lines,
In the message frame transmitted from the electronic control unit, a bus identifier indicating the transmission destination CAN communication line is given to the upper bits of the arbitration field, and a message identifier for identifying the message is given to the lower bits following the bus identifier. ,
The in-vehicle communication system, wherein the relay connection unit starts transmission to a destination CAN communication line at the time of reading a bus identifier in an arbitration field of the received message frame.   The in-vehicle communication system according to claim 1, wherein the number of bits to which the bus identifier of the arbitration field of the message frame is set is set according to the number of CAN communication lines connected to the relay connection unit.   The in-vehicle communication system according to claim 2, wherein the number of bits to which the bus identifier is assigned is 4 bits or less.   The bus identifier specifies a CAN communication line for each bit in advance, and represents “0” when relaying is required for the specified CAN communication line, and “1” when relaying is not required. The in-vehicle communication system according to any one of items 3.   When a message that needs to be relayed to another CAN communication line and a message that does not need to be relayed to another CAN communication line are transmitted from a plurality of electronic control units connected to one CAN communication line, Each electronic control unit that transmitted the message performs arbitration by comparing the bus identifier of the arbitration field of the message frame transmitted by the electronic control unit with the signal level of the CAN communication line bit by bit, The in-vehicle communication system according to any one of claims 1 to 4, wherein a message frame that needs to be relayed to a CAN communication line is preferentially transmitted.   The electronic control unit connected to the CAN communication line transmits a message frame that does not need to be relayed to another CAN communication line, and at the same time, the electronic control unit receives the message frame received from the other CAN communication line by the relay connection unit. When transmitting to a CAN communication line to which a unit is connected, each of the electronic control units and the relay connection unit, the own electronic control unit or the bus identifier of the arbitration field of the message frame transmitted by the own relay connection unit, The in-vehicle communication system according to any one of claims 1 to 5, wherein arbitration is performed by comparing the signal level of the CAN communication line for each bit, and the relay connection unit preferentially transmits a message frame. .

Images