The Layout Design of Can Harness of PHEV Vehicle

In this paper, CAN bus technology is applied to the design of automobile body wiring harness, and the overall structure of the whole vehicle system, CAN data transmission mode and control process are described in detail, and the node circuit design and wiring harness direction design are completed.

1 Foreword

The interaction effectiveness between modules of electric vehicle directly affects the driving efficiency and driving feeling of the vehicle. Plug-in hybrid vehicles can be divided into three categories according to the layout of electric drive system and engine power system: series, parallel and series-parallel hybrid. This paper discusses the scheme of parallel hybrid power system, which has the characteristics of modularization of the original vehicle technology, convenient implementation and wide applicability.

2 Operative Language

Node: a collection of devices connected to a communication network and able to communicate through the network according to a certain communication protocol.

Bus voltage: Bus voltage is the voltage of CAN _ H or CAN _ L of CAN bus to the ground of respective CAN nodes.

Design of CAN Bus Network Topology Structure

CAN bus is a multi-master bus. Once the bus is idle, any CAN node can send data to the bus. The node that sends messages first in the CAN bus channel depends on the lossless bit-by-bit arbitration, which can save the conflict time, especially in the case of heavy network load, and can run smoothly, ensure the utilization rate of the signal channel and improve the real-time performance of the whole system.

For the control system of plug-in hybrid electric vehicle, the whole vehicle control module (HCU), power system and safety system need to be layered and planned in detail.

Generally, there are many kinds of communication network topologies, and the branch lines are complicated and tedious, while the bus often has strong detection and correction ability, good implementation signal and guaranteed reliability, which can effectively judge the wrong nodes and automatically correct simple errors. Therefore, designing the communication network as a bus-type CAN network structure can meet the requirements of timeliness and reliability of information transmission. According to the principle of system hierarchical control, the topology diagram of parallel hybrid CAN communication structure is designed.

4 Harness Layout Design Principles

4.1 Wire Harness Requirements

The layout design of wiring harness requires multiple on-board ecus and off-line tools in the network.

For CAN harness design, the general requirements are as follows:

1) the total length of can bus is < 40m;

2) ECU spacing < 20m;

3) Number of ECU nodes < 20;

4) Shielded wire (high-speed CAN) or twisted-pair wire (low-speed CAN) is used for wiring harness;

5) The wiring harness requires the branch line to be as short as possible; The diagnosis node is directly connected to the bus, and the port length should be as short as possible, and the maximum length is required to be LM. The connection between diagnostic instruments from the connector should also be as short as possible, and the longest should not exceed 5m.

6) When laying out the wiring harness, the CAN line should be kept as smooth as possible to avoid the CAN line folding back. Ensure that the connection point of CAN _ H and CAN _ L is kept at the same position of the trunk line as far as possible when each branch line is connected with the trunk line. In principle, the node distance D between nodes is not allowed to be of equal length, so it should be as far away from power lines and signal lines as possible, and parallel wiring should be avoided as far as possible; 7) Do not arrange CAN bus near the interference source. If it can't be avoided, use shielded wire. When using shielded wire, the shielding layer must be grounded at either end (or the shielding layers at both ends are grounded).

In order to avoid the interference of cable power signal, the nodes of CAN network should be as close as possible to the trunk line. In practice, short branch lines should be used to connect with the bus as much as possible. In order to reduce standing waves, the ECU in CAN network should not be placed at equal distance, and the tail of the cable should not be all leads of the same length.

4.2 Terminal Resistance

Terminals can be placed adjacent to or in the two on-line ecus with the longest distance. Optional connection of non-terminal ECU. According to the standard requirements, the terminal resistance provided to the CAN bus is 60Ω, so the two farthest nodes on the CAN bus of the whole vehicle must each have a terminal resistance of 120Ω (between CAN _ H and CAN _ L is required).

The size of the terminal is required to be 110Ω-130Ω. Typical value: 120ω.

Common fault tolerance performance of 5-line can fault

The actual CAN detection circuit is more complicated. First, the fault types to be detected should be determined, and then the detection circuit should be designed according to the fault types.

6 Concluding Remarks

To sum up, according to the characteristics and functional requirements of the whole vehicle system of plug-in hybrid electric vehicle, the CAN communication system of the whole vehicle of plug-in hybrid electric vehicle is designed, and its network structure layout is determined on this basis. According to the types of communication nodes, the effective network topology diagram of the vehicle is designed, which effectively meets the design requirements of the vehicle for the network system and is of great significance to the further development of plug-in hybrid electric vehicle.