In response to the national call for energy conservation and emission reduction, major automobile manufacturers have launched different types of new energy vehicles and applied advanced manufacturing technologies to convert the power source of vehicles from traditional fuels to electricity. The design and application plan of the high-voltage wiring harness of the whole vehicle mainly involves the direction of the wiring harness, the selection method of the path, the type of the high-voltage connector, the selection of the charging port, the shielding design, and the wiring groove design.

1　Wire Harness Design Scheme

1.1　High-voltage wiring harness design scheme

High-voltage wiring harness can provide high-voltage power for new energy vehicles, and its wiring harness design has extremely important significance. The following principles should be followed in the design process.

First, the direction and path design of the wiring harness. The high-voltage wiring harness design should adopt a dual-track system. At this time, the high-voltage electricity generated by the operating system has exceeded the tolerance of the human body, and the car body cannot be used as a grounding point for the whole vehicle.

Second, the selection of connectors. The connector is mainly connected to high-voltage current and is responsible for the safety of humans and machines in the operation of the high-voltage loop. Therefore, the designer should choose a high-voltage connector with high-voltage resistance, good waterproof effect, and tightly connected shielding layer.

Third, for shielding design. The designer should choose a high-voltage line with better shielding performance, and wrap the shielding net directly inside the high-voltage line. When installing the connector, it is necessary to ensure that the shielding layer is completely connected.

In addition, designers can start the design of high-voltage wiring harness from the following aspects: the rated value of the load line, the actual temperature of the wire conductor, the temperature of the surrounding air after the wiring harness is finished, the effect of the conduction rate when the wire is energized, and the bundled wiring harness Current reduction factor.

1.2　 low voltage wiring harness design scheme

The design plan can be divided into the following steps:

One is the way of designing the wiring harness;

The second is to choose the fixed buckle of the line;

The third is to carry out shielding design;

The fourth is to select the connector.

The low-voltage wiring harness based on this design scheme not only has the function of a traditional car, but also realizes the function of an electronic control unit module.

In the overall design process, designers should focus on the interference caused by high-voltage wiring harnesses, and follow the principle of configuring different low-voltage wires for different signal sources. High-voltage connectors can be divided into two types: shielded and unshielded. The internal structure of the unshielded connector is relatively simple, which saves the installation cost of the shielding function, and can be applied to parts that do not need the shielding function, such as the charging circuit, the inside of the controller, and the electrical appliance with a metal shell. Shielded connectors are the opposite, and are suitable for applications that require shielding functions such as high-voltage wiring harness connections. Any type of connector needs to have a waterproof function, and the connection position is different, and the waterproof level of the selected connector is also different.

1.3 　 high and low voltage wiring harness layout plan

This layout plan mainly involves the following links. The wiring harness layout scheme of the engine compartment belongs to the entire vehicle model, which is the difficulty and focus of the design work. It concentrates the connection wiring harness of the drive motor, PDU and other equipment; the cab, the design of this link is for the layout structure of the traditional vehicle; the luggage compartment, It involves wiring harness units of high-voltage lines, battery control systems, and vehicle-mounted systems.

2　 Selection and case analysis of shielded wires in low-voltage wiring harness layout

2.1　Layered wiring

When the low-voltage wiring harness is in a high-frequency signal, the designer should choose the twisted pair and foil layer shielding layer; when the low-voltage wiring harness is in a low-frequency signal, the designer should choose the twisted pair and the braided layer shielding layer.

In order to reduce the interference of the high-voltage wiring harness to the transmission of strong currents and avoid the risk of electromagnetic interference from the low-voltage wiring harness to the control unit, the layered wiring design of the high-voltage wiring harness and the low-voltage wiring harness is now carried out for pure electric vehicles, and the low-voltage wiring harness is 20cm at the bottom of the high-voltage wiring harness. about. After commissioning experiments, this design scheme can alleviate the interference of strong electric work.

2.2　 Parallel wiring

This scheme is more suitable for hybrid new energy vehicles. The designer connects the high-voltage wiring harness to the unit wiring range and makes it parallel to the wiring harness device of the engine, so that the overall operation system can avoid the influence of electromagnetic interference from the high-voltage wiring harness power supply.

2.3 　 case analysis

Case 1: The information reported by the motor temperature sensor is incorrect. Cause analysis: At this time, the high-voltage lines of the operating system are distributed in a loop, and the branch wiring harness of the temperature sensor can directly pass through the high-voltage area. The electromagnetic interference generated in the high-voltage environment will affect the normal operation of the sensor and display error messages.

Solution: Change the direction of the high-voltage line, apply a layered wiring method, and choose a braided shielded wire.

Case 2: High-voltage line wear caused by battery packs. Reason analysis: The position of the battery pack in the operating system is fixed, so the high-voltage line is always under the chassis of the vehicle body, causing wear and tear on the vehicle.

Solution: Use the bending pipe forming method to pass the high-voltage wire into the crimping plug-in after the metal conduit, so that it presents a curved structure at the wire passing part.

3　 EMC protection of new energy vehicles

3.1　The power distribution scheme for EMC protection of the whole vehicle

Whether it is a pure electric vehicle or a hybrid vehicle, it is powered by a power source to provide operating energy for the vehicle. How to realize the application of high-voltage wiring harness in the EMC protection design of the whole vehicle is a difficult problem faced by many designers. It can be seen in the EMC protection design of the vehicle that the radiation conduction design is the key research direction, so the designer should consider this factor at the beginning of the plan.

The design of the entire vehicle range first needs to consider whether each component meets the EMC standard, and then connect the various control units in the car operating system with a wire harness, and then apply a fixed protection method to connect the power supply loop and the grounding point together, and then complete The configuration of the protective power supply works.

3.2　The wiring harness design scheme for EMC protection of the whole vehicle

The wiring harness design needs to meet the overall layout of the car and the needs of man-machine construction engineering. For the high-voltage wiring harness arranged in the chassis part, the designer needs to apply a special configuration method, fully considering the vehicle's wading depth, chassis wear rate, and sand splashing. Conditions and other factors, and adopt the form of plastic trunking or metal elbow to improve the safety of the wiring harness, consider the feasibility of the trunking design method, and use the slot design method to fix the high-voltage wiring harness on the vehicle floor.

In the choice of wire harness manufacturing materials, in order to avoid electromagnetic interference, designers should choose twisted-pair wires and arrange the circuit loops of the twisted-pair wires on the outermost side of other wire harnesses in the system. Most of the current conducted and emitted by the wiring harness of the vehicle is related to the power cord. Therefore, designers need to observe the following precautions when designing EMC protection harnesses: handle the switching part of the power supply, and give priority to the loop control method in the structural design; if the circuit system involves sensitive signals, you need to select shielded wires The cable is used for transmission, and all-round lap processing is done in its shielding layer; if the distance between the signal cable and the high-voltage network and strong interference signals is long, the coupling wiring needs to be reasonably configured; filter Relevant work to reduce the inductance of the system leads; in the cable design, it is necessary to maintain a sufficient trust-to-ground ratio, and the designer needs to analyze the problems that may occur in the design process, and make reasonable arrangements and configurations as soon as possible. The designer can analyze and answer the above-mentioned questions as soon as possible to avoid the risks in the later design as soon as possible.

4　 Conclusion

Through the configuration of the new energy vehicle wiring harness design scheme and the study of EMC protection methods, the interference generated during the operation of the strong wiring harness has been effectively reduced. In addition, in the experiment of the loading platform and the actual vehicle experiment, the designer is constantly carrying out the configuration of the wiring harness. optimization. At present, the wiring harness design methods and EMC protection measures used in new energy vehicles have been widely recognized by the industry.