Internal wiring harness design and layout analysis of power battery
In recent years, with the increasing development of new energy vehicles, we actively respond to the call of national energy conservation and emission reduction, promotion and use of new energy, and development of circular economy. Auto manufacturers have launched their own new energy vehicle products, including pure electric vehicles and hybrid vehicles. And with the gradual improvement of technology, electric power has tended to replace the traditional fuel as the power source of cars. For the design and research of the wiring harness in the power battery pack of new energy vehicles, there are various design problems and the birth of new design concepts. The wiring harness in the battery pack serves as the signal transmission of the power battery and realizes the effective output of the power. The power consumption and mileage of the power battery in the battery pack are effectively monitored. In the design process, it also faces the test of design scheme, layout trend, EMC protection and other aspects.
1. Analysis of wiring harness design scheme
At present, the number and structure of modules and monomers in the battery pack are determined according to the preliminary design objectives of the new energy vehicle power battery pack. The cooling forms of the battery pack are divided into air-cooled battery pack and water-cooled battery pack. For the wiring harness design inside the package, different from the traditional gasoline vehicle wiring harness, there are high voltage wiring harness and low voltage wiring harness. Different forms of battery pack internal wiring harness design adopts different forms of design and layout scheme.
1. 1. High voltage wiring harness design scheme in battery pack
High voltage wiring harness mainly provides high voltage and strong electric power supply for new energy vehicles. Therefore, it is particularly important for the design and layout of wiring harness. It mainly follows the following principles:
1) wiring harness trend design: the high-voltage wiring harness design adopts the dual-track system. As the high-voltage has exceeded the human body safety voltage, the body cannot be used as the iron point for the whole vehicle, so the high-voltage wiring harness design inside the package must strictly implement the dual-track system for the dc high-voltage circuit. The high voltage wiring harness inside the package can be divided into high voltage total positive and high voltage total negative.
2) selection of high-voltage connector: high-voltage connector is mainly responsible for high-voltage high-current connection and transmission, and responsible for man-machine safety of high-voltage loop. Therefore, high-voltage wire harness connectors are currently used for high-voltage resistance, high waterproof level, loop interlocking, shielding layer connection and other functions.
3) shielding design: use shielded high-voltage wire, and the shielding network is covered inside the high-voltage wire. , connector connection to achieve the connection of the shielding layer. Considering the electromagnetic interference, the whole hv wire harness system is completely covered by the shielding layer.
4) high-voltage line layout:
Considering safety and electromagnetic interference, high-voltage and low-voltage wiring harness are separated and arranged.
1. 2. Design scheme of low-voltage wiring harness in battery pack
1. 2. 1. According to the working principle and design structure of the battery, the internal wiring harness is divided into:
1) BMU (BMS motherboard) wiring harness: the main function is responsible for battery status estimation (SOC SOP SOH, etc.), actuator control, thermal management strategy, high voltage safety, fault diagnosis and other main control functions of BMS.
2) LMU (BMS slave board) wiring harness: mainly responsible for single voltage, battery temperature collection and monitoring.
3) HCU (BMS high pressure plate) information collection wiring harness: high voltage collection, insulation monitoring.
4) high voltage relay coil control wiring harness: responsible for controlling on and off of high voltage circuit.
5) current sensor wire harness: hall sensor or shunt is available, mainly responsible for collecting current information.
6) PTC controller: control PTC for heating
7) solenoid valve: control the on and off of air conditioning pipe of battery pack.
8) interlocking plugs of various high-voltage connectors: high-voltage loop interlocking signal transmission.
The above wiring harness layout is designed separately from the high voltage wiring harness in the battery pack to effectively avoid EMC interference.
1. 2. 2. Fixed low-voltage wiring harness and selected buckle type in battery pack:
Limited by the environment and structure inside the battery pack, the wire harness fixing method is miniaturized, easy to assemble and simple depending on the fixed structure.
1. 2. 3 shielding design:
The low-voltage wiring harness is responsible for the functional realization of the strong electric control unit module and the transmission of relevant signals. In the design and layout of low-voltage wiring harness, the interference protection caused by high-voltage wiring harness is considered. Different signal sources adopt different low-voltage shielded conductors.
High frequency signal: twisted pair wire is used for wiring harness and foil layer is used for shielding layer.
Low-frequency signal: the wire harness is twisted pair and the shielding layer is braided.
1. 2. 4. Grounding form of shielded conductor:
Single point grounding: low frequency signal adopts single point grounding.
Multipoint grounding: high frequency signal USES multipoint grounding.
Ii. High and low voltage wiring harness layout scheme
In order to avoid high voltage wire transmission of high-voltage electrical current to produce electromagnetic interference, lead to low voltage wiring harness on the control unit the power supply and signal transmission risk by electromagnetic interference, so our pure electric vehicle power battery pack USES the high voltage wire and low voltage wiring harness a hierarchical and paratactic type design, the design scheme effectively avoid the interference from high voltage. The layout is shown in figure 1.
2. 1 layering arrangement: high-voltage wiring harness and low-voltage wiring harness are divided into upper and lower hierarchical relations.
2. 1. 1. Layering wiring
In the early stage of battery pack layout, stratified wiring is taken into account of the high-voltage power supply and low-voltage signal acquisition of the battery module. Series wiring between modules ensures that the high-voltage connection line is under the module, low-voltage signal acquisition and other related low-voltage control wiring are on the upper layer of the module. The layered wiring can effectively protect EMC interference caused by high voltage line. Ensure the stability of power supply and signal transmission in the battery pack.
2. 2. Parallel layout:
2. 2. 1. Parallel arrangement of internal structure of battery pack attached.
The high voltage wiring of the front-end module and the low voltage wiring of the BMS motherboard are arranged in parallel to ensure that the high and low voltage wiring harness is parallel without crossing. Effectively protect the EMC interference to the controller when high voltage wiring harness is working.
3. Fixed design of high and low voltage wiring harness 3. 1. Selection of fastener in battery pack of wiring harness: fastening fastener, fastening stud fastener and fastening belt.
3. 1. 1. The tie belt is mainly used for the high and low voltage wiring harness. Through connecting the front and rear plastic air ducts, the internal structure of the air duct is made to provide clip connection type tie belt buckle to fix the wiring harness. The duct body reserves mounting holes for fixed wiring harness assembly.
3. 1. 2. Stud type stud clip is mainly used for the front and rear end of the battery module below, sheet metal bottom welding fixed stud fastening belt fixed wire harness.
3. 1. 3. The binding band is mainly used to fix the wiring harness with the upper cover plate of the back-end module for LMU signal acquisition from the board and HCU signal acquisition.
Iv. Design and analysis of high-low voltage wiring harness principle in battery pack
The high-voltage wiring harness adopts the dual-track system design, connecting the front and rear modules of the battery pack in series, PTC inside the battery pack, air-cooled FAN
, high-power maintenance switch, charging pre-charging circuit and so on to the principle circuit. And through the battery pack front end high voltage connector to provide the vehicle power supply. The high voltage connector is shielded by the plug-in body, and the high voltage interlock function is added to effectively protect EMC interference caused by high voltage current.
The principle design of low-voltage wiring harness inside the battery pack is the same as the conductor and selection principle used in the traditional external vehicle wiring harness. The difference lies in that the wiring harness inside the battery pack mainly carries out signal collection and the sensor components related to monitoring inside the battery pack. At present, high temperature resistant wire, shielded wire, twisted pair, etc. All the collected information will be exchanged to BMU for power supply, battery package heat management, package heat dissipation, battery charge and discharge and other related control.
4. 1. Power distribution scheme of wiring harness EMC protection in battery pack
Firstly, EMC of components within the scope of the whole vehicle is guaranteed to meet the standard requirements. All control units are connected together by wiring harness connection. In terms of power distribution, the protection method adopted is that the power supply loop and the connection point loop are arranged in the same connector.
4. 2 wiring harness design for EMC protection in battery pack
In order to effectively prevent electromagnetic interference caused by excessive current in the wiring harness, twisted pair wires are generally used in the selection of wiring harness materials, and twisted pair circuits are arranged to the outermost side of other wiring harnesses. In terms of high-frequency signals, twisted pair wires can be shielded.
90% of the transmission emission in the vehicle wiring harness is related to the power cord, so the following aspects should be paid attention to in the wiring harness evaluation and design
1) switch power supply part processing, design consideration loop control.
2) sensitive signals shall be transmitted by shielded cables, and the shielding layer shall be well overlapped 360 degrees.
3) the signal cable is far away from the high voltage network and strong interference source, and tightly coupled with the ground reasonably.
4) do a good job in filter "iron" grounding treatment measures to reduce lead inductance.
5) ensure sufficient signal to ground ratio in the cable, and make reasonable arrangements and configuration.
4. Design and analysis of power line conduction transient disturbance protection
At the beginning of the design, the transient immunity of power line conduction should also consider the protection design of surge and pulse when the new energy vehicles work at high and low pressure.
4. Pulse interference protection
In the process of opening or closing the switch relay and fuse in the battery pack, due to the interference pulse generated by the arc, the protection considered in the initial wiring harness design is also required.
Through the development of new energy in the battery pack wiring harness design rationalization of wiring harness design and layout, as well as the principle of high and low pressure inside the battery pack the focus of the design phase of EMC protection, effectively avoid the interference generated in high voltage wiring harness, and through carrying platform, real vehicle certification, constantly optimize the wiring harness layout scheme and the design of EMC. The current wiring harness layout and EMC protection schemes and measures have been fully verified and recognized in batch production projects.