Engineering Machinery Electrical Wire Harness Assembly

As users of construction machinery have higher requirements for operational comfort, energy saving, and safety, the electrical systems of construction machinery are gradually moving closer to the characteristics of automotive electrical systems. The layout of the wire harness should be fully considered during the wiring harness design stage of the complete machine electrical system. After the electrical components of the entire machine are selected, a comprehensive consideration is given to the layout of the electrical components based on the specific conditions of the vehicle body structure. After the electrical device layout is completed, the wiring design is carried out. Considering possible problems during the assembly process of electrical components and wiring harnesses, the installation positions of electrical components need to be adjusted accordingly after product trial production to ensure a reasonable layout of the electrical system of the entire machine.

Electric power engineering vehicle wiring harness

Design engineering vehicle wiring harness

Automotive audio system wiring harness

The overall direction of the wiring harness is reasonable and the appearance is neat:
The wiring harness of engineering machinery should be routed along the inner side of the frame, beams and other fixed positions of the body (the wiring tube or wiring trough designed on the frame). Avoid squeezing force on the wire harness or friction and interference of moving parts.
The main line layout direction should be horizontal and vertical in the projection direction, and the H-shaped wiring structure can be used to reduce the length of the wire harness. The wiring harness layout should be consistent with the pipelines and surrounding components.
The gaps are even and reasonable to achieve a neat appearance.

The wiring harness fixing points are reasonably arranged and fixed reliably:
According to the actual installation position of the wire harness on the vehicle, protection is provided to prevent the wire harness from sagging due to its own weight, axial movement due to vibration, and passing through sharp edges on the vehicle body. Reasonable and sufficient fixing points must be established to fix the wiring harness.
Set fixed points according to the direction of the wire harness and the specific structure of the car body. The bending radius of the wire harness at the bend (measured according to the inner arc of the wire harness) should not be too large. Refer to Table 1 for principle layout.
The distance between two fixed points on a straight line without a fulcrum is generally not greater than 300mm. In order to prevent interference caused by the inflection point of the wire harness, a fixed point must be set at the inflection point. Two fixed points need to be set at the right-angle inflection point, and the position of the fixed points should be within 100mm from the inflection point. A fixed point can be set for the obtuse-angle inflection point in this range, but it must be ensured that there is no interference after the wiring harness is installed, and the occurrence of acute-angle inflection points should be avoided.
Set a fixed point on the main line where the fulcrum exists, and the distance between the fixed point and the fulcrum should not be greater than 100mm. The connectors connected to other wire harnesses should be fixed on the car body, and a fixing point should be set at a suitable location no larger than 100mm in front of the connectors.
Select the fixed wire clip according to the size of the wire harness, and mark the wire clip fixing point on the wire harness. In order to standardize the fixed position of the wire harness, guide assembly operations, and improve assembly efficiency, the fixed points can be marked by pre-winding tape on the wire harness. The tape can be chosen in easily identifiable colors such as white or red to facilitate identification during assembly operations (Figure 1). During the three-dimensional wiring stage, the fixed points are pre-marked, and during the assembly and trial production stage, the wire harness structure and fixed points are optimized again based on assembly maneuverability.

The wiring harness should avoid interference with surrounding components:
1) After the wiring harness is fixed, it should not be in direct contact with the sharp edges of the car body. First, there should be a gap between the wire harness and the sharp edges and corners. The second is to increase the protection of the wiring harness to prevent the sharp edges of the car body from damaging the external insulation layer of the wiring harness, causing short circuit accidents.
2) The reserved length of the wire harness installed on the vibrating components (engine, vibratory roller frame, etc.) should be determined based on the amplitude of the vibrating components. Avoid virtual connections in internal contacts due to vibration transmitted by the wire harness, and try not to set the fixed point of the connector on the vibrating component.
3) The wire harness installed in the high-temperature area of the engine accessories should consider the high-temperature resistance characteristics of the wire harness, and the wire harness should be designed according to the reference standard: QC/T29106-2004 (Table 2). The engine wiring harness should be arranged on the low temperature side of the engine. The distance between the wiring harness and the exhaust manifold should be greater than 50mm, and the distance from the engine parts with a temperature greater than 150°C should be greater than 50mm.
4) The wiring harness does not use the same fixed points as the engine fuel pipeline, especially the wiring harness connection part and the oil line connection part, and does not cross or contact the fuel pipeline. The wiring harness should be routed to the upper side of the fuel line. Avoid line surface damage, short circuit, oil leakage or evaporation density that may cause fire when certain conditions are reached.

The assembly process and maintenance process of wire harness:
1) Do not pull the wire harness too tight during assembly (especially on moving parts such as work equipment). The reserved length of the wire harness in the moving parts should ensure that the wire harness does not bear tension or extrusion when the component moves to the extreme position. After the wiring harness is assembled, there should be enough clearance around it, especially near the working device and control system. The gap between the wire harness and adjacent moving parts should be greater than 25mm to ensure that it is not squeezed by other parts or pulled by the control link, etc. Avoid wiring harness insulation layer Figure 1 Bulldozer floor frame wiring harness being pinched, worn or broken to cause grounding and other faults.

2) In order to facilitate inspection and maintenance, the connectors are arranged in an easy-to-operate position. If the installation space of the electrical device is sufficient, the wiring harness can be directly plugged into the electrical device. If the installation space is small and the location is concealed, the wires of the electrical components need to be lengthened appropriately so that the connectors connected to the wiring harness are arranged in a location that is convenient for installation and maintenance. The connectors should be arranged as horizontally as possible and should not be arranged in rainwater gathering areas or outside the vehicle body to avoid direct contact with external environments such as rainwater and oil. When it must be arranged in the above-mentioned areas, protective measures must be taken, such as waterproof plug-ins, rubber plugs or rubber sleeves, etc. to prevent water from entering the plug-in and oxidizing the terminal surface.

3) When arranging the wire harness in the instrument box, determine the length of the reserved wire harness according to the installation depth of the instrument, the position and direction of the plug interface, and the space from the rear panel after installation. Considering the convenience of operation, the space in the plugging direction must be greater than 2 times the length of the plug, and a certain length must be reserved for the wiring harness.

4) The wiring harness hole must be larger than the size of the largest connector that needs to pass through, and the wiring hole should be designed with rubber protective parts such as rings. If passing through the sheet metal hole from the cab to the outside, the external wire harness must be lower than the wire passing hole, and corresponding rubber protection and seals must be designed to avoid vibration and wear of the hole. Avoid dripping or spilling liquid on the wiring harness, and the possibility of liquid entering the vehicle interior.

Other notes:
1) There must be a gap of no less than 20mm between the battery positive terminal and the electrical compartment cover, and the gap between the battery positive cable and moving parts must be more than 25mm. Avoid short circuit causing instantaneous large current discharge of the battery, causing the battery to explode. The positive terminal of the battery must be equipped with an insulating plastic protective cover or other protective measures that are not easily deformed, and at the same time ensure that the protective measures are not easy to break away. The negative terminal of the battery must be connected to the vehicle body separately. The negative terminal must be fixed with bolts or nuts, and the terminals must be free of paint and corrosion.
2) To avoid interference, instrument signal lines, engine control module signal lines, etc. should be kept away from sources of electromagnetic interference (speakers, starter motors, etc.)). Also keep high current cables (engine starter harness) as far away as possible. At the same time, the signal lines use twisted pairs and multi-layer shielded lines to effectively prevent electromagnetic interference.
3) The grounding point should be arranged on large structural parts such as the chassis or car body, but it should avoid rainwater gathering areas or the outside of the car body to prevent poor contact due to corrosion of the grounding point. The grounding point should also be away from the fuel pipeline to avoid safety hazards caused by fuel leakage. At the same time, before connecting the ground wire, check to ensure that there is no paint or rust on the ground point to prevent poor contact.
4) Ensure the convenience of replacing fuses and relays for frequently used electrical appliances. The fuses and relays are arranged in the fuse box so that they are easy to find and replace. For electrical appliances that are used frequently, work for a long time, and have large load currents, the distance between fuses and relays should be appropriately increased when arranging them. Or arrange them at intervals with fuses and relays that are used less frequently, work for a short time, and have a small load current. Avoid heat accumulation and slow dissipation, causing local temperature rise and reducing the performance and life of fuses and relays. At the same time, the rise in temperature will also cause the fuse box body to deform and carbonize, reduce the position accuracy of the installation parts, and increase the contact electricity. This will further cause the heat generation of fuses and relays to increase, and the fuse box will be scrapped.

Conclusion
The harsh working environment and changing working conditions cause frequent failures in the electrical system of construction machinery. Reasonable wiring harness layout and standardized assembly operations are important measures to improve the reliability of electrical systems. Different construction machinery should combine their unique working environment and structural characteristics, use three-dimensional wiring for wire harness layout design, and follow the above basic principles to rationally arrange wire harnesses and standardize assembly operations. Improving the craftsmanship of wire harness assembly and later maintenance during the product trial production stage can effectively improve the rationality and reliability of the electrical system.