What is the crossbar assembly located under the rear floor of the car?
The lower crossbeam assembly of the car's rear floor can be understood as a transverse beam-like structure assembly installed beneath the rear floor of the vehicle and arranged along the width of the vehicle body. It is part of the bottom frame of the vehicle body and is usually composed of crossbeam frames, crossbeam plates, and various connecting components.
Its core function is to enhance the rigidity and collision safety of the vehicle body. When sitting at the bottom of the rear seat and stepping down, these transverse metal beams are hidden beneath the floor. They are cross-connected with the front and rear longitudinal beams and the threshold beams, transforming the bottom of the vehicle body into a grid-like structure. This not only enhances the rigidity of the vehicle body and reduces the ride bumpiness but also disperses and absorbs impact forces during a collision, protecting the occupants' safety.
Depending on different vehicle models and patent schemes, its structure and functions may vary:
Structure composition: Common schemes include double-layer crossbeam structures (such as the first and second crossbeams in BYD's patent), or an assembly structure consisting of crossbeam frames, crossbeam plates, and cable clamping components; some designs may also incorporate carbon fiber layers and polyamide fiber layers to enhance the fixation capacity.
Core function: In addition to enhancing structural strength and anti-side impact, anti-bending, and anti-compression performance, some components also integrate cable clamping functions, used for fixing wiring or providing installation support for rear seats.
Manufacturing process: The material is mostly high-strength steel formed by stamping, and in recent years, there have been aluminum alloy integrated die-casting schemes, which ensure strength while achieving lightweighting.
It should be noted that this belongs to the vehicle body structure component. If this component is damaged in a severe rear-end collision, professional equipment is required for correction during repair, and the strength of the repaired part usually cannot fully reach the original factory level.
The main functions of the lower crossbeam assembly of the car's rear floor are: to bear the vehicle body and seats, to enhance the overall rigidity and collision safety, and to integrate installation functions. It is equivalent to the "skeletal support" at the rear bottom of the vehicle, not a single beam, but a structure assembly consisting of crossbeams, longitudinal beams, and connecting components.
Bearing and supporting: The crossbeams connect the rear longitudinal beams on both sides to form a stable framework, used to bear the weight of the rear seats and occupants, and provide installation points for the rear subframe, suspension, and other components.
Enhancing the overall rigidity: The crossbeams can ensure the torsional stiffness and bending strength of the frame, reducing ride bumpiness and vehicle deformation, and helping with handling stability.
Collision safety and force transmission: In the event of a rear-end collision or side collision, the crossbeams and longitudinal beams work together to collapse and absorb impact forces, distributing them to other parts of the vehicle body, protecting the passenger compartment and the battery (especially for electric vehicles).
In addition, this assembly also integrates cable clamping components (for wiring fixation), seat installation brackets, and suspension installation points, facilitating assembly and wiring layout.
Please note: The design of the rear floor crossbeam of different vehicle models varies significantly. Electric vehicles and fuel vehicles, as well as the structural emphasis of the body-mounted and non-body-mounted types, are different. Specific details should be based on the actual vehicle.
When there is a fault with the lower crossbeam assembly of the car's rear floor, the core principle is: first, determine the extent of the damage, then decide whether to perform repair or cutting replacement， and such structural component repairs must be completed by professional repair shops or 4S stores. It is not recommended to handle it yourself.
This type of crossbeam belongs to the vehicle body structure component and plays a bearing and protective role in a collision. If the damage is not repaired properly， the strength will decrease， and the protection effect for the occupants in the next accident will be compromised. When dealing with the issue， mainly determine the type of damage：
First， determine the fault type
Minor deformation or dent： such as small-area scratches or dents， without cracking， can be restored through cold processing of sheet metal (hammering， suction pull) and have relatively less damage to the original vehicle's anti-corrosion layer.
Severe deformation， cracking， or rusted perforation： such as bending of the crossbeam due to a collision， or cracking of the weld points， or rust through， requires cutting the damaged part， welding a new piece， or using a beam alignment instrument to stretch and correct.
Serious accident damage: If the deformation affects the main load-bearing structures such as the rear longitudinal beam, or if the damage area is too large, it may be necessary to replace the entire section of the beam directly. This is a highly challenging repair that requires the use of original factory or components of the same quality.
General process of professional repair
If it is confirmed that repair is necessary, the regular process is as follows:
Assess damage: Use equipment such as body electronic measuring instruments to determine the deformation amount, twisting degree and crack situation of the crossbeam, and then formulate a plan.
Remove related components: Remove the rear bumper, rear panel, tail lights, suspension components, etc., to create an operation space.
Correct or cut: For severe deformation, use the beam correction instrument to pull it back to its original position; if it cannot be pulled back, precisely cut off the damaged part.
Welding repair: Perform full welding or plug welding on the cut area to ensure the strength of the weld seam and smooth the surface.
Anti-corrosion and rust prevention treatment: This is a very crucial step. Welding will damage the original anti-corrosion layer, so it is necessary to reapply anti-corrosion treatment, such as applying epoxy primer, applying sheet metal glue, filling the cavity with wax, etc. Otherwise, it is prone to rust from the inside later.
Painting and assembly: Reapply the paint and reinstall all the removed components.
Comprehensive inspection and positioning: After the repair, a four-wheel alignment must be performed, and the chassis, suspension and other systems must be inspected to ensure driving safety.
Special risks to be noted
The crossbeam is a safety structural component. After repair, the strength is difficult to fully restore to the original factory level, posing safety hazards. Generally, it is recommended to directly replace the damaged component. Do not try to repair it at an unprofessional small shop for the sake of low cost. If the welding process and rust prevention treatment are not done properly, it is prone to rust again or pose safety risks in the future.
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