Pickup truck three kinds of body structure: load-bearing, non-load-bearing, semi-loaded

Since 2019, China's pickup truck industry has undergone earth-shaking changes, and the new trend characterized by passengerization and diversification has become the leading idea in the industry. Under the new development pattern, domestic pickup trucks have gradually expanded outward from traditional non-load-bearing models, deriving highly passenger-oriented load-bearing models and relatively low-end semi-load-bearing models, and the three body structures correspond to different demand directions.

Non-loaded

The non-loader is the most commonly used body frame for pickup trucks and is also the most widely used design in the history of the automotive industry. Before the 1980s, almost all automotive products used non-load-bearing structures, and the bearing-bearing structure gradually became mainstream with the continuous development and improvement of the front-drive layout. The transverse front drive model significantly reduces the cost of large-scale production and makes the use of space more efficient. After the advantages of low cost and high comfort of the bearing structure are gradually revealed, the non-bearing structure gradually withdraws from the historical stage of passenger cars, but the advantages of anti-torsional rigidity and high load carrying capacity make it always the preferred structure for off-road vehicles, pickup trucks and other vehicles.

"Non-bearing" as the name suggests is the meaning of "not bearing", the frame body does not directly or completely withstand the impact, under the frame body there is an independent layout of the "girder" responsible for bearing the force from one direction, the power system and the walking system are integrated and installed on a frame, and then the frame as the base of the vehicle assembly, connected with the body. The non-load-bearing chassis generally adopts rectangular or trapezoidal style, the two longitudinal beams extend from the front to the rear, and the number and position of the beams vary according to the technical characteristics of each manufacturer. "Beam" is generally a stout steel "large square pipe", horizontal and vertical arrangement welded as a whole, with the continuous upgrading of manufacturing technology will use a considerable proportion of high-strength and ultra-high-strength steel, to provide enough strong torsional resistance and bearing.

The frame body of the non-load-bearing model and the independent girder are mostly flexible connections, and the impact force generated during off-road or heavy load mainly plays a role in the chassis girder, and some of the force will be transmitted to the frame body part through the shock absorption cushioning components, and the body mainly provides collision protection and cushioning energy absorption. Since most of the force is absorbed by the extremely strong chassis girder, and the frame body is flexibly connected, the body torsional deformation amplitude is very small, which can greatly reduce the force distortion and metal fatigue of the frame body, so that the vehicle can have sufficient stability, durability and safety when carrying out high-load movements.

Good non-loader models are not easy to build. First of all, the frame and the body are two independent systems, and the frame is a flat structure, the body is a cage structure, so the energy absorption and collapse of the upper and lower parts of the non-bearing vehicle in the face of various impacts are two different forms, if not well combined, it will inevitably lead to secondary injury. Secondly, the mechanical structure of the power system of non-load-bearing vehicles is more complex, and the components such as gearbox, rear axle, transmission shaft transfer box, front axle and front half shaft are mechanical structures, and at the moment when electronic components are popular, more mechanical structures mean high costs.

Bearer

Bearing type and non-load type is a relative concept, bearing type design eliminates the independent chassis, the frame is both the body and the chassis, completely relying on the frame body to withstand the impact and load of the undulating road surface, so the load type structure design is more difficult, the material strength, structural design requirements are higher. The bearing structure is mostly made of steel plate stamping, using multi-layer steel plate superposition to improve the overall strength, and using special geometry to differentiate the force to achieve the purpose of improving the flexibility and rigidity of the frame. Due to the cancellation of the independent girder design, the load-bearing body can effectively reduce the chassis, so that the engine, transmission, and suspension position are closer to the ground, so the use of the load-bearing body has more advantages in fuel economy and control face, and at the same time, it is also better in the utilization of space in the car.

The bearing structure gives the vehicle a high degree of integrity through flexible design, making the vehicle more suitable for driving on a road in good condition, providing sufficient comfort and safety protection for drivers and passengers, but the pursuit of flexibility is also doomed to have insufficient rigid structure to cope with the impact of not paved roads. Metal material is not worried about hard collision, but very worried about bending and twisting, bearing body due to the lack of rigid resistance structure, the face of impact can only rely on metal flexible pull resistance, high frequency non-equilibrium twisting will make the body steel plate metal fatigue, so that the bearing body light steel plate metal structure "become loose", that is, the vehicle will also appear with the use of "osteoporosis" phenomenon.

Nearly 90% of the failures of metal components and structures are caused by fatigue with cyclic stress amplitudes much lower than the tensile strength of the materials involved, and are often subject to a large amount of accumulated, irreversible damage during cyclic deformation. Mechanical parts under the action of alternating pressure, after a period of time, in the local high stress area to form a tiny crack, and then gradually expanded by the tiny crack to break, light will affect the driving quality of the vehicle, heavy may cause frame deformation. Fatigue damage has the characteristics of suddenness in time, locality in position and sensitivity to environment and defects, so fatigue damage is often not easy to be found in time and easy to cause accidents.

However, this does not mean that the bearing structure is completely isolated from the off-road environment, and although the gap between the physical structures is difficult to overcome through technical means, it can be infinitely close. As technology continues to evolve, so does the overall strength of the load-bearing body. For example, Ford's new small pickup truck Maverick uses a load-bearing body, its load capacity and towing level is not inferior to that of traditional pickup trucks, and Ford also plans to launch a high-performance off-road version of the car. The new Land Rover Defender has also changed its previous style, abandoning the previous girder structure and adopting a bearing structure, so in theory, as long as the body strength is large enough, then the load-bearing body can be very hard, and it can achieve both urban driving and off-road road conditions.

Semi-loader

Semi-loader body structure is rare nowadays, the concept is to embed the "chassis" in the frame of the load-bearing body, which belongs to the recessed girder, and the general model will be presented as a front suspension as McPherson, but the rear is a leaf spring. The purpose of this design structure is to achieve the effect of 1+1>2 using frame strength + low standard girder, and some microcards use this type of structure. The semi-load-bearing structure theoretically seems to be better than the non-carrier-bearing type, but in fact, the overall strength is slightly inferior, and the lack of frame vibration absorption and buffering forces leads to comfort that is not as good as the load-bearing model, and finally in addition to the relatively low production cost, there is not much advantage, so the semi-loaded type is not suitable for ordinary household vehicles, and the civilian field is only suitable for low-end tool vehicles.

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