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Automotive Architecture
Published in Patrick Hossay, Automotive Innovation, 2019
Nevertheless, overall, the body-on-frame approach has been superseded. The vast majority of today’s cars are manufactured as a unitized body, or unibody. The idea is to integrate the frame and body together, so the entire assembly serves as an integral load-carrying structure. The result is a more three-dimensional structure that offers improved structural geometry and can therefore forgo heavy beams and beefy cross-members. Eliminating the need for a heavy lower frame significantly reduces vehicle weight. And because the entire body can absorb the impact of a crash, it also offers improves safety. The overall structure also lends itself well to mass production, building on a stamped floor pan and welding on various panels to define the body. Suspension and drivetrain components connect with discrete structural modules, called subframes (Image 7.1). These connect at integrated hardpoints to spread the load of an axle or engine over a wide area of the body sheet structure, providing strength and NVH isolation. So, unibody construction is cost-effective, able to incorporate crash protection well, capable of accommodating a large and flexible cabin design, and lends itself well to mass production; and as a result, it has been nearly universal among major production cars for quite some time.
Car Body Structures
Published in Raghu Echempati, Primer on Automotive Lightweighting Technologies, 2021
The unibody design concept [3] uses a system of box sections, bulkheads, and tubes to provide strength to the vehicle (Figure 5.3). Unibody is a design technique that the body is integrated into a single unit with the chassis rather than have the body on frame. Unibody design is similar to monocoque design. Most modern automobiles are not pure monocoques; rather, they are unibody construction. In some cases, unibody and monocoque are interchangeable but according to a few views, there are slight differences. In monocoque construction, the outer shell (Class A surface) is actually part of the body structure whereas, in unibody construction, the Class A surface is not.
Tailoring the impact response of a spaceframe vehicle structure towards optimum crashworthiness
Published in International Journal of Crashworthiness, 2023
Sunday M. Ofochebe, Solomon C. Nwigbo, Samuel O. Enibe, Onyemazuwa A. Azaka, Ikenna J. Akuchi
Some conventional vehicles are produced based on the unibody (or integral body) structure due to some economic advantages it offers such as; weight reduction, drive energy efficiency and reduced manufacturing cost. In addition, unibody cars are considered safer compared to the alternative body-on-frame vehicles given that they allow the entire body to absorb crash energy, which gives the designer more flexibility in making decisions on how to redirect the impact energy away from the vehicle occupants. The spaceframe vehicle structure is a special class of unibody structure that uses high number of tubular frames to achieve high structural rigidity that may be needed in severe working environments [3]. Tubular spaceframes are preferred choice in structural applications that require high strength-weight ratio. They are widely applied in production of high-performance sports cars, racing vehicles, armoured vehicles, bridges, tunnels, roof trusses etc [4–6]. Vehicle structures are generally designed such that in a frontal crash, the front end undergoes full-plastic deformation to provide primary mechanism for impact energy absorption, making the impact less impulsive. Spaceframe vehicle structures are prone to two types of elastic instabilities when subjected to a heavy impact load: global and local instabilities. Global instability leads to bending collapse (or global buckling) and significant loss of load carrying capacity, while local instability triggers localised buckling which results in high energy absorption in favour of crashworthiness. Many ways to improve on the energy absorption characteristics of metallic tubes for crash energy management were reported recently in literature [7–10]. Previous related studies have shown that high number of frames applied in production of a spaceframe vehicle structure results in high structural rigidity which amounts to a great risk of high occupants’ acceleration in collisions involving rigid barriers. Therefore, a matching design effort is required to tailor the impact response of a spaceframe vehicle structure for improved structural crashworthiness.