Body in White

    In the usual configuration, a body in white is an assembly of a frame and panels，madeup of homogeneous materials (for instance, steel or aluminum sheets or composites). Asan example, in Fig. 2. 1 a 3-door steel body and the frame of a 5-door aluminum body are shown.

    Many detachable components are fitted to the body, such as the so-called movableparts (e.g.doors, decklid，liftgate，hood，fuel filler flap and related locks and hinges)，external components（bumpers，windshield，windows，weather strips，grilles，spoilers，moldings，mirrors，lamps，windshield wipers，lamp wipers) and interior trim (instrumentpanel，seats, carpets，trimpanels，safety belts，airbags)，together constituting the vehiclebody.

    The chassis frame，the bearing structure of the vehicle，has to provide all mountingpoints for mechanical components and to carry on the complete body, which could beconsidered at that time as a dead weight. In addition，the chassis frame has to favor asound organization of the assembly work.

    A number of different configurations of the underbody can be identified：

    A) Unitized body or unibody, in which the chassis parts cannot be physically removedfrom the upper body parts. In this case，suspensions and other mechanical parts aredirectly fitted（using brackets) to body frame. The main advantage of such solution isrelatively low weight，while the main disadvantage is a lower dimensional precision ofsuspension attachment，due to body tolerance and the lower filtering performance ofsuspension fittings，reducing the insulation of vibrations due to road-wheel excitation.

    B) Body on frame, where the chassis frame is connected to upper body frame by boltswith or without the inter-position of rubber bushes. Such a solution offers the mainadvantage of allowing the adoption of one chassis for different body shapes，providingbenefits in terms of mechanical parts standardization and simplification of the assemblyprocess of a mechanical chassis, before being matched to the upper body. This kind ofsolution is commonly used for cargo vehicles，off-road and SUV. The main disadvantage isthe increased weight with respect to configuration A)．

    C) Body with ancillary subframes, for powertrain and suspension systems；connectionsbetween the subframe and the body can be either rigid or through elastic bushes. The mainadvantages are modularity and the division of the assembly process between parallel lines,enabling components to be mounted on the subframes. The resulting sub-assemblies canbe tested before integration with main body. Moreover, the relative ease in which elasticand damping devices between subframe and body can be inserted, provide an improvedinsulation from noise and vibration. Again, the main disadvantage is increased weight，butto a lower extent than configuration B).

    D) Dual frame body, in which body and chassis are separate and connected throughelastic and damping bushes. In this configuration, the structural，safety, propulsion anddriving functions are concentrated and optimized in the chassis，with priority to front andrear crash absorption, torsional stiffness and resistance to stress induced through thesuspension and powertrain attachments. The suspension articulation can be designed to beextremely stiff and precise，since the filtering of road-surface-induced excitation is achievedby incorporating elastic connections between chassis and body. The weight of upper bodycan be reduced, since the structural task is limited to its own inertial stresses and to thoseinduced by tiansported components，people and load.  The same chassis can also beadopted by different bodies of similar inertia properties. Although the increase of chassisweight remains a disadvantage, it is partially counterbalanced by the reduction in theweight of upper body.