A well-designed chassis frame along with the suspension system, steering and brake system prevent most of the accidents of the fast moving vehicles. The power unit of an automobile connected with the transmission system is generally mounted on a structural frame, which is fitted to the axles either directly or indirectly through the media of suspension system. On this frame, the body and the cabin are fastened by bolts and nuts or by welding. However the term chassis therefore, includes the power unit, transmission system, and suspension system, steering and brake systems so as to enable a vehicle to move on the road safely during the day or night time.
The chassis frame mounted on the axles carries the power unit, transmission system and certain parts of the suspension system. It also carries the body and the cabin in which certain amount of load is further carried to and fro. Depending on the method of mounting the chassis frame to the axles, the height is either reduced or decreased. There are two types of chassis frame and they can be classified as Conventional type and Mono construction type. In both the cases they are mounted on the axles and carry the operating units, body, driver’s cabin, etc., which are necessary for the vehicle to carryout its function as designed.
Various Types Of Frames
The Conventional Type. This type of frame is usually manufactured and fitted to the axles in order to form the structure of a vehicle. In the earlier types, they were plain and rectangular in shape and constructed mainly from two lengths of side members having channel or U section and interconnected with few cross members of similar section or tubular section. Such types of frames are still being used on some heavy vehicles and generally known as built-up chassis frame, since the cross members are either bolted or riveted to the side members and can be easily dismantled if necessary.
Frame. The term chassis although formerly used to refer to the frame only is now taken as the vehicle body to make it a self-propelling unit. The Frame is a special metal structure made of pressed steel, on which power plant, transmission, axles, suspension etc. are mounted.
The basis of all chassis construction is the frame and consists of two side members of channel or shallow ‘U’ section interconnected by similar or tubular section cross members either welded or riveted to the side members reinforced to the frame and also provide support for the engine and wheels. The frame is extremely rigid so that it can withstand the shock, blows, twist, vibrations and other strains to which is subjected. The side member of varying depth, is in general deeper towards the middle of the vehicle, where the bending tendency is greater due to the weight of the body and load components.
Cruciform Chassis. The earlier frames with plain cross members are found to be insufficiently strong in resisting forces tending to distort the frame along a diagonal from corner to corner. This lead to the introduction of the cruciform chassis. The cruciform bracing is formed from the two lengths of channel section, each shaped into a vide ‘V’ and fastened together at the apexes by plates riveted or welded to the upper and lower flanges, while the end of the channels are fastened to the side members by either a welded or riveted joint, with ‘Gusset Plates’. A further development of the chassis body or mono-construction in which the under frame or floor of the basic structure. Side member, cross member, floor and other components such as seat rails and suspension brackets are welded together as a complete assembly and most of larger components are dished or ribbed to add strength and rigidity. The pressed steel body is then welded to this structure, the whole forming integral unit.