INTRODUCTION TO CHASSIS & FRAME
The chassis is connected to the road wheels through the medium of spring and axle and it is such medium which with the wheels and tyres constitutes the suspension system of any vehicle. Although the axle are an integral part of the suspension system. They also incorporate other functions i.e .steering in the case of front axle and final drive in the case of rear axle. In any suspension system the aim is to obtain maximum comfort to the driver and passengers with the minimum stress on the frame and springs. On this frame the body and the cab are fastened by bolts and nuts or by welding. The height of it is reduced or decreased method and suitable wheels and tyres are fitted at the ends of the axles.
TYPES OF CHASSIS
The chassis frame is the main structure of the vehicle. There are two types of chassis frame and they can be classified as
(a) Conventional Type. This type of frame is usually manufactured and fitted to the axle in order to form the structure of a vehicle. They are rectangular in shape and constructed mainly from two lengths of side member having channel or U section and interconnected with few cross members of similar section or tubular section such type of frame are still being used on some heavy vehicles and generally known as built up type chassis frame since the cross members are either bolted or riveted to the side members can be easily dismantled if necessary .the built up type chassis has been found unfit to use on light and faster vehicles.
(b) Mono construction Type. 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 rigidly. The pressed steel body is then welded to this structure, the whole forming integral unit.
MAINTENANCE OF CHASSIS
(a) Check the chassis visually and by listening the regular or irregular run of the chassis and moving parts.
(b) Check visually fixed parts of the vehicle for damage, defect or loosening.
(c) Check leakage of fuel and air pipe lines which are fastened with the chassis.
(d) Check the oil level (SAE-90) of front axle differential and top-up weekly.
(e) Check tyre pressure daily. Always check when the tyres are cool to avoid error, as pressure builds up due to high temperature of tyres on operation.
(f) Oil and grease are particularly harmful to rubber, paraffin being almost instantaneous in its effect any oil which may be thrown on the tyre should be removed at the earliest by a rag, dipped in a little petrol.
(g) Inspect tyres regularly for cuts, imbedded nails or stones chips and at times for fairly big stones imbedded between dual tyres.
(a) In Swept. The frame viewed from the plan is invariably tapered inwards towards the front of the vehicle. i.e .front ends of both the side members are brought closer than the rear. This is done in order to enable the front wheels, which are almost of the same distance apart as the rear wheel, to be steered to a greater angle without touching the frame.
(b) Up Swept. In order to keep the vehicle as low as possible and to allow the axle to be moved up and down due to the road irregularities, the front and rear of the both side members are given upswept in the form of an arc just over the front and rear axle.
(c) Dump Iron. Sometimes the front ends of the chassis side members are strengthened by riveted metal forging known as dump iron.
(d) Gusset Plate. Reinforcement plates used at the junction of two members (side &cross) to stiffen the joints.
(e) Bracing. This is the method of joining the side and cross members of the chassis frame this may be riveting or welding.
(f) Cruciform Chassis. The earlier frame 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 to the cruciform chassis. The cruciform bracing is formed from the two lengths of the channel section, each shaped in to a vide’ V ’and fastened together at the apexes by plates riveted or welded to the upper and lower flanges while the ends of the channels are fastened to the side members by either welding or riveted joint with Gusset plates.