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Chapter 1 General Design of Automobiles & tractors

1.1.1. Classification of Automobiles

An automobile (car or truck) is a self-propelled (motor) vehicle intended for transporting goods or people and for carrying out special tasks.

As tо purpose, motor vehicles are divided into transport vehicles, special-purpose vehicles, and competition vehicles. Transport vehicles are classed in several types:

1. cars – motor vehicles intended for carrying small groups of people (up to eight in number);

2. buses – passenger service vehicles designed for carrying large groups of people (more than eight in number);

(c) trucks – motor vehicles intended for carrying various cargos.

According to cargo (load-carrying) capacity, trucks are in turn divided into the following classes: pick-up trucks (up to 0.5t), light trucks (from 1 to 2t), medium trucks (from 2 to 5t), heavy trucks (from 5 to 15t), and overweight trucks (more than 15t). Trucks used to carry loose and sticky goods are equipped with tipping bodies and are referred to as dump trucks. Special-purpose vehicles, as their name implies, are intended for special work and are equipped accordingly. This group includes truck cranes, tank trucks, seed-filler trucks, etc. These are modifications of standard transport vehicle models. Competition vehicles are cars specially designed for racing.

As tо the type of chassis, motor vehicles may be either framed or frameless. Framed vehicles have a support structure, called frame, to which all the component parts of the vehicle are attached. Frameless (unit-construction) vehicles have no frame, and all their component parts are attached directly to the vehicle body. The body in this case is referred to as unitized.

As tо the prime mover, automobiles may be powered by carburetor engines, diesel engines, or electric motors. Carburetor engines operate mainly on gasoline (petrol), diesel engines run on diesel fuel, and electric motors are supplied from storage batteries. Accordingly, automobiles are divided into gasoline-powered, diesel-powered, and battery-powered types.

1.1.2. Classification of Tractors

A tractor is a wheeled or tracked self-propelled vehicle used as a power means for moving agricultural, road-building, and other machines equipped with special tools, and also for towing trailers. The tractor engine can be used as a prime mover for active (moving) tools or stationary farm machinery through the intermediary of the power take-off (PTO) shaft or belt pulley.

The uses of the tractor in agriculture are many, and so different types of tractor are needed to do different types of farm work. Farm tractors are classified as follows.

As to the purpose, modern farm tractors are classed in three groups: general-purpose (land utility) tractors, universal-row-crop (row-crop utility) tractors, and special-purpose tractors. Land utility tractors are used for major farm operations common to the cultivation of most crops, such as tillage, disking, general cultivations, harrowing, sowing, and harvesting. The tractors are characterized by a low ground clearance, increased engine power, and good traction, thanks to their wide tires or tracks enabling them to develop a high pull.

Universal-row-crop tractors are intended for row-crop work, as well as for many other field tasks. For this purpose, some row-crop utility tractors are provided with replaceable driving wheels of different tread widths – wide for general farm work and narrow for row-crop work. In order not to damage plants, the tractors have a high ground clearance and a wide wheel track that can be adjusted to suit the particular inter-row distance.

Special-purpose tractors are modifications of standard land or row-crop utility tractor models and are used for definite jobs (e. g., in vineyards, cotton fields) or for various jobs under certain conditions (e. g., on marshy soils, hillsides). Thus, special tractors used to mechanize the cultivation of cotton have a single front (steerable) wheel, swamp tractors are equipped with wide tracks enabling them to operate on marshy soils, and hillside tractors are designed to work on hillsides sloping at up to 16°.

As to the design of the running gear, tractors are divided into crawler (track-laying) and wheeled types. Crawler tractors are distinguished by a large ground contact area and therefore have a good track adhesion; they crush and compact the soil insignificantly. Such tractors show a high cross-country power and are capable of developing a high pull. Wheeled tractors are more versatile and can be used for both field and transport work, but their traction is lower than that of crawler tractors.

As to the design of the undercarriage, tractors may be framed, semi-framed or frameless. The body of framed tractors is essentially a riveted or welded frame, that of semi-framed tractors is made up of two short longitudinal beams (side members) bolted or welded to the rear axle housing, while in frameless tractors, the body is formed by bolting together the casings of individual tractor mechanisms.

As to the nominal drawbar (DB) pull, tractors are divided into several classes differing in design.