1.2. Main Component Parts of Tractors & Automobiles
Both the tractor and the automobile are complex self-propelled machines consisting of separate interacting mechanisms and units that can be combined into certain groups.
The arrangement of the main component parts (groups of mechanisms) of the tractor is shown in Fig.1. Irrespective of particular design features, all tractors consist of engine 1, drive line 4, running gear 6, steering mechanism 2, working attachments 5, and auxiliary equipment 3.
The engine converts thermal energy into mechanical energy.
The drive line comprises a set of mechanisms which transmit the torque* developed by the engine to the driving wheels or tracks and change the driving torque both in magnitude and direction. The drive line includes the clutch, flexible coupling, transmission (gearbox) and rear axle.
The clutch serves to disconnect the engine shaft from the transmission for a short period of time while the driver is shifting gears and also to connect smoothly the flow of power from the engine to the driving wheels or tracks when starting the tractor from rest.
The flexible coupling incorporates elastic elements allowing connecting the clutch shaft and the transmission drive shaft with a slight misalignment.
The transmission makes it possible to change the driving torque and the running speed of the tractor by engaging different pairs of gears. With the direction of rotation of the engine shaft remaining the same, the transmission enables the tractor to be put in reverse.
The rear-axle mechanisms increase the driving torque and transmit it to the driving wheels or tracks at right angles to the drive shaft. In most tractors, the rear axle also comprises brakes.
In the wheeled tractor, as distinct from its crawler counterpart, the drive line includes the differential which enables the driving wheels to revolve with different speeds when making turns or running over a ragged terrain, at which time the left- and right-hand wheels must travel different distances during one and the same time.
crawler tractor;
wheeled tractor; 1 - engine;
2 - steering mechanism;
3 - auxiliary equipment;
4 - drive line;
5 - working (live) attachments;
6 - running gear
The running gear is needed for the tractor to move. The rotation of the driving wheels (or the movement of the tracks) in contact with the ground is converted into the translation motion of the tractor.
The steering mechanism serves to change the direction of movement of the tractor by turning its front wheels (in wheeled tractors) or by varying the speed of one of the tracks (in crawler tractors).
The working attachments of the tractor are used to utilize the useful power of the tractor engine for various farm tasks. They include the power takeoff shaft, drawbar (hitch device), implement-attaching (mounting) system, and belt pulley.
The tractor auxiliaries include the driver's cab with a spring-mounted seat and heating and ventilation equipment, hood, lighting equipment, tell tales (indicators), horns, etc.
Fig.2. Main component parts of the automobile
1 - driver's cab;
2 - cargo body;
3 - clutch;
4 - transmission (gearbox);
5 - propeller (cardan) shaft;
6 - final drive (driving axle)
The arrangement and purpose of the main component parts of the automobile (Fig.2) are in principle the same as those of the wheeled tractor. In the automobile, the drive line, running gear, steering mechanism, and braking system are referred to collectively as the chassis. The steering mechanism serves to change the direction of travel and the braking system, to slow down the running speed of the automobile or to stop it.
The auxiliaries of the automobile include a winch, cab heating and ventilation equipment, hitch bar, etc.
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* Torque is a moment of force which tends to produce rotation of a body. It is measured by multiplying the magnitude of the force by its arm, i.e., the perpendicular distance from the line of action of the force to the axis of rotation.