Road construction vehicles

Road construction vehicles classified in this category have a laden mass of less than three tones: this group is the main subject for this text. A wide range of different body shapes and sizes come into this light vehicle category these range from two-seater cars to personnel carriers (mini-buses) and small trucks.

Layout of components.

The layout of this vehicle, which is based on a minibus, is a comparatively simple construction. This is chosen to enable the reader to see the location, and study the duty, of each of the main components. Once this foundation has been established it will be possible to appreciate the finer details of the more sophisticated systems in common use.

Wheels.

Most light vehicles run on four wheels fitted with hollow rubber tyres filled with air under sufficient pressure to support the load they have to carry. These provide grip to the road and absorb shocks caused by small road irregularities. Larger shocks are taken by suspension springs and these allow the wheels to move vertically in relation to the rest of the Road construction vehicles.

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Front axle. This arrangement supports the front of the vehicle and is also used for steering. The axle is mounted on leaf-type springs to form the flexible suspension system needed to absorb the road shocks. Each wheel is carried on a stub axle: this is pivoted to the extremity to the front axle by a king pin. The two stub axles are linked together by steering arms which are joined together by a track rod and connected to a linkage coupled to the driver`s steering wheel.

On most modern light vehicles the one-piece axle beam has been superseded by a suspension arrangement that allows each front wheel to rise and tall with its own spring without affecting the other front wheel. This arrangement is called independent front suspension.

Rear axle.

This carries the wheels and supports the weight of the rear of the vehicle. The axle type shown is tubular in section and contains two axle shafts (half shafts), one for each side, to drive the roadwheels.

On the  Road construction vehicles centre line the axle is enlarged to house the final drive. This pair of gears turns the drive through 90 C and reduces the driving speed to that which is suitable for the size of the road wheels.

When the vehicle is turning a corner the inner and outer road wheels travel at different speeds. When the two road wheels are both rigidly connected to one axle shaft, the greater distance covered by the outer wheel causes one or both wheels to slip on the road.

Power unit. The normal source of power is provided by an internal combustion engine. The petrol (gasoline) engine is the most popular for its superior performance but if the vehicle is used extensively, the excellent fuel economy given by diesel (compression ignition) engine makes this type attractive. The economy feature of the diesel engine offsets the higher initial cost and slightly reduced output.{jcomments on}