UNIT I CLASSIFICATION AND REQUIREMENTS OF OFF ROAD VEHICLES

Transcription

1 UNIT I CLASSIFICATION AND REQUIREMENTS OF OFF ROAD VEHICLES INTRODUCTION It is a common fact that we find a wide variety of construction machines on every construction sites, which make the construction jobs easy, safe and quicker. Depending on the application, construction machines are classified into various categories which we are discussing here. A. Earthmoving equipments B. Construction vehicles C. Material handling equipments D. Construction equipments Vehicle power plant

2 There are two limiting factors to the maximum tractive effort of the vehicle: Maximum tractive effort that the tire-ground contact can support Tractive effort that the maximum torque of the power plant can produce with the given driveline gear ratios. The smaller of these factors will determine the performance potential of the vehicle. Usually it is the second factor that limits the vehicles performance. The classification of various types of power plants used in a vehicle is shown in Figure Figure 1: Classification of vehicle power plat In selecting a suitable power plant, the following factors are considered: Operating performance Economy Environment friendliness For vehicular applications, the ideal performance characteristic of a power plant is constant power output over the full speed range. Consequently, the torque varies hyperbolically with respect to speed as shown in Figure 2. This ideal performance characteristic of the power plant will ensure that the maximum power is available at any vehicle speed, thus resulting in optimal vehicle performance. In practice however, the torque is constrained to be constant a low speeds. This is done so as not to be over the maxima limited by the adhesion between the tyre -ground

3 contact areas. The internal combustion (IC) engines are the most commonly used power plants for the land vehicles. In hybrid and electric vehicle technology, the electric motor is used. Figure 2: Ideal performance characteristics for a vehicle power plant CHASSIS Chassis is a French term which denotes the whole vehicle except vehicles additional fitting in the body Chassis consists of engine, brakes, steering system & wheel mounted on the frame, differential, suspension other electronics are mounted. themselves, not the physical structure. disk drives & other equipments are mounted CLASSIFICATION OF CHASSIS According to control: conventional-forward chassis Semi-forward chassis

4 Full-forward chassis Engine at front Engine fitted in front but crosswise Engine fitted at the centre of the chassis Engine fitted at the back According to the Number of Wheels fitted in the vehicles and the number of driving wheels 4x2 drive chassis vehicle. 4x4 drive chassis vehicle. 6x2 drive chassis vehicle. 6x4 drive chassis vehicle Transmission The mechanism by which power is transmitted from an engine to the axle in a motor vehicle. Multivalve Vehicle Multi-valve or multivalve engine is one where each cylinder has more than two valves. A multi-valve engine has better breathing and may be able to operate at higher revolutions per minute (RPM) than a two-valve engine, delivering more power.

5 UNIT V VEHICLE SYSTEMS, FEATURES Braking system: Braking is the mechanism in the motor vehicle which is used to slowing down and stopping the vehicle to rest in the shortest possible distance. Principle of Braking system: While operating the braking system the KINETIC ENERGY of moving vehicle is converted in to HEAT ENERGY. Functions of Brakes: Brakes have the following functions. 1. It is used to stop the vehicle. 2. It is used to control the speed where and when required. 3. It is used to control the vehicle while descending along the slope. 4. To park the vehicle and held it in stationary position without the presence of Driver. Requirements of Automobile Brakes: 1. It should work efficiently irrespective of road condition and quality. 2. The retardation must be uniform throughout its application. 3. The pedal effort must be within the convenient capacity of the driver. 4. It must be reliable and should not be effected by heat water and dust. 5. It should be in minimum weight. 6. It should have long life. 7. It should be easy to maintain and adjust. 8. Noise and vibrations are to be minimum. 9. There should be provision for secondary brake or parking brake. Classification of Brakes: The following are the classifications of Brakes: 1. By method of power a) Mechanical brakes b) Hydraulic brakes c) Vacuum brakes d) Air brakes

6 e) Electrical brakes f) Magnetic brakes g) Air assisted hydraulic brakes 2. By method of application: a) Service or foot brakes b)parking or hand brakes 3. By method of operation: a) Manual b) Servo c) Power operation 4. By method of Braking contact a. Internal Expanding Brakes b. External Contracting Brakes 5. By Method of Applying Brake force: a.single Acting Brakes. b. Double Acting Brakes. Types of Mechanical Brakes: a.drum Brakes (Internal Expanding or External Contracting) b. Disc Brakes (Single or Two calipers) DISC BRAKES 1. Dry Disc Brakes 2. Wet Disc Brakes In a disc brake, the fluid from the master cylinder is forced into a caliper where it presses against a piston. The piston in turn squeezes two brake pads against the disc (rotor), which is attached to wheel, forcing it to slow down or stop.

7 Most modern multi-plate disc brakes run in oil to transfer the heat away from the friction plates but that hasn t always been the case. The enclosed nature of the brake does require consideration of heat dissipation though. We will only discuss wet brakes here. There are two fundamental types of multi-plate brakes, servo and non servo. Purpose of a multi plate disc brake is the same as the more conventional caliper. It has to retard, stop and hold the vehicle. The fundamental difference is that it is self contained and cooled by oil. In principle it s not too different to a motorcycle clutch but of course the details are very different. The braking faces are between a number of interleaved friction discs and counter plates alternately keyed to the housing or splined to a driveshaft. The plates are clamped together to produce a braking torque either by an annular piston which is coaxial with the driveshaft or by a ball and ramp mechanism. Many vehicles using this type of brake have hub reduction gearing so it is common for oil immersed brakes to be inboard of this gearing and as such they run at five or six time wheel speed. Hydraulic hooklift hoists are mounted on heavy duty trucks to enable haulers to change out flatbeds, dumpster bodies, and similar containers. Primarily used in conjunction with tilt frame bodies and specialized containers, generally designed for the transportation of materials in the waste, recycling, scrap and demolition industries. The system employs a series of hydraulic rams to hook, lift and hoist the container onto the chassis of the truck. There are several configuration options, and strict guidelines. This must be followed to ensure that the container is secured on the truck in transit This is a SAMPLE (Few pages have been extracted from the complete notes:-it s meant to show you the topics covered in the full notes and as per the course outline

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