SSC Marks Memo

Andhra Pradesh

SSC Marks Memo

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Layout of Automobile Chassis

Various loads acting on the frame:

Various loads acting on the frame are

Short duration Load  Momentary duration LoadImpact LoadsInertia LoadStatic LoadsOver Loads

Short duration Load

While crossing a broken patch.

Momentary duration Load

While taking a curve.

Impact Loads

Due to the collision of the vehicle.

Inertia Load 

While applying brakes.

Static Loads 

Loads due to chassis parts.

Over Loads

Beyond Design capacity.

State the different bodies used in automobiles:   The Automobile bodies are divided in two groups i.e.

According to Chassis design the body can divided into

1.       Conventional Type

2.       Integral Type

3.       Semi- Integral Type

 

According to other usage:

1.       Light vehicle Bodies - cars, jeeps

2.       Heavy vehicle Bodies – Busses, Lorries

3.       Medium vehicle Bodies - Vans, Matadors

Requirements of bodies for various types of vehicle:

The body of the most vehicles should fulfill the following requirements:

1.       The body should be light.

2.       It should have minimum number of components.

3.       It should provide sufficient space for passengers and luggage.

4.       It should withstand vibrations while in motion.

5.       It should offer minimum resistance to air.

6.       It should be cheap and easy in manufacturing.

7.       It should be attractive in shape and colour.

8.       It should have uniformly distributed load.

9.       It should have long fatigue life.

10.   It should provide good vision and ventilation.

Unitized Body Design

Introduction:

The suspension system must provide proper steering control and ride quality. Performing these functions is extremely important to maintain vehicle safety and customer satisfaction. Some vehicles, such as rear-wheel-drive cars, sport utility vehicles (SUVs), and trucks, have a frame that is separate from the body. Other vehicles have a unitized body that combines the frame and body in one unit, eliminating the external frame.

 

Unitized body design

In a unitized body, the body design rather than a heavy steel frame provides strength and rigidity.All parts of a unitized body are load-carrying members, and these body parts are welded together to form a strong assembly.

 

 

 

The frame or unitized body serves the following purposes:

1. Allows the vehicle to support its total weight, including the weight of the vehicle and cargo.

2. Allows the vehicle to absorb stress when driving on rough road surfaces.

3. Enables the vehicle to absorb torque from the engine and drive train.

4. Provides attachment points for suspension and other components.

 

The unitized body provides a steel box around the passenger compartment to provide passenger protection in a collision.Modern automotive bodies use a wide variety of materials, such as hydroformed aluminum rails, magnesium roof frames, and carbon fiber-balsa wood composite floor panels.In most unitized bodies, special steel panels are inserted in the doors to protect the vehicle occupants in a side collision.Some unitized body components are manufactured from high-strength or ultra-high-strength steels.The unitized body design is typically used in small- and mid-sized front-wheel-drive cars.A steel cradle is mounted under the front of the unitized body to support the engine and transaxle. Rubber and steel mounts support the engine and transaxle on the cradle.Large rubber bushings are mounted between the cradle and the unitized body to help prevent engine vibration from reaching the passenger compartment. Some unitized bodies have a partial frame mounted under the rear of the vehicle to provide additional strength and facilitate the attachment of rear suspension components.

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Vertical and Horizontal Engines

Introduction:
Horizontal and vertical engines are identified by the line of the stroke. If the line of stroke of an engine piston is vertical, then it is a vertical engine. The line of stroke of the horizontal engine is horizontal.

In a reciprocating type of engine, primary and secondary forces of the reciprocating parts exist. These forces act along the line of stroke and depend on the crank position. These primary and secondary forces combine together and give maximum force to the engine crank when the crank is at TDC.

Air Conditioning system

Introduction:

The signal to activate the air-conditioning system comes from the occupant. Activation of the air-conditioning system is achieved under some specific conditions.

System activation

Activation is completed by the onboard Electronic Control Unit (ECU).The ECU has a number of inputs which send electronic signals based on sensed conditions, e.g. temperatures, pressures, speeds, positions.Based on this information the ECU will either activate or deactivate (if already operating) the system. If the system does not activate then a fault in the form of a code will be stored in the computer and on some systems a light will be activated to tell the driver a fault exists.Advanced systems may use telematics to send a signal to a call centre.Operators at the centre will advise the customer of the required action, i.e. urgency on visiting a dealership, often via telephone.

Activation of the air-conditioning system is achieved under some or all of the following conditions:

● the outside air temperature is above 9°C

● the engine has been running for more than 5 seconds

● the temperature of the evaporator is above 4°C (no ice forming over the surface)

● the engine coolant temperature is approximately between 40°C and 105°C

● the vehicle is not rapidly accelerating or the engine is under high load (overtaking etc.)

● the air-conditioning activation button has been selected and the interior fan is on.

The sensors in the air-conditioning system have acknowledged that the system is under pressure assuming that a quantity of refrigerant exists inside the system and that it has not leaked out to the atmosphere (sensed by either pressure switches or sensors).

● No fault codes exist in the ECU.

Simple electronic circuit

1. Upon activation current flows from the vehicle battery through fuses, switches fitted to the A/C system and often an A/C relay to a magnetic clutch.
2. The A/C relay is generally controlled by an onboard computer, which makes the ultimate decision to allow the A/C system to be activated based on system integrity, that is, the system has no faults and conditions are right for system activation.
3. The clutch is positioned behind the compressor pulley and once activated will make a physical connection between the compressor pulley, which is driven by the engine, and the internal pumping elements.

WHEEL BEARINGS

Introduction:

Two main types of bearings are used in rear wheels: Ball and Roller (or tapered roller) bearings.

Axle Shafts:

Axle shafts transmit drive from the differential to the rear wheel hubs. An axle shaft has to 

withstand:

1. Torsional stress due to driving and braking forces
2. Shear and bending stress due to the weight of the vehicle
3. Tensile and compressive stress due to cornering forces

A number of bearing layouts are used on the fixed live alive (driven) of a rear wheel drive car,

to handle these stresses.

Wheel bearing:

semi-floating:

• With this design, the axle shaft has to withstand all the forces.the shaft is therefore strengthened and designed to do this

•  An oil seal is incorporated because oil from the final drive can work its way along the shaft.
• The seal prevents the brakes being contaminated. 

Wheel bearing: three-quarter floating

The three-quarter floating bearing reduces the main shear stresses on the axle shaft but the other stresses remain. The bearing is mounted on the outside of the axle tube. An oil seal is included to prevent the brake linings from being contaminated.

Wheel bearing: fully floating

Fully floating systems are generally used on heavy or off-road vehicles. This is because the stresses on these applications are greater. Two widely spaced bearings are used, which take all the loads, other than torque, off the axle shaft. Bolts or studs are used to connect the shaft to the wheel hub. When these are removed, the shaft can be taken out without jacking up the vehicle.

Front hub (rear-wheel drive) with tapered roller bearings

The front hubs on rear-wheel drive cars consist of two bearings. These are either ball or tapered roller. The roller types are generally used on earlier vehicles. They have to be adjusted by tightening the hub nut and then backing it off by about half a turn.

Front hub with ball bearings

The more modern hub bearings, known as contact-type ball races, do not need adjusting. This is because the hub nut tightens against a rigid spacer. This nut must always be set at a torque specified by the manufacturer.

The most common systems for rear-wheel drive cars are semi-floating rear bearings at the rear and twin ball bearings at the front. The front bearings are designed to withstand side forces as well as vertical loads. Front-wheel drive cars have a dead axle at the rear so, typically, two taper bearings are used, or a double-race ball bearing

Automobile Engineering

CRDI (Common Rail Direct Injection):-

CRDi stands for Common Rail Direct Injection meaning, direct injection of the fuel into the cylinders of a diesel engine via a single, common line, called the common rail which is connected to all the fuel injectors.

Whereas ordinary diesel direct fuel-injection systems have to build up pressure anew for each and every injection cycle, the new common rail (line) engines maintain constant pressure regardless of the injection sequence.

Advantages & Disadvantages

Advantages:-

CRDi engines are advantageous in many ways. Cars fitted with this new engine technology are believed to deliver 25% more power and torque than the normal direct injection engine. It also offers superior pick up, lower levels of noise and vibration, higher mileage, lower emissions, lower fuel consumption, and improved performance.

In India, diesel is cheaper than petrol and this fact adds to the credibility of the common rail direct injection system.

Disadvantages:-

Like all good things have a negative side, this engine also have few disadvantages. The key disadvantage of the CRDi engine is that it is costly than the conventional engine. The list also includes high degree of engine maintenance and costly spare parts. Also this technology can’t be employed to ordinary engines.

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DRUM BRAKE:-

  

A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum.

The term drum brake usually means a brake in which shoes press on the inner surface of the drum. When shoes press on the outside of the drum, it is usually called a clasp brake. Where the drum is pinched between two shoes, similar to a conventional disc brake, it is sometimes called a pinch drum brake, though such brakes are relatively rare. A related type called a band brake uses a flexible belt or "band" wrapping around the outside of a drum The modern automobile drum brake was first used in a car made by Maybach in 1900, although the principle was only later patented 1902 by Louis Renault. He used woven asbestos lining for the drum brakes lining, as no alternative dissipated heat like the asbestos lining, though Maybach has used a less sophisticated drum brake. In the first drum brakes, levers and rods or cables operated the shoes mechanically. From the mid-1930s, oil pressure in a small wheel cylinder and pistons (as in the picture) operated the brakes, though some vehicles continued with purely mechanical systems for decades. Some designs have two wheel cylinders.

The shoes in drum brakes wear thinner, and brakes required regular adjustment until the introduction of self-adjusting drum brakes in the 1950s. In the 1960s and 1970s, disc brakes gradually replaced drum brakes on the front wheels of cars. Now practically all cars use disc brakes on the front wheels, and many use disc brakes on all wheels. However, drum brakes are still often used for handbrakes, as it has proven very difficult to design a disc brake suitable for holding a parked car. Moreover, it is very easy to fit a drum handbrake inside a disc brake so that one unit serves as both service brake and handbrake.

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DTSi 4 - VALVE TECHNOLOGY

Pulsar 135 LS is incorporated with World’s First DTSi 4 valve Engine –designed for better performance than an equivalent capacity 2 Valve Engine.

This engine has 2 intake & 2 Exhaust valves compare to 1 intake & 1 Exhaust Valve of a 2 valve engine. These valves are smaller & light weight compared to that of 2 valve engine. 4 Valves (2 Intake & 2 Exhaust valves) are introduced to improve breathing means - intake & Exhaust process of engine.

A typical 2 valve engine has just 1/3 combustion chamber head area covered by the valves, but a 4 valve head increases that to more than 50% area.

Because of this flow area of intake & Exhaust port / passages leading to valves also get increased. This facilitates induction of more quantity of charge (air-fuel mixture) and also evacuation of all burnt gases inside the combustion chamber ensure faster, cleaner & more efficient combustion.

The result is increased engine performance-power, throttle response, pick up of all engine speeds.Moreover the 4 valve engine can be revved up to much higher rpm easily, there by allowing the rider to enjoy light sports bike performance.

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GLOW PLUG :-

Diesel engines, unlike petrol engines which rely on a spark to ignite the air-fuel mixture, function due to the auto-ignition of diesel fuel when subjected to high pressures. Under high pressure, the temperature of the diesel fuel increases to a point where the fuel self-combusts. In cold weather however, this temperature is not always achieved and glow plugs assist by heating the air-fuel mixture to assist in cold starting.

Put simply, glow plugs are small heaters.

So,  basic function of a glow plug is to raise the temperature inside the cylinder, so that sufficient heat is generated to ignite the diesel fuel on starting.

How it works?

A glow plug is an electrical resistor. When electricity passes through it the resistance creates heat causing the glow plug to heat up. A light bulb filament works the same way.The reason glow plugs help start the engine is because diesel engines use heat that is created from compressing air in order to ignite the fuel. Glow plugs help warm a cold part of the engine to aid starting. When the engine is cold the metal in the engine absorbes the heat caused from compression causing the air to not reach the temperature necessary in order to ignite the fuel. If the fuel does not ignite the engine will not run. A warm engine does not assorb as much heat and therefore the engine will start and run just fine. The glow plugs help the engine to start so that it can warm up and supply its own heat.