An automobile is a combination of large number of parts. It can be broadly divided into components i.e chassis and the body.
The chassis of an automobile consists of following
(A) Basic frame structure.
(B) Engine or power unit.
(C) Transmission system.
(D) Auxiliaries.
(E) Controls.
The body is that part where passengers have their seats or the luggage and cargo to be The above components are briefly discussed in the following pages.
(A) BASIC FRAME STRUCTURE
It consists of the frame, suspension system, axles, and wheels. The other components are attached to this in order to make a complete automobile. The details of the components of basic frame structure are as follows:
l . Frame.
The frame provides a base for the engine and the body of the vehicle. Following are the two types of frames which are commonly used:
(a) Body and frame type
(b) Unit type (frameless structure also known as monocoque body).
In the body and frame type design, the body is bolted to a separate frame which is a part of chassis. Most of the suspension, bumper and brake loads are transmitted to the frame. This type of construction is actually still used for trucks and some off road vehicles.
The following are the two types of body and frame type designs:
1). Ladder frame.
It consists of two long rails connected by a number of connecting pieces called cross members, as shown in Fig. This design is often called a ladder frame arrangement because it resembles a step ladder. This type of design has a disadvantage that it cannot sustain force of crash from the side.
2). X-member frame.
It uses two cross members, which are welded to the side rails under the centre of the vehicle to strengthen the ladder frame as shown in Fig.
In the unit type (i.e. frame less) design, the sheet metal parts are welded together, forming a framework to which an outer skin is attached. In other words, the chassis frame is integral to the body as shown in Fig, The frame less construction is possible only in the case of closed cars since the roof, windshield, pillars, and rear panel are essentially load taking parts of the structure.
The following are the advantages and disadvantages of the unit type (frameless) construction.
Advantages of unit type construction
1) It enables reduction in body weight, and consequently improves the fuel consumption.
2) It increases the safety levels because of better impact absorption.
3) The manufacturing cost is less.
4) It ensures lower body position which increases stability of the automobile and makes driving easy.
Disadvantages of unit type construction
1) It has less strength and durability.
2) The cost of repair is high in case of damage to the body during accidents.
2. Suspension system.
The suspension is located between the wheels and body of the vehicle. The suspension system includes springs, shock absorbers and their mountings. The purpose of a suspension system is to improve driving comfort and to reduce the amount of vibration and impact forces that are transmitted to the body. It also ensures that the wheels are always firmly in contact with the road surface and regulates the inclination of the body in order to improve the stability of the vehicle in any possible driving condition including acceleration, braking, and cornering.
The suspension system may be divided into two major types based on the design, i.e. rigid axle type and independent type suspension systems.
In the rigid axle type suspension system, the left and right wheels are connected to a single axle and the load directed to the wheels is supported by this system.The rigid axle suspension is more effective when it is desired to maintain a large suspension stroke in vehicles which exhibit large variation in load as a result of changes in cargo weight or passenger numbers. Thus, it is mainly employed in large or medium-sized trucks and buses. The drawback of this type of suspension system is that the driving comfort and stability are inferior to that of independent type suspension system.
In the independent type of suspension system, there is no axle connecting the left and right wheels, hence the load directed to the wheels is supported by the suspension arms. Thus, each wheel can move independently in response to its specific road condition. Though this type of suspension System is more complicated in terms of design than the rigid axle type, yet the unsprung mass is lighter and wheel-to-ground contact is better. Accordingly, the driving comfort and stability are superior when this type of suspension is adopted.
3. Axles.
The axles are the shafts on which road wheels are mounted. The axles m as dead axles and live axles. The dead axles are those axles which do not contain differential and it merely supports the load. The front axle is usually a dead axle, used in heavy vehicles. The live axles are those axles which contain the differential and it supports the load and transmits rotary motion to the road wheels. The live rear axles are referred to as floating axles, which are of the following three types:
(1) Semi floating type
(2) Three quarter floating type
(c) Full floating type.
4. Wheels.
The tyre and wheel rim assembly is generally referred to as a wheel. The tyre is fitted around the wheel rim and it provides a cushion between the vehicle and the road. It takes the load of the vehicle and transfer traction and braking forces to the road surface. The wheels support the whole weight of the vehicle and convert the rotary motion into longitudinal motion.
The chassis of an automobile consists of following
(A) Basic frame structure.
(B) Engine or power unit.
(C) Transmission system.
(D) Auxiliaries.
(E) Controls.
The body is that part where passengers have their seats or the luggage and cargo to be The above components are briefly discussed in the following pages.
(A) BASIC FRAME STRUCTURE
It consists of the frame, suspension system, axles, and wheels. The other components are attached to this in order to make a complete automobile. The details of the components of basic frame structure are as follows:
l . Frame.
The frame provides a base for the engine and the body of the vehicle. Following are the two types of frames which are commonly used:
(a) Body and frame type
(b) Unit type (frameless structure also known as monocoque body).
In the body and frame type design, the body is bolted to a separate frame which is a part of chassis. Most of the suspension, bumper and brake loads are transmitted to the frame. This type of construction is actually still used for trucks and some off road vehicles.
The following are the two types of body and frame type designs:
1). Ladder frame.
It consists of two long rails connected by a number of connecting pieces called cross members, as shown in Fig. This design is often called a ladder frame arrangement because it resembles a step ladder. This type of design has a disadvantage that it cannot sustain force of crash from the side.
2). X-member frame.
It uses two cross members, which are welded to the side rails under the centre of the vehicle to strengthen the ladder frame as shown in Fig.
In the unit type (i.e. frame less) design, the sheet metal parts are welded together, forming a framework to which an outer skin is attached. In other words, the chassis frame is integral to the body as shown in Fig, The frame less construction is possible only in the case of closed cars since the roof, windshield, pillars, and rear panel are essentially load taking parts of the structure.
The following are the advantages and disadvantages of the unit type (frameless) construction.
Advantages of unit type construction
1) It enables reduction in body weight, and consequently improves the fuel consumption.
2) It increases the safety levels because of better impact absorption.
3) The manufacturing cost is less.
4) It ensures lower body position which increases stability of the automobile and makes driving easy.
Disadvantages of unit type construction
1) It has less strength and durability.
2) The cost of repair is high in case of damage to the body during accidents.
2. Suspension system.
The suspension is located between the wheels and body of the vehicle. The suspension system includes springs, shock absorbers and their mountings. The purpose of a suspension system is to improve driving comfort and to reduce the amount of vibration and impact forces that are transmitted to the body. It also ensures that the wheels are always firmly in contact with the road surface and regulates the inclination of the body in order to improve the stability of the vehicle in any possible driving condition including acceleration, braking, and cornering.
The suspension system may be divided into two major types based on the design, i.e. rigid axle type and independent type suspension systems.
In the rigid axle type suspension system, the left and right wheels are connected to a single axle and the load directed to the wheels is supported by this system.The rigid axle suspension is more effective when it is desired to maintain a large suspension stroke in vehicles which exhibit large variation in load as a result of changes in cargo weight or passenger numbers. Thus, it is mainly employed in large or medium-sized trucks and buses. The drawback of this type of suspension system is that the driving comfort and stability are inferior to that of independent type suspension system.
In the independent type of suspension system, there is no axle connecting the left and right wheels, hence the load directed to the wheels is supported by the suspension arms. Thus, each wheel can move independently in response to its specific road condition. Though this type of suspension System is more complicated in terms of design than the rigid axle type, yet the unsprung mass is lighter and wheel-to-ground contact is better. Accordingly, the driving comfort and stability are superior when this type of suspension is adopted.
3. Axles.
The axles are the shafts on which road wheels are mounted. The axles m as dead axles and live axles. The dead axles are those axles which do not contain differential and it merely supports the load. The front axle is usually a dead axle, used in heavy vehicles. The live axles are those axles which contain the differential and it supports the load and transmits rotary motion to the road wheels. The live rear axles are referred to as floating axles, which are of the following three types:
(1) Semi floating type
(2) Three quarter floating type
(c) Full floating type.
4. Wheels.
The tyre and wheel rim assembly is generally referred to as a wheel. The tyre is fitted around the wheel rim and it provides a cushion between the vehicle and the road. It takes the load of the vehicle and transfer traction and braking forces to the road surface. The wheels support the whole weight of the vehicle and convert the rotary motion into longitudinal motion.
1 Comments
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