Disc brakes | Construction | Features

Construction : 

A disc brake can be made of a cast-iron disc bolted to the wheel hub and a stationary housing called calliper. The calliper is connected to some stationary part of the vehicle, like the axle casing or the stub axle and is cast in two parts, each part containing a piston. 

In between each disc and the piston, there is a friction pad held in position by retaining pins, spring plates etc. Passages are drilled for the fluid in the calliper to enter or leave each housing. These passages are also connected to another passage for bleeding. Each cylinder contains a rubber sealing ring between the cylinder and the piston. 

When the brakes are applied, hydraulically actuated pistons move the friction pads into contact with the disc, and later applying equal and opposite forces. On releasing the brakes, the rubber sealing rings act as return springs and retract the friction pad and pistons away from the disc. 

For this type of brake, 

T  = 2 µ p a R

Where, 

µ = fluid pressure 

a = cross-sectional area of one piston 

R = distance of the longitudinal axis from the wheel axis of the piston 

For special types of disc brakes include the swinging calliper type and the sliding calliper type. 

In-swinging calliper type the calliper is hinged about a fulcrum pin and one of the friction pads is fixed to the calliper. The fluid under pressure presses against the disc to the other pad to apply the brake. The reaction the calliper causes it to move the fixed pad inward slightly, applying equal pressure to the other side of the disc. The calliper automatically adjusts its position by swinging around the pin. 

In the sliding calliper type, there are two pistons between which the fluid under pressure is sent which presses on friction pad directly onto the disc, whereas the other pad is pressed indirectly via the calliper. Both these types are adjusting and have resulted in a simpler and lighter construction. 

Features : 

The discs of the brakes have made of pearlitic grey cast iron. The material is anti-wear properties. Cast steel discs have also been employed in certain cases, which are still less and provided a higher coefficient of friction, yet the big drawback in their case is the less frictional behaviour. 

Recently material like ceramics and carbon fibre have also found their way into automotive brakes. The greatest advantage of these materials is the weight reduction which greatly improves vehicle dynamics and steering characteristics, due to the reduction in unsprung mass. 

Two types of discs have been employed in various makes of disc brakes, for example, solid or the ventilated type. The ventilated type no doubt provides better cooling. It is seen that using a ventilated disc results in a reduction of about 30% in the pad temperature, as compared to solid discs. This results in a longer pad life. Whereas the ventilated discs also have certain disadvantages. They are usually thicker and even sometimes heavier than the solid discs. 

Some disc brakes use such friction pads as contain metallic contact inside. The contact is exposed when the pad wears down to the specified thickness and thereby completes an electrical circuit which lights up a warning lamp on the instrumental panel, indicating to the driver that the pads need replacement. 

Some large pistons for disc brakes are made of hard plastic whereas in some other cases, these are precision ground and plated with nickel-chrome which provides them with a hard surface which is durable. 

Drum brakes | Construction and Types | Factors

Construction and Types : 

In this types of brakes, a brake drum is attached concentrically to the axle hub whereas on the axle casing is mounted a backplate. In case of the front axle, the brakes plate is bolted to the steering knuckle. The backplate is made of pressed steel sheet and is ribbed to increase rigidity and to provide support for the expander, anchor and the brake shoes are protects the drum and shoe assembly from dust and mud. 

However, it absorbs the complete torque reaction of the shoe due to which reason it is sometimes also called a torque plate. Both brake shoes are anchored on the backplate. Friction linings are mounted on the brake shoes. Retractor springs are used to serve to keep the brake shoes away from the drum when the brakes are not applied. The brake shoes are anchored at one end whereas on the other hand force F is applied by means of some brake actuating mechanism. Which forces the brake shoe against the revolving drum, and hence applying the brakes. An adjuster is also provided to compensate for wear of friction lining with use. 

The relative braking torque obtained at the shoes for the same force applied at the pedal varies depending upon whether the expander is fixed to the brake plate or floating If the anchor is fixed or floating and then the shoes are leading or trailing. 

A

• Fixed expander type : 

To understand the action of this type it is necessary to understand the terms 'leading' and 'trailing' shoes. 

It is seen that a leading shoe tip is dragged along the drum even when there is no braking force, while the tip of the trailing shoe is thrown off the brake drum. Thus when the brakes are applied, the net force exerted on the leading shoe becomes more than the net force exerted on the trailing shoe and as such unequal braking effect is produced at the two shoes. With increased braking effect and consequently higher temperatures, the coefficient of friction gets reduced more with prolonged application in case of the leading shoe, due to which reason, leading shoe fades quicker than the trailing shoe. 

• Floating expander type :

In this type, the expander is not fixed on the backplate but is kept floating. In this way, the unequal braking effects at the two shoes are automatically balanced and made equal. Even if the lining on one shoe is worn more than on the other, the floating expander will move to one side so that the shoes still share equally the actuating force. However, the lining wear on two shoes is still unequal. 

• Floating anchor type :  

In this type of shoe operating mechanism, the two shoes are linked together at the floating anchor and have a common fixed anchor. For the direction of rotation, it is seen that both the shoes become leading, the details including merits and demerits of which are given below under separate bread since the shoes can be made leading by other means also. 

• Two leading shoe type : 

For this type, the leading shoe experiences an added breaking force or self energization. Thus if both the shoes are made leading, it definitely increases the braking torque. The lining wear also becomes uniform on both the shoes. However, the disadvantages are that firstly when the vehicle is moving in reverse, both the shoes will become trailing shoes and the braking effect is considerably decreased. This may not matter much because generally the vehicles in reverse are driven at comparatively slow speeds where the braking torque required is also less. Secondly, this type is sensitive to the coefficient of friction changes and thus will not be best suited for brakes meant for prolonged applications. 

• Two trailing shoe type :

In this type, both the shoes are trailing shoes as a result of which the braking effort at the wheels is decreased for the same force applied at the brake pedal as in case of two leading shoe type. That is why this type of brake is used generally with servo brakes or power brakes so that the driver is not fatigued. 
Apart from the above disadvantage of the decreased braking effort, this type has got a definite advantage. It has better anti-fade properties than the two leading shoe type and thus provides more consistent braking. 


Factors affecting braking effect : 

• The radius of the brake drum and the wheel 

Where Retarding force produced on a brake drum F = F_B * R_b / R_w

• The area of the brake lining and the amount of pressure applied at the brake lining increases the braking effect directly. 
• The higher coefficients of friction between braking surfaces and between tyre and road are also useful in increasing the braking effect, but two high coefficient may cause locking of wheels, which must be avoided. 

Types of brakes

There are different types of automotive brakes may be used according to the following considerations :

• Purpose
• Location 
• Construction 
• Method of actuation 
• Extra braking effort 

According to purpose : 

From this point of view, the brakes may be classified as the service or the primary and the parking or secondary brakes. The service brakes are the main brakes used for stopping the vehicle while vehicle in motion whereas the parking brakes are meant to hold the vehicle on the slop. 

According to the location : 

From this point of view, the brakes may be located either at the transmission or at the wheels. The wheel brakes are definitely better from dissipation point of view on account of two reasons. First, the location of transmission brakes from this viewpoint is very poor and secondary there is only one brake drum, whereas in the case of wheel brakes we may have four brake drums. Second, in case of transmission brakes, the whole of the braking torque has to be transmitted through the universal joints, propeller shaft, differential and the rear axle, suitable provision must be made in their design and their sizes increased proportionally.

However, if the brakes are located on the transmission, the braking torque is equally divided automatically between the two wheels and no special compensation is needed. Further because of the reduction at the differential, the transmission brakes would be stronger than the brakes of similar capacity at the wheels. 

Consideration the case of automobiles, the wheel brakes are used universally. 

According to construction : 

From this point of view brakes divided into two categories: One is drum brakes and another one is disc brakes. 

According to actuation : 

From this point of view brakes divided into following types : 

• Mechanical brakes 
• Hydraulic brakes 
• Electric brakes 
• Vacuum brakes 
• Air brakes 

According to the extra braking effort : 

When the weight of the vehicle is more that time driver can not apply the brakes comfortably without fatigue his effort is supplemented with some source of energy which makes the application of brakes easier. This types of brakes are called servo-brakes or power-assisted brakes. 

Brake efficiency and stopping distance

Braking efficiency : 

The maximum retarding force applied by the brake at the wheels F depends on the coefficient of friction between the road and the tyre surface µ. The weight of the vehicle on the wheel is W. 

F = µ F 

If the coefficient of friction achieved unity, the total retarding force produced at the wheels is equal to the vehicle weight itself, which is equal to the gravitational experienced by the falling body of the mass equal to that of the vehicle. 

If this is the case, the vehicle experiences a deceleration equal to the acceleration due to gravity g and the brakes are said to be 100 % efficient. Thus theoretical limit for brake efficiency is 100%.

In actual practice, the efficiency of 100% is rarely used for ordinary vehicles requirements like the safety of passengers in public vehicles. 

The brake efficiency usually varies from 50 to 80 % which enable the vehicle to stop within a reasonable distance. 

Stopping Distance : 

Approximate stopping distance at different vehicle velocities for various conditions of brakes are different. However, the minimum allowable limit of brake efficiency for any vehicle is 50 % for foot brakes and 30% for hand brakes. 

However, during emergency braking, the reaction of the driver and response time of the brakes also an important part. The stopping distance in case of emergency braking may be divided into 3 types : 

• Distance traversed during the reaction time of the driver. 
• Distance traversed during the time elapsed between the driver pressing the brake pedal and the brake being actually applied at the wheels. 
• Net stopping distance, depending upon the deceleration. 

Stopping distance mainly depends upon following factors :

• Vehicle speed
• Condition of tyre
• Condition of the road surface
• Coefficient of friction between tyre and road 
• Coefficient of friction between the brake drum and the brake lining 
• Braking force applied by the driver

Braking requirements

The braking system has a requirement for the correct breaking that will following below :

1. The brakes must be strong enough to stop the vehicle within a minimum distance in an emergency condition but this should also be consistent with safety. The driver must have proper control over the vehicle during emergency braking condition and the vehicle must not skid. 
2. The brakes must have good anti-fade characteristics like effectiveness should not decrease with the constant prolonged application and also descending hills. This requirement of the braking system demands the cooling of the brakes should be very efficient. 

Principle of braking system

The braking system is one of the most important control components of the vehicle. There are different types of brakes are used in various need. They are required to stop the vehicle within the smallest possible distance and this can be done by converting the kinetic energy of the vehicle into the heat energy which is dissipated into the atmosphere. 

Thermodynamics important questions

Question No 1 :

The following are examples of some intensive and extensive properties :

1. Pressure
2. Temperature
3. Volume
4. Velocity
5. Electronic charge
6. Magnetisation
7. Viscosity
8. Potential energy

Which one of the following sets gives the correct combinations of Intensive and Extensive properties?

Option A : Intensive - 1 2 3 4 Extensive - 5 6 7 8

Option B : Intensive - 1 3 5 7 Extensive - 2 4 6 8

Option C : Intensive - 1 2 4 7 Extensive - 3 5 6 8

Option D : Intensive - 2 3 6 8 Extensive - 1 4 5 7

Explanation : 

Intensive properties : Independent of mass 

Extensive properties : Dependent of mass 

Question No 2 :

In an isothermal process, internal energy?

Option A: Increases

Option B: Decreases 

Option C: Remain constant

Option D: Gradually increases

Explanation: Decreases

Question No 3 : 

A reversible process?

Option A: Must pass through a continuous series of equilibrium states

Option B: Leaves no history of the events in surroundings 

Option C: Must pass through the same states on the reversed path as on the forward path 

Option D: All of these

Explanation: All of the above

Question No 4 : 

The specific heat of water with rising of temperature?

Option A: Increases

Option B: Decreases 

Option C: First decreases to a minimum then increases

Option D: Remain constant 

Explanation: Decrease to a minimum first then increase 

Question No 5 : 

When two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This statement is :

Option A: Zeroth law of thermodynamics 

Option B: First law of thermodynamics 

Option C: Second law of thermodynamics 

Option D: None of the above 

Explanation: This is the statement of the zeroth law of thermodynamics 

Question No 6 : 

Kelvin-Plank's law deals with?

Option A: Conversion of work into heat

Option B: Conversion of heat into work 

Option C: Conversion of work 

Option D: Conversion of heat 

Explanation: Conversion of heat into work 

Question No 7 : 

According to the kinetic theory of gases, at absolute zero?

Option A: Specific heat of molecules reduces to zero 

Option B: Volume of gas reduce to zero

Option C: Kinetic energy of molecules reduces to zero 

Option D: Pressure of gas reduces to zero 

Explanation: Kinetic energy of molecules reduces to zero 

Question No 8 :

In a throttling process?

Option A : W = 0 

Option B : H = 0 

Option C : E = 0 

Option D : All of the above 

Explanation : At throttling all W, H, E = 0 

Question No 9 : 

In all reversible process, the entropy of the universe?

Option A: Increases 

Option B: Decreases 

Option C: Remains the same 

Option D: None of the above 

Explanation: Increases

Question No 10 : 

Efficiency of Carnot cycle is given by :

Option A : T1 + T2 / T1 

Option B : T1 - T2 / T1 

Option C : T1 / T1 + T2

Option D : T1 / T1 - T2 

Explanation : T1 - T2 / T1 

Question No 11 : 

The Carnot cycle consists of two reversible adiabatic processes and 

Option A: Two reversible isothermal processes 

Option B: Two reversible constant pressure processes 

Option C: Two reversible constant volume processes 

Option D: One reversible constant pressure processes

Explanation: Two reversible isothermal processes

Question No 12 : 

Carnot cycle has maximum efficiency for?

Option A : Petrol engine 

Option B : Diesel engine 

Option C : Reversible engine 

Option D : Irreversible engine 

Explanation : Reversible engine 

Question No 13 :

In the Carnot cycle, the algebraic sum of the entropy changes for the cycle is?

Option A: Positive

Option B: Negative 

Option C: Zero 

Option D: None of the above 

Explanation: Zero 

Question No 14 : 
In the Carnot cycle, the process carried at extremely slow speed is 
Option A: Isothermal compression 
Option B: Adiabatic compression 
Option C: Adiabatic expansion 
Option D: All of these 
Explanation: All are extremely slow speed processes

Question No 15 :
Control volume refers to a 
Option A: Specific mass
Option B: Fixed region in the space
Option C: Closed system 
Option D: NONE 
Explanation: Fixed region in the space

Question No 16 : 
The internal energy of a perfect gas depends upon
Option A: Temperature only
Option B: Temperature and pressure 
Option C: Temperature, pressure and specific heats
Option D: NONE
Explanation: Temperature only

Question No 17 :
Joule Thomson coefficient for an ideal gas having equation pV=RT is 
Option A: Zero
Option B: 0.5
Option C: Unity
Option D: Infinite 
Explanation: Zero

Question No 18 :
The temperature of a gas is a measure of 
Option A: Average distance between gas molecules 
Option B: Average kinetic energy of gas molecules
Option C: Average potential energy of gas molecules
Option D: NONE
Explanation: Average kinetic energy of gas molecules

Question No 19 :
A gas, which obeys kinetic theory perfectly is 
Option A: Pure gas
Option B: Real gas
Option C: Perfect gas
Option D: All of these
Explanation: Real gas

Question No 20 : 
The temperature at which, the volume of a gas becomes zero, is called
Option A: Absolute temperature
Option B: Absolute zero temperature
Option C: Absolute scale of temperature
Option D: NONE of these
Explanation: Absolute zero temperature

Question No 21 :
The absolute zero pressure exists 
Option A: At sea level
Option B: At -273 K
Option C: At vacuum condition 
Option D: When the molecular momentum of the system becomes zero 
Explanation: When the molecular momentum of the system becomes zero 

Question No 22 :
Specific heat of gas, Cp = Cv, at
Option A: Absolute zero
Option B: Critical temperature
Option C: Triple point
Option D: All temperatures
Explanation: Absolute zero

Question No 23 : 
The gas constant R is equal to the
Option A: Sum of two specific heats
Option B: Difference of two specific heats
Option C: Product of two specific heats
Option D: Ratio of two specific heat 
Explanation: Difference of two specific heats

Question No 24 : 
Triple point 
Option A: Occurs in a mixture of two or more gases
Option B: In the point, where three phases exist together
Option C: Occurs in sublimation
Option D: None of the above
Explanation: In the point, where three phases exist together

Question No 25 : 
For a pure substance at its triple point, the number of degrees of freedom is 
Option A: 0
Option B: 1
Option C: 2
Option D: None of these
Explanation: Zero 
Consider a system consisting of pure gas, say A. It is, evidently, a one-component, one phase system. The two variable required to be specified will be temperature and pressure. The composition will remain invariable A. The degree of freedom will be 2 if the system will be bivariant. One component system having two phases called mono variant and three phases coexist defines the system completely, therefore, is said to be non-variant or invariant or degree of freedom is zero.  

Question No 26 : 
The efficiency of a Rankine cycle 
Option A: Increases with decreasing temperature of heat rejection
Option B: Decreases with decreasing temperature of heat rejection 
Option C: Decreases with increasing temperature of heat rejection
Option D: None of the above
Explanation: Increase with decreasing temperature and decrease with increasing temperature of heat rejection.

Question No 27 : 
Rankine cycle efficiency for a power plant is 29%. The Carnot cycle efficiency will be
Option A: Less
Option B: More 
Option C: Equal 
Option D: NONE of the above
Explanation: Carnot cycle efficiency is more than the Rankine cycle for the power plant. 

Question No 28 : 
The ideal efficiency of a simple gas turbine cycle depends upon
Option A: Pressure ratio
Option B: Cut-off ratio
Option C: Both A & B
Option D: None of the above
Explanation: Pressure ratio

Question No 29 : 
A system is said to be consisting of a pure substance when 
Option A: It is homogeneous in composition
Option B: It is homogeneous and invariable in chemical aggregation
Option C: It has only one phase
Option D: It has more than one phase
Explanation: It is homogeneous and invariable in chemical aggregation
A pure substance is one which is
Homogeneous in composition 
Homogeneous in chemical aggregation
Invariable in chemical aggregation

Question No 30 :

At its critical point, any substance will 

Option A: Exist all the three phases simultaneously

Option B: Change directly from solid to vapour

Option C: Lose phase distinction between liquid and vapour

Option D: Behave as an ideal gas

Explanation: Lose phase distinction between liquid and vapour

Difference between automatic and manual transmission

Before buying a car there is some tough decision you have to make regarding what you want in your vehicle. There are two types of transmission one is automatic transmission and another one is manual transmission so choose one between these two is important to know the difference between manual and automatic transmission. 

The basic difference between two transmissions is that in manual transmission the driver uses a clutch to change the gears whereas in automatic transmission adjusts the gears automatically based on the engine speed. 

Now let we check some difference between them one by one pointwise below.

Difference : 

• Fuel consumption is more in automatic transmission as compared with manual transmission. 
• A manual transmission gives greater control of the car and auto gearing give lesser control but promises comfort and convenience. 
• A manually transmitted car is cheaper than the same automatically transmitted vehicle.
• Maintenance and repair cost for the automatic transmission is more as compared with manual transmission.  
• In a manual transmission, the gear is located on the floor whereas the location of gear is at the steering or on the floor in the automatic transmission. 
• Manual transmission cars give more mileage than automatic transmission cars. 
• Manual transmission box is lighter than automatic transmission. 
• It is much easier for an automatic transmission to overheat.
• Automatic cars are more often used in sports than manual cars.
• The driver needs to drive with both hand and feet engaged in a manual transmission car where the left foot is totally free in an automatic transmission car. 

What is production system

The production system of an industrial organization is that part which produces products of an organization. The production system has the following characteristics :

• Production is an organized activity, so every production system has an objective. 
• The system transforms various inputs into useful outputs. 
• It does not operate in isolation from the other organization system.

Classification of production system :

1. Job Shop Production 
2. Batch Production 
3. Mass Production 
4. Continuous Production 

Definition of production management

Production is the process which combines and transforms various resources like raw material used in the production system of the industrial organization into finished product or value-added service in a controlled manner as per the policies of the industrial organization.

The set of interrelated management activities, which are involved in manufacturing certain products is called production management. The same concept is extended to services management is called operations management.

Production management deals with converting raw materials into finished products of goods. It brings men, money, machines, materials, methods and markets to satisfy the wants of the people. 

Productivity measurement

Productivity can be measured by two types which are following below :

• By aggregate basis 
• On an individual basis

which is called total and partial measure. 

Total productivity Index / Measure = Total output / Total input 

It can also be measured by Total production of goods and services / Labour + material + capital + Energy + management 

Labour productivity Index / Measure = Output in unit / Man hours worked 

Machine productivity Index / Measure = Total output / Machine hours worked 

Management productivity Index / Measure = Output / Total cost of management 

Land productivity Index / Measure = Total output / Area of land used 

Partial measure can be measure by :

• Output / Labour  
• Output / Capital 
• Output / Materials 
• Output / Energy

Benefits of productivity

For the survival of any industrial organization productivity ratio must be at least 1. If it is more than 1 the organization is in a comfortable position. The ratio of output produced to the input resources utilized in the production.

Benefits derived from higher productivity are as follows :

• Improve profits because productivity helps to cut down cost per unit. 
• Gains from productivity can be transferred to consumers in the form of lower-priced products or better quality products. 
• Paying workers or employees at a higher rate because gains can be shared with them.
• A more productive entrepreneur can have better chances to exploit expert opportunities. 
• Generate more employment opportunity. 
• Overall productivity reflects the efficiency of the production system. 
• More output is produced with the same or less input. 
• The same output is produced with lesser input. 
• More output is produced with more input. 
• The proportional increase in the output is more than the proportional increase in input. 
• It is greatly helpful in achieving overall prosperity and growth of an economy.