Week-11 Challenge: Braking

ANSWER-1

Braking The function of the braking system is to retard the speed of the moving vehicle or bring it to rest in the shortest possible distance whenever required. The vehicle can be held on an inclined surface against the pull of gravity by the application of a brake. Brakes are mechanical devices for increasing the frictional resistance that retards the turning motion of the vehicle wheels. It absorbs either kinetic energy or potential energy or both while remaining in action and this absorbed energy appears in the form of heat. While moving down a steep gradient the vehicle is controlled by the application of brakes. In this case brakes remain in action for a longer period making it imperative to dissipate the braking heat to the atmosphere as rapidly as possible. Automobiles are fitted with two brakes; the service or foot brake and the emergency or hand brake. The foot brake is used to control the speed of the vehicle and to stop it, when and where desired, by the application of force on the brake pedal. The hand brake, applied by a lever, is used to keep the vehicle from moving when parked. Hand brakes are called emergency brakes because they are applied when the service brake fails. Virtually all vehicles are now equipment with 4-wheel brakes. The front brakes must operate without interfering with the steering action. The brakes must be capable of decelerating a vehicle at a faster rate than the engine is able to accelerate it. Normally brakes have to absorb three times the amount of engine horsepower energy in its equivalent form. Kinetic energy is the force that keeps the vehicle moving. This energy is provided by the engine in order to accelerate the vehicle from a standstill to desired speed. Kinetic energy is dissipated as heat by the brakes during application of breaks

Kinetic energy

All moving objects have kinetic energy. The kinetic energy E_k of an object with a mass of 'm' and a velocity of 'v' can be calculated as follows.

Ek=1/2*mv^2

In other words, an object's kinetic energy is proportional to the mass of the object and proportional to the square of the speed.

Stopping distance

When you try to stop the car, the car does not stop immediately. "Stopping distance" refers to the distance the vehicle travels while the brake is operating.
By definition of work (work = force x distance), the car's kinetic energy is equal to the braking force multiplied by the stopping distance.

Kinetic energy=1/2mv^2=braking force X stoppingdistance

Assuming that the braking force is constant, the stopping distance is proportional to the square of the car's speed.
In other words, when the speed is doubled, tripled, or quadrupled, the stopping distance increases by 4, 9, or 16 times. That's why it's dangerous when accidents happen on the highway.

Braking in motor vehicles

Mechanical braking

The most common method of braking in motor vehicles is mechanical or friction braking. In this method, some or all of the vehicles wheels are fitted with brake pads which apply a friction force that inhibits the motion of the wheels. Frictional braking results in a conversion of the kinetic energy gained from fuel consumption to thermal energy. This thermal energy then dissipates to the atmosphere in the form of waste heat.

Large friction forces can be needed to inhibit a vehicle's motion, particularly in large machines and trucks which have a high mass and therefore high kinetic energy. The brake pads, which are responsible for applying the friction force, experience wear over the course of their life due to this friction force. The brake pad wear causes the brakes to become less effective over the course of their life and need regular replacement.

Regenerative braking

Regenerative braking system involves the removal of the kinetic energy of a moving object by converting it into another form of useful energy, such as electric, pneumatic, or stored kinetic energy. The use of regenerative braking can increase the overall efficiency of a motor vehicle by conserving some of its kinetic energy which can then be used to bring the vehicle back up to speed.

Excel sheet of drive cycle:

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ANSWER-2 Electric motor can't develop braking torque at high speed similar to starting because Braking torque is applied in he opposite direction of the rotation. We can use a mechanical brake to produce a braking torque. We can also do it Electrically by regenarating brakingThe electric motor can't develop braking torque at high speed similiar to starting because once the electric supply is pulled off from the motor,it acts as a generator and due to the flux weakening effect of the electric generator,the generator produces low torque as expected.

Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy into a form that can be either used immediately or stored until needed. In this mechanism, the electric traction motor uses the vehicle's momentum to recover energy that would otherwise be lost to the brake discs as heat This contrasts with conventional braking systems, where the excess kinetic energy is converted to unwanted and wasted heat due to friction in the brakes, or with dynamic brakes, where the energy is recovered by using electric motors as generators but is immediately dissipated as heat in resistors. In addition to improving the overall efficiency of the vehicle, regeneration can significantly extend the life of the braking system as the mechanical parts will not wear out very quickly. The most common form of regenerative brake involves an electric motor functioning as an electric generator. In electric railways, the electricity generated is fed back into the traction power supply. In battery electric and hybrid electric vehicles, the energy is stored chemically in a battery, electrically in a bank of capacitors, or mechanically in a rotating flywheel. Hydraulic hybrid vehicles use hydraulic motors to store energy in the form of compressed air. In a hydrogen fuel cell powered vehicle, the electrical energy generated by the motor is used to break waste water down into oxygen and hydrogen which is recycled back into the fuel cell for later reuse.

The most common form of regenerative brake involves using an electric motor as an electric generator. The working of the regenerative braking system depends upon the working principle of an electric motor, which is an important component of the system. The electric motor gets activated when some electric current is passed through it. But, when some external force is applied to activate the motor (during the braking), then it behaves as a generator and generates electricity. This means that whenever the motor runs in one direction, the electric energy gets converted into mechanical energy, which is then used to accelerate the vehicle, and whenever the motor runs in the opposite direction, it performs functions of a generator, which then converts mechanical energy into electrical energy, which makes it possible to utilize the rotational force of the driving axle to turn the electric motors, which results in regenerating electric energy for storage in the battery and simultaneously reducing the speed of the car with the regenerative resistance of the electric motors. This electricity is then used for recharging the battery.

Coordination of Electric and Mechanical Brake: In an electric Motor, the Total Brake distribution is in two aspects which are Electrical Brake which is called Regenerative Brake, and Mechanical Brake or Classical Brake with a hydraulic cylindrical system. Brake Force distribution must be uniform, If the Regenerative braking power requirement is more than the charging limit of the battery or more than the regenerative capacity of the machine we must apply Mechanical brakes as well. In a practical case, the combination of these two is applied. So usually it is a combined response of Mechanical brake and Regenerative brake. The reason for how this braking force is combined, that particular phenomena are called Brake Control Strategies. There are two Brake Control Strategies, which are Series - In case of Series, we apply Mechanical brake and Regenerative electric brake one after another. We can apply only one brake strategy at a time either apply Regeneratively or apply Mechanical brake. The Series Brake Control Strategy has a further classification, that is based on whether we want the comfort of driver or Brake behavior compared to energy efficiency. Parallel - In the case of Parallel, we apply both brakes simultaneously. This Particular Parallel braking is going to happen both at a time. Electric Driven Intelligent Brake (EDIB) is a combination of Hydraulic brake or Mechanical brake along with a Regenerative brake. It is a Parallel braking technique. The Control criteria such that at low speed use regenerative braking higher and at high speed or during the initial braking period we actually combine the both.

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ANSWER-3

MATLAB CODE:

close all;

clear all;

clc;

Torque= linspace(1,250,250) ; %lnput Torque
Speed= linspace(1,2000,250) ; %lnput Speed
[w,T]= meshgrid (speed,Torque); %Converting to 2D array

Kc= 0.3; % Coppper loss constant
Ki= 0.009; % Iron loss Constant
Kw= 0.00005; % Windage loss constant
C=30; % constant loss

Pout= w.*T; %Output Power

C_loss=Kc*(T.^2); %Copper loss
I_loss=Ki*w; %Iron loss
w_loss=Kw*(w.^3); %Windage loss

Pin=Pout+C_loss+I_loss+w_loss+C; %Input power
eff=Pout./Pin

contour(Speed, Torque,eff)
title('Torque-speed-efficincy Contor of the induction motor');
xlabel('RPM*);
ylabel('TORQUE (N-m)');

Syntax Explanation:-In this program we are plotting speed Vs torque characteristic with the efficiency values. For this, first we are defining speed and torque values of motor. Then as we need to draw a contour, we convert this ID array to 2D array using "MESHGRID" command. Then we are defining the Cu constants for losses, like Cu loss constants, iron loss constant and windage loss constant.

Pi=Pout+Kc*T^2 + Ki*w + Kw*^3 + Constat loss

Using this formula, we calculate the efficiency and then plot the contour.

Result:-