Week-11 Challenge: Braking

SOLUTION 1.

Calculating the Energy required for braking of UDDS Drive Cycle:-

BRAKING:- Braking is the condition to slow down or stop a moving vehicle as required. There are several techniques to apply brakes, which can be Mechanical and Electrical. The most commonly used technique is by applying friction. It consumes energy. The consumed Kinetic Energy can be derived as the following Equation.

BRAKING ENERGY=(1/2)*M*V^2 (JOULES)

Where Braking Energy is the Kinetic Energy only.

M=Total mass of the vehicles (Vehicle mass+Pay load) in the unit of KG.

V=(Initial Velocity-Final Velocity) in m/sec

For Example:

If the initial speed of the vehicle is 20m/sec and the final speed is 10m/sec. The mass of the vehicle is 500kg.Then the required Kinetic Energy for Braking is:

=(1/2)*500*(20-10)^2

=25000J

=25 KILO JOULES

SOLUTION 2.

AC-MOTOR (TORQUE Vs SPEED ) DC-MOTOR (TORQUE Vs SPEED)

From the above plots, we can see that for both cases of AC or DC there is no torque at maximum speed, gradually the torque decreases as speed increases.This situation does not occurs at the beginning of acceleration because most of the torque is used to increase the kinetic energy of the load. But when the speed is already high & no extra load is applied it is not possible to increase the torque as well as to develop braking torque. The braking operation happens in the motion which is been distributed as per proportion in the brake energy & the regenerative braking.

THERE ARE TWO TYPES OF BRAKING:-

1) MECHANICAL BRAKING

2) ELECTRICAL BRAKING

MECHANICAL BRAKING:-

Mechanical Brakes all act by generating frictional forces as two surfaces rub against each other. The stopping power of a brake depends largely on the surface area of frictional surfaces as well as on the actuation force applied. Mechanical brakes are assemblies consisting of mechanical elements for the slowing or stopping of shafts in equipment drives. There are several types of mechanical brakes:-

1)BAND BRAKES

2)DRUM BRAKES

3)DISC BRAKES

BAND BRAKES:-

These are the simplest brake configuration, have a metal band lined with heat and wear resistance friction materials.

DRUM BRAKES:- These are commonly used on automobile rear wheels, work when shoes press against a spinning surface called a drum.

DISC BRAKES:- These are constructed of brake pads, a caliper and a rotor. During operation, the brake pads are squeezed against the rotor.

ELECTRIC BRAKING:- Electric brakes are devices that use an electric current or magnetic actuating force to slow or stop the motion of a rotating component. They are used in industrial and vehicular braking applications that require fast response times and precise tension control. The wire tap directly into the wiring. When electricity is on, it magnetizes the brake magnet. The magnet is attracted to the Drum's face. When it contacts this area, the friction causes it to rotate, which moves the actuating arm, and pushes the shoes out against the Drum. Those shoes have special brake pad material on them that resists the heat caused by friction. When the shoes press against the inside of the drum, they prevent the hub, and consequently the wheel that's touching the ground.

A very beautiful electric braking scheme called the REGENERATIVE BRAKING is now being employed for electric braking. Here during the braking action, the motor is operated as a generator. As we know that during the generating action a counter torque is produced. so this counter-torque opposes the motion of the motor and the motor comes to halt. Moreover, the brake energy is converted to electrical energy which can be fed back to the source using power converters.

ELECTRICAL AND MECHANICAL BRAKE COORDINATION:-

There are mainly 2 ways by which Electric vehicles could be braked:-

• SERIES:- Regenerative braking and mechanical braking both are applied one after another.
• PARALLEL:-Regenerative braking and mechanical braking both are applied simultaneously.

When the brake pedal is pressed the hydraulic fluid reaches the brake pistons and created the braking pressure on the wheels and the same kinetic energy is been used by the Regenerative braking for generating more power using the Bi-directional motor which operates as a generator while braking.

SOLUTION 3.

MATLAB PROGRAM WHICH PLOTS CONTOUR OF GIVEN MOTOR SPEED,TORQUE AND EFFICIENCY VALUES :-

clear all
close all
clc

speed= linspace(0,1000);
torque= linspace(0,500);

kc= 0.2;
ki=0.006;
kw=0.000010;
k=20;

[x,y] = meshgrid(speed,torque);
copper_loss= (y.^2)*kc;
iron_loss= x*ki;
windage_loss= (x.^3)*kw;

output_power= x.*y;
input_power= (copper_loss+iron_loss+windage_loss+output_power+k);
efficiency=(output_power./input_power);

n=linspace(0.7,0.95,10);
contourf(x,y,efficiency,n);
title('speed-torque efficiency')
xlabel('speed (rad/s)');
ylabel('torque (Nm)');
colorbar

OUTPUT PLOT:-