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AIM : To perform the various operations corresponding to an Electric vehicle inorder to fulfill the required objectives that were provided. OBJECTIVE : To calculate the energy required for braking. To brief about how electric and mechanical brakes are coordinated. To make a MATLAB program to plot…
Yogesh S
updated on 12 Feb 2021
AIM :
To perform the various operations corresponding to an Electric vehicle inorder to fulfill the required objectives that were provided.
OBJECTIVE :
1. Calculation of Energy required for Braking
Braking system :
A brake system is designed to slow and halt the motion of vehicle. To do this, various components within the brake system must convert vehicle’s moving energy into heat. This is done by using friction.
Friction is the resistance to movement exerted by two objects on each other. Two forms of friction play a part in controlling a vehicle: Kinetic or moving, and static or stationary. The amount of friction or resistance to movement depends upon the type of material in contact, the smoothness of their rubbing surfaces and the pressure holding them together.
Thus, in a nutshell a car brake works by applying a static surface to a moving surface of a vehicle, thus causing friction and converting kinetic energy into heat energy. The high-level mechanics are as follows.
As the brakes on a moving automobile are put into motion, rough-textures brake pads or brake shoes are pressed against the rotating parts of vehicle, be it disc or drum. The kinetic energy or momentum of the vehicle is then converted into heat energy by kinetic friction of the rubbing surfaces and the car or truck slows down.
When vehicle comes to stop, it is held in place by static friction. The friction between surfaces of brakes as well as the friction between tires and roads resist any movement. To overcome the static friction that holds the car motionless, brakes are released. The heat energy of combustion of in engine is converted into kinetic energy by transmission and drive train, and the vehicle moves.
The Governing equation to find braking energy is,
Braking Energy = 12mv2 kWh
Where m is the mass of the vehicle in kg
v is the velocity of the vehicle in m/s
The MATLAB program for Calculating the Braking Energy was attached,
close all
clear all
clc
M = 1500; % mass of the vehicle
T = 100; % Time period
Dc = xlsread('DriveCycle'); % Reading the drive cycle
time = Dc(1:T,1); % Time velues
v= Dc(1:T,2); % Velocity values
t = (1:96);
dec_velocity = zeros(1,T);
Change_in_time = zeros(1,T);
braking_energy = zeros(1,T);
for i = (1:length(v)-1)
if v(i)>v(i+1)
dec_velocity(i) = v(i+1)-v(i);
Chnage_in_time(i)= time(i+1)-time(i);
deceleration(i) = dec_velocity(i)/ Chnage_in_time(i);
Braking_energy(i) = 0.5*M*((v(i))^2-(v(i+1))^2) / 3600;
end
end
figure(1)
subplot(3,1,1)
plot(time,v,'linewidth',2)
title('DRIVE CYCLE')
xlabel('Time')
ylabel('Speed')
subplot(3,1,2)
plot(t,deceleration,'color','y','linewidth',2)
title('DECELERATION VALUES')
xlabel('Time')
ylabel('Deceleration')
subplot(3,1,3)
plot(t,Braking_energy,'color','r','linewidth',2)
title('BRAKING ENERGY VALUES')
xlabel('Time')
ylabel('Braking Energy')
fprintf('The total braking energy required is %0.3f kWh',sum(Braking_energy))
The value of Braking energy from the command window output was,
The Output plot representing the Drive cycle, Deceleration and Braking energy with respect to time was also attached,
Thus the Total Braking Energy for the given cycle was calculated using a MATLAB program.
2. Coordination of Electric and Mechanical brakes
Mechanical Braking :
Mechanical brakes all act by generating frictional forces as two surfaces rub against each other. The stopping power or capacity of a brake depends largely on the surface area of frictional surfaces as well as on the actuation force applied. The friction and wear encountered by the working surfaces are severe. Thus, the durability of a brake or service life between maintenance depends heavily on the type of material used to line the shoe or pad.
Mechanical brakes are assemblies consisting of mechanical elements for the slowing or stopping of shafts in equipment drives. They use levers or linkages to transmit force from one point to another. Braking slows or stops the movement of the coupled shafts. There are several types of mechanical brakes. Band brakes, the simplest brake configuration, have a metal band lined with heat and wear resistant friction material. Drum brakes, which are commonly used on automobile rear wheels, work when shoes press against a spinning surface called a drum. Disc brakes are constructed of brake pads, a caliper, and a rotor.
Electrical Braking :
If the load is removed from an electric motor and supply to it be disconnected, it will continue to run for some time due to inertia. The time elapsing before it stops will be especially long if the motor is massive and has run at high speed.
It is essential, however, in many cases that the motor and its driven machine be stopped quickly (in machine tools, cranes, hoists etc). In fact, quick stopping of a motor is more essential than quick starting. Delay in starting up a motor only causes the machinery to stand idle; a delay in stopping a motor may result in heavy damage to equipment or to the manufactured products and even the loss of human life.
Coordination of Brakes :
Conventional port hybrid vehicles can’t ef fectively recycle tremendous kinetic energy brought by car brake due to the limitation of energy storage element and energy conversion form in energy recovery braking system. A parallel hydraulic hybrid power control system is designed to solve the contradiction between braking safety stability and realizing the maximum energy recovery. The linear proportional electromagnetic valve is adopted to control the hydraulic pressure of the hydraulic cylinder of the brake. The numerical control of the frictional braking force is realized, and the braking force control strategy can be realized with the braking control system. The experimental results show that the system improves the stability of friction braking and energy recovery.
The coordination of these brakes can be achieved using two methods
Electric motor braking :
Electric motor can’t develop braking torque at high speed similar to starting because the torque of the induction motor is inversely propotional to the square of the rotor speed.
Thus at higher speed the torque will be less, this justifies the given statement.
3. Plotting contour of given motor speed, torque and efficiency values
In this program a contour plot was obtained which includes motor speed, torque and efficiency values
Power = Speed * Velocity
Copper loss = Kc.T2
Iron loss = Ki.ω
Windage loss = Kw.ω3
Constant loss = C
Where,
ω - Speed (rad/s)
T - Torque (Nm)
Kc - Copper loss constant
Ki - Iron loss constant
Kw - Windage loss constant
The MATLAb code was attached below,
close all
clear all
clc
s = linspace(0,1000); % Motor speed
t = linspace(0,250); % Torque
% Constants
kc = 0.3; % Copper loss
ki = 0.008 % Iron loss
kw = 0.0001;% Windage loss
c = 20; % Motor loss
% Creating 2D Array
[W,T] = meshgrid(s,t);
op = (W.*T);
% Calculating losses
cu_loss = kc*(T.^2);
Fe_loss = W.*ki;
Windage_loss = (W.^3)*kw;
ip = op + cu_loss + Fe_loss + Windage_loss + c'
Eff = op./ip
% Eff Curves value
V = [0.70,0.75,0.80,0.85,0.875,0.90,0.91,0.92,0.93]
% Plotting
box off
grid off
contourf(W,T,Eff,V);
colorbar
xlabel('Motor Speed (rpm)');
ylabel('Torque (Nm)');
zlabel('Efficiency');
title('Contour plot - Motor speed, Torque and Efficiency')
From this code the following parameters were calculated ,
The contour plot was obtained as shown below,
CONCLUSION :
All the given objectives were satisfied with atmost perfection.
The images and files were attached wherever necessary.
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