Week-11 Challenge: Braking

AIM:

1. For a defined driving cycle, calculate the energy required for braking.
2. Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?
3. Make a MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.

FOR QUESTION1:-

1. For a defined driving cycle, calculate the energy required for braking.

Answer:

A driving cycle is a series of data points representing the speed of a vehicle versus time. Driving cycles are produced by different countries and organizations to assess the performance of vehicles in various ways, as for instance fuel consumption, electric vehicle autonomy and polluting emissions.Driving cycles are important components for evaluation and design of vehicles. They determine the focus of vehicle manufacturers, and indirectly they affect the environmental impact of vehicles since the vehicle control system is usually tuned to one or several driving cycles.

There are two types of driving cycles:

1. Transient driving cycles involve many changes, representing the constant speed changes typical of on-road driving.
2. Modal driving cycles involve protracted periods at constant speeds.

energy required for braking:

braking energy=1/2*m*v^2

where, the braking energy is the kinetic energy in unit of joule

m=total mass of the vehicle (vehicle mass+pay load) in unit of kg.

v=(intial velocity-final velocity) in unit m/s8

for example if intial speed of a vehicle is 2o m/s and final speed is 10 m/s.the mass of the vehicle is 500 kg.then the required kinetic energy for braking is (1/2)*500*(20-10)^2=25000j=25kj

here for a drive cycle the required braking energy is calculated for each second of time to slow down or stop the vehicle-braking energy calculation for UDDS Driving cycle.

FOR QUESTION2:-

2)Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?

* Electric motor can’t develop braking torque at high speed similar to starting

So Electric motor can't develop braking torque at high speed similar to starting, because Braking Torque of an EV Motor is not as high as the Acceleration Torque. Therefore Regenerative braking is cannot happen so effectively that we can get all the power back to the battery. TheDC motor has high starting torque.In a series motor the same current flows through the armature and the field winding. The torque is therefore proportional to the square of the current. The current is set by the supply voltage and the back-emf generated in the armature.

DC motor torque vs speed characteristics:

here for both AC or DC there is no torque at maximum speed,gradually the torque decreses at high speed tends to be maximum speed.this situation does not occur at the begining of acceleration because most of the torque is used to increse the kinetic energy of the load.but when the speed is alredy high and no extra load is applied it is not possible to increse 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 and the regenerative braking.

in the mechanical brakings are2 types braking system .they are:

a)Mechanical braking:

The mechanical braking system powers the hand brake or emergency brake. It is the type of braking system in which the brake force applied on the brake pedal is carried to the final brake drum or disc rotor by the various mechanical linkages like cylindrical rods, fulcrums, springs etc. In order to stop the vehicle.What are the types of braking systems? The braking system can be classified into the mechanical brake, disc brake, hydraulic brake, power-assisted brake, air brake, electric, and hand brake system.

there are several types of mechanical brakes:

A)band brakes:

A band brake system resembles a drum brake system, except instead of using brake shoes to press against the inside of a rotating drum, the band brake uses a flexible band on the outside of the drum. When the brakes are initiated by pulling or pushing a lever, this creates tension in the band.

B) drum brake:

The drum brake has a primary function, namely as a medium for friction with the brake pads for the purpose that the wheels will stop on the road. Drum brakes last longer because drum brakes have increased friction contact area than a disc. Drum brakes are cheaper to manufacture than disc brakes. Rear drum brakes generate lower heat. Drum brakes have a built-in self energizing effect that requires less input force (such as hydraulic pressure.

C)disc brakes:

b)electrical braking:

A system in which a braking action is applied to an electric motor by causing it to act as a generator.Electric brakes use a sensor controlled by the tow vehicle's brake lights. When the lights activate, so does the brake controller. This sends power down a separate heavy-duty circuit to the trailer brakes.

The braking is the process of reducing the speed of an induction motor. In braking, the motor works as a generator developing a negative torque which opposes the motion of a motor. The braking of an induction motor is mainly classified into three types. They are. Regenerative Braking.

The brake system takes the kinetic energy of your moving vehicle and converts it to thermal energy through friction. That energy is used to slow and stop your four-thousand-pound-plus metal machine. The concept is the same; the equipment, well that is a bit more complex

electric and mechanical brake cordination:

There are mainly 2 ways by which the electric vehicles cloud be braked:

• series-regenerative braking and mechanical braking both are appiled one after another
• parallel-regenerative braking and mechanical braking both are appiled simultaneously.

When brake pedal is pressed the hydraulic fluid reaches the brake pistons and credited 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.

FOR QUESTION 3:

3)Make a MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.

MATLAB CODE:

clear all
close all
clc
%speed array
omega=linspace(0 ,300 ,100);
%torque array
T=linspace(0 ,2000 ,100);
%meshgrid
[X,y]=meshgrid(T,omega);
%loss coefficient
cu=0.17; %copper losses
fe=0.006; %iron coefficient
win=0.000016; %windage coefficient
%losses
cu_loss=cu*(y.^2); %copper losses
fe_loss=fe*(X.^2); %iron losses
win_loss=win*(X.^3); %windage losses
cond_loss=18; %conduction losses
%output power
p_out=(X.*y);
%Inputpower
p_in=p_out+(cu_loss)+(fe_loss)+(win_loss)+(cond_loss);
%efficiency
n=((p_out)./(p_in));

%efficiency values for contour
w=linspace(0.75 ,0.95 ,10);
%contour plot
contour(X,y,n,w)
xlabel('angular speed,rad/s')
ylabel('torque, Nm')
title('speed,torque and efficiency characterictics of motor');

Result :

code explanation:

In this MATLAB script,we create arrays for the speed aand the torque of the motor.they each also have a characteristics constant of proportionality which are all assumed for the following calculations and represnted as 'K' .in each calculation ,the speed and the torque are represented respectively as w&T.

copper losses=K.cu.w2

iron losses=K.Fe.T2

windage losses=Kw.T3

the values of coefficient are taken as general values.conduction losses are assumed to be 18 joules

We plot the contour with the 'contour' command.in condition ,an array for the efficency values we want to plot for is created called 'W' and is assigned for values ranging from an efficiency level of 0.65 to 0.95 .this array is used in the creation of the contour.axis labels and a title also made for better reliability.

OUTPUT:

From this contour plot we can see the highest level of efficiency arises in the ineermost contour plot and this efficiency decreses as the contours increses in size from the innermost contour.

CONCLUSION:

1. WE define thw driving cycle, calculate the energy required for braking.
2. We learn about the electric motor can’t develop braking torque at high speed similar to starting and How electric and mechanical brakes are coordinated.
3. we write the MATLAB program which plots contour of given motor speed, torque and efficiency values. Attach the code as a .m file attach a screenshot of all the plots.