Week-11 Challenge: Braking

AIM:-

• To defined driving cycle, calculate the energy required for braking.
• Why electric motor can’t develop braking torque at high speed similar to starting.
• How electric and mechanical brakes are coordinated.
• Make a MATLAB program which plots contour of given motor speed, torque and efficiency values.

EXPLAINATION:-

1.Introduction Driving Cycle:-

The braking performance is one of the most important concerns in vehicle safety. In urban area driving, a significant amount of energy is consumed in braking. Electrification of vehicles makes it feasible to recover some of the energy lost in braking. A hybrid braking system was developed to ensure the efficient braking of the vehicle and recovering the braking energy. The design and control objectives of such a hybrid braking system are to ensure sufficient braking force to quickly reduce the vehicle speed, properly distributing the brake force to the front and rear axle, and also recover as much braking energy as possible. So understanding of braking energy of a driving cycle is important. Now, it is also important to mention that braking energy also depends upon the type of driving cycle i.e. the higher number of time the vehicle will have rapid speed changes and will come to rest then the braking energy will automatically rise for that particular drive cycle than other driving cycle where the rapid speed changes don't occur.

Calculate the energy required :-

It consumes energy .The consumed kinetic Energy can be derived as following equation-

Braking Energy = (1/2)*m*v^2

Where, 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= (Initial Velocity-final Velocity) in unit m/s.

For Example if Initial speed of a vehicle is 20m/s and final speed is 10m/s. The mass of the vehicle is 500kg. Then the required kinetic energy for Braking is (1/2)*500*(20-10)^2 = 25000 J =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.

2.Why electric motor can’t develop braking torque at high speed similar to starting.

At High speed, the torque will be less & operates at a constant power region hence it is difficult to bring the vehicle to rest or decelerate immediately. The peak acceleration torque is greater than the peak deceleration torque. Hence Braking torque of the EV motor is not as high as the acceleration Torque.

This situation does not occur at the beginning of acceleration because most of the torque is used to increase the kinetic energy of the load (and motor). But when the speed is already high and 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 and the regenerative braking.

The term braking comes from the term brake. We know that brake is a piece of equipment to reduce the speed of any moving or rotating equipment, like vehicles, locomotives. The process of applying brakes can be termed braking. Now coming to the term or question what is braking. First of all, we can classify the term braking into two parts.

Mechanical braking is mostly used in scooters, motor vehicles, and motorcycles where small power is required. It is essential in manufacturing power transmission applications, material handling, etc. It delivers forces to the axle or a wheel to stop motion. It helps to reduce the speed of the system slowly by the mechanical process when compared to electrical braking. The working of a mechanical brake depends on the pedal. When the pedal is pressed, the brake shoes are pushed outwards and rotates against the drum which is connected to the wheels. Hence the machine or vehicle gets slow down and stopped. And when the pedal is released, it goes to a normal position due to the pullback action of spring shoes.

• Drum braking
• Disk braking
• Band braking
• Pawl and Ratchet braking

There are several types of mechanical brakes.

1) Band brakes: These are the simplest brake configuration, have a metal band lined with heat and wear-resistant friction material.

2.Drum brakes: These are commonly used on automobile rear wheels, which work when shoes press against a spinning surface called a drum.

3.Disc brakes: These are constructed of brake pads, a caliper, and a rotor. During operation, the brake pads are squeezed against the rotor.

Electrical Braking is used to reduce the speed of the machine depending on flux and torque. This type of braking is mainly used for functional braking to control the speed of the machine. It is easy to handle and comfortable. But it cannot be used for emergency braking and parking braking.

• Plugging type braking
• DC injection type braking
• Eddy current braking
• Dynamic resistor type braking
• Regenerative braking
• Sharing DC bus type braking

1. 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.

code:-

clear all

clc

%speed Arry

omenga=linspace(0,300,100);

%Torque Arry

T=linspace(0,200, 100);

% Meshgrid

[X,Y]=meshgrid(T,omega);

%Loss Coefficients

cu_loss=cu*(y.^2); % copper coefficient

fe=0.006; % Iron coefficient

win=0.000015; % 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; %condition losses

%output power

P_out=(x.*y);

% input power

P_in=P_out+ (cu_loss )+(win_loss)+( cond_loss);

%Efficiency

n=((P_out)./(P_in));

%Efficiency value for contour

W=linspace(0.75,0.95,10);

%Contour Plot

contour(x,y,n,W)

xlabel('Angular speed ,rad/s')

ylabel ('Torque,Nm')

tittle ('speed,Torque and Efficiency characteristics of Motor ')

graph:-