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.

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

ANS:

Driving cycle:

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, for instance, fuel consumption, electric vehicle autonomy and polluting emissions.

Calculate the energy required for braking:

We have been able to use the energy which is been disappeared at the point of breaking. The kinetic energy which helps the vehicle to run also gets wasted while the braking is done. Though it depends on various parameters on how effective the braking would be it can be depended upon.

1. Number of Brake Pistons
2. Duration and Degree of Brake Pedal been Pressed
3. Road Condition
4. Temperature
5. Brake Pad and Disc Condition
6. Mass of the Vehicle

Still with a basic operation where the vehicle is in motion and the brakes are applied the same efficiency could be calculated by the given equations,

where,

BE=braking energy,

m=mass of the vehicle,

v = velocity.

In this manner, the same calculation is carried out for calculating the brake efficiency required at the peak point. It is a drive cycle with speed variations the braking power required would vary but still, the highest braking power required is mentioned below.

Please refer to the attached excel sheet for complete calculation of deacceleration energy require in the UDDS cycle.

Braking Energy Required:

• To reduce speed from 80 to 40 kmph in 20 sec =292 KJ.
• To reduce speed from 80 to 0 kmph in 0 sec =560 KJ.

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

ANS:

Electric motor can't develop braking torque at a high speed similar to starting:

When the motor is at rest and it has to operate from a standstill position to reach the moderate speed the higher torque is required to bring the motor into operation. Whereas when the vehicle is already at high speed the capping or the limit is reached by the motor operation and thus any further higher torque could not be obtained while braking. The braking operation happens in the motion which is been distributed as per proportion in the brake energy and the regenerative braking.

Electric and mechanical brakes:

In Mechanical braking which we usually see and experience in all vehicles, the brake pedal in the vehicle cabin helps us to engage or disengage the brakes. Currently, braking technology has done wonders by inventing life-saving braking technologies such as ABS, EBD, BA and many others. All these technologies play a vital role in stopping the vehicle and coming back to rest at a high speed. In all these vehicles when the driver applies the brakes using brake pads come closer to the disc connected with the driving disc. The brake pads usually help inefficient braking.

There are two generic methods by which the vehicle could be braked in the ELECTRIC BRAKES are,

1.Series Braking - The Regenerative Braking of the Mechanical Braking are applied one after another.

2.Parallel Braking - The Regenerative Braking or the Mechanical Braking both are applied Parallely.

When the brake pedal is pressed the hydraulic fluid reaches the brake piston 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 An example of the proposition of Regenerative Braking and the Mechanical Braking.

NISSAN LEAF EDIB (ELECTRONIC-DRIVEN INTELLIGENT BRAKING):

EDIB (Electric Driven Intelligent Brake) controls the regenerative brake and friction brake to support both of these requirements. Further, it also controls the reactive force from the pedal in order to unify the feeling when stepping down on the pedal and the sense of deceleration.

Q.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.

ANS:

MATLAB program that plots the contour of given motor speed, torque and efficiency values:

Explanation of Matlab Program:

In this program, we are plotting speed Vs torque characteristics with the efficiency values. For this, first, we are defining the speed and torque values of the motor.

Then, as we need to draw a contour, we convert this 1D array to a 2D array using the "MESH GRID" command.

Then we are defining the Cu constants for losses, like Cu loss constants, iron loss constant and windage loss constant.

The Input Power is,

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

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

Workspace:

In workspace all the input, output variable values as well as result variables are stored. we can also save it separately for further uses.

Result:

Speed-Torque Characteristics:

Conclusion:

By using Matlab, we plotted the contour of motor speed, torque and efficiency characteristics of motor.

From the contour plot, we can conclude that motor operates efficiently in specific regions for a specified values of torque and speed of motor.