Week-11 Challenge: Braking
1. calculate the energy required for braking.
Driving Cycle,
A driving cycle is a set of vehicle speed parameters with respect to time. It is used to calculate the fuel consumption of vehicle, which is later compared with other vehicles. The following driving cycle points,
1. To observe the performance of the vehicle (Fuel and emission test).
2. To analyze the battery status and energy consumption.
3. To Simulate the vehicle design.
Braking:
The IC vehicles involves the conversion of kinetic energy into thermal energy (heat). When stepping on the brakes, the driver commands a stopping force several times as powerful as the force that puts the car in motion and dissipates the associated kinetic energy as heat.
Kinetic energy E = 1/2 *m*v^2
where,
m = mass of the vehicle in Kg
v = velocity of the vehicle in m/s
E(kinetic) = Kinectic energy in KJ
Ex. if the Initial speed of a vehicle is 30m/s and final speed is 10m/s. The mass of the vehicle is 1000kg. Then the required kinetic energy for Braking is (1/2)*1000*(30-10)^2 = 25000 J =25KJ
2. Why electric motor can’t develop braking torque at high speed similar to starting? How electric and mechanical brakes are coordinated?
Here for both in case of AC or DC there is no torque at maximum speed, gradually the torque decreases at high speed as the speed tends to be maximum speed. 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.
There are two types of Braking,
1. 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. 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.
2. Electrical Braking,
Electric brakes are devices that use an electrical 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 magnet in the backing plate has 2 conductor wires which tap directly into the wiring. When electricity is on, it magnetizes the brake magnet. The magnet is attracted to the drum 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 a special brake pad material on them that resists the heat caused by that friction. When the shoes press against the inside of the drum, they prevent the hub, and consequently the wheel that's touching the ground.
Combination of Electric and Mechanical Braking,
There are two main ways by which Electric Vehicle braked,
1. Series Regenerative,
Regenerative braking and mechanical braking both are applied one after another.
2. Parallel Regenerative,
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.
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 Program, (Graph Plot attached)
Explanation:
In this MATLAB script, we create arrays for the speed and the torque of the motor using the ‘linspace’ command. For the speed, consider a range of values from 0 to 2000 radians per second whereas for the torque, consider a range of values from 0 to 300Nm.These arrays are then used to create 2D grid coordinates using the ‘meshgrid’ command. These coordinates will help in the creation of the contour plot. In order to find the efficiency of the motor, we need to consider the various losses that occur in the motor’s operation. These are:
Copper losses
Iron losses
Windage losses
Conduction losses
These various losses are dependent on the speed and the torque of the motor. They each also have a characteristic constant of proportionality which are all assumed for the following calculations and represented as 'K'. In each calculation, the speed and the torque are represented respectively as: ω and T.
Copper losses = KCu⋅ω2
Iron losses =KFe⋅T2
Windage losses =Kw⋅T3
The values of coefficients are taken as general values. Conduction losses are assumed to be 18 Joules.
Finally we plot the contour with the 'contour' command. In addition, an array for the efficiency values we want to plot for is created called 'W' and is assigned for values ranging from an efficiency level of 0.75 to 0.95. This array is used in the creation of the contour. Axis labels and a title is also made for better readability.