Week-11 Challenge: Braking
1.
Braking: Braking is a condition to slow down or stops a moving vehicle as required. There are several techniques to apply brakes, which can be mechanical or electrical. The most commonly used technique is by applying friction. 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 40m/s and final speed is 15m/s. The mass of the vehicle is 1000kg. Then the required kinetic energy for Braking is (1/2)*1000*(40-15)^2 = 312500 J =312KJ
2.
Speed - Torque Characteristics of DC Motor
Speed - Torque Characteristics of AC Motor
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:
(i)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.
(ii) 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 shoe 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.
There are mainly 2 ways by which the Electric Vehicles could be braked:
* Series- Regenerative braking and mechanical braking both are applied one after another.
* Parallel- Regenerative braking and mechanical braking both are applied simultaneously.
When 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.
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 = KCu x w^2
Iron losses = KFe x T^2
Winding losses = Kw x T^3
Conduction losses is taken as 20J.
From this contour plot, we can see that the highest level of efficiency arises in the innermost contour plot and this efficiency decreases as the contours increase in size from the innermost contour.