Week-11 Challenge: Braking

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

Answer:

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

Answer:

Electric motor can't develop braking torque at high speed similar to starting, because Braking torque is applied in the opposite direction of the rotation. We can use a mechanical brake to produce a braking torque.

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.

Types of braking

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.

Band brakes:

These are the simplest brake configuration, have a metal band lined with heat and wear resistant friction material.

Drum brakes:

These are commonly used on automobile rear wheels, work when shoes press against a spinning surface called a drum

Disc brakes:

These are constructed of brake pads, a calliper, and a rotor. During operation, the brake pads are squeezed against the rotor.

This thermal energy generates heat, but since the main components are exposed to the atmosphere, this heat can be diffused efficiently. This heat-dissipating property reduces brake fade, which is the phenomenon where braking performance is influenced by the heat. Another advantage of disc brakes is its resistance to water fade, which occurs when the water on the brakes significantly reduces braking force. When the vehicle is in motion, the rotor spins at high speeds and this rotational motion discharges the water from the rotors themselves, resulting in stable braking force.

The brake rotor (disc) which rotates with the wheel, is clamped by brake pads (friction material) fitted to the caliper from both sides with pressure from the piston(s) (pressure mechanism) and decelerates the disc rotation, thereby slowing down and stopping the vehicle.

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.

A very beautiful electric braking scheme called Regenerative Braking is now being employed for electric braking. Here during the

braking action, the motor is operated as generator. As we know that during generating action, a counter torque is produced. So this

counter torque opposes the motion of motor and motor comes to halt. Moreover, the brake energy is converted to electrical energy

which can be fed back to the source using power converters.

Electric and Mechanical brake coordination:

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.

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.

Answer:

Plot: