Electric Brake

1.10. Electric Brakes

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.

Electric braking starts with applying a current proportional to the desired brake force to the electromagnet. The braking force asserted is caused by the friction between the electromagnet and the face of the drum which depends on the current through the electromagnet.

Fig:   Electric drum brake

1. Brake shield/drum

2. Reactor springs

3. Brake shoe

4. Actuating arm

5. Electromagnet

6. Adjuster

7. Adjuster spring

In an electric brake the current from the battery is utilized to energize an electromagnet within the brake drum. This actuates a cam to expand the brake shoes. As pedal is pressed more, hydraulic pressure actuates the rheostat to increase current to the electromagnet.

When current is stop, the cam and brake shoes are returned to the release position by retractor springs. The severity of braking is controlled by means of a rheostat, which is operated by the driver through the foot pedal.

As the brakes are applied for the main vehicle, it slows down due to which the weight or pendulum in the trailer brake control device moves forward, exposing a light-sensitive diode to more of the light beam. This increases the current to the electromagnet in the trailer brake, thereby applying a brake.

As an alternative to the foot -operated rheostat, hydraulic pressure has also been used to apply electric brakes. This type of brakes, though not very popular, as service brakes, has been commonly used on trailers. One such example is Warner electric brake.

Types of Electric Brakes:

There are two main types of electric brakes-

 1. Magnetic Brakes
 2. Electrically Actuated friction Brakes

Magnetic brakes are non-contact brakes that use magnetic fields to actuate the braking components. It is further divided into four types-

 a. Permanent Magnet Brakes

 b. Electromagnetic Brakes

 c. Eddy Current Brakes

 d. Hysteresis Powered Brakes

Although many electric brakes use mechanical methods for actuation, others rely upon friction. Electric Friction Brake is also divided into four types-

 a. Band Brakes

 b. Drum Brakes

 c. Disc Brakes

 d. Cone Brakes

1.10.1.  Advantages, limitations and applications of electric brakes:

1.10.1.1.     Advantage:

1. Simple in design and installation.

2. Simplified operating linkage (only one cable for each drum).

3. Less time-lag between the pressing of brake pedal and application of brakes at the wheels.

4. Much better control over the braking effort.

5. Absence of grab.

6. No adjustment required during its lining life.

7. For trailer brakes, this type offers much simplified connections; simply one cable has to be carried to the trailer side.

1.10.1.2.     Limitations:

1. Electric brakes are not very popular, as service brakes.

2. Necessary requirement of battery during brake operation.

3. Initial cost is high.

1.10.1.3.     Application:

1. These brakes are commonly used on trailers.
2. New electric modern trends cars like Tesla Motors (sedan car).

Fig:  Electric Drum Brake (Original View)