How Car Parts Work: July 2016

Shock absorber (also known as damper) is a hydraulic device used commonly in automobiles to absorb and dampen the vibrations which a vehicle experiences while traveling on irregular surfaces. Kinetic energy is converted into heat energy and the heat is dissipated.

A shock absorber is usually used in conjunction with coil springs. It actually absorbs the natural frequency of the spring and dampens the unwanted spring motion. Imagine a car with only springs. The drive will be a lot bouncy without shock absorbers.

Design of a Shock Absorber:

Twin tube shock absorber is the most commonly used type of shock absorber. So let’s discuss the working of a twin tube shock absorber. As the name suggests, it consists of two tubes. The outer tube, also known as reserve tube mount is connected to the frame of the vehicle, whereas the inner tube (also known as pressure tube) is connected to the wheel axle.

The reserve tube is internally connected to a piston via a piston rod. The reserve tube with a piston sits on the pressure tube filled with hydraulic fluid. Orifices of very small diameters are pocketed out in the piston.

Working of a Shock Absorber:

When a vehicle hits a bump, all the kinetic energy from the spring is transferred to the reserve tube. The kinetic energy is then transferred to the piston. To explain in a simple way, the reserve tube exerts a lot of force on the pressure tube. The hydraulic fluid in the pressure tube is compressed and a small amount of fluid escapes through the tiny orifices in the piston under a great pressure. Since only a small amount of fluid escapes to the reserve tube, the piston moves down slowly and hence the spring movement is dampened.

Every time we hit the brakes on a moving car, all the energy that the engine has supplied to the wheels goes to waste. In other words, the kinetic energy that is used to power the wheels is converted into heat when brakes are applied. The heat generated is of no use and thus we waste valuable energy.

Engineers have come up with a method to use the braking energy to be converted into electrical energy and recharge the battery. This method of utilizing the braking energy to be converted into electrical energy is known as Regenerative Braking. This system captures most of the kinetic energy and converts into electricity, which can recharge the battery. This system is used more commonly in hybrid and electric cars because it is imperative to recharge the batteries to make the car run longer.

How does braking waste energy?

Any normal guy driving a car would think that he is not wasting much energy in applying the brakes, because he is just using his foot to press the pedal. It doesn’t require a huge amount of force to apply pressure on the brake pedal and bring the car to a stop. So how are we wasting energy while braking?

Look at the above scenario from an engine’s perspective. Engine does all the work to generate power and supply it in the form of kinetic energy to the wheels. A lot of energy in the form of fuel is used to provide the momentum to the wheels. When brakes are applied, the car’s momentum is lost and it either slows down or comes to a halt. All the kinetic energy is wasted in the form of heat due to the friction between the brake pads and the drum. Now to start the car again from the start requires more fuel to provide the momentum. Hence, we are wasting a lot of valuable energy while braking.

Regenerative Braking System:

As already mentioned, regenerative braking technology is used in hybrid and electric cars because the wheels of these cars are powered by electric motors. The electric motors convert the electrical energy from the battery into kinetic energy which drives the wheels. During braking action, instead of using brake pads, the electric motor starts rotating in reverse direction.

When the driver steps on the brake pedal, the electric motor switches to generator mode by reversing its direction of rotation. Through its rotation, the generator converts a portion of the kinetic energy into electrical energy. This electrical energy is then stored in a high voltage battery. As a result of this electricity generation, generative braking torque is produced by the motor which decelerates the wheels. However, the generative braking torque won’t be sufficient to completely halt the vehicle. Therefore, once the vehicle is decelerated to a low speed, conventional friction brakes (disc or drum brake) further assist in stopping the wheels.

In the case of emergency where vehicle has to be stopped immediately, only friction brakes will be used. Regenerative brakes are more useful in stopping a slow moving vehicle.

Advantages of Regenerative Braking:

· It enables an extended battery range in electric vehicles.

· Reduces fuel consumption and CO₂ emissions in hybrid vehicles.