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An airbag is a safety device that protects the passenger in the event of a collision, by restricting their movement and inducing a slow reduction of the body’s momentum as opposed to coming to an abrupt halt. The greatest thing about an air bag is that along with the seat belt, it can reduce death in a collision by about 30%.

How does an airbag help in safety?
During a collision, the body of the passenger would continue to move forward, even if the vehicle has come to a sudden halt. This is because of the momentum carried by the body. So, in a collision, the upper part of the body hits the steering wheel or the dashboard hard causing fatal injuries or death. In high speeds, the passenger’s head even collides with the wind shield. This is extremely dangerous.

An airbag prevents the passenger from being thrown toward the dashboard. It also slows down the process of the body’s motion coming to zero velocity.

How is an airbag deployed?
There are collision detectors installed along with the airbags. When a collision happens, these sensors detect it, and send the signal to the airbag. In the airbag, this signal triggers a reaction between sodium azide and potassium nitrate. This reaction releases nitrogen gas which inflates the air bag. All of this happens under a fraction of a second and after the deployment, the nitrogen gas escapes through holes in the airbag to cause deflation in order for the passenger to move.

Different types of airbags

Frontal airbag
Frontal air bags are designed to prevent occupants from anything that is at the front portion of the car, like dashboard, steering wheel or wind shield. Since 1998, frontal airbags have been a standard in all the vehicles. Frontal airbags do not eliminate the need for seat belts. And they also do not protect the passenger in rear collision or a rollover. The amount of protection an airbag can offer depends a lot on whether the seat belt is fastened or not. Seat belts keep the passenger in the proper position to ensure protection by the airbag. An important thing to keep in mind is, if the seat belt is not on while in a collision, airbags can cause fatal injuries to the passenger.

Side torso airbag
This protects the passenger from injury to the ribcage and the pelvis. This airbags deploys in between the passenger and the door. Special designs are being included recently and these protect the passenger even in a roll over crash.

Side curtain airbag
The side curtain airbag deploys from the roof and protects the passenger from rollover injuries. Roll sensing side curtain bags are usually used in SUVs and pickup trucks because they are prone to rollovers. But in case the driver in taking the vehicle off road, he can disable the feature.

Knee airbag
This airbag is meant to protect the knees since the knee too is highly exposed while in a collision. These airbags deploy just below the steering wheel. The knee airbag has been increasingly used in cars since 2000.

Seat cushion airbag
The seat cushion airbag prevents the pelvis from diving below the lap belt in a collision.

Center airbag
This is meant to protect the rear passengers from head injuries. It deploys from the rear center seat. In 2012, General Motors introduced a center airbag which deploys from the driver seat.

Seat belt airbag
This is actually a seat belt that can be used like any other seat belt. But in a collision, the seat belt inflates and offers extra protection.

Pedestrian airbag
Pedestrian airbags are different in that they protect the pedestrian as opposed to the passengers. It was introduced in Volvo V40 in 2012 and it deploys from the car bonnet, so that the impact of the car on the pedestrian’s body is reduced.
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A hydraulic brake system is one that uses brake fluid to transfer pressure to the wheels. In this system, when the brake pedal is pressed, force is exerted on the push rod, which in turn pressurizes the brake fluid, which pushes the pads against the rotor disc to stop the vehicle. A hydraulic braking system has the following parts.

• Master cylinder
  This consists of a cylinder filled with brake fluid, a brake fluid reservoir, one or two pistons, ports from the main cylinder to the brake fluid reservoir and a return spring. The master cylinder receives pressure from the brake lever and conveys it to the hydraulic lines that start from it.

• Wheel cylinder
  Similar to the master cylinder, the wheel cylinder receives pressure from the brake fluid and pushes the brake caliper pistons against the disc.

• Brake fluid (or brake oil) pipelines
  These pipelines carry the brake fluid and connect the master cylinder to the wheels cylinder in each wheel.

• Caliper assembly
  The caliper assembly contains the brake caliper pistons and the rotor disc. The caliper assembly is the component which is actually involved in the process of slowing down the wheel.

Working
When the brake pedal is pressed, the push rod presses the master cylinder’s piston. The piston pressurizes the brake fluid in the cylinder. The fluid moves through the pipelines and reaches the caliper assembly. At the caliper assembly, there are two pistons one on each side of the rotor disc and they are connected to the brake fluid. The brake fluid pressurizes each of the pistons from both the sides, and pushes them towards the rotor disc. Since there is a one way movement of the brake fluid due to the pressure from the brake lever, it is displaced in the brake fluid reservoir. This process leads to a frictional motion between the brake calipers and the rotor disc, and thus braking happens. And when the brake lever is released, the return spring in the master cylinder pushes the master piston to its original position and the displaced brake fluid returns back to the pipelines.

Brake fade
Brake fading is a common disadvantage of the hydraulic braking system. It is caused due to the following reasons:

• When hydraulic brakes are subjected to heavy work like descending down a steep inclination, they produce a lot of heat. This might, in extreme conditions, vaporize the braking fluid. This causes ineffective or weak pressure in the caliper assembly and thus faded braking.
• Due to continuous usage, the pads which cause friction over the rotor disc may become soft due to wearing. This also causes ineffective braking. It thus becomes important to check the brake pads regularly, and if necessary, replace it.

Did you ever think how the wheels of your car initiated to move ahead. The rotational force is passed from the transmission to the differential. The drive-shaft also known as a propeller shaft or cardan shaft is a device that transfers rotational force from the transmission system to the differential. Technically, a drive-shaft transfers torque and rotation to parts of the vehicle that are far from the transmission system. In automobiles, it is a longitudinal shaft from an engine/transmission to the other end of the vehicle before it goes to the wheels. Physically, it is tubular in design, with an outside metal housing that protects an interior metal cylinder.

Parts of a differential:

Flange: The flange is a collar like structure that fastens the drive-shaft to the pinion gear.

Pinion gear: This is just a normal gear and rides on the larger ring gear at a 90 degree angle.

Side gears: Side gears receive the rotation directly from the ring gear and transfer it to the axle.

Ring Gear: The biggest gear in the differential. This is the gear that receives the rotation from the drive-shaft.

Left and right axle shaft: Axle shafts on both the sides of the vehicle.

Spider Gears: Spider gears hold both the axles intact and allow the two axles to rotate at two different speeds.

Why is a differential needed?
The need for a differential arises due to a single, simple reason. While the vehicle turns towards the right or left, the wheels don’t rotate in the same speed. While taking a turn, the distance traveled by the front wheels is always a little more than the rear wheels. Since distance is directly proportional to the speed, the wheels spin at different speeds.

Now, if all the wheels had been fixed in order to spin at the same speed, at turns, the slow-spinning wheels have to drag on the ground, since their necessity to undergo spinning is less. If the vehicle is making a right turn, the order of speeds in each wheel is Front Left>Front Right>Rear Left>Rear Right. In case of the absence of differentials, in hard surfaces such as tar, the drag faced by the wheel that undergoes less spin is more intense. This induces wear and tear on the tire and driving on such conditions is also difficult.

The drive-shaft carries the rotating motion from the engine crankshaft to the differential. At the differential, the Ring gear along with the side gear and pinion gear breaks the flow of rotational motion in between so that, the wheels can rotate at different speeds while the differential receives a single speed of rotation.
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Unlike other transmission systems, CVT does not have a set of gears. The common CVT uses a pulley system to transmit rotation. So theoretically, the number of gears a continuous variable transmission system offers is infinity. While riding a vehicle with a CVT system, you would find the transmission to be smooth and you does not feel the gear shift like in automatic and manual systems. There are basically three kinds of CVT systems.
a)Pulley based b) Toroidal and c) Hydrostatic

The pulley-based system
The pulley based system consists of two pulleys, the driving pulley, (also called the driving pulley) and the driven pulley (output pulley). A triangular shaped belt runs around them. The triangular shape is because the pulley groves taper towards the inside and so to have maximum friction.

The distance between the center of the pulleys where the belt makes contact in the groove is known as the pitch radius. When one pulley increases its radius, the other decreases its radius in order to keep the belt tight. So relatively, both the pulleys change their radii resulting in gear shifting. For example, when the pitch radius is small on the driving pulley and large on the driven pulley, the rotational speed of the output pulley decreases and vice-versa. The introduction of metal belts further enhances the performance of the belt. These flexible belts are composed of several (typically nine or 12) thin bands of steel that hold together high-strength, bow-tie-shaped pieces of metal.

Toroidal CVT
Toroidal CVT are very similar to the pulley-based model. There are two discs, one called as the input disc and the other called as the output disc replacing the input and output pulleys of the pulley based system. The discs are cone shaped structures with the tapered ends facing each other, and they have a curved surface. The rollers or wheels are rotating structures fixed to an external axis and are placed between the discs. They act like a gear wheel and transmit rotational force from the input disc to the output disc. The rollers while rotating on the external axis can also tilt themselves between the discs touching different places of the disc offering various speeds of rotation. For example,When the wheels touch the driving disc near the rim, they must contact the driven disc near the center, resulting in an increase in speed and a decrease in torque (i.e., overdrive gear). A simple tilt of the wheels, then, incrementally changes the gear ratio, providing for smooth, nearly instantaneous ratio changes.

Hydrostatic CVTs
Both pulley-based and toroidal models are friction based. But a hydrostatic CVT is a little different because it uses variable-displacement pumps and a hydrostatic motor. The rotational motion of the engine operates a pump and the pump converts this motion into fluid flow. This flow is then converted into rotating motion by a motor on the driven side. This system is usually used along with a planetary gear set as a hybrid system. Hydro-transmissions are good for heavy-performance vehicles which is why they are used in tractors.
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