To enhance the efficiency of the braking system a new system was designed called power brake system. It is also called ‘power assisted” brakes. This system uses the power of engine and also battery to increase the efficiency of braking system. Earlier power brakes were not required as most of the vehicles had drum brakes.
The power brake system is a modern braking tool for cars that’s designed to make braking safer and easier. A power braking system works to exert far more force upon a set of brake pads or shoes than is exerted upon the brake pedal by the driver. A Power brake system come equipped with a master cylinder, which pumps brake fluid through a series of tubes connected to each wheel, and a power brake booster. With a working power brake system, one merely needs to tap on a brake pedal to exert considerable pressure on the brakes.
How Brake Systems Work
When a driver pushes down on the brake pedal, brake fluid is released from a holding tank into the master cylinder, which houses two pistons that compress the fluid and force it through a series of tubes linked to each wheel. The pressure created by the brake fluid is immense, acting with great force upon each wheel’s set of pistons and calipers. When the fluid reaches the wheels, it causes calipers and pistons to exert force upon the braking apparatuses—called pads in the case of disk brakes, and shoes in drum brakes. Most cars use disk brakes in the front, which slow a tire down in much the same fashion as brakes on a bicycle, and drum brakes in the back.
The power brake booster adds even more braking pressure. It sucks air in through a one-way vacuum and uses that air to exert force upon the brakes when the brake pedal is depressed. The power brake booster also serves as a back-up power brake system in the event of engine failure. When an engine fails, the car is unable to pump brake fluid, thus eliminating power brakes. The power brake booster, however, keeps a reserve of air in such an event, giving the driver enough easy pumps of the brake pedal to come to a stop. If the booster’s air supply is exhausted, the brakes are still functional but much harder to operate.
Power brakes require a very particular type of hydraulic oil to operate. Brake fluid has special properties that are able to withstand different environments as well as the pressure a power braking system imposes. Brake fluid is designed to boil only at extremely high temperatures, up to 460 degrees Fahrenheit (238 degrees Celsius), much higher than a car would create. It’s also designed to keep its fluidity even at extremely low temperatures. Other types of fluid don’t meet the particular needs of a braking system, and if used in place of brake fluid could jeopardize passengers by causing total and immediate brake failure.
The Vacuum Booster
The vacuum booster is a metal canister that contains a clever valve and a diaphragm. A rod going through the center of the canister connects to the master cylinder piston on one side and to the pedal linkage on the other.
Brake booster is the most important element of power brake system. It is located at the back side of the engine compartment on the driver’s side of the car. Vacuum from the engine is used by brake booster to multiply the force that your foot applies to the master cylinder. Brake booster is placed on firewall behind the master cylinder. The power brake booster along with master cylinder is connected with brake pedal. The main purpose of the brake booster is to amplify the available foot pressure applied to the brake pedal. As a consequence, a large vehicle can be stopped with little foot pressure. Engine vacuum is used as power for the booster. Vacuum produced by automobile engine can be used freely in powering accessories such as the power brake booster.
The booster is an empty shell that is divided into two chambers by a rubber diaphragm. When the foot of the driver is off the brake pedal, the valve in the diaphragm remains open so that vacuum is allowed to fill both the chambers. When the driver depresses the brake pedal, the valve in the diaphragm closes, separating the two chambers and another valve opens to allow air in the chamber on the brake pedal side.
Check Valve
Another major element of the power brake is the check valve. With the help of a rubber hose the check valve is connected to the engine and acts as a one-way valve that allows vacuum to enter the booster but does not let it escape. If the engine is stopped or a leak forms in a vacuum hose, the check valve ensures that air does not enter the vacuum booster. Because of this valve the vacuum booster provides enough strength to the driver to make several stops in the event that the engine stops running.
The photo above shows the check valve, which is a one-way valve that only allows air to be sucked out of the vacuum booster. If the engine is turned off, or if a leak forms in a vacuum hose, the check valve makes sure that air does not enter the vacuum booster. This is important because the vacuum booster has to be able to provide enough boost for a driver to make several stops in the event that the engine stops running — you certainly don’t want to lose brake function if you run out of gas on the highway. In the next section, we’ll see how the booster
The Booster in Action
The vacuum booster is a very simple, elegant design. The device needs a vacuum source to operate. In gas powered cars, the engine provides a vacuum suitable for the boosters. In fact, if you hook a hose to a certain part of an engine, you can suck some of the air out of the container, producing a partial vacuum. Because diesel engines don’t produce a vacuum, diesel-powered vehicles must use a separate vacuum pump.
On cars with a vacuum booster, the brake pedal pushes a rod that passes through the booster into the master cylinder, actuating the master-cylinder piston. The engine creates a partial vacuum inside the vacuum booster on both sides of the diaphragm. When you hit the brake pedal, the rod cracks open a valve, allowing air to enter the booster on one side of the diaphragm while sealing off the vacuum. This increases pressure on that side of the diaphragm so that it helps to push the rod, which in turn pushes the piston in the master cylinder.
As the brake pedal is released, the valve seals off the outside air supply while reopening the vacuum valve. This restores vacuum to both sides of the diaphragm, allowing everything to return to its original position. However, there are some other factors which contribute to a loss of power assist. The engine must be running in order to have power assist. If the engine stops or stalls while driving, there will have small reserve of power assist for two or three pedal applications but, after that, it will be very difficult to depress the brakes.
Finally
Vehicles that require a power brake system are the ones that have disk brakes at least on the front wheels. Different types of power brakes are vacuum boosters, air suspended, hydraulic booster, and electrohydraulic booster. Albeit power brakes are costly as compared to other brakes they are used, nowadays, in most cars.
