Tuesday, September 17, 2013
Principles of Power Brakes
An automobile is a collection of systems working together to accomplish a few simple tasks: to stop, go, turn and not fall apart in the process. Each system relies on multiple scientific principles to control and convert energy from one source and apply it to another. A power brake system uses energy from the drivers leg and from the engine to force hydraulic fluid through brake lines. That energy expresses itself on the pistons in the brake calipers, which force the brake pads against rotors. This process completes a complex dance of physics and sheer necessity, expressed in a very ordinary way.
Conservation of Energy
Otherwise known as the "First Law of Thermodynamics," this principle states that energy can never appear or disappear, it can only change forms. When a car accelerates, its using the chemical energy stored in gasoline and converting it into momentum, or kinetic energy. To stop the car, you need to convert that kinetic energy into another form. A braking system uses brake pads to squeeze down on a smooth surface known as the rotors or drums to create frictional heat, thus converting the cars kinetic energy into thermal energy. That heat, at some point transfers to either the air around the rotor or into the components and fluid adjacent to the pads and rotor.
Incompressible Fluids
The difference between a gas and a liquid is that liquids are a solid mass of molecules or atoms, theres no empty space between them. This means that no matter how hard you squeeze a liquid, it never gets any smaller or compresses. Power brake systems use this principle known as hydraulics to transfer energy imparted onto the brake master cylinder or main hydraulic ram to another set of cylinders in the brake calipers. When the driver puts his foot down on the pedal, the energy he puts into it travels through the master cylinder, through the lines, into the brake calipers and ultimately expresses on the brake pads and rotors.
Differential Pressure as Energy
Most power brake systems use vacuum suction created by the engine to pull on a diaphragm, which is connected to the back of the master cylinder. When the driver pushes the brake pedal, a valve opens in one chamber of the diaphragm. Engine vacuum pulls on the diaphragm and subsequently the master cylinder piston, imparting energy of its own to the braking system, thus reducing the amount of energy the driver must expend to push fluid through the lines.
Vacuum as an entity doesnt actually exist; "vacuum" is a term to describe the absence of air and air pressure. When the vacuum valve opens in the diaphragm chamber, atmospheric air pressure, which is about 14 psi at sea level, pushes on the other side of the diaphragm membrane. The engine itself actually provides the energy, since it took energy from the gasoline to create the vacuum in the first place. Atmospheric pressure is just a static factor. Think of this like doing a push-up. You, as the engine, actually provide the energy that causes your body to move; the floor or atmospheric pressure, is simply the surface upon which you express that energy.
No comments:
Post a Comment