Difference between revisions of "Category:Brakes"

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Brakes decelerate the vehicle by converting kinetic energy into heat. This is done by having the driver press on the brake pedal, where brake fluid pressure is created in the master cylinder. This pressure acts on the brake piston via brake lines, and a net force pushes the brake cylinder into the brake pad and consequently into the brake rotor. This forced interface slows the vehicle by friction between the pad and the rotor, resisting the motion of the rotor, and therefore the wheel, and consequently the vehicle body.

The brake system is comprised of several components. In the body of the vehicle, there must be a brake pedal, a balance bar, and master cylinder(s). In Formula Student, it is standard by rules to have a minimum of two master cylinders (check your competitions rules for more details) – one for the front axle and one for the rear axle. There is also usually a balance bar adjustment dial on the vehicle dash for the driver to adjust brake balance while in motion. The master cylinders transmit pressure via the brake hydraulic system. This is usually comprised of a combination of hard and soft brake lines, and fitments that allow the joining or splitting of brake lines. The brake lines must be routed though the vehicle and/or along suspension arms to connect with the brake calipers.

The front wheels must have a brake caliper mounted rigidly on the suspension upright, where the brake pads can apply their clamping force onto the rotor. The rotor will be mounted on some part of the rotating wheel assembly, usually the wheel hub, but it as been seen to be done that it could be mounted from the wheel rim.

At the rear, the set up will have more options and depend on the drivetrain design. If the team uses a spool (locked differential) then it is allowable to use one brake caliper and rotor assembly, mounted on the sprung body, as the braking force will be transmitted to both wheels. If there is a differential or some other set up (for example, in-hub motors) where the rear wheels could possibly move at different speeds, then two are required. The packaging of the drivetrain will usually dictate if the brakes should be mounted inboard (on the sprung chassis mass) or outboard (inside the wheel assembly, like the front wheels).

Brake Pads

Brake Rotors

Brake rotors, or just rotors, are the discs that rotate with the wheel and provide a surface for the brake pads to apply friction to. They can be made using a wide variety of materials and manufacturing methods depending on the system they are used in, mostly dependent on the brake pad material.

Materials

The selection of material is highly dependent on the engineer's design goals for rotor operating temperature, pad-rotor coefficient of friction, material strength and other properties.Rotors can be constructed using the following materials:

• Steels of low to high carbon %
  
• Chromoly (4130 Steel) or other alloys
• Cast Iron
• Aluminum Alloys
• Carbon ceramic

Typically pad-rotor coefficients of friction and ideal pairings will be specified by the brake pad manufacturer, but this can also be physically tested and verified in-house by teams who have the resources to do so.

Post-Processing

Lightening

A common practice is the drilling of holes or slots into or all the way through the rotor. This practice has several effects on brake performance:

• Decreasing the area of contact between the pad and rotor, thus impeding the flow of heat into the rotor but also venting heat off the pad
• Adds a shaving effect to keep the pad surface clean
• Increases rotor temperatures through reduction of mass
• Decreases rotational inertia of system, wheel becomes easier to roll

A common misconception among designers is that doing this increases cooling effects on the brake rotor by increasing it's surface area. While drilling holes in the rotor does increase surface area, unless there is some form of air actively being guided through those holes either by brake/wheel ducts or winglets, there is no significant airflow through the holes of the rotor. Reducing the mass reduces the overall thermal capacity of the rotor, which leads to an increase in temperature during use. However, there are ways of increasing airflow through such slots and holes. For example, a wheel center that is designed to act as a propeller, sucking air into the wheel assembly and sending it through the rotor can change the direction of airflow from across the rotor's surface to through it's holes and slots, making the process more effective. This can also be done by adding the holes and slots at an angle, creating a slight suction effect as the disc rotates.

Venting

Vented rotors are rotors with fins in between either contact surface that allow air to pass inside the rotor itself. The way air travels through the rotor is dependent on the configuration of the fins inside.

Brake Calipers

please don't drill lightening holes in your brake calipers

Master Cylinders

please don't drill lightening holes in your master cylinder

Brake Balancing

More front brake = More rear cornering capacity, balance goes towards understeer under braking but could reduce braking times

More rear brake = More front cornering capacity, balance goes towards oversteer under braking but could increase braking times - try braking earlier first, rear brake will not fix a late braking problem from the driver