| Lead | Members | Reviewers | Status | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Saif Hafeez | Neeraj Nair Yiyi Zeng Christopher Tham kevin bui | J.T. Malcolm (Unlicensed) |
|
Overview
MSXII failed to meet the standard required at FSGP for minimum stopping distance. In order to properly meet (and exceed) this standard for MSXIV, a re-evaluation of the brake architecture is needed. In order to correctly evaluate necessary braking forces, line pressures, and eventual pedal input, a full mathematical model will be necessary. Before this can be done, an examination of the predicted brake architecture is required (some of this may be redundant to those who have worked on MSXII). Note that this excludes any regenerative braking, as the braking test must be passed using purely mechanical braking.
The following includes a basic list of all the fundamental components used in braking, and how they will need to be used for the kinematics/fluid dynamics problems to generate braking curve. This is a good baseline for anyone looking to understand how a mechanical set of brakes function, and how the calculations/curves evaluating potential braking inputs will be derived.
List of Components
1. Tires
Perhaps the single variable with the largest impact on stopping distance, the tires are always the limiting factor on the ability to comfortably stop a moving vehicle vs. uncomfortably slide uncontrollably into the nearest object. Assuming no slip, it is generally agreed that the tires are rotating at a fixed speed in revolutions per second that is equal to the speed divided by the diameter*pi. This is will be important for calculating rotor speed. The tire and its resulting coefficient of STATIC friction (remember, we want rolling, not sliding) between the surface are what will limit our maximum achievable braking acceleration and thus braking distance/time.
Important variables: Coefficient of friction between tire & road
2. Rotors
The next component that will be featured on the car is the rotor. The rotor is generally a cylinder that has been attached to the axle. The cylinder rotates with the same radial speed (revs/sec) as the wheel and tire.
Important variables: Coefficient of friction between pads & rotors, rotor diameter, contact patch between pad and rotor
3. Pads
The brake pad is generally a steel plate with some type of friction material (normally some type of composite) laid on one side. The pad is held in a position by the caliper where, at 0 input, it does not touch the rotor and allows the rotor to spin freely. As pressure is applied through the caliper and the pistons contract (see below), the pad is forced against the spinning rotor and causes friction to occur. The energy from the spinning rotor is converted into heat, and as the rotor loses energy, it slows. As a basic kinematics question would demonstrate, the magnitude of the frictional forces are directly proportional to the force input, or, how hard the piston is clamping the pad against the rotor. This allows for variable braking (i.e. when you lightly tap a brake pedal, the vehicle responds by coasting to a stop, whereas if you step on it aggressively, the magnitude of deceleration is much higher, and your head bounces off the steering wheel).
Important variables: Coefficient of friction between pads & rotors
4. Calipers
The caliper is what holds the rotor in place. As previously mentioned, they generally contain a number of pistons that can expand and contract based on the fluid pressure in the caliper. This is used to apply a force to the pads and generate friction. On one side of each caliper, there is a pipe fitting that connects to the brake lines.
Important variables: Coefficient of friction between pads & rotors
5 Brake lines
Brake lines refer to flexible hoses that are attached to the master cylinder (see below). They contain brake fluid which allows for compression of the master cylinder to be translated into pressurizing the caliper.
Important variables: Cross sectional area
6 Brake Fluid
Brake fluid refers to the liquid that fills the caliper, master cylinder, and brake lines at all times. As the master cylinder is compressed, the brake fluid is pressurized and exacts a pressure inside the caliper, causing the pistons to contract.
Important Variables: Viscosity, volume, pressure, etc
7 Master Cylinder
The master cylinder can be simplified to be a piston. Essentially, when the plunger is pushed, the pressure in the cylinder increases, and thus the tubes and the caliper pressure increases. The diameter of the plunger and the amount of depression directly affect the braking force.
Important Variables: Diameter
8 Pedal
The pedal is simply a swing arm that is almost directly connected to the master cylinder designed to allow for a foot to apply pressure (with appropriate feedback caused by the opposing forces occurring in the master cylinder).
Important Variables: Travel distance ratio (pedal travel to cylinder travel)
Component Selection & Justification
TBDMaster Cylinder: Remote Tandem Master Cylinder w/ Pushrod
( https://www.wilwood.com/MasterCylinders/MasterCylinderProd?itemno=260-14241-BK )
- able to mount resivour seperately to cylinder for ease access etc
- able to add on proportioning valve if we need one
- has tantum outputs (2 outputs) one for rear and front
- has varying bore sizes from ⅞ to 1-⅛”