BRAKE SYSTEM DESIGN – PHASE 1
October 27, 2003
The approach taken during the design of the braking system for the
BMW M3 is to act as an aftermarket company that specializes in
performance brake designs and is improving the current design of BMW
M3’s braking system. Considerations will be given to braking
performance, safety, the parking brake sub-system, and the actuating
Crambo specializes in aftermarket braking solutions for performance
cars. Through technology, innovation, design, and engineering
excellence, Crambo continues to push the envelope in brake systems.
Crambo brake systems have one of the highest reliability and safety
records in the industry.
The 2003 e46 BMW M3 is a 2 door, 5 passenger luxury sports car available
in two trims – convertible or hard top. The “e46” refers to the model
year of the vehicle. For example, this BMW (e46) is of production model
year 2000 to present. The design of these brakes will focus on the hard
top vehicle as this has the highest production numbers of the two trims.
The brake system of a car is one of the most critical components and as
such it is important to take into account factors such as safety,
reliability, quality, performance, and cost, to efficiently design a
brake system. At Crambo, engineers ensure that these factors are mated
together with perfection.
The problem Crambo will discuss in this report is to propose a design
that is superior to the current brake system in the current production
e46 BMW M3. The key objectives will be to determine the current brake
specifications of the M3, discuss brake torque, temperature rise, energy
dissipation and parking brake force. Also, an analysis of the various
methods of improving the current M3 components will be required. A final
design will then be proposed.
BMW enthusiasts often enjoy taking their cars to races and autocross
events. These enthusiasts demand the highest performance from their cars
in all aspects. In order satisfy and profit from this niche, Crambo has
undertaken a design project to replace the stock BMW M3 brake system
with a performance braking system that is both race worthy and street
worthy. An improved braking system will reduce lap times, since the car
can approach a corner faster before applying the brakes. The improved
braking system will also improve stopping distance and braking
response.. This enhances safety and performance both on the track and on
Phase 1, this report, will discuss and analyze the many options
available to improve the e46 M3 brakes such as disc material, disc
diameter and thickness, disc heat dissipations characteristics, brake
lines, etc. Final selections will take place completing phase 1. Full
calculations of braking force, stopping distance, and actuating force
will be performed in phase 2 of the report to confirm the final
selection of phase 1. If a different design is justified through phase 2
the proposed design of phase 1 will be replaced.
2.1 Functions of a Brake System
A vehicle is connected to the roadway by the traction forces produced by
the tires. Any braking force must be generated by the small tire tread
area contacting the road surface. Only forces equal to or less than the
product of the normal force and the tire-road friction coefficient can
be transmitted by the tire treads and wheels. Even an ideal braking
system cannot utilize more traction than what the tire and the road
provides . Brakes convert the vehicle’s kinetic and potential energy
in to thermal energy.
The basic functions of the brake system are to slow a vehicles speed, to
maintain speed during downhill operation, and to hold a vehicle
stationary. A good braking system determines how much control of the car
a driver has while driving.
There are two types of brake systems; service brakes, and parking
brakes. Service brakes are used for standard braking while driving,
whereas parking brakes are used to hold a vehicle stationary, but may be
used for slowing down in an emergency.
2.2 Components of a Brake system
There are two types of friction brakes; drum brakes and disc brakes.
Drum brakes use brake shoes that are pushed out in a radial direction
against the drum (figure 1). Disc brakes use pads that are pressed
axially against a disc (figure 2). The primary advantage of a disc brake
is that it is lightweight, easy to manufacture, low cost, has better
thermal dissipation, and performs better. Thus disc brakes are essential
used in all modern performance and sports cars. For these reasons Crambo
only works with disc brakes.
Figure 1 Typical Drum Brake Components 
Figure 2 Typical Disc Brake Components
A typical automotive brake system consists of service brakes and the
parking brake. The service brake consists of several key components. The
brake pedal connects to the master cylinder, and converts driver’s pedal
effort into hydraulic force. Brake boost assist systems are used to add
pressure to the master cylinder, which affectively multiplies the driver
pedal force. Thus the driver has to apply less force on the pedal to
achieve a larger braking force. The hydraulic fluid in the system flows
through flexible brake hoses from one component to the next. After the
boost, the hydraulic fluid flows into each of the brake callipers. The
callipers work like a C-clamp to squeeze the brake pads on to the rotor.
The pad rubs against the rotating disc to slow it down, effectively
converting the rotor’s kinetic energy in to thermal energy. See figure 3
for an overview of a general braking system.
The parking brake is a cable-activated system used to hold the brakes
continuously in the applied position. The parking brake activates the
brakes on the rear wheels. Instead of hydraulic pressure, a cable
(mechanical) linkage is used to engage the brake discs. When the
parking-lever is pulled, a steel cable draws the brake pads firmly
against the rotors. The release lever or button slackens the cables and
disengages the brake pads.
2.3 Layout of a Brake System
A typical brake system layout is shown in figure 3 below.
3 Typical Brake System Layout .