The Design of Light Weight Automotive Brake Pedal

Coventry University Faculty of Engineering and

Computing

- MSc Dissertation in

Manufacturing Systems Engineering

'The Design of Light Weight

Automotive Brake Pedal'

Submitted By: Nurfaizey A. Hamid

Project Supervisors: Dr. Gumail Singh Assc. Prof. Ir. Mustafar Abdul Kadir Dr. Janatul Islah Mohammad

10th September 2007

ABSTRACT

In recent years, people concerns on emissions are growing. As vehicles are one of

the contributors, some governments had introduced legislations pertaining to the matter.

Corporate Average Fuel Economy (CAFE) for example was introduced by the National

Highway Traffic Safety Administration (NHTSA) of the United States in order to

encourage car manufacturers to improve their product's efficiency, thus reducing

emissions. Higher efficiency means less fuel consumption without compromising

vehicles' performance. One of the solutions is to design the vehicles using smaller engine

and light weight design. Conventional heavy materials can be replaced with new

advanced materials to reduce weight.

This dissertation is concerned with the design of light weight automotive brake

pedal. Later we will be looking at how a new material can be selected as replacement for

conventional material. Material selection will be carried out systematically using CES

Edupack to search for potential materials. Material properties and manufacturing process

are the two factors which will be considered during material selection process.

An actual steel brake pedal sample from a passenger car will be used as example.

The component will be measured using coordinate measuring machine before a 3D model

can be generated using Solidworks. A new brake pedal will be designed using alternative

material. Both current and new design of brake pedal will be analysed using ABAQUS.

Linear static stress analysis will be performed to study the behaviour of the component

when subjected to extreme foot load. Based on analysis results, a polymer based

composite material was found as a suitable material to produce light weight brake pedal.

CHAPTER I

INTRODUCTION

1.1 History of Automotive Brake System

In the early days, wagons and other animal drawn vehicles relied on the animal's

power to both accelerate and decelerate the vehicle. Eventually there was the

development of basic supplemental braking system consisting of a hand lever to push a

wooden fiiction pad directly against the metal tread of the wheels. Over the years, as the

level of transportation technology has increased the braking system used to slow down

vehicles has also been improved.

In 1902 in New York, Ransom E. Olds had invented a brake system known as

external brake. It used a single flexible stainless-steel band, wrapped around a drum on

the rear axle. When the brake pedal was applied, the band contracted to grip the drum.

Although it ground down solid rubber tires pretty quickly, the tire brake was popular on

THE DESIGN OF LIGHT WEIGHTAUTOMOTIVE BRAKE PEDAL

carriages and many early autos. By 1904, practically all car makers were building cars

with an external brake on each rear wheel [I].

However, the external brake demonstrated some serious flaws in everyday use.

On hills, for example, the brake unwrapped and gave way rapidly. Another drawback to

the external brake was it had no protection from dirt so its bands and drums quickly wore.

A brake job every 200 to 300 miles was considered normal. The problems associated

with the external brake were overcome by the internal brake or drum brake as it is now

known. And, since brake parts were inside drums and protected from dirt, drivers could

go over 1,000 miles between brakes overhauls [l].

Since those days, drum brakes became all-dominant in the United States. In

Europe, particularly in Great Britain, it had to share the stage with disc brakes. The first

record of the disc brake was in 1902 in England where Dr. F.W. Lanchester patented a

design for a disc brake. However, these early disc brakes were not as effective at stopping

as the contemporary drum brakes of that time. Its major problem was noise. Metal-to-

metal contact between his copper linings and the metal disc caused an intense screech

that sent chills through anyone within earshot. The problem was solved in 1907 when

Herbert Frood, another Englishman, came up with the idea of lining pads with asbestos.

The new material was quickly adopted by car manufacturers on both drum and disc

brakes. Asbestos linings also outlasted other friction materials by a wide margin up to

10,000-mile [I].

As roads improved and cars began to be driven at high speeds, engineers

recognized the need for even better braking system. In 1918, a young inventor named

Malcolm Lougheed (or Lockheed) applied hydraulics to braking. He used cylinders and

tubes to transmit fluid pressure against brake shoes, pushing the shoes against the drums.

In 1921, the first passenger car the Model 'A' Duesenberg was equipped with four-wheel

hydraulic brakes [I]. The basic braking system we have today is based on this technology.

The modern automotive brake system today is the result of improvement for over 100

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Typical Disk Brake Typical Drum Brake

Front Brakes I I

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Rear Brakes

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Brake Lines

Typical Automotive Braking System

Figure 2 - Typical Brake System [5]

There are three subsystems in automotive brake system:

a) Leverage system

b) Hydraulic system

c) Friction

In an emergency stop, the forces that have to be applied to the brake shoes in

order to produce the maximum deceleration are very large. Approximating to the weight

of the vehicle, and to enable the driver to produce these forces with an effort which

cannot exceed 700 N and which is normally kept down to about one-third of that amount,

the brake system must be able to provide a considerable leverage [2]. The force

multiplication processes take place in two areas; leverage system and hydraulic system.

1.3.1 Leverage System

Leverage system is a foot pedal mechanism which is designed in such a way that

it can multiply the force from driver's foot several times before it is transmitted to the

1.3.2 Hydraulic System

Hydraulic system consists of a master cylinder, brake lines and braking unit at

each wheel. Figure 5 shows hydraulic system and a typical master cylinder in automotive

brake system. Due to the fact that fluid cannot be compressed, the force transmitted from

the foot pedal can be manipulated for an even greater force and then transferred to the

braking unit at each wheel. Figure 6 explains this process. To determine the

multiplication factor in Figure 6, start by looking at the size of the pistons. Assume that

the piston on the left is 2 inches (5.08 cm) in diameter (1-inch 12.54 cm radius), while the

piston on the right is 6 inches (1 5.24 cm) in diameter (3-inch I 7.62 cm radius). The area

of the two pistons is 71 * 3. Therefore piston on the right is nine times larger than the piston on the left [6]. This means that if 100 lbs force is applied to the left-hand piston, a

900 lbs force will come out on the right-hand piston.

U

Typical Master Cylinder

Figure 5 - Hydraulic system and a typical master cylinder [5]

inches

Figure 6

Force inches

I I - I I I I 2 1 1 in. I I I 6 in. I I i

- Force multiplication in hydraulic system [6]

1.3.3 Friction

Friction happens when force from the brake fluid press the brake pads or friction

linings against the rotor or drum. Friction also happens between tires and road surface.

Friction is a measure of how hard it is to slide one object over another [6] . The coefficient

of friction is the ratio of the limiting friction to the normal reaction between the sliding

surfaces. It is constant for a given pair of surfaces.

Coefficient of fiction = Friction force I Normal load

Friction force (F) = p. Normal load (N)

The friction force is proportional to normal load. Therefore, the heavier the

vehicle, the greater force is needed to decelerate the vehicle. This concept applies to the

brake system where the more force applied at the brake pads or linings, the greater the

friction force or braking force generated.


1.4 The Project Objectives

Corporate Average Fuel Economy (CAFE) was introduced by the National

Highway Traffic Safety Administration (NHTSA) of the United States in order to

encourage car manufacturers to improve their product's efficiency, thus reducing

emissions. CAFE is the sales weighted average fuel economy, expressed in miles per

gallon (mpg), of a manufacturer's fleet of passenger cars or light trucks with a gross

vehicle weight rating (GVWR) of 8,500 lbs (3,855 kg) or less, manufactured for sale in

the United States [lo]. According to [9], the trend toward lightweight materials continues

to grow each day. Whether it is for the Corporate Average Fuel Economy (CAFE)

standards in the automotive industry or just an OEM's drive to improve product

performance by increasing efficiency though weight reduction [9].

This project is concerned with the design of light-weight automotive brake pedal.

Most of the cars today have pedals that are made of steel. In some performance cars,

aluminium has been used to replace steel due to its higher strength to weight ratio. In this

project, we will be looking at a polymer-based material as the replacement material for

steel. A product sample from an average production car will be used as reference. The

main advantages of using this material are light-weight and ease of manufacture.

However, there are few problems that need to be considered such as limitation in material

properties, reliability and cost.

The aim of this project is to come out with a successful design of light-weight

automotive brake pedal using polymer-based material with acceptable level of

performance. In achieving this aim, project objectives are set as below:

To understand the working principles, components, standards and theories

through a literature study.

To analyse current design and its material properties.

To select an alternative materials using a systematic selection method.

THE DESIGN OF LIGHT WEIGHT AUTOMOTIVE BRAKE PEDAL

To develop and analyse new component design using CAD and CAE applications.

To clearly justify the results and conclusions.

Knowledge gained from this project is to be able to understand the steps needed to

design new brake pedal with new material from systematic material selection. The use of

CAD and CAE for design and analysis will help to minimise design time.

1.5 Current Developments in Brake Pedal Design

Efficiency of a car can be improved through weight reduction. In this perspective,

manufacturers are searching out opportunities to replace conventional materials with new

and lighter materials without compromising its mechanical and physical properties. An

example of reducing weight through new material application can be seen in the

manufacturing of Chevrolet Corvette. The Chevrolet Corvette is the sport car range that

has been manufactured by Chevrolet since 1953. It has been proclaimed to be the

"America's Sports Car" [l 11. The recent model Chevrolet Corvette C6 is shown in Figure

Figure 7 - Chevrolet Corvette C6 [8]

Chevrolet will take another step forward through the next generation of Chevrolet

Corvette C7 which will be launched in 2010. It was reported by [9], the conventional

brake pedal which was made of steel will be replaced with B356 aluminium. To solve


structural and mechanical property concerns, modified alloy chemistries and heat

treatment cycles were used with permanent mould casting to achieve the mechanical

properties of 35 ksi tensile strength, 25 ksi yield strength and 7% elongation [9]. Another

advantage other than light weight is the exceptional appearance which is important as it is

a visible component. Secondary cosmetic process such as spray painting will be no longer

required.

Figure 8 - Aluminium cast brake pedal to be used by the next generation Corvette C7 [9]

It is reported in [12] titled 'Concurrent design and manufacturing process of

automotive composite components' which had used concurrent engineering in the

development of polymeric based composite automotive clutch pedal. The research

objective was to demonstrate the use of Computer Aided Design (CAD) and Computer

Aided Engineering (CAE) to help designers in the design process. The chosen product

was a cable operated automotive clutch pedal which was converted from conventional

material to polymer based composite. Several engineering computer applications were

used from conceptual design until prototyping such Pro Engineer, LUSAS, Mould Flow

Analysis, and Stereolithography (SLA) and 3D Printer for rapid prototyping.

There were two conceptual designs considered; the 'T' profile and the 'I' profile.

Highlighted by [12] that based on analysis, the 'T' profile design was stiffer compared to

the 'I' profile. The analysis was done using LUSAS finite element analysis software.

Another interesting finding was the addition of ribs to the design to improve stiffness and

rigidity. The use of ribs enables designers to compensate the effect of reducing section

thickness to improve design efficiency. However, S.M. Sapuan [12] did not discuss the

overall performance of the new component in comparison with the original component.

1.6 Report Structtire

4 Chapter5 Ulapter 6 w e r 7

NEW DESIGN AND ANALYSIS DISCUSSION CONCLUSIONS AND FUTURE

RECOMMENDATIONS

Figure 9 - Report Structure

Chapter I lNTROWCTlON

Chapter 1 is the introduction chapter. A brief literature review on brake system

has been carried out focusing on history, hndamental theory and brake subsystems. The

project objectives and current developments in brake pedal design had also been

discussed.

h - 3 MEASUREMENT. GEOMETRY GENERATION AND ANALYSIS OF CURRENT COMPONENT

Chapter 2 explained about the current steel brake pedal with an actual brake pedal

used as example. The material properties and manufacturing process of the current brake

pedal will be discussed in detail.

- Chapter4 NEW WTERIAL SELECTION I

Chapter 3 is about measurement, geometry generation and finite element analysis

of current brake pedal. Coordinate Measuring Machine (CMM) will be used for

measurement, ~ o l i d ~ o r k s ' 2003 for geometry generation and ABAQUS for finite

element analysis.

Chapter 2 CURRENT COMPONENT \


also the mounting place of hydraulic master cylinder (not shown in figure) of the brake

system and brake light switch. The spring is used to retain brake pedal assembly at its

original position. When the brake pedal is depress, the spring will provides slight load to

the brake pedal. When brake pedal is released, it will move back to its original position.

Bolt and nut, pivot shaft and plastic bearings anchored the brake pedal assembly to the

bracket. Grease was applied at this area to minimise friction.

Figure 10 - Proton Wira (known as Persona in the UK) [14]

J

Figure 1 1 - Proton Wira brake pedal assembly


Figure 14 - Brake light switch mounting area

Figure 15 - Location of spring

The size of the brake pedal assembly is about 370 mm x 148 mm with overall

weight of 944.4 grams. Brake pedal assembly consists of three components; brake pedal,

rubber foot pad and switch contact pad. The main body of brake pedal is made of steel

plate with thickness 6 mm. It consists of three subcomponents joint by welding. The

welding areas are shown in Figure 17. Rubber foot pad is used to prevent foot slip while

switch contact pad is used to absorb noise as the result of contact between pedal and

brake light switch.


Figure 16 - Brake pedal asse&bly: (a) Brake pedal (b) Rubber foot pad (c) Switch

contact pad

Figure 17 - Three areas of welding

THE DESIGN OF LIGHT W?ZIGHTAUTOMOTIVE BRAKE PEDAL

2.3 Material Properties

A good design should always accompanied with the correct choice of material.

Selecting the wrong material will result in higher product cost, poor product performance

or even product failure. It was stated by [15] that normally the choice of material is

dictated by the design, but sometimes the other way around. Since the number of

engineering materials is large at an estimated over 120,000 materials are available, the

material selection process can be a difficult task without guidance. Ashby [IS] also

explained that a method of screening those materials is by understanding the design

requirements for a component by an analysis of function, constraints, objectives and free

variables. Table 1 explains what those criteria are while Table 2 shows the design

requirements for a brake pedal.

Table 1 - Function, constraints, objectives and free variables [15]

Table 2 - Design requirements for a brake pedal

Function

Constraints

Objective

Free variables

What does component do?

What non-negotiable conditions must be met?

What negotiable but desirable conditions.. ..?

What is to be maximised or minimized?

What parameters of the problem is the designer free to change?

Function

Constraints

Objective

Free variables

Brake pedal (load transfer)

No failure, meaning able to withstand load

High Young's modulus

Good tensile strength

Low material cost

Choice of material

Choice of design


Table 3 - Material properties of Low Carbon Steel AISI 101 0 [18]

Maximum -

Properties

General:

I Density I *7800 I 7900 Minimum

I Fe (Iron) I *99.13 I 99.62

Price

Composition:

C (Carbon)

Mn (Manganese)

P (Phosphorus)

*0.25

Units

___I 0.45

S (Sulphur)

Si (Silicon)

Mechanical:

Young's Modulus

Compressive Strength

Tensile Strength

Poisson's Ratio

GPa I

2.4 Manufacturing Process

Note: Value marked * are estimates

*O

0

*205

*255

3 10

0.285

Steel brake pedals are manufactured using press forming. Press forming covers a

range of sheet forming processes performed by means of a die and press. Processes used

include blanking, shearing, drawing, bending, forming, coining and swaging. These

processes may be performed consecutively to form complex shapes. However, all shapes

produced by this process have a uniform cross-sectional thickness. Tools are dedicated

and, therefore, tooling costs are high. Only materials available in sheet form can be

stamped and the thickness is limited to available sheet size 1181. More detail information

on press forming is attached in Appendix 2.

0.05

0.05

215

315

430

0.295


Deep drawing Blanking

Die Blank

Bending Stretching

Figure 19 - Process schematic of press forming [18]

The overview of current component as well as the material properties and

manufacturing process had been explained earlier in this chapter. In the next chapter, the

current component will be measured to get the actual dimensions. These data will be used

to generate the 3D model for stress analysis. The analysis will simulates the component's

behaviour when it is subjected to load exerted by the driver's foot.


CHAPTER 3

MEASUREMENT, GEOMETRY GENERATION AND ANALYSIS OF CURRENT

COMPONENT

3.1 A Brief History of Finite Element Method

This section presents a brief history of the Finite Element Method (FEM).

Although 'finite element' terminology was first used in 1960 by R.W. Clough in a paper

on plane elasticity problems [19], the ideas were dated back much further. A. Hrennikoff

in 1941 and D. McHenry in 1943 used a latticed of line elements for the solution of

stresses in continuous solids. Meanwhile R. Courant in 1943 had proposed setting up the

solution of stresses in a variational form. He used piecewise interpolation functions over

triangular sub-regions making up the whole region as a method to obtain approximate

numerical solutions [20]. Since then more and more researchers involved in FEM. Table

4 summarizes the important findings made by early researchers.


Table 4 - Brief History of Finite Element Method [20]

Name of researchers

A. Hremikoff and

D. McHenry

R. Courant

S. Levy

J.H. Argyris and S.

Kelsey

M.J. Turner

R.W. Clough

M.J. Turner

R.J. Melosh

R.H. Gallagher

R.H. Gallagher and

J. Padlog

P.E. Grafton and

D.R. Strome

Martin, Gallagher,

Melosh and Argyris

R.W. Clough, Y.

Rashid, E.L. Wilson

J.S. Archer

O.C. Zienkiewicz

B.A Szabo and Lee

T. Belytschko

Year

1941-1943

1943

1947-1 953

1954

1956

1960

, 1960

1961

1962

1963

1963

1961-1964

1965

1965

1968

1969

1976

Findings

Latticed of line elements for the solution of stresses

in continuous solids

Interpolation functions over triangular sub-regions as

a method to obtain approximate numerical solutions

Force method and displacement method

Matrix structural analysis using energy principles

Direct stzfiess method for obtaining total structure

stifiess matrix

Introduction ofJinite element using both triangular

and rectangular elements for plane stress analysis

Large deflections and thermal analysis

Flat rectangular-plate bending-element stiffness

matrix

Material nonlinearities

Introduction of buckling problems

Curved-shell bending-element stiffness matrix for

axisymmetric shells and pressure vessels

Extension of the FEM to three-dimensional

problems

Special case of axisymmetric solids

Dynamic analysis in consistent-mass matrix

Visco-elasticity problems

Weighted residual methods

Large-displacement nonlinear dynamic behaviour

The Design of Light Weight Automotive Brake Pedal

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