Transcript

Coventry University

Faculty of Engineering and
Computing

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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.

In 1902 in New York. Although it ground down solid rubber tires pretty quickly. Ransom E. Over the years. It used a single flexible stainless-steel band. the tire brake was popular on . When the brake pedal was applied.CHAPTER I INTRODUCTION 1. wagons and other animal drawn vehicles relied on the animal's power to both accelerate and decelerate the vehicle. the band contracted to grip the drum.1 History of Automotive Brake System In the early days. wrapped around a drum on the rear axle. Olds had invented a brake system known as external brake. 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. as the level of transportation technology has increased the braking system used to slow down vehicles has also been improved.

drivers could go over 1. The modern automotive brake system today is the result of improvement for over 100 . The new material was quickly adopted by car manufacturers on both drum and disc brakes. the external brake demonstrated some serious flaws in everyday use. came up with the idea of lining pads with asbestos.000 miles between brakes overhauls [l]. In 1921. And. The first record of the disc brake was in 1902 in England where Dr. However. By 1904. another Englishman. The basic braking system we have today is based on this technology. The problem was solved in 1907 when Herbert Frood. pushing the shoes against the drums. Lanchester patented a design for a disc brake. 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. drum brakes became all-dominant in the United States. F. In 1918.W. for example. the first passenger car the Model 'A' Duesenberg was equipped with four-wheel hydraulic brakes [I]. since brake parts were inside drums and protected from dirt. engineers recognized the need for even better braking system. He used cylinders and tubes to transmit fluid pressure against brake shoes. However. practically all car makers were building cars with an external brake on each rear wheel [I]. As roads improved and cars began to be driven at high speeds. Since those days. particularly in Great Britain. On hills.000-mile [I]. it had to share the stage with disc brakes. Its major problem was noise.THE DESIGN OF LIGHT WEIGHTAUTOMOTIVE BRAKE PEDAL carriages and many early autos. The problems associated with the external brake were overcome by the internal brake or drum brake as it is now known. these early disc brakes were not as effective at stopping as the contemporary drum brakes of that time. Asbestos linings also outlasted other friction materials by a wide margin up to 10. the brake unwrapped and gave way rapidly. a young inventor named Malcolm Lougheed (or Lockheed) applied hydraulics to braking. In Europe. Metal-tometal contact between his copper linings and the metal disc caused an intense screech that sent chills through anyone within earshot.

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the forces that have to be applied to the brake shoes in order to produce the maximum deceleration are very large. I I Rear Brakes V Brake Lines Typical Automotive Braking System Figure 2 .Typical Disk Brake Front Brakes Typical Drum Brake -. Approximating to the weight of the vehicle. leverage system and hydraulic system. 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.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 brake system must be able to provide a considerable leverage [2].3. The force multiplication processes take place in two areas.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.

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while the piston on the right is 6 inches (15.Hydraulic system and a typical master cylinder [5] .1.62 cm radius).3. To determine the multiplication factor in Figure 6. The area of the two pistons is 71 * 3. Figure 6 explains this process. U Typical Master Cylinder Figure 5 . brake lines and braking unit at each wheel. Due to the fact that fluid cannot be compressed.24 cm) in diameter (3-inch I 7.54 cm radius). Figure 5 shows hydraulic system and a typical master cylinder in automotive brake system. start by looking at the size of the pistons.08 cm) in diameter (1-inch 12. Assume that the piston on the left is 2 inches (5. a 900 lbs force will come out on the right-hand piston. This means that if 100 lbs force is applied to the left-hand piston. Therefore piston on the right is nine times larger than the piston on the left [6]. 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.2 Hydraulic System Hydraulic system consists of a master cylinder.

Therefore. Coefficient of fiction = Friction force I Normal load Friction force (F) = p.Force multiplication in hydraulic system [6] 1. the greater the friction force or braking force generated. the heavier the vehicle. Friction is a measure of how hard it is to slide one object over another [ 6 ] . Normal load (N) The friction force is proportional to normal load. . i II Figure 6 .3 Friction Friction happens when force from the brake fluid press the brake pads or friction linings against the rotor or drum. It is constant for a given pair of surfaces. This concept applies to the brake system where the more force applied at the brake pads or linings.3.Force inches I I 1 I inches - I 2 in.The coefficient of friction is the ratio of the limiting friction to the normal reaction between the sliding surfaces. the greater force is needed to decelerate the vehicle. Friction also happens between tires and road surface. I I II 1 6 in.

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. reliability and cost. components. To select an alternative materials using a systematic selection method. 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]. the trend toward lightweight materials continues to grow each day. In some performance cars. standards and theories through a literature study. A product sample from an average production car will be used as reference. CAFE is the sales weighted average fuel economy.855 kg) or less. we will be looking at a polymer-based material as the replacement material for steel. manufactured for sale in the United States [lo]. project objectives are set as below: To understand the working principles. According to [9]. To analyse current design and its material properties. thus reducing emissions.THE DESIGN OF LIGHT WEIGHTAUTOMOTIVE BRAKE PEDAL 1.500 lbs (3. . of a manufacturer's fleet of passenger cars or light trucks with a gross vehicle weight rating (GVWR) of 8.4 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. Most of the cars today have pedals that are made of steel. However. In this project. there are few problems that need to be considered such as limitation in material properties. aluminium has been used to replace steel due to its higher strength to weight ratio. expressed in miles per gallon (mpg). This project is concerned with the design of light-weight automotive brake pedal. In achieving this aim. The main advantages of using this material are light-weight and ease of manufacture.

The Chevrolet Corvette is the sport car range that has been manufactured by Chevrolet since 1953. the conventional brake pedal which was made of steel will be replaced with B356 aluminium. In this perspective. 1. manufacturers are searching out opportunities to replace conventional materials with new and lighter materials without compromising its mechanical and physical properties. To solve . The use of CAD and CAE for design and analysis will help to minimise design time. 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 . An example of reducing weight through new material application can be seen in the manufacturing of Chevrolet Corvette.5 Current Developments in Brake Pedal Design Efficiency of a car can be improved through weight reduction. To clearly justify the results and conclusions.THE DESIGN OF LIGHT WEIGHT AUTOMOTIVE BRAKE PEDAL To develop and analyse new component design using CAD and CAE applications.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]. 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.

. Secondary cosmetic process such as spray painting will be no longer required. Mould Flow Analysis. Several engineering computer applications were used from conceptual design until prototyping such Pro Engineer. The chosen product was a cable operated automotive clutch pedal which was converted from conventional material to polymer based composite. LUSAS. 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 DESIGN OF LIGHT WEIGHT AUTOMOTIVE BRAKE PEDAL 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. and Stereolithography(SLA) and 3D Printer for rapid prototyping. 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. Another advantage other than light weight is the exceptional appearance which is important as it is a visible component. 25 ksi yield strength and 7% elongation [9].

Coordinate Measuring Machine (CMM) will be used for ' for geometry generation and ABAQUS for finite measurement. Another interesting finding was the addition of ribs to the design to improve stiffness and rigidity. Highlighted by [12] that based on analysis. Sapuan [12] did not discuss the overall performance of the new component in comparison with the original component. hndamental theory and brake subsystems. Chapter 2 explained about the current steel brake pedal with an actual brake pedal used as example. GEOMETRY GENERATION AND ANALYSIS OF CURRENT COMPONENT Chapter4 NEW WTERIAL SELECTION I 4 Chapter5 NEW DESIGN AND ANALYSIS Ulapter 6 DISCUSSION w e r7 CONCLUSIONS AND FUTURE RECOMMENDATIONS Figure 9 .M.There were two conceptual designs considered. S.6 Report Structtire Chapter I lNTROWCTlON - Chapter 2 CURRENT COMPONENT \ h-3 MEASUREMENT. The project objectives and current developments in brake pedal design had also been discussed. However. geometry generation and finite element analysis of current brake pedal. A brief literature review on brake system has been carried out focusing on history. the 'T' profile design was stiffer compared to the 'I' profile. the 'T' profile and the 'I' profile. Chapter 3 is about measurement. The use of ribs enables designers to compensate the effect of reducing section thickness to improve design efficiency. ~ o l i d ~ o r k s 2003 element analysis. 1. . The analysis was done using LUSAS finite element analysis software.Report Structure Chapter 1 is the introduction chapter. The material properties and manufacturing process of the current brake pedal will be discussed in detail.

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When the brake pedal is depress. pivot shaft and plastic bearings anchored the brake pedal assembly to the bracket.Proton Wira (known as Persona in the UK) [14] J Figure 11 . The spring is used to retain brake pedal assembly at its original position. it will move back to its original position. When brake pedal is released. Bolt and nut. Figure 10 . Grease was applied at this area to minimise friction.THE DESIGN OF LIGHT WEIGHTAUTOMOTIVEBRAKE PEDAL also the mounting place of hydraulic master cylinder (not shown in figure) of the brake system and brake light switch. the spring will provides slight load to the brake pedal.Proton Wira brake pedal assembly .

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.Location of spring The size of the brake pedal assembly is about 370 mm x 148 mm with overall weight of 944.THE DESIGN OF LIGHT WEIGHTAUTOMOTIVE BRAKE PEDAL Figure 14 .4 grams.Brake light switch mounting area Figure 15 . It consists of three subcomponents joint by welding. The main body of brake pedal is made of steel plate with thickness 6 mm. Brake pedal assembly consists of three components. The welding areas are shown in Figure 17. brake pedal. 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. rubber foot pad and switch contact pad.

THE DESIGN OF LIGHT WEIGHTAUTOMOTIVE BRAKE PEDAL Figure 16 .Three areas of welding .Brake pedal asse&bly: (a) Brake pedal (b) Rubber foot pad (c) Switch contact pad Figure 17 .

.3 Material Properties A good design should always accompanied with the correct choice of material.Function. Since the number of engineering materials is large at an estimated over 120. meaning able to withstand load Constraints High Young's modulus Good tensile strength Objective Free variables Low material cost Choice of material Choice of design . objectives and free variables [15] Function Constraints What does component do? What non-negotiable conditions must be met? What negotiable but desirable conditions.000 materials are available. the material selection process can be a difficult task without guidance. Selecting the wrong material will result in higher product cost. .THE DESIGN OF LIGHT W?ZIGHTAUTOMOTIVEBRAKE PEDAL 2. constraints. Table 1 explains what those criteria are while Table 2 shows the design requirements for a brake pedal.. poor product performance or even product failure. It was stated by [15] that normally the choice of material is dictated by the design. 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. objectives and free variables. but sometimes the other way around.Design requirements for a brake pedal Function Brake pedal (load transfer) No failure.? Objective What is to be maximised or minimized? Free variables What parameters of the problem is the designer free to change? Table 2 . Table 1 . constraints.

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05 Si (Silicon) 0 0.05 Young's Modulus *205 215 Compressive Strength *255 315 Tensile Strength 3 10 430 Poisson's Ratio 0. Only materials available in sheet form can be stamped and the thickness is limited to available sheet size 1181.THE DESIGN OF LIGHT WEIGHT AUTOMOTIVE BRAKE PEDAL Table 3 . drawing.25 I 7900 I 99.13 *0.285 0. shearing. Press forming covers a range of sheet forming processes performed by means of a die and press. Tools are dedicated and. therefore.295 Mechanical: GPa Note: Value marked * are estimates 2. all shapes produced by this process have a uniform cross-sectional thickness. More detail information on press forming is attached in Appendix 2.45 Composition: I Fe (Iron) C (Carbon) Mn (Manganese) P (Phosphorus) S (Sulphur) *O 0. tooling costs are high. coining and swaging. Processes used include blanking. However.4 Manufacturing Process Steel brake pedals are manufactured using press forming. These processes may be performed consecutively to form complex shapes.Material properties of Low Carbon Steel AISI 1010 [18] - Minimum Properties Maximum General: I Density Price I *7800 I *99. bending.62 Units ___I 0. forming. I .

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.Process schematic of press forming [18] and The overview of current component as well as the material properties manufacturing process had been explained earlier in this chapter. the current component will be measured to get the actual dimensions. .THE DESIGN OF LIGHT WEIGHT AUTOMOTIVE BRAKE PEDAL Deep drawing Blanking Die Bending Blank Stretching Figure 19 . In the next chapter.

A. the ideas were dated back much further. Meanwhile R.W. Table 4 summarizes the important findings made by early researchers. Clough in a paper on plane elasticity problems [19]. Since then more and more researchers involved in FEM. GEOMETRY GENERATION AND ANALYSIS OF CURRENT COMPONENT 3.THE DESIGN OF LIGHT WEIGHTAUTOMOTIVE BRAKE PEDAL CHAPTER 3 MEASUREMENT.1 A Brief History of Finite Element Method This section presents a brief history of the Finite Element Method (FEM). Courant in 1943 had proposed setting up the solution of stresses in a variational form. Although 'finite element' terminology was first used in 1960 by R. . He used piecewise interpolation functions over triangular sub-regions making up the whole region as a method to obtain approximate numerical solutions [20]. Hrennikoff in 1941 and D. McHenry in 1943 used a latticed of line elements for the solution of stresses in continuous solids.

W. Gallagher and J. Melosh and Argyris R. McHenry 1941-1943 1943 R. Levy 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 1947-1953 Force method and displacement method J. Argyris and S. Clough 1960 M. 1963 1961-1964 matrix Curved-shell bending-element stiffness matrix for axisymmetric shells and pressure vessels Extension of the FEM to three-dimensional problems 1965 Special case of axisymmetric solids J.Brief History of Finite Element Method [20] Year Name of researchers A. Hremikoff and D.W. E. Turner Findings . 1960 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 R. Turner 1956 R.S.H.L. Wilson . Zienkiewicz 1968 Visco-elasticity problems B. Archer 1965 Dynamic analysis in consistent-mass matrix O.E. Gallagher 1962 Material nonlinearities 1963 Introduction of buckling problems R.H. Strome Martin.A Szabo and Lee 1969 Weighted residual methods T.R.J. Melosh 1961 R.THE DESIGN OF LIGHT WEIGHT AUTOMOTIVE BRAKE PEDAL Table 4 . Y.J. Courant S. Clough.J. Grafton and D. Padlog P. Belytschko 1976 Large-displacement nonlinear dynamic behaviour Rashid.C.H. Gallagher. 1954 Kelsey M.