Undergraduate Research Report

Spring 2010

Presented to: Dr. Ngaile | By: Anthony Katsaros and Philip Smith

NC STATE UNIVERSITY POWERTRAIN MOUNTING BRACKET DESIGN

Powertrain Mounting Bracket Design May 5, 2010 MAE 496 EcoCAR Project

NCSU Mechanical and Aerospace Engineering Department Page 1

Executive Summary The power train components on North Carolina State University’s EcoCar, a heavily modified Saturn Vue, need to be supported with a custom bracket. The following report follows the iterative process of designing this bracket to the required specifications. These specifications include space constraints, a factor of safety minimum, and weight/cost reduction. The iterative process included creating many designs followed by conducting finite element analysis on each one. New designs were created based on knowledge gained from previous designs. The most optimum design found in this report was Design 3D and was constructed from AISI 1045 steel.

This report includes a background section, description of constraints (including how the constraints were obtained), design alternatives and iterations (including FEA output of each design), a concluding section, and appendices (with machine drawings of each and every part).



Table of Contents 1 Introduction ................................................................................................................................................................... 5

1.1 Background ............................................................................................................................................................. 5 1.2 Objectives ................................................................................................................................................................ 5 1.3 Approach .................................................................................................................................................................. 6 1.4 Design Methodology ........................................................................................................................................... 7

2 Free Body Diagrams and Constraints .............................................................................................................. 8 2.1 Assumptions ........................................................................................................................................................... 8 2.2 Flexrail Goemetry ................................................................................................................................................. 8 2.3 Free Body Diagrams .......................................................................................................................................... 11 2.4 Solving for the Load .......................................................................................................................................... 14

3 Design Alternatives and Optimization .......................................................................................................... 16 3.1.1 Design Goal .................................................................................................................................................. 16 3.1.2 Finite Element Approach ....................................................................................................................... 17

3.2 Design Alternative 1 .......................................................................................................................................... 17 3.3 Design Alternative 2 .......................................................................................................................................... 20 3.4 Design Alternative 3 .......................................................................................................................................... 23 3.5 Design Optimization .......................................................................................................................................... 25

3.5.1 Design Iteration 3A .................................................................................................................................. 26 3.5.2 Design Iteration 3B .................................................................................................................................. 28 3.5.3 Design Iteration 3C .................................................................................................................................. 30 3.5.4 Design Iteration 3D .................................................................................................................................. 31 3.5.5 Design Iteration 3E .................................................................................................................................. 34

3.6 Material Selection and Cost ............................................................................................................................ 36 3.7 Design for Production ...................................................................................................................................... 38 3.8 Design Conclusion .............................................................................................................................................. 39

4 Manufactured Design .............................................................................................................................................. 40 5 Concluding Remarks ............................................................................................................................................... 41 6 Bibliography ................................................................................................................................................................ 42 7 Appendices ................................................................................................................................................................... 43

7.1 MATLAB Program .............................................................................................................................................. 43 7.2 Machine Drawings ............................................................................................................................................. 45

7.2.1 Design 1 ........................................................................................................................................................ 45 7.2.2 Design 2 ........................................................................................................................................................ 48 7.2.3 Design 3 ........................................................................................................................................................ 51 7.2.4 Design 3A ..................................................................................................................................................... 55 7.2.5 Design 3B ..................................................................................................................................................... 57 7.2.6 Design 3C...................................................................................................................................................... 58 7.2.7 Design 3D ..................................................................................................................................................... 60 7.2.8 Design 3E ..................................................................................................................................................... 62



Table of Figures Figure 1 - FlexRail Mounting System ............................................................................................................................... 6Figure 2 - CAD of Passenger's Side Mounting System from below ..................................................................... 7Figure 3 - Example of how the Geometric Center was found ................................................................................ 9Figure 4 - Isometric View of Diesel, Belt Box, and Generator Mounting ........................................................ 12Figure 5 - Free Body Diagram from the Right Side View ...................................................................................... 12Figure 6 - Free Body Diagram From the Front View ............................................................................................... 14Figure 7 - Diesel Bolt pattern and Passenger's side rail ........................................................................................ 16Figure 8 - Design 1 ................................................................................................................................................................ 18Figure 9 - FEA of Design 1 - Downward 3 g’s ............................................................................................................. 18Figure 10 - FEA of Design 1 - Forward 3 g’s ............................................................................................................... 19Figure 11 - FEA of Design 1 - Rightward 3 g’s ........................................................................................................... 19Figure 12 - Design 2 .............................................................................................................................................................. 20Figure 13 - FEA of Design 2 - Downward 3 g’s .......................................................................................................... 21Figure 14 - FEA of Design 2 - Forward 3 g’s ............................................................................................................... 21Figure 15 - FEA of Design 2 - Rightward 3 g’s ........................................................................................................... 22Figure 16 - Design 3 .............................................................................................................................................................. 23Figure 17 - FEA of Design 3 - Downward 3 g's .......................................................................................................... 24Figure 18 - FEA of Design 3 - Forward 3 g's ............................................................................................................... 24Figure 19 - FEA of Design 3 - Rightward 3 g's ........................................................................................................... 25Figure 20 - Design Iteration 3A ....................................................................................................................................... 26Figure 21 - FEA of Design Iteration 3A - Downward 3 g's .................................................................................... 26Figure 22 - FEA of Design Iteration 3A - Forward 3 g's ......................................................................................... 27Figure 23 - FEA of Design Iteration 3A - Rightward 3 g's ..................................................................................... 27Figure 24 - Design Iteration 3B ........................................................................................................................................ 28Figure 25 – FEA of Design Iteration 3B - Downward 3 g's ................................................................................... 28Figure 26 – FEA of Design Iteration 3B - Forward 3 g's ........................................................................................ 29Figure 27 – FEA of Design Iteration 3B - Rightward 3 g's .................................................................................... 29Figure 28 - Design Iteration 3C ........................................................................................................................................ 30Figure 29 – FEA of Design Iteration 3C - Downward 3 g's ................................................................................... 30Figure 30 – FEA of Design Iteration 3C - Forward 3 g's ........................................................................................ 31Figure 31 – FEA of Design Iteration 3C - Rightward 3 g's ..................................................................................... 31Figure 32 - Design Iteration 3D ....................................................................................................................................... 32Figure 33 - FEA of Design Iteration 3D - Downward 3 g's .................................................................................... 32Figure 34 - FEA of Design Iteration 3D - Forward 3 g's ......................................................................................... 33Figure 35 - FEA of Design Iteration 3D - Rightward 3 g's ..................................................................................... 33Figure 36 - Design 3E ........................................................................................................................................................... 34Figure 37 - FEA of Design Iteration 3E - Downward 3 g's .................................................................................... 34Figure 38 - FEA of Design Iteration 3E - Downward 3 g's .................................................................................... 35Figure 39 - FEA of Design Iteration 3E - Downward 3 g's .................................................................................... 35Figure 40 - FEA of Design 3D - Rightward 3 g's - Using 1020 Steel .................................................................. 36Figure 41 - FEA of Design 3d - Rightward 3 g's - Using 1045 Steel .................................................................. 37Figure 42 - FEA of Design 3d - Rightward 3 g's - Using 4140 Steel .................................................................. 37Figure 43 - Picture of Design 3 Installed in Vehicle ................................................................................................ 40Figure 44 - Design 1 .............................................................................................................................................................. 45Figure 45 - Design 1 Part 1 ................................................................................................................................................ 45



Figure 46 - Design 1 Part 2 ................................................................................................................................................ 46Figure 47 - Design 1 Part 3 ................................................................................................................................................ 46Figure 48 - Design 1 Part 4 ................................................................................................................................................ 47Figure 49 - Design 1 Part 6 ................................................................................................................................................ 47Figure 50 - Design 2 .............................................................................................................................................................. 48Figure 51 - Design 2 Part 1 ................................................................................................................................................ 48Figure 52 - Design 2 Part 2 ................................................................................................................................................ 49Figure 53 - Design 2 Part 3 ................................................................................................................................................ 49Figure 54 - Design 2 Part 4 ................................................................................................................................................ 50Figure 55 - Design 2 Part 5 ................................................................................................................................................ 50Figure 56 - Design 3 .............................................................................................................................................................. 51Figure 57 - Design 3 Part 1 ................................................................................................................................................ 51Figure 58 - Design 3 Part 2 ................................................................................................................................................ 52Figure 59 - Design 3 Part 3 ................................................................................................................................................ 52Figure 60 - Design 3 Part 4 ................................................................................................................................................ 53Figure 61 - Design 3 Part 5 ................................................................................................................................................ 53Figure 62 - Design 3 Part 6 ................................................................................................................................................ 54Figure 63 - Design 3A ........................................................................................................................................................... 55Figure 64 - Design 3A Part 7 ............................................................................................................................................. 56Figure 65 - Design 3B ........................................................................................................................................................... 57Figure 66 - Design 3C ........................................................................................................................................................... 58Figure 67 - Design 3C Part 5 ............................................................................................................................................. 59Figure 68 - Design 3D Part 7 ............................................................................................................................................. 59Figure 69 - Design 3D ........................................................................................................................................................... 60Figure 70 - Design 3D Part 7 ............................................................................................................................................. 61Figure 71 - Design 3D ........................................................................................................................................................... 62Figure 72 - Design 3E Part 8 ............................................................................................................................................. 63Figure 73 - Design 3E Part 9 ............................................................................................................................................. 63



1 INTRODUCTION

1.1 BACKGROUND

In 2009 the United States Department of Energy and General Motors created a national competition called EcoCAR, “The NeXt Challenge” with the goals of advancing vehicle technology and promoting the reduction of greenhouse gasses. The competition is being managed by the Argonne National Laboratory. The headline sponsors are Department of Energy and General Motors with the aid of plenty of lesser sponsors such as Snap-On, igus, the National Science Foundation, A123 Systems, and National Instruments.

Sixteen accredited engineering universities across the United States and Canada were chosen to participate in the competition, and North Carolina State University was fortunate enough to be chosen. Each university is given an identical Saturn Vue hybrid vehicle with the objectives of improving efficiency, reducing harmful emissions, and retaining customer appeal.

The competition is to take place over three years. During the first year teams are to design their vehicle system using computer aided software. The second and third years are intended for construction and optimization. This FlexRail mounting bracket design is taking place during the second half of year one.

This report focuses on one component of the vehicle’s construction, the powertrain mounting system. One bracket of this mounting system will be designed using iterations and will take into account material, manufacturing, costs, etc.

1.2 OBJECTIVES

The goal of this project is to design a bracket used to secure the passenger’s side of the diesel engine to the frame of the vehicle.

There are several design constraints/objectives which need to be addressed. The bracket must also:

• The bracket must fit within the allotted space. The vehicle’s engine bay is composed of thousands of parts, each of them essential to the vehicle’s operation and safety. The bracket must be designed not to interfere with any existing components.

• The bracket must be able to withstand three times the force caused by the acceleration of gravity and have a safety factor of three. The vehicle may be put under extreme loading, for example during a crash or while driving over bumps or holes in the road surface. These forces are assumed to be three times the force caused by gravity or less. Due to the importance of safety during all engineering endeavors, the factor of safety was set at three.

• The bracket must be able to be manufactured and assembled. The EcoCAR team at North Carolina State University has a limited amount of resources available, and the cheaper and faster the part can be made, the better.



1.3 APPROACH

The stock Saturn Hybrid Vue has a two-mode hybrid system and was designed to use only three frame mounting locations on the to attach the drivetrain to the vehicle’s frame. In order to have a safe and secure drivetrain, it was decided that the electric motor (ETS), diesel engine, generator, and belt box were to use only the three existing frame mounting locations. This would ensure a safe, firm grip to the frame and it would also reduce vibration in the car because the stock mounting locations included a damper.

In order to make a simple and consistent way to mount these components, two steel rails were attached to the chassis and were called “Flex Rails”. As shown in Figure 1, the symmetric Flex Rail Mounting System also simplifies the design and installation of component brackets, as all of the under hood components can mount to a common location. The 1½ inch square tube rail will be attached to the chassis on the passenger’s and driver’s side, approximately three feet apart (track width). Running from the front to the rear of the engine bay, the rails will be oriented parallel to the ground. The bracket being designed is the bracket attaching the chassis to the driver’s side rail and is circled with red in Figure 1, below.

FIGURE 1 - FLEXRAIL MOUNTING SYSTEM

In Figure 2, below, the bracket under consideration is colored red and is labeled as “A”. The passenger’s side flex rail is colored yellow and is labeled as “B”.



FIGURE 2 - CAD OF PASSENGER'S SIDE MOUNTING SYSTEM FROM BELOW

1.4 DESIGN METHODOLOGY

To find the best design possible many designs must be made and tested. This particular approach includes making three designs utilizing large changes, then to make three designs using smaller changes. The ideas will progress as the lessons learned from the first will carry on to the second, and then to the third etc. Finite element analysis will be completed after each design and will yield important to be considered and used to progress to the next design.

The design methodology for this project will be to: define the problem, come up with design alternatives, iterate the best design alternative, conduct materials/manufacturing studies, and conclude with the best possible solution.

The first and most important part of the design process is to define the problem. The problem at hand is that the powertrain components for NCSU’s EcoCAR need to be safely mounted. Design constraints were determined by analyzing CAD of the entire vehicle and were given by GM. The minimum factor of safety was given as 3, and the minimum force experienced by the car was given as 3g’s.

Several preliminary designs were developed using hand sketches and computer automated design software (SolidWorks). The designs were analyzed using FEA and more were produced. Once a suitable enough design alternative was determined, design iterations began on the best design alternative. This process continued until a most perfect design was achieved. Considerations of cost, manufacturability, weight, and material selection were then included. After analyzing all possible solutions, a “best solution” was determined.



2 FREE BODY DIAGRAMS AND CONSTRAINTS

In order to analyze the different designs using finite element analysis, first, the load on the bracket must be known. To find this load the whole bracket and powertrain system must be analyzed, since information such as distances, moments, and masses of different components at different locations all effect the load transferred to the bracket.

2.1 ASSUMPTIONS

During analysis of the entire FlexRail system and all the powertrain components, several assumptions had to be made.

• The brackets were assumed to have no mass. Due to the relative low mass of the brackets in relation to the larger components, it was assumed that their mass was negligible.

• The mass of the components: diesel engine, belt box, electric motor, and generator were assumed to centrally located at its geometric center.

2.2 FLEXRAIL GOEMETRY

The vehicle was already designed in the CAD program “NX”. This assembly was used to obtain the necessary dimensions for the free body diagrams. An origin was already set and was located on the “ground”, in front of the car, and slightly to the driver’s side of the vehicle.

To determine the geometric center of each engine component (the diesel engine, the electric motor, the generator, and the belt box) six points on each component were found. The x, y, and z dimensions of the left, right, top, bottom, front, and back (rear) sides were found and using the average of each position, the center of that component was found.



FIGURE 3 - EXAMPLE OF HOW THE GEOMETRIC CENTER WAS FOUND

TABLE 1 - POINT LOCATIONS ON DIESEL

Description Point X (mm) Y (mm) Z (mm)

Diesel Top 1479.81 63.33 846.86

Diesel Bottom 1269.83 83.08 215.53

Diesel Left 1270.93 -153.25 428.28

Diesel Right 1261.64 412.80 645.83

Diesel Front 1019.92 7.50 636.93

Diesel Back 1523.75 -62.36 590.90

Table 1, above, displays the actual point locations found during the analysis of the diesel motor using the program NX. Table 1 shows the process used to determine the center points of each component. This analysis was also preformed to the belt box, electric motor, and the generator. The distances between components could be determined from all of this information.

Table 2, below, displays the point locations for each of the components under review. These points were determined by taking the average between 2 meaningful parts of 2 of the 6 points found for each components. For example, the front of the Diesel was (1019.92,7.50,636.93) and the back was



(1523.75,-62.36,590.90). The front to rear axis is the x axis, therefore the average between the two x dimensions were found to find the geometric center point in the x direction. (1019.92+1523.75)/2=1271.86

TABLE 2 - CENTERPOINT LOCATIONS

Centerpoint X (mm) Y (mm) Z (mm)

ETS 1664.27 8.40 343.90

Diesel 1271.86 121.91 526.91

Belt Box 1513.22 -164.61 642.74

Generator 1661.49 -52.16 766.36

TABLE 3 - IMPORTANT DISTANCE INFORMATION

X mm Y mm

dx4 136.55 dy4 224.87

dx5 153.07 dy5 224.87

dx6 14.08 dy6 272.44

dx7 404.31 dy7 174.07

dx8 256.05 dy8 286.53

Figure 7, above, displays many very important dimensions used in the free body diagram section. These dimensions were determined by analyzing distances and center of masses of all of the systems. These distances will be described in more detail in Figure 5 and Figure 6.



TABLE 4 - COMPONENT MASSES

Component Name

Variable Mass Unit

ETS Em 114 kg

Diesel Dm 140 kg

Belt Box Bm 10 kg

Generator Gm 45 kg

Table 4, shown above, shows the masses used in the free body diagrams below.

2.3 FREE BODY DIAGRAMS

The free body diagrams are required to determine just how much force is being transmitted to each bracket. The free body diagrams are shown below in Figure 5 and Figure 6. The centers of masses of the three components below are displayed as blue circles with cross hatches.

The figures below use a unique nomenclature used to help clarify points and systems. The letters “G”, “B”, and “D” denote center of masses of various components. The “G” denotes the center of mass of the generator, the “B” is for the belt box, and the “D” is for the diesel engine. The “R”s display where a reaction force is found. All of the “R”s are located at where a bracket attaches to the diesel engine. A reaction force is an internal force which is usually not known. It exists only because a force is being applied to a component and a bracket is there to hold the body in equilibrium. RD1 and RD2 are two brackets located on the driver’s side of the diesel engine and connect to the driver’s side rail. RD3 is what is most important for this study. RD3 is the force experienced by the bracket being designed in this report. Figure 4, below, displays the overall positioning system of the Diesel, Generator, and Belt Box.



FIGURE 4 - ISOMETRIC VIEW OF DIESEL, BELT BOX, AND GENERATOR MOUNTING

FIGURE 5 - FREE BODY DIAGRAM FROM THE RIGHT SIDE VIEW



Figure 5, show above, displays the first free body diagram. This free body diagram uses a right side profile view of the vehicle. As displayed in this view, the vehicle would be traveling to the left. The distances, dx4 through dx8, can be found in Table 3. The masses can be found in Table 4.

Equations 1 and 2, below, are determined by analyzing Figure 5.

Taking the Sum of the forces in the Z direction:

zGzBzDzDzDzDz gmgmgmRRRF 9990 321 −−−++==∑

Then the known and unknown values were separated. The known variables were brought to the right side of the equation and the unknown values were brought to the left.

zGzBzDzDzDzD gmgmgmRRR 999321 ++=++ (1)

Taking the Sum of the moments about the center of gravity of the Diesel center of gravity:

zBxzGxzDxzDxzDxD gmdgmdRdRdRdM 990 87362514 −−++−==∑

Then the known and unknown values were separated. The known variables were brought to the right side of the equation and the unknown values were brought to the left.

zBxzGxzDxzDxzDx gmdgmdRdRdRd 99 87362514 +=++− (2)

Figure 6, below, was used to determine the next equation. Figure 6 displays the vehicle as if it was traveling upwards, out of the page. This new view allows for another, unique equation to be made and for the system to be solvable. Distances dy4 through dy8 can be found in Table 3 and all masses can be found in Table 4.



FIGURE 6 - FREE BODY DIAGRAM FROM THE FRONT VIEW

In order to obtain another useful equation, the vehicle view was rotated 90 degrees. Figure 6 was used to find one more equation. The sum of the moments about the center of gravity of the Diesel engine was found.

zByzGyzDyzDyzDyD gmdgmdRdRdRdM 990 87362514 −−−+==∑

The unknown values were brought to the left side of the equation and the knowns were moved to the right.

zByzGyzDyzDyzDy gmdgmdRdRdRd 99 87362514 +=−+ (3)

So, in order to create a solvable matrix, equations 1, 2, and 3 were then combined.

zGzBzDzDzDzD gmgmgmRRR 999321 ++=++ (1)

zBxzGxzDxzDxzDx gmdgmdRdRdRd 99 87362514 +=++− (2)

zByzGyzDyzDyzDy gmdgmdRdRdRd 99 87362514 +=−+ (3)

2.4 SOLVING FOR THE LOAD



To help solve for the unknowns, equations 1, 2 and 3 above can be combined together to form a system of equations. The unknown values, RD1z, RD2z, and RD3z, are separated from their variables forming two matrices on the left side of the equation. The left side of the matrix equations becomes a three by three matrix and a three by one matrix. The right side of the matrix equations becomes one three by one matrix.

The matrix below shows what Equations 1, 2, and 3 become when combined together. The coefficients were brought off of RD1z, RD2z, and RD3z.

++

++=

−−

zByzGy

zBxzGx

zGzBzD

zD

zD

zD

yyy

xxx

gmdgmdgmdgmd

gmgmgm

RRR

dddddd

9999999111

87

87

3

2

1

654

654

Next, the matrices were rearranged to solve for the unknowns, RD1z, RD2z, and RD3z.

++

++

−−=

−

zByzGy

zBxzGx

zGzBzD

yyy

xxx

zD

zD

zD

gmdgmdgmdgmd

gmgmgm

dddddd

RRR

9999999111

87

87

1

654

654

3

2

1

For a more accurate and expedient way of solving the systems of equations MATLAB was used. The MATLAB program itself can be found below in the Appendix 7.1, titled MATLAB code . The program defined the matrices shown above, defined all necessary variables as found in Table 3 and Table 4, and solved for the unknown reaction forces RD1z, RD2z, and RD3z. The most important number output from the equation was RD3z. RD3z represents the amount of force the bracket will be experiencing from above. It is the load which will be applied in FEA analysis to determine if the bracket is strong enough. The load was determined to be 2,058 Newtons (462.66 pounds).



3 DESIGN ALTERNATIVES AND OPTIMIZATION

To find the best design possible many designs must be made and tested. This approach includes making three designs utilizing large changes, then to make three designs using smaller changes. The ideas will progress as the lessons learned from the first will carry on to the second, and then to the third etc. Finite element analysis will be completed after each design and will yield important to be considered and used to progress to the next design.

It is important to note that within the infinite number of possible designs, only a few were considered and the most optimum was chosen from those. Given an infinite amount of time and resources a more perfect design could always be designed and optimized.

3.1.1 DESIGN GOAL

All potential designs, regardless to how different they are, must secure the passenger’s side of the diesel motor to the passenger’s side rail. The passenger’s side rail is a three foot long square tubing at 1 and ½ inch by 1 and ½ inch and is parallel with the ground. The diesel mount is a spot on the diesel engine which was designed to have a mount attached to it. It has a three bolt hole pattern spanning about 8 inches. Figure 3 below shows how the two components are in relation to each other.

FIGURE 7 - DIESEL BOLT PATTERN AND PASSENGER'S SIDE RAIL

The green, purple, and yellow section in Figure 7 show the passenger’s side of the diesel engine. The yellow plate shows the bolt hole pattern which needs to be connected to the blue rail at the bottom. The two components, the passenger’s side of the diesel and the passenger’s side rail, are shown here in correct relation to each other.



3.1.2 FINITE ELEMENT APPROACH

The Finite Element Analysis program imbedded within SolidWorks was used to complete the FEA. It was very efficient because fewer steps were required for testing as compared to by using a separate program.

The FEA analysis results are displayed in a color coded pattern. The more blue a location is means that it is experiencing less stress/deformation/factor of safety etc, and the more red it is the more stress/deformation/factor of safety etc. it is experiencing. The legend to the right of each image helps explain what the extremes of the colors represent, i.e. the units/meaning of the color. It is important to note that the color is a relative point of reference, meaning that a particular color or shade of color may represent a totally different stress value in one analysis then it does in another. This is because the colors help represent the total spectrum of stresses experienced by that part with that particular load, and the units are specific to that scenario.

Various viewing angles are presented during the following FEA analysis section. This is done to better display where that particular design’s most critical stresses are located. Depending on the design, the most critical sections vary greatly.

The FEA analysis assumed ASTM 1045 steel for all of the three designs. This steel was chosen because it is a commonly used steel. The primary use of FEA analysis is to compare one design to another, and their relative stresses. Therefore the which material doesn’t matter at this time. It is only during the material selection section where the optimum material will be chosen.

During the following finite element analysis studies, the brackets will be tested under 3 different types of loads: downwards, rightwards, and forwards. These loads have the same magnitude, but are applied in different directions. All the FEA models have the bottom part of the bracket constrained, meaning that it will not move. The bolt holes will experience a force which was determined in the “Solving for the Load” section. The direction of the force will change, depending on how the part is tested. It is important for the bracket to be strong enough in not just one direction, but in all three (the x, y, an z direction). The primary focus will be to focus on the forces acting downward, since gravity acts downwards. Rightwards and forward forces will be of secondary concern, as long as they pass the minimum FOS set by GM, it will be fine.

3.2 DESIGN ALTERNATIVE 1

As seen below in Figure 8, Design Alterative 1 is a very simple design. In order to ease material ordering and make fabrication as inexpensive as possible, the entire design is cut from ½ inch thick (12.7mm) plate steel. A slightly modified box frame was constructed in order to provide as much stability as possible from the geometry. The tops of the side supports are cut at a 9 degree angle to properly support the mounting plate, which must be tilted to account for the angling of the diesel mount. Finally, a large backing plate keeps the box frame square, as well as tying the base of the bracket to the FlexRail for increased strength.

With this design configuration, the bracket would be simple, stable, and strong. Design 1 mounts to the FlexRail on two sides, allowing ample space to weld as well as providing a fully constrained base. This



design would be just as strong in forward loading as it is in down loading. This design seems less stable from loading on the sides, but should be able to sustain a large enough load.

FIGURE 8 - DESIGN 1

FIGURE 9 - FEA OF DESIGN 1 - DOWNWARD 3 G’S

Figure 9, above, clearly shows how over designed this bracket is. Although the downward mode is the most critical mode, this design exceeds the necessary factor of safety by five times. Using such an overdesigned bracket would hurt the design goals in multiple ways. Not only does the excess material add to the cost of the bracket, but it also adds to the weight of the design and thus makes the overall vehicle less efficient.



FIGURE 10 - FEA OF DESIGN 1 - FORWARD 3 G’S

FIGURE 11 - FEA OF DESIGN 1 - RIGHTWARD 3 G’S

Examining Figure 10 and Figure 11 show similar results. In rightwards loading, this design has a minimum FOS of 11, and in forward loading the minimum FOS is 28. It is also quite evident by looking at the factor of safety plots that the minimum factors of safety only occur in a few distinct corners of the bracket. The majority of the bracket is very overdesigned, as it has a FOS closer to 100. In order to design a more consistent and efficient bracket, the stress should be more evenly spread across the bracket.




FIGURE 12 - DESIGN 2

Design 2 was created with the lessons learned from the analysis on Design 1 in mind. In order to remove excess bulk material and weight, Design 2 was created out of rectangular tubing instead of plate stock and a simple H design was incorporated. Similar to Design 1, the rails in Design 2 were kept vertical, with a perpendicular support. The excess bulk was removed from Design 1 to remove weight and save on price. Finally, since Design 1 depended on the base plate to tie the bracket to the FlexRail, Design 2 incorporates a section of square tubing that fits over the FlexRail to allow more area for the bracket to attach to the FlexRail. The rectangular tubing was hypothesized to increase strength due to the increased surface to surface contact with the rail.



FIGURE 13 - FEA OF DESIGN 2 - DOWNWARD 3 G’S

In the downward loading mode, as pictured in Figure 13, there is too much stress acting on the forward side on the bolt plate (on the left side in Figure 13) and on the forward vertical rail. Design 2 is not strong enough to support the entire load, although it is closer to the desired goal than Design 1. The minimum FOS is 1.8, and most of the stress concentration is occurs in the front of the bracket, indicating that the bracket is supporting too much of the load on the front of the bracket and not spreading enough to the back vertical column.

FIGURE 14 - FEA OF DESIGN 2 - FORWARD 3 G’S



FIGURE 15 - FEA OF DESIGN 2 - RIGHTWARD 3 G’S

Figure 14 and Figure 15, above, show Design 2 experiencing a rightward and a forward load, respectively. This FEA analysis shows similar results as excess stress concentrations are towards the front of the bracket (left side in the figures above). The minimum FOS for Design 2 loaded in the rightward direction is 1.6, and the FOS for Design 2 loaded in the forward direction is 1.7. Neither of these are acceptable.

Design 2 does not effectively spread the load across its geometry; it only supports itself in a few areas. It is in improvement from Design 1 because it is much lighter and cheaper, however it is not quite strong enough.





As seen above in Figure 16, Design 3 was created with the same basic principles of Design 2. Additionally, a new issue became apparent to the team; more space left on the FlexRail would be optimal to allow for other components in the engine compartment. To address this issue and in an attempt to distribute the load a basic H-frame was used, as in Design 2, except the H-frame was tilted 9 degrees towards the front of the vehicle. Nine degrees was chosen because it would allow a perfect right angle connection at the top bolt hole panel. The tilted H-frame reduces the required FlexRail mounting space, which allows for other vehicle components to be mounted in the space vertically below the diesel engine.

Another difference between Design 2 and Design 3 is the interface with the FlexRail. Reviewing the FEA from Design 2 shows that the square tube interface is much stronger than necessary as almost the entire square tubing was blue and not being stressed. Instead of the tubing, as in Design 2, a piece of angle iron (an “L” shape) was used, such as in Design 1. This also saves weight on the vehicle, and allows for a greater weld surface.

After trying minor alterations to the FEA analysis of Design 2, it was found that adding ribs to the top bolt plate greatly increased the strength and rigidity of the entire assembly. The ribs help distribute the load and increase strength without significantly increasing weight.



FIGURE 17 - FEA OF DESIGN 3 - DOWNWARD 3 G'S

Figure 17, pictured above, shows just how much adding the ribs help the design. The FOS jumped up from 1.82 to 3.72. This is just where it needs to be, right around and above 3. The slanted H frame spread the stress distribution more evenly, and the ribs really helped spread out the load across the vertical braces.

FIGURE 18 - FEA OF DESIGN 3 - FORWARD 3 G'S



FIGURE 19 - FEA OF DESIGN 3 - RIGHTWARD 3 G'S

Figure 18 and Figure 19, above, show the minimum FOS and the stress distribution for the other loading modes. Even in these conditions, the FOS’s are acceptable, at 5.20 and 3.29.

It is clear that Design 3 is a big improvement from both Design 1 and Design 2. It is comparable to Design 2 in weight, but is much stronger since the stresses are spread out better. It is just as strong as it needs to be, unlike Design 1, and uses much less material. Design 1 used too much material and was therefore not as cost effective as Design 3.

3.5 DESIGN OPTIMIZATION

To optimize the design further, Design 3 was slightly altered, or “iterated”, using various techniques to create a more prefect design. The overall Design 3 idea was the basis of these modifications. Design A, B, and C represent a series of modifications made to Design 3.



3.5.1 DESIGN ITERATION 3A

FIGURE 20 - DESIGN ITERATION 3A

It was decided that due to the primary stresses occurring on the top of the bracket, that section should be reinforced. The bolt holes themselves could not be interfered with since the bolts and washers needed to be inserted through those holes and some of the surrounding area. The underside of the top bolt hole panel could not be interfered with either since the diesel bracket mates on that side. The top side of the bolt hole panel was the only place to improve.

The simplest way to strengthen Design 3 was to add a 0.23 inch (6 mm or about ¼ inch) thick and 0.47 inch (12 mm or about ½ inch) tall strip along the top section. Two strips were used to retain symmetry and add even more strength.

FIGURE 21 - FEA OF DESIGN ITERATION 3A - DOWNWARD 3 G'S



As seen above in Figure 21, the FOS shot up from 3.72 to 7.02. The strength increase was great, but the actual material increase was minimal. This is what is most desired in the design process, to invoke the most positive change in performance with the least amount of effort or material cost.

FIGURE 22 - FEA OF DESIGN ITERATION 3A - FORWARD 3 G'S

Figure 22 pictured above shows how much the forward loading increased. The factor of safety rose from 5.20 to 6.13. The primary stresses are at the connections in the H-frame. The red areas are concentrated around the edges of the horizontal section as well as at the bottom front of the H.

FIGURE 23 - FEA OF DESIGN ITERATION 3A - RIGHTWARD 3 G'S

Figure 23 shows how the rightward load is distributed along the bracket. The bracket meets the minimum FOS requirement at 3.26, but the change from Design 3 to Design 3A did not effect this



loading much at all. The vertical strips at the top are not near the maximum stress for sideways loading.

3.5.2 DESIGN ITERATION 3B

FIGURE 24 - DESIGN ITERATION 3B

Design 3B utilized another set of ribs. The two ribs added for Design 3 from Design 2 seemed to help the model out very much without increasing the weight or cost very much, so more ribs were added to obtain Design 3B.

FIGURE 25 – FEA OF DESIGN ITERATION 3B - DOWNWARD 3 G'S



FIGURE 26 – FEA OF DESIGN ITERATION 3B - FORWARD 3 G'S

As seen in Figure 25 and Figure 26, the FOS increased again. The extra two ribs added in Design 3B increased the downward loading strength and the forward loading strength.

FIGURE 27 – FEA OF DESIGN ITERATION 3B - RIGHTWARD 3 G'S

Figure 27 shows that the FOS for rightward loading did not change at all. The ribs apparently have no effect on rightward loading. The maximum stress is obviously located far away from the rib locations.



3.5.3 DESIGN ITERATION 3C

FIGURE 28 - DESIGN ITERATION 3C

Design 3C came from the notion that Design 3A and 3B were too strong. In order to save material and become more efficient, the ribs and the rails on the top were reduced in size. It was thought that reducing their size would maintain the added strength, but decrease the cost of the material used. The factor of safety is 3 and it can be viewed that any more than 3 is undesirable since it would increase the cost.

FIGURE 29 – FEA OF DESIGN ITERATION 3C - DOWNWARD 3 G'S

Figure 29 shows how Design 3C acts under downward loading. This is the most primary loading condition and it is above 3 at 8.65. This shows that the



FIGURE 30 – FEA OF DESIGN ITERATION 3C - FORWARD 3 G'S

FIGURE 31 – FEA OF DESIGN ITERATION 3C - RIGHTWARD 3 G'S

As seen in Figure 30 and Figure 31, above, the changes made in Design 3C do not affect the forward and rightward loading conditions.



3.5.4 DESIGN ITERATION 3D

FIGURE 32 - DESIGN ITERATION 3D

Design 3D used a more convenient method of attaching the ridge along the top panel. The method shown above would be much easier to weld and only utilizes one strip instead of two. It also gives the bolts and washers more room to be inserted and tightened. The strip along the edge is as long as the top panel and is ¼ inch wide and 1 ½ inch tall. The strip on the top is the only change from Design 3C. Design 3D includes the four thinner triangular ribs.

FIGURE 33 - FEA OF DESIGN ITERATION 3D - DOWNWARD 3 G'S

As seen above in Figure 33, the factor of safety for Design 3D has remained almost unchanged. The FOS for the downward loading direction is 8.38, and has decreased only slightly from 3C at 8.65. The



downward loading direction is the primary cause for concern and the 8.38 FOS is better than it needs to be.

FIGURE 34 - FEA OF DESIGN ITERATION 3D - FORWARD 3 G'S

The factor of safety for forward loading has increased slightly to 5.84. This FOS for forward loading on this design is acceptable.

FIGURE 35 - FEA OF DESIGN ITERATION 3D - RIGHTWARD 3 G'S

The rightwards loading has remained unchanged from before. Figure 35 shows a very similar view as that of rightwards loading of Design 3A, 3B, and 3C in figures Figure 23, Figure 27, and Figure 31, respectively. The factor of safety for all three of these designs remains at 3.26.



3.5.5 DESIGN ITERATION 3E

FIGURE 36 - DESIGN 3E

Design 3E, seen in Figure 36, tried to increase the rightwards loading factor of safety. All previous designs have shown a factor of safety at 3.26 in rightward loading, which is acceptable, but if all the factor of safeties were similar, then it may be possible to degrade the material selection to save money. Since all previous designs showed great red areas along the sides of the two vertical sections of the H-frame, it was decided to extend the outside triangular ribs to make the vertical sections of the H-frame more sturdy. This goal was to help give the bending more area to act on and reduce the stress at one particular area.

FIGURE 37 - FEA OF DESIGN ITERATION 3E - DOWNWARD 3 G'S



The downward loading of Design 3E, pictured in Figure 37, shows how the extended ribs do not help or hurt the bracket withstand downward loading. The FOS changed from 8.38 in Design 3D to 8.36 in Design 3E. The change here is not significant.


The change in the forward loading is also insignificant. The FOS changed from 5.84 in Design 3D to 5.88 in Design 3E (Figure 38). The extended ribs obviously have very little effect on forward loading.


Figure 39 shows how adding the ribs did not increase the factor of safety. The picture section shows how the stresses are more spread out along the entire edge of the vertical H-frame sections, but looking at the legend to the right shows that the minimum factor of safety decreased to 1.19, which is an unacceptable level. It seems that even though it may seem like adding the extended ribs would help the



bracket, it actually decreases the FOS, and therefore Design 3E is a step backwards and not an improvement. Design 3E will therefore not be added upon and Design 3D should be considered the most acceptable design.

3.6 MATERIAL SELECTION AND COST

To determine the most effective material various metals were tested and evaluated. The factor of safety required remains at 3, but various other factors were considered. There is no such thing as one, perfect solution. Infinite possibilities are plausible, and a few are considered most optimal. Compromises must be made, weather in cost, weight, strength, finish, weldability, machinability, availability, etc. All options have advantages and disadvantages.

SAE steels beginning with the number “1” specifies them as carbon steels and the “10” prefix means that it is plain carbon with 1% or less Manganese.

SAE 1006 to 1035 carbon steels are considered to be general purpose low carbon steel and are easiest to weld and machine. The low carbon steels provide a good balance between price and workability. Below, in Error! Reference source not found., the rightward loading for SAE 1020 steel is shown. The rightward loading fails the FEA test since the minimum factor of safety is 1.75.

FIGURE 40 - FEA OF DESIGN 3D - RIGHTWARD 3 G'S - USING 1020 STEEL

SAE 1045 steel is a medium carbon steel and is stronger and less expensive than the lower carbon steels, but it is harder to machine and weld. The finite element analysis for all designs was done in SAE 1045 steel. This was done only to compare one design to another, not necessarily to specify the material. Below, in Figure 41, the downward loading for SAE 1045 steel is shown. The minimum FOS is 3.26, which is above 3 and therefore is acceptable.




4140 and 4142 Alloy steel is a more advanced type of steel, but costs the most. A steel beginning with 41 is considered a “Chromoly” steel since it alloyed with 0.5% to 0.95% Chromium and 0.12% to 0.3% Molybdenum. This gives it good fatigue, abrasion, and impact resistance. These qualities make it great for the power train applications since the engine vibrations will need to be absorbed by the bracket, but the bracket did not withstand rightward loading well enough. Below, in Figure 42, the downward loading for SAE 4140 steel is shown.




TABLE 5 - STEEL PROPERTIES

Steel Machinability Weldability Formability

1018/1020 Good Good Good

1045 Good Fair Difficult

4140/4142 Good Fair Fair

TABLE 6 - AVERAGE STEEL COST PER CUBIC INCH

SAE Steel Average cost

per in^3

1020 $1.26

1045 $1.14

4140 $1.58

Table 5 and Table 6, shown above, summarize the information discussed above as well as prices found from McMaster-Carr.com.

3.7 DESIGN FOR PRODUCTION

Creating a well engineered mounting bracket for the NCSU EcoCAR team was only one of the goals for this semester. In order to give the team a competitive edge, a design was needed which was easy to produce in house. Although there was the ability to out-source our work, the team would greatly benefit from the reduced cost and the quick turn-around time. As such, all of the design alternatives were made to be produced with the limited resources of a basic machine shop.

Primarily, the designs were composed of metal stock which was readily available. As such, a basic metal alloy and basic shapes were used. Also, there could not be any complicated features in any of the components, and the brackets had to be created in a way such that its final dimensions would not be drastically affected by tolerance stack-up. Finally, the metal parts had to be cut with an air compressor- driven cut off tool or a reciprocating saw, and had to be welded with a basic 110 V gas welder or a TIG welder.



3.8 DESIGN CONCLUSION

Design 1 has a factor of safety which was much too high. A new H-frame concept was developed and integrated to make Design 2. Design 2 was not strong enough, so it was modified to make Design 3. A design similar to Design 3 was actually constructed and installed into the EcoCAR. In order to find a more optimized solution, Design 3 was altered many different ways.

Design 3A, 3B, 3C, 3D, and 3E were created from the basic Design 3 idea. Each successive design was modified and perfected slightly. Design 3A added two support bars to the upper side of the bolt plate. Design 3B added another two triangular ribs to the center of the design. Design 3C reduced the thickness of both the two support bars from 3A and the four triangular ribs from Design 3B. Design 3D replaced the two thin support bars on the top of the bolt plate and replaced it with one thicker support bar attached at a more convenient location. Design 3E extended two of the four triangular ribs from Design 3D.

As seen in Table 7, all successive design iterations improved the previous design, except for Design 3E. For this reason and since several other designs were tested, but did not make it into this report for the sake of conciseness, Design 3D was found to be the most optimum design.

Once Design 3D was determined to be the best design, the material selection needed to be made. Design 3D was tested using three different material, SAE 1045, 1020 and 4140 Steel. The results from these tests can be shown below in Table 7. As seen in this table, Design 3D passed all tests for all materials, except rightward loading for both SAE 1020 and SAE 4140 steel. Therefore, since GM set the minimum required factor of safety at 3 the only acceptable material is SAE 1045 steel.

It was found for this study that Design 3, as seen in Figure 32, is the most optimum design, and that SAE 1045 steel is the most optimum steel choice.

TABLE 7 - FEA FACTOR OF SAFETY RESULTS

Design Steel Downward Forward Rightward Average

1 1045 15.53 28.06 10.95 18.18

2 1045 1.82 1.7 1.62 1.71

3 1045 3.72 5.2 3.29 4.07

3A 1045 7.02 6.13 3.26 5.47

3B 1045 10.15 6.00 3.26 6.47

3C 1045 8.65 5.66 3.26 5.86

3D 1045 8.38 5.84 3.26 5.83

3E 1045 8.36 5.88 1.19 5.14

3D 1020 4.32 3.87 1.75 3.31

3D 4130 5.12 4.59 2.56 4.09



4 MANUFACTURED DESIGN

FIGURE 43 - PICTURE OF DESIGN 3 INSTALLED IN VEHICLE

During the design process, time restraints required a final design to be chosen in order to complete the vehicle on time. Design 3 was the most optimal design at the time of necessity and therefore was chosen to be built and installed. It is proving itself to be reliable and efficient enough to serve its purpose at this time. The picture in Figure 43 depicts this bracket as it is installed in the vehicle. It was constructed out of various low carbon steels, comparable to SAE 1020 steel. As seen in the bottom of Figure 43, it was determined that the actual bracket was not strong enough. As a result the team decided to add an extra plate steel bracing to the bracket.



5 CONCLUDING REMARKS

Various designs and aspects of the designs were considered throughout this report. Many lessons have been learned and a dependable bracket design has been optimized. The final design is proven to be more optimized than the implemented design. According to the FEA analysis, Design 3D if constructed out of SAE 1045 steel should perform better than the Design 3 made out of low carbon steel.

It must be noted that GM’s requirements of having a vehicle experiencing a force of 3 g’s with a factor of safety of 3 in all three directions seems like it may be too much. It is understood that GM is focused on safety, but these requirements may be too drastic for various reasons. Regardless of this observation, all the analysis was done to GM’s specifications.

Although Design 3 has already been built and installed on the EcoCAR, this bracket and others could be modified and optimized. Year 3 for the EcoCAR competition is designated as “design optimization,” and the suggestions and lessons learned in this report may benefit the EcoCAR team. This report could give insight into how this part could be optimized, as well as provide an approach to optimize other powertrain mounting brackets.



6 BIBLIOGRAPHY

"About EcoCAR." EcoCAR Challenge. Argonne National Laboratory, n.d. Web. 5 May 2010. <http://www.ecocarchallenge.org/index.html>.

Beer, Ferdinand P., E. Russell Johnston, and John T. DeWolf. Mechanics of Materials. 3rd ed. New York, NY: McGraw-Hill, 2002. Print.

"Steel." McMaster-Carr. N.p., n.d. Web. 5 May 2010. <http://www.mcmaster.com/#steel/>.

Oberg, F.; Jones, F.; Horton, H.; Ryffel, H. Machinery’s Handbook. 28th Ed. New York: Industrial Press. 2008. Print. (Peyrache )



7 APPENDICES

7.1 MATLAB PROGRAM

% Force Solver clc syms re1z re2z re3z rd1z rd2z rd3z rc1z rc2z r3 c3 g3 format short %constants %known x measurements in mm dx1=104.654; dx2=102.906; dx3=102.715; dx4=136.548; dx5=254.027; dx6=14.081; dx7=404.311; dx8=256.046; % dx9=; dx10=; %dx11=; dx12=; dx13=; %known y measurements in mm dy1=196.8826; dy2=242.977176; dy3=271.423676; dy4=111.355176; dy5=111.355176; dy6=385.948924; dy7=174.0743; dy8=286.527; % dy9=; dy10=; %dy11=; dy12=; %masses kg gz=9.81; me=114; md=140; mb=10; mg=45; %matrices derived from FBD %ETS c1=[1 1 1 ; -dx1 dx2 -dx3 ; dy1 dy2 -dy3]; r1=[re1z ; re2z ; re3z]; g1=[9*me*gz ; 0 ; 0]; r1=inv(c1)*g1 re1z=r1(1,1) re2z=r1(2,1) re3z=r1(3,1) %Diesel+ Belt Box +Gen c2=[1 1 1; -dx4 dx5 dx6; dy4 dy5 -dy6]; r2=[rd1z rd2z rd3z]; g2=[9*md*gz+9*mb*gz+9*mg*gz; dx7*9*mg*gz+dx8*9*mb*gz; dy7*9*mg*gz+dy8*9*mb*gz] r2=inv(c2)*g2 rd1z=r2(1,1) rd2z=r2(2,1) rd3z=r2(3,1) %Passengers Beam %rc3z=rd3z+re3z %Drivers Beam %c3=[1 1; dx8 dx10]; %r3=[rc1z; rc2z]; %g3=[rd1z-rd2z-re1z; dx9*rd1z+dx11*rd2z+dx12*re1z]; %r3=inv(c3)*g3 %rc1z=r3(1,1) %rc2z=r3(2,1) PROGRAM OUTPUT: r1 = 1.0e+003 * 0.3076 5.0308



4.7267 re1z = 307.6410 re2z = 5.0308e+003 re3z = 4.7267e+003 g2 = 1.0e+006 * 0.0172 1.8324 0.9446 r2 = 1.0e+003 * 5.3045 9.9564 1.9557 rd1z = 5.3045e+003 rd2z = 9.9564e+003 rd3z = 1.9557e+003



7.2 MACHINE DRAWINGS

7.2.1 DESIGN 1


FIGURE 45 - DESIGN 1 PART 1











7.2.2 DESIGN 2













7.2.3 DESIGN 3
















7.2.4 DESIGN 3A

FIGURE 63 - DESIGN 3A

For Design 3A Part 1 see Figure 57








FIGURE 64 - DESIGN 3A PART 7



7.2.5 DESIGN 3B

FIGURE 65 - DESIGN 3B

For Design 3B Part 1 see Figure 57









7.2.6 DESIGN 3C

FIGURE 66 - DESIGN 3C

For Design 3C Part 1 see Figure 57






FIGURE 67 - DESIGN 3C PART 5


FIGURE 68 - DESIGN 3D PART 7



7.2.7 DESIGN 3D

FIGURE 69 - DESIGN 3D

For Design 3D Part 1 see Figure 57








FIGURE 70 - DESIGN 3D PART 7



7.2.8 DESIGN 3E

FIGURE 71 - DESIGN 3D










FIGURE 72 - DESIGN 3E PART 8

FIGURE 73 - DESIGN 3E PART 9

Documents

Undergraduate Research Report