car brake pedal design excercise

Autodesk Inventor®

Tutorial Exercise

SAE Car Brake Pedal Exercise. Autodesk Inventor

® Finite Element Analysis

Optimization

OBJECTIVE: To create simulations of various pedal designs that focus on

reducing the mass of the current design. The exercise involves

adding machined pockets on both sides of the pedals and

validating the design change in the Stress Analysis environment.

SAE Car Brake Pedal Exercise: Autodesk Inventor® Finite Element Analysis Optimization

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Contents TOPIC .......................................................................................................................................................... 3

OPTIMIZING THE MASS OF A BRAKE PEDAL .............................................................................. 3

OBJECTIVE ........................................................................................................................................ 3

DESCRIPTION ................................................................................................................................... 3

DATASET ............................................................................................................................................ 4

DESIGN CRITERIA ............................................................................................................................... 4

KEY TERMS ........................................................................................................................................... 4

EXERCISE .................................................................................................................................................. 6

DESIGN CRITERIA ............................................................................................................................... 6

Create a New Simulation ...................................................................................................................... 6

Review the Materials ............................................................................................................................. 7

Add Constraints ...................................................................................................................................... 7

Add Loads ............................................................................................................................................... 8

Run a Simulation .................................................................................................................................... 9

CONCLUSION: ..................................................................................................................................... 10

Create an Extrusion ............................................................................................................................. 10

Run the Second Simulation ................................................................................................................ 11

CONCLUSION: ..................................................................................................................................... 12

Create a Second Extrusion ................................................................................................................. 12

Run the Third Simulation ..................................................................................................................... 12

CONCLUSION: ..................................................................................................................................... 13


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TOPIC

OPTIMIZING THE MASS OF A BRAKE PEDAL

OBJECTIVE

To create simulations of various pedal designs that focus on reducing the mass of the current

design. The exercise involves adding machined pockets on both sides of the pedals and

validating the design change in the Stress Analysis environment.

DESCRIPTION

The current design of the pedals is overbuilt and the new designs are focused on maintaining

the design specifications of the current design, while reducing the mass of the part.

Using Autodesk Inventor, Stress Analysis will be used to determine the stress, displacement

and safety factor of the design. The work flow will be repeated until the mass of the pedal

design is optimized against the design criteria. The initial mass of the brake pedal is 0.311 kg.

The optimized mass is 1.51 kg, a reduction of 51%. The design changes include:

1. Add a machined pocket to each side of the brake pedal.

2. Add a machined cut-out.


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DATASET

brakes_pedal_tray.iam

The part to be analyzed is brakes_brake_pedal.ipt.

DESIGN CRITERIA

YIELD STRENGTH (MPa) DEFLECTION (mm) SAFETY FACTOR

276 (AL 6061) 1.25 2.0

KEY TERMS

KEY TERM DESCRIPTION

assembly Two or more components (parts or subassemblies) considered as a single model. An assembly typically includes multiple components positioned absolutely and relatively (as required) with constraints that define both size and position. Assembly components may include features defined in place in the assembly. Mass and material properties may be inherited from individual part files. The brake pedal is the part being analyzed. It is a part within the brake tray assembly.

Stress analysis An analysis showing that the model is statically and dynamically stable and free from divergence on application of external loads and frequencies.

In this optimization, we are using stress analysis to ensure that the material and geometry of the pedal can handle the loads without deforming and failing.


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Simulation In the context of Autodesk Inventor, the term Simulation has grown to be an equivalent term to analysis. The analysis of the brake pedal uses Stress Analysis to optimize the mass of the pedal. Stress Analysis is used to analyze the material at the point of maximum load on the pedal.

von Mises Stress Three-dimensional stresses and strains build up in many directions. A common way to express these multidirectional stresses is to summarize them into an Equivalent stress, also known as the von-Mises stress. A three-dimensional solid has six stress components. Sometimes a uniaxial stress test finds material properties experimentally. In that case, the combination of the six stress components to a single equivalent stress relates the real stress system.

displacement Displacement is the amount of stretching that an object undergoes due to the loading. For this simulation a maximum deflection of 1.25 mm is allowed.

safety factor All objects have a stress limit depending on the material used, which are presented as material yield or ultimate strengths. If aluminum has a yield limit of 276 MPa, any stresses above this limit result in some form of permanent deformation. If a design is not supposed to deform permanently by going beyond yield (most cases), then the maximum allowable stress in this case is 276 Ma. The safety factor is how much stronger the system is than it needs to be for a given load. You can calculate a factor of safety as the ratio of the maximum allowable stress (Yield Strength) to the equivalent stress (von-Mises) under the maximum load.. In the final design iteration of the end cap, the Yield Strength of the material is 276 MPa and the von Mises value is 70.34 MPa. This gives a minimum safety factor of 3.91.


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EXERCISE In this exercise, you review a design for the

brake pedal in the Formula SAE race car

built by the Oklahoma University Sooner

Racing Team. The objective is to reduce the

mass of the pedal which is currently 0.311

kg.

Note that your results may vary slightly than

the figures quoted here.

DESIGN CRITERIA

The following table lists the maximum

allowable stress and displacement values

and the minimum allowable safety factor for

this exercise.

STRESS DISPLACEMENT SAFETY FACTOR

276 MPa 1.25 mm 2.0

The completed exercise

Create a New Simulation

In this section of the exercise, you open the

current version of the pedal assembly.

1. Make Brake Pedal.ipj the active project.

2. Open Brake Pedal Tray.iam.

3. In the graphics window, right-click the

red brake pedal assembly. Click Open.

4. In the browser, expand Representations

> Level of Detail: Master. This

representation was created to suppress

the parts that are not required for the

simulation.

5. Double-click StressAnalysis.

6. On the Environments tab, Begin panel,

click Stress Analysis.


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7. On the Manage panel, click Create

Simulation.

8. For Name, enter Pedal Simulation 1.

Ensure the default values of Single

Point Design Objective and Static

Analysis are selected.

9. Click OK.

10. On the Contacts panel, click Automatic.

Since there are no moving parts to be

considered in this assembly, you can

generate contacts automatically.

11. In the browser, expand the Contacts >

Bonded folder and review the contacts.

12. Collapse the Contacts > Bonded folder.

Review the Materials

In this section of the exercise, you review

the currently assigned materials.

1. On the Material panel, click Assign.

2. Review the Assign Materials dialog box.

For this simulation the Aluminum 6061

is correct.

3. Under the Safety Factor column, ensure

that Yield Strength is selected for all

parts.

Note: The Safety Factor is calculated on the Yield Strength or Ultimate Tensile Strength of the material. For example, if the Yield Strength of the material is 276 MPa and the von-Mises equivalent stress is 138 MPa the safety factor is 2.0 (276/138 = 2.0).

4. Click Cancel to close the Assign

Materials dialog box.

Add Constraints

In this section of the exercise, you add a pin

constraint and a frictionless constraint to the

pedal.

1. On the Constraints panel, click Pin.

2. Select the face of the hole as shown.

3. Click OK.

4. On the Constraints panel, click

Frictionless.


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5. Select the bottom face of the pedal as

shown.

6. Click OK. This constraint is required on

the bottom face of the pedal to meet the

requirements of the simulation and

ensure the design is not

underconstrained.

Add Loads

In this section of the exercise, you add

loads to the pedal.

1. On the Loads panel, click Force.

2. Select the face of the pedal as shown.

3. In the Force dialog box, for Magnitude,

enter 450 N.

Note: This value is typical of the force

applied to a brake pedal in an emergency

braking operation.

4. Click OK. The force load is added and is

displayed as a glyph on the face of the

part.

5. On the ViewCube, click the top-left

corner.

6. Zoom into the area on the pedal as

shown.

7. On the Loads panel, click Force.

8. Select the face as shown.

9. In the Force dialog box, for Magnitude,

enter 45.

Note: This force is applied to represent the

resistance force from the brake cylinders as

you apply force to the brake pedal.

10. Click Apply.

11. Rotate the assembly and select the

same face on the other side of the part,

as shown.


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12. Click OK.

13. On the ViewCube, click Home.

Run a Simulation

In this section of the exercise, you run a

simulation.

1. On the Solve panel, click Simulate.

2. Click Run.

3. In the browser, review the Results

folder. By default, Von Mises Stress is

active.

4. Review the Maximum and Minimum

values (your results may vary

slightly).The values are 73.81 MPa and

0.04 MPa respectively. Comparing

these values to the supplied design

criteria shows that the design is

compliant.

5. In the browser, double-click

Displacement.


values. The values are 0.4493 mm and

0 mm respectively. Comparing these

values to the supplied design criteria

shows that the design is compliant.

7. In the browser, double-click Safety

Factor.

8. Review the Minimum value. The value is

3.73. Comparing this value to the

supplied design criteria shows that the

design is compliant.

9. On the Exit menu, click Finish Stress

Analysis.

10. In the browser, right-click

brakes_brake_pedal:1. Click Open. This

opens the part without the trunion

cages.

11. Right click on the part and select

iProperties.

12. On the Physical tab, click Update.

The mass of the brake pedal is 0.311

kg.

13. Click Close.


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14. Close the brakes_brake_pedal.ipt file.



16. In the browser, double-click Von Mises

Stress.

17. On the Result panel, click Animate.

18. On the Animate Results dialog box, click

Play.

19. Repeat the animation for Displacement

and Safety Factor.

20. Close the Animate Results dialog box.

CONCLUSION:

The design results indicate that

modifications can be made to reduce the

mass of the pedal. The first modification is

to create 2 machined pockets on the upper

part of the pedal.

Create an Extrusion

In this section of the exercise, you extrude a

sketch to create a pocket on one side of the

pedal.

1. In the browser, if required, expand

brakes_brake_pedal_assm.iam

(StressAnalysis).

2. Right-click brakes_brake_pedal:1. Click

Open.

3. In the browser, right-click Sketch3. Click

Visibility.

4. On the Model tab, Create panel, click

Extrude.

5. Select inside the sketch profile as

shown.

6. Drag the distance arrow to the right to

create a cut and until 12 is displayed as

the depth.

7. Click the check mark.

8. On the Pattern panel, click Mirror.

9. In the graphics window, select the

extruded feature you just created.

10. In the Mirror dialog box, click Mirror

Plane.


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11. In the browser, select the Work Plane

entry.

12. Click OK.

13. Rotate the part to review the mirrored

feature.

14. On the ViewCube, click Home.

15. Save the part and close the file.

Run the Second Simulation

In this section of the exercise, you run the

second simulation by carrying over the

constraints, loads, and contacts that you’ve

already defined.

1. On the Quick Access Toolbar, click

Local Update.


3. Click Run.


values. The values are 73.02 MPa and




compliant.


Displacement.







Factor.






Analysis.


brakes_brake_pedal:1. Click iProperties.

(without opening the part).



kg. This is a 47% reduction from the

mass of the initial design.

12. Click Close.


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Note: You’ll notice that the value of the

maximum stress is lower than the first

simulation. Stress is now more evenly

distributed on the pedal. To view the area of

maximum stress, you can probe for the

maximum value.

CONCLUSION:

The design results indicate that further

modifications can be made to optimize the

design. The next modification is to create a

machined opening around the lower pivot.

Create a Second Extrusion

In this section of the exercise, you extrude

an existing sketch to create an opening

around the pivot.

1. In the browser, if required, expand

brakes_brake_pedal_assm.iam

(StressAnalysis).

2. Right-click brakes_brake_pedal:1. Click

Open.

3. In the browser, right-click Sketch6. Click

Visibility.

4. On the Model tab, Create panel, click

Extrude.

5. Select inside the sketch profile as

shown.

6. Select Cut from the list.

7. Select Through All from the list.

8. Click the check mark.

9. Save the part and close the file.

Run the Third Simulation

In this section of the exercise, you run the

third simulation by carrying over the

constraints, loads, and contacts that you’ve

already defined.


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2. Click Run.


values. The values are 70.34 MPa and




compliant.


Displacement.







Factor.






Analysis.


brakes_brake_pedal:1. Click iProperties.



kg. This is a 51% reduction from the

mass of the initial design.

11. Click Close.

12. Save and close the file.

CONCLUSION:

The objective was to reduce the mass of the

pedal and that has been achieved. The

current design is 51% lighter than the

original design. What more can be done to

reduce the mass? In this assembly the

overall dimensions are controlled by 2

design criteria.

a. The length of the pedal which is

required for leverage.

b. The base of the pedal houses a

number of bearings that permit

easy rotation of the pedal in

operation. However, the overall

dimensions restrict any further

reduction of the pedal in that

area.

The stress, displacement, and safety factors

are all well within the design criteria, but the

design criteria prevent and more meaningful

reductions in the mass of the pedal. It is

now just 0.151 kg and further modifications

would not represent a significant reduction

for the cost and effort required.

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car brake pedal design excercise

Documents

design criteria

design change

current design

new simulation

stress analysis environment

contents topic

machined pockets

key terms