P09310: Automatic Shift Controls for ATV
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Mechanical System Analysis

Table of Contents

Cylinder System Analysis

The current design uses an electric solenoid cylinder that works like pneumatic system, but relieves our design of a pump, pressure tank, two solenoids, air cylinder, and air lines. This reduces the number of components, weight, and size of the system.

To determine the correct cylinder size required analysis on the following:

1. Maximum force to complete a shift
2. Distance traveled during the shift

The following sections outline this analysis process.

Spring Torque

Since our design incorporates the use of the existing gear shift lever, we needed to determine the internal transmission shift spring torque in order to calculate the require shift force. Polaris indicated that the spring created a torque of 150 in-lbs about the shift lever mounting location.

In order to test the spring, the ATV was run with the drive wheels lifted off the ground. A torque wrench was set to a desired torque used to shift through the gears by applying a torque to the shift lever mounting bolt. If the torque wrench clicked it meant more torque than the wrench setting was used to shift the gear. We began the test with the wrench set at 50 in-lbs and increased in increments of 10 in-lbs until the wrench no longer clicked when shifting through the gears. When this point was reached, the torque required to shift was less than the setting on the wrench. Therefore, the wrench setting was reduced by 5 in-lbs until it clicked again. Again increasing the torque, in 1 in-lb increments allowed us to narrow down to a torque greater than 142 in-lbs. The test matrix is shown below. This was very close to the value of 150 in-lbs, so we are comfortable with the test results. To be safe we used 145 in-lbs in our analysis.

Note: Values were recorded for each gear shift up and down, the highest torque was used.

Shift Torque Test Matrix

Shift Torque Test Matrix

Shift Lever Rotation

Image of Internal Case Stops

Image of Internal Case Stops

The original rotation angle was stated to be 20 degrees per shift, 40 degrees from upshift to downshift. By visual inspection, this seemed to be more than required and the actual angle was investigated using the extra transmission case. Built into the transmission case half are internal stops which the shift lever mechanism hits during and upshift and downshift. These are safety features designed into the case by KTM to prevent excessive rotation and strain on the shift drum and shift forks. The stops are considered Point B and point A is the internal mechanism which rotates to make contact with the stop. A full downshift, a mark was drawn across both the stop and mechanism to create a mate line. The lever was then released to the neutral position. A point C was located as the center of the shift lever mounting hole.

The following distances were measured:
C to A
C to B
A to B

This provided us with an isoceles triangle where line CA = line CB. Using the formula shown below and an angle of rotation was determined. This was repeated for an upshift. Finally, This was repeated three times for each shift and an average value of 15.5 was yielded. Additionally, an angle level was used to measure directly on the shift lever the rotation angle. This was determined to be around 15.5 degrees. To be safe a value of 16.5 degrees was used to determined the required throw length.

Angle Calculations

Angle Calculations

Shift Force Calculations

Using this 145 in-lb internal spring torque and a 16.5 degrees rotation angle, the required shift force and throw distance to complete a shift was calculated. Using this information a cylinder could specified and a manufacturer could be determined. Required force was determined using the moment equation, M = F*d. The cylinder throw distance was found using right triangles and the arc length formula S = r*theta. Since our design allows for pivoting of the cylinder during extension and retraction the actual distance traveled will be closer to the distance found using right angles, which do not account for total arc length. As shown by the calculations, these two distances are very close. The hand calculations are shown below and on the calculation spreadsheet.

Image of Internal Spring

Image of Internal Spring

Shift Lever Mounting Location

Shift Lever Mounting Location

Required Shift Torque & Throw Distance

Required Shift Torque & Throw Distance

Tabulated Force Requirements

Tabulated Results from Force Table

Tabulated Results from Force Table

Excel Spreadsheet to allow for parameter changes and easier iterations for specific design changes:

Force and Flow Calculations.xls Right Click and Save File as Excel Sheet

ANSYS Stress Calculations

Shift Tab Mounting System

The shift tab design is incorporated into the existing shift lever by removing the original extruding toe piece and replacing it with our non-folding tab. The tab has an extruding clevis pin where the cylinder will apply a bearing load of 40 lbs to the tab.

ANSYS Parameters:

Material Properties: Aluminum Alloy T6 6061

Young's Modulus 1.e+007 psi
Poisson's Ratio 0.33
Density 9.75e-002 lbm/in
Tensile Yield Strength 40000 psi
Compressive Yield Strength 40611 psi
Tensile Ultimate Strength 45000 psi

Stress Results

Type Equivalent Von-Mises Stress Total Deformation Maximum Principal Stress
Minimum 3.2858e-005 psi 0 in -851.58 psi
Maximum 2304 psi 9.8542e-004 in 2927.1 psi

The equivalent Von Mises Stress is a maximum at the radius just below the tab and at the outside edges of the constrained mounting hole as expected.

Equivalent Von Mises Stress

Equivalent Von Mises Stress

Equivalent Von Mises Stress

Equivalent Von Mises Stress

Below shows the actual deformation of the shift tab with the applied load. There is almost no deformation to the human eye.

Total Deformation Front View Actual

Total Deformation Front View Actual

The below images show 66 times the actual deformation. The vector also shows the direction of deflection. With a downward force on the clevis pin, the deflection direction is expected.

Total Deformation Top View: 66 Times Actual

Total Deformation Top View: 66 Times Actual

Total Deformation Vector Top View: 66 Times Actual

Total Deformation Vector Top View: 66 Times Actual

Our shift tab design shows a minimum factor of safety of 15.

Factor of Safety for our Design

Factor of Safety for our Design

Conclusion

Our shift tab design will handle the required force of 40 lbs applied by the cylinder. There is a minimum amount of deflection associated with this force and with a factor of safety of 15 this offers us some areas which can be redesigned to reduce the overall weight and increase manufacturability.

Prototype Redesign Plans:

1. Create a three piece design (toe, rectangle block, and plate) for ease of manufacturing and lower the material costs
2. Investigate a reduction in the plate thickness to reduce weight of design

Note: Deflection is equal and opposite for an upshift.

Cylinder Bracket Mounting System

ANSYS was again used to test the stresses applied to the two piece cylinder mounting design. A bearing load was applied to the cylinder mounting hole to simulate the force applied to the part by the cylinder creating a shift. This is the worst case scenario. All degrees of freedom were constrained at the two mounting bolt locations to simulate installation on the ATV. Below is a table of properties and results.

ANSYS Parameters:

Material Properties: Aluminum Alloy T6 6061

Young's Modulus 1.e+007 psi
Poisson's Ratio 0.33
Density 9.75e-002 lbm/in
Tensile Yield Strength 40000 psi
Compressive Yield Strength 40611 psi
Tensile Ultimate Strength 45000 psi

Stress Results

Type Equivalent Von-Mises Stress Total Deformation Maximum Principal Stress
Minimum 8.442e-002 psi 0 in -235.5 psi
Maximum 1606 psi 8.62e-003 in 2146 psi
Total Deformation of Bracket -66 Times Actual

Total Deformation of Bracket -66 Times Actual

The total Deformation is not significant and similar to that seen in the shift tab. The deformation is so small that it should not create any misalignment issues during shifting. As expected the maximum deflection is at the top and this be equal and opposite for an upshift.

Equivalent Von-Mises Stress

Equivalent Von-Mises Stress

Minimum and Maximum Principle Stresses

Minimum and Maximum Principle Stresses

The maximum stresses occur at the rear mounting tab because of the sharp decrease in thickness required to mate to the original mounting location. This stress is far below the yield stress and will not cause any mechanical failures.
Total Factor of Safety of Bracket

Total Factor of Safety of Bracket

Similar to the shift tab the bracket also has an overall factor of safety of 15. Therefore, the design thickness could possibly be reduced for weight and cost reasons.

Conclusion

This bracket was modeled as a single piece unit and shows that the bracket is able to withstand the worst case scenario of loading with our shifting design. The factor of safety is large enough to allow for some redesign in areas for improved strength, asthetics, reduced weight, and ease of manufacturing.

Our prototype design will incorporate a two piece design to reduce our material costs and machining time. It is understood that the customer would have the ability to mass produce a single one piece cast aluminum piece that would provide the same characteristic, but with decreased material waste and cost.

Other Mechanical Analysis

This section is various other mechanical analysis.

Bolt Strength

Pure Shear Analysis on Cylinder Pivot Mounting Bolts

Pure Shear Analysis on Cylinder Pivot Mounting Bolts

Clamp Bolt Torque

Required Clamp Bolt Torque to Secure Cylinder

Required Clamp Bolt Torque to Secure Cylinder

Pneumatic System Analysis

The original design plan was to use a pneumatic operated shift cylinder, but this was replaced with an electric cylinder for simplicity. There will be reduced part count, weight, and items causing possible failure. For an initial analysis click the link below.

Pneumatic System Analysis