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Detailed Design

Table of Contents 1 Drawings, Schematics, Flow Charts, Simulations 2 Material Selection 3 Microcontroller Selection 4 Sensor Selection 5 Sensors and Electronics Data Sheets 6 Bill of Materials (BOM) 7 Testing

Drawings, Schematics, Flow Charts, Simulations

Circuit Architecture

Circuit Schematic

PCB Layout

Theoretical Area Calculations with Sensitivity

The following plots show the relationships between the angular position of the control disk and the amount of open area in the output port. The step size used is 0.5°. This step size was chosen because previous testing of the position sensor by Alphacon LLC, as well as our own testing for verification, has shown that at least this amount of accuracy can be achieved.

To determine how our device would function if it isn't machined to the nominal dimensions, a sensitivity analysis was included. One critical dimension that we chose to look at is the radius of hole in the output port. Using a standard drilled holes tolerance size chart, we found that our hole would have a tolerance of +0.006"/-0.001". The other critical dimension that we looked at is the slot in the control disk. After talking with the staff in the Brinkman Lab and NTID Machine Shop, we found out that at most, the tolerance of the slot will be ±0.002 at most. We concluded that this is so small that it will have a negligible effect on our results.

Drawing Package

Exploded View

2D Part Drawings

Main Housing

Control Disk

Output Port

Output Fitting

Distribution Plate

3D PDFs

Top Level Assembly

Distribution Plate

(Note: Need to right click > save link as > open through Adobe Reader, not through web browser)

Material Selection

Main Case

• Selection
  • Aluminum 6061 w/ Black Oxide Coating - It is strong enough for the application and also is considerably light amongst common metals. 6061 is also easy to machine which will be important with the amount of features on the casing. The casing will need to be coated to protect the device from corrosion in a harsh automotive environment. Black Oxide coating adds at most a 10 millionth of an inch to the dimensions of the part it is coating. Black oxide is also the most reliable form of coating for the cost, not to mention the nice looking finish it puts on the part.

Control Disk

• Selection
  • Aluminum 6061 - Need a light metal to reduce the total inertia placed on the actuator. With less inertia that the actuator needs to overcome, less power will be needed to power the actuator.

Output Port / Spring Seat

• Selection
  • Nylon - It is the most used of the common engineering plastics. It has the highest coefficient of friction when in contact with solids (0.35). Nylon, due to its stiffer nature, is less susceptible to wear due to shock and vibrations, which is significant for an automotive environment.
• Alternatives
  • Teflon (PTFE) - It has one of the lowest coefficients of friction against solids (0.05 - 0.10) of all of the common engineering plastics. It is also more resistant to sliding wear than nylon. The downside to Teflon is that it is extremely soft and most susceptible to wear amongst other engineering plastics.

Spring

• Selection - The spring material selection will be determined based on price and availability of the spring applicable for our design. The following two materials would be a suitable choice of material for the spring:
  • Stainless Steel - It has a high resistance to corrosion and can last for well past the life of the product.
  • Zinc Plated - It also has a high resistance to corrosion, but often a shorter life; zinc plated is often slightly cheaper than stainless steel

Fittings

• Selection - For fittings, the material selection will be decided through price and availability of the fitting, the following two materials will be considered when selecting material of fittings.
  • Stainless Steel - It has a high resistance to corrosion and can last for well past the life of the product.
  • Brass - It also has a high resistance to corrosion; brass is cheaper than stainless steel.

Microcontroller Selection

To evaluate the performance of each controller, a program was developed in C and Arduino that has each controller execute 3000 floating point mathematical operations. The controller that could do this the fastest would be the controller we use.

Testing the Teensy showed that the time lost due to the background code tied to the Arduino language did not have a visible impact on the controller speed. Testing the C2000x was inconclusive because we were unable to obtain the necessary header files needed to configure the controller. Therefore, the Teensy 3.1 is the controller that was selected.

Sensor Selection

Delphi Coolant Temperature Sensor

• Many coolant temperature sensors were found that met the temperature requirements for our device. The main reason this sensor was selected because it uses a common 3/8-18 NPT fitting, allowing us to easily find adapters to accommodate it, and we could find the datasheet on it, which are scarce among the coolant temperature sensors we found.

Measurement Specialties Pressure Transducer

• Many pressure transducers were found, but most did not fit into our budget. This sensor was selected due to the fact it was the cheapest that met our pressure requirements and had a datasheet available. Also, some of the pressure transducers we found could only be purchased in large quantities, but the minimum purchase quantity of this one was only 1 unit.

Sensors and Electronics Data Sheets

Sensors

CTS Rotary Actuator

CTS Rotary Position Sensor

Delphi Coolant Temperature Sensor

Measurement Specialties Pressure Transducer

Electronics

Teensy 3.1 Microcontroller Development Board

Teensy 3.1 Microcontroller Development Board Layout

On Semiconductor Voltage Regulator

Freescale H-Bridge

Bill of Materials (BOM)

The most up to date BOM can be found here

Testing

Test Setup

Test Set Up Explanation

1. An air compressor will be used to supply air compressed at 4 bar to the prototype. The 4 bar was a specified testing parameter to be followed. The accuracy of the air pressure gage does not need to be completely accurate as the pressure transducer will be used in testing.
2. In order to have all sensors connected to the prototype for testing, a “cross” fitting will be needed to connect the air compressor to the temperature and pressure sensors as well as the prototype.
3. Pressure and temperature sensors will record data and send it to the Teensy microcontroller. These readings will help determine the mass flow rate that the prototype will deliver. The pressure transducer has an error of 0.25% which will most likely be ignored because the flow will be choked and once flow is choked the difference in pressure makes such a minimal change in flow. The temperature sensor is accurate to 0.6 °C. This uncertainty can be accounted for even though such a small change in temperature will not affect the density of the air too greatly.
4. The prototype will be clamped to a table to reduce the chance of any movement. A standard table clamp will be used in.
5. The position sensor will be used to measure the current position of the rotating disk. This information will be sent to the Teensy microcontroller. The sensor is accurate to within 0.5°. This will be the biggest source of error within our flow measurement.
6. The Teensy microcontroller will compute all of the data received from the three sensors. The microcontroller needs nanoseconds to compute the information so this allows for the majority of the 50ms dedicated for response time to the mechanical aspects of the prototype. The microcontroller will send a signal to the actuator within the prototype to rotate to a given angle which will allow air to flow out of the output port.
7. A monitor will be showing all of the data that is being recorded from the sensors
8. A 1” diameter PVC pipe of at least one foot long will be attached to the output fitting of the prototype. This needs to be done in order to reduce the velocity so a measurement can be made. A quick roundness check of the tube will be made on the output end of the PVC pipe to ensure an accurate area measurement. There should be minimal uncertainty with the measured area but should still be accounted for.
9. A hot wire anemometer will be used to measure the velocity of the air coming out of the PVC pipe. There is a variable uncertainty with the hot wire anemometer that will be used; the velocity range we expect to see will result in an uncertainty within 0.25m/s.
10. The area calculated from the PVC pipe, the velocity reading from the anemometer, and the data from the temperature and pressure sensors will be able to calculate the mass flow rate coming from the prototype within a specified uncertainty.

Estimated Error in Proposed Test Setup

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