I. Introduction

The idea of the digital dynamometer was conceived by the need to have actual engine performance data used in the Clean Snowmobile Competition (CSC) Modeling group’s system model. Coupled with the track dyno, this combination of digital tools will help isolate inefficiencies in the drive train.

The existing dyno in the shop was incapable of delivering output data, due to mechanical nature. The concept of mapping engine performance was limited to an operator standing at the controls, watching for peak horsepower. With the use of a digital diagnostic tool, we can gather engine performance data as fast and accurate as the data acquisition hardware allows us to.

Furthermore, we want this engine dyno to not only work on the Arctic Cat 660 we use in the CSC, but also as a stand alone dyno for whatever projects come into the lab, requiring engine data acquisition. This requires that the dyno have the ability to be run through a gear box.

II. Design Objective

The goals of this project was to develop a fully digital engine dynamometer and diagnostic tool which runs off a stand alone computer program to monitor engine performance and gage the engines reaction to inertial effects. The computer program has to be able to collect, organize, and output data in such a manner that allows the system modeling team to take the output text file, and directly feed it into their MatLab computer model.

1) Provide output engine data to the CSC computer model to predict engine performance for any suggested modification.

2) Run as a stand alone engine dyno for any work output shaft (either directly off the engine or through a gear box) that will fit the Land And Sea water brake.

3) Create a software interface that’s user friendly and scalable to future needs.

III. Inputs and Outputs

Figure 3.1 shows the input/output diagram used to base our design. We are gathering information from the engine, feeding it through our data acquisition board and then outputting our results, both raw data and power calculations to LabView.

Figure 3.1: Input output diagram of dynamometer system.

The ability to monitor the engine temperature and RPM’s is critical to the safe operation of an engine pull, with respect to the crew members and the snowmobile. Accurate, real time data helps insure the safe operation.

IV. Hardware

1) WATER BRAKE

Figure 4.1: Land and Sea water brake used in our engine dyno.

The Land and Sea water brake, pictured in Figure 4.1, provides a load for the engine. An engine under no load produces very little torque and horsepower. The water brake has an impeller that gets attached to the drive shaft of a vehicle. When there is no water in the brake drum there is no load, as water is pumped into drum it increases the resistance of the impeller which in turn increases the resistance to the shaft. Although this is not the most precise way to load the engine it is extremely versatile and generally much less expensive the AC or DC electric motors, eddy current brakes.

2) DAQ

The Data Acquisition unit (DAQ) is the heart and soul of the dynamometer. This electronic device collects and sends all of the desired data to the PC. This is done by programming blocks in LabView. The DAQ receives analog voltage information from up to 8 different sources at +- 10V. Each of the 8 channels of the DAQ have an analog to digital converter which changes the analog voltage signal to a digital signal that the computer can read. Since this is now digital data, programming in LabView must be done to change the digital data to engineering units that we can use. Once the data is in engineering units we can manipulate it by formulas or Fast Fourier Transforms to get the desired output.

Figure 4.2: The Measurement Computing 1608-FS DAQ board used in this dynamometer

The DAQ that we chose was the Measurement Computing 1608-FS, pictured in Figure 4.2. It is capable of recording up to 12,500 samples per second per channel. The maximum speed the engine will be running at is 7500 RPM or 125 sparks per second, the sampling rate is more than adequate for our snowmobile. In fact it can even be used to capture data from engines that can run even faster. Since its best to triple the sampling rate compared to the actual rate we could run an engine at 250,000 RPM and still get accurate data, this is way over anything that would be run in our shop.

3) LOAD CELL

Figure 4.3: Transducer Technique’s S-Type load cell, MN: SBO-200-C

A Transducer Technique’s S type load cell, shown in Figure 4.3, was used to measure the force exerted by the water brake torque arm. A load cell is classified as a force transducer, converting force or weight into an electrical signal. At the heart of all load cell is a set of strain gauges. These gauges change resistance when stressed.

This load cell can measure 0-200lbs and outputs 0-10Volts, therefore at 200lbs the DAQ would be reading 10V. Using this information we can develop a linear formula to calculate the force that the torque arm is producing. When you multiply the length of the torque arm by the force, we obtain the torque produced by the engine.

4) INDUCTIVE PICKUP

Figure 4.4: Land and Sea Inductive Pickup MN: 430-136

There are two inductive pickups located on the Dynamometer. The first one measures the engine RPM while the second measures the shaft RPM. It is very important to measure both the engine and shaft RPM for a couple of reasons. First we need to know how hard we a turning the engine so that we do not have a catastrophic failure. Secondly, for our dyno to be run through a gear box, we need to accurately measure the shaft RPM as well. When power is transmitted through a gear box, the engine and shaft RPM’s may be different.

An inductive pickup, as seen in Figure 4.4, works by sensing the magnetic field that is caused by current running through a wire. For the engine RPM, each time a spark plug fires a magnetic field is created. This field is sensed by the pickup and a 5 volt spike is recorded by the DAQ. In order to calculate the RPM we count the frequency of the spikes.

The shaft RPM works on a similar principal. There is a fixed inductive pickup sensor mounted on the water brake. On the center collar of the water brake a magnet is mounted so that it rotates with the output shaft. Each time the magnet passes the pickup sensor a voltage spike is recorded. Again we count the frequency of the spikes and we obtain the RPM of the shaft.

5) THERMOCOUPLES

Our dynamometer uses two different types of thermocouples, K and J. The K thermocouple is used to measure the exhaust gas temperature while the J thermocouple is used to measure the oil temperature. Although they are measuring different heat ranges they work using the same principals.

About 150 years ago T.J. Seebeck figured out electric current flows in a closed circuit of two metals that are dissimilar, when the junctions are heated. The magnitude and direction of the current depends on the temperature difference between the two metals and their difference in thermal properties. Thermocouples actually produce a low voltage, measurable current that is proportional to the temperature they are measuring. The K type thermocouple is capable of measuring up to 1024°C while a J type thermocouple can measure temperatures up to 500°C.

6) SIGNAL CONDITIONING

Figure 4.5: Measurement Computing Signal Conditioners.

As stated above a thermocouple outputs a low measurable voltage. Since our DAQ measures +_ 10V the thermocouple voltage needs to be amplified. To do this we chose Measurement Computing signal conditioners seen in Figure 4.5. These modules take the voltage from the thermocouple, linearize it, and amplify it to a 0-5 volt output. This allows us to obtain much more accurate measurements of our temperatures.

7) POWER SUPPLY

The dynamometer had two power supplies; one is a 110V to 12V “chopper” supply, while the other is a 12V to 5V DC to DC converter. The chopper power supply takes 110V source and turns it into a 12V supply. Although this is very convenient it poses a large noise problem. When the DAQ is capable of measuring millivolts all noise has to be eliminated. To do this, a 12V to 5V DC to DC converter was used. Not only did the converter “clean” up the signal, it also dropped the voltage so that it could be used for all of our components. With this set up, all of the voltages outputted by the DAQ are accurate to +- 2mV.

V. Programming

1) PROGRAMMING LANGUAGE

LabView was chosen as the programming language for two main reasons. The first is the ease of use. Instead of writing thousands of lines of code, the program is broken up into about 50 subprograms, or sub VI’s as they are called in LabView. Each block has its own specific wiring terminals. Programming is as simple as finding the right VI’s and connecting all the wire terminals with virtual wire. Not only does this make it extremely simple to write or build the program it also makes it very easy to make changes to the structure or the function.

The second reason is the amount of flexibility and power that are included in this package. The possibilities are endless. Doing frequency analysis or FFT’s are as simple as dragging the blocks and connecting up the terminals. There only limit to this program is the sky. In building the Virtual Instrument for our dynamometer we have just scratched the surface to what this program can do.

2) FLOW CHART

Please see Figure A-1, in Appendix A

3) LOGIC&STRUCTURE

The program logic is fairly straightforward. The constants such as channel number, board number, voltage range, etc. are all located outside of the loop so that they only run when the run button is first pressed. Everything else, data collection, file writing, graphing, and formulas are inside the loop. Each time the loop executes all of these actions happen. A wait timer of .001 seconds is programmed into the loop so that all of the data can be written and taken simultaneously. This is sufficiently low so that no lag can be seen in the loop when taking data.

Once the data is read, a Sub-VI transforms the digital data to engineering units. Since we are acquiring data from 7 channels everything is input into a matrix, then broken up into different single row elements. After the data is in the elements we can apply the frequency analysis, formulas, or whatever other kind of transforms need to be done to the data to display the proper numbers for a desired gage.

Along with displaying all of the diagnostic and calculated information on screen, torque, shaft RPM, and horsepower are all used to create a time stamped “.txt” file which can be read directly in the MatLab model. Since data is collected every .001 seconds and the engine is firing at a max of 1 time per .008 seconds there is no data lost. In fact the wait timer can even be adjusted so that files do not get too large on machines where memory is at a premium.

VI. Results

Engine Dynamometer Testing Set Up:

Please reference the set up manual for details and step by step instructions. A general overview of the set up is as follows: The water brake is connected to the drive shaft. A collar is placed over the driven shaft. Then a load cell is connected to the driven shaft’s collar, and a mounting block on the water brake torque arm. We then attached the inductive pick up sensor to the spark plug wires to gage engine RPM. Please see Figure 6.1 for the schematic of our physical set up.

Please see Table B-1 in Appendix B for a complete list of our instrumentation.

Figure 6.1: Conceptual schematic of experimental setup

Calculations:

Please note, all of our calculations were programmed into LabView, so for every data point the system took, all of our calculations were made simultaneously.

To determine the torque:

The force was obtained from the strain gage, and the moment arm was input at 1ft, .5 inches.

To determine the horsepower of the engine:

We multiply the torque by the engine RPM and unit conversion to obtain engine horsepower.

1) Engine Test Results

Using our dynamometer we are able to repeatedly produce, a maximum sustainable power of 53.5 HP at ~6650 RPM. Figure 6.2 below shows a sample of our highest pull in both torque and horsepower as a function of RPM.

Figure 6.2: Output of torque and horsepower curves created by the engine dyno.

While at the Clean Snowmobile Competition, a dynamometer similar to our set up was used in the emissions testing. They were able to produce a maximum power of 52.2 HP. With our results coming so close to a professional pull, we are quite confident in the accuracy of our numbers.

2) Track Test Results

Testing the snowmobile on the eddy current track dyno, with no load, yields a maximum track power of about 34 HP. Figure 6.3 below shows the track HP as a function of RPM at different loads.

Figure 6.3: Horsepower at the track as a function of mph. Created by the track dyno software WinPEP 7.0

Figure 6.3: Track HP obtained from track dyno as a function of RPM

To obtain our drive train efficiency at 10% load for example:

This efficiency equates to a 75% loss in power between the drive shaft and the ground due to the drive train as it currently exists. There also may be inaccuracies in the data since no support was given from Land and Sea.

These inefficiencies are directly related to clutching as well. However, with the use of the CSC computer model, we are able to tune the clutch to desired performance characteristics. With the pull on the track dyno shown above, the clutch was tuned to maximum fuel efficiency. If we then consider the clutch as no longer a source for power loss, because it’s giving the desired performance, then the next step is to engineer an alternative drive train.

VII. Conclusion

All of our objectives have been met. Throughout this past year, we created a digital dynamometer designed towards the ongoing goal of isolating drive train inefficiencies for the Clean Snowmobile Competition.

We have developed a physical setup that can be run directly off of an engine drive shaft, or through a gear box, while maintaining safe operating conditions for the engine while producing accurate calculations.

Also we’ve created a user friendly dyno operating program that supplies output data to the CSC computer model.

This program and physical set up is accurate to its current uses and is scalable to future needs.

VIII. Future Work

Future projects should include proper installation of the oil pressure sending unit. This was supposed to be one of our inputs, however due to time constraints we could not get this working properly. Every time it was connected to the system, the 110V to 12V power supply was destroyed.

The torque arm distance needs to be made either adjustable, with accurate measurements, or made fixed so that it does not move. Software adjustments need to be made in either circumstance to account for the solution.

Finally, a feedback control loop could be implemented to control both the water brake load valve and throttle position. This would allow for canned test cycles to be created. The advantage to this set up would allow for specific programmed test pulls to be made repeatable, by eliminating the need for an operator on the snowmobile to control these inputs.

Appendix B - Maintenance Manual

Setup of Computer

If Insta-Cal in not installed install Insta-Cal

Insert the Insta-Cal CD in the CD-ROM drive
Follow the on screen instructions

If the LabView Runtime Engine is not installed install the LabView Runtime Engine

Double Click the LVEngine Icon
Follow the on-screen instructions

Plug the USB cable from the Dyno Box into the USB port on the desired computer
Double Click on the Instal-Cal Icon
Check to see if board is recognized
Minimize the Insta-Cal screen
Double Click on the Dyno VI

LabView Troubleshooting (See help files in LabView)

Due to the complexity of LabView the help section that is in LabView should be referenced. However here are some simple troubleshooting tips

If running VI for a different vehicle, be sure to change the moment arm length in the setup screen.
Be sure the Count and Rate numbers are multiples of 31
Be sure the board number matches the board number in Insta-Cal
If you want to clear the graph press the clear graph button
Be sure the Locations on the Setup Page equal the channel that the sensor is on the DAQ.
Be sure the range is set to +-10V
If using all 8 channels make sure HighChan

is 7.

Wiring Diagram of Individual Components and Entire Setup

Proper Equipment Installation

For instructions on proper equipment instillation, refer to the Setup Manual included in this document.

Parts List

Qty	Company	Product	Part #	Price
1	Measurement Computing	Conditioning Board	ISO-Rack-08	$ 149.00
1	Measurement Computing	EGT Signal Conditioner	ISO-5B47-K-14	$ 199.00
1	Measurement Computing	USB 8Ch DAQ	PMD-1608FS	$ 399.00
1	Transducer Techniques	S type Load Cell	SBO-200-C	$ 325.00
2	Measurement Computing	J Type Thermocouples Conditioner	ISO-5B47-J-02	$ 199.00
1	Measurement Computing	500 Hz Frequency Module	ISO-5B47-J-02	$ 179.00
1	E-bay	12x12x8 Enclosure
2	Amphernol	Connector		$ 70.00
1	Omega	Strain Meter w/Analog Out	DP25B-S-A	$ 325.00
1		Oil Pressure Sending Unit		$ 5.00
1		DC DC Converter		Donated
1		12V Power Supply		Donated
1	Land And Sea	Inductive Pickup	430-136	$199.00

Table B-1: Parts list and instrumentation

A Digital Dynamometer Data Acquisition System