Customer Solutions

NI Products Enable Rapid Development of Cam and Crank Timing Test Cart

Author(s):

John Niezgoski, Roush Industries Inc.

Industry:

Automotive

Product:

Data Acquisition, LabVIEW

The Challenge:

Designing and fabricating a portable test cart to validate the cam and crank timing relationship of nearly 14,000 complete V6 automotive engines within two weeks.

The Solution:

Leveraging the rapid software prototyping power of LabVIEW, along with the integration of custom-fabricated hardware and E-series data acquisition (DAQ) boards, to quickly create a mobile cam and crank timing test cart.

Cam Gear Replacement
When a design change required the retrofit of a new cam gear on approximately 14,000 completely assembled, uninstalled automotive engines, the primary hurdles we faced were throughput and critical timing constraints. The replacement of the cam gear required the tensioner and belt to be held static by the technician while we installed the new gear. Any slippage during the process could easily result in timing changes and ultimately catastrophic failure of the engine upon final installation.

The existing end-of-line (EOL) test machines were not practical for the retesting of the engines because the process was too time consuming and costly. The engine manufacturer then turned to Roush engineers to create a portable test cart for the validation of the cam gear replacement and cam and crank timing of the V6 automotive engines. None of the assumptions pertaining to conventional EOL test machines were applicable - the apparatus needed to be lightweight and maneuverable, relatively low cost and maintenance free, require very little or no training to use, and flexible enough to detect every failure mode known for the UUT. The greatest challenge for the development team was the project timing. Due to housing limitations and lost revenue, the test carts had to be completed within two weeks of project commencement.

A Portable Hardware System
The signals required to accurately and repeatedly test the engines were as follows:

• CAM signal - (0 to Excitation Voltage) Pulse train representing the position on the cam gear. Acquired from the factory cam sensor on the engine block
• CRANK signal - (0 to Excitation Voltage) Pulse train representing the position of the crank. Acquired from the factory cam sensor on the engine block
• External Battery Voltage - Battery voltage level of the onboard power source used to crank the engines

We based our decision to use the National Instruments E-series DAQ device AT-MIO-16E-2 on the relatively simple I/O requirement coupled with the cost constraint. We placed the DAQ card in a rugged, lunch box-style computer and tethered it to an SCB-68 for ease of connectivity. The SCB-68 also provided access to the 5V excitation available on the DAQ card that we used to excite the cam and crank sensors.

Since the engine tests were to be cold tests, the hardware complement needed to crank the engines without combustion to generate the cam and crank signals. We determined that the engines had to be cranked a minimum of eight revolutions but could not exceed twelve revolutions to conserve battery life. With these conditions in mind, we fabricated a fixture that interfaced directly with transmission mounting bolts found on the engine. We fitted a reverse-spinning starter to the mount, ensuring proper mesh with the exposed flywheel and the starter gear. As a final step, we implemented a hand-held trigger device to permit the user to enable/disable the starter motor. The entire assembly was stable enough to achieve the large torque required for engine crank but also lightweight enough to be quickly and easily moved from one UUT to the next without the use of any tools.

Minimal User Interaction Interface
The primary goals of the custom LabVIEW application were as follows:

• Efficiently acquire cam and crank signal pattern with minimal engine revolutions (max of 10 revs)
• Calculate cam/crank relationship without the aid of an encoder to identify engine position
• Perform testing with minimal user interaction
• Execute complete test in less than one minute
• Log results in an SQL-compatible database for future analysis

Since the testing was to be done by end users without a lot of technical training, we designed all processes to be transparent and require no input from the operator. We accomplished this by first automating the process by which the tracing number and part number of the UUT was entered. We implemented a hand-held bar code scanner to enter the information.

Once scanning of the bar codes was complete, the user simply pulled the trigger of the starter gun to commence the test as instructed via the main screen. After acquiring the minimum amount of data required to accurately determine the cam and crank timing relationship, the user was instructed to terminate the test and to tag the UUT with the test results. Although the actual timing test required only seconds, a complex algorithm performed steps that were transparent to the user.

Most tests of this nature utilize an external encoder to easily render the engine position at any given time. Since an external encoder would have required an extended setup time for each engine, the calculation was done programmatically instead. The falling edges of the cam and crank signals coupled with the known pattern that exists between them permitted the proper determination of the timing characteristics.
With National Instruments LabVIEW and hardware, we were able to complete this application in an extremely short period of time without sacrificing functionality and reliability. The rapid prototyping capability of LabVIEW enabled Roush engineers to provide immense cost and time savings to the customer.

For more information, contact:

John Niezgoski

Roush Industries, Inc.

Tel: (734) 779-7494

E-Mail: jcniez@roushind.com

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