Customer SolutionsDeveloping a Dual-Dynamometer Road Load Simulator for Heavy-Duty Tracked Vehicles
Author(s):Douglas Eberle, Southwest Research Institute
Industry:Automotive
Product:Data Acquisition, LabVIEW, PXI/CompactPCI, Signal Conditioning
The Challenge:Updating a dual-dynamometer system for repeatable, reliable testing of heavy-duty tracked vehicles, such as bulldozers or armored military vehicles like tanks.
The Solution:Developing a PC-based acquisition and control system using an SCXI and DAQ system controlled by LabVIEW.Introduction The dynamics of tracked vehicles are very different from that of wheeled vehicles. Tracked vehicles experience the same road loads as other vehicles, but also undergo "scrubbing" - the frictional force encountered by the tracks as the vehicle performs a turn. During a turn, the tracks slide across the ground as they roll to propel the vehicle forward. Much research has been done to create equations that predict the amount of torque required to overcome scrubbing, based vehicle geometry and ground conditions. Using SCXI, we achieved a channel count of 370 in a relatively simple setup. The associated SCXI terminal blocks gave us ready access for wiring as well as for troubleshooting with a handheld meter. Although the company is not likely to use all of the channels, they wanted a lot of options for configuring different test setups. We provided: Although some channels are dedicated to fixed hardware in the test setup (control of dynos and accessories), the user can custom configure most channels from the set-up screen, including renaming channels and providing scale factors. Input channels provide error checking for low/high alarm and alert threshold values, and output channels provide for specification of a default value. Upon crossing an alarm threshold on an input, all outputs revert to the specified default values. Fixed analog input channel sensors include left/right dyno torque, left/right dyno speed, and gearbox temperatures. Fixed digital inputs include oil pressure limit switches, filter differential pressure limit switches, oil level switches, oil temperature limit switches, dyno air temperature limit switches, and dyno air flow switches. The client will likely use the generic input channels to monitor various vehicle temperatures, pressures, fluid levels, and speeds, as well as environmental conditions such as humidity, barometric pressure, and temperature. We took advantage of the extensive indicator-attribute features of LabVIEW to customize the graphical user interface. With the large potential channel count for this application, it is impossible to fit all of the channels on the screen simultaneously; moreover, many of the channels do not need to be seen on screen. By using the attribute node feature of the front panel indicators, the operator can define which channels he or she would like to monitor on screen, as well as where they should be placed. We used array clusters in the set-up program as a scrollable form from, which the operator can define channel names and features. We use global variables to store all system constants and to pass data from one subroutine to another. The program also contained a calibration routine so the technician could monitor and adjust each signal on a channel-by-channel basis and then store the calibration parameters to a file. We used buffered acquisition to read all of the defined input channels at 100 Hz. The main program loops operated at 10 Hz, and performed 10-point averaging of the data to help eliminate any noise. The program saved data to a file every two seconds. In addition, it maintained a circular buffer of the most recent 400 10Hz data points. In the event of an alarm, this data in the buffer could help determine what went wrong.
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