Although chassis dynamometers used in vehicle emissions testing employ calibration routines that check the dynamometer's functionality and calibration, the standard calibration checks that are performed do not ensure that the transient or steady-state loads applied by the dynamometer during a test meet response time or loading accuracy requirements. For example, a dynamometer can pass all of the standard calibration and quality assurance checks, but the response time of the dynamometer may be so poor that there is a large error in loading during transient testing. The Sierra Research Dynamometer Tester (U.S. Patent 6,601,441) is designed to measure these errors as well as confirm important dynamometer calibration and testing functions, all in a simple, compact, and portable system.
The Sierra Research Dynamometer Tester is capable of high-speed data collection (samples can be recorded at 64 ms intervals) during a vehicle test on a dynamometer, and can independently measure speed and record force at the roll surface on two-wheel drive (2WD) and four-wheel-drive (4WD) dynamometers. Based on the recorded data, the dynamometer tester calculates the actual force applied and compares this to the theoretical force that should have been applied based on vehicle operating parameters entered by the operator. The software allows for setting pass/fail criteria, and accommodates both full-inertia simulation (both positive and negative), as well as positive-inertia-only simulation (i.e., for eddy current power absorber dynamometers), calculating error appropriately for each type. The average (over the entire drive trace) and instantaneous (over a small, user-defined time interval) error during a driving cycle is calculated and a plot is produced showing second-by-second speed, theoretical instantaneous load, actual instantaneous load, and error, as well as overall average error and pass/fail status.
Figure 1. Dynamometer Tester Data Collection System Diagram, U.S. Patent 6,601,441
The dynamometer test system incorporates the following components and features:
- Laptop computer for running the software and storing test data.
- Hardware to directly measure speed via encoder pulse signals, or optional dual photo-tachometers for recording speed from each roll set of a 4WD dynamometer.
- Hardware to directly measure load signals from both roll sets of a 4WD dynamometer.
- Ability to sample and record four additional analog DC signals at 12 bit resolution with dynamometer test data.
- Easy portability with included suitcase-sized Pelican case.
- Ability to be operated on battery power.
Figure 2. Components of Sierra's Portable Dynamometer Tester, U.S. Patent 6,601,441
SYSTEM SOFTWARE CAPABILITIES
The test system software uses an MS Windows platform and contains the following functions:
- Ability to test both 2WD and 4WD dynamometers.
- Ability to test transient (certification, IM240) and steady-state (ASM) type dynamometers.
- User interface incorporating simple prompts for required user inputs.
- Ability to measure dynamometer parasitic drag.
- Ability to measure dynamometer roll speed(s).
- Ability to measure dynamometer load cell signals.
- Ability to measure dynamometer simulation error over a fixed time interval and graphically display achieved versus expected results.
- Ability to measure cumulative dynamometer simulation error over a drive cycle.
- Test data saved to ASCII text files for additional analysis as desired by user.
Figure 3. Dynamometer Tester Software Sample Screen, U.S. Patent 6,601,441