Measuring and testing – Vehicle chassis – Steering
Reexamination Certificate
2000-08-31
2003-08-05
McCall, Eric S. (Department: 2855)
Measuring and testing
Vehicle chassis
Steering
C073S123000, C073S862080
Reexamination Certificate
active
06601441
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device and method for verifying the proper operation of dynamometers. The inventive device and method have particular application to the field of automobile and engine testing.
BACKGROUND OF THE INVENTION
Measurement of the exhaust emissions, fuel consumption, and performance of automobiles requires the accurate simulation of on-road operating conditions in a fixed location. Simulation of on-road operation is typically accomplished using a treadmill-like device called a chassis dynamometer.
A dynamometer, which applies a resistance (or “load”) to the vehicle wheels as they turn one or more rollers, can be used to simulate a variety of driving conditions or testing scenarios including transient (i.e., “stop and go”) drive cycles. Dynamometer devices are described in U.S. Pat. Nos. 5,861,552, 5,450,748, 5,101,660, 6,044,696, which are hereby incorporated by reference in their entirety.
In recent years, the use of chassis dynamometers has been required in state-mandated testing programs for the identification and repair of vehicles with excessive emissions. This requirement has stimulated a large increase in the number of dynamometers in use and a corresponding need to assure their proper operation.
In emissions testing, transient drive cycles are employed to simulate the conditions observed in normal driving and are characterized by variations in vehicle speed and dynamometer load as a function of time. However, if the load is applied improperly, the test yields inaccurate results that may lead to falsely passing a defective vehicle in an emission test or falsely failing a vehicle that should have passed the test. Consequently, proper operation of the dynamometer is necessary to assure accurate simulation of vehicle operation and accurate measurement of emissions.
The key to proper dynamometer operation is application of the appropriate load at the proper vehicle speed over a given driving cycle. A variety of methods exist to accurately load dynamometers. These methods are described in U.S. Pat. Nos. 5,375,460, 5,385,042, 5,531,107, 4,466,294, 5,542,290, 5,657,227, and 5,375,461 which are hereby incorporated by reference in their entirety.
A dynamometer may apply two types of load known as inertia load and road load to the vehicle under test. The inertia load simulates the power required to accelerate the vehicle. The road load simulates the power required to overcome frictional load on the vehicle. The dynamometer roller(s) supply some of the inertial load with the remainder of the load typically provided by flywheels driven by the dynamometer roller(s). A device commonly referred to as a power absorption unit (PAU) provides the road load. The PAU is typically an electric motor, eddy current brake or a water pump (usually called a water brake). With adequate control, the PAU can also be used to provide the inertia load, thereby eliminating the need for heavy flywheels to simulate the weight of the vehicle being tested.
A dynamometer controller controls the amount of load provided by the PAU. The controller adjusts the power absorbed by the PAU based on the specified vehicle characteristics (e.g., weight) and the vehicle speed and acceleration rate being simulated. The relationship between vehicle characteristics (such as weight, frontal area, and aerodynamic drag coefficient), the speed-time profile being simulated, and the target value of power absorbed by the dynamometer can be calculated from standard equations representing the dynamics of linear motion. (See e.g.,
Automotive Handbook
by Robert Bosch GmbH, 1996, available at www.sae.org). The proportion of total dynamometer load provided by the PAU is dependent on whether or not flywheels are used to supply the inertia load.
Although the description of how a dynamometer is controlled may seem relatively simple, in fact, accurate control of a dynamometer is difficult. Dynamometer controllers must compensate for inter alia PAU response times and must respond very quickly to changes in vehicle speed when the PAU is used to supply inertia load. The dynamometer must also be “tuned” so that the PAU load properly accounts for dynamometer-specific factors which may change over time as the dynamometer components age and wear. Proper tuning requires an independent means of measuring dynamometer performance. However, an appropriate test device or method to carry out such testing has, until relatively recently, not been available.
In fact, little has been done to assure proper dynamometer performance during an actual test without using a dynamometer tester. In the past, manufacturers made and sold dynamometers without providing customers with the ability to independently verify whether the dynamometer was operating properly. If problems were suspected with a particular dynamometer system (e.g., an anomalous test result, such as abnormally high vehicle failure rates, was obtained), the commonly used means to crudely check performance was to employ a “cross-check” vehicle. In this test, a single cross-check vehicle was tested on several different systems to determine whether a statistically significant difference existed between emission levels produced with different dynamometers. However, this method is confounded by measurement errors in the vehicle exhaust sampling system and cannot identify the cause of the test discrepancy. Clearly, there is a need for a device and method to test the performance of dynamometers to verify their proper operation, and to assist in the diagnosis of problems if found.
One such test device was recently developed under contract to the California Bureau of Automotive Repair (BAR) (See e.g., BAR RFP Solicitation Package #95/96-001 “Solicitation Package For the Selection of a Contractor to Assist the State in the Design and Development of Device(s) or System for Performing Certification Testing of Dynamometers and Dynamometer Controls”, Sep. 15, 1995, Department of Consumer Affairs, Bureau of Automotive Repair, 10240 Systems Parkway, Sacramento, Calif. 95827). The BAR test device quantifies dynamometer performance by measuring the accuracy with which a dynamometer performs transient loading simulation. The BAR test device operates by sitting on the dynamometer rollers like a car and controls both the speed and acceleration of the dynamometer while simultaneously measuring the dynamometer's load using the BAR test device's own load cell (which measures the torque from the dynamometer tester's electric motor). The BAR test device uses an external fifth wheel to quantify speed and determines dynamometer performance during transient simulation by integrating the speed and load signals and comparing them to the theoretical loading for the selected vehicle characteristics. This device is further described in Society of Automotive Engineers (SAE) paper 970268 (“DynoCal—A Chassis Dynamometer Calibrator”, SAE International Congress and Exposition proceedings, Feb. 24-27, 1997, available at www.sae.org) which is hereby incorporated by reference.
The BAR test device identified a variety of problems with dynamometers that had never before been known or quantified. For example, the dynamometer control system, which was previously discussed, is often either under-damped or over-damped. Over-damped systems are slow to respond and reach the target load, whereas under-damped systems over-react to system inputs and behave erratically. In addition to dynamometer control problems, problems affecting vehicle loading accuracy were also readily apparent for the first time using the BAR test device. For example, during a typical vehicle test an independent computer instructs the dynamometer controller on which vehicle parameters to use. If this external computer selects the wrong parameters, the dynamometer will apply the wrong load even if the dynamometer is working correctly. This problem cannot be easily detected on transient tests without using a dynamometer tester such as the BAR test device.
In short, the development and use of the BAR test device
St. Denis Michael J.
Torgerson Garrett D.
McCall Eric S.
Morgan & Finnegan , LLP
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