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The DynoCal system for auditing chassis roll dynamometers has been developed for the California Bureau of Automotive Repair. It evaluates performance of new dynamometer designs and operational dynamometers in the field. The system includes a 50 kW electric motor with torque, thrust, and speed instrumentation. It functions as a vehicle to drive the chassis rolls under computer-controlled test modes. A trailer transports the system and houses the battery power supply, chargers, flux vector power converter, and computer. The controls are user-friendly, with graphic displays and high-speed data acquisition. Among other functions, this unique test instrument measures dynamometer road load and inertia simulation accuracy.

“Specifications for Electric Chassis Dynamometers, Attachment A” was issued by the USEPA in 1991. Although the primary purpose of the document was to serve as a Request for Proposal, it has subsequently been used as a general procedural manual to assess the road-simulation accuracy of electric chassis dynamometers. Significant strides have been made in the development of electric dynamometers since 1991. Procedures are needed to demonstrate that a chassis dynamometer is indeed capable of required accurate road simulation. Procedures for assessing dynamometer calibration, evaluating dynamometer response time, and measuring simulation error are reviewed. Novel methods are proposed for determining dynamometer torque measurement response and overall dynamometer system response to a simulated instantaneous change in vehicle thrust. This is offered to help dynamometer users evaluate the performance of their machines.

The chassis dynamometer described in this paper incorporates the latest design improvements in instrumentation for certification applications. Unlike other large-roll chassis dynamometers, this machine fits into a pit that is only slightly larger than the dynamometer itself. All serviceable components are accessible from the top and there is no need, or reason, to require maintenance personnel to enter a pit. Advantages of the small pit approach are (1) improved safety, (2) enhanced access to serviceable components, (3) increased mechanical stability, and (4) lower installation cost. Other noteworthy design features in the dynamometer are (1) AC flux-vector power converter employing isolated gate bipolar transistors (IGBT's), (2) motorized trunnion mounting in which bearing hysteresis is eliminated and no warm-up is required, (3) lag-lead control algorithm, and (4) graphics oriented user interface.