An AC electric motor drive system has been evaluated as a means of engine loading for production engine hot testing. It has been demonstrated that an 80% reduction in test cycle stabilization time is possible when compared with the water brake dynamometer that is commonly used in production engine testing.
Hot testing is normally a bottleneck in engine assembly, and the number of test stands is a direct function of the length of the test cycle. The steady state cycle that is used for engine testing may be reduced by quickly stabilizing the speed/load settings. The cycle may be further reduced by shortening the duration of the steady state sampling condition when the speed/load setting is held more accurately (fewer samples are required).[1,2] The AC drive demonstrated a set point stabilization time of 4 seconds or less and speed control accuracy of 0.25%.
The drive system evaluated is an AC adjustable speed drive with adjustable frequency static conversion. The drive will absorb power from the engine and deliver it to the AC power line through automatic regeneration as well as motor the engine as required. The transition from motoring to absorption is automatically controlled. Speed is regulated with the AC motor and torque is regulated with the engine via the throttle.
Advantages of the AC drive; in addition to fast stablizaton time, include: energy savings due to regeneration, elimination of the need for a seperate starting system, ability to measure frictional torque, more accurate timing setting and prevention of “green” engine stall-out during rapid speed/load changes.
Data in this paper include speed and torque control results with an eight-cylinder 5.0L and four-cylinder 1.6L and 2.3L engines in both steady state and transient operations. Comparisons are made with a water brake test system.