In the field of heavy duty diesel engines for trucks, fuel economy and high output power are required and have been improved. In the past, exhaust gas regulations have mainly applied to spark ignition engines. Recently, their main targets have changed to diesel engines. Especially, the new U.S. reguration in 1991 and 1994 are very severe ones. Engine makers of the world are challenging this new target vigorously.
These emission regurations demand more from the turbocharger. In addition to improved efficiency, better air fuel ratio control is required. The variable geometry turbocharger (VGT) gives an improvement in air fuel ratio control, but it's effectiveness can be limited by the control system, IHI has a VGT in production with a 4 step control. The fuzzy control adjusts the vanes continuously and it's development is the subject of this paper.
The controller consists of a micro processor, sensors and a stepping motor to drive nozzles. The driving mechanism of the nozzles is completely different from the present step control in which system the nozzles are driven by air cylinders. This controller adopts the “fuzzy control” method for reasoning the target nozzle opening position.
Full acceleration response tests on the engine bench indicates 3 A/F's improvement in contrast with the present 4 step control. Therefore, lower exhaust smoke level during transient operation is expected. This paper describes the 1st step of VGT fuzzy controller development.