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This paper describes a newly developed hydraulic variable valve timing control (VTC) system, targeting the internal combustion gasoline engine, with an optimum angular position locking mechanism to reduce tailpipe emissions (TPE). In general, emission control catalysts are used as one measure to reduce TPE. However, there is the issue that catalysts cannot remove pollutants before reaching its light-off temperature at cold engine start. To address this issue, we have been using a method of increasing the valve overlap period between intake valve opening (IVO) and exhaust valve closing (EVC) by operating a VTC system at engine start. This brings engine-out emissions (EOE) back to the combustion chamber to be burned, thereby reducing EOE levels. However, this method requires about 3 seconds for the sufficient hydraulic pressure to start VTC operations.

In order to significantly reduce NOx levels by EGR (Exhaust Gas Recirculation), while maintaining good fuel economy and driveability, the EGR flow rate must be properly and accurately controlled under a variety of engine operating conditions. Toward this objective, a new EGR control system was developed. It utilizes a carburetor venturi vacuum for a stable reference signal that represents the engine operating condition and it controls the EGR flow rate by using a feedback principle to obtain sufficient flexibility compatible with several different engines. Its control characteristics were mathematically analyzed. And it has also been confirmed that the system can automatically compensate for the drift in EGR characteristics. This EGR control system has been utilized in Nissan’s emission control systems in order to comply with the 1978 Japanese Emission Standards and the 1980 U.S. Federal and California Emission Standards.