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This paper describes the emission reduction technologies applied to 4- and 6-cylinder engines used on Japanese market models certified as ultra-low emission vehicles (U-LEVs) in Japan. To qualify for this rigorous U-LEV certification, a vehicle must reduce hydrocarbon (HC) and nitrogen oxide (NOx) emissions by an additional 75% from the levels mandated by Japan's 2000 exhaust emission regulations. Nearly all Nissan Japanese models fitted with a gasoline engine, ranging from in-line 4-cylinder engines to V6 engines, have now been certified as U-LEVs. This has been accomplished by further improving the emission reduction technologies that were developed for the Sentra CA, which was launched in the U.S. market in 2000 as the world's first gasoline-fueled vehicle to qualify for Partial Zero Emission Vehicle (P-ZEV) credits from the California Air Resources Board. The specific new technologies involved are as follows.

The thinnest wall thickness of automotive catalyst substrates has previously been 30 μm for metal substrates and 50 μm for ceramic substrates. This paper describes a newly developed catalyst substrate that is the world's first to achieve 20-μm-thick cell walls. This catalyst substrate features low thermal capacity and low pressure loss. Generally, a thinner cell wall decreases substrate strength and heat shock resistance. However, the development of a “diffused junction method”, replacing the previous “wax bonding method”, and a small waved foil has overcome these problems. This diffused junction method made it possible to strengthen the contact points between the inner waved foil and the rolled foil compared with previous substrates. It was also found that heat shock resistance at high temperature can be much improved by applying a slight wave to the foil instead of using a plane foil.

This paper describes the second generation of the partial zero emission vehicle (P-ZEV) technology that was developed for use on the Nissan Sentra CA sedan sold in California.1,2 The second-generation engine has been adopted on a mass-produced model marketed in Japan. Besides continuing the super ultra low emission vehicle (SULEV) performance of the Sentra CA, the second-generation technology incorporates a compact, two-stage HC trap catalyst system. The system has been substantially reduced in size and cost as a result of improving the catalyst and the substrate and reducing the total catalyst volume by optimizing the control method. Moreover, the second-generation P-ZEV technology includes an electrically actuated continuously variable swirl control valve of the high-speed jet type, a high-response electrically actuated EGR valve and catalyst model control based on the use of an air-fuel ratio sensor.

It is projected that compliance with Japanese new exhaust emission regulations set to be enforced in 2000 year will be difficult for turbocharged engines with conventional technologies. This is mainly because of the delay in catalyst lightoff at engine start due to the lower exhaust gas temperature of turbocharged engines compared with that of their naturally aspirated counterparts. Compliance will be particularly difficult for V-6 engines on account of the large heat mass of the exhaust system, resulting in a slower temperature rise. Previously, improvement of hydrocarbon (HC) conversion rates following engine start depended solely on the low-temperature characteristic of the catalyst. The catalyst system described here adopts a completely new mechanism that traps HCs before the catalyst lights off and then desorbs them for conversion after the engine warms up.

This paper presents firstly the newly developed “Timing and injection Rate Control System” for heavy duty diesel engine. In this system, a new concept of diesel fuel injection … variable pre-stroke mechanism. … is applied. As a result, this new system enables higher injection pressure at lower engine speeds, and accurate and fast injection timing control. Design concept of the injection pump itself, actuators and ECU will be described together with some experimental data. Secondly, the classification of diesel fuel injection systems is considered based on the function of features of each system. This illustrates the characteristics of the new injection system described in this paper.