Search Results

The development of environmental improvement technologies in the automobile industry is underway. These technologies are also developed for internal combustion engines, which remain the mainstream power source for most vehicles. Nissan Motor Company has developed a multi-locking hydraulic VTC (Valve Timing Control) system and adopted it on the newly developed QR25DER engine of the Pathfinder and Infiniti JX hybrid vehicles. The implementation of the developed system allows for an optimized variable valve timing at both, cold engine start, and idle stop re-start from EV mode. This paper describes an outline, the principle, and effects of the multi locking hydraulic VTC system.

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.

The disc brake pad is a part that is expected to exert the stable performance in a wide variety of working conditions, for example, in a wide speed range and in a wide temperature range. In addition to these working conditions, the stable performance in a variety of humid conditions has also been demanded. This is because most non-asbestos brake pads have the low friction coefficient μ in high humid conditions, which affects the performance of the disc brake pad. This study notes the film of the friction material on the disc rotor as the reason of a decrease in friction coefficient μ in the high humid environment and discusses the mechanism of the decrease in friction coefficient μ.

Resolving the brake squeal that occurs under various environments is a major topic, and a resolution method is eagerly anticipated. We focused on the phenomenon that, amid various environmental conditions, squeal occurs easily when an automobile has been left standing in a cold environment. We checked the details focusing on the friction coefficient (hereafter, μ). As a result, we found that μ increases when squeal is generated, and that the sliding surface film contributes to the μ behavior. We studied measures to be taken to increase the μ in cold conditions.