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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.

The concept of the Early or late Intake valve closing cycle has been examined over the years as a technique for improving fuel economy in conjunction with the use of a three-way catalyst for excellent exhaust emission performance. With this concept, the intake valve closing (IVC) timing is set either before or after bottom dead center. With the emergence of continuously variable valve timing and lift (VEL) systems in recent years, the Early IVC cycle has become a more familiar concept. However, the Early IVC cycle has an intrinsic drawback in that, although pumping losses decrease when charging efficiency is reduced in connection with IVC control, combustion performance deteriorates due to the decline in the effective compression ratio. In recent years, full-scale research has been undertaken on variable compression ratio systems as a new type of variable engine mechanism separate from variable valving.

As technologies for simultaneously maintaining the current high thermal efficiency of diesel engines and reducing particulate matter (PM) and nitrogen oxide (NOX) emissions, many new combustion concepts have been proposed, including premixed charge compression ignition (PCCI) and low-temperature combustion[1]. However, it is well known that since such new combustion techniques precisely control combustion temperatures and local air-fuel ratios by varying the amount of air, the exhaust gas recirculation (EGR) ratio and the fuel injection timing, they have the issues of being less stable than conventional combustion techniques and of performance that is subject to variance in the fuel and driving conditions. This study concerns a system that addresses these issues by detecting the ignition timing with in-cylinder pressure sensors and by controlling the fuel injection timing and the amount of EGR for optimum combustion onboard.

There has been strong public demand for reduced hazardous exhaust gas emissions and improved fuel economy for automobile engines. In recent years, a number of innovative solutions that lead to a reduction in fuel consumption rate have been developed, including in-cylinder direct injection and lean burn combustion technologies, as well as an engine utilizing a large volume of exhaust gas recirculation (EGR). Furthermore, a homogeneous charge compression ignition (HCCI) engine is under development for actual application. However, one of the issues common to these technologies is less stable combustion, which causes difficulty in engine management. Additionally, it is now mandatory to provide an onboard diagnosis (OBD) system. This requires manufacturers to develop a technology that allows onboard monitoring and control of the combustion state. This paper reports on an innovative combustion diagnostic method using an in-cylinder pressure sensor.

Achieving a multi-cylinder engine with excellent noise/vibration character sties and low friction at the main bearings requires an optimal design not only for the crankshaft construction but also for the bearing support system of the cylinder block. To accomplish that, it is necessary to understand crankshaft system behavior and the bearing load distribution for each of the main bearings. Crankshaft system behavior has traditionally been evaluated experimentally because of the difficulty in performing calculations to predict resonance behavior over the entire engine speed range. A coupled crankshaft-block analysis method has been developed to calculate crankshaft system behavior by treating vibration and lubrication in a systematic manner. This method has the feature that the coupled behavior of the crankshaft and the cylinder block is analyzed by means of main bearing lubrication calculations. This paper presents the results obtained with this method.

A new Variable Valve Event and Lift (VVEL) system has been developed as an effective technology for reconciling environmental performance such as lowering the fuel consumption and exhaust emissions with driving performance. This system can continuously vary both the intake valve lift and event angle (valve opening duration) over a wide operating range to flexibly control the valve timing and lift for a substantial improvement in engine performance. In developing the variable valve lift control system, the essential merit is based on the fundmental configuration of multiple-link mechanism. However, it is required to resolve tribological issues for the specific mechnism. This paper describes the structure of the VVEL system and its operating and motion conversion principles. It also explains the mechanism analysis, dynamic stress analysis and lubrication simulation techniques used in developing the VVEL system, the materials adopted and the surface treatment techniques applied.

A variable compression ratio (VCR) technology, that has a new piston-crankshaft mechanism with multi links, has been patented and developed by Nissan for some years (This technology has been detailed in previous SAE paper 2003-01-0921 and 2005-01-1134). This paper will present the use of this VCR technology for Diesel engine. The objective set with the use of VCR for Diesel engine is mainly to reduce as much as possible engine out emission to prepare for long-term, more strict emission standards. Results presented will include the description of the 2l Diesel VCR engine and its VCR mechanism adapted to Diesel constraints. Combustion tests have been performed with the use of HCCI (Homogeneous Charge Compression Ignition) combustion. This technology is still in a research phase in Renault: the adaptation of VCR technology to a Diesel engine consists in the modification of several parts with the addition of lower links, control links and control shaft.

Modern engine bearings have been operating under very harsh conditions. Consequently, a bearing wear propagates for a short time and a fatigue sometimes occurs on high loaded region. To reproduce the bearing damage in actual engines, the operating conditions of engine bearing were simulated on a rig test machine. The bearing wear was measured until the fatigue crack occurred in the simulation test. The wear progressed at the edges of the bearing length and the crack also was observed near the edges. The bearing damage is influenced by the bearing design and operating conditions. The experiment was conducted to change the design parameters in conditions. The experimental results were compared to the calculated results based on the elastohydrodynamic lubrication (EHL) theory. The correlation between bearing damage and bearing performance by theoretical analysis were investigated on effects of the design parameters.

In spark-ignition engine pumping loss increases and fuel economy decreases during partial load operation. Methods to reduce this pumping loss by controlling the intake-valve closing timing are currently under study. The authors, also, have confirmed that pumping loss can be reduced by controlling the amount of intake air-fuel mixture through making changes in the in Cake-valve closing timing. However, when pumping loss was reduced by controlling intake-valve closing timing, an improvement in fuel economy equivalent to the reduction in pumping loss was not obtained. In this study, it was found that the major contributing factor to this phenomenon was the deterioration of the combustion, namely, increase in combustion duration and in combustion fluctuation.

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.

A multiple-link variable compression ratio (VCR) mechanism is suitable for a long-stroke engine by providing the following characteristics: (1) a nearly symmetric piston stroke and (2) an upper link that stays vertical around the time of the maximum combustion pressure. These two characteristics work to reduce force inputs to the piston. The maximum inertial force around top dead center is reduced by the effect of the first characteristic. The second characteristic is effective in reducing piston side thrust force and helps ease piston pin lubrication. Because of the combined effect of these characteristics, the piston skirt can be made smaller and the piston pin can be shortened. That makes it possible for the piston skirt and piston pin to move between the counterweights, resulting in a downward extension of the piston stroke. As a result, a longer-stroke engine mechanism can be achieved without making the cylinder block taller.

This paper describes a new variable valve system that enables continuous control of valve events, i.e. time periods when the valve is open. In this system, valve events are controlled by varying the camshaft angular speed by means of an offset between the center of the camshaft and that of the medium member that transfers crankshaft torque to the camshaft. The medium member, a rotating disk, has a drive pin to enable the transfer of torque. The system has a mechanism that produces an offset between the center of the rotating disk and that of the camshaft as well as an actuator that drives the mechanism. This makes it possible to develop a compact system that can be installed in existing DOHC direct-acting valve train engines without making any major cylinder head modifications.

Reducing friction in the crankshaft main bearings is an effective means of improving the fuel efficiency of reciprocating internal combustion engines. To realize these improvements, it is necessary to understand the lubricating conditions, in particular the oil film pressure distributions between crankshaft and bearings. In this study, we developed a thin-film pressure sensor and applied it to the measurement of engine main bearing oil film pressure in a 4-cylinder, 2.5 L gasoline engine. This thin-film sensor is applied directly to the bearing surface by sputtering, allowing for measurement of oil film pressure without changing the shape and rigidity of the bearing. Moreover, the sensor material and shape were optimized to minimize influence from strain and temperature on the oil film pressure measurement. Measurements were performed at the No. 2 and 5 main bearings.

The possibility of predicting engine bearing durability by elastohydrodynamic lubrication (EHL) calculations was investigated with the aim of being able to improve durability efficiently without conducting numerous confirmation tests. This study focused on the connecting rod big-end bearing of an automotive engine. The mechanisms of wear and fatigue, which determine bearing durability, were estimated by comparing the results of EHL analysis and experimental data. This comparison showed the possibility of predicting the wear amount and the occurrence of fatigue by calculation.

It is important to understand the influence of housing stiffness on bearing performance, particularly for the connecting rod bearings of automotive engines. It is known that the engine lubricant shows a piezoviscous characteristic whereby its viscosity changes under the influence of pressure. Engine bearings under a heavy load are apt to be influenced in this way. In this study, the effects of connecting rod stiffness and lubricant piezoviscosity on bearing performance were examined by elastohydrodynamic lubrication (EHL) analysis under conditions corresponding to the high-speed operation of an actual engine. The results indicated that under such heavy load conditions housing stiffness greatly affects friction loss because of lubricant piezoviscosity. It was also found that the piezoviscosity of the lubricant has a large effect on bearing performance, as does its viscosity under atmospheric pressure.

The authors have previously proposed an engine system that uses a new piston-crank system incorporating a multiple-link mechanism to vary the piston's motion at top dead center and thereby obtain the optimum compression ratio matching the operating conditions. This multiple-link variable compression ratio (VCR) mechanism can be installed without increasing the engine size or weight substantially by selecting a suitable type of link mechanism and optimizing the detailed specifications. Previous papers by the authors have made clear the features of the VCR mechanism that facilitates continuously variable control of the compression ratio [1][2]. It was shown that engine friction attributable to piston-side thrust can be reduced through an upright orientation of the upper link in the expansion strokes.

A new variable valve event and lift (VVEL) system has been developed by applying a multiple-link mechanism. This VVEL system can continuously vary the valve event angle and lift over a wide range from an exceptional small event angle and small lift and to a large event angle and large lift. This capability offers the potential to improve fuel economy, power output, emissions and other parameters of engine performance. The valve lift characteristics obtained with the VVEL system consist of a synthesis of the oscillatory motion characteristics of the multiple-link mechanism and the oscillating cam profile. With the multiple-link mechanism, the angular velocity of the oscillating cams varies during valve lift, but the valve lift characteristics incorporate both gentle ramp sections and sharp lift sections, the same as a conventional engine.

A new variable valve actuation system that varies valve lift and timing events continuously has been devised and confirmed to substantially improve power and reduce fuel consumption when applied to a SI engine. The variable valve event and lift (VEL) system is a simple mechanism consisting of oscillating cams and linkages, enabling it to operate the valves smoothly even at high speed. Its compact size facilitates application to direct-acting valve trains and its ability to vary valve lift from a deactivated state (0) to a large lift amount allows the system to be used with a wide range of engine concepts. In this study, VEL was combined with a phase shifting function to enable the valve lift characteristic to be varied virtually arbitrarily, and test results showed that fuel consumption of a SI engine was reduced by nearly 10%.

A continuously variable valve event and lift (VEL) system, actuated by oscillating cams, can provide optimum lift and event angles matching the engine operating conditions, thereby improving fuel economy, exhaust emission performance and power output. The VEL system allows small lift and event angles even in the engine operating region where the required intake air volume is small and the influence of valvetrain friction is substantial, such as during idling. Therefore, the system can reduce friction to lower levels than conventional valvetrains, which works to improve fuel economy. On the other hand, a distinct feature of oscillating cams is that their sliding velocity is zero at the time of peak lift, which differs from the behavior of conventional rotating cams. For that reason, it is assumed that the friction and lubrication characteristics of oscillating cams may differ from those of conventional cams.

Engine bearings today are operating under very harsh conditions. Consequently, a wear propagates for a short time and a fatigue sometimes occurs on the bearings. In present study, on the rig test machine, the operating conditions of engine bearing were simulated to reproduce the bearing damage. The bearing wear was measured until the fatigue crack occurred. The bearing wear increased at the edges of the bearing length and the crack also was observed near the edges. The experimental results were compared to the calculated results based on the elastohydrodynamic lubrication (EHL) theory. The correlations between the bearing damage and the bearing performances by the theoretical analysis were investigated.