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To improve the fuel economy, we developed a turbo-charged spark ignition engine combined with a low pressure loop EGR system. A negative pressure control valve has been applied to achieve high EGR ratio in wide engine operation condition. In this paper, a new developed model-based control system for low pressure loop EGR with a negative pressure control valve will be described.

Fuel economy can be improved by reducing engine displacement, thanks to the resulting smaller friction losses and pumping losses. However, smaller engines frequently operate at high-engine speed and high-load, when pressure on the accelerator increases during acceleration and at high speed. To protect exhaust system components from thermal stress, exhaust gas temperature is reduced by fuel enrichment. To improve fuel economy, it is important to increase the frequency of stoichiometric operation at high-engine speed and high-load. Usually, the start timing of fuel enrichment is based upon temperature requirements to protect the catalyst. In the high-engine speed and high-load zone, the threshold temperature of catalyst protection is attained after some time because of the heat mass. Therefore, stoichiometric operation can be maintained until the catalyst temperature reaches the threshold temperature.

This paper describes the motor and inverter system developed for the Nissan LEAF that has been specifically designed as a mass-produced electric vehicle. The system produces maximum torque of 280 Nm and maximum power of 80 kW. The motor achieves a small size, high power, and high efficiency as a result of adopting the following in-house technologies. The magnetic circuit design was optimized for an interior magnet synchronous motor to attain the maximum performance figures noted here. The material technologies of the rotor and the stator facilitate high efficiency and the production technology achieves high density winding. The cooling mechanism is optimally designed for a mass-produced electric vehicle. The inverter incorporates the following original technologies and application-specific parts to obtain cost reductions combined with reliability improvements. The power module has an original structure with the power devices mounted directly on the busbars.

In order to satisfy increasing customer demands on ride quality as well as expectations for off-road performance of sport-utility vehicles (SUVs), it is necessary to develop technologies which offer enhanced levels of both performances. For ride quality, it is important to minimize body roll angle during cornering, which is achieved by suppressing suspension travel, and also to reduce vertical motion during straight-ahead travel. While for off-road performance, it is necessary to allow a long suspension stroke to allow a high level of off-road traction by delivering driving force reliably to the surface. These two performance parameters require a tradeoff with respect to vehicle roll stiffness. To reconcile these conflicting performance requirements, for first time in the world we adopted for production vehicles the system which connects the four shock absorbers together.

To promote widespread use of fuel cell vehicles (FCVs), further improvement of cold start capability is required for operation in various extreme temperature regions all over the world. Sub-freezing, cold start issues of fuel cells must be resolved through gaining a better understanding of the physical phenomena taking place in a cell during cold start and by elucidating the mechanisms hindering cold startup. Nissan has improved its understanding of the physical phenomena occurring in a fuel cell (FC) during cold startup by a laboratory-scale FC experiment at subfreezing temperatures and a numerical calculation that expresses various transport processes in a fuel cell, including those of the reactant gases, water, electrons and heat. The results have identified several necessary conditions for mass transport in a cell during cold startup and the factors that limit and govern the phenomena involved.

It is difficult for a conventional robust control algorithm to assure the performance of a slip speed control system, because the plant (lockup system) includes the nonlinear characteristics of the hydraulic system and large changes in the parameters of the slip model at low vehicle speed. The purpose of this study is to reduce the fuel consumption and improve the drivability of vehicles at takeoff by using a slip speed control system. Providing a large feedback gain is effective in reducing the influence of nonlinearity. However, since the operating parameters of the lockup clutch change depending on the driving conditions, that is not possible. A feedback compensator with a gain-scheduled H∞ control method was used in this study to solve these problems. The effectiveness of the slip speed control system was demonstrated in driving tests. Using this control system, the slip speed can be controlled with high accuracy, thereby reducing unnecessary revving of the engine.

A new control system for the coasting range was designed with the μ-synthesis technique to achieve robust stability, based on the slip speed control system that was reported in our previous paper.(1) The results of driving tests conducted with the fuel supply cut off while coasting confirm that the new control system is able to avoid engine stall even under sudden hard braking on a low friction road (μ<0.1) at a vehicle speed of 20 km/h and a turbine speed of 1000 rpm. The system also allows the lock-up clutch to slip stably at a certain target slip speed at anytime while coasting and achieves robust performance against characteristic variations of the lock-up mechanism. This slip speed control system thus makes it possible to extend the fuel cut-off range to a lower engine speed of 800 rpm, down from 950 rpm, thereby improving fuel economy by about 1%.

To reduce quenching distortion, step gas quenching has been proposed in recent years, which refers to rapid gas cooling of steel from austenitizing temperature to a point above or below Ms temperature, where it is held for a specific period of time, followed by gas cooling. In this study, by using infrared thermography combined with conventional thermocouple, a new temperature monitoring and control system was developed to realize the step gas quenching process of a hypoid ring gear after low pressure carburizing. The test production results indicate that by using the new monitoring and control system, we can control the gas quenching process and the distortion of carburized gear treated by step gas quenching can be reduced significantly compared with standard gas quenching.

Various driver assistance systems have been developed for maintaining a vehicle in its lane. For example, systems that apply force to the steering gear to help the driver keep the vehicle in the center of its lane are becoming popular. On the other hand, direct yaw-moment control systems have been developed for use in stabilizing the vehicle in extremer conditions where loss of control is detected. This paper deals with a system for aiding drivers in recovering from lane departure and maintaining the vehicle in its lane by utilizing direct yaw-moment control. The system uses a CCD camera to recognize lane makers and detects lane departures based on the positional relationship between the vehicle and the lane. When a lane departure is detected, the system applies force to the wheels to generate a yaw moment in the vehicle, so that it turns towards the original lane.

A study was made on a control method for an adaptive cruise control (ACC) system that uses vehicle-to-vehicle communication to achieve a substantial improvement in string stability and natural headway distance response characteristics at lower levels of longitudinal G. A control system using model predictive control was constructed to achieve this desired ACC vehicle behavior. Control simulations were performed using experimental data obtained in vehicle-following driving tests conducted on a proving ground course using a platoon of three manually driven vehicles. The results showed that the proposed ACC system satisfactorily achieved higher levels of required ACC performance.

This paper presents a newly developed adaptive cruise control system with low-speed following capability that is designed to reduce the driver's workload in low-speed driving such as in congested traffic. This system incorporates a forward-looking sensor with a wider range of view for improved detection of a preceding vehicle in the same lane. It also has a control algorithm that achieves natural vehicle behavior without any disconcerting feeling, as a result of being constructed on the basis of analyses of driving behavior characteristics at low speed like that of congested traffic. Evaluations conducted on a driving simulator have confirmed that the system is effective in reducing the driver's workload.

Driving tests were conducted using an experimental vehicle equipped with an adaptive cruise control system incorporating low-speed following capability in order to evaluate drivers' trust in a driver support system. The results revealed that the drivers' trust in the system declined in cases where the control algorithm produced vehicle behavior that was inconsistent with their expectations. However, that decline in trust ceased to be observed as the drivers' understanding of the system improved. This result suggests a correlation between their understanding of the system and trust in it.

Lock-up operation of an automatic transmission is known as one good method of improving fuel economy. However, locking up the transmission at low vehicle speeds can often cause undesirable vibration or booming noise. Slip control of the lock-up clutch can resolve these problems, but the speed difference of the lock-up clutch needs to be controlled at a certain value. This control system has to overcome large changes in the parameters of the lock-up system at low vehicle speeds and also changes with regard to the speed ratio in a continuously variable transmission (CVT). In this study, this complex non-linear system has been modeled as a first-order linear parameter varying (LPV) system. A robust control algorithm was applied taking various disturbances into account to design a new slip lock-up control system.

One important development area for obtaining better fuel economy is to reduce mechanical friction losses in engine components. The valvetrain is a significant source of mechanical friction loss in an automobile engine, especially at low speeds where fuel economy is most important. This paper describes the potential use of diamond-like carbon (DLC) coatings at the cam/follower interface in a bucket-type valvetrain. Using a pin-on-disk tester, a motored valvetrain friction apparatus and a bench test rig, the frictional performance of DLC coatings was tested. Experimental data indicate that under a lubricated condition, DLC coatings produced by a plasma CVD (chemical vapor deposition) technique did not show a sufficient effect on reducing friction (only a 20-25% reduction) contrary to our expectations. DLC coatings prepared by arc-ion plating and containing less hydrogen showed superior frictional performance compared with CVD-DLC coatings under a lubricated condition.

This paper describes an integrated switch system by which the audio control system, air-conditioner control system and navigation control system can be operated with a smaller number of switches. This system resolves several issues resulting from the incorporation of information technology into vehicles, including the increased visual load due to the greater amount of information presented and the poorer operability resulting from increased functionality. A usability evaluation was conducted and the results indicated that the integrated switch system can reduce visual load.

This paper describes a newly developed adaptive cruise control (ACC) system using continuously variable transmission (CVT) gear ratio control. This system provides excellent headway distance control performance at a reasonable cost. With this system, headway distance is measured with a laser radar, and the throttle position and CVT gear ratio are controlled under both acceleration and deceleration situations. The new ACC system consists of a target headway distance calculator, a headway distance controller, a vehicle velocity controller and a drive torque controller. Using a drive torque control method that was newly developed based on integrated control of engine torque and the CVT gear ratio, the following benefits are obtained. (1) It provides smoother acceleration and deceleration. (2) It maintains the target vehicle velocity on steep uphill and downhill grades. As a result, sufficient ACC performance can be attained even in 2.0-liter class vehicles.

This paper describes the new inline 4-cylinder QR engine series that is available in 2.0-liter and 2.5-liter versions. The next-generation QR engine series incorporates new and improved technologies to provide an optimum balance of power, quietness and fuel economy. Its quiet operation results from the adoption of a compact balancer system and the reduced weight of major moving parts. Power and fuel economy have been enhanced by a two-stage cooling system, a continuous variable valve timing control system, a dual close coupled catalyst system, electronic throttle control and an improved direct-injection system. The latter includes an improved combustion chamber concept and improved fuel spray characteristics achieved by driving the injector by battery voltage. A lightweight and compact engine design has been achieved by adopting a high-pressure die cast aluminum cylinder block, resin intake manifold and rocker cover and a serpentine belt drive.

This paper describes the method used to design the basic control algorithm of a lane-keeping support system that is intended to assist the driver's steering action. Lane-keeping control has been designed with steering torque as the control input without providing a minor loop for the steering angle. This approach was taken in order to achieve an optimum balance of lane-keeping control, ease of steering intervention by the driver and robustness. The servo control system was designed on the basis of H2 control theory. Robustness against disturbances, vehicle nonlinearity and parameter variation was confirmed by μ - analysis. The results of computer simulations and driving tests have confirmed that the control system designed with this method provides the intended performance.

Every fuel injection system for DI gasoline engines has a DC-DC converter to provide high, stabile voltage for opening the injector valve more quickly. A current control circuit for holding the valve open is also needed, as well as a large-capacity capacitor for pilot injection. Since these components occupy considerable space, an injector drive unit separate from the ECU must be used. Thus, there has been a need for a fuel injection system that can inject a small volume of fuel without requiring high voltage. To meet that need, we have developed a dual coil injector and an opening coil current control system. An investigation was also made of all the factors related to the dynamic range of the injector, including static flow rate, fuel pressure, battery voltage and harness resistance. Both efforts have led to the adoption of a battery voltage-driven fuel injector.

An Adaptive Cruise Control system with stop-and-go capability has been developed to reduce the driver's workload in traffic jams on expressways. Based on an analysis of driving behavior characteristics in expressway traffic jams, a control system capable of modeling those characteristics accurately has been constructed to provide natural vehicle behavior in low-speed driving. The effectiveness of the system was evaluated with an experimental vehicle, and the results confirmed that it reduces the driver's workload. This paper presents an outline of the system and its effectiveness along with the experimental results.