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To explore the measures that can be used to improve the fuel economy of internal combustion engines, we investigated how friction at the piston ring-cylinder liner interface is influenced by the boundary lubrication performance of engine oils. We formulated several engine oils with varying boundary lubrication performance and tested them for ring-liner friction by using a floating liner friction tester. We used friction modifiers (FMs) to modify the boundary lubrication performance of engine oils. We found that ring-liner friction is well correlated with the friction coefficients in boundary lubrication regimes when measured by a laboratory friction tester. We also found that the impact of the boundary lubrication performance of engine oils was emphasized in low viscosity engine oils. It makes it possible for improved boundary lubrication performance to inhibit or overcome the viscosity reduction-induced increase of friction energy.

Energy conserving performance by engine oils is required even for motorcycles from the viewpoint of environmental issues. The fuel efficiency of passenger car engine oils has been improved through lower viscosity and usage of friction modifiers. However, engine oils containing friction modifiers such as Mo compounds may not be applied to four-stroke motorcycles, because motorcycles normally have a wet clutch system inside the crankcase and such engine oils can decrease the clutch capacity. Therefore, it is important to investigate the effects of oil formulation in order to develop motorcycle engine oils, which can improve fuel efficiency and preserve clutch capacity1)∼2). In this study, fuel efficiency of prototype oils was evaluated with a motorcycle engine motoring tester. In addition, friction coefficients of engine oils formulated with different additives such as dispersants and detergents in clutch system were evaluated with an SAE No. 2 clutch friction tester.

The energy conserving by engine oils has been required from the viewpoint of the environmental issue. The fuel efficiency of passenger car engine oils has been improved by adding friction modifiers. However, engine oils containing friction modifiers can not be applied to 4-stroke motorcycles. Because motorcycles normally have a wet clutch system inside the crankcase and such engine oils can decrease the clutch capacity.1) ∼ 2) Therefore, it is important for motorcycle engines to investigate additives, which can increase friction coefficient on paper-based friction materials. In this study, friction coefficients of engine oils formulated with different additives such as dispersants and detergents were evaluated with a reciprocating friction tester. Several types of polybutenyl succinimides, sulfonates, phenates and salicylates were used as dispersants and detergents.

In the Japan Clean Air Program II (JCAP II) Diesel WG, effects of fuel properties on the performance of two types of diesel NOx emission aftertreatment devices, a Urea-SCR system and a NOx storage reduction (NSR) catalyst system, were examined. For a Urea-SCR system, the NOx emission reduction performance with and without an oxidation catalyst installed in front of the SCR catalyst at low exhaust gas temperature operation was compared. For an NSR catalyst system, the effect of fuel sulfur on both emissions and fuel economy during 50,000 km driving was examined. Furthermore, effects of other fuel properties such as distillation on exhaust emissions were investigated. The results show that sulfur is the influential factor for both devices. Namely, high NOx emission reduction performance of the Urea-SCR system with the oxidation catalyst at low exhaust gas temperature operation is influenced by sulfur.

High viscosity index(HVI) petroleum base stock, with excellent temperature-viscosity characteristics, oxidation resistance, and low-evaporation properties, offers advantages as the base stock for high fuel economy engine oils, particularly because of its low-friction properties in the boundary and/or “E.H.L (Elastohydrodynamic Lubrication)” area due to its rheological characteristics. This research evaluated HVI base stock's low-friction properties. Upgrading the oil from 5W-30 to 5W-20 was also investigated. The friction properties of the HVI base stock were measured by a unit friction platform. The results show a 28% reduction in friction coefficient compared with the conventional, solvent refined oil, which is attributable to the high-pressure viscosity of the base oil.

Gasoline engine downsizing combined with a turbocharger is one of the more effective approaches to improve fuel efficiency without sacrificing power performance. The benefit comes from lower pumping loss, lower mechanical friction due to ‘downsizing’ of the engine displacement and ‘down-speeding’ of the engine by using higher transmission gear ratios which is allowed by the higher engine torque at lower engine speeds. However abnormal combustion referred to as Low-Speed Pre-ignition (LSPI) is known to be able to occur in low-speed and high-torque conditions. It is a potential restriction to maximize the engine performance and its benefit, therefore prevention of LSPI is strongly desired for long-term durability of engine performance. According to recent technical reports, auto-ignition of an engine oil droplet in a combustion chamber is believed to be one of major contributing factors of LSPI and its formulations have a significant effect on LSPI frequency.

1 Fuel savings by engine oil have been requested for two-wheeled vehicles from the viewpoint of environmental issues. In four-wheeled vehicles, reduction of oil viscosity and addition of friction modifiers have been effective in improving fuel efficiency. However, direct application of engine oil for four-wheeled vehicles to two-wheeled vehicles is difficult. In a four-cycle two-wheeled vehicle, the transmission, gears, and a wet clutch system are imbedded within the engine1). Engine oil must display a remarkable performance as it is required to function as transmission oil and to improve anti-metal fatigue life and clutch performance2), 3). If fuel efficiency is improved by reducing the viscosity of engine oil used in two-wheeled vehicles, the fatigue life tends to worsen. Therefore, reduction in oil viscosity is difficult to achieve.

Nissan has developed a practical and available toroidal continuously variable transmission (T-CVT) for passenger vehicles for the first time in the world. This CVT is applicable to engines having an output of torque larger than 400 N-m and makes it possible to use a lock-up clutch at low vehicle speed, resulting in marked improvements in drivability and fuel economy. The authors have developed the T-CVT fluid, which is in this application, having excellent traction coefficient and sufficient capacity as the transmission fluid. This paper mainly describes the traction coefficient measurement procedure and the performance of the newly developed fluid.

To comply with increasingly strict emission regulations, diesel vehicles are equipped with Diesel Particulate Filters (DPF) to capture fine particulate matter (PM) from exhaust gas. However, due to the limited capacity of DPF to capture soot, periodic regeneration processing is required to burn it off. The ash created by metal-based additives in engine oil accumulates in DPF, leading to issues such as increased regeneration frequency and decreased fuel efficiency. To solve this problem, researchers have developed diesel engine oil with reduced ash content. However, the authors are taking it a step further and developing a diesel engine oil without metal-based detergents and anti-wear additives, for even more significant environmental impact reduction. This paper describes the development of an ashless engine oil with DH-2 performance, the effects of the developed engine oil on DPF, and the results of engine and actual field tests.