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Soot accumulation in diesel engine crankcase is the dominant factor which governs engine oil drain interval. So, efficient soot elimination from crankcase oil can be a practical way to achieve drain interval extension. Combination of high performance oil filter and low soot dispersancy oil results in an effective measure to trap soot efficiently. In this paper, the behavior of newly developed high performance diesel engine oil having low soot dispersancy is reported. Prior to oil development, an evaluation method of soot dispersancy in oil was elaborated. Based on relative viscosity defined as ratio of soot containing oil viscosity to soot eliminated oil viscosity, dispersancy parameter was determined. Oil dispersancy evaluated on this parameter agreed with the results obtained from particle size analyzer. Secondly, a method to obtain oil filter soot trap rate to total soot contaminated into crankcase (trap rate) was established.

Because of smaller ratios of tread to height of gravitational center, longer wheel-bases, and larger moment of inertia, vehicle roll is the most important characteristics governing truck controllability and stability. And longer wheel-bases result in a reduction in vehicle body torsional stiffness. Hence, the influence of vehicle body torsional stiffness on vehicle roll characteristics is investigated. We carried out a simulation analysis and vehicle test on medium-duty trucks, in studying the vehicle frequency response characteristics by changing vehicle design parameters. The results show that a reduction in body torsional stiffness increases the steady state gain of the front roll angle without affecting the yaw and lateral characteristics of vehicle motion. Accordingly, even if body torsional stiffness is unavoidably lowered, reducing the front roll angle by increasing the roll stiffness of the front suspension can maintain appropriate vehicle controllability and stability.

This paper studies the feasibility of improving vehicle ride comfort and vehicle dynamics by applying mechanically controlled hydropneumatic suspension to a medium-duty truck. Both front and rear suspensions consist of hydraulic cylinders, small gas accumulators and leaf springs. Hydraulic pressure In the cylinder is controlled by a hydraulic pressure difference between diagonally located hydraulic cylinders. Vehicle test results show that this suspension system reduces vertical vibration in the frequency range of 3 to 10 Hz, the pitch motion during braking, and the roll angle during a steady turn, when compared those the conventional suspension system. However, due to a response lag in the hydraulic control system, this system causes an unfavorable vehicle motion when there is a rapid steering operation, such as an abrupt lane change.

A heavy-duty, naturally aspirated diesel engine was converted into a turbocharged, aftercooled, compressed natural gas engine. Engine test results show that excess air ratio and ignition timing strongly affect NOx and THC emissions. Leaning the air-fuel mixture reduces NOx emission, but it increases THC emission and combustion becomes unstable above a certain excess air ratio. Retarding the ignition timing reduces both the NOx and THC emissions. Dual-plug ignition improves brake thermal efficiency. The NOx emission level can be reduced to meet the Japanese long-term emission regulation limit for heavy-duty gasoline engines with a sufficient safety margin by appropriately selecting the air-fuel ratio and ignition timing so as to keep the THC emission level below the regulation limit without using any after-treatment. The engine full torque characteristics were almost the same as the base engine throughout the engine speed range, while the maximum exhaust gas temperature was lower.

This study establishes the feasibility of improving the motion characteristics of commercial vehicles by applying rear axle steering. A model-matching control algorithm for rear axle steering was used to achieve the desired yaw rate response to steering action. Simulations with a two-degree-of-freedom model evaluated the effectiveness of the control method. Results of vehicle tests on an experimental medium-duty truck with rear axle steering proved that this control method can improve vehicle yaw response. However, the simulation results did not well represent the vehicle test results, because the simulation model was too simple. Adding the roll effect to the model reduced the discrepancy between the simulation and vehicle test results.

A reduction in vehicle weight sometimes results in a reduction in truck body torsional stiffness. Hence, the authors investigate the influence of vehicle body torsional stiffness on vehicle controllability and stability. A simulation analysis and vehicle test are carried out on a medium-duty truck, and the frequency response characteristics of the vehicle are studied by changing vehicle design parameters. The results show that a reduction in body torsional stiffness does not affect the yaw and lateral characteristics of vehicle motion, but increases the steady state gain of the front roll angle. Accordingly, even if body torsional stiffness is unavoidably lowered, appropriate controllability and stability can be maintained by increasing the roll stiffness of the front suspension, thereby reducing the front roll angle.

Evaporative cooling was applied to a heavy duty diesel engine to investigate the feasibility of this cooling method. Engine test results showed the following benefits of this cooling method: Reduction of the size of theradiator and cooling fan is feasible. The maximum temperature of the combustion chamber wall did not increase, though the coolant temperature rose by 20°C. The fuel consumption could be reduced especially at partial load. Engine warm-up performance was significantly improved. An oil cooler rig test was also conducted to investigate the heat transfer characteristics of the oil cooler with evaporative cooling.