Search

An optimal shift control strategy for electric vehicles with the two-speed dual-clutch transmission is proposed to reduce the vehicle jerk and friction work during gear shift. The dynamic model of the powertrain considering the stick–slip friction of clutch is built. The developed control scheme is divided into two stages. For the upper level control, a finite-time linear quadratic regulator (LQR) is designed to optimize the target trajectories of torque and speed of motor and clutch by integrating both jerk and friction work in the cost function. Considering that the clutch torque is necessary for calculating the target trajectories but cannot be measured directly, the Kalman filter is employed to estimate the clutch torque. For the lower level control, a combination of torque feedforward and speed feedback controller is constructed to control the motor torque and clutch pressure. To validate the effectiveness of the proposed strategy, comparisons with the strategies based on the polynomial method and unsmooth LQR are carried out. Simulation results and hardware-in-loop test reveal that the jerk and friction work are both reduced, indicating better shift performance. [ABSTRACT FROM AUTHOR]

In this study, the floating liner method is utilized to measure the friction generated in the piston assembly of a single-cylinder gasoline engine. The piston assembly is subjected to combustion pressure, lubricating friction, and asperity friction during engine operation and reciprocates within the cylinder. Therefore, the main goal of this study is to investigate the effect of engine combustion and lubricant conditions on piston friction. First, we analyze how the combustion pressure, obtained by changing the combustion load and the ignition timing, affects piston friction. Second, by adjusting engine speed and coolant/oil temperature, we analyze how each condition affects piston friction. Through the experiments for each case, it was confirmed that the friction increased as the combustion pressure increased under the same lubrication conditions. It was also confirmed that the piston friction was significantly measured due to the increase in lubrication friction as the engine speed increased. Finally, it was confirmed that as the temperature decreased, the oil viscosity increased, resulting in a large friction loss. [ABSTRACT FROM AUTHOR]

—Hydrodynamic lubrication is simulated under the contact conditions that the direction of contact velocity reverses with a sudden high applied load in the contact of piston top ring and cylinder liner. Hydrodynamic lubrication film formation and pressure between piston ring and cylinder liner at the top dead center (TDC) location are investigated in detail because most friction loss and wear damage happen at this location due to the thin-film thickness resulting from the slow-down and reversal contact velocities as well as high applied load. The surface roughness on the cylinder liner by the honing process that is similar scale to the lubrication film thickness at TDC location is considered. Around the TDC location, laser surface textured (LST) surface that is larger scale than the surface roughness is designed for the favorable film formation. These two surface roughness parameters are simulated to study the effects of favorable film formation and less frictional loss of piston top ring at TDC location where most of damage and friction loss occur. Frictional power loss and minimum film thickness of the cylinder surfaces of the honed roughness are compared with those of patterned designs. [ABSTRACT FROM AUTHOR]

In order to reduce unsprung mass and ensure driving comfortability, a novel electrical vehicle (EV) drive system, which integrated the wheel-side reducer and a single trailing arm, was studied in this paper. Firstly, the general structure of the drive system was studied, in which the reducer not only worked as a wheel-side reducer but also as the single trailing arm. Then, the transmission power losses were modeled by integrating different load-independent and load-independent models of power losses. Next, the experiment of the power losses test for the wheel-side drive system was conducted, which declared the patterns of power losses of electric motor and the whole drive system. Finally, the power losses of wheel-side reducer based on NEDC are studied, which illustrates oil churning and gear sliding power losses are the main types of transmission power losses. At low rotational velocities, gear friction power losses are larger than oil churning power losses. While at high rotational velocities, oil churning power losses are dominant. The transmission efficiency of the reducer based on NEDC varies among the range of 78 ∼ 95 %, which depends on the torque and rotational velocity transmitted from the driving motor to EV's wheel. [ABSTRACT FROM AUTHOR]

This paper deals with the power loss evaluation in gearshift assistant mechanism applied in automated manual transmission. The originalities include building the numerical models of gearshift assistant mechanism efficiency analysis for cost penalty evaluation and designing gear ratio matching algorithm to match the gear ratios of epicyclic mechanism with desired ones, which is expected to minimize the clutch friction losses by reducing the angular velocity differences between two clutch pads. In the numerical models, gear meshing losses and friction losses are considered the main power sink. By the kinematic relationships and power flow analysis, a set of generalized efficiency calculating formulas of simple epicyclic mechanism in six working modes with respect to teeth numbers are summarized, which are useful computer-aided tools in calculating multiple simple epicyclic mechanisms' efficiency. The matched gear ratios and the efficiency models are tested on a powertrain simulation model and several simulation results are reported. Finally, this paper summarized the merits and further research targets of the proposed transmission, which is a promising structure to achieve swift and smooth gearshift with low power losses. [ABSTRACT FROM AUTHOR]

This study examined the physical and chemical properties of engine oil with a submicron-sized carbon particle lubricant mixture. Spherical carbon particles were added to engine oil to lower the friction and wear losses. In the current study, morphological and chemical analyses of these carbon particles were performed using field emission scanning electron microscopy and energy dispersive spectroscopy. The results clearly demonstrated that these spherical particles consist of a pure carbon element. In addition, the size distribution and dispersion stability of the carbon particles in the engine oil were investigated. The results revealed that the carbon particles have a diameter in the range of 200 to 700 nm, and they maintain their suspension in the engine oil for about 240 hours without using surfactants. Rheological studies were conducted to explore the effect of carbon particles on the rheological properties of the baseline oil at different temperatures and shear rates. The viscosity measurements, at temperature ranging from 5 to 60 °C, for the baseline oil and the oil-carbon particle lubricant mixture were almost identical (less than 4 % difference). Furthermore, a wettability analysis was performed to examine the effect of carbon particles on the wetting behavior of the baseline oil on a steel substrate. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to reduce friction losses by adding carbon nanotubes to engine oil. Extremely favorable tribological properties of carbon nanotubes have been extensively studied on the microscopic scale and using tribometers, have not yet been verified in the engine. Enriching oil with nanotubes can lead to significant, exceeding 7 %, reduction in the motoring torque of the engine at low crankshaft rotational speed. The phenomena associated with the dispersion of carbon nanotubes in the engine are stated and discussed. It has been shown that the oil shear during normal operation of the engine can effectively improve the dispersion of nanotubes. At the same time the oil filtration system removes agglomerates of nanotubes very quickly. [ABSTRACT FROM AUTHOR]

Clutch engagement control is critical during launching process in a vehicle equipped with an automated manual transmission (AMT), which is a problem including muti-objective optimization and nonlinear control. In this paper, a optimal launching-intention-aware control strategy is proposed for clutch engagement. Firstly, a launching-intention-aware machine (LIAM) based on artificial neural network (ANN) is designed to identify the driver's launching intentions. Then the optimal laws of clutch engagement for different launching conditions are obtained based on the dynamic programming (DP), which regard friction loss, vehicle shock, angular acceleration of engine and engine torque as the optimizing indexes. Next, a slidingmode controller (SMC) is designed for the clutch engagement. Finally, the performances of the optimal laws and the SMC are validated by the joint simulation of Simulink-AMESim, and the results show that the requirements of vehicle launching are met. The proposed clutch engagement control strategy would provide a better theoretical support for the practical-extended application of AMT. [ABSTRACT FROM AUTHOR]

FTP75 driving cycle is used in many countries for evaluation of vehicle fuel economy. FTP75 has 3 phases, where the Phase 1 and the Phase 3 have a same velocity profile, but the Phase1, which is known as cold start phase, shows lower fuel efficiency than the Phase 3. In order to analyze the difference of fuel economy between Phase 1 and Phase 3, vehicle tests are performed. The test results show that the differences of fuel economy is ranging from 3.9% to 18.5%. The factors of the difference of fuel economy for gasoline automatic transmission vehicles are analyzed in this research. The key factors affecting the difference of fuel economy are engine friction loss, torque converter loss and accessory loss. The quantitative analysis of these factors is performed. [ABSTRACT FROM AUTHOR]