Model development and experimental research on an air spring with auxiliary reservoir

This paper focuses on the dynamic stiffness and overall equivalent damping of an air spring connected to an orifice and an auxiliary reservoir, with respect to the displacement excitation frequency, orifice area, and auxiliary reservoir volume. A theoretical model of this air spring with its auxiliary reservoir is derived by utilizing the energy conservation equation, gas state equation, and orifice flow rate equation. Simulation results from the presented model reveal that, when the air spring is subject to harmonic displacement excitation, its dynamic stiffness increases with an increase in excitation frequency and decrease in orifice area. Smaller orifice areas and lower excitation frequencies result in higher overall equivalent damping. A validation experiment is also implemented. When compared with experimental results, simulations show consistent varying trends of the dynamic stiffness and overall equivalent damping. The model developed here can correctly describe the behavior of the air spring with auxiliary reservoir, indicating that it is reasonable and feasible.     

Development of an idle speed engine model using in-cylinder pressure data and an idle speed controller for a small capacity port fuel injected SI engine

An idle speed engine model has been proposed and applied for the development of an idle speed controller for a 125 cc two wheeler spark ignition engine. The procedure uses the measured Indicated Mean Effective Pressure (IMEP) at different speeds at a constant fuel rate and throttle position obtained by varying the spark timing. At idling conditions, IMEP corresponds to the friction mean effective pressure. A retardation test was conducted to determine the moment of inertia of the engine. Using these data, a model for simulating the idle speed fluctuations, when there are unknown torque disturbances, was developed. This model was successfully applied to the development of a closed loop idle speed controller based on spark timing. The controller was then implemented on a dSPACE Micro Autobox on the actual engine. The Proportional Derivative Integral (PID) controller parameters obtained from the model were found to match fairly well with the experimental values, indicating the usefulness of the developed idle speed model. Finally, the optimized idle speed control algorithm was embedded in and successfully demonstrated with an in-house built, low cost engine management system (EMS) specifically designed for two-wheeler applications.     

Torque-based optimal vehicle speed control

This paper describes an optimal vehicle speed controller that uses torque-based control concepts. The controller design was divided into two steps: first, for a given vehicle speed trajectory, the engine torque demand was determined; in the second stage, a torque controller was implemented to track this torque demand. The torque demand was determined by a primary component and a correction component. The primary component was determined by solving an off-line optimization problem, and the correction component was added to compensate for the error caused by the off-line optimization. A modelbased proportional-integral (PI) feedback torque controller was employed to realize the engine torque tracking. Simulation results generated by a benchmark simulator were given to demonstrate performance of the optimal vehicle speed controller and a conventional PI speed controller that was included for comparison.     

Computational study of charge stratification in early-injection SCCI engines under light-load conditions

Under light-load conditions in early-injection stratified-charge compression-ignition (SCCI) engines, excessive premixing can lead to undesirable levels of unburned hydrocarbons (UHC) and carbon monoxide (CO) emissions. Optimal stratification can reduce these emissions. In this work, the effects of changes in swirl, injection pressure, injector hole-size and number of holes, injection timing, and piston geometry on stratification are computationally investigated. It is shown that these parameters affect the stratification through their influence on the rate of spray penetration, drop vaporization, and fuel/air mixing. The outcome is characterized by examining the evolution of the spatial distribution of the fuel vapor in the chamber and its mass-based distribution function. All other parameters remaining the same, decreasing drop size leads to faster vaporization and richer mixtures. Increasing penetration leads to greater spreading and leaner mixtures. Increasing spray included-angle leads to greater spreading and leaner mixtures. Increasing injection pressure leads to increased mixing and leaner mixtures. Increasing injector hole-size leads to richer mixtures at lighter loads because the duration of injection is reduced and the fuel is confined closer to the axis. Increasing swirl leads to faster breakup of the head-vortex and confinement of the fuel closer to the axis, and hence richer mixture.     

Influential factors for HLA pump up in a roller finger follower engine

In an HLA (hydraulic lash adjuster) piston engine, “pump up” can occur when a valve is opened by the HLA when it should be closed. HLA pump up is more frequently encountered with exhaust valves than with intake valves. When HLA pump up in occurs in the exhaust valve, exhaust gas from the exhaust manifold enters the cylinder on the intake stroke, and fresh air-fuel mixture exits through the exhaust manifold on the compression stroke and is burned in the catalyst, causing partial burning, misfire, catalyst melting and power drop. HLA pump up occurs when the force on the valve from the HLA is higher than the force on the HLA from the valve. HLA pump up is related to design parameters, such as oil pressure, rocker ratio, spring load, spring surge, and both intake and exhaust valve timing. In this study, valve lift and load on a roller finger follower were measured at varying engine firing conditions to evaluate HLA pump up. The results indicated that effective measures to reduce HLA pump up include a higher rocker ratio, a lower oil supply pressure to the HLA, a higher spring installation load and a lower spring surge.     

Numerical and experimental investigation of lubricating oil flow in a gerotor pump

Gerotor pumps are widely used in the automotive industry for engine oil lubrication, due to their high volumetric efficiency and smooth pumping action. In many cases, the lubricating oil from the sump is mixed with contaminants, such as dust and tiny solid particles, or becomes thickened, due to aging. These problems will lead to critical situations, such as increased noise, enhanced wear and erosion, and poor lubrication of the engine. These critical situations were studied by conducting a detailed CFD integrated investigation on a gerotor pump’s performance at different operating conditions in three phases, and the results are presented in this paper. In first phase, a CFD model of a gerotor pump was developed with a dynamic mesh for the rotary movement of both the inner and outer rotors. The effects on pump flow rate of important parameters, such as rotor speed, fluid viscosity and number of ports, were simulated using non-contaminated oil at room temperature and an elevated temperature of 140oC. The relationship between flow rate and pressure at different rotor speeds was predicted and validated with test data for further parametric study. The pressure ripples at different time steps were measured at different angular positions of the rotors to examine the model accuracy. It was found that the flow rate increased and pressure pulsation, as well as flow recirculation, was reduced when ports were added to the cover plate. A suction pipe with a strainer was added for the second phase to capture the undesired changes in flow behavior, such as cavitation, which is caused by negative suction at the inlet region of pump. A suitable size for the inlet suction pipe for this pump was chosen after performing tests to characterize the flow behavior with single and double ports. Next, the relationship between pressure drop and strainer porosity was determined using different porosity values for the strainers. In the final phase, oil with different concentrations of solids was simulated to measure the effect of solid particles on flow rates and pressure losses. It was observed that the intensity of the recirculation was reduced at the suction end at the higher concentration of 0.04%, due to particle inertial effects. It was also found that particle size distribution affected the overall efficiency and pressure head of the pump.     

Breakup modeling of a liquid jet in cross flow

We propose a novel breakup model to simulate the catastrophic breakup regime in a supersonic cross flow. A developed model has been extended from an existing Kelvin-Helmholtz/Rayleigh-Taylor (K-H/R-T) hybrid model. A new mass reduction rate equation, which has critical effects on overall spray structure, is successfully adopted, and the breakup length, which is an important parameter in existing model, is replaced by the breakup initiation time. Measured data from the supersonic wind tunnel with a dimension of 762×152×127 mm was employed to validate the newly developed breakup model. A nonaerated injector with an orifice diameter of 0.5 mm is used to inject water into a supersonic flow prescribed by the momentum flux ratio of the liquid jet to free stream air, q ₀ . The conservation-element and solution-element (CE/SE) method, a novel numerical framework for the general conservation law, is applied to simulate the supersonic compressible flow. The spray penetration height and average droplet size along with a spray penetration axis are quantitatively compared with data. The shock train flow structures induced by the presence of a liquid jet are further discussed.     

Reducing the memory footprint of OSEK-based systems via stack sharing and light-weight ready queues

OSEK OS (Offene Systeme und deren Schnittstellen für die Elektronik in Kraftfahrzeugen Operating System) is an open, real-time operating system standard for ECU software in vehicles. Because it was originally designed to be used in an extremely resource-constrained environment, an OSEK-compliant operating system must incur low processing overhead and memory usage. Unfortunately, as OSEK OS has evolved over time, it now specifies nontrivial kernel features along with multiple conformance classes and application modes. This may lead to unwanted dynamic resource usage in a system using OSEK OS unless the standard is carefully interpreted and designed into an OSEK OS implementation. In this paper, we analyzed the various kernel features of OSEK OS and their interactions to identify areas in the standard that warrant further resource usage optimization. In particular, we attempted to reduce the run-time memory footprint. Based on our analyses, we present two kernel mechanisms: (1) stack sharing among tasks and (2) light-weight ready queue handling specialized for OSEK OS conformance classes. We also offer implementation methods for the proposed mechanisms by extending OIL and associated tools. Finally, we show the effectiveness of the proposed mechanisms via extensive experiments. Our mechanisms allow OSEK-based systems to use only 36% of the memory requirements of conventional OSEK-based systems on average.     

Model referenced adaptive control to compensate slip-stick transition during clutch engagement

Clutches are widely used in various vehicle powertrains. The engagement process of a friction clutch has three phases, i.e., open, slipping, and sticking. Transitions between different phases introduce a discontinuity to the powertrain dynamics, which has been neglected in previous research. A model referenced adaptive controller (MRAC), based on Popov hyper-stability criterion, is designed to compensate the discontinuity. MRAC adjusts the frictional torque along with the errors of the state variables compared with those of a referenced model. The designed MRAC is applied to a clutch in a bus. Simulation and experimental results under fast and slow startup cases show that MRAC can simultaneously reduce vehicle jerk and frictional dissipation when compared with the conventional controller.     

Numerical simulation of fluid flow caused by buoyancy forces during vacuum arc remelting process

The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0 software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.