• Journal of Auto-vehicle Safety Association
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• v.13 no.1
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• pp.6-13
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• 2021

This paper presents yaw moment control for modification of steering characteristic in rear-driven vehicle with front in-wheel motors (IWMs). The proposed control algorithm is designed to modify yaw rate response of the test vehicle. General approach for modification of steering characteristic is to define the desired yaw rate and track the yaw rate. This yaw rate tracking method can cause the chattering problem because of the IWM actuator response. Large overshoot and settling time in IWM torque response can amplify the oscillation in control input and yaw rate. To resolve these problems, open-loop IWM controller for cornering agility was designed to modify the understeer gradient of the vehicle. The proposed algorithm has been investigated via the computer simulations and the vehicle tests. The performance evaluation has been conducted on dry asphalt using E-segment test vehicle. The performance of the proposed algorithm has been compared to general yaw rate tracking algorithm in the vehicle tests. It has been shown that the proposed control law improved the cornering agility without chattering problem.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.17-24
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• 2011

TMED(Transmission Mounted Electric Device) parallel hybrid configuration can realize EV(Electric Vehicle) mode by disengaging the clutch between an engine and a transmission-mounted motor to improve efficiencies of low load driving and regenerative braking. In the EV mode, however, jerk can be induced since there are insufficient damping elements in the drive-train. Though the jerk gives demoralizing influence upon driving comport, adding a physical damper is not applicable due to constraints of the layout. This study suggests the jerk reduction control, composed of active damping method and torque profiling method, to suppress the jerk without hardware modification. The former method creates a virtual damper by generating absorbing torque in the opposite direction of the oscillation. The latter method reduces impulse on the mated gear teeth of the drive-train by limiting the gradient of traction torque when the direction of the torque is reversed. To validate the effectiveness of the suggested strategy, a series of vehicle tests are carried out and it is observed that the amplitude of the oscillation can be reduced by up to 83%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.10
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• pp.888-893
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• 2012

This paper described the wind tunnel testing apparatus and technique to acquire the dynamic stability derivatives of large slenderness ratio air vehicle such as the guided missiles or rockets. There have been few difficulties in conducting wind tunnel testing for slender long rocket due to the size limitation of the test section size and the installation of oscillation equipments. In this study, the dynamic stability balance was used as the wind tunnel technique for obtaining the dynamic stability derivatives. Through the wind tunnel testing, the experimental apparatus for slender air vehicle's oscillation is established. The measured data showed that it is possible to acquire the dynamic stability derivatives of large slenderness ratio rocket, properly.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.7
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• pp.796-804
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• 2011

Railway vehicles are capable of indicating several types of instability. This phenomenon, which is called hunting motion, is a self excited lateral oscillation that is caused by the running velocity of the vehicle and wheel frail interactive forces. The interactive forces act to change effectively the damping characteristics of railway vehicle systems. This paper will show the impact of instability on the transfer function behavior using damping characteristics of secondary suspension. The vehicle dynamics are modeled using a 17 degree of freedom considering linear wheel/rail contact. The paper deals with certain condition of the damper characteristics that one is about various damping coefficient and another is equipped damper direction.

• Journal of Auto-vehicle Safety Association
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• v.12 no.2
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• pp.27-32
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• 2020

This paper presents steering system requirements to ensure the stabilized lateral control of autonomous driving vehicles. The two main objectives of a lateral controller in autonomous vehicles are maintenance of vehicle stability and tracking of the desired path. Even if the desired steering angle is immediately determined by the upper level controller, the overall controller performance is greatly influenced by the specification of steering system actuators. Since one of the major inescapable traits that affects controller performance is the time delay of the steering actuator, our work is mainly focused on finding adequate parameters of high level control algorithm to compensate these response characteristics and guarantee vehicle stability. Actual vehicle steering angle response was obtained with Electric Power Steering (EPS) actuator test subject to various longitudinal velocity. Steering input and output response analysis was performed via MATLAB system identification toolbox. The use of system identification is advantageous since the transfer function of the system is conveniently obtained compared with methods that require actual mathematical modeling of the system. Simulation results of full vehicle model suggest that the obtained tuning parameter yields reduced oscillation and lateral error compared with other cases, thus enhancing path tracking performance.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.75-80
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• 2011

In the area of wheel on rail vehicle, hunting stability which is generated by lateral motion is one of important characteristics for running safety. It might cause not only oscillation of vehicle but also derailment in an unstable area of the high speed. A Maglev vehicle is usually controlled the voltage to maintain the air gap between electromagnet and track. However, in Maglev system, an occurrence possibility of hunting motion could be high, because Maglev vehicle is not controlled directly lateral force between electromagnet and track in the curved guideway. In this paper, running safety is evaluated when Maglev vehicle run on guideway at high speed according to installment of damper between maglev vehicles and bogies, and to analyze the effect of it. Also, the parametric study is carried out for selecting effective lateral damper properties through the simulation. To accurately predict the running safety, 3d multibody dynamics models which are included air spring, guideway conditions and irregularities profile are used. With the results acquired, suggestions were made whether to adopt the damper and how to optimize the damping characteristics.

• Structural Engineering and Mechanics
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• v.54 no.3
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• pp.561-577
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• 2015

The main objective of this paper is to study the dynamic load allowance (DLA) calculation methods for bridges according to the dynamic response curve. A simply-supported concrete bridge with a smooth road surface was taken as an example. A half-vehicle model was employed to calculate the dynamic response of deflection and bending moment in the mid-span section under different vehicle speeds using the vehicle-bridge coupling method. Firstly, DLAs from the conventional methods and code provisions were analyzed and critically evaluated. Then, two improved computing approaches for DLA were proposed. In the first approach, the maximum dynamic response and its corresponding static response or its corresponding minimum response were selected to calculate DLA. The second approach utilized weighted average method to take account of multi-local DLAs. Finally, the DLAs from two approaches were compared with those from other methods. The results show that DLAs obtained from the proposed approaches are greater than those from the conventional methods, which indicate that the current conventional methods underestimate the dynamic response of the structure. The authors recommend that the weighted average method based on experiments be used to compute DLAs because it can reflect the vehicle's whole impact on the bridge.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.181-184
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• 2006

High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation and reattachment, shock and expansion waves. The general cavity flow phenomena include the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity' flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions, The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio(L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyized and compared with the results of Rossiter's Eq.

• Journal of computational fluids engineering
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• v.11 no.4 s.35
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• pp.62-66
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• 2006

High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation, reattachment, shock waves and expansion waves. The general cavity flow phenomena includes the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions. The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio (L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyzed and compared with the results of Rossiter's Eq.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.5
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• pp.463-468
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• 2009

Torsional oscillations of the drivetrain in electric vehicles are generated under rapid driving conditions. These lead to an uncomfortable jerking of the vehicle and an increased stress of the mechanical components. To suppress torsional oscillations, the low pass and notch filters between the torque command from the acceleration pedal and electric motor input torque are suggested. The filter parameters are optimized based on Taguchi method with $L_{18}(3^5)$ orthogonal array. The signal to noise (S/N) ratio mainly depends on slew rate of motor input torque, damping ratio and natural frequency of notch filter. With the proposed suppression control scheme, the S/N ratio is shown to be increased by 4.7dB and the torque overshoot of the drive shaft is reduced to 30%.