• 한국자동차공학회논문집
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• 제13권3호
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• pp.102-109
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• 2005

Wheel-slip control systems are able to control the braking force more accurately and can be adapted to different vehicles more easily than conventional ABS systems. But, in order to achieve the superior braking performance through the wheel-slip control, real-time information such as the tire braking force is required. For example, in the case of EHB (Electro-Hydraulic Brake) systems, the tire braking force cannot be measured directly, but can be approximated based on the characteristics of the brake disk-pad friction. The friction characteristics can change significantly depending on aging of the brake, moisture on the contact area, heat etc. In this paper, a wheel slip The proposed wheel slip control system is composed of two subsystems: braking force monitor and robust slip controller In the brake force monitor subsystem, the tire braking forces as well as the brake disk-pad friction coefficient are estimated considering the friction variation between the brake pad and disk. The robust wheel slip control subsystem is designed based on sliding mode control methods and follows the target wheel-slip using the estimated tire braking forces. The proposed sliding mode controller is robust to the uncertainties in estimating the braking force and brake disk-pad friction. The performance of the proposed wheel-slip control system is evaluated in various simulations.

• 자동차안전학회지
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• 제16권3호
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• pp.32-37
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• 2024

Braking judder vibration caused by thermal deformation of disc has been a major problem in brake system for a long time and many researchers have analyzed its mechanisms and developed solutions. However, judder vibration still occurs due to harsher vehicle driving conditions like increased power of EV (Electric Vehicle) and various environmental characteristics. In particular, in the case of eco-friendly vehicles such as EV, it is predicted that judder vibration will become a bigger problem due to the quiet driving condition compared to ICE (Internal Combustion Engine) vehicles. In addition, existing studies on judder vibration have been focused on the capacity and thermal deformation of the braking friction surface. So, the influence analysis of thermal deformation on the non-friction surface of the brake disc is relatively insufficient. In this study, we attempt to secure braking characteristics that are insensitive to thermal deformation in terms of the non-friction surface of the disc, focusing on the coning characteristic that occurs during braking thermal deformation. For this purpose, various factors of the non-friction surface of the disc are analyzed using robust design. The design standard for the robustness of the brake disc against judder vibration is proposed through the research results.

• Journal of Mechanical Science and Technology
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• 제15권11호
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• pp.1490-1498
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• 2001

In this paper, a regenerative braking algorithm is presented and performance of a hybrid electric vehicle (HEV) is investigated. The regenerative braking algorithm calculates the available regenera tive braking torque by considering the motor characteristics, the battery SOC and the CVT speed ratio. When the regenerative braking and the friction braking are applied simultaneously, the friction braking torque corresponding to the regenerative braking should be reduced by decreasing the hydraulic pressure at the front wheel. To implement the regenerative braking algorithm, a hydraulic braking module is designed. In addition, the HEV powertrain models including the internal combustion engine, electric motor, battery, CVT and the regenerative braking system are obtained using AMESim, and the regenerative braking performance is investigated by the simulation. Simulation results show that the proposed regenerative braking algorithm contributes to increasing the battery SOC which results in the improved fuel economy. To verify the regenerative braking algorithm, an experimental study is performed. It is found from the experimental results that the regenerative braking hydraulic module developed in this study generates the desired front wheel hydraulic pressure specified by the regenerative braking control algorithm.

• 한국철도학회논문집
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• 제9권6호
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• pp.677-681
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• 2006

In general, the braking system of high speed train has an important role for the safety of the train. To stop the train safely at its pre-decided position, it is necessary to combine the various brakes properly. The Korean high speed train (HSR-350x) has adopted a combined electrical and mechanical (friction) braking system. In this study, the measuring method that can obtain the disc braking forces and friction coefficient between disc and pad during on-line test of HSR-350x has been suggested and verified through the comparison of the results obtained from this method and those of the results of the dynamo-tests.

• 대한교통학회지
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• 제27권1호
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• pp.43-51
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• 2009

이 논문은 타이어-노면간 마찰계수(drag factor)와 노면에 발생된 스키드마크를 통해 제동직전 속도(pre-braking speed) 산정을 정확하게 하기 위한 방법론을 제시하고자 한다. 제동직전 속도(pre-braking speed)와 활주직전 속도(pre-skidding speed)간 어떠한 상관관계가 있는지 판단하기 위해 실차 주행 및 제동실험을 통해 데이터가 수집되었다. 두 대의 차량에 fifth wheel(오륜) 장비, 스피드건, vericom 2000 등 다양한 측정장비를 탑재하여 제동실험이 수행되었으며, 자동차 속도, 제동거리, 활주거리, 감속도 등이 정밀 측정되었다. 실험자료의 분석을 통해 노면 마찰계수값과 활주직전 속도를 산정하고, 이후 활주직전 속도와 제동직전 속도를 비교하여 이들간의 상관관계를 규명하였다. 결과적으로 산정된 마찰계수값은 현재 일반적으로 적용되고 있는 0.8보다 높았으며, 제동직전 속도는 활주직전 속도보다 $5{\sim}10km/h$ 정도 높은 것으로 나타났다. 향후에는 다양한 차종과 노면조건에 대한 후속실험을 통해 더욱 정교한 한국형 분석모형의 개발과 실무적용이 필요할 것으로 판단된다.

• Tribology and Lubricants
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• 제14권1호
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• pp.70-78
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• 1998

Two different friction materials (organic and low-metallic pads) for automotive brakes were studied to investigate the anti-fading phenomena during stop. The anti-fading phenomena were pronounced more in the case of using low metallic friction materials than organic friction materials. The main cause of the anti-fading phenomena was the high dependence of friction coefficient on a sliding speed. The anti-fading was prominent when the initial brake temperature was high in the case of low-metallic friction materials due to the strong stick-slip event at high temperature. On the other hand, the anti-fading was not severe in organic friction materials and the effect was reduced at high braking temperature due to the thermal decomposition of organic friction materials. The strong stickslip phenomena of low metallic friction materials at high temperature induced high torque oscillations during drag test. During this experiment two different braking control modes (pressure controlled and torque controlled modes) were compared. The type of the control mode used for brake test significantly affected the friction characteristics.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.87-92
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• 2000

In this paper, we investigated the braking performance of a composite brake shoe for power car. Laboratory bench test and field tests were carried out to characterize the braking performance by the parameters such as friction coefficient, wear rate, braking temperature and stopping distance. Density distribution was found to have a significant influence on the wear rate. The composite brake shoe with even density distribution showed better braking performance. The braking performance of a composite brake shoe was also compared with that of a cast iron brake shoe which is currently being used. The result indicated the performance of the composite brake shoe is better than the cast iron brake shoe.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 추계학술대회 논문집(II)
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• pp.779-786
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• 2002

The Friction Brake Pad of High Speed Train is the most important parts in brake system, which is usually made of Cu-based Sintered friction material. This study has been carried out about the formulation effects of sintered friction material and made lots of sample brake pads. Then, we have done the performance test of the developed product by using full scale inertia Dynamo-meter. This performance test (braking speed 300km/h) was conducted as GEC Alsthom Standard test procedure and High Speed Brake Test (braking speed 350km/h) was done at "Poli" in Italy. The friction properties of this product was almost identical with the brake pad which is currently used to TGV. And the temperature of brake disk on braking speed 350Km/h was a little higher.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 추계학술대회 논문집
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• pp.1761-1765
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• 2008

In the braking of a railroad car, mechanical brake systems using wheel tread and brake disk are applied as well as electrical brake systems by regenerator and rheostat. It is very important to consider the frictional characteristic because kinetic energy of the vehicle is dissipated as converted thermal energy through friction between disk and brake pad during disk braking. A friction coefficient and wear characteristic are decided from the interrelationship of disk and friction material in the disk brake system. Lab-scale dynamometer test on developed brake disk materials for increasing heat resistance was performed in this study. Each candidate material was tested at various braking speeds and pressures and we obtained the friction coefficient and wear characteristic. And we executed comparative evaluation of the result from the test.

• Tribology and Lubricants
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• 제18권4호
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• pp.305-311
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• 2002

Three different kinds of brake discs including two coated brake discs and one steel disc were tested under the same experimental conditions on a reduced scale braking test bench. A braking test bench was specially designed to analyse thermo-mechanical and frictional behaviors of two types of brake with different sizes in stop and hold braking modes. Plasma spray coating technique was also used to coat the discs with ceramic powder. During the test four commercial brake pads were coupled with discs. Ceramic coated discs showed good stability in friction coefficient at high speed and high energy braking conditions. But they caused large wear loss of pad mass compared with the steel disc. It was shown that thermal barrier effect in ceramic coated discs adjusted the thermal partition between pad and disc. For a steel disc. it showed fluctuating friction coefficient at high speed but small wear loss of pad mass compared with ceramic coated discs.