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Technical Paper

Coordinated Control under Transitional Conditions in Hybrid Braking of Electric Vehicle

2018-10-05
2018-01-1869
In the hybrid brake system of electric vehicle, due to the limitation of the motor braking force when the motor is at high speed and the failure of the regenerative braking force when the motor is at low speed, there are three transitional conditions in hybrid braking: the hydraulic brake system intervenes the braking, the hydraulic brake system withdraws the braking and the regenerative braking force withdraws the braking. Due to the response speed of the hydraulic system is slower than that of the motor, there is a large braking impact (the derivative of braking deceleration) in the transitional conditions of hybrid braking, which deteriorates the smoothness and comfort in braking. Aiming at the impact caused by the poor cooperation between the hydraulic braking force and the motor braking force, a coordinated strategy of double closed-loop feedback and motor force correction is proposed in this paper.
Technical Paper

Correlation of Objective and Subjective Evaluation in Automotive Brake Pedal Feel

2018-10-05
2018-01-1889
In order to establish the correlation between objective and subjective evaluation of brake pedal feel for passenger cars, road tests of brake pedal feel were carried out and an evaluation method was proposed. In the road tests, subjective scores and objective measurements were obtained under the conditions of uniform and emergency braking. The objective measurements include pedal preload, low deceleration pedal force and travel, moderate deceleration pedal force and travel, brake response time and brake linearity. Using the theory of analytic hierarchy process (AHP), the design process of the evaluation method was established. Key setups including the hierarchical structure model, the judgement matrix and the score calculation method of objective measurements were described in detail. Then, the correlation between subjective and objective scores was analyzed. It can be concluded that the evaluation method is effective and it can be applied to brake pedal feel assessment and adjustment.
Technical Paper

Open-Loop Characteristics Analysis and Control of High Speed On-Off Valve

2018-10-05
2018-01-1868
In the process of ABS control, the Anti-lock braking system (ABS) of the vehicle adjusts the wheel cylinder brake pressure through the hydraulic actuator so as to control the movement of the wheel. The high-speed on-off valve (HSV) is the key components of the Anti-lock braking system. HSV affects the performance of the hydraulic actuator and the valve response characteristics affects the Anti-lock braking system pressure response as well as braking effect. In this paper, the electromagnetic field theory and flow field theory of HSV are analyzed, and simulation analysis of electromagnetic field characteristics of HSV is done by ANSYS. Combined with the ANSYS analysis results, a precise physical model of HSV is constructed in AMESim. Meanwhile, the valve response characteristics are analyzed. Moreover, the influence of different wheel cylinder diameter and PWM carrier frequency on hydraulic braking force characteristics are analyzed.
Technical Paper

Study on Brake Disc Dynamics under Asymmetric Thermal Loads

2018-10-05
2018-01-1901
In order to explore the generation mechanism of hot-spots on the automotive brake disc, disc tests under non-frictional thermal loads are carried out on the brake dynamometer test bench. In the tests, the oxy-acetylene flame is used as the heat source, and the distribution characteristics of the disc temperature and displacement are measured and analyzed. To confirm the mechanism of the disc deformation, a disc thermal buckling model using finite element method is established, and the key factors for the disc thermal buckling under thermal loads are further analyzed. It is found that the temperature circumferential gradient is small but the temperature radial gradient is large. The disc presents waviness deformation mode with 5th order in circumferential direction, which is the first thermal buckling mode of the disc. A method using spatial frequency spectrum has been proposed to find the critical time and load of thermal buckling.
Technical Paper

Precise Steering Angle Control of Lane Change Assist System

2017-09-23
2017-01-2002
After obtaining the optimal trajectory through the lane change decision and trajectory planning, the last key technology for the automatic lane change assist system is to carry out the precise and rapid steering actuation according to the front wheel angle demand. Therefore, an automatic lane change system model including a BLDCM (brushless DC motor) model, a steering system model and a vehicle dynamics model is first established in this paper. Electromagnetic characteristics of the motor, the moment of the inertia and viscous friction etc. are considered in these models. Then, a SMC (Sliding Mode Control) algorithm for the steering system is designed to follow the steering angle input. The control torque of the steering motor is obtained through the system model according to steering angle demand. After that, the control current is calculated considering of electromagnetic characteristics of the BLDCM. Debugging and optimization of the control algorithm are done through simulations.
Technical Paper

The Trajectory Planning of the Lane Change Assist Based on the Model Predictive Control with Multi-Objective

2017-09-23
2017-01-2004
The automatic lane change assist system is an intelligent driving assistance technology oriented to traffic safety, which requires trajectory planning of the lane change maneuver based on the lane change decision. A typical scene of lane change for overtaking is selected, where the front vehicle in the same lane and the rear vehicle in the left lane are deemed to be potential dangerous vehicles through the lane change. Lane change trajectory equation is first established according to the general law of steering wheel angle through lane changes. Based on the relative position, velocity and acceleration information of the dangerous vehicles and the lane change vehicle, motions of these surrounding dangerous vehicles are predicted. At the same time, a multi-objective optimization function is established based on the relative longitudinal safety boundary. The objectives are the minimum safety distance, the lane change time and the front wheel angle.
Technical Paper

Control Optimization of a Compound Power-Split Hybrid Transmission for Electric Drive

2015-04-14
2015-01-1214
A novel compound power-split hybrid transmission based on a modified Ravigneaux gear set is presented. The equivalent lever diagrams are used to investigate the electric operating modes for the hybrid powertrain, and then its dynamic and kinematic characteristics as well as efficiency characteristics are described in equations. A brake clutch mounted on the carrier shaft is proposed to enhance the electric driving efficiency for the hybrid transmission. Three types of electric operating mode are analyzed by the simplified combined lever diagrams and the system efficiency and torque characteristics for these electric operating modes are compared. A major influence on output torque of the hybrid transmission derived from the torque capability of motors and brake clutch is depicted.
Technical Paper

Mechanism Study on Time-Varying Characteristics of Frictional Squeal in Pin-on-Disc System

2014-09-28
2014-01-2517
Disc brake squeal has always been a great challenge to the automotive industry. Based on the pin-on-disc system, a series of frictional squeal bench tests are carried out, which show significant time-varying characteristics on occurrence, sound pressure and frequency of frictional squeal. To investigate the generation mechanism of time-varying characteristics of frictional squeal, a four-degree-of-freedom (4DOF) lumped parameter model considering the time-varying tangential contact stiffness, the normal contact stiffness and the friction coefficient is established in this paper. Through both the system stability analysis and the transient response analysis, the time-varying frictional squeal is predicted successfully, and the generation mechanism and the key impact factors are also investigated in depth.
Technical Paper

Analysis and Design of Dual-Motor Electro-Hydraulic Brake System

2014-09-28
2014-01-2532
In this paper, by analyzing multiple electro-hydraulic brake system schemes in detail, the idea of dual-motor electro-hydraulic brake system is proposed. As a new solution, the dual-motor electro-hydraulic brake system can actively simulate pedal feel, make the most of pedal power (from the driver), and reduce the maximum power output of each active power source remarkably, which is a distinctive innovation compared to most current electro-hydraulic brake systems. Following the proposed concept, a general research thought and method is conceived, and then a dual-motor electro-hydraulic brake system is designed. Finally, the simulation model is set up in AMESim software and its feasibility is simulated and verified.
Journal Article

The Influence of Vacuum Booster Design Parameters on Brake Pedal Feel

2014-09-28
2014-01-2499
Brake pedal feel characteristic is determined by the structural and kinetic parameters of the components of the brake system. As the servo power component of the brake system, vacuum booster has a significant influence on the brake pedal feel. In this paper, a brake system model for brake pedal feel which has a detail vacuum booster mathematical description is established in the software MATLAB/Simulink. The structure gaps, spring preload, friction force and reaction disc characteristics of vacuum booster are considered in this model. A brake pedal feel bench test under different input velocity and vacuum pressure is completed in order to validate the prediction of the model.
Journal Article

Prediction of Temperature Field Inside Lithium-Ion Battery Based on Similarity Theory

2014-04-01
2014-01-1841
To accurately and efficiently predict the temperature fields inside a lithium-ion battery is key technology for the enhancement of battery thermal management and the improvement of battery performances. The dimensional analysis method is applied to derive similarity criterions and the similarity coefficients of battery interior temperature fields, based on the governing partial differential equations describing the three dimensional transient temperature field. To verify the correctness of similarity criterions and the similarity coefficients, 3D finite element models of battery temperature field are established with a prototype and scale model, on the assumption that the battery cell has single-layer structure and multi-layers structure separately. The simulation results show that the similarity criterions and the similarity coefficients are correct.
Journal Article

Torque Vectoring Control for Distributed Drive Electric Vehicle Based on State Variable Feedback

2014-04-01
2014-01-0155
Torque Vectoring Control for distributed drive electric vehicle is studied. A handling improvement algorithm for normal cornering maneuvers is proposed based on state variable feedback control: Yaw rate feedback together with steer angle feedforward is employed to improve transient response and steady gain of the yaw rate, respectively. According to the feedback coefficient's influence on the transient response, an optimization function is proposed to obtain optimum feedback coefficients under different speeds. After maximum feedforward coefficients under different speeds are obtained from the constraint of the motor exterior characteristic, final feedforward coefficients are calculated according to an optimal steering characteristic. A torque distribution algorithm is presented to help the driver to speed up during the direct yaw moment control.
Journal Article

Strain Rate Effect on Forming Limit Diagram for Advanced High Strength Steels

2014-04-01
2014-01-0993
The Forming limit diagram (FLD) is a powerful tool for describing the formability of sheet materials in the automobile industry, which provides fundamental data for die design and Finite Element (FE) simulation. However, traditional FLD testing is typically conducted at quasi-static strain rates from 0.001/s to 0.01/s, which are much lower than the industrial stamping process with strain rates about 1-10/s. In this research, FLDs at various punch speeds (from 1mm/s to 100mm/s or 120mm/s) were obtained for three kinds of AHSS, Quenched and Partitioned steel, Dual Phase 980 and Dual Phase 590 and three kinds of conventional steels, Low Alloy High Strength steel, Bake Hardening steel and IF steel. The results show that FLDs at a typical industrial stamping speed (100mm/s or 120mm/s) are considerably lower than the quasi-static test speed for the Advanced High Strength Steels (AHSS).
Technical Paper

Evaluation of Global and Local Deformation Behaviors of Similar Laser Welded Joints using Digital Image Correlation

2014-04-01
2014-01-0832
Similar laser welded blanks with same material and same gauge have been extensive applied in automobile body for improving the material utilization and extending maximum coil size. It is known that, for TWBs with dissimilar material and thicknesses, the difference of material properties and/or thickness of the welded blanks, change of the material properties in the weld seam and heat-affected zones (HAZ) as well as location and orientation of the weld seam are reasons for reduced formability. However, the plastic deformation capacity of TWBs is reduced even when the material and thickness are the same. The aim of this paper is to evaluate the deformation behaviors of similar laser welded joints. Uniaxial tensile of five laser welded joints, with 90°,60°,45°,30°and 0°weld orientations, were tested by using optical measurement-DIC (Digital Image Correlation). Strain /strain ratio distribution and evolution of each joint was analyzed and compared with base material.
Technical Paper

Numerical Investigation of Air Purifier Affecting Ultrafine Particle Transport in Vehicle Cabins

2014-04-01
2014-01-0682
Air purifier has been prevalently used in the passenger vehicle cabins to reduce in-cabin UltraFine Particle (UFP) concentration. In this study, Computational Fluid Dynamics (CFD) was applied to simulate the in-cabin UFP transport and distribution under different ventilation modes with different characteristics of the air purifier. Ventilation settings, air purifier settings, and air purifier location were identified as the important factors determining the in-cabin UFP distribution and transport. Downward ventilation airflow direction and smaller ventilation air velocity can be considered by the drivers for a lower in-cabin UFP concentration. Upward airflow direction from the air purifier's inlet and larger air velocity were recommended since it led up to 50% in-cabin UFP reduction. Air purifier installed at middle ceiling of the cabin develops the most efficient airflow for UFP removal.
Technical Paper

Study of the Combustion and Emission Characteristics of a Quasi ICRC Engine Under Different Engine Loads

2014-04-01
2014-01-1202
A novel reciprocating engine version of oxy-fuel combustion cycle combined with water direct injection (known as internal combustion rankine cycle) is presented in this paper. Water is injected near top dead center to control the reaction rate of the oxy-fuel mixture, as well as the peak in-cylinder temperature. The evaporation of the water mist will increase the mass of working gas inside the cylinder, and enhances the thermo efficiency and MEP. Moreover, the injected water is heated up through heat exchangers by both engine coolant and exhaust gas, and the waste heat is effectively recovered this way. This study investigates the combustion and emission characteristics of ICRC under different engine loads based on a single-cylinder, air-cooled SI engine fueled with propane. An extra diesel injector is employed to inject water with high injection temperature (160°C).
Technical Paper

Hybrid Brake System Control Strategy in Typical Transient Conditions

2014-04-01
2014-01-0267
The control in transient conditions when hydraulic brake and regenerative brake switch mutually is the key technical issue about electric vehicle hybrid brake system, which has a direct influence on the braking feel of driver and vehicle braking comfort. A coordination control system has been proposed, including brake force distribution correction module and motor force compensation module. Brake force distribution correction module has fixed the distribution results in hydraulic brake force intervention condition, hydraulic brake force evacuation condition and regenerative brake force low speed evacuation condition. Motor compensation module has compensated hydraulic system with motor system, which has fast and accurate response, thus the response of whole hybrid system has been improved.
Technical Paper

Study on Statistical Analysis of Uncertainty of Disc Brake Squeal

2014-04-01
2014-01-0030
Brake squeal shows a significant uncertainty characteristic. In this paper, a series of bench tests were carried out to study the uncertainty of brake squeal on a multi-function brake inertia dynamometer test bench. Then based on time-frequency analysis results, a creative squeal confirmation and determination method was presented, which can show the squeal variations in the domains of time, frequency and amplitude together. An uncertainty analysis method was also established, in which the statistical parameters of squeal frequency and sound pressure level (SPL), and probability density evaluation of frequency based on Quantile-Quantile Plot (QQ plot) were given. And a judgment method of the frequency doubling was devised based on numerical multiple and occurrence concurrence, as well as the uncertainty statistical analysis method considering frequency doubling. All the methods established were applied to the uncertainty analysis of brake squeal.
Technical Paper

Fatigue Design and Analysis of the Vehicle Exhaust System's Hanger

2013-10-14
2013-01-2609
The weight of an exhaust system on a modern vehicle is increasing because of all kinds of reasons, like engine power's increasing, more catalysts for emission control and more NVH (Noise, Vibration and Harshness) performance requirements. After the engine starting, the exhaust system was not only bearing a cyclical load from the engine, which mainly causing the vibration of the exhaust system, but also the loads from the road, which was transferred through the wheels, the suspension system and the body. Because the exhaust system always worked in these bad conditions, its structural strength, durability and life-time were analyzed in the paper, by numerical simulation and physical correlation. By discretizing the exhaust system's CAD model, a finite element model was built. After restrict the finite element model as it in a real load condition, complete the structure stress analysis and Fatigue analysis of exhaust system's hanger with FEA analysis tools.
Technical Paper

On Chaos and Bifurcation in Nonlinear Driver-Vehicle System Probabilistic Dynamics

2012-04-16
2012-01-0522
The vehicle system is actually a strongly nonlinear system with stochastic parameters. In this paper, the nonlinearities of suspension, tire and seat are analyzed, and the nonlinear dynamics model of driver-vehicle system with 8 degrees of freedom (DOFs) is built. The bifurcation and chaotic motion of the deterministic system under Sinusoid excitations considering the time delay between the front and rear tires are studied. Then, the stochastic feature of the equivalent stiffness and damping coefficients of suspension, tire and seat are assumed to be the normal distribution, and the nonlinear model with random parameters is obtained. The nonlinear dynamics of stochastic nonlinear driver-vehicle system is analyzed and compared through numerical simulation.
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