Shorter Stopping Distance Research Articles

On the Benefits of Active Aerodynamics on Energy Recuperation in Hybrid and Fully Electric Vehicles

In track-oriented road cars with electric powertrains, the ability to recuperate energy during track driving is significantly affected by the frequent interventions of the antilock braking system (ABS), which usually severely limits the regenerative torque level because of functional safety considerations. In high-performance vehicles, when controlling an active rear wing to maximize brake regeneration, it is unclear whether it is preferable to maximize drag by positioning the wing into its stall position, to maximize downforce, or to impose an intermediate aerodynamic setup. To maximize energy recuperation during braking from high speeds, this paper presents a novel integrated open-loop strategy to control: (i) the orientation of an active rear wing; (ii) the front-to-total brake force distribution; and (iii) the blending between regenerative and friction braking. For the case study wing and vehicle setup, the results show that the optimal wing positions for maximum regeneration and maximum deceleration coincide for most of the vehicle operating envelope. In fact, the wing position that maximizes drag by causing stall brings up to 37% increased energy recuperation over a passive wing during a braking maneuver from 300 km/h to 50 km/h by preventing the ABS intervention, despite achieving higher deceleration and a 2% shorter stopping distance. Furthermore, the maximum drag position also reduces the longitudinal tire slip power losses, which, for example, results in a 0.4% recuperated energy increase when braking from 300 km/h to 50 km/h in high tire–road friction conditions at a deceleration close to the limit of the vehicle with passive aerodynamics, i.e., without ABS interventions.

Fostering Drivers' Trust in Automated Driving Styles: The Role of Driver Perception of Automated Driving Maneuvers.

This study investigated the impact of driving styles of drivers and automated vehicles (AVs) on drivers' perception of automated driving maneuvers and quantified the relationships among drivers' perception of AV maneuvers, driver trust, and acceptance of AVs. Previous studies on automated driving styles focused on the impact of AV's global driving style on driver's attitude and driving performance. However, research on drivers' perception of automated driving maneuvers at the specific driving style level is still lacking. Sixteen aggressive drivers and sixteen defensive drivers were recruited to experience twelve driving scenarios in either an aggressive AV or a defensive AV on the driving simulator. Their perception of AV maneuvers, trust, and acceptance was measured via questionnaires, and driving performance was collected via the driving simulator. Results revealed that drivers' trust and acceptance of AVs would decrease significantly if they perceived AVs to have a higher speed, larger deceleration, smaller deceleration, or shorter stopping distance than expected. Moreover, defensive drivers perceived significantly greater inappropriateness of these maneuvers from aggressive AVs than defensive AVs, whereas aggressive drivers didn't differ significantly in their perceived inappropriateness of these maneuvers with different driving styles. The driving styles of automated vehicles and drivers influenced drivers' perception of automated driving maneuvers, which influence their trust and acceptance of AVs. This study suggested that the design of AVs should consider drivers' perceptions of automated driving maneuvers to avoid undermining drivers' trust and acceptance of AVs.

Ship-stopping algorithm utilizing VecTwin rudder system for automatic collision prevention

In this study, an algorithm for automatic ship stopping in an emergency is developed utilizing a VecTwin rudder system. Timing the emergency stop and determining the stopping capability of the ship equipped with the VecTwin rudder system are critical elements of the proposed stopping algorithm. The dangerous area of collision (DAC) between the ship and other ships is calculated to determine ship emergency stop. The algorithm is constructed such that the ship stops automatically after DAC, which is calculated based on the navigation situation between the own ship and the surrounding other ships, enters the emergency stopping region (ESR). The stopping capability of the subject ship equipped with the VecTwin rudder system was confirmed by a free-running model experiment with ship speeds determined by analyzing actual operational data. To validate the developed algorithm, two collision risk scenarios were selected—coastal navigation and in-port navigation—and simulations and free-running model tests were conducted for each scenario. It was demonstrated that the emergency stop algorithm developed for ships equipped with the VecTwin rudder system can reliably avoid collisions automatically. In addition, it was also confirmed that a shorter stopping distance was achieved than in the case of crash astern emergency stopping.

Probability Based Survey of Braking System: A Pareto-Optimal Approach

Active brake control systems are able to use more accurate control designs on the real-time knowledge of wheel slip such as tire braking forces and external momentums. A multi-objective Pareto type optimization approach is used to evaluate the inconsistent points of the optimization design namely those of minimizing the directional deviation while achieving maximum braking forces on wheels. Moreover, the optimal target slip values defined by the braking purposes like as shorter stopping distance and stability increment by keeping the vehicle in the straight line. This gets by the control of the longitudinal and lateral slip dynamics of each wheel concerning to the road conditions. A controller is optimally brought up by manipulating optimal control law with weights of two control inputs with mathematical and probabilistic characterization. The first-passage probability of critical response levels is used to directly control the vehicle directional stability. An impressive simulation technique based on Monte Carlo method named asymptotic sampling is applied to define the required first-passage probabilities and the Latin Hypercube sampling is used to design of experiments and to cover the design space. Afterwards, a Pareto-type optimization approach is applied to a trade-off between the inconsistent points of the optimization design. The simulation is conducted by the validated vehicle model and the results are indicated that the probability-based control design is represented as a preferable braking performance in comparison with the other systems for braking in sever conditions.

Modelling of automatic car braking system using fuzzy logic controller

The increasing rate of road accident is alarming and any vehicle without an effective brake system is prone to accident with apparently disastrous effect following. This is due to human errors in driving which involves reaction time delays and distraction. Automatic braking system will be developed to keep the vehicle steerable and stable and also prevent wheel lock and collision with an obstacle. The objectives of this study are to: design an obstacle detection model using ultrasonic sensors, model an antilock braking system, develop fuzzy logic rules for both detection and antilock braking system, and simulate the developed model using Simulink in MATLAB software to achieve high braking torque, optimal slip ratio and shorter stopping distance and time. The results show 22% improvement in braking torque thereby giving a shorter stopping time and distance when compared to the normal PID control. Keywords: Slip ratio, Model, Ultrasonic Sensor, Antilock Braking System, Fuzzy logic, wheel lock

Comparison of braking performance between mechanical and dynamic braking for Electric Powered Wheelchair

Braking is the necessary system need to install as the safety feature for the moving transportation. Using the mechanical braking only as primary braking system in Electric Transportation (ET) is insufficient due to some issues such as low strength users hand gripping and abruptly tire locking during braking especially on wet surface condition. In this paper, the performance between mechanical and electrical braking which is by using dynamic braking concept is proposed to enhance the braking performance of Electric Powered Wheelchair (EPW). The experiments were conducted during descending on the slope under wet and dry pavements. From the results of slip ratio, the slipping time between mechanical and dynamic braking in dry pavement is recorded 0.9 seconds and 0.7 seconds respectively. Meanwhile, it is observed that tire is fully locked-up for mechanical braking under the wet surface. However, by using the dynamic braking, the wheel does not lock-up and the slipping time was recorded 1.4 seconds. It can be considered that, mechanical and dynamic braking give their own merit. The high braking torque from mechanical braking is suitable to use under the dry pavement for the short stopping distance. The other sides, braking under the wet pavement, dynamic braking is more efficient compare to the mechanical braking in term of short slipping time and does not cause tire to lock-up while braking.

Driving at night with a cataract: Risk homeostasis?

Driving with a cataract can be dangerous, especially at night when road lighting and automotive lighting produce glare. Disability glare alters visual performance, while discomfort glare contributes to restricted mobility, with drivers avoiding driving at night. The present study was focused on the visual effects of an early cataract, and aimed at comparing three driving performance indexes at night, under glare conditions, with and without a simulated cataract. Two indexes directly referred to road safety, while a measure could be related to behavioral adaptation.Using a driving simulator, twenty-six participants were asked to drive in simulated night-time conditions, under controlled photometric conditions where the adaptation luminance and the glare level were consistent with a two-lane rural road at night with oncoming traffic. The visual effects of a bilateral cataract were simulated using goggles which were in the range of an early cataract in terms of light scattering, light transmission, visual acuity and contrast sensitivity loss. Participants were asked to avoid virtual pedestrians on the road, both with and without a simulated cataract. Three performance indexes were considered: the rate of pedestrian crashes, the distance to the pedestrian when the participant avoided the crash, and the mean speed, which allowed to control for a possible behavioral adaptation to the reduced visual performance. For a better understanding of the visual functions responsible for the degraded driving behavior, contrast sensitivity and time-to-collision performance were also measured in glare conditions.While simulated cataract resulted in slightly slower speeds, poorer driving performance was observed with the goggles than without, with more pedestrians being hit and shorter stopping distances. Time-to-collision estimates at 90 km/h were found to be predictive of stopping distances with a simulated cataract, while contrast sensitivity in glare conditions at 13 cycles per degree was found to be associated with the occurrence of a crash with cataract.The decrease in speed with a simulated cataract was real but ineffective in terms of driving safety, which suggests that the behavioral adaptation to the degraded visual performance was insufficient. The precise impact of a cataract on driving abilities remains to be further studied, to provide scientific knowledge to help practitioners determine the moment when the individuals should forego driving.

Fuzzy Scheduled Optimal Control of Integrated Vehicle Braking and Steering Systems

The safe hard braking of a turned vehicle requires short stopping distance while maintaining the vehicle in the path. To achieve the first aim, a wheel slip controller is designed to calculate the maximum braking force of each wheel according to the tire/road conditions. For the second aim, a new optimal multivariable controller for integrated active front steering and direct yaw moment control is analytically developed to control the vehicle directional stability directly. Since the required stabilizing external yaw moment has to be produced by reducing the maximum achievable braking forces of one side wheels, it leads to increase the stopping distance and should be kept as low as possible. In an effective way to manage the integrated control inputs, a fuzzy logic is defined to determine the weight factor of each control input in the integrated optimal control law. This logic is defined using the stability index obtained by the phase plane analysis of nonlinear vehicle model. Therefore, the proposed controller can be tuned automatically for different driving conditions. The simulation results carried out using a validated vehicle model demonstrate that the integrated control system has a better performance compared with stand-alone braking and steering systems to attain the desired purposes.

Model-based braking control of a heavy commercial road vehicle equipped with an electropneumatic brake system

Heavy commercial road vehicles have a longer stopping distance, owing to the inherent time lag associated with the conventional air brake system used in them. In general, electropneumatic brake systems would respond more quickly, resulting in a shorter stopping distance; these are the focus of this study. In an earlier work, the best configuration of the electropneumatic brake system was determined, considering both response and cost perspectives. This study focuses on the development of an experimentally corroborated mathematical model for this brake system. Non-linear model-based deceleration and brake chamber pressure control schemes were subsequently developed and their performance evaluated using a hardware-in-loop system. The model-based analysis and the control schemes presented in this article will assist in the development of advanced and cost-efficient active safety systems for heavy commercial road vehicles.

Incorporating Braking Distance Evaluation into Pavement Management System for Safe Road Operation

Maintaining a sufficiently short stopping distance is an important requirement for safe road operation. Stopping sight distances of road sections are decided during the highway alignment and roadway geometric design phase of the road development process. A pavement friction coefficient is used in the calculation of the stopping distances. Since pavement friction coefficient deteriorates with time under traffic action, and the available friction also reduces in wet weather, it is important for pavement maintenance engineers to ensure that sufficient skid resistance is maintained under actual operating conditions so that the stopping distances of road sections are less than the required safe stopping distance. This result requires pavement engineers to monitor regularly the available pavement skid resistance and the corresponding stopping distance of individual road sections. Because skid resistance is an accepted pavement condition to be measured in a pavement management system, it is proposed in this study that braking distance assessment be included as a part of the pavement condition monitoring program of a pavement management system. The proposed procedure consists of two parts: ( a) measurement of skid resistance and evaluation of braking distance and stopping distance and ( b) monitoring of the deterioration trends of individual road sections. The detailed procedure and the analytical tools necessary for the evaluation and prediction of braking and stopping distances, including a finite element skid resistance simulation model, are presented. A numerical example is presented to illustrate the concept and working of the proposed procedure.

A Highly Efficient and Reliable Power Scheme Using Improved Push-Pull Forward Converter for Heavy-Duty Train Applications

Electronically controlled pneumatic (ECP) brake systems have become popular in heavy-duty train applications because of their advantages, which include shorter stopping distances, improved handling, and less brake-shoe and wheel wear. In ECP brake systems, an improved power supply is required to support efficient and reliable operations. In this paper, we propose a new power converter for ECP brake systems, which is derived from a conventional push-pull converter. As opposed to conventional push-pull converters, we insert a clamping capacitor into the proposed circuit. This clamping capacitor simultaneously enables a greater number of operation modes for the proposed converter and absorbs the voltage spikes in the switch. The proposed converter is more suited for ECP brake applications that require high power, low voltage ripple, and high impedance. We theoretically analyze the proposed converter, and present the design guidelines. Further, we discuss the modeling and control aspects. We demonstrate the operations of the proposed model by performing both simulations and experiments.

Estimation of tire–road friction coefficient and its application in chassis control systems

Knowledge of tire–road friction conditions is indispensable for many vehicle control systems. In particular, friction information can be used to enhance the performance of wheel slip control systems, for example, knowledge of the current maximum coefficient of friction would allow an anti-lock brake system (ABS) controller to start braking with the optimal brake pressure, meaning the early cycles of operation are more efficient, resulting in shorter stopping distances. Also, from a passive safety perspective, it may be useful to present the driver with friction information so they can adjust their driving style to the road conditions. Hence, it is highly desirable to estimate friction using existing onboard vehicle sensor information. Many approaches for estimating tire–road friction estimation have been proposed in the literature with different sensor requirements and relative excitation levels. This paper aims at estimating the tire–road friction coefficient by using a well-defined model of the tire behavior. The model adopted for this purpose is the physically based brush tire model. In its simplest formulation, the brush model describes the relationship between the tire force and the slip as a function of two parameters, namely, tire stiffness and the tire–road friction coefficient. Knowledge of the shape of the force–slip characteristics of the tire, possibly obtained through the estimation of both friction and tire stiffness using the brush model, provides information about the slip values at which maximum friction is obtained. This information could be used to generate a target slip set point value for controllers, such as an ABS or a traction control system. It is also important to realize that a model-based approach is inherently limited to providing road surface friction information when the tire is exposed to an excitation with high utilization levels (i.e. under high-slip conditions). To be of greatest use to active safety control systems, an estimation method needs to offer earlier knowledge of the limits. In order to achieve the aforementioned objective, an integrated approach using an intelligent tire-based friction estimator and the brush tire model-based estimator is presented. An integrated approach gives us the capability to reliably estimate friction for a wider range of excitations (both low-slip and high-slip conditions).

Braking Performance of a Biomimetic Squid-Like Underwater Robot

In this study, the braking performance of the undulating fin propulsion system of a biomimetic squid-like underwater robot was investigated through free run experiment and simulation of the quasi-steady mathematical model. The quasi-steady equations of motion were solved using the measured and calculated hydrodynamic forces and compared with free-run test results. Various braking strategies were tested and discussed in terms of stopping ability and the forces acting on the stopping stage. The stopping performance of the undulating fin propulsion system turned out to be excellent considering the short stopping time and short stopping distance. This is because of the large negative thrust produced by progressive wave in opposite direction. It was confirmed that the undulating fin propulsion system can effectively perform braking even in complex underwater explorations.

Effects of Communications-Based Train Control and Electronically Controlled Pneumatic Brakes on Railroad Capacity

Railroads are increasingly using new technologies to improve capacity and operating efficiency. To plan their investments and prepare for the implementation of these technologies, railroads must understand their net effect on operations. This requires understanding both the particular aspects of these technologies that affect capacity and the characteristics of the systems into which they are being introduced. Two important technologies in this regard are communications-based train control (CBTC) and electronically controlled pneumatic (ECP) brakes. Each element of CBTC and ECP brakes with the potential to affect capacity was identified, and its effect under various implementation scenarios was evaluated. The potential impact of each element was assessed and compared with the various baseline conditions and conventional technologies to understand the incremental effect. An extensive review of the literature on the subject was conducted in support of these evaluations. CBTC implementation with enforcement braking will generally result in a loss of capacity, but as these systems become more fully integrated, the potential for capacity enhancement improves. ECP brakes will provide benefits under most operational scenarios because of the shorter braking distances and thus the potential for the closer spacing of trains. The two technologies have a potential interactive effect: CBTC may make it possible to more effectively take advantage of one of the principal benefits of ECP brakes: shorter stopping distances. The results for either technology will be route and network specific, so individual railroads will need to conduct analyses to understand the net effect on the capacity of their systems.

Straight-line braking dynamic analysis of a partly filled baffled and unbaffled tank truck

The straight-line braking performance characteristics of a partly filled tank truck with and without transverse baffles are investigated in the presence of transient fluid slosh within the tank. The dynamic interactions of the floating cargo with the vehicle are evaluated by integrating a dynamic fluid slosh model of the partly filled tank with and without transverse baffles with the seven-degrees-of-freedom pitch plane model of a tridem truck. The dynamic fluid slosh within the tank containing equally spaced four curved single-orifice baffles with flow equalizer is modelled using three-dimensional Navier—Stokes equations coupled with the volume-of-fluid equation and analysed using the FLUENT software. The coupled tank—vehicle model is subsequently analysed to determine the straight-line braking properties for different fill volumes, magnitudes of braking treadle pressure, and road surface adhesion coefficients, while the cargo load is considered to be constant. The results show interactions of the sloshing cargo with the vehicle. A degradation of the braking performance of the partly filled tank truck is evident in the presence of transient fluid slosh, particularly in the absence of baffles. The braking performance, however, is highly dependent upon the fill volume, presence of baffles, and severity of braking input. For a clean-bore tank truck, the stopping distance increases monotonically with decreasing fill volume, while the addition of transverse baffles in general results in considerably shorter stopping distance. The baffled tank truck, however, reveals a relatively shorter stopping distance under an intermediate fill condition (approximately 52.1 per cent), compared with the lower and higher fill volumes. Although the analyses are limited to conventional single-orifice baffles, the proposed coupled vehicle—tank model could serve as an important tool for exploring alternative baffle designs and layouts.

Assessing the validity of road safety evaluation studies by analysing causal chains

This paper discusses how the validity of road safety evaluation studies can be assessed by analysing causal chains. A causal chain denotes the path through which a road safety measure influences the number of accidents. Two cases are examined. One involves chemical de-icing of roads (salting). The intended causal chain of this measure is: spread of salt → removal of snow and ice from the road surface → improved friction → shorter stopping distance → fewer accidents. A Norwegian study that evaluated the effects of salting on accident rate provides information that describes this causal chain. This information indicates that the study overestimated the effect of salting on accident rate, and suggests that this estimate is influenced by confounding variables the study did not control for. The other case involves a traffic club for children. The intended causal chain in this study was: join the club → improve knowledge → improve behaviour → reduce accident rate. In this case, results are rather messy, which suggests that the observed difference in accident rate between members and non-members of the traffic club is not primarily attributable to membership in the club. The two cases show that by analysing causal chains, one may uncover confounding factors that were not adequately controlled in a study. Lack of control for confounding factors remains the most serious threat to the validity of road safety evaluation studies.

An In Situ Comparison between VUV Photon and Ion Energy Fluxes to Polymer Surfaces Immersed in an RF Plasma

Absolutely calibrated vacuum ultraviolet (VUV) spectroscopy has been used to determine the energy fluxes of VUV photons at an electrically floating substrate in a low-pressure 13.56-MHz radiofrequency plasma reactor used for polymer surface treatments. These fluxes have been compared with the positive ion flux that was reported in an earlier study. At the typical operating parameters of 10-mTorr pressure and 10-W power, the total VUV energy flux is 2.2 mW cm-2, compared with a value of 3.3 mW cm-2 from the ions. With increasing power (from 0.5 to 12 W), both the ion and VUV energy fluxes increase monotonically. However, as the pressure increases, (1−100 mTorr), the ion energy flux declines, while the VUV component increases. At discharge powers of 10 W, and pressures greater than 25 mTorr, the greater part of the energy flux to the surface is from the VUV photons. These measurements are used to determine which of the plasma components, VUV or ions, will be most effective in the treatment of polystyrene surfaces in a pure Ar plasma. Because of the low VUV absorption coefficient of polystyrene most of the photon flux penetrates through the outermost 2 nm of the polymer surface without attenuation. Consequently, we calculate that under typical plasma operating parameters, the ions play the major role in the modification of polystyrene surfaces because of their shorter stopping distances.

Investigation of the Influence of Various Braking Regulations on Accident-Avoidance Performance

Passenger car braking regulations promulgated by the United States and various European countries are analyzed to determine the incompatibilities in brake proportioning that derive from the performance requirements of the regulations. Two vehicles, one produced in the U.S. and the other in Europe, with extreme loading conditions (as derive from option selection and vehicle loading) were considered. The analysis shows that the European regulations require a larger forward bias in brake proportioning than FMVSS 105-75. Computer simulations were used to predict the differences in braking performance which result from proportioning the example vehicles to comply with the different regulations. Conditions of straight-line braking, braking in a turn, and three surface friction levels were considered. In general, both vehicles were capable of achieving shorter stopping distances when proportioned to meet FMVSS 105-75 than when proportioned to comply with the European regulations, but the differences were small and could be considered trivial when a car is driven by an ordinary driver. When proportioned to meet FMVSS 105-75, the rear wheels of the two study cars sometimes locked up first, a result that the European regulations are designed to prevent. Braking-in-a-turn test procedures (which have been discussed both in the U.S. and abroad) were also studied through computer simulations and found to be relatively insensitive to the fore-aft proportioning of brake torques.