Aerodynamic Forces Impact on Vehicle Braking Longitudinal Dynamics with a Sliding Mode Controller

This paper presents a novel piezoactuator-based valve for vehicle ABS. The piezoactuator located in one side of a rigid beam makes a displacement required to control the pressure at a flapper-nozzle of the pneumatic valve. In order to obtain the wide control range of the pressure, a pressure modulator comprised of dual-type cylinder and piston is proposed. The governing equation of the piezovalve system which consists of the proposed piezoactuator-based valve and the pressure modulator is obtained. The longitudinal vehicle dynamics and the wheel slip condition are then formulated. In order to evaluate the performance of the proposed piezovalve system from the viewpoint of the vehicle ABS, a sliding mode controller is designed for wheel slip control. The tracking control performances for the desired wheel slip rate are evaluated and the braking performances in terms of braking distance are then presented on different road conditions (dry asphalt, wet asphalt, and wet jennite). It is clearly shown that the desired wheel slip rate is well achieved and the braking distance and braking time can be significantly reduced by using the proposed piezovalve system associated with the slip rate controller.

<div class="section abstract"><div class="htmlview paragraph">The longitudinal dynamics control is an essential task of vehicle dynamics control. In present, it is usually applied by adjusting the slip ratio of driving wheels to achieve satisfactory performances both in stability and accelerating ability. In order to improve its performances, the coordination of different subsystems such as engine, transmission and braking system has to be considered. In addition, the proposed algorithms usually adopt the threshold methods based on less road condition information for simpleness and quick response, which cannot achieve optimal performance on various road conditions.</div><div class="htmlview paragraph">In this paper, an integrated longitudinal vehicle dynamics control algorithm with tire/road friction estimation was proposed. First, a road identification algorithm was designed to estimate tire forces of driving wheels and the friction coefficient by the method of Kalman Filter and Recursive Least Squares (RLS). Then, a rule based integrated control algorithm which coordinate the engine torque control, brake pressure control and transmission shifting control was built to improve the vehicle driving performance.</div><div class="htmlview paragraph">During the longitudinal dynamics control procedure, the transmission shifting control algorithm firstly decided whether the vehicle starting up at the 1st or the 2nd gear based on the road condition. Then, the engine torque control algorithm was applied to adjust the slip ratio of driving wheels. Its process was divided into three phases. In each phase, different control rules with integration of engine torque and brake torque were set by the combined feed forward and feedback methods to meet with requirements of accuracy, rapidity and stability. The brake pressure was determined by method of sliding mode control (SMC) for its rapid adjustment characteristic, in the meanwhile, it was also an important component to be considered in engine torque feedback control.</div><div class="htmlview paragraph">Finally, the algorithm was verified by using Matlab/Simulink and CarSim co-simulation, the results show that the proposed control algorithm could regulate slip ratios of driving wheels fast and accurately, and the vehicle driving performance could be improved effectively.</div></div>

Estimating vehicle braking distance over wet and rutted pavement surface through back-propagation neural network

The problem of estimating brake pad wear of cars has been considered, using friction work approximated from the product of longitudinal braking force and distance travelled during braking. The braking force is estimated from a longitudinal dynamics model with inputs from an inertial measurement sensing unit with Kalman filter based sensor fusion, and standard vehicle on-board diagnostics data. Wear coefficients are fitted with Bayesian linear regression on measurements from two series: (I) 16 measurements of previously worn pads over approx. 4,800 km with average wear of approx. -0.5 mm and (II) seven measurements of almost new pads over approx. 1,850 km and approx. -0.15 mm of wear. The approximated friction work appears to correlate well with the wear. The wear coefficients converge quickly after just 4-5 measurements. Coefficients ranging from −4.95⋅10−5mm3/J to −2.08⋅10−5mm3/J are obtained across the cases, when assuming a coefficient of friction μ=0.6 obtained through pin-on-disc (POD) tests. The wear coefficients are validated using POD tests, showing good agreements with the indirectly estimated wear coefficients from vehicle longitudinal dynamics. Data from series (II) is used for prediction of remaining useful life (RUL), where one additional measurement is carried out after 16,552 km. The RUL prediction requires knowledge of the relationship between usage feature and distance travelled. Different approaches are investigated for the predictions: wear based on only distance travelled, linear relationship between usage feature and distance, and three levels of braking severity based on the usage data. Four of the approaches underestimate the distance significantly at around 4,000 to 8,000 km against the actual distance of 16,552 km, while the low severity estimate is closest at 20,460 km, agreeing with expectations due to the driving being primarily on highways.

<div class="htmlview paragraph">This paper presents an atomization mechanism of a spray injected into the low-pressure field, as the subject of injection system in a suction manifold of gasoline engine. Pure liquid fuel, which is n-Pentane or n-Hexane is injected into quiescent gaseous atmosphere at room-temperature and low- pressure through pintle type electronic control injector. Fuel sprays are observed by taking photographs for variation of the back pressure and the changes in spray characteristics with the back pressure below atmospheric pressure are examined in detail. In particular, in the case of the back pressure below the saturated vapor pressure of fuel, the atomization mechanism is discussed from a viewpoint of flash boiling phenomena, those are bubble growth rate and so on. The results show that the saturated vapor pressure of fuel is the most significant factor and the spray characteristics can be arranged with the pressure difference between the back pressure and the saturated vapor pressure for various fuels, corresponding to the intensity of the flash boiling. Then, in the case of the back pressure below the saturated vapor pressure, the atomization process can be explained in terms of the nucleation process and the growth rate of cavitation vapor bubbles due to the flash boiling, corresponding to the pressure difference between the back pressure and the saturated back vapor pressure. Further a certain model describing the fuel vapor formation rate is proposed considering the distribution of initial bubble nuclei in the fuel and the bubble growth process, based upon the cavitation bubble analysis in the flash boiling phenomena.<span class="xref">*</span> Number in bracket designate references at end of paper.</div> <div class="htmlview paragraph">RECENTLY, A MULTI-POINT INJECTION SYSTEM has become to be applied in gasoline engines predominantly owing to its high response and control quality of fuel supply. In this system, liquid fuel is injected into the relative low-pressure atmosphere through an electronic control injector. And in some operating conditions of engine, a great deal of unburnt hydrocarbon is emitted with exhaust gas because of its low quality of the spray atomization. Therefore, it is important to reveal the atomization process of the spray injected into the low-pressure field and especially to examine the changes in spray characteristics with the surrounding back pressure with reference to performance and exhaust emissions of the engine.</div> <div class="htmlview paragraph">In general, injected fuel from the pintle type injector appears in the form of fuel film with conical shape near the injector and the breakup of fuel film into droplets is not completed immediately. In fact, aerodynamic forces and the instability of fuel film due to the turbulence provided at the injector exit and the resistance by the atmospheric density cause unstable wave growth leading to the disruption of the film flow resulting to liquid ligaments and to droplets. However, when liquid fuel is injected into the back pressure below the equilibrium pressure, so-called the saturated vapor pressure, for the liquid temperature, the liquid spray disintegrates into fine droplets by evolution of the vapor owing to flash boiling. The flash boiling phenomena, that is vapor bubble growth by cavitation, occur when a liquid, initially in a subcooled state, is rapidly depressed to a pressure below the saturated vapor pressure to initiate a rapid boiling process.</div> <div class="htmlview paragraph">In connection with the flash boiling fuel injection, superheated liquid jets have often been researched as the subject of the study. For instance, Brown & York [<span class="xref">1</span>]<span class="xref">*</span> have described the relation between the droplet mean size and the growth rate constant of the bubbles, and Lienhard & James [<span class="xref">2</span>] have presented the breakup length of the flashing superheated jets. And then, Sudo et al. [<span class="xref">3</span>] have measured the droplet size distribution in Methanol flash boiling spray. Further, the effects of the nuclei number and the idle time of bubble growth rate on the atomization process have been reported by Suzuki et al. [<span class="xref">4</span>], and research on analytical bubble growth rate for practical injectors has been conducted by Oza & Sinnamon [<span class="xref">5</span>].</div> <div class="htmlview paragraph">This study is intended for investigating the atomization mechanism of the spray injected into room-temperature and low-pressure field through a pintle type electric control injector. In particular, the change in spray characteristics with the back pressure below the atmospheric pressure are examined in detail. And, when the back pressure is below the saturated vapor pressure of fuel, the spray characteristics are discussed from a viewpoint of flash boiling, consisting the nucleation process and the bubble growth rate. In addition, a model which describes the fuel vapor formation rate is proposed by considering the distribution of initial bubble nuclei in the fuel and the bubble growth process, based upon the cavitation bubble analysis in the flash boiling phenomena. Experiments were performed using two fuels, n-Pentane and n-Hexane.</div>

<div class="htmlview paragraph">This article describes an application of <i>sliding mode</i> techniques to the design of an air/fuel ratio control system for a 4-stroke engine, to minimize exhaust gas and emissions.</div> <div class="htmlview paragraph">This technique allows to achieve good control performance in terms of precision, robustness, and fast transient response.</div> <div class="htmlview paragraph">To support <i>sliding mode control</i> a second PI stage was added, based on the signal of a second oxygen sensor installed after the catalytic converter.</div> <div class="htmlview paragraph">Experimental results were better than those obtained with a conventional PI control, currently used on production applications.</div> <div class="htmlview paragraph">The new control algorithm (<i>sliding mode</i> based on the first oxygen sensor, and PI on the second) is very versatile because the approach chosen allows to calculate the parameters values for the ECU using computer simulation.</div>

<div class="section abstract"><div class="htmlview paragraph">The work presented here is a further step in a continuing effort by the authors to study and document the aerodynamic effect of varying aspect ratio, ground clearance, and underbody roughness for basic rectangular shapes with radiused edges in ground effect.</div><div class="htmlview paragraph">Previous papers by the authors have presented extensive wake data for a range of aspect ratios and underbody roughness conditions. Force and moment data have been published for various aspect ratios, underbody roughness, and ground clearance. In this paper, additional wake data showing the effects of variation in ground clearance is presented. The focus of this paper is on analyses to make progress toward a rational correlation between body characteristics, the forces, and the measured wake properties.</div><div class="htmlview paragraph">A parametric analysis is presented linking the effects of the parameters varied in the study to the changes in the aerodynamic forces and moments. Results show correlations between the wake flows and the force results.</div></div>

<div class="htmlview paragraph">Thick airfoils are commonly used for wind turbine and propeller blade inboard sections, and for struts on aircraft. These airfoils are sometimes truncated for manufacturing convenience, or to save weight. The purpose of this investigation was to study the effects of systematic truncation on airfoil performance. In order to investigate these effects two basic airfoil shapes representative of wind turbine designs were tested: the NACA 23024 and the NACA 64<sub>3</sub>-621. The trailing edges of the models were truncated in steps up to the maximum thickness point. Aerodynamic forces and pitching moments were measured for angles of attack from -10° to 90° for each truncated model. Wind tunnel tests were conducted in the Wichita State University 2.13m × 3.05m (7′ × 10′) Walter Beech Memorial Wind Tunnel, using constant chord reflection plane models. Tests were conducted at a nominal dynamic pressure of 718 Pa (15 psf), which corresponds to a Mach number of 0.10 and a Reynolds number of 0.65 × 10<sup>6</sup> based on the full airfoil chord.</div> <div class="htmlview paragraph">Test results show relatively small changes in the aerodynamic force and moment coefficients for chord reductions up to 10%. For larger chord reductions, stalling angle and C<sub>LMAX</sub> values increase dramatically. C<sub>D</sub> shows large increases, as expected. C<sub>M</sub> changes are related to changes in camber associated with trailing edge truncation. For high angles of attack, the aerodynamic center moves aft for all configurations, an expected consequence of separation. Changes in C<sub>N</sub>, normal force coefficient, are similar to changes in lift. C<sub>S</sub>, leading-edge suction force coefficient shows surprisingly small change for moderate truncation. These results have important implications for rotor and strut design.</div>

<div class="section abstract"><div class="htmlview paragraph">The new BMW Aerodynamisches Versuchszentrum (AVZ) wind tunnel center includes a full-scale wind tunnel, "The BMW Windkanal" and an aerodynamic laboratory "The BMW AEROLAB." The AVZ facility incorporates numerous new technology features that provide design engineers with new tools for aerodynamic optimization of vehicles. The AVZ features a single-belt rolling road in the AEROLAB and a five-belt rolling road in the Windkanal for underbody aerodynamic simulation. Each of these rolling road types has distinct advantages, and BMW will leverage the advantages of each system. The AEROLAB features two overhead traverses that can be configured to study vehicle drafting, and both static and dynamic passing maneuvers. To accurately simulate "on-road" aerodynamic forces, a novel collector/flow stabilizer was developed that produces a very flat axial static pressure distribution. The flat static pressure distribution represents a significant improvement relative to other open jet wind tunnels. In addition, improved performance for reducing open jet plenum pressure fluctuations was achieved by incorporating and tuning Helmholtz resonators to selected low frequencies. The AVZ also includes a 32,000 m₂ support building with space for workshops, vehicle preparation, storage and offices. The close coupling of the support building to the wind tunnels improves the internal workflow within the vehicle design development process.</div></div>

<div class="htmlview paragraph">An important element in nearly all engine control systems is the lambda control feedback system and its associated switching exhaust gas oxygen sensor (EGO). This feedback loop is necessary to keep the mean value of the normalized air/fuel ratio close to one. This is a necessary condition for proper operation of the three-way catalyst systems which are a part of nearly all production emissions control systems.</div> <div class="htmlview paragraph">Currently many systems are based on using classical proportional-integral (PI) controllers in lambda control feedback loops which are self-oscillating. Proper design of such systems is dependent on knowing the time delay between the injection time and the time when a corresponding signal appears at the engine exhaust EGO sensor. Recently a new method of designing the vital larnbda control loop has emerged which is claimed to be very robust with respect to the injection/exhaust time delay. The method is based on modem geometric control techniques and is called a sliding mode controller.</div> <div class="htmlview paragraph">In this paper the previous work on sliding mode controllers (SMC) for the exhaust air/fuel ratio is extended and a sliding mode controller with improved steady state performance is developed. The sliding mode controller is compared to a conventional PI based controller on the same engine at a number of different operating points during different aggressive driving scenarios. It is shown that a SMC has desirable speed and robustness characteristics compared to conventional PI lambda controllers.</div>

<div class="section abstract"><div class="htmlview paragraph">The aerodynamics of a rotating tire can contribute up to a third of the overall aerodynamic force on the vehicle. The flow around a rotating tire is very complex and is often affected by smallest tire features. Accurate prediction of vehicle aerodynamics therefore requires modeling of tire rotation including all geometry details. Increased simulation accuracy is motivated by the needs emanating from stricter new regulations. For example, the upcoming Worldwide harmonized Light vehicles Test Procedures (WLTP) will place more emphasis on vehicle performance at higher speeds. The reason for this is to bring the certified vehicle characteristics closer to the real-world performance. In addition, WLTP will require reporting of CO<sub>2</sub> emissions for all vehicle derivatives, including all possible wheel and tire variants. Since the number of possible derivatives can run into the hundreds for most models, their evaluation in wind tunnels might not be practically possible. Therefore, simulations are very appealing alternative especially since their use is allowed by WLTP.</div><div class="htmlview paragraph">As a first step in order to meet these escalating demands, the current study uses a Lattice Boltzmann method (LBM) based computational fluid dynamics (CFD) solver using an immersed boundary method (IBM) based approach to simulate and validate a standalone rotating treaded tire. Preliminary wake plane prediction results are in good agreement with experimental wake plane measurements. Effect of tire loading on wake results is also discussed.</div></div>

<div class="section abstract"><div class="htmlview paragraph">With the development of brake-by-wire technology, electro-hydraulic composite braking technology came into being. This technology distributes the total braking force demand into motor regenerative braking force and hydraulic braking force, and can achieve a high energy recovery rate. The existing composite braking control belongs to single-channel control, i.e., the four wheel braking pressures are always the same, so the hydraulic braking force distribution relationship of the front and rear wheels does not change. For single-axle-driven electric vehicles, the additional regenerative braking force on the driven wheels will destroy the original braking force distribution relationship, resulting in reduced braking efficiency of the driven wheels, which are much easier to lock under poor road adhesion conditions. The integrated Electro-Hydraulic Braking system (iEHB) is the current advanced brake-by-wire system, which can build brake hydraulic pressure by its motor, and independently adjusts the four wheel braking pressures through the solenoid valves. Based on the characteristics of the iEHB, a composite braking control strategy for front-wheel-driven electric vehicles is proposed, which adjusts the braking force distribution relationship dynamically. Firstly, the structure of the iEHB system and the wheel braking pressure control principle are analyzed. Secondly, a composite braking control strategy that adjusts the braking force distribution relationship based on current regenerative braking force and wheel braking pressures is designed. Finally, simulations are carried out with the proposed control strategy and the single-channel composite braking control strategy. The simulation results show that the proposed composite braking control strategy can improve the braking efficiency of the driven wheels and improve the energy recovery rate.</div></div>

<div class="section abstract"><div class="htmlview paragraph">CVT is a transmission system widely applied in automobiles due to its better efficiency of the vehicle available power. That happens because of the continuously variation of the transmission since its pulleys mechanisms makes it possible for them to open or close according to engine speed and resistive forces. This paper presents a dynamical analysis of a CVT Transmission that utilizes a rubber belt. It is considered that the influence of the pulley’s mechanisms and the axial movement of the belt, and these effects in the vehicle longitudinal dynamics.</div></div>

<div class="htmlview paragraph">The investigation is concerned with dependencies between a friction coefficient of the tire with a road, μ, and wheel slip, s.</div> <div class="htmlview paragraph">The analysis of μ-s-dependencies is given in the paper. The conventional approach to their presentation contains some discordance with real physical processes. On the basis of the external friction theory it is possible to offer another concept of potential μ-s-curves. The potential μ-s-curve is a function of the deformative, adhesion and transverse components of tire grip, the absolute slip velocity and the road reaction. Over the interrelation character of the given components it is possible to evaluate a current road-operational situation.</div> <div class="htmlview paragraph">In addition the recommendations for practical use of the potential μ-s-dependencies for the Systems of Active Safety are given.</div>

This research presents a rule-based Anti-lock Braking System (ABS) algorithm towards active vehicle safety in Heavy Commercial Road Vehicles (HCRVs). Wheel Slip Regulation (WSR) algorithms, that are constituents of an ABS, are typically either model-based or rule-based. Model-Based Algorithms (MBAs) utilise mathematical models that characterise vehicle dynamics and are intensive in their demand for real-time information. On the other hand, Rule-Based Algorithms (RBAs) operate on set rules with pre-defined thresholds and utilise data from sensors that are typically available on the vehicle. A great deal of advancement has been reported in literature related to MBAs. However, most commercially available RBAs are proprietary in nature and the finer details are seldom revealed. Hence, this work proposes an RBA, which is a combined Slip and Wheel Acceleration Threshold Algorithm (SWATA), including a framework for identifying the importance of thresholds and their magnitudes. SWATA was tested on a Hardware-in-Loop (HiL) setup across varying road and loading conditions, and it provided a maximum of 36% braking distance improvement compared to a case where it was inactive. An adaptive version – ASWATA – is also proposed that can adapt the thresholds according to the particular tyre-road interface. Additionally, a quantitative comparison of the proposed RBA with a Sliding Mode Control (SMC) based MBA, which was developed and tested on the same HiL setup, is presented. It was observed that the performance of the RBA was on par with that of the MBA for most test cases, but with minimal data requirements.