Drivability Improvement Research Articles

Coordinated clutch actuation for drivability improvement and energy management of a novel multi-mode hybrid electric vehicle and HIL validation

This article presents a novel architecture of a particular class, i.e., multi-mode hybrid electric propulsion systems that utilize two planetary gear sets, multiple clutches, two electric motors, and an internal combustion engine. Although this class of propulsion systems offers architectural compactness, improved fuel economy, and operational versatility, it faces a drivability issue arising from simultaneous clutch engagement and disengagement during mode shift events. Such drivability issues cannot be addressed by baseline motor-torque compensation-based coordinated control that is typically employed to address the drivability issues in power-split and parallel hybrid propulsion systems. Therefore, this article proposes an enhanced version of the coordinated control that includes the clutch’s torque capacity control. The enhanced coordinated control module augments with the energy management system, making the mode shift schedule drivable and near-optimal. A real-time hardware-in-the-loop test bench is developed to accurately evaluate the enhanced coordinated control’s impact on the energy management system’s performance. Test bench results demonstrate that the enhanced coordinated control is more effective than the baseline coordinated control in attenuating the propulsion system’s perturbations during mode shift events and making the overall mode shift schedule drivable. The enhanced energy management system consumes 7%–8% more fuel while transforming the mathematically optimal mode shift schedule into a drivable one.

Target State Optimization: Drivability Improvement for Vehicles with Dual Clutch Transmissions

Vehicles with dual clutch transmissions (DCT) are well known for their comfortable drivability since gear shifts can be performed jerklessly. The ability of blending the torque during gear shifts from one clutch to the other, making the type of automated transmission a perfect alternative to torque converters, which also comes with a higher efficiency. Nevertheless, DCT also have some drawbacks. The actuation of two clutches requires an immense control effort, which is handled in the implementation of a wide range of software functions on the transmission control unit (TCU). These usually contain control parameters, which makes the behavior adaptable to different vehicle and engine platforms. The adaption of these parameters is called calibration, which is usually an iterative time-consuming process. The calibration of the embedded software solutions in control units is a widely known problem in the automotive industry. The calibration of any vehicle subsystem (e.g., engine, transmission, suspension, driver assistance systems for autonomous driving, etc.) requires costly test trips in different ambient conditions. To reduce the calibration effort and the accompanying use of professionals, several approaches to automize the calibration process are proposed. Due to the fact that a solution is desired which can optimize different calibration problems, a generic metaheuristic approach is aimed. Regardless, the scope of the current research is the optimization of the launch behavior for vehicles equipped with DCT since, particularly at low speeds, the transmission behavior must meet the intention of the driver (drivers tend to be more perceptive at low speeds). To clarify the characteristics of the launch, several test subject studies are performed. The influence factors, such as engine sound, maximal acceleration, acceleration build-up (mean jerk), and the reaction time, are taken into account. Their influence on the evaluation of launch with relation to the criteria of sportiness, comfort, and jerkiness, are examined based on the evaluation of the test subject studies. According to the results of the study, reference values for the optimization of the launch behavior are derived. The research contains a study of existing approaches for optimizing driving behavior with metaheuristics (e.g., genetic algorithms, reinforcement learning, etc.). Since the existing approaches have different drawbacks (in scope of the optimization problem) a new approach is proposed, which outperforms existing ones. The approach itself is a hybrid solution of reinforcement learning (RL) and supervised learning (SL) and is applied in a software in the loop environment, and in a test vehicle.

Application of Light Metal Alloy EN AW 6063 to Vehicle Frame Construction with an Innovated Steering Mechanism.

Nowadays the automotive industry is mainly focused on competition, and this fact forces vehicle producers to constantly look for improvements in the areas of quality and reliability. Life-span, flawless operation, and safety are directly interconnected. Therefore, much attention and resources are spent on research factors that affect the stated properties. Significant capital is invested in the optimization of the constructional solutions and innovative material applications related to the safety and durability of the constructions. This paper presents the results obtained while developing a new ecological three-wheeled vehicle. The main research areas were focused on replacing the original material with a light aluminum alloy, while achieving a substantial improvement in drivability for the three-wheeled vehicle by implementing a modified front wheel steering system. The submitted research achieved a weight reduction of the frame by 40 kg by applying light material substitution (EN AW 6063.T66), which will naturally have a positive impact on the range of the designed electric vehicle; furthermore, we implemented an innovative steering mechanism optimized during the experimental operations.

Optimal Design of a Novel Hybrid Electric Powertrain for Tracked Vehicles

Tracked vehicles have been widely used in construction, agriculture, and the military. Major problems facing the industry, however, are high emissions and fuel consumption. Hybrid electric tracked vehicles have thus become increasingly popular because of their improved fuel economy and reduced emissions. While the series hybrid system has drawn the most attention and has been applied in most cases, the low efficiency caused by energy conversion losses and large propulsion motors has limited its development. A novel multi-mode powertrain with two output shafts controlling each side of the track independently is first proposed. The powertrain is a three-planetary-gear power-split system with one engine, three motors, and an ultracapacitor pack. Compared with the existing technologies, the proposed powertrain can realize skid steering without an extra steering mechanism, and significantly improve the overall efficiency. To demonstrate the advantages of the novel powertrain, a topology-control-size integrated optimization problem is solved based on drivability, fuel economy, and cost. Final simulation results show that the optimized design with downsized components can produce about a 30% improvement in drivability and a 15% improvement in fuel economy compared with the commonly used series hybrid benchmark. Moreover, the optimized design is verified to be much more economical taking cumulative cost into account, which is very attractive for potential industrial applications in the future.

Drivability Improvement Control for Vehicle Start-Up Applied to an Automated Manual Transmission

Drivability is the key factor for the automated manual transmission. It includes fast response to the driver’s demand and the driving comfort. This paper deals with a control methodology applied to an automated manual transmission vehicle for drivability enhancement during vehicle start-up phase. Based on a piecewise model of powertrain, a multiple-model predictive controller (mMPC) is designed with the engine speed, clutch disc speed, and wheel speed as the measurable input variables and the engine torque reference and clutch friction torque reference as the controller’s output variables. The model not only includes the clutch dynamic, the flexible shaft dynamic, but also includes the actuators’ delay character. Considering the driver’s intention, a slipping speed trajectory is generated based on the acceleration pedal dynamically. The designed control strategy is verified on a complete powertrain and longitudinal vehicle dynamic model with different driver’s torque demands.

The High-Performance Asymmetric Capacitors with Lithium-Intercalated Metal-Organic Framework Electrodes

Text: High-power energy storage devices can provide an improvement of drivability and a load-levelling system in an electric vehicle, a hybrid electric vehicle, and a fuel-cell vehicle.1 Asymmetric capacitors known as lithium-ion capacitors (LIC), in which a faradaic, battery-type electrode is combined with a non-faradaic, capacitor-type electrode, are up-and-coming devices because they show faster charge and discharge responses than lithium ion batteries and larger energy densities than electric double-layer capacitors (EDLC).1 Safety is also an important factor for the onboard devices. However, LICs using conventional graphite carbon negative electrodes operating at 0.1 V have the risk of a metallic Li deposition causing internal short circuits. Thus, we have studied lithium-intercalated metal-organic frameworks (iMOFs)2 and reported the novel negative electrode of 2,6-naphthalene dicarboxylate dilithium (2,6-Naph(COOLi)2), whose operating potential (0.8 V vs. Li/Li+) is expected to suppress a metallic Li deposition. In this report, we will introduce a novel iMOF negative electrode for asymmetric capacitors, a 4,4’-biphenyl dicarboxylate dilithium (4,4’-Bph(COOLi)2), which is fast responsible because of the remarkably low internal resistances. 4,4’-Bph(COOLi)2 can be prepared from biphenyl-4,4’-dicarboxilic acid by the deprotonation in LiOH under methanol solution. The powder X-ray diffraction of 4,4’-Bph(COOLi)2 and the corresponding Rietvelt refinement revealed the repeating structure of organic p-stacked biphenyl moieties and inorganic tetrahedral LiO4 units (Figure 1a). 4,4’-Bph(COOLi)2 has a larger lattice parameter of the a-axis direction than 2,6-Naph(COOLi)2because of the longer aromatic unit. The charge/discharge curve of a Li/4,4’-Bph(COOLi)2 cell indicates that the 4,4’-Bph(COOLi)2 electrode shows reversible two-electron transfer reaction at a potential of 0.7 V vs. Li/Li+, which is 0.1 V lower operating potential than that of 2,6-Naph(COOLi)2 (Figure 1b). Compared to the polarization of the 2,6-Naph(COOLi)2 electrode, 4,4’-Bph(COOLi)2 electrode exhibits small and large polarization in the deep and shallow depth of discharge (DOD), respectively (Figure 1b). For further study, the internal resistances of 2,6-Naph(COOLi)2 and 4,4’-Bph(COOLi)2 electrodes were examined by using the electrochemical impedance spectroscopy using symmetric cells. The symmetric cells were constructed of two iMOF electrodes lithiated up to DOD 50% under the same condition. The results showed the charge transfer resistances of 4,4’-Bph(COOLi)2 were lower than 2,6-Naph(COOLi)2. The activation energy of the charge transfer resistance obtained from Arrenius plots was slight lower in 4,4’-Bph(COOLi)2 than in 2,6-Naph(COOLi)2 or graphite. The low internal resistance with low activation energy of 4,4’-Bph(COOLi)2electrode seems to be suitable for the negative electrode of high-power devices, and can lead a high-rate performance even at a low temperature. The asymmetric capacitors composed of the positive electrodes of active carbon (AC), and the negative electrodes of 4,4’-Bph(COOLi)2 (4,4’-Bph(COOLi)2/AC cell) or 2,6-Naph(COOLi)2 (2,6-Naph(COOLi)2/AC cell) were prepared. The 4,4’-Bph(COOLi)2/AC cell showed 56 Wh L－ 1 energy density at 1C and 2.3 kW L－ 1 power density at 60C (Figure 1d). 4,4’-Bph(COOLi)2/AC cell showed higher energy density at 60C than conventional EDLC, LIC4, LTO/AC cell, and 2,6-Naph(COOLi)2/AC cell. Interestingly, 4,4’-Bph(COOLi)2/AC cell maintained a high-rate performance at a low temperature of 0°C compared with 2,6-Naph(COOLi)2/AC cell, which could derive from the low internal resistance with the low activation energy of 4,4’-Bph(COOLi)2. The capacity retention of 4,4’-Bph(COOLi)2/AC cell was 86 % after 1000 cycles at 10C. In summary, the asymmetric capacitor with 4,4’-Bph(COOLi)2electrode can be safer than the LIC using graphite, and showed high power capability and favorable low-temperature performance, therefore our proposed capacitors will be promising for the future capacitors.

Coordinated control strategies for a full hybrid electric vehicle with single motor during mode changes

This paper presents the coordinated control strategies for a full hybrid vehicle with single motor during mode changes. The mode changes between various driving modes are firstly divided into three types according to the similar characteristics of mode transitions. For the first type of mode change, a coordinated control strategy expressed as the combination of clutch pressure fuzzy control and motor torque compensation is proposed. For the second type of mode change, a coordination control strategy of motor speed closed-loop control and clutch pressure control is developed. The coordinated control strategy expressed as the engine throttle opening rate control and motor torque compensation is adopted for the third type of mode change. Performance of these proposed control strategies is validated by experimental tests based on the test bench of the full hybrid drivetrain. The results show a remarkable improvement in drivability of the full hybrid vehicle during mode changes.

Torque and Center of Combustion Evaluation Through a Torsional Model of the Powertrain

The continuous development of modern internal combustion engine (ICE) management systems is mainly aimed at combustion control improvement. Nowadays, performing an efficient combustion control is crucial for drivability improvement, efficiency increase (critical for spark ignited engines), and pollutant emissions reduction (critical in compression ignited engines). The most important quantities used for combustion control are engine load (indicated mean effective pressure (IMEP) or torque delivered by the engine) and center of combustion, i.e., the angular position in which 50% of fuel burned within the engine cycle is reached. Both quantities can be directly evaluated starting from in-cylinder pressure measurement, which could be performed using the newly developed piezoresistive pressure sensors for on-board applications. However, the use of additional sensors would increase the cost of the whole engine management system. Due to these reasons, over the past years, a methodology that allows evaluating both engine load and the center of combustion with no extra cost has been developed. This approach is based on engine speed fluctuation measurement, which can be performed using the same speed sensor already mounted on-board. The methodology is general and can be applied to different engine–driveline systems with different architectures and combustion orders. Furthermore, it is compatible with on-board requirements, since the evaluation of only one specific harmonic component of interest is required (depending on the engine–driveline configuration under investigation). In order to clarify all the issues related to the application of the presented approach, it has been applied to some different engines, both compression ignited and spark ignited, taking also into account the case of combustion not evenly spaced. For all the analyzed configurations, the results obtained using the estimation algorithm seemed to be adequate to feedback a closed-loop methodology for optimal combustion control.

Modeling and Identification of Longitudinal Responses of an Electric Vehicle for Drivability Improvement

This paper develops a control-oriented drivability model for an electric vehicle. First, we establish a discrete-time nonlinear input-output mechanism model through investigating the longitudinal dynamic characteristics of the vehicle. Second, we use the least squares method to identify the model parameters based on the data obtained from a real electric vehicle. The model is built in Simulink and its accuracy is validated by CRUISE. The calibration results demonstrate that the identified model is capable of predicting longitudinal vehicle responses that affect drivability and useful in control algorithm design.

Origin of Stress Memorization Mechanism in Strained-Si nMOSFETs Using a Low-Cost Stress-Memorization Technique

Implementation of strained-Si MOSFETs with optimum low-cost stress-memorization technique for a 40-nm technology CMOS process was demonstrated. Devices fabricated on (1 0 0) substrate with 〈1 0 0〉channel orientation provide additional 8% current drivability improvement for strained-Si nMOSFETs without any degradation of pMOSFETs performance. The stress-memorization technique (SMT) mechanism was experimentally verified by studying the impact of layout geometry (length of source/drain L <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> and polyspacing) on the device performance. In the SMT devices with L <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> down to 0.11 μm and polyspace reduced to 120 nm, no obvious current improvement and more performance degradation are observed compared with control device (only strained contact etch-stop layer), indicating that the benefit of the SMT is substantially eliminated and showing that the SMT-induced stress is mainly originated from the source/drain region in our case.

Improvement of drivability and fuel economy with a hybrid antiskid braking system in hybrid electric vehicles

When braking on wet roads, Antilock Braking System (ABS) control can be triggered because the available brake torque is not sufficient. When the ABS system is active, for a hybrid electric vehicle, the regenerative brake is switched off to safeguard the normal ABS function. When the ABS control is terminated, it would be favorable to reactivate the regenerative brake. However, recurring cycles from ABS to motor regenerative braking could occur. This condition is felt to be unpleasant by the driver and has adverse effects on driving stability. In this paper, a novel hybrid antiskid braking system using fuzzy logic is proposed for a hybrid electric vehicle that has a regenerative braking system operatively connected to an electric traction motor and a separate hydraulic braking system. This control strategy and the method for coordination between regenerative and hydraulic braking are developed. The motor regenerative braking controller is designed. Control of regenerative and hydraulic braking force distribution is investigated. The simulation and experimental results show that vehicle braking performance and fuel economy can be improved and the proposed control strategy and method are effective and robust.

Low Contact Resistivity with Low Silicide/p+-Silicon Schottky Barrier for High-Performance p-Channel Metal–Oxide–Silicon Field Effect Transistors

A current drivability improvement of p-channel metal–oxide–silicon field effect transistors (MOSFETs) is necessary for the performance enhancement of complementary metal–oxide–semiconductor (CMOS) circuits. In this paper, we present the key technology for fabricating indispensable CMOS circuits with a small Schottky barrier height and a low contact resistance for p-type silicon using Pd2Si. We fabricated a Pd2Si gate Schottky barrier diode and a Kelvin pattern on silicon. The measured Schottky barrier height is 0.29 eV for p-type silicon. We also realized a very low contact resistivity of 3.7 ×10-9 Ω cm2 for the p+ region of silicon. The p-channel MOSFET with Pd2Si source/drain contacts realized a good characteristic, that is, a small off current. The technology developed in this work involves silicide formation for source/drain contacts of p-channel MOSFETs, which is expected to realize the performance enhancement of MOSFETs.

Characteristics of Nano-Grating N-Channel MOSFETs for Improved Current Drivability

Drivability-improved MOSFETs were successfully fabricated by using nano-grating silicon wafers. There was almost no additional process change in device fabrication when the height of the gratings was less than the conventional macroscopic wafer surface roughness. The MOSFETs with the grating height of 35 nm showed 21% improvement in current drivability compared to the conventional one with the same device occupancy area. And the roll-off characteristic of threshold voltage of nano-grating device held the line of conventional one in despite of the 3-D channel structure. The technology provides great advantages for drivability improvement without paying much tradeoff of process cost. This proposal will be useful to CMOS-LSIs with high performance in general.

A Study on Fatigue Strength Improvement of Aluminum Alloy Resistant Spot Welds by Cold Working

Resistance spot welds (RSW) have been widely used in the sheet metal joining process due to high productivity, low cost and convenience. The application of aluminum alloys in automobile manufacturing has resulted in the reduction of weight in vehicle, fuel economy and improvement of drivability and driving performance. Therefore, the resistance spot weld (RSW) process has attracted attention to fabrication of aluminum structures. However, applications of Al RSW are limited due to the unreliable durability of the weld-bonded joints. This study presents an experimental investigation on the use of a post-weld cold working process to improve the fatigue strength of Al RSW. The post-weld cold working process includes a pair of uniquely shaped indenters that are pressed or driven into the structure in order to induce the compressive residual stresses around the RSW. The mechanical properties of the post-weld cold worked Al RSW were investigated, including the experimental results of fatigue. The effect of the post-weld cold working process parameters on the fatigue strength of the Al RSW was also investigated. Comparisons of the mechanical properties and qualitative results between the as-welded RSW specimens and the post-weld cold worked RSW specimens of each post-cold working parameter have been carried out. Also, discussions on the experimental results using the finite element method (FEM) for the post-weld cold working parameters are performed.

Drivability improvement in Schottky barrier source/drain MOSFETs with strained-Si channel by Schottky barrier height reduction

Due to an extra barrier between source and channel, the drivability of Schottky barrier source/drain MOSFETs (SBMOSFETs) is smaller than that of conventional transistors. To reach the drivability comparable to the conventional MOSFET, the Schottky barrier height (SBH) should be lower than a critical value. It is expected that SBH can be effectively reduced by a bi-axially strain on Si. In this letter, p-channel MOSFETs with PtSi Schottky barrier source/drain, HfAlO gate dielectric, HfN/TaN metal gate and strained-Si channel are demonstrated for the first time using a simplified low temperature process. Devices with the channel length of 4μm have the drain current of 9.5μA/μm and the transconductance of 14μS/μm at Vgs−Vth=Vds=−1V. Compared to the cubic Si counterpart, the drain current and the transconductance are improved up to 2.7 and 3.1 times respectively. The improvement is believed to arising from the reduced barrier height of the PtSi/strained-Si contact and the enhanced hole mobility in the strained-Si channel.

A Dual-Gate Complementary Metal-Oxide-Semiconductor Technology with Novel Self-Aligned Pocket Implantation which Takes Advantage of Elevated Source/Drain Configurations

A dual-gate complementary metal-oxide-semiconductor technology with novel self-aligned pocket implantation is demonstrated which takes advantage of the elevated source/drain (S/D) configurations. Using the present procedure, S/D junction capacitance and leakage current were significantly suppressed for p-channel metal-oxide-semiconductor field-effect-transistors (MOSFETs) as well as for n-channel MOSFETs without degradation of the short channel characteristics. These results are interpreted in terms of the fact that the pocket impurity profiles shift to the upper positions in the deep S/D regions, though the impurity distribution at the gate edges was hardly varied. Furthermore, the suppression effects were more marked for a higher pocket implantation dosage, which will be required to suppress the short channel effects in future MOSFETs. In addition, improvement of drivability due to the reduction of the parasitic S/D resistance, an original benefit of the elevated S/D engineering, is maintained by the present technique. The present self-aligned pocket procedure is very promising as a key technology beyond the 0.1 µm node.

Drivability improvement on deep-submicron MOSFETs by elevation of source/drain regions

Deep submicron MOSFETs with elevated source/drain (S/D) structures, where S/D extension regions were partially elevated besides deep S/D regions, were fabricated by use of Si selective epitaxial growth technique. As fairly compared with a well-developed conventional MOSFET, we clarify an advantage of the elevated S/D structures, i.e., improvement upon driving performance with keeping excellent short-channel characteristics, which is enhanced for decrease in gate sidewall spacer width. The experimental results are explained in terms of the reduction in S/D parasitic resistance by addition of the Si epitaxial layer where the impurity profile is suitable.

Dual-polycide gate technology using regrowth amorphous-Si to suppress lateral dopant diffusion

Process techniques for dual-polycide gate CMOS have been developed. The origin of lateral dopant diffusion is analyzed, and an enlarged-grain dual-polycide gate technology using regrowth amorphous-Si (a-Si) is proposed. Reduction of the dopant absorption into the silicide layer has been observed in the regrowth of a-Si polycide gate structure. Lateral dopant diffusion has been suppressed to less than 0.1 /spl mu/m, and, as a result, 0.2 /spl mu/m n-MOS/p-MOS spacing has been realized under an 850/spl deg/C furnace annealing process. This technology can also achieve current drivability improvement by suppressing the gate depletion simultaneously. Suppression of boron penetration through the gate oxide to the channel region from the p/sup +/ gate has been realized by gate doping ion implantation into the a-Si, and no threshold voltage lowering with small standard deviation has been confirmed. It has been recognized that the above techniques are a possible solution for the dual-polycide gate CMOS structure.