Powertrain system optimization for a heavy-duty hybrid electric bus

This research concerns the design of a powertrain system for a plug-in parallel diesel hybrid electric bus equipped with a continuously variable transmission (CVT) and presents a new design paradigm for the plug-in hybrid electric bus (HEB). The criteria and method for selecting and sizing powertrain components equipped in the plug-in HEB are presented. The plug-in HEB is designed to overcome the vulnerable limitations of driving range and performance of a purely electric vehicle (EV), and it is also designed to improve the fuel economy and exhaust emissions of conventional buses and conventional HEBs. Optimization of the control strategy for the complicated and interconnected propulsion system in the plug-in parallel HEB is one of the most significant factors for achieving higher fuel economy and lower exhaust emissions in the hybrid electric vehicle (HEV). In this research, the proposed control strategy was simulated to prove its validity using the ADVISOR (advanced vehicle simulator) analysis simulation tool.     

Development of a path planning system using mean shift algorithm for driver assistance

The longitudinal and lateral vehicle control techniques have been widely used in several active driver assistance systems. The adaptive cruise control, lane keeping assistant control, vehicle platooning and stop-and-go control are typical examples of the most important applications. In this study, a novel path planning method is proposed considering the driving environment such as road shape, ego vehicle and surrounding vehicles’ movement. The relative distance and velocity between the ego vehicle and surrounding vehicles are identified with respect to the predicted lane shape in front of the ego vehicle. Based on the identified information, the road shape and surrounding vehicles are mapped into the intensity image and the desired vector for the ego vehicle’s movement is determined by the maximum intensity density tracing method. The desired vehicle path is followed by the acceleration/deceleration control and the steering assist control, respectively. In order to evaluate the performance of the proposed system, simulations are conducted and compared with ACC systems.     

Optimization of drying performance considering driving conditions

Compressed air can be used as an energy source for brake systems in medium-heavy and heavy-duty commercial vehicles. The moisture in compressed air, which is due to high temperature and humidity, can be eliminated by using an air dryer. In this paper, drying performance data for a cartridge were obtained and used to develop a drying performance program, to predict the moisture and relative humidity in the air tanks of vehicles. The on-load time, off-load time, air flow, duty cycle, humidity and dew point temperature were calculated according to air consumption. The validity of the program was verified, and it was shown to be able to predict humidity changes in the air tank. The air tank capacity was increased from 100 to 130 to reduce the duty cycle. Therefore, the regeneration rate decreased from 18% to 15%, but the dew point depression temperature (ΔT) remained above 30°C. The duty cycle decreased from 50% to 43%, and the total operation time and power consumption of the air compressor were reduced. In conclusion, fuel savings were obtained by changing the parameters to optimize the system.     

Manoeuvring characteristics of twin-rudder systems: rudder-hull interaction effect on the manoeuvrability of twin-rudder ships

With a recent increase in ship capacity and propulsion performance, a wide-beam ship fitted with a twin-rudder system has been adopted in many cases. However, to improve ship manoeuvring, it is still necessary to have a better understanding of rudder-hull interactions in twin-rudder ships. Captive model tests (oblique towing and circular motion test) as well as free-running tests with a single-propeller twin-rudder ship and a twin-propeller twin-rudder ship are carried out. The effect of drift angle on the rudder forces and some peculiar phenomena concerning rudder normal force for twin-rudder ships are evaluated. A method for estimating the hull-rudder interaction coefficients based on free-running experimental results is proposed.     

Influence of pilot injection on combustion characteristics and emissions in a DI diesel engine fueled with diesel and DME

This work experimentally investigates how the dwell time between pilot injection and main injection influences combustion and emissions characteristics (NOx, CO, THC and smoke) in a single-cylinder DI diesel engine. The experiments were conducted using two fuel injection systems according to the fuel type, diesel or dimethyl ether (DME), due to the different fuel characteristics. The injection strategy is accomplished by varying the dwell time (10°CA, 16°CA and 22°CA) between injections at five main injection timings (?4°CA aTDC, ?2°CA aTDC, 0°CA aTDC, 2°CA aTDC and 4°CA aTDC). Results from pilot-main injection conditions are compared with those shown in single injection conditions to better demonstrate the potential of pilot injection. It was found that pilot injection is highly effective for lowering heat-release rates with smooth pressure traces regardless of the fuel type. Pilot injection also offers high potential to maintain or increase the BMEP; even the combustion-timing is retarded to suppress the NOx emission formation. Overall, NOx emission formation was suppressed more by the combustion phasing retard effect, and not the pilot injection effect considered in this study. Comparison of the emissions for different fuel types shows that CO and HC emissions have low values below 100 ppm for DME operation in both single injection and pilot-main injection. However, NOx emission is slightly higher in the earlier main injection timings (?4°CA aTDC, ?2°CA aTDC) than diesel injections. Pilot injection was found to be more effective with DME for reducing the amount of NOx emission with combustion retardation, which indicates a level of NOx emission similar to that of diesel. Although the diesel pilot-main injection conditions show higher smoke emission than single-injection condition, DME has little smoke emission regardless of injection strategy.     

Hot judder simulation of a ventilated disc and design of an improved disc using sensitivity analysis

In a disc brake system, thermal expansion of the material is caused by friction energy that is generated by the sliding contact between a disc and pad during braking. This phenomenon, thermo-elastic instability, can lead to hot spots on the disc surface and a hot judder phenomenon. Transient finite element analysis has been used to simulate this phenomenon. Three dimensional finite element models of a disc, pad, and cylinder were created. Each part was connected by a joint. Contact condition was applied to the disc and pad with a friction coefficient (μ) of 0.4. A convective heat transfer coefficient was set as 40 W/m²K. Using a commercial program SAMCEF, the simulation of the thermo-mechanically coupled system was performed. In order to find the sensitive parameters of brake judder, sensitivity analysis was carried out with consideration for disc design parameters. As a result, the hot spot phenomenon was confirmed and hot judder was predicted. Moreover, the more sensitive parameters of the hot judder phenomenon were presented. Finally, an improved disc model and an analysis technique were verified by comparison to dynamo test results.     

Comparison on rating methods for female dummy in NCAP frontal impact test

From MY2010 US-NCAP, the 5th percentile female Hybrid III dummy has been used for the safety evaluation of the right front passenger position in the frontal impact test. In Korea, the Ministry of Land, Infrastructure and Transport (MLIT) decided to evaluate the safety of the 5th percentile female dummy in the frontal impact test from 2013 KNCAP. In this paper, using the frontal NCAP data for the 5 vehicles available from the NHTSA test database, the safety of the 5th percentile female dummy were examined. Using the evaluation and rating method by the KNCAP, 5 vehicles received 5 stars. Using the evaluation and rating method by the US-NCAP, only one vehicle received 5 stars and the remaining 4 vehicles received 4 stars. In the US-NCAP, the N_ij was the most influential factor for the star rating. In the KNCAP, the evaluation and rating method for the 5th percentile female Hybrid III dummy is less stringent than the method of the US-NCAP. The evaluation and rating method is proposed to increase the stringency of the star rating for the female dummy in the KNCAP.     

On-road chasing measurement of exhaust particle emissions from diesel,CNG, LPG,and DME-fueled vehicles using a mobile emission laboratory

We designed and applied a mobile emission laboratory for on-road measurements of exhaust particles emitted from conventional diesel, compressed natural gas (CNG), liquefied petroleum gas (LPG), and dimethyl ether (DME)-fueled vehicles. Fuel type and vehicle driving conditions significantly affected the particle size distribution and the number concentrations of the nucleation mode. For all buses, the size distributions of particles in the exhaust under idling conditions had larger mode diameters than at constant speed conditions of 50 km/h or 80 km/h. The nucleation mode (< 50 nm) fraction of diesel, CNG, LPG, and DME at a constant speed of 50 km/h was 53%, 63%, 79%, and 99%, respectively, indicating that the DME-fueled bus emitted the most nanoparticles. As the vehicle speed increased from 50 km/h to 80 km/h, the nucleation mode fraction of diesel, CNG, LPG, and DME changed to 43%, 99%, 99%, and 99%, representing a significant increase in the number concentrations of nanoparticles in the CNG and LPG-fueled vehicles. The particle size distributions in the exhaust of diesel, CNG, LPG, and DME-fueled vehicles were not affected by increase in the chasing distance.     

Characteristics on NOx adsorption and intermediates of LNT catalyst

Several NOx reduction technologies under development in recent years have now been commercialized, including selective catalytic reduction (SCR) with NH₃ or hydrocarbons, and Lean NOx Trap. The aim of the present study is to investigate characteristics on NOx adsorption according to the oxygen concentration, de-NOx performance according to lean/rich injection cycle and toxic intermediates at LNT downstram for lean-burn gasoline engine. Under oxygen of 6%, NOx storage capacity was the highest, showed the highest NOx conversion of 98%. The reason for this phenomena is because the excited oxygen atoms at high oxygen concentration increased oxidizing power of NO. Under low temperature of 205°C, LNT catalyst showed the least NOx conversion of 14% because its activity became lower, while the generation rate of toxic HNCO was highest as CO which is generated during the rich condition, reacts with NOx stored on Ba site.     

On the structure of weekly activity/travel patterns

Understanding the process of activity scheduling is a critical pre-requisite to an understanding of changes in travel behavior. To examine this process, a computerized survey instrument was developed to collect household activity scheduling data. The instrument is unique in that it records the evolution of activity schedules from intentions to final outcomes for a weekly period. This paper summarizes an investigation of the structure of activity/travel patterns based on data collected from a pilot study of the instrument. The term “structure” refers to the sequence by which various activities enter one’s daily activity scheduling process. Results of the empirical analyses show that activities of shorter duration were more likely to be opportunistically inserted in a schedule already anchored by their longer duration counterparts. Additionally, analysis of travel patterns reveals that many trip-chains were formed opportunistically. Travel time required to reach an activity was positively related to the scheduling horizon for the activity, with more distant stops being planned earlier than closer locations.