Browse Topic: Bus systems
This bus doesn’t use wheels to move around, but a CubeSat can’t get anywhere without it. In the world of these small, standardized, inexpensive satellites, a “bus” refers to the hardware foundation that provides it with power, communications, thermal stability, and other “services” a payload needs to function. Whether enabling data transfer for internet-enabled appliances, such as thermostats and refrigerators or tracking weather conditions, CubeSats continue to mature and support everyday services.
Growing environmental concerns and stringent vehicle emissions regulations has created an urge in the automotive industry to move towards electrified propulsion systems. Reducing and eliminating the emission from public transportation vehicles plays a major role in contributing towards lowering the emission level. Battery electric buses are regarded as a type of promising green mass transportation as they provide the advantage of less greenhouse gas emissions per passenger. However, the electric bus faces a problem of limited range and is not able to drive throughout the day without being recharged. This research studies a public bus transit system example which servicing the city of Ann Arbor in Michigan and investigates the impact of different electrification levels on the final CO2 reduction. Utilizing models of a conventional diesel, hybrid electric, and battery electric bus, the CO2 emission for each type of transportation bus is estimated. Vehicle speed data collected from various bus drives over different routes under different driving conditions are used to investigate the variability of drive conditions on performance metrics. Finally, recommendations are made for charge requirements of battery electric buses considering the variation in drive conditions which can result to an increase in the required charging time as high as 20%.
The bus sector is currently lagging behind when it comes to implementing autonomous systems for improved vehicle safety. However, in cities such as London, public transport strategies are changing, with requirements being made for advanced driver-assistance systems (ADAS) on buses. This study discusses the adoption of ADAS systems within the bus sector. A review of the on-road ADAS bus trials shows that passive forward collision warning (FCW) and intelligent speed assistance (ISA) systems have been successful in reducing the number of imminent pedestrian/vehicle collision events and improving speed limit compliance, respectively. Bus accident statistics for Great Britain have shown that pedestrians account for 82% of all fatalities, with three quarters occurring with frontal bus impacts. These statistics suggest that the bus forward collision warning system is a priority for inclusion in future vehicles to enhance the driver’s direct vision, and to increase reaction time for earlier brake application. Almost 80% of bus occupant casualties occurred in non-impact situations, mainly during acceleration/deceleration events. Therefore, care must be taken in implementing autonomous braking in buses, to ensure that it does not cause an increased number of deceleration events beyond the safe stability limits for passengers. Real on-road drive cycle data has shown that while instances of unsafe braking events do not occur regularly, there are instances of braking events that would present a hazard to both seated and standing passengers, therefore systems that would mitigate these issues would have real benefits to both passenger comfort and safety. During tests to simulate the use of the vehicle retarder for an autonomous braking system, deceleration rates largely remained safely within standee and seated passenger stability limits, whereas an emergency stop test showed a peak deceleration 3.5 times the limit of a standee supported by a vertical handrail, and 4 times the limit for a forward/backward facing seated passenger.
In-vehicle networks (IVN) have been standardized from the beginning. The story of IVN standardization started at the beginning of the 90s. Today, several IVN technologies have been internationally standardized by ISO (International Organization for Standardization) including the related conformance test plans. But as all electronic technologies, IVNs are a matter of improvement and change due to new requirements and gained experiences. This makes it difficult to always keep the standard backwards compatible, in particular if immature approaches are submitted. Furthermore, new communication protocols are knocking on the door of international standardization bodies. The automotive industry itself is conservative and adapts new IVNs slowly. There are also concerns regarding too many different bus systems and networks in one vehicle. This paper discusses the benefits and challenges of the standardization of IVNs.
Public transport has been considered the preferred strategy to reduce congestion and pollution from urban road traffic. For low to medium capacity, bus systems are considered the most affordable and flexible mode. Currently, diesel based systems still dominate transit bus market, due to their high productivity, low deployment costs, technological maturity, operational reliability and flexibility (high daily ranges, fast refuelling and no infrastructure requirement along the routes). However, although some important improvements in engine technology and aftertreatment devices, enforced by emission standards improvements (Euro VI, US 2010 and those related), have been achieved, it is well known that there is a limit to cleaning exhaust diesel buses exhaust. In this context, transit authorities and operators have been under pressure to shift for more environmental friendly technologies. Electric traction meet deserved operational and environmental features, with its high motor efficiency (allied with regenerative braking), torque (specially desired for stop and go cycles and hilly cities), low/zero emission (dependent on electricity mix) and low noise levels. Trolleybus systems are considered a well known and proven electric driven technology, that have been intensively used in the past, but that have been discontinued due to the massification of internal combustion engine vehicle use, with its inherent operational flexibility, albeit with an environmental burden, that was not appropriately weighted until recently. Currently, with an increasingly pressure to the adoption of environmental friendly transport systems, as well as due to technological/operational improvements (hybrid trolleybus configurations - which allows a free overhead wire range, ac motors, regenerative brake approach) trolleybus reemerges as an environmental friendly (zero local emission) transport system for medium to high loaded corridors, as Bus Rapid Transit - BRT. This is specially true for countries with a large share of renewable energy into electricity generation mix. This work presents a technical overview of modern trolleybus systems, with a detailed assessment of technological features of vehicles and infrastrucuture, as well as an economical evaluation focused on their fixed and variable costs, followed by a SWOT matrix analysis. Finally, it is presented an overview of some worldwide cities’ trolleybus bus experiences, with emphasis to the main operational and environmental drivers.
The way to autonomous driving is closely connected to the capability of verifying and validating Advanced Driver Assistance Systems (ADAS), as it is one of the main challenges to achieve secure, reliable and thereby socially accepted self-driving cars. Hardware-in-the-Loop (HiL) based testing methods offer the great advantage of validating components and systems in an early stage of the development cycle, and they are established in automotive industry. When validating ADAS using HiL test benches, engineers face different barriers and conceptual difficulties: How to pipe simulated signals into multiple sensors including radar, ultrasonic, video, or lidar? How to combine classical physical simulations, e.g. vehicle dynamics, with sophisticated three-dimensional, GPU-based environmental simulations? In this article, we present current approaches of how to master these challenges and provide guidance by showing the advantages and drawbacks of each approach. Therefore, we discuss different ADAS setups and show ways of how to implement HiL test benches for these. We discuss two categories: 1) Hardware level: we focus on the communication structure between the simulated plant model and the Unit under Test (UuT). We show possible interfaces into the sensor units and involved bus systems. 2) Software level: we focus on how to provide the data the UuT expects. This results in rendering images, creating data lists or providing ray-tracing based point clouds. This article provides solutions for current and up-coming challenges when dealing with HiL-based validation of ADAS and presents an overview of current test-approaches.
Urban Mobility is one of the most critical issues at the present. Public transport in connection with feeder bus system is proposed to be one of the main solution. Chulalongkorn University has a fleet of electric feeder bus in operation for a few years now. The fleet service is, however, to be improved because of current limitations in battery energy capacity and long battery charging time. This paper aims to examine the total cost of ownership (TCO) of the electric feeder buses using various types of energy storage. The results on the sensitivity analysis highlight the major parameters that exert strong influence in the TCOs. The fast charging system using supercapacitor battery bus shows the lowest TCO for the present bus fleet. The travel distance (km/year) and operational years were illustrated to be the top two parameters that exert major influence towards the TCO.
Current massive urbanization process concentrates high amount of population and impose an increased demand on transport systems. In this context, transit bus system plays an important role, as the most dynamic and less capital intensive transit option available. At the same time, it is strongly dependant on fossil fuels, predominantly diesel fuel, with its intrinsic polluting and greenhouse (climate change) effects. This has boosted research and investments for alternative and renewable fuels. One solution currently receiving widespread recognition is biogas use in transit bus fleets, as it allows the use of a renewable fuel, made from substrates derived basically from waste and sewage that otherwise would produce methane released to the atmosphere. Biogas contains basically methane, carbon dioxide, trace amounts of hydrogen sulfides and water, and to be used as engine fuel need to be upgraded, which means increasing the methane content up to 97% and removing water and other gases, when its composition becomes similar to fossil natural gas. From a technological perspective, biogas engines are predominantly spark ignited - SI and can be used in both lean burn (diesel derived) and stoichiometric (SI derived) combustion concept, as well the so called Diesel Dual Fuel - DDF technology, which uses a mix of natural gas and diesel fuel as a “liquid glow plug”, each one with its own strengths and weakness related to efficiency, thermal loads and cleanness (emission potential). The most suitable technology will depend basically on the emission targets to be achieved as well on the flexibility desired. Investment costs with biogas buses are generally higher, while operational costs use to be lower than those of baseline diesel buses, with the net value dependant on the size of the fleet relative to the installed infrastructure (bus garage, distribution, storage and filling system) as well as the cost of biogas production and engine maintenance. This paper is supposed to give an overview of biogas potential as a renewable fuel and its potential production chains, a technological heavy duty gas engine roadmap as well as an alternative fuel cost analysis.
The growing concentration of population in world metropolis caused by increasing urbanization rates has pushed the demand for high capacity and efficient public transport systems. At the same time, environmental concerns have led to increasingly stricter emission standards. In this context, transit authorities have become strongly focused on making their bus fleets more efficient and cleaner, by incorporating new alternative fuels and clean propulsion technologies. This has led to increased interest in electric driven technologies, with their intrinsic efficient, quiet and environment friendly features. Trolleybuses, a well proven mature electric technology already adopted in some cities, although efficient and clean, are burdened by high infrastructure costs and operational inflexibility. Hydrogen fuel cell buses, an infant technology, currently on a precommercial status, still presents some hurdles on hardware durability and hydrogen supply, which need to be surpassed before reach commercial status. At the same time, there has been significant technical progress into development of the electromobility concept for transit bus systems, through the use of pure electric drivetrains supported by the improvement of range, durability, charging procedures and cost of energy storage systems - ESS (batteries or/and supercapacitors), considered the core components of the so called pure electric buses. In this scenario, pure electric driven bus technology has aroused interest of transit industry, as a strategy for improving efficiency and environmental performance of transit bus fleets. Although not yet commercially competitive with diesel buses, there has been significant technical progress in development of pure electric buses, notably with improvements observed in the so called Lithium Ion battery (with their variants), supercapacitors technology and charging procedures, both under a technical and cost perspective. This work is supposed to present an overview of pure electric traction bus technology, with a focus on technical, operational, environmental and economical features, highlighting the pathways to be followed to reach commercial feasibility in order to comply with stricter environmental targets already scheduled and consolidate the electromobilty concept for transit bus industry. Moreover, it will be presented an overview of the main ongoing electromobility bus experiences in some important cities around the world.
Today, the Controller Area Network (CAN) is a widely used in-vehicle network. However, due to the constraint of the theoretical upper bound speed of CAN, we proposed Scalable-CAN (SCAN), which employs round-robin scheduling to improve upper bound speed while keeping the compatibility with traditional CAN. Moreover, we proposed the worst-case response time (WCRT) analysis for a single SCAN bus system and showed the real-time performance. In this paper, to apply SCAN to a next-generation in-vehicle network composed of a SCAN bus and a CAN bus, we first propose a schedulability analysis method for the integrated network system. Second, we show its real-time performance and highlight the effects of the bandwidth extension and throughput performance of the SCAN integrated system. Finally, we conclude that SCAN achieves lower latency, high schedulability, and high integrity toward a next-generation in-vehicle network.
This paper describes a study on electrical power management for the More Electric Aircraft (or MEA) and the More Electric Engine (or MEE). This study explored power management solutions based on an integrated engine/power control system and a permanent magnet motor. In recent years, electrical power management has emerged as a key aspect of aircraft system design. In cases in which the Electromechanical Actuator (or EMA) systems are used for flight control, the power bus systems must also be designed to dissipate the power regenerated from flight control systems. In their study, the authors focused on achieving an optimal balance between aircraft power management and operational requirements of the aero-engines. The study results suggest an effective and novel power control concept based on integrated engine control technologies that ensure stable power systems.
The increasing number of electronic control units (ECUs) in vehicles leads to more and more complex systems with a steadily growing demand for data exchange. This growth includes the number of bus participants, the amount of data and hence the data transfer rates. In addition, the trend towards car-to-x connectivity reinforces the need for new in-vehicle communication solutions. Since the early 1990s Controller Area Network (CAN) is the most widely used powertrain bus system. Since 2000 FlexRay is used in addition to CAN in the premium segment. For classic powertrain applications, the data transfer rates of these bus systems are sufficient; however the utilization is sometimes difficult and gateways are often required. For new applications like hybrid and electric vehicles and the next generation of external communication applications (e.g. telematics services) new concepts based on the existing bus systems or completely new solutions are needed. Looking outside of automotive business, Internet Protocol over Ethernet (IPoE) is the current standard technology for consumer and industry applications. IPoE has, compared to the currently used systems in powertrain area, very high data transfer rates and has the potential for further system cost reduction using standardized solutions. A first automotive application of IPoE was introduced in the market in 2008 for external communication. So far, IPoE is expensive compared to CAN and FlexRay due to higher hardware costs. Since a new transceiver technology enables the introduction of Ethernet in vehicles and Ethernet communication controller integrated into the microcontroller will be available for future powertrain ECUs, both evolutions together can be the enabler for Ethernet sub-bus systems in vehicles. Major technical challenges for the introduction of Ethernet in powertrain are the achievement of the necessary robustness under automotive conditions (electromagnetic compatibility (EMC), temperature range, mechanical vibrations) and the fulfillment of automotive real time, security and safety requirements. In addition, the capability of fast and easy adaptation to different vehicle configurations is mandatory. At the same time, the cooperation between original equipment manufacturer (OEM) and supplier needs to be considered to ensure an efficient integration and development. This paper analyses applications and the communication extend in current powertrain systems. A forecast for the future demand of communication capacity is calculated. Based on this, requirements are extracted and applied to Ethernet as well as IPoE. The result is an uncompromising approach to migrate in-vehicle powertrain communication to Ethernet and IPoE. Technical and process related requirements are considered to obtain a coherent picture.
The increasing demand for urban mobility, combined with the constriction of investment capacity of transit authorities and private companies make bus based systems a great option for public transport systems, since they allow the provision of high quality services at a fraction of the costs of rail based systems. In this scenario, Bus Transit System - BTS and Bus Rapid Transit - BRT allow the implementation of transport networks at considerably lower costs than their rail system counterparts. This is specially true to developing-nation cities, that have infrastructure costs as a pre-eminent decision-making factor in technology selection. From an environmental perspective, traction technology and fuel option are decisive to define systems' performance. Unlike rail based systems, that are generally electrified, bus based systems allow the use of a variety of traction options, like Diesel and Otto engines, Trolleybus, Hybrid (Diesel-Electric) and Fuel Cell Engine as well as fuels, like diesel, low sulfur diesel, natural gas, biodiesel, ethanol, hydrogen and electricity, each option presenting its own operational and environmental performance trade-offs. The prime objective of this paper is to present the potential of bus based technologies from a capacity and performance perspective, showing some examples of BTS and BRT systems around the world and a review of traction technologies and their performance, followed by some bus system experiences, focusing on traction technologies strategies and their economical approaches, including both retrofitting and upgrade programs. This study is structured in a way that it presents the state of art technologies, followed by some case studies around the world. Finally, Life Cycle Analysis is performed in order to allow an evaluation from a technical-economical perspective. This work is supposed to be a technical reference to those involved in planning or operating bus based systems.
Public transportation system and specifically transit bus systems are key element of the national transportation network in United States. Buses are one of the safest forms of transportation. Nonetheless, bus crashes resulting in operator injuries and fatalities do occur. According to National Transportation Statistics from 1990-2002, the number of transit motor buses in the U.S. has increased by 30% [1]. The majority of fatal crashes involving transit buses result from frontal crashes which could be fatal for bus operators. Therefore, crashworthiness research is a continuing effort. Research has been performed to analyze and improve the safety of transit bus operators. This paper describes the design, analysis and testing of an inflatable restraint system for a bus operator. At present a three point restraint is the only safety feature implemented on transit buses. The primary objective was to study the level of safety provided by the present safety system. To do this a physical environment of a bus operator compartment was manufactured and this was tested using a 50th percentile and a 95th percentile ATD for 18mph frontal impact condition. Acceleration pulse for the sled testing was obtained from a validated finite element model of a typical transit bus [2]. A finite element model of the operator compartment was generated and validated against the test results. This model was used as base line to design the inflatable restraint. A multibody model was created for the same using multibody code MADYMO to run design of experiment to optimize the inflatable restraint system. After achieving a satisfactory design, prototypes were manufactured for further validation of the design. Sled tests were conducted as per the test plan generated based on the simulation results. Results for present design and new design were compared to find the improvement on the level of safety.
The task-specific nature of an embedded system application typically defines a narrow scope of performance requirements. But the range of options for achieving those requirements are broad — from multicore processors and rugged single board computers (SBCs) to I/O devices and the bus systems that tie everything together. And the choices to be made are critical in their impact on cost, on performance efficiency in compute-intensive operations, and on the ability to function reliably in hot, cold, dusty or wet environments.
Bus systems like CAN or FlexRay allowed great advances in automotive electronics over the last 20 years. In order to function in an environment which requires the communication medium to tolerate one safety-relevant fault, these bus systems require a second, redundant bus to act as a backup for the original unit. With the network approach presented in this paper (SafeNet) it is possible to use the network intrinsic redundancy to keep the network fail-safe after at least one safety relevant fault in the network. To ensure this, messages are relayed to every node in the network. Even though the message delivery times in the network are not deterministic, it is shown that it is suitable for safety-relevant applications like drive-by-wire. Due to the simple point-to-point connections used to connect the nodes, high speeds can be achieved. The network approach is compared to both CAN and FlexRay under different aspects.
This paper presents model-based predictions of the performance of diesel, compressed natural gas (CNG), and hybrid buses on bus routes in the City of San Francisco. The bus route details were obtained by recording time-series measurements of speed and grade during actual runs of buses on the city streets under different traffic conditions. The transit buses' physical and mechanical characteristics were obtained from manufacturers' data and chassis dynamometer testing of the buses on different city cycles. Both the bus routes and the bus performance characteristics were put into the simulation package ADVISOR from the National Renewal Energy Laboratory (NREL). The most extreme results were for the San Francisco routes that have high grades. The high grades cause performance and emissions problems for both the diesel and CNG buses relative to the hybrid bus. A large portion of the performance and emissions problems can be directly related to the hydraulic torque converter that is currently used on most diesel and CNG city buses. At conditions that are typical of high grades, the hydraulic torque converters have quite poor efficiencies. Since the hybrid bus has a direct electric drive system, it does not suffer the efficiency problems to the same degree as the diesel and CNG buses. This paper also illustrates that bus performance modeling has reached a stage where it can help city bus systems evaluate bus performance before the buses are put into service. For example, it is expected that global positioning systems (GPS) will provide detailed time, speed, location, and grade information for all the bus routes in typical cities during different times of the day with different traffic conditions. This information can then be used with both old and new specifications for bus technologies to predict performance on the actual routes for which they could be used. In this way, a bus transit system could optimize bus routing assignments to minimize cost and emissions on a wide variety of routes.
SAE 100 Future look: In the early 1970s the foundations of what is now MTS Sensors began with the development of magnetostrictive technology and its application in industrial position-sensing applications. Much has been written about the adoption and benefits of electrohydraulic systems in off-highway vehicles, and an equal amount of attention has been given to the sensor technologies needed to effectively complete those systems. In many cases, these sensors are inherently “behind the scenes,” both technologically and economically. All the same, the advancements in both technology and economics are helping to transform off-highway vehicles-and the pace of change is accelerating. In the early 1970s the foundations of what is now MTS Sensors began with the development of magnetostrictive technology and its application in industrial position-sensing applications. These sensors are still known as Temposonics, and although the fundamental principle of the sensing technology has not changed, the materials science, electronics design, and manufacturing methods have evolved dramatically.
The ability to use one module to control two CAN nodes provides benefits including reduced hardware and software requirements, improved functionality, and lower CPU load, according to Infineon researchers. Automotive applications that use a large number of coupled functional units with different tasks typically contain more than one independent bus system. This allows developers to regroup the functional units and optimize each communication channel according to application-specific requirements. One of the buses is generally built as a high-speed (500 kbit/s to 1 Mbit/s) system to control powertrain modules for engine management, fuel injection, or ignition. Slower modules that operate from 50 to 250 kbit/s are used for body/convenience applications such as electrical seat-positioning systems, heating/ventilation, air conditioning, or door modules. Controller area network (CAN) bus systems provide for easy connection between the functional electronic control units (ECU) via their built-in multimaster capability. They enable easy communication between modules (called CAN nodes), since all CAN chips communicate with each other according to a standard protocol (Figure 1).
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