Shankar C. Subramanian

Modeling the Pneumatic Subsystem of an S-cam Air Brake System

This paper deals with the development of a fault-free model of the pneumatic subsystem of an air brake system that is used in commercial vehicles. Our objective is to use this model in brake control and diagnostic applications. The development of a diagnostic system would be useful in automating enforcement inspections and also in monitoring the condition of the brake system in real-time. This paper presents a detailed description of the development of this model and of the experimental setup used to corroborate this model for various realistic test runs.

Estimation of bus travel time incorporating dwell time for APTS applications

Congestion has become a serious problem in the context of urban transport around the world. As more and more vehicles are being introduced into the urban streets every year, the mode share of the public transportation sector is declining at an alarming rate. Particularly in developing countries, more people have moved to personalized mode since it is becoming easily affordable and the quality of service offered by the public transit is not improving. To attract more people, the public transit should provide a high level of quality service to the passengers. One way of achieving this is by using Advanced Public Transport Systems (APTS) applications such as providing accurate real-time bus arrival information to the passengers which will improve the service reliability of the public transit. Travel time prediction has been a well-renowned topic of research for years. However, studies which were model based and incorporating dwell times at bus stops explicitly for heterogeneous traffic conditions are limited. The present study tries to explicitly incorporate the bus stop delays associated with the total travel times of the buses under heterogeneous traffic conditions. This will help in obtaining a reliable algorithm which can be adopted for bus arrival time prediction under Indian conditions.

Prediction of traffic density for congestion analysis under Indian traffic conditions

Traffic congestion is a serious problem which traffic engineers all over the world are trying to solve. Congestion increases the uncertainty in travel times leading to human stress and unsafe traffic situations. Better management of traffic through Intelligent Transportation Systems (ITS) applications, especially by predicting the congestion on various roads and informing the travelers regarding the same is one possible solution. Accurate and quick prediction is one of the important factors on which the reliability of such a system depends. If one is able to predict congestion on a roadway, then the travelers can be warned of the same either pre-trip or enroute so that they can take well informed travel decisions. The number of vehicles in a given stretch of a roadway (usually referred to as “traffic density”) is one of the most commonly used congestion indicator. Also, the travelers in general will be more interested to know what they can expect when they make the trip in future rather than the present scenario. This makes the short term prediction to future time intervals important. In this study, some of the reported techniques for density prediction under homogeneous traffic conditions are attempted under heterogeneous traffic conditions in order to determine their feasibility under the Indian traffic scenario.

A note on the flow through porous solids at high pressures

In this study we propose an equation for the flow through a porous solid that includes the equations due to Darcy and Brinkman as special sub-cases. The model is particularly well suited for describing the flow when the range of the pressure is sufficiently large, as it takes into account the possibility that the viscosity and the drag coefficient can be functions of the pressure. We can see a marked departure in the pressure field with respect to the classical Darcy solution with a narrow boundary layer within which the pressure suffers most of its drop.

Cooperative control of regenerative braking and friction braking for a hybrid electric vehicle

In this paper, a rear-wheel-driven series hybrid electric vehicle which has a mechanically operated friction brake system is studied. A new cooperative control of regenerative braking and friction braking called ‘combined braking’ is proposed for this vehicle configuration. A mechanism to adjust the proportions of regenerative braking and friction braking was proposed in this paper. Further, the braking force distribution between the front wheels and the rear wheels was analysed to ensure stable braking. The brake system characteristics were considered to ensure that the driver’s feel remains the same in the new proposed combined braking strategy. The simulation results under urban driving and across the Modified Indian Driving Cycle and vehicle road testing results show that the proposed combined braking can regenerate more than twice the braking energy of conventional parallel braking. Also, with combined braking, the braking force distribution between the front wheels and the rear wheels is closer to the ideal braking force distribution curve, which is desirable to ensure stable braking.

Degradation of an Elastic Composite Cylinder due to the Diffusion of a Fluid

We study the degradation of a composite elastic cylinder due to the diffusion of a fluid through it. The composite is assumed to be comprised of two linearized elastic bodies whose material moduli at a particular location depend on the concentration of fluid at the location, the value of the moduli decreasing with increasing fluid content. Unlike previous studies, we simultaneously solve the problem of the diffusion of fluid and the deformation of the composite cylinder. The study has relevance to the diffusion of moisture in composites as well as that of gases and solvents that can cause degradation of the composite. We find that significant changes take place over time with regard to the displacement, strain, and stress fields in the interior of the annular cylindrical composite that is subject to stress or displacement boundary conditions.

A model based approach to predict stream travel time using public transit as probes

Travel time is one of the most preferred traffic information by a wide variety of travelers. Travel time information provided through variable message signs at the roadside could be viewed as a traffic management strategy designed to encourage drivers to take an alternate route. At the same time, it could also be viewed as a traveler information service designed to ensure that the driver has the best available information based on which they can make travel decisions. In an Intelligent Transportation Systems (ITS) context, both the Advanced Traveler Information Systems (ATIS) and the Advance Traffic Management Systems (ATMS) rely on accurate travel time prediction along arterials or freeways. In India, currently there is no permanent system of active test vehicles or license plate matching techniques to measure stream travel time in urban arterials. However, the public transit vehicles are being equipped with Global Positioning System (GPS) devices in major metropolitan cities of India for providing the bus arrival time information at bus stops. However, equipping private vehicles with GPS to enable the stream travel time measurement is difficult due to the requirement of public participation. The use of the GPS equipped buses as probe vehicles and estimating the stream travel time is a possible solution to this problem. The use of public transit as probes for travel time estimation offers advantages like frequent trips during peak hours, wide range network coverage, etc. However, the travel time characteristics of public transit buses are influenced by the transit characteristics like frequent acceleration, deceleration and stops due to bus stops besides their physical characteristics. Also, the sample size of public transit is less when compared to the total vehicle population. Thus mapping the bus travel time to stream travel time is a real challenge and this difficulty is more complex in traffic conditions like in India with its heterogeneity and lack of lane discipline. As a pilot study, a model based approach using the Kalman filtering technique to predict stream travel time from public transit is carried out in the present study. Since it is only a pilot study, only twowheeled vehicles have been considered as they constitute a major proportion in the study area. The prediction scheme is corroborated using field data collected by carrying GPS units in two-wheelers traveling along with the buses under consideration. The travel time estimates from the model were compared with the manually observed travel times and the results are encouraging.

Traffic density estimation under heterogeneous traffic conditions using data fusion

Data fusion is one of the recent approaches in traffic analysis for the accurate estimation and prediction of traffic parameters. In this approach, the parameters are estimated using the data from more than one source for better accuracy. This paper discusses a model based approach to estimate the parameters of heterogeneous traffic using both location data and spatial data using data fusion. The proposed method uses the Kalman filtering technique for the estimation of traffic density. Traffic density is a spatial parameter which is difficult to measure directly from field and can be measured only using aerial photography. Hence, it is usually estimated from other easily measurable parameters such as speed, flow, etc., or from a combination of such parameters. The present study estimates density using the flow values measured from video and the travel time obtained from Global Positioning System (GPS) equipped vehicles. The study also reports density estimation using flow and Space Mean Speed (SMS) obtained from location based data alone without fusing with spatial data, using the Extended Kalman filter technique. The estimates are corroborated using actual values and the results show data fusion performing better while estimating density.

Development and modelling of an electropneumatic brake system

The brake system is the primary system in an automobile which ensures its safety on the road. The ideal brake system should operate with the least effort from the driver and should stop the vehicle within the minimum possible distance. This paper deals with the air brake system which is widely used in commercial vehicles such as trucks, buses and tractor-trailers. One of the important parameters which affect the stopping distance of a vehicle is the brake response time. The work presented focuses on the development of an electropneumatic brake which would decrease the response time of the air brake system thereby providing a reduced stopping distance. A mathematical model that correlates the pressure transients in the brake chamber to the voltage input provided to the electropneumatic brake has been developed. The efficacy of this model is tested by comparing its results with experimental data obtained from various test runs.

Modeling the pneumatic subsystem of a s-cam air brake system

The air brake system is one of the critical components in ensuring the safe operation of any commercial vehicle. This work is directed towards the development of a fault-free model of the pneumatic subsystem of the air brake system. This model can be used in brake control and diagnostic applications. Current enforcement inspections are done manually and hence are time consuming and subjective. The long-term objective is to develop a model-based, performance-based diagnostic system that will automate enforcement inspections and help in monitoring the condition of the air brake system. Such a diagnostic system can update the driver on the performance of the brake system during travel and with recent advancements in communication technology, this information can be remotely transferred to the brake inspection teams. The model of the pneumatic subsystem correlates the pressure transients in the brake chamber with the brake pedal actuation force and the brake valve plunger displacement. An experimental test bench was set up at Texas A&M University and the experimental data is used to corroborate the results obtained from the model.