This thesis presents the results of high supply (up to 84 bar) pressure testing of hole-pattern annular gas seals performed at the Texas A & M Turbomachinery Laboratory in College Station, TX. The test variables were chosen to determine the influence of pressure ratio, rotor speed, and negative preswirl on seal performance. Preswirl signifies the circumferential fluid flow entering a seal, and negative preswirl indicates a fluid swirl in the direction opposite of rotor rotation. Changes in pressure ratio had only small effects on most rotordynamic coefficients. Cross-coupled stiffness showed slightly different profiles through the mid-range of excitation frequencies. Pressure ratio showed some influence on direct and cross-coupled damping at low excitation frequencies. Rotor speed significantly affected both cross-coupled stiffness and cross-coupled damping. As rotor speed increased, the magnitude of cross-coupled rotordynamic coefficients increased due to the positive fluid swirl induced by rotor rotation. For the low rotor speed, negative inlet preswirl was able to overpower the positive rotor induced fluid rotation, producing a negative cross-coupled stiffness. This outcome showed that, for hole-pattern seals, positive fluid swirl does indeed produce positive cross-coupled stiffness coefficients and negative fluid swirl produces negative cross-coupled stiffness coefficients. The addition of negative preswirl greatly reduced cross-coupled rotordynamic coefficients, while direct rotordynamic terms were unaffected. Cross-over frequency signifies the excitation frequency where effective damping transitions from a negative value to a positive value with increasing excitation frequency. Peak effective damping was increased by 50 percent and cross-over frequency reduced by 50 percent for high-negative preswirl versus zero preswirl results. This led to the conclusion that a reverse swirl could greatly enhance the stability of hole-pattern balance piston seals. A two-control-volume model that uses the ideal gas law at constant temperature (ISOT) was used to predict rotordynamic coefficients and leakage. This model predicted direct rotordynamic coefficients well, but greatly under predicted cross-coupled rotordynamic coefficients especially at high negative preswirls. The model predicted seal leakage well at low pressure ratios, but showed increasing error as the pressure ratio was increased. These results showed that the prediction model could not adequately estimate cross-coupled rotordynamic coefficients for a hole-pattern seal with negative inlet preswirl and requires modification to do so.

Road and rail vehicles and aircraft rely mainly or solely on friction brakes. These brakes pose several problems, especially in hybrid vehicles: significant wear, fading, complex and slow actuation, lack of fail-safe features, increased fuel consumption due to power assistance, and requirement for anti-lock controls. To solve these problems, a contactless magnetic brake has been developed. This concept includes a novel flux-shunting structure to control the excitation flux generated by permanent magnets. This brake is wear-free, less-sensitive to temperature than friction brakes, has fast and simple actuation, and has a reduced sensitivity to wheel-lock. The present dissertation includes an introduction to friction braking, a theory of eddy-current braking, analytical and numerical models of the eddy-current brake, its excitation and power generation, record of experimental validation, investigation and simulation of the integration of the brake in conventional and hybrid vehicles.

This thesis deals with the development of a mathematical model for an air brake system in the presence of leaks. Brake systems in trucks are crucial for ensuring the safety of vehicles and passengers on the roadways. Most trucks in the US are equipped with S-cam drum brake systems and they are sensitive to maintenance. Brake defects such as leaks are a major cause of accidents involving trucks. Leaks in the air brake systems affect braking performance drastically by decreasing the peak braking pressures attained and also increasing the time required to attain the same, thereby resulting in longer stopping distances. Hence there is a need for detecting leaks in an air brake system. In this thesis, a mathematical model for an air brake system in the presence of leaks is developed with a view towards developing an automatic leak detection system in the near future. The model developed here builds on an earlier research at Texas A&M University in which a "fault free" model of an air brake system is developed, i.e., a mathematical model of an air brake system that predicts how the pressure in the brake chamber evolves as a function of the brake pedal input when there are no leaks in the air brake system.In order to develop a model for an air brake system in the presence of leaks, one must characterize a "leak". A leak may be characterized by the location and its size. Since the pipes are short, the location of the leak does not significantly affect the evolution in the brake pressure as much as its size. For this reason, "effective area" of the leak was chosen as a characteristic of the leak. It was estimated by fitting an empirical relation for leak with leak flow measurement data. The supply pressure and effective area of leak comprised the inputs to the model along with the displacement of the foot pedal (treadle valve plunger). The model was corroborated with the experimental data collected using the setup at Texas A&M University.

Thesis--Technische Universität Dresden, 2007. / Includes bibliographical references.

The theme of Master project is very actual nowadays, cause a safety of human life is the biggest purpose in the world. That’s why engineers of automative industry seeks to find newer and newer solutions to create the level of safety as high as possible. And engineers knows, the main system in the vechile to make safely driving – brake system. Nowadays the most efective brake system type – disk brake system. That means disk brake pads are very important part also. The are a lot of manufacturers of brake pads and linings in the world. Commonly the technologycal procedure of brake pads manufacturing can be described as follows: steel back preparation, friction material mixing, preforming, pressing curing, baking, grinding and grooving, painting, printing and packing. The main purpose of this job is to analyze materials for friction material on brake pads and to make efectiveness tests of two different friction materials. Material No.2 mostly consists of steel wool, while material No.1 has just a little bit of steel wood in it. This material is replaced by fibre “Lapinus” and filler – barytes. Comparing the testing results it is obvious the highest friction coefficient has material No.2. Explanation of such results can be following: steel wool creats higher friction level. This analysis is a small part in the brake pads manufacturing world and always there will be newer improvements in this area.

Emergency braking of a vehicle is bound with many factors, such as the behaviour of the driver, the drive of the vehicle braking system, the braking mechanisms, the condition of the tyres, and the properties of the pavement. This process involves all parameters of the system “the driver – the vehicle – the road”. In order to investigate the efficiency of braking process upon specific conditions, it is necessary to examine all physical processes that take place in the vehicle on pressing the brake pedal. Upon the completion of the experimental and theoretical investigation on emergency braking of vehicles a general mathematical model of vehicle with hydraulic braking system on its emergency braking had been developed. The dynamic, thermodynamic in solid systems and fluid hydrodynamic processes were assessed. The model enables to examine various cases of emergency braking with assessment of the driver’s reaction, parameters of the vehicle’ technical condition and the pavement condition. A general mathematical model of vehicle with hydraulic braking system that’s computing is realized in the system of the applied software Compaq Visual Fortran Professional system provides possibilities for research the hydrodynamic processes that take place in the system of braking; enables to define more closely the movement parameters of the vehicle in the emergency braking mode and may be applied for analysis of traffic events, improvement of vehicle braking systems as well as a manual for... [to full text]

Emergency braking of a vehicle is bound with many factors, such as the behaviour of the driver, the drive of the vehicle braking system, the braking mechanisms, the condition of the tyres, and the properties of the pavement. This process involves all parameters of the system “the driver – the vehicle – the road”. In order to investigate the efficiency of braking process upon specific conditions, it is necessary to examine all physical processes that take place in the vehicle on pressing the brake pedal. Upon the completion of the experimental and theoretical investigation on emergency braking of vehicles a general mathematical model of vehicle with hydraulic braking system on its emergency braking had been developed. The dynamic, thermodynamic in solid systems and fluid hydrodynamic processes were assessed. Model enables to examine various cases of emergency braking with assessment of the driver’s reaction, parameters of the vehicle’ technical condition and the pavement condition. A general mathematical model of vehicle with hydraulic braking system that’s computing is realized in the system of the applied software Compaq Visual Fortran Professional v 6.3 system provides possibilities for research the hydrodynamic processes that take place in the system of braking; enables to define more closely the movement parameters of the vehicle in the emergency braking mode and may be applied for analysis of traffic events, improvement of vehicle braking systems as well as a manual... [to full text]

No description available.

Universiẗat, Diss., 2002--Stuttgart.

Failure of a parked unattended vehicle to remain stationary, otherwise known as vehicle rollaway, can result in property damage, injury or even fatality. Although the incidence of vehicle rollaway may be under reported, around 8% of drivers and 13% of Approved Driving Instructors surveyed indicated they had experienced a vehicle rollaway event. Unlike previous studies which focused only on the mechanical factors that may contribute to this phenomenon, the research presented in this thesis employed a more comprehensive, systems approach to explore additional factors related to the driver s interaction with the parking brake system at various interface levels. A mixed methods strategy collated data through two online surveys and three observational studies to explore the organisational, mechanical and driver related factors identified in a fault tree framework. The results indicated that current driver practice and interaction with the parking brake system may be contrary to legislative requirements and manufacturer s instruction. The findings suggested that a past experience of vehicle rollaway or parking brake system failure, had a statistically significant influence on whether the driver complied with the recommended practice. Driver interaction and the holding capability of the parking brake system were observed in 53 vehicles parked on three test gradients. The observations indicated that drivers were able to apply sufficient force to the parking brake lever to hold the vehicle stationary and that an additional degree of confidence in the system was provided by parking in gear. But, after driving a short commuting route, when the vehicle was parked with the parking brake lever applied to the lowest position to hold the vehicle and a gear was not selected, 63% of vehicles fitted with disc brakes rolled as the temperature returned to ambient. Discussion relates to the organisational, driver related and mechanical components of the parking brake system and in reference to Reason s Swiss Cheese model, considers how latent failures within the defensive layers of the system can contribute to rollaway. The research findings contributed to a change in UK driving standards and since 2015, drivers are recommended to park in gear at all times to reduce the risk of rollaway. This recommendation is likely to require a change in practice for up to 80% of Approved Driving Instructors who would not normally instruct new drivers in this way. Although this research focused on the manually operated parking brake system, the studies have uncovered results that can contribute to knowledge and are applicable to interaction with electronic parking brake systems. As parking brake systems develop, the Human Factors systems approach can be applied retrospectively and proactively to explore that interaction and prevent passenger vehicle rollaway.