Reference Governor Strategies for Vehicle Rollover Avoidance

This paper addresses the problem of vehicle rollover avoidance using reference governors (RGs) applied to modify the driver steering input in vehicles with an active steering system. Several RG designs are presented and tested with a detailed nonlinear simulation model. The vehicle dynamics are highly nonlinear for large steering angles, including the conditions where the vehicle approaches a rollover onset, which necessitates RG design changes. Simulation results show that RG designs are effective in avoiding rollover. The results also demonstrate that the controllers are not overly conservative, adjusting the driver steering input only for very high steering angles. IEE

ATV Dynamics and Pediatric Rider Safety

It has been observed through numerous academic and governmental agency studies that pediatric all-terrain vehicle ridership carries significant risk of injury and death. While no doubt valuable to safety, the post-hoc approach employed in these studies does little to explain the why and how behind the risk factors. Furthermore, there has been no prolonged, widespread, organized, and concerted effort to reconstruct and catalog the details and causes of the large (20,000+) number of ATV-related injuries that occur each year as has been done for road-based motor vehicle accidents. This dissertation takes the opposite approach from a meta-analysis and instead examines the injury risk factors through a two-pronged, a priori, physics-based approach. Specifically, this dissertation study sought to: 1) experimentally determine whether age is an effective metric for assessing proper rider fit on an ATV, and 2) demonstrate experimentally and analytically how the combined dynamics of the ATV and riders can contribute to vehicular instability. These two studies were conducted using instrumented human subjects and ATVs and measured in a biodynamics laboratory. The key finding from the rider versus ATV size study was:1) contrary to publicly circulated engine size and age-based fit guidelines, age is not an effective metric for assessing rider fit on ATVs; instead, stature is the more reliable measure. The key findings from the rollover propensity study were: 2a) the combination of common terrain and throttle input can easily lead to a rearwards rollover, with or without additional riders sitting behind the ATV driver, and 2b) the minimum turning radius before initiating a sideways rollover can be easily be exceeded when ATVs are driven on commonly-encountered terrain and at surprisingly low speeds. The results of this dissertation study thus provide new evidence for mitigating two root causes of ATV injury by informing better parental guidance: first, clearly revealing that stature and not age is the key metric for who fits on what ATV model, and second, revealing the ease with which backward and sideways rollovers can occur

Development of a vehicle dynamics controller for obstacle avoidance

As roads become busier and automotive technology improves, there is considerable potential for driver assistance systems to improve the safety of road users. Longitudinal collision warning and collision avoidance systems are starting to appear on production cars to assist drivers when required to stop in an emergency. Many luxury cars are also equipped with stability augmentation systems that prevent the car from spinning out of control during aggressive lateral manoeuvres. Combining these concepts, there is a natural progression to systems that could assist in aiding or performing lateral collision avoidance manoeuvres. A successful automatic lateral collision avoidance system would require convergent development of many fields of technology, from sensors and instrumentation to aid environmental awareness through to improvements in driver vehicle interfaces so that a degree of control can be smoothly and safely transferred between the driver and vehicle computer. A fundamental requirement of any collision avoidance system is determination of a feasible path that avoids obstacles and a means of causing the vehicle to follow that trajectory. This research focuses on feasible trajectory generation and development of an automatic obstacle avoidance controller that integrates steering and braking action. A controller is developed to cause a specially modified car (a Mercedes `S' class with steer-by-wire and brake-by-wire capability) to perform an ISO 3888-2 emergency obstacle avoidance manoeuvre. A nonlinear two-track vehicle model is developed and used to derive optimal controller parameters using a series of simulations. Feedforward and feedback control is used to track a feasible reference trajectory. The feedforward control loops use inverse models of the vehicle dynamics. The feedback control loops are implemented as linear proportional controllers with a force allocation matrix used to apportion braking effort between redundant actuators. Two trajectory generation routines are developed: a geometric method, for steering a vehicle at its physical limits; and an optimal method, which integrates steering and braking action to make full use of available traction. The optimal trajectory is obtained using a multi-stage convex optimisation procedure. The overall controller performance is validated by simulation using a complex proprietary model of the vehicle that is reported to have been validated and calibrated against experimental data over several years of use in an industrial environment

Reference governors: Theoretical Extensions and Practical Applications.

As systems become downsized and operate at the limits of performance, control systems must be designed to ensure that system state and control constraints are satisfied; however, conventional control schemes are often designed without taking constraints into account. Reference governors and the related, more flexible, extended command governors are add-on, constraint enforcement schemes that modify reference signals to conventionally designed, closed-loop systems for the purpose of enforcing output constraints. The focus of this dissertation is on theoretical and methodological extensions of reference and extended command governors, and on their practical applications. Various theoretical results are presented. The first is the development of reduced-order reference and extended command governors, which enables constraint enforcement schemes using simplified models. The second, related development is that of reference governors for decentralized systems that may or may not communicate over a network. The third considers command governors with penalty functions that are used to enforce prioritized sets of constraints, as well as reference governors that are applied to a sequence of prioritized references. The fourth considers the often overlooked case of applying reference governors to linear systems subject to nonlinear constraints; various formulations of constraints are considered, including quadratic constraints and mixed logical-dynamic constraints. The final theoretical development considers using contractive sets to design reference governors for systems with time-varying reference inputs or subject to time-dependent constraints. Numerical simulations are used throughout to illustrate the theoretical advances. The design of reference governor schemes for three systems arising in practical applications is also presented. The first scheme enforces compressor surge constraints for turbocharged gasoline engines, ensuring that the compressor does not surge. The second scheme is designed for an airborne wind energy system that is subject to various flight constraints including constraints on altitude and angle of attack. The third and final scheme is designed for the constrained control of spacecraft attitude, whose discrete-time dynamics evolve on the configuration space SO(3). In the case of the first application, experimental vehicle results are reported that show successful avoidance of surge. For the other two applications, nonlinear model simulation results are reported that show enforcement of system constraints.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113518/1/kalabic_1.pd

Central bank financial independence

Central bank independence is a multifaceted institutional design. The financial component has been seldom analysed. This paper intends to set a comprehensive conceptual background for central bank financial independence. Quite often central banks are modelled as robot-like maximizers of some goal. This perspective neglects the fact that central bank functions are inevitably deployed on its balance sheet and have effects on its income statement. A financially independent central bank exhibits the adequate balance sheet structure and earnings generation capacity to efficiently perform its functions. From a long-term perspective, as far as the demand for banknotes is maintained seignorage waters down any central bank financial independence concern. However, from a short-term perspective central bank financial vulnerability may condition its effective independence. Vulnerability may be real or accounting based. However, no matter its origin, institutional solutions are needed to minimize their impact. Adequate capitalization turns out to be a key issue. Alternatively, contingent capital in the form of institutional arrangements to bear central bank losses may be a (second-best) solution. The paper analyses in the context of simple VAR model the interplay between capitalization, accounting rules and dividend distribution. This analysis is preceded by a thorough discussion of the risk-return profile of central banks net return on assets. Three main conclusions shape the input to the capitalization model. Central banks return on assets can be very volatile from a short term perspective. From a medium term perspective, natural earnings generation cycles dampen down volatility. On average, central banks net return on assets typically exhibits a discount over government debt financing cost. These observations shape the central bank financing planning problem as follows. Namely, the size of the discount relative to the social costs that would arise in case of a lack of central bank independence, along with central bank exposure to risks and the volatility thereof, determine the incentives of the government to maintain an excess of financial assets in the form of central bank capital. Actually, the working of smoothing mechanisms operating across time on central banks earnings leads to a distinction between short-term and medium term capital, i.e. the optimum capital solution is a band. In the same vein, the need to maintain optimal consistence between central bank financial strength and dividends distribution policy leads also to smoothing proporsals for pay-policy

Potential Terrorist Uses of Highway-Borne Hazardous Materials, MTI Report 09-03

The Department of Homeland Security (DHS) has requested that the Mineta Transportation Institutes National Transportation Security Center of Excellence (MTI NTSCOE) provide any research it has or insights it can provide on the security risks created by the highway transportation of hazardous materials. This request was submitted to MTI/NSTC as a National Transportation Security Center of Excellence. In response, MTI/NTSC reviewed and revised research performed in 2007 and 2008 and assembled a small team of terrorism and emergency-response experts, led by Center Director Brian Michael Jenkins, to report on the risks of terrorists using highway shipments of flammable liquids (e.g., gasoline tankers) to cause casualties anywhere, and ways to reduce those risks. This report has been provided to DHS. The teams first focus was on surface transportation targets, including highway infrastructure, and also public transportation stations. As a full understanding of these materials, and their use against various targets became revealed, the team shifted with urgency to the far more plentiful targets outside of surface transportation where people gather and can be killed or injured. However, the team is concerned to return to the top of the use of these materials against public transit stations and recommends it as a separate subject for urgent research