Improving driver comfort in commercial vehicles : modeling and control of a low-power active cabin suspension system

Comfort enhancement of commercial vehicles has been an engineering topic ever since the first trucks emerged around 1900. Since then, significant improvements have been made by implementing cabin (secondary) and seat suspensions. Moreover, the invention of the air spring and its application to the various vehicle's suspension systems also greatly enhanced driver comfort. However, despite these improvements many truck drivers have health related Problems, which are expected to be caused by their exposure to the environmental vibrations over longer periods of time. The most recent suspension improvements in commercial vehicles date back more than a decade and the possibilities for further improvements using passive devices (springs and dampers) seem nearly exhausted. Consequently, in line with developments in passenger cars, truck manufacturers are now investigating semi-active and active suspension systems. Herein, active suspensions are expected to give the best performance, but also come at the highest cost. Especially the high power consumption of market-ready devices is problematic in a branch where all costs need to be minimized. In this dissertation the field of secondary suspension design and controllable suspensions for heavy vehicles is addressed. More specifically, the possibilities for a low power active cabin suspension design are investigated. The open literature on this topic is very limited in comparison to that of passenger cars. However, as heavy vehicle systems are dynamically more challenging, with many vibration modes below 20 Hz, there is great research potential. The dynamic complexity becomes clear when considering the developed 44 degrees of freedom (DOF) tractor semi-trailer simulation model. This model is a vital tool for suspension analysis and evaluation of various control strategies. Moreover, as it is modular it can also be easily adapted for other related research. The main vehicle components all have their own modules. So, for example, when evaluating a new cabin suspension design, only the cabin module needs to be replaced. The model has been validated using extensive tests on a real tractor semi-trailer test-rig. The control strategy is a key aspect of any active suspension system. However, the 44 DOF tractor semi-trailer model is too complex for controller design. Therefore, reduced order models are required which describe the main dynamic properties. A quarter truck heave-, half truck roll-, and half truck pitch-heave model are developed and validated using a frequency-domain validation technique and the test-rig measurements. The technique is based on a recently developed frequency domain validation method for robust control and adapted for non-synchronous inputs, with noise on the input and output measurements. The models are shown to give a fair representation of the complex truck dynamics. Furthermore, the proposed validation method may be a valuable tool to obtain high quality vehicle models. As a first step, in search of a low power active cabin suspension system, various suspension concepts are evaluated under idealized conditions. From this evaluation, it follows that the variable geometry active suspension has great potential. However, the only known physical realization - the Delft Active Suspension - suffers from packaging issues, nonlinear stiffness characteristics, fail-safe issues and high production cost. Recently, a redesign - the electromechanical Low-Power Active Suspension (eLPAS) - was presented, which is expected to overcome most of these issues. This design is modeled, analyzed and a controller is designed, which can be used to manipulate the suspension force. Feasibility of the design is demonstrated using tests on a hardware prototype. Finally, the validated reduced order models are used to design suitable roll and pitch-heave control strategies. These are evaluated using a combination of the 44 DOF tractor semi-trailer and eLPAS models. Four eLPAS devices are placed at the lower corners of the cabin and modal input-output decoupling is applied for the controller implementation. It is shown, that driver comfort and cabin attitude behavior (roll, pitch and heave when braking, accelerating or steering) can be greatly improved without consuming excessive amounts of energy. So, overall these results enforce the notion that the variable geometry active suspension can be effectively used as low power active cabin suspension. However, there are still some open questions that need to be addressed before this design can be implemented in the next generation commercial vehicles. Durability and failsafe behavior of the eLPAS system, as well as controller robustness to variations in the vehicle parameters and environmental conditions, are some of the topics that require further study

Adaptive and Robust Braking-Traction Control Systems

The designs of commercial Anti-Lock Braking Systems often rely on assumptions of a torsionally rigid tire-wheel system and heavily rely on hub-mounted wheel speed sensors to manage tire-road slip conditions. However, advancements in high-bandwidth braking systems, in-wheel motors, variations in tire/wheel designs, and loss of inflation pressure, have produced scenarios where the tire\u27s torsional dynamics could be easily excited by the braking system actuator. In these scenarios, the slip conditions for the tire-belt/ring will be dynamically different from what can be inferred from the wheel speed sensors. This dissertation investigates the interaction of tire torsional dynamics with ABS & traction controllers and offers new control designs that incorporate schemes for identifying and accommodating these dynamics. To this end, suitable braking system and tire torsional dynamics simulation models as well as experimental test rigs were developed. It is found that, indeed, rigid-wheel based controllers give degraded performance when coupled with low torsional stiffness tires. A closed-loop observer/nonlinear controller structure is proposed that adapts to unknown tire sidewall and tread parameters during braking events. It also provides estimates of difficult to measure state variables such as belt/ring speed. The controller includes a novel virtual damper emulation that can be used to tune the system response. An adaptive sliding-mode controller is also introduced that combines robust stability characteristics with tire/tread parameter and state estimation. The sliding mode controller is shown to be very effective at tracking its estimated target, at the expense of reducing the tire parameter adaptation performance. Finally, a modular robust state observer is developed that allows for robust estimation of the system states in the presence of uncertainties and external disturbances without the need for sidewall parameter adaptation

Combining Sensors and Multibody Models for Applications in Vehicles, Machines, Robots and Humans

The combination of physical sensors and computational models to provide additional information about system states, inputs and/or parameters, in what is known as virtual sensing, is becoming increasingly popular in many sectors, such as the automotive, aeronautics, aerospatial, railway, machinery, robotics and human biomechanics sectors. While, in many cases, control-oriented models, which are generally simple, are the best choice, multibody models, which can be much more detailed, may be better suited to some applications, such as during the design stage of a new product

Advances and Trends in Mathematical Modelling, Control and Identification of Vibrating Systems

This book introduces novel results on mathematical modelling, parameter identification, and automatic control for a wide range of applications of mechanical, electric, and mechatronic systems, where undesirable oscillations or vibrations are manifested. The six chapters of the book written by experts from international scientific community cover a wide range of interesting research topics related to: algebraic identification of rotordynamic parameters in rotor-bearing system using finite element models; model predictive control for active automotive suspension systems by means of hydraulic actuators; model-free data-driven-based control for a Voltage Source Converter-based Static Synchronous Compensator to improve the dynamic power grid performance under transient scenarios; an exact elasto-dynamics theory for bending vibrations for a class of flexible structures; motion profile tracking control and vibrating disturbance suppression for quadrotor aerial vehicles using artificial neural networks and particle swarm optimization; and multiple adaptive controllers based on B-Spline artificial neural networks for regulation and attenuation of low frequency oscillations for large-scale power systems. The book is addressed for both academic and industrial researchers and practitioners, as well as for postgraduate and undergraduate engineering students and other experts in a wide variety of disciplines seeking to know more about the advances and trends in mathematical modelling, control and identification of engineering systems in which undesirable oscillations or vibrations could be presented during their operation

The application of neural networks in active suspension

This thesis considers the application of neural networks to automotive suspension systems. In particular their ability to learn non-linear feedback control relationships. The speed of processing, once trained, means that neural networks open up new opportunities and allow increased complexity in the control strategies employed. The suitability of neural networks for this task is demonstrated here using multilayer perceptron, (MLP) feed forward neural networks applied to a quarter vehicle simulation model. Initially neural networks are trained from a training data set created using a non-linear optimal control strategy, the complexity of which prohibits its direct use. They are shown to be successful in learning the relationship between the current system states and the optimal control. [Continues.

Compendium in Vehicle Motion Engineering

This compendium is written for the course “MMF062 Vehicle Motion Engineering” at Chalmers University of Technology. The compendium covers more than included in that course; both in terms of subsystem designs and in terms of some teasers for more advanced studies of vehicle dynamics. Therefore, it is also useful for the more advanced courses, such as “TME102 Vehicle Modelling and Control”.The overall objective of the compendium is to educate engineers that understand and can contribute to development of good motion and energy functionality of vehicles. The compendium focuses on road vehicles, primarily passenger cars and commercial vehicles. Smaller road vehicles, such as bicycles and single-person cars, are only very briefly addressed. It can be mentioned that there exist a lot of ground-vehicle types not covered at all, such as: off-road/construction vehicles, tracked vehicles, horse wagons, hovercrafts, and railway vehicles.Functions are needed for requirement setting, design and verification. The overall order within the compendium is that models/methods/tools needed to understand each function are placed before the functions. Chapters 3-5 describes (complete vehicle) “functions”, organised after vehicle motion directions:\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 3:\ua0Longitudinal\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 4:\ua0Lateral\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 5:\ua0Vertical\ua0dynamicsChapter 1 introduces automotive industry and the overall way of working there and defines required pre-knowledge from “product-generic” engineering, e.g. modelling of dynamic systems.Chapter 2 also describes the subsystems relevant for vehicle dynamics:• Wheels and Tyre\ua0• Suspension\ua0• Propulsion\ua0• Braking System\ua0• Steering System\ua0• Environment Sensing SystemThe compendium is released in a new version each year, around October, which is the version your read now. A "latest draft" is more frequently updated and often includes some more, sometimes unfinished, material: https://chalmersuniversity.box.com/s/6igaen1ugcjzuhjziuon08axxiy817f

Compendium in Vehicle Motion Engineering

This compendium is written for the course “MMF062 Vehicle Motion Engineering” at Chalmers University of Technology. The compendium covers more than included in that course; both in terms of subsystem designs and in terms of some teasers for more advanced studies of vehicle dynamics. Therefore, it is also useful for the more advanced course “TME102 Vehicle Modelling and Control”.The overall objective of the compendium is to educate vehicle dynamists, i.e., engineers that understand and can contribute to development of good motion and energy functionality of vehicles. The compendium focuses on road vehicles, primarily passenger cars and commercial vehicles. Smaller road vehicles, such as bicycles and single-person cars, are only very briefly addressed. It should be mentioned that there exist a lot of ground-vehicle types not covered at all, such as: off-road/construction vehicles, tracked vehicles, horse wagons, hovercrafts, or railway vehicles.Functions are needed for requirement setting, design and verification. The overall order within the compendium is that models/methods/tools needed to understand each function are placed before the functions. Chapters 3-5 describes (complete vehicle) “functions”, organised after vehicle motion directions:\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 3:\ua0Longitudinal\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 4:\ua0Lateral\ua0dynamics\ub7\ua0\ua0\ua0\ua0\ua0\ua0\ua0\ua0 Chapter 5:\ua0Vertical\ua0dynamicsChapter 1 introduces automotive industry and the overall way of working there and defines required pre-knowledge from “product-generic” engineering, e.g. modelling of dynamic systems.Chapter 2 also describes the subsystems relevant for vehicle dynamics:• Wheels and Tyre\ua0• Suspension\ua0• Propulsion\ua0• Braking System\ua0• Steering System\ua0• Environment Sensing Syste

Analysis on actuator dynamics in active wheelsetcontrol

This thesis presents details of an investigation conducted to evaluate the applicability and requirements of actuators in the implementation of active solid–axle wheelset control systems, for primary suspensions of the railway vehicles, and the effects of actuator dynamics on the overall active control system. The research is focused on the use of electric–mechanical (EM) actuators and it addresses on two main aspects when designing active control systems for this application. One aspect is the detailed study on actuator dynamics and parameter optimisation to improve the effectiveness/efficiency of actuator performances while the second aspect is the development of a state observer to estimate key feedback signals, for the control of actuators, which are difficult to measure using readily available sensing techniques. The study of the actuator dynamics and its optimisation is conducted by varying key factors of the electro–mechanical (EM) actuator used in this application such as gear ratio, inertial values of the motor rotor/gear–wheel and stiffness/damping at the actuator–wheelset (load) connection, while assessing key actuator performance indicators such as output torque and power consumption. This analysis provides insight in to the task of finding optimal actuator parameter values for this particular application of active wheelset control such that the effectiveness, efficiency and robustness of the overall active wheelset control system can be improved. In order to assess the developed system comprehensively, both a two–axle vehicle model and a full bogie vehicle model are being evaluated individually in the study In addition, a state observer is developed in this study to estimate the output torque of the electro–mechanical (EM) actuator since feedback measurements are essential for the actuator control system developed in this case in order to ensure that actuator responds appropriately by delivering accurate and fast control efforts to maintain the stability of wheelsets. The formulation and design of the observer is done based only on the use of the actuator model such that it substantially reduces the complexity and difficult uncertainties related to the full model of a rail vehicle. Furthermore, a robustness assessment of the state observer is undertaken by conducting an assessment of its performance when key parameters of the model used to develop the state observer is varied within reasonable margins. The performance and robustness assessments of the state estimator integrated with the full active wheelset control system and with optimised actuator parameters are carried out with the use of both two–axle vehicle model and the full bogie vehicle model with different operational track features such as curved track and straight track with lateral irregularities with various travel speeds