This Special Issue addresses the use of hybrid systems in an important industrial domain of embedded systems: automotive control. Hybrid systems are a fascinating topic of research that has captured the attention of the research community in the past few years. Important theory results have been obtained but applying them to industrial strength control problems has been challenging. Automotive control has been the first field where hybrid systems have revealed their potential. The contributions published in the Special Issue span a number of applications in automotive control: from design flows to traffic control, from engine to suspension control.
In Hybrid systems in automotive electronics design, A. Balluchi, L. Benvenuti, A. Ferrari and A.L. Sangiovanni-Vincentelli present a broad view of the development process for embedded control systems in the automotive industry with the purpose of identifying challenges and opportunities for hybrid systems. Critical steps in the design flow are identified and a number of open problems where hybrid system technology might play an important role are pointed out.
In Verification of cooperating traffic agents, W. Damm, H. Hungar and E.-R. Olderog exploit design patterns used in coordinating autonomous transport vehicles to ease the burden of verifying cooperating hybrid systems. The authors present a verification rule explicating the essence of employed design patterns, guaranteeing global safety properties of the kind “a collision will never occur”, and whose premises can either be established by off-line analysis of the worst-case behavior of the involved traffic agents, or by purely local proofs, involving only a single traffic agent.
In Hybrid control of homogeneous charge compression ignition (HCCI) engine dynamics, J. Bengtsson, P. Strandh, R. Johansson, P. Tunestal and B. Johansson consider real-time control of a six-cylinder heavy-duty HCCI engine on a cycle-to-cycle basis. The authors compare different combustion controllers obtained by considering possible choices for sensors (ion current and cylinder pressure), actuators (dual-fuel and variable valve actuations) and control structures (MPC, PID and LQG). While satisfying the constraints on cylinder pressure, both control of the combustion phasing and control of load torque were achieved with simultaneous minimization of the fuel consumption and emissions.
In Automotive engine hybrid modelling and control for reduction of hydrocarbon emissions, P.R. Sanketi, J.C. Zavala and K. Hedrick develop hybrid models for engine control that incorporate time and events in their formulation. The resulting hybrid controllers have the capability of switching between two alternative control modes. The first mode is designed to reduce the raw HC (hydrocarbon) emissions while the second mode tries to increase the temperature of the catalytic converter as rapidly as possible during the initial transient or “cold start” period. Reachability, as a tool for system analysis, is used to verify the properties of the closed loop system.
In Constrained optimal control of an electronic throttle, M. Vašak, M. Baotić, M. Morari, I. Petrović and N. Perić propose a constrained optimal control problem formulation for a discrete-time piecewise affine model of the throttle valve. The optimal control is represented by look-up tables for on-line implementation. The reference tracking controller significantly outperforms a tuned PID controller with feed-forward compensation of non-linearities in terms of the response speed while preserving the response quality regarding the absence of an overshoot and the static accuracy within the measurement resolution.
In Modelling and control of auxiliary loads in heavy vehicles, N. Pettersson and K. Johansson evaluate the benefits of driving auxiliary units with electricity instead of mechanically are evaluated in terms of fuel saving. A Modelica library of the energy consumption of the auxiliaries is presented. A case study on optimal control of the cooling system is illustrated. Control actuators are the electrical generator, the cooling fan and the water pump. It is evaluated through simulations with external variables collected from experiments. The results show that significant energy savings can be obtained.
In Observability analysis and state observers for automotive powertrains with backlash: a hybrid system approach, G. Ferrari-Trecate and M. Gati analyse the observability properties of automotive powertrains. The powertrain is modeled as a hybrid system in the piecewise affine form and measurements of the engine torque and speed are used to compute the maximal set of observable states. This set captures in a precise way how the main variables and parameters of the driveline influence the possibility of estimating the shaft twist. Then, the authors show how to exploit the knowledge of observable states in order to build computationally efficient driveline deadbeat observers.
In Modelling and simulation of static and Coulomb friction in a class of automotive systems, R. Morselli, R. Zanasi and P. Ferracin propose a method for the efficient simulation of a wide class of automotive mechanical systems with static and Coulomb friction phenomena. The modelling approach is based on the port-Hamiltonian representation of the dynamic systems. The computation of the friction forces requires only zero-crossing detection. A slight approximation allows faster and sufficiently accurate simulations even without accurate zero-crossing detection. The proposed approach is used to simulate the behaviour of a complex gearbox provided by farm tractors.
In Hybrid model predictive control application towards optimal semi-active suspension, N. Giorgetti, A. Bemporad, E. Tseng and D. Hrovat model the constrained quarter-car semi-active suspension as a switching affine system where the switching is determined by the activation of passivity constraints, force saturation, and maximum power dissipation limits. The performance of different finite-horizon hybrid MPC controllers is tested in simulation using mixed-integer quadratic programming and compared to various semi-active controllers in the literature including the well-known “clipped-optimal”. For horizon equal to one, the explicit MPC control law corresponds to clipped LQR.
In Integrated vehicle control using steering and brakes, G. Burgio and P. Zegelaar consider the integration of brakes and steering actuators in vehicle lateral dynamics control. This control problem is of primary relevance and is challenging since it is MIMO, intrinsically non-linear due to tires characteristic and with high plant uncertainty due to variations of major parameters. An application of the state feedback linearization technique to the control problem is presented and some experimental results are reported. The controller results globally stable, smooth and effective with the steering actuator and uses the braking correction only in critical cases.
A good proportion of the papers in the special issue were presented in a workshop organized in May 2005 in Rome by the HYCON Network of Excellence. All papers were peer-reviewed and went through two round of review. We wish to thank the reviewers for their dedication. We also wish to thank Francoise Lamnabhi-Lagarrigue for her support and determination in pushing the publication of this special issue. Last but not least we acknowledge the support of Alkis Konstantellos, a constant inspiration in the European Community for the control research groups, and of Rolf Riemenschneider of the EU.