Jim Winkelman

Stability of linear feedback systems with random communication delays

Integral control of large-scale systems implies coordination of activities by information exchange via communication networks. Usually these networks are shared with other users. Thus traffic conditions in the network may introduce time-varying random delays in the control loop with adverse effects on its performance and stability. Hence, the control must be designed to compensate for these delays. Recent work in modelling integrated control and communication systems has shown that the communication specific phenomena inducing random communication delays (such as multirate sampling, vacant sampling and message rejection) may be encompassed by finite-dimensional linear discrete-time models, provided that the plant and the controller are linear and time invariant. Existing approaches to the design of integrated control systems rely on conservative stability tests, because only sufficient stability conditions were found for systems with random time-varying delays. In this paper, necessary and sufficient cond...

Stability of Linear Feedback Systems with Random Communication Delays

Integral control of large-scale systems implies application of control and information exchange via communication networks in which random delays may exist. The design of such systems rely on conservative sufficient stability tests for systems with random, time-varying delays. In this report, necessary and sufficient conditions are found for zero-state mean-square exponential stability of the considered class of control systems. Numerical tests for zero-state stability are outlined and illustrated by a simple example. Finally, the results are also demonstrated on specific hardware, multiprocessor real-time control network which has been recently developed.

Stochastic limit control and its application to spark limit control using ionization feedback

Spark timing of an internal combustion (IC) engine is often limited by engine knock in advanced direction and by partial burn and misfire in retard direction. The ability to operate the engine at either its advanced (borderline knock) spark limit or its retard (partial-burn or misfire) spark limit is the key for improving emissions and fuel economy. Due to combustion cycle-to-cycle variations, IC engine combustion behaves similar to a random process. For example, the combustion stability metric covariance of indicated mean effective pressure (IMEP) is calculated from in-cylinder pressure signals, assuming that IMEP is a random process. Presently, the spark limit control of IC engines is deterministic in nature. The controller does not utilize stochastic information associated with control variables such as knock intensity for advanced limit control and combustion stability for retard limit control. This paper proposes a stochastic limit control strategy to maintain engine operation in a normal region. It also presents a simple stochastic model for evaluating the proposed stochastic controller. The stochastic limit control is applied to both borderline knock limit control and combustion stability retard limit control on a 3.0L V6 engine.

Adaptive automotive speed control

An adaptive algorithm for adjusting the gains of a vehicle speed control system is presented. By continuously adjusting the proportional-integral control gains, speed control performance can be optimized for each vehicle and operating condition. This helps the design of a single speed control module that does not need additional calibration or sacrifices in performance for certain car lines. It also allows improved performance for changing road conditions not possible with a fixed-gain control or other types of adaptive control. The results of initial vehicle testing confirm the performance improvements and robustness of the adaptive controller. >

Automotive suspension control through a computer communication network

Closed-loop stability and performance-related studies performed on a multiplex communication network called Carlink, being considered for automotive applications, are discussed. Tests done on an automotive suspension control model, in which the active control signal is applied through the multiplex network as a real-time hybrid computer/hardware-in-the-loop experiment are outlined. The stability of the system is considered using analytical approaches developed by the authors (1991).<<ETX>>

Closed-Loop Ignition Timing Control for SI Engines Using Ionization Current Feedback

Minimal advance for best torque (MBT) timing for an internal combustion (IC) spark ignition (SI) engine is the minimum advance of spark timing for the best torque or, in other words, for the best fuel economy. But MBT timing is often limited by engine knock in the advanced direction and spark timing is also constrained by partial burn and misfire in the retard direction. It is preferred to operate IC engines at MBT timing when it is not knock limited and at borderline knock limit when it is knock limited. During cold start conditions it is desired to operate IC engines at its maximum retard limit subject to combustion stability constraints to reduce catalyst light-off time. Traditionally, both MBT timing and retard spark limit are open-loop feedforward controls whose values are experimentally determined by conducting spark sweeps at different speed and load points, and at different environmental conditions. The borderline knock limit is controlled by a dual-rate count-up/count-down closed-loop control utilizing information from engine knock sensor signals. A closed-loop control architecture for spark timing is proposed in this paper. Using in-cylinder ionization signals both borderline knock and retard spark limits are regulated using closed-loop stochastic limit controls. MBT timing is also controlled closed-loop using an MBT criterion derived from in-cylinder ionization signals. The proposed control strategy and architecture was experimentally validated on a 3.0-L V6 engine for steady state and slow transient conditions

Wheel slip control for antispin acceleration via dynamic spark advance

Abstract One of the problems that might occur during acceleration is wheel spin. While the wheels are spinning, the driving force on the tires reduces considerably and the vehicle cannot speed up as desired. It may even become very difficult to control the vehicle under these conditions. The acceleration characteristics of a vehicle can be improved without changing its physical capabilities with a suitable engine control algorithm that has no additional sensor inputs. This paper presents several control strategies for the wheel slip control problem. The torque output of an engine is modulated to prevent the wheel spin caused by rapid increases in the throttle input. The spark time is varied dynamically to adjust the engine torque and therefore the problem is often referred to as dynamic spark advance (DSA). Variable structure control theory is used for the controller design purposes and simulation results are provided.

MBT Timing Detection and its Closed-Loop Control Using In-Cylinder Ionization Signal

Maximum Brake Torque (MBT) timing for an internal combustion engine is the minimum advance of spark timing for best torque. Traditionally, MBT timing is an open loop feedforward control whose values are experimentally determined by conducting spark sweeps at different speed, load points and at different environmental operating conditions. Almost every calibration point needs a spark sweep to see if the engine can be operated at the MBT timing condition. If not, a certain degree of safety margin is needed to avoid pre-ignition or knock during engine operation. Open-loop spark mapping usually requires a tremendous amount of effort and time to achieve a satisfactory calibration. This paper shows that MBT timing can be achieved by regulating a composite feedback measure derived from the in-cylinder ionization signal referenced to a top dead center crank angle position. A Pi (proportional and integral) controller is used to illustrate closed-loop control of MBT timing. The test results show that the control, using the ionization current based feedback signal, not only maintains the engine average ignition timing at its MBT timing but also reduces the cycle-to-cycle variations.

Adaptive Control of a Pneumatic Valve Actuator for an Internal Combustion Engine

Electro-pneumatic valve actuators are used to eliminate the cam shafts of a traditional internal combustion engine. They are used to control the opening timing, duration, and lift of both intake and exhaust valves. In order to develop model-based control strategies, a control oriented model was developed by piece-wisely linearizing the physics-based nonlinear system model. In this paper, an adaptive valve lift control strategy was developed to improve the intake valve lift repeatability. The model reference adaptive system identification technique was employed to estimate system parameters needed for generating feedforward control signals for the closed-loop control scheme. The closed-loop lift control strategies, along with the model reference feedforward control, were developed and implemented in a prototype controller, and validated on a valve test bench with multiple reference valve lifts at both 1200 and 5000 r/min engine speeds. The experiment results showed that the actual valve lift reached the reference lift within 0.5 mm of lift error in one cycle at 1200 r/min and in two cycles at 5000 r/min. The maximum steady-state lift errors were less than 0.4 mm at high valve lift and less than 1.3 mm at low valve lift. Furthermore, the closed-loop valve lift control improved valve lift repeatability with more than 30% reduction of standard deviation over the open-loop control.

Nonstandard control inputs in the integrated design of vehicles

We consider a vehicle equipped with rear steering, variable drive/brake torque proportioning, and normal force control. Using extensive nonlinear and linear models, and using the notion of reachable sets, an open-loop analysis is conducted to investigate the possible benefits of these nonstandard control inputs in enhanced maneuverability and handling.