J. Christian Gerdes

Integrating Inertial Sensors With Global Positioning System (GPS) for Vehicle Dynamics Control

This paper demonstrates a method of estimating several key vehicle states-sideslip angle, longitudinal velocity, roll and grade-by combining automotive grade inertial sensors with a Global Positioning System (GPS) receiver. Kinematic Kalman filters that are independent of uncertain vehicle parameters integrate the inertial sensors with GPS to provide high update estimates of the vehicle states and the sensor biases. Using a two-antenna GPS system, the effects of pitch and roll on the measurements can be quantified and are demonstrated to be quite significant in sideslip angle estimation. Employing the same GPS system as an input to the estimator, this paper develops a method that compensates for roll and pitch effects to improve the accuracy of the vehicle state and sensor bias estimates. In addition, calibration procedures for the sensitivity and cross-coupling of inertial sensors are provided to further reduce measurement error The resulting state estimates compare well to the results from calibrated models and Kalman filter predictions and are clean enough to use in vehicle dynamics control systems without additional filtering.

A UNIFIED APPROACH TO DRIVER ASSISTANCE SYSTEMS BASED ON ARTIFICIAL POTENTIAL FIELDS

This paper presents an approach to vehicle control based upon the paradigm of artificial potential fields. Using this method, the dynamics of the vehicle are coupled with the environment in a manner that ensures that the system exhibits safe motion in the absence of driver inputs. The driver remains in control of the vehicle, however, with the control systems presenting a predictable and safe set of dynamics. With the control approach presented here, integration of various assistance systems can be easily achieved through simple superposition of individual potential and damping functions. A simple example of a combined lanekeeping and stability system demonstrates how this can be accomplished. Preliminary simulation results suggest that both safety and driveability are achievable with such a system, prompting further investigation.

Estimation of Tire Slip Angle and Friction Limits Using Steering Torque

Knowledge of the vehicles lateral handling limits is important for vehicle control systems which aim to enhance vehicle handling and passenger safety. This paper presents a model-based estimation method that utilizes pneumatic trail information in steering torque to identify a vehicles lateral handling limits, which are defined by the tire slip angle and peak lateral force limits. This method uses measurements available on many current production vehicles. Most importantly, it takes advantage of the early friction information encoded in the tire pneumatic trail. Pneumatic trail decreases as a function of the tire parameters even in the linear handling region, enabling early detection of the limits before they are reached. Experimental results on an independent front steering steer-by-wire research vehicle demonstrate the observers ability to provide accurate real-time estimates of tire slip angle up to the limits of handling. Testing conditions include maneuvers performed on dry, flat paved road, as well as on lower-friction, dry gravel.

The use of GPS based velocity measurements for measurement of sideslip and wheel slip

Summary This paper details a novel method for measuring three key vehicle states – wheel slip, body sideslip angle, and tire sideslip angle – using GPS velocity information in conjunction with other sensors. Based on initial noise data obtained from the system components, a prediction of the accuracy of the angle measurements is obtained. These results demonstrate that the errors due to stochastic noise in the GPS signal are below one degree for meaningful vehicle speeds and approach a tenth of a degree at highway speeds. Hence the limiting factor for measuring these states is not the GPS receiver, but the manner in which other implementation issues – such as bias elimination, off-axis dynamics and dead-reckoning during loss of satellite visibility – are handled. Subsequent experiments validate both the error analysis and the methodology for obtaining the measurements. The experimental results for this preliminary implementation of GPS-based state estimation compare favorably to theoretical predictions, suggesting that this technique has potential for future implementation in vehicle diagnostic and, ultimately, safety systems.

Optimal Rollover Prevention With Steer by Wire and Differential Braking

This paper uses Model Predictive Control theory to develop a framework for automobile stability control. The framework is then demonstrated with a roll mode controller which seeks to actively limit the peak roll angle of the vehicle while simultaneously tracking the driver’s yaw rate command. Initially, control law presented assumes knowledge of the complete input trajectory and acts as a benchmark for the best performance any controller could have on this system. This assumption is then relaxed by only assuming that the current driver steering command is available. Numerical simulations on a nonlinear vehicle model show that both control structures effectively track the driver intended yaw rate during extreme maneuvers while also limiting the peak roll angle. During ordinary driving, the controlled vehicle behaves identically to an ordinary vehicle. These preliminary results shows that for double lane change maneuvers, it is possible to limit roll angle while still closely tracking the driver’s intent.Copyright

Dynamic Modeling of Residual-Affected Homogeneous Charge Compression Ignition Engines with Variable Valve Actuation

One practical method for achieving homogeneous charge compression ignition (HCCI) in internal combustion engines is to modulate the valves to trap or reinduct exhaust gases, increasing the energy of the charge, and enabling autoignition. Controlling combustion phasing with valve modulation can be challenging, however, since any controller must operate through the chemical kinetics of HCCI and account for the cycle-to-cycle dynamics arising from the retained exhaust gas. This paper presents a simple model of the overall HCCI process that captures these fundamental aspects. The model uses an integrated Arrhenius rate expression to capture the importance of species concentrations and temperature on the ignition process and predict the start of combustion. The cycle-to-cycle dynamics, in turn, develop through mass exchange between a control volume representing the cylinder and a control mass modeling the exhaust manifold. Despite its simplicity, the model predicts combustion phasing, pressure evolution and work output for propane combustion experiments at levels of fidelity comparable to more complex representations. Transient responses to valve timing changes are also captured and, with minor modification, the model can, in principle, be extended to handle a variety of fuels.

Autonomous Vehicle Control at the Limits of Handling

Racecar drivers have the ability to operate a vehicle at its friction limit without losing control. If autonomous vehicles or driver assistance systems had similar capabilities, many fatal accidents could be avoided. To advance this goal, an autonomous racing controller is designed to gain insights into vehicle control at the friction limits. A bicycle model and a ‘ g-g ’ diagram are used to mimic racecar drivers’ internal vehicle model. Lanekeeping steering feedback and wheel slip feedback controllers are used to imitate drivers making steering and throttle corrections according to the vehicle responses. Experimental results on a low friction surface demonstrate that the controller can robustly track a path while operating at the limits of tyre adhesion and provide insights for the future development of vehicle safety systems.

Handwheel Force Feedback for Lanekeeping Assistance: Combined Dynamics and Stability

Lanekeeping assistance could save thousands of lives each year by maintaining lane position in the absence of driver steering commands. In order to work smoothly with the driver, handwheel force feedback must be an integral part of such a system. Here we combine force feedback with a lanekeeping controller based on lateral and heading error. In addition to force feedback replicating the feel in a conventional vehicle, the force can be based on the level of lanekeeping assistance being given. This coupling ofthe force feedback and assistance systems can destabilize the vehicle if not designed properly. Linear modeling verified by experiments shows the effect of varying the gains on both the force feedback and the lanekeeping assistance itself. In this analysis we show that within a range of values that feel reasonable to the driver, changes to the lanekeeping controller or force feedback can have marked effects on the response of the vehicle. It also shows that stability of the system can be ensured by injecting artificial damping or reproducing the on-center characteristics of a conventional vehicle. The analysis allows the force feedback designer to determine a range of stable force feedback gains, from which a set most acceptable to the driver can be chosen.

Pushing the limits: From lanekeeping to autonomous racing

Abstract The success of Electronic Stability Control (ESC) has demonstrated the potential life-saving benefits of vehicle control systems. Lanekeeping presents an obvious next step in vehicle control, but the performance of such systems must be guaranteed before lanekeeping can be viewed as a safety feature. This paper demonstrates that simple lookahead control schemes for lanekeeping are provably robust even at the limits of tire adhesion. By responding to the heading error relative to the desired path, these schemes provide the countersteer behavior necessary to compensate for rear tire saturation and stabilize the vehicle. Using a Lyapunov-based analysis, vehicle stability can be proven even with a highly saturated tire. Taking this a step further by developing a desired path based on the racing line, this lookahead controller can be coupled with longitudinal control based on path position and wheel slip to create an autonomous racecar. The performance of this algorithm shows the potential for lanekeeping control that can truly assist even the best drivers.

Physics-Based Modeling and Control of Residual-Affected HCCI Engines

Homogeneous charge compression ignition (HCCI) is a novel combustion strategy for IC engines that exhibits dramatic decreases in fuel consumption and exhaust emissions. Originally conceived in 1979, the HCCI methodology has been revisited several times by industry but has yet to be implemented because the process is difficult to control. To help address these control challenges, the authors here outline the first generalizable, validated, and experimentally implemented physics-based control methodology for residual-affected HCCI engines. Specifically, the paper describes the formulation and validation of a two-input, two-state control-oriented system model of the residual-affected HCCI process occurring in a single engine cylinder. The combustion timing and peak pressure are the model states, while the inducted gas composition and effective compression ratio are the model inputs. The resulting model accurately captures the system dynamics and allows the simultaneous, coordinated control of both in-cylinder pressure and combustion timing. To demonstrate this, an H 2 optimal controller is synthesized from a linearized version of the model and used to dictate step changes in both combustion timing and peak pressure within about four to five engine cycles on an experimental test bed. The application of control also results in reductions in the standard deviation for both combustion timing and peak pressure. The approach therefore provides accurate mean tracking, as well as a reduction in cyclic dispersion. Another benefit of the simultaneous coordination of both control inputs is a reduction in the control effort required to elicit the desired response. Instead of using a peak pressure controller that must compensate for the effects of a combustion timing controller, and vice versa, the coordinated approach optimizes the use of both control inputs to regulate both outputs.