CEmACS Project
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Information Society Technologies Sixth Framework Programme

Vehicle control for Active Safety

Improving driver and passengers safety by accident avoidance and accident mitigation is one of the most important long term research issues in the automotive industry. The main objective of this work package is to experimentally test and evaluate novel multivariable control and nonlinear state observervation approaches to stabilise cars close to the physical limits for increased active safety.

Roll-over protection

The main objective is the development of compensation strategies that prevent dangerous lateral acceleration and roll motion which may lead to rollover. Different actuator concepts will be considered such as brake-by-wire, steer-by-wire, active suspension, active stabilisors and combinations of those actuator concepts, however the main emphasis will be put on braking and active steering. The roll dynamics of a vehicle depend crucially on its mass and the position of its center of gravity. As difference to existing approaches (which follow a conservative worst case strategy) a load adaptive stabilisation control will be designed. It is assumed that information about the vehicle load is available from external estimators, the estimation error might be large in particular in the initial phase or in situations where there is not enough persistent excitation. Thus, uncertainties and errors in load estimation will have to be compensated by a combination of robust control and adaptation strategies. The rollover stabilisation should also work in critical situations where one or two wheels have already lost ground contact. Evaluation of the different methods will be carried out for a realisic simulation of a commercial van. In addition, the control system will be implemented in one of the experimental vehicles. The objective of the experimental evaluation will be to show that lateral acceleration and roll angle can be kept within pre-specified constraints.

Collision avoidance

The objective of this workpackage is to track the vehicle along a prescribed trajectory in order to avoid an impending collision. Possible scenarios for collision avoidance are
  1. to automatically start an evasion/dodging manoeuvre to avoid hitting an obstacle in cases when braking alone is not sufficient anymore,
  2. to automatically control the attitude of the vehicle in such a way that the impact is least harmful in cases when the crash has become unavoidable.
The basic idea is that in emergency situations automatic systems will respond faster and more reliably than the average driver. In many cases collision avoidance will require to control the vehicle outside the normal driving envelope in ranges where the vehicle dynamics become very nonlinear and the vehicle is close to the physical limits in terms of acceleration and tyre contact forces. In these ranges the average driver will often fail to stabilise the vehicle. Collision avoidance by active steering is still a long-term research objective. The task of collision avoidance involves control problems at different levels of hierachy as shown in the figure. Collision avoidance dynamics structure The normal operational mode of the vehicle is lane keeping and speed/distance control achieved either manually or by an autonomous cruise controller as a comfort function. At this level the command signals for the subordinate control systems are generated. In the event of automatically detecting an obstacle, decision making and trajectory generation for collision avoidance has to take place. On this level a set of possible reference trajectories is generated for the vehicle dynamics controller. The vehicle dynamics controller stabilises and tracks the system along a reference trajectory at the same time taking into account and adapting to the time varying road conditions. In particular, changes in road friction will impose physical limits on the achievable accelerations leading to constraints on the set of realisable trajectories. Collision avoidance heavily relies on efficient obstacle detection and situation assessment algorithms based on environmental information processing. This is currently the subject of extensive research in the fields of image processing, sensor fusion, communication etc. and will not be discussed here. From the previous remarks it is evident that a fully operational collision avoidance system is outside the scope of the project in terms of project structure and resources. Only a sub-task of the vehicle dynamics control problem will be considered in this project with the focus on developing enabling control technologies. This task includes the generation of a physically feasible trajectory and the compensation of environmental disturbances such as changes in the road conditions. The states to be controlled are yaw rate, side slip angle and vehicle speed, the control inputs are the steering angle and the pressure at the four wheel brakes. Vehicle speed and side slip angle are not directly measurable in production cars. Control performance will thus crucially depend on reliable methods of state estimation. An automatic lane change close to the physical limits can be demonstrated using one of the test vehicles. The designed controller will be experimentally verified by carrying out an automatic lane change manoeuvre at the physical limits using one of the test vehicles.

Vehicle Active Safety

Integrated Chassis Control

Control Design

Vehicle State Observation

DaimlerChrysler AG Hamilton Institute University of Glasgow Lund University SINTEF