Driver-centred Motion Control of Heavy Trucks

Doktorsavhandling, 2017

Traffic accidents constitute one of the leading global causes of death. Deadly traffic accidents occur, even in countries that have implemented far-reaching countermeasures, at a rate that cannot be tolerated. Improved safety of heavy trucks is an important remedy, as these vehicles are involved in a large part of all fatal accidents. Human error forms the leading cause of these accidents. Yet, the human ability to handle unstructured elements is unparalleled. The focus of this thesis is to develop a method for controlling the longitudinal and directional motion of the truck combination. The method combines the strength in human flexibility and a computer's ability to act fast in structured situations. Furthermore, the method is derived from observations of how drivers behave in normal and critical situations. This approach is defined as driver-centred motion control. The underlying theory of how drivers behave is based on prior art and two additional studies. In a first study the role of the dimensions of the vehicle is analysed. Furthermore, theories about how steering wheel torque should scale as vehicle properties change are established in more detail. The role of steering wheel size is one such aspect. In a second study the behaviour of the driver is analysed when the vehicle is decelerating and at the same time is exposed to a yaw disturbance. This naturally occurs when braking on split friction, after a front tyre blow out, or when differential braking is applied. The most important common conclusions drawn from these studies are the following. Steering wheel torque can be used as a means of changing driver behaviour. Yet, this requires that the action of the torque coincides with the cognitive objectives of the driver. A consequence of this is that the applied torque must change slowly in order to have a potential effect on the motion. Differential braking proves to be a much more effective approach when fast directional changes are required. This calls for a combination of differential braking and slowly varying steering wheel torque guidance, which is how the developed method operates. The control method has been implemented and evaluated in three studies. The first study was carried out in a moving base driving simulator, involving 39 professional truck drivers, where an oncoming collision between a car and a truck combination was staged. Half of the subjects driving the truck were not given any support. This resulted in a 100% crash rate. The other half were supported by the developed controller in order to initiate a steering avoidance manoeuvre. This reduced the crash rate by 78%. In a second study directional stability control was tested on a frozen lake where the developed controller was compared to a standard stability control system. Several manoeuvres were completed. The deviation from the intended course was reduced in all cases. A more balanced combination of braking and steering forces has been identified as one of the underlying factors. In a third study, the ability of the method to handle varying levels of driver attention during split friction braking was demonstrated in a series of simulations.