Abstract
KEYWORDS – Human-Machine-Interface, Brake-by-wire, customer study, force sensitive actuation, customisation
ABSTRACT
Today most electric and hybrid electric vehicles offered on market are equipped with a brake-by-wire system for efficient and comfortable braking. The characteristic generated by the pedal simulator often is described in studies as synthetic and not authentic, although today’s systems usually try to simulate conventional characteristics in case of an authentic and safe feeling. That’s why we defined two main objectives for our research: First eliminate the pedal simulator respectively the problems getting out of it. Second find an appropriate HMI with its optimal characteristic that additionally should be set up for customisation.
Conventional pedal and brake characteristics are too complex for customisation by the driver himself, because of the interrelation between their different parameters and their gradients against the pedal travel. So the idea is to reduce the degrees of freedom (DOF) of the characteristic from three (travel – force – deceleration) to two for getting it much more simple to vary. Furthermore the pedal simulator should be removed. As result we prefer a force sensitive brake pedal actuation without any pedal travel. With this kind of HMI customer studies with our self-built street-legal demonstrator were done. A small preliminary study determines the possible resolution of the pedal force compared to pedal travel by the driver’s foot. In the main study the customer acceptance of a personalised force sensitive brake pedal and the preferred force level has been checked via questionnaire and measurement.
So we acquired one hand objective statistical results and on the other hand subjective ratings. Both suggest a benefit for the driver. There is a wide range of variation of the adjusted force level. Furthermore it depends on actual traffic situation. This suggests no clear optimal pedal force level for all test persons in all situations. The answers to the questionnaires showed a very good acceptance of the customised force sensitive brake pedal. With the handling of this alternative HMI all subjects were fine.
In this study, test persons had to drive relatively short distances. Therefore, the effect on fatigue and comfort has to be analysed in further experiments.
In difference to known studies, done by the author or other scientists, in this study the subjects have to adjust their preferred brake pedal force level itself. So they are not forced to decide for pretended parameters. That’s why the results presented here are more representative. Another advantage of the presented method is the time savings for customer studies.
The purpose was to find an alternative HMI concept for brake-by-wire systems without the known disadvantages of benchmarked pedal simulators. The performed customer studies proved the benefits of the presented concept and method that were well accepted by the drivers.