The Multifunctional Human-Machine-Interface is supposed to bridge the gap between head-up displays and future virtual projection screens. It consists of a LED-matrix, which is applied beneath the windshield.

In current driver information and driver assistant systems, the implementation of the Human-Machine-Interface (HMI) providing visual advices and warnings usually works by means of head-down displays. They are prevailingly integrated into the instrument board (speed indicator etc.) or into the vehicle's center console. Head-up displays (HUD) are increasingly applied for further display. They project the information onto the windshield and generate a virtual image directly in front of the vehicle by means of an elaborate optical characteristic (see image 1). Those two concepts of displaying information differ with respect to the driver's level of distraction. Head-up display systems operate less distracting than head-down displays, as they are spatially closer to the traffic situation.
 

Image 1: Head-down display in the Mercedes-Benz S-Class (left) and a Siemens VDO head-up display (right). [Source: Daimler, Continental]

 

Despite of this advantage, head-up displays are subject to certain restrictions as well. For ergonomic and technical reasons, they are able to display the relevant information only in a small area of the driver's visual field. Therefore, spatially directed information, which for instance indicates hardly visible pedestrians in the dark, is presentable only in an indirect way.

A depiction on a virtual projection screen could be of great advantage in such a case. It would display the desired information on the windshield, directly at the visual axis between driver and object (e.g. hardly visible pedestrian). As such forms of depiction are hardly practicable so far, researchers at the Interdisciplinary Center for Advanced Driver Assistant Systems have developed a display form, which is designed as a preliminary stage of a virtual projection screen.

The  display is composed of several adjunctive LED modules forming a matrix and it is located at the lower edge of the windshield. Each of the matrix's modules is equipped with 256 ultra-bright LEDs and 96x96 millimeters in size. Every LED is able to indepentently depict 27 colors and shades of grey. According to the requirements, eight individual grades of brightness can be implemented. Several microcontrollers are applied to access the matrix and to generate symbols. By means of a CAN-bus interface, they receive data concerning the position and the display mode of different grafic information. Such a configuration permits maximum flexibility and at the same time simple control of the HMI throughout the entire period of research and development. Image 2 shows a prototype of the system applied to the research vehicle carai in Chemnitz.
 

Image 2: llustration of the Multifunctional HMI (left) and a first prototype of the HMI inside the research vehicle carai in Chemnitz (right).

The multifunctional HMI is able to display information and warnings which support the driver on various levels of driving. At the same time, it is able to communicate relevant information about the vehicle's condition from the board computer to the driver. The extension over the driver's entire frontal field of vision is what thereby distinguishes it from conventinal head-up or head-down displays.

As an assisting function on the level of navigation, the driver can be given indications concerning route guidance. Furthermore, information about traffic jams or suboptimal road conditions on the scheduled route is possible. By interacting with the vehicle's surroundings (car-to-infrastructure), it is also possible to include traffic light signals and apply an assistant for a so called progressive signal system. On the level of manoeuvering, the display offers the possibilty to depict information concerning road signs (e.g. no passing) or the occupancy of neighboring lanes (e.g. lane changing systems). In terms of turning at a crossroad, the display can indicate pedestrians or bicyclists within the blind spot.