Head-up Displays for Cars by Continental: production principles and safety guide lines
The head-up display reduces driver distraction and increases driver safety.
To read an instrument cluster, for at least a brief moment you have to take your eyes off the road. Your eyes need to adjust to the shorter distance (known as accommodation) before the information flow can begin. This process reoccurs when your eyes readjust to the greater visual distance to take in the traffic environment. This process takes time and tires the eyes if it happens frequently. Reading a display, including accommodation of the eye occurring twice, requires at least half a second with a conventional instrument cluster. This means that when drivers avert their gaze at a speed of 120 km/h they will be driving blind for about 33 meters. A head-up display (HUD) shows information exactly where you need it – directly in the line of sight. Drivers get all the important information such as speed, warning signals and indicator arrows for navigation without looking down to the instrument cluster or the secondary display. In the case of a windscreen head-up display drivers see a virtual image, but not as a flat, static picture on the windshield, but rather, as “floating” over the hood at a distance of about two meters. In the case of an augmented-reality head-up display the information of the windshield-HUD is enriched with a layer of information right on the street in front of the car. For Continental the HUD represents a key technology for its holistic approach for the human-machine-interface which will lead to a dialogue without word between the driver and his vehicle.
Always in control, always informed
Our head-up displays also make driving more comfortable. You will feel better protected, because you have all the information directly in their line of sight and therefore can recognize and catch critical situations even faster. With improved feedback regarding the driving situation and the status of your car, it will become harder to miss important information. Speed limits for example, can be displayed in the HUD and you will be warned if you drive above the speed limit. Information from the adaptive cruise control assures you that you are driving the correct distance from the car in front of you and gives you an early warning if you are not. Our lane departure warning system gives immediate feedback if you are going to leave the lane. The usability of navigation systems also improves with a better visual feedback regarding the road ahead, especially with our augmented reality head-up display, where navigation information is seamlessly integrated in to the environment in front of your car. Continental head-up displays can be easily adjusted to the needs and preferences of drivers. This allows to customize the positioning of the virtual image on the windshield, according to the own preferences. It is also possible to adjust the contrast and the brightness. Last but not least, you can configure what information is displayed on the HUD by turning off single information like speed limit or navigation.
From a technical point of view, the HUD is a master stroke. In order to create a distortion-free image, the windshield, a curved free-form surface from an optical point of view, requires very exact images from the concave mirror in the HUD. As a result, the tolerances in the manufacturing of the large mirror are correspondingly narrow: Continental produces this large asphere in plastic injection molding with a tolerance of under 5 micrometers (0.005 mm) across the entire surface. Due to the large dynamic range of ambient brightness, extreme luminance and excellent brightness control are required for the HUD (depending on the brightness of the background of the virtual display) in order to produce an image that can be easily read. Any optical distortions through the shield are electronically corrected on the display. A lot of research and development has primarily gone into optimizing the picture generating unit (PGU), consisting of a heat sink, printed circuit board, LED matrix, and TFT color display and light guide. The latest development in a follow-up solution for an existing HUD is a display that has already reached 3.1˝ and 800 x 480 pixel resolution. During optimization, the existing 1.8˝ PGU has not only seen its performance improve – it is now more efficient as well. Compared to the first generation, the LED matrix in the TFT display in the second generation has already reached 1,300 candela per watt (cd/W). Since 2013, the next stage of development has been based on an efficiency of 1,700 cd/W, and in a few years a brightness of 3,000 cd/W will be a realistic target. This explains why only 8 watts of electrical power are needed for a contemporary standard series HUD, despite the intense brightness of the display. Thanks to increasing efficiency in LED technology, the luminance of the visible display in the series has already reached more than 10,000 cd/m2.
Continental has a broad portfolio of head-up displays. We develop windshield head-up displays, combiner head-up displays and augmented reality head-up displays. One main focus of our strategy is an aim to provide head-up displays for all vehicles classes, from luxury cars to small vehicles. Consequently we were one of the first manufacturers to deliver mid range vehicle HUDs, for example for the BMW 3 Series. The key to producing HUDs for smaller, less expensive vehicle classes as well, was to optimize costs, and also, more importantly, to reduce installation space. As a result, the second generation of Continental HUDs require just over half the space needed for the first generation of HUDs. Our combiner-HUD is the latest step on the path towards having a HUD in every car and therefore improved safety, regardless of the size or value of the car. The combiner-HUD further reduces installation space and is flatter than a windshield-HUD, something that is crucial for all vehicles types, where space in the cockpit is very limited. It is also very cost-effective as it only requires a small plastic or glass screen in order to fulfill the optical requirements for adequately reflecting the light as opposed to the windscreen itself.