Automotive Engineer

Premium vehicles can provide drivers with almost limitless information but the space available to do so is finite. Some of the most innovative solutions to this problem are reconfigurable instrument clusters based on thin-film transistor (TFT) screens.

Unlike analogue displays, virtual instruments can change the information they present – the rev counter, for instance, can be replaced by navigation data as the vehicle approaches a junction.

Tier Ones such as Visteon have proved the efficacy of the technology in applications such as the Jaguar XJ sedan, but are working hard on next-generation systems. Consumer expectations for graphics quality increase all the time.

More powerful graphics processors – and more suppliers of them – are available now, thanks to the explosion in the smartphone and tablet markets, but they still have to be made robust enough to meet automotive standards.

Thermal management will become more challenging, in part because of the heat dissipated by the LED backlighting that TFT screens require. 

Dedicated cooling fans are not common now but may become integrated into the clusters in future.

Developing systems using a common platform, as Visteon does, helps to reduce cost. Further savings will come from implementing the graphics that OEMs’ designers come up with into the displays in weeks instead of months.

The technology will migrate to the C-segment and even premium B-segment vehicles as comfort and safety feature content keeps increasing, and as consumers demand greater connectivity.

The technology can also help OEMs to reduce the cost of electric and hybrid variants developed from mainstream models: graphics to display range, recharging station locations, and the motifs used to reward eco-driving style are easily integrated into reconfigurable clusters.

1. Lens
Moulded from PMMA, typically 50% smoked to protect from the sun’s UV rays and to enhance the perception that the display is floating in space.

2. Mask
Forms one half of the casing, to which the lens is a snap-fitting. The mask also mounts the light sensors. The sensors detect ambient light levels, helping to manage the display’s contrast ratio through the amount of backlighting required in any condition. Fixed backlighting would generate excessive heat.

3. Chimes speaker
Provides the sound effects for the direction indicators. Aural quality is important in luxury vehicles so polyphonic tones may be used.

4. TFT assembly
Comprises the LCD glass itself, display drivers and the LED backlighting module. The TFT display is traditional 1,280 x 480 pixel technology – effectively two wide VGA screens manufactured as a single panel. Legislation requires the display to be up and running quickly. If the display knows the doors are unlocked it can initiate the start-up processes. Integrating most of the drivers onto the PCB cuts cost.

5. Heat exchanger
A simple aluminium extrusion conducts the heat generated by the LED backlighting: around 10-20W, depending on demand. Thermocouples on the panel measure its temperature, which is fed to the cluster’s thermal management system.

6. PCB
The brains. May feature several chips; Visteon’s has just two. A vehicle interface microprocessor gets everything going and, via CAN and MOST networks, takes vehicle data, decides if it’s needed for updating the display and, if yes, sends it to the graphics microprocessor. This takes the data and builds the next frame to be stored ready to go to the display. Direct-access memory ensures that graphics load quickly. The PCB can run around five different voltages, making development challenging.

7. Back cover
Typically injection-moulded, glass-reinforced polyamide 6,6. This part can be vented to let heat escape. Cooling fans could be mounted here in future.