BMW patents 'virtual side-view mirror' that projects images onto car windows

Currently, automakers have been experimenting with virtual car mirror technology. According to foreign media reports, BMW recently applied for a patent that aims to better replicate the classic car mirror experience while providing virtual car mirror technology with the same advantages.

BMW car (Image source: thedrive.com)

The automotive industry has been thinking about replacing side-view mirrors with cameras and screens inside cars, and several automakers are working on the technology. The benefit of this technology is that it allows automakers to replace bulky side-view mirrors with sleeker camera modules to reduce air drag, giving car designers more freedom in styling. For example, Audi has installed the technology on its e-Tron SUV, which is now sold in multiple markets around the world. Although virtual side-view mirrors are not yet legal in the United States, the National Highway Traffic Administration (NHTSA) began testing the technology in 2019.

Like other virtual rearview mirror designs, BMW's patent uses cameras instead of side mirrors, but the difference is that the video is not displayed on a normal screen mounted on the door or A-pillar in the driver's line of sight. Instead, the video is sent to a hidden display and then projected onto a semi-mirror area on the side window of the car, creating a virtual image 0.5 to 2 meters away from the driver's line of sight, similar to the head-up display projected onto the car windshield. Although the system is likely to use a camera mounted on the car column to provide side-view video content, the image projection will be completed through a display inside the car, as shown in the figure below.

BMW patent Figure 1 (Image source: thedrive.com)

The system has many advantages over traditional side mirrors and more common virtual mirror systems, such as retaining the beneficial function of reducing wind resistance because such side mirrors can be made smaller while retaining a large field of view compared to traditional mirrors. In addition, the system allows the driver's eyes to focus on the distant road while looking at the mirror, reducing eye fatigue and reducing the time required for the driver to switch from viewing close-up to viewing distant situations. At the same time, the system also allows drivers familiar with ordinary mirrors to adapt to using the system more quickly because the system projects the image right where the ordinary side mirror is located.

BMW patent Figure 3 (Source: thedrive.com)

The patent also mentions that another major benefit of the system is the ability to overlay useful data on the virtual car mirror display, which may involve navigation instructions, parking warnings, and even the distance between the driver and nearby vehicles to achieve safer lane changes. Of course, this technology is not unique to BMW and can also be used in any other virtual car mirror system that uses a normal screen.

Some people may think that there is a basic problem with this system, that is, what happens when the window is rolled down? The patent shows that according to one of the usage scenarios of the display system, the mirror area is arranged in a part of the side window that is stationary. To be more specific, the half-mirror area of ​​the window will not move, that is, the virtual side-view mirror will always be in the same position. The purpose is to make the reflectivity of the side-view mirror area variable, so that the brightness of the virtual car mirror can be adjusted according to the external light conditions, so that the image can be seen during the day and it will not be too bright at night.

A key drawback of the virtual mirror system is the fixed field of view. Unlike traditional side-view mirrors, the screens used in virtual mirror designs do not react when the user moves their head because the cameras are fixed regardless of the driver's head position. However, this drawback can be compensated by head tracking technology, which is already a mature technology used in fighter jets and virtual reality equipment. Or it may be simple that drivers can adapt to using fixed side-view cameras as long as they provide a comfortable large field of view.

BMW is no stranger to virtual car mirror technology. As early as 2016, it launched a concept car i8 without car mirrors at CES. Each door of the car is equipped with a camera, which, combined with a screen that replaces the central rearview mirror, can provide a 180-degree view behind the car, allowing the driver to clearly see what is happening behind the car.

It’s unclear when BMW plans to bring the technology to real cars, but the hope is that it will first be available on cutting-edge electric models, similar to its previous innovative laser headlight technology.