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Japan Says Yes To Mirrorless Cars (carscoops.com)
An anonymous reader writes: Last month, Japan became one of the first countries to allow vehicles to use cameras instead of mirrors. "Video mirrors" will no longer be reserved for concept cars. They will likely turn into a huge marketplace for tech businesses and suppliers now that the "Land of the Rising Sun" gave Japanese companies the green light by allowing mirrorless vehicles. While many would argue that glass mirrors work just fine, video mirrors do have some real-world advantages. They can reduce drag and improve fuel efficiency (Warning: source may be paywalled) while improving the looks of a vehicle in the process. In addition, they can capture a wide-angle view that can see blind spots, and they can improve visibility by digitally compensating for glare, darkness or even rainy weather. The first company to supply digital mirrors will be Ichikoh. Their first product will be an interior rear-view mirror named the Smart Rear View Mirror that will enter production on June 28th.
Having a camera installed in a car that doesn't have one is a pain, because they have to put in the wiring for it. But once that's done, it's not difficult to just swap out the module. If these are anything like backup cameras, it's about the size of a GoPro (or smaller), and probably about as expensive. Judging by what I paid to replace one of my side mirrors, it's likely going to be roughly on par.
one of the downsides of rear screens is that your eye has to change its focal distance. With a mirror, your eye is focusing at a true distance of the objects behind you. With a screen, you have to adjust to the distance of the screen. It's minor, but it can fatigue your eyes, and you lose all depth perception. Hopefully the enhanced field of view will outweigh the shortcomings.
Back of the envelope estimation here... the mirrors are probably 1% of the drag cross section of the car and the drag is maybe ~50% of the total energy loss in the car. So my guess would be around 0.5% reduction in fuel consumption. Over its life, your car might burn about 20,000 liters of gas, so you'd save about 100 liters, or about $100 (depending on exact prices). Of course, I'm likely to be off by more than a factor of two (but probably less than a factor of 10).
Actually side view mirrors account for about 2-7% of the drag cross section for typical passenger cars (cars vary a lot in drag cross section), but only about 9-19%of the energy produced by burning gasoline makes is used to overcome drag (about 65% is lost in the engine itself). However, the rest of the typical passenger car is becoming more aerodynamic all the time so that 7% number is going up all the time.
As an example, there is a big win is for semi-trucks where their large side view mirrors can account for up to 10% of the drag cross section (after the rest of the truck is already streamlined) and every 2% reduction in drag results in a 1% increase in fuel economy. This is because over 50mph, drag becomes the most significant factor affecting fuel economy and truck spend much more of their time at speed than a typical passenger car.
There is a case for cameras to eventually replace mirrors in passenger cars, though. The cameras will likely be there already (for Advanced Driver Assist Systems required by the emerging New Car Assessment Program standards) and bulking up the various pillars (already required by the NHTSA for improved rollover crush resistance) is easier/cheaper if they widen them (unfortunately widening pillars creates larger blind spots which need to be accommodated by automotive architects), so if they just don't need to install mirrors, it is one less thing to install in the car and one less constraint on the automotive architects.