We’re still shopping for a new car to supplement the (awesome) 2018 Honda Odyssey. As we mull the options (waiting to test-drive the Mazda CX-30, for example), one thing that jumps out at me is that AWD (four-wheel drive) continues to be implemented via mechanical driveshafts, differentials, gears, etc. We’re about 12 years into the modern electric car era (Tesla Roadster was launched in 2008). Given the volumes of all-electric cars currently being produced by multiple manufacturers, shouldn’t it be cheaper to implement AWD via low-horsepower electric motors at the back wheels to supplement a conventional FWD system?
A car at highway speeds uses only about 20 hp (source). Thus, even for providing a certain amount of improved handling in slippery conditions, wouldn’t a 10 hp motor on each rear wheel be sufficient for escaping an icy driveway and touching up handling dynamics on the road? Acura announced this for high-performance cars in 2011 with 27 hp per rear wheel (Car and Driver), but the typical consumer just wants to overcome fear of getting stuck (FOGS). It seems that Acura is currently shipping this system in their MDX vehicle, using 36 hp per rear wheel (source). The MDX weighs over 4,000 lbs. For a lighter vehicle with fewer aspirations to greatness, shouldn’t 10 hp per rear wheel be enough? Why isn’t that cheaper than all of the mechanical parts to transmit power from the engine to the back of the car and then distribute between the wheels? A bit of searching on Alibaba shows that a 10 hp electric motor costs about $150 in small quantities. Presumably a car manufacturer would pay much less.
Plainly it actually is cheaper to do it the 1970s mechanical way. But why?