16-10-2023, 08:18 PM
Don't worry - my comments about VED were in reply to Jeffrey's points. I should have quoted, but was in a hurry to leave.
Since getting home, I've been reviewing my YouTube history, looking for a video I saw which explained the issues of hub motors in cars really well. Giving up now, as it must have been longer ago than I thought. It's definitely not impossible, but it'll be a while before it's in mass production, if ever. Many challenges.
As it is, some EVs (e.g. Rivian) have 4 motors, but mounted inboard. That's a half-way house, but it's debatable what you gain. The losses in a differential driving half-shafts aren't terrible - are they worse than the penalty of the extra weight of another motor? From what I've seen, 4-motor setups are more about power than efficiency. Personally, I'd rather focus on the latter - we all know that EVs can be crazy-fast, but that gets boring quickly - efficiency and range are what matters to most users of public roads.
For 4WD, I haven't seen one that uses front-rear prop shaft and differential like ICE - they all use separate front/rear motor/final drive assemblies. Probably because the battery is in the way! Most seem to only use 4WD for tearing away from a standstill, and drop back to one (usually the front) for normal driving. So they are quite a lot simpler than conventional 4WD cars. I'd wager there's a lot more moving parts in the simplest ICE engine than any EV motor, and of course the "gearbox" is only a fixed gear and differential, as there's no need to shift gears. The trouble is, it's easy to forget how complicated ICE engines and drivechains are, even in a relatively simple thing like a Yaris, because we don't strip them down any more. The last engine I worked on was an 8 valve from 1984, and I only needed to strip and rebuild the head - that was complicated enough, though it was my first (and only) time getting that involved. I've been watching quite a few teardown and restoration videos of engines over the years, ranging from simple to high-end, and they are so much more involved than an EV motor. Especially if you are replacing rod and main bearing shells. Kudos to the people doing that! Really, the complexity now is in the electronics and software, plus the cooling system. In terms of parts count alone, the cooling system is probably the most involved part of an EV, with lots of hoses, pumps and valves. Tesla have done a good job of integrating lots of these parts into one fairly large single component with the so-called "Super Manifold". Of course, it's not just about cooling the batteries, motor and inverter; the same system provides the cabin heating/cooling via a heat pump (and can heat the batteries to condition them as needed before driving and charging). Is that system more complicated than an ICE vehicle with air-con? Not sure, but certainly in a similar ballpark...
Since getting home, I've been reviewing my YouTube history, looking for a video I saw which explained the issues of hub motors in cars really well. Giving up now, as it must have been longer ago than I thought. It's definitely not impossible, but it'll be a while before it's in mass production, if ever. Many challenges.
As it is, some EVs (e.g. Rivian) have 4 motors, but mounted inboard. That's a half-way house, but it's debatable what you gain. The losses in a differential driving half-shafts aren't terrible - are they worse than the penalty of the extra weight of another motor? From what I've seen, 4-motor setups are more about power than efficiency. Personally, I'd rather focus on the latter - we all know that EVs can be crazy-fast, but that gets boring quickly - efficiency and range are what matters to most users of public roads.
For 4WD, I haven't seen one that uses front-rear prop shaft and differential like ICE - they all use separate front/rear motor/final drive assemblies. Probably because the battery is in the way! Most seem to only use 4WD for tearing away from a standstill, and drop back to one (usually the front) for normal driving. So they are quite a lot simpler than conventional 4WD cars. I'd wager there's a lot more moving parts in the simplest ICE engine than any EV motor, and of course the "gearbox" is only a fixed gear and differential, as there's no need to shift gears. The trouble is, it's easy to forget how complicated ICE engines and drivechains are, even in a relatively simple thing like a Yaris, because we don't strip them down any more. The last engine I worked on was an 8 valve from 1984, and I only needed to strip and rebuild the head - that was complicated enough, though it was my first (and only) time getting that involved. I've been watching quite a few teardown and restoration videos of engines over the years, ranging from simple to high-end, and they are so much more involved than an EV motor. Especially if you are replacing rod and main bearing shells. Kudos to the people doing that! Really, the complexity now is in the electronics and software, plus the cooling system. In terms of parts count alone, the cooling system is probably the most involved part of an EV, with lots of hoses, pumps and valves. Tesla have done a good job of integrating lots of these parts into one fairly large single component with the so-called "Super Manifold". Of course, it's not just about cooling the batteries, motor and inverter; the same system provides the cabin heating/cooling via a heat pump (and can heat the batteries to condition them as needed before driving and charging). Is that system more complicated than an ICE vehicle with air-con? Not sure, but certainly in a similar ballpark...
