SoylentNews is people
SoylentNews
An Anonymous Coward writes:
Until now, electric cars could be broken down nicely -- at the high end there is Tesla S & X, and then there is everything else (possibly including Tesla 3). A few possible competitors either quit early (Fisker) or haven't made it to production yet (Lucid, Faraday Future). This split covered price, luxury and range. Now there is a serious competitor from Jaguar and Motor Trend tested the I-Pace in Europe. While they report trouble finding charging points (it's a new car after all), they generally seemed to be impressed.
As BEV platforms go, the I-Pace’s skateboard layout is conventional. There’s a motor at each end, one driving the front wheels, the other the rear, and in between is a liquid-cooled 90-kW-hr battery pack with 432 lithium-ion cells that also provides structural integrity for the chassis. The Jaguar-developed motors are synchronous permanent magnet units with concentric transmissions that align the motors with the axles. Total output is 394 hp and 512 lb-ft.
[...] Much of Germany’s autobahn is subject to speed limits, so we spend a lot of time at 75–80 mph. There’s not much wind today, but the higher speed boosts consumption to 43 kW-hr per 100 miles. On one derestricted stretch I wind the I-Pace up near its 124-mph Vmax. It gets there easily, but I burn 6 miles of range in the process (and yes, a gasoline version would also burn fuel with such a surge). Feeling guilty at the extravagance, I back off and settle down to 75–80 mph again.
(Score: 4, Interesting) by Anonymous Coward on Saturday June 09 2018, @02:11PM (6 children)
> I thought the future of electric was going to be in-hub motors...
The allure of hub motors is packaging space, but that is not the full story. The ratio of unsprung weight (tire/wheel/hub/suspension_parts) to sprung weight (the rest of the vehicle) is fundamental to good road holding -- where this is defined as maintaining a roughly constant force between tire and road. Of course there are many other contributing factors, but (at high speed) adding the mass of an in-hub motor would make any vehicle skittish on rough roads, particularly one as fast as this Jag.
From the suspension designer's point of view, the styling trend to large diameter wheels is bad enough--they weigh considerably more than "traditional" wheels of 13" to 15" diameter. When the "dubs" aftermarket fad started (22" wheels) some years back, there were reports of suspension and suspension-mount (body/frame structure) failures in vehicles that had not been designed for or tested with such heavy wheels and/or such low-aspect-ratio vertically-stiff tires. It took a few years for the manufacturers to catch on and design for the increased loads.
There have been many prototype "city cars" build with hub motors and they are probably OK for city speeds. Just don't expect them to be good on a rough freeway.
> ... with the differential electronically controlled
It's a safety thing--if an electronic diff fails, the car can become one wheel drive (or other asymmetric situations with all wheel drive). Since all the wheels are offset from the centerline of the car, additional drive force at any one wheel will tend to steer the car, sometimes violently. A normal "open" differential is inherently safe in this respect since it splits torque nearly evenly between the two outputs. Of course there are edge cases that can cause other problems (drive will be lost with one wheel on ice or lifted off the ground) but these are inconveniences, not an instant spin-out.
Electronic diffs offer a lot of control, with a new vehicle. Around here we have a lot of salt on winter roads and the idea of relying on electronics for a safety critical function, in a wet salty environment, is not something that I would consider buying. For the long term I'll take good old high strength steel (in the diff) over silicon (computer and power electronics) and insulated wiring.
(Score: 2) by Arik on Saturday June 09 2018, @03:50PM (5 children)
Which is exactly why I had expected something a bit more sophisticated than simply sticking the wheel in the hub, but retaining the concept of independent engines for each wheel. It seems to me that if you put the engine at the other end of a short shaft, just a shaft with no gears or other complications, just to put a little distance between it and the wheel, then mount this assembly to the suspension in between the two correctly; you could actually tune your effective ratio by shifting the attachment point one way or the other just a touch, and your 'drivetrain' of 4 quite short and simple shafts should still be considerably lighter and easier to construct than a conventional drive train. Thought there was a name for this design but I can't seem to remember it or rediscover it quickly.
"Electronic diffs offer a lot of control, with a new vehicle. Around here we have a lot of salt on winter roads and the idea of relying on electronics for a safety critical function, in a wet salty environment, is not something that I would consider buying. For the long term I'll take good old high strength steel (in the diff) over silicon (computer and power electronics) and insulated wiring."
I take your point there, but the strong trend in industry seems to be to ignore folks like us. And IIRC Subaru AWD has been computer controlled for a long time, in terms of transmission and differential it's all automatic and it's all computer controlled and it works well. As long as it stays isolated and doesn't wind up getting integrated into the entertainment system or rewritten in css or something, it should be possible to adapt that sort of system to 4 independent motor packages driving 4 independent wheels and see it work just as well, no?
I am not an automotive engineer.
If laughter is the best medicine, who are the best doctors?
(Score: 1, Interesting) by Anonymous Coward on Saturday June 09 2018, @04:05PM (1 child)
> It seems to me that if you put the engine at the other end of a short shaft, just a shaft with no gears or other complications,
As a minimum it's going to need a constant velocity (CV) joint at the wheel for steering and reasonable suspension geometry. For a non-steered (rear) wheel there is swing axle suspension (Beetle, Corvair, etc) that has no outer joints, but expectations for handling have gone beyond swing axles...
> IIRC Subaru AWD has been computer controlled for a long time
Audi, Subaru and many others have used electric/electronically controlled diffs for quite awhile. I believe that these generally (don't know about every kind) default to a reasonable passive system *when* the electronics fails.
(Score: 3, Interesting) by Arik on Saturday June 09 2018, @05:45PM
Well yes, correct, I should have been less categorical, let's say *minimum* of gears and other complications, obviously there has to be a linkage to let the shaft change attitude without tilting the wheel and vice versa, but that's something every (modern) car has regardless if I'm not badly mistaken here. I looked up swing-axle and this is nothing like what I am thinking of. It would basically be a wishbone suspension, well I guess it really would be a wishbone suspension, because what would change is only the bit that's carrying the power, not the suspension itself.
Reading back on that, I'm sure my wording is confusing and that's not entirely unrelated to the writer being a bit confused as well. But the basic point I'm trying to make is that four engines per wheel does not require actually mounting in the hubcap to eliminate a lot of heavy gear, just mounting them closer to the wheel would still eliminate a lot of heavy and expensive gear. You can even tune the weight-distribution by moving them in or out slightly, even if the way I described it initially was confused. And since it's going to be computer controlled either way, whether with a central powerplant and drivetrain or separate powerplants, that doesn't seem like a good objection.
"Audi, Subaru and many others have used electric/electronically controlled diffs for quite awhile. I believe that these generally (don't know about every kind) default to a reasonable passive system *when* the electronics fails."
I mentioned Subaru because it's the one I have a lot of experience with. It's always worked very well for me and I'm not aware of any major problems with it. I was skeptical when they went to that - I LIKED my fully manual Subaru I learned to drive on that car and I knew I could trust it. But the new transmissions have earned respect, they have always worked quite well for me.
Of course when I say 'new' transmission that's all relative, I haven't drive a truly recent one. For all I know they have finally rewritten it in javascript as a webapp running through the entertainment system already.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by Runaway1956 on Saturday June 09 2018, @05:17PM (2 children)
I can't say that I've seen you write a lot of silly stuff. But, you've screwed things up this time.
Javascript, man. You may choose between Chrome/Chromium, or Mozilla, but it's going to be javascript, either way. Javascript is the future!
(Score: 3, Funny) by Arik on Saturday June 09 2018, @05:47PM
If laughter is the best medicine, who are the best doctors?
(Score: 2) by MostCynical on Saturday June 09 2018, @09:45PM
differential need oil change and virus removal!
"I guess once you start doubting, there's no end to it." -Batou, Ghost in the Shell: Stand Alone Complex