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I guess the answer is: How much more and how long to wait? I have AWD and it really makes a difference on our often-wet roads.
shark2k
Member
Seeing as there are still 2 years before this car comes out, for me the waiting would depend on how long after the car is released. If the car does get released in 2011 (Signature series and whatnot) and in 2012 they will have the option available, I would wait. If it was 2013, I might wait also. Of course for me, waiting another year would probably be a good idea since I'm jobless right now and the extra time would allow me to save more money. Just my $0.02.
-Shark2k
From a performance standpoint most awd systems won't handle as well as a similarly setup rear wheel drive version. A good example is BMW's 335 the rear wheel drive actually handles better on tarmac although it won't have as much traction in the snow. This is because the front tires get overworked in many situations as they are trying to accelerate and turn resulting in pushing.
With some of the modern systems in performance ICE cars i.e. the nissan GTR, STi, EVO and Porsche 911 turbo etc. Electronically controlled differentials, accelerometers, and abs systems have allowed the power to be distributed wherever needed allowing at any given time for the car to essentially be either entirely or almost fwd or rwd. The Nissan GTR is a good example of how the extra weight doesn't hinder a well designed AWD system.
With the 4 motor electric design you would be able to almost instantly modulate where torque is distributed with one system which is what you want from an engineering standpoint.
Tdave
Member
Thanks, elirentz, well written.
And that's why an AWD electric sports car is the holy grail of performance nirvana, with a motor at each wheel with small drive shaft, with all the stability control, traction control, and ABS controlled through software to the almost instantly modulated power/regen of the motors.
Neutral handling at all times. I've driven a RWD ICE car on the race track a fair bit for fun. The thought of the above gets me so excited, I really don't want to wait the 5 years it will take to get us there.
And that's why an AWD electric sports car is the holy grail of performance nirvana, with a motor at each wheel with small drive shaft, with all the stability control, traction control, and ABS controlled through software to the almost instantly modulated power/regen of the motors.
Neutral handling at all times. I've driven a RWD ICE car on the race track a fair bit for fun. The thought of the above gets me so excited, I really don't want to wait the 5 years it will take to get us there.
But why would 4 motors be superior to 2 motors with electronically-controlled differentials? The difference in driveshaft lengths has got to be minimal. Are the differentials significantly slower to allocate torque? I just don't see big benefits here.
For the record, the reason *not* to have 4 motors is that electric motors get less efficient as they get smaller. So for a given target horsepower 2 motors will weigh less than 4. Obviously this holds true with 1 motor vs. 2 as well, but assuming AWD is the goal we'd be talking about a very long and heavy driveshaft and two extra differentials, which more than offsets the extra weight of a second motor. I guess that means the question is whether at the target horsepower the increased weight of multiple motors/PEMs is greater or less than that of the somewhat longer driveshafts and the two differentials. Of course the PEM reliability issue is another factor, and cost is probably the elephant in the room...so if it's even a close question I'd expect the 2-motor solution to win out.
As an aside, in your first post on the subject you talk about the fact that braking and acceleration distances would be equal in such a scenario (using regen only). I suppose that's right...but you seem to assume that accel distances would decrease to current stopping distances, which seems wrong. I would expect the reverse...your braking performance would suddenly be limited to the power of the motor, so it would take a half-mile to run a quarter-mile sprint...one quarter accel and one quarter decel. That's why we still have friction brakes...there simply aren't any motors available that can rob as much kinetic energy in as short a time. If you want the car to accelerate to 60mph in 120ft, you're going to need an obscenely powerful motor(s) any way you slice it. Also, do note that none of this is affected by the number of motors in the car.
Well one thing is differentials create parasitic drive train power loss. Whether or not they are more efficient than having four motors IDK. I know, for example, with my car a subaru STi (w/ performance AWD) the output of the motor at the crank on average has been 300 hp+ and on average on most dyno's the car outputs ~240-260 hp to the wheels. That's a 60-40 hp loss because of the transmission and differentials, that's pretty significant.
Having direct drive motors would eliminate this problem.
Having direct drive motors would eliminate this problem.
Now, tell me how this "electronicaly controlled differential" alocates torque per wheel. Let's say, I want 20% on the left and 80% on the right. After 0.3s I want 76% on the left and only 24% on the right. After that I don't want any torque on the right and 100% on the left. In the next second I want 20% negative torque on the left and 100% positive on the right.
Now go and do this with "electronicaly controlled differential". You are "screwed". Some of it could be acomplished through brakes but it is slow, unreliable and inefficiant (wastes energy) while some of it (negative/positive torque) just cannot be done via differential.
A "motor per wheel" concept is not just equivalent to differentials, it is much more capable design.
Well, to be honest, we don't know that yet. It is much simpler design, mechanicaly speaking, but there is also lots of electronic.
Electronic absolutely hate heat, vibration, moisture, big temperature changes. There is plenty of all of that in a car. This is not unsolvable problem, but will take some thought and experience to get it right. I'm not sure the industry have them yet.
The most likely AWD candidate
Notable - BorgWarner Electrifies Transmissions - 04/09
BorgWarner makes the Roadster transmission and this is their AWD transmission for electric cars. Who else would they be making it for?
Tesla S: a model citizen - Los Angeles Times
From this article I read it looks like Tesla is committed to the liquid cooled multi-cell battery pack design like the Roadster. I hope they change their mind on this one because it is old school. This, of course, like the article states, eliminates the possibility of the 440V rapid recharge scenario. To top it off they say they are not looking into a battery swapping station scenario, read "we are not going to get in bed with Project Better Place". So what does this do for the car. It makes me reconsider my $5000 downpayment, is what it does. They have effectively made this another expensive toy to tool around the city instead of making it a true competitor against ICE vehicles. I hope they reconsider the battery choice, especially now with Toshiba producing Lithium Titanate batteries superior to Altairnano and they have the capacity to mass produce them to drive costs down, not to mention produce packs the size more friendly to motorcycles and cars.
Toshiba ups the Lithium Titanate battery ante | Sequence Omega
I seriously hope to hear a news article soon stating that Tesla has decided to go with Toshiba.
Notable - BorgWarner Electrifies Transmissions - 04/09
BorgWarner makes the Roadster transmission and this is their AWD transmission for electric cars. Who else would they be making it for?
Tesla S: a model citizen - Los Angeles Times
From this article I read it looks like Tesla is committed to the liquid cooled multi-cell battery pack design like the Roadster. I hope they change their mind on this one because it is old school. This, of course, like the article states, eliminates the possibility of the 440V rapid recharge scenario. To top it off they say they are not looking into a battery swapping station scenario, read "we are not going to get in bed with Project Better Place". So what does this do for the car. It makes me reconsider my $5000 downpayment, is what it does. They have effectively made this another expensive toy to tool around the city instead of making it a true competitor against ICE vehicles. I hope they reconsider the battery choice, especially now with Toshiba producing Lithium Titanate batteries superior to Altairnano and they have the capacity to mass produce them to drive costs down, not to mention produce packs the size more friendly to motorcycles and cars.
Toshiba ups the Lithium Titanate battery ante | Sequence Omega
I seriously hope to hear a news article soon stating that Tesla has decided to go with Toshiba.
Tdave
Member
Yeah, that implies it's for the Model S. But am I reading that right? Their AWD transaxle would use a single motor to drive all 4 wheels? Oh my, why on earth would they opt for that design?
Here I am excited about the possibilities of a motor per wheel with a short drive shaft, reluctantly admitting to myself that the first AWD EVs would probably opt for two motors, one per axle. And now this, implying Tesla will use the least progressive design, one stuck in the past using a single power source mechanically distributed to all 4 wheels.
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Wow. Great first Post kabalah70.
Curious that the redline 14,000 RPM of the Roadster is double of this new system at 7,500 RPM.
Toshiba and Panasonic keep having great battery press. At the same time there are lesser
"brand" companies also doing some cool things. Tesla's take on the Roadster was to go with tried and true commodity batteries to eliminate any problems with new technology. Really smart for the first round. Must they be this cautious on the next one or have they learned enough to go for something exciting?
Curious that the redline 14,000 RPM of the Roadster is double of this new system at 7,500 RPM.
Toshiba and Panasonic keep having great battery press. At the same time there are lesser
"brand" companies also doing some cool things. Tesla's take on the Roadster was to go with tried and true commodity batteries to eliminate any problems with new technology. Really smart for the first round. Must they be this cautious on the next one or have they learned enough to go for something exciting?
This looks to me like BW is doing a solo at what they are good at - transmissions. Tesla said their AWD will be "another smaller motor in front". No long driveshafts, thank you.
Actually, if you read the description properly, it sounds like it's for a "through the road" hybrid. They aren't that clear about it, but I believe they're describing something like a FWD IC engine and a rear electric motor with this transaxle. There's no long drive shaft. Just a secondary electrically driven axle than can provide some electric boost and regen.
