notyper
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RolledaNsx wrote:
traxtar614
The ECU and ABS will keep the tire from locking up.
When you brake the weight of the car goes forward so the front brakes does most of the work or one tire is on a bad surface it would help in those situations.
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traxtar614 is correct. While the ABS can prevent lockup, it cannot increase the available traction to improve stopping distances.
In fact, in _perfect_ circumstances, an ABS activated stop will be slightly longer than one where ABS does not activate, simply because ABS must release the brakes to prevent lockup. Of course, perfect almost never occurs, which is why ABS is better for pretty much everyone, pretty much all the time.
But back to my and traxtar's point - If you can invoke ABS on a given tire with an existing braking system, all the additional braking force in the world will not matter because the tires will simply lockup. I appreciate your point about heat management, but in this case you're simply moving the heat from the brake rotors to the regen motor/batteries. You'll still have to shed heat, just from a different place. And of course, you can only dump so much energy, so fast, into the batteries. To slow an 1800 kg vehicle travelling at 120 mph to 60 mph at about 1g of deceleration requires shedding energy at continuous 400 kW. In reality, the peak load will be somewhat higher and then taper down as speed drops.
Now, I'm no battery expert like some folks here who make a living in the industry, but unless I miss my guess, charging rates for modern Li-Ion cells are about 4 watts continuous per cell for a 3.6v/4.2v cell. Now, I don't know how many cells would be used. 250? 1000? 2000? Even with thousands of cells, you're not going to be able to dump more than a fraction of the energy lost to braking into the batteries at high speeds.
In summary, regen braking has its uses, especially when it comes to efficiency, but as a performance enhancer, well, I don't think that's a benefit that would stand up to much scrutiny.
SC
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RolledaNsx
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notyper and traxtar 614
LOL you guys are taking it to far
Everybody in the auto business know that regen can't replace fiction braking......(where are you going to put the energy? a semi-truck size battery? LOL , and regen can't brake to a complete stop).
Its just going to help
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notyper
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You said it's going to make a big difference in braking distances. I argue that braking distance is one area that regen definitely _won't_ make a difference. That is all.
SC
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P54
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notyper wrote:
You said it's going to make a big difference in braking distances. I argue that braking distance is one area that regen definitely _won't_ make a difference. That is all.
SC
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This is what he said:
Its just making the braking better just like adding carbon rotors every little thing in the end helps with stopping distance. :)
Maybe it's only 3 feet but 3 feet could save a live or win a race.
Im sorry if i came across as if it was going to be around 20 feet or more. |
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Nick GravesX
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I can understand how the 'damping' effect of motoers can reduce the tendency to lock up on bumpy services, compared to friction brakes.
But I've always assumed the only way Honda could meet its performance claims is via some sort of battery/supercap combination.
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Nick GravesX
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I can understand how the 'damping' effect of motoers can reduce the tendency to lock up on bumpy services, compared to friction brakes.
But I've always assumed the only way Honda could meet its performance claims is via some sort of battery/supercap combination.
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notyper
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Go back about 4 posts P54 where he said it could "lower braking distances a lot".
Just because he tries to pull back the claim doesn't mean the original wasn't incorrect.
SC
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sadlerau
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notyper wrote:
Go back about 4 posts P54 where he said it could "lower braking distances a lot".
Just because he tries to pull back the claim doesn't mean the original wasn't incorrect.
SC
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We have to remember that RolledaNSX is most likely from a sales background, so his comments need to be filtered with that in mind. As Nick has pointed out, there may be the odd situation where re-gen braking may help with braking distances, and judging on how bumpy the Nurburgring is, that track may be one place where this is a fact? And that track with it's high speeds and very frequent braking events, may well lend itself to a "performance hybrid"?
Let's be thankful that RolledaNSX is giving us the little tit bits that he does, because without him we would have diddly squat.
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RolledaNsx
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Yes..... the word was "could" not " it will".
You have to remember all your experience for "Hybrids" from day one was the IMA or the 2WD full hybrid system.
To get help in braking the hybrid system must be 4WD to be helpful and not attached to the petrol engine.
So the Porsche 918 and the NSX will be the first.
Now in a commuter car or EV why waste the money on the program mapping.....
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RolledaNsx
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June 2012 Car and Driver mag
The two electric motors decelerate the 918 up to .5 g versus .15 g in the Panamera Hybrid.
The Porsche 918 has a 6.8 KWH battery
not that big of battery?
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JIRZLEE
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notyper wrote:
RolledaNsx wrote:
traxtar614
The ECU and ABS will keep the tire from locking up.
When you brake the weight of the car goes forward so the front brakes does most of the work or one tire is on a bad surface it would help in those situations.
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an ABS activated stop will be slightly longer than one where ABS does not activate, simply because ABS must release the brakes to prevent lockup. Of course, perfect almost never occurs, which is why ABS is better for pretty much everyone, pretty much all the time.
SC
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I think you just pointed out an area of opportunity for improving stopping distances. Having additional braking force applied to the driveshaft can allow the ABS to more effectively walk the fine line between lockup and release.
Of course tire traction is always going to be the limiting factor, but what can more precise control of wheel speed do?
I'm not an expert but I'd be inclined to think that it could improve braking by a few feet or a bit more over rough surfaces.
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Grace141
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The shortest braking distance for any car is still with all brakes locked and tires sliding, and tire traction is still the end-all limiting factor for braking distances. I think the point here is that while ABS is better than inputs from most drivers it's still a pattern of on and off applications; as far as I know the current ABS tech still consists of uniform pulses regardless of speed. A 3-phase AC system could use phase de-coupling in a manner to provide an infinitely variable ABS - that's how it works in the first place to govern speed. I would think this would be included in the Sport mode software and I would think it could be adaptive to the tractive force offered by replacement tires. In fact you could have apparently three independently variable ABS channels in place to keep a car in a curve under full braking effort assuming the motors driving the front wheels are also capable of generating current to be captured.
Honda's KERS system made perfect sense with the two exceptions of controlling the heat generated and developing the means for quickly processing the energy captured.
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notyper
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Nope, disagree. You're still limited by the tires. The only way to know when you need ABS is when the tire begins to lock. Once a tire begins to lock you must release it until it begins to roll again. You're limited by the dynamics of the tire - it's grip, the time it takes to lock/unlock, it's ability to maintain grip on various surfaces/textures/bumps.
Responding more effectively to rough surfaces and such involves _predictive_ abilities which will require road reading sensors feeding into the braking system, whatever it might be.
As for the Porsche 918, note the _up to_ 0.5g. Some other hybrids can already do 0.3 g on regen. But that's also an _up to_. The regen has a certain amount of braking power available. The slower you're going, the greater the braking g's that fixed amount of braking power will be able to generate. But the faster you go, the less it will be able to contribute. And faster is where heat really affects the braking system in terms of thermal capacity.
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Nick GravesX
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That's true.
One point is that stock Hondas (especially my poor S2000!) tend to suffer from brake fade on the track. It has excellent brakes and I abuse that a bit. A lot.
Possibly, the benefit described may be a tendency for the regen. to help 'save' the service brakes when pounding the 'Ring.
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WingZ
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Nick Graves wrote:
That's true.
One point is that stock Hondas (especially my poor S2000!) tend to suffer from brake fade on the track. It has excellent brakes and I abuse that a bit. A lot.
Possibly, the benefit described may be a tendency for the regen. to help 'save' the service brakes when pounding the 'Ring.
S2K's have to have track pads and hi temp fluid. I had a KW suspension on my S2K CR and just perfect with that set up. I would chase Ferraris on small tracks ;-)
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JIRZLEE
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notyper wrote:
Nope, disagree. You're still limited by the tires. The only way to know when you need ABS is when the tire begins to lock. Once a tire begins to lock you must release it until it begins to roll again. You're limited by the dynamics of the tire - it's grip, the time it takes to lock/unlock, it's ability to maintain grip on various surfaces/textures/bumps.
Responding more effectively to rough surfaces and such involves _predictive_ abilities which will require road reading sensors feeding into the braking system, whatever it might be.
As for the Porsche 918, note the _up to_ 0.5g. Some other hybrids can already do 0.3 g on regen. But that's also an _up to_. The regen has a certain amount of braking power available. The slower you're going, the greater the braking g's that fixed amount of braking power will be able to generate. But the faster you go, the less it will be able to contribute. And faster is where heat really affects the braking system in terms of thermal capacity.
SC
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Not sure who you are disagreeing with but yes tires will always be the final limiting factor. Up to that point though, I think you are simplifying it a bit.
Other factors such as hysteresis, modulation rate, and slip ratio effect braking distances of ABS systems. We are talking about a whole new variable being thrown into the mix and you don't expect the end result to change?
I don't expect it to change the basic principles of how the system works either, but rather work more effectively over a wider range of vehicle speeds and surface textures due to reduced load on the conventional system as well as more precise control of wheel speed (slip ratio).
A tire that is locked up does not brake as effectively or as short as one held at 20% slip. Less load on the conventional system could mean less hysteresis and tighter slip ratio over a wider range of conditions.
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Nick GravesX
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You explained that far better than my attempt, Jirzlee!
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notyper
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JIRZLEE wrote:
Other factors such as hysteresis, modulation rate, and slip ratio effect braking distances of ABS systems. We are talking about a whole new variable being thrown into the mix and you don't expect the end result to change?
I don't expect it to change the basic principles of how the system works either, but rather work more effectively over a wider range of vehicle speeds and surface textures due to reduced load on the conventional system as well as more precise control of wheel speed (slip ratio).
A tire that is locked up does not brake as effectively or as short as one held at 20% slip. Less load on the conventional system could mean less hysteresis and tighter slip ratio over a wider range of conditions.
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No, I don't. Because once you reach a certain point (which IMO was reached about 10 years ago) it doesn't matter how fast you can cycle the brakes because the tire doesn't respond fast enough for it to matter. It's the _tire_ that needs to respond and stop sliding. It's the flex in the carcass and tread rubber that add a delay in response from lock to unlock.
This is the overarching theme here. You can increase your brake force cycling rate (or sampling/feedback) to 10,000 Hz but the tire isn't going to be able to respond or recover that fast. As I said, the only to dramatically improve braking is to create a predictive system that can anticipate changing traction conditions and alter braking force in advance. Theoretically this could be done now for the _rear_ tires on a car, but for the front, the sensor technology is probably a little too expensive.
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TonyEX
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notyper wrote:
JIRZLEE wrote:
Other factors such as hysteresis, modulation rate, and slip ratio effect braking distances of ABS systems. We are talking about a whole new variable being thrown into the mix and you don't expect the end result to change?
I don't expect it to change the basic principles of how the system works either, but rather work more effectively over a wider range of vehicle speeds and surface textures due to reduced load on the conventional system as well as more precise control of wheel speed (slip ratio).
A tire that is locked up does not brake as effectively or as short as one held at 20% slip. Less load on the conventional system could mean less hysteresis and tighter slip ratio over a wider range of conditions.
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No, I don't. Because once you reach a certain point (which IMO was reached about 10 years ago) it doesn't matter how fast you can cycle the brakes because the tire doesn't respond fast enough for it to matter. It's the _tire_ that needs to respond and stop sliding. It's the flex in the carcass and tread rubber that add a delay in response from lock to unlock.
This is the overarching theme here. You can increase your brake force cycling rate (or sampling/feedback) to 10,000 Hz but the tire isn't going to be able to respond or recover that fast. As I said, the only to dramatically improve braking is to create a predictive system that can anticipate changing traction conditions and alter braking force in advance. Theoretically this could be done now for the _rear_ tires on a car, but for the front, the sensor technology is probably a little too expensive.
SC
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OK, I claim some knowledge here having actually paid some attention to Mechanics in between daydreaming about heel and toeing an Alfa Romeo (don't laugh, I learned how to heel and toe that year while daydreaming in ElectroMagnetism, I passed the class (two semesters) too!).
It's more than using model based prediction, is also fundamental issue of pulsed vs. analog ABS systems. (And cost as you have noted). And, oh yeah... LEGAL implications.
There are some neat figures here...
http://ffden-2.phys.uaf.edu/211_fall2002.web.dir/ben_townsend/staticandkineticfriction.htm
This is the important graph
The trick for ABS is to keep the tire at the peak force, which is under its static friction mode, just before it starts to slide and shifts into kinetic friction. As you can see static friction is greater, hence the reason why once a car starts to slide it no longer slows down as much.
Once the tire starts to slide it won't come back for quite a while, likely when the car is in the ditch or after undesirably mating with another object... hence it's extremely important that the ABS algorithm keep the tire away from it's peak force by the maximum error that the particular ABS system is capable of.
That is:
Let MBF be Maximum Braking Force
Then, Max allowable MBC = (Max tire MBC - ABS system margin of error - legal safety margin ).
Where the legal safety margin is a compromise between what your lawyers and engineers say.
And Max allowable MBC is what your ABS algorithms are set to. Never push the tire past that number so as to not risk going into a slide.
So, the question is, how can we make sure that Max allowable MBC is as close as possible to Max tire MBC?
Turns out, only in a racing team can you even approach it.
Let's think about that.
Now, forgetting for a second that friction on a tire is about both longitudinal and side forces... just look at friction strictly as a scalar - I realize this takes out of context that the tire's construction means that lateral and longitudinal forces are handled very differently.
Current ABS systems, so far as I've experienced, pulse the brakes, letting the tire integrate the total forces... if you know electronics, this is like a PCM amplifier (class D) switching a PS and letting the crossover (RC circuit) of a speaker integrate the pulses into an analog signal.
As Shawn points out -not directly- this is but a first order approximation, and as such it must fall into the conservative side, hence an ABS will always err to the safe side and will back off from the peak static friction forces that a tire can generate.
I think a simple solution here would be to implement a servo circuit that monitor a number of parameters and perhaps provides some model of the tire and suspension... currently ABS measure the rotation of the tire only, but perhaps they should take accelerometers into play. I think a maximally defined model of the tire would be night impossible except for a well funded race enterprise, so in the open world the ABS model would again have to be dialed back from maximum performance.
Another thing that IMHO would work in ABS is not to run it in pulse mode (ON/OFF) but to run it in analog mode by modulating the brake pressure... NEVER really turning the brakes off.
I think this would help tremendously because it would remove the shock pulses that travel through the tire when the brakes are cycled. This kind of behavior would keep the tire working in its linear mode at all times. Shock pulse create distortions in the tire that surely create situations where the tire may exceed the its limits of static friction thus sending it sliding...
Again, IMO, pulse modulation of the brakes induces non linear behavior in the tire with peak behavior that exceeds its limits of static friction, hence pulsed ABS systems need to be dialed back from the optimal braking point for a tire in order not to risk skids.
But, a fast acting analog ABS system surely must be expensive because it must modulate a fluid.. hmm... it needs to be fast acting (high rise time) but at the same time handling a viscous fluid (ie: gooey, slow acting). Pulsed systems are much easier to build.
Conclusion- Pulsed ABS systems can never keep the tire at the optimal braking point for a commercial vehicle due to legal implications. Analog ABS systems are more efficient but much more expensive. Predictive algorithms get very expensive as you attempt to maximize the efficiency of the braking system (keeping the tire at its peak forces).
Another side... since brakes are designed to overwhelm the propulsion system, engine braking is just not so important, it's likely an order of magnitude less important... except of course in a racing environment with something like KERRS... but again, the solution then is to include the braking component of KERRS into the equation and the above conclusions all stand.
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TonyEX
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Grace141 wrote:
The shortest braking distance for any car is still with all brakes locked and tires sliding, and tire traction is still the end-all limiting factor for braking distances. I think the point here is that while ABS is better than inputs from most drivers it's still a pattern of on and off applications; as far as I know the current ABS tech still consists of uniform pulses regardless of speed. A 3-phase AC system could use phase de-coupling in a manner to provide an infinitely variable ABS - that's how it works in the first place to govern speed. I would think this would be included in the Sport mode software and I would think it could be adaptive to the tractive force offered by replacement tires. In fact you could have apparently three independently variable ABS channels in place to keep a car in a curve under full braking effort assuming the motors driving the front wheels are also capable of generating current to be captured.
Honda's KERS system made perfect sense with the two exceptions of controlling the heat generated and developing the means for quickly processing the energy captured.
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Suuure...
This is because the car will run into a ditch or something else.
That's really a quick stop...
Really, did you proof read what you wrote?
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RolledaNsx
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TonyE
You get a cookie.
It's just helps to take it closer to the "max".
Closer to a race set up.
Hint: its with the bias and tire load.
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sadlerau
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And then you hit a patch of oil, or greasy tar, or better yet black ice :)
The thing that never ceases to amaze me, is with all the hopeless drivers out there traveling with huge momentum, it's a wonder there aren't more serious accidents every day.
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RolledaNsx
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And while turning.
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sadlerau
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RolledaNsx wrote:
TonyE
You get a cookie.
It's just helps to take it closer to the "max".
Closer to a race set up.
Hint: its with the bias and tire load.
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I have to wonder if the use of "regen" braking doesn't add a smoothing component to the ABS pulses, especially on the less utilsed rear axle??
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RolledaNsx
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Have you ever crash?
I was testing a NSX-R at the Ring in 94 and lost it and rolled it for about 300 m and walked away.
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JIRZLEE
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notyper wrote:
JIRZLEE wrote:
Other factors such as hysteresis, modulation rate, and slip ratio effect braking distances of ABS systems. We are talking about a whole new variable being thrown into the mix and you don't expect the end result to change?
I don't expect it to change the basic principles of how the system works either, but rather work more effectively over a wider range of vehicle speeds and surface textures due to reduced load on the conventional system as well as more precise control of wheel speed (slip ratio).
A tire that is locked up does not brake as effectively or as short as one held at 20% slip. Less load on the conventional system could mean less hysteresis and tighter slip ratio over a wider range of conditions.
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No, I don't. Because once you reach a certain point (which IMO was reached about 10 years ago) it doesn't matter how fast you can cycle the brakes because the tire doesn't respond fast enough for it to matter. It's the _tire_ that needs to respond and stop sliding. It's the flex in the carcass and tread rubber that add a delay in response from lock to unlock.
This is the overarching theme here. You can increase your brake force cycling rate (or sampling/feedback) to 10,000 Hz but the tire isn't going to be able to respond or recover that fast. As I said, the only to dramatically improve braking is to create a predictive system that can anticipate changing traction conditions and alter braking force in advance. Theoretically this could be done now for the _rear_ tires on a car, but for the front, the sensor technology is probably a little too expensive.
SC
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So long answer made short - your opinion is that ABS systems are already 100% efficient in all conditions 100% of the time, beyond some advanced sensing capabilities (that I'm not even getting into)?
You may be right but I just want to be sure I'm getting your take on this.
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JIRZLEE
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notyper wrote:
RolledaNsx wrote:
traxtar614
The ECU and ABS will keep the tire from locking up.
When you brake the weight of the car goes forward so the front brakes does most of the work or one tire is on a bad surface it would help in those situations.
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traxtar614 is correct. While the ABS can prevent lockup, it cannot increase the available traction to improve stopping distances.
In fact, in _perfect_ circumstances, an ABS activated stop will be slightly longer than one where ABS does not activate, simply because ABS must release the brakes to prevent lockup. Of course, perfect almost never occurs, which is why ABS is better for pretty much everyone, pretty much all the time.
But back to my and traxtar's point - If you can invoke ABS on a given tire with an existing braking system, all the additional braking force in the world will not matter because the tires will simply lockup. I appreciate your point about heat management, but in this case you're simply moving the heat from the brake rotors to the regen motor/batteries. You'll still have to shed heat, just from a different place. And of course, you can only dump so much energy, so fast, into the batteries. To slow an 1800 kg vehicle travelling at 120 mph to 60 mph at about 1g of deceleration requires shedding energy at continuous 400 kW. In reality, the peak load will be somewhat higher and then taper down as speed drops.
Now, I'm no battery expert like some folks here who make a living in the industry, but unless I miss my guess, charging rates for modern Li-Ion cells are about 4 watts continuous per cell for a 3.6v/4.2v cell. Now, I don't know how many cells would be used. 250? 1000? 2000? Even with thousands of cells, you're not going to be able to dump more than a fraction of the energy lost to braking into the batteries at high speeds.
In summary, regen braking has its uses, especially when it comes to efficiency, but as a performance enhancer, well, I don't think that's a benefit that would stand up to much scrutiny.
SC
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Did you make this statement under the assumption that the driver would be able to hold the brakes an an ideal amount of slip? Locked-up braking is not as effective as ABS braking in ideal/high-traction conditions. Only if the driver was able to hold the brakes at about 10 to 30% slip ratio would your statement be true.
Generally speaking, a perfectly effective ABS system would maintain braking in this 10 to 30% slip range. It would not lock and unlock the wheels as you stated in other posts.
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JIRZLEE
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RolledaNsx wrote:
And while turning.
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Weight transfer to the outer front tire and the extra braking from regen holding that tire as close as possible to max braking force.
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sadlerau
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RolledaNsx wrote:
Have you ever crash?
I was testing a NSX-R at the Ring in 94 and lost it and rolled it for about 300 m and walked away.
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Luckily I've never had a big one, on the road or the track. Had some close calls on the track, but always had the luck to avoid that last big thump :)
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Mikeydred
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RolledaNsx wrote:
Have you ever crash?
I was testing a NSX-R at the Ring in 94 and lost it and rolled it for about 300 m and walked away.
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Question Rolled does your screen name pay homage to this event?
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