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Antilock-breaking (ABS) vs Stabilty Control (ESP) vs Traction Control Video
mikiem:
My current car has an automatic transmission, and not only have I heard it performing engine braking on its own while in cruise control, but I was successfully able to perform it using the manual override this morning to keep my speeds down and compensate for the loss of braking power.
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Automatic transmissions use a torque converter -- oversimplified imagine two propellers in a liquid, one powered, & the other connected to the transmission. A locking torque converter [which most vehicles have nowadays] tries to do just that, lock at higher speeds. A manual transmission uses a clutch, where a disc with a material similar to brake lining on both sides is squeezed by spring tension between the engine's flywheel & the transmission's input shaft. When you step on the clutch pedal you release that spring tension -- the more you press down the more spring tension is reduced.
So... you should be able to see or imagine why a torque converter might be less ideal for downshifting &/or braking. Will it work? Yes, but it's better suited to limiting the gear to a lower range, limiting speed going downhill in the mountains.
We've already had much discussion about ABS being able to stop a vehicle faster ... but the problem is - from a truly holistic defensive driving stand point - that's irrelevant. Because the real reason that ABS was originally explored as an option for cars, was to resolve an issue with steering control during hard breaking. Once the wheels lock due to excessive braking the ability the steer the vehicle is completely lost.
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ABS attempts to stop a skid -- sometimes, in some conditions, releasing & reapplying the brakes *may* help, by essentially giving the tires a 2nd, 3rd etc. chance to grab. For it to work traction must already be lost. Skids can be intentional, sometimes directed, sometimes controlled, and skids to some extend can often be countered. Control is not always completely lost, though it requires the driver not panic, & it obviously helps of they've prepared themselves beforehand, e.g. by practicing to know their vehicle's characteristics & limits.
I do agree about defensive driving, but wanted to mention personal responsibility as well -- it is the driver's responsibility to make sure the vehicle they're driving is operating optimally & is well maintained. People skimp on brake work, & they skimp on tires, & most don't research either the same way they might research say a video card.
Due to weight bias under breaking, the front wheels provide 70% of a vehicles stopping power
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Basic physics really -- the best example I can think of is when you lock front & rear brakes on a bicycle, & if you were going fast enough the rear tire will come off the ground. Momentum carries the total mass forwards, while the stopping point is where the tires meet the road or ground -- that's where the center of gravity comes in, the lower the better. The suspension, when there is one, matters too -- the more the nose can dive because of suspension travel, the more the nose will dive, the more the problem is pronounced.
Regardless the front wheels have always been where the majority of the stopping power is, with the rear brakes almost entire purpose keeping you stopping in a straight line -- that's why so many cars & trucks have front discs but rear drum brakes. [BTW, many rear drum brakes are Only adjusted when you use the parking or hand brake. And yes, drum brakes Have to be adjusted.]
Florida law says that if you rear-end someone, then the accident is automatically your fault.
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Ahh, but did you know FL traffic laws also favor direction, as in North or South? I got broadsided at a 4-way stop. Traditional common sense would say that they idiot who hit me was at fault, but in FL, Not So. That everyone was at a complete stop was never in dispute -- that I got there 1st was never in dispute. But because I was traveling East->West [as far as I can remember] the idiot who hit me had the right of way!
And as for engine-braking, I recall him saying that it was to be avoided at all costs, as, not only could it make for really jerky driving and risk hurting passengers' necks, but also, with constant use, it would destroy the transmission as you were making it do something it was not designed to do (it was designed to transfer the engine's energy to push the car forwards, not slow it down).
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May sound logical to someone without mechanical knowledge, but say that to a decent mechanic to make him/her laugh. Did he know how unnecessarily hard it would be to manufacture gears that had only one face of the teeth hardened?
mikiem:
Right from the start it needed new brakes, and one of the brake lines got changed at that time because I had to cut the line to get the caliper hose off. But for the most part the only time I even look at the underside of it is when I think there is something odd happening, and having the brake lines rot out and pop like this happens every couple years.
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What you need to consider is total age & condition plus the possibility of contaminants. If one PC case fan goes out, myself I'll replace all the others that are the same age rather than assume it was a fluke. If one rubber brake line rotted, assume all are the same age & replace them. BTW, heat + penetrating oil + a crows foot type fitting socket connected to a small impact help loosen rusted fittings. The impact can be key because of the rapid impacts -- not raw horsepower.
I mentioned contaminants... ANYTHING but pure brake fluid [of the correct type for your car/truck] can trigger chemical reactions that will swell &/or eat rubber seals & lines. THIS IS IMPORTANT. Rubber lines rarely go bad -- I can't remember replacing one in years running dealer service. It could be a combination of age & environment, e.g. in the Detroit area winter road salt wrecks havoc, but if you're repeatedly having problems with rubber lines consider the possibility that water or something else has gotten into the brake fluid, &/or that the wrong type of fluid has been added. I have seen where that led to ONE of the brakes locking on -- at high speed! Imagine what happens when a wheel stops turning!
SeraphimLabs:
My current car has an automatic transmission, and not only have I heard it performing engine braking on its own while in cruise control, but I was successfully able to perform it using the manual override this morning to keep my speeds down and compensate for the loss of braking power.
--- End quote ---
Automatic transmissions use a torque converter -- oversimplified imagine two propellers in a liquid, one powered, & the other connected to the transmission. A locking torque converter [which most vehicles have nowadays] tries to do just that, lock at higher speeds. A manual transmission uses a clutch, where a disc with a material similar to brake lining on both sides is squeezed by spring tension between the engine's flywheel & the transmission's input shaft. When you step on the clutch pedal you release that spring tension -- the more you press down the more spring tension is reduced.
So... you should be able to see or imagine why a torque converter might be less ideal for downshifting &/or braking. Will it work? Yes, but it's better suited to limiting the gear to a lower range, limiting speed going downhill in the mountains. -mikiem (October 26, 2014, 11:46 AM)
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And this is one place that automation can improve considerably. On a vehicle where the PCM is able to recognize when engine braking is about to take place, the torque converter can be instructed to lock up and stay locked once the transmission is in a suitable gear. I suspect my car is able to do this, since I've seen it engine braking all by itself while in cruise control and going down a steep hill.
Like so, engine braking with an automatic transmission is as practical as it is on a manual transmission, because the only difference between the two is the slightly higher slip factor resulting from the design.
Designs that don't do that though, you are indeed correct that engine braking with an automatic is less effective than on the same vehicle equipped with a manual transmission. Usually you end up going a gear or two lower into the range of options with an automatic in order to bring the RPM up enough to make the torque converter couple it back to the engine.
And as for engine-braking, I recall him saying that it was to be avoided at all costs, as, not only could it make for really jerky driving and risk hurting passengers' necks, but also, with constant use, it would destroy the transmission as you were making it do something it was not designed to do (it was designed to transfer the engine's energy to push the car forwards, not slow it down).
--- End quote ---
May sound logical to someone without mechanical knowledge, but say that to a decent mechanic to make him/her laugh. Did he know how unnecessarily hard it would be to manufacture gears that had only one face of the teeth hardened?
-mikiem (October 26, 2014, 11:46 AM)
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There actually is a mechanical concern to engine braking an automatic now that I think about it. It has to do with the way automatic transmissions shift- using bands similar to brake pads to grab different areas of the planar assembly in order to change the gear ratio without ever actually meshing or unmeshing the gears.
If you apply too much torque to this assembly, it can cause the bands to slip. This results in increased transmission wear and heating, and could indeed ruin the transmission.
However, this only applies to automatic transmissions, and really is only a concern in a scenario where the transmission is already worn out to a point where it is already experiencing internal slippage problems. A transmission that still has plenty of band-meat left and is operating at or above its optimum shifting pressure will have sufficient resistance to internal slip that engine braking won't hurt it any more than smoking the tires at the redlight- because again the tires will lose traction long before anything bad happens mechanically inside the transmission.
Right from the start it needed new brakes, and one of the brake lines got changed at that time because I had to cut the line to get the caliper hose off. But for the most part the only time I even look at the underside of it is when I think there is something odd happening, and having the brake lines rot out and pop like this happens every couple years.
--- End quote ---
What you need to consider is total age & condition plus the possibility of contaminants. If one PC case fan goes out, myself I'll replace all the others that are the same age rather than assume it was a fluke. If one rubber brake line rotted, assume all are the same age & replace them. BTW, heat + penetrating oil + a crows foot type fitting socket connected to a small impact help loosen rusted fittings. The impact can be key because of the rapid impacts -- not raw horsepower.
I mentioned contaminants... ANYTHING but pure brake fluid [of the correct type for your car/truck] can trigger chemical reactions that will swell &/or eat rubber seals & lines. THIS IS IMPORTANT. Rubber lines rarely go bad -- I can't remember replacing one in years running dealer service. It could be a combination of age & environment, e.g. in the Detroit area winter road salt wrecks havoc, but if you're repeatedly having problems with rubber lines consider the possibility that water or something else has gotten into the brake fluid, &/or that the wrong type of fluid has been added. I have seen where that led to ONE of the brakes locking on -- at high speed! Imagine what happens when a wheel stops turning!
-mikiem (October 26, 2014, 12:06 PM)
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I've never seen rubber brake lines. Its always steel, sometimes copper or plastic coated in a futile attempt to stop them from rotting out so fast. If only I could get stainless steel brake lines without breaking the bank, they'd stay pristine for the entire lifetime of the car.
Usually whenever I have to work on the brakes at all, I'll bleed the system down to nothing and refill it with fresh fluid from a sealed container. Contaminants eat calipers and master cylinders, and even if you keep the system tight they still manage to get in there. Fluid is cheap, and if it keeps me from having to change anything more expensive than the lines I don't mind paying that much.
Money is tight for me though. Simply replacing things whenever I happen to think about it would leave me completely broke. Though I prefer to not have it break in the first place, when you're limited on cashflow its best to stick to if it ain't broke don't fix it. And then make a point of learning how to ride out any failures that do happen, cause it will break no matter what you do it.
Stoic Joker:
Florida law says that if you rear-end someone, then the accident is automatically your fault.
--- End quote ---
Ahh, but did you know FL traffic laws also favor direction, as in North or South? I got broadsided at a 4-way stop. Traditional common sense would say that they idiot who hit me was at fault, but in FL, Not So. That everyone was at a complete stop was never in dispute -- that I got there 1st was never in dispute. But because I was traveling East->West [as far as I can remember] the idiot who hit me had the right of way!-mikiem (October 26, 2014, 11:46 AM)
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Hmmm... I'm not so sure about that bit. The only fine print in FL law about intersections is that if two people stop at the exact same time, the person on the right has the right of way.
I've never seen rubber brake lines.-SeraphimLabs (October 26, 2014, 12:14 PM)
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There's always that last bit that goes from the axel to the chassis (rear) or the chassis to the wheel (front) where the suspension travel requires it to be flexible. :)
40hz:
ABS attempts to stop a skid -- sometimes, in some conditions, releasing & reapplying the brakes *may* help, by essentially giving the tires a 2nd, 3rd etc. chance to grab. For it to work traction must already be lost. Skids can be intentional, sometimes directed, sometimes controlled, and skids to some extend can often be countered. Control is not always completely lost, though it requires the driver not panic, & it obviously helps of they've prepared themselves beforehand, e.g. by practicing to know their vehicle's characteristics & limits.
-mikiem (October 26, 2014, 11:46 AM)
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+1
I've generally found the ABS feature on Fords to be more startling for the driver than actually useful. I'm a big believer in anticipating and preparing in advance whenever possible. As the Top Gun school allegedly says: You don't rise to the occasion - you default to your level of training. So first snowfall, I make it a point to get a little "skid practice" as soon as I'm in a safe place to do it. Especially since people seem to be stupidest after that first coating of snow. After they get some experience with it over the following day or two, 90% are fine. So the sooner you're prepared the better off you are.
Same goes for a 'new' car. An empty lot and a spare hour getting a real feel for the individual vehicle is time well spent.
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