electronic throttle
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From: jim beam on 7 Mar 2010 11:24 On 03/07/2010 08:10 AM, Bill Putney wrote: > jim beam wrote: >> On 03/06/2010 08:26 PM, Bill Putney wrote: > >>> I don't necessarily disagree with the rest of your post, but that part >>> of your post is definitely incorrect. Have you ever played with your >>> power brakes while simultaneously pressing the accelerator? Anything >>> more than one or two initial stabs at the brakes depletes the vacuum >>> stored in the booster, and with even slight power simultaneously being >>> demanded of the engine, the vacuum is not enough to directly power the >>> brakes, much less re-charge the vacuum in the booster. >> >> i have done this. with the engine off, the vacuum remains until the >> pedal is released - thus if you stomp the pedal and keep it there, you >> don't need to keep replenishing the vacuum. and you will stop the car. >> with the engine running, there is no vacuum issue, and the brakes are >> still powerful enough to stop the car. on my honda anyway. > > I have real trouble believing that a large majority of people would, in > a sudden inadvertent acceleration situation, be content to press the > brakes one time and not try to pump them once or twice. why? if the car in front of you suddenly jams on their brakes, do you apply then release your pedal? i think your answer is "no" - unless you're skidding and know what cadence braking is. and if you know what cadence braking is, you should know that to stop a car with the engine on full throttle, you apply the brakes hard and quickly - you don't monkey about with multiple brake applications that can cause excess heating and fade. > After that, the > brakes will be almost totally ineffective because of loss of vacuum. no. fade maybe, but vacuum is always present if the engine is running. even if it's not, you still have vacuum reserve for three applications. > >>> People don't believe that, but try it on your car: On a deserted road at >>> highway speed, stab the brake pedal a couple of times while holding the >>> gas pedal down a little bit to load the engine slightly (this works >>> anywhere from slight to WOT throttle). I guarantee you (unless your >>> brake booster gets its vacuum from something besides the intake vacuum - >>> like a separate electric motor-driven vacuum pump) that after two or >>> more stabs at the brake pedal, the braking power will be extremely low - >>> so low that the engine will have no trouble overpowering the brakes. No >>> vacuum in the booster essentially equals no brakes. >> >> with respect, i think you're confusing vacuum with fade... > > No - I'm not. While you could certainly induce fade with a certain > prolonged script of usage of the brakes, what I'm talking about is true > over what I would say would be the real world typical scenario (before > the fade issue becomes real - which - yes - it would over a longer > period, but not likely if the 2 or 3 stabs had already occurred in the > relatively short period that I would expect). It is a fact that the > vacuum cannot recharge with almost no vacuum in the intake - it doesn't > recharge by magic. I guarantee you that after a third stab of the brakes > on an engine vacuum-driven power brake car, the brakes will loose the > fight with the engine - fade has nothing to do with that over the first > few seconds that we would be talking about (during which the first 2 or > 3 stabs would occur real world). if that is your experience, then i think you must have a vacuum leak. even with wide open throttle, there is sufficient vacuum in the manifold to create significant braking assist. > > i've >> experienced that too, one particular time on a major hill in san >> francisco approaching a busy intersection. yes, it's scary stuff. but >> when i changed the pads on my civic from after-market to oem, all fade >> problems disappeared. even fully loaded, repeatedly decelerating from >> speed. [i learned my "honda oem is best" lesson that way.] >> >> >>> >>> Also, once the booster is depleted of vacuum during that experiment, the >>> vacuum charge in the booster will remain depleted until a second or so >>> after the throttle is released - IOW - deplete it and continue applying >>> the throttle (again - doesn't have to be anywhere near WOT) for several >>> seconds. Every once in a while, while still applying the throttle, try >>> the brakes again. You will not have any effective braking until *after* >>> you release the throttle. >>> >>> I urge anyone who doesn't believe what I claim above to try it before >>> commenting. >> >> i have. my results and comments are as above. > > And both of us could design the script to create either end result we > wished. I submit that in the real world, most people would try pumping > the brakes in desperation if the sudden acceleration scenario actually > happened - the depleting stabs would occur before fade became a factor. > sorry dude, it's incredibly rare for a panicking driver to pump their brakes. that's why abs exists - abs does that for them, and only in the event of traction limit being exceeded.. -- nomina rutrum rutrum
From: jim beam on 7 Mar 2010 11:39 On 03/07/2010 08:13 AM, Bill Putney wrote: > jim beam wrote: >> On 03/06/2010 08:36 PM, Bill Putney wrote: >>> Jeff Strickland wrote: >>> >>>> ...We have not explored the interaction of traction control and >>>> antilock brakes preventing the brakes from stopping a car with a >>>> throttle intent on being set to the maximum setting. We also have not >>>> looked at the issue of brake fade that comes from the brakes getting >>>> hot. If the brakes locked the front tires, the ABS would sense this >>>> and unlock them. The driver might keep his foot planted firmly on the >>>> brake pedal which has sunk to the floor, but the car still would not >>>> stop. The brakes get hot and fade badly, and the car wouldn't even >>>> slow down... >>> >>> Read my previous post. With throttle applied (even partial throttle), >>> the booster vacuum gets depleted *rapidly*. There is no way to use the >>> brakes to stop a car with an engine of any power at all with throttle >>> applied since, with throttle applied, intake vacuum drops to close to >>> zero. No vacuum = essentially no brakes. Try the experiment I described >>> in my previous post. >>> >> >> no dude. even with no engine running to replenish vacuum, there is >> still sufficient vacuum reserve in the booster to apply the brakes >> full-on three times. unless you have a leak of course, which could >> also be affecting your experience. >> > > By the second stab, typically brake effectiveness is reduced > considerably. By third stab - engine overpowers brakes - power assist is > negligible. No leaks, i'll bet you haven't actually tested that. all you know from driving is that there is sufficient vacuum for the brakes to appear to work ok, i.e., evacuation rate > leak rate. it's only when leak rate > evacuation rate that people notice anything. in the mean time, a slow leak might be sufficient to lose vacuum in 30 seconds or less. > multiple cars in perfect condition. > -- nomina rutrum rutrum
From: Bill Putney on 7 Mar 2010 12:44 jim beam wrote: > On 03/07/2010 08:10 AM, Bill Putney wrote: >> jim beam wrote: >>> i have done this. with the engine off, the vacuum remains until the >>> pedal is released - thus if you stomp the pedal and keep it there, you >>> don't need to keep replenishing the vacuum. and you will stop the car. >>> with the engine running, there is no vacuum issue, and the brakes are >>> still powerful enough to stop the car. on my honda anyway. >> >> I have real trouble believing that a large majority of people would, in >> a sudden inadvertent acceleration situation, be content to press the >> brakes one time and not try to pump them once or twice. > > why? if the car in front of you suddenly jams on their brakes, do you > apply then release your pedal? i think your answer is "no" - unless > you're skidding and know what cadence braking is. and if you know what > cadence braking is, you should know that to stop a car with the engine > on full throttle, you apply the brakes hard and quickly - you don't > monkey about with multiple brake applications that can cause excess > heating and fade. We aren't talking about what the savvy drive does and knows about. What I've said still stands for the scenario we are talking about and for many drivers. We weren't talking about what the best thing would be to do. >> After that, the >> brakes will be almost totally ineffective because of loss of vacuum. > > no. fade maybe, but vacuum is always present if the engine is running... Not enough for any effectiveness of brakes. Do you even know what happens to plenum vacuum at light, moderate, and heavy throttle? If you knew the numbers, then you wouldn't be saying that an engine running (with throttle open) will have enough vacuum to run the brakes - because it simply isn't true. Anyone who has used a vacuum gage to any extent knows that vacuum plummets when the throttle is open. > even if it's not, you still have vacuum reserve for three applications. That part is arguably true. I'd say you're loosing effectiveness after 2, but what's one more jab of the brakes between friends. The result will be that the booster will absolutely *not* charge back to any usable level under acceleration. Plenum vacuum is just too low. Again - you don't seem to know that - if you want to argue that point, then give me some numbers for vacuum for a common engine of your choice at idle, and in gear under light, moderate, and heavy acceleration. If the numbers you come back with are honest, you will prove what I'm saying. >>> with respect, i think you're confusing vacuum with fade... >> >> No - I'm not. While you could certainly induce fade with a certain >> prolonged script of usage of the brakes, what I'm talking about is true >> over what I would say would be the real world typical scenario (before >> the fade issue becomes real - which - yes - it would over a longer >> period, but not likely if the 2 or 3 stabs had already occurred in the >> relatively short period that I would expect). It is a fact that the >> vacuum cannot recharge with almost no vacuum in the intake - it doesn't >> recharge by magic. I guarantee you that after a third stab of the brakes >> on an engine vacuum-driven power brake car, the brakes will loose the >> fight with the engine - fade has nothing to do with that over the first >> few seconds that we would be talking about (during which the first 2 or >> 3 stabs would occur real world). > > if that is your experience, then i think you must have a vacuum leak... That is simply not the case. > even with wide open throttle, there is sufficient vacuum in the manifold > to create significant braking assist. That is profoundly incorrect - period. >> i've >>> experienced that too, one particular time on a major hill in san >>> francisco approaching a busy intersection. yes, it's scary stuff. but >>> when i changed the pads on my civic from after-market to oem, all fade >>> problems disappeared. even fully loaded, repeatedly decelerating from >>> speed. [i learned my "honda oem is best" lesson that way.] >>>> I urge anyone who doesn't believe what I claim above to try it before >>>> commenting. >>> >>> i have. my results and comments are as above. >> And both of us could design the script to create either end result we >> wished. I submit that in the real world, most people would try pumping >> the brakes in desperation if the sudden acceleration scenario actually >> happened - the depleting stabs would occur before fade became a factor. > sorry dude, it's incredibly rare for a panicking driver to pump their > brakes... That's your *theory*, or you have something to back that statement up? Admittedly, my theory that some percentage of drivers would pump the brakes is not provable as far as I know, but I do state it as conjecture, not as fact as you are stating your argument. > that's why abs exists - abs does that for them, and only in the > event of traction limit being exceeded.. You're not talking about the same situation. Trying to stop a vehicle with runaway acceleration is not the same setup as emergency accident avoidance as far as paniced driver psychology. (Yes - there are similarities, but don't turn that similarity into being equal.) -- Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')
From: Jeff Strickland on 7 Mar 2010 12:45 "Ed Pawlowski" <esp(a)snetnospam.net> wrote in message news:GfedncnS4KVktg7WnZ2dnUVZ_s2dnZ2d(a)giganews.com... > > > "Jeff Strickland" <crwlrjeff(a)yahoo.com> wrote >> Brake interlocks are a relatively new thing. I drove cars for 30 years >> before I had one with a brake pedal interlock. Your elderly customer also >> drove for a very long time with cars that had no brake interlock, and he >> wasn't aware that his new car had one. My guess is that he wasn't aware >> that any car had one ... > > True > >> >> There is no inherent accident waiting to happen without the brake >> interlock. > > Elderly person, foot on gas, put car in gear. Crash Happens too > frequently. > > We had cars built for almost 90 years before brake interlocks came around. The occurance of a car shifting out of P was relatively rare, and almost always involved children playing in the car and moving the gear selector while the engine was not even ON. Yes, a person could take the car out of P while the engine was running, but as a practical matter, this almost never happened. Almost never. > >> Brake interlocks were put in to prevent children from moving the car from >> P and allowing it to roll down the driveway, they were not put in to keep >> the driver from being an idiot. > > Perhaps, but the side effects are good. Absolutely, but the purpose was the children playing in the car, not the inattentive driver. The gear selector has gates that are there for the driver to make him press a button or move the lever sideways to get out of P. A child playing in the car can press the button or move the lever sideways while the vehicle was parked, this is the condition for which the brake interlock was created.
From: Jeff Strickland on 7 Mar 2010 12:52
"jim beam" <me(a)privacy.net> wrote in message news:xbWdnV8Xic4E3Q7WnZ2dnUVZ_rGdnZ2d(a)speakeasy.net... > On 03/06/2010 08:36 PM, Bill Putney wrote: >> Jeff Strickland wrote: >> >>> ...We have not explored the interaction of traction control and >>> antilock brakes preventing the brakes from stopping a car with a >>> throttle intent on being set to the maximum setting. We also have not >>> looked at the issue of brake fade that comes from the brakes getting >>> hot. If the brakes locked the front tires, the ABS would sense this >>> and unlock them. The driver might keep his foot planted firmly on the >>> brake pedal which has sunk to the floor, but the car still would not >>> stop. The brakes get hot and fade badly, and the car wouldn't even >>> slow down... >> >> Read my previous post. With throttle applied (even partial throttle), >> the booster vacuum gets depleted *rapidly*. There is no way to use the >> brakes to stop a car with an engine of any power at all with throttle >> applied since, with throttle applied, intake vacuum drops to close to >> zero. No vacuum = essentially no brakes. Try the experiment I described >> in my previous post. >> > > no dude. even with no engine running to replenish vacuum, there is still > sufficient vacuum reserve in the booster to apply the brakes full-on three > times. unless you have a leak of course, which could also be affecting > your experience. > Doesn't matter. Even if the driver holds the brake pedal, the brakes get hot and fade, and this will cause them to stop doing the job they are supposed to do. The ONLY acceptable condition is that the engine return to idle when the gas pedal is released. The condition that is REQUIRED, no matter what sort of linkage -- mechanical or electronic -- is that the engine speed up when the pedla is pressed, hold steady when the pedal is set to any mid-scale position, and slow when the pedal is released. Unless these conditions happen in 100% of the instances, the mechanism is faulty. Period. Nobody should ever be exposed to a runaway car, either as a bystander or an occupant of the car. We don't know the causes of the runaway Toyotas, but whatever the causes, they do not appear to be operator induced. And the operators seem to have been unable to counteract whatever the causes were. |