electronic throttle
in [Technical]
|
From: clare on 7 Mar 2010 18:11 On Sun, 07 Mar 2010 15:42:12 -0500, Bill Putney <bptn(a)kinez.net> wrote: >jim beam wrote: >> On 03/07/2010 09:44 AM, Bill Putney wrote: > >> then you're making generalizations from your own exceptional experience >> that are not representative of most vehicle, and certainly not vehicles >> with standard tuning. vacuum decreases significantly at w.o.t, is >> sufficient to give brake boost. >> >> besides, how much vacuum do you think you need for a brake booster? with >> a 9" diameter diaphragm, [on the small side by modern standards], that's >> 63 sq inches. how much pressure delta do you think you need to double a >> person's braking force? > >You'd have to know the mechanical advantage in the pedal from basic >lever math and a bunch of other stuff that is beyond what either of us >wants to get into here. Without the absolute numbers for all that >stuff, it suffices to ratio things: When the booster is designed to >properly operate at 7 times the vacuum that you'll get from an engine >under acceleration, I say your assist is going to be close to useless - >the engine will likely overcome the brakes in being able to sustain >highway speeds (and this is before fade comes into the picture). > >Saying that 63 sq. in. is a big surface area and so even a tiny little >vacuum will give you huge force means nothing. Fact is the assist force >on the diaphragm with the very low vacuum under acceleration is less >than 15% of what it was designed to use under normal stored vacuum >conditions. > >> you're supposed to apply the brakes and keep them on. only if you >> release do you lose vacuum. > >Right or wrong, many people were taught to pump the brakes. Some people >will in fact pump the brakes, for any number of reasons. > >>> 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. >> >> see above. > >Yes - please see it. > >>>> 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. >> >> again, if that's your experience, i think you're working with something >> not representative of most vehicles. certainly not anything post 1980. > >Nope. Your assumptions are wrong on both counts. > > >>>> 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? >> >> where is your "theory" that people pump brakes? i saw someone on a >> freeway in rain in los angles one time, skating along with their brakes >> locked, car gently rotating, and the look on her face was that of >> someone trying to break the pedal off she was pushing it so hard. >> there's no way that person, as an average driver, was going to let off >> that pedal, and thus, even though she was going to crash, she was not >> going to lose vacuum. > >You keep throwing in scenarios totally different than what we're talking >about. Again - you can't prove your claim that hardly anyone pumps the >brakes any more than my claim that a lot of people would pump the brakes >- so from that standpoint, it's what we each want to believe until >someone presents some hard evidence. Your observations in life are no >more or no less valid than mine are - so quit belittling mine and >touting your just as anecdotal observations as more than they are. The problem is the average driver is going to attempt to CONTROL THE SPEED of the car with the brakes. THIS can NOT be done. The brakes CAN stop the car. Controlling the speed would involve applying and releasing (or modulating" the brakes. This loses vacuum and assist. Stopping the car involves a single, massive application of the brakes utilizing the full reserved vacuum assist of the power brake unit. > >>> 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. >> >> with respect, you're projecting your own behavior as representative of >> everyone. it's not true. > >Oh - I see - so no one pumps there brakes, either in accident avoidance >situations or if faced with runaway acceleration. Got it. (I don't buy >it.) > >>>> 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.) >> >> indeed, but i'm pointing out the fact that refutes your supposition - >> typical panicked drivers do not let off the brake pedal. > >That's your theory and your belief. No more or less valid than mine of >the opposite.
From: clare on 7 Mar 2010 18:14 On Sun, 07 Mar 2010 13:39:08 -0800, jim beam <me(a)privacy.net> wrote: >On 03/07/2010 12:42 PM, Bill Putney wrote: >> jim beam wrote: >>> On 03/07/2010 09:44 AM, Bill Putney wrote: >> >>> then you're making generalizations from your own exceptional >>> experience that are not representative of most vehicle, and certainly >>> not vehicles with standard tuning. vacuum decreases significantly at >>> w.o.t, is sufficient to give brake boost. >>> >>> besides, how much vacuum do you think you need for a brake booster? >>> with a 9" diameter diaphragm, [on the small side by modern standards], >>> that's 63 sq inches. how much pressure delta do you think you need to >>> double a person's braking force? >> >> You'd have to know the mechanical advantage in the pedal from basic >> lever math and a bunch of other stuff that is beyond what either of us >> wants to get into here. Without the absolute numbers for all that stuff, >> it suffices to ratio things: When the booster is designed to properly >> operate at 7 times the vacuum that you'll get from an engine under >> acceleration, I say your assist is going to be close to useless > >how did you manage before the days of vacuum assist? > Before the days of vacuum assist, master cyls had larger pistons and pedals had longer travel, providing more mechanical advantage. In most cases they also had self energizing (servo action) drum brakes, which provide SIGNIFICANTLY more initial brake effectiveness than disc brakes (but suffer much more from temperatire induced fade) >
From: Bill Putney on 7 Mar 2010 18:16 clare(a)snyder.on.ca wrote: > One throttle position sensor of the simplest design (a simple > potentiometer) can provide 2 signals - one the inverse of the other. Clare - I followed the rest of your explanation, but, as a circuit designer, I had trouble following that part. That would have to be two potentiometers ganged on one shaft? You're not saying that one potentiometer provides two signals, right? I'm picturing a TPS pot. with ground on one end, Vref on the other, and the wiper signal. I don't see getting two signals from the one pot, inverse or otherwise. What did I miss? -- Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')
From: Bill Putney on 7 Mar 2010 18:25 clare(a)snyder.on.ca wrote: > The problem is the average driver is going to attempt to CONTROL THE > SPEED of the car with the brakes. THIS can NOT be done. > > The brakes CAN stop the car. Controlling the speed would involve > applying and releasing (or modulating" the brakes. This loses vacuum > and assist. > > Stopping the car involves a single, massive application of the brakes > utilizing the full reserved vacuum assist of the power brake unit. Yep - I can see that. Like was demonstrated in that Popular Mechanics video that "ED" linked earlier today (http://www.popularmechanics.com/automotive/how_to/4348214.html). -- Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')
From: Bill Putney on 7 Mar 2010 18:29
Bill Putney wrote: > clare(a)snyder.on.ca wrote: > >> One throttle position sensor of the simplest design (a simple >> potentiometer) can provide 2 signals - one the inverse of the other. > > Clare - I followed the rest of your explanation, but, as a circuit > designer, I had trouble following that part. That would have to be two > potentiometers ganged on one shaft? You're not saying that one > potentiometer provides two signals, right? I'm picturing a TPS pot. > with ground on one end, Vref on the other, and the wiper signal. I > don't see getting two signals from the one pot, inverse or otherwise. > What did I miss? Actually, after some thought, I can see how it might be done with a single pot: Pot wiper gets tied to ground, and you run constant current into each end terminal. The voltages read at the two end terminals will be inverse of each other (as wiper is moved in one direction, voltage of one end terminal goes from 0 to R x I, voltage of the other end goes in the opposite direction). Not saying that the designers would have realized that it could be done like that, but that's the only way I could think of using a single pot. -- Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x') |