electronic throttle
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From: John Burns on 7 Mar 2010 08:42 You're a bit behind the times, our E34 Alpina B10 had an electronic throttle, it was a 1989 car! > if you buy all this fear-mongering idiocy that electronic throttle is a > problem, and that brakes, transmissions and ignition kill switches can > all simultaneously fail causing a driver to lose control, it might be > worth auto manufacturers of all stripes to adopt a slightly different > implementation of electronic throttle [e.t.] - if not for mechanical > reasons, but to shut the idiots up. -- Who needs a life when you've got Unix? :-) Email: john(a)unixnerd.demon.co.uk, John G.Burns B.Eng, Bonny Scotland Web : http://www.unixnerd.demon.co.uk - The Ultimate BMW Homepage! Need Sun or HP Unix kit? http://www.unixnerd.demon.co.uk/unix.html www.Strathspey.co.uk - Quality Binoculars at a Sensible price
From: Don Stauffer on 7 Mar 2010 10:39 jim beam wrote: > if you buy all this fear-mongering idiocy that electronic throttle is a > problem, and that brakes, transmissions and ignition kill switches can > all simultaneously fail causing a driver to lose control, it might be > worth auto manufacturers of all stripes to adopt a slightly different > implementation of electronic throttle [e.t.] - if not for mechanical > reasons, but to shut the idiots up. > > first, lets understand e.t. functionality: > > 1. open the throttle when demanded > 2. close throttle when demanded > 3. allow "demand" to account for additional requirements like > a. de-throttle on shifting for automatics, > b. throttle appropriate to load at high demand [eg. full throttle at > low rpms can choke an engine and significantly reduce output - thus > de-throttle until revs support full open] > > if we analyze the above [which is not exhaustive, but representative], > we find that in almost all situations, an e.t. needs to be more closed > than demanded, but seldom, if ever, more open. thus the "solution" to > the fear-mongering might be to have the throttle opened mechanically - > i.e. old fashioned cable linkage, but have the computer control a closer > device. thus, all the above can be implemented electronically, but > whenever the driver lifts their foot, the mechanical closure cannot be > over-ridden. and the throttle can never be more open than the > mechanical throttle command. > > this would not only address the "potential" for a runaway failure > [although how exactly a computer is supposed to fail such that it won't > switch off, disables brakes, disables transmission select, but still > runs its injection code is something i have never seen explained, even > by the most strident "but it must be the electronics" crowd], but it > would also remove the single most annoying thing i have ever experienced > in any vehicle driving experience: chevy's idiot idea that they need a > multi-second delay between foot pedal movement and e.t movement. anyone > that's ever tried to drive a chevy hhr on a winding mountain road knows > what i mean. > > y'all can now wait for at least 10 years for arrival, but i throw it out > there for what it's worth. > > In my Prius I am unaware of any 'kill' switches. There is just the normal power on-off switch. It is a simple sp-st switch that acts (through the computer) as an alternating switch.
From: Bill Putney on 7 Mar 2010 11:10 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. After that, the brakes will be almost totally ineffective because of loss of vacuum. >> 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). 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. -- 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 11:13 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, multiple cars in perfect condition. -- 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 11:16
dsi1 wrote: > I certainly believe you. You can get a feel for the amount of reserve > vacuum boost on your car by simply repeatedly pressing down on the > brakes without starting your engine. If your brakes are working > properly, you'll feel the pedal getting firmer until you'll only be able > to move the brake pedal a couple of inches of deflection. At that point, > you'll have used up all your vacuum reserve. I figure that you should be > able to get around 3 stabs at the brakes with mostly full boost. This > means you'll only get maybe two chances for full braking after the > initial attempt at braking. That's the breaks I guess. :-) My recollection is that boost is noticeably diminished after the second stab, greatly diminished by the third stab - engine overpowers brakes for most common vehicles. -- Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x') |