electronic throttle
in [Technical]
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From: dizzy on 10 Mar 2010 21:32 David Skelton wrote: >I thought the main reason for ABS is to maintain steering control when the >brakes were pressed too hard, so hazards could be avoided. Yes. >But, ABS does not >work so well in the very wet or icy conditions. Sure it does. It can't perform miracles, however.
From: clare on 10 Mar 2010 22:01 On Thu, 11 Mar 2010 01:51:29 +0000 (UTC), "Rodan" <Rodan(a)Verizon.NOT> wrote: > >>clare(a)snyder.on.ca wrote: >> >>Toyota throttle has 2 hall effect sensors. The output of one tracks the >>other but is offset. In other words, one starts at say, 0 volts, and the >>other at, say 1 volt - and they increase in step with each other. That way >>the CPU can tell if one has failed, and if the two outputs are shorted >>together (one bypassed) If either accelerator sensor fails, the CEL comes >>on >>and the vehicle is limited to 1/4 throttle. If both fail, the throttle >>gets set to a fast idle position and the rpm is controlled to normal idle >>speed by programmed [missfire] (injector cut) The throttle position >>sensor >>(throttle feedback) also has 2 hall effect sensors 0 and they have >>[different] "rates" - the primary gives a higher signal linear from closed >>to open, while the secondary reads full by about half throttle. >>If the CPU senses a single TPS failure the engine is reduced to a fast >>idle. >>iF BOTH tps fail, it is returned to base idle - and if the ECU determines >>that the throttle has NOT closed - the engine is shut off. The ECU has 2 >>CPUs. the main monitors all sensors and [controlls] the entire >>power-train - >>engine, transmission, cruise control, traction control, etc. The "sub" >>monitors all sensors and all outputs - and monitors the main CPU via a >>"watchdog" program. The sub ALSO controls the electronic throttle. >>Both >>cpus control an output transistor that feeds power to the throttle control >>motor - BOTH must be turned on in order to open the throttle. They are >>series connected). If either CPU senses a problem and shuts down, there >>is >>no throttle. Gets pretty darn difficult to envision any electronic error >>that could cause uncontrolled [accelleration], particularly without >>registering a code and turning on the CEL. >>_________________________________________________________________________ >> >>Once upon a time there was a cable from the gas pedal to the >>throttle that operated the throttle butterfly. The throttle >>shaft had a position sensor that told the computer how much >>power the driver was demanding. >> >>Someone figured they could save money by eliminating the >>cable and attaching a position sensor to the gas pedal to tell >>the computer the driver's gas pedal position. The throttle >>shaft still had to have a position sensor to let the computer >>know its state compared to the pedal position, so the cost >>tradeoff was one less cable and one more position sensor. >> >>But there were more costs. The throttle butterfly no longer >>had the driver's foot power to move it, so they had to add a >>servo device to the throttle to provide power to the butterfly, >>and controlling power transistors to drive the servo, plus >>a reprogrammed computer to keep track of it. >> >>More complexity, added electromechanical hardware, higher >>cost, multiple new interfaces, and more computer operations. >>The whole thing sounds like a joke invented by Rube Goldberg. >> >>Rodan. >____________________________________________________________________ > >clare(a)snyder.on.ca wrote: > >Would be true, except it had NOTHING to do with saving money, >and the throttle position sensor doesn't tell how much power is >required - just how impatient the driver is!! >____________________________________________________________________ > >You're right, of course. It had nothing to do with saving money. >It costs more, it's more complex, it adds more electromechanical >hardware and increases electrical, mechanical, and computer interfaces. >It introduces multiple new failure modes, while yielding no significant >improvement in gas mileage or pollution control. It is a money pit, >a maintenance nightmare and a death trap waiting for a victim. > >So why would anyone other than Rube Goldberg build such a useless >(and dangerous) contraption? My guess is that the automakers are >trying to develop a generic accelerator pedal that would work for any >automotive power plant combination. A single pedal would indicate >the driver's intention to a gas engine, electric motor, hybrid, steam >engine, or rear-engine system, or an engine powered by tram cables. > >Unfortunately, in their zeal to prove the concept, they chose to dismantle >and scrap the simple, proven, reliable gas pedal-to-cable mechanism for >their experiment, resulting in more danger for conventional automobiles. > >Regarding the throttle position sensor - until fly-by-wire took throttle >position control away from the driver it did indicate the driver's wishes >for the power level to be applied. Stepping on a gas pedal to open >the throttle is necessary to merge into traffic, to maneuver, and to >maintain separation and safety in traffic conditions. Opening the >throttle doesn't automatically prove that a driver is impatient. > >Rodan. > > EVERYONE is using drive by wire, or has plans to. It has MANY advantages - and is no more prone, by design, to failure than a cable. A very simple electrical fault can totally screw up a mechanical cable connection too. A bad ground can allow fault current to flow through the throttle cable, melting the plastic sheath, causing a sticking throttle. It has happened. I've seen it. Mechanical devices are MORE subject to failure than electronics As for my saying the throttle just shows how impatient the driver is, there is NO reason for the throttle on virtually any car to be "floored" under normal driving conditions.
From: jim beam on 10 Mar 2010 23:10 On 03/10/2010 06:32 PM, dizzy wrote: > David Skelton wrote: > >> I thought the main reason for ABS is to maintain steering control when the >> brakes were pressed too hard, so hazards could be avoided. > > Yes. > >> But, ABS does not >> work so well in the very wet or icy conditions. > > Sure it does. not always dude. stopping distances with abs can be considerably longer, especially in conditions like snow. > It can't perform miracles, however. > -- nomina rutrum rutrum
From: E. Meyer on 10 Mar 2010 23:26 On 3/10/10 3:39 PM, in article qm3gp5pvfpppr52dftviqvt7k3iom4nkfr(a)4ax.com, "Bob Flumere" <rflumere(a)comcast.net> wrote: > On Wed, 10 Mar 2010 09:52:49 -0600, "E. Meyer" <e.p.meyer(a)verizon.net> > wrote: > >> On 3/9/10 8:34 PM, in article hn70gb$ea0$1(a)panix2.panix.com, "Scott Dorsey" >> <kludge(a)panix.com> wrote: >> >>> Dave <hairy411(a)hotmail.com> wrote: >>>> >>>> You're imagining things. I made no comparisons. jim beam says that as long >>>> as an engine is running, it's creating plenty of vacuum to run accessories. >>>> Even at WOT. > > > Absolutely not so with any naturally aspirated internal combustion > engine. > > Manifold vacuum depends entirely on the air moving through the engine > and being "throttled" by the butterfly in the intake. This vacuum or > low pressure (below atmospheric) only exists because the engine is > pumping out air that cannot be resupplied through the closed or > partially closed throttle plate(s). > > Throttle open (stuck, actuated improperly, or opened wide by driver) > always equals ZERO (or certainly very low) manifold vacuum. > > Low manifold vacuum means zero power assist from a vacuum assisted > brake booster. There is a check valve to hold the (low) pressure in > the booster housing during low manifold vacuum events. However, the > booster housing holds only enough volume to fully assist only the > first or second brake pedal application. This gives the driver a very > hard brake pedal after only couple of strokes and causes a major > reduction of the amount of brake line pressure that the average person > can muster with only leg power. ie: the common feeling that the > brakes have "failed". > > Unless there is some kind of a vacuum backup assist pump.. (some > trucks and buses), not that I'm aware of on Toyotas, or the brakes are > power boosted by some other means, hydroboost etc. there is going to > be little or no power assistance to help the driver control the > "runaway" vehicle if the throttle is in the opened position. > > Neutraling the runaway engine, allowing the RPM to rise until there is > some other limiting factor STILL won't produce much, if any intake > manifold vacuum. It would of course help the driver to regain control > (if only with little or no power assist to the brakes). > > Switching "off" may stop the engine and if the still engaged > transmission allows it to stop turning, there still won't be any brake > assistance because there STILL won't be any vacuum as long as the > throttle is (stuck?) open. Furthermore, if the engine should stop > turning when switched "off", we now have the added element of no power > steering asist, (if the steering is assisted by an engine driven > hydraulic pump). > > Hope this somewhat basic expanation helps to explain what the driver > of a "runaway" feels and experiences. > > Bob Flumere > rflumere(a)comcast.net If you are going to clip the entire text of my post, at least do me the courtesy or removing my name as well.
From: jim beam on 10 Mar 2010 23:28
On 03/09/2010 10:15 PM, Rodan wrote: > clare(a)snyder.on.ca wrote: > > Toyota throttle has 2 hall effect sensors. The output of one tracks the > other but is offset. In other words, one starts at say, 0 volts, and the > other at, say 1 volt - and they increase in step with each other. how can that be true??? http://en.wikipedia.org/wiki/Hall_effect hall effect sensors are used for gross position detection, not small scale linear deflections. they can be used for "wot" detection, but their ability to work over a wide positioning range is limited. that's why they're used in timing for things like crank position [rotational] sensors where you're counting pulse rates, not graduation functions. > That way > the CPU can tell if one has failed, and if the two outputs are shorted > together (one bypassed) If either accelerator sensor fails, the CEL comes on > and the vehicle is limited to 1/4 throttle. If both fail, the throttle > gets set to a fast idle position and the rpm is controlled to normal idle > speed by programmed [missfire] (injector cut) The throttle position sensor > (throttle feedback) also has 2 hall effect sensors 0 and they have > [different] "rates" - the primary gives a higher signal linear from closed > to open, while the secondary reads full by about half throttle. > If the CPU senses a single TPS failure the engine is reduced to a fast idle. > iF BOTH tps fail, it is returned to base idle - and if the ECU determines > that the throttle has NOT closed - the engine is shut off. The ECU has 2 > CPUs. the main monitors all sensors and [controlls] the entire power-train - > engine, transmission, cruise control, traction control, etc. The "sub" > monitors all sensors and all outputs - and monitors the main CPU via a > "watchdog" program. The sub ALSO controls the electronic throttle. Both > cpus control an output transistor that feeds power to the throttle control > motor - BOTH must be turned on in order to open the throttle. They are > series connected). If either CPU senses a problem and shuts down, there is > no throttle. Gets pretty darn difficult to envision any electronic error > that could cause uncontrolled [accelleration], particularly without > registering a code and turning on the CEL. you can have a hall effect sensor at the end of the rotational travel for wot, and you can compare that output with the potentiometer output, but the graduated positional sensing is typically done with a potentiometer. > _________________________________________________________________________ > > Once upon a time there was a cable from the gas pedal to the > throttle that operated the throttle butterfly. The throttle > shaft had a position sensor that told the computer how much > power the driver was demanding. > > Someone figured they could save money by eliminating the > cable and attaching a position sensor to the gas pedal to tell > the computer the driver's gas pedal position. The throttle > shaft still had to have a position sensor to let the computer > know its state compared to the pedal position, so the cost > tradeoff was one less cable and one more position sensor. > > But there were more costs. The throttle butterfly no longer > had the driver's foot power to move it, so they had to add a > servo device to the throttle to provide power to the butterfly, > and controlling power transistors to drive the servo, plus > a reprogrammed computer to keep track of it. > > More complexity, added electromechanical hardware, higher > cost, multiple new interfaces, and more computer operations. > The whole thing sounds like a joke invented by Rube Goldberg. > > Rodan. > > > -- nomina rutrum rutrum |