Motorists, experts say throttles to blame

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Originally Posted By: Gary Allan
..but I will never willingly buy a "drive by wire" system'd car if alternatives are available. Nope. Cars are much too cheaply built.


Problem is, they're all E-throttle now and have been for some time.

Joel
 
Most of the aircraft you all fly on have electronic throttles as well as electronic fly by wire with no mechanical back-ups. However,there is a significant level of redundancy in those systems. When I scanned my Saturn Astra which is Throttle By Wire (TBW) I was reassured to see that the gas pedal and TPS systems were dual channel systems. Much like a modern FADEC on a jet engine. In Fadecs, the throttle lever positions are only allowed to deviate a certain amount from each other. This and the fault handling response is handled in software as well as an arbiter model to help determine which channel is correct based upon engine RPM, and MAP. I would hope that this same logic would be applied to automotive applications. My first thought would be when the channel disagree exceeds the limits, the arbiter model is used to select the properly functioning channel, failing that, the throttle would be reduced to idle. This could be dangerous on an interstate and cause serious accidents as well. There is no way I would trust a single channel throttle system in anything. Cruise control is easy to implement in these systems since it does not require a separate servo actuator as in the old days. Traction control, torque limiting, linearization, and other driveability enhancements are easily implemented in TBW. Really it all depends on the vulnerability of the hardware to a single point failure or disturbance and the level of sophistication of the software. Reducing the throttle to idle on brake application would be easy to impliment in software provided the FMEA says its the safest thing to do for all situations, provided the throttle servo is operational and the butterfly is not stuck (no butterfly on direct injected engines). You could always do a fuel cut as well. Sorry for being long winded, but I love engine controls AND I just bought a new Tacoma (manual trans).

Note that direct injected engines are becoming popular now. They have no throttle plate to move so TBW is about the most practical throttle control. With regards to electrical noise causing the malfunctions, the automotive manufacturers also subject their vehicles to pretty harsh EMI testing from both internally generated and externally generated (i.e. lightning, cell phones, etc...). For the event vehicles, I'd like to see the data from the vehicle event recorders that are being installed in cars/trucks now. These are similar to flight data recorders. You can bet that toyota seized these out of the accident vehicles to try to figure out what happened. There is a little blurb in my toyota owners manual about when and how this data can be used and who can have access to the data.
 
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Originally Posted By: JetStar
..Note that direct injected engines are becoming popular now. They have no throttle plate to move so TBW is about the most practical throttle control.


Dunno about that. AFAIK a gasoline, SI, recip engine still needs a throttle plate, manifold vacuum, etc. In regards to the TBW, all the ones I've seen have 2 position sensors in the throttle body and one for the accelerator pedal. In the event of system failure they fail to a fast idle only mode.

Joel
 
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Uh.... I like msot of what you said, JetStar, but (not 100% sure...) But I do believe that DI use throttle valves.... Because the amount of air still controls the power output of the engine. Not like in a diesel where the amount of fuel determines the power.
 
Originally Posted By: rudolphna
Uh.... I like msot of what you said, JetStar, but (not 100% sure...) But I do believe that DI use throttle valves.... Because the amount of air still controls the power output of the engine. Not like in a diesel where the amount of fuel determines the power.


Since I don't own a DI vehicle, I have to go by what I read. It is my understanding that the gains in DI engines are due to very precise injection volume and timing and no throttle plate losses. See theory of operation here.
http://en.wikipedia.org/wiki/Gasoline_direct_injection
http://www.canadiandriver.com/2005/08/31/auto-tech-gasoline-direct-injection.htm
 
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More info on DI from Ford:
What it is: Direct Injection (DI) refers to fuel injected directly into the combustion chamber above the piston. Direct Injection has long been used on large diesel engines. Smaller diesels are increasingly adopting direct injection (vs. indirect injection into a pre-chamber). Direct Injection also can be used in spark ignition (generally gasoline) engines instead of port fuel injection- for improved fuel economy, increased full throttle torque and power and potentially for better fuel economy with lean-burn operation. Ref-Port Fuel Injection (PFI): By comparison, Port Fuel Injection (used spark-ignition engines) have injectors in the intake port near the valve. During the intake stroke, fuel sprayed into the port enters the combustion chamber along with the air charge. Direct Injection: With Direct Injection Spark Ignition (DISI) engines, fuel is injected in one of two ways, depending on operating conditions. With lean burn operation (at low to mid loads), the engine is run unthrottled (similar to diesel) with fuel injected after the air has entered, causing a higher fuel concentration near the spark plug for easy ignition. This is known as the stratified charge mode. The overall air/fuel ratio is lean for better fuel consumption. At mid to high engine loads, fuel is injected during the air intake stroke to promote good mixing. This process is known as the homogenous mode of operation. Fuel injected and evaporating directly in the combustion chamber cools the air slightly for higher volumetric efficiency and power. It also allows a slightly higher compression ratio for improved fuel efficiency. Since all fuel being injected goes directly into the cylinder, it can be metered more precisely, promoting improved transient control for reduced engine-out emissions. Customer benefit: Better fuel efficiency, improved driveability and more power. Ford status: Under development.
 
Some of the technologies may be different, but here's a GM DI engine where you can clearly see the throttle plate in the TBW throttle body:
2010%202.4L%20I4%20VVT%20DI%20LAF%20LAC%20LoR.jpg


The 3.5L DI Isuzu Rodeo engine also had a throttle plate (and TBW).

Joel
 
I stand corrected on the DI and throttle plates and aplogize for derailing this thread. I did more research last night and found that some use throttle plates and some dont, so I cannot say in a blanket statement that none of them have throttle plates. What I did find out is that in the stratified charge mode (ultra lean burn)a throttle plate is not required, but in the other two modes a plate does help.
 
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Originally Posted By: JetStar
For the event vehicles, I'd like to see the data from the vehicle event recorders that are being installed in cars/trucks now. These are similar to flight data recorders. You can bet that toyota seized these out of the accident vehicles to try to figure out what happened. There is a little blurb in my toyota owners manual about when and how this data can be used and who can have access to the data.


As long as I'm conscious any wreck I'm in will have the car towed to my house, not impounded, and my (personal injury) attorney would get first crack at any of my black boxes.

If the pedal position sensor says "floored" and the black box records that, the investigation team will say a floor mat got caught. Potentiometers can be "scratchy" and clean themselves so any followup investigation on the pedal might be inconclusive.
 
I agree about keeping control of the data in the VER, but I don't know how that would work out depending on state laws. There is a lot of info on the web about this.
I would hope that the gas pedal system is two channels and is not a cheesy unsealed pot. I'd prefer an LVDT/RVDT like what is used on aircraft.
I'm curious if these events were preceeded by a normal driver commanded WOT. The VER could rule out uncommanded throttle movement among other things
 
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Originally Posted By: wapacz
actually the space shuttle isn't that safe. out of the 130 times it launched it had catastrophic failure 2 times.


I agree (that's my point)..but based on million miles/death ...it's probably the SAFEST form of transportation that the world has ever known. One orbit is at minimum (not accounting for altitude) 25k miles X 6 (plus "guests") is 150k/orbit. How many orbits have all shuttles traveled?

That statistic is worthless in assessing safety since it uses mileage as the metric. If it used events ..then a car would manage much better in spite of much higher fatalities per mile. A plane crashes with virtually 100% fatalities. A car crashes with rarely a fatality.
 
Originally Posted By: eljefino
Originally Posted By: JetStar
For the event vehicles, I'd like to see the data from the vehicle event recorders that are being installed in cars/trucks now. These are similar to flight data recorders. You can bet that toyota seized these out of the accident vehicles to try to figure out what happened. There is a little blurb in my toyota owners manual about when and how this data can be used and who can have access to the data.


As long as I'm conscious any wreck I'm in will have the car towed to my house, not impounded, and my (personal injury) attorney would get first crack at any of my black boxes.

If the pedal position sensor says "floored" and the black box records that, the investigation team will say a floor mat got caught. Potentiometers can be "scratchy" and clean themselves so any followup investigation on the pedal might be inconclusive.


Here is your state law on VER's
http://www.harristechnical.com/downloads/ME.pdf
 
Theres got to be a glitch somewere between the computer and throttle body is my guess. What ever happenend to keeping things simple. My Tacoma has a cable...if it fails the TB closes, not stick open.
 
Originally Posted By: JetStar

Here is your state law on VER's
http://www.harristechnical.com/downloads/ME.pdf


Interesting:

F. The data are retrieved by a law enforcement officer acting pursuant to authority
recognized under applicable statutory or constitutional law; or

G. The data are requested as part of routine civil or criminal discovery.

This pretty much means any dramatic wreck, someone's going to read the box. It would then be a mismosh of "experts" interpreting the data to their own ends. I'd be pretty irritated if the cops came to the conclusion that I was racing or hotdogging or whatever, if I got up to 110 MPH at WOT before wrecking. Then years later enough dud cars established a pattern that vindicated me.
 
Originally Posted By: ARB1977
Theres got to be a glitch somewere between the computer and throttle body is my guess. What ever happenend to keeping things simple. My Tacoma has a cable...if it fails the TB closes, not stick open.


emissions and safety standards.
 
Originally Posted By: wapacz
Originally Posted By: ARB1977
Theres got to be a glitch somewere between the computer and throttle body is my guess. What ever happenend to keeping things simple. My Tacoma has a cable...if it fails the TB closes, not stick open.


emissions and safety standards.

And elimination of separate mechanisms for stability control and cruise control (both are done by the ECU).

And the car's electronics can intelligently select a throttle position and a gear ratio together based on your driving habits.

And rev limits or speed limits can be imposed more smoothly.
 
Originally Posted By: ARB1977
My Tacoma has a cable...if it fails the TB closes, not stick open.

No, it can also fail open. Many a mechanic has kinked the cable during underhood repair. A kinked cable has caused many 'throttle stuck open' scenario. Probably more common than a broken cable scenario.
 
Dumb question and statement from an old gezzer who doesn't understand all this electronic stuff.

But do we add all these electronic controls just for the simple reason "that we can".
 
They even have Submarines now that are all drive by wire.

Regardless, I have one drive by wire car the rest have a Cable.
I like the cable. My 89 even has a TV cable, no computer involved in shifting a TH400.
 
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