Self Driving Uber Fatality - Thread IV 7

[IRstuff]

This thread is continued from thread815-438410

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[GregLocock]

There is no torque converter.

Cheers

Greg Locock


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[BrianPetersen]

If the aforementioned vehicle has a VW DSG transmission, the clutches default to "open" (uncoupled) and in a key-off situation, that's what happens. YES, this is the reverse of what happens with a manual-transmission clutch. The VW DSG clutches require active energisation in order to engage. Key-off? No torque transmitted. No bump-start for you. It will not command the clutches to engage if you attempt to bump-start the car.

Re auto trans being used for bump starting ... Keep in mind that they are not only reliant upon the torque converter being filled with oil but they are also reliant upon the correct internal multi-plate clutches being supplied with hydraulic pressure in order to transmit any torque, whether due to the engine driving or in over-run coasting (or in an attempt to bump-start).

If you go back to the dawn of hydraulic-controlled automatic transmissions, up to the early 1960s, they had a front pump driven by the engine and a rear pump driven by the drive shaft, expressly to permit bump-starting. You shifted to "drive" (no electronic controls in those days), had someone push the car, the rear pump developed pressure which engaged the clutches and then hopefully back-drove the engine to start it. It would have to be pushed fast enough for the torque converter (or, originally, fluid coupling) to transmit enough torque to get over that first compression stroke ...

In the mid sixties, the rear pump was deleted, and that was the end of bump-starting. If the engine is not running, the pump is not running, therefore there is no hydraulic pressure to engage the clutches. Doesn't matter what gear range was selected, doesn't matter how fast you spin the drive shaft in an attempt to back-drive and bump start. Pump not running -> no pressure -> no clutches engaged -> nothing happens.

Now, add to that the electronic controls, which also default to "off" in a key-off situation.

The thing that I don't know, is on a vehicle that has complete automation (switching the key off doesn't actually key-off anything), if you commanded engine-stop while rolling forward, is whether it would detect this and leave the transmission coupled in the interest of keeping the power steering and power brakes working, or whether it would simply cut all solenoid power to the transmission, in which case all solenoids go off, and all clutches disengage.

 

[GregLocock]

No, there was no engine braking. As you say, no power means no clutches engaged. I'd forgotten about the 2 pump malarkey on early autos, I've only ever worked on hydraulic 4 speeds and above, which had just the one pump.

Cheers

Greg Locock


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[LionelHutz]

LionelHutz, I didn't say I wouldn't buy a car with an electronic throttle. 3 of my cars do have them (btw, it was a 2002 model that I said had a mechanical throttle, not a 2009).

Sigh, see below...

The ECU very likely does control the throttle based on a suggestion from a pot or magnetic pickup at the accelerator pedal and/or the simultaneous application of the brake.

Not on any of my vehicles. All of mine have a mechanical linkage to the butterfly valve in the throttle body. Of course, the newest vehicle I have is a 2009, so some newer vehicles may be set up that way.

Yes, you did say you wouldn't own a vehicle with an electronic throttle.

Yes, you also said you had a 2009 with mechanical linkage.

 

[thebard3]

I don't understand the angst associated with an electronic throttle. The actuator for my afore-mentioned 2003 Silverado once suffered an intermittent failure. The throttle fails in a spring-return position to above idle, and a diagnostic message displayed that says 'Reduced engine power'. If the ECU indeed still has throttle control, it can only drive it down to idle but not above the spring return position thereby keeping it from exploding the engine. Also in this situation, the engine does provide enough power to get you off of the road albeit at reduced speed. I assume the failure mine experienced was a loss of position feedback, in which condition would keep any ECU controlled car from running properly. A couple of cycles returns the engine operation to normal. I purchased a replacement Delco throttle for $135 and it took me all of 1/2 hour to replace it. This all happened after I had over 150K miles on it so I don't consider any of that to be unacceptable.

Brad Waybright

It's all okay as long as it's okay.

 

[BridgeSmith]

Yes, you did say you wouldn't own a vehicle with an electronic throttle.

Yes, you also said you had a 2009 with mechanical linkage.

My apologies. I thought I had edited that post before submitting it. I looked at the pedals in my cars and realized I was mistaken about my newer vehicles, and apparently newer vehicles in general. Given the substantial number of vehicles successfully using the electronic throttle, I don't have the hesitation about them that I did. Perhaps, when the steering control systems (for parallel parking and such) have had a widespread successful history, I'll be ok with driving a vehicle that has it (still don't think I'd ever use it), but I don't think I'll ever trust a computer to drive me somewhere, though.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[dgallup]

The only stuck throttle I've ever experienced was my '79 Mustang when the "automatic" choke fell off the carb body and kept the throttle about 1/4 open. I managed to drive it home (only a couple of miles to go) by turning the ignition on and off to modulate the power. Fortunately it was late at night so little traffic and I just ran the red lights. No way I could park it like that so I drove up over the curb and left it in the front yard. Damn those unreliable mechanical systems.

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[3DDave]

One thing I enjoy about electronic engine control systems are the videos of what mechanics have to go through to see what the reason for a fault is, sometimes requiring the use of an oscilloscope. My favorite was a "Reduced Engine Power" failure display that was eventually traced to the redundant throttle position sensors; apparently if there was more than a slight disagreement between the two sensors, the ECU would basically paralyze the vehicle. While they can be very reliable, when they fail they can be maddeningly difficult to diagnose and can be horrifically expensive to repair.

 

[thebard3]

dgallup-
Try driving a 60's or 70's era pickup with a straight 6 and a broken engine mount, causing trottle, shifter and clutch linkages all to jam up at once!

Brad Waybright

It's all okay as long as it's okay.

 

[dgallup]

Oh, I drove several of them without a broken engine mount and had to pull over to un-jam the worn shifter linkage.

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[IRstuff]

My Charger(Arrow) would routinely break its front engine mount, but that didn't seem to incur any other damage.

A REALLY TINY disaster -- that car was sold in America, with American lug nuts, but it had metric-threaded studs, so I once got a flat and took out the wrench to remove the lug nuts, but SOMEONE had lost one of the OEM nuts during a previous repair and replaced it with the metric-threaded metric nut, which, of course, didn't fit my wrench. So, being in the pre-cellphone era, I had to wait, and wait, and wait, for AAA to come and help with installing the spare tire. Turned out the OEM lug nuts were actually metric nuts wrapped with a chromed cover that made it look like a US lug nut.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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