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#1 of 2264 Unintended Acceleration - Find the Cause
Mar 02, 2010 (12:26 pm)
Every car company has received complaints from consumers relating to vehicles that suffered unintended acceleration. Many incidents are not fully addressed by recalls. NHTSA is responding to the challenge with more of what they have already done: additional investigations.
Isnít it time to try a different approach? We at Edmunds.com think so.
#3 of 2264 Re: Unintended Acceleration - Find the Cause [steve_]
Mar 02, 2010 (1:38 pm)
Steve...now, that's one way to get inundated....offer money....lots of it, to show UA in Toyotas.
Me thinks you'll be hearing from Dr.Gilbert very soon.
For that kind of dough, I may go out and buy a Corolla and do it myself.
#4 of 2264 My explanation of Toyota's electronics control problems
Mar 02, 2010 (2:04 pm)
Many people think it's good to go with digital on everything. It's not always the case.
Let's start with a very simple control in every electronics, the volume control. In the old products, the volume control is a simple potentiometer. If you turn it slowly, you can change volume in indefinitely small steps (fine adjustment). If you turn it really fast, you can bring the volume from min to max in one revolution and in less than half a second. That's the beauty of analog (mechanical) controls.
Now let's see how a digital volume control works. The volume knob turns a digital encoder which has certain contacts at certain position. Let's say the encoder has 8 contact positions in a revolution (at 12, 1:30, 3, 4:30, 6, 7:30, 9, 10:30 o'clock position). The CPU would check periodically where the current contact position is and compare with the past position to determine which direction the volume knob is turning and how many steps; the CPU would change volume accordingly.
You can see two major problems of digital volume already:
1) Fine adjustment vs. fast change: if you want to make very fine changes in volume, say 8000 steps from min to max. Then the knob needs to be turned 1000 revolutions for that! If you want to make less total turns to one revolution like the analog volume, then you only have 8 steps!
2) Rotation direction and speed detection: let's say the CPU checks the encoder position 4 times a second (CPU needs to multi-tasking with many controls). The 1st time the CPU found the contact is at 12 o'clock; 2nd time is at 9 o'clock. Then the CPU assumes the volume is turned down by 2 clicks. But the user may have turned the knob up (clockwise) very fast from 12 o'clock to 9 o'clock between the 1/4 second CPU checks the encoder! You can see that the CPU could easily and totally miss-interprets the user action in the opposite way and wrong number of steps!
These are the 2 exact challenges when designing the car's pedal, steering and brake into digital (electronics) controls.
Camry unintended acceleration is probably due to the CPU miss-interpret the driver pedal action in the wrong direction.
Prius brake hesitation is probably due to the CPU not checking the brake encoder (sensor) fast enough.
Corolla steering problem is probably due to not enough fine steps in the steering encoder (sensor).
I challenge Toyota engineers to post their solution to the problems I listed above in their car design.
#5 of 2264 Re: Unintended Acceleration - Find the Cause [graphicguy]
Mar 02, 2010 (2:06 pm)
>I may go out and buy a Corolla
But think how bad the resale value is likely to be on a toyota now.
#6 of 2264 Re: My explanation of Toyota's electronics control problems [xlu]
by Stever@Edmunds HOST
Mar 02, 2010 (2:17 pm)
That analog knob fails when you are trying to tune a radio station however, especially if you are using a short wave radio. Or if you are trying to dial in a planetary or star position with your telescope.
And if the potentiometer jams on high, you get unintended acceleration "really fast."
In the good old days, a relatively common complaint was a "flat spot" in the accelerator. Drive by wire can avoid that issue. A mechanic device can kink or break or have an object dislodge and jam the throttle cable. So there's cons to heading back in that direction too.
#7 of 2264 Re: Unintended Acceleration - Find the Cause [graphicguy]
Mar 02, 2010 (2:16 pm)
I strongly suspect that at the end of the day it will be found that there is no "single" causative factor. Confluence of factors would be my guess. For instance, simultaneous opening of the A/C compressor clutch relay and startup of the ABS pumpmotor. Lots of RFI/EMI "spewed" about within the engine compartment and within the 12 volt wiring due to the inductive "kick" of the electromagnetic A/C clutch coil, while at the same time a HUGE load on the 12 volt system dragging it down to a minimum voltage.
Personally I would start by adding voltage "snubber" devices to the various inductive devices, A/C clutch, transaxle solenoids, DC motors, etc. I would also provide SOLID ground/supply wires directly from the battery post to the engine/transaxle control module, fused directly at the battery.
#8 of 2264 Re: My explanation of Toyota's electronics control problems [xlu]
Mar 02, 2010 (2:23 pm)
xlu, it seems to me that you are proposing ideas in the right direction and that you give examples of things that can cause "glitches".
However I think the root cause issues are substantially more complex than you have described and involve both race-conditions (software bugs relating to unexpected timing of separate processes) and multiple simultaneous electronic failures or "glitches".
That is, I don't think the problem occurs due to "single point of failure" of either software or hardware, else we would be seeing way more catastrophic failures, and failures that were easily repeatable.
Instead I think the catastrophic failures are something like a "cascade" of worst-case/corner-case race-conditions.
That professor dude seems to be demonstrating this empirically.
BTW, I think Toyota engineers are doing (and redoing) the exact same kind of tests and that they are diligent, skilled, and ethical engineers.
#9 of 2264 Re: My explanation of Toyota's electronics control problems [xlu]
Mar 02, 2010 (2:34 pm)
Wrong on both counts.
1. Fine adjustment vs fast change.
Check you PC mouse setup. You can have it set for very fine resolution AND fast change. The more distance you move the cursor the more rapid the cursor accelerates....
2. Rotational encoders, optical and mechanical, ALWAYS have two outputs, 90 degrees in phase separation, so direction of rotation can be discerned..
Proper hardware and software design is almost magical.
The gas pedal sensors are not "encoders" in your sense of the word, but hall effect position sensors. The two sensor outputs are intentionally displaced in voltage output by ~0.80 volts but otherwise track each other linearly as the pedal moves from idle to full depression. So it is not possible for the firmware, correctly written firmware, to miss-interpret the gas pedal position.
#10 of 2264 Re: My explanation of Toyota's electronics control problems [wwest]
Mar 02, 2010 (5:00 pm)
Your response seems to be too absolute.
In the 1st point, yes, I checked the mouse, both mechanical and optical. In the mechanical mouse, the movement in each axle is sensed by a small bar which drives a wheel with many holes. The optical sensor would read the hole counts. The resolution for one rotation is a fixed number (say 16); so no matter how you set it up, there's only 16 steps in one resolution. When you make the mouse faster, each step just jumps a bigger distance. The optical mouse works with the fixed amount of steps as well. The ball has many small dots which reflect lights. Again, fixed number of steps. You won't get more total steps no matter what you do.
In the 2nd point, I do not agree that the encoder ALWAYS have 2 outputs. I designed hundreds of products with the encoders of 1 output.
I'm not an auto engineer so I do not know if they use hall sensor in car design. If they do, there could be even bigger problems because Hall sensor is very sensitive to the EMI interferences.