Toyota's runaway-car worries may not stop at floor mats-LA TIMES

"Quick! What's the number for 911?", said in your best Homer Simpson voice.

Tom

 

excellent point ... i shall make them available to friends as well

 

At 100mph and full throttle, sticking the selector in neutral shuts the engine down all nice and safe and all the reving stops. It's nice and smooth too.

 

you're smooth

 

Like Rob Thomas and Santana Smooooth?

 

Or smooth like Jiffy peanut butter on a glass doorknob?

Tom

 

More like Rico . . . . . . . . . . . Suave



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The Engine ECU (electronic control unit; sometimes known as Engine Control Module or ECM) has complete responsibility for fuel pump, fuel injection, spark, and, on drive-by-wire cars, throttle opening angle. On cars with VVTi it manages the oil control valve, which governs the cam position that affects the valve timing. It manages the various pumps and valves in the fuel system, e.g. for the charcoal canister. It controls the cooling fans (in co-operation with the Air Conditioning Amplifier, which is an ECU). On the North American Gen 2 Prius it also manages the coolant thermos valve and pump.

There may well be other ECUs doing other jobs on the car, but on a conventional car, you lose the engine ECU, you lose the engine, you lose drive. That was the context of the message.

It's somewhat more complex on a Prius - please remember that the context of the accident was a non-hybrid Lexus sedan - because the engine ECU is no longer master, it's slave to a Hybrid Vehicle ECU (HV ECU). The HV ECU monitors the accelerator pedal and decides how much power it wants the engine to provide; the engine ECM responds by controlling the throttle as appropriate.

The HV ECU is in constant communication with the engine ECU (they're strapped back-to-back but they are separate modules) and in addition, the NE+ and G2 signals, from the crankshaft and camshaft position sensors respectively, are buffered by the engine ECU and read by the HV ECU so it knows how to time the motors for a smooth engine shutdown and startup next time. Throttle control signals are sent over the Controller Area Network communication bus. Each ECU is expecting a pretty constant stream of data from the other: the HV ECU will log DTC U0100 if it doesn't get a reply from the ECM to a request within 0.1 seconds, or if there's a problem sending one, and if it doesn't see anything for 1.91 seconds. The ECM will log U0293 if it doesn't see anything from the HV ECU for 0.68 seconds. (Times and codes from Gen 2.)

If you lose the HV ECU, you really will go nowhere, because it controls the three-phase signals for the electric motors directly. It has to keep the three waveforms for each motor going with exactly the right voltage, frequency, and phase, to have them drive at all. Mechanically the Prius cannot drive on just the engine. MG1 must be providing physical resistance or the transmission just spins.

There are hints that there are separate CPUs for providing the drive waveforms for the main drive motor (MG2) and generator (MG1), within the one ECU box. DTC P0A1D deals with internal ECU faults, and various subcodes refer to different components. Subcode 180-186 refer to a 'rotation angle CPU'. I, at least, would not design it so that those parts would operate autonomously for any length of time, that if they lost communication with the master processor, they would shut down safely.

There are plenty of other ECUs in the car - cars with HID headlamps have one for each headlamp! - but none of them are involved in the powertrain. On the Prius there is still a Transmission Control ECU but it's basically a stub - it only controls the parking pawl. The Park button and shifter are actually monitored by the HV ECU which instructs the Transmission Control ECU to apply or release the parking pawl as appropriate. Reverse is a software state, not a mechanical action (the HV ECU drives the main drive motor MG2 the other way).

There are a bunch of other ECUs that deal with the keyfob slot, power button, and (if fitted) smart key, but they pretty much only tell the HV ECU that it's OK to, and when to, go READY.

 

All you need is a scantily-clad Megan Fox in there and you've got a Michael Bay movie on your hands.


I have't read the whole thread - has anyone actually tried the two methods 1. turning off the car with the 3-sec button push and 2. shifting to Neutral at highway (70mph) speeds yet?

 

At least read the page you posted on... Sheesh!
Post #283

Hill, Gerardo was pretty Suave back in the day. lol

"So please don't judge a book by its cover
There's more to being a latin lover
You got to know how to deal with a woman
That won't let go
The price you pay for being a gigolo"

 

Mike, great post.
Although I have always just assumed/taken-for-granted that the MG motors on the Prius are in effect the starter motors for the engine, and that there is no separate "starter" motor on the Prius. My thought process never went any further because that is an easy concept to grasp. However, your post just caused me to ponder something ... RPM. MG velocity depends upon the velocity of the car's wheels (when the drivetrain is engaged; in "Drive." When starting an engine, usually, a given velocity is best, right? Or, does the Prius just jam the clutch in and squirt gasoline and fire the spark plugs at whatever velocity the transmission happens to be traveling at?
(I apologize for any redundancy, as I'm sure that if I used the search box and scrolled through dozens of pages, I could find the answer - but, I don't feel like doing that right now)
Thanks.

 

There is no clutch. The Prius PSD 'transmission' is nothing like a normal transmission, being more closely related a common differential.

Like a differential, the PSD has three input/output shafts, not the two of a common transmission. Very generically speaking (ignoring gear ratios and rotation directions), the speed of any one shaft is the sum of the other two. All three shafts can turn at once, or any one can be held stationary while the other two turn.

Also like a regular differential, if one shaft spins freely with no resistance (Differential: one wheel lifted off ground. PSD: MG1 electrically disconnected, with no motor or generator function), then no power or torque can be transmitted between the other two shafts. The result is the same on the Prius and on the common differential -- no power can get from the engine to the drive wheel.

When a Prius is rolling and its ICE is stopped, MG1 is spinning fast. To spin up the ICE before fueling and igniting it, MG1 is commanded to spin slower, forcing the ICE crankshaft to make up the difference.

 

The Prius transaxle takes the engine shaft and puts it between MG1 and the gears that power the wheels. When MG1 is electrically off, the engine spins MG1 and no torque goes to the wheels. As soon as MG1 begins working like a generator, the resistance torque causes part of the engine torque to go to the wheels ... the car moves forward. The power generated by MG1 needs to go somewhere so the car routes it to MG2 that is on the wheel side and adds it to turn the wheels. This is called "power split." Changing the amount of power generated by MG1 controls how much torque goes to the wheels.

The power split device is a planetary gear, which means there is a center, sun gear, a set of spider gears on a middle planetry gear carrier, and an outer, ring gear. The engine shaft connects to the middle gear carrier and MG1 connects to the center, sun gear. When MG1 is electrically idle, the engine turns the spider gear or planetary gear carrier and they spin MG1 insanely fast. The outer ring gear connected to the wheels remains stationary as the rest of the gears, the inner gears, rotate like mad. But as soon as MG1 starts to generate electricity, the counter torque at the sun gear causes the spider gears to apply torque to the outer ring gear and on to the wheels.

With MG1 generating power, it needs to go somewhere and that is to MG2 that is connected to the gears that drive the wheels. MG2 works as a motor to help turn the wheels. So other than energy conversion and gear friction, no significant energy is lost. All of the engine power goes to the wheels. Computers control all of this so no mechanical clutches are needed.

Brilliant people have already worked out that about 28% of the power flows through MG1 and thus 72% goes to the wheels via the ring gear. But this 28% of power goes to MG2 and rejoins the 72% to power the wheels. So the electrical losses apply only to 28% of the power and is typically around 3% ... about the same as three gears transferring power.

Computers control MG1, MG2 and the engine in a mad dance of spinning gears and invisible torque. Yet it works to give the smooth power of our Prius without shift points and no more moving parts than a manual transmission. It works.

Bob Wilson

ps. Clarification: Torque vs Power

Imagine MG1 is working as a generator and in applying counter torque against the ICE, the vehicle speed and gearing causes MG1 rpm to drop to or approach zero, which happens in certain speed ranges. But without fast enough rotation, MG1 as a generator can not make the counter torque needed except by making extremely high currents at too low voltage. It can happen if MG1 works as a motor. When MG1 rotation slows enough, the power for MG1 counter torque comes from one of two sources: MG2 or briefly, the traction battery.

The definition of Power is Work, force times distance (actually the dot product) over time. The Work occurs where the ICE powered spider gears engage the sun gear teeth. In that boundary, we find the torque is equal and opposite and the distance is the circumference of circle where the gear teeth engage and does not change. The time for both ICE and MG1 torque is identical and this means the MG1 power out as a generator or in as a motor remains be the same as the ratio of the torques, 28%.

 

Have you tried the power button?

 

No way man! That's nuts! Hahaha

Nah, I have not tried that yet. I didn't want to have to pull off the freeway or stop to restart the car.

 

Tell you what . . . if I have time, I'll take our Lexus hybrid out tonight ... gun it (on the freeway) up to speed, and while accelerating, I'll throw it in neutral ... then post the results ... if everyone promises to put this unkillable zombie thread down into the grave where I'd hoped it'd end many many days ago.



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Well, it's been nice knowing you. I predict that you will burst into flames, your eyes will pop out of your head, and you and the Lexus will teleport into another dimension populated by Korean cars.

On the other hand, maybe nothing will happen.

Tom

 

you have my unflinching support ... oh, don't forget your unicorn

 

i read in consumers report today it would be unsafe to press start button to quit as you would have no control of the car.also do not pump brakes but hit brakes hard and shift to neutral stop with brakes and then shut car off.makes a lot of sense to me

 

Which is what Toyota recommends.
Shift to N, Apply Brake till it stops or slows down enough, Power-off (3secs).
I told my wife this since she is the primary driver now of our Prius.