Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' in SD

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

"..disconnects the engine.."

There is no "disconnect", clutch.

In order for the Prius to "sit still" and not move in neutral with the ICE running the sum of the MG's must be counter to the engine RPM rate and direction.

Rev up the ICE in neutral and the MG's "sum" must rise accordingly.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

That doesn't sound like 'neutral' to me. We don't need the wheels to stop. We need the power to cease being applied to the wheels. If the ICE engine is stuck on, and neutral is broken such that it doesn't stop the engine, the car needs to turn both the MG into generators. The torque being created by the engine is split to both of them, and one of the is connected directly to the wheels. If one of the MGs is not spinning (one HAS to be) it can be brought up to speed at a reasonable rate, in fact it has to be. The HSD controls the load on the generator smoothly all the time in normal operation.

Only if Toyota is completely stupid. Given that there really isn't a 'neutral' where the engine is disconnected from the wheels, Toyota created a 'neutral' simulation, why would they make it such that the car flipped if put into neutral at high speed? That is insane.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

This Toyota Prius - Power Split Device is one of the online simulators of the PSD. So long as the car is moving all of the units connected to the ring gear will still move in proportion to the speed of the car. Putting the car into neutral will not change that. Of course if more power is applied to one of the units, the rotation of the other units will change but only so much as the speed of the car is changed.

But stepping on the brake will disengage a stuck throttle from the engine of a Prius unless there is a fault with the car's computer which there was not in this case. The throttle is actuated by the computer not a hard linkage. That is the key. A sudden failure of the computer which causes a runaway to maximum throttle of the engine AND an inability to disengage the throttle with the brake is extremely unlikely.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

Looking at the numbers:

Assume the worst case scenario: The engine is in full mutiny. It is running at maximum throttle, and won't stop for any reason.

Speed: 70 MPH
Engine: 4500 RPM
MG1: 5469 RPM
MG2: 4128 RPM (connected directly to the wheels)

In order to reduce speed we need to decrease the MG2, and increase MG1. No motor/generator is abruptly changing speed, certainly not going into reverse. If we tried to decrease the speed of MG1 the car would go faster (and MG2 is linked to the speed of the car).

Speed: 63 MPH
Engine 4500 RPM
MG1 6500 RPM
MG2 3736 RPM

Now we have slowed, but the MG1 is at maximum RPM, to continue to slow down, we need to slow both MGs, and overload the engine. This is done by causing both the MGs to become generators.

There is no way to have the engine at full RPMs and the car at a standstill, and the MGs within their approved RPM range (with no brakes). The best that can be managed is:

Speed: 0 MPH
Engine 1800 RPM
MG1 6500 RPM
MG2 0 RPM

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

"..Only if Toyota is completely stupid.."

You mean like requiring a 3 second depression of the PB to stop the engine rather than using 3 seconds to both start and stop...?

Other than the above method, how would, why would, the Toyota engineers know to plan for an ICE to be producing MAX HP with the gas pedal seemingly fully depressed and have the driver suddenly shift into neutral.

Anyone tried that, or like Sikes, too "chicken".

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

"..was not in this case.."

Indeterminate, not determined.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

"...This is done by causing both MGs to become generators.."

Two questions arise.

1. Can the battery pak absorb a charge rate cognizant with ICE max RPM and ~70 MPH road speed..?

2. Even should it be able to do that what happens when full SOC is (quickly..??) reached..?

"..overload the engine..."

How do you overload a ~70HP ICE with only 35HP of electric drive or generation capability..?

"...Engine 1800 RPM.."

Are you saying that above 1800 RPM a neutral CVT/PSD output cannot be accomplished..??

Wow, according to the simulator 61 MPH is the minimum road speed if the ICE is stuck at WOT RPM.

Unless you "blow up" MG1..!!

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

The MGs have 80 HP. And relevant quality is in fact torque, of which the MGs has 295 ft-lbs. 35 HP is the power limit of the batteries.

Basing it strictly on the relationships between the various motors and approved RPM ranges, yes. There are likely some subtleties of which I am unaware. And remember, there is no way to GET 1800 RPM in neutral.

So we are all agreed there will be no 'flipping', right?

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

No that is a design decision that you happen to disagree with. I mean stupid, as in it wouldn't pass safety inspections.

Firstly, ICE don't produce max HP at max RPM. Secondly, just having the gas pedal fully depressed wouldn't do it. Neutral, under normal circumstances, just slows and shuts off the engine, no problem. The worse case here requires the ICE at max RPM, the fuel still being provided (at least two other systems broken in unlikely ways), and presumably other things to go specifically wrong. Thirdly, Toyota needs to make a 'neutral' which acts reasonably close to what people expect in order to pass safety inspections. Here is an example: what happens when you shift into reverse in a manual transmission while traveling forward? You grind your gears, doing damage to you car. In a Prius, you go into neutral instead. No damage, no problems. If you are going slow enough, you go into reverse, and the car just slows and then reverses. Since it is just an electric motor changing speeds and then direction, there isn't even anything to go wrong. It is like changing directions on a fan (only better controlled).

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

In order to do a logical analysis we are forced to assume the ICE is "out of control" (throttle plate stuck fully open) and running at or near maximum RPM. In that situation wouldn't you agree that the minimum speed, even shifting into neutral, would be 61MPH.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

The point is that any sensible person aware of the CVT/PSD operation might well suspect a sudden severe front braking event (flipping, w/no ABS) should the system be shifted into neutral at ~70MPH.

And it would be that "suspicion" that would keep you from shifting into neutral.

Plus the simulator indicates that one of the MGs would have to go seriously OVERSPEED to produce an "idle" drive level at the CVT/PSD output if one were to shift into neutral at 70MPH and the ICE remain out of control.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

"..there is no way to GET 1800 RPM in neutral.."

But, also, there is NO WAY to GET neutral with the ICE above 1800 RPM...!!

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

Only is you assume no load, and assume that the MGs are better protected against overspinning than the engine. I would expect given the life-and-death nature of the worst case scenario, that an engineer might program the ECU to let the MG1 overspin in that case. How many things do we have going wrong in very specific ways at this point?

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

Of course there is. Get the engine above 1800 RPMs. Shift to neutral. The engine slows to a stop, and the MGs slow the car.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

Anyone who understands the PSD operation, knows what will happen. Nothing. Anyone who doesn't understand the PSD, but does understand the concept of neutral, will expect nothing to happen. And they will be right. The only people who could possibly get things wrong are people who are ignorant and arrogant at the same time.

Well at least we have moved from 'he knows more than you all' to 'he might incorrectly suspect'

Incorrect. The MG1 doesn't need to go overspeed until the speed decreases to 63. Seriously though, at the point where all those things have gone wrong, I wouldn't be worried about cutting a few years of the lifespan of my MG1 by letting wind up as fast as it needs to. I am sure Toyota's engineers felt the same.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

"..better protected against overspinning.."

The MGs have multiphase (3?) stators and permanent magnet rotors, the only way to prevent overspinning, "driven" overspinning, is by loading them up, CHARGING the hybrid battery.

The early FEH had a clutch (still does ??) that would disengage the drive if the vehicle were stuck from behind with such force that the MGs would overspin and produce such a high charging rate, voltage, that the electronics would be damaged.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

The case we're currently discussing has the ICE out of control and at WOT maximum RPM.

Yes,if the ICE will react to the shift into neutral and decline below 1800 RPM the the shift to neutral will be effective.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

You're missing the point, entirely. How much braking effect might you have on the front wheels during the period it takes for MG1 to go from 6500 RPM to the point wherein it begins disintegrating.

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

And...

Would the control software even allow (prevent an overspin) a "shift" into neutral until, unless, the ICE RPM drops to or below 1800RPM...??

 

Re: Toyota Offers Preliminary Findings From Technical Field Examination of Alleged 'Runaway Prius' i

My estimate would be 50,000 miles.

Those motors will bring the car up to 60 MPH in 10ish seconds (not with standard Toyota software) I don't envision them having any trouble doing the reverse. Even after choking off the engine. The brakes do it after all.

This hypothetical just keeps getting more outrageous. MG1 is an electric motor designed with a life of 300,000 miles, Toyota engineers want it to last that long therefore they set limits on its RPM. If this entire laundry list of things goes wrong, and it hits an unloaded RPM of 10,000 is it going to explode? No. It might get too hot, and possibly ruin the magnets. The bearing might suffer a bit. But we are talking about coasting down to zero from 70 MPH. Maybe a minute tops.

Then what? I am going to call Toyota to come get their misbehaving machine.
I get rid of cars that try to kill me. A bit of abuse of the MG1 is not an issue.