Coasting and tranny ???

No, that's correct. There is a fixed clutch between the ICE and the PSD. This clutch allows a bit of slip when the ICE fires up, to help avoid shock load and jerkiness. It is never disengaged or "thrown out", but instead just slips a bit when necessary.

Tom

 

that is interesting

i suppose that is controlled slip, akin to slip of clutch pack in a top fuel car, except this slip in prius is probably just in a duration of a second or 2 to avoid harsh engagement/disengagement

is this about right?

 

There is no clutch and no slipping.
There is a tortional damper which looks like the centre of a clutch plate in a manual car but this just smooths the power delivery of the ICE through springs. There is no friction material and no slipping just springs.

 

That's good to know. I assume the torsional damper allows a small amount of rotational displacement before the springs pull it back into alignment. Is this correct? That would work exactly as described above, but without the wear and maintenance issues of a clutch and frictional surfaces.


Tom

 

OK, there seems to be a lot of conjecture about what happens when you shift into N over 42 mph.

The N mode just changes modes in the computer. It prevents any power from being used for forward propulsion, and prevents any regenerative braking from slowing the car. It's like a forced glide. There is NO WAY that the engineers at Toyota would design the software to allow you to overspeed any components of the drivetrain just by moving a lever. just imagine the warrenty costs they would have to deal with!

According to my scangauge, when running at highway speeds in neutral the engine will run at a low RPM. As you coast to a stop the engine eventually will stop.

I use the N position all the time when coasting down hills, or any time I want to maximize my coasting. No problems.

 

Tom

Similar torsional dampers are used on centrifugal blowers and other large equipment at industrial plants. With a +200 HP electric motor, the bearings wouldn't last long if there wasn't a way to minimise the startup and shutdown harmonics

Cheaper couplings just use an elastomer material inbetween splined metal fingers. They work but don't last, and the failure mode is usually a catastrophic one

The question I have is this: why on earth would anybody want to or need to shift into N at highway speeds while driving a Prius? At the very least, you prevent charging the traction battery

jay

 

I will be glad to try it when the opportunity arises. What I think you are missing is that the ICE doesn't have to start. MG2 (it is MG2 isn't it?) will spin up to prevent an MG1 overspeed condition. That will spin up the ICE without actually using fuel.
Anyway, if the situation presents itself I'll to the test and report the scangauge data.

 

MG2 is tied directly to the drive train. Its speed is not controlled by the ECU. Only MG1's speed is controllable. The speed of the ICE is a product of the relative speeds of MG2 and MG1. That's why MG1 goes so fast when you coast without the ICE spinning. If the ECU slows down MG1, then the ICE will start to turn. That works without question. The question is whether the ECU will limit the speed of MG1, or rigidly stick with the no-starting-in-neutral rule that is otherwise enforced. Evan's experience suggests that the ECU will not limit the speed of MG1. This makes sense since MG1 is not powered in this mode, but is merely freewheeling.

Tom

 

Jayman,

Many marine engines use this sort of damper to connect the engine to the propeller shaft. In this case they are usually the cheap ones with the elastomer.

Our marine diesel has the prop shaft bolted directly to the drive flange of the engine. Our engine is also directly bolted to wooden engine logs. Must be that we enjoy vibration. :dance:

Tom

 

Actually, so long as the wheels are turning MG2 is always spinning. Furthermore, MG2 rpm is in direct proportion to the rpm of the front wheels (assuming that both front wheels are spinning at the same speed).

At any given constant speed MG1 and the ICE balance against each other. As the ICE changes speed, MG1 must change speed to compensate. If the shaft of the ICE is not spinning at all, then all changes in vehicle speed much be compensated for with a change in MG1 speed.

At 62 MPH, if the ICE is not spinning (because the driver chose the Neutral drive setting below 42 MPH when the ICE wasn't spinning), then one of three things will have to happen.

1) Neutral will no longer keep the ICE shaft from spinning and the ICE will suddenly be allowed to spin. (through testing with various tachometer solutions it has been confirmed that prior to 62 MPH this does not occur)

2) The vehicle will apply some form of braking mechanism to prevent exceeding 61 MPH. (regen? automatic application of friction brakes without driver input?)

3) MG1 will exceed the 10,000 rpm it is rated for and risk of failure will increase substantially.

Now, I'm not sure what the original source of the information is, but it seems to be generally excepted here at PriusChat that if the ICE shaft is not spinning and the Neutral gear selector is chosen, then the ICE shaft will not spin again until a non-neutral selector is chosen (Park or Drive). It is also generally accepted that the vehicle will not under any circumstances engage in HV battery charging while the Neutral gear selection is chosen. If both these are true, that only leaves option number 3 above.

I assume that you are indicating a belief that option number 1 above is what the engineers are likely to have designed into the vehicle?

It appears that there is some mechanism in place prior to 62 MPH that holds the ICE shaft in place and keeps it from spinning. Your belief seems to indicate that this mechanism will suddenly release, allowing the ICE shaft to spin freely as needed at 62 mph. Additionally there must be some sort of mechanism to maintain MG1 at or below 10,000 rpm to provide the resistance necessary to transfer force to the ICE shaft to accelerate it and acquire the appropriate rpm from the ICE?

 

Come on, how about taking one for the team.

I don't know if this is OT or not, but interesting to consider is that N in the Prius is not a mechanical state of the transmission, but a disconnection of the electrical field current in both MGs. That is why the car cannot start the engine in N; there is no field current to power MG1.

Also, I doubt that an even 10k rpm is the magic number that the MG will catastrophically explode; someone at Toyota has probably tested this on a few transaxles and then derated the actual speed limit to give a margin of safety. That isn't to claim that you aren't doing some damage at that speed though; you might get away with it a few times, then get your catastrophic failure at lower speed because you initiated a crack a few months before.

I think I will just leave mine in D.

 

Speaking of torsional damping and MG1 cranking ICE:

I wonder, since Evan got MG1 to 9960 RPM with ICE at 0 RPM, would damping between MG1 and ICE be enough if ICE started from 0 RPM while MG1 is @ 10k RPM? Or would there be further risk damaging the drivetrain or motors by allowing a shock like that? I know ICE routinely starts and stops with MG1 around 6500 RPM, so maybe another 4k is not enough to stress about.

But I have to wonder if that's part of the design decision to limit to ICE-on at higher speeds, not just avoid high RPMs in MG1.

 

So I just bought a 2008 that has a transmission position labled "B". I haven't even finished reading the manual, so I havent' gotten to that part yet, but when reading this thread it made me wonder why nobody is referring to this. Is this setting new?

 

B mode is not new; it is on all Prius. It is analogous to "2" (or possibly 1) in a 'normal' automatic transmission.

For more info read this

 

Tom

A low speed application, that should be ok. A surprising number of high speed (3600 rpm) +200 hp electric motors are hooked up to centrifugal multi-stage blowers that way, which is *not* a good idea

Kind of historic and romantic to have this 1-2 cylinder iron horse diesel knocking away. As a kid, I remember one of my uncles having an ancient Lister diesel on his farm to run a water pump

The Lister had pushrods external to the block, and you could watch them go up and down. For a kid, it provided hours of entertainment. It was built like a brick s***house, for under 20 hp it weighed around 800 lbs. Easy to take apart, clean/rebuild, and reassemble

jay

 

And according to my Scangauge even when no power flow arrows appear on the display the battery is being pulled at about 6 amps. When N is selected that drops to just below 1 amp with nothing but the radio on. (More with lights, fans etc.) When doing lots of pulse and glide it seems that N helps keep the traction battery from draining.