As already pointed out, only below ~64 km/h (~40 mph) can one shift into Neutral without the ICE needing to spin in order to protect MG1 from over-revving. Normally it would be spun by MG1 with electrical power supplied by MG2. Droid13 and Pete4 make the interesting point that, since in 'N' all power flow to/from the MG's (and consequently also your regenerative braking) is supposedly cut, the ICE cannot be spun in this way by MG1, and must thus be fired up under gasoline power to protect MG1. But how can this be done without using MG1 to restart the ICE? Well, if the car was in fuel-cut mode when it was put into 'N', then the ICE was already spinning at ~1000 rpm, and so could presumably be fired up instantaneously without any problem. This is just how the TCH normally switches into and out of "fuel-cut" mode while driving in 'D' (see below). But if the car was accelerating in 'READY' and 'N' under gravity from rest down a hill, starting with the ICE off, how would it start the ICE to protect MG1? I don't know. I'd guess that, since the NiMH battery and all electronics are still active because the car is still in READY, it would go ahead and use MG1 to start up the ICE for protective purposes when the speed reached ~64 km/h. Would someone like to check this out?

Talking about "heretical" mode, without instrumentation more sophisticated than the car's MFD or a ScanGauge, I don't think it's easy to determine exactly when the TCH is in this mode. In addition to the ICE's speed, one needs to be able to monitor MG1's speed, and also its direction of rotation. I believe that heretical mode is commonly employed when travelling at steady high speeds on relatively flat highways. It should not be confused with fuel-cut mode which can occur at speeds above ~64 km/h when the car is coasting (or, at least, when the accelerator is only very lightly pressed). In fuel-cut mode, all fuel flow to the ICE is stopped, but it is being spun at ~1000 rpm by MG1 (powered by electricity from MG2), in order to prevent it from the over-revving that would occur were the ICE allowed to stop completely. Fuel-cut mode can be detected unambiguously from the fact that ScanGauge shows "open-loop" ICE operation, and the dash's FE gauge simultaneously reads precisely zero fuel usage (0 L/100 km or 60 mpgUS). In both cases, electrical power is flowing from MG2 to MG1. The open-loop indication would, however, clearly distinguish fuel-cut mode from heretical mode.

Stan

 

The whole concept of "Neutral" in the Toyota technology requires a pretty large shift from conventional thinking. There never occurs a mechanical detatchment of the axle and power components in this system. To faithfully replicate a conventional transmission in "neutral" therefore requires some pretty smart decisions on the part of the ppowertrain computer. It has to: 1) supply no driving force to the axle, either positive or negative (sounds easy until you consider number 3 below); 2) protect MG1 from overspeed; 3) simulate a coasting condition if the vehicle is in motion from kenetic energy; and 4) respond correctly to braking inputs, either by the "normal" braking combination, or by the friction brake alone.

I strongly suspect that neutral on the TCH is largely a computer software concept, and that all of the powertrain components remain active, but under different rules for operation. Such a software rule set would require the protection portions to take a priority and the no-power application (Positive or Negative) to the ring gear to be a second, lower priority portion. I do not think that a total removal of the MG2 - MG1 Iinteraction would be desirable or even feasible. Can you start the ICE by making a power demand with the accelerator in neutral while the TCH is at a dead stop?

What we are really talking about is the computer responding to its sensors in such a mannor that no forces are applied to the wheels -- so long as the brakes are not applied and the powertrain is within the limits established for its protection. An interesting subject that this suggests is an investigation of the failure modes associated with sensor failures for MG1/2 RPM sensors, varoius current limiters, the computer, etc.

 

I think that when in neutral, the braking is done entirely by the friction brakes. It has been recommended in various forums that a few stops from speed while in neutral can help clean off your rotors (they can get rusty from lack of use) and eliminate some grabbiness.

 

I assume no regen takes place when braking in N because I don't see any arrows and the brakes feel different (smoother) and you don't hear the WRRR of the motor like you do under regen. Also, when in N and at a dead stop (ICE off), stomping on the accelerator does absolutely nothing. No ICE startup or rev at all. This indicates that the ICE most likely is cut when the wheels are moving, at any speed?

The easiest way to test all this is for someone with a ScanGauge to investigate!

After reading all the replies on this thread and the new one about Heretical mode (and fuel-cut?!! need to get me a scangauge!), I've been driving by the MPG meter instead of the spedo, and getting 45-50mpg (instant) for highway stretches doing 65-75mph!

 

I would imagine there must be a way to start (and keep running) the ICE for trubleshooting...nt that helps us with this discussion...just a curiosity

 

Well, try this: While stopped, shift to B, press and and hold the brake pedal while momentarily pressing on the gas. The ICE will start and stay running on my TCH if I do this.

 

Thanks to you, Ed, and the other fellows here for the information on the TCH. My car should be arriving by mid July. I have used the scan gauge with my last two cars. One was a 4-cyl, '03 Corolla and the other a '06 Ford Five Hundred V6. Strange, but both got peak mileage at 48 - 50 mph. The mpg would slowly fall off above 55 mph and even more at 60. I run 35 psi in my tires when cool. With the TCH I may go near maximum psi. I read that many run the max pressure here in the greenhybrid forms.

I wish I had bought the TCH when they came out. I could have had a years experience behind the wheel.

burt

 

spiff72 — It's also my understanding that when in 'N' all braking is done by the friction brakes — no regen.

greyghostTCH — In my TCH I can't force the ICE to start when in 'N,' but in either 'D' or 'B' it will start, as mentioned by nash, if the accelerator is pressed momentarily.

jbollt — I believe that, using Toyota's Intelligent Tester, the technician can indeed put the TCH into a test mode that allows all manner of things to be done that the driver cannot do! Things like running the ICE for troubleshooting, etc. The Repair Manual discusses this (offhand I can't say precisely where).

Stan