Guys, the TCH has no pulleys, clutches, variable gears, or drive belts. The CVT also has no ICE disconnect capability. The ICE, MG1 and MG2 are always coupled to the three shafts of the Power Split Device — a planetary-gear set. There's a mathematical relationship between the speeds of these three shafts. One shaft is always coupled to the wheels and to MG2. As the car speeds up in pure-EV mode, and if the ICE is not spinning, then the MG1 shaft reaches speeds that Toyota considers to be undesirable ("over revving"). So, they arrange to slow down MG1 electrically to prevent this from happening. This causes the ICE to be spun in fuel-cut mode (absolutely no fuel is being used!). This happens above 64 km/h (~40 mph) in 'D.' I'm sure that MG1 is safe from physically flying apart until much higher speeds, but I wouldn't want to test it out myself. From what you're saying, it seems that, if you put the car in 'N' while you're in pure-EV mode, and let it accelerate downhill, the ICE does not get spun by MG1, and the protection is disabled. (Or else, it is in fact being spun, and you don't realize it!) This isn't free, by the way. You're losing kinetic energy in the form of engine braking if the ICE is being spun in this way. If the ICE is indeed not being spun, then there's no such energy loss, and the car is then just coasting freely. As I said, I wouldn't want to do this at speed in my TCH. It may also be illegal. The FE gauge reads precisely 0 L/100 km (60 mpg) when you're in fuel-cut mode, and sits at the very bottom of the blue area when you're in pure-EV mode. Only when it rises above 0 L/100 km in the metric version is fuel being used. I assume that the US version treats a reading of exactly 60 mpg as the fuel-cut indication too.

There's a lot of discussion of these matters elsewhere in this forum, by the way, and it's not fruitful to repeat it all here. (Look at the thread "Heretical Mode," for example.)

Stan

 

Here is a link to a similar discussion on PC a while back. This should pretty much clear up the neutral gliding discussion. It's a quick read. If you have any questions about real world hybrid function with proof check out the prolific postings of people like Hobbit and Ken1784 on the other sites around. I don't recall the question of gliding at high speed in neutral has ever come upon this site. Please do not resurrect that heretical mode thread!

 

Good point on the fact that using neutral looses the kinetic energy stored in the motion of the vehicle and the fact that the transmission is really a "power split device" and never is ever really disconnected from the drive shaft. Hopefully that will put to rest any further discussion on this matter.....!! It just doesn't make sense to drive in neutral. Case closed!!

 

Thanks SPL for the info. I had assume there was still some sort of linkage that disconncted the transmission from the output, but I guess not.

It's curious that the system will not charge in "neutral". (at least according to the manual). You would think if everything was still connected, it could.

And yeah, sounds like high speed coasting in neutral with the engine off is a bad thing. (....not that it's a good thing in any car.)

Later!

Dang

 

Ok, I give up!! I'll keep it in D from now on.

 

Dang — In 'N, the motor control electronics are disabled from both receiving power from (i.e., regeneration), or sending power to (i.e., motoring), the MGs. In this sense it's like 'N' in a regular car, where the ICE is completely physically disconnected from the wheels. In the TCH, however, a physical disconnect cannot occur; 'N' provides an "electrical disconnect," which achieves the same goal. It's probably done for reasons of safety, such as when servicing the car. So, it follows that MG1 cannot start the ICE in 'N,' even if the car's speed exceeds 64 km/h. I had wondered, in a previous post in another thread, what might happen under these circumstances, but was unwilling to test it myself!

Stan

 

Stan, you have it right, but you are confusing yourself.

All correct, a perfect description. But your later post:

Mabe a little combat fatigue here.

MG1 and MG2 are never disconnected from the ECU. If any selected configuration of driver controls and vehicle dynamics attempts to overspeed MG1 the ECU will protect it by using power from MG2 to provide an MG1 electrial load that will setup an MG1/MG2 ratio that will spin the ICE in fuel-cut, period.

What the "N" position on the selector primarily does is:
1> Place the ICE in fuel cut and keeps it there to prevent an ICE start (this is the power off state for the fuel valve solenoid); and 2> shuts off the regen circuit from MG2 that is used during regen coasting and regen braking; and 3> shuts down the ability of MG1 or MG2 to be electrically driven from the traction battery.

As you correctly stated in your post, the reason is saftey. This combination of electrial cuts ensures that the ICE cannot start. when the car is stationary neither MG is turning and no fuel is available. When the car is moving, the engine may rotate, but will not produce power as no fuel is available. However, it may be used by the ECU to provide a brake effect to protect MG1 -- because MG2 is turning and can make the power necessary to set the necessary electrical field on MG1 to achieve the difference in speed on the sun gear necessary to spin the ICE.

IMHO, If we disregard the legal issue for the moment, there is one, and only one, situation where selecting N may offer a benefit. When under 42 miles per hour, by removing all of the regen from braking and coasting, the artificial engine drag that Toyota put in the TCH to simulate a conventionally driven vehicle is removed, and thus the coasting speed and/or range can be increased somewhat. Coasting in this manner is effectively similiar to "stealth" mode, but is much easier to maintain than when in "D" in the TCH. If it can be maintained over a descent period, without exceeding the 42 miles per hour speed that will start spinning the ICE in fuel cut, then the efficiency loss of sending regen to the battery and then reclaiming it to drive MG2 will be avoided. To achieve this, the grade must permit sustained speeds that are fast enough for the traffic conditions, but not faster than the 42 miles per hour ECU limit.

One other thing -- Once the ICE starts spinning, it will not stop spinning if you simply slow below 42MPH again. See the "Heretical Mode" thread for the reasons.

 

The original post stated that the the engine did not rotate, even at 55mph. I've seen this myself although not at these speeds. My question is this. With the engine rpm=0, MG2 rpm = fast (lets say your doing 70 miles per hour), what is the speed of MG1?

 

If it were possiible at 70 miles per hour that the ICE was not turning, then MG1 would be at around -10816 RPM. It would not be below the -6500 RPM ECU limit until the ICE was in fuel cut at approximately 1200 RPM or so.

At 55 miles per hour, if you could get there without the ICE turning, then MG1 would be at -8600 RPM or so. In theory an ICE spin of about 600 RPM would put it back in range, but I do not know if the ECU will permit fuel cut to operate the ICE in a slow RPM range like this. It may adjust the MG2/MG1 ratio to get the miminum ICE idle RPM of around 1000 RPM, even in fuel cut. That would put MG1 at a very safe -4980 or so.

 

FastMover — I'm afraid that you misinterpreted what I was trying to say. Perhaps my colloquial use of the phrase "electrically dsiconnected" was a poor choice, but I intended this to signify that the driving circuitry was placed in an "open circuit" state, so that electrically it was the same as if it had actually been disconnected. As you say, there's no actual "breaking" of any electrical path other than by switching the solid-state (transistor) path to "off." Indeed, this raises another issue that probably is germane. When the electrical load on the MGs is removed, being permanent-magnet types, they still produce an open-circuit voltage at their terminals. At high MG rpm's, this voltage can become excessive, and cause electrical breakdown in the MGs or their solid-state driving circuitry. This is, I believe, the reason for the limitation on wheel-down towing speed for the Toyota hybrids. I suspect that this electrical breakdown limitation may be more serious than the possibility of mechanical damage to the MGs from over-revving while freewheeling at high speed in 'N.'

There's another possibility that you didn't mention. If the ICE is idling (not in fuel-cut) when the car is placed in 'N,' it continues to run. I agree with you about complete freewheeling in 'N' below 64 km/h (~40 miles per hour). There's then no slight retarding regenerative drag (to simulate normal automatic-transmission drag), and thus no slowing of the car from this cause. I said as much in my post #31.

Except when it's not turning at all, I've never seen the ICE spinning slower than ~900 rpm. It idles with fuel ~1000 rpm. In fuel-cut in 'D' it is spun at ~1000 rpm too, presumably so that it can be "fired up" again undetectably. The formula that gives the relation between the Road Speed (RS) of the car, the speed Ns (rpm) of MG1, and the speed Ne (rpm) of the ICE was given in my post #40 in the thread "Heretical Mode." It is:

Ns = 3.60 Ne - 73.37 RS for RS in km/h] = 3.60 Ne - 118.08 RS [for RS in miles per hour]

A ScanGauge can give you the ICE's rpm Ne. Knowing RS and Ne, you can then compute MG1's speed Ns from the formula above. In my post #66 in the "Heretical Mode" thread, I gave a table of values from which you can determine when MG1's direction of rotation reverses — that is, when the car enters "heretical mode" behavior.

Stan