How much power is used to spin ICE at 42 mph plus?

At 42 mph and greater, ICE spins at a little less than 1000 rpm when not burning fuel. How much hp/Kw is used to spin it? Can Torque Pro indications be used to compute this?
Thanks in advance!
Lain

 

“Fuel-cut is maintained, and the retarded intake cam timing reduces the amount of air sucked in around the throttle flap and through the engine to almost zero. This is a very low-resistance state for the engine to be in, and it only takes a kilowatt or two to keep all that merrily turning. Since the regenerative drag is reduced or eliminated, the car will coast along a lot farther -- still losing speed on the flat, but fairly slowly, and one can easily maintain speed or accelerate going downhill. It's really the higher-speed equivalent of "glide" with perhaps a little more brought in from the battery to compensate for the spinning dead weight of
the engine.”
Hobbit, Warp Stealth: a Prius driver's guide, H* 060522

Thank you Leadfoot. And thank you ChapmanF for your detailed and instructive response. I’m not familiar with data-logging, and I especially appreciate your remark about values not being simultaneous.
Likely, someone such as BWilson has already refined Hobbit’s above “kilowatt or two.” But I haven’t found any discussion.
Could determining “Warp Stealth” engine-spin power loss be as simple as reading Torque Pro’s MG1 Power?
Intuitively, it should take the same kW to spin the engine at 950 rpm regardless of road speed. Likely, density-altitude is a small variable in pumping loss.
During Hobbit’s “Warp Stealth,” torque exerted by MG1 through the planet carrier on the ring gear might appear to complicate the issue. Yet this torque would just contribute to motive force, lessening power demand on MG2, or conversely—depending on deceleration and road gradient--recirculate power through the inverter to MG1).
Thanks again for help in sorting this out!
Lain

 

Whoops! My apologies! I have that backwards: It'll take power from BOTH MG1&2 to spin the engine.
As ChapmanF suggests, it's not so simple.
Thanks!
Lain

 

Thanks to ALL for your comments! Thanks especially to ChapmanF and fuzzy1 for clarifications and suggestions.

An excerpt from bwilson4web’s 2014 executive summary on optimal speeds gives more context:

· 39-44 mph (indicated) - avoid because it brackets the hybrid threshold speed, 42 mph, (and) can lead to inefficiencies optimal speed for economy, Gen 1? | PriusChat
​

In the weeks since last posting, I installed Hybrid Assistant to augment Torque Pro. I also bought an OBDLink LX adapter.
Nearby for road trials here, is a straight, three-mile, downhill. The gradient is ideal: once at speed, it’s all straight-ahead coasting; no ICE required. Likely, this isn’t really Warp Stealth, since it requires no foot finesse. Still, I’ll use “W/S” in the following as convenient short-hand for a passively spinning engine. Below, are results from two apps and two adapters.

A.) Initial road trials with Torque Pro and a Panlong adapter indicate that my Gen2 ICE almost always spins at a steady 990 rpm in W/S. In contrast, MG-1 torque indications exhibit rapid excursions, some to values as low as 2.4 ft-lbs. Most indications, however, are about 3 ft-lbs/4Nm. For now, I’ll use these latter numbers.

As ChapmanF observed above, “The power-split device is a fixed torque split, so if you know MG-1’s torque, you know the engine’s . . .” Multiplying MG1 torque by a factor of 3.6 yields the torque imposed by the planet carrier on the engine. Thus, it appears that the carrier applies about 10.8 ft-lbs, or 14.4 Nm. At 990 rpm, this equals 2 hp, or 1.5kW.

B.) A trial with Hybrid Assistant and OBDlink LX yielded similar results: the ICE almost always spins at 990 rpm. Nine screenshots yield an average MG1 torque of 3.98 Nm. (Most screens showed either 4.0 or 4.1 Nm).
Hybrid Assistant also displays ICE negative power, the power that the engine is absorbing. Fourteen screenshots yielded an average of minus 1.45kW.

So, two sets of equipment produced similar results. Issues beyond my ken may cloud these, but I tentatively conclude that a Gen-2 engine in W/S absorbs about 2 hp or 1,500 watts.

Thus, Hobbit’s 2006 approximation of a “kilowatt or two” appears to have been right on the mark.

Please note that elevation here is about 6,000 ft. msl. Density is 80% that of sea-level air, so the engine might absorb somewhat more power at lower elevations. Also, one or more of my down-hill runs may not have been at operating temperature, so results may be somewhat skewed.

My understanding of power flow:

Stabilized on my local down-hill, MG1 & 2 functioned simply as generators. Power from the wheels followed a mechanical path to the ring gear, planets, and carrier. The carrier conveyed torque to the engine, and the engine’s resistance caused the planets to spin the sun & MG1 in reverse. MG1 controlled this spin, thereby holding engine rpm constant, while at the same time generating electricity.

True Warp-Stealth-ing, however, entails careful accelerator action. As I understand it, an educated foot would not only override HSD “fake drag,” but could also apply some battery power as motive force. MG2 would then work as a motor, gently propelling the car. As before, MG1 would continue to oppose sun-gear torque, hold ICE rpm steady, and generate electricity.

In other words, a small amount of mechanical power would flow from MG2 through the ring gear and carrier to spin the engine. The ring-gear would also spin the planets, hence the sun & MG1. MG1 would regulate this spin, and send electricity to the inverter, and then on to MG2. This circular path in the transaxle & inverter is similar to “energy re-circulation,” but smaller, and opposite in direction.

I hope that readers will flag my mistakes, as well as direct me to better commentaries.

Thanks in advance!
Lain

 

Thank you ChapmanF and fuzzy1 for your kind replies!

ChapmanF, thanks too for reiterating your suggestion on logging throttle angle. Yesterday evening, I took fifteen screenshots showing throttle angle in "Warp Stealth." Torque Pro offers four throttle-position indications, three of which were active. These were "Absolute Throttle Position," "Relative Throttle Position B," and "Throttle Position (Manifold)." Almost all of the fifteen screens--taken over about four minutes--showed exactly the same throttle values. RPM and Mass Air Flow varied slightly. Below, Warp Stealth data is in bold. (For comparison, I've copied data from an "up-hill" screenshot in parentheses. This single screen was at 47 mph, with the ICE nominally developing 35.3 hp.)

W/S Absolute Throttle Position: 48.63% (72.94%)
W/S Relative Throttle Position B: 0.00% (19.22%)
W/S Throttle Position (Manifold): 15.29% (34.51%)
W/S MAF, grams per second 2.2 +/- (20.8)
W/S RPM 990 +/- (2,792)

Indicated RPM ranged from 934 to 1,083. MAF varied from 3.0 to 2.1 A majority of values, however, were at 2.2 grams per second.

I don't understand Torque Pro's "Throttle Position (Manifold)." Perhaps readers might explain the difference between this and "Relative Throttle Position B." Yet another consideration is intake-valve timing, but I haven't any way of monitoring this.

fuzzy1, as I understand it, your Gen3 relies in part on manifold pressure data to control your high-volume, cooled EGR. Does this system function to reduce pumping loss by increasing MAP with inert gas?

Thanks!
Lain