Heretical mode on third gen Prius, what do we know?

FYI,
Since, the standard tires and the final gear ratios are different among Prius generations, I made following tables about the speed vs ICE rpm combination at the zero MG1 rpm condition.

I use "dynamic load tire diameter" for the math, because it is 3% smaller than "no load tire diameter".

(note: Gen3 195/65R15 dynamic load tire diameter=615.5mm final ratio=3.267)

	mph	km/h	ring gear rpm	ICE rpm
1	70	113	3172	2291
2	65	105	2945	2127
3	60	97	2719	1963
4	55	89	2492	1800
5	50	80	2266	1636

(note: Gen2 185/65R15 dynamic load tire diameter=602.9mm final ratio=4.113)

	mph	km/h	ring gear rpm	ICE rpm
1	70	113	4077	2944
2	65	105	3785	2734
3	60	97	3494	2524
4	55	89	3203	2313
5	50	80	2912	2103

(note: Gen1 175/65R14 dynamic load tire diameter=565.6mm final ratio=3.905)

	mph	km/h	ring gear rpm	ICE rpm
1	70	113	4125	2979
2	65	105	3831	2767
3	60	97	3536	2554
4	55	89	3241	2341
5	50	80	2947	2128

Ken@Japan

 

Thank you,

Notice how 65 mph corresponds nicely with the transition between ICE efficiency of the the 1.5L, NHW11 engine:


It turns out that 65 mph also corresponds to a "knee" in the NHW11 mileage curve:

Note that the NHW20 has a lower coefficient of drag, more efficient transmission and the data points were collected at significantly higher temperatures at higher altitudes. They did have the AC running.

Bob Wilson

 

I get "heretical" mode all the time. The engine drives the wheels "directly" and the battery gets recharged (yes it does!). The energy flow goes from the engine to the wheels and from the motor to the battery. No flow from the electrical motor to the wheels.
BTW: on pages 190-1 of the user's manual, this mode is not shown. Only the mode in which the battery is completely full and the engine drives "directly" the wheels is shown (and hardly achievable, honestly speaking...).

It happens when I am driving more than 60km/h and I reduce the gas instead of completely removing and the reapplying it (to have only "electric mode" gliding/coasting).
The engine simply reduces the "whir" and you feel a distinct change in the drive - you feel then that you are in "overdrive". You can apply some gas, but always very gently otherwise the motor starts getting current from the battery. Depending on the decline/incline of the road, you can easily be always under 5L/100km (all the way down to 2.5L/100km when the road is completely flat) when in this mode but go up to 7L/100km when hitting an incline before the motor kicks in to help the ICE.

 

very intriguing...the system that we have in the genIII Prius is the Gen I HSD system and had been modified since then but the principle nature of the system remain the same. If I'm correct : This is the system broken down into a simple chart.

Chart and description from Wikipedia based source...and information subject to change.

http://upload.wikimedia.org/wikipedia/en/2/2a/THS_evol_1.png


ICE = Internal Combustion Engine
MG1 = Motor / Generator 1 (typically "closer" to the engine and "smaller")
MG2 = Motor / Generator 2
R = Ring Gear
C = Carrier Gear
S = Sun Gear

"The basic design of the Toyota Hybrid System / Hybrid Synergy Drive has not changed since its introduction in the 1997 Japanese-market Toyota Prius, but there have been a number of refinements.
The schematic diagrams illustrate the paths of power flow between electric motor-generator 1 (MG1), gasoline internal combustion engine (ICE), planetary gearset "power split device" elements (S: central "sun", C: planetary carrier, R: outer ring) and motor-generator 2 (MG2)."


"The Atkinson cycle engine itself was also designed specifically to minimize engine drag via an offset crankshaft to minimize piston drag during the power stroke, and a unique intake system to prevent drag caused by manifold vacuum versus the normal Otto cycle in most engines. Furthermore, the Atkinson cycle recovers more energy per cycle than the Otto because of its longer power stroke. The downside of the Atkinson cycle is much reduced torque, particularly at low speed; but the HSD has enormous low-speed torque available from MG2"

which i associate as the typical layout for MG2 as a power booster at low speeds...

The chart shows that MG2 is imposable to generate power for MG1...most people will agree. I did too.

HOWEVER...the problem is that MG1 in joint power mode with the ICE is acting on their own to create power to the wheels if it's getting from the ICE that is a power draw and not Efficient...from the battery? No such luck either because that would force the battery charge down and would not be sustained for long durations...there is only one answer that MG2 is indeed powering MG1 in Joined power mode to generate the power FOR MG1...which equals no load on the battery and no load on the ICE...


Brilliant.

 

In layman's terms...MG1 Must get power from somewhere...it cant be the battery nor can it be from the ICE...where else can it get is source?

 

I wonder what would happen if MG1 and MG2 where rebuilt with Superconductor magnets That will active at much lower voltage levels...and loop the energy back the to axles of MG1-MG2 with a type of mag-lev barring system to reduce drag even more with even faster response...and a battery pack capable of faster charge/discharge rates and twice the voltage. hmmmmmmmmmmmmmmmmmmmm!!!

 

MG2 *can* be used as a generator. We know this because it is used for regenerative braking. There is absolutely no reason it can't also generate when the ICE is running.

As for superconducting magnets in the MGs, the cost of carrying around cryogenic coolant might outweigh the benefit.

While I say that somewhat in jest, I do have a fair amount of experience with superconducting magnets. I used to head up the design group for a large MRI company. All of our magnets were superconducting.

Tom

 

I just think it be neat to see what would happen...LOL

 

Now we can read the MG1/2 torque with the SG II on the Gen III cars, it should be easy to see this switch. During normal acceleration, MG2 shows a positive torque value ... so if you are still accelerating and you see a negative torque value on MG2 that means your are in the heretical mode ... (I assume, LOL)

 

Would certainly be hard as they heat up quite a bit from use and just with the casing being in contact of the engine. With just casual driving around in LA traffic (not a fully warmed up engine) I saw MG2 at 125F ... I assume with extended drives they end up near the coolant temp of 190F....

 

MG1 can generate from the ICE, but isn't MG2 on the other side of the ring gear? I don't see how it could generate power from the ICE unless the ring is spinning - is that possible when the wheels aren't moving?

 

It's zero MG2 rpm condition and it is not a Heretical mode.
The MG1 rotates same direction as ICE.

Ken@Japan

 

There are three modes

• vehicle stopped and less than ~25 mph - engine runs and MG1 turns, generating power and counter torque needed to spin ring gear. The power from MG1 races to MG2 and also turns to move the car forward. The ICE sees no loss of torque.
• vehicle ~25 mph (NHW11) - MG1 rpm is falling off, so too is torque, however MG2 is spinning quite rapidly. The back EMF is inhibiting further power from the weaking MG1 and the torque needed to pass ICE torque to the ring gear. With the traction battery briefly providing the power, MG1 changes from a generator to a motor. The control electronics reverses the flow so MG2 begins working as a generator and passing power to MG1 to provide the torque needed. The engine sees no loss of torque.
• vehicle above ~25 mph (NHW11) - MG1 direction reaches zero and reverses but the torque against the ICE remains constant and keeps the ICE on the operating line, an efficient part of the BSFC surface. The ICE sees no loss of torque.

Bob Wilson

 

Sorry - I misunderstood the previous posts (thought someone was discussing use of MG2 for home power generation)...

But am I correct in stating that MG2 can only generate power when the wheels & ring gear are turning?

 

No. MG2 is connected to the drive wheels. If they aren't moving, MG2 is not moving. However, as stated above, this has absolutely no bearing on the topic of this thread, which is discussing a situation where MG2 and the drive wheels *must* be turning.

In a stationary situation, all electrical generation comes from MG1.

Tom

 

awh darn...that means we need to go to the future steal Doc Browns MR fusion LOL...

 

You're correct.
power = torque X rpm
The zero rpm means no generation power input.

Ken@Japan

 

yeah

 

There has been speculation that if MG1 were clamped at 0 rpm, all power would flow through the power split device, no electrical bypass, and improve transaxle efficiency. However, to vary the vehicle speed, the ICE rpm would have to vary and it is likely this would put it in poor BSFC regions.

Bob Wilson

 

As you know, for a given power request, i.e. constant speed, you can end up at quite different MG1 RPM and both, in heretical mode o normal mode, with largely different results in FE.
So , a typical trick to make ICE making more torque than requested is to pass the target speed and then holding back slighty, what we call "Pulse & Release", allowing MG1 to turn at negative numbers.
But is quite easy to fall back to normal mode, and pass the reversing points indicated by Ken. Too easy.

Now i'm trying to understand few things:
1) Is it the e-CVT geometry that makes so easy the fall from grace or the software set-up?
2) Are there software parameters (or PIDs by chance) that can be tweaked to force ICE to increase his torque without the prompt RPM ramping up?
3) Any PSD's (adjustable) parameter can be found in TECHSTREAM (i have software and OBD2 cable)?


Thanks.
M.