Using traction battery for reverse only

I checked Carista and don’t see that as a configurable setting.

 

Nope. When they say it's a hybrid, they mean it. The engine and the electric motors are both essential.

 

Absolutely impossible. The power splitting device (which Toyota calls the eCVT) does not shift gears. The gas engine is essentially permanently in top gear while the electric motor adds torque for acceleration. If you disabled electric power going forward, you would barely able to get going.

 

I’m curious, why would you even want to do this?

 

anything is possible

 

The engine really never pushes against the wheels, it adds it's power by pushing against (usually) M/G2 or (rarely) M/G1. When they have no power, that is N, and the engine has nothing to push against.

 

It's not completely silly to think about operating the transmission without much battery involvement; in fact, the car will do something close to that at times when the battery is really cold or really overheated.

What's important for the tranny to function as a tranny is for the inverter to be able to shuttle electric power back and forth between MG1 and MG2. When those flows are balanced, there's pretty much nothing going to or coming from the battery, and the tranny can still do what it does. It's only if you even break the electrical path between the MGs and the inverter (which is what the N shift position does) that it can only freewheel.

It's a bit of overstatement to speak as if there is only a "top gear" and the tranny can't match the torque to the driving conditions. Sometimes people mix up these two questions: "do the metal gears in the tranny ever shift?" (they don't) and "can the tranny overall, from input shaft to output shaft, match speed and torque across a whole range from a high ratio to a low ratio?" (absolutely can and does, that's what it's there for. Instead of sliding gears around, it's just the timing of electrical pulses that does it.)

So the car would be somewhat driveable ... it would just feel about like you'd expect for 3000 pounds of car and 76 HP of engine. Yawn.

 

I never said the entire "tranny" is in top gear, just the gas engine. I also said that the electric motor provides torque as needed. Bottom line, we are in agreement on how the "eCVT" works and that it would't work properly without the electrical component.

 

Right, so the basic hack the OP is looking for might be achieved by spoofing the battery temperature sensors such that it thinks the battery should not be charged or discharged, knowing that Toyota has already tested and provided operating code to let the car drive (with limits) in those circumstances. Obviously the car will bend that rule for reversing and ICE startup within that program, but it sounds promising.

It might not completely eliminate battery dependency but the reduction may be enough to support the OP's demands, and the bigger point is that the car is still operating within parameters that Toyota planned and tested.

 

(re #9) I hope we are ... I struggle a bit to find the sense in talking about what "gear" an engine is in.

The engine is the thing that has a somewhat fixed torque-speed-power curve that not much can be done about, while the tranny is the thing with the job of matching those to whatever's needed at the wheels, by varying ratio as necessary. The Prius transmission does do that, and even when it is flowing net zero from or to the battery.

 

O.K. The engine itself is not in a gear. To clarify, the engine output that is sent to the wheels does so through a fixed gear ratio in the planetary gear set in the eCVT,

I know what I was trying to say and I still believe that it does not disagree with what you have described but we humans often have a hard time communicating.

 

Ok, but the point is? This is saying that somewhere inside the transmission, there are some gears meshed in a fixed ratio.

That's true of most kinds of transmission.

Does it mean there's a fixed ratio between the engine and the wheels, or a variable one?

For anyone who isn't sure, there are a couple easy things to try:

- take a Prius out on a flat road, and accelerate smoothly from a standstill to a cruising speed, holding the engine at the same rpms the whole time (either by ear, or watching rpm on a ScanGauge).

- take the Prius out on a hilly road, set the cruise control to hold a fixed speed (wheels), and listen to the engine (or watch rpms on a ScanGauge) up and down the hills.

What do you notice about the relationship between engine rpm and wheel speed?

 

I never said that there is a fixed ratio between engine speed and wheel speed. But there is a consequence to that fixed gear ratio, it is not insignificant. The consequence is that the amount of torque that is mechanically transmitted from the engine to the wheels can't be increased by shifting to a different mechanical gear ratio and therefore the torque required for initial or hard acceleration must be supplemented by the electrical motor.

Here is a link to a description of how the eCVT works: Graham's Toyota Prius (You have to go to "Understanding your Prius" and then "Power Split Device" to get to my quote below.)

From that article: "The torque multiplication effect of a true CVT is absent and it replaced by electric motor assist."

That is all that I was trying to point out.

 

To the OP, as you can see, it is somewhat meaningless to discuss gear ratios and such in a Prius, most of what would be handled by gears is handled by software controlling the Inverter and powering the Motor/Generators. The engine is one component of all this, but is not able to work alone, as you seem to want.

 

Graham has been an incredibly valuable contributor from the earliest days, and we've all been using a lot of his analysis, and his 72% / 28% torque split at the PSD, for years. But it can happen that a person gets a whole lot of stuff right and nonetheless falls into a mental trap, which you can recognize because it doesn't square with the rest of even his own (correct) information. So it is with the "it's not a CVT, it can't multiply torque" canard.

It's also possible with Graham (and I think more likely, given the otherwise pretty complete spot-on-ness of his analysis) that he had not really confused himself, but he goes for that style of explanation where you hold the reader's interest by dropping in some curiosity-piquing, not-quite-right partial conclusions along the way, and doubling back to clear up the story. You can throw in "we cannot multiply up the ICE torque" or "equivalent to always being in top gear!", meaning something more like "this is what you might be thinking at this point in the story," and then proceed with telling the rest of the story. Which is pretty much exactly what he goes on to do.

The one downside to that style of explanation is that you can make up such colorful, memorable misdirections in the middle that they end up being what the reader remembers and takes away, even after you finish laying out the real story.

The part of his site where he has pretty much all of the necessary argument in one place is the "Understanding the Prius" / "Continuously Variable Transmission" section.

An important thing he says clearly is in the last paragraph under his heading The "Power Split Device" (or the paragraph just before his Always in Top Gear heading): he's very careful to clarify that the fixed 72% / 28% ratio applies to torque, not power, because power is torque ✕ rpm and the rpm relationships are not fixed.

Another thing about power: it isn't coming from nowhere, and it isn't vanishing to nowhere. Most people have heard the "no such thing as a free lunch" aphorism, and at the same time, there's nobody stealing your lunch either. Other than the painstakingly minimized mechanical and electrical losses along the way, all of the power being delivered by the engine into the transmission is also getting delivered out of the transmission.

Even the small amount of power claimed by friction and electrical loss is not vanishing to nowhere; it's becoming heat. The sums add up.

At times in a Prius, the engine will be producing some more power than you need at the wheels, and the difference is going to charge the battery. At other times, you want some more power at the wheels than the engine is producing, and the difference is coming from the battery.

But: we can also focus on the times when the net in/out with the battery is near zero. That's very much the case during much of a typical drive. The engine is producing power, the power is going through the transmission and coming out at the wheels, and the battery is doing very little to distract us from that picture.

You can even experience that when moving off from a standstill. Most of the time, you'll be getting some battery boost in those conditions, but if the battery is way hot or at way low SoC, you won't. And the car will still move off from a standstill. Not as peppily as you're used to, but also definitely not like a car stuck in high gear. So what's going on?

As you move off from that standstill, the engine is revving high, and the final drive is barely turning. The product (engine rpm ✕ engine torque) is the power going into the transmission. The product (final drive rpm ✕ final drive torque) is the power coming out. But for the small losses, these power figures are equal. And if the final drive rpm is only a fraction of the engine rpm, what does that tell you about the final drive torque?

It has been multiplied. By the same factor the rpm is reduced by.

Imagine if that weren't the case, but you could somehow have the revs reduced and the torque not increased. At that point, you would be delivering from the transmission only a fraction of the power going in. How is the rest disappearing? You do not have forty horsepower of heat wafting away from the transmission. You'd notice that. And you would not be posting your MPG figures on Fuelly....

So, there's more torque showing up at the final drive than you can explain by the 72% imparted by the planets to the ring, right? How'd it get there? That's the next question to work out.

But while working it out, keep in mind that this simple need to account for the power is not optional. It may be possible to get tied up in knots thinking about gear teeth and MGs, but if you come out concluding the power sums don't work out, that's the sign to give it another go.

Graham, right after he drops the colorful, memorable "equivalent to always being in top gear!", fills in the rest of what's really happening in the very next paragraph.

Because the ring gear is turning very slowly, even at 72% of engine torque there, the torque ✕ rpm product is just a small fraction of the engine output power following that path. The only other place engine power is going is MG1. That's only getting 28% of engine torque, but at much higher rpm, so a lot of the engine power is going there.

And where does that engine power go next? It goes up through three orange cables to a box on top of the transmission. It goes down through three more orange cables back into the transmission again, to the windings of MG2.

And what does that engine power do there?

It makes a strong magnetic field. It pulls tangentially on permanent magnets built into MG2's rotor. Those are a certain distance out from the center of the shaft, so the force pulling those magnets tangentially ✕ the radius from the rotor center to the magnets is ...

Torque!

And the engine power being delivered as magnetic torque at MG2 adds to the engine power being delivered by the planet gears to the ring gear, and lo, the total torque there times the rpm there equals the engine output torque times the engine rpm, and hooray, we have built ourselves a CVT.

Keep in mind there is no Department of CVT Police that look at different ways of building a CVT and say "ah, no, you had some of the power go out of the box on orange wires there and then come right back in, you're busted, not allowed to do it that way!"

If your box takes one product of torque ✕ speed coming in at one end, and a different speed ✕ different torque coming out the other, and the ratios can be varied without steps, and the products come out equal (all but for the small real-world losses), your box is a CVT. And this box does exactly that.

So what was up with Graham's presentation? Did he just come up with some memorable misdirections for mid-story, and forget to sum up clearly enough at the end "so I've just finished filling in what happened to the rest of the power, and you can see what was wrong with those earlier descriptions", so that too many people remembered the misdirections instead of the story, and they keep popping up on PriusChat eighteen years later?

Or was he, himself, actually stuck in one of those misapprehensions, not even noticing his own explanation was complete enough to lay it to rest?

I'm pretty sure it was the first of those two choices ... but both things do happen to people, and I might never really know.

 

Hold the HV Ev button for like 5 secounds and it will go into engine only mode

 

Kind of feel I'll regret asking, but exactly why would anyone want to apply these parameters to their Prius?

I mean if you want a vehicle that the engine will "handle all the power needed to move forward", why not just buy....well...a regular ICE car?

Usually the question being asked is just the opposite.
Most people want to find secret Prius handshakes that lead to increased Battery Powered movement. This is a rare post asking for just the opposite.

Oh well......

 

Not on OP's 2009 Prius. In any case, it is a very perplexing first question to ask to this community. lol