Gen I stealth question

No, that's not an official definition at all. The term "stealth" is sometimes used by enthusiasts and bloggers, but that's about it. Same with "Classic Prius", "Iconic Prius", "warp stealth", and so on.

 

I've been playing with shifting into neutral lately. First of all, this car rolls amazingly well in N! It seems to take off like a rocket. I tried neutral for the first time yesterday on a fairly long downhill and was able to coast for a long time - much farther than when in drive. I usually get anywhere from 58-61 for my daily commute. Yesterday with only using neutral when possible for the last 1/3 of the trip, I finnished with 62mpg. On the way in this morning I tried neutral as much as possible and by the time I got to work I was actually 2-3mpg lower than normal. I'll report back what I end up with at home tonight.

 

My typical protocol:

• 0-50 seconds - while the catalytic convert lights off, accelerate keeping the ICE rpm < 1,400 rpm to the fastest comfortable speed, ~38-40 mph. Then shift into "N" when speed is reached to preserve traction battery charge. Avoid trying to maintain speed on traction battery, use it just for acceleration.
• 50-300 seconds (first 5 minutes or until 70C coolant is reached) - alternate between power and shifting into "N" until the car reaches hybrid mode.
• 300+ seconds - keep speed 38 mph and lower for normal, excessive Prius MPG, or 45-65 mph for honest, 52 MPG. Try to keep ICE rpm < 2,600 rpm but it is OK to go up to ~3,800 rpm. Anything over 3,800 rpm, should be used for insane clown-car chasing.

My expectations, 52 MPH year round. It is better in the Spring, Summer, and Fall. Not so hot when temperatures dip below 50F.

GOOD LUCK!
Bob Wilson

 

Well so much for that experiment. I ended up with 57mpg for my 22 mile commute. Maybe I need to make sure the ICE and cat are warmed up before I start throwing it in neutral on downhills? Not sure why this would matter, but something isn't adding up.

 

You are using the HV battery on the climb uphills and N on downhills, so you aren't regaining any of that charge on the HV battery. I think N is better on flat runs because letting off the gas in D just slows you down a lot and doesn't capture that much charge. I'd be curious the best speeds to use N because it seems over 38 mph, the ICE has to spin and there is extra friction.. But I still haven't fully read up on understood all of Bob's experiments.

 

Uphill is either ICE+HV or ICE only. I can only use HV only on downhill, flat or VERY slight incline.

 

The actual threshold is 42 mph. Below 42, the ICE can shutoff but once you reach 42 mph, the control laws want the engine running. You can observe this if you have instrumentation:

• At top of hill, start descent at under 40 mph.
• Keep speed under 40 mph and in "D" until ICE stops.
• Keep in "D" and foot on floor and watch ICE start at 42 mph.
  • If the hill isn't steep enough, briefly shift into "N" to let speed increase and then test with "D"

Our understanding is above 42 mph, the ICE has to run to keep MG1 rpm under the 6,500 rpm limit. However, I've been up to 50 mph and it hasn't 'exploded.' Still, treat ICE off above 42 mph as ... not what you want to do in regular driving.

Will you be getting a Scangauge II or equivalent OBD scanner? It makes a lot of sense to do these tests with instrumentation so you cans exactly what I and others have seen. <wink>

One comment, I prefer to descend large hills, 500 ft, in "B" or shift between "B" and "D" on the descent for 'feet on the floor' speed control. The reason is charging the traction battery is exothermic, they can and do get hot. By using "B", you'll minimize the risk of heat-pumping by charging the traction battery.

Also, I prefer to assend hills at the same speed as a heavy truck ... IF I'm after fuel economy. But with instrumentation, you'll be able to monitor ICE rpm and keep it under 3,900 rpm for excellent engine thermodynamic efficiency.

Bob Wilson

 

I don't understand why sometimes the ICE runs forever and refuses to shut down, and other times will seem to go forever without the ICE. Funky software I'm guessing.
I can sometimes score as high as 75mpg in the city. A recent lunchtime trip for example to a store about a mile from work; of course the ICE ran the entire time going TO lunch, but was shut down almost the entire return trip at up to 35mph. ( can sometimes cruise up to 40mph on electric motor alone). averaged 74mpg!

 

The Prius will use the ICE much less when fully warmed up. Sounds like that's what is happening. Search here for the different stages of warm up.

 

I'm sure that warm up has a lot to do with it, just seems inconsistant. There are times when the engine has been driven 15 miles or more and still won't shut down. I'm aware it has to meet certain conditions; the engine must be at operating temp + the demand for heat/cool in the passenger cabin must be satisfied + the battery must be fully charged. its just goofy.
The other thing is this'; when I first start the car and move out it will accelerate with the ICE at idle to about 35mph exhausting the drive battery before the ICE kicks in with a bit of a lurch. under the driving conditions during my commute I can imagine the possibilitiies if it would do this at every stop sign would help MPG greatly! But it seems to be a program to help the ICE warm up before it goes to work.

 

• catalytic converter too cold - during this 45-55 second time the O{2} sensors are too cold to measure oxygen levels, they need to be at several hundreds of degrees C. To minimize emissions yet let the engine exhaust warm them up to operating temperature, all Prius try to use traction battery, EV power., while keeping the engine running. As good as this is, it has limits. So modest acceleration, keeping the engine RPM < 1,300 rpm, lets you reach a reasonable street speed. BUT then you need to not draw any more traction power than you necessary because the engine will have to run to generate the replacement charge. I usually shift into "N" and let momentum carry me forward (often to a stop sign or traffic light so no real loss.)
• coolant warm-up - during the 300-360 second time, the engine control laws try to bring the mechanical parts and lubricants up to 70C, the normal minimum for hybrid operation. Our NHW11 is especially dumb and runs the engine constantly until 70C is reached. All you can do is maximize use of "idle" although sometimes at a light, shifting into "R" holding the brake and hitting the accelerator will stop the engine. Again, after reaching a street speed, I like to shift into "N" as traffic allows. The car is rolling but at minimum fuel burn, idle. The NHW20 has a thermos with stored, hot coolant and the ZVW30 has an exhaust heat exchanger. Both of these more recent models can stop the engine when the car is at a light before 70C is reached. The goal is to quickly as possible get the engine warm-enough that ordinary hybrid control laws apply so the car can turn off the engine.

Bob Wilson

 

Jh,
I don't know if you've read this b4 but, I had similiar questions and this really helped explain it for me. What you have to remember is the Prius focuses on emissions first then efficiency. Emissions has a higher priority than efficiency (despite that, it is very efficient). The reason the ICE seems to go forever w/out shutting down is due to the emissions bias of the hybrid system. The best thing you can do is to get to S4 ASAP. This is done by coming to a complete stop for 7-10 seconds once the ICE is fully warmed up. The time you got 75mpg, you were in S4. Many people make the mistake of driving around in S3 for lengthy periods (I did too).

Read this to better help you understand how the system places emissions first and use that info to your advantage.

The Five Stages of Prius Hybrid Operation | PriusChat

 

There is a flat road 35 mph right before I reach home. Every time I come off the highway and on this road, the HV battery is fully charged and the car likes to do this whole mile in EV only mode. So yes, you can get "75 mpg" which really is meaningless because when you park the car the HV battery will be at half charge and when you start it the next day, the engine will work extra hard to recharge the HV battery again and you will get 25 mpg to recharge back up to 60% SOC. So people really really should quit worrying about short term mpg.. It should be banned from the forum even mentioning mpg that aren't average over 100 miles in my opinion.

I could force charge the car and drive around and post stupid 100 mpg average pics even over a 200 mile trip if you use the car display and force charge it at stops. People are too obsessed about "bragging" and the displayed mpg (which Toyota is typically lying to you by 5% more mpg than the real numbers).

Anyways the reason you can get longer stealth drives depends on the temp of the battery the S4 mode and the SOC. If you step on the gas with a colder battery, the kW requested will be too much for the HV battery and the ICE will assist. (ie. the IB requested cause the voltage to drop too much and it kicks on the ICE). After a freeway drive (especially with offramp regen) the HV battery will be quite warm and also at a very high SOC. (On the freeway it has been constantly charging to a high threshold voltage, then dumping current into MG2 when the battery gets to whatever the max SOC/voltage is. repeat over and over again). So when you drive in that state, the HV battery has no problem handling higher currents and will stay in stealth until you try to accelerate too much or hit a hill or until the SOC is below a threshold voltage. (this is all under 40mph driving).

(Also this behavior is dependent on A/C and coolant temp and how far you press the pedal).

 

I've read it before but I don't "understand" why emissions needs to be a priority if you use LESS fuel in the first place???! Seems counterproductive to me.

 

I totally agree but, CARB and the EPA don't care about that. They only do a test on the emissions that come out of the tailpipe while the ICE is running. Accounting for emissions saved due to less fuel use is not part of their agenda (and probably way too complicated for them as well).