Accelerating from a red light

The Prius gasoline Atkinson cycle engine to run betwen 992 to 4000 rpm.

A Dept of Energy Argonne Labs determine the most energy efficient torque/RPM range for a 2010/3rd gen Prius is to be from about 100o rpm to 200o rpm ( from 15% to 38% of the chemical energy is translated into mechnical energy). Because the Prius often has to travel in stop and go traffic and at low speed often it is easier modulate/control the accelerator at a less than optimal 1088 to 1280 RPMs to optimize fuel efficiency. Howver, if driving conditions permit the Prius can delivers more torque at a efficient energy conversion in burst mode when running between 1280 to 1700 RPM. However, at those power levels - the Prius often starts going at speeds higher than 45 mph and wind resistance starts to be more of a problem...

The most efficient way to use the gas engine is to accelerate to a target speed and then set the Prius to..

a) low rpm/power setting to maintain a speed
(low Rpm is from 995 rpm to 1180 rpm, it uses from .50 to .80 gallons per hour and is often
used in a hypermiling technique called stealth highway mode)
b) turn off the gasoline engine and let the Prius momentum and gravity keep it moving
(rpm =0, it uses .02 to .00 gallons per hour)

 

^^ Look at a SFC map. If you want a simple truism, it is this: run at high torque.
The regular car equivalent is easier to understand, it is highest gear without the car lugging. Since you cannot set the gear in a Prius, I think the best approach is to shoot for a constant engine load and let the e-transmission settle itself.

 

Lugging is where the vehicle is moving too slowly for the engine and gear. It happens in manual transmission cars because there's essentially a direct connection between the engine and the wheels, so the engine can only turn as the wheels can turn. If the engine is moving but can't transmit its motion effectively the car will jerk. Naturally lots of lugging is bad for the engine. If it really can't handle it the engine will stall. (Lugging and stalling doesn't happen in (working) automatics because the car picks gears, idles the engine for you and the transmission allows for "slip" so that the wheels and engine can move at different speeds. With a manual transmission, it's the clutch that allows the slip.)

That's where torque comes in. I think of "torqueyness" of an engine as how well it can transmit its power to the wheels and force them to move and torque numbers in Nm or ft-lbs as combining engine power and a torque-to-power ratio. So, when Sage writes that you run at high torque, he means that you're running the engine at a rate that doesn't just give you more power per gallon but gives you more wheel rpms per gallon.

I still don't really understand it, but when dieselheads and EV fanatics get excited about torque I presume it's because they like acceleration more than they like speed.

Specific fuel consumption - Wikipedia, the free encyclopedia

Engine efficiency varies with rpm. But to maximize efficiency in a car with a combustion engine you balance engine efficiency and aerodynamic drag.

So you run the engine at high torque and it'll cause your car to accelerate, but aerodynamic drag increases with speed so you don't want to keep accelerating. Instead you stop the engine and the car gradually slows down. Then you start the process again. That's pulse and glide.

 

When I'm in warp stealth I think it's usually at 992rpm.

It's hard to know you're in WS without a Scangauge. The ICE is still spinning but you need a GPH (Gallons Per Hour) display to see that there is no fuel flow. It happens only under very light load when the car is fully warmed up and traveling above the speed where the ICE will shut down (45mph??). Once you're in WS, it helps enormously to have a load display so you can try to keep the load light enough to stay in WS.

EDIT: Sorry, I don't know what I was thinking! I should have said: "Once you're in WS, it helps enormously to have a GPH display so you can try to keep the load light enough to stay in WS." When trying to hold WS, the horizontal bar in the HSI display is adequate as a load indicator. Probably has to be held in the first 25% to stay in WS.

The LOD display in the Scangauge can be useful for the pulses in Pulse & Glide. I used to use it for that in my Subaru, but since I don't know how to do P&G in the Prius I don't use it for that.

Sorry for the confusion!!

 

Shut up and drive. Just kidding, couldn't resist.

I use PWR for regular driving, get up to speed (limit plus 5) as fast as possible and then try and keep it at 100mpg as best can.

When it's hot out (last couple days, upper 80's AC on 72) I use ECO so it better controls the power to the AC.

I average 56 mpg right now so you don't have to over think it to get good gas mileage, have sporty acceleration at the lights and be comfortable in hot weather.

 

If you are averaging 58mpg calculated then you are probably doing the right things already. I think the biggest thing you can do to assure good fuel efficiency is slow down and learn how to glide at every opportunity that presents itself. Freeway overpasses are a prime example of lost mpg if you are not gliding down the other side.

 

I find that the best way to accelerate is to either do so very very gently or otherwise much more aggressively to trigger the ICE. Moderate pulse tends to deplete the battery somewhat disproportionately and is therefore less efficient.

 

Warp Stealth(WS) is when the ICE is off (GPH=0.02 to 0.00) but the electric motors are running to push the Prius at 35mph to 45 mph. As long as the Prius is going under 46 mph the ICE wont automatically turn on or use gas; at about 46 mph the ICE will turn at RPM =992 but it still will not use any gas (GPH=0) the problem keeping the Prius at this tipping point speed of 46 mph because when the Prius starts going above 46 mph the ICE will start to run at about GPH=0.20-0.31 -- it is easier just to keep the Prius under 46 mph. I try to avoid WS unless the Prius SOC is greater than 55% (5 bars) and the Prius is going downhill because it can drain the HV battery very quickly and can push the Prius into an automatic HV battery recharge state. Going downhill the electric motors gets more MPH out of every kwh it uses. WS will only work after the Prius ICE has been warmed up. IMHO P&G and DWL is more sustainable hypermiling technique than WS.

It is possible to roughly do WS with just a HSI display. Anytime Prius is running with the HSI display is on the right side, past the ECO capsule the ICE is on. Anytime the Prius is running on the left side of HSI display at less than 1/4-1/3 of the ECO bar but not in the RECHG bar its running the electric motors. To get into the WS, start at the top of a long downhill stretch (.1-.5 miles) and pulse-accelerated to 45 mph using the ICE. Once at 45 mph, release the accelerator so the HSI display moves to the very far left end of the ECO bar but not in the RECHG bar (at this point the electric and IcE are both off and the Prius is coasting/gliding - stay here for P&G). To go into WS - increase the pressure on the accelerator so that the HSI is between 1/4 to 1/3 the way on the left side but not under the ECO capsule - this will trigger the electric motor but not start the ICE. As long as the Prius is on the left side of the ECO bar the ICE will not go on (you'll hear the ICE go on if the accelerator is pushed too far). The electric motors don't have enough torque to keep the Prius going uphill so WS won't work going uphill.

 

Yes - it is all part of a continuum of driving techniques

CC = cruise control - steady speed
SHM = pulse with ICE @hi power, glide phase with ICE @low power
WS = pulse with ICE @hi power , glide phase assisted with electric motors@hi power.
P&G= pulse with ICE @ hi power, glide phase with electric motors off or @low power.
DWL = pulse with ICE @hi power on top uphill, glide phase with electric motors off or @low speed downhill, in valley pulse ICE@hi power then set ICE@low power on long uphill
NICE = pulse with ICE @ hi power, glide phase with transmisson in neutral
(ICE-electric motor detached to reduce internal resistance)

 

Warp stealth was coined to indicate when the stealth threshold (speed of 42 mph back then) was exceeded, the engine was spinning, but no gas was being consumed.

 

Warp stealth (WS) IMO is over- rated. Sure it is fun while it lasts, but you have to replete the battery eventually and unless you are careful the repletion phase is inopportune and inefficient. Moreover, the traction battery is heating up from continuous use, which may not be good for long term reliability.

You want over the top numbers ? Maximize gliding, meaning coasting at speeds below automatic ICE spin with no arrows moving, or minimal electric movement. When the ICE is used, shoot for RPM values of 1600 - 2200. Try to schedule the ICE use for at least 15 seconds* firing to give the e-transmission time to find best efficiency.

*pulled out of my hat

 

All this is really difficult to pull off without a scangaugeII or something similar.

 

WS is actually quite useful for those who do a lot of highway driving. The energy loss is fairly low and still more efficient than just riding your brakes, regening, or accelerating above the speed limit. Because my commute has such a large uphill section of road over 7miles long, I have to utilize WS or else I am wasting fuel. I also find it very conveient for large overpasses. I cannot allow my speed to drop while driving up one side of the overpass like you normally would when DWL so to recover some of the lost energy I enter WS at the top of the overpass and glide down the other side while maintaining or even gaining a little speed. I then reapply ICE when the road begins to level and I sense my speed is about to drop.

 

Does this mean you keep the HSI between 1/4-1/3 on the left side when gliding uphill?

Freeways here in Phoenix metro have a lot of short 1/5 to 1/2 mile uphill/downhill stretches.
Where I live the terrain is a very gradual high elevation traveling on freeways north & east.
If I want to go 65mph on the freeway I will anticipate the uphills and increase my speed around 70-73mph and go uphill with the HSI a tiny bit past half way point to the right, by then my speed may go down to about 55-60 and I'll increase back to 65 until the next hill.
Since I just got a SGII I can see my exact iMPG...so what I do now is give it a little more gas than I use to on the uphill so I don't lose as much speed.
If you or anyone have a more efficient way for freeway driving with many short hills I'd like to hear it.

 

I just drive nomally when accelerating, keeping up with the flow of
traffic, and my last tank was 54+ mpg
calculated.