Any idea to save fuel while frequent stop-go`s?

You could do it with the EV button but only the odd one or two times before the HV battery gets too low and requires the petrol engine to work harder to charge it up. It is better just to let the car work out the best times. With the gen3 Prius there is an 'Eco' button which holds the car on electric a little longer than normally and this would be helpful in the situation you describe.

My Prius spent 95% of its time in similar traffic conditions to what you describe and in really heavy traffic was quite hard on the HV battery causing the engine to run. The way I look at it is that in a traditional car (especially with an automatic gearbox) you will be getting very poor fuel economy in town. With the Prius it will be poor also but not as poor. Remember, once the engine has charged the HV battery it will switch off again for a while, whereas a traditional car always has the engine running.

 

Heavy stop and go is bad for any car.

- If you can time the lights and keep rolling, do so. Maintaining momentum helps efficiency.
- If you know where you're going to stop you want to pulse and glide your way to it: brisk acceleration, followed by a glide. Don't worry about the large gap building ahead of you: if you get there and the traffic's stopped you haven't held up the people behind you.

However, do note that gliding can make the other people behind you consume more gas as they have to overcome their engine drag by using gas to keep the car moving. Unless they turn the engine off, in which case they'll glide like you. Or they can shift to neutral: it's not as good as your Prius glide, but it'll help.

 

Here's a few tips.

1. If you're fully warmed up but not in "stage 4", than make sure you stop in "D" for at least 7 to 10 seconds until the engine cuts out (placing it into "hybrid stage 4"). This makes sure the engine cuts instantly that you back off the accelerator whatever speed you're going.

2. Use EV mode sparingly. For example, if you're stopped at a crossing and there are red lights just ahead then you might crawl forward in EV until the lights change and then kick it. Be careful about using EV mode on uphill sections, as you can dump all your charge really quickly.

3. As always, try to maximize the length of your glide to stops. That is, if you see red lights ahead then back off the accelerator early and let it coast up to a stop.

 

I measured it for 12 months and it came in about 49 mpg UK which is about 41 or 42 mpg USA. Not sure what it is in litres.

 

just thought i'd share my recently-added post in another thread that might also help achieve this. Try it, it works.

But first,

In creeping pace, a knowledge of the concept of Traffic Waves and practicing it will help

In stop-and-go/heavy traffic, the "Coasting Regen - PC Glide - Neutral Glide" technique might just work for you. (see last paragraph)

If in case the inevitable happens (your SOC drops to 45%-47% and holding a glide is difficult), just do pulse-and-glide. Let the car in front accelerate first and create a good gap for you to do a quick pulse to just the right speed so that by the time he's already stopped or slowing down, and you're still half-way through, release the accelerator and just let the car coast to a stop. Sometimes, just a 1-2 second moderate pulse will do in most stop-and-go situations.

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I only use N-glide for bumper-to-bumper traffic. Coasting or PC-gliding to a stop, i monitor the amp in/out through the SGII so that just before the car reaches 6-7mph, i engage to neutral because the SGII is telling me that either there is no more regen happening or that PC-gliding to a halt still uses around 2.5 - 4.0 even if the speed is almost zero. so at around 6-7mph, i engage to N so that current draw will drop down to only 1.2 - 1.5 to conserve juice. it really helps in heavy traffic especially if you time it right. I'll also confirm as per JimboK's tests, is that N has more friction because there's no more of the unseen (as per MFD screen) minimum current draw to keep the car in a "gliding" state. This can be felt at really slow/creeping speeds when N is engaged. The car decelerates more than when PC-gliding. So take this into consideration if you decide to employ N-glides into stop-and-go traffic.

 

That would be 5.77 l/100 km.

 

Not quite.
In theory, consumes less during this "power" stage than other vehicles (better BSFC).
In practice, some energy goes to or comes from the battery pack also during this stage, so we may not be looking at all the picture.

My experience is that doing "pulse" and "glide" when possible gives the better results. Also switching off some energy-load peripherals, such as AC does keep SOC level during high traffic conditions.
The adequate use of N (eg.in descents) may be good in bumper-to-bumper crawl.

 

The Prius does not HAVE a true transmission with gears. All power changes are done electronically via MG1/MG2. The only danger of frequent shifts from neutral to D, etc is wearing out the shift knob.

 

Hi Bojan, there's no need to change to neutral in order to do "pulse and glide".

 

Depends on the character of the stop'n go. I usually get great mileage on So. California freeways using a combination of pulse & glide and electric, as long as there is enough go to keep the traction battery charged. When the glides become as short as the pulses, the efficiency of this process is lost.

 

Raise psi up to max sidewall to reduce rolling resistance.
Glide, glide, glide.

 

Turn the Climate Control OFF.
* The heater takes heat out of the engine. The HSD wants coolant
temps above 145 degF. It will start the ICE when car is stopped to raise
coolant temps.
* The HSD also wants the HV battery SOC to be around 60% in warm
outside air temps, and 65% SOC when its cold. The air conditioning is
powered directly from the HV battery.

Try to drive with all gas consumption being used to directly move the
car. This means no power, yellow arrows, going into or out of the HV
battery.
Power going into and out of the HV battery comes with a stiff penalty
due multiple energy-state conversion losses:
Kinetic (car in motion) ->Mechanical (wheels) -> Electrical
(Motor/Generator) -> Chemical (battery) -> Electrical
(Motor/Generator) -> Mechanical (wheels)

This can even be done when accelerating by playing

"The Snake Game:"
See the upright yellow arrow arrow showing power going into the HV
battery as a cobra poised to strike... bad.
So, step on its head by depressing the go-pedal a little...
Snake disappears and no power is going into the HV battery.
See the horizontal yellow arrow showing power being fed to the wheels
as the cobra slinking away... good.
Encourage that by easing up a little on the go-pedal.
Snake disappears and no power is being used to move the car.
If the snakes are switching back and forth, hold the go-pedal position
for a few seconds and things will settle down.
Make corrections as necesssary.

It is better to put a little energy into the HV battery than take it out
when accelerating. If the SOC level is low the HSD will find sneaky
ways to put some energy back. It does this by diverting through the
Power split Device to MG1 operating as a generator. You can't stop this
little game.

On the other hand if the SOC level is high the HSD will also play sneaky
little games to your FE advantage. When you're trying to maintain a no-
arrows-glide and encounter power transients (actually torque demand
transients) like a slight rise or change in wind pressure, the HSD will
tap into the HV battery for a few seconds rather than fire up the ICE.

Hope this helps.