Why is the engine active so often at slower speeds?

I am a prius n00b myself, but the battery bars are the SOC (State of Charge) of the battery. Full green 8 bars is 80% full and empty blue is 40% (Not sure on the bottom number here). Toyota tries to keep it within these ranges to prolong battery life.

The gas depends on how hard you push the accelerator. You can crawl from stop to 25 on electric only then gas will kick in, or if you put in an EV button you can go much more speedily from battery to 35mph before gas kicks in. Just remember all that electricity comes from the ICE (gas engine, internal combustion engine) so it is not always most efficient to use electric only and in some cases detrimental to fuel efficiency. Some people suggest a "pulse-n-glide" technique which I myself have not mastered. But I think it involves briskly accelerating to 40mph, then "gliding" or keeping your foot where no regenerative braking happens and no power is applied (the energy screen has no arrows at all) until you slow down to 35-30mph, then "pulse" back up to speed, and glide back down.

I dont know how people manage to do that, but living on a mountain it just doesnt work for me, or maybe I dont understand it well enough yet. But I am averaging 45mpg at 7000ft-10000ft above sea level on the side of a mountain driving it like a semi-normal car. Exception being I use the EV mode to get from my garage to the start of the huge downward hill and go from 3 bars to full recharge by the bottom. Also use EV only in parking lots and quiet neighbourhoods at night out of courtesy, not fuel efficiency.

 

Good post, Probably pretty dumb question, but what is EV mode and where is the EV button?

 

One thing to keep in mind is that the programming is really designed to minimize emissions, fuel economy is just a side benefit. When the engine is cold, the programming is designed to run so that the catalytic converter will be warmed up into the operating range as quickly as possible.

Once warmed up, sometimes the engine will run to recharge the HV battery, and the engine will run more when the AC system is on and the heat is needed to warm the interior. If the defroster is on, the engine will run more than normal also.

 

It all boils down to the PSD...



You'll discover those moving parts offer a wide variety of power options, which can rapidly change since the carriers are often rotating anyway.

There's more animations and some illustrated documents available on my website.
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+1, well said.

 

Great discussion. Since the topic of bars and wheels is up, I thought I could hijack the thread politely and ask what does it mean when you have yellow arrows only (from battery to electric motor to wheels, wheels turning) when at a stoplight. This happens on occassion. 2007 owner for 7 weeks.

 

It means you need to step a little harder on the brake pedal to turn the arrows off.

 

Its basically the car trying to creep forward.

 

Why does the car try to creep forward? The ICE shuts off when the car is stopped. The electric motor shouldn't be doing anything either, it seems to me. Isn't it wasting power?

Or are they just trying to make it "act like a normal car"?

 

The latter. Same reason for the car to simulate engine pumping loss by slowing the car down with regenerative braking when you lift your foot from the accelerator.

 

This is it exactly. The designers of the Prius tried to make it operate as much like a "normal" car as possible. If you know the details, it's pretty amazing.

Tom

 

Thank you for the response. The feel of the engine braking is almost the same as it was in the 2001 Honda Civic I traded in for the Prius.

I drove a friend's 2002 and was surprised by how much the car slowed down when I took my foot off the gas pedal. So I guess Toyota must have tweaked that function by Gen III, because it feels really natural to me.

 

Thank you. Can you point me to an article on this? I'm at work and don't want to spend a lot of time Googling. As a former mechanical engineer (now a computer programmer) I find this stuff fascinating.

 

Combustion engine use has nothing to do with speed, it has to do with how much torque (strain) you're putting on the engine, and it varies depending upon how fully charged the battery is.

You can drive the Prius at ten MPH or higher around a track, completely on battery power. But eventually the battery depletes, and the gas engine has to kick in.

If you drive with the HIB display on the 2010 model, you'll see that, usually, when you're below the 50% point, the car will run only on the battery. To make it do this, when you decelerate, you have to lift your foot off the accelerator pedal (kills the gas engine), and then gently accelerate. As soon as you hit the midpoint, the gas engine will start up. I've been able to run as fast as 37 mph uphill in battery-only mode, but only for a few blocks.

These observations of mine are only generalities, and the car won't always follow these rules. The Prius isn't an electric car, and it can't run in all-electric mode for long.

 

Here is a good place to start:

[ame=http://en.wikipedia.org/wiki/Hybrid_Synergy_Drive]Hybrid Synergy Drive - Wikipedia, the free encyclopedia[/ame]

Tom

 

From the Wikipedia article, an excellent technical description of the Gen I and II vehicles. This appears to be a Toyota training document. The same website has more articles about Prius, fairly technical.

 

Very good resource for everyone to read. As another engineer, it is always facinating to learn the "inner workings" of the system you are driving.