A new owner with some questions

You're absolutely correct.

Electric only won't get you very far very fast.

I mainly use it for parking lots and for helping maintain speed
during a glide (if needed).

I'm not sure about the poor mileage situation. Maybe someone else has
had the same problem and will chime in.

 

There are many posts on the forum talking about how to get good mileage. Any of them will help. If you drive your Prius like a normal car, you will do pretty well. Most new drivers make the mileage worse by trying to out-think the hybrid system. You don't have to do that. If you want to try for super mileage, then you can advance to the tricks of the hyper-milers.

Driving on the electric system is inefficient. The more you drive in electric mode, the worse will be your mileage. The electric portion of the hybrid system is there to augment the gas engine, recover energy during braking, and allow the gas engine to shut off when the car is stopped or moving slowly. Remember that all of the energy used by the Prius comes from the gas internal combustion engine (ICE); all of it, even the energy stored in the battery. When you drive on electric power, you are using energy that started as gas, was converted to mechanical power by the ICE, was converted again to electrical power by the motor-generator (MG1 & MG2), converted again to chemical energy stored in the battery, converted again to electrical power as it comes back out of the battery, converted to mechanical energy by MG2, and finally sent to the drive wheels. That's not an extremely efficient process. Ideally you want the energy to go right from the ICE to the wheels, but real world driving presents many obstacles to that ideal, so the hybrid synergy drive (HSD) uses a balanced combination of electrical and mechanical drive, and overall does a better job than a normal transmission.

Some simple techniques and concepts to help your mileage:
1) Avoid short trips. Short trips are mileage killers since the engine and emissions system has to warm up just as much for a short trip as a long one. Try to group several short errands into one longer trip.

2) Don't warm up your engine before driving. Just take it easy with the throttle for the first five minutes.

3) Don't try to force the HSD into electric mode. For most driving conditions, it's better to let the computer do its thing and decide what is most efficient.

4) Accelerate briskly up to speed when the road is clear ahead. Slow starts are less efficient than ones putting the ICE into its efficient RPM range.

Those should get you started. I'll let others chime in with more ideas.

Tom

 

Once you know how the whole system works you will realize that running on battery is counterintuitive. All battery power ultimately comes from the gas engine, either directly, or from braking. Energy is lost each step of the way when it is converted from motion to electricity to chemistry, and again when it is converted back. There for the most efficient mode is not to use the battery at all.

Pulse and glide is ideally a pure gas engine endeavor - accelerate with gas engine at max efficiency, and glide using no power at all.

Electricity is used to take up the slack when you have to slow down, and during short periods where you can avoid the gas engine from kicking in for very short periods of time when it is really not needed. The EV switch gives you some control over this.

 

I'd like to chime in, if I may. I've had my Prius for 6 wks, and am developing an appreciation for these subtleties. My question: without a tach, how can I develop a sense for the optimally efficient rpm range for the ICE?

TIA,
David

 

These suggestions seem very strange. If your goal is to use only the gas engine, why get a Hybrid at all? Would a Corolla with the Prius transmission (that allows a true glide as opposed to an engine slow-down) do as well as a Prius on MPG?

My limited experience with the Prius shows I get better mileage around town if I force the car into EV mode (back off the accelerator and then gently back on) and coast to stops to charge up the battery. The one thing you are not mentioning is driving on EV is more efficient because at least some of the energy is recovered (Regen braking, coasting) while none is when using the ICE.

Also, when on the Highway, I get better mileage if I can get the engine in a low RPM mode so it is just charging the battery and providing little thrust.

 

One rule of thumb is to keep your instantaneous MPG as shown on the MFD above half the vehicle speed. See this thread for an in-depth discussion.

Since that thread was begun, I've begun to question the second part of the rule -- that is, keeping iMPG below 1.2 x vehicle speed. Between that being a slightly more difficult mental calculation to make on the fly and recent reports of good results in sub-1400 RPM ranges, I think the first part of the rule is sufficient for most without added instrumentation. (I'll probably add an update to that thread accordingly.)

 

Good question but there is a clear answer. The Prius engine is a very efficient engine because it only works over a very limited rpm range. The HSD design allows this by using the transaxle to convert a very narrow range of engine rpms into the very wide range of wheel rpms. A non-hybrid needs an engine that works over a very wide rpm range and this really hurts efficiency. Additionally, the hybrid part also allows recovering most all the braking energy....can't do this if you do not have a battery.