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Discussion Starter · #1 ·
Please correct me if I say anything wrong.

As I understand it, both the Prius and Insight transmission have the engine capable of generating electricity and storing the energy in a battery.

The Prius uses a power split mechanism so the engine can constantly run at THE most efficient rpm. If the load is light, the extra power from the engine gets generated into electricity and stored in the battery. This is a significant advantage.

What about the Honda hybrid powertrain? Can it allow the engine the always work at a single rpm? Obviously it cannot if it has a manual transmission. What about the one with the CVT? Can the engine just run at its highest efficiency rpm and have the CVT match that with the vehicle speed? And the extra power get generated by the motor and get stored in a battery?

408 Posts
Yea, all true automatics to date (correct me if I'm wrong) will have a lower efficiency than their manual counterparts. Whether it's due to a torque convertor or just more friction. To my knowledge, the CVT will run the engine at a certain rpm depending on throttle position and the assist will also run when the throttle exceeds a certain limit. The assist motor is mounted driectly onto the drivshaft before the transmission (which allows for the engine to charge the battery when idling) so the assist motor will spin at the same speed as the engine. As for storing excess power to the battery, the Insight is only 3 cylinders. Moreover, it's very efficient so there is little or no excess power. The assist motor is used as an alternator when cruising so the 12V battery can be kept up as well as the big battery. So basically, it works the same as the Prius.

I think the Prius has a sort of 3 way mini transmission where it can switch engine and assist with the output. This way, it can drive the car on engine or assist but I still don't think that the assist and engine can opperate at different rpm's.

Premium Member
1,631 Posts
I do have a CVT and have read about how it works...A couple of things
to consider when comparing the CVT to the manual about efficiency:
1) The engines are not the same (The manual has two more horsepower)
(Also has 1 lb.-ft more torque)
2) The manual ECM (main computer) is programmed for lean burn.
3) The CVT doesn't seem to use as much IMA during acceleration
4) All CVTs have air conditioning.

We are not comparing apples to apples. The reason why I mention air
conditioning is not if you use it or not but the additional weight. Now there
are some manuals that have A/C installed as an option but the CVT still
weighs more because the CVT transmission itself weighs more than the
manual - manual with no A/C 1850 lbs - manual with A/C 1881 lbs - and
the CVT 1975 lbs . That means the CVT transmission weighs 94 lbs MORE
than the manual. In a car where everyone is thinking lightweight parts,
this extra weight and less horsepower can and does make the car a little
slower from 0-60...But it could be worse (much slower) if Honda used a
conventional automatic transmission. Here, the CVT shines...If both
models had the same egine, I believe the CVT would actually perform
better than manual because there is no power loss while changing ratios
(or shifting gears in manual terms)

To remark about previous statements:

1) There is no torque converter. The Hondamatic uses a series of clutches
to simulate a torque converter giving the feeling of "creeping" forward.
2) The CVT can change the ratio to match maximum performance based
upon your current style of driving (max mileage or max performance)
3) The CVT does step up the ratio to give the engine more rpm when you
are comming to a stop so the IMA can charge the battery more. I think
CVTs does a better job at keeping the battery charged than the manual.
(Just look at all the images on Ebay of SOC - State of charge - between
the manual and CVT models.)

Here is a good link to explain this stuff better than I can

JoeCVT - Just your average CVT owner

Premium Member
2,332 Posts
Unclehan: The Prius "transmission" is less efficient than a manual transmission. The planetary gear is almost 100 percent efficient but running an electric motor continously to vary a gear ratio is not. The Prius must generate electricity all the time to power the main electric motor or the electric motor would spin backwards and the car would not move! Drawing this energy from the hybrid batteries is not efficient so the synergy system has a secondary electric generator/motor. Otherwise if the hybrid batteries failed or got too low on energy the "transmission" would "fail". If the IMA batteries fail in a Honda you can use the 12 volt system to start and run the car. There is no "secondary" IMA motor.

If the Prius engine just ran at a constant RPM and power for maximum efficiency and stored excess electricity, the battery would quikly overcharge. :shock: Turning available engine power into stored electricity is not efficient. The system losses are too great. Toyota does not have an advantage there. Where Toyota gains is by using a really efficient but sluggish engine and coupling this to a relatively massive and high torque electric motor. The net result is a wonderfully smooth and capable system.

What you have described would more likely be found in a "plug in" hybrid with massive batteries where the gas motor is used as a range extender and where the primary engine is the electric motor. Toyota is moving in that direction.

I"ll be surprised if we don't hear from John 1701 on this post. :wink:
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