Toyota eCVT vs. Ford HF35 transmission

Here is the chart:

 

According to: Toyota Prius - Power Split Device
At 62 MPH the Prius MG1 would be spinning at -9578 RPM if the ICE were off. At 85 MPH it would be spinning at -13144 RPM if the ICE were off. The FFH Gen RPMs are lower due to the different size/design of Ford's planetary gear set.

 

Hmm, if they could just add a couple of clutches to detach MG2 and the wheels from the ring gear....

 

What do you mean?

 

Instead of compromising the power split gearing ratios to slow down MG1 and increase the engine-off EV speed they could do something similar to the Volt.

In the Prius HSD, the big motor (MG2) and the output to the reduction gearing, differential and the wheels are all tied to the main planetary ring gear. Conceptually, they could add a clutch to allow all that to be detached from the ring gear so the wheels and MG2 would not cause MG1 to spin. A second clutch/brake would allow the ring gear to be locked to the HSD case so that MG1 on the Sun gear can force the planetary carriers attached to the engine to turn and start the engine and likewise allow the engine to spin MG1 to generate electricity in serial mode when needed.

This would allow hybrid gearing to be optimized as in a non-plugin and allow EV driving to have less internal transmission drag and no rpm EV speed limitations. This is similar to what the Volt does. The downside is some added hardware complexity and software to control the clutching and gear speed matching during transitions. Also, the Volt uses a somewhat different relationship (output-split vs input-split) between the various drivetrain components and the planetary gears. That allows the Volt to power-split between just MG1 and MG2 at speeds above 60 mph for better efficiency (by lowering MG2 rpm). There are doubtless other tradeoffs between the two power-splitting approaches.

It probably isn't worth doing it until you have a battery pack around the same size as the Volt that can put out enough EV mode sustained power to make the electric motor the main traction source when the battery is charged up (EREV-style).

I predict Toyota and Ford will do something like this in a few years when the necessary batteries come down further in price and can be packaged to allow full rear seating and acceptable rear storage space.

 

Honda's dual motor system in the Accord hybrid does this, albeit without the complexity of a planetary gear set. If it lives up to its EPA rating, adding a clutch as you propose very well may be worth it for a non PHV.

 

AFAIk Toyota "overprotected" MG1 and has already relaxed the max Ev limit in the plugin version which has the same powertrain.

 

They may have relaxed it in the Japanese market Aqua/c. The new Fit hybrid had beat it out on the Japan test cycle, but the latest model year is on top again.

 

Gas engine was tuned for max efficiency above 62 mph. Below that is for EV where aero loss is not major. It makes the best use of both the battery and the gas engine.

As battery cost gets lower and density increases, that balance should change.

Ford Energi went with 85 mph EV and gave up some cargo as a compromise. Both the EV and gas efficiencies took some hit to increase EV ratio (range).

Volt went even more extreme. The good thing is each plugins are tuned differently across the spectrum for us.

 

Can you provide MG1 vs ICE and MG2 vs MPH graphs?

 

The truth will never come out from Toyota or Ford statements. There is too much wiggle room for spin.

E.g., if the Ford is 99% Toyota developed and 1% Ford, then it would be quite true that Ford did not simply copy the HSD. One interesting side-effect of the PAICE litigation Vs Ford might be some light on this question.

 

I will look into it. It will take some time to gather enough data.

 

The Generator RPM is variable when the ICE is on. There is not a fixed ratio of Gen RPM to ICE RPM. It all depends how much of the ICE torque is going to the wheels versus going to the generator. The FFH likes to charge the battery with about 30-40 amps of current (8700-11,600 watts @ 290 volts). The Generator RPM can be as low as 30-50 RPM and still put 30-40 amps into the HVB. When this happens, nearly 100% of the electricity from the generator must be flowing to the HVB and almost 0% of it must be going to the traction motor. In city driving the Gen RPM is often 5000-6000 because the ICE is sending almost 0% of its torque to the wheels. In city driving the ICE primarily only spins the generator and then the generator sends some electricity to the battery and some to the traction motor to power the wheels. In typical highway driving there is a split of the ICE torque and the Gen RPM is usually 1000-2500 depending on how the car decides to split the power.

 

Here is the equation based on the 3000 or so data points from a couple trips plus another 10,000 or so data points of (0,0) to get the equation to pass through that point or as close as possible since that's the one data point that we actually know is correct:
Gen RPM = -120*MPH
Note that in theory the intercept should be exactly 0 because when speed is 0 the Gen RPM is also 0. But this is very close to 0 and can probably just be ignored as noise. It's very hard to get the measurements exactly in sync which creates noise in the data.
This means that the previous FFH max Gen RPM was: -7440 @ 62 MPH
Now the max Gen RPM is: -10,200 @ 85 MPH
Here is the chart: