Feasibility of conversion to PHEV with L110 transmission

[Miyuki]

Hi folks,
I wonder how feasible it is to convert old ICE with Lexus L110 transmission to PHEV. It would be nice to have about a 50 to 100 km EV range and keep the engine for nice sound, longer trips, or extra power.
I'm aware there will be some additional work, like power steering conversion, probably to electric. Electric vacuum pump for brake booster and AC compressor.
Did anybody do such a thing? EV drive is well documented and straightforward, but running in hybrid mode while relatively simple in theory will have plenty of issues.

[Jacobsmess]

There are more complications and overall more work than a straight up EV conversion. The controls are also a pain and you'd want to implement the CVT control somehow (currently not achieved) in order to modulate the gearing and make your ICE usable at low speeds.

[Miyuki]

If there is a possibility to run MG1 at a constant speed and monitor the current size and direction, then it shall be relatively simple math.
With the engine running just set MG1 to match it (in the opposite direction) and then just apply throttle to the engine.
Lexus states they run it in 8-speed emulation mode. So while running then just calculate MG1 speed according to the selected speed's gear ratio.
Selecting speed is a simple lookup table of speed, throttle, and some hysteresis.
Trying to implement take-off will need to simulate some form of slippage, but it shall be circumvented by just using only MG2 at low speed.

It seems doable on the paper. But tuning it to behave reasonably will probably take an awful lot of time.

[Jacobsmess]

It's the integration of the control systems that's the difficulty, the math and the theory isn't an issue but to make it work and in a usable fashion is the problem, which is why no one (I know of) has a working hybrid conversion thus far....

[Miyuki]

I see, I have tuned a few control processes and it can be quite a pain to get it working as desired especially when there will be regulation delays and inertia. Even car manufacturers sometimes have issues to fine-tune throttle response.
Plus PHEVs are somewhat ugly ducklings hated by both sides, so nobody wants to have it as a fun project.
But it shall perfectly suit my uses and avoid legal hustle as the original engine remains.

And another complication can be to keep the engine from turning backward in some transitional states in EV mode as MG1 probably has nonnegligible inertia. There probably will have to be some at least slow engine rotation in the right direction to be safe.

[jrbe]

There's the work being done to try to use the BMW i3 range extender (rex) to charge a battery. That should eliminate a lot of the integration efforts to be able to use ice to increase range.
See viewtopic.php?t=3749
Or if you do a true hybrid and pull it off that would be a great addition to this forum.

[Woodfie]

Hi, this may give some insight
operating a factory Gs450h, with 98 Lipo4, switched parallel to the Nimh 288v, judicially when voltages are acceptably matched.
The Boost converter limits the available power to 37kw.
This is a bit low for some driving circumstances , maybe 5%. . Stratagem was to avoid percieved problems like steep hill starts, etc.
Have operated in this mode for many months as a test program, when gathering some idea if how it all works, and it worked well for me. Have some ideas to increase the usability, on the project list..much to learn..

A thought had been to include the ability to run standard system, and then switch control, oil pump ,HV power to bypass the boost, and separate vcu to control basic drive function as an ev... initial investigations had not achieved the power steering to still operate, work on other related projects has put this on hold at present.

[Miyuki]

There's the work being done to try to use the BMW i3 range extender (rex) to charge a battery. That should eliminate a lot of the integration efforts to be able to use ice to increase range.
See viewtopic.php?t=3749
Or if you do a true hybrid and pull it off that would be a great addition to this forum.

I also thought about REX or other small ICE, but having the combined power of both motors seems like a fun thing to drive. This can be overcome with a stronger motor than this one for pure EV.
Plus there is that legal aspect of things, when I pull the engine out I will have to do custom vehicle certification which can be more complicated and expensive than conversion itself.
And with full EV when you want to go further then fast charging is a desired feature and that looks like a problematic thing.
This way I can use a small 20kWh pack capable of 15s burst at 8C and sustained 1C build from safe LiFePO4 without active cooling.

//edit: I wonder how the efficiency of running eCVT MG>inverter>MG compared to common automatic transmission with torque converter. I expect it will be way better at least at city speeds when the converter is open.

[Miyuki]

I did some calculations to see how power splitting would behave with my engine and final drive
Table showing maximum power MG1 and Engine can deliver to wheels and percentage of that power relative to total engine power.
At higher speeds and low engine RPM are those percentages over 100% because MG1 acts as a motor.

And output torque of combined MG1 and Engine

It did surprise me a little but it makes sense to be optimized to transfer the majority of power when ICE RPM is at peak efficiency around 3000-4000 RPM
It behaves as a constant torque device and it is very nice. I did not realize that.
It also simplifies control algorithms as the stock inverter takes commands in torque.
Acceleration is then just setting constant torque to MG1 and the engine throttle shall also remain stationary.

When I look at the RPM limitations and consider MG1 will have a 10,000 RPM limit then ICE can rew 1000-3000 RPM from stationary to max speed, this is nice.
High ICE RPMs will be available only at really high vehicle speeds, as ICE at 6000RPM will cause 10,600RPM at MG1 even at 149 km/h, and for 5000RPM the speed has to be at least 105 km/h to be in the limit of MG1.