BMW 6x6 SDU Conversion

[thecoolx3]

I am building a BMW 7 series (E38) 6x6. Per the reason I am posting here, it will be a hybrid. I have a twin-turbo V12 mated to a ZF8 auto trans with a BMW Xdrive system powering the traditional 4 wheels, and I intend to put the Tesla SDU on the rearmost axle. I am considering an LDU but I think space is a limiting factor as I have to contain the motor within the original subframe. I have the engine and the rest of the vehicle controlled by a mix of OEM and standalone hardware. I am thinking that the electric side will almost operate as a mostly standalone system. I do not necessarily want the ECU and the openinverter to talk via Can or other means, as I don't think they need to, but I want to ensure I am not oversimplifying it. In my mind, I will just send the open inverter the same throttle signal that goes to my ECU, and that would get me roughly in the ballpark of everything playing nice. The rest would just come to tuning the systems together.

Has a hybrid setup like this been done before? I don't see why it wouldn't work but I am expecting significant pains in tuning the two systems to play nice with each other.

I am not looking to drive the truck as a pure EV. The motor is there to give more umpf when I am looking for fun or while I am towing and to provide an additional source of braking. My engine makes about 600HP, but it is a turbocharged gasoline engine, so torque isn't immediately available, my goal for the motor is to help alleviate this. Is it possible for the openinverter to have configurable 'drive modes'? I would like to have something like a regen-only mode, low power, and full power. I will likely have around 25kWh worth of pack on board.

Thank you for the advice in advance! Here https://www.youtube.com/channel/UCOucit ... OviNuH_cAQ is my Youtube if you're interested in more of the engineering of the project.

[crasbe]

In my mind, I will just send the open inverter the same throttle signal that goes to my ECU, and that would get me roughly in the ballpark of everything playing nice. The rest would just come to tuning the systems together.

Has a hybrid setup like this been done before? I don't see why it wouldn't work but I am expecting significant pains in tuning the two systems to play nice with each other.

A hybrid setup like this has not been done yet and you correctly identified the main issue: Getting the systems play nicely.

I'm afraid you are oversimplifying it with the idea to only use the throttle input. At least with the goal of providing additional "boost" when the turbo doesn't give much boost yet.
The main problem I see here is that you essentially need the knowledge of what the driver "wants". So for example if you're starting from a slow speed and push the throttle to the maximum, you want maximum torque from the electric motor until the boost hits. But as soon as it does, the assistance can/should be lower. But on the other hand, if you're already driving with say quarter throttle and push it, the boost might hit quicker and you don't want as much assistance from the electric motor.

Long story short: It's very possible to build it as a proof-of-concept, but having a well-behaved system probably requires the control of the V12 and the control of the electric motor to be a little more intertwined.

I think a possibility to make this happen is the interface between the ECU and the transmission controller. I don't know what you are using and how they are internally working, but often automatic transmission control units require a torque estimate from the ECU. Sometimes you'll have a torque setpoint from the ECU as well. The difference between the torque estimate and the torque setpoint would be exactly what you require as an input to the inverter controller (obviously through some kind of mapping function).


By the way: Your car looks really wild, I love it

[thecoolx3]

You make a really great point about the integration. My plan was, and I am unsure if openinverter has this ability, to reduce output power as wheel speed increases. I figured with the tuning of the throttle response and power by speed, I should be able to create a predictable acceleration.

I am using a MAXX ECU to control the engine with a CANTCU for the ZF8. My intention was to calculate the output torque of the motor given my calibrations and add that to the torque factor calculations. According to the guys at CANTCU, there is some level of "it will just figure it out", and I'm heavily banking on that to pick up any slop.

Thank you for the reply!

A hybrid setup like this has not been done yet and you correctly identified the main issue: Getting the systems play nicely.

I'm afraid you are oversimplifying it with the idea to only use the throttle input. At least with the goal of providing additional "boost" when the turbo doesn't give much boost yet.
The main problem I see here is that you essentially need the knowledge of what the driver "wants". So for example if you're starting from a slow speed and push the throttle to the maximum, you want maximum torque from the electric motor until the boost hits. But as soon as it does, the assistance can/should be lower. But on the other hand, if you're already driving with say quarter throttle and push it, the boost might hit quicker and you don't want as much assistance from the electric motor.

Long story short: It's very possible to build it as a proof-of-concept, but having a well-behaved system probably requires the control of the V12 and the control of the electric motor to be a little more intertwined.

I think a possibility to make this happen is the interface between the ECU and the transmission controller. I don't know what you are using and how they are internally working, but often automatic transmission control units require a torque estimate from the ECU. Sometimes you'll have a torque setpoint from the ECU as well. The difference between the torque estimate and the torque setpoint would be exactly what you require as an input to the inverter controller (obviously through some kind of mapping function).


By the way: Your car looks really wild, I love it