[Pankrivoklat]

Currently driving F90 M5 with its awesome M xDrive and I am curious how is all four wheel magic done in this new i4 M50. I understand there is no VTG transfer case and each axle is powered directly via 1 speed gearbox by separate electric motor. I tried to find some more info about four wheel solution in i4 M50 but unfortunatelly with no success. Does anybody know a little more about this? Eg:

1) Are there any basic principles/logic how the torque of both electro motor is synchronised? What exactly substitutes xDrive transfer case on software/control base?

2) Are there any “maps” inside of related control module which says how much power should be where (front/rear) in different conditions? I mean speed, cornering, acceleration/deceleration etc.

3) Does electro powered drive train utilize some kind of torque vectoring on each wheel? How it is done?

Thnx for ANY related info or shortcut to.
Tomas

[motzus]

I have wondered many of the same things myself. BMW has not really provided any answers to the above questions so far. Or if they have none of the normal reviewers have though it was significant enough to report. With one electric motor per axle there is no way to vector torque without mechanical assistance. That mechanical assistance may come via some form of limited slip differential (geared, mechanical clutch, electronic clutch), some other fancy geared setup or via the brakes. Given that BMW has not mentioned some sort of fancy limited slip differential in their marketing material I would assume that they are running open differentials and will be using standard traction control (which cuts power) and braking of wheels (to transfer torque across the axle). Given the torque that the electric motors provide I wonder how fast the brakes would heat up during spirited driving to move the torque across the axle.

[techwhiz1]

Originally Posted by motzus

I have wondered many of the same things myself. BMW has not really provided any answers to the above questions so far. Or if they have none of the normal reviewers have though it was significant enough to report. With one electric motor per axle there is no way to vector torque without mechanical assistance. That mechanical assistance may come via some form of limited slip differential (geared, mechanical clutch, electronic clutch), some other fancy geared setup or via the brakes. Given that BMW has not mentioned some sort of fancy limited slip differential in their marketing material I would assume that they are running open differentials and will be using standard traction control (which cuts power) and braking of wheels (to transfer torque across the axle). Given the torque that the electric motors provide I wonder how fast the brakes would heat up during spirited driving to move the torque across the axle.

So I do know from reading that the DSC, ABS, etc is built into the motor and not out at the wheel.

[Pankrivoklat]

Originally Posted by motzus

BMW has not really provided any answers to the above questions so far.

There must be some significant intelligence somewhere between those two separate axles which provides all the 4WD stuff. Its not easy task to sync two separate engines (rated at different power output) to drive seamlessly and safe 4 wheels of one car when there is not direct mechanical connection between them. And yes, BMW is very loudly quiet about it. Weird

Originally Posted by techwiz1

So I do know from reading that the DSC, ABS, etc is built into the motor and not out at the wheel.

Interesting. Any closer details? Regular recuperation brake has not enough stopping power to deliver ABS/DSC like functionality. Is ABS pressure hoses connected somewhere inside to electro-engine? I dont think so.

[motzus]

So I do know from reading that the DSC, ABS, etc is built into the motor and not out at the wheel.

I remember reading the same thing. I also remember thinking how / why? Depending on what BMW considers at the "motor" I don't know how it could be done. Looking at the pictures of the "motor" it looks like there is only one gear that comes out of the motor. I don't know how you'd be able to measure wheel spin for two different wheels coming from one gear. Unless BMW also considers the differential as part of the "motor." If the differential is part of the motor then they could measure wheel spin at the two outputs of the differential. Why they would measure wheel spin at the differential as opposed to the wheels would be interesting. Given how similar the i4 is to the 4 series grand coupe I don't know why they would go with different configurations for DSC and ABS sensors between the two cars. You would think that it would be cheaper to reuse the 4 series DSC and ABS configuration. Unless the iX and the i4 are sharing electric drive train technology and BMW implemented DSC and ABS in the electric motor for the iX and just moved it over to the i4 to save cost. Who knows, but as an engineer I'd love to know the reasoning.

[techwhiz1]

Originally Posted by motzus

I remember reading the same thing. I also remember thinking how / why? Depending on what BMW considers at the "motor" I don't know how it could be done. Looking at the pictures of the "motor" it looks like there is only one gear that comes out of the motor. I don't know how you'd be able to measure wheel spin for two different wheels coming from one gear. Unless BMW also considers the differential as part of the "motor." If the differential is part of the motor then they could measure wheel spin at the two outputs of the differential. Why they would measure wheel spin at the differential as opposed to the wheels would be interesting. Given how similar the i4 is to the 4 series grand coupe I don't know why they would go with different configurations for DSC and ABS sensors between the two cars. You would think that it would be cheaper to reuse the 4 series DSC and ABS configuration. Unless the iX and the i4 are sharing electric drive train technology and BMW implemented DSC and ABS in the electric motor for the iX and just moved it over to the i4 to save cost. Who knows, but as an engineer I'd love to know the reasoning.

Unlike the ICE car, you can directly control output to the wheels. Also measuring at the motor/trans assembly doesn't require outboard sensors.

[Pankrivoklat]

Originally Posted by techwhiz1

Unlike the ICE car, you can directly control output to the wheels. Also measuring at the motor/trans assembly doesn't require outboard sensors.

No way you can provide ABS functionality directly inside electro-engine. Basic principle of ABS si to interrupt pressure of brake fluid when you lock wheels using your brake pedal. Which is totally separated from power/torque coming from engine to axles.

Similar with Electronic stability control ESC (DSC, ESP, whatever) - it applies brake force individually on each wheel. You cant do anything close to that by adjusting output power of electro-engine. Its impossible even inside differential mechanism.

All my questions remain unanswered

PLEASE, ANYBODY?

[techwhiz1]

Originally Posted by Pankrivoklat

No way you can provide ABS functionality directly inside electro-engine. Basic principle of ABS si to interrupt pressure of brake fluid when you lock wheels using your brake pedal. Which is totally separated from power/torque coming from engine to axles.

Similar with Electronic stability control ESC (DSC, ESP, whatever) - it applies brake force individually on each wheel. You cant do anything close to that by adjusting output power of electro-engine. Its impossible even inside differential mechanism.

All my questions remain unanswered

PLEASE, ANYBODY?

From the BMW technical specifications.
Before you start talking crap about me not knowing what I'm talking about; you should research. It is integrated into the motor management system and hence the near the motors and not outboard like conventional systems.

Also in an ICE car you cannot but with an electric motor and shafts exiting the housing you can measure things like rotational speed, delivered torque and do computation directly from sensors at the motor. Also there is ZERO connection on this car from brake pedal to the actual brake system. Brakes along with regen is under computer control.

Why do people argue when they haven't read the technical briefs?

https://www.press.bmwgroup.com/usa/a...language=en_US

The BMW-developed near-actuator wheel slip limitation, which in combination with the electric all-wheel drive, enables the car to maintain optimum traction in a straight line. Specially configured for the instantaneous power delivery of electric motors, this traction control system is integrated into the motor management. This eliminates the long signal paths to the control unit for the DSC (Dynamic Stability Control), meaning that the corrective inputs are applied up to ten times faster than in conventional systems.

Near-actuator wheel slip limitation is fitted on both the rear-wheel-drive BMW i4 eDrive40 and the all-wheel-drive BMW i4 M50. The near-actuator wheel slip limitation is designed to bring the advantages of rear-wheel drive to the world of electric mobility in the BMW i4 eDrive40, whereas in the BMW i4 M50 it is set up for optimum, rear-biased distribution of drive torque between the two axles.

[Pankrivoklat]

Unfortunatelly all this PR bullshits brings more questions than answers It is VERY UNCLEAR what “near-actuator wheel slip limitation” really means in technical manners of electro car like i4. BMW uses the same technology (called ARB) even in ICE cars like 1 series and even 2 series so its nothing unique to electro cars. Hence it leads me to thoughts it is more about location of sensors and control module than about mechanical technology of solution. Thats the reason BMW primary mentiones eliminating the long signal paths to the control units etc.

Can you please help me find those informations in BMW press info?

1. What exactly causes reduce of braking power on each wheel at mechanical basis to reach ABS functionality? Eg. what kind of ABS technology is BMW i4 M50 equipped?
   
2. If the answer is “somewhere somewhat inside” i ask - is there some clutches inside? Or additional brake mechanism? Or does it rely just on stopping power of recuperation? Is it enough for ABS/ESP functionality?
   
3. What kind of differential is located (inside or outside) of each i4 M50 axle?

[techwhiz1]

Originally Posted by Pankrivoklat

Unfortunatelly all this PR bullshits brings more questions than answers It is VERY UNCLEAR what “near-actuator wheel slip limitation” really means in technical manners of electro car like i4. BMW uses the same technology (called ARB) even in ICE cars like 1 series and even 2 series so its nothing unique to electro cars. Hence it leads me to thoughts it is more about location of sensors and control module than about mechanical technology of solution. Thats the reason BMW primary mentiones eliminating the long signal paths to the control units etc.

Can you please help me find those informations in BMW press info?

1. What exactly causes reduce of braking power on each wheel at mechanical basis to reach ABS functionality? Eg. what kind of ABS technology is BMW i4 M50 equipped?
   
2. If the answer is “somewhere somewhat inside” i ask - is there some clutches inside? Or additional brake mechanism? Or does it rely just on stopping power of recuperation? Is it enough for ABS/ESP functionality?
   
3. What kind of differential is located (inside or outside) of each i4 M50 axle?

1. BMW says the motor control is part of the system.

2. The transmission is integrated with the motor. So nobody currently knows what's inside.

3. There is no need for outboard rings with hall effect sensors at the wheels to detect rotational difference. You can place that at the transmission and reduce wiring and points of failure. (That's what I would do.)

4. Since the brake pedal isn't mechanically connected and is drive by wire and the braking is fully integrated with regeneration; ABS is going to be an combination of maximum braking and regenerative recovery.

[4monks]

Folks - I suspect a couple of things are being muddled here...

a) Sensors -- for the BEV version, the rotaional sensors can be in the motor for the driven wheels. For the ICE version, more traditional wheel located sensors (also for the non driven wheels for the 2WD BEV).

b) Slip limitation - when it refers to slip limitation being done at the electric motor, this is almost certainly for acceleration and regen braking with no pad braking). For ABS braking, when the pads are being used aggressively causing lock up, this will almost certainly be pad pulsing per normal.

Regarding the original question, synchronisation of electric power to front / rear and balancing is far easier for electric motors than ICE motors because of the virtually instantaneous nature of applying / removing power under electronic control. That said, the left / right balance is more traditional when served by a single motor and diff, so ABS braking might be used to limit over rotation in such a situation. We will need for details on the L/R diff to confirm this.

[footie]

Originally Posted by Pankrivoklat

There must be some significant intelligence somewhere between those two separate axles which provides all the 4WD stuff. Its not easy task to sync two separate engines (rated at different power output) to drive seamlessly and safe 4 wheels of one car when there is not direct mechanical connection between them. And yes, BMW is very loudly quiet about it. Weird

I was wondering the same thing which makes what Porsche/Audi have done with their Taycan/E-Tron GT all the more impressive as their rear motor has a two speed gearbox.

[Pankrivoklat]

I heard it was VERY difficult task during development of BMW i8 to sync its ICE with the electro-motor in one car on two separate axles. So i was wondering if the same logic is used nowadays in i4 etc.

[techwhiz1]

Originally Posted by Pankrivoklat

I heard it was VERY difficult task during development of BMW i8 to sync its ICE with the electro-motor in one car on two separate axles. So i was wondering if the same logic is used nowadays in i4 etc.

ICE would be more difficult; but in that case I would sync the electric motor to ICE as that is the easier of the two. In that case you let the ICE be the independent and the electric motor be dependent. You read the instantaneous speed and position of the ICE and match that with the electric. It's even easier now with faster processors.

Syncing two electric motors with position and speed sensors in them is something that is done all the time in computers. Spindle synchronized hard drives come to mind.

You have a control system with feedback.
Both motors running off the same.controller monitoring position and speed.

[gunslinger1976]

I can’t answer any of these questions but I’ve got an i4 M50 ATM on loan and took it out for a good run tonight and it’s very good indeed. I’ve owned various M cars and whatever they’ve done feels almost identical to a mechanical LSD at the rear. I will be buying one.

[Rickardg]

Hi,
Any new knowledge in the topic of power distrubution between front and rear axle?
They do use the "good old" rotation sensors at the wheel hubs, so i guess that the "near actuator wheel slip" story is about that its controlled by the inverter that is integrated in the engine/bearbox case.

[Rickardg]

Found this info that gives some info about how the functionality of the electric powertrain is set up.

[freshxdough]

Originally Posted by Rickardg

Hi,
Any new knowledge in the topic of power distrubution between front and rear axle?
They do use the "good old" rotation sensors at the wheel hubs, so i guess that the "near actuator wheel slip" story is about that its controlled by the inverter that is integrated in the engine/bearbox case.

I'm sure the gearbox and electrical machine also has rotation sensors as well which would likely transmit far faster than the wheel speed sensors.

[Wunsch]

I'm curious about this too. One of the things I really like about my current gas-powered xDrive car is the way it takes steering angle into consideration when allocating power between the front and rear. When the steering wheel is turned, it shifts a lot of the power to the rear to avoid overloading the front tires (which also has the benefit of giving more of a RWD feel). As you unwind the steering wheel coming out of the corner, the power transfers smoothly forward to help you accelerate out.

This is a lot easier to feel if you're driving in the snow, because you can do it at much lower speeds. It's also completely hidden by the regular DSC system, but if you switch to a DTC mode, there it is.

So I'm really hoping they've kept all of this intact as they recreate it in software for their electric vehicles.

[cruzer666]

Originally Posted by Wunsch

I'm curious about this too. One of the things I really like about my current gas-powered xDrive car is the way it takes steering angle into consideration when allocating power between the front and rear. When the steering wheel is turned, it shifts a lot of the power to the rear to avoid overloading the front tires (which also has the benefit of giving more of a RWD feel). As you unwind the steering wheel coming out of the corner, the power transfers smoothly forward to help you accelerate out.

This is a lot easier to feel if you're driving in the snow, because you can do it at much lower speeds. It's also completely hidden by the regular DSC system, but if you switch to a DTC mode, there it is.

So I'm really hoping they've kept all of this intact as they recreate it in software for their electric vehicles.

See if this answers your question. It doesn't go into crazy technical details, it's only a 3 minute video, but describes what happens with power distribution when you're turning.