How does the REx work?

[ThomasNurburgring]

Hello i3 owners,

Currently I am helping with a PhD project and a part of this research is concerned with electric vehicles.
At the moment I have to research the range extender of the i3 and I have several questions I hope I can ask here:

1. The range extender of the i3 does not power the wheels directly, but charges the battery. Is that correct?
2. Is it the only electric car that has a range extender that does this (the Volt's range extender can power the wheels directly if I am not wrong)?
3. Is the range extender engine coupled to a generator?
4. If so, what generator? Does anyone have a name or specifications of it?

I hope I am allowed to ask this kind of questions here and all help is greatly appreciated!

Thanks in advance,
Thomas

 

[RonRPH]

1) range extender only charges the battery. And only charges to 6% (if it can; at some levels- high speeds and hills it may not be able to maintain this) or if coded, to a selected value of 75% or below- again maintaining it if possible.
2) I believe you are right.
3) Coupled to a generator to generate electricity of course.
4) Sorry, do not know the name. From what I gather it is a very efficient generator. If you search in the forum I am sure there are values for the maximum power it will supply.

 

[PDXelectric]

1) range extender only charges the battery. And only charges to 6% (if it can; at some levels- high speeds and hills it may not be able to maintain this) or if coded, to a selected value of 75% or below- again maintaining it if possible.
2) I believe you are right.
3) Coupled to a generator to generate electricity of course.
4) Sorry, do not know the name. From what I gather it is a very efficient generator. If you search in the forum I am sure there are values for the maximum power it will supply.

I believe the Volt engine can either generate for the battery or couple to the drivetrain depending on conditions. The big difference is that the i3 is designed to be electric only with the engine as a "range extender" for backup purposes. I believe most i3 Range Extender users rarely use the extender during daily commutes, etc.

 

[jadnashuanh]

The Volt's engine/motor/transmission control logic is fairly complex. Normally, the engine only charges the battery when required, but at higher speeds, the transmission will enable the engine to help power the vehicle directly via the transmission...from what I've read, that situation doesn't occur very often, and it does it because it can let the electric motor run slower, since at higher rpm, it starts to become less efficient. The number I seem to remember is a max of 10% engine power to the wheels, the rest electric, which it being all-electric most of the time.

The powertrain in the i3 is more similar to an electric locomotive in that the engine is only hooked to a generator, and never directly drives the wheels - the electric motor does that...I think they call that a serial hybrid powertrain.

 

[ThomasNurburgring]

Thanks a lot for all the replies!

Now I completely understand how the drivetrain of the i3 functions (and how it differs from the Volt's drivetrain).
I hope I will be able to find the name and specifications of the generator.
If anyone knows more about the generator, all help is welcome of course!

 

[imolazhp]

Magic

 

[janner]

The generator is a synchronous permanent magnet machine. The ReX generates between idle speed (2200rpm/2400rpm) and a max continuous of 3600rpm with 4300rpm used at very low battery SOC. The ReX Electronics (REME) converts the generator AC to DC to charge the battery or drive into the motor electronics. The generator is max 94% efficient (and probably made in-house by BMW?) and the REME is max 96% efficient and designed and manufactured by Bosch.

 

[ian4x4]

If you haven't already discovered there is quite a lot of information on line.

Try googling 'BMW i3 manufacturing'

or 'BMW i3 munro'

for some interesting videos.

example
https://www.bing.com/videos/search?q=bmw+i3+manufacture&&view=detail&mid=01F4E99AFCCF6FC5AAA701F4E99AFCCF6FC5AAA7&FORM=VRDGAR

 

[louisgrenier]

Some say that the engine is made by Rotax. Might be true.

 

[Stevei3]

Hi,
the engine is made for BMW by Kymco.
Regards, Steven

 

[ThomasNurburgring]

Thanks for the help!

After contacting BMW about 5 times, they shared some specifications:
Brand: Valeo
Voltage: 250V
Cont. power DC: 23.300W (at 330V and 4.800rpm)
Efficiency: 94%
Diameter: 300mm
Length: 115mm
Mass: 26kg

Unfortunately, this is not a standard generator that can be bought.
Since our project requires us buying one with comparable specs, we are now looking for a similar one.
So, if anyone knows how to buy one of a BMW i3 or a comparable one, please let me know!

 

[janner]

Are you sure it wasn't 4300rpm and not 4800rpm?

Designation Unit W20K06U0


Design R2
Displacement [cm3] 647
Firing order 1-2
Bore/stroke [mm] 79/66
Power output [kW (HP)] 25(34) at engine speed [rpm] 4300
Torque [Nm (lb-ft)] 55 (40) at engine speed [rpm] 4300
Compression ratio [ε] 10.6
Valves per cylinder 4
Fuel rating [RON] 95
Fuel [RON] 87- 98
Exhaust emissions legislation SULEV II
Additional range in REX driving [km] (miles) 120-150 (74–90)
Digital Motor Electronics RDME