Damien takes Zombie GS450h on dyno

[SuperV8]

Messing with wheel torque calculations, i'm just not seeing it?

From the numbers i'm looking at here (best guess ofcourse based on published figures) a RWD ID.4 puts down circa 4000nm wheel torque from start upto whenever it hits the power limit (info is vague but assuming its all pretty linear, somewhere around 5000rpm or ~35mph).

This dyno pull suggests the E39 is putting down less than 2000nm wheel torque given the diff ratio guess above and various assumptions (ie factory tyre size and the dyno speed plot being accurate)

Perhaps my numbers arent perfect and i'm happy to be corrected if i've missed something?

Using your 2.81 diff ratio and 1.9 gear reduction (5.339 total reduction) and 255/40 17 tyres I make it about 7200 motor rpm at 100mph.
Using low gear of 3.9 (10.96 total gear reduction) basically halves the speed at 7200rpm to 49mph - or double the wheel torque.
Assuming 225hp at 7200 I make it about 222Nm motor torque at 7200rpm - which would be 1185Nm wheel torque in high (at 100mph) or 2432Nm in low gear (at 49mph).

The ID4 rear motor is 310Nm max torque I believe and has a gear reduction of 10:1 which gives a good off the line wheel torque/force of 3100Nm
Max speed of 112mph
Large tyres of 235/60/18
At that top speed the motor will be turning at 13000 - some way short of its 16,000 max.
Using the same 100mph and using the higher power version of 204hp it will be turning at 12000rpm which would be 121Nm motor torque - which would be 1210Nm wheel torque so basically the SAME wheel torque as the beached whale - but going through much larger wheel diameters!

This is an interesting graph of the GS450h gearbox of how the gear ratios relate to torque and speed.

[Aragorn]

yeah

So my numbers suggested 12.9:1 reduction on the ID4, with the 310nm figure and a max speed of 99. Those came from a VW technical PDF.
Giving a bit over 4000nm from standstill to about 30mph or so, at which point you'd hit the 200hp power limit and transition into power limited mode with declining torque. I dont know if it can maintain 200hp all the way to the maximum speed, but one imagines it manages to maintain most of that 200hp in the main accelleration zone from 30-70ish.

The Dyno plot can be converted to wheel torque easily enough if we have a tyre size and speed. Using the standard E39 tyre size of 235/45r17 and the speed from the dyno run, we get circa 1800nm wheel torque in the torque limited section from the start of the run at ~60kph to peak power at 120ish. So one can surmise it was making 1800nm from 0 all the way to 120kph. Which is why i felt it was somewhat lacking.

A shorter diff ratio would help no end to get that up to a nicer figure, and get the motor moved more into its "ideal" window. Currently its geared for extremely high speeds and its losing usable performance as a result.

Low gear would ofcourse be the alternative, however from what i understand, managing shifting for that doesnt yet exist? The gearing in Damiens car is tall enough that he could almost run it in low all the time!

[rstevens81]

I'm sure Damian would improve performance on the Dyno if you were to fund him a high ratio LSD, driveshafts and the Dyno cost.

[royhen99]

Just did some rough calculations taking traction into account.

With slicks ( 0.9 coeff friction ) max torque 2170nm

with typical road tyres ( 0.7 coeff. friction ) max torque 1520nm

So 1800nm will potentially give wheel spin on a dry road with the current gearing

Calcs assume mass=1530Kg and wheel radius of 0.322m

[Aragorn]

I'm sure Damian would improve performance on the Dyno if you were to fund him a high ratio LSD, driveshafts and the Dyno cost.

Can we not have a discussion without it turning into barbs? We're all here to understand things.

Many have asked about the performance of this transmission, and Damien has very helpfully provided some data regarding its performance. Ofcourse that is fantastic.

Are we somehow not allowed to analyse that data and pose questions around it? Compare it with other machines and explore possibilities for improving it? Investigate any areas that look unusual or odd? Isnt that the entire point?

My immediate thought looking at the plot, was that it spends too long in the torque limited zone (the result of which being far less "area under the curve"). So i wanted to explore why that was, and after a bit of discussion its become evident that its geared extremely tall.

If damiens happy with the car then thats great. My take away from the dyno and subsequent discussion is that gearing is important, and that someone building with this trans should be trying to get their gearing into a nice area. Ideally hitting maximum gearbox RPM at say 100mph. My proposed project has ~4.2:1 reduction and slightly taller tires, so actually quite close to the ideal zone.

From this discussion and the points made around wheel torque i then decided to graph wheel torque of the existing ICE and Autobox, and compared it to simulations of a factory EV like the ID4 and also damiens dyno plot. That helps me visually model the system and understand how it might perform. I was going to post them, but it would seem people dont really care for such discussion.

[tom91]

all the info you guys could wish for is just a google away...

https://slideplayer.com/slide/14432904/

So the MG1 Planetary set Output rotational speed before being fed into the output shaft is 1:-0.436 (note reversing)

MG2 can do 1.9:1 or 3.90:1 ratio to the output shaft.


This means the following:
Gear selected has no impact on MG1 speed, MG1 is fixed ratio to the output shaft. This will limit the max vehicle speed.

Relative to output shaft
MG1 speed is -2.29:1
MG2 speed can be 1.9:1 or 3.9:1

A very good doc with info
https://www.osti.gov/servlets/purl/947393

MG2 is rated at 300Nm and max 10,230 rpm
MG1 info is sparse as it is not meant to drive the vehicle and only used to do E-CVT things and start the vehicle. Thus it would be smart to use the same speed limit as MG2.

this means that Mg1 should be viewed as the motor limiting top speed, with a max allowed output rotation of the gearbox being 4460rpm

[Aragorn]

Your suggestion of MG2 Max at 10230 is interesting. As discussed in the other thread about max RPM (did you mean to post this over there?), the advertised top speed of the GS450h is 155mph.

Working back from the tyre size (255/40r18) and diff ratio (3.26), the propshaft/gearbox output needs to be turning a bit over 6500rpm to achieve 155mph. Which suggests MG2 would be doing near 12500rpm at that point?

Perhaps the discrepancy is the OSTI doc is talking about the LS600h? Perhaps it has different gearing and thus ends up with a different max speed?

Ofcourse MG1 limits are less clear and arent coupled to road speed (in the factory application), so that part is harder to nail down, and given the 2.29 ratio vs 1.9, means it'll be turning faster than MG2, so as you say, MG1 is probably the limiting factor for gearbox speed, we just dont know exactly where that limit lies.

[tom91]

we just dont know exactly where that limit lies.

Correct.

In the end all you can do is make estimations based on information gathered. My "suggestion" is from gearbox information derived out of a presentation not a suggestion. If there are no clear published facts you can deduce things from various sources, so information might vary.

No body here will warrant what you decide to do with your setup so it is up to you to decide on safety margins and the reliability of the data.

Yes your math checks out. Then this does not really matter as it is MG2 which has a speed ratio of 0.83 to MG1.

This does mean that MG1 will limit top speed and even if you assume 12.5K or 14K rpm working the maths backs it yields 5458 or 6113 rpm on gearbox output.

[Clrs]

The dyno results are disappointing. MG2 is rated at 165kw and 300nm. MG1 is locked I guess (input shaft)? So it must give another 100kw and 200nm. Where are they? If MG1 is not locked and only MG2 is driving the car, the transmission loss is around 25%? Pretty much for RWD car.

If MG1 limits top speed, it sucks and must not be locked and used then. Lexus LS600h with the same L110F gearbox is capable of 270km\h easily. So MG2 is ok with that speed. Moreover just checked the GS450h is also 270km\h capable.

Maybe for those who need top speed (me) and a bit of power, it's a good idea to use two MG2s from two L110 gearboxes connected to one another and cut the MG1 as useless to save weight?