It is very easy to calculate dRPM / dt, which is proportionate to torque. However, when doing tuning runs, you want to be able to compare the result after changes (like changes in ignadv).
Analyzing the logged runs, in RPM-bins, in a similar way as lambda, VE and ignadvn is tuned is very helpful. Something like this (except for real data, and colored nicely):
| RPM | 3000 | 3500 | 4000 |
| MAP | 110 | 140 | 170 |
| ignadv | 24 | 25 | 27 |
| EGT(C) | 552 | 603 | 612 |
| lambda | 0.82 | 0.81 | 0.8 |
| torque dRPM/dt | 1600 | 3100 | 3900 |
RPM => power calculation is very simple
Some of the input parameters are often estimated though (a well known such parameter: m=mass, you can measure that too, of course)
- P=F*v
- F=m* (dv/dt + anull) + Fnull
- where anull = g*slopepercent (like g*0.04 for a 4% slope to keep the car climbing without deceleration)
- Fnull = some force to keep the car running without decel even on a 0 slope. Fnull=500N means that 500N * 20m/s = 10kW sounds reasonable below 100km/h (at high speed this climbs as v**2, due to air drag)
- so P=v* (m* (dv/dt+anull) + Fnull)
- v = RPM * const
- where, with audi in gear2: const = 1/2.13/4.11 * wheel_circumference
- wheel_circumference=1.87m (if you measure diameter and calculate 0.6m * pi, you get 1.885m, but remember the tyre is somewhat pressed in)
- so the audi wheelspeed at 7000 RPM and gear2: 7000 / 60 /2.13/4.11 * 1.87 = 24.9 m/s = 89.7 km/h
dRPM/dt => Nm (torque) calculation
So (with the 1600kg audi in gear2) what is the const in the torque=const * dRPM/dt to get the result in Nm ?
- dRPM / dt is given
- as in the upper formula, force on the wheels: F=m* (dv/dt + anull) + Fnull
- wheel torque Mwheel = F * wheelradius
- motor torque Mengine = Mwheel / drivetrain = Mwheel / 2.13/4.11
- v (in m/s) = RPM/60 / 2.13/4.11 * wheel_circumference
- m=1600kg (1400kg + spare tyre + fuel + 2 persons)
- wheelradius = 0.3m
- Fnull = 500N
- the uphill we use for tuning: anull = 0.03 * 9.81 m/ss
- this contributes to less than 10% of the power, at dRPM/dt = 1000 RPM/sec it is like 3.6 + 0.29 for the accel and the climb components
octave snippet:\nÿ1ÿ
..
Evaluation
The gear can be seen very clearly. Torque 200-ish is gear2, and 300+ is gear1 (the calc is made for gear2 so these that are in fact gear1 are not real numbers). Considering the value of (dRPM/dt) / avgMAP, it could be automatically judged (unless the terrain has very tricky slopes)
TODO-s:
- better filtering. Sometimes a +-80 RPM spike (which is otherwise harmless, eg at 5500 RPM) can cheat the calculation, because it's based on appr dRPM/dt=450 RPM in appr 0.400 sec
- for very same reason, the given run sometimes ends a bit earlier than in real (a small downspike makes the algorithm think the acceleration has ended)
- better annotation of input files (the time in seconds is already seen, but we should see which file it was from)
- parametrization of input data: currently wired in for mass and gear2 drivetrain ratio and wheelsize of Marcell's audi200
- also, input files currently must be c:\races\*.log and output is always c:\races.csv
- colored display inside v3GUI: currently saved to csv, takes 3 click to open in spreadsheet and use "freeze-panes"
- proper non-debug release. Now [v3gui-debug] is not for human consumption. It contains big debug-dlls, but lacks mainframe.xrc (copy from a v3gui release). The program automatically processes c:\races\*.log upon startup to c:\races.csv output file (will be in experimental/loganalysis menu, with some widgets for input data: these data must be saved to session, so it does not need to be retyped every time)