trends from race data. One point I haven’t touched
on is how we deal with a ride height sensitive aero map. Believe it or not, it’s actually not all that difficult. You need to export dampers and wheel loads. If you have them, you need to know the look-up table of drag for front and rear ride height. The only challenge is you’ll need to do this with either a Visual basic, Matlab or Maple script. This is now well beyond what you can do with a maths channel.
Figure 2: required channels for engine curve calculation
resistance drag in equation 2. I have done this for two reasons. Firstly, as a rough rule of thumb, aero drag usually dominates everything. I’ve only dealt with a couple of racecars where rolling drag has had a significant effect. The second reason is for simplicity. Yes, you can add rolling drag into equation 2, the only drawback being you need pushrod loads to determine the rolling drag. The important thing is I want you to do this, which is why I’m keeping it simple. When you have done this, you
Figure 3: engine power curve from race data
plot rpm vs torque and engine power and do a curve fit. It will
THEORY INTO PRACTICE But how does this stack up in real life? To see, a sample ChassisSim simulation is shown with the power curve generated in figure 3. While this isn’t perfect, the acceleration is very close and the speeds are within a km/h. Again, because this is live data I’ve had to remove all the scales. What is abundantly clear, though, is that you have something you can start using to think about gear ratios and use for sensible vehicle performance analysis. I think you can also see we have obtained quite a bit of data on what the car is doing. We can also see that this is a very effective work around when we don’t have engine data.
"Something you can start
using to think about gear ratios"
Figure 4: example of simulated vs actual data using a race data-generated power curve So all we need to do now is
convert each individual bit of data (speed and acceleration) into SI units, for which you can easily create a column. Then you need to create a new column with this formula and you are done. If you
are feeling brave, you can put a column next to it and convert this into either kW or bhp. Before I discuss results,
let me briefly cover what we have discussed here. You’ll notice I haven’t included rolling
look something like figure 3. First things first, my apologies
for blanking out the data, but unfortunately, the specifics are confidential. However, what it does illustrate is that you can get some very clear and discernable
In closing then, calculating an engine curve from nothing isn’t hard. All we need is some rough idea of maximum power, some good data and the appropriate channels and we are well on our way. While this is not perfect – and I don’t claim that it is – this technique will get you a significant way down the road so you have a usable engine curve you can use to engineer the car. Also, the beauty of what we have discussed is that you can make it as simple or as complicated as you like. It also provides a valuable tool that you can put in your analytical tool set.
May 2012 •
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