TECHNOLOGY – DATABYTES /* Throttle ON
Constant Throttle full is the threshold set which determines what throttle percentage is deemed as ‘’ON’’ */ choose ( [Throttle Percentage] > CONST (Throttlefull) , 1 , 0) /* Time ON Throttle */ integral ( [Throttle ON] , Hold ) /* Distance ON Throttle */ integral([Throttle ON] * ([XKart Speed]/3.6), Hold)
Figure 4: histogram of the real rpm spread with the calculated ones alongside. This can give vital clues about gearing
channel calculates the difference in time at a set distance. For example, if datum data set A takes one second to travel 10m, and data set B takes 1.5 seconds, the compare time channel will give a delta time of -0.5 seconds at 10m. This compare time trace can then be differentiated and plotted on a track map to highlight where time is being lost or gained at a high rate. After the areas that need
improving have been identified, vehicle performance needs to be analysed, and a very useful channel to analyse engine performance is rpm.
SPEED AND RPM Traditionally, the rpm trace is simply plotted on a time / distance plot to identify maximum and minimum rpm on straights and corners and where the rev limiter is active. This
CHALLENGE – identify these Kart circuits 1
Figure 5: it is interesting to look at how the driver’s use of the pedals directly impacts the lap time, especially the time spent using neither pedal, described as the coasting time
information is very useful, but when speed and rpm are combined, more advanced information can be found. On a Kart, using speed, rpm,
front and rear sprocket values and rear tyre circumference, a prediction can be made as to how the rpm range will change when a sprocket change is made. This information is track specific and uses the speed trace with a known gear ratio from an outing to calculate how the rpm trace will change when gearing is changed. This can then be plotted on a histogram for easy analysis. If the power output along the
2
rpm range is known, a look-up table can be used in conjunction with this to plot the engine torque produced for the different gear ratios. This makes selecting the optimal gear ratios for a circuit even simpler.
PEDAL TRACES As well as looking at vehicle characteristics, analysing driver inputs can yield significant performance advantages, too. If throttle and brake traces are
4 3
logged, a useful technique is to use maths channels to calculate the time and the distance spent using each pedal per lap. This allows a quick overview of how the driver is using the pedal inputs throughout a session. The distance on the brakes channel can then be used in further, more detailed analysis, such as to
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www.racecar-engineering.com • May 2012
calculate braking efficiency at a particular circuit. Using a tabular outing report, pedal information can be analysed in a concise and simple way, which gives a perspective not otherwise attained from looking at the raw traces on a time distance plot. Using the three maths channels below, the throttle on distance and throttle on time can be calculated. By using the same principals for the brake pedal and combining brake and throttle channels, coasting information can also be determined.
OVERVIEW By using the techniques outlined in this article, engineers can make sure they make the most use of the data they are collecting. It also shows that, with just a few inputs and the right analysis tools, an engineer can gain far more insight from seemingly basic vehicle data than most assume. This additional information, once analysed and understood, can be translated into set-up changes and focussed driver coaching, which ultimately will make the racecar go faster.
Produced in association with Cosworth Tel: +44 (0)1954 253600 Email:
ceenquiries@cosworth.com Website:
www.cosworth.com/motorsport
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