Results
5.1 RaceLap
5.1.1 Front Grip Factor
Racing tyres are usually available in different compounds. Each tyre model provided by the manufac- turer is divided in categories that correspond to the grip level of the tyre, called compounds or treads.
The categories are usually separated inSoft, MediumandHard, with decreasing level of grip. ASoft tyre has more grip but a shorter life-span than a Hard tyre. Different compounds also correspond to distinct optimal operation conditions like pressure and temperature.
As stated in the introductory text of this chapter, in order to approximate the tyre model to the medium
compound used in the front axle, the grip of such tyres in the simulation must be multiplied by a factor.
The first choice criteria is the smallest factor that gives the same minimum corner velocities verified in the real lap. These points are located before mid-turn (or before the appex) after the deceleration phase when entering the corner and before the acceleration phase when exiting [16]. This is analysed here for these are the points of a lap where the car’s behaviour is fully dependent on the tyre’s capability to generateFyand therefore other parameters are not a source of error.
Figure 5.2 shows the resulting velocity profile for five different grip factors as well the real lap for comparison.
0 500 1000 1500 2000 2500 3000 3500 4000 4500
Track Length (m) 50
100 150 200 250 300
Velocity (km/h)
Real Sim Sim×1.1 Sim×1.2 Sim×1.4 Sim×1.5
Figure 5.2: Real and RaceLap simulated laps for different front tyres grip factor.
The results for a 1.1 and 1.2 factor (also for 1.3 but not shown for simplicity) are close to be identical, with the same happening for 1.4 and 1.5. All of the results shown get identical appex velocities with the main difference being the velocity slope right before the finishing line. Considering this, the final decision for the grip factor will be between 1.1 and 1.4 because those are the smaller values within each group and a second choice criteria must be met.
The 1.1 and 1.4 grip factors, highlighted in Figure 5.3 profiles diverge in the beginning and end of the lap which correspond to points in the main straight line. The 1.4 velocity slope at the start of the lap is identical to the slope of the real lap but the top speed is more accurate for the 1.1 profile. This could mean that when testing, the real car was not in ideal conditions in terms of straight line behaviour (powertrain related issues, for example). To analyse it further, the same simulation was performed for the Le Mans track. Also called the Circuit the La Sarthe[17], the famous 24 Hours of Le Mans semi- permanent race track is characteristic for very long straights. This particularity of the french circuit makes this track ideal to assess the impact of the two grip factors in straight line behaviour. It was observed from the Le Mans simulation with different vehicles that the 1.4 grip factor results, for some cases, in an unusual behaviour in the straights, with the velocity profile suffering of several slope changes during a
0 500 1000 1500 2000 2500 3000 3500 4000 4500 Track Length (m)
50 100 150 200 250 300
Velocity (km/h)
Real Sim*1.1 Sim*1.4
Figure 5.3: Real and RaceLap simulated laps for 1.1 and 1.4 front tyres grip factor.
straight line. This lead to achieving lower speeds in longer straights. It was concluded that using a 1.4 grip factor might induce in unrealistic simulations and so the grip level chosen to simulate the medium tyre compound for the front tyres was set to be 1.1.
5.1.2 Final Results
Finally are presented the final main results from the RaceLap simulation in Figure 5.4. Despite always achieving higher velocities, the simulation gives a slower time. This can be justified by the extra 100 meters of the trajectory simulated. Taking the mean of the RaceLap velocity, 46.59 m/s, the extra 100 meters account for an extra 2.146 seconds, giving a lap time prediction of 1:37.442 for the same trajectory that was done in the best lap of the real test. This result is given in Table 5.1 under ”Predicted real trajectory time”. The top speed registered in the real lap was 257 km/h, with the simulation giving 256.6 km/h. The main difference between the profiles is in the positive acceleration stages whereas in the braking stages the profiles are more similar. All main results are presented in Table 5.1.
Applying equation (1.4), the amount of energy needed at the wheels to perform a lap as simulated in RaceLap is 5.62 kWh. Assuming 100% efficiency for an electric powertrain, this is would be the calculated amount of energy consumed from a battery if AD03 was an electric vehicle. Because this energy actually comes from a combustion engine, this value has to be divided by the efficiency of the powertrain (tank-to-wheel) that is far from the electric vehicles values that come close to 100%. Advised
0 500 1000 1500 2000 2500 3000 3500 4000 4500 Track Length (m)
50 100 150 200 250 300
Velocity (km/h)
Real - 1:38.295 RaceLap - 1:39.588
Figure 5.4: Velocity profiles of both RaceLap simulation (1:39.588) and the real lap (1:38.295).
by the engine manufacturer company, the engine efficiency is considered to be 30%. The gearbox must also be accounted for, in this case with an efficiency of 96.04%. The total energy consumption of the simulated lap is then
E = 5.62
0.3·0.9604= 19.51kW h (5.1)
Because there is no information about the track elevation and the engine shaft moment of inertia, the hill climb and angular inertia terms of equation (1.4) were not accounted for. The resulting energy consumption calculated value is 73.18% from the linear inertia term, 24.52% from aerodynamic drag and 2.3% from tyres rolling resistance.
Table 5.1: RaceLap main results
Real RaceLap Error (%)
Lap Time (min:sec) 1:38.295 1:39.588 1.32
Predicted real trajectory time1(min:sec) - 1:37.442 -0.87
Average Speed (km/h) 164.5 167.7 1.95
Top Speed (km/h) 257 256.6 -0.16
Energy Consumption (kWh) 19.22 19.51 1.5
1Prediction for the real trajectory by subtracting time corresponding to travelling 100 meters at the simulation average velocity from the simulation Lap Time.