Performance Indices for Motorsport Drivers Analysis

Performance Indices for Motorsport Drivers Analysis Flavio Farroni, Ernesto Rocca, Aleksandr Sakhnevych, and Francesco Timpone(&) University of Napoli, Naples, Italy {flavio.farroni,ernesto.rocca,ale.sak, francesco.timpone}@unina.it Abstract. The present paper aims to propose performance indices able to characterize the driving abilities of a car driver in the motorsport ambit. These indices could be used both to improve drivers performances and to conduct comparative analyses between professional and non-professional drivers. The data used for the analysis come from a Formula 4 vehicle and have been acquired by means of a specific data logger. Some indices, suggested by the specific literature in the motorsport vehicles, have been analyzed and employed on the data acquired on track during races. The results were not so satisfactory especially to evaluate the performance of a non-professional driver. The proposed indicators defined as the product of the accelerations along one determined direction (longitudinal or lateral) for the corresponding velocities seem to be suitable to be used as performance indices for the pilot in all the three main phases of a curve. The analysis of the data shows that these indices are quite reliable even if, in some particular cases, they show little discrepancies. This happens because the indices must be interpreted differently in dependence of the various types of curve, which are diversely approached (e.g. a chicane or a hairpin). Further development will improve the indicators according to the type of curve, trying to give an overall performance indicator for each curve. Keywords: Driver Key Performance Indices (DKPI) Travelling in curve
Vehicle dynamics 1 Introduction In the highly competitive motorsport ambit one of the most important challenges is the definition of driver performance indicators useful to characterize the driving abilities and the style of a pilot. Usually during motorsport competitions numerous signals coming out from various sensors positioned on board are acquired to characterize the vehicle behavior, while, as concerns the driver performance, just one indicator is commonly used: the lap time or the split time. The definition of reliable and objective driver performance indices, not only based on time, could be very useful for different reasons. First of all they could be used to improve driver performance, moreover they could be useful to make comparisons © Springer Nature Switzerland AG 2019 G. Carbone and A. Gasparetto (Eds.): IFToMM ITALY 2018, MMS 68, pp. 123–129, 2019. https://doi.org/10.1007/978-3-030-03320-0_13 124 F. Farroni et al. among different professional pilots or between a professional and a nonprofessional pilot - in the latter case with the aim to train and improve abilities of young motorsport drivers. In the vehicles dynamics literature there are some studies concerning the analysis of the driver behavior in the traffic [1] or inattentive (cell phones, noise, etc.) [2–6], while it is quite difficult to find studies [7–14] concerning the definition of pilot performance indices in motorsport. Some indices, proposed and adopted by the specific literature for sport vehicles, employing experimental data acquired on track during races, appear in some cases not so satisfactory, especially for evaluating the performance of a nonprofessional driver [7]. The present study takes origin from these considerations and its main aim is to define proper objective performance indices able to characterize the driving style of the driver and the performance of the driver on a competition vehicle to describe the driving abilities and the behavior of the pilot driving on a track. The test activity was conducted on track and then continued with the processing of data acquired both during some private tests sessions and during the competition weekends of the Italian Formula 4 championship. To process the data acquired by a data logger (produced by AiM Tech Srl), a MATLAB script able to evaluate the necessary parameters and performance indicators has been developed. 2 Experimental Set-up The system installed on the vehicle and employed for data acquisition is detailed and described here below. The adopted data logger is the EVO4 model by AiM (Fig. 1). It is a modular acquisition device with an integrated GPS, a triaxial accelerometer, five channels for analogic inputs, two wheel speed inputs, a magnetic or optical sensor input, ECU input for the acquisition data coming from the Engine Control Unit (ECU) via CAN, EXP for the external expansion modules, RPM for motor rpm acquisition, USB for downloading the acquired data. Fig. 1 AIM EVO4 data logger Performance Indices for Motorsport Drivers Analysis 125 The internal memory of the data logger is 16 Mb, while its sampling rate is 5 kHz. The sampling frequency of the signals coming from the brake pressure sensor and from the potentiometer measuring the rotation of the steering wheel was 50 Hz, while the sampling frequency of the signals coming from the GPS module, the triaxial accelerometer and the engine control unit (ECU) was 10 Hz. The GPS module of the data acquisition unit allowed to obtain the following measurements: “GPS Speed”: speed; “GPS LatAcc”: lateral acceleration; “GPS LonAcc”: longitudinal acceleration; “GPS Slope”: slope of the road; “GPS Heading”: vehicle direction in degrees (± 180); “GPS Gyro”: yaw rate in degrees/s. This value is calculated from the tangent to the trajectory traveled by the vehicle unlike the measurement coming from the gyro sensor calculated from the curvature of the vehicle. The triaxial accelerometer allowed to measure lateral, longitudinal and vertical accelerations. This sensor was positioned very near to the center of mass and the acquired accelerations were reported to the center of mass. 3 Performance Indices 3.1 Throttle Acceptance The throttle acceptance [7] is a parameter to evaluate the performance of the driver in the curve exit. It can be defined as the amount of lateral acceleration where the driver is able to reach full throttle (curve exit) compared with, or better expressed as a percentage of the maximum lateral acceleration developed by the vehicle during the entire curve. This indicator must be as close as possible to one hundred percent to minimize the curve travel time (when the driver does not accelerate or brake). This parameter works well for curves travelled at low and medium speed, a little less for fast curves. In Fig. 2 is reported a comparison between the Throttle Acceptance values evaluated for the 8 curves of a track in two laps (on the x- axis is indicated the curve numbered sequentially on the circuit, on the y-axis is reported the value of the Throttle Acceptance for each curve), the blue one by a professional driver, the red by a nonprofessional one. It is possible to see that it is quite difficult to correlate the TA with the best driver performance because not always the professional driver has a higher value of the TA even if its lap time is shorter. 3.2 Brake Pressure The brake pressure, measured by sensors located downstream of the two pumps (one for the front and the other for the rear brakes) is one of the most important parameters to evaluate braking performance. The ability to develop a high value of this signal, allowing to delay the braking phase, decreases the space needed to brake and therefore 126 F. Farroni et al. Fig. 2 Throttle Acceptance for two laps (blue: professional driver, red: nonprofessional driver) the lap time. The two most important parameters affecting braking are the braking length and the maximum pressure reached. Generally for high performance it is desired to get a high brake pressure value and a low brake length value. An interesting indicator of driver braking performance is obtained dividing the maximum pressure value in the braking phase by the distance traveled in the same phase; a high value of this indicator translates into an increase in performance and a reduction in lap time. 3.3 Proposed Indicators The performance indicators proposed in this paper Px and Py are defined as the product between the acceleration along one determined direction (longitudinal or lateral) and the corresponding speed [15, 16] when describing a curve, they are very useful to analyze both the apex and the exit phase of the curve. Px = Ax
Vx Py = Ay
Vy To improve the performance reducing the time intervals in which the driver does not use the accelerator or the brake pedal, it is necessary to have a high speed during cornering, but this may affect the exit curve phase. Analyzing these indicators, it has been seen that, a high peak of them during curve travel, very often corresponds to a high peak at the curve exit. By a physical point of view the above parameters, multiplied by the total mass (vehicle and pilot), give a power. So, the indicators represent a specific power, measured in W/kg. They can be considered as specific powers associated with the vehicle undergoing certain accelerations at determined speeds values in a curve. This implies that at a fixed speed a higher value of this indicators means to be able to develop a higher interaction forces between the tires and the road, bringing the vehicle closer to the limit of grip. Performance Indices for Motorsport Drivers Analysis 127 4 Case Studies Results In Fig. 3 it is reported, as an example, the comparison between the Px indicators evaluated in two different laps, the first one performed by a professional driver (green curve), the second one by a nonprofessional driver (red curve) driving the same vehicle, with the same set-up on the same day of testing. The conditions of the asphalt were about the same, as well as the weight of the two pilots. Fig. 3 PX indicator for two laps (green professional driver, red nonprofessional driver) As can be seen in Fig. 3 the value of the longitudinal performance indicator is always higher for the best lap except in one case. This last is a curve very particular since at the curve exit the vehicle is on the curb at full change of direction, this means that, despite the peak value of the Px, this circumstance does not imply any advantage for the lap time. 5 Conclusions In the paper two performance indicators to characterize the driving abilities of a car driver in the motorsport ambit have been described and tested. The indices have been obtained by multiplying the accelerations with the speed along a particular direction in the curve, so representing a specific power. Some comparisons with other indices, suggested by the specific literature, have been conducted by adopting experimental data coming from a Formula 4 vehicle during a track race. The proposed indicators seem to be suitable to be used as performance indices for all the three main phases of a curve to the pilot. Results were so satisfactory especially for evaluating the performance of a non-professional driver. 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