Engine calibration and driveability evaluation of a racecar 2019-36-0126
The passenger car automakers are always competing to excel in vehicle characteristics related to passenger comfort and driveability aspects. The engine calibration is a theoretical and experimental procedure with the intention to extract maximum efficiency from the engine and guarantee satisfactory levels of driving for both conventional and racing cars. This paper describes the calibration procedure of a Formula SAE race car engine. The engine was a four cylinder 600 cm3 four-strokes with modified intake and exhaust systems, controlled by an engine control unit (Motec M800 ECU). These engines present optimized characteristics for high speed, in exchange for some combustion degradation in some specific operating conditions at low speed that may impair vehicle driveability. Therefore, good tip-in reaction and the progression of the torque delivery are fundamental criteria to increase the vehicle performance, specially, to those submitted to short acceleration distances. The related criteria to the vehicle dynamic comfort has objective values to measure the abrupt engine speed transactions, jerks and acceleration variability related to torque variation. Improvement on such parameters can be obtained by means of main factors that influence in the combustion such as the air/fuel ratio control and the spark timing. In reality, the variations or instabilities in the torque delivery can be verified by analyzing instabilities in engine speed. This paper describes the direct approach with the aim of reducing temporal engine speed variability and compare it to the driveability criteria. Thus, accelerometers were used to quantify the vehicle longitudinal accelerations, decelerations and critical track conditions, such as low speed traction, to evaluate the engine calibration and correlate data in favor of the driveability and performance improvements.