Application Research On The Tolerances Back-stepping Design Of Engine Precision Manufacture Based On Engine Performance Requirements

With the growing importance of energy conservation and emissionsreduction, China’s automobile engine industry keeps upgrading andchanging the way of production, so engine manufacturing precision hasreceived more and more attention. Engine parts design tolerance not onlyinfluences the production quality and manufacturing costs, but also is thekey factor in improving engine performance consistency. Generally, enginecalibration is only conducted on one engine, and its calibration results,such as the ignition Angle and inlet valve timing, are just directly copied tothe other engines’ ECU. Even if in the same batch of engine, due to thedifferences of manufacturing precision, compression ratio will also havecertain or even high fluctuations. So In the same batch, the operationvariables like ignition angle of the others engines may be not as optimal asthat of the calibration engine, causing fluctuations in performance and fuelconsumption of the same batch engines or even causing some enginesknock. So it’s practically significant that improving the manufacturingaccuracy of components and parts that affect engine compression ratio andimproving the consistency of the compression ratio. What’s more, in thesame multi-cylinder engine, the fluctuations of engine components and parts cause the fluctuations of compression ratios in the same engine.However, in the engine test bench calibration, only the cylinder that hasthe maximum compression ratio will be made the standard for calibrationand surely can work in the best operating parameters, while the othercylinders may not. As a result, the engine’s fuel economy and powerperformance and the consistency between the cylinder and the cylinderengine performance may be bad. Therefore, this paper investigates how tobuild a model that connects those component tolerances and engineperformance fluctuations by using compression as a middle factor. Thenthe engine performance uniformity can be improved by optimizing the keydimension tolerance.In this paper, a1.2L displacement4-cylinder gasoline engine wasused to build a geometrical correlation between the relevant dimensionsand the compression ratio, as well as the simulation model between thecompression ratio and engine performance using AVL-BOOST. Based onthose models, the tolerance requirement of the compression ratio wasderived from the required engine performance consistency; then thetolerance of the key dimensions influencing the compression ratio wasoptimized using a DE algorithm. The Monte-Carlo method, combined withthe BOOST simulation, was used to verify the optimization results. Theoptimized key dimension tolerances could result in significant reductionson engine torque fluctuation of32.5%and fuel consumption fluctuation of31.8%, respectively, in average, which improves the engine performanceconsistency.