A Holistic Approach to Develop a Modern High-Power Density Diesel Engine to Meet Best-in-Class NVH Levels

The ever-increasing customer expectations put a lot of pressure on car manufacturers to constantly reduce the noise, vibration, and harshness (NVH) levels. This paper presents the holistic approach used to achieve best-in-class NVH levels in a modern high-power density 1.5 lit 4-cylinder diesel engine. In order to define the NVH targets for the engine, global benchmark engines were analysed with similar cubic capacity, power density, number of cylinders and charging system. Moreover, a benchmark diesel engine (considered as best-in-class in NVH) was measured in a semi-anechoic chamber to define the engine-level NVH targets of the new engine. The architecture selection and design of all the critical components were done giving due consideration to NVH behaviour while keeping a check on the weight and cost. Extensive 1D crank-train simulations were carried out to ensure that the crankshaft torsional amplitude was contained less than the NVH limit of 0.1 degree for higher-order excitations. Similarly, the flywheel-end speed irregularity was confirmed to be within acceptable limits. A complete engine-level simulation was carried out to simulate the surface velocities which could help to identify the areas with high noise radiation. Based on the results, potential improvement areas were identified and modified to reduce surface velocity. Prototype engine testing in the semi-anechoic test chamber identified further potential improvement areas including the camshaft drive gears, injection pump, engine top, and damper pulley. Acoustic holography technique was extensively used to identify high noise radiating areas. With the incorporation of all these optimization measures, a best-in-class value of 65 dB(A) could be achieved as the average 1m engine noise at the low-idle condition. This paper explains the methodology used throughout the design and development of the engine to achieve the above-mentioned NVH levels.