Search Results

The paper quantifies the forces applied to the main bearings of three six-cylinder turbocharged diesel engines and reviews their exciting properties in both time and frequency domains. The engine structure response at the bearing supports and the outer engine surfaces are correlated. It is shown that the engine structure response is a transient phenomenon and is a maximum in the vicinity of the applied force. By representing the engine response in terms of displacement it is possible to recognise the applied force time history and thus the identification of the specific parts of the engine structure primarily excited by moments and by direct force. The displacement technique for quantifying engine response provides detailed information of the distortion of the running engine enabling the prediction of mechanical inputs which can control the turbocharged engine noise.

The paper exemplifies the necessity to quantify the various noise sources present in modern automotive engines. Results demonstrate the non-linearity problems associated with many of the non-running engine rig tests currently in use. A new technique is described for combustion induced noise simulation using hydraulic excite ion. Results obtained using this experimental method are compared with those measured on the running engine.

In this paper the noise of engines of different size, duty and combustion system are compared. Measured differences, not consistent with combustion charges, are analysed in detail and these differences are shown to be the result of mechanical impacts. Results suggest that the kinetic energy of impact is not the only significant parameter influencing mechanical noise, and in the general case the magnitude of the force accelerating a component across a clearance must also be considered. The analysis shows that the dominant parameters affecting the magnitude of the impact change with speed and size of engine and offers an explanation for the apparent discrepancies observed in some previously recorded data.

The paper divides into two parts. First the investigation of the noise of an unconventional design of two cycle diesel engine, including the results of applying known noise reducing features to it. Then taking one component of that engine, the scavenge blower, and re-designing it from first principles to produce a low noise machine suitable for the low noise engine. The final assembly of engine and blower demonstrated that the noise that has been regarded the characteristic of the two cycle engine is in fact that of the Roots type blower and when eliminated the noise level can be quite low. The present test bed noise level of 97/98 dBA at 1 metre shows promise of this type of engine meeting the legislative requirements of the 1980's.

Methods of reducing the noise level of a diesel engine include the suppression of the major modes of block vibration and treatment of the external surfaces. Design methods enable the frequencies and noise levels of these modes to be calculated for a conventionally designed engine. The important modes of vibration, the noise signature and the effect of block modifications of a standard production V-8 engine were found by experiments. These provided the basis for the design of an experimental low-noise engine. Design features include a suffer block, removal of the bottom part of the crankcase skirt, the addition of a single bearing beam, and the use of isolated panels and damped surfaces. The noise reduction obtained was 9 dBA. Most of this is due to the use of isolated and damped nonload carrying surfaces.

This paper describes the relation between the diesel engine structure design, its characteristics of vibration, and emitted noise. Special techniques developed for the investigation of the origins of noise and modes of vibration are discussed. On in-line engines the effect on noise and vibration of various design alternatives, such as wet and dry-liner, underslung crankshaft and skirted crankcases, intermains and without intermains crankshaft, designs, engine size, and number of cylinders are explored. On vee engines the origins of noise and the basic modes of vibration are established and the significance of the contribution of noise by covers is shown. A new form of in-line engine structure design has been investigated giving 10 dbA overall reduction of noise.