ディーゼル機関用歯車, 弾性継手およびクラッチについて

Abstract

In marine application the medium speed diesel engine requires gears to adapt its operational speed to the speed with which the propeller performs highest efficiency. There are many configurations of marine gears. They depend on kind and number of engines as well as on the engine room installation. Reverse reduction gears of very different design, single input reduction gears, vertical or horizontal offset or coaxial, twin or multiple input form the main groups of this section of gear designing. The single stage gear unit of today shows very compact design and a high load carrying capacity. This is due to the surface treatment of the tooth flanks by hardening processes. Outstanding experience has been collected with carburised teeth, which have been ground for accuracy achievement. Effective profile modification for the purpose of high bending resistance, protuberance milling to keep the roots of the teeth untouched by the grinding wheel result in utmost resistance against wear and rupture. So the specific loading agreed to by the classification societies are fully justified.The required accuracy of those gears even at their low circumferential velocity is to compare with the precision of turbine gears manufactured according to BSS 1807. Important are full contact areas between the teeth, this requires careful observation of shaft deflection, bearing clearance, thermal distortions and rigidity of housing, thrust block and foundation in the hull. Another important condition to be observed satisfactory performance of marine gears is the absence of major torsional vibrations producing overload torque or even torque reversal. With diesel engines as power sources excitations of torsional vibrations are very likely to interfere with one or another of the natural ferquencies of the propulsion system. The fundamental connections required to calculate torsional vibration and the rise of torques caused by them are well known. With increasing familiarization of computer technique the calculation procedure has been refined to handle even manifold systems easily and practically reliable.The necessary over-all-elasticity of the torsional vibrating system thus can be calculated and realised. More and more there are used torsionally elastic couplings to dislocate the natural frequencies to the region of low speed. Good performance showed rubber couplings with metal bonded contact surfaces of special design, which allows a prestressing of the bonded surfaces. Their high torsional elasticity and damping property assures an overcritical operation. At the same time they allow for misalignment without any maintenance trouble. In some cases where it is advisable to avoid the turbulence zone at low speed at all, there are torsional elastic clutches available. They consist of the same elastic rubber elements combined with a clutching device with friction cones and pneumatically operated ring cylinder. Thus, it is possible to engage the whole propulsion system only after having reached the engine service speed. With disengaging and re-engaging the clutch great advantage is obtained during “crashstop”-manouvre, because the time for propeller reversal is much reduced. In any case torsionally elastic clutches are required for twin or multiple engine installations, where they have been applied originally and have proven an ample reputation of reliability. Nowadays, the tedency to install unmanned engine rooms leads to immediate measuring of engine torque : this is relatively easy with highly elastic couplings of linear characteristic, the torsional angles of which are large enough to furnish significant values for the purpose of measurement.The lecture points out the recent development which has been achieved on the side of Gearing and Couplings adequate to the development of the medium speed diesel engines.