Europaisches Patentamt (19) European Patent Office Office europeenpeen des brevets EP 0 529 935 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) intci.6: F16C 5/00, F02B 75/32 of the grant of the patent: 15.05.1996 Bulletin 1996/20 (21) Application number: 92307594.9 (22) Date of filing: 19.08.1992 (54) Four-stroke cycle trunk piston type diesel engine Diesel-Viertaktmotor Moteur Diesel a quatre temps (84) Designated Contracting States: (56) References cited: CH DE DK GB LI DE-A-2 620 910 DE-C- 577 389 DE-U- 9 003 721 US-A-2 057 158 (30) Priority: 29.08.1991 JP 218587/91 US-A-2 410 565 (43) Date of publication of application: • "Bau und Berechnung von 03.03.1993 Bulletin 1993/09 Verbrennungsmotoren" 1983 • "Verbrennungsmotoren Band 1" 1990 (73) Proprietor: THE HANSHIN DIESEL WORKS, LTD. • "Krafte, Momente und deren Ausgleich in der Kobe, Hyogo 650 (JP) Verbrennungskraftmaschine" 1981 • "Motoren Technik Praxis Geschichte" 1982 (72) Inventor: Nakano, Hideaki • "Gestaltungen und Hauptabmessungen der Okubo-cho, Akashi, Hyogo 674 (JP) Verbrennunskraftmaschine" 1979 • Forscher Bericht VDI "Entwicklungsaspekte bei (74) Representative: Rackham, Anthony Charles Grossdieselmotoren" 1985 Lloyd Wise, Tregear & Co., • "The Motor Ship" Feb 1993 Commonwealth House, 1-19 New Oxford Street London WC1A 1LW (GB) DO lO CO O) O) CM LO Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice the Patent Office of the Notice of shall be filed in o to European opposition to European patent granted. opposition a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. a. 99(1) European Patent Convention). LU Printed by Jouve, 75001 PARIS (FR) 1 EP 0 529 935 B1 2 Description Furthermore, the cross-sectional area of the con- necting rod must be greatly enlarged to increase the The present invention relates to a low-revolution, buckling strength. This results in an increase in the over- long-stroke, four-stroke cycle diesel engine of the trunk all length of the engine, and in increases in the engine piston type suitable for use in marine applications. 5 size (external dimensions) and weight, which represent The diesel engines currently used for marine appli- a drop in operating economy. cations can be generally classified into two types ac- For these reasons, in order to satisfy the above re- cording to the type of the connection between the piston quirements, a trunk piston type diesel engine, which has and the crankshaft. The two types are the trunk piston an S/D ratio of only 2.0 or less, is currently required to type and cross-head type. 10 be connected with an expensive and heavy speed re- Fig. 11 of the accompanying drawings shows a con- duction gear. ventional two-stroke cycle diesel engine of the cross- DE-A-577389 shows an engine which is probably head type, in which the cylinder and crankcase are iso- of the crosshead type. It has an upper piston sliding in lated by a stuffing box SB. The small end of connecting a cylinder to form the combustion chamber with a lower rod CR is connected to a crosshead C which recipro- is part-cylindrical guide sliding in the lower part of the cyl- cates along a crosshead guide CG in the crankcase. inder. It suffers the problems noted above. The crosshead is connected via a rod R to the piston P. It is therefore an object of this invention to provide The provision of a crosshead makes it mechanically a long stroke four-stroke cycle trunk piston type diesel easy to lengthen the piston stroke. Currently, long- engine having a low overall height and a low rated rev- stroke crosshead type diesel engines having a stroke- 20 olution which can be used without a reduction gear. to-bore (S/D) ratio of approximately 3.8 are being prac- According to the invention there is provided a four- tically used. However, this type engine has a complicat- stroke trunk piston type diesel engine having a stroke- ed construction and is costly because it requires a stuff- to-bore ratio of at least 2.5, comprising: ing box, an auxiliary blower for scavenging, etc. Fig. 12 of the drawings shows a conventional four- 25 a cylinder having an upper portion and a lower por- stroke cycle diesel engine of the trunk piston type, in tion of the same diameter, which the small end of the connecting rod is connected an upper piston reciprocatable inside the cylinder directly to the piston. This type engine can generally portion and forming a combustion chamber there- have a lower overall height than a crosshead type diesel with, engine of the same output. The lower height decreases 30 a lower piston spaced from the upper piston by a the dead space on board the ship and increases the space and connected thereto to reciprocate there- available capacity. with inside the lower cylinder portion and part of the In recent years, in order to improve the propulsion upper cylinder portion, and the length of the lower efficiency of a ship propeller, there has been a trend to- piston plus the space between the upper and lower ward a marked reduction in the propeller revolution as 35 pistons being a least equal to the cylinder bore, compared with what was previously used. Accordingly, a rod connecting the lower piston to the crankshaft, main engines for marine applications are required to and have a low rated revolution. In order to respond to this the lower cylinder portion having a length substan- requirement without decreasing engine output, it is nec- tially equal to the length of the lower piston plus the essary to lengthen the piston stroke. 40 length of the space between the upper and lower Trunk piston type diesel engines are limited for con- pistons, and having recesses formed axially the- structional reasons to a stroke-to-bore (S/D) ratio of realong on both sides to avoid interference with the about 2.0 in practice. In the case of this type engine, it rod. is necessary to avoid the interference of the lower end (E in Fig. 1 2) of the cylinder liner with the connecting rod 45 Such an engine is simple, cheap and excellent in when the rod inclines. Therefore, if the S/D ratio increas- low load operation, load adaptability and fuel consump- es, the rod must be lengthened to avoid the interference. tion. It can also have a low overall height and a lower As pointed out by G. Wolf and other researchers noted rated revolution. in this field, if an attempt is made to increase the S/D Although the recesses reduce the area of the lower ratio (lengthen the stroke) of a trunk piston type diesel so cylinder portion on which the side thrust force is exerted, engine, as shown in Fig. 6, the connecting rod will be because the force is markedly low on this area, the force long on a quadratic curve with respect to the S/D ratio. per unit area does not increase substantially. This re- As shown in Fig. 7, when the S/D ratio increases sults in high reliability despite the recesses formed. past the point of approximately 2.5, the overall engine Preferred embodiments of the invention are shown height for the trunk piston type becomes greater than 55 in the accompanying drawings, wherein: even that of the crosshead type, thus eliminating the fea- tures and advantages of the trunk piston type diesel en- Fig. 1 a is a schematic view partially in axial section gine. of main parts of an engine according to one embod- 2 3 EP 0 529 935 B1 4 iment; es between the pistons 25 and 31 . Fig. 1 b is a sectional view taken along line 1 b-1 b of In order to reduce the height required to remove the Fig. 1a; pistons when overhauling the engine, the rod 43 is con- Figs. 2 and 3 are views similar to Fig. 1 a, but show- nected to the pin 39 via a flange 48 so as to be disas- ing some parts in different positions; 5 sembled. Fig. 4a is a perspective view of parts of an engine The cylinder 21 and liner 23 are longer than those according to another embodiment; of a conventional trunk piston type diesel engine by at Fig. 4b is a sectional view taken along lines 4b-4b least the length X between the bottoms of pistons 25 of Fig. 4a; and 31. Fig. 5a is a perspective view of parts of an engine 10 A bottom portion of cylinder 21 has triangular re- according to a further embodiment; cesses 49 formed in it on both sides. The corresponding Fig. 5b is an elevational view of parts of the engine bottom portion of liner 23 has slits 51 formed through it, shown in Fig. 5a; which are aligned with and have the same height as the Fig. 5c is a sectional view taken along line 5c-5c of recesses 49. The recesses 49 and slits 51 are slightly 5a; is wider than the thickness of rod 43, which does conse- Fig. 6 is a graph showing the relationship between quently not interfere with the cylinder 21 and liner 23 the length of the connecting rod divided by the bore when it inclines as shown in Fig. 2. and the stroke-to-bore ratio of a trunk piston type In these bottom portions, the side thrust force ex- diesel engine; erted by the lower piston 31 upon the liner 23 decreases Fig.