An internal combustion engine
The invention relates to an internal combustion engine having cylinders arranged in V-shape in two rows, wherein the fixed main structure of the engine is divided into a separate bedplate on which an engine frame box is mounted, and preferably further divided into a separate cylinder section mounted on the frame box, and wherein the separate main structural elements are clamped together by means of stay bolts extending from the cylinder section to the bedplate, and of which at least two extend obliquely in relation to the median plane of the engine.
V-engines have found their widest application within four-stroke trunk engines. They all have a fixed main structure integrally formed, that is as a single integral block which is formed with a relatively deep downward recess in which the crankshaft is mounted underslung and fastened to the main structure by means of loose lower main bearing parts clamped together with the main structure by means of heavy vertical bolts. These bolts are parallel and may extend up to the upper side of the fixed structure. Particularly in large V- engines, it is a disadvantage that the crankshaft is mounted underslung because it is not then possible to lower the shaft directly into place in the engine by means of a crane.
US-A-3 318 297 describes an engine of the type mentioned above. The engine is of the trunk type and is suitably small so that the crankshaft may be lifted without the use of a crane. The stay bolts on the inside of the cylinders cross over the crankshaft and are fastened to the bedplate at the outer side of the neighbouring cylinder. To enable removal of the crank¬ shaft without unclamping the stay bolts, the lower ends
of the innermost stay bolts are offset so far upwards that there is a free space above the crankshaft of such a size that the crankshaft may be lifted free of the main bearings and displaced longitudinally out through an opening in the end wall of the engine frame box.
The object of the present invention is to provide a large V-engine of the crosshead type.
In view of this object, the internal combustion engine according to the invention is characterized in that the engine is a two-stroke crosshead engine having guide planes mounted on a transverse stiffening in the frame box and extending obliquely in relation to the median plane of the engine over a substantial part of the height of the frame box, and that the stay bolts fastened in the bedplate pass longitudinally along and outside the guide plane of the associated cylinder which is outermost in the transverse direction.
For a crosshead engine it is of vital importance to obtain a very reliable operational control of the crossheads. The mounting of the guide planes on the transverse stiffening of the engine frame box renders possible a large transmission of force from the guide planes to the frame box without deformation of the latter to an extent which has an adverse effect on the planeness of the guide planes. It is known per se from large two-stroke crosshead engines of the in-line type that it is possible to obtain a secure fixation and stiffening of the guide planes to the transverse stiffening, but the known guide planes extend verti- cally, and on both sides of the longitudinal axis of each cylinder the frame box is supported by stay bolts positioned immediately outside the guide planes.
The invention is based on the surprising realiz¬ ation that it is possible to completely leave out the stay bolt on the inside of each cylinder, and that the
guide planes fastened to the transverse stiffening may be arranged with an oblique course in relation to the median plane of the engine. Leaving out the stay bolts on the inside of the cylinders makes room for a fasten- ing and stiffening of the guide planes to the transverse walls. As the outermost guide planes are influenced by substantially larger forces from the crosshead than the innermost guide planes, the absence of the innermost stay bolts does not lead to impermissible deformations of- the frame box. If it is necessary in consideration of the fixation of the cylinder section, the cylinder section may be clamped down towards the frame box on the inside of the cylinder by means of short bolts anchored in the frame box and not in the bedplate. In the engine according to the invention, the axes of the cylinders intersect the horizontal plane at an angle which differs from 90°. The effect of this is that the dominant cylinder forces may have horizontal components of a substantial magnitude. The oblique stay bolts permit transmission of the horizontal components of the cylinder forces to the bedplate so that the individual elements of the fixed main structure of the engine do not get displaced in relation to each other along the joining faces. The through-going stay bolts positioned on the outer side of the guide planes render it possible to use the same bolt force for joining elements which are divided at several joining faces, whereby the total number of bolts is kept down as far as possible. Compared with the known V-engines, the joining bolts will be uncommonly slender, that is the ratio between the length and the thickness of the bolts will be very high. As the bolt force has to be largely the same regardless of the bolt length, the elongation of the bolts at the tightening is proportional with the bolt length, so the very slender bolts are stretched
very much at their tightening which makes the tensioning force largely independent of settlings in threads and contact faces for nuts and of any wear between the parts and vibrations in the elements clamped together. This property in stay bolts is particularly important for the V-engines where the axes of the cylinders are not at right angles to the underlying joining faces between the main structural elements.
The position of the stay bolts on the outer side of the guide planes makes sufficient room for the stay bolts to pass down past the crankshaft for fastening at the bottom of the bedplate.
With a view to reducing the transverse loads in the main structure of the engine, the stay bolts suitably extend substantially in parallel with the guide planes.
In one embodiment, the cylinder sections of two neighbouring cylinders, each in its row, are designed as mutually separate units, and each of the cylinders has a bolt fastened in the engine frame box and extend- ing longitudinally along and on the inside of the guide plane of the cylinders which is innermost in the trans¬ verse direction. The bolt on the inside of the innermost guide plane is not a proper stay bolt fastened to the bedplate, and thus it does not contribute towards clamping the frame box and the bedplate together. Nevertheless, the inside bolt ensures that the cylinder section is securely fastened in the frame box without any possibility of tilting outwards owing to the influence from the stay bolts positioned at the outer side of the cylinders.
In a particularly simple embodiment, the cylinder sections of two neighbouring cylinders in respective rows are integrally formed, and seen in the transverse direction of the engine, all stay bolts are positioned outside of the guide plane of the associated cylinder
which is outermost in the transverse direction. The integral cylinder section renders it possible to leave out bolts in the area between the two neighbouring cylinders so that only a minimum of two stay bolts are required per cylinder pair. To prevent the dominant cylinder forces from offsetting the separate main structural elements in relation to each other during the running of the engine, the stay bolts may be tightened so hard that the stationary frictional force in the plane of the joint exceeds the components of the dominant cylinder forces in the same plane by a secure safety margin.
To facilitate the manufacture of the individual engine elements it is desirable that the partition face between the separate main structural elements extends substantially at right angles to the median plane of the engine, as that produces large horizontal joining faces which are easy to machine in conventional machines. However, the plane partition faces may make unsuitably high demands on the tensioning force required to prevent displacement of the individual elements in relation to each other, and therefore a preferred embodiment employs locking means positioned at the partition face to prevent mutual displacement of the structural elements in the plane of the partition face. Apart from reducing the requirements to the tensioning force of the stay bolts, the locking means facilitate the mounting of the engine, as the individual elements are positioned in relation to each other by the locking means, while the stay bolts are tightened, which might otherwise, owing to the oblique course of the stay bolts in relation to the joining face, lead to mutual displacement of the elements if the stay bolts were temporarily non-uniform- ly tightened.
According to a .preferred embodiment it is also possible to provide a geometrically defined locking between the separate main structural elements in that the partition face between these elements comprises at least two plane sections positioned at either side of the median plane of the engine and extending at an angle therewith. In this manner, the partition face may be given a kind of roof shape where a relative movement along one roof surface requires an opening of the other roof surface and a consequent extra stretching- of the associated stay bolts, which is normally impossible. This kind of interlocking of the separate elements is, of course, more cost-consuming to manufacture, but the locking provided is very efficient, which is particular- ly advantageous in V-engines with a relatively large angle between the two rows of cylinders. The component of the cylinder forces in the plane of the partition face may suitably be minimized by the plane sections of the partition face being substantially at right angles to the central axis of the associated cylinder.
The invention will now be explained in further detail with reference to the schematic drawing, in which Fig. 1 is a cross-sectional view through a first embodiment of an engine according to the invention, Fig. 2 is a corresponding view of another embodi¬ ment according to the invention, and
Fig. 3, on a larger scale, shows a partial view of the joining face between two elements.
Fig. 1 shows a two-stroke long-stroke V-engine 1 of the crosshead type, where the cylinders are mounted in a V-shape in two rows so that the pistons in two neighbouring cylinders 2, 3 are connected with a common crank pin journal 4 on a crankshaft 5. The pistons are connected with the journal 4 via piston rods 6 and connecting rods 7 which are mutually connected in
crossheads 8 guided in the transverse direction of the engine by guide shoes 9 sliding on guide planes 10. These guide planes are fastened to upright transverse walls 11 separating the individual cylinder pairs from each other in the longitudinal direction of the engine. The piston diameter is 90 cm, and the stroke of the engine is longer than 2.5 m, which gives the engine a total height of about 12 m. In a twelve-cylindered embodiment, the engine has a total length of just under 14 m, which should be compared with a total length of just under 24 m for the known twelve-cylindered engines of a corresponding output. It is immediately apparent that a substantial saving of space is obtained by means of the example shown of an engine according to the invention, which may produce an output of more than 70,000 BHP. Naturally, it is possible within the scope of the invention to make engines of other dimensions, both as regards piston diameter and output.
The fixed main structure of the engine is divided into a bedplate 12 and a cylinder section 13 as well as a frame box 14 positioned between the bedplate and the cylinder section and enclosing the crossheads with associated guides and stiffening. The division of the main structure into smaller elements makes it easier to manufacture and handle the individual elements.
The bedplate is designed with a central upward recess 15 through which the crankshaft 5 may be lowered for positioning in the lower parts of the main bearings which are mounted in the bedplate. Sideways outside the recess, the upper side 16 of the bedplate extends obliquely downwards towards the outer wall 17 of the bedplate. The two oblique sections of the upper side 16 positioned on either side of the median plane of the engine incline in respective directions in relation to
the median plane so that the upper side of the bedplate has a roof shape.
The bottom side of the frame box 14 is designed with two plane oblique sections 18, the inclination of which corresponds to the inclination of the upper side of the bedplate.
Similarly, the upper side 19 of the frame box is designed with two oblique sections 20 fitting together with similarly oblique sections 21 on the bottom side of- the cylinder section 13. The oblique sections 18, 20 and 21 extend at right angles to the longitudinal median plane 22 of each cylinder row.
The cylinder section 13 extends integrally over the transverse direction of the whole engine and comprises a scavenging air chamber 23 for each cylinder. The two scavenging air chambers associated with a pair of neighbouring cylinders are interconnected by a centrally positioned scavenging air receiver 24 supplied with air from a turbocharger 25. The cylinder section 13, the frame box 14 and the bedplate 12 are clamped together by means of two stay bolts at each transverse wall 11. The stay bolts extend inside stay bolt pipes,27 and at each end carry nuts 28 clamped against contact faces on the upper side of the cylinder section 13 and the bottom side of the bedplate 12, respectively. The stay bolts extend in parallel with a respective median plane 22 and are positioned at a suitable distance on the outer side of the median planes so that the lower sections of the stay bolts may pass beyond the crankshaft 5. As the two stay bolts are positioned like the legs of a V and extend transversely to the two mutually oblique sections 18 and 20 posi¬ tioned at respective joining faces, the three separate elements of the fixed main structure of the engine are geometrically interlocked so that the transverse forces
in the main structure produced by the cylinder forces are not able to overcome the forces locking the elements together.
Instead of using a stay bolt pipe arranged in the middle of the transverse wall 11, a pipe on either side of the transverse wall may be used together with twin stay bolts. It is also possible to anchor the stay bolts in the bedplate 12 at a level above the main bearings so that the latter are not loaded by the tensioning force of the bolts. If the cylinder section is designed as two separate units for each cylinder pair, it is also necessary to use a bolt (not shown) on the inside of the median plane of the cylinder for the individual cylin¬ der, and arranged specifically so that the bolt passes longitudinally along and inside of the innermost guide plane. The lower end of this internal bolt may, for example, be fastened to the frame box 14 in an area above the crankshaft and close to the longitudinal median plane of the engine. In the other embodiment shown in Fig. 2, one hundred has been added to the reference numerals for elements having the same function as the elements shown in Fig. 1. The following only describes how this embodiment differs from the embodiment of Fig. 1. The partition faces between the separate main structural elements, viz. the bedplate 112, the frame box 114, and the cylinder section 113, extend substan¬ tially at right angles to the median plane 129 of the engine. As shown in fig. 3, to prevent a mutual horizon- tal displacement between the individual elements, locking means 131 have been provided at the partition faces 130 in the form of a set bolt which is inserted largely without play in connected bores in flanges 132 and 133 on the frame box 114 and the cylinder section 113, respectively. The set bolts prevent mutual dis-
placement of the flange portions in the plane of the partition face. Even though only a single locking means has been indicated in Fig. 2, it is obvious that the number of locking means is adapted to the magnitude of the transverse forces to be received. The locking means may also be designed in any other manner, for example as fixed pins projecting from the flange of one element and passing into guide holes in the flange of the adjacent element.