The invention relates to a V-engine of the crosshead type with cylinders positioned obliquely in relation to the centre plane of the engine and arranged in two rows positioned beside each other and having pistons, of which each, through a piston rod extending in parallel with the associated cylinder axis, is connected with a crosshead guided in the transverse direction of the engine and connected directly via a connecting rod with a crank pin journal on the crank¬ shaft where the lower ends of the connecting rods associated with two neighbouring cylinders in respective rows are journalled on a common crank pin journal.

For many years it has been known to make V-engines of the trunk type in which the piston positioned in the cylinder is journalled at the top of a connecting rod, the lower end of which is journalled on a journal in a throw of the crankshaft. This form of connection between the piston and the crankshaft is relatively uncompli- cated and gives great liberty to arrange the cylinder in various ways in relation to the crankshaft, because angular rotations of the cylinder about a longitudinal axis of the engine are directly received in the journal connection between the connecting rod and the piston. Prior art comprises a V-engine of the crosshead type of the above kind manufactured by the company Schmidt-Bolness, in which the member acting as a crosshead is an air pump piston in a cylinder having a larger diameter than the working cylinder and lying in extension thereof. The piston and the air pump piston are connected via a relatively short piston rod, and the air pump piston is further connected with the crankshaft via a connecting rod. As the crosshead function is built into a piston, the crosshead function is limited by the

requirements necessary for the piston function, which means, among other things, that the lubricating oil film between the piston and the cylinder wall is thinner than between a conventional crosshead and the associated guide plane, which restricts the ability of the piston to receive transverse loads. The Bolness engine suffers from the same disadvantages as the well-known V-engines of the trunk type, viz. that the upper end of the connecting rod is fastened to a piston in a cylinder, which means that the angular variation of the connecting rod during an engine cycle is restricted by the lower cylinder rim. The consequence of the restricted angular variation of the connecting rod is that the stroke of the engine becomes relatively short and/or that the connecting rod has to be very long in relation to the stroke, so that the engine becomes very tall. The air pump piston of the Bolness engine is fastened in the horizontally extending wall which closes the crank housing upwards. This structure is not suited for the absorption of large transversal forces.

As mentioned above, the ratio between the stroke and the cylinder diameter in the known V-engines is restricted by the fact that the connecting rod has to clear the associated cylinder. From large long-stroke crosshead engines with the cylinders arranged in a single row it is known per se to obtain a long stroke in relation to the cylinder diameter by having the piston rod extending completely out of the cylinder and down to a crosshead which is guided in the transverse direction by guide planes fastened to the engine frame box. It has always been a basic characteristic of these engines that the guide planes extend vertically.

Since 1928 it has been known from GB patent No. 292 772 that a crosshead engine may have two parallel rows of vertical cylinders, the pistons of which are con-

nected in pairs with a common crank pin journal via a rod which connects the crosshead with a separate journal on a bifurcate connecting rod, the upper end of which is journalled in the engine frame box via a horizontally extending connecting link. The crosshead is of the type which has a stiffening member extending transversely from a central portion of the crosshead pin and engaging with a unilaterally positioned double-acting slot in a guide plane which is fastened on the longitudinally extending side wall of the engine frame box in such a position that the piston rod, the connecting rod and the guide plane are positioned in the same transverse plane. The guide planes also extend vertically in this engine, and the connection between the piston rod and the crank pin journal is very complicated. The engine has a large width in relation to the stroke, because the angular movement of the connecting rod has to be on the internal side of the guide plane, which is, of course, positioned in the same plane as the connecting rod. The object of the invention is to provide a high- powered V-engine with a good fuel economy and small outer dimensions seen in relation to its power.

This object is obtained by the V-engine mentioned in the introduction being characterized in that it is a large two-stroke engine having a ratio between the stroke and the cylinder diameter of at least S/B = 2, that the engine frame box is reinforced by an internal transversal vertical stiffening, preferably in the form of plate walls, that the crossheads are guided in the transverse direction by elongated guide planes which are fastened to the vertically extending stiffening, and that the lower ends of the guide planes are positioned at such a distance from the centre plane of the engine that the direction of movement of the crosshead associ- ated with the guide plane is offset outwards in the

transverse direction of the engine in relation to the rotational axis of the crankshaft.

With the invention, it has surprisingly been acknowledged that the guiding of the crossheads known from large two-stroke in-line engines may be used in a V-engine despite the fact that the guide planes will then extend obliquely in relation to the centre plane of the engine.

The long stroke in relation to the cylinder diameter gives the engine a good fuel economy, but at the same time makes special demands on the guiding of the crosshead, because there has to be space for the angular variation of the connecting rod during an engine cycle. The positioning of the guide planes on the internal transverse stiffening in the engine frame box results in a separation of the connecting rod and the guide planes in the longitudinal direction of the engine so that the connecting rod may oscillate in the trans¬ verse direction of the engine in any desired manner quite unimpeded by the guide planes. The vertically extending transverse stiffening supports and braces the guide planes along all their extent in the direction of height of the engine, which renders it possible to transfer large transversal forces from the crosshead via the guide planes to the transverse walls out into the engine frame box without any risk of undesired deforma¬ tions of the guide planes.

The oblique cylinders and the associated angular positioning of the guide planes in relation to the centre plane of the engine leads to a novel space problem at the lower sections of the guide planes, as the upper ends of the connecting rods must not collide when the pistons are close to their lower dead centre position. The connecting rods may be made so long that in their lowest position the crossheads are sufficiently

far from each other, but this results in an engine of large height. The outward offset of the lower sections of the guide planes in relation to a position in which the longitudinal axes of the cylinders intersect the rotational axis of the crankshaft provides a separation between the upper ends of the connecting rods near the lower dead centre position so that the guide planes may end at such a short distance above the crankshaft that the engine has an advantageously small height. As explained below, the outward offset has the further advantage that the stroke of the engine becomes longer than double the centre distance between the main bearing journal and the crank pin journal in the crankshaft, which also contributes to making the engine compact. The outward offset also leads to a more vertical position of the longitudinal axes of the cylinders, which facilitates overhauling of pistons, cylinders, exhaust valves, etc., because the components in question do not have to be lifted or lowered quite so obliquely as was otherwise the case without the above offset. Finally, the offset results in a smaller total width of the engine.

The invention renders it possible to manufacture V-engines with powers far exceeding the power of the largest known engines, without any substantial increase of the dimensions of the engine. It is possible, for example, to manufacture an internal combustion engine with an output of about 100,000 kW, which does not deviate substantially in height, length and width from the largest in-line engines of about 50,000 kW of the present day.

In a preferred embodiment, the centre lines of the guide planes associated with two neighbouring cylinders extend in the same angle in relation to the centre plane of the engine, and the centre lines intersect this plane

at the same low level below the rotational axis of the crankshaft. The symmetrical structure about the centre plane of the engine facilitates its manufacture, and the uniform course of the neighbouring cylinders in relation to the centre plane promotes a uniform load on the engine components.

Examples of embodiments of the invention will now be described in further detail below with reference to the schematic drawings, in which Figs. 1 and 2 show a partially cross-sectional view through an engine near the upper and lower dead centre positions, respectively,

Fig. 3 shows a cross-sectional view corresponding to Fig. 2 of another embodiment according to the invention, and

Fig. 4 is an illustration of the relation between the stroke of the engine and the course of the guide planes of the crossheads.

Fig. 1 shows a two-stroke crosshead engine of the V-type generally designated 1 having an engine frame box

3 mounted on a bedplate 2 and carrying on its upper side two rows of cylinders 4 which are mounted in pairs in a V-manner on the engine frame box. The pistons of each cylinder pair are journalled via respective piston rods 5 with associated crossheads 6 at the top of connecting rods 7, the lower ends of which are journalled on a crank pin journal 8 common to the cylinder pair and positioned on the crankshaft 9. The crosshead is guided in the transverse direction of the engine by means of crosshead shoes 10 sliding on associated guide planes

11 which are fastened on upright transverse walls 12 in the engine frame box. The back of the guide planes 11 is reinforced by means of plate sections 13 welded onto the transverse wall. The ratio between the stroke S of the engine and the cylinder diameter B (not shown, but

B is identical to the bore of the cylinder) is at least S/B = 2, and in the case shown of about S/B = 2.7. The long stroke gives the engine good fuel economy, but necessitates an accurate guiding of the movement of the piston and the piston rod. This guiding is provided by means of the guide planes which extend substantially in parallel with the longitudinal axis of the associated cylinder and have a length longer than the stroke.

The upper end of the connecting rod 7 is journalled on a crosshead pin rigidly connected with the piston rod and extending in the longitudinal direction of the engine and carrying one crosshead shoe 10 on either side of the connecting rod which may oscillate in the transverse direction in relation to the crosshead pin unimpeded by the guide shoes. Each crosshead shoe 10 has two bearing faces 14 which are guided in the transverse direction via contact with a respective guide plane 11. The guide planes 11 protrude such a distance from the transverse wall 12 that the bearing faces 14 are fully supported, but that the connecting rod 7 completely clears the guide planes. The two guide planes for each shoe extend in parallel, and the centre line 15 between the two guide planes determines the direction of movement of the centre of the crosshead. It may be seen from Fig. 1 that the centre line 15 and thus the direction of movement of the crosshead does not inter¬ sect the rotational axis 16 of the crankshaft, but, on the contrary, passes it at a distance d in the trans¬ verse direction of the engine. This results in a horizontal distance between the lower sections of the guide planes which is sufficient to enable the connect¬ ing rods, as shown in Fig. 2, to have a suitable distance from each other when the pistons are moved through their lower dead centre position. The outward offset by the distance d of the direction of movement

of the crosshead in relation to the rotational axis 16 results in the centre line 15 intersecting the centre plane of the engine at the point 18 which is positioned at a lower level than the axis 16. The guide planes of the two neighbouring cylinders, the connecting rods 7 of which are journalled directly on the same journal 8, are symmetrical about the centre plane 17, so that both lines 15 intersect the centre plane at the same level below the rotational axis. From the description with reference to Fig. 4 it will appear that this position of the guide planes 11 also results in a longer stroke for the engine.

For absorption of the transverse forces from the crosshead it is substantial that the guide planes 11 are securely fixed along their full length, which is effected through the above fastening to the transverse wall 12. In the longitudinal direction of the engine, the engine frame box 3 has a vertically extending through-going transverse wall 12 between each pair of neighbouring cylinders. Below each transverse wall, the crankshaft is supported by coaxially positioned main bearings mounted in the bedplate 2. The transverse walls give the frame box 3 the required rigidity for absorp¬ tion of the transverse forces from the crossheads. Preferably, the transverse walls 12 are single-layer through-going plate walls, as such walls are simple to manufacture, but it is also possible to use a transverse stiffening in the form of double-walled frame profiles which are not necessarily through-going in the trans- verse direction. However, the profiles must have an extent sufficient to achieve a good fixation of the guide planes 11.

In Fig. 2, the crankshaft has rotated to such a position that the left piston in the drawing is close to its lower dead centre position. In this position,

there is a good clearance between the upper ends of the connecting rods. By making the guide planes 11 and the associated bearing faces 14 on the shoes 10 wider in the longitudinal direction of the engine, it is possible to provide a bearing area which is sufficiently large for transmission of larger transverse forces from the crossheads to the transverse walls. As shown in Fig. 3, this may be utilized to make the connecting rods so short that their upper ends almost touch each other near the lower dead centre position. This will make the guide planes 11 end at a very short distance from the rotational axis 16 of the crankshaft, whereby the engine obtains an extremely small ^' height in relation to its stroke. At the same time, the width of the engine is reduced slightly, because the oblique cylinders are finished at a lower level. In the second embodiment shown in Fig. 3, the same reference numerals have been used as in Figs. 1 and 2 for elements having the same function. In Fig. 4, the outline marked A shows the position of the guide planes in a crosshead engine where the direction of movement of the crosshead intersects the rotational axis 216 of the crankshaft, and outline B illustrates an embodiment where the direction of movement of the crosshead is offset in relation to the shaft 216.

Outline A shows the case where the stroke S of the engine corresponds to double the distance between the rotational axis 216 and the axis of symmetry 218 of the crank pin journal. In the two outlines, similar crank¬ shafts and connecting rods of the same length have been used. Consequently, the position of the crosshead nearest to the crankshaft must be located on the circular arc 219 regardless of the location of the guide planes 211, and the position of the crosshead farthest

away from the crankshaft must be located on the circular arc piece 220, the radius of which corresponds to the length of the connecting rod plus the distance between the axes 216 and 218. The radius of the circular arc piece 219 corresponds to the length of the connecting rod less the distance between the axes 216 and 218. In the engine outlined in A, the crosshead is moved according to a radius through the rotational axis 216. By changing the location of the guide planes 211 in such a manner that the crosshead is no longer moved according to a radius through the rotational axis 216 of the crankshaft, it is immediately seen that the stroke of the engine is increased, as the shortest distance between two concentric circles is found along the radii of the circles.

Outline B shows a case where the upper dead centre of the crosshead is located at the same distance from the centre plane 217 of the engine as in outline A, but in outline B the lower sections of the guide planes are displaced outwards in the transverse direction of the engine so that the direction of movement of the centre of the crosshead has been offset by a distance c in relation to the rotational axis 216. This is seen to increase the stroke by the distance ΔS_ corresponding to an increase of the original stroke of about 14.5 per cent. As the upper dead centre position of the crosshead is unchanged in relation to outline A, the height of the engine in the two outlines is substantially the same despite the fact that the stroke in outline B has been increased by just under 15 per cent.

It may be seen from Fig. 4, that the width and height of the engine and the stroke may be adapted largely according to need by choosing suitable upper and lower dead centres for the crosshead and mounting the guide planes 211 in the engine frame box accordingly.

It may also be seen that the stroke is increased substantially at an increasing offset of the lower dead centre position of the crosshead in the transverse direction of the engine. Apart from this, a result of the offset is also that the guide planes may end at a lower level above the rotational axis 216, because the outward offset gives better space for the connecting rods. This renders possible a further reduction of the engine height in relation to the stroke.