Technical field

The present invention concerns a bearing element for the small end of a con necting rod that connects a piston of a piston engine to a crankshaft in accord ance with the preamble of claim 1 . The invention also concerns a lubrication arrangement and a piston engine.

Background

Each piston of a piston engine is attached to a crankshaft by means of a con necting rod. A main bearing connects the connecting rod to the crankshaft. The crankshaft end of the connecting rod is often referred to as big end and the other end is referred to as small end. At the small end, the piston is at tached to the connecting rod by means of a gudgeon pin. The small end is provided with a bearing, which allows rotational motion of the connecting rod relative to the piston. The bearing at the piston end of the connecting rod is often referred to as a small end bearing.

Piston cooling in large medium speed engines is typically arranged through drillings in the crankshaft, connecting rods and gudgeon pins. The cooling oil introduced into the piston via the connecting rod also lubricates the small end bearing.

In high speed engines, piston cooling is often implemented by utilizing oil jets. Jet cooling is advantageous also in medium speed engines, since it omits the need for oil drillings in the crank gear components and allows thus higher load ing and lower manufacturing costs. In a typical jet cooling arrangement, the cooling arrangement is provided with a separate oil system for piston cooling. Oil injection nozzles for spraying the cooling oil are arranged inside the engine block. Through the injection nozzles, the oil is sprayed onto the bottom side of each piston. The piston skirt is provided with a space for receiving the oil. Drill ings from the oil receiving space lead into a piston crown cooling gallery.

In jet cooled engines, the lubrication of the small end bearings differs from engines, in which the piston cooling is arranged via the connecting rods. In jet cooled engines, the oil flows from the cooling gallery into a middle part of the piston and from there onto the connecting rod and further into the small end bearing.

Figure 3 shows a prior art bearing element. The bearing surface on the inner perimeter of the bearing element is provided with oil an groove, which distrib utes lubricating oil on the bearing surface. The lubricating oil is introduced into the oil groove through an oil supply hole at an upper end of the oil groove, from which it flows downwards along the oil groove by gravity. A problem with the bearing element of figure 3 is that when the piston is in accelerating motion towards bottom dead center, the oil flows due to mass forces to the oil supply hole, which may have an adverse effect on the lubrication of the bearing.

Summary of the invention

An object of the invention is to provide an improved bearing element for the small end of a connecting rod that connects a piston of a piston engine to a crankshaft. The characterizing features of the bearing element according to the invention are given in the characterizing part of claim 1 . Other objects of the invention are to provide an improved lubrication arrangement for a bearing that connects a piston to a connecting rod of a piston engine and an improved piston engine.

The bearing element according to the invention comprises a bearing surface, which bearing surface is configured to cooperate with a surface of a gudgeon pin for allowing rotational motion of the connecting rod relative to the gudgeon pin, the bearing element comprising at least one oil supply hole for allowing lubricating oil to be supplied radially through the bearing element onto the bear ing surface, and an oil groove connected to said oil supply hole for distributing lubricating oil on the bearing surface, the oil groove comprising a first portion, which extends from the oil supply hole to a direction, which allows in a mounted state of the bearing element lubricating oil to flow from the oil supply hole along the first portion by gravity, and a second portion connected to the first portion. The second portion is shaped so that in a mounted bearing element accelera tion of the piston towards bottom dead center causes part of the lubricating oil to be trapped in the second portion. The bearing element according to the invention prevents that all the fuel flows back to the oil supply hole during accelerating movement of the piston towards bottom dead center. This improves lubrication of the small end bearing.

According to an embodiment of the invention, in a mounted bearing element the first portion extends in a direction that is parallel to the longitudinal direction of the connecting rod.

According to an embodiment of the invention, in a mounted bearing element the second portion extends from the first portion to a direction, which is at an angle of 90-140 degrees relative to a direction from the big end of the con necting rod towards the small end of the connecting rod. The second portion thus extends sidewards from the first portion in a horizontal direction or in a direction inclined downwards. This distributes the lubricating oil effectively over the bearing surface.

According to an embodiment of the invention, the second portion comprises a sub-portion, which is shaped to receive and trap lubricating oil that flows into the sub-portion due to the acceleration of the piston towards bottom dead cen ter.

According to an embodiment of the invention, the sub-portion forms an end portion of the second portion and extends in a mounted bearing element to a direction, which is at an angle of 0-80 degrees relative to a direction from the big end of the connecting rod towards the small end of the connecting rod. The sub-portion is thus inclined upwards.

According to an embodiment of the invention, the sub-portion is formed by a cutout extending in a mounted bearing element from the rest of the second portion towards the small end of the connecting rod.

According to an embodiment of the invention, the oil groove comprises a third portion that is connected to the first portion and the second portion and the third portion are arranged mirror-symmetrically about the first portion. Lubricat ing oil is thus distributed to two directions from the first portion.

According to an embodiment of the invention, the bearing element comprises two oil grooves, which are arranged mirror-symmetrically about an imaginary plane that coincides in a mounted bearing element with the longitudinal center axes of the bearing element and the connecting rod.

The lubrication arrangement according to the invention comprises a bearing element defined above and an opening arranged in the connecting rod for re- ceiving lubricating oil from the piston and supplying the lubricating oil to the bearing element.

According to an embodiment of the invention, the lubrication arrangement comprises an injection nozzle for injecting lubricating oil onto the bottom side of the piston. A piston engine according to the invention comprises a lubrication arrange ment defined above.

Brief description of the drawings

Embodiments of the invention are described below in more detail with refer ence to the accompanying drawings, in which Fig. 1 shows a cross-sectional view of a piston and part of a connecting rod of a piston engine,

Fig. 2 shows a cross-sectional view of a piston and part of a connecting rod of a piston engine from another direction,

Fig. 3 shows a prior art bearing element for the small end of a connecting rod, Fig. 4 shows a bearing element according to an embodiment of the invention for a small end of a connecting rod,

Fig. 5 shows a bearing element according to another embodiment of the in vention, and

Fig. 6 shows a bearing element according to still another embodiment of the invention. Detailed description of embodiments of the invention

Figures 1 and 2 show cross-sectional views of a piston 4 and part of a con necting rod 2 of a piston engine. The engine is a large internal combustion engine, where the cylinder bore is at least 150 mm.

The piston 4 is arranged to move in a reciprocating manner within a cylinder 7. The piston 4 moves between a top dead center position, which is shown in figures 1 and 2, and a bottom dead center position. The cylinder 7 does not need to be arranged vertically, but it can be inclined from a vertical direction, such as in V-engines. The piston 4 is connected to a connecting rod 2. Another end of the connecting rod 2 is connected to a crankshaft (not shown). The connecting rod 2 converts the reciprocating motion of the piston 4 into a rota tional motion of the crankshaft. The connecting rod 2 has a longitudinal direc tion. When the piston 4 is at top dead center or bottom dead center, the lon gitudinal direction of the connecting rod 2 is parallel to the longitudinal direction of the cylinder 7.

The crankshaft end of the connecting rod 2 can be referred to as a big end. The piston end of the connecting rod 2 can be referred to as a small end. The big end is provided with a main bearing, which connects the connecting rod 2 to the crankshaft. The small end is provided with a small end bearing.

The small end bearing allows rotational motion of the connecting rod 2 relative to the piston 4. The small end bearing is a slide bearing. The small end bearing comprises a bearing element 1 . The bearing element 1 is arranged into a loop at the small end of the connecting rod 2. The inner perimeter of the bearing element 1 forms a bearing surface 1a. The bearing surface 1a is configured to cooperate with a surface of a gudgeon pin 3. The gudgeon pin 3, which can also be referred to as a wrist pin or piston pin, connects the piston 4 to the connecting rod 2. The bearing element 1 can rotate about the gudgeon pin 3. The piston 4 is attached in a rotationally fixed manner to the gudgeon pin 3.

The piston 4 of the engine of figures 1 and 2 is jet cooled. An oil injection nozzle (not shown) is arranged to inject cooling oil onto the bottom side of the piston 4. In figure 2 can be seen a cooling oil channel 8, through which the cooling oil injected onto the bottom side of the piston 4 can flow further into a cooling gallery 9 and further into a middle part 10 of the piston 4. The cooling oil also functions as lubricating oil for the small end bearing. The small end of the connecting rod 2 is provided with an opening 11 . The opening 11 extends through the end of the connecting rod 2 in the longitudinal direction of the connecting rod 2. Through the opening 11 , the oil can flow from the middle part 10 of the piston 4 onto the outer perimeter of the bearing element 1 . Rotational motion of the connecting rod 2 facilitates distributing the oil on the outer perimeter of the bearing element 1.

The bearing element 1 is provided with oil supply holes 5a, 5b, 5c, 5d, 5e. Each oil supply hole 5a, 5b, 5c, 5d, 5e extends radially through the bearing element 1 . Via the oil supply holes, the oil can flow onto the bearing surface 1 a. Figures 4 to 6 show bearing elements 1 according to different embodiments of the in vention. Lubricating oil is mainly supplied onto the bearing surface 1 a via those oil supply holes 5a, 5c, 5e that are arranged in the upper half of the bearing element 1 . The expression “upper half” refers to that half of the bearing ele ment 1 , which is positioned in a mounted bearing element 1 closer to the small end of the connecting rod 2.

The bearing element 1 comprises an oil groove 6 for distributing lubricating oil on the bearing surface 1a. The oil groove 6 is connected to an oil supply hole 5a. The oil groove 6 comprises a first portion 6a, which extends from the oil supply hole 5a to a direction, which allows in a mounted state of the bearing element 1 lubricating oil to flow from the oil supply hole 5a, 5c along the first portion 6a by gravity. The first portion 6a thus extends downwards from the oil supply hole 5a. In the embodiments of the figures, the first portion 6a extends in a direction, which is parallel to the longitudinal direction of the connecting rod 2. However, the first portion 6a could also extend obliquely downwards from the oil supply hole 5a. In the embodiments of the figures, the oil supply hole 5a is at an end of the first portion 6a of the oil groove 6. In the embodi ments of the figures, the first portion 6a is straight.

When lubricating oil is introduced onto the outer surface of the bearing element 1 , it flows along the outer perimeter and part of the oil can enter through the oil supply hole 5a onto the bearing surface 1a. On the bearing surface 1a, the oil can flow downwards by gravity.

A second portion 6b is connected to the first portion 6a. From the first portion 6a, the oil can flow further into the second portion 6b. The second portion 6b is configured so that the lubricating oil can flow into the second portion 6b by gravity.

When the piston 4 is in accelerating motion towards bottom dead center and the acceleration exceeds the acceleration of gravity, the lubricating oil in the oil groove 6 is forced towards the oil supply hole 5a. However, in the bearing element 1 according to the invention, the second portion 6b is shaped so that the acceleration of the piston 4 towards bottom dead center causes part of the lubricating oil to be trapped in the second portion 6b. This prevents that all the lubricating oil in the oil groove 6 flows back to the oil supply hole 5a.

In the embodiment of figure 4, the second portion 6b of the oil groove 6 extends from the first portion 6a to a direction, which is at an angle of 120 degrees relative to a direction from the big end of the connecting rod 2 towards the small end of the connecting rod 2. The second portion 6b is thus directed side wards from the first portion 6a and sloping downwards. Because the first por tion 6a is in the embodiment of figure 4 vertical, the angle between the first portion 6a and the second portion 6b is 120 degrees. The angle between the second portion 6b and the direction from the big end of the connecting rod 2 towards the small end of the connecting rod 2 could be, for instance, in the range of 90-140 degrees. The second portion 6b could thus be directed side wards from the first portion 6a either in a horizontal direction or sloping down wards. In case of a downwards sloping second portion 6b, the lubricating oil flows in the second portion 6b by gravity. However, even if the second portion 6b is horizontal, the lubricating oil is spread in the second portion 6b by gravity and the kinetic energy received in the first portion 6a of the oil groove 6.

The second portion 6b comprises a sub-portion 6b’, which is shaped to receive and trap lubricating oil that flows into the sub-portion 6b’ due to the acceleration of the piston 4 towards bottom dead center. In the embodiment of figure 4, the sub-portion 6b’ forms an end portion of the second portion 6b and extends in a mounted bearing element 1 to a direction, which is at an angle of approxi mately 30 degrees relative to the direction from the big end of the connecting rod 2 towards the small end of the connecting rod 2. The angle could be, for instance, in the range of 0-80 degrees.

The lubricating oil flows by gravity to the lowermost part of the second portion 6b. When the piston 4 is in accelerating motion towards bottom dead center, part of the lubricating oil flows back to the first portion 6a and further to the oil supply hole 5a. However, part of the lubricating oil flows towards the end of the sub-portion 6b’ of the second portion 6b and is thus trapped in the second portion 6b of the oil groove 6.

The embodiment of figure 5 is similar to the embodiment of figure 4. In the embodiment of figure 5, the sub-portion 6b’ of the second portion 6b receiving and trapping the oil is formed by a cutout extending in a mounted bearing ele ment 1 from the rest of the second portion 6b towards the small end of the connecting rod 2. In the embodiment of figure 5, the lower edge of the second portion 6b extends in the same direction as in the embodiment of figure 4, but the upper edge of the second portion 6b is provided with a cutout 6b’. Also in this embodiment, the sub-portion 6b’ traps part of the lubricating oil, but part of the oil can flow back to the first portion 6a of the oil groove 6.

In the embodiment of figure 6, the second portion 6b extends from the first portion 6a to a direction, which is at an angle of 90 degrees relative to the direction from the big end of the connecting rod 2 towards the small end of the connecting rod 2. The second portion 6b is thus directed sidewards from the first portion 6a in a horizontal direction. In the embodiment of figure 6, the sub portion 6b’ of the second portion 6b receiving and trapping the oil is formed by a cutout extending in a mounted bearing element 1 from the rest of the second portion 6b towards the small end of the connecting rod 2. However, the sub portion 6b’ could also be formed as an end portion of the second portion 6b in a similar way as in the embodiment of figure 4.

In the embodiments of the figures, the oil groove 6 comprises a third portion 6c that is connected to the first portion 6a, and the second portion 6b and the third portion 6c are arranged mirror-symmetrically about the first portion 6a. The third portion 6c comprises a sub-portion 6c’ that is configured to receive and trap lubricating oil. The third portion 6c functions in the same way as the second portion 6b.

In the embodiments of the figures, the bearing element 1 is mirror-symmetrical about a plane that is parallel to the longitudinal direction of the connecting rod 2 and perpendicular to the longitudinal center axis, i.e. the rotation axis of the bearing element 1. In the embodiments of the figures, the bearing element 1 is also mirror-sym metrical about a plane that coincides in a mounted bearing element 1 with the longitudinal center axis of the bearing element 1 and with a longitudinal center axis of the connecting rod 2. The bearing element thus comprises a second oil groove, which is arranged opposite to the oil groove 6 described above. The two oil grooves are identical with each other. The second oil groove receives lubricating oil through oil sup ply hole 5c.

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims.