Technical field

The invention relates to a piston bearing arrangement for an internal combustion engine, including a piston with at least an upper part and a lower part being tightly fixed to each other, and a connecting rod having an upper end provided with piston pin means (fitted between and) turnably journalled to the piston in accordance with the preamble of claim 1.

Background art

With reference to the attached figures 1 a and 1 b illustrating a typical prior art arrangement in an internal combustion engine force transmission between a piston 1 ' and a crank shaft (not shown) is arranged by means of a connecting rod 2', one end of which, in this connection called the lower end, is turnably at- tached to the crank shaft and the other end respectively, here called the upper end 2'a, is turnably attached to the piston 1 ' by means of a piston pin 3'. The arrangement includes a bearing surface 10' between the upper end 2'a of the connecting rod and the piston pin 3' as well as bearing surfaces 11 ' between the piston pin 3' and the piston 1 '. As illustrated in figure 1 b by arrows most of the bending loads on the piston pin 3' come from the gas forces in the cylinder, less from inertia and side forces from the crank mechanism. With increased need for higher cylinder outputs and higher cylinder maximum pressures there is a need for increased bearing surface areas to conform to the increased bending forces. Increased cylinder pressure affects most on the upper halves on the bearing surfaces. The bearing loads on the lower bearing halves, however, do not increase with increased cylinder pressure, but with piston weight and higher speed on the engine.

A known solution for increasing the bearing area is to utilise spherical bearing surfaces in the upper end of the connecting rod. A drawback with this solution is increased weight of the upper end of the connecting rod, whereby the connecting rod must be reinforced and balancing of the engine must be increased. Manufacturing of spherical bearing surfaces is also more challenging than conventional cylindrical bearing surfaces.

An object of the invention is to provide a novel piston bearing arrangement, which solves the above mentioned and other problems of the prior art. It is also an object of the invention to provide a reliable solution for coping with increased cylinder pressures and speeds utilised in internal combustion engines, specifically large diesel engines.

Disclosure of the invention

The objects of the invention can be met substantially as is disclosed in claim 1 and in the other claims presenting more details of different embodiments of the invention.

The basic idea of the invention is to separate the way forces are transferred depending on the direction of the forces in each case. Hereby different bearing diameters and areas can be utilised so as to better conform to the different load requirements respectively and the whole construction may be optimised in accordance with the load conditions.

According to the invention the upper end of the connecting rod is provided with a first bearing surface turnably engaged with an inner surface of the upper part of the piston. The piston pin means include also a second and a third bearing surfaces placed on either side of the connecting rod and being located on the opposite side of the piston pin means with regard to the first bearing surface. Hereby the first bearing surface is utilised for taking up the load resulting from the combustion process in the cylinder in question, whereas the second and third bearing surfaces take up forces affecting in the direction of movement of the piston upwards. Since the downward forces are transferred directly to the connecting rod there are no bending loads in the piston pin. The bearing surfaces have substantially the form of half a cylinder making them easy to manufacture. In addition the radius of curvature of the first bearing surface is with advantage made substantially bigger than that of the second and third bearing surfaces. Hereby the difference in load can be taken account of by different bearing areas respectively so that the first bearing surface is designed to have relatively larger bearing area.

In practice the radius of curvature of the first bearing surface is with advantage at least 60-70% bigger than the radius of the second and third bearing surfaces.

Further, the bearing surfaces have the same center of curvature which is pref- erably also the center of rotation of the upper end of the connecting rod.

In one practical embodiment the piston pin means comprise a separate piston pin inserted in the upper end of the connecting rod. Then the second and third bearing surfaces may with advantage overlap partly the first bearing surface in the direction of the axis of the piston pin means, whereby also the area of these bearing surfaces can be increased.

In another embodiment the piston pin means are arranged as an integral part of the upper end of the connecting rod. In this case machining on the upper end of the connecting rod may be more complicated, but on the other hand there is no bending or tension loads resulting from the drilling through the upper end of the connecting rod.

The piston pin means are provided with a relief at the position of the second and third bearing surfaces on the opposite side thereof with regard to the axis of the piston pin means. Since this part of the piston pin means is not involved with taking up forces and is thus not provided with bearing surfaces, material can with advantage be machined away to decrease the weight respectively.

The upper part and lower part of the piston are with advantage provided with separate bearing shell elements at the position of the bearing surfaces, said bearing shell elements being pressed to the respective bearing seats in said parts of the piston by bolting the upper part and the lower part together. Brief Description of Drawings

In the following the invention will be described, by way of example only, with the reference to the accompanying schematic drawing, in which

- figures 1 a and 1 b illustrate a typical prior art piston bearing arrangement,

- figure 2 illustrates schematically an upper end of a connecting rod in a piston bearing arrangement according the invention and the affecting forces,

- figure 3 illustrates a piston bearing arrangement according to the invention as a sectional view, and

- figures 4 and 5 illustrate some details of the upper end of a connecting rod.

Detailed Description of Drawings

In the figures 2 - 5 reference numeral 1 indicates a piston of an internal combustion engine having an upper part 1 a and a lower part 1 b fixed together by tension bolts 8. An upper end 2a of a connecting rod 2 is turnably attached to the piston 1 . For this purpose it is provided with a first bearing surface 2a1 which is turnably engaged with the upper part 1 a of the piston by means of a bearing shell element 4 fitted to a bearing seat 1 a1 in the inner surface of the upper part 1 a of the piston. In addition the upper end 2a of the connecting rod 2 is provided with piston pin means 3 having a second and a third bearing surfaces 3a arranged to cooperate with bearing shell elements 5 arranged in bearing seats 1 b1 in the lower part 1 b of the piston 1.

As specifically apparent from figure 2 the bearing surfaces 2a1 and 5 are cylinder formed and cooperate with bearing shell elements 4 and 5 having cylindrical surfaces as well. Arrow 6 illustrates the load from the not-shown cylinder of an internal combustion engine. This load is taken up directly be the upper end 2a of the connecting rod, whereby it can be provided with a much larger bearing area 2a1 in comparison with the bearing area 10' arranged in the piston 1 ' according to the conventional arrangement shown in figure 1. As a consequence, since the larger load indicated by the arrow 6 and resulting mainly from the cylinder pressure affect directly on the upper end of the connecting rod with a lar- ger than normal bearing surface area, any bending of the piston pin can be avoided.

On the other hand when the piston is moving upwards there are only inertia forces depending on the weight of the piston affecting on the lower surfaces of the piston pin means 3, illustrated by arrows 7 in figure 2. Thus these bearing surfaces 3a may be designed as in a conventional piston pin design.

As obvious from figure 4 the radius of curvature R1 of the bearing surface 2a1 is substantially larger than the radius of curvature R2 of the bearing surfaces 3a. The larger is the radius R1 the larger is the area of the bearing surface 2a1 enabling it to take up bigger loads respectively. On the other hand with in- creased radius R1 also the weight of the upper end 2a on the connecting rod will increase, whereby the connecting rod must be reinforced for the added weight requiring rebalancing of the engine. As apparent the bearing surfaces have with advantage the same center of curvature which is also the center of rotation of the upper end 2a of the connecting rod.

Figure 5 illustrates two optional ways of implementing the piston pin means 3. It may be a separate piston pin locked in the upper end 2a of the connecting rod 2. In this case more material can be machined away from the connecting rod as illustrated by broken line resulting in an additional bearing surface 3b, whereby increased load can be taken up respectively if needed. As apparent from the figure 5 the joint bearing surfaces 3a and 3b overlap a bit with the bearing surface 2a1 in the direction of the axis of the piston pin, but this is has no negative effect since these bearing surface are operable in different moving directions of the connecting rod and the piston.

Alternatively the piston pin means 3 may be implemented as integral part of the upper end 2a of the connecting rod 2. In this case machining of the upper end

2a is more complicated and the lower bearing surfaces 3a remain relatively smaller. An advantage is, however, that hereby bending load resulting from the drilling through the upper end 2a of the connecting rod to make a hole for the piston pin can be avoided. In addition no traditional bending loads, as illustrated by the broken line 9 in figure 4, appear.

Whichever is the implementation of the piston pin means 3 the arrangement according to the invention allows for making a relief 3a2 (cf. figure 5) since no material is needed here due to the bearing surface 2a1 taking all the loads from upwards. Hereby the connecting rod can be made lighter. In case of a separate piston pin suitable locking means may be utilised to prevent rotation of the pis- ton pin relative to the connecting rod so that the bearing surfaces 3a and 5 (cf. figures 2 and 3) remain mutually aligned.

It is clear that the invention is not limited to the examples mentioned above but can be implemented in many other different embodiments within the scope of the inventive idea.