Technical field

The invention relates to a method of installing and turnably journaling a connecting rod to a piston according to preamble of claim 1.

Background art

In an internal combustion engine force transmission between a piston and a crank shaft is typically arranged by means of a connecting rod, one end of which is turnably attached to the crank shaft of the engine and the other end respectively is turnably attached to the piston by means of a piston pin. The arrangement includes a bearing surface between the upper end of the connecting rod and the piston pin as well as bearing surfaces between the piston pin and the piston. Most of the bending loads on the piston pin 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 gas forces from the combustion. 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. Hereby the upper end of the connecting rod can be turnably journalled directly to the bearing surface arranged inside the piston, and thus, no separate piston pin is needed. The area of a curved bearing surface is wider than a cylindrical one allowing utilisation of increased cylinder pressures. A drawback with this kind of traditional solution is increased weight of the upper end of the connecting rod, whereby the connect- ing rod must be reinforced and balancing of the engine must be increased. Prior solutions are also complicated and the installation is awkward and time consuming.

An object of the invention is to provide a novel solution for utilising curved bearing surfaces for turnably journaling a connecting rod to a piston, applicable in an internal combustion engine, and installation thereof so that the drawbacks in the prior solutions can be minimised.

Disclosure of the invention

The objects of the invention can be met substantially as is disclosed in claim 1 and in the other claims.

The basic idea of the invention is to make use of curved bearing surfaces in a new way so that the design and the dimensions utilised allow easy and quick installation of the end part of the connecting rod and the piston together with its bearing member located inside. In accordance with the invention the piston is provided with a bearing member having a curved bearing surface to be turnably engaged with an end part of the connecting rod provided with similar bearing surface. The bearing member has a ring-like shape with a cut-out at the side of the connecting rod. The end part of the connecting rod is arranged through the cut-out into the piston in a position, in which the end part of the connecting rod and the bearing member are essentially perpendicular with regard to each other. The connecting rod or the piston is then moved further so that the end part of the connecting rod becomes in contact with the bearing member. Thereafter the end part of the connecting rod and the bearing member are arranged to their final position by means of relative turning movement between the connecting rod and the piston so that the mutual bearing surfaces are aligned and substantially correspond to each other.

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

- Figure 1 a illustrates the first phase of the installation of a connecting rod to be turnably journalled with a piston in accordance with the invention, - Figure 1 b is section A-A of figure 1 a,

- Figure 2a illustrates the second phase of the installation of a connecting rod to be turnably journalled with a piston in accordance with the invention,

- Figure 2b is section B-B of figure 2a,

- Figure 3a illustrates as a 3D version the principle of the first phase of installa- tion according to figures 1 a and 1 b,

- Figure 3b illustrates as a 3D version the principle of the second phase of installation according to figures 2a and 2b, and

- Figure 4 illustrates the finishing phase of the installation and corresponds to the view of figure 2b.

Detailed Description of Drawings

In the figures the reference numeral 1 indicates a piston of an engine, which is provided with a bearing member 3 arranged inside of the piston 1 for turnably journaling an end part 2a of a connecting rod 2 thereto. The bearing member 3 is a ring-like piece having a cut-out 3a located at the side of the connecting rod 2. With reference to the figures the installation of the connecting rod 2 to be turnably journalled with the piston 1 takes place as follows.

The mutual turning position of the end part 2a of the connecting rod 2 and the piston 1 with the bearing member 3 is arranged such that the end part 2a is roughly perpendicular with regard to the bearing member 3 (cf. figures 1 a, 1 b, and 3a). In other words the turning axis 5 of the end part 2a of the connecting rod 2 is perpendicular with regard to the axis 6 of the curvature of the bearing member 3. From the viewpoint of the invention, in principle, it is of no consequence which of the pieces is turned, i.e. the connecting rod 2 or the piston 1. In practice, especially in case the connecting rod is already installed on the crank shaft of the engine, it may be easier to turn the piston 1 relative to the connect- ing rod 2 than vice versa. In this mutual position of the pieces the end part 2 of the connecting rod 2 is taken through the cut-out 3a of the bearing member 3. Again, in practice, the piston 1 is with advantage moved relative to the connecting rod 2 so that the end part 2a of the connecting rod 2 reaches into contact with the bearing member 3 as illustrated in figures 1 a and 3a. In the second phase the bearing surfaces of the bearing member 3 and the end part 2a are aligned by mutual relative turning movement between the piston 1 and the connecting rod 2, as illustrated in figures 1 a, 2a and 3b. In practice the piston 1 together with the bearing member 3 is with advantage turned with regard to the connecting rod 2 so that the mutual position shown in figures 2a, 2b, 3b and 4 is reached. In this position the axes 5 and 6 are also aligned. Then, in order to finish the installation a locking member 4 is inserted in the piston 1 as shown in figure 4. The locking member 4 prevents turning of the piston 1 around its longitudinal axis relative to the connecting rod 2 during operation of the engine. Figure 4 illustrates also dimensioning of the separate pieces and elements. Thus, the width of the bearing member 3 is dimensioned so that its total circumference covers at most 180 degrees in the cross-sectional plane of the longitudinal axis of the piston 1 taken at the position of the turning axis 5 of the end part 2a of the connecting rod 2 after installation. Correspondingly the end part 2a of the connecting rod 2 is formed so that on both sides of its curved bearing surface there is a planar side surface 2b (cf. the figures). Hereby the curved bearing surfaces can be much wider than cylindrical ones utilised in connection with a piston pin. The bearing member 3 is, however, easier to manufacture than a spherical bearing surface and it allows for insertion of the end part 2a of the connecting rod 2 through the cut-out 3a at lower part of the piston 1 (cf. figures 1 a and 3a). For this purpose the cut-out 3a should be dimensioned likewise so that it allows said insertion. In practice the cut-out 3a may with advan- tage be dimensioned to roughly correspond to the width of the end part 2a of the connecting rod 2 in the direction of its turning axis 5 (cf. figures 1 a and 3a). In this case the mutual bearing surfaces at the lower part of the arrangement next to the cut-out 3a are still sufficient for taking the inertia forces and crank forces resulting from operation of the engine. These forces may with advantage be decreased by providing the end part 2a of the connecting rod with reliefs 2c by machining some material away to thereby decrease the weight of the connecting rod 2.

The figures show only the principles of the invention. Thus the invention is not limited to the embodiment shown but variations are feasible within the scope of the inventive idea.