A CRANKSHAFT BEARING ARRANGEMENT OF A COMBUSTION ENGINE

Technical Field

The present disclosure relates to a crankshaft bearing arrangement of a combustion engine, and especially to a crankshaft bearing arrangement of an internal combustion engine of a hand-held motor-driven tool .

Background In the development of combustion engines for motor-driven tools, such as chainsaws, hedge trimmers, grass trimmers etc., bearing sleeves have been used to eliminate the need for after-treatment of bearing seats of crankshaft bearings after the bearings seats have been manufactured. In US4974973 and WO97/45649 crankshaft bearing arrangements have been described using such bearing sleeves. In the bearing arrangement of e.g. US4974973, a bearing can be arranged in a bearing sleeve, which is formed as a tin cup with a rubber coated outer periphery. The rubber coated outer periphery is arranged to compensate for tolerances, e.g. size variations in the production of e.g. bearing seats and to seal against the cylinder and the crankcase. Also, the arrangement has an internal periphery provided with a sealing ring to seal against the crankshaft. Even if such arrangements have a lot of advantages, a couple of problems may occur:

Due to the rather large tolerances in such an arrangement, there is a risk that the bearing is either too loosely arranged in the sleeve, with a result that the bearing may rotate in the bearing sleeve or that the bearing including the bearing sleeve will rotate in the bearing seat, or that the bearing will press too hard in the sleeve, risking obliqueness of the bearing or that the bearing and/or the

bearing sleeve is squeezed in the bearing seat such that the bearing and/or the bearing sleeve finally breaks .

- Even if dimensions are achieved for which a proper squeezing of the bearing and the bearing sleeve is achieved, it may be difficult to seal such an arrangement. As a result, it may be necessary to seal during operation with exceptionally much silicone glue between bearing seat and bearing sleeve.

Also, such a solution is rather expensive to produce, since an expensive kind of rubber has to be used for the rubber-coated outer periphery.

Summary

An object of the invention is to create an improved crankshaft bearing arrangement which solves the above mentioned problems.

This is solved by a crankshaft bearing arrangement according to claim 1.

According to a first aspect of the invention, defined in claim 1, a crankshaft bearing arrangement is arranged such that at least one part of the bearing seat has a reinforcement arranged in the bearing seat, and a surface of the at least one part of the bearing seat, which surface bears against the bearing, is made of a plastic material. The bearing arrangement also has a sealing arrangement for sealing against crankshaft and bearing seat

By having such a reinforcement, it would be possible to use a plastic material for the surface of the bearing seat without risking a compression set in the plastic material. Another advantage compared to the prior art solutions using a tin cup as bearing sleeve, is that such a bearing sleeve can be omitted in this solution, resulting in smaller tolerances between bearing seat and bearing, i.e. manufacturing size variations. Still existing construction tolerances can be

received by the nature of the plastic material. Also, the plastic material can be produced without after-treatment with a low tolerance compared to e.g. a metallic material. Thereby, with the arrangement according to the invention, there is low risk that the bearing is too loosely held in the bearing seat, such that it may rotate or that is too hardly held and is tilted or damaged in any other way. Since the position of the bearing is well defined, a proper function of the crankshaft assembly including piston rod, and good cooperation of crankshaft assembly and cylinder is ensured, which will result in good engine characteristics and low emissions.

Another advantage with this arrangement is that the diameter of the bearing arrangement can be reduced since there is no bearing sleeve, which results in a more cost-effective arrangement. Also, when there is no bearing sleeve, the arrangement will be lighter and more cost-effective.

By arranging the surface of plastic material as a layer between the bearing and the reinforcement, as defined in claim 2, the arrangement will be more resistant to loads, i.e. it may be exposed to rather high loads without risking a compression set in the plastic material. This is especially true if the plastic material is a fibre-reinforced plastic material as defined in claim 4.

By having a sealing arrangement arranged according to claim 7, a cost-efficient sealing arrangement can be used, which can be produced from simple rubber materials and still achieve a satisfactory sealing against bearing seats and crankshaft. Also, such a sealing arrangement can be produced as one unit at the same manufacturing occasion. By arranging the sealing arrangement such that it has at least one protrusion arranged in a pushing engagement with the bearing, according to claim 8, tolerances in the axial direction of the crankshaft can be received by the protrusions .

By arranging the at least one protrusion of the sealing arrangement such it bears against an outer ring of the bearing, according to claim 9, a displacement can be achieved between an outer ring and an inner ring of the bearing. Thereby, when the bearing is realized as a ball bearing, it is ensured that the balls of the ball bearing will be in contact with both the inner and the outer ring of the bearing. Due to this measure, the bearing will achieve a long life.

By arranging a number of protrusions forming a discontinuous ring bearing against an outer ring of the bearing, according to claim 10, the sealing arrangement will contribute to centering the bearing in an axial direction of the crankshaft.

By arranging the at least one protrusion with a tapered shape, according to claim 11, a compression that is proportional to the pressure from the bearing will be achieved. Thereby, dimension variations in an axial direction due to manufacturing tolerances can be well received independent of the size of the dimension variations. According to a second aspect of the invention, an internal combustion engine is provided, comprising a crankshaft and at least one arrangement according to any of the embodiments described in this document.

According to third aspect of the invention, a hand- held motor-driven tool is provided, comprising an internal combustion engine having a crankshaft and at least one arrangement according to any of the embodiments described in this document.

Brief Description of the Drawings

The invention will in the following be described in more detail with reference to the enclosed drawings, wherein:

Figure 1 shows an embodiment of the crankshaft bearing arrangement of the invention in a vertical cross-sectional

view in an axial plane of a crankshaft at which the bearing arrangement is arranged.

Figure 2 shows an embodiment of the crankshaft bearing arrangement of the invention in a vertical cross-sectional view in section I-I of figure 1.

Figure 3 shows an enlargement of a part of figure 1 describing a part of a sealing arrangement according to an embodiment of the invention.

Figure 4 illustrates a schematic front view of a side of a sealing arrangement facing the bearing, according to an embodiment of the invention.

Description of Embodiments

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements.

In the embodiment of the invention described in the figures, a crankshaft 16 is shown, which is journalled in two bearings 10, in the form of ball bearings. Although, other types of bearings might also be used. Between the two bearings 10, and mounted on the crankshaft is a crankshaft assembly 14 with piston rod and counterweights. The bearings 10 are inserted in a bearing seat, which in this embodiment comprises an upper half 15, which is a lower part of a cylinder of an internal combustion engine, and a lower half 11, which is a part of a crankcase of a tool in which the arrangement is installed. Each bearing is supported by the two halves of the

bearing seat in such a way that the bearing seat houses the bearings .

According to the invention, the lower half 11 of the bearing seat has a reinforcement 12 arranged as a layer of metal inside the bearing seat for receiving a pressure force from each bearing. The reinforcement is coated by a plastic material, which provides a surface 13 of the lower half of the bearing seat, which surface bears directly against the bearing. Thereby, the surface 13 of plastic material is arranged as a layer between the bearing 10 and the reinforcement layer 12. The surface 13 is of a fibre- reinforced plastic material, which can endure high loads and temperatures that may occur in a held-held motor-driven tool, such as a chainsaw. The surface is made as thin as possible for the manufacturing process . Typically, when using an injection casting procedure, the plastic surface 13 will be 1- 1,5 mm. Typically, the reinforcement layer 12 has a thickness of approximately 2-6 mm, depending e.g. on the size of the engine. The surface of plastic material bearing against the bearing may be made of the same plastic material as the rest of the crankcase. Thereby, the reinforcement will be embedded in the plastic material of the crankcase, and the surface of the plastic material will be arranged as a layer between the bearing and the reinforcement. In the embodiment described in the figures, the lower half of the bearing seat 11 has two reinforcements, each arranged close to each bearing 10 as a metal layer inside the bearing seat.

In the embodiment described in the figures, see e.g. figure 2, the cylinder 15 rests on the upper part of the crankcase 11. For this reason, the crankcase has an upper surface comprising four metal areas 17, two at each bearing, on which the cylinder stands, called the cylinder foot plane. By arranging the plastic surface layer such that it extends to

also cover the area around these four metal areas, there is no risk of leakage at the cylinder foot plane.

The embodiment described in the figures also shows two separate sealing arrangements 20, arranged against a side of each bearing 10, which side faces away from the crankshaft assembly 14, both sealing arrangements being arranged around the crankshaft 16. Each sealing arrangement 20 is arranged as one unit to seal against the crankshaft 16 and the bearing seat 11, 15. The sealing arrangement 20 shown in the embodiment described in the figures is arranged as a sealing ring having a diameter substantially equal to the diameter of the bearing 10.

Figure 4 shows a side of the sealing ring which, when the sealing ring is arranged on the crankshaft, faces the bearing 10. As could be seen in figure 3 and 4, the sealing ring has a number of protrusion 21 arranged at a certain radius of the ring such that the protrusions 21 bear against an outer ring of the bearing 10. Due to this measure, the protrusions 21 help to push an outer ring of the bearing 10 in an axial direction of the crankshaft 16 towards the crankshaft assembly 14, such that the bearings are pushed into a proper position, which results in a long life for the bearings, the crankshaft assembly and the cylinder. The protrusions 21 preferably form a discontinuous ring bearing against the outer ring of the bearing 10. According to other embodiments, the protrusions might also have other forms, such as a continuous ring.

The protrusions 21 preferably have a tapered shape in a direction towards the outer ring of the bearing. Although, the protrusions 21 might have other shapes, such as squared.

In the embodiment described above, the cylinder is manufactured from a metal, which means that it has a surface of metal bearing against the bearing 10. This surface has to be after-treated after the cylinder has been produced in e.g.

a die casting procedure to get low tolerances and a fine surface against the bearing. Although, a cylinder of an internal combustion engine has to be after-treated anyhow, regarding other parts of a cylinder, and to make more after- treatment of a part that anyhow experiences after-treatment is more cost-efficient than to start an after-treatment process of a part that does not have to be after-treated.

In the embodiment described, only the lower half of the bearing seat has a plastic material surface bearing against the bearing and a reinforcement arranged in the bearing seat close to the surface. Although, such an arrangement might also be used for an upper part of the bearing seat, or for parts of the lower or upper part of the bearing seat.

In the embodiment described, the bearing seat comprises a lower half of a cylinder and an upper half of a crankcase, which are connected at a horizontal section. In an alternative embodiment, the invention is adapted to be suitable for crankshaft arrangements in which a bearing seat is arranged coaxially onto a crankshaft as one integral part housing one bearing. In such arrangements the internal combustion engine comprises two bearing seats, one first bearing seat preferably housing a first bearing and one second bearing seat preferably housing a second bearing, arranged in such a way that each bearing seat supports one respective bearing. Further, in this alternative embodiment the first bearing seat is integrated in a first crankcase half and the second bearing seat is integrated in a second crankcase half, wherein the two crankcase halves are connected at a vertical section to form the crankcase. For such arrangements, the whole or part of the surface of the bearing seat may be coated with a plastic material, and correspondingly, the whole or part of the bearing seat may have a reinforcement arranged in the bearing seat. If the reinforcement is arranged in the whole of one bearing seat, it may be arranged as a ring of e.g. metal,

arranged close to the surface of plastic material. Such a ring reinforcement would be easy to manufacture and there would not be necessary with any after-treatment of a surface bearing against the bearing. The plastic material of the surface of the bearing seat bearing against the bearing is preferably any kind of reinforced plastic material, such as a carbon fibre reinforcement, a glass fibre reinforcement or a nano-composite material. The surface may be of any kind of plastic material that has a high heat distortion temperature. The higher the heat distortion temperature of the material and the thinner the layer of plastic material, the less the plastic material will be deformed.

In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.