JP6398934B2 - Crankshaft support structure for internal combustion engines - Google Patents

Description

  The present invention relates to a crankshaft support structure for an internal combustion engine, and more particularly to a technique for preventing oil film breakage of a crankshaft bearing and maintaining a liquid lubrication state.

  Generally, lubricating oil is supplied to a bearing of a crankshaft of an internal combustion engine, and a thin oil film is formed on the inner peripheral surface of the bearing. This oil film serves to reduce the friction between the sliding surfaces of the crankshaft and the bearing and to cool the heat generated by the friction. If the oil film runs out, there is a risk that seizure will occur due to frictional heat between the sliding surfaces of the crankshaft and the bearing. Therefore, the bearing of the crankshaft of the internal combustion engine is required to avoid solid lubrication due to oil film breakage and maintain a liquid lubrication state in which an oil film is formed.

  2. Description of the Related Art Conventionally, there has been known a bearing device that supplies lubricating oil with a sufficient flow rate to a bearing in order to prevent an oil film breakage of the bearing of the crankshaft (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-30419

  In the conventional bearing device, there is a problem that the work of the oil pump for increasing the supply amount of the lubricating oil is increased, and the mechanical resistance of the entire internal combustion engine is increased. On the other hand, in a supercharged engine or a high compression ratio engine, the load applied to the bearing of the crankshaft of the internal combustion engine tends to increase, and there is a concern that the oil film may break at the bearing. Accordingly, it is necessary to increase the load capacity of the bearing (wear resistance, seizure resistance, etc.).

  In view of the above problems, the present invention maintains a liquid lubrication state by preventing oil film breakage of a crankshaft bearing with a comparatively simple structure without using a mechanism for increasing the supply amount of lubricating oil. Is an issue.

A crankshaft support structure for an internal combustion engine according to an aspect of the present invention includes a crankshaft having a main journal and a pin journal, a crankshaft bearing that rotatably supports the main journal, and a connecting rod that rotatably supports the pin journal. a bearing, and a oil path for supplying lubricating oil to the crankshaft bearings and connecting rod bearings, at least one of the main journals and pin journals, Ri Oh axial vertical cross section in oval journals oval piston dead point In this state, the angle formed between the minor axis of the elliptical cross section of the elliptical journal and the reciprocating direction axis of the piston is −50 in the rotational direction of the elliptical journal with the reciprocating direction axis of the piston being 0 °. It is in the range of not less than 20 ° and not more than 20 °.

According to this, it is possible to secure a large minimum oil film thickness region formed between the lower end of the outer peripheral surface of the elliptical journal and the lower end of the inner peripheral surface of the bearing, thereby reducing the frictional force between the journal and the bearing as compared with the prior art. Can increase the load capacity of the journal .

In addition, the friction loss average effective pressure can be reduced, and a friction loss reduction effect can be obtained.

  In the crankshaft support structure of the internal combustion engine, it is more preferable that the minor axis of the elliptical cross section of the elliptical journal is inclined in the range of −30 ° to less than 0 ° with respect to the rotational direction of the elliptical journal.

  According to this, the friction loss average effective pressure can be minimized, and the maximum friction loss reduction effect can be obtained.

A crankshaft support structure for an internal combustion engine according to another aspect of the present invention includes a crankshaft having a main journal and a pin journal, a crankshaft bearing that rotatably supports the main journal, and the pin journal. An elliptical journal comprising a connecting rod bearing that freely supports and an oil passage that supplies lubricating oil to the crankshaft bearing and the connecting rod bearing, wherein at least one of the main journal and the pin journal has an elliptical vertical cross section. The elliptical journal bearing is an elliptical bearing having an elliptical cross section in the axial direction, and the curvature of the minimum curvature portion of the elliptical journal is equal to the curvature of the minimum curvature portion of the elliptical bearing.

According to this, it is possible to secure a larger minimum oil film thickness region formed between the lower end of the outer peripheral surface of the elliptical journal and the lower end of the inner peripheral surface of the bearing, and the frictional force between the journal and the bearing is smaller than before. Thus, the load capacity of the journal can be increased.

  According to the present invention, without using a mechanism for increasing the supply amount of lubricating oil, it is possible to maintain a liquid lubrication state by preventing oil film breakage of the bearing of the crankshaft with a comparatively simple structure.

Side surface sectional drawing of the crankshaft support structure of the internal combustion engine which concerns on one Embodiment of this invention Perspective view of crankshaft support structure with lower structure (lower block) removed Perspective view of crankshaft support structure with upper structure (cylinder block) removed Crankshaft perspective view VV sectional view of FIG. Diagram comparing the minimum oil film thickness area of a perfect circle journal (conventional example) and an elliptical journal (embodiment) Schematic diagram showing oil film pressure distribution around the journal bearing A graph showing the relationship between the inclination of the elliptical journal and the friction loss mean effective pressure

  Hereinafter, embodiments will be described in detail with reference to the drawings as appropriate. However, more detailed explanation than necessary may be omitted. For example, detailed descriptions of already well-known matters and repeated descriptions for substantially the same configuration may be omitted. This is to avoid the following description from becoming unnecessarily redundant and to facilitate understanding by those skilled in the art.

  The inventor (s) provides the accompanying drawings and the following description in order for those skilled in the art to fully understand the present invention, and these are intended to limit the subject matter described in the claims. Not what you want. In addition, the dimensions, thicknesses, detailed shapes of details, and the like of each member depicted in the drawings may be different from actual ones.

  FIG. 1 is a side sectional view of a crankshaft support structure 100 for an internal combustion engine according to an embodiment of the present invention. The crankshaft support structure 100 is divided into an upper structure (cylinder block 20) and a lower structure (lower block 30) at the axial center of the crankshaft 10. FIG. 2 is a perspective view of the crankshaft support structure 100 with the lower structure (lower block 30) removed. FIG. 3 is a perspective view of the crankshaft support structure 100 with the upper structure (cylinder block 20) removed.

  The crankshaft support structure 100 for an internal combustion engine according to this embodiment is a crankshaft support structure for an in-line four-cylinder four-stroke engine (internal combustion engine) in which four cylinders (cylinders 21) are arranged in series. The first cylinder, the second cylinder, the third cylinder, and the fourth cylinder are arranged in this order from the front (left side in FIG. 1) of the crankshaft support structure 100. FIGS. 1 to 3 show the first cylinder and the fourth cylinder. This represents a state where the piston 40 is at the top dead center position and the pistons 40 of the second and third cylinders are at the bottom dead center position (state where the crank angle is 0 °).

  The piston 40 slides in the cylinder 21 and reciprocates. A small end portion of a connecting rod (connecting rod) 50 is connected to the piston 40, and a large end portion of the connecting rod 50 is connected to a pin journal 12 (see FIG. 4) of the crankshaft 10. Thereby, the reciprocating motion of the piston 40 is converted into the rotational motion of the crankshaft 10 via the connecting rod 50. When the piston 40 is at the dead center position (top dead center or bottom dead center), the connecting rod 50 is in a straight state with respect to the reciprocating direction of the piston 40, that is, in an upright state.

  The cylinder block 20 is a structure in which four cylinders 21 and an outer wall are integrally molded. A semicircular cutout for supporting the crankshaft 10 is provided in the lower part of the cylinder block 20. A halved flat bearing (bearing metal) 22a is provided in the notched portion.

  The lower block 30 is a structure in which a bearing of the crankshaft 10 and an outer wall are integrally formed. A semicircular cutout for supporting the crankshaft 10 is provided on the upper portion of the lower block 30. A halved flat bearing (bearing metal) 22b is provided in the notched portion.

  The crankshaft bearing 22 is formed by vertically combining the bearing metal 22a on the cylinder block 20 side and the bearing metal 22b on the lower block 30 side. The crankshaft bearing 22 is a bearing that rotatably supports the main journal 11 (see FIG. 4) of the crankshaft 10.

  The large end of the connecting rod 50 is divided into a top and bottom by a connecting rod body 51 and a connecting rod cap 53. The connecting rod main body 51 is provided with a half-split flat bearing (bearing metal) 52a. The connecting rod cap 53 is provided with a split-type flat bearing (bearing metal) 52b. A connecting rod bearing 52 is formed by vertically combining a bearing metal 52a on the connecting rod body 51 side and a bearing metal 52b on the connecting rod cap 53 side. The connecting rod bearing 52 is a bearing that rotatably supports the pin journal 12 (see FIG. 4) of the crankshaft 10.

  A crankcase may be used as the lower structure of the crankshaft support structure 100 in place of the lower block 30. In that case, a bearing beam and a bearing cap are provided on the crankcase, and a bearing metal 22b is provided on the bearing cap.

  FIG. 4 is a perspective view of the crankshaft 10. The crankshaft 10 is composed of five main journals 11 and four pin journals 12 alternately arranged. The main journal 11 is supported by a bearing (crankshaft bearing 22) formed by combining the cylinder block 20 and the lower block 30 vertically. The pin journal 12 is supported by a bearing (a connecting rod bearing 42) formed at the large end of the connecting rod 41. A piston 40 is connected to the small end of the connecting rod 41 (see FIGS. 1 and 3).

  The main journal 11 and the pin journal 12 are connected by a crank arm 13. A part of the crank arm 13 is provided with a counterweight 14 on the side opposite to the pin journal 12.

  Oil supply holes 15 are provided on the outer peripheral surfaces of the main journal 11 and the pin journal 12. The oil supply hole 15 of the main journal 11 and the oil supply hole 15 of the adjacent pin journal 12 are connected by an oil passage 16 (see FIG. 1) inside the crankshaft 10, and the end of the oil passage 16 is a blind plug. 17 (see FIG. 1).

  Lubricating oil is supplied by pressure from a main gallery (not shown) provided in the cylinder block 20 to a bearing (crankshaft bearing 22) of the main journal 11 through an oil passage 23 (see FIG. 5). A part of the lubricating oil enters the oil supply hole 15 of the main journal 11, and is ejected from the oil supply hole 15 of the pin journal 12 through the oil passage 16, so that the bearing of the pin journal 12 (the connecting rod bearing 42) is also injected. Lubricating oil is supplied.

  A camshaft drive 18 as a sprocket or crank gear is attached to the front end of the crankshaft 10. A crank pulley (not shown) for driving various auxiliary machines can be attached to the front end of the crankshaft 10. On the other hand, a flange 19 to which a flywheel (not shown) is fastened is provided at the rear end portion of the crankshaft 10.

  5 is a cross-sectional view taken along the line VV in FIG. As shown in the drawing, the vertical cross section in the axial direction of the main journal 11 of the crankshaft 10 is elliptical. Specifically, the shape of the cross section in the axial direction of the main journal 11 is an ellipse in which the upper and lower sides of a 50 mm perfect circle are shortened by 5 μm (short axis) and the left and right are lengthened by 5 μm (long axis). As will be described later, the main journal 11 is adjusted so that the elliptical shape of the axial vertical cross section is slightly inclined around the rotation axis of the crankshaft 10 in a state where the piston 40 is at the dead center position. Note that the pin journal 12 of the crankshaft 10 may have an elliptical vertical cross section in the same manner as the main journal 11.

  Hereinafter, for convenience, a journal having an elliptical cross section in the axial direction as in the present embodiment is referred to as an “elliptical journal”. On the other hand, a journal having a circular vertical cross section in the axial direction as in the conventional example is referred to as a “perfect circle journal”. FIG. 6 is a diagram comparing minimum oil film thickness regions of a perfect circle journal (conventional example) and an elliptical journal (embodiment). For convenience, the space between the journal (main journal 11 or pin journal 12) and the bearing (crankshaft bearing 22 or connecting rod bearing 52) is drawn extremely wide. Further, as shown in the figure, the axial vertical cross section of the journal bearing (crankshaft bearing 22 or connecting rod bearing 52) may be elliptical. Hereinafter, this is referred to as “elliptical bearing”.

  When the intake and compression of the air-fuel mixture into the cylinder 21 are finished, the piston 40 is at the top dead center position. When the air-fuel mixture is ignited and combusted, the combustion gas expands and the piston 40 is pushed down to the bottom dead center. At this time, an explosion load is applied to the crankshaft 10, and the largest load is applied to the lower end portion of the inner peripheral surface of the crankshaft bearing 22 that supports the main journal 11. An oil film of lubricating oil is formed in the gap between the outer peripheral surface of the main journal 11 and the inner peripheral surface of the crankshaft bearing 22, but the oil film thickness at the lower end portion of the inner peripheral surface of the crankshaft bearing 22 that receives a large load is the thinnest. (Minimum oil film thickness region).

  Comparing the conventional perfect circle journal and the elliptic journal according to the present embodiment, since the perfect circle journal has the same curvature in every part, the minimum oil film thickness region is relatively small. By making the minimum curvature portion of the elliptical journal contact the lower end of the inner peripheral surface of the crankshaft bearing 22 when an explosion load is applied to the shaft 10, a relatively large minimum oil film thickness region can be secured. Therefore, according to the present embodiment, the frictional force between the main journal 11 and the crankshaft bearing 22 is made smaller than before and the main journal 11 is made smaller while preventing the oil film from being cut off at the place where the main journal 11 and the crankshaft bearing 22 are rubbed. 11 load capacity can be increased.

  In particular, it is preferable that the journal bearing (crankshaft bearing 22 or connecting rod bearing 52) is an elliptical bearing so that the curvature of the minimum curvature portion of the elliptical journal is equal to the curvature of the minimum curvature portion of the elliptical bearing. As a result, a larger minimum oil film thickness region can be secured, the frictional force between the main journal 11 and the crankshaft bearing 22 can be reduced, and the load capacity of the main journal 11 can be further increased.

  Although the main journal 11 and the crankshaft bearing 22 have been described as examples, the same applies to the pin journal 12 and the connecting rod bearing 52. That is, by making the pin journal 12 an elliptical journal, the frictional force between the pin journal 12 and the connecting rod bearing 52 is made smaller than before, while preventing the oil film from being cut off at the location where the pin journal 12 and the connecting rod bearing 52 are frictioned. Thus, the load capacity of the pin journal 12 can be increased. Furthermore, by using the connecting rod bearing 52 as an elliptical bearing, the frictional force between the pin journal 12 and the connecting rod bearing 52 can be reduced, and the load capacity of the pin journal 12 can be further increased.

  FIG. 7 is a schematic diagram showing the oil film pressure distribution around the journal bearing. When the elliptical journal (main journal 11 or pin journal 12) is rotating, the lubricating oil between the outer peripheral surface of the elliptical journal and the inner peripheral surface of the bearing (crankshaft bearing 22 or connecting rod bearing 52) has its viscosity. Is pulled into the tapered gap in the journal rotation direction. As a result, a pressure (wedge oil film pressure) as illustrated in the lubricating oil is generated at the lower end portion of the inner peripheral surface of the bearing. As described above, an area where the oil film pressure is small in the region where the oil film pressure develops by making the vicinity of the minimum curvature portion of the elliptical journal come into contact with the lower end of the inner peripheral surface of the bearing when an explosion load is applied to the crankshaft 10. Can be increased, and the minimum oil film thickness region can be increased.

  Here, in the elliptical journal, the axis of reciprocating motion of the piston 40 is Ax_rec, the short axis of the elliptical cross section of the elliptical journal with the piston 40 in the dead center position is Ax_mr, and the angle formed by Ax_rec and Ax_mr is φ , Φ is preferably other than ± 90 °. A specific range of φ will be described later.

  FIG. 8 is a graph showing the relationship between the inclination of the elliptical journal and the friction loss mean effective pressure (FMEP). The friction loss average effective pressure is related to the friction loss of the journal. The smaller the friction loss average effective pressure, the greater the effect of reducing the journal friction loss. For comparison, the average effective pressure of friction loss of a perfect circle journal is also shown.

  Since every round journal has the same curvature, the average effective frictional loss pressure is constant. On the other hand, in the case of an elliptical journal, the curvature varies depending on the portion. A negative value φ represents that the elliptical journal is tilted in the opposite direction of rotation while the piston 40 is at the dead center position. A positive value φ indicates that the elliptical journal is tilted in the rotational direction with the piston 40 in the dead center position. It can be seen from the graph in the figure that when φ is in the range of −50 ° to 20 ° (including both end values), the friction loss average effective pressure is smaller than that of the conventional example (a perfect circle journal). In particular, when φ is in a range of −30 ° or more and less than 0 °, the friction loss average effective pressure can be minimized. Therefore, the reciprocating direction axis of the piston 40 is 0 °, and the angle formed by the short axis of the elliptical cross section of the elliptical journal and the reciprocating direction axis of the piston 40 is −50 ° or more and 20 ° in the rotational direction of the elliptical journal. The following range is preferable, and it can be said that it is more preferable to incline the minor axis of the elliptical cross section of the elliptical journal in the range of −30 ° to less than 0 ° in the rotational direction of the elliptical journal.

  As described above, the embodiments have been described as examples of the technology in the present invention. For this purpose, the accompanying drawings and detailed description are provided.

  Accordingly, among the components described in the accompanying drawings and the detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to illustrate the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

  Moreover, since the above-mentioned embodiment is for demonstrating the technique in this invention, a various change, replacement, addition, abbreviation, etc. can be performed in a claim or its equivalent range.

10 Crankshaft 11 Main Journal (Oval Journal)
12 pin journal (ellipse journal)
22 Crankshaft bearing (elliptical bearing)
40 Piston 52 Connecting rod bearing (Oval bearing)
53 Oil passage 100 Crankshaft support structure

Claims (3)

A crankshaft having a main journal and a pin journal;
A crankshaft bearing for freely supporting the main journal;
A connecting rod bearing that rotatably supports the pin journal;
An oil passage for supplying lubricating oil to the crankshaft bearing and the connecting rod bearing,
Wherein at least one of the main journals and the pin journals, axial vertical cross section Ri Oh elliptical journal oval,
In the state where the piston is at the dead center position, the angle formed between the minor axis of the elliptical cross section of the elliptical journal and the reciprocating direction axis of the piston is 0 ° with respect to the reciprocating direction axis of the piston. A crankshaft support structure for an internal combustion engine, wherein the crankshaft support structure is in a range of -50 [deg.] To 20 [deg.] In the rotational direction . 2. The crankshaft support structure for an internal combustion engine according to claim 1 , wherein a minor axis of the elliptical cross section of the elliptical journal is inclined in a range of −30 ° to less than 0 ° with respect to the rotational direction of the elliptical journal. A crankshaft having a main journal and a pin journal;
A crankshaft bearing for freely supporting the main journal;
A connecting rod bearing that rotatably supports the pin journal;
An oil passage for supplying lubricating oil to the crankshaft bearing and the connecting rod bearing,
At least one of the main journal and the pin journal is an elliptical journal having an elliptical cross section in the axial direction,
The elliptical journal bearing is an elliptical bearing having an elliptical cross section in the axial direction,
The crankshaft support structure for an internal combustion engine, wherein the curvature of the minimum curvature portion of the elliptical journal is equal to the curvature of the minimum curvature portion of the elliptical bearing .

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