Lower link of an internal combustion engine

Abstract

The lower link (6) has an oil hole (30) in the crank pin bearing portion (11) for supplying injection oil to the joint portion of the upper pin (4) and the upper link (3). The oil hole (30) is composed of a first oil hole (31) extending linearly from the inner peripheral surface of the crank pin bearing portion (11) to the outer side in the radial direction, and a second oil hole (32) extending linearly from the outer side surface of the lower link (6) so as to intersect the front end portion of the first oil hole (31). The inclination angle (θ) of the first oil hole (31) with respect to the split surface (14) is small, so the position of the oil inlet (3113) where stress concentration becomes a problem is a position close to the split surface (14) where stress is low. Thus, stress concentration at the oil inlet (3113) is mitigated.

Description

TECHNICAL FIELD

[0001] The present application relates to an improvement of a lower link constituting a multi-link piston-crank mechanism of an internal combustion engine. BACKGROUND

[0002] As a prior art that links a piston pin of a reciprocating internal combustion engine and a crank pin by a multi-link piston-crank mechanism, Patent Document 1 and the like previously proposed by the present applicant are known. It has: an upper link linked with the piston pin of a piston; a lower link linking the upper link and a crank pin of a crankshaft; and a control link having one end supported to the internal combustion engine main body side in a swingable manner and the other end linked with the lower link. Further, the upper link and the lower link are rotatably linked with each other via an upper pin, and the control link and the lower link are rotatably linked with each other via a control pin.

[0003] The lower link of such a multi-link piston-crank mechanism takes the combustion pressure received by the piston from the upper pin via the upper link, and transmits the force to the crank pin as a kind of "lever" action with the control pin as a fulcrum.

[0004] In Patent Document 1, a structure is disclosed in which, in a crank pin bearing portion into which the crank pin is fitted, an oil hole that ejects lubricating oil to the outside when coinciding with an oil hole on the crank pin side is formed penetrating in the radial direction. The lubricating oil ejected from the oil hole lubricates the bearing portion between the upper pin and the upper link.

[0005] If the direction of movement of the piston is set as the "up-down" direction, the combustion load is input to the upper pin at one end of the lower link toward the lower side, and the reaction force of the combustion load also acts on the control pin at the other end of the lower link toward the lower side. Further, the reaction force of the combustion load acts on the crank pin bearing portion into which the crank pin of the form between the upper pin and the control pin is fitted toward the upper side. With the input of such a load, a large stress concentrates on the opening edge of the oil hole on the crank pin side of the crank pin bearing portion formed penetratingly as a tensile stress, a bending stress. Therefore, the opening of the oil hole on the crank pin side becomes a weak point in terms of the strength of the lower link, and the high output of the internal combustion engine having the multi-link piston-crank mechanism is limited.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-196888 SUMMARY

[0007] Regarding the lower link to which the present application relates, the oil hole that supplies lubricating oil from the oil supply hole of the crank pin toward the linking portion of the upper pin and the upper link is composed of a first oil hole that extends linearly from the inner circumferential surface of the crank pin bearing portion to the radial direction outside and a second oil hole that intersects the front end portion of the first oil hole, opens one end as an oil outlet on the outside surface of the lower link, and extends linearly.

[0008] In other words, the oil hole of the lower link is formed in an approximate L shape by combining a first oil hole and a second oil hole each formed in a straight line. Lubricating oil supplied from the crank pin is supplied toward the joint of the upper pin and the upper link, which is a lubrication target, through the first oil hole and the second oil hole.

[0009] With this structure, compared with a case where the oil hole is formed in a simple straight line from the crank pin side toward the joint of the upper pin and the upper link, which is a lubrication target, the inclination angle of the first oil hole, which opens in the inner peripheral surface of the crank pin bearing portion (i.e., which inclines toward the direction away from the piston), can be relatively reduced. The circumferential distribution of stress generated in the crank pin bearing portion by the load input described above is large at a position in the direction from the center of the crank pin toward the piston, and thus the inclination angle of the first oil hole is reduced so that the opening position of the first oil hole becomes a position where the stress is relatively small.

[0010] Therefore, stress concentration at the opening edge of the oil hole of the crank pin bearing portion, which is a weak point in terms of strength of the lower link, is mitigated, and this is advantageous in terms of ensuring the strength of the lower link and high output of the internal combustion engine. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a structural explanatory view of a multi-link type piston-crank mechanism of an embodiment.

[0012] Figure 2 is an oblique view of a lower link of the first embodiment.

[0013] Figure 3 is a cross-sectional view of the lower link of the first embodiment.

[0014] Figure 4 is a cross-sectional view of an upper portion of the lower link of the first embodiment.

[0015] Figure 5 is an oblique view of a bearing metal piece.

[0016] Figure 6 is a cross-sectional view of the lower link of the first embodiment assembled with the bearing metal piece.

[0017] Figure 7 is a cross-sectional view of a lower link of the second embodiment.

[0018] Figure 8 is a cross-sectional view of an upper portion of the lower link of the second embodiment.

[0019] Figure 9 is a cross-sectional view of the lower link of the second embodiment assembled with the bearing metal piece. DETAILED DESCRIPTION

[0020] Next, an embodiment of the present application will be described in detail based on the drawings.

[0021] Figure 1 A structural element of a multi-link piston-crank mechanism to which the present application is applied is shown. The multi-link piston-crank mechanism itself is a well-known structure according to the aforementioned Patent Literature 1 or the like, and has an upper link 3 whose one end is linked with a piston 1 via a piston pin 2, a lower link 6 whose other end is linked with the upper link 3 via an upper pin 4 and is linked with a crank pin 5 of a crankshaft, and a control link 7 that restricts a degree of freedom of the lower link 6. One end of the control link 7 is swingably supported to a support pin 8 on an engine main body side, and the other end is linked with the lower link 6 via a control pin 9. Further, the multi-link piston-crank mechanism can be configured as a variable compression ratio mechanism by making a position of the support pin 8 variable.

[0022] As shown in Figure 2 and Figure 3 The lower link 6 has a cylindrical crank pin bearing portion 11 in which the crank pin 5 is fitted in the center, and an upper pin pin boss portion 12 and a control pin pin boss portion 13 are provided at positions on opposite sides of the crank pin bearing portion 11 at approximately 180° from each other. The lower link 6 is formed as a parallelogram close to a rhombus, and is divided into a lower link upper portion 6A including the upper pin pin boss portion 12 and a lower link lower portion 6B including the control pin pin boss portion 13 at a division surface 14 passing through the center of the crank pin bearing portion 11. The lower link upper portion 6A and the lower link lower portion 6B are fastened to each other by two bolts 21 and 22 on both sides of the crank pin bearing portion 11 with the crank pin 5 fitted in the crank pin bearing portion 11 via a bearing metal member 16 described later. The two bolts 21 and 22 extend in directions orthogonal to the division surface 14, i.e., the bolt center lines are parallel to each other. Further, the bolt 21 on the upper pin pin boss portion 12 side penetrates a bolt hole 23 on the lower link lower portion 6B side and is screwed into a screw hole 24 on the lower link upper portion 6A side. The bolt 22 on the control pin pin boss portion 13 side penetrates a bolt hole 25 on the lower link upper portion 6A side and is screwed into a screw hole 26 on the lower link lower portion 6B side.

[0023] The aforementioned upper pin boss 12 and control pin boss 13 are formed in a two-strand structure, clamping the upper connecting rod 3 and control connecting rod 7 at the axial center. A pair of bearing flanges 12a and 13a, which support the axial ends of the upper pin 4 and control pin 9 respectively, extend along the axial end face of the lower connecting rod 6. That is, each bearing flange 12a and 13a constituting the pin bosses 12 and 13 is connected to the two axial ends of the cylindrical crank pin bearing portion 11. The bearing flanges 12a and 13a each have circular through holes 12b and 13b, into which the cylindrical ends of the upper pin 4 and control pin 9 are pressed. Furthermore, the upper connecting rod 3 and control connecting rod 7 are oscillating in the grooves 17 and 18 formed between the pair of bearing flanges 12a and 13a.

[0024] The aforementioned crank pin bearing portion 11 is engaged with the crank pin 5 via a pair of semi-cylindrical bearing metal parts 16 (see reference). Figure 5 , Figure 6 The crank pin 5 has an internal lubrication passage for supplying pressurized lubricating oil, and the front end of the lubrication passage extending radially serves as an oil supply hole 29 (see reference). Figure 1 The crank pin 5 has an opening on its outer peripheral surface. As will be described later, an oil hole 30 is formed through the crank pin bearing portion 11. The oil hole 30 is configured such that when it coincides with the oil supply hole 29 on the crank pin 5 side, lubricating oil is sprayed from the oil hole 30 as so-called injection oil.

[0025] Regarding the lower connecting rod 6, the combustion load is transferred from the upper connecting rod 3 via the upper pin 4 to the upper pin boss 12, causing it to swing with the control pin 9 as the fulcrum. This transmits the force to the crank pin 5 in a lever-like motion. Therefore, the combustion load... Figure 1 The lower side acts on the upper pin boss 12, and the combustion load reaction force also acts towards... Figure 1 The force acts on the lower side of the control pin boss 13, and in contrast, the reaction force from the crank pin 5... Figure 1 The stress acts on the upper side near the center of the crankpin bearing portion 11, thereby generating significant stress around the crankpin bearing portion 11 in the upper part 6A of the lower connecting rod. The circumferential distribution of stress in the crankpin bearing portion 11 is greatest roughly from the center of the crankpin 5 towards the piston 1, and more specifically, slightly towards the vicinity of the upper pin 4. On the other hand, the stress is relatively reduced in the portion of the crankpin bearing portion 11 near the dividing surface 14.

[0026] Figure 4 This is a cross-sectional view of the upper part 6A of the lower connecting rod having the oil hole 30 of the first embodiment in the crank pin bearing section 11 (a cross-sectional view along a plane orthogonal to the axial direction of the crank pin 5).

[0027] The oil hole 30 is used to lubricate the sliding surface between the upper pin 4 and the upper link 3 at the joint portion of the upper link 3 and the lower link 6, and is formed in a substantially L shape by the first oil hole 31 and the second oil hole 32.

[0028] The first oil hole 31 is a non-through (i.e., the front end 31a is closed) hole extending linearly from the inner circumferential surface 11a of the crank pin bearing portion 11 to the radially outer side, and the base end is opened at the inner circumferential surface 11a of the crank pin bearing portion 11 as an oil inlet 31b. In one embodiment, the first oil hole 31 is inclined with respect to the division surface 14 and is formed along the radial line of the crank pin bearing portion 11. In this way, the first oil hole 31 is arranged along the radial line of the crank pin bearing portion 11 so that the oil inlet 31b is substantially opened in a pure circle.

[0029] In addition, regarding the first oil hole 31, in order to avoid a portion having a high stress in the circumferential distribution of the stress of the above-described crank pin bearing portion 11, the inclination angle of the lower link 6 (for example, the inclination angle θ with the division surface 14 as a reference) is set to be small. In the illustrated first embodiment, the inclination angle θ of the first oil hole 31 with the division surface 14 as a reference is 10°. In this way, the inclination angle θ is small, and therefore the extension line of the center line of the first oil hole 31 is formed in a direction that does not intersect the outer circumferential surface of the upper pin 4. In detail, the extension line of the center line of the first oil hole 31 passes through the lower side (the opposite side of the piston 1) of the upper pin 4.

[0030] The second oil hole 32 is a non-through (i.e., the front end 32a is closed) hole extending linearly from the outer side surface of the lower link 6, in detail, the bottom surface 17a of the groove portion 17 opposite the upper pin 4, to the inside of the lower link 6, and the base end is opened at the above-described bottom surface 17a as an oil outlet 32b. In the inside of the lower link 6, the front end portion (i.e., the portion on the front end 32a side) of the second oil hole 32 and the front end portion (i.e., the portion on the front end 31a side) of the first oil hole 31 intersect each other. That is, the second oil hole 32 communicates with the first oil hole 31.

[0031] The extension line of the center line of the second oil hole 32 is formed in a direction that intersects the outer circumferential surface of the upper pin 4, and in the illustrated example, the second oil hole 32 points to the vicinity of the center of the upper pin 4. In addition, in the illustrated embodiment, the second oil hole 32 extends in a direction orthogonal to the division surface 14, and therefore is parallel with respect to the center axis of the adjacent bolt 21 and the corresponding screw hole 24. In this way, the second oil hole 32 is parallel with respect to the adjacent screw hole 24, and therefore the thickness therebetween is constant in the axial direction, and it is possible to avoid local thinning and thus a decrease in local strength.

[0032] The first oil hole 31 and the second oil hole 32 are formed along a plane orthogonal to the axial direction of the crank pin 5. For example, the first oil hole 31 and the second oil hole 32 are located on the above-mentioned plane passing through the center of the axial dimension of the crank pin bearing portion 11. Further, in the present application, the first and second oil holes 31, 32 can be formed in an inclined direction having a certain angle with respect to the above-mentioned plane, but it is preferable to form them along the above-mentioned plane in terms of ensuring the strength of the oil inlet 31b of the first oil hole 31.

[0033] The angle formed by the first oil hole 31 and the second oil hole 32 intersecting each other is greater than 90°. For example, the inclination angle θ of the first oil hole 31 with respect to the split surface 14 is 10°, and if the second oil hole 32 is orthogonal to the split surface 14, the first oil hole 31 and the second oil hole 32 intersect at an angle of 100°. Such an obtuse angle intersection makes the loss at the intersection with respect to the flow of lubricating oil smaller.

[0034] The first oil hole 31 and the second oil hole 32 are formed by secondary machining using a drill, for example, after the lower link upper portion 6A is formed by forging. In addition, the lower link upper portion 6A is subjected to carburizing treatment (carburizing quenching) for improving the surface hardness, but it is preferable to perform the drilling before the carburizing treatment.

[0035] Here, in a preferable embodiment, the diameter of the second oil hole 32 is set to be relatively larger than the diameter of the first oil hole 31. By thus increasing the diameter of the second oil hole 32, the rigidity around the second oil hole 32 decreases, a relatively large deformation occurs, and thus the stress around the first oil hole 31 (particularly, the oil inlet 31b thereof), which is the most problematic in terms of stress concentration, decreases. That is, compared to the case where the diameters of both are the same, or the case where, on the contrary, the diameter of the first oil hole 31 is smaller than that of the second oil hole 32, the stress of the oil inlet 31b is alleviated.

[0036] In addition, by thus making the diameter of the second oil hole 32 relatively larger than the diameter of the first oil hole 31, even if there is a machining error or a tolerance, the communication state can be reliably ensured at the intersection of both, and a prescribed passage cross-sectional area can be stably obtained.

[0037] Further, in the illustrated example, according to the case of drilling, the front end 32a of the second oil hole 32 further extends slightly across the first oil hole 31, but if machining is possible, such a remaining passage portion is not required.

[0038] With the above-described embodiment, at a prescribed crank angle, the oil supply hole 29 on the side of the crank pin 5 coincides with the oil inlet 31b of the first oil hole 31, and the pressurized lubricating oil passes through the first oil hole 31 and the second oil hole 32 and is ejected from the oil outlet 32b as injection oil toward the upper pin 4. The injection oil is used to lubricate between the upper pin 4 and the upper link 3.

[0039] Here, the inclination angle θ of the first oil hole 31 with respect to the split surface 14 is small, and the oil inlet 31b is opened at a position close to the split surface 14, so stress concentration of the opening edge of the oil inlet 31b is mitigated. For example, on the premise of the same arrangement of the upper pin 4 and the like, if the oil hole is formed linearly in a direction intersecting the upper pin 4 along a radius line of the crank pin bearing portion 11, the inclination angle θ with respect to the split surface 14 is an angle of about 40°. This angle direction passes through a portion where stress is relatively high from the stress distribution in the circumferential direction of the crank pin bearing portion 11. In contrast, in the above-described embodiment, the oil hole 30 is composed of the first oil hole 31 and the second oil hole 32, so the oil inlet 31b is at a position close to the split surface 14, and this is advantageous in terms of suppressing stress concentration. Figure 4

[0040] However, as described above, if the inclination angle θ of the first oil hole 31 with respect to the split surface 14 is reduced, the circumferential speed of the oil inlet 31b with respect to the crank pin 5 increases (for example, compared to the case where the inclination angle θ is about 40°) in the swinging motion of the lower link 6 and the swinging motion of the crank pin 5. Therefore, there is a tendency that the time when the oil supply hole 29 on the side of the crank pin 5 coincides with the oil inlet 31b is shortened, and the amount of lubricating oil is reduced. Therefore, in a preferred embodiment, as shown in FIG. 6, the communication hole 41 of the bearing metal piece 16 is formed as an elongated hole that is long in the circumferential direction. Figure 5

[0041] That is, the bearing metal piece 16 is divided into two parts by 180° in such a manner that the whole is formed in a cylindrical shape, and is assembled to the lower link upper portion 6A and the lower link lower portion 6B, respectively, in a non-rotating state. In order to make the oil supply hole 29 on the side of the crank pin 5 and the oil inlet 31b of the lower link 6 communicate with each other, the communication hole 41 is formed in the bearing metal piece 16 at a position corresponding to the oil inlet 31b. Further, the communication hole 41 is formed as an elongated hole that extends in the circumferential direction. Thus, the oil supply hole 29 on the side of the crank pin 5 and the oil inlet 31b of the lower link 6 are kept in a communicating state over a prescribed angular range. In other words, the time when the oil supply hole 29 on the side of the crank pin 5 and the oil inlet 31b of the lower link 6 communicate with each other is extended. Therefore, an adequate amount of lubricating oil can be ensured.

[0042] In one embodiment, as shown in FIG. 7, the communication hole 41 of the bearing metal piece 16 is formed as a plurality of holes that are arranged in the circumferential direction. Figure 6 ​​As shown, one end of the communication hole 41 formed as an elongated hole is positioned at a position corresponding to the oil inlet 31b, and the other end extends to a position where the inclination angle θ with the split surface 14 as a reference is large.

[0043] Further, if the communication hole 41 is excessively increased, the surface pressure as a bearing is increased, and thus it is not preferable.

[0044] In the above-described first embodiment, the inclination angle θ of the first oil hole 31 with the split surface 14 as a reference is described as an example of 10°, but in the present application, the inclination angle θ of the first oil hole 31 is not limited to a particular angle. Figures 7-9 The lower link 6 of the second embodiment in which the inclination angle θ of the first oil hole 31 along the radius line of the crank pin bearing portion 11 is set to 24°, for example. The other structures are substantially the same as those of the first embodiment. The extension line of the center line of the first oil hole 31 still points in a direction not intersecting the upper pin 4, and the lubricating oil is guided to the upper pin 4 side via the second oil hole 32.

[0045] In this second embodiment, the intersection angle of the first oil hole 31 and the second oil hole 32 at the intersection portion is larger than that of the first embodiment, and the pressure loss accompanying the change in flow direction is small. In addition, the passage length of the second oil hole 32 is shorter than that of the first embodiment, and based on this point, the pressure loss is also reduced. Conversely, the position of the oil inlet 31b of the first oil hole 31 is close to a portion where the stress is high. Therefore, it is preferable to set the inclination angle θ in consideration of both.

[0046] In the second embodiment, the communication hole 41 of the bearing metal piece 16 is also formed as an elongated hole, but the inclination angle θ of the first oil hole 31 is larger than that of the first embodiment, and thus the oil inlet 31b of the first oil hole 31 is positioned near the circumferential center of the communication hole 41 formed as an elongated hole (see Figure 9 ).

[0047] Further, the lower link upper portion 6A (lower link 6) of the first and second embodiments has an oil hole 28 for supplying injection oil toward the piston 1 (see Figure 1 ) or the cylinder inner wall surface in addition to the above-described oil hole 30. This oil hole 28 is positioned at a position closer to the control pin 9 than a position where the maximum combustion load reaction force acts in the circumference of the crank pin bearing portion 11. Therefore, the stress concentration at the opening edge based on the aforementioned combustion load and combustion load reaction force is small. Therefore, the oil hole 28 is formed as a simple straight line. The communication hole 42 of the bearing metal piece 16 corresponding to this oil hole 28 is formed as a pure circle (see Figure 5 , Figure 6 , Figure 9 ).

[0048] The above describes one embodiment of the application in detail, but the application is not limited to the above-described embodiment and can be appropriately changed. For example, in the above-described embodiment, the first oil hole 31 is formed along the radius line of the crankpin bearing portion 11, but can be slightly inclined with respect to the radius line of the crankpin bearing portion 11 or can be configured to slightly move parallel with respect to the radius line.

[0049] In addition, the second oil hole 32 can also not strictly along the direction orthogonal to the split surface 14 (i.e., the direction parallel to the bolt 21).

Claims

1. A lower link of an internal combustion engine, which is the above-mentioned lower link of a piston-crank mechanism of an internal combustion engine, the piston-crank mechanism having: an upper link whose one end is linked with a piston of the internal combustion engine via a piston pin; a lower link whose other end is linked with the upper link via an upper pin, and which is linked with a crank pin of a crankshaft; and a control link whose one end is swingably supported to an engine main body side, and whose other end is linked with the above-mentioned lower link via a control pin, a crank pin bearing portion that is rotatably fitted with the above-mentioned crank pin is provided between the above-mentioned upper pin and the above-mentioned control pin, an oil hole that supplies lubricating oil from an oil supply hole of the above-mentioned crank pin toward a joint portion of the above-mentioned upper pin and the above-mentioned upper link is formed through the above-mentioned crank pin bearing portion, wherein the above-mentioned oil hole is constituted by: a first oil hole that extends in a straight line from an inner peripheral surface of the above-mentioned crank pin bearing portion to the outside in a radial direction; and a second oil hole that intersects with a front end portion of the above-mentioned first oil hole, and that extends in a straight line, one end of the second oil hole being opened to the outside in a lower link outer surface as an oil outlet, an angle at which the above-mentioned first oil hole intersects with the above-mentioned second oil hole is greater than 90°.

2. The lower link of an internal combustion engine according to claim 1, wherein a diameter of the above-mentioned second oil hole is relatively larger than a diameter of the above-mentioned first oil hole.

3. The lower link of an internal combustion engine according to claim 1 or 2, wherein the lower link is divided into a lower link upper portion including a pin boss portion for the upper pin, and a lower link lower portion including a pin boss portion for the control pin, in a division surface that passes through a center of the above-mentioned crank pin, and the above-mentioned two portions are fastened to each other by a plurality of bolts that extend in a direction orthogonal to the above-mentioned division surface, the above-mentioned first oil hole extends in a direction inclined with respect to the above-mentioned division surface, and the above-mentioned second oil hole extends in a direction orthogonal to the above-mentioned division surface.

4. The lower link of an internal combustion engine according to claim 1 or 2, wherein an extension line of a center line of the above-mentioned first oil hole is formed in a direction that does not intersect with an outer peripheral surface of the above-mentioned upper pin, and an extension line of a center line of the above-mentioned second oil hole is formed in a direction that intersects with the outer peripheral surface of the above-mentioned upper pin.

5. The lower link of an internal combustion engine according to claim 1 or 2, wherein the above-mentioned first oil hole is formed along a radius line of the above-mentioned crank pin bearing portion.

6. The lower link of an internal combustion engine according to claim 1 or 2, wherein the above-mentioned crank pin bearing portion is fitted with the above-mentioned crank pin via a bearing metal piece, and in the above-mentioned bearing metal piece, an elongated hole-shaped communication hole that keeps the oil supply hole of the above-mentioned crank pin and the above-mentioned first oil hole in a communication state over a prescribed angle range is opened. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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