Patent Description:
As a conventional technology in which a multi-link piston crank mechanism connects between a crank pin and a piston pin of a reciprocation type internal combustion engine, one described in a patent document <NUM> previously proposed by the present applicants has been publicly known. This multi-link piston crank mechanism includes an upper link connected to a piston pin of a piston, a lower link which connects the upper link with a crank pin of a crankshaft, and a control link of which one end is swingably supported on the engine body side and the other end is connected to the lower link. Then, the upper link and the lower link are rotatably connected to each other via an upper pin, and the control link and the lower link are rotatably connected to each other via a control pin.

Such a lower link in the multi-link piston crank mechanism receives combustion pressure, which is received by the piston, from the upper pin via the upper link, and transmits force to the crank pin by motion like leverage with the control pin as a fulcrum.

In the patent document <NUM>, there is disclosed a configuration in which an oil hole for injecting lubricating oil to the outside when it meets an oil hole on the crank pin side is formed through a crank pin bearing portion, which is fitted to a crank pin, along a substantially radial direction. The lubricating oil injected from the oil hole lubricates the bearing portion between the upper pin and the upper link.

When the moving direction of the piston is up and down direction, a combustion load is input to the upper pin of one end of the lower link toward the down direction, and the reaction force of the combustion load acts on the control pin of the other end of the lower link toward the down direction similarly. Then, the reaction force of the combustion load acts on the crank pin bearing portion to which the crank pin positioned between the upper pin and the control pin is fitted, toward the substantially up direction. By such a load input, a large stress as tensile stress or bending stress is concentrated at the opening edge on the crank pin side of the oil hole formed through the crank pin bearing portion. Therefore, the opening on the crank pin side of the oil hole is a weak point on the strength of the lower link, and an increase in the output of the internal combustion engine having a multi-link piston crank mechanism is limited.

Patent Document <NUM>: Japanese Patent Application Publication <CIT>.

Prior art document <CIT> refers to a multi-link piston-crank mechanism of an internal combustion engine wherein a crank throw is shortened by the use of a multi-link mechanism, a stress concentration caused by a torsional torque in the vicinity of a pin-side opening of an oil passage, which is open at the outer peripheral surface of a crankpin, is alleviated. The crank throw from the axis of a main journal to the axis of the crankpin is set shorter than one-half of a piston stroke. The oil passage is formed to supply lubricating oil to a bearing portion of the crankpin. The pin-side opening of the oil passage, which is open at the outer peripheral surface of the crankpin, is formed in ranges other than angular ranges of <NUM>°, <NUM>°, <NUM>°, and <NUM>° with respect to a reference line extending from the axis of the main journal toward the axis of the crankpin in a decentering direction of the crankpin.

Prior art document <CIT> shows a lubricating mechanism of a multilink piston-crank mechanism for an internal combustion engine. At a predetermined crank angle at which the crank pin oil passage and the lower link oil passage are communicative, viewed in the direction of the crankshaft, along a straight line connecting the center of rotation of the crank shaft and the end of the lower link oil passage at the side opposed to the pin boss opposing surface, the pin boss portion is disposed as the lubricating object. On the axial side of the pin boss portion, a recess portion is provided.

Prior art document <CIT> describes a lubricating structure that is configured to ensure hardness of a pin boss portion and to improve lubrication performance to a pin shaft bearing part, with a structure which injects and supplies lubricant from a lower link to the pin boss portion of an upper link. On a lower link, a lower link oil passage penetrating a pin boss opposite surface opposing to a pin boss portion of an upper link, and a bearing surface of a crank pin is formed. At a predetermined crank angle, a crank pin oil passage formed on the crank pin and the lower link oil passage are communicated to inject and supply lubricant to the pin boss portion. At that time, on a straight line connecting a rotation center of a crank shaft and an end portion on the pin boss opposite surface side of the lower link oil passage, the pin boss portion to be supplied the lubricant is disposed. On an axial side surface of the pin boss portion, a recessed portion depressed in an axial direction is provided.

Prior art document <CIT> discloses a double-link piston crank mechanism, wherein an opening on one end side of a pin-boss oil passage opens to an inner circumferential surface of a pin boss part of an upper link, while an opening on the other end side thereof opens to the outer circumferential surface of the pin boss part of the upper link. A lower-link oil passage has a one-end-side opening structured to open to a pin-boss-facing surface of the lower link facing the outer circumferential surface of the pin boss part of the upper link and its other-end-side opening structured to open to a crankpin bearing surface. The lower-link oil passage is configured to point, at a prescribed crank angle, to a specified end edge of end edges of the other-end-side opening of the pin-boss oil passage, the specified end edge facing one end side of the upper link.

The object underlying the present invention is achieved by a lower link of an internal combustion engine according to independent claim <NUM>. Preferred embodiments are defined in the respective dependent claims.

A lower link according to the present invention is provided with an oil hole for supplying lubricating oil from an oil supply hole of a crank pin toward the connecting portion between an upper pin and a upper link, and the oil hole is composed of a first oil hole linearly extending from the inner peripheral surface of a crank pin bearing portion outwardly in the radial direction, and a second oil hole linearly extending so as to intersect a distal end portion of the first oil hole and having one end opened to the outer surface of the lower link as an oil outlet.

In other words, the oil hole of the lower link is formed in a substantially L shape formed by combining the first oil hole and the second oil hole each having a liner shape. The lubricating oil supplied from the crank pin is injected and supplied to the connecting portion between the upper pin and the upper link, which is a lubrication object, through the first oil hole and the second oil hole.

In such a configuration, as compared with case where an oil hole having a simple liner shape is formed from the crank pin side toward the connecting portion between the upper pin and the upper link which is a lubrication object, the angle of the inclination of the first oil hole opened to the inner peripheral surface of the crank pin bearing portion can be relatively small (that is, it is inclined in the direction away from a piston). The circumferential distribution of stress generated at the crank pin bearing portion by the above-mentioned load input becomes mostly large in an area in a direction from the center of the crank pin toward the piston, and by reducing the inclination angle of the first oil hole, the opening position of the first oil hole becomes a part at which stress is relatively small.

Accordingly, the stress concentration at the opening edge of the oil hole in the crank pin bearing portion that becomes a weak point in the strength of the lower link is alleviated, with advantageous for securing the strength of the lower link and for increasing in output of the internal combustion engine.

In the following, one embodiment of the present invention will be explained in detail based on the drawings.

In <FIG>, there is shown a component element of a multi-link piston crank mechanism to which the present invention is applied. This multi-link piston crank mechanism itself has been publicly known, for example, by the above-mentioned patent document <NUM>, and is provided with an upper link <NUM> having one end connected to a piston <NUM> via a piston pin <NUM>, a lower link <NUM> connected to the other end of upper link <NUM> via an upper pin <NUM> and connected to a crank pin <NUM> of a crankshaft, and a control link <NUM> for regulating the freedom degree of lower link <NUM>. One end of control link <NUM> is swingably supported on a supporting pin <NUM> on the engine body side, and the other end is connected to lower link <NUM> via a control pin <NUM>. In addition, the multi-link piston crank mechanism can be configured as a variable compression ratio mechanism by making the position of supporting pin <NUM> variable.

As shown in <FIG> and <FIG>, lower link <NUM> includes, in the middle thereof, a cylindrical crank pin bearing portion <NUM> which is fitted to crank pin <NUM>, and a pin boss portion <NUM> for an upper pin and a pin boss portion <NUM> for a control pin, and upper-pin pin boss portion <NUM> is disposed at a position on the side opposite to control-pin pin boss portion <NUM> by approximately <NUM>° with crank pin bearing portion <NUM> sandwiched therebetween. Lower link <NUM> as a whole has a shape of a parallelogram similar to a rhombus, and is formed of two parts of a lower link upper 6A having upper-pin pin boss portion <NUM> and a lower link lower 6B having control-pin pin boss portion <NUM> by being divided at a divided surface <NUM> passing through the center of crank pin bearing portion <NUM>. These lower link upper 6A and lower link lower 6B are fastened to each other by two bolts <NUM> and <NUM> positioned at respective both sides of crank pin bearing portion <NUM>, after crank pin bearing portion <NUM> is fitted to crank pin <NUM> via the after-mentioned bearing metal <NUM>. Two bolts <NUM> and <NUM> each extend in the direction orthogonal to divided surface <NUM>, and bolt center lines of bolts <NUM> and <NUM> are parallel to each other. In addition, bolt <NUM> positioned on the upper-pin pin boss portion <NUM> side passes through a bolt hole <NUM> on the lower link lower 6B side, and is screwed to a screw hole <NUM> on the lower link upper 6A side. Bolt <NUM> positioned on the control-pin pin boss portion <NUM> side passes through a bolt hole <NUM> on the lower link upper 6A side, and is screwed to a screw hole <NUM> on the lower link lower 6B side.

Upper-pin pin boss portion <NUM> and control-pin pin boss portion <NUM> are formed in bifurcated shapes so as to sandwich upper link <NUM> and control link <NUM> in the middle part in the axial direction, and a pair of bearing flange portions 12a and a pair of bearing flange portions 13a respectively supporting upper pin <NUM> and control pin <NUM> extend along the end surfaces in the axial direction of lower link <NUM>. That is, bearing flange portions 12a and 13a respectively forming pin boss portions <NUM> and <NUM> are connected to the end portions in the axial direction of crank pin bearing portion <NUM> having a cylindrical shape. Bearing flange portions 12a and 13a have circular through holes 12b and 13b respectively, and cylindrical end portions of upper pin <NUM> and control pin <NUM> are press-fitted into through holes 12b and 13b respectively. Then, upper link <NUM> and control link <NUM> are swingably moved in groove portions <NUM> and <NUM> respectively which are formed between a pair of bearing flange portions 12a and between a pair of bearing flange portions 13a respectively.

Crank pin bearing portion <NUM> is fitted to crank pin <NUM> via a pair of semicylindrical bearing metals <NUM> (see <FIG> and <FIG>). Crank pin <NUM> is provided with, in the inside thereof, a lubrication oil passage to which pressurized lubricating oil is supplied, and a distal end portion of the lubrication oil passage extending in the radial direction is opened to the outer peripheral surface of crank pin <NUM> as an oil supply hole <NUM> (see <FIG>). As will be mentioned below, an oil hole <NUM> is formed through crank pin bearing portion <NUM>, and when oil hole <NUM> meets oil supply hole <NUM> on the crank pin <NUM> side, lubricating oil is injected from oil hole <NUM> as oil jet.

Combustion load acts on upper-pin pin boss portion <NUM> from upper link <NUM> via upper pin <NUM>, and lower link <NUM> swings with control pin <NUM> as a fulcrum so as to transmit force to crank pin <NUM> by motion like leverage. Consequently, the combustion load acts on upper-pin pin boss portion <NUM> in the lower direction in <FIG> and combustion reaction force acts on control-pin pin boss portion <NUM> in the lower direction in <FIG> similarly. On the other hand, reaction force from crank pin <NUM> acts on the vicinity of the center of crank pin bearing portion <NUM> in the upper direction in <FIG>, and consequently, a large stress is generated around crank pin bearing portion <NUM> of lower link upper 6A. The circumferential distribution of stress of crank pin bearing portion <NUM> becomes maximum in an area in a direction from the center of crank pin <NUM> toward piston <NUM>, more specifically, in an area in a direction slightly close to upper pin <NUM>. On the other hand, in an area close to divided surface <NUM> of crank pin bearing portion <NUM>, stress becomes relatively small.

In <FIG>, there is shown a sectional view of lower link upper 6A (sectional view along a surface orthogonal to the axial direction of crank pin <NUM>) in which an oil hole <NUM> in a first embodiment is provided to crank pin bearing portion <NUM>.

Oil hole <NUM> is formed to lubricate the connecting portion of upper link <NUM> connected to lower link <NUM> in upper-pin pin boss portion <NUM>, namely, the sliding surface between upper link <NUM> and upper link <NUM>, and is formed in a substantially L shape by a first oil hole <NUM> and a second oil hole <NUM>.

First oil hole <NUM> is a non-through hole (that is, a distal end 31a is sealed) linearly extending from an inner peripheral surface 11a of crank pin bearing portion <NUM> outwardly in the radial direction, and the base end is opened to inner peripheral surface 11a of crank pin bearing portion <NUM> as an oil inlet 31b. In one embodiment, first oil hole <NUM> is obliquely inclined with respect to divided surface <NUM>, and is formed along the radial line of crank pin bearing portion <NUM>. In this way, by arranging first oil hole <NUM> along the radial line of crank pin bearing portion <NUM>, oil inlet 31b is opened in a form of substantially true circle.

In addition, the inclination angle of first oil hole <NUM> (for example, an inclination angle θ of first oil hole <NUM> with divided surface <NUM> set as a reference) in lower link <NUM> is set so as to be relatively small, to avoid being positioned in an area where stress is high in the above-mentioned circumferential distribution of stress of crankpin pin bearing portion <NUM>. In the illustrated first embodiment, inclination angle θ of first oil hole <NUM> with divided surface <NUM> set as a reference is <NUM>°. In this way, since inclination angle θ is small, first oil hole <NUM> is formed such that the extension line of the center line of first oil hole <NUM> extends in a direction not intersecting the outer peripheral surface of upper pin <NUM>. Specifically, the extension line of the center line of first oil hole <NUM> passes through the lower side of upper pin <NUM> (opposite side of piston <NUM>).

Second oil hole <NUM> is a non-through hole (that is, a distal end 32a is sealed) linearly extending from the outer surface of lower link <NUM> to the inside of lower link <NUM>. Specifically, it extends from a bottom surface 17a of a groove portion <NUM> facing upper pin <NUM> to the inside of lower link <NUM>, and the base end of second oil hole <NUM> is opened to bottom surface 17a as an oil outlet 32b. In the inside of lower link <NUM>, the distal end portion of second oil hole <NUM> (that is, a portion on the distal end 32a side) and the distal end portion of first oil hole <NUM> (that is, a portion on the distal end 31a side) intersect each other. That is, second oil hole <NUM> communicates with first oil hole <NUM>.

Second oil hole <NUM> is formed such that the extension line of the center line of second oil hole <NUM> extends in a direction intersecting the outer peripheral surface of upper pin <NUM>, and, in the illustration, it is directed to the vicinity of the center of upper pin <NUM>. In addition, in the illustrated embodiment, second oil hole <NUM> extends along the direction orthogonal to divided surface <NUM>, so as to be parallel to the center axial line of bolt <NUM> adjacent thereto and screw hole <NUM> corresponding to bolt <NUM>. In this way, since second oil hole <NUM> extends parallel to screw hole <NUM> adjacent thereto, the thickness therebetween is fixed in the axial direction, and it is possible to suppress the occurrence of partial thinning and partially lowering of strength.

First oil hole <NUM> and second oil hole <NUM> are formed along one plane orthogonal to the axial direction of crank pin <NUM>. For example, first oil hole <NUM> and second oil hole <NUM> are positioned on the plane passing through the middle of the dimension in the axial direction of crank pin bearing portion <NUM>. In addition, in the present invention, although first and second oil holes <NUM> and <NUM> may be formed in an oblique direction so as to have angles to the plane slightly, it is desirable to formed them along the plane in order to secure the strength in oil inlet 31b of first oil hole <NUM>.

The angle formed by first oil hole <NUM> and second oil hole <NUM> intersecting each other is larger than <NUM>°. For example, inclination angle θ of first oil hole <NUM> with divided surface <NUM> set as a reference is <NUM>°, and when second oil hole <NUM> is orthogonal to divided surface <NUM>, second oil hole <NUM> intersects first oil hole <NUM> at the angle of <NUM>°. In this way, first oil hole <NUM> intersects second oil hole <NUM> at an obtuse angle, and consequently, the loss of flow of lubricating oil at the intersection becomes small.

First oil hole <NUM> and second oil hole <NUM> are each formed, for example, by secondary machining with a drill after forming lower link upper 6A by forging. In addition, although carburization treatment (carburization quench hardening) is conducted to lower link upper 6A for increasing surface hardness, it is desirable to perform drilling before the carburization treatment.

Here, in one preferable embodiment, the diameter of second oil hole <NUM> is set to be larger than that of first oil hole <NUM>. In this way, when second oil hole <NUM> is formed so as to have a larger diameter, the rigidity around second oil hole <NUM> is lowered, and a relatively large deformation occurs, as a result of which stress around first oil hole <NUM> (in particular, around oil inlet 31b of first oil hole <NUM>) where stress concentration as the largest problem arises is lowered. That is, as compared with case where the diameter of first oil hole <NUM> is the same as that of second oil hole <NUM>, or case where the diameter of first oil hole <NUM> is smaller than that of second oil hole <NUM>, stress at oil inlet 31b is alleviated.

In addition, by setting the diameter of second oil hole <NUM> so as to be larger than that of first oil hole <NUM>, even if there is some machining error or tolerance, a communication state at the intersecting portion therebetween can be surely secured, and a predetermined passage sectional area can be stably obtained.

In addition, in the illustrated example, although distal end 32a of second oil hole <NUM> passes through and slightly extends from first oil hole <NUM> further due to drilling, such an excess passage part is not necessary if working can be performed.

In lower link <NUM> of the embodiment configured as above, at a predetermined crank angle, oil supply hole <NUM> on the crank pin <NUM> side meets oil inlet 31b of first oil hole <NUM>, and, as oil jet, pressurized lubricating oil is injected from oil outlet 32b toward upper pin <NUM> through first oil hole <NUM> and second oil hole <NUM>. By this oil jet, lubrication is performed between upper pin <NUM> and upper link <NUM>.

Here, since inclination angle θ of first oil hole <NUM> with respect to divided surface <NUM> is relatively small and oil inlet 31b is opened at a position close to divided surface <NUM>, the stress concentration at the opening edge of oil inlet 31b is alleviated. For example, when an oil hole was linearly formed penetrating in a direction intersecting upper pin <NUM> along the radial line of crank pin bearing portion <NUM>, assuming that the positions of upper pin <NUM> and the like are the same as those shown in <FIG>, inclination angle θ with respect to divided surface <NUM> would be approximately <NUM>°. In this angle direction, the oil hole passes through an area where stress is high in the stress distribution in the circumferential direction of crank pin bearing portion <NUM>. In contrast to this, in the above embodiment, by forming oil hole <NUM> from first oil hole <NUM> and second oil hole <NUM>, oil inlet 31b is located at a position close to divided surface <NUM>, and it is advantages in suppressing stress concentration.

Here, when, as mentioned above, inclination angle θ of first oil hole <NUM> with divided surface <NUM> set as a reference is small, the circumferential velocity of oil inlet 31b with respect to crank pin <NUM> becomes high during the swinging movement of lower link <NUM> and rotation movement of crank pin <NUM> (as compared with case where inclination angle θ is, for example, approximately <NUM>°). Consequently, the time during which oil supply hole <NUM> on the crank pin <NUM> side meets oil inlet 31b becomes relatively short, and the amount of lubricating oil tends to decrease. Therefore, in one preferable embodiment, as shown in <FIG>, a communicating hole <NUM> of bearing metal <NUM> is formed in a long hole shape which is circumferentially long.

That is, bearing metal <NUM> is formed by being divided into two parts by <NUM>° so as to have a cylindrical shape as a whole, and they are assembled to respective lower link upper 6A and lower link lower 6B in a non-rotation state. Bearing metal <NUM> is formed with communicating hole <NUM> located at a position corresponding to inlet 31b, in order to communicate oil supply hole <NUM> on the crank pin <NUM> side and oil inlet 31b of lower link <NUM> with each other. In addition, communicating hole <NUM> has a long hole shape extending in the circumferential direction. Accordingly, oil supply hole <NUM> on the crank pin <NUM> side and oil inlet 31b of lower link <NUM> are kept in a communication state over a predetermined angle range. In other words, the time during which oil supply hole <NUM> on the crank pin <NUM> side and oil hole 31b of lower link <NUM> communicate with each other becomes long. Consequently, a sufficient amount of lubricating oil can be secured.

In one embodiment, as shown in <FIG>, one end of communicating hole <NUM> having a long hole shape is located at a position corresponding to oil inlet 31b, and the other end extends to a position at which inclination angle θ with divided surface <NUM> set as a reference becomes larger.

In addition, when communicating hole <NUM> is excessively enlarged, surface pressure as a bearing becomes high, and it is therefore not preferable.

Although, as an example, first embodiment in which inclination angle θ of first oil hole <NUM> with divided surface <NUM> set as a reference is <NUM>° has been explained, in the present invention, inclination angle θ of first oil hole <NUM> is not limited to a specific angle. <FIG> show lower link <NUM> in a second embodiment in which inclination angle θ of first oil hole <NUM> along the radial line of crank pin bearing portion <NUM> is set, for example, to <NUM>°. Other configurations are basically the same as those of the first embodiment. First oil hole <NUM> is also formed such that the extension line of the center line of first oil hole <NUM> is directed in a direction not intersecting upper pin <NUM>, and lubricating oil is guided toward the upper pin <NUM> side via second oil hole <NUM>.

In the second embodiment, the intersecting angle at the intersection portion between first oil hole <NUM> and second oil hole <NUM> is larger than that of the first embodiment, and pressure loss caused by a change in a flow direction is small. In addition, the passage length of second oil hole <NUM> becomes shorter than that in the first embodiment, as a result of which pressure loss also becomes small. However, oil inlet 31b of first oil hole <NUM> is positioned close to the area where stress is high. It is therefore preferable to set inclination angle θ while considering these matters.

In the second embodiment, although communicating hole <NUM> of bearing metal <NUM> is also formed in a long hole shape, inclination angle θ of first oil hole <NUM> is large as compared with the first embodiment, and oil inlet 31b of first oil hole <NUM> is positioned in the vicinity of the middle in the circumferential direction of communicating hole <NUM> having a long hole shape (see <FIG>).

In addition, lower link upper 6A (lower link <NUM>) of the first embodiment and the second embodiment is provided with, in addition to oil hole <NUM>, an oil hole <NUM> for supplying oil jet toward piston <NUM> (see <FIG>) or the inner wall surface of a cylinder. Oil hole <NUM> is positioned closer to control pin <NUM> than the position at which the maximum combustion load reaction in the circumference of crank pin bearing portion <NUM> acts. Consequently, the stress concentration at the opening edge of oil hole <NUM> by the combustion load and combustion load reaction mentioned above is relatively small. Oil hole <NUM> is therefore formed so as to simply extend linearly. An communicating hole <NUM> of bearing metal <NUM> which corresponds to oil hole <NUM> is formed in a true circle (see <FIG>, <FIG> and <FIG>).

As the above, although one embodiment of the present invention has been explained in detail, the present invention is not limited to the above embodiments, and various changes can be made to the embodiments. For example, although, in the above embodiments, first oil hole <NUM> is formed along the radial line of crank pin bearing portion <NUM>, it may be slightly inclined with respect to the radial line of crank pin bearing portion <NUM> or may be arranged so as to be slightly displaced in parallel with respect to the radial line.

Claim 1:
A lower link (<NUM>) of an internal combustion engine, which is included in a piston crank mechanism of the internal combustion engine,
- the piston crank mechanism including: an upper link (<NUM>) having one end connected to a piston (<NUM>) of the internal combustion engine via a piston pin (<NUM>); the lower link (<NUM>) connected to an other end of the upper link (<NUM>) via an upper pin (<NUM>), and connected to a crank pin (<NUM>) of a crankshaft; and a control link (<NUM>) having one end swingably supported on an engine body side, and an other end connected to the lower link (<NUM>) via a control pin (<NUM>),
- the lower link (<NUM>) comprising: a crank pin bearing portion (<NUM>) rotatably fitted to the crank pin (<NUM>) between the upper pin (<NUM>) and the control pin (<NUM>),
- wherein an oil hole (<NUM>) for supplying lubricating oil from an oil supply hole (<NUM>) of the crank pin (<NUM>) toward a connecting portion between the upper pin (<NUM>) and the upper link (<NUM>) is formed through the crank pin bearing portion (<NUM>),
- wherein the oil hole (<NUM>) includes:
- a first oil hole (<NUM>) linearly extending from an inner peripheral surface of the crank pin bearing portion (<NUM>) outwardly in a radial direction; and
- a second oil hole (<NUM>) linearly extending so as to intersect a distal end portion of the first oil hole (<NUM>), and having one end opened to an outer surface of the lower link (<NUM>) as an oil outlet (32b).