Patent Application
20120111143
The present invention relates to a crankshaft of an internal combustion engine provided with a multi-link piston-crank mechanism.
The applicants of the present invention are studying to realize optimized piston stroke characteristic and variable compression-ratio control by the use of a multi-link piston-crank mechanism (hereinafter referred to as “multi-link mechanism”), by which a piston pin of a piston and a crankpin of a crankshaft are linked to each other via a plurality of links, as a primary kinetic system in which the piston and the crankshaft of an internal combustion engine are linked to each other.
As described in Patent Literature 1, in the case of a single-link piston-crank mechanism (hereinafter referred to as “single-link mechanism”, by which a piston pin and a crankpin are linked to each other via a single link (a connecting rod), a crankthrow, corresponding to a distance from the axis of a crankshaft main journal to the axis (a rotation center) of a crankpin, is one-half (½) of the piston stroke, except a specific case that the axis of the main journal is offset from the cylinder centerline. In contrast, in the case of a multi-link mechanism, by the action of a leverage of the multi-link mechanism, comprised of an upper link, a lower link, and the like, it is possible to set a crankthrow shorter than one-half of the (maximum) piston stroke. Therefore, by virtue of the shortened crankthrow, it is possible to attain downsizing, enhanced engine mountability, and high-compression-ratio engine. Also, due to the shortened crankthrow, the main journal and the crankpin can be laid out so as to approach each other in a decentering direction of the crankpin, and hence, as viewed in the axial direction of the crankshaft, the overlapping area, in which the main journal and the crankpin are overlapped with each other, tends to become greater, thus ensuring the enhanced rigidity and strength of the crankshaft.
By the way, the crankshaft is formed with oil passages for lubricating bearing portions of crankpins. Regarding each of the oil passages, lubricating oil is supplied from the cylinder-block side to the oil passage. One end of the oil passage, that is, the oil-passage pin-side opening is configured to be open at the outer peripheral surface of the crankpin. Note that a large magnitude of combustion load acts on the crankshaft in a decentering direction of the crankpin whose axis is displaced from the axis of the main journal. In order to avoid a stress concentration arising from the combustion load, as described in Patent Literature 2, the oil-passage pin-side opening is generally formed at an angular position of 90° or −90° with respect to a reference line extending in the crankpin decentering direction, that is, on either side of diametrically-opposing positions of both sides of the crankpin in the crankpin transverse direction perpendicular to the crankpin decentering direction.
However, in the case that a crankthrow is set shorter than one-half of a (maximum) piston stroke, the inventors have discovered that the following problems arise. These problems are hereunder described in reference to
Hence, in the case of a crankshaft of an internal combustion engine to which is a multi-link mechanism is applied, the influence of a load P caused by the previously-discussed torsional torque T and acting in the crankpin transverse direction as well as a load caused by an explosive power and acting in the crankpin decentering direction X must be fully taken into account. Assume that, as described in Patent Literature 2, in order to avoid a stress concentration arising from the explosive load (combustion load), the oil-passage pin-side opening, configured to be open at the outer peripheral surface of the crankpin, is formed at a position of 90° or −90° (i.e., 270° crankangle in the crank rotation direction) with respect to a reference line extending in the crankpin decentering direction. In such a case, owing to torsional torque T, a stress concentration occurs in the vicinity of the oil-passage pin-side opening. Additionally, owing to the shortened crank arm (the shortened crankthrow) of the multi-link mechanism, there are several drawbacks, namely, an increase in load caused by torsional torque T and acting in the crankpin transverse direction Y, and a locally high mechanical strength of either side of diametrically-opposing portions of the crankpin in its transverse direction, arising from the increased overlapping area of the crankpin and the main journal as viewed in the crank axial direction. From this point of view, assuming that the pin-side opening is formed on either side of the crankpin in the crankpin transverse direction, a stress concentration tends to be easily induced in the vicinity of the pin-side opening. As a countermeasure against such a stress concentration, to ensure the appropriate rigidity and mechanical strength, there is a necessity of increasing the diameter of the crankpin. This leads to the difficulty of providing a compact internal combustion engine including a multi-link mechanism.
The present invention has been realized, while paying its attention to a demerit newly caused by a crankthrow shortened by using a multi-link mechanism. That is, the present invention relates to a crankshaft of an internal combustion engine employing a multi-link piston-crank mechanism having an upper link whose one end is linked to a piston via a piston pin, a lower link linked to the other end of the upper link via an upper pin and also linked to a crankpin of a crankshaft, and an auxiliary link, one end of the auxiliary link being pivotally supported on a main-body side of the engine, and the other end of the auxiliary link being linked to the lower link via an auxiliary pin.
A crankthrow from the axis of a main journal of the crankshaft to the axis of the crankpin is set shorter than one-half of a stroke of the piston. Additionally, as viewed in the crank axial direction, the crankpin and the main journal are overlapped with each other.
Owing to the shortened crankthrow, a load caused by torsional torque and acting in a transverse direction of the crankpin tends to become great, and the overlapping area of the crankpin and the main journal in the crankpin transverse direction also tends to increase. Therefore, regarding oil passages for supplying lubricating oil to bearing portions of crankpins, assuming that the oil-passage pin-side opening, configured to be open at the outer peripheral surface of the crankpin, is formed on either side of diametrically-opposing portions of the crankpin in the crankpin transverse direction, that is, at a position of 90° or −90° with respect to a reference line directed from the axis of the main journal toward the axis of the crankpin and extending in the crankpin decentering direction, a stress tends to concentrate in the vicinity of the pin-side opening.
Thus, in a crankshaft of the invention, the pin-side opening is formed in ranges other than angular ranges of 90° or −90° with respect to the reference line extending from the axis of the main journal toward the axis of the crankpin in the crankpin decentering direction, that is, formed in ranges other than both sides of the crankpin in its transverse direction.
According to the invention, regarding a crankshaft of an internal combustion engine having a crankthrow shortened by using a multi-link mechanism, a pin-side opening of an oil passage, configured to be open at an outer peripheral surface of a crankpin, is formed in ranges other than both sides of the crankpin in the crankpin transverse direction, thereby suppressing or alleviating a stress concentration occurring in the vicinity of the pin-side opening owing to torsional torque, and consequently achieving the compactified crankpin whose diameter is properly reduced, while ensuring a required strength and rigidity.
FIG.
The preferred embodiments of the invention are hereinafter described in reference to the drawings.
As described in the previously-noted JP2008-224015, a multi-link piston-crank mechanism is well-known. Briefly speaking, the multi-link mechanism is comprised of an upper link 6 whose one end is linked to the piston 8 via a piston pin 7, a lower link 4 linked to the other end of the upper link 5 via an upper pin 6 and also linked to a crankpin 3 of the crankshaft 1, and an auxiliary link 10, one end (the lower end) of the auxiliary link being pivotally supported on the side of cylinder block 14, corresponding to a main-body side of the internal combustion engine, and the other end (the upper end) of the auxiliary link being linked to the lower link 4 via an auxiliary pin 11. Regarding crankshaft 1, main journal 2 and crankpin 3 are connected via a crank web 14.
Hereupon, L1 denotes a crankthrow from the axis of main journal 2 to the axis of crankpin 3, L2 denotes a distance from the geometric center of the crankpin bearing portion of lower link 4 to the geometric center of the upper-pin bearing portion of lower link 4, L3 denotes a distance from the geometric center of the auxiliary-pin bearing portion of auxiliary link 10 to the geometric center of an eccentric shaft portion 12B, L4 denotes a distance from the geometric center of the crankpin bearing portion of lower link 4 to the geometric center of the auxiliary-pin bearing portion of lower link 4, L6 denotes a distance from the geometric center of the piston-pin bearing portion of upper link 5 to the geometric center of the upper-pin bearing portion of upper link 5, and x4 denotes an offset amount of the center of piston pin 7 (reciprocating along a cylinder centerline) from the crankshaft main journal centerline.
As compared to a single-link mechanism in which a piston pin and a crankpin are connected by one connecting link, such a multi-link mechanism, in which piston pin 7 and crankpin 3 are connected via a plurality of links, has a higher degree of freedom of piston stroke characteristic settings. By optimizing the piston stroke characteristic, for instance, by tuning the piston stroke characteristic to a characteristic close to a simple harmonic oscillation, it is possible to remarkably attenuate noise and vibrations.
The previously-noted crankthrow L1 is set shorter than one-half of the (maximum) piston stroke. Hence, in comparison with a popular single-link mechanism in which a crankthrow is one-half of a piston stroke, in the case of the multi-link mechanism, for the same engine compression ratio, by virtue of the shortened crankthrow L1, it is possible to attain the enhanced rigidity and strength and downsizing. Also, for the same length of crankthrow L1, it is possible to attain high-compression-ratio engine. As a result of the shortened crankthrow, as viewed in the crank axial direction, the crankpin and the main journal are overlapped with each other. Thus, the crankshaft has such an overlapping area (denoted by ΔOL in
Furthermore, a journal portion 12A of auxiliary shaft 12, which extends continuously over the plurality of cylinders, is rotatably supported on the cylinder block 14 via support members (not shown). Auxiliary shaft 12 has the previously-discussed auxiliary shaft portion 12B provided for each engine cylinder. The other end of auxiliary link 10 is pivotably linked to the associated eccentric shaft portion 12B. Hence, by changing the rotational position of auxiliary shaft 12 by means of an actuator (not shown) depending on engine operating conditions, the position of eccentric shaft portion 12B, serving as a fulcrum of oscillating motion of auxiliary link 10, can be changed, and therefore an engine compression ratio can be changed owing to a change in a motion-restriction condition that motion of lower link 4 is restricted by means of auxiliary link 10 (variable compression ratio means). As discussed above, it is possible to easily realize variable engine-compression-ratio control by the use of a multi-link piston-crank mechanism.
The specific construction, operation and effects of the embodiments are hereunder described in detail. As clearly shown in
First of all, regarding the specific construction, common to all of the embodiments, as shown in
As discussed above, in the crankshaft that crankthrow L1 is shortened by the use of the multi-link mechanism, assume that the pin-side opening is formed in angular ranges Q2 and Q4 in the crankpin transverse direction Y, that is, in angular ranges Q2 and Q4, corresponding to diametrically-opposing portions of both sides of the crankpin in the crankpin transverse direction. A stress concentration tends to occur in the vicinity of the pin-side opening owing to a load caused by torsional torque and acting in the crankpin transverse direction Y. Also, this leads to the difficulty of ensuring an oil film in the vicinity of the pin-side opening. Due to such an inadequate oil film (a lack of oil film), there is a tendency for the fluid-lubrication performance to be lowered. In the case of the multi-link mechanism, on the one hand, by virtue of the shortened crankthrow, the overlapping area ΔOL increases and thus the strength and rigidity thereof also increase. On the other hand, owing to the shortened crankthrow, the rigidity of the overlapping area of crank web 14 for the load, caused by torsional moment and acting in the crankpin transverse direction perpendicular to both the crank axial direction and the crankpin decentering direction, tends to become locally high, and thus a stress concentration tends to be induced in the section other than the locally-high-rigidity section. Especially, a stress tends to concentrate in an oil passage formed to penetrate in the crankpin transverse direction. Therefore, by forming pin-side opening 21 in ranges other than angular ranges Q2 and Q4, corresponding to diametrically-opposing portions of both sides of the crankpin in the crankpin transverse direction, such a stress concentration can be suppressed and alleviated, thereby reducing the diameter of the crankpin, while ensuring a required strength and rigidity, and consequently achieving compactification. Additionally, it is possible to suppress a lack of oil film in the vicinity of the pin-side opening 21, thus enabling a good fluid-lubricating action. That is, the oil-passage opening on the side of crankpin 3 is formed in angular ranges in the crank rotation direction, in which a stress concentration cannot be produced in the oil passage without an inadequate oil film in the vicinity of pin-side opening 21 of oil passage (oil hole) 20.
Also, in angular ranges Q1 and Q3 in the crankpin decentering direction X, great combustion load and/or inertial load acts near the top dead center (TDC) and the bottom dead center (BDC). Thus, assuming that the pin-side opening is formed in angular ranges Q1 and Q3 in the crankpin decentering direction X, owing to the leverage of the multi-link mechanism, a further increased magnitude of combustion load/inertial load tends to repeatedly act on the pin-side opening near the piston TDC position and the piston BDC position of each engine cylinder. That is, as discussed previously, there is a risk of the occurrence of stress concentration and lowered fluid-lubrication performance arising from an inadequate oil film. In contrast to the above, when the pin-side opening 21 is located and formed in ranges other than angular ranges Q1 and Q3 in which great combustion load and/or inertial load acts, the combustion load and/or inertial load never acts directly in the vicinity of the pin-side opening 21. Thus, it is possible to suppress a lack of oil film in the vicinity of the pin-side opening 21, while alleviating and reducing a stress concentration in the vicinity of the pin-side opening 21, thus enabling a good fluid-lubricating action.
The technical term “angle” described later, basically means an angle measured in the crank rotation direction α with respect to the reference line X1 extending from the crankpin center taken as an origin.
In the first embodiment shown in
As discussed previously, in comparison with a single-link mechanism, in the case of the multi-link mechanism, by virtue of the shortened crank-arm (shortened crankthrow L1), the overlapping area ΔOL increases and thus the strength and rigidity thereof also increase. Hence, it is possible to easily form the previously-noted oil passage 20 by way of which the outer peripheries of main journal 2 and crankpin 3 are connected each other straightly and directly. Additionally, by forming the oil passage 20 within the overlapping range ΔOL, there is a less risk of reducing the strength and rigidity owing to formation of oil passage 20. Furthermore, machining the straight oil passage 20 eliminates the need for forming additional radial oil passages in the crankpin and/or the main journal. This contributes to the reduced machining time and costs, and also ensures a required strength and rigidity.
In the second embodiment shown in
According to the second embodiment, radial oil passage 24 is formed to straightly penetrate crankpin 3 in the diametral direction of the crankpin, thus facilitating machining. Additionally, oil can be supplied to the crankpin bearing portion through the two opposite pin-side openings 24A-24B of both ends of radial oil passage 24, thus resulting in an increase in the lubricating-oil amount.
In to similar manner to the second embodiment, in the third embodiment shown in
By the way, in the internal combustion engine having the multi-link mechanism, the crankangle, corresponding to the piston TDC position, tends to phase-retard with respect to the reference position of revolution of the crankshaft (exactly, the crankangle at which the crankpin decentering direction X is identical to the crankshaft main journal centerline). As seen from the load diagram of
As compared to the second embodiment, the third embodiment is superior for the reasons discussed below. That is, in the third embodiment, radial oil passage 25 is formed to be obliquely inclined by 45 degrees in the crank rotation direction with respect to the crankpin decentering direction X, such that the pin-side openings 25A-25B are formed in the respective angular ranges, substantially corresponding to 45 degrees and 225 degrees. Thus, it is possible to suppress or alleviate the openings from being affected by combustion load acting in the angular range substantially corresponding to 315 degrees (−45 degrees).
In the fourth embodiment shown in
Referring to
Also, lower link 4 has a peripheral oil groove 27 and a splash hole 28 formed therein. Peripheral oil groove 27 is formed as a radially-outward recessed groove in the crankpin bearing surface of lower link 4 in a manner so as to extend in the peripheral direction over an angular range of 90 degrees. Splash hole 28 is provided to inject and supply lubricating oil toward a designated bearing portion, that is, the bearing portion of upper pin 6 in the fifth embodiment. One opening end of splash hole 28 is configured to open into the bottom face of peripheral oil groove 27, whereas the other opening end of splash hole 28 is configured to open into the bottom face of the forked pin-boss portion that supports the upper pin 6. Thus, lubricating oil, supplied from peripheral oil groove 27 to splash hole 28, can be injected and fed toward the upper-pin side (upper pin 6).
In this manner, four pin-side openings 24A, 24B, 25A, and 25B are formed in the outer peripheral surface of crankpin 3 in a manner so as to be circumferentially equidistant-spaced from each other every predetermined angular intervals, such as 90 degrees. Peripheral oil groove 27 is circumferentially recessed in the lower-link side (lower link 4) over the same angular range (i.e., 90 degrees) as the angular interval between the two adjacent openings of these pin-side openings 24A, 24B, 25A, and 25B. Hence, during operation, either one of pin-side openings 24A, 24B, 25A, and 25B approaches the peripheral oil groove 27 in a manner so as to be brought into fluid-communication with the peripheral oil groove 27. For instance, at given degrees of crankangle shown in
More preferably, a radially-penetrating upper-link side oil passage 29 may be formed in the pin-bearing portion of upper link 5 for upper pin 6, in a manner so as to be oriented substantially in the oil-splay direction of splash hole 28, and hence part of lubricating oil splayed from splash hole 28 can be more certainly supplied through the upper-link side oil passage 29 to the upper-pin bearing portion (upper pin 6).
Referring to
In the seventh embodiment shown in
With the previously-discussed oil-passage structure, lubricating oil, supplied from the crankpin-side (crankpin 3) oil passage to peripheral oil groove 27 of lower link 4, can be delivered into the oil-sump portion 30 by virtue of rotation of crankpin 3. Additionally, due to a shearing stress arising from viscosity, part of lubricating oil is flown out in such a manner as to be dragged in the direction of sliding motion of the crankpin (i.e., in the rotation direction of crankpin 3 relative to the crankpin bearing portion of lower link 4), that is, in the direction opposite to the direction of sliding motion of the crankpin bearing portion, thus ensuring stable supply of lubricating oil to the crankpin bearing portion.
By the way, oil-sump portion 30 is formed in ranges of the crankpin bearing surface other than the above-mentioned angular ranges R1, R2, and R3, in which a large magnitude of load acts, for example, in either one of angular ranges, substantially corresponding to 0°, 90°, 180° and 315°. Hence, it is possible to avoid a large magnitude of load from acting directly on the oil-sump portion 30.
In the eighth embodiment shown in
In the ninth embodiment shown inn
As appreciated from the eighth and ninth embodiments, by virtue of a plurality of splash holes 28 formed in lower link 4, it is possible to effectively inject and supply lubricating oil toward a plurality of moving parts to be lubricated and cooled.
1 . . . CRANKSHAFT
2 . . . MAIN JOURNAL
3 . . . CRANKPIN
4 . . . LOWER LINK
5 . . . UPPER LINK
6 . . . UPPER PIN
7 . . . PISTON PIN
8 . . . PISTON
10 . . . AUXILIARY LINK
11 . . . AUXILIARY PIN
20 . . . OIL PASSAGE
21 . . . PIN-SIDE OPENING
22 . . . JOURNAL-SIDE OPENING
24, 25 . . . RADIAL OIL PASSAGES
24A, 24B, 25A, 25B . . . PIN-SIDE OPENINGS
27 . . . PERIPHERAL OIL GROOVE
28 . . . SPLASH HOLE
X . . . CRANKPIN DECENTERING DIRECTION
Y . . . CRANKPIN TRANSVERSE DIRECTION
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-168674 | Jul 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/059247 | 6/1/2010 | WO | 00 | 1/12/2012 |
