JP4714609B2 - Variable compression ratio mechanism of internal combustion engine - Google Patents

Description

  The present invention relates to a variable compression ratio mechanism for an internal combustion engine.

  In Patent Document 1 by the present applicant, an upper link connected to a piston via a piston pin, a lower link connected to the upper link and a crankpin of a crankshaft, and a crankshaft substantially along the cylinder row direction. A control shaft extending in parallel, a control link having one end pivotably connected to the control shaft and the other end connected to the lower link, and an actuator that rotationally drives the control shaft using reciprocation of the actuator shaft, An internal combustion engine in which the center of swing of the control link with respect to the control shaft is decentered from the center of rotation of the control shaft, and the engine compression ratio is variably controlled by a relative position change of the center of swing of the control link accompanying rotation of the control shaft An engine variable compression ratio mechanism is disclosed. In this Patent Document 1, the actuator is a so-called feed screw that reciprocates the actuator shaft by forming a male screw portion on the proximal end side of the actuator shaft and rotationally driving the cylindrical portion of the actuator that is screwed to the male screw portion. It has a structure.

  In the variable compression ratio mechanism disclosed in Patent Document 1, the in-cylinder pressure in the combustion chamber and the inertial force of the reciprocating piston apply a load to each link component, and also act as a load in the shaft bending direction on the actuator shaft. This bending load causes deformation in the entire axial direction of the shaft, and the deformation also reaches the male thread portion of the actuator shaft.

  Also, a load acts on the cylindrical portion that is screwed into the male thread portion of the actuator shaft due to the bending deformation of the actuator shaft.

  Here, since the screwing position of the actuator in the axial direction of the actuator shaft with respect to the male screw changes according to the position corresponding to the compression ratio within the variable range, the position of the portion where the high stress acts also varies. become. On the other hand, the bending displacement of the actuator shaft is always under a relatively high stress in the same region regardless of the compression ratio setting.

Therefore, the stress condition of the actuator shaft is relatively severe between the actuator shaft and the cylindrical portion of the actuator. In order to reduce the stress of the actuator shaft, the diameter of the male screw portion is increased, and the surface pressure of the surface where the male screw portion of the actuator shaft and the female screw portion of the cylindrical portion contact each other (hereinafter referred to as a contact surface) is reduced. It is conceivable to increase the cross-sectional area of the actuator shaft while lowering it.
JP 2002-115571 A

  If the diameter of the actuator shaft is increased, the diameter of the male thread can be increased, the surface pressure of the contact surface can be reduced under the same load, and the strength can be increased under the same load by increasing the cross-sectional area of the actuator shaft. -Durability is also advantageous.

  However, actuators that have a feed screw structure are also important in terms of operation response, and under the same actuator shaft feed speed. Increasing the screw diameter is equivalent to increasing the peripheral speed, and there is a concern about an increase in PV value in considering the wear performance on the contact surface. Here, the PV value is an index value that can be expressed by the product of P, which is the sliding surface pressure, and V, which is the sliding speed. The surface pressure of the contact surface is P, and the cylindrical portion with respect to the male screw portion of the actuator shaft The rotation speed can be regarded as V.

  In other words, the increase in the diameter of the male thread portion does not simply contribute to the reduction of the PV value and does not improve the strength and durability when applied to an actuator structure that requires a high feed rate. .

  Accordingly, an object of the present invention is to improve the strength and durability of an actuator shaft under high stress without increasing the diameter of the actuator shaft.

The present invention includes an upper link coupled to a piston via a piston pin, a lower link coupled to the upper link and a crankpin of the crankshaft, and a control shaft extending substantially parallel to the crankshaft along the cylinder row direction. A control link having one end pivotably coupled to the control shaft and the other end coupled to the lower link, and an actuator that rotationally drives the control shaft using the reciprocating motion of the actuator shaft. A variable compression ratio mechanism for an internal combustion engine that eccentrically controls the swing center of the control link from the rotation center of the control shaft and variably controls the engine compression ratio by the relative position change of the swing center position of the control link accompanying the rotation of the control shaft in the actuator, the actuator shaft coupled to the control shaft, engaged with the threaded portion formed on the actuator shaft An actuator shaft driving member rotatable in the circumferential direction of the actuator shaft, and reciprocatingly moving the actuator shaft by rotationally driving the actuator shaft driving member. The film treatment is performed so that the film thickness differs in the axial direction .

  According to the present invention, the strength and durability of an actuator shaft under high stress can be improved without increasing the diameter of the actuator shaft. In addition, when a coating process is performed on the outer peripheral surface of the actuator shaft, for example, a film that is subjected to a dipping process has good workability.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a basic configuration as a premise of a variable compression ratio mechanism of an internal combustion engine according to the present invention, and shows an application example to an in-line four-cylinder engine. FIG. 1 shows a state in the vicinity of the top dead center of the piston when the maximum compression ratio is set.

  In the cylinder block 11, a cylindrical cylinder 12 is formed for each cylinder, and a water jacket 13 is formed around each cylinder 12. A piston 14 is disposed in each cylinder 12 so as to be movable up and down. The piston pin 15 of each piston 14 and the crankpin 17 of the crankshaft 16 are mechanically connected via a multi-link variable compression ratio mechanism. It is linked to. Reference numeral 18 denotes a counterweight.

  The variable compression ratio mechanism includes a lower link 21 that is externally fitted to the crankpin 17 so as to be relatively rotatable, an upper link 22 that links the lower link 21 and the piston pin 15, and a cylinder row direction parallel to the crankshaft 16. A control shaft 23 extending inward, an eccentric cam 24 provided eccentric to the control shaft 23, a control link 25 linking the eccentric cam 24 and the lower link 21, and rotating the control shaft 23 within a predetermined control range. And an actuator 30 as a driving means for driving and holding at a predetermined rotational position. The control shaft 23 is manufactured by forging or casting.

  The upper end portion of the rod-like upper link 22 is connected to the piston pin 15 so as to be relatively rotatable, and the lower end portion is connected to the lower link 21 via the connecting pin 26 so as to be relatively rotatable. One end of the control link 25 is coupled to the lower link 21 via a coupling pin 38 so as to be relatively rotatable, and the other end of the control link 25 is externally fitted to the eccentric cam 24 so as to be relatively rotatable.

  FIG. 2 is an explanatory view showing an essential part of an actuator mechanism including an actuator shaft 32 (described later) and a cylindrical member 34 (described later) extracted from the variable compression ratio mechanism shown in FIG.

  As shown in FIG. 2, the control shaft 23 includes a substantially rod-shaped shaft portion 27 that is rotatably supported by the lower portion of the cylinder block 11, and protrudes radially outward from the outer peripheral surface of the shaft portion 27. The connecting portion 28 is connected to one end of the shaft 32.

  The shaft portion 27 is roughly composed of a main shaft 29 rotatably supported by a main bearing portion (not shown) provided at a lower portion of a cylinder spacing wall (not shown) of the cylinder block 11 and the eccentric cam 24 described above. The rotation center P of the eccentric cam 24 is eccentric with respect to the rotation center Q of the main shaft 29.

  The connecting portion 28 includes a pair of flanges 40 that are separated from each other in the axial direction of the control shaft 23 and are opposed to each other. The pair of flanges 40 and 40 are respectively provided with slits 37 that are elongated in the radial direction of the control shaft 23. Is formed. That is, each flange 40, 40 is formed to have a substantially bifurcated shape.

  As shown in FIG. 1, the actuator 30 includes an actuator shaft 32 that can be moved forward and backward in the casing 31, and a female screw portion 36 that is screwed into a male screw portion 33 on the base end side (rear end) of the actuator shaft 32. And a cylindrical member 34 formed on the inner peripheral surface. The cylindrical member 34 corresponds to an actuator driving member, and is rotationally driven around an axis by a driving source such as a motor or a hydraulic pump based on a control signal from a control unit (engine control unit) (not shown). The

  As shown in FIG. 2, the actuator shaft 32 is disposed along a direction orthogonal to the control shaft 23, and reciprocates along its own longitudinal direction (axis direction of the actuator shaft 32). One end (tip) of the actuator shaft 32 has a cylindrical shape, and a rod-like pin 35 is disposed on the inner surface of the cylinder so as to be rotatable. The actuator shaft 32 and the control shaft 23 are pinned so that one end of the actuator shaft 32 is sandwiched between a pair of flanges 40 and 40 provided on the connecting portion 28 of the control shaft 23 and is rotatably arranged on the inner surface of the cylinder. Both ends of 35 are connected to each other by slidably engaging with a pair of slits 37, 37 formed in the flanges 40, 40 respectively. Note that both ends of the pin 35 have substantially the same width as the sliding surface 37 a of the slit 37.

  Here, the operation of the variable compression ratio mechanism will be briefly described. When the cylindrical member 34 is rotationally driven by the control unit, the actuator shaft 32 screwed into the cylindrical member 34 reciprocates. Specifically, the actuator 30 realizes the reciprocating motion of the actuator shaft 32 by a so-called feed screw structure constituted by the actuator shaft 32 and the cylindrical member 34. As a result, the control shaft 23 rotates in a predetermined direction via the connecting portion 28 while being accompanied by a sliding operation of the pin 35 in the slit 37. In order to prevent the actuator shaft 32 from reciprocatingly moving inadvertently, the actuator 30 performs the rotational movement of the actuator shaft 32 via the screwed portion between the male screw portion 33 and the female screw portion 36 of the cylindrical member 34. It is the structure converted into reciprocating motion.

  Then, by rotating the control shaft 23 according to the engine operating state, the swing fulcrum of the control link 25 fitted on the eccentric cam 24 is changed, and the postures of the lower link 21 and the upper link 22 are changed. The compression ratio of the combustion chamber defined above 14 is variably controlled.

  In this variable compression ratio mechanism, the compression ratio is continuously increased when the actuator shaft 32 moves forward, and the compression ratio is continuously decreased when the actuator shaft 32 moves backward.

  In such a variable compression ratio mechanism, since the piston pin 15 and the crankshaft 16 are linked by only two links 22 and 21, the configuration is simplified as compared with, for example, one using three or more link members. The In addition, because the control link 25 is connected to the lower link 21, the control link 25 and the control shaft 23 can be disposed on the lower side of the engine with a relatively large space, which makes engine mounting easier. Are better.

  When a load (load load) such as pulling and bending due to torsional torque from the link mechanism is input to the actuator shaft 32, the actuator shaft 32 undergoes bending deformation as shown in FIG. Will occur.

  Here, the actuator shaft 32 itself is a non-rotating member (only reciprocating motion), and when a load load as described above is input, as shown in FIG. Stress sites are always concentrated on the same site. Further, the tensile stress and the compressive stress of the actuator shaft 32 tend to be large in the direction in which the load is applied, and the stress condition of a specific part is always severe.

  On the other hand, the cylindrical member 34 that is screwed to the actuator shaft 32 receives a compressive stress as a reaction of a load applied to the actuator shaft 32 at a meshing portion (female screw portion 36) with the actuator shaft 32 (see FIG. 4). ). However, the cylindrical member 34 is a rotating member, and different portions are subjected to high stress depending on the reciprocating position of the actuator shaft 32, that is, the set compression ratio.

  Therefore, in the actuator shaft 32, the specific portion is always under high stress regardless of the set value of the compression ratio, whereas the cylindrical member 34 is also compressed in a portion where high stress is similarly seen. Since its own rotational position differs depending on the ratio setting, the stress condition of the actuator shaft 32 is overwhelmingly severe compared to the cylindrical member 34 when viewed from the engine life.

  Therefore, in the present invention, focusing on the actuator shaft 32 with more severe stress conditions, by applying a film treatment only to the surface of the male thread portion 33 of the actuator shaft 32, high stress can be effectively dealt with.

  In a so-called feed screw structure constituted by the actuator shaft 32 and the cylindrical member 34, an appropriate gap (backlash) exists between the threads of the actuator shaft 32 and the cylindrical member 34.

  In the variable compression ratio mechanism as described above applied to the present invention, an alternating torque (direction) is applied to the control shaft 23 particularly during operation at a low load and high rotation where the combustion pressure is low and the link inertia force is dominant. And torque whose magnitude changes with time). This alternating torque acts as an alternating load on the actuator shaft 32, causing backlash in the feed screw structure and causing abnormal noise.

  As this noise reduction measure, reduction of backlash can be considered, but simply reducing this backlash is effective in reducing noise, but from the increase of friction in the feed screw structure. The driving energy also increases, and there is a possibility that the loss in the entire actuator system cannot be ignored.

  In addition, when machining the male thread portion 33 on the actuator shaft 32, it is technically possible to incorporate a process that reduces backlash only on the low compression ratio side (the right side in the axial direction of the actuator shaft 32 of the male thread portion 33 in FIG. 3). However, it is very difficult and cost rise is inevitable.

  FIGS. 5A and 5B show an example of the case where a ball screw and a trapezoidal screw are applied to the feed screw structure, that is, the male screw portion 33 of the actuator shaft 32 and the female screw portion 36 of the cylindrical portion 34, respectively. It is explanatory drawing which showed typically the example of a film processing which becomes.

(A) When the film thickness on the high compression ratio side is increased Although the coating treatment is performed on the entire length of the male screw portion 33 in the axial direction, the film thickness on the high compression ratio side (left side in FIG. It is relatively thicker than the film thickness on the low compression ratio side (right side in FIG. 5).

  Since the high compression ratio side (left side in FIG. 5) of the male screw portion 33 is particularly stressed under high load conditions, the wear resistance is improved by, for example, hard chrome plating.

(B) Increasing the film thickness on the low compression ratio side Although the coating treatment is performed on the entire length of the male screw portion 33 in the axial direction, the film thickness on the low compression ratio side (right side in FIG. It is relatively thicker than the film thickness on the high compression ratio side (left side in FIG. 5).

  In order to suppress the generation of abnormal noise due to the alternating load at the time of the low compression ratio, the low compression ratio side (the right side in FIG. 5) of the male screw portion 33 needs to reduce backlash. Therefore, the backlash amount is changed in the axial direction of the actuator shaft 32 by making the film thickness of the treatment film thicker on the low compression ratio side than on the high compression ratio side of the male screw portion 33, thereby reducing the low compression ratio side of the male screw portion 33. Reducing the backlash amount of.

As a result, the backlash can be reduced as much as possible on the low compression ratio setting side that is affected by the alternating load. Further, on the high compression ratio setting side where the load is high, in order to suppress the drive energy of the actuator shaft 32 , the backlash is appropriately given by reducing the film thickness, and between the male screw portion 33 and the female screw portion 36. Friction can be made lower than that on the low compression ratio side.

(C) When the coating treatment is performed only in the vicinity of the low compression ratio side The coating treatment is performed only on the low compression ratio side (right side in FIG. 5) of the male screw portion 33, and the high compression ratio side of the male screw portion 33 (see FIG. 5). The left side) is not coated. As a result, the same effect as when the film treatment is performed as in the above (b) can be obtained, and the cost can be reduced by performing the film treatment and reducing the treatment area as compared with the above (b). .

  In any of the cases (a) to (c), DLC (diamond like carbon) treatment can be applied. When this DLC treatment is applied, it is possible to obtain a substantially constant friction coefficient regardless of oil properties. . The fact that the friction coefficient can be made substantially constant means that, for example, in the case of an actuator of a variable compression ratio mechanism, when the set compression ratio is held at a constant value, it is easy to predict and manage the held energy, and in particular, variable compression ratio. It is effective in combination with a ratio mechanism. When, for example, a trapezoidal screw is applied to the feed screw structure, the holding energy can be easily controlled if the friction coefficient of the contact surface between the male screw portion 33 and the female screw portion 36 is stable.

  Further, different types of coating treatment may be performed on the male thread portion 33 of the actuator shaft 32 in the axial direction of the actuator shaft 32.

  And the processing cost can be reduced by making the said feed screw structure into a general trapezoidal screw or a ball screw. Also, by changing the feed lead, the required responsiveness can be easily set and controlled. In particular, when the feed lead is a lower lead than the JIS standard series (JIS B 0216, JIS B 1192), the rotation angle of the cylindrical member 34 increases from the standard lead due to the load acting on the actuator shaft 32. The cylindrical member 34, which becomes a tendency and is combined with the actuator shaft 32 in the axial direction and the direction perpendicular to the axial direction, can change the rotation angle quickly even with a small axial displacement and support a high stress portion in a higher range. Therefore, it can be avoided that high stress is concentrated on a part. Further, avoiding concentration of high stress at a specific part leads to a reduction in the number of repetitions in fatigue strength, and contributes to a long life of the actuator 30.

  In the above-described embodiment, the actuator 30 including the actuator shaft 32 and the cylindrical member 34 is disposed on the side of the engine so as to be substantially parallel to the cylinder 12 axis. It is also possible to arrange with respect to the engine as shown in FIG. FIG. 6 shows the actuator 30 disposed on the side of the engine in a state of being inclined with respect to the cylinder 12 axis. FIG. 7 shows the actuator 30 disposed below the engine.

  In the variable compression ratio mechanism to which the present invention is applied, the length of the internal thread portion 36 of the cylindrical member 34 (length in the axial direction of the screw) is set to the length of the external thread portion of the actuator shaft 32 (in the axial direction of the screw). In the case where the female screw portion 36 is always screwed into the male screw portion 33 in the entire axial direction of the screw, the male screw portion 33 of the actuator shaft 32 is subjected to a film treatment so as to be cylindrical. The film life can be made relatively longer than when the film treatment is applied to the female thread portion 36 of the member 34.

  The technical idea of the present invention that can be grasped from the above embodiment will be listed together with the effects thereof.

  (1) an upper link coupled to the piston via a piston pin, a lower link coupled to the upper link and a crankpin of the crankshaft, a control shaft extending substantially parallel to the crankshaft along the cylinder row direction, A control link having one end pivotably connected to the control shaft and the other end connected to the lower link, and an actuator that rotationally drives the control shaft using the reciprocating motion of the actuator shaft. In a variable compression ratio mechanism of an internal combustion engine in which the link compression center is decentered from the rotation center of the control shaft and the engine compression ratio is variably controlled by the relative position change of the control link swing center position accompanying the rotation of the control shaft. The actuator shaft connected to the control shaft is subjected to a film treatment. Thereby, the strength and durability of the actuator shaft under high stress can be improved without increasing the diameter of the actuator shaft. In addition, when a coating process is performed on the outer peripheral surface of the actuator shaft, for example, a film that is subjected to a dipping process has good workability.

  (2) In the variable compression ratio mechanism for an internal combustion engine according to (1), the actuator includes an actuator shaft and an actuator that engages with a screw portion formed on the actuator shaft and can rotate in a circumferential direction of the actuator shaft. And a shaft driving member that reciprocates the actuator shaft by rotationally driving the actuator shaft driving member, and the threaded portion of the actuator shaft is coated.

  In the variable compression ratio mechanism, the combustion load applied to the piston and the inertial force of the main motion system components such as the piston act as torque on the control shaft. A resultant force in the perpendicular direction acts. This resultant force causes bending deformation to act on the actuator shaft.

  In an actuator shaft that reciprocates only without rotating itself, a specific part always has high stress. On the other hand, the actuator drive member (cylindrical member 34) that is combined with the actuator shaft and rotates on the circumference of the actuator shaft changes the rotation angle in a timely manner depending on the axial position of the actuator shaft. Extensive. Therefore, by applying a coating process to the threaded portion (male threaded portion 33) on the actuator shaft side that is constantly exposed to high stress, the strength and durability can be improved while suppressing the number of processing steps.

  (3) In the variable compression ratio mechanism for an internal combustion engine described in (2) above, the threaded portion of the actuator shaft is coated so that the film thickness differs in the direction of the actuator shaft axis. Thus, the backlash amount can be easily adjusted by changing the film thickness of the film treatment on the threaded portion of the actuator shaft in the axial direction of the actuator shaft. In the variable compression ratio mechanism where the setting of the compression ratio changes, the load load on the actuator differs depending on the compression ratio, but the process according to the load load that changes depending on the compression ratio is applied to the actuator. It can be applied to the shaft.

  (4) The variable compression ratio mechanism of the internal combustion engine according to (2) or (3) is more specifically compressed as the actuator driving member is positioned at one end side in the actuator shaft axial direction of the threaded portion of the actuator shaft. The ratio is a relatively low compression ratio, and the coating is applied to at least one end side of the screw shaft in the axial direction of the actuator. As a result, it is possible to suppress the generation of abnormal noise when setting a low compression ratio at which an alternating load acts.

  (5) In the variable compression ratio mechanism for an internal combustion engine according to any one of (1) to (4), the treatment film applied to the actuator shaft is a DLC film.

  As a result, a substantially constant friction coefficient can be maintained regardless of the properties of the lubricating oil. In addition, since the friction can be greatly reduced, the drive energy of the actuator shaft can be suppressed.

  (6) In the variable compression ratio mechanism for an internal combustion engine according to any one of (2) to (5), specifically, the thread portion of the actuator shaft is a trapezoidal screw.

  (7) In the variable compression ratio mechanism for an internal combustion engine according to any one of (2) to (5), specifically, the thread portion of the actuator shaft is a ball screw.

Explanatory drawing which shows the basic composition of the variable compression ratio mechanism of the internal combustion engine which concerns on this invention. The disassembled perspective view which shows the connection part of the control shaft and actuator shaft in the variable compression ratio mechanism of the internal combustion engine which concerns on this invention. It is explanatory drawing which showed typically an example of the deformation | transformation condition when a load acts on an actuator shaft. It is explanatory drawing which showed typically an example of the stress distribution of an actuator shaft and a cylindrical member when a load acts on an actuator shaft. Explanatory drawing which shows the example of the film processing to the external thread part of an actuator shaft. Explanatory drawing which shows the modification of the variable compression ratio mechanism of the internal combustion engine which concerns on this invention which changed the arrangement position of the actuator with respect to FIG. Explanatory drawing which shows the modification of the variable compression ratio mechanism of the internal combustion engine which concerns on this invention which changed the arrangement position of the actuator with respect to FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 14 ... Piston 17 ... Crank pin 21 ... Lower link 22 ... Upper link 23 ... Control shaft 25 ... Control link 27 ... Shaft part 28 ... Connection part 30 ... Actuator 32 ... Actuator shaft 33 ... Male screw part 34 ... Cylindrical member 36 ... Female screw part

Claims (5)

An upper link connected to the piston via a piston pin, a lower link connected to the upper link and the crankpin of the crankshaft, a control shaft extending substantially parallel to the crankshaft along the cylinder row direction, and one end controlled A control link connected to the shaft in a swingable manner and having the other end connected to the lower link, and an actuator that rotationally drives the control shaft using the reciprocating motion of the actuator shaft. In a variable compression ratio mechanism of an internal combustion engine in which the dynamic center is decentered from the rotation center of the control shaft and the engine compression ratio is variably controlled by the relative position change of the swing center position of the control link accompanying the rotation of the control shaft.
The actuator includes an actuator shaft coupled to the control shaft, and an actuator shaft driving member that engages with a screw portion formed on the actuator shaft and is rotatable in the circumferential direction of the actuator shaft. Reciprocating the actuator shaft by rotationally driving,
A variable compression ratio mechanism for an internal combustion engine, characterized in that a film treatment is applied to a thread portion of an actuator shaft so that the film thickness varies in the axial direction of the actuator shaft . The variable compression ratio mechanism is such that the compression ratio becomes relatively low as the actuator driving member is positioned on one end side in the actuator shaft axial direction of the threaded portion of the actuator shaft, and the coating treatment is performed at least on the threaded portion. The variable compression ratio mechanism for an internal combustion engine according to claim 1 , wherein the variable compression ratio mechanism is provided on one end side in the actuator shaft axial direction. The variable compression ratio mechanism for an internal combustion engine according to claim 1 or 2 , wherein the treatment coating applied to the actuator shaft is a DLC coating. The variable compression ratio mechanism for an internal combustion engine according to any one of claims 1 to 3 , wherein the threaded portion of the actuator shaft is a trapezoidal screw. The variable compression ratio mechanism for an internal combustion engine according to any one of claims 1 to 3 , wherein the threaded portion of the actuator shaft is a ball screw.

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