JP2008163768A - Variable valve opening characteristic internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable valve opening characteristic internal combustion engine improved in the degree of freedom in setting valve opening characteristics while employing comparatively simple structure. <P>SOLUTION: A roller 28 is brought into rolling contact with the cam lobe 4a of an exhaust camshaft 4. A roller shaft 27 is brought into rolling contact with a circular arc slipper surface 6a formed on an exhaust rocker arm 6. The rotational center of the exhaust camshaft 4 is positioned in a direction facing the slipper surface 6a. Within the moving range of a control shaft 25, with the roller 28 brought into rolling contact with the base circle Cb of the cam lobe 4a, the circular arc center Ps of the slipper surface 6a is offset obliquely upward in drawing with respect to the center Pc of the base circle Cb. Therefore, the radius of curvature R of the slipper surface 6a is set significantly large in comparison with the case where the center Pc of the base circle Cb conforms with the circular arc center Ps of the slipper surface 6a. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a variable valve opening characteristic internal combustion engine, and more particularly to a technique for improving the degree of freedom in setting a valve opening characteristic while adopting a relatively simple configuration.

  In recent years, internal combustion engines such as gasoline engines and diesel engines (hereinafter simply referred to as engines) are equipped with various valve opening characteristic variable mechanisms in order to improve output and fuel consumption and reduce harmful exhaust gas components. is increasing. As a valve opening characteristic variable mechanism, there is a mechanism that switches between a low speed type cam and a high speed type cam according to the operating condition, but in recent years it has been opened in order to further improve the transient characteristics and reduce the throttle. Some have continuously changed the valve characteristics (valve lift and valve timing).

This type of valve opening characteristic variable mechanism includes a swing type control link in which a roller or roller shaft at the tip is interposed between the camshaft and the rocker arm, and a control that serves as a swing fulcrum for the control arm. One that rotates a shaft around a support shaft is known (see Patent Documents 1 and 2). In the valve opening characteristic variable mechanism of Patent Document 1, the roller is brought into contact with the cam lobe of the camshaft, and the roller shaft coaxial with the roller is brought into contact with the concave arcuate slipper surface formed on the rocker arm. The center of the arc of the slipper surface and the rotation center of the camshaft coincide with each other in a state of rolling contact with the base circle of the cam lobe. In the valve opening characteristic variable mechanism disclosed in Patent Document 2, the roller is brought into contact with the cam lobe of the camshaft, but the tappet roller coaxial with the roller is brought into contact with the convex slipper surface formed on the rocker arm. .
JP 2001-164911 A JP 2005-344702 A

  In automotive engines, the valve clearance is reduced by reducing the valve clearance during high lift to reduce the impact load of the valve system, or increasing the valve clearance and closing the valve instantaneously during low lift. It is desirable to change the valve clearance according to the above. However, in the variable valve opening characteristic mechanism of Patent Document 1, the arc center of the slipper surface and the rotation center of the camshaft coincide with each other, so that the valve clearance does not depend on the position of the control shaft (that is, the magnitude of the valve lift). In addition to being constant, there is a problem that a new cam lobe (that is, a camshaft) is required when changing the valve lift characteristics. On the other hand, in the valve opening characteristic variable mechanism of Patent Document 2, since the tappet roller is in rolling contact with the convex slipper surface of the rocker arm, the valve lift characteristic is greatly deviated only by a slight deviation of the initial position of the tappet roller. There was a problem such as.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a variable valve opening characteristic internal combustion engine that can improve the degree of freedom in setting the valve opening characteristic while adopting a relatively simple configuration. To do.

The invention of claim 1 is formed on the camshaft, has a cam having a predetermined base circle, a valve pressing portion that presses the valve in the valve opening direction, and a rocker arm that swings around the support shaft, A roller link that rotatably holds a first roller that is in rolling contact with the cam, a second roller that is in rolling contact with a concave arc-shaped slipper surface formed on the rocker arm, and a base end of the roller link. A variable valve opening characteristic internal combustion engine comprising a control shaft that is slidably held and a control shaft driving means that moves the control shaft along a predetermined movement locus, in a direction opposite to the slipper surface. In the state where the rotation center of the cam is located and the first roller is in rolling contact with the base circle in the movement range of the control shaft Characterized in that the arc center of said sliding surface of said base circle is offset.

  Further, the invention according to claim 2 is the valve opening characteristic variable internal combustion engine according to claim 1, wherein the first roller is in rolling contact with the base circle in the moving range of the control shaft. The gap between the valve pressing portion and the valve is within 0.35 mm.

  According to the first aspect of the present invention, the relative position between the center of the base circle and the center of the arc of the slipper surface is appropriately set, which causes a large deviation in the valve lift characteristics due to the deviation of the initial position of the second roller. In addition, the value of the valve clearance with respect to the valve lift can be changed relatively freely, and the valve lift characteristics can be changed without newly manufacturing a camshaft. Further, according to the invention of claim 2, the valve can be instantaneously closed within a range in which an excessive impact load does not act on the valve operating system.

Hereinafter, an embodiment of the present invention and a partial modification thereof will be described in detail with reference to the drawings.
FIG. 1 is a perspective view of a main part showing an upper part of an engine according to the embodiment, FIG. 2 is a longitudinal section showing an upper part of the engine according to the embodiment, and FIG. 3 shows a main part of the VLC mechanism according to the embodiment. FIG. 4 is a longitudinal sectional view showing a main part of the VLC mechanism according to the embodiment.

<< Configuration of Embodiment >>
<Overall configuration>
An engine (variable valve opening characteristic internal combustion engine) E shown in FIG. 1 is a four-cycle in-line four-cylinder engine for automobiles. As shown in FIG. 2 and an intake valve 3, and a DOHC 4-valve type valve operating mechanism is provided in which the valves 2 and 3 are driven by an exhaust camshaft 4 and an intake camshaft 5. An exhaust rocker arm 6 is interposed between the exhaust valve 2 and the exhaust camshaft 4, and an intake rocker arm 7 is interposed between the intake valve 3 and the intake camshaft 5. The exhaust valve 2 and the intake valve 3 are always urged in the closing direction by the valve springs 8 and 9, respectively. In FIG. 1, a member denoted by reference numeral 10 is a rocker shaft that serves as a swing fulcrum of the exhaust rocker arm 6.

  Five cam holders (support members) 11 to 15 are fastened to the upper surface of the cylinder head 1, and the cam shafts 4 and 5 and the rocker arms 6 and 7 are supported by the cam holders 11 to 15 so as to be rotatable or swingable. ing. In the present embodiment, among the cam holders 11 to 15, the right end one is the front cam holder 11, the center one is the center cam holder 13, the left end one is the rear cam holder 15, and the other two are the middle cam holder 12, And 14 respectively. A flat base plate 18 is installed on the upper surfaces of the cam holders 11 to 15, and the valve mechanism is covered with the base plate 18 and the head cover 19.

  The engine E of the present embodiment is equipped with a variable valve lift control (VLC) mechanism 20 that variably controls the lift amount of the exhaust valve 2 as a valve opening characteristic variable mechanism.

<VLC mechanism>
As shown in FIG. 3, the VLC mechanism 20 includes an electric motor 21 installed on the upper surface of the base plate 18 (not shown in FIG. 2) in parallel with the camshafts 4 and 5 and a reduction gear mechanism (not shown). A pair of left and right gear links 23, 24 each having a gear shaft 22 driven to rotate by the electric motor 21, driven gear portions 23 a, 24 a meshing with a gear 22 a formed on the gear shaft 22, and shaft holder portions 23 b, 24 b, respectively. The control shaft 25 is rotatably supported by the shaft holder portions 23b and 24b of the gear links 23 and 24, the roller link 26 is inserted into the base end of the control shaft 25, and the tip of the roller link 26 is provided. A roller (first roller) 28 rotatably supported by a roller shaft (second roller) 27 The are the main components.

  1 is a sensor (rotary encoder) that detects the rotation amount of the electric motor 21, and an engine ECU (not shown) determines the position of the control shaft 25 based on the detection signal of the sensor 29, The supply current to the electric motor 21 is feedback controlled. 2 and 3 is a support pin for supporting the gear links 23 and 24 on the cam holders 11 to 15 in a swingable manner. A member denoted by reference numeral 31 is an adjustment screw (valve pressing portion), which is attached to the exhaust rocker arm 6 and presses the stem end 2a of the exhaust valve 2.

  Both gear links 23 and 24 rotate steplessly between a position shown by a solid line (minimum lift position) and a position shown by a broken line (maximum lift position) in FIG. The shaft holder portions 23b and 24b) pivot about the support pin 30. The roller link 26 swings around the minimum lift point Pg1 when the gear links 23 and 24 are at the minimum lift position, and centered at the maximum lift point Pg2 when the gear links 23 and 24 are at the maximum lift position. Rocks.

  The roller 28 is in rolling contact with the cam lobe 4 a of the exhaust camshaft 4. The roller shaft 27 is in rolling contact with an arc-shaped slipper surface 6 a formed on the exhaust rocker arm 6. In the case of the present embodiment, the rotation center of the exhaust camshaft 4 is located in the direction facing the slipper surface 6a, and the roller 28 is in rolling contact with the base circle Cb of the cam lobe 4a in the moving range of the control shaft 25. In FIG. 4, the arc center Ps of the slipper surface 6a is offset obliquely to the upper left in FIG. 4 with respect to the center Pc of the base circle Cb. Accordingly, the radius of curvature R of the slipper surface 6a is set to be significantly larger than the case where the center Pc of the base circle Cb and the arc center Ps of the slipper surface 6a coincide.

<< Operation of Embodiment >>
When the engine E of the automobile is started, the engine ECU sets the target lift amount of the exhaust valve 2 based on various operation information such as the depression amount of the throttle pedal and the coolant temperature by the driver, and the electric motor of the VLC mechanism 20 The drive current is output to 21. Then, the gear shaft 22 is rotationally driven by the electric motor 21 via a reduction gear mechanism (not shown), and the gear links 23 and 24 engaged with the gear 22a of the gear shaft 22 by the driven gear portions 23a and 24a are directed in either the forward or reverse direction. Driven by rotation.

  When reducing the valve lift during idling or the like, the engine ECU rotates the gear links 23 and 24 to the minimum lift position and swings the roller link 26 around the minimum lift point Pg1, as shown in FIG. I will let you. As a result, even when the roller 28 is pushed down by the cam lobe 4a, the roller shaft 27 rolls along the slipper surface 6a as shown by the arrow in FIG. 2 lift amount) is minimized.

  On the other hand, when increasing the valve lift during high load operation or the like, the engine ECU rotates the gear links 23 and 24 to the maximum lift position as shown in FIG. 6, and the roller link 26 around the maximum lift point Pg2. Oscillate. Thus, when the roller 28 is pushed down by the cam lobe 4a, the roller shaft 27 hardly rolls along the slipper surface 6a, so that the lift amount of the exhaust valve 2 is maximized.

  In the present embodiment, as described above, when the roller 28 is in rolling contact with the base circle Cb of the cam lobe 4a, the arc center Ps of the slipper surface 6a is offset obliquely upward with respect to the center Pc of the base circle Cb. . As a result, when the position of the control shaft 25 (that is, the swing fulcrum of the roller link 26) fluctuates, the roller shaft 27 rolls on the slipper surface 6a, and the gap between the adjustment screw 31 and the stem end 2a of the exhaust valve 2 ( That is, the valve clearance S changes. Then, when the roller link 26 swings around the minimum lift point Pg1, the valve clearance S becomes relatively large (for example, 0.35 mm) as shown by the solid line in FIG. When swinging around the lift point Pg2, it becomes almost 0 as shown by a two-dot chain line in FIG.

  As a result, in the present embodiment, at the time of the minimum lift, as shown by the solid line in FIG. 8, the exhaust valve 2 is instantaneously closed to increase the pressure wave, thereby improving the pulsation effect. Further, at the time of the maximum lift, as shown by a two-dot chain line in FIG. 8, the exhaust valve 2 is smoothly opened and closed, and the impact of the valve operating system (between the adjustment screw 31 and the stem end 2a, etc.) The load has been reduced.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, in the above embodiment, the present invention is applied to an in-line four-cylinder DOHC gasoline engine that variably controls only the lift amount on the exhaust valve side, but the lift amount on the intake valve side is also variably controlled. Of course, the present invention can also be applied to SOHC engines and diesel engines. Further, the positional relationship between the center of the base circle of the cam and the arc center of the slipper surface is not limited to the example in the above embodiment, and can be arbitrarily set as long as it does not depart from the gist of the present invention. is there. In the above embodiment, the spur gear mechanism is used for driving the power transmission member by the actuator, but a worm reduction mechanism, a chain drive mechanism, a cam mechanism, or the like may be used. Further, the specific configuration and the like of the variable valve opening characteristic mechanism can be changed as appropriate without departing from the gist of the present invention.

It is a principal part perspective view which shows the upper part of the engine which concerns on embodiment. It is a longitudinal section showing the upper part of the engine concerning an embodiment. It is a perspective view which shows the principal part of the VLC mechanism which concerns on embodiment. It is a longitudinal cross-sectional view which shows the principal part of the VLC mechanism which concerns on embodiment. It is operation | movement explanatory drawing of a VLC mechanism. It is operation | movement explanatory drawing of a VLC mechanism. It is a figure which shows the change of the valve clearance accompanying the action | operation of a VLC mechanism. It is a valve lift-valve timing diagram concerning an embodiment.

Explanation of symbols

1 Cylinder head 2 Exhaust valve 3 Intake valve 4 Exhaust camshaft 4a Cam lobe (cam)
6 Exhaust rocker arm 6a Slipper surface 20 VLC mechanism 21 Electric motor 22 Gear shaft 23 Gear link 24 Gear link 25 Control shaft 26 Roller link 27 Roller shaft (second roller)
28 Roller (first roller)
31 Adjustment screw (valve pressing part)
Cb Base circle E Engine

Claims (2)

A cam formed on the camshaft and having a predetermined base circle;
A rocker arm that has a valve pressing portion that presses the valve in the valve opening direction and swings around the support shaft;
A roller link that rotatably holds a first roller that is in rolling contact with the cam and a second roller that is in rolling contact with a concave arc-shaped slipper surface formed on the rocker arm;
A control shaft for swingably holding the base end of the roller link;
A variable valve opening characteristic internal combustion engine comprising a control shaft driving means for moving the control shaft along a predetermined movement locus,
The rotation center of the cam is located in a direction facing the slipper surface;
In the range of movement of the control shaft, the center of the base circle and the arc center of the slipper surface are offset when the first roller is in rolling contact with the base circle. organ.   The movement range of the control shaft is characterized in that a gap between the valve pressing portion of the rocker arm and the valve is within 0.35 mm when the first roller is in rolling contact with the base circle. 1. A variable valve opening characteristic internal combustion engine described in 1.

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