JP2816876B2 - Valve drive device for DOHC type internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Field of the Invention The present invention relates to a valve mechanism for a so-called double overhead camshaft (DOHC) type four-stroke internal combustion engine.
In particular, the present invention relates to a valve driving device that changes both valve timing and valve lift of an intake valve and an exhaust valve.

(2) Prior Art It is known that valve timing and valve lift of an intake valve and an exhaust valve in a four-cycle internal combustion engine are significant factors that affect the performance of the internal combustion engine.

However, since the required optimum valve timing and valve lift change with the change in the rotation speed of the internal combustion engine, if the valve timing and valve lift suitable for a specific rotation range are selected, sufficient performance is obtained in other rotation ranges. There is a problem that it cannot be obtained. In order to cope with such a problem, there has been proposed a valve drive device capable of adjusting a valve timing and a valve lift of an intake valve or an exhaust valve in accordance with a change in the number of revolutions of an internal combustion engine (Japanese Utility Model Publication No. 44-44).
No. 23442).

The above-mentioned valve drive device is a camshaft provided with a cam abutting on a rocker arm and a cam gear meshing with an idler gear, and a base end portion of which is pivotally supported on a distal end portion of a camshaft support arm pivotally supported on a rotation shaft of the idler gear. The camshaft support arm is configured to swing around the rotation axis of the idler gear according to a change in the rotation speed of the internal combustion engine.

According to the valve drive device, when the camshaft support arm swings, the cam provided on the camshaft moves along the slipper surface of the rocker arm so as to approach or separate from the fulcrum of the rocker arm, and the lever ratio changes. However, the valve lift can be increased or decreased. Also, when the camshaft support arm swings, the cam gear provided on the camshaft meshes with the idler gear and rotates.
The phase angle of the cam that rotates integrally with this cam gear changes,
The valve timing of the exhaust valve and the intake valve can be changed.

(3) Problems to be Solved by the Invention However, the above-mentioned conventional valve drive device is a so-called single overhead camshaft (SOHC) type internal combustion engine in which an intake valve and an exhaust valve are driven via one camshaft. Since it is applied, the degree of freedom in adjusting the valve timing and valve lift of the intake valve and the exhaust valve is small, and it has been difficult to make full use of the features.

The present invention has been made in view of the above circumstances, and in a double overhead camshaft type internal combustion engine,
It is an object of the present invention to provide a valve drive device for a DOHC type internal combustion engine, in which the valve timing and valve lift of an intake valve and an exhaust valve can be adjusted to have relatively large degrees of freedom, respectively, so that functional performance can be improved. .

B. Configuration of the Invention (1) Means for Solving the Problems In order to achieve the above object, according to the valve drive device for an internal combustion engine of the present invention, the valve drive device is disposed above a cylinder head and meshes with a common idler gear. Two camshafts driven by a pair of cam gears, a rocker arm abutting on a cam provided on each camshaft and swinging about a fulcrum, and an intake valve and an exhaust valve driven abutting on these rocker arms. In the internal combustion engine provided with, each of the camshafts is mounted on the tip of an integral camshaft support arm pivotally supported coaxially with the rotation shaft of the idler gear, and the support arm drive mechanism is used in accordance with a change in the rotation speed of the internal combustion engine. By swinging the camshaft support arm and changing the cam phase angle and the rocker arm lever ratio, the valve timing and valve lift of the intake and exhaust valves can be reduced. It is first to be changed
In addition to this feature, the second feature is that the valve timing of the intake valve and the exhaust valve is delayed and the valve lift of both valves is increased with the increase in the rotation speed of the internal combustion engine. .

(2) Operation According to the first feature, when the camshaft supporting arm that supports the two camshafts at the tip thereof is swung with the rotation speed of the internal combustion engine, the cam gear fixed to the camshaft is rotated. Meshes with the idler gear and rotates, whereby the phase angle of the cam changes, and the valve timing of the intake valve and the exhaust valve can be changed. At the same time, the position of the contact portion between the rocker arm and the cam changes due to the swing of the camshaft support arm, and the lever ratio of the rocker arm changes, so that the valve lift can be increased or decreased. By simultaneously controlling both the valve timing and the valve lift of the internal combustion engine in this manner, it is possible to control the time area of the valve overlap.

Further, according to the second feature, the timing of closing the intake valve is earlier at the time of low-speed rotation and later at the time of high-speed rotation. Therefore, the tuning rotational range is expanded by the intake inertia effect, and flat torque characteristics and high output can be obtained. . Further, the change in the valve lift makes it possible to increase the output during high-speed rotation and reduce the exhaust noise in the low-speed rotation range. Furthermore, since the time area of the valve overlap in the low-speed rotation region is reduced, fresh air passing therethrough is reduced, and harmful components in the exhaust gas are reduced.

(3) Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 to 4 show an embodiment of the present invention.
FIG. 1 is a cross-sectional view of the valve driving device, and FIG. 2 is II in FIG.
FIG. 3 is an explanatory view of the operation, and FIG. 4 is a graph showing valve characteristics.

As shown in FIGS. 1 and 2, the double overhead camshaft type four-stroke internal combustion engine E includes a cylinder head 3 joined on a cylinder block 2 on which a piston 1 slides, and a head cover 4 covering an upper part thereof. Have.

A combustion chamber 5 is formed in the cylinder head 3 so as to face the top surface of the piston 1. A pair of intake ports 6 and an exhaust port 7 that open into the combustion chamber 5 respectively have a pair of intake valves 8 a and a pair of intake valves 8 a. An exhaust valve 8b is mounted. The intake valve 8a and the exhaust valve 8b are urged in the valve closing direction by valve springs 9a and 9b, and are swingable at their upper ends by an intake side rocker arm shaft 10a and an exhaust side rocker arm shaft 10b which are supported by the cylinder head 3 at the upper end thereof. Tapper clearance adjustment screws 12a, 12b for the intake side rocker arm 11a and the exhaust side rocker arm 11b
Is in contact.

A camshaft support arm 17 is pivotally supported by a pair of bosses 15 and 16 fixed to bolts 13 and 14 on the cylinder head 3. The camshaft support arm 17 is composed of two substantially sector-shaped side plates 18 and 19 and two connecting members 20 for connecting the upper portions of both side plates 18 and 19, and the boss 1 is provided at the lower end of the side plates 18 and 19.
The intake side camshaft 21a and the exhaust side camshaft 21b are rotatably supported between the upper ends of the side plates 18, 19 while being rotatably supported by the side plates 5, 16. An idler gear 22 that rotates in conjunction with the crankshaft is supported by the one boss 16 via a ball bearing 23.
An intake cam gear 24a fixed to the intake camshaft 21a and an exhaust cam gear 24b fixed to the exhaust camshaft 21b mesh with 22. Intake side camshaft 21a
The intake side cam 25a provided on the intake side rocker arm 11a has a slipper surface concentric with the idler gear 2 formed on the intake side rocker arm 11a.
In addition to being connected to the exhaust side camshaft 21b, the exhaust side cam 25b provided on the exhaust side camshaft 21b is connected to the same concentric arc-shaped slipper surface 25b formed on the exhaust side rocker arm 11b.
As is clear from FIG. 1, both rocker arm shafts 10a, 10b
Are provided on the same side (right side in the figure) with respect to both camshafts 21a and 21b, and both camshafts 21a and 21b
b is driven counterclockwise.

A worm gear shaft 28 connected to a servomotor 27 such as a step motor and rotating above the head cover 4.
Is supported, and a worm gear 29 formed on the outer periphery thereof
Meshes with a sector gear 30 formed on one side plate 19 of the camshaft support arm 17. Thus, when the servo motor 27 is driven to rotate the worm gear 29,
The camshaft support arm 17 carrying the camshafts 21a and 21b swings about the bosses 15 and 16.

Next, the operation of the embodiment of the present invention having the above-described configuration will be described.

The rotation of the idler gear 22, which is interlocked with the rotation of the crankshaft in association with the operation of the engine E, is transmitted to the camshafts 21a, 21b via a pair of cam gears 24a, 24b. Drive at a rotational speed of. Cams 25a, 25b that rotate with the camshafts 21a, 21b
The rocker arms 11a and 11b that abut against the rocker arm shafts 10a and 1
0b, and the intake valve 8a and the exhaust valve 8b pressed by the rocker arms 11a and 11b are connected to the crankshaft 2a.
Open the valve once per rotation. At this time, the intake side cam 25
1 and the exhaust-side cam 25b both rotate counterclockwise in FIG. 1, but the phase angle of the exhaust-side cam 25b is different from that of the intake-side cam 25a.
About 90 ° ahead of the phase angle of the exhaust valve 8a.
The opening period of the intake valve 8a precedes the opening period of the intake valve 8a. The opening period of the exhaust valve 8b and the opening period of the intake valve 8a slightly overlap with each other.
A valve overlap period in which both the valve 8b and the intake valve 8a open is formed.

Now, as shown in FIG. 3 (a), when the internal combustion engine is in the low-speed rotation range, the camshaft support arm 17 is in a state of swinging to the left, and both the cams 25a, 25b are at the tip side of the rocker arms 11a, 11b. (Left side in the figure). In this state, the cams 25a and 25b and the rocker arm are moved from the rocker arm shafts 10a and 10b.
Since the distance to the contact point of 11a, 11b increases, the swing angle of the rocker arms 11a, 11b decreases, and as a result, the intake valve 8a
And the valve lift of the exhaust valve 8b decreases as indicated by the solid line in the graph of FIG.

When a sensor (not shown) detects an increase in the number of revolutions of the engine E, the servomotor 27 is driven to rotate the worm shaft 28, and the camshaft support arm 17 is centered on the bosses 13 and 14 via the worm gear 29 and the sector gear 30. Fig. 3 (b)
Swings clockwise to the position. Then, the intake-side camshaft 21a and the exhaust-side camshaft 21b provided on the camshaft support arm 17 swing together to move the contact point between the two cams 25a, 25b and the rocker arms 11a, 11b toward the rocker arm shafts 10a, 10b. As a result, the rocking angles of the rocker arms 11a and 11b increase, the valve lifts of the intake valve 8a and the exhaust valve 8b both increase as shown by the broken line in FIG. 4, and the time area of valve overlap also decreases in the low speed rotation range. Increase compared to. At the same time, the clockwise swing of the camshaft support arm 17 causes the intake-side cam gear 24a and the intake-side cam gear 24b to mesh with the idler gear 22.
Rotates slightly in the clockwise direction, that is, in the direction opposite to the driving direction of the camshafts 21a and 21b, so that the phase angle between the intake cam 25a and the exhaust cam 25b moves to the lag side, and the valve timing is delayed.

In this manner, in the low speed rotation range, the valve lift decreases and the valve opening speed of the exhaust valve 8b decreases, so that the blowdown of exhaust gas becomes slow and exhaust noise can be reduced, and the cam 25a, The contact pressure of the contact portion between the contact surface 25b and the slipper surfaces 26a, 26b is reduced, so that the lubrication can be easily performed. Further, since the time area of the valve overlap in the low-speed rotation region can be reduced, not only fresh air passing through the intake port 6 to the exhaust port 7 decreases, but also harmful components in the exhaust gas decrease. The sneak of the exhaust pressure wave into the intake system is reduced and noise is prevented.

On the other hand, in the high-speed operation range, the valve timing of the intake valve 8a can be delayed as compared with the low-speed rotation, so that the tuning rotation range in which the intake inertia effect is exhibited is expanded, and flat torque characteristics and high output can be obtained. .

As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various small design changes can be made without departing from the present invention described in the claims. It is possible to do.

For example, the driving of the camshaft support arm 17 does not necessarily need to be performed electrically, but may be hydraulically driven. Further, instead of forming the slipper surfaces 26a, 26b of the rocker arms 11a, 11b with arcuate surfaces concentric with the idler gear 22, the center of curvature of the slipper surfaces 26a, 26b is shifted from the center of the idler gear 22, so that the low-speed rotation and the high-speed rotation are performed. The valve clearance during rotation can be changed. In addition, the intake valve
The numbers of the exhaust valves 8a and the exhaust valves 8b do not necessarily have to be two, and may be one each.
And the other may be two. The power transmission from the crankshaft to the idler gear 22 can be performed via either a gear or a chain.

C. Effects of the Invention As described above, according to the first aspect of the present invention, two camshafts each having a cam that abuts on a rocker arm and drives an intake valve and an exhaust valve can swing freely. Since the cam gears fixed to the respective camshafts are meshed with the idler gears while being supported at the tip of the support arm, the valve timing and valve lift of the intake valve and the exhaust valve can be changed with a simple configuration.

Further, according to the second feature of the present invention, the timing of closing the intake valve can be early during low-speed rotation and late during high-speed rotation,
The tuning rotation range is expanded by the intake inertia effect, and flat torque characteristics and high output can be obtained. In addition, the output at the time of high-speed rotation increases due to the change in the valve lift, and the exhaust noise in the low-speed rotation range and the lubrication of the cam and the slipper surface can be facilitated. Furthermore,
Even if the time area of valve overlap is sufficiently secured in the high-speed rotation range to improve the volumetric efficiency, the time area of valve overlap in the low-speed rotation range can be reduced, reducing the fresh air passing through. As a result, the harmful components in the exhaust gas can be reduced, and the exhaust pressure wave can be prevented from sneaking into the intake system to reduce noise.

[Brief description of the drawings]

1 to 4 show an embodiment of the present invention. FIG. 1 is a cross-sectional view of the valve driving device, and FIG. 2 is II- in FIG.
FIG. 3 is a sectional view taken along the line II, FIG. 3 is an explanatory diagram of the operation, and FIG. 4 is a graph showing valve characteristics. 3 ... Cylinder head, 8a, 8b ... Valve, 11a, 11b ... Rocker arm, 17 ... Camshaft support arm, 21a, 21b ... Camshaft, 22 ... Idler gear, 24a, 24b ... Cam gear, 25a, 25b …… Cam

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenji Nishida 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-64-53009 (JP, A) 62-116103 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01L 13/00 301 F01L 1/12 F01L 1/34 F01L 1/04

Claims (2)

(57) [Claims] 1. An apparatus according to claim 1, wherein said cylinder head is disposed above said cylinder head.
Two camshafts (21) driven by a pair of cam gears (24a, 24b) meshing with a common idler gear (22)
a, 21b), rocker arms (11a, 11b) which abut on cams (25a, 25b) provided on the respective camshafts (21a, 21b) and swing around fulcrums, and these rocker arms (11a, 11b).
Intake valve (8a) and exhaust valve (8b) driven in contact with
And a camshaft (21a, 21b) is connected to an idler gear (2
2) The camshaft support arm (17) is attached to the tip of an integral camshaft support arm (17) pivotally supported coaxially with the rotation axis, and the camshaft support arm (17) is swung by a support arm drive mechanism in accordance with a change in the rotation speed of the internal combustion engine. The cam (25a, 25b) and the rocker arm (11
a, 11b) by changing the lever ratio, the intake valve (8a)
And a valve timing of the exhaust valve (8b) and a valve lift of the DOHC type internal combustion engine, respectively. 2. The valve timing of an intake valve (8a) and an exhaust valve (8b) is delayed and the valve lift of both valves (8a, 8b) is increased with an increase in the rotation speed of the internal combustion engine. The valve drive device for a DOHC internal combustion engine according to claim 1, wherein