JPH0458006A - Variable valve timing device - Google Patents

Abstract

PURPOSE:To stabilize combustion to improve thermal efficiency and obtain high torque in all operating regions by providing a low speed cam and a high speed cam having base circles of the same diameter to a cam shaft to make it possible for a roller follower to move. CONSTITUTION:A low speed cam 8 and a high speed cam 9 having base circles of the same diameter are provided integrally to a cam shaft 6. A roller follower 13 is held by shifter arms 15a, 15a of a shifter 15. When an engine runs at low speeds, a rocker arm 10 oscillates through a roller follower 13 by the low speed cam 8, and the valve has characteristics of low lift and narrow opening angle. Furthermore, when the engine is operated at high speeds, the roller follower 13 is slidably brought into contact with the high speed cam 9. As a result, the rocker arm 10 oscillates through the roller follower 13 by the high speed cam 9, and the valve has characteristics of high lift and wide opening angle. Thermal efficiency, along with charging efficiency are thus improved to increase output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable valve timing device having a low and high speed cam, and more particularly to smooth switching when switching between low and high speed cams.

[Conventional technology]

In the past, many proposals have been made for variable valve timing devices that change the opening and closing timing of intake and exhaust valves, and Japanese Patent Application Laid-Open No. 58-211516 discloses a method of selectively switching between two cams by moving a rocker arm. Additionally, Japanese Utility Model Application Publication No. 6269003 discloses a system using rollers (roller followers) to reduce friction in a valve train.

[Problem to be solved by the invention]

However, in the above-mentioned first prior art, the rocker arm that rotates the rocker arm in the axial direction is relatively large, and thus a large force (actuator reaction force) is required to shorten the switching time.

In addition, since the rocker arm is a center pivot type rocker arm, the force in the direction perpendicular to the rocker arm axis when the valve train operates is (
(cam reaction force) + (valve reaction force), and a large force acts on the rocker arm shaft. For this reason, the rocker arm shaft must have a large diameter, and there are also problems such as increased friction when switching the rocker arm.

Note that the second prior art is a valve operating device that operates two valves simultaneously using a bifurcated swing arm, and is not a variable valve timing device.

However, interposing rollers between the cam and the swing arm is effective in reducing friction.

The present invention has been made in view of the above-mentioned problems, and is a variable valve timing device in which a roller follower is movably mounted in order to reduce the switching force of a switching means that selectively switches between a low-speed cam and a high-speed cam. The purpose is to provide

[Means to decide the issue]

In order to achieve this object, the present invention provides an engine valve operating device in which a roller follower provided on a rocker arm and a cam formed on a camshaft are in sliding contact, wherein the camshaft has a base circle of the same diameter. The roller follower is provided with a low-speed cam and a high-speed cam, and a shifter is interposed in the roller follower, and the shifter is operated based on the operating state of the engine, thereby selectively switching the roller follower between the low-speed cam and the high-speed cam. It is characterized by moving and sliding contact with.

[For production]

In the variable valve timing device of the present invention, at low speeds, the roller follower attached to the rocker arm slides against the low speed cam to operate the valve, thereby obtaining valve characteristics of low lift and narrow opening angle.

Furthermore, at high speeds, the roller follower is moved via a shifter by hydraulic or electrical means and slides into contact with the high speed cam to operate the valve, thereby obtaining high lift and wide angle valve characteristics.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a valve mechanism without showing the first embodiment of the present invention, FIG. 2 is a view taken in the direction of the Z arrow in FIG. 1, and FIG.
It is an arrow view. In the figure, reference numeral 1 indicates an intake valve (or exhaust valve), 2 a valve stem, 2a a stem end, 3 a valve spring, 4 a retainer, and 5 a valve seat. Further, 6 indicates a camshaft rotated by a crankshaft of an engine (not shown) via a timing belt, and 7 indicates a rocker shaft parallel to the camshaft 6.

The camshaft 6 is integrally provided with a low speed cam 8 and a high speed cam 9 having base circles of the same diameter.

A rocker arm 10 that is rocked by a low-speed cam 8 or a high-speed cam 9 is pivotally supported on the rocker shaft 7, and the tip of the rocker arm 10 is attached to the stem end 2a of the valve stem 2. Intake valve 1
An adjustment screw 11 is installed to adjust the clearance.

Here, the rocker arms 10 are left and right arms 10a.

10b is integrally connected with the tip 10C, and is formed in a concave shape, and is parallel to the rocker shaft 7 and the roller shaft 12 pivotally supported by the left and right arms IOa and tab at the intermediate part between the rocker shaft 7 and the adjustment screw 11. It is set in. A roller follower 13 that selectively slides on the low-speed cam 8 or the high-speed cam 9 is attached to the roller shaft 12 via a needle 14.

The roller follower 13 is the theater arm 15a of the shifter 15.
, 15a, and a piston 16 is fixed to the boss portion 15b of the shifter I5. When the piston 16 is moved, the roller follower 13 moves in the axial direction of the roller shaft 12 together with the needle 14. The piston 16 is fitted into a hydraulic cylinder 17 press-fitted into one am IOa side of the rocker arm IO, and a return spring 18 is provided between the right arm 10b of the rocker arm 10 and the shifter 15b. A pressure chamber 10d formed between the bottom of the hydraulic cylinder 17 and the piston 16 communicates with the oil gear gallery 7b of the rocker shaft 7 via the opening 17a of the hydraulic cylinder I7 and the oil passage 7a, and is connected to the oil gear gallery 7b of the rocker shaft 7, and is connected to an oil pump (not shown). The oil pressure of the pumped lubricating oil, the oil gear gallery 7b, the oil passage 7a, the opening 17a1, the oil pressure chamber 10
d on the piston 16.

At low speeds, the switching valve (not shown) is closed and the hydraulic pressure does not reach the hydraulic chamber 10d, so that the shifter 15 is moved by the return spring 18 to the left arm 1 of the rocker arm 10. The roller follower 13 is pressed toward the Oa side, and as shown in FIG. 3, the roller follower 13 is in sliding contact with the low speed cam 8. Further, when the switching valve opens at high speed, the piston 16 moves the shifter 15 against the return spring 18 by the hydraulic pressure of the lubricating oil introduced into the hydraulic chamber 10d, as shown in FIG. The roller follower 13 is brought into sliding contact with the high speed cam 9.

Next, the operation of the variable valve timing device according to the present invention will be explained based on an embodiment configured as described above.

At low speeds, including when the engine is stopped, the switching valve of the oil passage communicating with the oil carriage b of the rocker shaft 7 is closed, and as shown in FIG. 18 through the shifter 15 to the low speed cam 8 side.

Therefore, the rocker arm 10 is swung by the low-speed cam 8 via the roller follower 13, and as shown by a in FIG.
The actual opening timing of the intake valve 1 is delayed, the amount of valve lift is small, and the actual closing timing is also early, resulting in a valve characteristic of low lift and narrow opening angle. Therefore, the overlap between the intake and exhaust valves is reduced, the actual compression ratio is increased, combustion is stabilized, and thermal efficiency is improved.

Also, at high speed, the switching valve opens and the oil gear lary 7b,
Lubricating oil is supplied to the hydraulic chamber 10d through the oil passage 7a and the opening 17a.
The oil pressure of the lubricating oil causes the piston 16 to return the shifter 15 to the rocker arm L)0(F) against the spring 18.
The right arm 10b is moved to the side, and the roller follower 13 is brought into sliding contact with the high speed cam 9 as shown in FIG. Therefore, the rocker arm 10 is moved to the roller follower 1 by the high speed cam 9.
As shown in Fig. 5b, the actual valve opening timing of the intake valve I becomes earlier, the valve lift amount is also large, and the actual valve closing timing is also delayed, resulting in a high lift and wide angle. The valve characteristics are as follows. Therefore, the overlap between the intake and exhaust valves increases, improving gas exchange, improving charging efficiency, and increasing output.

In addition, in the present invention, the movement operation of the roller follower 13 is performed because the friction between the roller follower [3] and the low-speed cam 8 or the high-speed cam 9 during the valve lift is larger than the thrust force due to the hydraulic pressure during the switching operation. The control is performed only during the contact period between the base circles of the low-speed cam 8 and the high-speed cam 9 and the roller follower 13.

6 to 9 show a second embodiment of the present invention, in which low speed cams 8a, 8b and high speed cam 9 are shown.
a, 9b are arranged alternately on the camshaft 6, and the cam widths of the low-speed cams 8a, 8b and the high-speed cams 9a, 9b are each formed into a narrow cam width 1, for example, 172 mm, which is the cam width of the first embodiment. ing.

Further, a roller follower 13 movably attached to a roller shaft 12 parallel to the rocker shaft 7 at an intermediate portion of the rocker arm 10 has a roller 13a that can slide into two low-speed cams 8a8b or high-speed cams 9a and 9b.

13b, and in the middle part of these rollers 13a, 13b, when the roller follower 3 is in sliding contact with the low speed cams ga, 8b or the high speed cams 9a, 9b, a low speed cam 8 is installed.
A small diameter portion 13c is formed so that the high speed cam 9a or the low speed cam 8b disposed between the portions a and 8b does not come into contact with each other.

Furthermore, the roller follower 13, as shown in FIG.
The needle 14 is supported via thrust receiving plates 21 provided on both end faces, and the needle 14 is not pulled out when the roller follower 13 is moved. Further, the shifter 15 for moving the roller follower 13 is formed with a shifter arm 15a that engages with a small diameter portion 13c formed between the rollers 13a and 1.8b.

The operation of the second embodiment configured as described above is similar to that of the first embodiment already described, and at low speed, as shown in FIG. 8, the rollers 13a and 1 of the roller follower 13 are
3b is in sliding contact with low-speed cams 8a and 8b, and at high speed, the 9th cam
As shown in the figure, the roller 13a of the roller follower 13,
13b is in sliding contact with the high speed cams 9a and 9b.

However, the rollers 13a and 13b of the roller follower 13
Since the small diameter part 13c of the high speed cam 9 is formed in the middle part of the
The roller follower 13 is connected to the low speed cam 8a, 8b or the high speed cam 9a, 9b to the high speed cam 9a, 9b or the low speed cam 8a.

When moved to 8b, since the cam width is narrow, it immediately slides into contact with high speed cams 9a, 9b or low speed cams 8a, 8b.

Therefore, the amount of movement of the roller follower 13 is approximately half that of the first embodiment, and the amount of movement can be reduced to shorten the switching time.

In this embodiment, the shifter 15 is moved by applying hydraulic pressure to the piston 16 fixed to the shifter 15, but instead of hydraulic pressure, electric means such as a solenoid may be used.

〔Effect of the invention〕

As explained above, in the valve timing device of the present invention, the camshaft is provided with a low speed cam and a high speed cam having base circles of the same diameter, and the low speed cam and high speed cam are selected depending on the operating condition of the engine. By making the roller follower movable, the valve features low lift and narrow opening angle at low speeds, resulting in stable combustion and improved thermal efficiency.

In addition, at high speeds, the valve characteristics of high lift and wide opening angle are obtained, which improves filling efficiency and improves output.
High torque can be obtained in all operating ranges.

Furthermore, when making the valve timing variable, the roller follower is moved based on the engine operating condition and the low-speed cam or high-speed cam is selected, so since the mass of the roller follower is small, the low-speed cam and high-speed cam can be switched with a small switching force. It is possible to switch between

Furthermore, since the roller shaft supporting the roller follower only receives the cam reaction force compared to the rocker shaft, the shaft diameter can be made smaller, and the variable valve timing device can be made more compact.

Furthermore, the low-speed cams and high-speed cams each have two low-speed cams and two high-speed cams each having a narrow cam width, and are arranged alternately in the axial direction of the camshaft, and are selectively connected to the two low-speed cams or the high-speed cams. The roller follower that comes into sliding contact with the
Since the roller follower is made movable by engaging the shifter arm of the shifter in the small diameter section, the movement of the roller follower is reduced due to the narrow cam width, and the switching response time between low-speed and high-speed cams is shortened. Ru.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a valve mechanism showing a first embodiment of the present invention, FIG. 2 is a Z-arrow view showing the main parts of FIG. 1, and FIG. 3 shows the main parts of FIG. 1. FIG. 4 is an explanatory diagram of the main parts showing the state at high speed, FIG. 5 is a valve characteristic diagram according to the present invention, FIG. 6 is an explanatory diagram of the second embodiment, and FIG. 7 is an explanatory diagram of the second embodiment. FIG. 6 is a view in the direction of the P arrow showing the main parts of FIG. 6, FIG. 8 is a view in the direction of the Q arrow showing the main parts of FIG. 6, and FIG. 9 is an explanation of the main parts showing the state of the second embodiment at high speed. It is a diagram. l...Intake valve (exhaust valve), e-camshaft, 7...rocker shaft, 8, 8a, gb...
・Low speed cam, 9.9a9b・・High speed cam, 10・・Rocker arm, 12・・Roller shaft, 13・・Roller follower, 15・Shifter, 16・・Piston, 17・
・Hydraulic cylinder, 18...Return spring.

Claims (3)

[Claims] (1) In an engine valve train in which a roller follower provided on a rocker arm and a cam formed on a camshaft are in sliding contact, a low-speed cam and a high-speed cam having base circles of the same diameter are installed on the camshaft. A shifter is interposed in the roller follower, and the roller follower is selectively brought into sliding contact with the low-speed cam and the high-speed cam by operating the shifter based on the operating state of the engine. variable valve timing device. (2) Low-speed cams and high-speed cams have two low-speed cams and two high-speed cams each with narrow cam widths, and are arranged alternately in the axial direction of the camshaft. A roller follower that selectively makes sliding contact is divided into two parts by a small diameter part, and a shifter arm of a shifter is engaged with the small diameter part to make the roller follower movable.
1) The variable valve timing device described above. (3) The variable valve timing device according to claims (1) and (2), wherein the shifter is moved by hydraulic or electrical means.