JPH07116926B2 - Variable valve device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a variable valve operating device that changes the valve timing of an intake / exhaust valve of an internal combustion engine according to operating conditions.

(Prior Art) In general, a device for improving intake / exhaust efficiency and the like in a low speed region and a high speed region by changing valve timings of intake / exhaust valves of an internal combustion engine according to operating conditions,
It is proposed by JP-A-55-96310.

In order to change the valve timing, a three-dimensional cam whose cam profile changes in the axial direction of the cam shaft is created, and by moving this in the axial direction according to the operating conditions,
For example, the valve opening period and lift are reduced in the low speed range, and the valve opening period and lift are increased in the high speed range to improve fuel economy and exhaust composition in the low speed range, intake and exhaust efficiency in the high speed range, and the like.

(Problems to be Solved by the Invention) However, according to the normal valve operating device, the intake / exhaust valve is opened by the cam, but the valve closing is performed by using the biasing force of the valve spring. A large driving force was required when moving in the direction. In particular, during valve lift, a large frictional force is applied by the valve spring, so an actuator that overcomes this frictional force is required to move the three-dimensional cam, and a larger driving force is required to switch the response in a responsive manner. Become.

In the case of a multi-cylinder internal combustion engine, all cylinders are common, the frictional force between the cam and intake / exhaust valve is the smallest, and the period in the cam base circle is extremely short. It was also very difficult.

Also, since the cam surface is inclined in the axial direction, the cam contact part (cam follower) such as the rocker arm of the intake / exhaust valve.
Requires point contact, or a pivot type tip capable of following the cam surface must be interposed, the former requires wear due to high surface pressure, and the latter requires measures such as complicated structure and assembly.

An object of the present invention is to provide a variable valve operating device for an internal combustion engine, which can smoothly move in the camshaft direction when changing the valve timing.

(Means for Solving the Problem) According to the present invention, a camshaft that rotates in synchronization with engine rotation is provided with a cam for opening a valve and a cam for closing a valve, respectively, and the cam for opening the valve and the cam for closing the valve are shafts. The rocker arm for rocking is formed by a three-dimensional cam whose cam profile changes in a direction, and is provided with a driving means for axially displacing the cam shaft, and at the same time, a rockable arm for rocker opening that makes point contact with the cam for opening the valve via an arc portion. Of the rocking valve rocker arm for swinging close to the valve shaft of the intake or exhaust valve in the direction of pushing down, and point contact with the cam for closing the valve via the circular arc portion. Locked in.

(Operation) Therefore, the intake or exhaust valve is driven in the valve opening direction by the valve opening rocker arm that responds to the valve opening cam, and is returned in the valve closing direction by the valve closing rocker arm that responds to the valve closing cam.

When changing the valve timing of intake or exhaust, the solid cam is moved in the axial direction together with the cam shaft. As a result, the contact position of the valve opening / closing rocker arm with the cam changes, and the intake or exhaust valve lifts due to the different characteristics of the cam profile. At this time, since the rocker arm is configured to make point contact with the cam surface via the arc portion, both the valve opening and closing rocker arms can accurately open and close the valve with the same lift characteristics in any part of the cam profile. Activate.

Further, in this case, since there is no valve spring that biases the intake or exhaust valve toward the cam, the contact pressure of the rocker arm with respect to the cam is low, the cam shaft moves smoothly, and the contact pressure is small in this way. Therefore, even in the structure in which the rocker arm and the cam are in point contact with each other, the wear is suppressed and high durability is secured.

(Example) Hereinafter, the present invention will be described based on some examples.

In the first embodiment shown in FIGS. 1 and 2, reference numeral 1 is a camshaft, and one camshaft is provided above the valve (intake or exhaust valve) 4 of each cylinder. Open the cam 2 for valve opening and 2 on both sides by sandwiching the cam 2 for opening the valve.
The three valve closing cams 3 are integrally formed.

The rocker arm 5 for opening the valve, which is in contact with the cam 2 for opening the valve via the cam follower portion 5a, has its swinging tip abutted against the end portion of the valve shaft 4a of the valve 4, and its swinging base end is an adjusting screw. It is swingably supported by a pivot (spherical surface receiver) 7 via 6 and pushes down the valve 4 depending on the rotational position of the camshaft 1.

On the other hand, the valve-closing rocker arm 15 that comes into contact with the two valve-closing cams 3 via the bifurcated cam follower portion 15a has the intermediate portion of the valve-closing rocker arm 15 via the support shaft 16 and is connected to the valve-opening rocker arm 5. While swingably connected in the middle,
The oscillating tip contacts (locks) the retainer 17 attached to the valve shaft 4a from the bottom surface, and the valve 4 moves depending on the rotational position of the camshaft 1.
Pull up.

It should be noted that when the valve opening cam 2 pushes down the valve 4, the valve closing cam 3 does not interfere with this, and the valve closing cam 3 does not interfere with the valve 4.
Each of the valve opening cams 2 is formed with a cam profile so as not to hinder the valve opening cam 2 when it is pulled up, whereby the up-and-down movement of the valve 4 is driven by the cam together without the valve spring.

By changing the screwing position of the screw portion 6a of the adjusting screw 6, the swing center position of the valve opening rocker arm 5 is adjusted, and the adjusting screw 6 is fixed by the locking nut 8 screwed to the screw portion 6a. . The pivot 7 is inserted into the support hole 9a of the cylinder head (engine body) 9 to receive a load, and the lubricating oil guided to the support hole 9a lubricates the contact surface of the adjusting screw 6 with the spherical receiving portion 11.

By the way, as shown in FIG. 3 (A), the valve-opening and valve-closing cams 2 and 3 formed on the camshaft 1 are formed by a three-dimensional cam 10a whose cam profile continuously changes in the axial direction. It That is, the cam profile in contact with the rocker arms 5 and 15 is slightly different depending on the axial position of the camshaft 1, and the valve opening period and the lift amount of the valve 4 can be gradually changed. Depending on the axial position of the camshaft 1, each cam profile is set such that both the valve opening period and the lift are small in the engine low speed region, while the valve opening period and the lift are large in the high speed region. In the low speed range, valve overlap is eliminated to improve fuel efficiency and exhaust composition, and in the high speed range, intake and exhaust efficiency is increased to improve the maximum engine output.

FIG. 3 (B) shows the cams 2 and 3 for opening and closing the valve.
The cam profile of is set to two, one for low speed and the other for high speed, and a three-dimensional cam with two-stage switching that is continuous by a slope between them.
It is 10b. In this case, the processing of the cam profile is easier than that of FIG. 3 (A), and general biaxial processing can be used.

The follower parts of the rocker arms 5 and 15 for the valve opening cam 2 and the valve closing cam 3 shown in FIGS. 3 (A) and 3 (B).
5a and 15a are given a circular arc shape in the axial direction of the cam shaft by crowning so that the cams 2 and 3 and the rocker arms 5 and 15 are in point contact with each other, whereby relative displacement in the axial direction is achieved. The cam surface is smoothly followed, and the valve opening side and valve closing side operate accurately with the same lift characteristics.

In addition, the two cam followers 15 of the rocker arm 15 for closing the valve
Guides 19a and 19b are provided on both sides of a so as to prevent positional displacement so that the rocker arms 5 and 15 do not move together when the camshaft 1 is displaced.

In order to displace the camshaft 1 in the axial direction according to the operating conditions, a drive mechanism as shown in FIGS. 4 (A) and 4 (B) is provided.

FIG. 4 (A) shows that the camshaft 1 is driven by an electromagnetic actuator 20a. When a signal from the controller 21 is output to the actuator 20a via the drive circuit 22, the actuator 20a operates accordingly. Then, the camshaft 1 is displaced. The displacement amount is detected by the stroke sensor 23 and fed back to the controller 21 via the conversion circuit 24 and the movement determination circuit 25, whereby the movement of the camshaft 1 is controlled so as to match the target value.

Signals representing various operating conditions such as engine speed, load, and temperature are input to the controller 21, and the target position of the camshaft 1 in the axial direction is calculated based on these signals.

In FIG. 4 (B), a hydraulic actuator 20b is provided instead of the electromagnetic actuator 20a.
The switching valve 26 for controlling the hydraulic pressure supplied to 0b is switched by the output of the drive circuit 22.
Incidentally, 27 is a hydraulic pump, and 28 is a reservoir.

It is configured as described above, and the operation will be described below.

As the cam shaft 1 rotates, the valve 4 is pushed down by the valve opening cam 2 via the rocker arm 5 to open the valve.
Then, the valve 4 is pulled up by the valve closing cam 2 via the rocker arm 15 to close the valve.

In this way, the opening and closing of the valve 4 is performed by the cams 2 and 3, and the conventional valve spring is not required. Therefore, the opening and closing of the valve 4 can be stably performed even in the high rotation range without causing surging or the like. It can be carried out.

On the other hand, when the camshaft 1 is axially driven by the signal from the controller 21 via the actuator 20a (20b) in accordance with the operating condition of the engine, the opening that contacts the cam follower portions 5a, 15a of the rocker arms 5, 15 is performed. The cam profiles of the valve-closing and valve-closing cams 2 and 3 change, and the valve timing changes accordingly.

That is, the valve timing is changed so that the valve opening period and lift of the valve 4 are small in the low engine speed range, and the valve opening period and lift are large in the high engine speed range, ensuring optimum valve characteristics according to the operating conditions. Is done.

Since the valve 4 is not always urged in the closing direction by the valve spring, each rocker arm 5, 15 and the cam 2,
The contact pressure with 3 is extremely small. Therefore, even if the driving force for displacing the camshaft 1 in the axial direction is small, the camshaft 1 moves smoothly and the valve timing can be switched with good response. Further, since the contact pressure is low as described above, the rocker arm 5, which comes into contact with the cams 2 and 3,
Even if the 15 cam follower parts 5a, 15a are arc parts,
High surface pressure does not occur, and problems such as fluctuation of valve clearance due to wear hardly occur.

The embodiment of FIGS. 5 and 6 will now be described in which rocker arms 5 and 15 are independent of each other and rocker shafts 30 and 31 are provided.
It is an example in which it is swingably supported.

Also in this case, the opening and closing of the valve 4 is controlled by the rocker arms 5 and 15 that respond to the valve opening and valve closing cams 2 and 3.
Also, by moving the camshaft 1, each rocker arm 5, 15
The valve timing is variably controlled by a three-dimensional cam so that the cam profiles of the cams 2 and 3 that come into contact with the cam change. The positions of the rocker arms 5 and 15 are regulated by the end surface of the support boss portion 32 of the rocker shaft 30 (31) so as not to be displaced in the thrust direction when the cam shaft 1 is displaced.

In this embodiment, the rocker arm 15 for closing the valve is biased in the returning direction by the weak spring 33.
However, it is the closing cam 3 that drives the valve 4 in the closing direction. Therefore, the spring load of the spring 33 is much larger than that of a normal valve spring. Since it may be small, the cam shaft 1 can be smoothly moved in the axial direction as in the first embodiment.

In the above description, the setting of the valve timing in the low speed region and the high speed region is merely an example, and can be freely set according to the purpose.

(Effects of the Invention) As described above, according to the present invention, the cam profile of the three-dimensional cam changes by axially displacing the camshaft,
It is possible to freely change the valve timing of the intake or exhaust valve according to operating conditions.In this case,
Since there is no valve spring that biases the intake or exhaust valve toward the cam in the closing direction, the contact pressure of the rocker arm against the cam is low, and the camshaft can move smoothly and responsively.As a result, the camshaft is driven. The size and weight of the mechanism can be reduced.

Further, since the contact frictional force between the rocker arm and the cam is small, sufficient durability can be ensured even if the rocker arm is point-contacted with the cam through the arc portion, thus simplifying the structure and improving the assemblability. , It is possible to perform accurate opening / closing operation by matching lift characteristics in both opening and closing directions with respect to each of the valve opening and valve closing cams whose cam profile changes three-dimensionally by such a point contact contact structure. Therefore, the accuracy and reliability of the valve operating mechanism can be improved.

[Brief description of drawings]

1 is a sectional view showing a first embodiment of the present invention, FIG. 2 is a plan view of the same, FIGS. 3 (A) and 3 (B) are plan views of a three-dimensional cam, and FIG. 4 (A) and FIG. (B) is a block diagram of the drive means of a camshaft, respectively. FIG. 5 is a sectional view of the second embodiment, and FIG. 6 is a plan view of the same. 1 ... Cam shaft, 2 ... Valve opening cam, 3 ... Valve closing cam, 4 ... Valve (intake and exhaust valves), 5 ... Rocker arm, 5a ... Cam follower part, 9 ... Cylinder head, Ten
a, 10b: Solid cam, 15: Rocker arm, 15a: Cam follower part, 20a, 20b: Actuator, 21: Controller.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Komatsu, 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Kosaburo Okawa, 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (56) References Japanese Patent Laid-Open No. 61-223210 (JP, A) Actually published 63-132808 (JP, U)

Claims (1)

[Claims] Claims: 1. A camshaft that rotates in synchronism with engine rotation is provided with a cam for opening a valve and a cam for closing a valve, and the cam for opening and closing the cam has a three-dimensional cam profile that changes in the axial direction. A cam is provided with drive means for axially displacing the cam shaft, while a swingable rocker opening rocker arm that comes into point contact with the cam for opening the valve via an arc portion is used for the intake or exhaust valve shaft. A rocking valve rocker arm for swinging, which is brought into contact with the valve closing direction in a downward direction and is in point contact with the valve closing cam via an arc portion, is also locked in the pulling direction with respect to the valve shaft. A variable valve device for an internal combustion engine.