JPH0247206Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention relates to a camshaft drive device for a DOHC engine.

(Prior art and problems to be solved) <First conventional technology and problems to be solved> As a conventional technology in this field, U.S. Patent No.
There is one described in the specification of No. 1398651. In this case, the two camshafts are directly connected by gears, and one of the camshafts is further connected to the crankshaft by multiple gears, so that all of the driving force of the crankshaft is transmitted to the two camshafts by the gears. It is something.

This first prior art has the disadvantage that a gear hitting sound is generated due to the existence of a bump due to the rotational fluctuation of each of the two camshafts, and this hitting sound generates a large noise. Here, the main reasons why rotational fluctuations occur in each camshaft are as follows.

That is, in the valve opening process where the camshaft pushes down the valve lifter against the elastic force of the valve spring as shown in Fig. 4, the camshaft receives torque from the valve spring in the opposite direction to the rotational driving direction. As shown in the figure, during the valve closing process in which the valve lifter is pushed up by the elastic force of the valve spring, the elastic force of the valve spring generates a torque in the direction of accelerating the rotation of the camshaft, temporarily increasing the rotation speed. Since such rotational fluctuations occur at different times in the two camshafts, the teeth of the gears of the two camshafts that mesh with each other collide with each other within the range of collision, producing a knocking sound.

<Second Prior Art and Problems to be Solved> Another conventional technology is the technology described in Japanese Utility Model Publication No. 38-7203. In this system, two camshafts are gear-coupled to each other, but not directly but via an intermediate idle gear, and the idle gear (intermediate shaft) and crankshaft are connected by a chain. be.

In this second prior art, since the intermediate idle gear is used, the distance between the two camshafts becomes large, which becomes an obstacle to making the engine more compact. Further, similar to the first prior art, there is a problem in that gear hitting noise occurs between each gear of the two camshafts and the idle gear due to the above-mentioned rotational fluctuation, and this causes a large amount of noise.

If the chain were able to absorb and attenuate the gear hammering sound, the above noise could be reduced, but this mechanism, which connects the idle gear and the crankshaft through a chain, would not exhibit the hammering noise reduction effect. . The reason is as follows.

As shown in FIG. 6, for example, when a tooth d hits a tooth i due to rotational fluctuation in the counterclockwise direction of the camshaft D shown by the solid line in the figure, the idle gear I connected to the chain has to absorb the collision force. Even if an attempt is made to rotate clockwise, if the other camshaft C causes a rotational fluctuation in the clockwise direction indicated by the dotted line arrow in the figure, this will prevent the clockwise rotation of this idle gear I, and therefore transfer the collision force to the idle gear. It cannot be absorbed or attenuated by the chain through the rotation of I. In other words, since the idle gear I is coupled with a plurality of different rotation axes C and D,
In response to rotational fluctuations of one rotating shaft D, rotation of the idle gear I is hindered by rotational fluctuations of the other rotating shaft C. Furthermore, the other rotating shaft C becomes a so-called stopper for the idle gear I, and the teeth d of the one rotating shaft D collide with the teeth i in the same way as they hit a rigid body that does not have a rotation absorption function, causing a large Generates a banging sound. As described above, since the collision force between the gears cannot be converted into the rotation of the idle gear, the chain connected to the idle gear cannot absorb or attenuate the collision force of the gear teeth and thus the hammering sound.

As mentioned above, in the first prior art, there is no idea of absorbing or attenuating gear hitting sound with a chain (the chain itself does not exist), and in the second prior art, there is no chain. However, since the chain is wrapped around an intermediate shaft, the gears that mesh with the chain interfere with the chain's ability to absorb and attenuate hitting sounds.
In the end, it can be said that there is no concept of using a chain as a means of reducing hitting noise.

The problem to be solved by the present invention is to provide a camshaft drive device in which the distance between two camshafts is small (compact) and gear noise accompanying rotational fluctuations of each of the two camshafts can be reduced. There is a particular thing.

(Means for solving the problem) The configuration for solving this problem can be summarized as follows.

Two camshafts, each of which undergoes rotational fluctuations, are connected directly (without an intermediate gear) with gears of the same diameter, one camshaft is directly provided with a sprocket or pulley, and the other camshaft and crankshaft are connected by a chain or belt. This transmits the driving force of the crankshaft to one camshaft, and drives the other camshaft via that camshaft.

(Function/Effect) If you do this, the distance between the two camshafts will be
Not only can it be short and compact by direct gear coupling, but it can also be connected to a chain or belt (hereinafter referred to as "chain"), which eliminates the gear rattling sound caused by the aforementioned rotational fluctuations occurring in each of the two camshafts without being interfered with by other gears. can be effectively and effectively absorbed and attenuated.

In other words, the chain in the present invention is not only used as a driving force transmission means for transmitting the rotational driving force of the crankshaft to each camshaft, but also as an absorption/damping means for reducing gear hitting noise. It is designed to fulfill its role. Absorbing this gear sound
A more concrete explanation of the damping effect is as shown in FIG. 3.

In Fig. 3, when tooth b hits tooth a due to rotational fluctuation of the driven side camshaft (driven gear 17) (temporary acceleration in the counterclockwise direction indicated by the solid line arrow in the figure), the The collision force is absorbed by the drive gear 16 (camshaft to which the chain is connected) as it rotates clockwise in the figure.
By being attenuated, the hitting sound between teeth b and teeth a is reduced. Further, the collision force between teeth a and teeth b due to rotational fluctuations of the drive gear 16 in the counterclockwise direction in the figure (dotted line arrow) is also attenuated by the chain directly connected to the drive gear 16. In this way, since the driven gear 17 is the only gear that meshes with the drive gear 16 to which the chain is directly connected, the rotation of the drive gear 16 to absorb the gear tooth collision force is not hindered by other gears, and the chain This provides an effective gear knocking noise reduction effect.

In short, the key points of the present invention are the direct connection of both camshafts by gears, and the structure with a chain that functions as a means to absorb and attenuate the sound of these gears.

(Example) An example of this invention will be described below based on the drawings. In the figure, 1 is the cylinder head of the DOHC engine, 2 is the cam housing, 3 is the first camshaft, 3a is the first cam, 4 is the second camshaft, 4a is the second cam, 5 is the first intake valve, 6 is the second
It is an intake valve. Note that the DOHC engine of this embodiment has the above two intake valves 5, 6 and 1 per cylinder.
The exhaust valve is provided with a double exhaust valve, which exhaust valve is located at 21 in FIG. The first intake valve 5 is driven by the first cam 3a via the lifter 7, pad 9, and valve spring 11. Further, the second intake valve 6 is driven by the second cam 4a via a lifter 8, a pad 10, and a valve spring 12. The exhaust valve 21 also has a similar structure. 13 is a first intake port, 14 is a second intake port, 15 is an exhaust port, and the first intake valve 5 is connected to the first intake port 13.
The second intake valve 6 opens and closes the second intake port 14, and the exhaust valve 21 opens and closes the exhaust port 15. A drive gear 16 is attached to the first camshaft 3, and a driven gear 17 that has the same size as the drive gear 16 and meshes with the drive gear 16 is attached to the second camshaft 4. A sprocket 18 having a larger diameter than both gears 16 and 17 is attached to the first camshaft 3 in front of the drive gear 16. This sprocket 18 is driven by a sprocket attached to the crankshaft of an engine, also not shown, via a chain, not shown. 19 is a spark plug, and 20 is a wedge type combustion chamber.

In the above configuration, the first camshaft 3 is driven by the sprocket 18 by the rotation of the engine crankshaft. 1st camshaft 3
Drive gear 16 and driven gear 1 due to the rotation of
The second camshaft 4 rotates via 7. Therefore, the first intake valve 5, the second intake valve 6, and the exhaust valve 2 in each cylinder are controlled by the first cam 3a and the second cam 4a.
1 is driven, and a predetermined phase difference is given to the valve operation timing of each cylinder.

The distance between the axes of both camshafts 3 and 4 is approximately the same as the pitch circle diameter of the drive gear 16 or driven gear 17. The number of teeth, width, and pitch circle diameter of both gears 16 and 17 may be set so as to withstand the driving torque of the first camshaft 3.

Then, when the above-mentioned rotational fluctuation occurs in the first camshaft 3 or the second camshaft 4, the collision force between the gear teeth at that time and the gear rattling noise are based on the rotational displacement of the drive gear 16 (first camshaft 3). This is absorbed and attenuated by the damping action of the chain, which acts as a minute displacement absorber, thereby reducing the vibration and noise of the camshaft drive section.

Note that the above description is literally just an example, and it goes without saying that the present invention can be implemented with various modifications based on the knowledge of those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 shows a plan view of an embodiment of this invention.
FIG. 2 shows a sectional view taken along the line -- in FIG. Also,
Fig. 3 is an explanatory diagram specifically showing the gear knock noise reduction effect according to the present invention, Figs. 4 and 5 are explanatory diagrams showing the causes of rotational fluctuations of each camshaft, and Fig. 6 is an explanatory diagram showing each gear in the conventional example. FIG. 3...First camshaft, 4...Second camshaft, 16...Drive gear, 17...Driven gear, 21...Exhaust valve.

Claims (1)

[Scope of utility model registration request] Two camshafts are arranged in parallel above the cylinder head of the engine, and the rotation of these camshafts opens and closes the intake and exhaust valves.
In a DOHC engine, one camshaft is driven by the engine crankshaft via a chain or belt, so a sprocket or pulley is fixed concentrically to one camshaft, and the other camshaft is connected to one camshaft. A camshaft drive device, characterized in that the camshaft drive device is directly engaged with the sprocket or pulley by a gear having the same diameter but smaller in diameter than the sprocket or pulley.