JP2000002234A - Bearing device for camshaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a striking noise of a camshaft to a thrust bearing face. SOLUTION: This bearing device 5 supports both a first camshaft 1 interlockingly driven with a crank shaft and a second cam shaft 2 interlocked with the first camshaft 1 through a pair of helical gears 3 with both the camshafts 1, 2 oriented in a thrust direction. In this bearing device 5, when the camshafts 1, 2 are displaced toward a thrust action direction at the time of driving through helical gears 3, one of bearing flanges 8, 9 abuts on either upper or lower thrust bearing face (shown in one way hatched lines). Otherwise, when the camshafts 1, 2 are displaced toward the opposite direction, the bearing flanges 8, 9 abut on both the upper and lower thrust bearing faces (shown in crossed hatched lines).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camshaft bearing device and, more particularly, to a camshaft bearing device for reducing a tapping noise on a thrust bearing surface of a camshaft interlocked via a helical gear pair.

[0002]

2. Description of the Related Art In an overhead cam mechanism, an exhaust camshaft for opening and closing an exhaust valve and an intake camshaft for opening and closing an intake valve are generally arranged in parallel with a cylinder head, and a cam pulley fixed to a front end of the exhaust camshaft is provided. The exhaust camshaft and the intake camshaft are interlocked via a helical gear pair while being configured to be driven in conjunction with the crankshaft. A bearing device that rotatably supports these camshafts includes a bearing portion formed on a lower cylinder head and an upper bearing cap.Furthermore, in a bearing portion at a front end portion of these camshafts, For example, actual Kaihei 1-1
As disclosed in Japanese Patent No. 24308 or the like, a pair of bearing flanges are provided on a cam shaft at an appropriate interval in the axial direction, a bearing portion and a bearing cap are fitted between the bearing flanges, and these cam shafts are mounted. It is configured so as to be rotatable in the radial direction and to support the thrust force acting on the helical gear pair.

By the way, the bearing flange of the camshaft, the thrust bearing surfaces on both sides of the bearing portion of the cylinder head, and the thrust bearing surfaces on both sides of the bearing cap ensure smooth rotation while facilitating assembly of the camshaft. Figure 4
As shown in FIG. 5, the gap between the pair of bearing flanges 12 and 13 provided at the front end of the camshaft 11 and the bearing cap 14 are fitted in a state where a minimum gap δ required for assembling the bearing cap 14 is generated. The pair of bearing flanges 12, 13 and the bearing portion 15 formed on the cylinder head 20 are fitted in a state where a considerably large gap Δ is formed so that the cam shaft 11 can be easily assembled to the cylinder head 20. When the camshaft 11 is displaced by a thrust force acting when the camshaft 11 is driven via the helical gear pair, one of the bearing flanges 13 is provided with the thrust bearing surfaces 15 of both the bearing portion 15 and the bearing cap 14.
b and 14b.

Accordingly, in a state where the thrust force due to the reaction force of the driving force of the helical gear pair is acting on the camshaft 11, one of the bearing flanges 13 is applied to both the thrust bearing surfaces 15b, 14b of the bearing portion 15 and the bearing cap 14. In the state where the camshaft 11 receives the rotational biasing force in the opposite direction due to the biasing force of the valve spring of the intake valve, as shown in FIG. Abuts only on the thrust bearing surface 14a of the cap 14 and between the thrust bearing surface 15a of the bearing portion 15 and (Δ
−δ), and a one-sided contact state occurs only at the upper portion.

[0005]

In the above construction, the exhaust camshaft is driven to rotate, and the intake camshaft is rotated in conjunction with the helical gear pair, whereby the exhaust valve and the intake valve are biased by the valve spring. When the intake camshaft is driven by the exhaust camshaft, the direction of the thrust force applied by the helical gear pair when the intake camshaft is driven, and conversely, the intake camshaft is urged to rotate by the valve spring. The direction of the thrust force acting by the helical gear pair when the exhaust camshaft is received by the exhaust camshaft via the helical gear pair is opposite to each other,
Each of the camshafts repeatedly moves in the axial direction by the gap δ, and each time the bearing flange 12 of the camshaft 11 collides with the thrust bearing surface 14a of the bearing cap 14, and the bearing flange 13 forms the bearing cap 14 or the bearing portion. 15 thrust bearing surfaces 14b, 1
There was a problem that a hitting sound colliding with 5b was generated and the resulting noise was loud.

[0006] In order to investigate noise generation due to hammering noise as a countermeasure for noise reduction, the displacement of the exhaust camshaft and the intake camshaft in the thrust direction and the magnitude of the generated noise were measured. As shown in the figure, the exhaust (EX) camshaft is displaced to the front (Fr) side and the intake (IN) camshaft is displaced to the rear (Rr) side by the thrust force applied when driving (positive torque) by the helical gear pair, and the thrust bearing is displaced. The noise generated when colliding with the surface is small. Conversely, when the intake camshaft is rotationally urged by the valve spring (negative torque), it is displaced in the opposite direction by the thrust force acting and collides with the thrust bearing surface. It was found that the generated noise was much higher.

Further, the cause is that the collision speed (β) at the negative torque is larger than the collision speed (α) at the positive torque, and the driving by the helical gear pair (positive torque) ), The upper and lower ends are in contact with each other. On the contrary, when the intake camshaft is rotationally urged by the valve spring (negative torque), only the upper portion is in a single contact state. It was found that the buffer effect of the oil film was small.

The present invention has been made in consideration of the above-described conventional problems, and has as its object to provide a camshaft bearing device that reduces the impact noise of a camshaft against a thrust bearing surface.

[0009]

SUMMARY OF THE INVENTION A camshaft bearing device according to the present invention comprises a first camshaft driven in conjunction with a crankshaft and a first camshaft interlocked with the first camshaft via a helical gear pair. 2. A bearing device for supporting the camshaft 2 in the thrust direction, wherein when the camshaft is displaced in a direction in which a thrust force acts upon driving via a helical gear pair, the camshaft contacts one of the upper and lower thrust bearing surfaces. When the camshaft is displaced in the opposite direction, it comes into contact with both the upper and lower thrust bearing surfaces.

According to such a configuration, when driven by the helical gear pair (positive torque), only one of the upper and lower portions is brought into contact with each other. However, since the collision speed against the thrust bearing surface is relatively low, the noise generated is low, and When the intake camshaft is urged to rotate by the valve spring (negative torque), the collision speed against the thrust bearing surface is large, but since the upper and lower parts hit against the thrust bearing surface,
The area of the buffer oil film on the thrust bearing surface is large, and the generated noise can be reduced. Therefore, the overall noise due to the striking sound of the camshaft on the thrust bearing surface can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a camshaft bearing device according to the present invention will be described below with reference to FIGS.

In FIG. 1, reference numeral 1 denotes an exhaust cam shaft for opening and closing an exhaust valve, and reference numeral 2 denotes an intake cam shaft for opening and closing an intake valve, which is arranged in parallel with a cylinder head 10 (see FIG. 2). At the end on the front (Fr) side of the exhaust cam shaft 1,
A cam pulley 4 is fixed, is configured to be driven in conjunction with a crankshaft (not shown), and the exhaust camshaft 1 and the intake camshaft 2 rotate in conjunction with each other via a helical gear pair 3. It is configured to be.

The camshafts 1 and 2 are rotatably supported by a plurality of bearing devices 5 arranged at appropriate intervals from the front (Fr) to the rear (Rr) side.
As shown in FIG. 2, the bearing comprises a bearing portion 6 formed on a lower cylinder head 10 and an upper bearing cap 7. Further, in the front end bearing device 5 disposed forward of the helical gear pair 3 of the camshafts 1 and 2, a pair of front and rear bearing flanges 8 are provided at appropriate intervals in the axial direction of the camshafts 1 and 2. A bearing portion 6 and a bearing cap 7 are fitted between the bearing flanges 8 and 9 to support the camshafts 1 and 2 rotatably in the radial direction and to act on the helical gear pair 3 in the thrust direction. It is configured to support the force of

The bearing 6 of the cylinder head 10 has a pair of bearing flanges 8, 9 and thrust bearing surfaces 6a, 6b on both sides of the bearing 6 so that the camshafts 1, 2 can be easily assembled to the cylinder head 10. The width of the thrust bearing surface 7a, 7b on both sides of the bearing cap 7 is set such that the bearing cap 7 is fitted between the pair of bearing flanges 8, 9 so that a relatively large gap Δ is generated therebetween. Is set so that a minimum gap δ required for assembly is generated.

When the intake camshaft 2 is driven via the helical gear pair 3 as shown by arrows a and b in FIG. 1, a thrust force is applied to the camshafts 1 and 2 in the directions shown by outline arrows c and d. When these camshafts 1 and 2 are displaced by the action, as shown by the oblique lines in FIG.
As shown in FIG. 2, the bearing abuts only on the thrust bearing surface 7 b behind the bearing cap 7, and the bearing flange 8 on the front of the intake camshaft 2.
Abuts only on the front thrust bearing surface 7 a of the bearing cap 7, and a gap of (Δ−δ) is formed in the lower bearing 6.

On the contrary, in a state in which the intake camshaft 2 is reversely driven by the urging force of the valve spring of the intake valve, and the exhaust camshaft 1 receives the reverse driving force via the helical gear pair 3, FIG. As indicated by the cross hatching, the front bearing flange 8 of the exhaust camshaft 1 abuts both the bearing portion 6 and the front thrust bearing surfaces 6a, 7a of the bearing cap 7,
The rear bearing flange 9 of the intake camshaft 2 is in contact with both the bearing portion 6 and the rear thrust bearing surfaces 6b, 7b of the bearing cap 7, so that both upper and lower contact states are established.

According to the above construction, the exhaust camshaft 1 is driven by the cam pulley 4, and at the same time, the helical gear pair 3
When the intake camshaft 2 is driven through the positive torque, the bearing flange 9 behind the exhaust camshaft 1 is used as shown in FIGS.
Is only on the thrust bearing surface 7b behind the bearing cap 7,
The front bearing flange 8 of the intake camshaft 2 comes into a single contact state in which the front bearing flange 8 abuts only on the front thrust bearing surface 7a of the bearing cap 7. However, at the time of this positive torque, the generated noise is low because the collision speed of the bearing flanges 9 and 8 against the thrust bearing surfaces 7b and 7a is relatively low. On the other hand, when the intake camshaft 2 is rotationally urged by the valve spring and the negative torque is received by the exhaust camshaft 1 via the helical gear pair 3, the collision speed against the thrust bearing surface is large, but the rearward of the intake camshaft 2 A bearing flange 9 is provided on both the thrust bearing surfaces 6b and 7b behind the bearing portion 6 and the bearing cap 7, and a bearing flange 8 in front of the exhaust camshaft 1 is provided with a thrust bearing surface 6a in front of the bearing portion 6 and the bearing cap 7. Since both the upper and lower parts 7a come into contact with each other, the area of the buffer oil film on the thrust bearing surface is large, and the noise generated can be reduced. Therefore, the camshaft 1,
2, it is possible to reduce the overall noise due to the tapping sound on the thrust bearing surfaces 6a, 6b, 7a, 7b.

The actual noise reduction effect will be described with reference to FIG. 3. The permissible noise level depends on the engine speed.
The value is set to a larger value as the engine speed increases, and an allowable level is set for each engine speed. In the conventional example, as shown by the solid line, when the engine speed exceeds 1000 rpm, the allowable level may not be able to be cleared. The noise level can be reduced by the engine speed,
Especially in the general-purpose range and the relatively high noise level of 1000 to 1000
The noise level was significantly reduced in the range of the engine speed of 2500 rpm. As a result, even when the engine speed exceeded 1000 rpm, the allowable level could be cleared lightly, and the noise could be reduced at all engine speeds.

[0019]

According to the camshaft bearing device of the present invention, when the camshaft is displaced in the direction in which the thrust force acts at the time of positive torque driven via the helical gear pair as described above, one of the upper and lower parts is used. Abuts one thrust bearing surface,
When the camshaft is displaced in the opposite direction, it comes into contact with both the upper and lower thrust bearing surfaces. The generated noise is low. Conversely, when the intake camshaft is negatively urged to rotate by the valve spring, the impact speed against the thrust bearing surface is large, but the upper and lower parts hit against the thrust bearing surface. , The area of the buffer oil film is large, and the generated noise can be reduced. Therefore, it is possible to reduce the noise due to the tapping noise on the thrust bearing surface of the camshaft at a low cost without adding a complicated configuration only by a simple design change.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of a main part of a camshaft bearing device according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a bearing unit in the embodiment.

FIG. 3 is a comparison diagram of noise levels between the embodiment and a conventional example.

FIG. 4 is a schematic configuration diagram of a conventional camshaft lubrication device.

FIG. 5 is an explanatory diagram showing a relationship between displacement operation of an exhaust camshaft and an intake camshaft and generated noise in the conventional example.

[Explanation of symbols]

 Reference Signs List 1 exhaust cam shaft 2 intake cam shaft 3 helical gear pair 5 bearing device 6 bearing portion 6a, 6b thrust bearing surface 7 bearing cap 7a, 7b thrust bearing surface 8 bearing flange 9 bearing flange 10 cylinder head

Claims (1)

[Claims] 1. A bearing device for supporting a first camshaft driven in conjunction with a crankshaft and a second camshaft linked to the first camshaft via a helical gear pair in a thrust direction. When the camshaft is displaced in the direction in which the thrust force acts when driven through the helical gear pair, the camshaft is in contact with one of the upper and lower thrust bearing surfaces, and when the camshaft is displaced in the opposite direction, the upper and lower thrust bearings are displaced. A camshaft bearing device characterized in that it contacts both thrust bearing surfaces.