JP2004245385A - Device for preventing skipping of timing chain - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve at once the problems of assembling operability, dimension precision requirement, and noises, related to a skip preventive guide for the timing chain of an internal combustion engine. <P>SOLUTION: A slack guide 12 provides a tension to a timing chain 9 by pressurizing the one side of the timing chain 9 using a hydraulic actuator 13 while an engine is operated. The bottom of an inside member 12B of it is extended downward to integrally form a skip preventive guide 14 along the lower part of the winding section of a crankshaft sprocket 7 and the timing chain 9. When the engine is stopped, a clearance c1 is provided for preventing skipping. When the engine is operated, the clearance is increased by clockwise rotation as shown in the figure along with a slack guide 12, resulting in preventing interference between the skip preventive guide 14 and the timing chain 9. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for preventing a timing chain from coming off from a lower sprocket of a timing chain (tooth jump).
[0002]
[Prior art]
In an internal combustion engine mounted on a vehicle or the like, the timing of the crankshaft sprocket (lower sprocket) and the timing of the camshaft sprocket (upper sprocket) are used to rotate the camshaft of the valve mechanism in synchronization with the rotation of the crankshaft. There is something around the chain.
[0003]
In this device, when the upper sprocket is removed, the timing chain is positioned below the lower wrapped portion to prevent the timing chain from dropping downward and coming off the lower sprocket (tooth skipping). Thus, a tooth jump prevention guide is provided (see Patent Document 1).
[0004]
[Patent Document 1]
JP-A-5-86893
[Problems to be solved by the invention]
In recent years, the timing chain has a small engagement depth with a sprocket of about 1 to 2 mm for quietness and the like. It must be smaller than the depth.
[0006]
As a result, the assemblability of parts is poor and the requirements for dimensional accuracy are strict.In addition, by reducing the clearance in this way, the timing chain and the tooth jump prevention guide interfere during operation and generate abnormal noise There was a problem of doing.
[0007]
That is, as a problem in assembling parts, since the tooth skip prevention guide prevents the timing chain from coming off from the sprocket, the timing chain cannot be attached after the sprocket and the tooth skip prevention guide are attached. Constraints).
[0008]
Also, as a problem of dimensional accuracy requirements, in order to balance the clearance to prevent the timing chain from coming off the sprocket and the clearance to prevent the tooth skipping prevention guide from constantly contacting the timing chain due to manufacturing variations and assembly variations of parts. In addition, high component accuracy is required.
[0009]
Furthermore, as a problem of generating abnormal noise due to interference between the timing chain and the tooth jump prevention guide, the timing chain flaps due to a decrease in hydraulic pressure supplied to a slack guide which presses the side of the timing chain during engine operation to eliminate slack. In the case where the tooth jump prevention guide has a small clearance, the timing chain comes into contact with the tooth jump prevention guide and an interference sound is generated.
[0010]
SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and a tooth skipping prevention device for a timing chain which has simultaneously solved the above-described problems of assembling the components, a problem of dimensional accuracy requirement, and a problem of generation of abnormal noise. The purpose is to provide.
[0011]
[Means for Solving the Problems]
Therefore, according to the present invention, the clearance between the tooth jump prevention guide and the timing chain is switched so that the clearance from the lower sprocket of the timing chain can be prevented when the engine is stopped, and larger when the engine is operating than when the engine is stopped. Possible movable structure.
[0012]
In this way, the clearance between the tooth jump prevention guide and the timing chain can be switched, so that if the clearance is large, the timing chain can be wound around the sprocket even after the tooth jump prevention guide is attached, Restrictions on the assembly procedure are eliminated.
[0013]
In addition, the clearance should be set only for the size that can prevent the timing chain from coming off the lower sprocket when the engine is stopped, and for the clearance that prevents the tooth jump prevention guide from constantly contacting the timing chain. Since there is no need, the required degree of dimensional accuracy can be reduced and cost can be reduced.
[0014]
In addition, when the engine is running, the slack guide functions to apply tension to the timing chain, so it is tightly wound around the sprocket. By doing so, interference with the tooth jump prevention guide due to flapping of the timing chain is prevented, and generation of abnormal noise can be prevented.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
1 and 2, an internal combustion engine 1 has an intake camshaft 5 and an exhaust cam mounted on a cylinder head 4 connected above the cylinder block 2 while a crankshaft 3 is pivotally supported below the cylinder block 2. The shaft 6 is supported in parallel.
[0016]
On the front surface of the internal combustion engine 1, a crankshaft sprocket 7 is provided on the crankshaft 3. An intake camshaft sprocket 8 and an exhaust camshaft sprocket 9 are provided on the intake camshaft 5 and the exhaust camshaft 6, respectively.
[0017]
The crankshaft sprocket 7, the intake camshaft sprocket 8, and the exhaust camshaft sprocket 9 are used to rotate the intake camshaft 5 and the exhaust camshaft 6 of the intake / exhaust valve mechanism in synchronization with the rotation of the crankshaft 3. , The timing chain 10 is wound.
[0018]
In order to prevent the timing chain 10 from loosening and swinging during operation, an arcuate chain guide 11 for pressing one side (the right side in the figure) of the timing chain 10 inward is fixed to the front wall of the engine 1, The slack guide 12, which presses the other side surface of the chain 10 inward during operation, is disposed so as to pivotally support a lower portion of the slack guide 12 on the front wall. The slack guide 12 is made of a material having high rigidity such as metal. An inner member 12B made of a lubricating resin material is fixed inside the formed outer member 12A, and the inner surface of the inner member 12B slides with the timing chain 10. The outer member 12A has a lower end pivotally supported by a support shaft 12C, and an upper end connected to a telescopic operating rod of a hydraulic actuator 13 fixed to a front wall of the engine 1.
[0019]
When the engine is stopped, as shown in FIG. 1, the operating rod of the hydraulic actuator 13 is at the retracted position. However, when the engine is operating, as shown in FIG. The rod extends. As a result, the slack guide 12 rotates clockwise in the drawing, and the inner surface of the inner member 12B presses the timing chain 10 inward, applying a predetermined tension to the timing chain 10 and preventing the timing chain 10 from being loosened.
[0020]
The tooth jump prevention guide 14 according to the present invention is integrally provided with the slack guide 12 having such a basic function.
That is, the lower end of the inner member 12B formed of the resin material is provided to extend downward, and the arc-shaped tooth jump prevention guide 14 extends along the lower part of the timing chain 10 around the portion around the crankshaft sprocket 7. Is formed.
[0021]
Here, in the state shown in FIG. 1 when the engine is stopped, the clearance c1 between the arc-shaped tooth skip prevention guide 14 and the timing chain 10 is set smaller than the engagement depth between the timing chain 10 and the crankshaft sprocket 7. It is.
[0022]
As a result, when the upper intake camshaft sprocket 7 and the exhaust camshaft sprocket 8 are removed, the timing chain 10 is prevented from falling down by the tooth skipping prevention guide 14 and the winding around the crankshaft sprocket 7 is released. (Tooth jump) can be prevented. Also, when the engine is started at an extremely low speed, such as when the engine is started, the operating rod of the hydraulic actuator 13 is retracted because the hydraulic pressure is still low, and a state in which tension is not applied to the timing chain 10 occurs. Since the clearance c1 between the tooth skipping prevention guide 14 and the timing chain 10 is small, the tooth skipping can be prevented and no trouble occurs.
[0023]
In addition to the basic tooth jump prevention function of the tooth jump prevention guide, the tooth jump prevention guide 14 is configured to be rotatable integrally with the slack guide 12 as a configuration according to the present invention. When the timing chain 10 is wound around, the tooth jump prevention guide 14 is manually rotated together with the slack guide 12 in the counterclockwise direction as shown in FIG. What is necessary is just to increase the clearance c2, whereby the winding becomes possible and the restriction on the assembling procedure is eliminated.
[0024]
When the engine is started from the engine stopped state in FIG. 1, after the engine is started, the hydraulic pressure rises due to the rotation increase, the operating rod of the hydraulic actuator 13 is extended, and the slack guide 12 is rotated clockwise in the figure. The tension is applied to the timing chain 10. At the same time, the tooth jump prevention guide 14 also rotates integrally with the slack guide 12, and the clearance c2 between the tooth jump prevention guide 14 and the timing chain 10 increases as shown in FIG.
[0025]
As described above, the tension is applied to the timing chain 10 by the slack guide 12 during the operation of the engine, so that the tooth skip does not occur even if the clearance c2 is large.
[0026]
On the other hand, since the clearance c2 is large, interference with the tooth jump prevention guide 14 due to flapping of the timing chain 10 can be prevented, and generation of abnormal noise due to the interference can be prevented.
[0027]
Further, as described above, the accuracy of the clearance only needs to consider the minimum clearance c1 for preventing tooth skipping, and there is no need to consider interference between the tooth skipping prevention guide 14 and the timing chain 10. That is, when interference is considered, there is a restriction on the direction in which the clearance is narrowed. However, since it is not necessary to consider interference, the clearance can be sufficiently reduced within the range of manufacturing variation and assembly variation. Therefore, the problem of dimensional accuracy requirement is solved.
[0028]
Further, as an effect according to the present embodiment, conventionally, it was necessary to provide a dedicated tooth skipping prevention guide, but in the present embodiment, since the tooth skipping prevention guide 14 is provided integrally with the slack guide 12, the number of parts is reduced. it can. In particular, the present invention includes a device in which the tooth jump prevention guide according to the present invention is provided separately from the slack guide, but in that case, it is necessary to provide a mechanism for varying the clearance between when the engine is stopped and when the engine is running. Therefore, the number of parts increases as compared with the conventional case. In this regard, in the present embodiment, by providing the tooth jump prevention guide 14 integrally with the slack guide 12, the variable clearance mechanism (hydraulic actuator 13) can be shared, the number of parts can be reduced, and the cost can be reduced.
[0029]
Further, in particular, since the tooth jump prevention guide 14 is integrally formed with the inner member 12B formed of the resin material of the slack guide 12, the fluttering of the timing chain 10 greatly interferes with the tooth jump prevention guide 14 due to an operation failure of the engine. Even in this case, the interference sound level is lower than that of the tooth jump prevention guide formed of aluminum or the like.
[0030]
In the above-mentioned Patent Document 1, a chain jump prevention guide is provided on the chain cover. In this case, however, the tooth jump prevention guide side becomes invisible when the chain cover is assembled. Since the position is very close for that purpose, the tooth jump prevention guide may hit the timing chain and be damaged when the chain cover is assembled. In this regard, in the present embodiment, the tooth jump prevention guide can be seen when the timing chain is assembled, so that such a situation can be avoided.
[0031]
3 and 4 show a second embodiment.
In this case, the tooth skipping prevention guide 14 'is formed integrally by extending the inner member 12B of the slack guide 12 downward, but the tooth skipping prevention guide 14' is formed in a bag shape with an open upper end. The structure is provided with an oil sump in which the portion where the timing chain 10 and the crankshaft sprocket 7 are wound is immersed.
[0032]
That is, in the transmission mechanism using the timing chain, it is necessary to reduce the noise and wear of the meshing between the timing chain and the sprocket, and to reduce the wear caused by sliding between the slack guide and the chain guide and the timing chain. For this reason, conventionally, an oil jet is provided to spray oil onto the timing chain to perform forced lubrication.
[0033]
On the other hand, if the oil reservoir 13a is provided in the tooth skipping prevention guide 14 'as described above, the oil falling during the operation of the engine is accumulated in the oil reservoir 13a. Therefore, the winding portion of the timing chain 10 and the crankshaft sprocket 7 is constantly immersed in oil, so that the meshing noise and wear between the timing chain 10 and the intake camshaft sprocket 7, the exhaust camshaft sprocket 8 and the crankshaft sprocket 7 are reduced. In addition, it is possible to reduce wear caused by sliding between the slack guide 12 and the chain guide 10 and the timing chain 10. This eliminates the need for a conventional oil jet, thereby reducing costs.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing one embodiment of the present invention, showing a state when an engine is stopped.
FIG. 2 is a diagram showing a state during engine operation of the embodiment.
FIG. 3 is an overall configuration diagram showing a second embodiment of the present invention, showing a state during engine operation.
FIG. 4 is a sectional view taken along line AA of FIG. 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 7 ... Crankshaft sprocket 8 ... Intake camshaft sprocket 9 ... Exhaust camshaft sprocket 10 ... Timing chain 12 ... Slack guide 12A ... Outer member 12B ... Inner member 12C ... Support shaft 13 ... Hydraulic actuator 14 ... Tooth jump prevention Guide 14 ': Tooth jump prevention guide 14a: Oil pool

Claims (5)

A tooth jump prevention guide provided below a portion where the lower sprocket is wound around the upper sprocket and the lower sprocket of the internal combustion engine is provided with a clearance between the tooth jump prevention guide and the timing chain. Tooth jump prevention device for a timing chain, characterized in that it has a movable structure capable of switching clearance so as to prevent detachment from the lower sprocket of the timing chain when stopped, and to make it larger when the engine is running than when the engine is stopped. . The tooth jump prevention guide is integrally provided at a lower end of a slack guide driven by hydraulic pressure rising by engine operation, swinging around a support shaft, pressing a side surface of the timing chain to eliminate looseness, and when the engine is stopped. The swing in the direction opposite to that during operation due to a decrease in oil pressure reduces the clearance between the tooth jump prevention guide and the timing chain to a size that can prevent the timing chain from coming off the lower sprocket. Item 2. The tooth skipping prevention device for a timing chain according to Item 1. 2. The tooth skipping prevention device for a timing chain according to claim 1, wherein the tooth skipping prevention guide is integrally formed of the same material as a member that slides with the timing chain of the slack guide. 4. An oil reservoir structure in which the tooth jump prevention guide is formed in a bag shape having an open upper end so that a winding portion between the timing chain and the lower sprocket is immersed therein. 3. The tooth skipping prevention device of the timing chain described in (1). 5. The tooth skipping prevention device for a timing chain according to claim 1, wherein the upper sprocket is a camshaft sprocket, and the lower sprocket is a crankshaft sprocket. 6.

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