JPH0749101Y2 - Engine timing belt device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an engine timing belt device that transmits the rotation of a crankshaft to a camshaft to control the opening / closing timing of a valve.

[Conventional technology]

In this type of conventional engine timing belt device,
For example, as disclosed in Japanese Utility Model Laid-Open No. 60-121547, a timing belt between a crank sprocket and a cam sprocket is provided with a tensioner that pushes the timing belt from the outside and pulls it inward. Has been. This tensioner is composed of a rubber that abuts on the timing belt and a lever to which the rubber is attached. Then, the back surface of the lever of the tensioner is pressed by an adjuster mechanism having a pressing rod.

[Problems to be solved by the invention]

However, due to torque fluctuations caused by load fluctuations in the valve operating system, the timing belts described above alternately increase and decrease in tensile force on the return side of the timing belt that moves from the cam sprocket to the crank sprocket, that is, on the so-called tension side. Occurs. This is because in each stroke of rotating the engine, the valve that can be opened for intake and exhaust into the cylinder is
Since the cam opens the valve against the valve closing means that presses the valve, which is provided to keep the inside of the cylinder substantially sealed, a load fluctuation occurs in the valve operating system as the valve opens and closes. It is a thing.

For example, in a so-called DOHC engine in which the intake valve and the exhaust valve are driven by different camshafts, if the number of cylinders whose camshaft driven by the timing belt opens and closes the valve is n, The above tensile force increases or decreases at the timing of the n / 2th order with respect to the rotation speed of the crank sprocket. This is natural considering that, assuming a 4-cycle engine, an explosion occurs once every two revolutions of the crank, and the explosion strokes of each cylinder are performed at even intervals in order to smooth the revolution. That is, in the case of a DOHC engine with three in-line cylinders and six V-type cylinders (three cylinders per bank), as shown in FIG. 8, with respect to the engine speed, that is, with respect to the crank sprocket speed. It occurs periodically at the 3rd timing relative to the 1.5th order or the rotational speed of the cam sprocket. Due to this periodic fluctuation of tension, resonance occurs on the tension side of the timing belt at a specific rotation speed,
It causes inconveniences such as generation of abnormal noise, deformation of the tensioner lever and breakage of rubber, breakage or lock of the adjuster mechanism, elongation and breakage of the timing belt.

[Means for solving problems]

In order to solve the above problems, the engine timing belt device of the present invention is an engine timing belt in which a chain as a timing belt is stretched between a crank sprocket having engaging teeth on the outer periphery and a cam sprocket. In the device, the engagement teeth provided on the outer peripheral portion of the cam sprocket are divided into a plurality of engagement portions composed of one or more engagement teeth, and within each engagement portion, the engagement teeth are separated from the center of the cam sprocket. Of the plurality of different engaging portions formed on the same cam sprocket, the smallest diameter engaging portion having the smallest diameter valley portion has the same diameter up to the valley portion between the mating teeth. While the sprocket is provided with the same number of different valve driving timings of the cam during one rotation, the cam sprocket is depressed when the cam is pushing down the valve. As Tsu bets are driven at the minimum diameter engaging portion, it is characterized in that position where the minimum diameter engaging portion is configured with a camshaft.

[Action]

According to the above configuration, the load fluctuation of the valve operating system, that is, the cyclic increase that increases to open the valve against the pressing force of the cam closing means, and decreases to close the valve in a cyclic manner. When the valve opening operation is performed, the cam sprocket is always driven in the minimum diameter engagement portion against the fluctuation of the drive resistance of the cam shaft.

When switching from an engagement part other than the minimum diameter engagement part to driving to the minimum diameter engagement part, that is, from the radius of the valley part in the engagement part that was driven until immediately before, to a position closer to the center Is changed, the tension on the pulling side of the chain is reduced during driving by the minimum diameter engaging portion. On the contrary, when the valve is closed, the driving resistance is reduced by being assisted by the pressing force of the valve closing means, but at that time, from the smallest diameter engagement portion to the engagement portion having a larger diameter at the valley portion. Due to the switching, the tension on the pull side of the chain increases.

In other words, depending on the size of the root of the cam sprocket, when the tension of the chain is relatively high in the load fluctuation of the valve train, it acts to reduce the tension, and when the tension of the chain is relatively low, the tension is reduced. Since it acts in the increasing direction, fluctuations in the tensile force applied to the chain are reduced, and resonance that occurs in the chain can be prevented.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

As shown in FIG. 2, a DOHC engine has a crank sprocket 1 attached to the crankshaft at the bottom and cam sprocket 2/3 attached to each of the two camshafts at the top. It is provided. An endless chain 4 is stretched around each of the sprockets 1, 2, and 3. A chain guide 5 guides between the crank sprocket 1 and the cam sprocket 3 in the chain 4, that is, the pulling side 4a.
Further, the chain 4 between the crank sprocket 1 and the cam sprocket 2, that is, the slack side 4b is pulled inward by the tensioner 6 pressed by the adjuster 7.

As shown in FIG. 1, the cam sprockets 2 and 3 have engaging teeth 9 ... Engaging with the chain 4 on the outer peripheral portion. The outer peripheral portions of the cam sprockets 2 and 3 are equally divided into six engaging portions for each central angle of 60 °. The three engaging portions present at every other engaging portion are large-diameter engaging portions 12, ..., And the three engaging portions existing between these large-diameter engaging portions 12 ... Joint part 13 ... Large diameter engaging part 12 ...
As shown in FIG. 3, the valleys 10 between the engagement teeth 9 that engage with the rollers 5a of the chain are formed to be shallower than the valleys 11 of the small-diameter engagement portions 13. There is. Therefore, the radius of the large-diameter engaging portions 12 of the cam sprocket 2 to the valleys 10 is larger than the radius of the small-diameter engaging portions 13 to the valleys 11.

In the present embodiment, with respect to the cam angle, 10 ° ~ 70 °, 13
Large diameter engagement part 12 in the range of 0 ° -190 ° and 250 ° -310 ° ...
, 70 ° -130 °, 190 ° -250 ° and 310 °
The small-diameter engagement portion 13 is in the range of up to 10 °. Therefore,
The cam sprocket wheels 2 and 3 described above are such that when the pulling side 4a of the chain 4 undergoes a pulling fluctuation in which the pulling force becomes large, the chain 4 has a small-diameter engaging portion of the cam sprocket wheels 2 and 3.
It is designed to engage with 13 ...

In the above configuration, when the engine is started and the crankshaft rotates, this rotation is transmitted to the camshaft via the crank sprocket 1, the chain 4 and the cam sprockets 2 and 3, and each valve is driven.

At this time, as shown by the curve a in FIG.
Tension and slack are about to be applied to the tension side 4a at the timing of 1.5th order with respect to the engine speed. In contrast,
When pulling on the chain 4, the cam sprocket 2
Since the small-diameter engagement portions 13 ... of 3 are set to engage with the chain 4, the fluctuation of the pulling force indicated by the curve b in the figure with respect to the chain 4 from the cam sprocket 2/3 side. Join. Therefore, the fluctuation of the tensile force applied by the load fluctuation of the valve train and the fluctuation of the tensile force applied from the cam sprockets 2 and 3 cancel each other out, and as shown in FIG. Will be reduced.

Note that the timing belt device of the present engine is not limited to the above-mentioned configuration. For example, as shown in FIG. 6, an SOHC type engine provided with only one cam sprocket 2 or FIG. As shown, the configuration shown in FIG. 2 can also be applied to a V-type DOHC engine provided with a pair of V-types.

Further, the diameters of the large-diameter engagement portion 12 and the small-diameter engagement portion 13 of the cam sprockets 2 and 3 are not uniform diameters.
It is also possible to adopt a configuration in which the diameter gradually changes according to the load fluctuation of the valve train.

[Effect of device]

As described above, the engine timing belt device of the present invention is the engine timing belt device in which the chain as the timing belt is stretched between the crank sprocket and the cam sprocket having the engaging teeth on the outer periphery as described above. The engagement teeth provided on the outer peripheral portion of the cam sprocket are divided into a plurality of engagement portions composed of one or more engagement teeth. Within each engagement portion, the valley between the engagement teeth from the center of the cam sprocket is divided. Among the plurality of different engaging portions formed on the same cam sprocket, the minimum diameter engaging portion having the valley of the minimum diameter makes one rotation of the cam sprocket. While the same number of different valve drive timings of cams are provided,
When the cam pushes down the valve, the position where the minimum diameter engaging portion is provided with respect to the cam shaft is set so that the cam sprocket is driven in the minimum diameter engaging portion.

Therefore, it is possible to prevent the resonance caused in the chain due to the load fluctuation of the valve train. As a result, it is possible to reduce the damage to the peripheral members of the chain and the generation of noise caused by the resonance of the chain, and it is possible to improve the reliability of the engine.

[Brief description of drawings]

1 to 7 show an embodiment of the present invention. FIG. 1 is a front view of a cam sprocket, and FIG. 2 is a first view.
FIG. 3 is an explanatory view showing a chain stretched state in a DOHC type engine equipped with a cam sprocket, FIG. 3 is an explanatory view of main parts of the cam sprocket shown in FIG. 1, and FIG. A graph showing the relationship between the fluctuation in the tensile force applied to the chain by the curve (curve a) and the fluctuation in the tensile force applied from the cam sprocket to the chain (curve b),
Fig. 5 is a graph showing the damping state of the pulling force in the chain, Fig. 6 is an explanatory view showing an example in which this device is applied to a SOHC type engine, and Fig. 7 is a V type DOHC type engine. FIG. 8 is an explanatory view showing a provided example, and FIG. 8 is a graph showing a conventional example and showing a torque variation of a valve train with respect to a cam angle. 1 is a crank sprocket, 2 is a cam sprocket, 4 is a chain, 6 is a tensioner, 9 is an engaging tooth, 10
Reference numeral 11 is a valley portion, 12 is a large diameter engaging portion, and 13 is a small diameter engaging portion (minimum diameter engaging portion).

Claims (1)

[Scope of utility model registration request] 1. A timing belt device for an engine, wherein a chain as a timing belt is stretched between a crank sprocket having engaging teeth on the outer peripheral portion and a cam sprocket, and the engagement provided on the outer peripheral portion of the cam sprocket. The teeth are divided into a plurality of engaging portions made up of one or more engaging teeth, and within each engaging portion, the diameter from the center of the cam sprocket to the valley between the engaging teeth is the same as each other. Of the plurality of different engaging portions formed on the same cam sprocket, the smallest diameter engaging portion having the smallest diameter valley is the same as the different valve drive timing of the cam during one rotation of the cam sprocket. The number of camshafts is set to the minimum, but when the cam pushes down the valve, the cam sprocket is driven in the minimum diameter engagement part. On the other hand, the engine timing belt device is characterized in that the position at which the minimum diameter engaging portion is provided is set.