JP3168935B2 - Camshaft drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a camshaft drive for driving a camshaft of an internal combustion engine.

[0002]

2. Description of the Related Art In a four-cycle internal combustion engine (reciprocating engine), in particular, an engine having high engine performance, two camshafts for intake and exhaust are provided above a cylinder head, and intake and exhaust are respectively provided. A dedicated camshaft drives an intake valve and an exhaust valve.

[0003] In driving such a camshaft, a timing belt (an endless rubber belt having teeth formed on the inside) is used to transmit power from the crankshaft to the camshaft because of its advantage of excellent noise reduction. Many transmission structures are used.

More specifically, a driven sprocket is provided at two camshaft ends for intake and exhaust, a driving sprocket is provided at an end of a crankshaft, and a timing belt is wound between these sprockets to form a crankshaft. The rotation required to open and close the intake and exhaust valves from the shaft to each camshaft is transmitted.

[0005] Incidentally, the timing belt has a resistance on the positive side such that the intake / exhaust valve is pushed down via the cam of the camshaft against the valve spring or the intake / exhaust valve is pushed up by the return of the valve spring. In order to perform the work which fluctuates periodically to the negative side, the tension fluctuates periodically (positively and negatively) in the circumferential direction.

Therefore, the timing belt has a natural frequency due to valve timing, valve spring, valve train layout, timing belt layout, and the like, and there is an engine speed that causes resonance.

[0007]

On the other hand, in the internal combustion engine, in order to increase the volumetric efficiency, the lift amount of the intake valve or the opening time of the intake valve has been increased. In the valve train that increases the lift amount and the valve opening time, the load on the timing belt increases, and the load fluctuation difference of the timing belt, that is, the amplitude of the load that fluctuates periodically tends to increase.

However, when the amplitude of the load increases, the load applied to the timing belt tends to increase rapidly as approaching the resonance point of the internal combustion engine.
The belt load may exceed the allowable load of the timing belt.

Therefore, in Japanese Utility Model Laid-Open No. 1-95538, an oval sprocket is used as a crank sprocket, and a change in the tension and an opposite phase that occur due to a change in the relationship between the winding angle and the winding length of the timing belt. A structure has been proposed which is applied to a timing belt to reduce the belt load.

However, in this structure, the tension variation is applied not only to the tension side but also to the loose side at the same time.
As a result, the auto-tensioner (or the tensioner) has an adverse effect such as vibration due to a change in tension, and the effect of reducing the belt load is difficult to obtain unless the difference in the length of the oval sprocket is increased.

When the difference between the lengths of the oval sprockets is increased, the amount of movement of the belt in the radial direction of the sprocket is increased, and vibration of the belt in the radial direction of the sprocket is generated. If this vibration occurs, the belt will be disengaged if resonance occurs during high-speed rotation of the engine. In the worst case, it can cause the belt to "jump".

Accordingly, it is not preferable to use an oval sprocket for the crank sprocket. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a camshaft driving device capable of sufficiently reducing a fluctuation load of a timing belt.

[0013]

According to a first aspect of the present invention, there is provided a camshaft driving device, comprising: a timing belt extending between a driving sprocket of a crankshaft and a driven sprocket of a camshaft; Oval sprockets that apply a tension in the circumferential direction of the timing belt in the circumferential direction and a phase opposite to the circumferential direction of the timing belt are wound around the belt portion between the driven sprocket and the driving sprocket located on the tension side to vary the tension. The reason is that the offset effect is sufficiently exhibited.

That is, according to the camshaft driving device of the first aspect, the belt length of the belt portion between the driven sprocket and the driving sprocket is changed by the rotation of the oval sprocket in accordance with the tension fluctuation. Variable.

At this time, with the rotation of the oval sprocket, a load is applied to the belt portion between the driven sprocket and the driving sprocket, where the belt returns from the tensioned state (tensed state) to the retracted state (relaxed state). Since the behavior in which the fluctuation easily occurs is formed, a tension having a high reverse phase corresponding to the timing of the tension fluctuation of the timing belt can be obtained without increasing the difference between the major axis and the minor axis.

Therefore, the oval sprocket can obtain a tension in a reverse phase of a load sufficient to offset the tension fluctuation of the timing belt while suppressing the load on the timing belt.

In addition to the above object, the camshaft driving device according to the second aspect of the present invention provides a camshaft driving device which is provided between the driven sprocket and the driving sprocket located on the other loose side in order to realize more stable running of the timing belt. The belt portion is biased by an auto-tensioner that keeps the belt tension constant to adjust the change in belt length caused by the opposite-phase tension fluctuation.

A camshaft driving device according to a third aspect of the present invention drives the water pump in order to easily obtain the opposite-phase tension by utilizing the existing parts attached to the internal combustion engine in addition to the above objects. The sprocket to be used is an oval sprocket.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on a first embodiment shown in FIGS. FIG. 1 shows a camshaft driving device of, for example, a four-cycle internal combustion engine (reciprocating engine) to which the present invention is applied. In the drawing, reference numeral 1 denotes a crankshaft on which a piston 2 is mounted, and 3 denotes a crankshaft provided at an end of the crankshaft 1. Crankshaft sprocket (corresponding to the drive side sprocket).

Reference numerals 4a and 4b denote two camshafts for intake and exhaust, and reference numerals 5a and 5b denote camshafts 4a and 4b.
b is a cam sprocket (corresponding to a driven sprocket) provided at each end.

These crankshaft sprockets 3,
Between the camshafts 5a and 5b, a timing belt 6 (endless rubber belt having teeth formed on the inside) wound around, for example, a cocked belt or the like is wound, and the power from the crankshaft 1 is supplied. The intake and exhaust valves 7, 8 are opened and closed at a predetermined timing by transmitting the signals to the cams 4c of the respective camshafts 4a, 4b as indicated by arrows in the drawing (camshaft drive system).

The cam sprocket 5b on the belt pulling side
A water pump (W / P) sprocket 9 connected to a water pump (not shown) is wound around a belt portion 6a between the crankshaft sprocket 3 and the crankshaft sprocket 3, and the timing belt 6 also drives the water pump. is there. Reference numeral 10 denotes an idler pulley for winding the belt portion 6a around the water pump sprocket 9 in a predetermined manner.

The water pump sprocket 9 employs an oval (elliptical) sprocket A. In the drawings, the difference between the major axis and the minor axis is exaggerated, and the actual difference is several mm.

If the oval sprocket A generates a tension that periodically fluctuates between positive and negative with the driving of the camshafts 4a and 4b as shown in FIG. The belt portion 6a is attached at an angle such that the belt length of the belt portion 6a is reduced during a period in which the torque for driving the shafts 4a and 4b is positive (the side where the valve is pushed down and rotation of the cam is hindered).

Here, since a sprocket whose major axis and minor axis are symmetrical is used for the oval sprocket A, the tension fluctuation of the timing belt 6 as shown in FIG. A tension that fluctuates in a cycle of the opposite phase is generated.

A tensioner for keeping the belt tension constant, for example, an auto tensioner for pressing (biasing) the pulley 11a against the belt portion 6b with a spring force is provided on the belt portion 6b opposite to the oval sprocket A with the crankshaft sprocket 3 interposed therebetween. 11 are provided to allow for changes in belt length caused by opposite phase tension.

Next, the operation of the camshaft device configured as described above will be described. Now, it is assumed that the piston 2 reciprocates and power is output from the crankshaft 1.

Then, the timing belt 6 is driven by the crankshaft sprocket 2 and rotates as shown by the arrow in FIG. Thus, the camshafts 4a, 4b on the intake / exhaust side are rotated through the cam sprockets 5a, 5b, and the cams 4c open and close the intake / exhaust valves 7, 8 at a timing corresponding to a predetermined combustion process.

At this time, the intake / exhaust valves 7 and 8 are depressed against a valve spring (not shown) to open the valve or to close the valve when the valve spring returns. The decrease results in a fluctuation of the tension that periodically changes between the positive side and the negative side, and causes the timing belt 6 to vibrate in the circumferential direction as shown in FIG. This vibration is accompanied by resonance.

On the other hand, the timing belt 6 as shown in FIG.
A tension which fluctuates in the opposite phase to the tension fluctuation of the above occurs. When the intake / exhaust valves 7 and 8 are pushed down to delay the belt, the belt is wound around the long diameter portion of the oval sprocket A as shown in FIG. When the belt tries to advance rapidly due to the return of the spring, the behavior of delaying the belt from winding the belt around the short diameter portion of the oval sprocket A as shown in FIG.

Further, at this time, as can be seen from the difference between FIGS. 2A and 2B, the belt is returned from the tensioned state (tensed state) to the retracted state (relaxed state).
Since a behavior in which a load change is likely to occur is formed, a tension having a high antiphase is generated.

As a result, without increasing the difference between the major axis and the minor axis of the oval sprocket A, a large antiphase load capable of sufficiently exhibiting the canceling effect is secured. The tension fluctuation having a high antiphase is combined with the fluctuation of the tension of the timing belt 6 by the camshafts 4a and 4b to cancel the fluctuation of the tension as shown in FIG. The amplitude of is reduced.

Therefore, it is possible to reduce the load on the timing belt 6 while effectively reducing the belt load (the load due to the resonance of the tension fluctuation using the torque fluctuation as the vibrating force) while reducing the load on the timing belt 6.

Therefore, even if the internal combustion engine is provided with a structure for increasing the lift amount of the intake valve or increasing the opening time of the intake valve, the internal combustion engine is rotated up to the resonance point as shown in FIG. However, unlike the conventional tension fluctuation indicated by the broken line X, a peak behavior such as a sudden rise as indicated by the belt load indicated by the solid line Y does not appear, so that the belt load exceeds the allowable load of the timing belt 6. Can be suppressed.

In addition, since the belt portion 6b on the opposite side is urged by the auto tensioner 11, the change in the belt length caused by the tension fluctuation in the opposite phase is adjusted by the tension of the belt portion 6b, so that it is stable. Timing belt 6
Is promised.

In addition, since the oval sprocket A merely changes the existing water pump driving sprocket attached to the internal combustion engine, it is possible to obtain the tension fluctuation in the opposite phase with a simple structure.

Next, a second embodiment will be described with reference to FIG. FIG. 5 is a diagram for explaining a camshaft driving device of a V-type engine. 5c and 5 are both cam sprockets.

As in the first embodiment, the power from the crankshaft sprocket 3 is transmitted to each of the camshaft sprockets 5a, 5b, 5c and 5d as indicated by arrows in FIG. It is made to let.

The belt portion 6 between the sprocket 5d on the belt pulling side and the crankshaft sprocket 3
A water pump sprocket 9 is wound around a, and the water pump is driven by the timing belt 6. Reference numeral 10 denotes an idler pulley for winding the belt portion 6a around the water pump sprocket 9 in a predetermined manner.

The water pump sprocket 9 also employs an Ovals (elliptical) sprocket A, has the operation as described with reference to FIGS. 2 (a), 2 (b) and 3 and is a belt added to the timing belt 6. The load can be effectively reduced.

[0041]

As described above, according to the first aspect of the present invention, a large load having an opposite phase that can sufficiently exhibit a canceling effect without increasing the difference between the major axis and the minor axis of the oval sprocket. Can be secured.

Therefore, it is possible to effectively reduce the belt load applied to the timing belt while reducing the load on the timing belt. For example, it is possible to increase the lift amount of the intake valve in the internal combustion engine or to open the intake valve. Even if the internal combustion engine is rotated up to the resonance point by providing a structure for increasing the time, the belt load can be suppressed from exceeding the allowable load of the timing belt, so that the timing belt can be provided with high reliability.

According to the invention described in claim 2, according to claim 1
In addition to the effects of the invention described in (1), the change in the belt length caused by the tension fluctuation in the opposite phase can be adjusted, so that the timing belt can run stably.

According to the third aspect of the present invention, in addition to the effects of the first and second aspects of the present invention, an existing component of the internal combustion engine can be used to easily achieve a high antiphase. Tension fluctuations can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a camshaft driving device according to a first embodiment of the present invention.

FIG. 2 is a view for explaining the movement of an oval sprocket for canceling a tension fluctuation generated in a timing belt.

FIG. 3 is a view for explaining that a tension fluctuation generated in the timing belt is reduced by an opposite-phase tension fluctuation caused by an oval sprocket.

FIG. 4 is a diagram for explaining that a belt load is reduced.

FIG. 5 is a view for explaining a camshaft driving device according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Crankshaft 3 ... Crankshaft sprocket (drive side sprocket) 4a, 4b ... Camshaft 5a, 5b, 5c, 5d ... Cam sprocket (driven side sprocket) 6 ... Timing belt 10 ... Idler pulley 11 ... Auto tensioner A ... Oval sprocket.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02B 67/06 F16H 7/08 F16H 7/02

Claims (3)

(57) [Claims] A timing belt is wound between a driving sprocket provided on a crankshaft of an internal combustion engine and a driven sprocket provided on a camshaft of the internal combustion engine, and power is transmitted from the driving sprocket to the driven sprocket. A transmitting camshaft drive system, and a periodic tension fluctuation in the circumferential direction of the timing belt provided around the belt portion between one driven sprocket located on the tension side of the timing belt and the driving sprocket. And an oval sprocket for applying an opposite phase tension to the camshaft driving device. 2. The apparatus according to claim 1, wherein a belt portion between the other driven side sprocket and the driving side sprocket is urged by an auto-tensioner that keeps the tension of the timing belt constant. Camshaft drive. 3. The camshaft driving device according to claim 1, wherein the oval sprocket is a sprocket for driving a water pump.