JPH0650408A - Variable valve timing mechanism - Google Patents

Abstract

PURPOSE:To obtain a variable valve timing mechanism which can vary a valve lifting characteristic in a simple structure according to operation conditions, and prevents generation of clattering noises which may be caused by a cam shaft fluctuation torque. CONSTITUTION:An intake cam shaft 1 is driven by means of a driving shaft 3 which performs constant velocity rotation through either true circle gears 5a, 5b or non-circle gears 7a, 7b. When the cam shaft 1 is driven through the non-circle gears 7a, 7b, the cam shaft 1 performs variable velocity rotation. A valve lifting characteristic is different from that of the case where the shaft is driven through the true circle gears 5a, 5b. The true circle gears 5a, 5b and the non-circle gears 7a, 7b are changed over by moving a piston 11 and a sleeve 19 through hydraulic pressure according to operation conditions, and a required valve lifting characteristic is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camshaft drive mechanism for an internal combustion engine, and more particularly to a variable valve timing mechanism capable of changing valve lift characteristics according to operating conditions.

[0002]

2. Description of the Related Art A variable valve timing mechanism has been conventionally devised so that an optimum valve lift characteristic such as a valve lift period (valve opening period) can be obtained according to an operating condition of an internal combustion engine. In general, the valve lift characteristic is determined by the cam profile of the cam shaft, so in order to change the valve lift period, a cam with a different profile is formed in advance on the cam shaft, and these can be switched for use. A method is used in which the rocker arm is switched so that the valve lift has a different working angle to drive the valve. However, these methods are difficult to apply to a so-called direct OHC type valve operating mechanism in which a cam directly pushes a valve without using a rocker arm.

On the other hand, a variable valve timing mechanism adapted to vary the valve lift period by rotating the camshaft at a non-constant speed is also applicable to these direct OHC type camshafts. For example, as an example of this type of variable valve timing mechanism, Japanese Patent Laid-Open No. 3-20
There is one disclosed in Japanese Patent No. 6311. In the device of the publication, a planetary gear mechanism that makes a swinging motion is provided in a rotation transmission path to a cam shaft, and the swinging motion of the planetary gear is added to the uniform speed rotation of the engine output shaft and transmitted to the cam shaft. By doing so, it is possible to obtain the non-uniform rotational movement of the cam shaft. The camshaft is caused to rotate unequally, for example, the camshaft rotation speed is increased while the valve is closed, and the camshaft rotation speed is decreased while the valve is open, resulting in an increase in the valve opening period. The same effect as changing the cam profile can be obtained.

[0004]

However, in the device disclosed in Japanese Patent Laid-Open No. 3-206311, it is necessary to install a planetary gear mechanism that causes a swing motion in the camshaft drive path.
There is a problem that the structure becomes complicated. Further, torque variation occurs due to the valve drive reaction force on the cam shaft, and if there is a gear meshing portion, tooth variation collision noise (catching sound) is generated due to torque variation. Is transmitted through a large number of planetary gear meshing portions, so that there are many places where the rattling noise is generated and it is difficult to take countermeasures.

In view of the above problems, it is an object of the present invention to provide a variable valve timing device which can change the valve lift characteristic with a simple structure and which can easily cope with the collision noise of tooth surface.

[0006]

According to the present invention, there is provided a mechanism for transmitting engine output shaft rotation to a cylinder valve driving cam shaft, the first shaft being capable of transmitting the output shaft rotation to the cam shaft. A gear device and a second gear device; and a switching means for selectively switching the first gear device and the second gear device according to engine operating conditions to drive the cam shaft,
At least the first gear device is provided with a pair of non-circular gears meshing with each other for converting the uniform speed rotation of the engine output shaft into a non-uniform speed rotation in which the speed changes in accordance with the engine output shaft rotation angle. The variable valve timing mechanism is provided in which the meshing portion of each of the first and second gear devices is configured as a scissors gear.

[0007]

The operation of the present invention will be described with reference to FIGS. 4 to 7. FIGS. 4A and 4B show the shape of a non-circular gear used in the first gear device that transmits rotation to the camshaft.
FIG. 4A shows a two-leaf (elliptical) gear, and FIG. 4B shows a four-leaf gear having a shape in which two ellipses are combined. Also, FIG. 4 (C)
FIG. 3 is a diagram showing the definition of ellipticity e used in this specification. As shown in FIG. 4C, the ellipticity e is 1 + e = R ₁ / R, using the major radius R ₁ and the minor radius R ₂ of the ellipse of the gear.
It is represented as 1-e = R ₂ / R (R = (R ₁ + R ₂ ) / 2).

FIGS. 5A and 5B respectively show FIGS. 4A and 4B.
The velocity diagram when rotation is transmitted using the non-circular gear of FIG. As shown in FIG. 5, when the input shaft is rotated at a constant speed, the output shaft of the two-leaf gear of FIG. 4A is twice per rotation (every 180 degrees), and of the four-leaf gear of FIG. 4B. When the input shaft rotational speed is set to 1 (1-e / 1 + e) when the input shaft rotational speed is 1 when the variable speed rotational motion is performed in which the rotational speed changes periodically in 4 cycles per rotation (every 90 degrees) ~ (1 + e / 1
-E).

Therefore, by forming a cam on the output shaft side of the gear device and driving the valve in each non-uniform speed rotation section, different valve lift periods and characteristics can be obtained using the same cam profile. . In this case, the two-leaf gear can be used for a two-cylinder engine and the four-leaf gear can be used for a four-cylinder engine. However, in the case of other number of cylinders, the present invention is applied if a non-circular gear having the same number of leaves as the number of cylinders is used. it can.

Next, the operation of changing the valve lift characteristic by the non-circular gear will be described with reference to FIG. In FIG. 6, the horizontal axis represents the input shaft rotation angle θ of the non-circular gear device, and the vertical axis represents the output shaft (cam shaft) rotation angle φ. Now, assuming that a non-circular gear is not used and a perfect circular gear having the same number of teeth is used to transmit the rotation, the input shaft rotation angle θ and the output shaft rotation angle φ have a relationship of θ = φ, and in FIG. It is represented by a straight line passing through the origin and having an inclination of 45 degrees (line I in FIG. 6).

However, when non-circular gears are used,
The output shaft rotation angle φ is obtained by adding the fluctuation component shown in FIG. 5 to the input shaft rotation angle θ, and as shown by the curve II in FIG. It will rotate (Fig. 6, II shows the speed change in the case of 4-leaf gear). Figure 6
Shown by III and IV are the lift curves of the cams provided on the output shaft side. Actually, the number of cams equal to the number of gear leaves (number of cylinders) is provided on the output shaft, but in this figure, only one is shown for simplicity, and the case where the cam formation position is changed is illustrated. Further, the valve lift period is 90 degrees in terms of the output shaft rotation angle φ.

Now, assuming that the output shaft is driven by using a true circle gear and constant speed transmission is performed, there is a relation of θ = φ (straight line I). Therefore, the lift curve of the cam is converted into the input shaft rotation angle θ. The case is the same as III. On the other hand, when the non-circular gears are used to perform the non-uniform speed transmission as shown by the curve II, the lift curve of the cam changes depending on the position where the cam is formed (angle position of φ).

That is, when the cam is formed in the range of φ shown by III in FIG. 6, since the motion is unequal speed, the lift curve of the cam converted to the input shaft rotation angle θ has a shape like III '. At the beginning and end, the speed is slow and near the maximum lift, the speed is so-called "lean lift curve". When a cam is formed in the range of φ shown by IV in FIG. 6, when converted to θ, the speed is fast at the start and end of the lift and slow near the maximum lift. Therefore, it is possible to improve the performance when rotating at high speed.

In the case of FIG. 6, the valve lift period is set to 9
Since the shape of the lift curve is changed to 0 degrees (in the case of 4 leaves), the lift period converted to θ remains 90 degrees and does not change. However, when the lift period is other than 90 degrees, the lift period for θ can be changed together with the shape of the lift curve.

FIG. 7 shows a case where the cam lift period is set to 135 degrees (in the value of φ) as a value close to the actual valve lift period of a 4-cylinder engine. At the position shown in FIG.
When converted to, the lift starts late and ends early, so the lift period becomes shorter than 135 degrees, and I'in FIG.
As shown in, the minimum angle is about 112 degrees. Conversely, if a cam is formed at the position shown in FIGS. 7 and II, the lift period becomes longer, and as shown by II 'in FIG.
It will be about degree.

In the present invention, by utilizing the above, the cam shaft is driven by selectively using the non-circular gear and another gear (for example, a perfect circular gear or another non-circular gear having a different phase, shape, etc.). As a result, lift characteristics and periods of cylinder valves such as intake valves and exhaust valves can be switched according to operating conditions. In addition, in the present invention, since one set of non-circular gears installed in the camshaft driving force transmission path is sufficient in principle and only one meshing portion is provided, scissors gears can be easily configured, resulting in a rattling noise of the tooth surface. Will be reduced.

[0017]

1 to 3 show a first embodiment of the present invention. FIG. 1 shows a sectional view of the variable valve timing mechanism of the present invention. In FIG. 1, reference numeral 1 is a cam shaft for driving an intake valve, 3 is a drive shaft, which is driven from a crank shaft (not shown) via a belt, a gear, etc., and the cam shaft 1 is driven via gears 5a, 5b, 7a, 7b. It is rotating. In the double overhead camshaft engine, instead of providing the independent drive shaft 3, the exhaust valve drive camshaft is driven by the crankshaft,
Using the exhaust valve drive cam shaft as the drive shaft 3, the gear 5a,
The intake camshaft 1 may be driven via 5b, 7a, 7b.

In the present embodiment, the gears 5a and 5b are configured as true circle gears that mesh with each other, and the gears 7a and 7b are four lobes that mesh with each other as shown in FIG. 2, assuming an in-line four-cylinder engine. It is configured as a gear. Also, the gear 5
a and 7a are integrally joined, and further fixed to the cam shaft 1 via a pin 9 so as not to rotate. Also,
The gears 5b and 7b are formed as separate bodies, and are individually fitted to the drive shaft 3 in a freely rotatable manner.

The drive shaft 3 has a hollow structure and is provided with a piston 11 slidable inside the hollow portion. Further, the hollow portions on both sides of the piston 11 have hydraulic passages 13a, 1
The hydraulic pressure supply source and the drain are selectively connected via 3b and a hydraulic pressure switching valve (not shown). For example, when hydraulic pressure is supplied to the passage 13a side, the piston 11 moves to the right in the drawing, and when hydraulic pressure is supplied to the passage 13b side, the piston 11 moves to the left in the drawing. Further, the piston 11 is a pin 1 that penetrates an elongated hole 15 provided on the wall surface of the drive shaft 3.
A sleeve 19 fitted around the outer periphery of the drive shaft 3 is connected by 7 so that the sleeve 19 moves in the axial direction together with the piston 11.

FIG. 3 shows a cross section taken along line III-III in FIG. As shown in FIG. 3, the sleeve 19 is configured as a deformed spline having protrusions 21a, 21b, 21c extending in the axial direction on the outer peripheral portion, and the protrusions 21a, 21b of the sleeve 19 are formed on the bosses of the gears 5b and 7b. Grooves 23a to 23c and 25a to 25c (only 23a and 25a are shown in FIG. 1) that engage with 21b and 21c are formed, respectively.

At the position where the hydraulic pressure is supplied to the hydraulic passage 13b and the piston 11 moves leftward in the drawing, the protrusions 21a to 21c of the sleeve 19 engage only with the grooves 23a to 23c of the gear 5b and the grooves 25a to 25c of the gear 7b. Does not engage. Therefore, the driving force applied to the cam shaft 1 is transmitted from the side wall of the elongated hole 15 of the drive shaft 3 to the sleeve 19 via the pin 17 and the sleeve 1
9 protrusions 21a to 21c on the outer periphery and the groove 2 of the boss portion of the gear 5b
3a to 23c and transmitted to the gear 5b, and the gear 5b
Is transmitted to the camshaft through the gear 5a and the pin 9.

Therefore, when the piston 11 is moved to the left side, the cam shaft 1 makes a uniform rotational movement at the same speed as the drive shaft 3, and the gear 7b is idling with respect to the drive shaft 3.
On the other hand, the hydraulic pressure is supplied to the hydraulic passage 13a, and the piston 11
Is moved to the right in the figure, the camshaft 1 is driven from the drive shaft 3 via the gears 7b and 7a, and the gear 5b is reversed.
Becomes idle with respect to the drive shaft 3. As described above, in the present embodiment, the gears 7a and 7b are configured as four-leaf non-circular gears, and therefore the cam shaft makes a non-uniform rotational motion at this time.

As is apparent from the above description, according to the present embodiment, for example, in the low-medium speed operation, the camshaft 1 is driven via the true circle gears 5a and 5b, and the normal valve lift characteristic (see FIG. 7, I) is obtained.
I) is obtained, the hydraulic pressure is switched during high-speed rotation to rotate the camshaft 1 through the gears 7a and 7b at a non-constant speed, and the valve lift period is increased as shown in FIG. Can be obtained.

Next, the scissors gear structure adopted in this embodiment will be described with reference to FIGS. A reaction force of valve opening / closing drive is applied to the cam shaft 1, and this reaction force acts on the cam shaft 1 as reaction force torque that fluctuates between positive and negative values. For this reason, when there is backlash in the gear meshing portions of the gears 5a, 5b, 7a, 7b, etc., the varying reaction torque causes the tooth surface to touch within the backlash, producing a collision sound (a rattling noise).

In this embodiment, the gears 5a and 7a are constituted as scissors gears to prevent the rattling noise. The gear 7a will be described below, but the gear 5a
Has a similar structure. Gear 7a as shown in FIG.
Is actually configured such that two gears 71a and 72a are axially overlapped. Gear 71a (main gear) and 7
The gear 2a (sub gear) and the gear 7a, which are integral with each other, have the same sectional shape as a shape obtained by cutting and dividing the gear 7a along the axis.
The main gear 71a and the sub gear 72a are axially overlapped with each other with a ring-shaped leaf spring 73 interposed therebetween, and one end of the leaf spring 73 is a pin 74 fixed to the main gear 71a.
The other end is engaged with a pin 75 fixed to the sub gear 72a to press the main gear 71a and the sub gear 72a in a direction in which the tooth traces of the main gear 71a and the sub gear 72a are displaced. Therefore, when the gear 7a is in mesh with the gear 7b, the tooth surface of the gear 7b is set to the main gear 71a and the sub gear 72a.
The tooth surface of “a” is sandwiched and pressed from both sides, and the backlash of the meshing portion can be maintained at zero. Therefore, if the biasing force of the leaf spring 73 is set appropriately, the camshaft 1
Even if a fluctuating torque is applied to the tooth surface, the tooth flank is not shaken and the rattling noise is prevented.

As described above, according to this embodiment, the cam shaft is
The valve lift characteristic and the lift period of the intake valve can be changed with a simple structure by switching between the non-uniform speed rotational motion by the non-circular gear and the uniform speed rotary motion by the perfect circle gear. Further, since the gear can be easily made into a scissors gear, it is possible to effectively prevent rattling noise of the tooth surface due to camshaft torque fluctuation.

Next, FIG. 8 shows a second embodiment of the present invention.
In the figure, the same reference numerals as those shown in FIGS. 1 to 3 denote the same elements, and thus the details thereof will be omitted. In the present embodiment, the case where two-leaf gears are used for a four-cylinder engine is shown. Since the two-leaf gears 7a and 7b are used, the drive shaft 3
Is, for example, from the exhaust valve drive cam shaft 2 to the speed increasing gears 81a, 81
It is driven via b and rotates at twice the speed of the exhaust cam shaft 2. Further, the driven shaft 4 reduces the speed to 1/2 through the reduction gears 82a and 82b to drive the intake cam shaft 1.
By rotating only the non-circular gear portion at a speed twice that of the camshaft in this way, as in the case of using the four-lobed gear (Fig. 1), the speed fluctuation of four cycles per one rotation of the camshaft is reduced. Obtainable.

As the number of leaves of the non-circular gear increases, the setting of the pitch circle of the gear is restricted, the ellipticity e cannot be set to a large value, and the speed fluctuation width of the non-uniform rotational motion tends to become small. . Also, if the number of leaves is large, it becomes difficult to make a non-circular gear. In the present embodiment, in consideration of the above, the rotational speed is increased only in the non-circular gear portion so that the same effect as the multi-leaf gear can be obtained with a gear having a small number of leaves. In this embodiment, the two-leaf gear is used for the four-cylinder engine, but it is also possible to use the three-leaf gear for the in-line six-cylinder engine with the same configuration.

Further, in this embodiment, for example, the exhaust cam shaft 4
Drive the drive shaft 3 via the speed increasing gears 81a and 81b to increase the speed to twice the speed of the cam shaft. The drive shaft 3 is directly driven from the engine crankshaft via a belt, chain or the like. It may be done. In the above-mentioned embodiments, the non-circular gears 7a and 7b and the perfect circle gears 5a and 5b are used by switching, but both the gears 7a and 7b and 5a and 5b are non-circular gears. It goes without saying that it is possible to use In this case, there is an advantage that the lift period and the switching range of the characteristics can be further increased.

[0030]

According to the variable valve timing mechanism of the present invention, the valve lift period and lift characteristics can be changed according to operating conditions with a simple structure, and noise such as rattling noise of tooth flanks can be prevented. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a diagram showing an example of the shape of a non-circular gear used in the present invention.

FIG. 5 is a diagram for explaining a non-uniform speed rotational motion by a non-circular gear.

FIG. 6 is a diagram showing an example of a change in valve lift characteristics due to a non-circular gear.

FIG. 7 is a diagram showing a change in valve lift period due to a non-circular gear.

FIG. 8 is a diagram showing a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intake cam shaft 2 ... Exhaust cam shaft 3 ... Drive shaft 4 ... Driven shaft 5a, 5b ... True circular gear 7a, 7b ... Non-circular gear 9 ... Pin 11 ... Piston 13a, 13b ... Hydraulic passage 15 ... Oblong hole 17 ... Pin 19 ... Sleeve 21a, 21b, 21c ... Protrusion 23a, 23b, 23c ... Groove 25a, 25b, 25c ... Groove 71a ... Main gear 72c ... Sub gear 73 ... Leaf spring 74 ... Pin 75 ... Pin 81a, 81b ... Speed increasing gear 82a, 82b ... Reduction gear

Claims (1)

[Claims] 1. A mechanism for transmitting engine output shaft rotation to a cylinder valve driving cam shaft, the first gear device and the second gear device capable of respectively transmitting the output shaft rotation to the cam shaft, Switching means for driving the cam shaft by selectively switching between the first gear device and the second gear device according to engine operating conditions, and at least the first gear device is the engine output. The shaft includes a pair of non-circular gears meshing with each other, which converts a constant speed rotation of the shaft into a non-uniform speed rotation whose speed varies according to the rotation angle of the output shaft of the engine. A variable valve timing mechanism in which the meshing portion is configured as a scissors gear.