JPH10141030A - Variable valve system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To change a valve lift in accordance with a driving condition by providing a cam shaft with plural cams neighboring one another and arranging a connection switch means between mutually neighboring cam followers individually put in slide contact with the cams for connection or disconnection therebetween in a switchable manner. SOLUTION: Lock pistons 12a, 12b can be moved by turning on or off oil pressure on oil holes 10a, 10b with an oil pressure control valve, in a period when the base circle of a cam contacts a tappet. During turning-on, a high speed cam follower 7 and a low speed cam follower 6 are joined together to make a valve driven by a high speed cam 5. During turning-off, the low speed cam follower 6 and the high speed cam follower 7 are mutually independently moved to drive the valve to be open/closed by low speed cams 4a, 4b. In this way, independent cams with two types of profiles can be switched in accordance with the driving condition of an engine, or the increase and decrease of speed and load, and if required, to develop high torque at low-to-high speeds.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a camshaft, which is rotatably driven in synchronization with the rotation of an engine, integrated with a cam corresponding to an intake valve or an exhaust valve. The present invention relates to a valve train for an engine in which a cam directly drives an intake valve or an exhaust valve via a tappet.

[0002]

2. Description of the Related Art In a valve train of an engine, a valve diameter, a valve lift amount, a valve opening / closing timing, a total opening angle of a valve, and the like at high speed, medium speed, low speed, a load state, etc. Generally, the optimum value differs depending on the operating conditions of the machine.

[0003] In order to solve this problem, a valve actuating device of the type that opens and closes a valve via a rocker arm has been switched to a rocker arm as disclosed in, for example, Japanese Patent Publication No. 2-50282. There is known a mechanism in which a mechanism is built in and a plurality of cams are switched to operate.

However, in a valve train in which a cam directly opens and closes a valve via a tappet, such a switching mechanism does not exist, so that the phase of the camshaft is relatively shifted from the phase of the crankshaft. And so on. However, only by changing the phase of the fixed cam profile, the cam lift, the valve opening angle, and the valve closing angle cannot be changed independently, and the full opening angle of the valve is also fixed. There were no shortcomings.

[0005]

In the above-mentioned prior art, there is no technique for changing the valve lift in a direct acting valve train. Considering the friction loss of the internal combustion engine, the valve drive loss accounts for nearly 30% of the total loss, especially at low speeds, and generally decreases as the speed increases. The loss can be reduced by reducing the valve lift. Reduction of friction loss leads to improvement of engine efficiency. When considering internal combustion engines for automobiles, the frequency of use in the low speed range is particularly important because it is high, including in urban areas.

The present invention has been made in view of such circumstances, and even in a direct valve driving device, a valve lift, a valve opening angle, a valve closing angle, and a total valve opening angle are subdivided into operating regions. To control the valve operation to improve the overall output of the motor,
It is an object of the present invention to provide a valve train for an engine that can reduce fuel consumption and emission of harmful exhaust gas.

[0007]

According to the present invention, a plurality of cams are provided adjacent to each other on a camshaft, and at least one tappet having a rotation preventing function is individually slidably contacted with each cam. A cam follower is provided, and connection switching means for switching between connection and disconnection between the two cam followers is provided.

[0008]

[Operation] By operating the connection switching means in accordance with the operating state of the engine, a different cam profile suitable for the operating state of the engine can be selected. Valve operation control becomes possible.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. A first embodiment of the present invention is shown in FIGS. FIG. 1 is a front view showing an arrangement of a tappet including a plurality of cams and a plurality of cam followers. A valve 1 is disposed on a cylinder head 9 of the internal combustion engine. The valve 1 is provided with a low-speed cam 4a, 4b or a high-speed cam 4 of the same shape provided on a camshaft 3 driven in synchronization with the rotation of the engine. The cam 5 is driven to open and close via the low-speed cam followers 6a and 6b or the high-speed cam follower 7, respectively.

FIG. 2 is a sectional view taken along the line II-II of FIG. The high-speed cam follower 7 is incorporated in a groove formed at the center of the low-speed cam followers 6a and 6b formed as one body. The low-speed cam followers 6a and 6b have piston holes I15 into which the lock pistons 12a and 12b slide.
a, 15b are provided respectively, and the lock pistons 12a, 1
Clips 13a and 13b for regulating the position of 2b are provided respectively. In the cylinder head 9, switching control hydraulic passages 10a and 10b and locking pin grooves 11a and 11b are provided.
The low-speed cam followers 6a and 6b are provided with hydraulic transfer grooves 14a and 14b, respectively. The high-speed cam follower 7 is provided with piston holes II 16a and 16b having a projecting stopper 19 and a hydraulic release hole 20 at the center, and a piston spring 18 is installed with both ends supported by spring receivers 17a and 17b. Detent pins 8a, 8 sliding into retaining pin grooves 11a, 11b
b is fixed.

FIG. 3 is a sectional view taken along the line III-III of FIG. The high-speed cam follower 7 has a spring hole 21a,
A high-speed cam follower spring 22a, 22b is provided for pushing the high-speed cam follower 7 toward the high-speed cam 5 by pushing the low-speed cam follower 6 and the high-speed cam follower 7 apart. The lower center portion of the low-speed cam follower 6 is in contact with the top of the valve 1 via the shim cover 23 and the shim 24. Shim 24 is used to adjust tappet clearance.

FIG. 4 is a sectional view taken along the line IV-IV of FIG. FIG. 4 shows a state in which the base circles of the cams 4a, 4b, 5 are in contact with the tappet and the hydraulic pressure of the switching control hydraulic passages 10a, 10b, that is, the hydraulic pressure of the hydraulic transfer grooves 14a, 14b is off. The lock pistons 12a and 12b are connected to the piston spring 1 via spring receivers 17a and 17b.
8, the position restricted by the clips 13a, 13b, that is, the piston hole I1 of the low-speed cam follower 6.
5a, 15b, and are located at positions not protruding outside. Piston hole II16a, 1 of high-speed cam follower 7
The spring receivers 17a and 17b in the 6b are regulated by the lock pistons 12a and 12b, and are located opposite to each other, that is, in the piston holes II16a and 16b of the high-speed cam follower 7 so as not to protrude outside. In this state, the high-speed cam follower 7 can move up and down relative to the low-speed cam follower 6.

FIG. 5 shows the state of FIG.
Rotate and the top of the cam contacts the tappet.
The low-speed cam follower 6 is pushed down by the low-speed cams 4a and 4b, and the valve 1 is opened via the shim cover 23 and the shim 24. Since the high-speed cam 5 has a higher lift than the low-speed cams 4a and 4b, the high-speed cam follower 7 has a greater amount of depression than the low-speed cam follower 6, but the high-speed cam follower spring 18 only flexes the high-speed cam follower spring 18 by the difference. The cam follower 7 is in an idle state.

The high-speed cam follower spring 18 always presses the high-speed cam follower 7 so as to contact the high-speed cam 5, but its force is small as compared with the valve spring 2, so that the friction loss is small. Low speed cams 4a, 4
Since the valve drive loss due to b is low, the valve drive loss is reduced as compared with the case where the entire area is driven by a high-speed cam.

FIG. 6 shows a state in which the base circle of the cam 3 is in contact with the cam followers 6 and 7 (corresponding to FIG. 4), the hydraulic pressure is turned on to the switching control oil holes 10a and 10b, and the lock pistons 12a and 12b are turned on. Overcomes the drag of the piston spring 18 and places the spring receivers 17a, 17b in the stopper 1
9 until the piston holes I15a, 15b
And the camshaft 3 is rotated in a state where the high-speed cam follower 7 and the low-speed cam follower 6 are integrally coupled to each other, and the top of the cam is a tappet. Shows the state of contact with. The high-speed cam 5 pushes down and opens the valve 1 via a high-speed cam follower 7 and a low-speed cam follower 6 integrally connected thereto. Since the low-speed cams 4a and 4b have a lower lift than the high-speed cam 5, they do not contact the low-speed cam followers 6a and 6b and are in an idle state.

According to this embodiment, when the hydraulic pressure to the oil holes 10a and 10b is turned on and off by the hydraulic control valve (not shown), the base circle of the cam contacts the tappet (corresponding to FIG. 4). When the lock pistons 12a and 12b are turned on, the high-speed cam follower 7 and the low-speed cam follower 6 are integrally connected when the lock pistons are turned on, and the valve 1 is driven by the high-speed cam 5 as shown in FIG. State. When the hydraulic pressure is off, as shown in FIG. 5, the low-speed cam follower 6 and the high-speed cam follower 7 move independently of each other, the high-speed cam follower 7 enters an idle state, and the valve 1 operates at a low speed by the low-speed cams 4a and 4b. It is opened and closed via a cam follower 6.

As described above, according to the present embodiment, in a direct-acting valve drive device in which a cam directly opens and closes a valve via a tappet, an independent cam having two types of profiles is used to change the operating state of the engine, that is, the magnitude of speed. , The magnitude of the load, and the like, can be arbitrarily switched as required, so that a high torque from a low speed to a high speed can be obtained. Especially at low speeds and at low and medium loads, the profile of the low-speed cam is optimally set without sacrificing the output at high speeds to improve the inflow speed of air and air-fuel mixture into the combustion chamber. By promoting the turbulence, the combustion speed can be improved and more complete combustion can be performed, and the improvement of engine efficiency and reduction of harmful exhaust gas can be expected. In addition, the lift of the low-speed cam can be set lower than that of the normal cam, so that there is an effect that the valve driving loss at the time of driving the low-speed cam can be reduced.

FIGS. 7 to 9 show a second embodiment of the present invention. FIG. 7 is a sectional view corresponding to FIG. Referring to FIG. 7, a high-speed cam follower 37 is incorporated in a groove formed at the center of the integrally formed low-speed cam followers 36a and 36b. The high-speed cam follower 37 is provided with a piston hole I45,
The lock pistons 42a and 42b are in sliding contact. The cylinder head 39 is provided with a hydraulic passage 40 for switching control and grooves 41a, 41b for a detent pin, and the high-speed cam follower 37 is provided with hydraulic transfer grooves 44a, 44b, respectively. The groove 44b has an oil hole 55a and a piston hole I4.
5. The oil hole 55b communicates with the groove 44a, and both grooves are kept at the same hydraulic pressure, which helps to maintain the balance of the hydraulic pressure acting on the high-speed cam follower 37. The low-speed cam followers 36a and 36b are provided with piston holes IIa and 46b, respectively, into which the lock pistons 42a and 42b slide, and support the piston springs 48a and 48b, the spring receivers 47a and 47b, and the springs 48a and 48b, and at the same time, support the spring receivers 47a and 48b. Clips 43a, 43b for regulating the positions of the lock pistons 42a, 42b via the 47b and hydraulic release holes 50a, 50b are provided, respectively, and detent pins 38a, 38b slidingly engaged with the detent pin grooves 41a, 41b are fixed. Is established.

FIG. 8 is a sectional view taken along the line VIII-VIII of FIG. Spring hole 5 in high-speed cam follower 37
High-speed cam follower springs 52a and 52b are provided to push the high-speed cam follower 37 toward the high-speed cam 35 by pushing out the space between the low-speed cam follower 36 and the high-speed cam follower 37. You. The lower center portion of the low-speed cam follower 36 contacts the top of the valve 31 via the shim cover 53 and the shim 54. Shims 54 are used to adjust tappet clearance.

FIG. 9 is a sectional view taken along the line IX-IX of FIG. FIG. 7 shows that the high-speed cam follower 37 and the low-speed cam follower 36 move independently while the hydraulic pressure of the switching control hydraulic passage 40, that is, the hydraulic pressure of the hydraulic transfer grooves 44a and 44b is off, and the high-speed cam follower 37 enters an idle state. Shows a low speed operation state driven by the low speed cams 34a and 34b. FIG. 9 shows a state where the control oil pressure is turned on and the base circles of the cams 34a, 34b, 35 are in contact with the tappet, and the lock pistons 42a, 42b are connected to the piston springs 48 via the spring receivers 47a, 47b.
a, 48b, the piston holes II 46a, 46
b, the high-speed cam follower 37 and the low-speed cam follower 36 are integrally connected, and show a high-speed operation state driven by the high-speed cam 35 as a whole.

FIG. 10 shows a third embodiment of the present invention.
This figure is a sectional view corresponding to FIG. In this example, the top surface of the tappet is formed in a rectangular shape instead of a circular shape as a whole. The advantage in this example is that since the ratio of length and width can be changed, the degree of freedom of design is increased, and the area of the cam follower slidingly contacting the cam surface can be made effective. The shape is not limited to a rectangle, and may be an oval or the like.

FIGS. 11 and 12 show a fourth embodiment of the present invention. In this embodiment, in an engine having two intake valves or exhaust valves per I cylinder, one tappet drives two intake valves or exhaust valves.

FIG. 11 is a sectional view corresponding to FIG. Referring to FIG. 11, a high-speed cam follower 67 is provided at the center of a groove formed at the center of a low-speed cam follower 66a, 66b formed as a single body, and medium-speed cam followers 86a, 86b are provided adjacent to both sides thereof. Is incorporated. The low-speed cam followers 66a, 66b have piston holes II into which lock pistons III 72a, 72b slide.
I75a and 75b, respectively, and the lock piston II
Clips 73a, 7 for regulating the positions of I72a, 72b
3b are installed respectively.

The cylinder head 69 is provided with a first switching control hydraulic passage 70a, 70b and a second switching control hydraulic passage 70c, and the low speed cam followers 66a, 66b are provided.
Are provided with first hydraulic transfer grooves 74a and 74b, respectively. The middle-speed cam followers 86a and 86b have stoppers 79a and 79b projecting from the center and a hydraulic release hole 80 at the center.
piston holes IV76a, 76b, 76 having a, 80b
c, 76d, and piston springs 78a, 7
8b are spring receivers 77a, 77b, 77c at both ends.
Each is supported and supported by 77d.

The high-speed cam follower 67 has a piston hole V
75c are provided, the lock pistons V72c, 72d are slid, and second hydraulic transfer grooves 74c, 74d are provided, respectively. The groove 74d has an oil hole 85a and a piston hole V75c.
The oil hole 85b communicates with the groove 74c, and both grooves are kept at the same oil pressure, which helps to maintain the balance of the force by the oil pressure acting on the high-speed cam follower 67.

FIG. 12 is a sectional view taken along the line XII-XII of FIG. The low-speed cam followers 66a and 66b are integrally formed (66), and slidably contact the low-speed cams 64a and 64b, and have two bottom shim covers 83a and 83b.
And it contacts with the valves 61a and 61b via the shims 84a and 84b. The medium-speed cam followers 86a and 86b are medium-speed cam follower springs 8 provided between the medium-speed cam followers 86a and 86b and the low-speed cam followers 66, respectively.
8a, 88b, 88c, 88d, the medium speed cam 87a,
87b. High Speed Cam Follower 67
Are high-speed cam follower springs 8 installed between high-speed cam followers 67 and low-speed cam followers 66, respectively.
2 presses against the high-speed cam 65.

In this state, the first switching control hydraulic passage 70
a, 70b and the hydraulic pressure to the second switching control hydraulic passage 70c are all off, and the lock pistons III 72a, 72
b is the piston hole I of the low-speed cam followers 66a and 66b.
II 75a, 75b, lock piston V7
2c and 72d are piston holes V of the high-speed cam follower 67
75c, a low-speed cam follower 66, a medium-speed cam follower 86a, 86b, and a high-speed cam follower 67
Move independently of each other, and the valves 61a and 61b are simultaneously driven by the low speed cams 64a and 64b via the low speed cam follower 66, and the high speed cam follower 67 and the medium speed cam followers 86a and 86b are in the idle state. Cam drive suitable for the operating state can be realized.

When the hydraulic pressure to the first switching control hydraulic passages 70a and 70b is turned on and the hydraulic pressure to the second switching control hydraulic passage 70c is turned off, the lock pistons III72a and
72b is a piston spring 7 by hydraulic pressure applied to the back surface.
8a, 78b, medium speed cam follower 86a,
The low-speed cam followers 66a and 66b and the medium-speed cam followers 8 inserted into the piston holes IV76a and 76d of the 86b
6a and 86b are integrally connected by lock pistons III 72a and 72b. In this state, the valves 61a, 6
1b is driven by medium speed cams 87a and 87b, and the low speed cams 64a and 64b and the high speed cam follower 67 are in an idle state, so that cam driving suitable for a medium speed operation state can be realized.

When the hydraulic pressures to the first switching control hydraulic passages 70a and 70b and the second switching control hydraulic passage 70c are both on, the lock pistons V72c and 72
d is pushed by the hydraulic pressure and piston holes IV76b and 7
6c, the high-speed cam follower 67 and the medium-speed cam followers 86a, 86b
It is integrally connected by 72b. In this state, the valve 6
1a and 61b are driven by the high-speed cam 65, and the low-speed cams 64a and 64b and the medium-speed cams 87a and 87b are in an idle state, so that cam driving suitable for a high-speed operation state can be realized.

Although the illustrated embodiment has been described above,
The present invention is not limited to this. One valve can be driven by one tappet, two valves can be driven by one tappet at the same time, two-stage cam profile switching, three-stage cam profile switching, and the like can be freely implemented.

[0031]

As described above, according to the present invention, a plurality of cams are provided adjacent to each other on a camshaft in a direct-acting valve drive apparatus in which a cam directly pushes down a valve via a tappet. The tappet is divided into a plurality of cam followers which are individually slidably contacted with the respective cams, and are provided adjacent to each other. Between the mutually adjacent cam followers, connection switching means capable of switching connection and disconnection between the two is provided. Since this is provided, the valve speed control can be performed by subdividing the engine speed range into a plurality of ranges, and the engine output can be improved and the fuel consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a front view of a first embodiment of the present invention.

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

FIG. 3 is a sectional view taken along the line III-III of FIG. 1;

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is a cross-sectional view showing a state in which the camshaft has rotated from FIG. 4 and the cam top has been in contact with the tappet, and shows a state during low-speed operation.

FIG. 6 is a sectional view corresponding to FIG. 4, showing a high-speed operation state.

FIG. 7 is a sectional view corresponding to FIG. 2, showing a second embodiment of the present invention.

FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 7;

FIG. 9 is a sectional view taken along line IX-IX of FIG.

FIG. 10 is a sectional view corresponding to FIG. 7, showing a third embodiment of the present invention.

FIG. 11 is a sectional view corresponding to FIGS. 2 and 7 showing a fourth embodiment of the present invention.

FIG. 12 is a sectional view taken along the line XII-XII in FIG. 11;

[Explanation of symbols]

1 is a valve 2 is a valve spring 3 is a camshaft 4a, 4b is a low speed cam 5 is a high speed cam 6 is a low speed cam follower 6a, 6b is one side of a low speed cam follower 7 is a high speed cam follower 8a, 8b is a detent pin 9 Is a cylinder head 10a, 10b is a switching control oil hole 11a, 11b is a locking pin groove 12a, 12b is a lock piston 13a, 13b is a clip 14a, 14b is a hydraulic transfer groove 15a, 15b is a piston hole I 16a, 16b Piston holes II 17a and 17b are spring receivers 18 are piston springs 19 are stoppers 20 are hydraulic release holes 21a and 21b are spring holes 22a and 22b are high-speed cam follower springs 23 are shim covers 24 are shims 31 are valves 34a and 34b are for low speed One side of the cam 35 is a high speed cam 36 is a low speed cam The followers 36a, 36b are one side of a low-speed cam follower 37 is a high-speed cam follower 38a, 38b is a detent pin 39 is a cylinder head 40 is a hydraulic control oil hole 41a, 41b is a detent pin groove 42a, 42b is a lock piston 43a , 43b are clips 44a, 44b are hydraulic transfer grooves 45 are piston holes I 46a, 46b are piston holes II 47a, 47b are spring receivers 48a, 48b are piston springs 50a, 50b are hydraulic release holes 51a, 51b are spring holes 52a, 52b is a high speed cam follower spring 53 is a shim cover 54 is a shim 55a, 55b is an oil hole 61a, 61b is a valve 64a, 64b is a low speed cam 65 is a high speed cam 66 is a low speed cam follower 66a, 66b is one side of a low speed cam follower 67 Is high The speed cam follower 69 is a cylinder head 70a, 70b is a first hydraulic control oil hole 70c is a second hydraulic control oil hole 72a, 72b is a lock piston III 72c, 72d is a lock piston V 73a, 73b is a clip 74a, 74b is The first hydraulic transfer grooves 74c, 74d are second hydraulic transfer grooves 75a, 75b are piston holes III 75c are piston holes V 76a, 76b, 76c, 76d are piston holes IV 77a, 77b, 77c, 77d are spring receivers 78a, 78b. Are piston springs 79a and 79b are stoppers 80a and 80b are hydraulic release holes 82a and 82b are high speed cam follower springs 83a and 83b are shim covers 84a and 84b are shims 85a and 85b are oil holes 86a and 86b are medium speed cam followers 87a and 87b Is medium speed Cam 88a, 88b, 88c, 88d medium-speed cam follower spring

Claims (7)

[Claims] A camshaft is integrated with a camshaft that is driven to rotate in synchronization with rotation of an engine, the cam corresponding to an intake valve or an exhaust valve, and the intake valve or the exhaust valve is operated in accordance with the rotation of the cam. Is a direct-acting valve train of an engine driven directly by opening and closing via a tappet.
One or more cams are provided adjacent to each other, and the direct-acting tappet is divided into a portion that slides on each cam, that is, a cam follower, and is pivotally supported so as to be adjacent to each other. The present invention provides a variable valve operating device for an engine, comprising a connection switching means capable of switching between connection and disconnection between the two. 2. A tappet comprising a plurality of cam followers has at least one or more detent functions.
A low-speed cam is provided on the camshaft adjacent to the high-speed cam, and a high-speed cam follower that slides on the high-speed cam is installed at the center of the tappet. The cam follower is integrally formed, the low-speed cam follower slides on the low-speed cam and abuts on the intake valve or the exhaust valve, and the high-speed cam follower has a pressing means for urging and urging toward the high-speed cam. 2. The variable valve gear of an engine according to claim 1, wherein the pressing means is interposed between the high-speed cam follower and the low-speed cam follower. 3. An at least one hydraulic transfer portion is provided on an outer peripheral surface of the tappet, and at least one piston is slidably incorporated in at least one cam follower, and at least one piston is slidably incorporated in an adjacent cam follower. The piston is slidably slidably provided with a hole, and the connection and disconnection between the cam followers is controlled by a hydraulic switching valve. The hydraulic pressure is applied to or released from the piston via the hydraulic transfer unit. 2. The variable valve actuation device for an engine according to claim 1, wherein the variable valve actuation is performed. 4. An outer peripheral surface of the tappet or an inner surface of a hole with which the tappet slides is provided with at least one pair of grooves at symmetric positions, and the pair of grooves is configured to always have the same hydraulic pressure,
4. The variable valve operating device for an engine according to claim 3, wherein one or both of the pair of grooves functions as a hydraulic transfer portion. 5. A motor having a direct-acting valve train having a plurality of intake valves or exhaust valves per cylinder, wherein one tappet simultaneously contacts a plurality of intake valves or exhaust valves. The variable valve operating device for an engine according to claim 1, wherein 6. An engine having a direct-acting valve train having a plurality of intake valves or exhaust valves per cylinder, wherein one direct-acting tappet simultaneously contacts a plurality of intake valves or exhaust valves. A plurality of cams are integrated corresponding to the tappet, a middle speed cam is arranged adjacent to both sides of the high speed cam, and a low speed cam is arranged adjacent to the outside of both middle speed cams. . The tappet has a high-speed cam follower sliding on the high-speed cam at the center of the tappet, and a medium-speed cam follower sliding on the medium-speed cam on both sides of the high-speed cam follower,
A low-speed cam follower slidably provided on the low-speed cam adjacent to the outside of both medium-speed cam followers. Both low-speed cam followers are integrally formed and abut against a plurality of intake valves or exhaust valves. The medium-speed cam follower has a pressing means for being urged toward the medium-speed cam and the high-speed cam follower toward the high-speed cam. A first connection switching means is provided between both low-speed cam followers and both medium-speed cam followers, which can switch connection and disconnection between the two.
A second connection switching means is provided between the two medium-speed cam followers and the high-speed cam follower, which can switch connection and disconnection between the two. The variable valve gear of an engine according to claim 1, characterized by the above. 7. The actuation according to claim 6, wherein the pressing means is interposed between the high-speed cam follower and the low-speed cam follower, and between the medium-speed cam follower and the low-speed cam follower, respectively. Variable valve gear of the machine.