WO2015162820A1

WO2015162820A1 - Valve gear for engine

Info

Publication number: WO2015162820A1
Application number: PCT/JP2014/082447
Authority: WO
Inventors: 正義奥見
Original assignee: 株式会社マキタ
Priority date: 2014-04-24
Filing date: 2014-12-08
Publication date: 2015-10-29
Also published as: JP6220309B2; JP2015209768A

Abstract

Provided is a valve gear with which it is possible to vary the valve opening characteristics of an engine valve in accordance with the operating state of an engine. A valve gear for an engine includes a cam gear (32) having a gear part (321) and a cam part (322), the valve gear opening and closing an engine valve via a cam follower member (33) that abuts against the outer peripheral surface of the cam part (322). The cam gear (32) is rotatably supported on a first support shaft (11) and is capable of moving over the first support shaft (11). The outer peripheral surface of the cam part (322) has a tapered surface part inclined from one end side toward the other end side in the axial direction of the first support shaft (11) (the rotational axis direction of the cam gear (32)). The valve gear moves the cam gear (32) over the first support shaft (11), thereby varying the abutting position of the outer peripheral surface of the cam part (322) and the cam follower member (33) in the axial direction of the first support shaft (11), and varying the valve opening characteristics of the engine valve.

Description

Engine valve gear

The present invention relates to an engine valve operating device, and more particularly to an engine valve operating device that changes the valve opening characteristics of an engine valve in accordance with the operating state of the engine.

Patent Document 1 describes an example of an engine used for a prime mover (drive source) such as a work machine. In the engine described in Patent Document 1, the cam gear rotates with the rotation of the crankshaft, and the cam provided on the cam gear moves the push rod up and down via a member that abuts the outer peripheral surface thereof. The engine valve (intake valve, exhaust valve) is opened and closed.

Japanese Patent Laid-Open No. 10-299626

However, in the engine described in Patent Document 1, the valve opening characteristics (lift amount and opening / closing period) of the engine valve during operation of the engine are constant. For example, the engine valve is changed to a more preferable valve opening characteristic according to the operating state of the engine. Can not do it.

Therefore, an object of the present invention is to provide an engine valve operating device capable of changing the valve opening characteristics of an engine valve in accordance with the operating state of the engine.

According to an aspect of the present invention, an engine that includes a cam member and includes a cam member that rotates in conjunction with a crankshaft, and opens and closes an engine valve via a cam follower member that contacts the outer peripheral surface of the cam member. A valve operating apparatus is provided. In the valve operating apparatus of the engine, the cam member is movable in a rotation axis direction, and the outer peripheral surface of the cam portion of the cam member is directed from one end side to the other end side in the rotation axis direction. An inclined tapered surface portion is formed. In the engine valve operating apparatus, when the cam member moves in the rotation axis direction, a contact position between the outer peripheral surface of the cam portion and the cam follower member in the rotation axis direction changes. The engine valve is configured to change the valve opening characteristic.

According to the valve operating apparatus of the engine, the valve opening characteristic of the engine valve can be changed by moving the cam member in the direction of the rotation axis. For this reason, by providing the said taper surface part suitable for the said outer peripheral surface of the said cam part of the said cam member, and setting it as the structure which moves the said cam member suitably according to the driving | running state of the said engine, A preferable valve opening characteristic of the engine valve according to the operating state can be obtained.

1 is a schematic cross-sectional view of an engine to which a valve gear according to an embodiment of the present invention is applied. FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG. It is a principal part enlarged view of the said valve operating apparatus. FIG. 4 is a sectional view taken along line BB in FIG. 3. It is an enlarged view which shows the structure of the cam gear of the said valve operating apparatus. It is a figure which shows the state of the valve operating apparatus at the time of engine low rotation (including the time of engine stop). It is a figure which shows the lift curve of the engine valve (intake valve, exhaust valve) at the time of engine low rotation. It is a figure which shows the state of the valve operating apparatus at the time of engine high rotation. It is a figure which shows the lift curve of the engine valve (intake valve, exhaust valve) at the time of engine high rotation.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic cross-sectional view of an engine 1 to which a valve gear according to an embodiment of the present invention is applied, and FIG. 2 is a schematic cross-sectional view taken along line AA of FIG. The engine 1 is mainly used as a drive source (prime mover) of a portable work machine such as a brush cutter. The engine 1 is provided with a valve operating device 30 for opening and closing an engine valve, that is, an intake valve 2 and an exhaust valve 3 of the engine 1.

The valve gear 30 includes a drive gear 31, a cam gear 32, a cam follower member (first cam follower member 33, second cam follower member 34), push rods (first push rod 35, second push rod 36), and a rocker arm. (First rocker arm 37, second rocker arm 38).

The drive gear 31 is attached to the crankshaft 4 of the engine 1 and rotates together with the crankshaft 4. The cam gear 32 integrally includes a gear portion 321 in which gear teeth meshing with the drive gear 31 are formed on the periphery (outer peripheral surface) and a cam portion 322 having the outer peripheral surface as a cam surface. The cam gear 32 is rotatably supported by the first support shaft 11 and rotates around the first support shaft 11 in conjunction with the rotation of the crankshaft 4 (drive gear 31). That is, in the present embodiment, the axis of the first support shaft 11 is the rotation axis of the cam gear 32.

The first cam follower member 33 and the second cam follower member 34 are swingably supported by the second support shaft 12 disposed above the first support shaft 11, respectively. The first cam follower member 33 and the second cam follower member 34 are in contact with the outer peripheral surface (cam surface) of the cam portion 322 of the cam gear 32, and are linked to the rotation of the cam gear 32 (cam portion 322). It swings (rotates) around twelve. In the present embodiment, the first cam follower member 33 contacts the outer peripheral surface of the cam portion 322 from the upper left, and the second cam follower member 34 contacts the outer peripheral surface of the cam portion 322 from the upper right (see FIG. 1). ). That is, the first cam follower member 33 and the second cam follower member 34 swing with a predetermined phase difference.

One end of the first push rod 35 is connected to the first cam follower member 33 and the other end is connected to one end of the first rocker arm 37, and the swing motion of the first cam follower member 33 is transmitted to the first rocker arm 37. To do. The second push rod 36 has one end connected to the second cam follower member 34 and the other end connected to one end of the second rocker arm 38, and the second cam follower member 34 can be swung to the second rocker arm 38. To communicate. The other end of the first rocker arm 37 is connected to the intake valve 2, and the other end of the second rocker arm 38 is connected to the exhaust valve 3.

In the present embodiment, the drive gear 31, the cam gear 32, the first cam follower member 33, and the second cam follower member 34 are accommodated in a valve drive chamber 15 provided on the side of the cylinder 14 that accommodates the piston 13 so as to reciprocate. Has been. The first rocker arm 37 and the second rocker arm 38 are accommodated in the valve operating chamber 16 provided above the cylinder 14. The first push rod 35 and the second push rod 36 are respectively disposed in the first communication path 17 and the second communication path 18 that communicate the valve drive chamber 15 and the valve train chamber 16. The valve drive chamber 15, the valve train chamber 16, the first communication passage 17, and the second communication passage 18 are supplied with, for example, lubricating oil (oil mist) that is misted in a crank chamber that houses the crankshaft 4. The above-described components constituting the valve gear 10 are lubricated by the supplied oil mist.

When the engine 1 (crankshaft 4) rotates, the cam gear 32 is rotationally driven via the drive gear 31. When the cam gear 32 rotates, the first cam follower member 33 and the second cam follower member 34 that are in contact with the outer peripheral surface of the cam portion 322 are swung around the second support shaft 12, whereby the first push rod 35 and the second cam follower member 32 are swung. Each push rod 36 moves in the axial direction (vertical direction). The first rocker arm 37 opens and closes the intake valve 2 as the first push rod 35 moves in the axial direction, and the second rocker arm 38 opens and closes the exhaust valve 3 as the second push rod 36 moves in the axial direction. To do. In this way, the valve gear 30 opens and closes the intake valve 2 and the exhaust valve 3 of the engine 1.

Here, in the present embodiment, the cam gear 32 is provided so as to be movable on the first support shaft 11, in other words, movable in the direction of the rotation axis. Then, the valve gear 30 moves the cam gear 32 on the first support shaft 11, that is, moves in the direction of the rotation axis, whereby the valve opening characteristics of the intake valve 2 and the exhaust valve 3 (lift amount and / or valve opening). (Period) is changed at the same time. Hereinafter, the configuration of the valve gear 30 will be further described.

FIG. 3 is an enlarged view of a main part of the valve operating apparatus 30, and FIG. In FIG. 3, the second cam follower member 34 and the second push rod 36 are omitted for convenience of explanation.

As shown in FIG. 4, in this embodiment, a cover member 21 is attached to the outer surface of the cylinder member 20 in which the cylinder 14 is formed, and the valve drive chamber 15 is provided between the cylinder member 20 and the cover member 21. Is formed. In the valve drive chamber 15, the first support shaft 11 that rotatably supports the cam gear 32 is supported at both ends by the cylinder member 20 and the cover member 21, and the first cam follower member 33 (and a second cam follower not shown). The second support shaft 12 that supports the member 34) is erected on the outer surface of the cylinder member 20. The valve gear 30 further includes a holding plate 39, a plurality of centrifugal weights 40, and a spring member 41 in addition to the above-described components such as the cam gear 32.

FIG. 5 is an enlarged view showing the configuration of the cam gear 32.
As described above, the cam gear 32 is configured by integrating the gear portion 321 and the cam portion 322, and includes a side surface (hereinafter referred to as “gear side surface”) 32 a on the gear portion 321 side and a cam portion 322 side. And a side surface (hereinafter referred to as “cam side surface”) 32b. The cam gear 32 has a shaft insertion hole 323 through which the first support shaft 11 is inserted. Here, the gear portion 321 has a predetermined width (thickness) so as to mesh with the drive gear 31 even when the cam gear 32 moves on the first support shaft 11.

In the present embodiment, the outer peripheral surface of the cam portion 322 of the cam gear 32 has a tapered surface portion 322a that is inclined downward in a direction away from the gear portion 321. In other words, the outer peripheral surface of the cam portion 322 is different from one end side in the axial direction of the first support shaft 11 (that is, the rotational axis direction of the cam gear 32) in a state where the cam gear 32 is supported by the first support shaft 11. A tapered surface portion 322a inclined toward the end side is formed.

Further, a plurality (six in this case) of guide grooves 324 extending in the radial direction from the vicinity of the shaft insertion hole 323 are formed on the gear side surface 32 a of the cam gear 32. In other words, each guide groove 324 extends in a direction orthogonal to the axis of the first support shaft 11 (that is, the rotation axis of the cam gear 32) in a state where the cam gear 32 is supported by the first support shaft 11. In the present embodiment, the plurality (six) of guide grooves 324 are arranged at equal intervals in the circumferential direction. Further, the bottom portion 324a of each guide groove 324 is inclined so as to gradually become shallower as the distance from the insertion hole 323 increases, that is, as the distance from the axis of the first support shaft 11 (the rotation axis of the cam gear 32) increases.

Returning to FIG. 4, the holding plate 39 is formed in a disk shape and attached to the first support shaft 11. The holding plate 39 is disposed closer to the cylinder member 20 than the cam gear 32, and one surface faces the gear side surface 32 a of the cam gear 32 with a predetermined gap. Further, the other surface of the holding plate 39 is in contact with the convex portion 20 a of the cylinder member 20, whereby the movement of the holding plate 39 in the direction away from the cam gear 32 is restricted. Preferably, the holding plate 39 is fixed to the first support shaft 11. The holding plate 39 only needs to be restricted from moving in the direction away from the cam gear 32. For example, by using the first support shaft 11 as a stepped shaft, the direction of the holding plate 39 away from the cam gear 32 is limited. You may make it regulate movement of.

The plurality of centrifugal weights 40 are each formed in a spherical shape and disposed between the cam gear 32 and the holding plate 39. As the centrifugal weight 40, for example, a steel ball used for a bearing can be adopted. In the present embodiment, each of the plurality of centrifugal weights 40 is disposed so as to be slidable and rollable in each guide groove 324 formed on the gear side surface 32 a of the cam gear 32. That is, each centrifugal weight 40 can move along the guide groove 323 in which it is housed, and can roll at any position within the guide groove 323 in which it is housed.

The spring member 41 is disposed on the opposite side of the holding plate 39 across the cam gear 32, that is, between the cam side surface 32b of the cam gear 32 and the cover member 21. The spring member 41 is mounted on the first support shaft 11, and one end is in contact with the cam side surface 32 b of the cam gear 32 and the other end is in contact with the cover member 21 on the inner surface. The spring member 421 biases the cam gear 32 toward the holding plate 39, whereby the plurality of centrifugal weights 40 are sandwiched between the cam gear 32 and the holding plate 39. Here, each centrifugal weight 40 is held at the innermost position in each guide groove 324 (position closest to the rotation axis of the cam gear 32) when the cam gear 32 is not rotating.

Next, the operation of the valve gear 30 according to the present embodiment will be described with reference to FIGS.
FIG. 6 shows a state of a main part of the valve gear 30 at the time of engine low rotation (including when the engine is stopped), and FIG. 7 shows lift curves of the intake valve 2 and the exhaust valve 3 at the time of engine low rotation. Yes. FIG. 8 shows a state of a main part of the valve gear 30 at the time of high engine rotation, and FIG. 9 shows lift curves of the intake valve 2 and the exhaust valve 3 at high engine speed.

As shown in FIG. 6, the cam gear 32 is urged by the spring member 41 and is in a position closest to the holding plate 39 at the time of low engine rotation. Each centrifugal weight 40 is located on the innermost side in the radial direction in the guide groove 323 of the cam gear 32 (located closest to the rotation axis of the cam gear 32). For this reason, the first cam follower member 33 has a small distance from the rotation axis of the outer peripheral surface of the cam portion 322 (more specifically, the tapered surface portion 322a) on the cover member 21 side, that is, the outer peripheral surface of the cam portion 322. Abuts the area. Similarly, the second cam follower member 34 also abuts on the cover member 21 side portion of the outer peripheral surface (taper surface portion 322a) of the cam portion 322. Accordingly, during the low engine speed, the swing amount of the first cam follower member 33 and the second cam follower member 34 is small. For this reason, the lift amount of the intake valve 2 and the exhaust valve 3 is small, and the valve opening period (lift period) is also shortened. Further, the valve overlap (amount) is also reduced (see FIG. 7).

When the engine speed increases, the centrifugal weights 40 move radially outward in the guide grooves 323 of the cam gear 32 by the action of centrifugal force. As the centrifugal weights 40 move, the cam gear 32 moves on the first support shaft 11 in a direction away from the holding plate 39 against the urging force of the spring member 41. That is, the cam gear 32 moves in a direction away from the holding plate 39 by the action of centrifugal force according to the engine speed. Then, the region where the first cam follower member 33 and the second cam follower member 34 abut on the outer peripheral surface (tapered surface portion 322a) of the cam portion 322 changes.

When the engine rotates at a high speed, as shown in FIG. 8, the centrifugal weights 40 are positioned at the radially outermost side in the guide groove 323 of the cam gear 32, and the cam gear 32 is positioned farthest from the holding plate 39. . Therefore, the first cam follower member 33 comes into contact with a portion of the outer peripheral surface (tapered surface portion 322a) of the cam portion 322 on the gear portion 321 side, that is, a region where the distance from the rotation axis of the outer peripheral surface of the cam portion 322 is large. Therefore, the swing amount of the first cam follower member 33 and the second cam follower member 34 becomes large at the time of high engine rotation, and as shown in FIG. The lift amount of the exhaust valve 3 increases, and the valve opening period (lift period) also increases. In addition, the valve overlap (amount) also increases. In addition, the broken line in FIG. 9 has shown the lift curve of the intake valve 2 and the exhaust valve 3 at the time of engine low rotation.

In this embodiment, the cam gear 32 corresponds to the “cam member” of the present invention, the holding plate 39 corresponds to the “opposing member” of the present invention, and the spring member 41 corresponds to the “biasing member” of the present invention. The plurality of centrifugal weights 40 correspond to the “driving member” of the present invention.

According to the valve gear 30 according to the present embodiment, the valve opening characteristics of the engine valves (the intake valve 2 and the exhaust valve 3) can be changed according to the operating state of the engine 1, particularly the engine speed. For this reason, by appropriately setting the biasing force of the spring member 41 and the outer peripheral surface shape of the cam portion 322 of the cam gear 32, a preferable valve opening characteristic of the engine valve corresponding to the operating state (engine speed) of the engine 1 is obtained. It is done.

Further, in the valve gear 30 according to the present embodiment, the outer peripheral surface of the cam portion 322 of the cam gear 32 is inclined from one end side to the other end side in the axial direction of the first support shaft 11 (the rotational axis direction of the cam gear 32). The tapered surface portion 322a is provided. Then, the valve gear 30 moves the cam gear 32 on the first support shaft 11, so that the outer peripheral surface of the cam portion 322 in the axial direction of the first support shaft 11 and the cam follower member (first cam follower member 33, second The contact position with the cam follower member 34) changes to change the valve opening characteristics of the engine valve. Specifically, the cam gear 32 is configured such that the plurality of centrifugal weights 40 move radially outward in the guide groove 323 by the action of a centrifugal force according to the rotational speed of the engine 1, thereby biasing the spring member 41. To move away from the holding plate 3. Therefore, it is possible to obtain the valve opening characteristics of the intake valve 2 and the exhaust valve 3 according to the operating state of the engine 1 with a relatively simple configuration without requiring complicated control.

By the way, in the said embodiment, although the outer peripheral surface of the cam part 322 of the cam gear 32 has one taper surface part 322a, the outer peripheral surface of the cam part 322 may have several taper surface parts from which an inclination angle differs. it can. The tapered surface portion may be formed as a curved surface.

Further, in the above embodiment, the valve gear 30 has the holding plate 39. However, it is not limited to this. A member having the same function as that of the holding plate 39, that is, a member having a facing surface facing the gear side surface 32 a of the cam gear 32, movement in a direction away from the cam gear 32 is restricted, and a plurality of centrifugal weights 40 between the cam gear 32. Instead of the holding plate 39, a member that can hold can be employed. The holding plate 39 may be omitted, and a part of the outer surface of the cylinder member 20 may have a function as the holding plate 39.

Furthermore, in the above embodiment, the centrifugal weight 40 is formed in a spherical shape, but is not limited thereto. The centrifugal weight 40 is only required to be slidable and rollable in the guide groove 323, and may have a shape other than a spherical shape (for example, a roller shape).

Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications and changes can be made based on the technical idea of the present invention. is there.

DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Intake valve, 3 ... Exhaust valve, 4 ... Crankshaft, 11 ... 1st support shaft, 12 ... 2nd support shaft, 30 ... Valve operating apparatus, 31 ... Drive gear, 32 ... Cam gear, 33 ... 1st cam follower member, 34 ... 2nd cam follower member, 35 ... 1st push rod, 36 ...

2nd push rod

36, 37 ... 1st rocker arm, 38 ... 2nd rocker arm, 39 ... Holding plate, 40 ... Centrifugal weight, 41 ... Spring member, 321 ... Gear part, 322 ... Cam part, 322a ... Tapered surface part

Claims

A valve operating apparatus for an engine that includes a cam member that includes a cam member that rotates in conjunction with a crankshaft, and that opens and closes an engine valve via a cam follower member that contacts the outer peripheral surface of the cam portion of the cam member,
The cam member is movable in the rotational axis direction thereof,
The outer peripheral surface of the cam portion of the cam member is formed to have a tapered surface portion inclined from one end side to the other end side in the rotation axis direction,
As the cam member moves in the direction of the rotation axis, the contact position between the outer peripheral surface of the cam portion and the cam follower member in the direction of the rotation axis changes to change the valve opening characteristics of the engine valve. A valve operating device for an engine, which is configured as follows.
The engine valve operating apparatus according to claim 1, further comprising a drive member that moves the cam member in the direction of the rotation axis in accordance with the rotational speed of the engine.
An opposing member having an opposing surface facing one side surface of the cam member and restricted from moving in a direction away from the cam member;
A plurality of centrifugal weights disposed between the one side surface of the cam member and the opposing surface of the opposing member, and movable in a direction orthogonal to the rotation axis;
A biasing member that biases the cam member toward the opposing member so as to sandwich the plurality of centrifugal weights between the cam member and the opposing member;
Have
The plurality of centrifugal weights move in a direction perpendicular to the rotation axis by the action of centrifugal force according to the rotational speed of the engine, so that the cam member resists the urging force of the urging member from the opposing member. It is configured to move in a direction away from the outer peripheral surface of the cam portion and the cam follower member in the rotation axis direction, thereby changing the valve opening characteristic of the engine valve. The valve gear for an engine according to claim 1.
The one side surface of the cam member is formed with a plurality of guide grooves each extending in a direction orthogonal to the rotation axis and gradually becoming shallower as the bottom portion thereof is inclined and separated from the rotation axis.
4. The valve gear for an engine according to claim 3, wherein each of the plurality of centrifugal weights is arranged to be slidable and rollable in each guide groove. 5.
The valve operating apparatus for an engine according to claim 4, wherein each of the plurality of centrifugal weights is formed in a spherical shape.
The cam member integrally includes the cam portion and a gear portion to which a driving force from the crankshaft is transmitted, and is rotatably supported by a predetermined support shaft.
The opposing member is mounted on the support shaft;
Each of the plurality of centrifugal weights moves in each guide groove in the radial direction of the support shaft by the action of a centrifugal force according to the rotational speed of the engine, whereby the cam member resists the urging force of the urging member. Then, it moves in a direction away from the opposing member on the support shaft, whereby the contact position between the outer peripheral surface of the cam portion and the cam follower member in the axial direction of the support shaft changes, and the engine valve The valve operating apparatus for an engine according to claim 4, wherein the valve opening characteristic of the engine is changed.