JP2971146B2 - Variable valve timing mechanism - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable valve timing mechanism which varies a valve timing by causing a rotational phase difference between a camshaft and a crankshaft of an engine.

[0002]

2. Description of the Related Art Hitherto, various proposals have been made to make the valve timing of an engine variable. One such technique is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-185914.
As disclosed in Japanese Patent Application Laid-Open Publication No. H10-260, a camshaft-side member and a rotary drive member are respectively provided on a camshaft side and a crankshaft side for a driving force transmission mechanism for transmitting rotational driving force from a crankshaft to a camshaft. Provided so as to be relatively rotatable, the sleeve-shaped camshaft-side member and the rotary drive member rotate relative to each other to generate a rotational phase difference between the camshaft side and the crankshaft side, thereby changing the valve timing. Such is known.

In such a variable valve timing mechanism, a driving force transmitting portion for transmitting a rotational driving force from a crankshaft to a camshaft to generate the above-mentioned rotational phase difference is usually provided between a camshaft side and a crankshaft. A relative rotation is caused between the side. As its structure, a transmission member for transmitting a driving force is provided between the rotation drive member on the crankshaft side and the member on the camshaft side, and this transmission member is connected to the member on the camshaft side and the rotation drive member. An engagement means for engaging each is provided. At least one of these engaging means is constituted by an inclined cam surface extending obliquely in the axial direction and an engaging portion slidably in contact with the inclined cam surface. Further, there is provided moving means for moving the transmission member in the axial direction so as to move the contact position between the inclined cam surface and the engaging portion, and the contact position is moved on the inclined cam surface by this moving means. Accordingly, relative rotation occurs between the two members.

[0004]

However, in this case,
Along with the torque for driving the camshaft, a component force in the axial direction of the camshaft driving torque generated by the inclination angle of the inclined cam surface always acts on the contact surface between the engaging portion and the inclined cam surface.
Therefore, after switching the valve timing, the transmitting member is moved in the axial direction by the component force in the axial direction, so that the contact position is displaced and the valve timing is not changed. A large holding force for holding the transmission member is required. Further, when the abutment position moves at the time of switching the valve timing, the axial component of the camshaft drive torque and the static friction force act on the abutment surface, so that the movement for moving the transmission member is started. Sometimes requires a large driving force. Further, since a large force is always applied to the contact surface where the engagement portion and the inclined cam surface come into contact with each other, problems such as abrasion and fixation of the contact surface occur.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a variable valve timing for changing a valve timing by causing a rotational phase difference between a camshaft and a crankshaft. In the mechanism, while reducing the axial component of the camshaft driving torque in the driving force transmission unit to reduce the holding force after switching the valve timing and the driving force when switching the valve timing, wear of the contact surface and The purpose is to prevent sticking.

[0006]

Means for Solving the Problems To achieve the above object, a solution taken by the invention according to claim 1 is that a rotational driving force from a crankshaft is applied to a camshaft to rotate between the camshaft and the crankshaft. As a variable valve timing mechanism that changes the valve timing by generating and transmitting a phase difference, the variable valve timing mechanism is provided rotatably on the camshaft and immovable in the axial direction,
A rotary drive member to which a rotary drive force from a crankshaft is transmitted; a camshaft-side member rotatably provided integrally with the camshaft; and a camshaft between the rotary drive member and the camshaft-side member. A transmission member provided rotatably and axially movably on the transmission member; first engagement means for engaging the transmission member slidably in the axial direction with the rotation driving member; and the transmission member. A second engaging means for slidably engaging the camshaft-side member in the axial direction; and a moving means for moving the transmission member in the axial direction. And the moving means is
The camshaft is provided so as to be rotatable and immovable in the axial direction.
And is screwed to the transmission member along the cam shaft center.
The supporting member, and rotating the supporting member with respect to the transmission member.
At least one of the first and second engaging means has an inclined cam surface extending inclining in the axial direction and a rotational phase difference contacting the inclined cam surface in a slidable manner. , And at least both ends of the inclined cam surface are formed as flat portions substantially parallel to the axial direction.

Further, in the invention of claim 2, in addition to the constituent features of the invention of claim 1, at least one flat portion substantially parallel to the axial direction is provided in the middle of the inclined cam surface.

[0008]

According to the above construction, in the first aspect of the invention, the rotational driving force from the crankshaft is transmitted from the rotational driving member to the transmitting member via the first engaging means, and further transmitted from the transmitting member to the second engaging member. The rotation is transmitted to the camshaft side member via the means to rotate the camshaft. At least one of the first and second engaging means includes an inclined cam surface extending inclining in the axial direction, and an engaging portion which slidably abuts the inclined cam surface to generate a rotational phase difference. It is made from. Because of this, the support
The material is rotated relative to the transmission member by the rotary drive means
As a result, when the transmission member screwed to the support member is moved in the axial direction, the contact position between the inclined cam surface and the engaging portion moves on the inclined cam surface, and the camshaft and the crank are moved. A rotational phase difference occurs between the shaft and the shaft, and the valve timing is changed. In this case, when the valve timing is switched in two stages, the contact position between the inclined cam surface and the engaging portion after the valve timing is switched is one of both ends of the inclined cam surface. Since at least both ends are formed as flat portions substantially parallel to the axial direction, the flat portions of the inclined cam surface become the contact positions after the valve timing is switched. Therefore, the axial force of the camshaft driving torque does not act on the contact surface, so that the force for moving the transmission member in the axial direction is reduced, and a large holding force is required for holding the transmission member. Does not require power. In addition, in the holding state of the valve timing, since the axial component of the camshaft driving torque is lost, only the static friction force acts on the contact surface when the contact position is moved at the time of switching the valve timing. Therefore, a large driving force is not required at the start of the movement for moving the transmission member, and the driving force of the moving means is reduced. Furthermore, the contact surface between the engaging portion and the inclined cam surface does not always receive an extra axial component force while the valve timing is maintained, so that abrasion and sticking of the contact surface occur. Is suppressed.

According to the second aspect of the present invention, at least one flat portion substantially parallel to the axial direction is formed in the middle of the inclined cam surface, and the flat portion comes into contact with the inclined cam surface and the engaging portion. Since the position is easily held, by setting the flat portion at an appropriate position in the middle of the inclined cam surface, the intermediate state of the desired valve timing can be reliably and stably set, and multi-stage valve timing control is performed. Is easily performed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a variable valve timing mechanism according to a first embodiment of the present invention. In the figure, 1 is a cam shaft,
Reference numeral 2 denotes a cam sprocket serving as a rotation drive member rotatably provided on the cam shaft 1 and immovable in the axial direction. The cam sprocket 2 receives a rotation drive force from a crank shaft (not shown) on a timing belt. Is transmitted via Reference numeral 3 denotes a hub fixed to the camshaft 1 as a camshaft-side member. The hub 3 has a claw portion 3 extending in the axial direction.
a,... An advancing plate 4 is provided on the camshaft 1 so as to be rotatable and axially movable by engaging with both the cam sprocket 2 and the tab 3a of the hub 3. Then, the rotational driving force from the crankshaft is transmitted from the cam sprocket 2 to the hub 3 via the advancing plate 4 via the advancing plate 4 to be transmitted to the camshaft 1, and the camshaft 1 is rotationally driven.
As a result, a cam (not shown) formed integrally with the camshaft 1 drives the intake and exhaust valves to open and close at a predetermined timing.

5 is the advancing plate 4
And a drum serving as a supporting member for moving the advancing plate 4 in the axial direction, the drum 5 being rotatably provided on the camshaft 1 and rotating relative to the advancing plate 4. Has become. A coil unit 21 (rotation driving means) including an annular solenoid coil 22 is provided on the inner periphery of the drum 5 so as to be rotatable and concentric with respect to the drum 5. Fixed on the side. The drum 5 is made of a magnetic material such as iron, and the drum 5 and the coil unit 21 constitute an electromagnetic clutch 20 (moving means) . Further, reference numeral 6 denotes a spiral spring, which is arranged concentrically with the camshaft 1.
The outer peripheral end of one end of the spiral spring 6 is engaged with the drum 5, and the inner peripheral end of the other end of the spiral spring 6 is engaged with the hub 3. As a result, the drum 5 is urged in the same direction as the rotation direction of the cam sprocket 2.

As shown in FIG. 4, engagement projections 10,... Are formed on the outer periphery of the advancing plate 4, and engagement protrusions extending in the axial direction are formed on the inner periphery of the cam sprocket 2. A groove (not shown) is formed, and by engaging the engaging protrusion 10 with the engaging groove, the advancing plate 4 rotates integrally with the cam sprocket 2 while the advancing plate 4 It is provided movably in the direction. The engagement protrusions 10 and the engagement grooves constitute first engagement means 18 for engaging the advancing plate 4 as a transmission member with the cam sprocket 2 as a rotation drive member in an axially slidable manner. ing. Further, helical grooves 12,... Inclined with respect to the axial direction are formed on the outer periphery of the advancing plate 4, and as shown in FIG.
The helical groove 12 and the inclined cam surface 13 of the claw portion 3a are brought into contact with and engaged with each other. By moving in the axial direction, the inclined cam surface 1
As the contact position with the hub 3 moves, the hub 3 rotates relative to the hub 3. By the helical groove 12 and the inclined cam surface 13 formed in the claw portion 3a of the hub 3, the advancing plate 4 as a transmission member is slidably engaged in the axial direction with respect to the hub 3 as a cam shaft side member. Second
The engaging means 19 is constituted. In addition, the helical groove 1
Reference numeral 2 functions as an engaging portion that slidably abuts against the inclined cam surface 13 to generate a rotational phase difference. As shown in FIG. 5, flat portions 14a and 14b substantially parallel to the axial direction are formed at both ends of the inclined cam surface 13.

Further, an internal thread is formed on the inner circumference of the advancing plate 4, and a male thread 15 is formed on the outer circumference of the drum 5, as shown in FIG. The advancing plate 4, which is screwed and is axially movable by the relative rotation of the advancing plate 4 and the drum 5, is moved in the axial direction. The relative rotation between the drum 5 and the advancing plate 4 is caused by the operation of the electromagnetic clutch 20. That is, the solenoid coil 22 is energized to generate a magnetic force, and the drum 5 is attracted to the coil unit 21 by the magnetic force, and the clutch surface 5a of the drum 5 and the coil unit 21 come into contact with each other. As a result, the drum 5 is braked against the urging force of the spiral spring 6, causing a rotation delay with respect to the advancing plate 4 and relative rotation with the advancing plate 4.

With the above arrangement, in the above embodiment, the rotational driving force of the crankshaft is transmitted from the cam sprocket 2 to the advancing plate 4 by the first engaging means 18 and further by the second engaging means 19. The power is transmitted from the advancing plate 4 to the camshaft 1. In this case, when the engine speed is lower than the predetermined engine speed N, the electromagnetic clutch 20 is not operated, and the advancing plate 4
Is held at one end of the drum 5 and the second engaging means 1
In 9, the engagement is at a flat portion 14 a on one end side of the inclined cam surface 13. In this state, the valve timing is set to the low-speed valve timing. On the other hand, when the engine speed is higher than the predetermined engine speed N, the electromagnetic clutch 20 is actuated, and the drum 5 rotates relative to the advancing plate 4 on the delay side in the rotation direction against the urging force of the spiral spring 6. The advancing plate 4 is axially moved to and held by the other end of the drum 5, and is engaged by the second engaging means 19 with a flat portion 14 b on the other end of the inclined cam surface 13. As a result, the camshaft 1 and the cam sprocket 2, that is, the crankshaft rotate relative to each other to generate a rotational phase difference, and the valve timing is switched from the low-speed valve timing, and in this state, the high-speed valve timing is set. When the operation of the electromagnetic clutch 20 is stopped due to a decrease in the engine speed, the drum 5 rotates relative to the advancing plate 4 in the rotational direction by the urging force of the spiral spring 6, and The sing plate 4 is moved to and held at one end, and is switched to the low-speed valve timing.

Here, when the valve timing is held at the low-speed valve timing or the high-speed valve timing, the second engagement means 19 of the advancing plate 4 is held.
The contact positions with the helical groove 12, which is the engagement point in the above, are flat portions 14a, 14b substantially parallel to the axial direction of both ends of the inclined cam surface 13 formed in the claw portion 3a of the hub 3.
Therefore, an axial component of the camshaft driving torque for rotating the camshaft 1 does not act on the contact surfaces of the flat portions 14a and 14b, and the advancing plate 4 is moved in the axial direction. The holding force for holding the advancing plate 4, that is, a large clutch capacity of the electromagnetic clutch 20 is not required, and the mounting of the electromagnetic clutch 20 in a limited space is facilitated. Can be. Further, at the start of the valve timing switching, when the contact position is moved,
Only the static frictional force acts on the flat portions 14a and 14b, which are the contact surfaces, without the axial component of the camshaft driving torque, and the driving force at the start of the movement for moving the advancing plate 4, that is, The clutch force of the electromagnetic clutch 20 does not need to be large.
Power consumption during operation can be reduced. In addition, in the holding state of the valve timing, there is no need to apply an extra component force in the axial direction at all times, and the holding force and the driving force can be reduced. Can be suppressed.

FIG. 6 shows a second embodiment of the present invention, which is different from the first embodiment only in the shape of the inclined cam surface formed on the claw portion 3a of the hub 3, and the other structure is the same. In the figure, flat portions 16a, 16b, and 16c are formed in the claw portion 3a at both ends and a central portion thereof, respectively. The flat portions 16a, 16b, and 16c are substantially parallel to the axial direction. The inclined cam surfaces 17a and 17b extending in the axial direction are formed therebetween. Thus, in this embodiment, the advancing plate 4 can be easily and stably held on the central flat portion 16c in addition to the same operation and effect as the first embodiment. As the timing, the intermediate-speed valve timing intermediate between the low-speed valve timing and the high-speed valve timing of the first embodiment can be reliably and stably added, and the valve timing can be accurately adjusted in multiple stages. Control can be performed.

In the first and second embodiments,
Although the electromagnetic clutch is used, in the present invention, a hydraulic drive type clutch may be used instead of the electromagnetic clutch. In the second embodiment, one flat portion is formed in the middle of the inclined cam surface. However, in the present invention, a plurality of flat portions may be formed.

[0019]

As described above, according to the first aspect of the present invention, when the valve timing is switched between two stages, the contact position between the inclined cam surface and the engagement portion after the valve timing is switched is determined by the inclination cam surface. It is one of both ends,
Since at least both ends of the inclined cam surface are formed as flat portions substantially parallel to the axial direction, no component force in the axial direction of the camshaft driving torque acts on the contact surface, and the transmission member is moved in the axial direction. The force to move the transmission member is reduced, and a large holding force is not required to hold the transmission member. In addition, in the holding state of the valve timing, there is no axial component of the camshaft driving torque, so that only the static friction force acts on the contact surface when the contact position is moved at the time of switching the valve timing. Thus, a large driving force is not required at the start of the movement for moving the transmission member, and the driving force of the moving means can be reduced. Further, the contact surface between the engaging portion and the inclined cam surface is not always subjected to an extra axial component force in a state where the valve timing is held.
It is possible to suppress the occurrence of abrasion and sticking of the contact surface of each part.

According to the second aspect of the present invention, at least one flat portion substantially parallel to the axial direction is formed in the middle of the inclined cam surface, and the flat portion comes into contact with the inclined cam surface and the engaging portion. Since the position is easily held, by setting the flat portion at an appropriate position in the middle of the inclined cam surface, the intermediate state of the desired valve timing can be reliably and stably set, and multi-stage valve timing control is performed. Can be easily performed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a variable valve timing mechanism according to a first embodiment of the present invention.

FIG. 2 is a diagram showing engagement between an advancing plate and a hub.

FIG. 3 is a diagram illustrating a screw engagement between an advancing plate and a drum.

4 is a view as viewed from an arrow A in FIG. 3;

FIG. 5 is an enlarged view of a claw portion.

FIG. 6 is a diagram corresponding to FIG. 5 of a second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 camshaft 2 cam sprocket (rotation drive member) 3 hub (camshaft side member) 4 advancing plate (transmission member) 5 drum (support member) 10 engagement protrusion 12 helical groove (engagement portion) 13 inclined cam surface 14a , 14b Flat portions 16a, 16b, 16c Flat portions 17a, 17b Inclined cam surface 18 First engaging means 19 Second engaging means 20 Electromagnetic clutch (moving means) 21 Coil unit (rotation driving means)

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunori Kanda 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Corporation (56) References JP-A-3-225007 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) F01L 1/34

Claims (2)

(57) [Claims] 1. A variable valve timing mechanism for changing a valve timing by transmitting a rotational driving force from a crankshaft to a camshaft by generating a rotational phase difference between the camshaft and the crankshaft, A rotary drive member rotatably provided on the camshaft and immovable in the axial direction, to which a rotary drive force from a crankshaft is transmitted; and a camshaft-side member rotatably provided integrally with the camshaft. A transmission member rotatably and axially movable on a cam shaft between the rotation driving member and the cam shaft side member; and sliding the transmission member in the axial direction with respect to the rotation driving member. First engagement means for movably engaging the first transmission means, second engagement means for slidably engaging the transmission member with the camshaft-side member in the axial direction, and moving the transmission member in the axial direction. and a moving unit for, the move The means is rotatably and axially mounted on the camshaft.
Along the cam shaft center.
A support member screwed to the transmission member, and the transmission member
Rotating means for rotating the member with respect to the material, at least one of the first and second engaging means is slidably contacting the inclined cam surface extending inclining in the axial direction. A variable valve timing mechanism, comprising: an engaging portion that contacts and generates a rotational phase difference; at least both ends of the inclined cam surface are formed as flat portions that are substantially parallel to the axial direction. 2. The variable valve timing mechanism according to claim 1, wherein one or more flat portions substantially parallel to the axial direction are provided in the middle of the inclined cam surface.