JP2005155432A - Variable valve device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to omit a stopper mechanism for mechanically locking excessive rotation of a control shaft 12. <P>SOLUTION: The variable valve device is equipped with a variable valve mechanism for varying a variable lift property according to a rotational position of the control shaft 12 equipped with a control eccentric shaft part. A worm gear mechanism for linking the control shaft 12 to an actuator is equipped with a worm wheel 15b which rotates with the control shaft 12, and a worm which meshes with a worm gear 15c formed on the outer periphery of the worm wheel 15b. A gear forming section θ1 of the worm gear 15c includes a dead center P1 which turns over in the direction wherein reaction force torques working toward the control shaft 12 come close to each other, and is off a change point P2 in the direction wherein the reaction force torques separate from each other. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a variable valve device used for an intake valve and an exhaust valve of an internal combustion engine, and more particularly to a variable valve device capable of continuously and variably controlling lift characteristics.

  For example, Patent Literature 1 and Patent Literature 2 disclose variable valve operating apparatuses that can continuously and variably control the lift characteristics of intake valves. This device rotates in conjunction with a crankshaft and has a drive shaft having a drive eccentric shaft portion, a control shaft having a control eccentric shaft portion whose rotational position is controlled within a predetermined actual use section by an actuator, A rocker arm that is swingably attached to the control eccentric shaft portion, a swing cam (valve cam) that is swingably supported by the drive shaft, and a first link that links the drive eccentric shaft portion and one end of the rocker arm. And a second link that links the other end of the rocker arm and the swing cam. The intake valve is driven to open and close by a swing cam that swings with the rotation of the drive shaft, and the rotational position of the control shaft (control eccentric shaft portion) is changed by the actuator, so that the lift of the intake valve is adjusted to its operating angle. It is comprised so that it may increase / decrease with.

Further, Patent Document 3 discloses a variable valve operating device capable of continuously variably controlling the operating angle with a constant lift amount as a valve lift characteristic. This device is rotatably supported by the internal combustion engine body and is rotated in synchronization with the rotation of the internal combustion engine, and is also controlled by the actuator so that the rotation angle is controlled by the actuator. The rotation of the shaft and the drive shaft is transmitted via a pin to rotate, and the center position of the rotation relative to the internal combustion engine body changes as the intermediate member changes according to the rotation angle of the control shaft. A disc and a cam that rotates in accordance with the rotational movement of the annular disc and presses the intake valve, and the annular disc and the cam further rotate at a constant speed by changing the rotational center position of the annular disc. However, the valve opening / closing timing and the operating angle are changed.
JP 2000-213314 A JP 2003-148233 A JP-A-8-260923

  In the variable valve system that variably controls the valve lift characteristics via the control shaft as described above, the reaction force torque due to the valve spring reaction force and the inertial force of each component acts on the control shaft, causing the control shaft to rotate. Try to. Therefore, conventionally, for example, a stopper mechanism for mechanically restricting the rotation range of the control shaft is provided so that the control shaft does not rotate excessively beyond a predetermined actual use section. For example, if the control shaft tries to rotate excessively beyond a predetermined operating use section, a locking pin of a stopper mechanism fixed to the engine body such as a cylinder head contacts and locks a part of the control shaft. Prevent and regulate further rotation of the control shaft.

  However, the provision of such a mechanical stopper mechanism is not so preferable in terms of layout, functionality, reliability, and cost, particularly when the actuator is linked to the control shaft via a worm gear mechanism. Absent. The reason for this is that if the control shaft is held in a locked state by the stopper mechanism due to reaction torque acting on the control shaft, the worm gear mechanism, particularly the meshed portion of the worm and worm gear, is excessive. Will be in a state where a large force is applied. Accordingly, the worm gear mechanism is required to have high rigidity and strength so as not to cause deformation of the worm and worm wheel, leading to an increase in size, weight, and cost. In addition, the friction of the meshing portion increases, which may cause local wear of the meshing portion, and may cause the control shaft to be fixed or locked, which is not preferable in terms of functionality and reliability.

  The present invention has been made in view of such problems. The variable valve operating apparatus for an internal combustion engine according to the present invention includes a variable valve mechanism whose valve lift characteristics change according to the rotational position of a control shaft rotatably supported by the internal combustion engine body, and a worm gear mechanism on the control shaft. And an actuator that drives the control shaft in the rotational direction and holds the rotational position. The worm gear mechanism includes a worm wheel that rotates together with the control shaft, a worm gear formed on the outer periphery of the worm wheel, and a worm that meshes with the worm gear. The worm gear is formed only in a predetermined gear forming section that is a part in the circumferential direction of the worm wheel.

  According to the present invention, since the worm gear is formed only in a predetermined gear forming section that is a part of the worm wheel in the circumferential direction, for example, by considering the reaction torque acting on the control shaft, the machine as described above It is possible to omit a typical stopper mechanism. Therefore, it is possible to reduce the number of parts and the cost, and to improve layout performance / functionality and reliability.

  Hereinafter, an embodiment in which the present invention is applied to an intake valve of an automobile internal combustion engine will be described. FIG. 1 is a configuration explanatory view showing the overall configuration of the variable valve operating apparatus. The variable valve operating apparatus includes a variable lift / operating angle mechanism 1 that changes a lift / operating angle of an intake valve as a variable valve operating mechanism. The lift / operating angle variable mechanism 1 has been previously proposed by the present applicant and the like, and is known by, for example, the above-mentioned Patent Document 1 and Patent Document 2, so only the outline thereof will be described.

  The lift / operating angle variable mechanism 1 is rotatably supported by a cam bracket (not shown) at the upper part of the cylinder head, and extends above the intake valve 11 in the cylinder row direction. The drive eccentric shaft portion 3 fixed by the drive shaft 2 and rotated integrally with the drive shaft 2, and a control shaft rotatably supported by the same cam bracket at a position above the drive shaft 2 and arranged in parallel with the drive shaft 2 12, a control eccentric shaft portion 18 that is fixed to the control shaft 12 by press-fitting or the like and rotates integrally with the control shaft 12, and a rocker arm 6 as an intermediate member that is swingably supported by the control eccentric shaft portion 18. And a swing cam (valve cam) 9 attached to the drive shaft 2 so as to be swingable. The drive eccentric shaft portion 3 and one end of the rocker arm 6 are linked by an arm-shaped first link 4, and the other end of the rocker arm 6 and the swing cam 9 are linked by a second link 8 having a ring shape at one end. Has been.

  The drive shaft 2 is driven by an engine crankshaft via a timing chain or timing belt (not shown), and rotates around the shaft in conjunction with the crankshaft. The drive eccentric shaft portion 3 has a circular outer peripheral surface, and the center of the outer peripheral surface is eccentric from the axis of the drive shaft 2 by a predetermined amount. The rocker arm 6 is supported at its substantially central portion by a control eccentric shaft portion 18 so as to be swingable. A first link 4 is connected to one end of the rocker arm 6 via a connecting pin 5, and a second link 8 is connected to the other end via a connecting pin 7. The control eccentric shaft portion 18 is eccentric from the axis of the control shaft 12 by a predetermined amount. Therefore, the rocking center of the rocker arm 6 changes according to the angular position of the control shaft 12.

  The tip of the swing cam 9 and the second link 8 are connected via a connecting pin 17. On the lower surface of the swing cam 9, a base circle surface concentric with the drive shaft 2 and a cam surface extending in a predetermined curve from the base circle surface are continuously formed. These base circle surfaces and cam surfaces are opposed to and abutted against the upper surface of the tappet 10 according to the swing position of the swing cam 9. That is, the base circle surface is a section where the lift amount becomes 0 as a base circle section. When the swing cam 9 swings and the cam surface contacts the tappet 10, the intake valve resists the valve spring reaction force. When pushed down, the intake valve gradually lifts.

  The lift / operating angle control actuator 13 has a function of driving the control shaft 12 in the rotation direction and maintaining the rotation position thereof, and is composed of an electric motor such as a servo motor, for example, and is a worm gear which is a mechanical interlocking mechanism. It is linked to the control shaft 12 through a mechanism 15. As shown in FIGS. 2 and 3, the worm gear mechanism 15 is fixed to the output shaft 13a of the actuator, and is fixed to the control shaft 12 by press fitting or the like, and the worm 15a that rotates integrally with the output shaft 13a. And a worm wheel 15b that rotates together with the control shaft 12. A worm gear 15c that meshes with the worm 15a is formed on the outer periphery of the worm wheel 15b. As will be described later, the worm wheel 15b is a so-called sector gear having a substantially fan shape in which the worm gear 15c is formed only in a predetermined gear formation section θ1 that is a part of the circumferential direction.

  Referring to FIG. 1 again, the rotation angle (rotation position) of the control shaft 12 and the control eccentric shaft portion 18 is detected by the rotation angle sensor, that is, the control shaft sensor 14, and based on the detected actual rotation position. Thus, the actuator 13 is controlled by the control device (control means) 21 so that the rotational position of the control shaft 12 becomes the target rotational position.

  The operation of the lift / operating angle variable mechanism 1 will be briefly described. When the drive shaft 2 rotates, the swing cam 9 moves via the drive eccentric shaft portion 3, the first link 4, the rocker arm 6, and the second link 8. Swing. The tappet 10 is pressed by the swing cam 9 and the intake valve 11 is pushed down against the spring force of a valve spring (not shown) to open and close. Further, when the angle position of the control shaft 12 is changed by the lift / operation angle control actuator 13, the initial position of the rocker arm 6 is changed, and the valve lift characteristic by the swing cam 9 is continuously changed. That is, the lift and the operating angle can be continuously expanded and contracted simultaneously. Depending on the layout of each part, for example, the opening timing and closing timing of the intake valve 11 change substantially symmetrically as the lift and operating angle change.

  A valve spring reaction force acts on the swing cam 9 along with the valve lift of the intake valve 11. The valve spring reaction force increases as the lift / operation angle increases, and also acts on the control shaft 12 via the links 4, 8 and the rocker arm 6. In addition to the above valve spring reaction force, a reaction force due to the inertial force of each component also acts on the control shaft 12. The load on the control shaft 12 due to these reaction forces changes according to the rotational position of the control shaft 12 corresponding to the lift / operation angle, and increases as the rotational position becomes a large lift / operation angle. On the other hand, since the load applied to the control shaft 12 is strictly received by the control eccentric shaft portion 18, it acts on the control shaft 12 as a reaction torque.

  As shown in FIG. 4, when the center of the drive shaft 2 that is the rotation center of the swing cam 9 is the cam center O1, and the center of the control shaft 12 is the control shaft center O2, the load acting on the control shaft 12 (in the cycle) The direction of the average load (or the maximum load) F generally coincides with a reference line L1 connecting the cam center O1 and the control axis center O2, and is a direction from the cam center O1 toward the control axis center O2. The reaction torque acting on the control shaft 12 via the control eccentric shaft portion 18 due to the load F varies depending on the angular position of the control shaft, that is, the center position of the control eccentric shaft portion 18. For example, when the center position of the control eccentric shaft portion 18 is on the left side of the reference line L1, the acting direction T1 of the reaction force torque is clockwise, and the center position of the control eccentric shaft portion is from the reference line L1. 4 is also on the right side of FIG. 4, the reaction direction T2 of the reaction force torque is counterclockwise. That is, the first position P1 farthest from the cam center O1 in the circumferential position of the control shaft 12 becomes a dead point where the reaction torques are reversed in directions approaching each other, and is closest to the cam center O1. The second position P2 becomes a change point where the reaction torque is reversed in a direction away from each other.

  The lift operating angle decreases as the center of the control eccentric shaft portion 18 (the angular position of the control shaft 12) approaches the first position P1, that is, away from the cam center O1, and the center of the control eccentric shaft portion 18 becomes the first. The lift operation angle increases as the position approaches the second position P2, that is, the closer to the cam center O1. Further, the actual motion use section θ2 that can be taken by the target rotation position of the control shaft 12 by the control device 21 is approximately 90 °.

  As a characteristic configuration of the present embodiment, the worm gear 15c is formed only in a predetermined gear formation section θ1 that is a part in the circumferential direction of the worm wheel 15b. The worm wheel 15b has a small diameter so that the worm 15a and the worm wheel 15b idle without being engaged with each other in a region outside the gear formation section θ1 including both ends of the gear formation section θ1. Therefore, if the worm 15a reaches both ends of the gear formation section θ1, the worm 15a and the worm wheel 15b are idled without being engaged with each other.

  The gear formation section θ1 includes the above-described actual operation use section θ, and extends in the circumferential direction beyond the actual operation use section θ2. However, unlike the conventional sector gear, the dimensional accuracy of the portion deviating from the actual use section is not low, and the desired dimensional accuracy is provided over the entire length of the gear formation section θ1 including the portion deviating from the actual use section θ2. Set to maintain.

  The first position P1, which is a dead center, exists in the gear formation section θ1. That is, the gear forming section θ1 extends in the circumferential direction by a predetermined first extending section θ3 (for example, 40 to 50 °, preferably 45 °) beyond the first position P1. Therefore, even if the control shaft 12 rotates excessively from the actual use section θ2 beyond the dead point P1 to the small lift operating angle side, the reaction torque in the direction T2 toward the actual use section θ2 is applied to the control shaft 12. Therefore, the control shaft 12 is quickly returned in the direction toward the actual use section θ2 (counterclockwise direction in FIG. 4). Further, since the gear formation section θ1 extends beyond the dead point P1 by a predetermined first extension section θ3, the meshing state of the worm and the worm gear is maintained in this section θ3, and the reliability and stability are excellent. ing.

  If the control shaft 12 tries to rotate further toward the small lift operating angle side beyond the first extension section θ3, the worm and the worm wheel are idled without meshing, and the control shaft is directed toward the dead center P1. Since the reaction torque of T2 acts, there is no possibility that the control shaft 12 is further displaced to the small lift operating angle side, and the control shaft is returned toward the dead center P1.

  The second position P2, which is the thought point, is out of the gear formation section θ1. That is, the gear forming section θ1 is not extended to the second position P2. Accordingly, even if the control shaft 12 excessively rotates to the large lift operating angle side beyond the actual use section θ2, the reaction torque in the direction T1 toward the actual use section θ2 always acts on the control shaft 12. Therefore, the control shaft 12 is forcibly and quickly returned to the direction of the actual use section θ2. Since the gear formation section θ1 does not reach the thought point P2, even if the control shaft 12 rotates excessively toward the large lift operating angle side, the direction of the reaction force torque acting on the control shaft 12 is away from the actual use section θ2. There is no risk of reversing in the direction T2. Further, in the gear formation section θ1, a predetermined extension section θ4 (for example, 40 to 50 °, more preferably 45 °) is secured on the larger lift operating angle side than the actual use use section θ2, so it is assumed that the control shaft Even if 12 exceeds the actual use section θ2 and rotates excessively toward the large lift operating angle, the meshing state between the worm and the worm gear is stably maintained.

  As described above, in this embodiment, the gear formation section θ1 is set in consideration of the reaction torque acting on the control shaft (positional relationship with the cam center O1). It is possible to omit a biasing means such as a return spring for returning the rotational position to the actual use section θ2. That is, the rotation region of the control shaft can be substantially limited / restricted using the reaction force torque without depending on the stopper mechanism or the biasing means. Therefore, the number of parts and the cost are reduced and the layout, functionality, and reliability are remarkably improved as compared with the case where these mechanical stopper mechanisms and urging means are provided.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, the present invention can be similarly applied to a variable valve mechanism of the type described in Patent Document 3 described above. In the above embodiment, the worm is directly fixed to the output shaft of the actuator. However, for example, a speed reduction mechanism may be provided between the actuator and the worm.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows one Example of the variable valve operating apparatus of the internal combustion engine which concerns on this invention. The front view which shows the worm gear mechanism which links an actuator and a control shaft. Sectional drawing which follows the III-III line | wire of FIG. Explanatory drawing which shows the gear formation area which makes the principal part of a present Example.

Explanation of symbols

1. Lift / operating angle variable mechanism (variable valve mechanism)
9 ... Oscillating cam (valve cam)
DESCRIPTION OF SYMBOLS 12 ... Control shaft 13 ... Actuator 15 ... Worm gear mechanism 15a ... Worm 15b ... Worm wheel 15c ... Worm gear 18 ... Control eccentric shaft part 21 ... Control apparatus (control means)
θ1 ... Gear formation section θ2 ... Actual use section T1, T2 ... Direction of reaction force torque P1 ... First position (dead center)
P2 ... Second position (thinking point)

Claims (8)

A variable valve mechanism whose valve lift characteristics change according to the rotational position of a control shaft rotatably supported by the internal combustion engine body, and the control shaft are linked via a worm gear mechanism to drive the control shaft in the rotational direction. And an actuator for holding the rotational position,
The worm gear mechanism has a worm wheel that rotates together with the control shaft, and a worm that meshes with a worm gear formed on the outer periphery of the worm wheel,
The variable valve operating apparatus for an internal combustion engine, wherein the worm gear is formed only in a predetermined gear forming section that is a part of the worm wheel in the circumferential direction.   The variable valve operating apparatus for an internal combustion engine according to claim 1, wherein the worm and the worm wheel are idled at both ends of the gear forming section without meshing.   The dead point where the reaction force torque acting on the control shaft including the valve spring reaction force in the circumferential direction position of the control shaft reverses in a direction approaching each other exists in the gear forming section. 3. A variable valve operating apparatus for an internal combustion engine according to 2.   2. A thought point in which a reaction torque acting on the control shaft including a valve spring reaction force in a circumferential direction of the control shaft is reversed in a direction away from each other is out of the gear forming section. The variable valve operating apparatus for an internal combustion engine according to any one of? The variable valve mechanism has a valve cam that pushes down an intake valve or an exhaust valve against a valve spring reaction force,
The variable valve operating apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein a first position farthest from a center of the valve operating cam among circumferential positions of the control shaft exists in the gear forming section. The variable valve mechanism has a valve cam that pushes down an intake valve or an exhaust valve against a valve spring reaction force,
The variable valve operating apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein a second position closest to a center of the valve operating cam among circumferential positions of the control shaft is out of the gear forming section. . Control means for controlling the actuator so that the rotational position of the control shaft becomes a predetermined target rotational position according to the engine operating state;
The variable valve operating apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the gear formation section is set so as to exceed an actual operation use section that the target rotational position can take. The variable valve mechanism is
A control eccentric shaft portion that rotates integrally with the control shaft and is eccentric with respect to the center of the control shaft;
A rocker arm swingably attached to the control eccentric shaft,
A drive shaft rotatably supported by the internal combustion engine body and rotating in conjunction with the crankshaft;
A valve cam that is swingably attached to the drive shaft and pushes down the intake valve or exhaust valve against the reaction force of the valve spring;
A drive eccentric shaft portion that rotates integrally with the drive shaft and is eccentric with respect to the center of the drive shaft;
A first link linking one end of the rocker arm and the drive eccentric shaft portion;
A second link linking the other end of the rocker arm and the valve cam;
A variable valve operating apparatus for an internal combustion engine.

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