JP2006292012A - Ball screw mechanism and valve system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw mechanism and an actuator which maintain a long rolling fatigue life even under comparatively poor lubricating conditions. <P>SOLUTION: The force F that presses a ball 6 between an internal thread groove 5b and an external thread groove 4a forming one rolling passage, and the force F that presses the ball 6 between an internal thread groove 5a and the external thread groove 4a forming the other rolling passage, arise respectively due to a deviation Δ. Since the force F has components opposed to an axial direction, even if high frequency force whose direction is changeable in two normal and reverse directions arises between a nut 5 and a screw shaft 4, the occurrence of noise is suppressed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a ball screw mechanism and a valve mechanism, for example, a variable valve timing type valve mechanism that is installed in an engine of an automobile and is driven by an actuator, and a ball screw mechanism that is suitable for use therewith.

  In internal combustion engines mounted on vehicles in recent years, a variable valve timing type valve operating mechanism that changes the opening / closing timing of a valve in accordance with the engine speed and load has increased. In such a valve operating mechanism, for example, by applying hydraulic pressure, the phases of the sprocket and camshaft synchronized with the crankshaft can be changed, thereby making it possible to vary the valve timing and the like.

  However, in the valve mechanism of the above prior art, hydraulic pressure is required to make the valve timing variable, and therefore it is necessary to provide a hydraulic pump. In an internal combustion engine, a hydraulic pump for lubricating each part is generally installed, but if hydraulic pressure is used to achieve variable valve timing etc., a larger capacity hydraulic pump is required, Since the power is extracted from the crankshaft, there is a problem that fuel consumption is deteriorated accordingly.

On the other hand, a mechanism for changing the valve timing or the like using the power of the electric motor is known as disclosed in, for example, Patent Document 1 below. According to such a technique, by changing the valve timing or the like using the power of the electric motor, it is not necessary to take out the power from the crankshaft, and the fuel efficiency can be improved.
JP 2002-256832 A

  However, in the mechanism disclosed in Patent Document 1, the driving force of the electric motor is transmitted to a control shaft that can vary valve timing and the like via a screw shaft and a nut. Here, when power transmission is performed via the screw shaft and the nut, there is a problem that power saving cannot be achieved due to the friction generated therebetween. Therefore, by combining a screw shaft having a thread groove on the outer peripheral surface and a nut having a thread groove on the inner peripheral surface, and rolling a plurality of balls on a transfer path formed by both opposing screw grooves, It is conceivable to use a ball screw mechanism that can convert rotational motion and linear motion with a small frictional force.

  However, when such a ball screw mechanism is used, the control shaft of the variable valve mechanism of the internal combustion engine generates a high-frequency force generated by the camshaft drive, the direction of which can be changed in two forward and reverse directions. Then, it is also transmitted to the ball screw mechanism engaged with the control shaft. The force transmitted from the control shaft to the ball screw mechanism causes a relative movement between the nut and the screw shaft, but since the direction is not unidirectional, the screw shaft, nut, There was a problem that the collision with the ball was repeated, thereby generating abnormal noise and noise.

  The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a ball screw mechanism and a valve mechanism that can suppress noise and abnormal noise.

The ball screw mechanism of the present invention is
A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a plurality of rolling paths formed between the opposing screw grooves, and
A plurality of circulating members attached to the nut and returning the ball from one end of the rolling path to the other end;
When the female thread groove forming one rolling path is extended along the lead, the female thread groove forming another rolling path is displaced.

  In the ball screw mechanism of the present invention, when the female screw groove forming one rolling path is extended along the lead, the female screw groove forming the other rolling path is displaced, so that Due to such deviation, the ball pressing force between the female screw groove and the male screw groove forming one rolling path, and the ball between the female screw groove and the male screw groove forming another rolling path. Therefore, even when a high-frequency force is generated between the nut and the screw shaft, the direction of which can be changed in two forward and reverse directions, the generation of noise and abnormal noise can be suppressed. it can.

  Furthermore, in the axial cross section of the screw shaft, the normal line of the point where the ball contacts in the female thread groove forming one rolling path, and the point where the ball contacts the female thread groove forming another rolling path The normal line is preferably at least facing outward in the axial direction. In this case, the line of contact between the nut, ball and screw shaft in one rolling path (matches the normal) and the line of contact of the nut, ball and screw shaft in another rolling path (matches the normal) ) Intersects the axis of the screw shaft at positions separated from each other. Such an intersection is called an action point. The distance between the two action points becomes larger than the action point distance of the conventional ball screw mechanism in which the female screw groove is not displaced when extended along the lead, and can receive a larger moment load.

  Furthermore, it is preferable that the female thread groove forming one rolling path and the female thread groove forming another rolling path are discontinuous.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a valve operating mechanism capable of changing valve timing and valve lift using the ball screw mechanism and actuator according to the present embodiment. In FIG. 1, for easy understanding, two valves on the intake side of one cylinder of the internal combustion engine are illustrated.

  In FIG. 1, a drive shaft 101 rotatably attached to a cylinder head (not shown) and a control shaft 102 extend in parallel. A disc-shaped eccentric cam 101 a is formed on the drive shaft 101, and a disc-shaped eccentric cam 102 a is also formed on the control shaft 102. An upper portion of the first link 103 having a hole 103a that engages with the eccentric cam 101a of the drive shaft 101 extends to the control shaft 102 side, and a rocker having a hole 104a that engages with the eccentric cam 102a of the control shaft 102 The arm 104 is pivotally attached to one end. The upper end of the second link 105 is pivotally attached to the other end of the rocker arm 104, and the lower end of the second link 105 is attached to an output cam 106 that is swingably attached to the drive shaft 101. It arrange | positions so that it may contact | abut. The output cam 106 is in contact with the upper surfaces of a pair of cylindrical valve lifters 107, and each valve lifter 107 is in contact with the upper end of the stem of the valve 108.

  A position sensor 109 that detects the rotational position is attached to one end of the control shaft 102 that is a driven member, and a nut 5 is attached via a third link 110. The nut 5 and the screw shaft 4 are connected so as to be able to convert rotational motion and axial motion, and the screw shaft 4 and the electric motor 1 give a predetermined reduction ratio via the worm gear mechanism (2, 3). So that they are connected. The ECU 111 receives a signal from the position sensor 109 and controls the drive of the electric motor 1 accordingly.

  A worm 2 is formed at the tip of the rotating shaft 1a of the electric motor 1 fixed to a housing (not shown). The worm 2 meshes with the worm wheel 3. The worm wheel 3 is connected to a screw shaft 4, and a nut 5 is disposed around the screw shaft 4. The lower end of the third link 110 (also serving as a detent for the nut 5) is connected to the outer periphery of the nut 5, and the upper end thereof is connected to rotate integrally with the control shaft 102. The worm 2 and the worm wheel 3 constitute a worm gear mechanism.

  2 is a partial cross-sectional perspective view of a ball screw mechanism used in the valve mechanism of FIG. In FIG. 2, the ball screw mechanism includes a screw shaft 4 having a male screw groove 4a formed on the outer peripheral surface, and two female screw grooves 5a and 5b which are arranged so as to surround the screw shaft 4 and are discontinuous on the inner peripheral surface. Along with the formed nut 5 and a plurality of balls 6 arranged so as to be freely rollable along two rolling paths formed between the opposing screw grooves 4a, 5a and 5b, the nut 5 is attached to the nut 5. It consists of two circulation members (tops) 7 and 7 for returning the ball 6 from one end of the runway to the other end.

  FIG. 3 is an enlarged view showing an axial cross section of the ball screw mechanism according to the present embodiment. In FIG. 3, when the right female screw groove 5b is extended along the lead (with a constant lead angle), a virtual female screw groove (5B) is formed at a position indicated by a dotted line in the cross section of the figure. However, in the present embodiment, another female screw groove 5a is formed at a position shifted by a distance Δ with respect to the virtual female screw groove 5B. If the amount of deviation Δ is too large, the ball 6 will not enter any of the rolling paths, so it is desirable to set the amount of deviation Δ so that no play occurs when the balls 6 are loaded on the two rolling paths. . The male screw grooves 4a and the female screw grooves 5a and 5b all have the same pitch of 3 mm. Such female thread grooves 5 a and 5 b can be formed by using a tool that can move three-dimensionally within the nut 5.

  The operation of the valve mechanism of the present embodiment will be described. When the drive shaft 101 rotates in synchronization with a crankshaft (not shown), the eccentric cam 101a performs an eccentric motion to reciprocate the first link 103 up and down. When the first link 103 reciprocates up and down, the rocker arm 104 swings accordingly. As the rocker arm 104 swings, the second link 105 reciprocates up and down to swing the output cam 106. As the output cam 106 swings, the valve 108 reciprocates via a valve lifter 107 that abuts on the output cam 106.

  As described above, when the electric motor 1 is driven by the drive control of the ECU 111 and the rotating shaft 1a rotates, the meshed worm 2 and worm wheel 3 rotate, and the rotational force is transmitted to the screw shaft 4. . The rotation of the screw shaft 4 is smoothly converted into the axial movement of the nut 5 via the ball 6, and the lower end of the third link 110 swings, so that the control shaft 102 is rotationally displaced. Since the eccentric cam 102a is rotationally displaced according to the rotational position of the control shaft 102, and thereby the rocker arm 104 is displaced, a desired valve timing or the like can be set accordingly.

  FIG. 4 is a diagram illustrating changes in the position of the rocker arm 104 and the lift amount of the valve 108. For example, Δ1 (FIG. 4B), which is the difference between the top dead center (a) and the bottom dead center (b) when the control shaft 102 is set to the positions of FIGS. Compared to Δ2 (FIG. 4 (d)), which is the difference between the top dead center (c) and the bottom dead center (d) when the control shaft 102 is set to the position of FIGS. 4 (c) and 4 (d). can do. Furthermore, by rotating the control shaft 102 in synchronism with the drive shaft 101, the valve timing and phase can be changed.

  As shown in FIG. 3, due to the deviation Δ, a force F pressing the ball 6 between the female thread groove 5b and the male thread groove 4a forming one rolling path, and the female thread groove 5a and the male thread forming the other rolling path. A force F that presses the ball 6 is generated between the groove 4a and the force F has a component that opposes the axial direction, so that the direction is in two directions, the forward and reverse directions, between the nut 5 and the screw shaft 4. Even when a high-frequency force that can be changed is generated, the generation of noise and abnormal noise can be suppressed.

  FIG. 5 is an axial sectional view of a ball screw mechanism shown as a comparative example. In this comparative example, when the right female screw groove 5b ′ is extended along the lead, another female screw groove 5a is formed at a position shifted from the lead, but the ball is formed in the female screw groove 5b ′. The surface 6 contacts (the right side surface in FIG. 5) faces the surface (the left side surface in FIG. 5) where the ball 6 contacts the female thread groove 5a ′ outward in the axial direction.

  FIG. 6 is a cross-sectional view in the axial direction of the ball screw mechanism according to the present embodiment. In the present embodiment, the surface is the same as that shown in FIG. 3, but the surface on which the ball 6 contacts the female screw groove 5b (the left side surface in FIG. 6) is the surface on which the ball 6 contacts the female screw groove 5a (FIG. 6). And the right side surface).

  Here, when an axial force is generated between the screw shaft and the nut, the action line connecting the contact point between the female screw groove and the ball and the contact point between the male screw groove and the ball (matches the normal line at the contact point) The point that extends and intersects the axis of the screw shaft is defined as the point of action. As shown in FIG. 3, in the present embodiment, the direction of force is different in the two rolling paths, and there are two left and right, so two action points are generated.

  In the embodiment shown in FIG. 6 with respect to the comparative example shown in FIG. 5, the direction of the action line is reversed. Therefore, the action point P2 of the present embodiment is determined from the interval A between the action points P1 and P1 of the comparison example. , P2 has a larger interval B. This means that when the nut 5 receives the moment force M (see FIG. 2) with respect to the screw shaft 4, the present embodiment has higher rigidity than the comparative example. That is, according to the present embodiment, even when the nut 5 receives a moment force via the third link 110 of FIG.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

It is a perspective view of the valve operating mechanism which can change the valve timing and valve lift which are this Embodiment. It is a fragmentary sectional perspective view of the ball screw mechanism used for the valve operating mechanism of FIG. It is a figure which expands and shows the axial direction cross section of the ball screw mechanism concerning this Embodiment. It is a figure which shows the rocker arm 104 position and the change of the lift amount of the valve | bulb 108. FIG. It is an axial direction sectional view of a ball screw mechanism shown as a comparative example. It is a figure which expands and shows the arrow VI part of the structure of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric motor 1a Rotating shaft 2 Worm 3 Worm wheel 4 Screw shaft 4a Male thread groove 5 Nut 5B Virtual female thread groove 5a Female thread groove 5b Female thread groove 6 Ball 7 Circulating member 101 Drive shaft 101a Eccentric cam 102 Control shaft 102a Eccentric cam 103 Link 103a Hole 104 Rocker arm 104a Hole 105 Link 106 Output cam 107 Valve lifter 108 Valve 109 Position sensor 110 Link

Claims (4)

A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a plurality of rolling paths formed between the opposing screw grooves, and
A plurality of circulating members attached to the nut and returning the ball from one end of the rolling path to the other end;
A ball screw mechanism characterized in that when the female thread groove forming one rolling path is extended along the lead, the female thread groove forming another rolling path is displaced.   In the axial cross section of the screw shaft, the normal of the point where the ball contacts in the female thread groove forming one rolling path and the method of the point where the ball contacts the female thread groove forming another rolling path The ball screw mechanism according to claim 1, wherein the wire is opposed to at least an axially outward direction.   The ball screw mechanism according to claim 1 or 2, wherein the female screw groove forming one rolling path and the female screw groove forming another rolling path are discontinuous. A valve operating mechanism comprising the ball screw mechanism according to claim 1.

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