JP2004218651A - Ball screw mechanism and valve system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact ball screw mechanism of an excellent assembly property, and a valve system mechanism capable of obtaining variable valve timing or the like using an electric motor while saving energy. <P>SOLUTION: A roller bearing 11 having a plurality of rollers 11b is disposed between a housing 10 and a nut 5. The outer circumferential surface of the nut 5 forms the rolling surface of the roller bearing 11, and the nut 5 is assembled so as to be relatively movable in the axial direction to the roller bearing 11. After the bearing is assembled with the housing, the nut can be assembled therewith, and the assembly property becomes excellent while achieving a compact configuration by omitting an inner ring of the roller bearing 11. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ball screw mechanism and a valve operating mechanism, and more particularly to a valve operating mechanism capable of changing the opening / closing timing of a valve and a ball screw mechanism suitable for use in the valve operating mechanism.
[0002]
[Prior art]
2. Description of the Related Art In recent years, an internal combustion engine mounted on a vehicle often uses a variable valve timing type valve operating mechanism that changes a valve opening / closing timing according to an engine speed or a load. In such a valve operating mechanism, for example, by applying a hydraulic pressure, the phase between the sprocket and the camshaft synchronized with the crankshaft can be changed, thereby making the valve timing variable.
[0003]
However, in the above-described conventional valve operating mechanism, a hydraulic pressure is required to make the valve timing and the like variable, and therefore, it is necessary to provide a hydraulic pump. In an internal combustion engine, a hydraulic pump for lubricating various parts is generally installed.However, if hydraulic pressure is used to achieve variable valve timing or the like, a larger capacity hydraulic pump is required, and Since the motive power is taken out from the crankshaft, there is a problem that fuel consumption is deteriorated accordingly.
[0004]
On the other hand, a valve operating mechanism that changes valve timing or the like using the power of an electric motor is known as disclosed in, for example, Non-Patent Document 1 below. According to this technique, by changing the valve timing and the like using the power of the electric motor, it is not necessary to directly take out the power from the crankshaft, and the fuel efficiency can be improved.
[Non-patent document 1]
Journal of the Society of Automotive Engineers of Japan, Vol. 56, no. 2, 2002, P44-49
[0005]
[Problems to be solved by the invention]
By the way, in the valve train disclosed in Non-Patent Document 1, the driving force of the electric motor is transmitted to a control shaft that changes valve timing and the like via a ball screw mechanism including a screw shaft and a nut. ing. Here, in order to incorporate such a valve train into an internal combustion engine, it is necessary to incorporate each component more compactly. However, for example, a nut in a tube circulation type ball screw mechanism generally has a nut for returning a ball moving along a rolling path between the screw shaft and the nut on its outer periphery. Since the outer circumference is non-circular, there is a problem that the surrounding space cannot be effectively used. Therefore, in Patent Document 1 below, by using an end cap circulation type ball screw mechanism, the outer shape of the nut is made circular, and further, the inner raceway surface of the bearing is formed directly on the outer peripheral surface of the nut to reduce the dimension in the nut radial direction. It offers a compact configuration that is kept low.
[Patent Document 1]
JP 2000-310310 A
However, when the end cap type ball screw mechanism described in Patent Document 1 is used for the above-described valve mechanism, there is a problem in assembling the nut and the bearing into the housing. More specifically, after the bearing is assembled to the nut, the bearing is inserted into the housing. However, since the nut also serving as the inner ring of the bearing is long in the axial direction and is not completely cylindrical, the ball and the outer ring are connected to a normal bearing. It takes more time to assemble than when assembling to the inner ring. Also, when inserting the nut assembled into the housing with the bearing into the housing, if the outer ring and the housing are tightly fitted, they must be inserted using a jig, which is troublesome and costly. Increase. For example, if the outer ring is bisected in the axial direction, and the ball aligned with the inner ring raceway surface of the nut is sandwiched between the two axially opposite sides of the nut by the bisected outer ring, it is possible to further assemble the ball bearing around the outer periphery of the nut. Although easier to do, the difficulties of incorporating such nut and ball bearing assemblies into the housing still remain.
[0007]
The present invention has been made in view of the problems of the related art, and it is possible to achieve a variable valve timing and the like using an electric motor while achieving a compact ball screw mechanism with excellent assemblability and energy saving. It is an object of the present invention to provide a valve operating mechanism that can be used.
[0008]
[Means for Solving the Problems]
The ball screw mechanism of the present invention includes a screw shaft having a thread groove formed on an outer peripheral surface, a nut disposed to surround the screw shaft and having a thread groove formed on an inner peripheral surface, and a ball screw mechanism formed between the opposed screw grooves. In a ball screw mechanism having a plurality of balls arranged rotatably,
A bearing having a plurality of rolling elements is arranged between the housing and the nut, and an outer peripheral surface of the nut has a rolling surface of a rolling element of the bearing having a cylindrical or tapered shape. The nut is attached by moving the bearing relative to the bearing in the axial direction.
[0009]
[Action]
In the ball screw mechanism of the present invention, a bearing having a plurality of rolling elements is arranged between the housing and the nut, and an outer peripheral surface of the nut is a cylindrical or tapered rolling element of the bearing. Since the nut is assembled by moving the nut relative to the bearing in the axial direction, the nut is assembled after the bearing is assembled to the housing. This makes it possible to achieve a compact structure by omitting the inner ring of the bearing, while improving the ease of assembly. In order to assemble the nut by moving the nut relative to the bearing in the axial direction, if the bearing is a roller bearing, it is sufficient to simply provide the nut outer periphery with a highly accurate cylindrical surface, thereby reducing costs. However, an angular ball bearing may be used.
[0010]
Further, it is preferable that a gear for transmitting driving force is attached to an outer peripheral surface of the nut.
[0011]
Preferably, the gear is a worm wheel.
[0012]
Further, it is preferable that the ball screw mechanism is an end cap circulation type ball screw mechanism.
[0013]
Further, a valve mechanism capable of changing the open / close state of the valve is rotationally displaced, whereby a control shaft for changing the open / close state of the valve, an electric motor, and power for transmitting the power of the electric motor to the control shaft. Since the power transmission mechanism includes a worm gear mechanism and the above-described ball screw mechanism, by appropriately setting the worm lead of the worm gear mechanism, a stronger force is transmitted than the control shaft. Even in such a case, the transmission of the force to the electric motor is suppressed, whereby the rotational position of the control shaft can be maintained without constantly energizing the electric motor, thereby saving energy. The “open / closed state of the valve” refers to a valve timing, a valve lift amount, a phase, and the like, but is not limited thereto.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
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 including a ball screw mechanism according to the present embodiment and capable of changing valve timing and valve lift. In FIG. 1, two valves on the intake side of one cylinder of the internal combustion engine are illustrated for easy understanding.
[0015]
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 101a is formed on the drive shaft 101, and a disc-shaped eccentric cam 102a is also formed on the control shaft 102. A locker having an upper portion of a first link 103 having a hole 103a for engaging with the eccentric cam 101a of the drive shaft 101, extending toward the control shaft 102, and having a hole 104a for engaging with the eccentric cam 102a of the control shaft 102. The arm 104 is pivotally attached to one end. An upper end of a second link 105 is pivotally attached to the other end of the rocker arm 104, and a lower end of the second link 105 is connected to an output cam 106 that is swingably attached to the drive shaft 101. It is arranged to 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 stem upper end of the valve 108.
[0016]
At one end of the control shaft 102, a position sensor 109 for detecting its rotational position is attached, and is connected to the screw shaft 4 via a third link 110. The nut 5 and the screw shaft 4 are connected so as to be able to convert between rotational movement and axial movement, and the screw shaft 4 and the electric motor 1 have a predetermined reduction ratio via the worm gear mechanism (2, 3). Linked to give. The ECU 111 receives a signal from the position sensor 109 and drives and controls the electric motor 1 in accordance with the signal.
[0017]
FIG. 2 is a partial cross-sectional view showing a drive unit in the valve train of FIG. FIG. 3 is a diagram of the driving unit of FIG. 2 as viewed from the direction of arrow III. In FIG. 3, a worm 2 is formed at the tip of the rotating shaft 1a of the electric motor 1 fixed to the housing 10. The worm 2 meshes with the worm wheel 3. Note that the worm 2 and the worm wheel 3 constitute a worm gear mechanism.
[0018]
As shown in FIG. 2, the worm wheel 3, which is a gear for transmitting driving force, is press-fitted to a first outer peripheral surface 5f of a nut 5, which is a cylindrical upper surface, so as to rotate integrally. The nut 5 is rotatably supported by the second outer peripheral surface 5g, which is a cylindrical surface having a diameter larger than that of the first outer peripheral surface 5f, with the roller bearing 11 interposed in the opening 10a of the housing 10. The roller bearing 11 includes an outer ring 11a fitted into the opening 10a, a plurality of rollers 11b as rolling elements, and a retainer (not shown). The inner ring raceway surface (also referred to as a rolling surface) of the roller bearing 11 is provided. , 5 g of the second outer peripheral surface of the nut 5. Therefore, the outer diameter of the roller bearing 11 is reduced by the absence of the inner ring, which contributes to downsizing of the present embodiment.
[0019]
A third link 110 connected to the end of the screw shaft 4 passing through the nut 5 is pin-connected to a position other than the center of the control shaft 102. Four outer thread grooves 4a are formed on the outer peripheral surface of the screw shaft 4 (simplified and shown), and four inner thread grooves 5a are formed on the inner peripheral surface of the nut 5 surrounding the screw shaft 4. A large number of balls 6 are rotatably arranged in a space (rolling path) formed by the outer screw groove 4a and the inner screw groove 5a. The nut 5 has caps 5b at both ends, and the ball 6 is connected to one end of the thread grooves 4a, 5a via a passage 5c in the cap 5b and a passage 5d formed inside the nut 5. It is circulated to the end side.
[0020]
Assuming that the screw shaft 4 moves to the left in FIG. 2 in accordance with the nut 5 that rotates relatively, the screw shaft 4 moves about half the circumference (0) of the nut 5 along the first and second thread grooves 4a, 5a. The ball 6 which has been rolled for 0.5 times is scooped up by the passage of the end cap 5b at the position of one end of the nut 5, passes through the passage extending in the nut 5 in the axial direction, and passes through the other end of the nut 5. At the position, the screws are returned to the third and fourth thread grooves 4a and 5a, respectively.
[0021]
That is, in the case of the present embodiment, both ends of the rolling path formed of the first thread groove and the rolling path formed of the third screw groove in the nut 5 are connected to each other. Both ends of the rolling path formed of the second threaded groove and the rolling path formed of the fourth threaded groove in the nut 5 are connected to form a closed circuit. However, the pattern of the closed circuit is not limited to the above. The screw shaft 4, the nut 5, and the ball 6 constitute an end cap circulation type ball screw mechanism. Further, a power transmission mechanism is constituted by the end cap circulation type ball screw mechanism and the worm gear mechanism described above.
[0022]
The operation of the valve train will be described. When the drive shaft 101 rotates in synchronization with a crankshaft (not shown), the eccentric cam 101a moves eccentrically and reciprocates the first link 103 up and down. When the first link 103 reciprocates up and down, the rocker arm 104 swings accordingly. Due to the rocking movement of the rocker arm 104, the second link 105 reciprocates up and down, and rocks the output cam 106. The swing of the output cam 106 causes the valve 108 to reciprocate via the valve lifter 107 abutting on the output cam 106.
[0023]
As described above, when the electric motor 1 is driven by the drive control of the ECU 111 and the rotating shaft 1 a rotates, the meshed worm 2 and the worm wheel 3 rotate, and the torque is transmitted to the screw shaft 4. . The rotation of the screw shaft 4 is converted into the axial movement of the nut 5, and the control shaft 102 is rotationally displaced by moving the third link 110 along the axis. Since the eccentric cam 102a is rotationally displaced in accordance with 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.
[0024]
FIG. 4 is a diagram showing the position of the rocker arm 104 and the change in the lift amount of the valve 108. For example, Δ1 (FIG. 4 (b)), which is the difference between the top dead center (a) and the bottom dead center (b) when the control shaft 102 is set at the positions shown in FIGS. When the control shaft 102 is set at the positions shown in FIGS. 4C and 4D, it is larger than Δ2 (FIG. 4D), which is the difference between the top dead center (c) and the bottom dead center (d). can do. Further, by rotating the control shaft 102 in synchronization with the drive shaft 101, the valve timing and the phase can be changed.
[0025]
According to the present embodiment, for example, after the control shaft 102 is set at an arbitrary rotation position, even if a large force is applied to the rocker arm 104, the characteristic of the worm mechanism causes the screw shaft 4 to move from the screw shaft 4 to the electric motor 1 side. Since the transmission of the force is prevented, it is not necessary to always energize the electric motor 1, and energy can be saved. Further, in the present embodiment, the screw shaft 4 and the nut 5 have four thread grooves 4a, 5a, and the ball rolled from one end of the nut 5 to the other end along one thread groove. Since the nut 6 is returned to another thread groove, the axial length of the nut 5 can be shortened, and a compact valve mechanism can be provided.
[0026]
When assembling the nut 5 to the housing 10, the roller bearing 11 is first mounted in the opening 10a of the housing 10 (the rollers 11b are held at equal intervals by a retainer (not shown)), and then the roller bearing is mounted. The nut 5 is assembled by being moved relative to the inside of the nut 11 in the axial direction. According to the present embodiment, since the second outer peripheral surface 5g, which is the rolling surface of the roller 11b, is cylindrical, even if the roller bearing 11 is assembled to the housing 10, the nut 5 inwardly extends in the axial direction. Since smooth insertion is allowed, the nut 5 can be easily assembled.
[0027]
As described above, the present invention has been described with reference to the embodiments. However, the present invention should not be construed as being limited to the above embodiments, and it is needless to say that modifications and improvements can be made as appropriate. For example, the second outer peripheral surface 5g of the nut 5 may not be cylindrical but may be tapered in one direction. In this case, the roller bearing 11 is not a cylindrical roller bearing but a tapered roller bearing. Further, the number of threads and the number of turns of the screw groove are not limited to the above, and various combinations can be considered. Further, the present invention can be applied to a tube circulation type ball screw mechanism, but an end cap circulation type ball screw mechanism is more effective. In addition, any type of mechanism for changing the valve timing, the valve lift, the phase, and the like can be used regardless of the type shown in FIG.
[0028]
【The invention's effect】
In the ball screw mechanism of the present invention, a bearing having a plurality of rolling elements is arranged between the housing and the nut, and an outer peripheral surface of the nut is a rolling element of the bearing having a cylindrical or tapered shape. Since the nut is assembled by moving the nut relative to the bearing in the axial direction, the nut is assembled after the bearing is assembled to the housing. This makes it possible to achieve a compact structure by omitting the inner ring of the bearing, and to improve the assemblability.
[0029]
Further, a valve mechanism capable of changing the open / close state of the valve is rotationally displaced, whereby a control shaft for changing the open / close state of the valve, an electric motor, and power for transmitting the power of the electric motor to the control shaft. Transmission mechanism, the power transmission mechanism includes a worm gear mechanism and the above-described ball screw mechanism, so that even when a stronger force is transmitted than the control shaft due to the characteristics of the worm gear mechanism, the force is reduced to Transmission to the electric motor is suppressed, whereby the rotational position of the control shaft can be maintained without constantly energizing the electric motor, thereby saving energy.
[Brief description of the drawings]
FIG. 1 is a perspective view of a valve operating mechanism that can change a valve timing and a valve lift according to the present embodiment.
FIG. 2 is a partial cross-sectional view showing a drive unit (including a power transmission mechanism) in the valve train of FIG.
FIG. 3 is a view of the driving unit of FIG. 2 as viewed from a direction of an arrow.
FIG. 4 is a diagram showing a change in the position of the rocker arm 104 and a lift amount of a valve 108.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electric motor 2 Worm 3 Worm wheel 4 Screw shaft 5 Nut 6 Ball 10 Housing 11 Roller bearing 101 Drive shaft 102 Control shaft 104 Rocker arm 106 Output cam 108 Valve 111 ECU

Claims (5)

A screw shaft having a thread groove formed on the outer peripheral surface, a nut arranged to surround the screw shaft and having a thread groove formed on the inner peripheral surface, and a plurality of rollers arranged to be rotatable between the opposed screw grooves. And a ball screw mechanism having
A bearing having a plurality of rolling elements is arranged between the housing and the nut, and an outer peripheral surface of the nut has a rolling surface of a rolling element of the bearing having a cylindrical or tapered shape. The ball screw mechanism is characterized in that the nut is assembled by moving the nut relative to the bearing in the axial direction. The ball screw mechanism according to claim 1, wherein a gear for transmitting driving force is attached to an outer peripheral surface of the nut. The ball screw mechanism according to claim 2, wherein the gear is a worm wheel. The ball screw mechanism according to any one of claims 1 to 3, wherein the ball screw mechanism is an end cap circulation type ball screw mechanism. In a valve operating mechanism that can change the open / close state of the valve,
A control shaft that changes the open / close state of the valve by rotating and displacing,
An electric motor,
A power transmission mechanism for transmitting the power of the electric motor to the control shaft,
5. The valve train according to claim 1, wherein the power transmission mechanism includes a worm gear mechanism and the ball screw mechanism according to claim 1.

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