JP2014020405A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple ball screw capable of saving a space and energy, and having a braking function.SOLUTION: In the ball screw including a nut 20 having a spiral thread groove 20a on its inner periphery, and a screw shaft 18 internally inserted to the nut through a number of balls 19, and having a spiral thread groove 18a on its outer periphery, a braking nut 21 is connected to the nut 20 by a connection plate 27 through a small gap in the rotating direction and the radial direction while being free in the axial direction, and has a spiral thread groove 21a corresponding to the thread groove 18a of the screw shaft 18 on its inner periphery, a number of balls 19 are placed between both thread grooves, the gap between the braking nut 21 and the balls 19 is larger than the gap of the nut 20, a pin hole 25 penetrating to an outer peripheral face 21b is formed on the thread groove 21a of the braking nut 21, and the pin 26 is press-fitted thereto to be engaged in the thread groove 18a at its tip portion.

Description

  The present invention relates to a ball screw used in an actuator for a drive unit of a general industrial electric motor or automobile, and more specifically, an actuator such as an automobile transmission or a parking brake. It relates to a ball screw to be converted into

  In actuators used in various drive units, a gear mechanism such as a trapezoidal screw or a rack and pinion is generally used as a mechanism for converting the rotational motion of an electric motor into a linear motion in the axial direction. Since these conversion mechanisms involve a sliding contact portion, the power loss is large, and it is necessary to increase the size of the electric motor and increase the power consumption. Therefore, a ball screw has been adopted as a more efficient actuator.

  As a conventional actuator, for example, a nut constituting a ball screw can be driven to rotate by an electric motor supported by a housing, and the output member coupled to the screw shaft is displaced in the axial direction by rotating the nut. Possible (normal operation).

  With trapezoidal screws with sliding contact parts, the nut does not rotate even if axial force is applied to the screw shaft via the output member, and braking can be performed against the axial force. The nut is easily rotated (reverse operation) by the thrust load (axial force) acting on the output member side, so it is necessary to hold the output member when the electric motor is stopped. The position cannot be held. Thus, it can be said that there is a trade-off between good force transmission efficiency and position holding.

  Therefore, for example, a brake means is provided in an electric motor, or a low-efficiency thing such as a worm gear is provided as a transmission means. An actuator for a step transmission is known. This continuously variable transmission actuator is applied to a belt-type continuously variable transmission. A movable sheave 53 in which a main drive side V-groove pulley around which a transmission belt 51 is wound and a fixed sheave 52 is paired with an electric motor 54. A housing 55 to be fixed and a ball screw 56 provided in the housing 55 are provided.

  The fixed sheave 52 is restrained in the axial direction with respect to the housing 55, and the shaft portion 52 a is rotatably supported by the housing 55 by a pair of bearings 57 and 58. Rotational torque is transmitted to the shaft 52a from an input shaft (not shown) that is rotated according to the rotational speed of the engine (not shown).

  The movable sheave 53 is arranged coaxially with the fixed sheave 52 and is fitted to the shaft portion 52a of the fixed sheave 52 by a ball spline 59 so as to be slidable in the axial direction.

  The housing 55 has a cylindrical inner peripheral surface 55a provided at the same center as the axis of the movable sheave 53, and the cylindrical inner peripheral surface 55a is detachable. An inner shaft 61 connected via a bearing 60 fitted to the movable sheave 53 is inserted inside the cylindrical inner peripheral surface 55a. A shaft portion 52 a of the fixed sheave 52 is inserted through the inner periphery of the middle shaft 61. The movable sheave 53 and the middle shaft 61 are in a connected state in which only the relative rotation of the movable sheave 53 with respect to the middle shaft 61 is permitted by the bearing 60, and both the 53 and 61 move integrally in the axial direction.

  In the electric motor 54, the motor shaft 54 a is arranged in parallel with the axis of the fixed sheave 52, and the drive gear 62 provided on the motor shaft 54 a is rotatably supported by the pair of bearings 63 and 64 with respect to the housing 55. The intermediate gear 65 is engaged.

  The ball screw 56 includes a hollow screw shaft 66 having a helical thread groove 66a formed on the outer peripheral surface thereof, and a nut 67 having an outer peripheral surface formed with a helical screw groove 67a. And a large number of balls 68 accommodated in a rolling path formed by the opposing screw grooves 66a and 67a. The screw shaft 66 is supported so as not to rotate relative to the housing 55 and to be movable in the axial direction. The nut 67 is supported so as to be rotatable relative to the housing 55 and not movable in the axial direction.

  The driven gear 69 is formed on the outer periphery of the nut 67 and meshes with the intermediate gear 65. When the electric motor 54 rotates, the rotational power is transmitted from the drive gear 62 to the nut 67 through the intermediate gear 65 at a reduced speed. In this way, the screw shaft 66 is converted into a linear motion when the nut 67 is rotationally driven.

  The screw shaft 66 is formed integrally with a cup-shaped holder 71 that holds the double rows of balls 70 a and 70 b between the outer periphery of the middle shaft 61 and the cylindrical inner peripheral surface 55 a of the housing 55. On the outer periphery of the middle shaft 61, a pair of conical engagement surfaces 61a, 61b in the axial direction are formed so as to be continuous on the small diameter side.

  The retainer 71 has pockets 71a for equally arranging double rows of balls 70a and 70b in the circumferential direction. The pockets 71a are formed between a pair of engagement surfaces 61a and 61b and a cylindrical inner peripheral surface 55a. The double-row balls 70a and 70b are held in the wedge space.

  FIG. 12A is an enlarged view of the pocket 71a in a state where the electric motor 54 and the movable sheave 53 are stopped, with the cage 71 as the center. The double rows of balls 70a and 70b held in the pocket 71a are biased in a direction to engage with the wedge space by an elastic member 72 interposed therebetween.

  The convex engaging portion 73 protruding to the inner periphery of the cage 71 is fitted into a concave engaging portion 74 provided on the outer periphery of the middle shaft 61. That is, the convex engaging portion 73 is made of a transmission member press-fitted into the cage 71, and the concave engaging portion 74 is made of a concave hole formed on the outer periphery of the intermediate shaft 61.

  The convex engaging portion 73 and the concave engaging portion 74 are always engaged in the rotational direction and the radial direction, and are provided so as to face each other in the axial direction. An axial gap b larger than the axial pocket gap a of 71a is provided.

  Here, from the state of FIG. 12A, as shown in FIG. 12B, the electric motor 54 rotates in either the forward or reverse direction, and the nut 67 transmits the rotational power transmitted through the intermediate gear 65 to the driven gear. 69, when the screw shaft 66 moves to the right in the axial direction as indicated by an arrow in the figure, the retainer 71 also moves to the right in the axial direction together with the screw shaft 66.

  When the retainer 71 moves the distance b, the distance of the axial pocket gap a has already been moved, and the engagement with the wedge space is released by pushing the rear ball 70a in the integral movement direction. Yes. Further, when the retainer 71 moves in the same direction, since the convex engaging portion 73 and the concave engaging portion 74 are engaged in the axial direction, axial propulsive force is transmitted to the intermediate shaft 61, and the intermediate shaft 61 is movable. The sheave 53 is integrally moved to the right in the axial direction by the connection via the bearing 60 (see FIG. 11).

  Here, while the retainer 71 and the middle shaft 61 are moving together, even if the rear ball 70a in the integral movement direction tries to engage with the wedge space, the retainer 71 hits first and does not allow it. The integral movement of the movable sheave 53 continues. Therefore, the ball 70a on the rear side in the integral movement direction and the wedge space are not repeatedly engaged / disengaged, and vibration input to the screw shaft 66 is prevented.

  On the other hand, when the movable sheave 53 is rotated and the electric motor 54 is stopped, the middle shaft 61 itself is not rotating and the double row balls 70a and 70b are engaged with the wedge space. Even if 53 and the middle shaft 61 try to move together in the axial direction, the middle shaft 61 is instantly locked in the axial direction. That is, the movable sheave 53 and the middle shaft 61 do not move in the axial direction. Therefore, it is not necessary to generate a holding torque in the electric motor 54 to prevent the nut 67 from rotating, and the electric motor 54 can be reduced in size and power consumption can be reduced (see, for example, Patent Document 1).

JP 2007-263268 A

  In such a conventional continuously variable transmission actuator, a complicated braking mechanism is used to hold the movable sheave 53 in position when the electric motor 54 stops so that the nut 67 does not rotate easily due to a thrust load acting on the movable sheave 53. Not only is it necessary, but also a space for assembling the braking mechanism including the center shaft 61 and the retainer 71 and an assembling work are required.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a ball screw having a braking function while being simple and saving space and energy.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a nut having a spiral thread groove formed on the inner periphery, and is inserted into the nut via a large number of balls. A ball screw including a screw shaft formed with a spiral screw groove corresponding to the screw groove of the nut, wherein the nut is braked freely through the axial direction and through a slight gap in the rotational direction and the radial direction. And a braking mechanism that locks between the thread groove of the braking nut and the thread groove of the screw shaft during reverse operation.

  Thus, a nut having a spiral thread groove formed on the inner periphery, and a plurality of balls inserted into the nut, and a spiral thread groove corresponding to the thread groove of the nut formed on the outer periphery. In a ball screw provided with a screw shaft, a braking nut is connected to the nut through a slight gap in the axial direction and in a rotational direction and a radial direction. Since it has a lock mechanism that locks between the thread groove of the braking nut and the thread groove of the screw shaft, the braking nut can be easily used without causing adverse effects unless axial force is applied to the screw shaft. In addition to being able to rotate, when an axial force is applied to the screw shaft, friction is generated on the braking nut side, and the rotational resistance becomes very large. As a result, the axial force applied to the screw shaft up to a specific magnitude is not converted into the rotation of the braking nut, the position remains maintained, and the braking function can be exhibited against the axial force. Therefore, since the braking function is added to the ball screw alone, an extra device for braking is not required as in the prior art, and the structure can be simplified and the space can be saved. Here, the electric motor rotates the nut constituting the ball screw, and the movement of displacing the drive shaft coupled to the screw shaft by the rotational drive of the nut in the axial direction is defined as a normal operation, and the drive shaft The movement of the nut rotating by the acting thrust load (axial force) is defined as reverse operation.

  Preferably, as in the invention described in claim 2, a connecting plate is fixed to one of the nut and the braking nut, and the connecting plate is interposed through a slight gap in the rotation direction of the other nut. For example, the rotation of the nut can be efficiently converted into an axial force and the axial force is not converted into the rotation of the braking nut, and a braking function can be exerted on the axial force.

  Further, as in the invention described in claim 3, a slight clearance in the rotational direction of the nut and the braking nut is δr, an axial clearance of the braking nut is δa, and a ball center diameter of the nut is D. If the nut and the braking nut are connected via a slight gap δr consisting of δr = δa / L × Dπ, the backlash at the time of switching the rotation direction can be reduced and the brake can be sufficiently applied. Function.

  According to a fourth aspect of the present invention, the breaking nut is formed with a spiral thread groove corresponding to the thread groove of the screw shaft on the inner periphery, and a large number of balls are formed between the both thread grooves. A pin hole that is accommodated and has a clearance between the braking nut and the ball set to be larger than a clearance between the nut and the ball, and penetrates the outer peripheral surface of the braking nut in the thread groove of the braking nut If the pin is press-fitted into these pin holes and the tip of the pin is bulged into the thread groove of the screw shaft, the ball is restricted from moving in the circumferential direction and circulates on the thread groove. The braking function can be exhibited effectively.

  According to a fifth aspect of the present invention, the braking nut is formed in a cylindrical shape, and pin holes that penetrate from the inner peripheral surface to the outer peripheral surface are formed, and the pins are press-fitted into these pin holes. In addition, if the tip ends of these pins are formed into a convex spherical surface and bulge into the thread groove of the screw shaft, friction will not occur unless an axial force is applied to the screw shaft, and the braking nut is easy. When an axial force is applied to the screw shaft, friction occurs between the braking nut and the screw shaft like a slide screw, resulting in a very large rotational resistance and a braking function. can do.

  According to a sixth aspect of the present invention, the braking nut is formed in a cylindrical shape, and a spiral protrusion corresponding to the thread groove of the screw shaft is formed on the inner periphery. If the tip of the screw is engaged with the screw groove, when an axial force is applied to the screw shaft, friction occurs between the braking nut and the screw shaft like a slide screw, resulting in a very large rotational resistance. The braking function can be demonstrated.

  According to a seventh aspect of the present invention, a spiral groove is formed in a land surface between the screw grooves of the screw shaft, the braking nut is formed in a cylindrical shape, and an inner periphery of the screw shaft is formed. If a spiral groove that engages with the spiral groove is formed, the braking nut and the screw shaft are configured by a mechanism that locks the spiral shaft with each other, and friction is not caused unless axial force is applied to the screw shaft. The nut can be easily rotated, and when an axial force is applied to the screw shaft, friction is generated between the braking nut and the screw shaft, and the rotational resistance becomes very large. As a result, the axial force applied to the screw shaft is not converted into the rotation of the braking nut, the position is maintained, and the braking function can be exhibited against the axial force.

  A ball screw according to the present invention includes a nut having a spiral thread groove formed on the inner periphery thereof, and a spiral screw that is inserted into the nut via a number of balls and corresponds to the thread groove of the nut on the outer periphery. In a ball screw including a screw shaft formed with a groove, a braking nut is coupled to the nut through a slight gap in the axial direction and in a rotational direction and a radial direction. During reverse operation, it has a lock mechanism that locks between the thread groove of the braking nut and the thread groove of the screw shaft. The braking nut can easily rotate, and when an axial force is applied to the screw shaft, friction is generated on the braking nut side and the rotational resistance becomes very large. As a result, the axial force applied to the screw shaft up to a specific magnitude is not converted into the rotation of the braking nut, the position remains maintained, and the braking function can be exhibited against the axial force. Therefore, since the braking function is added to the ball screw alone, an extra device for braking is not required as in the prior art, and the structure can be simplified and the space can be saved.

1 is a longitudinal sectional view showing a first embodiment of a continuously variable transmission including a ball screw according to the present invention. It is a longitudinal cross-sectional view which shows the actuator part of FIG. It is a longitudinal cross-sectional view which shows the ball screw of FIG. 3A is a left side view of FIG. 3, FIG. 3B is a cross-sectional view taken along line IV-IV of FIG. 3, and FIG. 3C is a right side view of FIG. FIG. 4 is a perspective view, partly in section, showing the ball screw of FIG. 3. FIG. 6 is a perspective view, partly in section, showing a modification of FIG. 5. FIG. 7 is a perspective view, partly in section, showing another modification of FIG. 5. It is a longitudinal cross-sectional view which shows 2nd Embodiment of the continuously variable transmission provided with the ball screw which concerns on this invention. It is a longitudinal cross-sectional view which shows the actuator part of FIG. FIG. 10 is a perspective view, partly in section, showing the ball screw of FIG. 9. It is a longitudinal cross-sectional view which shows the actuator for continuously variable transmission provided with the conventional ball screw. (A) is an operation view showing a state where the electric motor and the movable sheave in FIG. 11 are stopped, and (b) is a state when the cage is moved from the state (a) in the direction of the arrow in the figure. FIG.

  A nut in which a spiral thread groove is formed on the inner periphery, and a screw shaft in which a spiral thread groove corresponding to the thread groove of the nut is formed on the outer periphery is inserted into the nut via a large number of balls. The braking nut is connected to the nut by a connecting plate that is axially free and has a slight gap in the rotational direction and radial direction, and the braking nut is connected to the screw on the inner periphery. A spiral thread groove corresponding to the thread groove of the shaft is formed, and a large number of balls are accommodated between the both thread grooves, and the clearance between the braking nut and the ball is larger than the clearance between the nut and the ball. And a pin hole penetrating the outer peripheral surface of the braking nut is formed in the thread groove of the braking nut, and a pin is press-fitted into these pin holes, and the tip portion thereof is the screw shaft. It is bulged in the screw groove.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a first embodiment of a continuously variable transmission for an automobile equipped with a ball screw according to the present invention, FIG. 2 is a longitudinal sectional view showing an actuator portion of FIG. 1, and FIG. 2 is a longitudinal sectional view showing the ball screw of FIG. 2, FIG. 4 (a) is a left side view of FIG. 3, (b) is a transverse sectional view taken along line IV-IV of FIG. 3, and (c) is a diagram. 3 is a perspective view showing a part of the ball screw shown in FIG. 3, FIG. 6 is a perspective view showing a modification of FIG. 5, and FIG. It is the perspective view which cut down a part showing other modifications.

  A continuously variable transmission 1 for an automobile shown in FIG. 1 includes a housing 2, an electric motor 3 attached to the housing 2, and an output gear 5 that meshes with an input gear 4 attached to a motor shaft 3 a of the electric motor 3. A reduction mechanism 6 comprising: a ball screw 8 for converting the rotational movement of the electric motor 3 into a linear movement in the axial direction of the drive shaft 7 via the reduction mechanism 6; and an actuator body 9 provided with the ball screw 8. I have.

  The housing 2 is formed by die casting from an aluminum alloy such as A6061 or ADC12, and is heated to a high temperature to form a solid solution, a quenching process in which it is rapidly cooled in water, and then kept at room temperature or at a low temperature ( A so-called precipitation hardening treatment, in which a large lattice strain is generated in the precipitate phase and hardened by a heat treatment composed of an age hardening treatment (tempering treatment) that is heated to 100 to 200 ° C. for precipitation, is performed. As a result, the mass productivity can be improved and the cost can be reduced. In addition, the strength can be increased to reduce the amount of aluminum used, and the weight can be reduced.

  The motor shaft 3a of the electric motor 3 has an input gear 4 made of a spur gear attached to its end so as not to be relatively rotatable by press fitting, and an output gear 5 meshing with the input gear 4 constitutes a ball screw 8 described later. It is fixed to the nut 20.

  The continuously variable transmission 1 is configured such that a primary sheave V-groove pulley around which a transmission belt 10 is wound and a stationary sheave 11 are paired with a movable sheave 12, and the movable sheave 12 is rotatable by a rolling bearing 15 including a deep groove ball bearing. And a sliding rod 14 to be supported. The sliding rod 14 is disposed coaxially with the fixed sheave 11 and is fitted to the housing 2 so as to be slidable in the axial direction by a ball spline 16.

  The fixed sheave 11 is constrained in the axial direction and is rotatably supported by a rolling bearing 13 formed of a deep groove ball bearing with respect to the shaft portion 11a. Rotational torque is transmitted to the shaft portion 11a from an input shaft (not shown) that is rotated according to the rotational speed of an engine (not shown).

  The drive shaft 7 is integrally formed with a screw shaft 18 constituting a ball screw 8 described later, and one end portion (left end portion in the figure) of the screw shaft 18 is integrally coupled to the sliding rod 14 via a connecting pin 17. The screw shaft 18 is supported so as not to rotate but to be movable in the axial direction.

  As shown in an enlarged view in FIG. 2, the ball screw 8 includes a screw shaft 18, and a nut 20 and a braking nut 21 that are externally inserted to the screw shaft 18 via a ball 19. The screw shaft 18 is formed with a spiral thread groove 18a on the outer periphery, and is supported so as to be axially movable and non-rotatable. On the other hand, the nut 20 and the braking nut 21 are extrapolated to the screw shaft 18, and spiral screw grooves 20a, 21a corresponding to the screw grooves 18a of the screw shaft 18 are formed on the inner periphery. A large number of balls 19 are accommodated between 21a and 18a so as to roll freely. The nut 20 and the braking nut 21 are supported on a housing (not shown) via support bearings 22 and 23 made of deep groove ball bearings so as to be rotatable and not movable in the axial direction. Reference numeral 24 denotes a piece member that constitutes a circulation member by connecting the screw grooves 20a of the nut 20 and the piece member 24 can circulate an infinite number of balls 19 infinitely.

  The cross-sectional shape of each thread groove 18a, 20a, 21a may be a circular arc shape or a gothic arc shape, but here a gothic arc in which the contact angle with the ball 19 is large and the axial gap can be set small. It is formed into a shape. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The nut 20 and the breaking nut 21 are made of case-hardened steel such as SCM415 and SCM420, and the surface thereof is subjected to hardening treatment in the range of 55 to 62HRC by vacuum carburizing and quenching. Thereby, the buffing etc. for the scale removal after the heat treatment can be omitted, and the cost can be reduced. On the other hand, the screw shaft 18 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and its surface is hardened in the range of 55 to 62 HRC by induction hardening or carburizing hardening.

  A small-diameter portion 20d is formed on the outer peripheral surface 20b of the nut 20 via a shoulder portion 20c. The output gear 5 constituting the speed reduction mechanism 6 is fitted and fixed to the small-diameter portion 20d until it abuts against the shoulder portion 20c, and the support bearing 22 is brought into contact with the side surface of the output gear 5 via a predetermined shimiro. It is press-fitted. On the other hand, a support bearing 23 is press-fitted into the outer peripheral surface 21b of the braking nut 21 via a predetermined squeeze. Thereby, even if a thrust load is applied from the drive shaft 7, it is possible to prevent the axial displacement between the support bearing 22 and the output gear 5. Further, the two support bearings 22 and 23 are constituted by sealed deep groove ball bearings having shield plates 22a and 23a attached to both ends, and leakage of the lubricating grease sealed inside the bearings from the outside This prevents wear powder from entering the bearing.

  Here, the gap between the braking nut 21 and the ball 19 is set larger than the gap between the nut 20 and the ball 19. In this embodiment, the size of the ball 19 is the same, and the dimension (curvature radius) of the thread groove 21 a of the braking nut 21 is set larger than the dimension (curvature radius) of the thread groove 20 a of the nut 20. Note that the size of the ball 19 may be changed by making the dimensions of the screw grooves 20a and 21a the same. In the former case, by using the balls 19 of the same size, problems such as misassembly can be prevented and assembly workability can be improved. In the latter case, the size of the ball 19 is appropriately adjusted to easily reduce the gap and eliminate the occurrence of play when assembling.

  Further, among the screw grooves 21 a of the braking nut 21, pin holes 25, 25 penetrating from the screw grooves 21 a, 21 a on the end surface side to the outer peripheral surface 21 b are formed, and the pins 26, 26 are formed in these pin holes 25, 25. Is press-fitted. The tip of the pin 26 is bulged into the screw groove 18 a of the screw shaft 18. Thereby, the movement of the ball 19 in the circumferential direction is restricted, the ball 19 is prevented from circulating on the screw groove 21a, and the ball 19 slides on the screw groove 21a by the rotation of the screw shaft 18. Further, as in the present embodiment, by forming the pin holes 25 in the screw grooves 21a and 21a on the end face side and press-fitting the pins 26, the balls 19 can be packed without gaps in the circumferential direction. Circumferential backlash can be eliminated.

  In the present embodiment, the nut 20 and the braking nut 21 are connected by a connecting plate 27. Specifically, as shown in FIGS. 3 and 4, a pair of flat surfaces 28, 28 are formed opposite to the outer peripheral surface 21 b of the braking nut 21, and in the axial direction on the outer peripheral surface 20 b of the nut 20. A pair of extending grooves 29, 29 are formed to face each other. A pair of connecting plates 27 are straddled between the flat surfaces 28 and 28 of the braking nut 21 and the concave grooves 29 and 29 of the nut 20, and are fixed to the braking nut 21 side by fixing bolts 30.

  Here, the connecting plate 27 is connected to the rotation direction (circumferential direction) of the nut 20 via a “slight gap”, and is not connected in the axial direction and the radial direction. Specifically, the concave groove 29 of the nut 20 is formed to be slightly 2E wider than the width dimension of the connecting plate 27, and the outer peripheral surface 20b of the nut 20 and the connecting plate 27 have a degree of freedom in both the axial direction and the radial direction. Is engaged. That is, the breaking nut 21 and the nut 20 are arranged with an axial interval A, the connecting plate 27 and the shoulder 20c of the nut 20 and a predetermined axial gap B, and the outer peripheral surface 20b and a predetermined radial gap. C is engaged via C.

  In order to connect the nut 20 and the breaking nut 21 freely in the axial direction, a slight axial gap A is provided between them, but in order to make the ball screw 8 more compact, the nut 20 and the breaking nut 21 are provided. The axial distance A can be reduced to half the distance of the lead length L of the ball screw 8 during assembly. It is not always necessary to provide a slight axial gap A between them, and for example, an elastic member such as synthetic rubber may be interposed. The same applies to the gap in the rotational direction.

  In addition, the smaller the clearance in the rotational direction between the connecting plate 27 and the nut 20, the smaller the backlash when switching the rotational direction, but conversely, the clearance in the rotational direction is limited to a specific range. Without this, the braking function cannot be fully exhibited. A “slight gap” that satisfies both conditions can be obtained by the following equation. Here, δr = δa / L × Dπ, where δr is a slight clearance in the rotational direction between the connecting plate 27 and the nut 20, δa is a clearance in the axial direction of the braking nut 21, and D is a ball center diameter of the nut 20. It is represented by

  In this way, in the ball screw 8, as shown in FIG. 5, in addition to the normal nut 20, a lock mechanism (pin 26 and screw groove 18a for locking between the screw groove 20a of the nut 20 and the screw groove 18a of the screw shaft 18 is provided. A braking nut 21 having an engagement structure) is set, the clearance between the braking nut 21 and the ball 19 is set larger than the clearance between the nut 20 and the ball 19, and the ball 19 on the braking nut 21 side is set. Is restricted by the pin 26 so as not to circulate, so that unless the axial force is applied to the screw shaft 18, it does not cause an adverse effect of friction, and the clearance with the ball 19 is large, so that it can easily rotate. Can do. However, when an axial force is applied to the screw shaft 18, the ball 19 on the braking nut 21 side does not circulate, so that friction occurs like a so-called slide screw and the rotational resistance becomes very large. As a result, the axial force applied to the screw shaft 18 to a specific magnitude is not converted into the rotation of the braking nut 21, and the position remains maintained, so that the braking function can be exhibited against the axial force.

  As a result, the position of the screw shaft 18 (drive shaft 7) of the ball screw 8 can be held without applying torque to the electric motor 3, so that the power consumption of the electric motor 3 to be used can be reduced and energy can be saved. The state of the apparatus can be maintained even when the power supply fails or the electric motor 3 is damaged. In addition, since the braking function is added to the ball screw 8 alone, an extra device for braking is not required as in the prior art, and the structure can be simplified and space saving can be achieved.

  When such a braking nut 21 is combined with a normal nut 20, specifically, as described above, a connecting plate 27 is fixed to the breaking nut 21, and the connecting plate 27 and the nut 20 are connected to each other in the rotational direction and radius. When a rotational torque is applied to a normal nut 20 by connecting with a slight gap in the direction and with a degree of freedom in the axial direction, the load generated between the nut 20 and the screw shaft 18 is the normal load. However, no load is applied to the braking nut 21 side.

  On the other hand, since the normal nut 20 and the braking nut 21 are connected in the rotational direction, the braking nut 21 rotates with the rotation of the nut 20. In this case, the braking nut 21 can be driven with a torque-axial force conversion efficiency almost equal to that of a normal ball screw with only a slight friction.

  On the other hand, when an axial force is applied in a state where there is no rotational torque, the nut 20 first slightly reversely rotates in the direction of releasing the load, but the braking nut 21 does not rotate. This is because the nut 20 and the braking nut 21 are connected by the connecting plate 27 and a clearance in the rotational direction is provided between the connecting plate 27 and the nut 20. Thus, the fully rotated nut 20 escapes from the load, and as a result, the axial load is transferred to the remaining braking nut 21. In this case, as described above, the braking nut 21 that has received the axial force exhibits a braking function, so that the axial force is not changed to rotation. Even after the braking function is exhibited, it can be released by applying a rotational torque of a specific magnitude or more to the nut 20 side. Therefore, since this type of action is a continuous process of gradually removing the frictional force, there is no sudden release of braking.

  Here, the embodiment in which the connecting plate 27 is fixed to the braking nut 21 and the nut 20 and the braking nut 21 are connected by the connecting plate 27 is illustrated, but the connecting plate 27 is not necessarily used. The nut 20 and the braking nut 21 may be connected via a slight gap in the rotational direction. For example, the braking nut may be provided with a protrusion extending in the axial direction, or may be connected with a pin or the like. . Further, the illustrated connecting plate 27 is not necessarily fixed to the braking nut 21 side, and may be fixed to the nut 20 to adopt the connecting method as described above.

Next, the case where the ball screw 8 according to the present invention is applied to a control mechanism of a continuously variable transmission of an automobile will be described with reference to FIG.
A transmission belt 10 that transmits torque of the continuously variable transmission 1 is sandwiched between a fixed sheave 11 and a movable sheave 12. Since the transmission belt 10 transmits force due to friction between the fixed sheave 11 and the movable sheave 12, a tension is always applied. A predetermined inclination is formed on the surface of the stationary sheave 11 and the movable sheave 12 on the side in which the transmission belt 10 is slidably contacted. There is a force to separate them. This force is transmitted to the screw shaft 18 of the ball screw 8 through the sliding rod 14.

  In the control mechanism, the position of the movable sheave 12 must be appropriately controlled while receiving such a load on the screw shaft 18. This control is performed by converting the torque applied from the electric motor 3 into the axial force of the screw shaft 18 via the nut 20 of the ball screw 8. With this axial force, the position of the movable sheave 12 can be moved by driving the screw shaft 18 of the ball screw 8 beyond the load received from the sliding rod 14.

  However, once the torque of the electric motor 3 is released, the screw shaft 18 tries to retreat (right side in the figure) again after the torque is released. As described above, this is nothing but the force that keeps the fixed sheave 11 and the movable sheave 12 away from each other always works. In order to prevent the screw shaft 18 from retreating, the braking nut 21 receives a load, and the ball screw 8 alone exhibits a braking function. Therefore, it is not necessary to keep driving the electric motor 3 in order to maintain the torque, and the electric motor 3 can be prevented from being damaged due to overheating and the system can save power.

  Even after braking is applied, if the torque of the electric motor 3 is further increased, the screw shaft 18 of the ball screw 8 can be moved forward (left side in the figure). At this time, braking is quickly and smoothly released. On the other hand, when it is desired to retract the screw shaft 18, it is only necessary to reversely rotate the electric motor 3. At this time, although the braking nut 21 exhibits a braking function, it can be driven easily with the help of the load from the sliding rod 14. Therefore, there is no problem that the braking is suddenly released and an impact or vibration occurs.

  FIG. 6 is a modification of the above-described embodiment (FIG. 5). This ball screw 31 is basically different from the above-described ball screw 8 only in the configuration of the braking nut side, and other parts and parts having the same parts or parts having the same functions are denoted by the same reference numerals. The detailed explanation is omitted.

  The ball screw 31 includes a screw shaft 18, and a nut 20 and a braking nut 32 that are externally inserted to the screw shaft 18 via a ball 19. The screw shaft 18 is formed with a spiral thread groove 18a on the outer periphery, and is supported so as to be axially movable and non-rotatable. On the other hand, the nut 20 and the braking nut 32 are extrapolated to the screw shaft 18, and a helical screw groove 20 a corresponding to the screw groove 18 a of the screw shaft 18 is formed on the inner periphery of the nut 20. A large number of balls 19 are accommodated so as to roll between the grooves 20a and 18a. The nut 20 and the braking nut 32 are supported so as to be rotatable with respect to the housing (not shown) and not movable in the axial direction.

  The breaking nut 32 is formed in a cylindrical shape, is made of case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62HRC by vacuum carburizing and quenching.

  Here, pin holes 25, 25 penetrating from the inner peripheral surface 32 a of the braking nut 32 to the outer peripheral surface 21 b are formed, and the pins 33, 33 are press-fitted into these pin holes 25, 25. The tip 33 a of the pin 33 is formed into a convex spherical surface and bulges into the screw groove 18 a of the screw shaft 18. As in the above-described embodiment, the gap between the braking nut 32 and the screw groove 18 a of the screw shaft 18 is set larger than the gap between the nut 20 and the ball 19. In this embodiment, the radius of curvature of the tip 33 a of the pin 33 is set smaller than the radius of the ball 19. As a result, as long as no axial force is applied to the screw shaft 18, friction does not occur, and the braking nut 32 can easily rotate. When an axial force is applied to the screw shaft 18, the brake nut 32 is braked like a slide screw. Friction is generated between the nut 32 and the screw shaft 18, and the rotational resistance becomes very large. That is, it has a lock mechanism (an engagement structure of the pin 33 and the screw groove 18a) that locks between the screw groove 20a of the nut 20 and the screw groove 18a of the screw shaft 18. As a result, as in the above-described embodiment, the axial force applied to the screw shaft 18 is not converted into the rotation of the braking nut 32, and the position remains maintained, and the braking function can be exerted on the axial force. it can.

  FIG. 7 shows another modification of the above-described embodiment (FIG. 5). This ball screw 34 is basically different from the above-described ball screw 8 only in the configuration of the braking nut side, and other parts and parts having the same parts or parts having the same functions are denoted by the same reference numerals. The detailed explanation is omitted.

  The ball screw 34 includes a screw shaft 18, and a nut 20 and a braking nut 35 that are externally inserted to the screw shaft 18 via a ball 19. The nut 20 and the braking nut 35 are extrapolated to the screw shaft 18, and a helical screw groove 20 a corresponding to the screw groove 18 a of the screw shaft 18 is formed on the inner periphery of the nut 20. , 18a, a large number of balls 19 are accommodated so as to roll freely. The nut 20 and the braking nut 35 are supported so as to be rotatable with respect to a housing (not shown) and not movable in the axial direction.

  The breaking nut 35 is made of case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62HRC by vacuum carburizing and quenching. The braking nut 35 is formed in a cylindrical shape, and a spiral ridge 36 corresponding to the thread groove 18a of the screw shaft 18 is formed on the inner periphery. Moreover, the front-end | tip part 36a of the protruding item | line 36 is formed in the predetermined gothic arc shape corresponding to the shape of the thread groove 18a, and is engaged with the thread groove 18a.

  As in the above-described embodiment, the gap between the braking nut 35 and the screw groove 18 a of the screw shaft 18 is set larger than the gap between the nut 20 and the ball 19. In the present embodiment, the radius of curvature of the tip 36 a of the ridge 36 is set to be smaller than the radius of the ball 19. As a result, unless the axial force is applied to the screw shaft 18, friction does not occur, and the braking nut 35 can easily rotate. When the axial force is applied to the screw shaft 18, the braking nut 35 and the screw Friction occurs between the shafts 18 and the rotational resistance becomes very large. As a result, as in the above-described embodiment, the axial force applied to the screw shaft 18 is not converted into the rotation of the braking nut 35, and the position remains maintained, and the braking function can be exerted on the axial force. it can.

  FIG. 8 is a longitudinal sectional view showing a second embodiment of a continuously variable transmission for an automobile equipped with a ball screw according to the present invention, FIG. 9 is a longitudinal sectional view showing an actuator part of FIG. 8, and FIG. FIG. 10 is a perspective view, partly in section, showing the ball screw of FIG. 9. In addition, the same code | symbol is attached | subjected to the component and site | part which has the same component same part as embodiment mentioned above, or the same function, and detailed description is abbreviate | omitted.

  The continuously variable transmission for an automobile shown in FIG. 8 includes a housing 2, an electric motor 3 attached to the housing 2, and an output gear 5 meshing with an input gear 4 attached to a motor shaft 3a of the electric motor 3. A speed reduction mechanism 6, a ball screw 38 that converts the rotational motion of the electric motor 3 into a linear motion in the axial direction of the drive shaft 37 via the speed reduction mechanism 6, and an actuator body 39 including the ball screw 38. ing.

  The motor shaft 3a of the electric motor 3 has an input gear 4 made of a spur gear attached to the end of the motor shaft 3a so as not to rotate relative to the motor shaft 3a, and an output gear 5 meshing with the input gear 4 constitutes a ball screw 38 to be described later. It is fixed to the nut 20.

  The drive shaft 37 is integrally formed with a screw shaft 40 constituting a ball screw 38 to be described later, and one end portion (left end portion in the figure) of the screw shaft 40 is connected to the sliding rod 14 constituting the continuously variable transmission. The screw shaft 40 is supported so as to be non-rotatable and movable in the axial direction.

  As shown in an enlarged view in FIG. 9, the ball screw 38 includes a screw shaft 40, and a nut 20 and a braking nut 41 that are externally inserted through the ball 19 to the screw shaft 40. The screw shaft 40 is formed with a spiral thread groove 18a on the outer periphery thereof, and is supported so as to be movable in the axial direction and not rotatable. On the other hand, the nut 20 and the braking nut 41 are extrapolated to the screw shaft 40, and a helical screw groove 20 a corresponding to the screw groove 18 a of the screw shaft 40 is formed on the inner periphery of the nut 20. A large number of balls 19 are accommodated so as to roll between the grooves 20a and 18a. The nut 20 and the braking nut 41 are supported by a housing (not shown) via the support bearings 22 and 23 so as to be rotatable and not movable in the axial direction.

  Here, the screw shaft 40 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and the spiral groove 42 is formed on the outer peripheral surface of the screw shaft 40, that is, the land surface between the screw grooves 18a and 18a. ing. And the hardening process is given to the range of 55-62HRC on the surface by induction hardening or carburizing hardening.

  The breaking nut 41 is made of case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62HRC by vacuum carburizing and quenching. The braking nut 41 is formed in a cylindrical shape, and a spiral groove 43 that engages with the spiral groove 42 of the screw shaft 40 is formed on the inner periphery.

  As in the above-described embodiment, the gap between the braking nut 41 and the screw shaft 40 is set larger than the gap between the nut 20 and the ball 19. In the present embodiment, as shown in FIG. 10, the braking nut 41 and the screw shaft 40 are formed by a sliding screw between the spiral grooves 42 and 43, so that friction is applied unless an axial force is applied to the screw shaft 40. The braking nut 41 can be easily rotated without being raised, and when an axial force is applied to the screw shaft 40, friction is generated between the braking nut 41 and the screw shaft 40, and the rotational resistance becomes very large. . As a result, as in the above-described embodiment, the axial force applied to the screw shaft 40 is not converted into the rotation of the braking nut 41, the position is maintained, and the braking function can be exerted on the axial force. it can.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  An electric linear actuator according to the present invention is used in a drive unit of a general industrial electric motor, automobile, etc., and has a ball screw mechanism that converts rotational input from an electric motor into linear motion of a drive shaft via the ball screw mechanism. It can be applied to the provided electric linear actuator.

DESCRIPTION OF SYMBOLS 1 Continuously variable transmission 2 Housing 3 Electric motor 3a Motor shaft 4 Input gear 5 Output gear 6 Reduction mechanism 7, 37 Drive shaft 8, 31, 34, 38 Ball screw 9, 39 Actuator body 10 Transmission belt 11 Fixed sheave 11a Shaft DESCRIPTION OF SYMBOLS 12 Movable sheaves 13 and 15 Rolling bearing 14 Sliding rod 16 Ball spline 17 Connection pin 18, 40 Screw shaft 18a, 20a, 21a Thread groove 19 Ball 20 Nut 20b Nut outer peripheral surface 20c Shoulder portion 20d Small diameter portion 21, 32, 35, 41 Brake nut 21b Brake nut outer peripheral surfaces 22, 23 Support bearings 22a, 23a Shield plate 24 Block member 25 Pin holes 26, 33 Pin 27 Connecting plate 28 Flat surface 29 Groove 30 Fixing bolt 32a Inner circumference of the brake nut Surface 33a Pin tip 36 ridge 36a ridge Tip portions 42, 43 spiral groove 51 transmission belt 52 fixed sheave 52a shaft portion 53 movable sheave 54 electric motor 54a motor shaft 55 housing 55a cylindrical inner peripheral surface 56 ball screw 57, 58, 60, 63, 64 bearing 59 ball spline 61 Middle shaft 61a, 61b Engagement surface 62 Drive gear 65 Intermediate gear 66 Screw shaft 66a, 67a Thread groove 67 Nut 68, 70a, 70b Ball 69 Driven gear 71 Retainer 71a Pocket 72 Elastic member 73 Convex engagement part 74 Concave engagement part A Axial spacing between braking nut and nut a Cage pocket clearance B Axial clearance b between connecting plate and nut groove b Axial clearance C between convex engaging portion and recessed engaging portion C Outer peripheral surface of connecting plate and nut Clearance in the radial direction of the ball D Center diameter of the ball nut E Clearance between the groove of the nut and the connecting plate L Lead length of the ball screw δa Axial clearance of the nut δr Slight clearance in the rotational direction of the connecting plate and nut

Claims (7)

A nut having a spiral thread groove formed on the inner periphery;
In a ball screw provided with a screw shaft that is inserted into the nut via a large number of balls and on the outer periphery of which a spiral screw groove corresponding to the screw groove of the nut is formed.
A braking nut is connected to the nut through a slight gap in the axial direction and in a rotational direction and a radial direction. When the braking nut is in reverse operation, the thread of the braking nut and the screw A ball screw characterized by having a lock mechanism for locking between screw grooves of a shaft.   The ball screw according to claim 1, wherein a connecting plate is fixed to one of the nut and the braking nut, and the connecting plate is connected via a slight gap in the rotation direction of the other nut.   When the slight clearance in the rotational direction of the nut and the braking nut is δr, the axial clearance of the braking nut is δa, and the ball center diameter of the nut is D, the nut and the braking nut are δr = δa The ball screw according to claim 1, wherein the ball screws are connected via a slight gap δr composed of / L × Dπ.   The braking nut is formed with a spiral thread groove corresponding to the thread groove of the screw shaft on the inner periphery, and a large number of balls are accommodated between both the thread grooves, and there is a gap between the braking nut and the ball. The pin is set to be larger than the gap between the nut and the ball, and a pin hole penetrating the outer peripheral surface of the braking nut is formed in the thread groove of the braking nut, and the pin is press-fitted into these pin holes. The ball screw according to any one of claims 1 to 3, wherein a tip portion thereof is bulged into a screw groove of the screw shaft.   The braking nut is formed in a cylindrical shape, and pin holes penetrating from the inner peripheral surface to the outer peripheral surface are drilled. The pins are press-fitted into these pin holes, and the tips of these pins are convex spherical surfaces. The ball screw according to claim 1, wherein the ball screw is formed and bulged in a thread groove of the screw shaft.   The braking nut is formed in a cylindrical shape, and a spiral protrusion corresponding to the thread groove of the screw shaft is formed on the inner periphery, and the tip of the protrusion is engaged with the thread groove. The ball screw according to any one of claims 1 to 3.   A spiral groove is formed on the land surface between the screw grooves of the screw shaft, the braking nut is formed in a cylindrical shape, and a spiral groove that engages with the spiral groove of the screw shaft is formed on the inner periphery. The ball screw according to any one of claims 1 to 3.

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