Direct drive

Abstract

A direct drive type driver has a ball screw device having a screw, a nut, and a plurality of balls, a piston installed to one end of the screw, and a stroke limiting mechanism that sets a work start time in a first direction in which the screw is directed to the one end. The nut has an end surface facing the first direction and a protruding portion protruding from the end surface. The piston has an opposite surface facing a second direction opposite to the first direction and opposite to the end surface, an avoidance groove portion recessed from the opposite surface in the first direction and extending in a rotation direction with the screw as a center, and a step surface disposed at an end portion of the avoidance groove portion in one direction in the rotation direction among wall surfaces surrounding the avoidance groove portion and facing the other direction in the rotation direction. The protruding portion and the step surface abut to constitute the stroke limiting mechanism.

Description

Technical Field

[0001] This invention relates to a direct-acting drive equipped with a ball screw device. Background Technology

[0002] A direct-acting actuator is a device equipped with a ball screw mechanism that converts rotary motion into linear motion. In a direct-acting actuator, when the nut rotates, the amount of protrusion of the screw protruding from the nut changes. As a result, an object mounted at the end of the screw is displaced along the axial direction. A piston can be used as the object mounted at the end of the screw. Such a direct-acting actuator is used in a brake booster, as shown, for example, in Patent Document 1.

[0003] As shown in Patent Document 2, the direct-acting drive has a stroke limiting mechanism. By employing this stroke limiting mechanism, the start time of the lead screw's movement (the start time of operation) can be kept constant.

[0004] To elaborate further, in the stroke limiting mechanism of Patent Document 2, a protrusion is provided on the end face of the nut. On the other hand, an anti-rotation member is installed at the end of the lead screw. The anti-rotation member has a locking portion protruding radially outward from the end of the lead screw. When the amount of protrusion of the lead screw decreases due to the rotation of the nut, the anti-rotation member approaches the nut, and the locking portion contacts the protrusion. Thus, the rotation of the nut is restricted, and the position of the lead screw in the axial direction is fixed.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2016-014437

[0008] Patent Document 2: Japanese Patent Application Publication No. 2019-113168 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] In the stroke limiting mechanism of Patent Document 2, the anti-rotation member is independent of the lead screw. Furthermore, since the anti-rotation member is mounted on the lead screw, its weight becomes an obstacle when improving the operability of the direct-acting drive. Additionally, because the anti-rotation member is mounted at the end of the lead screw, space is required for arranging the lead screw and the anti-rotation member.

[0011] The present invention was made in view of the above-mentioned problems, and its object is to provide a direct-acting actuator that can reduce the number of components, reduce weight and miniaturize.

[0012] Solution for solving the problem

[0013] To achieve the above objectives, one technical solution of the present invention provides a direct-acting actuator, wherein the direct-acting actuator comprises: a ball screw assembly having a screw, a nut, and a plurality of balls; a piston mounted at one end of the screw; and a stroke limiting mechanism for setting the start time of operation of the screw in a first direction pointing to the one end. The nut has an end face facing the first direction and a protrusion protruding from the end face. The piston has: an opposing face facing a second direction opposite to the first direction and opposite to the end face; a clearance groove recessed from the opposing face in the first direction and extending in a rotational direction centered on the screw; and a stepped surface disposed at the end of the wall surrounding the clearance groove in one of the rotational directions and facing the other direction of rotation. The protrusion and the stepped surface abut against each other to form the stroke limiting mechanism.

[0014] By employing this invention, a stepped surface is provided on the piston instead of an anti-rotation member. This reduces the number of components. Furthermore, the operability of the direct-acting actuator is improved by making the lead screw lighter compared to conventional methods. Additionally, since the anti-rotation member is absent, the direct-acting actuator can be miniaturized. Moreover, by contacting the protrusion, the load input to the stepped surface is distributed across the piston. Therefore, stress concentration at the stepped surface area can be suppressed.

[0015] As a preferred embodiment of the aforementioned direct-acting actuator, the piston has a bottom surface that surrounds the avoidance groove in the first direction. At least a portion of the bottom surface is inclined in a spiral shape in the first direction as it is oriented toward one of the rotational directions.

[0016] According to the aforementioned structure, compared to the case where the recess amount of the avoidance groove is constant in the circumferential direction, the recess amount of the avoidance groove can be reduced. In other words, it is possible to prevent the piston volume from becoming smaller. Consequently, the load input to the step surface becomes easier to distribute, and stress concentration can be suppressed.

[0017] As a preferred embodiment of the aforementioned direct-acting actuator, the piston has a bottom surface that surrounds the avoidance groove in the first direction. At least a portion of the bottom surface is stepped in the first direction as it moves toward one of the rotational directions, thus forming a stepped shape.

[0018] According to the aforementioned structure, compared to the case where the recess amount of the avoidance groove is constant in the circumferential direction, the recess amount of the avoidance groove can be reduced. In other words, it is possible to prevent the piston volume from becoming smaller. Consequently, the load input to the step surface becomes easier to distribute, and stress concentration can be suppressed.

[0019] As a technical solution for the aforementioned direct-acting actuator, the piston may also have a bottom surface that surrounds the avoidance groove in the first direction. At least a portion of the bottom surface is flat.

[0020] As a technical solution for the aforementioned direct-acting actuator, the piston may also have a stop member, the surface of which faces another direction of rotation becoming the stepped surface.

[0021] As a preferred embodiment of the aforementioned direct-acting actuator, the piston has an inner cylinder portion located radially inward of the stop member, and has a fitting hole that opens in the second direction and allows one end of the lead screw to engage. The radially inward end of the stop member is connected to the inner cylinder portion.

[0022] According to the structure described, the load acting on the stop is distributed throughout the inner cylinder. Therefore, stress concentration on the stop can be suppressed.

[0023] As a preferred embodiment of the aforementioned direct-acting actuator, the piston has an outer cylinder portion located radially outward from the stop member, and the outer circumferential surface of the outer cylinder portion slides relative to the housing. The radially outward end of the stop member is connected to the outer cylinder portion.

[0024] According to the structure described, the load acting on the stop is distributed across the outer cylinder. Therefore, stress concentration on the stop can be suppressed.

[0025] As a preferred embodiment of the aforementioned direct-acting actuator, the piston has a first end face facing the first direction. On this first end face, a protrusion extending in the first direction is provided at a position overlapping the avoidance groove when viewed from an axis parallel to the lead screw. The amount of protrusion of the protrusion corresponds to the amount of recess in the avoidance groove.

[0026] According to the aforementioned structure, the thickness in the axial direction of the portion forming the avoidance groove can be made uniform. Furthermore, since the stepped surface and the stop are covered by the outer cylinder, they cannot be visually identified during lead screw assembly. Therefore, determining the phase of the stepped surface and the stop becomes difficult during lead screw assembly. However, the phase of the stepped surface and the stop can be determined based on the shape of the protrusion. Therefore, determining the phase of the stepped surface and the stop becomes easy during lead screw assembly.

[0027] As a preferred embodiment of the aforementioned direct-acting actuator, the protrusion has an abutting surface that abuts against the stepped surface. When viewed from an axis parallel to the lead screw, the stepped surface is parallel to a first imaginary line extending radially and is positioned in another direction within the rotational direction. When viewed from the axial direction, the abutting surface is parallel to a second imaginary line extending radially and is positioned in another direction within the rotational direction. The distance between the stepped surface and the first imaginary line is greater than the distance between the abutting surface and the second imaginary line.

[0028] According to the structure, the stepped surface and the abutting surface are in contact with each other on their radially inner sides. Therefore, loads are less likely to be applied to the radially outer sides of the stepped surface and the abutting surface, respectively.

[0029] As a preferred embodiment of the aforementioned direct-acting actuator, the nut is made of an iron-based material. The piston is made of an aluminum alloy.

[0030] According to the structure, when the protrusion comes into contact with the stepped surface, the stepped surface (piston) is easily plastically deformed.

[0031] The effects of the invention

[0032] The direct-acting actuator of the present invention enables the reduction of the number of components, weight reduction, and miniaturization. Attached Figure Description

[0033] Figure 1 It is a cross-sectional view obtained by cutting the direct-acting drive of Embodiment 1 along the axial direction.

[0034] Figure 2 This is a perspective view of the nut in Embodiment 1 viewed from an oblique angle in the first direction.

[0035] Figure 3 This is a perspective view of the piston in Embodiment 1 from a second oblique angle.

[0036] Figure 4 yes Figure 3 Sectional view in direction IV-IV.

[0037] Figure 5 This is a three-dimensional view of the piston in modified example 1, viewed from an oblique angle in the second direction.

[0038] Figure 6 This is a three-dimensional view of the piston in modified example 2, viewed from an oblique angle in the second direction.

[0039] Figure 7 This is a three-dimensional view of the piston in modified example 3, viewed from an oblique angle in the second direction.

[0040] Figure 8 This is a three-dimensional view of the piston in modified example 4, viewed from an oblique angle from the second direction.

[0041] Figure 9 This is a plan view of the piston in modified example 5 as viewed from the second direction.

[0042] Figure 10 This is a cross-sectional view obtained by cutting the piston of deformed example 6 along the axial direction.

[0043] Figure 11 This is a plan view of the piston in modified example 7 as viewed from the second direction.

[0044] Figure 12 This is a plan view of the nut in modified example 7 as viewed from the first direction.

[0045] Figure 13 This is a cross-sectional view showing the state in which the stop and the protrusion are in contact in the direct-acting drive of Modified Example 7.

[0046] Figure 14 This is a cross-sectional view showing the state in which the stop and the protrusion are in contact in the direct-acting drive of the comparative example.

[0047] Figure 15 This is a plan view of the piston in modified example 8 as viewed from the first direction.

[0048] Figure 16 This is a cross-sectional view of the direct-acting drive according to Embodiment 2.

[0049] Figure 17 This is a perspective view of the nut in Embodiment 2.

[0050] Figure 18 This is a perspective view of the piston in Embodiment 2. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings. Furthermore, the present invention is not intended to be limited to the manner in which it is carried out (hereinafter referred to as the embodiments). Additionally, the constituent elements in the following embodiments include elements readily conceived by those skilled in the art, substantially the same elements, and elements of so-called equivalent scope. Moreover, the constituent elements disclosed in the following embodiments can be appropriately combined.

[0052] Figure 1 It is a cross-sectional view obtained by cutting the direct-acting drive of Embodiment 1 along the axial direction. Figure 2 This is a perspective view of the nut in Embodiment 1 viewed from an oblique angle in the first direction. Figure 3 This is a perspective view of the piston in Embodiment 1 from a second oblique angle. Figure 4 yes Figure 3 Sectional view in direction IV-IV.

[0053] (Implementation Method 1)

[0054] The direct-acting actuator 100 of embodiment 1, mounted in a vehicle, is a brake booster that generates hydraulic pressure corresponding to the amount of pressure applied to the brake pedal. For example... Figure 1 As shown, the direct-acting drive 100 includes a motor 101, a transmission device 102, a housing 103, a ball screw device 110, a piston 120, and a stroke limiting mechanism 140.

[0055] Hereinafter, the direction parallel to the axis O of the lead screw 112 of the ball screw assembly 110 will be referred to as the axial direction. In addition, the direction in the axial direction in which the piston 120 is arranged when viewed from the nut 111 of the ball screw assembly 110 will be referred to as the first direction X1, and the direction opposite to the first direction X1 will be referred to as the second direction X2.

[0056] Motor 101 includes a stator (not shown), a rotor (not shown), and an output shaft 101a. Power is supplied to motor 101 from a power source (not shown) to rotate the rotor and output shaft 101a. Motor 101 is supported on housing 103, and output shaft 101a is parallel to lead screw 112.

[0057] The transmission device 102 includes a first gear 104 that engages with the output shaft 101a of the motor 101 and a second gear 105 that engages with the outer periphery of the nut 111. The second gear 105 is a gear with a diameter larger than that of the first gear 104. Therefore, the transmission device 102 reduces the rotational motion generated by the motor 101 and transmits it to the nut 111.

[0058] The ball screw assembly 110 includes a nut 111, a screw 112, and a plurality of balls 113. The nut 111 is cylindrical about an axis O. An inner circumferential track surface 111a is provided on the inner circumferential surface of the nut 111. The nut 111 is supported by a bearing 106 that fits into the inner circumferential surface of the housing 103. Thus, the nut 111 can rotate freely about the axis O of the screw 112.

[0059] The following explanation of the rotation direction of nut 111 is based on the view from the first direction X1. Furthermore, as... Figure 2 As shown, when viewed from the first direction X1, the direction of rotation to the left with respect to axis O is called the first rotation direction L1. The direction of rotation to the right with respect to axis O is called the second rotation direction L2.

[0060] like Figure 2 As shown, the nut 111 has an end face 116 facing a first direction X1. A protrusion 117 protruding in the first direction X1 is provided on the end face 116. The protrusion 117 is approximately trapezoidal in shape when viewed from the axial direction. The protrusion 117 has an abutment surface 118 facing the first rotational direction L1.

[0061] like Figure 1 As shown, the lead screw 112 is a solid shaft component that passes through the nut 111. The lead screw 112 includes a lead screw body 114 with an outer peripheral track surface 114a on its outer peripheral surface and a mounting portion 115 extending from the end face of the lead screw body 114 in the first direction X1. The lead screw body 114 is supported on the housing 103 in a manner that allows it to move freely along the axial direction but prevents it from rotating about the axis O, which is not shown in detail.

[0062] The inner circumferential track surface 111a and the outer circumferential track surface 114a form a spiral track. Multiple balls 113 are arranged on this spiral track. When the nut 111 rotates, the inner circumferential track surface 111a presses against the outer circumferential track surface 114a along the axial direction via the balls 113. This causes the lead screw 112 to move along the axial direction. Furthermore, in this embodiment, when the nut 111 rotates along the second rotational direction L2, the lead screw 112 moves along the first direction X1. On the other hand, when the nut 111 rotates along the first rotational direction L1, the lead screw 112 moves along the second direction X2.

[0063] The diameter of the mounting portion 115 is smaller than the diameter of the lead screw body 114. Therefore, an annular stepped surface 115a facing the first direction X1 is provided at the boundary between the mounting portion 115 and the lead screw body 114.

[0064] The piston 120 is a cylindrical component coaxially arranged with the shaft O. The piston 120 is preferably manufactured by forging, but it can also be formed by known machining methods such as cutting. The piston 120 is located inside the cylinder body 107 at the end closest to the second direction X2. Furthermore, in this embodiment, the cylinder body 107 and the housing 103 are integrally formed, but in this invention, the cylinder body 107 and the housing 103 can also be independent of each other. Brake fluid (not shown) is stored inside the cylinder body 107. The piston 120 has a first end face 121 facing the first direction X1 and a second end face 122 facing the second direction X2.

[0065] A concave surface 121a is provided on the first end face 121, which is recessed in the second direction X2. The concave surface 121a faces the bottom surface 107b of the cylinder body 107. A helical spring (not shown) is disposed between the concave surface 121a and the bottom surface 107b. When the piston 120 is pressed in the first direction X1, the piston 120 moves against the force of the helical spring (not shown). Alternatively, the piston of the present invention may not have the concave surface 121a.

[0066] like Figure 3 As shown, a fitting hole 123 opening in the second direction X2 is provided at the center of the second end face 122. A mounting part 115 (one end of the lead screw 112) is inserted into the fitting hole 123 (see reference). Figure 1The inner diameter of the fitting hole 123 is slightly smaller than the outer diameter of the mounting portion 115, and an interference fit is provided. Therefore, the piston 120 moves integrally with the lead screw 112 along the axial direction without separating from the lead screw 112.

[0067] Hereinafter, the portion of the piston 120 that engages with the mounting portion 115 (the cylindrical wall surrounding the outer periphery of the engagement hole 123) will be referred to as the inner cylinder portion 124. Figure 1 As shown, the end face 124a of the inner cylinder portion 124 in the second direction X2 abuts against the annular stepped surface 115a of the lead screw 112.

[0068] like Figure 1 As shown, the outer circumferential surface of the piston 120 slidably abuts against the sealing member 108 on the inner circumferential side of the cylinder 107. Thus, brake fluid (not shown) is sealed and does not flow towards the side where the nut 111 and lead screw 112 are located.

[0069] The outer diameter of piston 120 is larger than the outer diameter of nut 111. An annular outer cylinder portion 125 protrudes in a second direction X2 and surrounds the outer periphery of nut 111 on the second end face 122 of piston 120. That is, the outer periphery of piston 120 extends in the second direction X2 through the outer cylinder portion 125. Therefore, even if piston 120 moves in the first direction X1, the outer cylinder portion 125 and sealing member 108 will slide in contact, thereby maintaining a seal.

[0070] A portion of the second end face 122 of the piston 120 becomes a facing face 126 opposite to one end face 116 of the nut 111. The facing face 126 is located radially outside the inner cylinder portion 124 and radially inside the outer cylinder portion 125.

[0071] like Figure 3 As shown, a portion of the opposing surface 126 has a recessed avoidance groove 127 extending in the first direction X1. The avoidance groove 127 extends in the rotational direction with the axis O as the center, and appears as an arc (C-shape) when viewed from the axial direction. This avoidance groove 127 is a space for avoiding contact with the protrusion 117 of the nut 111. Hereinafter, the wall surface surrounding the avoidance groove 127 from the first direction X1 will be referred to as the bottom surface 129.

[0072] like Figure 3 , Figure 4As shown, the depth of the recess in the avoidance groove 127 gradually increases from the opposing surface 126 toward the first rotational direction L1. Therefore, the bottom surface 129 of the avoidance groove 127 also becomes a spiral surface located in the first direction X1 as it moves toward the first rotational direction L1. Furthermore, a stepped surface 130 is provided at the end of the avoidance groove 127 in the first rotational direction L1 between the opposing surface 126 and the bottom surface 129. On the other hand, an edge line 131 serving as the boundary line between the opposing surface 126 and the bottom surface 129 is provided at the end of the avoidance groove 127 in the second rotational direction L2.

[0073] As described above, the avoidance groove 127 is a space used to avoid contact with the protrusion 117. Therefore, the inclination angle of the bottom surface 129 of the avoidance groove 127 is set to be perpendicular to the inner circumferential track surface 111a (see reference). Figure 1 The tilt angle is the same as that of the inner circumferential track surface 111a, or it is set to be greater than the tilt angle of the inner circumferential track surface 111a.

[0074] The portion of the opposing surface 126 without the avoidance groove 127 becomes the stop 128. The side surface of the stop 128 in the second rotational direction L2 becomes the stepped surface 130. When viewed from the axial direction, the stop 128 has a generally trapezoidal shape. Figure 3 As shown, the radially inner end of the stop member 128 is connected to the inner cylinder portion 124. The radially outer end of the stop member 128 is connected to the outer cylinder portion 125.

[0075] Next, the operation of the direct-acting actuator 100 of Embodiment 1 will be described. When the motor 101 is driven, the rotational motion is transmitted to the nut 111 via the transmission device 102. This causes the nut 111 to rotate. Furthermore, when the rotation direction of the nut 111 is the second rotational direction L2, the lead screw 112 moves along the first direction X1. Simultaneously, the piston 120 also moves along the first direction X1, increasing the hydraulic pressure of the brake fluid. As a result, the hydraulic pressure of the brake fluid is transmitted to an external device through the through-hole 107a.

[0076] On the other hand, as the nut 111 rotates along the first rotation direction L1, the lead screw 112 moves along the second direction X2. Simultaneously, the piston 120 moves along the second direction X2, reducing the hydraulic pressure of the brake fluid. Furthermore, the distance between the second end face 122 of the piston 120 and one end face 116 of the nut 111 gradually decreases. Also, the protrusion 117 of the nut 111 enters the avoidance groove 127 of the piston 120 while rotating along the first rotation direction L1.

[0077] After entering the avoidance groove 127, the protrusion 117 rotates further along the first rotation direction L1 and contacts the stepped surface 130 of the stop member 128. As a result, the rotation of the nut 111 in the first rotation direction L1 stops. Furthermore, after the rotation of the nut 111 stops, the contact surface 118 of the nut 111 and the stepped surface 130 of the piston 120 come into contact (see reference). Figure 4 Therefore, the rotation of the nut 111 in the first rotational direction L1 is restricted. Correspondingly, the movement of the lead screw 112 in the second direction X2 is also restricted. Thus, when the direct-acting drive 100 is about to perform its next operation, it will begin from the state where the protrusion 117 and the stepped surface 130 are in contact. In this way, the starting time of the axial movement of the lead screw 112 (the start time of operation) is constant. That is, the protrusion 117 (the contact surface) and the stop 128 (the stepped surface 130) constitute the stroke limiting mechanism 140.

[0078] Furthermore, when the protrusion 117 contacts the stepped surface 130, the load is input from the protrusion 117 to the stop 128. Since the stop 128 is integrally formed with the piston 120, the load is distributed to the piston 120. In addition, the stop 128 is continuous with the inner cylinder 124 and the outer cylinder 125, so the load is easily distributed to the inner cylinder 124 and the outer cylinder 125. Therefore, the load input to the stop 128 is distributed in various parts, and the stress does not concentrate on the stop 128.

[0079] The direct-acting actuator 100 of Embodiment 1 includes: a ball screw assembly 110 having a screw 112, a nut 111, and a plurality of balls 113; a piston 120 mounted on one end of the screw 112; and a stroke limiting mechanism 140 that sets the start time of operation of the screw 112 in a first direction X1 pointing towards one end. The nut 111 has an end face 116 facing the first direction X1 and a protrusion 117 protruding from the end face 116. The piston 120 has: a facing surface 126 facing a second direction X2 opposite to the first direction X1 and facing an end face 116; a recessed groove 127 extending from the facing surface 126 in the first direction X1 and extending in the rotational direction with the lead screw 112 as the center; and a stepped surface 130 disposed in the wall surrounding the recessed groove 127 at the end of one direction (first rotational direction L1) of the rotational direction of the recessed groove 127 and facing the other direction (second rotational direction L2). The protrusion 117 and the stepped surface 130 abut against each other to form a stroke limiting mechanism 140.

[0080] According to Embodiment 1, the direct-acting drive 100 does not require an anti-rotation component. Therefore, the number of parts can be reduced, and assembly time is decreased. Furthermore, the lead screw 112 becomes lighter, improving the operability of the direct-acting drive 100. Moreover, miniaturization of the direct-acting drive 100 is also possible.

[0081] Furthermore, the piston 120 in Embodiment 1 includes: a stop member 128, the surface of which facing the other direction of rotation (the second rotation direction L2) is a stepped surface 130d; an inner cylinder portion 124, located radially inward of the stop member 128, having a fitting hole 123 opening towards the second direction X2 and fitting one end of the lead screw 112; and an outer cylinder portion 125, located radially outward of the stop member 128, the outer peripheral surface of which slides relative to the housing 103. The radially inward end of the stop member 128 is connected to the inner cylinder portion 124. The radially outward end of the stop member 128 is connected to the outer cylinder portion 125.

[0082] According to the direct-acting driver 100 of Embodiment 1, the load input to the stop 128 is distributed between the inner cylinder portion 124 and the outer cylinder portion 125. Therefore, stress does not concentrate on the stop 128.

[0083] The direct-acting actuator 100 of Embodiment 1 has been described above, but the present invention is not limited to the examples shown in the embodiments. For example, the piston 120 of Embodiment 1 has an inner cylinder portion 124 and an outer cylinder portion 125, but the present invention may also be a piston having only an inner cylinder portion, or a piston having only an outer cylinder portion, or a piston without both an inner cylinder portion and an outer cylinder portion. The shape of the avoidance groove portion of the piston is also not limited to the examples shown in the embodiments. Hereinafter, a modified example in which the avoidance groove portion is deformed will be described. Furthermore, in the modified example, in order to easily observe the shape of the avoidance groove, a case in which the piston does not have an outer cylinder portion is given.

[0084] (Variation Example 1)

[0085] Figure 5 This is a perspective view of the piston of Modified Example 1 viewed from a second oblique angle. In the piston 120A of Modified Example 1, the amount of recess in the avoidance groove 127A is constant in the circumferential direction. That is, the bottom surface 129A of the avoidance groove 127A is a flat surface facing the direction of rotation. Even in this Modified Example 1, as in Embodiment 1, it is possible to reduce the number of parts and miniaturize the direct-acting actuator without the need for an anti-rotation member.

[0086] Furthermore, the end of the avoidance groove 127A in the second rotational direction L2 becomes a stepped surface 131A between the bottom surface 129A and the opposing surface 126. Additionally, according to Modification 1, the recess amount of the avoidance groove 127A is greater than the recess amount of the avoidance groove 127 in Embodiment 1. That is, the volume of the piston 120 in Embodiment 1 is greater than the volume of the piston 120A in Modification 1. Therefore, from the viewpoint of suppressing stress concentration, the shape of the avoidance groove 127 in Embodiment 1 is more desirable.

[0087] (Variation Example 2)

[0088] Figure 6 This is a three-dimensional view of the piston in modified example 2, viewed from an oblique angle in the second direction. (See image below.) Figure 6 As shown, in the piston 120B of Modified Example 2, the bottom surface 129B of the avoidance groove 127B has a helical surface 129a and a flat surface 129b. That is, the helical surface 129a extends from the ridge line 131 along the first rotational direction L1, and the flat surface 129b extends from the end of the helical surface 129a along the first rotational direction L1. Even in this Modified Example 2, the same effect as in Embodiment 1 can be obtained. In other words, the bottom surface of the present invention can be composed of a combination of two or more surfaces.

[0089] (Variation Example 3)

[0090] Figure 7 This is a three-dimensional view of the piston in modified example 3, viewed from an oblique angle in the second direction. (As shown...) Figure 7 As shown, in Modified Example 3, the recessed amount (depth) of the avoidance groove 127C of the piston 120C from the opposing surface 126 increases in a stepped manner as it moves toward the first rotational direction L1. In other words, the bottom surface 129C of the avoidance groove 127C becomes a stepped surface located in the first direction X1 in a stepped manner as it moves toward the first rotational direction L1. Even in this Modified Example 3, the same effect as in Embodiment 1 can be obtained.

[0091] Furthermore, the amount of recess in the avoidance groove 127C is approximately equal to the amount of recess in the avoidance groove 127 of Embodiment 1, and the volume of the piston 120C is approximately equal to the volume of the piston 120 of Embodiment 1. Therefore, it is a shape that easily suppresses stress concentration, similar to Embodiment 1. In addition, regarding the manufacturing of the piston 120C in Modified Example 3, when the avoidance groove 127C is formed by cutting the outer peripheral surface of the piston 120C (cutting from the radially outer side), it is easier to form than the spiral bottom surface 129 of Embodiment 1. Therefore, it is possible to reduce the cost of manufacturing the piston 120C.

[0092] (Variation Example 4)

[0093] Figure 8 This is a three-dimensional view of the piston in modified example 4, viewed from an oblique angle in the second direction. (For example...) Figure 8 As shown, in the piston 120D of Modified Example 4, the bottom surface 129D of the avoidance groove 127D is a combination of a helical surface 129a, a stepped surface 131A, and a flat surface 129b. That is, the amount of recess in the avoidance groove 127D changes significantly in the middle, forming a stepped surface 131A. As a result, a thick-walled reinforcing portion 131D is partially retained in the first rotational direction L1 of the stop member 128. Therefore, in Modified Example 4, compared with the piston 120 of Embodiment 1, a lighter weight can be achieved, and on the other hand, compared with the piston 120A of Modified Example 1, it has a shape that can suppress stress concentration.

[0094] The above describes a variation of the avoidance groove (bottom surface). Next, we will describe an example after changing the shape of the contact surface and the step surface.

[0095] (Variation Example 5)

[0096] Figure 9 This is a plan view of the piston in modified example 5, viewed from the second direction. (See diagram below.) Figure 9 As shown, the stepped surface 130E of the piston 120E in Modified Example 5 forms an arc shape when viewed from the second direction X2. That is, the radial center portion 132 of the stepped surface 130E protrudes in the second rotational direction L2. Therefore, when the protrusion 117 contacts the stop member 128E, the abutment surface 118 contacts the center portion 132 of the stepped surface 130E. Furthermore, with repeated contact, the center portion 132 of the stepped surface 130E is gradually crushed, and the stepped surface 130E becomes a flat surface. Thus, according to Modified Example 5, the stepped surface 130E has a shape in which the contact portion that contacts the abutment surface 118 of the protrusion 117 gradually increases in size. In addition, even in Modified Example 5, the same effect as in Embodiment 1 can be obtained.

[0097] Furthermore, in modified example 5, it is preferable that the nut 111 is made of an ferrous material and the piston 120E is made of an aluminum alloy. Therefore, when the protrusion 117 contacts the stepped surface 130E, the stepped surface 130E deforms more easily. This accelerates the flattening (plastic deformation) of the stepped surface 130E. Additionally, by using an aluminum alloy, a damping effect (vibration absorption) is generated when the abutting surface 118 of the protrusion 117 contacts. Therefore, contact noise can be reduced.

[0098] Furthermore, as an example of a shape where the stepped surface is easily plastically deformed, an arc-shaped stepped surface 130E is given in Modification Example 5, but the present invention is not limited to this. For example, the stepped surface can also be a generally flat surface with a relatively large surface roughness. According to this example, the stepped surface has fewer irregularities (smaller surface roughness) due to repeated contact with the protrusion 117.

[0099] Alternatively, fine irregularities can be formed on the step surface 130E. Thus, the irregularities only undergo plastic deformation when excessive torque is applied, making the contact surfaces close together and thereby dispersing stress.

[0100] (Variation Example 6)

[0101] Figure 10 This is a cross-sectional view obtained by cutting the piston of deformed example 6 along the axial direction. For example... Figure 10 As shown, in Modified Example 6, the corner 133 between the stepped surface 130 and the bottom surface 129 of the piston 120F is rounded. This increases the volume of the corner 133 portion, thus suppressing stress concentration.

[0102] (Variation Example 7)

[0103] Figure 11 This is a plan view of the piston in modified example 7 as viewed from the second direction. Figure 12 This is a plan view of the nut in modified example 7 as viewed from the first direction. Figure 13 This is a cross-sectional view showing the state in which the stop and the protrusion are in contact in the direct-acting drive of Modified Example 7. Figure 14 This is a cross-sectional view showing the contact between the stop and the protrusion in the direct-acting drive of the comparative example.

[0104] like Figure 11 As shown, in the piston 120G of Modified Example 7, the stepped surface 130G is a surface parallel to the surface containing the axis O and the imaginary line M1 extending perpendicularly from the axis O. Therefore, when viewed from the axial direction, the edge of the stepped surface 130G in the first direction X1 and the edge in the second direction X2 overlap. Furthermore, when viewed from the axial direction, the stepped surface 130G of the piston 120G of Modified Example 7 is positioned in the second rotational direction L2 (offset towards the second rotational direction L2) relative to the imaginary line M1 passing through the circumferential center portion 128a of the stop member 128 and the axis O, and is parallel to the imaginary line M1. The distance between the imaginary line M1 and the stepped surface 130G is a.

[0105] like Figure 12As shown, in the nut 111G of Modified Example 7, the abutment surface 118G is a surface parallel to the surface containing the axis O and the imaginary line M2 extending perpendicularly from the axis O. Therefore, when viewed from the axial direction, the edge of the abutment surface 118G in the first direction X1 and the edge in the second direction X2 overlap. Furthermore, when viewed from the axial direction, the abutment surface 118G of the nut 111G of Modified Example 7 is offset in the second rotational direction relative to the imaginary line M2 passing through the axis O, and is parallel to the imaginary line M2. The distance between the imaginary line M2 and the abutment surface 118G is b. Additionally, the distance a is greater than the distance b (a > b).

[0106] According to this modified example 7, when the protrusion 117G contacts the stop 128G, the contact area becomes the radially inner portion of both the protrusion 117G and the stop 128G. Therefore, the load acting on the radially outer portion of both the protrusion 117G and the stop 128G is reduced.

[0107] In addition, such as Figure 14 As shown, assuming distances a and b are equal (a=b), the contact surface 1118 of the protrusion 1117 and the stepped surface 1130 of the stop 1128 are in parallel contact (surface contact). Therefore, it is impossible to reduce the load acting on the radially outer portion. Next, an example of deforming the first end face of the piston will be described.

[0108] (Variation Example 8)

[0109] Figure 15 This is a plan view of the piston in modified example 8, viewed from the first direction. (See diagram below.) Figure 15 As shown, the piston 120H in Modified Example 8 has a protrusion 134 protruding in the first direction X1 on its first end face 121. The protrusion 134 extends in the rotational direction and is arc-shaped (C-shaped). When viewed from the axial direction, the protrusion 134 and the avoidance groove 127 (see reference) Figure 3 Therefore, the plane 137 disposed between the two ends of the protrusion 134 in the direction of rotation overlaps with the stop 128 (see reference). Figure 3 , Figure 4 )overlapping.

[0110] The protrusion of the protrusion 134 gradually increases as it moves toward the first rotation direction L1. That is, the protruding surface 134a of the protrusion 134 becomes a helical surface. Therefore, a stepped surface 135 is provided at the end of the protrusion 134 in the first rotation direction L1, between the protruding surface 134a and the plane 137. On the other hand, a ridge line 136 formed by the protruding surface 134a and the plane 137 is provided at the end of the protrusion 134 in the second rotation direction L2.

[0111] The amount by which the protrusion of the protrusion 134 protrudes in the first direction X1 is equal to the amount by which the recess of the avoidance groove 127 is recessed in the first direction X1. That is, the thickness in the axial direction from the protruding surface 134a of the protrusion 134 to the bottom surface 129 of the avoidance groove 127 is constant in the circumferential direction.

[0112] According to this modified example 8, the thickness in the piston 120H is uniform in the axial direction. Furthermore, in the piston 120 (refer to...) which has an outer cylinder portion 125... Figure 3 In the assembly of piston 120 and lead screw 112, stop 128 and stepped surface 130 are covered by outer cylinder 125 and cannot be visually identified (see reference). Figure 1 Therefore, determining the phase of the stop 128 and the step surface 130 during assembly becomes difficult. On the other hand, according to Modified Example 8, the stop 128 and the step surface 130 can be grasped using the plane 137 (protrusion 134). Therefore, determining the phase of the stop 128 and the step surface 130 becomes easy.

[0113] Furthermore, variations that facilitate the determination of the phase between the stop member 128 and the stepped surface 130 are not limited to the above-described embodiments. For example, the piston of the present invention may also have a keyway for preventing rotation on its outer peripheral surface. Moreover, according to this piston, it can be configured to allow the phase between the stop member and the stepped surface to be determined with reference to the keyway. In addition, markings may be made on the first end face 121 and the outer peripheral surface of the piston 120.

[0114] (Implementation Method 2)

[0115] Figure 16 This is a cross-sectional view of the direct-acting drive according to Embodiment 2. Figure 17 This is a perspective view of the nut in Embodiment 2. Figure 18 This is a perspective view of the piston in Embodiment 2. Figure 1 This is a cross-sectional view of the direct-acting drive 1 according to the embodiment. (See attached image.) Figure 16 As shown, the direct-acting drive 1 has a ball screw device 2, a stroke limiting mechanism 3, a piston 4, a motor 5, and a housing 6.

[0116] The ball screw assembly 2 comprises a screw 7, a nut 8, and multiple balls 9. The screw 7 has an outer peripheral track surface (first thread groove) 10 on its outer circumferential surface. The screw 7 passes through the nut 8. The nut 8 has an inner peripheral track surface (second thread groove) 11 on its inner circumferential surface, corresponding to the outer peripheral track surface (first thread groove) 10. The outer peripheral track surface (first thread groove) 10 and the inner peripheral track surface (second thread groove) 11 form a helical track (rolling path). The multiple balls 9 roll on the track (rolling path). The ball screw assembly 2 is supported on the housing 6 via ball bearings 12. The inner ring 13 of the ball bearing 12 is fitted into both ends of the nut 8, and the outer ring 14 of the ball bearing 12 is fitted into the housing 6. Thus, the screw 7 and the nut 8 can move smoothly relative to each other. Alternatively, the inner ring 13 can be integrally formed with the nut 8.

[0117] The travel restriction mechanism 3 consists of protrusion 15 (see reference). Figure 17 The screw 7 is composed of a protrusion 15 and a locking part 16. The protrusion 15 is provided on one end face of the nut 8 and is located radially outward. The locking part 16 is provided on the piston 4, which will be described later. Thus, at the end of the stroke in the retraction direction of the screw 7, the relative displacement between the screw 7 and the nut 8 is restricted.

[0118] like Figure 18 As shown, the piston 4 is provided with a locking portion 16. The locking portion 16 is concave on the end face of the piston 4. The locking portion 16 is formed by a stepped surface (abutment portion) 17 and a clearance groove 18. The stepped surface (abutment portion) 17 contacts the protrusion 15. The depth of the clearance groove 18 increases accordingly based on the lead of the outer peripheral track surface (first thread groove) 10. The piston 4 is connected at one end of the lead screw 7 to a mounting portion (shaft portion) 19 that is coaxially arranged with the lead screw 7. The piston 4 has a bottomed cylindrical shape, and the mounting portion (shaft portion) 19 is inserted into the inner diameter side of the piston 4. The piston 4 and the mounting portion (shaft portion) 19 are joined by serrated engagement and pressing, and are joined in such a way that the piston 4 and the mounting portion (shaft portion) 19 cannot rotate and the mounting portion (shaft portion) 19 cannot be dislodged from the piston 4 along the axial direction. The material of the piston 4 is preferably aluminum alloy or the like. Furthermore, the depth of the entire surface of the avoidance groove 18 can be set to be the same, or it can be set to a certain depth to the extent that it does not contact the protrusion 15.

[0119] Motor 5 is mounted in housing 6. Motor 5 has an output shaft (drive shaft) 20. A first gear (drive gear) 21 is provided at the end of the output shaft (drive shaft) 20. The first gear (drive gear) 21 meshes with a second gear (driven gear) 22 located on the outer circumferential surface of nut 8. The first gear (drive gear) 21 transmits the rotation of motor 5 to nut 8 via the second gear (driven gear) 22. When nut 8 rotates, lead screw 7 moves along the axial direction. Thus, ball screw device 2 converts rotary motion into linear motion.

[0120] The housing 6 is composed of a first housing 23 and a second housing 24. The first housing 23 has a first large-diameter recess 25 and a first small-diameter recess 26. The first large-diameter recess 25 engages with a ball bearing 12 at one end of the nut 8. The first small-diameter recess 26 is equipped with a motor 5. The first large-diameter recess 25 has a second small-diameter recess 27 with a diameter smaller than that of the first large-diameter recess 25. The piston 4 is slidably engaged in the second small-diameter recess 27. The second small-diameter recess 27 functions as a cylinder. The second housing 24 has a second large-diameter recess 28 with the same diameter as the first large-diameter recess 25 of the first housing 23. The second large-diameter recess 28 engages with a ball bearing 12 at the other end of the nut 8.

[0121] Furthermore, in this embodiment, the stroke limiting mechanism 3 is composed of a protrusion 15 provided on one end face of the nut 8 and a locking part 16 provided on the piston 4. However, the protrusion 15 of the nut 8 and the locking part 16 of the piston 4 can also be arranged in reverse order. Alternatively, instead of directly providing the protrusion 15 on the end face of the nut 8, a hole can be opened on the end face of the nut 8, and a pin can be inserted into the hole to form the protrusion 15. Furthermore, the locking part 16 that abuts against the pin-shaped protrusion 15 can be designed as an arc shape accordingly.

[0122] As described above, the direct-acting drive 1 of this embodiment includes a ball screw assembly 2, a stroke limiting mechanism 3, a piston 4, a motor 5, and a housing 6. The ball screw assembly 2 includes a screw 7, a nut 8, and a plurality of balls 9. The stroke limiting mechanism 3 consists of a protrusion 15 provided on one end face of the nut 8 and a locking portion 16 provided on the piston 4. The locking portion 16 is concave on the end face of the piston 4. The locking portion 16 is formed by a stepped surface (abutment portion) 17 and a clearance groove 18.

[0123] Therefore, by providing a locking part 16, which is a separate component from the conventional piston 4, on the piston 4, the strength of the locking part 16 can be increased without increasing the size of the component. Thus, excessive stress concentration in the stroke limiting mechanism 3 can be prevented with a simple structure.

[0124] Furthermore, by providing the locking part 16 on the piston 4, the number of separate components that would have been present in the conventional locking part 16 can be reduced, that is, the number of components can be reduced. Moreover, by reducing the number of separate components that would have been present in the conventional locking part 16, the direct-acting drive 1 can be miniaturized.

[0125] Furthermore, the lead screw 7 is connected to the piston 4 via a mounting portion (shaft portion) 19 located at one end of the lead screw 7, thereby guiding the displacement of the lead screw 7 in the axial direction by the piston 4. Therefore, the wobbling of the ball screw device 2 can be suppressed, the contact between the protrusion 15 in the stroke limiting mechanism 3 and the stepped surface (abutment portion) 17 becomes stable, and the wear between the protrusion 15 and the stepped surface (abutment portion) 17 can be reduced.

[0126] Explanation of reference numerals in the attached figures

[0127] 1. Direct-acting drive; 2. Ball screw assembly; 3. Stroke limiting mechanism; 4. Piston; 5. Motor; 6. Housing; 7. Screw; 8. Nut; 9. Ball; 10. Outer peripheral raceway (first thread groove); 11. Inner peripheral raceway (second thread groove); 12. Ball bearing; 13. Inner ring; 14. Outer ring; 15. Protrusion; 16. Locking part; 17. Stepped surface (abutment part); 18. Avoidance groove; 19. Mounting part (shaft part); 20. Output shaft (Drive shaft); 21. First gear (drive gear); 22. Second gear (driven gear); 23. First housing; 24. Second housing; 25. First major diameter recess; 26. First minor diameter recess; 27. Second minor diameter recess; 28. Second major diameter recess; 100. Direct-acting actuator; 101. Motor; 102. Transmission device; 103. Housing; 107. Cylinder; 110. Ball screw assembly; 111, 111G, Nut; 111a. Inner circumferential track surface; 112, lead screw; 113, ball; 116, one end face; 117, 117G, protrusion; 118, 118G, abutment surface; 120, 120A, 120B, 120C, 120D, 120E, 120F, 120G, 120H, piston; 121, first end face; 122, second end face; 123, fitting hole; 124, inner cylinder; 125, outer cylinder; 126, opposing surface; 127, 127A 127B, 127C, 127D, Avoidance groove; 128, 128G, Stop; 129, 129A, 129B, 129C, 129D, Bottom surface; 129a, Spiral surface; 129b, Flat surface; 130, 130E, 130G, Stepped surface; 131, Edge; 131A, Stepped surface; 133, Corner; 134, Protrusion; 135, Stepped surface; 136, Edge; 137, Plane; 140, Stroke limiting mechanism.

Claims

1. A direct-acting drive, wherein, This direct-acting drive has: A ball screw device having a screw, a nut and a plurality of balls, the nut being rotatable in a rotational direction, the rotational direction including a first rotational direction and a second rotational direction opposite to the first rotational direction; A piston, which is mounted at one end of the lead screw; and A stroke limiting mechanism sets the position of the lead screw at the start of operation in the first direction pointed to by one end. The nut has one end face facing the first direction and a protrusion extending from the one end face. The piston has: The opposite face faces a second direction opposite to the first direction and is opposite to one end face; An avoidance groove is recessed from the opposing surface in the first direction and extends along the rotation direction with the lead screw as the center. as well as The stepped surface is the wall surface of the wall that divides the avoidance groove portion, located at the end of the avoidance groove portion in the first rotation direction, and facing the second rotation direction. The protrusion and the stepped surface abut against each other to form the travel limiting mechanism.

2. The direct-acting drive according to claim 1, wherein, The piston has a bottom surface that divides the avoidance groove from the first direction in one of the wall surfaces that divides the avoidance groove. At least a portion of the bottom surface is inclined in a spiral shape in a manner that it is located in the first direction as it moves toward the first rotational direction.

3. The direct-acting drive according to claim 1, wherein, The piston has a bottom surface that divides the avoidance groove from the first direction in one of the wall surfaces that divides the avoidance groove. At least a portion of the bottom surface is positioned in a stepped manner in the first direction as it moves toward the first rotation direction, thus becoming stepped.

4. The direct-acting drive according to claim 1, wherein, The piston has a bottom surface that divides the avoidance groove from the first direction in one of the wall surfaces that divides the avoidance groove. At least a portion of the bottom surface becomes a flat surface.

5. The direct-acting drive according to claim 1, wherein, The piston has a stop, the surface of which faces the second rotation direction and becomes the stepped surface.

6. The direct-acting drive according to claim 5, wherein, The piston has an inner cylinder portion located radially inward than the stop member, and has a fitting hole that opens in the second direction and allows one end of the lead screw to engage. The radially inner end of the stop member is connected to the inner cylinder portion.

7. The direct-acting drive according to claim 5, wherein, The piston has an outer cylinder portion located radially outward from the stop member, and the outer peripheral surface of the outer cylinder portion slides relative to the housing. The radially outer end of the stop member is connected to the outer cylinder portion.

8. The direct-acting drive according to any one of claims 1 to 7, wherein, The piston has a first end face facing the first direction. On the first end face, a protrusion extending in the first direction is provided at a position overlapping the avoidance groove when viewed from an axis parallel to the lead screw. The amount of protrusion of the protrusion corresponds to the amount of indentation of the avoidance groove.

9. The direct-acting drive according to any one of claims 1 to 7, wherein, The protrusion has an abutting surface that abuts against the stepped surface. When viewed from an axis parallel to the lead screw, the stepped surface is parallel to a first imaginary line extending radially and positioned in the second rotation direction. When viewed from the axial direction, the abutment surface is parallel to and positioned in the second imaginary line extending radially in the second rotational direction. The distance between the stepped surface and the first imaginary line is greater than the distance between the abutting surface and the second imaginary line.

10. The direct-acting drive according to any one of claims 1 to 7, wherein, The nut is made of ferrous materials, and the piston is made of aluminum alloy.

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