Valve actuator motor

Abstract

To provide a motor for a valve actuator, which is mounted on a valve actuator, and in which a pinion gear can be firmly fixed to an output side shaft without applying special processing to the shaft even when the shaft has a small diameter, and cracks are prevented during and after mounting of the pinion gear to improve the strength.SOLUTION: A motor is mounted on a valve actuator 1. A substantially-cylindrical coupling 11 having a through hole 21 in the center is provided between a shaft 10, which is the output shaft of the motor, and a pinion gear 12. The shaft 10 is press-fitted into a through hole 21a on one end side of the coupling 11, and teeth 12b of the pinion gear 12 are press-fitted into a through-hole 21b on the other end side of the coupling 11, so that rotation from the shaft 10 can be transmitted to the pinion gear 12 through the coupling 11.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a motor for a valve actuator, and more particularly to a fixing structure for a pinion gear provided on the tip side of an output shaft of the motor. [Background technology]

[0002] Generally, electric actuators are used to automatically open and close valves such as butterfly valves. Such valve actuators are equipped with an electric motor for driving, and the rotation of this motor is output from a pinion gear fixed to an output shaft. The rotation of the pinion gear is transmitted to a reducer equipped with a reduction gear train, and the rotation reduced by this reducer is output from an output shaft. The output shaft is connected to the stem of the valve, and the stem is rotated by the rotation of this output shaft, and the disk is opened and closed by a rotation angle of, for example, 90°.

[0003] In this case, in particular, actuators for butterfly valves are often set to an intermediate opening for flow control, and therefore it is required to be able to stop the valve at the desired rotation angle. Here, since the moment of inertia of a motor shaft increases in proportion to the square of the shaft diameter, it becomes difficult to control the rotation of the motor when the output shaft has a large diameter. This makes it difficult to stop the valve at the desired rotation angle, and the rotating rotor (permanent magnet) also becomes larger, which further increases the moment and leads to further deterioration of controllability. For these reasons, in valves that require control of an intermediate opening, it is effective to make the shaft as thin as possible to reduce the moment of inertia and improve control performance. In addition, as a drive motor, a DC motor is easy to control the output of and generates high torque from the start of movement, making it suitable for accurate control.

[0004] When providing a pinion gear on the shaft of the motor described above, the pinion gear may be formed directly on the tip of the shaft by cutting. In this case, the portion of the shaft where the pinion gear is formed is formed with a slightly larger diameter, and the pinion gear is integrally provided on the shaft by cutting this large diameter portion.

[0005] Meanwhile, there is known a technique for a fixing structure of a pinion gear of a motor in which the pinion gear is formed as a separate member from the shaft, and the tip side of the shaft is fitted into a central hole formed in the pinion gear to integrate the two. As an example of this type of valve actuator motor, Patent Document 1 discloses, for example, that in this motor, a D-cut is provided on the drive shaft, while a D-cut hole corresponding to the D-cut is provided in the shaft fitting hole of the pinion gear, and the drive shaft and pinion gear are fixed so that they can rotate together by fitting the D-cut into the D-cut hole.

[0006] The motor of Patent Document 2 is configured such that a knurled portion is formed on the outer periphery of the output shaft. In this case, when the output shaft is press-fitted into an insertion hole formed in the pinion gear, the knurled portion is engaged with the insertion hole to firmly connect the shaft and the pinion gear. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2000-81113 A [Patent Document 2] Utility Model Registration No. 2563569 Summary of the Invention [Problem to be solved by the invention]

[0008] In the motor for the above-mentioned electric valve actuator, when the pinion gear is directly formed on the tip end of the shaft by cutting, it becomes difficult to machine the pinion gear if the shaft has a small diameter. For this reason, when the shaft has a small diameter, it becomes necessary to fix a separate pinion gear to the tip of the shaft by fitting it in. In this case, in order for the pinion gear to withstand repeated rotational movements many times, it becomes necessary to increase the surface hardness of the tooth flank, and therefore the tooth flank is often subjected to heat treatment.

[0009] However, when the pinion gear has a small diameter (compact), not only the tooth surface but also the center side of the teeth and the thin parts between the teeth are easily affected by the heat treatment, and while the heat-treated parts harden, they also easily become embrittled. Therefore, particularly when the heat treatment affects the thin parts between the teeth, the pinion gear receives a force (tensile force) in the direction of expanding the diameter from the inner diameter side when the shaft is pressed in, and is prone to cracking if it cannot withstand this force.

[0010] In Patent Documents 1 and 2, when the shaft and pinion gear of these motors are made of metal materials, the problem of embrittlement of the pinion gear described above occurs when the shaft has a small diameter, and the shaft becomes even thinner when D-cut or knurled, resulting in a decrease in strength. Furthermore, processing problems arise in that the small diameter of the shaft makes it difficult to perform D-cut or knurling.

[0011] The present invention was developed to solve the problems of the related art, and its purpose is to provide a motor for a valve actuator that is mounted on a valve actuator, and that can firmly fix a pinion gear without requiring special processing on the output shaft even when the shaft has a small diameter, and that has improved strength by preventing cracks during and after installation of the pinion gear. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention according to claim 1 is a motor mounted on a valve actuator, in which a substantially cylindrical coupling having a through hole in the center is provided between a shaft serving as an output shaft of the motor and a pinion gear, the through hole of the coupling includes a small diameter through hole disposed on the base side of the shaft and a large diameter through hole provided on the tip side of the shaft and having a larger diameter than the small diameter through hole, On one end of this coupling Small diameter The shaft is press-fitted into the through hole, and the other end of the coupling Large diameter The teeth of the pinion gear are press-fitted into the through hole, With a base side of the shaft being press-fitted into the small diameter through hole of the coupling, a tip side of the shaft is inserted into an insertion hole formed in the pinion gear, and the pinion gear is provided so as to be held substantially concentric with the shaft when integrated with the coupling, This is a motor for a valve actuator, which is provided so that rotation from the shaft can be transmitted to the pinion gear through a coupling.

[0013] The invention according to claim 2 is characterized in that the base side of the shaft is a coupling. Small diameter With the shaft pressed into the through hole with a tight fit, the tip of the shaft is inserted into the insertion hole formed in the pinion gear with a loose fit. was This is a motor for a valve actuator.

[0014] The invention according to claim 3 is characterized in that the coupling is made of a material softer than the pinion gear, and the teeth of the pinion gear are Large diameter This is a motor for a valve actuator that is provided in a state where it bites into the inner circumferential surface of a through hole.

[0015] The invention according to claim 4 is characterized in that the tip side of the tooth of the pinion gear on the coupling press-fit side is cut out to form a reduced diameter tooth, and the tooth tip of this reduced diameter tooth is connected to the coupling. Large diameter This is a motor for a valve actuator in which, when pressed into the inner peripheral surface of the through hole, a locking step formed at the boundary between the reduced diameter teeth and the meshing teeth of the pinion gear abuts against the end face of the coupling, thereby positioning the pinion gear axially relative to the coupling.

[0016] The invention according to claim 5 is a motor for a valve actuator, in which the end face side of the pinion gear close to the shaft is engaged with a step formed on the outer circumference of the shaft, and the pinion gear is positioned axially relative to the shaft together with the coupling. Effect of the Invention

[0017] According to the invention of claim 1, the shaft, which is the output shaft of the motor, is fixed to the pinion gear through a coupling provided separately from the shaft, so that when the shaft has a small diameter, the pinion gear can be provided without forming the pinion gear directly on the shaft or performing special processing. In this case, a coupling having a through hole is provided between the shaft and the pinion gear, and the shaft is press-fitted and fixed to one end of the coupling, and the teeth of the pinion gear are press-fitted and fixed to the other end, so that the rotation from the shaft can be transmitted to the pinion gear through the coupling. Since the pinion gear is fixed while being subjected to a force from the outer diameter direction by the coupling, the rotation of the motor can be transmitted to the pinion gear while preventing cracking and deformation of the pinion gear. The teeth of the pinion gear are heat-treated to increase the surface hardness, so that even if the thin-walled portion between the teeth of the pinion gear becomes embrittled, it is possible to provide a motor for a valve actuator with excellent durability that prevents damage such as cracking and deformation of the pinion gear and suppresses wear. In addition, with the base side of the shaft pressed into the small diameter through hole of the coupling, the tip side of the shaft is inserted into an insertion hole formed in the pinion gear, thereby achieving the effect of the pinion gear being arranged to maintain a roughly concentric state with the shaft while being integrated with the coupling.

[0018] According to the invention of claim 2, the base side of the shaft is connected to the coupling. Small diameter The coupling is pressed into the through hole with an interference fit, and the tip of the shaft is inserted into the pinion gear insertion hole with a clearance fit, so that the pinion gear is held approximately concentric with the shaft while integrated with the coupling, and so when the coupling rotates together with the shaft and the pinion gear fixed to the coupling rotates, the tip of the shaft acts as a guide for the pinion gear, and even if a force in the swinging direction acts on the pinion gear due to gear meshing, the tip of the shaft located inside the pinion gear insertion hole acts as a support to prevent the pinion gear from wobbling. This allows rotation to be transmitted with high efficiency through the pinion gear.

[0019] According to the invention of claim 3, the coupling is made of a softer material than the pinion gear, so that when the shaft is inserted into the through hole of the coupling, the two fit well together, while the teeth of the pinion gear can easily be inserted into the through hole, and the pinion gear and shaft are press-fitted into the coupling, so that the coupling is less likely to crack or deform even if stress is applied to the coupling in the outer diameter direction from inside the through hole. This makes it possible to firmly and easily connect the pinion gear to the coupling even when a large press-fit margin is provided, and the pinion gear rotates as a unit while preventing slippage relative to the coupling.

[0020] According to the invention of claim 4, the pinion gear and the coupling can be assembled in a predetermined positioning state by pressing in the pinion gear until the locking step abuts the end face of the coupling, and by integrating them in advance, they can be easily attached to the shaft.

[0021] According to the invention of claim 5, the pinion gear can be positioned in the axial direction with respect to the shaft by engaging the end face side closer to the shaft with a step on the outer periphery of the shaft, and the coupling integrated with the pinion gear can be attached to a predetermined position on the shaft. This makes it possible to mount the coupling and pinion gear in the appropriate positions on the shaft while preventing loosening between the respective components, thereby efficiently transmitting output to the secondary side. [Brief description of the drawings]

[0022] [Figure 1] 1 is a cross-sectional view, with some parts omitted, showing an embodiment of a valve actuator. [Diagram 2] 2 is an enlarged cross-sectional view of the motor of the valve actuator in FIG. 1, with a portion thereof omitted. [Diagram 3] (a) is a perspective view of a pinion gear, (b) is a plan view of (a), and (c) is a cross-sectional view taken along line AA of (b). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The motor for a valve actuator of the present invention will be described in detail below based on an embodiment. Fig. 1 shows one embodiment of the valve actuator of the present invention, and Fig. 2 shows an enlarged cross-sectional view of the vicinity of a pinion gear fixing position of the motor in Fig. 1 with some parts omitted.

[0024] 1, valve actuator 1 is mounted on a valve such as a butterfly valve (not shown), and has a motor body 2 provided inside. Motor body 2 is attached to the top side of a base body 3 for mounting components by means of a mounting plate 4 and bolts (not shown). A shaft 10 for transmitting rotation is provided on the output side of motor body 2, and a pinion gear 12 for transmitting power is fixed to this output side shaft 10 via a coupling 11.

[0025] The rotation of the motor body 2 is capable of being transmitted by the pinion gear 12 to a reducer (not shown) provided between the pinion gear 12 and an output shaft 13. The reducer is provided within the base body 3, a reduction mechanism is provided inside the reducer, and an output shaft 13 connected to a stem of a butterfly valve (not shown) is provided on the output side of the reducer. As a result, the rotation of the motor body 2 is reduced in speed by the reduction mechanism from the pinion gear 12 and output from the output shaft 13. A cover 14 is detachably provided on the base body 3, and this cover 14 covers the upper side of the motor body 2 and other internal parts.

[0026] The motor body 2 in this embodiment is an electric motor, and a general-purpose DC type motor with a relatively small shaft outer diameter, which is the output shaft, and a simplified internal structure is used. When a DC motor is used as the motor body 2 in this way, output control becomes easy and it becomes possible to control the motor to a predetermined intermediate opening. In addition, since it generates high torque from the moment it starts moving, it is particularly suitable for controlling butterfly valves.

[0027] 2, a tapered step 20 is formed near the middle of the outer periphery of the shaft 10, with a larger diameter on the base side and a smaller diameter on the tip side of the step 20. The outer diameter φDS1 on the base side of the shaft 10 is smaller than the outer diameter φDP1 of a tip circle of the meshing teeth 12a formed on the pinion gear 12, which will be described later.

[0028] A coupling 11 and a pinion gear 12 are attached to the shaft 10 at a portion that protrudes from the motor body 2, and the overall length LS1 of this protruding portion is set to 17.8 mm, for example. More specifically, for example, the length LS2 on the base side from the step 20 is 7.8 mm, the outer diameter φDS1 is φ5 mm, the length LS3 on the tip side from the step 20 is 8 mm, the outer diameter φDS2 is φ3 mm, and the length LS4 of the step is 2 mm.

[0029] The coupling 11 is made of a material softer than the pinion gear 12 described later and is formed in a generally cylindrical shape, with a through hole 21 formed in the center thereof. The through hole 21 includes a small diameter through hole 21a disposed on the base side of the shaft 10 and a large diameter through hole 21b disposed on the tip side of the shaft 10 and larger in diameter than the small diameter through hole 21a. The small diameter through hole 21a has an inner diameter φdC1 that is equal to or slightly smaller than the outer diameter φDS1 of the base side of the shaft 10 so that the base side of the shaft 10 can be press-fitted therein. On the other hand, the large diameter through hole 21b has an inner diameter φdC2 that is slightly smaller than the reduced diameter teeth 12b of the pinion gear 12 described later so that the reduced diameter teeth 12b can be press-fitted therein. A flat annular end face 22 is formed on the side of the coupling 11 where the pinion gear 12 is attached.

[0030] The coupling 11 is formed from a metal material such as S45CF, and, for example, has an axial length LC of 9 mm, an inner diameter φdC1 of the small through hole 21a of φ5 mm, and an inner diameter φdC2 of the large through hole 21b of φ6 mm.

[0031] In the pinion gear 12 shown in FIG. 3, in FIG. 3(a) and FIG. 3(c), the meshing teeth 12a are formed on the lower side, and the reduced-diameter teeth 12b, which are reduced in diameter than the meshing teeth 12a, are formed on the upper side. The reduced-diameter teeth 12b are formed by cutting the tip side of the meshing teeth 12a by lathe processing or the like. A flat locking step 23 is formed at the boundary between the meshing teeth 12a and the reduced-diameter teeth 12b, and the locking step 23 is provided so as to be able to abut against the annular end surface 22 of the coupling 11. The outer diameter φDP2 of the tooth tip circle of the reduced-diameter teeth 12b is formed slightly larger than the inner diameter φdC2 of the large-diameter through hole 21b, and is provided so as to be able to be press-fitted into the large-diameter through hole 21b. On the other hand, the outer diameter φDP1 of the tooth tip circle of the meshing teeth 12a is set to a size that provides a tooth profile that can mesh with an input gear (not shown) of the reduction mechanism of the secondary side reducer.

[0032] An insertion hole 24 is formed in the center of the pinion gear 12. This insertion hole 24 has an inner diameter φdPH that is slightly larger than the outer diameter φDS2 of the tip side of the shaft 10. The tip side of the shaft 10 can be inserted into this insertion hole 24. A flat end face 25 is formed at the tip of the pinion gear 12 on the side where it is attached to the coupling 11 , and this end face 25 close to the shaft 10 is arranged so as to be able to come into contact with the shaft step portion 20 .

[0033] The pinion gear 12 is formed from a metal material such as S45CF, and has a total length LP1 of 8 mm, which is approximately the same as the length LS3 of the shaft tip side. The inner diameter φdPH of the insertion hole 24 is φ3 mm, the outer diameter φDP1 of the tip circle of the meshing tooth is φ7.1 mm, the axial length LP2 of the reduced diameter tooth 12b is 3 mm, and the outer diameter φDP2 of the tip circle of the reduced diameter tooth is φ6 mm.

[0034] The pinion gear 12 is formed from the same material as the coupling 11 described above, but the pinion gear 12 has been subjected to heat treatment such as quenching, thereby making it harder, whereas the coupling 11 has not been subjected to heat treatment such as quenching, thereby making it softer than the pinion gear 12 and more durable. For this reason, in the present invention, "the coupling 11 is formed of a material softer than the pinion gear 12" means "the coupling 11 is formed of a material having softer properties than the pinion gear 12", and therefore the coupling 11 and the pinion gear 12 do not necessarily need to be made of materials with different compositions, and may be made of the same material as in this embodiment.

[0035] Here, the hardness of each member refers to the indentation hardness measured by a prescribed hardness test method, and any test method such as Brinell hardness, Vickers hardness, etc. can be applied for comparing hardness. In other words, "the coupling 11 is made of a softer material than the pinion gear 12" means that when the hardness of each material (materials treated under the same conditions in the case of members that are subjected to prescribed treatment such as heat treatment) is measured by the same hardness test method, the material of the pinion gear 12 is found to be harder than the material of the coupling 11.

[0036] 1 and 2, the motor main body 2 has a coupling 11 provided between an output side shaft 10 and a pinion gear 12, and the shaft 10 is press-fitted and fixed into an inner circumferential surface 30 of a small diameter through hole 21a which is a through hole on one end side of the coupling 11, while the tooth tips 12c of reduced diameter teeth 12b of the pinion gear 12 are press-fitted and fixed into an inner circumferential surface 31 of a large diameter through hole 21b which is a through hole on the other end side. This allows the rotation from the shaft 10 to be transmitted to the pinion gear 12 through the coupling 11.

[0037] When attaching the pinion gear 12 to the coupling 11, the pinion gear 12 is attached to the coupling 11 by press-fitting the tooth tips 12c of the reduced-diameter teeth 12b into the inner circumferential surface 31 of the coupling 11. At this time, the pinion gear 12 is press-fitted into the coupling 11 until the locking step 23 abuts against the coupling end face 22, and by abutting the locking step 23 and the coupling end face 22, the pinion gear 12 is press-fitted to a predetermined position while being positioned axially in the coupling 11, and the pinion gear 12 and the coupling 11 are integrated.

[0038] In this case, the dimensions and dimensional tolerances are set so that the outer diameter φDP2 of the tip circle of the reduced-diameter teeth 12b of the pinion gear 12 is always larger than the inner diameter φdC2 of the large-diameter through hole 21b of the coupling 11, so that the tips 12c of the reduced-diameter teeth 12b are reliably pressed into the large-diameter through hole 21b in a so-called interference fit state. Moreover, since the coupling 11 is made of a material softer than the pinion gear 12, the tips 12c of the pinion gear 12 are in a state of biting into the inner circumferential surface 31. In addition, the material of the coupling 11 that is pushed out by the biting of the tips 12c moves to the valleys between the tips 12c of the pinion gear 12, and as a result, the coupling 11 and the pinion gear 12 are strongly fixed to each other.

[0039] When connecting these integrated pinion gear 12 and coupling 11 to shaft 10, the coupling 11 is oriented with the upper side and the pinion gear 12 with the lower side, and with the tip surface of the pinion gear 12 abutting against a specified surface, the tip side of the shaft 10 is inserted through the small diameter through hole 21a of the coupling 11, and the pinion gear 12 and coupling 11 are attached from below the shaft 10.

[0040] When inserting, when shaft 10 is inserted until its tip abuts the surface on which pinion gear 12 is placed, end face 25 of pinion gear 12 reaches the position of step 20 on the outer circumference of shaft 10, and this end face 25 side engages with step 20, positioning pinion gear 12 axially relative to shaft 10, and pinion gear 12 and coupling 11 are fixed in the specified positions on shaft 10.

[0041] Although the step portion 20 is tapered, the tip of the shaft 10 abuts against the underside at the same position as the tip surface of the pinion gear 12, preventing the shaft 10 from being inserted any further. This prevents the step portion 20 from being pushed into the insertion hole 24 of the pinion gear 12 more than necessary, thereby preventing the pinion gear 12 from cracking, etc.

[0042] At this time, the coupling 11 and the pinion gear 12 are fixed to the shaft 10 with the inner surface 30 of the small diameter through hole 21a of the coupling 11 positioned on the base side outer surface 32 of the shaft 10, and the inner surface 24a of the insertion hole 24 of the pinion gear 12 positioned on the tip side outer surface 33 of the shaft 10.

[0043] In this case, the dimensions and dimensional tolerances are set so that the outer diameter φDS1 of the base side outer peripheral surface 32 of the shaft 10 and the inner diameter φdC1 of the small diameter through hole 21 of the coupling 11 are at least the same size, and therefore the base side outer peripheral surface 32 of the shaft 10 is pressed into the small diameter through hole 21a by an interference fit.

[0044] On the other hand, since the dimensions and dimensional tolerances are set so as to provide at least a gap between the outer diameter φDS2 of the tip outer peripheral surface 33 of the shaft 10 and the inner diameter φdPH of the inner peripheral surface 24a of the insertion hole 24 of the pinion gear 12, the tip outer peripheral surface 33 of the shaft 10 is inserted into the insertion hole 24 of the pinion gear 12 with a clearance fit.

[0045] As described above, the base side outer peripheral surface 32 of the shaft 10 is press-fitted into the coupling 11 with an interference fit, and the pinion gear 12 is press-fitted into this coupling 11 in an interference fit state, thereby fixing the shaft 10, the coupling 11, and the pinion gear 12. At this time, the tip side outer peripheral surface 33 of the shaft 10 is inserted into the insertion hole 24 of the pinion gear 12 with a clearance fit, so that the pinion gear 12 is provided so as to maintain a substantially concentric state with the shaft 10 while being integrated with the coupling 11.

[0046] In the above embodiment, the shaft 10 does not necessarily have to have the step 20, the large-diameter base-side outer circumferential surface 32, and the small-diameter tip-side outer circumferential surface 33, and a motor body having a shaft of the same outer diameter (not shown) may also be used. In this case, it is also possible to cut a shaft of the same outer diameter to provide a step, a large-diameter base-side outer circumferential surface, and a small-diameter tip-side outer circumferential surface. When using the motor body 2 of the above-mentioned embodiment, an existing general type of motor body 2 having a step portion 20, a large-diameter base-side outer peripheral surface 32, and a small-diameter tip-side outer peripheral surface 33 can be used without processing the shaft 10.

[0047] In order to press-fit the pinion gear 12 into the coupling 11, the coupling 11 mounting side of the pinion gear 12 is cut to form reduced-diameter teeth 12b. However, it is also possible to provide a configuration in which the meshing teeth 12a of the pinion gear 12 can be directly press-fitted into the coupling 11 without machining such reduced-diameter teeth 12b.

[0048] The motor body 2 may be of an AC type, and a motor other than a general-purpose motor may be used in accordance with characteristics such as the torque required for rotating the valve disc.

[0049] Next, the operation of the motor for the valve actuator of the present invention in the above embodiment will be described. In the motor body 2 in the above embodiment, the pinion gear 12 provided separately from the shaft 10 is fixed to the output side shaft 10 by the coupling 11, and the rotation of the shaft 10 is transmitted to the pinion gear 12 through the coupling 11, so there is no need to machine the pinion gear 12 directly on the shaft 10, and the outer diameter of the shaft 10 (the outer diameter φDS1 which is the maximum diameter) can be formed to be small. This keeps the moment of inertia small when the shaft 10 rotates, and particularly when the motor body 2 is a DC motor, it is possible to significantly improve the control performance and easily drive the motor to the desired intermediate opening with high precision.

[0050] Since the shaft 10 and the pinion gear 12 are provided separately, the outer diameter of the pinion gear 12 (outer diameter φDP1 of the tip circle of the meshing teeth) can be made larger than the outer diameter of the shaft 10 (outer diameter φDS1), and the meshing teeth 12a of the pinion gear 12 can be made thick. Therefore, when the pinion gear 12 is subjected to heat treatment such as quenching, it is possible to harden the entire gear while suppressing embrittlement, thereby improving the strength of the teeth. The pinion gear 12 may be made of various materials other than S45CF depending on the performance of the motor body 2, such as the output torque and rotation speed, to further improve characteristics such as strength.

[0051] Since the coupling 11 is attached by press-fitting the output shaft 10 into the small diameter through hole 21a at one end of the coupling 11 and press-fitting the reduced diameter teeth 12b of the pinion gear 12 into the large diameter through hole 21b at the other end, a force in the diameter-reducing direction (compressive force) is applied to the pinion gear 12 from the coupling 12, which provides higher strength than when a force in the diameter-expanding direction (tensile force) is applied. Therefore, even when the pinion gear 12 is provided with a small diameter, durability is improved and cracks and deformation are less likely to occur.

[0052] The base side outer peripheral surface 32 of the shaft 10 is pressed into the small diameter through hole 21a of the coupling 11 with an interference fit, and the tip side outer peripheral surface 33 of the shaft 10 is inserted into the insertion hole 24 of the pinion gear 12 with a clearance fit, and the pinion gear 12, which rotates integrally with the coupling 11, is arranged to maintain a substantially concentric state with the shaft 10. Therefore, when the shaft 10 rotates, the coupling 11 rotates integrally with the base side of the shaft 10, and the pinion gear 12 rotates integrally with the coupling 11 while also rotating in sync with the tip side of the shaft 10.

[0053] In this case, as described above, an extremely small gap is created between the outer peripheral surface 33 at the tip end of the shaft 10 and the insertion hole 24 of the pinion gear 12 due to the relationship between the upper and lower dimensional tolerances. Even if such a small gap exists, if the pinion gear 12 vibrates due to gear meshing or the like when the pinion gear 12 rotates, the outer peripheral surface 33 at the tip end of the shaft 10 comes into contact with the inner peripheral surface 24a of the insertion hole 24 of the pinion gear 12, suppressing excessive vibration. This makes it possible to transmit the rotation of the shaft 10 to the pinion gear 12 with high efficiency and control the rotation of the butterfly valve with high precision.

[0054] The coupling 11 is made of a softer material than the pinion gear 12, and when the pinion gear 12 is press-fitted into the large-diameter through-hole 21b of the coupling 11, the teeth 12c of the pinion gear 12 bite into the inner peripheral surface 31, improving the joining strength between the pinion gear 12 and the coupling 11. This allows them to be firmly connected and rotate together, and prevents cracking and deformation. The coupling 11 does not come into contact with other gears or other parts, so there is no need to perform heat treatment for hardening or the like.

[0055] Furthermore, the reduced-diameter teeth 12b are formed by cutting out the tip side of the teeth of the pinion gear 12 on the side where the pinion gear 12 is pressed into the coupling 11, so that the dimension of the outer diameter φDP2 of the tip circle of the reduced-diameter teeth 12b is stable. Therefore, when the reduced-diameter teeth 12b are pressed into the inner peripheral surface 31 of the large-diameter through-hole, the pinion gear 12 can be attached with high precision while being reliably concentric with the coupling 11. At this time, the locking step 23 is abutted against the coupling end surface 22 to be positioned in the axial direction, and the pinion gear 12 can be accurately assembled into the coupling 11. If the pinion gear 12 is provided in a state where it is integrated with the coupling 11 in advance, it can be easily attached to the shaft 10 of the motor body 2, which is an existing general-purpose motor.

[0056] The end face 25 of the pinion gear 12 is engaged with a step 20 on the outer periphery of the shaft 10, and the pinion gear 12 is positioned axially relative to the shaft 10 together with the coupling 11. This makes it possible to position the meshing teeth 12a of the pinion gear 12 at a predetermined position on the shaft 10 and accurately mesh the pinion gear 12 with the input gear of the secondary side reduction mechanism.

[0057] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the description of the embodiment, and various modifications can be made without departing from the spirit of the invention described in the claims of the present invention. [Explanation of symbols]

[0058] 1 Valve actuator 2 Motor body 10 Output shaft 11 Coupling 12 Pinion gear 12a Biting teeth 12b Reduced diameter teeth 12c Tooth Tip 20 steps 21 Through hole 21a Small diameter through hole 21b Large diameter through hole 22 Coupling end face 23 Locking step 24 Insertion hole 25 Pinion gear end face 30 Inner surface of small diameter through hole 31 Inner surface of large diameter through hole 32 Shaft base outer periphery 33 Shaft tip outer periphery

Claims

1. A motor is mounted on a valve actuator, and a substantially cylindrical coupling having a through hole in the center is provided between a shaft, which is an output shaft of the motor, and a pinion gear. the through hole of the coupling includes a small diameter through hole disposed on a base side of the shaft and a large diameter through hole provided on a tip side of the shaft and having a larger diameter than the small diameter through hole, The shaft is press-fitted and fixed in the small diameter through hole on one end side of the coupling, and the teeth of the pinion gear are press-fitted and fixed in the large diameter through hole on the other end side of the coupling, a tip end side of the shaft is inserted into an insertion hole formed in the pinion gear with a base end side of the shaft press-fitted into the small diameter through hole of the coupling, and the pinion gear is provided so as to be substantially concentric with the shaft when integrated with the coupling, 2. A motor for a valve actuator, comprising: a motor for transmitting rotation from said shaft to said pinion gear through said coupling;

2. 2. The motor for a valve actuator according to claim 1, wherein a base side of the shaft is press-fitted into the small diameter through hole of the coupling by an interference fit, and a tip side of the shaft is inserted into an insertion hole formed in the pinion gear by a clearance fit.

3. 3. The motor for a valve actuator according to claim 1, wherein the coupling is made of a material softer than the pinion gear, and teeth of the pinion gear are disposed in a state in which they bite into an inner circumferential surface of the large diameter through hole.

4. 4. The motor for a valve actuator according to claim 1, wherein a tip side of a tooth of the pinion gear on a side where the pinion gear is pressed into the coupling is notched to form a reduced-diameter tooth, and with the tip of the reduced-diameter tooth pressed into the inner circumferential surface of the large-diameter through hole of the coupling, a locking step formed at a boundary between the reduced-diameter tooth and the meshing tooth of the pinion gear abuts against an end face of the coupling, thereby positioning the pinion gear in the axial direction with respect to the coupling.

5. 5. The motor for a valve actuator according to claim 4, wherein an end face side of the pinion gear close to the shaft is engaged with a step formed on the outer periphery of the shaft, and the pinion gear is axially positioned relative to the shaft together with the coupling.

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