Power meter

Abstract

To provide a watt-hour meter that can significantly reduce manufacturing costs compared to conventional techniques. [Solution] A watt-hour meter comprising a meter body and a terminal block that are separable from each other, a current bar that is fixed to the meter body and electrically connected to a terminal fitting of the terminal block, and the current bar is configured to be fixed to the terminal fitting via a fixing screw member, wherein the fixing screw member has a head, a male threaded portion, and a non-male threaded portion that is provided between the head and the male threaded portion and does not have a male thread, the outer diameter of the non-male threaded portion is smaller than the outer diameter of the male threaded portion, the current bar has a female threaded portion with a thread groove that mates with the thread of the male threaded portion, and the female threaded portion has an inner diameter that is larger than the inner diameter of the male threaded portion specified in the JIS standard.

Description

[Technical Field]

[0001] The present invention relates to a watt-hour meter having a meter body and a terminal block that are separable from each other, and in particular, to a watt-hour meter in which a current bar is fixed to the meter body and electrically connected to a terminal fitting of a terminal block, and the current bar is fixed to the terminal fitting via a fixing screw member. [Background technology]

[0002] Generally, watt-hour meters are known in which the meter body and the terminal block are configured to be separable from each other. For example, in such watt-hour meters, a current bar fixed to the meter body can be fixed to a terminal fitting of the terminal block by a fixing screw member. For example, to fix the current bar, the current bar can be arranged so as to overlap the front surface of the terminal fitting, and the fixing screw member can be inserted into a screw hole of the terminal fitting through an opening in the current bar and tightened into the screw hole.

[0003] Regarding the above-mentioned fastening method, a fall-off prevention structure for preventing a fixing screw member from falling off the current bar is known. An example of a typical screw fall-off prevention structure is described in, for example, Patent Document 1. In this example, a screw member includes a cylindrical non-externally threaded portion, which is smaller in diameter than the externally threaded portion and does not have an external thread, between the externally threaded portion at the tip and the head. A mounting plate is provided on the front side of an installation plate having a threaded hole for fastening the externally threaded portion. A through hole is formed in the installation plate to allow the screw member to pass through. A female thread is formed in the through hole of the installation plate. In this configuration, the male thread portion of the screw member passes through the through hole of the installation plate and is fastened to the screw hole of the installation plate. The non-externally threaded portion is held within the through hole of the installation plate. The female thread of the through hole interferes with the male thread portion of the screw member, preventing the screw member from falling off the installation plate.

[0004] In a conventional screw fall-out prevention structure for an electricity meter, a screw member having a configuration similar to that of the screw member of Patent Document 1 can be used as the fixing screw member. That is, the fixing screw member has, between the male threaded portion at the tip and the head, a cylindrical non-male threaded portion that is smaller in diameter than the male threaded portion and does not have a male thread formed thereon.

[0005] Furthermore, a female thread is formed in the opening of the current bar to prevent the fixing screw member from falling off. Conventionally, the female thread portion of the current bar is formed to have the same thread dimensions as the screw hole of the terminal fitting so that it can mate with the male thread portion of the fixing screw member. For example, JIS B0205-4 specifies the reference dimensions of general-purpose metric threads. Furthermore, JIS B0209-1 and JIS B0209-2 specify the tolerances of general-purpose metric threads. The female thread portion of a conventional current bar is formed to have an inner diameter specified in these JIS standards relative to the male thread portion of the fixing screw member.

[0006] In a screw member for fixing a current bar of a watt-hour meter, the non-external thread portion is generally formed by rolling, which is a type of plastic processing.

[0007] However, because rolling is a plastic process, there is a limit to the outer diameter of the component that can be formed. Therefore, there is a problem in that the non-male threaded portion after rolling is likely to interfere with the female threaded portion of the current bar. If the non-male threaded portion interferes with the female threaded portion of the current bar, the fixing screw member cannot move freely within the opening of the current bar. This hinders the assembly work of the watt-hour meter. To solve this problem, the outer diameter of the non-male threaded portion after rolling has traditionally been machined. This requires an additional process in addition to rolling, significantly increasing the manufacturing cost of the fixing screw member and, ultimately, the manufacturing cost of the watt-hour meter. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 10-75077 Summary of the Invention [Problem to be solved by the invention]

[0009] According to one embodiment of the present invention, it is possible to provide a watt-hour meter that can significantly reduce manufacturing costs compared to the prior art. [Means for solving the problem]

[0010] According to one embodiment of the present invention, there is provided an electricity meter including a meter body and a terminal block that are separable from each other. A current bar is fixed to the meter body and electrically connected to a terminal fitting of the terminal block, and the current bar is configured to be fixed to the terminal fitting via a fixing screw member. The fixing screw member has a head, a male thread portion, and a non-male thread portion provided between the head and the male thread portion and not formed with a male thread, the outer diameter of the non-male thread portion being smaller than the outer diameter of the male thread portion. The current bar has a female thread portion formed with a thread groove that mates with the thread of the male thread portion. The female thread portion has an inner diameter larger than the inner diameter of the male thread portion specified in the JIS standard. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view showing an overall outline of a watt-hour meter according to an embodiment of the present invention. [Figure 2] FIG. 2 is a side view showing an example of a fixing screw member. [Figure 3] 10 is a partial cross-sectional side view of the watt-hour meter, illustrating the tightening operation of the fixing screw member. FIG. [Figure 4] FIG. 10 is an image diagram showing the clearance between the non-male thread portion and the first female thread portion. [Figure 5] 10A and 10B are diagrams illustrating possible orientations of the meter body during assembly of the watt-hour meter. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described below with reference to Figures 1 to 5. Note that the following description is merely an example and is not intended to limit the technical scope of the present invention to the following embodiment. Furthermore, in the drawings, identical or corresponding components are designated by the same reference numerals, and redundant description will be omitted.

[0013] [Overview of electricity meters] FIG. 1 is a perspective view showing an example of a watt-hour meter according to an embodiment of the present invention. In this embodiment, the watt-hour meter 10 includes a meter body 2 and a terminal block 4 that are separable from each other. A power distribution line (not shown) is electrically connected to the meter body 2 via the terminal block 4. The illustrated watt-hour meter 10 may be, for example, a single-phase three-wire type. However, the type of the watt-hour meter 10 is not particularly limited in this embodiment.

[0014] The watt-hour meter 10 is used in a state where it is installed on a wall or the like of a building. The meter body 2 and the terminal block 4 may be connected in advance and installed on a wall or the like via, for example, an installation plate (not shown). Alternatively, only the terminal block 4 may be installed in advance, and then the meter body 2 may be connected to the terminal block 4. Furthermore, the meter body 2 may be removed from the terminal block 4 installed on a wall or the like, for example, for periodic replacement. In the following description of the watt-hour meter 10, the side facing the wall or the like when installed on a wall or the like is referred to as the back side, and the side opposite the back side is referred to as the front side. Furthermore, in the installed state of the watt-hour meter 10, the side on which the terminal block 4 is located is referred to as the lower side, and the side on which the meter body 2 is located is referred to as the upper side. FIG. 1 is a perspective view of the meter body 2 and terminal block 4, which are separated from each other, viewed from the bottom of the watt-hour meter 10.

[0015] The meter body 2 includes a housing 21 made of a non-conductive material such as resin. Devices (not shown) for measuring electric energy, such as a current transformer and a circuit board, are built into the housing 21. The measured electric energy value and other values ​​can be viewed through a display window 22 provided on the front of the housing 21. The terminal block 4 includes a housing 41 made of a non-conductive material such as resin, and terminal fittings 42 fixed to the housing 41. As an example, insertion openings 43 into which the power distribution line is inserted are formed on the underside of the housing 41 of the terminal block 4, aligned laterally with the housing 41. The power distribution line inserted through the insertion opening 43 of the housing 41 is received in hollow portions 45 (not shown in FIG. 1 ) of the terminal fittings 42, and is fixed to the terminal fittings 42 with screws 44 or the like.

[0016] The meter body 2 may include a current bar 23 that protrudes and extends from, for example, the bottom surface of the housing 21. The meter body 2 can be electrically connected to the terminal block 4 by bringing the current bar 23 into contact with a terminal fitting 42. The energy meter 10 includes a fixing screw member 24 for fixing the current bar 23 to the terminal fitting 42. As shown in FIG. 1 , the fixing screw member 24 can be held in an opening in the current bar 23.

[0017] [About fixing screws] An example of the fixing screw 24 is shown in FIG. 2. FIG. 2 is a side view of the fixing screw 24. The fixing screw 24 includes a head 24a configured to be rotatable with a screwdriver or the like, a male-threaded portion 24b having male threads and forming the tip of the fixing screw 24, and a non-male-threaded portion 24c provided between the male-threaded portion 24b and the head 24a. The non-male-threaded portion 24c has a cylindrical surface on which no male threads are formed. As shown in FIG. 2, the outer diameter of the non-male-threaded portion 24c is smaller than the outer diameter of the male-threaded portion 24b. Here, the outer diameter of the male-threaded portion 24b refers to the diameter of an imaginary cylinder that contacts the crest of the male thread of the male-threaded portion 24b. In the fixing screw 24, at least the non-male-threaded portion 24c may be formed solely by rolling.

[0018] For example, a general-purpose metric screw can be used as the male thread portion 24b of the fixing screw member 24. The male thread portion 24b of the fixing screw member 24 may have a nominal diameter specified in the JIS standard according to the rated current value of the watt-hour meter 10. For example, the reference dimensions of general-purpose metric screws are specified in JIS B0205-4. Furthermore, the tolerances of general-purpose metric screws are specified in JIS B0209-1 and JIS B0209-2. The male thread portion 24b may have dimensions specified in these JIS standards.

[0019] [About the current bar] 1, the current bar 23 can electrically connect the meter body 2 to the terminal block 4 by coming into contact with the terminal fittings 42. In this embodiment, the conductive rod-shaped members for electrically connecting the meter body 2 to the terminal block 4 (specifically, the terminal fittings 42) are collectively referred to as the current bar 23.

[0020] The current bar 23 has an opening 23a (see FIG. 3 ) for passing the fixing screw member 24, and a female thread is formed in this opening 23a. The female thread of the opening 23a has a thread groove that can mate with the threads of the male thread portion 24b of the fixing screw member 24. In this embodiment, the opening 23a of the current bar 23 with the female thread formed is also referred to as the first female thread portion 23a. The first female thread portion 23a may be formed using a conventionally known tool, such as a cutting tap or a rolling tap. The male thread portion 24b of the fixing screw member 24 can pass through the first female thread portion 23a by rotation. Once the male thread portion 24b passes through the first female thread portion 23a, it interferes with the first female thread portion 23a and is prevented from falling off the current bar 23. This allows the fixing screw member 24 to be held on the current bar 23. Furthermore, in this embodiment, the inner diameter of the first female thread portion 23a (in other words, the diameter of an imaginary cylinder in contact with the crest of the thread of the first female thread portion 23a) is set larger than the inner diameter of the female thread portion of a fixing member 46 (to be described later) to which the fixing screw member 24 is fastened. The operation of this configuration will be described later.

[0021] [About terminal blocks] 3A and 3B are partial cross-sectional side views of the energy meter 10, particularly illustrating the interior of the terminal block 4. The terminal block 4 has a second female threaded portion having a thread groove that can mate with the threads of the male threaded portion 24b of the fixing screw 24. The current bar 23 can be fixed to the terminal fitting 42 by tightening the male threaded portion 24b of the fixing screw 24 into the second female threaded portion. In this embodiment, the second female threaded portion is provided on an inner peripheral portion 46a of a fixing member 46 provided on the terminal block 4. The fixing member 46 can be provided, for example, on the back side of the terminal fitting 42, at a step between the first surface 41a and the second surface 41b of the housing 41, as shown in FIGS. 3A and 3B. However, according to other embodiments, the fixing member 46 can be omitted, and the second female threaded portion can be formed on the terminal fitting 42. The fixing member 46 can be formed of a conductive or non-conductive material.

[0022] As an example, the terminal fitting 42 includes a through-hole 42a sized to receive the male threaded portion 24b and the non-male threaded portion 24c of the fixing screw member 24. No threads may be formed in the through-hole 42a. The male threaded portion 24b can be advanced beyond the through-hole 42a and tightened into the second female threaded portion 46a of the fixing member 46.

[0023] [Operation of this embodiment] Thus, in this embodiment, the current bar 23 of the meter body 2 has a first female thread portion 23a, and the fixing member 46 of the terminal block 4 has a second female thread portion 46a. The first female thread portion 23a and the second female thread portion 46a each have a thread groove that can mate with the threads of the male thread portion 24b of the fixing screw member 24. The second female thread portion 46a has an inner diameter specified by the JIS standard relative to the male thread portion 24b so that the male thread portion 24b can be tightened into the second female thread portion 46a to fix the current bar 23 to the terminal fitting 42. In contrast, the first female thread portion 23a has an inner diameter larger than the inner diameter specified by the JIS standard relative to the male thread portion 24b. In other words, the inner diameter of the first female thread portion 23a is set larger than the inner diameter of the second female thread portion 46a. This prevents the non-male threaded portion 24c of the fixing screw member 24 after rolling from interfering with the first female threaded portion 23a, thereby enabling the fixing screw member 24 to be tightened smoothly.

[0024] FIG. 4 is an image diagram showing the clearance C between the surface of the non-male threaded portion 24c and the crest of the thread of the first female threaded portion 23a when the non-male threaded portion 24c is arranged coaxially with the first female threaded portion 23a. In FIG. 4, the symbol 23a indicates an imaginary circle tangent to the crest of the thread of the first female threaded portion 23a, and therefore indicates the inner diameter of the first female threaded portion 23a. The symbol 24c indicates the outer diameter of the non-male threaded portion 24c. The dashed line indicates the inner diameter of the second female threaded portion 46a. The inner diameter of the first female threaded portion 23a is determined so as to create sufficient clearance C between the non-male threaded portion 24c and the first female threaded portion 23a and so that the thread groove of the first female threaded portion 23a can engage with the thread of the male threaded portion 24b.

[0025] In this embodiment configured as described above, even if the instrument body 2 is separated from the terminal block 4, as shown in FIG. 1, the fixing screw 24 is held to the current bar 23 by interference with the first female thread portion 23a. As shown in FIG. 3(A), the male thread portion 24b of the fixing screw 24 is inserted into the through hole 42a of the terminal fitting 42 to electrically connect the current bar 23 to the corresponding terminal fitting 42 (in other words, to bring the current bar 23 into conductive contact with the terminal fitting 42). While the fixing screw 24 is advanced, the non-male thread portion 24c can pass through the first female thread portion 23a and enter the through hole 42a of the terminal fitting 42 without interfering with the first female thread portion 23a. Then, the male thread portion 24b is tightened into the second female thread portion 46a by rotating the head 24a of the fixing screw 24 manually or with an appropriate tool such as a screwdriver. As a result, the current bar 23 is fixed to the terminal fitting 42, completing the fastening operation (FIG. 3(B)).

[0026] As described above, conventionally, the male threaded portion of the fixing screw member and the corresponding female threaded portions of the current bar and terminal block are formed to dimensions specified in JIS standards, such as JIS B0205-4. Therefore, in conventional watthour meters, the female threaded portion of the current bar through which the male threaded portion of the fixing screw member passes and the female threaded portion of the terminal block to which the male threaded portion is fastened have substantially the same inner diameter. However, in this case, the non-male threaded portion after rolling, which has limitations in outer diameter machining, is prone to interference with the female threaded portion of the current bar. Therefore, the non-male threaded portion after rolling is machined to reduce its outer diameter. This requires an additional process in addition to the rolling process, significantly increasing the manufacturing costs of the fixing screw member and, ultimately, the watthour meter.

[0027] In contrast, in this embodiment, the first female thread portion 23a, through which the male thread portion 24b passes, has an inner diameter larger than the inner diameter of the male thread portion 24b specified in the JIS standard. Therefore, as shown in FIG. 4, for example, the non-male thread portion 24c of the fixing screw member 24 after rolling can pass through the first female thread portion 23a without the conventional interference problem. Therefore, an additional process for cutting the non-male thread portion 24c is not required. This significantly reduces the manufacturing costs of the conventional fixing screw member, and ultimately the manufacturing costs of the watt-hour meter.

[0028] The first female threaded portion 23a does not require axial force for tightening because it is provided to prevent the fixing screw member 24 from falling off. Therefore, the inner diameter of the first female threaded portion 23a can be made large as long as the thread groove of the first female threaded portion 23a can fit with the thread of the male threaded portion 24b.

[0029] The male thread portion 24b of the fixing screw member 24 may be configured as a general-purpose metric thread having a nominal diameter and pitch specified in a JIS standard, such as JIS B0205-4. In this case, the second female thread portion 46a may have an inner diameter specified in the JIS standard corresponding to the nominal diameter and pitch of the male thread portion 24b. Here, the "inner diameter specified in the JIS standard" includes the dimensional tolerance range specified in the JIS standard. Therefore, for example, the inner diameter of the second female thread portion 46a may be within the dimensional tolerance range of the female thread inner diameter for general-purpose metric threads according to JIS B0209-1 or JIS B0209-2.

[0030] In contrast, the inner diameter of the first female thread portion 23a is different from the inner diameter of the second female thread portion 46a and is larger than the inner diameter specified in the JIS standard corresponding to the nominal diameter and pitch of the male thread portion 24b. For example, JIS B0209-2 specifies the maximum and minimum values ​​of the inner diameter of the female thread for general-purpose metric coarse threads. Therefore, the inner diameter of the first female thread portion 23a may be set larger than the maximum value of the nominal inner diameter of the female thread specified in JIS B0209-2 corresponding to the nominal diameter of the male thread portion 23a.

[0031] Although the embodiments of the present invention have been described above, the above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit thereof, and the present invention naturally includes equivalents thereof. Furthermore, any combination or omission of the components described in the claims and specification is possible within the scope of solving at least part of the above-described problems or achieving at least part of the effects.

[0032] The present invention includes the following aspects. 1. A watt-hour meter comprising a meter body and a terminal block that are separable from each other, a current bar that is electrically connected to a terminal fitting of the terminal block is fixed to the meter body, and the current bar is configured to be fixed to the terminal fitting via a fixing screw member; The fixing screw member has a head, a male thread portion, and a non-male thread portion provided between the head and the male thread portion and not having a male thread, and the outer diameter of the non-male thread portion is smaller than the outer diameter of the male thread portion, The current bar has a female threaded portion formed with a thread groove that mates with the threads of the male threaded portion, and the female threaded portion has an inner diameter larger than the inner diameter specified in the JIS standard with respect to the male threaded portion. Electric energy meter. 2. A watt-hour meter as described in 1 above, wherein the non-male thread portion of the fixing screw member is formed solely by rolling. [Industrial Applicability]

[0033] The present invention is broadly applicable to energy meters that include a current bar connecting the meter body to a terminal block. [Explanation of symbols]

[0034] C Clearance 10 Energy meter 2 Instrument body 21. Cabinet 22 Display window 23 Current Bar 23a Opening (first female threaded portion) 24 Fixing screw member 24a head 24b male thread 24c non-male thread 4 terminal blocks 41 Case 41a First Surface 41b Second Surface 42 Terminal fittings 42a Through hole 43 Insertion port 44 screws 45 Cavity 46 Fixing member 46a Inner circumference (second female thread)

Claims

1. A watt-hour meter comprising a meter body and a terminal block that are separable from each other, a current bar that is electrically connected to a terminal fitting of the terminal block is fixed to the meter body, and the current bar is configured to be fixed to the terminal fitting via a fixing screw member, The fixing screw member has a head, a male threaded portion, and a non-male threaded portion provided between the head and the male threaded portion and not having a male thread, and the outer diameter of the non-male threaded portion is smaller than the outer diameter of the male threaded portion, The current bar has a female thread portion formed with a thread groove that mates with the threads of the male thread portion, The male thread portion has a nominal diameter and a pitch specified in the JIS standard, and the inner diameter of the female thread portion is larger than the inner diameter specified in the JIS standard corresponding to the nominal diameter and the pitch of the male thread portion. Electric energy meter.

2. An electricity meter as described in claim 1, wherein the JIS standard is JIS B0205-4.

3. 3. A method for manufacturing the watt-hour meter according to claim 1, comprising forming the non-external thread portion of the fixing screw member solely by rolling.

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