JP7554705B2 - Spindle unit of machine tool - Google Patents

Description

This invention relates to a spindle unit that is installed in a machine tool that performs cutting on a workpiece made of metal and in which tools are changed by an automatic tool changer, for example.

In this specification and claims, the side of the spindle where the tool attachment portion is provided, i.e. the left side in Figure 1, will be referred to as the front, and the opposite side as the rear.

A conventional spindle device for a machine tool includes a hollow spindle that is rotatably supported by a housing and has a tool attachment at its tip, a drawbar that is coaxially arranged within the spindle so as to be movable axially relative to the spindle and that clamps and unclamps a tool to the tool attachment by axial movement, a number of disc springs that move the drawbar in the clamping direction, an actuator that has a piston and moves the drawbar in the unclamping direction against the biasing force of the disc spring, and a through-coolant path that supplies coolant from the outside to the tool fixed to the tool attachment. In such a known spindle device, a rotary joint is provided between the rear end of the drawbar and the housing, and the through-coolant path is formed by coolant passages provided in the housing, the rotary joint, and the drawbar.

In the case of known spindle devices such as those described above, if the rotary joint becomes dirty or stiff after long-term use, coolant can leak from the rotary joint when machining the workpiece, and the coolant can seep into the bearings that support the spindle or the motor that drives the spindle, causing the spindle device to break down.

In order to solve such problems, the applicant proposed a spindle unit for a machine tool, which is characterized in that, in the above-mentioned known spindle unit, a branch path is provided in the cleaning air path, which is connected to the space in which the rear end of the drawbar moves back and forth, and a coolant discharge path is provided in the housing that connects the space with the outside of the housing, so that when machining is completed and the drawbar is moved forward by the actuator to unclamp, coolant that has leaked into the space from the rotary joint during machining can be discharged to the outside of the housing via the coolant discharge path by compressed air sent into the space via the branch path (see Patent Document 1).

JP 2009-202301 A

However, in the spindle device described in Patent Document 1, the coolant that leaks from the rotary joint during machining is discharged outside the housing after machining is completed, so the coolant that leaks during machining cannot be discharged outside the housing while machining is continuing.

The object of this invention is to solve the above problem and provide a spindle device for a machine tool that can discharge coolant that leaks from the through-coolant path during machining to the outside of the housing while machining continues.

The present invention has the following aspects to achieve the above objectives.

1) A spindle unit of a machine tool comprising: a hollow spindle rotatably supported by a housing and having a tool mounting portion at its tip; a draw bar arranged coaxially within the spindle so as to be movable in the axial direction relative to the spindle, and which clamps and unclamps a tool to and from the tool mounting portion by axial movement; first moving means for moving the draw bar in a clamping direction; and second moving means for moving the draw bar in an unclamping direction; the spindle unit being provided with a through-coolant path for supplying coolant from an outside to a tool fixed to the tool mounting portion, a cleaning air path for supplying air from an outside to the tool mounting portion, and a purge air path for guiding coolant leaking from the through-coolant path to a drain hole provided in the housing by air supplied from the outside,
a flow rate of air flowing through the cleaning air path and the purge air path is changed by the movement of the draw bar in a clamping direction by the first moving means and the movement of the draw bar in an unclamping direction by the second moving means ,
the first moving means comprises biasing means for biasing the draw bar in the clamping direction, the second moving means comprises an actuator having a piston which moves in the front-rear direction and which moves the draw bar in the unclamping direction against the biasing force of the biasing means, the piston being adapted to move between a first position at which the draw bar is permitted to move in the clamping direction by the first moving means to clamp the tool, and a second position at which the draw bar is moved in the unclamping direction to unclamp the tool,
a spindle device of a machine tool, wherein a cleaning air flow passage which becomes part of the cleaning air path is formed in the piston, and when the piston is in the first position, air flows into the purge air path and the flow of air to the cleaning air flow passage is blocked, and when the piston is in the second position, air flows into the cleaning air flow passage and some of the air flowing into the cleaning air flow passage flows into the purge air path .

2) A spindle unit of a machine tool as described in 1) above, wherein a purge air flow passage which becomes part of the purge air path and a cleaning air flow passage which becomes part of the cleaning air path are formed in parallel in the piston, and when the piston is in the first position, air flows into the purge air flow passage and the flow of air to the cleaning air flow passage is blocked, and when the piston is in the second position, air flows into the cleaning air flow passage and at least a part of the flow of air to the purge air flow passage is blocked .

3) a rotary joint is provided between the housing and the draw bar, a coolant flow passage that is a part of the through coolant path is formed between the draw bar and the rotary joint, and a drain chamber that receives coolant leaking from the rotary joint and communicates with the drain hole is provided between the housing and the piston,
a plate protruding radially outward is fixedly provided at a rear portion of the draw bar, and when the piston is at the first position, a labyrinth portion is formed between the plate and the piston and between the draw bar and the piston, and the labyrinth portion is formed which is in communication with the purge air path and the drain chamber,
A spindle device of a machine tool according to 1) or 2) above, wherein, when the piston is in the first position, purge air is blown from the purge air path through the labyrinth portion into the drain chamber, and coolant leaking from the rotary joint is guided to the drain hole by the pressure of the purge air blown into the drain chamber.

4) A spindle unit of a machine tool as described in 3) above, further comprising a branch air path which branches off from the cleaning air path, is blocked when the piston is in the first position, and communicates the cleaning air path with the drain chamber when the piston is in the second position.

5) An annular wall protruding rearward is provided on the outer circumferential edge of the rear surface of the plate of the draw bar, and a recess is formed surrounded by the annular wall,
the piston comprises a pressure-receiving portion disposed in a cylinder chamber provided in the housing, and a cylindrical rod portion provided in the pressure-receiving portion and extending forward, the rod portion comprising: a cylindrical pressing portion that presses a rear surface of the annular wall of the plate when the piston moves from the first position to the second position; a cylindrical fitting portion provided on a radially inner portion of the pressing portion so as to protrude forward of the pressing portion and fitted into the recess so as to be movable in the front-rear direction; and an inward flange portion that protrudes radially inward from a front end of the fitting portion,
A spindle unit of a machine tool according to 3) or 4) above, wherein a portion of the purge air is formed to penetrate the fitting portion in the front-rear direction, the cleaning air flow path is formed to penetrate the pressing portion in the front-rear direction, and the drain chamber is formed between an internal space of the rod portion and the housing.

According to the spindle device of the machine tool described above in 1) to 5) , when the draw bar is moving in the clamping direction during machining, the purge air path is opened and the cleaning air path is closed, changing the flow rate of air flowing through the cleaning air path and the purge air path, so that air flows through the purge air path and the flow of air through the cleaning air path is blocked. The flow rate of air flowing through the purge air path becomes relatively large, and the coolant leaking from the through coolant path is guided to the drain hole by the air pressure and discharged to the outside of the housing. Therefore, the coolant leaking from the through coolant path during machining can be discharged to the outside of the housing while machining is continued. As a result, the coolant leaking from the through coolant path during machining is prevented from entering the bearings supporting the spindle or the motor for driving the spindle while machining is continued, causing a breakdown of the spindle device. The coolant leaking from the through coolant path during unclamping when the draw bar is moving in the unclamping direction is discharged to the outside of the housing as described above during subsequent machining.

In addition, if coolant leaks from the through-coolant path during unclamping while the drawbar is moving in the unclamping direction, the cleaning air path is opened and only part of the purge air path is closed, changing the flow rate of air through the cleaning air path and the purge air path. When air flows through the cleaning air path and part of the air flows through the purge air path, the pressure of the purge air guides the coolant leaking from the through-coolant path to the drain hole and discharges it outside the housing.

According to the spindle device of the machine tool described above in 4) , it is possible, with a relatively simple structure, to open the cleaning air path and close only a part of the purge air path during unclamping when the draw bar is moving in the unclamping direction.

The machine tool spindle devices described above in 3) and 5) have a relatively simple structure.

1 is a vertical sectional view showing the overall configuration of a spindle device of a machine tool according to the present invention, illustrating a state in which a tool is clamped (upper half) and a state in which the tool is unclamped (lower half). [0023] FIG. FIG. 2 is a vertical sectional view showing a main part of a spindle device with a tool clamped thereon. FIG. 4 is a vertical sectional view showing a main part of a spindle device in a state where a tool is unclamped. FIG. 11 is a longitudinal sectional view of a main portion of a modified example of the spindle device of the machine tool according to the present invention, showing a state in which a tool is clamped. 5A and 5B show a state in which the tool of the spindle device in FIG. 4 is unclamped, and FIG. 5A is a vertical sectional view of the main part, and FIG. 5B is a sectional view taken along line A-A in FIG. 5A.

The following describes an embodiment of the invention with reference to the drawings.

Figure 1 shows the overall configuration of a spindle unit of a machine tool according to the present invention, with the upper half showing the state in which the tool is clamped and the lower half showing the state in which the tool is unclamped. Figure 2 shows the main parts of Figure 1 with the tool clamped, and Figure 3 shows the main parts of Figure 1 with the tool unclamped.

In FIG. 1, the spindle unit 1 comprises a housing 2 provided on a spindle head (not shown) of a machining center or the like, and a hollow spindle 3 arranged rotatably within the housing 2. The front and rear of the spindle 3 are rotatably supported relative to the housing 2 by rolling bearings 4 and 5, respectively. A motor 6 for rotating the spindle 3 is provided between the front bearing 4 and the rear bearing 5 within the housing 2.

At the front end of the spindle 3, a tapered hole 8 (tool attachment portion) into which the tapered shank 7a of the tool holder 7 holding a tool (not shown) is fitted is formed so as to communicate with the axial hole 9, and a collet 11 is disposed as a clamping mechanism for clamping/unclamping the fitted tool holder 7. The tool holder 7 is formed with a coolant passage 7b that penetrates it in the front-rear direction.

A drawbar 12 for clamping/unclamping the collet 11 is arranged coaxially within the axial hole 9 of the spindle 3 so that it does not rotate relative to the spindle 3 but can move back and forth, which is the axial direction of the spindle 3. When in the retracted position, the drawbar 12 clamps the collet 11 and draws and fixes the tapered shank 7a of the tool holder 7 into the tapered hole 8 (see the upper half of Figure 1). When in the forward position, the drawbar 12 unclamps the collet 11 and allows the tapered shank 7a of the tool holder 7 to be removed from the tapered hole 8.

The drawbar 12 is moved in the clamping direction (rearward) by a number of disc springs 15 (biasing means, first moving means) arranged between a rearward step 13 formed at the front of the inner circumferential surface of the axial hole 9 of the spindle 3 and a forward step 14 formed at the rear of the outer circumferential surface of the drawbar 12, and is moved in the unclamping direction (forward) against the biasing force of the disc springs 15 by an actuator 16 (second moving means) provided at the rear of the drawbar 12.

As shown in Figures 2 and 3, the rear of the drawbar 12 protrudes slightly rearward from the main shaft 3, and a plate 17 that protrudes radially outward is fixed to this protruding portion. An annular wall 18 is provided on the rear outer peripheral edge of the rear surface of the plate 17, and a recess 19 is formed surrounded by the annular wall 18.

The actuator 16 is provided in the housing 2 and includes a cylinder chamber 21 to which pressure oil is supplied from a hydraulic source (not shown), and a piston 22. The piston 22 is composed of a pressure-receiving portion 23 disposed in the cylinder chamber 21 and a cylindrical rod portion 24 provided on the pressure-receiving portion 23 and extending forward, and moves between a first position (see the upper half of FIG. 1 and FIG. 2) (retracted position) in which the draw bar 12 is permitted to move in the clamping direction by the disc spring 15 to clamp the tool, and a second position (see the lower half of FIG. 1 and FIG. 3) (advanced position) in which the draw bar 12 is pushed forward to move in the unclamping direction to unclamp the tool.

The rod portion 24 of the piston 22 includes a large cylindrical portion 25 and a small cylindrical portion 27 that is integrally provided via a connecting portion 26 on the radial inside of the large cylindrical portion 25 and whose inner peripheral surface is in sliding contact with the outer peripheral surface of the cylindrical portion 2a provided in the housing 2. The front end of the large cylindrical portion 25 is a pressing portion 28 that presses the rear surface of the annular wall 18 of the plate 17 when the piston 22 moves from the first position to the second position. The rear end surface of the small cylindrical portion 27 is on the same plane as the rear end surface of the connecting portion 26. The front end of the small cylindrical portion 27 is provided with an insertion portion 29 that protrudes forward from the connecting portion 26 and is inserted into the recess 19 of the plate 17 so as to be movable in the front-rear direction. An inward flange 31 that protrudes radially inward is provided at the front end of the insertion portion 29, and a surrounding wall 32 that protrudes forward from the inner peripheral edge of the inward flange 31 and surrounds the rear end of the drawbar 12 is provided.

When the piston 22 is in the first position, the drawbar 12 is biased by the disc spring 15 to move to a retracted position where the tool is clamped. When the piston 22 is in the second position, the drawbar 12 is pushed by the piston 22 to move to a forward position where the tool is unclamped.

Inside the piston 22, a rotary joint 33 is arranged so that most of it, except for the front end, is located within the cylindrical portion 2a of the housing 2. The rotary joint 33 contacts the drawbar 12 in the retreated position when the piston 22 moves to the first position and separates from the drawbar 12 in the forward position when the piston 22 moves to the second position. A drain chamber 34 is provided between the piston 22 and the housing 2 to accommodate coolant leaked from the rotary joint 33 and to communicate with the drain hole 2b provided in the housing 2. When the piston 22 is in the first position, the internal space of the cylindrical portion 2a becomes the drain chamber 34, and when the piston 22 is in the second position, the internal space of the cylindrical portion 2a and the space between the front end of the cylindrical portion 2a and the inward flange 31 become the drain chamber 34. The drain chamber 34 communicates with the drain hole 2b via a coolant discharge passage 2c formed in the housing 2.

When the piston 22 is in the first position, a drain chamber 34 and a labyrinth portion 35 leading to a purge air path 60 described later are formed between the plate 17 and the inward flange 31 and surrounding wall 32 of the piston 22, and between the draw bar 12 and the surrounding wall 32.

The spindle device 1 is provided with a through-coolant path 40 that supplies coolant from an external coolant supply means (not shown) to the tool clamped to the front end of the spindle 3, a cleaning air path 50 that supplies air to the tapered hole 8 from an external air supply means (not shown), and a purge air path 60 that guides the coolant that has leaked from the through-coolant path 40 and is contained in the drain chamber 34 to the drain hole 2b provided in the housing 2 by air supplied from the outside.

The through coolant path 40 is composed of a first coolant passage 41 formed in the housing 2 and connected to the coolant supply means, a second coolant passage 42 formed in the rotary joint 33 and connected to the first coolant passage 41, and a third coolant passage 43 formed at the axis of the draw bar 12 and whose front end is connected to the coolant passage 7b of the tool holder 7. When the piston 22 moves to the first position and the draw bar 12 is in the retracted position, the second coolant passage 42 and the third coolant passage 43 are connected, and when the piston 22 moves to the second position and the draw bar 12 is in the forward position, the second coolant passage 42 and the third coolant passage 43 are separated.

The cleaning air path 50 is composed of a first air flow path 51 formed in the housing 2 and connected to the compressed air supply means, a plurality of second air flow paths 52 (cleaning air flow paths) formed in the pressing portion 28 of the piston 22 at intervals in the circumferential direction and penetrating in the front and rear directions, with the front end opening to the front surface of the pressing portion 28 and the rear end opening to the rear surface of the pressing portion 28 and leading to the inside of the piston 22, a plurality of third air flow paths 53 formed in the plate 17 at intervals in the circumferential direction, a plurality of fourth air flow paths 54 formed in the rear part of the draw bar 12 at intervals in the circumferential direction so as to lead to the third air flow path 53 and whose tips open to the step portion 34 of the draw bar 12, a fifth air flow path 55 consisting of a space in which the disc spring 15 is arranged in the axial hole of the main shaft 3, and a sixth air flow path 56 formed in the front part of the draw bar 12 so as to lead to the fifth air flow path 55 and whose tip opens into the tapered hole 8. The first air flow path 51 of the cleaning air path 50 consists of a first straight section 511 extending forward from the rear surface of the housing 2, an annular section 512 connected to the front end of the first straight section 511, and multiple second straight sections 513 formed at intervals in the circumferential direction, with rear ends connected to the annular section 512 and tips opening to the front surface of the radially outer portion of the cylindrical section 2a.

When the piston 22 moves to the first position and the draw bar 12 is in the retreated position, the pressing portion 28 of the piston 22 moves away from the rear surface of the annular wall 18 of the plate 17, and the rear end opening of the second air passage 52 is blocked by the front surface of the radially outer portion of the cylindrical portion 2a of the housing 2, thereby blocking the flow of air to the third air passage 53. On the other hand, when the piston 22 moves to the second position and the draw bar 12 is in the advanced position, the first air passage 51 and the second air passage 52 communicate with each other through a space 57 formed between the front surface of the radially outer portion of the cylindrical portion 2a of the housing 2 and the rear surface of the pressing portion 28 and the small cylindrical portion 27 of the rod portion 24 of the piston 22, and the second air passage 52 and the third air passage 53 communicate with each other, and air is supplied into the tapered hole 8 through the cleaning air path 50.

The purge air path 60 includes the first air flow path 51 of the cleaning air path 50 and a plurality of purge air flow paths 61 formed at intervals in the circumferential direction and penetrating the small cylindrical portion 27 of the rod portion 24 of the piston 22 in the front-rear direction. The front end openings of the purge air flow paths 61 and the first air flow paths 51 are located at the same circumferential position.

When the piston 22 moves to the first position and the draw bar 12 is in the retracted position, the purge air passage 61 communicates with the first air passage 51 of the cleaning air passage 50, and the front surface of the radially outer portion of the cylindrical portion 2a of the housing 2 is in close contact with the rear surface of the pressing portion 28 and the small cylindrical portion 27 of the rod portion 24 of the piston 22, blocking the rear end opening of the second air passage 52. Furthermore, the purge air passage 61 communicates with the drain chamber 34 through the labyrinth portion 35 formed as described above. This opens the purge air passage 60, sends air to the drain chamber 34, and the coolant leaking from the through coolant passage 40 is guided by the air pressure to the drain hole 2b and discharged to the outside of the housing 2.

As described above, according to the spindle device 1, during machining when the draw bar 12 is moving in the clamp direction, the purge air path 60 is opened and the cleaning air flow path 52 is closed, so that air flows through the purge air path 60 and the flow of air to the cleaning air path 50 is blocked, and the coolant that has leaked from the through coolant path 40 and is contained in the drain chamber 34 is guided by the air pressure to the drain hole 2b and is discharged to the outside of the housing 2 through the coolant discharge path 2c. Therefore, the coolant that has leaked from the through coolant path 40 during machining can be discharged to the outside of the housing 2 while machining is continuing. As a result, it is possible to prevent the coolant that has leaked from the through coolant path 40 during machining from entering the bearings that support the spindle 3 or the motor 6 for driving the spindle while machining is continuing, thereby causing a breakdown of the spindle device 1.

In addition, any coolant that leaks out of the through coolant path 40 during unclamping when the drawbar 12 is moving in the unclamping direction is discharged to the outside of the housing 2 during subsequent machining, in the same manner as described above.

Figures 4 and 5 show modified examples of the spindle device of a machine tool.

4 and 5, the spindle unit 100 is provided with a branch air path 110 that is closed when the piston 22 is in the first position and that connects the cleaning air path 50 to the drain chamber 34 when the piston 22 is in the second position. The branch air path 110 is formed at a position offset in the circumferential direction from the purge air flow path 61 of the purge air path 60, and is composed of a through hole 111 whose one end opens into the second air flow path 52, which is the cleaning air flow path of the piston 22, and whose other end opens into the inner circumferential surface of the small cylindrical portion 27 of the rod portion 24.

The rest of the configuration of the spindle unit 100 is the same as that of the spindle unit 1 shown in Figures 1 to 3, and is designated by the same reference numerals.

According to the spindle unit 100 of the machine tool shown in Figures 4 and 5, even when the piston 22 is in the second position and the draw bar 12 is moving in the unclamping direction, part of the air flowing through the cleaning air path 50 flows through the branch air path 110 into the drain chamber 34, and the coolant leaking from the through coolant path 40 and contained in the drain chamber 34 due to the air pressure is guided to the drain hole 2b and discharged to the outside of the housing 2 through the coolant discharge path 2c.

The spindle device of this invention is suitable for use in machine tools that perform cutting on metal workpieces.

1, 100: spindle device, 2: housing, 2b: drain hole, 3: spindle, 8: tapered hole (tool attachment portion), 12: draw bar, 15: disc spring (first moving means, biasing means), 16: actuator, 17: plate, 18: annular wall, 19: recess, 22: piston, 23: pressure receiving portion, 24: rod portion, 28: pressing portion, 29: fitting portion, 31: inward flange portion, 33: rotary joint, 34: drain chamber, 35: labyrinth portion, 40: through coolant path, 42: second coolant path, 43: third coolant path, 50: cleaning air path, 51: first air path, 52: second air path (cleaning air path), 53: third air path, 60: purge air path, 61: purge air path

Claims (5)

a hollow spindle supported rotatably by a housing and having a tool mounting portion at its tip; a draw bar arranged coaxially within the spindle so as to be movable in the axial direction relative to the spindle, and clamping and unclamping a tool to and from the tool mounting portion by axial movement; first moving means for moving the draw bar in a clamping direction; and second moving means for moving the draw bar in an unclamping direction, wherein a through-coolant path supplies coolant from an outside to a tool fixed to the tool mounting portion, a cleaning air path for supplying air from an outside to the tool mounting portion, and a purge air path for guiding coolant leaking from the through-coolant path to a drain hole provided in the housing by air supplied from the outside,
a flow rate of air flowing through the cleaning air path and the purge air path is changed by the movement of the draw bar in a clamping direction by the first moving means and the movement of the draw bar in an unclamping direction by the second moving means ,
the first moving means comprises biasing means for biasing the draw bar in the clamping direction, the second moving means comprises an actuator having a piston which moves in the front-rear direction and which moves the draw bar in the unclamping direction against the biasing force of the biasing means, the piston being adapted to move between a first position at which the draw bar is permitted to move in the clamping direction by the first moving means to clamp the tool, and a second position at which the draw bar is moved in the unclamping direction to unclamp the tool,
a cleaning air flow passage that forms part of the cleaning air path, and when the piston is in the first position, air flows into the purge air path and the flow of air to the cleaning air flow passage is blocked, and when the piston is in the second position, air flows into the cleaning air flow passage and some of the air flowing into the cleaning air flow passage flows into the purge air path . 2. A spindle unit of a machine tool according to claim 1, wherein a purge air flow passage which is a part of the purge air path and a cleaning air flow passage which is a part of the cleaning air path are formed in parallel in the piston, and when the piston is in the first position, air flows into the purge air flow passage and the flow of air to the cleaning air flow passage is blocked, and when the piston is in the second position, air flows into the cleaning air flow passage and at least a part of the flow of air to the purge air flow passage is blocked. a rotary joint is provided between the housing and the draw bar, a coolant flow passage that is a part of the through coolant path is formed between the draw bar and the rotary joint, and a drain chamber is provided between the housing and the piston for receiving coolant that has leaked from the rotary joint and communicating with the drain hole,
a plate protruding radially outward is fixedly provided at a rear portion of the draw bar, and when the piston is at the first position, a labyrinth portion is formed between the plate and the piston and between the draw bar and the piston, and the labyrinth portion is formed which is in communication with the purge air path and the drain chamber,
3. A spindle device of a machine tool according to claim 1 or 2, wherein when the piston is in the first position, purge air is blown from the purge air path through the labyrinth portion into the drain chamber, and coolant leaking from the rotary joint is guided to the drain hole by the pressure of the purge air blown into the drain chamber . 4. A spindle unit of a machine tool according to claim 3, further comprising a branch air passage which branches off from the cleaning air passage, is blocked when the piston is in the first position, and communicates the cleaning air passage with the drain chamber when the piston is in the second position . a rearwardly protruding annular wall is provided on an outer peripheral edge of the rear surface of the plate of the draw bar, and a recess is formed surrounded by the annular wall,
the piston comprises a pressure-receiving portion disposed in a cylinder chamber provided in a housing, and a cylindrical rod portion provided in the pressure-receiving portion and extending forward, the rod portion comprising: a cylindrical pressing portion that presses a rear surface of the annular wall of the plate when the piston moves from the first position to the second position; a cylindrical fitting portion provided on a radially inner portion of the pressing portion so as to protrude forward of the pressing portion and fitted into the recess so as to be movable in the front-rear direction; and an inward flange portion that protrudes radially inward from a front end of the fitting portion,
5. A spindle unit of a machine tool according to claim 3 or 4, wherein a part of the purge air path is formed so as to penetrate the fitting portion in the front-rear direction, the cleaning air flow path is formed so as to penetrate the pressing portion in the front-rear direction, and the drain chamber is formed between an internal space of the rod portion and the housing .

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