JPH091433A - Apparatus for incorporating piston in engine - Google Patents

Abstract

PURPOSE: To provide an apparatus for incorporating pistons having various outer diameters in a cylinder block. CONSTITUTION: A piston incorporating unit 16 provided in the opposite position to an opening part of a cylinder 2 is provided with a movable base 37 moved by a pitch feeding mechanism 30, a band 80 provided on the movable base 37 and a piston extruding mechanism 122. The band 80 having the length capable of winding around the whole periphery of a piston 3 is looped by at least one turn. The first end of the band 80 is connected to a first support mechanism 51 and the second end is connected to a second support mechanism 52. The second support mechanism 52 can be moved in the direction of separating from the first support mechanism 51. When the second support mechanism 52 is lifted by a drive mechanism 46, the second end of the band 80 is pulled up to make the band 80 wind around the piston 3 while the diameter of a piston ring is adapted to be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston assembling device for inserting a piston into a cylinder of a cylinder block in an engine assembling process.

[0002]

2. Description of the Related Art As illustrated in FIG. 9, a cylinder block 1 of an engine is formed with a number of cylinders 2 corresponding to the number of cylinders, and a piston 3 is housed in each cylinder 2. Each piston 3 is provided with a connecting rod 4, and each piston 3 is connected to the crankshaft 6 by fixing a connecting rod cap 5 to the end of the connecting rod 4 with a bolt (not shown).

A piston ring 8 is mounted in a piston ring groove formed in the head of the piston 3. Since the outer diameter of the piston ring 8 in the free state is larger than the inner diameter of the cylinder 2, it is necessary to reduce the outer diameter of the piston ring 8 by some means when inserting the piston 3 into the cylinder 2.

For the above-mentioned reasons, conventionally, when inserting a piston into a cylinder, for example, a cylindrical guide jig having a tapered inner diameter is set at the open end of the cylinder, and the piston is mounted on the guide jig. By pushing in, the diameter of the piston ring is reduced along the tapered inner surface. In this case, the piston is inserted into the cylinder with the diameter of the piston ring being reduced by pushing the piston into the cylinder from the other end of the guide jig by the piston pushing member.

Further, as described in Japanese Utility Model Publication No. 60-165166 and Japanese Utility Model Publication No. 62-178086, the piston ring is contracted by a tightening band capable of expanding and contracting the diameter of the piston. A piston insertion jig that can be inserted into a cylinder has also been proposed.

[0006]

Since the cylindrical guide jig having the tapered inner surface must be of a size corresponding to the outer diameter of the piston, it is necessary to use the cylindrical guide jig depending on the type (size) of the piston. Different types of guide jigs are required, which not only makes jig management complicated and costly, but also requires the guide jigs to be replaced every time the type of piston changes, which makes work setup for that. It takes a lot of work.

Further, the piston insertion jig using the above-mentioned tightening band can be used substantially only for a piston having one outer diameter, and the jig is replaced every time the size of the piston changes. It had to be versatile because it had to be used.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a highly versatile piston assembling device which allows pistons of various sizes to be inserted into each cylinder by one piston assembling device.

[0009]

The present invention, which was developed to achieve the above object, is an apparatus for assembling a piston having a piston ring mounted therein to a cylinder block of an engine, the cylinder opening of the cylinder block. And a first support mechanism provided on the base and near a side portion of the piston, and a piston provided on the base and with respect to the first support mechanism. A second support mechanism that is relatively movable in a plane along the radial cross section of the piston, and has a length that allows it to be wound around the entire circumference of the piston, and is wound in a loop and has one end side of the first support mechanism. Between the one end side and the other end side of the band, which is fixed to the support mechanism and the other end side of which is fixed to the second support mechanism and which covers the outer peripheral side of the piston ring. It has a drive mechanism that draws the band to a position where the piston ring contracts by driving the support mechanism in the unfolding direction, and a piston pushing member that is provided so as to be able to move forward and backward facing the end surface of the piston. And a piston pushing mechanism including an actuator that advances the piston pushing member to a position where the piston enters the cylinder.

[0010]

The piston skirt side portion is inserted into the opening of the cylinder in advance, and the cylinder block is set so that the piston pushing member is located directly in front of the piston. At this time, the first support mechanism and the second support mechanism are located close to each other, and the band is made to stand by in a state where the band is wider than the outer diameter of the piston. Then, the band is put on the outside of the piston ring.

By driving the first support mechanism and the second support mechanism away from the above state, the band is reduced in diameter,
Shrink the piston ring by wrapping the band around the outside of the piston ring. In this case, even if the size of the piston varies, the amount by which the band is narrowed only changes, so the piston ring can be reduced in diameter using the same band. With the piston ring contracted, the actuator of the piston pushing mechanism moves in the forward direction, so that the piston pushing member pushes the piston into the cylinder.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The piston assembly apparatus 10 shown in FIG. 1 is used to insert the piston 3 into each cylinder 2 of the cylinder block 1 as shown in FIG. 9, for example. The cylinder block 1 in the illustrated example is an in-line 6 cylinder, and the cylinders 2 are provided at the same pitch in the length direction of the cylinder block 1.

The cylinder block 1 is conveyed to a predetermined position in front of the piston assembling apparatus 10 in a posture in which the cylinder block 1 is placed on the support base 11 and tilted sideways, that is, in a posture in which the axis of the cylinder 2 is horizontal. Before each piston 3 is conveyed to the piston assembly device 10, the skirt side portion of the piston 3 is inserted into the cylinder 2 in advance.

Each of the pistons 3 has a No. 1 in relation to the rotation angle of the crankshaft 6. 1 piston and No. 6 pistons in the same phase, No. 2 pistons and No. 5 pistons have the same phase, and No. 3 pistons and no. The four pistons are attached to the crankshaft 6 so that they have the same phase. That is, the positional relationship is such that every time the crankshaft 6 rotates by 120 °, two pistons for each of the above phases reach the bottom dead center in sequence. For this reason, the piston assembling apparatus 10 of this embodiment has a structure in which two pistons having the same phase can be simultaneously assembled in the cylinder block 1.

That is, as shown in FIG. 1 and the like, the piston assembling apparatus 10 is provided with a pair of left and right piston assembling units 16 and 17 on a base frame 15, and the piston assembling units 16 and 17 form pistons. Two cylinders can be inserted into each cylinder 2.

The base frame 15 includes a base 20 fixed to the floor of the factory and pillars 21 and 2 standing on the base 20.
2 is provided. A guide rod 25 extending horizontally and the first lead screw 2 are provided on the upper ends of the pillars 21 and 22.
6, 27 are provided. Each lead screw 26,
The columns 27 are supported by the columns 21 and 22 so that they can be rotated separately.

The lead screws 26, 27 are rotated by a desired rotation amount in either forward or reverse directions by a pitch feed drive mechanism 28, 29 capable of controlling the rotation amount like a servo motor having an encoder. You can do it. The lead screws 26 and 27 and the drive mechanisms 28 and 29 are the pitch feed mechanism 3 for moving the piston assembly units 16 and 17 in the arrangement direction of the cylinder 2.
0.

In FIG. 1, the first piston assembly unit 16 located on the right side and the second piston assembly unit 17 located on the left side are symmetrical with respect to each other, but have substantially the same structure and operation. Therefore, the first piston assembly unit 16 will be described below as a representative.

The piston assembly unit 16 has a movable base 37 having an upper portion 35 and a lower portion 36, as shown in FIG. As shown in FIG. 1 and the like, the movable base 37 is arranged at a position facing the opening of the cylinder 2. A thrust bearing 40 is provided above the movable base 37, and a guide rod 25 is fitted to the bearing 40 so as to be relatively movable in the horizontal direction.

A nut portion 41 screwed onto the lead screw 26 is provided on the upper portion of the movable base 37.
As the lead screw 26 rotates, the movable base 37 moves in the horizontal direction along the guide rod 25 in accordance with the rotation direction and the number of rotations.

A second base extending vertically on the movable base 37.
Lead screw 45 is provided. The lead screw 45 is a drive mechanism 4 including a servomotor and the like.
By means of No. 6, the gear mechanism 47 for power transmission can be rotated in both forward and reverse directions by a desired number of revolutions.

As shown in the front view of FIG. 4 and the side view of FIG. 7, a first support mechanism 51 is provided below the lead screw 45. A second support mechanism 52 is provided above the lead screw 45. The first support mechanism 51 is located near the side of the piston 3 and includes a movable frame 55 that can be raised and lowered.

The movable frame 55 has a guide member 56 (shown in FIG. 4) extending in the vertical direction, is relatively movable in the axial direction (vertical direction) with respect to the lead screw 45, and has a return spring (not shown). Or movable frame 5
It is urged toward the descending position shown in FIGS. 4 and 7 by its own weight or the like.

A first advancing / retreating head 60 is provided on the front side of the movable frame 55. The advancing / retreating head 60 is movable in the front-rear direction of the movable frame 55 along a rod-shaped guide member 61 (only the front end is shown in FIG. 4) extending in the front-rear direction (the left-right direction in FIG. 7).
A reciprocating actuator 62 such as a fluid pressure cylinder provided on the back side of the valve 5 allows driving from the retracted position shown in FIGS. 1 and 7 to the advanced position shown in FIGS. 2 and 8.

The advancing / retreating head 60 is provided with a guide member 65 extending horizontally (left and right in FIG. 4), a floating member 66 movable horizontally along the guide member 65, a return spring 67 and the like. ing. The return spring 67 urges the floating member 66 toward the initial position (the direction away from the piston 3) shown in FIG. The initial position of the floating member 66 can be adjusted by a stopper 68 that can adjust the amount of protrusion in the horizontal direction. These advancing / retreating heads 60 and guide members 6
5, the floating member 66, and the like form a first floating unit.

A bracket 75 is provided on the floating member 66. The bracket 75 extends diagonally rightward in FIG. The bracket 75 is provided with a first arm 76. The first arm 76 is movable in the up-down direction along the bracket 75 (the direction intersecting with the direction in which the floating member 66 moves), and by turning the adjusting screw 78 of the height adjusting mechanism 77, the arm with respect to the bracket 75 is moved. The height of 76 can be set variably. Then, one end side of the band 80, that is, the first end 81 is fixed to the first arm 76.

As shown in FIG. 7 etc., the first movable frame 5
A second movable frame 85 is provided above 5.
The movable frame 85 includes a nut portion 86 screwed to the lead screw 45 and a guide member 87 extending in the vertical direction.
(Shown in FIG. 4), and when the lead screw 45 rotates, the second screw is rotated according to the rotation direction and the rotation speed.
The movable frame 85 is vertically movable to a desired position.

As shown in FIGS. 4 and 7, the second
A second advancing / retreating head 90 is provided on the front side of the movable frame 85. This advancing / retreating head 90 also has a rod-shaped guide member 91 extending in the front-rear direction (only the front end is shown in FIG. 4).
It is provided so as to be able to move forward and backward along. The advancing / retreating head 90 is driven from the retracted position shown in FIGS. 1 and 7 to the advanced position shown in FIGS. 2 and 8 by a reciprocating actuator 92 such as a fluid pressure cylinder provided on the back side of the movable frame 85. I am able to do it.

The advancing / retreating head 90 is provided with a guide member 96 extending in the horizontal direction (the left-right direction in FIG. 4) and constituting a second floating means, and is movable in the horizontal direction along the guide member 96. A floating member 97, a return spring 98, etc. are provided. The return spring 98 biases the floating member 97 toward the initial position shown in FIG. 4, and the initial position (position before movement) of the floating member 97 can be adjusted by the stopper 100.

The second arm 1 is attached to the floating member 97.
01 is provided, and the band 8 is attached to the second arm 101.
The other end side of 0, that is, the second end 102 is fixed by a fixing member 103.

The band 80 has a thickness of, for example, 0.8 mm ±.
It is made of a stainless steel strip-shaped metal plate of about 0.2 mm, and has a first end 81 and a second end 1 as conceptually shown in FIG.
02, so that the second end 102 can move with respect to the first end 81 in a plane along the radial cross section of the piston 3. A slightly wider portion 105 is provided on the first end 81 of the band 80, and the second end 102 side of the band 80 is passed through this wide portion 105 and pulled upward to loop the band 80 in a ring shape. I am letting you. Further, the wide portion 105 is provided with an ear portion 106 protruding to the outer peripheral side of the band 80, and the ear portion 106 is fixed to the first arm 76 by an appropriate fixing component 107 such as a bolt.

On the front edge side (piston side) of the band 80, a plurality of convex portions 110 are provided at appropriate intervals in the circumferential direction of the band 80. These convex portions 110 project to the outer peripheral side of the band 80. A spring locking portion 111 is provided on the upper portion on the trailing edge side of the band 80. The lower end of the band lifting spring 112 is connected to the spring locking portion 111. The upper end of the band lifting spring 112 has a second advancing / retreating head 90.
It is locked to the spring receiving portion 113 provided in the above, and the tension is generated in the direction of pulling up the band 80.

As shown in FIG. 6 and the like, the band 80 is provided with an overlapping portion 115 by looping 360 ° or more so as to overlap over a certain length on the outer peripheral side of the first end 81.

The upper end of the overlapping portion 115 and the band 80
If the angle between the line segment M1 connecting the center C of the band 80 and the line segment M2 connecting the center C of the band 80 and the center of the ear portion 106 of the first end 81 is θ, the present inventors have studied. It has been found that when θ is in the range of 20 ° ± 10 °, the load for pulling up the first end 81 can be small when the band 80 is contracted.

When θ is out of the above range, the load for pulling up the first end 81 at the time of reducing the diameter of the band 80 remarkably increases, and in extreme cases, the diameter of the band 80 may not be reduced. . Therefore, θ is 2 with a center value of 20 °.
It is recommended to set it in the range of 0 ° ± 10 °.

A cylindrical piston pushing member 120 (a part of which is shown in FIGS. 1, 2 and 7 and 8) is provided on the front side of the movable base 37. The push-out member 120 faces the end face of the piston 3, and the push-out member 1
The center of 20 is located on an extension of the center of the piston 3. The piston push-out member 120 has a movable base 37.
Piston pushing mechanism 122 provided with a reciprocating actuator 121 such as a fluid pressure cylinder provided on the back side of the
It is possible to move forward and backward. That is, when the piston 3 is inserted into the cylinder 2, the piston pushing member 120 can be advanced in the direction of the cylinder 2 by the actuator 121, and can be retracted to the position shown in FIGS. 1 and 7 after the piston is inserted. It has become.

The drive mechanisms 28, 29, 46 and the actuators 62, 92, 121, etc. described above are sequence-controlled in the following operation sequence by a controller 125 having a control program such as a microcomputer incorporated therein.

Next, the operation of the piston assembling apparatus 10 having the above structure will be described. This piston assembly device 10 is
For example, when assembling the piston 3 to the cylinder block 1 as shown in FIG. 1 piston and No. After assembling the 6-piston, 2 pistons and No. Assemble 5 pistons, and then No. 3 pistons and no. Assemble 4 pistons. Each piston 3
Is transferred to a predetermined position in front of the piston assembly device 10 in a state where the skirt side portion is horizontally inserted into the opening of the cylinder 2.

No. 1 piston and No. When assembling the 6 pistons, the pitch feed mechanism 30 reads the lead by the pitch feed mechanism 30 based on the pulse command from the controller 125 so that the piston pushing members 120 of the piston assembling units 16 and 17 are located directly in front of the pistons 3. Screw 2
6, 27 are rotated by a predetermined amount. At this time, the crankshaft 6 is previously No. 1 crank and No. Rotate the 6 cranks to the bottom dead center position.

The first movable frame 55 and the second movable frame 85 are in the initial positions shown in FIGS. 4 and 7, respectively, and the band 80 is in a spread state. The advancing / retreating heads 60, 90 are both actuators 62,
It stands by at 92 in the retracted position shown in FIGS.

From the above initial state, the advancing / retreating heads 60, 90 are simultaneously advanced by the actuators 62, 92 as shown in FIG. 2, whereby the band 80 is advanced and covers the outer peripheral surface of the piston ring 80. That is, as shown in FIG. 4, the band 80 in an expanded state surrounds the outside of the piston ring 80. In this case, since the band 80 is prevented from hanging down by the band lifting spring 112, the shape of the band 80 is kept circular to some extent.

After that, the second lead screw 45 is rotated by the drive mechanism 46 in the direction of raising the second movable frame 85. Since the piston 3 is inserted into the cylinder 2 and its movement in the radial direction is restrained, when the second movable frame 85 rises, the diameter of the band 80 shrinks.

As the band 80 winds around the outer peripheral surface of the piston 3, the first end 81 of the band 80 gradually approaches the outer peripheral surface of the piston 3. The first end 81 is movably supported in the horizontal direction by the floating member 66, and further, the first movable frame 55 can move upward, so that the first end 81 moves in the direction in which it contacts the piston 3. acceptable.

When the diameter of the band 80 is reduced in this way, the second end 102 tends to be displaced leftward in FIG. Here, since the floating member 97 of the second support mechanism 52 is movable in the horizontal direction, the second end 102 can be displaced in this direction. For this reason, the band 80 is wound around the entire circumference of the piston ring 8 in a substantially evenly tight state. The drive mechanism 46 inserts the piston 3 into the cylinder 2 by rotating the lead screw 45 by a predetermined amount in response to a command pulse from the controller 125 and reducing the outer diameter of the piston ring 8 to about the same as the outer diameter of the piston 3. The state becomes possible (state shown in FIGS. 5 and 8).

After that, the actuator 121 of the piston pushing mechanism 122 moves in the forward direction, so that the piston pushing member 120 pushes the piston 3 into the cylinder 2. At this time, since there is a slight gap between the opening edge of the cylinder 2 and the outer peripheral surface of the piston 3, the front edge of the band 80 may be caught in this gap unless some measures are taken. However, in this embodiment, the convex portion 110 is provided on the front edge portion of the band 80, and since the convex portion 110 abuts the opening edge of the cylinder 2, the band 8 is provided in the gap.
The problem that 0 is bitten can be avoided.

After the piston 3 is inserted all the way into the cylinder 2 through the series of operations described above, the connecting rod cap 5 is fixed to the end of the connecting rod 4 by a bolt (not shown).

No. 1 piston and No. After 6 pistons are inserted into each cylinder 2, the piston pushing mechanism 12
The second actuator 121 operates in the backward direction, and the second movable frame 85 is returned to the initial position shown in FIGS. 4 and 7 by the drive mechanism 46. Further, the first movable frame 55 also descends to the initial position shown in FIGS. 4 and 7. The floating members 66, 97 are springs 6 for returning.
Return to the initial position by 7,98.

After that, by the pitch feed mechanism 30,
The piston assembly units 16 and 17 are No. 2 pistons and No. It can be moved right in front of the 5 piston. In addition, the crankshaft 6 can be manually or mechanically
By rotating it by 0 °, the No. 2 cranks and No.
Position 5 cranks at bottom dead center. Then, by repeating the same piston insertion step as described above, the No. 2 pistons and No. Five pistons are inserted in each cylinder 2.

After that, by the pitch feed mechanism 30,
The piston assembly units 16 and 17 are No. 3 pistons and no. It can be moved right in front of the 4 pistons. Also, by rotating the crankshaft 6 by 120 °, N
o. 3 cranks and No. Position 4 cranks at bottom dead center. Then, by repeating the same piston insertion step as described above, No. 3 pistons and no. Four pistons are inserted in each cylinder 2.

When the size (outer diameter) of the piston 3 is small, the piston assembling apparatus 10 having the above-described structure has the band 80 having a smaller diameter according to the piston outer diameter as shown by a two-dot chain line A in FIG. Since the piston ring can be contracted, the diameter of the piston ring can be reduced similarly to a large-sized piston. In order that the overlapping portion 115 of the band can always maintain the above-mentioned angle θ (about 20 °) regardless of the outer diameter of the piston 3, the height adjusting mechanism 77 adjusts the angle depending on the outer diameter of the piston. The height of the second arm 101 may be adjusted.

In the piston assembly apparatus 10 of this embodiment, the movement of the first end 81 and the second end 102 can be allowed by the free movement of the floating members 66 and 97 when the band 80 is wrapped around the piston. Therefore, it is possible to avoid applying an excessive load to the band 80, and it is possible to pull the band 80 with a force as small as possible.

Moreover, the piston assembly device 10 of the above embodiment
Has a pair of left and right assembling units 16 and 17, so that in a cylinder block having an even number of cylinders such as four cylinders or six cylinders, two pistons can be simultaneously inserted in accordance with the phase of the crankshaft. Because it is possible, it has good work efficiency.

[0053]

According to the present invention, regardless of the size of the piston, the diameter of the piston ring can be reduced to an outer diameter substantially matching the outer peripheral surface of the piston, and pistons of various sizes can be inserted into desired cylinders. be able to. Further, by adopting the floating means as claimed in claims 2 and 3, it is possible to smoothly reduce the diameter of the piston ring without causing excessive stress in the band.

Further, when the overlapping portions of the bands having the contact angle θ are provided as described in claim 4, the movement of the bands when the bands are reduced in diameter becomes smoother, and the load is as small as possible. The piston ring can be contracted by. Further, if a pair of assembling units are provided as described in claim 5, two pistons can be simultaneously inserted into the cylinder block of the even-numbered cylinder in accordance with the rotational position of the crankshaft. The work can be further speeded up.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a piston assembling apparatus according to an embodiment of the present invention with a part cut away.

FIG. 2 is a perspective view of the apparatus shown in FIG. 1 with an advancing / retreating head advanced.

FIG. 3 is a perspective view schematically showing a band and a support mechanism of the device shown in FIG.

FIG. 4 is a front view of a part of the piston ring assembly unit of the device shown in FIG.

FIG. 5 is a front view of the assembly unit shown in FIG. 4 in a state where the band has a reduced diameter.

6 is a front view of the first support mechanism in the device shown in FIG. 1. FIG.

7 is a side view of a first support mechanism and a second support mechanism of the apparatus shown in FIG.

8 is a side view showing an operating state of the first support mechanism and the second support mechanism shown in FIG. 7. FIG.

FIG. 9 is a perspective view showing a cylinder block and a piston.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylinder block 2 ... Cylinder 3 ... Piston 8 ... Piston ring 10 ... Piston assembly device 16, 17 ... Piston assembly unit 30 ... Pitch feed mechanism 46 ... Drive mechanism 51 ... First support mechanism 52 ... Second support Mechanism 55 ... First movable frame 66 ... Floating member 80 ... Band 81 ... First end 85 ... Second movable frame 97 ... Floating member 102 ... Second end 115 ... Band overlapping part 122 ... Piston pushing mechanism

Claims (5)

[Claims] 1. A device for assembling a piston, to which a piston ring is attached, to a cylinder block of an engine, the base being disposed at a position facing a cylinder opening of the cylinder block, and the base being provided on the base. A first support mechanism arranged near the side of the piston, and a second support mechanism provided on the base and movable relative to the first support mechanism in a plane along the radial cross section of the piston. A support mechanism and a length that allows it to be wound around the entire circumference of the piston, and is wound in a loop shape. One end side is fixed to the first support mechanism and the other end side is the second support mechanism. Fixed to the piston ring and covered on the outer peripheral side of the piston ring, and by driving the support mechanism in a direction of increasing the distance between one end side and the other end side of the band, the piston Drive mechanism that draws the band to a position where the inner ring contracts, and a piston push-out member that can move forward and backward facing the end face of the piston, and pushes the piston until the piston enters the cylinder. An piston assembly apparatus for an engine, comprising: a piston pushing mechanism having an actuator for moving a member forward. 2. The first support mechanism is provided with a movable frame provided movably in the radial direction with respect to the piston, and movable with respect to the movable frame in a direction intersecting the moving direction of the movable frame. The piston assembling apparatus according to claim 1, further comprising: a floating member having an arm whose one end side is fixed, and a return spring for urging the floating member in a direction of expanding the band. 3. The piston assembly apparatus according to claim 2, wherein the floating member is provided with an adjusting mechanism capable of adjusting the position of the arm in a direction intersecting the moving direction of the floating member. . 4. The loop is formed by looping the band by 360 ° or more to provide an overlapping portion, and an angle formed by a line segment connecting both ends of the overlapping portion and the center of the band is 20.
The piston assembling apparatus according to claim 1, wherein the range is ± 10 °. 5. A first piston assembly unit having the first support mechanism, the second support mechanism, a band, a drive mechanism, and a piston pushing mechanism is provided on the base, and
A second piston mounting unit having a mechanism substantially similar to that of the first piston mounting unit is provided on a base different from the base, and both piston mounting units are arranged in a cylinder block of a cylinder block. The piston assembling apparatus according to claim 1, further comprising a pitch feed mechanism that can be moved in any direction.