JP3686703B2 - Position-dependent hydraulic shock absorber - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an improvement of a position-dependent hydraulic shock absorber that makes a generated damping force variable depending on its expansion / contraction position.
[0002]
[Prior art and its problems]
For example, in the case of a hydraulic shock absorber mounted on a vehicle such as a truck where the vehicle height often changes due to a change in the load load, the damping force generated by the hydraulic shock absorber responds to the above vehicle height change. It is preferable to be configured to change.
[0003]
Therefore, for example, although JP 56-39330 Patent position dependent of the hydraulic shock absorber in Japanese is disclosed, in this hydraulic shock absorber, from its structure, a so-called malfunction is expressed, attenuation settings as there is a possibility that the occurrence of force can not be expected.
[0004]
That is, in this conventional hydraulic shock absorber, when the load acting on the hydraulic shock absorber is less than a predetermined load, that is, 1 G or less, the piston rod tends to protrude from the cylinder. in the field above the oil chamber serving extension side oil chamber Haizai spring becomes shrinkage tendency made, a spool of Haizai the extension side oil chamber side of the piston in the biasing force of the spring is placed in the lowered position, The spool opens a so-called bypass path that bypasses the main damping valve disposed in the piston, and as shown by the solid line in FIG. 5, each of the damping force on the expansion side and the compression side generates low damping force (soft). It is supposed to be maintained in a state.
[0005]
Further, when the load becomes 1G or more , it is not affected by the urging force of the upper extending spring, but the spool is raised so as to retreat by the urging force of the lower spring, At this time, the bypass path is closed by the spool, and as shown by a broken line in FIG. 5, each of the damping force on the extension side and the compression side is maintained in a state of high damping force generation (hard).
[0006]
Therefore, for example, in a vehicle such as a large truck where the vehicle height often changes greatly due to a change in the load, when the load becomes large, in particular, the damping force on the compression side should be increased. So-called bottoming in the hydraulic shock absorber can be prevented in advance.
[0007]
In the case of the hydraulic shock absorber, when the loading load on the vehicle such as the above-mentioned large truck is lost, the damping force on the extension side is particularly reduced, and the rugged feeling caused by the hydraulic shock absorber is reduced. This can improve ride comfort.
[0008]
However, in the conventional hydraulic shock absorber described above, the spool for opening and closing the bypass passage is configured to be Zaisa distribution in expansion side oil chamber side of the piston, the spool is under the biasing spring biasing force The spool is forcibly lowered against the urging force of the lower urging spring due to a so-called hydraulic pressure difference between the extension side oil chamber and the pressure side oil chamber when it should be maintained in the raised state by There is a possibility.
[0009]
As a result, in the conventional hydraulic shock absorber described above, when the spool is maintained in the raised state and the compression side damping force must be maintained in the hard state, the spool is in the lowered state. There is a possibility that the compression side damping force may be switched to a soft state. Therefore, even if the generated damping force is changed in a position-dependent manner, it may not be possible to expect the damping force generation as set.
[0010]
The present invention was devised in view of the above-described circumstances, and the object of the present invention is to expect generation of damping force as set when the generated damping force is made variable by making it position-dependent. Needless to say, in addition, it is possible to give the flexibility to set each of the damping force on the expansion side and the compression side to be hard or soft, and it is optimal for mounting on a vehicle such as a truck. Another object of the present invention is to provide a position-dependent hydraulic shock absorber suitable for use as a seat damper.
[0011]
[Means for Solving the Problems]
In order to achieve the above-described object, the position-dependent hydraulic shock absorber according to the present invention includes a cylinder connected to a wheel side in a vehicle, a piston rod connected to a vehicle body side in the vehicle and retracted into and out of the cylinder, a piston defining a extension side oil chamber and the compression side oil chamber in the cylinder is slidably accommodated in the cylinder while being held in the front end spigot portion of the piston rod, the extension side damping valve of Haizai to the piston and a bypass passage that allows communication between the extension side oil chamber and the compression side oil chamber while bypassing the compression side damping valve, a spool is Zaisa distribution in the bypass path, the first to constantly biasing the spool in the downward direction it has a spring and a second spring for raising the spool against the biasing force of the first spring when the load acting on the piston rod is equal to or higher than a predetermined load In the position-dependent hydraulic shock absorber, with a vertical hole in the axial center portion of the front end spigot portion of the piston rod forming the bypass passage is formed by perforated in, said longitudinal hole of the piston rod while being communicated with the compression side oil chamber is perforated in a radial direction to the tip socket portion becomes in communication with an extension side oil chamber via the communication hole serving as the vertical, while the spool is slidably accommodated in a vertical direction in a vertical hole of the axial a cylindrical sliding portion of the inner passage of the formed part is opened to the compression side oil chamber, distribution to the first lower pressure side oil chamber while locking the spring is provided continuously to the lower end outer periphery of the tubular sliding portion And a hook portion that can lock the upper end of the second spring, and when the spool is raised in the vertical hole by the urging force of the second spring, the inner path is The spool is in the vertical hole by the urging force of the first spring. Inner passage when descending is communicated communication hole of the lower, or first with the inner passage when the spool by urging force of the second spring is increased in the vertical hole communicating with the communication hole of the lower When the spool descends in the vertical hole due to the urging force of the spring, the inner passage communicates with the upper communication hole, and the upper communication hole prevents the flow of hydraulic oil from the expansion oil chamber side below the check communicates with the distribution standing under the valve extension side oil chamber, the distribution standing under the compression side check valve to prevent outflow of the extension side oil chamber of the hydraulic fluid from the communication hole side downward該伸side oil chamber Suppose that it communicates with the communication hole side .
[0012]
[Action]
Therefore, in the position-dependent hydraulic shock absorber, since the spool is disposed in the cylinder on the pressure side oil chamber side which is the lower oil chamber defined by the piston, the spool is provided with the extension side oil chamber. The oil pressure is not affected by a so-called hydraulic pressure difference between the pressure side oil chamber and the pressure side oil chamber, and abnormal movement due to the hydraulic pressure difference, that is, abnormal operation does not occur.
[0013]
In the position-dependent hydraulic shock absorber, when the load acting on the position-dependent hydraulic shock absorber is less than a predetermined load, that is, 1 G or less, the sliding position of the piston in the cylinder is relatively raised, and the spool is The lowering state is maintained by the urging force from the first spring without being affected by the urging force from the second spring.
[0014]
Then, the load is a predetermined load or more, i.e., when more than 1G, the sliding position of the piston is relatively lowered position, the second spring said spool overcomes the biasing force of the first spring It is maintained in a rising state in response to the biasing force.
[0015]
Whether the spool is in the lowered or raised state, the inner path is set as a bypass path, while the selection of whether the spool is raised or lowered allows communication to the extension side oil chamber of the bypass path Therefore, the damping force on the extension side or the damping force on the compression side can be freely set to either a high damping force generation (hard) state or a low damping force generation (soft) state.
[0016]
And since the 2nd spring is distribute | arranged to the compression side oil chamber in a cylinder, it functions also as a spring which buffers the bottom of a piston near the time of the most compression in this position-dependent hydraulic shock absorber.
[0017]
【Example】
In the following, the present invention will be described based on an embodiment shown in the drawings. The position-dependent hydraulic shock absorber shown in FIG. 2, it has a piston 3, further, in this embodiment, the spool 4, has a first spring 5, and a second spring 6.
[0018]
When the position-dependent hydraulic shock absorber is mounted on a vehicle, the cylinder 1 is connected to the wheel side of the vehicle, although the lower end side is connected to the wheel side of the vehicle. In this case, a so-called cylinder body is formed (in the case of the present embodiment) or a single cylinder type.
[0019]
When the position-dependent hydraulic shock absorber is mounted on the vehicle, the piston rod 2 is connected to the vehicle body side of the vehicle at its upper end, which is always projected outside the cylinder 1, As shown in the drawing, the tip end side which is the lower end side is inserted into the cylinder 1 so as to be able to appear and retract.
[0020]
The piston 3 is slidably accommodated in the cylinder 1 while being held by the leading inlay portion 2a of the piston rod 2, and defines an extension side oil chamber U and a pressure side oil chamber L in the cylinder 1, and The side oil chamber U and the pressure side oil chamber L can communicate with each other under the arrangement of the expansion side damping valve 3a and the pressure side damping valve 3b.
[0021]
Incidentally, in this embodiment, the piston 3 is interposed in the tip inlay portion 2a of the piston rod 2 , but at this time, one end is locked to the tip base 2b side of the piston rod 2 and the other. The end is locked to the side of the piston nut 7 screwed to the tip thread portion 2c of the piston rod 2, and is fixed in a fixed state at a predetermined position.
[0022]
In this embodiment, the piston nut 7 is formed so as to have an empty portion 7a on the inner circumference on the lower half side in consideration of the accommodation of the spool 4 described later.
[0023]
Therefore, the position-dependent hydraulic shock absorber is a compression in which the piston rod 2 is immersed in the cylinder 1 and the pressure-side oil chamber L becomes the high-pressure side when the configuration of the spool 4 and a bypass path related thereto are not considered. During operation, the hydraulic oil from the pressure side oil chamber L flows into the expansion side oil chamber U via the pressure side damping valve 3b, and at this time, the pressure side damping force having a predetermined magnitude by the pressure side damping valve 3b. Is generated.
[0024]
Further, when the piston rod 2 protrudes from the cylinder 1 and the extension side oil chamber U becomes the high pressure side, the hydraulic oil from the extension side oil chamber U enters the pressure side oil chamber L via the extension side damping valve 3a. will flow out, this time, the extension side damping force becomes the predetermined size by the extension side damping valve 3a is generated.
[0025]
By the way, the position-dependent hydraulic shock absorber according to the present invention has a bypass path that bypasses the expansion-side damping valve 3a and the compression-side damping valve 3b disposed in the piston 3 by sliding the spool 4 so as to bypass the expansion-side or pressure-side bypass path. And the damping force on each side is changed.
[0026]
That is, the spool 4 includes a main body serving as a cylindrical shape is slidably accommodated in the vertical direction of the piston 3 to the perforated in has been vertical hole in 2d the axis of the tip fitting portions 2a of the piston rod 2 causes interposed and the sliding portion 4a, it has a flange portion 4b for sliding contact with the outer periphery are provided continuously to the lower end periphery of the cylindrical sliding portion 4a on the inner circumference of hollow portion 7a of the piston nut 7, a cylindrical An inner path R is formed in the shaft core portion of the sliding portion 4a, and the hook portion 4b is engaged with a locking portion for locking a lower end of a first spring 5 described later, and an upper end of the second spring 6 is engaged. The locking part is set to be stopped.
[0027]
Further, the spool 4 exposes the lower end of the cylindrical sliding portion 4a to the pressure side oil chamber L in the cylinder 1 so that the inner path R is opened to the pressure side oil chamber L in the cylinder 1 and communicates with it. The upper end portion of the cylindrical sliding portion 4a has a communication hole 4c that is opened in the radial direction and communicates the inner path R with the outer peripheral side of the cylindrical sliding portion 4a.
[0028]
In the meantime, the spool 4 is assumed to be locked to the stopper 7b disposed on the inner periphery of the lower end of the piston nut 7 so that the spool 4 is prevented from dropping, that is, dropping from a predetermined position.
[0029]
The spool 4, which is the vertical hole 2d in the vertical direction when sliding the communication hole 4c of the piston rod 2 of the distal end spigot end of the vertical which is perforated in a radially 2a communicating holes 2e, 2f, That is, it is configured to selectively face either the upper communication hole 2e or the lower communication hole 2f , and set the inner path R as either the expansion side or the pressure side bypass path.
[0030]
That is, of the communication holes 2e and 2f, the upper communication hole 2e is opened and closed by the check valve 8 on the extension side that prevents the hydraulic oil from the extension side oil chamber U side from flowing into the communication hole 2e side. The lower communication hole 2f is closed so as to be openable and closable by a pressure-side check valve 9 that prevents hydraulic oil from the communication hole 2f from flowing out to the expansion-side oil chamber U. .
[0031]
Therefore, in this embodiment, as shown in FIG. 1, when the spool 4 is lowered and the communication hole 4c is collated with the lower communication hole 2f , the upper communication hole 2e is closed. At the same time , the inner passage R is set as an extension-side bypass passage having the pressure-side check valve 9 to allow hydraulic oil from the extension-side oil chamber U to flow into the pressure-side oil chamber L, but to prevent backflow. becomes, on the other hand, as shown in FIG. 2, when the spool 4 is communicating hole 4c is raised is collated over the communicating hole 2e, together with the lower communication hole 2f is placed in the closed state, said inner passage R is set to the bypass path of the compression side with the extension side check valve 8, the hydraulic oil from the compression side oil chamber L is allowed to flow into the expansion side oil chamber U to prevent the backflow Will be.
[0032]
In view of the above, in the present invention, the bypass path can be independently set to either the expansion side or the compression side bypass path , and therefore, the damping force on the expansion side and the compression side can be independently changed , that is, As will be described later, in the case of the illustrated embodiment, as shown in FIG. 1, when the load is 1 G or less and the spool 4 is lowered, the bypass path becomes the bypass path on the extension side, and the extension side As shown in FIG. 2, when the load is 1G or more and the spool 4 is rising, the bypass path becomes the pressure side bypass path and the pressure side damping force is reduced .
[0033]
The first spring 5 maintains the spool 4 formed as described above in the lowered state, and the first spring 5 is accommodated in the empty portion 7a of the piston nut 7, It is assumed that the lower end is locked to the flange portion 4 b of the spool 4.
[0034]
The upper end of the first spring 5 is locked to the inner periphery of the upper end of the empty portion 7a in the piston nut 7.
[0035]
Attributable to, when the first spring 5 to maintain the spool 4 in the lowered position, the load acting on the position-dependent hydraulic shock absorber is less than a predetermined load, i.e., in a case where equal to or less than 1G, this time, consists in the cylinder 1 tends to piston rod 2 projects, therefore, the sliding position of the piston 3 in the cylinder 1 is relatively raised position, the influence of the biasing force from the second spring 6 in the lower I will not receive it.
[0036]
The second spring 6 maintains the spool 4 in the raised state against the urging force of the first spring 5, and the second spring 6 is arranged below the spool 4. The lower end is locked to the lower end side of the cylinder 1 while the upper end is locked to the flange 4b.
[0037]
Incidentally, when the second spring 6 maintains the spool 4 in the raised state against the urging force of the first spring 5, the load acting on the position-dependent hydraulic shock absorber is a predetermined load or more, that is, 1G or more. At this time, the piston rod 2 tends to be largely immersed in the cylinder 1, so that the sliding position of the piston 3 in the cylinder 1 is relatively lowered, and the second The biasing force of the spring 6 affects the spool 4.
[0038]
Further, since the second spring 6 is disposed in the pressure side oil chamber L in the cylinder 1 in this embodiment, the so-called hydraulic pressure difference between the extension side oil chamber U and the pressure side oil chamber L is reduced. It is not affected and abnormal movement due to the hydraulic pressure difference, that is, it does not operate abnormally, and near the maximum compression time of the position-dependent hydraulic shock absorber, this cushions the bottom of the piston 3. It will also function as a spring.
[0039]
In the illustrated example, the base valve portion 10 is disposed inside the lower end of the cylinder 1, and the lower end of the second spring 6 is locked to the valve seat member 10 a constituting the base valve portion 10. However, instead of this, although not shown, the lower end of the second spring 6 may be locked to an appropriate so-called stopper member that is fixedly disposed on the lower end side of the cylinder 1.
[0040]
The position-dependent hydraulic shock absorber according to this embodiment formed as described above has a tendency that the piston rod 2 protrudes from the inside of the cylinder 1 due to the distribution of the suspension spring, although not shown in the drawings when mounted on the vehicle. It is biased in the extension direction .
[0041]
From this state, when the load acting on the position-dependent hydraulic shock absorber is 1 G or less, as shown in FIG. 1, the sliding position of the piston 3 in the cylinder 1 is set to the relatively raised position, and the spool 4 The second spring 6 disposed below the second spring 6 is not in contact with the spool 4, and the spool 4 is lowered by the urging force of the first spring 5.
[0042]
As a result, the spool 4 collates the communication hole 4c opened in the cylindrical sliding portion 4a with the communication hole 2f below the opening in the piston rod 2, and is formed in the cylindrical sliding portion 4a. The inner path R is set as an extension-side bypass path.
[0043]
Accordingly, when the piston 3 slides in the cylinder 1 in this state, the extension side damping force during the extension operation becomes soft, whereas the compression side damping force during the compression operation becomes hard. It becomes the state of.
[0044]
Further, when the load becomes 1G or more, as shown in FIG. 2, the sliding position of the piston 3 in the cylinder 1 is relatively lowered, and the second spring disposed below the spool 4. 6 contacts the spool 4, and therefore the spool 4 is raised by the biasing force of the second spring 6 that exceeds the biasing force of the first spring 5.
[0045]
As a result, contrary to the above , the spool 4 collates the communication hole 4c with the communication hole 2e above the piston rod 2 and sets the inner path R as a pressure-side bypass path. Therefore, when the piston 3 slides in the cylinder 1 in this state, the compression side damping force during the compression operation becomes a soft state, whereas the extension side damping force during the extension operation. Is in a hard state.
[0046]
FIG. 3 shows that the inner path R is set to the expansion side or the pressure side bypass path by sliding the spool 4, and the setting of the extension side or the pressure side of the bypass path to the sliding of the spool 4 is the same as that in the above-described embodiment. An embodiment in which the case is reversed is shown.
[0047]
In this embodiment, since the configuration other than the spool 4 is the same as that of the above-described embodiment, the same portions of the configuration are the same in the drawing except where necessary. The detailed description will be omitted.
[0048]
That is, in the embodiment shown in FIG. 3 , the spool 4 is formed in an annular shape on the outer periphery of the upper end in addition to the communication hole 4c that is opened in the radial direction at the upper end and communicates with the inner path R. The hole 4c is a so-called different route, and has a notch 4d that communicates with the inner path R.
[0049]
In this embodiment, as shown in the figure, when the spool 4 is in the lowered state, the notch 4d is collated with the communication hole 2e above the opening of the piston rod 2, and at this time, The communication hole 4c is set so as not to be matched with the communication hole 2f below the opening of the piston rod 2.
[0050]
Further, in the embodiment shown in FIG. 3, although not shown, when the spool 4 is placed in raised position, the above-described communication hole 4c and is collated hole 2f of the lower of the, at this time, the notch 4d are set so as not to match the communication hole 2e of the upper.
[0051]
Therefore, in the embodiment shown in FIG. 3, the setting of the expansion side or the pressure side of the bypass path by sliding of the spool 4 can be made by slightly changing the design of the spool 4. Conversely, it can be set.
[0052]
Note that the basic operation of the embodiment shown in FIG. 3 is the same as that of the embodiment shown in FIG.
[0053]
As described above, in the present invention, either when the spool 4 is in the lowered state (the state shown in FIGS. 1 and 3) or when the spool 4 is in the raised state (the state shown in FIG. 2). However, depending on whether the spool 4 is set to the expansion side or the compression side, the damping force on the expansion side or the compression side can be freely set to either a hard state or a soft state. Become.
[0054]
As a result, the position-dependent hydraulic shock absorber load acting predetermined load or less, i.e., when: 1G, as shown by a solid line in FIG. 4, to set the damping force of the extension side in soft On the other hand, the damping force on the compression side can be set to a hard state, or as shown by the solid line in FIG. 5, both the damping force on the expansion side and the compression side can be set to a soft state, and when the load is more than 1G, as shown by a broken line in FIG. 4, to set the damping force of the compression side in soft relative to setting the damping force of the extension side of the state of the hard, or FIG. As indicated by a broken line in FIG. 5, it is possible to set both the extension side and compression side damping forces to a hard state .
[0055]
And, as is well known, enabling the damping characteristics shown in FIG. 4 to be realized enables a rapid decrease in energy in the motion system of this type of hydraulic shock absorber, that is, the damping effect. This makes it possible to match the characteristics when increasing.
[0056]
In the above description, the position-dependent hydraulic shock absorber according to the present invention has been described as an example in which the position-dependent hydraulic shock absorber is mounted as a suspension for a vehicle such as a truck whose vehicle height changes due to a change in the load load. Therefore, by changing the design of other configurations including appropriately setting the urging forces of the first spring 5 and the second spring 6, a large truck with a large vehicle height change or a small vehicle height change is small. The position-dependent hydraulic shock absorber can be used for any small truck.
[0057]
In addition, the position-dependent hydraulic shock absorber can be moved up and down such as the track by changing the design of other structures including appropriately setting the urging forces of the first spring 5 and the second spring 6 described above. It can also be used as a damper for a moving vehicle seat.
[0058]
【The invention's effect】
As described above, in the present invention, since the spool that sets the bypass path to either the expansion side or the pressure side is disposed on the pressure side oil chamber side defined by the piston in the cylinder, The spool is not affected by the so-called hydraulic pressure difference between the expansion side oil chamber and the compression side oil chamber, and therefore, the abnormal operation of the spool moving abnormally due to the hydraulic pressure difference is not manifested. Allows damping force to be generated as set.
[0059]
In the position-dependent hydraulic shock absorber, when the load acting on the position-dependent hydraulic shock absorber is below a predetermined load or above the predetermined load, that is, when the spool is in the lowered state or in the raised state. However, depending on whether the spool is set to either the expansion side or the compression side, the expansion side damping force or the compression side damping force can be freely set to either a hard state or a soft state.
[0060]
In the position-dependent hydraulic shock absorber, the second spring is disposed in the compression side oil chamber in the cylinder. There is an advantage that it also functions as a spring for cushioning.
[Brief description of the drawings]
FIG. 1 is a partial longitudinal sectional view of a position-dependent hydraulic shock absorber according to one embodiment of the present invention.
FIG. 2 is a partially enlarged longitudinal sectional view showing a state where the spool in FIG. 1 is raised.
FIG. 3 is a partially enlarged longitudinal sectional view showing another embodiment of the open / close state of the bypass passage by the spool.
FIG. 4 is a characteristic diagram of a generated damping force in the position-dependent hydraulic shock absorber according to the present invention.
FIG. 5 is a characteristic diagram of a generated damping force in a conventional position-dependent hydraulic shock absorber.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston rod 2a Tip | blade leading part 2d Vertical hole 2e, 2f Communication hole 3 Piston 3a Extension side damping valve 3b Pressure side damping valve 4 Spool 4a Cylindrical sliding part 4b Eave part 5 1st spring 6 2nd spring 8 , 9 Check valve L Pressure side oil chamber R Inner passage constituting the extension side bypass passage or the pressure side bypass passage U Extension side oil chamber

Claims (1)

A cylinder connected to a wheel side of the vehicle, a piston rod which is infested in the cylinder is connected to the vehicle body in a vehicle, slidably is accommodated in the cylinder while being held in the front end spigot portion of the piston rod allowing the piston to define a extension side oil chamber and the compression side oil chamber in the cylinder, the communication between the extension side oil chamber and the compression side oil chamber while bypassing the extension side damping valve and the compression side damping valve of Haizai to the piston a bypass passage, a spool that is Zaisa distribution in the bypass path, and a first spring for constantly biasing the spool in the downward direction, the load acting on the piston rod above when equal to or greater than a predetermined load first in a position-dependent hydraulic shock absorber comprising a second spring for raising the spool against the biasing force of the spring, the upper the axis of the tip fitting portions of the piston rod With longitudinal holes, which are perforated in constituting a bypass passage, Shin via the communication holes said longitudinal hole becomes vertical is perforated in the radial direction at the distal end spigot portion of the piston rod while being communicated with the compression side oil chamber A cylindrical sliding portion that communicates with the side oil chamber and opens the inner passage formed in the shaft core portion to the compression side oil chamber while the spool is accommodated in the vertical hole so as to be slidable in the vertical direction; have a flange portion that allows locking the upper end of the second spring to be Zaisa distribution in the first pressure side oil chamber while locking the lower end of the spring is provided continuously to the lower end outer periphery of the tubular sliding portion When the spool is raised in the vertical hole by the urging force of the second spring, the inner passage communicates with the upper communication hole, and the spool is moved into the vertical hole by the urging force of the first spring. The inner passage communicates with the lower communication hole when descending at 2 or the second spring The inner passage communicates with the lower communication hole when the spool ascends in the vertical hole by the urging force, and the inner passage opens upward when the spool descends in the vertical hole by the urging force of the first spring. The upper communication hole communicates with the extension-side oil chamber under the arrangement of the extension-side check valve that prevents the inflow of hydraulic oil from the extension-side oil chamber, and the extension-side oil chamber A position-dependent hydraulic shock absorber characterized in that it communicates with a lower communication hole side under the presence of a pressure-side check valve that prevents the hydraulic oil from flowing out from the communication hole side to the extension side oil chamber .

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