JP6082546B2 - Hydraulic cylinder - Google Patents

Description

  The present invention relates to a hydraulic cylinder that is extended by a pressurized hydraulic fluid introduced from an external hydraulic pressure source.

  For example, in a hydraulic cylinder (lift cylinder) that is provided on a forklift and lifts a load, a piston type single unit that expands and contracts by supplying and discharging hydraulic fluid to and from the bottom side chamber of the rod side chamber and the bottom side chamber partitioned by the piston. A dynamic hydraulic cylinder is used.

  As this type of hydraulic cylinder, the one disclosed in Patent Document 1 is such that the hydraulic fluid flows in the vicinity of the stroke end and the cushion pressure is generated in the rod side chamber (cushion pressure chamber). The impact that occurs when the vehicle stops when it is fully extended is alleviated.

  When manufacturing the hydraulic cylinder, the rod side chamber is filled with a predetermined amount of the working fluid for cushioning. However, depending on the usage conditions of the hydraulic cylinder, etc., there is a possibility that the hydraulic fluid in the rod side chamber leaks into the bottom side chamber beyond the piston seal ring provided in the piston, and the amount of hydraulic fluid stored in the rod side chamber is insufficient. is there.

  For this reason, a hydraulic cylinder is provided with the replenishment hole opened to a cylindrical cylinder tube, and the plug which obstruct | occludes this replenishment hole (refer FIG. 1 of patent document 1). When the working fluid filled in the rod side chamber is insufficient, the plug is removed and the working fluid can be replenished from the outside to the rod side chamber through the replenishing hole.

  At the time of manufacturing the cylinder tube, a threaded hole constituting a replenishing hole and a seating surface on which the plug is seated are formed by cutting.

JP 2010-242803 A

  However, in the above hydraulic cylinder, since the cylinder tube is a long and large cylindrical member, it is difficult to form a replenishment hole and a seating surface by cutting the outer periphery of the cylinder tube, There is a problem that this operation takes a long time.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a hydraulic cylinder that can shorten the working time for forming a replenishing hole and the like.

The present invention is a single-acting hydraulic cylinder that is extended and operated by the pressure of hydraulic fluid guided from an external hydraulic pressure source to a bottom side chamber among a rod side chamber and a bottom side chamber partitioned by a piston, and the piston slides A cylindrical cylinder tube that is freely housed and has a bottom side chamber and a rod side chamber inside, a cylindrical piston rod that is connected to the piston and protrudes slidably from the opening end of the cylinder tube, and inside the piston rod The rod inner chamber that is defined and communicates with the rod side chamber through the communication passage, the rod head that closes the opening end of the piston rod and seals the rod inner chamber, the rod head penetrates, and the working fluid is supplied from the outside into the rod. and replenishing hole capable refill the chamber, to a sealing member for sealing the refill hole, assume Rueki圧cylinder equipped with a.
A recess is formed on the end face of the rod head, a seating surface in which a replenishment hole is opened is formed at the bottom of the recess, and a plug for sealing the replenishment hole as a sealing member is seated on the seating surface.
In addition, the valve opens as the pressure difference between the rod inner chamber and the bottom chamber rises above a predetermined value, and the return check valve returns the working fluid in the rod inner chamber to the bottom chamber, and the rod inner chamber moves upward from the piston. And a return tube connected to the inlet of the return check valve, and is offset so that the outlet of the replenishing hole that opens into the rod inner chamber and the inlet of the return tube are not arranged coaxially extending in the vertical direction. It is characterized by that.
The replenishing hole has an inlet that opens to the side of the rod head and an outlet of the replenishing hole that opens to the rod inner chamber.
In addition, the sealing member includes a replenishment check valve that is opened by a hydraulic pressure filled in the replenishment hole from the outside.

  In the present invention, when the amount of hydraulic fluid stored in the rod side chamber is insufficient, the hydraulic fluid is filled from the outside into the rod inner chamber through the replenishment hole, so that the hydraulic fluid passes from the rod inner chamber through the communication path to the rod side chamber. The shortage of hydraulic fluid can be resolved.

  At the time of manufacturing the hydraulic cylinder, the operation of forming the replenishment hole in the rod head having a small diameter smaller than that of the cylinder tube is easily performed, and the work time for forming the replenishment hole can be shortened.

It is sectional drawing of the hydraulic cylinder which concerns on 1st Embodiment of this invention. 1 is a plan view of a hydraulic cylinder according to a first embodiment of the present invention. It is sectional drawing of the hydraulic cylinder which concerns on 2nd Embodiment of this invention. It is sectional drawing of the rod head which concerns on 3rd Embodiment of this invention. It is sectional drawing of the rod head which concerns on 4th Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a sectional view showing the entire hydraulic cylinder (hydraulic cylinder) 1. The hydraulic cylinder 1 is expanded and contracted by a piston rod 20 projecting slidably from one end of the cylinder tube 10.

  The hydraulic cylinder 1 is used as a lift cylinder that lifts and lowers the load of a forklift. The hydraulic cylinder 1 has a cylinder tube 10 connected to a forklift vehicle body (not shown) via a stay 70, and a piston rod 20 connected to a fork (not shown) on which a load is placed. The hydraulic cylinder 1 is mounted on the body of the forklift so that the central axis O extends in the vertical direction. The fork is moved up and down by the expansion and contraction of the hydraulic cylinder 1.

  FIG. 2 is a plan view of the hydraulic cylinder 1 as viewed from below. The stay 70 has an annular portion 72 that fits to the outer peripheral surface of the cylinder tube 10 and a pair of flange portions 71 that project left and right from the annular portion 72, and bolts (not shown) that pass through the flange portion 71. Is fastened to the vehicle body side.

  The annular portion 72 of the stay 70 is fixed to the outer periphery of the cylinder tube 10 by upper and lower welded portions 73 and 74.

  A cylindrical cylinder head 60 is screwed and coupled to the upper end of the cylindrical cylinder tube 10.

  An O-ring 64 is interposed between the cylinder tube 10 and the cylinder head 60. The O-ring 64 seals between the outside and the rod side chamber 6.

  The piston rod 20 is inserted into the cylinder tube 10 via the cylinder head 60. A cylindrical bush (bearing) 61 is interposed on the inner periphery of the cylinder head 60. The piston rod 20 is slidably supported by the cylinder head 60 via the bush 61.

  A main seal 62 and a dust seal 63 that are in sliding contact with the outer peripheral surface 28 of the piston rod 20 are interposed on the inner periphery of the cylinder head 60. The rod side chamber 6 in the cylinder tube 10 is sealed by the main seal 62. The dust seal 63 prevents dust and the like from entering.

  A piston 40 is coupled to a proximal end portion of the piston rod 20 inserted into the cylinder tube 10.

  The piston 40 is formed in a bottomed cylindrical shape having a cylindrical piston outer ring portion 43 fitted to the outer periphery of the piston rod 20 and a disk-shaped piston bottom portion 44 on which the lower end of the piston rod 20 is seated.

  The inner periphery of the piston outer ring portion 43 is fitted to the outer periphery of the piston rod 20, and the snap ring 19 is interposed therebetween. The snap ring 19 is fitted over an annular groove opened on the inner circumferential surface of the piston outer ring portion 43 and an annular groove opened on the outer circumferential surface of the piston rod 20, and the piston rod 20 is fitted to the piston 40. On the other hand, the upward movement in the direction of the central axis O is locked.

  A bush (bearing) 41 is interposed on the outer periphery of the piston 40. The piston 40 is slidably supported on the inner peripheral surface 11 of the cylinder tube 10 via the bush 41.

  An end block 50 is coupled to the lower end of the cylinder tube 10. The end block 50 has an inlay portion 51 that fits to the inner peripheral surface 11 of the cylinder tube 10, and the outer periphery thereof is fixed to the lower end of the cylinder tube 10 by a welded portion 53.

  A space inside the cylinder tube 10 is partitioned into a bottom side chamber 5 and a rod side chamber 6 by a piston 40.

  The bottom side chamber 5 is defined between the piston 40 and the end block 50 inside the cylinder tube 10.

  The end block 50 is formed with a supply / discharge port 52 for supplying / discharging hydraulic fluid to / from the bottom side chamber 5. A pipe extending from a hydraulic pressure source (not shown) is connected to the supply / discharge port 52.

  The hydraulic cylinder 1 uses oil as hydraulic fluid supplied and discharged from the hydraulic pressure source, but hydraulic fluid such as water-soluble alternative fluid may be used instead of oil.

  When the hydraulic fluid pressure led from the hydraulic pressure source rises, the hydraulic fluid is supplied from the supply / discharge port 52 to the bottom chamber 5, and the piston rod 20 moves upward with respect to the center axis O with respect to the cylinder tube 10. 1 is extended, and the load is lifted through a fork interlocked therewith.

  On the other hand, when the hydraulic fluid pressure led from the hydraulic pressure source decreases, the piston rod 20 moves downward by its own weight and load and the hydraulic cylinder 1 contracts, and the hydraulic fluid pressure in the bottom side chamber 5 is supplied and discharged. The fluid is discharged from the port 52 to the hydraulic pressure source. FIG. 1 shows a state in which the hydraulic cylinder 1 is most contracted and the piston rod 20 is at the stroke end.

  The rod side chamber 6 is defined between the outer periphery of the piston rod 20, the cylinder head 60, and the piston 40 inside the cylinder tube 10.

  A predetermined amount of hydraulic fluid (cushion oil) and gas (air) are placed in the rod side chamber 6. As the hydraulic cylinder 1 expands and contracts, the gas enclosed in the rod side chamber 6 is compressed and expanded, so that the volume of the rod side chamber 6 is reduced and expanded.

  The hydraulic fluid put into the rod side chamber 6 is the same as the hydraulic fluid guided from the hydraulic pressure source to the bottom side chamber 5.

  A piston seal ring 42 is interposed on the outer periphery of the piston 40. When the piston seal ring 42 is in sliding contact with the inner peripheral surface 11 of the cylinder tube 10, the space between the bottom side chamber 5 and the rod side chamber 6 is sealed.

  A rod inner chamber 7 is defined inside the hollow piston rod 20. The piston rod 20 includes a cylindrical hollow rod 25 and a rod head 30 that closes the upper opening end of the hollow rod 25. The hollow rod 25 is formed using a pipe material extending in a right cylindrical shape, and the volume of the rod inner chamber 7 is ensured to the maximum.

  A communication passage 23 is provided between the rod side chamber 6 and the rod inner chamber 7 to communicate the both. In the lower part of the hollow rod 25, a port 21 and an orifice 22 are formed as a communication path 23.

  The orifice 22 is formed so as to open at the lowermost part of the portion of the hollow rod 25 facing the rod side chamber 6. A tapered portion 43 </ b> A is formed on the inner periphery of the piston outer ring portion 43 to which the hollow rod 25 is fitted so as to face the opening end of the orifice 22.

  The port 21 is formed at a predetermined distance above the orifice 22 and is disposed so as to be immersed in the hydraulic fluid stored in the rod side chamber 6.

  During the extension operation of the hydraulic cylinder 1, the piston 40 and the piston rod 20 are moved upward in the direction of the central axis O by the hydraulic pressure introduced to the bottom side chamber 5, and the pressure in the rod side chamber 6 is increased. The hydraulic fluid flows into the rod inner chamber 7 through the port 21 and the orifice 22.

  When the piston rod 20 approaches the stroke end during the extension operation of the hydraulic cylinder 1, the port 21 is closed by the bush 61, and the working fluid in the rod side chamber 6 flows into the rod inner chamber 7 through the orifice 22. The orifice 22 provides resistance to the flow of the hydraulic fluid, and the piston rod 20 is decelerated by increasing the cushion pressure in the rod side chamber 6. Thus, the impact when the piston rod 20 reaches the stroke end is reduced.

  On the other hand, when the hydraulic cylinder 1 is contracted, the piston 40 and the piston rod 20 move downward, and the pressure in the rod side chamber 6 decreases, so that the hydraulic fluid in the rod inner chamber 7 passes through the port 21 and the orifice 22. It flows into the rod side chamber 6.

  Depending on the state of the piston seal ring 42, as the expansion and contraction operation of the hydraulic cylinder 1 is repeated, the hydraulic fluid in the bottom side chamber 5 leaks into the rod side chamber 6 over the piston seal ring 42, and the rod side chamber 6 and the bottom side chamber There is a possibility that the amount of hydraulic fluid intervening 5 increases from the set storage amount.

  In order to cope with this, a return tube 9 and a return check valve 8 are provided in order to return excess hydraulic fluid accumulated in the rod inner chamber 7 to the bottom side chamber 5.

  The return check valve 8 is accommodated in a valve housing 80 interposed in the piston 40. A mounting hole 47 is formed at the center of the piston bottom 44. The outer periphery of the cylindrical valve housing 80 is fitted into the mounting hole 47. The snap ring 17 is fitted in an annular groove formed in the mounting hole 47 to prevent the valve housing 80 from coming off.

  An O-ring 18 is interposed between the mounting hole 47 and the valve housing 80. The space between the bottom chamber 5 and the rod inner chamber 7 is sealed by the O-ring 18.

  The return check valve 8 includes a seat communicating with the rod inner chamber 7 and the bottom side chamber 5 and a valve body (ball) pressed against the seat by a biasing force of a spring. When the pressure difference between the rod inner chamber 7 and the bottom side chamber 5 exceeds a predetermined valve opening pressure, the valve body is separated from the seat.

  A mounting hole 82 is formed in the central portion of the valve housing 80. A straight cylindrical return tube 9 is press-fitted into the attachment hole 82 and attached. Thus, the return tube 9 is erected on the piston 40 and disposed on the central axis O. The return tube 9 is connected to the inlet of the return check valve 8 through the mounting hole 82.

  When the hydraulic fluid in the bottom side chamber 5 leaks over the piston seal ring 42 to the rod side chamber 6 and the liquid level of the hydraulic fluid accumulated in the rod side chamber 6 and the rod inner chamber 7 exceeds the upper end of the return tube 9, the hydraulic fluid returns. It flows down into the tube 9. When the pressure in the rod inner chamber 7 is increased from the bottom side chamber 5, the return check valve 8 is opened, and excess hydraulic fluid accumulated in the return tube 9 is returned to the bottom side chamber 5. Thereby, the liquid level of the hydraulic fluid which accumulates in the rod side chamber 6 and the rod inner chamber 7 is maintained in the vicinity of the upper end of the return tube 9, and the hydraulic fluid storage amount is kept below the set value.

  By the way, depending on the state of the piston seal ring 42, the hydraulic fluid in the rod side chamber 6 leaks into the bottom side chamber 5 beyond the piston seal ring 42, and the amount of hydraulic fluid stored in the rod side chamber 6 and the rod inner chamber 7 is set. It may decrease from the value.

  In response to this, the hydraulic cylinder 1 is formed with a replenishment hole 45 penetrating the rod head 30, and a plug 65 is provided as a sealing member for sealing the replenishment hole 45. As a result, when the amount of hydraulic fluid in the rod side chamber 6 is insufficient, the plug 65 can be removed and the hydraulic fluid can be filled into the rod inner chamber 7 through the replenishment hole 45.

  Hereinafter, the configuration of the rod head 30 will be described.

  The block-shaped rod head 30 includes an inlay portion 31 that fits to the inner periphery of the hollow rod 25, an annular step portion 32 that comes into contact with the upper end surface of the hollow rod 25, and a bracket portion 33 that is connected to the counterpart member. Have.

  A snap ring 35 is interposed between the hollow rod 25 and the spigot 31 as a locking means for preventing the rod head 30 from coming off. The snap ring 35 is fitted over an annular groove opened on the inner peripheral surface of the hollow rod 25 and an annular groove opened on the outer peripheral surface of the spigot portion 31, and the rod head 30 is attached to the hollow rod 25. To move upward in the direction of the central axis O. A seal ring 36 is interposed between the hollow rod 25 and the inlay portion 31 along with the snap ring 35, and the rod inner chamber 7 is sealed by the seal ring 36.

  The bracket portion 33 protruding from the upper end of the hollow rod 25 is formed in a columnar shape, and a part of the upper end surface is brought into contact with a mating member (not shown) provided on the fork. In addition, the bracket part 33 is formed in the shape according to the other party member (not shown) to which this is connected not only in column shape. Actually, a plurality of types of rod heads 30 are provided according to the vehicle type or specification of the forklift.

  A recess 38 is formed on the upper end surface 37 of the rod head 30, and a seating surface 39 is formed on the bottom of the recess 38.

  The replenishment hole 45 is formed coaxially with the central axis O of the hydraulic cylinder 1 extending in the vertical direction. The replenishing hole 45 has an inlet 45 </ b> A that opens to the seat surface 39 and faces the outside, and an outlet 45 </ b> B that opens to the lower surface of the rod head 30 and faces the rod inner chamber 7. The outlet 45B of the refill hole 45 and the inlet 9A of the return tube 9 are arranged coaxially with each other.

  A female screw portion 46 is formed at an end portion of the replenishing hole 45 that opens to the seating surface 39. A plug 65 that is screwed into the female screw portion 46 and seated on the seat surface 39 is provided. The plug 65 constitutes a sealing member that seals the working fluid flowing out from the rod inner chamber 7 through the refill hole 45.

  In a state where the hydraulic cylinder 1 is mounted on the forklift, the refill hole 45 is arranged so that the plug 65 can be attached and detached without interfering with the forklift members.

  Hereinafter, the manufacturing process of the hydraulic cylinder 1 will be described.

  In the process of processing the rod head 30, the rod head 30 formed in a block shape is placed on a processing table of a cutting machine (not shown), positioned to the rod head 30, the refill hole 45, the female screw portion 46, The seating surface 39 is cut.

  Thereby, compared to the case where the seat surface and the supplementary hole are formed on the outer peripheral surface (curved surface) of the long and large diameter cylinder tube 10 as in the conventional apparatus, the supplementary hole 45 and the seating surface 39 are formed in the short small-diameter rod head 30. Etc. can be easily performed, and this operation time can be greatly shortened and the cost of the product can be reduced.

  In the process of assembling the hydraulic cylinder 1 after the processing of the rod head 30 is completed, the rod head 30 is fitted and attached to the open end of the piston rod 20 (hollow rod 25) via the snap ring 35.

  After the assembly of the hydraulic cylinder 1 is completed, a predetermined amount of hydraulic fluid is externally filled into the rod inner chamber 7 through the refill hole 45, and the plug 65 is attached to the rod head 30 to seal the refill hole 45.

  In the step of inspecting the operation of the hydraulic cylinder 1, the sealing performance of the piston seal ring 42 is inspected as follows.

  First, in a state where a load is applied to the hydraulic cylinder 1, the supply / discharge port 52 is connected to a hydraulic pressure source through a pipe to increase the pressure of the hydraulic fluid guided to the bottom side chamber 5.

  In this state, the plug 65 is removed from the rod head 30, and it is detected whether there is a gas flow flowing out through the refill hole 45.

  In this inspection, if the flow of gas flowing out through the refill hole 45 is detected, the sealing failure of the piston seal ring 42 occurs, and the hydraulic fluid in the bottom side chamber 5 leaks into the rod side chamber 6. Determined. On the other hand, when the flow of gas flowing out through the refill hole 45 is not detected, it is determined that the sealing by the piston seal ring 42 is normally performed.

  The hydraulic cylinder 1 manufactured as described above is assembled to a forklift. During the operation of the forklift, the hydraulic cylinder 1 expands and contracts by supplying and discharging hydraulic fluid from the hydraulic pressure source, and lifts and lowers the load via the fork.

  During the operation of the forklift, resistance is given to the flow of hydraulic fluid by the orifice 22 near the stroke end where the hydraulic cylinder 1 is extended, and cushion pressure is generated in the rod side chamber 6 so that the hydraulic cylinder 1 is fully extended and stopped. The impact that occurs when doing so is mitigated.

  When the piston rod 20 approaches the stroke end when the hydraulic cylinder 1 is extended, if the piston rod 20 is not sufficiently decelerated, the amount of hydraulic fluid stored in the rod side chamber 6 and the rod inner chamber 7 May be lower than the set value.

  In this case, the plug 65 is removed from the rod head 30 while the hydraulic cylinder 1 is still mounted on the forklift, and the working fluid is filled from the outside into the rod inner chamber 7 through the replenishment hole 45. The hydraulic fluid filled in the rod inner chamber 7 flows into the rod side chamber 6 through the communication path 23, and a predetermined amount of hydraulic fluid is stored in the rod inner chamber 7 and the rod side chamber 6. Thereby, the shortage of the hydraulic fluid amount in the rod side chamber 6 is eliminated, and the impact generated when the hydraulic cylinder 1 is fully extended and stopped is reduced as set.

  According to the above 1st Embodiment, there exists an effect shown below.

  [1] A piston-type single-acting hydraulic cylinder 1 that is extended by a pressurized hydraulic fluid guided from an external hydraulic pressure source. The hydraulic cylinder 1 is defined inside a piston rod 20 and communicates with a rod side chamber 6. 23, the rod inner chamber 7 that communicates through the rod 23, the rod head 30 that closes the open end of the piston rod 20, seals the rod inner chamber 7, passes through the rod head 30, and hydraulic fluid enters the rod inner chamber 7 from the outside. Since the replenishment hole 45 that can be replenished and the plug 65 (sealing member) that seals the working fluid that flows out from the rod inner chamber 7 through the replenishment hole 45 is provided, the rod inner chamber 7 and the rod side chamber 6 store. When the amount of the hydraulic fluid to be used is insufficient, the hydraulic fluid is replenished from the outside to the rod inner chamber 7 through the replenishment hole 45 by hand, and this hydraulic fluid is transferred from the rod inner chamber 7 to the rod side chamber 6 through the communication passage 23. Inflow Lack of the working fluid volume is eliminated.

  When manufacturing the hydraulic cylinder, the operation of forming the replenishment hole 45 in the rod head 30 is easily performed, and the operation of forming the replenishment hole 45 compared to the case of forming the replenishment hole in the long large diameter cylinder tube 10. Time can be shortened and product costs can be reduced.

  [2] The piston rod 20 is provided with a throttle (orifice 22) that provides resistance to the flow of hydraulic fluid flowing from the rod side chamber 6 into the rod inner chamber 7 through the communication passage 23 near the stroke end during the extension operation. As the pressure approaches, the throttle (orifice 22) imparts resistance to the flow of hydraulic fluid flowing from the rod side chamber 6 into the rod inner chamber 7, and the cushion pressure in the rod side chamber 6 increases, whereby the piston rod 20 is decelerated. . When the amount of hydraulic fluid that causes this cushion pressure is insufficient, the hydraulic fluid is replenished from the outside to the rod inner chamber 7 through the replenishment hole 45 by hand, so that the shortage of hydraulic fluid is eliminated. The impact that occurs when 1 fully extends and stops is mitigated as set.

  [3] A recess 38 is formed in the end surface 37 of the rod head 30, and a seat surface 39 in which the replenishment hole 45 is opened is formed in the bottom of the recess 38, and a plug 65 that seals the replenishment hole 45 is seated as a sealing member. Since the seat 65 is seated on the surface 39, the plug 65 accommodated in the recess 38 does not protrude from the end surface 37 of the rod head 30 and is prevented from interfering with a mating member to which the rod head 30 is coupled.

  By the way, in the hydraulic cylinder 1 according to the first embodiment, the outlet 45 </ b> B of the refill hole 45 and the inlet 9 </ b> A of the return tube 9 are coaxially arranged, so that the rod inner chamber 7 is refilled through the refill hole 45. There is a possibility that a part of the hydraulic fluid flows down into the return tube 9 and flows out to the bottom side chamber 5 through the return check valve 8.

(Second Embodiment)
The second embodiment of the present invention is made in response to the problem of the hydraulic cylinder 1 according to the first embodiment. Hereinafter, a second embodiment of the present invention will be described with reference to FIG. Below, it demonstrates centering on a different point from the said 1st Embodiment, the same code | symbol is attached | subjected to the structure same as the hydraulic cylinder of the said 1st Embodiment, and description is abbreviate | omitted.

  In the hydraulic cylinder 101 according to the second embodiment, the outlet 145B of the replenishing hole 145 and the inlet 9A of the return tube 9 are offset so as not to be arranged coaxially. The replenishment hole 145 extends in parallel with the central axis O and is formed to be offset from the central axis O. In addition, the replenishing hole 145 may be formed so as to be inclined with respect to the central axis O and the outlet 145B of the replenishing hole 145 is offset with respect to the central axis O.

  When the amount of the hydraulic fluid stored in the rod inner chamber 7 and the rod side chamber 6 is insufficient, the hydraulic fluid is replenished from the outside to the rod inner chamber 7 through the replenishment hole 145 by hand, and this hydraulic fluid is supplied to the rod inner chamber. 7, the rod side chamber 6 is filled through the communication passage 23, so that the shortage of hydraulic fluid can be solved.

  According to the above 2nd Embodiment, while exhibiting the effect of said [1] [2] similarly to 1st Embodiment, there exists the effect shown below.

  [4] Since the outlet 145B of the replenishing hole 145 and the inlet 9A of the return tube 9 are offset so as not to be arranged on the same axis extending in the vertical direction, one of the hydraulic fluid filled in the rod inner chamber 7 through the replenishing hole 45 It is avoided that the portion flows down into the return tube 9 and flows out from the return tube 9 into the bottom side chamber 5 via the return check valve 8. Thereby, the hydraulic fluid to be replenished can be stored in the rod side chamber 6 without waste.

(Third embodiment)
Next, a second embodiment of the present invention will be described with reference to FIG. Below, it demonstrates centering on a different point from the said 1st Embodiment, the same code | symbol is attached | subjected to the structure same as the hydraulic cylinder of the said 1st Embodiment, and description is abbreviate | omitted.

  In the rod head 230 provided in the hydraulic cylinder according to the third embodiment, a concave portion 238 is formed on the side portion (outer periphery) of the bracket portion 233, and a seat surface 239 is formed on the bottom portion of the concave portion 238. The seating surface 239 is formed on the outer peripheral surface of the bracket portion 233 by cutting. Since the rod head 230 is smaller than the cylinder tube, it takes less time to perform positioning by positioning on the curved surface.

  The replenishing hole 245 includes a through hole 246 extending in a direction orthogonal to the central axis O of the hydraulic cylinder, and a through hole 247 extending coaxially with the central axis O of the hydraulic cylinder.

  In the replenishing hole 245, one end of the through hole 246 opens to the seat surface 239 as an inlet 245 </ b> A, and one end of the through hole 247 opens to the lower surface of the rod head 230 as the outlet 245 </ b> B to face the rod inner chamber 7.

  The outlet 245B of the refill hole 245 and the inlet of the return tube are arranged on the central axis O.

  Note that the present invention is not limited to the above-described configuration, and the outlet 245B of the replenishing hole 245 may be offset from the central axis O so that the return tube inlet is not coaxially disposed.

  A female screw portion 248 is formed at the end of the through hole 246 that opens to the seating surface 239. A plug 65 that is screwed into the female screw portion 248 and seated on the seating surface 239 is provided. The plug 65 constitutes a sealing member that seals the working fluid flowing out from the rod inner chamber 7 through the replenishing hole 245.

  When the amount of hydraulic fluid stored in the rod inner chamber and the rod side chamber is insufficient, the plug 65 is removed while the hydraulic cylinder is still mounted on the forklift, and the hydraulic fluid passes through the replenishment hole 245 to the rod inner chamber. Filled. This hydraulic fluid flows from the rod inner chamber into the rod side chamber through the communication passage, and the shortage of hydraulic fluid is eliminated.

  Since the inlet 245A of the replenishing hole 245 is disposed on the side of the rod head 230, the entire upper end surface 237 of the rod head 230 can be brought into contact with a mating member (not shown) provided on the fork.

  According to the above 3rd Embodiment, while exhibiting the effect of said [1] [2] similarly to 1st Embodiment, there exists the effect shown below.

  [5] Since the replenishment hole 245 has an inlet 245A that opens to the side of the rod head 230 and an outlet 245B that opens to the rod inner chamber 7, the orientation of the inlet 245A of the replenishment hole 245 relative to the hydraulic cylinder is a product. Can be dealt with by adjusting the rotational position around the central axis O of the rod head 230 attached to the piston rod. Thereby, a common rod head 230 can be used among products with different specifications, and a hydraulic cylinder can be produced efficiently.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIG. Below, it demonstrates centering on a different point from the said 1st Embodiment, the same code | symbol is attached | subjected to the structure same as the hydraulic cylinder of the said 1st Embodiment, and description is abbreviate | omitted.

  The rod head 330 provided in the hydraulic cylinder according to the fourth embodiment is provided with a replenishment check valve 350 that opens as a sealing member by hydraulic fluid filled in the replenishment hole 345 from the outside.

  The replenishment check valve 350 includes a seat 351 that communicates between the rod inner chamber and the bottom chamber, and a valve body (ball) 352 that is pressed against the seat 351 by a biasing force of a spring 353.

  The rod head 330 is formed with a replenishment hole 345 and a valve accommodation hole 346 coaxially with the central axis O. A valve body 352, a first retainer 361, a spring 353, a second retainer 362, and a retaining ring 363 are interposed in the valve housing hole 346. The second retainer 362 is prevented from coming off via a retaining ring 363. The coiled spring 353 is compressed and interposed between the first retainer 361 and the second retainer 362.

  The replenishment check valve 350 is not limited to the configuration described above.

  When the amount of hydraulic fluid stored in the rod inner chamber and the rod side chamber is insufficient, the pressurized hydraulic fluid is sent to the replenishment hole 345 via a filler (not shown). The valve body 352 is separated from the seat 351 against the spring 353 by the pressure of the hydraulic fluid, and the replenishment check valve 350 is opened. As a result, the hydraulic fluid is filled into the rod inner chamber through the replenishment hole 345, and the hydraulic fluid flows into the rod side chamber from the rod inner chamber through the communication path, thereby eliminating the shortage of the hydraulic fluid amount.

  The replenishment check valve 350 constitutes a sealing member that seals the working fluid flowing out from the rod inner chamber 7 through the replenishing hole 345.

  According to the above 4th Embodiment, while exhibiting the effect of said [1] [2] similarly to 1st Embodiment, there exists the effect shown below.

  [6] Since the replenishment check valve 350 is opened as the sealing member by the working fluid pressure filled in the refilling hole 345 from the outside, the refilling hole is provided when the working fluid is refilled into the rod inner chamber through the refilling hole 345. The replenishment check valve 350 is opened by the hydraulic fluid pressure filled in 345. When the hydraulic cylinder is operated, the replenishment check valve 350 is closed, and the working fluid in the rod inner chamber is prevented from flowing out through the replenishment hole 345. Thereby, the plug (plug body) with which the replenishment hole 345 is mounted | worn can be abolished.

  The present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea.

  In the first to fourth embodiments, the replenishment hole replenishes the hydraulic fluid that generates the cushion pressure near the stroke end of the hydraulic cylinder. The hydraulic cylinder of the present invention is not limited to this configuration, and the replenishment hole may replenish the rod side chamber with hydraulic fluid (lubricating oil) that lubricates, for example, the piston seal ring.

  The hydraulic cylinder of the present invention is not limited to a lift cylinder provided in a forklift, but can be used in a cylinder provided in another machine or facility.

DESCRIPTION OF SYMBOLS 1 Hydraulic cylinder 5 Bottom side chamber 6 Rod side chamber 7 Rod inner chamber 9 Return tube 9A Inlet 10 Cylinder tube 20 Piston rod 22 Orifice (throttle)
23 Communication path 30, 230, 330 Rod head 37 End surface 38 Recess 39 Seat surface 40 Piston 45, 145, 245, 345 Replenishment hole 65 Plug (sealing member)
145B, 245B Outlet 245A Inlet 350 Refill check valve (sealing member)

Claims (4)

Among the rod side chamber and the bottom side chamber partitioned by the piston, a single-acting hydraulic cylinder that is extended by the pressure of the hydraulic fluid guided from the external hydraulic pressure source to the bottom side chamber,
A cylindrical cylinder tube in which the piston is slidably housed and has the bottom side chamber and the rod side chamber inside;
A cylindrical piston rod connected to the piston and slidably protruding from an open end of the cylinder tube;
The rod inner chamber defined inside the piston rod and communicating with the rod side chamber through a communication path;
A rod head that closes the open end of the piston rod and seals the inner chamber of the rod;
A replenishment hole penetrating the rod head and capable of replenishing the rod inner chamber with hydraulic fluid from the outside;
A sealing member for sealing the replenishment hole,
A recess is formed on the end face of the rod head,
A seating surface in which the replenishment hole opens is formed at the bottom of the recess,
A hydraulic cylinder, wherein a plug for sealing the replenishment hole as the sealing member is seated on the seating surface . Among the rod side chamber and the bottom side chamber partitioned by the piston, a single-acting hydraulic cylinder that is extended by the pressure of the hydraulic fluid guided from the external hydraulic pressure source to the bottom side chamber,
A cylindrical cylinder tube in which the piston is slidably housed and has the bottom side chamber and the rod side chamber inside;
A cylindrical piston rod connected to the piston and slidably protruding from an open end of the cylinder tube;
The rod inner chamber defined inside the piston rod and communicating with the rod side chamber through a communication path;
A rod head that closes the open end of the piston rod and seals the inner chamber of the rod;
A replenishment hole penetrating the rod head and capable of replenishing the rod inner chamber with hydraulic fluid from the outside;
A sealing member for sealing the replenishment hole;
A return check valve that opens as the pressure difference between the rod inner chamber and the bottom side chamber rises above a predetermined value and returns the working fluid in the rod inner chamber to the bottom side chamber;
A return tube protruding upward from the piston in the rod inner chamber and connected to the inlet of the return check valve;
The hydraulic cylinder according to claim 1, wherein an outlet of the replenishing hole opened in the rod inner chamber and an inlet of the return tube are offset so as not to be arranged coaxially extending in a vertical direction . Among the rod side chamber and the bottom side chamber partitioned by the piston, a single-acting hydraulic cylinder that is extended by the pressure of the hydraulic fluid guided from the external hydraulic pressure source to the bottom side chamber,
A cylindrical cylinder tube in which the piston is slidably housed and has the bottom side chamber and the rod side chamber inside;
A cylindrical piston rod connected to the piston and slidably protruding from an open end of the cylinder tube;
The rod inner chamber defined inside the piston rod and communicating with the rod side chamber through a communication path;
A rod head that closes the open end of the piston rod and seals the inner chamber of the rod;
A replenishment hole penetrating the rod head and capable of replenishing the rod inner chamber with hydraulic fluid from the outside;
A sealing member for sealing the replenishment hole,
The refill hole is
An inlet opening to the side of the rod head;
A hydraulic cylinder , comprising: an outlet of the replenishing hole that opens into the rod inner chamber . Among the rod side chamber and the bottom side chamber partitioned by the piston, a single-acting hydraulic cylinder that is extended by the pressure of the hydraulic fluid guided from the external hydraulic pressure source to the bottom side chamber,
A cylindrical cylinder tube in which the piston is slidably housed and has the bottom side chamber and the rod side chamber inside;
A cylindrical piston rod connected to the piston and slidably protruding from an open end of the cylinder tube;
The rod inner chamber defined inside the piston rod and communicating with the rod side chamber through a communication path;
A rod head that closes the open end of the piston rod and seals the inner chamber of the rod;
A replenishment hole penetrating the rod head and capable of replenishing the rod inner chamber with hydraulic fluid from the outside;
A sealing member for sealing the replenishment hole,
The hydraulic cylinder according to claim 1, wherein the sealing member includes a replenishment check valve that is opened by an operating hydraulic pressure filled in the replenishing hole from the outside .

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