CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based on and claims priority from Korean Patent Application No.
10-2008-0007192, filed on January 23, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated
herein in its entirety by reference.
BACKGROUND OF THE INVENTION
Field of the invention
[0002] The present invention relates to a hydraulic cylinder having a rod safety device,
which can improve the safety of a hydraulic cylinder by adding a joint connection
means to a bonding part in which a rod head and a rod body of the hydraulic cylinder
are joint-connected by welding.
[0003] More particularly, the present invention relates to a hydraulic cylinder having a
rod safety device, in which a screw engagement part (e.g. a screw is used) is formed
in center parts of mutual contact surfaces of a rod head and a rod body of the hydraulic
cylinder in a shaft direction, and an outer surface of a joint connection part of
the rod head and the rod body is welded, so that a free falling of an arm and a bucket
is prevented by a screw engagement part when a welding part is broken to protect a
cab and an operator.
Description of the Prior Art
[0004] As illustrated in FIG. 1, a general hydraulic cylinder includes a tube 2 accommodating
a cylinder rod 1 that slides in a set stroke range; a cover 3 connected by weld joint
to one end part of the tube 2 (corresponding to a side of a rod head 1a); an end cover
4 connected by weld joint to the other end part of the tube 3 (corresponding to a
side of a piston 5); and a piston 5 fastened to one end part of the cylinder rod 1
to reciprocate along an inner periphery of the tube 2.
[0005] As illustrated in FIG. 2, in the conventional hydraulic cylinder, outer part of mutual
contact surfaces of a rod head 1a and a rod body 1b of the cylinder rod 1 are connected
by weld joint.
[0006] In this case, if stress is generated in the weld joint part due to high impact and
vibration repeatedly generated during the operation of the hydraulic cylinder, fatigue
fracture of the weld joint part occurs to greatly deteriorate the durability of the
weld joint part 13, so that the life span of the hydraulic cylinder is shortened and
the safety is degraded.
[0007] As illustrated in FIG. 5, the cylinder rod 1 receives a complex load, such as a tensile
force, a compression force, and a bending load in a shaft direction. At this time,
a relatively large force acts on the outer surface (i.e. an edge part) of the weld
joint part 13 of the rod body 1b rather than the center of the weld joint part 13
in the shaft direction.
[0008] Accordingly, a relatively large force is applied to the mutual weld parts of the
rod head 1a and the rod body 1b. Also, in unexpected environments, such as in welding
defects of the weld joint part 13 of the rod head 1a and the rod body 1b, an abrupt
damage of the weld joint part may precedently occur.
[0009] As described above, even if the weld joint part 13 of the cylinder rod 1 of the hydraulic
cylinder (e.g. an arm cylinder 8 of an excavator) mounted on the equipment is broken
due to the welding defects and so on, the safety of the operator in the cab is not
threatened by the bucked and so on in view of the working radius of a standard working
device that is provided by manufacturers of heavy equipment.
[0010] However, as illustrated in FIG. 6, in order to efficiently use the expensive equipment,
an owner of the equipment may mount a working device optionally remodeled to cope
with diverse working environments (so called "special attachments") on a bucket 7
and so on.
[0011] In this case, if the weld joint part 13 of the arm cylinder 8 is broken due to the
welding defects and so on, a mechanical free falling of an arm 9 and the bucket 7
around a point 0 occurs, and this may cause the damage of the cab 6 and the threatening
of the operator's life.
SUMMARY OF THE INVENTION
[0012] Accordingly, the present invention has been made to solve the above-mentioned problems
occurring in the prior art while advantages achieved by the prior art are maintained
intact.
[0013] One object of the present invention is to provide a hydraulic cylinder having a rod
safety device, in which a screw engagement part is formed in center parts of mutual
contact surfaces of a rod head and a rod body of the hydraulic cylinder in a shaft
direction, and an outer surface of a joint connection part of the rod head and the
rod body is welded, so that a free falling of an arm and a bucket is prevented by
fastening members when a welding part is broken to prevent the damage of a cab and
to protect an operator from an accident.
[0014] Another object of the present invention is to provide a hydraulic cylinder having
a rod safety device, which can improve the reliability of equipment by preventing
a free falling of an arm and a bucket when a welding part of a cylinder rod is broken
due to welding defects and so on, even if an owner of the equipment optionally remodels
a working device to cope with divers working environments.
[0015] In order to accomplish the objects, there is provided a hydraulic cylinder having
a rod safety device, according to embodiments of the present invention, which includes
a cylinder rod sliding within a set stroke range in a tube and composed of a rod head
and a rod body joint-connected to the rod head; a cover connected by weld joint to
one end part of the tube; an end cover connected by weld joint to the other end part
of the tube; a piston fastened to one end part of the cylinder rod to reciprocate
along an inner periphery of the tube; and a connection means composed of a screw engagement
part formed in center parts of mutual contact surfaces of the rod head and the rod
body in a shaft direction to joint-connect the rod head and the rod body by screw-engaging
the rod head and the rod body, and a weld joint part joint-connecting the rod head
and the rod body by welding outer peripheries of the contact surfaces of the rod head
and the rod body.
[0016] The screw engagement part may include screw holes respectively formed in the center
parts of the mutual contact surfaces of the rod head and the rod body in the shaft
direction, and a connection bolt engaged into the screw holes to screw-engage the
rod head and the rod body.
[0017] The screw engagement part may include a screw hole formed in one of the center parts
of the contact surfaces of the rod head and the rod body, and a connection bolt fixed
by welding to the other of the center parts of the contact surfaces of the rod head
and the rod body to correspond to the screw hole.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and advantages of the present invention will
be more apparent from the following detailed description taken in conjunction with
the accompanying drawings, in which:
FIG. 1 is a schematic view illustrating a general hydraulic cylinder;
FIG. 2 is a view illustrating a main portion of a joint part of a conventional hydraulic
cylinder;
FIG. 3 is an exploded perspective view illustrating a main portion of a hydraulic
cylinder having a rod safety device according to an embodiment of the present invention;
FIGS. 4A and 4B are sectional views illustrating a main portion of a hydraulic cylinder
as illustrated in FIG. 3;
FIG. 5 is a view explaining generation of a load on a weld joint part of a cylinder
rod; and
FIG. 6 is a view explaining that a cab and an operator may be threatened by a working
device freely falling when the weld joint part of the hydraulic cylinder is broken
due to welding defects and so on.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] Hereinafter, preferred embodiments of the present invention will be described with
reference to the accompanying drawings. The matters defined in the description, such
as the detailed construction and elements, are nothing but specific details provided
to assist those of ordinary skill in the art in a comprehensive understanding of the
invention, and thus the present invention is not limited thereto.
[0020] As shown in FIGS. 3, 4A and 4B, a hydraulic cylinder having a rod safety device according
to an embodiment of the present invention includes a cylinder rod 1 sliding within
a set stroke range in a tube 2 and composed of a rod head 1a and a rod body 1b joint-connected
to the rod head 1a; a cover 3 connected by weld joint to one end part of the tube
2; an end cover 4 connected by weld joint to the other end part of the tube 2; a piston
5 fastened to one end part of the cylinder rod 1 to reciprocate along an inner periphery
of the tube 2; and a connection means composed of a screw engagement part 10 formed
in center parts of mutual contact surfaces of the rod head 1a and the rod body 1b
in a shaft direction to joint-connect the rod head 1a and the rod body 1b by screw-engaging
the rod head 1a and the rod body 1b, and a weld joint part 13 joint-connecting the
rod head 1a and the rod body 1b by welding outer peripheries of the contact surfaces
of the rod head 1a and the rod body 1b.
[0021] In a preferred embodiment of the present invention, the screw engagement part 10
includes screw holes 11 respectively formed in the center parts of the mutual contact
surfaces of the rod head 1a and the rod body 1b in the shaft direction, and a connection
bolt 12 engaged into the screw holes 11 to screw-engage the rod head 1a and the rod
body 1b.
[0022] The hydraulic cylinder having a rod safety device according to an embodiment of the
present invention, except for the screw engagement part 10 including the screw holes
11 respectively formed in the center parts of the mutual contact surfaces of the rod
head 1a and the rod body 1b in the shaft direction, and the connection bolt 12 engaged
into the screw holes 11 to screw-engage the rod head 1a and the rod body 1b, is substantially
the same as the conventional hydraulic cylinder as illustrated in FIGS. 1 and 2, and
thus the detailed description thereof will be omitted. In the description of the present
invention, the same drawing reference numerals are used for the same elements across
various figures.
[0023] Hereinafter, the operation of the hydraulic cylinder having a rod safety device according
to an embodiment of the present invention will be described in detail with reference
to the accompanying drawings.
[0024] As illustrated in FIGS. 3, 4A and 4B, the rod head 1a and the rod body 1b are joint-connected
by screw-engaging the connection bolt 12 into the screw holes 11 respectively formed
in the center parts of the mutual contact surfaces of the rod head 1a and rod body
1b of the cylinder rod 1. The outer surfaces of the contact surfaces of the rod head
1a and the rod body 1b, which are in close contact with each other and are joint-connected
by the connection bolt 12, are fixed together by welding.
[0025] That is, the rod head 1a and the rod body 1b are firstly joint-connected by the connection
bolt 12 that is screw-engaged with the center parts of the mutual contact surfaces
of the rod head and the rod body in a shaft direction, and are secondly joint-connected
by the weld joint part 13 that fixes by welding the outer surfaces of the contact
surfaces of the rod head 1a and the rod body 1b to each other.
[0026] During working of the equipment, if external forces, such as a tensile force, a compression
force, a bending load, and the like, are repeatedly applied to and accumulated on
the weld joint part 13 of the cylinder rod 1, the weld joint part 13 may be broken
or damaged due to welding defects and so on.
[0027] As described above, even in the case where the weld joint part 13 is broken in unexpected
environments, the rod head 1a and the rod body 1b can be kept in a joint connection
state by the connection bolt 12 that is screw-engaged with the inner center portion
of the weld joint part 13 in a shaft direction.
[0028] Accordingly, even in the case where the weld joint part 13 of the rod head 1a and
the rod body 1b of the cylinder rod 1 is broken, the arm and the bucket are prevented
from freely falling by the connection bolt 12, and thus a cab or an operator can be
protected from safety accidents.
[0029] As illustrated in FIG. 4B, the screw engagement part 10, which is formed in the center
parts of the mutual contact surfaces of the rod head 1a and the rod body 1b in a shaft
direction to joint-connect the rod head 1a and the rod body 1b through screw-engagement,
may a screw hole 11 formed in one of the center parts of the contact surfaces of the
rod head 1a and the rod body 1b (e.g. formed in the rod head 1a), and a connection
bolt 12 fixed by welding to the other of the center parts of the contact surfaces
of the rod head 1a and the rod body 1b to correspond to the screw hole 11.
[0030] In this case, the construction, except for the screw engagement part 10 composed
of the screw hole 11 formed in the center of the contact surface of the rod head 1a
and the connection bolt 12 fixed by welding to the center of the contact surface of
the rod body 1a, is substantially the same as that as illustrated in FIGS. 3 and 4A,
the detailed description thereof will be omitted. In the description of the present
invention, the same drawing reference numerals are used for the same elements across
various figures.
[0031] As described above, the hydraulic cylinder having a rod safety device according to
the embodiments of the present invention has the following advantages.
[0032] Since the screw engagement part is formed in the center parts of the mutual contact
surfaces of the rod head and the rod body of the hydraulic cylinder in the shaft direction
(i.e. in a direction of extension and compression of the cylinder rod), and the outer
surface of the joint connection part of the rod head and the rod body is welded, a
free falling of the arm and the bucket is prevented by the fastening members when
the welding part is broken, so that the cab is prevented from being damaged, and the
operator is protected from an accident.
[0033] Also, even if an owner of the equipment optionally remodels a working device to cope
with divers working environments, the reliability of the equipment is improved by
preventing a free falling of the arm and the bucket when the welding part of the cylinder
rod is broken due to welding defects and so on.
[0034] Although preferred embodiment of the present invention has been described for illustrative
purposes, those skilled in the art will appreciate that various modifications, additions
and substitutions are possible, without departing from the scope and spirit of the
invention as disclosed in the accompanying claims.