Implements or apparatus for applying pushing or pulling force – Hoisting truck – Single throw lever
Reexamination Certificate
2001-10-04
2003-06-24
Hail, III, Joseph J. (Department: 3723)
Implements or apparatus for applying pushing or pulling force
Hoisting truck
Single throw lever
C254S00200C, C254S00200C, C254S00800R
Reexamination Certificate
active
06581909
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention pertains to hydraulic lifting jacks and, in particular, a simplified hydraulic circuit for a quick-rise type lifting jack. The novel construction of the hydraulic circuit positions two discharge valves that control two stages of the lifting operation of the jack in the same valve housing in a base of the jack and thereby significantly reduces the costs involved in manufacturing and assembling the hydraulic circuit of the jack.
(2) Description of the Related Art
FIG. 1
shows a typical hydraulic jack commonly referred to as a service jack. Hydraulic jacks of this type are well known in the art and examples of the constructions of such jacks are shown in the Tallman U.S. Pat. No. 4,018,421, issued Apr. 19, 1997, and the John U.S. Pat. No. 4,131,263, issued Dec. 26, 1978. Generally, hydraulic jacks of the type shown in
FIG. 1
are operated by manually oscillating the lever arm
12
of the jack upwardly and downwardly. The oscillating movement of the lever arm
12
is transferred to a reciprocating pump
14
that draws hydraulic fluid from a reservoir of the jack and compresses the fluid. The compressed fluid unseats a discharge valve of the jack hydraulic circuit causing the pressurized hydraulic fluid to travel through the hydraulic circuitry machined in a base
16
of the jack. The hydraulic circuitry routes the pressurized hydraulic fluid to a lifting cylinder where the pressurized hydraulic fluid acts on a ram or lifting piston of the jack. Extension of the ram or lifting piston of the jack from the cylinder while being acted on by hydraulic fluid under pressure pumped from the pump
14
causes a lifting arm
18
to rise through a mechanical connection between the lifting piston and the arm. In many hydraulic jacks of the type shown in
FIG. 1
, the lever arm
12
is rotatable in its connection to the jack. Rotation of the arm
12
in a counter-clockwise direction opens a release valve that allows the pressurized hydraulic fluid in the lifting cylinder of the jack to be vented back to the hydraulic fluid reservoir, thereby allowing the lifting arm
18
to be lowered. Rotating the lever arm
12
counter-clockwise after the lifting arm
18
has been lowered reseats the release valve and the jack is again ready for its lifting operation.
There are many different types of hydraulic fluid jacks of the type shown in FIG.
1
. In addition, there are similar types of jacks commonly referred to as bottle jacks due to their appearance. These jacks do not employ a lifting arm
18
that raises as the ram or lifting piston is extended from the lifting cylinder of the jack, but instead employ the ram or lifting piston as the lifting component of the jack. Operation of the lever arm of a bottle jack causes the ram or lifting piston to be extended vertically from the lifting cylinder and thus the lifting force of the lifting piston is applied directly to the object to be raised and not through a mechanical linkage such as the lifting arm
18
of the jack of FIG.
1
.
All jacks of the type described above employ a circuit of conduits and valves to control the delivery of hydraulic fluid pressurized by the pump of the jack to the lifting cylinder of the jack. The hydraulic conduits and valve housings are commonly constructed by machining or drilling holes into a cast solid metal base of the jack. The conduits and valve housings are then sealed closed at the exterior of the base by screw threaded plugs or set screws that are screwed into internal screw threading of the conduits and valve housings adjacent the exterior of the base. More simplified hydraulic jack constructions require only a few conduits and valve housings machined into the base of the jack and therefore the machining costs of the more simplified hydraulic jacks are relatively small when compared to other jack constructions.
More complex jack constructions, for example, a hydraulic jack that has a quick-rise feature where the ram or lifting piston is extended quickly from the lifting cylinder on oscillation of the jack lever arm until it encounters a resisting load, and then is extended more slowly from the lifting cylinder as the hydraulic fluid is pressurized by the lever arm and pump to lift the load require a more elaborate hydraulic circuit in the jack base. The more elaborate circuit of a quick-rise lifting jack requires additional conduits to be machined into the base of the jack and additional valve housings to control the two stage lifting function of the jack. Jacks of this type will have increased manufacturing costs over that of more simplified jacks due to the additional machining steps needed to construct the hydraulic circuit and the additional assembly steps needed to assemble the valve elements into the valve housings of the hydraulic circuit.
FIG. 2
shows a schematic representation of a hydraulic circuit for a prior art quick-rise lifting jack. The circuit is formed into the base (not shown) of the jack in the known manner of machining conduits and valve housings into the base from the exterior of the base. All hydraulic circuits of this type basically operate by drawing hydraulic fluid from a fluid reservoir into a pump, and then pressurizing the fluid forcing it through the hydraulic circuit to the lifting cylinder where the pressurized fluid causes a ram or piston to be extended from the cylinder. As explained earlier, the lifting piston is mechanically connected to a lifting arm of the jack or acts directly on the load being lifted by the jack. In operation of the circuit shown in
FIG. 2
, the lifting piston is quickly extended out of the lifting cylinder until it encounters the load to be raised. On subsequent operation of the pump of the hydraulic circuit, the lifting cylinder is raised at a slower rate but exerts a greater force on the object to be raised.
The hydraulic circuit shown in
FIG. 2
includes a pump
22
comprised of a pump cylinder
24
and a pump plunger
26
mounted in the cylinder for reciprocating movement therein. The reciprocating movement of the pump plunger
26
is caused by oscillating movements of the arm
12
shown in FIG.
1
.
The pump cylinder
24
communicates through a conduit
32
with a relief valve
34
. The relief valve
34
includes a cavity machined into the base (not shown) of the jack that contains a relief ball valve
36
that is held against a valve seat by a spring
38
. The cavity is sealed closed by a screw threaded plug
42
. The cavity also communicates with the hydraulic fluid reservoir R of the jack through a conduit
44
that is behind the relief ball valve
36
when the ball valve is positioned on its valve seat as shown in FIG.
2
.
The pump cylinder
24
also communicates through a conduit
46
with a discharge valve
48
. The discharge valve
48
includes a discharge ball valve
52
that is biased against a valve seat by a spring
54
that is contained in a cavity machined into the jack base. The cavity is closed by a screw threaded plug
56
. At the bottom of the discharge valve cavity is a suction valve cavity containing a pump suction ball valve
58
that seats on a valve seat separating the suction valve cavity, the pump cylinder
24
and the conduit
46
communicating the pump cylinder with the discharge valve cavity and suction valve cavity from the reservoir R.
A further length of conduit
62
extends downstream from the discharge valve
48
. This length of conduit
62
communicates with the release valve
64
, a gravity valve
66
, a second stage ball valve
68
and an interior ram
72
of the jack lifting mechanism
74
.
The release valve
64
contains a release valve element
76
that is shown in
FIG. 2
seated against a valve seat that is machined into the base. The release valve element
74
is permitted to move away from the valve seat when the lever arm
12
of the jack is rotated in a counter-clockwise direction as explained earlier. This unscrews the release valve element
74
away from its valve seat and opens communication of the downstream conduit
62
to t
Bryan Cave LLP
Clore Automotive, LLC
Hail III Joseph J.
Shanley Daniel
LandOfFree
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