Structural improvements of a hydraulic four-wheel jack which protects the jack from damage resulting from overloading and/or overpumping, while offering a compact configuration having minimal space requirements. The jack incorporates a hydraulic unit assembly of the piston-and-cylinder variety in which the piston extends in an upwardly direction and bears against a cross-wise shaft being pivotably mounted between parallel cantilever arms, which carry on their respective free ends a lift assembly. The jack further incorporates a base having a unique series of interior passages provided with one-way, spring loaded ball-check-valves, whereby fluid communication is provided for the hydraulics of the jack.

FIELD OF THE INVENTION 
The present invention relates to structural improvements to hydraulic jacks 
and, in particular, to structural improvements to hydraulic four-wheel 
jacks. 
BACKGROUND OF THE INVENTION 
Hydraulic jacks comprise usually three types: The vertical type, the 
four-wheel type and the large type, respectively. The four-wheel types are 
normally designed to be carried within a vehicle for use at home or on the 
road wherever and whenever needed. At the present time, these type of 
four-wheel jacks have several disadvantages in that they are relatively 
bulky and expensive. 
Accordingly, there remains a need to provide a four-wheel jack which 
requires less storage space, is less bulky and is less expensive than 
present four-wheel jacks, and is easier and more convenient to use. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to alleviate the 
deficiencies of the prior art by producing an improved four-wheel jack 
which achieves the following advantages: (1) it reduces the storage space 
by about one-third, thereby facilitating storage in the trunk of a sedan 
or other light-weight vehicle; (2) it reduces fabrication and 
transportation costs; and (3) it reduces the bulk and weight, thereby 
facilitating easier operation and handling. 
It is another object of the present invention to provide a four-wheel jack 
which, by changing the position of the application of force prevailing in 
conventional devices and utilizing a different execution of the principles 
of levers permits the introduction of a relatively smaller pump piston as 
compared with that of the prior art devices. 
It is yet another object of this invention to provide a four-wheel jack, of 
the piston-and-cylinder variety, which has an improved hydraulic system 
that protects the jack from damage resulting from overloading and/or 
overpumping. 
In accordance with the teachings of the present invention, a hydraulically 
operated lifting device is provided of the type having a four-wheeled 
carriage which includes a pair of substantially parallel side plates. A 
pair of elongated cantilever arms extend above the side plates and each 
has a pair of end portions. Means are provided for pivotably mounting one 
end portion of each of the arms between the side plates (near one end of 
the carriage) and a lift assembly is provided on the other free end of 
each of the arms. A pair of elongated stabilizing struts are parallel with 
the cantilever arms and are pivotably connected between the side plates 
and the lift assembly. Within this structure, the improvement of the 
present invention includes a hydraulic cylinder pivotably mounted between 
the side plates intermediate the ends thereof. A piston is disposed within 
the cylinder and is operatively associated therewith. A shaft, which is 
substantially rectangular in cross-section and has a plurality of flat 
faces, is pivotably mounted crosswise on the cantilever arms intermediate 
the end portions thereof. The piston extends in a substantially upwards 
direction and engages one of the flat faces on the shaft thereby raising 
the cantilever arms, struts and lift assembly. 
In accordance with the further teachings of the present invention, a 
hydraulically operated lifting device is provided, having a first extended 
position and a second collapsed position. This jack has a four wheeled 
carriage and includes a pair of substantially parallel side plates. A pair 
of parallel elongated cantilever arms extend above the side plates, and 
each has a pair of end portions. Means are provided for pivotally mounting 
one end portion of each of the arms between the side plates (near one end 
of the carriage), and a lift assembly is provided on the other free end of 
each of the arms. A pair of elongated stabilizing struts are parallel with 
the cantilever arms and are pivotably connected between the side plates 
and the lift assembly. Within this structure, the improvement includes a 
hydraulic actuator, having an outer annular oil supply reservoir and an 
inner cylinder, pivotably mounted between the side plates intermediate the 
end of the carriage. A piston is disposed within the inner cylinder and is 
operatively associated therewith. A shaft, substantially rectangular in 
cross-section and having a plurality of flat faces, is pivotably mounted 
cross-wise on the cantilever arms intermediate the end portions thereof, 
whereby the piston extends in a substantially upwardly direction engaging 
one of the flat faces on the shaft. Hydraulic fluid is disposed in the 
outer reservoir. A reciprocating pump means is provided for pumping 
hydraulic fluid from the outer reservoir and into the inner cylinder. A 
pressure release valve having a first closed position, whereby oil 
pressure in the inner cylinder is maintained, and a second open position, 
whereby hydraulic fluid is allowed to flow from the inner cylinder, is 
provided. A base is disposed beneath the hydraulic cylinder, and secured 
thereto. The base has at least one first interior passage positioned 
between, and in fluid communication with, the outer reservoir, the 
reciprocating pump means and the inner cylinder. At least two (2) one-way, 
spring-loaded ball-check-valves are disposed in the first interior 
passage. The base also has at least one, second interior passage 
positioned between, and in fluid communication with, the inner cylinder 
and the reservoir. At least one, one-way, spring-loaded ball-check-valve 
and the pressure release valve are disposed in the second interior 
passage. The base further has at least one, third interior passage 
positioned between, and in fluid communication with, the inner cylinder 
and the reservoir. At least one, one-way, spring-loaded ball-check-valve 
is disposed in the third interior passage. These interior passages provide 
fluid communication between the inner cylinder and outer reservoir for 
raising and lowering the lift assembly. 
These and other objects of the present invention will become apparent from 
a reading of the following specification, taken in conjunction with the 
enclosed drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIGS. 1 and 2, there is a hydraulically operated lifting 
jack 10 of the type having a wheeled carriage including wheels 11, a pair 
of substantially parallel side plates 12 and 13 and a pair of elongated 
cantiliver arms 14 and 15. One end of each of the cantiliver arms 14 and 
15 is pivotably mounted on a shaft 16 between the side plates 12 and 13 
near one end of the carriage. The other, respective free ends of the 
cantilever arms 14 and 15 pivotably carry the lift assembly 17 on a second 
shaft 18. 
A pair of elongated stabilizing struts 19 and 20 are positioned parallel 
with the cantilever arms 14 and 15. Each of the struts 19 and 20 is 
pivotably connected at their one end to the side plates 12 and 13. The 
other free ends are pivotably secured by a shaft 61 to the lift assembly 
17. 
A base 21 is rotatably positioned and secured between the side plates 12 
and 13 intermediate the ends of the carriage. A hydraulic cylinder 22 is 
positioned above, and is integral with, the base 21. The cylinder 22 
carries a piston 23 that bears against a cross-wise shaft 24 rotatably 
mounted between the cantilever arms 14 and 15. 
A pressure release valve rod 25 is positioned within and projecting from 
the base 21, whereby pressure within the hydraulic cylinder 22 may be 
adjusted so that the jack may be raised or collapsed, as desired. 
A reciprocating pump 28, with two ends, has its one end carried within the 
base 21. Its other end is pivotably mounted to one end of a bracket 26. 
The other end of the bracket 26 carries a socket 27 for operational 
contact threrwith, whereby rocking the socket 27 in an up and down motion 
actuates the piston 23 thereby extending the jack and lifting the article 
desired. 
A return spring 35 is provided, one end of which is secured to a projection 
(not shown) of the side plate 12. The other end of the return spring 35 is 
established on a cantilever arm 14 whereby pull is provided to reset the 
cantilever arms 14 and 15 and struts 19 and 20 to the zero position. 
A dust cover 36 is also provided, being positioned on the jack in the 
manner illustrated in FIG. 1, having been removed for clarity of 
understanding. 
Now with reference to FIG. 12, in addition to FIG. 1, the handle, generally 
designated 29, has an upper member 30 and a lower member 31. The upper 
member 30 has a grip means 32 at its one end, and at its other, tapered 
end, a pin 33 projecting therefrom. The lower member 31 carries at its one 
end a pin 34. At its other end, is an "L" shaped indentation for receiving 
the pin 33 of the upper member 30. To couple the members, the tapered end 
of the upper member, is inserted into the lower member 31 so that the pin 
33 is received in the indentation and turned for coupling, whereby a 
handle 29 is formed for insertion into the socket 27. 
As illustrated in FIG. 3, the piston 23 is received within, and bears 
against an indentation on a face of the rotatably set cross-wise headed 
shaft 24 where it is secured in place by a cotter pin 37. 
With reference to FIG. 4, the hydraulic subassembly is provided with a 
pressure release valve rod 25. A base 21 is positioned beneath and 
integral with, a hydraulic cylinder 22 which carries a piston 23. 
The hydraulic cylinder has an inner cylinder 38 and an outer annular oil 
supply reservoir 39 as illustrated in FIG. 5. The piston 23, removed for 
clarity of understanding, is carried by the inner cylinder 38. Openings in 
the inner cylinder 40 and 41 and in the reservoir 42, 43 and 44 are 
aligned with interior passages housed within the base for fluid 
communication therewith. The reciprocating pump 28 is inserted into an 
opening 45 in the base being provided for that purpose. 
With reference to FIGS. 6, 7 and 8, the base 21 is provided with a series 
of interior passages for fluid communication between the inner cylinder 
38, the reservoir 39, the reciprocating pump 28 and the pressure release 
valve 46 to provide the hydraulics for raising and lowering of the lift 
assembly. 
With reference to FIG. 6, a first interior passage 47 is provided for 
lifting the piston 23 in the direction indicated by the arrows. This 
passage is provided with two oil holds 48 and 49, each housing a one-way, 
spring-loaded ball-check-valve 50 and 51. To raise the lift assembly, one 
first turns the pressure release valve rod 25 in a clockwise direction, 
thereby placing the pressure release valve 46 in a closed position (see 
FIG. 7) whereby oil pressure in the inner cylinder 38 is maintained. Then 
the handle 29, carried by the socket 27, is rocked in an upwardly 
direction, drawing the pump 28 outwardly from the base 21 whereby the 
first ball-check-valve 50 is unseated, and oil in the reservoir 39 is 
drawn by vacuum through a filter 52, the opening 42 and into the first 
passage 47, filling the first passage 47, including the oil hold 48, to 
occupy all the space that the pump 28 has emptied. When the pump 28 is 
inwardly pushed by a downwards rocking motion on the handle 29, the first 
valve 50 is forced back into its seated position (as seen in FIG. 6) 
preventing oil flow back into the reservoir and the second valve 51 is 
unseated allowing oil to flow through the second oil hold 49 of the first 
passage 47, and the second opening 40, respectively, and into the inner 
cylinder 38. The oil filling the inner cylinder 38 forces the piston 23 
upwardly in the direction of the arrow, thereby raising the lift assembly 
17 so that the desired object may be lifted. 
With further reference to FIG. 6 there is also presented a bypass hole 53 
in the wall between the inner cylinder 38 and the reservoir 39. This 
bypass hole 53 is provided to prevent damage from occurring to the device 
in the event of overpumping of oil into the inner cylinder 38. As oil is 
forced into the inner cylinder 38 there is a relative upward movement of 
the entire assembly, including the cross-wise headed shaft 24. This 
movement is due to the action of the piston 23 moving in the direction of 
the arrow which causes the cantilever arms 14 and 15 to raise the load 
carried by the lift assembly 17. This movement continues until a point is 
reached where the bypass hole 53 comes into registry with the fluid level 
in the inner cylinder 38. At that point, the continued operation of the 
reciprocating pump 28 merely forces additional oil from the inner cylinder 
38 through the bypass hole 53 and back into the reservoir 39. In this 
manner, no further lifting can take place, thus there is no chance of the 
piston 23 being forced completely out of the cylinder 22. Furthermore, 
there is no excessive buildup of pressure which might cause the device to 
break down, because any further attempt to pump fluid into the cylinder 38 
merely causes it to flow directly back into the reservoir 39 through the 
bypass hole 53. 
Referring now to FIG. 7, the base 21 is provided with a second, interior 
passage 54 which houses the pressure release valve 46. This second passage 
54 is in fluid communication with the inner cylinder 38 and the reservoir 
39 whereby, when the valve 46 is unseated, lowering of the piston 23 may 
be effected so that the device can be collapsed for storage, etc. The 
valve 46 is a ball-check-valve. It is unseated by turning the pressure 
release valve rod 25 in a counter-clockwise direction and manually 
applying force downwardly on the piston 23. This motion forces oil out of 
the inner cylinder through the third opening 41, the second passage 54, 
and the fourth opening 43, respectively and into the outer reservoir 39, 
so that the device may be collapsed. 
Referring now to FIG. 8, a third interior passage 55 is provided, being 
positioned in fluid communication with the first passage 47 and the outer 
reservoir 39 to protect the jack at times when the jack is subjected to a 
load greater than its designed capacity. This third passage 55 houses a 
third, one-way spring-loaded ball check-valve 56. In a preferred 
embodiment, the spring of this valve 56 is of a heavier gauge than the 
spring of the other spring-loaded ball-check valves 50 and 51. This valve 
56 only permits oil flow into the outer reservoir 39. 
At times when an overload occurs, oil drawn into the first passage 47 by 
the reciprocating pump 28 cannot, due to the pressure of the oil already 
present in the inner cylinder 38, unseat the second valve 51, (see FIG. 6) 
in order to proceed into the second oil hold 49. Instead, the oil is 
forced from the first passage 47 into the third passage 55. There it 
unseats the third valve 56 and flows through the passage 55 and fifth 
opening 44, respectively and into the reservoir 39. 
With reference to FIG. 9, the cantilever arms 14 and 15 and the stabilizing 
struts 19 and 20 are connected at their respective one end to the lift 
assembly 17. The base 21 is seen carrying the pressure release valve rod 
25 and the reciprocating pump 28. The socket 27 is also shown with a 
handle 29 inserted therein. 
In FIG. 10, the structure of the socket 27 is best illustrated. The socket 
27 has an "L" shaped indentation into which a pin 34, positioned on the 
exterior of the lower member 31 of the handle, is inserted and turned, 
whereby the handle is coupled to the socket 27 for operational contact 
therewith. 
In FIG. 11, the lift assembly 17 can be seen being positioned on a plane 
located substantially lower than that of the cross-wise shaft 24 when the 
device is in its fully collapsed position. 
In FIG. 13 is the jack in its fully extended position. In that position the 
cantilever arms 14 and 15 and their parallel struts 19 and 20 extend above 
the side plates 12 and 13 with the lift assembly 17 positioned on the 
raised end. 
Lower bracing members 57 are positioned between the side plates 12 and 13 
and mounted thereto as shown in FIG. 14, whereby additional support for 
the carriage is provided. 
As seen in FIG. 15, the lift assembly 17 has a lift saddle 58 mounted to a 
lift base 59 for rotational movement thereon by means of an "I" pin 60. 
The lift base 59 is positioned between the cantilever arms 14 and 15 and 
stabilizing struts 19 and 20. The base is pivotably mounted thereto by a 
pair of shafts 61 and 18, whereby raising of the cantilever arms and the 
struts raises the lift assembly 17. It will be appreciated by those 
skilled in the art that this lift assembly could be of any suitable design 
or material consonant with the teachings of this invention. 
With reference to FIG. 16, each of the wheels 11 is provided with an 
aperture through its center. This aperture is aligned with a corresponding 
aperture in each of the side plates. These apertures carry a bolt axle 62 
which is secured to the jack by nuts, whereby wheels 11 for the carriage 
are provided. 
Obviously, many modifications may be made without departing from the basic 
spirit of the present invention. Accordingly, it will be appreciated by 
those skilled in the art, that within the scope of the appended claims, 
the invention may be practiced other than has been specifically described 
herein.