Hydraulic lifting jack including a safety device for an elevator therein

A hydraulic lifting jack on wheels, comprising a pair of frame plates, an elevator pivotally mounted on the frame plates, a lifting saddle arranged in the free end of the elevator, and a hydraulic power unit for lifting the elevator, in which a safety device for the elevator is further provided and comprises a support block member pivotally mounted to the elevator, and step block members, each having stop steps in its front slope surface, secured to the frame plates. The support block member is pivoted by a lever into an engaging or disengaging position wherein the support block member engages or disengages with or from the step block members. When the support block member is positioned in the engaged position, the raised elevator is prevented from falling down by the support block member, the bottom of which is supported by the stop steps of the step block members.

BACKGROUND OF THE INVENTION 
This invention relates to a hydraulic lifting jack including a safety 
device for an elevator therein. 
With a conventional lifting jack, most accidents happens when elevator of 
the lifting jack fails or accidentally rides down, which is very 
dangerous. Further, when an operator operates a wrong lever by mistake, 
the elevator of the lifting jack goes down against his, which will often 
bring about the same fatal results. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a hydraulic lifting 
jack including a safety device for an elevator therein free from the 
aforementioned disadvantages, and one which is simple in construction and 
reliable and safe in operation. 
According to the present invention there is provided a hydraulic lifting 
jack on wheels, comprising: a pair of frame plates; an elevator which is 
pivotally mounted to the frame plates; a lifting saddle arranged in the 
free end of the elevator; and a hydraulic power unit, mounted to the frame 
plates, for lifting the elevator. The safety device for the elevator, 
comprising a support block means which is pivotally mounted to the 
elevator, and a step block means having stop steps in its front slope 
surface, which is secured to the frame plates, wherein the support block 
means is adapted to be pivoted into an engaging or disengaging position 
wherein the support block means engages or disengages with or from the 
step block means, and wherein, when the support block means is positioned 
in the engaged position, the raised elevator is prevented from falling 
down by the support block means the bottom of which is supported by the 
stop steps of the step block means.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, in which the same numerals denote the same 
parts, there is shown in FIGS. 1 and 2 a hydraulic lifting jack comprising 
a pair of frame plates 1; a pair of front wheels 2 which are rotatably 
mounted to the frame plates 1 through a shaft 3; a pair of casters 4 with 
rear wheels 4a, mounted to the rearward portions of the frame plates 1; an 
elevator 5, pivotally mounted to the frame plates 1, for lifting an 
object; a lifting saddle 6 arranged in the free end of the elevator 5; a 
hydraulic power unit 7 for lifting the elevator 5, which is mounted to the 
frame plates 1 by a mounting member 7a; and a handle 8 including a handle 
rod for lowering the elevator 5, which is mounted to the frame plates 1 in 
its end portion by a yoke 9. 
The hydraulic power unit 7 is of substantially conventional construction 
and comprises an oil pump means 10 actuated by the handle 8, an oil 
cylinder 11 connected thereto, and an actuating rod 12 connected thereto. 
When the elevator 5 is raised, the handle 8 is turned up and down many 
times for actuating the oil pump means 10 via a coupling rod 13 and a link 
14, and thereby pushing the oil cylinder 11. Then, the actuating rod 12 is 
extended forwards, i.e. the right hand side direction in FIG. 1, by the 
oil cylinder 11, and thereby the elevator 5 coupled to the actuating rod 
12 is raised, as hereinafter described. 
When the elevator is lowered, a lever 17 connected to the handle rod of the 
handle 8 is pivoted in a horizontal plane, and then a cam plate 19 which 
is engaged with the lower end of the handle rod is rotated 
counterclockwise in FIG. 1 around a shaft 15. Then, a coupling rod 18 
connected to the cam plate 19 is pulled in the left hand side direction, 
and thus the by-pass of the oil pump means 10 is opened, with the result 
that the actuating rod 12 is retreated or withdrawn while the elevator 5 
is lowered. 
The elevator 5 is of substantially conventional construction and comprises 
two elevator arms 20 of which the upper parts of one end portions are 
connected to a pivot member 22 on a pivot shaft 21 which is pivotally 
mounted to the frame plates 1 by nuts 21a, and the other ends of which are 
pivotally mounted to a bracket 24 of the saddle 6 via pivot pins 23, and a 
pair of link bars 25, one ends of which are pivotally connected to the 
frame plates 1 via pivot pins 26 by nuts 27, and the other ends of which 
are pivotally mounted to the bracket 24 via pivot pins 28. The tops of the 
elevator arms 20 are covered by a cover plate 30. 
To the one ends of the elevator arms 20 is secured a link shaft 29 which is 
pivotally coupled to the front end portion 12a of the actuating rod 12. 
While the elevator 5 is raised by the forward movement of the actuating rod 
12, the lifting saddle 6 is always kept horizontal by a parallelogram link 
mechanism with four vertexes, i.e. the pivot shaft 21 and the pivot pins 
23, 26 and 28. 
As clearly shown in FIG. 3, a safety device for the elevator 5 comprises a 
pair of step block members 31, each having hollow stop steps 31a in its 
inclined front surface and a lower slope 31b in its foot, secured to the 
frame plates 1, and a support block member 32 pivotally mounted to the 
elevator arms 20 via bosses 34 secured thereto by pivot pins 33. To the 
top of the support block member are connected a horizontal rod 35a 
extending outwards via a short rod 35c in its one side and a bend rod 35b 
having a bent in its free end, in its the other side. 
A pair of springs 37 are disposed between the horizontal rod 35a, the top 
of the bend rod 35b, and the stop pins 38 mounted to the link bars 25. The 
outer end of the horizontal rod 35a is pivotally connected to one end of a 
coupling rod 36 the other end of which is connected to an actuating lever 
39 through a hole of a guide member 40 mounted to the frame plate. 
When the lever 39 is pushed, the safety device is operated, that is, the 
support block member 32 is pivoted clockwise about the pivot pin 33 as 
shown in FIG. 3 against the springs 37 and into an engaged position 
wherein the lower end portion of the support block members 32 is engaged 
with the step block members 31 by the springs 37, as clearly shown by the 
solid lines in FIG. 3. 
Meanwhile, when the lever 39 is pulled, the safety device does not work, 
that is, the support block member 32 is pivoted counterclockwise about the 
pivot pin 33 as shown in FIG. 3 against the springs 37 through a dead 
point, i.e. the stop pins 38, into a disengaged position wherein the lower 
end portion of the support block member 32 is disengaged from the step 
block members 31 by the springs 37, as clearly shown by the two-dotted 
lines in FIG. 3. 
As the elevator 5 is lifted from the bottom while the safety device is 
operated, the bottom of the support block member 32 is raised from the 
ground upwardly along the front surfaces of the step block members 31 in 
contact with their lower slopes 31a and then their stop steps 31a. 
When the raised elevator 5 is suddenly lowered by an accident, a mistake of 
operation, or the like, the fall downward of the elevator 5 is stopped by 
the support block member 32, the bottom of which is stopped by the stop 
steps 31a of the step block members 31. 
When the elevator is lowered, the bottom of the support block member 32 is 
pivoted upwards away from the step block members 31 by pulling the lever 
39, as described above. 
Although the present invention has been described in some detail by way of 
illustration and example for purposes of clarity of understanding, it 
will, of course, be understood that various changes and modifications may 
be made in the form, details, and arrangements of the parts without 
departing from the scope of the invention as set forth in the following 
claims.