Safety device for control lever of construction machines

A safety device for the control lever of a construction machine having hydrostatic transmission which comprises a casing provided on the machine and a control rod rotatably connected at one end thereof with the control lever associated with the hydrostatic transmission, said control rod being formed with a slender portion at the other end portion which is slidably accommodated by the casing, said slender portion having a coil spring interposed within the casing, and said coil spring being stressed sufficiently to automatically return the control lever to the neutral position when the operator takes his hands off the control lever.

FIELD OF THE INVENTION 
This invention relates to a safety device for the control lever of 
construction machines such as a pedestrian-type road roller or a compactor 
having a hydrostatic transmission. The safety device of the present 
invention prevents said construction machines from running away. 
BACKGROUND OF THE INVENTION 
The above construction machines are driven by an operator, while the 
operator is walking. The machines have a possibility of running away, in 
case the operator tumbles over and cannot control it any more or in case 
he turns on the starter with the control lever keeping at the forward or 
backward position. 
To solve the above problem, a conventional machine has been equipped with 
the safety device as shown in FIG. 5. The safety device comprises a 
control box 20, a control lever 30, a safety rod 40, and a safety arm 50. 
The control lever 30 is swingably supported by an axis in the control box 
20. The safety rod 40 is slidably supported on the rear wall of the 
control box 20 and extends from the outside through the inside of the rear 
wall. The safety rod 40 interposes a stressed coil spring 41 in the 
housing 42. The upper portion of the control lever 30 is adjacent to the 
end of the safety rod 40 inside the control box 20 when the lever 30 is 
shifted to the backward position as indicated by dashed line. The safety 
arm 50 has a V-like shape and is pivotally supported at the corner of the 
V-like shape by an axis in the lower portion of the control box 20 
adjacent to the front wall of the control box 20. The upper portion of the 
safety arm 50 inwardly extends in the control box 20. The lower end of the 
control lever 30 is adjacent to the upper portion of the safety arm 50 
when the lever 30 is shifted to the backward position as indicated by 
dashed line. The lower portion of the safety arm 50 extends from the 
bottom to the outside of the control box 20. In case the operator is 
sandwiched between an obstacle and the machine moving backwardly, pushing 
the safety rod 40 changes the position of the control lever 30 to the 
neutral or forward position and then keeps the operator safe. In case the 
operator tumbles over and cannot operate the control lever, pushing the 
safety arm 30 changes the position of the control lever 30 to the neutral 
or forward position and then keeps the operator safe. 
However the above-mentioned conventional safety device requires the 
operator to immediately touch another portion than the control lever 30, 
that is, the safety rod 40 or the safety arm 50, in order to prevent the 
machine from running away. If the operator unfortunately has no chance to 
touch such portions, it is impossible to stop the machine running away. 
Moreover, the safety rod 40 and the safety arm 50 are encumbrances for 
ordinary operations, since they extend out of the control box 20. And such 
structure is complicated and large, and makes the manufacturing cost 
expensive. 
U.S. Pat. No. 4,267,804 issued to Rypka discloses a safety system which 
prevents a construction machine from being turned on unless the control 
lever is in a neutral position, thereby making the operator reminded to 
place the control lever in the neutral position before attempting to start 
the machines. Rypka provides a solution to prevent accidents which occur 
when the machine is started, but does not give the solution to prevent 
accidents which occur while the machine is in operation, e.g. when the 
operator in operation tumbles over. 
SUMMARY OF THE INVENTION 
The present invention provides a safety device which is adapted to a 
construction machine having hydrostatic transmission which normally 
comprises fluid pressure pump and hydraulic motor. The safety device 
according to the present invention comprises a casing and a control rod. 
The control rod is slidably accommodated in the casing and extends from 
the inside through the outside of the casing. The control rod is rotatably 
connected at the end extending outside of the casing with an end of the 
control lever. The control rod has a slender portion where a stressed coil 
spring is interposed. The control lever connectes with and controls the 
fluid pressure pump of the hydrostatic transmission. The coil spring is 
stressed sufficiently to have the control lever to automatically return to 
the neutral position where no fluid is supplied with the fluid pressure 
pump, when an operator takes his hand off the control lever. 
According to a preferred embodiment, the coil spring is provided at both 
ends thereof with washers. Each washer engages with each engaging portion 
formed on the interior wall of the casing because of the force of the 
stressed coil spring so that the control rod may return to the neutral 
position when the operator takes his hands off the control lever. 
It is an object to provide a safey device which automatically makes the 
control lever return to the neutral position only if the operator takes 
his hands off the lever, thereby stopping the movement of the machine. 
It is another object to provide a safety device which is simple in 
structure, small-sized, easy to manufacture and low in cost. 
According to the present invention, all the operator has to do in case of 
an accident is only to take his hands off the control lever. Even if the 
operator tumbles over or is sandwiched between an obstacle and the 
machine, the operator do not have to handle any portion of the machine.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Hereinafter, the present invention is more particularly set forth with 
reference to the accompanying drawings wherein preferred embodiments are 
shown. 
In FIG. 1, the numeral 1 generally indicates a inventive safety device 
which automatically returns the control lever from the forward or backward 
position to the neutral position. The device 1 includes a casing and a 
control rod, which are generally indicated at 2 and 3, respectively. The 
casing 2 is rotatably connected at the forward end 21 thereof with an 
appropriate portion of the body of a construction machine. The control rod 
3 is slidably inserted into the casing 2. The rearward end 31 of the 
control rod 3 which extends out of the casing, is rotatably connected to 
the lower end of the control lever 5. The control lever 5 is rotatably 
supported by an axis 4. 
The casing 2 comprises a cylindrical member 6 and a cap member 7. The 
cylindrical member 6 consists of a wide portion 61 and a narrow portion 
62. The connecting portion of the wide portion 61 and the narrow portion 
62 forms a rear engaging portion 8a inside the cylindrical member 6. The 
cap member 7 is threadably mounted into the cylindrical member 6 and has 
an inner diameter smaller than that of the wide portion 61 so that the rim 
of the cap member forms a forward engaging portion 8b inside the 
cylindrical member 6. 
The control rod 3 has a forward slender portion 9. The slender portion 9 
forms a step portion 15 of the rod 3 and is provided at the end thereof 
with a snap ring 10. In the slender portion 9, a stressed coil spring 11 
is interposed between the snap ring 10 and the step portion 15. The 
stressed coil spring 11 is provided at both ends thereof with washers 12a 
and 12b, each of which engages with the snap ring 10 and the step portion 
15. The control lever 5 is connected with the control rod 3 so as to be in 
the neutral position when the washers 12a and 12b engage with the engaging 
portions 8a and 8b respectively. 
The control rod 3 is provided therearound adjacent to the rear end of the 
cylindrical member 6 with an annular friction member 13 made of such 
material as urethane rubber and is provided adjacent to the friction 
member 13 with an adjusting ring 14 which covers the friction member 13. 
The adjusting ring 14 is threadably connected with the cylindrical member 
6. Rotation of the adjusting ring 14 varies the slide speed of the control 
rod 3 depending on the pressure of the friction member 13 to the control 
rod 3. 
As best shown in FIG. 2, when the control lever 5 is positioned in the 
forward direction as drawn by full line, the lower end of the control 
lever 5 moves backwardly around the axis 4 and actuates the control rod 3 
backwardly. At this time, the washer 12a engages with the engaging portion 
8a and the washer 12b moves backwardly while engaging with the snap ring 
10 and compressing the coil spring 11 between the washers 12a and 12b. On 
the other hand, when the control lever 5 is positioned in the rearward 
direction as drawn by dashed line, the lower end of the control lever 5 
moves forwardly around the axis 4 and actuates the contorl rod 3 
forwardly. At this time, the washer 12b engages with the engaging portion 
8b and the washer 12a moves forwardly while engaging with the step portion 
15 and compressing the coil spring 11 between the washers 12a and 12b. In 
the latter position of the control lever 5, if the operator is sandwiched 
between the machine and an obstacle behind him or tumbles over, he only 
has to take his hands off the control lever 5, and the control lever 5 
automatically returns to the neutral position shown in FIG. 1 thanks to 
the resilience of the spring coil 11 so that the machine stop. 
FIG. 3 diagramatically shows a pedestrian-type vibrarion roller 100 having 
a hydrostatic transmission, which is connected with the safety device 1 
according to the present invention. The safety device is mounted with a 
bolt 21 on a flange in the control box 101 of the roller 100. The control 
lever 5 is fixed at one end of the shaft 4 which is rotatably supported on 
a bearing 102 within the control box 101. An arm 103 is fixed with bolts 
and the like on the other end of the shaft 4. And, the arm 103 is 
connected via a wire 107 having a guide tube to the lever 106 of the fluid 
pressure pump 105 which varies the amount and the direction of fulid to be 
supplied with the hydraulic motor. Thus, when the control lever 5 is in 
forward or backward position as shown in FIG. 2, the hydrostatic 
transmission drives the machine in a foward or backward direction by way 
of the control lever 5, the shaft 4, the arm 103, the wire 107 and the 
lever 106. 
Even if the operator tumbles over or is sandwiched between the roller and 
an obstacle during the operation of the roller 100 of FIG. 4, all the 
operator has to do to stop the roller is to take his hands off the control 
lever 5. Because, only if he takes his hands off, the control lever 5 
automatically returns to the neutral position by virtue of the stressed 
coil spring 11 and places the lever 106 at the position where no fluid is 
pumped to the hydraulic motor by way of the wire 107, thereby stopping the 
movement of the roller 100. 
FIG. 4 shows another embodiment of the safety device according to the 
present invention. Of course, the safety device of FIG. 4 can be applied 
to the roller of FIG. 3 in place of the safety device of FIG. 1. In FIG. 
3, the numerals denote the members corresponding to FIGS. 1 and 2. This 
embodiment has the same structure as the embodiment of FIGS. 1 and 2, 
except that the coil spring 11 has a washer 12 adjacent to the snap ring 
10 and the other end of the coil spring 11 directly engages with the step 
portion 15 of the control rod 3. When the control lever 5 is positioned in 
the backward direction, the lower end of the control lever 5 moves 
forwardly around the axis 4 and actuates the control rod 3 forwardly. At 
this time, the washer 8 engages with the rim 8 of the cap member 7 while 
the coil spring 11 is compressed between the portion 15 and the washer 12. 
At the above state, if the operator takes his hands off the control lever 
5, the control lever 5 automatically returns to the neutral position 
thanks to the resilience of the coil spring 11. However, when the control 
lever 5 is positioned in the forward direction, this embodiment does not 
allow the control lever 5 to return to the normal position automatically. 
It is understood that the embodiment of FIG. 3 is designed to ensure the 
safety only during the backward drive and is, therefore, suitable to 
attain an efficient work. 
It should be understood that the inventor intend to cover by the appended 
claims all modifications falling within the true spirit and scope of the 
present invention.