Brakes – Operators – Fluid pressure
Reexamination Certificate
1999-12-30
2002-05-14
Rodriguez, Pam (Department: 3613)
Brakes
Operators
Fluid pressure
C091S431000, C060S401000, C060S462000
Reexamination Certificate
active
06386346
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a brake valve device for use in industrial vehicles, and more particularly to a spool-out type booster brake valve device in which a valve spool is upwardly moved in accordance with the depression of a brake pedal, thereby causing high pressure working fluid to be introduced into a booster chamber to forcibly extend a master piston so that a brake fluid existing in a master chamber can be discharged under pressure into a brake actuator.
DESCRIPTION OF THE PRIOR ART
Generally, industrial vehicles such as forklift trucks are equipped with a pump for discharging high pressure working fluid. The working fluid discharged from the pump is supplied to a steering system, a brake system, and a variety of working implements so that it can be used as a power source for desired tasks to be conducted. The brake system typically includes a pedal adapted to be depressed by the foot of a user, a brake actuator adapted to apply a brake force to the wheels of a vehicle, and a brake valve device adapted to feed a brake fluid under pressure to the brake actuator in response to the depression of the pedal, thereby causing the brake actuator to conduct its braking function. The brake valve device may be either of a booster type in which the hydraulic force of the working fluid is used to force the brake fluid under pressure to the brake actuator, or a non-booster type in which only the depression force of the pedal is relied upon to direct the brake fluid to the brake actuator. The brake valve device may also be of a spool-in type in which a spool incorporated in the brake valve device is inwardly moved in accordance with the depression of the pedal, or a spool-out type in which the spool is outwardly moved in accordance with the depression of the pedal.
Referring to
FIG. 1
, a conventional brake valve device is illustrated which is of a spool-in booster type. As shown in
FIG. 1
, this brake valve device includes a valve body
10
which is defined with a booster chamber
12
and a master chamber
14
. The booster chamber
12
is selectively connected to a pump
18
through a working fluid inlet
16
or to a reservoir tank
22
through a working fluid outlet
20
. A valve spool
24
is slidably arranged in the valve body
10
in such a fashion that it can be shifted between an idle position and an operating position thereof. The valve spool
24
is normally biased toward the idle position by a return spring
24
a.
When the valve spool
24
is at its idle position, as shown in
FIG. 1
, the booster chamber
12
is shut off from the pump
18
while communicating with the reservoir tank
22
. In this state, accordingly, no pressure is applied to the booster chamber
12
. As the valve spool
24
is moved from its idle position to its operating position in accordance with the depression of a brake pedal
26
, the pump
18
is connected to the booster chamber
12
so that high pressure working fluid can be supplied to the booster chamber
12
. A pressure reducing valve
28
is arranged between the working fluid inlet
16
of the valve body
10
and the pump
18
. The pressure reducing valve
28
serves to reduce the pressure of the working fluid supplied to the booster chamber
12
to a predetermined level or less.
In the meantime, the master chamber
14
of the valve body
10
is connected to a brake actuator
32
via a backflow control valve
30
while being connected to the valve spool
24
via a pilot line
34
. The master chamber
14
also communicates with a brake fluid reservoir tank
36
to receive a brake fluid from the reservoir tank
36
. A booster piston
38
and a master piston
40
are slidably received in the booster chamber
12
and the master chamber
14
, respectively. These pistons
38
and
40
are connected to each other by means of a connecting rod
42
so that they can move as a unit. The booster piston
38
and the master piston
40
are always biased toward their retracted positions by return springs
38
a
and
40
a,
respectively. When the driver of a vehicle, to which the brake valve device is applied, depresses the brake pedal
26
to shift the valve spool
24
from the idle position to the operating position, the pump
18
is rendered to communicate with the booster chamber
12
to feed high pressure working fluid to the booster chamber
12
. As a result, both the booster piston
38
and the master piston
40
are extended against the return springs
38
a
and
40
a
by a distance proportional to the displacement of the valve spool
24
, thus causing the brake fluid in the master chamber
14
to be fed under pressure to the brake actuator
32
which in turn applies brake force to vehicle wheels.
On the contrary, when the depression force
26
is removed from the brake pedal, the valve spool
24
returns to its idle position by virtue of the biasing force of the return spring
24
a.
This allows the working fluid in the booster chamber
12
to be discharged to the reservoir tank
22
. At this time, the booster piston
38
and the master piston
40
are moved to their retracted positions by virtue of the urging force of the return springs
38
a
and
40
a,
respectively, whereby the brake fluid is returned back to the master chamber
14
from the brake actuator
32
to make the latter inoperative.
In the case of the above mentioned spool-in type booster brake valve device, it is necessary to use an independent brake fluid reservoir tank for storage of brake fluid to be supplemented in the master chamber, as well as a pressure reducing valve for decreasing the pressure of the working fluid to be supplied to the booster chamber. Use of such elements tends to make the brake valve device complicated in structure and costly to manufacture. Moreover, it is unavoidable to replace overall link mechanism with a new one when an attempt is made to retrofit the existing spool-out type brake valve devices through the use of the spool-in type valve device referred to supra.
SUMMARY OF THE INVENTION
With the above-identified problems in mind, it is an object of the invention to provide a brake valve device for industrial vehicles capable of allowing pump-discharged working fluid to be used as a brake fluid, thereby eliminating the need to use a separate brake fluid fill-up unit.
Another object of the invention is to provide a brake valve device for industrial vehicles that permits pump-discharged working fluid to be supplied to a booster chamber without any pressure reduction thereof, thereby avoiding the use of a pressure reducing valve.
A further object of the invention is to provide a brake valve device for industrial vehicles which can be advantageously used in retrofitting existing spool-out type booster brake devices.
In accordance with the present invention, there is provided a brake valve device for use in industrial vehicles equipped with a fluid pump, a reservoir tank and a brake actuator, comprising: a valve body having an inlet port, a drain port, a brake port, a booster chamber communicatable with the pump via the inlet port and a master chamber communicatable with the brake actuator via the brake port, the master chamber selectively connectable to the pump to receive working fluid therefrom; a valve spool slidably fitted in the valve body through the booster chamber and the master chamber for extending and retracting movement with respect to the valve body, the valve spool shiftable between an idle position and an operating position; and slider means axially displaceably fitted to and movable together with the valve spool for, in response to the shifting movement of the valve spool into the operating position, decreasing the volume of the master chamber so that the fluid present in the master chamber can be extruded into the brake actuator via the brake port.
REFERENCES:
patent: 3050944 (1962-08-01), Schwartz et al.
patent: 3119235 (1964-01-01), Lewis et al.
patent: 3159974 (1964-12-01), Rodgers
patent: 3638426 (1972-02-01), Belart
patent: 3774736 (1973-11-01), Ito et al.
patent: 4007593 (1977-02-01), Baker
Hong Jeong Hee
Jang Dal Sik
Kim Tae Kyung
Park Sung Ha
Daewoo Heavy Industries Ltd.
King Bradley
Rodriguez Pam
Staas & Halsey , LLP
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