Pumps – Condition responsive control of drive transmission or pump... – Having condition responsive pumped fluid control
Reexamination Certificate
1999-02-05
2001-10-02
Walberg, Teresa (Department: 3742)
Pumps
Condition responsive control of drive transmission or pump...
Having condition responsive pumped fluid control
C417S218000
Reexamination Certificate
active
06296455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pump enable system and method; and more particularly, a pump enable system and method for variable-displacement piston pumps.
2. Description of Related Art
FIG. 1
schematically illustrates a well-known variable-displacement piston pump
10
such as Vickers Incorporated's Model No. PVE19R930CVPC. The piston pump
10
includes a pump
12
having a plurality of pistons (not shown). The pump
12
is connected between a suction line
14
and a pressure line
16
, and is driven by an engine
18
. Oil leaking in the pump
12
is drained via a drain line
20
.
As is well-known, a swash plate
22
(also known as a wobble plate), connected to the pistons in the pump
12
, controls the displacement of the pistons; and thus, the flow rate of the pump
12
. More specifically, the position of the swash plate
22
determines the displacement of the pistons in the pump
12
. A servo piston
24
controls the movement of the swash plate
22
based on hydraulic pressure (i.e., fluid) supplied thereto.
As shown in
FIG. 1
, a pressure compensation valve
26
and a flow compensation valve
28
cooperatively regulate the supply of hydraulic pressure generated by the pump
12
to the servo piston
24
based on the hydraulic pressure in a load sense line
30
. The load sense line
30
, for instance, is connected to a directional control valve (not shown), which when placed in a state requiring hydraulic pressure supplies hydraulic pressure to the load sense line
30
. Both the pressure and flow compensation valves
26
and
28
are two-state valves.
When a load is placed on the pump
12
, the pressure compensation valve
26
and the flow compensation valve
28
are both placed in a first state as shown in FIG.
1
. In this first state, the hydraulic pressure generated by the pump
12
is not supplied to the servo piston
24
, and the servo piston
24
is connected with the drain line
20
to remove hydraulic pressure therefrom. As a result, the servo piston
24
retracts and the swash plate
22
moves to an inclined position, which increases the displacement of the pistons in the pump
12
and increases the flow rate of the pump
12
.
When no load is placed on the pump
12
, the pressure compensation valve
26
and the flow compensation valve
28
both attain a second state. While not shown as being in the second state,
FIG. 1
does illustrate the second states of the pressure and flow compensation valves
26
and
28
. In this second state, the hydraulic pressure generated by the pump
12
is supplied to the servo piston
24
. As a result, the servo piston
24
extends and moves the swash plate
22
to a more vertical position, which reduces the piston displacement in the pump
12
and decreases the flow rate of the piston pump
12
. When fully stroked, the servo piston
24
moves the swash plate
22
to a position which reduces the hydraulic pressure generated by the pump
12
to a stand-by pressure.
Whether the pressure and flow compensation valves
26
and
28
are placed in the first or second state depends on the hydraulic pressure in the load sense line
30
and the pressure line
16
. Namely, the hydraulic pressure generated by pump
12
is supplied to first control inputs
40
and
44
of the pressure compensation valve
26
and the flow compensation valve
28
, respectively, and the hydraulic pressure in the load sense line
30
is supplied to a second control input
42
of the pressure compensation valve
26
. First and second springs
45
and
46
bias the pressure and flow compensation valves
26
and
28
, respectively, to the right in FIG.
1
.
When no load is placed on the load sense line
30
, the hydraulic pressure generated by the pump
12
causes the pressure and flow compensation valves
26
and
28
to move to the left in
FIG. 1
(i.e., the second state). However, when a load is placed on the load sense line
30
, the hydraulic pressure applied to the second control input
42
of the pressure compensation valve
26
causes the pressure compensation valve
26
to move to the right (i.e., the first state). As a result, the hydraulic pressure applied to the first control input
44
of the flow compensation valve
28
is exhausted to the drain line
20
via the pressure compensation valve
26
, and the flow compensation valve
28
moves to the right (i.e., the first state).
The hydraulic pressure generated by the pump
12
and supplied via the pressure line
16
typically powers hydraulically operated machinery. As discussed above, the variable-displacement piston pumps
10
can be connected to a directional control valve. The directional control valve applies hydraulic pressure to the load sense line
30
depending on the need for hydraulic pressure from the variable-displacement piston pump
10
. Unfortunately, if the directional control valve sticks in an open state for operating machinery connected thereto when an operator wants the directional control valve closed, the variable-displacement piston pump
10
continues to supply hydraulic pressure.
As such, it is desirable, such as in emergency conditions, to immediately stop operation of that machinery. Often this is accomplished by removing the supply of hydraulic pressure necessary to operate the machinery.
FIG. 1
illustrates a conventional dump system for removing the supply of hydraulic pressure.
As shown in
FIG. 1
, a dump valve
32
is connected between the pressure line
16
and a reservoir
34
. In a closed state, the dump valve
32
prevents hydraulic pressure from flowing to the reservoir
34
from the pressure line
16
. However, in an open state, as shown in
FIG. 1
, the dump valve
32
permits hydraulic pressure to flow to the reservoir
34
, which substantially eliminates hydraulic pressure in the pressure line
16
. By placing the dump valve
32
in the open state, operation of machinery utilizing the hydraulic pressure in the pressure line
16
can be brought to a halt.
FIG. 2
schematically illustrates another well-known variable-displacement piston pump
110
such as Parker Hannifin Corporations Model No. PAVC65X29948. The piston pump
110
includes a pump
112
having a plurality of pistons (not shown). The pump
112
is connected between a suction line
114
and a pressure line
116
, and is driven by an engine
118
. Oil leaking in the pump
112
is drained via a drain line
120
.
As is well-known, a swash plate
122
, connected to the pistons in the pump
112
, controls the displacement of the pistons; and thus, the flow rate of the pump
112
. More specifically, the position of the swash plate
122
determines the displacement of the pistons in the pump
112
. A servo piston
124
controls the movement of the swash plate
122
based on hydraulic pressure (i.e., fluid) supplied thereto.
As shown in
FIG. 2
, a differential adjustment valve
126
regulates the supply of hydraulic pressure generated by the pump
112
to the servo piston
124
based on the hydraulic pressure in a load sense line
130
. The load sense line
130
, for instance, is connected to a directional control valve (not shown), which when placed in a state requiring hydraulic pressure supplies hydraulic pressure to the load sense line
130
.
The differential adjustment valve
126
is a two-state valve. When no load is placed on the pump
110
, the differential adjustment valve
126
is placed in a first state. While
FIG. 2
does not illustrate the differential adjustment valve
126
in the first state,
FIG. 2
does illustrate the first state. Specifically, because no hydraulic pressure is supplied to the control input
140
of the differential adjustment valve
126
by the load sense line
130
, a spring
142
biases the differential adjustment valve
126
down in
FIG. 2
(i.e., biases the differential adjustment valve
126
towards the first state). This connects the servo piston
124
to the drain line
120
, and hydraulic pressure at the servo piston
124
exhausts via the drain line
120
. As a result, the servo piston
124
retract
Backer Robert D.
Hall David Alan
Johnston Robert William
Campbell Thor
Grove U.S. L.L.C.
Walberg Teresa
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