Note: Descriptions are shown in the official language in which they were submitted.
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Description
3~L~
And Flow Reduction
Technical Field
This invention relates to a control system
which will allow upstaging of one of a plurality of
working circuits fed from a variable displacement pump
with concomitant flow reduction.
Background Art
A number of vehicles have a plurality of
work circuits each supplied in interrupted series or
in parallel from a single pressure compensated variable
displacement pump. It is known to have some of the
work circuits operable at higher pressures than other
of the work circuits. For example, the track drive of
an excavator may be required to operate at higher
pressure than the hydraulic motor which controls the
stick or the boom. To accomplish this, the prior art
has provided hydraulic control circuitry which will
supply a higher pressure, and at times a lower flow
rate as well, to a track drive working circuit and a
relatively lower pressure to a stick motor or a boom
motor. U.S. Patent 4,107,924, issued August 22, 197~
to J.E. Dezelin illustrates a hydraulic circuit for an
earthworkiny vehicle having such characteristics.
In certain circumstances, it is desirable for
an operator to be able to supply additional pressure
to one of the hydraulic motors, for example, to the
boom motor of an excavator when the boom is being
raised. In fact, in such a situation it is desirable
to be able to supply a higher pressure to the boom
motor than is normally supplied even to the track drive.
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While such a capability has been available with systems
which normally operate at only a single pressure level,
for example, as shown in U.S. Patent 4,123,907, issued
November 7, 1978 to D. L. Bianchetta, et al., it has
not been available in a hydraulic system which has work
circuits which already operate at two different
pressure levels. Further, such pressure control
circuitry as is known to the prior art for raising the
pressure and lowering the flow rate from a variable
displacement pump to a hydraulic circuit which has a
work circuit normally operating at only a single
pressure range, is not readily adaptable to more
complex systems which normally have a hydraulic circuit
supplying working circuits which operate at two
different pressure ranges.
It therefore follows that it would be
advantageous to be able to selectively provide an
upstage pressure in one of at least three work circuits
of a hydraulic system, wherein the work circuits of the
system normally operate in at least two different
pressure ranges. It would be further advantageous if
such could be accomplished along with a concomitant
reduction in pump displacement (output flow), so that
during upstaged pressure operation various components,
e.g., the boom, being moved would not be overstrained
and possibly damaged. A further advantage would be
obtained if all of the above could be accomplished
while protecting the relatively lower pressure
operating work circuits of the system from the
upstaged pressure. Still further, it would be
advantageous if the above set out operation were
accomplished with safety features built in so that
operator error could not lead to improper application
of excessive pressure to any of the work circuits.
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Disclosure of Invention
The present invention is directed to
overcoming one or more of the problems as set forth
above.
According to one aspect of the present
invention, there is provided a hydrualic system having
a variable displacement pump, a plurality of fluid work
circuits including first, second and third fluid work
circuits, means for delivering pressurized fluid from
said pump to selectively engage said first, second and
third work circuits and pressure relief means for
normally limiting each of (a) said first of said
circuits to normally operate up to a first pressure
level, (b) said second of said circuits to normally
operate up to a second pressure level which is less
than said first pressure level and (c) said third of
said circuits to normally operate up to a third
pressure level which is no greater than said first
pressure level, the improvement comprising means for
selectively operating said third circuit at an upstaged
pressure level which exceeds said first pressure level;
and means for preventing operation of said third
circuit at said upstaged pressure level in response to
engagement of either one of said first circuit and said
second circuit.
Brief Description of Drawing
The single figure of the drawing is a
diagrammatic view, partially in section, of a hydraulic
circuit which includes an improvement in accordance
with an embodiment of the present invention.
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Best Mode for Carrying Out the Invention
Adverting to the figure, there is shown
therein a hydraulic system 10 which is particularly
adapted for use with an earthworking vehicle such as an
excavator. The hydraulic system 10 includes a
conventional pressure compensated variable displacement
pump 12 for pumping hydraulic fluid from a sump via
pressurized fluid delivery means 16 to selectively
engage at least three work circuits 18. In the
embodiment illustrated, the three work circuits 18 are
a first work circuit 20, a second work circuit 22 and a
third work circuit 24.
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114126i5
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In a manner which will shortly become
apparent, the first work circuit 20 is normally
operable up to a first pressure, e.g., 28,000 kPa
(4,061 psi) and the second work circuit 22 is normally
operable up to a second pressure, e.g., 25,000 kPa
(3,626 psi), which is less than the first pressure.
The pump 12 conventionally internally adjusts
displacement dependent upon its output pressure. The
first work circuit 20 might typically be a track drive
circuit of an excavator the second circuit 22 might
be a stick control circuit and the third circuit 24
might be a boom control circuit.
The pressurized fluid delivery means 16
delivers the fluid in interrupted series flow to main
control valves 26c, 26b and 26a, respectively of work
circuits 24, 22 and 20. That is, the valve 26c
controls flow therethrough to the valve 26b, which in
turn controls flow therethrough to the valve 26a.
Hence, even if the valve 26c is partially shifted
downwardly or upwardly, flow still passes therethrough
to the valve 26b, and therethrough to the valve 26a.
In the embodiment illustrated, the main
control valves 26a, 26b and 26c are controlled
respectively by pilot control valves 28a, 28b and 28c
which receive pressurized fluid flow from a pilot pump
30. When flow from pilot pump 30 is being supplied
via pilot control valve 28a to first work circuit 20,
either line 32a or line 34a is pressurized. The
pressure of the hiqher pressure of lines 32a and 34a
is supplied by a resolver 36 to a pressure control line
38. This pressure is later utilized, in a manner which
will become apparent, for limiting the pressure
delivered by the pressurized fluid delivery means 16
to the work circuits 20, 22 and 24.
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When the pilot control valve 28b is operated,
either line 32b or line 34b is pressurized. A resolver
40 delivers the higher of these pressures to a conduit
42. The pressure in the conduit 42 andthe pressure in
the pressure control line 38 are both fed to a resolver
44. The higher of these pressures is delivered to an
upstaged pressure blocking conduit 46 and utilized in
a manner which will be explained below.
When the pilot control valve 28c is operated,
either line 32c or ]ine 34c is pressurized. Line 34c
is pressurized during boom lifting operation.
In normal (nonupstaged) operation, pressure
relief valve circuitry 48 limits the pressure supplied
by the pressurized fluid delivery means 16. Fluid
from the pump 12 passes into a main conduit 50 from
whence it flows to a first end 52 of a bore 54 in a
body 56. A main dump spool 58 sits in reciprocal
relationship within the bore 54. A spring 60 acts
between a second end 62 of the bore 54 and the spool
58. Thus, the spring 60 serves as means for biasing
a first end 64 of the spool 58 into blocking relation
with the first end 52 of the bore 54. A restricted
orifice 66 communicates the first end 64 of the spool
58 with a second end 68 thereof. As pressure builds
up in the main conduit 50, pressurized fluid passes
via the restricted orifice 66 through the dump spool
58. Thereby, a similar pressure builds up at the
second end 62 of the bore 54.
A first relief valve 70, e.g., a poppet
relief valve, is provided which is set to open at the
first pressure (e.g., 28,000 kPa). The first relief
valve 70 communicates via a conduit 72 with the second
end 62 of the bore 54. Thus, the first relief valve
70 is exposed to the pressure in the main conduit 50.
The first relief valve 70 thereby serves as a first
pilot stage of the main dump spool 58.
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A second relief valve 74, e.g., a poppet
relief valve, is set to open at the second pressure
(e.g., 25,000 kPa). The second relief valve 74
communicates with the second end 62 of the bore 54
via a conduit 76 and a continuation conduit 78. The
second relief valve 74 thereby serves as a second
pilot stage of the main relief dump spool 58.
An upstaged pressure (e.g., 31,000 kPa or
4,496 psi) opening relief valve 80, e.g., a poppet
relief valve, communicates with the second end 62 of
the bore 54 via the conduit 76 and a continuation
conduit 82. The upstaged pressure opening relief
valve 80 thereby serves as an upstaged pilot stage
of the main relief dump spool (58).
When either the first relief valve 70, the
second relief valve 74, or the upstaged pressure
opening relief valve 80 is opened by an appropriate
pressure being exerted thereupon, a pressure
differential is created across the dump spool 58
which lifts it upwardly in the drawing against the
force of the spring 60. A plurality of holes 84
through the side of the dump spool 58 adjacent the
first end 64 thereof and a conduit 86 then serve as
means for communicating the first end 52 of the
bore 54 with the sump 14 responsive to upward
movement of dump spool 58.
Means 90 are provided for blocking off
communication of the second end 62 of the bore 54 with
the second check valve 74 responsive to engagement of
the first circuit 20. When the first circuit 20 is
engaged, pressure from the pressure control line 38 is
delivered via a resolver 92 and a pressure delivery
conduit 94 to a first end 96 of a blocking spool 98
which fits in a bore 100. A spring 102 acts against
a second end 104 of the blocking spool 98 to force it
upwardly into the position shown in the drawing. When
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pressure (pilot pressure) is applied in the pressure
delivery conduit 94, this forces the blocking spool 98
downwardly thus blocking off the continuation conduit
78. When the continuation conduit 78 is blocked off,
this prevents pressure from the second end 62 of the
bore 54 from being applied to the second relief valve
74. Thus, the dump spool 58 does not dump pressure
from the main conduit 50 at the lower pressure, i.e.,
at the aforementioned second pressure (e.g. 25000 kPa).
Instead, when the pressure in the main conduit 50
reaches the first pressure (e.g., 28,000 kPa), the
first relief valve 70 opens which causes the dump
spool 58 to limit the pressure delivered by the pump
12 to the first pressure.
Means 106 are provided for blocking flow
from the second end 62 of the bore 54 past both the
first relief valve 70 and the second relief valve 74
responsive to engagement of the third circuit 24 at
the upstaged pressure. Referring to the drawing, to
place the third circuit 24 in the upstage pressure
mode of operation, the pilot control valve 28c is
shifted upwardly which in turn shifts the main oontrol
valve 26c upwardly. Further, a solenoid actuated
valve 108 is shifted rightwardly from the position
shown, on operator activation of a switch. The
pressure in line 34c is delivered via a branch conduit
110 against a first side 112 of a two position valve
114. If either the first circuit 20 or the second
circuit 22 is operating, pressure in the upstage
pressure blocking conduit 46 opposes the pressure in
the branch conduit 110 and the two position valve 114
remains in the position shown, due to the biasing of
a spring 116 and the pressure in the blocking conduit
46 which acts against a second side 118 thereof.
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So long as neither the first circuit 20 nor
the second circuit 22 is operating, there is no
pressure in the upstage pressure blocking conduit 46.
In this situation, the pressure in the branch conduit
110 forces the two position valve 114 leftwardly.
This delivers pilot pressure via a conduit 120 to the
solonoid actuated valve 108. With the solenoid
actuated valve 108 in its actuated position, i.e.,
shifted rightwardly, flow continues from the conduit
120 via a conduit 122 to the resolver 92. Since there
is now no pressure in the pressure control line 38
(as the first circuit 20 is not operating), the
pressure from the conduit 122 is supplied via the
resolver 92 to the pressure delivery conduit 94. In
accordance with the previously described mode of
operation, this forces the blocking spool 98
downwardly and blocks off the second relie~valve 74.
Pressure in the conduit 122 also acts via a branch
conduit 124 against an auxiliary blocking valve 126
and forces the auxiliary bloeking valve 126
leftwardly in the drawing. This blocks off any
possibility of flow past the first relief valve 70.
Thus, the first relief valve 70 is likewise
incapacitated. Flow can still, however, oceur from
the second end 62 of the bore 54 to the upstage
pressure opening relief valve 80. And, when pressure
reaehes its upstage value (e.g., 31,000 kPa), the
upstage relief valve 80 opens, whereby the dump
spool 58 opens, thereby regulating pressure in the
main conduit 50 to be the upstage pressure.
Pressure in the conduit 122 is also supplied
via a displacement control conduit 128 to a
conventional pump displacement control 130. Responsive
to the pressure in the displacement control conduit
128, the variable displacement pump 12 shifts to a
lower displacement and thereby supplies pressurized
b.~
g
fluid at a lower flow rate. This assures that when
upstaged pressure operation is taking place in the
third circuit 24, it is taking place at a reIatively
slow rate so that the various structural components
being moved by third circuit 24 are not strained
beyond their limits.
It will be noted that a two position valve
132 is positioned in the pressure control line 38.
The two position valve 132 serves to assure that when
the second circuit 22 is engaged, the pressure
delivered by the pump 12 to the main conduit 50 is
limited to the second pressure. If, for example,
the first circuit 20 is engagedl the main line 50
will be limited to the first pressure (e.g., 28,000
kPa) as has been previously explained. If the pilot
control valve 28b is now moved to engage the second
circuit 22, pressure from the conduit 42 is applied
via a branch conduit 134 against the two position
valve 132, in opposition to the biasing thereof by
a spring 136. The pressure in the branch conduit
134 overcomes the force of the spring 136 and
forces the two position valve 132 upwardly. This
blocks off pressuxe from the pressure control line
38 and stops it from reaching the pressure delivery
conduit 94. As a result, the blocking spool 98
moves upwardly and pressure begins to be delivered
again to the continuation conduit 78 and the second
check valve 74. Since the second check valve 74 is
set at the second pressure te.g., 25,000 kPa), which
is lower than the first pressure, the pressure at the
mainline 50 is limited to the setting of the second
relief valve 74. In this manner, it is assured
that the second circuit 22 can not be exposed to a
pressure over that for which it is normally designed.
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It follows that the solenoid actuated valve
108, in combination with the two position valve 114
and various conduits as previously described, serves
as means for selectively operating the third circuit
24 at an upstaged pressure which exceeds the first
pressure. Further, the displacement control conduit
128 then serves as means for reducing the displacement
of the pump 12, in response to the third circuit 24
being operated at the upstaged pressure.
It also follows that the two position valve
114 serves as means for preventing operation of the
third circuit 24 at the upstaged pressure when either
the first circuit 20 or the second circuit 22 is
engaged. That is, whenever there is pressure in the
upstaged pressure blocking conduit 46, which
corresponds to either the first circuit 20 or the
second circuit 22 beinq enqaqed, the two position
valve 114 is blocked, thus preventing upstaged
operation of the third circuit 24.
Furthermore, the third circuit 24 is
normally operated only up to a third pressure, which
is generally no greater than the aforementioned
first pressure and usually no greater than the
aforementioned second pressure. That is, ihe pilot
control valve 28c motivates the main control valve
26c, which receives pressurized fluid at a pressure
determined by either first relief valve 70 or second
relief valve 74 in the absence of shifting of
solenoid valve 108 rightwardly and shifting of main
control valve 26c upwardly, to place third circuit
24 in the upstaged mode of operation. If it is
desired to limit operation of the third circuit 24
to the second pressure, this can be accomplished
by duplicating two position valve 132 or providing
an appropriate resolver from line 32c and from
conduit 42 to branch conduit 134.
It should be noted that when the first
circuit 20 is engaged, the resulting pressure in the
upstaged pressure blocking conduit 46 assures that
the pressure delivered by the pump 12 to the main
conduit 50 is reduced to the first pressure. It
should further be noted that when the second circuit
22 is engaged, this overrides the pressure reducing
due to engagement of the first circuit 20 and assures
that the pressure must be reduced further to the
second pressure.
It should also be noted that when either
the first circuit 20 or the second circuit 22 is
engaged, the pump displacement reduction is
terminated since there is no signal in the
displacement control conduit 128, due to the
blockage of the two position valve 114.
Industrial Applicability
The aforementioned and described improved
hydraulic system is particularly useful with an
excavator and wherein the first circuit is a track
drive circuit, the second circuit is a stick
control circuit and the third circuit is a boom
control circuit. Further, in such an excavator
the upstaged operation of the boom control circuit
is normally selectable only on boom raising
operation.
