Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02571609 2006-12-15
LOAD SENSING HYDRAULIC SYSTEM
Field of the Invention
The invention relates generally to a versatile load sensing hydraulic
system capable of being adapted to a variety of possible configurations for
vehicle mounted implements such as plow/spreader type vehicles or the like.
Background of the Invention
The operation of vehicles such as those used for plowing or scraping snow
and/or ice from roads, airport runways and similar surfaces and for spreading
traction enhancing materials such as sand and/or salt requires the
installation of
a hydraulic system that supplies power to operate the various components of
spreader and plow equipment. The usual installation includes a single gear
pump that pushes hydraulic fluid through an open center valve with a power
beyond connection, which is used to operate the plow functions. The power
beyond is connected to the pressure pressure of the spreader valve, from where
it returns to a hydraulic fluid tank or reservoir, or is partially routed to
the
spreader's hydraulic motors. The principal problem of this circuit is the
stoppage
of the spreader when any plow function is operated. Various solutions have
been
used to remedy this problem.
Tandem pumps may be used in two completely separate hydraulic circuits.
One pump supplies the plow hydraulic functions, the other one supplies the
spreader only. Simultaneous operation is rendered possible for both the plow
and the spreader, but several major inconveniences remain. The system is more
expensive, more complicated, requires a larger hydraulic fluid reservoir and
consumes more energy.
Another solution is the use of a variable displacement piston pump that is
usually controlled by sensing the load. The load sensing pump works in
conjunction with closed center valves that share a common pressure supply,
which is the pump. This constitutes a normal load sensing circuit, with all
its usual
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benefits. The main problem associated with this solution is the very high cost
of
load sensing valves and pumps.
Therefore, there is a need for a cost effective load sensing hydraulic
system capable of providing hydraulic fluid to operate the various components
of
plow/spreader type equipment.
Summary of Invention
This invention is directed to a hydraulic system for operating vehicle
mounted hydraulic equipment such as that mounted on plow/spreader or sander
type equipment. Other hydraulically operated accessories may likewise be
operated from this system, such as sweepers, wetting systems and any kind of
other equipment requiring hydraulic flow. In one aspect, the hydraulic system
comprises a reservoir for hydraulic fluid, a flow and pressure compensated
variable displacement pump, referred to commonly as a load sensing pump, for
pumping hydraulic fluid from the reservoir and a plow on/off valve apparatus
having a pressure port coupled to the pump for receiving hydraulic fluid under
pressure. The plow valve apparatus comprises a manifold having a fluid channel
with a pressure port and a number of return ports. Further the plow valve
apparatus further includes one or more on/off valves coupled to the manifold
return ports, each valve being adapted to control fluid flow therein to
operate a
respective component of the plow equipment, and a stroke valve coupled to a
manifold return port, the stroke valve being adapted to operate in conjunction
with one or more of the on/off valves for providing a load sensing pressure
signal
to the pump.
Further, the hydraulic system in accordance with one embodiment of the
present invention may comprise a load sensing spreader valve having a pressure
port coupled to the pump for receiving hydraulic fluid under pressure. The
spreader valve comprises a device for controlling fluid flow through the
spreader
valve for operating the spreader and a port for providing a load sensing
pressure
signal. The hydraulic system further includes a shuttle valve arrangement for
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receiving the load sensing pressure signal from the spreader valve and the
load
sensing pressure signal from the plow on/off valve apparatus, and for applying
a
resultant load sensing pressure signal to the pump.
In addition, the hydraulic system may comprise a plow load sensing valve
apparatus having a pressure port coupled to the pump for receiving hydraulic
fluid under pressure. The plow load sensing valve apparatus comprises one or
more load sensing valves adapted to control fluid flow therein to operate
components of the plow equipment, and a port for providing a load sensing
pressure signal from the plow load sensing valves.
One aspect of the present invention provides for a hydraulic system for
operating hydraulic functions of plow/spreader type equipment comprising:
a) a reservoir means for hydraulic fluid;
b) a load sensitive variable displacement pump means for pumping
hydraulic fluid from the reservoir; and
c) a plow on/off valve means having a pressure port coupled to the
pump means for receiving hydraulic fluid under pressure, the plow valve
means including:
i) a manifold means having a fluid channel coupled to the plow
valve means pressure port and further having a number of return
ports;
ii) one or more on/off valve means coupled to the manifold
means return ports, each valve means being adapted to control
fluid flow therein to operate a respective component of the plow
equipment; and
iii) a stroke valve means coupled to a manifold means return
port, the stroke valve means being adapted to operate in
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conjunction with one or more of the on/off valve means for providing
a load sensing pressure signal to the pump means.
Another aspect of the present invention provides for a hydraulic system for
controlling hydraulic functions comprising:
a) a reservoir means for hydraulic fluid;
b) a load sensing variable displacement pump means for pumping
hydraulic fluid from the reservoir;
c) a unitised valve block having a pressure port coupled to the pump
means, the unitised valve block comprising at least one hydraulic function
valve
means for controlling at least one hydraulic function; and
d) a stroke valve means for providing a load sensing pressure signal
to the pump means, the stroke valve being operated based on the operation of
each function valve means.
Other aspects and advantages of the invention, as well as the structure
and operation of various embodiments of the invention, will become apparent to
those ordinarily skilled in the art upon review of the following description
of the
invention in conjunction with the accompanying drawings.
Brief Description of the Drawings
Figure 1 shows a schematic drawing illustrating one embodiment of the present
invention;
Figure 2 shows a hydraulic schematic drawing illustration another embodiment
of
the present invention;
Figure 3 shows a hydraulic schematic drawing illustration another embodiment
of
the present invention;
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Figure 4 shows a hydraulic schematic drawing illustration another embodiment
of
the present invention; and
Figure 5 shows a hydraulic schematic drawing illustration another embodiment
of
the present invention.
Detailed Description
Figure 1 shows a schematic according to one illustrative embodiment of
the current invention. A load sensing variable displacement pump 11, pumps
hydraulic fluid from a reservoir 14 to a stroke valve 45 and a hydraulic
function
valve 5. Port T of the stroke valve 45 is connected to the reservoir, port P
of the
stroke valve 45 is connected to either the function valve input or output
port, and
the working port of the stroke valve 45 is connected to the load sensing input
port
of the pump. The stroke valve 45 may be a 3 way 2 position valve. The function
valve 5 controls the flow of hydraulic fluid to and from a hydraulic function
3, and
may be any suitable type of closed center valve. The hydraulic function 3 may
be
any suitable function controlled or operated by the flow of hydraulic fluid
such as
a hydraulic piston, a hydraulic motor, a hydraulic driven compressor, etc. A
interconnector 7, brings the function valve 5 and the stroke valve 45 into
communication, such that when the function valve 5 is operated the stroke
valve
45 is also operated. If the stroke valve 45 is a solenoid on/off valve the
interconnector 7 may be an electrical signal provided by the function valve 5.
If
the function valve 5 is controlled electrically, the signal to the
interconnector 7
may be the same as the electrical signal to the function valve 5. If the
function
valve 5 is not controlled electrically, the controller of the function valve 5
may be
readily adapted to provide an electrical signal to the interconnector 7
whenever
the function valve is operated. If the stroke valve is of a type other then a
solenoid on/off valve, the interconnector 7 may be suitably adapted to operate
the stroke valve 45 when required. This may include a mechanical linkage,
pilot
pressure signals, pneumatic control, etc.
CA 02571609 2006-12-15
When the function valve 5 is operated to allow hydraulic fluid to flow
through the valve to the hydraulic function 3, the stroke valve 45 is also
operated
to connect the P port of the stroke valve 45 to the working port of the stroke
valve
45. As a result the pump 11 receives a load sensing signal from the stroke
valve
45 and controls the flow of hydraulic fluid to the function valve 5.
Although described as controlling only a single hydraulic function 3, the
function valve 5 may comprise multiple function valves controlling different
hydraulic functions as set out below.
Through the use of the stroke valve 45 in the configuration as described,
non-load sensing valves may be used in conjunction with a load sensing pump.
The hydraulic system as described may be used advantageously in
numerous applications. One application that benefits from the described
hydraulic system is the hydraulic system of a vehicle, which has a
substantially
continuous hydraulic function as well as on-demand hydraulic functions, such
as
a vehicle used for plowing and sanding roads. The sander of the vehicle runs
substantially continuously, as such an economic benefit may be achieved
through the use of a load sensing variable displacement pump. By using the
hydraulic system of the current invention, the same pump may be used to
control
other hydraulic functions of the vehicle, such as raising and lowering of the
plow.
This is achieved using non-load sensing closed center valves.
Figure 2 shows a hydraulic schematic of a first illustrative embodiment of
the current invention. The embodiment is directed to a hydraulic system for
operating plow/spreader type equipment. The plow/spreader embodiment has a
valve apparatus or block for controlling the spreader equipment. The spreader
valve apparatus comprises load sensing valves, and the spreader valve
apparatus provides a load sensing signal to control the pump. A load sensing
apparatus, for example a load sensing valve stack, comprises load sensing
valves to control various functions. The load sensing apparatus also provides
a
load sensing pressure signal to control the pump. An on/off valve apparatus,
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such as a manifold valve stack comprises non-load sensing on-off valves to
control various plow functions. The on/off valve apparatus comprises a stroke
valve for providing a load sensing pressure signal to control the pump.
A shuttle valve arrangement is connected to the load sensing pressure
signals and provides the highest pressure signal to the load sensing pressure
port of the load sensing pump to control the fluid flow of the pump.
The plow/spreader hydraulic system in accordance with the present
embodiment is illustrated in figure 2. A pumping unit 10 includes a load
sensing
variable displacement pump 11 having a load sensing pressure port 12. The
pump 11, which is driven either directly off of a motor 13, such as a truck
engine
or off of an automatic transmission via a power take-off, pumps hydraulic
fluid or
oil from a reservoir 14 out of a port P1. The pressure detected at the sensing
pressure port 12 controls the fluid flow from the pump 11 in order to maintain
the
desired pressure differential. Pumps of this type are readily available in the
market, one example of such a pump is manufactured by Parker as model
number PAVC65RH.
The hydraulic circuit includes fluid lines that connect the pump return
pressure port P1 to pressure ports P2, P3 and P4 of three groups of valves, a
load sensing valve stack 20, a load sensing spreader valve 30 and a manifold
valve stack 40. The circuit further includes fluid lines that connect the
return
ports of the load sensing valve stack 20 (T2) and the manifold valve stack 40
(T4)
to reservoir 14. Spreader valve 30 must have a drain port T3B if the valve 30
incorporates a bleed-off line in order to prevent trapped oil in the LS signal
line
from maintaining pressure when the valve is off (de-energised). This ensures
that
stand-by pressure is as low as possible when the spreader is not used.
The load sensing valve stack 20 is used to operate the plow equipment
that requires proportional control such as for example a wing front post lift,
a side
wing lift, the truck box hoist. What functions are controlled proportionally
and
which ones are on-off may be determined based on the user's preference and/or
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budget and/or requirement. Typical functions found on plow sander trucks are:
wing front post lift, wing rear lift, reversible front plow, variable pitch
front plow,
front plow lift, banking tower, under body scraper lift, under body left-right
orientation, quick hitch lock-unlock, roll-on-roll-off winch, roll-on-roll-off
locking
pins, detachable harness tilt, dump body hoist, inside lift for side dump four
season bodies, and the like. Usually not all the above listed functions are
present
on given equipment. Any function that is not controlled proportionally will be
controlled on/off, which is much less expensive. The stack 20 includes a
number
of load sensing valve units 21A, 2113, 21C, three being shown, one for each
component of the equipment to be operated proportionally. These valves may be
controlled electrically, mechanically or by any other manner. The valve units
21A,
21 B, 21 C include shuttle valves 22A, 22B, 22C which are connected in series
to
provide the highest pressure detected at the valves 21 A, 2113, 21C to the
stack
20 LS4 port. The LS4 port is connected to a shuttle valve 50. Valve stack 20
further includes a pressure section 23 having a relief valve 24. The pump
feeds
fluid to the valve stack 20 through pressure port P2 and the fluid is returned
to
the reservoir 14 from return port T2.
For certain applications where valves of different capacity are required, the
valve stack 20 may be divided into different sections, wherein the valves in
each
respective section are of the same capacity. Note that for valves of a given
model
there may exist spools of different maximum flows that allow precise speed
control for various functions. In certain applications, it may be determined
that
few if any components of a selected piece of plow/spreader equipment actually
require proportional control. Since the valve stack 20 only includes load
sensing
proportional valves, the valve stack 20 would not be required if the plow
equipment does not need proportional control. An example of the valve 21A,
21 B, 21 C that may be used with the present invention is the Danfoss PVG 32
valve or the Walvoil DLS8 valve.
The load sensing spreader valve 30 is shown as having a first and a
second branch with metering devices 31 and 32. Metering devices 31 and 32
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may be proportionally controlled valves. Metering device 31 controls fluid
flow to
a motor 34 for a material transporting device such as a conveyor, an auger or
a
combination of both, through return port P51, while metering device 32
controls
fluid flow to a spinner motor through return port P32. Valve 30 further
includes a
shuttle valve 33 such that the highest pressure at the outlets of the metering
devices 31 and 32 is transferred through a load sensing port LS3 to the
shuttle
valve 50, which transfers the highest pressure signal it detects to a further
shuttle
valve 51. Though spreader valve 30 has been shown as having two branches, it
may have further branches. For instance, a third branch may be used to control
a liquid dispenser.
Examples of spreader valves 30 that do not have a bleed-off by-pass line
are the Vickers ICSV3000, and the Danfoss 2FFC12 or FFLC12 valves. Valves
without internal bleed-off require the addition of an external drain in order
to
prevent any residual pressure in the LS signal line when the sander valve is
turned off. Examples of spreader valves with a by-pass line incorporated in
the
design of the spreader valve itself are the 800 VALACE-2LS or in the 800
VALACE-3LS.
The manifold valve stack 40 operates the plow equipment that requires
on/off control. The manifold 40 includes a mounting block 41 having an
pressure
port P4 and a return port T4 at each end of the mounting block 41 that are
connected to a pair of separate channels 42A and 42B are located within the
mounting block 41 along its length. As only one pressure port P4 and return
port
T4 are connected, the other one must be plugged. Openings to the surface of
the mounting block from the channels 42A and 42B form a series of pressure and
return ports P4A and T4B. The required number of ports P4A and T4B will
depend on the number of components in the plow equipment to be operated by
the manifold valve stack 40 in any particular application, and may number up
to
12 per manifold. Closed center valves are mounted onto the mounting block 41
and connect to their respective ports P4A and T4B. For most components in the
plow equipment, 4 way 3 position valves 43A, 43B, 43C may be used, however
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for some functions 4 way 2 position valves 44 will suffice. In this particular
embodiment, the components operated by the manifold valve stack 40 may be
the front plow lift, the front plow left-right orientation, the detachable
harness
using 4 way 3 position valves 43A, 43B, 43C and the quick hitch lock using a 4
way 2 position valve 44.
It is to be noted that none of the valves 43A, 43B, 43C or 44, which may
be of the Denison A4D01 model, or Hystar DSG01 model, are load sensing
valves. Instead, a stroke valve 45, which is a 4 way 2 position closed centre
valve, is also located on the mounting block 41, and is controlled so as to
receive
a signal to open at the same time as any one of the other valves 43A, 43B, 43C
or 44. When valve 45 is operated, it sends a pressure signal to the shuttle
valve
51, which also receives a pressure signal from shuttle valve 50 to provide a
pressure signal to the pump 11 through the load sensing pressure port 12. In
this
way, the pump receives a pressure signal increase whenever any one or more of
the components of the plow/spreader equipment are operated.
The valve size CETOP03 is suggested for this application as shown in the
sample models given, due to its low cost, adequate flow capacity, ready
availability and the possibility to meet special requirements by adding
sandwiches with various auxiliary valves such as counterbalance or reliefs.
Other
valve sizes may be used using the same concept of the stroke valve.
Though the system has been described as having one manifold 41, further
valve manifolds may be incorporated into the system, however only one of the
manifolds 41 needs to have a stroke valve 45.
All of the valves 43A, 43B, 43C, 44 and 45 are of the "closed center"
configuration, which means that in their neutral position there is no oil flow
going
through the valve. In its neutral position, the stroke valve 45 fluidly
connects P4A
to working port B, and working port A to T4B. In order to block any flow with
the
stroke valve 45 in neutral, a plug 46 is installed in the B port.
CA 02571609 2006-12-15
In operation, through its load sensing pressure port 12, pump 11 senses
pressure changes whenever spreader valve 30 and/or a valve 21 A, 2113, 21C in
the valve stack 20 is operated under the control of the vehicle operator who
applies a signal to the respective valve either electrically, mechanically or
by
some other manner determined by the system. In the manifold valve stack 40,
when a signal is sent to any one of the operating valves 43A, 43B, 43C, 44 of
the
manifold 41, a signal is simultaneously sent to the stroke valve 45; this
signal
causes the spool in the valve 45 to shift, connecting the P4A port to A. With
the A
port of valve 45 connected to the shuttle valve 51, and the load sensing lines
of
the plow valve stack 20 and the spreader valves 30 connected to the shuttle
valve 50, which in turn is also connected to shuttle valve 51, the highest
load
sensing pressure of all of the valves is connected to the pump load sensing
pressure port 12. This will cause the pump 11 to stroke until it reaches its
pressure compensator setting, which is the maximum system pressure.
The stroke valve 45 is energized every time one of the other manifold
valves 43A, 43B, 43C, 44 is energized to operate a plow function. This can be
accomplished by using a solenoid to control the valve. The controls of the
manifold valves 43A, 43B, 43C and 44 may be modified to send a signal to the
solenoid whenever they are operated. Every time a work port is opened to
operate a plow equipment component, such as the wing banking cylinder, the
stroke valve 45 causes the pump pressure to increase to the pump compensator
setting. If, for example, 500 psi is required to extend the front plow lift
cylinder
and the pump 11 compensator is adjusted to, for example 2000 psi, the front
plow lift cylinder speed can be very accurately adjusted by choosing an
orifice
size. The plow weight requires a certain pressure in order to raise it, for
example
500 psi. Knowing that there is 2000 psi on the valve side of the orifice and
that
500 psi is required to get the cylinder to move, there exists a pressure drop
of
1500 psi every time the system is operated. A constant pressure drop of 1500
psi
across a given orifice size results in a constant flow rate, which when
properly
selected gives good speed control. It should be noted that the figures given
in
this example were for the front plow raise function. When the plow is powered
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down, there is speed control for the same reason: The weight adds to the
hydraulic pressure, but as the rod end of the cylinder is pushed, induced
pressure on the piston side is lower than system pressure, but with the help
of
the plow weight almost identical speed in both directions is obtained.
The spreader valve 30 and the plow valve stack 20 can be affected by the
action of the stroke valve 46 if they are not pressure compensated. If the
valves
are pressure compensated, the pressure compensator eliminates the various
pressure differentials and maintains constant flow. Non-compensated valves
will
show an increase in oil flow. As the plow valve is controlled by the operator,
the
operator may adjust the functions speed to his liking. With a closed loop
spreader
control system, the electronics will compensate for any valve variations.
The versatility of the load sensing hydraulic system in accordance with the
present invention is clearly evident. As many equipment components as desired
may be added to the vehicle and operated by adding valves to the hydraulic
system. As long as the pump 11 has enough flow capacity to supply all actuated
components with oil to maintain stand-by pressure all components will work
simultaneously at their predetermined speed. If oil flow drops below demand,
the
lowest pressure requirements will be met first. In practical use the operator
will
likely never be able to use more than a maximum of three functions
simultaneously due to the layout of the controls and the size of the
operator's
hand. Manifold valve stacks 41 may be added as required by simply plugging P
and T ports into Tees. Because the stroke valve 45 is activated every time any
other functional on/off valve is activated, the system permits the possibility
of
adding an unlimited number of non-load sensing valves to the system.
Figure 3 illustrates a hydraulic schematic according to another
embodiment of the present invention. The embodiment provides for the ability
to
utilize both high and low-flow non-load sensing valve blocks with a load
sensing
variable displacement pump.
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The hydraulic system has a load sensitive variable displacement pump 11,
a reservoir 14, a load sensitive valve block 301, a unitised valve block 310,
a
remote manifold 330 and a shuttle valve 51.
The load sensitive valve block 301 is connected to the pump 11 and the
reservoir 14 and includes a load sensitive valve 303 to control a hydraulic
function 305. The load sensitive block 301 provides a load signal 302 as is
well
known in the art. The load sensitive valve block 301 is also connected to the
reservoir 14 through a bleed off orifice for bleeding off hydraulic fluid
trapped in
the load signal channel when the load sensitive valve is not operating. The
load
sensitive valve block 301 may comprise more than one load sensitive valve 303,
however, usually comprises at least two load sensitive valves. Each load
sensitive valve 303 controls a hydraulic function 305.
The unitised valve block 310 includes an adapter block 312 connected to a
first valve block and a second valve block. In the present embodiment the
first
valve block is a high-flow valve block 314 and the second valve block is a low-
flow valve block 316. The first and second valve blocks need not be different.
For example two low flow valve blocks may be connected to the adapter block.
Furthermore only one valve block may be connected to the adapter block.
The stroke valve 45 is located within the adapter block 312. The function
and operation of the stroke valve 45 is the same as previously described. When
a function valve 5a, 5b of either the high or low-flow valve block 314, 316 is
operated the stroke valve 45 is operated. When in operation the stroke valve
45
connects an input line of the adapter block, which is connected to the P port
of
the stroke valve, to a load signal port 318 of the adapter block 312, which is
connected to the working port of the stroke valve 45. The load signal port 318
provides a load signal for controlling the load sensitive pump 11. When not in
operation, the stroke valve 45 connects the load signal port 318 to the
reservoir
14 through the T port of the stroke valve. A bleed off orifice is not required
since
the stroke valve T port is separated from the pressure port. This releases any
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trapped hydraulic fluid in the load signal line when the stroke valve is not
operated.
In the present embodiment the adapter block 312 has a pressure port 317,
a return port 319 and a load signal port 318. The pressure port 317 is
connected
to the output from the pump 11. The return port 319 is connected to the
reservoir
14. The load signal port 318 is connected to the load signal port 12 of the
pump
11. The load signal port 318 may be connected directly to the pump 11 if there
is
only one load signal line in the hydraulic system. If there is more than one
load
signal line, such as when a load sensitive valve block 301 is incorporated, a
shuttle valve 51 is used to connect the load signal line with the highest
pressure
to the load signal port 12 of the pump as set out below.
In the current embodiment comprising both the unitised valve block 310
and the load sensitive valve block 301, a shuttle valve 51 must be used to
connect the load signal line with the highest pressure to the load signal port
12 of
the pump 11. One input of the shuttle valve 51 is connected to the load signal
port 304 of the load sensitive valve block 301 and the other input of the
shuttle
valve 51 is connected to the load signal port 318 of the unitised valve block
310.
The output of the shuttle valve 51 is connected to the load signal port 12 of
the
pump 11. Multiple shuttle valves may be required depending on the number of
pressure signals present in the hydraulic system.
The hydraulic system may also include one or more remote manifolds 330
for operating other hydraulic functions 332. The remote manifold 330 may
contain any number of remote function valves 334 for controlling hydraulic
functions 332. The remote manifold 330 does not require a separate stroke
valve. When operated, the remote function valves 334 provide a signal (not
shown) to the stroke valve 45 of the adapter block 312 so that the stroke
valve 45
is operated as well.
The adapter block 312 has pressure channels 350 formed therein to
connect the input port 317 of the adapter block 312 to the P ports of the
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connected high- and low-flow valve blocks 352, 353 respectively. Separate
outlet
channels 355 are formed in the adapter block 312 connecting the T ports of the
connected high and low-flow valve blocks 357, 358 respectively to the return
port
319 of the adapter block 312.
The high-flow valve block 314 may be comprise one or more SD16
sandwich valves manufactured by Walvoil. The outlet cover of the SD16 valve
block is replaced with the adapter block 312. The adapter block 312 is
manufactured such that the pressure 350 and outlet 355 channels of the adapter
block 312 are in fluid communication with the P and T ports of the SD16 when
it
is secured to the adapter block 312.
The low-flow valve block 316 may be one or more SD100 sandwich valves
manufactured by Walvoil. The outlet cover of the SD100 is also replaced with
the
adapter block 312. The adapter block 312 is manufactured such that the
pressure 350 and outlet 355 channels of the adapter block 312 are in fluid
communication with the P and T ports of the SD100 as well when it is secured
to
the adapter block.
Replacing the outlet covers of the SD16 and SD100 valve blocks has the
advantage of maintaining the original inlet covers. The pressure cover of the
SD16 has the option of providing a full flow main relief valve that may be
used in
conjunction with the current hydraulic system. The pressure cover of the SD100
can be provided with a pressure reducing cover to provide pilot pressure
necessary when using electro-proportional controls. By retaining the inlet
sections of the SD16 and SD100, a number of different types of function
control
devices may be included in the valve block. These may include: manual,
pneumatic proportional, electric on-off and electro-proportional devices.
Although the outlet covers of both the SD16 and the SD100 have been
described as being replaced with the adapter block, one skilled in the art
will
realize that the inlet covers of either the SD16 or the SD100 could be
replaced
with the adapter block 312 instead of the outlet cover.
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The stroke valve 45 has been described as a 3 way 2 position solenoid
valve when installed in an adapter block. It is to be understood that other
types
of controls are possible, such as a mechanical linkage, pilot pressure
control,
pneumatic control, etc., for operating the stroke valve. Furthermore, the 3
way
valve may be replaced with a 4 way valve that has a work port plugged. The
function valves 303, 5a, 5b,334 of the various blocks 301, 310, 330 are closed
center valves.
Although the pump 11 is described as being connected to the adapter
block 312 it may be connected to the pressure cover of the SD16 as shown in
Figure 4, which illustrates an alternate embodiment provided by the present
invention. This configuration may be desirable depending on the plumbing and
space limitations for a particular installation.
Figure 5 shows another alternate embodiment of the present invention
wherein the adapter block 312b contains the load sensitive function valve 303b
to
control the hydraulic function 305. Those skilled in the art will realize that
more
than one load sensitive function valve 303b may be included in the adapter
block
312b. An adapter block 312b containing a load sensitive function valve 303b
may reduce the plumbing requirements necessary for a particular installation.
If
the load sensitive valves 303b are incorporated into the adapter block 312b
shuttle valve may also be included in the adapter block 312b to provide the
highest pressure signal between the stroke valve 45 and the load sensitive
valves 303b to the load signal port 12 of the pump 11. At least one shuttle
valve
must be used in order to make sure the load sensing pump receives a load
sensing pressure signal. If the adapter block 312b is not provided with a
shuttle
valve, an additional load signal return port 318b may be provided for the
pressure
signal from the load sensing valves. A shuttle valve 51 b may then be provided
remotely from the adapter block for providing the highest pressure signal to
the
load sensing pressure of the pump.
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The hydraulic system as described above may advantageously be used to
control the flow of hydraulic fluid to other hydraulic functions, such as for
example
a street sweeper. Depending on the hydraulic flow requirements there are
various possibilities: If the sweeper broom requires flow within the flow
capacities
of the sander valve 301 the flow if the sander valve may be used. When higher
flow is required, an unused port of the high flow valve 5a may be used. This
would activate the stroke valve for flow. If the low flow block meets the flow
requirements, it may be used for the control of the sweeper. For an
application
having unidirectional flow an extra high flow section 5a may be added, and a
load
sense signal derived from its used work port. This signal may be used to
stroke
the pump through an additional shuttle valve 51 in order to maintain a
constant
pressure differential across the work spool. Similar set-ups may be used for
the
use of an auger, a hydraulic hammer, various street cleaning attachments and a
variety of other implements.
The benefits of using a load sensitive variable displacement pump are well
known in the art. By using the stroke valve 45 as described herein, non-load
sensing function valves may be used in place of more expensive load sensing
valves, while maintaining the benefits of the load sensitive variable
displacement
pump.
While the invention has been described according to what is presently
considered to be the most practical and illustrative embodiments, it must be
understood that the invention is not limited to the disclosed embodiments.
Those
ordinarily skilled in the art will understand that various modifications and
equivalent structures and functions may be made without departing from the
spirit
and scope of the invention as defined in the claims.
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