U.S. patent application number 13/705766 was filed with the patent office on 2014-06-05 for hydrostatic circuit flushing flow cancellation.
This patent application is currently assigned to CATERPILLAR INC.. The applicant listed for this patent is CATERPILLAR INC.. Invention is credited to Jason Mark Buckmier, Christopher Mark Elliott, Richard Ryan Evenson, Paul Alan Rousseau.
Application Number | 20140150880 13/705766 |
Document ID | / |
Family ID | 50824245 |
Filed Date | 2014-06-05 |
United States Patent
Application |
20140150880 |
Kind Code |
A1 |
Rousseau; Paul Alan ; et
al. |
June 5, 2014 |
Hydrostatic Circuit Flushing Flow Cancellation
Abstract
Flushing circuits for closed loop hydrostatic circuits enable
overriding of the normal function of the flushing circuit during
certain machine operational events where flushing can cause
undesirable performance issues. The disclosed flushing circuits may
prevent flow from leaving the flush valve, may prevent flow from
leaving the flushing circuit, may prevent flow from entering the
flushing circuit, may prevent the flush valve from shifting from a
normally closed position to an open position or may replace the
hydro-mechanical control of the flush valve with an electronic
control. Cancellation of the flushing function may be commanded by
a controller based on fluid temperatures, pressures, turning
commands, engine speed, etc.
Inventors: |
Rousseau; Paul Alan;
(Raleigh, NC) ; Elliott; Christopher Mark; (Apex,
NC) ; Evenson; Richard Ryan; (Apex, NC) ;
Buckmier; Jason Mark; (Cary, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CATERPILLAR INC. |
Peoria |
IL |
US |
|
|
Assignee: |
CATERPILLAR INC.
Peoria
IL
|
Family ID: |
50824245 |
Appl. No.: |
13/705766 |
Filed: |
December 5, 2012 |
Current U.S.
Class: |
137/2 ;
137/565.11 |
Current CPC
Class: |
Y10T 137/85986 20150401;
Y10T 137/0324 20150401; F03C 1/26 20130101; F16H 61/4008 20130101;
F16H 61/4165 20130101; F16H 61/4104 20130101; F04B 49/002
20130101 |
Class at
Publication: |
137/2 ;
137/565.11 |
International
Class: |
F04B 23/00 20060101
F04B023/00 |
Claims
1. A hydrostatic circuit comprising: a hydrostatic pump connected
to first and second input/output lines; the first and second
input/output lines connected to a hydrostatic motor to form a loop;
a flush valve, a control valve and a flush outlet; the first and
second input/output lines also connected to one of the flush valve
or the control valve, the flush valve and control valve configured
to perform three functions including providing communication
between the first input/output line and the flush outlet, providing
communication between the second input/output line and the flush
outlet and isolating the first and second input/output lines from
the flush outlet; a controller in communication with the control
valve for opening the control valve and providing communication
between the flush valve and the flush outlet, for closing the
control valve and isolating the flush valve from the flush outlet
and for reestablishing communication between one of the flush valve
and the flush outlet.
2. The hydrostatic circuit of claim 1 wherein the control valve is
a normally open proportional solenoid control valve.
3. The hydrostatic circuit of claim 1 further including a flush
flow regulator valve disposed downstream of the flush valve.
4. The hydrostatic circuit of claim 1 further including a flush
flow regulator valve disposed downstream of the control valve.
5. The hydrostatic circuit of claim 2 wherein the normally open
proportional solenoid control valve is in communication with the
controller and is disposed between the flush valve and the flush
outlet, the normally open proportional solenoid control valve being
adjustable between a fully open position providing full flow
between the flush valve and the flush outlet and a fully closed
position stopping flow between the flush valve and the flush
outlet.
6. The hydrostatic circuit of claim 5 further including a flush
flow regulator valve disposed downstream of the normally open
proportional solenoid control valve.
7. The hydrostatic circuit of claim 6 wherein the flush flow
regulator valve is pilot operated.
8. The hydrostatic circuit of claim 1 further comprising a
temperature sensor linked to the controller for communicating a
temperature of fluid in the hydrostatic circuit to the controller,
and if the temperature of the fluid is below the predetermined
temperature, the controller closes the control valve, and if the
temperature of the fluid is above the predetermined temperature,
the controller opens the control valve.
9. The hydrostatic circuit of claim 1 further including a first
pressure sensor in the first input/output line and a second
pressure sensor in the second input/output line, the first and
second pressure sensors being linked to the controller, and if a
first pressure in the first input/output line and a second pressure
in the second input/output line are both below a predetermined
pressure, the controller closes the control valve.
10. The hydrostatic circuit of claim 1 further including a first
pressure sensor in the first input/output line and a second
pressure sensor in the second input/output line, the first and
second pressure sensors being linked to the controller, the
controller having a memory programmed to calculate differences
between pressures sensed by the first and second pressure sensors
and if said difference is less than about 20 bar, the controller
closes the control valve.
11. The hydrostatic circuit of claim 1 wherein the controller is
linked to a steering mechanism, the steering mechanism for
communicating an operator command for machine steering to the
controller, wherein, upon receiving an operator command for machine
steering from the steering mechanism, the controller closes the
control valve.
12. The hydrostatic circuit of claim 11 wherein if the steering
command exceeds a predetermined time period, the controller opens
the control valve.
13. The hydrostatic circuit of claim 11 wherein if the controller
receives a straight command from the steering mechanism after
receiving an operator command for machine steering from the
steering mechanism, the controller opens the control valve.
14. The hydrostatic circuit of claim 1 wherein the flush outlet is
connected to a fluid tank, the fluid tank including a temperature
sensor that is linked to the controller, wherein if the temperature
in the tank is below a predetermined temperature, the controller
closes the control valve and if the temperature in the tank is
above the predetermined temperature, the controller opens the
control valve.
15. A hydrostatic circuit comprising: a hydrostatic pump connected
to first and second input/output lines; the first and second
input/output lines connected to a hydrostatic motor to form a loop;
the first and second input/output lines also connected to a flush
valve, the flush valve including a spool that is moveable between a
first position providing communication between the first
input/output line and a flush outlet line, a second position
providing communication between the second input/output line and
the flush outlet line and a third position wherein the flush valve
isolates the first and second input/output lines from the flush
outlet line; the flush outlet line terminating at a flush outlet; a
controller linked to at least one flush valve override component
selected from the group consisting of a normally open solenoid
control valve disposed downstream of the flush valve and upstream
of the flush outlet and in communication with the controller and
being moveable to a closed position for stopping flow from the
flush valve to the flush outlet, a normally open solenoid control
valve disposed upstream of the flush valve and in communication
with the controller and being moveable to a closed position for
stopping flow from the first and second input/output lines to the
flush valve, a normally open solenoid control valve disposed
upstream of the flush valve and in communication with the
controller and being moveable to a closed position for preventing
communication between the first and second input/output lines and
the flush valve, and a pair of solenoids disposed at opposing ends
of the flush valve and in communication with the controller for
maintaining the flush valve in its normally closed position; and at
least one temperature sensor linked to the controller for
communicating a temperature of fluid in the hydrostatic circuit to
the controller, and a plurality of pressure sensors linked to the
controller for communicating pressures in the first and second
input/output lines to the controller.
16. The hydrostatic circuit of claim 15 wherein the normally open
solenoid control valve disposed downstream of the flush valve and
upstream of the flush outlet is a normally open proportional
solenoid control valve that is adjustable between a fully open
position providing full flow between the flush valve and the flush
outlet and a fully closed position stopping flow between the flush
valve and the flush outlet.
17. The hydrostatic circuit of claim 15 further including a flush
flow regulator valve disposed downstream of the flush valve.
18. The hydrostatic circuit of claim 17 wherein the override
component is disposed downstream of the flush flow regulator
valve.
19. A method for overriding a flushing function of a flush valve of
a closed loop hydrostatic circuit, the method comprising:
overriding the flushing function in response to at least one
operating condition selected from the group consisting of: a)
measuring a temperature of a fluid in the circuit, if the
temperature of the fluid is below a predetermined minimum
temperature, sending a signal to stop any flushing flow from the
circuit to a flush outlet, b) measuring a loop pressure of the
fluid in the circuit, if the loop pressure is below a predetermined
minimum loop pressure, sending a signal to stop any flushing flow
from the circuit to the flush outlet, c) measuring pressures in
first and second input/output lines of the circuit, calculating a
difference (.DELTA.P) between the pressures in the first and second
input/output lines, if the .DELTA.P is below a predetermined
minimum .DELTA.P, sending a signal to stop any flushing flow from
the circuit to the flush outlet, d) receiving a turning command,
sending a signal to stop any flushing flow from the circuit to the
flush outlet, e) receiving a turning command, sending a signal to
stop any flushing flow from the circuit to the flush outlet, timing
a duration of the turning command, if the duration of the turning
command exceeds a predetermined maximum turning time period,
sending a signal to initiate flushing flow from the circuit to the
flush outlet, receiving a straight steering command, sending a
signal to initiate flushing flow from the circuit to the flush
outlet.
20. The method of claim 19 wherein the receiving and sending is
performed by a controller.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This disclosure relates generally to flushing systems for
hydrostatic circuits and various means for overriding such flushing
systems during certain machine operational events.
[0003] 2. Description of the Related Art
[0004] In the art of hydrostatics, oil or fluid is pumped by
mechanical hydrostatic pumps for the purpose of causing a
hydrostatic motor to revolve, a hydrostatic cylinder to extend, or
for other useful purposes. A common aspect of many tractors,
earthmoving machines and the like is a hydrostatic transmission. In
its most basic form, a hydrostatic transmission consists of a
hydrostatic pump which is normally driven by an internal combustion
engine, and provides a source of pressurized fluid flow which
causes one of more hydrostatic motors to rotate. The rotation of
these one or more hydrostatic motors will cause the machine to
travel forward or reverse as commanded by the operator of the
machine.
[0005] Hydrostatic transmissions typically operate in what is known
as a closed loop circuit. In a closed loop circuit, pressurized
fluid or oil from a hydrostatic pump flows directly (or through one
or more valves) through one line and through a hydrostatic motor
before the fluid is returned from the motor through a second line
to the pump. The hydrostatic pump and motor are typically of the
bidirectional and variable displacement type. This system is known
as closed loop circuit because the fluid circulates in a closed
path formed by the two lines between the pump and the motor without
passing through a fluid reservoir on each pass. This closed loop
circuit differs from an open loop circuit where a pump draws the
fluid from a fluid reservoir and pumps the fluid through a motor
before the fluid is returned to the fluid reservoir. Even in a
closed circuit, a small reservoir and a charge pump are needed to
collect a small amount of fluid which leaks out of the closed loop
and to replace the leaked fluid so that the closed loop remains
full of fluid at all times.
[0006] When a hydrostatic transmission is operated under heavy
loads for an extended period of time, it is possible for the fluid
to become heated to an extent which may not be desirable. This
heating occurs due to friction and other processes. The fluid may
degrade more quickly when maintained at excessive temperatures,
thus requiring premature replacement of the fluid. Further, at
elevated temperatures, hydrostatic fluid may lose certain
lubricating properties including, but not limited to, viscosity.
When a hydrostatic fluid loses viscosity, it compromises the
fluid's ability to prevent damaging wear to the hydrostatic
machinery, such as the pump, motor and valves. In order to remove
hot fluid from the closed loop hydrostatic circuit, a "controlled
leak" or loop-flushing system is employed to remove fluid from the
closed circuit. This fluid is then cooled in a reservoir and
returned to the closed circuit through the charge pump.
[0007] As shown in FIG. 2 of U.S. Pat. No. 6,430,923, a flushing
system 32 may include a flush valve in the form of a
spring-centered shuttle spool 34 that is connected to both the high
pressure and low pressure fluid paths A, B on the closed loop
hydrostatic circuit. The flush valve 34 may be configured to draw
fluid from the low pressure line of the two hydrostatic circuit
pressure lines A, B of the closed loop system. The flush valve 34
may be connected to a flushing flow regulator valve 36 that may be
in communication with a reservoir, a cooler, motor case, etc. The
flushing flow regulator valve 36 may control the release of fluid
from the loop. The flushing flow regulator valve 36 may also serve
to provide a minimal flushing flow of hot fluid from the loop while
the charge pump 28 replaces the flushed hot fluid with cool fluid
to maintain the fluid in the loop at an appropriate
temperature.
[0008] Hydrostatic systems include several deficiencies. For
example, current loop flushing systems that incorporate a flush
valve and a relief valve are not intelligently controlled.
Typically, the pressure in the high pressure fluid path dictates
when flushing occurs because the system is not intelligently
controlled, the loop flushing action occurs whenever the
transmission is operational and cannot be overridden. During
certain machine operational events, the flushing function can cause
performance issues including, but not limited to jerky steering,
slow steering response, reduced fluid pressure in the closed loop
and sluggish transitions between forward and reverse movements.
[0009] Therefore, there is a need for an improved hydrostatic
circuit with a flushing function that can be canceled or overridden
to avoid the problems noted above.
SUMMARY OF THE DISCLOSURE
[0010] In one aspect, a hydrostatic circuit is disclosed that is
capable of cancelling its flushing function. The disclosed circuit
may include a hydrostatic pump connected to first and second
input/output lines. The first and second input/output lines may be
connected to a hydrostatic motor to form a loop. The circuit may
also include a flush valve, a control valve and a flush outlet. The
first and second input/output lines may also be connected to one of
the flush valve or the control valve. The flush valve and the
control valve may be configured to perform three functions
including providing communication between the first input/output
line and the flush outlet, providing communication between the
second input/output line and the flush outlet and isolating the
first and second input/output lines from the flush outlet. The
circuit may also include a controller in communication with the
control valve for opening the control valve and providing
communication between the flush valve and the flush outlet, for
closing the control valve and isolating the flush valve from the
flush outlet and for reestablishing communication between the flush
valve and the flush outlet.
[0011] In another aspect, a hydrostatic circuit is disclosed which
is also capable of overriding or cancelling the flushing function.
The disclosed circuit may include a hydrostatic pump connected to
first and second input/output lines. The first and second
input/output lines may be connected to a hydrostatic motor to form
a loop. The first and second input/output lines may also be
connected to a flush valve. The flush valve may include a spool
that is moveable between a first position providing communication
between the first input/output line and the flush outlet line. The
spool may also be moveable to a second position providing
communication between the second input/output line and the flush
outlet line. Finally, the spool may be moveable to a third position
wherein the flush valve isolates the first and second input/output
lines from the flush outlet line. The flush outlet line may
terminate at a flush outlet. The circuit may further include a
controller that is linked to at least one flush override component
selected from the group consisting of: a normally open solenoid
control valve disposed downstream of the flush valve and upstream
of the flush outlet and in communication with the controller and
being moveable to a closed position for stopping flow from the
flush valve to the flush outlet; a normally open solenoid control
valve disposed upstream of the flush valve and in communication
with the controller and being moveable to a closed position for
stopping flow from the first and second input/output lines to the
flush valve; a normally open solenoid control valve disposed
upstream of the flush valve and in communication with the
controller and being moveable to a closed position for preventing
communication between the first and second input/output lines and
the flush valve; and a pair of solenoids disposed at opposing ends
of the flush valve and in communication with the controller for
maintaining the flush valve in its normally closed position. The
circuit may further include at least one temperature sensor linked
to the controller for communicating a temperature of fluid in the
hydrostatic circuit to the controller and a plurality of pressure
sensors linked to the controller for communicating pressures in the
first and second input/output lines to the controller.
[0012] In another aspect, a method for overriding a flushing
function of a flush valve of a closed loop hydrostatic circuit is
disclosed. The method may including overriding the flushing
function in response to at least one operating condition selected
from the group consisting of: measuring a temperature of a fluid in
the circuit and, if the temperature of the fluid is below a
predetermined temperature, sending a signal to stop any flushing
flow from the circuit to a flush outlet; measuring a loop pressure
of the fluid in the circuit and, if the loop pressure is below a
predetermined minimum loop pressure, sending a signal to stop any
flushing flow from the circuit to the flush outlet; measuring
pressures in first and second input/output lines of the circuit,
calculating a difference (.DELTA.P) between the pressures in the
first and second input/output lines and, if the .DELTA.P is below a
predetermined minimum .DELTA.P, sending a signal to stop any
flushing flow from the circuit to the flush outlet; receiving a
turn command and sending a signal to stop any flushing flow from
the circuit to the flush outlet; receiving a turn command, sending
a signal to stop any flushing flow from the circuit to the flush
outlet, timing a duration of the turn command and, if the duration
of the turn command exceeds a predetermined maximum turning time
period, sending a signal to initiate flushing flow from the circuit
to the flush outlet and, optionally, receiving a straight steering
command and sending a signal to initiate flushing flow from the
circuit to the flush outlet in response to receiving the straight
steering command.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic illustration of a closed loop
hydrostatic circuit equipped with a prior art flushing circuit, but
which can be equipped with any of the disclosed flushing
circuits.
[0014] FIG. 2 is a schematic illustration of a first disclosed
flushing circuit that may be incorporated into the hydrostatic
circuit of FIG. 1.
[0015] FIG. 3 is a schematic illustration of a third disclosed
flushing circuit that may be incorporated into the hydrostatic
circuit of FIG. 1.
[0016] FIG. 4 is a schematic illustration of a third disclosed
flushing circuit that may be incorporated into the hydrostatic
circuit of FIG. 1.
[0017] FIG. 5 is a schematic illustration of a fourth disclosed
flushing circuit that may be incorporated into the hydrostatic
circuit of FIG. 1.
[0018] FIG. 6 is a schematic illustration of a fifth disclosed
flushing circuit that may be incorporated into the hydrostatic
circuit of FIG. 1.
[0019] FIG. 7 is a schematic illustration of a sixth disclosed
flushing circuit that may be incorporated into the hydrostatic
circuit of FIG. 1.
[0020] FIG. 8 is a flow chart illustrating the cancellation of the
flush function when the loop pressure is below a predetermined
value.
[0021] FIG. 9 is a flow chart illustrating the cancellation of a
flushing function if a difference in pressures between the first
and second input/output lines is less than a predetermined value
and the activation of the flushing function when the tank/loop
temperature is above a predetermined value regardless of the low
pressure differential between the two input/output lines.
[0022] FIG. 10 is a flow chart illustrating the cancellation and
activation of the flushing function in response to the fluid
temperature.
[0023] FIG. 11 is a flow diagram illustrating the cancellation and
activation of the flushing function in response to turn commands
from the operator or steering mechanism.
[0024] FIG. 12 is another flow diagram illustrating the
cancellation and activation of flushing in response to various
parameters including charge pressure, turn commands, pressure
differential between the two input/output lines, and fluid
temperature.
DETAILED DESCRIPTION
[0025] FIG. 1 illustrates a closed loop hydrostatic circuit 10 for
background purposes as FIG. 1 also illustrates typical flushing
circuit 11. It will be noted that the hydrostatic circuit 10 may
not be the only type of hydrostatic circuit 10 that requires a
flushing function. While the flushing circuits 111, 211, 311, 411,
511, 611 illustrated in FIGS. 2-7 may be incorporated into the
hydrostatic circuit 10 of FIG. 1, it will be noted that the
flushing circuits illustrated in FIGS. 2-7 are not limited to
incorporation into the hydrostatic circuit 10 of FIG. 1, but may be
incorporated into other hydrostatic circuits as well.
[0026] Referring to FIG. 1, the hydrostatic circuit 10 includes a
hydrostatic charge pump 12 that is connected to a first
input/output line 13 and a second input/output line 14. The lines
13, 14 are described as input/output lines 13, 14 as the
hydrostatic charge pump 12 illustrated in FIG. 1 is a variable
displacement pump capable of directing flow in either direction,
i.e., from the pump 12 through the line 13 to the hydrostatic motor
15 or from the pump 12, through the line 14 to the hydrostatic
motor 15. Similarly, the hydrostatic motor 15 is also a two way
variable displacement hydrostatic motor that may rotate a shaft or
other component 16 in either direction as indicated by the arrows
17. While the circuit 10 is described herein as a closed loop
circuit, the hydrostatic fluid or oil flowing through the circuit
10 may need to be filtered or cleaned or the circuit 10 may need to
be cooled by removing hot fluid and replacing the removed hot fluid
with cooler fluid from a tank or reservoir 18. The reservoir 18 is
in communication with a makeup pump 19 which draws fluid from the
reservoir 18 and delivers it to the input/output lines 13, 14 via
the makeup lines 21, 22 respectively. The makeup lines 21, 22 may
be equipped with check valves 23, 24 respectively to prevent
backflow from the input/output lines 13, 14 to the makeup pump 19.
The makeup lines 21, 22 may also be in communication with a charge
relief valve 25 that may be a normally closed, pilot operated
pressure relief valve as shown and that may provide communication
between the line 26 that is in communication with the makeup lines
21, 22, and the reservoir 18, or an alternative tank or reservoir
(not shown).
[0027] FIG. 1 also illustrates a conventional flushing circuit 11
that may include a flush valve 27 that may be pilot operated as
shown with a shuttle spool 28 that may be moved between three
positions. The flush valve 27 is shown in its normally closed
position in FIG. 1 wherein flow from the first and second flush
lines 31, 32 to the flush outlet line 33 is blocked. In the event
the pressure in the first input/output line 13 exceeds a
predetermined value, the pressure will be communicated from the
line 13, through the line 31 to the first pilot line 34 which will
shift the shuttle spool 28 downward in the orientation of FIG. 1
thereby overcoming the bias of the spring or biasing element 35
thereby establishing communication between the lower pressure
second flush line 32 and the flush outlet line 33. Similarly, in
the event the pressure in the second input/output line 14 exceeds a
certain value, that pressure will be communicated through the
second flush line 32 to the second pilot line 36 which may then
cause the shuttle spool 28 to be shifted upwards in the orientation
of FIG. 1 thereby overcoming the bias of the spring or biasing
element 37 and providing communication between the lower pressure
first flush line 31 and the flush outlet line 33. The flushing
circuit 11 may also include a flush flow regulator valve 38 that
may also be pilot operated and used to control the flow from the
flush outlet line 33 to the flush outlet 41. In short, if the
pressure in the flush outlet line 33 exceeds a certain value, that
pressure will be communicated through the pilot line 42 which
causes the normally closed flush flow regulator valve 38 to be
shifted to an open position thereby overcoming the bias of the
spring or biasing element 43. The flush flow regulator valve 38 may
also include a flow control device 44 that may be a fixed orifice
that limits the amount of flow that could be passed from the flush
outlet line 33 through the flush flow regulator valve 38. Further,
because the flush flow regulator valve 38 may be pilot operated, it
also acts as a low pressure relief valve that prevents flush flow
to the flush outlet 41 during events that may reduce the charge
pressure of the circuit 10 below a predetermined pressure
value.
[0028] During certain operations of a machine or work implement in
which a hydrostatic circuit 10 is incorporated, the flushing
function can cause undesirable performance issues including, but
not limited to jerky steering, slow steering response, loss of
desired charge pressure and sluggish forward/reverse transition
responses. Therefore, to avoid these problems, improved
intelligently controlled flushing circuits 111, 211, 311, 411, 511,
611 are disclosed in FIGS. 2-7 which include override components
that override the normal hydro-mechanical function of the flushing
circuit 11. The disclosed flushing circuits 111, 211, 311, 411,
511, 611 may operate in a variety of ways including, but not
limited to preventing flushing flow from exiting the flush valve 27
or the shuttle spool 28, preventing flushing flow from leaving the
flushing circuit 11, preventing flow from entering the flushing
circuit 11, preventing the shuttle spool 28 from shifting and/or
electronically shifting the shuttle spool 28 as opposed to
hydro-mechanically shifting the shuttle spool 28. Various
parameters for overriding the normal hydro-mechanical function of
the flushing circuits 11, 211, 311, 411, 511 and 611 are discussed
below in connection with FIGS. 7-12.
[0029] Turning first to FIG. 2, a disclosed flushing circuit 111
may include a hydro-mechanically operated flush valve 27 as
illustrated in FIG. 1. A flush valve override component is provided
in the form of a control valve 50 disposed in the flush outlet line
33 and downstream of the flush valve 27. The control valve 50 may
be a normally open solenoid control valve equipped with a biasing
element 51 and a solenoid 52 that is in communication with a
controller 53. As shown in FIG. 2, the control valve 50 is moveable
between two positions including the open position shown in FIG. 2
and a closed position which is achieved by the controller 53
sending a signal to the solenoid 52 thereby shifting the valve 50
upward in the orientation of FIG. 2 thereby placing the check valve
54 or other blocking element in the flush outlet line 33 to prevent
or block communication between the flush valve 27 and the flush
outlet 41. When the valve 50 is de-energized, the flushing circuit
111 functions normally. When the controller 53 energizes the
solenoid 52 thereby shifting the valve 50 to a closed position, the
valve 50 prevents flushing flow from exiting the shuttle spool 28
and reaching the flush outlet 41.
[0030] Turning to FIG. 3, another flushing circuit 211 is disclosed
that includes a flush valve 27 and flush flow regulator valve 38 as
illustrated in FIG. 1. In the flushing circuit 211 of FIG. 3, the
control valve 50 is disposed downstream of the flush flow regulator
valve 38 or between the flush flow regulator valve 38 and the flush
outlet 41. Thus, if a two position/two way normally open solenoid
valve like that shown at 50 in FIGS. 2-3 is utilized as the flush
valve override component, such a control valve 50 may be disposed
upstream or downstream of the flush flow regulator valve 38 as
shown in FIGS. 2-3 respectively.
[0031] Turning to FIG. 4, yet another flushing circuit 311 is
disclosed that may be equipped with a flush valve 27 and flush flow
regulator valve 38 as described above. Instead of the two
position/two way normally open solenoid valve 50 as shown in FIGS.
2-3, the flush valve override component of the flushing circuit 311
of FIG. 4 is a two position/four way normally open solenoid control
valve 60 that may be disposed upstream of the flush valve 27. The
control valve 60 includes a biasing element 61 that maintains the
valve 60 in a normally open position as shown in FIG. 4 and a
solenoid 62 that may be linked to the controller 53. When the
controller 53 sends a signal to the solenoid 62, the control valve
60 is shifted upward from the orientation of FIG. 4 to a closed
position thereby blocking flow from the first and second flush
lines 31, 32 to the flush valve 27. Thus, when the control valve 60
is de-energized, the flushing circuit 311 operates normally. When
the controller 53 sends a signal to the solenoid 62, the control
valve 60 may be shifted to a closed position thereby preventing
flow from the hydrostatic circuit 10 (FIG. 1) from entering the
flush valve 27.
[0032] Turning to FIG. 5, yet another flushing circuit 411 is
disclosed that is similar to the flushing circuit 311 of FIG. 4.
Specifically, a two position/four way normally open solenoid
control valve 60 is disposed upstream of the flush valve 27, but in
communication with the pilot lines 34, 36 as opposed to the flush
lines 31, 32. Again, the control valve 60, when de-energized, is in
the open position shown in FIG. 5. If the pressure in the first
flush line 31 exceeds a certain value, that pressure will be
communicated through the open control valve 60 and through the
first pilot line 34 to shift the shuttle spool 28 downward thereby
establishing communication between the second flush line 32 and the
flush outlet line 33 as the second flush line 32 is at a lower
pressure than the first flush line 31. Conversely, if the second
flush line 32 is at a pressure that exceeds a certain value, that
pressure will be communicated through the open control valve 60 and
through the second pilot line 36 thereby shifting the shuttle spool
28 upward in the orientation of FIG. 5 and thereby establishing
communication between the lower pressure first flush line 31 and
the flush outlet line 33. When energized by a signal being sent
from the controller 53 to the solenoid 62, the control valve 60
shifts downward in the orientation of FIG. 5 thereby blocking
communication between the first and second flow lines 31, 32 and
the first and second pilot lines 34, 36 respectively so that the
normally closed flush valve 27 remains in its normally closed
position as shown in FIG. 5. Thus, the control valve 60 of the
flushing circuit 411 maintains the flush valve 27 in its normally
closed position when the control valve 60 is energized.
[0033] Turning to FIG. 6, yet another flushing circuit 511 is
illustrated which also acts to maintain a flush valve 127 in its
normally closed position when the flushing function needs to be
overridden. Specifically, the flush valve 127 of FIG. 6, as opposed
to the flush valves 27 of FIGS. 2-5, is electrically or
electronically activated as the flush valve 127 includes solenoids
71, 72 disposed at either end of the shuttle spool 128. The
controller 53 controls the entire flushing function. That is, if
pressure in the first flush line 31 exceeds a certain value, that
value will be detected by the sensor 81, communicated to the
controller 53, which will then send a signal to the solenoid 71
thereby shifting the shuttle spool 128 downward and providing
communication between the lower pressure second flush line 32 and
the flush outlet line 33. Conversely, when the pressure in the
second flush line 32 exceeds a certain value, it will be detected
by the sensor 82, communicated to the controller 53, which will
then send a signal to the solenoid 72 thereby shifting the shuttle
spool 128 upwards and establishing communication between the lower
pressure first flush line 31 and the flush outlet line 33.
[0034] Finally, turning to FIG. 7, another flushing circuit 611 is
illustrated which includes the pilot operated flush valve 27 and
the pilot operated flush flow regulator valve 38 as described
above. The flush valve override component is provided in the form
of a normally open proportional flow solenoid control valve 90
downstream of the flush valve 27. It will be noted that the control
valve 90 could also be disposed downstream of the flush flow
regulator valve 38 as well. The controller 53 is in communication
with an actuator 91 which, when fully energized, shifts the control
valve 90 upward to a closed position where the check valve or other
blocking element 92 blocks flow from exiting the flush valve 27.
When the actuator 91 is de-energized, the control valve 90 assumes
the open position shown in FIG. 7. Variable command current may be
utilized to proportionally control the flushing flow rate based on
system conditions. That is, instead of completely overriding the
flushing function, the flushing flow rate may be reduced to an
acceptable level which will not present the problems of jerky
steering, slow steering response, low charge pressure and/or
sluggish forward/reverse transition responses as discussed above.
Thus, along with flow cancellation, the flushing circuit 611
includes the additional function of variable flushing flow.
[0035] Still referring to FIG. 7, the various disclosed methods for
cancelling and activating the flushing flow function will now be
described. It will also be noted that the disclosed methods for
cancelling and activating the flushing flow function are also
applicable to the flushing circuits 111, 211, 311, 411 and 511 of
FIGS. 2-6. The controller 53 may be linked to a plurality of
sensors including a pressure sensor 92 that may be coupled to the
flush line 31 in FIG. 7 but could also be placed in the first
input/output line 13 shown in FIG. 1. The controller 53 may also be
linked to a temperature sensor 93 that is also shown coupled to the
flush line 31, but could also be disposed along the first
input/output line 13 (FIG. 1). Similarly, the controller 53 may be
linked to a pressure sensor 94 that may be coupled to the flush
line 32 as well as a temperature sensor 95 that may be coupled to
the flush line 32. The pressure and temperature sensors 94, 95
could also be coupled to the second input/output line 14. The
controller 53 is also linked to pressure sensors 96, 97, disposed
on the other side of the hydrostatic charge pump 12 for measuring
the charge pressure or pressure in the first and second
input/output lines 13, 14. Thus, pressure sensors 96, 97 can also
be used to measure loop pressure in a manner similar to the
pressure sensors 92, 94. The controller 53 may also be linked to a
temperature sensor 98 that may be coupled to the flush outlet 41 or
fluid reservoir 18 for measuring the temperature of the fluid in
the circuit 10 similar to the temperature sensors 93, 95. While
three temperature sensors 93, 95, 98 are shown in FIG. 7, only a
single temperature sensor may be needed in a closed hydrostatic
circuit like the one shown at 10 in FIG. 1. Finally, the controller
53 is also linked to a steering mechanism 99 which communicates
turn commands, forward and reverse commands and straight (no turn)
commands to the controller 53. The importance of the variables
provided by the various sensors shown in FIG. 7 will be described
in connection with the flow charts of FIGS. 8-12.
[0036] Turning to FIG. 8 while still referring to FIG. 7, at part
130, the controller 53 may receive a pressure reading of fluid in
the hydrostatic loop from one of the pressure sensors 92, 94, 96,
97 or another appropriately placed pressure sensor for measuring
the pressure of the fluid in the circuit 10. After the controller
53 receives a pressure signal, the controller 53 determines whether
the pressure is less than the predetermined pressure value at part
131. If the pressure is below a predetermined value, the flushing
function is cancelled at part 132. The method illustrated in FIG. 8
may be particularly applicable when the engine speed is low thereby
resulting in a low charge pressure and/or high load situations with
substantial leakage of fluid. These situations can occur in certain
machines such as skid steer loaders, track type loaders, various
types of tractors, small wheel loaders and others. A low charge
pressure can cause a work implement to pop out of a float position
or a position where the implement is following the ground. Further,
when the charge pressure is too low, the parking brake of certain
machines may automatically be applied and, if the machine is
moving, undue wear to the parking brake may occur.
[0037] Turning to FIG. 9, a method is disclosed for cancelling
flushing in the event the pressure difference (.DELTA.P) between
the first and second input/output lines 13, 14 is too small. At
part 133 the controller 53 receives pressure signals from two
pressure sensors, such as the sensors 92, 94 or the sensors 96, 97.
At part 140, the .DELTA.P is circulated. At part 134, the
controller 53 determines whether the .DELTA.P is less than a
predetermined level and, if so, the flushing is cancelled at part
135. If the .DELTA.P is greater than the predetermined level at
part 134, the method may go on to determine whether the fluid
temperature is above the predetermined level at part 136. If so,
flushing is actuated at part 137 to avoid over heating of the
fluid.
[0038] Turning to FIG. 10, a method for cancelling flushing in the
event the fluid temperature is too low is disclosed. At part 138,
the controller 53 receives a temperature signal from at least one
of the temperature sensors 93, 94 or 98. If the reservoir 18 and
flush outlet 41 are in communication with one another, the
temperature sensor 98 also reflects the temperature fluid passing
through the makeup pump 19. After the temperature signal is
received at part 138, the controller 53 determines whether the
temperature is below a predetermined value at part 139 and, if so,
flushing is cancelled at part 141. If the fluid temperature is
determined to be above a predetermined value at part 139 or part
142, then flushing is activated at part 143. If the temperature of
the fluid in the circuit 10 is too low, it will cause slow shifting
of the flushing spool and certain machines may be subject to
uncommanded motion detection or, in other words, the flushing spool
moves so slowly that the machine may not be able to follow an
operators command quickly enough.
[0039] Turning to FIG. 11, a method for cancelling flushing while a
machine is being steered or turned is disclosed. At part 145, the
controller 53 receives a signal from the steering mechanism 99 that
the operator has inputted a turning command. Flushing is then
cancelled at part 146 in response to the turning command. Flushing
is cancelled during turning of certain machines, such as small
track type tractors and skid steer loaders, because the loss of
pressure and fluid caused by flushing can cause steering hesitation
or a sticking or hang up of the shuttle spool 28. However, the
controller 53 may include a timer and if the turning command has
been applied longer than a predetermined time period at part 147,
flushing may be activated at part 148 to avoid overheating the
fluid. If a straight command or a return to a straight pathway
command has been received at part 149, then flushing is activated
at part 151.
[0040] Turning to FIG. 12, the controller 53 receives the charge
pressure, most likely from either of the sensors 96, 97 at part
153. If the charge pressure is less than a predetermined minimum
value at 154, then the flushing is cancelled at 155. If the charge
pressure is sufficient, the controller 53 then checks to see
whether it has received a turn command from the steering mechanism
99 at part 156. If so, the controller 53 determines whether the
steering command has been extended past a predetermined time period
at part 157. If so, flushing may be cancelled at part 158. The loop
pressures and .DELTA.P are measured and calculated at part 159 and
if the .DELTA.P is less than a predetermined minimum value at part
161, flushing may be cancelled at part 162. The controller 53 then
may check the fluid temperature at part 163 and if the temperature
is less than a predetermined minimum value at part 164, flushing
may be cancelled at part 165. If the temperature is of a sufficient
value, then the system may be flushed at part 166 in a normal
fashion. While the above method were described in connection with
FIG. 7, they are also applicable to the flushing circuits 111, 211,
311, 411 and 511 as shown in FIGS. 2-6.
INDUSTRIAL APPLICABILITY
[0041] As noted above, closed loop hydrostatic circuits 10 require
a flushing function for purposes of maintaining clean fluid in the
circuit 10, maintaining a sufficient amount of fluid in the circuit
10 in the case of leakage, controlling circuit heat by removing hot
fluid and replacing it with cooler fluid, etc. However, during
certain machine operational events, automated flushing circuits
like that shown at 10 in FIG. 1 can be activated and cause unwanted
performance issues such as jerky steering, slow steering response,
low charge pressure and sluggish responses during forward and/or
reverse transitions. The disclosed flushing circuits 111, 211, 311,
411, 511, 611 override the normal hydro-mechanical function of a
typical flush valve 27, 127 during machine operational events when
flushing is not desired but which would otherwise trigger the
flushing function. The disclosed flushing circuits 111, 211, 311,
411, 511, 611 may prevent flushing flow from leaving the flush
valve 27, 127 or prevent flushing flow from leaving the flushing
circuit 111, 211, 311, 411, 511, 611 downstream of the flush valve
27, 127. The disclosed flushing circuits 111, 211, 311, 411, 511,
611 may also prevent flow from entering the flushing circuit 111,
211, 311, 411, 511, 611 or entering the flush valve 27, 127. The
disclosed flushing circuits 111, 211, 311, 411, 511, 611 may also
prevent the flush valve 27, 127 from shifting or the
hydro-mechanical function of the typical flush valve 27 may be
replaced by electronic control as shown by the flush valve 127 of
FIG. 6. Finally, in addition to flow cancellation during certain
operational events, a proportional flow solenoid control valve 90
(FIG. 7) may provide variable flushing flow control so that limited
flushing can occur during machine operational events when a full
flushing operation would be undesirable.
[0042] Various issues may arrive during the operation of a machine
that may call for cancellation of the flushing function. For
example, at slow speeds, low engine speeds, small or no load,
bucking or instability may occur if the pressure difference between
the first and second input/output lines 13, 14 is not sufficient.
Thus, the methods of FIGS. 9 and 12 may avoid this problem.
Further, during a steering operation or a turning command,
insufficient pressure may be available to move the shuttle spool
28, 128, causing it to hang up. This can result in a delay in the
steering of the machine (e.g., causing the machine to proceed in a
straight direction as opposed to the desired turn direction).
Hence, the methods of FIGS. 11 and 12 may be employed to avoid
these problems. Cold fluid also causes slow shifting of the shuttle
spool 28, 128 which may cause the machine to do something different
than what it is being commanded to do. Thus, the methods of FIGS.
10 and 12 may avoid these problems. Further, low charge pressure
can cause all sorts of problems including control pressures, and
unintended application of the parking brake (not shown), thereby
causing undue wear to the parking brake. Thus, the methods of FIGS.
8 and 12 may avoid these problems.
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