METHOD FOR OPERATING A HYDRAULIC ACTUATION POWER SYSTEM
EXPERIENCING PRESSURE SENSOR FAULTS
TECHNICAL FIELD
[001] The present invention relates to hydraulic actuation systems, and, more
particularly, to operational modes for hydraulic actuation systems employed in
machinery experiencing pressure sensor faults.
BACKGROUND OF THE INVENTION
[002] Hydraulic actuation systems, as employed to operate lifting arms in load
transferring equipment, such as construction machinery, typically include a pressure
source such as a pump, a fluid tank and at least one fluid cylinder to control a lifting
arm of the subject machine.
[003] It is known in the art to utilize pressure sensors for controlling the
operation of such hydraulic actuation systems. Typically, the pressure sensors are
employed in the control of valves that manage, based on loads, fluid flow between the
fluid cylinder, pressure source, and fluid tank. It is, however, conceivable that such a
pressure sensor may experience a malfunction, and render the system inoperative.
SUMMARY OF THE INVENTION
[004] A method for operating a hydraulic actuation system during a pressure
sensor malfunction is provided. The hydraulic actuation system includes a pressure
source, such as a pump, arranged to supply fluid flow in response to a fluid flow
demand, a reservoir arranged to hold fluid, and first and second work-ports. The
pressure source is in fluid communication with the reservoir and with the first and
second work-ports.
[005] The hydraulic actuation system also includes a valve system capable of
controlling fluid flow. The valve system has a first orifice arranged between the
pressure source and the first pressure chamber, a second orifice arranged between the
pressure source and the second pressure chamber, a third orifice arranged between the
first pressure chamber and the reservoir, and a fourth orifice arranged between the
second pressure chamber and the reservoir.
[006] The hydraulic actuation system also includes a pressure sensor system
capable of sensing pressure (Ps) of the fluid supplied by the pressure source, pressure
(Pa) of the fluid supplied to the first pressure chamber, and pressure (Pb) of the fluid
supplied to the second pressure chamber. The hydraulic actuation system additionally
includes a controller arranged to regulate the pressure source and the valve system
based on the fluid flow demand and on determined differences between Ps, Pa, Pb,
and pressure (Pt) of the fluid returned to the reservoir.
[007] The method includes detecting a malfunction of solely a sensor arranged to
sense Pa, closing the second and third orifices, and regulating the pressure source to
generate fluid flow corresponding to maximum Ps. The method additionally includes
assigning a value for the difference between Ps and Pa that is equivalent to a value
within an attainable range for difference between the two pressures. Moreover,
regulating the first orifice and the fourth orifice in response to the fluid flow demand
is included, such that the system continues to operate despite the malfunction of the
sensor arranged to sense Pa.
[008] According to the method, replating the fourth control valve may be
accomplished by generating flow through the fourth orifice that is equivalent to the
flow demand multiplied by the ratio between areas of the first and second work-ports.
Additionally, a malfunction signal may be generated in response to said detecting a
malfunction of the sensor arranged to sense Pa.
[009] The method may further include detecting a malfunction of solely a sensor
arranged to sense Pb, closing the second and third orifices, directing the pressure
source to generate fluid flow corresponding to Ps > Pa, and assigning a value for the
difference between Pb and Pt that is substantially equivalent to a maximum attainable
value. In such a case, the method also includes regulating the first orifice in response
to fluid flow demand, and regulating the fourth orifice to generate Pb, such that the
system continues to operate despite the malfunction of the sensor arranged to sense
Pb. Furthermore, regulating the fourth orifice is accomplished by holding Pa below
its maximum value. The method may also include generating a malfunction signal in
response to said detecting a malfunction of the sensor arranged to sense Pb.
[0010] If the reservoir employed within the hydraulic actuation system operates
above a minimum known pressure, the pressure sensor system may additionally
include a pressure sensor capable of sensing pressure Pt.
[0011] The above method may be applied to a machine operated via a hydraulic
actuation system. The hydraulic actuation system of the machine employs an
actuator having first and second opposing pressure chambers that are arranged to
operate an arm of the machine in response to the fluid flow controlled according to
the above description.
[0012] The above features and advantages and other features and advantages of
the present invention are readily apparent from the following detailed description of
the best modes for carrying out the invention when taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Figure 1 is a schematic diagram illustrating a hydraulic actuation system
employing valves with pressure sensors for controlling system function;
|0014] Figure 2 is a flowchart of a method for controlling a hydraulic actuation
system experiencing a second pressure sensor fault; and
[0015] Figure 3 is a flowchart of a method for controlling a hydraulic actuation
system experiencing a third pressure sensor fault.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Referring to the drawings wherein like reference numbers correspond to
like or similar components throughout the several figures, Figure 1 illustrates a
schematic diagram illustrating a hydraulic actuation system 10 employing a valve
system and pressure sensors for controlling system function. Hydraulic actuation
system 10 is commonly employed in earth moving or construction machines (not
shown) to raise and/or lower the machine's arm in order to transfer a load.
[0017] Hydraulic actuation system 10 includes a fluid reservoir 12 in fluid
communication with a pressure source, such as a pump 14 via a fluid passage 13. The
pressure source 14 is in fluid communication with a first pressure sensor 18 via a fluid
passage 16. Sensor 18 is arranged to sense pressure Ps of the fluid supplied by the
pressure source 14. The sensor 18 is in fluid communication with an orifice 22 via a
fluid passage 20. The orifice 22 is in fluid communication with a second pressure
sensor 24. The pressure sensor 24 is arranged to sense pressure Pa of the fluid
supplied to a hydraulic actuator 28 via a fluid passage 26.
[0018] The hydraulic actuator 28 includes a moveable piston 30 that includes a
piston head 30a and a rod 30b. The piston 30 separates the hydraulic actuator into a
first work-port or pressure chamber 32 on the side of the piston head 30a, and a
second work-port or pressure chamber 34 on the side of the piston rod 3 0b.
Specifically, the pressure Pa sensed by the pressure sensor 24 corresponds to pressure
of the fluid inside the first pressure chamber 32.
|0019] The sensor 18 is additionally in fluid communication with an orifice 38 via
a fluid passage 36. The orifice 38 is in fluid communication with a third pressure
sensor 40. The pressure sensor 40 is arranged to sense pressure Pb of the fluid
supplied to the hydraulic actuator 28 via a fluid passage 42. Specifically, the pressure
Pb sensed by the pressure sensor 40 corresponds to pressure of the fluid inside the
second pressure chamber 34.
[0020] The sensor 24 is also in fluid communication with an orifice 46 via a fluid
passage 44. The orifice 46 is in fluid communication with a fourth pressure sensor
48. Pressure sensor 48 is arranged to sense pressure Pt of the fluid returned to the
reservoir 12 via a fluid passage 50. The orifice 22 and the orifice 46 may be separate
control valves configured to regulate fluid flow between the pressure source 14, the
reservoir 12 and the first pressure chamber 32, or be combined into a single control
valve structure.
[0021 ] The sensor 40 is also in fluid communication with an orifice 54 via a
fluid passage 52. The orifice 54 is in fluid communication with the pressure sensor
48. The orifice 38 and the orifice 54 may be separate control valves configured to
regulate fluid flow between the pressure source 14, the reservoir 12 and the second
pressure chamber 34, or be combined into a single control valve structure.
[0022] Together, the orifices 22,38,46 and 54 form a valve system for managing
fluid flow through the hydraulic actuation system 10. A controller 56, such as an
electronic control unit (ECU), is programmed to regulate the pressure source 14 and
the orifices 22, 3 8,46 and 54. As understood by those skilled in the art, controller 56
regulates the pressure source 14 and the orifices 22, 38,46 and 54 based on
differences between pressures Ps, Pa, Pb and Pt calculated by the controller, as well as
according to the fluid flow demand. The fluid flow demand is generally established
by a request from a construction machine's operator, for example, to raise or lower a
particular load.
[0023] The pressure data sensed and communicated to the controller 56 is
additionally employed to determine which of the two chambers 32 and 34 of actuator
28 is subjected to a load. In order to raise a load, hydraulic actuation system 10 is
regulated to supply fluid to chamber 32 such that the pressure generated within
chamber 32 exceeds the pressure seen by chamber 34. As known by those skilled in
the art, the velocity with which a load is to be raised is controlled by the difference in
pressure between Pa, Pb, Ps and Pt. It is to be additionally appreciated that when
raising a specific load, chamber 32 is required to operate against the force of gravity
to handle the load, i.e., the load is "passive", and thus operates an upstream work-port
connecting to pressure source 14. In such a situation, chamber 34 operates as a
downstream work-port connecting fluid flow to reservoir 12. On the other hand,
when lowering a load, the force of gravity assists operation of the chamber 32, i.e., the
load is "overrunning", and thus operates as a downstream work-port, while chamber
34 operates as an upstream work-port,
[0024] At least one of the pressure sensors, 18,24,40 and 48, preferably contains
a temperature sensor (not shown) in order to detect temperature of the pressurized
fluid and provide such data to the controller 56. Having such temperature data,
enables the controller 56 to calculate viscosity of the fluid. As appreciated by those
skilled in the art, with fluid viscosity, as well as position of and pressure drop across
each particular orifice being known, fluid flow across each orifice may be calculated.
The calculated fluid flow across each particular orifice, in combination with
communicated flow rate demand, is employed by controller 56 to regulate fluid flow,
and thus the pressure Ps provided by the pressure source 14. Operation of the
hydraulic actuation system 10 is subject to the maximum fluid flow capacity or
capability of the pressure source 14. Therefore, fluid flow to actuator 28, as well as to
other actuators in an expanded system, is reduced in order to ensure that the
maximum capacity of the pressure source is not exceeded, and the machine operator's
request to handle a particular load is satisfied.
[0025] Figures 2 and 3 depict methods 100 and 200, respectively, for operating
the hydraulic actuation system 10 in the event either pressure sensor 24 or pressure
sensor 40 develops a malfunction. Typically, a loss of data from one of the sensors 24
and 40 results in deactivation of the hydraulic actuation system 10, because with the
loss of control via pressure regulation, control over the fluid flow is similarly lost.
Additionally, with the loss of such data, the capability to recognize whether the load is
passive or overrunning is similarly lost, as is the capability to determine the amount of
pressure Ps required to overcome and translate such a load. Methods 100 and 200, on
the other hand, by putting both chambers 32 and 34 in flow-control mode, i.e., where
fluid flow to both chambers is actively controlled, at a minimum, permit an operator
of the machine to complete the job in progress.
[0026] Method 100 shown in Figure 2 commences with a frame 102 where a
malfunction of the sensor 24 is detected. The malfunction of sensor 24 is detected by
the controller 56 either via registering a loss of pressure signal that is otherwise
continuously communicated to the controller, or via registering a signal that is out of
the expected range. Following frame 102, the method proceeds to frame 104, where
the orifice 38 and orifice 46 are closed. Then, after closing orifices 38 and 46, the
method advances to frame 106, where the pressure source 14 is regulated to generate
fluid flow corresponding to maximum Ps. Maximum Ps is a maximum pressure that
the pressure source 14 is capable of providing,
|0027] From frame 106, the method advances to frame 108, where the difference
between Ps and Pa, i.e., (Ps - Pa), is set to a value that is equivalent to a value within
an attainable range for difference between the two pressures. The set value of (Ps -
Pa) is assumed and assigned in place of an unknown value for (Ps - Pa) for use by the
controller 56. The set value of (Ps - Pa) is chosen based on a recognition that,
although likely not the actual value for (Ps - Pa), the chosen value enables the
controller 56 to continue to regulate the hydraulic actuation system 10, The (Ps - Pa)
value may be set to a mean value or midpoint of the attainable range for the subject
difference, as a default, Following frame 108, the method proceeds to frame 110.
[0028] In frame 110, orifice 22 is regulated by controller 56 in response to the
fluid flow demand, as directed by the operator of the machine. After frame 110, the
method advances to frame 112, where the orifice 54 is regulated by the controller 56
to generate flow through the fourth orifice that is equivalent to the flow demand offset
by the ratio between areas of the first and second chambers 32 and 34. In other
words, the flow at orifice 54 is set to flow demand multiplied by the ratio between
areas of the first and second chambers 32 and 34. The ratio between areas of
chambers 32 and 34 is a known fixed quantity. As a result of implementation of
method 100, in spite of the malfunction of sensor 24, the hydraulic actuation system
10 is controlled to operate actuator 28 and support a load or extend an arm of the
construction machine.
[0029] Method 200 shown in Figure 3 commences with frame 202, where a
malfunction of the sensor 40 is detected. Similar to the malfunction of sensor 24
above, the malfunction of sensor 40 is detected by the controller 56 either via
registering a loss of pressure signal that is otherwise continuously communicated to
the controller, or via registering a signal that is out of the expected range. Following
frame 202, the method proceeds to frame 204, where the orifice 38 and 46 are closed.
After closing orifices 38 and 46, the method advances to frame 206.
[0030] In frame 206, the pressure source 14 is regulated to generate fluid flow
corresponding to Ps > Pa, i.e., such that the fluid pressure generated by pressure
source 14 is greater than the pressure seen at sensor 24. Setting pressure of the
pressure source 14 to greater than the pressure seen at sensor 24 permits to ensure that
the pressure generated by the pressure source 14 will be sufficient to support a load at
the first pressure chamber 32. From frame 206, the method advances to frame 208.
|0031] In frame 208, a value for the difference between Pb and Pt, i.e., (Pb - Pt),
is set to a maximum attainable value for the subject difference. The maximum value
of (Pb - Pt) is assumed and programmed into the controller 56. The maximum value
of (Pb - Pt) is chosen based on a recognition that, although likely not the actual value
for (Pb - Pt), the chosen value enables the controller 56 to continue to regulate the
hydraulic actuation system 10. Following frame 208, the method proceeds to frame
210.
[0032] In frame 210, orifice 22 is regulated by controller 56 in response to the
fluid flow demand, as directed by the operator of the construction machine. After
frame 210, the method advances to frame 212, where the orifice 54 is regulated by the
controller 56 to keep Pa at or below its maximum allowable pressure. Thus, the
method 200 employs the control of pressure Pa to regulate the pressure within the
chamber 34, in what is termed as "cross-axis" control. As a result of implementation
of method 200, and similar to method 100 described above, in spite of the malfunction
of sensor 40, the hydraulic actuation system 10 is controlled to operate actuator 28
and support a load or extend an arm of the construction machine.
[0033] Because methods 100 and 200 are enabled by assigning assumed pressure
differences for controlling the hydraulic actuation system 10, the respective pressures
generated in pressure chambers 32 and 34 are not matched precisely to the handled
load. As a result of employing assumed values to control the operation of hydraulic
actuation system 10, the amount of movement of piston 32 within the actuator 28 and
the velocity with which the piston translates may differ somewhat from the expected
outcome. Such loss of precision typically results in a reduction of the hydraulic
actuation system's operating efficiency. Operation with reduced efficiency
nonetheless maintains the functionality of the construction machine, and permits the
machine to complete a prescribed task despite experiencing a pressure sensor
malfunction.
[0034] While maintaining operation of the hydraulic actuation system 10 despite a
malfunction of either the pressure sensor 24 or the pressure sensor 40, both methods
100 and 200 may provide for a generation of a malfunction signal to the machine's
operator. Such a malfunction signal may be displayed as a visual and/or an audible
alert, preferably on an instrument panel of the subject machine.
[0035] While the best modes for carrying out the invention have been described in
detail, those familiar with the art to which this invention relates will recognize various
alternative designs and embodiments for practicing the invention within the scope of
the appended claims.
We Claim:
1. A method for operating a hydraulic actuation system 10 during a
pressure
sensor malfunction, the hydraulic actuation system 10 including:
a pressure source 14 arranged to supply fluid flow in response to a fluid flow
demand, a reservoir 12 arranged to hold fluid, a first work-port 32 and a second work-
port 34, wherein the pressure source 14 is in fluid communication with the reservoir
12 and the first and second work-ports 32, 34; a valve system capable of controlling
fluid flow having a first orifice 22 arranged between the pressure source 14 and the
first work-port 32, a second orifice 38 arranged between the pressure source 14 and
the second work-port 34, a third orifice 46 arranged between the first work-port 32
and the reservoir 12, and a fourth orifice 54 arranged between the second work-port
34 and the reservoir 12; a pressure sensor system capable of sensing pressure (Ps) of
the fluid supplied by the pressure source 14, pressure (Pa) of the fluid supplied to the
first work-port 32, and pressure (Pb) of the fluid supplied to the second work-port 34;
and a controller 56 arranged to regulate the pressure source 14 and the valve system
based on the fluid flow demand and on determined differences between Ps, Pa, Pb,
and pressure (Pt) of the fluid returned to the reservoir 12;
the method comprising:
detecting a malfunction of solely a sensor 34 arranged to sense Pa;
closing the second and third orifices 38,46;
regulating the pressure source 14 to generate fluid flow corresponding to a
maximum Ps;
assigning a value for the difference between Ps and Pa that is equivalent to a
value within an attainable range for the difference between Ps and Pa;
regulating the first orifice 22 in response to the fluid flow demand; and
regulating the fourth orifice 54 in response to the fluid flow demand, such that
the system continues to operate despite the malfunction of the sensor 24 arranged to
sense Pa.
2. The method according to claim 1, wherein said regulating the fourth
orifice 54 is accomplished by generating flow through the fourth orifice 54 that is
equivalent to the flow demand multiplied by the ratio between areas of the first and
second work-ports 32, 34.
3. The method according to claim 1, further comprising generating a
malfunction signal in response to said detecting a malfunction of the sensor 24
arranged to sense Pa.
4. The method according to claim 1, further comprising:
detecting a malfunction of solely a sensor 40 arranged to sense Pb;
closing the second and third orifices 38,46;
directing the pressure source 14 to generate fluid flow corresponding to Ps >
Pa;
assigning a value for a difference between Pb and Pt that is substantially
equivalent to a maximum attainable value for the difference;
regulating the first orifice 22 in response to the fluid flow demand; and
regulating the fourth orifice 54 in response to the fluid flow demand, such that
the system continues to operate despite the malfunction of the sensor 40 arranged to
sense Pb.
5. The method according to claim 4, wherein said regulating the fourth
orifice is accomplished by holding Pa at or below its maximum value.
6. The method according to claim 4, further comprising generating a
malfunction signal in response to said detecting a malfunction of the sensor 40
arranged to sense Pb.
7. The method according to claim 1, wherein the pressure sensor system
further comprises a pressure sensor 48 capable of sensing pressure Pt.
8. A system for operating a hydraulic actuation system 10 during a
pressure
sensor malfunction, the system including:
a pressure source 14 arranged to supply fluid flow in response to a fluid flow
demand, a reservoir 12 arranged to hold fluid, a first work-port 32 and a second work-
port 34, wherein the pressure source 14 is in fluid communication with the reservoir
12 and the first and second work-ports 32,34; a valve system capable of controlling
fluid flow having a first orifice 22 arranged between the pressure source 14 and the
first work-port 32, a second orifice 38 arranged between the pressure source 14 and
the second work-port 34, a third orifice 46 arranged between the first work-port 32
and the reservoir 12, and a fourth orifice 54 arranged between the second work-port
34 and the reservoir 12; a pressure sensor system capable of sensing pressure (Ps) of
the fluid supplied by the pressure source 14, pressure (Pa) of the fluid supplied to the
first work-port 32, pressure (Pb) of the fluid supplied to the second work-port 34, and
pressure (Pt) of the fluid returned to the reservoir 12; and a controller 56 arranged to
regulate the pressure source 14 and the valve system based on the fluid flow demand
and on determined differences between Ps, Pa, Pb, and Pt;
the controller 56 adapted for:
detecting a malfunction of solely a sensor 24 arranged to sense Pa;
closing the second and third orifices 38,46;
regulating the pressure source 14 to generate fluid flow corresponding to a
maximum Ps;
assigning a value for the difference between Ps and Pa that is equivalent to a
value within an attainable range for the difference between Ps and Pa;
regulating the first orifice 22 in response to the fluid flow demand;
regulating the fourth orifice 54 in response to the fluid flow demand, such that
the hydraulic actuation system 10 continues to operate despite the malfunction of the
sensor 24 arranged to sense Pa; and
generating a malfunction signal in response to said detecting a malfunction of
the sensor 24 arranged to sense Pa;
wherein said regulating the fourth orifice 54 is accomplished by generating
flow through the fourth orifice 54 that is equivalent to the flow demand multiplied by
the ratio between areas of the first and second work-ports 32, 34.
9. The system according to claim 8, wherein the controller 56 is further
adapted for:
detecting a malfunction of solely a sensor 40 arranged to sense Pb;
closing the second and third orifices 38,46;
directing the pressure source 14 to generate fluid flow corresponding to Ps >
Pa;
assigning a value for a difference between Pb and Pt that is substantially
equivalent to a maximum attainable value for the difference;
regulating the first orifice 22 in response to the fluid flow demand; and
regulating the fourth orifice 54 in response to the fluid flow demand, such that
the system 10 continues to operate despite the malfunction of the sensor 40 arranged
to sense Pb.
10. The system according to claim 9, wherein said regulating the fourth
orifice 54 is accomplished by holding Pa at or below its maximum value.

ABSTRACT

A method for operating a hydraulic actuation system 10 during a pressure
sensor malfunction is provided. The hydraulic actuation system 10 includes a pump
14, a reservoir 12, a first work-port 32 and a second work-port 34, a valve system
with individual orifices 22,38,46, 54, a pressure sensor system, and a controller 56
for regulating the hydraulic actuation system 10 based on fluid flow demand and on
determined pressure differences. The method includes detecting a malfunction of a
pressure sensor 22 for the first work-port 32, closing second and third orifices 22,46,
and regulating the pump 14 to generate fluid flow corresponding to maximum
pressure generated by the pump. The method also includes assigning a value for the
difference between pump pressure and the pressure of the subject work-port 32 that is
equivalent to a value within an attainable range for difference between the two
pressures. Furthermore, the method includes regulating a first orifice 22 and a fourth
orifice 54 in response to the fluid flow demand.