CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is being filed on May 6, 2015, as a PCT International Patent
application and claims priority to U.S. Patent Application Serial No. 61/989,215 filed on
May 6, 2014, the disclosure of which is incorporated herein by reference in its entirety.
BACKGROUND
[0002] Work machines, such as fork lifts, wheel loaders, track loaders, excavators,
backhoes, bull dozers, and telehandlers are known. Work machines can be used to move
material, such as pallets, dirt, and/or debris. The work machines typically include a work
implement (e.g., a fork) connected to the work machine. The work implements attached to
the work machines are typically powered by a hydraulic system. The hydraulic system
can include a hydraulic pump that is powered by a prime mover, such as a diesel engine.
In some applications, the hydraulic pump alternately powers both the work functions and
the driving functions of the work machine. In some operational modes of such systems,
excessive or undesirable noise can be generated by the hydraulic pump. Improvements are
desired.
SUMMARY
[0003] A hydraulic pump radiant noise reduction method for a forklift or other work
machine is disclosed. One step includes providing a hydraulic system having a variable
displacement pump in selective fluid communication with a plurality of hydraulic branch
circuits, wherein each of the hydraulic branch circuits has a control valve assembly and
contains hydraulic fluid at a hydraulic fluid pressure. Another step includes determining
that the pump displacement is in a zero displacement position and that an operator is not
demanding flow from any of the hydraulic branch circuits. Yet another step includes
initiating a noise control algorithm that is enabled as long as the pump displacement
remains in the zero displacement position and an operator is not demanding flow from any
of the hydraulic branch circuits. When the noise control algorithm is enabled, the method
includes the step of opening the control valve assembly associated with the hydraulic
branch circuit having the lowest hydraulic fluid pressure in relation to the hydraulic fluid
pressures of all other hydraulic branch circuits while ensuring that all remaining control
valve assemblies are in a closed position. In some implementations, for example, where a
hybrid forklift work machine is provided with a hydraulic pump that powers both the
driving and work functions, the valve associated with the lowest pressure function can be
the valve that is opened when the noise control algorithm is activated. In an alternative
embodiment, a drain valve assembly is provided that is opened when the noise control
algorithm is activated while the remaining valves are placed in or remain in the closed
position.
DESCRIPTION OF THE DRAWINGS
[0004] Non-limiting and non-exhaustive embodiments are described with reference to
the following figures, which are not necessarily drawn to scale, wherein like reference
numerals refer to like parts throughout the various views unless otherwise specified.
[0005] Figure 1 is a schematic view of a work machine having features that are
examples of aspects in accordance with the principles of the present disclosure.
[0006] Figure 2 is a schematic view of a hydraulic system suitable for use in the work
machine shown in Figure 1.
[0007] Figure 3 is a schematic of a modified version of the hydraulic system shown in
Figure 2.
[0008] Figure 4 is a schematic of a modified version of the hydraulic system shown in
Figure 2.
[0009] Figure 5 is a schematic view of an electronic control system for use with the
hydraulic systems shown in Figures 2, 3, and/or 4.
[0010] Figure 6 is a process flow chart showing a method of operation of the hydraulic
system shown in Figure 2, 3, and/or 4.
DETAILED DESCRIPTION
[0011] Various embodiments will be described in detail with reference to the
drawings, wherein like reference numerals represent like parts and assemblies throughout
the several views. Reference to various embodiments does not limit the scope of the
claims attached hereto. Additionally, any examples set forth in this specification are not
intended to be limiting and merely set forth some of the many possible embodiments for
the appended claims.
General Description
[0012] As depicted at Figure 1, a work machine 300 is shown. Work machine 300
includes a work attachment 301 for performing a variety of work tasks. In one
embodiment, work machine 300 is a fork lift truck and work attachment 301 comprises
two forks. However, one skilled in the art will appreciate that work attachment may be any
hydraulically powered work implement.
[0013] Work machine 300 is also shown as including at least one drive wheel 305 and
at least one steer wheel 306. In certain embodiments, one or more drive wheels 305 may
be combined with one or more steer wheels 306. The drive wheels are powered by an
engine 308 in power communication with a pump 12 and a hydraulic motor 312 via a
hydraulic propel circuit 204. Pump 12 is mechanically coupled to the engine 308 while
hydraulic motor 312 is connected to the engine 308 via a hydraulic system 10. Motor 312
is also mechanically coupled to the drive wheel(s) 305 via axles 316, differential 318, and
drive shaft 320.
[0014] In one embodiment, a work circuit 104 and a steering circuit 324 are also in
fluid communication with the hydraulic system 10. The work circuit 104 actuates the
work attachment 301 such that the work tasks can be performed while the steering circuit
324 allows for the work machine 300 to be selectively steered in a desired direction.
Hydraulic System Description
[0015] Referring to Figure 2, a first embodiment of the hydraulic system 10 is
illustrated as a schematic diagram. As shown, hydraulic system 10 includes a pump 12
configured to provide pressurized fluid to at least a first hydraulic branch circuit 100
having a first control valve assembly 102 and a second hydraulic branch circuit 200
having a second control valve assembly 202. In the embodiment shown, pump 12 is
shown as a variable displacement axial pump. However, other types of pumps may be
used for pump 12, such as an over-center pump. As configured, the hydraulic pump 12
includes an inlet (i.e., a low pressure side) that receives hydraulic fluid from a reservoir
14, and the hydraulic pump 12 includes an outlet (i.e., a high pressure side) that is
connected to the first and second control valve assemblies 102, 202 via respective
hydraulic supply lines 18, 19. When the pump 12 is rotated, hydraulic fluid is drawn from
the reservoir 14 into the inlet of the hydraulic pump 12 and expelled from the outlet of the
hydraulic pump 12 at a higher pressure.
[0016] Still referring to Figure 2, the control valve assembly 102 is shown as being
upstream of the first hydraulic circuit 104 which is configured as a work circuit 104, while
the second control valve assembly 202 is shown as being upstream of the second hydraulic
circuit 204 which is configured as a propel circuit 204. Fluid is returned from the circuits
104, 204 by a respective reservoir line 20, 21.
[0017] The work circuit 104 is provided to control and actuate the various work
functions of the work machine via actuators, such as the lift actuator, the tilt actuator, and
the side shift actuator for a work attachment (e.g. forks) of a fork lift truck. One example
of a work circuit 104 is described in US Patent Application Publication US 2012/0204549
entitled CONDITIONAL LOAD SENSE CONTROL, the entirety of which is hereby
incorporated by reference. The work circuit 104 can be configured with one or more valve
sections corresponding to one or more individual work circuit sections that are used to
actuate various functions of a work machine. The work circuit sections can be configured
to activate hydraulic motors and/or hydraulic actuators. For example, the work circuit 104
can include three individual work circuit sections corresponding to lift, tilt, and shift
functions of a fork lift.
[0018] The propel circuit 204 is provided to power the drivetrain of the work machine.
In the embodiment shown, the second hydraulic branch circuit 200 includes an
accumulator 206 that functions to store hydraulic fluid at high pressure for use when the
pump 12 is unavailable or has insufficient capacity to power the drivetrain. In one
embodiment, the propel circuit includes one or more hydraulic motors.
[0019] In the embodiment shown at Figure 1, the first control valve assembly 102 and
the second control valve assembly 202 are configured as two-position, two-way valves
having a closed position A and open position B. When the first control valve assembly
102 is in the open position B, hydraulic fluid is allowed to pass from the pump 12 to the
work circuit 104. Correspondingly, when the first control valve assembly 102 is in the
closed position A, fluid is blocked from flowing from the pump 12 to the work circuit 104
and vice versa. When the second control valve 202 is in the open position B, hydraulic
fluid is allowed to pass from the pump 12 to the propel circuit 204 and/or the accumulator
206. When the second control valve 202 is in the closed position A, hydraulic fluid is
prevented from flowing between the pump and the propel circuit 204 and the accumulator
206. In applications where an accumulator 206 is present in the second hydraulic branch
circuit 200 and the pressure at the second hydraulic circuit is greater than the pressure in
the first hydraulic branch circuit 100, the closed position A of the second control valve
assembly 202 prevents hydraulic fluid from undesirably migrating from the accumulator
206 to the reservoir 14 via the first hydraulic branch circuit 100.
[0020] In one embodiment, the first control valve assembly 102 is provided with a
biasing spring 102a and an actuator 102b. As shown, the biasing spring 102a functions to
bias the first control valve assembly 102 to the closed position A while the actuator 102b
functions to drive the first control valve assembly 102 to the open position B against the
force of the biasing spring 102a. However, it is noted that the biasing and control
functions could be oppositely arranged, if desired, such that the valve 102 is biased to the
open position B and actuated to the closed position A. In one embodiment, the first
control valve assembly 102 is a spool type valve in which the biasing spring 102a and the
actuator 102b act on opposite ends of a spool within a sleeve. In the embodiment shown,
the actuator 102b is a variable force solenoid valve (i.e. a proportional control valve) or
voice coil. However, it is to be understood that the actuator 102b could be a hydraulic
actuator or another type of electric or electro-hydraulic actuator.
[0021] In one embodiment, the second control valve assembly 202 is provided with a
biasing spring 202a and an actuator 202b. As shown, the biasing spring 202a functions to
bias the seond control valve assembly 202 to the open position B while the actuator 102b
functions to drive the second control valve assembly 202 to the closed position A against
the force of the biasing spring 202a. However, it is noted that the biasing and control
functions could be oppositely arranged, if desired, such that the valve 202 is biased to the
closed position and actuated to the open position. In one embodiment, the second control
valve assembly 202 is a spool type valve in which the biasing spring 202a and the actuator
202b act on opposite ends of a spool within a sleeve. In the embodiment shown, the
actuator 202b is a variable force solenoid valve (i.e. a proportional control valve) or voice
coil. However, it is to be understood that the actuator 202b could be a hydraulic actuator
or another type of electric or electro-hydraulic actuator.
[0022] As shown in Figure 3, the hydraulic system 10 may include any number (“x”)
of desired hydraulic circuits, as represented by hydraulic circuit 604, for example up to
twenty hydraulic circuits. In one embodiment, one of the additional hydraulic circuits 604
can be the steering circuit 324 of the work machine 300. Hydraulic circuit 604 may be
provided with a control valve assembly 602 and a pressure sensor 610 that are similar to
those described in relation to those shown for the first and second branch circuits 100, 200
at Figure 1. For example, control valve assembly 602 may include an actuator 602b and a
biasing spring 602a to move the valve assembly between a closed position A and an open
position B. The hydrauclic circuit(s) 604 may also be placed in fluid communication with
the pump 12 via a supply line 23 and placed in fluid communication with the reservoir 14
via drain line 25. It is noted that the schematic shown at Figure 3 shows the second
hydraulic circuit 204 without the use of the accumulator 206 and that the control valve
assemblies 102, 202, 602 are biased to the closed postion A by their respective biasing
springs 102a, 202a, 602a.
[0023] With reference to Figure 4, the hydraulic system 10 may further include a
dedicated drain valve assembly 702. As shown, the drain valve assembly 702 is
configured as a two-position, two-way valve having a closed position A and and open
position B. When the drain valve assembly 702 is in the open position B, hydraulic fluid
is allowed to pass directly from the pump 12 to the reservoir 14. Correspondingly, when
the drain valve assembly 702 is in the closed position A, fluid is blocked from flowing
from the pump 12 to the reservoir via the drain valve assembly 702.
[0024] In one embodiment, the drain valve assembly 702 is provided with a biasing
spring 702a and an actuator 702b. As shown, the biasing spring 702a functions to bias the
drain valve assembly 702 to the closed position A while the actuator 702b functions to
drive the drain valve assembly 702 to the open position B against the force of the biasing
spring 702a. However, it is noted that the biasing and control functions could be
oppositely arranged, if desired, such that the valve 702 is biased to the open position B and
actuated to the closed position A. In one embodiment, the drain valve assembly 702 is a
spool type valve in which the biasing spring 702a and the actuator 702b act on opposite
ends of a spool within a sleeve. In the embodiment shown, the actuator 702b is a variable
force solenoid valve (i.e. a proportional control valve) or voice coil. However, it is to be
understood that the actuator 702b could be a hydraulic actuator or another type of electric
or electro-hydraulic actuator.
The Electronic Control System
[0025] The hydraulic system 10 operates in various modes depending on demands
placed on the work machine 300 (e.g., by an operator). The electronic control system
monitors and allows for the various modes to be initiated at appropriate times. An
electronic controller 50 monitors various sensors and operating parameters of the
hydraulic system 10 to configure the hydraulic system 10 into the most appropriate mode
of operation.
[0026] Referring to Figure 5, the electronic controller 50 is schematically shown as
including a processor 50A and a non-transient storage medium or memory 50B, such as
RAM, flash drive or a hard drive. Memory 50B is for storing executable code, the
operating parameters, the input from the operator interface while processor 50A is for
executing the code. Electronic controller 50 is also shown as having a number of inputs
and outputs that may be used for implementing the work circuit operational modes. As
shown, the electronic controller 50 includes a first hydraulic circuit pressure input 500, a
second hydraulic circuit pressure input 502, and up to “X” hydraulic circuit pressure
inputs 504. Electronic controller is also shown as having a plurality of work machine
inputs 506 which may include: one or more levers 62 such as a lift lever 62a, a tilt lever
62b, and a side shift lever 62c; an accelerator pedal position 63; and a steering wheel
position 65. In one embodiment, the lever position input(s) is a direct digital signal from
an electronic lever. The work lever 62 provides a user indication to the controller 50 that a
work operation by hydraulic actuator(s) associated with the work circuit 104 is desired.
One skilled in the art will understand that many other inputs are possible. For example,
measured engine speed may be provide as a direct input into the electronic controller 50 or
may be received from another portion of the control system via a control area network
(CAN). The measured pump displacement, for example via a displacement feedback
sensor, may also be provided. In one embodiment, the electronic controller 50 is
configured to include all required operational inputs for the various circuits 104, 204, 604.
[0027] Still referring to Figure 5, a number of outputs from the electronic controller 50
are shown. One output is a pump output command 510 which is for adjusting the output
pressure of the pump 12. In one embodiment, pump pressure output can be controlled by
adjusting the angle of the swash plate in a variable displacement axial piston pump.
Additional outputs shown are the first control valve assembly position command 512; the
second control valve assembly position command 514; the “X” control valve assembly
position command 516; and the drain valve assembly position command 518. Other
outputs are possible as well. In one embodiment, the electronic controller 50 is configured
to include all required operational outputs for the various circuits 104, 204, 604.
[0028] The electronic controller 50 may also include a number of maps or algorithms
to correlate the inputs and outputs of the controller 50. For example, the controller 50 may
include an algorithm to control the position of the valves 102, 202, 602, and/or 702 based
on predicted noise output levels and measured pressures at sensors 110, 210, and/or 610,
as described further in the Method of Operation section below.
[0029] The electronic controller 50 may also store a number of predefined and/or
configurable parameters and offsets for determining when each of the modes is to be
initiated and/or terminated. As used herein, the term “configurable” refers to a parameter
or offset value that can either be selected in the controller (i.e. via a dipswitch) or that can
be adjusted within the controller.
Method of Operation
[0030] Referring to Figures 6, method 1000 for operating the control valve assemblies
102, 202, 602, and/or 702 is shown. It is noted that although Figure 6 diagrammatically
shows the method steps in a particular order, the methods are not necessarily intended to
be limited to being performed in the shown order. Rather at least some of the shown steps
may be performed in an overlapping manner, in a different order and/or simultaneously.
[0031] In a first step 1002 of the method 1000, the electronic controller 50 determines
that the hydraulic pump 12 is in a zero displacement state, meaning that the pump 12 has
either been commanded to produce no output flow or that the various control valves are at
zero flow and/or are in a closed position because the operator is not requesting an
operation. It is noted that in actual implementations of a hydraulic system utilizing a
variable displacement axial piston pump, a completely or true zero flow state at the pump
12 does not occur and that some flow is produced by the pump in this condition.
Therefore, the terms “zero output position” and “zero displacement position” include those
positions of the hydraulic pump that are near to no displacement or flow but where a slight
positive hydraulic flow is still generated by the pump 12. Because of this circumstance,
and because no relief valves are shown as being provided in the hydraulic system 10, at
least one of the control valves 102, 202, 602, and/or 702 must be commanded at least
partially open to allow the minimal flow from the pump 12 to flow back to the reservoir
14.
[0032] At a step 1004, a determination is made as to whether the operator is
demanding flow from any of the hydraulic branch circuits 100, 200, 600. In one
embodiment, this determination can be made based on the above described inputs 506 to
the electronic controller 50 wherein the inputs indicate that no function at the hydraulic
circuit 104, 204, 604 of the work machine 300 is being requested. If flow is being
demanded from any of the branch circuits 100, 200, 600, then the method returns to step
1002.
[0033] At a step 1006, a low noise control or noise reduction algorithm is initiated
within the controller 50. The noise reduction algorithm will remain active as long as the
pump 12 remains in a zero displacement state and no demand from the operator is
detected. The noise reduction algorithm is for reducing noise at the pump 12 caused by
high pressure differential between the hydraulic branch circuits and the inlet side of the
pump 12. It is noted that radiant noise generated by the pump 12 increases as the
differential pressure across the inlet and outlet of the pump 12 increases. Accordingly,
when the pump 12 is exposed to a branch circuit at a relatively high pressure, the noise
output of the pump will be greater than the noise produced when the pump 12 is exposed
to a branch circuit at a relatively lower pressure.
[0034] At a step 1008, the control valve associated with the lowest branch line
pressure is opened to allow the minimal pump flow to return to the reservoir while
ensuring that all remaining control valves for branch circuits served by the pump are in a
closed position. The closed position can be accomplished by actuating the valve assembly
or assemblies to the closed position or by providing a valve that is biased to the closed
position. In one embodiment, the lowest branch line pressure can be determined by
comparing the inputs from the pressure sensors 110, 210, and/or 610. As stated above,
opening the control valve associated with the lowest pressure will result in the lowest
noise generation at the pump 12. For the particular configuration shown in Figure 2,
which includes an accumulator 206 to maintain a high pressure, the first hydraulic branch
circuit 100 would normally be expected to be at a lower pressure than the second hydraulic
branch circuit 200. As such, the first control valve assembly 102 may be chosen as a
default valve assembly to open once the noise reduction control algorithm is implemented
instead of or in addition to performing a direct comparison of branch circuit pressures.
For the particular configuration shown in Figure 3, which includes an additional drain
valve assembly 702, an alternate step 1008a may be implemented rather than step 1008.
In step 1008a, the drain valve assembly 702 is opened to allow the minimal pump flow to
return to reservoir once the noise reduction algorithm has been implemented at step 1006,
wherein the valve assemblies associated with the hydraulic branch circuits are commanded
to the closed position or left in the default closed position.
[0035] The above described method can result in a substantial reduction in the radiant
sound output from the hydraulic pump, as compared to typical hydraulic systems which do
not implement any type of noise reduction control strategy.
[0036] The various embodiments described above are provided by way of illustration
only and should not be construed to limit the claims attached hereto. Those skilled in the
art will readily recognize various modifications and changes that may be made without
following the example embodiments and applications illustrated and described herein, and
without departing from the true spirit and scope of the disclosure.

What is claimed is:
1. A hydraulic pump radiant noise reduction method including the steps of:
(a) providing a hydraulic system having a variable displacement pump in selective
fluid communication with a plurality of hydraulic branch circuits, each of the
hydraulic branch circuits having a control valve assembly and containing
hydraulic fluid at a hydraulic fluid pressure;
(b) determining that the pump displacement is in a zero displacement position and
that an operator is not demanding flow from any of the hydraulic branch
circuits;
(c) initiating a noise control algorithm that is enabled as long as the pump
displacement remains in the zero displacement position and an operator is not
demanding flow from any of the hydraulic branch circuits; and
(d) the noise control algorithm including, opening the control valve assembly
associated with the hydraulic branch circuit having the lowest hydraulic fluid
pressure in relation to the hydraulic fluid pressures of all other hydraulic
branch circuits while ensuring that all remaining control valve assemblies are
in a closed position.
2. The hydraulic pump radiant noise reduction method of claim 1, wherein the step of
opening the control valve assembly associated with the hydraulic branch circuit having
the lowest hydraulic fluid pressure includes opening a control valve assembly that is
predetermined as having the lowest hydraulic fluid pressure.
3. The hydraulic pump radiant noise reduction method of claim 1, wherein the step of
opening the control valve assembly associated with the hydraulic branch circuit having
the lowest hydraulic fluid pressure includes comparing the hydraulic pressures at each
branch circuit.
4. The hydraulic pump radiant noise reduction method of claim 1, wherein the step of
providing a hydraulic system includes providing a pressure sensor for each of the
plurality of hydraulic branch circuits.
5. The hydraulic pump radiant noise reduction method of claim 1, wherein the step of
providing a hydraulic system includes providing a first branch circuit and a second
branch circuit, wherein the second branch circuit includes an accumulator.
6. The hydraulic pump radiant noise reduction method of claim 5, wherein the step of
providing a hydraulic system includes providing a first control valve assembly for the
first branch circuit and providing a second control valve assembly for the second
branch circuit, wherein the first control valve assembly is biased to a closed position
and wherein the second control valve assembly is biased to an open position.
7. The hydraulic pump radiant noise reduction method of claim 6, wherein the step of
opening the control valve assembly associated with the hydraulic branch circuit having
the lowest hydraulic fluid pressure includes opening the first control valve assembly.
8. The hydraulic pump radiant noise reduction method of claim 4, wherein the step of
providing a hydraulic system includes providing a first branch circuit, a second branch
circuit, and a third branch circuit.
9. The hydraulic pump radiant noise reduction method of claim 5, wherein the step of
providing a hydraulic system includes providing a first control valve assembly for the
first branch circuit, providing a second control valve assembly for the second branch
circuit, and providing a third control valve assembly for a third branch circuit, wherein
the first, second, and third control valve assemblies are biased to a closed position.
10. A hydraulic pump radiant noise reduction method including the steps of:
(a) providing a hydraulic system having a variable displacement pump in selective
fluid communication with a plurality of hydraulic branch circuits, each of the
hydraulic branch circuits having a control valve assembly and containing
hydraulic fluid at a hydraulic fluid pressure;
(b) providing a drain valve assembly positioned and arranged to selectively place
the variable displacement pump in fluid communication with a hydraulic fluid
reservoir;
(c) determining that the pump displacement is in a zero displacement position and
that an operator is not demanding flow from any of the hydraulic branch
circuits;
(d) initiating a noise control algorithm that is enabled as long as the pump
displacement remains in the zero displacement position and an operator is not
demanding flow from any of the hydraulic branch circuits; and
(e) the noise reduction algorithm including, opening the drain valve assembly
while ensuring that the control valve assemblies associated with the hydraulic
branch circuits are in the closed position.
11. The hydraulic pump radiant noise reduction method of claim 10, wherein the step of
providing a hydraulic system includes providing a first control valve assembly for a
first branch circuit and providing a second control valve assembly for a second branch
circuit, wherein the first and second control valve assemblies are biased to a closed
position.
12. The hydraulic pump radiant noise reduction method of claim 11, wherein the step of
providing a hydraulic system includes providing a third control valve assembly for a
third branch circuit, wherein the third valve assembly is biased to a closed position.
13. A forklift hydraulic pump radiant noise reduction method including the steps of:
(a) providing a forklift having a hydraulic system having a variable output pump in
selective fluid communication with:
i. a first hydraulic branch circuit including a first control valve assembly
and a work circuit for powering at least lifting and tilt functions of the
forklift; and
ii. a second hydraulic branch circuit including a second control valve
assembly, an accumulator, and a propel circuit for powering driving
functions of the forklift; and
(b) determining that the pump output is in a near zero flow state and that an
operator is not demanding flow from any of the hydraulic branch circuits;
(c) initiating a noise control algorithm that is enabled as long as the pump
displacement remains in the zero displacement position and the operator is not
demanding flow from any of the hydraulic branch circuits; and
(d) the noise control algorithm including, opening the first control valve to allow
minimal pump flow from the pump to return to a reservoir while ensuring that
th d t l l bl i i l d iti
14. The forklift hydraulic pump radiant noise reduction method of claim 13, wherein the
step of providing a forklift having a hydraulic system includes the first control valve
assembly being biased to a closed position and the second control valve assembly
being biased to an open position.
15. The forklift hydraulic pump radiant noise reduction method of claim 14, wherein the
first and second control valve assemblies each include a biasing spring and an actuator.
16. The forklift hydraulic pump radiant noise reduction method of claim 15, wherein each
actuator of the first and second control valves is a solenoid type control valve.