U.S. patent application number 13/866757 was filed with the patent office on 2013-10-24 for hydraulic system.
This patent application is currently assigned to J.C. BAMFORD EXCAVATORS LIMITED. The applicant listed for this patent is J.C. BAMFORD EXCAVATORS LIMITED. Invention is credited to Harish Narotham.
Application Number | 20130280097 13/866757 |
Document ID | / |
Family ID | 46261777 |
Filed Date | 2013-10-24 |
United States Patent
Application |
20130280097 |
Kind Code |
A1 |
Narotham; Harish |
October 24, 2013 |
HYDRAULIC SYSTEM
Abstract
A method includes providing a hydraulic pump with an outlet, a
main orifice having an inlet communicating with the pump outlet,
and a main orifice outlet. Further provided are a flow orifice, an
amplification orifice, and an amplification orifice outlet, means
for generating an output signal representative of a fluid pressure,
and a pump controller for controlling the hydraulic pump in
response to the output signal. The flow orifice and the
amplification orifices each define an area, with these areas
defining a ratio, and with the main orifice and the ratio being
variable. The method includes operating the system in a first mode
so as to define a first mode ratio and operating the system in a
second mode so as to define a second mode ratio, so that the ratio
is controlled differently in the first mode and the second
mode.
Inventors: |
Narotham; Harish;
(Uttoxeter, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
J.C. BAMFORD EXCAVATORS LIMITED |
Uttoxeter |
|
GB |
|
|
Assignee: |
J.C. BAMFORD EXCAVATORS
LIMITED
Uttoxeter
GB
|
Family ID: |
46261777 |
Appl. No.: |
13/866757 |
Filed: |
April 19, 2013 |
Current U.S.
Class: |
417/1 |
Current CPC
Class: |
F15B 11/165 20130101;
F15B 2211/50536 20130101; F15B 2211/6051 20130101; F15B 2211/651
20130101; F15B 2211/20546 20130101; F15B 2211/6058 20130101; F15B
11/168 20130101; F15B 2211/20538 20130101; F15B 2211/253 20130101;
F15B 2211/40507 20130101; F15B 2211/40515 20130101; F15B 2211/653
20130101; F04B 49/00 20130101 |
Class at
Publication: |
417/1 |
International
Class: |
F04B 49/00 20060101
F04B049/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 24, 2012 |
GB |
1207161.9 |
Claims
1. A method of operating a hydraulic system including providing a
hydraulic pump having a pump outlet, a main orifice having a main
orifice inlet in fluid communication with the pump outlet and a
main orifice outlet for supplying pressurized fluid to a service, a
flow orifice having a flow orifice inlet for sensing a pressure
representative of a pressure at the pump outlet and a flow orifice
outlet, an amplification orifice having an amplification orifice
inlet in fluid communication with the flow orifice outlet and an
amplification orifice outlet for sensing a pressure representative
of a pressure at a service, means for generating an output signal
representative of a fluid pressure between the flow orifice outlet
and the amplification orifice inlet, and a pump controller for
controlling the hydraulic pump in response to the output signal,
the flow orifice defining a flow orifice cross section area and the
amplification orifice defining an amplification orifice cross
section area, the flow orifice cross section area and the
amplification orifice cross section area defining a ratio, in which
the main orifice is variable and the ratio is variable, the method
further comprising the steps of operating the system in a first
mode so as to define a first mode ratio regime and operating the
system in a second mode so as to define a second mode ratio regime,
so that the first mode ratio regime is different to the second mode
ratio regime.
2. A method as defined in claim 1 wherein when operating the system
in the first mode the first mode ratio regime is to have a fixed
ratio.
3. A method as defined in claim 2 wherein the first mode ratio
regime fixes the ratio at one of greater than 1 and less than 1 and
equal to 1.
4. A method as defined in claim 1 wherein when operating the system
in the first mode the first mode ratio regime is to have a variable
ratio.
5. A method as defined in claim 4 wherein the variable ratio
excludes a ratio of one of greater than 1 and less than 1.
6. A method as defined in claim 1 wherein when operating the system
in the second mode the second mode ratio regime is to have a fixed
ratio.
7. A method as defined in claim 1 wherein when operating the system
in the second mode the second mode ratio regime is to have a
variable ratio.
8. A method as defined in claim 1, the method further comprising
the steps of operating the system in a third mode so as to define a
third mode ratio regime so that the ratio is controlled differently
in the first mode and the second mode and the third mode wherein
when operating the system in the third mode the third mode ratio
regime is to have a fixed ratio.
9. A method as defined in claim 1, the method further comprising
the steps of operating the system in a third mode so as to define a
third mode ratio regime so that the ratio is controlled differently
in the first mode and the second mode and the third mode wherein
when operating the system in the third mode the third mode ratio
regime is to have a variable ratio.
10. A method as defined in claim 1 wherein the amplification
orifice outlet is in fluid communication with a service.
11. A method as defined in claim 1 in which the flow orifice is
variable.
12. A method as defined in claim 11 in which the amplification
orifice is variable.
13. A method as defined in claim 1 in which the flow orifice is
fixed.
14. A method as defined in claim 1 in which the amplification
orifice is fixed.
15. A method as defined in claim 1 wherein the hydraulic pump is a
variable displacement hydraulic pump having a pump margin pressure
and the controller is configured to vary a margin pressure of the
main orifice relative to the pump margin pressure in response to
the output signal.
16. A method as defined in claim 1 in which the hydraulic pump is a
fixed displacement hydraulic pump, having a pump margin pressure
defined by a bypass regulator valve and the controller is
configured to vary a margin pressure of the main orifice relative
to the pump margin pressure in response to the output signal.
17. A method as defined in claim 15 wherein the controller is
configured to increase the margin pressure of the main orifice
relative to the pump margin pressure in response to the output
signal.
18. A hydraulic system including a hydraulic pump having a pump
outlet, a main orifice having a main orifice inlet in fluid
communication with the pump outlet and a main orifice outlet for
supplying pressurized fluid to a service, a flow orifice having a
flow orifice inlet for sensing a pressure representative of a
pressure at the pump outlet and a flow orifice outlet, an
amplification orifice having an amplification orifice inlet in
fluid communication with the flow orifice outlet and an
amplification orifice outlet for sensing a pressure representative
of a pressure at a service, means for generating an output signal
representative of a fluid pressure between the flow orifice outlet
and the amplification orifice inlet, and a pump controller for
controlling the hydraulic pump in response to the output signal,
the flow orifice defining a flow orifice cross section area and the
amplification orifice defining an amplification orifice cross
section area, the flow orifice cross section area and the
amplification orifice cross section area defining a ratio, in which
the main orifice is variable and the ratio is variable, the main
orifice defining a main orifice margin pressure, the system being
configured to vary the main orifice margin pressure by varying the
ratio.
19. A hydraulic system as defined in claim 18 wherein the pump
defines a pump margin pressure and the system is configured to vary
the main orifice margin pressure relative to the pump margin
pressure.
20. A hydraulic system as defined in claim 19 wherein the main
orifice margin pressure is greater than the pump margin pressure.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a hydraulic system, in
particular a hydraulic system used on working machines.
BACKGROUND OF THE INVENTION
[0002] A typical working machine may include a hydraulic system
having a hydraulic pump and one or more hydraulically operated
services (such as actuators) coupled to the hydraulic pump. One or
more control valves are used to control the supply of hydraulic
fluid from the hydraulic pump to the or each actuator. Thus, an
operator may use a control interface to control operation of the
one or more control valves to cause actuation of one or more of the
actuators.
[0003] The actuators may be coupled to parts of the working
machine. For example, the actuation of an actuator may cause
movement of a working arm of the working machine.
[0004] Known load sensing hydraulic systems aim to keep a constant
flow for a given position of a control valve, in particular for a
given position of a spool of a directional control spool valve.
This is done by maintaining a constant pressure difference known as
(valve) margin pressure, across the orifice made by the spool.
[0005] The associated pump has a control valve that automatically
keeps the pump pressure and flow at a level needed to fulfill the
system load and flow needs. When none of the hydraulic circuits are
being used the pump will be operating at a "stand by" pressure,
typically be somewhere the range 20-30 bar. When a hydraulic
service is being used a signal representative of the pressure
demanded at the service is sent to the pump control valve which
then controls the pump to operate at the required pump pressure and
flow. The pump outlet pressure will typically be somewhere in the
range 20-30 bar above the pressure at the service and the
difference between the pump supply pressure and the service
pressure is called the pump margin pressure. In known load sensing
systems the pump margin pressure and the valve margin pressures are
usually identical (ignoring any line losses).
[0006] On a variable displacement hydraulic pump the margin
pressure is set by a load sense controller bias spring. On a fixed
displacement hydraulic pump the margin pressure is set by a bypass
regulator valve bias spring. It is not possible to adjust the
spring pressure of the load sense controller bias spring or the
bypass regulator valve bias spring whilst the machine is in
operation i.e. whilst the machine is being used and as such the
spring pressure is fixed whilst the machine is being used.
[0007] Typically a service will react more quickly with a higher
valve margin pressure than with a lower valve margin pressure. A
higher margin pressure can be advantageous in some circumstances,
for example when a loading shovel is being used to load loose
material, such as earth. However, under other circumstances a
higher margin pressure can be disadvantageous. For example, where
an operator needs to carefully control the position of a service.
With a higher margin pressure the service can react too quickly to
operator inputs making precise control of the service difficult.
Additionally, higher margin pressures for low flow requirements
represent an unnecessary energy loss. An example where careful
control of a service is required would be operative of a loading
shovel during a grading operation (i.e. an operation where a ground
surface is leveled off or graded by taking a thin skim off the
ground). In such prior art systems the margin pressure has to be
set at a compromise.
[0008] Other prior art has attempted to vary the margin pressure at
the pump, and so affect the valve margin pressure to offer
additional levels of flow control, but they suffer from a lack of
range (i.e. they start at the pre-set level and allow only a
gradual reduction in margin pressure, towards zero, by offsetting
the spring load by electrical solenoid or hydraulic pilot pressure
means.
[0009] Operation of the hydraulic pump consumes fuel (the hydraulic
pump is typically coupled to an engine of the working machine which
drives the hydraulic pump). Therefore, there is a desire to operate
the hydraulic pump and valves as efficiently as possible.
[0010] There is also a desire to provide hydraulic fluid quickly
with minimal transmission losses when it is required to avoid any
significant lag between, for example, an operator using a control
interface to cause actuation of an actuator and the actuator
actuating as a result.
[0011] The distribution of hydraulic fluid between a plurality of
control valves and associated actuators is difficult as, for
example, the termination of the operation of one actuator can have
a significant impact on the pressure of the hydraulic fluid in the
hydraulic system and, hence, the operation of the other actuators.
There is a desire to reduce the unwanted impact of changes in the
demand for hydraulic fluid on the operation of actuators of a
hydraulic system.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is to overcome one or
more problems associated with the prior art.
[0013] Thus, according to one aspect of the present invention there
is provided a method of operating a hydraulic system including
providing a hydraulic pump having a pump outlet, a main orifice
having a main orifice inlet in fluid communication with the pump
outlet and a main orifice outlet for supplying pressurized fluid to
a service, a flow orifice having a flow orifice inlet for sensing a
pressure representative of a pressure at the pump outlet and a flow
orifice outlet, an amplification orifice having an amplification
orifice inlet in fluid communication with the flow orifice outlet
and an amplification orifice outlet for sensing a pressure
representative of a pressure at a service, means for generating an
output signal representative of a fluid pressure between the flow
orifice outlet and the amplification orifice inlet, and a pump
controller for controlling the hydraulic pump in response to the
output signal, the flow orifice defining a flow orifice cross
section area and the amplification orifice defining an
amplification orifice cross section area, the flow orifice cross
section area and the amplification orifice cross section area
defining a ratio, in which the main orifice is variable and the
ratio is variable, the method further comprising the steps of
operating the system in a first mode so as to define a first mode
ratio regime and operating the system in a second mode so as to
define a second mode ratio regime, so that the first mode ratio
regime is different to the second mode ratio regime.
[0014] The method may include operating the system in the first
mode when the first mode ratio regime is to have a fixed ratio.
[0015] The method may include the first mode ratio regime which
fixes the ratio at greater than 1 or less than 1 or equal to 1.
[0016] The method may include operating the system in the first
mode when the first mode ratio regime is to have a variable
ratio.
[0017] The method may include the variable ratio including a ratio
of greater than 1 and/or including a ratio of less than 1 and/or
including a ratio equal to 1.
[0018] The method may include the variable ratio excluding a ratio
of greater than 1 or wherein the variable ratio excluding a ratio
of less than 1.
[0019] The method may include operating the system in the second
mode when the second mode ratio regime is to have a fixed
ratio.
[0020] The method may include the second mode ratio being greater
than 1 or less than 1, or equal to 1.
[0021] The method may include operating the system in the second
mode when the second mode ratio regime is to have a variable
ratio.
[0022] The method may include having a variable ratio which
includes a ratio of greater than 1 and/or includes a ratio of less
than 1 and/or includes a ratio equal to 1.
[0023] The method may include having a variable ratio which
excludes a ratio of greater than 1 or wherein the variable ratio
excludes a ratio of less than 1.
[0024] The method may further comprise the steps of operating the
system in a third mode so as to define a third mode ratio regime so
that the ratio is controlled differently in the first mode and the
second mode and the third mode wherein when operating the system in
the third mode the third mode ratio regime is to have a fixed
ratio.
[0025] The method may include the third mode ratio being greater
than 1 or less than 1, or equal to 1.
[0026] The method may further comprise the steps of operating the
system in a third mode so as to define a third mode ratio regime so
that the ratio is controlled differently in the first mode and the
second mode and the third mode wherein when operating the system in
the third mode the third mode ratio regime is to have a variable
ratio.
[0027] The method may include the variable ratio including a ratio
of greater than 1 and/or including a ratio of less than 1 and/or
including a ratio equal to 1.
[0028] The method may include the variable ratio excluding a ratio
of greater than 1 or wherein the variable ratio excludes a ratio of
less than 1.
[0029] The method may include the amplification orifice outlet is
in fluid communication with a service.
[0030] The method may include the flow orifice being variable.
[0031] The method may include the amplification orifice being
variable.
[0032] The method may include the flow orifice being fixed.
[0033] The method may include the amplification orifice being
fixed.
[0034] The method may include the main orifice being variable only
between a first position and a second position.
[0035] The method may include the flow orifice being variable only
between a first position and a second position.
[0036] The method may include the amplification orifice being
variable only between a first position and a second position.
[0037] The method may include the first position being a closed
position.
[0038] The method may include the main orifice being variable
between a first position, a second position and a third
position.
[0039] The method may include the flow orifice being variable
between a first position, a second position and a third
position.
[0040] The method may include the amplification orifice being
variable between a first position, a second position and a third
position.
[0041] The method may include the first position being a closed
position.
[0042] The method may include the main orifice being continuously
variable.
[0043] The method may include the flow orifice being continuously
variable.
[0044] The method may include the amplification orifice being
continuously variable.
[0045] The method may include the hydraulic pump being a variable
displacement hydraulic pump having a pump margin pressure and the
controller is configured to vary a margin pressure of the main
orifice relative to the pump margin pressure in response to the
output signal.
[0046] The method may include the hydraulic pump is a fixed
displacement hydraulic pump, having a pump margin pressure defined
by a bypass regulator valve and the controller is configured to
vary a margin pressure of the main orifice relative to the pump
margin pressure in response to the output signal.
[0047] The method may include the controller being configured to
increase the margin pressure of the main orifice relative to the
pump margin pressure in response to the output signal.
[0048] According to a further aspect of the present invention there
is provided a hydraulic system including a hydraulic pump having a
pump outlet, a main orifice having a main orifice inlet in fluid
communication with the pump outlet and a main orifice outlet for
supplying pressurized fluid to a service, a flow orifice having a
flow orifice inlet for sensing a pressure representative of a
pressure at the pump outlet and a flow orifice outlet, an
amplification orifice having an amplification orifice inlet in
fluid communication with the flow orifice outlet and an
amplification orifice outlet for sensing a pressure representative
of a pressure at a service, means for generating an output signal
representative of a fluid pressure between the flow orifice outlet
and the amplification orifice inlet, and a pump controller for
controlling the hydraulic pump in response to the output signal,
the flow orifice defining a flow orifice cross section area and the
amplification orifice defining an amplification orifice cross
section area, the flow orifice cross section area and the
amplification orifice cross section area defining a ratio, in which
the main orifice is variable and the ratio is variable, the main
orifice defining a main orifice margin pressure, the system being
configured to vary the main orifice margin pressure by varying the
ratio.
[0049] The hydraulic system may include the pump defining a pump
margin pressure and the system being configured to vary the main
orifice margin pressure relative to the pump margin pressure.
[0050] The hydraulic system may include the main orifice margin
pressure being greater than the pump margin pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] Aspects of embodiments of the present invention as
described, by way of example, with reference to the accompanying
drawings, in which:
[0052] FIG. 1 shows a working machine incorporating a hydraulic
system according to the present invention;
[0053] FIG. 2 shows an embodiment of a hydraulic system according
to the present invention,
[0054] FIG. 3 shows a hydraulic system according to the present
invention, and
[0055] FIG. 4 shows a hydraulic system according to the present
invention.
[0056] With reference to FIG. 1, there is shown a working machine
10.
DETAILED DESCRIPTION
[0057] The working machine 10 may be a machine as generally
depicted in FIG. 1; however, it will be appreciated that
embodiments of the present invention may be used in relation to
other types of working machine and the machine depicted in FIG. 1
is merely shown by way of example.
[0058] The working machine 10 includes a main body 12 which may
include a cab 14 mounted thereon. The main body 12 of the machine
carries an engine 16. The main body 12 may include a ground
engaging arrangement 18. The ground engaging arrangement may
comprise, for example, a plurality of wheels mounted on a plurality
of axles and/or may comprise one or more endless tracks. The ground
engaging arrangement 18 is coupled to the engine 16 which is
configured to drive the ground engaging arrangement 18 with respect
to a ground surface to cause movement of the main body across the
ground surface.
[0059] The working machine 10 may include one or more working arms
20 on which may be mounted respective working tools or implements
22. The working machine may include two working arms 20, for
example, as depicted in FIG. 1. The or each working arm 20 may
comprise a plurality of arm sections coupled to each other--for
example, with the distal end of one arm section coupled in a
pivotable configuration to a proximal end of another arm section.
The or each working arm 20, or a part thereof, may be configured
for movement with respect to the main body 12 of the working
machine 10. A working arm 20 may comprise a boom coupled to a
dipper arm.
[0060] Movement of the or each working arm, or part thereof, may be
driven by a respective service such as an actuator 24 which may be
a hydraulic actuator 24.
[0061] Other services may be provided to drive movement of other
components of the working machine 10.
[0062] A hydraulic system 30 (see FIG. 2) is provided to control
and drive a hydraulic service of the working machine such as one or
more of the or each actuator 24 of the working machine 10.
[0063] Hydraulic system 30 includes a hydraulic pump 32 driven by
the engine and having a pump outlet 60 and a pump inlet 65 in fluid
communication with a source of hydraulic fluid 34 in the form of a
tank. The hydraulic pump supplies pressurized fluid to a hydraulic
service (in this case an actuator 24) primarily via main orifice 43
as described below.
[0064] The hydraulic system has a main fluid path 61 and a
secondary fluid path 62. The main fluid path is in fluid
communication with the pump outlet 60 and includes a main orifice
43. The secondary fluid path 62 is in parallel with the main
orifice 43. The secondary fluid path includes a flow (or pilot)
orifice 44 and an amplification orifice 45 in series with the flow
orifice. Means 63 is capable of generating an output signal
representative of the fluid pressure in the secondary fluid path 62
between the flow orifice 44 and the amplification orifice 45 in
this case means 63 is a port connected to pressure sensing line 66.
A pump controller 64 is capable of controlling the pump flow in
response to the output signal. The main orifice 43 is variable and
at least one of the flow orifice 44 and amplification orifice 45 is
a variable orifice.
[0065] Pump 32 may be a variable displacement pump or it may be a
fixed displacement pump.
[0066] When the pump 32 is a variable displacement pump the pump
controller 64 may act to vary the pump flow. For example where pump
32 is a variable displacement swash plate pump then the pump
controller 64 may act to vary the angle of the swash plate, thereby
varying the pump flow.
[0067] Where the pump 32 is a fixed displacement pump the fixed
displacement pump may include a bypass valve through which excess
fluid flow can pass on route to a reservoir (or tank) of hydraulic
fluid (such as source of hydraulic fluid 34). The pump controller
64 may vary the relief pressure of the bypass valve, thereby
varying the amount of excess fluid flow that passes to tank.
[0068] As mentioned above the main orifice 43 is a variable
orifice, which may be variable between just two orifice areas, or
it may be variable between two or more discreet orifice areas, or
it may be continuously variable over a range of orifice areas. The
smallest orifice area of the main orifice may be zero (i.e. the
main orifice may be closable) or the smallest orifice area may be a
non zero area (i.e. the main orifice may not be closable). The main
orifice 43 may be varied manually or electrically, or via a pilot
pressure.
[0069] The flow orifice (or pilot orifice) 44 may be a fixed
orifice or may be a variable orifice. When the flow orifice 44 is a
variable orifice, it may be variable between just two orifice
areas, or it may be variable between two or more discreet orifice
areas, or it may be continuously variable over a range of orifice
areas. When the flow orifice 44 is a variable orifice the smallest
orifice area may be zero (i.e. the flow orifice may be closable) or
the smallest orifice area may be a non zero area (i.e. the flow
orifice may not be closable). Where flow orifice 44 is variable it
may be varied manually, or electrically, or via a pilot
pressure.
[0070] The amplification orifice 45 may be a fixed orifice or may
be a variable orifice. When the amplification orifice 45 is a
variable orifice, it may be variable between just two orifice
areas, or it may be variable between two or more discreet orifice
areas, or it may be continuously variable over a range of orifice
areas. When the amplification orifice 45 is a variable orifice the
smallest orifice area may be a non zero area (i.e. the
amplification orifice may not be closable). Where amplification
orifice 45 is variable it may be varied manually, or electrically,
or via a pilot pressure.
[0071] Where two or more of main orifice 43, flow orifice 44 and
amplification orifice 45 are variable, they may be varied together
or they may be varied independently.
[0072] The means 63 for generating an output signal representative
of the fluid pressure in the secondary fluid path between the flow
orifice and amplification orifice may be a tapping generating a
pilot pressure signal or may be a pressure sensor that generates an
electrical signal.
[0073] Table 1 below shows three options with regard to the main
orifice, flow orifice and amplification orifice being either
variable or fixed.
TABLE-US-00001 TABLE 1 Flow Orifice Amplification Options Main
Orifice (pilot orifice) Orifice 1 V V V 2 V F V 3 V V F V =
variable F = fixed
[0074] Consideration of FIG. 2 shows that: [0075] hydraulic lines
50, 61A and 62A will all be at the same hydraulic pressure namely
the pump outlet pressure, [0076] hydraulic lines 61B, 62C and 51
will all be at the same hydraulic pressure namely the service
pressure, or load sense pressure, i.e. the pressure sensed at the
load (or service).
[0077] When the service is being operated the pump will be pumping
hydraulic fluid along line 50, and line 61A, through the main
orifice 43 along line 61B and line 51 to the service 24. Because
there will be a pressure drop across the main orifice as the
hydraulic fluid passes through the orifice then the pump outlet
pressure will be higher than the service pressure, the difference
between the pump outlet pressure and service pressure being the
margin pressure.
[0078] The pressure in the line 62B between the flow orifice will
be less than the pump outlet pressure but will be greater than the
service pressure.
[0079] The actual value will depend upon the relative cross
sectional areas of the flow and amplification orifices.
[0080] Thus if the flow orifice cross section area is larger than
the amplification orifice cross section area then the pressure in
line 62B will be nearer the pump outlet pressure than the service
pressure.
[0081] Conversely if the cross section area of the flow orifice is
smaller than the cross section area of the amplification orifice
then the pressure in line 62B will be nearer the service pressure
than the pump outlet pressure.
[0082] Thus by varying the ratio of the cross section area of the
flow orifice and amplification orifice the pressure in the line 62B
(the intermediate pressure) between the flow orifice and amp
orifice can be varied and will be less than the pump outlet
pressure but more than the service pressure. This intermediate
pressure can then be communicated to the pump via line 66 so that
the pump swash setting is controlled to match the flow demands.
[0083] The present invention allows the system to be operated in a
first mode and in a second mode such that the ratio is controlled
differently in the first mode and the second mode.
[0084] As mentioned above, in prior art load sensing systems, the
pump margin pressure and valve margin pressure are usually
identical (ignoring any line losses). The present invention allows
the valve (or orifice) margin pressure to be varied relative to the
pump margin pressure. This is done by varying the flow orifice area
to amplification orifice area ratio. Thus the valve margin pressure
equals the pump margin pressure plus (the area ratio squared times
the pump margin pressure), in other words:
valve margin pressure = pump margin pressure + ( ( area ratio ) 2
.times. pump margin pressure ) ##EQU00001## or ##EQU00001.2## valve
margin pressure = pump margin pressure .times. ( 1 + flow orifice
area 2 amplification orifice 2 ) ##EQU00001.3##
[0085] Thus the first mode of operation defines a first mode ratio
regime and the second mode defines a second mode ratio regime which
is different from the first mode ratio regime.
[0086] In one embodiment in one mode the cross section area of the
flow orifice may be 3 mm2 and the cross section area of the
amplification orifice may be set to 4 mm2, giving a ratio of 3:4
i.e. 0.75. This ratio remains constant, setting a fixed valve
margin pressure (in this case equivalent to the pump
margin.times.(1+0.752), different to the pump margin pressure
proportional to the ratio. When operating the machine in this mode
with orifice 43 varying from zero to some max value flow control of
the service is established. In this mode the valve orifice 43 will
have a relatively low margin pressure of about 1.56 times the pump
margin pressure across it and hence this mode is suitable for
precision work, such as grading. In this mode the ratio regime is
to have a fixed ratio i.e. when operating in this mode the ratio
does not change, i.e. the ratio remains constant.
[0087] In another mode, the cross section area of the flow orifice
may be 3 mm2 and the cross section area of the amplification
orifice may be set to 1 mm2, giving a ratio of 3:1 i.e. 3. This
ratio remains constant when operating the machine in this mode. In
this mode the valve orifice 43 will have a relatively high margin
pressure (about 10 times the pump margin) across it and hence this
mode is suitable for fast work such as loading. In this mode the
ratio regime is to have a fixed ratio i.e. when operating in this
mode the ratio does not change, i.e. the ratio remains
constant.
[0088] In another mode, the cross section area of the flow orifice
may be 3 mm2 and the cross section area of the amplification
orifice may vary between 4 mm2 at a relatively low displacement of
an associated spool and 1.5 mm2 at a relatively high displacement
of an associated spool. Under these circumstances the ratio will
vary between 3:4, i.e. 0.75 at relatively low displacements and
3:1, i.e. 3 at relatively high displacements. Under these
circumstances, the valve orifice 43 will have a relatively low
margin (of about 1.56 times the pump margin pressure across it) at
low spool displacement and will have a relatively high margin (of
about 10 times the pump margin across it) at high spool
displacement and hence this mode is suitable for precision work
such as grading at low spool displacement and is suitable for fast
work, such as loading at high spool displacement spool. The spool
may typically be a control spool for controlling the service (such
as an actuator). In this mode the ratio regime is to have a
variable ratio i.e. when operating in this mode the ratio changes
i.e. the ratio does not remain constant.
[0089] In the above example it will be appreciated for all three
modes of operation the flow orifice cross section area is 3 mm2,
i.e. the flow orifice cross section area is fixed. By controlling
the amplification orifice in three different ways (set at 4 mm2,
set at 1 mm2, variable between 1 mm2 and 4 mm2) then it is possible
to control the ratio in three different ways (the ratio fixed at
0.75, the ratio fixed at 3, the ratio variable between 0.75 and 3)
i.e. it is possible to have three different ratio regimes by being
able to control the ratio in three different ways (i.e. by having
three different ratio regimes) then the pressure at the means 63
and in hydraulic lines 66 can be controlled in three different ways
allowing the valve margin pressure across orifice 43 to be
controlled in three different ways.
[0090] In the example above the main orifice is variable, the
amplification orifice is variable and the flow orifice is fixed and
this equates to option 2 in table 1 above. In an alternative
embodiment the amplification orifice could be fixed and the flow
orifice could be variable as in option 3 in table 1 above. In one
mode the cross section area of the flow orifice may remain constant
during operation in this mode. In a different mode of operation the
cross section area of the flow orifice may remain constant at a
different cross section area. In an alternative mode the cross
section area of the flow orifice may vary dependent upon a
characteristic of machine (for example dependent upon the position
of associated spool). By controlling the cross section area of the
flow orifice in different ways allows control of the ratio of cross
section area of the flow orifice and amplification orifice in
different ways and this in turn allows the valve margin pressure
across orifice 43 to be controlled in different ways.
[0091] In option 1 in table 1 above, both the flow orifice and the
amplification orifice are variable. Under these circumstances in
one embodiment in one mode, the cross section area of the flow
orifice may be set to 2 mm2 and the cross section area of the
amplification orifice may be set to 4 mm2 giving a ratio of 2:4 or
0.5. This ratio remains constant when operating the machine in this
mode. In this mode the valve will have a relatively low pressure
margin and hence this may be suitable for precision work, such as
grading.
[0092] In another mode the cross section area of the flow orifice
may be set to 4 mm2 and the cross section area of the amplification
orifice may be set to 2 mm2 giving a ratio of 4:2 i.e. 2. This
ratio remains constant when operating the machine in this mode. In
this mode the valve will have a relatively high margin and hence
this mode is suitable for fast work such as loading.
[0093] In another mode the cross section area of either the
amplification orifice or the flow orifice or both orifices may vary
depending upon a characteristic of the machine, for example
depending upon the position of an associated spool. In one mode the
cross section area of the amplification orifice may vary whilst
cross section area of the flow orifice remains constant. In another
mode the cross section area of the flow orifice may be variable
whilst the cross section area of the amplification orifice remains
constant. In another mode the cross section area of the
amplification orifice may vary and the cross section area of the
flow orifice may vary. As will be appreciated, by arranging for the
cross section area of the flow orifice to be variable and the cross
section area of the amplification orifice to be variable allows the
system to be operated in a first mode and in a second mode such
that the ratio is controlled differently in the first mode and the
second mode.
[0094] With reference to FIG. 3 there is shown a further hydraulic
system 230 according to the present invention with components that
fulfill the same function as hydraulic system 30 being labeled 200
greater. Pump 232 is a fixed displacement pump. A bypass regulator
270 allows excess fluid flow to pass to tank and is controlled via
a port 263 between the flow orifice 244 and amplification orifice
245 and pressure sensing line 266. The flow orifice and
amplification orifice are in series with the amplification orifice
being downstream of the flow orifice.
[0095] In this case there are two main orifices 243A and 243B. The
main orifice 243A is defined by orifice 243A1 and orifice 243A2 of
control valve 271. Orifice 243B is defined by orifice 243B1 and
243B2 contained within control valve 272.
[0096] Load sensing copy valve 277 is provided. Copy valves are
known per se and act to replicate the pressure either side of the
valve. Thus, the pressure at C is replicated by the copy valve such
that the pressure at C' is the same as the pressure at C.
[0097] Control valve 271 controls service 273 and control valve 272
controls service 274. A compensator 275 is associated with control
valve 271 and a compensator 276 is associated with control valve
272. Compensators per se are known and act to reduce pressure being
supplied to the associated service under certain conditions. Thus,
for the purpose of explanation, it is assumed that service 273
requires a higher pressure than service 274. Accordingly, the spool
of compensator 275 will be positioned as shown in FIG. 3 and when
the control valve 271 is operated, then hydraulic fluid will pass
through the control valve 271, through the compensator 275 (without
any significant loss in pressure) through control valve 271 to
service 273.
[0098] However, because, in this example, service 274 operates at a
lower pressure, the spool of compensator 276 will be positioned
towards the left when viewing FIG. 3 i.e. the spool will move to
the middle position shown and may move nearly to the fully closed
position (the right hand box symbol) since the pressure at D in the
hydraulic circuit will be less than the pressure at A and therefore
the pressure at C' will cause the spool of the compensator to move
left when viewing FIG. 3. This will result in fluid flowing through
compensator 276 dropping the pressure between A and D.
[0099] Hydraulic system 330 includes a known drain regulator 280
which is arranged to drain trapped pressure when no service spool
is actuated thus allowing pump pressure to fall back to a low
standby value.
[0100] Relief valves 281 and 282 are provided to protect service
274. Relief valves 283 and 284 are provided to protect service 273.
Relief valve 285 acts to limit the pressure in line 266 but can be
temporarily overridden by a "boost" valve 286, which, when actuated
by the operator results in a pressure drop across the valve thereby
enabling the pressure in line 266 to increase above the relief
valve pressure setting of relief valve 285. This "boost" valve is
used in circumstances where extra system pressure is temporarily
required, for example, during a digging operation.
[0101] Consideration of FIG. 3 shows the following:
[0102] The main orifice 243A and 243B are in fluid communication
with the pump outlet. Each main orifice 243A and 243B supplies
pressurized fluid to its associated service 273 and 274. The flow
orifice 244 has a flow orifice inlet which senses a pressure
representative of the pressure of the pump outlet, i.e. in this
case it senses the pressure of the pump outlet. The flow orifice
has an outlet. The amplification orifice 245 has an inlet in fluid
communication with the flow orifice outlet. The amplification
orifice outlet senses a pressure, C' representative of a pressure C
at a service (in the above example, the pressure at service 273).
Means in the form of port 263 generate an output signal
representative of the fluid pressure between the flow orifice
outlet and the amplification orifice inlet. A pump controller (in
this case bypass regulator 270) controls the hydraulic pump in
response to the output signal. The flow orifice defines a flow
orifice cross section area in this case a fixed cross section area.
The amplification orifice defines an amplification orifice cross
section area, in this case a variable cross section area. The flow
orifice cross section area and the amplification cross section area
define a ratio. The main orifice 243A, 243B is variable. The ratio
is variable (by virtue of varying the amplification orifice 245).
The hydraulic system 30 can be operated in a first mode and in a
second mode such that the ratio is controlled differently in the
first mode and the second mode. The ratio is controlled differently
by virtue of controlling the cross section area of the
amplification orifice differently in the first and second modes. In
one mode, the amplification orifice can be controlled by
maintaining the amplification orifice cross section area at a
specified value. In the second mode of operation the amplification
orifice may be maintained at a specified value different from the
value when operating in first mode. In another mode of operation
the cross section area of the amplification orifice may be
variable.
[0103] In further embodiments in addition to the amplification
orifice being variable the flow orifice may be variable.
[0104] In further embodiments the amplification orifice may be
fixed and the flow orifice may be variable.
[0105] When the flow orifice is variable it may operate in a first
mode where the cross section area of flow orifice is fixed. The
system may operate in a second mode where the cross section area of
the flow orifice is fixed at a different value to when operating
the first mode. The system may operate in a mode where the cross
section area of the flow orifice is variable.
[0106] The bypass regulator 270 includes a spring 290 which sets a
basic pump pressure margin. In the present invention this basic
setting may be relatively low, for example 4 bar. The pressure in
line 266 acts to assist spring 290 thereby increasing the pump
pressure i.e. the pump pressure will always be 4 bar higher than
the pressure in line 266. Because the ratio of cross section areas
between the flow orifice and amplification orifice can be varied
depending upon which mode of operation this system is being
operated under, then the pressure in line 266 varies depending upon
the mode of operation in which the system is operating and hence
the valve orifice 243A1 and 243B1 margin pressure can be varied
depending upon the mode of operation in which the system is being
operated.
[0107] With reference to FIG. 4 there is shown a further hydraulic
system 330 with components that fulfill the same function as
hydraulic system 230 being labeled 100 greater.
[0108] The only difference between hydraulic system 230 and
hydraulic system 330 is that hydraulic system 330 includes a
variable pump with associated hydraulic circuitry whereas hydraulic
system 230 has a fixed pump with associated hydraulic circuitry.
Thus, pump 332 is a variable displacement pump. In this case pump
332 has a swash plate 394, the angle of which is controlled by
swash plate controller 395. The basic pump margin pressure is set
by spring 390 and the spring pressure of spring 390 will be
supplemented by the pressure in line 366 to increase the pump
pressure as required. The hydraulic system 330 can operate in the
first mode where the ratio of the cross section area of the flow
orifice and amplification orifice is controlled in a first manner
and can operate in a second mode where the ratio of the flow
control orifice cross section area and amplification orifice cross
section area is controlled in a second manner.
[0109] In further embodiments in addition to the amplification
orifice being variable the flow orifice may be variable.
[0110] In further embodiments the amplification orifice may be
fixed and the flow orifice may be variable.
[0111] When the flow orifice is variable it may operate in a first
mode where the cross section area of flow orifice is fixed. The
system may operate in a second mode where the cross section area of
the flow orifice is fixed at a different value to when operating
the first mode. The system may operate in a mode where the cross
section area of the flow orifice is variable.
[0112] As mentioned above, the outlet from the amplification
orifice 45 senses the pressure representative of a pressure at
service 24. In this case the outlet of amplification orifice 45
senses the pressure by being in fluid communication with the
service.
[0113] These can be contrasted with the outlet from amplification
orifice 245 and 345, which, whilst also sensing a pressure
representative of a pressure at a service (in the example the
pressure representative of pressure at the respective service 273,
373), the outlet from the amplification orifice 245 and 345 is not
in fluid communication with respective service 273, 373.
[0114] As described above one ratio regime is to keep the ratio (or
ratio value) fixed. In the example above the ratio value was 0.75
and this ratio value remained constant when operating the system in
this mode. As described above, another, different ratio regime is
to keep the ratio (or ratio value) fixed at a different value, in
the example case the ratio value was 3 and this ratio value
remained constant when operating the system in this mode. Thus, it
is possible to have two different ratio regimes even though the
value of the ratio does not change when operating under each of the
regimes. The regimes are different because the value of the ratio
when operating under each regime is different.
[0115] As described above, one ratio regime is to vary the ratio
(or vary the ratio value). The example above the ratio value was
varied between 0.86 and 2. As will be appreciated, another,
different ratio regime would be to vary the ratio differently, for
example the ratio could vary between 0.5 and 2 to provide a
different ratio regime, the ratio could vary between 0.68 and 3 to
provide a different ratio regime. Where the ratio regime has a
variable ratio value, the ratio value may vary dependent upon a
first machine characteristic in a first ratio regime and may vary
dependent upon a second machine characteristic in a second ratio
regime.
[0116] Clearly if one ratio regime has a fixed ratio and another
ratio regime has a variable ratio, then these two ratio regimes
will necessarily be different regimes.
* * * * *