U.S. patent application number 09/760308 was filed with the patent office on 2001-05-24 for pressure regulating method.
This patent application is currently assigned to LUK GETRIEBE-SYSTEME GMBH. Invention is credited to Eidloth, Rainer, Frietsch, Thomas, Kemmner, Benjamin.
Application Number | 20010001394 09/760308 |
Document ID | / |
Family ID | 7872489 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001394 |
Kind Code |
A1 |
Kemmner, Benjamin ; et
al. |
May 24, 2001 |
Pressure regulating method
Abstract
The pressure of hydraulic fluid which is supplied to the
continuously variable transmission in the power train of a motor
vehicle is regulated by an apparatus wherein an adjustable pilot
valve can receive fluid from a pilot conduit leading to a pressure
reducing valve. The pilot conduit normally receives fluid from a
further conduit, wherein the pressure of fluid is at least
substantially constant, by way of a flow restrictor. A branch
conduit serves to evacuate fluid from the pilot conduit into the
pilot valve when the latter is at least partially open. The
fluid-discharging end of the flow restrictor confronts the inlet of
the branch conduit, and such inlet is narrowed to reduce the
likelihood of turbulence developing in the fluid stream flowing
from the pilot conduit, across the further conduit and into the
inlet of the pilot valve.
Inventors: |
Kemmner, Benjamin;
(Baden-Baden, DE) ; Frietsch, Thomas; (Oberkirch,
DE) ; Eidloth, Rainer; (Bamberg, DE) |
Correspondence
Address: |
DARBY & DARBY P.C.
805 Third Avenue
New York
NY
10022
US
|
Assignee: |
LUK GETRIEBE-SYSTEME GMBH
|
Family ID: |
7872489 |
Appl. No.: |
09/760308 |
Filed: |
January 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09760308 |
Jan 11, 2001 |
|
|
|
09344186 |
Jun 24, 1999 |
|
|
|
Current U.S.
Class: |
137/82 ;
137/625.64 |
Current CPC
Class: |
Y10T 137/2278 20150401;
Y10T 137/8659 20150401; G05D 16/2097 20190101; Y10T 137/0396
20150401; G05D 16/2022 20190101; Y10T 137/86614 20150401; G05D
16/024 20190101 |
Class at
Publication: |
137/82 ;
137/625.64 |
International
Class: |
G05D 016/18 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 1998 |
DE |
198 29 148.5 |
Claims
What it claimed is:
1. A method of controlling the pressure of a hydraulic fluid in a
pilot conduit which receives fluid at an at least substantially
constant pressure from a constant-pressure conduit by way of a flow
restrictor and a pilot valve which is adjustable to permit outflow
of fluid from the pilot conduit through a branch conduit at a
variable rate and to thus lower the static pressure of fluid in the
pilot conduit in response to increasing rate of fluid outflow from
the pilot conduit, comprising the steps of: establishing for the
flow of fluid from the pilot conduit to the pilot valve a path
extending from the pilot conduit, first through the flow restrictor
and thereupon through the branch conduit into and through the pilot
valve; and varying the speed of fluid flowing through the flow
restrictor to thus influence the static pressure of fluid in the
pilot conduit.
2. The method of claim 1, wherein said speed varying step includes
adjusting the pilot valve to select the rate of fluid flow from the
branch conduit into the pilot valve.
3. The method of claim 1, further comprising the step of collecting
the fluid flowing through the pilot valve.
4. The method of claim 1, wherein the fluid includes a
lubricant.
5. Apparatus for controlling the pressure of a hydraulic fluid,
comprising: a pilot valve having an inlet, an outlet and means for
varying the rate of fluid flow from said inlet to said outlet; a
source of constant-pressure hydraulic fluid including a first
conduit having an outlet; a branch conduit connecting the outlet of
said first conduit with the inlet of said pilot valve; a pilot
conduit which is arranged to receive fluid from said branch conduit
and wherein the static pressure of fluid decreases in response to
increasing rate of fluid outflow from the pilot conduit; and a flow
restrictor establishing an evacuating path for the outflow of fluid
from said pilot conduit into said branch conduit.
6. The apparatus of claim 5, wherein said flow restrictor is
installed between said first conduit and said pilot conduit.
7. The apparatus of claim 5, wherein said first conduit establishes
a second path for the flow of fluid to at least one of said first
conduit and said branch conduit, said evacuating path crossing said
second path.
8. The apparatus of claim 5, wherein said first conduit includes a
portion constituting a portion of said pilot conduit, said flow
restrictor being provided in said portion of said first
conduit.
9. The apparatus of claim 8, wherein said branch conduit has an
inlet positioned to receive fluid flowing along said evacuating
path from said pilot conduit, through said flow restrictor and
across said first conduit, said branch conduit further having an
outlet connected with the inlet of said pilot valve.
10. The apparatus of claim 9, wherein the inlet of said branch
conduit has a first cross-sectional area and said branch conduit
further includes a portion adjacent said inlet of said branch
conduit and having a second cross-sectional area greater than said
first cross-sectional area.
11. The apparatus of claim 5, wherein said branch conduit includes
means for opposing the development of turbulence in said evacuating
path.
12. The apparatus of claim 5, wherein said pilot valve has a body
an said means for varying the rate of fluid flow from the inlet to
the outlet of said pilot valve comprises a valving element which is
reciprocable in said body.
13. The apparatus of claim 12, wherein said pilot valve further
comprises means for moving said valving element relative to said
body.
14. The apparatus of claim 13, wherein said means for moving
comprises at least one magnet.
15. The apparatus of claim 14, wherein said at least one magnet is
an electromagnet.
16. The apparatus of claim 5, wherein said first conduit and said
pilot conduit include portions which are at least substantially
normal to said branch conduit.
17. The apparatus of claim 5, wherein said branch conduit has at
least one bend between said flow restrictor and said inlet of said
pilot valve.
18. The apparatus of claim 5, wherein said branch conduit is
straight and has an inlet communicating with said pilot conduit and
an outlet communicating with the inlet of said pilot valve.
19. The apparatus of claim 5, further comprising a regulating valve
having an inlet arranged to receive fluid from said pilot conduit
and an outlet, a consumer of fluid, and a control conduit
connecting the outlet of said regulating valve with said
consumer.
20. The apparatus of claim 19, wherein said consumer includes a
transmission in a power train of a motor vehicle.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to improvements in pressure
regulating methods and apparatus.
[0002] It is often necessary to design a hydraulic control system
in such a way that a regulating or control valve (e.g., a pressure
reducing valve) is installed downstream of a pilot valve or servo
valve (hereinafter called pilot valve). The latter serves to select
fluid pressure in a (pilot) conduit which is connected with an
inlet of the regulating valve. An outlet of the regulating valve
serves to convey fluid to one or more consumers, e.g., to a
so-called continuously variable transmission (CVT). Reference may
be had, for example, to commonly owned U.S. Pat. No. 5,667,448
(granted Sep. 16, 1997 to Oswald Friedmann for "POWER TRAIN") and
to commonly owned U.S. Pat. No. 5,674,155 (granted Oct. 7, 1997 to
Dieter Otto et al. for "METHOD OF AND APPARATUS FOR TRANSMITTING
TORQUE IN THE POWER TRAINS OF MOTOR VEHICLES"). The disclosures of
the just enumerated US patents as well as of all other patents and
patent applications (including commonly owned pending German
priority patent application Ser. No. 198 29 148.5 filed Jun. 30,
1998) are incorporated herein by reference.
[0003] A conventional pilot valve-regulating valve combination can
employ a pilot valve having an inlet connected to a source of
constant-pressure (or substantially constant-pressure) fluid by a
constant-pressure conduit which contains a flow restrictor) e.g.,
an adjustable diaphragm, and can communicate with a pilot conduit
serving to convey fluid to the regulating valve. An adjustable
valving element of the pilot valve can divert varying quantities of
fluid from the pilot conduit (downstream of the flow restrictor) to
a sump or to another destination so that the pilot valve can select
the pressure of fluid entering the body of the regulating
valve.
[0004] A drawback of heretofore known pressure regulating methods
and apparatus of the just outlined character is that (for example,
due to often unavoidable leakage of fluid from the pilot valve
and/or from other parts of the apparatus), the pressure in the
pilot conduit (between the pilot valve and the regulating valve)
cannot match the pressure of fluid in the constant-pressure
conduit. Moreover, even if the valving element of the pilot valve
is moved to a fully open position (in which the valving element
does not interfere with the flow of fluid from the pilot conduit,
through the pilot valve, and on to to the sump), the pilot pressure
of fluid (in the pilot conduit) still exceeds zero pressure. Such
residual pressure in the pilot conduit is attributable to losses
developing in the region of the flow restrictor, e.g., to losses in
the path defined by the constant-pressure conduit, by the flow
restrictor, by a branch conduit connecting the constant-pressure
conduit (downstream of the flow restrictor) to the inlet of the
pilot valve, and by the conduit connecting the outlet of the pilot
valve with the sump or with another receptacle for hydraulic
fluid.
[0005] A further drawback of the aforedescribed conventional
pressure regulating apparatus is that, due to turbulence which
develops in the fluid path in the region of the flow restrictor, at
least a high percentage of kinetic energy of the fluid (such as
oil) is ultimately converted into heat.
OBJECTS OF THE INVENTION
[0006] An object of the invention is to provide a novel and
improved method of regulating the pressure of hydraulic fluid which
is utilized in cylinder-and-piston units and/or other constituents
of transmissions and/or other fluid-operated components, e.g., in
the power trains of motor vehicles.
[0007] Another object of the invention is to provide a method which
can be practiced without the generation of appreciable, noticeable
or even any quantities of heat.
[0008] A further object of the invention is to provide a method
which can be practiced by resorting to a relatively simple, compact
and inexpensive apparatus.
[0009] An additional object of the invention is to provide a method
which renders it possible to reduce the pilot pressure between the
pilot valve and the regulating valve of the appparatus to a
threshold value below that achievable by resorting to heretofore
known methods.
[0010] Still another object of the invention is to provide an
apparatus which can be utilized for the practice of the above
outlined method and is designed in such a way that the
aforedescribed drawbacks of conventional apparatus can be avoided
in a simple, effective and inexpensive manner.
[0011] A further object of the invention is to provide a novel and
improved pilot valve-regulating valve combination for use in the
above outlined apparatus.
[0012] Another object of the invention is to provide the improved
apparatus with a novel combination of a flow restrictor and
conduits for conveying hydraulic fluid from a source of fluid at an
at least substantially constant pressure (e.g., from a valve) to
the pilot valve and from the pilot valve to the regulating
valve.
[0013] An additional object of the invention is to provide an
apparatus which can be utilized in the power trains of motor
vehicles as a superior substitute for the aforedescribed and other
conventional pressure regulating apparatus.
[0014] Still another object of the invention is to provide a
fluid-consuming or fluid-operated unit, such as a continuously
operable transmission, which embodies an apparatus of the above
outlined character.
[0015] A further object of the invention is to provide an apparatus
which exhibits the advantages but does not embody the drawbacks of
standard fluid pressure regulating apparatus utilizing combinations
of pilot valves and regulating valves in the path of hydraulic
fluid flow from a source of constant-pressure fluid to a consumer
requiring fluid at two or more different pressures.
[0016] Another object of the invention is to provide a motor
vehicle, such as a passenger car, having a power train embodying a
unit which consumes or is operated by a hydraulic fluid and which
receives hydraulic fluid from the above outlined apparatus in
accordance with a method of the present invention.
SUMMARY OF THE INVENTION
[0017] One feature of the instant invention resides in the
provision of a method of controlling the pressure of a hydraulic
fluid (e.g., a fluid which includes or constitutes a lubricant such
as oil) in a pilot conduit which receives fluid at an at least
substantially constant pressure from a constant-pressure conduit by
way of a flow restrictor and a pilot valve which is adjustable to
permit outflow of fluid from the pilot conduit through a branch
conduit at a variable rate and to thus lower the static pressure of
fluid in the pilot conduit in response to increasing rate of fluid
outflow from the pilot conduit. The improved method comprises the
steps of (a) establishing for the flow of fluid from the pilot
conduit to the pilot valve a path extending from the pilot conduit
first through the flow restrictor and thereupon through the branch
conduit into and through the pilot valve, and (b) varying the speed
of the fluid flowing through the flow restrictor to thus influence
the static pressure of fluid in the pilot conduit.
[0018] The speed varying step can include adjusting the pilot valve
to select the rate of fluid flow from the branch conduit into the
pilot valve. The fluid which is permitted to flow from the pilot
conduit, through the branch conduit and through the pilot valve can
be confined in (i.e., collected by) a suitable receptacle, e.g., in
a sump.
[0019] Another feature of the invention resides in the provision of
an apparatus for controlling the pressure of a hydraulic fluid,
e.g., a transmission fluid, a lubricant or the like. The apparatus
comprises a pilot valve having an inlet, an outlet and means for
varying the rate of fluid flow from the inlet to the outlet, a
source of constant-pressure hydraulic fluid including a first
conduit having an outlet, a branch conduit connecting the outlet of
the first conduit with the inlet of the pilot valve, a pilot
conduit which is arranged to receive fluid from the branch conduit
and wherein the static pressure of fluid decreases in response to
increasing rate of fluid outflow from the pilot conduit, and a flow
restrictor which establishes an evacuating path for the outflow of
fluid from the pilot conduit into the branch conduit.
[0020] The flow restrictor is installed between the first conduit
and the pilot conduit. The latter establishes a second path for the
flow of fluid to at least one of the first conduit and the branch
conduit; the evacuating path can be oriented in such a way that it
crosses the second path.
[0021] In accordance with a presently preferred embodiment, the
first conduit includes a portion which constitutes a portion of the
pilot conduit (for example, such portions of the first and pilot
conduits can be disposed back-to-back), and the flow restrictor is
provided in such portion of the first conduit. The inlet of the
branch conduit in such apparatus is positioned to receive fluid
flowing along the evacuating path from the pilot conduit, through
the flow restrictor and across the first conduit; the outlet of
such branch conduit is connected with the inlet of the pilot vave.
The dimensions of the just described branch conduit can be selected
in such a way that its inlet has a first cross-sectional area and
that the branch conduit further includes a portion adjacent the
inlet of the branch conduit (e.g., extending all the way from the
inlet of the branch conduit and to the inlet of the pilot valve)
and having a second cross-sectional area greater than the first
cross-sectional area.
[0022] The just described inlet and portion of the branch conduit
constitute a means for opposing the development of turbulence (such
as vortices) in the evacuating path.
[0023] The means for varying the rate of fluid flow from the inlet
to the outlet of the pilot valve can include a valving element
(e.g., a piston which is reciprocable in the housing or body of the
pilot valve) and means for moving the valving element relative to
the body of the pilot valve. The moving means can comprise at least
one magnet, e.g., an electromagnet.
[0024] The orientation of the first conduit and the pilot conduit
can be such that these conduits include portions which are at least
substantially normal to the branch conduit. The latter can have at
least one bend between the flow restrictor and the inlet of the
pilot valve. Alternatively, the branch conduit can be a straight
conduit having an inlet communicating with the pilot conduit and an
outlet communicating with the inlet of the pilot valve.
[0025] The improved apparatus can further comprise a regulating
valve having an inlet arranged to receive fluid from the pilot
conduit and an outlet, a consumer of fluid, and a control conduit
connecting the outlet of the regulating valve with at least one
inlet of the consumer. For example, the consumer can comprise a
transmission in the power train of a motor vehicle, e.g., a
so-called continuously variable transmission (CVT). A typical
example of a continuously variable transmission is a transmission
employing two parallel shafts each of which carries an adjustable
pulley, and an endless belt or chain which is trained over the
pulleys. The fluid which is supplied by the regulating valve by way
of the control conduit can be utilized to vary the ratio of the
transmission and/or to select the extent of frictional engagement
between the flanges of the adjustable pulleys and endless chain or
belt.
[0026] The novel features which are considered as characteristic of
the invention are set forth in particular in the appended claims.
The iproved apparatus itself, however, both as to its construction
and its mode of operation, together with numerous additional
features and attributes thereof, will be best understood upon
perusal of the following detailed description of certain presently
preferred specific embodiments with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a fragmentary schematic partly elevational and
partly sectional view of a conventional fluid pressure regulating
apparatus;
[0028] FIG. 2 is a diagram wherein the curve represents the
relationship between the changes of fluid pressure in the pilot
conduit and the changes in the setting of the pilot valve in the
apparatus of FIG. 1;
[0029] FIG. 3 is a fragmentary schematic partly elevational and
partly sectional view of second conventional apparatus;
[0030] FIG. 4 is a view similar to that of FIG. 3 but showing
certain constituents of an apparatus which embodies one form of the
invention;
[0031] FIG. 5 is a diagram wherein the curve denotes the
relationship between the changes of pressure in the pilot conduit
and the changes in the setting of the pilot valve in the apparatus
of FIG. 4; and
[0032] FIG. 6 is a fragmentary schematic partly elevational and
partly sectional view of a novel apparatus which constitutes a
modification of the apparatus shown in FIG. 4.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0033] FIG. 1 shows certain component parts of a conventional
apparatus which includes a pump 6 serving to draw hydraulic fluid
(such as oil and hereinafter referred to as fluid) from a source 7,
e.g., a sump. The outlet of the pump 6 delivers a stream of fluid
into a main conduit 8 at a pressure which can exceed the pressure
required in a control conduit 28 serving to deliver at least one
stream of pressurized fluid to at least one inlet of a consumer 29,
e.g., a continuously variable transmission (CVT) of the type
disclosed in the commonly owned U.S. Pat. No. 5,667,448 or
5,674,155.
[0034] The main conduit 8 supplies pressurized fluid to an inlet of
a constant-pressure valve 10 (this valve can be replaced with a
pressure regulating valve, not shown) having an outlet connected
with the inlet or intake end of a (first) constant-pressure conduit
12. The valve 10 supplies fluid at an at least substantially
constant pressure. The discharge end or outlet of the
constant-pressure conduit 12 delivers fluid to the inlet of a pilot
conduit 20 by way of a flow restrictor of throttle 14 having a
passage with a fixed or variable effective cross-sectional area for
the flow of fluid from the constant-pressure valve 10 to the pilot
conduit 20.
[0035] The outlet of the pilot conduit 20 (i.e., the outlet of the
constant-pressure conduit 12 downstream of the flow restrictor 14)
is further connected with an inlet of a pilot valve 16 by a branch
conduit 22. The valve 16 has an outlet 24 which can discharge fluid
into the sump 7 when a reciprocable valving element (such as a
piston) 18 in the housing or body 19 of the valve 16 permits at
least some fluid to flow along a path extending from the pilot
conduit 20, through the branch conduit 22, between the inlet of the
housing 19 and the outlet 24, and from the outlet 24 into the sump
7.
[0036] The valving element 18 is movable by a magnet, preferably an
electromagnet having at least one coil 30 arranged to receive
electric current from a suitable source 32. The sump 7 (or at least
that portion of the sump which can receive fluid from the outlet
24) can be replaced with a tank or any other suitable receptacle
for hydraulic fluid which flows along the aforementioned
(evacuating) path from the pilot conduit 20 to and beyond the
outlet 24 when the pilot valve 16 is at least partially open. At
such time, the valving element or piston 18 is spaced apart from a
seat of the housing 19; the seat is adjacent the respective end of
the branch conduit 22, i.e., it is located at the left-hand end of
the cylinder chamber for the reciprocable valving element 18 in the
housing 19.
[0037] When the pump 6 is driven and the pilot valve 16 is at least
substantially sealed, the conduit 12 delivers a stream of fluid to
the pilot conduit 20 via flow restrictor 14. The outlet of the
conduit 20 delivers fluid to one inlet of a pressure reducing valve
26 (e.g., a slide valve) having an outlet connected with the
consumer 29 by way of the aforementioned control conduit 28. The
valve 26 regulates the pressure of fluid in the conduit 28 and in
the consumer 29.
[0038] The exact construction of the valves 10, 16 and 26 is known
and, therefore, need not be described here. The pilot valve 16 is
normally closed, i.e., the valving element 16 dwells in the
left-hand end position so that the branch conduit 22 is at least
substantially sealed from the outlet 24 in the housing 19 of the
valve 16. The valving element 18 is held in the left-hand end
position when the intensity of the magnetic field established by
the coil or coils 30 assumes a maximum value.
[0039] FIG. 3 shows a portion of another conventional fluid
pressure regulating apparatus. All such parts which are identical
with or clearly analogous to those shown in FIG. 1 are denoted by
similar characters. The only difference is that straight portions
of the conduits 12, 20 are adjacent each other and that the flow
restrictor 14 is arranged to convey fluid between such straight
portions.
[0040] The mode of operation of the apparatus shown in FIGS. 1 and
3 will be explained with reference to the coordinate system of FIG.
2 wherein the fluid pressure (in bar) in the pilot conduit 20 is
measured along the ordinate, and the current (in Amperes) supplied
to the coil or coils 30 is measured along the abscissa.
[0041] It is assumed that the fluid pressure in the first conduit
12 is at least substantially constant and amounts to between about
5 and 5.3 bar. The flow restrictor 14 can constitute an adjustable
diaphragm and is assumed to be set for the establishment of a
circular or substantially circular opening with a diameter of
approximately 0.8 mm.
[0042] When the intensity of the magnetic field established by the
coil or coils 30 reaches a maximum value (e.g., when the current
furnished to the terminal(s) 32 has a strength in the range of one
Ampere, the valving element 18 engages its seat and thus seals or
substantially seals the branch conduit 22 from the outlet 24 of the
housing 19. Consequently, the pressure of fluid in the conduits 20
and 22 is maintained at a maximum value, e.g., at slightly less
than 5 bar. The pressure of fluid in the conduits 20, 22 cannot
rise to the pressure of fluid in the first (constant-pressure)
conduit 12 due to leakage of the pilot valve 16 and/or due to other
leak or leaks in the apparatus embodying the structure shown in
FIG. 1 or FIG. 3.
[0043] If the strength of the current flowing through the coil or
coils 30 is reduced, the valving element 18 proceeds to move away
from the seat in the housing 19. This establishes a flow of fluid
from the pilot conduit 20, through the branch conduit 22, from the
inlet to the outlet 24 of the housing 19, and into the sump 7. When
the pilot valve 16 is fully open, the residual pressure of fluid in
the pilot conduit 20 amounts to between about 0.2 and 0.4 bar. The
existence of such residual pressure is attributable to friction
between the fluid in the path from the pilot conduit 20 into the
sump 7 (via pilot valve 16), and the surrounding surfaces.
[0044] Furthermore, and as shown in FIG. 3 by arrows 15, kinetic
energy of the fluid flowing through the flow restrictor 14 causes
the generation of turbulence (such as eddies or vortices
immediately downstream of the flow restrictor) which, in turn,
entails a heating of the conduits 12, 20 and a heating of the
conveyed fluid.
[0045] The characteristic curve 40 in the coordinate system of FIG.
2 indicates that, when the valving element 18 is remote from its
seat in the housing 19, the relationship between the amperage of
the current supplied by the coil or coils 30 and the pressure in
the pilot valve 16 deviates from a linear relationship.
[0046] FIG. 4 shows a portion of an apparatus which embodies one
form of the present invention. The reference characters utilized in
FIG. 4 are largely identical with those shown in FIG. 1 or 3 except
for the numeral 34 which denotes a portion or wall of the conduit
20 of one piece with and thus constituting a portion of the conduit
20. Furthermore, the flow restrictor or nozzle 14 is provided in
the common portion 34 of the conduits 12, 20 in such a way that it
can discharge fluid from the conduit 12, across the conduit 20 and
directly into the inlet of the branch conduit 22. The latter has a
bend 22a between its inlet (at 14) and its outlet (i.e., the inlet
of the pilot valve 16). Thus, when the valve 16 is open to an
extent determined by the intensity of magnetic field being then
established by the coil or coils 30, the fluid can flow from the
constant-pressure conduit 12, across the pilot conduit 20 (via flow
restrictor 14) and directly into the inlet of the branch conduit 22
to thereupon flow to the sump 7 along the path established by the
housing 19 of the pilot valve 16.
[0047] The speed of the fluid flowing from the conduit 12 into the
conduit 22 across the conduit 20 is very high (because the orifice
defined by the flow restrictor 14 is preferably small). Due to such
elevated speed of the fluid flowing into the branch conduit 22, the
static pressure in the conduit 20 is reduced in accordance with the
Bernoulli theorem; this causes the flow restrictor 14 to act as a
jet pump and to draw liquid from the conduit 20 into the branch
conduit 22.
[0048] FIG. 5 shows a coordinate system corresponding to that shown
in FIG. 2, except that the fluid pressure (measured in bar) in the
conduit 20 of FIG. 4 is related to the amperage of the current
supplied to the coil(s) 30 shown in FIG. 4. When the pilot valve 16
of FIG. 4 is at least nearly fully open, the pressure in the pilot
conduit 20 drops below the pressure indicated in FIG. 2. Thus, and
a shown in FIG. 5, the pressure can drop below the zero value. This
ensures that the relationship between the pilot pressure in the
conduit 20 and the amperage of the current being supplied to the
coil(s) 30 remains linear even when the fluid pressure in the pilot
conduit 20 is very low, i.e., when the valving element 18 is remote
from its seat in the valve housing 19. This amounts to a widening
of the operating range of the improved apparatus beyond the
operating range of conventional apparatus. When the pressure of
fluid in the pilot conduit 20 is relatively high, the difference
between the corresponding portions of the curves 40 and 40A
respectively shown in FIGS. 2 and 5 is or can be negligible. The
reason is that when the fluid pressure in the conduit 20 is
relatively high (because the valve 16 is fully or nearly fully
closed), the speed of fluid flow from the conduit 20 via conduit 22
and valve 16 (in the apparatus of FIG. 4) is low or negligible.
[0049] An advantage of the improved method and apparatus is that
they render it possible to widen or broaden the operating range
within which one can control, by means of the pilot pressure, the
operations of other valves such as slide valves or the pressure
reducing valve and/or other components of the apparatus and the
power train. Moreover, one can establish a more predictable linear
relationship between the pressure in the pilot conduit 20 and the
(magnetic) force with which the valving element 18 is urged to its
operative (sealing) position of engagement with the seat in the
housing 19 to thus prevent or reduce the rate of fluid flow from
the pilot conduit 20, through the branch conduit 22 and out of the
housing 19 via outlet 24.
[0050] It is clear that the aforedescribed advantages of the
improved method and apparatus become even more pronounced if the
velocity of the fluid stream flowing from the pilot conduit 20,
through the branch conduit 22 and through the housing 19 of the
pilot valve 16 increases.
[0051] FIG. 6 illustrates a portion of an apparatus which
constitutes a modification of the novel apparatus shown in FIG. 4.
One difference between the apparatus of FIGS. 4 and 6 is that the
branch conduit 22 of FIG. 6 includes an end portion 36 merging into
the adjacent straight portion of the pilot conduit 20 and a
straight portion 22A which extends to the inlet of the body or
housing 19 of the pilot valve 16. The cross-sectional area of the
passage defined by the inlet 36 is smaller than that of the passage
defined by the portion 22A. The straight branch conduit 22 of FIG.
6 renders it possible to dispense with the bend of the type shown
at 22a in FIG. 4. A bend (such as 22a) might be necessary under
certain circumstances (e.g., to take advantage of the space which
is avaiable for the apparatus); however, such bend or bends
necessarily affect the velocity of the fluid flowing from the pilot
conduit 20 toward and into the valve 16.
[0052] An advantage of the smaller-diameter inlet 36 of the branch
conduit 22 of FIG. 6 is that it enhances the velocity of the fluid
stream flowing through the conduit 22 and into the body 19 of the
pilot valve 16. The internal surface of the inlet 36 is preferably
rounded and smooth. Moreover, the inlet 36 enables the branch
conduit 22 of FIG. 6 to act as a highly effective jet pump, i.e., a
pump generating a suction much more pronounced than that achievable
with the branch conduit 22 and flow restrictor 14 shown in FIG. 1
or 3.
[0053] The flow restrictor 14 of FIG. 6 is provided in that portion
of the constant-pressure conduit 12 which is common to the pilot
conduit 20, the same as in FIG. 4.
[0054] It has been found that the operation of the improved
apparatus is particularly satisfactory (especially as concerns
savings in enery) if the pressure in the pilot conduit 20 is zero
bar when the current strength in the coil or coils 30 is at least
very close to 0 mA.
[0055] It is also desirable to design the improved apparatus in
such a way that the pilot pressure in the conduit 20 is zero bar
when the strength of the current flowing in the coil or coils 30 is
slightly above 0 mA. This is of particular advantage in the event
of variations of temperature and/or viscosity of the conveyed
fluid. Under such circumstances, the 0-bar operating point can be
caused to conform (i.e., it can be adapted) to the operating
conditions by varying the strength of the current in the windings
of the coil or coils 30.
[0056] To summarize, one of the important advantages of the
improved method and apparatus is that the fluid pressure in the
pilot conduit 20 can be lowered below that in the pilot conduit of
a conventional apparatus when the pilot valve 16 offers little or
no resistance to the flow of fluid from the conduit 20, via conduit
22, through the valve 16 and into the sump 7. This is accomplished
in that the kinetic energy of the stream of fluid flowing from the
conduit 12, through the flow restrictor 14 and branch conduit 22
into and from the valve 16 is utilized to further reduce the fluid
pressure in the conduit 20.
[0057] Without further analysis, the foregoing will so fully reveal
the gist of the present invention that others can, by applying
current knowledge, readily adapt it for various applications
without omitting features that, from the standpoint of prior art,
fairly constitute essential characteristics of the generic and
specific aspects of the above outlined contribution to methods of
and apparatus for regulating the pressure of hydraulic fluid and,
therefore, such adaptations should and are intended to be
comprehended within the meaning and range of equivalence of the
appended claims.
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