PRESSURE-SENSING HOSE
Cross Reference To Related Applications
This application is being filed on 22 November 201 1, as a PCT
International Patent application in the name of Eaton Corporation, a U.S. national
corporation, applicant for the designation of all countries except the U.S., and, Luis
R. Pereira, a citizen of Venezuela, Hassan Al-Atat, a citizen of Lebanon, and Mark
A. Juds, a citizen of the U.S., applicants for the designation of the U.S. only, and
claims priority to U.S. Patent Application Serial No. 61/415,991 filed on 22
November 2010, the disclosure of which is incorporated herein by reference in its
entirety.
Technical Field
The present disclosure relates to methods and systems for measuring
characteristics of a hose; in particular, the present disclosure relates to a pressuresensing
hose.
Background
High pressure reinforced hydraulic hose is typically used on a variety
of fluid power operated machines, such as earth-moving machines, to provide a
flexible connection between several moving parts of a hydraulic circuit employed on
or within the machine. Such hoses may include a hollow polymeric inner tube on
which successive cylindrical layers of reinforcing material, such as wire or textile,
are concentrically applied to contain the radial and axial pressures developed within
the inner tube.
Many applications are demanding hose constructions with both high
burst strength and long term fatigue resistance. Using conventional technology, the
burst strength of a hose design may be increased by adding additional reinforcing
material and/or layers, a practice which is generally discouraged because of its
negative impact on the flexibility of the hose, or by universally increasing the tensile
strength of each layer of reinforcement material, which may come at the expense of
hose fatigue resistance.
An impulse test measures a hose design's resistance to fatigue failure by cyclically
subjecting the hose to hydraulic pressure. A burst test, on the other hand, is a
destructive hydraulic test employed to determine the ultimate strength of a hose by
uniformly increasing internal pressure until failure. Based on these and other tests, a
manufacturer can estimate a hose life that can be used to determine when a hose has
reached the end of its life and may require replacing.
In some circumstances, it is desirable to detect, in a non-destructive
and non-disruptive manner a likelihood of failure of a hydraulic hose. One solution
providing this capability is discussed in U.S. Patent No. 7,555,936, and discloses
connecting a monitor circuit between two parallel, at least partially-conductive
layers of a hose wall. A change in an electrical property observed by that monitor
circuit may indicate a change in a property of the hose wall structure that might
indicate impending failure of the hose wall. However, even with this solution, it can
be difficult to determine whether the changed electrical property is in fact due to a
change in a physical feature of a hose wall, or if the changed electrical property is
due to a change in the sensing electronics, a change in an electrical property of a
harness connecting the monitoring circuit to the hose wall, or simply degradation of
an electrical connection to the hose wall. In these cases, there may be a change in an
electrical property observed, even when hose wall integrity is not compromised, but
instead is due to a change in position or pressure within the hose. This is because
existing solutions do not account for pressure within a hose, either for monitoring
purposes or for compensating for pressure effects on failure sensing circuitry.
Summary
In a first example aspect, a pressure sensing hose assembly includes a
hose assembly including a hose having first and second conductive layers and a
circuit electrically connected to the first and second conductive layers of the hose
assembly. The circuit generates an electrical signal across the first and second
conductive layers of the hose assembly, which generates an electrical response to the
electrical signal. The pressure-sensing hose assembly further includes a computing
system configured to receive the electrical response and estimate a pressure within
the hose assembly based on the electrical response.
In a second example aspect, a method of sensing an internal pressure
of a hose assembly includes applying an electrical signal to a hose assembly and
calculating at least one electrical property of the hose assembly based on a response
of the hose assembly to the electrical signal. The method also includes estimating a
pressure within the hose assembly based on the electrical response.
In a third example aspect, a method of sensing an internal pressure of
a hose assembly includes applying a voltage across first and second concentric
conductive layers of a hose assembly separated by an elastomeric insulating layer,
and determining a voltage drop across the hose assembly. The method further
includes calculating a resistance and a capacitance of the hose assembly based on the
voltage drop across the hose assembly, and estimating a change in wall thickness of
the hose assembly based at least in part on the resistance and the capacitance. The
method also includes applying a hysteresis model to the estimated change in wall
thickness to estimate pressure within the hose assembly.
Brief Description of the Drawings
FIG. 1 is a partial cross-sectional view of an exemplary hose
assembly employing a fault detector having exemplary features of aspects in
accordance with the principles of the present disclosure.
FIG. 2 is a perspective view, partially cut away, illustrating an
exemplary hose employing a braided conductive layer that is suitable for use with
the hose assembly of FIG. 1.
FIG. 3 is a perspective view, partially cut away, illustrating an
exemplary hose employing a spiral wire conducting layer that is suitable for use with
the hose assembly of FIG. 1.
FIG. 4 is a schematic cross-sectional view of a model of the hose
assembly of FIGS. 1-3.
FIG. 5 is an electrical schematic model of the hose assembly of FIG.
4.
FIG. 6 is a schematic axial cutaway view of a portion of a hose
assembly, according to an example embodiment.
FIG. 7 is a schematic cross-sectional view of a model of a pressurized
hose assembly.
FIG. 8 is an electrical schematic model of a pressurized hose
assembly.
FIG. 9 is a hysteresis model illustrating elasticity responsiveness of
an insulating layer included in a hose assembly according to embodiments of the
present disclosure.
FIG. 10 is a chart illustrating an example input pressure wave applied
to a hose assembly.
FIG. 11 is a chart illustrating a change in voltage observed at a hose
in response to the input pressure wave of FIG. 11.
FIG. 12 is a chart illustrating example hysteresis curves illustrating
responsiveness of an insulating layer included in a hose assembly based on the input
pressure wave of FIG. 11.
FIG. 13 is a flowchart of an method for sensing and computing an
internal pressure of a hose assembly, according to an example embodiment.
FIG. 14 is a chart illustrating an example input pressure wave applied
to a hose assembly.
FIG. 15 is a chart illustrating an example measured voltage response
of a hose assembly in response to the input pressure wave of FIG. 14.
FIG. 6 is a chart illustrating estimated thickness of an elastomer
layer positioned between conductive layers based on the measured voltage
illustrated in FIG. 15.
FIG. 17 is a chart illustrating estimated pressure within a hose
assembly after applying a hysteresis model on the thickness calculations shown in
FIG. 16.
Detailed Description
Reference will now be made in detail to the exemplary aspects of the
present disclosure that are illustrated in the accompanying drawings. Wherever
possible, the same reference numbers will be used throughout the drawings to refer
to the same or like structure.
Generally, the present disclosure relates to methods and systems for
determining an internal pressure of a hose assembly. According to various
embodiments discussed herein, a hose assembly including concentric conductive
layers can be modeled as a coaxial cable having an electrical response that changes
with pressure. By accounting for hysteresis effects of an elastomer layer between
the conductive layers, it is possible to estimate a current pressure within the hose
assembly based on the electrical response of the hose over time. This allows a user
of a hydraulic hose to be able to monitor pressure within the hose with reasonable
accuracy, and without requiring a separate pressure gauge or other instrument.
Referring now to FIG. 1, an exemplary hose monitoring system,
generally designated 10, is shown. The hose monitoring system 10 includes a hose
assembly, generally designated 12, and a monitoring assembly 14 in electrical and
physical communication with the hose assembly 12. The hose monitoring system 10
can be used, for example, to determine current operational characteristics of the hose
assembly 12, such as the current pressure within the hose assembly 12, or to monitor
degradation and/or failures in the hose assembly.
The hose assembly 12 includes a hose, generally designated 16,
having a multi-layer construction. In the subject embodiment, the hose 16 is
generally flexible and includes an inner tube 18 made from a polymeric material,
such as rubber or plastic, or another material depending on the requirements of the
particular application, a first conductive layer 20, an intermediate layer 22, a second
conductive layer 24 and an outer cover 26. The first and second conductive layers
20, 24 define an electrical characteristic of the hose assembly 12, such as
capacitance, inductance and/or resistance (impedance).
In the subject embodiment, the first conductive layer 20 overlays the
inner tube 18 and the intermediate layer 22 overlays the first conductive layer 20.
The second conductive layer 24 overlays the intermediate layer 22. The first and
second conductive layers 20, 24 may be configured as reinforcing layers. The outer
cover 26 may overlay the second conductive layer 24, and may include, for example,
an extruded layer of rubber or plastic. The outer cover 26 may itself include a
reinforcing layer.
The intermediate layer 22 operates to at least partially insulate
electrically the first and second conductive layers 20, 24 from one another. The
intermediate layer 22 may have any of a variety of constructions. For example, the
intermediate layer 22 may consist of a single layer of an electrically resistive
material. The intermediate layer 22 may also consist of multiple layers, wherein at
least one of the layers exhibits electrical insulating properties. Certain composite
materials may also be employed in the intermediate layer 22, such as a woven fabric
bonded to a polymeric material. Composite materials having various other
constructions may also be utilized. Composite materials may also be used in
combination with other materials to form the intermediate layer 22.
The first and second conductive layers 20, 24 generally extend the
entire length and span the entire circumference of the hose. This is generally the case
when the conductive layer also functions as a reinforcement layer. The intermediate
layer 22 may also extend over the entire length and circumference of the hose. There
may be instances, however, where at least one of the first and second conductive
layers 20, 24 extends only over a portion of the hose length and/or a portion of its
circumference. In that instance, the intermediate layer 22 may also be configured to
generally extend over the region of the hose containing the partial conductive layer
20, 24. The partial intermediate layer 22 may be positioned within the hose so as to
separate the first and second conductive layers 20, 24 from one another.
Referring now to FIGS. 2 and 3, the first and second conductive
layers 20, 24 may include, for example, an electrically conductive braided
reinforcement material, such as shown in FIG. 2, or alternating layers of electrically
conductive spiral reinforcement material, such as shown in FIG. 3. The braided
reinforcement material may consist of a single layer or may include multiple layers.
Although a two-wire spiral reinforcement arrangement is depicted in FIG. 3, it shall
also be appreciated that other configurations, such as four and six wire
arrangements, may also be utilized.
The first and second conductive layers 20, 24 may each have the
same configuration, or each layer may be configured differently. For example, the
first and second conductive layers 20, 24 may each include the braided material
shown in FIG. 2, or one of the first and second conductive layers 20, 24 may include
the braided material while the other of the first and second conductive layers 20, 24
may include the spiral reinforcement material shown in FIG. 3. Additionally, the
first and second conductive layers 20, 24 may include a single ply or multiple plies
of reinforcement material. The first and second conductive layers 20, 24 may
comprise metal wire, natural or synthetic fibers and textiles, and other reinforcement
materials, provided the selected material is electrically conductive.
Referring again to FIG. 1, the hose assembly 1 may include a hose
fitting, generally designated 30, for fluidly coupling the hose 6 to another
component. The hose fitting 30 may have any of a variety of different configurations
depending, at least in part, on the requirements of the particular application.
In the subject embodiment, the hose fitting 30 includes a nipple,
generally designated 32, that engages the inside of the hose 16 and a socket,
generally designated 34, that engages the outside of the hose 16. The nipple 32
includes an elongated cylindrical end portion 36 that engages the inner tube 18 of
the hose 16. A cylindrically shaped end portion 38 of the socket 34 engages the
outer cover of the hose 16. The socket 34 and nipple 32 may be constructed from an
electrically conductive material.
The socket 34 and nipple 32 can be secured to the hose 16 by
crimping the end portion 38 of the socket 34 overlaying the hose 16. The crimping
process deforms the end portion 38 of the socket 34, thereby compressing the hose
16 between the nipple 32 and the socket 34. In the subject embodiment, the portions
of the nipple 32 and the socket 34 that engage the hose 16 include a series of
serrations that at least partially embed into the relatively softer hose material when
the socket 34 is crimped to help secure the hose fitting 30 to the hose 16. The
serrations may be configured to prevent the serrations from penetrating the inner
tube and outer cover and contacting the first and second conductive layers 20, 24.
In the subject embodiment, the socket 34 includes an inwardly
extending circumferential lug 40 positioned near an end 42 of the socket 34 adjacent
an end 44 of the hose 16. The lug 40 engages a corresponding circumferential slot
46 formed in the nipple 32 for securing the socket 34 to the nipple 32. The end 42 of
the socket 34 having the lug 40 is initially formed larger than the nipple 32 to enable
the socket 34 to be assembled onto the nipple 32. During the assembly process the
end 42 of the socket 34 is crimped, which deforms the socket 34 and forces the lug
40 into engagement with the corresponding slot 46 in the nipple 32. The socket 34
can be electrically insulated from the nipple 32 by positioning an electrically
insulating collar 48 between the socket 34 and nipple 32 at the point the lug 40
engages the slot 46.
The hose fitting 30 also includes a nut 50 attached to the nipple 32.
The nut 50 provides a means for securing the hose assembly 12 to another
component.
The first conductive layer 20 may be configured to extend beyond the
end of the inner tube of the hose 16. The first conductive layer 20 may engage the
nipple 32 to create an electrical connection between the nipple 32 and the first
conductive layer 20. Similarly, the second conductive layer 24 may be configured to
extend beyond an end of the outer cover of the hose 16. The second conductive layer
24 may engage the socket 34 to create an electrical connection between the socket
34 and the second conductive layer 24.
To help prevent the portions of the first and second conductive layers
20, 24 that extend beyond the end of the hose 16 from contacting one another, an
electrically insulating spacer 52 may be positioned between the exposed ends of the
first and second conductive layers 20, 24. The spacer 52 may be integrally formed as
part of the collar 48 used to electrically insulate the socket 34 from the nipple 32.
The spacer 52 may also be formed by extending the intermediate layer 22 of the
hose 16 beyond an end of the inner tube 18 and outer cover 26. The spacer 52 may
also be configured as a stand alone component separate from the collar 48 and the
intermediate layer 22 of the hose 16.
The monitoring assembly 4 may have any of a variety of
configurations. In general, the monitoring assembly 14 is connectable over a portion
of the hose assembly 12, in particular the portion illustrated in FIG. 1. The
monitoring assembly 14, when installed over hose assembly 12, forms a physical
and electrical connection with the hose assembly 12, and in particular to nipple 32
and socket 34, respectively. Generally, the monitoring assembly 14 detects an
electrical characteristic of the hose assembly 12, while validating the connection to
the nipple 32 and socket 34. An exemplary monitoring assembly 14 is described in
further detail below, in connection with FIGS. 4-17.
Referring now to FIGS. 4-5, schematic representations of the hose
assembly 12 and a monitoring circuit that can be included in a monitoring assembly
14 are provided. In FIG. 4, a cross-sectional, schematic physical representation of a
hose assembly 100 is shown. The hose assembly 100 schematically appears as a
coaxial cable, with concentric first and second conductive layers 102, 104,
respectively. The first and second conductive layers 102, 104 can, in some
embodiments, correspond to layers 20, 24 of FIGS. 1-3, above.
An elastomeric layer 106 resides between the first and second
conductive layers 102, 104, and acts as an insulator electrically separating the layers.
Accordingly, and as shown in FIG. 5, the hose assembly 100 can be represented as a
parallel capacitor 1 0 and resistor 120 (i.e., modeled on a coaxial cable
arrangement).
It is noted that, in FIG. 4, the facing portions of conductive layers
102, 104 separated by the elastomeric layer 106, would act as separated capacitor
plates, with a separate resistive component. Accordingly, as shown in FIG. 5, a
monitoring circuit 200 can take the form of a voltage (V sen sor) 202 and resistance
(Rsensor) 204 applied to a first of the conductive layers, and a response can be
detected on the second of the conductive layers. As such, a voltage (Vh 0Se) at the
point between the resistance 204 and the hose assembly 100 (represented
schematically by the parallel resistor 120 and capacitor 140) indicates the proportion
of the overall voltage (V sen sor) 202 attributable to a drop across the resistance (R sen sor)
204 or across the hose assembly 100.
To assess the electrical response of the hose assembly of FIGS. 4-5,
various physical characteristics of the hose assembly are accounted for, including
the resistivity (p) of the elastomer layer 106, as well as the permittivity (e) of the
elastomer, and the length (L) of the hose. Additionally, the radial position of the
conductive layers 102, 104 is also accounted for (distances a and b, respectively).
As such, when a D C voltage, such as voltage (V sen sor) 202 is applied in the
monitoring assembly 200, the resistor (Rhose) 120 and capacitor (Chose) 0 can be
represented by the following equations:
(resistor 120)
2weL
(capacitor 140)
As such, based on the change in distances a and b, as pressure within the hose
assembly 100 increases, resistance 120 of the hose assembly 100 decreases, but
capacitance 140 increases.
Additionally, due to the capacitive effect of the hose assembly 100,
the hose assembly has an electrical characteristic that is responsive to voltage
changes over time. In particular, when a voltage is initially applied, the voltage
response across the hose as a function of time can be represented by the voltage
divider and RC ircuit equation express low:
Accordingly, when the switch is closed, the current going through the
capacitor will spike and exponentially decrease until the capacitor is fully charged to
the settling (DC) voltage. The time it takes the capacitor to fully charge to the
settling voltage is dependent on time constant t, which can be detected from:
I
Although the model described in FIGS. 4-5 provides an accurate
estimate of electrical response of a hose assembly in the event where conditions
remain constant, it does not account for changes in the electrical properties if a hose
assembly in the event of pressure changes within the hose assembly. In particular,
when the fluid passes through the hose it exerts an internal pressure on the walls of
the hose. The internal pressure will cause stress in the walls of the hose and would
thus cause the walls to contract. As illustrated in FIGS. 6-9, various geometrical
features of a hose assembly 100 may change as pressure within the hose assembly
changes. In FIG. 6, an axial cross-section of one wall of a hose assembly is shown,
with first and second conductive layers 102, 104 positioned at distances a and b from
a center axis of the hose assembly, and separated by the elastomeric layer 106. As
pressure changes in the hose assembly, both the first and second layers may be
compressed, and may change thickness by different amounts Aa, Ab, respectively.
Additionally, as illustrated in FIG. 7, the thickness of the elastomer layer 106 can be
represented as the difference between distances b and a (i.e., distances from the
center axis of the hose to the center axis of each of the conductive layers 102, 104),
as adjusted by half the compression distance of the conductive layers:
Ab Aa
T — b —a
In addition, since resistance and capacitance are proportional to the
natural log of the proportion of distances (ln (b/a)), the proportional resistance and
capacitance can be expressed as a function of the thickness of the elastomer layer:
As specifically illustrated in FIG. 7, because pressure varies as a
function of time t, it will cause X2(t) to change, which refers to a change in
elastomer thickness over time. This will accordingly cause the elastomer thickness
(T- X2(t)) to vary. So, the quantity Ln(b/a) will vary over time with pressure
changes as follows
As observed, as pressure increases, the distance X2 decreases, and
therefore the thickness (T- X2(t)) will decrease. Additionally, the resistance will
decrease by AR, and capacitance will increase by AC. Specifically, a hose resistance
will change as follows:
Rhose
Additionally, the change in thickness of the elastomer will change as
follows:
Act Ab
X 2(t) = a + T e
2 2
Accordingly, both the resistance and capacitance of the hose
assembly will change in response to changes in pressure internal to the hose.
Referring specifically to FIG. 8, a modified electrical schematic model of the hose
assembly 100 is illustrated, as compared to the arrangement shown in FIG. 5. As
shown, an additional adjustment to the capacitance 145, illustrated as AC, and an
additional adjustment to the resistance (shown as AR, as a portion of resistor 120)
are illustrated.
In FIG. 8, it is noted that the settling time for the hose assembly 100
varies according to the particular pressure present in the hose as well. Specifically,
the settling time of the voltage drop across the hose will vary according to the
resistance 120 (Rhose):
nose r sensor
hose V )
ho e ^sesnsor
Additionally, the hose resistance will change over time as a function of pressure:
( f
Rsensor * Vhose
-J ~ y
sensor hose
This leads to a model of a change in thickness of the elastomer layer 106 being a
function of various hose parameters and sensed voltages as follows:
In addition to the above estimate of a change in thickness of the
elastomer layer 106 as a function of sensed voltages, it is possible to then extrapolate
an estimate of pressure within the hose assembly 100 based on those same observed
voltages. However, due to the elastomeric nature of the insulating elastomer layer
106, the relationship between displacement of the elastomer layer 106 and the fluid
pressure within the hose assembly 100 is not perfectly correlated, but instead follows
a hysteresis model. Referring now to FIG. 9, a chart 300 showing a first
experimental example of observed hysteresis illustrating elasticity responsiveness of
an insulating layer included in a hose assembly according to embodiments of the
present disclosure. As illustrated, the example uses the values outlined in Table 1,
below, to empirically derive a hysteresis model for the elastomeric layer 106 of the
hose assembly. For example, a switching input pressure can be applied to a hose
assembly 100 and a voltage response recorded to determine the resistance and
capacitive effect of the hose assembly.
Hose Geometry Input Meters
Mean Diameter D i 1.000 0.0254
Length L In 4 00 1.2192
Thickness T in 0.100 0.002$
Hose Materia) Properties In r ut
Dielectric Constant s r . .
t Spring Constant k ps i 1 00E+ 2 .00E 12
2nd Spring Constant k2 P n 2 > 20,000
Damping Constant k3 ps !n ec) . 2 0.b00
Pressure y e Input
Peak Pressure P pel 1,000
Cvcle Tme to sec
Steady State Detection X2max in 0.0500
Constants
Pe r Vit of Space 8 0 f/m 85E 12
Table 1: Experimental Characteristics of Hose Assembly for Hysteresis Model
From this measurement of pressure and calculation of capacitance as
a function of the response of Vhose to a switching pressure input, a relationship can
be extrapolated from the chart 300 as follows:
Furthermore, a compression of the elastomeric layer 106 of the hose
assembly can be represented as a function of the thickness of the layer 106 at
atmospheric pressure as adjusted by the hose pressure as affected by constants
dictated by the parameters relating to materials used in the hose assembly:
x x e-lik + (— + -)(1 - e
As illustrated in chart 300, as pressure is increased from 0 to 1000
psi, capacitance slowly increases. However, as pressure is decreased from 1000 psi
to 0 psi, capacitance slowly decreases, and does not return to the original value
immediately due to hysteresis effects.
It is noted that, although in FIGS. 5 and 8 a particular voltage divider
circuit is illustrated in which a resistor 120 (R sen sor) positioned on a high voltage
side of the hose assembly 100, which has a first conductive layer 102 connected to
the resistor 120 and a second layer 04 connected to ground, in alternative
embodiments other circuit arrangements could be used as well. For example, a
circuit could be employed in which additional components are included, or in which
the voltage divider arrangement is reversed (i.e., the resistor 1 0 is positioned
between the hose assembly 100 and ground.
Referring to FIGS. 10-12, additional examples of hysteresis are
shown. In particular, in FIG. 10, an input pressure wave 400 is illustrated in which
periodic high pressure occurrences are illustrated. In particular, the input pressure
wave 300 illustrates a change from about 0.2 to about .2 MPa, or between about 0
and 2000 psi. As shown, the input pressure wave includes a low pressure condition
402, a rising pressure condition 404, a high pressure condition 406, and a dropping
pressure condition 408.
FIG. 11 depicts a chart 500of an output hose voltage (Vh0Se)
compared to pressure over time. In the context of the present disclosure, it is
assumed that the output hose voltage (Vh0Se) about 4.5 V or above if the pressure
within the hose is about 0 psi, as illustrated in region 502 (i.e., corresponding to a
response to an input pressure region 402). However, as pressure is increased in the
hose (e.g., in region 404 of FIG. 10), the voltage slowly drops in region 504. At a
maximum pressure (in region 406), voltage continues to decrease in region 506. In a
decreasing pressure region (e.g., region 408), voltage slowly increases (region 508).
As can be seen in FIG. 11, at a same pressure, different voltage readings could occur
based on a previous pressure within the hose assembly. As such, a chart 600 of
hysteresis curves are illustrated in FIG. 12, which define a creep model analogous to
that described above in FIG. 9. The creep model tracks an elastomeric compression
change over time based on a previous compression, the current pressure P(t), and
constants a and b, which are experimentally determined for each set of materials
used to form the hose assembly 100. Specifically, the elastomeric compression
change can be illustrated as:
X {t) = X 2 (t - l ) * e-' , / + P(t) * a * ( - e ~'' )
As such, a hysteresis model can be applied to any hose model whose
reaction is being tracked and whose hose characteristics are known, to allow for
computation of a current thickness of the elastomer layer based on a tracked voltage
response of the hose assembly 100 over time, and subsequently estimating an
internal pressure of a hose assembly by applying a hysteresis model to the results of
that elastomer layer thickness computation.
Referring now to FIG. 13, a flowchart of a method 700 for sensing
and computing an internal pressure of a hose assembly is shown, according to an
example embodiment. T e method 700 can be performed, in various embodiments,
using a microcontroller associated with a hose, or a computing system
communicatively connected to a signal acquisition system associated with a hose
assembly 100. In embodiments where a computing system separate from the hose
assembly 100 is used, the computing system could be used to manage a model of
one or more hoses and provide updates regarding an estimated pressure of each hose
such that abnormal pressures or other issues that may indicate failure or malfunction
of the hose may be detected.
In the embodiment shown, the method 700 includes inputting an
electrical signal from an electrical source onto a conductive layer of a hose assembly
(step 702), and measuring a response of the hose assembly (step 704). This can
include, for example, applying a voltage across the hose assembly, using a
monitoring circuit such as those shown in FIGS 5 and 8, and monitoring a change in
an output voltage V h0Se as a function of time. The method 700 can also include
applying a signal processing algorithm to the output voltage V 0se to determine the
electrical properties of the hose over time, including its resistance and capacitance at
each time (R(t) and C(t)), for example using the estimates provided above and
discussed with respect to FIG. 8 (step 706).
In the embodiment shown, the method 700 includes applying an
algorithm based on the calculated estimates of resistance and capacitance over time
to determine an estimated thickness of the elastomer layer that is positioned between
conductive layers of the hose assembly 100 (step 708). This can include, for
example, determining a change in thickness over time X (t), as discussed above in
connection with FIG. 8, and determining that effect on thickness T of the elastomer
layer 106.
In some embodiments, the method 700 also includes developing an
estimate of pressure within the hose assembly 00 based on the change in thickness
of the elastomer layer 106 over time, using a hysteresis model derived as above (step
710).
Although in FIG. 13, the method 700 discloses applying an
algorithm to determine wall thickness and a subsequent hysteresis model for
determining internal pressure of a hose assembly, it is noted that in alternative
embodiments models could be used which calculate pressure directly from an
electrical response of the hose assembly and characteristics of the hose assembly. In
such embodiments, hysteresis and/or hose thickness considerations may be built into
the model of electrical response of the hose assembly.
Referring now to FIGS. 14-17, charts illustrating an example process
of performing method 700 of FIG. 3 are shown using a varying input pressure
wave. In FIGS. 14-17, lengths of hose of 24 and 60 inches were used. FIG. 14
illustrates a chart 800 of an input pressure wave, showing periodic changes in input
pressure between 0 and 0.6 MPa. In FIG. 15, a chart 900 illustrates a voltage
response at V h0Se to the change in pressure within the hose, keeping input voltage
sensor constant. As can be seen in the periodic response voltage shown, at a time of
switching to a high pressure, the hose voltage will spike to a maximum voltage and
settle back to a settling voltage representing a direct current voltage, indicating that
the hose assembly capacitive effects have settled. Additionally, upon switching to
the low pressure, the hose voltage will initially drop, but the voltage will drop
further over time as the capacitive effect of the hose assembly 100 discharges.
FIG. 16 illustrates a chart 1000 of the estimated value of X2(t) based
on the observed voltage and known characteristics of the hose assembly being
tested. As seen in this chart, the response of X2(t) is generally inverse that of the
sensed voltage Vhose over time. Finally, to estimate pressure, a hysteresis model is
applied, and the results of which are illustrated in FIG. 1 . In particular, FIG. 17
shows a chart 1100 illustrating a first waveform 1 02 that represents the estimated
pressure based on calculations of hysteresis and elastomer layer thickness, and a
second waveform 1104 illustrating an actual input pressure into the hose assembly.
As seen in the chart 1100, pressure within the hose assembly can be determined with
reasonable accuracy based on monitoring of a voltage response from conductive
layers of a hose, since the resistive and capacitive effects of that hose can be used to
determine a distance between the conductive layers. Once hysteresis in an
elastomeric insulative layer between the conductive layers is compensated for,
pressure within the hose can be extrapolated from mathematical models of the hose.
This allows continuous monitoring of internal pressure within the hose without
requiring expensive pressure sensing equipment or gauges.
Referring now to FIGS. 1-17 generally, it is noted that although in the
embodiments described herein two conductive layers are discussed, in alternative
embodiments within the scope of the present disclosure, the hose assembly 100 can
include more than two conductive layers. In such arrangements, each of the
conductive layers can be separated from adjacent conductive layers by separate
insulative layers, and the resistive and capacitive features of such a hose assembly
(as well as the hose construction variables) may vary accordingly, within the general
concepts as disclosed herein and as encompassed by the appended claims.
The above specification, examples and data provide a complete
description of the manufacture and use of the composition of the invention. Since
many embodiments of the invention can be made without departing from the spirit
and scope of the invention, the invention resides in the claims hereinafter appended.
Claims:
1. A pressure-sensing hose assembly comprising:
a hose assembly including a hose having first and second conductive
layers;
a circuit electrically connected to the first and second conductive
layers of the hose assembly, the circuit generating an electrical signal across the first
and second conductive layers of the hose assembly, wherein the hose assembly
generates an electrical response to the electrical signal;
a computing system configured to receive the electrical response and
estimate a pressure within the hose assembly based on the electrical response.
2. The pressure-sensing hose assembly of claim 1, wherein the pressure
is a hydraulic pressure within the hose assembly.
3. The pressure-sensing hose assembly of claim 1, wherein the
computing system is configured to apply an algorithm to estimate a wall thickness of
the hose assembly, the computing system further configured to apply a hysteresis
model to estimate the pressure based on a change in wall thickness over time.
4. The pressure-sensing hose assembly of claim 1, wherein the first and
second conductive layers comprise concentrically disposed inner and outer
conductive layers.
5. The pressure-sensing hose assembly of claim 4, further comprising an
insulative elastomer layer positioned between the first and second conductive layers.
6. The pressure-sensing hose assembly of claim 5, wherein the wall
thickness includes a thickness of the insulative elastomer layer.
7. The pressure-sensing hose assembly of claim 6, wherein the thickness
of the elastomer layer is calculated based on an electrical response across the hose
assembly and one or more physical characteristics of the hose assembly.
8. The pressure-sensing hose assembly of claim 7, wherein the one or
more physical characteristics of the hose assembly include a length of the hose and
radii of the first and second conductive layers.
9. The pressure-sensing hose assembly of claim 7, wherein the one or
more physical characteristics of the hose assembly include materials used in the hose
assembly.
10. The pressure-sensing hose assembly of claim 1, wherein the circuit
comprises a monitoring circuit including a voltage source and a scalar resistor.
11. A method of sensing an internal pressure of a hose assembly, the
method comprising:
applying an electrical signal to a hose assembly;
calculating at least one electrical property of the hose assembly based
on a response of the hose assembly to the electrical signal;
estimating a pressure within the hose assembly based at least in part
on the electrical property.
12. The method of claim 11, wherein applying an electrical signal to the
hose assembly comprises applying a voltage across first and second conductive
layers of the hose assembly using a monitoring circuit.
13. The method of claim 11, wherein the monitoring circuit includes a
voltage source and a scalar resistor.
14. The method of claim 11, wherein calculating at least one electrical
property of the hose assembly includes calculating a resistance of the hose assembly.
15. The method of claim 11, wherein estimating the pressure within the
hose assembly includes:
estimating a change in wall thickness of the hose assembly based at
least in part on the electrical property; and
applying a hysteresis model to the estimated change in wall thickness
to estimate pressure within the hose assembly.
16. The method of claim 15, wherein estimating a change in wall
thickness of the hose assembly is based at least in part on the resistance.
17. The method of claim 16, wherein calculating at least one electrical
property of the hose assembly includes calculating a capacitance.
18. The method of claim 17, wherein estimating a change in wall
thickness of the hose assembly is based at least in part on the resistance and the
capacitance.
19. The method of claim 15, wherein the hysteresis model is empirically
determined for a particular set of materials used in the hose assembly.
20. The method of claim 5, wherein the hysteresis model relates to
responsiveness of a change in thickness of an elastomeric layer positioned between
first and second conductive layers of the hose assembly.
2 1. The method of claim 20, wherein the hysteresis model is represented
by the following equation:
X 2{t) = X t - \) * ~'* + P(t) * a * (l - e-' )
22. A method of sensing an internal pressure of a hose assembly, the
method comprising:
applying a voltage across first and second concentric conductive
layers of a hose assembly separated by an elastomeric insulating layer;
determining a voltage drop across the hose assembly;
calculating a resistance and capacitance of the hose assembly based
on the voltage drop across the hose assembly;
estimating a change in wall thickness of the hose assembly based at
least in part on the resistance and capacitance; and
applying a hysteresis model to the estimated change in wall thickness
to estimate pressure within the hose assembly.