U.S. patent application number 09/740483 was filed with the patent office on 2002-06-20 for hydraulic cylinder life prediction.
Invention is credited to Muller, Thomas P..
Application Number | 20020077734 09/740483 |
Document ID | / |
Family ID | 24976706 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020077734 |
Kind Code |
A1 |
Muller, Thomas P. |
June 20, 2002 |
Hydraulic cylinder life prediction
Abstract
Maintenance requirements for hydraulic cylinders used to actuate
heavy equipment may be predicted by measuring actual use of the
cylinders. Sensors measuring piston position within each cylinder
are interrogated and the results stored in histograms bins to
provide a permanent record of motion. Hydraulic pressure and
temperature are also recorded. Data are downloaded periodically and
compared with data from laboratory tests and/or from other units in
the
Inventors: |
Muller, Thomas P.;
(Montgomery, IL) |
Correspondence
Address: |
CATERPILLAR INC.
100 N.E. ADAMS STREET
PATENT DEPT.
PEORIA
IL
616296490
|
Family ID: |
24976706 |
Appl. No.: |
09/740483 |
Filed: |
December 19, 2000 |
Current U.S.
Class: |
701/29.5 |
Current CPC
Class: |
G07C 3/00 20130101; F15B
15/14 20130101; F15B 19/005 20130101 |
Class at
Publication: |
701/30 ;
701/35 |
International
Class: |
G01M 017/00 |
Claims
1. A method for predicting service intervals for hydraulic systems
on machinery using pressurized hydraulic fluid to actuate hydraulic
cylinders for control functions comprising: sensing the position of
a piston in an hydraulic cylinder at intervals of time and
recording the position of the piston as a function of time;
determining the direction of travel of said piston and calculating
the distance traveled by said piston over a period of time;
calculating the acceleration and deceleration rates for said piston
over each period of time corresponding to movement in a direction;
recording the acceleration; sensing the pressure of the hydraulic
fluid at intervals of time; recording the sensed pressure of the
fluid at each interval of time; calculating the average, maximum
and minimum pressure over all recorded intervals of time; sensing
the temperature of the hydraulic fluid at intervals of time;
recording the sensed temperature of the hydraulic fluid at said
intervals of time; collecting the recorded data for position,
distance, acceleration, pressure and temperature; and comparing the
collected data to pre-established standards to determine the time
for the next service.
2. A method according to claim 1 wherein the position of a piston
is determined by use of a sensor device selected from the group
consisting of rotary position sensors, magnetostrictive sensors,
radiofrequency sensors, linear potentiometers, variable impedance
transducers linear variable displacement transducers, and cable
displacement transducers.
3. A method according to claim 1 wherein pressure is measured using
a strain gauge.
4. A method according to claim 1 wherein temperature is measured
using a device selected from the group consisting of thermocouples
and thermisters.
5. A method according to claim 1 wherein data is collected and
processed in a microprocessor.
6. A method according to claim 1 further comprising downloading the
stored data to a portable recording device.
7. A method according to claim 1 further comprising downloading the
stored data to a central location via satellite.
8. A method according to claim 1 further comprising display of data
indicating excursions from desired ranges of pressure and
temperature within an operator's work station.
Description
TECHNICAL FIELD
[0001] This invention relates to hydraulic cylinders on mobile or
stationary equipment and more particularly to data collection of
the activity of the cylinders which is used to predict the time
remaining before the next service or impending component
failure.
BACKGROUND ART
[0002] There are numerous advantages to recording operational data
for mechanical and electrical systems and components thereof. The
availability of electronic devices, more particularly
microprocessors or "black boxes" has facilitated the obtention and
recordation of such information. Particularly in the area of heavy
equipment such as wheel loaders, back hoes, dozers and other moving
equipment having implements which are operated through the use of
hydraulic cylinders, the accumulation of data on use is very
valuable for the prediction of failures, and for the determination
of need for routine maintenance and for other out-of-service
events.
[0003] U.S. Pat. No. 5,987,394 to Takakura et al., granted Nov. 16,
1999, is directed to a system for downloading electronic control
units on motor vehicles which is adaptable to different vehicles
having different specifications and different numbers of
modules.
[0004] U.S. Pat. No. 5,748,496 to Takahashi et al., granted May 5,
1998, is directed to a diagnosis system for monitoring the
operation of a manufacturing facility in which the system predicts
future changes and potential production defects on the basis of
sensed information. This information is depicted in a simplified
form to expedited a proper response from line employees.
[0005] U.S. Pat. No. 5,506,773 to Takaba et al, granted Apr. 9,
1996, is directed to a self-diagnosis system for a motor vehicle
and particularly to the storage of date indicating malfunctions and
relating them to error codes.
[0006] U.S. Pat. No. 5,852,793 to Board et al., granted Dec. 22,
1998, is directed to life cycle measurements of rotating or
reciprocating machinery using transducers detecting vibration,
friction and shock waves and provides necessary filters to
eliminate extraneous data.
[0007] The prior art discloses either real time expert systems,
event flags which have been "collected" during operation of a
vehicle or other device or revert to the time-honored process of
simply measuring engine hours. There remains a need for data
collection in the field from hydraulic devices which can be related
to parameters established in laboratory on a test stand and/or to
recorded histories of equivalent hydraulic devices in the field.
The present invention is directed to overcoming the problems and
disadvantages associated with the prior art as set forth above.
DISCLOSURE OF THE INVENTION
[0008] The invention relates to methods for predicting service
intervals for hydraulic systems in machinery using pressurized
hydraulic cylinders to control various operational functions. Data
are collected and compiled from operating parameters including but
not limited to position of pistons, total travel of a piston,
acceleration and deceleration, fluid pressures and fluid
temperatures. Data are collected over discrete intervals reflecting
the type of use cycle and may be further processed to indicate
average values over a cycle, high and low excursions. Other factors
such as ambient temperatures which may relate to the selected
operational parameters also may be collected.
[0009] Data are periodically downloaded from an electronic storage
module and compared to date collected on other similar devices on
test stands or from other machinery in the field. Comparisons are
used to identify decrements in system performance, specific
component deterioration and to predict time to service and the
extent of service required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a plan view of a wheel loader showing the
components of the hydraulic system and the location of hydraulic
cylinders to which this invention is directed.
[0011] FIG. 2 shows the components of an hydraulic cylinder.
BEST MODE FOR CARRYING OUT THE INVENTION
[0012] The elements of the invention and the method of their use
are applicable to any operating system which uses hydraulic
cylinders to move components. For purposes of this invention, the
elements and method will be described in terms of a wheel loader, a
type of work vehicle having groupings of hydraulic cylinders
applied to different functions.
[0013] FIG. 1 is a plan view of a typical wheel loader 1. The
loader has two basic components articulated at a hitch 2. The
engine frame 3 carries engine, transmission and cab (not shown).
The loader tower 5 carries bucket 7, lift arms 9, 9', dump cylinder
11, and lift cylinders 13, 15 and is supported by a front axle.
[0014] The steering for the loader is accomplished using right
steering cylinder 17 and left steering cylinder 19.
[0015] The example chosen has two hydraulic systems having separate
pressurized oil tanks 21, 23 and hydraulic pumps 25, 27. The number
of hydraulic systems is not critical to the invention but he use of
two serves to illustrate certain advantages of this invention. The
operation of the hydraulic system is controlled by valves such as
steering control valve 29, dump control valve 31, and brake control
valve 33.
[0016] The hydraulic cylinder to which this invention is applied is
illustrated in FIG. 2. The cylinder 101 has a housing 103 which
typically is circular in cross section. A shaft 105 passes through
a seal 107 in end plate 109. The shaft ends in a rod end fitting
(not shown) which is moved by movement of the shaft. At the
opposite end of the cylinder housing 103 is an ear 115 mounted on a
second end plate 117. Hydraulic lines 111, 113 provides paths for
hydraulic oil flow to ends of the cylinder. A seal 119 on mounted
piston 121 on shaft 105 divides the cylinder into a return pressure
chamber 123 and an extension pressure chamber 125.
[0017] The primary measurement useful in predicting the life of an
hydraulic cylinder is the total displacement of or "mileage" on the
rods. Wear on the seals 107 at the end plate through which the rod
passes (109) is caused by abrasion. Wear on the seal 119 on the rod
end is also a function of the mileage as the piston moves within
the cylinder. In addition, over the stroke of the rod there is
inevitable oblique force pushing the rod into misalignment with the
cylinder, causing uneven wear and "egging" of the seals and bore
holes. Finally, grit is an unavoidable enhancer of wear and, all
else being equal, damages as a function of the number of times the
grit is rubbed between a seal and a metal surface.
[0018] The position of a rod and ultimately the position of the
driven component, can be measured in a number of ways which provide
electronic signals which can be processed and stored using
state-of-the art microprocessors. Included in a list of measurement
techniques are rotary position sensors, magnetostrictive sensors,
radiofrequency (RF) sensors, captive or floating sliding magnets
(linear potentiometers) variable impedance transducers, linear
variable displacement transducers (LVDT) and cable displacement
transducers (string pot yo-yo's).
[0019] Rotary potentiometers are mounted over a linkage pin at the
end of a rod to measure the angular rotation of the joint. Using
simple trig functions, the angularity is related to the rod
extension. Examples of rotary potentiometers used to measure
location include U.S. Pat. No. 3,834,345. An example of the use of
such a device in determining the position of a bucket of a loader
is U.S. Pat. No. 5,727,387.
[0020] Magnetostrictive sensors measure the movement of a magnet.
The measuring system may be mounted within the cylinder for
protection against the external environment or externally on the
rod. Commercial systems are available from MTS Systems Corporation,
Minneapolis, Minn. and Berlin, Germany, under the tradename
TEMPOSINICS.RTM. and Balluf, Inc., Florence, Ky., under the
tradename MICROPULSE.RTM.. These products are integrateable into
available Canbus systems to enable both measurement and
control.
[0021] RF sensors are acoustical sensors which measure the location
of the piston within the hydraulic cylinder using reflected sound
waves within the cylinder. Because of the geometry of the cylinder,
RF sensors treat the cylinder as a resonance chamber and rely upon
some frequency shift corrections to reach accurate results. The
frequency used and the positions of sender and receiver may be
varied and the correlations obtained electronically. Cylinders of a
characteristic size and using a specified hydraulic fluid can be
carefully tuned and corrected for temperature changes. Some
non-limiting examples of the use of RF sensing to determine the
position of a piston is an hydraulic cylinder are U.S. Pat. No.
5,710,514 to Crayton et al., which uses sender and sensor located
near the end plate 109 and correlates the location of the piston on
the basis of a look-up table. U.S. Pat. No. 5,856,745 to Morgan et
al. locates the rod support, an extension of the resonance cavity
and optionally, the electromagnetic wave couplers, piston stop and
hydraulic input-output port within a single mechanical structure at
the end of piston travel. The objective is to improve reliability
by locating critical components beyond the reach of a piston being
"banged" to the end of travel. Banging of the dump cylinder is a
technique frequently employed to obtain quantative transfer from a
bucket. U.S. Pat. No. 6,119,579 to Pawelski employs an ultrasonic
transducer positioned on a side of an hydraulic cylinder and
receiving signals resonating within the cylinder. The sending mode
is pulsed and then receiving mode analyzes the echoes. The computed
result determines position and may be integrated into a control
function such as automatic implement positioning.
[0022] Linear potentiometers are external analog sensors which move
with the rod. They are a type of magnetostrictive sensor and are
available form MTS Sensors.
[0023] Variable impedance transducers which are available from
Automatic Systems Laboratories, Milton Keynes, United Kingdom
[0024] Linear variable displacement transducers (LVDT) are mutual
inductor devices with three coils and a core. LVDT's measure
distances fore and aft of a null point by voltage difference.
[0025] Cable displacement transducers or string pot yo-yo' are
cable actuated sensing devices. A cable rotates a cable drum which
in turn rotates a precision potentiometer to provide and output
proportional to cable travel. They may be external to the cylinder
or internal.
[0026] The output from the above-described devices is processed
electronically in a microprocessor to produce a result in terms of
distance, distance over unit time, or any other result desired
including but not limited to strokes, full strokes, partial
strokes, acceleration and deceleration rates and percentage of
total travel utilized. The results may be displayed in the cab
and/or stored in memory and downloaded as desired. Storage may be
simplified by recording date in histogram bins reflecting high and
low values and one or more mid-range values. Separate bins may
reflect discrete units of time over an operational cycle.
[0027] Pressure may be measured using pressure transducers or
strain gauges anywhere in the hydraulic system. Suitable locations
are the pump(s), at the oil tank(s) and at the control valves.
Display in the cab or other work station, using a high and lower
pressure warning light and/or sound generator, as well as storage
of all data in a microprocessor are preferred. Pressure losses or
fluctuations indicate one or more of deterioration of a pump,
improper ramping of a variable displacement pump, leaking seals,
deterioration of hydraulic lines and deterioration or contamination
of hydraulic fluid. Drift in pressure over time is a measure of
overall system deterioration. Fluctuations over daily cycles may
indicate operator inattention, poor technique or overloading.
[0028] Hydraulic fluid temperatures may be measured using
thermocouples or thermisters. Valuable information is obtained from
average temperature as measured at the fluid tank. Extremes
indicate whether suitable fluids are being used in consideration of
the local temperatures as well as the work load of the vehicle.
Excessively high temperatures may indicate overloading or
mechanical deterioration (wear). Low temperatures, especially with
lower maximum fluid pressure, strongly suggests contamination with
lower boiling liquids. Hydraulic fluid temperature is displayed in
the cab or other work station and may be coupled with a warning
lamp or sound generating device.
[0029] The collected data is downloaded periodically to an external
recording device through a connector or may be transmitted
periodically via satellite to a central location.
[0030] Industrial Applicability
[0031] When the equipment is started, the position sensors are
zeroed by the operator or automatically by microprocessor (ECU).
Beginning with start-up, or at a selected time-of-day for equipment
operated continuously, a new set of position data is stored. Output
from each sensor is recorded individually at pre-established time
intervals, usually every 10-20 msec. or serially. Data may be
stored as raw data for subsequent processing or divided into
groupings indicating piston location. Acceleration data may be
stored raw but is preferably sorted into at least three data
sets.
[0032] When downloaded, the "mileage" on each cylinder is analyzed
and compared to standards established during bench testing of each
component type. In addition, the results may be compared to that
obtained from other units in the field. Service intervals, e.g.,
time to next service, may be predicted from actual usage data, and
costly out-of-service time can be scheduled when actually needed
based upon use, not on hours or time since last service. Pressure
and temperature readings likewise commence with start-up or
periodically for continuously running equipment. These too are
downloaded to determine wear and fluid contamination or
deterioration. Simple service can be performed when collected data
indicate that immediate service should be performed. Fluid purge
and fill can be done on the spot if downloaded on site or scheduled
as required if reported by satellite. In-frame service can be
scheduled based on actual need and parts ordered prior to required
service. Comparison with similar equipment in the field may
indicate improper selection of equipment, improper operation or
manufacturing or engineering problems prior to costly work
stoppages or recalls.
[0033] Other aspects, objects and advantages of this invention can
be obtained from a study of the drawings, the disclosure and the
appended claims.
* * * * *