SYSTEM AND METHOD FOR ASSIGNING A SERVICE LIFE ESTIMATE OF A HYDRAULIC CYLINDER

Abstract

A system for monitoring a hydraulic cylinder in a work machine is disclosed. The system calculates a normalized seal damage for the hydraulic cylinder based on a normalized wear coefficient. An estimated degradation rate is determined from normalized seal damage calculations performed over a timestep during operation of the work machine, and the estimated degradation rate is compared to a degradation model formed from population hydraulic cylinder data. A service life estimate of a seal of the hydraulic cylinder is identified based on the alignment of the estimated degradation rate within the degradation model.

Claims

1. A work machine having a system for monitoring a hydraulic cylinder in the work machine, the work machine comprising: a frame; a boom movably attached to the frame; an engine mounted on the frame; an undercarriage supporting the frame; an implement movably attached to the boom; a hydraulic cylinder operatively associated with the boom and including a cylinder barrel, a piston moveably disposed in the cylinder barrel, a seal provided with the hydraulic cylinder, and a pressure sensor configured to monitor a pressure of a fluid in the hydraulic cylinder; and an electronic control unit, the electronic control unit in communication with the pressure sensor, the electronic control unit programed to: receive pressure signals from the pressure sensor, determine a piston displacement of the piston, calculate a normalized seal damage based on the received pressure signals, the determined piston displacement, and a normalized wear coefficient, determine an estimated degradation rate of the seal from the calculated normalized seal damage, compare the estimated degradation rate to a degradation model, and identify a service life estimate to the seal based on the alignment of the estimated degradation rate within the degradation model.

2. The work machine of claim 1, in which the normalized wear coefficient is calculated from merged population data of population hydraulic cylinders of the same cylinder type as the hydraulic cylinder.

3. The work machine of claim 2, in which the degradation model is constructed by calculating a normalized population seal damage of at least two population hydraulic cylinders of the same cylinder type as the hydraulic cylinder, compiling normalized population seal damage data over a timestep that includes at least two normalized population seal damage calculations for each population hydraulic cylinder, and calculating the population degradation rate for each population hydraulic cylinder for the timestep from the compiled data.

4. The work machine of claim 3, in which constructing the degradation model further includes bucketizing the calculated population degradation rates into ranges of machine operation hours.

5. The work machine of claim 4, in which the identification of the service life estimate to the seal is based on the alignment of the estimated degradation rate within a bucket of the degradation model.

6. The work machine of claim 1, in which prior to calculating the normalized seal damage, the electronic control unit enables a service life estimate based on one or more of a preset range of the cylinder displacement, cylinder pressure, oil temperature, and operator commands.

7. The work machine of claim 1, in which after the service life estimate is identified, the electronic control unit configured to display the assigned service life estimate on an external display.

8. The work machine of claim 1, in which the hydraulic cylinder further includes a displacement sensor in the hydraulic cylinder that sends displacement signals to the electronic control unit for use in determining the piston displacement.

9. The work machine of claim 1, in which the electronic control unit makes an estimate of the piston travel distance for the determined piston displacement.

10. The work machine of claim 1, in which the degradation rate is calculated at the end of a predetermined timestep, and the degradation rate includes multiple calculations of the normalized seal damage calculated during the timestep.

11. The work machine of claim 10, in which the timestep is between 50 and 100 hours of operating the work machine.

12. The work machine of claim 1, in which the service life estimate is a range of work machine operation hours that the seal is estimated to need to be replaced at.

13. The work machine of claim 1, in which the normalized seal damage is calculated from merged population data of population hydraulic cylinders of the same hydraulic cylinder type, and the merged population data includes mean pressure data and mean piston displacement data collected from the population hydraulic cylinders.

14. A system for identifying a service life estimate to a seal of a hydraulic cylinder of a work machine, the system comprising: a degradation model constructed by periodically calculating a normalized population seal damage of a population of hydraulic cylinders of the same cylinder type as the hydraulic cylinder of the work machine, and periodically determining the population degradation rate for the population of hydraulic cylinders based on the normalized population seal damage calculations; the hydraulic cylinder for the work machine including a cylinder barrel, a piston moveably disposed in the cylinder barrel, a seal provided with the hydraulic cylinder, and a pressure sensor configured to monitor a pressure of a fluid in the hydraulic cylinder; and an electronic control unit, the electronic control unit in communication with the pressure sensor, the electronic control unit configured to receive pressure signals from the pressure sensor, determine a piston displacement of the hydraulic cylinder for the work machine, calculate a normalized work machine seal damage based on the received pressure signals, the determined piston displacement, and a normalized wear coefficient, determine an estimated degradation rate of the seal from the calculated normalized seal damage, compare the estimated degradation rate to the degradation model, and identify the service life estimate to the seal based on the alignment of the estimated degradation rate within the degradation model.

15. The system of claim 14, in which the hydraulic cylinder for the work machine is part of a hydraulic circuit of the work machine that includes multiple hydraulic cylinders.

16. The system of claim 15, in which each hydraulic cylinder in the hydraulic circuit includes at least two seals, and the system identifies a service life estimate for each seal in the hydraulic circuit.

17. A method of assigning a service life estimate to a seal of a hydraulic cylinder of a work machine, the method including: constructing a degradation model by periodically calculating a normalized population seal damage of population hydraulic cylinders of the same cylinder type as the hydraulic cylinder of the work machine, determining the estimated population degradation rate of the population hydraulic cylinders based on the normalized population seal damage calculations, and bucketizing the estimated population degradation rates; periodically calculating a normalized work machine seal damage during operation of the work machine based on received pressure signals as they are received from at least one pressure sensor on the hydraulic cylinder, a piston displacement of a piston of the hydraulic cylinder as it is determined by an electronic control unit of the work machine, and a normalized wear coefficient; determine an estimated degradation rate of the seal based on the periodic normalized work machine seal damage calculations; and identify a service life estimate to the seal based on the alignment of the estimated degradation rate within the bucketized population degradation rates.

18. The method of claim 17, in which the normalized population seal damage calculation is calculated based on pressure measurements of the population hydraulic cylinders, piston displacement of the population hydraulic cylinders, and the normalized wear coefficient.

19. The method of claim 18, in which the normalized wear coefficient is calculated from the mean merged pressure measurements and mean piston displacement of the population hydraulic cylinders.

20. The method of claim 17, in which prior to calculating the normalized seal damage during operation of the work machine, the electronic control unit determines the work machine is in an operating mode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a diagrammatic, cross-sectional view of a hydraulic cylinder, in accordance with an exemplary embodiment of the present disclosure.

[0011] FIG. 2 is a block diagram of an exemplary system for assigning a service life estimate to an hydraulic cylinder, in accordance with an exemplary embodiment of the present disclosure.

[0012] FIG. 3 is a schematic diagram illustrating an exemplary system for communicating amongst a fleet of work machines and monitoring service center, in accordance with an exemplary embodiment of the present disclosure.

[0013] FIG. 4 is a decision tree diagram illustrating exemplary system for assigning a service life estimate of a hydraulic cylinder seal according to the present disclosure.

[0014] FIG. 5 is a graph illustrating a normalized damage calculated on a population of hydraulic cylinders over time, in accordance with an exemplary embodiment of the present disclosure.

[0015] FIG. 6 is a graph illustrating an estimate damage rate of a population of hydraulic cylinders, in accordance with an exemplary embodiment of the present disclosure.

[0016] FIG. 7 is a graph illustrating a degradation model, in accordance with an exemplary embodiment of the present disclosure.

[0017] FIG. 8 is a graph illustrating a normalized damage calculated on a hydraulic cylinder of a work machine, in accordance with an aspect of the present disclosure.

[0018] FIG. 9 is graph illustrating the seal service life of a population of boom cylinders of excavator machines, in accordance with an aspect of the present disclosure.

[0019] FIG. 10 is a graph illustrating estimate damage rates over time of a hydraulic cylinder of a work machine compared to a degradation model.

[0020] FIG. 11 is a flow chart illustrating an exemplary method for assigning a seal service life estimate, in accordance with an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

[0021] Referring to FIG. 1, an exemplary hydraulic cylinder constructed in accordance with the present disclosure referred to by reference numeral 10. The hydraulic cylinder 10 includes a piston 12 connected to a rod 14, both of which are adapted to reciprocate in a cylinder barrel 16. The hydraulic rod includes a head end (HE) 18 and a rod end (RE) 20 which includes head apertures 22 and rod aperture 23, respectively. The space defined by the head end 18 and piston 12 is referred to as a head space 25, while the space defined by the rod 14 and cylinder barrel 16 is referred to as rod space 26. In order to seal the head space 24 from the rod space 26, a piston seal 28 is provided around the piston 12 and proximate the cylinder barrel 16. Similarly, to seal the rod space 26 from the environment, a rod seal 30 is provided around the rod 14 and proximate the rod end 20 of the cylinder barrel 16. A wiper 31 is also provided to seal the cylinder 10.

[0022] The piston 12 is caused to move one direction or the other within the barrel 16 in order to perform useful work depending on the machinery to which the cylinder 10 is attached. The piston 12 is caused to move by introduction and evacuation of hydraulic fluid from the head space 24 and rod space 26. More specifically, it will be noted that a first port 32 is in communication with the head space 24 and a second port 34 is in communication with the rod space 26. Pressurized hydraulic fluid provided by a hydraulic piston pump, accumulator, or the like is in communication with the ports 32 and 34 and enables ingress and egress of hydraulic fluid to both. In so doing, if hydraulic fluid is introduced to the head space 24 and removed from the rod space 26, the piston 12 is caused to move to the right (in FIG. 1) and conversely if hydraulic fluid is introduced to the rod space 26 and removed from the head space 25, the piston is caused to move to the left (in FIG. 1). A hydraulic circuit 36 may include hydraulic components (not shown) which are well known in the industry such as, but not limited to, one or more control valves, one or more hydraulic actuators, at least one pump fluidly coupled to a hydraulic fluid reservoir and any other such components consistent with a hydraulic circuit.

[0023] The hydraulic circuit 36 may thus be configured to pump or otherwise transport the hydraulic fluid from hydraulic circuit 36 into the head space 24 and rod space 26 of the hydraulic cylinder 10 via the ports 32, 34. In some embodiments, a valve 38 is configured as a two-position, one-way valve including an open position and a closed position to assist in doing so. When the valve 38 is selectively moved to the closed position, the valve 38 is capable of removing fluid from the head space 24 and introducing the hydraulic fluid into the rod space 26. On the other hand, when the valve 38 is selectively moved to the open position, the hydraulic fluid is caused to leave the rod space 26 and enter the head space 24. As a result, during operation the fluid levels within the head space 24 and rod space 26 may each be increased or decreased to define a piston displacement 40, or in other words, an operational travel range, or distance, of the piston 12. As used herein, the piston displacement 40 refers to the displacement of the piston 12 during operation of the hydraulic cylinder 10.

[0024] FIG. 2 illustrates one non-limiting example of a system 42 capable of assigning a service life estimate to the hydraulic cylinder 10. The hydraulic cylinder 10 is in communication with a head end pressure sensor 4, a rod end pressure sensor 6, a displacement sensor 48, a temperature sensor 50, and a operating mode determiner 8. In some embodiments the displacement sensor 48 may be a position sensor. Also, in some embodiments, as shown in FIG. 1, head end pressure sensor 4 may be disposed in the head space 24 of the hydraulic cylinder 10 and is configured to monitor and measure the pressure of the fluid in the head space 24. Alternatively, in some embodiments, the head end pressure sensor 4 may be disposed in a first connected space 100 between the head space 24 and the valve 38. An example of such an alternative disposition of the head end pressure sensor 4 may also be seen in FIG. 1 where the head end pressure sensor 4 is shown in broken line. The rod end pressure sensor 6 may be disposed in the rod space 26 of the hydraulic cylinder 10 and is configured to monitor and measure the pressure of the hydraulic fluid in the rod space 26. Alternatively, in some embodiments, the rod end pressure sensor 6 may be disposed in a second connected space 102 between the rod space 26 and the valve 38. An example of such an alternative disposition of the rod end pressure sensor 6 may also be seen in FIG. 1 where the rod end pressure sensor 46 is shown in broken line. The displacement sensor 48 may be disposed in the barrel 16, for example in the rod space 26, and be configured to monitor and measure the movement and/or position of the rod 14 or piston 12. In some embodiments, the temperature sensor 50 may be disposed in the head space 24 (as shown in the broken line in FIG. 1) and is configured to monitor and measure the temperature of the hydraulic fluid. Alternatively, an embodiment of the hydraulic cylinder 10 may include the displacement sensor 48 disposed in the dead space 24 to monitor and measure the position of the piston 12. Another embodiment of the hydraulic cylinder 10 may include the temperature sensor 50 in the rod space 26 (see FIG. 1) to monitor and measure the temperature of the hydraulic fluid. In a further embodiment, the temperature sensor 50 is an oil temperature sensor that measures the oil temperature of a work machine 88 in which the hydraulic cylinder 10 is located on. In a further embodiment, in lieu of the displacement sensor 48, a machine linkage sensor (not shown) may be provided and cylinder displacement can be calculated based on machine linkage positions of the work machine 88.

[0025] Furthermore, the head end pressure sensor 4, the rod end pressure sensor 6, the displacement sensor 48, the temperature sensor 50, and the operating mode determiner 8 are all in communication with an electronic control unit 52. The electronic control unit 52 is configured to receive and process pressure signals 9 from one or more of pressure sensors 44, which includes the head end pressure sensor 4 and the rod end pressure sensor 6, with the pressure sensors 44 monitoring or measuring the pressure of the fluid inside of the hydraulic cylinder 10.

[0026] Additionally, the electronic control unit 52 is configured to receive and process a piston position signal 2 to determine the piston displacement. The electronic control unit 52 is also configured to receive a temperature sensor signal 3 from the temperature sensor 50 to determine the temperature of the hydraulic fluid or oil temperature of the work machine 88.

[0027] The electronic control unit 52 is further configured to receive an operating mode signal 5 from the operating mode determiner 8 to determine which operating mode the work machine 88 is in. The operating modes may include any transport or work operating modes common in work machines 88 in the construction or heavy machinery industries. The system 42 is a dynamic system such that the electronic control unit 52 is configured to monitor current status, operation, performance, health, and identify a service life estimate of the seals 28, 30, 31 of the hydraulic cylinder 10 via, in part, dynamic, real-time feedback of the pressure signals 9, piston displacement signals 2, the temperature signals 3, and/or the operating mode signals 5.

[0028] As shown best in FIG. 3, the electronic control unit 52, which includes a processor, memory and input and outputs as is conventional, may be provided on-board the work machine 88. The work machine 88 is depicted as an excavator as an example, but it is to be understood that the work machine 88 may be any number of earth moving or other heavy industry machines including but not limited to track-type tractors, bull dozers, bucket loaders, and the like. With any such work machine, it will include one or more hydraulic cylinders 10 for performing useful work. As depicted, the work machine 88 includes multiple hydraulic cylinders 10 for moving the boom 90, arm 92 and implement 94. Moreover, the work machine 88 includes an engine 96 and operator cabin 98 mounted on a frame 104 supported by a driven undercarriage 105.

[0029] As will also be noted from FIG. 3, the work machine 88 and electronic control unit 52 may be in communication with a remote monitoring service center 106 by way of a satellite 108 or other communication network. In so doing, if a operating company has a fleet of work machines 88, each can be monitored at the service center 106 so that when the system herein disclosed determines that the hydraulic cylinder needs to be replaced, such maintenance can be scheduled.

[0030] With respect to the algorithm itself, whereas normal seal wear can be calculated as a function of geometry, normal load, sliding speed, time and other factors using the known wear law:

[00001]$W=k\frac{P_{n}S}{H}={\mathrm{cP}}_{n}S$ [0031] the present disclosure uses a new equation developed using normalized seal damage. That equation for normalized seal damage (h.sub.norm) is represented mathematically as

[00002]$h_{\mathrm{norm}}=\mathrm{Pdx}$$\mathrm{or}$$=\frac{1}{\mathrm{mean}\left(\mathrm{Pdx}\right)}$ [0032] where mean (Pdx) is found by merging population work order data with measured data from the work machine in question. In other words, as there are hundreds of thousands of work machines and hydraulic cylinders in service, the data coming back from maintenance work orders and the like showing when hydraulic cylinders have failed, that population work order data is merged with the actual machine data as measured to normalize the overall data set. In so doing, the model can be more easily applied to different applications with minimal calibration and testing efforts.

[0033] Turning now to FIG. 4, a decision tree is depicted outlining the approach of the present invention. In a first step 200, the seal damage is estimated using the aforementioned algorithm. This algorithm, referred to as a recursive least squares algorithm 202 is applied to the data every timestep to estimate the damage accumulation rate. The timestep may be any suitable increment, for example, every second although other increments are possible. The model then determines in a step 204 if the accumulated operating hours of the machine is greater than a predetermined threshold. For example, the severity level may be estimated every 50-100 machine hours (or other interval) using thresholds set by evaluating a statistical distribution. If the operational hours are indeed greater than that threshold, the model them asks if the normalized damage rate is greater or less than a damage threshold to medium life rate as shown in steps 206 and 208, and based on those comparisons the seal service life estimate can be bucketized into ranges of remaining machine hours. For example, a high estimate could be 4000-6000 hours, a medium range estimate could be 2000-4000 hours, and a low estimate could be less than 2000 hours remaining. Of course, such buckets are only example ranges and other values are certainly possible and consistent with the present invention. Based on those bucketized estimates, the monitoring service center can schedule replacement of the cylinder seal at the appropriate time and thereby minimize any potential downtime for the machine.

[0034] The present invention can also be further understood graphically with reference to FIGS. 5-10, where FIG. 5 is a graph illustrating a normalized damage calculated on a population of hydraulic cylinders over time, in accordance with an exemplary embodiment of the present disclosure; FIG. 6 is a graph illustrating an estimate damage rate of a population of hydraulic cylinders, in accordance with an exemplary embodiment of the present disclosure; FIG. 7 is a graph illustrating a degradation model, in accordance with an exemplary embodiment of the present disclosure; FIG. 8 is a graph illustrating a normalized damage calculated on a hydraulic cylinder of a work machine, in accordance with an aspect of the present disclosure; FIG. 9 is graph illustrating the seal service life of a population of boom cylinders of excavator machines, in accordance with an aspect of the present disclosure; and FIG. 10 is a graph illustrating estimate damage rates over time of a hydraulic cylinder of a work machine compared to a degradation model.

INDUSTRIAL APPLICABILITY

[0035] In operation, the present invention can find applicability in many industries including but limited to work machines used in earth moving, heavy industry, agricultural and the like. For example, work machines such as excavators and the like typically include multiple hydraulic cylinders used to perform useful work depending on the implements attached to the machine. Being able to accurately predict the remaining life of such cylinders will enable the operator and/or fleet management to plan accordingly in terms of maintenance and replacement of same to optimize the up-time of the machine.

[0036] With that in mind, FIG. 11 depicts a sample sequence of steps which may be practiced by the method 1000 of the present invention. Starting with a step 1002, the method first involves constructing a degradation model for use by the algorithm. It does so by analyzing the accumulated population data. Based on that population data and degradation model, in a step 1004, a normalized seal damage value for a given hydraulic cylinder is calculated. In addition, at a step 1006 an estimated degradation rate of the given seal is also determined.

[0037] With those values calculated, the damage rate severity level for the seal can be identified by comparing the estimated degradation rate to the constructed degradation model as shown by a step 1008. Finally, the estimated remaining service life for the seal can be determined. Such estimation can be enabled based on a preset range of piston displacement, cylinder pressure, oil temperature and operator commands. Once known, the operator can then schedule to have maintenance performed, or the seal replaced, in a timely manner so as to mitigate any necessary downtime for the work machine.

[0038] While the preceding text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of protection is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every embodiment since describing every embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims defining the scope of protection.

[0039] It should also be understood that, unless a term was expressly defined herein, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to herein in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term be limited, by implication or otherwise, to that single meaning.