Patent Application
20180223501
The present disclosure relates generally to pull-slip control in a tractor, and more particularly to reducing a pull-slip ratio error by way of selectively engaging a back ground-engaging implement of the tractor with material of an underlying substrate.
Tractors such as track-type tractors are used in a great many different operations, ranging from pushing loose material or debris about a worksite to grading, production dozing or scraping where materials are dug from a substrate, and still other applications related to site preparation, forestry, mining, and general civil engineering. Track-type tractors offer the advantage of a rugged build and substantial capacity for drawbar pull and traction in challenging underfoot conditions, steep terrain, and when towing or pushing large loads.
Due to the nature of the service environment within which track-type tractors operate, the tracks typically experience some slip relative to the underlying substrate. It has been discovered that the extent of track slip in relation to drawbar pull affects operating efficiency of the track-type tractor. If a track-type tractor is experiencing close to 100% track slip, then the track-type tractor is not presently traveling and therefore not likely moving any material or otherwise performing any useful work. On the other hand, if the track-type tractor is experiencing close to 0% track slip the track-type tractor may be traveling but is likely not moving any load apart from the tractor's own weight. Along a so-called pull-slip curve between 100% slip and 0% slip there is a window or zone of greatest efficiency. Different pull-slip curves may be applied to different machine conditions or different service conditions, with the idea that certain machine or operating parameters can be varied in real time to cause the track-type tractor to operate as efficiently as is practicable. U.S. Pat. No. 8,983,739 to Faivre discloses real-time pull-slip curve modeling based upon information as to soil conditions. Establishing an accurate, real-time pull-slip curve theoretically enables an operator or autonomous controller to vary machine parameters, such as track speed, more effectively to achieve efficiency or other aims. Despite advancements taught by Faivre and others, there remains ample room for advancement in controls technology for track-type tractors and related implements.
In one aspect, a method of operating a tractor having a hydraulically actuated implement system includes receiving data indicative of a pull-slip ratio of a tractor during traversing a substrate with at least one of a front ground-engaging implement or a back ground-engaging implement of the hydraulically actuated implement system engaged with material of the substrate. The method further includes calculating an error between the pull-slip ratio indicated by the data and a target pull-slip ratio, and commanding engagement of the back ground-engaging implement with the material of the substrate to reduce the error between the pull-slip ratio indicated by the data and the desired pull-slip ratio.
In another aspect, a tractor includes a frame, and ground-engaging elements coupled to the frame. A hydraulically actuated implement system of the tractor includes a front ground-engaging implement, and a back ground-engaging implement. A pull-slip control system of the tractor includes a first sensing mechanism configured to monitor a drawbar pull parameter of the tractor, a second sensing mechanism configured to monitor a slip parameter of the tractor, and a control mechanism coupled with the hydraulically actuated implement system. The control mechanism is configured to compare a pull-slip ratio indicated by data produced from the first sensing mechanism and the second sensing mechanism with a target pull-slip ratio, and command engagement of the back ground-engaging implement with material of the substrate, such that an error between the pull-slip ratio indicated by the data and the target pull-slip ratio is reduced.
In still another aspect, a pull-slip control system for a tractor having a hydraulically actuated implement system with a front ground-engaging implement and a back ground-engaging implement includes a first sensing mechanism configured to monitor a drawbar pull parameter of the tractor, a second sensing mechanism configured to monitor a slip parameter of the tractor, and a control mechanism. The control mechanism is configured to receive data from each of the first sensing mechanism and the second sensing mechanism, and to determine a pull-slip ratio of the tractor based on the data received from the first sensing mechanism and the second sensing mechanism. The control mechanism is further configured to compare the determined pull-slip ratio with a target pull-slip ratio, and command engagement of the back ground-engaging implement with material of a substrate underlying the tractor, such that an error between the pull-slip ratio indicated by the data and the target pull-slip ratio is reduced.
Referring to
In the illustrated embodiment, front ground-engaging implement (hereinafter “implement”) 24 is shown in the context of a known dozing blade of a type suitable for production dozing, however, the present disclosure is not thereby limited. Another hydraulic actuator(s) 29 may be provided for raising and lowering back ground-engaging implement (hereinafter “implement”) 26, and yet another hydraulic actuator(s) 31 provided for pivoting implement 26 about a horizontal axis. Other hydraulic actuators could also be provided for varying a position or orientation of implement 26 in three-dimensional space according to additional degrees of freedom. In the illustrated embodiment implement 26 includes a ripper, oriented so as to penetrate a tip 27 into material of a substrate 90. Those skilled in the art will be familiar with conventional applications for a ripper mounted upon a track-type tractor, including cutting and/or fracturing soil, aggregate, or other types of substrate materials. Other types of back ground-engaging implements such as blades, claws, discs, plows, or the like might alternatively be used. In the illustrated embodiment, a height of implement 24 can be adjusted in a vertical range generally referred to in the art as grade and shown by way of arrow 70 in
Tractor 10 may further be equipped with a pull-slip control system 40 that is a part of or otherwise coupled with certain of the components of hydraulically actuated implement system 22. As further discussed herein, pull-slip control system (hereinafter “control system”) 40 is configured to receive and gather data relating to present or anticipated operating conditions or operating state of tractor 10, and exploit such data for purposes relating to optimizing efficiency to a particular task. It is contemplated that tractor 10 may be manually operated or autonomously operated, or operated such that certain tasks relating to control of hydraulically actuated implement system 22 are performed autonomously by control system 40.
Referring now to
Also shown in
Control system 40 further includes a second sensing mechanism 50 configured to monitor a track slip parameter of tractor 10. Second sensing mechanism 50 may include a first sensor 52 configured to monitor a ground speed of tractor 10, a second sensor 54 configured to monitor a track speed of a first one of ground-engaging tracks 20, and a third sensor 56 configured to monitor a track speed of another one of ground-engaging tracks 20. Comparisons of ground speed with track speed can be used to determine track slip. Other known techniques could be applied as well. Control system 40 further includes a control mechanism 60 that includes at least one computing device 62 such as a processor, microcontroller, etc., that is coupled with hydraulically actuated implement system 22 and also coupled with each of first sensing mechanism 42 and second sensing mechanism 50 to receive data produced from first sensing mechanism 42 and second sensing mechanism 50.
Also shown in
As noted above, control mechanism 60 is configured to receive data from each of first sensing mechanism 42 and second sensing mechanism 50. Control mechanism 60 may be further configured to determine a pull-slip ratio of tractor 10 based on the data received from first sensing mechanism 42 and second sensing mechanism 50. Control mechanism 60 may be still further configured to calculate an error between the pull-slip ratio indicated by the data and a target pull-slip ratio. Calculating a difference between numerical ratios to determine an error term is a routine mathematical operation. Control mechanism 60 may also be configured to command engagement of implement 26 with material of an underlying substrate that tractor 10 is traversing while at least one of implement 24 and 26 is engaging material of the substrate, such that the error is reduced. Another way to understand these principles is that control mechanism 60, while tractor 10 is traversing a substrate and one or both of implement 24 and implement 26 is engaged with material of the substrate, can initiate engagement of implement 26 or change a pattern of engagement of implement 26, with the substrate to reduce the error in the pull-slip ratio. In one further embodiment, the data includes an expected pull-slip ratio, and the engagement of implement 26, such as dropping of implement 16 into engagement, with the material of the substrate may be initiated prior to occurrence of the expected pull-slip ratio.
Those skilled in the art will appreciate that operating efficiency can vary relatively dramatically where a track-type tractor is operating outside of a relatively narrow window or region along an optimum pull-slip curve. By exploiting the capability of implement 26 to reduce the error, efficiency can be improved over alternative strategies. As noted above, tractor 10 may be operated in the usual course to traverse a substrate with one or both of implement 24 and implement 26 engaged with material of the substrate. It is contemplated that control mechanism 60 can be used to command engagement of implement 26 by commanding dropping implement 26 into engagement with the material of the substrate to reduce an effective drawbar pull force of tractor 10, thus reducing the error. It is also contemplated that control mechanism 60 can command a change in a pattern of engagement of implement 26 with material of the substrate, such as commanding varying a depth of penetration of implement 26.
Referring now to
As noted above, in
Tractor 10, and more particularly control mechanism 60, may also be configured to gather data as to undercarriage surface conditions by operating tractor 10 to traverse substrate 90 with implement 26 lowered into engagement with material of substrate 90. In
As suggested above, still other instances where it is desirable to command initiating engagement or ceasing engagement of a back ground-engaging implement, or changing a pattern of engagement such as a depth of engagement, are contemplated beyond the exemplary work cycle described herein. For example, as a part of the work cycle depicted in
Referring now to
Referring now to
An undercarriage surface condition or undercarriage surface condition value can be determined based on estimated information from a work assignment system, or potentially from a neighboring machine by way of machine-to-machine communication systems. Real-time surface information can also be derived when a ripper is lowered down in a work position, in engagement with material of the underlying substrate, as discussed above. If the substrate surface is extremely slippery, when the ripper is lowered down, a track-type tractor may not be capable of moving at all. The ripper can be elevated to relieve the slip, and the height/grade of the ripper and the relative speed of the tractor utilized to derive the surface condition. On-board sensors monitoring ground speed, track speed, track slip, and other factors as discussed herein are employed for these purposes of gathering and storing data of the surface condition. Use of the ripper (implement 26) to derive a real-time pull-slip ratio is considered advantageous, as the information may be more accurate than information passed from other machines or from a work assignment system. Moreover, when a track-type tractor acquires the accurate real-time pull-slip ratio before a load phase by engaging the ripper at the end of a return phase, less time will likely be required for an autonomous machine to set an accurate grade for a blade when the load phase starts.
Drawbar pull force 254 may be computed on the basis of a transmission gear ratio 260, an engine output power 258, and stored machine cycle patterns 256, as described herein. Engine output power 258 might be estimated according to a fueling map and present engine speed. The stored machine cycle patterns could be based upon empirical testing of tractor operation under varying conditions, such as varying undercarriage or substrate conditions relating to moisture or soil hardness or toughness, for instance, slope or inclination conditions, and still others.
At a block 270 the derived real time pull-slip ratio 210 is compared with the target pull-slip ratio 250 to calculate an error value 272 corresponding to a pull-slip ratio error. At a block 274 a target grade of the blade/implement 24 and also a target grade of the ripper/implement 26 is determined, on the basis of the pull-slip ratio error 272. At a block 276 the target grades are compared with real time grade positions from a block 290, to produce actuator commands or control signals for actuators 26, 28, 29 or such other actuators as might be used, based on the error term calculated at block 276. Control signals may be sent to block 278, and the electrical currents for driving the appropriate actuators according to the control signals generated at a block 278. At block 282 grade adjustment of blade/implement 24 occurs and in parallel at block 280 grade adjustment of ripper/implement 26 occurs.
It should be appreciated that control mechanism 60, or another suitable control mechanism, receives data indicative of a grade of implement 26 and a grade of implement 24 at block 290, calculates the error between the indicated grades of each of implement 26 and implement 24 and target grades at block 276, and then reduces the errors by way of adjusting implement 26 and implement 24 in a closed loop fashion. Meanwhile the pull-slip ratio error calculated at block 270 is being reduced in a closed loop fashion. As described above, the reduction in the pull-slip error may be achieved by way of commanded engagement of implement 26 with material of the underlying substrate. It should also be appreciated, however, that the operation of tractor 10 may be changing at the same time, as the grade of implement 24 may be adjusted to transition tractor 10 between phases in a work cycle, such as between a load phase and a carry phase as depicted in
Turning now to
From block 315 the logic may advance to block 320 to determine the target pull-slip ratio. From block 320 the logic may advance to block 325 to query is the pull-slip ratio in the optimum window? If yes, the logic may advance to block 350 to maintain current operation. If no, the logic may advance to block 330 to query is the current operation at the end of load or return segment? If yes, the logic may advance to block 335 to set the grade targets for both the blade and the ripper. If no, the logic may advance to block 340 to set either the grade target of the blade or the grade target of the ripper. From either of block 335 or block 340 the logic may advance to block 345. At block 345 the logic may query whether the grade target or targets are within tolerance? If yes, the logic may advance to block 350 to maintain current operation. If no, the logic may advance to block 355 to adjust one or both of implement 24 and implement 26 as appropriate. From block 355 the logic may advance to block 360 to monitor grade information, and thereafter return to block 345, exit, or execute still another operation.
The present description is for illustrative purposes only, and should not be construed to narrow the breadth of the present disclosure in any way. Thus, those skilled in the art will appreciate that various modifications might be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. As noted above, the teachings set forth herein are applicable to a variety of different traction-producing off-highway machines utilizing a variety of different implements than those specifically described herein. Other aspects, features and advantages will be apparent upon an examination of the attached drawings and appended claims. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.
