This invention relates to a method and apparatus for controlling an implement connected to a tractor, and more particularly, to a method and apparatus for determining the draft force exerted on the tractor by the implement.
Reference to the term xe2x80x9ctractorxe2x80x9d is meant to include any vehicle capable of propelling a ground or soil engaging implement for the purpose of processing the ground or soil, or objects (e.g. crops, forage, shellfish) lying on or in the ground or soil. Typically a tractor is a four wheel drive vehicle having a hitch for attachment of an implement behind the vehicle. It is also well known for tractors to push implements, such as furrow presses. The typical configuration of a tractor includes an operator cab mounted at the rear of the vehicle, and a forward-mounted engine and transmission system. However, it is also known to provide a multi-purpose vehicle, that may function as a tractor, having a forward mounted cab and underslung engine and transmission systems beneath a load carrying deck. Other forms of tractors include two wheeled, two wheel drive devices and tracked vehicles that may be coupled to pull or push implements. The invention relates to and embraces within its scope all such tractors.
Tractor/implement combinations are widely used in various processes in agriculture. One of the most common of these is plowing, in which a plow is towed behind a tractor. However, tractors may be used for a great variety of other operations such as spraying, furrow pressing, harrowing, raking, seeding and a number of specialized operations such as arise e.g. in vineyards and estuaries, in which specially designed ground-engaging implements are used. Consequently, references made herein to the term xe2x80x9cimplementxe2x80x9d is intended to include, but not be limited to, plows, harrows, furrow presses, rakes, seed drills, and indeed virtually any device that may be attached to or operated by a tractor and that has the effect of increasing the energy demand of the tractor by virtue of engagement of the implement with the ground or soil or with objects thereon or therein.
Electronic control of the subsystems of tractors is becoming more and more common. For example, EP-A-0 838 141 (the entire disclosure of which is incorporated herein be reference) discloses an integrated control system for tractors by means of which a programmed microprocessor (or series of microprocessors) maximizes the workrate of a tractor e.g. during plowing operations, by comparing the implement draft force against a steady state reference model, and performing implement working width and transmission ratio adjustments in order to maintain a maximal workrate while also maintaining a predetermined implement working depth.
The method and apparatus of EP-A-0 838 141 is most effective when it is possible to obtain an accurate, real time indication of the proportion of the tractor engine output that is attributable to the implement draft force; and the proportion that is attributable to other losses. One way of generating a signal indicative of the implement draft force is to provide a draft force sensing pin (including e.g. a strain gauge forming part of a per se known bridge circuit) in the lower link of the tractor three point hitch. The accuracy of the signal generated from such a sensing pin is acceptable when the implement is a fully-mounted one such as a fully-mounted plow. The accuracy of the draft force sensing pin arrangement is worse for semi-mounted implements such as a semi-mounted plow; and of no use whatsoever with trailed or pushed equipment, that does not place a load on the lower link of the tractor three point hitch.
EP-A-0 741 286 (the entire disclosure of which is incorporated herein by reference) discloses one form of a torque sensor securable to or constituting part of the flywheel of a tractor engine. An arrangement, such as that disclosed in EP-A-0 741 286, that generates a signal indicative of the flywheel torque, is more suitable, than the above-mentioned lower link pin sensor, for control systems controlling a tractor/implement combination, since the engine loading xe2x80x9cseenxe2x80x9d by the flywheel torque sensor is a total loading value, regardless of whether the implement is trailed, semi-mounted, fully-mounted or propelled in some other way (such as pushed in front of the tractor instead of towed behind the tractor). However, the generated torque signal is dependent upon the selected tractor transmission ratio and tire circumference (or the effective circumference of another driven, ground engaging member if present). Also, the tractor flywheel torque is dependent upon both the implement-imposed drive line load (that tractor/implement control software may seek to maintain constant); and vehicle rolling resistance (RR) and frictional/parasitic losses in the tractor transmission and drive line.
It is possible to devise software in a tractor/implement control system that compensates for variations in the flywheel torque signal arising from the choice of tire circumference and the selected transmission ratio. The compensations needed to account for these variations are likely to be invariant, and may be dealt with in the software algorithm by means of a simple factoring by memory-stored values relating to tire size and transmission ratio. On the other hand the vehicle rolling resistance and frictional/parasitic losses are unlikely to remain constant during operation of the tractor. The rolling resistance component of the flywheel torque is significant, accounting for up to 25% of the flywheel torque.
It is an object of this invention to provide for the storing of calibration data indicative of the rolling resistance and frictional/parasitic losses acquired when the tractor/implement combination operates in a particular field condition. The stored rolling resistance and-frictional/parasitic loss value may then be subtracted from the real time flywheel torque sensor output signal during use of the tractor in the field in order to give an accurate indication of the engine loading due to the implement draft. The resulting, corrected torque signal may then be used in software and apparatus, e.g. as disclosed in EP-A-0 838 141, as a measure of the implement draft load.
It is a feature of this invention that the tractor includes more than one transmission ratio to vary the draft force with changes in transmission ratio.
It is another feature of this invention to provide calibration data obtainable for more than two transmission ratios.
It is an advantage of this invention to permit a control method to operate an implement with greater accuracy and efficiency.
It is another object of this invention to allow for calculation of the draft force notwithstanding variations in the torque loading caused by the choice of tractor tire (or other driven, ground engaging member) effective circumference and the overall transmission ratio between the tractor engine flywheel and the driven ground engaging member, respectively.
It is still another feature of this invention to store the rolling radius and overall transmission ratio data as one or more lookup tables in a memory forming part of or operatively connected to a control device such as a microprocessor.
It is another advantage of this invention to use the implement draft force signal to initiate or augment a control operation.
It is still another object of this invention to calculate the implement draft force signal according to the formula:                                                         Implement              ⁢                              xe2x80x83                            ⁢                              Draug                ⁢                ht                            ⁢                              xe2x80x83                            ⁢                              (                kN                )                                      =                                                            [                                                                                                                                          Instantaneous                            ⁢                                                          xe2x80x83                                                        ⁢                            Flywheel                                                                                                                                                                            Torque                            ⁢                                                          xe2x80x83                                                        ⁢                                                          (                                                              N                                .                                m                                                            )                                                                                                                                            -                                                                                                                        Calibration                            ⁢                                                          xe2x80x83                                                        ⁢                            Flywheel                                                                                                                                                                            Torque                            ⁢                                                          xe2x80x83                                                        ⁢                                                          (                                                              N                                .                                m                                                            )                                                                                                                                                            ]                                xc3x97                PR                                            Rear                ⁢                                  xe2x80x83                                ⁢                Tire                ⁢                                  xe2x80x83                                ⁢                Rolling                ⁢                                  xe2x80x83                                ⁢                Radius                ⁢                                  xe2x80x83                                ⁢                                  (                  m                  )                                xc3x97                1000                                              ⁢                      
                    ⁢                      here:-                    ⁢                      xe2x80x83                    ⁢                      
                    ⁢                                                                      PR                  ≡                                                                                                                                                                          The                          ⁢                                                      xe2x80x83                                                    ⁢                          tractor                          ⁢                                                      xe2x80x83                                                    ⁢                          powertrain                          ⁢                                                      xe2x80x83                                                    ⁢                          ratio                                                ,                                                  xe2x80x83                                                ⁢                                                                              i                            .                            e                            .                                                          xe2x80x83                                                        ⁢                            the                                                    ⁢                                                      xe2x80x83                                                    ⁢                          transmission                                                                                                                                                                        and                        ⁢                                                  xe2x80x83                                                ⁢                        entire                        ⁢                                                  xe2x80x83                                                ⁢                        driveline                        ⁢                                                  xe2x80x83                                                ⁢                        ratio                        ⁢                                                  xe2x80x83                                                ⁢                        from                        ⁢                                                  xe2x80x83                                                ⁢                        the                        ⁢                                                  xe2x80x83                                                ⁢                        flywheel                        ⁢                                                  xe2x80x83                                                ⁢                        to                        ⁢                                                  xe2x80x83                                                ⁢                        the                                                                                                                                                                          axle                          ⁢                                                      xe2x80x83                                                    ⁢                          end                                                ;                                                                                                                          ⁢                      xe2x80x83                    ⁢                      
                    ⁢                                                                      Instantaneous                                                                                                  Flywheel                    ⁢                                          xe2x80x83                                        ⁢                    Torque                                                                        ≡                          “                              Uncorrected                ⁢                                  xe2x80x83                                ⁢                Flywheel                ⁢                                  xe2x80x83                                ⁢                Torque                            ”                                ⁢                      xe2x80x83                    ⁢                      
                    ⁢          nd          ⁢                      xe2x80x83                    ⁢                      "IndentingNewLine"                    ⁢                                                                      Calibration                                                                                                  Flywheel                    ⁢                                          xe2x80x83                                        ⁢                    Torque                                                                        ≡                                                                                Transmission                    ⁢                                          xe2x80x83                                        ⁢                    gear                    ⁢                                          -                                        ⁢                    specific                    ⁢                                          xe2x80x83                                        ⁢                    flywheel                    ⁢                                          xe2x80x83                                        ⁢                    torque                                                                                                                    value                    ⁢                                          xe2x80x83                                        ⁢                    derived                    ⁢                                          xe2x80x83                                        ⁢                    during                    ⁢                                          xe2x80x83                                        ⁢                    a                    ⁢                                          xe2x80x83                                        ⁢                                          “                                              Rolling                        ⁢                                                  xe2x80x83                                                ⁢                        Resistance                                            ”                                                                                                                                        Calibration                    ⁢                                          xe2x80x83                                        ⁢                                          Procedure                      .                                                                                                          ⁢                  xe2x80x83                                    (        1        )            
It is still another advantage of this invention that maintenance of a generally constant implement depth value may be achieved by carrying out a control operation including adjusting or maintaining one or more variable subsystems.
It is another advantage of this invention that the step of detecting the torque at the tractor engine flywheel and generating a signal indicative thereof, while the tractor/implement combination advances across the surface with a first tractor transmission ratio selected, takes place with the tractor engine governor set at approximately a xe2x80x9cfull throttlexe2x80x9d setting.
It is yet another advantage of this invention that the calibration of the tractor/implement combination with the tractor operating at a full throttle setting avoids the need to compensate the flywheel torque value for variations in the governor setting.
It is another feature of this invention to carry out the step of detecting the torque at the tractor engine flywheel and generating a signal indicative thereof while the tractor/implement combination advances across a surface with the implement disengaged from the surface, at a throttle setting less than maximum, whereby the calibration of the tractor/implement combination is normalized to a reference or datum throttle setting, that in practical embodiments is equivalent to a full throttle setting.
It is an object of this invention to use a power shift automatic transmission to provide more accurate control of the tractor/implement combination if the method is temporarily interrupted during transmission shifts.
It is yet another feature of this invention to include a sensor for detecting the selected tractor transmission ratio and generating a signal indicative thereof, the processor optionally or additionally being programmed to compensate the value of the corrected flywheel torque signal for variations arising from the transmission ratio selected.
It is yet another object of this invention to permit adjustment and/or maintenance of the implement working depth and the tractor transmission ratio in order to maximize tractor/implement combination workrate while maintaining an optimal implement draft.
It is a further feature of this invention to store in the memory of the tractor/implement combination a steady state reference model.
It is still a further object of this invention to calculate the degree of wheelslip by subtracting the true vehicle speed value from a theoretical value simply derived from the wheel speed. If the degree of wheelslip exceeds an operator inputted or software imposed limit, control software may operate an actuator in order to reduce wheelslip to within acceptable limits. This ensures an efficient tractive effort and assists in maximizing workrate of the tractor/implement combination.
It is still another feature of this invention to raise the three point hitch of the tractor to reduce wheelslip in an attempt to reduce the implement draft force and consequently reduce wheelslip.
It is yet another feature of this invention to control a mid-axle mounted wheel, mounted on an actuator strut whose length is adjustable by means of an hydraulic remote service valve by controlling the working depth of the rear section of the implement.
It is an advantage of this invention that the change in implement draft force resulting from the raising operations, that in turn reduces the tractor wheelslip, is less pronounced and results in a greater efficiency of the tractor/implement combination operation.
It is a feature of this invention that the length adjustable actuator includes a fluid actuator whereby the step of lowering the second portion of the semi-mounted implement includes exhausting fluid from the actuator via the spool valve.
These and other objects, features and advantages are accomplished according to the instant invention by providing a control for a tractor/implement combination in which the real-time data on the true draft force generated by engagement of an implement with the ground. A method of controlling a tractor/implement combination includes obtaining and storing calibration data on the torque generated at the tractor flywheel, while the implement is disengaged from the ground, including such data the rolling resistance and frictional/parasitic losses between the flywheel and driven wheel axle of the tractor. During subsequent operation of the tractor/implement combination, the calibration data is subtracted from instantaneous data to generate a signal indicative of the implement draft force. The draft force signal may be factored to take account of the tractor power train ratio and the rolling radius of the tractor tires. The method allows generation of accurate draft force data, regardless of the nature and mounting location of the implement.