Abstract:
A method of calibrating the control current startup threshold in a proportionally controlled drive system for a work vehicle is disclosed. To determine a current threshold value for use in the system a control current exhibiting a relatively low value is first applied to the system. Subsequently, the steps of repetitively increasing the control current to a control current start value at which system motion starts and decreasing the control current to a control current stop value at which system motion substantially stops are repetitively conducted. The resultant control current start values and control current stop values are stored in a memory. The stored control current start values and control current stop values are is then averaged to determine a control current threshold value for use in controlling the system.

Description:
BACKGROUND  
         [0001]    The disclosures herein relate generally to the field of control systems for work vehicles. More particularly, the disclosures herein relate to a system and method for quickly determining the threshold control current necessary to actuate a proportional control system such as a hydro-mechanical system on a work vehicle.  
           [0002]    To operate a modern hydraulic control system it is important to determine the startup threshold current of devices such as pumps, clutches, valves and other mechanisms which are controlled via control signals. These devices have a common operating requirement, namely that they all require some minimum amount of current, i.e. the startup threshold current, to start operating. The conventional approach to determining such startup threshold currents is to employ an automatic calibration process to measure the startup threshold current for a hydraulic system by ramping up the control signal slowly until the controlled device starts to move. This ramping step is repeated several times and the results are averaged to yield an average startup threshold current. Unfortunately, this calibration process takes a relatively large amount of time to obtain accurate results. Since hydraulic systems exhibit system dynamics and nonlinear characteristics, the ramp up speed is essential to the accuracy of threshold current calibration.  
           [0003]    What is needed is a methodology for more quickly automatically determining the startup threshold currents for controlled devices without sacrificing calibration accuracy. Such a methodology would be especially useful in work vehicles such as combines and other agricultural implements requiring calibration of their hydraulic, pneumatic and other proportional control systems.  
         SUMMARY  
         [0004]    Accordingly, in one embodiment a method of operating a proportional control drive system is disclosed which includes applying a control current to a controlled device; repetitively increasing the control current to a control current start value at which system motion starts and decreasing the control current to a control current stop value at which system motion substantially stops; storing in a memory the control current start values and control current stop values; and averaging the control current start values and control current stop values to determine a current threshold value.  
           [0005]    A principal advantage of the embodiment disclosed herein is significantly expedited threshold current determination. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a perspective view illustrating an embodiment of an agricultural harvesting vehicle.  
         [0007]    [0007]FIG. 2 is a block diagram of a control system for the vehicle of FIG. 1.  
         [0008]    [0008]FIG. 3 is a pump coil current vs. time graph depicting the time history for pump coil startup threshold current calibration.  
         [0009]    [0009]FIG. 4 is a pump displacement (or angle) vs. pump coil current graph for the control system of FIG. 2.  
         [0010]    [0010]FIG. 5 is a clutch current vs. time graph showing the time history for the clutch startup threshold current calibration.  
         [0011]    [0011]FIG. 6 is a flow chart depicting how the startup threshold current calibration method fits into the operation of a controller employed in the control system of FIG. 2.  
         [0012]    [0012]FIG. 7A is a flow chart showing the process for determining the startup control current threshold for the positive coil of the rotor pump.  
         [0013]    [0013]FIG. 7B is a flow chart showing the process for determining the startup control current threshold for the negative coil of the rotor pump.  
         [0014]    [0014]FIG. 7C is a flow chart showing the process for determining the startup control current threshold for a clutch mechanism of the vehicle. 
     
    
     DETAILED DESCRIPTION  
       [0015]    While being generally applicable to systems under proportional control, the disclosed methodology is described with respect to the hydro-mechanical drive system of agricultural equipment such as a combine by way of example.  
         [0016]    Agricultural work vehicles such as combines utilize a header or other implement to perform various operations on a field. Combines often employ an implement such as a harvester or header attached to a feeder to harvest a crop or other plant-related matter. The feeder receives the cut or harvested crop from the header and provides the harvested crop to various pieces of equipment within the combine which perform assorted operations on the harvested crop such as sorting, separating, spreading, storing, or other agricultural functions.  
         [0017]    Generally, combines have a combustion engine or mechanical power source indirectly driving the various pieces of equipment which operate on the harvested crop. The various pieces of equipment can include, but are not limited to, a feeder which receives the harvested crop from the header and transports the harvested crop to within the combine, a rotor which receives the harvested crop from the feeder and spins axially to thresh or separate the seed from the non-seed material of the harvested crop, a shoe shaker which separates additional seed from the non-seed material from the rotor, a straw spreader which spins to throw the non-seed material received from the shoe shaker out of the combine, a tailings elevator which conveys seed from the shoe shaker to the rotor, a clean grain elevator which transports seed from the rotor to the grain storage tank or external grain storage area, a discharge beater, a chopper which cuts the non-seed material for spreading by the straw spreader, a cleaning fan which provides cross air movement across the seed material to clean the seed material as it is conveyed through the combine, a rotary air screen fan which provides cooling for the combustion engine, as well as other types of devices which are driven by the engine. An unloader apparatus, typically a swingable auger tube, is stowed alongside the combine in a plane parallel with the combine&#39;s wheels. This unloader tube is capable of swinging from the stowed position to a position which is approximately 90 degrees perpendicular to the stowed position. The unloader tube is swung back and forth by the operator over a grain receiving bin in a storage vehicle which is positioned alongside the combine.  
         [0018]    As shown in FIG. 1, a work vehicle, namely agricultural vehicle  10 , includes a pair of drive wheels  12  located at the front end of vehicle  10 , a pair of steerable wheels  14  located at the rear end of vehicle  10 , a machinery and grain storage compartment or housing  16 , a grain elevator/auger and grain unloading tube  18 , an operator cab  20 , and a support frame or chassis  21  for joining and supporting the above-listed components.  
         [0019]    Attached to a feeder  29  at the front end of the frame of vehicle  10  (i.e., the front-most end of vehicle  10  along its forward direction of travel during harvesting) is a header  22  such as a grain harvesting header. Header  22  is positioned relative to vehicle  10  and/or the surface  23  upon which vehicle  10  is moving (i.e., the ground from which the respective plant related matter, grain or vegetation, is being harvested). Header  22  includes a reel  27  for gathering the cut crop. The harvested crop is provided to feeder  29  which includes an auger or conveyor mechanism for transporting the harvested crop from header  22  to within combine  10 . Vehicle  10  includes a straw spreader  40  as shown. Vehicle  10  includes an engine  50  to provide motive power to move vehicle  10  and power to operate the various components included therein, such as straw spreader  40 , for example.  
         [0020]    Agricultural vehicle  10  includes a control system  11  mounted in an interior  13  of cab  20 . Control system  11  is coupled to a display  17  preferably located within interior  13  of cab  20  easily visible to the operator. Display  17  can be also be located on a vertical post within the interior  13  of cab  20 . Display  17  is conveniently implemented as a liquid crystal display (LCD), a light emitting diode (LED) array, an incandescent lamp array, a cathode ray tube (CRT), a plasma display or other display devices. Information regarding the status of the various mechanical and electrical systems of vehicle  10  is conveniently provided to the operator on display  17 .  
         [0021]    A work vehicle such as combine  10  is illustrated in block diagram form in FIG. 2. Combine  10  includes a number of hydraulic systems which require startup threshold current calibration. For example, hydraulic rotor pump  100  and engine-to-ring (ETR) clutch  105  form part of a rotor control system which requires startup current threshold current calibration. In more detail, combine  10  includes a rotor controller  110  that controls a rotor  115  which is driven by engine  50 . Rotor  115  is a cylindrically shaped device which facilitates the threshing of the crop ingested by combine  10 . Concaves (not shown), positioned close to the rotor, scrape and separate grain from the chaff as the rotor rotates. Rotor  115  is controlled electronically and hydraulically as now explained. Typical instructions carried out by controller  110  to control the operation of rotor  115  include 1) rotor accelerate, 2) rotor decelerate 3) de-slug—namely, to slowly rotating the rotor forward or reverse to flush compacted crop between the rotor and the concaves, and 4) calibrate. Rotor controller  110  receives these instructions from another controller (not shown) via controller area network (CAN)  120  and controller  110  provides status information such as rotor speed and direction to other controllers in combine  10  and to display  17  over the same CAN bus of CAN  120 .  
         [0022]    Rotor controller  110  includes a central processing unit (CPU)  116  which is coupled to a random access memory (RAM)  117  that provides temporary storage for information. CPU  116  is also coupled to a read only memory (ROM)  118  in which control software is permanently stored. Control software governs the operation of controller  110  and rotor  115  as will be discussed later in more detail. A electronically erasable programmable read only memory (such as EEPROM)  119  is included in controller  110 .  
         [0023]    As shown in FIG. 2, engine  50  is coupled to gear box  130 . Gear box  130  drives engine-to-ring clutch  105  which drives ring gear  140  when the clutch is engaged under the control of rotor controller  110 . A planet gear set  145  (multiple planet gears connected by carrier  152 ) is coaxially mounted within ring gear  140 . Planet gear set  145  is coaxially mounted to sun gear  150 . Ring gear  140 , planet gear set  145  and sun gear  150  are concentric, each being coaxially mounted with respect to the other. Together ring gear  140 , planet gear set  145  and sun gear  150  are collectively referred to as planetary  151 . Rotor motor  155  drives sun gear  155  as directed by rotor controller  110  via the rotor pump  100 . In more detail, rotor pump  100  is coupled to and controlled by rotor controller  110 . Rotor pump  100  is connected to rotor motor  155  to drive sun gear  150 . A motor speed sensor  160  is connected to rotor motor and rotor controller  110  so that the rotational velocity of rotor motor  155  can be reported back to controller  110 .  
         [0024]    A ring-to-frame brake  165  is mechanically connected to ring gear  140  and electrically connected to rotor controller  110  so that controller  110  can control the braking and hence the deceleration of rotor  115 . As seen in FIG. 2, rotor  115  is mechanically connected by a multi-speed gearbox  170  to carrier  152 . A rotor speed sensor  175  is connected to rotor  115  and controller  110  to report the rotational velocity of rotor  115  back to controller  110 . External loads driven by rotor  115  are indicated collectively as external loads  180 .  
         [0025]    More detail is now provided with respect to selected components of vehicle  10 . Rotor pump  100  is used in conjunction with rotor motor  155  to hydrostatically accelerate rotor  115  from rest through planetary  151  and gear box  170 . Rotor pump  100  is also employed in conjunction with rotor motor  155  to hydrostatically adjust the rotor speed after initial hydrostatic acceleration since engine  50  at this point provides the majority of the power for rotor  115  via engine-to-ring clutch  105 , planetary  151  and rotor gear box  170 .  
         [0026]    The purpose of the ring-to-frame brake  165  is to hold ring gear  140  of planetary  151  stationary. This allows rotor pump  100 , rotor motor  155 , planetary  151  and gear box  170  to drive rotor  115  hydrostatically either during initial start-up of is rotor  115  when a separator switch (not shown) is engaged, or to control the rotor  115  in a “de-slug” mode of operation should too much crop be ingested at one time for the rotor to properly separate the crop, or to allow rotor controller  110  to calibrate the rotor system.  
         [0027]    The purpose of engine-to-ring (ETR) clutch  105  is to engage engine  50  with planetary  151  after ring-to-frame (RTF) brake  165  is disengaged to drive rotor  115  through planetary  151  and rotor gear box  170 . With ETR clutch  105  engaged and RTF brake  165  disengaged, engine  50  provides the majority of the rotor&#39;s power and rotor pump  100  and rotor motor  155 , at that time, are only used to make small changes to the rotor&#39;s speed by controlling the speed and direction of the planetary&#39;s  151  sun gear  150 .  
         [0028]    A high level overview of an automatic calibration process for setting the startup threshold current of hydraulic devices such as rotor pump  100  and ETR clutch  105  is now presented with reference to FIGS. 3, 4 and  5 . The process is implemented by control software stored in ROM  118  and executed by CPU  116  of controller  110 . To begin the process of start rotor pump threshold current calibration for spinning forward or reverse, the control current, I C1 , supplied to rotor pump  100  initially jumps to a value 1 (FIG. 3) which is predetermined to be below any possible startup threshold current. FIG. 3 is a graph depicting control current, I C1 , vs. time. As seen in FIG. 3, when controller  110  commences calibration it initially sets the control current, I C1 , to a value designated at 1. Controller  110  then permits the control current to increase rapidly until rotor motor  155  starts to move at 2. Controller  110  can readily ascertain when motor  155  commences rotation by monitoring the motor speed signal received from motor speed sensor  160 . Then, as seen in FIG. 3, the control current decreases slowly as designated at 3 until rotor motor  155  ceases rotation. The control current value observed at the point in time when the motor ceases rotation is saved in memory (RAM)  117  as a command current value or stop value. Controller  110  again increases the control current, I C1 , to commence motor rotation but this time slowly until the motor begins rotating as indicated at 4. The control current value observed when the motor begins rotating this second time is also stored in RAM  117  as a command current value or start value. The above described process is repeated several times. The stored command current values which include both stopping and starting command current values are averaged to determine a nominal startup threshold current. The process is terminated after several start-stop cycles at time, T1. FIG. 4 is a graphical representation of rotor pump  100  displacement (or angle) vs. the coil current of pump  100  showing a hysteresis effect between starting and stopping.  
         [0029]    A high level overview of an automatic calibration process for setting the startup threshold current of hydraulic devices such as ETR clutch  105  is now presented with reference to FIG. 5. FIG. 5 is a graph depicting control current, I C2 , vs. time. The calibration process is implemented by control software stored in ROM  118  and executed by CPU  116  of controller  110 . To begin the process of clutch threshold current calibration under control of rotor controller  110  the control current, I C2 , supplied to ETR clutch  105  initially jumps to a value 5 which is predetermined to be below any possible startup threshold current. The control current, I C2 , then increases quickly at 6 until the output side of the clutch starts to move. At this point, the command current value is saved in RAM  117  as a reference value. Next, rotor controller  110  commands ETR clutch  105  to release and the control current, I C2 , goes to zero at 7. After the output side of the clutch slows down, the control current, I C2 , suddenly jumps to a value indicated at 8, a function of, the previous reference value stored in RAM. Then, rotor controller  110  increases the control current, I C2 , slowly until the output of ETR clutch  105  starts moving as indicated at 9. At the point where the output of clutch  105  starts moving the command current value is again stored in RAM  117 . This process of releasing the clutch and increasing the control current is repeated several times and the stored data is averaged to determine a nominal startup threshold current for clutch  105 .  
         [0030]    [0030]FIG. 6 is a flow chart depicting how the startup threshold calibration method fits into the operation of controller  110  at a high level. Rotor controller  110  is initialized at start block  200 . Controller  110  monitors rotor speed via sensor  175  as indicated at decision block  205  until rotor speed falls below 20 rpm. When rotor speed is less than 20 rpm, process flow continues and ring-to-frame brake  165  is engaged as per block  210 . Controller  110  monitors to determine if calibration is requested as per decision block  215 . If calibration is requested then controller  110  resets parameters, namely the data values stored in RAM  117  as per block  220 . A test is conducted at decision block  225  to see if calibration is complete, or if there is a system error, or a stop calibration request is received. If any of these conditions occur, then the calibration process is halted as per block  230 . Results and status are displayed as per block  240  and the process ends. Otherwise, the calibration process depicted in more detail in the flowchart of FIGS. 7A, 7B and  7 C continues to completion after the test at decision block  225 .  
         [0031]    As shown in FIG. 7A, the calibration process carried out by controller  110  begins at start block  300 . A test is conducted at decision block  305  to determine if the separator switch is on. If the separator switch is determined to be on, then process flow continues to block  310  at which an initial current control command is applied to the positive (+) coil terminal of rotor pump  100 . A test is conducted to determine if the rotor velocity is greater than 1 rpm at decision block  315 . If the rotor velocity is not greater than 1 rpm then controller  110  increases the control current through the coil of rotor pump  100  by 0.1 A/sec as per block  320 . When the rotor velocity exceeds 1 rpm then a second test is conducted at decision block  325  to determine if the rotor velocity is now less than 1 rpm. If the rotor velocity is not found to be less than 1 rpm, then controller  110  decreases the control current through the coil of rotor pump  100  by 0.01 A/sec as per block  330 . When the rotor velocity ultimately decreases to the point where it is less than 1 rpm then the control current value corresponding to that point is stored in RAM  117  or in a temporary register in CPU  116  as per block  335 .  
         [0032]    A test is then conducted at decision block  340  to determine if the rotor velocity has increased to more than 1 rpm. If the rotor velocity has not so increased, then controller  110  increases the control current through the + terminal of the pump coil by 0.01 A/sec as per block  345 . When decision block  340  finds that the control current has now increased to a point at which the rotor velocity is greater than 1 rpm, then the control current value corresponding to that point is stored in RAM  117  or in a temporary register in CPU  116 . The above described sequence is repeated several times and the control current values from each cycle are averaged together to obtain the control current threshold value to be used by vehicle  10 . More specifically, a test is run at decision block  350  to determine if 3 high-low cycles have been conducted. If so, the pump (+) coil control current threshold calibration is complete as per block  360 . The average of the saved control current thresholds from each cycle is stored for later use as the positive (+) control current threshold. The command current is set back to zero in preparation for determining the control current threshold for the negative (−) terminal of the pump coil.  
         [0033]    The flowchart continues on FIG. 7B which depicts the steps carried out to determine the control current threshold for the negative (−) terminal of pump coil  100 . A test is conducted at decision block  405  to determine if the rotor velocity is less than 1 rpm. If the rotor velocity is less than 1 rpm then flow continues to block  410  at which an initial current control command is applied to the negative (−) terminal of the rotor pump&#39;s coil. A test is conducted to determine if the rotor velocity is greater than 1 rpm at decision block  415 . If the rotor velocity is not greater than 1 rpm then controller  110  increases the control current through the coil of rotor pump  100  by 0.1 A/sec as per block  420 . When the rotor velocity exceeds 1 rpm then a second test is conducted at decision block  425  to determine if the rotor velocity is now less than 1 rpm. If the rotor velocity is not found to be greater than 1 rpm, then controller  110  decreases the control current through the coil of rotor pump  100  by 0.01 A/sec as per block  430 . When the rotor velocity ultimately decreases to the point where it is less than 1 rpm then the control current value corresponding to that point is stored in RAM  117  or in a temporary register in CPU  116  as per block  435 .  
         [0034]    A test is then conducted at decision block  440  to determine if the rotor velocity has increased to more than 1 rpm. If the rotor velocity has not so increased, then controller  110  increases the control current through the negative (−) terminal of the pump coil by 0.01 A/sec as per block  445 . When decision block  440  finds that the control current has now increased to a point at which the rotor velocity is greater than 1 rpm, then the control current value corresponding to that point is stored in RAM  117  or in a temporary register in CPU  116 . The above described sequence is repeated several times and the control current values from each cycle are averaged together to obtain the control current threshold value to be used by vehicle  10 . More specifically, a test is run at decision block  450  to determine if 3 high-low cycles have been conducted. If so, the pump negative (−) coil control current threshold calibration is complete as per block  460 . The average of the saved control current thresholds from each cycle is stored for later use as the negative control current threshold.  
         [0035]    The flowchart continues on FIG. 7C which depicts the steps carried out to determine the control current threshold for ETR clutch  105 . Controller  110  waits for 10 seconds as per block  500  to allow rotor  115  to speed up by way of the hydraulic dragging between two sides of ETR clutch  105 . Controller  110  then saves the current rotor velocity in RAM  117  as a reference as per block  505 . Controller  110  applies an initial command to the coil in ETR clutch  105  to cause current to flow in the coil as per block  510 . A test is then conducted at decision block  515  to determine if the velocity difference between the rotational velocity of rotor  115  and the reference rotor speed mentioned above is greater than 15 rpm. If the velocity difference is not greater than 15 rpm, the control current through the clutch coil is increased by 0.1 A/sec as per block  520 . When the velocity difference ultimately exceeds 15 rpm, then the present clutch control current value is saved in RAM  117  as a reference control current value as per block  525 . The clutch current value applied to ETR clutch  105  is reset to zero as per block  530 . A test is conducted at decision block  535  to determine if the absolute value of the velocity difference is less than 5 rpm. When the absolute value of the velocity difference decreases to less than 5 rpm, then controller  110  applies a starting command to the coil of ETR clutch  105 . As per block  540  the stored reference current is used in this command.  
         [0036]    A test is then conducted at decision block  545  to determine if the rotor velocity has increased to greater than 15 rpm. If not, as per block  550  the control current through the clutch coil is increased by 0.01 A/sec. When test block  545  ultimately finds that the velocity difference has increased to greater than 15 rpm, the present control current value applied to the rotor coil is saved in memory as per block  555 . The above test sequence is conducted several times and the control current values determined in each test sequence are saved. A test is carried out at decision block  560  to determine if the test sequence has been conducted 3 times. If not, process flow continues back to block  530  and the test is repeated. However, when decision block  560  finds that the test sequence has been conducted 3 times, process flow continues to block  565  at which 1) for rotor pump  100 , the average of the high threshold pump control current values, the average the low pump control current threshold values, and an overall average or median threshold value is calculated from all stored pump control current values, and 2) the nominal control current threshold value for ETR clutch  105  is calculated by averaging the stored threshold control current values for the clutch. These values are then saved in an electronically erasable programmable read only memory (EEPROM)  119  in controller  110  as per block  570 . This completes the automatic determination of startup control threshold currents for rotor pump  100  and ETR clutch  105  as noted in block  575 . The values thus determined are used subsequently as the startup threshold control currents for the pump and clutch respectively.  
         [0037]    The processes described by the flowcharts mentioned above are not limited to pumps containing two coils but rather by reversing the direction of current, the same process would apply to single coil pumps. Moreover, this process can be adaptive for successive calibrations of the same coil or coil type. The reference current value, from a first calibration, can be used for successive calibrations to significantly reduce the amount of calibration time. Additionally, the incremental current rates can be modified to more quickly realize the max/min thresholds by first “jumping” to a current close to the threshold and then slowly incrementing to the anticipated current threshold.  
         [0038]    Advantageously, the process described herein achieves a significantly expedited threshold control current determination. Moreover, the method can be applied to different proportional control systems, whether they are hydraulic, pneumatic or otherwise. The method readily adapts to different systems having different control current requirements and thresholds.  
         [0039]    Although illustrative embodiments have been shown and described, a wide range of modification, change and substitution is contemplated in the foregoing disclosure and in some instances, some features of an embodiment may be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the embodiments disclosed herein.