Abstract:
A computer calibration method and apparatus for calibrating one or more auxiliary hydraulic valves on a work vehicle includes the steps of selecting a first auxiliary hydraulic valve, applying a valve opening signal to that valve, measuring a pressure in a flow restricted signal circuit coupled to the valve, comparing the first pressure with a predetermined pressure to see if the valve is cracked open and if the valve is not cracked open, incrementing the signal to a second level and repeating the foregoing steps until the first valve cracks open. The final step is saving a value indicative of the signal at which the valve just cracked open.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates generally to work vehicles. More particularly, it relates to auxiliary hydraulic valves and controllers for work vehicles. Even more particularly, it relates to automated methods and structures for calibrating the auxiliary valves for such vehicles.  
         FIELD OF THE INVENTION  
         [0002]    This invention provides a way for automatically calibrating electronically controlled remote hydraulic valves. It is adaptable for use on all agricultural and construction vehicles equipped with electronically controlled remote hydraulic valves.  
           [0003]    Remote hydraulic valves provide auxiliary hydraulic flows to implements that are coupled to vehicles for performing various tasks. Typically, such a vehicle will have several such valves, typically varying between two and eight. These valves are controlled in an operator station typically in the cab of the vehicle, most commonly by manipulating a lever or knob that provides a signal proportional to the movement of the lever or knob and indicates a desired flow rate to or from an auxiliary hydraulic valve. The hydraulic valves are typically connected to a manifold or manifolds, most commonly located at the rear of the vehicle, to which hydraulic actuators are mounted. These hydraulic actuators include such things as hydraulic motors and cylinders. By varying the position of the lever or knob, the operator can vary the flow rate to the manifold, and thence to the hydraulic actuators located on the implement.  
           [0004]    Another common user input device located at the operator station is a flow rate control. The flow rate control is typically a small dial or knob that is set by the operator and indicates a maximum flow rate through the valve. Thus, by rotating the flow rate control, the operator can limit the operating range of the lever or knob from a flow rate of zero (0) to a positive maximum flow rate indicated by the flow rate control, and a negative maximum flow rate, also indicated by the flow rate control.  
           [0005]    Vehicle operators usually expect the same flow rate curve from all the auxiliary hydraulic valves. Flow variations between valves may be severe, however, due to the tolerances of the valves, the actuators and the controls.  
           [0006]    A typical problem that is commonly found with auxiliary hydraulic valves is that of hysteresis. From the operator&#39;s perspective, hysteresis appears when the operator moves the lever or knob away from a zero flow rate position towards either a positive or negative flow rate and no flow passes through the valve.  
           [0007]    The initial small movements of the lever or knob generate equivalent small electrical signals that are applied to the valve coil. These small initial signals are insufficient to overcome the valve&#39;s static friction and therefore these initial small movements of the lever or knob will not cause the valve to open.  
           [0008]    As the operator continues to move the lever or knob, indicating a higher flow rate, and generating a larger valve signal, the valve will still remain closed until the applied signal is sufficient to overcome the static friction, at which point a low flow rate begins to pass through the valve.  
           [0009]    In some cases, the valve spool may indeed move when a signal is applied, but due to the location of the various lands and grooves, this movement may not be sufficient to open up a fluid flow path. The effect, from the operator&#39;s perspective, is the same: movement of the lever or knob does not result in an equivalent flow rate.  
           [0010]    In addition, a strong spring used in the valve may resist the movement of the spool and also result in no valve opening when small valve signals are applied.  
           [0011]    During this movement of the lever or knob, the valve signal applied to the valve is indeed increasing. However, due to frictional effects in the valve, the resistance of the spring, or the location of the various lands and grooves, no hydraulic flow through the valve may occur. This region of no valve flow when the lever or knob is moved is often called a “dead-band.” 
           [0012]    A way to cancel out this dead-band is needed in order to make the whole range of motion of the lever or knob provide an proportional flow rate.  
           [0013]    The dead-band can be modeled as a constant valve signal offset that must be added to any signal sent by the controller. If the valve resists opening until a small positive valve signal is applied, this offset should be added to any signal transmitted by the lever or knob. In this manner, whenever the operator moves the proportional controlled lever or knob, even a small amount, some flow will begin to pass through the valve.  
           [0014]    Determining this offset for a particular valve in a particular vehicle, generally requires actually applying a signal to the valve until the valve just opens or “cracks”. If one could observe the valve “cracking” and identify the actual signal that was applied to the valve at the same time, the signal could be saved in the valve controller for later addition to the signal received from the proportional control lever or knob.  
           [0015]    Identifying the valve “cracking” point would normally require the attachment of a loop-back tool to each of the valves. When the valve cracks open, fluid will begin to flow through the valve, out through the quick-connect coupling, through the loop-back tool, back into the adjacent quick-connect coupling, back through the valve and then to a hydraulic reservoir or tank. This, however, would require that an additional tool be attached to the vehicle. During assembly of the vehicle, and when calibrating the vehicle in the field, it is awkward to use such a tool.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0016]    What is needed, therefore, is a method and apparatus for calibrating auxiliary hydraulic valves without the necessity of attaching a loop-back tool to the auxiliary hydraulic manifold. It is an object of this invention to provide such a method and apparatus.  
           [0017]    It is also an object of this invention to provide a method and apparatus for sequentially and automatically calibrating each of the auxiliary hydraulic valves under computer control.  
           [0018]    In accordance with the first embodiment of the invention, a method of computer calibrating at least one auxiliary hydraulic control valve is provided that includes the steps of selecting a first valve from a plurality of hydraulic control valves, applying a signal to that valve that is equivalent to a first degree of desired valve opening, measuring a first pressure in a restricted flow rate circuit, comparing the pressure with a predetermined pressure to identify a pressure change that indicates the cracking of the valve, incrementing the signal if the valve is not cracked and repeating the foregoing steps until the first valve cracks open, and finally saving a value indicative of the increment signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:  
         [0020]    [0020]FIG. 1 illustrates a work vehicle, shown as a tractor, having an auxiliary hydraulic valve calibration system in accordance with the present invention;  
         [0021]    [0021]FIG. 2 is a top-level schematic diagram of an auxiliary hydraulic valve control and calibration system;  
         [0022]    [0022]FIG. 3 is a detailed schematic of a microprocessor-based control system and operator controls for driving the auxiliary hydraulic valves;  
         [0023]    [0023]FIG. 4 is a detailed embodiment of a hydraulic pump and valve arrangement together with a load sensing and control circuit for regulating the specific displacement of the pump; and  
         [0024]    [0024]FIG. 5 is a flow chart showing the mode of operation of the system when calibrating each of the auxiliary hydraulic valves.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    Referring now to FIG. 1, a vehicle  10  is shown having an engine  12  drivingly engaged to a transmission  14  by a drive shaft  16 . These are mounted on a chassis  35 . The transmission  14  is in turn coupled through drive shafts  18  and  20  to front differential  22  and rear differential  24 . Front wheels  26  are coupled to and driven by differential  22  and rear wheels  28  are coupled to and driven by differential  24 . A hydraulic pump  30  is coupled to and driven by engine  12 . This pump provides hydraulic fluid to the auxiliary valves.  
         [0026]    Inside cab  32  is an operator station  33  that includes a proportional control lever  34  and a flow rate control  36 . These controls are coupled to electronic controller  38  which receives the operator commands and converts the operator commands into valve signals which are applied to auxiliary hydraulic control valves  40 . Valves  40  regulate the flow of fluid between pump  30  and auxiliary valve manifold  42  located at the rear of the vehicle. Manifold  42  typically includes quick-connect couplings that provide bi-directional flow to implements (not shown) that have mating hydraulic connectors.  
         [0027]    A load sensing and control circuit  44  is fluidly coupled to valves  40  and pump  30 . It receives fluidic signals from each of the auxiliary hydraulic valves and transmits a signal indicative of the hydraulic load on the valves to pump  30 . Pump  30 , in turn, varies its specific hydraulic output (i.e., the volume of hydraulic fluid per single revolution or cycle of pump  30 ) in accordance with the load signal that it receives.  
         [0028]    Referring now to FIG. 2, at least one proportional control lever or knob  34  and flow rate control  36  are coupled to electronic controller  38 . A pressure sensor  46  is also coupled to controller  38  and provides a signal indicative of the pressure in load signal line  54 . Controller  38  is electrically coupled to valves  40  and generates a valve signal indicative of the degree of desired valve opening for each of the valves. FIG. 2 shows two individual valves for ease of illustration. It should be understood that the system is not limited to any particular number of auxiliary hydraulic control valves. Controller  38  transmits a signal to valve actuators  50 . These valve actuators typically include an electrical coil responsive to the current transmitted from controller  38  and open the valve proportional to the current flowing through the actuators. In this manner, controller  38  can selectively apply individual signals to each of the valves causing them separately and independently to open or close.  
         [0029]    Each valve is connected to quick-connect couplings  52  located at manifolds  42 . There are typically two hydraulic lines extending between each valve and the manifold. As shown by the arrows on the hydraulic lines extending between the valves and the couplings, bi-directional flow is provided in each hydraulic line and depending upon the position of the valve.  
         [0030]    The hydraulic valves are also fluidly coupled to load sensing and control circuit  44 . The circuit receives a signal from each of the valves that indicates the load placed on the valve on signal lines  54 . The signal lines for each valve are combined and are provided to pump  30  on signal line  48 . Pump  30 , in turn, responds to the load on the valves provided on signal line  48  and regulates its specific displacement based on that load. In this manner, pump  30  need only put out as much pressurized hydraulic fluid as is required to feed each of the hydraulic valves. Each of hydraulic valves  40  are also connected to a hydraulic reservoir or tank  56  for receiving fluid returned from the implement (not shown) that is coupled to quick-connect couplings  52 .  
         [0031]    Referring now to FIG. 3, a preferred arrangement of electronic controller  38  is shown having two separate microprocessor based controllers  58  and  60 . While all of the functionality of the invention claimed herein could be provided by single microprocessor based controller, it is preferable to have several of them. Controllers  58  and  60  communicate over a serial communications link  62 , typically configured to carry signals as packets of data in accordance with the SAE J1939 standard. Each controller  58  and  60  includes a communication circuit  64  which converts the packetized data on communications link  62  into a form useable by the microprocessor. Each of controllers  58  and  60  also includes a microprocessor  66  connected to circuits  64  over control/data/address bus  68 . A random access memory (RAM)  70  is provided for each controller  58  and  60  and is also coupled to bus  68  to provide working memory for the microprocessors  66 . A read only memory (ROM)  72  is also provided in each of controllers  58  and  60  to store the programmed instructions executed by microprocessors  66 . Controller  60  includes a driver circuit  74  that is also coupled to bus  68  and responds to signals generated by microprocessor  66 . Driver circuit  74  generates the signals on a plurality of signal lines  76  that are coupled to valve actuators  50 . Controller  58  also includes a signal conditioning circuit  78  that is coupled to and conditions the signals received from proportional control lever  34  and flow rate control  36 . Note that in this embodiment, more than one proportional control lever  34  and flow rate control  36  are coupled to controller  38 . In a typical embodiment, one lever  34  and one control  36  is provided for each of the auxiliary hydraulic valves in the system. In operation, the operator moves a lever  34  to indicate a desired flow rate to one of valves  40 . This signal, typically an electrical signal, is received by circuit  78  and is transmitted to microprocessor  66  in controller  58 . Microprocessor  66  transmits the value over bus  68  to communications circuit  64  in controller  58 . This circuit creates a digital packet including a numeric value indicative of the position of lever  34 . Circuit  64  places this packet on serial communications link  62  and it is transmitted to a similar communications circuit  64  in controller  60 . Circuit  64  in controller  60  extracts the numeric value from its packetized form and provides it to microprocessor  66  in controller  60 . Microprocessor  66 , in turn, generates a valve signal indicative of the desired flow rate through the valve corresponding to the lever that was moved and transmits that signal to driver circuit  74 . Driver circuit  74 , in turn, amplifies that signal and produces a valve signal which is applied on one of signal lines  76  to the appropriate valve actuator  50  (see FIG. 2). In this manner, electronic controller  38  responds to operator commands and generates an appropriate valve signal.  
         [0032]    Once the system has been calibrated, and a value indicative of the dead-band of the valve has been saved in ROM  72 , microprocessor  66  will add this as a calibration or offset value to the signal generated by lever  34 . This signal, which is a composite of the operator&#39;s command and the calibration value, is then provided to driver circuit  74  and thence to actuator  50 , as described above. The calibration value can be stored in any of the memory circuits on busses  68 . In addition, the combining of the offset value and the command generated by lever  34  can be performed by either of the microprocessors. If the calibration value and the operator&#39;s command from lever  34  combined in controller  58 , the combined value is packetized and sent over serial communications link  62  to controller  60 .  
         [0033]    Flow rate controls  36  also generate a signal proportional to the degree of deflection by the operator. In the present system, flow rate controls  36  may be a potentiometer which generates an electrical signal proportional to the degree of deflection of the potentiometer. It may also be an optical encoder that typically sends out pulses for each increment of deflection. In the case it is a digital device, such as a shaft encoder, controller  58  will add to (or subtract from) the pulses as they are received to determine how far the operator has moved the flow rate control. Alternatively, it could be a monolithic digital device incorporating a shaft encoder-like element that transmits a digital value that&#39;s magnitude is proportional to the degree of deflection. All such devices and similar ones for converting a deflection or rotation into a value indicative of the total degree of deflection are well-known in the art. The proportional control lever or knob is similarly constructed.  
         [0034]    Referring now to FIG. 4, two hydraulic valves  40  are connected to a hydraulic fluid supply conduit  80 , which supplies hydraulic fluid under pressure to the valves from hydraulic pump  30 . Check valves  82  are disposed in a hydraulic supply conduit to prevent the back flow of hydraulic fluid from the valves to the pump. Depending upon the position of valves  40 , fluid from the hydraulic pump is provided to conduits  84  or  86 , which extend between valves  40  and quick-connect couplings  52  located in manifold  42 .  
         [0035]    Hydraulic fluid returning from the actuators coupled to couplings  52  is conducted to hydraulic tank or reservoir  56  through hydraulic conduits  88  that are coupled to and between tank  56  and valves  40 . During calibration, actuators  50  cause the valve mechanism to shift from the closed position “A” to either of positions “B” or “C”. Calibration can occur, and preferably does occur, with no device attached to couplings  52  and thus with no fluid flowing either to a loop-back tool or to an implement. Nonetheless, as valve  40  shifts, a flow path between conduit  80  and signal conduit  54  begins to open. Hydraulic fluid flows into conduit  54  as the valve is physically cracked and is applied to load sensing circuit  44 . Signal conduit  54  is common to both of the valves  40  shown in FIG. 4. As each valve is separately cracked during calibration, they are joined together at bi-directional check valve  92  in such a manner that the cracking of either valve causes hydraulic fluid to flow into conduit  54  which is therefore common to both the illustrated valves. Although there are only two valves shown in FIG. 4, for convenience, any number of auxiliary valves can connected to a common load sensing circuit by a signal line  54 .  
         [0036]    The particular load sensing circuit  44  shown in FIG. 4 uses two valves to control the specific output of pump  30 : valves  94  and  98 . As one or the other (or both) of valves  40  are cracked, pressure is applied to signal line  54  and is communicated to valve  94 . This signal line pressure is applied to the valve causing it to shift toward the position shown in FIG. 4. As a result, signal line  48  is connected through valves  98  and  94  to tank  56  via conduit  100 . This causes piston and cylinder arrangement  102  to change its position as fluid travels from arrangement  102  to tank  56  through valves  94  and  98 . Arrangement  102  is coupled to the other components of pump  30  to vary the specific output of the pump.  
         [0037]    Sensor  46  is coupled to signal line  54  and detects hydraulic fluid pressure fluctuations in that signal line. It is a fluid node common to both (all) of valves  40  due to the construction of signal line  54  and thus can be used to measure the cracking open of each of the valves  40 . As a result, when a valve  40  being calibrated just cracks open, hydraulic fluid will flow from conduit  80  into that valve, then out of that valve on signal line  54  to load sensing circuit  44 . This causes a pressure fluctuation on signal line  54 , which is, in turn, detected by pressure transducer  46 . A pressure fluctuation measured at transducer  46  is therefore indicative of any of valves  40  just cracking open. Note that this sensing of actual valve opening is independent of any flow through quick-connect couplings  52 . In this manner, pressure transducer  46  and controller  38  can sense actual valve opening regardless of any flow or lack thereof through couplings  52 . This permits the elimination of a separate loop-back testing tool that might otherwise be required to be connected to couplings  52 .  
         [0038]    In FIG. 5, a flow chart of the calibration process performed by controller  38  is illustrated. In the first step, Step  106 , controller  38  selects a valve to be calibrated. Controller  38  then reads the initial pressure at transducer  46  indicative of pressure on a load sensing signal line. This value is saved and is used as reference in future calibration calculations for that valve.  
         [0039]    In Step  110 , controller  38  applies an initial small signal to the valve that was selected for testing in Step  106 . Once the signal is applied, controller  38  reads the pressure at pressure sensor  46  in Step  112  to determine whether the pressure has changed. The pressure measured in Step  112  is compared with the initial pressure measured in Step  108  in Step  114 . If the pressure has changed sufficiently, as shown in Step  116 , controller  38  saves a value indicative of the signal applied to actuator  50  in Step  118 . The selected valve is now calibrated.  
         [0040]    On the other hand, if the controller&#39;s comparison of the two pressures does not indicate that the valve is cracked open, controller  38  increments the signal applied to the valve in Step  120  and processing returns to Step  110 . With this incremented valve signal, controller  38  again reads the pressure in Step  112  and compares the initial pressure with the new pressure in step  114 . This process of incrementing the valve signal, (the signal applied to the valve actuators  50 ), is repeated until controller  38  determines that a sufficient difference between the initial or reference pressure and the newly measure pressure at transducer  46  exists. At which point, a value indicative of the signal applied to actuator  50  that was just sufficient to crack the valve is saved in Step  118 , as described above.  
         [0041]    Once one valve has been calculated, controller  38  then determines if there are more valves to be calculated in Step  122 . If there are, processing returns to Step  106  and the new valve is selected. The pressure is incremented until this new valve cracks as described in the paragraphs above.  
         [0042]    Controller  38  again checks whether there are additional valves in Step  122 , and if there are, it again repeats the calibration process of the Steps  106  through  118 .  
         [0043]    Ultimately, all the auxiliary hydraulic valves in the system will be calibrated and the answer to the question in block  122  will be “no”. At this point, the calibration process ends at block  124 .  
         [0044]    While the embodiments illustrated in the FIGURES and described above are presently preferred, it should be understood that these embodiments are offered by way of example only. The invention is not intended to be limited to any particular embodiment, but is intended to extend to various modifications that nevertheless fall within the scope of the appended claims.