Patent Publication Number: US-6671641-B1

Title: Method for calibrating hydraulic actuators

Description:
TECHNICAL FIELD 
     The present invention relates generally to vehicle hydraulic fluid management systems. 
     BACKGROUND OF THE INVENTION 
     Modern motor vehicles are equipped with numerous fluid based systems, e.g., anti-lock brake systems, ride control systems, or traction control systems, that provide comfort and safety to drivers and passengers of these vehicles. Each of these systems require numerous hydraulic actuators that direct the flow of hydraulic fluid between the system components when necessary. For example, a typical anti-lock brake system can include several hydraulic actuators to control the fluid pressure in the individual components, e.g., a master cylinder, and a plurality of wheel cylinders. 
     The memory of an actuator control system includes numerous look-up tables which allow the control system to know what electric signals, e.g., current values, to apply to the actuators in order to yield specific actuation pressures. Typically, these look-up tables are generic tables that are not tailored to the individual actuators in the fluid system. These generic tables are created to account for worst-case part-to-part variances, manufacturing variances, and system variances. Thus, the tolerances of the values contained in the tables are relatively large and result in less than optimal performance of the actuators. 
     As recognized by the present invention, very expensive actuators can be used to decrease part-to-part variances, but the overall system tolerances remain larger than the tolerances that can be obtained by individually calibrating less expensive actuators to create customized look-up tables for each actuator. 
     The present invention has recognized the prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies. 
     SUMMARY OF THE INVENTION 
     A method for calibrating a hydraulic actuator includes applying a series of electrical signals to the actuator. For each applied electrical signal, the actuation pressure of the actuator is measured. Then, based on predetermined pressure values, unwanted signals are filtered out to create a customized look-up table for the actuator. 
     In a preferred embodiment, the customized look-up table is stored in a database. Preferably, multiple actuators are assembled to form a module assembly and the customized look-up table for each actuator is accessed. Based on the customized look-up tables, electrical signals are applied to each actuator and an actuation pressure is measured for each electrical signal. Based on the measured actuation pressures, the customized look-up tables are adjusted and then, the adjusted customized look-up tables are stored in a database. In a preferred embodiment, the electrical signals include a current sweep from a minimum value to a maximum value back to the minimum value. In another aspect of the present invention, the electrical signals include a voltage duty cycle sweep from a minimum value to a maximum value back to the minimum value. 
     In yet another aspect of the present invention, an actuator device test system includes a test stand. An actuator device is installed in the test stand. In this aspect of the present invention, the test stand includes a control circuit that includes logic means for creating a customized look-up table for the actuator device. 
     In still another aspect of the present invention, an actuator module assembly is calibrated. Initially, a customized look-up table is established for each hydraulic actuator in the actuator module assembly. Then, the actuators are assembled to form the module assembly. Thereafter, signals are applied to each actuator. Based on the responses of the actuators to the signals, an adjusted customized look-up table is established for each actuator. 
    
    
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an actuator test system; 
     FIG. 2 is a block diagram of a module assembly test system; 
     FIG. 3 is a flow chart showing the actuator calibration logic; and 
     FIG. 4 is a flow chart showing the module assembly calibration logic. 
    
    
     DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
     Referring initially to FIG. 1, an actuator test system is shown and generally designated  10 . As shown in FIG. 1, the actuator test system  10  includes an actuator test stand  12  having an actuator  14  placed therein. It is to be appreciated that the actuator  14  is, e.g., a PWM actuator, a variable bleed actuator, or a variable force actuator, used in a hydraulic management system. When placed in the actuator test stand  12 , the actuator  14  is connected to a signal generator  16  that provides a current or voltage signal to the actuator  14  during the actuator calibration process described below. As shown in FIG. 1, the actuator test stand  12  is connected to a central database  18  in which look-up tables generated during the calibration process are stored. FIG. 1 also shows that the actuator test stand  12  includes a first control circuit  20  that undertakes the actuator calibration logic described below. 
     FIG. 2 shows a module assembly test system generally designated  22 . As shown in FIG. 2, the module assembly test system  10  includes a module test stand  24  and a module assembly  26 , consisting of multiple actuators  12 , disposed therein. When placed in the module test stand  24 , the module assembly  26  is connected to a vehicle electronics package  27  that provides current or voltage signals to the module assembly  26  during the module calibration process described below. The vehicle electronics  27  also includes a memory  28  and a second control circuit  29 . As shown in FIG. 2, the module test stand  24  is connected to the central database  18 . Accordingly, as described below, the look-up tables generated during the actuator  12  calibration process are retrieved from the central database  18  and temporarily stored in the vehicle electronics  27 . Thereafter, the look-up tables may be adjusted before being permanently stored in the vehicle electronics  27 . It is to be understood that the second control circuit  29  that executes the module assembly calibration logic described below. 
     The method for calibrating hydraulic actuators  12 , disclosed below, may be executed as a series of instructions by a digital processor on the actuator test stand  12  and the module test stand  24 . These instructions may reside, for example, in the control circuits  20 ,  29  of the test stand  12  and vehicle electronics  27 , which, when programmed with the present logic, establishes a computer program product. 
     Alternatively, the instructions may be contained on a data storage device with a computer readable medium, such as a computer diskette having a data storage medium holding computer program code elements. Or, the instructions may be stored on a DASD array, magnetic tape, conventional hard disk drive, electronic read-only memory, optical storage device, or other appropriate data storage device. In an illustrative embodiment of the invention, the computer-executable instructions may be lines of compiled C++ compatible code and/or micro-code. As yet another equivalent alternative, the logic can be embedded in an application specific integrated circuit (ASIC) chip or other electronic circuitry. 
     Referring now to FIG. 3, the individual actuator calibration logic is shown. Commencing at block  30 , a do loop is entered wherein the succeeding steps are completed for each actuator  14 . Moving to block  32 , the actuator  14  is installed in the actuator test stand  12 . Thereafter, at block  34  a current sweep or voltage duty cycle sweep is performed on the actuator  14  by applying a series of signals to the actuator  14  from the signal generator  16 . The current sweep preferably is performed from zero amps to one amp back to zero amps (0A-1A-0A) and the voltage duty cycle sweep preferably is performed from zero percent to one hundred percent back to zero percent (0%-100%-0%). It is to be appreciated that either signal sweep is performed in increments small enough to obtain a satisfactory resolution. 
     Continuing the description of the actuator calibration logic, at block  36  the pressure values obtained during either sweep, or both sweeps, are temporarily stored in the memory of the actuator test stand  12 . Proceeding to block  38 , this data is filtered in order to obtain the exact current values or percentage duty cycle values which, when applied to the actuator  14 , yield the sought after pressure values. In other words, during the current sweep performed at block  34 , a series of pressure values are obtained, as shown in Table 1. Thereafter, to meet predetermined requirements it is necessary to remove any current values which do not correspond to the desired pressure values, shown in Table 2. Thus, only the current values which correspond to the desired pressure values remain, as shown in Table 3. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Exemplary Current Values vs. Pressure Values 
               
               
                 (0.0 A to 0.40 A) 
               
            
           
           
               
               
               
            
               
                   
                 Current (A) 
                 Pressure (psi) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 0.000 
                 93.33 
               
               
                   
                 0.025 
                 93.15 
               
               
                   
                 0.050 
                 92.97 
               
               
                   
                 0.075 
                 92.63 
               
               
                   
                 0.100 
                 92.09 
               
               
                   
                 0.125 
                 91.76 
               
               
                   
                 0.150 
                 91.28 
               
               
                   
                 0.175 
                 90.97 
               
               
                   
                 0.200 
                 90.49 
               
               
                   
                 0.225 
                 90.01 
               
               
                   
                 0.250 
                 89.10 
               
               
                   
                 0.275 
                 88.45 
               
               
                   
                 0.300 
                 88.12 
               
               
                   
                 0.325 
                 87.91 
               
               
                   
                 0.350 
                 87.12 
               
               
                   
                 0.375 
                 86.99 
               
               
                   
                 0.400 
                 84.88 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Exemplary Desired Pressure Values 
               
               
                 Pressure (psi) 
               
               
                   
               
             
            
               
                 93.0 +/− 0.1 
               
               
                 92.0 +/− 0.1 
               
               
                 91.0 +/− 0.1 
               
               
                 90.0 +/− 0.1 
               
               
                 89.0 +/− 0.1 
               
               
                 88.0 +/− 0.1 
               
               
                 87.0 +/− 0 1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Exemplary Filtered Look-up Table 
               
            
           
           
               
               
               
            
               
                   
                 Pressure (psi) 
                 Current (Amp) 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 93.0 +/− 0.1 
                 0.050 
               
               
                   
                 92.0 +/− 0.1 
                 0.100 
               
               
                   
                 91.0 +/− 0.1 
                 0.175 
               
               
                   
                 90.0 +/− 0.1 
                 0.225 
               
               
                   
                 89.0 +/− 0.1 
                 0.250 
               
               
                   
                 88.0 +/− 0.1 
                 0.325 
               
               
                   
                 87.0 +/− 0.1 
                 0.375 
               
               
                   
                   
               
            
           
         
       
     
     Returning to the actuator calibration logic shown in FIG. 3, at block  39  each actuator is serialized, i.e., each actuator is assigned a serial number that allows each actuator to be identified later. Thereafter, at block  40  the filtered data, e.g., the data shown in Table 3, is stored in the central database  18  as a customized look-up table for that particular actuator  14 . Each look-up table stored in the central database  18  is linked to the serial number of its corresponding actuator  12 . The customized look-up table for each actuator  14  is then retrieved at the module test stand during the module assembly calibration logic described below. It is to be appreciated that by filtering the data, a graph of the pressure values versus the current values, or percentage duty cycle values, can be made to take nearly any shape, e.g. curved, dual-slope, flat, and linear. 
     Referring now to FIG. 4, the module assembly calibration logic is shown, and commencing at block  50  multiple actuators  12  are assembled to form a module assembly  26 . At block  52 , the module assembly  26  is installed in a module test stand  24 . Moving to block  54 , the serial number for each individual actuator  12  is determined. Thereafter, at block  56 , the customized look-up table for each actuator  14  is retrieved from the central database  18 , based on the serial numbers determined at block  52 . At block  57 , each look-up table is temporarily stored in the vehicle electronics  27 , e.g., in the memory  28 . 
     Continuing to block  58 , a do loop is entered wherein for each actuator  14  comprising the module assembly  26  the succeeding steps are performed. At block  60 , the current values or percentage duty cycle values from the look-up table are applied to the module assembly  20  by the vehicle electronics  27 . Moving to decision diamond  62 , it is determined whether the pressure values for each actuator  14  fall within the predetermined tolerance windows, e.g., plus or minus one-tenth pound per square inch (+/−0.1 psi). If so, the logic ends proceeds to block  64  where the current or voltage duty cycle values are permanently stored in the vehicle electronics  27 , e.g., in the memory  28 . Thereafter, the logic ends at state  66 . 
     If at decision diamond  62 , if the pressure values do not fall within the predetermined windows the logic proceeds to block  68  where the current or percentage duty cycle applied to the actuator  14  is adjusted so that the pressure values fall within the specified windows. Then, at block  64  the adjusted current values or percentage duty cycle values are permanently stored in the vehicle electronics  27 . The logic then ends at state  66 . 
     With the configuration of structure and logic described above, it is to be appreciated that the method for calibrating hydraulic actuators can be used create customized look-up tables for hydraulic actuators. When the actuators are assembled to form module assemblies, the customized look-up tables can be used to further create adjusted customized look-up tables depending on the response of the module assemblies to signals from the vehicle electronics. Either the customized look-up tables or the adjusted customized look-up tables are stored in the vehicle electronics memory. Thus, the tolerances of the module assemblies are reduced and their performance is increased. 
     While the particular METHOD FOR CALIBRATING HYDRAULIC ACTUATORS as herein shown and described in detail is fully capable of attaining the above-described objects of the invention, it is to be understood that it is the presently preferred embodiment of the present invention and thus, is representative of the subject matter which is broadly contemplated by the present invention, that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural and functional equivalents to the elements of the above-described preferred embodiment that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it is to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. section 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”