Patent Publication Number: US-2020276980-A1

Title: Method for calibrating a characteristic diagram ofa work machine and work machine

Description:
This application is a National Stage completion of PCT/EP2018/078331 filed Oct. 17, 2018, which claims priority from German patent application serial no. 10 2017 220 485.0 filed Nov. 16, 2017. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method for calibrating a characteristic diagram of a working machine and to a working machine with an electronic control unit for carrying out the method. 
     BACKGROUND OF THE INVENTION 
     From automotive technology, working machines such as forklift trucks, wheel loaders or other special vehicles are known, which are equipped with a hydrodynamic drive unit. The hydrodynamic drive unit usually consists of a drive motor, a hydrodynamic torque converter and a transmission downstream therefrom. In the known working machines it is usual for low travel speeds to be required when picking up certain loads, but in that driving condition the working hydraulic system needs maximum power in order to take up the loads or to carry out other working operations. In order to limit the traction force or torque of the hydrodynamic drive unit at high rotational speeds, the downstream transmission can comprise a friction clutch. 
     In a driving condition in which high rotational speeds are demanded from the drive motor, the friction clutch is operated in the slipping range in order thereby to make it possible to drive the working machine at a slow speed even when the motor rotational speed is high. For that purpose, in known working machines the control pressure in the friction clutch is reduced in order correspondingly to reduce the clutch torque. The pressure level set at the clutch is determined by the pedal displacement of the brake pedal. In that way, propulsion of the vehicle is controlled by the drive input clutch by way of the pressure level as a function of the pedal position. With this type of control the pressure level set depends on the friction coefficient of the clutch linings and also on the tolerances of the pressure regulators used and of the hydraulic control system. Thus, for the pressure preselected by means of the pedal position, as a function of the tolerances a different torque is obtained at the clutch whereas the pedal position corresponds to a desired torque or clutch torque, the so-termed torque specification, which is transmitted to an electronic control unit and the electronic control unit associates this specification with a corresponding pressure and emits that pressure or the pressure specification to the clutch or the hydraulic valve of the clutch. 
     From WO 2005/078304 A1 a drive machine is known, which drives both consumers and drive wheels by way of a clutch device. When a brake pedal is actuated an electronic control device determines an input torque of the clutch device and actuates the clutch device in the opening direction when the brake pedal reaches a defined value that depends on the input signal. The value can preferably be obtained from a calculated characteristic which can be readjusted manually. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention can be achieved by the characteristics specified in the independent claims. Further advantageous design features emerge from the subordinate claims and the drawings. 
     A method is proposed for calibrating a characteristic diagram for a working machine such as an agricultural or construction machine. The characteristic diagram is preferably stored in an electronic control unit. The characteristic diagram comprises a brake pedal characteristic of a brake system and at least one clutch characteristic of a drive input clutch. Preferably, in the characteristic diagram a braking torque of the brake system as a function of a pedal position of the brake system is stored. In the calibrated condition, the brake pedal characteristic and the clutch characteristic have a nominal relationship to one another. To calibrate the two characteristics, a drive output torque on the wheel side is determined first. With reference to this drive output torque an actual brake pedal characteristic is then determined. By comparing the actual brake pedal characteristic with a nominal brake pedal characteristic, an actual relationship that deviates from the nominal relationship is inferred. The nominal relationship or the relationship of the nominal brake pedal characteristic to the nominal clutch characteristic represents an ideal behavior of the system which, however, changes with the duration of the working machine&#39;s service, in particular due to wear. On the basis of the measurement results the actual brake pedal characteristic and/or the clutch characteristic is/are calibrated so that the actual relationship corresponds to the nominal relationship and hence to optimized efficiency. The calibration of the characteristic diagram is preferably carried out automatically by the electronic control unit, in particular so that mass-produced vehicles can be used in an optimum manner throughout their useful life. 
     The behavior of the drive input clutch of the working machine can be inexpensively optimized by means of this method, so that it can be operated up to the limit of its power without risk of overloading the drive input clutch and thereby damaging it. The characteristic diagram stored in the control unit is essentially tailor-made for the vehicle concerned and can be adjusted as often as desired in order to achieve improved efficiency of the working machine. 
     Advantageously, a nominal clutch characteristic remains unchanged and/or the actual brake pedal characteristic is calibrated to match the nominal brake pedal characteristic. The nominal clutch characteristic is essentially that set in the factory. Alternatively, the actual brake pedal characteristic remains unchanged and the nominal clutch characteristic is calibrated to match an actual clutch characteristic. The actual clutch characteristic is the clutch characteristic calibrated and adapted to the actual measurement results, by means of which the efficiency of the working machine can be optimized. By calibrating the brake pedal characteristics and/or the clutch pedal characteristics, the system can be operated permanently with low consumption. 
     It is advantageous if, to determine the drive output torque, from a converter characteristic stored in the electrical control unit, a turbine wheel torque of a hydrodynamic torque converter upstream from the drive input clutch in the power flow direction is determined. By virtue of the turbine torque and the drive output torque, the braking torque, which has a decisive influence with regard to the efficiency of the system, can be determined indirectly. 
     It is advantageous for the drive output torque to be calculated with reference to the turbine wheel torque, at least one clutch parameter of the drive input clutch and/or with reference to at least one transmission parameter of a transmission downstream from the hydrodynamic torque converter. The parameters required for the calculation can be, for example, a pressure increased by a brake valve as a function of the pedal displacement, friction coefficients, or piston forces for producing the braking force. 
     It is advantageous if, by way of the drive output torque, a brake characteristic magnitude, in particular a braking torque, also referred to as a brake torque, is determined. With reference to the brake characteristic magnitude, a braking torque of the brake system can be determined indirectly or directly. 
     Furthermore it is advantageous if, to determine the actual brake pedal characteristic, a value of the brake characteristic magnitude that corresponds to at least one brake pedal position is determined for that brake pedal position. With this additional value the respective brake pedal position can be plotted as a Bezier control point in the characteristic diagram. Thus, the characteristic diagram is always matched individually to the operating and/or wear condition of the working machine at the time, so that it can be operated ideally. 
     It is also advantageous for the brake pedal characteristic to be determined by a discrete method in which several Bezier control points are determined. The various Bezier control points preferably depict relevant system points. The number of Bezier control points preferably depends on the desired accuracy of the characteristic diagram. The discrete method can be carried out manually by a driver or automatically by the electric control unit, so mass-produced vehicles can be operated with optimized efficiency throughout their useful life. 
     It is advantageous if, in the discrete method, to determine a Bezier control point the brake pedal position is set to a value and during the determination of the corresponding value of the brake characteristic magnitude it is kept constant at that value. At the beginning of the process the working machine is preferably at rest, and the brake pedal is kept depressed for example by 100%, 75% or 50% of its travel. 
     With the working machine at rest, advantageously a gear of the transmission is engaged and a motor rotational speed is increased, in particular by means of an accelerator pedal, until rolling of the vehicle is recognized. Rolling is preferably detected by means of a drive output rotational speed indicator associated with one or more tires. Alternatively the rolling can be detected by a movement sensor. 
     When rolling is detected, the transmission is advantageously automatically shifted to idling mode by the electronic control unit. The value of the brake characteristic magnitude that exists at the moment when rolling begins, in particular the braking torque, is then determined and stored. This forms the first Bezier control point of the actual brake pedal characteristic. With reference to this procedure the characteristic diagram can be updated in a simple manner. 
     Furthermore, it is advantageous for the actual brake pedal characteristic to be determined in a continuous process, in which the brake pedal position is changed continually and at the same time the corresponding values of the brake characteristic magnitude are determined. 
     In addition, it is advantageous to accelerate the working machine up to the maximum speed attainable in a gear and then brake it to rest during a deceleration phase by continually increasing the actuation of the brake pedal. The corresponding values of the brake characteristic magnitude are determined during this deceleration phase. The deceleration phase is the test period during which the brake pedal is actuated. In essence, this produces a curve that represents the actual brake pedal characteristic and enables the characteristic diagram to be calibrated. 
     It is advantageous to carry out the continuous method, in particular in order to determine an initiation point of the actual brake pedal characteristic, first at a first motor rotational speed and then at a motor rotational speed higher than the first motor rotational speed. 
     Furthermore a working machine is proposed, in particular an agricultural or construction machine. The working machine comprises a drive unit, a hydrodynamic torque converter, a drive input clutch, a transmission, a brake system and an electronic control unit. The brake system is in particular hydraulic. In the control unit is stored a characteristic diagram which comprises a brake pedal characteristic of the brake system and at least one clutch characteristic of the drive input clutch. In the calibrated condition the brake pedal characteristic and the clutch characteristic have a nominal relationship to one another. The electronic control unit is designed in accordance with the foregoing description, wherein the features mentioned can exist individually or in any desired combination. 
     The working machine is designed to have a long useful life with optimized efficiency by virtue of the characteristic diagram that can be calibrated automatically. If increased wear or higher fuel consumption are noticed, the working machine can be brought to its calibration condition and the characteristic diagram corrected virtually automatically by the control unit. 
     For this it is advantageous for a converter characteristic of the torque converter to be stored in the electronic control unit. The converter characteristic is preferably a plot of torque of a turbine wheel of a torque converter against the rotational speed ratio between an impeller and the turbine wheel. On the basis of the converter characteristic, the turbine wheel torque and hence the torque at the drive output of the transmission can be determined. From the transmission drive output, conclusions can be drawn about the braking torque, which is relevant for the design of the characteristic diagram of the working machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Below, the invention is explained in greater detail with reference to drawings, which show: 
         FIG. 1 : A schematic view of a drive-train of a working machine, and 
         FIG. 2 : A characteristic diagram for the working machine in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a drive-train  1  of a working machine  2 . The drive-train  1  comprises a drive unit  3 , which drives one or more consumers by way of a hydrodynamic torque converter  4  and a drive input clutch  5 . The working machine  1  drives wheels  6  and at least one power take-off  7  such as hydraulic pumps for actuating loading scoops. 
     The torque converter  4  is on the one hand functionally connected to the drive unit  3  so that torque of the drive unit  3  can be transmitted to an impeller  8  of the torque converter  4 . On the other hand, on the wheel side the torque converter  4  is connected to the drive input clutch  5  and/or to a transmission  9 . A turbine wheel  10  of the hydrodynamic torque converter  4  receives the flow energy produced by the impeller  8  and supplies it in the form of mechanical energy to the drive input clutch  5  and the transmission  9 , whereby preferably at least one wheel  6  is driven. 
     On the drive input side, the power take-off  7  is connected upstream from the torque converter  4  and drives for example a high-pressure pump, a concrete mixer or a moving blade. The torque supplied to the power take-off  7  is preferably a function of the torque of the drive unit  3  transmitted to the impeller  8  of the torque converter  4 . 
     Connected upstream from the wheels  6  is a hydraulic brake system  11  such that the wheels  6 , for example during driving, can be braked in accordance with the position of a brake pedal (not shown) or prevented from rotating when the vehicle is at rest. To brake the wheels  6 , the brake system  11  produces a braking pressure by means of which the braking process takes place. 
     In addition the working machine  2  comprises an electronic control unit  12  by means of which a calibration process can be carried out. In the control unit  12  at least one characteristic diagram  13  (see  FIG. 2 ) of the working machine  2  is stored, which enables the braking torque of the brake system  11  to be determined. 
       FIG. 2  shows the characteristic diagram  13  for the working machine  2 , wherein by comparison with  FIG. 1  the same indexes are used for features whose design and/or mode of operation is identical or at least comparable. Insofar as these are not again explained in detail, their design and/or mode of operation corresponds to the design and mode of operation of the features already described earlier. 
     The x-axis of the characteristic diagram  13  represents a pedal displacement of the brake system  11  and the y-axis represents the braking torque of the brake system  11  (see  FIG. 1 ). The characteristic diagram  13  comprises a nominal brake pedal characteristic  14  of the hydraulic brake system  11  and at least a first actual clutch characteristic  17  of the drive input clutch (see  FIG. 1 ). In the calibrated condition the nominal brake pedal characteristic  14  and the actual clutch characteristic  17  have a nominal relationship with one another. In the calibrated condition an actual brake pedal characteristic  16  and/or an actual clutch characteristic  17  are compared with the respective nominal brake pedal characteristic  14  and/or the nominal clutch characteristic  15 . The nominal relationship depicts at least one point of intersection  18  between the nominal brake pedal characteristic  14  and the actual clutch characteristic  17 . The position of the point of intersection  18  represents the pedal position at which the drive input clutch  5  is released. The calibrated characteristic diagram  13  makes it possible to determine the braking torque of the brake system  11  independently of the major tolerances thereof. 
     The nominal brake pedal characteristic  14  has an initiation point  24 , which indicates from which pedal position of the brake system  11  the latter engages and thus brakes the working machine  2  or keeps it at rest (see  FIG. 1 ). 
     To get to the calibrated condition, a wheel-side drive output torque is determined. In the control unit  12 , a converter characteristic (not shown) of the hydrodynamic torque converter  4  is stored, which represents the relationship of the rotational speed ratio between the impeller  8  and the turbine wheel  10  on the one hand, and the torque of the turbine wheel  10  on the other hand (see  FIG. 1 ). The drive output torque is calculated with reference to the turbine torque and/or at least one clutch and/or transmission parameter of the drive input clutch  5  or the transmission  9 . The clutch and/or transmission parameters are for example the transmission ratio, the pressure at a brake valve which increases in line with pedal displacement, friction values, and/or piston values for producing the braking force. 
     The drive output torque determined enables the determination of a brake characteristic magnitude, in particular the brake pressure, by means of which a braking torque of the brake system  11  can be characterized. 
     With reference to the drive output torque an actual brake pedal characteristic  16  can be determined, and for that purpose the brake characteristic magnitude is determined for at least one brake pedal position and a value that corresponds to that brake pedal position. This can be done with the help of a discrete and/or a continuous method. 
     In the discrete method, the actual brake pedal characteristic  16  is determined by determining several Bezier control points  19 ,  20 ,  21 ,  22  and plotting those points in the characteristic diagram  13 . 
     At the beginning of this method the working machine according to  FIG. 1  is preferably at rest. By the control unit  12 , which is configured for calibration, or by a driver (not shown), the calibration process is started in that the brake system  11 , specifically its brake pedal, is actuated to a first Bezier control point  19 . To reach the first Bezier control point  19  the brake system  11  is actuated in such manner that the brake pedal is fully depressed as far as the maximum pedal displacement. At least during the next step the brake pedal remains constantly held at the maximum pedal displacement. 
     With the working machine  2  at rest a gear is now engaged in the transmission  9 . Preferably, the gear engaged is that gear in which the maximum sustainable traction force is produced by the brake system  11 . For this, the drive unit  3  is accelerated in the form of a motor rotational speed increase until rolling of the working machine  2  is detected. For that purpose a drive output rotational speed indicator (not shown) or a sensor is preferably installed, in order to be able to detect rotation of at least one wheel  6 . The drive input of the drive unit  3  can for example be produced manually by way of an accelerator pedal or brought about automatically by the control unit  12 . 
     When rolling of at least one wheel  6  is detected, the transmission  9  is automatically shifted to idling mode by the electronic control unit  12 . At the point when the rolling of the wheel  6  is detected, the associated drive output torque is stored in the control unit  12 . The drive output torque is determined by way of the turbine wheel torque stored in the converter characteristic, which in turn in determined by the pump and turbine rotational speed of the impeller  8  and the turbine wheel  10  of the torque converter. Then, from the established drive output torque a braking torque is determined, with reference to which a braking torque of the brake system  11  (see  FIG. 1 ) can be determined. The value existing at the moment of rolling, that corresponds to the braking characteristic magnitude, specifically the brake pressure, is determined and plotted as a braking torque into the characteristic diagram  13  along the y-axis. 
     Thus, in the characteristic diagram  13  the braking force or braking torque is determined by way of the pedal displacement at a first Bezier control point  19 . Preferably the steps, from setting a particular pedal displacement of the brake system  11  while at rest, engaging a gear of the transmission  9  and operating the drive unit  3  at an elevated motor rotational speed until rolling movement of the wheel  6  is first detected, are carried out for different pedal displacements. As shown in  FIG. 2 , this is carried out a number of times for different pedal displacements of 75%, 60% and 23% to obtain additionally at least a second, third and fourth Bezier control points  20 ,  21  and  22 . The number of Bezier control points  19 ,  20 ,  21 ,  22  can be varied arbitrarily in order to determine as exact an actual brake pedal characteristic  16  as possible. 
     After determining the actual brake pedal characteristic  16 , the actual clutch characteristic  17  is calibrated by forming a nominal clutch characteristic  15  on the basis of the actual brake pedal characteristic  16 . Since the nominal relationship is defined by the common point of intersection  18  of the two characteristics  14  and  17 , the actual brake pedal characteristic  16  is calibrated on the basis of the nominal brake pedal characteristic  14 , in particular in the characteristic diagram  13  displaced in parallel so that the actual clutch characteristic  17 , together with the actual brake pedal characteristic  16 , form the original point of intersection  18  which essentially represents the nominal relationship. 
     Displacement of the actual brake pedal characteristic  16  preferably takes place along an offset  25  between the initiation point  24  and a mirror point  26  relative thereto. In the characteristic diagram  13  or  FIG. 2 , for the sake of simplicity the offset  25  is displaced along the brake pedal characteristics  14 ,  16 . The initiation point  24  of the brake system  11  depends decisively on the wear of the brake system. The greater the wear, as a rule the later the brake system  11  engages or the higher must be the braking torque. Thus, if the actual brake pedal characteristic  16  deviates from the nominal brake pedal characteristic  14 , the initiation point  24  also is displaced to the mirror point  26 . In the characteristic diagram  13  the mirror point  26  and the initiation point  24  are connected with one another by the offset  25 . Preferably, the offset  25  remains the same size throughout the length of the nominal and actual brake pedal characteristics  14 ,  16 . To calibrate the actual brake pedal characteristic  16 , it is displaced by the offset  25  relative to the nominal brake pedal characteristic  14 , so that the drive input clutch  5  is released at the ideally chosen pedal position corresponding to the intersection point  18  of the actual relationship. 
     Alternatively, it is conceivable to displace the actual clutch characteristic  17  along the offset  25  relative to a nominal clutch characteristic  15 , so that a new calibration point  23  is defined at which the actual relationship corresponds to the nominal relationship at the intersection point  18 . 
     The calibration of the characteristic diagram  13  takes place by the continuous method as previously described, but the actual brake pedal characteristic  16  is determined in this case by continuously varying the brake pedal position instead of moving to individual, discrete Bezier control points  19 ,  20 ,  21 ,  22  as before. At the same time as the continuous variation of the pedal displacement, the corresponding values of the braking characteristic magnitudes, in particular the braking pressure, are determined in order to determine the braking torque. The working machine  2  is accelerated by the drive unit  3  up to the maximum speed attainable in the gear of the transmission  9  engaged at the time. Then, the working machine  2  is slowly braked to rest by continuously increasing the actuation of the brake system  11 , in particular its brake pedal (see  FIG. 1 ). During this deceleration phase, in which the working machine  2  is progressively braked, the values of the braking magnitudes that correspond to the pedal displacement are determined so that the braking torque as a function of the pedal displacement can be documented in the characteristic diagram  13 . This produces an essentially flowing actual brake pedal characteristic  16 , which can be corrected in accordance with the previously described calibration method. 
     The calibration takes place by correcting either the actual clutch characteristic  17  or the actual brake pedal characteristic  16 , in such manner that the actual relationship corresponds to the nominal relationship. 
     By means of the discrete or the continuous method, the initiation point  24  of the actual brake pedal characteristic  16  can be determined. This enables the calibration of the characteristic diagram  13  to be carried out, so that the opening of the drive input clutch  5  is permanently matched to the braking force or pedal displacement of the brake system  11  and wear or the brake system  11  is prevented. The readjustment of the drive-train  1  can if necessary take place several times during the service life of the working machine  2 , so that it is optimally calibrated for any driving situation. The adjustment process takes place at least partially automatically. 
     The present invention is not limited to the example embodiments illustrated and described. Variations within the scope of the claims are also possible, such as a combination of features, even where these have been illustrated and described in different example embodiments. 
     INDEXES 
     
         
           1  Drive-train 
           2  Working machine 
           3  Drive unit 
           4  Torque converter 
           5  Drive input clutch 
           6  Wheel 
           7  Power take-off 
           8  Impeller 
           9  Transmission 
           10  Turbine wheel 
           11  Brake system 
           12  Control unit 
           13  Characteristic diagram 
           14  Nominal brake peal characteristic 
           15  Nominal clutch characteristic 
           16  Actual brake pedal characteristic 
           17  Actual clutch characteristic 
           18  Point of intersection 
           19  First Bezier control point 
           20  Second Bezier control point 
           21  Third Bezier control point 
           22  Fourth Bezier control point 
           23  Calibration point 
           24  Initiation point 
           25  Offset 
           26  Mirror point