Patent Publication Number: US-10767345-B2

Title: Device and method for controlling work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase application of International Patent Application No. PCT/EP2016/059939 filed May 3, 2016, which claims priority to Japanese Patent Application No. 2015-095797 filed May 8, 2015, both of which are incorporated by reference herein in their entireties for all purposes. 
     TECHNICAL FIELD 
     The present invention relates to a device and a method for controlling a work machine that has a fluid pressure system including a fluid pressure actuator for operating the work machine and a pump for discharging a working fluid for operating the fluid pressure actuator, and an engine for driving the pump. 
     BACKGROUND ART 
     A conventional work machine such as a hydraulic shovel executes various tasks using a work device and also turns the upper revolving body with respect to the lower traveling body by operating hydraulic actuators such as a hydraulic cylinder and a hydraulic motor with hydraulic oil that is discharged from a hydraulic pump driven by the engine. 
     In some cases the operator of such work machine does not need to perform leveling (smoothing of the ground) or crane operations using the maximum power of the hydraulic system or at the maximum speed thereof. In such a case, while the power required in the hydraulic system is low because the amount of lever operation by the operator is small and the speeds of the hydraulic actuators are low, the energy loss of the hydraulic system is high because the amount of hydraulic oil to be bled off to a tank through, for example, a control valve is high or the energy loss is high in the pump due to the lowered efficiency. Therefore, the hydraulic system is required to be used at its efficient point in accordance with the work amounts of the hydraulic actuators associated with the operation of the lever by the operator. 
     For example, a configuration has been known in which each task is identified using fuzzy inference based on the amount of lever operation by the operator [(see, for example, PTL 1 to PTL 5)]. However, the known configurations aim to identify the type of task and improve the operability merely by controlling pump flow rates or changing the state of an engine auto deceleration control, so the use of the hydraulic system at its efficient point is not taken into consideration. 
     SUMMARY OF THE INVENTION 
     However, the configurations described in PTL 1 to PTL 5 aim to identify the type of the task and improve the operability, and merely control the pump flow rates or change the validity/invalidity of so-called engine auto deceleration control, and the use of the hydraulic system at its efficient point is not taken into consideration. 
     The present invention has been contrived in view of these circumstances, and an object thereof is to provide a device and a method for controlling a work machine that are designed to curb energy loss of a fluid pressure system. 
     The present disclosure describes a control device and method for controlling a work machine having a fluid pressure system that includes a fluid pressure actuator for operating the work machine and a pump for discharging a working fluid for operating the fluid pressure actuator, and an engine for driving the pump, the control device having: estimation means for estimating a work amount of the work machine by using fuzzy inference based on an operation amount the fluid pressure actuator is operated by operation means; and setting means for setting a setting signal by using fuzzy inference, the setting signal being used for setting the engine speed in accordance with the work amount estimated by the estimation means. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram showing an embodiment of a control device for controlling a work machine according to the present invention. 
         FIG. 2  is a block diagram showing an internal structure of a part of the control device. 
         FIG. 3  is an explanation diagram showing weighting means of the control device. 
         FIG. 4  is an explanation diagram showing estimation means of the control device. 
         FIG. 5  is a graph showing an example of a membership function used in the control device. 
         FIG. 6  is a flowchart of a control method used by the control device. 
         FIG. 7  is a side view of the work machine having the control device. 
         FIG. 8( a )  is a graph showing the amount of a stick-in operation as an example of the control device,  FIG. 8( b )  is a graph showing the amount of a stick-out operation,  FIG. 8( c )  is a graph showing a temporal change in adaptation level with respect to the low level,  FIG. 8( d )  is a graph showing a temporal change in adaptation level with respect to the medium level,  FIG. 8( e )  is a graph showing a temporal change in adaptation level with respect to the high level, and  FIG. 8  is a graph showing a temporal change in centroid value obtained based on  FIGS. 8( c ) to 8( e ) . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present invention is described hereinafter in detail based on an embodiment shown in  FIGS. 1 to 8 . 
       FIG. 7  shows a work machine  11  as a hydraulic shovel. This work machine  11  has a hydraulically-operated (fluid pressure-driven) chassis  12  and a hydraulically-operated (fluid pressure-driven) work device  13  mounted to the chassis  12 . In the chassis  12 , an upper revolving body  16  is provided on a lower traveling body  14  with a revolving bearing  15  therebetween, in such a manner as to be revolved by a revolving hydraulic motor  16   m . A cab  17  configuring an operator&#39;s station and a machine room  18  are mounted in the upper revolving body  16 , wherein an engine  19  shown in  FIG. 1  and (first and second) pumps P 1 , P 2  driven by this engine  19  are mounted in the machine room  18 . 
     The work device  13  has a boom  21  that is axially supported by the upper revolving body  16  and rotated by a boom cylinder  21   c , a stick  22  that is axially coupled to a tip of the boom  21  and rotated by a stick cylinder  22   c , and a bucket  23  that is attached to a member axially coupled to a tip of the stick  22  and rotated by a bucket cylinder  23   c.    
     The pumps P 1 , P 2  are of variable swash plate type or variable capacity pumpshaving capacity controllers ϕ 1 , ϕ 2  such as swash plate regulators. These pumps P 1 , P 2  are connected to an output shaft  19   a  of the engine  19  and driven by the engine  19 . Output channels  27 ,  28  of these pumps P 1 , P 2  are connected to a control valve CV. Through this control valve CV, hydraulic oil as a working fluid is supplied to the revolving hydraulic motor  16   m  functioning as a revolving motor, which is a fluid pressure actuator, the boom cylinder  21   c  functioning as a hydraulic cylinder, which is a fluid pressure actuator, the stick cylinder  22   c  functioning as a hydraulic cylinder, which is a fluid pressure actuator, and the bucket cylinder  23   c  functioning as a hydraulic cylinder, which is a fluid pressure actuator. In the present embodiment, the pump P 1 , for example, supplies the hydraulic oil to the boom cylinder  21   c  and the bucket cylinder  23   c , and the pump P 2  supplies the hydraulic oil to the revolving hydraulic motor  16   m  and the stick cylinder  22   c.    
     Displacement of the control valve CV is controlled in accordance with the operation amounts of operation means (operation levers) L 1  to L 4  such as hydraulic or electric levers provided in the operator&#39;s station (i.e., the inclination angles or the levels of displacement of the respective operation means (operation levers) with respect to a neutral position). One of the control valve CV consists of a spool or the like provided slidably in, for example, a single block, controls the direction and flow rate of the hydraulic oil supplied by each of the pumps P 1 , P 2 , and then supplies the resultant hydraulic oil to the revolving hydraulic motor  16   m , the stick cylinder  22   c , the boom cylinder  21   c , and the bucket cylinder  23   c . In the control valve CV, connection from the pump P 1 , P 2  to a tank T is established through center bypass lines, not shown, that are formed in each of the spool. Negative flow control pressure (NFC pressure) obtained from the center bypass lines are fed back from, for example, a control device CT to the capacity controllers ϕ 1 , ϕ 2  of the pumps P 1 , P 2 . The NFC pressure is configured to control the discharge flow rates of the pumps P 1 , P 2  in such a manner that the NFC pressure is maximum when the spool of the control valve CV is at the neutral position, that the greater the level of displacement of the spool, the lower the NFC pressure becomes, that the higher the NFC pressure, the lower the pump flow rates are made by the capacity controllers ϕ 1 , ϕ 2  of the pumps P 1 , P 2 , and that the lower the NFC pressure, the higher the pump flow rates are (NFC system). The inside of the block is also provided with spools and the like for controlling the direction and flow rate of hydraulic oil to be supplied to left and right traveling hydraulic motors (not shown) functioning as fluid pressure actuators, which are provided in, for example, the lower traveling body  14  of the chassis  12 , and the operation means are provided in the operator&#39;s station so as to correspond to these spools. However,  FIG. 1  only shows the circuits and operation means L 1  to L 4  corresponding to the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c , and omits the illustration of the other circuits and operation means. Although the present embodiment describes the control valve CV corresponding to the NFC system, the present embodiment is not limited to the NFC system and therefore can be applied to other control valves CV. 
     The control device CT has a rotational frequency control function for controlling the engine speed  19 , and a discharge amount control function for controlling the amounts of hydraulic oil discharged from the pumps P 1 , P 2  by controlling the capacities of the pumps P 1 , P 2 . Specifically, the control device CT generates a setting signal  30  based on the rated rotational frequency and the differential rotational frequency set beforehand while detecting the engine speed  19  by using a rotational frequency sensor, not shown. The setting signal  30  is an electrical signal (such as a current) for controlling the fuel injection timing and injection amount of a fuel injector installed in the engine  19 . The control device CT also controls the discharge flow rates of the pumps P 1 , P 2  by outputting, to the capacity controllers ϕ 1 , ϕ 2  of the pumps P 1 , P 2 , an electrical signal (such as a current) corresponding to the NFC pressure detected by a pressure sensor, not shown. The control device CT also generates an electrical signal (such as a current) such as the foregoing control signals in accordance with the operation amounts of the operation means L 1  to L 4 , i.e., the operation amount of at least any of the spools of the control valve CV or, in the present embodiment, the operation amount of each of the spools. 
     How the rotational frequency control function of the control device CT sets the engine speed  19  is now described specifically. As shown in  FIG. 2 , the control device CT has an input unit  31 , an environment setting unit  32 , a weighting unit  33  functioning as the weighting means, an estimation unit  34  functioning as the estimation means, an output unit  35  and the like. The estimation unit  34  and the output unit  35  configure a setting unit  36  that functions as the setting means for setting the setting signal  30  by using fuzzy inference, the setting signal  30  being used for setting the engine speed of engine  19  in accordance with the work amount estimated by the estimation unit  34 . The control device CT estimates the work amount of the work machine  11 , i.e. the work amounts of the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c , by using fuzzy inference and in accordance with the operation amount of each of the operation means L 1  to L 4 , and sets the engine speed  19  in accordance with the estimated work amount. 
     The input unit  31  receives input of discharge pressures  41 ,  42  of the pumps P 1 , P 2  that are detected by pressure sensors  37 ,  38  provided in the output channels  27 ,  28 , a left revolution operation amount  43  and a right revolution operation amount  44  of the revolving hydraulic motor  16   m , such as pilot pressures or electrical signals, which are set in accordance with the operation amount of the operation means L 1  that is obtained when revolving the upper revolving body  16  to the left with respect to the lower traveling body  14 , a boom lifting operation amount  45  and a boom lowering operation amount  46  of the boom cylinder  21   c , such as pilot pressures or electrical signals, which are set in accordance with the boom lifting and lowering operation amounts obtained through the operation means L 2 , a stick-in operation amount  47  and a stick-out operation amount  48  of the stick cylinder  22   c , such as pilot pressures and electrical signals, which are set in accordance with the stick-in and stick-out operation amounts obtained through the operation means L 3 , a bucket-in operation amount  49  and a bucket-out operation amount  50  of the bucket cylinder  23   c , such as pilot pressures or electrical signals, which are set in accordance with the bucket-in and bucket-out operation amounts obtained through the operation means L 4 , and a determination flag (status flag)  51  for determining whether the operation means L 1  to L 4  are operated or not. The values that are input to this input unit  31  are each A/D-converted and output to the weighting unit  33  and the output unit  35 . 
     The environment setting unit  32  sets various numerical values to be used by the estimation unit  34 . For instance, the environment setting unit  32  sets a predetermined time period (e.g., 15 seconds) TP during which the work amount of the work machine  11  based on the operation amounts of the operation means L 1  to L 4  is detected, sampling rates SR for sampling the operation amounts of the operation means L 1  to L 4 , weighting factors Wl, Wm, Wh corresponding to the fuzzy rules of the consequent parts of the fuzzy inference, and the like. The numerical values set by the environment setting unit  32  are stored in storage means (memory) not shown, and can be rewritten. 
     The weighting unit  33  weights the operation amounts of the operation means L 1  to L 4 . As shown in  FIG. 3 , the weighting unit  33  outputs, to the estimation unit  34 , the maximum element out of the values obtained by multiplying operation amounts  43  to  50 , which are set in accordance with the operation amounts of the operation means L 1  to L 4 , by weighting coefficients (gains)  53  to  60  respectively. In other words, the weighting unit  33  outputs the maximum operation amount  61  to the estimation unit  34 . These weighting coefficients  53  to  60  are set according to the operations of the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c  that are operated by the operation means L 1  to L 4 . In the present embodiment, the weighting coefficients  53  to  55 ,  57 , and  59  corresponding to the operation amounts  43  to  45 ,  47 , and  49  are set at 1, the weighting coefficient  56  corresponding to the boom lowering operation amount  46  at 0, and the weighting coefficients corresponding to the stick-out operation amount  48  and the bucket-out operation amount  50  at a predetermined value less than 1. 
     The estimation unit  34  is a fuzzy inference computation unit that estimates and computes the work amount of the work machine  11  by using fuzzy inference, based on the operation amounts of the operation means L 1  to L 4  operating the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c . Specifically, as shown in  FIG. 4 , the estimation unit  34  has a membership function introduction unit  62  that introduces a membership function F to the maximum operation amount  61  input from the weighting unit  33 , adaptation level calculation units  63  to  65  that calculate the adaptation levels (average value) to the antecedent parts of the fuzzy rules in the predetermined time period TP by using the numerical values input from the environment setting unit  32  and the membership function F introduced by the membership function introduction unit  62 , a centroid value calculation unit  66  that performs defuzzification by calculating the centroid values of the consequent parts of the fuzzy rules using the adaptation levels calculated by the adaptation level calculation units  63  to  65  and the numerical values input by the environment setting unit  32 , and an amplifier  67  for amplifying the centroid value calculated by the centroid value calculation unit  66 . In the estimation unit  34 , therefore, the membership function introduction unit  62  functions as an antecedent part computation unit for computing the antecedent parts of the fuzzy inference of the control device CT, and the adaptation level calculation units  63  to  65  and the centroid value calculation unit  66  function as consequent part computation units for computing the consequent parts of the fuzzy inference of the control device CT. 
     The membership function F used by the membership function introduction unit  62  quantitatively indicates the levels of requirement for the speeds of the revolving hydraulic motor  16   m  and cylinders  21   c  to  23   c . In the present embodiment, as illustrated by the example in  FIG. 5 , for instance, the membership function is constituted of a function F 1  representing the adaptation level when the levels of requirement for the speeds are low (referred to as “low level,” hereinafter), a function Fm representing the adaptation level when the levels of requirement for the speeds are moderate (referred to as “medium level,” hereinafter), and a function Fh representing the adaptation level when the levels of requirement for the speeds are high (referred to as “high level,” hereinafter). 
     The adaptation level calculation units  63  to  65  each detect the low level, medium level, and high level of the membership function F introduced by the membership function introduction unit  62  for each sampling rate within the predetermined time period TP input from the environment setting unit  32 , and obtains the adaptation levels (average value for each predetermined time period TP) Gl, Gm, Gh by dividing each of the detected levels by the predetermined time period TP. 
     The centroid value calculation unit  66  uses, for example, the adaptation levels Gl, Gm, Gh obtained by the adaptation level calculation units  63  to  65 , to calculate a centroid value W based on, for example, W=(Wh*Gh+Wm*Gm+Wl*Gl)/(Gh+Gm+Gl). In the present embodiment, three fuzzy rules are set: (1) the engine speed  19  is kept as is in case of the high level, (2) the engine speed  19  is lowered in case of the medium level, and (3) the engine speed  19  is lowered significantly in case of the low level. In the present embodiment, therefore, the estimation unit  34  uses the fuzzy inference to calculate the amount of reduction in the engine speed  19 , i.e., the differential rotational frequency. The weighting factors Wh, Wm, Wl are set in accordance with the consequent parts of these three fuzzy rules. In the present embodiment, these weighting factors are equal to or less than 0 and set such as Wh&gt;Wm&gt;Wl. 
     The amplifier  67  outputs a differential rotational frequency  68 , which is an output value obtained by amplifying the centroid value W by a predetermined amplification degree (e.g., 1), to the output unit  35  shown in  FIG. 2 . 
     Then, only when the determination flag  51  determines that the operation means L 1  to L 4  are operated, the output unit  35  outputs the setting signal  30 , an electrical signal obtained by processing the differential rotational frequency  68 . The fuel injection timing and injection amount of the fuel injector installed in the engine  19  are controlled based on the setting signal  30  output from the output unit  35  and a predetermined rated rotational frequency that is set beforehand by setting means such as an acceleration dial, not shown, thereby controlling the engine speed  19  to a target rotational frequency ((rated rotational frequency+(differential rotational frequency)). 
     Next, the control method according to the present embodiment is described with reference to the flowchart shown in  FIG. 6 . The numbers in the circles shown in  FIG. 6  represent the step numbers. 
     Step 1 
     First, the control device CT calculates the average value of the maximum values of the operation amounts of the operation means L 1  to L 4  within the predetermined time period TP. In so doing, the estimation unit  34  causes the adaptation level calculation units  63  to  65  to calculate the average value within the predetermined time period TP with respect to the maximum operation amount  61  corresponding to the maximum values of the operation amounts of the operation means L 1  to L 4  that are weighted by the weighting unit  33 . 
     Step 2 
     Next, using the membership function F introduced by the membership function introduction unit  62 , the control device CT causes the adaptation level calculation unit  63  to  65  of the estimation unit  34  to determine the adaptation levels Gl, Gm, Gh with respect to each level of the average value of the operation amounts of the operation means L 1  to L 4  that are obtained in step  1  (fuzzification). Note that, using the membership function F introduced by the membership function introduction unit  62 , the control device CT may calculate the adaptation levels corresponding to the levels of the operation amounts of the operation means L 1  to L 4  and then calculate the average value of these adaptation levels within the predetermined time period TP. 
     Step 3 
     The control device CT also causes the centroid value calculation unit  66  of the setting unit  36  (the estimation unit  34 ) to quantify the centroid value W by using the adaptation levels Gl, Gm, Gh obtained in step  2  and the weighting factors Wl, Wm, Wh set by the environment setting unit  32  (defuzzification). 
     Step 4 
     The control device CT causes the output unit  35  to convert the value corresponding to (proportional to) the centroid value W quantified in step  3 , into the setting signal  30 , and then operates the engine  19  at the target rotational frequency that is set based on this setting signal  30  and the signal into which the value corresponding to the rated rotational frequency is converted. 
     Specifically, a case is considered in which when leveling (smoothing of the ground) is performed, the stick-in operation amount  47  and the stick-out operation amount  48  of the stick cylinder  22   c  fluctuate as shown in  FIG. 8( a )  and  FIG. 8( b ) . As shown by the pilot pressures in  FIG. 8( a )  and  FIG. 8( b ) , when these operation amounts fluctuate between −1.5 MPa to 1.5 MPa from 0 to 40 seconds, between −1.0 MPa to 1.0 MPa from 40 to 80 seconds, and between −4.0 MPa to 4.0 MPa from 80 to 120 seconds, the adaptation levels Gl, Gm, Gh corresponding to the average value of the operation amounts within the predetermined time period TP (15 seconds) are obtained with respect to the low level, medium level, and high level as shown in  FIGS. 8( c ) to 8( e ) . In the present embodiment, the centroid value W for each time is obtained as shown in  FIG. 8( f )  by establishing, for example, Wh=0, Wm=−100, and Wl=−200 with respect to these adaptation levels Gl, Gm, Gh. Then, the engine speed of the engine  19  is controlled to the target rotational frequency obtained by adding the rotational frequency corresponding to (proportional to) this centroid value W to the rated rotational frequency. 
     As described above, according to the foregoing embodiment, the work amount of the work machine  11  is estimated by the estimation unit  34  using fuzzy inference based on the operation amounts of the operation means L 1  to L 4  operating the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c , and then the setting signal for setting the engine speed of the engine  19  is set by the setting unit  36  using fuzzy inference in accordance with the estimated work amount. Therefore, the engine speed can be optimized in accordance with the intention of the operator in operating the operation means L 1  to L 4 . In other words, the efficient parts of the engine  19  and the pumps P 1 , P 2  can be used. 
     Specifically, in a case where the operation amounts of the operation means L 1  to L 4  are low, the operating speeds of the revolving hydraulic motor  16   m  and cylinders  21   c  to  23   c  are almost the same, although the engine speed varies depending on the operation such as the stick-out operation. For this reason, when the amounts the operation means L 1  to L 4  are operated by the operator are low, the levels of requirement for the speeds the revolving hydraulic motor  16   m  and cylinders  21   c  to  23   c  are basically low as well, and the required power of the hydraulic system does not need to be high. However, reducing the flow rates of the pumps P 1 , P 2  with the intention of reducing the energy loss caused by bleeding the hydraulic oil off to the tank T leads to a decrease in efficiency of the pumps P 1 , P 2  themselves, resulting in not being able to reduce the energy loss. The present embodiment, on the other hand, employs the NFC system, to reduce the engine speed of the engine  19 . Thus, the efficiency of the pumps P 1 , P 2  is not lowered easily because the swash plates of the variable capacity-type pumps P 1 , P 2  start to rise naturally even when the operation amounts of the operation means L 1  to L 4  are the same. 
     As a result, the energy loss of the hydraulic system including the pumps P 1 , P 2 , the revolving hydraulic motor  16   m , and the cylinders  21   c  to  23   c  can be reduced. 
     Specifically, the accuracy of estimating the work amount of the work machine  11  can be further improved by causing the estimation unit  34  to estimate the work amount of the work machine  11  based on the average value of the maximum values of the operation amounts of the operation means L 1  to L 4  obtained within the predetermined time period TP and the membership function F representing the predetermined levels of requirement for the speeds of the revolving hydraulic motor  16   m  and cylinders  21   c  to  23   c.    
     Particularly, the estimation accuracy can be further improved by using the weighted operation amounts of the operation means L 1  to L 4  to estimate the work amount of the work machine  11  using the estimation unit  34 . As a result, the engine speed can be controlled to the rotational frequency that fits with the operations of the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c  operated by the operation means L 1  to L 4 . Consequently, not only it is possible to reduce the energy loss of the hydraulic system more reliably, but also the engine speed with respect to the operation means L 1  to L 4  is prevented from changing drastically. 
     Therefore, the engine speed can be controlled to the rotational frequency suitable for a task, improving fuel consumption. 
     According to the foregoing embodiment, the membership function F, the weighting factors Wl, Wm, Wh and the like can be set arbitrarily based on the set fuzzy rules. 
     The levels of requirement for the speeds of the revolving hydraulic motor  16   m  and the cylinders  21   c  to  23   c  do not have to be three (low level, medium level, high level), and two, four or more levels can be set. 
     The present invention is suitable for a hydraulic shovel-type work machine and can also be applied to a wheel-type work machine as long as it has a work device protruding from the chassis. 
     INDUSTRIAL APPLICABILITY 
     The present invention is industrially applicable to all businesses that are concerned in manufacturing and sales of work machines equipped with fluid pressure systems having fluid pressure actuators and pumps.