Patent Publication Number: US-11643792-B2

Title: Wheel loader configured to determine a reduction value of a traveling drive force

Description:
TECHNICAL FIELD 
     The present invention relates to a wheel loader. 
     BACKGROUND ART 
     As the background art of the technical field to which the present invention belongs, for example, Patent Literature 1 describes a “driving force control device for controlling driving slip of wheels of a four-wheel drive vehicle, comprising: a longitudinal acceleration detecting means for estimating or detecting longitudinal acceleration occurring in the vehicle; a road surface gradient estimating means for estimating the gradient of a road surface; a vehicle body speed estimating means for correcting the longitudinal acceleration detected by the longitudinal acceleration detecting means in consideration of the road surface gradient estimated by the road surface gradient estimating means and estimating the vehicle body speed based on a correction value; and a driving force control means for controlling driving force transmitted from each wheel to the road surface based on determination of driving slip using the vehicle body speed estimated by the vehicle body speed estimating means”. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 2001-82199 A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, if merely applying the conventional technique described in Patent Literature 1 to a wheel loader having a working device on the front side of a vehicle body, it is impossible to attain balance between slip suppression and excavation performance during excavation work of the earth and sand by the wheel loader. This is because when performing the excavation work by the wheel loader, it is necessary to take into consideration balance between penetration into the earth and sand by traveling traction force and thrust of a hydraulic cylinder associated with lifting operation of the working device after the penetration. In a state in which the lifting operation of the working device is not sufficiently performed after the penetration into the earth and sand, the reaction force of the working device load handling force is not applied to wheels. Meanwhile, when the lifting operation of the working device is performed after the penetration into the earth and sand, the working device load handling force increases accordingly, and thereby the reaction force of the working device load handling force, which is applied to the wheels, also increases. As described above, after the penetration into the earth and sand, slip limit traveling drive force changes in accordance with the change of grounding force of the wheels. If simply limiting the traveling drive force at start of the slip, the slip is suppressed but the force for penetration into the earth and sand is not sufficiently obtained in accordance with the limitation of the traveling drive force, and as a result, sufficient excavation performance is not exhibited. 
     An objective of the present invention is to provide a wheel loader capable of exhibiting sufficient excavation performance while suppressing slip during excavation. 
     Solution to Problem 
     In order to achieve the objective described above, a wheel loader according to the present invention is configured to comprises: a vehicle body to which wheels are attached on a front side and a rear side thereof, respectively; a working device provided on the front side of the vehicle body; a hydraulic cylinder configured to drive the working device; an engine serving as a power source, configured to generate traveling drive force of the vehicle body and thrust of the hydraulic cylinder; an acceleration sensor configured to detect acceleration of the vehicle body; a rotational speed sensor configured to detect rotational speed of the wheels; a thrust sensor configured to detect thrust of the hydraulic cylinder; and a control device configured to control the traveling drive force of the vehicle body, wherein the control device is configured to: determine a reduction value of the traveling drive force based on first vehicle body acceleration of the vehicle body calculated using the acceleration detected by the acceleration sensor, second vehicle body acceleration of the vehicle body calculated using the rotational speed of the wheels detected by the rotational speed sensor, and the thrust of the hydraulic cylinder detected by the thrust sensor; and reduce the traveling drive force based on the reduction value and output the reduced traveling drive force. 
     Advantageous Effects of Invention 
     According to the wheel loader of the present invention, it is possible to exhibit sufficient excavation performance while suppressing slip during excavation. Problems, configurations, and effects other than those described above will be clarified by the following description of an embodiment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a side view of a wheel loader according to an embodiment of the present invention. 
         FIG.  2    is a block diagram schematically illustrating hardware configuration of a controller. 
         FIG.  3    is a block diagram illustrating functional configuration of a controller. 
         FIG.  4    is an analytical model diagram for calculating an inclination angle and first vehicle body acceleration. 
         FIG.  5    is an analytical model diagram for correcting a reduction value of driving force of an engine. 
         FIG.  6    is an analytical model diagram for correcting a reduction value of driving force of an engine. 
         FIG.  7    illustrates a reduction value data table. 
         FIG.  8    illustrates a reduction value correction data table. 
         FIG.  9    illustrates a flowchart showing a procedure of control processing for engine driving force performed by a controller. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of a wheel loader according to the present invention will be described with reference to the drawings. 
       FIG.  1    is a side view of a wheel loader  1  according to the embodiment of the present invention. As illustrated in  FIG.  1   , the wheel loader  1  includes a front frame (vehicle body)  5  having a pair of lift arms  2 , a bucket  3 , a pair of front wheels  4 , etc., and a rear frame (vehicle body)  9  having an operator&#39;s cab  6 , an engine compartment  7 , a pair of rear wheels  8 , etc. An engine  25  is mounted in the engine compartment  7 , and a counterweight  10  is attached to the rear of the rear frame  9 . The operation of the engine  25  is controlled by an engine control unit (hereinafter, referred as ECU)  70 . 
     The pair of lift arms  2  is rotated in the vertical direction (tilting movement) by the driving of a pair of lift arm cylinders  11 , and the bucket  3  is rotated in the vertical direction (clouding or dumping) by the driving of a bucket cylinder  12 . A link mechanism including a bell crank  13  is interposed between the bucket cylinder  12  and the bucket  3 , and the bucket cylinder  12  rotates the bucket  3  via the link mechanism. A working device  14  is constituted by the pair of lift arms  2 , the bucket  3 , the pair of lift arm cylinders  11 , the bucket cylinder  12 , the bell crank  13 , etc. 
     A lift arm angle sensor (not illustrated) is attached to a connecting portion between the lift arm  2  and the front frame  5 , which is configured to detect the rotation angle of the lift arm  2 . In addition, the lift arm cylinder  11  is provided with a bottom side pressure sensor (thrust sensor)  33  for detecting pressure on the bottom side and a rod side pressure sensor (thrust sensor)  34  for detecting pressure on the rod side (see  FIG.  3   ). These pressure sensors  33 ,  34  are configured to detect working device pressure (object handling load) applied to the working device  14 . The bucket cylinder  12  is provided with a proximity switch (not illustrated), so that when the rod of the bucket cylinder  12  is shortened by a predetermined amount, the proximity switch is turned on and the posture of the bucket  3  can be detected. 
     A rotational speed sensor  32  for detecting the rotational speed of the front wheels  4  and the rear wheels  8  is also provided. In the present embodiment, the rotational speed sensor  32  is configured to detect the rotational speed of an output shaft of a transmission (not illustrated) connected to an output shaft of the engine  25  via a torque converter (not illustrated), and convert the detected rotational speed of the output shaft of the transmission into the rotational speed of the front wheels  4  and the rear wheels  8 . Meanwhile, the rotational speed sensor  32  may be configured to directly detect the rotational speed of the front wheels  4  and the rear wheels  8 . 
     The front frame  5  and the rear frame  9  are rotatably connected to each other by a center pin  15 , and the front frame  5  is swiveled in the left and right direction with respect to the rear frame  9  by expansion and contraction of a steering cylinder (not illustrated). The operator&#39;s cab  6  mounted on a front portion of the rear frame  9  includes such as an operator&#39;s seat on which an operator is seated, a steering wheel for controlling a steering angle of the wheel loader  1 , a key switch for starting and stopping the wheel loader  1 , a display device for providing the operator with information (none of them are illustrated). The operator&#39;s cab  6  also includes a controller (control device)  50  for controlling the entire operation of the wheel loader  1 , an IMU (Inertial Measurement Unit)  31  for detecting the vehicle body acceleration and the vehicle body angular velocity. 
       FIG.  2    is a block diagram schematically illustrating hardware configuration of the controller  50 . As illustrated in  FIG.  2   , the controller  50  is constituted by hardware including a CPU (Central Processing Unit)  50 A configured to perform various calculation for controlling the entire operation of the vehicle body, a storage device such as a ROM (Read Only Memory)  50 B configured to store a program for executing the calculation by the CPU  50 A, a RAM (Random Access Memory)  50 C serving as a work area when the CPU  50 A executes the program, and an input and output interface  50 D configured to input and output various information and signals to/from an external device. 
     In the above-described hardware configuration, the program stored in the ROM  50 B is read out to the RAM  50 C and operated in accordance with the control by the CPU  50 A so that the program (software) and the hardware cooperate, and thereby the functional block which realizes the function of the controller  50  is constituted therein. 
       FIG.  3    is a block diagram illustrating functional configuration of the controller  50 . As illustrated in  FIG.  3   , the controller  50  includes an inclination angle calculating section  51  configured to calculate an inclination angle θ of the vehicle body, a vehicle body acceleration calculating section  52  configured to calculate first vehicle body acceleration of the vehicle body, a vehicle body acceleration estimating section  53  configured to estimate second vehicle body acceleration of the vehicle body, an acceleration difference comparing and determining section  54  configured to compare and determine acceleration difference between the first vehicle body acceleration calculated by the vehicle body acceleration calculating section  52  and the second vehicle body acceleration estimated by the vehicle body acceleration estimating section  53 , a driving force reduction value determining section  55  configured to temporarily determine a reduction value of the driving force (output torque) output from the engine  25 , a lift arm cylinder thrust calculating section  56  configured to calculate thrust of the lift arm cylinders  11 , and a driving force reduction value correcting section  57  configured to correct the reduction value of the driving force temporarily determined by the driving force reduction value determining section  55 , a target driving force output section  58  configured to output target driving force (target output torque) of the engine  25 , a reduction value data table  59 , and a reduction value correction data table  60 . 
     Hereinafter, the functional configuration of the controller  50  will be described in detail mainly with reference to  FIG.  3   , and appropriately with reference to  FIGS.  4  to  6   .  FIGS.  4  to  6    illustrate analytical models for performing various calculations, specifically,  FIG.  4    is an analytical model diagram for calculating an inclination angle θ and first vehicle body acceleration av 1 , and  FIGS.  5  and  6    are analytical model diagrams for correcting the reduction value of the driving force of the engine  25 . 
     The inclination angle calculating section  51  inputs each data of acceleration ay of the y-direction component and angular velocity co which are detected by the IMU  31  to a Kalman filter, and calculates an inclination angle θ (see  FIG.  4   ). Since the processing by the Kalman filter is well known, the description thereof is omitted here. 
     The vehicle body acceleration calculating section  52  calculates first vehicle body acceleration av 1  by substituting the acceleration ay of the y-direction component detected by the IMU  31  and the inclination angle θ calculated by the inclination angle calculating section  51  into the following Equation 1.
 
 av 1= ay−g× sin θ  [Equation 1]
 
     The vehicle body acceleration estimating section  53  calculates (estimates) second vehicle body acceleration av 2  by substituting rotational speed N (rpm) of the front wheels  4  and the rear wheels  8  detected by the rotational speed sensor  32  into the following Equation 2. The second vehicle body acceleration av 2  is an estimation value based on data detected by the rotational speed sensor  32 . 
                     av   ⁢   2     =       d   [     α   ×   N     ]     dt             [     Equation   ⁢         2     ]               
Here, α is a vehicle body speed conversion factor.
 
     The acceleration difference comparing and determining section  54  subtracts the first vehicle body acceleration av 1  calculated by the vehicle body acceleration calculating section  52  from the second vehicle body acceleration av 2  estimated by the vehicle body acceleration estimating section  53  to calculate acceleration difference (difference) Δa between the first vehicle body acceleration av 1  and the second vehicle body acceleration av 2 , and compares and determines whether the acceleration difference Δa is equal to or greater than a predetermined value. 
     The driving force reduction value determining section  55  refers to the reduction value data table  59  illustrated in  FIG.  7   , and temporarily determines a target driving force reduction value Δf from the acceleration difference Δa calculated by the acceleration difference comparing and determining section  54 . Here, the reduction value data table  59  illustrated in  FIG.  7    is a characteristic in which the driving force reduction value Δf increases in proportion to the acceleration difference Δa. That is, in the present embodiment, as the acceleration difference Δa increases, the driving force is reduced since it is assumed that slip is occurring. The reduction value data table  59  is stored in advance in the ROM  50 B. The driving force reduction value determining section  55  can calculate the driving force reduction value Δf by substituting the acceleration difference Δa into the following Equation 3, without referring to the reduction value data table  59 .
 
Δ f=αmΔa   [Equation 3]
 
     Here, m is the mass of the vehicle body, and α is a correction factor. 
     The lift arm cylinder thrust calculating section  56  calculates lift arm cylinder thrust (hydraulic load) ph by substituting pressure phb on the bottom side of the lift arm cylinders  11  detected by the bottom side pressure sensor  33  and pressure phr on the rod side of the lift arm cylinders  11  detected by the rod side pressure sensor  34  into the following Equation 4. 
     Note that calculation of ph is performed by multiplication of a factor, etc. in consideration of pressure receiving areas on the bottom side and the rod side of the lift arm cylinders  11 .
 
 ph=phb−phr   [Equation 4]
 
     The driving force reduction value correcting section  57  corrects the driving force reduction value Δf temporarily determined by the driving force reduction value determining section  55  based on the lift arm cylinder thrust ph calculated by the lift arm cylinder thrust calculating section  56 , and outputs a corrected driving force reduction value Δf′ to the target driving force output section  58 . Since the load (excavation reaction force) during object handling work such excavation acts on the vehicle body, in particular, the grounding force of the front wheels  4  with respect to the ground increases, so that slip is less likely to occur. Accordingly, when the load during the object handling work is applied to the vehicle body, the driving force can be increased as compared with the case where the load during the object handling work is not applied to the vehicle body. In other words, the driving force reduction value Δf temporarily determined can be reduced during the object handling work. Accordingly, the driving force reduction value correcting section  57  corrects the reduction value of the driving force to be small in accordance with the hydraulic load (object handling load) acting on the lift arm cylinders  11 . A specific calculation method will be described in the following, appropriately with reference to  FIGS.  5  and  6   . 
     When the load Wf is applied to the front wheels  4  by the object handling work, slip is less likely to occur, so that the driving force can be increased. The increase of the driving force by the load Wf can be calculated by the following Equation 5.
 
 Δf−Δf′=μΔWf   [Equation 5]
 
Here, ΔWf is increase in the load applied to the front wheels  4 , and μ is a friction factor.
 
     From the Equation 5, Δf′ can be expressed by the following Equation 6.
 
 Δf′=Δf−μΔWf   [Equation 6]
 
     Referring to  FIG.  5   , ΔWf can be expressed by the following Equation 7 from moment balance. 
                     Δ   ⁢   Wf     =       (     L   +   WB     )     ×     W     (   WB   )                 [     Equation   ⁢         7     ]               
Here, L is object handling load point length, WB is wheel base length, and W is object handling load.
 
     When substituting the Equation 7 into the Equation 6, the corrected driving force reduction value Δf′ can be expressed by the following Equation 8. 
                     Δ   ⁢     f   ′       =       Δ   ⁢   f     -       μ   ⁡   (     L   +   WB     )     ×     W     (   WB   )                   [     Equation   ⁢         8     ]               
Referring to  FIG.  6   , the object handling load W can be expressed by the following Equation 9 according to mechanism calculation.
 
                     W   =       ph   ×   Ma   ⁢   5         l   ⁢   2     -     l   ⁢   1   ×       Ma   ⁢   1     R             ⁢   
     〈     R   =       Ma   ⁢   2   ×   Ma   ⁢   4       Ma   ⁢   3         〉             [     Equation   ⁢         9     ]               
Here, ph is lift arm cylinder thrust (hydraulic load), and  11 ,  12 , and Ma 1  to Ma 5  are mechanical parameters determined by the load handling posture.
 
     When substituting the Equation 9 into the Equation 8, the corrected driving force reduction value Δf′ can be expressed by the following Equation 10. 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                       f 
                       ′ 
                     
                   
                   = 
                   
                     
                       Δ 
                       ⁢ 
                       f 
                     
                     - 
                     
                       
                         μ 
                         ⁡ 
                         ( 
                         
                           L 
                           + 
                           WB 
                         
                         ) 
                       
                       × 
                       
                         W 
                         
                           ( 
                           WB 
                           ) 
                         
                       
                       × 
                       
                         
                           ph 
                           × 
                           Ma 
                           ⁢ 
                           5 
                         
                         
                           
                             l 
                             ⁢ 
                             2 
                           
                           - 
                           
                             l 
                             ⁢ 
                             1 
                             × 
                             
                               
                                 Ma 
                                 ⁢ 
                                 1 
                               
                               R 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     10 
                   
                   ] 
                 
               
             
           
         
       
     
     In this manner, the driving force reduction value correcting section  57  can calculate a value by correcting the driving force reduction value Δf using the Equation 10, that is, the corrected driving force reduction value Δf′. In the present embodiment, the calculation for correcting the driving force reduction value Δf is simplified by using the reduction value correction data table  60  illustrated in  FIG.  8   . More specifically, the reduction value correction data table  60  illustrated in  FIG.  8    has a characteristic in which the correction factor (Δf′/Δf) increases in inverse proportion to the lift arm cylinder thrust ph. That is, in the present embodiment, the larger the load handling load (excavation reaction force) is, the more difficult it is for slip to occur, so that the correction factor becomes small. As a result, the corrected driving force reduction value Δf′ becomes small. When the corrected driving force reduction value Δf′ is small, the value of the target driving force to be output becomes large, so that it is possible to make the wheel loader  1  travel with the large driving force as compared with the case where the object handling load is small. The reduction value correction data table  60  is stored in advance in the ROM  50 B. 
     The target driving force output section  58  outputs a target torque command T* or a target rotational speed command N* to the ECU  70  so as to reduce the driving force by the corrected driving force reduction value Δf′ corrected by the driving force reduction value correcting section  57 . The ECU  70  controls the driving force of the engines  25  in accordance with this command. 
     Next, a procedure of the control processing by the controller  50  will be described.  FIG.  9    illustrates a flowchart showing the procedure of the control processing for engine driving force performed by the controller  50 . When the key switch of the wheel loader  1  is turned on, the controller  50  starts the processing illustrated in  FIG.  9   . 
     Firstly, in step S 1 , the inclination angle calculating section  51  calculates an inclination angle θ of the vehicle body based on each data of the acceleration ay and the angular velocity co input from the IMU  31 . The vehicle body acceleration calculating section  52  calculates first vehicle body acceleration av 1  based on the inclination angle θ and the acceleration ay. 
     Next, in step S 2 , the vehicle body acceleration estimating section  53  calculates (estimates) second vehicle body acceleration av 2  based on data of rotation speed N input from the rotation speed sensor  32 . 
     Next, in step S 3 , the acceleration difference comparing and determining section  54  subtracts the first vehicle body acceleration av 1  from the second vehicle body acceleration av 2  to obtain acceleration difference Δa, and determines whether the acceleration difference Δa is equal to or greater than a predetermined value. Here, the predetermined value is set as a threshold value for determining whether the wheel loader  1  is slipping, and is predetermined by calculation or experience in consideration of specifications such as weight and size of the wheel loader  1 . The predetermined value is stored in advance in the ROM  50 B. 
     When the difference Δa is equal to or greater than the predetermined value (step S 3 /Yes), it is determined that the wheel loader  1  is slipping, and a processing for reducing the driving force is performed. Specifically, in step S 4 , the driving force reduction value determining section  55  refers to the reduction value data table  59  and determines a driving force reduction value Δf. Next, in step S 5 , the lift arm cylinder thrust calculating section  56  calculates lift arm cylinder thrust ph based on the bottom side pressure data and the rod side pressure data of the lift arm cylinders  11  detected by the pressure sensors  33 ,  34 . 
     Next, in step S 6 , the driving force reduction value correcting section  57  refers to the reduction value correction data table  60  and calculates a corrected driving force reduction value Δf′ based on the driving force reduction value Δf and the lift arm cylinder thrust ph. When the lift arm cylinder thrust ph is zero, the corrected driving force reduction value Δf′ calculated in step S 6  has the same value as the driving force reduction value Δf, and accordingly, the output target driving force becomes traveling drive force necessary for slip suppression when the object handling work is not considered. 
     Next, in step S 7 , the target driving force output section  58  outputs a target driving force signal to the ECU  70  so as to reduce the traveling drive force by the corrected driving force reduction value Δf′, and repeats the steps of S 5  to S 8  until a certain period of time elapses in step S 8 . 
     Here, the certain period can be set to a time required for single excavation work performed by the wheel loader  1 . For example, at the time of performing V-shaped excavation work, it can be set to a time (for example, about 5 seconds to 10 seconds) until the wheel loader  1  is switched to reverse after advancing to thrust the bucket  3  into a pile of the earth and sand or the like, scooping the earth and sand or the like by the bucket  3 , and moving up the bucket  3 . In this way, it is possible to perform the object handling work efficiently while reliably preventing slip until the single excavation work is completed. 
     When the certain period of time elapses (step S 8 /Yes), the processing returns to the start. If NO in step S 3 , the acceleration difference comparing and determining section  54  determines that no slip has occurred. Then, the processing proceeds to the return and returns to the start. 
     As described above, according to the present embodiment, even when the wheel loader  1  is slipping, since the traveling drive force is corrected so as to increase in accordance with the object handling load (excavation reaction force), it is possible to exhibit sufficient excavation performance while suppressing slip during excavation. Furthermore, since the thrust of the lift arm cylinders  11  is calculated by the pressure sensors  33 ,  34  on the bottom side and the rod side of the lift arm cylinders  11 , which are usually provided in the wheel loader  1 , and the traveling driving force is corrected, it is unnecessary to provide a separate sensor for calculating the object handling load, which makes it possible to suppress the cost. Still further, there is an advantage that the load of the calculation processing by the controller  50  can be reduced by performing the calculation using the reduction value data table  59  and the reduction value correction data table  60 . 
     It should be noted that the embodiments as described above are examples of the present invention, and are not intended to limit the scope of the present invention only thereto. Those skilled in the art can practice the present invention in various other ways without departing from the concept of the invention. 
     For example, if preparing a plurality of the reduction value data table  59  and the reduction value correction data table  60  so that the operator can select them in accordance with the environment (road surface condition, etc.) in the object handling work, it is possible to perform the object handling work efficiently while suppressing slip with higher accuracy. Furthermore, instead of using the IMU  31 , an acceleration sensor for detecting the acceleration ay of the vehicle body, an inclination sensor for detecting the inclination angle θ of the vehicle body, etc. may be separately provided. In addition, by providing a vehicle speed sensor instead of the rotational speed sensor  32 , it is possible to calculate the rotational speed of the wheels from the vehicle speed detected by the vehicle speed sensor. 
     In the present invention, the reduction of the traveling drive force is performed until a certain time of time elapses. Meanwhile, it also can be configured to detect that the wheel loader  1  is switched from advancing to reversing, and thereby the reduction of the traveling drive force is ended. 
     LIST OF REFERENCE SIGNS 
     
         
           1  wheel loader 
           2  lift arm 
           3  bucket 
           4  front wheel (wheels) 
           8  rear wheel (wheels) 
           5  front frame (vehicle body) 
           9  rear frame (vehicle body) 
           11  lift arm cylinder (hydraulic cylinder) 
           12  bucket cylinder (hydraulic cylinder) 
           13  bell crank 
           14  working device 
           25  engine 
           31  IMU (acceleration sensor) 
           32  rotational speed sensor 
           33  bottom side pressure sensor (thrust sensor) 
           34  rod side pressure sensor (thrust sensor) 
           50  controller (control device)