Patent Publication Number: US-11384512-B2

Title: Work machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National stage application of International Application No. PCT/JP2019/042802, filed on Oct. 31, 2019. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-215047, filed in Japan on Nov. 15, 2018, the entire contents of which are hereby incorporated herein by reference. 
     BACKGROUND 
     Field of the Invention 
     The present invention relates to a work machine. 
     Background Information 
     A work machine, such as a bulldozer, includes a hydraulic pump, a hydraulic actuator, and a work implement, as shown in Japanese Laid-Open Patent Publication No. H4-285304. The hydraulic actuator is driven by hydraulic fluid discharged from the hydraulic pump to operate the work implement. In addition, a load sensing valve is provided in the work machine. The load sensing valve controls the discharge displacement of the hydraulic pump so that a differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the hydraulic actuator is held at a predetermined set pressure. 
     SUMMARY 
     However, a hydraulic motor and a fan are provided in the work machine. The hydraulic motor is driven by hydraulic fluid discharged from the hydraulic pump to rotate the fan. Therefore, the hydraulic fluid discharged from the hydraulic pump is distributed to the hydraulic actuator for the work implement and to the hydraulic motor for the fan. 
     In the work machine described above, the set pressure of the load sensing valve is set to a suitable value when driving the work implement that applies a large load to the hydraulic actuator. Therefore, when the work implement is not operated and only the hydraulic motor for the fan is driven, the hydraulic pump discharges the hydraulic fluid at an excessive pressure. As a result, the energy loss of the hydraulic pump is great. 
     An object of the present invention is to reduce the energy loss of a hydraulic pump in a work machine. 
     A work machine according to one aspect includes a variable displacement hydraulic pump, hydraulic actuators, a work implement, a fan, a control valve, a regulator, a load sensing valve, a set pressure control device, and a controller. The hydraulic actuators include a work implement actuator and a hydraulic motor and are driven by hydraulic fluid discharged from the hydraulic pump. The work implement is connected to the work implement actuator. The fan is connected to the hydraulic motor. The control valve controls the flow rate of the hydraulic fluid supplied from the hydraulic pump to the hydraulic actuators. The regulator controls the discharge displacement of the hydraulic pump. The load sensing valve controls the regulator in accordance with a differential pressure between a discharge pressure of the hydraulic pump and a load pressure of the hydraulic actuators to maintain the differential pressure at a set pressure. The set pressure control device controls the set pressure. The controller controls the set pressure control device so that the set pressure is reduced more when a determination condition, which includes the fact that the work implement is not being operated, is satisfied than when the work implement is being operated. 
     According to the present invention, energy loss of the hydraulic pump in the work machine can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of the work machine. 
         FIG. 2  is a block diagram illustrating a configuration of the work machine. 
         FIG. 3  is a schematic view of a configuration of the pump control device. 
         FIG. 4  illustrates a determination condition for controlling a set pressure control device. 
         FIG. 5  illustrates a control method for a fan. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A work machine  1  according to an embodiment will be discussed below with reference to the drawings.  FIG. 1  is a side view of the work machine  1 . The work machine  1  according to the present embodiment is a bulldozer. The work machine  1  includes a vehicle body  2 , a travel device  3 , and a work implement  4 . The vehicle body  2  includes an operator&#39;s cab  11  and an engine compartment  12 . The engine compartment  12  is disposed in front of the operator&#39;s cab  11 . The travel device  3  is attached to a bottom portion of the vehicle body  2 . The travel device  3  includes a pair of left and right crawler belts  13 . Only the crawler belt  13  on the left side is illustrated in  FIG. 1 . The work machine  1  travels due to the rotation of the crawler belts  13 . 
     The work implement  4  is attached to the vehicle body  2 . The work implement  4  has a lift frame  14  and a blade  15 . The lift frame  14  is attached to the vehicle body  2  in a manner that allows movement up and down. The lift frame  14  supports the blade  15 . The blade  15  is disposed in front of the vehicle body  2 . The work machine  1  includes work implement actuators  16  to  18 . The work implement actuators  16  to  18  include a lift cylinder  16 , a tilt cylinder  17 , and an angle cylinder  18 . The lift cylinder  16 , the tilt cylinder  17 , and the angle cylinder  18  are connected to the work implement  4 . 
     Specifically the lift cylinder  16  is coupled to the vehicle body  2  and the lift frame  14 . The blade  15  moves up and down (referred to below as “lifting motion”) due to the extension and contraction of the lift cylinder  16 . The tilt cylinder  17  is connected to the lift frame  14  and the blade  15 . The left and right ends of the blade  15  moves up and down and the blade  15  tilts (referred to below as “tilting motion”) due to the extension and contraction of the tilt cylinders  17 . The angle cylinder  18  is connected to the lift frame  14  and the blade  15 . The left and right ends of the blade  15  move forward and backward and the blade  15  tilts (referred to below as “angling motion”) due to the extension and contraction of the angle cylinder  18 . 
       FIG. 2  is a block diagram of a configuration of a control system of the work machine  1 . As illustrated in  FIG. 2 , the work machine  1  includes an engine  21 , a hydraulic pump  22 , a power transmission device  23 , a control valve  24 , and a controller  25 . 
     The engine  21  is an internal combustion engine, such as a diesel engine. The output of the engine  21  is controlled by adjusting an injection amount of fuel from a fuel injection device  26 . The adjustment of the fuel injection amount is performed by the controller  25  controlling the fuel injection device  26 . The hydraulic pump  22  is driven by the engine  21  to discharge hydraulic fluid. The hydraulic fluid discharged from the hydraulic pump  22  is supplied to the work implement actuators  16  to  18  via the control valve  24 . The work implement actuators  16  to  18  are driven by hydraulic fluid discharged from the hydraulic pump  22 . 
     The hydraulic pump  22  is a variable displacement hydraulic pump. The displacement of the hydraulic pump  22  is controlled by controlling a tilt angle of a swash plate  27 . The displacement of the hydraulic pump  22  signifies the discharge amount of hydraulic fluid per one rotation of the hydraulic pump  22 . The discharge displacement is determined by the angle of the swash plate  27 . A pump control device  28  is connected to the hydraulic pump  22 . The tilt angle of the swash plate  27  of the hydraulic pump  22  is controlled by the pump control device  28 . A detailed explanation of the pump control device  28  is provided below. 
     The power transmission device  23  transmits the driving power of the engine  21  to the travel device  3 . The power transmission device  23  may be a hydrostatic transmission (FIST), for example. Alternatively, the power transmission device  23 , for example, may be a transmission having a torque converter or a plurality of speed change gears. 
     The work machine  1  includes a cooling device  31 , a hydraulic motor  32 , a fan  33 , and a temperature sensor  34 . The cooling device  31  is, for example, a radiator and cools cooling water for the engine  21 . The hydraulic motor  32  is driven by hydraulic fluid discharged from the hydraulic pump  22 . The fan  33  is connected to the hydraulic motor  32 . The fan  33  is rotationally driven by the hydraulic motor  32  thereby generating an air flow for cooling the cooling water in the cooling device  31 . The temperature sensor  34  detects the temperature of the cooling water. The temperature sensor  34  outputs a detection signal indicative of the detected temperature of the cooling water. 
     The control valve  24  is controlled by command signals from the controller  25 . The control valve  24  is connected to the hydraulic actuators  10  and the work implement pump  22  through a hydraulic circuit. The hydraulic actuators  10  include the above-mentioned work implement actuators  16  to  18  and the hydraulic motor  32 . The hydraulic fluid discharged from the hydraulic pump  22  is supplied to the work implement actuators  16  to  18  and the hydraulic motor  32  via the control valve  24 . The control valve  24  changes the opening degree of the control valve  24  in accordance with the command signals from the controller  25 . Consequently, the control valve  24  controls the flow rate of hydraulic fluid supplied from the hydraulic pump  22  to the work implement actuators  16  to  18  and the hydraulic motor  32 . The control valve  24  may also be controlled by supplying a pilot hydraulic pressure. 
     Specifically, the control valve  24  includes a fan control valve  41 , a first control valve  42 , a second control valve  43 , and a third control valve  44 . The fan control valve  41  controls the flow rate of the hydraulic fluid supplied from the hydraulic pump  22  to the hydraulic motor  32 . The first control valve  42  controls the flow rate of the hydraulic fluid supplied from the hydraulic pump  22  to the lift cylinder  16 . The second control valve  43  controls the flow rate of the hydraulic fluid supplied from the hydraulic pump  22  to the tilt cylinder  17 . The third control valve  44  controls the flow rate of the hydraulic fluid supplied from the hydraulic pump  22  to the angle cylinder  18 . 
     The work machine  1  includes a work implement operating member  45  and a travel operating member  46 . The work implement operating member  45  and the travel operating member  46  are disposed in the operator&#39;s cab  11 . The work implement operating member  45  is a member for operating the work implement  4 . The work implement operating member  45  is manually operable in the operating positions for the lifting motion, the tilting motion, and the angling motion of the blade  15 . The work implement operating member  45  receives an operation from an operator for driving the work implement  4  and outputs an operation signal corresponding to the operation. 
     The travel operating member  46  is, for example, a travel lever and is a member for operating the travel device  3 . The travel operating member  46  is manually operable in a forward travel position, a reverse travel position, and a neutral position. The travel operating member  46  receives an operation from the operator for driving the work machine  1  and outputs an operation signal corresponding to the operation. The operation signal of the work implement operating member  45  and the operation signal of the travel operating member  46  are outputted to the controller  25 . 
     The controller  25  is programmed to control the work machine  1  based on acquired data. The controller  25  includes a processor  51  and a memory  52 . The processor  51  is, for example, a CPU and executes processing for controlling the work machine  1 . The memory  52  includes, for example, a volatile memory and a non-volatile memory. The memory  52  records computer commands that are executable by the processor and that are for controlling the work machine  1 . 
     The controller  25  acquires operation signals from the work implement operating member  45  and the travel operating member  46 . The controller  25  controls the travel device  3 , the engine  21 , and the power transmission device  23  in accordance with the operation signals from the travel operating member  46  to travel the work machine  1 . The controller  25  controls the control valve  24  in accordance with the operation signals from the work implement operating member  45  to move the work implement  4  and the fan  33 . The work implement operating member  45  and the travel operating member  46  are not limited to levers and may be other members, such as a pedal or a switch. The work implement operating member  45  and the travel operating member  46  are not limited to outputting electrical operation signals and may output pilot hydraulic pressures that correspond to the operations. In this case, the controller  25  may detect the pilot hydraulic pressures from the work implement operating member  45  and the travel operating member  46  with a hydraulic pressure sensor and may acquire operation signals indicative of the pilot hydraulic pressures. 
     A configuration of the pump control device  28  will be explained next. The pump control device  28  controls the angle of the swash plate  27  so that the differential pressure between the discharge pressure of the hydraulic pump  22  and the load pressure of the hydraulic actuators  10  is constant. The load pressure of the hydraulic actuators  10  may be the greatest among the load pressures of the work implement actuators  16  to  18  and the hydraulic motor  32 . Alternatively, the load pressure of the hydraulic actuators  10  may be another pressure determined based on the load pressures of the work implement actuators  16  to  18  and the hydraulic motor  32 . 
       FIG. 3  is a schematic view illustrating a configuration of the pump control device  28 . As illustrated in  FIG. 3 , the pump control device  28  has a regulator  53 , a load sensing valve  54  (referred to below as “LS valve  54 ”), and a set pressure control device  55 . 
     The regulator  53  is a servo piston and controls the discharge displacement of the hydraulic pump  22 . The regulator  53  includes a piston  56  and a cylinder  57 . The piston  56  is coupled to the swash plate  27 . A first chamber  53   a  and a second chamber  53   b  are provided inside the cylinder  57  with the piston  56  interposed therebetween. The piston  56  is urged from the first chamber  53   a  side toward the second chamber  53   b  side by a spring  58 . As a result, the position of the piston  56  inside the cylinder  57  is determined by the balance between the resultant force of the spring force of the spring  58  and the force of the hydraulic pressure inside the first chamber  53   a , and the force of the hydraulic pressure inside the second chamber  53   b . When the piston  56  moves to the second chamber  53   b  side (toward the left in  FIG. 2 ), the angle of the swash plate  27  increases and the discharge displacement of the hydraulic pump  22  increases. Alternatively, when the piston  56  moves to the first chamber  53   b  side, the angle of the swash plate  27  decreases and the discharge displacement of the hydraulic pump  22  decreases. 
     The LS valve  54  maintains a differential pressure at a set pressure by controlling the regulator  53  in accordance with the differential pressure between the discharge pressure of a hydraulic pump  22  and the load pressure of the hydraulic actuators  10 . The LS valve  54  controls the angle of the swash plate  27  so that the differential pressure is constant at the set pressure. The LS valve  54  includes a first pilot port P 1 , a second pilot port P 2 , and a third pilot port P 3 . The first pilot port P 1  is connected to the discharge side of the hydraulic pump  22  through a first pilot circuit  61 . The discharge pressure of the hydraulic pump  22  is applied to the first pilot port P 1  as a pilot pressure through the first pilot circuit  61 . The second pilot port P 2  is connected to the load side of the control valve  24  through a second pilot circuit  62 . The load pressure of the hydraulic actuators  10  is applied to the second pilot port P 2  as a pilot pressure through the second pilot circuit  62 . The third pilot port P 3  is connected to the set pressure control device  55 . 
     The LS valve  54  is switched between a state S 1  and a state S 2 . The LS valve  54  connects the second chamber  53   b  of the cylinder  57  to a drain circuit  63  in the state S 1 . Consequently, the hydraulic fluid from the second chamber  53   b  is exhausted and the hydraulic pressure of the second chamber  53   b  decreases. The LS valve  54  connects the second chamber  53   b  to the first pilot circuit  61  in the state S 2 . Consequently, hydraulic fluid is supplied to the second chamber  53   b  and the hydraulic pressure of the second chamber  53   b  increases. 
     A spring  59  is provided to the LS valve  54  and urges the LS valve  54  toward the state S 1 . The set pressure of the LS valve  54  is determined by the urging force of the spring  59  and the pilot pressure applied to the third pilot port P 3 . When the differential pressure is less than the set pressure of the LS valve  54 , the LS valve  54  enters the state S 1 . In this state, the hydraulic pressure of the second chamber  53   b  of the regulator  53  decreases and the piston  56  moves toward the left in  FIG. 3 . As a result, the angle of the swash plate  27  increases and the discharge displacement of the hydraulic pump  22  increases. 
     In addition, when the differential pressure is greater than the set pressure, the LS valve  54  switches to the state S 2 . In this state, the LS valve  54  supplies hydraulic fluid to the second chamber  53   b  of the regulator  53  through the first pilot circuit  61 . Consequently, the hydraulic pressure of the second chamber  53   b  increases and the piston  56  inside the regulator  53  moves to the right in  FIG. 3 . As a result, the angle of the swash plate  27  decreases and the discharge displacement of the hydraulic pump  22  decreases. 
     The set pressure control device  55  controls the set pressure of the above-mentioned LS valve  54 . Specifically, the set pressure control device  55  switches the set pressure between a predetermined first pressure and a predetermined second pressure. The second pressure is smaller than the first pressure. The set pressure control device  55  is an electromagnetic control valve controlled by command signals from the controller  25 . 
     The set pressure control device  55  switches between an off-state and an on-state in accordance with the command signals from the controller  25 . The set pressure control device  55  causes the third pilot port P 3  of the LS valve  54  to be in communication with a drain circuit  64  in the off-state. At this time, no pilot pressure is supplied from the set pressure control device  55  to the third pilot port P 3 , and the set pressure of the LS valve  54  is set to the first pressure determined by the spring  59 . 
     In addition, the set pressure control device  55  causes the third pilot port P 3  of the LS valve  54  to be in communication with a pilot circuit  65  in the on-state. The pilot circuit  65  is connected to the hydraulic pump  22  or to another hydraulic pump which is not illustrated. When the set pressure control device  55  is in the on-state, a predetermined pilot pressure is supplied from the set pressure control device  55  to the third pilot port P 3 . As a result, the set pressure of the LS valve  54  is reduced from the first pressure to the second pressure. 
     The control of the set pressure performed by the controller  25  will be explained next. The controller  25  controls the set pressure control device  55  so as to reduce the set pressure more when a predetermined determination condition is satisfied than when the determination condition is not satisfied. The predetermined determination condition is that the work implement  4  is not being operated and the travel device  3  is in the reverse travel state. 
     The controller  25  determines whether or not the work implement  4  is being operated based on the operating amount of the work implement operating member  45 . The controller  25  determines that the work implement  4  is not being operated when the operating amount of the work implement operating member  45  is zero. The controller  25  may determine that the work implement  4  is not being operated when the operating amount of the work implement operating member  45  is approximately zero. The controller  25  determines that the travel device  3  is in the reverse travel state when the travel operating member  46  is positioned in the reverse travel position. 
     In  FIG. 4 , “F” represents the forward travel position, “N” represents the neutral position, and “R” represents the reverse travel position “OFF” indicates that the predetermined determination condition is not satisfied, that is, that the set pressure control device  55  enters the off-state. “ON” indicates that the predetermined determination condition is satisfied, that is, that the set pressure control device  55  enters the on-state. As illustrated in  FIG. 4 , when the work implement  4  is being operated, the controller  25  sets the set pressure control device  55  to the off-state even if the travel operating member  46  is in any of the forward travel position, the neutral position, or the reverse travel position. Therefore, the controller  25  sets the set pressure control device  55  to the off-state and sets the set pressure to the first pressure when the work implement  4  is being operated. Consequently, the pump control device  28  controls the discharge displacement of the hydraulic pump  22  so that the differential pressure is held at the first pressure. 
     Moreover, even when the work implement  4  is not being operated, the controller  25  sets the set pressure control device  55  to the off-state if the travel operating member  46  is in the forward travel position or the neutral position. Therefore, the controller  25  sets the set pressure to the first pressure when the travel operating member  46  is in the forward travel position or the neutral position regardless of whether the work implement  4  is being operated or not. 
     When the work implement  4  is not being operated and the travel operating member  46  is in the reverse travel position, the controller  25  sets the set pressure control device  55  to the on-state and sets the set pressure to the second pressure which is less than the first pressure. Consequently, the pump control device  28  controls the discharge displacement of the hydraulic pump  22  so that the differential pressure is maintained at the second pressure. 
     The control of the fan control valve  41  performed by the controller  25  will be explained next. The controller  25  determines a target rotation speed of the fan  33  in accordance with the temperature of the cooling water, and controls the fan control valve  41  in accordance with the target rotation speed. As illustrated in  FIG. 5 , the controller  25  has target rotation speed data D 1  and control valve command data D 2 . The target rotation speed data D 1  defines a relationship between the temperature of the cooling water and the target rotation speed of the fan  33 . The controller  25  refers to the target rotation speed data D 1  and determines the target rotation speed from the temperature of the cooling water. The target rotation speed data D 1  may define a relationship between the temperature of the hydraulic fluid and/or the air intake temperature of the engine  21 , and the target rotation speed of the fan  33 , without being limited to the temperature of the cooling water. The controller  25  may refer to the target rotation speed data D 1  and determine the target rotation speed from the temperature of the hydraulic fluid and/or the air intake temperature of the engine  21 . 
     The control valve command data D 2  defines a relationship between a command current to the fan control valve  41  and the target rotation speed of the fan  33 . The command current to the fan control valve  41  represents the opening degree of the control valve  24 . The smaller the command current, the greater the opening degree of the control valve  24 . The control valve command data D 2  includes first command value data D 21  and second command value data D 22 . The second command value data D 22  defines a command current that is smaller than the first command value data D 21  with respect to the same target rotation speed. That is, the second command value data D 22  defines an opening degree that is larger than that of the first command value data D 21  with respect to the same target rotation speed. 
     The controller  25  refers to the first command value data D 21  and determines the opening degree of the control valve  24  when the set pressure control device  55  is in the off-state. The controller  25  refers to the second command value data D 22  and determines the opening degree of the control valve  24  when the set pressure control device  55  is in the on-state. Therefore, when the set pressure control device  55  is in the on-state, the controller  25  controls the fan control valve  41  so that the opening degree of the fan control valve  41  increases more than when the set pressure control device  55  is in the off-state. 
     In the work machine  1  according to the present embodiment explained above, the set pressure is reduced to the second pressure when the work implement  4  is not being operated more so than when the work implement  4  is being operated. Therefore, the discharge displacement of the hydraulic pump  22  is controlled so that the differential pressure between the discharge pressure of the hydraulic pump  22  and the load pressure of the hydraulic actuators  10  is reduced when the work implement  4  is not being operated. Accordingly, energy loss of the hydraulic pump  22  can be reduced. In addition, even when the set pressure is set to the second pressure, a differential pressure for properly actuating the hydraulic motor  32  is assured. Consequently, the cooling capacity by the fan  33  can be sufficiently assured. Furthermore, when the work implement  4  is being operated, the set pressure is not reduced to the second pressure and is maintained at the first pressure. Consequently, a reduction in the operability of the work implement  4  can be suppressed. 
     The set pressure is reduced when the work implement  4  is not being operated and the travel device  3  is in the reverse travel state. In the work machine  1 , the work implement  4  is not operated very often when the travel device  3  is in the reverse travel state. As a result, when the travel device  3  is in the reverse travel state, the set pressure is reduced whereby a reduction in the operability of the work implement  4  can be suppressed. 
     When the set pressure control device  55  is in the on-state, the controller  25  causes the opening degree of the fan control valve  41  to increase more than when the set pressure control device  55  is in the off-state. Therefore, the set pressure is reduced whereby a reduction in the rotation speed of the fan  33  can be suppressed even when the differential pressure is reduced. 
     Although an embodiment of the present invention has been described so far, the present invention is not limited to the above embodiment and various modifications may be made within the scope of the invention. The work machine  1  is not limited to a bulldozer and may be another vehicle such as a hydraulic excavator, a wheel loader, or a motor grader or the like. The travel device  3  is not limited to crawler belts and may include other members such as tires. The work implement  4  is not limited to a blade and may include another member such as a bucket. 
     The hydraulic actuators are not limited to the above-mentioned lift cylinder, tilt cylinder, and angle cylinder, and may include other actuators. The configuration of the pump control device is not limited to that of the above-mentioned embodiment and may be modified. For example, the configuration of the hydraulic circuit of the pump control device may be modified. The set pressure control device may be capable of continually changing the set pressure. 
     The determination conditions are not limited to the above embodiment and may be modified. For example, the condition pertaining to the travel operating member may be modified or omitted. Alternatively, another condition may be added to the determination conditions. 
     According to the present invention, energy loss of the hydraulic pump in the work machine can be reduced.