Work vehicle, controller for work vehicle, and speed control method for work vehicle

Abstract

A speed control method of a work vehicle includes receiving a setting stage set by a first operation member among a plurality of speed stages, obtaining a target moving direction of a work vehicle that is determined by a speed difference between a target rotation speed of a first hydraulic motor and a second hydraulic motor, determining an operating range of a first control parameter and an operating range of a second control parameter based on the setting stage when a second operation member is operated so that deviation amount between the target moving direction and the straight direction is within first range, and determining a boost stage among the plurality of speed stages that corresponds to target rotation speeds higher than the target rotation speeds of the setting stage when the second operation member is operated so that deviation amount is out of the first range.

What is claimed is: 
     
         1 . A speed control method for a work vehicle, comprising:
 receiving a setting stage set by a first operation member among a plurality of speed stages, the plurality of speed stages corresponding to a plurality of sets of target rotation speeds at which a first hydraulic motor and a second hydraulic motor respectively rotate to move the work vehicle straight, the first hydraulic motor being configured to drive a first traveling device provided on a left side of a vehicle body of the work vehicle, the second hydraulic motor being configured to drive a second traveling device provided on a right side of the vehicle body;   obtaining a target moving direction of the work vehicle by receiving information corresponding to the target moving direction from a sensor to detect operation of a second operation member via which the target moving direction is set, the target moving direction being determined by a speed difference between a target rotation speed of the first hydraulic motor and a target rotation speed of the second hydraulic motor;   determining an operating range of a first control parameter and an operating range of a second control parameter based on the setting stage when the second operation member is operated such that a deviation amount between the target moving direction and a straight direction is within a first range predetermined, a displacement volume of the first hydraulic pump configured to supply hydraulic fluid to the first hydraulic motor being determined by the first control parameter, a displacement volume of a second hydraulic pump configured to supply hydraulic fluid to the second hydraulic motor being determined by the second control parameter;   determining a boost stage among the plurality of speed stages based on the deviation amount to determine at least one operating range based on the boost stage, when the second operation member is operated such that the deviation amount is out of the first range, each of the at least one operating range being an operating range of each of at least one control parameter of the first control parameter and the second control parameter, the boost stage corresponding to a set of target rotation speeds higher than the target rotation speeds of the setting stage;   controlling the first control parameter within the operating range of the first control parameter determined based on the boost stage or the setting stage;   controlling the second control parameter within the operating range of the second control parameter determined based on the boost stage or the setting stage; and   setting a displacement volume of the first hydraulic motor and a displacement volume of the second hydraulic motor to respective constant volumes regardless of the plurality of speed stages to drive the first traveling device and the second traveling device by rotating the first hydraulic motor and the second hydraulic motor, respectively.   
     
     
         2 . The speed control method according to  claim 1 ,
 wherein the first range is a range of the deviation amount that is predetermined such that rotation of at least one of the first hydraulic motor and the second hydraulic motor is operable when the setting stage is set to a minimum speed stage among the plurality of speed stages, the minimum speed stage corresponding to a set of rotation speeds lowest among the target rotation speeds of the plurality of speed stages.   
     
     
         3 . The speed control method according to  claim 2 ,
 wherein, when the deviation amount is out of the first range, the boost stage is determined such that a difference in stages between the boost stage and the setting stage increases as the deviation amount increases.   
     
     
         4 . The speed control method according to  claim 3 ,
 wherein the difference in stages is determined such that rotation of at least one of the first hydraulic motor and the second hydraulic motor is operable within a range of the deviation amount based on which the boost stage is determined.   
     
     
         5 . The speed control method according to  claim 3 ,
 wherein a maximum value of the difference in stages is n+1,   wherein n represents a number of speed stages whose target rotation speeds are higher than the target rotation speeds of the minimum speed stage and lower than the target rotation speeds of a minimum turnable speed stage of the plurality of speed stages, and   wherein the minimum turnable speed stage corresponds to a set of rotation speeds lowest among the target rotation speeds of the plurality of speed stages at which rotation of at least one motor of the first hydraulic motor and the second hydraulic motor is operable regardless of operation of the second operating member.   
     
     
         6 . The speed control method according to  claim 1 ,
 wherein the first control parameter is a first high pilot pressure which is a higher one of two pilot pressures and by which the displacement volume of the first hydraulic pump is determined, and   wherein the second control parameter is a second high pilot pressure which is a higher one of two pilot pressures and by which the displacement volume of the second hydraulic pressure pump is determined.   
     
     
         7 . The speed control method according to  claim 1 ,
 wherein the first control parameter is a first pilot effective pressure obtained by subtracting a first low pilot pressure from a first high pilot pressure, the first low pilot pressure being a lower one of first two pilot pressures by which the displacement volume of the first hydraulic pump is determined, the first high pilot pressure being a higher one of the first two pilot pressures, and   wherein the second control parameter is a second pilot effective pressure obtained by subtracting a second low pilot pressure from a second high pilot pressure, the second low pilot pressure being a lower one of second two pilot pressures by which the displacement volume of the second hydraulic pump is determined, the second high pilot pressure being a higher one of the second two pilot pressures.   
     
     
         8 . A work vehicle comprising:
 a vehicle body;   a first traveling device and a second traveling device provided on a left side and a right side of the vehicle body, respectively;   a first hydraulic motor configured to drive the first traveling device;   a second hydraulic motor configured to drive the second traveling device;   a first hydraulic pump configured to supply hydraulic fluid to the first hydraulic motor;   a second hydraulic pump configured to supply the hydraulic fluid to the second hydraulic motor;   a control mechanism configured to control a displacement volume of the first hydraulic pump and a displacement volume of the second hydraulic pump;   a prime mover configured to rotate the first hydraulic pump and the second hydraulic pump;   a storage configured to store a plurality of speed stages corresponding to a plurality of sets of target rotation speeds at which the first hydraulic motor and the second hydraulic motor respectively rotate to move the work vehicle straight;   a first operation member configured to receive an input corresponding to a setting stage of the plurality of speed stages;   a second operation member configured to receive an input corresponding to a target moving direction of the work vehicle determined by a speed difference between a target rotation speed of the first hydraulic motor and a target rotation speed of the second hydraulic motor;   a sensor configured to detect an operation of the second operation member; and   a hardware processor configured to control the motor and the control mechanism;   the hardware processor being configured to:
 receive the setting stage from the first operation member; 
 receive information corresponding to the target moving direction from the sensor to obtain the target moving direction; 
 determine an operating range of a first control parameter and an operating range of a second control parameter based on the setting stage when the second operation member is operated such that a deviation amount between the target moving direction and a straight direction is within a first range predetermined, a displacement volume of the first hydraulic pump being determined by the first control parameter, a displacement volume of the second hydraulic pump being determined by the second control parameter; 
 determine a boost stage among the plurality of speed stages based on the deviation amount to determine at least one operating range based on the boost stage, when the second operation member is operated such that the deviation amount is out of the first range, each of the at least one operating range being an operating range of each of at least one control parameter of the first control parameter and the second control parameter, the boost stage corresponding to a set of target rotation speeds higher than the target rotation speeds of the setting stage; 
 control the control mechanism such that the first control parameter is within the operating range of the first control parameter and the second control parameter is within the operating range of the second control parameter, the operating ranges of the first control parameter and the second control parameter being determined based on a boost stage or the setting stage, and 
 set a displacement volume of the first hydraulic motor and a displacement volume of the second hydraulic motor to respective constant volumes regardless of the plurality of speed stages to drive the first traveling device and the second traveling device by rotating the first hydraulic motor and the second hydraulic motor, respectively. 
   
     
     
         9 . The work vehicle according to  claim 8 ,
 wherein the first range is a range of the deviation amount that is predetermined such that rotation of at least one of the first hydraulic motor and the second hydraulic motor is operable when the setting stage is set to a minimum speed stage among the plurality of speed stages, the minimum speed stage corresponding to a set of rotation speeds lowest among the target rotation speeds of the plurality of speed stages.   
     
     
         10 . The work vehicle according to  claim 9 ,
 wherein, when the deviation amount is out of the first range, the boost stage is determined such that a difference in stages between the boost stage and the setting stage increases as the deviation amount increases.   
     
     
         11 . The work vehicle according to  claim 10 ,
 wherein the difference in stages is determined such that rotation of at least one of the first hydraulic motor and the second hydraulic motor is operable within the range of the deviation amount based on which the boost stage is determined.   
     
     
         12 . The work vehicle according to  claim 10 ,
 wherein a maximum value of the difference in stages is n+1,   wherein n represents a number of speed stages whose target rotation speeds are higher than the target rotation speeds of the minimum speed stage and lower than the target rotation speeds of a minimum turnable speed stage of the plurality of speed stages, and   wherein the minimum turnable speed stage corresponds to a set of rotation speeds lowest among the target rotation speeds of the plurality of speed stages at which rotation of at least one motor of the first hydraulic motor and the second hydraulic motor is operable regardless of operation of the second operating member.   
     
     
         13 . The work vehicle according to  claim 8 ,
 wherein the control mechanism comprises:
 a pilot pump configured to supply pilot oil to the first hydraulic pressure pump and the second hydraulic pressure pump; 
 a first pilot hydraulic circuit connecting the pilot pump and two pilot ports of the first hydraulic pump; 
 a second pilot hydraulic circuit connecting the pilot pump and two pilot ports of the second hydraulic pump; 
 at least one first pressure control valve provided in the first pilot hydraulic circuit and configured to control a first high pilot pressure that is a higher one of two pilot pressures respectively applied to the two pilot ports of the first hydraulic pump, and at least one second pressure control valve provided in the second pilot hydraulic circuit and configured to control a second high pilot pressure that is a higher one of two pilot pressures respectively applied to the two pilot ports of the second hydraulic pump, 
   wherein the prime mover is configured to rotate the pilot pump,   wherein the first control parameter is the first high pilot pressure, and   wherein the second control parameter is the second high pilot pressure.   
     
     
         14 . The work vehicle according to  claim 8 ,
 wherein the control mechanism includes:
 a pilot pump configured to supply pilot oil to the first hydraulic pressure pump and the second hydraulic pressure pump; 
 a first pilot hydraulic circuit to connect the pilot pump and two pilot ports of the first hydraulic pressure pump; 
 a second pilot hydraulic circuit to connect the pilot pump and two pilot ports of the second hydraulic pressure pump; 
 at least one third pressure control valve provided in the first pilot hydraulic circuit and configured to control a first pilot effective pressure which is a difference between two pilot pressures applied to the two pilot ports of the first hydraulic pressure pump, and 
 at least one fourth pressure control valve provided in the second pilot hydraulic circuit and configured to control a second pilot effective pressure which is a difference between two pilot pressures applied to the two pilot ports of the second hydraulic pressure pump, 
   wherein the prime mover is configured to rotate the pilot pump,   wherein the first control parameter is the first pilot effective pressure, and   wherein the second control parameter is the second pilot effective pressure.   
     
     
         15 . The work vehicle according to  claim 13 ,
 wherein at least one control parameter includes the first control parameter and the second control parameter.   
     
     
         16 . The work vehicle according to  claim 13 ,
 wherein the second operation member is an operation lever rotatable in the front-rear and right-left directions,   wherein the two pilot ports of the first hydraulic pump include a first port and a second port, the pilot oil being supplied through the first port to move a swash plate of the first hydraulic pump so that the first hydraulic motor drives the first traveling device in a forward direction when the first hydraulic pump is rotated, the pilot oil being supplied through the second port to move the swash plate of the first hydraulic pump so that the first hydraulic motor drives the first traveling device in a backward direction when the first hydraulic pump is rotated,   wherein the two pilot ports of the second hydraulic pump include a third port and a fourth port, the pilot oil being supplied through the third port to move a swash plate of the second hydraulic pump so that the second hydraulic motor drives the second traveling device in the forward direction when the second hydraulic pump is rotated, the pilot oil being supplied through the fourth port to move the swash plate of the second hydraulic pump so that the second hydraulic motor drives the second traveling device in the backward direction when the second hydraulic pump is rotated,   wherein the first pilot hydraulic circuit includes
 a first pilot oil passage connecting the pilot pump to the first port, 
 a second pilot oil passage connecting the pilot pump to the second port, 
   wherein the second pilot hydraulic circuit includes
 a third pilot oil passage connecting the pilot pump to the third port, 
 a fourth pilot oil passage connecting the pilot pump to the fourth port, 
   wherein the work vehicle further includes
 a first hydraulic sensor configured to detect a first forward pilot pressure which is a pilot pressure applied to the first port, 
 a second hydraulic sensor configured to detect a first backward pilot pressure which is a pilot pressure applied to the second port, 
 a third hydraulic sensor configured to detect a second forward pilot pressure which is a pilot pressure applied to the third port, 
 a fourth hydraulic sensor configured to detect a second backward pilot pressure which is a pilot pressure applied to the fourth port; 
   wherein the hardware processor is configured to
 acquire the first forward pilot pressure from the first hydraulic sensor, 
 acquire the first backward pilot pressure from the second hydraulic sensor, 
 acquire the second forward pilot pressure from the third hydraulic sensor, 
 acquire the second backward pilot pressure from the fourth hydraulic sensor, 
 determine based on the first forward pilot pressure, the first backward pilot pressure, the second forward pilot pressure, and the second backward pilot pressure, which of a first instruction, a second instruction, a third instruction, and a fourth instruction is input as an input instruction via the operation lever, the first instruction being to rotate the first hydraulic motor so as to drive the first traveling device in the forward direction and to rotate or stop the second hydraulic motor so as to drive the second traveling device in the backward direction with respect to the first traveling device, the second instruction being to rotate the first hydraulic motor so as to drive the first traveling device in the backward direction and to rotate or stop the second hydraulic motor so as to drive the second traveling device in the forward direction with respect to the first traveling device, the third instruction being to rotate the second hydraulic motor so as to drive the second traveling device in the forward direction and to rotate or stop the first hydraulic motor so as to drive the first traveling device in the backward direction with respect to the second traveling device, the fourth instruction being to rotate the second hydraulic motor so as to drive the second traveling device in the reverse direction and to rotate or stop the first hydraulic motor so as to drive the first traveling device in the forward direction with respect to the second traveling device, 
 determine an operation degree from at least two pressures of the first forward pilot pressure, the first backward pilot pressure, the second forward pilot pressure, and the second backward pilot pressure, the operation degree corresponding to a target value of the speed difference between the rotation speed of the first hydraulic motor and the rotation speed of the second hydraulic motor in the input instruction, and 
 determine the deviation amount such that the larger the deviation amount is as the larger the operation degree is. 
   
     
     
         17 . The work vehicle according to  claim 13 ,
 wherein the at least one first pressure control valve includes a first pressure reducing valve, a second pressure reducing valve, and a first relief valve,   wherein the first pressure reducing valve is provided in the first pilot oil passage and configured to convert a primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the second pressure reducing valve is provided in the second pilot oil passage and configured to convert the primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the first relief valve is connected to the first pilot oil passage between the first pressure reducing valve and the first port and to the second pilot oil passage between the second pressure reducing valve and the second port, and is configured to reduce the secondary pressure exceeding a first set pressure to the first set pressure when at least one of the secondary pressure input to the first pressure reducing valve and the secondary pressure input to the second pressure reducing valve exceeds the first set pressure,   wherein the at least one second pressure control valve includes a third pressure reducing valve, a fourth pressure reducing valve, and a second relief valve,   wherein the third pressure reducing valve is provided in the third pilot oil passage and configured to convert the primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the fourth pressure reducing valve is provided in the fourth pilot oil passage and configured to convert the primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the second relief valve is connected to the third pilot oil passage between the third pressure reducing valve and the third port and to the fourth pilot oil passage between the fourth pressure reducing valve and the fourth port, and is configured to decrease the secondary pressure exceeding a second set pressure to the second set pressure when at least one of the secondary pressure input to the third pressure reducing valve and the secondary pressure input to the fourth pressure reducing valve exceeds the second set pressure, and   wherein the hardware processor is configured to:
 control the first control parameter such that the first set pressure is set to an upper limit value of the operating range, when the at least one control parameter includes the first control parameter, and 
 control the second control parameter such that the second set pressure is set to an upper limit value of the operating range, when the at least one control parameter includes the second control parameter. 
   
     
     
         18 . The work vehicle according to  claim 13 ,
 wherein the at least one first pressure control valve includes
 an electromagnetic pressure control valve provided in the first pilot oil passage and configured to change the pilot pressure supplied by the pilot pump in accordance with a first signal from the hardware processor, and 
 a second electromagnetic pressure control valve provided in the second pilot oil passage and configured to change the pilot pressure supplied by the pilot pump in accordance with a second signal from the hardware processor, 
   wherein the at least one second pressure control valve includes
 a third electromagnetic pressure control valve provided in the third pilot oil passage and configured to change the pilot pressure supplied by the pilot pump in accordance with a third signal from the hardware processor, and 
 a fourth electromagnetic pressure control valve provided in the fourth pilot oil passage and configured to change the pilot pressure supplied by the pilot pump in accordance with a fourth signal from the hardware processor, and 
   wherein the hardware processor configured to generate
 the first signal or the second signal corresponding to the first high pilot pressure based on the deviation amount and an upper limit value of the operating range, and 
 the third signal or the fourth signal corresponding to the second high pilot pressure based on the deviation amount and an upper limit value of the operating range. 
   
     
     
         19 . The work vehicle according to  claim 13 ,
 wherein the at least one first pressure control valve includes a first pressure reducing valve and a second pressure reducing valve,   wherein the first pressure reducing valve is provided in the first pilot oil passage, and is configured to convert a primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the second pressure reducing valve is provided in the second pilot oil passage, and is configured to convert a primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the at least one second pressure control valve includes a third pressure reducing valve and a fourth pressure reducing valve,   wherein the third pressure reducing valve is provided the third pilot oil passage, and is configured to convert a primary pressure supplied by the pilot pump into a secondary pressure according to a rotation direction and a rotation amount of the operation lever,   wherein the fourth pressure reducing valve is provided in the fourth pilot oil passage, and is configured to convert the primary pressure supplied by the pilot pump into the secondary pressure in accordance with a rotation direction and a rotation amount of the operation lever,   wherein the at least one first pressure control valve and the at least one second pressure control valve include a primary pressure control valve provided to be connected to both the first pilot hydraulic circuit and the second pilot hydraulic circuit, and is configured to set the primary pressure to a set pressure, and   wherein the hardware processor controls the primary pressure control valve so that the set pressure is an upper limit value of the operating range.   
     
     
         20 . A controller for a work vehicle, comprising:
 a hardware processor configured to:
 receive a setting stage set by the first operation member among a plurality of speed stages, the plurality of speed stages corresponding to a plurality of sets of target rotation speeds at which a first hydraulic motor and a second hydraulic motor respectively rotate to move the work vehicle straight, the first hydraulic motor being configured to drive a first traveling device provided on a left side of a vehicle body of the work vehicle, the second hydraulic motor being configured to drive a second traveling device provided on a right side of the vehicle body; 
 obtain a target moving direction of the work vehicle by receiving information corresponding to the target moving direction from a sensor to detect operation of a second operation member via which the target moving direction is set, the target moving direction being determined by a speed difference between a target rotation speed of the first hydraulic motor and a target rotation speed of the second hydraulic motor; 
 determine an operating range of a first control parameter and an operating range of a second control parameter based on the setting stage when the second operation member is operated such that a deviation amount between the target moving direction and a straight direction is within a first range predetermined, a displacement volume of the first hydraulic pump configured to supply the hydraulic fluid to the first hydraulic motor being determined by the first control parameter, a displacement volume of the second hydraulic pump configured to supply the hydraulic fluid to the second hydraulic motor being determined by the second control parameter; 
 determine a boost stage, which is among the plurality of speed stages based on the deviation amount to determine at least one operating range based on the boost stage, when the second operation member is operated such that the deviation amount is out of the first range, each of the at least one operating range being an operating range of each of at least one control parameter of the first control parameter and the second control parameter, the boost stage corresponding to a set of target rotation speeds higher than the target rotation speeds of the setting stage; based on the magnitude of the deviation amount, and determines an operation range of at least one control parameter of the first control parameter and the second control parameter based on the boost stage when the second operation member is operated such that the deviation amount is out of the first range, 
 control the control mechanism such that the first control parameter is within the operating range of the first control parameter determined based on the boost stage or the setting stage; 
 control the control mechanism such that the second control parameter is within the operating range of the second control parameter determined based on the boost stage or the setting stage; 
 control a prime mover configured to rotate the first hydraulic pump and the second hydraulic pump to drive the first hydraulic pump and the second hydraulic pump such that the first hydraulic motor and the second hydraulic motor of which the displacement volumes are set to respective constant volumes regardless of the plurality of speed stages.