Wheel loader

Abstract

Provided is a wheel loader having an HST type driving system. In order to make it possible to improve working efficiency in an eco mode when a power mode and the eco mode have been set in the wheel loader, the wheel loader is provided with a controller 18 which has an eco mode characteristic line 31, a power mode characteristic line 32, and a lifting operation characteristic line 34 having a matching point C located between a matching point A between a working device operating engine torque characteristic line 30 and the eco mode characteristic line 31 and a matching point B between the working device operating engine torque characteristic line 30 and the power mode characteristic line 32. The controller 18 includes a control portion which controls an HST pump 11 in accordance with the lifting operation characteristic line 34 when lifting operation of a lift arm 4 is detected in the condition that the eco mode has been selected by a work mode selecting portion 22.

1 . A wheel loader comprising:
 a vehicle body frame ( 11 );   wheels ( 9 ,  10 );   a working device ( 3 ) which is attached to the vehicle body frame ( 10 ) and which has a lift arm ( 4 ) capable of being rotated in an up/down direction;   an engine ( 17 ) which is attached to the vehicle body frame ( 10 );   an HST traveling device in which a variable displacement type HST pump ( 11 ) driven by the engine ( 17 ) and an HST motor ( 14 ) driving the wheels ( 9 ,  10 ) are connected to each other in a closed circuit, and which has an HST pump control portion ( 15 ) controlling input torque of the HST pump ( 11 ); and   a working machine pump ( 13 ) which is driven by the engine ( 17 ) to discharge pressure oil for operating the working device ( 3 ); wherein:   the wheel loader further comprises:   a work mode selecting device ( 22 ) which selects one from a power mode and an eco mode, the power mode serving as a work mode when the workload is a heavy load, the eco mode serving as a work mode when the workload is a light load;   a detecting device ( 23 ) which detects lifting operation of the lift arm ( 4 ) of the working device ( 3 ); and   a control device ( 18 ) which makes control so that the input torque of the HST pump ( 11 ) can be controlled in accordance with a preset eco mode characteristic by the HST pump control portion ( 15 ) when the eco mode is selected by the work mode selecting device ( 22 ), and the input torque of the HST pump ( 11 ) can be controlled in accordance with a preset power mode characteristic by the HST pump control portion ( 15 ) when the power mode is selected by the work mode selecting device ( 22 ), but the input torque characteristic of the HST pump ( 11 ) can be controlled in accordance with a lifting operation characteristic in place of the eco mode characteristic when the lifting operation of the lift arm ( 4 ) is detected by the detecting device ( 23 ) after the eco mode has been selected.   
     
     
         2 . A wheel loader according to  claim 1 , wherein:
 the control device ( 18 ) has a storage portion ( 28 ) which stores an eco mode characteristic line ( 31 ), a power mode characteristic line ( 32 ), and a lifting operation characteristic line ( 34 ); each of the eco mode characteristic line ( 31 ), the power mode characteristic line ( 32 ) and the lifting operation characteristic line ( 34 ) includes a characteristic line expressing a relation between engine speed and the input torque of the HST pump ( 11 ); and the lifting operation characteristic line ( 34 ) is set as a characteristic in which a matching point as an intersection point of the lifting operation characteristic line ( 34 ) with a working device operating engine torque characteristic line ( 30 ) obtained by subtracting torque of the working machine pump ( 13 ) from torque of the engine ( 17 ) is provided between a matching point as an intersection point between the eco mode characteristic line ( 31 ) and the working device operating engine torque characteristic line ( 30 ) and a matching point as an intersection point between the power mode characteristic line ( 32 ) and the working device operating engine torque characteristic line ( 30 ).   
     
     
         3 . A wheel loader according to  claim 1 , further comprising:
 a multistage transmission which is connected to the HST motor ( 14 ) and which has a plurality of speed stages including a high speed stage and a low speed stage;   a speed stage detecting device ( 20 ) which detects that the multistage transmission has been changed over to the low speed stage; and   a forward movement detecting sensor ( 21 ) which detects that the wheel loader is in a state of forward movement;   
       wherein:
 the HST motor ( 14 ) includes a variable displacement type hydraulic motor; 
 the HST traveling device has an HST motor control portion ( 16 ) which controls tilting of the HST motor ( 14 ); and 
 when it is detected by the speed stage detection device ( 20 ) that the multistage transmission has been changed over to the low speed stage and it is detected by the forward movement detecting sensor ( 21 ) that the wheel loader is in a state of forward movement, the control device ( 18 ) makes control so that minimum tilting of the HST motor ( 14 ) can be set as minimum tilting larger than minimum tilting in the eco mode by the HST motor control portion ( 16 ). 
 
     
     
         4 . A wheel loader according to  claim 1 , wherein:
 the lifting operation characteristic line ( 34 ) is provided to diverge from the middle of the eco mode characteristic line ( 31 ).   
     
     
         5 . A wheel loader according to  claim 2 , wherein:
 the lifting operation characteristic line ( 34 ) is provided to diverge from the middle of the eco mode characteristic line ( 31 ).   
     
     
         6 . A wheel loader according to  claim 2 , further comprising:
 a multistage transmission which is connected to the HST motor ( 14 ) and which has a plurality of speed stages including a high speed stage and a low speed stage;   a speed stage detecting device ( 20 ) which detects that the multistage transmission has been changed over to the low speed stage; and   a forward movement detecting sensor ( 21 ) which detects that the wheel loader is in a state of forward movement;   
       wherein:
 the HST motor ( 14 ) includes a variable displacement type hydraulic motor; 
 the HST traveling device has an HST motor control portion ( 16 ) which controls tilting of the HST motor ( 14 ); and 
 when it is detected by the speed stage detection device ( 20 ) that the multistage transmission has been changed over to the low speed stage and it is detected by the forward movement detecting sensor ( 21 ) that the wheel loader is in a state of forward movement, the control device ( 18 ) makes control so that minimum tilting of the HST motor ( 14 ) can be set as minimum tilting larger than minimum tilting in the eco mode by the HST motor control portion ( 16 ). 
 
     
     
         7 . A wheel loader according to  claim 3 , wherein:
 the lifting operation characteristic line ( 34 ) is provided to diverge from the middle of the eco mode characteristic line ( 31 ).   
     
     
         8 . A wheel loader according to  claim 6 , wherein:
 the lifting operation characteristic line ( 34 ) is provided to diverge from the middle of the eco mode characteristic line ( 31 ).