Engine speed control device and motor grader including the same

A motor grader comprising:

• an engine;
• at least a pair of front and rear travelling wheels;
• a transmission having a plurality of manually shiftable low speed stages and at least one high speed stage, the transmission being configured to switch between a manual mode for manually selecting one of all the speed stages and an automatic shifting mode for automatically shifting a predetermined speed stage and higher, and to change and transmit power from the engine to at least either of the at least a pair of front and rear travelling wheels;
• a working unit;
• and
• an engine speed control device comprising an upper limit engine speed control unit configured to:
• set an upper limit engine speed to be an out-of-service travelling-use upper limit engine speed at the at least one high speed stage;
• and
• set the upper limit engine speed to be a working-use upper limit engine speed at any one of the low speed stages, the working-use upper limit engine speed being lower than the out-of-service travelling-use upper limit engine speed, wherein
• a matching torque point is set on higher engine speed side than a maximum torque point of an engine torque curve for the engine, the matching torque point being an intersection between the engine torque curve and a regulation line where the upper limit engine speed is set to be the working-use upper limit engine speed.

A motor grader comprising:

• an engine;
• at least a pair of front and rear travelling wheels;
• a transmission having a plurality of manually shiftable low speed stages and at least one high speed stage, the transmission being configured to switch between a manual mode for manually selecting one of all the speed stages and an automatic shifting mode for automatically shifting a predetermined speed stage and higher, and to change and transmit power from the engine to at least one of the front and rear travelling wheels;
• a torque converter including a lock-up clutch, the torque converter configured to transmit driving force from the engine to the transmission;
• a working unit;
• an engine speed detection unit configured to detect an engine speed;
• a lock-up clutch control unit configured to disengage the lock-up clutch when the engine speed becomes lower than or equal to a lock-up release engine speed set to be lower than the low idle engine speed while the lock-up clutch is engaged;
• and
• an engine speed control device comprising an upper limit engine speed control unit configured to:
• set an upper limit engine speed to be an out-of-service travelling-use upper limit engine speed at the at least one high speed stage;
• and
• set the upper limit engine speed to be a working-use upper limit engine speed at any one of the low speed stages, the working-use upper limit engine speed being lower than the out-of-service travelling-use upper limit engine speed.