Grass mower

1. A grass mower comprising:

a drive wheel unit;

a variable speed drive mechanism for driving the drive wheel unit;

a mower unit having a cutter blade;

a cutter blade drive mechanism for rotatably driving the mower unit;

a man-operable vehicle speed controlling tool which is operated in a range from a zero vehicle speed position to a maximal vehicle speed position;

an operation detection section for detecting an operational position of the man-operable vehicle speed controlling tool;

a vehicle speed instruction value calculation section for generating a vehicle speed instruction value including a maximal vehicle speed, based on the operational position of the man-operable vehicle speed controlling tool detected by the operation detection section;

a mode selection section for selecting a control mode from a plurality of control modes;

a control table in which a plurality of control parameters are set, the control parameters being provided for the respective control modes, each of the control parameters including a rotational speed value of the cutter blade and a maximal vehicle speed value corresponding to the rotational speed value;

a vehicle speed control target value calculation section configured to calculate a vehicle speed control target value, based on a vehicle speed instruction value generated by the vehicle speed instruction value calculation section and a selected control parameter corresponding to the control mode selected by the mode selection section;

a traveling control section configured to control the variable speed drive mechanism based on the vehicle speed control target value;

a cutter blade control target value calculation section configured to calculate a rotational speed control target value for the cutter blade, based on the selected control parameter; and

a cutter blade control section configured to control the cutter blade drive mechanism based on the rotational speed control target value.

2. The grass mower of claim 1 , further comprising:

a maximal vehicle speed value changing section for changing the maximal vehicle speed value in the control table, based on a cutter blade rotational speed which is a detected rotational speed of the cutter blade.

3. The grass mower of claim 2 , wherein in the control table, there are set a low cutter blade rotational speed range in which the maximal vehicle speed is increased as the cutter blade rotational speed becomes higher, and a high cutter blade rotational speed range in which the maximal vehicle speed is maintained constant irrespectively of the cutter blade rotational speed.

4. The grass mower of claim 3 , wherein:

the control modes include a full power mode for obtaining high grass cutting performance, and an eco mode for energy saving and noise reduction; and

a maximal vehicle speed value in the high cutter blade rotational speed range in the full power mode is set higher than a maximal vehicle speed value in the high cutter blade rotational speed range in the eco mode.

5. The grass mower of claim 1 , wherein the cutter blade control target value calculation section calculates the rotational speed control target value, based on a rotational load to the cutter blade.

6. The grass mower of claim 1 , further comprising:

a battery;

wherein each of the variable speed drive mechanism and the cutter blade drive mechanism includes an electric motor associated therewith connected to the battery as its drive source.