Control system, work vehicle, control method and computer program

A control method for controlling an operation of a power transmission of a work vehicle, the power transmission including a hydrostatic transmission including a hydraulic pump to which rotation generated by an internal combustion engine is transmitted to discharge hydraulic fluid in accordance with an angle of a swash plate, and a hydraulic motor to which the hydraulic fluid is supplied from the hydraulic pump to generate rotation, a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic transmission are transmitted to generate multiple types of rotations corresponding to a plurality of gear ratios, and a hydraulic clutch mechanism to switch a transmission gear of the planetary transmission, the control method comprising:

• controlling the hydraulic clutch mechanism so as to perform switching of the transmission gear based on a relationship between a ratio between a rotational speed of a predetermined component on a power transmission path to transmit the rotation of the planetary transmission to wheels and a rotational speed of the internal combustion engine, and a plurality of switching points, which are points at which a transmission gear of the planetary transmission is switched, the plurality of switching points including a first switching point;
• when the ratio changes to approach a first value corresponding to the first switching point, estimating a first time period required for the ratio to reach the first value;
• and
• controlling the hydraulic clutch mechanism so as to start hydraulic fluid charging to perform switching of the transmission gear before the ratio reaches the first value based on the estimated first time period.

A non-transitory computer readable medium including a computer program to cause a computer to control an operation of a power transmission of a work vehicle, the power transmission including a hydrostatic transmission including a hydraulic pump to which rotation generated by an internal combustion engine is transmitted to discharge hydraulic fluid in accordance with an angle of a swash plate, and a hydraulic motor to which the hydraulic fluid is supplied from the hydraulic pump to generate rotation, a planetary transmission to which the rotation generated by the internal combustion engine and the rotation generated by the hydrostatic transmission are transmitted to generate multiple types of rotations corresponding to a plurality of gear ratios, and a hydraulic clutch mechanism to switch a transmission gear of the planetary transmission, the computer program causing the computer to perform:

• controlling the hydraulic clutch mechanism so as to perform switching of the transmission gear based on a relationship between a ratio between a rotational speed of a predetermined component on a power transmission path to transmit the rotation of the planetary transmission to wheels and a rotational speed of the internal combustion engine, and a plurality of switching points, which are points at which the transmission gear of the planetary transmission is switched, the plurality of switching points including a first switching point;
• when the ratio changes to approach a first value corresponding to the first switching point, estimating a first time period required for the ratio to reach the first value;
• and
• controlling the hydraulic clutch mechanism so as to start hydraulic fluid charging to perform switching of the transmission gear before the ratio reaches the first value based on the estimated first time period.