A device for controlling a gear ratio of a hydrostatic mechanical power-split transmission comprises an input switch (1) which, when rotated, produces a particular transmission characteristic and, at the same time, limits the maximum pressure. The selected position of the input switch (1) selects a particular maximum pressure curve from a large number of stored maximum pressure curves.

A device for controlling a gear ratio of a hydrostatic mechanical power-split transmission comprises an input switch (1) which, when rotated, produces a particular transmission characteristic and, at the same time, limits the maximum pressure. The selected position of the input switch (1) selects a particular maximum pressure curve from a large number of stored maximum pressure curves.

A hydraulic drive system includes: a first hydraulic motor and a second hydraulic motor configured to be driven by working oils respectively discharged from a first hydraulic pump and a second hydraulic pump; a first pump control unit and a second pump control unit configured to control discharge volumes and discharge directions of the first hydraulic pump and the second hydraulic pump; a signal pressure generating unit configured to generate a signal pressure for adjusting command pressures to control the first pump control unit and the second pump control unit in accordance with the sum of discharge pressures of the first hydraulic pump and the second hydraulic pump; and a first pressure adjusting unit and a second pressure adjusting unit configured to adjust the command pressures in accordance with the signal pressure.

A hydraulic drive system includes: a first hydraulic motor and a second hydraulic motor configured to be driven by working oils respectively discharged from a first hydraulic pump and a second hydraulic pump; a first pump control unit and a second pump control unit configured to control discharge volumes and discharge directions of the first hydraulic pump and the second hydraulic pump; a signal pressure generating unit configured to generate a signal pressure for adjusting command pressures to control the first pump control unit and the second pump control unit in accordance with the sum of discharge pressures of the first hydraulic pump and the second hydraulic pump; and a first pressure adjusting unit and a second pressure adjusting unit configured to adjust the command pressures in accordance with the signal pressure.

A hydraulic system in a work machine includes a travel operation device provided in a pilot oil path between a hydraulic pump a travel pump and including an operation member and configured to generate a pilot pressure supplied via the pilot oil path and an additional pilot pressure in accordance with an operation amount of the operation member. The travel pump is to control a flow direction of hydraulic oil supplied to a travel motor based on the pilot pressure and the additional pilot pressure. A pressure selection valve is provided in a first coupling oil path to select a selected pressure from the pilot pressure and the additional pilot pressure to apply the selected pressure to the pilot hydraulic oil in the second coupling oil path. A pressure adjustment valve is provided in a second coupling oil path to control the selected pressure to be an adjusted pilot pressure.

A hydraulic system in a work machine includes a travel operation device to generate a pilot pressure and an additional pilot pressure in accordance with an operation amount of the operation member. A travel pump is to control a flow direction of hydraulic oil supplied to a travel motor based on the pilot pressure and the additional pilot pressure. A pressure selection valve is provided in a first coupling oil path to select a selected pressure from the pilot pressure and the additional pilot pressure to apply the selected pressure to the pilot hydraulic oil in a second coupling oil path. A pressure adjustment valve is provided in the second coupling oil path to control the selected pressure to be an adjusted pilot pressure. A differential pressure generation valve is provided in the second coupling oil path to generate differential pressure upstream or downstream relative to the pressure adjustment valve.

A method is provided for operating a drive device for a working machine having a conventional maximum traction force curve, where the maximum permissible traction force of the drive device increases as the output speed of the drive device decreases. The method includes receiving an activation signal for activating a grading operation of the working machine, where the grading operation has a limited maximum traction force curve in which the maximum permissible traction force of the drive device increases less sharply than with the conventional maximum traction force curve as the output speed of the drive device decreases. A currently maximum permissible traction force is ascertained based on the limited maximum traction force curve and a current traction force is compared with the currently maximum permissible traction force. The transmission ratio of the gearbox is adjusted toward a lower output speed of the drive device based on the comparison.

A method is provided for operating a drive device for a working machine having a conventional maximum traction force curve, where the maximum permissible traction force of the drive device increases as the output speed of the drive device decreases. The method includes receiving an activation signal for activating a grading operation of the working machine, where the grading operation has a limited maximum traction force curve in which the maximum permissible traction force of the drive device increases less sharply than with the conventional maximum traction force curve as the output speed of the drive device decreases. A currently maximum permissible traction force is ascertained based on the limited maximum traction force curve and a current traction force is compared with the currently maximum permissible traction force. The transmission ratio of the gearbox is adjusted toward a lower output speed of the drive device based on the comparison.