An automatic transmission where the control portion controls the adjustment solenoid valve so that the circulation hydraulic pressure equals to a second circulation hydraulic pressure higher than the first circulation hydraulic pressure when the rotational speed difference between the output rotational speed of the fluid transmission device and the rotational speed of the driving source is more than the predetermined rotational speed.

A hydraulic control circuit includes: a shift valve configured to be switched between a state of supplying oil pressure to a clearance adjusting chamber of an LR brake and a state of discharging the oil pressure from the clearance adjusting chamber of the LR brake; and a linear SV configured to control the oil pressure supplied to a pressing chamber of the LR brake. The hydraulic control circuit further includes a source pressure oil passage through which oil pressure equal to the oil pressure supplied from the shift valve to the clearance adjusting chamber is supplied to a source pressure port a of the linear SV. By discharging the oil pressure in the clearance adjusting chamber at the time of opening malfunction of the linear SV, the oil pressure in the pressing chamber is also discharged through a drain port of the shift valve.

Methods and systems for a hydromechanical transmission are provided herein. In one example, the transmission operating method includes asynchronously shifting between a first pair of drive ranges in the transmission via operation of two clutches and a variable displacement hydraulic pump in a hydrostatic assembly. In the method, asynchronously shifting between the two drive ranges includes a plurality of phases that include a swiveling phase where a speed of the hydrostatic assembly is inverted.

Described herein are control systems and methods for self-propelled windrowers and other types of agricultural dual-path machines that improve drive efficiency of the machines through automated control of propulsion, steering, or engine speed. In some embodiments, a control system improves drive efficiency by adjusting engine speed and pressure and flow of a hydraulic propulsion system. In such embodiments and others, a controller controls the engine speed and pressure and flow of the hydraulic propulsion system in left and right drive pumps and motors of the dual-path machine according to setpoints and adjustment factors. The adjustment factors in such examples and others are not allowed to exceed respective thresholds, such as a fixed percentage of a raw command, to prohibit immobilizing the machine while disabling or limiting the controller. The adjustment factors are based on feedback signals from various sensors of the machine.