A hydrostatic transmission pressure monitoring system includes a hydrostatic transmission and a pressure sensor data source. The hydrostatic transmission includes, in turn, a transmission casing, a pivoting yoke assembly rotatably mounted in the transmission casing, a hydrostatic pump-motor arrangement containing a hydraulic pump-motor circuit at least partially formed in the pivoting yoke assembly, and a pressure scaling device fluidly coupled to the hydraulic pump-motor circuit. The pressure scaling device is configured to generate a pressure-scaled output signal substantially proportional to a peak circuit pressure within the hydraulic pump-motor circuit. The pressure sensor data source is fluidly coupled to the pressure scaling device and is configured to generate pressure sensor data indicative of the pressure-scaled output signal.

Methods and systems for controlling a hydromechanical transmission are proposed. In one example, a control method for a hydrostatic unit of a hydromechanical variable transmission (HVT) is presented, comprising controlling the hydrostatic unit via a feedforward control architecture including a non-linear, multi-coefficient model, wherein the hydrostatic unit comprises a hydrostatic pump and a hydrostatic motor. A desired differential pressure of the hydrostatic unit or a desired hydraulic pump displacement may be used as inputs for the model, where the model's output is a pressure difference for a pump control piston coupled to a swash plate of the hydrostatic unit. Use of the non-linear model permits the hydrostatic unit to be controlled based on load, speed, and/or torque, thereby increasing the adaptability of the control system.

The controller determines whether the vehicle is in a shuttle motion from the operating position of the forward/reverse travel operating member and the actual traveling direction of the vehicle. The controller determines a target braking force when the vehicle is in the shuttle motion. The controller determines at least one of a target displacement of the travel pump and a target displacement of the travel motor based on the target braking force.

An HST circuit has a hydraulic pump that converts a drive force of an engine into energy of oil, and a hydraulic motor that converts the energy of the oil converted by the hydraulic pump into drive energy. Pressure sensors detect a pressure of the oil within the HST circuit. A variable charge pump replenishes the oil into the HST circuit. A controller controls a capacity of the variable charge pump based on the pressure of the oil within the HST circuit detected by the pressure sensors.

An HST circuit has a hydraulic pump that converts a drive force of an engine into energy of oil, and a hydraulic motor that converts the energy of the oil converted by the hydraulic pump into drive energy. Pressure sensors detect a pressure of the oil within the HST circuit. A variable charge pump replenishes the oil into the HST circuit. A controller controls a capacity of the variable charge pump based on the pressure of the oil within the HST circuit detected by the pressure sensors.

A working machine is provided, which includes a prime mover, a first traveling pump driven by power of the prime mover to supply operation fluid through a connector fluid tube, a traveling motor including first and second ports connected to the connector fluid tube, the traveling motor configured to be switched in a first speed and a second speed higher than the first speed, a first pressure detector to detect first traveling-pump pressure near the first port, a second pressure detector to detect second traveling-pump pressure near the second port, and a controller configured, with the traveling motor switched in the second speed, to automatically shift down the traveling motor from the second speed to the first speed, when a differential pressure between the first traveling-pump pressure and the second traveling-pump is equal to or more than a deceleration threshold.

A hydrostatic transmission pressure monitoring system includes a hydrostatic transmission and a pressure sensor data source. The hydrostatic transmission includes, in turn, a transmission casing, a pivoting yoke assembly rotatably mounted in the transmission casing, a hydrostatic pump-motor arrangement containing a hydraulic pump-motor circuit at least partially formed in the pivoting yoke assembly, and a pressure scaling device fluidly coupled to the hydraulic pump-motor circuit. The pressure scaling device is configured to generate a pressure-scaled output signal substantially proportional to a peak circuit pressure within the hydraulic pump-motor circuit. The pressure sensor data source is fluidly coupled to the pressure scaling device and is configured to generate pressure sensor data indicative of the pressure-scaled output signal.

A drum drive system includes a controller configured to selectively control an engine, a variable displacement pump, and a variable displacement motor of a vehicle to provide a target drum speed for a drum of the vehicle. To provide the target drum speed, the controller is configured to: (i) initially operate the variable displacement motor at a maximum motor displacement and operate the variable displacement pump at a pump displacement that provides the target drum speed without needing to actively manipulate an engine speed of the engine; (ii) increase the pump displacement and decrease a motor displacement without needing to actively manipulate the engine speed while still providing the target drum speed; and (iii) increase the engine speed in response to the pump displacement reaching a maximum pump displacement and the motor displacement reaching a minimum motor displacement if necessary to maintain the target drum speed.

A work vehicle includes a power source, a travel device, a power transmission device, and a control device. The power transmission device includes a hydrostatic continuously variable transmission having a relief valve capable of setting a relief pressure, and is configured to transmit power of the power source to the travel device. The control device includes a relief pressure setting unit configured to set the relief pressure of the relief valve in accordance with a target output value of the travel device.

A transmission (21) as a power transmission device for a vehicle comprises an input shaft (22), an output shaft (23), a planetary continuously variable transmission mechanism (31), a direct connecting mechanism (27), and an idler gear (29). The direct connecting mechanism (27) comprises a direct connecting clutch (30). The planetary continuously variable transmission mechanism (31) comprises a planetary gear mechanism (32), a pump side clutch (33), a hydraulic pump (36), a hydraulic motor (38), and a motor side clutch (40). The hydraulic pump (36) and the hydraulic motor (38) are connected via a pair of main lines (37A, 37B). An electromagnetic on-off valve (41) capable of switching between a communicating state and a blocking state between the pair of main lines (37A, 37B) is provided between the pair of main lines (37A, 37B).