A milling machine has a frame, ground engaging tracks that support the frame, a first actuator connecting the frame to a first track of the ground engaging tracks and a second actuator connecting the frame to a second track from the ground engaging tracks. The milling machine has an orientation sensor that determines an orientation of the frame. The milling machine has a controller that operates the first and second actuators to raise or lower the frame. The controller determines the frame orientation using the orientation sensor. The controller also determines a velocity error between actuator velocities of the first and second actuators based on the frame orientation and a target orientation of the frame. The controller determines a control parameter for the second actuator based on the velocity error and operates the second actuator using the determined control parameter.

A hydraulic control system includes a first hydraulic cylinder, a second hydraulic cylinder, a fluid supply apparatus, a first control valve bank, a second control valve bank, a third control valve bank, and a first check valve. The first control valve bank is configured to independently control the first hydraulic cylinder; the second control valve bank is configured to independently control the second hydraulic cylinder; and the third control valve bank is configured to synchronously control the first hydraulic cylinder and the second hydraulic cylinder. Synchronous volume control is implemented through series connection of the hydraulic cylinders, and has quite high synchronization precision, which is measured to be up to two percent.

A landing gear lifting/lowering EHA system includes: a hydraulic actuator configured to lift and lower the leg of an aircraft; at least one electrically operated hydraulic pump; a hydraulic path; a pressure sensor attached to the hydraulic actuator or the hydraulic path and configured to output a measurement signal corresponding to hydraulic pressure; and a controller configured to output a control signal to the electrically operated hydraulic pump, wherein, when a state in which the hydraulic pressure exceeds a set pressure continues for a set time, the control unit stops the electrically operated hydraulic pump in operation and resumes the operation of the electrically operated hydraulic pump after the hydraulic pressure drops to or below a second set pressure after the electrically operated hydraulic pump is stopped.

A hydraulic circuit includes a hydraulic power unit, a first cylinder pair coupled with the hydraulic power unit, and a second cylinder pair coupled with the hydraulic power unit in parallel with the first cylinder pair. Re-phasing valves coupled with each cylinder of the first and second cylinder pairs are activated when a respective one of the cylinders reaches one of a fully extended or a fully retracted position. The hydraulic circuit incorporates the serially plumbed, re-phasing cylinders for synchronized movement in a system with multiple pairs of cylinders.

A hydraulic system of a work machine includes a first hydraulic device to operate in a first operation mode while pressure of hydraulic oil supplied from a hydraulic pump via a first oil passage is equal to or higher than a first pressure threshold. The hydraulic oil in the first oil passage is to be discharged via a second oil passage. A pilot check valve is provided in the second oil passage and has a pilot port to receive a pilot pressure of the hydraulic oil. The pilot check valve is closed to stop discharging the hydraulic oil in the first oil passage through the second oil passage while the pilot pressure is lower than the fourth pressure threshold. The pilot check valve is opened while the pilot pressure is higher than or equal to the fourth pressure threshold. The first hydraulic device is a ride control device.

The subject matter of this specification can be embodied in, among other things, a method that includes controlling, by a first fluid valve, a first fluid flow to a first fluid actuator, actuating, by the first fluid actuator, an output, controlling, by a second fluid valve, a second fluid flow to a second fluid actuator, and actuating, by the second fluid actuator, the output.

A hydraulic control circuit operable to selectively hydraulically link first and second hydraulic actuators and to bypass that hydraulic link.

A drive system with multiple hydraulic cylinders applying torque to the drive shaft of a machine. Each cylinder is attached at one end to the frame of the machine by a clevis that pivots and the other end is rotationally connected to a shaft fixed to a crank arm, fixed to the drive shaft. Each cylinder either pushes or pulls-the crank arm shaft producing torque on the drive shaft in the form of a moment about centerline. As the drive shaft rotates, each cylinder alternately pushes and pulls on the crank arm shaft, depending on the rotational position of the crank arm with respect to the cylinders. The direction of force applied by each hydraulic cylinder is determined by an electro/hydraulic direction control valve, driven by a programmable logic controller, using a signal from a sensor to detect the rotational position of the drive shaft.

A mobile hydraulic system includes a hydraulic actuator coupled to a load, and a control unit coupled to the load and/or to the hydraulic actuator. The control unit is adapted to anticipate an over-center transition of the load relative to a gravity vector prior to the over-center transition through the use of sensors configured with accelerometers, gyroscopes and magnetometers. In some examples, the over-center transition is from an overrunning driving of the load to a passive driving of the load. In some examples, the over-center transition is from a passive driving of the load to an overrunning driving of the load. In some examples, the control unit is adapted to control change in a metered flow through one or more ports of the associated actuator to minimize and/or prevent one or more hydraulic effects of the anticipated over-center transition. In some examples, the control unit controls the metered flow by causing one or more actuators (e.g., a solenoid) to shift one or more valve positions to change the flow through one or more ports of the associated actuator.

A switching valve module which is part of a switching valve control system for use with reciprocating slat-type conveyors is disclosed herein. Disclosed herein is a switching valve module that includes an inner control valve and an outer control valve. A spool is positioned within the inner control valve and a spool positioned within the outer control valve. Movement of each the spool creates both a spool-type seal and a poppet-type seal between the spool and the respective control valve.