A hydraulic control apparatus is disclosed that controls a hydraulic pump in a construction machine in which a hydraulic actuator is connected to the hydraulic pump via a directional control valve of a closed center type, and in which a position of the directional control valve is changed according to an operation amount of an operation member. The hydraulic control apparatus includes a virtual negative control pressure calculating part configured to calculate, based on the operation amount of the operation member and a discharge pressure of the hydraulic pump, a virtual negative control pressure when a negative control system is assumed; and a part configured to calculate a control command value for the hydraulic pump based on the virtual negative control pressure.

A counter balance valve (71L) is located between a directional control valve (23) and a hydraulic motor (32L) and provided on the way of a pair of supply/discharge lines (25A, 25B). The counter balance valve (71L) allows a spool (72L) to be displaced axially based on a pressure difference between the supply/discharge lines (25A, 25B). The counter balance valve (71L) includes a communicating passage (73L) for communicating the supply/discharge lines (25A, 25B) when the displacement of the spool (72L) exceeds a predetermined amount (X.sub.CM), based on a pressure difference between the supply/discharge lines (25A, 25B). The communicating passage (73L) is provided in the spool (72L) of the counter balance valve (71L).

A device for varying the swept volumes of first and second hydraulic machines, whose swept volumes depends upon pivoting positions of adjustable axes thereof which can be connected to one another by first and second lines. The axes can be coupled to a piston-cylinder device which is adjustable by a control valve unit for pivoting the axes. Pressures in the area of the hydraulic machines can be limited by the control valve unit. The control valve unit can be coupled to a respective first or second line with the highest pressure. A device for determining an existing actual pressure is located upstream of the control valve unit, at least in the area of one of the first and the second lines that connects with the first and the second hydraulic machines. The control valve unit can be actuated based on the actual pressure value determined by the device.

A hydraulic system for use with an agricultural harvester header is provided. The hydraulic system includes a reversible hydraulic pump that drives a reversible hydraulic motor in a forward or harvesting direction and a reverse or header cleaning direction. The system can further include a second reversible pump similarly driving a second reversible hydraulic motor in forward and reverse directions. The pumps and motors can be used to operate various header implements, e.g., the first pump and motor may be used to operate at least a crop cutting knife and the second pump and motor can be used to operate at least one conveyor. The pumps and motors operate within hydraulic circuits which share their hydraulic fluid with the harvester's hydraulic fluid reservoir, thereby reducing system weight, complexity and maintenance requirements.

A hydraulic system for use with an agricultural harvester header is provided. The hydraulic system includes a reversible hydraulic pump that drives a reversible hydraulic motor in a forward or harvesting direction and a reverse or header cleaning direction. The system can further include a second reversible pump similarly driving a second reversible hydraulic motor in forward and reverse directions. The pumps and motors can be used to operate various header implements, e.g., the first pump and motor may be used to operate at least a crop cutting knife and the second pump and motor can be used to operate at least one conveyor. The pumps and motors operate within hydraulic circuits which share their hydraulic fluid with the harvester's hydraulic fluid reservoir, thereby reducing system weight, complexity and maintenance requirements.

A counter balance valve (71L) is located between a directional control valve (23) and a hydraulic motor (32L) and provided on the way of a pair of supply/discharge lines (25A, 25B). The counter balance valve (71L) allows a spool (72L) to be displaced axially based on a pressure difference between the supply/discharge lines (25A, 25B). The counter balance valve (71L) includes a communicating passage (73L) for communicating the supply/discharge lines (25A, 25B) when the displacement of the spool (72L) exceeds a predetermined amount (X.sub.CM), based on a pressure difference between the supply/discharge lines (25A, 25B). The communicating passage (73L) is provided in the spool (72L) of the counter balance valve (71L).

A hydrostatic transmission system includes a fluid-driven motor and an integrated pump assembly connected to the fluid-driven motor to provide fluid to operate the fluid-driven motor. The integrated pump assembly includes a pump with at least one fluid driver comprising a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from a first port of the pump to a second port of the pump. The pump assembly also includes two valve assembles to isolate the pump from the system. The hydrostatic transmission system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover to exclusively adjust at least one of a flow and a pressure in the hydrostatic transmission system to an operational set point.

A hydrostatic transmission system includes a fluid-driven motor and an integrated pump assembly connected to the fluid-driven motor to provide fluid to operate the fluid-driven motor. The integrated pump assembly includes a pump with at least one fluid driver comprising a prime mover and a fluid displacement assembly to be driven by the prime mover such that fluid is transferred from a first port of the pump to a second port of the pump. The pump assembly also includes two valve assembles to isolate the pump from the system. The hydrostatic transmission system also includes a controller that establishes at least one of a speed and a torque of the at least one prime mover to exclusively adjust at least one of a flow and a pressure in the hydrostatic transmission system to an operational set point.

A harvester is provided with a draper head that has a frame extending substantially across a working width of the draper head. Cutting elements are arranged at a front side of the draper head and connected to the frame. Conveying surfaces and conveying members transport cut crop from the cutting elements to a discharge location of the draper head. A reel extends transversely to a working direction of the draper head across the working width of the draper head. Reel support arms are pivotably supported on the frame and support the reel. A hydraulic adjusting drive is operatively connected to the reel support arms to pivot the reel support arms to carry out a height adjustment of the reel. A hydraulic circuit is operatively connected to the hydraulic adjusting drive and has a hydraulic valve that is able to lock the hydraulic circuit.

The present disclosure relates to an apparatus for controlling/regulating the travel speed of a utility vehicle comprising at least one drive motor, at least one hydraulic pump, at least one control slide valve, at least one hydraulic travel motor, at least one further hydraulic drive, as well as at least one controller. In accordance with the present disclosure, the travel speed of the at least one hydraulic travel motor is controlled/regulated via at least the speed of the drive motor, while the at least one further hydraulic drive does not provide any drive power.