The present disclosure relates to a blended or hybrid power system with increased operating efficiency. The blended power system combines the advantages of electrical power with the advantages of hydraulic power when delivering power to a hydraulic actuator. The hydraulic power provides higher power density and the electrical power provides high efficiency and control accuracy in the blended power system. In a blended power system, a control system may be configured to select different modes of operation based on the loads encountered in the combined hydraulic and electrohydrostatic system. The blended power system also allows for smooth and uninterrupted transitions between the different modes of operation within the blended power system. Thus, jerkiness in the blended power system may be minimized or eliminated.

The present invention relates to an electrohydrostatic system having a hydraulic cylinder comprising a first cylinder chamber and a second cylinder chamber. Furthermore, the electrohydrostatic system has a fluid hydraulic supply device for providing a hydraulic fluid, a fluid hydraulic motor pump unit, designed to provide a fluid hydraulic volume flow in order to move the hydraulic cylinder. A motor control device is designed to provide a rated current for an electrical drive of the fluid hydraulic motor pump unit. Moreover, the electrohydrostatic system has at least one fluid hydraulic safety valve, which on a first valve side is connected to one of the cylinder chambers of the hydraulic cylinder and on a second valve side is connected to the fluid hydraulic motor pump unit. The fluid hydraulic safety valve can be bridged via a bypass connection with a fixed orifice plate, wherein the bypass connection is connected to the first valve side and to the second valve side of the at least one fluid hydraulic safety valve. Moreover, the electrohydrostatic system has a pressure sensor that is connected to one of the cylinder chambers of the hydraulic cylinder. The pressure sensor is designed to detect a fluid hydraulic pressure on one of the cylinder chambers and, according to the detected fluid hydraulic pressure, to provide an enabling signal for the motor control device to provide the rated current for the electrical drive of the fluid hydraulic motor pump unit.

A closed-circuit, self-contained hydraulic axis includes an electric motor, a hydraulic cylinder configured to be connected to a load and a main pump driven by the electric motor to pump hydraulic fluid through the circuit. Pressure connections of the pump are connected to the respective chambers of the cylinder such that the cylinder rod is configured to extend and retract depending on a direction of flow of the hydraulic fluid through the main pump. The hydraulic axis includes a main accumulator connected to the pump via first control valve, an energy storage accumulator connected to the pump via a second control valve, and a charge pump. The hydraulic axis is switchable between a first operating mode that is free of energy storage in the energy storage accumulator, and a second operating mode in which energy is stored in the energy storage accumulator.

A construction machine that makes it possible for an operator to linearly push a bucket simply by operating an arm in a pushing direction is provided. A controller 50 is configured to, in a case where a straight locus is selected by a bucket locus selecting device 52, calculate a constant flow rate ratio α according to a boom initial angle that is an angle of a boom 2 sensed by a boom angle sensor 33 at a time point when an arm 4 is operated in a pushing direction by an operation device 51, and control the delivery flow rate of a first hydraulic pump 12 such that a hydraulic fluid is discharged from a cap chamber 1a of a boom cylinder 1 at a flow rate Qb obtained by multiplying a flow rate Qa of a flow supplied to a cap chamber 3a of an arm cylinder 3 by the flow rate ratio α while the arm 4 is operated in the pushing direction by the operation device 51 and there is not an instruction for operation of the boom 2.

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 present invention relates to a hydraulic system with a feed pump for feeding hydraulic fluid, wherein the feed pump is driven by a hydraulic drive motor. The invention furthermore comprises a method for feeding hydraulic fluid into a hydraulic system via a feed pump, wherein the feed pump is driven by a hydraulic drive motor.

In a hydraulic system which is biased to a minimum system pressure using a bias valve or other flow obstruction disposed in a tank line, there is provided in a bypass line to the bias valve an evacuating and filling valve through which the hydraulic system is first evacuatable and subsequently fillable with a hydraulic fluid. The valve closes the bypass when a differential pressure overcomes a preadjusted force of a spring element. For this purpose, the valve possesses a displaceably mounted valve body with an integrated throttle and a seal face which closes a through opening when the valve body is shifted against the bias force of the spring element due to the pressure difference.

When hydraulic fluid discharged from a hydraulic actuator is to be recovered for driving a different hydraulic actuator, the recovery frequency is increased to achieve further energy saving. To this end, a pressure increasing circuit 36 is provided in which a communication pressure increasing valve 12 is disposed in a communication passage 26 that connects a bottom side line 23 of and a rod side line 24 a boom cylinder 4. A recovery control valve 11 is controlled such that, when a first operation unit 5 is operated in a boom lowering direction (own weight falling direction of the boom) and a second operation unit 6 is operated simultaneously, only if the pressure at the bottom side of the boom cylinder 4 is higher than the pressure at the arm cylinder side that is a recovery destination of hydraulic fluid, the recovery control valve 11 is opened to recover the flow rate discharged from the bottom side of the boom cylinder 4 to the arm cylinder side.

A shuttle valve connects a second flowpath and a drain flowpath when the hydraulic pressure in a first flowpath is greater than the hydraulic pressure in the second flowpath. The shuttle valve connects the first flowpath and the drain flowpath when the hydraulic pressure in a second flowpath is greater than the hydraulic pressure in the first flowpath. The ratio between the pressure receiving area of a first pressure section and the pressure receiving area of a second pressure section is the same as the ratio between the pressure receiving area of a first chamber side and the pressure receiving area of a second chamber side of a cylinder rod.

To provide a construction machine that has a hydraulic system mounted thereon in which a closed-circuit pump, and an open-circuit pump and a proportional valve are arranged as a pair, and that makes it possible to use an unused open-circuit pump or proportional valve to accelerate the speed of a single rod hydraulic cylinder when the single rod hydraulic cylinder and a hydraulic motor are driven simultaneously. A controller (51) controls a cap-side selector valve (46) and a rod-side selector valve (47) such that a particular open-circuit pump (15) not connected to a single rod hydraulic cylinder (3) is connected to the single rod hydraulic cylinder, and controls an opening area of a particular proportional valve (49) provided on a flow line that connects a delivery port of the particular open-circuit pump to a tank, when the single rod hydraulic cylinder and a hydraulic motor (7) are driven simultaneously.