Patent application number | Description | Published |
20140123639 | HYDRAULIC DRIVE SYSTEM - A hydraulic driving system includes a hydraulic cylinder with a cylinder tube and a cylinder rod, a main pump, a hydraulic-fluid path, a charge pump, a stroke position detecting unit, and a pump control unit. The hydraulic-fluid path forms a closed circuit between a main pump and the hydraulic cylinder. The cylinder rod expands or contracts depending on how hydraulic fluid is supplied and exhausted to and from first and second chambers. The charge pump replenishes hydraulic-fluid in the hydraulic-fluid path. The pump control unit performs flow-rate reduction control in which the pump control unit reduces a suction flow rate so that a suction flow rate of the main pump is equal to or less than a maximum discharge flow rate of the charge pump when the stroke position becomes closer to a stroke end of the cylinder rod than a prescribed reference position during the flow rate reduction control. | 05-08-2014 |
20140123847 | HYDRAULIC EXCAVATOR - In a hydraulic excavator, a hydraulic cylinder drives a boom via a hydraulic fluid discharged from a first hydraulic pump. A first hydraulic circuit connects the first hydraulic pump and the hydraulic cylinder and forms a closed circuit therebetween. A hydraulic motor rotates a revolving upper unit with hydraulic fluid discharged from a second hydraulic pump. A second hydraulic circuit independent from the first hydraulic circuit connects the second hydraulic pump and the hydraulic motor. A motor hydraulic pressure reduction unit reduces the driving hydraulic pressure of the hydraulic motor when a predetermined condition is satisfied. The predetermined condition is a condition in which an operation of the boom operating member to raise the boom and an operation of the rotation operating member to rotate the revolving upper unit are conducted together and an operation amount of the boom operating member is equal to or greater than a predetermined threshold. | 05-08-2014 |
20140130487 | HYDRAULIC DRIVE SYSTEM - A hydraulic driving system includes a hydraulic pump, a driving source, a hydraulic cylinder, a closed circuit hydraulic path between the pump and cylinder, a pump-flow-rate control unit controlling a discharge flow rate of the pump, a flow rate control valve between the pump and the cylinder in the fluid path, a directional control unit, a target flow rate setting unit and a control device. The directional control unit allows a flow of fluid from the pump to the cylinder and prohibits a flow of fluid from the cylinder to the pump when fluid is supplied from the pump to the cylinder via the flow rate control valve. The control device controls fluid flow to the cylinder with the flow rate control valve when the target flow rate is within a prescribed range, and with the pump-flow-rate control unit when the target flow rate is greater than the prescribed range. | 05-15-2014 |
20140283510 | HYDRAULIC DRIVE SYSTEM - 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. | 09-25-2014 |
20140345265 | HYDRAULIC DRIVE SYSTEM - An operating state determining unit determines whether a hydraulic cylinder is in operation or not in operation. A discharge pressure reducing unit reduces the discharge pressure of a charge pump. A discharge pressure control unit controls the discharge pressure reducing unit when the hydraulic cylinder in not in operation to reduce the discharge pressure of the charge pump to a low pressure lower than a normal pressure. The normal pressure is the discharge pressure of the charge pump when the hydraulic cylinder is in operation. An accumulator is connected to a charge flowpath. A one-way valve is disposed between the accumulator and the charge pump. The one-way valve allows the flow of hydraulic fluid from the charge pump to the accumulator and prohibits the flow of hydraulic fluid from the accumulator to the charge pump. | 11-27-2014 |
20150013320 | HYDRAULIC DRIVE SYSTEM - A hydraulic cylinder causes a work implement to be lowered due to the exhaust of hydraulic fluid from a first chamber and the supply of hydraulic fluid to a second chamber. A hydraulic fluid flowpath has a first flowpath and a second flowpath. The first flowpath connects a first pump port and the first chamber. The second flowpath connects a second pump port and the second chamber. The hydraulic fluid flowpath configures a closed circuit between a hydraulic pump and the hydraulic cylinder. A bleed-off flowpath branches off from the first flowpath. A portion of hydraulic fluid exhausted from the first chamber when lowering the work implement flows into the bleed-off flowpath. | 01-15-2015 |
20150176610 | HYDRAULIC DRIVE SYSTEM - A hydraulic fluid flowpath includes a first flowpath and a second flowpath. The first flowpath connects a first pump port and a first chamber in a hydraulic cylinder. The second flowpath connects a second pump port and a second chamber in the hydraulic cylinder. The hydraulic fluid flowpath forms a closed circuit between a hydraulic pump and the hydraulic cylinder. A bleed-off flowpath bleeds off a portion of the hydraulic fluid from the second flowpath. A control valve connects the second flowpath to the bleed-off flowpath via a throttle when an operation amount of an operating member for lowering a work implement is less than a predetermined operation amount so that a hydraulic pressure in second flowpath is maintained at less than a relief pressure. The predetermined operation amount is less than or equal to the maximum operation amount for lowering the work implement. | 06-25-2015 |