Patent ID: 9683585
Date: 2017-06-20
CPC Classifications: E02F,F15B

Claim:
1. A hydraulic driving system comprising: a hydraulic pump; a driving source configured to drive the hydraulic pump; a hydraulic cylinder configured to be driven by hydraulic fluid discharged from the hydraulic pump; a hydraulic fluid path forming a closed circuit between the hydraulic pump and the hydraulic cylinder, the hydraulic fluid path including a pump-flow-rate control unit configured to control a discharge flow rate of the hydraulic pump in response to a first command signal; an adjustment flow rate control unit arranged and configured to control a flow rate of hydraulic fluid supplied to the adjustment path from the hydraulic pump, the adjustment flow rate control unit including a pilot port connected to the pilot flow path, the adjustment flow rate control unit being further configured to a flow rate control valve arranged to provide an adjustable opening degree in the hydraulic fluid path between the hydraulic pump and the hydraulic cylinder, the flow rate control valve being arranged and configured to connect the pump path to the cylinder path and to connect the cylinder path to the pilot path, the flow rate control valve being configured to control a flow rate of hydraulic fluid supplied to the hydraulic cylinder from the hydraulic pump by varying the opening degree of the flow rate control valve in response to a second command signal; a directional control unit configured to allow a flow of hydraulic fluid from the hydraulic pump to the hydraulic cylinder and prohibit a flow of hydraulic fluid from the hydraulic cylinder to the hydraulic pump when hydraulic fluid is supplied from the hydraulic pump to the hydraulic cylinder via the flow rate control valve; and a controller configured to control the flow rate of hydraulic fluid supplied to the hydraulic cylinder from the hydraulic pump based on a target flow rate by the controller being further configured such that when the target flow rate is within the prescribed range, the controller controls the pump-flow-rate control unit to set a discharge flow rate of the hydraulic pump to a flow rate greater than the target flow rate such that hydraulic fluid from the hydraulic pump is divided between the hydraulic cylinder and the adjustment path, a differential hydraulic pressure between the pump path and the cylinder path being greater than the prescribed set pressure when the target flow rate is within the prescribed range, and the differential hydraulic pressure between the pump path and the cylinder path being equal to or less than the prescribed set pressure when the target flow rate is greater than the prescribed range.