# US 9,518,593 B2 · Hydraulic drive system for construction machine > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,518,593 B2 - Document ID: US9518593B2 - Status: Granted - Kind: B2 - Application number: 14/236,685 - Filed: 2012-08-28 - Published: 2014-06-26 - Granted: 2016-12-13 - Earliest claimed: 2011-08-31 - Assignees: Hitachi Construction Machinery Co., Ltd. - Applicants: Kazushige Mori; Kiwamu Takahashi; Yoshifumi Takebayashi; Natsuki Nakamura - Inventors: Kazushige Mori; Kiwamu Takahashi; Yoshifumi Takebayashi; Natsuki Nakamura - Web page: https://patentgrep.com/patent/US9518593B2 ## CPC - F15B 15/02: Mechanical layout characterised by the means for converting the movement of the fluid-actuated element into movement of the finally-operated member - E02F 3/325: {Backhoes of the miniature type} - E02F 9/207: {of the type electric propulsion units, e.g. electric motors or generators} - E02F 9/2075: {of the hybrid type (for vehicles in general B60W20/00)} - E02F 9/2217: {with energy recovery arrangements, e.g. using accumulators, flywheels} - E02F 9/2232: {using one or more variable displacement pumps} - E02F 9/2285: {Pilot-operated systems} - E02F 9/2296: {Systems with a variable displacement pump} - F04B 49/06: Control using electricity (regulating by means of floats actuating electric switches F04B49/04) - F15B 11/163: {for sharing the pump output equally amongst users or groups of users, e.g. using anti-saturation, pressure compensation} - F15B 11/168: {with at least one load sense pressure being derived from a work port load pressure but not being the work port load pressure itself} - F15B 21/14: Energy-recuperation means - F15B 2211/20546: variable capacity - F15B 2211/30535: the pressure compensating valve is arranged between pressure source and directional control valve - F15B 2211/329: actuated by fluid pressure - F15B 2211/6058: with isolator valves - F15B 2211/71: Multiple output members, e.g. multiple hydraulic motors or cylinders - F15B: SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR - E02F: DREDGING; SOIL-SHIFTING (winning peat E21C49/00) - F04B: POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS (machines for liquids, or pumps, of rotary-piston or oscillating-piston type F04C; non-positive-displacement pumps F04D; pumping of fluid by direct contact of another fluid or by using inertia of fluid to be pumped F04F) ## Abstract A hydraulic motor (52) is arranged in a control hydraulic line (51) connecting a second hydraulic fluid supply line (4a) (for supplying the hydraulic fluid delivered from the main pump (2) to flow control valves (26a to 26h)) to a tank (T). A generator (53) connected with the rotating shaft (52a) of the hydraulic motor (52). Maximum load pressure (PLmax) is detected by a pressure sensor (54). Power generation control of the generator (53) is performed by a second control device (55) so that the hydraulic motor (52) rotates when the delivery pressure of the main pump (2) exceeds target control pressure (Pun) determined by adding a preset value (Pb) to the maximum load pressure (PLmax). AC power generated by the generator (53) is stored in a battery (41). ## Claims ### Claim 1 A hydraulic drive system for a construction machine including a prime mover, a main pump of the variable displacement type driven by the prime mover, a plurality of actuators driven by hydraulic fluid delivered from the main pump, a plurality of flow control valves that respectively control the flow of the hydraulic fluid supplied from the main pump to the actuators, and a pump control device that performs load sensing control for a delivery flow rate of the main pump in such a manner that a delivery pressure of the main pump becomes higher than a maximum load pressure of the actuators by a target differential pressure, comprising: a hydraulic motor arranged in a control hydraulic line connecting a hydraulic fluid supply line for supplying the hydraulic fluid from the main pump to the flow control valves, to a tank, the hydraulic motor being drivable by the hydraulic fluid delivered from the main pump; a generator connected with a rotating shaft of the hydraulic motor; a control device that performs power generation control of the generator in such a manner that the hydraulic motor is driven by the hydraulic fluid delivered from the main pump when the delivery pressure of the main pump becomes higher than a target control pressure; a pressure sensor that detects the maximum load pressure; and an electricity storage device that stores electric power generated by the generator, wherein the control device calculates the target control pressure by adding a preset value to the maximum load pressure detected by the pressure sensor, calculates a power generation torque of the generator having a magnitude overcoming a rotating torque of the hydraulic motor caused by the target control pressure, and performs the power generation control of the generator in such a manner that the power generation torque is achieved. ### Claim 2 (depends on 1) The hydraulic drive system for the construction machine according to claim 1, further comprising: a correction device that corrects the target differential pressure of the load sensing control in such a manner that the target differential pressure decreases with a decrease in a revolution speed of the prime mover, wherein the control device corrects the preset value in such a manner that the preset value decreases with the decrease in the revolution speed of the prime mover. ### Claim 3 (depends on 1) The hydraulic drive system for the construction machine according to claim 1, wherein: the prime mover includes an electric motor, and the electricity storage device is a power supply for the electric motor. ### Claim 4 (depends on 2) The hydraulic drive system for the construction machine according to claim 2, wherein: the prime mover includes an electric motor, and the electricity storage device is a power supply for the electric motor.