ELECTRIC DRIVE UNIT FOR CONSTRUCTION MACHINE

• US 20140046552A1
• Filed: 05/10/2012
• Published: 02/13/2014
• Est. Priority Date: 05/25/2011
• Status: Active Grant

• Current Assignee: Hitachi Construction Machinery Tierra Co.,Ltd. (Hitachi Construction Machinery (China) Co., Ltd.)
• Original Assignee: Hitachi Construction Machinery Company Limited (Hitachi, Ltd.)
• Inventors: Tsuruga, Yasutaka, Takahashi, Kiwamu, Takishita, Tatsuo, Kurikuma, Hajime
• Granted Patent: US 9,347,203 B2
• Time in Patent Office: Days
• US Class Current: 701/50
• CPC Class Codes: B60L 1/003 to auxiliary motors, e.g. for pumps, compressors
• CPC Class Codes: B60L 15/2009 for braking
• CPC Class Codes: B60L 2200/40 Working vehicles
• CPC Class Codes: B60L 2240/421 Speed
• CPC Class Codes: B60L 2250/24 by lever actuation
• CPC Class Codes: B60L 2270/142 acoustic
• CPC Class Codes: B60L 2270/145 Structure borne vibrations
• CPC Class Codes: B60L 53/65 involving identification of vehicles or their battery types
• CPC Class Codes: B60L 7/14 for vehicles propelled by ac motors
• CPC Class Codes: E02F 3/325 Backhoes of the miniature type
• CPC Class Codes: E02F 9/207 of the type electric propulsion units, e.g. electric motors or generators
• CPC Class Codes: E02F 9/2091 Control of energy storage means for electrical energy, e.g. battery or capacitors energy recovery arrangements in hydraulic or pneumatic drives E02F9/2217
• CPC Class Codes: E02F 9/2246 Control of prime movers, e.g. depending on the hydraulic load of work tools
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility
• CPC Class Codes: Y02T 90/12 Electric charging stations
• CPC Class Codes: Y02T 90/14 Plug-in electric vehicles
• CPC Class Codes: Y02T 90/16 Information or communication technologies improving the operation of electric vehicles
• CPC Class Codes: Y02T 90/167 : Systems integrating technologies related to power network operation and communication or information technologies for supporting the interoperability of electric or hybrid vehicles, i.e. smartgrids as interface for battery charging of electric vehicles [EV] or hybrid vehicles [HEV]
• CPC Class Codes: Y04S 30/14 : Details associated with the interoperability, e.g. vehicle recognition, authentication, identification or billing

Abstract

An electric drive unit for a construction machine is capable of increasing the operating time of the construction machine. The electric drive unit has an electricity storage device, a hydraulic pump of the fixed displacement type which is driven by a motor/generator, a plurality of directional control valves which respectively control the flow of hydraulic fluid supplied to a plurality of hydraulic actuators, a bidirectional converter which performs variable control on the revolution speed of the motor/generator, and an LS control device which controls the bidirectional converter so that LS differential pressure Pls equals a target value Pgr. The bidirectional converter performs regeneration control for converting the inertial force of the rotor of the motor/generator into electric power thereby charging the electricity storage device when the revolution speed of the motor/generator is decreased in response to an excess of the LS differential pressure Pls over the target value Pgr.

Claims

1. An electric drive unit for a construction machine equipped with an electricity storage device (7), a motor/generator (29) which supplies and receives electric power to/from the electricity storage device (7), a hydraulic pump (30) which is driven by the motor/generator (29), a plurality of hydraulic actuators (22, 23), a plurality of operating means (37A, 37B) which command the operation of the hydraulic actuators (22, 23), and a plurality of directional control valves (33, 34;

33A, 34A) which respectively control the direction and the flow rate of hydraulic fluid supplied from the hydraulic pump (30) to the hydraulic actuators (22, 23) according to operating directions and operation amounts of the plurality of operating means (37A, 37B), the electric drive unit comprising;

motor/generator control means (28) which performs variable control on the revolution speed of the motor/generator (29); and

command control means (45;

45A;

66;

70) which calculates a command value for the motor/generator control means (28) according to the change in a demanded flow rate determined based on operation command levels from the plurality of operating means (22, 23),

wherein the motor/generator control means (28) performs regeneration control for converting inertial force of a rotor of the motor/generator (29) into electric power and thereby charging the electricity storage device (7) when the revolution speed of the motor/generator (29) is decreased in response to a decrease in the demanded flow rate.

2. The electric drive unit for a construction machine according to claim 1, comprising:

a plurality of pressure compensating valves (35, 36;

35A, 36A) which perform control so that differential pressure across each of the directional control valves (33, 34) equals load sensing differential pressure defined as differential pressure between delivery pressure of the hydraulic pump (30) and the maximum load pressure of the hydraulic actuators (22, 23); and

differential pressure detecting means (40;

40A;

40B;

40C) which detects the load sensing differential pressure, wherein;

the command control means (45) calculates the command value for the motor/generator control means (28) according to the difference between the load sensing differential pressure detected by the differential pressure detecting means (40;

40A;

40B;

40C) and a preset target value so that the load sensing differential pressure equals the target value, and

the motor/generator control means (28) performs the regeneration control for converting the inertial force of the rotor of the motor/generator (29) into electric power and thereby charging the electricity storage device (7) when the revolution speed of the motor/generator (29) is decreased in response to an excess of the load sensing differential pressure over the target value.

3. The electric drive unit for a construction machine according to claim 1, comprising:

a plurality of pressure compensating valves (35A, 36A) which perform control so that differential pressure across each of the directional control valves (33, 34) equals load sensing differential pressure defined as differential pressure between delivery pressure of the hydraulic pump (30) and the maximum load pressure of the hydraulic actuators (22, 23);

delivery pressure detecting means (58) which detects the delivery pressure of the hydraulic pump (30); and

maximum load pressure detecting means (59) which detects the maximum load pressure of the hydraulic actuators (33, 34), wherein;

the command control means (45A) sets a target value for the delivery pressure of the hydraulic pump (30) based on the maximum load pressure of the hydraulic actuators (33, 34) detected by the maximum load pressure detecting means (59) and calculates the command value for the motor/generator control means (28) according to the difference between the delivery pressure of the hydraulic pump (30) detected by the delivery pressure detecting means (58) and the target value so that the delivery pressure of the hydraulic pump (30) equals the target value, and

the motor/generator control means (28) performs the regeneration control for converting the inertial force of the rotor of the motor/generator (29) into electric power and thereby charging the electricity storage device (7) when the revolution speed of the motor/generator (29) is decreased in response to an excess of the delivery pressure of the hydraulic pump (30) over the target value.

4. The electric drive unit for a construction machine according to claim 1, wherein the directional control valves (33A, 34A) are valves of the open center type, and the electric drive unit comprises:

a restrictor (63) which is arranged in a downstream part of a center bypass line of the directional control valves (33A, 34A);

control pressure detecting means (64) which detects pressure on the upstream side of the restrictor (63), changing according to the change in the control level of at least one of the directional control valves (33A, 34A) switched on the upstream side of the restrictor (63), as control pressure;

revolution speed acquisition means (28) which acquires the revolution speed of the motor/generator (29); and

delivery flow rate calculation means (66) which calculates the delivery flow rate of the hydraulic pump (30) based on the revolution speed of the motor/generator (29) acquired by the revolution speed acquisition means (28), wherein;

the command control means (66) sets a target value for the control pressure based on the delivery flow rate of the hydraulic pump (30) calculated by the delivery flow rate calculation means (66) and calculates the command value for the motor/generator control means (28) according to the difference between the control pressure detected by the control pressure detecting means (64) and the target value, and

the motor/generator control means (28) performs the regeneration control for converting the inertial force of the rotor of the motor/generator (29) into electric power and thereby charging the electricity storage device (7) when the revolution speed of the motor/generator (29) is decreased in response to an excess of the control pressure over the target value.

5. The electric drive unit for a construction machine according to claim 1, comprising:

maximum operation amount detecting means (69) which detects the maximum operation amount of the plurality of operating means (37A, 37B);

revolution speed acquisition means (28) which detects the revolution speed of the motor/generator (29); and

delivery flow rate calculation means (70) which calculates the delivery flow rate of the hydraulic pump (30) based on the revolution speed of the motor/generator (29) detected by the revolution speed acquisition means (28), wherein;

the command control means (70) sets the demanded flow rate based on the maximum operation amount of the plurality of operating means (37A, 37B) detected by the maximum operation amount detecting means (69) and calculates the command value for the motor/generator control means (28) according to the difference between the delivery flow rate of the hydraulic pump (30) calculated by the delivery flow rate calculation means (70) and the demanded flow rate so that the delivery flow rate of the hydraulic pump (30) equals the demanded flow rate, and

the motor/generator control means (28) performs the regeneration control for converting the inertial force of the rotor of the motor/generator (29) into electric power and thereby charging the electricity storage device (7) when the revolution speed of the motor/generator (29) is decreased in response to an excess of the delivery flow rate of the hydraulic pump (30) over the demanded flow rate.