Electric construction machinery

Abstract

To provide an electric construction machine which improves pump efficiency of a hydraulic pump when an electric motor drives a hydraulic pump, and can achieve energy saving without impairing original performance of a construction machine.SOLUTION: A pressure sensor 10 detects a pressure of pressure oil of a pressure oil supply path 5 as a discharge pressure of a pump device 1 composed of first and second pumps 1a and 1b, a vehicle body controller 20 drives at least the first pump 1a between the first and second pumps 1a and 1b when the discharge pressure is lower than PL (first threshold), drives only the second pump 1b when the discharge pressure is equal to or more than the PL, and controls the capacity of the first pump 1a and engine speeds of first and second electric motors 2a and 2b so as to perform such output restriction control to continuously decrease a discharge flow rate of the pump device 1 composed of the first and second pumps 1a and 1b as the discharge pressure is raised and so as to restrict output of the pump device 1 to a maximum output M or less, when the discharge pressure is equal to or more than PL0 (second threshold).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electric construction machine powered by electricity. [Background technology]

[0002] In order to reduce greenhouse gas emissions, electric construction machinery, in which the engines of conventional construction machinery such as hydraulic excavators have been replaced with electric motors, has been developed and commercialized.

[0003] Patent Document 1 describes a technology that includes a mode switching means for setting three types of work modes, namely, a travel mode, an excavation mode, and an excavation eco mode, and that sets the rotation speed of the electric motor to a first rotation speed in the travel mode, sets the rotation speed of the electric motor to a second rotation speed lower than the first rotation speed in the excavation mode, and sets the rotation speed of the electric motor to a third rotation speed even lower than the second rotation speed in the excavation eco mode, thereby reducing waste of power used by the electric motor and achieving energy conservation. Patent Document 1 also mentions changing not only the rotation speed of the electric motor but also the output of the electric motor depending on the work mode.

[0004] Patent Document 2 has an objective of increasing the efficiency of a hydraulic pump by operating the engine in a region where pump efficiency is high, and discloses a technology in which, in an engine control device that controls the engine so as to move the matching point, where the engine output torque and the hydraulic pump absorption torque are balanced, on an engine torque diagram with engine speed on the horizontal axis, a target torque line is set in a region on the torque diagram where the engine speed decreases and the hydraulic pump capacity increases, and the engine is controlled so as to match at a point on this target torque line. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5851843 [Patent Document 2] JP 2004-150304 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, Patent Document 1 proposes that in an electric construction machine, the rotation speed or the rotation speed and output of the electric motor are changed depending on the work mode, thereby reducing the power consumption of the electric motor and achieving energy conservation.

[0007] However, while reducing the rotation speed or the rotation speed and output of an electric motor certainly reduces the power consumption of the electric motor, this alone may result in a decrease in work efficiency due to insufficient power of the construction machinery, and the original performance of the construction machinery, such as its digging power, may be impaired, and it cannot be said that true energy conservation has been achieved.

[0008] In Patent Document 2, the engine is controlled so as to match a point on a target torque line set in a region on a torque diagram where the engine speed decreases and the hydraulic pump capacity increases, thereby increasing pump efficiency.

[0009] However, this proposed technology also reduces the engine speed, and there is a possibility that the original performance of the construction machine, such as the excavation force, may be impaired, such as a decrease in work efficiency due to insufficient power of the construction machine. In addition, Patent Document 2 proposes an "engine control device" as an invention, and does not intend to use an electric motor instead of an engine as a prime mover. Even if an electric motor is used instead of an engine as a prime mover, it is necessary to reduce the output of the electric motor to a matching point on the target torque line, so when the hydraulic load of the hydraulic pump increases during work such as excavation, the electric motor will not be able to support the hydraulic load of the hydraulic pump, and the system will not be established.

[0010] An object of the present invention is to provide an electric construction machine that improves the pump efficiency of a hydraulic pump when an electric motor drives the hydraulic pump, thereby achieving energy savings without compromising the original performance of the construction machine. [Means for solving the problem]

[0011] In order to solve such problems, the present invention provides an electric construction machine including a first variable displacement hydraulic pump, a first electric motor supplied with power from a power source and driving the first hydraulic pump, a plurality of hydraulic actuators driven by oil discharged from the first hydraulic pump, a plurality of operating devices for instructing the operation of a plurality of driven bodies driven by the plurality of hydraulic actuators, and a control valve for controlling the flow of pressure oil supplied from the first hydraulic pump to the plurality of hydraulic actuators by operating the plurality of operating devices, the electric construction machine further comprising: a second fixed displacement hydraulic pump, a second electric motor supplied with power from the power source and driving the second hydraulic pump, a pressure oil supply passage through which the discharge oil of the first hydraulic pump and the discharge oil of the second hydraulic pump are joined and supplied to the control valve, and a pressure sensor for detecting the pressure of the pressure oil in the pressure oil supply passage as the discharge pressure of a pump device consisting of the first and second hydraulic pumps. and a vehicle body controller that controls the capacity of the first hydraulic pump and the rotation speeds of the first electric motor and the second electric motor based on the operation of the operating device and the discharge pressure detected by the pressure sensor, wherein the vehicle body controller drives at least the first hydraulic pump of the first and second hydraulic pumps when the discharge pressure is lower than a first threshold value, controls the first and second electric motors to drive only the second hydraulic pump when the discharge pressure is equal to or higher than the first threshold value, and controls the capacity of the first hydraulic pump and the rotation speeds of the first and second electric motors so that, when the discharge pressure is equal to or higher than a second threshold value that is lower than the first threshold value, a discharge flow rate of the pump device consisting of the first and second hydraulic pumps is continuously reduced as the discharge pressure increases, and performs output limiting control to limit an output of the pump device to a preset maximum output or less.

[0012] In this way, by dividing the operating range of the first hydraulic pump and the second hydraulic pump, and controlling the capacity of the first hydraulic pump and the rotation speed of the first electric motor and the second electric motor based on the discharge pressure of the pump device consisting of the first and second hydraulic pumps, the first and second hydraulic pumps operate more frequently in the operating ranges of the first and second hydraulic pumps where the pump capacity (flow rate) is large and the pump efficiency is high, and energy saving can be realized by reducing waste of power consumption of the first and second electric motors compared to the case where output limit control is performed with one pump. In addition, it is possible to suppress a decrease in work efficiency due to insufficient power of the construction machine. This improves the pump efficiency of the hydraulic pump when the electric motor drives the hydraulic pump, and realizes energy saving without impairing the original performance of the construction machine. Effect of the Invention

[0013] According to the present invention, the pump efficiency of the hydraulic pump when the electric motor drives the hydraulic pump can be improved, and energy savings can be achieved without impairing the original performance of the construction machine. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a diagram showing a crawler type hydraulic excavator as an example of an electric construction machine according to the present invention. [Diagram 2] 1 is a diagram showing an overall system including a hydraulic system and its control system mounted on an electric construction machine according to a first embodiment of the present invention. FIG. [Figure 3A] FIG. 1 is a diagram showing pump iso-efficiency curves superimposed on a characteristic diagram of output limit control of a conventional hydraulic system. [Figure 3B] FIG. 4 is a diagram showing pump equal efficiency lines superimposed on a characteristic diagram of output limit control of the hydraulic system according to the first embodiment. [Figure 3C] FIG. 4 is a diagram showing pump iso-efficiency curves superimposed on flow rate characteristics when the fixed displacement second hydraulic pump used in the hydraulic system of the first embodiment is driven over the entire range of discharge pressures. [Figure 4]FIG. 4 is a diagram showing an algorithm of a vehicle body controller according to the first embodiment. [Figure 5A] 13 is a diagram showing the relationship between the discharge pressure and the target capacity set in a calculation table of the target capacity calculation unit. FIG. [Figure 5B] 13 is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in a calculation table of the limit rotation speed of the first electric motor of the limit rotation speed calculation unit. FIG. [Figure 5C] 13 is a diagram showing the relationship between the requested rotation speed N1req and the corrected rotation speed N1cor of the first pump, which is set in a calculation table of the requested rotation speed limiting unit. FIG. [Figure 6A] 13 is a diagram showing the relationship between the requested rotation speed N2req and the corrected rotation speed N2cor of the second pump, which is set in a calculation table of the limit rotation speed of the requested rotation speed limiting unit. FIG. [Figure 6B] 13 is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in a calculation table of the limit rotation speed of the second electric motor of the limit rotation speed calculation unit. FIG. [Figure 7A] 5 is a diagram showing the operating characteristics of the first pump when the first pump and the first electric motor are controlled by a variable pump control section. FIG. [Figure 7B] 13 is a diagram showing the operating characteristics of the second pump when the second electric motor is controlled by a fixed pump control section. FIG. [Figure 8] FIG. 11 is a diagram showing an overall system including a hydraulic system and its control system that is mounted on an electric construction machine according to a second embodiment of the present invention. [Figure 9] FIG. 4 is a diagram showing a control logic for switching an electromagnetic switching valve set in a vehicle body controller. [Figure 10] FIG. 11 is a diagram showing an overall system including a hydraulic system and its control system that is mounted on an electric construction machine according to a third embodiment of the present invention. [Figure 11] FIG. 3B is a view similar to FIG. 3B illustrating the operating principle of the third embodiment of the present invention; [Figure 12] FIG. 13 is a diagram showing an algorithm of a vehicle body controller according to the third embodiment. [Figure 13A]13 is a diagram showing the relationship between the discharge pressure and the target capacity set in a calculation table of the target capacity calculation unit. FIG. [Figure 13B] 13 is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in a calculation table of the limit rotation speed of the first electric motor of the limit rotation speed calculation unit. FIG. [Figure 14] 13 is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in a calculation table of the limit rotation speed of the second electric motor of the limit rotation speed calculation unit. FIG. [Figure 15A] 5 is a diagram showing the operating characteristics of the first pump when the first pump and the first electric motor are controlled by a variable pump control section. FIG. [Figure 15B] 13 is a diagram showing the operating characteristics of the second pump when the second electric motor is controlled by a fixed pump control section. FIG. [Figure 16A] FIG. 11 is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in a limit rotation speed calculation unit of a variable pump control unit in a modified example of the first embodiment. [Figure 16B] FIG. 11 is a diagram showing the relationship between the discharge pressure and the limited rotation speed set in a fixed pump control section in the modified example of the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. <First embodiment> ~Construction machinery~ Fig. 1 is a diagram showing a crawler-type hydraulic excavator as an example of an electric construction machine according to the present invention. Note that the present invention is not limited to crawler-type hydraulic excavators, and can also be applied to electric construction machines such as wheel-type hydraulic excavators, hydraulic cranes, and wheel loaders.

[0016] 1, the hydraulic excavator is composed of an articulated front device 100A consisting of a boom 100a, an arm 100b, and a bucket 100c that each rotate in the vertical direction, and a vehicle body 100B consisting of an upper rotating body 100d and a lower traveling body 100e, and the base end of the boom 100a of the front device 100A is supported on the front part of the upper rotating body 100d so as to be rotatable in the vertical direction, and the upper rotating body 100d is mounted on the lower traveling body 100e so as to be rotatable. The boom 100a, the arm 100b, the bucket 100c, the upper rotating body 100d, and the lower traveling body 100e are driven by a boom cylinder 103a, an arm cylinder 103b, a bucket cylinder 103c, a swing motor 103d, and left and right traveling motors 103e and 103f, respectively. The movement of the boom 100a, arm 100b, bucket 100c, and upper rotating body 100d is commanded by operating pilot pressure generated by front / swing operating lever devices 104a, 104b (see Figure 2), and the movement of the lower traveling body 1e is commanded by operating pilot pressure generated by traveling operating lever / pedal devices 105a, 105b (see Figure 2).

[0017] ~ Overall system (hydraulic system and control system) ~ 2 is a diagram showing the entire system including the hydraulic system and its control system mounted on the electric construction machine of this embodiment. The hydraulic system is indicated by reference numeral 200, and the control system is indicated by reference numeral 300.

[0018] In this embodiment, the hydraulic system 200 includes a variable displacement first hydraulic pump 1a, a first electric motor 2a that receives power from a battery 8 serving as a power source and drives the first hydraulic pump 1a, a plurality of hydraulic actuators (the above-mentioned boom cylinder 103a, arm cylinder 103b, bucket cylinder 103c, swing motor 103d, left and right traveling motors 103e, 103f) that are driven by the discharge oil of the first hydraulic pump 1a, and a plurality of driven actuators (the above-mentioned boom cylinder 103a, arm cylinder 103b, bucket cylinder 103c, swing motor 103d, left and right traveling motors 103e, 103f) that are driven by the plurality of hydraulic actuators 103a to 103f. The hydraulic excavator 100 is equipped with an operating device (the above-mentioned operating lever devices 104a, 104b and operating lever / pedal devices 105a, 105b) that instructs the operation of the above-mentioned boom 100a, arm 100b, bucket 100c, upper rotating body 100d and lower traveling body 1e, which are the above-mentioned main bodies, and a control valve 4 that is supplied with oil discharged from the first hydraulic pump 1a and has multiple spool valves built in that control the pressurized oil supplied to the multiple hydraulic actuators 103a to 103f in response to the operation of the operating devices 104a, 104b, 105a, 105b.

[0019] The first hydraulic pump 1a is equipped with a regulator 7, and the regulator 7 variably adjusts the capacity (for example, the tilt of the swash plate) of the first hydraulic pump 1a.

[0020] The hydraulic system 200 also includes a fixed displacement second hydraulic pump 1b, a second electric motor 2b that receives power from a battery 8 serving as a power source and drives the second hydraulic pump 1b, and a pressurized oil supply path 5 that merges the oil discharged from the first hydraulic pump 1a and the oil discharged from the second hydraulic pump 1b and supplies the resulting oil to the control valve 4.

[0021] The pressurized oil supply passage 5 has a first oil passage 5a connected to the first hydraulic pump 1a, a second oil passage 5b connected to the second hydraulic pump 1b, a third oil passage 5c connecting the first oil passage 5a and the second oil passage 5b to the control valve 4, and a check valve 6 arranged in the first oil passage 5a for preventing backflow of pressurized oil from the third oil passage 5c to the first hydraulic pump 1a when the first hydraulic pump 1a is stopped.

[0022] The control system 300 includes a pressure sensor 10 that detects the pressure of the pressurized oil in the pressurized oil supply path 5 as the discharge pressure of the pump device 1 consisting of first and second hydraulic pumps 1a, 1b, a shuttle valve block 11 that extracts the highest pressure among the operating pilot pressures of the operating devices 104a, 104b, 105a, 105b, a pressure sensor 12 that detects the operating pilot pressure extracted by the shuttle valve block 11, first and second inverters 15a, 15b that convert the DC current of the battery 8 into three-phase AC and control the rotation speed of the first and second electric motors 2a, 2b, and a vehicle body controller 20.

[0023] The pressure sensor 10 is provided in the third oil passage 5c of the pressure oil supply passage 5, and detects the pressure of the pressure oil flowing through the third oil passage 5c as the discharge pressure of the pump device 1 consisting of the first and second hydraulic pumps 1a, 1b. Note that, although the "pump device 1 consisting of the first and second hydraulic pumps 1a, 1b" is defined as such for convenience of explanation, the first and second hydraulic pumps 1a, 1b constituting the "pump device 1" do not need to be a mechanically integrated device, and the first and second hydraulic pumps 1a, 1b may each be an individual pump.

[0024] The shuttle valve block 11 and the pressure sensor 12 detect the operation of the operating devices 104a, 104b, 105a, 105b by the pressure sensor 12 detecting the highest pressure among the operating pilot pressures of the operating devices 104a, 104b, 105a, 105b extracted by the shuttle valve block 11.

[0025] The vehicle body controller 20 controls the capacity of the first hydraulic pump 1a and the rotation speeds of the first electric motor 2a and the second electric motor 2b based on the operation of the operating devices 104a, 104b, 105a, 105b detected by the shuttle valve block 11 and the pressure sensor 12, and the discharge pressure detected by the pressure sensor 10.

[0026] ~Operating Principle~ The operating principle of the present invention will be described with reference to Figures 3A, 3B and 3C. In the following, the "hydraulic pump" will be simply referred to as the "pump" as appropriate.

[0027] Fig. 3A is a diagram showing pump iso-efficiency lines superimposed on a characteristic diagram of output limit control of a conventional hydraulic system, and Fig. 3B is a diagram showing pump iso-efficiency lines superimposed on a characteristic diagram of output limit control of the hydraulic system of this embodiment. The conventional hydraulic system has one hydraulic pump (a variable displacement hydraulic pump), while this embodiment has two pumps (a variable displacement first pump 1a and a fixed displacement second pump 1b). Fig. 3C is a diagram showing pump iso-efficiency lines superimposed on flow characteristics when the fixed displacement second pump 1b used in the hydraulic system of this embodiment is driven over the entire range of discharge pressure.

[0028] 3A to 3C, the horizontal axis represents the discharge pressure of each pump, and the vertical axis represents the discharge flow rate of each pump. In this embodiment using two pumps, the discharge pressure on the horizontal axis represents the pressure of the third oil passage 5c through which the discharge oil flows. The required pump output is the same in both the case of FIG. 3A and the case of FIG. 3B, but the pump output is generated by one pump in FIG. 3A, and is generated by two pumps in FIG. 3B.

[0029] The curve indicated by the symbol A is an isopower line, and PL0 (second threshold value) indicated on the horizontal axis is the start pressure of the output limit control. Pmax is the maximum pressure (maximum pump discharge pressure) of the pressure oil supply passage 5 determined by a main relief valve (not shown) provided in the hydraulic system. Q1max on the vertical axis is the discharge flow rate when the capacity of the first pump 1a is maximum and the first pump 1a is driven at a reference rotation speed (e.g., 1800 rpm).

[0030] In a hydraulic excavator equipped with a variable displacement pump driven by an engine, the pump capacity (flow rate) is limited as the discharge pressure increases in order to prevent engine stall during high load such as excavation. Specifically, a maximum output M permitted from the engine output, the load of the auxiliary equipment, and the pump efficiency (pump efficiency) is set, and when the discharge pressure becomes equal to or higher than PL0, the flow rate is reduced as the discharge pressure increases, and the pump capacity (flow rate) is controlled so that the pump output does not exceed the maximum output M (so that the pump discharge flow rate does not exceed the maximum flow rate calculated by M / discharge pressure), thereby limiting the pump output to M. This control is generally called horsepower limit control (referred to as output limit control in this specification). The maximum output M of this output limit control is shown by the iso-power curve A shown in FIG. 3A. If the pump flow rate is always inside the iso-power curve A (toward the origin) over the entire range of the pump discharge pressure, the pump output will not exceed M, and engine stall can be prevented.

[0031] The same is true for pumps driven by electric motors, and by setting an equal power line A as shown in Figure 3A, the pump capacity and rotation speed are controlled so that the pump output does not exceed the maximum output M. This prevents the electric motor from being unable to support the hydraulic load of the pump when the hydraulic load of the hydraulic pump increases during work such as excavation, and enables work such as excavation to be performed efficiently.

[0032] On the other hand, pump efficiency is a value determined by volumetric efficiency and torque efficiency, and it is known that the larger the pump capacity, the better the volumetric efficiency and torque efficiency, and thus the higher the pump efficiency (see, for example, the above-mentioned Patent Document 2, "JP 2004-150304 A"). As shown in FIG. 3A, pump efficiency is highest when the flow rate (capacity) is high at an intermediate discharge pressure, and pump efficiency decreases in areas where the discharge pressure and flow rate are low.

[0033] In Fig. 3B, Q2max shown on the vertical axis is the flow rate (reference flow rate) when the fixed displacement second pump 1b in this embodiment is driven at a reference rotation speed (e.g., 1800 rpm). As shown in Fig. 3C, when the second pump 1b is driven at the reference rotation speed over the entire range of discharge pressure, it always discharges a constant flow rate Q2max. PL (first threshold value) shown on the horizontal axis is the pressure (hereinafter referred to as switching pressure) at which the drive mode of the first and second pumps 1a, 1b is switched in this embodiment.

[0034] In the present invention, as shown in Fig. 3B, the operating ranges of the first and second pumps are divided, and when the discharge pressure is lower than PL, at least the first pump 1a of the first and second pumps 1a, 1b is driven, and when the discharge pressure is PL or higher, the first and second electric motors 2a, 2b are controlled to drive only the second pump 1b. Also, when the discharge pressure is PL0 (second threshold value) or higher, the capacity of the first pump 1a and the rotation speed of the first and second electric motors 2a, 2b (the rotation speed of the first pump 1a and the second pump 1b) are controlled so that the discharge flow rate of the pump device 1 consisting of the first and second pumps 1a, 1b is continuously reduced as the discharge pressure increases, and output limit control is performed to limit the output of the pump device 1 to a preset maximum output M or less.

[0035] When output limit control is performed with one pump, the region where the pump efficiency is high overlaps with the region where output limit control is performed, so the pump must be operated in a region where the pump efficiency is relatively low. However, if two pumps (first and second pumps 1a, 1b) with appropriate operating ranges are selected and operated as described above, the region where the pump efficiency is high can be used even when output limit control is performed.

[0036] As a result, in the respective operating ranges of the first and second pumps 1a, 1b, the first and second pumps 1a, 1b operate more frequently in areas with large capacity (flow rate) and high pump efficiency, thereby reducing wasteful power consumption of the first and second electric motors 2a, 2b compared to when output limiting control is performed on a single pump, achieving energy savings, and also suppressing a decrease in work efficiency due to insufficient power of the construction machinery.

[0037] Here, the fixed displacement of the second pump 1b is set so as to have a reference flow rate near an operating point on the equal power curve A when the discharge pressure exceeds PL.

[0038] Furthermore, the switching pressure PL may be set, taking into consideration the distribution of load pressure that changes with the work load and the efficiency characteristics of the pumps used, so as to optimize the pump efficiency when the first and second pumps 1a, 1b perform output limit control as one pump 1. Specifically, in Fig. 3B showing a characteristic diagram of output limit control, the equal-power line A is a hyperbola expressed by Q=M / P, and it is preferable that the switching pressure PL (first threshold value) is set to a value higher than the pressure at the maximum curvature point X of the equal-power line A and lower than 3 / 5 of the maximum discharge pressure Pmax. In this embodiment, as an example, the switching pressure PL is set to 1 / 2 of the maximum discharge pressure Pmax.

[0039] By setting the fixed capacity and switching pressure PL (first threshold value) of the second pump 1b in this manner, the pump efficiency can be optimized, and switching from the first pump 1a to the second pump 1b is performed in a region on the equal output line A where the flow rate change is small, thereby suppressing fluctuations in the discharge flow rate when switching pumps and enabling smooth pump switching.

[0040] ~Car Controller~ The vehicle body controller 20 controls the capacity of the first pump 1a and the rotation speeds of the first and second electric motors 2a, 2b (the rotation speeds of the first pump 1a and the second pump 1b) so as to realize the above-mentioned operating principle.

[0041] More specifically, the vehicle body controller 20 controls the first and second electric motors 2a, 2b to drive at least the first pump 1a of the first and second pumps 1a, 1b when the discharge pressure detected by the pressure sensor 10 is lower than PL (first threshold value), and drives only the second pump 1b when the discharge pressure is equal to or higher than PL (first threshold value). Also, when the discharge pressure is equal to or higher than PL0 (second threshold value), the vehicle body controller 20 controls the capacity of the first pump 1a and the rotation speed of the first and second electric motors 2a, 2b (the rotation speed of the first pump 1a and the second pump 1b) so that the discharge flow rate of the pump device 1 consisting of the first and second pumps 1a, 1b is continuously reduced as the discharge pressure increases, and output limiting control is performed to limit the output of the pump device 1 to a preset maximum output M or less.

[0042] In order to realize the above control, in this embodiment, the vehicle body controller 20 controls the first and second electric motors 2a, 2b so that when the discharge pressure is lower than PL (first threshold), the second pump 1b is stopped and only the first pump 1a is driven, and when the discharge pressure is equal to or higher than PL (first threshold), the vehicle body controller 20 controls the capacity of the first pump 1a and the rotation speed of the first electric motor 2a so that the output of the first pump 1a does not exceed the maximum output M of the output limit control when the discharge pressure is between PL0 (second threshold) and PL (first threshold), and controls the rotation speed of the second electric motor so that the output of the second pump 1b does not exceed the maximum output M of the output limit control when the discharge pressure is equal to or higher than PL (first threshold).

[0043] 4 is a diagram showing an algorithm for the vehicle body controller 20 to perform the above-mentioned control. This algorithm is repeatedly executed within the vehicle body controller 20.

[0044] The vehicle body controller 20 has a required flow rate calculation unit 20a, a variable pump control unit 20b, and a fixed pump control unit 20c. Each of these will be described in order below.

[0045] Requested flow rate calculation section 20a The required flow rate calculation unit 20a has a calculation table of the required flow rate, and inputs the operating pilot pressure Pi detected by the pressure sensor 12 to calculate a target flow rate Qreq according to the operating pilot pressure Pi. The target flow rate Qreq is the combined target flow rate of the two pumps 1a, 1b. In the calculation table of the required flow rate, a relationship between the operating pilot pressure Pi and the target flow rate Qreq is set so that the target flow rate Qreq increases as the operating pilot pressure Pi increases.

[0046] Variable pump control section 20b The variable pump control unit 20b has a target capacity calculation unit 50 for the first pump 1a, a limit rotation speed calculation unit 51 for the first electric motor 2a, a division unit 53, a required rotation speed limit unit 54 for the first electric motor 2a, and a minimum value selection unit 55.

[0047] The target capacity calculation unit 50 includes a calculation table for the target capacity of the first pump 1a, receives the pressure of the third oil passage 5c detected by the pressure sensor 10 as the discharge pressure Ps of the first pump 1a, and calculates the target capacity q1 of the first pump 1a according to the discharge pressure Ps. The target capacity q1 of the first pump 1a is output to the regulator 7 as a capacity command. The target capacity q1 of the first pump 1a is also sent to a division unit 53.

[0048] 5A is a diagram showing the relationship between the discharge pressure and the target capacity set in the target capacity calculation table. In the target capacity calculation table, the relationship between the discharge pressure Ps and the target capacity q1 is set so that while the discharge pressure Ps is between 0 and PL0, the target capacity q1 is constant at the maximum capacity qmax, while while the discharge pressure Ps is between PL0 and PL, the target capacity q1 gradually decreases from the maximum capacity qmax to a capacity qa, and while the discharge pressure Ps is between PL and the maximum Pmax, the target capacity q1 is constant at a capacity qa. The capacity qa is set to a value equal to the fixed capacity q2 of the second pump 1b described later.

[0049] The limit rotation speed calculation unit 51 has a calculation table for the limit rotation speed of the first electric motor 2a, and inputs the pressure of the third oil passage 5c detected by the pressure sensor 10 as the discharge pressure Ps of the first pump 1a to calculate the limit rotation speed N1 of the first electric motor 2a according to the discharge pressure Ps.

[0050] 5B is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in the calculation table of the limit rotation speed of the first electric motor 2a. In the calculation table of the limit rotation speed, the relationship between the discharge pressure Ps and the limit rotation speed N1 is set so that while the discharge pressure Ps is between 0 and PL0, the limit rotation speed N1 is constant at the maximum rotation speed N1amax of the output limit control, while while the discharge pressure Ps is between PL0 and PL, the limit rotation speed N1 gradually decreases from the maximum rotation speed N1amax to the intermediate rotation speed Na1, and while the discharge pressure Ps is between PL and Pmax, the limit rotation speed N1 becomes zero (the first electric motor 2a stops).

[0051] Here, when the discharge pressure Ps is at PL0, the first pump 1a is at the maximum capacity qmax in Fig. 5A, the first electric motor 2a is at the maximum rotation speed N1amax in Fig. 5B, and the first pump 1a discharges the maximum flow rate Q1max in Fig. 3B. The relationship between qmax, N1amax, and Q1max at this time is expressed by the following formula.

[0052] Q1max=qmax×N1amax In addition, when the discharge pressure Ps drops to PL, the first pump 1a is at the capacity qa in Fig. 5A, the first electric motor 2a is at the intermediate rotation speed Na1 in Fig. 5B, and the first pump 1a discharges a flow rate equal to the flow rate Q2max (reference flow rate of the second pump 1b) in Fig. 3B. The relationship between qa, Na1, and Q2max at this time is expressed by the following formula.

[0053] Q2max = qa × Na1 N1amax is the reference rotation speed of the first electric motor 2a (for example, 1800 rpm).

[0054] The rate of change of the capacity q1 of the first pump 1a and the limit rotation speed N1 of the first electric motor 2a while the discharge pressure Ps changes from PL0 to PL is set so that the product (output) of the discharge pressure Ps and the limit rotation speed N1 is equal to the maximum output M on the equal output curve A in Figure 3B.

[0055] A division unit 53 divides the target flow rate Qreq calculated by the required flow rate calculation unit 20a by the target capacity q1 of the first pump 1a calculated by the target capacity calculation unit 50 to calculate a required rotation speed N1req of the first pump 1a.

[0056] The required rotation speed limiting unit 54 has a limit table for the required rotation speed of the first electric motor 2a, inputs the required rotation speed N1req of the first pump 1a calculated by the division unit 53, and calculates a corrected rotation speed N1cor by limiting the minimum and maximum values ​​of the required rotation speed N1req.

[0057] 5C is a diagram showing the relationship between the required rotation speed N1req and the corrected rotation speed N1cor of the first pump 1a, which is set in the required rotation speed calculation table. In the required rotation speed limit table, the relationship between the required rotation speed N1req and the corrected rotation speed N1cor is set so that while the required rotation speed N1req is between zero and rotation speed N0, the corrected rotation speed N1cor increases as the required rotation speed N1req increases while the required rotation speed N1req is between N0 and rotation speed Nr, and when the required rotation speed N1req exceeds the rotation speed Nr, the corrected rotation speed N1cor becomes constant at the maximum allowable rotation speed N1max.

[0058] The maximum rotation speed N1amx of the output limit control shown in Fig. 5B is set to a value slightly smaller than the maximum allowable rotation speed N1max. N1amx may be set to a value equal to N1max.

[0059] The minimum value selection unit 55 selects the smaller of the limit rotation speed N1 calculated by the limit rotation speed calculation unit 51 and the corrected rotation speed N1cor calculated by the required rotation speed limit unit 54 as the target rotation speed command for the first electric motor 2a, and outputs the target rotation speed command to the inverter 3a of the first electric motor 2a.

[0060]

[0061] When the discharge pressure is equal to or lower than PL0, the output represented by the product of the discharge pressure and the pump capacity is smaller than the maximum output M of the constant output line A, and the first pump 1a operates according to the required flow rate in the region where the discharge pressure in FIG. 3B is equal to or lower than PL0.

[0062] Fixed pump control unit 20c The fixed pump control unit 20c includes a division unit 56, a required rotation speed limitation unit 57 for the second electric motor 2b, a limited rotation speed calculation unit 58 for the second electric motor 2b, and a minimum value selection unit 59.

[0063] The division unit 56 divides the target flow rate Qreq calculated by the required flow rate calculation unit 20a by the fixed capacity q2 of the second pump 1b to calculate the required rotation speed N2req of the second pump 1b.

[0064] The required rotation speed limitation unit 57 includes a limitation table for the required rotation speed of the second electric motor 2b, inputs the required rotation speed N2req of the second pump 1b calculated by the division unit 56, and calculates a corrected rotation speed N2cor that limits the minimum and maximum values of the required rotation speed N2req.

[0065] 6A is a diagram showing the relationship between the requested rotation speed N2req and the corrected rotation speed N2cor of the second pump 1b, which is set in a calculation table of the limit rotation speed of the requested rotation speed. In the limit table of the requested rotation speed, the relationship between the requested rotation speed N2req and the corrected rotation speed N2cor is set so that, similarly to the requested rotation speed limiting unit 54 of the first electric motor 2a, while the requested rotation speed N2req is between zero and the rotation speed N0, the corrected rotation speed N2cor increases as the requested rotation speed N2req increases while the requested rotation speed N2req is between the rotation speed N0 and the rotation speed Nr, and when the requested rotation speed N2req exceeds the rotation speed Nr, the corrected rotation speed N2cor becomes constant at the maximum allowable rotation speed N2max.

[0066] The limit rotation speed calculation unit 58 has a calculation table for the limit rotation speed of the second electric motor 2b, and inputs the pressure of the third oil passage 5c detected by the pressure sensor 10 as the discharge pressure Ps of the second pump 1b to calculate the limit rotation speed N2 of the second electric motor 2b according to the discharge pressure Ps.

[0067] 6B is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in the calculation table of the limit rotation speed of the second electric motor 2b. In the calculation table of the limit rotation speed, the relationship between the discharge pressure Ps and the limit rotation speed N2 is set so that while the discharge pressure Ps is between 0 and PL, the limit rotation speed N2 is zero, and while the discharge pressure Ps is between PL and Pmax, the limit rotation speed N2 gradually decreases from the maximum rotation speed N2bmax of the output limit control to the minimum rotation speed N2min of the output limit control.

[0068] Here, when the discharge pressure Ps is at PL, the second pump 1b with a fixed displacement q2 discharges the maximum flow rate Q1max in Fig. 3B. The relationship between N2bmax and Q1max at this time is expressed by the following formula.

[0069] Q2max=q2×N2bmax N2bmax is set to a value slightly smaller than the maximum allowable RPM N2max. N2bmax may be set to a value equal to N2max.

[0070] Also, when the discharge pressure Ps is at Pmax, the second pump 1b with a fixed capacity q2 discharges the minimum flow rate Q2min in Fig. 3B. The relationship between N2min and Q2min at this time is expressed by the following formula.

[0071] Q2min = q2 × N2min The change rate of the limit rotation speed N2 of the second electric motor 2b while the discharge pressure Ps changes from PL to Pmax is set such that the product (output) of the discharge pressure Ps and the limit rotation speed N2 is equal to the maximum output M on the constant output line A in Fig. 3B.

[0072] The minimum value selection unit 59 selects the smaller value between the limit rotation speed N2 of the second electric motor 2b calculated by the limit rotation speed calculation unit 58 and the corrected rotation speed N2cor calculated by the required rotation speed limit unit 57 as the target rotation speed command for the second electric motor 2b, and outputs the target rotation speed command to the inverter 3b of the second electric motor 2b.

[0073] As a result, while the discharge pressure Ps is from zero to PL, the discharge flow rate of the second pump 1b becomes zero, and while the discharge pressure Ps is from PL to Pmax, in the range where N2cor < N2, the second pump 1b operates inside the constant output line A in Fig. 3B, and in the range where N2cor ≧ N2, the second pump 1b operates on the constant output line A in Fig. 3B.

[0074] Fig. 7A is a diagram showing the operating characteristics of the first pump 1a when the first pump 1a and the first electric motor 2a are controlled by the variable pump control unit 20b. Fig. 7B is a diagram showing the operating characteristics of the second pump 1b when the second electric motor 2b is controlled by the fixed pump control unit 20c.

[0075] In Fig. 7A, while the discharge pressure Ps is from PL0 to PL, the output of the first pump 1a is limited to the maximum output M on the constant output line A, and when the discharge pressure Ps reaches PL, the first pump 1a stops.

[0076] In FIG. 7B, while the discharge pressure Ps is between zero and PL0, the second pump 1b is stopped, and when the discharge pressure Ps reaches PL, the second pump 1b starts rotating, and while the discharge pressure Ps is between PL and Pmax, the output of the second pump 1b is limited to the maximum output M on the isopower line A.

[0077] By combining the operating characteristics of the first pump 1a and the second pump 1b that operate in this manner, the operating characteristics shown in FIG. 3B are obtained.

[0078] ~Effects~ According to this embodiment, the following effects can be obtained.

[0079] 1. In this embodiment, the vehicle body controller 20 drives at least the first pump 1a of the first and second pumps 1a, 1b when the pressure (discharge pressure) of the pressure oil in the pressure oil supply passage 5 is lower than PL, and controls the rotation speeds of the first and second electric motors 2a, 2b to drive only the second pump 1b when the discharge pressure becomes PL or higher. In addition, the vehicle body controller 20 controls the capacity of the first pump 1a and the rotation speeds of the first and second electric motors 2a, 2b (the rotation speeds of the first pump 1a and the second pump 1b) so that the first and second pumps 1a, 1b perform output limiting control as a single pump when the discharge pressure becomes PL0 (second threshold value) or higher.

[0080] As a result, in the operating ranges of the first and second pumps 1a, 1b, the first and second pumps 1a, 1b operate more frequently in the ranges where the pump capacity (flow rate) is large and the pump efficiency is high, and energy saving can be achieved by reducing wasteful power consumption of the first and second electric motors 2a, 2b compared to the case where the output limit control is performed with one pump as shown in Fig. 3A. In addition, a decrease in work efficiency due to insufficient power of the construction machine can be suppressed.

[0081] As described above, according to this embodiment, the pump efficiency of the hydraulic pump driven by the electric motor is improved, and energy savings can be achieved without compromising the inherent performance of the construction machine.

[0082] 2. In addition, in this embodiment, the battery 8 is used as the power source, and the energy saving described above reduces the power consumption of the battery 8, making it possible to extend the operating time of the construction machine.

[0083] When a commercial power source is used as the power source, the amount of power used is reduced, and therefore the power bill can be reduced.

[0084] 3. In this embodiment, the fixed displacement of the second pump 1b is set to have a reference flow rate near the operating point on the equal power line A when the discharge pressure exceeds PL. The switching pressure PL is set to a value higher than the pressure at the maximum curvature point X of the equal power line A and lower than 3 / 5 of the maximum discharge pressure Pmax. As an example, the switching pressure PL is set to 1 / 2 of the maximum discharge pressure Pmax. This optimizes the pump efficiency, and since the first pump 1a is switched to the second pump 1b in a region on the equal power line A where the flow rate change is small, the variation in the discharge flow rate during pump switching can be suppressed, and the pump can be switched smoothly.

[0085] 4. Furthermore, in this embodiment, a check valve 6 is provided in the first oil passage 5a, which is the pressure oil supply passage for the first pump 1a, to prevent backflow of pressure oil from the third oil passage 5c to the first pump 1a when the first pump 1a is stopped. This prevents the oil discharged from the second pump 1b from flowing back to the first pump 1a when the discharge pressure exceeds PL (first threshold value) and the first pump 1a is stopped and the second pump 1b is driven, making it possible to supply the entire amount of oil discharged from the second pump 1b to the actuator.

[0086] <Modification> 5B and 5C, in the variable pump control section 20b, the limit rotation speed calculation section 51 reduces the limit rotation speed N1 to zero in a stepwise manner (the first electric motor 2a stops) when the discharge pressure Ps rises to Pmax, and in the fixed pump control section 20c, the limit rotation speed calculation section 58 increases the limit rotation speed N2 to N2bmax in a stepwise manner when the discharge pressure Ps reaches PL. However, the limit rotation speeds N1 and N2 may be set to change at a predetermined rate of change at the switching pressure PL.

[0087] 16A and 16B are diagrams showing the relationship between the discharge pressure and the limit rotation speed when the limit rotation speeds N1 and N2 are set in this way.

[0088] In the calculation table of the limited rotation speed of the limited rotation speed calculation unit 51, as shown in FIG. 16A, the relationship between the discharge pressure Ps and the limited rotation speed N1 is set so that when the discharge pressure Ps becomes PL or more, the limited rotation speed N1 decreases from the intermediate rotation speed Na along the diagonal line H1. In addition, in the calculation table of the limited rotation speed of the limited rotation speed calculation unit 58, as shown in FIG. 16B, the relationship between the discharge pressure Ps and the limited rotation speed N2 is set so that when the discharge pressure Ps becomes PL or more, the limited rotation speed N1 increases from zero along the diagonal line H2. The change rate of N1 of the diagonal line H1 and the change rate of the diagonal line H2 are set so that the sum of the product (=flow rate) of N1 and the target capacity q1 of the first pump 1a at that time and the product (=flow rate) of the fixed capacity q2 of the second pump 1b coincides with the flow rate on the equal power line A shown in FIG. 3B. This makes it possible to further suppress the flow rate fluctuation when the discharge pressure Ps exceeds PL and the hydraulic pump is switched from the first pump 1a to the second pump 1b.

[0089] <Second embodiment> A second embodiment of the present invention will be described with reference to FIGS.

[0090] 8 is a diagram showing an entire system including a hydraulic system and its control system mounted on an electric construction machine according to a second embodiment of the present invention. The hydraulic system is indicated by reference numeral 200A, and the control system is indicated by reference numeral 300A. The vehicle controller is indicated by reference numeral 20A.

[0091] In this embodiment, in addition to the components of the hydraulic system 200 of the first embodiment shown in FIG. 2, the hydraulic system 200A further includes an accumulator 60, a pressure oil supply passage 61 connecting the accumulator 60 to the third oil passage 5c of the pressure oil supply passage 5, and an electromagnetic switching valve 62 arranged in the pressure oil supply passage 61 and switchable between an open position and a closed position.

[0092] The hydraulic system 200A also includes a pressure oil return line 63 that is arranged in parallel with the pressure oil supply line 61 and connects the bottom side of the boom cylinder 103a, which may be driven in the boom lowering direction by the inertial load of the boom 101a (see Figure 1), to the accumulator 60, and a check valve 64 that is installed in this pressure oil return line 63 and opens when the pressure on the bottom side of the boom cylinder 103a becomes equal to or greater than the pressure in the pressure oil supply line 61, to recover and accumulate a portion of the pressure oil on the bottom side of the boom cylinder 103a in the accumulator 60.

[0093] The hydraulic actuator connected to the pressure oil recovery path 63 may be an actuator other than the boom cylinder 103a, such as the arm cylinder 103b shown in FIG. 1, the swing motor 103d, or a combination thereof, so long as it is an actuator that can be driven by the inertial load of a driven member.

[0094] FIG. 9 is a diagram showing a control logic for switching the solenoid switching valve 62, which is set in the vehicle body controller 20A.

[0095] The vehicle body controller 20A sets the switching pressure of the electromagnetic switching valve 62 to a pressure equal to the aforementioned switching pressure (first threshold value) PL, and when the discharge pressure, which is the pressure of the third oil passage 5c of the pressure oil supply passage 5, is lower than the first threshold value PL, outputs a close command to hold the electromagnetic switching valve 62 in the closed position, and when the discharge pressure becomes equal to or higher than the third threshold value PL, outputs an open command to switch the electromagnetic switching valve 62 from the closed position to the open position.

[0096] In the present embodiment configured as described above, when the pressure in the third oil passage 5c of the pressure oil supply passage 5 exceeds the switching pressure PL (first threshold value) and the first pump 1a is stopped and the first and second electric motors 2a, 2b are controlled to drive only the second pump 1b, the vehicle body controller 20A simultaneously outputs an open command to the electromagnetic switching valve 62 to switch the electromagnetic switching valve 62 to the open position and merges the pressure oil stored in the accumulator 60 into the pressure oil supply passage 5. This absorbs pressure fluctuations that occur when the hydraulic pump supplying pressure oil to the control valve 4 is switched from the first pump 1a to the second pump 1b, making it possible to more smoothly switch between the first and second pumps 1a, 1b.

[0097] In addition, since the accumulator 60 accumulates pressure by utilizing the pressure oil discharged and recovered from the hydraulic cylinder 103a, no special hydraulic source is required, and energy savings can be achieved.

[0098] <Third embodiment> A third embodiment of the present invention will be described with reference to Figs. 10 to 15B.

[0099] ~ Overall system (hydraulic system and control system) ~ FIG. 10 is a diagram showing an entire system including a hydraulic system and its control system mounted on an electric construction machine according to a third embodiment of the present invention.

[0100] In Fig. 10, the vehicle body controller is indicated by the reference symbol 20B, and the control system including the vehicle body controller 20B is indicated by the reference symbol 300B. In this embodiment, the algorithm of the vehicle body controller 20B is different from that of the first embodiment. The other configurations are the same as those of the first embodiment.

[0101] ~Operating Principle~ FIG. 11 is a diagram similar to FIG. 3B, in which a pump iso-efficiency line is superimposed on a characteristic diagram of the output limit control of the hydraulic system of this embodiment. In this embodiment, when the discharge pressure is equal to or less than PL, both the first pump 1a and the second pump 1b are driven, and when the discharge pressure exceeds PL, the first pump 1a is stopped and the first and second electric motors 2a, 2b are controlled so that only the second pump 1b is driven.

[0102] Even when the operating ranges of the two pumps 1a, 1b are separated in this manner, the first pump 1a is not driven when the discharge pressure exceeds PL, and only the fixed displacement second pump having a reference flow rate near the operating point on the equal power line A when the discharge pressure exceeds PL is driven, and when the discharge pressure is equal to or lower than PL, not only the first pump 1a but also the second pump 1b is driven. This further increases the frequency with which the first and second pumps 1a, 1b operate in the ranges where the pump capacity (flow rate) is large and the pump efficiency is high, within the respective operating ranges of the first and second pumps 1a, 1b.

[0103] In addition, in this embodiment, since the second pump 1b operates over its entire discharge range, no fluctuations in the discharge flow rate occur during pump switching when the first pump 1a stops at the switching pressure PL, and pump switching can be performed extremely smoothly.

[0104] ~Car Controller~ The vehicle body controller 20B controls the capacity of the first pump 1a and the rotation speeds of the first and second electric motors 2a, 2b (the rotation speeds of the first pump 1a and the second pump 1b) so as to realize the above-mentioned operating principle.

[0105] More specifically, the vehicle body controller 20B drives both the first pump 1a and the second pump 1b when the pressure (discharge pressure) of the pressure oil in the pressure oil supply passage 5 is lower than the switching pressure PL (first threshold value), and stops the first pump 1a and controls the first and second electric motors 2a, 2b to continue driving the second pump 1b when the discharge pressure is equal to or higher than PL (first threshold value). In addition, when the discharge pressure is between PL0 (second threshold value) and PL (first threshold value), the vehicle body controller controls the capacity of the first pump 1a and the rotation speed of the first and second electric motors 2a, 2b so that the total output of the first pump 1a and the second pump 1b does not exceed the maximum output M of the output limit control, and when the discharge pressure is equal to or higher than PL (first threshold value), controls the rotation speed of the second electric motor 2b so that the output of the second pump 1b does not exceed the maximum output M of the output limit control.

[0106] FIG. 12 is a diagram showing an algorithm of the vehicle body controller 20B that realizes the above-mentioned operating principle.

[0107] In FIG. 12, this embodiment differs from the algorithm of the first embodiment shown in FIG. 4 in the following points.

[0108] 1. In the variable pump control unit 20Bb, a limit rotation speed calculation unit 51B is provided instead of the limit rotation speed calculation unit 51 of the first electric motor 2a, and a subtraction unit 52 which was not provided in the first embodiment is provided, and the calculated value of the subtraction unit 52 is input to a division unit 53.

[0109] 2. The fixed pump control unit 20Bc includes a rotation speed limit calculation unit 58B instead of the rotation speed limit calculation unit 58 of the second electric motor 2b.

[0110] Fig. 13A is a diagram showing the relationship between the discharge pressure and the target displacement set in the calculation table of the target displacement of the target displacement calculation unit 50 of the first pump 1a in the variable pump control unit 20Bb. Fig. 13A is the same as Fig. 5A of the first embodiment, but is shown again to facilitate understanding of the explanation related to the rotation speed limit calculation unit 51B of the first electric motor 2a.

[0111] FIG. 13B is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in the calculation table for the limit rotation speed of the first electric motor 2a in the limit rotation speed calculation unit 51B.

[0112] In FIG. 13B, in the limit rotation speed calculation table of the limit rotation speed calculation unit 51B, the relationship between the discharge pressure Ps and the limit rotation speed N1 is set so that while the discharge pressure Ps is between 0 and PL0, the limit rotation speed N1 is constant at the maximum rotation speed Ncmax of the output limit control, and while the discharge pressure Ps is between PL0 and PL, the limit rotation speed N1 decreases from the maximum rotation speed Ncmax to zero (the first electric motor 2a stops).

[0113] Here, when the discharge pressure Ps is at PL0, the first pump 1a is at the maximum capacity qmax in Fig. 13A, the first electric motor 2a is at the maximum rotation speed Ncmax in Fig. 13B, and the first pump 1a discharges the maximum flow rate Q1max-Q2max in Fig. 11. If Q1max-Q2max is expressed as Q3max (Q3max=Q1max-Q2max), the relationship between qmax and Ncmax and Q3max at this time is expressed by the following formula.

[0114] Q3max=qmax×Ncmax That is, Ncmax is smaller than the maximum rotation speed N1amax (FIG. 5B) in the first embodiment, and is a value expressed by Q3max=qmax×Ncmax.

[0115] Furthermore, when the discharge pressure Ps is at PL, the first pump 1a is at a capacity qa in FIG. 13A, the rotation speed of the first electric motor 2a becomes zero as shown in FIG. 13B, and the discharge flow rate of the first pump 1a becomes zero at the operating point of the flow rate Q2max of the second pump 1b in FIG. 11.

[0116] The rate of change of the capacity q1 of the first pump 1a and the limit rotation speed N1 of the first electric motor 2a while the discharge pressure Ps changes from PL0 to PL is set so that the product (output) of the discharge pressure Ps and the limit rotation speed N1 is equal to the maximum output M on the equal output line A in Figure 3B.

[0117] A subtraction unit 52 subtracts a flow rate (reference flow rate) Q2max when the fixed displacement second pump 1b is driven at a reference rotation speed from the target flow rate Qreq calculated by the required flow rate calculation unit 20a to calculate a required target flow rate Qreq1 of the first pump 1a. A division unit 53 divides the target flow rate Qreq1 by the target capacity q1 of the first pump 1a calculated by the target capacity calculation unit 50 to calculate a required rotation speed N1req of the first pump 1a.

[0118] The required rotation speed limiting unit 54 receives the required rotation speed N1req of the first pump 1a calculated by the division unit 53, and calculates a corrected rotation speed N1cor by limiting the minimum and maximum values ​​of the required rotation speed N1req. The calculation content of the required rotation speed limiting unit 54 is the same as that of the required rotation speed limiting unit 54 in the first embodiment.

[0119] FIG. 14 is a diagram showing the relationship between the discharge pressure and the limit rotation speed set in the calculation table for the limit rotation speed of the second electric motor 2b in the limit rotation speed calculation unit 58B.

[0120] In Figure 14, the limit rotation speed calculation table sets the relationship between the discharge pressure Ps and the limit rotation speed N2 so that while the discharge pressure Ps is between 0 and PL, the limit rotation speed N2 is constant at the maximum rotation speed N2bmax of the output limit control, and while the discharge pressure Ps is between PL and Pmax, the limit rotation speed N2 gradually decreases from N2bmax to the minimum rotation speed N2min of the output limit control.

[0121] Here, when the discharge pressure Ps is at PL, the second electric motor 2b is at the maximum rotation speed N2bmax in Fig. 14, and the second pump 1b with a fixed displacement q2 discharges the maximum flow rate Q2max in Fig. 11. The relationship between N2bmax and Q2max at this time is expressed by the following equation.

[0122] Q2max=q2×N2bmax Furthermore, when the discharge pressure Ps is at Pmax, the second electric motor 2b is at the minimum rotation speed N2min in Fig. 14, and the second pump 1b with a fixed displacement q2 discharges the minimum flow rate Q2min in Fig. 11. The relationship between Nbmin and Q2min at this time is expressed by the following equation.

[0123] Q2min = q2 × N2min The rate of change of the limit rotation speed N2 of the second electric motor 2b while the discharge pressure Ps changes from PL to Pmax is set so that the product (output) of the discharge pressure Ps and the limit rotation speed N2 is equal to the maximum output M on the equal output line A in Figure 11.

[0124] The calculation content of the requested rotation speed limiting unit 57 is the same as that of the requested rotation speed limiting unit 57 in the first embodiment.

[0125] Fig. 15A is a diagram showing the operating characteristics of the first pump 1a when the first pump 1a and the first electric motor 2a are controlled by the variable pump control unit 20Bb, and Fig. 15B is a diagram showing the operating characteristics of the second pump 1b when the second electric motor 2b is controlled by the fixed pump control unit 20Bc.

[0126] In FIG. 15A, while the discharge pressure Ps is between zero and PL0, the first pump 1a has a maximum flow rate of Q3max (=Q1max-Q2max) and discharges a flow rate less than Q3max. While the discharge pressure Ps is between PL0 and PL, the output of the first pump 1a is limited to the maximum output M on the iso-output line A. When the discharge pressure Ps reaches PL, the first pump 1a stops.

[0127] In FIG. 15B, while the discharge pressure Ps is between zero and PL, the second pump 1b discharges a flow rate of maximum flow rate Q2max, and when the discharge pressure Ps reaches PL, the second pump 1b begins to operate on the isopower line A, and while the discharge pressure Ps is between PL and Pmax, the output of the second pump 1b is limited to the maximum output M on the isopower line A.

[0128] By combining the operating characteristics of the first pump 1a and the second pump 1b that operate in this manner, the operating characteristics shown in FIG. 11 are obtained.

[0129] In this embodiment configured as above, when the discharge pressure becomes equal to or higher than PL, the first pump 1a is not driven, and only the fixed displacement second pump having a reference flow rate near the operating point on the equal power line A when the discharge pressure is equal to or higher than PL is driven, and when the discharge pressure is lower than PL, not only the first pump 1a but also the second pump 1b is driven. As a result, in the respective operating ranges of the first and second pumps 1a, 1b, the first and second pumps 1a, 1b operate more frequently in the ranges where the pump capacity (flow rate) is large and the pump efficiency is high, and energy savings can be achieved without impairing the original performance of the construction machine.

[0130] In addition, in this embodiment, since the second pump 1b operates over its entire discharge range, no fluctuations in the discharge flow rate occur during pump switching when the first pump 1a stops at the switching pressure PL, and pump switching can be performed extremely smoothly. [Explanation of symbols]

[0131] 1a First hydraulic pump 1b No. 2 hydraulic pump 2a First electric motor 2b Second electric motor 4. Control valve 5 Pressure oil supply path 5a 1st oilway 5b 2nd oilway 5c 3rd oilway 6 Check valve 7 Regulator 8 Battery (power source) 10 Pressure Sensor 11 Shuttle valve block 12 Pressure Sensor 20, 20A, 20B Vehicle controller 20a Demand flow calculation section 20b Variable pump control section 20c Fixed pump control section 50 Target capacity calculation unit for first pump 1a 51 First electric motor 2a rotation speed limit calculation unit 52 Subtraction section 53 Division section 54 First electric motor 2a required rotation speed limiting unit 55 Minimum value selection section 60 Accumulator 61 Pressure oil supply line 62 Solenoid controlled valve 63 Pressure oil recovery passage 64 Check valve 103a to 103f Multiple hydraulic actuators 104a, 104b, 105a, 105b Multiple operating devices A isopower line M Maximum output for output limit control PL 1st Threshold PL0 Second Threshold X maximum curvature point

Claims

1. A first hydraulic pump of a variable displacement type; a first electric motor that receives electric power from a power source and drives the first hydraulic pump; A plurality of hydraulic actuators driven by the discharge oil of the first hydraulic pump; A plurality of operation devices that instruct the operation of a plurality of driven bodies driven by the plurality of hydraulic actuators; a control valve for controlling a flow of pressure oil supplied from the first hydraulic pump to the plurality of hydraulic actuators by operating the plurality of operating devices, A second hydraulic pump of a fixed displacement type; a second electric motor that receives electric power from the power source and drives the second hydraulic pump; a pressure oil supply line through which the discharge oil of the first hydraulic pump and the discharge oil of the second hydraulic pump are joined together and supplied to the control valve; a pressure sensor that detects the pressure of the pressure oil in the pressure oil supply line as a discharge pressure of a pump device including the first and second hydraulic pumps; a vehicle body controller that controls a displacement of the first hydraulic pump and a rotation speed of the first electric motor and the second electric motor based on an operation of the operating device and the discharge pressure detected by the pressure sensor, The vehicle body controller includes: When the discharge pressure is lower than a first threshold value, at least the first hydraulic pump of the first and second hydraulic pumps is driven, and when the discharge pressure is equal to or higher than the first threshold value, the first and second electric motors are controlled to drive only the second hydraulic pump; an electric construction machine characterized in that, when the discharge pressure is equal to or higher than a second threshold value lower than the first threshold value, the capacity of the first hydraulic pump and the rotation speeds of the first and second electric motors are controlled so that, as the discharge pressure increases, the discharge flow rate of the pump device consisting of the first and second hydraulic pumps is continuously reduced, and output limiting control is performed to limit the output of the pump device to a preset maximum output or less.

2. 2. The electric construction machine according to claim 1, The vehicle body controller includes: When the discharge pressure is lower than the first threshold value, the second hydraulic pump is stopped and only the first hydraulic pump is driven, and when the discharge pressure is equal to or higher than the first threshold value, the first hydraulic pump is stopped and only the second hydraulic pump is driven, and the first and second electric motors are controlled; when the discharge pressure is between the second threshold value and the first threshold value, controlling the displacement of the first hydraulic pump and the rotation speed of the first electric motor so that the output of the first hydraulic pump does not exceed a maximum output of the output limiting control; an output limiting control unit configured to limit the rotation speed of the second electric motor so that the output of the second hydraulic pump does not exceed a maximum output of the output limiting control when the discharge pressure is equal to or higher than the first threshold value.

3. 2. The electric construction machine according to claim 1, The pressure oil supply passage includes: A first oil passage connected to the first hydraulic pump; A second oil passage connected to the second hydraulic pump; a third oil passage connecting the first oil passage and the second oil passage to the control valve; a check valve disposed in the first oil passage and configured to prevent backflow of pressurized oil from the third oil passage to the first hydraulic pump when the first hydraulic pump is stopped.

4. 2. The electric construction machine according to claim 1, An accumulator; a pressure oil supply passage connecting the accumulator to the pressure oil supply passage; The pressure oil supply passage further includes an electromagnetic switching valve that is arranged in the pressure oil supply passage and can be switched between an open position and a closed position. The vehicle body controller includes: an electric construction machine characterized in that, when the discharge pressure is lower than the first threshold value, a close command is output to hold the electromagnetic switching valve in the closed position, and, when the discharge pressure becomes equal to or higher than the first threshold value, an open command is output to switch the electromagnetic switching valve from the closed position to the open position.

5. 2. The electric construction machine according to claim 1, The vehicle body controller includes: When the discharge pressure is lower than the first threshold value, both of the first hydraulic pump and the second hydraulic pump are driven, and when the discharge pressure is equal to or higher than the first threshold value, the first hydraulic pump is stopped and the second hydraulic pump is continued to be driven, and the first and second electric motors are controlled; when the discharge pressure is between the second threshold value and the first threshold value, controlling the displacement of the first hydraulic pump and the rotation speeds of the first and second electric motors so that the total output of the first hydraulic pump and the second hydraulic pump does not exceed a maximum output of the output limiting control; an output limiting control unit configured to limit the rotation speed of the second electric motor so that the output of the second hydraulic pump does not exceed a maximum output of the output limiting control when the discharge pressure is equal to or higher than the first threshold value.

6. 2. The electric construction machine according to claim 1, An electric construction machine characterized in that the first threshold value is set to a value higher than the pressure at the maximum curvature point of the iso-output line indicating the maximum output in a characteristic diagram of the output limiting control, and lower than a pressure that is 3 / 5 of the maximum discharge pressure.

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