Fluid pressure system

Abstract

To provide a hydraulic pressure system capable of suppressing an increase in the diameter of a shaft without impairing operability.SOLUTION: A hydraulic pressure system 1 comprises an electric motor 3, a shaft 6 rotated by the electric motor 3, a predetermined number of variable displacement hydraulic pumps 2 that are connected to the electric motor 3 via the shaft 6 and discharge hydraulic oil to operate a hydraulic actuator, and a controller 5 that controls the outputs of the hydraulic pumps 2 in response to an input command. The controller 5 allocates and controls the outputs of the hydraulic pumps 2 in response to the input command so that the upper limit of the sum of the outputs becomes approximately equal to the total output of the maximum outputs of a number of hydraulic pumps 2 that is less than a predetermined number.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a fluid pressure system in which a plurality of fluid pressure pumps are driven by an electric motor. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there are known hydraulic systems used in work machines and the like in which a plurality of hydraulic pumps are driven by a common engine or electric motor (see, for example, Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 59-177778 [Patent Document 2] Special Publication No. 7-84866 [Patent Document 3] JP 2002-81370 A [Patent Document 4] Special Publication No. 2002-515567 [Patent Document 5] JP 2011-75023 A Summary of the Invention [Problem to be solved by the invention]

[0004] In order to operate all the pumps at 100%, the shaft diameter connecting the power source and the pumps must be increased so that it can withstand the large torque applied to it. Increasing the shaft diameter leads to an increase in the size of the entire system and the work machine.

[0005] The present invention has been made in consideration of these points, and has an object to provide a fluid pressure system that can suppress an increase in the diameter of a shaft without impairing operability. [Means for solving the problem]

[0006] The invention described in claim 1 is a fluid pressure system comprising an electric motor, a shaft rotated by the electric motor, a predetermined number of variable displacement fluid pressure pumps connected to the electric motor via the shaft and discharging working fluid to operate a fluid pressure actuator, and a controller that controls the output of these fluid pressure pumps in response to an input command, wherein the controller allocates and controls the output of each fluid pressure pump in response to the input command so that the total upper limit of the outputs of the fluid pressure pumps is approximately equal to the total output of the maximum outputs of a number of fluid pressure pumps that is less than the predetermined number.

[0007] The invention described in claim 2 relates to a fluid pressure system according to claim 1, in which three or more fluid pressure pumps are set, and a controller controls the output of an electric motor so that the upper limit of the total output of each fluid pressure pump is approximately equal to the total output of the maximum outputs of the two fluid pressure pumps.

[0008] The invention described in claim 3 is such that the shaft in the fluid pressure system described in claim 1 extends on both sides of the electric motor, and a fluid pressure pump is connected to each of the shafts on one side and the shaft on the other side based on the electric motor.

[0009] The invention as set forth in claim 4 is such that any one of the fluid pressure pumps in the fluid pressure system as set forth in any one of claims 1 to 3 is connected in parallel to the shaft. Effect of the Invention

[0010] According to the invention described in claim 1, the torque applied to the shaft can be reduced, the uses of a specified number of fluid pressure pumps can be separated to make it easier to control the fluid pressure actuator, and the increase in the diameter of the shaft can be suppressed while ensuring operability.

[0011] According to the invention of claim 2, the uses of three or more fluid pressure pumps are independent, making it easier to control the fluid pressure actuator, and while ensuring operability, it is possible to suppress an increase in the diameter of the shaft.

[0012] According to the invention recited in claim 3, compared with the case where a fluid pressure pump is connected to only one side of an electric motor, it is possible to increase the number of locations where a reduced diameter shaft can be used.

[0013] According to the invention as recited in claim 4, compared with the case where a fluid pressure pump is connected in series to an electric motor, it is possible to increase the number of locations where a reduced diameter shaft can be used. [Brief description of the drawings]

[0014] [Figure 1] 1 is a circuit diagram showing a first embodiment of a fluid pressure system according to the present invention. [Diagram 2] 1A is a table showing an example of the output, torque, and minimum required diameter of each fluid pressure pump of the above-mentioned fluid pressure system, FIG. 1B is a table showing another example of the output, torque, and minimum required diameter of each fluid pressure pump of the fluid pressure system, and FIG. 1C is a table showing an example of the output, torque, and minimum required diameter of each fluid pressure pump of a conventional fluid pressure system. [Diagram 3] FIG. 4 is a circuit diagram showing a second embodiment of a fluid pressure system according to the present invention. [Figure 4] 1A is a table showing an example of the output, torque, and minimum required diameter of each fluid pressure pump of the above fluid pressure system, and FIG. 1B is a table showing another example of the output, torque, and minimum required diameter of each fluid pressure pump of the above fluid pressure system. [Diagram 5] FIG. 4 is a circuit diagram showing a third embodiment of a fluid pressure system according to the present invention. [Figure 6] 1A is a table showing an example of the output, torque, and minimum required diameter of each fluid pressure pump of the above fluid pressure system, and FIG. 1B is a table showing another example of the output, torque, and minimum required diameter of each fluid pressure pump of the above fluid pressure system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present invention will be described in detail below based on a first embodiment shown in Figures 1 and 2, a second embodiment shown in Figures 3 and 4, and a third embodiment shown in Figures 5 and 6.

[0016] First, the first embodiment will be described.

[0017] In Fig. 1, reference numeral 1 denotes a hydraulic system which is a fluid pressure system. The hydraulic system 1 is applied to a work machine such as a hydraulic excavator. The hydraulic system 1 includes hydraulic pumps 2 which are a predetermined number of fluid pressure pumps for discharging hydraulic oil which is a working fluid, and these hydraulic pumps 2 are driven by a common electric motor (electric motor) 3. In other words, the hydraulic system 1 is an electro-hydraulic system.

[0018] The hydraulic pump 2 is a variable displacement type having a displacement varying means 4 also called a regulator. A pump line connected to the hydraulic pump 2 is connected directly or indirectly via a control valve to a hydraulic actuator, which is a fluid pressure actuator such as a hydraulic cylinder or a hydraulic motor, and operates the hydraulic actuator by supplying the discharged hydraulic oil to the hydraulic actuator. Preferably, three or more hydraulic pumps 2 are set. In this embodiment, three hydraulic pumps 2 (hydraulic pumps 2a, 2b, 2c) are set. Each hydraulic pump 2 is capable of supplying hydraulic oil to a predetermined hydraulic actuator group. The hydraulic actuator group corresponding to each hydraulic pump 2 may be fixed, or may be switched by switching a valve in response to an operation by an operator of an operating device such as a lever or pedal for operating the hydraulic actuator.

[0019] The operations of the electric motor 3 and the hydraulic pump 2 are controlled by a controller 5. The controller 5 is a power controller unit, which generates a command signal for commanding a flow rate based on an input command (signal) input in accordance with the amount of operation of an operating device, and outputs the command signal to the capacity varying means 4, thereby controlling the output (horsepower) of the hydraulic pump 2, i.e., the amount of hydraulic oil discharged by the hydraulic pump 2. The electric motor 3 and the controller 5 are operated by power supplied from a battery.

[0020] The electric motor 3 is connected to the hydraulic pump 2 via a shaft 6. In the illustrated example, the shaft 6 extends to one side of the electric motor 3, and the hydraulic pump 2a is connected to the shaft 6a, the hydraulic pump 2b is connected to the shaft 6b connected to the hydraulic pump 2a, and the hydraulic pump 2c is connected to the shaft 6c connected to the hydraulic pump 2b. The shafts 6a, 6b, and 6c are arranged coaxially, and the hydraulic pumps 2a, 2b, and 2c are connected in series (tandem). The shafts 6a, 6b, and 6c are rotated by the electric motor 3 in the same direction at the same speed. Therefore, the torque of the hydraulic pump 2c is applied to the shaft 6c, the torque of the hydraulic pumps 2b and 2c is applied to the shaft 6b, and the torque of the hydraulic pumps 2a, 2b, and 2c is applied to the shaft 6a.

[0021] Here, if the torque applied to the shaft 6 is T, the shear stress is τ, and the polar section modulus is Zp, then τ=T / Zp, and if d is the diameter of the shaft 6, then Zp=πd 3 / 16, so d = (16T / πτ) 1 / 3 That is, the diameter d of the shaft 6 is proportional to the cube root of the torque T. Furthermore, the output of the hydraulic pump 2 is expressed as the product of the torque T and the rotation speed. Therefore, the diameter d of the shaft 6 is proportional to the cube root of the output of the hydraulic pump 2.

[0022] Therefore, in this embodiment, the controller 5 controls the output of the hydraulic pump 2 to suppress the torque T applied to the shaft 6, thereby making it unnecessary to increase the diameter d of the shaft 6.

[0023] Specifically, the controller 5 allocates and controls the outputs of the hydraulic pumps 2 in accordance with the magnitude relationship of the input commands so that the upper limit of the total output is approximately equal to the total output of the maximum outputs P of the hydraulic pumps 2 which is a number less than a predetermined plurality, for example, one less than the predetermined plurality. In this embodiment, the controller 5 controls the outputs of the hydraulic pumps 2 so that the upper limit of the total output P of the three hydraulic pumps 2 is approximately equal to the total output (=2P) of the maximum outputs P of the two hydraulic pumps 2. Note that "approximately equal" includes "equal".

[0024] The output of each hydraulic pump 2 is set in response to an input command for each hydraulic pump 2 based on an operation request to a hydraulic actuator.

[0025] In other words, the controller 5 sets the output of each hydraulic pump 2 to an output according to the input command if their sum is approximately 2P or less, and if their sum exceeds 2P, sets the input command to an output converted from the input command in accordance with the ratio between the sum and 2P.

[0026] For example, if the input commands (%) of the hydraulic pumps 2a, 2b, and 2c are I1, I2, and I3, and P·(I1+I2+I3) / 100=S, the outputs P1, P2, and P3 of the hydraulic pumps 2a, 2b, and 2c are Pi=(P·Ii / 100)·{2P / max(2P,S)}=Ii·4P 2 / 100(2P+S+|2P-S|), set as i=1,2,3.

[0027] For example, when there is a 100% input command for all hydraulic pumps 2a, 2b, and 2c, in the case of the conventional example shown in Fig. 2(c) where output allocation control by controller 5 is not performed, the output of hydraulic pump 2a, the output of hydraulic pump 2b, and the output of hydraulic pump 2c are each set to P, and the torque applied to shaft 6c (the maximum torque applied by hydraulic pump 2 alone operating at maximum output) is T, the torque applied to shaft 6a is 3T, and the torque applied to shaft 6b is 2T. Therefore, when the diameter of shaft 6c (diameter that can withstand the maximum torque T) is d, the minimum diameter required for shaft 6a is 1.44d, and the minimum diameter required for shaft 6b is 1.26d.

[0028] 2(a), the output of hydraulic pump 2a, the output of hydraulic pump 2b, and the output of hydraulic pump 2c are each set to 0.67P, the torque applied to shaft 6a is 2T, the torque applied to shaft 6b is 1.33T, and the torque applied to shaft 6c is 0.67T. Therefore, the minimum required diameter of shaft 6a is 1.26d, the minimum required diameter of shaft 6b is 1.1d, and the minimum required diameter of shaft 6c is 0.87d.

[0029] Also, for example, when there is a 100% input command to hydraulic pumps 2b and 2c, as shown in Fig. 2(b), the output of hydraulic pump 2a is set to 0, the output of hydraulic pump 2b and the output of hydraulic pump 2c are each set to P, the torque applied to shafts 6a and 6b is 2T, and the torque applied to shaft 6c is T. Therefore, the minimum diameters required for shafts 6a and 6b are 1.26d, and the minimum diameter required for shaft 6c is d. Note that, in this example, the output of hydraulic pump 2a is set to 0 for the sake of clarity, but in reality, some output is generated because hydraulic pump 2a needs to be operated to the extent that it does not burn out.

[0030] In this way, by allocating and controlling the output of each of a predetermined number of variable displacement hydraulic pumps 2 in response to an input command so that the upper limit of their total is approximately equal to the total output of the maximum outputs of a number of hydraulic pumps 2 that is less than the predetermined number, the torque applied to the shaft 6 can be reduced, the uses of the multiple hydraulic pumps 2 can be separated, making it easier to control the hydraulic actuator, and the diameter of the shaft 6 can be prevented from becoming large while ensuring operability.

[0031] Specifically, according to this embodiment, while driving three or more hydraulic pumps 2, for example three hydraulic pumps 2, in response to an input command, the torque applied to the shaft 6 can be suppressed to be equal to or less than the sum (2T) of the maximum torque T of two hydraulic pumps 2, thereby making it possible to suppress an increase in the diameter of the shaft 6. Therefore, by separating the uses of the three or more hydraulic pumps 2, it is possible to easily control the hydraulic actuator and to suppress an increase in the diameter of the shaft 6 while ensuring operability. For example, in this embodiment, for the shaft 6c, the torque applied can be set to be equal to or less than the maximum torque T and the diameter can be set to be equal to or less than d, and for the shafts 6a and 6b, the torque applied to each can be set to be equal to or less than 2T and the diameter can be set to be equal to or less than 1.26d.

[0032] Next, a second embodiment will be described. Note that the same components and functions as those in the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted.

[0033] In the hydraulic system 1 shown in FIG. 3, a shaft 6 extends on both sides of an electric motor 3, and one of the hydraulic pumps 2 is connected to the shaft 6 on one side and the shaft 6 on the other side based on the electric motor 3.

[0034] In the illustrated example, a hydraulic pump 2a is connected to a shaft 6a on one side of the electric motor 3, a hydraulic pump 2b is connected to a shaft 6b on one side connected to the hydraulic pump 2a, and a hydraulic pump 2c is connected to a shaft 6c on the other side of the electric motor 3. The shafts 6a, 6b, and 6c are arranged coaxially. The shafts 6a, 6b, and 6c are rotated in the same direction at the same speed by the electric motor 3. Therefore, the torque of the hydraulic pump 2b is applied to the shaft 6b, the torque of the hydraulic pumps 2a and 2b is applied to the shaft 6a, and the torque of the hydraulic pump 2c is applied to the shaft 6c.

[0035] For example, when a 100% input command is given to hydraulic pumps 2a and 2b, the output of hydraulic pump 2a and the output of hydraulic pump 2b are each set to P, and the output of hydraulic pump 2c is set to 0, as shown in FIG. 4(a). The torque applied to shaft 2a is 2T, the torque applied to shaft 6b is T, and the torque applied to shaft 6c is 0. Therefore, the minimum diameter required for shaft 6a is 1.26d, and the minimum diameter required for shaft 6b is d. Note that in this example, the output of hydraulic pump 2c is set to 0 for the sake of clarity, but in reality, some output is generated because hydraulic pump 2c needs to be operated to the extent that it does not burn out.

[0036] Also, for example, when a 100% input command is given to hydraulic pumps 2b and 2c, the output of hydraulic pump 2a is set to 0, the output of hydraulic pump 2b and the output of hydraulic pump 2c are each set to P, and the torque applied to shafts 6a, 6b, and 6c is each set to T, as shown in FIG. 4(b). Therefore, the minimum diameter required for shafts 6a, 6b, and 6c is each set to d. Note that in this example, the output of hydraulic pump 2a is set to 0 for the sake of clarity, but in reality, some output is generated because hydraulic pump 2a needs to be operated to the extent that it does not burn out.

[0037] In this way, according to the second embodiment, the outputs of each of a predetermined number of variable displacement hydraulic pumps 2 are allocated and controlled in response to an input command so that the upper limit of the total of the outputs is approximately equal to the total output of the maximum outputs of a number of hydraulic pumps 2 that is less than the predetermined number, in a manner similar to that of the first embodiment. This makes it possible to achieve the same effects as the first embodiment, such as preventing the shaft 6 from becoming larger in diameter without compromising operability.

[0038] Furthermore, in the shaft 6 protruding on both sides of the electric motor 3, by connecting one of the hydraulic pumps 2 to each of the shaft 6 on one side and the other side of the electric motor 3 as a reference, the torque applied to each shaft 6 can be reduced and the number of places where the small-diameter shaft 6 can be used can be increased, compared to the case where the hydraulic pump 2 is connected to only one side of the electric motor 3. For example, in this embodiment, for the shafts 6b and 6c, by having one hydraulic pump 2 connected in series, the torque applied to each can be made equal to or less than the maximum torque T and the diameter can be made equal to or less than d, and for the shafts 6a and 6b, the torque applied to each can be made equal to or less than 2T and the diameter can be made equal to or less than 1.26d.

[0039] Next, a third embodiment will be described. Note that the same reference numerals are used to denote the same configurations and operations as those in the respective embodiments, and the description thereof will be omitted.

[0040] In the hydraulic system 1 shown in Fig. 5, one of the hydraulic pumps 2 is connected in parallel to a shaft 6 via a shaft coupling 8. In this embodiment, the shaft 6 extends on both sides of the electric motor 3, and one of the hydraulic pumps 2 is connected to the shaft 6 on one side and the shaft 6 on the other side based on the electric motor 3, and the hydraulic pump 2 is connected in parallel to at least the shaft 6 on one side.

[0041] In the illustrated example, a hydraulic pump 2a is connected to a shaft 6a on one side of an electric motor 3, a shaft 6b is connected in parallel to the shaft 6a via a shaft coupling 8, a hydraulic pump 2b is connected to the shaft 6b, and a hydraulic pump 2c is connected to a shaft 6c on the other side of the electric motor 3. The shafts 6a and 6c are arranged coaxially. The shafts 6a, 6b, and 6c are rotated in the same direction at the same speed by the electric motor 3. Therefore, the torque of the hydraulic pump 2b is added to the shaft 6b, the torque of the hydraulic pump 2a is added to the shaft 6a, and the torque of the hydraulic pump 2c is added to the shaft 6c.

[0042] And, for example, when there is a 100% input command to the hydraulic pumps 2a and 2b, as shown in FIG. 6(a), the output of the hydraulic pump 2a is set to P, the output of the hydraulic pump 2b is set to P', and the output of the hydraulic pump 2c is set to 0. Here, P' is the output obtained by subtracting the loss due to the shaft coupling 8 from P and is a value smaller than P. The torque added to the shaft 2a is T, the torque added to the shaft 6b is T' (<T), and the torque added to the shaft 6c is 0. Therefore, the required minimum diameter of the shaft 6a is d, and the required minimum diameter of the shaft 6b is d' (<d). In this example, for the sake of clarity, the output of the hydraulic pump 2c is set to 0, but in reality, since it is necessary to operate the hydraulic pump 2c so that it does not seize, some output is generated.

[0043] Also, for example, when there is a 100% input command to the hydraulic pumps 2b and 2c, as shown in FIG. 6(b), the output of the hydraulic pump 2a is set to 0, the output of the hydraulic pump 2b is set to P', the output of the hydraulic pump 2c is set to P, the torque added to the shaft 6b is T', and the torque added to the shaft 6c is T. Therefore, the required minimum diameter of the shaft 6b is d' (<d), and the required minimum diameter of the shaft 6c is d. In this example, for the sake of clarity, the output of the hydraulic pump 2a is set to 0, but in reality, since it is necessary to operate the hydraulic pump 2a so that it does not seize, some output is generated.

[0044] In this way, according to the third embodiment, the outputs of each of a predetermined number of variable displacement hydraulic pumps 2 are allocated and controlled in response to an input command so that the upper limit of the total of the outputs is approximately equal to the total output of the maximum outputs of a number of hydraulic pumps 2 that is less than the predetermined number, in a manner similar to that of the first embodiment, thereby making it possible to suppress an increase in the diameter of the shaft 6 without impairing operability, and other similar effects to those of the other embodiments can be achieved.

[0045] Furthermore, by connecting the hydraulic pump 2 in parallel to the shaft 6, although some loss occurs due to the shaft coupling 8 for the parallel connection compared to connecting the hydraulic pump 2 in series to the electric motor 3, the torque applied to each shaft 6 can be reduced and the number of locations where the reduced diameter shaft 6 can be used can be increased.

[0046] In particular, since the shaft 6 extends on both sides of the electric motor 3 and multiple hydraulic pumps 2 are connected in parallel to the shaft 6, the torque applied to each shaft 6 can be reduced more than when the hydraulic pump 2 is connected to only one side of the electric motor 3, and compared to when the same number of hydraulic pumps 2 are connected in series, and the number of places where the small-diameter shaft 6 can be used can be increased. By allocating the three hydraulic pumps 2 so that two are connected in parallel to one side of the electric motor 3 and one is connected to the other side of the electric motor 3, the torque applied to each of all shafts 6a, 6b, 6c can be made equal to or less than the maximum torque T, and the diameter can be made equal to or less than d.

[0047] In the third embodiment, an example has been described in which the reduction ratio of the hydraulic pumps 2 connected in parallel by the shaft coupling 8 is 1, but the invention is not limited to this, and the reduction ratio may be increased when a larger torque is required for the hydraulic pumps 2 connected in parallel, and may be decreased when a higher rotation speed is required. In other words, the reduction ratio of the hydraulic pumps 2 connected in parallel may be set arbitrarily according to the torque and rotation speed required.

[0048] Furthermore, the hydraulic pumps 2 may be connected in parallel to the shafts 6 extending on both sides of the electric motor 3, respectively.

[0049] Furthermore, the shaft 6 is not limited to extending on both sides of the electric motor 3, but may extend on one side of the electric motor 3. In other words, the hydraulic pump 2 may be connected in parallel to the shaft 6a or the shaft 6b of the first embodiment via the shaft coupling 8.

[0050] Thus, according to each embodiment, there is a high degree of freedom in the layout of the hydraulic pump 2, and variations can be easily added. It is possible to improve the efficiency of the electro-hydraulic system by reducing weight and improving transmission efficiency, and it is possible to accommodate various changes in the form of the hydraulic system 1 due to electrification.

[0051] In each embodiment, the number of hydraulic pumps 2 is not limited to three, and may be four or more. [Industrial Applicability]

[0052] INDUSTRIAL APPLICABILITY The present invention is applicable to industries that manufacture and sell hydraulic systems in which a plurality of hydraulic pumps are driven by an electric motor, and work machines such as electric excavators equipped with such hydraulic systems. [Explanation of symbols]

[0053] 1. Hydraulic system, a fluid pressure system 2. Hydraulic pumps, which are fluid pressure pumps 3. Electric motor 5. Controller 6 Shaft

Claims

1. An electric motor; a shaft rotated by the electric motor; a plurality of predetermined variable displacement fluid pressure pumps connected to the electric motor via the shaft and discharging a working fluid for operating the fluid pressure actuator; a controller that controls the outputs of the hydraulic pumps in response to input commands; The controller controls and allocates the outputs of the hydraulic pumps in response to an input command so that the upper limit of the total of the outputs is approximately equal to the total of the maximum outputs of the hydraulic pumps that are less than a predetermined number.

1. A fluid pressure system comprising:

2. The hydraulic pump is configured to have three or more hydraulic pumps. The controller controls the output of the electric motor so that the upper limit of the total output of each hydraulic pump is approximately equal to the total output of the maximum outputs of the two hydraulic pumps.

2. The fluid pressure system according to claim 1.

3. The shaft extends on either side of the electric motor; A hydraulic pump is connected to each of the shafts on one side and the shaft on the other side of the electric motor.

2. The fluid pressure system according to claim 1.

4. One of the hydraulic pumps is connected in parallel to the shaft.

4. The fluid pressure system according to claim 1, wherein the fluid pressure system comprises:

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