JP4250797B2 - Inverter-driven hydraulic unit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inverter-driven hydraulic unit capable of controlling the flow rate and pressure of oil.
[0002]
[Prior art]
Conventionally, there is a hydraulic unit as shown in FIG. 4 that can control the flow rate and pressure of oil. The hydraulic unit includes a variable displacement hydraulic pump 2 driven by an induction motor 1 that rotates at a constant rotational speed, and a swash plate control cylinder that controls a swash plate that is a variable discharge amount control element of the variable displacement hydraulic pump 2. 3 and a pressure compensation valve 5 for controlling the oil supplied to the swash plate control cylinder 3. The swash plate control cylinder 3 is moved back and forth by the operation of the pressure compensation valve 5 so that the pressure of the pump line 7 of the variable displacement hydraulic pump 1 becomes a pressure corresponding to the spring force of the spring 5a of the pressure compensation valve 5. Thus, the discharge amount of the variable displacement hydraulic pump 2 is controlled. A hydraulic cylinder 9 is connected to the pump line 7 via a switching valve 8.
[0003]
[Problems to be solved by the invention]
However, since the conventional hydraulic unit requires the variable displacement hydraulic pump 1 and the pressure compensating valve 5, there is a problem that the structure is complicated, large, and expensive. The variable displacement hydraulic pump 1 requires a complicated and large variable displacement mechanism such as a swash plate or a swash plate control cylinder 3. Further, the pressure compensation valve 5 requires a pressure compensation mechanism, and its structure is more complicated than a relief valve.
[0004]
Further, in the above conventional hydraulic unit, the variable displacement hydraulic pump 1 is driven to rotate at a constant speed by an induction motor regardless of the required discharge flow rate, so that noise is great and energy loss and heat generation occur. There is a problem of being big.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to provide a hydraulic unit that is simple in structure, small in size, inexpensive, and has little noise, energy loss, and heat generation.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, an inverter-driven hydraulic unit according to the invention of claim 1 comprises:
A fixed displacement hydraulic pump;
A motor capable of controlling the rotational speed for driving the fixed displacement hydraulic pump;
An inverter controller for controlling the rotation speed of the motor;
A relief valve connected to the discharge line of the fixed displacement hydraulic pump ;
A pressure sensor for detecting the pressure of the discharge line of the fixed displacement hydraulic pump;
The inverter controller controls the rotational speed of the motor based on the output of the pressure sensor and the command signal, and uses the pressure override characteristic of the relief valve to release a small amount of oil from the relief valve to the tank. However, the oil pressure in the discharge line is feedback-controlled .
[0007]
[0008]
According to the inverter-driven hydraulic unit of the first aspect of the invention, the rotational speed of the fixed displacement hydraulic pump is controlled by controlling the rotational speed of the motor by the inverter controller in accordance with the command signal, and the required per unit time. An amount of oil is discharged from the fixed displacement hydraulic pump, and a small amount of oil is discharged from the relief valve to the tank to control the flow rate and pressure of the oil. By utilizing the pressure override characteristic of the relief valve, the pressure in the discharge line can be controlled by the rotation speed of the fixed displacement hydraulic pump.
[0009]
In this way, basically, the number of rotations of the motor is controlled according to the amount of oil required, and the fixed displacement hydraulic pump cannot be rotated at an unnecessarily high number of rotations. Because excess oil is hardly discharged unnecessarily, there is little energy loss and heat generation of the oil is small.
[0010]
When excessive oil pressure is generated in the discharge line due to impact load, etc., the relief valve operates and the oil is discharged to the tank, so that the motor is not overloaded and the motor is overcurrent. Does not flow.
[0011]
The inverter-driven hydraulic unit according to the first aspect of the invention drives the fixed displacement hydraulic pump while controlling the rotation speed via the motor with an inverter controller, and uses the pressure override characteristic of the relief valve to control the flow rate and pressure. Since the control does not require a complicated pressure compensation mechanism of the variable displacement hydraulic pump or a complicated pressure compensation mechanism of the pressure compensation valve, there is an advantage that the structure is simple, small, and inexpensive.
[0012]
[0013]
According to the inverter driving the hydraulic unit of the invention of claim 1, the inverter controller, based on the command signal and the output of the pressure sensor, a feedback control so that the pressure in the discharge line to the pressure corresponding to the command signal. Therefore, while discharging oil from the relief valve, the pressure of the discharge valve can be accurately controlled to a value corresponding to the command signal by utilizing the pressure override characteristic of the relief valve.
[0014]
An inverter-driven hydraulic unit according to a second aspect of the invention is characterized in that, in the inverter-driven hydraulic unit according to the first aspect, a bleed-off line having a restriction is connected to the discharge line.
[0015]
According to the inverter-driven hydraulic unit of the second aspect of the invention, oil is always leaked to the tank from the bleed offline having the throttle. Therefore, even if there is a limit on the minimum rotation speed of the motor by the inverter controller, that is, there is a limit on the minimum discharge amount from the fixed displacement hydraulic pump, the minimum discharge line flow rate is equivalent to the leakage flow rate from the bleed-off line The value of can be reduced.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0017]
As shown in FIG. 1, the inverter-driven hydraulic unit of this embodiment includes a fixed displacement hydraulic pump 11 and a synchronous motor 12 as an example of a motor that can control the rotation speed, that is, the rotation speed of the fixed displacement hydraulic pump 11. An inverter controller 13 for controlling the rotational speed of the synchronous motor 12, a relief valve 15 connected to the discharge line 7 of the fixed displacement hydraulic pump 11, and a pressure sensor 17 for detecting the pressure of the discharge line 7. I have. The inverter controller 13 receives AC power from an AC power supply 18 and rectifies and outputs DC power, and a switching transistor unit that receives DC power from the rectifier 13a and outputs a drive signal to the synchronous motor 12. 13b and the output signal from the pressure sensor 17 are received, and the switching transistor unit 13b is switched so that a drive signal having a frequency corresponding to the flow rate or pressure corresponding to the command signal is output to the synchronous motor 12. It has the control part 13c. A hydraulic cylinder 9 is connected to the discharge line 7 via a switching valve 8.
[0018]
In the above configuration, it is assumed that a flow rate command signal is input to the inverter controller 13 as a command signal. Then, the control unit 13c of the inverter controller 13 performs switching control of the switching transistor unit 13b so that the synchronous motor 12 and thus the fixed displacement hydraulic pump 11 rotate at a rotation speed according to the flow rate command signal. As a result, the fixed displacement hydraulic pump 11 rotates at a rotational speed corresponding to the speed command signal, discharges an amount of oil corresponding to the rotational speed, and causes the piston rod of the hydraulic cylinder 9 to respond to the flow command signal. Move at a different speed. At this time, the pressure in the discharge line 7 is roughly the pressure corresponding to the load of the hydraulic cylinder 9, and the relief valve 15 has a pressure override characteristic as shown in FIG. A quantity of oil is discharged into the tank 16.
[0019]
As described above, the rotation speed of the synchronous motor 12 is controlled by the inverter controller 13 so that the fixed displacement hydraulic pump 11 discharges an amount of oil corresponding to the flow rate command signal, and the fixed displacement hydraulic pump 11 is rotated at an excessive rotation speed. Since the hydraulic pump 12 cannot be rotated, noise is low, and excess oil is hardly discharged unnecessarily, so there is little energy loss and less heat is generated by the oil.
[0020]
Further, when the hydraulic cylinder 9 suddenly stops at the stroke end or when an impact load or the like is applied, an excessive hydraulic pressure is generated in the discharge line 7. At this time, the relief valve 15 operates. Since the oil is discharged into the tank 16, the synchronous motor 12 is not overloaded, and no overcurrent flows through the synchronous motor 12.
[0021]
On the other hand, for example, it is assumed that a pressure command signal is input as a command signal to the inverter controller 13 in order to cause the hydraulic cylinder 9 to perform a clamping operation. Then, the control unit 13c of the inverter controller 13 compares the output signal indicating the pressure of the discharge line 7 from the pressure sensor 17 with the pressure command signal, and controls the switching transistor unit 13b based on the comparison result. The rotational speeds of the synchronous motor 12 and the fixed displacement hydraulic pump 11 are increased or decreased so that the pressure of the discharge line 7 becomes a pressure corresponding to the pressure command signal. That is, when the pressure detected by the pressure sensor 17 is smaller than the pressure indicated by the pressure command signal, the rotational speed of the fixed displacement hydraulic pump 11 is increased, while the pressure detected by the pressure sensor 17 indicates the pressure command signal. When the pressure is larger than the pressure, feedback control is performed so as to reduce the rotational speed of the fixed displacement hydraulic pump 11. At this time, the relief valve 15 discharges to the tank 16 the amount of oil determined by the override characteristics shown in FIG.
[0022]
In this way, by utilizing the pressure override characteristic of the relief valve 15, the pressure in the discharge line 7 is fixed to the pressure sensor 17, the inverter controller 13, and the synchronous motor 12 while releasing a small amount of oil from the relief valve 15 to the tank 16. Since the feedback control is performed by the displacement hydraulic pump 11, the pressure of the discharge line 7 can be controlled to an accurate value corresponding to the pressure command signal while reducing energy loss.
[0023]
As described above, even during the pressure control by the pressure command signal, the rotation speed of the synchronous motor 12 and thus the fixed displacement hydraulic pump 11 is controlled by the inverter controller 13, and the fixed displacement hydraulic pump 11 is rotated at a rotation speed higher than necessary. Therefore, noise is low, and excess oil is hardly discharged unnecessarily, so there is little energy loss and heat generation of oil is small.
[0024]
Further, the inverter-driven hydraulic unit 10 drives the fixed displacement hydraulic pump 11 while controlling the rotation speed via the synchronous motor 12 by the inverter controller 13, and uses the pressure override characteristic of the relief valve 10 to change the flow rate. Since the pressure is controlled, the structure is simple, small and inexpensive. That is, this hydraulic unit does not require the complicated pressure compensation mechanism of the variable displacement hydraulic pump and the complicated pressure compensation mechanism of the pressure compensation valve as in the prior art, so the structure is simple, small and inexpensive. is there.
[0025]
FIG. 3 shows a modified example. In this modified example, only the structure of the relief valve 25 is different from the embodiment of FIG. 1, and other components are the same as those of the embodiment of FIG. Therefore, the same component uses FIG.
[0026]
The relief valve 25 includes a relief valve main body 21 and a bleed offline 23 having a throttle 24. Oil is always discharged from the discharge line 7 to the tank 16 through the bleed offline 23 and the throttle 24. Therefore, even if the minimum rotation speed of the synchronous motor 13 by the inverter controller 13 is limited, that is, the minimum discharge amount from the fixed displacement hydraulic pump 11 is limited, the discharge from the bleed offline 23 having the throttle 24 is performed. The value of the minimum flow rate supplied to the load such as the hydraulic cylinder 9 from the discharge line 7 can be reduced by the flow rate.
[0027]
In FIG. 3, the bleed offline 23 is provided in the relief valve 25, but may be provided separately from the relief valve.
[0028]
[0029]
The motor is not limited to a synchronous motor and may be any motor as long as the number of revolutions can be controlled by pulses from an inverter controller.
[0030]
【The invention's effect】
As is clear from the above, according to the inverter-driven hydraulic unit of the first aspect of the invention, the rotational speed of the fixed displacement hydraulic pump is controlled by controlling the rotational speed of the motor by the inverter controller in accordance with the command signal. And, by utilizing the pressure override characteristics of the relief valve, a small amount of oil is discharged from the relief valve to the tank, and the flow rate and pressure of the oil are controlled. Is not rotated, noise is small, and excess oil is hardly discharged unnecessarily, so there is little energy loss and less heat is generated by the oil.
[0031]
Further, according to the inverter driven hydraulic unit of the invention of claim 1, when an excessive hydraulic pressure is generated in the discharge line due to an impact load or the like, the relief valve is operated and the oil is discharged to the tank. The motor is not overloaded and no overcurrent flows through the motor.
[0032]
The hydraulic unit according to the invention of claim 1 requires a variable displacement hydraulic pump having a complicated variable displacement mechanism and a pressure compensation valve having a complicated pressure compensation mechanism using a fixed displacement hydraulic pump and a relief valve. Therefore, there is an advantage that the structure is simple, small and inexpensive.
[0033]
Further, according to the inverter driving the hydraulic unit of the invention of claim 1, while utilizing the pressure override characteristics of the relief valve, the inverter controller, on the basis of the command signal and the output of the pressure sensor, the rotation of the fixed displacement hydraulic pump Since the speed is controlled and feedback control is performed so that the pressure of the discharge line becomes a pressure corresponding to the command signal, the pressure of the discharge line can be accurately controlled to a value corresponding to the command signal.
[0034]
According to the inverter driven hydraulic unit of the invention of claim 2 , since oil is always leaked to the tank from the bleed offline having the throttle, even if the minimum rotational speed of the motor by the inverter controller is limited, that is, fixed. Even if the minimum discharge amount from the displacement hydraulic pump is limited, the value of the minimum flow rate in the discharge line can be reduced by the amount of leakage flow from the bleed-off line.
[Brief description of the drawings]
FIG. 1 is a block diagram of an inverter drive hydraulic unit according to an embodiment of the present invention.
FIG. 2 is a graph showing pressure override characteristics.
FIG. 3 is a circuit diagram of a modified example of the relief valve.
FIG. 4 is a circuit diagram of a conventional hydraulic unit.
[Explanation of symbols]
7 Discharge line 11 Fixed displacement hydraulic pump 12 Synchronous motor 13 Inverter controller 15, 25 Relief valve 23 Bleed offline 24 Restriction

Claims (2)

A fixed displacement hydraulic pump (11);
A motor (12) capable of controlling the rotational speed for driving the fixed displacement hydraulic pump (11);
An inverter controller (13) for controlling the rotational speed of the motor (12);
Relief valves (15, 25) connected to the discharge line (7) of the fixed displacement hydraulic pump (11) ;
A pressure sensor (17) for detecting the pressure of the discharge line (7) of the fixed displacement hydraulic pump (11);
The inverter controller (13) controls the rotational speed of the motor (12) based on the output of the pressure sensor (17) and a command signal, and utilizes the pressure override characteristic of the relief valve (15, 25). An inverter-driven hydraulic unit that performs feedback control of the oil pressure in the discharge line (7) while discharging a small amount of oil from the relief valve (15, 25) to the tank (16) . The inverter-driven hydraulic unit according to claim 1, wherein a bleed-off line (23) having a throttle (24) is connected to the discharge line (7).

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