Patent Description:
When a hydraulic pump is driven by a motor, it is known that pulsations occur in a discharge pressure of the hydraulic pump due to a discharge fluctuation of the hydraulic pump and a torque ripple of the motor (refer to, for example, PTL <NUM>).

If a motor that drives a pump is controlled by an inverter based on a detected pressure and/or flow rate of a fluid discharged from the pump when there is a pulsation in the discharge pressure of the pump, the stability of the pressure <CIT> discloses a fluid pressure unit comprising an inverter, a motor controlled by the inverter, a pump driven by the motor to discharge a hydraulic fluid, a detector configured to detect the pressure of the fluid, or a flow rate of the fluid, a controller configured to control the inverter such that a pressure of the pump or a flow rate of the pump, becomes a predetermined value, based on a detected value by the detector, and a suppressor configured to suppress a change in an output of the inverter caused by a pulsation frequency component of the fluid included in the detected value. <CIT>is a technological background document and relates to a drive device, fluid utilization device and air conditioner. and/or flow rate of the fluid discharged from the pump may be reduced.

The present disclosure provides a fluid pressure unit capable of suppressing a decrease in the stability of the pressure and/or flow rate of the fluid discharged from the pump.

The present disclosure provides a fluid pressure unit that includes an inverter, a motor controlled by the inverter, a pump driven by the motor to discharge a fluid, a detector configured to detect a pressure of the fluid, a flow rate of the fluid, or both, a controller configured to control the inverter such that a pressure of the pump, a flow rate of the pump, or both becomes a predetermined value based on a detected value by the detector, and a suppressor configured to suppress a change in an output of the inverter caused by a pulsation frequency component of the fluid included in the detected value.

According to this configuration, it is possible to suppress a decrease in stability of the pressure and/or flow rate of the fluid discharged from the pump.

In the above-described fluid pressure unit, the suppressor may reduce an amount of suppression at a frequency component that is higher than the pulsation frequency component in comparison with an amount of suppression at the pulsation frequency component.

According to this configuration, a responsiveness of the motor and the pump can be suppressed in a frequency range that is higher than the pressure pulsation frequency of the fluid.

In the above-described fluid pressure unit, the suppressor may be a band stop filter in which a frequency of the pulsation frequency component is included in a stop band.

According to this configuration, a responsiveness of the motor and the pump can be suppressed in a frequency range other than the stop band.

In the above-described fluid pressure unit, the band stop filter may be a notch filter in which the frequency of the pulsation frequency component is included in the stop band.

According to this configuration, a responsiveness of the motor and the pump can be further suppressed in a frequency range other than the stop band.

In the above-described fluid pressure unit, the stop band may vary according to a rotational speed of the pump.

According to this configuration, a decrease in stability of the pressure and/or flow rate of the fluid discharged from the pump can be suppressed even when the rotational speed of the pump changes.

In the above-described fluid pressure unit, the stop band may vary according to a product of the rotational speed of the pump and a number of teeth of the pump.

According to this configuration, a decrease in stability of the pressure and/or flow rate of the fluid discharged from the pump can be suppressed accurately even when the rotational speed of the pump changes.

In the above-described fluid pressure unit, the detector may include a pressure sensor to detect the pressure of the fluid.

According to this configuration, it is possible to accurately suppress a decrease in stability of the pressure of the fluid discharged from the pump.

In the above-described fluid pressure unit, the detector may include a flow rate sensor to detect the flow rate of the fluid.

According to this configuration, it is possible to accurately suppress a decrease in stability of the flow rate of the fluid discharged from the pump.

Hereinafter, embodiments will be described.

<FIG> is a diagram illustrating a configuration example of a system including a fluid pressure unit according to an embodiment. A system <NUM> illustrated in <FIG> causes an actuator <NUM> to perform a desired operation by a fluid supplied from a fluid pressure unit <NUM>. The system <NUM> includes the fluid pressure unit <NUM>, a control valve <NUM> and the actuator <NUM>. The actuator <NUM> is an example of a load operated by a fluid supplied from the fluid pressure unit <NUM>. The actuator <NUM> is connected to the fluid pressure unit <NUM> through a control valve <NUM>.

The fluid pressure unit <NUM> drives a pump <NUM> by a motor <NUM> controlled by an inverter <NUM> to supply the fluid from a tank <NUM> to the actuator <NUM>, such as a cylinder. If the fluid is oil, the fluid pressure unit is also referred to as a hydraulic unit. The fluid is not limited to liquids, such as oils, and may be a gas.

The fluid pressure unit <NUM> includes the inverter <NUM>, the motor <NUM>, the pump <NUM>, the tank <NUM>, the pressure sensor <NUM>, a controller <NUM>, and a suppressor <NUM>.

The inverter <NUM> controls the motor <NUM> according to a command (i.e., control signal) supplied from the controller <NUM>. The inverter <NUM> is a circuit for regulating the power supply to the motor <NUM> and includes, for example, a three-phase bridge circuit that outputs a three-phase alternating current.

The motor <NUM> is a synchronous motor controlled by the inverter <NUM> and is driven by an alternating current output from the inverter <NUM>.

The pump <NUM> is driven by the motor <NUM> controlled by the inverter <NUM> to discharge a fluid. For example, the pump <NUM> draws in and compresses the fluid from the tank <NUM> through a suction path <NUM> and discharges the compressed fluid to the actuator <NUM> through a discharge path <NUM> and the control valve <NUM>. The fluid output from the actuator <NUM> returns to the tank <NUM> through the control valve <NUM> and a return path <NUM>.

In the example illustrated in <FIG>, the discharge path <NUM> includes discharge pipes 15b, 15c, 15d, and 15e through which the fluid discharged from the pump <NUM> passes. The discharge path that passes through the discharge pipes 15b and 15c on the fluid pressure unit <NUM> side and the discharge path that passes through the discharge pipes 15d and 15e on the actuator <NUM> side are connected to each other at a connection point 15a. On the other hand, the return path <NUM> includes return pipes 9a and 9b through which the fluid output from the actuator <NUM> passes.

For example, the discharge pipes 15b and 15c have higher rigidity than the discharge pipes 15d and 15e. As an example, the discharge pipes 15d and 15e are hoses formed of an elastic body such as rubber or resin, and the discharge pipes 15b and 15c are pipes formed of a metal block that is more rigid than the elastic body. The return path <NUM> (the return pipes 9a and 9b) may be made of the same material as the discharge path <NUM> or a different material.

The pressure sensor <NUM> is an example of a detecting unit for detecting the pressure of the fluid discharged from the pump <NUM>, and outputs the pressure of the detected fluid (hereinafter, also referred to as a detected pressure Pd). The pressure sensor <NUM> detects the pressure of the fluid flowing into the discharge path <NUM>. In this example, the pressure of the fluid discharged from the pump <NUM> to the discharge pipe 15b of the discharge path <NUM> is detected through the discharge pipe 15c.

The controller <NUM> outputs a command for controlling the inverter <NUM> such that the pressure (a discharge pressure Po) of the fluid discharged from the pump <NUM> becomes a predetermined value, based on a detected pressure value (i.e., the detected pressure Pd in the example illustrated in <FIG>) by the pressure sensor <NUM>. For example, the controller <NUM> operates the inverter <NUM> to control the motor <NUM> such that the discharge pressure Po of the pump <NUM> becomes a target pressure, based on the detected pressure value by the pressure sensor <NUM>. The target pressure is specified, for example, by a pressure command supplied from outside the controller <NUM>. Further, the pressure at the input end of the actuator <NUM> from the pump <NUM> through the discharge path <NUM> is called a load pressure Pa.

When the pump is driven by the motor <NUM>, the detected pressure value by the pressure sensor <NUM> may include a pressure pulsation frequency component of the fluid because the discharge pressure Po of the pump <NUM> is pulsed by the drive of the pump <NUM>. In this case, when the controller <NUM> controls the inverter <NUM> based on the detected pressure value by the pressure sensor <NUM>, the stability of the discharge pressure Po of the pump <NUM> may get reduced due to the pressure pulsation frequency component included in the detected pressure value.

For example, by performing a method of controlling the inverter <NUM> so as to cancel the pulsation of the discharge pressure Po (i.e., a pulsation compensation method) based on the detected pressure value by the pressure sensor <NUM>, the controller <NUM> can suppress the pulsation of the discharge pressure Po and the load pressure Pa as illustrated in <FIG>. However, in the pulsation compensation method, when the frequency band of the pulsation of the discharge pressure Po increases, the control band of the inverter <NUM> by the controller <NUM> is insufficient, the discharge pressure Po and the load pressure Pa become unstable may become unstable as illustrated in <FIG>. For example, when the controller <NUM> controls the inverter <NUM> to cancel pulsations above the control band, a command (control signal) supplied from the controller <NUM> to the inverter <NUM> may vibrate and cause the discharge pressure Po and the load pressure Pa to hunt.

The fluid pressure unit <NUM> according to an embodiment illustrated in <FIG> includes a suppressor <NUM> configured to suppress the change in the output of the inverter <NUM> caused by the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM>. According to the suppressor <NUM>, since the change in the output of the inverter <NUM> caused by the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM> is suppressed, a decrease in stability of the discharge pressure Po and the load pressure Pa of the pump <NUM> can be suppressed.

<FIG> is a diagram illustrating an example of the change in the output of the inverter caused by the pulsation frequency component of the fluid included in the detected value. When the controller <NUM> controls the inverter <NUM> based on the detected pressure value by the pressure sensor <NUM>, the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM> may superimpose on the alternating current output from the inverter <NUM>. <FIG> illustrates a waveform in which the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM> is superimposed on an AC current iu of one phase output from the inverter <NUM>. A similar pressure pulsation frequency component is superimposed on the AC current of other phases (for example, AC current iv, AC current iw) output from inverter <NUM>.

Since the suppressor <NUM> illustrated in <FIG> suppresses the change in the output AC current of the inverter <NUM> caused by the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM>, the pressure pulsation frequency component superimposed on the output AC current can be suppressed as illustrated in <FIG>. Since the inverter <NUM> is not controlled to cancel the pulsation of the discharge pressure Po, a slight pulsation may remain in the discharge pressure Po, as illustrated in <FIG>. However, the load pressure Pa at the input end of the actuator <NUM> becomes substantially constant because the pressure pulsation is attenuated in the discharge path from the connection point 15a to the actuator <NUM>.

The suppressor <NUM> may reduce the suppression amount at a frequency component higher than the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM> in comparison with the suppression amount at the pressure pulsation frequency component of the fluid. According to this configuration, a reduction in a responsiveness of the motor <NUM> and the pump <NUM> can be suppressed in a frequency range that is higher than the pressure pulsation frequency of the fluid. For example, an abrupt operation of the motor <NUM> and the pump <NUM> can be suppressed from being inhibited.

The suppressor <NUM> may be a band stop filter that includes, in a stop band, the frequency of the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM>. According to this configuration, the reduction in the responsiveness of the motor <NUM> and the pump <NUM> can be suppressed in the frequency range other than the stop band.

The band stop filter may be a notch filter that includes, in the stop band, the frequency of the pressure pulsation frequency component of the fluid included in the detected pressure value by the pressure sensor <NUM>. Since the signal in the frequency range other than the stop band does not readily attenuate, the notch filter can further suppress the reduction in the responsiveness of the motor <NUM> and the pump <NUM> in the frequency range other than the stop band.

The stop band of the bandpass filter or notch filter may vary depending on a rotational speed of the pump <NUM>. According to this configuration, even when the rotational speed of the pump <NUM> changes, a decrease in stability of the discharge pressure Po of the pump <NUM> can be suppressed by being adjusted to an appropriate stop band in accordance with the rotational speed.

The stop band may vary depending on the product of the number of revolutions of the pump <NUM> and the number of teeth of the pump <NUM>. According to this configuration, even when the rotational speed of the pump <NUM> changes, a decrease in stability of the discharge pressure Po of the pump <NUM> can be accurately suppressed.

The number of teeth of the pump <NUM> is typically about <NUM> to <NUM>. For example, if the pump <NUM> is a positive displacement pump, a pulsation corresponding to the product of the rotational speed of the pump <NUM> and the teeth number of the pump <NUM> occurs in the discharge pressure Po. <FIG> illustrates a waveform in which the pulsation frequencies of <NUM> to <NUM> [Hz] × <NUM> [sheets] are superimposed on the output AC current of the inverter <NUM> when the number of teeth of the pump <NUM> is <NUM>.

The suppressor <NUM> may be configured by hardware or in cooperation with hardware and software.

<FIG> is a diagram illustrating a first configuration example of the fluid pressure unit. A configuration similar to that illustrated in <FIG> among the configurations illustrated in <FIG> is omitted. A fluid pressure unit 200A illustrated in <FIG> may include a speed sensor <NUM>. The speed sensor <NUM> detects a speed of the motor <NUM> and outputs the detected speed ωd.

The controller <NUM> includes a notch filter <NUM> that includes the frequency of the pressure pulsation frequency component included in the detected pressure Pd in the stop band. The notch filter <NUM> changes the stop band (notch frequency) in accordance with the speed ωd detected by the speed sensor <NUM>. Alternatively, the notch filter <NUM> changes the stop band (notch frequency) in accordance with a command speed ω* (more preferably, an old speed ω^ before the unit time of the command speed ω*). According to these configurations, the notch filter <NUM> can adjust the stop band to a frequency including the pressure pulsation frequency component that varies in accordance with the rotational speed of the pump <NUM>, thereby suppressing a decrease in the stability of the pressure and/or flow rate of the fluid discharged from the pump <NUM>.

The controller <NUM> controls the operation of the inverter <NUM> that drives the motor <NUM> based on the pressure Pd detected by the pressure sensor <NUM>, a flow rate Qd calculated based on the speed ωd detected by the speed sensor <NUM>, and a map <NUM> (also referred to as a PQ map) comprising a target pressure, a target flow rate, and a horsepower limit. The flow rate Qd calculated by the controller <NUM> represents an estimated value of the flow rate Q of the fluid discharged from the pump <NUM> to the discharge path <NUM>.

The controller <NUM> multiplies the detected speed ωd [<NUM>/s] and a volume q [m<NUM>] of the pump <NUM> by a multiplier <NUM> to determine the flow rate Qd [m<NUM>/s]. The volume q of the pump <NUM> is constant and therefore fixed. The controller <NUM> derives a target horsepower Rr from the PQ map <NUM> based on the target pressure Pr supplied from the outside and the flow rate Qd calculated by the multiplier <NUM>. On the other hand, the controller <NUM> multiplies the pressure Pd detected by the pressure sensor <NUM> and the flow rate Qd calculated by the multiplier <NUM> by a multiplier <NUM> to derive the detected horsepower Rd (= Pd × Qd). The controller <NUM> derives an error Re (= Rr - Rd) between the target horsepower Rr and the detected horsepower Rd by a subtractor <NUM>. The controller <NUM> includes a PID control unit <NUM> that derives the command speed ω* which brings the error Re close to zero by a PID control (in PID, P refers to proportional, I refers to integral, and D refers to derivative). The command speed ω* may be derived by PI control.

The controller <NUM> may calculate the old speed ω^ [<NUM>/s] before the unit time (for example, control period) by delaying the command speed ω* with a delay device (not illustrated), and may calculated the flow rate Qd [m<NUM>/s] by multiplying the old speed ω^ by the volume q [m<NUM>] of the pump <NUM> with the multiplier <NUM>.

The controller <NUM> includes a voltage setting unit <NUM> for setting a command voltage Vr for driving the inverter <NUM> that drives the motor <NUM> based on the command speed ω*.

The functions of each unit, such as the PID control unit <NUM>, provided by the controller <NUM> are implemented by operating a processor (for example, a central processing unit (CPU) by a program that is stored in the memory readably.

<FIG> is a diagram illustrating an example of a pressure-flow rate map. The PQ map <NUM> includes a maximum flow rate line corresponding to the maximum set flow rate Q0, a maximum horsepower curve comprising a curve corresponding to the maximum horsepower limit L0, and a maximum pressure line corresponding to the maximum set pressure P0. The flow rate Q corresponds to the product of the rotational speed ω (the number of rotations) of the motor <NUM> and the volume q of the pump <NUM> and is therefore equivalent to the rotational speed ω.

The controller <NUM> operates the inverter <NUM> that drives the motor <NUM> such that the pressure Pd detected by the pressure sensor <NUM> and the flow rate Qd calculated based on the detected speed ωd or the command speed ω* operate on a line consisting of a set pressure Pn, a set flow rate Qn, and a set horsepower curve Ln in the PQ map <NUM>.

<FIG> is a diagram illustrating a second configuration example of a fluid pressure unit. A configuration similar to the configuration illustrated in <FIG> and <FIG> among the configurations illustrated in <FIG> is omitted. A fluid pressure unit 200B illustrated in <FIG> includes a flow rate sensor <NUM>. The flow rate sensor <NUM> is an example of a detector that detects the flow rate Q of the fluid discharged from the pump <NUM> to the discharge path <NUM>, and outputs the flow rate Qd of the detected fluid (hereinafter, also referred to as the detected flow rate Qd). The flow rate sensor <NUM>, for example, detects the flow rate Q of the fluid flowing into the discharge pipe 15b of the discharge path <NUM>, but may detect the flow rate Q of the fluid flowing into the discharge pipe 15d or the discharge pipe 15e. The controller <NUM> calculates the detection speed ωd [<NUM>/s] by dividing the detection flow rate Qd [m<NUM>/s] by the volume q[m<NUM>] by the divider <NUM>.

The controller <NUM> includes a notch filter <NUM> that includes the frequency of the pulsation frequency component included in the detected pressure Pd in the stop band. The notch filter <NUM> changes the stop band (notch frequency) in accordance with the speed ωd detected by a divider <NUM> of the controller <NUM>. According to this configuration, the notch filter <NUM> can adjust the stop band to a frequency including the pulsation frequency component that varies with the rotational speed of the pump <NUM>, thereby suppressing a decrease in stability of the pressure and/or flow rate of the fluid discharged from the pump <NUM>.

Although a description has been given of the embodiments, it may be understood that various modifications may be made to the configurations and details thereof, without departing from the subject matter and scope of the claims.

For example, the controller <NUM> may control the inverter such that the pressure and/or flow rate of the pump <NUM> are at a predetermined value based on the flow rate value detected by the flow rate sensor <NUM>. This is because the controller <NUM> can calculate the pressure of the fluid from the flow rate detected by the flow rate sensor <NUM> by using a pipeline resistance of the discharge path <NUM>.

Claim 1:
A fluid pressure unit (<NUM>;200A;200B) comprising:
an inverter (<NUM>);
a motor (<NUM>) controlled by the inverter (<NUM>);
a pump (<NUM>) driven by the motor (<NUM>) to discharge a fluid;
a detector configured to detect a pressure of the fluid, a flow rate of the fluid, or both;
a controller (<NUM>) configured to control the inverter (<NUM>) such that a pressure of the pump (<NUM>), a flow rate of the pump, or both becomes a predetermined value, based on a detected value by the detector; and
a suppressor (<NUM>) configured to suppress a pulsation frequency component that is superimposed on an output alternating current of the inverter (<NUM>) caused by the pulsation frequency component of the fluid included in the detected value, wherein the pulsation frequency component is higher than the output alternating current.