Hydraulic unit

Abstract

To suppress power consumption of a hydraulic unit.SOLUTION: A hydraulic unit 1 includes a motor 3, a variable capacity type hydraulic pump 2 for discharging hydraulic pressure, the hydraulic pump 2 utilizing discharge pressure for reducing a discharge flow amount when the discharge pressure is a predetermined value or higher, a current sensor 5 for detecting a value for a current flowing in the motor 3, and a controller 6 where a first threshold value is set in a range from a value for the current as an upper limit when the discharge flow amount is maximum to a value for the current as a lower limit when the discharge pressure is full cut-off pressure, for reducing the speed of a motor 3 when the value for the current is lower than the first threshold value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a hydraulic unit. [Background technology]

[0002] A hydraulic unit is used to operate actuators, etc. In the hydraulic unit, a hydraulic pump pressurizes hydraulic oil and supplies it to the actuators, etc.

[0003] For example, in a system using a fixed displacement hydraulic pump, the rotation speed of the motor is controlled to adjust the output of the hydraulic pump. For example, in Patent Document 1, a variable displacement hydraulic pump is used to adjust the output of the hydraulic pump. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2003-172302 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional methods for controlling hydraulic units having hydraulic pumps tend to require large amounts of power consumption.

[0006] In view of the above problems, an object of the present invention is to provide a hydraulic unit capable of suppressing power consumption. [Means for solving the problem]

[0007] In order to solve the above problems, the hydraulic unit of the present invention comprises a motor, a variable displacement hydraulic pump that is rotationally driven by the motor to discharge hydraulic pressure, and that reduces a discharge flow rate by utilizing the discharge pressure when a discharge pressure reaches or exceeds a predetermined value, a current sensor that detects a value of a current flowing to the motor when the hydraulic pump is rotationally driven, and a controller that sets a first threshold within a range having an upper limit set to the value of the current when the discharge flow rate is at a maximum and a lower limit set to the value of the current when the discharge pressure is a full cutoff pressure, and that reduces the rotation speed of the motor from a state in which the hydraulic pump is rotationally driven when the value of the current falls below the first threshold.

[0008] The controller also reduces the rotation speed at a predetermined rate of change.

[0009] The controller also reduces the rotational speed to a lower limit of the hydraulic pump's rating.

[0010] Moreover, the controller increases the rotation speed when the value of the current becomes higher than a second threshold value set within the range after reducing the rotation speed.

[0011] Also, within the range, the first threshold is greater than the second threshold. Effect of the Invention

[0012] According to the hydraulic unit of the present invention, power consumption can be reduced. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a diagram showing an example of a configuration of a hydraulic unit according to the embodiment of the present invention. [Diagram 2] FIG. 4 is a diagram showing characteristics of a discharge flow rate and a load current with respect to a discharge pressure of a hydraulic pump. [Diagram 3] FIG. 3 is a diagram showing a first threshold value and a second threshold value in the characteristics of FIG. 2; [Figure 4] FIG. 4 is a diagram illustrating an example of the operation of a hydraulic unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In order to facilitate understanding of the description, the same reference numerals are used to designate the same components in each drawing, and duplicated description will be omitted as appropriate.

[0015] === Implementation form === <Hydraulic unit configuration> Fig. 1 is a schematic diagram showing an example of the configuration of a hydraulic unit 1 according to an embodiment of the present invention (hereinafter referred to as "this embodiment"). As shown in Fig. 1, the hydraulic unit 1 mainly includes a hydraulic pump 2, a motor 3, an inverter 4, a current sensor 5, and a controller 6. For example, the inverter 4 and the controller 6 are stored in a control panel 7 or the like. In this embodiment, the description will be given assuming that the destination of the hydraulic pressure supplied by the hydraulic unit 1 is an actuator, but the device to which the hydraulic pressure is supplied is not limited to an actuator.

[0016] The hydraulic pump 2 is a variable displacement hydraulic pump 2. The variable displacement hydraulic pump 2 has a mechanism for varying the displacement, such as a variable displacement piston pump or a variable displacement vane pump. Specifically, in this embodiment, the hydraulic pump 2 will be described using a swash plate type variable displacement piston pump as an example.

[0017] The hydraulic pump 2 is driven by a motor 3 to draw hydraulic oil from an oil tank 8, increase the pressure, and discharge the hydraulic pressure to supply it to the actuator side. The actuator performs a desired operation on a load using the supplied hydraulic pressure.

[0018] The hydraulic pump 2 is provided with an adjustment mechanism 9. That is, the hydraulic pump 2 has the function of the adjustment mechanism 9. The adjustment mechanism 9 is a mechanical pressure adjustment mechanism that reduces the discharge flow rate by utilizing the discharge pressure when the discharge pressure of the hydraulic pump 2 becomes equal to or higher than a predetermined value. The predetermined value is the cutoff start pressure. That is, the adjustment mechanism 9 performs cutoff control. For example, in a swash plate type variable displacement piston pump, when the discharge pressure reaches the pressure set by the pressure adjustment screw 11 biased by the spring 10, that is, the cutoff start pressure, the position of the swash plate, which is a discharge amount variable element, is mechanically controlled based on the discharge force (hydraulic force). Then, the discharge pressure and the discharge flow rate are mechanically controlled. Note that, when the hydraulic pump 2 is a variable displacement vane pump, the discharge amount variable element is a cam ring.

[0019] That is, in the adjustment mechanism 9, when the hydraulic oil is boosted and reaches the cutoff start pressure, the position of the discharge amount variable element is mechanically controlled by the discharge force, reducing the pump displacement and decreasing the discharge flow rate while adjusting the discharge pressure. In this way, by providing the adjustment mechanism 9 in the hydraulic pump 2, the discharge flow rate decreases due to the mechanical operation of the adjustment mechanism 9 in the region above the cutoff start pressure. Then, when the discharge pressure reaches the full cutoff pressure, the discharge flow rate becomes zero.

[0020] The motor 3 is a variable speed motor, and rotates and drives the hydraulic pump 2. The rotation speed (frequency) of the motor 3 is controlled by an inverter 4.

[0021] The inverter 4 rotates the motor 3. The motor 3 rotates based on the output frequency of the inverter 4, and the hydraulic pump 2 rotates in conjunction with this.

[0022] The current sensor 5 detects the value (current value) of a current flowing to the motor 3 as a load current. Specifically, the current sensor 5 detects the current flowing from the inverter 4 to the motor 3 as the load current in a state in which the motor 3 is driving and rotating the hydraulic pump 2. The detected current value of the load current is output to the controller 6.

[0023] The controller 6 controls the inverter 4. Specifically, the controller 6 outputs a rotation speed command to the inverter 4, thereby controlling the motor 3 and the hydraulic pump 2.

[0024] In particular, in a region equal to or higher than the cutoff start pressure, the controller 6 controls the rotation speed of the motor 3 based on the current value detected by the current sensor 5. Specifically, by referring to the current value detected by the current sensor 5, when the current value falls below a threshold value, the controller 6 executes control to reduce the rotation speed of the motor 3. This threshold value is also called a first threshold value.

[0025] The details of the control by the controller 6 will be described with reference to FIG. 2. FIG. 2 is a diagram showing the characteristics of the load current with respect to pressure changes in the hydraulic pump 2. In FIG. 2, the horizontal axis represents the discharge pressure, and the vertical axis represents the discharge flow rate and the load current. In FIG. 2, the characteristics of the discharge flow rate are shown as L1, and the characteristics of the current value of the load current are shown as L2. Also, the cutoff start pressure is shown as P1, and the full cutoff pressure is shown as P2. That is, P1 is the operating point of the adjustment mechanism 9 provided in the hydraulic pump 2. Note that the flow rate characteristics and load current characteristics in FIG. 2 show characteristics when the rotation speed is constant (maximum).

[0026] As shown by L1, the discharge flow rate gradually decreases with increasing discharge pressure in the low discharge pressure region. Then, when the discharge pressure reaches P1, which is the cutoff start pressure, the adjustment mechanism 9 operates, and the discharge flow rate decreases in the region above P1. Then, the discharge flow rate becomes zero and reaches the full cutoff pressure.

[0027] The load current also varies according to the discharge flow rate. Specifically, in the region below the cutoff start pressure P1, the load current increases as the discharge pressure increases. When the discharge pressure reaches the cutoff start pressure P1, the adjustment mechanism 9 operates and the load current decreases.

[0028] That is, when the discharge pressure reaches or exceeds the cutoff start pressure and the adjustment mechanism 9 operates, both the discharge flow rate and the load current decrease. In particular, at the full cutoff pressure indicated as P2, the load current decreases to IL. The controller 6 uses this characteristic to detect that the discharge pressure is close to the full cutoff pressure based on the current value of the load current.

[0029] Here, in the load current characteristic shown as L2, the range shown by IH and IL is close to the full cutoff pressure. For this reason, the range between IH and IL is set as the predetermined range R. Note that the predetermined range R includes the values ​​of IH and IL. The predetermined range R can be said to be the value of the load current corresponding to the pressure state just before the full cutoff pressure is reached.

[0030] For this reason, the threshold value A1 is set within this predetermined range R. The threshold value A1 is the above-mentioned first threshold value. That is, the controller 6 executes control to reduce the rotation speed of the motor 3 when the current value of the load current detected by the current sensor 5 becomes lower than the threshold value A1. When the current value becomes lower than the threshold value A1, the load current that was larger than the threshold value A1 becomes equal to or smaller than the threshold value A1. For example, the controller 6 reduces the rotation speed to a predetermined low-speed rotation speed. The low-speed rotation speed is, for example, the lower limit rotation speed of the rated hydraulic pump 2. As an example, when the hydraulic pump 2 is operated at the upper limit rotation speed of the rated hydraulic pump 2, the rotation speed is reduced to the lower limit rotation speed of the rated hydraulic pump 2. The upper limit rotation speed (frequency) of the rated hydraulic pump 2 is, for example, 60 Hz.

[0031] IH, which is the upper limit of the predetermined range R, is the current value of the load current when the discharge flow rate is at a maximum. In other words, IH is the current value of the load current when the actuator, which is the target device to which hydraulic pressure is supplied by the hydraulic pump 2, is in an unloaded state and the discharge flow rate of the hydraulic pump 2 is at a maximum. Because of the unloaded state, the discharge flow rate is at a maximum. In other words, IH can be said to be the value at which the load current is at a minimum in the region below the cutoff start pressure. The load current is at a maximum at the cutoff start pressure.

[0032] IL, which is the lower limit of the predetermined range R, is the current value of the load current when the discharge pressure is the full cutoff pressure. That is, IL is the current value of the load current when the discharge flow rate is zero and the discharge pressure of the hydraulic pump 2 reaches the set pressure and is in the full cutoff state. In other words, IL can be said to be the value at which the load current is minimum in the region equal to or higher than the cutoff start pressure.

[0033] In this way, by setting the upper and lower limits of the predetermined range R and setting the threshold within this range, it is possible to detect that the discharge pressure has dropped close to the full cutoff pressure. When this is detected, the rotation speed is reduced, making it possible to reduce power consumption. Furthermore, compared to when the discharge pressure is directly detected by a sensor, it is possible to eliminate the need for a pressure sensor, and it is also possible to simplify the system.

[0034] FIG. 3 is an enlarged view of the periphery of the predetermined range R in FIG. 2. As shown in FIG. 3, a threshold value A2 may be set as a second threshold value within the predetermined range R. That is, the controller 6 may execute control to increase the rotation speed of the motor 3 when the current value of the load current detected by the current sensor 5 becomes higher than the threshold value A2 after performing the above-mentioned process of reducing the rotation speed. When the current value becomes higher than the threshold value A2, the load current that was smaller than the threshold value A2 becomes equal to or larger than the threshold value A2. For example, the controller 6 increases the rotation speed up to a predetermined increased rotation speed. The increased rotation speed is, for example, the rated upper limit rotation speed of the hydraulic pump 2. For example, when the process of increasing the rotation speed is performed, the rotation speed returns to the rotation speed before the process of reducing the rotation speed is performed.

[0035] In addition, within the predetermined range R, it is preferable that the threshold A1, which is the first threshold, is larger than the threshold A2, which is the second threshold. In particular, it is preferable that, within the predetermined range R, the threshold A1 is set on the upper limit side of the middle of the predetermined range R, and the threshold A2 is set on the lower limit side of the middle. Setting the thresholds in this manner makes it easier to stabilize the system. In addition, the threshold A1 and the threshold A2 may be set to be equal, or the threshold A1 may be smaller than the threshold A2.

[0036] Fig. 4 is a diagram showing an example of the operation of the hydraulic unit 1. In Fig. 4, the horizontal axis represents time, and the vertical axis represents the discharge pressure, the discharge flow rate, the load current, and the rotation speed (frequency).

[0037] The rise starts from T1, and the inverter 4 increases the rotation speed. This increases the discharge pressure, discharge flow rate, and load current, and the discharge pressure rises to the full flow pressure, which is the operating pressure. Then, at T2, the rotation speed is constant at a predetermined speed (60 Hz) indicated as R1, and the discharge pressure becomes full flow pressure and the load current becomes full flow flow rate. Here, depending on the operating conditions, the cut-off start pressure is reached at T3, the adjustment mechanism 9 operates, and the discharge flow rate is reduced.

[0038] After the adjustment mechanism 9 operates, the load current also decreases, and at T4 it becomes lower than the threshold A1. The controller 6 monitors the load current by the current sensor 5, and detects that the load current becomes lower than the threshold A1 at T4. That is, it detects that the discharge pressure has increased and is approaching the full cutoff pressure. In response to this, control is executed to reduce the rotation speed. Therefore, the rotation speed decreases from T4 onwards. This reduction in the rotation speed is performed at a predetermined rate of change. That is, over the time from T4 to T5 (T5-T4), the rotation speed is reduced to R2, which is the low-speed rotation speed. When the rotation speed reaches R2 at T5, the rotation speed is maintained.

[0039] Here, it is assumed that the load current becomes higher than the threshold A2 at T6 due to the operating conditions. The discharge pressure decreases due to the operating conditions, and the load current increases accordingly. The controller 6 detects that the load current has become higher than the threshold A2, and performs a process to increase the rotation speed. As a result, the rotation speed increases at a predetermined rate of change from T6 onwards. That is, over the time from T6 to T7 (T7-T6), the rotation speed is increased to, for example, 60 Hz as an increased rotation speed. The rate of change when the rotation speed is decreased from T4 to T5 may be smaller than the rate of change when the rotation speed is increased from T6 to T7. That is, the change in the rotation speed becomes more gradual when the rotation speed is decreased.

[0040] <Action and effect> As described above, in this embodiment, the hydraulic unit 1 is a motor 3, a variable displacement hydraulic pump 2 that is rotationally driven by the motor 3 to discharge hydraulic pressure, and is equipped with the hydraulic pump 2 that utilizes the discharge pressure to reduce the discharge flow rate when the discharge pressure becomes equal to or higher than a predetermined value, a current sensor 5 that detects the value of current flowing to the motor 3 when the hydraulic pump 2 is being rotationally driven, and a controller 6 that sets a first threshold value, i.e., a threshold value A1, within a predetermined range R with an upper limit set to the current value when the discharge flow rate is at its maximum and a lower limit set to the current value when the discharge pressure is at the full cutoff pressure, and that reduces the rotation speed of the motor 3 from a state in which the hydraulic pump 2 is being rotationally driven when the current value becomes lower than the threshold value A1.

[0041] According to this configuration, when the current flowing through the motor 3 becomes lower than the threshold A1, the rotation speed of the motor 3 is reduced, and the current detects that the discharge pressure is approaching the full cutoff pressure, and the rotation speed is reduced. This makes it possible to avoid a state in which the rotation speed is excessively high near the full cutoff pressure, and to reduce power consumption. In particular, the predetermined range R is set to the current value when the discharge flow rate is maximum as the upper limit, and the current value when the discharge pressure is the full cutoff pressure as the lower limit, making it possible to detect that the discharge pressure is approaching the full cutoff pressure.

[0042] Moreover, in this embodiment, the controller 6 reduces the rotation speed at a predetermined rate of change.

[0043] According to this configuration, the rotation speed is reduced at a predetermined rate of change, so that the rotation rate can be changed while maintaining stability.

[0044] Moreover, in this embodiment, the controller 6 reduces the rotation speed of the hydraulic pump 2 to the lower limit of the rating.

[0045] According to this configuration, by lowering the hydraulic pump 2 to the lower limit of its rating, the effect of suppressing power consumption can be enhanced.

[0046] Furthermore, in this embodiment, after reducing the rotation speed, if the current value becomes higher than a threshold value A2, which is a second threshold value set within the predetermined range R, the controller 6 increases the rotation speed.

[0047] According to this configuration, the decrease in the discharge pressure is detected after the rotation speed is reduced, and the hydraulic pressure can be supplied to the actuator by increasing the two outputs of the hydraulic pump again.

[0048] In the present embodiment, within the predetermined range R, the threshold value A1, which is the first threshold value, is greater than the threshold value A2, which is the second threshold value.

[0049] According to this configuration, the operational stability of the hydraulic pump 2 can be improved.

[0050] === Variations === The present invention is not limited to the above-described embodiment. In other words, the above-described specific example may be modified by a person skilled in the art as appropriate, and the modifications may be included in the scope of the present invention as long as they include the features of the present invention. In addition, the elements of the above-described embodiment and the following modifications may be combined to the extent technically possible, and the combinations of these may be included in the scope of the present invention as long as they include the features of the present invention.

[0051] In the above embodiment, a swash plate type variable displacement piston pump has been described as an example of the hydraulic pump 2. However, as long as the hydraulic pump has the adjustment mechanism 9, it is not limited to a swash plate type variable displacement piston pump. [Explanation of symbols]

[0052] 1: hydraulic unit, 2: hydraulic pump, 3: motor, 5: current sensor, 6: controller, 9: adjustment mechanism, A1: threshold (first threshold), IH: upper limit, IL: lower limit, R: specified range, P1: specified value (cutoff start pressure), P2: full cutoff pressure

Claims

1. A motor; a variable displacement hydraulic pump that is rotationally driven by the motor to discharge hydraulic pressure, and that reduces a discharge flow rate by utilizing the discharge pressure when the discharge pressure becomes equal to or higher than a predetermined value; a current sensor that detects a value of a current flowing through the motor when the hydraulic pump is being rotationally driven; a first threshold is set within a range having an upper limit set to a value of the current when the discharge flow rate is at a maximum and a lower limit set to a value of the current when the discharge pressure is a full cutoff pressure, and when the value of the current becomes lower than the first threshold, a controller that reduces the rotation speed of the motor from a state in which the hydraulic pump is being rotationally driven; A hydraulic unit comprising:

2. The hydraulic unit according to claim 1 , wherein the controller reduces the rotational speed at a predetermined rate of change.

3. The hydraulic unit according to claim 1 or 2, wherein the controller reduces the rotational speed to a lower limit of the rating of the hydraulic pump.

4. 3. The hydraulic unit according to claim 1, wherein the controller increases the rotation speed when the value of the current becomes higher than a second threshold value set within the range after the rotation speed is reduced.

5. The hydraulic unit of claim 4 , wherein within the range, the first threshold is greater than the second threshold.

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