JP2001090670A - Hydraulic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic device aiming at the matching of the operation range required by a hydraulic pump with the operation area of a motor, and aiming at the miniaturization of a device and lowering of the cost while lowering the motor capacity. SOLUTION: This hydraulic device drives a hydraulic pump with a motor to be driven by an inverter, and as the motor, a switched reluctance motor 1 is used. The switched reluctance motor 1 can lower the reverse electromotive voltage of the motor with the weak magnetic flux control, and in a rectangular coordinate (torque-rotating speed) expressed with a figure 3, inverse proportional curve-like operation area can be realized. With this invention, operation rang matching with the operation (waiting to holding, holding to waiting) of a clamp of a lathe can be realized, and the motor capacity is reduced, and the cost is lowered, and miniaturization of the device is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic device for driving a hydraulic pump by a motor driven by an inverter.

[0002]

2. Description of the Related Art Conventionally, a hydraulic pump is driven by a constant speed motor. There is a pump control system in which a pump discharge pressure generated by the hydraulic pump is released by a relief valve or the like in accordance with a drive pressure required on the load side. There is also a pump control system in which a comparator valve for setting the discharge pressure of the hydraulic pump to a predetermined pressure is provided, and the pump swash plate is swung to control the pump discharge amount.

[0003] However, in the former pump control system, the pressure released by the relief valve becomes energy loss as it is,
Energy loss has occurred due to transmission efficiency between the hydraulic pump and the relief valve or between the hydraulic pump and the constant speed motor.

In the latter pump control system,
Energy loss has occurred due to transmission efficiency between the hydraulic pump and the constant speed motor.

In recent years, from the viewpoint of protection of the global environment, the need for energy saving in factories has been increasing, and an inverter hydraulic pump capable of saving energy by varying the rotation speed of a motor for driving the hydraulic pump by means of an inverter. A system has been proposed.

FIG. 7 shows an example of the inverter hydraulic pump system. This system includes an inverter-motor system having an inverter 101 and a motor 102, and a motor 102 driven at a variable speed by the inverter 101.
Is a system for driving the hydraulic pump 103. Pressure (or discharge amount) of hydraulic oil discharged by this hydraulic pump 103
Is converted into an electric signal and input to the hydraulic control unit 105. The hydraulic control unit 105 outputs a speed command signal to the speed control unit 106, and the speed control unit 106, the waveform control unit 1
07, electronic control is performed by the speed detection unit 108 such that the pressure (or discharge amount) of the hydraulic oil becomes a predetermined value.

The output capacity of the motor 102 for driving the hydraulic pump 103 has been determined so that the maximum pressure Pmax can be maintained when the hydraulic pump 103 has the maximum flow rate Qmax, as shown in FIG. Here, the pump pressure (M
Pa) is proportional to the motor torque τ (Nm), and the pump flow rate Q
(1 / min) is proportional to the rotation speed N (rps). Therefore, the operating range of the motor 102 is shown in FIG.
As in the case of (rotation speed) characteristics, a rectangular area has been required.

Therefore, the required capacity P of the motor 102
Is calculated as P = 2π · Nmax · τmax (1)

The operation of a lathe clamp, which is frequently used as an actuator driven by the hydraulic pump 103, will be described. This clamp is open
(Hereinafter, abbreviated as a standby state) and a state in which the work is fixed and held (hereinafter, abbreviated as a held state) requires a large pressure. On the other hand, the clamp is held from the standby state,
Alternatively, in the process from the holding state to the standby state (hereinafter abbreviated as a transition state), only the force required to move the clamp is required.

Therefore, in this transition state, although the required pressure may be low, the flow rate of the working oil is increased, the moving speed of the clamp is increased, and the work is replaced in a short time.

As shown in FIG. 6A, a series of (standby → hold, hold → standby) operations of this clamp
The (pressure) locus is an inclined line segment L1 connecting the point G1 of the flow rate Qmax (pressure Pmin) and the point G2 of the flow rate Qmin (pressure Pmax). This inclined line segment L1 is slightly bent toward the origin. Further, as shown by a solid line L2 in FIG.
During the above (standby → hold, hold → standby) operation, the required (torque-rotation speed) operation range of the motor is the maximum torque (τma
x), minimum torque from point X1 of minimum rotation speed (N0)
It is defined by a descending curve that reaches the point X2 at the rotation speed maximum (Nmax) at (τ0). Although the lathe clamp has been exemplified, hydraulic actuators used in other machine tools or industrial machines, such as a clamp in a machining center, have a locus similar to (flow-pressure).

Here, in the concept shown in FIGS. 5A and 5B, the motor capacity PN is calculated by the following equation (2).

PN = 2π · Nmax · τmax (2)

[0014]

However, in a lathe clamp, as shown in FIGS. 6A and 6B, the capacity PT required for the hydraulic pump is calculated by the following equation (3).

PT = Max (2π · N0 · τmax, 2π · Nmax · τ0) <PN (3) where Max (A, B) is a function for selecting a larger one of A and B. . As can be seen from the equation (3) and the comparison between FIG. 5 and FIG. 6, in the conventional concept shown in FIG. 5 and the equation (2), the motor capacity is excessive, and
There is a problem that the cost increases and the motor and the inverter device become larger.

Accordingly, an object of the present invention is to provide a hydraulic device capable of achieving matching between an operating range required for a hydraulic pump and an operating area of a motor, reducing motor capacity, and achieving cost reduction and downsizing. It is in.

[0017]

Means for achieving the above object will be described in detail. In general, the generated torque τM of a variable speed motor controlled by an inverter can be expressed as τM∝φf · iτ (10) where the field flux linkage number φf and the torque component current are iτ. The back electromotive voltage eM can be expressed as eM∝φf · ω (20), where ω is the rotational angular velocity of the motor. Here, in order to increase the motor torque τM, it can be seen from equation (10) that φf should be increased. Further, it can be seen from the equation (20) that when such a setting is made, the rate of increase of the back electromotive voltage eM of the variable speed motor with the rotation speed increases. That is, the field flux linkage number φf
Is set to a large value, the back electromotive voltage eM exceeds the maximum voltage of the inverter output at a lower speed, causing a disadvantage that current cannot flow to the motor. The maximum value of the output voltage of the inverter is determined by the DC voltage, and when this DC voltage is supplied from a capacitor input type diode rectifier circuit, it is determined by the (AC) power supply voltage to which the rectifier circuit is connected. To avoid the above inconvenience, φf is set small and iτ is increased. The phase of the output waveform of the inverter is controlled to reduce φf. However, in the former, the current density of the stator slot for mounting the motor winding increases with the increase of iτ, and a problem of heat generation occurs. When the slot area is increased and the current density is reduced, the motor is inevitably increased in size, and further, as the output current of the inverter increases, the rating of the switching element also increases. Therefore, the size and cost of the apparatus are increased. On the other hand, in the latter, the number of rotations of the field magnetic flux linkage φf is reduced by the phase control of the inverter waveform at a rotation speed at which the motor current cannot flow due to an increase in the back electromotive voltage (hereinafter, referred to as flux weakening control).
Therefore, the generated torque decreases. In the operation of the clamp, when the variable speed motor is accelerated to increase the flow rate, the torque required for the motor is reduced accordingly. By matching these two characteristics, a desired torque-rotation speed characteristic of the hydraulic pump can be obtained only by controlling the waveform phase of the inverter without increasing the size of the motor as in the former method. In order to achieve the above object, a hydraulic device according to the first aspect of the present invention is a hydraulic device that drives a hydraulic pump by a variable speed motor controlled by an inverter. It is characterized in that the inverter is controlled in order to reduce the generated back electromotive voltage. According to the first aspect of the present invention, the motor back electromotive voltage can be reduced by controlling the inverter so as to reduce the back electromotive voltage generated in the variable speed motor as the flow rate of the hydraulic pump increases. As shown, (torque-rotation speed)
In rectangular coordinates, an inversely proportional operating area can be realized. Therefore, according to the first aspect of the present invention, for example, an operation range matching the operation of the lathe clamp can be realized, the motor capacity can be reduced, and the cost and size can be reduced. The hydraulic device according to the second aspect of the present invention
A hydraulic device for driving a hydraulic pump by a motor driven by an inverter, wherein the motor is a brushless DC motor of an embedded magnet structure type.

According to the second aspect of the present invention, a brushless DC motor having an embedded magnet structure is employed as the motor.
This brushless DC motor of the embedded magnet structure type can reduce the motor back electromotive voltage by the magnetic flux weakening control, and as shown in FIG. 3, realizes an inversely proportional curve-shaped operation area in (torque-rotation speed) orthogonal coordinates. it can.

Therefore, according to the brushless DC motor of the embedded magnet structure type, for example, it is possible to realize an operation range matching the operation of the lathe clamp (standby → hold, hold → standby), and reduce the motor capacity. Thus, cost reduction and miniaturization can be achieved.

On the other hand, in the surface magnet type brushless DC motor, the effect of the magnetic flux weakening control is small in principle, and the increase of the motor back electromotive voltage due to the increase of the motor rotation speed cannot be sufficiently suppressed. Therefore, (torque-
(Rotation speed) In the rectangular coordinates, as shown in FIG. 4, in a clamp having a substantially trapezoidal operation region having a peak at the maximum torque and a maximum rotation speed point G3, and having a very small torque in the transition state, The motor capacity may be excessive.

According to a third aspect of the present invention, there is provided a hydraulic device for driving a hydraulic pump by a motor driven by an inverter, wherein the motor is a switch reluctance motor.

In the third aspect of the present invention, a switched reluctance motor is employed as the motor. In this switch reluctance motor, the motor back electromotive voltage can be reduced by the magnetic flux weakening control, and as shown in FIG. 3, an operation region having an inversely proportional curve can be realized in (torque-rotational speed) orthogonal coordinates. Therefore, according to this switch reluctance motor, for example, the (standby →
It is possible to realize an operation range that matches the operation of (hold, hold → standby), reduce the motor capacity, and achieve cost reduction and miniaturization.

According to a fourth aspect of the present invention, there is provided a hydraulic device for driving a hydraulic pump by a motor driven by an inverter, wherein the motor is an induction motor.

In the present invention, an induction motor is used as the motor. In this induction motor, the motor back electromotive voltage can be reduced by the flux-weakening control, and as shown in FIG. 3, an operation region having an inversely proportional curve can be realized in (torque-rotational speed) orthogonal coordinates. Therefore, according to this induction motor, for example, it is possible to realize an operation range that matches the operation of the lathe clamp (standby → hold, hold → standby), reduce the motor capacity, and achieve cost reduction and miniaturization.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 shows the structure of a switch reluctance motor 1 provided in an embodiment of the hydraulic apparatus of the present invention.
The hydraulic pump driven by the switch reluctance motor 1, the inverter driving the motor 1, and the control system have the same configuration as the inverter hydraulic pump device shown in FIG.

This switch reluctance motor 1
The outer stator 2 has twelve salient poles 3 and the inner rotor 5 has eight salient poles 7. The switch reluctance motor 1 rotates the rotor 5 by a rotating magnetic field generated in the stator 2.

As shown in the (torque-rotational speed) characteristic of FIG. 3, the switched reluctance motor 1 has a substantially triangular shape in which the inversely proportional region in which the maximum torque that can be generated decreases as the rotational speed increases becomes large. It has a shaped driving area. Therefore, this switch reluctance motor 1 can realize an operation area matching the (flow-pressure) locus of the hydraulic pump during the (hold-open) operation of the clamp as shown in FIG. Therefore, according to the hydraulic device of this embodiment, the motor capacity can be reduced, and the cost and size can be reduced.

It should be noted that a brushless DC motor 21 of an embedded magnet structure type shown in FIG. 2 may be employed in place of the switch reluctance motor 1 of the above embodiment. The brushless DC motor 21 includes a magnet 23 embedded and mounted in a rotor 22 and a stator 25 for generating a rotating magnetic field.
It is composed of The brushless DC motor 21 having this structure can obtain the maximum torque by utilizing the magnet torque and the reluctance torque. The magnet torque is a torque obtained by the magnet 23 mounted on the rotor 22 and the winding current, and the reluctance torque is a torque obtained by the core portion of the rotor 22 and the winding current. .

The brushless DC motor 21 of the embedded magnet type can reduce the motor back electromotive voltage by the magnetic flux weakening control, and like the switch reluctance motor 1,
FIG. 4 shows a characteristic (torque-rotational speed) of a substantially triangular operation area shown in FIG. Therefore, it is possible to realize an operation range that matches the operation of the lathe clamp (standby → hold, hold → standby), reduce the motor capacity, and achieve cost reduction and miniaturization.

Further, an induction motor may be used instead of the above-described brushless DC motor 21 of the embedded magnet type. This induction motor also exhibits an inversely proportional (torque-rotational speed) characteristic shown in FIG.
An operation range that matches the operation (hold, hold → standby) can be realized.

The brushless DC motor 21 of the embedded magnet type is more expensive than the switch reluctance motor 1 and the induction motor, but has the highest efficiency, so that energy can be saved particularly. On the other hand, the switch reluctance motor 1 is the cheapest of the three, and has an embedded magnet type brushless DC motor 21.
Next, since the efficiency is the highest, the balance in consideration of both the initial cost and the running cost is the best.

[0033]

As is apparent from the above description, the hydraulic device according to the first aspect of the present invention controls the inverter to reduce the back electromotive voltage generated in the variable speed motor as the flow rate of the hydraulic pump increases. Motor back electromotive voltage can be reduced,
As shown in FIG. 3, in the (torque-rotational speed) Cartesian coordinates, it is possible to realize an operation region having an inversely proportional curve shape. Therefore, according to the first aspect of the present invention, for example, an operation range matching the operation of the lathe clamp can be realized, the motor capacity can be reduced, and the cost and size can be reduced. The hydraulic device according to the second, third and fourth aspects of the present invention is a hydraulic device for driving a hydraulic pump by a motor driven by an inverter, wherein the motor is a brushless DC motor of an embedded magnet structure type, Reluctance motor and induction motor.

In the second, third and fourth aspects of the present invention, a brushless DC motor, a switch reluctance motor, and an induction motor having an embedded magnet structure are employed as motors. The brushless DC motor, switch reluctance motor, and induction motor of this embedded magnet structure type can reduce the motor back electromotive voltage by the magnetic flux weakening control, and as shown in FIG. An operation region having an inversely proportional curve can be realized. Therefore, according to the second, third, and fourth aspects of the present invention, it is possible to realize an operating range matching the operation of the lathe clamp (standby → hold, hold → standby) as shown in FIG. The capacity can be reduced to achieve cost reduction and miniaturization.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a switch reluctance motor constituting an embodiment of a hydraulic device of the present invention.

FIG. 2 is a diagram showing a structure of a brushless DC motor of an embedded magnet structure type adopted as a modification of the embodiment.

FIG. 3 is a (torque-rotational speed) characteristic diagram of the switch reluctance motor, the embedded magnet structure type brushless DC motor, and the induction motor employed in the embodiment.

FIG. 4 is a (torque-rotational speed) characteristic diagram of a surface magnet type brushless DC motor as a comparative example.

FIG. 5A shows the flow rate of a hydraulic pump in a conventional example.
FIG. 5B is a pressure characteristic diagram, and FIG. 5B is a torque-rotation speed characteristic diagram of a motor in a conventional example.

FIG. 6A is a flow rate-pressure characteristic diagram of a hydraulic pump corresponding to a holding-opening operation of a clamp of a lathe;
(B) is a torque-rotation speed characteristic diagram of the motor corresponding to the holding-opening operation of the clamp.

FIG. 7 is a block diagram showing a configuration of a conventional inverter hydraulic pump system.

[Explanation of symbols]

1: Switched reluctance motor, 2: stator, 3:
Salient pole, 5 ... Rotor, 7 ... Salient pole, 21 ... Brushless D
C motor, 22 ... rotor, 23 ... magnet, 25 ... stator.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3H044 AA02 CC19 DD18 DD21 3H045 AA05 AA09 AA12 AA24 BA28 BA33 CA01 CA06 CA21 DA07 5H619 AA01 BB01 BB05 BB15 BB22 BB24 PP02 PP04 PP08 5H621 AA02 BB09 GA04 GB10 H01

Claims (4)

[Claims] A hydraulic device for driving a hydraulic pump by a variable speed motor controlled by an inverter, wherein the variable speed motor (2)
A hydraulic device characterized by controlling an inverter to reduce a back electromotive voltage generated in (1, 1). 2. The hydraulic device according to claim 1, wherein the variable speed motor is a brushless DC motor of an embedded magnet structure type. 3. The hydraulic device according to claim 1, wherein the variable speed motor is a switch reluctance motor.
(1) A hydraulic device characterized by the following. 4. The hydraulic device according to claim 1, wherein the variable speed motor is an induction motor.