JPH0720393B2 - High-efficiency operation method for fluid transmission - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-efficiency operating method of a fluid variable speed device which is a combination of an induction motor and a fluid transmission such as a fluid coupling or a wet multi-plate clutch.

[Prior Art] As a fluid variable speed device of this type, there has conventionally been the one shown in FIG. FIG. 1 shows a conventional typical fluid variable speed device using a wet multi-plate clutch as a fluid transmission. 1 is a wet multi-plate clutch, 2 is an induction motor, 3 is a driven machine (fluid driven machine). In the example, a blower), 4 is a rotation speed (speed) detector, 5 is a rotation speed (speed) setting device, 6 is a comparison calculation circuit unit, 7 is a hydraulic pressure command circuit unit, 8 is a hydraulic operation motor, and 9 is a
Is a valve, F is a fluid (oil) source, and AC is a three-phase AC power supply.

In this configuration, the rotation speed of the output shaft 1A of the clutch 1 is detected by the rotation speed detector 4. The rotation speed signal output from the rotation speed detector 4 is compared and calculated with the set value of the rotation speed setting device 5 by the comparison calculation circuit unit 6, and the difference signal (speed adjustment signal) is supplied to the hydraulic pressure command circuit unit 7. The hydraulic pressure command circuit section 7 drives the hydraulic operation motor 8 so that the input difference signal becomes zero, whereby the opening degree of the hydraulic valve 9 is adjusted, the slip between the clutch plates, and hence the output shaft 1A. The rotation speed is controlled to the above set value.

[Problems to be solved by the invention]

When the fluid-driven machine 3 is a blower as in this example, the air volume is proportional to the number of revolutions, but the required power is three revolutions.
Proportional to the square. On the other hand, when a wet multi-plate clutch or a fluid coupling is used for the rotation speed control, its efficiency is proportional to the speed. Therefore, the required output of the induction motor 2 used for such a drive system depends on the rotation speed of the fluid driven machine 3. It changes with the square.

However, in the conventional motor, since the induction motor is operated at the rated voltage, its iron loss and excitation loss are constant even if the load is reduced, so in a light load region, low efficiency and low power factor operation are performed. There was a problem.

The present invention has been made to solve the above problems,
An object of the present invention is to provide a high-efficiency operating method for a fluid transmission capable of operating an induction motor at a maximum efficiency even in a light load region and increasing operating efficiency as compared with the conventional method.

[Means for solving problems]

In order to achieve the above object, the present invention obtains an optimum voltage that minimizes the input of the induction motor at full load in advance, calculates the input voltage of the induction motor from the rotation speed, and calculates the load factor of the induction motor. The voltage is controlled to a value obtained by multiplying the square root of the load factor by the optimum voltage.

[Action]

According to the present invention, since the primary terminal voltage of the induction motor changes in proportion to the load factor of the induction motor, the operating efficiency under light load is significantly improved.

Example of Invention

FIG. 1 shows an embodiment of the present invention. In the figure, 10 is a load factor calculation circuit for sending a voltage control signal to an ignition circuit 11. 12 is a phase control circuit (triac)
It is provided between the AC power supply AC and the input terminal of the induction motor 2. The load ratio calculation circuit 10 is guided by the speed adjustment signal generated by the comparison calculation circuit unit 6 and receives a load ratio l described later.
To calculate the voltage control signal E proportional to the square root of the load factor l.
Is sent. The ignition circuit 11 receives the voltage control signal and supplies the ignition angle control signal to the triac 12, which applies an AC voltage so that the terminal voltage V of the induction motor 2 changes in proportion to the square root of the load factor l. Phase control.

Now, when the reference voltage Vo is represented as 1, the voltage ratio (the voltage ratio between the terminal voltage V of the induction motor 2 and the reference voltage Vo) is e, and the total load (rated load) is 1 When the load factor is 1, the loss WT of the induction motor 2 is expressed by the following equation.

WT = Wmo + Wcoe ² ＋ 3r ₁ I ² ₂₀ e ^-2 l ² ＋ 3r ₁ I ² moe ² ＋ 3r ₂ I ² ₂₀ e ^-2 l ² (1) However, the first term of the above equation is mechanical loss, the second term Is the iron loss third term,
The fourth term is the primary copper loss, and the fifth term is the secondary copper loss. Wmo, Wco
Are the mechanical loss and iron loss values at the reference voltage, I ₂₀ , and I, respectively.
mo is the reference voltage, the secondary current at the rated load, and the exciting current, respectively.

When the above equation (1) is differentiated by voltage, Now, assuming that the voltage at which the loss WT is minimum at the rated load (l = 1) is found and the voltage is set to the reference voltage Vo = 1, the following formula is established at this point.

Wco + 3r ₁ I ² mo≈3 (r ₁ + r ₂ ) I ² ₂₀ (3) Therefore, e ^-2 l = 1, that is, the terminal voltage V of the induction motor 2 is proportional to the square root of the load factor l. If changed, the induction motor 2 can be operated at the highest efficiency point at the load factor.

By the way, the load factor (the required power of the induction motor 2) is proportional to the square of the rotation speed of the output shaft 1A of the wet multi-plate clutch 1. Generally, the rated output of the electric motor has a margin of 10 to 20% of the required power of the blower. Therefore, this margin ratio should be confirmed during the combination test of the two, and the load factor calculation circuit 10
If the calculation of is corrected, the load factor 1 can be uniquely determined for the rotation speed.

Further, the voltage Vo that causes the maximum efficiency of the electric motor may be measured by changing the terminal voltage by applying a full load during factory test.

Since the load factor calculating circuit 10 in the above embodiment calculates the load factor 1 based on the rotation speed of the output shaft 1A and creates the voltage control signal E in which the voltage Vo is changed by the square root of the load factor 1, The induction motor 2 can always be operated near the maximum efficiency point, and a significant power saving effect can be obtained.

FIG. 2 shows an example A of loss improvement when the present invention is implemented.
The case of KwHp is shown in comparison with the conventional case B.

As is clear from this figure, it is understood that particularly at a light load, a large power saving effect can be obtained.

〔The invention's effect〕

As described above, the present invention is a simple method in which the primary terminal voltage of the induction motor is changed in proportion to the load factor, but the induction motor is always operated near the maximum efficiency point even if the load changes. Because it is possible, especially in the light load area,
Compared with the conventional one, it is possible to obtain a significant power saving effect, and since the power factor is as high as that at the rated time, the input KVA at light load can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram of a blower control device embodying the present invention, FIG. 2 is a load factor-motor loss characteristic diagram, and FIG. 3 is a block diagram showing a conventional blower control device. In the figure, 1 ... Wet multi-plate clutch, 2 ... Induction motor, 3 ... Blower, 4 ... Rotation speed (speed) detector, 5 ...
… Rotation speed (speed) setter, 6 …… Comparison operation circuit, 7 ・ ・ ・
… Hydraulic pressure command circuit section, 10 …… Load factor calculation circuit, 11 …… Firing circuit, 12 …… Phase control circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A fluid variable speed device for controlling the amount of fluid supplied to the fluid transmission such that the number of revolutions of a fluid transmission driven by an induction motor is compared with a set speed so that they match each other. The optimum voltage that minimizes the input of the induction motor at full load is obtained, and the input voltage of the induction motor is
A high-efficiency operating method for a fluid transmission, comprising: calculating a load factor of an induction motor based on the rotational speed and performing voltage control to a value obtained by multiplying a square root of the load factor by the optimum voltage.