JP3332730B2 - Washing machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a washing machine and, more particularly, to a washing and dewatering tub which is provided at the bottom of the washing and dehydrating tub while discharging water from an outer tub having the washing and dewatering tub therein. The present invention relates to a washing machine that performs rinsing of laundry by rotating a rotor.

[0002]

2. Description of the Related Art Rinsing in a washing machine is roughly divided into:
There are three types of methods: so-called pool rinsing, water rinsing, and dehydrating rinsing (also called shower rinsing). The pool rinsing is a method of rinsing after a predetermined amount of water is injected into the washing and dewatering tub, stopping the water injection, and rotating a rotary blade provided at the bottom of the washing and dewatering tub. The water injection rinsing is a method of rinsing the rotating blades while discharging a predetermined amount of water into the washing and dewatering tub and discharging a part of the water in the washing and dewatering tub. In addition, dehydration rinsing is performed by first pouring water to the extent that water permeates the entire laundry, stopping water pouring, and rotating the washing and dewatering tub at high speed to perform dehydration, so that detergent water permeating the laundry is removed. This is a method of rinsing with water.

FIG. 7 is a side vertical sectional view showing the structure of a general fully automatic washing machine. An input unit 11 having operation keys is provided in front of the upper surface of the machine casing 10. An outer tub 12 is supported by four hanging rods (not shown) inside the machine casing 10, and a washing and dewatering tub 13 having a large number of dehydration holes in a peripheral wall is provided inside the outer tub 12. It is rotatably supported about a rotation shaft 14 provided on a wall. At the bottom of the washing and dewatering tub 13, a rotating blade 15 for stirring the laundry is arranged, and the rotation of the motor 16 is controlled by the motor and pulley 17, the belt 18, the main pulley 19, and the power switching mechanism 20. And transmitted to the rotary wing 15. The power switching mechanism 20 performs mechanical switching so as to rotate only the rotating blades 15 during washing and rinsing (excluding dehydration rinsing), and to rotate the washing and dewatering tub 13 and the rotating blades 15 integrally during dehydration.

A drain 21 is provided at the rear of the bottom of the outer tub 12, and the drain hose 2 is opened and closed by a drain solenoid valve 22.
Drainage is made to the outside through 3. An air trap 24 is provided at one corner of the bottom of the outer tub 12, and the air trap 24 is connected to a water level sensor 26 via a pressure hose 25. The water level sensor 26 detects the water level in the outer tub 12 by detecting the pressure of the air according to the water level.

[0005] A water supply pipe 27 provided with a water supply solenoid valve 28 is provided in the middle of the upper part of the machine frame 10, and tap water passing through the water supply pipe 27 is supplied from a water inlet 29 provided with a detergent container to a washing and washing port 29. Water is injected into the dehydration tank 13. Further, an overflow port 30 is provided at the upper rear of the outer tank 12, and the overflow port 30 is provided in the outer tank 1.
2 Drain hose 23 through drain pipe 31 formed on the back
It is connected to. Further, a circulating water passage 32 extending from the bottom wall to the top is provided at an appropriate location on the inner peripheral wall of the washing and dewatering tub 13.

[0006] The operation of the washing machine having the above configuration at the time of pouring and rinsing will be schematically described. First, the drainage electromagnetic valve 22 is closed, while the water supply electromagnetic valve 28 is opened, and tap water is injected into the washing and dewatering tub 13 from the water inlet 29. When the water level reaches a predetermined position, the motor 16 is driven to rotate, whereby the rotary wings 15 rotate, and the laundry in the washing and dewatering tub 13 is stirred. During the rotation of the rotor 15, the water injection is continued, and when the water level further rises and reaches the position of the overflow port 30, the water in the outer tank 12 overflows from the overflow port 30 and flows through the drain pipe 31. It is discharged to the outside via Therefore, while clean tap water is newly injected, the washing and dewatering tank 1
Since a part of the contaminated rinse water in 3 is discharged from the overflow port 30, the water in the washing and dewatering tub 13 gradually becomes transparent (contains no detergent).

However, for example, the external drain port to which the drain hose 23 is connected is clogged and the drainage capacity is reduced, or the amount of water supplied from the tap to the water supply pipe 27 is too large and the amount of water injected exceeds the amount of drainage. In this case, the water level in the washing and dewatering tub 13 may exceed the overflow water level at the position of the overflow port 30, and water may overflow from the washing and dewatering tub 13, that is, the outer tub 12. Therefore, in the conventional washing machine, the dangerous water level is set in advance at a position higher than the overflow water level, and when the water level detected by the water level sensor 26 reaches this dangerous water level, the water supply electromagnetic valve 28 is forcibly closed. And the injection was stopped.

[0008]

However, in the above-described washing machine, when the rotary wings 15 rotate, the outer tub 12 and the washing and dewatering tub 13 are pumped by the back blades on the back surface thereof.
Water in the gap between the washing and dewatering tub 1 is sucked downward.
3 flows into the washing and dewatering tub 13 from the opening in the bottom wall, and further rises in the circulating water channel 32, and from the upper opening thereof, the washing and dewatering tub 1
3 is released. In some cases, water is spouted from the vicinity of the center of the rotary wing 15 into the washing and dewatering tub 13. In any case, the water level of the gap between the outer tub 12 and the washing and dewatering tub 13 (hereinafter, this water level is referred to as “water level in the outer tub 12”) is lowered by the pump action, Water level rises, and there is a water level difference between the two.

Of course, the water in the washing and dewatering tub 13 is circulated to the outer tub 12 through the dewatering hole. However, since the pumping action of the rotor 15 is strong, a difference in water level cannot be avoided.
The higher the rotation speed of 5, the greater the water level difference. Also,
Normally, dehydration is performed before water rinsing. Therefore, at the start of water rinsing, laundry is stuck to the inner peripheral wall surface of the washing and dewatering tub 13 to close the dewatering holes. For this reason, especially when the amount of the laundry is large, the circulation of water from the washing and dewatering tub 13 to the outer tub 12 is interrupted, and the difference in water level is further increased.

When such a water level difference occurs, since the water level sensor 26 detects the water level in the outer tub 12, the water level in the washing and dewatering tub 13 exceeds the dangerous water level. The water level detected by the water level sensor 26 may be determined to be lower than the dangerous water level. As a result, water overflows from the upper end of the washing and dewatering tub 13, and the filled water is scattered around the washing machine by being stirred by the rotating blades 15.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a washing machine in which overflow and splash of water during rinsing with water are prevented.

[0012]

According to a first aspect of the present invention, there is provided a washing and dewatering tub in which water is discharged from an outer tub having a washing and dewatering tub therein. In addition, in a washing machine that performs rinsing by rotating a rotor provided at the bottom of the washing and dewatering tub, a) a water level detection unit provided in the outer tub, and b) a plurality of motors that rotationally drive the rotor. Rotation control means for controlling according to any of the drive control patterns of c), c) water level determination means for determining whether the water level detected by the water level detection means has reached a predetermined water level, the drive control of the rotation control means Water level determining means for changing the height of the predetermined water level according to the pattern; d) stopping water injection into the washing and dewatering tub when a result indicating that the detected water level has reached the predetermined water level is obtained by the water level determining means. Water injection control means It is characterized in.

[0013]

[0014]

[0015]

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a washing machine according to a first aspect of the present invention, a rotation control means rotationally drives a motor in accordance with a drive control pattern corresponding to the type of laundry fiber and the amount of laundry. That is, the intensity of the water flow generated in the washing / dewatering tub is adjusted by changing the drive control pattern. For example, the rotation control means performs one cycle of intermittent operation in which the motor is rotated for a first predetermined time and then stopped for a second predetermined time, and drive control of the motor is repeated so as to repeat this cycle. . The plurality of drive control patterns may have different ratios of the first predetermined time and the second predetermined time. When a strong water flow is required, the ratio of the first predetermined time is set relatively long, and when a weak water flow is required, the ratio of the second predetermined time is set relatively long.

When the water flow in the washing and dewatering tub is strong, the effect of the pump action is also strong, so that the difference between the water level in the outer tub and the water level in the washing and dewatering tub is large. Therefore, when determining the detected water level, the water level determination means lowers the height of the predetermined water level serving as a criterion for determination when the water flow is strong, and increases the height of the predetermined water level when the water flow is weak. I do. The plurality of predetermined water levels are dangerous water levels that are predetermined at a position higher than an overflow port provided at an upper portion thereof for discharging water in the outer tank to the outside. The criterion for determining the water level detected in the outer tub differs depending on the water flow, but the difference between the water level in the outer tub and the water level in the washing and dewatering tub also differs depending on the water flow. Regardless, when the water level in the washing and dewatering tub reaches substantially the same position, the water level determination means determines that the detected water level has reached the predetermined water level. And
Upon receiving the result, the water injection control means stops water injection by closing the water supply valve.

[0018]

[0019]

[0020]

[0021]

According to the washing machine of the first aspect of the present invention, the water injection is stopped when the water level in the outer tub reaches a predetermined water level, that is, a dangerous water level which differs according to the strength of the water flow. Therefore, even if the difference between the water level in the outer tub and the water level in the washing and dewatering tub is different due to the strength of the water flow, water injection is stopped when the water level in the washing and dewatering tub reaches substantially the same position. Because
In any of the water flows, it is possible to surely prevent the overflow of the water and the scatter of a large amount of water from flooding the surroundings of the washing machine.

[0022]

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

First, the electrical configuration of the washing machine according to the present invention will be described with reference to FIG. The control unit 40 is mainly configured by a microcomputer, and includes a water level determination unit 41, a rotation control unit 42, an opening / closing control unit 43, and a central processing unit 44. The water level detection signal from the water level sensor 26 is input to the water level determination unit 41, and the determination result is provided to the central processing unit 44. Further, the rotation control unit 42 and the opening / closing control unit 43
Receives a command from the central processing unit 44 and sends control signals to a motor driving unit 52 that drives the motor 16 and an electromagnetic valve driving unit 53 that drives the water supply electromagnetic valve 28 and the drainage electromagnetic valve 22, respectively. Output. A key input signal is input from the input unit 11 to the central processing unit 44, and a display control signal for monitoring the key input and the operation state is displayed on the display unit 51.
Output to The central processing unit 44 includes a memory storing an operation program, and executes each operation process of washing by receiving the key input signal and executing the operation program.

Next, the configuration of the input unit 11 and the display unit 51 will be described with reference to the external plan view of FIG. In FIG.
The input unit 11 includes a plurality of input keys, and the display unit 51 includes a plurality of LEDs for displaying a mode or a numerical value selected by operating the input keys. Only the input keys related to the characteristic operation of the washing machine according to the present invention will be described below.

The water level selection key 61 is used to change the amount of washing water at the time of rinsing or rinsing according to the amount of laundry to "extremely small", "small amount" or "low".
This is an input key for the user to select from among five modes of “medium” and “high”.
At the top of 1, the selected water level mode is illuminated. During automatic operation, an appropriate washing water level is automatically selected according to the amount of laundry detected by the load sensor, and the water level mode is displayed. The course selection key 62 is an input key for the user to select one of a plurality of washing courses in which washing time, water flow, and the like are determined in advance according to the type of laundry and the degree of dirt. The selected course is illuminated above the course selection key 62 in the display unit 51. In this laundry course, for example, a "solid" course is for washing and rinsing with a particularly strong current to wash a very dirty laundry, and a "dry" course is for washing clothes designated for dry cleaning at home. Washing and rinsing is performed with a very weak current.

Hereinafter, the processing operation of the control unit 40 at the time of water rinsing in the washing machine having the above-described configuration will be described with reference to FIGS. FIG. 4 is a schematic diagram showing a water level set in the washing and dewatering tub 13, FIG. 5 is a diagram showing an example of setting parameters for each washing course, and FIG. 6 is a waveform diagram showing an example of a drive control pattern of the motor 16. It is.

First, by closing the drainage electromagnetic valve 22 and opening the water supply electromagnetic valve 28, the washing and dewatering tub 13 is opened.
Water injection into the inside is started (step S10). At this time,
The motor 16 is stopped. After the start of water injection, the output of the water level sensor 26 is detected at predetermined time intervals, and it is determined whether or not a plurality of water levels as described below have been reached (step S1).
1). Here, if the predetermined time is too short, the water level rise during the water level determination is too small, which is not only inefficient, but also makes it difficult to secure time for performing other operation processing. On the other hand, if the time interval of the water level determination is too long, the detection of reaching the predetermined water level will be delayed. For this reason, it is preferable that this time interval is appropriately set in consideration of the range of the water injection speed, but for example, the value is set to about 0.5 seconds.

When the water injection proceeds and the detected water level reaches the washing water level L3, a control signal is output to the motor drive section 52 so that the motor 16 is intermittently operated in a predetermined cycle (step S12). Here, the washing water level is a water level previously selected from a plurality of water levels as described above.

The drive control pattern in the intermittent operation cycle of the motor 16 is determined according to the strength of the water flow generated in the washing and dewatering tub 13. Generally, one cycle is defined as rotating the motor 16 for a first predetermined time and then stopping the motor 16 for a second predetermined time.
Reversing the rotation direction for each cycle is a basic pattern. A washing course selected by operating the course selection key 62 from a plurality of drive control patterns in which the first predetermined time and the second predetermined time are appropriately determined, or
An appropriate item is selected according to the amount of laundry detected by a load amount sensor described later, and a control signal is given to the motor drive unit 52 according to the drive control pattern.

As an example of a drive control pattern corresponding to each washing course, the motor 16 is turned on / off in one cycle.
FIG. 5 shows the off-control time, and FIG. 6A shows the drive control pattern of the "standard" course. For example,
In the "standard" course, the time for one cycle of ON / OFF control of the motor 16 is set to 1.5 seconds / 0.5 seconds, and the rotation direction is reversed every cycle. That is, when the rotation direction is reversed, the motor stops for 0.5 seconds. It is preferable to change the ON / OFF control time more finely according to the amount of the laundry.

When the rotation drive of the motor 16 is started,
The timer of the first timer 45 starts (step S13).
Further, the height of the dangerous water level L5 is determined according to the strength of the water flow determined by the drive control pattern of the motor 16 (step S14). That is, as shown in FIGS. 4 and 5, a plurality of water levels (HHT1, HHT2, and HHT3) corresponding to the strength of the water flow are preset at positions higher than the overflow water level L4 corresponding to the overflow port 30. The water level corresponding to the drained water flow is selected as the dangerous water level L5. The plurality of water levels set in advance are the difference between the water level in the outer tub 12 and the water level in the washing and dewatering tub 13 caused by the strength of each water flow, and the rotation of the rotary wing 15 is stopped as described later. An appropriate position is determined in advance in consideration of the degree of decrease in the water level difference later. Basically, when the water flow is strong, the water level difference is large, so that the position is low (for example, HHT1). Conversely, when the water flow is weak, the water level difference is small, so that the position is high (for example, HHT3).

When the first timer 45 has counted 30 seconds (step S15), the cycle of the intermittent operation of the motor 16 is changed so as to lengthen the off time (step S15).
16). For example, in the case of the drive control pattern as shown in FIG. 5, the off time is set to 2.5 seconds except for the case of a weak water flow having a long off time. That is, the cycle of strong water flow is 2
Seconds / 2.5 seconds, the standard water flow cycle is 1.5 seconds / 2.
It is changed to 5 seconds (see FIG. 6B).

As described above, while the rotary blade 15 is rotating, the difference between the water level in the outer tub 12 and the water level in the washing and dewatering tub 13 is large due to the pumping action of the back blade.
The water level difference decreases as the water flow becomes gentle due to the stoppage of 5. Therefore, the longer the stop time of the rotary blade 15, the smaller the water level difference, and the water level detected by the water level sensor 26 approaches the actual water level in the washing and dewatering tub 13. For example, the off time is set to 2.
When extended to 5 seconds, the water level determination performed at 0.5 second intervals is performed at least five times during the off period of one cycle. Since the water level difference decreases with time after the motor 16 is controlled to be turned off, an accurate water level determination reflecting the water level in the washing and dewatering tub 13 is performed in the latter half of the five determinations. I can do it.

In steps S15 and S16,
The reason for changing the intermittent operation cycle 30 seconds after the start of the rotation of the rotor 15 is as follows. That is, extending the off-time of the motor 16 as described above is useful for accurately determining the water level.
Since the water flow is weaker than before, the rinsing performance is degraded. Therefore, in order to accurately determine whether or not the rinsing performance has reached the dangerous water level L5 as much as possible, the off-time is required until the water level in the washing and dewatering tub 13 reaches the vicinity of the dangerous water level L5. Motor 1 in short intermittent operation cycle
It is desirable to drive the motor 16 in an intermittent operation cycle with a long off-time after driving the motor 6 and near the dangerous water level L5. According to the above-described processing, the rotary wing 15
Rinsing performance is ensured for 30 seconds after
Thereafter, the stopping time of the rotary wing 15 becomes longer, the accuracy of the water level determination increases, and when the dangerous water level L5 is reached, it is quickly detected.

Since the rising rate of the water level actually depends on the flow rate of the injected water, the time required for changing the cycle of the intermittent operation in accordance with the flow rate of the injected water is required to improve the rinsing performance. It is preferable to change. As a configuration for this, for example, two levels of water levels are set in advance at a position lower than the washing water level L3, and the water injection flow rate is calculated by measuring the difference between the two water levels after the start of water injection. The time until the intermittent operation cycle is changed may be determined according to the flow rate of water injection.

By rotating the A motor 16, the rotor 15 rotates and the laundry in the washing and dewatering tub 13 is agitated. Thereafter, however, the water is continuously injected, and the water level further rises and the overflow water level increases. When the water reaches L4, discharge of water from the overflow port 30 starts.

It is determined whether or not the water level detected by the water level sensor 26 has reached the previously selected dangerous water level L5 (step S17). If the detected water level has not reached the dangerous water level L5, the flow proceeds to step S18. Then, the timer of the first timer 45 is checked to determine whether or not a predetermined rinsing time has elapsed. If the predetermined rinsing time, for example, 3 minutes, has not elapsed, the process returns to step S17, and it is determined whether the detected water level has repeatedly reached the dangerous water level L5. Step S1
If the predetermined rinsing time has elapsed at 8, the water supply electromagnetic valve 28 is closed, the rotation of the motor 16 is stopped, and the water injection rinsing is stopped.

On the other hand, if the detected water level has reached the dangerous water level L5 in step S17, the flow proceeds to step S19, in which the water supply is temporarily stopped by closing the water supply electromagnetic valve 28. At the same time, the second timer 46 starts counting time (step S20). The time of the second timer 46 is 3
When 0 second has elapsed, the process proceeds from step S21 to S23, and it is determined whether or not the detected water level has dropped below a water level L6 (not shown in FIG. 4) set at a position 20 mm lower than the dangerous water level L5. If the detected water level is equal to or lower than the water level L6, the water supply electromagnetic valve 28 is opened again to restart water injection (step S24). If the timer of the first timer 45 has passed the predetermined rinsing time before the detected water level falls below the water level L6, the process proceeds from step S23 to step S25, in which the rotation of the motor 16 is stopped to end the water rinsing.

After the water supply solenoid valve 28 is opened in step S24 and water injection is resumed, the flow returns to step S17 to monitor again so that the water level does not exceed the dangerous water level L5.

If the timer of the first timer 45 has passed a predetermined rinsing time before the timer of the second timer 46 reaches 30 seconds in step S21, the process proceeds to step S21.
To S22, the rotation of the motor 16 is stopped (the water supply electromagnetic valve 28 is in a closed state), and the water injection rinse is terminated.

In the above embodiment, the detection of the detected water level is performed at regular time intervals that are asynchronous with the drive control cycle of the motor 16. That is, the water level is determined even while the motor 16 is rotating. However, as described above, when the rotating blade 15 rotates, the water level in the outer tub 12 decreases, so that it is possible to quickly detect that the dangerous water level L5 has been reached during the period when the rotating blade 15 is stopped. . Therefore, in the cycle of the drive control of the motor 16, the water level may be determined at an appropriate time within the off-control of the motor 16. In this case, it is preferable to perform the water level determination at a time as long as possible after the motor 16 is turned off. Therefore, for example, 0.5 seconds (or more) than when the motor 16 shifts from the off state to the on state. It is better to make the water level judgment before (shorter time).

By the way, in the washing machine of the above embodiment, the height of the dangerous water level L5 is changed according to the strength of the water flow.
The difference between the water level in the outer tub 12 and the water level in the washing and dewatering tub 13 is also affected by the amount of the laundry. That is, as described above, when the amount of the laundry is large, the circulation of the water from the washing / dewatering tub 13 to the outer tub 12 through the dewatering hole stagnates, and the water level difference increases. Accordingly, a load amount sensor for detecting the amount of laundry is provided, and the dangerous water level L is determined according to the load amount.
It is also possible to adopt a configuration in which the height of 5 is selected.

This load amount sensor can also be used as a load amount sensor used for determining the washing water level according to the amount of the laundry put into the washing and dewatering tub 13 when executing the automatic operation. it can. The detection of the load amount by the load amount sensor is performed, for example, in the following procedure.

First, an appropriate amount of water (for example, up to the "minimum" water level, which is the lowest washing water level), is applied to the washing and dewatering tub 13.
After that, the rotation control unit 42 outputs a control signal to the motor drive unit 52 so that a predetermined voltage is applied to the motor 16 for a short time. As a result, the rotor 15 rotates instantaneously, but as the load on the rotor 15 increases, that is, as the amount of laundry increases, the rotor 15 stops earlier. Therefore, a pulse signal corresponding to the rotation of the motor 16 is obtained from a pulse generator provided in association with the motor 16, and the central processing unit 44 counts the number of the pulse signals. Then, the magnitude of the load amount is determined according to the count value.

For example, the central processing unit 44 classifies the load amount into three levels of “large”, “medium” and “small” according to the pulse count result, and sets the washing water level to “high”, In addition to "medium" and "low", the height of the dangerous water level L5 is set to "HHT1" or "HHT2" according to the load.
And "HHT3". That is, the selection of the dangerous water level L5 in step S14 of the flowchart of FIG. 3 is performed based on the load amount, and “HHT1,” “HHT2” and “HHT2” corresponding to the “large”, “medium” and “small” load amounts. "HHT
"3" is selected as the dangerous water level L5.

The embodiment described above is merely an example, and it is apparent that changes and modifications can be made as appropriate within the scope of the present invention.

[Brief description of the drawings]

FIG. 1 is an electric configuration diagram of a washing machine according to the present invention.

FIG. 2 is an external plan view of an operation panel of the washing machine according to the present invention.

FIG. 3 is a control flowchart of water rinsing in the washing machine.

FIG. 4 is a schematic view showing a water level set in a washing and dewatering tub.

FIG. 5 is a diagram showing an example of setting parameters for each washing course.

FIG. 6 is a waveform chart showing an example of a motor drive control pattern.

FIG. 7 is a side longitudinal sectional view showing a configuration of a general washing machine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 ... Outer tub 13 ... Washing and dehydration tub 15 ... Rotating blade 16 ... Motor 24 ... Air trap 25 ... Pressure hose 26 ... Water level sensor 28 ... Water supply solenoid valve 29 ... Filling port 30 ... Overflow port 40 ... Control unit 41 ... Water level judgment Unit 42: Rotation control unit 43: Open / close control unit 44: Central processing unit 52: Motor drive unit 53: Solenoid valve drive unit

Continuation of front page (56) References JP 8-33787 (JP, A) JP 8-889 (JP, A) JP 5-15695 (JP, A) JP 8-879 (JP) , A) JP-A-1-94895 (JP, A) JP-A-7-116378 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D06F 33/00-39/08

Claims (1)

(57) [Claims] 1. A method for injecting water into a washing and dewatering tub while draining water from an outer tub in which the washing and dewatering tub is provided, and rotating a rotating blade provided at a bottom portion of the washing and dewatering tub to perform rinsing. A) a water level detecting means provided in the outer tub, b) a rotation control means for controlling a motor for rotatingly driving the rotary wings according to any of a plurality of drive control patterns, and c) the water level detection. Water level determination means for determining whether the water level detected by the means has reached a predetermined water level, wherein the water level determination means changes the height of the predetermined water level according to a drive control pattern of the rotation control means; d) A water washing control unit that stops water injection into the washing and dewatering tub when a result indicating that the detected water level has reached a predetermined water level is obtained by the water level determining means.