Automatic water level control system for an automatic washer

An automatic water level control is provided which utilizes a single pneumatic pressure sensor for detecting minimum water level, maximum water level and tub motion during agitation. Relative tub movement change during agitation and filling is used to determine an optimum water level for washing. A horizontal portion of the sensor fills with water during the tub filling process and provides the arrangement for detecting tub motion. A microprocessor stores and compares successive peak pressure signals to determine relative changes in tub motion amplitude.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an automatic liquid control system for a clothes 
washing machine and more specifically to an automatic liquid level control 
system. 
2. Description of the Prior Art 
Various methods have been proposed in the past for controlling the amount 
of liquid added to a clothes washing machine to provide an optimum amount 
of wash liquid. U.S. Pat. No. 3,065,618 and a corresponding divisional 
case U.S. Pat. No. 3,093,841 disclose the use of a torque responsive 
system which senses the torque transmitted from the agitator to the wash 
tub by means of a mercury sensor switch in combination with a circuit hold 
relay and a time delay relay to energize the water control system and to 
introduce an appropriate amount of liquid into the tub for washing 
purposes. A separate minimum water level switch 90 and a maximum water 
level switch 92 are provided, agitation beginning and continuing upon 
operation of the minimum level switch 90. If sufficient water has not been 
added at the minimum level, torque will be transmitted from the agitator 
to the basket through the clothes load closing the mercury sensor switch 
70 causing additional water to be added to the tub while agitation 
continues. The time delay relay 100 will cause water to be added for a 
preselected length of time which is followed by additional sensing of the 
mercury switch. 
U.S. Pat. No. 3,093,841 describes an improvement in the mechanics of the 
device but the functioning remains the same. 
U.S. Pat. No. 3,316,569 discloses a torque responsive pneumatically 
operated water level control for an automatic washer in which a steel ball 
is seated on an outlet from an air bleed line, the ball being unseated in 
response to excessive movement of the tub caused by a transmission of 
torque from the agitator to the tub. A pressure switch 44 controls the 
initial fill and once a minimum water level is achieved agitation 
commences and continues uninterrupted. Excessive movement of the tub 
causes the air pressure leading to the pressure switch to be reduced 
thereby resulting in additional filling of the tub with water until the 
ball remains seated due to minimal tub movement. A separate maximum water 
level control switch 57 is provided. 
U.S. Pat. No. 3,497,884 discloses an automatic water level control for a 
washer which utilizes a sensor in the drive train of the washer between 
the motor and the agitator to detect the torque transmitted between the 
motor and the agitator. Torque sensors such as mechanical or electrical 
strain gages are used. A minimum water level switch is used to fill the 
water to a first level and subsequently agitation commences and continues 
interrupted, additional filling of water being controlled by the torque 
sensor. 
U.S Pat. No. 3,498,090 discloses a torque responsive water level control 
which senses the relative motion between the tub and the perforate basket 
mounted within the tub and uses this relative motion as a control for the 
water valve. 
U.S. Pat. No. 4,503,575 discloses an automatic water level control which is 
responsive to various parameters selected by the user of the washer in 
which an incoming water volume is continuously measured by a pressure 
transducer for an initial time period as the clothes are thoroughly 
wetted. The incoming water volume is continuously measured by the pressure 
transducer until a minimum level sensor pressure switch associated with 
the tub closes signaling that a volume of liquid plus clothes load has 
been received in the washer. This volume is stored in a microprocessor 
portion of the washer control. The water fill would continue and the 
volume continuously measured until the total volume of liquid in the 
washer reaches a precomputed desired volume finding the desired amount of 
liquid optimum for washing performance for the selected type of clothes 
load. This volume is determined by computation from the initial minimum 
level volume, the fabric type and a stored table of optimum values. 
SUMMARY OF THE INVENTION 
The present invention provides a double chamber sensor and algorithm in 
which the optimum water level within the tub for a given load can be 
determined by sensing the motion of the washer tub. The sensor used is an 
air dome having two chambers. A first chamber is attached to the tub and 
has two holes through which to exchange water with the tub. This first 
chamber is normally essentially full of water when the water level in the 
tub is above a predetermined minimum height and serves as a motion sensor 
with tub movement. The mass of water alternatively forces in and out of 
the tube which connects the first chamber to the second chamber. The 
second chamber is connected via a tube to an electronic pressure 
transducer and behaves as a normal air dome. The resulting waveform 
measured at the pressure transducer includes the water level information 
and tub motion information. Any other pressure signal, such as the 
agitator pressure and resulting varying water pressure due to splashing 
etc. has been practically eliminated by the double chamber air dome. That 
is, when the tub is held rigid during agitation, the signal has a nearly 
zero ripple. 
The algorithm uses the motion data derived from the pressure transducer to 
derive the optimum water level. The peak to peak amplitude of the pressure 
signal represents the amplitude of axial rotation of the tub about the 
agitator shaft. This amplitude can be represented by X and varies with 
cloth to water density and the type of fabric. That is, X equals F(V,M,F) 
where V is the water volume, M is the load weight and F is the fabric 
type. The value of X is greater for smaller water volumes and/or larger 
load sizes and in general rises to a maximum and then falls off as more 
water is added. 
In the preferred embodiment the desired water volume is that which enables 
maximum rollover for a given load size. This correlates with water volumes 
slightly above the volume at which the peak motion occurs. A microcomputer 
can be programmed to search for this optimum point and to terminate fill.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In FIG. 1, an automatic washing machine is shown generally at 10 comprising 
a cabinet or housing 12, and an imperforate tub 14, a concentrically 
mounted basket 16 with a vertical agitator 18, a water supply 19, an 
electrically driven motor 20 operably connected via a transmission to the 
agitator 18 and a pump 24 driven by the motor. 
An openable lid 26 is provided on the cabinet top for access into the 
basket 16 and controls 28 including a presettable sequential control means 
for use in selectively operating the washing machine through a programmed 
sequence of washing, rinsing and spinning steps are provided on a console 
panel 30. 
FIG. 2 is a schematic diagram showing a means for automatically filling the 
wash tub 14 to a desired level with wash liquid. There is a hot water 
supply 34 and a cold water supply 36 which direct water to pass through 
mixing valves 38 and 40 which may be operated automatically by the washer 
controls in response to a temperature parameter selected by the user when 
operating controls 28 and in response to a measured temperature of wash 
liquid. 
During the filling operation water enters the tub through a nozzle 42 and 
the water level is monitored by a pressure sensor 44. Once the pressure 
sensor detects a water level corresponding to approximately 40 liters of 
water, the agitator 18 is caused to start an oscillation in which the 
agitator rotates about its vertical axis through a predetermined angle of, 
for example 120.degree., and then reverses its direction of travel to 
rotate in an opposite direction of the same angle. 
The agitator 18 includes a plurality of radially extending vanes 46 which 
pump water outwardly during the oscillatory motion of the agitator, but 
which also carry the clothes load with the agitator and in effect couple 
the clothes load to the agitator. Thus, the clothes load within the wash 
basket 16 is moved in an oscillatory manner. 
The clothes load provides a coupling of the agitator to the wash basket 16 
and causes the wash basket 16 to also move in an oscillatory manner 
comprising partial rotation about the vertical axis of the agitator. 
During this stage of the wash cycle, the basket is held in a locked 
position relative to the wash tub 14 and thus the tub 14 moves with the 
basket. 
As the water continues to fill the wash basket and tub, there is achieved a 
point at which the outward pumping of the water by the vanes 46 causes a 
rollover of the clothes load within the basket. This rollover is a 
movement of the clothes load radially outwardly along a lower skirt 48 of 
the agitator, upwardly along the basket wall 16, inwardly toward the 
agitator 18 and downwardly along the height of the agitator. It is known 
that increased rollover improves the washing performance and thus an 
optimum water level within the tub is one in which maximum rollover is 
achieved. 
Applicants have determined that the maximum rollover rate of the clothes 
load can be determined by detecting the rotational movement of the wash 
tub. The wash tub movement is detected by using the pressure sensor 44 
which is constructed in a novel manner. 
As seen in FIGS. 1, 2 and 3, the pressure sensor 44 comprises two separate, 
but interconnected chambers 50, 52 which are connected by a conduit 54 
which has a diameter smaller than the chambers 50, 52. The first chamber 
or reservoir 50 is mounted to the tub 14 and has two relatively small 
openings 56 which provide the liquid communication with the interior of 
the tub 14. The use of two separate vertically spaced openings 56, one 
near a bottom of the chamber and one near a top of the chamber, is done to 
let water completely fill the first chamber 50 at least to a level above a 
connection point 58 of the connecting conduit 54 and also to permit the 
chambers 50, 52 to completely drain at the end of a wash cycle. A single 
vertical slit opening would also provide the same function. 
The connecting conduit 54 enters at a bottom point 60 of the second chamber 
52 which is at an elevated position relative to the connecting conduit 54. 
Another conduit 62 connects at top opening 64 of the second chamber 52 and 
is connected to an electronic pneumatic pressure transducer 64 which 
provides as an output a square wave whose frequency is a function of 
pressure and sends a signal to a microprocessor 68. Alternatively, an 
analog to digital converter could be used if the output of the transducer 
is an analog signal. 
As the water level within the tub 14 increases, the first chamber 50 will 
fill with water and water will pass through conduit 54 to partially fill 
the second chamber 52. Because air is trapped in the second chamber 52, as 
the water level in the tub increases, the trapped air within the second 
chamber 52 and conduit 62 will become increasingly pressurized and this is 
reflected by the signal sent from the pressure transducer 64 to the 
microprocessor 68. In the initial filling step of the washer, this 
pressure sensor 44 detects the water level in a static mode and is used to 
detect an initial or minimum fill of approximately 40 liters. 
Once the initial fill amount has been achieved, the microprocessor 68 
causes the motor 20 to be energized to oscillate the agitator 18 and, as 
mentioned above, the tub 14 also begins to oscillate. The connecting 
conduit 54 between the two chambers 50 and 52 has a horizontal component 
54A which is mounted to the tub below the second chamber 52 and below the 
minimum fill level. As the tub rotates back and forth, the water in this 
conduit is caused to move back and forth relative to the conduit due to 
inertia, thereby causing an oscillating signal to be sent from the 
pressure transducer 64 to the microprocessor. 
FIG. 4 illustrates the oscillating signal of the pressure transducer 64. 
The oscillating continuous line 70 represents the amplitude of the 
oscillating motion of the tub as a predetermined additional amount of 
water is added to the interior of the tub. A central dashed line 72 
represents the actual water level within the tub and a dotted line or 
curve 74 connecting the peak oscillation points of line 70 permits a 
determination of the optimum water level. 
It has been determined that for at least some wash speeds, as the water 
level increases and the clothes begin their rollover, the coupling between 
the agitator and basket is reduced thereby resulting in less oscillatory 
motion of the basket and tub. The peak to peak curve is illustrated in 
FIG. 5 for varying sized loads and it is seen that the degree of coupling 
and thus motion increases as water volume increases up to a certain point 
for each size load and then decreases after the maximum point. Applicants 
have determined that the optimum water volume for a given sized load is 
that water volume which is slightly greater than the water volume which 
results in maximum tub motion. Addition of water beyond this optimum value 
does not appreciably increase the number of rollovers in a given time 
period (and may decrease the number for small loads) and therefore this 
extra water is not necessary. 
During the addition of water after the initial fill agitation continues and 
the microprocessor 68 stores and compares successive peaks of the 
oscillating signal 70 to determined the slope of the peak to peak curve 74 
which represents the relative changes in amplitude of the tub rotation. 
During this sampling period the size of the load can be determined with 
some degree of accuracy in that loads of different sizes have distinctly 
different curves as is illustrated in FIG. 5. For example, a light load of 
approximately three pounds reaches a peak with a water volume 
substantially less than that required to produce a peak motion with a 
medium load of about six pounds. The medium load in turn has a peak motion 
at a lesser water volume than that of a heavy load which would be in the 
range of nine to twelve pounds. 
Thus, with a light load situation, the sampling during the additional 
filling step would detect a slope change from positive to negative 
indicating that an optimum water volume had been achieved with a 
relatively small addition, for example 10 liters. The water fill would be 
terminated and the wash cycle would continue with agitation at that water 
level. Sensing and comparison of the relative tub motion would continue 
for some preselected period of time so that in the event the user added 
clothes to the load during the initial stages of the wash cycle, this 
could be detected and additional water added if needed. 
Based upon the slope of the curve 74, it may be determined that a medium 
load is present in the wash tub. If this is the case, then agitation of 
the wash load is terminated and additional water is added of a 
predetermined amount, for example on the order of ten liters, based on an 
average level change. At about the time when approximately five liters of 
water remain to be added to the tub, agitation is restarted and the peak 
to peak pressure curve 74 is again sampled to determine the slope of the 
curve. If a slope change from positive to negative is detected, then water 
fill is terminated and the wash cycle continues. If the sensed slope 
indicates that additional water is required the same agitation termination 
and fill continuation steps are repeated and again the peak to peak 
pressure curve is sensed during the final portion of the additional 
filling step. 
If, during the initial additional filling step the slope of the curve 
indicates that a heavy load is present in the tub, then a predetermined 
water volume, on the order of twenty liters, will be added to the tub 
while the agitation is terminated. Again, during the final portion of such 
filling, agitation is resumed and sampling of the pressure curve 74 is 
continued for determination of the slope as described above. 
Since the center line 72 of the oscillating curve 70 indicates actual water 
volume in the tub, the single pressure sensor is used to monitor levels 
and additions during fill and as a maximum water level sensor to terminate 
water fill at a predetermined maximum level regardless of the slope of the 
pressure curve to prevent flooding. 
It has been determined that by using a dual chamber pressure sensor and a 
necked down entrance to the connecting conduit 54, agitator motion can be 
effectively filtered out of the pressure sensor reading so that the 
resulting signal is primarily tub motion. 
Thus, the present invention provides for an automatic water level control 
in which a single sensor can be utilized to determine water levels, 
(including minimum and maximum) and tub motion and, the information 
obtained from the sensor can be utilized to admit an optimum volume of 
water to the tub while reducing agitation of the load at a less than 
optimum water volume and to terminate the water fill operation once the 
optimum water level has been achieved. 
The present invention does not rely on absolute motion values or torque 
values which are dependent on machine characteristics, that is 
characteristics of different models or characteristics of differences 
between machines due to varying tolerances, but rather the motion sensor 
detects relative changes in motion within the subject machine. Agitation 
speed changes are compensated for automatically and varying sized loads 
are treated differently rather than attempting to utilize an identical 
motion level or amplitude for every size load. That is, referring to FIG. 
5, the motion of the tub with a heavy load at an optimum water volume 
V.sub.H is much greater than the motion of the tub with a light load at 
its optimum water volume V.sub.L. Prior devices world require the relative 
motion for the heavy load to be reduced to the amount of motion for the 
light load thus resulting in too much water for large loads or too little 
water for small loads. 
The determined size of the load can be stored during the current wash cycle 
to permit appropriate amounts of water to be admitted for subsequent 
rinsing steps to reduce excessive water usage and to optimize rinse 
effectiveness. 
It will be apparent to those skilled in the art that wash characteristics 
may vary from machine to machine and from speed to speed. While the 
foregoing exemplary embodiment describes a specific algorithm for 
determining the optimum water level for a wash load, it is within the 
contemplation of the invention that the apparatus of the present invention 
may be used to measure characteristics and use algorithms other than that 
disclosed, which may be determined to be more appropriate for some 
purposes. 
As is apparent from the foregoing specification, the invention is 
susceptible of being embodied with various alterations and modifications 
which may differ particularly from those that have been described in the 
preceding specification and description. It should be understood that we 
wish to embody within the scope of the patent warranted hereon all such 
modifications as reasonably and properly come within the scope of our 
contribution to the art.