Washing machine with dynamic water inlet control arrangement

Dishwashing machine including a valve (7) that is open during a water inlet phase and a circulation pump (11) that is energized during the water inlet phase. A control arrangement is driven by a signal (V) that is proportional to the outlet pressure of the circulation pump so as to close the inlet valve (7) when signal variations decrease below a pre-determined value. The circulation pump (11) is driven by a single-phase asynchronous motor (14) with a phase-shift capacitor (15) from which the signal (V) is derived. A further signal (U) can be derived from the capacitor (15) to drive the control arrangement so as to determine the correct de-energization of a discharge pump (18).

BACKGROUND OF THE INVENTION 
The present invention refers to a washing machine, such as clothes washing 
or dishwashing machine, of the type in which water being filled into a 
wash vessel is circulated in a closed circuit by a circulation pump and is 
finally let out by means of a discharge pump. In particular, the present 
invention refers to a washing machine provided with a control arrangement 
which is adapted to precisely determine the amount of water which is let 
into the wash vessel. 
A dynamic control arrangement is known, for instance from the disclosure in 
EP-A-O 118 719, that is adapted to control the operation of a water inlet 
valve of a dishwashing machine wherein the circulation pump is operating 
during the water inlet phase to be controlled. A specially provided 
transducer means delivers a control signal that is proportional to the 
delivery pressure of the pump and substantially comprises a direct-current 
component and damped oscillating component. When the amplitude of the 
variations of the control signal decreases below a predetermined value, 
the water inlet valve is shut off. 
Such a control arrangement may operate on the basis of any physical 
quantity that is representative of the delivery pressure of the water 
circulating pump. For instance, such a quantity may be correlated to the 
flow rate or the rotating speed of the pump, or to the active power input 
of the driving motor of the pump. In particular, the quantity may be the 
phase shift between the voltage and the current of said motor. 
In principle, such a control arrangement enables water fill phases to be 
carried out which are optimally and very accurately controlled regardless 
of the variables that may be introduced by the water supply system, such 
as for instance the delivery pressure of the water supply mains. On the 
other hand, such a control arrangement calls for the utilization of 
relatively expensive electronic components. In particular, it requires the 
use of a transducer of a particularly sophisticated type, which may not be 
reliable. Furthermore, the need arises for the application of special 
means adapted to amplify the control signal in order to provide an 
adequate definition of the same signa. 
SUMMARY OF THE INVENTION 
It would therefore be desirable, and is a purpose of the present invention, 
to provide a washing machine comprising a dynamic water inlet control 
arrangement, which is particularly accurate in its operation, although 
making use of only a small number of substantially simple, reliable and 
unexpensive component parts. 
It is a further purpose of the present invention to provide a washing 
machine of the above-cited kind, in which the dynamic water inlet control 
arrangement is capable of controlling also the operation of the discharge 
pump in a simple, but particularly effective manner. 
According to the present invention, such aims are reached in a washing 
machine with a dynamic water inlet control arrangement having the 
characteristics and features as recited in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With particular reference to FIG. 1, the washing machine described can be a 
clothes washing machine, but is preferably a household-type dishwashing 
machine. A wash vessel 5 can be supplied with mains water through a 
conduit 6 provided with an electromagnetic valve 7, or the like, 
controlled by a program sequence control unit 8 of the washing machine. 
In a known manner, the wash vessel 5 houses an upper rotating spray arm 9 
and a lower rotating spray arm 10. The spray arms are adapted to be 
supplied by a circulation pump 11 with water that the circulation pump 
takes in from the bottom of the wash vessel 5. In particular, the rotating 
spray arms 9 and 10 are connected with the delivery side (or outlet) 12 of 
the circulation pump 11 through appropriate conduits 13, 13'. 
The circulation pump 11 is driven by an electric motor 14, which is 
controlled by the program sequence control unit 8 of the machine, 
according to one feature of the present invention, the motor 14 is a 
single-phase asynchronous motor of the type adapted to be started to 
rotate by means of phase-shifting capacitor 15. As described in a more 
detailed manner further on, opposite terminals 16, 17 of the capacitor 15 
are preferably connected to corresponding driving inputs of the program 
sequence control unit 8. 
In a known manner, the dishwashing machine also includes a discharge pump 
18. The discharge pump is controlled by the program sequence control unit 
8 of the machine and is adapted to deliver to an outlet pipe 19 the water 
that had previously been filled into the wash vessel 5 of the machine. 
In a preferred manner, the discharge pump 18 is arranged so as to be driven 
by the asynchronous driving motor 14. For driving the two pumps 11, 18, 
the motor 14 is a reversing type, such as described in EP-A-0 268 835. In 
particular, the circulation pump 11 and the discharge pump 18 are capable 
of being driven selectively when the driving shaft of the motor 14 rotates 
in a first or in a second direction, respectively. In other words, when 
the motor 14 is driven to rotate in one direction, only the circulation 
pump 11 will be operating. On the contrary, when the motor 14 is caused to 
rotate in the opposite direction, only the discharge pump 18 will be 
driven. 
With reference also to FIG. 2, the asynchronous motor 14 includes a pair of 
stator windings 20, 21. An end of the pair is connected to an energization 
terminal 22. The opposite end of the one winding 20 is connected to a 
second energization terminal 23 (which in a preferred manner is connected 
to ground), as well as to one terminal 16 of the capacitor 15. 
The opposite end of the other winding 21 is connected to the opposite 
terminal 17 of the phase-shift capacitor 15. A substantially sine-wave 
supply voltage, such as for instance 220 VAC, is applied across the 
energization terminals 22 and 23. The second terminal 17 of the 
phase-shift capacitor 15 is connected, via an AC/DC converter 24, to a 
driving input 25 of a microprocessor 26. This microprocessor, together 
with the converter 24, forms a dynamic control arrangement, which is part 
of the program sequence control unit 8 of the machine and includes an 
output 27 that, in a known manner, is adapted to drive the electromagnetic 
or similar valve 7. 
Referring now also to FIG. 4, an example of the manner in which water is 
filled into the wash vessel 5 of the dishwashing machine is described. At 
an instant t.sub.0, the program sequence control unit 8 of the machine 
causes the electromagnetic valve 7 to open and, at an instant t.sub.1, the 
unit then causes the motor 14 to be energized. The motor 14 therefore 
starts to rotate, thereby driving the circulation pump 11 in a direction 
of rotation that is determined by the phase-shift capacitor 15. A voltage 
signal V substantially proportional to the water outlet or delivery 
pressure of the circulation pump 11 develops across the terminals 16, 17 
of the capacitors 15. Specifically, the voltage signal V is substantially 
inversely proportional to the water outlet pressure of the circulation 
pump 11. As a result, the voltage signal V tends to decrease with time, 
until, at an instant t.sub.2 at which the circulation pump 11 starts to 
prime, a damped oscillation starts to appear in the voltage signal V. The 
damped oscillation represents, in a substantially known manner, the 
operational conditions of the pump 11. 
Through the converter 24, the voltage signal V drives the microprocessor 26 
which, in a known manner thereby causes the electromagnetic valve 7 to 
close when, at an instant t.sub.3, the variations of the signal V decrease 
to a level below a pre-determined value. In other words, when the 
component parts involved are appropriately sized, the electromagnetic 
valve 7 is caused to close as soon as the smallest amount of water has 
been filled into the wash vessel 5 of the dishwashing machine as required 
to enable the circulation pump 11 to prime in an optimum manner. 
As already stressed above, this is an inherently known scheme. However, 
according to the present invention, the instant t.sub.3 is determined 
without any need for special transducer means to be employed in view of 
delivering a control signal which is proportional to the outlet or 
delivery pressure of the pump 11. The control signal V is directly derived 
(with respect to ground) at the second terminal 17 of the phase-shift 
capacitor 15 which therefore, according to the present invention, performs 
a double duty in that it starts the rotation of the motor 14 and supplies 
an appropriate control signal to the microprocessor 26. 
In addition, in a quite advantageous manner, the dynamic control 
arrangement of the washing machine according to the present invention does 
not require any amplifier for the control signal V, which is available 
across the terminals of the capacitor 15 in an already amplified form, for 
instance with a value of approximately 700 V. This is due particularly to 
the fact that, by applying a substantially sine-wave supply voltage (220 
V) to the energization terminals 22, 23, the same current I flows through 
impedances represented by the winding 21 and the capacitor 15 of the motor 
14. Correspondingly, across the terminals of the impedances 21 and 15 (an 
inductive impedance and a capacitive one, respectively) respective voltage 
drops form which are vectorially opposite with respect to each other and 
the modulus of which is directly proportional to the value of the 
respective impedances. In a normal single-phase asynchronous motor 14 the 
capacitive impedance 15 is substantially greater than the inductive 
impedance 21, therefore the absolute value of the voltage V derived at the 
terminals of the capacitor 15 is substantially amplified, as this has 
already been explained above. 
According to the present invention, therefore, the capacitor 15 also 
performs a further duty in that it amplifies the control signal V which, 
as a result, has an advantageously high definition and allows for an 
accurate driving of the dynamic control arrangement 24, 26. 
Through simple modifications, explained in greater detail with reference to 
FIG. 3, the washing machine according to the present invention can further 
be enabled to control effectively water outlet phases in which the water 
is let out of the wash vessel 5, particularly in the preferred case in 
which the circulation pump 11 and the discharge pump 18 are both driven by 
the same asynchronous motor 14, such as previously described. 
The motor 14 is reversible by a change-over switch or reversing switch 28 
controlled via a relay 29 or the like. The relay is driven by an 
additional output 30 of the microprocessor 26. The microprocessor has 
another input 31 that is connected, via another AC/DC converter 32, to the 
first terminal 16 of the phase-shift capacitor 15. In particular, the 
change-over switch 28 has a "disconnected" resting position shown in FIG. 
3 and can be selectively switched over to first and second operational or 
active positions in which the switch energizes the motor 14 via the first 
terminal 16 and the second terminal 17, respectively, of the phase-shift 
capacitor 15. 
When the change-over switch 28 is connected to the first terminal 16, the 
motor 14 is operated to rotate in a first direction of rotation, in which 
only the circulation pump 11 is operating. In this particular condition, 
the control signal V is derived at the second terminal 17 of the capacitor 
15 and drives the input 25 of the microprocessor 26 in the aforedescribed 
manner. 
When the change-over switch 28 is connected to the second terminal 17, the 
motor 14 is operated to rotate in the opposite direction of rotation, in 
which only the water discharge pump 18 is operating. In this particular 
condition, the input 31 of the microprocessor 26 is driven, via the 
converter 32, by a second voltage signal U derived at the first terminal 
16 of the phase-shift capacitor 15. 
Such a further voltage signal (indicated as U in FIG. 5) is inversely 
proportional to the water outlet pressure of the discharge pump 18. In 
particular, the voltage U reaches a given value V.sub.0 at the end of each 
water outlet phase, that is, when the discharge pump 18 starts to 
substantially unprime, thereby representing a reduced dynamic load for the 
driving motor 14. As a result, the microprocessor 26 can be easily set by 
anyone skilled in the art so as to switch the change-over switch 28 to its 
resting position when the input 31 thereof detects that the above-cited 
value V.sub.0 has been attained. Specifically, with reference to FIG. 5, 
at an instant t.sub.1 the program sequence control unit 8 operates the 
discharge pump 18 by switching the change-over switch 28 into contact with 
the second terminal 17 of the capacitor 15. The discharge pump is 
initially in an optimum priming condition and starts then to unprime in 
correspondence of an instant t.sub.2 at which the voltage U at the first 
terminal 16 reaches the above-cited value V.sub.0. At said instant 
t.sub.2, therefore, the microprocessor 26 energizes the relay 29 so as to 
switch the change-over switch 28 to its resting position. As a result, the 
discharge pump 18 stops operating. 
In traditional solutions, the water outlet phase has a fixed, 
pre-determined duration, at the end of which the discharge pump, in view 
of ensuring an adequate water outlet, keeps operating in a substantially 
unprimed state. It will be readily appreciated that this means that energy 
is thereby used to no avail and noise is undesirably generated in the 
washing machine. 
On the contrary, according to the present invention the discharge pump 18 
is operated in an efficient manner, whereby all of the main variables of 
the water flow and discharge system are duly kept into account. In 
particular, the operation of the discharge pump 18 is cut off as soon as 
the water contained in the vessel 5 is detected to have been substantially 
discharged, thereby avoiding a substantial, undesired generation of noise. 
It can be readily appreciated that the washing machine according to the 
present invention makes use of simple and reliable means to optimally 
control both the water inlet and the water outlet phases. 
It will be further appreciated that the above-described washing machine may 
undergo a number of modifications without departing from the scope of the 
present invention.