Patent Publication Number: US-2019179350-A1

Title: Dishwasher appliance having a pressure sensor

Description:
FIELD OF THE INVENTION 
     The present disclosure relates generally to dishwasher appliances, and more particularly to dishwasher appliances having features and methods for ensuring optimal fill levels. 
     BACKGROUND OF THE INVENTION 
     Dishwasher appliances generally include a tub that defines a wash chamber. Rack assemblies can be mounted within the wash chamber of the tub for receipt of articles for washing. Multiple spray assemblies can be positioned within the wash chamber for applying or directing wash fluid towards articles disposed within the rack assemblies in order to clean such articles. Dishwasher appliances are also typically equipped with at least one circulation pump for circulating fluid through the wash chamber, e.g., via one or more of the multiple spray assemblies, for washing or rinsing items contained in the wash chamber. For example, liquid can collect in a sump disposed at a bottom of the wash chamber during operation of the dishwasher appliance and the circulation pump can be operated to urge such liquid from the sump to selected spray assemblies. 
     In general, it is considered desirable for a dishwasher appliance to operate quietly. The noise level generated by the circulation pump is critical to such quiet operation. However, an undesirably high noise level may be generated if air is drawn into the circulation pump and becomes entrained in the circulated liquid. Air may be drawn into the circulation pump, for example, when the circulation pump operates at a speed that is too high relative to the rate of flow into the sump such that the liquid level in the sump is drawn down too low relative to the inlet of the circulation pump. It is also considered desirable for a dishwasher appliance to operate efficiently, for example, by using the least amount of water necessary to prime the circulation pump during the cleaning operation. Typical dishwasher appliances, however, are often configured to avoid entraining air by drawing additional water above the minimum amount required to prime the circulation pump. 
     Accordingly, dishwasher appliances that include features and methods for operating the circulation pump at an optimal speed and thereby ensuring optimal fill levels would be useful. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present disclosure provides a dishwasher appliance that includes features and methods for avoiding or minimizing air entrainment in the circulation pump without overfilling the sump. Additional aspects and advantages of the invention will be set forth in part in the following description, may be apparent from the description, or may be learned through practice of the invention. 
     In accordance with one exemplary embodiment, a method of circulating fluid in a dishwasher appliance is provided. The dishwasher appliance includes a circulation pump, a pressure sensor upstream of the circulation pump, and a diverter downstream of the circulation pump. The method includes operating the circulation pump at a first speed less than a target speed for a first amount of time. The method also includes determining a first minimum pressure value based on the first speed and a position of the diverter and monitoring a pressure upstream of the circulation pump with the pressure sensor. The method further includes operating the circulation pump at a second speed greater than the first speed when the monitored pressure continuously exceeds the first minimum pressure value for a second amount of time. The method also includes determining a second minimum pressure value based on the second speed and the position of the diverter after operating the circulation pump at the second speed for a third amount of time. 
     In accordance with another exemplary embodiment, a dishwasher appliance is provided. The dishwasher appliance includes a cabinet with a tub positioned within the cabinet. The tub defines a wash chamber for receipt of articles for washing. The dishwasher appliance also includes one or more spray assemblies and a circulation pump for circulating water to the one or more spray arm assemblies. A pressure sensor is upstream of the circulation pump and a diverter is downstream of the circulation pump. The dishwasher appliance also includes a controller communicatively coupled with the pressure sensor and the circulation pump. The controller is configured to operate the circulation pump at a first speed less than a target speed for a first amount of time, determine a first minimum pressure value based on the first speed and a position of the diverter, and monitor a pressure upstream of the circulation pump with the pressure sensor. The controller is also configured to operate the circulation pump at a second speed greater than the first speed when the monitored pressure continuously exceeds the first minimum pressure value for a second amount of time and determine a second minimum pressure value based on the second speed and the position of the diverter after operating the circulation pump at the second speed for a third amount of time. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures. 
         FIG. 1  provides a perspective view of an exemplary embodiment of a dishwasher appliance of the present disclosure with a door in a partially open position. 
         FIG. 2  provides a side, cross sectional view of the exemplary dishwasher appliance of  FIG. 1 . 
         FIG. 3  provides a cross sectional view of a circulation pump, a sump, and a pressure sensor of the dishwasher appliance of  FIGS. 1 and 2 . 
         FIG. 4  provides an enlarged view of a portion of  FIG. 3 . 
         FIG. 5  provides a flow diagram of an exemplary method according to one or more exemplary embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     As used herein, the term “article” may refer to, but need not be limited to dishes, pots, pans, silverware, and other cooking utensils and items that can be cleaned in a dishwashing appliance. The term “wash cycle” is intended to refer to one or more periods of time during which a dishwashing appliance operates while containing the articles to be washed and uses a detergent and water, preferably with agitation, to e.g., remove soil particles including food and other undesirable elements from the articles. The term “rinse cycle” is intended to refer to one or more periods of time during which the dishwashing appliance operates to remove residual soil, detergents, and other undesirable elements that were retained by the articles after completion of the wash cycle. The term “drain cycle” is intended to refer to one or more periods of time during which the dishwashing appliance operates to discharge soiled water from the dishwashing appliance. The term “wash fluid” refers to a liquid used for washing and/or rinsing the articles and is typically made up of water that may include other additives such as detergent or other treatments. Furthermore, as used herein, terms of approximation, such as “approximately,” “substantially,” or “about,” refer to being within a ten percent (10%) margin of error. 
       FIGS. 1 and 2  depict an exemplary dishwasher or dishwashing appliance  100  that may be configured in accordance with aspects of the present disclosure. For the particular embodiment of  FIGS. 1 and 2 , dishwasher  100  defines a vertical direction V, a lateral direction L, and a transverse direction T. Each of the vertical direction V, lateral direction L, and transverse direction T are mutually perpendicular to one another and form an orthogonal direction system. Dishwasher  100  includes a cabinet  102  having a tub  104  therein that defines a wash chamber  106 . As shown in  FIG. 2 , tub  104  extends between a top  107  and a bottom  108  along the vertical direction V, between a pair of side walls  110  along the lateral direction L (only one shown in  FIG. 2 ), and between a front side  111  and a rear side  112  along the transverse direction T. 
     Tub  104  includes a front opening  114  ( FIG. 1 ) and a door  116  hinged at its bottom for movement between a normally closed vertical position (shown in  FIG. 2 ), wherein the wash chamber  106  is sealed shut for washing operation and a horizontal open position for loading and unloading of articles from dishwasher  100 . Dishwasher  100  includes a door closure mechanism or assembly  118  that is used to lock and unlock door  116  for accessing and sealing wash chamber  106 . 
     As further shown in  FIG. 2 , tub side walls  110  accommodate a plurality of rack assemblies. More specifically, guide rails  120  are mounted to side walls  110  for supporting a lower rack assembly  122 , a middle rack assembly  124 , and an upper rack assembly  126 . Upper rack assembly  126  is positioned at a top portion of wash chamber  106  above middle rack assembly  124 , which is positioned above lower rack assembly  122  along the vertical direction V. Each rack assembly  122 ,  124 ,  126  is adapted for movement between an extended loading position (not shown) in which the rack is substantially positioned outside the wash chamber  106 , and a retracted position (shown in  FIGS. 1 and 2 ) in which the rack is located inside the wash chamber  106 . This is facilitated, for example, by rollers  128  mounted onto rack assemblies  122 ,  124 ,  126 , respectively. Although guide rails  120  and rollers  128  are illustrated herein as facilitating movement of the respective rack assemblies  122 ,  124 ,  126 , it should be appreciated that any suitable sliding mechanism or member may be used according to alternative embodiments. 
     Some or all of the rack assemblies  122 ,  124 ,  126  are fabricated into lattice structures including a plurality of wires or elongated members  130  (for clarity of illustration, not all elongated members making up rack assemblies  122 ,  124 ,  126  are shown in  FIG. 2 ). In this regard, rack assemblies  122 ,  124 ,  126  are generally configured for supporting articles within wash chamber  106  while allowing a flow of wash fluid to reach and impinge on those articles, e.g., during a cleaning or rinsing cycle. According to other exemplary embodiments, a silverware basket (not shown) may be removably attached to a rack assembly, e.g., lower rack assembly  122 , for placement of silverware, utensils, and the like, that are otherwise too small to be accommodated by rack  122 . 
     Dishwasher  100  further includes a plurality of spray assemblies for urging a flow of water or wash fluid onto the articles placed within wash chamber  106 . More specifically, as illustrated in  FIG. 2 , dishwasher  100  includes a lower spray arm assembly  134  disposed in a lower region  136  of wash chamber  106  and above a sump  138  so as to rotate in relatively close proximity to lower rack assembly  122 . Similarly, a mid-level spray arm assembly  140  is located in an upper region of wash chamber  106  and may be located below and in close proximity to middle rack assembly  124 . In this regard, mid-level spray arm assembly  140  is generally configured for urging a flow of wash fluid up through middle rack assembly  124  and upper rack assembly  126 . Additionally, an upper spray assembly  142  may be located above upper rack assembly  126  along the vertical direction V. In this manner, upper spray assembly  142  may be configured for urging and/or cascading a flow of wash fluid downward over rack assemblies  122 ,  124 , and  126 . As further illustrated in  FIG. 2 , upper rack assembly  126  may further define an integral spray manifold  144 , which is generally configured for urging a flow of wash fluid substantially upward along the vertical direction V through upper rack assembly  126 . 
     The various spray assemblies and manifolds described herein may be part of a fluid distribution system or fluid circulation assembly  150  for circulating water and wash fluid in tub  104 . More specifically, fluid circulation assembly  150  includes a circulation pump  152  for circulating water and wash fluid (e.g., detergent, water, and/or rinse aid) in tub  104 . Circulation pump  152  is located within sump  138  or within a machinery compartment located below sump  138  of tub  104 . Circulation pump  152  is in fluid communication with an external water supply line (not shown) and sump  138 . A water inlet valve  153  can be positioned between the external water supply line and circulation pump  152  to selectively allow water to flow from the external water supply line to circulation pump  152 . Additionally or alternatively, water inlet valve  153  can be positioned between the external water supply line and sump  138  to selectively allow water to flow from the external water supply line to sump  138 . Water inlet valve  153  can be selectively controlled to open to allow the flow of water into dishwasher  100  and can be selectively controlled to cease the flow of water into dishwasher  100 . Further, fluid circulation assembly  150  may include one or more fluid conduits or circulation piping for directing water and/or wash fluid from circulation pump  152  to the various spray assemblies and manifolds. For example, for the embodiment depicted in  FIG. 2 , a primary supply conduit  154  extends from circulation pump  152 , along rear  112  of tub  104  along the vertical direction V to supply wash fluid throughout wash chamber  106 . 
     As further illustrated in  FIG. 2 , primary supply conduit  154  is used to supply wash fluid to one or more spray assemblies, e.g., to mid-level spray arm assembly  140  and upper spray assembly  142 . However, it should be appreciated that according to alternative embodiments, any other suitable plumbing configuration may be used to supply wash fluid throughout the various spray manifolds and assemblies described herein. For example, according to another exemplary embodiment, primary supply conduit  154  could be used to provide wash fluid to mid-level spray arm assembly  140  and a dedicated secondary supply conduit (not shown) could be utilized to provide wash fluid to upper spray assembly  142 . Other plumbing configurations may be used for providing wash fluid to the various spray devices and manifolds at any location within dishwasher appliance  100 . 
     Each spray arm assembly  134 ,  140 ,  142 , integral spray manifold  144 , or other spray device may include an arrangement of discharge ports or orifices for directing wash fluid received from circulation pump  152  onto dishes or other articles located in wash chamber  106 . The arrangement of the discharge ports, also referred to as jets, apertures, or orifices, may provide a rotational force by virtue of wash fluid flowing through the discharge ports. Alternatively, spray arm assemblies  134 ,  140 ,  142  may be motor-driven, or may operate using any other suitable drive mechanism. Spray manifolds and assemblies may also be stationary. The resultant movement of the spray arm assemblies  134 ,  140 ,  142  and the spray from fixed manifolds provides coverage of dishes and other dishwasher contents with a washing spray. Other configurations of spray assemblies may be used as well. For example, dishwasher  100  may have additional spray assemblies for cleaning silverware, for scouring casserole dishes, for spraying pots and pans, for cleaning bottles, etc. 
     In operation, circulation pump  152  draws wash fluid in from sump  138  and pumps it to a diverter  156 , e.g., which is positioned within sump  138  of dishwasher appliance. Diverter  156  may include a diverter disk (not shown) disposed within a diverter chamber  158  for selectively distributing the wash fluid to the spray arm assemblies  134 ,  140 ,  142  and/or other spray manifolds or devices. For example, the diverter disk may have a plurality of apertures that are configured to align with one or more outlet ports (not shown) at the top of diverter chamber  158 . In this manner, the diverter disk may be selectively rotated to provide wash fluid to the desired spray device. 
     According to an exemplary embodiment, diverter  156  is configured for selectively distributing the flow of wash fluid from circulation pump  152  to various fluid supply conduits, only some of which are illustrated in  FIG. 2  for clarity. More specifically, diverter  156  may include four outlet ports (not shown) for supplying wash fluid to a first conduit for rotating lower spray arm assembly  134  in the clockwise direction, a second conduit for rotating lower spray arm assembly  134  in the counter-clockwise direction, a third conduit for spraying an auxiliary rack such as the silverware rack, and a fourth conduit for supply mid-level and/or upper spray assemblies  140 ,  142 , e.g., such as primary supply conduit  154 . 
     Drainage of soiled wash fluid within sump  138  may occur, for example, through drain assembly  166 . In particular, wash fluid may exit sump through a drain and may flow through a drain conduit  167 . A drain pump  168  may facilitate drainage of the soiled wash fluid by pumping the wash fluid to a drain line external to dishwasher  100 . 
     Dishwasher  100  is further equipped with a controller  160  to regulate operation of dishwasher  100 . Controller  160  may include one or more memory devices and one or more microprocessors, such as general or special purpose microprocessors operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In some embodiments, the processor executes programming instructions stored in memory. For example, the instructions may include a software package configured to execute a portion of the example method  300 , described below with reference to  FIG. 5 . The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller  160  may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. 
     Controller  160  may be positioned in a variety of locations throughout dishwasher  100 . In the illustrated embodiment, controller  160  may be located within a control panel area  162  of door  116  as shown in  FIGS. 1 and 2 . In such an embodiment, input/output (“I/O”) signals may be routed between the control system and various operational components of dishwasher  100  along wiring harnesses that may be routed through the bottom of door  116 . Typically, the controller  160  includes a user interface panel/controls  164  through which a user may select various operational features and modes and monitor progress of dishwasher  100 . In one embodiment, the user interface  164  may represent a general purpose I/O (“GPIO”) device or functional block. In one embodiment, the user interface  164  may include input components, such as one or more of a variety of electrical, mechanical or electro-mechanical input devices including rotary dials, push buttons, and touch pads. The user interface  164  may include a display component, such as a digital or analog display device designed to provide operational feedback to a user. The user interface  164  may be in communication with the controller  160  via one or more signal lines or shared communication busses. It should be noted that controllers  160  as disclosed herein are capable of and may be operable to perform any methods and associated method steps as disclosed herein. For example, in some embodiments, methods disclosed herein may be embodied in programming instructions stored in the memory and executed by the controller  160 . 
     It should be appreciated that the invention is not limited to any particular style, model, or configuration of dishwasher  100 . The exemplary embodiment depicted in  FIGS. 1 and 2  is for illustrative purposes only. For example, different locations may be provided for user interface  164 , different configurations may be provided for rack assemblies  122 ,  124 ,  126 , different spray arm assemblies  134 ,  140 ,  142  and spray manifold configurations may be used, and other differences may be applied while remaining within the scope of the present subject matter. 
       FIG. 3  provides a cross sectional view of sump  138 , circulation pump  152 , and a pressure sensor  200  of the dishwasher  100  of  FIGS. 1 and 2 . In particular,  FIG. 3  illustrates the relative vertical positions of an inlet  202  of the pressure sensor  200  and an inlet  151  of the circulation pump  152 . For example, as illustrated in  FIG. 3 , the inlet  202  of the sensor  200  may define a height HS relative to the sump  138  and the inlet  151  of the circulation pump  152  may define a height HP also relative to the sump  138 . In some embodiments, the height HS of the inlet  202  of the sensor  200  may be generally the same as the height HP of the inlet  151  of the circulation pump  152 . In other embodiments, the respective heights HS and HP may differ. 
       FIG. 4  provides an enlarged view of a portion of  FIG. 3 , in particular the pressure sensor  200  and the sump  138 . The pressure sensor  200  may be operable to measure hydrostatic pressure resulting from an accumulation of water within the sump  138 . Accordingly, in some exemplary aspects of the present disclosure, dishwasher  100 , and in particular the controller  160  thereof, utilizes outputs from pressure sensor  200  to estimate or calculate the hydraulic head of water within the sump  138 , which may be expressed in inches above the inlet  202  of the pressure sensor  200 , an example of which is illustrated by liquid depth D in  FIG. 4 . In various embodiments, the output from the pressure sensor  200  generally correlates to the liquid depth D in the sump  138 , whereby pressure values and thresholds may be used to ensure that the liquid depth D is sufficient to avoid or minimize air entrainment in the circulation pump  152 . In embodiments such as the example illustrated in  FIG. 3  where the respective heights HS and HP differ, such pressure values and thresholds may include an adjustment factor or offset to account for the difference in heights HS and HP. For example, as described in more detail below, an operating speed of the circulation pump  152  may be regulated according to one or more exemplary methods whereby the flow rate out of the sump  138  does not exceed the flow rate into the sump  138  from the wash chamber  106 , and as a result, the liquid in the sump  138  will not be drawn down low enough to expose the inlet  151  ( FIG. 3 ) of the circulation pump  152  to air. 
     Pressure sensor  200  is operatively configured to communicate the liquid depth D to controller  160  ( FIG. 2 ) via one or more signals. Thus, pressure sensor  200  and controller  160  are communicatively coupled. The pressure sensor  200  may send signals to controller  160  as a frequency, as an analog signal, or in another suitable manner or form. Pressure sensor  200  can be any suitable type of sensor capable of sensing the liquid depth D within dishwasher  100 . For example, pressure sensor  200  may be a pneumatic pressure sensor, a piezoelectric pressure sensor, or any other suitable sensor. 
       FIG. 5  provides a flow diagram of an exemplary method  300  of circulating fluid in a dishwasher appliance according to one or more exemplary embodiments of the present disclosure. For instance, the method  300  can be used to ensure an optimal fill level in the sump  138  of dishwasher appliance  100  as illustrated in  FIGS. 1 and 2 . Accordingly, the method  300  may advantageously prevent a surge of air in the dishwasher appliance  100  rather than reacting to a surge. To provide context to exemplary method  300 , the reference numerals used in  FIGS. 1 and 2  to describe the features of dishwasher  100  will be used below. It will be appreciated, however, that method  300  is not limited in scope to dishwasher  100  of  FIGS. 1 and 2 ; rather, method  300  is applicable to other suitable types and models of dishwashers. 
     As illustrated in  FIG. 5 , method  300  of circulating fluid in a dishwasher appliance includes an initial step  302  of starting circulation, e.g., by operating circulation pump  152  to supply wash fluid through diverter  156  to one or more of the spray assemblies  134 ,  140 ,  142 , and/or manifold  144  as described above, at a first speed less than a target speed, e.g., A % of the target speed. For example, the first speed may be about seventy-five percent (75%) of the target speed or less, such as about sixty percent (60%), such as about fifty percent (50%), such as about forty percent (40%) of the target speed or less. The first speed may advantageously be sufficiently less than the target speed to avoid creating a surge of air into the circulation pump  152 . Accordingly, by starting slow and gradually increasing the speed of circulation pump in response to pressure readings from the pressure sensor  200  as described in more detail below, the exemplary method  300  may avoid or minimize surging rather than reacting to surging while also avoiding excessive water consumption. The step  302  may also include operating the circulation pump  152  at the first speed for a first amount of time, e.g., X seconds. The first amount of time may be a predetermined amount of time. For example, the first amount of time may be about seven seconds or less, such as about five seconds, such as about three seconds. The first amount of time need not be particularly long, only long enough for the circulation pump  152  to ramp up and reach a generally steady state of operation. 
     The method  300  may also include a step  304  of determining a first minimum pressure value (P min ) based on the first speed and a position of the diverter  156 . As described above, the diverter  156  may be selectively positionable in one of several, e.g., four, positions to provide fluid flow to a selected one or combination of the spray assemblies  134 ,  140 ,  142 , and/or manifold  144 . Accordingly, one of skill in the art will understand that the flow rate and required minimum pressure may vary depending on the position of the diverter  156 . For example, supplying fluid to only one of the spray assemblies  134 ,  140 , or  142  requires a lesser or slower flow of liquid than supplying fluid to more than one of the spray assemblies  134 ,  140 ,  142 , and/or manifold  144  at the same time, and the required minimum pressure (P min ) is correspondingly lower when the flow rate is lower. Additionally, where the first speed is less than the target speed, the minimum pressure (P min ) to avoid air entrainment is also less than would be needed at full speed or the target speed. In some embodiments, determining the first minimum pressure value (P min ) may include looking up the first speed and the position of the diverter in a lookup table. As discussed in more detail below and as shown in  FIG. 5 , the method  300  may include returning to step  304 , e.g., to determine a second minimum pressure value. In such embodiments, subsequent minimum pressure values, e.g., a second minimum pressure value, third minimum pressure value, etc., may also be determined by looking up the current speed (e.g., a second speed, a third speed, etc.) and the position of the diverter in the lookup table 
     Method  300  may include, after the first amount of time has elapsed, monitoring a pressure upstream of the circulation pump  152 , e.g., in the sump  138 , with the pressure sensor  200 . For example, the pressure may be monitored by the controller  160 . Controller  160  can receive the pressure sensor output directly or indirectly from pressure sensor  200 . Preferably, controller  160  receives pressure sensor outputs continuously at a predetermined interval, such as e.g., every tenth of a second, every half second, every second, etc. In this way, dishwasher  100  constantly monitors pressure upstream of the circulation pump  152 , e.g., pressure in the sump  138 , with the pressure sensor  200 . Thus, method  300  may include a decision step at  306  of determining whether the pressure sensor output is less than or equal to the determined minimum pressure value (P min ) for a second amount of time, e.g., Y seconds, consecutively. If not, e.g., when the monitored pressure continuously exceeds the minimum pressure value for the second amount of time, the method  300  may include increasing the speed of the circulation pump. For example, as illustrated in  FIG. 5 , the method  300  may include a decision step at  308 , after determining at  306  that the pressure sensor output has not been less than or equal to P min  for Y seconds consecutively, of determining whether the current speed is greater than or equal to the target speed. For example, where the first speed is less than the target speed, the method  300  may include operating the circulation pump  152  at a second speed greater than the first speed when the monitored pressure continuously exceeds the first minimum pressure value for the second amount of time. The second amount of time may be about five seconds or less, such as about four seconds, such as about three seconds, such as about two seconds or less. 
     As illustrated at step  310  in  FIG. 5 , the second speed may be greater than the first speed by a fixed, predetermined amount. For example, the step  310  may include increasing the operating speed of the circulation pump  152  by B %, where B is a set number of percentage points. For example, B may be ten percent, such that if the first speed is fifty percent of the target speed, the second speed would be sixty percent of the target speed, a third speed would be seventy percent of the target speed, or the first speed may be about forty percent of the target speed and the second speed may be about fifty percent of the target speed, etc. Also by way of example, B may be five percentage points or any other suitable increment. 
     Method  300  may further include operating the circulation pump at the second speed for a third amount of time, e.g., Z seconds as illustrated at  312  in  FIG. 5 . After the third amount of time has elapsed, e.g., after waiting Z seconds at step  312 , the method  300  may then return to step  304  to determine a new P min  value. For example, the method may include determining a second minimum pressure value based on the second speed and the position of the diverter after operating the circulation pump at the second speed for the third amount of time. The third amount of time may be may be a predetermined amount of time. For example, the third amount of time may be about seven seconds or less, such as about five seconds, such as about three seconds. Depending on the overall duration of the selected cycle, the method  300  may reiterate step  304  any number of times. For example, the method  300  may also include calculating a third minimum pressure value based on a third speed, a fourth minimum pressure value based on a fourth speed, etc. As noted above, the minimum pressure will generally increase as the operating speed increases. Thus, for example, where the second speed is greater than the first speed, the second minimum pressure value will also be greater than the first minimum pressure value. 
     As mentioned above, the method  300  may include continuously monitoring the pressure sensor output. Accordingly, the method  300  may include monitoring the pressure upstream of the circulation pump  152  with the pressure sensor  200  while operating the circulation pump  152  at the second speed. Also, method  300  may return to step  306  and determine whether the monitored pressure while operating the circulation pump at the second speed continuously exceeds the second minimum pressure value for the second amount of time. If so, or as noted at  306  in  FIG. 5 , if the pressure sensor output is not less than or equal to P min , and the second speed is less than the target speed at  308 , e.g., if the current speed is not greater than or equal to the target speed, then the method  300  may return to step  310  and increase the speed by another increment of B %. For example, the method  300  may include operating the circulation pump  152  at a third speed greater than the second speed when the monitored pressure while operating the circulation pump  152  at the second speed continuously exceeds the second minimum pressure value for the second amount of time and when the second speed is less than the target speed. 
     When the decision or determination at step  308  is positive, the method  300  may continue from step  308  to steps  312  and  304 , e.g., as illustrated in  FIG. 5 , when the current speed is greater than or equal to the target speed, the method  300  may include waiting Z seconds at  312  and returning to  304  to determine a next consecutive minimum pressure value, e.g., a third minimum pressure value, based on the current speed, e.g., the third speed, and the position of the diverter. As noted above, Z seconds may also be referred to as the third amount of time. Accordingly, in some embodiments, when the third speed is greater than or approximately equal to the target speed, the method  300  may include determining a third minimum pressure value based on the third speed and the position of the diverter after operating the circulation pump at the third speed for the third amount of time. After determining the next consecutive minimum pressure value at  304 , the method  300  continues to monitor the pressure upstream of the circulation pump with the pressure sensor at step  306 , e.g., when the third speed is greater than or equal to the target speed, the method  300  may include monitoring the pressure upstream of the circulation pump with the pressure sensor while operating the circulation pump at the third speed. 
     In some instances, at any of the above-described operating speeds, it may be determined at step  306  that the pressure sensor output is less than or equal to the determined minimum pressure value (Pmin) for the second amount of time, e.g., for Y seconds consecutively. When the monitored pressure is less than P min , e.g., the first minimum pressure value, the second minimum pressure value, etc., for the second amount of time, the method  300  may include a step  314  of determining whether the current cycle of the dishwasher permits adding water. For example, the dishwasher  100  may be selectively operable in any one of a variety of modes or cycles, such as normal wash, heavy wash, eco, etc. In some cycles, such as the eco cycle, the dishwasher appliance  100  may prioritize efficiency, e.g., by not permitting additional water to be added. In other cycles, such as the heavy wash cycle, adding water may be permitted. When the current cycle of the dishwashing appliance  100  permits adding water, the method  300  may include opening the water valve  153  for a fourth amount of time, e.g., Q seconds as noted in  FIG. 5 . The fourth amount of time may be less than about three seconds, such as less than about two seconds, such as less than about one and a half seconds, such as about one second or less. The method  300  may also include a limit on the total amount of water used in the cycle. For example, the method  300  may include a step  316  of determining whether a cumulative on time for the water valve  153  during the entire cycle is less than or equal to a maximum on time, W max , and may activate the water valve  153  at step  318  only when the current cumulative on time is less than or equal to W max  at step  316 . Referring to some of the above examples for illustration, if or when the monitored pressure is less than or equal to the first minimum pressure value for the second amount of time at step  306  while operating the circulation pump  152  at the first speed, and when the current cycle of the dishwashing appliance permits adding water at step  314 , the method  300  may include opening the water valve  153  for the fourth amount of time at step  318  when a current cumulative water valve on time is less than a maximum water valve on time at step  316 . As another example, when the monitored pressure is less than the minimum pressure value corresponding to a higher speed for the second amount of time, e.g., Y consecutive seconds at step  306 , the method  300  may proceed to step  314  after more than one iteration of steps  308 ,  310 ,  312  and  304 , e.g., the method  300  may include opening the water valve  153  for the fourth amount of time at step  318  when the monitored pressure while operating the circulation pump at the third speed is less than the second minimum pressure value at step  306 , when a current cycle of the dishwashing appliance permits adding water at step  314 , and when a current cumulative water valve on time is less than a maximum water valve on time at step  316 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.