Patent Publication Number: US-3876148-A

Title: Dishwasher having epicyclic spray system

Description:
United States Patent Cushing et al. Apr. 8, I975 [5 DISHWASHER HAVING EPICYCLIC SPRAY 2.27911; 4/l942 Fisher l34/l79 x SYSTEM 2.967.024 l/l96l 3,05l.183 8/1962 [75] Inventors: Donald S. Cushing; Thomas E. 109 400 5/1963 Jenkins, both of Louisville, Ky. 3.496.949 2/1970 r a a Assigneez General Electric p y, 3.677.473 7/1972 Belaieff -39/ Sl L H .K Oulsvl e y Primary Examiner-M. Henson Wood, Jr. Flledi P 13, 1973 Assistant Examiner-Andres Kashnikow [2|] Appll NO: 396 823 Attorney, Agent or FirmFrancis H. Boos, Jr,  
  52 us. c1. 239/227; 134/179; 239/246; [57] ABSTRACT 239/261 There is disclosed a dishwasher having a spray arm 5| Int. Cl B08b 3/02; BOSb 3/06 providing a p y p g therein- The p y arm is [58] Field of Search 239/225, 97, 227, 236, mounted in order to move the Opening in an epicyclic 239/24344 243 249 25 253 255 25 spray path In one embodiment of the invention the 261 DIG 1; 134/17 79 cpicyclic spray arm is positioned low in the wash chamber. Another embodiment of the invention pro [56] Refere Cit d vides the epicyclie spray arm as elevated above a UNITED STATES PATENTS SPTaY 928,386 7/1909 Johnson 239/227 15 Claims, 13 Drawing Figures FIIENTEZAPR 8%975 7 ,1453  
 FIGJ  
 PATENTEU W575 3,876,148  
 SE&#39;EEY 8 BF 8 PRKJR ART DISHWASHER HAVING EPICYCLIC SPRAY SYSTEM The conventional dishwasher presently commercially available incorporates a spray arm having a plurality of spray openings therein. The spray arm is mounted for simple rotation. Each spray opening necessarily repeats or tracks its prior path during rotation and defines a circular trace, the radius of which is the dimension from the particular spray opening to the axis of rotation. Since the liquid spray emitting from any particular opening travels the same path during successive revolutions of the spray arm, it is not surprising that there is room for improvement in washing efficiency. The classic techniques for improving washing efficiency are to increase liquid volume through the spray device and to increase spray pressure.  
  This invention relates to an improved technique for moving a spray arm to provide an essentially nonrepeating path for a spray opening thereby improving area coverage during washing. There are devices in the prior art which, either intentionally or inherently, provide increased area coverage of individual spray openings. Typical disclosures are found in US. Pat. Nos. 2,279.6l9; 3,468,486; and 3,677,473 as well as US. application Ser. No. 252.824, filed May I2, 1972 now US. Pat. No. 3,771,725, which patent is owned by the assignee of this invention. In each of these disclosures, a main spray arm is mounted for rotation about a central axis and carries a secondary spray arm near an extremity of the primary spray arm. The second spray arm is rotated or indexed about its own axis while the primary spray arm is rotated about its axis. Consequently, the spray path defined by the openings in the secondary spray arm meanders in more or less predetermined fashion between limits comprising radii of different length from the central axis. The area coverage of compound spray arms of this type is improved as compared to the conventional spray arms which are mounted for simple rotation.  
  One difficulty with the compound spray arms of the prior art is poor water distribution. The annular spray zone of the compound spray arms of the prior art is quite large. Since the quantity of water emitting from any particular spray opening remains generally constant, the outer portions of the spray zone tends to be starved of wash water while the inner edge of the spray zone tends to be flooded.  
  Another difficulty with the prior art compound spray arms is that the inertia of the secondary spray arm is quite small compared to the inertia of the primary spray arm whereby the secondary spray arm is rotated very rapidly. Rotating the secondary spray arm too fast tends to break up the spray emitting from the secondary spray openings into a mist.  
  The improved spray system of this invention provides a meandering spray path between relatively narrow inner and outer limits. The spray path of the openings is epicyclic in nature.  
  It is an object of this invention to provide a dishwasher incorporating an improved spray system.  
  In summary, the dishwasher of this invention comprises wash chamber and means for spraying liquid into th chamber including a member having at least one spray opening therein, means mounting and moving the member for movement of the opening in a nonrepeating epicyclic spray path.  
 IN THE DRAWINGS:  
  FIG. 1 is an isometric view of a dishwasher. certain parts being broken away to expose the spray system of this invention;  
  FIG. 2 is a side view of the dishwasher of FIG. 1, certain parts being broken away;  
  FIGS. 3 and 4 are partial top plan views of the compound spray arm of this invention;  
  FIG. 5 is a partial exploded view of the mounting mechanism for the compound spray arm of this invention;  
  FIG. 6 is a vertical cross sectional view of the spray arms and mounting means therefor;  
  FIG. 7 is a trace of one of the spray openings illustrating the epicyclic path during thirty revolutions of the opening;  
  FIGS. 8 and 9 illustrate a trace of one of the spray openings for slightly in excess of one revolution;  
  FIG. 10 is a trace of one of the spray openings of a typical prior art compound spray arm;  
  FIG. I1 is a trace of the spray openings of another typical prior art compound spray arm;  
  FIG. 12 is a cross-sectional view of another embodiment of this invention; and  
  FIG. I3 is an isometric view of another embodiment of the spray arm of this invention.  
  Referring to FIGSv I and 2, there is illustrated a dish washer l0 comprised of a cabinet 12, a door 14 closing the front of the cabinet 12, a tub I6 in the cabinet 12 which cooperates with the door 14 to define a wash chamber I8 and means 20 for spraying liquid into the wash chamber 18. Suitable article receiving racks 22, 24 reside in the tub 16 for supporting tableware, kitchenware and the like.  
  The tub 16 includes a bottom wall 26 providing a sump 28 in communication with the inlet of a pump 30 positioned under the tub bottom 26. The pump 30 includes an outlet 32 in sealing engagement with the tub bottom 26 and in fluid communication with the spray means 20.  
  As shown best in FIGS. 1-6, the spray means 20 includes a spray arm or member 34 having a plurality of generally upwardly facing spray openings 36 therein spaced at different distances from the center of the arm 34. The spray arm 34 includes an interior passage 38 providing communication between the center of the arm 34 and the spray openings 36. One or more of the spray openings 36 may be laterally inclined with respect to the arm 34 for drivably rotating the same in a conventional manner. The size or cross sectional area of the upwardly facing openings 36, or the number of openings, preferably increases as the spacing thereof from the center of the arm 34 increases, for purposes more fully explained hereinafter.  
  As shown most clearly in FIGS. 5 and 6, the spray means 20 includes means 40 mounting the spray arm 34 for movement of the spray openings 36 in an epicyclic spray path.  
  As used herein. the term epicyclic path is defined as the trace of a point on the circumference of a first circle that rolls around the interior of the circumference of a second circle wherein the diameter of the first circle exceeds the radius of the second circle. The term non-repeating epicyclic path is here defined as an epicyclic path of the above type in which the trace does not track on successive revolutions.  
  The mounting means 40 includes a hub 42 on which the arm 34 is mounted for rotation about a first axis 44. The hub 42 is mounted by a retaining collar 46 onto a stub conduit 48 for rotation about a second axis 50.  
  The stub conduit 48 is conveniently molded plastic providing threads 52 received by the pump outlet 32, an interior passage 54 for transmitting washing liquid, an external flange 56 comprising part of a bearing assembly, and a lip 58 comprising part of a seal for preventing leakage through the bearing assembly. Accordingly, the mounting means 40 not only constrains the spray arm 34 for movement in the predetermined path but also acts to transmit pressurized washing liquid from the pump to the interior passage 38 of the spray arm 34.  
  The retaining collar 46 includes an interiorally projecting flange 60 which acts to captivate a plurality of ball bearings 62 and a bearing retainer 64 against the flange 56. The upper end of the retaining collar 46 is of enlarged internal diameter and provides screw threads 66 for receiving complementary screw threads 68 provided by the hub 42.  
  The hub 42 is also conveniently made of molded plastic and provides an interior axial passage 70, a first series of radially directed passages 72 providing communication between the passages 38, 70 and a second series of radially directed passages 74 providing communication between the passage 70 and a driving or auxiliary arm 76. The hub 42 carries a pair of seals 78, 80 for minimizing leakage between the hub 42 and the spray arm 34 and a seal 82 cooperating with the lip 58 for minimizing leakage between the hub 42 and the stub conduit 48. The hub 42 also provides a series of threads 84 adjacent the upper end thereof for securing the driving arm 76 to the hub 42.  
  The driving arm 76 provides an interior passage 86 leading to a laterally directed nozzle 88 for rotating the driving arm 76, the hub 42 and the retaining collar 46 about the second axis 50. The driving arm 76 may pro vide upwardly directed spray openings as desired.  
  Although the upper end of the driving arm may be sealed, as by a suitable closure, there is preferably provided a spray tower 90 in accordance with the disclosure of U.S. Pat. No. 3,077,200, to which reference is made for a more complete description thereof. In summary, the delivery of pressurized washing liquid to the interior of the mounting means causes the spray tower 90 to move upwardly therethrough into abutting engagement with a shoulder 92 provided by the driving arm 76. The spray tower 90 provides one or more ele vated spray openings in order to discharge washing liquid at an elevated location within the wash chamber 18. When the pump 30 is turned off and pressurized washing liquid ceases passing through the mounting means 40, the spray tower 90 falls by gravity through the passage 70 of the hub 42 and through the passage 54 of the stub conduit 48. Since the axes of the passages 54, 70 are offset to each other, the passage 54 is preferably substantially larger in order to receive the spray tower 90 in any position of the hub 42.  
  It should now be apparent that the spray arm 34 undergoes compound movement during the wash cycle of the dishwasher 10. Upon delivery of washing liquid through the mounting means 40, the spray arm 34 is drivably rotated about the first axis 44 while the first axis 44 is drivably rotated about the second axis 50.  
  It will be apparent that the distance of any particular spray opening 36 from the stationary axis 50 will vary depending on the position of the first axis 44 which in turn is dictated by the orientation of the hub 42. For purposes of illustration, it may be assumed that the spray opening 36a is positioned a distance A from the first axis 44 while the first axis 44 is spaced :1 distance B from the axis 50. If the spray arm 34 were held stationary and the hub 42 rotated as by rotating the driving arm 76, the trace of the spray opening 360 moves radially with respect to the axis 50 between a first distance A+B and a second distance A-B from the axis 50. Accordingly. the trace of spray opening 360 moves radially a distance equal to 2B as suggested from FIG. 7.  
  Analysis of the movement of the opening 360 during operation of the dishwasher It] reveals that the exact pattern or spray path depends on the speed ratio between the hub 42 and the spray arm 34. When the speed ratio between the hub 42 and the spray arm 34 is an integer, the trace of the spray opening 36a repeats or tracks at each revolution of the spray arm 34. Ac cordingly, the design speed ratio between the hub 42 and the spray arm 34 is not an integer. It is, of course, within the skill of the art to correlate the inertia of the arms 37, 76 and the frictional forces operating on the seals 78, 80, 82 and on the bearing assembly 56, 60, 62, the liquid volumes and pressures acting on the various reaction nozzles and the distance of the reaction nozzles to the axes of rotation to establish reasonably accurate rotational speeds for the arms 34, 76.  
  For example, with the spray arm 34 rotating at 30 revolutions per minute and the driving arm 76 rotating at 17 revolutions per minute, the speed ratio is somewhat less than l.8:1 and provides a l-minute or 30 revolution pattern similar to that shown in FIG. 7, although it must be admitted that the representation in FIG. 7 is somewhat more regular than the actual tracing obtaining with a model of this invention. At a speed ratio of exactly 1.8:], the trace of the spray opening 360 should theoretically begin to track or repeat after 18 revolutions.  
  In practice the trace of the spray opening 36a does not begin to track as quickly, if at all, as theory would indicate. The reason appears to be that the arms 34, 76 cannot be driven at precise constant rates. The fluctuation of pump outlet pressure or pump volume as well as the appearance of a gas bubble or food soil particle at the driving nozzles will affect the instantaneous rate of rotation of one or both of the arms 34, 76. Accordingly, the actual rate of rotation of the arms 34, 76 will fluctuate from the design rate thereof.  
  It is evident that it is highly desirable to provide as many consecutive non-tracking revolutions of the spray opening 360 as practicable. There appear to be two approaches which produce one-revolution traces of different configurations. The first approach is to provide an extremely large speed ratio between the spray arm 34 and the driving arm 76. The second approach is to provide a speed ratio between the arm 34 and the driving arm 76 of less than one.  
  In providing a very large speed ratio, there are several counterbalancing considerations. First, there are limits on how fast the spray arm 34 can be rotated. The inertia of the spray arm 34 is substantial since it is filled with water during rotation. Accordingly, driving the spray arm 34 at a very rapid rate consumes a significant amount of energy since the proportion of the pressurized water used to drive the spray arm 34 become appreciable. Another factor limiting the rate of speed of the spray arm 34 is that the spray emitting from the openings 36 can conceivably be converted to a mist in the wash chamber I8. This is obviously undesirable and constitutes a practical upper limit from the rate of rotation of the spray arm 34. Second. there are limits on how slow the driving arm 76 can be rotated. Since the frictional forces acting on the seal 82 and the ball bearing 62 fluctuate at the inception of rotation because of the change of static to dynamic friction, control over the rate of rotation of the arm 76 is erratic unless it is rotating fast enough. It is accordingly desirable to rotate the driving arm 76 fast enough to assure that the friction acting on the seal 82 and the ball bearings 62 is dynamic friction. The problem of static as opposed to dynamic friction forces acting on the seals 78, 80 can be resolved in a slightly different manner. If the driving arm 76 and the spray arm 34 are rotated in the same direction, the rotation sensed by the seals 78, 80 is the difference in the rate of rotation between the arms 34, 76. If the arms 34, 76 are driven in opposite directions, the rotation sensed by the seals 78, 80 is the sum of the rotational rates of the arms 34, 76. Accordingly, it is desirable to counterrotate the arms 34, 76 to assure that dynamic friction is acting on the seals 78, 80.  
  In practice, the driving arm 76 probably cannot be rotated slower than five revolutions per minute while the spray arm 34 probably cannot be rotated faster than 60 revolutions per minute giving a maximum speed ratio of I22 I. Preferably, the driving arm 76 is 1&#39;0- tated between ten and twenty revolutions per minute while the spray arm 34 is preferably rotated between twenty and forty revolutions per minute. Accordingly, the preferred speed ratio lies in the range of 1:l to 4:1. As previously mentioned, the speed ratio should not be an integer to prevent immediate tracking of the spray path on successive revolutions of the spray arm 34.  
  Referring to FIG. 8, there is illustrated a trace 94 covering a slightly more than one revolution of the spray opening 36a when the speed ratio between the spray arm 34 and the driving arm 76 is greater than 1:1. For purposes of convenience, the representation of FIG. 8 constitutes one revolution based on the same parameters as the thirty revolution representation of FIG. 7. For purposes of illustration, the spray arm 34 is illustrated as rotating in a counterclockwise direction commencing at a starting point 96. It will be appreciated that the axis 44 describes a circular trace 98 about the axis 50 during rotation of the arms 34, 76. For purposes of illustration, the starting point 96 is positioned at a distance A+B from the axis 50 which corresponds to the configuration illustrated in FIG. 6. The axis 44 is accordingly positioned at a point 100 on the trace 98 at the start of rotation. As the arms 34, 76 commence rotation, the distance from the spray opening 36a to the second axis 50 begins to shorten in accordance with the degree of relative rotation between the hub 42 and the spray arm 34. Assuming that the arms 34, 76 counterrotate, the minimum distance AB between the spray opening 36a and the axis 50 is designated by the point 102 on the trace 94. In this situation, the axis 44 has movedto a point 104 on the trace 98. The minimum distance between the axis 50 and the spray opening 360 is illustrated in the configuration of the arms 34, 76 in FIG. 3. The spray opening 36a moves along the trace 94 to about the point 106 while the axis 44 moves along the trace 98 to about the point 108.  
  Somewhat different considerations appear to establish practical limits on the speed ratio between the arms 34, 76 when operating at a speed ratio less than one. The problem of static friction acting on the seals 78, 80, 82 and on the bearing assembly 56, 60, 62 are no longer governing factors since the arm 76 is rotated relatively rapidly and since the arms 34, 76 can be counterrotated. The maximum rate of rotation of the arm 76 issomewhat higher than the maximum rate of rotation of the arm 34 since the inertia of the arm 76 is substantially less and since it is immaterial if the water passing through the nozzle 88 is converted to a mist. Although rotational rates of the arm 76 in excess of one hundred revolutions per minute appear practicable, rates in the range of 20-80 revolutions per minute seem desirable if for no reason other than conservation of energy. The arm 34 must be rotated at least fast enough to provide a substantial number of revolutions during each wash cycle of the dishwasher 10. For this reason, a rotational rate of less than five revolutions per minute for the arm 34 is deemed undesirable. Preferably, the spray arm 34 is rotated between l0 and 40 revolutions per minute. Accordingly, the preferred ratio lies in the range of lzl to 1:8.  
  Referring to FIG. 9, there is illustrated a trace I10 covering one revolution of the spray opening 360 utilizing a speed ratio of about I:3.8. It will be appreciated that the axis 44 describes a circular trace 112 about the axis 50 during rotation of the arms 34, 76. As in the representation of FIG. 8, the distance between any point on the trace and the axis 50 depends on the relative orientation of the hub 42 and the arm 34.  
  The movement described in FIGS. 8 and 9 is to be contrasted with that in FIG. 10 which is representative of the traces which are obtained from the disclosures in US. Pat. Nos. 2,279,619; 3,468,486 and 3,677,473 when the secondary spray arms counterrotate relative to the primary spray arm. An axis 114 illustrated in FIG. 10 corresponds to the axis of rotation of the primary spray arm. A trace 116 describes the path taken by one of the spray openings in the secondary spray arm. It will be apparent from a comparison of FIGS. 8-10 that the individual spray openings of this invention cover a relatively narrow annulus as compared to the relatively broad annulus between the inner and outer circles 118, 120. One disadvantage of the prior art spray patterns is poor water distribution. It is obviously desirable that the quantity of water emitting from each spray opening be substantially constant per unit area of dishes exposed to the spray.  
  For purposes of illustration, the radius r, of the inner circle 118 is assumed to be one unit, the radius r, of the circle 122 is assumed to be two units and the radius r; of the circle 120 is assumed to be three units. The circle 122 constitutes the trace of the axis of rotation of the secondary spray arm. Elementary calculations will reveal that the area of the annular segment rrr is greater than the area of the annular segment r r, by a factor of 1.67. It is apparent that the spray opening on the secondary spray arm resides exact half the time in the annular segment ry-r: and exactly half the time in the annular segment rrr Accordingly, the quantity of water sprayed in each annular segment ry-r, and rrr, are equal. Since the area of the outer annular segment r=,r, is substantially greater, the conclusion is unmistakable that the outer annular segment is relatively starved of wash water while the inner annular segment is relatively flooded with wash water. It is thus apparent that the water distribution pattern of the prior art is not desirable.  
  As may be seen from FIG. 10, the trace 116 is basically of clover leaf design and is illustrated as having six loops or leaves indicating a speed ratio of approximately six. It is apparent that the water distribution pattern of the prior art is not improved by changing the speed ratio between the primary and secondary spray arms since each secondary spray opening resides in the inner annular segment r r for exactly the same time that it resides in the outer annular segment r -,r independent of the number of loops or leaves on the trace 116.  
  As mentioned previously, the trace 116 is achieved with the primary and secondary arms counterrotating. As shown in FIG. 11, a trace 130 with somewhat different configuration is obtained if the primary and secondary spray arms of the prior art devices rotate in the same direction. An axis 132 corresponds to the axis of rotation of the primary spray arm with the spray zone being defined between inner and outer circles 134, 136. The loops or leaves of the trace 130 are inverted to intersect the inner circle 134 with the trace segment 138 between the loops being adjacent the outer circle 136. As in the configuration of FIG. 10, the circle 140 represents the trace of the secondary spray arm axis so that each spray opening resides for equal periods of time in the inner annular segment defined by the circles 134, 140 and the outer annular segment defined by the circles 140, 136. It will accordingly be apparent that a greater quantity of water per unit area is delivered to the inner annular segment than to the outer annular segment.  
  It will be noted that the traces 116, 130 intersect during one revolution thereof about the axis 114, 132 respectively. This is inherent in the prior art since the distance between the secondary spray opening and the secondary arm axis is less than the distance between the primary and secondary arm axes. For the same reason, the traces 116, 130 do not continuously proceed in the same direction about the axis 114, 132 respectively but instead proceed in the opposite direction adjacent the apex of each loop.  
  In contrast to the relatively wide spray zone of the prior art, each spray opening of this invention covers a relatively narrow annular spray zone of predetermined cross sectional area which may be calculated quite readily from the dimensions A, B as shown in FIGS. 6-8. Since the annular spray zone of each spray opening increases in area as the distance from the spray opening to the axis 50 increases, the spray openings 36 desirably increase in size (or number) as the distance thereof from the axis 50 increases so that the delivered water per unit area of each annular zone is relatively constant. The spacing between the spray openings 36, such as the openings 36a, 36b in FIG. 1, is preferably such that the corresponding annular spray zones 126, 128 illustrated in FIG. 7 abut or overlap to afford substantially complete area coverage. As is apparent from FIG. 7, the coverage of each spray opening 36 within its corresponding spray zone is quite good leading to good washing efficiency. Since the area coverage of each spray opening 36 is so complete, the openings 36 may be designed to create a solid jet of water rather than a fan-shaped spray. It will be evident that this provides substantial erosion action on food soil particles adhering to tableware and kitchenware in the racks 22, 24. Also contributing to good washing efficiency is that the spray jet passes each point in its zone at different angles of attack.  
  Another difference between the spray zones of this invention and that of the prior art resides in the mean diameter of the spray zones 126, 128. From FIG. 7, it is apparent that the mean diameter of the spray zone 126, which is the inner diameter plus one-half of the width of the spray zone, is the distance from the spray opening 360 to the axis 44 which is designated A in FIG. 6. Similarly, the mean diameter of the spray zone 128 is the distance between the axis 44 and the spray opening 36b. Consequently, the mean are of each of the spray zones of this invention re of different length. In the prior art spray patterns represented in FIG. 10, the mean diameter of the outermost opening spray zone on the secondary spray arm is the distance between the trace 122 and the axis 114 which is the distance between the axes of the primary and secondary spray arms. Assuming for purposes of illustration that the secondary spray arm of the prior art provides a spray opening closer to the axis of the secondary spray arm, this spray opening defines an annular spray zone having inner and outer diameters 142, 144 having a mean diameter corresponding to the trace 122. Conse quently, the spray zones of the prior art have a common mean diameter. Thus in a multi spray opening secondary spray arm of the prior art, there is a substantial quantity of water per unit area delivered between the diameters 118, 144. There is a relatively small quantity of water per unit area delivered in the annular zone defined by the diameters 120, 144.  
  It will accordingly be apparent that the spray zones of this invention may abut or overlap but none of the spray zones are of sufficient width to wholly encompass another of the annular spray zones.  
  Referring to FIG. 12, there is illustrated another embodiment of the invention comprising spray means 146 including a spray arm or member 148 having a plurality of generally upwardly facing spray openings 150 therein spaced at different distances from the center of the arm 148. The spray arm 148 includes an interior passage 152 providing communication between the center of the arm 148 and the spray openings 150. One or more of the openings 150 may be laterally inclined with respect to the arm 148 for drivably rotating the same in a conventional manner. The size or cross sec tional area of the spray openings 150 preferably increases as the distance thereof from the center of the arm 148 increases as previously discussed.  
  The spray means 148 includes means 154 mounting the spray arm 148 for movement of the spray openings 150 in an epicyclic spray path. The mounting means 154 includes a hub 156 on which the arm 148 is mounted for rotation about a first axis 158. The hub 156 is mounted by a retaining collar 160 onto a stub conduit 162 for rotation about a second axis 164. The stub conduit 162 is conveniently molded plastic and includes threads received by a pump outlet 166, an interior passage 168 for transmitting washing liquid, an external flange 170 comprising part of a bearing assembly, and a lip 172 comprising part of the seal for preventing leakage through the bearing assembly. Accordingly, the mounting means 154 not only constrains the spray arm 148 for movement in the predetermined path but also acts to transmit pressurized washing liquid from the pump (not shown) to the interior passage 152 of the spray arm 148.  
  The retaining collar 160 includes an interiorally projecting flange 174 which acts to captivate a plurality of ball bearings 176 and a bearing retainer 178 against the flange 170. The upper end of the retaining collar 160 is of enlarged internal diameter and provides screw threads for receiving complementary screw threads provided by the hub 156.  
  The hub 156 is also conveniently made of molded plastic and provides an interior axial passage 180 and a series of radially directed passages 182 providing communication between the passages 152, 180. The hub 156 carries a pair of seals 184., 186 for minimizing leakage between the hub 156 and the spray arm 148 and a seal 188 cooperating with the lip 172 for minimizing leakage between the hub 156 and the stub conduit 162. The hub 156 also provides an upstanding conduit 190 for cooperation with an extendable spray tower 192.  
  A major distinction between the embodiment of FIG. 12 and the previously described embodiment resides in the means for rotating the hub 156 and retaining collar 160 about the second axis 164. In the embodiment of FIG. 6, the driving arm 76 effects this rotation. In the embodiment of FIG. 12, there is provided a gear transmission 194 for rotating the hub 156 about the axis 164 in response to rotation of the spray arm 148 about the axis 158. The gear transmission 194 includes a first stationary annular gear 196 having inwardly projecting gear teeth provided by the stub conduit 162. The gear transmission 194 also includes a second movable annular gear 198 having inwardly projecting gear teeth provided by the rotatable spray arm I48. Interconnecting the annular gears 196, 198 is a member 200 comprising a first circular gear 202 rigid with an axle 204 which is inturn connected to a second circular gear 206. The axle 204 extends through a boss 208 rigid with the hub 156.  
  Rotation of the spray arm 148 rotates the movable annular gear 198 thereby rotating the first circular gear 202. Coaction between the gears 196, 206 constitutes a reaction member causing the axle 204 to orbit about the second axis 164. Since the axle 204 is received by the boss 208, orbiting of the axle 204 causes the hub 156 and the retaining collar 160 likewise to revolve about the second axis 164.  
  The gear reduction ratio afforded by the transmission 194 is selected to provide desirable spray patterns as previously discussed. In the particular design illustrated in FIG. 12, the ratio between the gears 198, 202 is greater than the ratio between the gears 196, 206 which provides for rotation of the hub 156 faster than the spray arm 148 providing a spray pattern similar to that shown in FIG. 9 where the trace of any particular spray opening 150 will intersect the inner and outer diameters of the spray zone more than once. For purposes of illustration, the gear 202 may comprise teeth, the gear 198 may comprise 112 teeth, the gear 206 may comprise teeth and the gear 196 may comprise 70 teeth. One revolution of the gear 198 causes 11.2 revolutions of the gear 202 which necessarily effects 11.2 revolutions of the gear 206. Eleven and two tenths revolutions of the gear 206 causes 2.4 revolutions of the axle 204 about the axis 164 thereby providing a speed ratio between the arm 148 and the hub 156 of 1:24.  
  The arrangement of FIG. 12 provides several advantages over the device of FIG. 6. A substantial advantage is that the speed ratio between the arm 148 and the hub 156 may be determined quite directly rather than taking into account all of the dynamically variable forces acting on the driving arm 76. Eliminating the driving arm 76 also provides a lower wash arm of lower profile which may be desirable in many instances.  
  Referring to FIG. 13, there is illustrated another embodiment of this invention comprising spray means 210 including a lower spray arm 212 spaced from an upper spray arm 214 by a central conduit 216. The length of the conduit 216 is preferably such that the upper spray arm 214 resides directly beneath an upper rack, such as the rack 22 illustrated in FIG. 2. The lower rack, such as the rack 24 in FIG. 2, is provided with a central slot in order to pass the conduit 216 allowing movement of the lower rack 24 into and out of the wash chamber 18 as is conventional.  
  The lower spray arm 212 includes a hub 218 mounted for simple rotation about an axis 220 on the pump outlet (not shown). Mounting of the hub 218 may be effected in substantially the same manner that the retaining collar 46 is mounted for rotation. The lower spray arm 212 provides a plurality of upwardly directed spray openings 222 for discharging wash liquid in the wash chamber and a reaction nozzle 224 for drivably rotating the spray arm 212 about the axis 220. It will accordingly be seen that the lower spray arm 212 may be of typical design.  
  The conduit 216 conveniently projects upwardly from the hub 218 concentric with the axis 220. The upper spray arm 214 provides a hub 226 mounting the spray arm 214 for rotation about an axis 228 offset with respect to the axis 220. The hub 226 may comprise a base 230 threaded into the top of the conduit 216 in much the same manner that the hub 42 is threaded into the top of the collar 46. Suitable seals are provided in the hub 226 for sealing between a rotating circumferential band 232 and a relatively stationary hub body 234. The spray arm 214 preferably includes a pair of balanced oppositely projecting arm segments 236, 238 providing a plurality of spray openings 240 and a reaction nozzle 242 respectively.  
  The embodiment of FIG. 13 has many functional similarities to the embodiment of FIG. 6. The lower spray arm 212 functions in much the same manner as the driving arm 76 to orbit the hub 236 about the axis 220. The speed ratio between the lower spray or driving arm 212 and the upper spray arm 214 is subject to control based on the design parameters discussed in relation to FIG. 6.  
  It will accordingly be seen that there is provided an improved spray system for dishwashers.  
 We claim:  
  1. A dishwasher comprising a wash chamber and means for spraying liquid into the chamber comprising a spray member having at least one spray opening therein, and means mounting and moving the member for movement of the opening in a non-repeating epicyclic path which does not intersect itself in one path revolution.  
  2. The dishwasher of claim 1 wherein the mounting means comprises a hub mounting the member for rotation about a first axis, means mounting the hub for rotation about a second axis parallel to and spaced from the first axis, the member extending away from the first axis a distance greater than the spacing between the axes, the spray opening being spaced from the first axis a distance greater than the spacing between the axes.  
  3. The dishwasher of claim 2 comprising means for drivably rotating the member about the first axis at a first rate and means for drivably rotating the hub at a second rate, the ratio of the first and second rates being other than an integer.  
  4. The dishwasher of claim 3 wherein the first mentioned rotating means comprises means driving the member in a first direction and the second mentioned rotating means comprises means driving the member in a second opposite direction.  
  5. The dishwasher of claim 4 wherein the first mentioned rotating means comprises a reaction nozzle on the member facing in the second direction and the second mention ed rotating means comprises an arm rigid with the hub having a reaction nozzle thereon facing in the first direction.  
  6. The dishwasher of claim 3 wherein the first mentioned rotating means comprises a reaction nozzle on the member and the second mentioned rotating means comprises a gear transmission interconnecting the member and the hub.  
  7. The dishwasher of claim 3 wherein the first mentioned rotating means comprises a reaction nozzle on the member, the second mentioned driving means comprising a driving arm rigid with the hub having thereon a reaction nozzle.  
  8. The dishwasher of claim 3 wherein the dishwasher comprises a pump having an outlet, the member comprising a hollow spray arm, the hub mounting means comprising a conduit in fluid transmitting relation to the pump outlet, and the hub including a passage in fluid transmitting relation between the conduit and the hollow spray arm.  
  9. The dishwasher of claim 3 wherein the path mean&#39; ders between inner and outer radii of the second axis, the radial distance between the inner and outer radii being twice the distance between the axes.  
  10. A dishwasher comprising a wash chamber and means for spraying liquid into the chamber comprising a member having at least one spray opening therein, means mounting the member for combined rotating and revolving movement about an axis for continuously moving the opening in a meandering path between inner and outer spaced limits comprising different radii of the axis, the path intersecting the limits periodically and proceeding continuously in the same direction about the axis.  
  H. A dishwasher comprising a wash chamber and means for spraying liquid into the chamber comprising a member having first, second and third spray openings therein spaced at decreasing distances from a fixed axis intersecting the member; means mounting and moving the member relative to the axis for movement of each opening in a continuously meandering path between inner and outer spaced diameters defining an annular spray zone, the outer diameter of the third opening spray zone extending at least as far from the axis as the inner diameter but not as far as the outer diameter of the second opening spray zone and the outer diameter of the second opening spray zone extending at least as far from the axis as the inner diameter but not as far as the outer diameter of the first opening spray zone.  
  12. A dishwasher comprising a wash chamber and means for spraying liquid into the chamber comprising a member having a plurality of spaced spray openings therein, means mounting the member for movement relative to an axis for moving the spray openings in meandering paths between inner and outer diameters defining a corresponding plurality of annular spray zones of different mean diameter.  
  13. The dishwasher of claim 12 wherein the width of all of the spray zones is substantially the same.  
  14. A dishwasher comprising a wash chamber and means for spraying liquid into the chamber comprising a member having at least one spray opening therein, means mounting the member for movement relative to an axis for moving the spray opening in a meandering path between inner and outer diameters defining an annular spray zone and means for delivering a substantially constant quantity of liquid per unit area throughout the spray zone.  
  15. The dishwasher of claim 14 wherein the member provides a plurality of spray openings spaced therealong and the delivering means includes means for delivering a substantially constant quantity of liquid per unit area throughout each spray zone.  
 a: s k