Patent Publication Number: US-11643799-B2

Title: Flush toilet

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a flush toilet, and in particular to such a flush toilet that the shelf surface of a bowl is formed to include linear portions. 
     Description of the Related Art 
     Recent flush toilets are adapted to perform washing with flush water at a small flow rate to discharge waste. However, it is necessary to favorably wash the whole bowl surface even when the flow rate of flush water is small. 
     In the flush toilet of Japanese Patent Laid-Open No. 2018-48518 (Patent Literature 1), by reducing the width of a shelf of a rear area of a bowl where waste easily adheres and, furthermore, increasing a curvature radius of an outer coupling portion that couples an end portion and a waste receiving surface, in the vertical direction in the rear area of the bowl, flush water spouted backward is caused to smoothly flow from the shelf into the rear area of the bowl so that the rear area of the bowl is sufficiently washed away. 
     In a flush toilet, it is necessary to perform washing with flush water and flow the flush water evenly on the whole surface of a bowl to discharge waste. However, when the flow rate of the flush water is small, there is a possibility that unwashed parts occur on the bowl. 
     In the flush toilet of Patent Literature 1 described above, it is prevented that unwashed parts occur in the rear area of the bowl. In the flush toilet, however, it is not possible to flow flush water evenly on the whole surface of the bowl, and further improvement is requested. 
     Especially, in such a flush toilet that the shelf of a bowl includes linear portions, since the flow path resistance of the linear portions of the shelf is small, it is difficult for a circulating flow of flush water to flow down to a waste receiving surface of the bowl, and, thereby, an unwashed parts may occur on the waste receiving surface of the bowl. Therefore, in the case of developing such a flush toilet that the shelf of the bowl includes linear portions, it is necessary to solve the above problem. 
     An object of the present invention is to provide a flush toilet capable of preventing occurrence of unwashed parts by flowing flush water evenly on the whole waste receiving surface of a bowl even if the flow rate of the flush water is small. 
     SUMMARY OF THE INVENTION 
     In order to achieve the above object, the present invention is a flush toilet for discharging waste by using flush water, the flush toilet including: a bowl including a waste receiving surface configured to receive the waste, a rim formed on a top edge of the waste receiving surface, and a shelf surface formed between the waste receiving surface and the rim, the shelf surface of the bowl including linear portions formed on a right side and a left side when seen from forward, a front arc portion connected to front ends of the linear portions, and a rear arc portion connected to rear ends of the linear portions; a rim spout portion configured to spout flush water from a rim spout port provided on the rim to the shelf surface to form a circulating flow; and a water conduit configured to guide flush water supplied from a flush water supply source to the rim spout portion; wherein flush water is spouted backward from the rim spout port of the rim spout portion along the linear portions of the shelf surface; and the shelf surface and the waste receiving surface are coupled by an inner coupling portion, and a curvature radius of the inner coupling portion along a vertical direction is set to a smaller value on a rear end of the bowl than on a front end thereof. 
     In the flush toilet in which the shelf surface of the bowl is formed by the linear portions formed on the right side and the left side when seen from forward, the front arc portion connected to the front ends of the linear portions, and the rear arc portion connected to the rear ends of the linear portions, when a circulating flow of flush water flows on the shelf surface, it is difficult for the flush water to flow down from the shelf surface to the waste receiving surface at the time of flowing from the front arc portion or the rear arc portion to the linear portions because the flow path resistance of the circulating flow is small on the linear portions (because the circulating flow is rectified). On the other hand, at the time of flowing from the linear portions to the front arc portion or the rear arc portion, it is easy for flush water to flow down from the shelf surface to the waste receiving surface because the circulating flow is disturbed on the front and rear arc portions. Since the rim spout port of the rim spout portion spouts flush water backward along the linear portions of the shelf surface of the bowl, it is difficult for the flush water to flow down on the waste receiving surface near the rim spout port, and unwashed parts easily occur. 
     Therefore, in the present invention, the curvature radius of the inner coupling portion that couples the shelf surface and the waste receiving surface, along the vertical direction is set to a smaller value at the rear end of the bowl than at the front end thereof. Therefore, in the case of washing the rear area of the bowl, flush water easily flows down at the rear end of the bowl because the flush water flows from the linear portions to the rear arc portion and has a momentum, and disturbance increases. However, by setting the curvature radius of the inner coupling portion to a smaller value than at the front end thereof, the flush water is prevented from flowing down too much. Furthermore, in the case of washing the front area of the bowl, since the momentum of flush water flowing from the linear portions to the front arc portion is weak, and disturbance is small at the front end of the bowl, it is difficult for the flush water to flow down. Therefore, by setting the curvature radius of the inner coupling portion to a larger value than at the rear end of the bowl, the flush water is caused to easily flow down. Furthermore, it is also difficult for flush water flowing from the front arc portion to the linear portions to flow down. Therefore, by increasing the curvature radius of the inner coupling portion at the front end of the bowl, the flush water is caused to easily flow down, and it is possible to prevent unwashed parts from occurring on the waste receiving surface near the rim spout port. 
     In the present invention, preferably, the curvature radius of the inner coupling portion that couples the shelf surface and the waste receiving surface is set so that a value increases from the rear end of the bowl toward the front end thereof. 
     In the present invention, flush water is spouted backward from the rim spout port. Therefore, flush water has a stronger momentum and is more largely disturbed in the rear area of the bowl than in the front area thereof, and the flush water easily flows down from the shelf surface to the waste receiving surface. In the front area of the bowl, flush water has a weaker momentum, and disturbance is smaller than in the rear area thereof. Therefore, it is difficult for the flush water to flow down from the shelf surface to the waste receiving surface. Therefore, in the present invention, the curvature radius of the inner coupling portion that couples the shelf surface and the waste receiving surface is set so that the value increases from the rear end of the bowl toward the front end thereof. Thus, flush water does not flow down too much in the rear area of the bowl, and it is easy for flush water to flow down in the front area, so that it is possible to prevent occurrence of unwashed parts on the waste receiving surface of the bowl. 
     In the present invention, preferably, the shelf surface and the rim are coupled by an outer coupling portion, and a curvature radius of the outer coupling portion along a vertical direction is set so that a value increases from the rear end of the bowl toward the front end thereof. 
     In the present invention configured as described above, the curvature radius of the outer coupling portion that couples the shelf surface and the rim, along the vertical direction is set so that the value increases from the rear end of the bowl toward the front end thereof. Therefore, when it is difficult for flush water to flow down from the shelf surface to the waste receiving surface in the front area of the bowl, it becomes easy for the flush water to flow down in the rear area of the bowl, and it is possible to, by causing an appropriate amount of flush water to flow down into the rear area of the bowl to wash away adhering waste. 
     In the present invention, preferably, the shelf surface is formed such that a shelf width thereof is the widest at the front end of the bowl and the narrowest at the rear end of the bowl. 
     In the present invention configured as described above, though the momentum of flush water is weak in the front area of the bowl, it is possible to, because the shelf width of the shelf surface is formed the widest at the front end of the bowl, maintain the flush water by the shelf surface and cause the flush water to whirl to the vicinity of the rim spout port and flow down. On the other hand, since the momentum of flush water is strong in the rear area of the bowl, the flush water does not flow down too much even though the shelf width of the shelf surface is formed to be the narrowest at the rear end of the bowl. 
     According to the flush toilet of the present invention, it is possible to prevent occurrence of unwashed parts by flowing flush water evenly on the whole waste receiving surface of the bowl even if the flow rate of the flush water is small. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is an overall schematic diagram showing a flush toilet according to an embodiment of the present invention; 
         FIG.  2    is a plan view showing the flush toilet according to the embodiment of the present invention; 
         FIG.  3    is a sectional view seen along line III-III in  FIG.  1   ; 
         FIG.  4    is a plan view showing a bowl and a shelf of the flush toilet according to the embodiment of the present invention; 
         FIG.  5    is a schematic plan view of the shelf for illustrating a flow of flush water on the shelf of the flush toilet according to the embodiment of the present invention; 
         FIG.  6    is a partial sectional view seen along line VI-VI in  FIG.  2   ; 
         FIG.  7    is a table showing relative heights H of a shelf surface on the entire circumference of the bowl; 
         FIG.  8    is a line graph showing the relative heights H of the shelf surface on the entire circumference shown in  FIG.  7   ; 
         FIG.  9    is a table showing widths W of the shelf surface on the entire circumference of the bowl; 
         FIG.  10    is a line graph showing the widths W of the shelf surface on the entire circumference shown in  FIG.  9   ; 
         FIG.  11    is a partial sectional view seen along line XI-XI in  FIG.  2   ; 
         FIG.  12    is a table showing curvature radii R 3  of an inner coupling portion that couples the shelf surface and a waste receiving surface, on the entire circumference of the bowl; 
         FIG.  13    is a line graph showing the curvature radii R 3  of the inner coupling portion on the entire circumference shown in  FIG.  12   ; 
         FIG.  14    is a table showing curvature radii R 4  of an outer coupling portion that couples the shelf surface and a rim, on the entire circumference of the bowl; and 
         FIG.  15    is a line graph showing the curvature radii R 4  of the outer coupling portion that couples the shelf surface and the rim, on the entire circumference shown in  FIG.  14   . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Next, a basic structure of a flush toilet according to an embodiment of the present invention will be described with reference to  FIGS.  1  to  3   . 
     First, as shown in  FIG.  1   , a flush toilet  1  according to one embodiment of the present invention is provided with a toilet main body  4  to which flush water is supplied from a flush water supply source such as a water tap via a flush water supply device  2 . 
     The following description will be made on the assumption that, in the plan view shown in  FIG.  2   , a side located on the left side when the toilet main body  4  is seen from forward is a left side, and a side located on the right side is a right side. 
     As shown in  FIGS.  1  and  2   , the toilet main body  4  has a bowl  6 , and the bowl  6  is provided with a waste receiving surface  8  that receives waste, a rim  10  formed on the top edge of the bowl  6  and a shelf surface  12  formed between the waste receiving surface  8  and the rim  10 . The shelf surface  12  is a flat surface that is slightly inclined inward, and the flat surface is formed on the entire circumference of the bowl  6 . 
     The toilet main body  4  is further provided with a water discharge trap pipe  14  that extends from the bottom portion of the bowl  6 . Above a communicating portion between the bottom portion of the bowl  6  and the water discharge trap pipe  14 , pooled water  15  is formed. 
     As shown in  FIGS.  1  to  3   , on the rim  10  of the bowl  6 , a rim spout portion  16  is formed which spouts flush water supplied from the flush water supply source into the bowl  6  to form a circulating flow in the bowl  6 . The rim spout portion  16  is provided on the rim  10  on the right side when the toilet main body  4  of the bowl  6  is seen from forward. Further, for the rim spout portion  16 , a rim water passage  18  through which supplied flush water passes is formed inside the rim  10 , and, on the downstream end of the rim water passage  18 , a rim spout port  20  for spouting flush water backward is formed. 
     In the present embodiment, the rim spout port  20  is a single spout port provided on the rim  10 . Therefore, flush water with a strong momentum can be spouted from the rim spout port  20 , and it becomes easy to wash the rear area of the bowl  6  that is easy to get dirty, and it is possible to reduce unwashed parts in an area X 2  (see  FIG.  5   ), as described later. 
     Inside the rim  10  on the right side when the toilet main body  4  is seen from the front side, the rim water passage  18  extends forward from the rear side of the toilet main body  4  and then bends inside at the middle toward the rear side, that is, forms a so-called U-turn shape. Furthermore, on the upstream side of the rim water passage  18 , a rim-side water supply passage  2   a  of the flush water supply device  2  described above is connected. Furthermore, on the immediately downstream side of the rim spout port  20  of the rim  10  and on the outer circumferential side of the shelf surface  12 , a spout port water passage surface  21  is formed. Over the spout port water passage surface  21 , the inner circumferential surface of the bowl  6  overhangs. Flush water supplied from the rim-side water supply passage  2   a  to the rim water passage  18  is spouted backward to the spout port water passage surface  21 , from the rim spout port  20 , and, after that, spouted into the bowl  6  via the shelf surface  12 . The flow rate of the flush water spouted from the rim spout port  20  is 10 L/min to 16 L/min. 
     As shown in  FIGS.  1  and  2   , the water discharge trap pipe  14  described above is provided with an inlet  14   a , an ascending conduit  14   b  and a descending conduit  14   c . A discharge socket  22  is connected to the descending conduit  14   c  of the water discharge trap pipe  14 , and the downstream end of the discharge socket  22  is connected to a discharge pipe  24  (wall drainage). In the present embodiment, in addition to the wall drainage, a discharge socket may be connected to the floor so that flush water may be discharged to a discharge pipe provided in the floor (floor drainage). 
     A jet water conduit  26  is formed on the bottom portion of the bowl  6  of the toilet main body  4 ; a jet spout port  26   a  is formed at the downstream end of the jet water conduit  26 ; and the jet spout port  26   a  is oriented toward the inlet  14   a  of the water discharge trap pipe  14 . Flush water is spouted from the jet spout port  26   a  toward the inlet  14   a  of the water discharge trap pipe  14  to perform jet spouting. 
     As shown in  FIG.  1   , a switching valve  27  is provided on the downstream side of the flush water supply device  2 , and supply of flush water is switched to between the rim-side water supply passage  2   a  and a tank-side water supply passage  2   b  by the switching valve  27 . 
     A reservoir tank  28  is provided on the downstream side of the tank-side water supply passage  2   b , and a pressurizing pump  30  is connected to the downstream side of the reservoir tank  28  via a pump water supply passage  2   c . A jet-side water supply passage  2   d  is connected to the downstream side of the pressurizing pump  30 , and flush water in the reservoir tank  28  is supplied to the jet water conduit  26  described above by the jet-side water supply passage  2   d.    
     The flush water supply device  2  described above is provided with a stop cock, a fixed flow valve, a diaphragm-type main valve, a solenoid valve and the like. The flush water supply device  2  is further provided with a controller  32 , and opening/closing operations of the various kinds of valves described above, switching operations of the switching valve  27  and the number of rotations, operation time and the like of the pressurizing pump  30  are controlled by the controller  32 . 
     Here, the switching valve  27  is also capable of supplying flush water to both of the rim-side water supply passage  2   a  and the tank-side water supply passage  2   b  at the same timing. In this case, the ratio of the amount of water supply to the rim side and to the tank side can be arbitrarily changed. 
     Due to the above, in the flush toilet  1  according to the present embodiment, flush water under direct water pressure is supplied to the rim spout port  20  from the rim-side water supply passage  2   a  of the flush water supply device  2  via the rim water passage  18  of the toilet main body  4  so that spouting from the rim spout port  20  (so-called “rim spouting”) can be performed. 
     Furthermore, after passing through the tank-side water supply passage  2   b  of the flush water supply device  2 , the reservoir tank  28 , the pump water supply passage  2   c  and the pressurizing pump  30 , flush water is supplied to the jet spout port  26   a  from the jet-side water supply passage  2   d  via the jet water conduit  26  of the toilet main body  4  so that spouting from the jet spout port  26   a  (so-called “jet spouting”) can be performed. 
     The flush toilet  1  according to the present embodiment is a so-called hybrid-type flush toilet  1  that is adapted to use both of rim spouting by flush water under direct water pressure and jet spouting by flush water from the reservoir tank  28 , which is pressurized by the pressurizing pump  30 . 
     As shown in  FIG.  1   , inside the reservoir tank  28 , an upper-side float switch  34  and a lower-side float switch  36  are arranged. The water level in the reservoir tank  28  can be detected by the float switches  34  and  36 . 
     The upper-side float switch  34  is switched to ON when the water level in the reservoir tank  28  reaches a predetermined reservoir water level, and the controller  32  detects the ON state of the upper-side float switch  34  and causes the solenoid valve of the flush water supply device  2  to be closed. 
     On the other, the lower-side float switch  36  is switched to ON when the water level in the reservoir tank  28  drops to a predetermined water level lower than a predetermined reservoir water level detected by the upper-side float switch  34 , and the controller  32  detects the ON state of the lower-side float switch  36  and causes the pressurizing pump  30  to stop. 
     The pressurizing pump  30  is adapted to be capable of, by absorbing flush water reserved in the reservoir tank  28  into the pump water supply passage  2   c  and pressurizing the flush water from the pump water supply passage  2   c  to the jet-side water supply passage  2   d , causing the flush water to be spouted from the jet spout port  26   a.    
     In the flush toilet  1  according to the present embodiment described above, at the time of washing the toilet bowl, the controller  32  detects an operation of a toilet bowl washing switch (not shown) or the like by a user and causes the flush water supply device  2  to operate to supply flush water from the flush water supply source to the toilet main body  4 . 
     Thereby, spouting from the rim spout port  20  and spouting from the jet spout port  26   a  are sequentially started, and flush water that has washed the waste receiving surface  8  of the bowl  6  is discharged from the water discharge trap pipe  14  to the outside together with waste in the bowl  6 . 
     Furthermore, after the washing ends, the controller  32  switches the switching valve  27  of the flush water supply device  2  to the tank-side water supply passage  2   b  side so that flush water is replenished into the reservoir tank  28 . 
     Then, when the water level in the reservoir tank  28  rises, and the upper-side float switch  34  detects the predetermined reservoir water level, the controller  32  stops replenishment of flush water by the flush water supply device  2  into the reservoir tank  28 . 
     Next, the structure of the shelf surface  12  of the bowl  6  and the like will be described in detail with reference to  FIGS.  4  and  5   . 
     First, as shown in  FIG.  4   , the shelf surface  12  of the bowl  6  is formed by a right-side linear portion  40   a  and a left-side linear portion  40   b  extending in parallel on the right side and left side of the bowl  6 , a front arc portion  42  connected to the front ends of the right-side and left-side linear portions  40   a  and  40   b , and a rear arc portion  44  connected to the rear ends of the right-side and left-side linear portions  40   a  and  40   b  when seen from the top surface. 
     Specifically, the front end of the right-side linear portion  40   a  and the front arc portion  42  are coupled by a coupling portion  46   a ; the rear end of the right-side linear portion  40   a  and the rear arc portion  44  are coupled by a coupling portion  46   b ; the rear arc portion  44  and the rear end of the left-side linear portion  40   b  are coupled by a coupling portion  46   c ; and the front end of the left-side linear portion  40   b  is coupled with the front arc portion  42  by a coupling portion  46   d.    
     Note that the right-side linear portion  40   a  and left-side linear portion  40   b  described above may be provided in a manner of extending “almost in parallel” on the right side and the left side. 
     Here, both of the front arc portion  42  and the rear arc portion  44  are formed with a single curvature radius R 1 . 
     Note that the front arc portion  42  and the rear arc portion  44  may be formed by combining a plurality of curvature radii. 
     To make a description more specifically, the shelf surface  12  of the bowl  6  is in a shape that is almost bilaterally symmetrical relative to a center line C 1  extending in the front-rear direction and is also in a shape that is almost symmetrical in the front-rear direction relative to a center line C 2  extending in the left-right width direction as shown in  FIG.  4   . The front arc portion  42  is in a semicircular shape with the single radius R 1  having a center O 1 , and, similarly, the rear arc portion  44  is in a semicircular shape with a single radius R 2  having a center O 2 . 
     Furthermore, in  FIG.  4   , a position A is the front end of the bowl  6 ; a position B is an intermediate position between the front end of the bowl  6  and the front end of the right-side linear portion  40   a ; a position C is the front end of the right-side linear portion  40   a ; a position D is an intermediate position of the right-side linear portion  40   a ; a position D 1  is the position of the rim spout port  20 ; and the position D and the position D 1  are almost the same position. A position E is an intermediate position between the rear end of the right-side linear portion  40   a  and the rear end of the bowl  6 ; a position G is the rear end of the bowl  6 ; a position H is an intermediate position between the rear end of the bowl  6  and the rear end of the left-side linear portion  40   b ; a position I is the rear end of the left-side linear portion  40   b ; a position J is an intermediate position of the left-side linear portion  40   b ; a position K is the front end of the left-side linear portion  40   b ; and a position L is an intermediate position between the front end of the left-side linear portion  40   b  and the front end of the bowl  6 . 
     Here, a length L 2  in the front-rear direction from the center line C 2  to the position G is longer than a length L 1  in the front-rear direction from the center line C 2  to the position A. Therefore, when a user excretes in a standing or sitting position, the waste receiving surface  8  in the rear area of the bowl  6  is large, and a sense of safety at the time of excretion can be increased. Further, a length L 3  in the front-rear direction from the position C to the position E and a length L 4  in the front-rear direction from the position I to the position K are almost the same. Furthermore, a length in the front-rear direction from the position E (the position I) to the position G (=R 2 ) and a length in the front-rear direction from the position C (the position K) to the position A (=R 1 ) are longer than the length L 3  in the front-rear direction and the length L 4  in the front-rear direction. In other words, the curvature radius R 1  of the front arc portion  42  and the curvature radius R 2  of the rear arc portion  44  are longer than the length L 3  of the right-side linear portion  40   a  in the front-rear direction and the length L 4  of the left-side linear portion  40   b  in the front-rear direction. As a result, when flush water flows from the linear portions  40   a  and  40   b  to the arc portions  42  and  44 , change in the flow of the flush water is gradual because the curvature radii R 1  and R 2  of the arc portions  42  and  44  are set long, and it is possible to prevent splattering of the flush water. 
     Next, the behavior of flush water flowing on the shelf surface  12  of the bowl  6  will be described with reference to  FIG.  5   . As shown in  FIG.  5   , the flow of flush water flowing from the right-side linear portion  40   a  to the rear arc portion  44  is indicated by F 1 ; the flow of flush water flowing from the rear arc portion  44  to the left-side linear portion  40   b  is indicated by F 2 ; the flow of flush water flowing from the left-side linear portion  40   b  to the front arc portion  42  is indicated by F 3 ; and the flow of flush water flowing from the front arc portion  42  to the right-side linear portion  40   a  is indicated by F 4 . 
     Here, it is difficult for flush water flowing on the right-side and left-side linear portions  40   a  and  40   b  of the shelf surface  12  to flow down to the waste receiving surface  8  because there is little flow path resistance. On the other hand, the flow of flush water flowing on the front arc portion  42  and the rear arc portion  44  is disturbed because the flow direction changes, and thus it is easy for the flush water to flow down to the waste receiving surface  8  due to the disturbance of the flow. The influence of the disturbance of the flow is greater than the influence of centrifugal force. 
     Therefore, as for the flows F 2  and F 4  of flush water flowing from the arc portions  42  and  44  to the linear portions  40   a  and  40   b , it is difficult for the flush water to flow down from the shelf surface  12 , but on the other hand, as for the flows F 1  and F 3  of flush water flowing from the linear portions  40   a  and  40   b  to the arc portions  42  and  44 , it is easy for the flush water to flow down from the shelf surface  12 . Due to such behavior of flush water, unwashed parts easily occur on the waste receiving surface  8  in areas X 1  and X 2  where flush water flows from the arc portions  42  and  44  to the linear portions  40   a  and  40   b.    
     Here, in the rear area (including the area X 2 ) of the bowl  6 , flush water is spouted backward from the rim spout port  20  provided at the position D 1 , and the distance from the rim spout port  20  is relatively short. Therefore, the flush water has a strong momentum and is disturbed much, and thus it is easy for the flush water to flow down from the rear arc portion  44 . Thus, it is difficult for unwashed parts to occur. On the other hand, in the front area (including the area X 1 ) of the bowl  6 , the momentum of flush water is weak, and the flush water is disturbed less. Therefore, it is difficult for the flush water to flow down from the front arc portion  42 , and thus unwashed parts easily occur. 
     In the present embodiment, the area X 1  in  FIG.  5   , that is, the shelf surface  12  located from the front arc portion  42  to the right-side linear portion  40   a  has a sloped surface (an ascending surface)  50  that ascends toward the rim spout port  20 . 
     The ascending sloped surface (the ascending surface)  50  will be described in detail with reference to  FIGS.  6  to  8   . 
     First, as shown in  FIGS.  6  to  8   , relative heights H on the entire circumference of the shelf surface  12  of the bowl  6  are not the same. The shelf surface  12  is the lowest at the front end of the bowl  6  (the position A), and the sloped surface (the ascending surface)  50  that ascends toward the rim spout port  20 , from the front end of the bowl  6  to the rim spout port  20  (the position D 1 ) (or the central position D of the right-side linear portion  40   a ) is formed. Furthermore, the shelf surface  12  is formed with the same height from the rim spout port  20  (the position D 1 ) (or the central position D of the right-side linear portion  40   a ) to the central position J of the left-side linear portion  40   b  via the rear end of the bowl  6  (the position G). Furthermore, the shelf surface  12  has a sloped surface (a descending surface)  52  that descends toward the front end, from the central position J of the left-side linear portion  40   b  to the front end of the bowl  6  (the position A). 
     Here, since the top portion of the rim  10  is formed almost the same, the front end of the rim  10  is higher than the rear end, relative to the shelf surface  12 . Therefore, at the time of excretion in a sitting position, urine and the like hit the front end of the bowl  6  and can be prevented from being splattered from the bowl  6 . 
     In the flush toilet  1  according to the present embodiment, since the shelf surface  12  has the ascending surface  50 , in the area X 1  (that is, an area across the coupling portion  46   a  where the front arc portion  42  and the right-side linear portion  40   a  are connected) as described above, the flow velocity of flush water decreases, and, thereby, it is possible to prevent unwashed parts from occurring on the waste receiving surface  8  that is a lower part of the shelf surface  12  that is in the area of the rim spout port  20  (or the central position D of the right-side linear portion  40   a ). 
     Here, as shown in  FIGS.  7  and  8   , the shelf surface  12  is the lowest at the front end of the bowl  6  (the position A) and is formed at a certain height higher than the position A, in an area from the central part of the right-side linear portion  40   a  (the position D) to the central part of the left-side linear portion  40   b  (the position J) via the rear end of the bowl  6  (the position G). 
     Furthermore, as shown in  FIGS.  7  and  8   , the relative heights of the shelf surface  12  of the right-side linear portion  40   a , the rear arc portion  44  and the left-side linear portion  40   b  are almost the same. 
     Though the above-described ascending sloped surface (the ascending surface)  50  the shelf surface  12  has extends from the front end of the bowl  6  (the position A) to the rim spout port  20  (the position D 1 ), the sloped surface (the ascending surface)  50  is not limited thereto and may be formed on the shelf surface  12  between the position A and the position D 1 . Furthermore, it is preferable that the ascending surface  50  is formed across the coupling portion  46   a  that connects the front arc portion  42  and the right-side linear portion  40   a.    
     It is preferable that an ascending height H 1  of the above-described ascending sloped surface (the ascending surface)  50  that the shelf surface  12  is provided with is 15 to 20 mm. 
     Next, shelf widths W of the shelf surface  12  will be described with reference to  FIGS.  9  and  10   . 
     As shown in  FIGS.  9  and  10   , the shelf width W of the shelf surface  12  is the widest at the front end of the bowl  6  (the position A) and the narrowest at the rear end of the bowl  6  (the position G). The shelf width W of the shelf surface  12  near the rim spout port  20  (the position D 1 ) is a little wider than other areas of the right-side linear portion  40   a  in order to stabilize spouting of flush water. 
     Here, it is preferable that the shelf width W of the shelf surface  12  at the front end of the bowl  6  (the position A) is 25 to 35 mm. Further, it is preferable that the shelf width W of the shelf surface  12  at the rear end of the bowl  6  (the position G) is 10 to 20 mm. 
     In the flush toilet  1  according to the present embodiment described above, though the momentum of flush water is weak at the front end of the bowl  6  (the position A), it is possible to cause the flush water to whirl to the vicinity of the rim spout port  20 , maintaining the flush water by the shelf surface  12 , and flow down, because the shelf width W of the shelf surface  12  is formed the widest at the front end of the bowl  6  (the position A). On the other hand, since the momentum of flush water is strong at the rear end of the bowl  6  (the position G), the flush water does not flow down too much even though the shelf width W of the shelf surface  12  is formed to be the narrowest at the rear end of the bowl  6 . 
     Furthermore, in the present embodiment, the shelf widths W of the rear arc portion  44  of the shelf surface  12  at the positions F, G and H are almost the same. By the shelf width W of the shelf surface  12  changing, it becomes easy for flush water to flow down, and, on the rear arc portion  44 , the direction of the flow of the flush water changes, so that disturbance easily occurs. Therefore, by causing the shelf width W of the shelf surface  12  at the positions F, G and H to be almost the same as described above, flush water is prevented from flowing down too much. 
     Next, an inner curvature radius R 3  of an inner coupling portion  54  that couples the shelf surface  12  and the waste receiving surface  8  on the entire circumference of the bowl  6  will be described with reference to  FIGS.  11  to  13   . 
     As shown in  FIG.  11   , the shelf surface  12  and the waste receiving surface  8  are coupled by the inner coupling portion  54 . The inner coupling portion  54  is formed by the curvature radius R 3  of a convex shape along the vertical direction. 
     As shown in  FIGS.  12  and  13   , the curvature radius R 3  of the inner coupling portion  54  has a smaller value at the rear end of the bowl  6  (the position G) than at the front end of the bowl  6  (the position A). 
     In the flush toilet  1  according to the present embodiment, the curvature radius R 3  of the inner coupling portion  54  that couples the shelf surface  12  and the waste receiving surface  8 , along the vertical direction has a smaller value at the rear end of the bowl  6  (the position G) than at the front end thereof (the position A). Therefore, in the case of washing the rear area of the bowl  6 , flush water easily flows down at the rear end of the bowl  6  (the position G) because the flush water flows from the right-side linear portion  40   a  to the rear arc portion  44  and has a momentum, and disturbance increases. The flush water is prevented from flowing down too much by setting a smaller value for the curvature radius R 3  of the inner coupling portion  54  than at the front end (the position A). 
     On the other hand, in the case of washing the front area of the bowl  6 , since the momentum of flush water flowing from the left-side linear portion  40   b  to the front arc portion  42  is weak, and disturbance is small at the front end of the bowl  6  (the position A), it is difficult for the flush water to flow down. Therefore, by setting the curvature radius R 3  of the inner coupling portion  54  to a larger value than at the rear end of the bowl  6  (the position G), the flush water is caused to easily flow down. Furthermore, it is also difficult for flush water flowing from the front arc portion  42  to the right-side linear portion  40   a  to flow down. Therefore, by increasing the curvature radius R 3  of the inner coupling portion  54  at the front end of the bowl  6  (the position A), the flush water is caused to easily flow down, and it is possible to prevent unwashed parts from occurring on the waste receiving surface  8  near the rim spout port  20 . 
     Furthermore, as shown in  FIGS.  12  and  13   , the value of the curvature radius R 3  of the inner coupling portion  54  increases from the rear end of the bowl  6  (the position G) toward the front end thereof (the position A). 
     Here, it is preferable that the curvature radius R 3  of the inner coupling portion  54  at the front end of the bowl  6  (the position A) is 40 to 45 mm. It is preferable that the curvature radius R 3  of the inner coupling portion  54  at the rear end of the bowl  6  (the position G) is 25 to 30 mm. 
     In the flush toilet  1  according to the present embodiment, flush water is spouted backward from the rim spout port  20  along the right-side linear portion  40   a  of the shelf surface  12 . Therefore, flush water has a stronger momentum and is more largely disturbed in the rear area of the bowl  6  than in the front area thereof, and the flush water easily flows down from the shelf surface  12  to the waste receiving surface  8 . In the front area of the bowl  6 , flush water has a weaker momentum, and disturbance is smaller than in the rear area thereof. Therefore, it is difficult for the flush water to flow down from the shelf surface  12  to the waste receiving surface  8 . Therefore, in the flush toilet  1  according to the present embodiment, the value of the curvature radius R 3  of the inner coupling portion  54  that couples the shelf surface  12  and the waste receiving surface  8  increases from the rear end of the bowl  6  (the position G) toward the front end (the position A) thereof. Thus, flush water does not flow down too much in the rear area of the bowl  6 , and it is easy for flush water to flow down in the front area, so that it is possible to prevent occurrence of unwashed parts on the waste receiving surface  8  of the bowl  6 . 
     Next, an inner curvature radius R 4  of an outer coupling portion  56  that couples the shelf surface  12  and the rim  10  on the entire circumference of the bowl  6  will be described with reference to  FIGS.  11 ,  14  and  15   . 
     As shown in  FIG.  11   , the shelf surface  12  and the rim  10  are coupled by the outer coupling portion  56 . The outer coupling portion  56  is formed by the curvature radius R 4  of a concave shape along the vertical direction. 
     As shown in  FIGS.  14  and  15   , the curvature radius R 4  of the outer coupling portion  56  has the smallest value near the rim spout port  20  (the position D 1 ) in the right-side area of the bowl  6 . Schematically, however, the value of the curvature radius R 4  increases from the front end of the bowl  6  (the position A) toward the rear end thereof (the position G). 
     On the other hand, in the left-side area of the bowl  6 , the curvature radius R 4  of the outer coupling portion  56  has the smallest value at the front end of the bowl  6  (the position A), and the value of the curvature radius R 4  increases toward the rear end of the bowl  6  (the position G). 
     Here, it is preferable that the curvature radius R 4  of the outer coupling portion  56  at the front end of the bowl  6  (the position A) is 6 to 8 mm. It is preferable that the curvature radius R 4  of the outer coupling portion  56  at the rear end of the bowl  6  (the position G) is 12 to 15 mm. 
     In the flush toilet  1  according to the present embodiment, the value of the curvature radius R 4  of the outer coupling portion  56  that couples the shelf surface  12  and the rim  10 , along the vertical direction increases from the rear end of the bowl  6  (the position G) toward the front end thereof (the position A). Therefore, when it is difficult for flush water to flow down from the shelf surface  12  to the waste receiving surface  8  in the front area of the bowl  6 , it becomes easy for the flush water to flow down in the rear area of the bowl  6 , and it is possible to, by causing an appropriate amount of flush water to flow down into the rear area of the bowl  6  to wash away adhering waste.