BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hinge mechanism suitable for supporting the seat or the seat lid of a toilet bowl. 
     2. Description of the Related Art 
     A known hinge mechanism for supporting the seat or the seat lid of a toilet bowl employs a torsion coil spring to urge the seat or the seat lid in an opening direction so that the seat or the seat lid can be lightly opened and may not slam down when closing the same. 
     Generally, the torque of a torsion spring varies linearly with twist angle and therefore the torque of the torsion spring does not match exactly with the rotation moment of the seat or the seat lid that varies in a gentle sinusoidal curve with angle. Since the torsion spring is twisted to a maximum extent when the seat or the seat lid is turned to its closed position, the seat or the seat lid is liable to be raised slightly from the closed position after closing, and the torque of the torsion spring exceeds the rotation moment of the seat or the seat lid when the seat or the seat lid is turned near to its open position and the seat or the seat lid is slammed against the water tank by the torsion spring. 
     When attaching a hinge mechanism employing a torsion spring to a toilet bowl after assembling the hinge mechanism and a seat or a seat lid, the hinge mechanism can be comparatively easily attached to the toilet bowl because the seat or the seat lid is held at a certain angular position relative to the hinge mechanism by the torsion spring. A hinge mechanism employing a combination of a compression spring and a sliding cam for controlling a seat or a seat lid like a hinge mechanism of the present invention requires difficult work for attaching the hinge mechanism to a toilet bowl after assembling the hinge mechanism and the seat or the seat lid, because the seat or the seat lid is able to turn through 360° relative to the hinge mechanism. 
     OBJECT OF THE INVENTION 
     It is a first object of the present invention to provide a hinge mechanism for supporting the seat or the seat lid of a toilet bowl, capable of enabling the seat or the seat lid to be turned lightly in the opening direction, of not springing up the seat or the seat lid when the seat or the seat lid is turned near to its fully open position, of making the seat or the seat lid turn gradually in the closing direction and of securely holding the seat or the seat lid at its closed position. 
     A second object of the present invention is to provide a hinge mechanism for supporting the seat or the seat lid of a toilet bowl, capable of enabling the seat or the seat lid to be turned lightly in the opening direction, of not springing up the seat or the seat lid when the seat or the seat lid is turned near to its fully open position, of making the seat or the seat lid turn in a predetermined limited angular range, of making the seat or the seat lid turn gradually in the closing direction and of securely holding the seat or the seat lid at its closed position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a hinge mechanism in a preferred embodiment of the present invention as attached to a toilet bowl; 
     FIG. 2 is an exploded perspective view of the hinge mechanism of FIG. 1; 
     FIG. 3 is a longitudinal sectional view of the hinge mechanism of FIG. 1; 
     FIG. 4 is a longitudinal sectional view of the hinge mechanism of FIG. 1 in a position where the seat or the seat lid supported thereon is at its closed position; 
     FIG. 5 is a longitudinal sectional view of the hinge mechanism of FIG. 1 in a position where the seat or the seat lid is opened in an upright position; 
     FIGS. 6 and 7 are perspective views of a slider and a cam member as viewed from different directions; 
     FIG. 8 is a sectional view of assistance in explaining the construction and the operation of a stopping mechanism; 
     FIG. 9 is a development of the cam contour of the cam member; and 
     FIG. 10 is a diagram showing the variation of the respective torques of the hinge mechanism of FIG. 1 and a seat supported on the same hinge mechanism with angle. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 showing a pair of hinge mechanism 4 in a preferred embodiment according to the present invention, a support member 2 provided with a pair of coaxial bores 2a at its opposite ends is fastened with a pair of bolts 2b to the substantially middle portion of the upper surface of the rear part of a toilet bowl 1, and cylindrical cases 3 of the pair of hinge mechanisms 4 are detachably inserted in the bores 2a, respectively, and held in place in the bores 2a with stopping projections 3a formed in the lower portions of the case 3 in engagement with stopping part 2c formed in the bores 2a, respectively, as shown in FIG. 3. 
     As shown in FIG. 1, one of the pair of hinge mechanisms 4 supports a seat 18 (FIG. 8) and the other supports a seat lid, not shown, and the pair of hinge mechanisms 4 are in mirror-image relationship with each other and are the same in construction. Therefore, only the hinge mechanism 4 supporting the seat 18 will be described below. 
     Referring to FIGS. 2 to 5, a shaft 5 is inserted in and supported on the case 3 for turning about its axis. The shaft 5 has a flange 5a fitted in its circumference with a sealing member 6, such as an O ring, an expanded section 5b extending from the flange 5a, a reduced section 5c having a substantially oval cross section and extending from the extremity of the expanded section 5b, and an oval hole 5d formed through the flange 5a into the expanded section 5b coaxially with the expanded section 5b. One end of a compression spring 7 is wound around the expanded portion 5b of the shaft 5, and a slider 8 having a center hole 8a having a shape corresponding to the substantially oval cross section of the reduced section 5c of the shaft 5 is slidably mounted on the reduced section 5c so as to be turned together with the shaft 5. The extremity of the reduced section 5c is supported in a bearing hole 3d formed in a bearing wall 3c formed within the case 3. The compression spring 7 is compressed between the flange 5a and the slider 8 to urge the slider 8 in one direction, i.e., to the right as viewed in FIG. 3. As best shown in FIGS. 6 and 7, the slider 8 has a pair of projections 8b axially projecting from diametrically opposite positions from the inner end surface of the slider 8. The extremity of the reduced section 5c of the shaft 5 is inserted in a hole 9d formed in a stopping plate 9 and having a shape corresponding to the substantially oval cross section of the reduced section 5c, and the stopping plate 9 is fastened through a washer 10a to the extremity of the reduced section 5c with a screw 10b, so that the shaft 5 is restrained from slipping out of the case 3 by the bearing wall 3c and the stopping plate 9 rotates together with the shaft 5. A cap 11 fitted in its circumference with a sealing member 16, such as an O ring, is fitted in the inner end of the case 3 to conceal the case 3 and to seal the case 3 from water and moisture. Part of the circumference of the stopping plate 9 is cut to form a recess 9a, a first shoulder 9b and a second shoulder 9c as shown in FIGS. 2 and 8. A projection 3f projecting from the inner surface of the case 3 is received in the recess 9a of the stopping plate 9 to form a stopping mechanism 17. 
     The first shoulder 9b comes into contact with the projection 3f when the stopping plate 9 is turned together with the shaft 5 in one direction to limit the turning of the shaft 5 in that direction and the second shoulder 9c comes into contact with the projection 3f when the stopping plate 9 is turned together with the shaft 5 in the opposite direction to limit the turning of the shaft 5 in that direction. Thus, the shaft 5 is able to turn a limited angular range defined by the stopping mechanism 17. The hinge mechanism 4 can be easily attached to the toilet bowl because the seat 18 is restrained from free turning relative to the hinge mechanism 4 when attaching the hinge mechanism 4 to the toilet bowl. Although the seat 18 needs to be turned through an angle of 110°, the hinge mechanism 4 allows the seat 18 to turn through an angle of 110°+10° as shown in FIG. 8. The stopping mechanism 17 may comprise, for example, a pair of projections projecting from the inner surface of the case 3 and spaced from each other by an appropriate angle, and a projection attached to or formed integrally with the shaft 5. When designing conditions permits, the stopping plate 9 may be substituted by a flange formed integrally with the shaft 5. 
     As shown in FIGS. 6 and 7, a cam member 12 has a pair of cam surfaces 12a formed diametrically opposite to each other in one end surface thereof, four projections 12b formed on the other end surface at equal angular intervals and a center hole 12c. As shown in FIG. 3, the four projections 12b of the cam member 12 are pressed in holes 3e formed in the inner surface of the bearing wall 3c. The reduced section 5c of the shaft 5 extends rotatably through the center hole 12c, and the cam surfaces 12a are in contact with the projections 8b of the slider 8, respectively. 
     As shown in FIGS. 1 and 3, a hinge pin 13 having a flange and an oval section is put through a round hole of a knuckle 15 of the seat lid and an oval hole of a knuckle 14 of the seat 18 and pressed in the oval hole 5d of the shaft 5. The knuckle 14 of the seat 18 is unable to turn relative to the hinge pin 13, and the knuckle 15 of the seat lid is able to turn on the hinge pin 13. As is obvious from FIG. 1, the other knuckle 14 of the seat 18 is able to turn on the other hinge pin 13 pressed in the shaft 5 of the other hinge mechanism 4 and the other knuckle 15 of the seat lid is unable to turn relative to the same hinge pin 13. 
     FIG. 4 shows the hinge mechanism 4 in a state where the seat 18 is at the closed position. In this state, the projections 8b of the slider 8 are in contact with the cam surfaces 12a of the cam member 12 at comparatively gently sloping positions slightly before the highest points of the cam surfaces 12b, respectively, and the projection 3f of the stopping mechanism 17 is about 10° before the first shoulder 9b of the recess 9a as shown in FIG. 8. As shown in FIG. 10, a torque produced by the compression spring 7 is slightly lower than the torque of the seat 18 in the angular range of 0° to about 80°, and a torque produced by the compression spring 7 is slightly lower than a maximum torque that can be produced by the compression spring 7 when the seat 18 is at the closed position as shown in FIG. 4. When the seat 18 is turned to the open position, the shaft 5 is turned counterclockwise, as viewed in FIG. 8, by the hinge pin 13 and the projections 8b of the slider 8 slides along the cam surfaces 12a to the lowest points 12d of the cam surfaces 12b, respectively. Since a reaction from the cam member 12 resulting from the pressure applied by the compression spring 7 through the slider 8 to the cam member 12 produces a torque to turn the shaft 5 counterclockwise, when the projections 8b of the slider 8 slides along the cam surfaces 12a to the lowest points 12d, the seat can be substantially weightlessly opened. 
     When the seat 18 is turned further in the opening direction beyond an 80° position, the projections 8b of the slider 8 slide along gently rising slopes 12e of the cam surfaces 12a, respectively, as shown in FIG. 9, so that the compression spring 7 starts being compressed to exert a braking force on the seat 18 in a direction opposite the opening direction and the torque resulting from the pressure applied by the compression spring 7 through the slider 8 to the cam member 12 exceeds the moment of the seat 18 as shown in FIG. 10. Therefore, the seat 18 does not spring up and does not slam against the water tank with large noise. When the seat 18 is turned to a 110° position, i.e., the fully open position, the projections 8b of the slider 8 come into contact with the sharply rising slopes of the cam surfaces 12a, respectively. In this state, the projection 3f of the stopping mechanism 17 is at a position about 10° before the second shoulder 9c of the recess 9a and spaced from the second shoulder 9c of the recess 9a. 
     When the fully opened seat 18 is turned in the closing direction, the projections 8b of the slider 8 turning together with the shaft 5 slide up the up slopes of the cam surfaces 12a, respectively, against the resilience of the compression spring 7. Since a varying torque produced by the resilience of the compression spring 7 and acting against the downward turning of the seat 18 is substantially equal to or slightly lower than the torque of the seat 18 varying with angle as shown in FIG. 10, the downward turning of the seat 18 is not accelerated and the seat 18 will not slam down. 
     The cam surfaces 12a of the cam member 12 are designed so that the torque produced by the reaction resulting from the pressure exerted on the cam surfaces 12a by the compression spring 7 is slightly lower than the torque of the seat 18 in most part of the angular range of turning of the seat 18, the compression spring 7 is compressed to a maximum extent when the seat 18 is turned to a position around a 15° position, and the compression spring 7 compressed to a maximum extent is allowed to expand slightly after the seat 18 is tuned in the closing direction beyond the 15° position. Therefore, the seat 18 turned to the closed position is not raised and rests securely at the closed position.
A hinge mechanism for a toilet bowl seat or seat lid has improved control of rotation due to torque exerted by a cam member working with a compression spring and slider, such that the torque varies depending on the angle of the seat or seat lid to the plane of the toilet bowl. The slider and cam member are mounted on a shaft having an axially directed oval hole in which a complementary shaped hinge pin is received to connect the seat and the seat lid to the mechanism. A stop mechanism prevents the shaft from turning beyond a predetermined angle.