Lip seal device for water pumps
BACKGROUND OF THE INVENTION 
     The present invention relates to a lip seal device for water pumps. 
     Heretofore, for sealing the water pump of an automobile, a mechanical seal device has been used. Generally, such devices include a follower ring slidably and axially provided within a case attached to a housing, and a sealing plate mounted on a rotary shaft passing through the shaft of the follower ring with the follower ring being brought into sliding contact with the sealing plate due to the elastic force of a coil spring, whereby the engine coolant is kept liquid-tight by the sealing surface between these members. An example of such a mechanical seal is shown in commonly assigned U.S. Pat. No. 4,733,873. 
     However, the mechanical seal device of the above structure has disadvantages in that since the follower ring is supported by the coil spring, it has a wide range of freedom of movement so that it can easily frictionally vibrate. Once the follower ring has begun to vibrate, the coil spring also vibrates in resonance therewith, resulting in transmitting an amplified vibration to all parts of the automobile engine. This phenomenon is especially bothersome when the engine is at idle or rotating at a low speed, that is, when the engine noise level is low. During such times, an abnormal &#34;creaking&#34; sound is liable to be heard. 
     Further disadvantages of the mechanical seal device are that since the follower ring is slidably mounted in the case so as to come into sliding contact with the sealing plate due to the elastic force of the coil spring, not only is the overall seal device unavoidably large, but also the structure thereof is complicated and expensive. 
     Further, a lip-type seal device is known for use in sealing an automotive compressor which uses no coil spring. An example of such a lip-type seal device is described in commonly assigned U.S. Pat. No. 4,721,314. However, such seal devices have not previously been used for sealing water pumps. That is, in a compressor, the liquid for which the seal is provided is a type of oil, which provides a much better lubricating effect for the seal than can water in the case of a water pump. If such a lip seal for a compressor were used in a water pump, leakage would unavoidably occur. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to eliminate the above-described disadvantages of the conventional mechanical seal device, and a principal object of the invention is to provide a lip seal device for use with an automobile water pump which can effectively prevent the generation of abnormal sounds yet which provides a good sealing effect. 
     The lip seal device according to the present invention comprises a rotary shaft rotatably supported in a housing, a case mounted in the housing and having an axial section through which the rotary shaft passes so as to freely rotate and at least one lip having its outside circumferential surface attached to the case and its inner circumferential surface held in sliding contact with a sleeve disposed around the outside circumferential surface of the rotary shaft. 
     The lip seal device of the present invention having the above-described structure attains substantially the same level of efficiency as the conventional mechanical seal device but, due the absence of any resonant part such as the coil spring of the conventional seal device, prevents the generation of abnormal noise while providing a good sealing effect. Further, since the structure thereof is simple, it can be manufactured with a compact size and at a low cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a water pump employing a lip seal device constructed according to a first embodiment of the invention; 
     FIG. 2 is an enlarged cross-sectional view of the lip seal device of the first embodiment; 
     FIG. 3 is a cross-sectional view of a portion of a lip seal device of a second embodiment of the invention; and 
     FIG. 4 is a cross-sectional view of a portion of a lip seal device of a third embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will now be described on the basis of first and second preferred embodiments thereof and with reference to the accompanying drawings. 
     The first embodiment of the present invention is shown in FIGS. 1 and 2. Referring to FIG. 1, a rotary shaft 4 is rotatably supported in a throughhole 2 formed in a water pump housing 1 through a bearing 3, and a pulley 5 is mounted on one end of the rotary shaft 1 projecting outside the housing 1 and interlocked with an engine crankshaft (not shown). 
     On the other end of the rotary shaft 4 located within the housing 1 there is mounted a rotor 6 for feeding liquid coolant, and at a portion between the rotor 6 and the bearing 3 in the throughhole 3 there is provided a seal lip device 8 for sealing a coolant passage 7. 
     As shown on a enlarged scale in FIG. 2, the seal lip device 8 includes a cylindrical case 10 fixed to the housing 1 and two sheets of seal lips 11 and 12 made of polytetrafluoroethylene (PTFE) disposed in the case 10. The case 10 includes a cylindrical main body 10a, a flange 10b extending radially and outwardly from the right end portion of the main body 10a, and a flange 10c extending radially and inwardly from the left end portion of the main body 10a. 
     The case 10 is fixed to the housing 1 in such a manner that it is press-fitted into the throughhole 2 until the flange 10b extending outwardly in the radial direction comes into contact with the inner wall of the housing 1. 
     The two seal lips 11 and 12 received within the cylindrical main body 10a of the case 10 are arranged such that the outside circumference of the lip 11 is held in contact with the flange 10c. A spacer 13 is inserted midway between the outside circumferences of the lips 11 and 12 and the lip 12 is supported by a spacer 14 press-fitted and fixed within the main body 10a of the case 10 so that the lip 11, spacer 13 and lip 12 are integrally fixed between the flange 10c and the spacer 14. As shown in FIGS. 2 and 3, spacer 14 has a flat side face 14a which faces the flange 10c. The flat side face has a radial thickness which is smaller than the radial thickness of the flange 10c and which is larger than the radial thickness of the main body 10a of the case 10. Further, the flat side face 14a has a radial thickness which is smaller than the axial width of the spacer 14. 
     Further, as shown in FIG. 2, the rotary shaft 4 passes through the case 10 in the axial direction so as to rotate freely, and a sleeve 16 made of a material having excellent antiabrasive and anticorrosive properties is fixed to the outside circumference of the rotary shaft 4 at the portion at which the rotary shaft 4 passes through the case 10 through a rubber seal member 15. For the material of the sleeve 16, it is preferred to employ a ceramic material, such as alumina or titanium carbide, or a metallic material, such as stainless steel, steel having a chrome plating, or a copper alloy, for example, a copper-tin alloy. In addition, a portion of the inner circumferential surface of each of the lips 11 and 12 is curved toward the coolant side from the radial direction, that is, toward the right in the axial direction, so that a portion of each lip is held in sliding contact with the outside circumferential surface of the sleeve 16 by its own elastic force. 
     With the above arrangement, since each of the lips 11 and 12 is in close contact with the sleeve 16 fixed to the rotary shaft 4 due to its own elastic force when the engine (not shown) is not running, the coolant in the passage 7 is prevented form leaking outside. 
     Further, when the engine is started, the rotary shaft 4 is driven to rotate through the pulley 5 to cause the rotor 6 to rotate therewith, the coolant in the passage 7 is supplied to all required parts of the engine. In this case, the lips 11 and 12 slide against the sleeve 16, but, even when the rotary shaft 4 is rotating, they constantly serve to prevent the coolant from leaking to the outside. 
     Thus, unlike the conventional mechanical seal devices, the lip seal device 8 of the above-described embodiment does not include a resonant member such as a coil spring, and therefore the generation of abnormal noise is prevented. Further, the device of the invention can be manufactured with a compact size and at low cost since the number of parts and the number of manufacturing steps are minimized. 
     A second embodiment of the present invention is shown in FIG. 3. As will be seen from this figure, the lip seal device of this embodiment is provided on the sliding outside circumferential surface with a spring 17 surrounding the rotary shaft 4 in lieu of the seal lip 11 and the spacer 13 of the first embodiment. The remaining parts are the same as those of the first embodiment, and the same operation and effects as those of the first embodiment can be attained by this embodiment. A single flange portion 15A is provided on the seal member 15 to prevent movement of the sleeve 16. The flange portion has a beveled portion 15C disposed at an inner circumferential surface of the seal member 15. As shown in FIG. 3, the length of the inner surface of the cylindrical portion of seal member 15 is greater than that of the sleeve 16. 
     In a third embodiment of the invention as shown in FIG. 4, the rubber seal member 15 is provided with two flange portions 15A and 15B, rather than the single flange portion 15A employed in the above-described embodiments. Although it is not absolutely to provide even the single flange portion, use of a flange portion is useful in that it prevents movement of the sleeve against pressure. The provision of two flange portions enhances this effect. 
     As described above, according to the lip seal device of the present invention, the generation of abnormal noise is prevented due to the elimination of a coil spring or the like. Moreover, the inventive lip seal device can be manufactured with a compact size, and, since it is not necessary to employ a rotary shaft having a precisely controlled diameter due to the use of the sleeve, the lip seal device of the invention can be produced at a low cost.