Clutch disk for a clutch and method of treating a facing of a clutch
BACKGROUND OF THE INVENTION 
     The present invention relates to a clutch for vehicles, and more particularly to a clutch disk for a clutch used in an automobile, in the clutch disk a rust preventive is impregnated. 
     There is a clutch disc having facings which are made of sintered steel. In such a clutch, moisture in the air tends to deposit on the sliding surfaces of the facings of the clutch disk, flywheel and pressure plate of the clutch moistening the surfaces, since these members are located closely to each other with an appropriate gap. Further the moisture inside the clutch of a vehicle hardly evaporates. Accordingly, rust easily forms on the inner parts. The rust formed on the sliding surfaces of the facings and flywheel causes both members to stick to each other and causes problems with the clutch such as failure of disengagement of the clutch if the vehicle is not driven for a long time. Therefore, rust preventives must be provided on the sliding surfaces during manufacturing the automobile to prevent rusting which will occur before it is given to a user. 
     In a conventional rust prevention method, sodium nitrite is impregnated into the facings of the clutch disk and the surfaces made of iron of the flywheel and pressure plate are kept in a passive state, so that the formation of rust on the surfaces is prevented. In such a clutch disk, a sufficient amount of sodium nitrite must be maintained in the facings to obtain a satisfactory anti-corrosion effect. 
     However, the rust preventive of sodium nitrite is apt to be removed from the facing by the sliding of the facing on the flywheel during the use of the clutch for the transportation of the automobile before transfer of it to a user. As a result, sufficient rust preventing effect is not expected. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a clutch disk having a sufficient rust preventive effect, even after the clutch is once used and stored for a time. 
     The present invention will be more apparent from the following description made with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is an exploded perspective view of a clutch; 
     FIGS. 2a and 2b are explanatory broken-away cross-sectional views showing conventional facings; and 
     FIGS. 3a and 3b are explanatory views showing facings according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PRESENT INVENTION 
     The conventional rust prevention treatment is explained with reference to the attached drawing. In FIG. 1 showing a clutch for an automobile, a flywheel 1 is connected with a crankshaft of an engine (not shown), and a ring gear 2 engaging with a starter (not shown) is fixed to the periphery of the flywheel 3. In the flywheel 1, there is a clutch disk 3 connected with a transmission input shaft and has facings 4 secured to both sides thereof. A pressure plate 5 is further attached to the flywheel 1 by screws 6. Each facing 4 is made of sintered steel in porous structure. FIGS. 2a and 2b show cross sections of one of the facings 4 which is impregnated with sodium nitrite 7. In FIG. 2a, which shows the state before the facing 4 has been used, sodium nitrite 7 appears on the surface of the facing 4. If such facings with sodium nitrite 7 on the surfaces are disposed between the flywheel 1 and the pressure plate 5, are prevented from rusting. However, after use of the clutch for moving the automobile, the surface of the facing 4 wears as shown in FIG. 2b and the sodium nitrite on the surface is removed. Therefore, unless sodium nitrite remaining inside the facing 4 comes out on the surface, rust prevention is not effected. Actually it takes a lot time before the sodium nitrite 7 inside the facing 4 comes on the surface. Therefore satisfactory rust prevention cannot be expected after sodium nitrite 7 has been removed from the surface and the formation of rust will occur on the members of the clutch when the automobile reaches to a user. 
     The object of the present invention is to seek to eliminate such a drawback of the conventional clutch disk. 
     Referring to FIG. 3a showing the facing 14 corresponding to the flywheel 1 according to the present invention, a rust preventive 8 which vaporizes at 200°-300° C. is (as discussed in the next paragraph) is impregnated in the facing 14. The rust preventive is, for example, dicyclohexylammonium nitrite (C 6  H 11 ) 2  NH 2  NO 2 . The facing 14 is submerged in an aqueous solution of dicyclohexylammonium nitrite until it is deeply impregnated into the porous structure of the facing 14 as well as appearing on the surface of the facing 14 as shown in FIG. 3a. 
     Before the clutch operates, the state of which is shown in FIG. 3a, the rust preventive 8 impregnated in the facing 14 appears on the surfaces of the facing 4. Therefore, the sliding surfaces of the flywheel and pressure plate are prevented from rusting by the rust preventive. When the clutch operates, the facings of both sides of the clutch disk engage with the flywheel 1 and the pressure plate 5 at a pressure about 2 Kg/cm 2 . Although the rust preventive is removed by sliding between these members, friction heat is generated on both of the facings 14. The friction heat raises the temperature to 200°-300° C. and the rust preventive in the facing is vaporized, forming a rust preventive layer on the surface of the facing as shown in FIG. 3b, thereby preventing rusting of the iron. Further, the higher the friction temperature caused by the clutch operation, the more the rust preventive 8 moves to the surface to compensate the loss of rust preventive so as to continuously prevent the rusting. Such a movement of the rust preventive 8 continues until all the rust preventive is exhausted and runs out. A required amount of rust preventive 8 may be impregnated in the facing in accordance with the period required to protect the sliding members. 
     In accordance with the present invention, a rust prevention film is formed on sliding surfaces of the flywheel 1 and pressure plate 5 to prevent rusting thereof, even if the clutch is used for the transportation of the automobile. Thus, rust prevention can be maintained for a long time.