Abstract:
A cylindrical member is placed in a dead-end hole formed in a housing made of a material such as aluminum. A peripheral portion of the hole is pressed down to plastically deform the housing material and to supply the deformed material into a groove formed on an outer periphery of the cylindrical member. The cylindrical member is calked to the housing in this manner. To supply a proper amount of deformed material into the groove for obtaining a quality calking, an inflection point of a calking curve indicating a relation of a calking force and a calking stroke is detected during the calking process. After the inflection point is detected, the calking is performed by giving a predetermined calking stroke or by adding a predetermined calking force.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
         [0001]    This application is based upon and claims benefit of priority of Japanese Patent Application No. 2000-231648 filed on Jul. 31, 2000, the content of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a method of fixing a cylindrical member in a hole by calking. For example, an electromagnetic valve of an ABS actuator is fixed by calking in a hole formed in a housing.  
           [0004]    2. Description of Related Art  
           [0005]    It is generally known to fix a cylindrical member in a hole by calking. In the conventional calking, either a calking force or a calking stroke is kept constant. The former is called constant pressure calking and the latter is called constant stroke calking. In both calking processes, however, it has been difficult to attain quality calking because dimensions of members to be calked are not always constant. It is especially important to attain quality calking when a high strength and a high sealing ability of a calked portion are required.  
           [0006]    To improve the calking quality, it could be possible to machine the members to be calked with high accuracy or to determine calking conditions according to dimensions of respective members. However, it is time-consuming and costly to employ such a process.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved calking method in which quality calking is attained in a simple manner.  
           [0008]    A member having a cylindrical portion is fixed by calking to a depressed portion formed in a housing. A groove is formed on the outer periphery of the cylindrical portion. A peripheral portion of the depressed portion is pressed down to plastically deform a part of the housing material such as aluminum and to supply the deformed housing material into the groove. Thus, the member having the cylindrical portion is fixed to the housing. This calking method is used, e.g., for fixing electromagnetic valves to an aluminum housing of an ABS actuator.  
           [0009]    In the process of deforming the housing material, a relatively large amount of calking force is required until the housing material begins to be supplied into the groove. On the other hand, a relatively small amount of calking force is required during the course of filling the groove with the housing material. This means that a calking curve showing the amount of calking force required relative to the calking stroke has an inflection point. In other words, an inclination of the calking curve is large up to the inflection point and becomes small after the inflection point.  
           [0010]    During the calking process, the calking force and the calking stroke are measured to detect the inflection point based on the inclination of the calking curve. A point where the inclination becomes lower than a predetermined value is determined as the inflection point. Alternatively, a point where the inclination changes considerably may be determined as the inflection point. After the calking process reached the inflection point, the calking is performed with a predetermined constant stroke. In this manner, a substantially constant amount of the deformed housing material is supplied into the groove, if there are certain dimensional deviations in members to be calked together. The constant stroke is predetermined, so that an adequate amount of the housing material for obtaining quality calking is supplied into the groove. Instead of setting the constant stroke, a predetermined constant calking force may be added after the inflection point.  
           [0011]    According to the present invention, the quality calking having a high mechanical strength and a high sealing ability is realized because a proper amount of the housing material is supplied into the groove.  
           [0012]    Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a plan view showing an ABS actuator having electromagnetic valves calked in depressed portions formed in a housing;  
         [0014]    [0014]FIG. 2A is a cross-sectional view showing a calking portion before members are calked;  
         [0015]    [0015]FIG. 2B is a cross-sectional view showing a calking portion after the members are calked;  
         [0016]    [0016]FIG. 3 is a cross-sectional view showing a calking portion where an electromagnetic valve is placed in a depressed portion of a housing;  
         [0017]    FIGS.  4 A- 4 C are cross-sectional views showing a process of calking;  
         [0018]    [0018]FIG. 5 is a graph showing relation between a calking stroke and a calking force; and  
         [0019]    [0019]FIG. 6 is a graph showing relation between a calking stroke and a calking force; one curve showing a situation where the members are calked with a small clearance and a deep groove, and the other curve with a large clearance and a shallow groove. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an ABS (anti-block braking system) actuator in which electromagnetic valves  2  are calked in depressed portions  1   b  formed in a housing  1 . plural braking fluid passages are formed in the aluminum housing  1 , and electromagnetic valves  2  for opening and closing the fluid passages are fixed to the housing  1  by calking. Among the plural electromagnetic valves  2 , four valves control communication in passages connecting a master cylinder and each wheel cylinder, and the other four valves control communication in passages connecting a reserve tank and each wheel cylinder. Since the electromagnetic valves  2  are disposed in a high pressure passages, they have to be liquid-tightly fixed to the housing  1  with a high sealing ability and a high mechanical strength.  
         [0021]    As shown in FIGS. 1, 2A and  2 B, each electromagnetic valve  2  is placed in a depressed portion  1   b  formed in the housing  1  and fixed to the housing  1  by depressing a peripheral portion  1   a  around the depressed portion  1   b . The calking process according to the present invention will be explained in detail with reference to FIGS.  2 A- 4 C.  
         [0022]    [0022]FIG. 2A shows a calking portion in which an electromagnetic valve  2  is placed in a depressed portion  1   b  formed in the housing  1 . The electromagnetic valve  2  has a cylindrical portion  2   a  at which the electromagnetic valve  2  is fixed to the housing  1  by calking. A triangular groove  2   b  is formed around the cylindrical portion  2   a . The diameter of the depressed portion  1   b  is a little larger than the outer diameter of the cylindrical portion  2   a . The thickness of the cylindrical portion  2   a  is made larger than the depth of the depressed portion  1   b , so that a part of the cylindrical portion  2   a  sticks out from the depressed portion  1   b.    
         [0023]    [0023]FIG. 2B shows the calking portion after the electromagnetic valve  2  is fixed to the housing  1  by calking. A peripheral portion  1   a  surrounding the depressed portion  1   b  is pressed down by a cylinder-shaped calking punch. The inner bore of the depressed portion  1   b  is deformed by the calking force, and a part of the housing material (aluminum in this embodiment) swells into the groove  2   b . In other words, the calking force causes plastic deformation of the housing material and the groove  2   b  is filled with the housing material. To give a liquid-tight sealing function to the calked portion, the groove  2   b  has to be filled with a sufficient amount of the housing material, and the housing material has to closely contact the surface of the groove  2   b.    
         [0024]    However, if too much housing material that generates an excessive pressure on the groove surface is supplied into the groove  2   b , the electromagnetic valve  2  is deformed by the pressure. Therefore, it is necessary to control the amount of housing material filling the groove  2   b  within a limited range. That is, the amount of housing material has to be precisely controlled. It is difficult, however, to precisely control the amount of housing material in the conventional calking process. This is because the dimensions of the cylindrical portion  2   a  and the depressed portion  1   b  somewhat varies from piece to piece. A clearance B between the cylindrical portion  2   a  and the depressed portion  1   b , the depth C of the depressed portion  1   b , and the thickness A of the cylindrical portion  2   a , all shown in FIG. 3, are not always constant. Those dimensions deviate piece by piece. Therefore, the amount of housing material cannot be kept constant in the conventional calking process.  
         [0025]    In order to realize a calking process in which the amount of housing material that fills the groove  2   b  is kept substantially constant, the calking mechanism is investigated in detail. The mechanism will be explained with reference to FIGS.  4 A- 4 C. First, as shown in FIG. 4A, the cylindrical portion  2   a  of the electromagnetic valve  2  is placed in the depressed portion  1   b  of the housing  1 , and a cylindrical calking punch  3  is positioned on the surface of the housing  1 . Then, as shown in FIGS. 4B and 4C, a calking force is applied to the punch  3  to press down the peripheral portion  1   a . The inner bore of the depressed portion  1   b  is plastically deformed by the calking force until the deformed housing material fills the groove  2   b.    
         [0026]    The deformed housing material only fills the clearance B during a period from the beginning of the deformation to the point where the deformed material starts to enter the groove  2   b . Therefore, during this period, a large calking force is required to make the deformation of the housing material. Once the deformed material beings to enter the groove  2   b  that has a large space, the punch  3  easily moves downward with a smaller calking force. The calking force versus the caking stroke is plotted in the graph in FIG. 5. As seen in the graph, the curve showing the relation between the calking stroke and the calking force has an inflection point. That is, the curve sharply rises up with a substantially constant inclination up to the inflection point, and it slowly rises after the inflection point. The inflection point corresponds to the point where the deformed housing material begins to enter the groove  2   b . Therefore, it is possible to control the amount of deformed material entering the groove  2   b  on the basis of the inflection point.  
         [0027]    According to the investigation results described above, the calking process of the present invention is carried out in the following manner. First, the cylindrical portion  2   a  of the electromagnetic valve  2  is placed in the depressed portion  1   b  of the housing  1 . Then, the calking force is applied to the punch  3 . The calking force applied to the punch  3  and the downward stroke of the punch  3  are measured to find the inflection point. After the inflection point is detected, the punch  3  is pressed down by a stroke which is suitable to supply a desired amount of the deformed material into the groove  2   b . Such a suitable stroke is predetermined through experiments.  
         [0028]    More particularly, the inclination of the calking curve is calculated during the calking process based on the measured calking force and stroke. A point where the calculated inclination becomes smaller than a predetermined threshold value is determined as the inflection point. Alternatively, the calking force F and the calking stroke S are measured with certain intervals (a sampling method), and the inclination of the calking curve is calculated. A point where an inclination difference between two neighboring measuring points exceeds a predetermined threshold value is determined as the inflection point.  
         [0029]    By pressing down the punch  3  by the predetermined stroke from the detected inflection point, the amount of the deformed housing material supplied to the groove  2   b  is kept substantially constant even if there are deviations in the dimensions A, B and C. As shown in FIG. 6, the calking curve in the case where the clearance B is small and the depth of the groove  2   b  is deep differs from the calking curve in the case where the clearance B is large and the depth of the groove  2   b  is shallow. Irrespective of the shape of the calking curve, the quality calking is realized according to the present invention, because the inflection point is always detected in each calking curve and the stroke is measured from the detected inflection point. Further, since the inflection point indicates the position of the groove  2   b , it is possible to detect the position of the groove  2   b  based on the inflection point.  
         [0030]    The present invention is not limited to the embodiment described above, but it may be variously modified as long as the amount of housing material supplied to the groove  2   b  is controlled on the basis of the inflection point. For example, an amount of calking force increase from the inflection point may be controlled at a constant value, or a predetermined amount of the calking force may be added to the calking force applied at the inflection point. Though the calking process for fixing the electromagnetic valve to the ABS actuator housing is shown in the foregoing embodiment, the calking process of the present invention may be applied to other similar members requiring a quality calking.  
         [0031]    While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.