Patent Publication Number: US-8118080-B2

Title: Control valve body of automatic transmission and manufacturing method therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 11/596,845, now U.S. Pat. No. 7,854,250 which is a national phase application of International Application No. PCT/JP2005/009114, filed May 12, 2005, and claims the priority of Japanese Application No. 2004-150931, filed May 20, 2004, the contents of all which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a control valve body of an automatic transmission, in which a channel groove for hydraulic oil for use in a speed change operation of the automatic transmission is formed between partitions, and also to a method for manufacturing the same. 
     BACKGROUND ART 
     Japanese Patent Laid-open Publication No. 2000-320502 discloses related art of a control valve body of an automatic transmission. According to this related art, a valve body member which has a hydraulic oil channel groove formed on at least one surface thereof and constituting a hydraulic circuit, and a cap member which is attached to the surface of the valve body member where the channel groove is formed and covers the channel groove, are provided. On the cap member, a supporting portion is formed, which has a side surface for supporting the partition between the channel grooves on the valve body member, against pressing pressure applied from an oil channel in the form of the channel groove. With this arrangement, the thickness of the partition formed on the valve body member, and accordingly the size and weight of the valve body member, can be reduced. 
     In addition to the above, Japanese Patent Laid-open Publication No. Hei 10-238628 discloses a control valve body of an automatic transmission. Further, as other background art, Japanese Patent No. 3286224 and Japanese Patent Laid-open Publication No. Hei 11-124692 disclose a magnesium-molded product. 
     A control valve body of an automatic transmission is generally manufactured through aluminum die-casting. A hydraulic oil channel groove defined on the valve body is formed using a steel casting mold. However, in an attempt to reduce the width of the channel groove in manufacturing the valve body through aluminum die-casting, the casting mold in use is readily deteriorated due to the reaction between the aluminum melted liquid and the steel casting mold and heat exhaustion or the like in a cooling and heating cycle. Therefore, it is not practicable to employ a valve body having a channel groove of a narrower width. 
     According to Japanese Patent Laid-open Publication No. 2000-320502, where size and weight reduction of the valve body is attempted by forming a thinner partition, a problem remains that sufficient size and weight reduction of the valve body cannot be readily achieved as employment of a channel groove having a narrower width is not practicable due to the above-described reason. 
     The present invention aims to provide a control valve body of an automatic transmission in which a hydraulic oil channel groove having a narrower width can be formed, and a method for manufacturing such a control valve body. 
     DISCLOSURE OF INVENTION 
     According to the present invention, there is provided a manufacturing method for manufacturing a control valve body of an automatic transmission where a channel groove for hydraulic oil for use in a speed change operation of the automatic transmission is formed between partitions, comprising a magnesium die-casting step of pouring, by means of pressure, melted liquid of magnesium or magnesium alloy into a hollow portion formed using a casting mold, to thereby mold a valve body having the partitions formed thereon, and in the magnesium die-casting step, the channel groove is formed due to a convex portion which is formed on the casting mold so as to project into the hollow portion. 
     According to the present invention, by pouring, by means of pressure, the melted liquid of magnesium or magnesium alloy into the hollow portion formed using a casting mold, a valve body where partitions for forming a hydraulic oil channel groove are formed is molded. 
     With the above, variation of the temperature of the mold during the cooling and heating cycle can be suppressed, and the reactivity between the melted liquid and the mold can be eliminated. Therefore, according to the present invention, the convex portion formed on the mold for formation of a channel groove is not deteriorated. This allows employment of a thinner convex portion, and accordingly, formation of a hydraulic oil channel groove having a narrower width. 
     In the method for manufacturing a control valve body of an automatic transmission according to the present invention, a piercing pin which projects into the hollow portion and pierces through the convex portion is provided on the casting mold, and in the magnesium die-casting step, a valve hole for allowing the valve to pierce through the partitions is formed by the piercing pin. 
     With this arrangement, it is possible to reduce the force (side force) which is perpendicular to the shaft of the valve and acts on the valve piercing through the partitions. 
     According to another aspect of the present invention, there is provided a control valve body of an automatic transmission where a channel groove for hydraulic oil which is used in a speed change operation of the automatic transmission is formed between partitions, wherein a valve body having the partitions formed thereon is made using magnesium or magnesium alloy. 
     According to the present invention, the valve body where partitions for forming a channel groove for hydraulic oil are formed is made using magnesium or magnesium alloy. This enables formation of a channel groove for hydraulic oil having a narrower width. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross sectional view schematically showing a structure of a control valve body of an automatic transmission according to an embodiment of the present invention; 
         FIG. 2  is a cross sectional view schematically showing a structure of a control valve body of an automatic transmission according to the embodiment of the present invention; 
         FIG. 3  is a cross sectional view schematically showing a structure of a magnesium die-casting device used in carrying out a method for manufacturing the control valve body of the automatic transmission according to the embodiment of the present invention; 
         FIG. 4  is a cross sectional view schematically showing a structure of a magnesium die-casting device used in carrying out a method for manufacturing the control valve body of the automatic transmission according to the embodiment of the present invention; and 
         FIG. 5  is a cross sectional view explaining a side force applied to the valve. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the following, a preferred embodiment of the present invention will be described with reference to the accompanied drawings. 
       FIGS. 1 and 2  are cross sectional views schematically showing a structure at different positions of a control valve body of an automatic transmission according to an embodiment of the present invention. A valve body  10  according to this embodiment has a plurality of partitions  12  formed on a base surface  10 - 1  of the valve body  10  thereof so as to project in a substantially vertical direction thereto, so that a channel groove  14  for hydraulic oil, which is used in a speed change operation of the automatic transmission, is defined between the partitions  12 . It should be noted that  FIGS. 1 and 2  show only a part of the valve body  10 , and that the overall shape of the valve body  10 , which can be realized in a known shape, is not shown. The valve body  10  according to this embodiment is used in a hydraulic control circuit for an automatic transmission such as a multi-speed AT, a CVT, or the like. 
     As shown in  FIG. 2 , a valve hole  18  is formed on some of the partitions  12 , so that the valve  16  passes through the valve holes  18  to thereby pass through the partitions  12  in the substantially vertical direction. When the valve  16  slides in the substantially vertical direction relative to the partitions  12  (that is, the direction substantially parallel to the base surface  10 - 1  of the valve body  10 ), oil grooves for use in a speed change operation of the automatic transmission can be switched. 
     In this embodiment, the valve body  10  having the partitions  12  formed thereon is made using magnesium or magnesium alloy. As an example of magnesium alloy, AZ group (AZ91D and so forth), or AM group (AM60 B an so forth) may be employed here. In addition, AS group (AS21 and so forth) having heat resistance imparted, or heat resistant alloy with Ca, Sr, RE (Ce, La, Pr, Nd), Sn or the like added thereto may also be applicable. Any alloy containing magnesium as a main component can be used as the material of the valve body  10  according to this embodiment. 
     In the following, a method for manufacturing the valve body  10  according to this embodiment will be described. The valve body  10  according to this embodiment can be manufactured through steps including a magnesium die-casting step. 
       FIGS. 3 and 4  are cross sectional views schematically showing a structure at different positions of a magnesium die-casting device which is used in carrying out a method for manufacturing the valve body  10  according to this embodiment. The die-casting device in this embodiment has a steel mold including a fixed side die  21  and a moving side die  22 . The fixed side die  21  and the moving side die  22  together form a hollow portion  23  for molding the valve body  10 . 
     A plurality of convex portions  27  are formed on the moving side die  22 , which project into the hollow portion  23 . Further, as shown in  FIG. 4 , a moving pin  28  is provided to the moving side die  22 , which projects into the hollow portion  23  while piercing through some of the convex portions  27  in the substantially vertical direction. 
     In the magnesium die-casting step, the melted liquid  29  of magnesium or magnesium alloy is poured into the hollow portion  23  by means of pressure from the plunger  26  for molding the valve body  10 . In the molding, the channel groove  14  is formed due to the convex portion  27 , and the melted liquid  29  poured into the space between the convex portions  27  forms the partition  12 . The valve hole  18  is formed due to the moving pin  28 . It should be noted that as the melted liquid  29  of magnesium alloy, the melted liquid  29  of the above described materials may be employed. 
     After the melted liquid  29  having been poured into the hollow portion  23  by means of pressure is consolidated through cooling, the moving pin  28  is pulled out from the moving side die  22 , and the moving side die  22  is moved to thereby release the hollow portion  23 . Then, known machining is carried out on the valve body  10  which is molded through magnesium die-casting. Through the above-described steps, the valve body  10  according to this embodiment can be manufactured. 
     Here, a case in which the valve body  10  is molded through aluminum die-casting is considered. In this case, due to the large heat capacity of the aluminum, the temperature of the dies  21 ,  22  may vary largely in a cooling and heating cycle. Further, the reaction between the melted aluminum liquid and the steel dies  21 ,  22  readily leads to formation of reactant on the surface of the dies  21 ,  22 . As a result, the dies  21 ,  22  (in particular, the convex portion  27  thereof) are readily deteriorated. Therefore, in the case where the valve body  10  is molded through aluminum die-casting, a die  22  having thinner convex portions  27  formed thereon is not appropriately employed. This makes it difficult to form a valve body  10  having a channel groove  14  with a narrower width. 
     Meanwhile, in this embodiment, magnesium die-casting is employed in molding of the valve body  10  having partitions  12  formed thereon. As magnesium has a smaller heat capacity than aluminum, the variation of the temperature of the dies  21 ,  22  in the cooling and heating cycle can be suppressed. Moreover, as the melted magnesium liquid  29  has no reactivity with respect to the steel dies  21 ,  22 , deterioration of the dies  21 ,  22 , in particular, of the convex portion  27  thereof, can be suppressed. Therefore, according to this embodiment, as the convex portion  27  is not deteriorated, a thinner convex portion  27  can be employed. This enables formation of a valve body  10  having a channel groove  14  having a narrower width d, and therefore, size reduction of the valve body  10  can be achieved. It should be noted that, in this embodiment, typically, the width d of the channel groove  14  can be reduced to smaller than 3 mm. 
     Further, in this embodiment, the use of magnesium, which has smaller relative density than aluminum, as the material of the valve body  10  enables reduction of the weight of the valve body  10 . 
     In addition, in the case where the valve body  10  is molded through aluminum die-casting, it is difficult to ensure a smaller draft angle due to the reactivity between the aluminum melted liquid and the steel dies  21 ,  22 . Specifically, when there is a draft angle defined on the partition  12 , as shown in  FIG. 5 , the width of the channel groove  14  becomes wider as it goes away from the base surface  10 - 1  of the valve body  10 . In this case, in consideration of the force (a side force) which is perpendicular to the shaft of the valve  16  and acts on the valve  16  due to the pressure of the hydraulic oil having been poured into the channel groove  14 , the side force A due to the pressure by the hydraulic oil near the tip end side of the partition  12  (upper in  FIG. 5 ) is larger than the side force A′ due to the pressure of the hydraulic oil near the base surface side  10 - 1  (lower in  FIG. 5 ). In other words, a side force which is directed from the tip end side of the partition  12  toward the base surface  10 - 1  side thereof acts on the valve  16 . This side force causes the friction of the valve  16  to increase, leading to deterioration of the oil groove switching capability. 
     Meanwhile, in this embodiment, as the valve body  10  having partitions  12  formed thereon is molded through magnesium die-casting, the reactivity between the magnesium melted liquid  29  and the steel dies  21 ,  22  can be eliminated. This makes it possible to ensure a smaller draft angle of the partition  12 . As a result, the channel groove  14  having constant widths on the tip end side of the partition  12  and the base surface  10 - 1  side can be formed. This makes it possible to reduce the above-described side force which acts on the valve  16 . Therefore, in this embodiment, the friction of the valve  16  can be reduced, and the oil groove switching capability can be enhanced. It should be noted that in this embodiment, typically, the draft angle of the partition  12  can be reduced to smaller than two degrees. 
     Further, in this embodiment, beside realization of a smaller draft angle, molding of the valve  10  through magnesium die-casting enables reduction of consumption of the mold release agent. 
     It should be noted that, although an embodiment to render the present invention into practice has been described in the above, the present invention is not limited to such an embodiment, and that a variety of modifications can be made to the present invention within the scope and gist of the present invention.