Abstract:
A method of manufacturing a valve sleeve is disclosed which is adapted to construct an oil rotary valve together with a valve rotor, and a valve sleeve of a configuration which is suitably formed by carrying out the method is also disclosed. The valve sleeve has an axially extending groove in its inner surface, and the bottom surface of the groove has a portion which is disposed at an angle with respect to the axis. The method of manufacturing comprises shaping a cylindrical member having an inner and an outer diameter, both of which are greater than those of a valve sleeve to be manufactured, inserting a punch into the material, and applying a compression to the material from the radially outside thereof to cause the internal surface of the material to bear against the punch.

Description:
This is a division of Ser. No. 870,200, filed June 2, 1986, now U.S. Pat. No. 4,706,487, issued Nov. 17, 1987. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a valve sleeve which forms an oil rotary valve and a method of manufacturing same. 
     An oil rotary valve as used in a power steering apparatus, for example, comprises a valve rotor in which a plurality of axial grooves are formed, and a valve sleeve which is rotatably fitted around the valve rotor and formed with axial grooves in its inner surface which can be aligned with the circumferentially opposite sides of a groove in the valve rotor. In response to a relative rotational displacement between the valve rotor and the valve sleeve, the supply and discharge of hydraulic fluid to or from a power cylinder can be controlled. The grooves formed in the valve sleeve are defined as blind grooves, namely, a groove in which only its middle portion is recessed to serve as a groove while the opposite ends must not be recesed. 
     A technique which forms such blind groove in the inner surface or a cylindrical valve sleeve is disclosed in Japanese Patent Publication No. 49,541/1974. In this technique, a cutter of a given size is repeatedly driven back and forth along an arcuate path of movement into the inside of a cylindrical material to form a single groove. A plurality of grooves are formed successively by synchronously rotating the cylindrical material. However, the described technique suffers from disadvantaes that an apparatus having a complex construction is required and an increased length of working time is necessary. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the invention to provide a method of manufacturing a valve sleeve having a blind groove in its inner surface, by a press operation which operates through a simple rectilinear motion. This object is achieved by inserting a punch into a cylindrical material having an inner and an outer diameter which are greater than those of a valve sleeve to be manufactured, and subsequently compressing the material radially from the outside to cause the inner surface of the material to abut against the punch. 
     It is another object of the invention to provide a valve sleeve having a configuration which is preferred for its manufacturing by a press operation having a rectilinear motion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a solid cylindrical material; 
     FIG. 2 is a longitudinal section illustrating a step of shaping a hollow cylindrical material; 
     FIG. 3 is a longitudinal secton of the cylindrical member; 
     FIG. 4 is a longitudinal section of the cylindrical member having a hole formed in its bottom; 
     FIG. 5 is a longitudinal section illustrating a first stage of a step of forming a blind groove; 
     FIG. 6 is an exploded perspective view of a punch; 
     FIG. 7 is a cross section of the stage shown in FIG. 5; 
     FIG. 8 is a cross section of a second stage; 
     FIG. 9 is a longitudinal section of a third stage; 
     FIG. 10 is a longitudinal section of a fourth stage; 
     FIG. 11 is a cross section of the stage shown in FIG. 10; 
     FIG. 12 is a longitudinal section of a fifth stage; 
     FIG. 13 is a longitudinal section of a valve sleeve; 
     FIG. 14 is a perspective view of another form of punch member; 
     FIG. 15 is a longitudinal section of a valve sleeve manufactured with the punch member shown in FIG. 14; 
     FIG. 16 is a perspective view of a further form of punch member; 
     FIG. 17 is a longitudinal section of a valve sleeve manufactured with the punch member shown in FIG. 16; 
     FIG. 18 is a persepctive view of still another form of punch member; 
     FIG. 19 is an exploded perspective view of a punch ued in a second embodiment; 
     FIGS. 20 to 25 are a series of longitudinal sections illustrating sequential steps of manufacturing according to the second embodiment; and 
     FIG. 26 is a longitudinal section of another form of cylindrical material. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to the drawings, several embodiments of the invention will now be described. Initially, a solid cylindrical material 2 as shown in FIG. 1 is formed by a machining, a cold or hot forging operation, and the material 2 is then placed in a press die 4 as shown in FIG. 2. A solid cylindrical punch 6 having a given outer diameter is then used to perform a press operation, whereby a hollow cylindrical material 8 having a bottom as shown in FIG. 3 is shaped. The inner diameter 4a of the press die 4 and the outer diameter 6a of the cylindrical punch 6 are greater than the outer diameter and the inner diameter. respectively, of a valve sleeve to be manufactured. Accordingly, the cylindrical material 8 which is shaped has an outer diameter 8a and an inner diameter 8b which are greater than the outer and the inner diameter of a valve sleeve to be manufactured. Where the bottom 8c of the cylindrical material 8 which is shaped by the press operation has a thickness greater than a desired value, the thickness is reduced to a given value by removing the material as by cutting operation. A through hole 8d is then formed centrally in the bottom 8c of the cylindrical material 8, resulting in a configuration as shown in FIG. 4. 
     In the next step, a plurality of axially extending blind grooves are formed in the inner surface of the cylindrical material 8 shown in FIG. 4. A press die 10 used in this step comprises a section 10a having an inner diameter greater than the outer diameter 8a of the cylindrical material 8, another section 10b having an inner diameter which is substantially identical with the outer diameter of a valve sleeve to be manufactured, and a tapered surface 10c which joins the both sections 10a and 10b, as indicated in FIG. 5. Accordingly, when the cylindrical material 8 is disposed inside the press dia 10, the material 8 comes to a stop upon abutment of the peripheral edge of the bottom thereof against the tapered surface 10c. A punch 12 which is shown in an exploded view in FIG. 6 is used to apply a press operation upon the material 8 which is thus disposed. 
     The punch 12 comprises a punch pin 14, six punch members 16 which are carried in the outer periphery of the punch pin 14, and a screw 18 which prevents the punch members 16 from being disengaged from the punch pin 14. The punch pin 14 has an outer diameter which is substantially identical to the inner diameter of a valve sleeve to be manufactured, and is formed with six axially extending notches 14a at an equal interval in its outer peripheral surface. These notches 14a are formed so that they exhibit a depth which gradually increases toward the front end of the punch pin 14, or to the left as viewed in FIG. 6. In other words, the bottom surface 14b of each of the six notches 14a is tapered toward the front end. In addition, the punch pin includes a projecting tapered portion 14c which continues from the bottom surfaces 14b of the notches and disposed at the front end of the punch pin. The notches 14a are shaped such that a width w 1  as measured around the outer surface is less than a width w 2  as measured along the bottom surface 14b. The punch member 16 includes a machining surface 16a which is chevron-shaped in longitudinal section, and a bottom surface 16e which is inclined at an angle of θ 1  with respect to a plane 16d which joins the both base lines 16b and 16c of the machining surface 16a. The angle θ 1  substantially matches an angle of inclination θ 2  of the tapered portion 14c of the punch pin 14. The bottom surface 16e has a width w 3  greater than a width w 4  of the machining surface 16a, and the both widths w 3  and w 4  are less than the width w 2  of the bottom surface and the width w 1  along the outer periphery of the notch 14a, respectively. Accordingly, by fitting each punch member 16 into an individual one of the notches 14a formed in the punch pin 14, and sliding the punch member relative to the notch 14a, it is possible to move the punch member 16 outward or inward in the radial direction of the punch pin 14. The width w 3  of the bottom surface 16e of the punch member 16 is greater than the width w 1  around the outer periphery of the notch 14a, whereby the disengagement of the punch member 16 radially outward from the punch pin 14 is prevented. The screw 18 has a head 18a of an outer diameter which is greater than the outer diameter 14e of a foremost end 14d of the projecting tapered portion 14c of the punch pin 14. Thus, after fitting the punch members 16 into the notches 14a in the punch pin 14 and clamping the screw 18, axial disengagement of the punch members 16 from the punch pin 14 is prevented while allowing the punch members to move together with the punch pin 14. 
     The process of plastically deforming the hollow cylindrical member 8 by a press operating using the press die 10 and the punch 12 will now be described. In FIG. 5, the material 8 is disposed within the press die 10, and the punch 12 is inserted into the material 8. The punch members 16 have travelled toward the front end of the punch pin 14 and thus remain at rest in abutment against the head 18a of the screw 18. Under this condition, the punch members 16 assume positions indicated in FIG. 7 where they have been retracted to the greatest extent toward the axis of the punch pin 14 and the machining surface 16a of the punch member 16 is clear from the inner surface 8e of the material 8. 
     Subsequently when the punch pin 14 is lowered, the individual punch members 16 cannot move down as a result of their abutment against the bottom 8c of the material 8, and hence they are raised relative to the punch pin 14. The tapered configuration of the notches 14a formed in the punch pin 14 causes the punch members 16 to be driven radially outward as they are raised relative to the punch pin 14, thus bringing the machining surface 16a of the punch member 16 into abutment against the inner surface 8e of the material 8 as shown in FIG. 8. 
     As the punch pin 14 is lowered further downward, the abutment of the punch members 16 against the upper end face 14f of the notches 14a prevent their movement relative to the punch pin, whereby the force applied to move the punch pin 14 down is effectively transmitted to the bottom 8c of the material, as a result of the abutment of the step 14g thereof against the bottom thus causing a downward movement of the material 8. As a consequence, the material 8 is gradually pressed into the area defined by the tapered surface 10c and thence into the reduced diameter portion 10b of the press die 10, as shown in FIG. 9, and is eventually pressed into the reduced diameter portion 10b completely, as shown in FIG. 10. The reduced diameter portion 10b has an inner diameter which is substantially equal to the outer diameter of a valve sleeve to be manufactured and which is less than the outer diameter of the material 8, so that the material 8 is compressed radially inward as it is driven downward, whereupon the machining surface 16a of the punch member 16 is forced into the internal surface of the material 8, thus forming an axial groove (see FIG. 11). It is to be noted that when the punch member 16 assumes its uppermost position relative to the punch pin 14, the projecting tapered portion 14c of the punch pin 14 and the screw 18 project downward through the opening 8d formed in the bottom 8c of the cylindrical member 8. 
     After the axial groove is formed in the internal surface of the material 8 in the manner mentioned above, the punch pin 14 is raised. Because the individual punch member 16 bite into the grooves 8f formed in the material 8, they cannot move upward, and thus move relative to the punch pin 14 toward the front end thereof. This allows the punch members 16 to retract radially inward, and as the punch pin 14 is raised further upward, the punch members engage the screw 18 to be disengaged from the grooves 8f, whereby they are capable of being carried upward by the punch pin 14 (see FIG. 12). 
     Subsequently, the cylindrical member 8 having axial blind grooves 8f formed therein may be removed from the press die 10 as by a knock-out pin, and then subject to a finishing operation for the internal and the external surface therof to complete a valve sleeve. As shown in FIG. 13, the valve sleeve manufactured as a result of the described steps has an axial blind groove 8f defined by a pair of bevelled surfaces 8h which exhibits the greatest depth at the axial center 8g thereof. Forming the groove 8f which has its bottom surface defined by the bevelled surfaces 8h provides an advantage that the withdrawal of the punch 12 is facilitated in that the punch 12 slides along the bevelled surfaces 8h. It will be appreciated that the formation of a blind groove in the internal surface of a valve sleeve which has been considered difficult to achieve can be accomplished in accordance with the invention by repeating a simple rectilinear motion. 
     In the described embodiment, the notch 14a formed in the punch in 14 has a width which is greater toward its bottom (w 2 ) than at its outer surface (w 1 ) to prevent the withdrawal of the punch members 16, but it should be understood that a blind groove can also be formed by using a notch which has a uniform width. While a valve sleeve having six blind grooves has been illustrated above, it will be appreciated that the number of blind grooves is not limited thereto. A variety of materials such as structural carbon steel or alloyed steel may be used for the cylindrical material 8. In addition, a hollow cylindrical, metallic material 8 having fitted therein a cylinder 8i of a different material such as formed of resin, as indicated in FIG. 26, may also be used. A choice of any desired material is enabled in this instance, in consideration of the machineability. 
     In addition, the configuration of the groove to be formed in the valve sleeve is not limited to one shown in FIG. 13. By way of example, a punch member 26 as illustrated in FIG. 14 may be used to form a groove 8f having a bottom surface which includes a constant depth portion 8j which is contiguous to bevelled portions 8h, as shown in FIG. 15. Furthermore, a punch member 36 as illustrated in FIG. 16 may be used to form a pair of bevelled surfaces 8h at the opposite ends of the groove 8f and which are joined by a portion 8j of a constant depth, located therebetween, as shown in FIG. 17. The grooves shown in FIG. 15 and 17 may be advantageous in that a greater volume is available within the groove. Finally, a punch member 46 having a pair of steps 46h at its opposite ends, as illustrated in FIG. 18, may be used to define a groove as shown in FIG. 13. Punch members 36, 46 as shown in FIG. 16 and 18 which exhibit symmetrical machining surfaces with rspect to the longitudinal center can be more easily manufactured. 
     A second embodiment of the invention will now be described which employs a punch shown in FIG. 19 to effect a press operation. A punch 20 shown comprises a punch pin 22, a punch sleeve 24 which is fitted around the punch pin 22, and six punch member 26. The punch pin 22 comprises a solid cylindrical main portion 22a, a tapered portion 22b which is located at the front end thereof, and a step 22c defined between the main portion 22a and the tapered portion 22b. The punch sleeve 24 has an inner diameter which is substantially equal to the outer diameter of the main portion 22a of the punch pin 22 and an outer diameter which is substantially equal to the inner of a valve sleeve to be manufactured, with axially extending, rectangular openings 24a formed toward its front end and equally spaced apart circumferentially. The punch member 26 includes a machining surface 26a which is chevron-shaped in cross section, and a pair of steps 26b, 26c which are located on the opposite ends of the machining surface 26a, as viewed lengthwise thereof. In addition, the punch member includes a bottom surface 26g which is inclined by an angle θ 3  with respect to a plane 26f which join the both base lines 26d and 26e of the chevron-shaped machining surface 26a. The angle θ 3  substantially matches the angle of inclination θ 4   of the tapered portion 22b as referenced to the main portion 22a of the punch pin 22. The punch 20 is assembled by fitting the individual machining surfaces 26a into the individual openings 24a with the end of the punch member 26 having an increased thickness oriented toward the front end of the punch sleeve 24 or to the left, as viewed in the drawing, and partly inserting the front end of the tapered portion 22b of the punch pin 22 into a space defined by the punch members 26. It is to be noted that the top of the punch sleeve 24 is formed with a portion 24b of an increased diameter as shown in FIG. 20 while the top of the punch pin 22 is formed with an annular projection 22d so as to be fitted into the portion 24b of the punch sleeve 24. A flange member 28 is secured around the punch sleeve 24, thus allowing the punch pin 22 to be displaced relative to the punch sleeve 24 through a distance defined between a step 24c  on the punch sleeve 24 and the lower surface 28a of the flange member 28. 
     A press operation which uses the punch 20 described above will now be described. Initially, the hollow cylindrical material 8 is disposed within the press die 10, and the punch 20 is inserted into the material 8 (see FIG. 20). As in the previous embodiment, the material 8 remains at rest in abutment against the tapered surface 10c of the press die 10 while the punch pin 22 assumes its uppermost position relative to the punch sleeve 24, with only its front end of the tapered section 22b inserted into a space defined by the punch members 26. Accordingly, the individual punch members 26 assume a most retracted position which is nearer the axis of the punch 20, and hence the machining surface 26a of the punch member 26 is clear from the internal surface 8e of the cylindrical material 8. The punch pin 22 is then driven downward. The downward movement of the punch pin 22 is not transmitted to the punch sleeve 24 until the annular projection 22e on the punch pin 22 bears against the step 24c on the punch sleeve 24, allowing only the punch pin 22 to be lowered, with the tapered portion 22b being driven further into the space defined by the punch member 26 to thereby spreading them radially outward to cause their machining surfaces 26a to contact the internal surface 8e of material (see FIG. 21). As the punch pin 22 is further driven downward, the punch sleeve 24 is also driven downward by the projection 22d on the punch pin 22, and the downward movement of the punch sleeve 24 is transmitted to the bottom 8c of the material 8, causing the material 8 to be gradually pressed into the tapered surface 10c and thence into the reduced diameter portion 10b of the punch die 10 (see FIG. 22). Finally, the material is completely pressed into the reduced diameter portion 10b (see FIG. 23). In the process of pressing the material 8 into the reduced diameter portion 10b of the press die 10, the material 8 is compressed radially inward, whereby the internal surface 8e thereof bears against the machining surfaces 26a of the punch members 26, which thus form axially extending blind grooves. 
     When the punch pin 22 is driven upward after the grooves have been formed in the internal surface 8e, only the pin 22 moves upward initially (see FIG. 24), followed by the abutment of the annular projection 22d on the punch pin 22 against the lower surface of the flange member 28 to cause an upward movement of the flange member 28 and its integral punch sleeve 24 and the punch members 26. Since the punch pin 22 have already been raised as indicated in FIG. 24, the punch members 26 are allowed to retract toward the axis, and thus can be easily disengaged from the blind grooves for upward movement, as indicated in FIG. 25. Thus, similar results can be achieved with this embodiment as mentioned previously. 
     While the invention has been illustrated and described above in connetion with several embodiments thereof, it should be understood that a number of changes, modifications and substitutions will readily occur to one skilled in the art without departing fromthe scope and spirit of the invention as defined by the appended claims.