Abstract:
An operation unit includes a case and an operation member molded integrally through injection molding. The operation member includes an outer surface and a slide portion supported by the case. The slide portion is slidable and movable relative to the case. The operation member further includes a knob operated by an operator, a parting line formed continuously from the slide portion to the knob along the outer surface, and a ridge line formed on the outer surface. At least part of the parting line is formed along the ridge line.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2011-173237, filed on Aug. 8, 2011, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an operation unit provided with an operation member including an outer surface having a parting line. 
     A typical vehicle includes electrical devices such as an air conditioner and audio equipment. An operation unit, which is arranged in the passenger compartment, is operated to control such a device. Japanese Laid-Open Patent Publication No. 2010-122992 describes an example of such an operation unit. 
     The operation unit of Japanese Laid-Open Patent Publication No. 2010-122992 includes a case and an operation member, which is held in a state slidable and movable relative to the case. Referring to  FIG. 8 , a cylindrical operation member  80  includes a slide portion  81 , a step portion  82 , and a knob  83 . The slide portion  81  is movable relative to the case. The step portion  82  is continuous with an upper part of the slide portion  81  and has a smaller diameter than the slide portion  81 . The knob  83  is continuous with an upper part of the step portion  82  and has a smaller diameter than the step portion  82 . Knurls  84  are formed on the outer surface of the knob  83  to prevent slipping. Each knurl  84  is pyramidal. A lubricant such as grease is applied to the outer surface of the slide portion  81  to reduce friction between the slide portion  81  and the case. This allows for smooth rotation of the operation member  80  relative to the case. 
     The operation member  80  of Japanese Laid-Open Patent Publication No. 2010-122992 is injection molded. Injection molding is performed by filling a plurality of molds with thermoplastic resin. This allows for easy molding of a product having a complicated shape. However, an elevated line referred to as a parting line is formed on a molded product at where molds meet. Four parting lines PL are formed on the outer surface of the operation member  80 . The four parting lines PL are formed at equal intervals in the circumferential direction. Each parting line PL extends straight from the slide portion  81  to the knob  83 . 
     The lubricant applied to the slide portion  81  may be transferred to the knob  83  along the parting lines PL due to capillary action. When the lubricant is transferred to the knob  83 , the lubricant may stick to a user&#39;s hand as the user operates the knob  83 . 
     To solve this problem, a through hole  85  extending through the operation member  80  from its outer surface to its inner surface is arranged on each of the four parting lines PL between the knurls  84  and the slide portion  81 . The through holes  85  block the capillary action of the lubricant along the parting lines PL. 
     Such an operation unit often includes a light source arranged in the operation member  80 . This forms a path of light in the operation member  80  and illuminates a panel (not shown), which is arranged in the vicinity of the distal end of the operation member  80 , from the rear. The light leaking through the panel allows the user to recognize the operation positions or the like of the operation member  80  especially in the nighttime. However, when the light source is arranged in the operation member  80 , the light emitted from the light source may also leak from the through holes  85 . The leaked light will illuminate the surrounding of the operation member. This is not preferable from an aesthetic viewpoint. Japanese Laid-Open Patent Publication No. 2010-122992 illustrates that the through holes  85  may be replaced by openings or recesses that do not extend through the wall of the operation member  80 . However, in this case, each parting line PL remains connected and is not split apart. That is, the capillary action of the lubricant that occurs along the parting line PL is not blocked. Thus, there is a demand for development of an operation unit that suppresses the occurrence of a capillary action without the through holes  85  and prevents lubricant from leaking to the exterior. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is an operation unit including a case and an operation member molded integrally through injection molding. The operation member includes an outer surface and a slide portion supported by the case. The slide portion is slidable and movable relative to the case. The operation member further includes a knob operated by an operator, a parting line formed continuously from the slide portion to the knob along the outer surface, and a ridge line formed on the outer surface. At least part of the parting line is formed along the ridge line. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
         FIG. 1  is a perspective view showing a passenger compartment including operation units; 
         FIG. 2A  is a cross-sectional view showing an operation unit according to one embodiment of the present invention; 
         FIG. 2B  is an enlarged cross-sectional view of  FIG. 2A  showing hooks; 
         FIG. 3A  is a perspective view showing an operation member of the operation unit; 
         FIG. 3B  is an enlarged view of  FIG. 3A  showing a knob; 
         FIG. 3C  is an enlarged view of  FIG. 3A  showing a region from a mounted portion to a step portion 
         FIG. 3D  is an enlarged view of  FIG. 3A  showing a region from the step portion to a slide portion; 
         FIG. 4  is a cross-sectional view of a mold used in a process for manufacturing the operation member; 
         FIG. 5A  is a cross-sectional view taken along line A-A in  FIG. 4 ; 
         FIG. 5B  is a cross-sectional view taken along line B-B in  FIG. 4 ; 
         FIG. 6  is a perspective view showing a modification of the operation member; 
         FIG. 7  is a cross-sectional view showing a process for manufacturing the operation member of  FIG. 6  taken along a plane corresponding to line B-B in  FIG. 4 ; and 
         FIG. 8  is a perspective view showing an operation member of the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An operation unit according to one embodiment of the present invention will now be described with reference to  FIGS. 1 to 5 . The operation unit is used to operate an air conditioner for a vehicle. 
     Referring to  FIG. 1 , an instrument panel  1  is arranged in a passenger compartment. Operation units  2  are arranged on the instrument panel  1  to adjust the temperature, change the direction of a blowing port, and adjust the airflow. 
     Referring to  FIG. 2A , each operation unit  2  includes a case  3 . The case  3  includes a main body portion  3   a , a cylindrical mounting portion  3   b , which extends upward from the main body portion  3   a , and a cylindrical distal portion  3   c , which extends upward from the mounting portion  3   b . The main body portion  3   a  is tetragonal. The distal portion  3   c  has a smaller outer diameter than the mounting portion  3   b . The interior of the mounting portion  3   b  is in communication with the interior of the main body portion  3   a . The interior of the distal portion  3   c  is in communication with the mounting portion  3   b . The case  3  includes an opening at the upper part of the distal portion  3   c  and an opening at the lower part of the main body portion  3   a . A panel  4  closes the opening of the distal portion  3   c . A housing  5  closes the opening of the main body portion  3   a . The housing  5  has a U-shaped cross-section and includes an upper opening and a bottom wall. A cable hole  5   a  extends through the central part of the bottom wall in the housing  5 . The case  3  is fixed to the vehicle so that the distal portion  3   c  projects into passenger compartment from the instrument panel  1 . 
     A rotation supporting portion  3   d  is formed around the mounting portion  3   b  on an upper surface of the main body portion  3   a . The rotation supporting portion  3   d  has a larger inner diameter than the outer diameter of the mounting portion  3   b . Further, four hooking portions  3   e  are arranged around the rotation supporting portion  3   d  on the upper surface of the main body portion  3   a .  FIG. 2A  shows only two of the hooking portions  3   e  that are located on opposite sides of the mounting portion  3   b  in the radial direction. The hooking portions  3   e  are separated from the rotation supporting portion  3   d . Further, the hooking portions  3   e  are arranged at equal angular intervals along a circle extending around the mounting portion  3   b . Each hooking portion  3   e  includes a distal part from which a hook  3   f  extends toward the mounting portion  3   b . The rotation supporting portion  3   d  has a height from the upper surface of the main body portion  3   a  that is less than the distance from the upper surface of the main body portion  3   a  to the hook  3   f  of the hooking portion  3   e.    
     A bearing  3   g  is formed on an inner circumferential surface of the mounting portion  3   b . A communication hole  3   h  is formed in the lower end of the mounting portion  3   b  communicating the inner side and outer side of the case  3 . The communication hole  3   h  is adjacent to the bearing  3   g.    
     An insulator  6  is accommodated in the void formed by the main body portion  3   a  of the case  3  and the housing  5 . The insulator  6  includes a flat fastening portion  6   a  and a cylindrical supporting portion  6   b . The fastening portion  6   a  extends along an inner bottom surface of the main bottom surface of the main body portion  3   a  of the case  3 . The supporting portion  6   b  extends downward from the lower surface of the fastening portion  6   a . A support shaft  6   c  is formed on the outer circumferential surface of the supporting portion  6   b . The fastening portion  6   a  includes an accommodation hole  6   d  that faces toward the support shaft  6   c  in the axial direction of the supporting portion  6   b . The insulator  6  is fixed to the inner bottom surface of the main body portion  3   a  in the case  3  so that the support shaft  6   c  is aligned with the bearing  3   g  in the axial direction of the mounting portion  3   b  (supporting portion  6   b ). 
     The bearing  3   g  of the case  3  and support shaft  6   c  of the insulator  6  rotatably support a reduction gear  7 . The supporting portion  6   b  of the insulator  6  rotatably supports an internal gear  8 . The reduction gear  7  includes a first gear portion  7   a  and a second gear portion  7   b . The first gear portion  7   a  includes teeth extending from its outer circumferential surface. The second gear portion  7   b  has a smaller diameter than the first gear portion  7   a . The second gear portion  7   b  includes teeth extending from its outer circumferential surface. The first gear portion  7   a  and the second gear portion  7   b  are formed integrally on the same shaft. The teeth of the first gear portion  7   a  are arranged in correspondence with the hooks  3   f  of the case  3 . The second gear portion  7   b  is engaged with the internal gear  8 . The internal gear  8  is cylindrical, closed at the bottom, and open toward the insulator  6 . An insertion hole  8   a  extends through the central part of the bottom wall in the internal gear  8 . A cylindrical coupling portion  8   b  extends toward the insulator  6  around the insertion hole  8   a . The coupling portion  8   b  has an inner diameter that is the same as the diameter of the insertion hole  8   a  and an outer diameter that is slightly smaller than the inner diameter of the supporting portion  6   b  of the insulator  6 . An annular projection  8   c  is arranged on the bottom of the insulator  6 . In a state in which the coupling portion  8   b  is arranged in the supporting portion  6   b  of the insulator  6  and the distal surface of the annular projection  8   c  is in contact with the bottom surface of the housing  5 , the insulator  6  and the housing  5  rotatably support the internal gear  8 . A cable (not shown) is arranged in the coupling portion  8   b . The cable extends out of the housing through the cable hole  5   a  of the housing  5  and is connected to the air conditioner. 
     An operation member  9  is mounted on the mounting portion  3   b  of the case  3 . Injection molding is performed to form the operation member  9 . The operation member  9  is cylindrical and has two open ends. Further, the operation member  9  includes a knob  10 , a mounted portion  11 , a step portion  12 , and a slide portion  13 . The knob  10  has an inner diameter that is slightly greater than the outer diameter of the distal portion  3   c . The mounted portion  11  has an inner diameter that is slightly greater than the outer diameter of the mounting portion  3   b . The mounted portion  11  has an outer diameter that is greater than the outer diameter of the knob  10 . The step portion  12  has an outer diameter that is greater than the outer diameter of the mounted portion  11 . Further, the outer diameter of the step portion  12  is slightly less than the distance between the hooks  3   f  of two of the hooking portions  3   e  arranged on opposite sides of the mounting portion  3   b  in the radial direction. The slide portion  13  has an outer diameter that is greater than the outer diameter of the mounted portion  11 . Further, the outer diameter of the slide portion  13  is greater than the distance between the hooks  3   f  of two of the hooking portions  3   e  arranged on opposite sides of the mounting portion  3   b  in the radial direction and slightly smaller than the distance between the two hooking portions  3   e . The slide portion  13  has an inner diameter that is slightly greater than the outer diameter of the rotation supporting portion  3   d.    
     The operation member  9  is mounted on the mounting portion  3   b  in a state in which the slide portion  13  is arranged at the inner side of the hooking portions  3   e  of the case  3 . Referring to  FIG. 2B , an upper surface  13   a  of the slide portion  13  located near the step portion  12  is engaged with the hooks  3   f  of the hooking portions  3   e . This secures the operation member  9 , in a rotatable state, to the mounting portion  3   b . As shown in  FIG. 3 , the slide portion  13  includes four thin parts  14  arranged at equal angular intervals in the circumferential direction. Each thin part  14  has a thickness that gradually decreases at lower locations. Alignment of the thin parts  14  with the hooks  3   f  facilitates the engagement of the upper surface  13   a  of the slide portion  13  with the hooks  3   f.    
     As shown in  FIG. 2A , teeth  12   a  extend from the inner surface of the step portion  12 . When the operation member  9  is mounted on the mounting portion  3   b , the teeth  12   a  are arranged in correspondence with the hooks  3   f  of the mounting portion  3   b  and engaged with the first gear portion  7   a  of the reduction gear  7 . 
     A resin knob top  15  is coupled to the distal part of the knob  10 . The knob top  15  includes a coupling portion  15   a , which is cylindrical and coupled to the inner surface of the knob  10 , and an annular flange  15   b , which is continuous with the upper part of the coupling portion  15   a . The flange  15   b  has an inner diameter that is greater than the outer diameter of the panel  4 . Further, the flange  15   b  has an outer diameter that is the same as the outer diameter of the distal part of the mounted portion  11 . When the knob top  15  is coupled to the operation member  9 , the flange  15   b  covers the distal part of the knob  10  and the peripheral part of the panel  4 . 
     The outer diameter of the knob  10  decreases at upper locations. As shown in  FIGS. 2A and 3B , pyramidal knurls  10 A are formed on the entire outer circumferential surface of the knob  10  to prevent slipping. 
     As shown in  FIG. 3A , parting lines PL are formed in the outer surface  9   a  of the operation member  9  extending over the slide portion  13 , the step portion  12 , the mounted portion  11 , and the knob  10 . Each parting line PL is an elevated line formed where molds meet when integrally molding the operation member  9  during injection molding. In the present example, two parting lines PL are formed at locations corresponding to two opposing ones of the four thin parts  14  (only one shown in the perspective view of  FIG. 3A ). The parting line PL extends upward and is continuous with the step portion  12 . 
     The upper surface of the step portion  12  includes an outer circumferential surface  12   b , which is continuous with the upper surface  13   a  of the slide portion  13 , and an upper surface  12   c , which is continuous with an upper part of the outer circumferential surface  12   b . As shown in  FIG. 3C , a ridge line  12   d  is formed as a peak extending continuously at the boundary between the outer circumferential surface  12   b  and the upper surface  12   c  throughout the entire circumference of the step portion  12 . The outer circumferential surface  12   b  and the upper surface  12   c  are arranged at a major angle of 270°. A major angle is an angle between 180° and 360°. As shown in  FIG. 3A , in the step portion  12 , parting lines PL are formed on the outer circumferential surface  12   b , the upper surface  12   c , and the ridge line  12   d . In detail, the parting lines PL formed on the outer circumferential surface  12   b  extend in the vertical direction. Each of the parting lines PL on the outer circumferential surface  12   b  have a lower part that is continuous with a parting line PL formed on the upper surface  13   a  of the slide portion  13  and an upper part that is continuous with a parting line PL formed along the ridge line  12   d . Each parting line PL formed along the ridge line  12   d  has a length corresponding to one fourth of the entire circumference of the ridge line  12   d . A central part in the circumferential direction of the parting line PL formed along the ridge line  12   d  is continuous with a parting line PL formed on the outer circumferential surface  12   b . The four parting lines PL formed on the upper surface  12   c  extend in the radial direction of the operation member  9  at equal angular intervals in the circumferential direction (only two shown in the perspective view of  FIG. 3A ). Each parting line PL formed on the upper surface  12   c  includes a radially outer end, which is continuous with one of two circumferential ends of a parting line PL extending on the ridge line  12   d , and a radially inner end, which is continuous with a parting line PL formed on the mounted portion  11  and the knob  10 . As shown in  FIG. 3D , the region where the upper surface  13   a  of the slide portion  13  is continuous with the circumferential surface  12   b  is finely curved. In the same manner, as shown in  FIG. 3C , the region where the upper surface  12   c  is continuous with the outer surface of the mounted portion  11  is finely curved. 
     In the present example, a recess  16  is formed in the outer circumferential surface  12   b  of the step portion  12  above two of the thin parts  14 . Each recess  16  has a V-shaped cross-section. Two parting lines PL are formed on the outer circumferential surface  12   b . These two parting lines PL extend across the recesses  16 . 
     Referring to  FIG. 2A , when the knob  10  is rotated, the operation member  9  rotates as the hooks  3   f  of the hooking portions  3   e  slide on the upper surface  13   a  of the slide portion  13 . A lubricant is applied between the hooking portion  3   e  and the outer surface of the slide portion  13 , which slides on the hooking portions  3   e  of the case  3 , to reduce friction of the slide portion  13 . 
     The rotation of the knob  10  of the operation member  9  rotates the reduction gear  7 . This rotates the internal gear  8 , which is engaged with the second gear portion  7   b  of the reduction gear  7 . The rotation of the internal gear  8  pulls a wire of the cable and switches the operation state of the air conditioner. 
     A method for manufacturing the operation member  9  will now be described. 
     A mold  20  shown in  FIG. 4  is used to integrally mold the operation member  9 . The mold  20  includes an outer surface formation mold  21 , an inner surface formation movable mold  22 , and a fixed mold  23 . The outer surface formation mold  21  is cylindrical and has two open ends. The inner surface formation movable mold  22  closes one end (lower end as viewed in  FIG. 4 ) of the outer surface formation mold  21 . The fixed mold  23  is partially fitted into the outer surface formation mold  21  and closes the outer end (upper end as viewed in  FIG. 4 ) of the outer surface formation mold  21 . 
     The outer surface formation mold  21  will now be described. 
     The outer surface formation mold  21  includes a total of four mold segments, namely, two first mold segments  31 , which are shown in  FIGS. 5A and 5B , and two second mold segments  32 , which are shown in  FIG. 5B . Each first mold segment  31  includes an upper molding portion  31   a , which is shown in  FIG. 5A , and a lower molding portion, which is shown in  FIG. 5B . As shown in  FIG. 4 , the upper molding portion  31   a  includes an inner surface corresponding to the outer circumferential surfaces of the knob  10  and the mounted portion  11 . The lower molding portion is formed by a step formation part  31   b , which includes an inner surface corresponding to the outer circumferential surface of the step portion  12 , and a slide portion formation part  31   c , which includes an inner surface corresponding to the outer circumferential surface of the slide portion  13 . As shown in  FIG. 5A , each second mold segment  32  includes only an upper molding portion  32   a . The upper molding portion  32   a  includes an inner surface corresponding to the outer circumferential surfaces of the knob  10  and the mounted portion  11 . 
     Referring to  FIG. 4 , the upper molding portions  31   a  and  32   a  define a knob formation part  33 . The second mold segments  32  and upper molding portion  32   a  are not shown in  FIG. 4 . The knob formation part  33  includes a plurality of pyramidal recesses  33   a . The two first mold segments  31  include two protrusions  37 , which are formed at the middle parts of the step formation parts  31   b  in the vertical direction at equal angular intervals in the circumferential direction. The protrusions  37  project in an inward direction. Further, the lower ends of the first mold segments  31  includes four partitioning projections  35  (only two shown in  FIG. 4 ) at the lower end of the slide portion formation part  31   c  at equal angular intervals in the circumferential direction. Each partitioning projection  35  includes an inner surface  35   a  including an inclined surface gradually inclined inward toward the distal end. Although not shown in  FIG. 4 , each first mold segment  31  includes a projection arranged at the middle part in the circumferential direction of the lower end of the slide portion formation part  31   c . The projection includes an inclined surface inclined gradually inward toward the distal end. 
     The two first mold segments  31  and the two second mold segments  32  are arranged in contact with one another in the circumferential direction to form the cylindrical outer surface formation mold  21 . This forms a single projection at each location where the two first mold segments  32  meet each other. A drive mechanism (not shown) moves the two first mold segments  31  and the two mold segments  32  in the radial direction of the operation member  9  shown by solid lines in  FIGS. 5A and 5B . The outward radial movement of one of the two first mold segments  31  separate a circumferential end surface  36  of the first mold segment  31  from the other first mold segment  31  and the two mold segments  32 . 
     As shown in  FIG. 4 , the two upper molding portions  31   a  and the two upper molding portions  32   a  form the outer surfaces of the knob  10  and the mounted portion  11 . The recesses  33   a  of the upper molding portions  31   a  and  32   a  form the knurls  10   a  of the knob  10 . Further, the two step formation parts  31   b  form the outer surface of the step portion  12 . The two slide portion formation parts  31   c  form the outer surface of the slide portion  13 . The protrusions  37  of the step portion formation parts  31   b  form the recesses  16  of the step portion  12 . The projection formed by two partitioning projections  35  adjacent to each other in the circumferential direction and formed on the two slide portion formation parts  31   c  or the projection (not shown) formed on the slide portion formation part  31   c  forms one of the thin parts  14  of the slide portion  13 . 
     The inner surface formation movable mold  22  will now be described. 
     Referring to  FIG. 4 , the inner surface formation movable mold  22  includes a base  41 , which has the form of a circular plate, and a mold projection  42 , which projects vertically from the upper surface of the base  41  and is fitted to the outer surface formation mold  21 . 
     The base  41  includes an opposing surface  41   a  opposing the outer surface formation mold  21 . The opposing surface  41   a  comes into contact with the lower end surface of the outer surface formation mold  21  (i.e., the two first mold segments  31 ), and the base  41  closes the lower opening of the outer surface formation mold  21 . The annular part of the opposing surface  41   a  of the base  41  that does not contact the lower end surface of the outer surface formation mold  21  forms the end surface of the operation member  9  at the side of the slide portion  13 . 
     The mold projection  42  is cylindrical and has a diameter that is smaller than the inner diameter of the outer surface formation mold  21 . The projection length of the mold projection  42  from the upper surface of the base  41  is set so that a distal end surface  42   a  of the mold projection  42  contacts the fixed mold  23  in a state in which the upper surface of the base  41  is in contact with the lower end surface of the outer surface formation mold  21 . The inner surface formation movable mold  22  is movable in the vertical direction. A drive mechanism (not shown) moves the inner surface formation movable mold  22  in the downward direction to separate the opposing surface  41   a  of the base  41  away from the outer surface formation mold  21  and the distal end surface  42   a  of the mold projection  42  away from the fixed mold  23 . 
     From the upper side, the mold projection  42  is formed by a first step  42   b , which corresponds to an inner surface of the knob  10 , a second step  42   c , which corresponds to an inner surface of the mounted portion  11 , a third step  42   d , which corresponds to an inner surface of the step portion  12 , and a fourth step  42   e , which corresponds to an inner surface of the slide portion  13 . In this manner, the mold projection  42  has the form of a ladder that includes four steps. The outer circumferential surface of the mold projection  42  forms the inner surface of the operation member  9 . In detail, the first step  42   b  forms the inner surface of the knob  10 , the second step  42   c  forms the inner surface of the mounted portion  11 , the third step  42   d  forms the inner surface of the step portion  12 , and the fourth step  42   e  forms the inner surface of the slide portion  13 . 
     The fixed mold  23  will now be described. 
     The fixed mold  23  has the form of a circular plate and closes the upper opening of the outer surface formation mold  21 . A cylindrical protrusion  23   a  protrudes from the central part of the lower surface of the fixed mold  23 . The protrusion  23   a  has a larger diameter than the first step  42   b . The movable mold contact surface  23   b  forms the inner surface of the upper part of the knob  10 , that is, the part where the knob top  15  is arranged, with the outer circumferential surface of the protrusion  23   a  and an annular part excluding the part of the movable mold contact surface  23   b  contacting the distal end surface  42   a  of the mold projection  42 . The fixed mold  23  includes a lower surface defining a mold segment contact surface  23   c , which extends around the protrusion  23   a . The mold segment contact surface  23   c  contacts the outer surface formation mold  21  (i.e., end surfaces of the first and second mold segments  31  and  32 ). 
     When manufacturing the operation member  9 , first, as shown in  FIG. 4 , the outer surface formation mold  21  (i.e., the two first mold segments  31  and the two mold segments  32 ) and the fixed mold  23  are brought into contact with the inner surface formation movable mold  22 . This forms a cavity having a shape corresponding to the shape of the operation member  9 . The cavity includes space for forming the mounted portion  11  of the operation member  9 , space for forming the step portion  12 , and space for forming the slide portion  13 . 
     Next, an injection apparatus (not shown) injects molten resin into the cavity. The molten resin is hardened. Then, the inner surface formation movable mold  22  is moved in a direction opposite to the projection direction of the mold projection  42 , and the first and second mold segments  31  and  32  are moved outward in the radial direction. This allows the operation member  9  to be removed from the outer surface formation mold  21 . The operation member  9  includes parting lines PL formed at locations where the upper portions of the first mold segments  31  meet the second mold segments  32  (total of four locations) and locations where the lower portions of the first mold segments  31  meet each other (total of two locations). The molten resin is not filled into parts of the cavity where the partitioning projections  35  and the projections (not shown) are arranged. These parts form the thin parts  14 . In the same manner, the molten resin is not fitted into parts of the cavity where the protrusions  37  are arranged. These parts form the recesses  16 . The thin parts  14  and the recesses  16  formed by the partitioning projections  35  include the partitioning lines PL. Finally, the operation member  9 , which is fixed to the mold projection  42  of the inner surface formation movable mold  22 , is moved in the projection direction of the mold projection  42  and removed from the mold projection  42 . This forms the operation member  9 . 
     The operation of the operation unit  2  will now be described. 
     As described above, a lubricant such as grease is applied to the operation member  9  between the outer surface of the slide portion  13  and the hooking portions  3   e  of the case  3  to reduce friction. The lubricant is transferred along the parting lines PL due to the usage environment, such as the temperature and the humidity. 
     It is know that a ridge line will hinder the transfer of a liquid such as the lubricant. The lubricant, which is applied to the slide portion  13 , is transferred from the slide portion  13  to the knob  10  along the parting lines PL. The step portion  12  is located between the slide portion  13  and the knob  10 . As shown in  FIG. 3 , the parting lines PL are formed along the ridge line  12   d  at the step portion  12 . Thus, the ridge line  12   d  hinders the transfer of the lubricant. This hinders the advancement of the lubricant toward the mounted portion  11  and the knob  10 . 
     Further, as shown in  FIG. 3 , the recesses  16  are formed at locations corresponding to the parting lines PL in the outer circumferential surface  12   b  of the step portion  12 . The recesses  16  collect the lubricant transferred from the slide portion  13  along the parting lines PL. In other words, the transfer of the lubricant from the slide portion  13  to the knob  10  along the parting lines PL is suppressed. 
     The present embodiment has the advantages described below. 
     (1) The parting lines PL of the slide portion  13  (step portion) are shifted from the parting lines PL of the mounted portion  11  (knob  10 ) in the circumferential direction at the ridge line  12   d . It is well known that a ridge line hinders the transfer of liquid. Thus, the ridge line  12   d  hinders the flow of the lubricant along the parting lines PL. Further, the transfer of the lubricant from the slide portion  13  to the knob  10  along the parting lines PL is suppressed. 
     (2) The parting lines PL of the slide portion  13  are shifted from the parting lines formed on the mounted portion  11 . The ends of each parting line PL formed on the ridge line  12   d  connects one end of a parting line PL formed on the slide portion  13  to one end of a parting line PL formed on the mounted portion  11 . Thus, the two ends of each parting line PL formed on the ridge line  12   d  form peaks at where the continuous parting line PL is bent. The peaks hinder the flow of the lubricant along the parting lines PL. Thus, the transfer of the lubricant from the slide portion  13  to the knob  10  along the parting lines PL is suppressed. 
     (3) Each parting line PL extending upward from the slide portion  13  is branched into two directions at the ridge line  12   d . Thus, more parting lines PL are formed at the step portion  12  than the slide portion  13 . This increases the paths along which the lubricant is transferred upward in the operation member  9  and increases the amount of lubricant required to be transferred upward. Thus, less lubricant leaks from the paths as compared to when the same amount of lubricant is applied to a slide portion  13  having less paths. Further, the parting lines PL include fine steps. This increases slide resistance when the number of the parting lines PL increases at the slide portion  13 . In this respect, the slide portion  13  includes a small number of the parting lines PL. This suppresses the slide resistance at the slide portion  13 . Accordingly, the operation unit is easy to operate and lubricant does not leak out of the operation unit. 
     (4) The corner formed between the upper surface  13   a  and the outer circumferential surface  12   b  and the corner formed between the upper surface  12   c  and the outer circumferential surface of the mounted portion  11  includes curved portions that are finely curved. The curved portions suppress the occurrence of a capillary action. In other words, the curved portions suppress the dispersion of the lubricant. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     In the above embodiment, the outer surface formation mold  21  includes the first mold segments  31  and the second mold segments  32  that have different shapes. Each parting line PL formed on the outer surface of the operation member  9  is branched into two directions at the ridge line  12   d . However, such branching is not necessarily required. For example, as shown in  FIG. 6 , four parting lines PL may extend from the slide portion  13  to the knob  10  at equal angular intervals in the circumferential direction. The four parting lines PL are shifted by 90° from one another at the ridge line  12   d . In this case, as shown in  FIG. 7 , the outer surface formation mold  21  includes four identical mold segments  70 . In comparison with the upper embodiment, this structure decreases the distance in which a drive mechanism (not shown) moves the mold segments  70  when forming the operation member  9 . This allows for reduction in size of a machine tool that forms the operation member  9 . 
     In the above embodiment, the parting lines PL are arranged in the ridge lines  12   d  of the step portion  12  but may be arranged at other locations. For example, a parting line PL may be arranged in the ridge line of the slide portion  13  or the knob  10  of the mounted portion  11 . Further, a plurality of parting lines PL may be arranged at these locations. Such a structure would have the same advantages as the above embodiment. 
     In the above embodiment, the ridge line  12   d  is formed by a portion at which a peak of 270° continues. However, the peak is not limited to 270° as long as the peak has a major angle of 180° to 360°. 
     In the above embodiment, the corner between the upper surface  13   a  and the outer circumferential surface  12   b  and the corner between the upper surface  12   c  and the outer circumferential surface of the mounted portion  11  are finely curved but do not have to be curved. Such a structure would still obtain advantages (1) to (3) of the above embodiment. 
     In the above embodiment, the outer surface of the operation member  9  excluding the slide portion  13 , namely, the outer surfaces of the knob  10 , the mounted portion  11 , and the step portion  12  do not have to be cylindrical. These outer surfaces may be polygonal and include ridge lines. For example, the outer surfaces may be hexagonal or octagonal. In this case, the formation of the parting lines PL on the ridge lines of the polygon will suppress the leakage of lubricant at the knob  10 . 
     In the above embodiment, the thin parts  14  and the recesses  16  are formed during injection molding. However, the thin parts  14  and the recesses  16  may be formed after injection molding the operation member  9  through, for example, machining, grinding, laser processing, thermal processing, or ultrasonic processing. Further, after injection molding the operation member  9 , part of the outer surface  9   a  of the operation member  9  may be eliminated or melted to divide apart the parting line PL. 
     The above embodiment is applied to an operation unit that rotates the operation member, that is, a rotary switch. However, the present invention may also be applied to an operation unit that pushes an operation member, that is, a push switch, as long as the outer surface of the operation member includes a slide portion and a parting line. 
     In the above embodiment, the operation unit  2  is used with the air conditioner but may be used for an in-vehicle device such as audio equipment to adjust the volume. The operation unit  2  may also be used as a switch unit for a device other than an in-vehicle device. 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.