Patent Publication Number: US-6336761-B1

Title: Knock-type writing instrument

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a knock-type writing instrument in which the writing extremity end is extended out of or retracted into the instrument through a knocking operation, and more particularly a knock-type writing instrument provided with a clip releasing mechanism for releasing said extended-out state when the clip is opened under a state in which the writing extremity end is extended out of the instrument. 
     2. Description of the Related Art 
     As this kind of knock-type writing instrument in the prior art, there has been provided, as already disclosed in the gazette of Japanese Patent Laid-Open No. Hei 10-264584, a writing instrument in which the outer peripheral surface of the rotor is axially provided with protrusions to be guided at the fixed cam slant surface of the inner surface of the barrel, and protruded engaging section formed at the front side of said protrusions and engaged with the concave engaged sections inside the ball at the extremity end of the clip. 
     This knock-type writing instrument is constituted such that an engaged state having said protruded engaging section at the outer peripheral surface of the rotor engaged with said concave engaging section of the clip is released to cause the extremity end of the writing instrument to be retracted by an opening operation of a clip when the writing instrument is put into the pocket in order to prevent the extremity end of the writing instrument from staining a cloth when the writing instrument is stored in a pocket of the cloth under a state in which the inner end of the writing instrument is being protruded by accident. 
     However, the aforesaid prior art knock-type writing instrument had a disadvantage that the axial length of the rotor is elongated due to the fact that the protrusion for use in guiding the fixed cam slant surface of the inner surface of the barrel and the protruded engaging section to be engaged with the concave engaged section inside the ball at the extremity end of the clip are separately arranged axially at the outer peripheral surface of the rotor. That is, since the axial space in the barrel was restricted by the rotor, this fact caused improvements of the writing instrument such as an increased ink volume in the writing instrument by extending the length of the refill or an arrangement of compact-sized writing instrument by shortening the length of the barrel and the like, for example, to be difficult. 
     In addition, in the case of the aforesaid prior art knock-type writing instrument, although the extremity end of the writing instrument was retracted into the barrel through the depressing operation at the knock part other than its practical use to protect by itself, there was a possibility that the writing extremity end was apt to be damaged when the writing instrument was dropped while the writing extremity end was being faced downward with the writing extremity end being exposed or when the writing was carried out with an excessive high writing pressure or when a load more than that required for writing operation directed toward the rear part of the barrel was applied to the writing extremity end. For example, in the case that the writing instrument was a ball-point pen, it was afraid that the extremity end edge of the tip was deformed, the ball was not rotated to cause the writing operation to become impossible or ink was flowed out between the ball and the extremity end. 
     SUMMARY OF THE INVENTION 
     The present invention has been invented in reference to the aforesaid circumstances and it is an object of the present invention to provide a knock-type writing instrument in which the cloth can be prevented from being stained with ink when the writing instrument is stored in a pocket and further the writing extremity end can be prevented from being damaged while it is being extended out of the barrel under an unintended state of use by a clip releasing mechanism having a compact structure. 
     The technical means of the present invention to resolve the aforesaid problems consists in a knock-type writing instrument having a clip releasing mechanism operated such that a knock rod arranged at the rear end of a barrel is knocked to enable a writing extremity end of a refill to be extended out of or retracted into an extremity end port of the barrel by a thrust lock mechanism provided with a rotor and a return spring, the rotor is engaged with a ball of a clip at the time of extended-out state and the engaged state of the rotor is released under an opening operation of said clip and this is characterized in that: 
     a window hole is opened at a peripheral surface of the barrel, the ball at the extremity end of the clip is provided with an inner protrusion which can be extended out of or retracted into said window hole; 
     the rotor is provided with a plurality of peripheral protrusions at its outer peripheral surface in a circumferential direction thereof to stop its rotation by being abutted against said inner protrusion of the clip when the writing extremity end is extended out of the barrel; 
     said thrust lock mechanism is provided with a fixed cam slant surface formed at the inner peripheral surface of the barrel, a thrust cam slant surface formed at the extremity end of the knock rod and axially slid in integral with said knock rod, a rotary cam slant surface formed at the rear end of the rotor, and a guiding slant surface formed at the surface of the writing extremity end at said inner protrusion; 
     said thrust lock mechanism causes the rotor to be rotated while said peripheral protrusion is guided by the fixed cam slant surface after said rotary cam slant surface is guided by the thrust cam slant surface when the knock operation for extending out the writing extremity end is carried out, one of said plurality of peripheral protrusions is abutted against said inner protrusion to cause the rotor to be stopped, and in turn when a knock operation for retracting the writing extremity end is carried out, one of said peripheral protrusions being abutted against the inner protrusion is guided by said guiding slant surface of the inner protrusion to cause the rotor to be rotated and said writing extremity end to be retracted after said rotary cam slant surface is guided by the thrust cam slant surface. 
     In accordance with the aforesaid technical means, the present invention has two functions, i.e. one function in which the peripheral protrusions of the rotor are guided by the fixed cam slant surface and the other function in which they are engaged with the ball at the extremity end of the clip. Then, when the writing extremity end is extended out of the barrel, a rotation of the rotor is stopped by abutting the peripheral protrusions at the outer peripheral surface against the inner protrusions of the clip. Accordingly, as the clip is opened, the inner protrusion of the clip is moved out of the barrel and is not abutted against the peripheral protrusions of the rotor, resulting in that the rotor is rotated to cause the writing extremity end to be retracted into the barrel. 
     In addition, in order to prevent the writing extremity end kept at its extended-out state from being damaged, there is provided a knock-type writing instrument having a clip releasing mechanism operated such that a knock rod arranged at the rear end of a barrel is knocked to enable a writing extremity end of a refill to be extended out of or retracted into an extremity end port of the barrel by a thrust lock mechanism provided with a rotor and a return spring, the rotor is engaged with a ball of a clip at the time of extended-out state and the engaged state of the rotor is released under an opening operation of said clip, wherein 
     a window hole is opened at a peripheral surface of the barrel, the ball at the extremity end of the clip is provided with an inner protrusion which can be extended out of or retracted into said window hole; 
     the rotor is provided with a plurality of peripheral protrusions at its outer peripheral surface to stop its rotation by being abutted against said inner protrusion of the clip when the writing extremity end is extended out of the barrel; and 
     the clip is constituted such that said inner protrusion is pushed up by said abutted peripheral protrusion when the writing extremity end at its protruded position is pushed in an axial rearward direction with a force of more than a predetermined load. 
     In this case, the aforesaid thrust lock mechanism is a mechanism constituted such that the extremity end of the knock rod and the rear end of the rotor, or the outer peripheral surface of the rotor and the inner peripheral surface of the barrel and the like are formed with cam slant surfaces to be engaged to each other, the rotor biased at the leading end side by a return spring is rotated under an engaging action of said cam slant surfaces, and the rotor is formed at a position where the writing extremity end of the refill installed at the extremity end of the rotor is extended out of the barrel extremity end port and another position where the writing extremity end is retracted from the barrel extremity end port. 
     In accordance with the aforesaid technical means, rotation of the rotor is prevented from being carried out by a method wherein the peripheral protrusions at the outer peripheral surface are abutted against the inner protrusions of the clip when the writing extremity end is extended out of the barrel. Accordingly, when the clip is opened, the inner protrusions of the clip are moved in an outward direction of the barrel and are not abutted against the peripheral protrusions of the rotor, resulting in that the rotor is rotated to cause the writing extremity end to be retracted into the barrel. 
     In addition, as the writing extremity end at the extended-out position is pushed rearwardly of the barrel with a force more than a predetermined load when the writing extremity end is extended out of the barrel, its pushing action becomes a rotating force for the rotor and the rotor is tried to rotate to push up the inner protrusions at the extremity end of the clip with the peripheral protrusions. Then, the clip is resiliently opened to cause the engaged state of the rotor to be released and the writing extremity end is retracted into the barrel. 
     Further, in order to attain a configuration of the clip in which said inner protrusions are pushed up with said peripheral protrusions being abutted when the writing extremity end at its extended-out position is pushed rearwardly of the barrel with a force more than a predetermined load, it is preferable that the abutted section between the aforesaid inner protrusion and the aforesaid peripheral protrusion is formed with a slant surface slidably contacted with the aforesaid peripheral protrusion and pushed up by it. In addition, it is satisfactory that said slant surface is of an R-shaped surface slidably contacted with the afore said peripheral protrusion and pushed up by it. Further, it does not show any problem to provide a configuration in which the inner protrusions are pushed up over the peripheral protrusions by making a proper setting of a tension force of the clip. 
     Further, preferably, the angle of said slant surfaces is set to be about 30°. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A to  1 C are longitudinal section for showing one example of a knock-type writing instrument of the present invention, wherein  1 A shows a state in which the writing extremity end is projected,  1 B shows a state in which the peripheral protrusions of the rotor push up the inner protrusions of the clip, and  1 C shows a state in which the engaged state of the rotor is released to cause the writing extremity end to be retracted into the barrel. 
     FIG. 2 is a sectional view taken along line ( 2 )—( 2 ) in FIG.  1 A. 
     FIG. 3 is a sectional view taken along line ( 3 )—( 3 ) in FIG.  1 B. 
     FIGS. 4A to  4 D are exploded view for showing the knock-type writing instrument, wherein  4 B is a sectional view taken along line IVB—IVB of FIGS. 4A,  4 C is a sectional view taken along line IVC—IVC of FIGS. 4A and 4D is a sectional view taken along line IVD—IVD of FIG.  4 . 
     FIGS. 5A to  5 C are developed view for showing an operation of a thrust lock mechanism in the knock-type writing instrument when the writing extremity end is projected, wherein  5 A shows a state before the writing extremity end is projected,  5 B shows a state in which the rotor is slid toward the leading end of the shaft to cause the writing extremity end to be projected and  5 C shows a state in which the peripheral protrusions of the rotor are engaged with the inner protrusions of the clip and the projected state of the writing extremity end is kept. 
     FIGS. 6A to  6 C are developed view for showing an operation of a thrust lock mechanism in the knock-type writing instrument when the writing extremity end is retracted into the barrel, wherein  6 A shows a state in which the engaged state between the peripheral protrusions of the rotor and the inner protrusions of the clip is released,  6 B shows a state in which the peripheral protrusions of the rotor are contacted with the guiding slant surfaces of the inner protrusions of the clip,  6 C shows a state in which the peripheral protrusions of the rotor are guided by the inner protrusion guiding slant surfaces of the clip to cause the rotor to be rotated and  6 D shows a state in which the rotor is slid in an axial direction to cause the writing extremity end to be retracted into the barrel. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     Referring now to the drawings, one preferred embodiment of the present invention will be described as follows. 
     FIGS. 1A to  6 D illustrate one example of a knock-type writing instrument of the present invention. 
     This knock-type writing instrument is a knock-type ball-point pen comprised of a barrel  10  having an extremity end port integrally formed with it, a refill  50  stored in the barrel  10  and biased by a return spring  70 , a rotor  20  installed at the rear end of the refill  50 , a knock rod  30  arranged at the rear side of the rotor  20 , a rear end shaft  40  fitted and fixed to the rear end of the inner peripheral surface of the barrel  10 , and a clip  60  fitted to the rear end shaft  40 , wherein there is provided a thrust lock mechanism in which the knock rod  30  is depressed with a force to cause the rotor  20  to be slid or rotated and then the writing extremity end  51   a  of the tip  51  is extended out of or retracted into the barrel extremity end port  12 , wherein a clip releasing mechanism for retracting the projected-out writing extremity end  51   a  under the opening operation of the clip  60 . 
     The barrel  10  is of a substantial cylindrical shape having a fine leading end port integrally formed with it, wherein its most-forward end has an extremity end port  12  of the barrel for use in extending out or retracting the writing extremity end  51   a,  the peripheral surface of the rear end of it has a substantial rectangular window hole  11 , and two slit holes  13 ,  13  arranged to hold the window hole  11  therebetween. 
     The refill  50  is constructed such that the tip  51  is connected to the extremity end of an ink storing pipe  53  through a coupler  52  of which diameter is reduced substantially by about a full size of the diameter of the ink storing pipe  53 , the return spring  70  having its extremity end engaged in the barrel is inserted around the coupler  52  and then the refill is stored in the barrel  10  under a state in which it is biased rearwardly of the barrel by the return spring  70 . 
     The rotor  20  is comprised of a cylinder  21  having an installing hole  21   c  into which the rear end of the refill  50  is installed, and a free fitting part  22  in which its diameter is reduced so as to be rotatably fitted into the knock rod  30  to be described later and it is integrally formed with the rear end of said cylinder  21 , wherein the outer peripheral surface of the cylinder  21  is formed with three peripheral protrusions  21   a  arranged in a circumferential direction at the outer peripheral surface of the cylinder  21  and projected in a direction of its diameter, the rear end of the cylinder  21  is formed with three rotary cam slant surfaces  21   b  projected rearwardly of the shaft and rotatably stored in the rear end of the barrel  10 . 
     The peripheral protrusion  21   a  is formed with a slant surface  21   a - 1  slidably contacted with a fixed cam slant surface  41   a - 1  of the rear end barrel  40  to be described later and a guiding slant surface  62   a - 2  of a ball part  62  at the extremity end of the clip  60  at the side surface of the rear part of the shaft. 
     In addition, the rotary cam slant surface  21   b  is a slant surface formed such that a location at the rear end of the cylinder  21  corresponding to each of the aforesaid peripheral protrusions  21   a  is projected like a triangle as seen in its front elevational view and its side part is slidably contacted with a thrust cam slant surface  31   a - 1  to be described later. 
     An inside part of the knock rod  30  is formed with a free fitting hole  30   a  into which a free fitting part  22  of the rotor  20  is rotatably fitted, its rear end is of a substantial closed cylindrical shape, its extremity end is formed with a thrust cam part  31  and its rear end is projected from the rear end barrel  40  so as to be operated with a knock. 
     The thrust cam part  31  has a plurality of protrusions  31   a  of substantial isosceles triangle projected toward the extremity end of the shaft, one side of each of the protrusions  31   a  forms a thrust cam slant surface  31   a - 1  for guiding the aforesaid rotary cam slant surface  21   b  and rotating the rotor  20 . 
     In addition, the peripheral surface of each of the aforesaid protrusions  31   a  is formed with a thrust protrusion  31   a - 2  engaged with an axial longitudinal groove  10   a  formed at the inner surface of the fixed cam  41  of the rear end barrel  40  and enabling the knock rod  30  to be axially slid. 
     The rear end barrel  40  is formed into a substantial cylindrical shape comprised of a fixed cam section  41  at the extremity end thereof and a cylindrical flange  42  at the rear end formed to have a substantial same outer diameter as an outer diameter of the barrel  10 , wherein the fixed cam section  41  is fitted to the rear end in the barrel  10  and at the same time the cylindrical flange  42  is fixed under a state in which it is projected from the rear end of the barrel  10 . 
     As shown in the developed figures of FIGS. 5A-5C and  6 A- 6 D, the fixed cam section  41  is formed such that its extremity end is formed into a corrugated shape, wherein the extremity end of each of the two protrusions  41   a  is formed with the fixed cam slant surface  41   a - 1  for guiding the aforesaid peripheral protrusions  21   a  and for rotating the rotor  20  (refer to FIGS. 5A-5C and  6 A- 6 D). 
     In addition, the cylindrical flange section  42  is formed, at its side surface, with a clip fitting section  42   a  into which an engaging piece  61   a  at the rear end of the clip  60  is inserted from the rear side and fitted, wherein this clip fitting part  42   a  is fitted into a recess  10   b  formed at the rear end of the barrel  10  and the rear end cylinder  40  is fixed in such a way that it may not be rotated in a peripheral direction (refer to FIG.  4 ). 
     The clip  60  is made such that a ball section  62  made of resin material is formed at the extremity end of the clip main body  61  comprised of a metallic plate. 
     The clip main body  61  is formed such that its rear end is bent into a U-shape and the bent extremity end is formed with an engaging piece  61   a  fitted to the clip fitting part  42   a  of the rear end barrel  40 . The engaging piece  61   a  is formed to have both side surfaces of saw-teeth shape in such a way that it may not be easily pulled out of the clip fitting part  42   a.    
     In addition, the ball section  62  is formed with an inner protrusion  62   a  arranged at a substantial central part of the plane of the ball section  62  at the barrel  10  and two longitudinal protrusions  62   b,    62   b  arranged to hold the inner protrusion  62   a,  wherein when the clip  60  is opened or closed, the inner protrusion  62   a  is extended out of or retracted into the window hole  11  at the peripheral surface of the barrel  10  and at the same time the longitudinal protrusions  62   b,    62   b  are extended out of or retracted into the slit holes  13 ,  13  at the peripheral surface of the barrel  10  (refer to FIGS.  2  and  3 ). 
     The aforesaid inner protrusion  62   a  is formed such that it may be projected out through the window hole  11  into the barrel  10 , wherein when the knock rod  30  is depressed to cause the writing extremity end  51   a  to be projected out of it, the side surface of the peripheral protrusion  21   a  of the rotating rotor  20  is abutted against said inner protrusion  62   a  to cause the rotation of the rotor  20  to be stopped. 
     In addition, the surface of the inner protrusion  62   a  at the writing extremity end  51   a  is formed with a guiding slant surface  62   a - 2 . This guiding slant surface  62   a - 2  causes the peripheral protrusion  21   a  moved toward the extremity end of the shaft together with the knock rod  30  when the knock rod  30  is depressed again to cause the writing extremity end  51   a  to be retracted under the engaged state of the aforesaid rotor  20 , thereby the rotor  20  is rotated (refer to FIGS. 5A-5C and  6 A- 6 D). 
     In addition, the abutting section of the peripheral protrusion  21   a  of the inner protrusion  62   a  is formed with a slant surface  62   a - 1  (refer to FIGS.  2  and  3 ). This slant surface  62   a - 1  is formed such that when the writing extremity end  51   a  is pushed toward the rear part of the shaft with a force more than the predetermined load, the inner protrusion  62   a  of the clip  60  is pushed up by the peripheral protrusion  21   a  of the rotor  20  with this load. That is, the clip  60  is constituted such that it is opened by a method wherein the inner protrusion  62   a  is pushed up by the slant surface  62   a - 1  while being slidably contacted with the peripheral protrusion  21   a.    
     In addition, it is preferable that the aforesaid load to cause the writing extremity end  51   a  to be pushed rearwardly of the shaft is 2.94N-29.4N (300 gf-3 kgf) and more preferably the value is set to 19.6 N (2 kgf) as applied in the preferred embodiment. A slant angle of the slant surface  62   a - 1  is set in such a way that the peripheral protrusion  21   a  of the rotor  20  pushes up the inner protrusion  62   a  of the clip  60  with this predetermined load to open the clip  60 , and more particularly, an angle α (refer to FIG. 2) formed between the side surface of the inner protrusion  62   a  at the cross section and the slant surface  62   a - 1  is set to be about 30°. 
     Then, an operation of the knock-type writing instrument having the aforesaid configuration will be described. 
     At first, referring to FIGS. 5A-5C and  6 A- 6 D, the thrust lock mechanism for extending out or retracting the writing extremity end  51   a  into the barrel through the barrel extremity end port  12  under a knock operation of the knock rod  30 . 
     As shown in FIG. 5A, as the knock rod  30  is depressed, the peripheral protrusion  21   a  of the rotor  20  is slid toward the leading side of the shaft along the side surface of the protrusion  41   a  of the fixed cam section  21  and as the peripheral protrusion  21   a  rides over the top part of the protrusion  41   a,  the rotary cam slant surface  21   b  is guided by the thrust cam slant surface  31   a - 1 , resulting in that the rotor  20  is rotated by a size H 1  shown in this figure and attains the state shown in FIG.  5 B. Then, as the pushing operation of the knock rod  30  is started, the peripheral protrusion  21   a  is abutted against the fixed cam slant surface  41   a - 1  of the protrusion  41   a  due to the fact that the rotor  20  is biased by the return spring  70  toward the rear part of the shaft. Then, the peripheral protrusion  21   a  is guided by the fixed cam slant surface  41   a - 1  to cause the rotor  20  to be rotated. Then, as shown in FIG. 5C, the rotor  20  causes one of the peripheral protrusions  21   a  (the central peripheral protrusion  21   a  in this figure) to be abutted against the inner protrusion  62   a  of the clip  60  and then its rotation is stopped at the time when the rotor  20  is rotated by a size H 2 . At this time, the state in which the writing extremity end  51   a  is extended out of the barrel extremity end port  12  is maintained (the state shown in FIG.  1 A). 
     Then, as the knock rod  30  is depressed again under the protruded state of the aforesaid writing extremity end  51   a,  the rotor  20  is slid toward the leading end of the shaft and as shown in FIG. 6A, the peripheral protrusion  21   a  abutted against the inner protrusion  62   a  rides over the top part of the inner protrusion  62   a  and the rotary cam slant surface  21   b  is guided by the thrust cam slant surface  31   a - 1  to cause the rotor  20  to be rotated by a size H 3 . Then, as the depressing operation of the knock rod  30  is released, since the rotor  20  is biased rearwardly of the shaft with the return spring  70 , the peripheral protrusion  21   a  is abutted against the guiding slant surface  62   a - 2  of the inner protrusion  62   a  (refer to FIG.  6 B). Then, the peripheral protrusion  21   a  is guided by the guiding slant surface  62   a - 2  to cause the rotor  20  to be rotated (refer to FIG.  6 C). Then, as the rotor  20  is further rotated to cause the sliding contacted state between the peripheral protrusion  21   a  and the inner protrusion  62   a  to be released, the rotor  20  and the peripheral protrusion  21   a  are slid toward the rear part of the shaft (refer to FIG.  6 D). Accordingly, the writing extremity end  51   a  occupies the retracted position (the state shown in FIG.  1 C). 
     Then, an operation of the clip releasing mechanism will be described as follows. 
     As the clip  60  is opened under a state in which one of the peripheral protrusions  21   a  of the rotor  20  is abutted against the inner protrusion  62   a  of the clip  60  (the state shown in FIG.  5 C), i.e. a state in which the writing extremity end  51   a  keeps its projected position, the inner protrusion  62   a  is moved outwardly of the shaft, resulting in that said peripheral protrusion  21   a  is not abutted against the inner protrusion  62   a.  Accordingly, each of the other two peripheral protrusions  21   a,    21   a  of the rotor  20  is guided by the fixed cam slant surface  41   a - 1  of the rear end barrel  40  to cause the rotor  20  to be rotated. As each of said two peripheral protrusions  21   a,    21   a  rides over the end part of the fixed cam slant surface  41   a - 1 , the rotor  20  and the peripheral protrusion  21   a  are slid toward the rear end of the shaft, resulting in that they become the state shown in FIG.  6 D. Thus, the writing extremity end  51   a  is retracted into the barrel extremity end port  12 . 
     In addition, when the writing extremity end  51   a  is pushed toward a rear part of the shaft with a force more than the predetermined load under a state in which one of the peripheral protrusions  21   a  of the rotor  20  is abutted against the inner protrusion  62   a  (the state shown in FIG.  5 C), i.e. the state in which the writing extremity end  51   a  keeps its projected position in the same manner as that described above, said inner protrusion  62   a  is pushed up while the slant surface  62   a - 1  of the inner protrusion  62   a  of the clip  60  is being slidably contacted with the peripheral protrusion  21   a  of the rotor  20  to be rotated under this load (refer to FIGS.  1 B and  3 ). That is, the clip  60  is opened, the operation of the aforesaid clip releasing mechanism is performed in the same manner as that above to attain the state shown in FIG.  6 A and the writing extremity end  51   a  is retracted into the barrel extremity end port  12 . 
     In addition, in the aforesaid preferred embodiment, it has been described about the embodiment in which the clip  60  is opened when the writing extremity end  51   a  at the projected position is depressed with a force more than a predetermined load, i.e. the embodiment concerning claims  2  to  4 . However, it is not necessarily required in claim  1  that there is provided the aforesaid preferred embodiment. In other words, in the case of claim  1 , it is satisfactory that the opening operation is not carried out when the writing extremity end  51   a  at its projected position is depressed under no formation of the aforesaid slant surface  62   a - 1  or increasing of tension force of the clip  60 . 
     In accordance with the present invention, since its constitution is made such that the plurality of peripheral protrusions are arranged at the outer peripheral surface of the rotor in a circumferential direction and one of these peripheral protrusions is abutted against the inner protrusion of the clip to cause the rotor to be stopped, it is not necessary to provide a constitution that the protrusions to be guided along the fixed cam slant surface of the inner surface of the barrel and the protruded engaging section to be engaged with the concave engaged section inside the ball section at the clip extremity end are separately installed in an axial direction at the outer circumferential surface of the rotor as found in the aforesaid prior art structure, resulting in that it is possible to prevent the writing instrument from staining the cloth when it is stored in the pocket of it by the clip releasing mechanism having a short axial length of the rotor and compact structure, and further elongated length of the refill facilitates an increased amount of ink in the writing instrument, and arranging of a short barrel as well as a compact-sized writing instrument and the like. 
     In addition, the constitution of the clip in which the inner protrusions of the clip are pushed up by the peripheral protrusions of the rotor to be abutted when the writing extremity end at the projected position is pushed toward the rear part of the shaft with a force more than a predetermined load causes the engaged state of the rotor to be released, the writing extremity end to be retracted and the writing extremity end to be protected in the case that a load applied to the rear part of the shaft more than the required load is applied to the writing extremity end such as in the case that the writing instrument is dropped with the projected writing extremity end being faced downward or in the case that the writing is carried out with an excessive writing pressure. 
     Having described specific preferred embodiments of the invention with reference to the accompanying drawings, it will be appreciated that the present invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one of ordinary skill in the art without departing from the scope of the invention as defined by the appended claims.