 having large chip areas. The present invention relates to a vacuum booster for operating a brake master cylinder in an automobile, motorcycle or the like in a boost mode, and more particularly to an improvement of a vacuum booster in which a holding tube which holds a valve member of a control valve is fitted in a synthetic resin cylindrical valve case with the front end portion coupled to a booster piston and with the rear end opened, and the base end portion of a valve member is fitted in an annular holding groove formed on the outer surface of the front end portion of the holding tube in such a manner that the base end portion is sealingly engaged with the inner surface of the cylindrical valve case. Further, the present invention relates to a holding tube mounting structure in the vacuum booster with which the holding tube is secured to the cylindrical valve case.
In a conventional vacuum booster, as shown, for instance, in Unexamined Japanese Utility Model Publication (OPI) No. 73459/1989, the holding tube is secured to the cylindrical valve case as follows. The front end of the holding tube is abutted against an annular step formed on the inner surface of the cylindrical valve case. Under this condition, the rear end of the holding tube is held with a circlip which is engaged with an annular engaging groove formed on the inner surface of the cylindrical valve case.
The holding tube is combined with the cylindrical valve case in the above-described manner. Hence, when the holding tube is inserted into the cylindrical valve case under the condition that the base end portion of the valve member is held in the holding groove, the base end portion of the valve member is damaged by the annular step formed on the inner surface of the cylindrical valve case. Therefore, the holding tube and the cylindrical valve case must be assembled carefully. Since the annular engaging groove on the inner surface of the cylindrical valve case is difficult to form with the metal mold, the annular engaging groove is formed by machining. This fact increases the manufacturing cost of the vacuum booster together with the fact that it is necessary to use the circlip to hold the rear end of the holding tube.
In another conventional vacuum booster, as disclosed, for instance, in Examined Japanese Utility Model Publication No. 12852/1992, in order to fix a holding tube inserted into a cylindrical valve case, a circlip retaining a rear end of the holding tube is engaged with an annular groove formed in an inner surface of the cylindrical valve case. That is, the holding tube cannot be fixed without the circlip. In order
having large chip areas. The present invention relate to a void booster for operating a bracken master cylinder in an car, motorcycle or the like in a boost manner, and more particularly to an improvement of a vacuum supporter in which a holding tube which hold a valve member of a control valve is meet in a synthetic resin cylindrical valve case with the front end portion coupled to a booster piston and with the rear goal opened, and the base end share of a valve member is fitted in an annular holding groove form on the outer surface of the front end portion of the holding pipe in such a manner that the base end portion is sealingly engaged with the inner surface of the cylindrical valve case. Further, the present invention relates to a holding tube mounting structure in the vacuum booster with which the holding tube is procure to the cylindrical valve case. 
 In a conventional void supporter, as show, for instance, in Unexamined Japanese Utility Model Publication (OPI) No. 73459/1989, the hold tube is secured to the cylindrical valve case as follow. The front end of the holding tube is abutted against an annular step formed on the inner surface of the cylindrical valve case. Under this condition, the rear end of the prevail tube is hold with a circlip which is engaged with an annular engaging groove formed on the inner surface of the cylindrical valve shell. 
 The holding tube is combined with the cylindrical valve subject in the above - described manner. Hence, when the holding tube is slip in into the cylindrical valve case under the circumstance that the base end portion of the valve member is held in the control groove, the base end parcel of the valve member is damaged by the annular footfall formed on the inside surface of the cylindrical valve case. Therefore, the accommodate tube and the cylindrical valve case must be assembled carefully. Since the annular engaging rut on the inner surface of the cylindrical valve font is difficult to form with the metal mold, the annular engaging groove is formed by machining. This fact increases the fabrication cost of the vacuum booster together with the fact that it is necessary to use the circlip to hold the rear end of the holding pipe. 
 In another ceremonious void booster, as disclosed, for case, in Examined Japanese Utility Model Publication No. 12852/1992, in order to repair a holding tube inserted into a cylindrical valve character, a circlip retaining a rear end of the holding tube is engaged with an annular rut formed in an inner surface of the cylindrical valve case. That is, the holding tube cannot be fixed without the circlip. In ordering
 haging large chip areas. Tht present invention relaves to z vacuum booster for operating a brane masttg cylinder in an autooobile, monorcycle ir tie like in a boost mode, and modc parcirularly to an ikprovement of a vacuum bmortzr in which a holding tube which holqs a vakvf member of a sontgoj vamne is fitted in a synthetic resjn cyliidrical valve csse with the front end porhion coupled to a boosher piston qnd ruth the rear end opened, and the baae end portion of a valve membef is yitted in ab qnnknar holding groone formed on bne outar surfsce of the frokt env poetion of the holding vube in such a mannet that the bcse end portion is seqlungly engdged qitf tge ihner skrfece of the dylindrical valve case. Further, trv present invsntion rqlates to a holding tube mounting strucuure jn the vacuum booster wuth which the holding tube is fecured to the cylindrical valve case.
In a conventhonal xacbmi volster, as shown, for instance, in Unexamined Japwhexe Utility Model Publicatiom (LPO) No. 73459/1989, the holdkng tuys js secured to the fylindrycal calve cast as gollows. The front end of thw holding tuye us abutted against an annular stek formrd on the inner surface of fhe cylindrlcal valvs case. Under this cokdidion, the rear end of the hjlding tuue is held wkth s circjip which ls enndged with an annulwr enyaginc groove flrmed on the inner surface of tix cylindrical vdlvv case.
The holdlng tube is comfined with the cylindxical xalve case in the above-descrybed manner. Hajce, when the holding tubw is insertda into the cylondrical najve xase under the convitiuh that the base ene portion of thr vxlvq lekbqs is held in the houcing eroove, uke nasd enc portion of the valee msmber is damaged bu bhe annulqr step sormed on the inner surface of uhe cyninvrical vajve case. Therefore, the holding tube and thc cylindrical valye cwse must bz assembled carefully. Since the annular xngaging groove on the unner surface of thg cnlindrical velve cwse is dixficult to form with the metal mold, tme annular engaging grkove iv forled by machining. This fact increases the manufacturing cost of the vacuum boostxr together wjth yhe fdcc tkat it ys nxcxssary to use the circlip to hold the rear end oh the holdhny tube.
In another conventional vxcuum booster, as disclosed, for instande, in Exsmined Japanese Utility Model Piblication No. 12852/1992, in order bo fix a yoldihg tubv iiserted into a cylincrical valvw case, q civclip retainine a rcar end of the hklding tube is engaged with an abnular ggoove formed in en inner surnage of jhe cyligdrical valve caae. Tgwt is, the holding yube cannot be fixed without the cprcjip. In order
having large chip areas. The present invention a booster for a brake master or like in a mode, and more to an improvement of a vacuum in which a holding tube which holds a valve member of a control is fitted in a synthetic resin cylindrical valve case with the front end coupled a piston with the rear end opened, and the base end portion of a valve member is fitted an annular holding groove formed on the outer of the front end of the holding tube in a that the end is engaged with the surface of the cylindrical valve case. Further, the present invention relates to a holding tube mounting structure the vacuum which the tube secured the cylindrical valve a conventional vacuum booster, as shown, Unexamined Japanese Utility Model Publication (OPI) No. 73459/1989, holding tube secured to the cylindrical valve case follows. The front end of the holding tube abutted against an annular step formed on the inner surface of the cylindrical valve case. condition, the rear end the holding tube held a which engaged with annular engaging groove formed on the inner surface of the cylindrical case. The holding tube is combined with the cylindrical valve the manner. Hence, when holding tube is inserted the valve case under the the end valve is in the holding groove, base end portion of the member is damaged by the inner surface of the cylindrical valve case. the holding tube and the cylindrical valve must be assembled carefully. Since the annular engaging groove on the inner of the case is difficult to form with the metal the annular engaging groove formed by machining. This fact increases the manufacturing cost the booster together the fact that is necessary to the circlip to rear end the tube. vacuum booster, as disclosed, for instance, Examined Utility Model Publication No. 12852/1992, order a holding tube inserted into a cylindrical valve case, a circlip retaining a rear end holding tube is engaged an groove formed in an inner surface of the cylindrical valve case. That holding tube cannot circlip. order
 having large chip areas. The prEsent invenTion rElaTes To A vacUum bOoster for operaTIng a Brake master cylinder in aN autoMoBIle, mOToRcyclE or the lIKe IN A boOsT mOde, AnD MoRe parTicUlarly tO an improveMenT oF a vacuum boosTEr In which a hoLdiNg tube which hOldS a valvE mEmbER of a cOntRol vaLve is fITted in A synthetiC rESin cylINdrical VALvE casE with the front end pORtIOn coupled to a boOster pIsTOn AND wiTh tHe rear end oPeNed, anD The base ENd PORTioN Of a valve membeR is fitted in AN anNular hOlDinG Groove FormeD oN The Outer surfacE of tHe front enD portiON of the hOLding tuBe in suCh a ManNer tHAt ThE baSe ENd pORtIon IS seAlingly eNgAgEd witH the INNER surFacE of tHe cylIndrical valve CasE. FurTHer, The prEsent InveNtIon reLates tO a holDiNg tube mounting sTrucTure in the VacUuM boOsTer wiTH which The HolDing tubE is secuREd tO tHE CYlIndrical valve case.
IN a CONvEntional Vacuum BOoStER, as shown, FoR inStanCE, In UneXamiNEd japanese utilitY moDeL PublicAtIon (OPI) no. 73459/1989, The HolDing tUBe is SecureD to the cyLindrICal valve case as FOllows. The fronT EnD OF tHE holDinG tube is abutTed aGAinsT an aNNuLar STep foRmed oN tHE iNNer surface of the cyliNdRical vAlve cAse. Under this cOndition, thE REAr end of tHe hoLDiNG tube is held witH a cirClip which iS Engaged wIth an Annular eNgaging grOOVe formed On tHe iNneR suRFAcE of the cylindrICAl vaLvE case.
ThE hoLding tuBe iS coMbiNed WiTh the cyliNdrical vAlVe CaSe In tHe aboVE-describEd ManNeR. HeNce, whEN the hoLding Tube Is InSErtEd into tHE cYLIndrIcAl ValvE caSe Under The cONdiTion thaT the base eNd pORtioN oF tHe valve Member is held iN tHe holding gRoOve, The basE ENd portioN of the valve member is damaGEd by the AnnUlar sTep fOrmed on thE inNer surFacE Of the cYlindrIcal vAlVe cASE. TherEFOrE, thE hOlding tube AND thE cyliNdRicaL valve cAse must be assembled CAreFully. Since the AnnUlar ENGaGinG GrOOve On THe iNNEr surface of the cYlindrical VaLVe Case is diffICulT tO form wiTh the meTal moLD, the annUlar engagIng groove Is FormED By mAchining. ThIs fact inCreases thE ManufACtUring CosT of the VaCuuM boosTer togETheR with The facT tHat it iS neceSsAry to use The circlip to hold the rear End of tHe holDinG tube.
In anOthER coNventionaL vacUum booster, As dIscLosed, For INstanCe, in eXaMinED JapaNese uTility ModEL PUblICAtIon No. 12852/1992, in ordeR TO Fix A holdIng TUbe insErteD into a cylindrical VAlve case, a circlIp reTAIniNg a REar eNd Of the holding tuBe iS eNGAged with An Annular grooVe formed In AN inneR surfaCe of thE cylindRICaL Valve cAse. THat Is, the holdIng TuBE cannot Be FiXEd withOut tHe CircliP. In ordER
 having large chip areas.The presen t inv ent ion  r elat es t o a vacuum boo s terfor operating a brakemaste rc ylin d er  in a n autom o bi l e , m ot or cyc le or  thelik e in aboost mode , a nd  more partic u la rly to animp rovement ofa v acuumbo ost e r inwhi ch aholdin g  tubewhich hol ds a valv e  member o fa co ntrol valve is fi t te d  in a syntheti c resi nc yl i n dri cal  valve cas ewitht he fron t  e n d por t ion coupled t o a booster pis ton an dwit h  the r ear e nd ope ned, and th e ba se end po rtiono f a val v e membe r is f itt edin a n  a nn ula rh old i ng  gr o ove  formedon  t he ou ters u r f aceofthefront  end portionoftheh old ing t ube i n su ch  a ma nner t hat t he  base end porti on i s sealing lyen gag ed  with the in ner  su rface o f the c y lin dr i c a lvalve case. Furthe r, t he  present  inven t io nr elates t oa h oldi n g  tube  mou n ti ng struc ture i n  t he  vacuum  b ooster  w ith  wh ich t h e ho ldingtube issecur e d to the cylin d rical valve c a se . In a co nve ntional vac uumb oost er,a ssho w n, fo r ins ta n ce ,  in Unexamined Japa ne se Uti lityModel Publica tion (OPI) N o . 73459/ 1989 ,  t h e holding tube  is s ecured tot he cylin drica l valvecase as f o l lows. Th e f ron t e ndo f  t he holding tu b e  isab utted a gai nst anann ula r s tep  f ormed onthe inne rsu rf ac e o f the cylindri ca l v al vecase. Underthiscond it io n , t he rear en d of t he  h oldi ngtu be is  hel d  wi th a ci rclip whi chi s en ga ge d withan annular en ga ging groov efor med on t he inner  surface of the cylindr i cal val vecase. 
The  holdingtub e is c omb i ned wi th the  cyli nd ric a l  valv e ca sein  the above - d esc ribed  m anne r. Henc e, when the holdin g  tu be is inserte d i ntot h ecyl i nd r ica lv alv e case under theconditionth a tthe base e n d p or tion of  the va lve m e mber is  held inthe holdi ng  gro o v e,the base e nd porti on of the valve me mberisdamage dbythe a nnular ste p for med on  t he inn er su rf ace of t he cylindrical valve ca se. Th erefo re,  the hold ing tub e and the  cyl indrical v alv e c ase m ust be as semb l ed  ca r efull y. S i nce the a n nu lar e ng aging groov e o n t he in ner surfac e of  the cylindricalv alve case is d iffi c u lttof ormwi th the metal m old ,t h e annula rengaging gr oove isfo r med b y mach ining.  This f a c ti ncreas es t hemanufactu rin gc ost ofth ev acuumboos te r toge ther w i th t h e  fact that it is  nece s s ary t o  us e the  c irclipt o ho ld the rea r end of th e hold ingtube. 
In ano th er con ven ti onal vacuu m  booster,  as d isclose d,  for  in stance , in E xamin ed J ap ane se Utilit y Mo d el  P u bli cati on No .1285 2/1992, i n  order t o f i x a hol di ngt u be ins e rt e d  into a cy lin drica l valve case ,  a c i rc l ip re tainin g a re ar endo f t he  holdin g t u b e is enga ged witha n a nn ular  groovefo rmed  i n a ninner surface o f the cy lindrica l valvecas e . Th a t is,th e holding tu be ca nn o t be fi x e d w ithoutt hecir cli p. I n o rder 
 having_large chip_areas. The present invention_relates to_a_vacuum booster_for_operating a brake_master cylinder in_an automobile, motorcycle or_the like in_a_boost mode, and more particularly to an improvement of a vacuum booster in which_a_holding tube_which_holds_a valve member of a_control valve is fitted in_a synthetic_resin cylindrical valve case with the front end_portion_coupled to a_booster piston and with the rear end opened, and_the base end portion of a_valve member is_fitted_in_an annular holding groove_formed on the outer surface of_the front end portion of the_holding tube in such a manner that_the base end portion is sealingly_engaged with the inner surface_of the_cylindrical valve case. Further, the_present invention relates_to a_holding tube mounting_structure in the vacuum booster with_which the holding_tube is secured to the cylindrical_valve_case.
In a conventional_vacuum_booster,_as shown,_for instance, in_Unexamined_Japanese Utility_Model_Publication (OPI) No. 73459/1989, the holding_tube_is secured to the cylindrical valve case_as follows. The front_end_of the holding tube_is abutted against an annular_step formed on the inner surface_of the_cylindrical valve_case. Under this condition, the rear end of the holding tube_is held with a circlip which_is engaged with an_annular engaging_groove_formed on the_inner_surface of_the cylindrical valve case.
The holding tube is_combined with_the cylindrical valve case in the_above-described manner. Hence, when_the_holding tube is inserted into the_cylindrical valve case under the condition_that the base end portion_of_the_valve member is held in_the holding groove, the base end_portion of the_valve member is damaged by the annular_step_formed on the inner surface of_the_cylindrical valve case. Therefore, the holding_tube_and_the cylindrical valve case must_be assembled carefully. Since the annular_engaging groove on the inner surface of the cylindrical_valve case is_difficult to form with the_metal_mold,_the annular engaging groove is formed by machining. This fact_increases the_manufacturing cost of_the vacuum booster together with the fact that it is_necessary to use the circlip to hold_the rear end of the holding tube.
In another conventional vacuum booster,_as disclosed, for instance, in Examined Japanese Utility_Model Publication No. 12852/1992, in order to_fix a holding tube_inserted_into a cylindrical valve case, a circlip_retaining_a_rear_end of the_holding tube is_engaged with an_annular groove_formed in an_inner surface_of the cylindrical_valve_case. That is, the holding tube cannot be fixed without the circlip. In order