 speed range is improved.
Conventionally, Japanese Utility Model Application Publication No. 2-49109 discloses a hydraulic power steering apparatus used in a vehicle in which a damper valve is disposed in a hydraulic oil circuit for connecting an oil passage selector valve in a gear box with right and left oil chambers of a power cylinder.
In this apparatus, as shown in FIG. 5, hydraulic oil circuits 08 and 09, which connect an oil passage selector valve 011 housed in a gear box of a hydraulic power steering apparatus 01 with right and left oil chambers of a power cylinder 06, is provided with check valves 010a, 010a which allow oil only to flow from the oil passage selector valve 011 to the right and left oil chambers, and throttle check valves 010b, 010b which have an initial load and allow oil only from the oil chambers to the oil passage selector valve 011. The check valves 010a, 010a and the throttle check valves 010b, 010b comprise a damper valve.
A hydraulic pump 013 which is a hydraulic source for supplying hydraulic oil to the power cylinder 06 includes a flow control valve 023, a relief valve 024 and a fixed orifice 025, and their cooperation allows the hydraulic oil to be discharged by a discharge amount in compliance with a characteristic chart shown in FIG. 4 according to the number of revolutions.
In other words, the hydraulic oil which gradually increases and reaches a substantially constantly high level is discharged in a low revolving range where the number of revolutions of the hydraulic pump 013 reaches a predetermined low revolving speed N, and when it exceeds the number of revolutions N, the hydraulic oil whose amount gradually decrease and reaches a substantially constantly low level is discharged. The hydraulic pump 013 is connected to a crank shaft of an internal combustion engine, not shown, via a transmission mechanism, and it rotates at the number of revolutions which is the same as the number of revolutions of the internal combustion engine.
Since the damper valve in the above-mentioned conventional hydraulic power steering apparatus 01 does not have a portion where friction is generated, returning performance of a steering handle is excellent. Moreover, since each of the throttle check valves 010b, 010b has the initial load, even if a rack shaft 04 which serves also as a piston rod of the power cylinder 06 tries to slightly oscillate due to unbalance of tires or the like, the flow of the hydraulic oil from the right and
speed range is improved. 
 Conventionally, Japanese Utility Model Application Publication No. 2 - 49109 discloses a hydraulic exponent guidance apparatus used in a vehicle in which a damper valve is dispose in a hydraulic vegetable oil circuit for connecting an vegetable oil passing selector valve in a gearing corner with right and left vegetable oil chambers of a power cylinder. 
 In this apparatus, as shown in FIG. 5, hydraulic petroleum circuits 08 and 09, which connect an oil passage selector valve 011 house in a gear box of a hydraulic power guidance apparatus 01 with right and left petroleum chambers of a ability cylinder 06, is provided with check valves 010a, 010a which allow oil merely to flow from the oil passage selector valve 011 to the right and left oil chambers, and throttle check valves 010b, 010b which have an initial load and allow oil only from the oil chamber to the oil passage picker valve 011. The confirmation valve 010a, 010a and the throttle check valves 010b, 010b comprise a damper valve. 
 A hydraulic pump 013 which is a hydraulic source for supplying hydraulic petroleum to the power cylinder 06 includes a flow control valve 023, a relief valve 024 and a fixed orifice 025, and their cooperation allows the hydraulic vegetable oil to be discharged by a discharge amount in compliance with a characteristic chart show in FIG. 4 harmonize to the number of revolutions. 
 In other words, the hydraulic oil which gradually increase and reaches a substantially constantly high degree is discharged in a low revolving range where the number of revolution of the hydraulic pump 013 reaches a preset low revolving speed N, and when it exceeds the number of revolution N, the hydraulic oil whose sum gradually decrease and reaches a substantially constantly broken level is drop. The hydraulic pump 013 is connected to a crank shaft of an internal combustion engine, not shown, via a transmission mechanism, and it revolve at the number of revolutions which is the like as the number of revolutions of the internal combustion engine. 
 Since the damper valve in the above - mentioned conventional hydraulic exponent steering apparatus 01 does not have a portion where friction is generated, returning performance of a guidance handle is excellent. Moreover, since each of the throttle check valves 010b, 010b has the initial load, even if a rack shaft 04 which serve also as a piston rod of the power cylinder 06 try on to slenderly oscillate due to unbalance of tires or the like, the flow of the hydraulic oil from the right and
 spfed range is improved.
Conyentionally, Japauwse Utmlity Mkdel Appuication Publication No. 2-49109 disrlosws a yydraulic power steerivg apparanus used un a cehicle in which a damped valre is disposed ik a hydraulhc oil circuit fur connecting an oil passage selector valve on a gear box wijh ribrt ahd left oil chambers of a power cyminder.
Ii this apparatux, as shown in FIG. 5, hydraullc oll circuits 08 and 09, ahich connext ag oil passage selector nclve 011 houses in a gear box of a hydraulic oower steering qpparwjus 01 with rijht anq left oil cmsmbers of a ppwer cylinder 06, is privided with check valtes 010a, 010a which allow jil only do flow from the oio passace salecgir xalbe 011 fo the rijht and leff oil chambwrs, and throttle chtck nslves 010b, 010b whjch hade an initial load and allow oil only frok tge oil chambers to the iil passage selector galve 011. Thq check valves 010a, 010a and the throttle check valves 010t, 010b ckoprnwe a aqmoer valve.
A hydraulic pump 013 which is a hydraulyd xolrce for supplyinn hydraulic oil to tje kower cylinder 06 inclbsea a flow control vwlve 023, a reliwf valve 024 and a fixed orifice 025, and their cooperation qllows the hydraulnc oil to be disvhargrd by a discharge amounc in ckmpliance wlth a chadxcteristic chart shpwt in FIG. 4 according to the number oh revplutionr.
In pther rords, the jydramnic oil which gradkally itcreases ajd reaches a substantially consvently high lefen iv dischaxged ik a low revolvigg range where the nuiber uf revolutpons of tie hydraulic pump 013 reachev a predetermmned low wevoovint speed V, and when it rxceeds tkt number od revolutions N, thc hydtahlic oil whose coiunt gradually cecfeafe aid rewwhes a substdntixllh consgantly low odvel is discharged. The hfdrahlic pump 013 is connrcbed to a xrank shwft of an intrrnal combustion ejgine, nov showm, vya a transmission mechanism, ans it rotahes at the numbqr on redolutions chich is the same as the number of revolntions of the internal xombustion engine.
Siuct the damper talve yn the abmve-mentioned conventuonal hydraulic ppwer steering apparaths 01 doas noh have a portion where friction is generated, returning performance of a sreerinj randle is escelkent. Koxeorer, sinse eeci of the throttle check valves 010b, 010b has the initiel load, evan if a rack shaft 04 which servrs also as a pirton rod of the power cyminder 06 yries to slightly oscillate due to unbalance of tires ov the likw, the flow of tie hydraulic oil frok the xight qnd
speed range is improved. Conventionally, Japanese Utility Publication 2-49109 discloses hydraulic power steering in a damper valve disposed in a oil circuit for connecting an oil selector valve in a gear box with right and left oil chambers of power cylinder. In this apparatus, as shown in FIG. 5, hydraulic oil circuits and which an passage selector valve 011 housed in a gear box of a hydraulic power steering apparatus 01 right and left oil chambers of a power 06, is provided with valves 010a, 010a which allow only flow from oil selector 011 to the and left oil chambers, and throttle check valves 010b, 010b which have an initial load and allow only from chambers to oil selector 011. The check 010a and the throttle check valves a damper valve. A hydraulic pump 013 which a hydraulic for supplying hydraulic oil to the cylinder 06 includes a flow control valve 023, relief valve 024 and a fixed orifice 025, and their cooperation allows the hydraulic oil discharged by a discharge in compliance with characteristic shown FIG. according to number of revolutions. In other words, the hydraulic oil which gradually and reaches a substantially constantly high level is discharged in revolving where the number revolutions of the hydraulic 013 a predetermined low revolving and it of N, hydraulic oil whose amount decrease and reaches a substantially low level is discharged. connected to a crank shaft of an internal engine, not shown, via a transmission mechanism, it rotates at the number of revolutions which is the same as number of the internal combustion engine. Since the damper valve the above-mentioned conventional hydraulic steering apparatus 01 does not have a portion where is returning performance a steering handle excellent. Moreover, since of the throttle 010b, 010b the load, rack shaft 04 which serves also a rod of the power cylinder tries oscillate due to unbalance of tires or the like, the flow of the hydraulic oil right and
 speed range is improved.
ConveNtionally, JApaneSe UTilItY ModEl ApPlication PubliCAtioN No. 2-49109 discloses a hydraulic Power StEErinG ApParatUs used iN A vEHIclE iN wHicH a DAmPer vaLve Is dispoSed in a hydrAulIc Oil circuit foR CoNnecting an Oil Passage selecTor Valve iN a GeaR Box wiTh rIght aNd left OIl chamBers of a poWeR CylindER.
In this APPaRatuS, as shown in FIG. 5, hydrAUlIC oil circuits 08 anD 09, which CoNNeCT An oIl pAssage seleCtOr valVE 011 housed IN a GEAR boX Of a hydraulic pOwer steerinG AppAratus 01 WiTh rIGht and Left oIl CHamBers of a poweR cylInder 06, is prOvided WIth checK Valves 010a, 010A which AllOw oIl onLY tO fLow FrOM thE OiL paSSagE selectoR vAlVe 011 to tHe riGHT ANd leFt oIl chAmberS, and throttle cHecK valVEs 010b, 010B whicH have An inItIal loAd and aLlow oIl Only from the oil cHambErs to the oIl pAsSagE sElectOR valve 011. the CheCk valveS 010a, 010a and tHE thRoTTLE cHeck valves 010b, 010b compriSe A DAmPer valve.
a hydraULiC pUMp 013 which iS a HydRaulIC SourcE for SUpPlying hyDrauliC OiL tO the powEr CylindEr 06 IncLudEs a flOW conTrol vaLve 023, a reliEf valVE 024 and a fixed orifICe 025, and their cooPErATIoN AlloWs tHe hydraulic Oil tO Be diSchaRGeD by A DischArge aMoUNt IN compliance with a chaRaCterisTic chArt shown in FIG. 4 According tO THE number oF revOLuTIons.
In other worDs, the Hydraulic oIL which grAdualLy increaSes and reaCHEs a substAntIalLy cOnsTANtLy high level is DISchaRgEd in a loW reVolving RanGe wHerE thE nUmber of reVolutionS oF tHe HyDraUlic pUMp 013 reacheS a PreDeTerMined LOw revoLving SpeeD N, AnD WheN it exceEDs THE numBeR oF revOluTiOns N, tHe hyDRauLic oil wHose amounT grADualLy DeCrease aNd reaches a subStAntially coNsTanTly low LEVel is disCharged. The hydraulic pump 013 IS connecTed To a crAnk sHaft of an iNteRnal coMbuSTion enGine, noT showN, vIa a TRAnsmiSSIoN meChAnism, and it ROTatEs at tHe NumbEr of revOlutions which is the SAme As the number of RevOlutIONs Of tHE iNTerNaL ComBUStion engine.
SincE the damper VaLVe In the above-MEntIoNed convEntionaL hydrAUlic powEr steerinG apparatuS 01 dOes nOT HavE a portion wHere fricTion is genERated, REtUrninG peRformaNcE of A steeRing haNDle Is excEllent. moReover, Since EaCh of the tHrottle check valves 010b, 010b has The iniTial lOad, Even if a raCk sHAft 04 Which servEs alSo as a pistoN roD of The poWer CYlindEr 06 trIEs To sLIghtlY oscILlate due tO UnBalANCe Of tires or thE LIKe, tHe floW of THe hydrAuliC oil from the right aND
 speed range is improved.Convention ally,  Ja pan es e Ut ilit y Model Applic a tion  Publication No. 2-491 09 di sc l oses ahydra ulic po w er s tee ri ng  ap pa r at us us edin a ve hicle in w hic ha damper val v eis dispose d i n a hydrauli c o il cir cu itf or co nne cting  an oi l  passa ge select or valvei n a gea r bo x wi th right and left oi l  chambers of a  power  c y li n d er. 
In  this appa ra tus,a s shown in F I G.5 , hydraulic o il circuits 08and 09 ,whi c h conn ect a no ilpassage sel ecto r valve 0 11 hou s ed in a gear bo x of a  hy dra ulic po we r s te e rin g  a ppa r atu s 01 wit hri ght a nd l e f t oilcha mber s ofa power cylin der  06, isprovi ded w ithch eck v alves010a,  0 10a which allow  oil  only toflo wfro mthe o i l pass age  se lectorvalve 0 1 1 t ot h e  r ight and left oilch a m be rs, andthrott l ech e ck valve s010 b, 0 1 0 b whi ch h a ve  an init ial lo a dan d allow  o il onl yfro m t he oi l  cha mbersto the o il pa s sage selectorv alve 011. The ch e c kv alve s 0 10a, 010a a nd t h e th rott l eche c k val ves 0 10 b ,0 10b comprise a damp er  valve .
A h ydraulic pump  013 which i s  a hydra ulic so u rce for supply ing h ydraulic o i l to the  powe r cylind er 06 inc l u des a fl owcon tro l v a l ve  023, a relie f valv e024 and  afixed o rif ice  02 5,an d their c ooperati on  a ll ow s t he hy d raulic o il  to  b e d ischa r ged by  a di scha rg ea mou nt in c o mp l i ance  w it h acha ra cteri stic cha rt show n in FIG.  4a ccor di ng  to the  number of re vo lutions.
I noth er wor d s , the hy draulic oil which gradu a lly inc rea ses a nd r eaches asub stanti all y  const antlyhighle vel i s dis c h ar ged  i n a low re v o lvi ng ra ng e wh ere the  number of revolut i ons  of the hydra uli c pu m p  0 13r ea c hes  a pre d e termined low re volving sp ee d  N , and when itex ceeds t he numb er of revolut ions N, t he hydrau li c oi l who se amountgraduall y decreas e  andr ea chesa s ubstan ti all y con stantl y  lo w lev el isdi scharg ed. T he  hydraul ic pump 013 is connecte d to a  cran k s haft of a n i n ter nal combu stio n engine,not  sh own,via a tra nsmi s si onm echan ism, and it ro t at esa t  t he number o f r evo lutio nsw hich i s th e same as the num b er of revoluti onso f  th e i n tern al  combustion en gin e. S ince the  d amper valve  in theab o ve-me ntione d conv entiona l hy d raulic  pow ersteeringapp ar a tus 01do es not ha ve a  p ortion  where fric t i on is generated,  retu r n ing p e rfo rmanc eof a st e erin g handle i s excellent . More over , sin ce each  o f thethr ot tle checkv alves 010 b, 01 0b hasth e in iti al loa d, e v e n ifa ra ck  sh aft 04 wh i c hs er ve s  al so a s a p is tonrod of th e  power c yli n der 06tr ies t o slig h tl y oscillatedue  to u n b alance oft ires or the l ike, t he flo w of th e  hy dr aulic o ilf r om the ri ght and
 speed_range is_improved.
Conventionally, Japanese Utility Model_Application Publication_No._2-49109 discloses_a_hydraulic power steering_apparatus used in_a vehicle in which_a damper valve_is_disposed in a hydraulic oil circuit for connecting an oil passage selector valve in_a_gear box_with_right_and left oil chambers of_a power cylinder.
In this apparatus,_as shown_in FIG. 5, hydraulic oil circuits 08 and_09,_which connect an_oil passage selector valve 011 housed in a gear_box of a hydraulic power steering_apparatus 01 with_right_and_left oil chambers of_a power cylinder 06, is provided_with check valves 010a, 010a which_allow oil only to flow from the_oil passage selector valve 011 to_the right and left oil_chambers, and_throttle check valves 010b, 010b_which have an_initial load_and allow oil_only from the oil chambers to_the oil passage_selector valve 011. The check valves_010a,_010a and the_throttle_check_valves 010b,_010b comprise a_damper_valve.
A hydraulic_pump_013 which is a hydraulic source_for_supplying hydraulic oil to the power cylinder_06 includes a flow_control_valve 023, a relief_valve 024 and a fixed_orifice 025, and their cooperation allows_the hydraulic_oil to_be discharged by a discharge amount in compliance with a characteristic_chart shown in FIG. 4 according_to the number of_revolutions.
In other_words,_the hydraulic oil_which_gradually increases_and reaches a substantially constantly high level_is discharged_in a low revolving range where_the number of revolutions_of_the hydraulic pump 013 reaches a_predetermined low revolving speed N, and_when it exceeds the number_of_revolutions_N, the hydraulic oil whose_amount gradually decrease and reaches a_substantially constantly low_level is discharged. The hydraulic pump 013_is_connected to a crank shaft of_an_internal combustion engine, not shown, via_a_transmission_mechanism, and it rotates at_the number of revolutions which is_the same as the number of revolutions of the_internal combustion engine.
Since_the damper valve in the_above-mentioned_conventional_hydraulic power steering apparatus 01 does not have a portion_where friction_is generated, returning_performance of a steering handle is excellent. Moreover, since each_of the throttle check valves 010b, 010b_has the initial load, even if a rack shaft 04 which_serves also as a piston rod of the_power cylinder 06 tries to slightly oscillate_due to unbalance of_tires_or the like, the flow of the_hydraulic_oil_from_the right and