 left oil chambers to the oil passage selector valve 011 is restricted, and thus the rack shaft 04 hardly moves. For this reason, slight oscillation of the steering handle, namely, a shimmy phenomenon, can be prevented. In this regard, reference numeral 012 is a reservoir tank.
However, since the conventional damper valve has a constant damper effect regardless of the number of revolutions of the internal combustion engine (the number of revolution of the hydraulic pump) and the speed of a vehicle, the damper effect is not required so much at the time of low-speed revolution of the internal combustion engine and in a low-speed operation of the vehicle. In fact the damper effect is required in the occasion opposite to the above one. However, in the past the damper effect could not be adjusted according to the degree of necessity. For this reason, there is a need to improve steering follow-up performance of the steering handle particularly, at the low speed of the vehicle.
The present invention is disclosed in order to solve the above problem. It therefore is an object of the present invention to provide a hydraulic power steering apparatus in which the damper effect of a damper valve is changeable according to the number of revolutions of an internal combustion engine so that steering follow-up performance of a steering handle, particularly in a low speed range of a vehicle can be improved, and stability of steering in a high speed range of the vehicle can be improved, and a shimmy phenomenon and the kick-back phenomenon can be prevented simultaneously.
The present invention relates to a hydraulic power steering apparatus which solves the above problem. The invention provides a hydraulic power steering apparatus, which is constituted so that a damper valve is disposed in hydraulic oil circuits for connecting an oil passage selector valve in a gear box with right and left oil chambers of a power cylinder, characterized in that: the damper valve is composed of a spool valve. A control oil chamber of the spool valve is connected with a hydraulic oil feed passage for connecting a hydraulic pump which is driven by an internal combustion engine so as to discharge hydraulic oil with the oil passage selector valve. Its back pressure chamber is connected with a hydraulic oil circulating passage for connecting the oil passage selector valve with a reservoir tank. Orifices are provided respectively in the connecting oil passages, and when a discharged oil pressure of the hydraulic pump rises, the opening of the spool valve increases.
Since the invention is constituted as mentioned above, the spool valve, which
left oil chambers to the oil enactment picker valve 011 is restricted, and thus the wrack shaft 04 barely moves. For this reason, little oscillation of the steering handle, namely, a shimmy phenomenon, can be prevent. In this regard, reference numeral 012 is a reservoir cooler. 
 However, since the conventional damper valve has a ceaseless damper consequence regardless of the number of revolutions of the internal combustion engine (the act of revolution of the hydraulic pump) and the speed of a fomite, the damper effect is not necessitate so a lot at the time of broken - speed revolution of the internal burning engine and in a low - speed operation of the vehicle. In fact the damper consequence is required in the occasion opposite to the above one. However, in the past the damper effect could not be adjusted according to the degree of necessity. For this reason, there is a motivation to improve steering play along - up operation of the guidance handle particularly, at the low speed of the vehicle. 
 The present invention is disclosed in order to solve the above trouble. It therefore is an object of the present invention to provide a hydraulic power steering apparatus in which the damper effect of a damper valve is changeable according to the number of revolutions of an internal burning engine so that steer follow - up performance of a steering handle, particularly in a low focal ratio range of a vehicle can be improved, and constancy of steering in a gamey speed range of the fomite can be improved, and a shimmy phenomenon and the kick - back phenomenon can be prevented simultaneously. 
 The present invention relates to a hydraulic ability steering apparatus which solve the above problem. The invention leave a hydraulic power guidance apparatus, which is constituted so that a damper valve is disposed in hydraulic oil circumference for connecting an vegetable oil passage selector valve in a gear box with right and left oil chambers of a power cylinder, qualify in that: the damper valve is composed of a spool valve. A command oil chamber of the bobbin valve is connected with a hydraulic oil feed passage for connecting a hydraulic pump which is driven by an internal combustion engine so as to discharge hydraulic oil with the petroleum enactment picker valve. Its back atmospheric pressure chamber is connected with a hydraulic oil circulating enactment for connecting the oil passage picker valve with a reservoir tank. orifice are provided respectively in the connecting oil passages, and when a discharged oil pressure of the hydraulic pump rise, the opening of the spool valve addition. 
 Since the invention is constituted as mentioned above, the spool valve, which
 levt oil chambers to the oll passage selecjoe valvx 011 is rsstrictea, and thus the rack shaft 04 herdlt movtf. For this reason, rlight osbillation of uhe steering handle, nameln, a sglmmy 'hxnomenon, can be prevented. In this regarg, feyerence numeral 012 is a reservoir tank.
Rowever, slnce the convegtiomwl dzmper valve has a constant damper sffect gegardless of the number of revolutions of hhe lnternal combustioj engine (thg nuiver of revoljtion of the hydraulic pump) and the speed of a vehicld, the damper efdext lv not requiced so much at the time of low-sperd revolution pf vhe unternal combustion eigine and in a low-spged operathou of the vehicle. In fqcr the dam[er ddfezt js rsquiref ii the occasjon oppositw to the above one. Norvfer, in the pzst thq qamper effect could not be adjusted accmrdjng to the degree of nexessity. For this reasln, there ys a need to improve steering follow-up performanca of vhd suecving yajdle particularly, at the low speed of the vehydlt.
Thv present inventijn is disclpsfd yn order to sulve tks zbove problem. It tjereforg is ab object jf tne present invention to procide a hydrallic power steering ap'aratus in wkich tne dakper effect of a damper valbe is changfable acckfding to the numcer ox revoluukons of an internwl combusvion zngine su thst steqring folllw-up iarformance of a stferiny hangle, particklarly in a low speed range of e vehicle can ba ikproved, cnd stsbility of stqering in a hiyh speed rangd of the vvhicle cai be improveq, and a shimmf phenomenon end the kyck-bqck phenomevun can be prevrnted simlluaneously.
Tye present inventipn temates to a hydrcbluc power steerimg xppwrwtns whywh solves tha abuve lrobldm. The invektiun ptovides a hydraulic [owed steering apparatis, which iw constieuted so that a damper valve is dispmsev in hudrwulic oil circuits for connectjng an oip pwssage seleceor yalvg in a gear box with right and left oil chambers oh a power cylinder, chatacterized in that: thg dsmper valve is cjmposed ox a spool valve. A cobtrol oil chamber of the spool valve ia connacted with a hydraulic oil feed passage for connecting a hydraulic pump which us driteg by an intsrnak comtufcion endine ro as to discharbe hydraulic oil with the oil pessage selaccor valve. Its back pressure cnaober is connezted with a hydraulic oim circulsting passage for connecting thr oil passage selector vslve wity a rsservopt tenk. Orifices are profided xespecrively un tme connecting uil pwssages, ajd wien a discharged oil pressure of thw hydrqupic pump rises, tie opening on uhe spokl valde increases.
Sincs ths invevtion is consyituted as menyioned above, the spoml valve, which
left oil chambers to the oil passage 011 restricted, and the rack shaft reason, oscillation of the handle, namely, a phenomenon, can be prevented. In this reference numeral 012 is a reservoir tank. However, since the conventional damper valve a constant damper effect regardless of the number of revolutions of the internal engine number revolution the hydraulic pump) and the speed of a vehicle, the damper effect is not required so at the time of low-speed revolution of the combustion engine and in low-speed operation of the vehicle. fact damper effect required the opposite to the one. However, in the past the damper effect could not be adjusted according to the degree of For this is a to steering performance of the particularly, at the low speed of present invention is disclosed in order to solve above problem. therefore is an object of the invention to provide a hydraulic power steering apparatus which the damper effect of a damper valve is changeable according to the number of an internal combustion engine that steering follow-up of steering particularly a low range of a vehicle can be improved, and stability of steering a high speed range of the vehicle can be improved, shimmy and the kick-back can be prevented simultaneously. present relates to a hydraulic apparatus solves The provides hydraulic power steering apparatus, is constituted so that a valve is disposed in an oil passage selector valve in a gear with right and left oil chambers of power cylinder, characterized in that: the damper valve is composed of a valve. A chamber of the spool valve is connected with hydraulic oil feed passage connecting a hydraulic pump which is driven by an combustion so as discharge hydraulic oil the oil passage valve. Its back is connected a oil connecting the oil passage selector valve a tank. Orifices are provided respectively the passages, and when a discharged oil pressure of the hydraulic pump rises, the opening of valve increases. Since the is as mentioned above, the spool valve, which
 left oil chambers to the oil paSsage selecTor vaLve 011 Is rEsTricTed, aNd thus the rack sHAft 04 hArdly moves. For this reasoN, sligHt OScilLAtIon of The steeRInG HAndLe, NaMelY, a SHiMmy phEnoMenon, caN be preventEd. IN tHis regard, refEReNce numeral 012 Is a Reservoir tanK.
HoWever, sInCe tHE convEntIonal Damper VAlve haS a constanT dAMper efFEct regaRDLeSs of The number of revoluTIoNS of the internal CombusTiON eNGIne (The Number of reVoLutioN Of the hyDRaULIC puMP) and the speed oF a vehicle, thE DamPer effEcT is NOt requIred sO mUCh aT the time of lOw-spEed revoluTion of THe interNAl combuStion eNgiNe aNd in A LoW-sPeeD oPEraTIoN of THe vEhicle. In FaCt The daMper EFFECt is ReqUireD in thE occasion oppoSitE to tHE abOve onE. HoweVer, iN tHe pasT the daMper eFfEct could not be adJustEd accordiNg tO tHe dEgRee of NEcessiTy. FOr tHis reasOn, there IS a nEeD TO ImProve steering folloW-uP PErFormance Of the sTEeRiNG handle pArTicUlarLY, At the Low sPEeD of the veHicle.
THE pReSent invEnTion is DiSclOseD in orDEr to Solve tHe above pRobleM. it therefore is aN Object of the prESeNT InVEntiOn tO provide a hyDrauLIc poWer sTEeRinG ApparAtus iN wHIcH The damper effect of a dAmPer valVe is cHangeable accoRding to the NUMBer of revOlutIOnS Of an internal coMbustIon engine sO That steeRing fOllow-up pErformancE OF a steeriNg hAndLe, pArtICUlArly in a low speED RangE oF a vehicLe cAn be impRovEd, aNd sTabIlIty of steeRing in a hIgH sPeEd RanGe of tHE vehicle CaN be ImProVed, anD A shimmY phenOmenOn AnD The Kick-bacK PhENOmenOn CaN be pRevEnTed siMultANeoUsly.
The Present inVenTIon rElAtEs to a hyDraulic power sTeEring apparAtUs wHich soLVEs the aboVe problem. The invention prOVides a hYdrAulic PoweR steering AppAratus, WhiCH is conStitutEd so tHaT a dAMPer vaLVE iS diSpOsed in hydrAULic Oil ciRcUits For connEcting an oil passage SEleCtor valve in a gEar Box wITH rIghT AnD LefT oIL chAMBers of a power cylInder, charaCtERiZed in that: tHE daMpEr valve Is compoSed of A Spool vaLve. A contrOl oil chamBeR of tHE SpoOl valve is cOnnected With a hydrAUlic oIL fEed paSsaGe for cOnNecTing a HydrauLIc pUmp whIch is dRiVen by aN inteRnAl combusTion engine so as to discharGe hydrAulic Oil With the oiL paSSagE selector ValvE. Its back prEssUre ChambEr iS ConneCted WItH a hYDraulIc oiL CirculatiNG pAssAGE fOr connectinG THE oiL passAge SElectoR valVe with a reservoir tANk. Orifices are pRoviDED reSpeCTiveLy In the connectinG oiL pASSages, and WhEn a dischargEd oil preSsURe of tHe hydrAulic pUmp riseS, THe OPening Of thE spOol valve iNcrEaSEs.
Since ThE iNVentioN is cOnStitutEd as meNTionED Above, the spool valVe, whiCH
 left oil chambers to theoil passag e sel ect orva lve011is restricted, andthus the rack shaft 04  hard ly move s .For t his rea s on , sli gh tosc il l at ion o f t he stee ring handl e,na mely, a shim m yphenomenon , c an be preven ted . In t hi s r e gard,  re feren ce num e ral 01 2 is a re se r voir t a nk.
How e v er , si nce the conventio n al damper valve h as a c on s ta n t  da mpe r effect r eg ardle s s of th e  n u m b ero f revolutions  of the int e rna l comb us tio n  engin e (th en umb er of revol utio n of thehydrau l ic pump )  and th e spee d o f a  veh i cl e,  th ed amp e reff e ctis not r eq ui red s o mu c h a t th e t imeof lo w-speed revol uti on o f  th e int ernal  com bu stion  engin e and  i n a low-speed o pera tion of t heve hic le . Inf act th e d amp er effe ct is r e qui re d i nthe occasion oppos it e to  the abo ve one .  H ow e ver, inth e p astt h e dam pere ff ect coul d notb ead justedac cordin gtothe  degr e e of  neces sity. Fo r thi s  reason, there is a need toi mp r o ve stee rin g follow-up  per f orma nceo fthe steer ing h an d le particularly, at th elow sp eed o f the vehicle .
The pres e n t  inventi on i s  d i sclosed in ord er to  solve the above pr oblem . It the refore is a n object  of  th e p res e n tinvention top r ovid ea hydra uli c power  st eer ing  ap pa ratus inwhich th eda mp er  ef fecto f a damp er  va lv e i s cha n geable  acco rdin gto the  number of r evol ut io ns o f a ninter nalc omb ustionengine so  th a t st ee ri ng foll ow-up perform an ce of a st ee rin g hand l e , partic ularly in a low speed r a nge ofa v ehicl e ca n be impr ove d, and  st a bility  of st eerin gina highs p ee d r an ge of thev e hic le ca nbe i mproved , and a shimmy phe n ome non and the k ick -bac k ph eno m en o n c an bep r evented simulta neously.
T he pr esent inve n tio nrelates  to a h ydrau l ic powe r steerin g apparat us  whi c h  so lves the a bove pro blem. The inven t io n pro vid es a h yd rau lic p ower s t eer ing a pparat us , whic h isco nstitute d so that a damper valv e is d ispos edin hydrau lic oil  circuits  for  connectin g a n o il pa ssa g e sel ecto r  v alv e  in a  gea r  box with ri ght a nd  left oil c h a m ber s ofa p o wer cy lind er, characterized in that: the d ampe r val vei s co mp osed of a spoo l v al v e . A cont ro l oil chamb er of th es poolvalveis con nectedw i th a hydr auli c o il feed p ass ag e  for co nn ec t ing ahydr au lic pu mp whi c h is d riven by an inte rnalc o mbust i onengin eso as t o  dis charge hyd raulic oilwith t he o il pa ssage s el ectorval ve . Its back pressurechamb er is c on nect edwith a  hyd r a ulicoilci rcu lating pa s s ag e  f or con nect ing t he  oil  passages electorval v e withares e r voir t a nk . Orifices a reprovi d e d respecti v elyi nt he co nnecti ng oil  passag e s,an d whena d i s charged o il pressu r e o fthehydrauli cpump  r ise s,  the opening of  the spo ol valve i ncreas es. Sinc e  the i nv ention is co nstit ut e d as me n t ion ed abov e , t hespo ol v alv e, w h ich
 left_oil chambers_to the oil passage_selector valve_011_is restricted,_and_thus the rack_shaft 04 hardly_moves. For this reason,_slight oscillation of_the_steering handle, namely, a shimmy phenomenon, can be prevented. In this regard, reference numeral_012_is a_reservoir_tank.
However,_since the conventional damper valve_has a constant damper effect_regardless of_the number of revolutions of the internal combustion_engine_(the number of_revolution of the hydraulic pump) and the speed of_a vehicle, the damper effect is_not required so_much_at_the time of low-speed_revolution of the internal combustion engine_and in a low-speed operation of_the vehicle. In fact the damper effect_is required in the occasion opposite_to the above one. However,_in the_past the damper effect could_not be adjusted_according to_the degree of_necessity. For this reason, there is_a need to_improve steering follow-up performance of the_steering_handle particularly, at_the_low_speed of_the vehicle.
The present_invention_is disclosed_in_order to solve the above problem._It_therefore is an object of the present_invention to provide a_hydraulic_power steering apparatus in_which the damper effect of_a damper valve is changeable according_to the_number of_revolutions of an internal combustion engine so that steering follow-up performance_of a steering handle, particularly in_a low speed range_of a_vehicle_can be improved,_and_stability of_steering in a high speed range of_the vehicle_can be improved, and a shimmy_phenomenon and the kick-back_phenomenon_can be prevented simultaneously.
The present invention_relates to a hydraulic power steering_apparatus which solves the above_problem._The_invention provides a hydraulic power_steering apparatus, which is constituted so_that a damper_valve is disposed in hydraulic oil circuits_for_connecting an oil passage selector valve_in_a gear box with right and_left_oil_chambers of a power cylinder,_characterized in that: the damper valve_is composed of a spool valve. A control oil_chamber of the_spool valve is connected with_a_hydraulic_oil feed passage for connecting a hydraulic pump which is_driven by_an internal combustion_engine so as to discharge hydraulic oil with the oil_passage selector valve. Its back pressure chamber_is connected with a hydraulic oil circulating passage for connecting the_oil passage selector valve with a reservoir tank._Orifices are provided respectively in the connecting_oil passages, and when_a_discharged oil pressure of the hydraulic pump_rises,_the_opening_of the spool_valve increases.
Since the_invention is constituted_as mentioned_above, the spool_valve, which