Characteristics on Hydro-mechanical Transmission in Power Shift Process

CHINESE JOURNAL OF MECHANICAL ENGINEERING●50●Vol. 22, No. 1, 2009DOI: 10.3901/CME.2009.01.050, available online at ww.jmenet.com www.cjmcnet.com.cnCharacteristics on Hydro-mechanical Transmission in Power Shift ProcessHU Jjibin*, WEI Chao, YUAN Shihua, and JING ChongboNational Key Laboratory of Vehicular Transmission, Beijing Institute of Technology, Bejing 100081, ChinaReceived September 16, 2008; revised January 4, 2009; accepted January 5, 2009; published lectronically January 5, 2009Abstract: To improve the vehicular power and acceleration performance and reduce the shift impact, the study of the characteristics onpower shift is necessary. Based on the flexible hydraulic unit of hydro-mechanical transmission, this paper explores the feasibility ofshift without power interuption. With the four models concerning displacement ratio, rotational speed, rotational torque and power atideal shift point, the characteristics on power shift in dfferent running conditions are analyzed, and the rules of power shift are revealed.The theoretical analysis and test results show that the hydro- mechanical transmission can shift without power interuption in differentnunning conditions. Furthermore, there exists an ideal shift point in theory, at which point the cycle power in hydro- mechanicaltransmission can't be generated, and the impact on the system can be reduced to the minimum. However, if before or afier this idealshift point, a cycle power can be generated.mechanical transmission. Based on the flexible hydraulicIntroductionunit of hydro-mechanical transmission, this paper exploresthe feasibility of running in the stage of dual range and thesystem characteristics on shift without power interruption.stepless transmission which is suitable for transmittingThe research results are supposed to theoretically supportlarge power. It consists of some ranges in which the speedthe study on control strategy served to improve the shiftratio can be changed continuously. And speed ratios ofquality.different ranges can be linked up by the correct shift control.In this way, the transmission can get a expanded range of2 Description of Power Shiftcontinuous speed ratiol-. At present, many scholars focusresearches on the scheme design, control method of speedFig. 1 is the drive diagram of one two range hydro-ratio, the shifing control strategy of clutches, and the mechanical transmission, which consists of two brakes,consolidated control strategy of power train system, etcl+ . three planetary gearsets, one variable- displacement pump,Their analysis results show thaarithmetic type and one fixed displacement motor.hydro-mechanical transmission applies to the variablesteering in the tracklayers for the sake of its constant.T2moment output and geometric one to the straight-linepropulsion! t0. The speed ratio follow-up control methodcan achieve the regulation of engine speed, and PID controlh[10-13] Aalgorthm is good at the speed ratio control。 Andshiting with the short overlapping time of clutches canKI K2K3Outputreduce the impact and decrease the time of powerinterruption"4. Up to now, there is no published theoretical影article about the feasibility of shift without powerinterruption of hydro-mechanical transmission.So far, the shifting control strategy of bhydro-mechanical. Puimtransmission is similar to the strategy of step automatic中国煤化工ngetransmission. So the step automatic transmission can't shiftwithout power interruption. Neither do the hydro-YHCNMHGsionWhen brake T1 is joined and brake T2 is declutched, theplanetary gearset Kl works, the hydro-mechanicalThis project is supported by National Key LaboratorTasission Foundaion of China (Grant No. 9140C3402050702)Chicular transmission works in hydraulic range. When brake T2 isCHINESE JOURNAL OF MECHANICAL ENGINEERING●51●joined and brake T1 is declutched, the planetary gearset K2 respectively.and K3 work, and the hydro-mechanical transmissionworks in hydro-mechanical range.3.2 Model of rotational speed in power shift processIf the brake T2 is joined firstly and then brake T1 isThe rotational speeds of motor nm and transmissiondeclutched in the shift process from hydraulic range to output shaft m are got according to the rotational speedhydro-mechanical range, there is a short stage in which the relation as follows:two brakes work together. Because the brake TI is joined inthis stage, the power is transmitted by planetary gearset KI."_=nmy=(1+k)(1+k)n。(2)And when brake T2 is joined, the planetary gearset K2(1+kj)(1+k +左)片'begins to transmit power. When brake T1 is declutched,planetary gearset KI doesn't transmit power any longer,1+khowever, the whole power is transmitted by planetary"q° (+k)1+h+k)后”。(3)gearset K2. In this process, the power is transmittedwithout any interruption. This kind of shift method is calledpower shift. The flexible hydraulic unit of hydro-Where nu and 1:1 are the rotational speeds of sun gear andmechanical transmission is applied to resolve mechanicalplanet carrier of K1, ne is the rotational speed ofconstrain in the process of power shift. Thus excessivetransmission input shaft, in is the speed ratio from planetendogenetic force can be avoided, mechanical componentscan be protected and at last the shift without powercarrier of K1 to the transmission output shaft.interruption can be realized in hydro-mechanicalSo the speed ratio of hydro-mechanical transmission istransmission. The component running situation in differentmodes is shown in Table.，= (1+h+k)X1+4)位(4)1+k2Table. Running table of hydro .mechanical transmissionRunning stateK2_ K3These analyses show that the speed ratio of hydro-Hydraulic range (H)mechanical transmission is constant in power shift processHydro-mechanical range (HM)even if displacement ratio of pump is changed. No matterPower shift processwhat the rotational speeds of transmission output shaft andmotor are in hydraulic range, the rotational speeds of3 Model of the Characteristics in Powertransmission output shaft and motor change into the valuewhich is determined by rotational speed of transmissionShift Processinput shaft, regardless of the displacement ratio of pump.Fig. 2 shows the rotational speeds of motor and3.1 Ideal shift pointThere exists an ideal displacement ratio in theory, whichtransmission output shaft in the power shift process fromdefines the rotational speed difference between drive andhydraulic range to hydro-mechanical range (e is representedslave part of later range brake as zero， and thithe displacement ratio of pump). According to Fig. 2(a),displacement ratio is called ideal shift point. Shift at thiswhen power shift is started at 8<&，the rotational speeds ofmotor and transmission output shaft can immediatelypoint will make the impact least.The ideal displacement ratio from bhydraulic range to increase to one constant value crreponding to power shithydro-mechanical range can be resolved according to the process. The rotational speeds of motor and transmissiondefinition that rotational speed of gear ring of K3 is zero atoutput shaft do not change when power shift is started atideal shift point, that isε=ε° from Fig. 2(b). And from Fig. 2(C), when power shiftis started at 8>ε，the rotational speeds of motor andtransmission output shaft can immediately decrease to one。=_ ,0(+2)(1+4) .. 上。constant value corresponding to power shift process. As“(1+2)(1+个+k) V'transmission turms into hydro-mechanical range from powershift process, the rotational speeds of motor andwhere iy is the speed ratio from input shaft of transmissiontransmission output shaft also respectively change intoto the shaft of variable- displacement pump, in is the speedvalues corresponding to_ hvdro-mechanical range (theratio from input shaft of tasmission to the shaft of sun displac中国煤化工ed as constant ingear of K3, Vm is the displacement of fixed-displacementpower sCNMHGmotor, Vpmax is the maximum displacement of variable-By thie cuauous 01 vUlIIC lw U1 pump ep=enp pmaxysdisplacement pump, k， k2 and kg represent motor Qm=nmVm, the relationship of the rotational speedcharacteristic parameter of three planetary gearsets, between pump and motor in power shift process is●52●HU Jibin, e al: Charateristics on Hydro mechanical Transmission in Power Shift Processrelation Qp<2m would be got. As a consequence, the pump盟_ (1+k)1+k.+k2)(5is driven by the flow coming from motor, which means the”(1+k)(1+k),function of pump and motor exchanges each other. Andnow, the original pump works as motor and the originalPower shiftrnge pocesmotor works as pump, and the relation of motor torqueTm<0 is got at the same time. If the displacement ratio ofnpump is larger than ideal displacement ratio e>ε , then therelation Qp>Qm would be got. As a result, the motor is stilldriven by the flow corming from pump. It means thefunction of pump and motor doesn't change, and therelation of motor torque T>0 is got at the same time.(旧) Curve of rtaional speed carateristic when eg'deduced:Fig.2. Curve of rotational speed characteristicin power shit processTq=(10)The displacement ratio of pump in the condition of1+k2 +所volume flow conservation law in power shift process isgiven as1/4+(1+k)mT=-1+k2+h(1)i,(l+k)(1+k) v_(1+k)(1+k+k)M Vrpax(6)r,=T/2+(1+k)Tm. 1+k2(12)1+h+k 1+k .The deduced result shows that Eq. (6) is equal to Eq. (),=.T/i+(1+k)Tm 1+kp T;ε. (13)so the volume flow of pump Qp is equal to that of motor中国煤化工only at the ideal shift point in power shift process. In themeanwhile, the motor torque Tm is equal to zero. However,CHCNMHGqs. (1u) 113 10w uIai uu wiyuc of each componentin the power shift process, if the displacement ratio ofcan be deduced by the torque of motor and load ofpump is less than ideal displacement ratio 80, theshift process and the hydro-mechanical transmission can equivalent torque of transmission input shaft calculatedwork in the same process for a long period without from torque of mechanical branch is negative all the time,component damaged.and the power of mechanical branch is transmitted inpostive direction. In addition, because of Tm<0, the3.4 Model of power in power shift processequivalent torque of transmission input shaft calculatedRegardless of power loss owing to volumetric efficiency from torque of hydraulic branch is positive all the time, andand mechanical eiciency， the output power of the power of hydraulic branch is transmitted in negativetransmission wouldn't change (eferring to Eq. (14)), but direction. Therefore there is only one type of power flowthe input power of transmission would change with the mode in this condition, that is the power of mechanicaldisplacement ratio of pump (efering to Eq. (15)):branch is transmitted in positive direction and power ofhydraulic branch is transmitted in negative direction1+k,(referring to Fig. 4).B=Ton=(l+k)Xl+k. +k)脑”-n.T,(14)Power transmitted byhydraulic breanchp.=1n.(1+k)[(1+K)Tm+T](15)(1+h +k.)1+k)i2Input powerPower transmittd byIn Eq. (15), the first item represents the power of hydraulicmechanical branchbranch. When the torque of motor is negative value, theFig. 4. Power flow diagram of power shiftpower of bydraulic branch is transmitted in negativebefore ideal shift point when Tu<0direction. When the torque of motor is positive value, thpower of hydraulic branch is transmitted in positive direction.The second item of Eq. (15) represents the power of4.2 Analysis of the characteristics at ideal shift pointmchanical banrch. The decion ofthe power ramitedo. Ifpower shift hppers at the ideal shit point, then Tc=0,mechanical branch is related to the torque of motor and loadso the power of hydraulic branch is zero, the whole inputpower is transmitted only by mechanical branch, and thereof ransmission, which will be elaborated later.is no cycle power in hydro-mechanical transmission. In this4 Analysis on the Characteristics in Powercondition, the system has the maximum ffciency. Thecurve of power flow of hydro-mechanical transmission isShift Processshown in Fig. 5. .4.1 Analysis of the characteristics before idealshift pointOutput powerHere, the load of transmission is supposed as 1 400N .m.Based on Eqs. (10)-(11), the relationship curves between2the torques of sun gear of K1 and K2 and the pressure ofmechanical banchhydraulic system are indicated in Fig.3.Fig. 5. Power flow diagram of power shiftat ideal shift point600-4.3 Analysis of the characteritics after idealHere, the load of transmission is supposed as 1 400 Nom.:200致二hydray中国煤化5B.6. The resut of-200figure-eased from positivePressure of bydrsulie sysyteom p/MPa30一40valueIYHC N M H Geased from negativevalue to larger negaive value. 1I 122U, then the equivalentFig. 3. Curves of Tt1 and T12 before idealtorque of transmission input shaft calculated from torque ofmechanical branch is negative, and the power 0●54.HU Jibin, et al: Characteristics on Hydro mechanical Transmission in Power Shift Processmechanical branch is transmitted in positive direction. In5 Test and Verificationaddition, because of Tm>0， the equivalent torque oftransmission input calculated from torque of hydraulicbranch is negative, and the power of hydraulic branch isThe test is done at 330 kW dynamic simulated test benchtransmitted in negative direction. Therefore, in this in National Key Laboratory of Vehicular Transmission ofcondition the input power of transmission is split intoBeiing Institute of Technology. The schematic diagram ofpower of mechanical branch and hydraulic branch, andtest bench is shown in Fig. 9, the two bydraulicthere is no cycle power in transmission. The direction ofsecondary-regulated units are used as driving instrumentpower flow is shown in Fig. 7.and loading instrument.20二=Hydraulicpump stationDrivingInartialLoadinginstrument TonqueTorquerinstrument~~、8--20islrensdu_ Hydro-.1 tansduce文片四H mechanical 四4-400-600Control30 40systemPressure of hydraulic syaytem p/MPaFig. 9. Diagram of test benchFig. 6. Curves of T and To after idealshift pointFig. 10 shows the test curve of power shift before idealPower tansmited byshift point, Fig. 10(a) shows the curve of pressure of brakeshydraulic branchand Fig. 10(b) shows the curve of rotational speed.Input powerOutput power2.0[Power shitrnge procesPower tasmitted bymechanical branchFig. 7. Power flow diagram of power shiftPafter ideal shift point when T2>05tIf Tr<0, the equivalent torque of transmission inputshaft calculated fom torque of mechanical branch is1T1spositive, and the power of mechanical branch is transmittedTime t1sin negative direction. In addition, because of Tm>0, the(a) Pressure curve of brake clutchequivalent torque of transmission input shaft calculatedfrom torque of hydraulic branch is negative, and the power80of hydraulic branch is transmitted in positive direction.700Therefore, in this condition the power of hydraulic branch， 600Input shaftis transmitted in positive direction, the power omechanical branch is transmitted in negative direction, and足400Power shiftthere is cycle power in transmission. The direction of300roge processpower flow is shown in Fig. 8.6 200Power transmitted byOutput safhydnulic branchisTime跆(b) Curve of rtaioal speedhput power)Fig. 10. Test curves of power shift二中国煤化工Fron.YHCNMHGeT1andT2workFig. 8. Power flow diagram of power shifttogether ftorm the time t=4.5 S to the time t=10 s (thisafter ideal shift point when Tp<0period is in power shift process). According to Fig. 10(b),CHINESE JOURNAL OF MECHANICAL ENGINEERING●55.the rotational speed of motor and transmission output shaft time t>8.2 s, the test curve is similar to the simulated resultrise immediately at the time [=4.5 s, from the time t=4.5 shown in Fig. 2(c).s to the time t=10 s the rotational speeds of motor andtransmission output shaft remain fixed value, and the2.Power shiftrotational speed of motor fall immediately, but thmaoge process,rotational speed of transmission output shaft rises again1.5immediately after the time t>10 s. Test curve is similar tothe simulated result shown in Fig. 2(a).E1.0' prPrzThe test curve of power shift at ideal shift point is shown导ξin Fig. 11. The period from the time r2.8 s to the timeE o.st=8 s is in the process of power shift according to Fig.11(a). And according to Fig. 11(b) there is no rotationalisspeed impact of motor and transmission output shaft in theTime 18power shift process. The result of analysis proves that(向) Pessre curve ofbrake clutchpower shift at ideal shift point wouldn't bring about anyshift impact.80luwwwmm.0Power shftl 600\ Motorange pocess400Inoput shafti 300rnange processs ξ10 PnPr200Output shaft互1000.Time t10I(6)Cunve of rtatioal speedTime IlsFig. 12. Test curves of power shft(a) Pessure curve ofbrake chutchafter ideal shift point00pThe results of test curve also show that the power shiftprocess may last for 6 s, there is no power interruption inMotorhis process and no any components are damaged.oolTherefore, the power shift of hydro-mechanicallaoput shafttransmission is the real shift without any power interruption.OUrtput shatIn addition, if the time of power shift process is too longrange proessbefore or after ideal shift point, the hydraulic pressure will00exceed the set value of safety valve and the safety valvewill work. In the actual application, the time of power shiftTime thprocess should be modulated by the specific condition to(6)Curve of roatioal spedhave a good performance.Fig. 11. Test curves of power shiftat ideal shift point6 ConclusionsFig. 12 is the test curve of power shift after ideal shiftpoint, Fig. 12(a) is the curve of pressure of brakes and Fig.According to the theoretical analysis and test verification,12(b) is the curve of rotational speed. From Fig. 12(a), itis the characteristics on power shift of hydro-mechanicalclear that brake T1 and T2 work together from the time transmission are discussed in the paper. Four importantt=1.5 s to the time t=8.2 s (this period is in power shift conclusions are drawn.process). According to Fig. 12(b), the rotational speed of(1) There is no power interruption in the process ofmotor and transmission output shaft decrease immediately power中国煤化工trasmssisni cean beat the time t=1.5 s, from the time t=1.5 s to the time in thetime without anyt=8.2 s the rotational speeds of motor and transmission compoYHCNMHGoutput shaft remain fixed value, and the rotational speed of(2) There exists an ideal shift point in theory, at whichmotor rises immediately, but the rotational speed of point the input power is transmitted by the mechanicaltransmission output shaft falls again immediately after the branch entirely, and no power in the bydraulic branch. Also,HU Jibin, et al: Characteristics on Hydro mechanical Trasmissio in Power Shift Processthe shift impact of transmission can be reduced to the[9] XU Liyou, ZHOU hili, ZHANG Mingzhu, et al. Reasonable329- -36.minimum. Therefore, it is the ideal shift way.(3) If power shift happens before ideal shift point, thematching of engine and hydro mechanical continuously variabletransmission system of tractor[J]. Transactions of the CSAE, 2006,mechanical branch transmits power in positive direction22(7): 109-113. (in Chinese)and the hydraulic branch transmits power in negative[10] YUAN Shibua, HU Jjbin, YANG Wenzheng. Conditions of ratiodirection. There exists a cycle power in transmission.changing continuously for multi-range split tasmission([]J. Journal(4) If power shift happens after ideal shift point, theof Beijing Instiute of Technology, 2000, 9(4): 358 :361. (inChinese)direction of power flow changes with the increase ofhydraulic pressure. When the hydraulic pressure is less than[1] HU Jibin, WEI Chao, DU Jiuyu, et al. A study on the speed ratiofollow-up cootrol system of hydro mechanical tasmissio[].certain value, the input power is transmitted respectively byTransactions of Bejing Instiute of Technology, 2008, 28(6): 481-hydraulic branch and mechanical branch, and there is no485. (in Chinese)cycle power. And when the hydraulic pressure is higherthan the certain value, the bydraulic branch still transmitshydrostatic-mechanical transmision: Us, 5671137[P/OL]. 19975-2-15[1997-9-23]. htp: /www.google com/patents?id= WaQeAAApower in positive direction, but the mechanical branchEBAJ &dq=5671137.transmits power in the negative direction, and there exists a[13] KRASNEVSKI L. The synthesis method of electro .hydraulic sche-cycle power in transmission.mes of mechatronic control systems for hydromechanical trans-missions[CV//Society of Automotive Engineers, Inc., Warre ndale,ReferencesPennsylwaria, USA, SAE 2003 World Congress, Detroit, Michigan,[1] KITA Y, SUGAWARA R Hydromechanical transmission: Us,March3- 6, 2003: 289 -295.4813306[P/OL].1986-10-21[1989-3-21]. htp: /1 www.google.com[14] GUO Xiaolin, PAN Hui, YANG Shujun, et al. Study on displace-/patent?ld=WKduAAAEBAJ&dq- KITA+, +SUGAWARA.ment control strategy of tw[2] COUTANT A R, GARNETT s C. Hydro -mechanical transmissontransnission[]. Transactions of the Chinese Society for Agriculur-having three planetaries and five members: US. 5890981[P/OL].ral Machinery, 2006, 37(9): 13-16. (in Chinese)196-11-2519994-6]. ht:/:/w/w googie com/patents?id=lqoWAAAAEBAJ&dq-Hydro mrhaitattsnsisthavingthere Biographical notesplanetaries+and+ fivetmembers.HU jibin, bom in 1970, is currently an associate professor in[3] MITSUYA H, OTANI K, ISHINO T, et al. Development of hydro- Beijing Institute of Technology, China. He received his PhDmecbanical transmission (HMT) for bulldozers[CV/Society of degree from Beiing Instiute of Technology, China, in 2002. HisAutomotive Engineers, Inc, Warrendale, Pennsylvania, USA, S4E research interests include the technology of vehicular transmissionIntermational 0Of-Highway and Powerplant Congress and and hydraulic transmission.Exposition, Milwaukee, Wisconsin, September 12-14, 1994:Tel: +86-10-68914786; E-mail: hujibin@bit.edu.cn159-168.[4] TANG Xinxing, ZHAO Dingxuan, HUANG Haidong, et al. WEI Chao, bom in 1980, is currently an instructor in BeiingTre-stage with geometric ratios hytrostati-mechanical compound Institute of Technology, China. He received his PhD degree fromrasmision for construction vehicle[JI. Journal of Jilin University Beijing Institute of Technology, China, in 2002. His research(Engineering and Techology Edition), 2006, 36(2); 56-61. (ininterest includes the technology of hydraulic tansmission.5] CAO Fuyi, WANG Jun. Power analysis of hydro mechanicalTel: +86-10-68914786; E-mail: weipeter1@bit.edu.cndifferential turing mechanism of Dongfanghong1302R tractor[].YUAN Shihua, bom in 1958, is currently a professor in BejingTransactions of The Chinese Society of Agriculural Engineering,Institute of Technology, China. He received his PhD degree from2005, 21(3): 99-104. (in Chinese)[6] XU Liyou, ZHOU Zhill, ZHANG Mingzhu. Design ofBeijing Institute of Technology, China, in 1999. His researchhydro-mechanical continuously variable tasmission of tractor[J].interests include the technology of vehicular transmission andTrarsactions of the Chinese Society for Agriculural Machinery,hydraulic transmission.Tel: +86-10-68914786; E-mail: yuanshihua@bit.edu.cn2006, 37(7): 5-8. (in Chinese)[7] TAKIYAMA T，MORITA s. Engine-CVT consolidated controlusing LQI control theory[]. Sociery of Aunomotive Enineersof JING Chongbo, bom in 1970, is curenty a PhD candidate inJapan, JSAE Review, 1999, 20(2): 251-255.Beijing Institute of Technology, China. His rescarch interest[8] PFIFFNER R Cuzzella L, ONDER C H. Fuel-optimal control of includes the tchnology of hydraulic tansmission.CVT powertainsJ]. Control Enginering Practice, 2003, 1(3):) Tel: +86-10- 68914786; E mail: weipeter1@bit.cdu.cn中国煤化工MYHCNMHG