Power flows and efficiency analysis of out- and input coupled IVT

Transcription

1 Ŕ periodica polytechnica Mechanical Engineering 53/ (9) 6 68 doi:.33/pp.me.9-. web: me c Periodica Polytechnica 9 flows and efficiency analysis of out- and input coupled IT EEAH ATILE eceied --8 Abstract ince late 995, when the high-powered (94 kw) Fendt Faorit 96 equipped with a ario transmission was launched, power machines with T (ontinuously ariable Transmission) hae appeared on the palette of all major tractor manufacturing companies as well. The T unit in the transmission of these power machines is not included directly in the power flow, but in one of the power branches after a split. By modifying the gear ratio of a properly selected T unit, the transmission can be geared neutral and the direction of progress of the ehicle can be changed. The transmission structure produced so is called power split IT (Infinitely ariable Transmission). The paper presents the ways of producing an IT drie and analyzes the Fendt ario driing mechanism with O- structure and the same elements but with I- structure. There is detailed analysis on both structures on power flows (power split, positie/negatie power circulating), the Geared Neutral and the backward operational stages, taking into account the significant states from efficiency calculation point of iew, together with changes thereof in function of output reolution. Based on these inestigations it is highlighted that the entire range of the course of the ehicle can be coered by an output coupled system adjusting the gear of the T unit within the high-efficiency range. The task is the same for input coupled systems, to be realized by planetary gears installed after the IT unit and by the proper control of their engagement. Keywords T IT power split efficiency power flow tractor Acknowledgement The authors wish to acknowledge the technical assistance of the Hungarian Institute of Agricultural Engineering. Furthermore thanks for the support of Hungarian cientific esearch Found (OTKA K6875). Zsolt Farkas György Kerényi Department of Machine and Product Design, BME, H- Budapest, Műegyetem rkp.3, Hungary Introduction Leonardo Dainci sketched the first T (ontinuously ariable Transmission) in 49 []. Long time has passed since the first records and continuously ariable transmission technology has been applied in more and more areas. The T mechanisms deeloped for agricultural power machines had no success until the 96s and 97s because of their low efficiency. In the 98s and 99s, hydrostatic-mechanical power split transmission mechanisms stepless by speed ranges were of higher efficiency, but they were only produced at prototype leel (e.g.: Hungarian AI-TAK 4x4, Jarchow transmission, Kirste enius: LTM Forschungs-Tractor, etc.). A real breakthrough was brought about by the serial production of 94 kw Fendt Faorit 96 with ario transmission, presented in late 995 []. And in the course of the past fourteen years, models with continuously ariable transmission appeared in the product palette of nearly all manufacturers (Table ). Ealuation of T mechanisms A T unit can be integrated into a drietrain in two ways. One of them is mounting directly into the power flow (Fig. a), the other is mounting into a branch created by power split (Figs. b and c). The continuously ariable power split transmission mechanisms thus produced can be diided into two further main groups. One of the main groups consists of single (Fig. b), the other of multiple power split transmission mechanisms (Fig. c). There are arious structural designs for T units [3]. Apart from one or two exceptions, the T unit of serially produced continuously ariable tractor transmission is hydrostatic (Table ). This transmission type ensures the most shifting options. The transmission structure so produced is called power split IT (Infinitely ariable Transmission). The IT produced as aboe can be used for arious purposes: to improe total efficiency; to increase the transmission ratio range. Unfortunately, these goals cannot be reached simultaneously, as the ratio range is reduced the efficiency increases, and an in- flows and efficiency analysis of out- and input coupled IT

2 Tab.. ommercially aailable T tractor models The Type of Transmission T Unit The Type of Tractor Fendt ario Dyna-T -tronic Techtar T M Hydrostatic (primary and secondary controls) Fendt ario 3, 4, 7, 8, 9 Massey Ferguson 74, 84 JB Fastrac 85 hallenger MT 5 B, 6 B laas HM laas Xerion teyr (ZF) -Matic teyr T, 3, 5, 7 Hydrostatic (primary controls) ase X, 3, 5, 7 Autoommand T M New Holland TT 35, 45, 55, 7, 9 ZF Eccom Hydrostatic (primary controls) John Deere 64, 66, 68, 69 Deutz Fahr Agrotron TT 3, 45, 6 laas Xerion 33, 5 Mcormick TX 7-9 Terrion ATM 7 John Deere AutoPowr Hydrostatic (primary controls) John Deere 7, 83 New Holland EasyDrie hain ariator (PI) New Holland Boomer arraro aryt Toroid ariator arraro T 5., T., T 5. altra Nordic Hydrostatic altra Direct NH Autoommand Hydrostatic (primary controls) New Holland T 7 Belarus - Electromechanical Belarus 33 plit i const plice plit / plice i const plice / plit i const a, direct integration b, single power split c, multiple power split Fig.. Options for mounting a T unit into the drietrain (schematic diagrams) creased ratio range results in the reduction of total transmission efficiency. Four basic structural components are required for producing the simplest IT structures (Fig. ), namely: coupling member of constant speed, coupling member of constant torque, power branch of constant gear and power branch of infinitely ariable gear. If the coupling member of constant speed is on the input side, the resulting system will be input coupled (I) (Fig. a) with split torque; if it is on the output side, the resulting system will be output coupled (O) (Fig. a) with split speed. Out of the models commercially aailable, transmission of Fendt is of the O ( oupled) type, all the rest are I ( oupled). Let us assume that the coupling member of constant torque is an EI type planetary gear (E means external, I means internal toothing) [4]. The planetary gear is indicated by P in Fig.. The abbreiations of the three basic elements of an EI type planetary gear according to the English terminology are the following: un gear, ing gear, arrier. In case of a stepless, constant gear, and input coupled (I) system, there are seeral ways of connecting the output shaft and in case of an output coupled (O) system, the input shaft to the three basic components (,, or ) of a EI type planetary gear of two degrees of freedom. Thus, by combining basic structural components, twele different structures can be created (Table ). The number of different structures due to kinematics equialence can be reduced to 6 Per. Pol. Mech. Eng.

3 haft onstant peed i const i b P haft onstant Torque haft onstant Torque i b P i const haft onstant peed a, input coupled (I) b, output coupled (O) Fig.. The two ground type of single power split infinitely ariable transmissions six. On the basis thereof, ario transmission is the structure indicated by the O- code (Fig. 3a). In the signage, O means output coupled, the first letter () refers to the connection with the T component, the second letter () to that with the component of constant gear, and the third letter () to that with the input shaft. 3 Analysis and modelling of the basic components of IT structures The basic components of an IT structure were examined one by one in detail. The input and the output of the basic components were analysed in iew of speed, torque and power. The gear ratio between output and input and efficiency were taken into consideration during modelling. 3. ariable gear In high-power machines, the ariable gear unit is a mechanical or hydrostatic transmission, except for the Belarus electromechanic transmission. The accurate modelling of a T unit is quite complicated due to parameters depending on both the speed of reolution and the torque. The most accurate results for the gear ratio between inputs and outputs and for efficiency alues would be proided by the results measured on the transmission test bench. Therefore the simulation model is built up to directly integrate the field alues of speed of reolution, torque, and the characteristic cure of efficiency yielded by measurements. In this study, the efficiency of the ariable gear unit was taken into consideration with a constant alue independent from the gear ratio and the applied torque. 3. Planetary gear The speed of reolution correlation between the basic components of the planetary gear (, and ), based on the Willis basic equation, is: ( i b ) n = n i b n () Where i b is the internal gear ratio of the planetary gear, which can be determined by the speeds of the basic components, applying them to a carrier by definition, and can also be expressed by the tooth numbers of basic components (). i b = n n n n = z z () The relation of torques is only determined by the internal gear ratio i b and efficiency η and η. The order of letters in the index shows the direction of power flow. From the torque balance of the planetary gear: T + T + T = (3) When carrier does not rotate, from the power balance in both power flow directions: For sun gear input: For ring gear input: T n = T n η (4) T n = T n /η (5) By summing up both efficiencies and introducing η W the torque relation independent of power flow direction will be: It follows from (3) and (6) that: T T = n n η w = i b η w (6) T T = i b η w (7) T T = i b η w (8) Based on the signs gien in the literature [5], the w index comes from the sign of the rolling power P w on the shaft of the sun gear. If P w >, rolling power flows from the sun gear to the ring gear; if P w <, it flows from the ring gear to the sun gear. The defnition of η w for calculations follows from this: w = + η w = η (9) w = η w = η () Eqs. () to () aboe can be used for calculating the speeds of the missing basic component(s) on the basis of input parameters Z, Z (sun-, ring gear tooth numbers) and input data; and on the basis of the tooth efficiency calculation described at the cylindrical cogwheel connection and the bearing loss of the planetary gear, torque and output alues can be determined by taking the power flow direction into account. flows and efficiency analysis of out- and input coupled IT

4 Tab.. ingle power split infinitely ariable transmission structures tructures: Internal gear ratio of the i b /i b i b /i b i b /i b i b /i b i b /i b i b /i b planetary gear: Equialent structures: I- I- I- O- O- O- 3.3 onstant gear Tooth efficiency can be determined on the basis of the tooth numbers of the connecting gears (Z and Z ), based on equation () were µ Z =,4 is the coefficient of friction. In case of an EI type gear connection the - sign, and in case of an EE type gear connection the sign + is required []. ( η =, µ Z ± ) Z Z 3.4 Bearing Friction in the rolling bearing is a determining factor, its influences the operating temperature. Bearing friction depends on load and other factors, the most important of which are the bearing type and size, the operating speed, the properties and quantity of the lubricant. The total resistance to rolling in a bearing is made up of the rolling and sliding friction in the rolling contacts, the friction in the contact areas between the rolling elements and the cage as well as on the guiding surfaces for the rolling elements and the cage, the friction in the lubricant and of the sliding friction of rubbing seals in the case of sealed bearings. The modelling of bearing loss is quite complex [6]. This study does not contain detailed modelling, only a simplified ersion thereof. This simplification was based on planetary gear tests performed at our department [7]. On the basis thereof, bearing losses were taken into consideration at per cent of rolling output power. 4 Testing of IT systems Three different operational states can be distinguished in T power split transmission mechanisms based on the power flows generated [8]. One of them is power split (P), when power flows along power branches of both the constant and the ariable gear. The other is power circulation, within which there are positie and negatie operational states. Positie power circulation (+P) means that the sum of power coming from the input shaft and of circulating power flows through the power branch of ariable gear. In case of negatie power circulation ( P), aggregate power passes through the power branch of constant gear, and the T unit is only loaded by circulating power. These operational states must be further broken down in order to accurately analyse and calculate efficiency. Particular attention must be paid to the state of geared neutral and to the clutch state of the planetary gear [9]. 5 Analysis of O- and I- transmissions Using basic structural components, the Fendt ario transmission of O- structure (Fig. 3a) and the I- structure, the mirror image of the former was examined (Fig. 4a) by using the same components. The double heay lines in the figures indicate the bearings in the tests. Test parameters were the tooth number of sun- and ring gear (Z = 5, Z = ), the speed of reolution of input shaft (n I N = 9 /min), the torque of input shaft (T I N = Nm) and the gear ratios (i = 3, i = ) (Fig. 3a and 4a). Fig. 3/b shows the analysing tables of O-, and Fig. 4b shows that of I-. The following assumptions are made in order to specify power flows: drie means that the direction of the actie force and of rolling point speed are identical. introduced into the transmission is always positie. drie means that the direction of the actie force and of rolling point speed are the opposite. power is always negatie. The first column of the tables on the input and output shafts of each basic component shows the signed alues of speed, the second those of torque, and the third those of power. The first row of the tables illustrates the operational state of (P); the second that of ( P); the third that of (+P), the fourth that of Geared Neutral (P onst = GN); and the fifth the one when no power flows through the branch of ariable gear (P ar = ). The operational state of power split should be further broken down for efficiency analysis, as this operational state includes the highest efficiency state of the planetary gear, namely the clutch state. This separates power flow from the sun gear to the ring gear and from the ring gear to the sun gear. Fig. 5a O- and 5.b I- shows the Kutzbach speed figures of these three operational states of the planetary gear. Our tests were performed separately by taking into consideration, the tooth efficiency, the efficiency of the component of ariable gear, and the friction losses of bearings. The efficiency of the component of ariable gear was taken into consideration as a alue η ar =.87 regardless of the gear ratio. Fig. 6a shows power proportions in function of output reolution for the O- structure, and Fig. 6b for the I- structure. 64 Per. Pol. Mech. Eng.

5 P IN i b i c i ar i c P OUT haft P i c n c nar i b n i c nc haft a, Transmission structure b, Analysing tables of the operational states Fig. 3. O- transmission P IN i ar i b i c i c P OUT haft n ar i c c n i c n c i b n P haft a, Transmission structure b, Analysing tables of the operational states Fig. 4. I- transmission n TP + ++ O max. max. n T P max. max. O P T P T P T P T P T PT Fig. 5. Kutzbach speed figures of the power split state of the planetary gear a, O- structure b, I- structure Fig. 7a shows ratio change of gear ratio of ariable gear in function of output reolution for the O- structure, and Fig. 7b for the I- structure. Fig. 8a shows efficiency changes in function of output reolution for the O- structure, and Fig. 8b for the I- structure. Let us note that the boundaries of changes between operational states are shifted by taking efficiency alues into consideration. In addition to taking tooth and bearing loss into consideration, Figs. 6, 7 and 8 indicate the boundaries corresponding to the figure of η ar =.87. Fig. 9a shows the total efficiency changes at different constant efficiency alues in the ariable gear unit as a function of output reolution for the O- structure, and Fig. 9b for the I- structure. 6 onclusions According to the analysis presented aboe the following conclusion can be drawn. Depending on the structure and applied operational state of the system, total transmission efficiency is affected by different way: First: by the efficiency of the components of ariable gear and by changes. flows and efficiency analysis of out- and input coupled IT

6 P ar. P T P onst. +P ar. +P onst. +P -P ar. -P onst. -P P P 35 + P P 35 - P + P 3 3 [kw] 5 5 [kw] Fig. 6. ratios of the transmissions in function of output reolution a, O- structure b, I- structure 5, 5,,, atio of ariable gear [-] 5,, , - P P -, + P atio of ariable gear [-] 5,, , -, P - P + P -5, -5, reolution [/min] reolution [/min] GN GN a, O- structure b, I- structure Fig. 7. atio change of ariable gear in function of output reolution (n I N =9 /min) econd: by the tooth friction. Third: by bearing friction, the alues of which increase as the speed increases. The third is loss by bearing friction, the alues of which increase as the speed increases. The finding for O-: At start, power flows through the branch of ariable gear ratio, therefore total transmission efficiency highly depends on the efficiency of this branch. By decreasing the gear ratio the ehicle starts and power is continuously lead through to the branch of constant gear haing higher efficiency, and total efficiency is improed in the meantime. At higher speeds, efficiency will considerably decrease due to speed-dependent losses and the negatie power circulation in the range of.36 < i ar <. By changing the gear ratio (i ar > ), a large gear range (< n OU T < /min) can be coered without drastically changing total efficiency (.83 < η <.96). Therefore this transmission should only be used in this range in forward gear. 3 By further changing the gear ratio (i ar <.36), the direction of motion of the ehicle will be changed. Efficiency will be further decreased from the initial alue more and more drastically (< η <.83), due to increased speed and the positie power circulation generated. Therefore this transmission should be operated for short periods and at low speeds in reerse drie. 66 Per. Pol. Mech. Eng.

7 P η tooth * η ar P η tooth * η ar * η bearing H -P η tooth * η ar -P η tooth * η ar * η bearing +P η tooth * η ar +P η tooth * η ar * η bearing P η tooth +P η tooth -P η tooth,,,9,8,7 - P P + P, Efficiency [-],9,8,7,6,5 P - P + P, Efficiency [-] a, O- structure b, I- structure a, O- structure b, I- structure Figure 8. Efficiency changes of the transmissions in function of output reolution Fig. 8. Efficiency changes of the transmissions in function of output reolution η ar=,95 η ar=,9 η ar=,85 H η ar=,8 η ar=,75,, Efficiency [-],9,8,7 - P P + P, ,9,8,7,6,5 P - P + P, a, O- structure b, I- structure Fig. 9. The total efficiency changes at different constant efficiency alues in the ariable gear unit as a function of output reolution Efficiency [-] flows and efficiency analysis of out- and input coupled IT

8 The finding for I-: At start, total transmission efficiency is ery low by reason of power circulation. By decreasing the gear ratio (i ar <-,733), the ehicle starts and the alue of power circulation will be lower and lower, therefore total efficiency will increase (η <,94). The best efficiency is proided in the case of i ar =, as no power will flow along the branch of ariable gear ratio. By further reducing the gear ratio, total efficiency will will decrease due to the power split state and higher speed. 3 By increasing the gear ratio (>i ar >-,733), the ehicle will start backward, the alue of power circulation will be lower and lower, therefore total efficiency will improe. 4 Therefore this transmission can be operated at higher efficiency,86< η <,94 and,9< η <,94 only in the range of i ar <-,4 and i ar >,4 which coers a small speed range (37 /min < n OU T < 36 /min) and does not include the starting state. Therefore this transmission can only be coered by breaking down the entire speed range into seeral speed ranges as required, and by applying seeral different planetary gear ratios. Deeloped models can be used for analysing and testing any kind of single power split transmission structure. eferences tuart B, Audi takes T from 5th century to st century, AE International, 7. enius K Th, Trends in Tractor Design with Particular eference to Europen, Journal of Agricultural Engineering esearch 57 (994). 3 Höhn B, tufenlos erstellbare mechanische Getriebe, DI Berichte Mr. 68 (986). 4 Terplán, Apró, Antal, Döbröczöni, Fogaskerék- bolygóműek, Műszaki Könykiadó, Budapest, Müller H W, Wirkungsgradberechnung on Planetengetriben, Antiebstechnik 34 (995), no KF General catalogue. 7 sobán A, Kozma M, Inestigation of the Energy Losses Generated by the Oil hurning, the Bearing and the Tooth Friction in Planetary Gear Dries, 7th International olloquium Tribology, Technische Akademie Esslingen,. 8 Birkle H G, Das Betriebserhalten der stufenlos einstellbaren Koppelgetriebe, 968. Dissertation TH Darmstadt. 9 Farkas Zs, Analysis of single power split Infinitely ariable Transmissions, X. International onference in Mechanical Engineering, OGÉT, 7. Niemann G, Winter H, Maschinenelemente II., pringer, Berlin, Per. Pol. Mech. Eng.