ENERGY SAVING IN THE HYDRAULIC CIRCUIT OR AGRICULTURAL TRACTORS: OCUS ON THE POWER SUPPLY GROUP. Massmo Borgh, Barbara Zardn, rancesco Pntore, Engneerng Department Enzo errar, Unversty of Modena and Reggo Emla barbara.zardn@unmore.t Abstract: Ths work ams to analyze a complete hydraulc system of a medum sze agrcultural tractor, n order to perform an energy dsspaton analyss and to suggest possbly alternatve confguratons and solutons. The fuel consumpton and energy dsspaton n off road vehcles have n fact become a key feature, gven the great attenton devoted to the need of reducng pollutant emssons, n order to satsfy the future emsson lmts. In ths work the focus s on the flud power supply group and the standard archtecture of ths unt has been compared wth an alternatve soluton, called varable pump margn strategy and compared on the bass of the power consumpton to perform the same duty cycle, showng that a relevant percentage of energy may be saved wth smple modfcatons n the hydraulc power generator group. Keywords: Agrcultural Tractor, Smulaton, Power Savng, Duty Cycle 1. Introducton Ths paper s ntended to descrbe part of the work done as a research program whose fnal am s to test and verfy the effectveness of some hgh effcency hydraulc archtectures n agrculture tractors. Hydraulc crcut n md-sze tractors has dfferent key roles: feedng the auxlary utltes, the htch valve, the traler brake, the steerng, the drvelne and PTO clutches, the lubrcaton lne and the plot lnes to control the electro-hydraulc valves. Tradtonal confguraton of ths crcut nvolves the use of separate pumps to feed the auxlary utltes lne, the htch valve and the steerng on one sde and lubrcaton on another sde and fnally the clutches and plot lnes. The frst step of the research s the analyss and the evaluaton of the energy dsspaton of the auxlary utltes of a standard crcut, whch s a typcal load sensng mult-actuators system. The load sensng concept has been ntroduced n the second half of the last century and t s stll used n hydraulc applcatons because t has proved to be more effcent than the hydraulc power system whch entrusted power management to dsspatve components (as the tradtonal pressure relef valve). At the same tme, hydraulc load sensng systems are robust and relable (see for nstance [1], [], [3] and [4]). Nevertheless, the need to lmt pollutant emssons of agrcultural machnes has become more and more pressng n the last years. Many researchers and manufacturers have focused ther efforts on reducng the energy consumpton n the system wthout compromsng ts functonalty and ts performance. rom ths pont of vew, the combned use of smulaton tools and expermental testng represents the most promsng way to develop alternatve solutons characterzed by lower energy consumpton (see for example works from [5] to [11], whch proposes dfferent solutons spannng from ndependent meterng valves to dsplacement controlled actuators). In ths knd of system, possbltes to acheve more energy savng lay on the fact that hgh dsspatve dstrbutors are used to manage the flow to the actuators and to mantan control of multple loads eventually workng together and that the flud power group must work under a fxed pressure margn that s hgher than the maxmum workng pressure generally of about -3 MPa; ths margn of pressure has to be suffcent to overcome all the pressure losses at the maxmum flow rate that the flow come across from the pump to the actuators. Possblty to reduce power losses lay hence both on the power generaton sde and n the power utlsaton sde. In ths paper the focus s more on the power generaton group mprovement. It s noteworthy to underlne that hydraulc crcut n a tractor can serve a wde range of actuators, dependng on the equpment connected at the moment on the tractor, for example a seeder, or a loader or a harrow. The actuators can be both motors and cylnders and standardzed duty cycles for these knd of crcut do not exst at the moment. Ths requres more efforts n the analyss to be devoted at the expermental measurement of the man hydraulc varables durng a workng cycle of the tractor wth dfferent equpment. On the bass of prevous analyss ([1], [13]), here t was chosen to adopt a standard duty cycle created analysng the whole lfe and average use of a md-sze power tractor. The alternatve solutons evaluated and compared wth the standard archtecture are bult through the adopton of electroncally controlled varable dsplacement pumps. In the future, the logcal followng step of ths work wll be to select the best solutons from the smulaton results and to realze them on the vehcle, expermentally testng on vehcle the ablty of new solutons of mantanng the vehcle performances besde the ntroducton of energy savng. The Standard Load Sensng Hydraulc System and ts Modellng Gven the complexty of the hydraulc crcut of the agrcultural tractor, t s convenent to use a top-down approach that dvdes the entre crcut n dfferent operatonal sectons. The hydraulc crcut s composed by a flud power supply grou and a complex whole of hydraulc actuators (hgh and low pressure users) and control valves. The power supply unt represents the heart of the tractor. Ths s composed of two pumps (a charge pump of the gerotor type and an axal pston pump) that generate the operatng flow rate requred by the users. The power supply unt s a typcal load sensng opencrcut group that nvolves the use of local pressure and flow compensators. Advantages and crtcal aspects of these knd of systems have been thoughtfully analyzed n lterature, for example n [14] and [15].When speakng of the energy dsspaton of these systems, the crtcal aspect s that they work at the pump delvery wth an hgher pressure level than the one requred by the load. These pressure dfference (pump margn) s regulated n order to be able to guarantee the maxmum flow rate request at the actuators and t strctly depends on the losses that flow encounters n the passage from the pump delvery to the user. In the standard hydraulc pum ths pressure dfference s fxed, even f t could be reduced when the flow request s not at ts maxmum level, thus reducng dsspaton. A prorty valve s placed after the hydraulc power supply unt; ths valve has the task of ensurng the proper operaton of the three man users of the agrcultural tractor: steerng system, traler brake and agrcultural equpment whose actuators are controlled wth auxlary dstrbutors. 9
The prorty valve, consstng of two sectons that work n parallel, sets lmts of operatng pressure and n emergency condtons guarantee a level of flow and pressure to the users wth a specfc prorty. In connecton wth the prorty valve are the followng utltes: steerng, traler brake valve and auxlary dstrbutor, wth ther respectve lnes of load pressure sensng. Dependng on the load detected, the valves n the prorty block are used to adjust the flow rate and the pressure comng from the power supply unt, ensurng a prorty order n the functons of power steerng, traler brake and auxlary utltes. The traler brake valve has the task of managng the pressure sgnal generated by the brake pedals n the cab and the pressure to be provded for the parkng brake of the machne. The auxlary actuators may work together hence local pressure compensators are ntroduced on each secton of the auxlary dstrbutor to guarantee the correct flow sharng. These elements, because of the geometry complexty ntroduced on the dstrbutor secton and of the multple ol passages needed to perform the control and to guarantee the flow, are crtcal for the dsspaton ntroduced ([16]). To complete the hydraulc crcut of the agrcultural tractor, the man accessory components are the flter and the heat exchanger. The hydraulc crcut of the tractor n ts standard confguraton s represented n gure 1, by means of a functonal representaton n whch the blocks descrbed before are recognzable. These blocks contan the mathematcal models that defne the components behavour, developed n LMS Imagne.Lab AMESm and AMESet, followng a lumped parameters approach (gure 1). A detaled hydraulc model s nstead realzed for the auxlary dstrbutors, snce they have shown from prevous analyss ([1]) to be qute dsspatve elements. The hydraulc model nvolve also the flter and lubrcaton secton not shown n gure 1. ocussng on the flud power grou n the followng a detaled descrpton s gven of the man pum the varable dsplacement swashplate axal pstons pump. The hydraulc model realzed n LMS Imagne. Lab AMESm envronment s an evoluton of the model presented by the authors n [17], consstng manly of three man sectons: -rotatng group of axal pston pum ncludng the pstons movng wthn the cylnder block, the valve plate, the swashplate -actuator that perform the adjustment of the dsplacement of the machne -flow and pressure compensators: t mplements the modellng of the 3 way valves that contrbute n the determnaton of the control pressure wthn the actuator chamber. The model allows the determnaton of the pressure transents n the pston chambers, the nstantaneous forces exerted between the movable parts of the pum the torques at the swashplate and at the shaft and the nstantaneous flow. The basc module s represented by the pston chamber whch s a typcal control volume that communcates wth hgh and low pressure ports through varable orfces, opportunely controlled n order to replcate the openng and closng of the flow areas due to the cylnder blocks and valve plate nterposton. or each control volume contnuty equaton can be wrtten under the hypothess of an ncompressble flud and consderng sothermal flow: dp B dv Qk, 1... N dt V k dt dp B d V k dv d Qk d dt (1) In equaton (1), B s the Bulk Modulus of the flud, Q k represents the generc flow comng n or out the pston chamber.the pston chamber volume s defned as a functon of the angular poston of the machne shaft θ and of the swashplate β, as n equaton () where V 0 s the dead volume of the chamber, R the cylnder block radus, β the swashplate angle, D p pston dameter, θ the angular poston of the pston and ω the angular speed. gure 1: Standard Hydraulc Crcut of a medum szed tractor The lumped parameters model s dvded n three man sectons. The frst one (orange block n the gure 1 named LUID POWER SUPPLY UNIT), ncludes the detaled model of the axal pston pump of the tractor, together wth the flow and pressure compensators, and the model of the charge pump. The nstantaneous pressure at the axal pston pump delvery and sucton, the flow rate and the torque transents are typcal output varables of ths block. The second secton (red block), named Prorty & Traler Brake Valve, ncludes the detaled model of the prorty valve and a functonal model for the traler brake valve. These models ensure the correct pressure settngs and flows-sharng towards the users. The green blocks contan the hydraulc models of the man users of the agrcultural tractor. The steerng user and traler user are modelled by means of varable orfces, sutably controlled and calbrated. V V0 R 1 cos tan D p 4 dv R 1 cos D sn tan p 4 d cos The flow through the valve plate ports s determned usng the equaton of flow through an orfce havng geometrcal passage equal to A: p Q Cd A sgnp In equaton (3) C d represents the dscharge coeffcent, varable as a functon of the Reynolds number as descrbed n equaton (4), where D h hydraulc dameter of the orfce, υ knematc vscosty e the flud densty; R ec the value assumed by the Reynolds number where the transton between lamnar and turbulent flow happens; C s the value of the dscharge coeffcent n fully turbulent flow condton across the orfce. () (3) 30
D p C C h d tanh( Re ), Re Rec Partcular care has also been devoted to the descrpton of the leakages through the lubrcatng gaps whose geometry (heght) s constant and has been defned on the bass of expermental and numercal comparson of data regardng the average flow, swashplate torque and shaft torque for dfferent operatng condtons. Equaton (5) s used to calculate the leakages across the slpper bearngs-swashplate gap; R ext and R nt represents the external and nternal slpper rad, the flud absolute vscosty, p nt and p ext the pressure values at the external and nternal radus of the slpper. 3 h pnt pext q 6 Rext ln Rnt A smlar expresson s used for the leakage across the pston ball jont-slpper ga consderng axally-smmetrc geometry and agan constant gap heght. Equaton (6) descrbe the leakage across the cylnder blockvalve plate ga where leakage may flow both to dran and to the adjacent pstons chambers. Equvalent geometrc dmensons have been defned to descrbe the ga the length l and the wdth b cy, and agan a constant hegth h cy (dstance between the cylnder block and the valve plate) has been consdered. 3 cy bcy h q 1 l p p D nally, equaton (7) expresses the flow across the gap between the pstons and the cylnder block, consderng a zero eccentrcty pston poston. In equaton (7) h p s as usual the gap hegth, l e the s length of the gap and P the pston speed: 3 p Dp h q 1 le D p p pd hp s P The pston-slpper assembly force, due to the chamber pressure, nerta, vscous frcton, determnes one of the contrbuton of the torques actng on the swashplate; the swashplate, modelled as a rotary nerta, receves also the contrbuton of the sprng and of the control actuator. The varaton of the swashplate poston s nstantaneously conveyed to the pston elements and all the cnematc varables are updated as a consequence. The man geometrcal parameters descrbng the valve plate, the cylnder block, the pstons are defned through a pre-processor module. Equatons (8) shows the dsplacement s p, speed and acceleraton of the pston: they are functon of the shaft angular poston and of the swashplate angular poston, calculated for a certan constant angular speed ω. s s s R R R R 1 cos tan R 1 cos sn tan cos cos tan sn R 1 cos R 1 cos cos tan Pston-slpper assembly undergoes the acton exerted from the pressure wthn the chamber, from the nerta contrbuton m,, from the vscous frcton that arses n the pston-cylnder block gap v,i, from the swashplate reacton R z,. (4) (5) (6) (7) (8) m, v, R p Dp 4 m s, z, D ple s h p m, v, 0 Equaton (10) descrbes the swashplate dynamc moton: I the moment of nerta, T c s the torque due to the actuator acton and sprng, T sw s the torque of the pston slpper assembles on the swashplate, as shown n equaton (11), T ν the vscous frcton torque, as expressed n equaton (1) where c s the vscous frcton coeffcent. I T T T T l sw, T sw slsw, N 1 R c T sw, cos c sw cos R z, 1 N cos slsw, l sw (10) (9) (11) (1) gure rame of reference and schematc vew of an axal pston swashplate pump. nally, detaled modellng of the flow and pressure compensators and of the control and bas actuators are added to the model of pump n order to be able to descrbe the dynamc varaton of the machne dsplacement durng pump operaton. 3 Alternatve Archtectures Varable Pump Margn (VPM) The load-sensng varable dsplacement pump s a very known and studed component, but n recent years t s undergong substantal changes for the ntroducton of advanced electronc for the control of the hydraulc power generaton. The electronc control allows an nfnte range of adjustments and controls, but a good ntegraton wth flud power components has to be studed and developed n order to guarantee the performances and robustness of the system. In a typcal LS power supply unt, the pump operates at a fxed pressure level hgher than the pressure actually requred by the user. Ths addtonal pressure, also called Pump Margn, s always fxed by the sprng preload of the flow compensator, gvng rse to energy losses, dependng on the duty cycle or the operaton carred out. 31
Here, the nomnal value of.5 MPa assgned to Pump Margn s the mnmum possble value of system pressure n the standard confguraton n order to overcome the losses caused by valves and the actuators connected to t when the flow rate s at ts maxmum value. gure 3: Contrbuton to buld up the pump margn The estmaton of the Pump Margn, as shown n the gure 3, s due to two fundamental components of the hydraulc crcut: the prorty valve and the local pressure compensator of the auxlary dstrbutors. The resultng energy losses are due to an hgh pressure drop across the two valves prorty & auxlary dstrbutors. The VPM strategy s based on the reducton of the pressure dfference between the delvery pressure of the pump and the actual pressure of the generc actuator, by adjustng the sprng preload of the flow compensator that equps the axal pston pum usng a solenod valve and an opportune strategy on the ECU (Electronc Control Unt) to control t. gure 4 Varable Pump Margn Concept Let's consder a request of flow rate Q L correspondng to a pressure p L, f the regulaton of the sprng preload of the pump flow compensator s equal to p M pressure, the man pump s workng at pressure p S gven by the sum of p L and p M. The power dsspated n standard workng condtons, s represented by the area ABCD between the levels of pressure p S and p L. Under pressure saturaton condton and consderng the maxmum pressure p max allowed n the system, the power loss s represented by the area EGH, between pressure levels p max and p max -p M. or the mplementaton of the VPM control strategy, t was decded to use a commercal valve, called Ex (Ex s a commercal valve that replace the flow compensator for the axal pston pump. or related and detaled note refer to http://www.boschrexroth.com), whch replaces the hydraulc compensator wth an electro-hydraulcally flow compensator controlled by a specfc control unt. The pressure margn can vary between.5 MPa to 1.5 MPa due to the acton of ths valve. The VPM control strategy provdes two types of control that can be mplemented on the ECU: fxed pont strategy and dynamc varaton strategy. The fxed pont strategy s based on the settng of a sngle value of reduced pump margn for the pump to be regulated when possble and wthout any possblty of dynamc adjustment. Ths strategy s possble only n the case of standby condton of the machne: n fact, n a generc operatng condton the lowerng of the pressure mposed by the VPM fxed pont strategy to the mnmum level, wll not be able to meet the flow requests comng from the auxlary and other users connected. A second control strategy for the VPM s ntroduced: through the use of pressure sensors (dslocated on the dscharge lne of the pump and on the man workng lnes)and readng va CAN net the control sgnals at the auxlary drectonal valves, t s possble to create an operatng map for the control unt (ECU). or a frst analyss, a lnear dependence has been used between the total requred capacty (easly obtanable through the Electro Hydraulc sgnals of the auxlary dstrbutors avalable va CAN network) and the current that has to be provded to the solenod for the dynamc varaton of the Pump Margn. The VPM dynamc strategy, allows to obtan a contnuous varaton of the Pump Margn as a functon of the requred flow and pressure from by the users. The dynamc varaton of the pressure, allows to ncrease the energy savng of the system n all the duty cycle stages, mmedately adaptng the Pump Margn to the new condtons of load. Despte ths soluton seems qute promsng, the mnmum level of Pump Margn assgnable n dynamc condtons, s lmted by the presence of the prorty valve. Hence a combned optmzaton process wll have to be developed to obtan the maxmum energy savng contrbuton from ths soluton. Electronc Dsplacement Control - EDC A further alternatve soluton related to flud power supply grou s based on the use of bgger pumps coupled wth the nternal combuston engne, n order to beng able to delver the same flow at lower speed, thus optmzng the pump-engne couplng and havng the chance of a more flexble management of the power and torque characterstcs of the engne. To do ths, an electro-hydraulc valve s ntroduced, able to set a lmt of the maxmum swash plate angle of the axal pston pump. The valve s screwed drectly nto the seat of the actuator control of the swashplate and through the regulaton current allows to vary the maxmum value of the stroke of the swash plate, thereby adjustng the maxmum flow suppled by the man pump. gure 5 Electronc Dsplacement Control Concept Usng ths concept, the EDC soluton allows to obtan the same flow, delvered by the power supply unt, at dfferent speeds of rotaton of the combuston engne connected to the power supply. 3
Settng the level of flow n the standard condtons, a rotatonal speed n 1 of the pump s obtaned. ollowng the lnear characterstcs of the machnes, the requred flow Q REQ can be acheved at a lower engne speed, equal to n, usng the machne wth hgher dsplacement and the EDC valve. Ths may for example allow to swtch from the maxmum power to the maxmum torque operatng condton. 4 Duty Thanks to the collaboraton between the Unversty of Modena and Reggo Emla and the manufacturer CNH Industral S.p.a, collecton of data from the feld has led to the defnton of a duty cycle that descrbes the usage of the tractor durng ts average lfe, dentfyng four man phases of work: transport, standby, work n low speed & work at hgh speed. Wth reference to the tractor lfe, the duty cycle defnes four man phases of work that occupy the whole lfetme of the tractor as descrbed n the followng: 5% transport, 0% standby, 5% work wth low engne speed and 30% work wth hgh engne speed. The followng subsectons wll descrbe the detals of how each work phase has been defned and then smulated wth the model. Transport In ths phase the portons of the hydraulc crcut that are workng, besde the flud power grou are the steerng system and eventually the traler system; the value of pressure and flow rate taken as reference n each workng phase are non-dmensoned wth respect to the maxmum pressure and flow of the hydraulc system: - steerng phase: the drver acts contnuously on the steerng to make correctons of the vehcle trajectory whle drvng. or ths reason, the steerng s qute stressed and t s consdered that ts usage covers the whole transport phase (100%). The operatng condtons n terms of flow rate and pressure level at the steerng are: flow rate 14 %Q max ; pressure 4 %p max. - traler system: durng transport, a traler may be attached to the agrcultural tractor. rom expermental data however the usage of the traler s qute lmted and covers only 1.5% of the transport phase under operatng condtons equal to: flow rate 1 %Q max ; pressure level 87 % p max. The tractor speed durng transport s consdered varyng between 1 and 40 km/h. Standby In ths work phase actually the system s not workng wth the hydraulc actuators, the axal pston pump s at ts mnmum dsplacement, delverng only the flow needed to compensate leakages and to allow regulaton of the flow and pressure compensators. The operatng condtons n terms of flow rate and pressure level are: flow rate 4%Q max, Pressure 1% p max. The engne speed s at ts mnmum value. Work at hgh engne speed The work phase at hgh engne speed nvolves the smultaneous use of the hydraulc actuators controlled by the auxlary dstrbutors and the steerng system: -steerng: n ths case the tractor s workng on feld, hence the contact between the tres and the ground s sgnfcantly dfferent from the transport phase. As a consequence, the duty cycle nvolves hgher pressure level and flow rate as operatng condtons: flow rate 14%Q max ; pressure 38% p max. The usage of the steerng system occupes the 50% of the phase of work at hgh engne speed. - auxlary users: the auxlary dstrbutors are ones of the most dsspatve components of the system and are used for approxmately the 7.5% of the phase of work at hgh engne speed, also consderng the smultaneous workng of more than one actuator. The operatng condtons are: flow rate 100%Q max ; pressure 48% p max. The tractor speed durng ths phase s varyng between 5 and 14 km/h. Work at low engne speed Also n ths phase, a smultaneous usage of auxlary dstrbutors and steerng s consdered but the operatng condtons are changed. -steerng: the use of the steerng system covers the 0% of the phase under the followng operatng condtons: flow rate 14%Q max ; pressure 48% p max. -auxlary users: the auxlary dstrbutors work occupes the 7.5% of ths phase, the operatng condtons are equal to the prevous ones: flow rate 14%Q max ; pressure 48% p max. The tractor speed durng ths phase s varyng between 0.05 and 5 km/h. The gure 6 shows the duty cycle subdvson just descrbed. gure 6 Duty Cycle specfcaton 5 Results The alternatve confguratons ntroduced n the prevous sectons have been modelled n LMS Imagne.Lab AMESm envronment and compared wth the standard confguraton. The comparson has been done usng the duty cycle prevously descrbed, chosen accurately and representatve of the average lfe cycle of an agrcultural tractor. Results are presented makng reference to the power consumpton at the flud power generator group shaft n percentage, vewed as the power consumpton of the alternatve archtecture wth respect to the power consumpton of the standard archtecture (100%); the power savng s the dfference between the percentage power consumpton of the standard verson and the percentage power consumpton of the alternatve archtectures. Varable Pump Margn - VPM The power savng acheved by the VPM fxed pont strategy n the standby phase s very low and does not justfy the nstallaton on the vehcle. As can be seen from the gure 7 the power savng achevable by ths confguraton s about 0.13%, whch s rrelevant for the chosen duty cycle. Ths s due to the fact that n the standby phase the flow dscharged by the pump s low and the ncdence of lowerng the pump margn s very lttle. 33
gure 7 Power consumpton: VPM fxed pont strategy In order to ncrease the amount of power saved, the best soluton reles on usng the control strategy wth dynamc varable pump margn. To show ths, a duty cycle where only the auxlary dstrbutors are workng has been supposed. The auxlary dstrbutors have been proportonally opened n order to gradually rse the flow request tll the maxmum value. the gure 8 shows the correspondent percentage of power savng as functon of the flow rate. gure 9 Power consumpton durng tractor lfetme: VPM Soluton The EDC strategy allows to ntroduce n the system an addtonal degree of freedom n order to provde the effcency of the nternal combuston engne-pump couplng. The user may decde to lmt the dsplacement of the man pump n order to get the same flow rate of workng flud at dfferent engne speeds. Generally, the ntroducton of a larger pump whch rotates at a lower engne speed, to keep fxed the flow, nvolves a reducton n the effcency of the same pump. The lowerng of effcency of the man pump can be consdered relatvely low compared to the possble benefts comng from an optmzed management of the engne speed. However, wth ths partcular duty cycle the power savng was about 1-%. gure 8 VPM Dynamc Soluton Usng the lnear mappng performed n the control unt (ECU), the maxmum avalable power savng s acheved at ntermedate flow rate request. or hgh flow rates all the avalable pump margn pressure s needed and therefore there s no possblty of obtanng a beneft wth respect to the standard confguraton. Wth reference to the duty cycle defned prevously, gure 9 shows there s no apprecable dfference between the control strategy wth VPM fxed pont (VPM standby) and the standard verson, whle obtanng a power savng of 19% n the case of usng a dynamc VPM adjustment. Durng the transport phase, the pressure and flow rate requests are ntermedate, so t s possble to acheve the maxmum power savng, as shown n gure 9. In all other work phases, pressure and flow rate levels are such as to mnmze the power saved adoptng of the VPM strategy. 6 Conclusons And uture Work The motvaton of ths work derves from the need to reduce energy consumpton n hydraulc crcut of agrcultural tractors. To do ths an ntense research work to evaluate the actual stuaton has been carred out and from the results obtaned suggestons for the mprovement of the hydraulc energy producton and usage n the vehcle are expected. In the target vehcle analyzed the hydraulc crcut has a typcal hydraulc load sensng mult-users archtecture where hydraulc power s provded by a group of fxed and varable dsplacement pumps and n ths paper the attenton has been focused on the varable dsplacement pump. A detaled lumped parameter model has been developed for the whole hydraulc crcut of the tractor, focusng n ths paper n partcular on the analyss of the pumps together wth the flow compensator. The study of the standard hydraulc layout hghlghted that many crtcal ssues are represented by the excessve pressure drop across the valves and an mproper management of the pressure levels between the man pump and the prnal loads. Some alternatve solutons are hence suggested. The standard archtecture of the flud power supply group n the tractor has been compared n terms of power consumpton wth some smple alternatves whch nvolve the mplementaton of an electronc control of the varable dsplacement pump. In relaton to the flud power supply unt, the alternatve soluton proposed s based on the analyss of the pump margn pressure of the axal pston pump. The ntellgent management of ths addtonal pressure between pump and load, leads to an energetc mprovement of the entre system: adoptng a dynamc varaton of the pump margn as functon of the requested flow rate by means of an electronc flow compensator, t s possble to acheve the maxmum energy savng. Wth the am of defnng a term of comparson of the standard and alternatve archtectures, an actual duty cycle has been defned consderng the entre lfe of the vehcle. rom the comparson, dependng on the type of the flow rate request and followng a lnear characterstc wthn the ECU, t s possble to reach the maxmum energy savng for the ntermedate pressure and flow rate levels by usng the Dynamc VPM strategy (19%). 34
In case of use of the Dynamc VPM strategy a crtcal aspect s the dffculty n some operatng condtons to ensure the correct flow rate levels: to solve ths problem a new archtecture, nvolvng a flexble prorty valve, able to mantan the correct pressure levels and flow rate levels request by the users, s under nvestgaton. These alternatve soluton of the flud power supply unt wll be expermentally tested on a prototype vehcle thanks to the manufacturer CNH Industral SpA. Bblography 1. Wu, D., Schoenau, G., Burton, R., Btner, D., 005, Model and Expermental Valdaton of a Load Sensng System wth a Crtcally Lapped regulator Spool, Internatonal Journal of flud Power, Volume 6, Number 3, November 005. ISSN 1439-9776.. Shenouda, A., Brook, W., 005, Energy Savng Analyss usng a four ndependent meterng confguraton controllng a hydraulc cylnder, SAE Paper 005-01-363, SAE Commercal Vehcle Congress and Exhbton, ISBN 0-7680-1678-9, 005. 3. Shenouda, A., 006, Quas-Statc Hydraulc Control Systems and Energy Savngs Potental Usng Independent Meterng our-valve Assembly, Ph.D. Thess, Woodruff School of Mechancal Engneerng, Georga Insttute of Technology, August 006. Of An Agrcultural Tractor, Proceedngs of the Bath/ASME Symposum on lud Power & Moton Control (PMC 010), 15th- 17th September 010, Bath, UK. 13. Borgh, M., Zardn, B., Mancarella,., Speccha, E., 010, Energy Consumpton of the Hydraulc Crcut of a Md-Sze Power Tractor, Proceedngs of 7th Internatonal lud Power Conference, Aachen 010. ISBN 978-3-950565-90-7. 14 Bonanno A.; Paoluzz R., Gess S.011. Global Smulaton Envronment for the Global Effcency Improvement n Agrcultural Tractors, Proceedngs of The Twelfth Scandnavan Internatonal Conference on lud Power, SICP11, May 18-0, 011, Tampere, nland, 167--179. Vol. 4. :, 011. 15 Wu D. 003. Modellng and expermental evaluaton of a load sensng and pressure compensated hydraulc system, Ph.D. Thess, Department of Mechancal Engneerng, Unversty of Saskatchewan. 16. Borgh, M., Zardn, B.,Pntore,., Belluzz,.,014, Energy Savngs n the Hydraulc Crcut of Agrcultural Tractors, Energy Proceda, Volume 45, pp. 35-361, ISSN1876-610. 17 Pntore,., Zardn, B., Borgh, M., 01, lud Power Supply Unt or Agrcultural Tractors: Towards Energy Savng Through Smulaton. Accepted for 7th Ph.D. Symposum on lud Power, Reggo Emla, 7-30 June 01. 4. Erksson, B., Larsson, J., Palmberg, J.-O., 006, Study on ndvdual pressure Control n energy effcent Cylnder drves, Proc. of the 4th Ph.D. Symposum, Sarasota, lorda. 5. Lnjama, M., Huova, M., Vlenus, M., 007, On Stablty and Dynamc Characterstcs of Hydraulc Drves wth Dstrbuted Valves, /ASME Symposum on lud Power and Moton Control. 6. Huova, M., Karvonen, Ahola, V., Lnjama, M., Vlenus, M., 010, Energy Effcent Control of Multactuator Dgtal Hydraulc Moble Machne, Proceedngs of 7th Internatonal lud Power Conference, Aachen 010. ISBN 978-3-950565-90-7. 7. Maran, P., Ansalon, G., Paoluzz, R., 008, Load Sensng wth Actve Regeneraton System, Proceedngs of the 7th JPS Internatonal Symposum on lud Power, TOYAMA 008. 8. Rahmfeld, R., Ivantysynova, M., Weber, J., 004, Dsplacement Controlled Wheel Loader - A Smple and Clever Soluton, 4th Internatonal lud Power Conference - Dresden, 004. 9. Wllamson, C., Zmmerman, J. and Ivantysynova, M., 008. Effcency Study of an Excavator Hydraulc System Based on Dsplacement- Controlled Actuators, Bath/ASME Symposum on lud Power and Moton Control. 10. Heybroek, K., Larsson, J., Palmberg, J.-O., 006, Open Crcut Soluton or Pump Controlled Actuators, Proc. of the 4th Ph.D. Symposum, Sarasota, lorda. 11. Erksson, B., Palmberg, J.-O., 010, How to Handle Auxlary unctons n Energy Effcent Sngle Pum low Sharng Moble Systems, Proceedngs of 7th Internatonal lud Power Conference, Aachen 010. ISBN 978-3-950565-90-7. 1 Borgh, M., Zardn, B., Mancarella,., 010, Energy Dsspaton Of The Hydraulc Crcut Of Remote Auxlary Utltes 35