1、92 FTM 3Reduced Fuel Consumption and Emissionsdue to Better Integration of Engine andTransmissionby: B. R. HiShnTechnical University Munich,GermanyAmerican Gear Manufacturers AssociationTECHNICAL PAPERReduced Fuel Consumption and Emissions due to BetterIntegration of Engine and TransmissionBernd-Rob
2、ert Hiihn, Technical University Munich, GermanyThe statements and opinions contained herein are those of the author and should not be construed as an official action oropinion of the American Gear Manufacturers Association.ABSTRACT:The need to reduce fuel consumption and emissions from combustion de
3、mands better integration of engine andtransmission. Gears with wider ratio range have three advantages:1. A large overdrive ratio range can reduce engine speed. The speedlimit in nearly every country makes this kind ofoperation of great importance, since mid-size and big-size cars need low engine sp
4、eed but high torque to deliver therequired power. This improves thermal efficiency of diesel and gasoline engines.2. The enlargement of the value of first gear improves acceleration without enlarging the engine, or makes a smallerengine possible if increased acceleration is not important. In either
5、case it is necessary that the gear box efficiency begood over the entire range of ratios.3. The wide ratio range gear box is optimal for a new hybrid driveline for passenger cars. Thisdrivelineconsistsofasmall electric engine, a normal combustion engine and the wide ratio range gearbox. City driving
6、, where lower power issufficient, can use the electric engine because the gearbox will provide adequate torque at the wheels. For accelerationand driving on the road, the normal combustion engine will be activated.With the proposed driveline, operation with partial load and poor thermal efficiency c
7、an be avoided.Copyright 1992American Gear Manufacturers Association1500 King Street, Suite 201Alexandria, Virginia, 22314October, 1992ISBN: 1-55589-583-2Reduced Fuel Consumption and Emissionsdue to Better Integration of Engine and TransmissionBernd-Robert H6hn, Professor Dr.-Ing.Technical University
8、 Munich, GermanyINTRODUCTION Many scientists predict dramatic effectson the world climate. In reality, humani-The increase of the global COz -.emission ty has only one option over the next 30and the feared influence on the climate years. This is to reduce energy consump-such as the higher COz - conc
9、entration tion. To demonstrate that it is our taskinduced green-house-effect in the atmos- to start reduction, we should remind our-phere, gives the discussion of saving selves of the fact that in the more in-energy a new dimension. During the 70s dustrialized countries, like the U.S.,energy reducti
10、on, especially in individu- Western Europe and Japan, energy consump-al traffic, had the target of improving tion per man is 50 times higher than inthe private economics. The objective is other countries.now a more political economic target. With such circumstances, the task of re-Fig. 1 shows the b
11、ig difference between ducing fuel consumption in cars will be-forecast and recommendation for COz - come the central target of future caremissions in the next 30 years, development. The potential for reductiondue to better drivelines will be shown inthis paper. A big reduction in fuel con-I /_Z fore
12、cas| O world- sumption is possible if you view the35 _ energy-c0nference whole system, which consists of internal(WEK1989 combustion engine and transmission. Theincrease of the separate efficiencies of3o - engine and transmission are very small._ However, if you make an evaluation of thesmall econom
13、ic system, a marked contribution could be25 progress made. System-Engineering for automobileoc _ drivelines would certainly contribute to- _ the reduction of energy-consumption._ System engineering for drivelines can be20 _ divided in two parts:_ a. Wide ratio overdrive gear to reducerecommendation1
14、5 chm01ee0nterence1988 engine speed and increase torque ofthe internal combustion engineandI 1990 2000 2010 2020year b. lower ist gear of the transmissionto increase wheel torque with lessFig. i: CO_ - Emission World Wide(Global Energy Perspectives, WEK engine torque.Montreal)I2. Reduction of fuel-c
15、onsumption with 300_ -7overdrive gear. I i I I i mox.powercurve I IA lot of engine-vehicle combinations are 250rated for their fuel reduction potential1, 2, 3, 4, 5, 6, 8, 9. In this paperit will be shown that even dealing with 200the very best economical engine, system J I J/ _ I nl /r0odrgs_slgoce
16、_Jengineering can reduce fuel consumption.2.1 DefinitionsA modern transmission can be character- _ i00_ized with 3 gear-stages or gear ratios:I. starting gear: ist 50_-/_-_-jT_e_-_this is the value of the first gearby manual and automatic transmis-sion.1000 2000 3000 mm-I LO002. high speed gear: ih
17、enginespeed nengThis is the gear ratio value of the Fig. 2: Torque and Specific Fuel Con-4th or 5th gear. With this gear maxi- sumption of a Diesel Enginemum speed can be attained, with Direct Injection andTurbocharges (TDI)3. overdrive gear: imi“This is the smallest value of a gear The minimum of t
18、he specific fuel consump-ratio in a transmission and the big- tion is at an operating condition withgest influence on fuel savings, maximum torque but low speed. The roadresistance curve of the high-speed gear ihTo design a future transmission you need lies far away from the optimum area ofthree ran
19、ge-values: fuel consumption. Only by acceleration isthe engine able to run at its lowest1. The driving range _d specific fuel-consumption. How much over-_ ist drive range, _o, is necessary to obtain_d lh this optimum for constant speed?Fig. 3 shows in the left diagram the roadThis is normal range of
20、 produced trans- resistance curve of a large-sized-car formissions, different road inclination and in theright diagram the fuel consumption of theinternal combustion engine.2. The overdrive range _0:ihimi n 90 /_o _iI _iThis is a measurement of the potential of 75 220 -a transmission to interact wit
21、h the en-glne at high torque but less speed in the _ road,nchnolion=partial-load area.m 2%/_so - o_3. The gearrange%:_g- iSt - _d_olmln _ _/- “ . illf _ I25The gear range is the most importantcri- / /terion for the gear-designer. This valuedetermines the number of gears or thekind of Continously Var
22、iable Transmission /(CVT)0 50 100 150kmlh200 0 1000 2000 3000 mJn- 50002.2 Definition of the optimal overdrive vehlclespeedv enginespeednengrangeFig. 3: Road Resistance and Power Char-Fig. 2 shows the specific fuel consump- acteristics of a Diesel Enginetion b of a diesel-turbo-engine with di- with
23、Direct Injection (TDI)oe ,rect in3ectlon.2heexamplegiveevidencethahenecessary power for a vehicle speed of 140 20km/h leads to a certain minimum speed ofthe engine of about 1700 min “I. The quo-tient of the engine speed net min -I andthe vehicle speed mentioned in revolu- _o“tions of the wheels nw s
24、in1, leads tothe required gear ratio. 70 ._ _0_0,_ _In Fig. 4 this gear ratio is plotted o 6againstvehiclespeed. _ 5 _30_ IThis diagram, which is very useful to the _ 4 60gear designer, brings together informa- _ 3tion about vehicle and engine, thus de- I _I I_ Itermining the necessary overdrive ran
25、ge specif,cfuelconsumpt,on=?20_ _ I _ Ifor this example. The point, where the 2- i , i ._ ill._._yA ._ivertical line touches the maximum powercurve, represents the gear ratio ih = 2,8 1.5for maximum speed.10 15 20 30 _-050 607080 100 150 200kin/h300vehicle speed v20_ Fig. 5: i-v-Graph for a Large-Si
26、zed Car_ withDieselEngine(TDI)at 2 %_ _ _ RoadInclinationlo . i 8 .b_ _a km/h to 177 km/h. Even under this hill- -_ climbing-condition an overdrive gear imi“o 6 “ b = 1,8 is required. The overdrive range_ 45 _ _ _ has a value of _o = 1,55. For this over-drive range, two additional gears in a_ _|4(_0
27、“_ _1 transmission are required. Consequently a3- |,_. 5-speed manual gear box would need to bespecificfuelconsumphon-J_I/2q0_= increased to a 7 speed-transmission.2 Based on experience with one overdrive_ _ gear in a manual transmission, it seemst5 necessary to automate the overdriveI g_l range. A
28、vehicle equipped with this gearklI II_ be_200 h _ runs with more engine torque and lowerI . _ I _, I engine speed. The engine torque is a10 15 20 30 _0 50 607080 100 150200ks/h300 function of the accelerator pedal. Invehiclespeed v these overdrive gears the customer has topull it down more than usua
29、l to reduceFig. 4: i-v-Graph for a Large-Sized-Car the fuel consumption. However, it is dif-with Diesel Engine (TDI) at 0 % ficult for the customer to see the rela-Road Inclination tionship between the accelerator pedaland fuel consumption. But automating canIf this vehicle is only driven at a speed
30、 solve this problem.of 130 km/h for example with the gear ih,it is impossible to reach the minimumspecific fuel consumption. To achievethis point, an overdrive gear of imin =1,6 and an overdrive spread of _o = 1,75 Fig. 6 shows the theoretically possibleis necessary. With such an overdrive fuel savi
31、ngs for this example.spread one can decrease the specific fuelconsumption from be = 250 g/kWh to be =205 g/kWh. The i-v-graph in Fig. 4 can beused to determine the overdrive range fora given vehicle-engine combination.Fig. 5 shows the i-v-graph for the samevehicle but with a 2 % road inclination.325
32、 TW = TE “ _S ist “ _T (i)% with TE = torque of the engine20_g = efficiency of thegearbox_15E “ = startinggearist10 _T = W. / W, = accelerationefficlencyW T = energy for car accel-eration60 80 100 120 140 kmlh 180 W E = energy output at thecrankshaft of thevehicle speed v engineFig. 6: Theoretically
33、 Possible FuelSavings for a Large-Sized Car W T can be determined withwith Diesel Engine (TDI)1 .v2The potential is about 15 - 20 % between WT = _ mF (2)60 km/h and 180 km/h. The wide range ofspeed is remarkable if you compare it toother cars with other engines. Even if a mF = mass of the cartransmi
34、ssion with wider gear range, _g_ v = vehicle speedhas a lower efficiency, a reduction o_fuel-consumption of about i0 - 15 % canbe obtained. WE is the output energy at the crankshaftand can be determined withS. Reduction of fuel consumptionthrough other starting gear 2 1WE = _I mF v2 + _2 (8A “wE + _
35、 8R “_) (3)The acceleration of a vehicle is influ-enced by two phases:1 The starting of the vehicle with 8A = inertia of the drive-“ line, engine andslipping clutch or torque converter, transmission reducedto motor rpm (wE)2. The acceleration after slippage ofthe clutch (or torque converter) in 8R =
36、 inertia of wheels,the starting gear, ist. half-shafts and dif-ferential reduced toThe larger the starting gear ratio, ist, wheel rpm (_w)is, the shorter phase 1 is, with greaterslippage and poor efficiency. Especially 8F = _F “ r2 = effectivein manual transmissions, phase 2 is more inertia of the v
37、ehi-important to the average driver than clephase i, which is only a concern to driv-ers of sport- and racing cars. The aver- r = radius of wheelsage driver tries to finish the slippagephase very quickly and then acceleratethe car with his accelerator pedal. Re- The efficiency _T can be written as:d
38、uction of fuel consumption may becomereality, when we achieve the same accel- 8Feration with a smaller engine but a dif- _T = (4), ist “8 Aferent starting gear ratio, 1st. The smal- F + 8_ + .2ler engine with less torque can producethe same wheel-torque as before, with a Then Tw follows:higher start
39、ing gear. The question is howto obtain the optimum first gear, because eFthe bigger the value of the starting Tw = T E “_g “ist (5).2gear, the shorter the operation time. As eF + _R + ist “Amore energy is used to accelerate therotating inertia of the engine less isavailable for acceleration of the v
40、ehi- The maximum of Tw can be determined with:cle. The torque TW at the output of thedifferential to the two half-shafts is d Tw _ 0 (6)d ist4With this equation the optimum starting It can be seen, that the optimum of thegear, ist, can be solved after some deri- starting gear is between istopt = 21.
41、 andvations to: ist“_t = 26 for different comblnatlon ofengine and cars. The tendency is thatlow-powered cars need higher values ofi the starting gear than high powered cars. - eF + 0R (7) The increase of wheel torque is betweenist opt- 8A 13 % and 19 % in comparison to the exis-ting starting gears.
42、Equation (4) is not only valid for theEquation (5) is plotted in Fig. 7 for two starting gear, ist, but also for all gearsvalues of the transmission efficiency, of a stepped gearbox. With this equationyou can determine what part of the enginepower really accelerates the car and what300o part acceler
43、ates the inertia of the en-gine after shifting into a new gear. Only_m using a CVT can you have the entire en-/0plimum glne power for car acceleration, after/slart,nggear reaching the point of maximum power withI_ istop| the starting gear.2000 _/r -7 Fig“ 9 shows the efficiency _T as a func-/_ tion
44、of the gear ratio.s=monufocluredslorting gear 11 g =o.gS _ 13 .121oooo lO 20 30 _o _ “/.slarlinggearist Fig. 7: Torque at the Wheels as a Func- _ 0.5 I_-/- mQnufGc_uredtionof GearRatio _ engine kIt can be seen that the maximum wheel-torque, ist_t, from equation (7) is faruaway from the first gear of
45、 an existinggearbox. The wheel-torque can be improved 0for this car by about i0 % if you compare 2 4 6 8 10 20 30= it to the existing cars. The short action geQrrahoi ti I me of _uu,_ starting gear *L,_b U n_u-essary to automate the gear 7, i0. Fig. 9: Acceleration Efficiency as aFunction of Gear Ra
46、tioFig. 8 shows some other examples. The dotted part cannot be used for caracceleration. It is necessary for engine20 acceleration.You can see that even in_ the 2_ or 3 rd gear of an existing manual% transmission 13 % or 7 % of the powerwould be needed for engine acceleration.How can this optimum st
47、artinggear istopt_15 _ _ be used for a reductionof fuel consump-l I;:_-_ tion? This is possible if you use a smal-,. ler internalcombustionenginewith less_1_ torque and power. This engine operates in_I0 the partial load area near its optimumfor more time than a largerengine,thus_ _lgiie_;l_ reducing
48、fuelconsumption.- If you use a CVT with a widerrangethereare two effects, when you have the goal5 - of not reducing acceleration time of the_, car.c I / gasohneeng,ne- 2.21gasohneengme _-231 / First the optimum starting gear ist o t per-. pwffhlurbocharger mits reduction of the englne between I0 %Ib
49、 _0 _0 _ and 19 % without loosing accelerationgear reho Ils_geor time. Next you have no gear shifting whenyou use a CVT and therefore more powerFig. 8: Increase of Wheel Torque for for car acceleration. One disadvantage isHigher Gear Ratios that such a CVT with a wide range has aworse efficiency. For the given example,5a large size car and a turbo-diesel-en- 4. Conclusion and outlookgine with direct injection, the accelera-tion time from 0 - I00 km/h should not be
