Taşıtlara aktarma organlarındaki dönen kütlelerin toplam ataletinin ve toplam verimin deneysel olarak bulunması
Başlık çevirisi mevcut değil.
- Tez No: 55875
- Danışmanlar: PROF.DR. ALİ G. GÖKTAN
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 149
Özet
ÖZET TAŞITLARDA AKTARMA ORGANLARINDAKİ DÖNEN KÜTLELERİN TOPLAM ATALETİNİN VE TOPLAM VERİMİN DENEYSEL OLARAK BULUNMASI Bu çalışmada ilk olarak, taşıtlarda güç iletimine dair seyir dirençleri, taşıt moment gereksinimi ve motor moment arzı konulan kısaca tanıtılmıştır. İçten yanmalı motor karakteristiklerinin taşıt gereksinimlerinin karşılanması amacıyla dönüştürülmesi hususuna değinilmiş ve tipik bir dönüştürücü olan alın dişli çark mekanizmalı kademeli moment değiştiricinin verim ve çevrim oranı gibi temel özellikleri açıklanmıştır. Daha sonra, gerekli tüm teknik özellikleri bilinen bir taşıtın belirli bir seyrine dair temel güç iletimi hesapları yapılmıştır. Ayrıca çalışmanın bir parçası olması bakımından, yine bu seyre ait seyir hızı, seyir ivmesi, vites konumu verileri ile ilgili çeşitli istatistiki değer ve karakteristikler aranmıştır. Bir kayıt donanımı vasıtasıyla taşıt seyir hızı, motor devir sayısı, hava kelebeği açıklığı ve soğutucu akışkan sıcaklığı gibi büyükülükler kaydedilerek elde edilmiş bulunan bu bir adet seyir kaydı, bu incelemelerin hareket noktası olmaktadır. Son bölümde ise, aktarma organlarının temel özelliklerinden olan dönen kütlelere ait eşdeğer kütlesel atalet momenti Jeş ve verim riK'nın, bir önceki bölümde sözü geçen taşıttaki kayıt donanımı imkanları çerçevesinde iki adet deney yapılarak, çeşitli vites konumlarındaki değerlerinin tespitine çalışılmıştır. X, aktarma organlarındaki dönen kütlelerin taşıtın ivmelenrnesine etkisini gösteren bir faktördür ve taşıtın ivme direncinin hesabında kullanılır. Â'nın bulunması amacıyla, aktarma organları sistemi için ilk deneyin şartları da göz önünde bulundurularak bir matematik model kurulmuş ve tahrik tekerleklerinin hareket denklemi çıkarılmıştır. Bu denklem analitik olarak çözülmüş, deney sonuçları ve bazı kabuller yardımıyla, sözü geçen deney taşıtının her bir vites konumuna tekabül eden X değerleri elde edilmiştir. Aktarma organları toplam verimi T^'nın bulunması amacıyla ise, ikinci deneyin şartları altında sistemdeki kayıplar etraflıca incelenmiş, bazı kabuller yapılarak, sadece deneye ait motor devir sayısı verilerinin kullanımı ile verimin eldesi yoluna gidilmiştir. xıı
Özet (Çeviri)
SUMMARY THE EXPERIMENTAL DETERMINATION OF THE REDUCED MOMENT OF INERTIA OF THE ROTATING MASSES AND THE OVERALL EFFICIENCY OF THE DRIVE TRAIN OF A VEHICLE The engine converts the energy of the fuel into mechanical energy, which is carried through the drive train to support tractive forces at the wheel-to-ground contact area. The components of the power train are used to carry torque from the engine to the driving wheels of the vehicle. Different arrengements are used for rear-wheel-drive and front-wheel-drive vehicles. For example in front-wheel-drive cars, the engine torque is carried by the clutch, transmission (gearbox), final drive gears and differential (which are also in the tranmission housing) and front drive shafts to the front wheels of the vehicle. The friction disc clutch is a friction type of coupling and uncoupling device and it consists basically of a disc held against the fly-wheel face to transmit engine power. The gearbox contains gears and shafts which provide different gear ratios between the engine and driving wheels. This is necessary with all internal combustion engines, because they produce not enough torque for the low speeds of the vehicle. Only one low gear ratio is naturally unsuitable for higher road speeds. For this reason, a number of gear ratios (generally 5 for forward speeds) are provided in the tranmission of passenger cars. Both in front- and rear- wheel-drive vehicles, a gear reduction also occurs in the final drive gears which are part of the gearbox in front-wheel-drive vehicles. In a passenger car fitted with a four speed tranmission, a typical overall gear ratio of the first gear could be 12:1. The first gear allows the vehicle to move off slowly and accelerate quickly. In cars which are fitted with five speed transmissions, the fifth gear is an overdrive gear which provides an increase of speed within the transmission, although there is still a reduction in the final drive unit. This arrengement enables the engine to operate at lower speeds under light-load and cruising conditions. The fundamental drag force on road vehicles at low speed is tyre rolling resistance. It is directly proportional to the weight of the vehicle. The tyre rolling resistance is expressed as follows, FR = fRG xiiiwhere fR rolling resistance coefficient and G the weight of the vehicle. Gradient resistance too, is proportional to weight and is given by Fs, = Gp. The air resistance of a vehicle İs proportional to the square of its driving speed v, cross section area A (projected frontal area normal to the direction of travel), drag coefficient cw and air density p and can be calculated by (in the case of that cross winds do not exist) FL = CwA(p/2)v2. Physical origin of air resistance on vehicles is derived from three sources: Drag resistance which is a function of aerodynamic shape; skin friction of the body (for typical surface finishes accounts for about %10 of the air resistance); air flow through the vehicle for engine cooling and interior ventilation purposes. It is of great importance reducing skin drag component of air resistance by smooting the outer surfaces of the vehicle. Typical values of A is 1.3-2. 7m2 and 0.3-0.5 for cw. The importance of aerodynamic drag at higher speeds becomes obvious. The resistance of acceleration (the inertia force to overcome), on acceleration of a vehicle is given by FB =A-m-\. where X the factor of rotational masses, m the mass of the vehicle and x the acceleration in the diriction of travel. The factor of rotational masses X is, X = 1 + »Vrj, where Jt the reduced moment of inertia of the whole power train, r the static radius of driven wheels, R the dynamic radius of driven wheels (by slipping). For a front-wheel-drive car, X is X=l + f T J +i2S +i2i2J ^ + ? Vra'^a rö*Ra J where Jr.a the moment of inertia of the non-driven rear wheels, Jx.e the moment of inertia of the front driven wheels and drive shafts. JD is the moment of inertia of the gearbox output shaft. Jm is the reduced total moment of inertia of the rotational masses of the engine (crankshaft, camshaft(s), flywheel etc.) and the gearbox input shaft. xivThe fundamental equation of longitudional vehicle dynamics is, ^MT.j x 1 Z = Z-Ti= FR+FL+Fst+FB= fR+p + /l-- -G + --/7-v2-cw-A j=ı r, \ g) 2 Z is the tractive force at the wheels of the vehicle which is acting at the wheel-to-ground contact surface. The vehicle requires the torque MT at its wheels to overcome the sum of the tractive resistances. The torque of the engine (Mm), which is transmitted by the power train, is multiplied by the gear ratios which are selected by the driver. (iŞfi, iD) In the case of positive engine torque however, the total gearbox efficiency tjk (tik=t1ş,İt1d) causes a decrease of the torque which is available at the driven wheels. This can be expressed as follows, Mt^T^îTIdİ^İdMm where iş,i is the gear ratio and rjş.i is the efficiency of the selected gear. In the case of negative engine torque and the need to decelerate, the torque at the wheels can be calculated by, MT=- - viDMM+Mfren where Mfren the total moment at the wheels which originates in the brakes of the vehicle. Reducing mechanical component and equipment weight, in turn reducing translational and rotational inertial drag on acceleration, as well as rolling resistance and gradient resistance is great importance of reducing fuel consumption. The fitting of a lighter system in one place of the vehicle could result in a mechanical change in another. A small engine car may have smaller brakes and wheels, it is also a compact and small car which has a reduced air resistance. In the section three some statistical values and characteristics are searched and the needed tractive force is determined for a given driving cycle recorded by an equipment which is connected to the electronic control unit of the test vehicles engine. The equipment can get and record the data in digital mode with a sampling rate of 0.15 seconds. The types of recorded values were, -time in seconds, -vehicle speed v in km/h, -engine speed n in rpm, -intake air throttle valve (accelerator pedal) displacement in Volts, -engine cooling liquid temperature in °C. xvThe acceleration values for the whole cycle are derived from the recorded vehicle speed values. The position of the gear lever during the cycle for each of the data sets are determined from calculated v/n ratios. Only the four characteristics which are listed below are obtained for the given driving cycle: - the frequency distributions of vehicle speed and acceleration values, - some statistics about gear shifting, - the distribution of vehicle speed on vehicle acceleration, - the distribution of gear position values on vehicle speed. A statistical chart which relates the gear usage during the cycle is given below as an example of performed studies. I -5 t I §.s Gear Usage for the given Cycle in seconds This type of distributions and values and others help researchers to derive driving patterns and cycles for big city traffic conditions. A lot of recorded driving cycles must be analyzed for this purpose. The standardized driving cycles is used to measure the emissions of the vehicles and to forecast the emissions from road traffic. On the next step, the tractive resistances for each of the speed and acceleration values in the cycle are calculated. It is known that, the test track has no inclination. The tyre rolling resistance, air resistance and acceleration resistance are calculated and summed up to obtain the tractive effort force Z at the wheels which the vehicle needs to perform this cycle. At the end of this chapter, the calculation of the engine torque from the tractive force values is discussed. The last chapter relates to two experiments which are suggested to obtain the factor of rotational masses X and the overall efficiency of the drive train r\K respectively. XVIThe X-Experiment. The driven wheels of the front-wheel-drive test vehicle is lifted. The recording equipment mentioned above is used to get the test data. The ^-experiment consists of two parts. This two parts differs from each other by the moment of inertia of the drive train system. The front wheels are dismantled in the second part. In both parts, the driver shifts gears and holds the gas pedal on a permanent position. For each gear position the driver pushes the clutch pedal to uncouple the drive train from the engine and waits until the speed of the wheels becomes zero. The stopping time values are used to calculate the reduced moment of inertia of the drive train. This calculations are performed with the help of the following equation which is relied on a simplified mathematical model of the drive train : *d» ^ 65.İ ".* T* T J ld Jeş,i Ta» and Td are the stopping times which are observed in the second and first parts of the experiment respectively. Jeş,i is the reduced moment of inertia of the drive train for each gear position. JT. is the moment of inertia of the two dismantled wheels. A,. = i+ - - /m r-R / The X values are calculated by using the equation above. Note that Jr,a and Jm are values that were estimated. The results achieved are very similar to those which can be estimated due to the related values in the literature. The rfK-Experiment : Many people who are dealing with car manufacturing and development are seeking currently for possibilities of minimizing the fuel consumption and exhaust emissions. A big part of energy is dissipated in the drive trains. The gearbox efficiency is presumed to be constant in many of the calculations which are done to obtain the tractive effort at the driven wheels. However, this assumption can not be made in the case of calculations that require high accuracy. The types of the power losses in the drive train are, -gear teeth losses, -bearing losses -and lubrication losses, xviiwhich depend on the load, engine speed and gearbox oil temperature. In this experiment too, the driven wheels of the front-wheel-drive test vehicle is lifted. The recording equipment is also used to get the test data. The ^-experiment consists of two parts. The second part of the experiment helps to understand the air drag effect of the rotating wheels which is normally excluded in the types of losses in the drive train. During the experiment the driver holds the gas pedal on a permanent position to obtain stable engine speed. At this gas pedal position the driver shifts the gear and waits at each gear until the engine speed becomes stable. This procedure is repeated at three positions of the gas pedal. Average values of every stable engine speed regions are calculated and this values are devided by the reference engine speed of each gas pedal position. This ratios are the efficiencies of each gear with the assumption of that the engine torque is constant at every gas pedal position. The reference engine speed represents the average speed by uncoupled engine and neutral gear for each of the gas pedal positions. The results obtained were : - The higher the gearbox losses the lower the engine speed at a given contant gas pedal position. - The higher the gear lever position (the higher the speed-dependent losses) the lower the efficiencies of the drive train. - The higher the gas pedal position (the higher the engine speed and load) the higher the efficiencies of the drive train. The main adventage of these two experiments is the non-existance of the tractive resistances during the measurements. xvui
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