Tahrik tekerleklerinin kayma dinamiği ve önleme olanakları
Slipping dynamics of driving wheels and the controlling technioues
- Tez No: 21973
- Danışmanlar: DOÇ. DR. AHMET GÜNEY
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 86
Özet
ÖZET Üç bölüm olarak hazırlanan bu çalışmada.önce kuvvet bağlantısı ve kayma değişkenlerine bağlı olarak taşıt dinamiğinin matematiksel bir modeli kurulmuştur. Daha * sonra bu matematiksel modele dayanan ve çeşitli tahrik mekanizmalarının, değişik yol şartları için simüle eden bir bilgisayar programı yazılmıştır. ikinci bölümde bu bilgisayar programının algoritması hakkında açıklamalara yer verilmiştir. Üçüncü bölümde ise belirtilen bilgisayar programında elde edilen değişik tahrik mekanizmalarının sonuçlarını gösteren grafikler verilmiştir. Daha sonra bu grafiklerin yorumlanması ve hangi tür yol şartlarında hangi tür tahrik mekanizmalarının daha iyi olduğu sonucuna gidilmiştir. ı !
Özet (Çeviri)
SUMMARY SLIPPING DYNAMICS OF DRIVING WHEELS AND THE CÖNTROLKE-NG :: TECHNIO.UES~:ı: in our vorld where we have limited sources of oil, the most important goal of the automobile manufacturing finns is to design cars whose fuel consumptions are low. Keeping fuel consumption low depends on designing light-structures and obtaining useful forces from the ground at the maximum level.- To obtain maximum useful force interaction between the tyres and the ground, different driving methods are being used. in this study; theoretical analysis of different driving mechanisms will be made which are new to our local automobile manufacturers. in the first part of the study, a mathematical model of a vehicle's dynamics in relation to force interactions and slipping variables is set up. By using this mathematical model, a computer program is prepared simulating different driving mechanisms on different road conditions. in the second part, the algorhythm of the computer program is explained. Finally, in the third part, the graphics that are obtained from the computer program are given. Coments on these graphics are made and the results (which driving mechanism is better on which road condition) is explained. As mentioned above, in the first part of the study, a theoretical analysis about the tyres and the vehicle is made. Here, the resistances that are analyzed are: 1.Tyre resistance 2.Rolling resistance 3. Other resistances (toe-in and water resistances) 4. Total tyre resistances Total tyre resitance is taken as approximately equal to rolling resistance. Then, the dynamics of the vehicle VIIIis analyzed. The mathematical statement of acceleration, tyre, slope, aerodynamic resistances that are interacting with the vehicle are found. The magnitude of slipping, which has an important role in the interaction of tyres and the ground is analyzed. The momentum and force that are necessary for the vehicle are found by using the eguations that have been found in the study mentioned above. Finally, using ali the eguations, the ideal momentum distribution in two-axles-drive (4x4) mechanism is analyzed, which is the main subject of this study. in the second part, the behaviour of the vehicle with the below given conditions and different driving mechanisms is analyzed: Velocity of the vehicle (at time 0) (V) = 5 m/s Aerodynamic resistance coefficient CxA = 0.7 Total mass of the vehicle = 880 kg The height of center of gravity = 0.2 m Dynamic tyre radius = 0.3 m Static tyre radius = 0.3 m Rolling resistance coefficient = 0.015 Time period = 10 s Total momentum= 2000 NM The parameters for the vehicle can be chosen at the beginning of the computer program for different road types and conditions. With the computer program, the behaviour of the vehicle for 4 different conditions is analyzed. First, the behavior of a vehicle with slipping control, ör wihthout slipping control, having 4-wheel-drive, front-wheel drive ör rear-wheel-drive on dry concrete ground are analyzed. The results of this analysis show that the best driving mechanism on dry concrete ground is 4x4, the next is rear-wheel-drive and the last is front-wheel-drive. Another result of this analysis is that, with the use of slipping control mechanism, the performance is higher and also fuel consumption is lower; as lower momentum was used. At the same time, wear of tyres and rotating parts is lower. The simulation of the slipping-control mechanism in the computer program is as follows; the momentum transmitted to the tyres is kept under control so that the value of the tyre slipping will not exceed the critical slipping value. IX-Secondly, front-wheel-drive, rear-wheel-drive, 4x4 (1:1), 4x4 (33:66) and 4x4 (ideal distribution) mechanisms are analyzed on wet asphalt ground. The results show that the driving mechanisms, when ordered according to their advantages in the above given condition (on wet asphalt ground) are: 4x4(ideal), 4x4 (33:66), 4x4 (1:1), rear-wheel-drive and front-wheel- drive, respectively. The positive effects of slipping control mechanism are also seen here. The results of the graphics are also very close to the theoretically found ones. Next, the effect of tyre inertia on the vehicle's dynamics is analyzed. The inertia of tyres, being small, has a positive effect on performance. in the situation of the vehicle analyzed above, 4 tyres were ali on the same type of ground condition. The analysis of a vehicle whose left tyres are on dry concrete ground, and the right tyres are on icy concrete ground is also made. The vehicle has front- wheel-drive. On such a ground condition, locked and unlocked differentils are compared. The result is that the locked differential provides extra performance which increases the vehicle's velocity 2 times and acceleretion 5 times. For the vehicles frequently used away from hard top roads, installation of the limited -slip differential has very significant advantages; -Its locking action comes into effect automatically whenever needed -it prevents the wheel on öne side of the vehicle from spinning when traction is applied, and greatly reduced tire wear, -Despite its locking action, the limeted slip differential continues to provide smooth traction when cornering, -The locking action of the limited-slip diferential is restricted to a given value'to prevent overloading of output-side transmission compenent on öne side of the vehicle when the device is in operation. -The locking action can be varied to süit specific vehicles and working conditins, -The limited-slip differential is no larger than a conventional differential assembly, so that it can be later installed if reguired, x-Limited-slip dif ferantials need no special maintenance. The limited-slip differential consist of all the components making up a conventinal differential-cage, side gear, and differential bevel pininons, differential shaft - with an additional braking system. Mult i disc brakes are mounted at the left and right on the side gears, and react to relative movement between them and the differential cage by generating a braking force dependent on torque. This braking movement has the effect of partially locking the output side concerned, and increasing the torque on the side with good wheel grip. The braking movement in other words, acts as a substitute for the torque reaction at the road wheel on the side with poor grip. The differential effect when cornering results from a super imposition of the external difference in speeds and a load dependent locking action. The multi disc brake consist of outer discs located in the cage and inner discs connected to the side gears in such a way that they can not rotate separately. These inner discs have a patented molybdenum coating on the friction faces to ensure a constant friction coefficient and thus maintain braking moment constant throughout the working life of the differential. The spreading force is obtained by transmission of the torque at the diferential by two thrust rings to the differential shafts, which are loosely located by inclined faces. The limited-slip differential is particularly suitable for vehicles intented for off road use, away from hard top surfaces. Without any action being needed on the part of the driver, the multi discs brakes automatically compansate for varying degrees of wheel grip on the left and right sides of the vehicle. As a result, much greater tractive force can be applied during vehicle operation, and wheelspin when one wheel encounters a slippery surface avoided. The limited-slip differential is suitable for all construction machines, tractors, self propelled machines of other kinds. The preffered locking ratio is % 45, but 25 %or 75 %can be specified if required. A 45 % locking is capable of compensating for a 1 : 2.6 difference in friction between the left and right wheels at the multi brakes. Compared with a conventinal differential, this means an increase in friction of approximetely 80 %. XIOn many construction machines with all wheel drive, for example shovel loaders, the limited-slip differential is specified for both the front and rear axle. The limeted-slip differential is described permits vehicles to be drxven smoothly and rapidly during operation, and improve the effective tractive force level by reducing wheel slip. Compared with the differential lock which has to be engaged and released by the driver, the limited -slip differential offers the advantages that loads on the half shafts are subject to an upper limit according to the locking action specified by the designer of the vehicle, and in addition the normal differential action is retained for concerning. The vehicle can be steered during operation with the same ease and precision as before. XII
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