DİFERANSİYEL 4X4, 4WD ve AWD

Transkript

1 MARMARA ÜNİVERSİTESİ TEKNOLOJİ FAKÜLTESİ DİFERANSİYEL 4X4, 4WD ve AWD Yrd. Doç. Dr. Abdullah DEMİR HAZIRLAYAN: Yrd. Doç. Dr. Abdullah DEMİR

2 The advantages and disadvantages of the different arrangements of power unit and transmission systems may be considered under the following general headings: Interior space Ease of handling Maintaining traction Balanced braking Other considerations

3 ADVANTAGES and disadvantages of front-wheel drive engine length limited by available space; there is load on the steered and driven wheels; good road-holding, especially on wet roads and in wintry conditions the car is pulled and not pushed; good drive-off and sufficient climbing capacity with only few people in the vehicle; tendency to understeer in cornering; insensitive to side wind; although the front axle is loaded due to the weight of the drive unit, the steering is not necessarily heavier (in comparison with standard cars) during driving; axle adjustment values are required only to a limited degree for steering alignment; simple rear axle design e.g. compound crank or rigid axles possible; long wheelbase making high ride comfort possible; short power flow because the engine, gearbox and differential form a compact unit; good engine cooling (radiator in front), and an electric fan can be fitted; effective heating due to short paths; smooth car floor pan; exhaust system with long path (important on cars with catalytic converters); a large boot with a favourable crumple zone for rear end crash. Automotive Engineering, 2009

4 The disadvantages are: under full load, poorer drive-off capacity on wet and icy roads and on inclines; with powerful engines, increasing influence on Steering; engine length limited by available space; with high front axle load, high steering ratio or powersteering is necessary; with high located, dash-panel mounted rack and pinion steering, centre take off tie rods become necessary or significantkinematic toe-in change practically inevitable; geometrical difficult project definition of a favourable interference force lever arm and a favourable steering roll radius (scrub radius); engine gearbox unit renders more difficult the arrangement of the steering package; the power plant mounting has to absorb the enginemoment times the total gear ratio; it is difficult to design the power plant mounting booming noises, resonant frequencies in conjunction with the suspension, tip in and let off torque effects etc., need to be suppressed; with soft mountings, wavy road surfaces excite the power plant to natural frequency oscillation (socalled front end shake ; there is bending stress on the exhaust system from the power plant movements during drive-off and braking (with the engine); there is a complex front axle, so inner drive shafts need a sliding CV joint; the turning and track circle is restricted due to the limited bending angle (up to 50) of the drive joints; high sensitivity in the case of tyre imbalance and nonuniformity on the front wheels; higher tyre wear in front, because the highly loaded front wheels are both steered and driven; poor braking force distribution (about 75% to the front and 25% to the rear); complex gear shift mechanism which can also be influenced by power plant movements. Automotive Engineering, 2009

5 Arkadan İtişli Araçlar: Arkadan itişli araçlarda; motor gücü, yönlendirme tertibatı olmayan arka dingilde bulunan tekerleklere aktarılır. Ayrıca araç arkadan itildiği için kararlı gidişi, önden çekiş ve dört çeker sistemlere göre daha düşüktür. Reading Text: FWD vs RWD 1- Load on tires: The biggest benefit to rear wheel drive is that it spreads the loads of the car across all four tires of a car, the rear wheel do the pushing while the front wheels are for the steering duties. In front wheel drive cars the front tires must perform both functions, the engine acceleration\deceleration forces act on the front wheels that s beside the steering duties. 2- Better weight balance: Rear wheel drive cars have the engine in the front and the drive components in the rear, but the front drive cars have every thing up front. So by balancing the front and rear of the car you can improve the handling, acceleration, braking and thus safety of the car. 3-Torque Steer: Front wheel Drive cars have a problem known as Torque Steer. This occurs when the acceleration of the engine effects the cars steering. Since the driveline is connected to the steering wheels the torque of the engine applies force to the front wheels causing the car to pull to the right during acceleration. Rear Drive cars do not have this problem since the engine is not connected to the steering gear.

6 Dört Tekerlekten Çekiş: Dört tekerlekten tahrikli sistemler; kısmi (Four Wheel Drive FWD, 4WD) ve daimi dört tekerlekten tahrikli sistemler (All Wheel Drive AWD) olarak ikiye ayrılır. Bu sistemlerde motordan gelen giriş torku vites kutusu vasıtasıyla merkezi diferansiyele iletilir. Dört tekerlekten çekişin faydasını anlamak kolaydır. Herhangi bir 4WD sisteminin temel parçaları; iki diferansiyel (ön ve arka) ve bir transfer kutusudur. Sürekli Dört Çeker (AWD): İki tekerlekten çekişli (2WD) araçlara göre, özellikle viraj alırken çeşitli avantajlara sahiptir. İki tekerlekten çekişli araçlarda dengesizlik görülmesi olasılığına karşın, gücün tüm tekerleklere iletildiği sürekli dört tekerlekten çekişli araçlarda, dönüşlerde önden kayma veya arkadan kayma daha az oluşur.

7 Four-Wheel Drive

8 All-Wheel Drive

9 KİA, 4WD 4WD Sistemi

10 Ağırlık Aktarımı ve Farklı 4WD Düzenekleri KİA, 4WD Aktarma sisteminin düzeni, ağırlık aktarımı bakımından otomobillerin davranışlarını etkiler.

11 Subaru - S y m m e t r i c a l AWD

12 Automotive Engineering, 2009 Four-Wheel Drive In four-wheel drives, either all the wheels of a passenger car or commercial vehicle are continuously in other words permanently driven, or one of the two axles is always linked to the engine and the other can be selected manually or automatically. This is made possible by what is known as the centre differential lock. If a middle differential is used to distribute the driving torque between the front and rear axles, the torque distribution can be established on the basis of the axle load ratios, the design philosophy of the vehicle and the desired handling characteristics. That is why Audi choose a 50%:50% distribution for the V8 Quattro and Mercedes-Benz choose a 50%:50% distribution for M class off-road vehicles, whereas Mercedes-Benz transmits only 35% of the torque to the front axle and as much as 65% to the rear axle in vehicles belonging to the E class. This section deals with the most current four-wheel drive designs. In spite of the advantages of four-wheel drive, suitable tyres as shown in Fig. 1 should be fitted in winter.

13 Fig. 1: With a loaded Vauxhall Cavalier on compacted snow (µx,w=0.2) driving forces are measured on the flat as a function of the slip (Fig. 2). The illustration shows the advantage of four-wheel drive, and the necessity, even with this type of drive, of fitting correct tyres. Regardless of the type of drive, winter tyres also give shorter braking (stopping) distances on these road surface conditions. Automotive Engineering, 2009

14 Fig. 2: Coefficient of friction µx,w of a summer tyre with 80 90% deep profile, measured at around 60 km/h and shown in relation to the slip on road surfaces in different conditions (see also Fig. 1). Wide tyres in the 65 series and below have the greatest friction at around 10% slip, which is important for the ABS function. Automotive Engineering, 2009

15 Advantages and Disadvantages In summary, the advantages of passenger cars with permanent four-wheel drive over those with only one driven axle are: better traction on surfaces in all road conditions, especially in wet and wintry weather (Figs. 1 and 3); an increase in the drive-off and climbing capacity regardless of load; better acceleration in low gear, especially with high engine performance; reduced sensitivity to side wind; stability reserves when driving on slush and compacted snow tracks; better aquaplaning behavior; particularly suitable for towing trailers; balanced axle load distribution; reduced torque steer effect; even tyre wear. Automotive Engineering, 2009 According to EU Directive 70/156/EWG, a towed trailer load of 1.5 times the permissible total weight has been possible for multipurpose passenger vehicles (four wheel passenger vehicles) since However, the system-dependent, obvious disadvantages given below should not be ignored: acquisition costs; around 6 10% higher kerb weight of the vehicle; generally somewhat lower maximum speed; 5 10% increased fuel consumption; in some systems, limited or no opportunity for using controlled brake gearing, for instance for anti-locking or ESP systems; not always clear cornering behaviour; smaller boot compared with front-wheeldrive vehicles. Predictability of self-steering properties even in variable driving situations, traction, toe-in stability and deceleration behaviour when braking, manoeuvrability, behaviour when reversing and interaction with wheel control systems are the principal characteristics of the

16 Four-Wheel Drive Automotive Technology, Four- and All-Wheel Drive, Prepared by Martin Restoule Algonquin College, 2007

17 Figure: Conventional arrangements of propeller shafts used with 4WD (GKN Hardy Spicer) TC to FA: Transfer Case to Front Axle Two Joint and Shaft Assembly. TC to RA: Transfer Case to Rear Axle Short Coupled Joint Assembly. T to TC: Transmission to Transfer Case Short Coupled Joint Assembly. TC to FA: Transfer Case to Front Axle Two Joint and Shaft Assembly. TC to RA: Transfer Case to Rear Axle Two Joint and Shaft Assembly M.J. Nunney, Light and Heavy Vehicle Technology, Fourth edition, 2007

18 Sağ Ön Teker Tahrik Mili Ön Diferansiyel Tahrik Mili Sol Ön Teker Motor Vites Kutusu Transfer Kutusu Üç Kanallı Dijital Kontrollü ABS Şaft Çeneli Kavrama Sağ Arka Teker Aks Mili Sağ / Sol Tork Bölünmeli Viskoz Kavrama Aks Mili Sol Arka Teker AWD ve 4WD Tahrik Algoritması The Transfer Case The transfer case itself is constructed similarly to a standard transmission. It uses shift forks to select the operating mode, plus splines, gears, shims, bearings, and other components found in manual and automatic transmissions. The outer case of the unit is made of cast iron, magnesium, or aluminum.

19 The Transfer Case An electric motor axle disconnect Automotive Technology, Four- and All-Wheel Drive, Prepared by Martin Restoule Algonquin College, 2007

20 4WD Operational Modes 2-high (2H) Vehicle operates like a normal twowheel drive vehicle. 4-high (4H) The front axle is connected to the driveline. 4-low (4L) The transfer case provides a lower gear ratio. Automotive Technology, Four- and All-Wheel Drive, Prepared by

21 KOLEOS Kullanım Kitabı

22 KOLEOS Kullanım Kitabı

23 4 tekerlek tahrik sistemi ile ilgili uyarılar: Sürüş koşullarına bağlı olarak sistem, 2 tekerlek tahriki modundan otomatik olarak 4 tekerlek tahriki moduna geçebilir. Bu durumda, 4WD ikaz ışığı yanmaz. Seçilen mod ne olursa olsun, arka tekerleklerin zeminde ve ön tekerleklerin boşlukta (araç kriko üzerinde) veya makaralar üzerinde olması halinde motoru çalıştırmayınız. Virajda, geri viteste veya tekerlekler patinaj halindeyken mod seçim butonuna basmayınız. Sadece aracın düz yolda sürülmesi durumunda 2WD, AUTO veya 4WD Lock modunu seçiniz. Motor ısındığında rölanti devrinde yükselme olması mümkündür. AUTO modu seçiliyken kaygan zeminli yolda aracın ilk kalkış anında veya seyir halindeyken dikkatli olunuz. Özellikle istenen teknik özelliklere uygun lastikler kullanınız. Kar zincirlerini sadece ön tekerleklere takınız. Bu fonksiyon, aracın tutumunu sürücünün isteğine uygun hale getirmeyi sağlamak için kritik sürüş koşullarında ilave bir yardımdır. Önemli Not: Bununla birlikte bu fonksiyon sürücünün yerine müdahalede bulunmaz. Bu fonksiyon, sizi, aracınızın limitlerini aşmaya ve daha hızlı kullanmaya yöneltmemelidir. Dolayısıyla bu fonksiyon, manevralar sırasında hiçbir durumda sürücünün özenini ve sorumluluğunu üstlenemez (sürücü, her zaman sürüş sırasında aniden meydana gelebilecek olaylara karşı dikkatli olmalıdır). *** Önemli Diğer Uyarılar: Düzgün zeminli yollarda 4WD Lock modunu sürekli olarak kullanmamanız tavsiye edilir. Dört tekerleğe de daima aynı teknik özelliklere sahip (marka, boyut, aşınma vs.) lastikler takınız. Ön ve arka ve/veya sol ve sağ tekerleklerde farklı boyutlarda lastik kullanılması, lastiklerde, vites kutusunda, aktarma organlarında ve arka diferansiyel dişlilerinde ağır hasarlara neden olabilir.

24 KOLEOS Kullanım Kitabı Güvenlik, konfor ve çekiş sistemleri ile ilgili Genel Uyarı Bu tür fonksiyonlar sürücünün yerine müdahalede bulunmaz. Bu fonksiyon, sizi, aracınızın limitlerini aşmaya ve daha hızlı kullanmaya yöneltmemelidir. Dolayısıyla bu fonksiyon, manevralar sırasında hiçbir durumda sürücünün özenini ve sorumluluğunu üstlenemez (sürücü, her zaman sürüş sırasında aniden meydana gelebilecek olaylara karşı dikkatli olmalıdır).

25 Okuma Parçası: Dört çeker ve önden çeker araçlarda yol tutuş nasıldır? (Honda CR-V, Toyota RAV4 veya Subaru Forester ) Toyota RAV4, aktif tork kontrollü dört çeker bir aktarma sistemine sahiptir. Arazi şartlarında otomatik olarak devreye giren dört tekerlekten çekiş sistemi anında tutunmayı üst limitlerine çıkartıyor. Öte yandan tekerleğin zemin ile temasını kaybetmesi halinde motor elektroniği tekerleklere aktarılan fazla gücü kısıyor. Şehrin gerekleriyle arazi araçlarının güçlü görünümlerini aynı potada eriten Forester da kullanılan Simetrik AWD, her bir tekerleğe aktarılan tork miktarının sürekli şekilde ve gerçek zamanlı olarak ayarlanması sayesinde, diğer AWD sistemlerine üstünlük sağlamaktadır. Simetrik sürekli dört tekerlekten çekiş sistemiyle; aracın savrulma momentinin azaltılması ve aracın virajı daha kolay dönmesi amaçlamıştır. Bu sayede daha dengeli ve temkinli bir direksiyon hakimiyeti elde edilir. Optimum aktarma sağlamasına rağmen 4x4 ve AWD gibi sistemler, daha ağır ve pahalı sistemlerdir. Ayrıca SUV özellikli araçların yol tutuş özellikleri daha zayıf olmakla birlikte devrilmeye de daha yatkındır. Bu araçlarda devrilme eğilimini azaltmak ve yol tutuşu iyileştirmek için araç daha fazla elektronik sistemlerle desteklenir. Gücün 4 tekerleğe birden aktarıldığı araçlar, özellikle kaygan zeminli virajlarda daha rahat kontrol edilebilir ve ESP nin daha geç müdahale etmesi sağlanır.

26 Active Differentials Active differentials employ electrohydraulically or electromechanically activated multi-disc clutches to limit differential slip. The additional traction provided by limited differential slip can be adjusted depending on conditions, up to and including full lockup. Such a system allows the dynamic influence of limited differential slip to be activated as required. Active differentials, however, can only transfer torque from the wheel with greater rotational velocity to the wheel with less rotational velocity. Bernd Heißing Metin Ersoy (Eds.), Chassis Handbook Fundamentals, Driving Dynamics, Components,Mechatronics, Perspectives, 1st Edition 2011.