4X4 - 4WD - AWD_2014-2015

MARMARA ÜNİVERSİTESİ
TEKNOLOJİ FAKÜLTESİ
DİFERANSİYEL
4X4, 4WD ve AWD
Yrd. Doç. Dr. Abdullah DEMİR
HAZIRLAYAN:
Yrd. Doç. Dr. Abdullah DEMİR
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
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
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
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.
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.
Four-Wheel Drive
All-Wheel Drive
4WD Sistemi
KİA, 4WD
Ağırlık Aktarımı ve Farklı 4WD Düzenekleri
KİA, 4WD
Aktarma sisteminin düzeni, ağırlık aktarımı bakımından otomobillerin
davranışlarını etkiler.
Subaru - S y m m e t r i c a l AWD
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.
Automotive Engineering, 2009
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
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
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 1994.
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
Four-Wheel Drive
Automotive Technology, Four- and All-Wheel Drive, Prepared by Martin Restoule Algonquin College, 2007
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
Çeneli
Kavrama
Üç Kanallı
Dijital Kontrollü
ABS
Şaft
Sağ Arka Teker
Aks
Mili
Sağ / Sol
Tork Bölünmeli
Viskoz Kavrama
Aks
Mili
Sol Arka Teker

Sağ Ön Teker
Transfer
Kutusu

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.
Motor
Vites
Kutusu
The Transfer Case

Tahrik
Mili
Ön Diferansiyel
Tahrik
Mili
Sol Ön Teker
AWD ve 4WD Tahrik
Algoritması
The Transfer Case
An electric motor axle disconnect
Automotive Technology, Four- and All-Wheel Drive, Prepared by Martin Restoule Algonquin College, 2007
4WD Operational Modes
 2-high (2H)
 Vehicle operates like a normal two-
wheel 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
KOLEOS Kullanım Kitabı
KOLEOS Kullanım Kitabı
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.
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).
KOLEOS Kullanım Kitabı
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.
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.