Four steering system is about the maneuvering of the wheel using all four wheel. Which allows the vehicle to take sharp turn at slow speed and decrease the rollover accident danger at higher speed.
3. INTODUCTION TO STEERING:-
Steering is the collection of components, linkages, etc. which allow
a vehicle (car, motorcycle, bicycle) to follow the desired course. An
exception is the case of rail transport by which rail tracks combined
together with railroad switches (and also known as 'points' in British
English) provide the steering function.
Requirement of steering-
•It should multiply the turning effort applied on the steering wheel by
the driver.
•It should be to a certain degree irreversible so that the shocks of the
road surface encountered by the wheels are not transmitted to the
driver’s hand.
•The mechanism should have self –rightening effect so that when the
driver release the steering wheel after negotiating the turn , the wheel
should try to achieve straight ahead position.
5. FOUR WHEEL STEERING:-
• Four-wheel steering (or all wheel steering) is a system
employed by some vehicles to improve steering response,
increase vehicle stability while maneuvering at high
speed, or to decrease turning radius at low speed. A 4-
wheel steering system is superior to a 2- wheel steering
system. It reduces the turning radius as well as the space
required for turning. It also enables to change road lane
while driving even at high speed.
• At lower speeds, turning the rear wheels in the opposite
direction to the front wheels results in a smaller turning
radius and faster cornering responses. At high speeds,
turning all four wheels in concert improves high-speed
stability.
6. The Four Wheel steering system offers a 21% reduction in turning
radius. So if a vehicle is capable of making a U-turn in a 25-foot
space. It allows the driver to do it in about 20 feet. . A front wheel
active steering function was added to Rear Active Steer adopted
on the Fuga. By controlling the steering angle of all four wheels,
this active steering system helps improve stability and response at
high speed and helps reduce driver’s steering workload at low
speed. To achieve precise vehicle
• Vehicles move smoothly and are easy to drive both in the city
and on winding roads.
• Added stability means vehicles can be driven safely on
expressways and when changing lanes.
• Quick and responsive control system will allow gentle steering
operation.
7. TURNING RADIUS:-
The turning radius of a vehicle is the radius of the smallest circular turn
(i.e. U-turn) that the vehicle is capable of making. it refers to the tightest
turn a vehicle can make and is dependent on several factors. One obvious
one is the width of the wheel base — that is, how far apart the front tires
are. All other things being equal, a smaller wheel base can offer a tighter
radius, while a large wheel base, such as those on large trucks, will have a
larger radius, regardless of other factors.
8. 4-WS SYSTEM PARTS: -
• Rack and pinion front steering,
• hydraulically controlled
• Rear-steering shaft
• Vehicle speed sensors
• Steering-phase control unit
• Centering lock spring
• Solenoid valve
9.
10. At higher speeds, the rear wheels turn in the same direction of the
front wheels to increase stability by preventing oversteer and fish
tailing. And reduces the turning radius.
AT HIGH SPEED:-
4-WS DRIVE AT DIFFERENT SPEED
11. At lower speeds, the rear wheel turn in the opposite direction
from the front wheels. This will help in easy maneuverability
of the vehicle during parking and taking a tight curve. The
turning radius of a vehicle can be reduced by a minimum of
20% by having this mechanism, which is a significant benefit
for bigger cars and trucks.
AT LOW SPEED
12. ADVANTAGES OF 4WS
• Speed can be varied
Slow Medium Fast
• Improved maneuverability
14. MODERN CARS WITH ACTIVE FOUR WHEEL
STEERING: -
•Acura RLX (P-AWS)
•BMW 850CSi (only Euro spec models)
•BMW 7-Series (2009 onward, part of sport package)
•BMW 5-series (2011 onwards, Integral Active Steering option)
•Toyota Camry / Vista JDM 1988–1999 (Optional)
•Toyota Carina ED / Toyota Corona EXiV (world's first dual-mode switchable
2WS to 4WS)
•Toyota Celica (option on 5th and 6th generation, 1990–1993 ST183 and
1994–1997 ST203) (Dual-mode, high and low speed)
•Toyota Soarer (UZZ32)
15. CONCLUSION: -
An innovative feature of this steering linkage
design and its ability to drive all four (or two)
wheels using a single steering actuator makes it
more efficient than 2WS. Though it is expensive
now but by producing it at big level cost may be
decreased. Its successful implementation will
allow for the development of a four-wheel, steered
power base with maximum maneuverability,
uncompromised static stability, front- and rear-
wheel tracking, and optimum obstacle climbing
capability.
