Steering
Assembly
(Recirculating
ball)
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Steering is the collection of components, linkages, etc. which allows
any 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. The primary purpose of the
steering system is to allow the driver to guide the vehicle.
Introduction
The most conventional steering arrangement is to turn the
front wheels using a hand–operated steering wheel which is positioned
in front of the driver, via the steering column, which may
contain universal joints (which may also be part of the collapsible
steering column design), to allow it to deviate somewhat from a straight
line. Other arrangements are sometimes found on different types of
vehicles, for example, a tiller or rear–wheel steering. Tracked
vehicles such as bulldozers and tanks usually employ differential
steering — that is, the tracks are made to move at different speeds or
even in opposite directions, using clutches and brakes, to bring about a
change of course or direction.
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Basic geometry
Caster angle θ indicates kingpin pivot line and gray area indicates
vehicle's tire with the wheel moving from right to left. A positive caster
angle aids in directional stability, as the wheel tends to trail, but a large
angle makes steering more difficult.
Curves described by the rear wheels of a conventional automobile. While
the vehicle moves with a constant speed its inner and outer rear wheels
do not.
The basic aim of steering is to ensure that the wheels are pointing in the
desired directions. This is typically achieved by a series of linkages, rods,
pivots and gears. One of the fundamental concepts is that of caster
angle – each wheel is steered with a pivot point ahead of the wheel; this
makes the steering tend to be self-centering towards the direction of
travel.
The steering linkages connecting the steering box and the wheels
usually conform to a variation of Ackermann steering geometry, to
account for the fact that in a turn, the inner wheel is actually travelling
a path of smaller radius than the outer wheel, so that the degree
of toe suitable for driving in a straight path is not suitable for turns. The
angle the wheels make with the vertical plane also influences steering
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dynamics (see camber angle) as do the tires.
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Recirculation Ball Type Steering.
A diagram of a recirculating ball mechanism
Recirculating ball, also known as recirculating ball and nut or worm and
sector, is a steering mechanism commonly found in older
automobiles, off-road vehicles, and some trucks. Most new cars use the
more economical rack and pinion steering instead, but some upmarket
manufacturers (such as BMW and Mercedes-Benz) held on to the design
until well into the 1990s for the durability and strength inherent in the
design. A few, including Chrysler and General Motors, still use this
technology in certain models including the Jeep Wrangler.
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Mechanism
The recirculating ball steering mechanism contains a worm gear inside
a block with a threaded hole in it; this block has gear teeth cut into the
outside to engage the sector shaft (also called a sector gear) which
moves the Pitman arm. The steering wheel connects to a shaft, which
rotates the worm gear inside of the block. Instead of twisting further
into the block, the worm gear is fixed so that when it rotates, it moves
the block, which transmits the motion through the gear to the Pitman
arm, causing the road wheels to turn.
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Thank You
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