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A reciprocal shock absorber system
called the “X-REAS” (Relative
Absorber System) enhances drivability
by eff ecting full four-wheel
control and is provided as optional
equipment on the 4Runner.
An air suspension that uses
pneumatic cylinders instead of
coil springs is provided as a set
option with the X-REAS in the rear
suspension.
The oil passages of the front
and rear shock absorbers of the
X-REAS are connected diagonally,
with a center control absorber
interposed.
This ensures a linear and
smooth response to the rolling
and pitching of the vehicle.
As a result, high levels of riding
comfort and controllability are
achieved.
The system consists of front
shock absorbers, rear shock absorbers,
center control absorbers
and a plumbed tube assembly.
The components are oil-fi lled and
a check valve is built into the tube
joints for serviceability.
In order to apply a damping
force to the two shock absorbers
that are connected to the center
control absorber, the center control
absorber consists of a valve,
free piston and a gas chamber.
DIAGONALLY
OPPOSITE PHASE
When the vehicle tilts, pitches
or rolls, a directional
diff erence
is created in the
pistons of the two
connected shock
absorbers. As a result,
oil fl ows from
the shock absorber
that is compressing
into the center
control absorber
and fl ows into the
shock absorber
that is extending (rebounding).
The resulting fl ow resistance
acts as a damping force in addition
to the damping force that
is generated by the connected
shock absorbers.
Somewhat similar to the way a
torsional anti-roll bar functions,
the compression side transfers
energy to the opposite side (extending
side) to minimize body
roll and to enhance handling and
response.
DIAGONALLY
EQUAL PHASE
If the two connected shock
absorbers are compressed in the
same direction with the same
amount of piston stroke, such
as when the vehicle is driven
over a bump or a dip in the road,
oil from both shock absorbers
will fl ow into the center control
absorber.
However, oil will pass through
Spring 2010 STAR Service News
TOYOTA TECHNICAL
the control absorber orifi ce due
to even oil fl ow.
The resulting pressure acts entirely
on the free piston, allowing
it to absorb shock without generating
a damping force.
DIAGONALLY EQUAL
PHASE WITH DIFFERENT
PISTON SPEEDS
If two diagonally connected
shock absorbers are in the same
phase but their piston speeds differ,
the oil fl ows from both shocks,
but at diff erent rates into the
center control absorber.
This causes the free piston in
the center absorber to move only
by an amount that corresponds to
the volume of oil fl owing in.
Because the volume that fl ows
in is diff erent, the volume of oil
that corresponds to the diff erence
passes through the orifi ce.
The resulting fl ow resistance acts
as a damping force in addition to
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