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TM 9-8000
suspension arms. When a load is applied to the bogie
31-4.  Torsion Bar Suspension. The torsion bars
wheels, the suspension arms pivot upward, transmitting
generally are mounted inside the vehicle and extend
the force directly to the spring, thereby compressing it.
completely across the width of the hull. Because of
Vertical displacement of only one road wheel changes
this configuration, the springs are protected from
the spring load, thereby changing the load on the other
damage such as road hazards and, to some extent,
wheel. The balance of forces in the suspension
land mines. Road wheels are mounted to crank-
mechanism results in a wheel motion that is a
shaped arms connected to the hull through antifriction
combination rocking motion and vertical deflection.
bearing mountings, which relieve the springs of all
except the torsional loads (fig. 31-2). One end of a
31-6.  Suspension  Snubbers.  Volute  suspension
torsion bar is splined to the pivoting axle of each
snubbers are mounted on brackets bolted to the hull
suspension arm. The other end of the bar is secured
above each road wheel position (fig. 31-3). The volute
rigidly to the opposite side of the hull. The means of
springs serve to cushion road wheel arm bottoming
securing the stationary end of the torsion bar are well
shock loads. Inboard stub spindles on the support arms
suited to applying mechanisms for varying the spring
contact the springs near the upper limit of the support
preload, thereby providing a means for adjusting the
arm travel. A double volute spring is used for the front
freestanding position of the vehicle to best suit the
road wheel arm, and a single volute spring at the other
operating conditions. Angular displacement of the
road wheel arm positions.
suspension arm is resisted by the torsional spring
force of the bar. Because the arms operate in sealed
31-7.  Shock Absorbers. Suspension  systems in
antifriction bearings, and because of the lack of friction
tracked vehicles employ either direct-acting, cam and
in the spring, little natural damping of the spring
lever, or double-acting shock absorbers, which are
system is available. This condition makes the use of
discussed in chapter 30, section VI.
shock absorbers essential to minimize bouncing and
pitching of the vehicle.
31-5. Horizontal Volute Spring Suspension. In the
horizontal volute spring suspension (fig.  31-1) the
spring is located between bellcranklike
designed to combine lockout, damping, and bump-stop
31-8. Purpose. The basic function of a suspension
functions for each road wheel arm.
lockout system is to bypass the suspension system
and attempt to lock the vehicle to the ground. When
(2) Damping is controlled through a three-way valve
the system is used in combat vehicles, it allows large
mounted in the driver's compartment.
guns to be fired from relatively light vehicles because
the recoil is transmitted directly to the ground with
(3) Control pressure is supplied from a hydraulic
minimum carriage movement. Suspension lockout
accumulator, through the three-way valve and a
systems also are used on lifting vehicles. When the
reducing valve to a common line, which supplies all
system is activated on such vehicles, it allows the
of the lockout cylinders.
operator to maneuver large objects without the
suspension compressing and possibly tipping over the
(4) To lock the cylinder, control pressure is applied to
the spool, depressing the spring until the spool land
closes the right-hand ports in the rod, trapping the
31-9. Hydraulic Lockout System.
fluid in both ends of the cylinder.
a. Operating Principles.
b. Construction. The construction of the system is that
of a double-rod-end cylinder with passages into the
(1) This unit uses a hydraulic cylinder
valve region in the rod from


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