Page 232 - The Tribology Handbook

Damping devices E315

PERFORMANCE OF HYDRAULIC DAMPERS FITTED WITH VALVES

4

3.5

3.0

2.5

2.0

1.5

1

3.5

a 0.5 1 1.5 2 2.5
FREQUENCY OF EXCITATION = t
FREQUENCY = NATURAL FREQUENCY fr

Figure 165 Curves of relative transmissibility for a number of representative V~SCQUS damping factors

If two components are connected by a spring system, such This damping factor is not affected by velocity for a
as a wheel and the body of a vehicle, the forces and damper of this kind, and consequently the relative tran-
oscillating movement transmitted by one to the other, will smissibility of forces and movements will depend mainly
depend on the frequency of the oscillations being tran- on the frequency ratio r, of the excitation frequency to the
smitted in relation to the natural frequency of the system, resonant frequency.
and the damping factor of any damping device which is For a system of this kind with resonance at T = 1,
incorporated. damping is desirable over the range T = 0 to r = 1.4. If r is
In a viscours hydraulic damper, in which F is propor- normally greater than 1.4 low D values become more
tional to V, the damping factor D is given by desirable. For conditions extending over a wide range of r,
values of D = 0.25 to 0.4 are found to give the best results.
Viscous hydraulic dampers of good design are available
with adjustable valves to give controlled relationships
between damping force and damper velocity.
where 6' = damping force per unit velocity N/ms-l
m = mass of the critical component kg
J = natural (resonant) frequency of the system

B15.2