Week 10 - suspension part 2

Question 1

What do dampers do?

Answer 1

Prevent oscillations for both the sprung and unsprung masses.

Question 2

How do viscous dampers operate?

Answer 2

They operate by forcing a fluid through an orifice producing a force proportional to velocity that restrains spring motion

Question 3

What is the equation for critical damping coefficient?

Answer 3

C crit = 4 pi * ms *fs

Question 4

What is the damping ratio?

Answer 4

Damping ratio = actual damping coefficient/ critical damping coefficient.

Question 5

What damping ratio can be expected for passenger cars and racing cars?

Answer 5

passenger vehicles = 0.25 for best trade between comfort and performance.0.65- 0.7, producing overshoot but returning to the neutral position as quickly as possible.

Question 6

What is compliance?

Answer 6

Compliance is the displacement/ the force. How much mass is displaced for a given force.

Question 7

What is mobility?

Answer 7

Velocity / the force. How quickly a mass is displaced for a given force.

Question 8

What is accelerance?

Answer 8

How much a mass accelerates for a given force.

Question 9

Derive the equations for accelerance, mobility and compliance for a single degree of freedom . Eg a car tyre and chassis as one rigid body

Answer 9

For accelerance: w^2/ ((-mw^2) + (cjw) +k)

Question 10

Apply Euler rule for displacement, velocity and acceleration

Answer 10

X = Xe^(jwt)
V = Xjw e^(jwt)
A =- X w^2 e^(jwt)

Question 11

What is transmissivity?

Answer 11

Displacement of the vehicle chassis from a bump in the road displacement of the unsprung mass. (Tyre moves up due to bump and the rigid body also moves , compare the two)

Question 12

Derive the equation for transmissivity. For resonance.

Answer 12

Derivation should give:
x/u = (cjw +k)/ cjw

Question 13

What is the resonance equation

Answer 13

ks - wn^2 * ms = 0