Vehicle Vibration 2 Flashcards
what are the three important performance criteria of a vehicle
- body acceleration
- working space
- dynamic tyre force
what is the rms body acceleration
- rms body acceleration = sqrt(E[z_doubledot_s^2])
what is the rms working space
- rms working space = sqrt(E[(z_s - z_u)^2])
what is the rms tyre force
- rms tyre force = sqrt(E[(k_t*(z_r - z_u))^2])
for pitch-plane analysis, what is the general equation of motion in matrix-vector notation
- Mx_dotdot + Cx_dot + Kx = Pu_dot + R*u
if you are operating under natural modes of vibration, meaning stiffnesses c_1 = c_2 = 0 and the displacements z_r1 = z_r2 = 0, how would you find a solution to the equation of motion
- take laplace transforms to get: M^-1Kx(jw) = w^2x(jw)
- solutions are the e-values and e-vectors of M^-1*K
in the special case of uncoupled equations where k_1a = k_2b, what is the frequency w^2 in pure bounce mode
- w^2 = k_1 + k_2 / m
in the special case of uncoupled equations where k_1a = k_2b, what is the frequency w^2 in pure pitch mode
- w^2 = k_1a^2 + k_2b^2 / I
what is z_r2(t) in terms of z_r1(t) where a is the distance between G and z_r1 at the front while b is the distance between G an z_r2 in the back
- z_r2(t) = z_r1(t)*(t - (a+b)/V)
what is the wavenumber n
- n = 1/λ = w/2pi*V
what is the normalised wavenumber N
- N = L/λ = L*n
what is the magnitude for the bounce gain
- bounce gain = sqrt(1+cos(2pi*N) / 2)
what is the magnitude for pitch gain
- pitch gain = sqrt(1-cos(2pi*N) / 2)
what is the body acceleration physically
- it is the acceleration of the sprung mass
- it is a proxy for discomfort in a vehicle
what is the working space physically
- the space available for relative displacement of the sprung and unsprung masses
what is the tyre force physically
- the ability of the tyres to generate breaking or cornering force
- this is reduced if the vertical tyre force oscillates
relating to contours of RMS body acceleration, when is body acceleration minimized
- when k and c are 0
what happens to the RMS body acceleration if damping is small but stiffness is not
- large values of acceleration occur
relating to contours of RMS working space, what does it rely on wrt to damping and stiffness
- only damping
- working space increases as damping decreases
what is the relationship between RMS working space and damping if suspension is locked
- damping is infinite
- so working space is 0
relating to contours of RMS tyre force, when is it minimized
- at a specific combination of non-zero damping and stiffness
- because the contours are circular
