Vehicle Vibration 4

Question 1

what are the advantages of coil springs

Answer 1

• theyre cheap and reliable

Question 2

what are the disadvantages of coil springs

Answer 2

• they have lightly damped modes of vibration
• leading to structurally transmitted noise

Question 3

how do you reduce the amplitude of coil resonances

Answer 3

• by placing an elastomer isolating pad between the spring and car body
• this dissipates the energy

Question 4

what is the advantage of air springs

Answer 4

• suspension static displacement can be adjusted by adding or releasing air via a valve

Question 5

what are the disadvantages of air springs

Answer 5

• more expensive than coil springs
• compressed air supply required

Question 6

how does a monotube damper work

Answer 6

• the oil displaced by the piston rod is accommodated by compression of the gas below the floating piston
• the gas pressure prevents cavitation and causes a static force

Question 7

what do the elastomer mountings on a monotube damper do

Answer 7

• they reduce transmission of high-frequency structure-borne noise

Question 8

how does a twin damper work

Answer 8

• the cavity between the concentric tubes provides space for the oil displaced by the piston rod

Question 9

how does a twin tube damper compare to a monotube damper

Answer 9

• larger diameter and shorter
• heavier
• lower static force
• cavitation is at risk
• must be mounted upright
• greater bending stiffness

Question 10

how does inerter suspension work

Answer 10

• an inerter generates a force proportional to the relative acceleration across the device

Question 11

how does a switchable damper work

Answer 11

• you can switch the damper valve between several fixed settings (automatic or manual)
• this allows the trade-off between performance criteria to be varied

Question 12

how does a continuously variable damper (specifically the magneto-rhetorical damper) work

Answer 12

• the piston contains an electromagnetic coil
• the MR fluid passes through and orifice and magnetic field
• the damper force can be adjusted depending on the strength of the field

Question 13

how does linked suspension work

Answer 13

• an anti-roll bar links the left and right wheels to increase roll stiffness
• linking the front and rear systems provides low warp stiffness

Question 14

how is wheel vibration managed to attenuate the force transmitted to the car body

Answer 14

• by using an elastomer mounting bush with slots

Question 15

if you were told to sketch a monotube damper, what would the inside of the body look like top to bottom

Answer 15

• the rod coming through the top with a piston and valve at the end of it
• the very top of the body is a region containing the rod seal
• the space between the rod seal region and the piston+valve is filled with oil
• in between the piston+valve and the floating piston below it is more oil
• in between the floating piston and the bottom is compressed gas at 30 bar

Question 16

what does the top and bottom of the monotube damper look like outside of the body

Answer 16

• the rod is connected to a top elastomer mounting
• below the body is a donut-shaped mounting eye with elastomer

Question 17

what is the key difference between the piston attached to the rod and the floating piston in a monotube damper

Answer 17

• the piston attached to the rod has valves so oil can flow through it
• the floating piston has seals so does not allow any flow through it

Question 18

if you were told to sketch a twin tube damper, what would the inside of the body look like top to bottom

Answer 18

• the rod coming through the top with a piston and extension valve at the end of it
• the very top of the body is a region containing the rod seal
• the space between the rod seal region and the postion+valve is filled with oil
• in between the pistion+valve and the compression valve the bottom is more oil
• the compression valve connects to a thin outer shell that is partially filled with low pressure oil
• the remainder of this shell is filled with low pressure gas

Question 19

what does the top and bottom of the twin tube damper look like outside of the body

Answer 19

• the same as a monotube damper
• top mounting with elastomer and bottom mounting eye with elastomer