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ACTIVE SUSPENSION
SYSTEMS

A historical leaf-type suspension

Vertical acceleration and its effect on traction

Vehicle motion

Vehicle motion (Roll and Pitch)

Comfort Issues

• motion sickness: ∼1 Hz

• head toss: ∼2–8 Hz

Passive Suspension Types

Spring-Damper mechanism

Suspension Links

Double – Wishbone type

MacPherson Type

Different spring types

Wheel Model

Free Body diagram of passive suspension system

Passive Suspension Model
ms zs  bp ( zs  zu )  k p ( zs  zu )  0

mu zu  kt ( zu  zr )  bp ( zs  zu )  k p ( zs  zu )  0

Passive Suspension Model

s 2 ms  Z s  sbp (Z s  Zu )  k p (Z s  Zu )  0

s mu  Zu  kt (Zu  Z r )  sbp (Z s  Zu )  k p (Z s  Zu )  0
2

Passive Suspension Model

Z s (s ms  sbp  k p )  Zu (sbp  k p )  0
2

s ms  sbp  k p
2

Zu  Z s

sbp  k p

Passive Suspension Model

Zu (s 2 mu  sbp  kt  k p )  Z s (sbp  k p )  Z r (kt )  0

Zs

s 2 ms  sbp  k p
sbp  k p

 ( s 2 mu  sbp  kt  k p )  Z s ( sbp  k p )  Z r (kt )

Passive Suspension Model
 ( s 2 ms  sbp  k p )  ( s 2 mu  sbp  kt  k p )  ( sbp  k p )  ( sbp  k p ) 
Zc 
  Z r (kt )
sbp  k p





sbp kt  k p kt
Zs
 4
Z r s ms mu  s 3 (msbp  mu bp )  s 2 (ms kt  ms k p  mu k p )  s (bp kt )  (k p kt )

s 

kp
ms

u 

kt
mu

Simulink Diagram of Passive Suspension System

Road disturbance (model)

btpu
ms
k

Passive Suspension Model

Passive Suspension Model Response

Semi-active Suspension

Magneto – Rheological Suspension

Active Suspension Systems

BMW ARC (Anti Roll Control) System

Active Suspension Systems
Hydraulic Systems:
Advantages
1) very high force density
2) ease of control
3) ease of design
4) commercial availability of the various parts
5) reliability
6) commercial maturity
Disadvantages
1) considered inefficient due to the required continuously
pressurized system
2) relatively high system time constant (pressure loss and
flexible hoses)
3) environmental pollution due to hose leaks and ruptures,
where hydraulic fluids are toxic
4) mass and intractable space requirements of the total
system, including supply system, even though it mainly
contributes to the sprung mass

Active Suspension Systems
Electromagnetic Systems
Advantages:
1) increased efficiency
2) improved dynamic behavior
3) stability improvement
4) accurate force control
5) dual operation of the actuator
Disadvantages:
1) increased volume of the suspension, since the force density
of the active part of hydraulics is higher than for
electromagnetic actuation, i
...
, system mass and volume
could be less
2) relatively high current for a 12- to 14-V system
3) conventional designs that need excitation to provide a
continuous force
4) higher system costs

Active Suspension Systems

BOSE Active Suspension

BOSE Active Suspension

Active Suspension Model (1/4 Car Model)

Active Suspension Model

ms  zs  kac ( zs  zu )  bac ( zs  zu )  U  FI  0

mu  zu  kt ( zu  zr )  kac ( zs  zu )  bac ( zs  zu )  U  0

Active Suspension Model
s 2ms  Zs  s  bac (Z s  Zu )  kac  (Z s  Zu )  U  FI  0

s mu  Zu  s  bac (Zs  Zu )  kac  (Z s  Zu )  kt (Zu  Zr )  U  0
2

Active Suspension Model

Zs (ms s 2  bac s  kac )  Zu (bac s  kac )  U  FI  0

Zu (mu s  bac s  kac  kt )  Zs (bac s  kac )  kt  Zr  U  0
2

Active Suspension Model

Zu (bac s  kac )  U  FI
Zs 
ms s 2  bac s  kac

Z r  kt  Z s (bac s  kac )  U
Zu 
mu s 2  bac s  kac  kt

Simulink Diagram of Active Suspension Model

Active Suspension Model

Comparison of active and passive suspension

Quarter car test setup

Full Car Pitch Model

Full Car Roll Model

Full Car Model
I   l f ( F1 fl  F1 fr )  lr ( F1rl  F1rr )  ms hs g  ms

I  h f ( F1 fl  F1 fr )  hr ( F1rl  F1rr )  ms ghs  0

ms zs  F1 fl  F1 fr  F1rl  F1rr  0
m2 fl z2 fl  F1 fl  F2 fl  0
m2 fr z2 fr  F1 fr  F2 fr  0

m2 rl z2 rl  F2 rl  F2 rl  0

m2 rr z2 rr  F1rr  F2 rr  0

dV
hs  0
dt

Full Car Model
F1 fl  k1 fl ( z1 fl  z2 fl )  c1 fl ( z1 fl  z2 fl )  Kaf (  ( z2 fl  z2 fr ) / 2hf ) / 2hf  f fl
F1 fr  k1 fr ( z1 fr  z2 fr )  c1 fr ( z1 fr  z2 fr )  Kaf (  ( z2 fl  z2 fr ) / 2h f ) / 2h f  f fr

F1rl  k1rl ( z1rl  z2 rl )  c1rl ( z1rl  z2 rl )  K ar (  ( z2 rl  z2 rl ) / 2hr ) / 2hr  f rl
F1rr  k1rr ( z1rr  z2 rr )  c1rr ( z1rr  z2rr )  K ar (  ( z2rr  z2rr ) / 2hr ) / 2hr  f rr

z1 fl  zs  l f   h f 
z1 fr  zs  l f   hf 

z1rl  zs  lr  hr
z1rr  zs  lr  hr
F2 fl  k2 fl ( z2 fl  wfl )

F2 fr  k2 fr ( z2 fr  wfr )
F2 rl  k2 rl ( z2 rl  wrl )

F2 rr  k2 rr ( z2 rr  wrr )



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