Transcript No Slide Title

ELECTRONICALLY MANAGED SUSPENSION
• introduction
• system overview
• sensors and control mechanisms
• checking procedures
tmc
ELECTRONICALLY MANAGED SUSPENSION
Introduction
The purpose of any suspension system is to ease the shock of the road
surface.
To improve riding comfort and stability.
To help the tyres hold the road.
Before we talk about active type suspension systems, lets think about some
basic systems. Functions:
• Connects the body of the vehicle to the wheel assembly.
• Absorbs and damps vibrations and shocks.
• Protects passengers and cargo.
• Transmits driving and braking forces generated
by friction between road and wheels to the vehicles
body.
• Transports body on axles and maintains proper
relationship between body and wheels.
ELECTRONICALLY MANAGED SUSPENSION
Shock Absorbers - Purpose
To improve ride handling and comfort by quickly
damping oscillations of the springs (up and down
movement).
A
M
P
L
I
T
U
D
E
Help tyres hold the road better.
TIME
With shock
absorbers.
Without shock
absorbers.
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Action of the shock
absorber and springs.
ELECTRONICALLY MANAGED SUSPENSION
On electronic systems shock absorbers must reconcile 2 requirements.
1 = passenger comfort, for which
dampening should be soft
(85% of use).
2 = performance dampening that
should be hard.
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ELECTRONICALLY MANAGED SUSPENSION
Upper Wishbone
Shock Absorber
Spring
Lower Wishbone
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Shock Absorbers - Types
Single action shock absorber. Damping
only occurs when the shock absorber
is extended. When the shock absorber
is compressed no damping force is
generated.
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Orifice
Valve
Fluid
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Valve is now open, fluid flows from the
lower chamber through the now open
valve and the orifice.
The flow resistance of the fluid moving
through the orifice creates a damping
force.
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Multi action shock absorbers.
Damping occurs when the shock
absorber is extended and when
it is compressed.
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Twin tube shock
absorbers.
Cylinder divided by
pressure tube and outer
tube into working chamber
(inner cylinder) and
reservoir chamber (inner
chamber).
When the piston is forced
down, oil which is
incompressible flows
through a check valve and
damps the descent of the
piston. This process is
reversed during rebound.
As the plunger enters the
cylinder an equivalent
amount of oil enters the
reservoir between the jacket
and the cylinder.
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Gas filled shock absorbers:
Charged with mainly Nitrogen gas.
There are 2 main types:
Low pressure - 142 to 213 psi.
High pressure - 284 to 427 psi.
The smaller the check valves the
stiffer the shock absorber.
The larger the valves the softer
the shock absorber.
ELECTRONICALLY MANAGED SUSPENSION
Normal
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Dive - braking
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Pitch - acceleration
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Pitching can also occur when the vehicle has gone over a hump or
obstacle in the road and continues to oscillate.
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The roll caused by an evasive
manoeuvre or rapid lane changing.
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Normal
Pitch - acceleration
Roll
Dive - braking
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Due to the fact that the check valves size, will
determine the stiffness of the suspension
conventional systems have to either have a balance
between the two or be one or the other.
Electronically controlled systems have the major
advantage of being able to deliver both.
It can alter the stiffness of the shock absorbers in a
fraction of a second depending upon driving style
and road profile.
ELECTRONICALLY MANAGED SUSPENSION
How does it work?
The twin tube shock absorber contains the following:
• Hollow plunger.
• Actuator.
• 16,000 rpm miniature electric motor.
• Reduction gear train, ratio 46 : 1.
• Torque limiter to cut power to the motor.
• Rotary valve.
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Actuator, rotates clockwise and
anti clockwise.
Channel closed damping is heavy.
SPORT position.
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Actuator, rotates clockwise and
anti clockwise.
Channel open damping is soft.
COMFORT position.
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Inputs for system
requirements.
Outputs from the
control unit.
Steering angle sensor
Damper motor n/s/f
Yaw / pitch sensor
Brake pressure switch
Pedal potentiometer
Vehicle speed sensor
Drivers selector switch
Electronic
Control
Unit
Damper motor o/s/f
Damper motor n/s/r
Damper motor o/s/r
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The speed sensor is an inductive device.
PERMANENT
MAGNET
WINDING
SOFT IRON CORE
It is a tiny alternator that
produces an AC waveform.
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The steering wheel sensor.
This is mounted on the
steering column and informs
the ECU of conditions that could
induce roll.
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The steering wheel sensor. This measures the steering wheel angle and
the speed in which it is rotated.
It consists of a Phonic
wheel fitted to the
steering column.
The phonic wheel
turns with the
steering wheel and
blocks or allows
the light through to
the transistors.
The sensor itself consists
of 2 LED’s and 2 photo
transistors.
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Yaw /pitch sensor - this measures suspension movement that may
induce pitching or yawing movement.
Its mounted on the front sub - frame and connected by a link to the anti - sway
bar.
During suspension travel the anti sway bar actuates the link. The link drives
a notched phonic wheel that blocks or allows through light from 4 LED’s.
SBY - LED’s
The trim height is
calculated from the
succession of signals.
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Yaw / Pitch sensor.
SBY - LED’s
The trim height is
calculated from the
succession of signals.
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Pedal potentiometer.
This evaluates the risk of front end lift or
dive.
It delivers 2 types of information:
•The rate which the pedal is being operated.
•The amplitude of any acceleration or deceleration.
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The brake pressure sensor limits dive.
It consist of a switch that when the pressure exceeds 15 bars it opens
the circuit.
What does the ECU do with this information?
The ECU has basic maps programmed
into it’s memory with reference points
for all the sensors.
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What does the ECU do with this information?
Steering Angle
Angular Velocity of the Steering Wheel
O
O/S
KM/H
KM/H
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Body Height
Amplitude of acceleration
O/S
H
5
4
3
KM/H
KM/H
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Amplitude and rate of deceleration
O/S
Braking pressure
Bar
15
KM/H
KM/H
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Consider the reference point for the steering wheel angle. It defines
2 zones a green zone and a blue zone.
The vehicle is travelling
at the same speed but now
enters a sharp bend with
a steering angle of 15°.
It is now in the blue zone.
Steering Angle
O
15
5
The vehicle enters a large
radius bend at 90km/h and
a steering angle of 90°.
The point P is in the green zone
normal ride dampening.
15
P
90
Sport position.
P
5
KM/H
90
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The ECU sends a
signal 150 m/s long
to the shock absorbers
when point P is in the
blue zone.
The valves of the
4 shock absorbers
close changing
to the sport position.
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When the ECU
senses a stable
condition for at
least 2 seconds it
sends a signal
300 m/s long which
closes the actuators
in the shocks.
These valves remain
closed for as long as
point P stays in the
blue zone.
If a fault is detected
in the systems the
ECU forces all the valves
closed - sport position.