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BRAKES
[M5B1] 4-4
ECU CONNECTOR
18 17
15 11
11 10 9
7
Z
1
4
5 3I
32
29 8 27
25 2.
7 21 0 19
TO
R~
Hydraulic unit
Master cylinder
Stop light
---
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t
F L Q
' ;
L----- +-----------------
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~-
iRLQ
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FR
FL
'FRQZ _ ;
FR
MV
FL
MV
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Wheel!
T~
RRQ
I
cylinder
a1y
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,r
Wheel
cylinder 1
-JL
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----
-----
--
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-
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-
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-
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r
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PV
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PV
L ---------_ '
Electronic
RL
i
RL
.
RR
RR
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--------
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"
control
(ECU)
unit
Wheel
I
My
MV
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Wheel
r~-
cytinderji ; ;~
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cylinder
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MR
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r
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VR M
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ie
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FR : Front ri ht
MV : M
l
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l
i
g
agnet va ve
amp
Warn ng
Alternato
..**
= Ignition-i.
F L: Front left
MP : Motor & pump
Battery
'
R L: Rear left
MR : Motor relay
Vehicle speed - Wheel speed
RR : Rear right
VR : Valve relay
Slip ratio =
X 100°~
Vehicle speed
PV : Proportioning valve
134-611
Fig. 21 ABS System diagram
3. THEORY OF ABS CONTROL
When the brake pedal is depressed during operation,
wheel speed as well as vehicle speed decreases . The
difference which occurs between wheel speed and
vehicle speed is called the "slip" phenomenon . The
magnitude of this action is expressed by "slip" the ratio
which is determined by the following equation :
Vehicle speed - Wheel speed
Slip ratio =
x 100%
Vehicle speed
When the "slip" ratio is 0% vehicle speed equals wheel
speed and the wheel rotates without any slippage .
When the "slip" is 100% the wheel locks and does not
rotate (wheel speed = 0) although vehicle speed exists .
The relationship between the frictional force of a wheel
in the fore-and-aft direction and the "slip" ratio is shown
by two characteristic curves in Figure 22 .
These curves are determined by the relationship be-
tween the wheel and road surface. Where the same
type of wheel are used ; the curve shown by a solid line
indicates wheels driven on asphalt or paved roads, the
curve shown by dotted lines refers wheels subjected to
slippery (snowy or icy) roads.
When different types of wheels are used, although the
road surface is the same, these curves will change . In
general, the frictional coefficient between wheel and
road surface in relation to an increase in the "slip ratio"
will reach the maximum value in the 8 - 30%range and
will tend to decrease after that.
Control zone by ASS
m
I
Asphalt road
do
.U
d `°
_ Ir
~
I
Ice-snow road
m
U . M
0
-
1001%1
Slip ratio
B4-034
Fig. 22
F
B- CONSTRUCTION AND OPERATION
1 . WHEEL SPEED SENSOR
The wheel speed sensor detects wheel speed and
consists of a permanent magnet, coil, tone wheel, etc.
The magnetic flux produced by the permanent magnet
varies with the tone wheel (which rotates together with
the wheel) and the sensor emits an alternating voltage
corresponding with the wheel speed by electromag-
netic induction .
13
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