Vehicle Speed Sensor; Reed Switch Type; Photocoupler Type - Toyota COMPUTER-CONTROLLED SYSTEM Training Manual

ELECTRONIC CONTROL SYSTEM - Vehicle Speed Senso r
VEHICLE SPEED SENSO R
This sensor senses the actual speed at which the
vehicle is traveling . It outputs an SPD signal,
which is used mainly to control the ISC system,
and to control the air-fuel ratio during
acceleration, deceleration, etc .
There are four types of speed sensor :
• Reed switch type
• Photocoupler typ e
• Electromagnetic pickup typ e
• MRE (magnetic resistance element) typ e
1 . REED SWITCH TYP E
This sensor is mounted in the analog
combination meter . It contains a magnet which
is rotated by the speedometer cable, turning the
reed switch on and off. The reed switch goes on
and off four times each time the speedometer
cable rotates once .
The magnet has the polarities shown in the
figure below . The magnetic force at the four
areas of transition between the N and S poles of
the magnet opens and closes the contacts of the
reed switch as the magnet rotates .
Q To speedometer cabl e
OHP 2 9
ELECTRICAL CIRCUITRY
Engine ECU
2 . PHOTOCOUPLER TYP E
This sensor is mounted in the combination
meter . It includes a photocoupler made from an
LED, which is aimed at a phototransistor . The
LED and phototransistor are separated by a
slotted wheel, which is driven by the
speedometer cable . The slots in the slotted
wheel generate light pulses as the wheel turns,
with the light emitted by the LED divided into 20
pulses for each revolution of the cable . These 20
pulses are converted to four pulses by the digital
meter computer, then sent as signals to the ECU .
Slo
tt
ed
wheel
OHP 29
ELECTRICAL CIRCUITR Y
+B
Combination
meter Puls e
Phototransistor
conversio n
circuit
Engine EC U
OHP 2 9
34 OHP 29