PREVOST X3-45 2016, Руководство по обслуживанию

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Section 12: BRAKE AND AIR SYSTEM
Section 12 Updated Sept. 2015 X3-45 Commuter PA1593 DOB 2400-2489
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31.2.1 Electronic Control Unit (ECU)
This control unit is located in the front electrical
compartment, (refer to figure 31 for location).
According to the data transmitted by the sensors
(number of pulses/sec is proportional to the
speed of each wheel), the electronic control unit
determines which wheel is accelerating or
decelerating. It then establishes a reference
speed (average speed) from each wheel data,
and compares the speed of each wheel with this
reference speed to determine which wheel is
accelerating or decelerating.
As soon as wheel deceleration or wheel slip
threshold values are exceeded, the electronic
control unit signals a solenoid control valve to
limit the excessive brake pressure produced by
the driver in the appropriate brake chamber.
Maintenance
No specific maintenance is required. The ECU is
not serviceable. When found to be defective,
replace.
FIGURE 32: ABS ECU LOCATION
06617
CAUTION
In order to protect the ABS electronic control
unit from voltage surges, always disconnect
before performing any welding procedure on
vehicle.
31.2.2 ABS Modulator Valve
This ABS system is equipped with four or five
modulator valves, located between the brake
chamber and the relay valve or quick release
valve (Fig. 32). Note that on the basic ABS
system, there is only one solenoid valve
controlling the drive and tag axle wheels on the
same side (tag axle is slave to drive axle).
This is an "On/Off" type valve, i.e., at brake
application, the valve exhausts air from the
brake chamber when the electronic unit senses
that the corresponding wheel speed is
decreasing in relation to the other wheels.
FIGURE 33: ABS MODULATOR VALVE
12221
Maintenance
Refer to Bendix Service Data sheet SD-13-4870
located at the end of this section.
31.2.3 Sensors
The sensors are mounted on the front, drive and
tag axle (if applicable) wheel hubs (Fig. 33). The
inductive sensors consist essentially of a
permanent magnet with a round pole pin and a
coil. The rotation of the toothed wheel alters the
magnetic flux picked up by the coil, producing an
alternating voltage, the frequency of which is
proportional to wheel speed. When wheel speed
decreases, magnetic flux decreases proportion-
ately. Consequently, the electronic control unit
will command the solenoid control valve to
decrease the pressure at the corresponding
brake chamber.
Maintenance
No specific maintenance is required for sensors,
except if the sensors have to be removed for
axle servicing. In such a case, sensors should
be lubricated with special grease (Prevost
#680460) before reinstallation. Refer to
paragraph “Sensor Installation” for details.