ANTILOCK BRAKING SYSTEMS LAB WORKBOOK
The components of the ABS system:
1-brake disc
2-wheel speed sensor
3-toothed rotor
4-hydraulic modulator
5-master cylinder
6-brake calliper
7-brake booster
Wiring diagram description:
Front Right Wheel Sensor has white/black wire
Front Left Wheel Sensor has green/red wire
Rear Left Wheel Sensor has blue/pink wire
Rear Right Wheel Sensor has yellow/brown wire
All the sensors are breaded in order to prevent interference from other sources of electrical signals. The ECU must read the wheel speed sensors signal precisely because of safety reason.
The ABS circuit above employ these fuses:
1.Main fusible link ( FL MAIN)
2.ABS fuse (50A)
3.Gauge fuse (10 A)
4.Dome fuse (10 A)
5.Stop fuse (15 A)
6.ECU-IG (15 A)
White/black earth wire is connected to the pin #1 of ABS actuator assembly ( ABS motor), and to the pins #10 and #7 of the ABS ECU.
Solenoids identification with wire colours and pin numbers:
Front Right Wheel: pin#9(a) white wire and pin#10(a) black wire
Front Left Wheel: pin#23 (a) green wire and pin #22(a) red wire
Rear Left Wheel: pin # 3(b) blue wire and pin #2(b) pink wire
Rear Right Wheel: pin#8(b) yellow wire and pin # 9(b) brown wire
Braking conditions and valves operations
1. Under normal braking condition the inlet valve is open and outlet valve is closed.
2. When the ABS is operating to reduce wheel brake pressure the inlet valve is closed and the outlet valve is open
3.When the ABS is operating to hold brake pressure the inlet valve is closed and the outlet valve is closed
4. When the ABS is operating to increase wheel brake pressure the inlet valve is open and the outlet valve is closed
The ABS motor will pump in the pressure when it is necessary to increase the pressure on the brake pads. There are types of ABS constructions when the ABS pump operates to reduce the pressure on the brake pads.
There is a digital signal on the graph below that switches 5 volts every 2 seconds
The analogue signal with a frequency of 0.5 Hz and a maximum of +3 volts is drawn on the graph below:
The ABS system of demonstrator we working on is equipped with inductive pick-up speed sensors.
Wheel Speed sensors connected to the ECU as follows:
Left Front ECU Pin #4and # 5
Left Rear ECU Pin # 7 and #9
Right Front ECU Pin # 11 and #21
Right Rear ECU Pin # 24 and #26
All these sensors work on the principle of inducing voltage in the winding by means of emf . Once the tab of the toothed rotor passes against the inductive pick-up it changes magnetic field in the pick-up winding. The sensor produces the sine-wave signal the same way as AC generator. When the rotor tooth is reaching the sensor the signal out increases, when the rotor tooth is getting further from the sensor signal decreases and then changes the polarity from positive to negative. As a result, we have sinusoid type voltage out with a shape of the signal pulse depending on the teeth shape. Clearance between the rotor and the inductive pick-up is also essential feature. It influences on the amplitude of the signal.
Left Front Wheel Speed sensor Waveform (pin#5)
As you can see from the photos above, we have experimented with two different oscilloscopes. The best one is so accurate that through the pattern you can examine the condition of the teeth surfaces, not to mention the clearance between the teeth and the sensor. Once I have tried to rub the rust from the teeth it has shown these small changes immediately. However, back to the main task of the experiment. The comparison between the signals highlighted that all the sensor produce different voltages due to difference in clearance and some disparities in state of teeth on the tone wheels.
AC Volts measured with multimeter:
Left Font (pin#5) : 3.433 V
Left Rear ( pin#7) : 2.542 V
Right Front ( pin #11) : 4.289 V
Right Rear ( pin #24) : 4.881 V
The oscilloscope patterns observing and analysis allows to note and to understand any small differences in toothed rotors conditions, clearance between tone wheel and speed sensor, frequency changes. The multimeter can only say if there is a signal out and what is the voltage of the signal. This is not enough for proper diagnostics very often.
ABS RELAYS
K39-system relay
K100-ABS pump relay
K38- ABS HCU solenoids relay
Power supply wire for the ECU is connected to the pin#1
Line #15 from the ignition switch controls the relay for the ABS ECU.
Line # 30 brings in the power to the ABS pump.
Through the pin#28 the ECU controls the relay for the ABS pump.
ABS HCU solenoids relay (K38) waveforms for both control circuit and switching circuit:
At the moment we switch the ignition key "on" the ABS starts self-test. The control cirsuit of the relay K38 (pin#6 of the HCU) is supplied with battery voltage (points "A"-"B"on the pattern from ch.1). The coil of the control circuit is grounded through the ECU ( point "B") . Once it happens the solenoid is "on"(point "E" from the pattern of ch.2). The emf occurs at the point "F". The second part of the ABS self-test comes to action when we turn the ignition key "off"( point "C", pattern ch.1) The solenoid is "off" ( point "G"). To die-out for the magnetic field in the relay control circuit takes time around the point "C". From this point to the point"D" on the pattern of the ch.1. we see battery voltage again.
ABS Pump Relay (K100) Waveform:
To control what is going on during the self-test on the ABS pump we checked out the patterns on the pins #9 and #11. Ch1 shows that when the ignition switch is "on" ( point "A) we've got a supply voltage from "A" to "B". Once the relay control circuit is grounded by the ECU the ABS pump is "on" ( point "G" on the Ch.2 pattern) For the pattern from the channel 1 the period "B"-"C" is time when the relay is grounded. From point "H" the ABS pump is "off" but not instantly, it takes time for the pump to stop. The failing part of the puls shows this. The second part of the self-test happens when the ignition key is "off"( point"D" on the pattern of the channel). The ABS pump is "on" again ("I"-"J") while the coil is grounded ("D"-"E" on the ch.1 pattern). "E"-"F" is supply voltage while the ABS pump is "off"("J") but not instantly. It takes time from "J" to "K" on the falling part of the ch.2 pattern.
The oscilloscope pattern when the ABS solenoid is actuated:
Provided we captured the pattern with division per scale on the time axes equal to 500 ms, the respond time of the solenoid on the voltage supplied is about 100 ms. This is actually the frequency of brake fluid pressure modulation. No one driver can be so fast at emergency braking situation.
From the gauges reading on this video we can conclude that HCU reduces the pressure in the line of the wheel which is locked up. It does it so fast, almost instantly. Once the wheel is free to rotate again, the pressure in the line rises to the same level as others wheels pressure.
On Vehicle Testing:
Mazda Familia 1998
ABS system components identification:
1. Wheel speed sensor:
2. ABS control unit:
4.ABS pump motor
5.Parking brake switch:
8.RPM sensor
9.Foot brake switch:
11.Main ABS control unit fuse:
Front Left wheel speed sensor gap : 0.661 mm ( 0.226 inches)
They both are within the specification ( 0.4-1.0 mm)
The patterns recorded from the wheel speed sensors are:
4 volts peak to peak analogue signal from the inductive type wheel speed sensor. Period of the signal is 4 ms what is equal to 250 Hz
The reading of the multimeter is:
Live data reading from Mazda Demio:
ABS solenoids control relay is off. This is the reason why ABS warning lamp is on. Apart from normal reading for others components we can see speed recorded from the left front wheel speed sensor ( 78 km/H ) and right front wheel speed sensor ( 78 km/H ). The car was stationary ( on the hoist) with rear wheels not running. That's why ABS module recognised that rear wheels did not rotate and recorded the fault which describes there is no coherency between rear sensors reading and front sensors reading. It's logical and understandable because our car didn't run on the road and this difference in speed of the wheels was created artificially during the test.
LAND ROVER 2003 ACTUATORS TEST
As it seen from the photos above we experimented on actuators by using AutoBoss scanner. First off all, we've read all the data to make sure what is the current condition of the ABS system. Once we found that right hand wheel speed sensor was out of order we decided to hold the test on the inlet valve ( solenoid). To do so we activated this solenoid by means of scan tool program and recorded two videos below.
If listen carefully you can hear clear such a specific clicking noise from the solenoid. That physically means actuations. Applying voltage to solenoid we opened it for a certain period of time. What we've learned extra is the opportunity to bleed an old generation ABS system hydraulic assembly providing actuation test. This is way how to release air from the system. Modern systems usually don't have this sort of problems with bleeding.
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