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نظام فرامل Abs

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    نظام فرامل Abs

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    اليوم اقدم لكم نظام فرامل ABS






    HOW ANTILOCK BRAKES WORKS
    All antilock brake systems control tire slip by monitoring the relative deceleration rates of the wheels during braking. If one wheel starts to slow at a faster rate than the others, or at a faster rate than that which is programmed into the antilock control module, it indicates the wheel is starting to slip and is in danger of breaking traction and locking up. The ABS system responds by momentarily reducing hydraulic pressure to the brake on the affected wheel or wheels.
    Electrically operated solenoid valves are used to hold, release and reapply hydraulic pressure to the brakes. This produces a pulsating effect, which can usually be felt in the brake pedal during hard braking. The driver may also hear a buzzing or chattering noise from the ABS hydraulic unit.
    The rapid modulation of brake pressure in the brake circuit reduces the braking load on the slipping wheel and allows it to regain traction, thus preventing lockup. It is the same as pumping the brakes, except that the ABS system does it automatically for each brake circuit, and at speeds that would be humanly impossible, up to dozens of times per second depending on the system (some are faster than others).
    Once the rate of deceleration for the affected wheel comes back in line with the others, normal braking function and pressure resume, and antilock reverts to a passive mode.



    WHO MAKES ANTILOCK BRAKES?
    The major OEM suppliers of antilock brakes are:
    Bendix, Acquired from Allied Signal by Bosch, used primarily on Chrysler and Jeep products.
    Bosch, Main supplier for most imports and assorted domestic vehicles.
    Delco, Now known as Delphi, is used exclusively on GM applications.
    Continental Teves, found on various Ford, GM, Chrysler and import applications.
    Kelsey-Hayes, supplier of rear-wheel ABS and four-wheel ABS systems on Ford, Chevy and Dodge trucks.
    Nippondenso, used on Infiniti and Lexus
    Sumitomo, found on certain Mazda and Honda applications, as well as Ford Escort.
    Toyota, rear wheel only ABS systems on Toyota pickups



    ANTILOCK BRAKE CONFIGURATIONS
    Regardless of who makes them, all ABS systems keep track of wheel deceleration rates with wheel speed sensors. On some applications, each wheel is equipped with its own speed sensor. This type of arrangement would be called a "four wheel, four channel" system since each wheel speed sensor would give its input into a separate control circuit (the word "channel" here actually refers to each individual electronic circuit rather than the individual hydraulic brake circuits).
    On other applications, fewer sensors are used. Many four-wheel ABS systems have a separate wheel speed sensor for each front wheel but use a common speed sensor for both rear wheels. These are called "three channel" systems. The rear wheel speed sensor is mounted in either the differential or the transmission. The sensor reads the combined or average speed of both rear wheels. This type of setup saves the cost of an additional sensor and reduces the complexity of the system by allowing both rear wheels to be controlled simultaneously.
    Another variation is the "single channel" rear-wheel only ABS system that is used on many rear-wheel drive pickups and vans. Fords version is called "Rear Antilock Brakes" (RABS) while GM and Chrysler call theirs "Rear Wheel Anti-Lock" (RWAL). The front wheels have no speed sensors and only a single speed sensor mounted in the differential or transmission is used for both rear wheels. Rear-wheel antilock systems are typically used on applications where vehicle loading can affect rear wheel traction, which is why it is used on pickup trucks and vans. Because the rear-wheel antilock systems have only a single channel, they are much less complex and costly than their three- and four-channel, four-wheel counterparts.




    INTEGRAL & NONINTEGRAL ANTILOCK BRAKES SYSTEMS
    Another difference in ABS systems is that some are "integral" and others are "nonintegral."
    Integral systems, which are found mostly on older full-size passenger car applications, combine the master brake cylinder and ABS hydraulic modulator, pump and accumulator into one assembly. Integral systems do not have a vacuum booster for power assist and rely instead on pressure generated by the electric pump for this purpose. The accumulators in these systems can contain over 2700 psi. The accumulator must be depressurized prior to doing any type of brake repair work by pumping the brake pedal 40 times while the key is off.
    Nonintegral ABS systems, which are sometimes refereed to as "add-on" systems, are used on most of the newer vehicles. Nonintegral ABS systems use a conventional master brake cylinder and vacuum power booster with a separate hydraulic modulator unit. Some also have an electric pump for ABS braking (to reapply pressure during the ABS hold-release-reapply cycle), but do not use the pumps for normal power assist.






    WHEEL SPEED SENSORS
    The wheel speed sensors (WSS) consist of a magnetic pickup and a toothed sensor ring (sometimes called a "tone" ring). The sensor(s) may be mounted in the steering knuckles, wheel hubs, brake backing plates, transmission tailshaft or differential housing. On some applications, the sensor is an integral part of the wheel bearing and hub assembly. The sensor ring(s) may be mounted on the axle hub behind the brake rotor, on the brake rotor itself, inside the brake drum, on the transmission tailshaft or inside the differential on the pinion shaft.
    The wheel speed sensor pickup has a magnetic core surrounded by coil windings. As the wheel turns, teeth on the sensor ring move through the pickup magnetic field. This reverses the polarity of the magnetic field and induces an alternating current (AC) voltage in the pickup windings. The number of voltage pulses per second that are induced in the pickup changes in direct proportion to wheel speed. So as speed increases, the frequency and amplitude of the wheel speed sensor goes up.
    The WSS signal is sent to the antilock brake control module, where the AC signal is converted into a digital signal and then processed. The control module then counts pulses to monitor changes in wheel speed.
    On applications where the wheel speed sensor is not part of the hub or wheel bearing assembly, it can be replaced if defective. Sensor problems can be caused by an accumulation of debris on the end (they are magnetic), incorrect air gap or faults in the wiring or connectors.

  2. [2]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    ABS CONTROL MODULE
    The ABS electronic control module (which may be referred to as an EBCM "Electronic Brake Control Module" or EBM "Electronic Brake Module") is a microprocessor that functions like the engine control computer. It uses input from its sensors to regulate hydraulic pressure during braking to prevent wheel lockup. The ABS module may be located in the trunk, passenger compartment or under the hood. It may be a separate module or integrated with other electronics such as the body control or suspension computer. On the newer ABS systems (Delphi DBC-7, Teves Mark 20, etc.), it is mounted on the hydraulic modulator.
    The key inputs for the ABS control module come from the wheel speed sensors and a brake pedal switch. The switch signals the control module when the brakes are being applied, which causes it to go from a "standby" mode to an active mode.
    When ABS braking is needed, the control module kicks into action and orders the hydraulic unit to modulate brake pressure as needed. On systems that have a pump, it also energizes the pump and relay.
    Like any other electronic control module, the ABS module is vulnerable to damage caused by electrical overloads, impacts and extreme temperatures. The module can usually be replaced if defective, except on some of the newest systems where the module is part of the hydraulic modulator assembly.

    HYDRAULIC MODULATOR
    The hydraulic modulator or actuator unit contains the ABS solenoid valves for each brake circuit. The exact number of valves per circuit depends on the ABS system and application. Some have a pair of on-off solenoid valves for each brake circuit while others use a single valve that can operate in more than one position. On Delco VI ABS systems, small electric motors are used in place of solenoids to drive pistons up and down to modulate brake pressure.
    On some systems, the individual ABS solenoids can be replaced if defective, but on most applications the modulator is considered a sealed assembly and must be replaced as a unit if defective.


    PUMP MOTOR & ACCUMULATOR
    A high pressure electric pump is used in some ABS systems to generate power assist for normal braking as well as the reapplication of brake pressure during ABS braking. In some systems, it is used only for the reapplication of pressure during ABS braking.
    The pump motor is energized via a relay that is switched on and off by the ABS control module. The fluid pressure that is generated by the pump is stored in the "accumulator." The accumulator on ABS systems where the hydraulic modulator is part of the master cylinder assembly consists of a pressure storage chamber filled with nitrogen gas.
    Should the pump fail (a warning light comes on when reserve pressure drops too low), there is usually enough reserve pressure in the accumulator for 10 to 20 power-assisted stops. After that, there is no power assist. The brakes still work, but with increased effort.
    On ABS systems that have a conventional master cylinder and vacuum booster for power assist, a small accumulator or pair of accumulators may be used as temporary holding reservoirs for brake fluid during the hold-release-reapply cycle. This type of accumulator typically uses a spring loaded diaphragm rather than a nitrogen charged chamber to store pressure.

    CARING FOR ABS
    Most vehicles with ABS require no special maintenance according to the vehicle manufacturers. But considering how expensive the hydraulic modulators are on many vehicles, many brake experts say changing the brake fluid every year or two for preventative maintenance can save consumers a bundle in brake repairs. Brake fluid absorbs moisture over time, which promotes internal corrosion in the system. So changing the fluid periodically can prolong the life of the ABS hydraulic components and minimize the risk of failure.
    Basic brake service is essentially the same on a vehicle equipped with ABS as that which does not have ABS. On some vehicles, special bleeding procedures are required. Replacement linings should have similar friction characteristics to the OEM linings. On applications where the wheel speed sensor rings are part of the rotors or drums, replacement rotors or drums must be the same (count the teeth to make sure!).
    If a vehicle has an integral ABS system where the ABS hydraulic modulator is part of the master cylinder, if either component fails the whole assembly must usually be replaced (which is very expensive). On nonintegral systems, the master cylinder may or may not be the same as the same vehicle application without ABS, so check your catalog carefully to make sure. Some antilock brake applications may have extra ports or connections on the master cylinder.

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    ان الله فى عون العبد ما دام العبد فى عون اخيه
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  3. [3]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    تشخيص نظام Abs

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  4. [4]
    mohamed abouzahra
    mohamed abouzahra غير متواجد حالياً
    عضو متميز
    الصورة الرمزية mohamed abouzahra


    تاريخ التسجيل: Nov 2006
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    NEW ABS DIAGNOSTIC TESTERS


    Although a scan tool is all that is needed to read and clear fault codes on most ABS systems, fault codes alone don't fix the problem. A code only tells you the system has self-diagnosed a problem in a particular circuit or component. It does not tell you what to replace. To fix the problem you have to refer to the step-by-step diagnostic checks in a service manual and isolate the fault by a process of elimination. Jump to conclusions and you may guess wrong.
    What's more, intermittent problems may not set a fault code. So if there is no code, don’t assume everything is fine. You have to check the operation of the system as well as individual components to figure out what is wrong.
    Point by point resistance and voltage checks can help you isolate problems with or without codes, but such tests can be very time-consuming and may not always reveal a problem. Dynamic tests are also impossible with this approach because you have no means of exercising or testing the operation of the ABS solenoids and valves. Such components may show the correct voltage and resistance readings, but may not be functioning correctly. So some means of testing their function may be necessary for an accurate diagnosis. That is where a bi-directional scan tool or dedicated ABS tester can make a big difference. Here are three such ABS testers you should know about:



    ABS READER
    One of the newest testers is OTC's ABS Reader. This hand-held tester includes "GM-approved" software for full bi-directional control on 1991-94 Delco VI and 1988-91 Powermaster III ABS systems. The tool can also be used to troubleshoot Bosch, Teves, Kelsey-Hayes and Mazda MECS ABS systems.
    The ABS Reader has an easy-to-read four line, 19-characters per line LCD display, with nine input buttons. The display shows diagnostic codes with descriptions along with live data stream information on ABS sensors and switches, plus record and playback of data stream. It also allows bi-directional inputs for the Delco ABS systems which provides the following:
    • Powermaster III; manual control, hydraulic control, Powermaster bleed, pump run tests (run cycle time, total time, leak down, cycles without brake), system identification, data stream and fault codes.
    • Delco VI; manual control, hydraulic control, electromagnetic brake (EMB), motor test, gear tension relief, relay test, voltage load test, lamp test, system identification, motor rehome, data stream and fault codes.
    • Mazda MECS; wiggle test plus fault codes.
    • Bosch & Teves; data stream and fault codes.
    • Kelsey-Hayes; fault codes only.
    On the Delco VI system, the manual control test checks each of the three motors to determine if they are operating properly. The EMB test and motor test can help you find problems with the motor pack. The gear tension relief test can find a defective hydraulic modulator. The relay test checks to see that the relay is supplying power to the ABS system. The motor rehome test opens up the ABS circuits so the modulator can be bled. The hydraulic control test lets you check the operation of all three ABS channels (left front, right front & rear) to detect problems. The voltage load test checks system voltage to verify that it is within specifications. The lamp test checks the lamp circuit and driver module. The system identification test provides information on the ABS control module, eliminating the need to check part numbers visually.
    The OTC ABS Reader retails for $449 (tool and manual only P/N #3758), or $599 with adapter cables & carrying case (P/N #3757). For further information, contact your OTC distributor or call

    ABS-TECH
    The ABS-TECH by Edge Diagnostic Systems is a dedicated computer-based ABS analyzer for diagnosing all current import and domestic ABS systems. The ABS-TECH diagnostic software module is actually an "add-on" enhancement for the SIMU-TECH computerized engine control system diagnostic pod that works in conjunction with a personal computer. The ABS-TECH system has been on the market for about five years, and is currently used by some OEMs for ABS diagnosis as well as Midas and Goodyear.
    One of the many features offered by this easy-to-use menu-driven system is the ability to perform an automated full system sweep of ABS sensor, actuator and signal circuits in about 60 seconds. The test results are then displayed with "pass" or "fail" ratings for each component based on vehicle specifications stored in the ABS-TECH data base. This feature allows a technician to pinpoint electrical problems quickly, saving valuable diagnostic time.
    Another unique feature of the ABS-TECH software is that it can do a fully automated dynamic ABS test, eliminating the need to test drive the vehicle. It does this by inputting simulated vehicle and wheel speed sensor signals into the ABS module, which allows the technician to see how the system responds during a simulated ABS stop.
    The system can also cycle and test all of the ABS solenoids for checking individual ABS hydraulic circuits.
    Other features on the ABS-TECH are:
    • A single point connection. The cable connects between the ABS module and wiring harness (which does require different adapters for various applications).
    • A fully self-configuring seven-trace lab scope for viewing live signal output waveforms. Up to 75 different signals inputs can be shown, seven at a time on the screen. There is also a stored library of known "good" waveforms for comparison purposes. The software allows you to record, play back, save and print all signals displayed. * Built-in custom meters, including volts, ohms, amps and frequency for pinpoint testing. Data can be displayed various ways; analog (waveform, bar chart, variation chart), digital (frequency, dwell, voltage, duty cycle, pulse width), and switch (on/off).
    • Online help covering recommended ABS brake bleeding procedures, control module locations, signal descriptions and more.
    The ABS-TECH is available through Snap-On distributors, and sells for around $2,000 as an add-on (if you already have SIMU-TECH) or from $8,000 to $12,000 for the complete system. Contact your Snap-On distributor or call 1-800-746-8832 for more details.
    Also available from Edge Diagnostics is their hand-held Personal Automotive Computer (PAC) diagnostic tool, which combines the functions of a scan tool with a four-channel lab scope. This unit can also be used to read ABS codes and display signal waveforms, but lacks the diagnostic capability of the ABS-TECH system.
    FAST-TRACK ABS TROUBLESHOOTER
    Snap-On’s Fast-Track ABS Troubleshooter (MT25002794) provides access to vehicle scan codes on domestic vehicles. Specific systems covered include GM (Bosch 2U, 2S & 3, ITT Teves Mark 2, Delco Powermaster III, Delco VI, Kelsey-Hayes RWAL & 4WAL), Ford (Teves Mark 2 & 4, Kelsey-Hayes RABS, and Sumitomo), Chrysler (Bendix 4, 6 & 10, Kelsey-Hayes RWAL, Bosch 3), Jeep (Bendix 9). For Asian import applications, there is a separate combination cartridge kit MT25004495. Adapter cables for domestic and import vehicles are available separately (cables can be purchased or leased from Snap-On).
    Introduced in 1995, the Fast-Track ABS troubleshooter cartridge is an add-on enhancement for Snap-On’s MT2500 hand-held Scanner and Domestic Combination Primary cartridge. Depending on the application, the Fast-Track ABS Troubleshooter can display codes, system data including wheel speed sensor readings, lamp and pump motor status, and valve positions, and perform functional tests for activating various ABS valves, relays and motors, and cycle the ABS solenoids when bleeding the brakes. The tester can handle brake bleeding on Delco VI, Bendix 4 & ABX-4 and Teves Mark 4 applications, actuator tests on Chrysler Bendix 4, 6 & 10 and Teves Mark 4 applications, plus many other tests.
    Each ABS menu in the Troubleshooter is organized to include:
    • Warning lights & initial checks—often overlooked checks that can lead to misdiagnosed problems, system specific lamp diagnostics and preroad test checks.
    • ABS brake service caution areas—things to avoid or be careful about when servicing the brakes, plus brake specifications.
    • Code tips—extensive, system specific code descriptions with code set conditions and repair tips.
    • Symptom tips—descriptions of and repair tips for frequently occurring problems that may not always set a code.
    • Tests and procedures—detailed subsystem test information such as wheel speed sensor, pump and valve assembly testing, including brake bleeding procedures.
    • Training information—description of how system works.

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    mohamed abouzahra
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