anti locking braking system full report
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Anti-lock-brakes.ppt (Size: 1.59 MB / Downloads: 1,621)
Anti-lock braking systems (ABS) take a lot of the challenge out of this sometimes nerve-wracking event. In fact, on slippery surfaces, even professional drivers can't stop as quickly without ABS as an average driver can with ABS.anti-lock braking system, or ABS is a safety system which prevents the wheels on a motor vehicle from locking up (or ceasing to rotate) while braking.A rotating road wheel allows the driver to maintain steering control under heavy braking by preventing a skid and allowing the wheel to continue interacting tractively with the road surface as directed by driver steering inputs. ABS offers improved vehicle control and decreases stopping distances on dry and especially slippery surfaces. However, on loose surfaces like gravel and snow-on-pavement, it can slightly increase braking distance while still improving vehicle control
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Regd no: 0501227541
An anti-lock braking system (ABS) is a safety system on motor vehicles which prevents the wheels from locking
The Anti-lock Braking System is designed to maintain vehicle
control, directional stability and optimum deceleration under
severe braking conditions on most road surfaces
It does so by monitoring the rotational speed of each wheel and controlling the brake line pressure to each wheel
during braking. This prevents the wheels from locking up.
A rotating road wheel allows the driver to maintain steering control under heavy braking
1929 Anti-lock braking systems were first developed for aircraft, by Gabriel Voisin,
1950 Dunlop's Maxaret introduced a system and still in use on some aircraft models
1960 A fully mechanical system used in the Ferguson P99 racing car, the Jensen FF and the Ford Zodiac, but saw no
further use; the system proved expensive and, in automobile use, somewhat unreliable
1964 Limited form of ABS in Austin 1800, utilizing a valve which could adjust front to rear brake force
distribution when a wheel locked
1971 Chrysler, and Bendix Corporation, introduced 1971 Imperial. Called "Sure Brake",
1971 ABS Systems based Mercedes design were later introduced on other cars. GM introduced the "Trackmaster" ABS on
their Cadillac models
1975 Ford also introduced ABS on the Lincoln Continental Mark III and the Ford LTD station wagon, called "Sure Trak
1978 Bosch and Mercedes-Benz introduced the first completely electronic 4-wheel multi-channel ABS system in trucks
and the Mercedes-Benz S-Class
1988 BMW became the world's first motorcycle manufacturer to introduce an electronic/hydraulic ABS system, this on
their BMW K100
1992 Honda launched its first ABS system, this on the ST1100 Pan European
1997 Suzuki launched its GSF1200SA (Bandit) with ABS
Today ABS has become a standard equipment even for small cars
When the car brakes (normally ) wheels exert a forward force on the street which less than maximum static
If the driver brakes very hard it can occur that the maximum static friction is surpassed and the wheels lose
their grip and begin sliding
The amount of traction which can be obtained for an auto tire is determined by the coefficient of static friction
between the tire and the road. If the wheel is locked and sliding, the force of friction is determined by the
coefficient of kinetic friction
The Anti-lock Braking System is designed to maintain vehicle control, directional stability and optimum
deceleration under severe braking conditions on most road surfaces It does so by monitoring the rotational speed of
each wheel and controlling the brake line pressure to each wheel during braking. This prevents the wheels from
The sensors - one at each wheel send a variable voltage signal to the control unit, which monitors these signals,
compares them to its program information, and determines whether a wheel is about to lock up
When a wheel is about to lock up, the control unit signals the hydraulic unit to reduce hydraulic pressure (or
not increase it further) at that wheelâ„¢s brake caliper. Pressure modulation is handled by electrically-operated
Wheel Speed Sensors
Abs Control Module
The ABS control module is a microprocessor and uses input from its sensors to regulate hydraulic pressure during
braking to prevent wheel lockup
The key inputs are 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.
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.
Pump Motor &
Wheel Speed Sensors
The wheel speed sensor pickup has a magnetic core surrounded by coil consist of a magnetic pickup and a toothed
sensor ring,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.
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.
ABS Control Module
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
The fluid pressure that is generated by the pump is stored in the "accumulator."
Anti-Lock Brake Types
By The Number Of Channels :
Four-channel, four-sensor ABS -Speed sensor on all four wheels and a separate valve for all four wheels. So
individual wheel monitoring and optimum braking forces
Three-channel, three-sensor ABS - Speed sensor and a valve for each of the front wheels, with one valve and one
sensor for both rear wheels
One channel one sensor ABS - One valve, which controls both rear wheels, and one speed sensor, located in the rear
Open and closed systems:
Open anti-lock system : The brake fluid released from the brakes during ABS stop is not returned to the brake
instead, the fluid is stored in an accumulator during the ABS stop, then returned to the master cylinder reservoir
This type is used in simple-real wheel-only ABS designs.
Closed system: Closed system has some means, generally an electrically powered pump, to restore hydraulic pressure
that's bled off during an ABS stop.
The pump supplies fluid to an accumulator, where it's stored under pressure until is needed to increase brake
Increased braking distances under some limited circumstances (snow, gravel, "soft" surfaces),
Creation of a "false sense of security" among drivers who do not understand the operation, and limitations of ABS.
The anti-lock brakes are more sensitive on the damper condition. the influence of the worn components on the
performance of the vehicle with anti-lock brakes is more significant than without anti-lock brakes, the stopping
distance with defective shocks is by meters longer for the presented simulation scenario
Modern Electronic Stability Control (ESC or ESP) systems
An evolution of the ABS concept. Here, a minimum of two additional sensors are added to help the system work:
these are a steering wheel angle sensor, and a gyroscopic sensor.
The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car does not
coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s)
(up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends.
The steering wheel sensor also helps in the operation of Cornering Brake Control (CBC), since this will tell the
ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much
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There is a strong possibility that the federal government will mandate the use of antilock brakes on certain vehicles in the near future. ABS has been in use for several years, and evidence mounts regarding its benefitsâ€specifically its ability to improve vehicle stopping distances and to maintain vehicle directional control under extremely slick road conditions.
These findings are not without controversy, however. Initial claims of the benefits of ABS were significantly overstated, and many drivers have found that ABS offers them little or no advantage in their particular situation. In this respect, the controversy is a little like the one that surrounded seat belts.
Additional systems have been developed that enhance the benefits of the basic ABS. One of these systems is automatic traction control, called ATC. ATC uses the same components as ABS, but works at the other end of the speed spectrumâ€getting a vehicle started under slippery conditions. In operation, it senses each wheel's speed to detect when one or more wheels "break loose" and start to spin. When that happens, it applies the brake on that wheel 12 to 15 times per second to let it slow down and regain traction. In demonstrations, vehicles have been held by blocks on an ice-covered grade. When the vehicles start and the blocks are pulled away, the vehicle without ATC spins its wheels and slowly slides backwards down the grade, while the ATC-equipped vehicle pulls its way up the ice.
It is expected that ABS, along with other new vehicle products, will continue to increase in popularity as the price goes down and the benefits become more apparent.
Borad Mayur D.
7th Mech L.D.C.E. Ahmedabad â€œ 15
Stopping safely is one of the most important functions a motor vehicle can perform. Failure of the brake system will almost invariably result in property damage, personal injury, or even death. Consequently, a great deal of consideration has been given to improving the brake system in trucks and passenger cars over the last nine decades. One of the latest improvements is an antilock brake system which, as the name suggests, prevents a vehicle's brakes from locking up and skidding during hard stops on wet or icy roads.
The problem of skidding reveals the one overwhelming weakness of all motor vehicle braking systems: they depend strongly on the coefficient of static friction between the tire and the road. If for any reason the tire momentarily loses its adhesion to the road while the brakes are applied, the friction of the brakes against the drums or rotors locks the wheel solidly and the tire begins skidding across the road. In this condition, the braking force of that wheel is dependent on the sliding friction between the tire and the road, which is much less than the static friction. Under wet or icy conditions, the sliding friction is reduced even further, resulting in significantly longer stopping distances. In addition, when the front wheels are in this condition, they cannot be used to steer the vehicle; regardless of the angle of the front wheels, the vehicle continues to skid in whatever direction its momentum sends it until either the driver releases the brakes or the vehicle collides with something solid enough to bring it to a halt.
Generations of drivers were taught to handle this condition by quickly applying and releasing, or pumping, the brakes during a skid. However, this training was often lost during panic situations. Additionally, even the calmest and best-trained driver could not pump the brakes faster than two or three times per second, which limited the effectiveness of the technique.
As the electronic and hydraulic portions of aircraft ABS became smaller and less expensive, truck and automobile manufacturers began to take interest. At first, antilock brake systems were developed only for heavy-duty trucks. Large semi trucksâ€truck tractor-trailer combinations weighing up to 80,000 pounds (36,364 kg)â€were especially hazardous to traffic around them when they skidded since they not only moved out of the driver's control, but also articulated, or jack-knifed, and frequently rolled over. Today, antilock brake systems are standard on many cars and trucks.
Regardless of manufacturer or the type of vehicle, all antilock brake systems operate in a similar manner. Wheel speed sensors are placed on each wheel that is to be controlled. Each speed sensor usually has a toothed wheel, like a gear, that rotates at the
same speed as the vehicle wheel or axle. Mounted close to, but not touching this toothed wheel, is a permanent magnet wrapped with a coil of wire, called the pick-up coil. As each tooth rotates past the permanent magnet, it causes the magnetic field to concentrate and increase slightly. This, in turn, induces a small pulse of current in the coil of wire. The number of pulses per second are directly proportional to the speed of the wheel. The faster the wheel turns, the faster the teeth pass the magnet and the higher the pulse rate.
The pulsed output from the wheel speed sensors goes to an electronic controller, which monitors each wheel's speed relative to the speed of the other wheels. As long as the brakes are not being applied and all of the monitored wheels are rotating at roughly the same speed, the system takes no action. If, however, the brakes are being applied and one or more of the monitored wheels suddenly begins to reduce speed at a higher rate than the othersâ€indicating a loss of traction with the road and an imminent wheel lockup and skidâ€the controller then activates the antilock system.
The antilock brake system on any vehicle is simply an additional monitoring and controlling function superimposed on the existing vehicle brake system. ABS is not a second brake system, nor does it replace the vehicle brake system. When all four wheels on an automobile are monitored and controlled, the system is called a four-channel ABS. If the front two wheels plus the rear axle (but not each rear wheel individually) are to be controlled, the system is called a three-channel ABS. On heavy trucks with two rear drive axles, the ABS is commonly a four-channel system which controls the front wheels and two of the four rear wheels. Trailers pulled by heavy truck tractors may also have their own separate ABS which must interconnect with the ABS on the tractor.
In an automobile, the brakes are actuated by hydraulic pressure. The ABS controller operates solenoid valves built into the high pressure side of the master brake cylinder. These valves are normally open and do not interfere with braking. When the controller senses that a wheel is locking up while braking, it first activates a solenoid to close a valve in the affected wheel's brake line which prevents the pressure from increasing any further. If the locked wheel continues to lose speed, the controller activates a second solenoid which bleeds pressure off the affected brake line, in effect releasing the brake for that wheel regardless of whether the driver is still pushing on the brake pedal. As soon as the wheel regains traction and its speed increases, the solenoids are de-activated, and normal braking resumes. Of course, if the conditions are such that the wheel starts to skid again, the brake will promptly begin to lock up and the ABS will take over. This cycle is repeated 12 to 15 times per second until either the road condition changes or the driver releases the brakes. The driver will be able to detect this rapid cycling as a vibration felt through the brake pedal, but will not have to take any action.
The ABS will minimize the skid and will allow the driver to maintain directional control of the vehicle.
The brakes on a heavy truck are actuated by air pressure, rather than hydraulic pressure. The antilock brake system on a truck works in a manner similar to the ABS on an automobile, except the antilock air pressure control valves are located on the vehicle frame rail, near each wheel.
A. What is an ABS?
Antilock braking systems (ABSs) are electronic systems thatmonitor and control wheel slip during vehicle braking. ABS scan improve vehicle control during braking, and reduce stopping distances on slippery (split or low coefficient of friction) road surfaces by limiting wheel slip and minimizing lockup. Rolling wheels have much more traction than locked wheels. Reducing wheel slip improves vehicle stability and control during braking, since stability increases as wheel slip decreases.
ABSs can be applied to nearly all types of vehicles and can be successfully integrated into hydraulic and air brake systems (including air over hydraulic). This document applies to the ABSs used with air brake systems on commercial vehicles.
The equipment requirements of FMVSS 121 specify that ABSs on truck-tractors and full trailers must control the brake pressures to at least one front axle and one rear axle. The ABSs on semi-trailers and dollies must control at least one axle of the vehicle. Additionally, the ABSs on tractors must control one of the rear axles with two modulator valves so that the brake pressure on one end of the axle is independent of the brake pressure on the other end. The performance requirements of FMVSS 121 can require an ABS on additional axles.
B. How Do ABSs Work?
An ABS consists of several key components: electronic control unit (ECU), wheel speed sensors, modulator valves, and exciter rings. Here's how these components work together:
Â¢ Wheel speed sensors constantly monitor and send electrical pulses to the ECU at a rate proportional to the wheel speed.
Â¢ When the pulse rates indicate impending wheel lockup, the ECU signals the modulator valve(s) to reduce and/or hold the brake application pressure to the wheel(s) in question.
Â¢ The ECU then adjusts pressure, seeking one which gives maximum braking without risking wheel lockup.
Â¢ When the ECU acts to modulate the brake pressure, it will also (on most vehicles) turn off the retarder (if so equipped) until the risk of lockup is over.
Â¢ The ECU continually checks itself for proper operation. If it detects malfunction/failure in the electrical/electronic system, it will shut down that partof the ABS affected by the problemâ€or the entire ABSâ€depending upon the system and the problem.
Â¢ When this happens, the ABS malfunction lamp lights.
Â¢ An ABS adjusts brake pressure much faster and more accurately than can drivers. It's faster because:
electronic controls are very fast and
ABS modulator valves are physically closer to the brakes than is the driver's foot brake valve. It is more effective, too, because an ABS can tailor the brake pressure to each wheel or set of wheels to provide maximum braking/stability. Some vehicles also use a traction control system in conjunction with the ABS. Traction control helps the ABS improve vehicle traction by minimizing wheel slip on the drive axle during acceleration. If a wheel on the drive axle starts to slip, the traction control system automatically brakes the wheel slightly, transferring engine torque to the wheels with better traction. If all the drive wheels start to slip, the traction control system may also reduce engine power.Traction control systems are referred to by several different names, depending on the manufacturer. These include:
a. Automatic Traction Control (ATC)
b. Traction Control (TC)
c. Automatic Slip Regulation/Anti-Spin Regulation (ASR)
C. How Should I Drive an ABS-equipped Vehicle During Road Tests?
It is the consensus of brake experts that drivers should brake an ABS-equipped vehicle just as they would brake a non- ABS equipped vehicle.The proper braking technique is to maintain a steady, modulated brake application. Modulated, in this case, means applying only the pressure required to achieve the desired deceleration. Do not slam on the brakes to make speed corrections or routine stops.
When operating on slippery surfaces, with or without an ABS, it is strongly recommended that drivers depress the clutch when braking. Engine braking itself can
cause drive wheels to slip. Usually, any retarder will automatically be disabled when the ABS is in use.
Much of what is taught about hydraulic ABSs doesn't apply to air ABSs. Thus, it's important to remember the following:
Brake as if no ABS is present, with a modulated application as described previously.
Unless c ertain that the entire c ombination vehicle has a working ABS, d on't stomp on the brakes in a panic situationâ€one or more wheels could lock and cause the vehicle to jackknife. Even then, be careful because you can still jackknife or lose control if the vehicle is travelling too fast. Do not expect to feel the brake pedal pulsing or hear strange sounds when the ABS activates on air-braked vehicles. These vehicles do not transmit pulsing presure to the driver's foot and the driver probably will not hear the system cycling.
Operate mixed combination vehicles (with and without an ABS) the same way one would operate totally non- ABS combination vehicles. Apply only the brake pressure needed to achieve the desired deceleration while ensuring vehicle stability. Monitor the combination vehicle behavior and back off the brake pedal, if possible, to keep the units under control.
D. What Are the Features and Benefits of ABSs?
wheel spin during acceleration, reducing the possibility of power skids, spins or jackknifes.
Self-diagnosing system Built-in system makes maintenance checks quick and easy.
Diagnostic tool compatibility ABSs are compatible with industry standard hand-held and computer-based diagnostic tools. Blink codes and other diagnostic schemes can also be used for troubleshooting, if other tools are not available.
ABS Malfunction Indicator Lamp Informs the driver or technician that an ABS fault has occured. The warning lamp may also transmit blink code information. It does not signal all possible faults.
E. With OR Without
ABS keeps the wheels from fully locking up while braking to allow the driver to maintain steering control. There are two basic types of ABS. Rear Wheel ABS prevents only rear wheels from locking. Four Wheel ABS prevents all four wheels from locking. Without ABS, too much force applied to the brake pedal can cause a wheel to stop turning (lockup) and begin skidding, greatly reducing the capability of the driver to steer or maintain stability. With ABS, the wheels are kept rolling and the driver maintains steering control within the limits of traction. Many light trucks use rear-wheel ABS to prevent rear wheel lockup.
Rear Wheel ABS does not help steering directly during hard braking, but it helps to keep the vehicle stable and reduces fishtailing and a loss of control.
Design of ABS
An antilock brake system is designed for a specific vehicle application. A truck which does not pull a trailer, like a cement mixer, would have a slightly different ABS than a truck tractor which pulls one or more trailers. Likewise, an antilock brake system for a trailer would have a different design.
ABS for automobiles may be even more specific and may be designed for a particular
Regardless of manufacturer or the type of vehicle, all antilock brake systems operate in a similar manner. Wheel speed sensors are placed on each wheel that is to be controlled. Each speed sensor usually has a toothed wheel that rotates at the same speed as the vehicle wheel or axle. If the brakes are applied and one or more of the monitored wheels suddenly begins to reduce speed at a higher rate than the others, the controller activates the antilock system.
brand name and model of car. Since ABS components must fit and function along with existing vehicle components on each model, the design and manufacturing process of a new antilock brake system is carried out in partnership between the automobile manufacturer and the ABS supplier.
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. 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.
WHEEL SPEED SENSOR
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.
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.
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.
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
The Manufacturing Process
The manufacturing process for antilock brake systems consists of manufacturing the component parts and then installing those parts on the vehicle. The parts are built in one
plant, then packaged and shipped to a vehicle assembly plant for installation. This is a typical process for an automobile antilock brake system.
Making the master brake cylinder
Â¢ 1 The master cylinder, including the base for the solenoid body, is cast as a single unit. The seating and sealing surfaces are machined smooth and the connection ports are threaded.
Â¢ 2 The individual primary and secondary pistons, solenoid coils, reservoir caps and seals, pressure accumulator, and any metering and proportioning valves are installed. The solenoid body has a cover which attaches to the master cylinder with four or more screws and is sealed with a gasket.
Making the wheel speed sensors
Â¢ 3 The toothed wheel is cast from iron. Minor machining may be required at the mounting points.
Â¢ 4 The pick-up coils are wound around the permanent magnet core in a machine called a coil winder. The entire assembly is encased, or potted, in plastic resin with an electrical connector attached.
Making the controller
Â¢ 5 The electronic controller components are soldered to a printed circuit board.
Â¢ 6 The board is connected inside a protective housing and mounted to the cast aluminum heat sink base. Extemal electrical connections are provided for the input wiring from each speed sensor and the out-put wiring to the solenoids in the master brake cylinder.
Installing the ABS
Â¢ 7 In the automobile assembly plant, the steel tubing brake lines are installed in the framework of the body. They run from the partition between the engine compartment and the occupant compartment, called the firewall, to the vicinity of each wheel. The electrical wires for the ABS are also run from the vicinity of each wheel to the controller location and from the controller to the firewall.
Â¢ 8 The brake master cylinder is bolted to the firewall in the engine compartment near the brake pedal. The brake lines are attached to the appropriate ports on the solenoid body, and the electrical wires are connected.
Â¢ 9 The toothed sensor wheels are pressed onto the outer constant velocity joints or the ends of the axle spindles so that they ride just inside the wheels. Once the axles are attached to the frame, the brake lines are attached and the pick-up coils are installed so that the end of the coils are close to the toothed wheels. The pickÃ‚Â¬up coils are then electrically connected to the wires to the controller.
II. ABS COMPONENT DESCRIPTIONS & OPERATION
When you complete this section, you should understand the purpose and function of all major ABS parts including: the ECU, the modulator valve, the wheel speed sensor, ABS malfunction/ indicator lamp, ABS diagnostic components, and traction control. Modern antilock braking systems all feature the following major components:
Â¢ ABS Malfunction
Â¢ Electronic Control Unit (ECU)
Â¢ Modulator Valves
Â¢ Wheel Speed Sensors (pickup and exciter)
A. Electronic Control Unit (ECU)
The ECU processes all ABS information and signal functions. It receives and interprets voltage pulses generated by the sensor pickup as the exciter teeth pass by, and uses this information to determine:
Â¢ Impending wheel lock-up and
Â¢ When/how to activate the ABS modulator valves. The ECU connects to the following ABS components: wheel speed sensors, ABS modulator valves, power source, ground, warning lamps, blink code switch, J1587* diagnostic connector, and retarder control device (usually by relay or the J1922**/ J1939*** datalink.) The ECU also makes self-diagnostic checks during normal operation.During braking, the ECU uses voltage pulses from each wheel speed sensor to determine wheel speed changes. If the ECU determines that the pulse rate of the sensed wheels indicates imminent lock-up, it cycles the ABS modulator valves to modify brake air pressure as needed to provide the best braking possible.
The ECU sends signals to the ABS malfunction indicator lamp or blink code lamp to communicate ABS faults. It also sends signals to the retarder control to disengage the retarder when the ABS is working. When the ABS stops modulating the brake pressure, the ECU permits retarder use once again.
Â¢ SAE J1587, Joint SAE/TMC Recommended Practice for Electronic Data Interchange Between Microcomputer Systems in Heavy-duty Vehicle Applications. (See Glossary of
TYPICAL TRACTOR ABS SCHEMATIC
ans can communicate with the ECU through a standard SAE J1587 diagnostic connector. Technicians can read and clear fault codes stored in the ECU and run various diagnostic tests with this connector. The type of ECU used and its location (in-cab or frame) by manufacturer and application. A detailed description of all the different ECU types used today is beyond the scope of this manual. Consult either the vehicle or componentmanufacturer's service i nformation for specifics.
B. Modulator Valves
ABS modulator valves regulate the air pressure to the brakes during ABS action. When not receiving commands from the ECU, the modulator valve allows air to flow freely and has no effect on the brake pressure. The ECU commands the
modulator valve to either:
Â¢ change the air pressure to the brake chamber, or
Â¢ hold the existing pressure.
However, it cannot automatically apply the brakes, or increase the brake application pressure above the level applied by the driver.
The modulator valve typically contains two solenoids. The modulator valve and relay valve may be incorporated into a single unit. The modulator valve may also be separate, inserted into the service line to the brake chamber(s) after any relay valve, located as close as practicable to the chamber(s) itself. When the modulator valve is separate, it has to control more air flow and, therefore, includes two larger diaphragm valves which are controlled by the solenoids. It usually has three ports: the supply port, the delivery port and the exhaust port.
Â¢ The supply port receives air from a quick release or relay valve.
Â¢ The delivery port sends air to the brake chambers.
Â¢ The exhaust port vents air from the brake chamber(s).
Â¢ Typically, when an ECU controlling a separate modulator valve detects impending wheel lockup, it activates the solenoids to close the supply port and open the exhaust port. When enough air is vented to prevent wheel lockup, the exhaust valve will close and the ECU willâ€depending on the situationâ€either:
Â¢ keep the supply port closed to maintain existing pressure, or
Â¢ open the supply port to allow brake application pressure to increase and repeat the cycle.
C. Wheel Speed Sensors
The wheel speed sensor has two main components: the exciter and the pickup. Other components include associated wiring and mounting equipment.
Exciterâ€The exciter is a ring with notched teeth. The most commonly used exciter has 100 evenly spaced teeth, but the number of teeth can vary depending on the system design. Thecomponent is known by several names: sensor ring, tooth wheel, tone ring, and exciter
Pickupâ€The pickup is commonly called "the sensor." It contains a wire coil/magnet assembly,
Exciter or Tooth Wheel
which generates pulses of electricity as the teeth of the exciter pass in front of it. The ECU uses the pulses to determine wheel speeds and rates of acceleration/deceleration. The strength of these electrical pulses decreases rapidly with slight increases in the gap between the pickup and the exciter.
Wheel speed sensor location varies. It can be located anywhere on the axle to sense wheel speed. The sensor can be an assembly containing both the exciter and the pickup with a fixed gap. Or, the pickup and the exciter can be mounted separately on different parts of the axle assembly. The sensor pickup is a sealed unit and typically of elbow or straight design.
On most ABS air-braked vehicles, the pickup is located in the mounting flange on the wheel end. The exciter usually is either mounted onâ€or integrated withâ€the wheel hub. Since the output of the pickup decreases so rapidly with slight increases in exciter-pickup gap, it is imperative that the wheel end and sensor gap be maintained within the manufacturer's specification. When the wheels o f o nly o ne t andem axle have wheel speed sensors, they are usually placed on the axle whose wheels are most likely to lock-up first during braking. On a tandem with a four-spring suspension, the sensors are generally on the lead axle. On a tandem with air suspension, the sensors are generally located on the trailing axle.
ABS configuration is defined by the arrangement and number of sensors and modulator valves used. The most common configurations for power units are:
Â¢ four sensors/four modulators (4S/4M),
Â¢ six sensors/four modulators (6S/4M), and
Â¢ six sensors/six modulators (6S/6M).
Â¢ Common configurations for trailers are 2S/1M, 2S/2M, 4S/
2M and 4S/3M.
D. ABS Malfunction Indicator Lamps
Vehicles required to have an ABS must have ABS malfunction indicator lamps. These lamps must be yellow and l i ght up when the ABS h as a " ' malfunction that affects
the generation or transmission of response or control s ignals" i n the ABS. ABS malfunction indicator lamps are not required to light up for every type of malfunction. However, they are required to light up for short periods of time for a bulb check whenever the ABS starts to receive electrical power. The warning lamps for trailers and dollies are not required to light up for a bulb check unless the vehicle is stopped.
All trailers/dollies built on or after March 1, 1998 must feature an external ABS malfunction indicator lamp as part of the ABS. All new trailers must be capable of activating an in-cab trailer warning lamp beginning in March 2001. The requirement for an external trailer/dolly indicator lamp expires in March 2009.
In-cab ABS indicator lamps are typically located on the instrument panel. The exact location and appearance vary by vehicle/component manufacturer. Consult the manufacturer's service information for specifics.
E. ABS Diagnostics
Although not required by law, all air brake ABSs have selfdiagnostic capability. On ruck-tractors and single-unit or straight trucks, an ABS provides this information to technicians
through the malfunction indicator lamp and/or an electronic diagnostic tool, which plugs into an on-board diagnostic connector. The connector is typically located inside the tractor cab just underneath the left end of the instrument panel. It is usually the same c onnector that's u sed to troubleshoot el ectronic e ngines.
Truck-tractors and trucks may also use the ABS malfunction indicator lamp to signal stored fault information through a blink code. Vehicles using this system have a switch to activate the blink code system. Other ABSs may also have light-emitting diode (LED) lamps on the ECU to indicate problems. ABSs used on trailers sometimes have a place to connect an electronic diagnostic tool. The connector is either on a pigtail to the ECU, on the outside of the ECU, or inside the ECU box. Others have either LED lamps on the ECU box or number codes displayed inside the ECU which give diagnostic information.
III. ABS TROUBLESHOOTING, MAINTENANCE &
Although an ABS generally requires no routine maintenance, it should be checked periodically like other components of the air brake system. In this section, we review various aspects of ABS troubleshooting, maintenance and inspection. When you complete this section, you should understand:
Â¢ General ABS troubleshooting principles
Â¢ Special concerns about connector repairs
Â¢ ABS error detection methods
Â¢ Common ABS errors and causes
Â¢ General ABS component adjustment, installation and removal procedures
A. ABS Troubleshooting
1. General Diagnostic Principles
This section describes general principles of electrical, electronic, and air system diagnostics to provide technicians with a plan of action for ABS troubleshooting. Chart 1 on page 15 illustrates these diagnostic principles in flow chart form. The following sub-sectionsâ€based o n T he Maintenance Council's Recommended P ractice TMC RP 1406, "Basic Electrical/ Electronic D iagnostic Procedures"â€cover this process in detail.
Step 1: Verify the problem or driver concern.
Establish the connection between the symptom and the underlying cause of the problem. Use the vehicle manufacturer's recommended i nformation c ollection methods for verification.
Step 2: Perform preliminary checks.
Operational, visual and audio checks are generally easy to perform, do not require the use of special tools and may result in a quick diagnosis. This is a critical step in the diagnostic process.
CHART 1: GENERAL DIAGNOSTIC PRINCIPLES
Step 3: Refer to service information.
Vehicle manufacturers provide service procedures which must be followed to ensure proper repair. Training/service information is readily available from various sources such as:
Â¢ Service newsletters
Â¢ Service manuals
Â¢ Manufacturers' and dealers' " 'Help Line P hone Numbers"
Â¢ Troubleshooting guides
Be sure to confirm that the reference material is applicable to the specific problem or vehicle being diagnosed. Also, ensure information is current. Vehicle and supplier manufacturers' service informationâ€specifically bulletins and newslettersâ€is very effective and may help shorten diagnosis.
Step 4: Perform electrical, electronic and air system checks.
Systems checks found in service manuals provide a systematic approach to identifying the probable cause of a system fault. This step is important to properly define the correct approach for the repair and to avoid unnecessary time-consuming repairs. Additionally, systems checks will help to define what the problem is not. Systems checks may require the use of original equipment manufacturer (OEM) service tools and should isolate a particular component in the system as a probable cause.
i. Electrical diagnostic procedures
Electrical problems are a common cause of ABS faults. It is beyond the scope of this document to explain electrical diagnostic procedures for all ABSs and vehicle manufacturers ingreat detail. References for diagnosing electrical systems can be readily obtained from component, vehicle, and test equipment manufacturers.
ii. Electronic diagnostic procedures
To diagnose an electronic system properly, specialized test equipment approved by the electronic system manufacturer may be required. Failure to use the correct diagnostic tool may result in inaccurate or incomplete diagnosis or cause ECU damage.
iii. Air system diagnostics
It is beyond the scope of this document to explain air system diagnostic procedures in great detail. However, several TMC Recommended Practicesâ€such as RP 619, " 'Air S ystem Inspection P rocedure"â€are a good source of general information on this topic. Other references for diagnosing air brake systems can be readily obtained from component, vehicle, and test equipment manufacturers.
If a suspect part can be easily installed and removed, remove and temporarily replace it with a known good part to see if the problem remains. If the problem disappears, reinstall the suspect component to see if the problem returns. If so, replace the suspect component.
Step 5: Find and isolate problem
For an active problem, the diagnosis should narrow and/or eliminate possible causes. Find and isolate the faulty part of the system or circuit by breaking the problem into smaller pieces. For an intermittent problem, attempt to simulate/recreate the conditions where the fault would exist. Monitor suspect circuits and components to pinpoint the probable cause while the problem is occurring.
Step 5a : Reexamine complaint
Review all information describing the complaint. When did the problem occur? What conditions are present when the symptom occurs? contact the driver, if necessary, to gather more information or to arrange a " ' show me" or te st rive interview.
Step 6: Repair and verify
Once the suspect component is found, carefully disconnect the old component and inspect its connections to the harness. If the component connections are OK, temporarily connect a known good component (without installing) to ensure the problem is corrected.
After the problem is corrected with the known good component, reconnect the suspect component to make sure the problem returns. Temporarily connecting a known good component, and then reconnecting the suspect component, will help reduce replacement of incorrect components. If reconnecting the suspect component does not cause the problem to recur, thoroughly inspect the connectors and harnessing for the cause of the problem. Reconnect the suspect component and move (jiggle) the harness while monitoring for the problem to return. If the problem returns with the connection of the suspect component, permanently install the new component.
Step 7: Clear fault codes.
Clear any codes stored in the ECU identifying the problem. Step 8: Implement any possible preventive measures.
Review the vehicle maintenance schedule for required service intervals and perform necessary maintenance. Check for other areas of apparent concern and notify the fleet Manager or fixâ€prior to release of vehicle.
2. Notes on Electrical/Electronic Connections
a. Wiring Termination Techniques
Termination is the process of either ending a wire or attaching a device to be used at the end of a wire. Wiring terminations are made in a variety of ways. Wires can be terminated with butt splices, the application of a terminal, and by simply "tinning" or sealing the wire's end. The primary considerations during a termination are mechanical strength, vibration resistance, electrical integrity, and environmental protection.
Â¢ Mechanical Strengthâ€Whenever a wire is terminated, the mechanical strength of the termination should meet or exceed the mechanical strength of the conductor without the termination.
Â¢ Vibration Protectionâ€Always place conductors back in any holding device that they were in prior to the modification/repair or attach the conductors to the vehicle in a manner which will prevent the conductor from vibrating during operation.
Â¢ Electrical Integrityâ€The termination must be able to fulfill the electrical needs of the circuit (for example, current-carrying capability, minimal voltage drop).
Whenever a termination or splice is made in a conductor, an inherent voltage drop will be present. Special connectors are available to minimize the voltage drop, but these connectors normally are cost prohibitive. Terminations made carefully normally provide an acceptable voltage drop.
Â¢ Environmental Protectionâ€Whenever a termination is made in a conductor which disturbs the integrity of the insulation on the conductor, measures must be taken to ensure that the termination is not susceptible to moisture damage or other damage which may result from the conductor or termination being exposed to its normal operating environment. Additionally, consideration must be given to the type of insulating material being used to ensure that it has an acceptable heat range and is compatible with the intended environment.
Â¢ Electromagnetic/Radio Frequency Interference Protectionâ€The ECU contains components that can detect radio waves and other electromagnetic "noise" and unintenionally send false signals because of them. To prevent radio frequency interference (RFI) and electromagnetic interference (EMI), ABS cables contain special shielding. When making repairs, take care to ensure the integrity of the shielding is not compromised. For terminations that are made to a threaded stud which is exposed to salt spray or other corrosive environments, a suitable coating material should be applied to the connection to ensure adequate service life.
Conventional Terminationsâ€Conventional terminations are terminations made using commercially available terminals such as ring terminals, spade terminals, etc. Terminals of this type are available through many different outlets.
Selection of good quality terminals is crucial to making a dependable connection. The selection should include the considerations mentioned in "Wiring Termination Techniques," as well as specific considerations about the location of the termination on the vehicle (for example, heat exposure). Some fleets have established specific methods for making terminations. These methods were developed to ensure consistent terminations which will yield an acceptable service life. These recommendations should be followed when applicable.
Proprietary Terminationsâ€Proprietary terminations are terminations made using proprietary terminals and connector nbodies. These terminations are very common on commercial vehicles and come in a variety of configurations. Multiple connections in one connector body are typical. Also, various types of proprietary terminations on the same vehicle are common. When repairing or replacing these terminations, special techniques are needed. These techniques include tools, special assembly methods and, many times, special training.
When servicing special connectors, use of OEM recommended tools is critical to making a good termination. Repair or replacement of these special terminations should no be attempted without the specific tools recommended. Manufacturers' service manuals and bulletins typically detail the techniques to be used for proper repair.
Butt Splicesâ€A butt splice i s any splice where wires are j oined together " ' end-to-end." In this case, the wires may be either twisted together and soldered, or crimped together using a commercially available terminal. Butt splices should always be covered with insulation and heat shrink tubing which has a meltable inner liner or another suitable protective insulation. The use of pressure sensitive tape is not recommended as the tape will likely deteriorate with time.
Conductor Terminationsâ€Terminations of conductors are made to attach the conductor to another conductor or to a device on the vehicle. These terminations must be carefull made in order to provide acceptable serviceability. Attaching a wire to another wire is an example of a conductor termination.
Terminations Without Terminalsâ€Occasionally a wire is terminated without a terminal to facilitate the attachment of the wire to an accessory. If this situation is unavoidable, the wire should be "tinned" to prevent fraying and breakage at the point of connection. Using a heat shrink process at the end of the wire is also acceptable.
b. Grounding Recommendations
Grounding problems occur in a variety of ways (such as corrosion or inadequate current-carrying capacity). As a result, grounding terminations should be coated with a suitable material to prevent corrosion as a result of exposure to salt spray or other corrosive environments.Whenever an additional grounding point is to be established on the vehicle, consult the vehicle manufacturer to ensure that the planned alteration does not result in an inadequate ground path for other components on the vehicle. This is especially important when establishing a grounding point between chassis and body.
c. Wiring Damage Caused During Repair
Mechanical damage to wiring must be avoided during vehicle repair. Insulation cuts and "pinchpoints" are common problems which may cause failure. Conductor insulation should not be pierced while troubleshooting electrical problems. Piercing of the protective covering results in corrosion which can cause circuit failure. If piercing of the insulation is unavoidable, suitable insulation to avoid water entry must be used at the point where the conductor was pierced.
d. Vehicle Repairsâ€Special Care
Many times vehicle repairs include welding operations. All welding on a vehicle should be done using methods and techniques which are acceptable to the OEM in order to avoid damage to the electrical and electronic system of the vehicle. This damage normally occurs due to unwanted circuit paths or to voltage spikes created in the electrical and electronic systems which cause component failure.
3. Error Detection Methods
One ABS benefit is the ability to electronically detect component or system failures. This electronic detection occurs either during self-test checks at start-up, or during continuous passive monitoring.
At start-up, the ECU will activate the ABS malfunction indicator lamp and briefly energize the ABS modulator valves (ignition-on blow down or "chuff test"). At the same time, the ECU checks the wheel speed sensors and other essential components for proper operation. If no problems are found, and the ECU detects that wheel speed sensors were functioning properly just prior to the last vehicle shutdown, the ABS malfunction indicator lamp will go out. On earlier systems, the lamp would not go out until the vehicle reached about 5 mph.
During vehicle operation, the various ABS components also continually monitor each other for failures and "out-of-range" operating parameters. Through this process, the ECU detects abnormalities during operation and activates the ABS malfunction indicator lamp as appropriate.
The ECU will generally detect two types of faults: active and stored. An active fault is a current and continuous failure in need of repair (such as a broken connector). A stored fault is a failure that affects ABS operation intermittently (such as a loose connector). Technicians typically can retrieve failure information either through blink codes or an electronic diagnostic tool. For explanations of manufacturer-specific diagnostic and troubleshooting tools and procedures, consult the appropriate manufacturer's service information.
Top 10 Most Commonly Encountered Problems That Trigger ABS Malfunction Indicator Lamps
o Abraded or cut wires in convuluted tubing near frame clamps. o Cut or corroded wires near sharp frame members and frame-mounted modulators.
o Wire jacket worn through from overlapping sensor and modulator wires near frame members and frame-mounted modulators
o Corroded connectors and connections not properly sealed or damaged seals.
o Damaged connector latches or connectors not completely sealed to mating assemblies.
o Terminals not completely latched or seated into connectors o Excessive sensor air gap, sensor clip tension or excessive wheel bearing endplay.
o Damage to exposed wires exiting or entering wire tubing. o Worn, chipped or damaged sensor or modulator. o Non-functioning controller (ECU).
CHART 3: SAMPLE ABS MALFUNCTION INDICATOR DIAGNOSTIC FLOW
TABLE 2: COMMON ABS ERRORS AND RESPONSES
DETECTED ERROR SYSTEM RESPONSE
Component or wiring failure ABS malfunction indicator lamp informs driver of fault. Affected wheel(s) is removed from ABS control and switched to normal braking. The remaining ABS valves may continue providing braking control at the wheels. The error is recorded as a fault code and stored in the ECU. The information can be recalled by the technician through the blink code lamp or an electronic diagnostic tool.
Power supply to ECU is interrupted or ABS connector not plugged in. All antilock and traction control systems would be inoperative. Normal, non-ABS controlled braking would be available at all wheels. ABS malfunction indicator lamp indicates system fault.
Individual electronic component fails internally in ECU. All or part of the ABS is shut off and that part of the vehicle reverts to normal, non-ABS braking. ABS malfunction indicator lamp indicates system fault.
Error not detected. ABS remains inoperative but warning light remains off Certain failures, mainly mechanical, can occur and cause the ABS to malfunction but not illuminate the indicator lamp. Depending on the fault, the ABS will be inoperable on one or more axles. In the rare event a valve hangs open, system air could be lost, impairing all braking.
4. Causes of Common ABS Sensor Problems
TABLE 3: COMMON ABS SENSOR PROBLEMS AND CAUSES
Sensor signal is erratic. Damaged tooth wheel, excessive hub runout, and/or sensor gap is too wide. Replace as needed. Check sensor adjustment, resistance. Check wheel bearing adjustment.
Open sensor circuit. Damaged sensor, cable or loose cable connections. Replace as needed.
Shorted sensor circuit. Damaged sensor, cable or cable connections. Replace as needed.
One sensor is not producing a signal when other sensors are producing signals, and sensor resistance is within specification. Improper air gap at non-producing sensor. Gaps should not exceed 2 mm (0.080 in.). Check sensor adjustment. Check wheel bearing adjustment.
ABS malfunction indicator lamp does not go out when vehicle reaches speed needed for minimum or " 'threshold" voltage (such as five mph.) All of the items listed above could be causes. Also, no tooth wheel or sensor installed. Install tooth wheel and sensor.
Sensor cap and cables lose elasticity, swell, or become mechanically sensitiv Corrosion of bushing, sensor, and/or sensor clip. Make any necessary replacements. C heck manufacturer's recommendations for proper lubricant.
Even if the space between the teeth of the exciter ring is full of dust and particles from the brake linings, the monitoring operation is not affected. In fact, the magnetic property of the dirt in the gaps is similar to that of air. The change in the magnetic field is determined by the spacing of the teeth of the exciter ring. The output voltage is unaffected by dirt. Therefore, an ABS fault cannot be remedied by cleaning the tooth wheel with compressed air. Dirt in the gaps doesn't affect voltage output, so removing it will not remedy an ABS fault.
B. ABS Maintenance and Inspection
1. ABS Sensor Pickup Adjustment
CAUTION: Follow all recommended safety warnings and cautions. To prevent eye
injury, always wear safe eye protection when performing maintenance or service. Do not work under a vehicle supported only by jacks. Jacks can slip or fall over and cause serious personal injury.
To adjust the ABS sensor pickup, gently push the sensor pickup in until it contacts the tooth wheel:
Â¢ On the steering axle, the sensor pickup may be Typical Senior Assembly accessible on the in-board side of the steering knuckle.* On the drive axle, the wheel and drum assembly must be pulled to gain access to the pickup. Prior to pulling the wheel and drum assembly, observe the output voltage of the pickup while rotating the wheel by hand. The amount of output voltage is dependent upon the sensor pickup gap and wheel speed. Refer to the manufacturer's recommendations for proper voltage levels.
2. ABS Sensor Pickup Removal & Installation
The following installation and removal procedure is a guideline only. When removing or installing a sensor pickup on your system, always follow the procedures detailed in the manufacturer's maintenance manual.
3. Sensor Pickup Removalâ€Front Axle
To remove the sensor pickup from the front axle:
1. Put wheel chocks under the rear tires to keep the vehicle from moving. Apply the parking brake.
2. Remove the pickup and spring clip from the steering knuckle. Use a twisting motion if necessary. Never pull or tug on the cable.
3. Disconnect the pickup cable from the chassis harness. Be careful not to criss-cross wiring.
4. Sensor Pickup Installationâ€Front Axle
To replace the sensor pickup in the front axle:
1. Connect the sensor cable to the chassis harness. Be careful not to criss-cross wiring.
2. Install the fasteners used to hold the sensor pickup cable in place.
3. Apply lubricant to the sensor spring clip and to the body of the pickup. NOTE: Use a mineral oil-based lubricant that contains molybdenum disulfide. The lubricant should have excellent anti corrosion and adhesion characteristics, and be capable of continuously functioning in a temperature range of -40Ã‚Â° to 300Ã‚Â°F (-40Ã‚Â°- 150Ã‚Â° C).
4. Clean and inspect the hole in the steering knuckle. Install the sensor pickup spring clip. Make sure the flange stops are on the inboard side of the vehicle.
5. Push the sensor spring clip into the bushing in the steering knuckle until the clip stops.
6. Push the sensor pickup completely into the sensor spring clip until it contacts the tooth wheel/exciter.
7. Install fasteners and straps to retain the pickup wiring.
8. Remove the wheel chocks.
5. Sensor Pickup Removalâ€Rear Axle
1. Put chocks under the front tires to keep the vehicle from moving.
2. Raise the rear tire off the ground. Put safety stands under the axle.
3. Release the parking brake and back off the slack adjuster to release the brake shoes.
4. Remove the wheel and tire assembly from the axle.
5. Remove the brake drum.
6. Remove the pickup from the mounting block in the axle housing. Use a twisting motion if necessary. Never pull or tug on the cable.
7. Remove the sensor spring clip from the mounting block.
8. Disconnect the fasteners that hold the sensor cable and the hose clamp to the other components.
9. Disconnect the pickup cable from the chassis harness.
6. Sensor Pickup Installationâ€Rear Axle
To reinstall the sensor pickup in the rear axle:
o Apply lubricant to the sensor spring clip and to the body of the pickup. Follow manufacturer's recommended lube specification ( See lubricant recommendation in previous s ection " ' S ensor Pickup Installationâ€Front Axle").
o Clean and inspect the hole in the mounting block. Install the sensor spring clip. Make sure the flange stops on the inboard side of the vehicle.
o Push the sensor spring clip into the mounting block until it stops.
o Push the pickup completely into the sensor spring clip until it contacts the tooth wheel. See figure at left.
o Insert the pickup cable through the hole in the spider and axle housing flange. Route the cable to the frame rail. Be sure to route the cable in a way that will prevent pinching or chafing, and will allow sufficient movement for suspension travel.
o Connect the pickup cable to the chassis harness.
o Install the fasteners that hold the pickup cable in place.
o Install the brake drum on the wheel hub.
7. Proper ABS Sensor Resistance
For most common types of ABS sensors, the sensor circuit resistance is between 700Ã‚Â¬3000 ohms. Resistance can be measured at the sensor connection when it is removed from the ECU, or right at the sensor when the extension cable is removed. Follow the manufacturer's specifications to determine the corect sensor resistance.
8. Modulator Valve/Routine Inspection
As part of a routine vehicle preventive maintenance program, ABS modulator valves should be checked for proper operation and condition. This inspection generally should include:
o Removal of contaminates and a visual inspection for excessive corrosion
and physical damage. o Inspection of all air lines and wiring harnesses for signs of wear or
o Testing for leakage and proper operation. For specific modulator valve inspection and testing procedures, consult the manufacturer's s ervice information.
9. Modulator Valve Removal and Installation
The following removal and installation information is offered as a guideline only. Always refer to the manufacturer's specific instructions when removing or instaling ABS modulator valves.
o Disconnect the harness connector from the modulator valve. Be careful
not to criss-cross wiring. o Disconnect the air supply and air delivery lines from their respective ports. o Remove modulator valve mounting fasteners. o Remove the modulator valve.
o Install the modulator valve with appropriate mounting fasteners. Tighten
to specified torque. o Connect the air supply and air delivery lines at their respective ports. o Connect the harness connector to the modulator valve. Be careful not to
o Check installation by applying the brakes, listening for\ leaks at the modulator valve.
o Turn the ignition on, and listen for the modulator valve to cycle. If the valve fails to cycle, check the electrical connection and any stored or active fault Â¢ codes. Drive the vehicle to verify that the ABS and its malfunction lamp operate properly.
10. Proper ABS
For most ABS modulator valves, the resistance range between each valve solenoid coil terminal and the ground on the ABS valve connector is between 3-10 ohms. To test this resistance, disconnect the wiring connector from the modulator and test the resistance between the two pins of each solenoid. Follow the manufacturer's i nstructions for d etermining valve resistance.
IV. ABS SPEC'ING CONSIDERATIONS
The F ederal Government's requirement for full-time electrical power to ABSs has prompted both equipment users and manufacturers to reconsider the way trailers are supplied with such power. Since a particular powering configuration is not required in the ABS rule, manufacturers and equipment users can decide for themselves how to achieve the full-time power requirement.
There are several different methods of supplying full time power to the trailer ABS:
Â¢ If the auxiliary circuit of the s even-pin connector is not in use, it can be used to supply full-time p ower as long as the circuit i s always " 'on" or " 'hot" when the key switch is "on." NOTE: Unless otherwise specified, many manufacturers wiil supply a "hot" auxiliary circuit as standard equipment. It is very important that vehicles use this option if they are commonly coupled to vehicles in other fleets.
Â¢ A second connector can be used specificaly to power the trailer ABS.
Â¢ A special connector which is compatible with the existing seven-pin connector can be used if it can accommodate additional circuits (for example, a 13-pin connector).
Each of these methods has certain advantages and m drawbacks. However, it is the consensus of the members of The Maintenance Council that the existing seven-pin connector design should be preserved if possible for important reasons of compatibility, safety, and maintainability.
Another important consideration is ensuring that adequate power is available for proper ABS function. Voltage drops between the battery and the last unit of a combination vehicle can impact the amount of power available for the ABS, especially in doubles and triples combinations.
For these reasons, TMC developed two recommended practices to promote power supply and connector standardizationâ€TMC RP 1 37, " ' Antilock Electrical Supply From Tractors Through the SAE J560 Seven-pin Connector," and TMC RP 1 41, "Trailer ABS Power Supply Requirements."
To ensure adequate power is provided to the trailer from the tractor, TMC RP 137 recommends that at least 12.5 volts be available at the J560 connector with a 10-amp load on both the stop lamp and auxiliary circuit. Industry consensus is that meeting this
minimum recommendation will ensure adequate power for trailer ABSs.
V. GLOSSARY OF ABS TERMS
The following terms are used by one or more manufacturers to describe different aspects
Â¢ Antilock Braking System (ABS): A system that monitors and controls wheel speed during braking so as to minimize wheel lockup while maximizing vehicle lateral stability. Plural formâ€ABSs.
Â¢ ABS Configuration: The arrangement of antilock braking system components, which varies by the number of sensors and modulator valves used. The following configurations for tractors are commonplace: 4S/4M, 6S/4M, and 6S/6M. For trailers, 2S/1M., 2S/2M, 4S/2M and 4S/3M. (S=sensor. M=modulator.)
Â¢ ABS Inline Valve: A modulator valve located in the service brake delivery line near the wheel's brake chamber which modifies brake pressure during an ABS event. Also see ABS Modulator Valve or ABS Relay Valve.
ABS Modulator Valve; An electro-pneumatic control valve that contains the solenoids used to precisely modulate brake air pressure during an ABS event. Also see ABS Inline Valve or ABS Relay Valve.
Â¢ ABS Relay Valve A valve that performs the service relay function as well as the ABS modulator valve function to modify brake air pressure during an ABS event. Also see ABS Modulator Valve or ABS Inline Valve Anti-Spin Regulation (ASR) See Traction Control.
Â¢ Axle Control That mode of ABS control whereby one modulator controls the air pressure to the brake chambers on both ends of a given axle. Also referred to as axle-by-axle control.
Â¢ Bracket Mounting The means of installing the ABS modulator-controller on the host vehicle by using a supplied, pre-formed bracket.
Â¢ Brake Proportioning The limiting of brake air pressure to a specific axle or tandem to compensate for varying vehicle loading. Brake proportioning is most beneficial during bobtail tractor operation.
Â¢ Braked Wheel Behavior The study of wheel reactions during braking, particularly between the road surface and the tire. Category (I, II, & III) A means of categorizing ABS performance used in Europe.
Â¢ Chamber Pressure The air pressure in the brake chambers during a brake application.
Â¢ Channel The electrical connection between the ECU and the modulator. The term is also used to describe the number of individual modulators in a particular antilock system. Chuff Test Also called ignition blowdown test. A testâ€ designed to simplify diagnosticsâ€used to exercise the ABS modulator(s) upon initial power-up. The " 'chuff sound i s made by air e scaping from rapid exercising of the exhaust solenoid (and supply solenoid) on each modulator.
Â¢ Coefficient of Friction A measure of the friction (such as between a tire and the road surface) available to use as surface retardation. The ratio is defined a s " 'Force Required to Overcome Friction/Weight" and is denoted by the Greek letter m. See also " 'Mu."
Â¢ Control Algorithm The specific configuration of logical decisions implemented to determine the characteristics of an ABS cycle. Apply, release, hold, etc., determinations are made in the control algorithm, which is implemented in the ABS software contained in the electronic control unit (ECU).
Â¢ Control Pressure The air pressure applied from the foot/hand valve which controls the brake applicati
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ANTI-LOCK BRAKES (4).ppt (Size: 728.5 KB / Downloads: 66)
ABS, (Anti-Lock brake system)
ABS allows the driver to maintain steering control of the vehicle while in hard braking situations .
Computerized ABS is designed to keep the wheels from locking as the brakes are applied.
A locked wheel provides very little or no directional control
The following slides show the common ABS components.
Some components are part of both the conventional and ABS system.
When operating a vehicle with ABS never pump the brakes.
Doing so will make the ABS system ineffective.
Always apply firm pressure
Drivers may experience a pulsation in the brake pedal, or pedal kick back during an ABS stop. This is normal and not to be confused with a conventional brake pedal pulsation
Major components of the anti-lock brake system consist of a
Brake control module,
Solenoid valve assembly,
Wiring, and the amber ABS brake warning light.
Brake Control Module:
The brake control module is a compute that receives information from the speed sensor and compares it to the speed of other wheels.
When one wheel is approaching lock-up pressure can be vented allowing the wheel nearing lock-up to speed up.
If a wheel is to fast pressure can be increased to slow down the wheel.
If both wheel are approximately the same speed the brake control module can enter a pressure hold mode of operation.
Solenoid Valve Assembly:
Is a pair of valves that can:
A. Increase pressure
B. Hold pressure steady
C. Decrease pressure
ABS system can maintain extremely high static pressure and must be disabled before attempting repairs.
Normally pumping brake 20-30 times will release pressure.
ABS brake system are
An integrated system has the master cylinder and control valve assembly made together.
A nonintegrated has the master cylinder and control valve assembly made separate.
ABS operates using the same hydraulic principal as conventional brakes.
ABS system only operates when wheel lock-up is emanate.
A bussing noise and bakes pedal vibration is normal during ABS operation.
To determine if wheel lock-up is about to occur vehicles a wheel speed sensor
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Joined: Aug 2012
18-08-2012, 10:24 AM
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