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AYOB AGHAZI 4848
15/11/12

Anti-Lock Brake System (ABS) & CAN

ANTI-LOCK BREAKING SYSTEM (ABS)

Theory:

Anti-lock Braking system (ABS) is a very important feature in modern vehicles. During sudden braking it allows for better control, steer-ability, and stability while stopping vehicle in the shortest distance and time. (Note ABS only kicks in when brakes are fully applied)

Types of ABS: There are 3 types

• 1 Channel
• 3 Channel
• 4 Channel

There are two main types of wheel sensors on modern vehicles and they are

1. Magnetic inductive pick up type (Analogue signal)
2. Hall Effect which sends an On/Off digital signal

On the graph below is an example of a hall effect type sensor that switches 5V every 2 seconds.

Below is an example of an analogue signal with a frequency of 0.5Hz and a maximum of 3volts

­Stopping a car in a hurry on a slippery road can be very challenging. 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.
In this article, the last in a six-part series on brakes, we'll learn all about anti-lock braking systems -- why you need them, what's in them, how they work, some of the common types and some associated problems

Anti-lock brake pump and

The ABS System

The theory behind anti-lock brakes is simple. A skidding wheel (where the tire contact patch is sliding relative to the road) has less traction than a non-skidding wheel. If you have been stuck on ice, you know that if your wheels are spinning you have no traction. This is because the contact patch is sliding relative to the ic. By keeping the wheels from skidding while you slow down, anti-lock brakes benefit you in two ways: You'll stop faster, and you'll be able to steer while you stop.
There are four main components to an ABS system:

• Speed sensors
• Pump
• Valves
• Controller

­Speed Sensors

The anti-lock braking system needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential. provide this information.

Valves

There is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:

• In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
• In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
• In position three, the valve releases some of the pressure from the brake.

Pump

Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.

Controller

The controller is a computer in the car. It watches the speed sensors and controls the valves.

ABS at Work

There are many different variations and control algorithms for ABS systems. We will discuss how one of the simpler systems works.
The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second.

Anti-Lock Brake Types

­Anti-lock braking systems use different schemes depending on the type of brakes in use. We will refer to them by the number of channels -- that is, how many valves that are individually controlled -- and the number of speed sensors.

­Four-channel, four-sensor ABS

This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

Three-channel, three-sensor ABS

This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
This sys­tem provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.

One-channel, one-sensor ABS

This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.
This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.

DO I pump the brake pedal when stopping in slippery conditions?

You absolutely should not pump the brake pedal in a car with ABS. Pumping the brakes ­is a technique that is sometimes used in slippery conditions to allow the wheels to unlock so that the vehicle stays somewhat straight during a stop. In a car with ABS the wheels should never lock in the first place, so pumping the brakes will just make you take longer to stop.
In an emergency stop in a car with ABS, you should apply the brake pedal firmly and hold it while the ABS does all the work. You will feel a pulsing in the pedal that may be quite violent, but this is normal so don't let off the brake.

­Anti-lock brake components

Anti-Lock Brake Diagram

Now let's put the parts together to see how anti-lock brakes work as a whole. This diagram provides both a closeup view and an example of where the brakes are located in your vehicle.
­For more information on anti-lock brakes and related topics, check out the links on the next page

Is anti-lock brakes really work?

Anti-lock brakes really do help you stop better. They prevent wheels from locking up and provide the shortest stopping distance on slippery surfaces. But do they really prevent accidents? This is the true measure of the effectiveness of ABS systems.
The Insurance compony for in united state(IIHS) has conducted several studies trying to determine if cars equipped with ABS are ­involved in more or fewer fatal accidents. It turns out that in a 1996 study, vehicles equipped with ABS were overall no less likely to be involved in fatal accidents than vehicles without. The study actually stated that although cars with ABS were less likely to be involved in accidents fatal to the occupants of other cars, they are more likely to be involved in accidents fatal to the occupants of the ABS car, especially single-vehicle accidents.
There is much speculation about the reason for this. Some people think that drivers of ABS-equipped cars use the ABS incorrectly, either by pumping the brakes or by releasing the brakes when they feel the system pulsing. Some people think that since ABS allows you to steer during a panic stop, more people run off the road and crash.
Some more recent information may indicate that the accident rate for ABS cars is improving, but there is still no evidence to show that ABS improves overall safety this is one type sensor.

 

 

 

 

Anti-Lock Brake Types

­Anti-lock braking systems use different schemes depending on the type of brakes in use. We will refer to them by the number of channels -- that is, how many valves that are individually controlled -- and the number of speed sensors.

­Four-channel, four-sensor ABS

This is the best scheme. There is a speed sensor on all four wheels and a separate valve for all four wheels. With this setup, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

Three-channel, three-sensor ABS

This scheme, commonly found on pickup trucks with four-wheel ABS, has a speed sensor and a valve for each of the front wheels, with one valve and one sensor for both rear wheels. The speed sensor for the rear wheels is located in the rear axle.
This sys­tem provides individual control of the front wheels, so they can both achieve maximum braking force. The rear wheels, however, are monitored together; they both have to start to lock up before the ABS will activate on the rear. With this system, it is possible that one of the rear wheels will lock during a stop, reducing brake effectiveness.

One-channel, one-sensor ABS

This system is commonly found on pickup trucks with rear-wheel ABS. It has one valve, which controls both rear wheels, and one speed sensor, located in the rear axle.
This system operates the same as the rear end of a three-channel system. The rear wheels are monitored together and they both have to start to lock up before the ABS kicks in. In this system it is also possible that one of the rear wheels will lock, reducing brake effectiveness.
This system is easy to identify. Usually there will be one brake line going through a T-fitting to both rear wheels. You can locate the speed sensor by looking for an electrical connection near the differential on the rear-axle housing.

Should I pump the brake pedal when stopping in slippery conditions?

You absolutely should not pump the brake pedal in a car with ABS. Pumping the brakes ­is a technique that is sometimes used in slippery conditions to allow the wheels to unlock so that the vehicle stays somewhat straight during a stop. In a car with ABS the wheels should never lock in the first place, so pumping the brakes will just make you take longer to stop.
In an emergency stop in a car with ABS, you should apply the brake pedal firmly and hold it while the ABS does all the work. You will feel a pulsing in the pedal that may be quite violent, but this is normal so don't let off the brake.

Do anti-lock brakes really work?

Anti-lock brakes really do help you stop better. They prevent wheels from locking up and provide the shortest stopping distance on slippery surfaces. But do they really prevent accidents? This is the true measure of the effectiveness of ABS systems.
The Insurance Institute for Highway Safety (IIHS) has conducted several studies trying to determine if cars equipped with ABS are ­involved in more or fewer fatal accidents. It turns out that in a 1996 study, vehicles equipped with ABS were overall no less likely to be involved in fatal accidents than vehicles without. The study actually stated that although cars with ABS were less likely to be involved in accidents fatal to the occupants of other cars, they are more likely to be involved in accidents fatal to the occupants of the ABS car, especially single-vehicle accidents.
There is much speculation about the reason for this. Some people think that drivers of ABS-equipped cars use the ABS incorrectly, either by pumping the brakes or by releasing the brakes when they feel the system pulsing. Some people think that since ABS allows you to steer during a panic stop, more people run off the road and crash.
Some more recent information may indicate that the accident rate for ABS cars is improving, but there is still no evidence to show that ABS improves overall safety
Reference-
google
ayob aghazi

controlled area net work can systems  The CAN Bus is an automotive bus developed by Robert Bosch, which has quickly gained acceptance into the automotive and aerospace industries. CAN is a serial bus protocol to connect individual systems and sensors as an alternative to conventional multi-wire looms. It allows automotive components to communicate on a single or dual-wire networked data bus up to 1Mbps.

Before CAN Bus Since the early 1940's, automakers have continually improved their vehicles' technology by integrating an increasing amount of electronic components. As technology progressed, the vehicles became more complex as electronic components replaced mechanical systems and provided additional comforts, convenience, and safety features. Up until the release of CAN Bus, vehicles contained enormous amounts of wiring which was necessary to interconnect all of the various electronic components. Due to the vast amount of wiring, an after market installation requires the installer not only to understand how the integrated systems communicate with each other, but also requires numerous connections to be made throughout the vehicle. To make matters worse, the vehicle wiring differs between vehicle years, makes, and even models. As a result, installers need to be highly knowledgeable and perform intensive labor for the most trivial after market equipment or the installation shop experiences countless hours of lost time on troubleshooting and sometimes even expensive claims for damaged OEM equipment. During this progression, installation shops have had an increasingly difficult time finding qualified staff that are able to perform everyday installations and as a result, have either had to increase their prices to compensate for the required specialization and labor, or simply had to turn away the customers who owned complex vehicles. Introducing CAN Bus The BMW 850 coupe was the first CAN Bus vehicle to enter the market in 1986. By reducing the vehicles wiring by 2km, the vehicles overall weight was significantly reduced by at least 50kg and using only half the connectors. For the first time, each of the vehicles systems and sensors were able to communicate at very high speeds (25kbps - 1Mbps) on a single or dual-wire communication line as opposed to the previous multi-wire looms. However, the introduction of CAN Bus also increased the vehicles complexity and made after market installations even more difficult and in many cases impossible to perform. In 2006, over 70% of all automobiles sold in North America will utilize CAN Bus technology. Beginning in 2008, the Society of Automotive Engineers (SAE) requires 100% of the vehicles sold in the USA to use the CAN Bus communication protocol while the European Union has similar laws. Several new after market devices have been introduced into the market that utilize the CAN Bus protocol but until now, there have been no new devices that assist the aging after market remote starter and alarm system technology. Now there is an after market module that offers remote starter and alarm connectivity to the CAN Bus communication protocol. The CAN SL is the first after market CAN Bus bypass kit to offer connectivity of aging remote starters and alarms to the new high speed CAN Bus communication protocol.   Modern vehicles are equiped with communication network system whereby various modules communicate with each other by way data bus system to monitor and control vehivle functions. All the communications is done in real time. CAN systen is a more efficient and less expensive (less wires) and has cut down the number of wiring looms used in modern vehicles. Waveform showing CAN High & CAN Low signal The two wave forms are mirror images of each other and their base voltages are 2.1V for CAN Low and CAN High 2.6V CAN High Yellow colour Can Low Blue colour CAN High speed (high priority) actuates such things as: ABS TPS ECT Brake switch light Traction control CAN Low speed (low priority) actuates things such as: Wiper motor Alarm Central locking power windows De-fog switch refrence. google and me