ABS Questions, Diagram & Components

ABS Questions

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. 

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.

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.

Anti-lock brake components

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.

Types, Advantages and Disadvantages of ABS

Types of Anti-Lock Brake System

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 probably the best ABS. There is a speed sensor on each of the four wheels and a separate valve for each wheel. With this system, the controller monitors each wheel individually to make sure it is achieving maximum braking force.

Three-channel, three-sensor ABS

This system is mostly found on pickup trucks with four-wheel ABS. It 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 are monitored together. 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. 

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.­

What are the advantages of ABS braking systems compared to other hydraulic braking systems?

• The advantages of ABS brakes (anti-lock braking system), are just as the meaning of their acronym implies, they eliminate or greatly reduce the possibility of brake lock up and therefore provide a better chance of steering out of trouble. 
• ABS brakes were designed to combat the problem of tire lock up and uncontrolled spins. Since brakes are most effective at slowing the car at a point just before wheel lock up, a system that provides for wheel braking while preventing wheel lock up is very desirable. 
• Use of ABS is simple you mash the brake pedal and the computer takes over. No matter what the surface, ABS adapts to it. Even professional race car drivers can not adapt as quickly as a computer to changing surfaces. Most of those who live in the snowier regions know what patchy snow can be like.
• Steer ability of the vehicle is very well maintained.

What are the disadvantages of ABS braking system?

Stop Times - Anti-lock brakes are made to provide for surer braking in slippery conditions. However, some drivers report that they find the stopping distances for regular conditions are lengthened by their ABS system, either because there may be errors in the system, or because the clunking or noise of the ABS may contribute to the driver not braking at the same rate.

Delicate Systems - It's easy to cause a problem in an ABS system by messing around with the brakes. Problems include disorientation of the ABS system, where a compensating brake sensor causes the vehicle to shudder, make loud noise or generally brake worse.

Cost - ABS systems require significantly more parts than a traditional braking system, meaning there are more opportunities for damage to occur. With regular maintenance and care, repair costs may be kept to a minimum, but if left alone for a significant amount of time, small problems can become larger and more expensive to fix. It is especially important to regularly check brake fluid and pads to reduce potential problems. Preventative maintenance is key to avoiding expensive repairs.

System damage - A variety of factors can cause the system to be less effective, and can present with everything from shuddering of the vehicle to loud noises while trying to stop. Diagnosing potential problems are also more difficult, a factor which can cause larger repair bills. Additionally, some electronics or other pieces may require the assistance of a specialist; making do-it-yourself repairs less likely. If one or more pieces fail, it may require a complete overhaul, which can quickly become a pricey prospect.

ABS Design and Advanced Application on ABS

Design

An anti-lock 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 anti-lock 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 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 anti-lock brake system is carried out in partnership between the automobile manufacturer and the ABS supplier.

Regardless of manufacturer or the type of vehicle, all anti-lock 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 anti-lock system.

Advanced Application on ABS

Security has become one the major concerns in modern vehicles. In order to provide maximum safety, braking plays an immense role. The main objective is to leave no chance to human errors on the road. Therefore Anti-lock braking systems will continue to evolve. The modern ABS algorithm and computers collect wide set of data to control the behavior of the ABS functionality. In the early stages it was just wheel speed and vehicle speed. Modern ABS systems are equipped with many sensors in brake pedal, all four wheels and the accelerator as well. They could be designed to capture weather conditions as an input signal to the algorithm to make it even accurate. The electronic stability control which could be identified as an extension of ABS, applies breaking separately to each wheel using advanced algorithm which helps the driver to keep the vehicle on the track at greater speeds and on sharp corners. Recently ABS systems are plugged in to motorcycles and result was more than 40% lesser accidents.  If your vehicle is also equipped with ABS and it’s well maintained, you don’t have to worry about skidding or controlling it when you apply breaks. All you have to do is just push the break paddle. ABS computer will do the hard part for you, and ensure maximums safety for your baby vehicle.

 

ABS vs No ABS

You may have heard that it's possible to slow down quicker in a car without ABS. This has elements of truth, but in practical terms the benefits of ABS massively outweigh the slightly longer braking distances. For road use, ABS is an absolute must as it will allow you to steer out of the way of unexpected hazards. 
Diagrams 2 and 3 below explain the practical reasons for ABS.

Diagram 2: Braking hard on a slippery surface with ABS

In the diagram above, the driver hits the brakes hard on a slippery surface (1), then steers (2), and successfully manages to avoid the obstacle. ABS prevents the wheels from locking, and this allows you steer.

Diagram 3: Braking hard on a slippery surface without ABS

Without ABS, as the driver applies the brakes the wheels lock (1). Despite applying steering lock, the car continues straight ahead due to the loss of steering control (2) and a collision results. 

This is another example;

• With Anti-Lock Braking Systems

 

•  Without Anti-lock Braking System
  

ABS on the track

If done correctly, threshold braking can slow a vehicle more quickly that a car fitted with ABS (in the right conditions). Many competitive racing drivers would say that they prefer their cars not to have the system. However, to gain maximum advantage you will need to practice the threshold braking technique repeatedly. A good test is to find a section of test-track, and mark out a cone which will act as the braking point. Accelerate to 60 or 70mph and brake as hard as you can in a car equipped with ABS, then repeat without ABS. Compare the stopping distances by having someone mark them on the side of the track, then practice threshold braking until you notice a marked improvement. If you do have ABS fitted, don't get into the habit of locking up wheels before entering a corner - this isn't the quickest way of slowing down and can unsettle the car.

ABS - Anti-lock Braking System

ABS (Anti-lock Braking System) is a life saving technology which allows the driver to steer while braking heavily

ABS multifunction occurs due to the unit's design imperfection and failure of the components when the system overloaded. However most ABS modulus are repairable and can be restored instead of replaced by and expensive unit.

Objective of ABS
The system primary aims are;

• miximize braking power.
• Allow the driver to maintain control on the steering by preventing the wheel from locking and skiding.
• Shorten braking distance under most conditions.

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.

The ABS system - overview

An ABS system consists of the following components:

• Some wheel speed sensors
• Brake calipers
• A hydraulic motor
• Some pressure release valves
• A quick thinking computer (or control module) which coordinates the whole process

Diagram 1: Brake caliper (1) and wheel speed sensor (2)

How ABS works

When the driver hits the brakes this pressurises the hydraulic system which causes the brake pads to squeeze against the discs which causes the car to slow down. If the ABS system detects that one wheel is slowing down more rapidly than the rest (a symptom of wheel-lock) it automatically reduces the brake pressure on this wheel by opening a pressure release valve in the hydraulic system. ABS also has the ability to build the pressure back up via the hydraulic motor. The system reacts remarkably quickly, and compared wheel speeds many times a second. ABS systems can act on just the front wheels (which do most of the braking work), or all four depending on what car you're in.

Diagram 2: Wheel speed sensor (A), ABS control module (B),
hydraulic motor and pressure release valves (C), Brake pipe leading to caliper (D)