How Harley-Davidson ABS brakes work

The ABS brake systems are already a standard on medium and large cylinder motorcycles, we will try to explain what they consist of and what are the advantages that are popularizing them even among the less sporty models, the custom motorcycles.

ABS are the acronyms of "Anti-Lock Braking System," i.e. Anti-Lock Braking System and was designed in 1929 for aircraft brakes. Its principle is to prevent the wheels from locking when braking, preventing the tyres from skating uncontrollably on the pavement and losing adhesion, thus achieving maximum friction (and therefore braking) and at the same time allowing to maintain balance and steering.

Components and Operation
We will now talk about what elements make up an ABS system on a motorcycle and how they work, although according to the brand and model there may be small variants, the principles are the same.
The system starts from a conventional pump and brake clamp, to which a Hydraulic Unit is attached in the conduit that connects them to each other that will allow to maintain, release and recover the braking pressure, while we press the brake handle or pedal.

This Hydraulic Unit is electronically controlled by the ECU or ABS switchboard.

At the same time, sensors are installed that control the speed of rotation of the wheels that can measure holes in the brake disc when rotating,

or read a few codified bearings magnetically, as in Harley-Davidson ABS systems.

The ECU of the ABS therefore knows at what speed each wheel spins. If one stops more quickly than would be advisable (locking and skid possibility) a signal is sent to the Hydraulic Unit to release pressure (even if the driver continues to tighten the brake), until the wheel turns a bit again, then the pressure is reset to continue with the braking.

If the possibility of skid continues, the process is repeated. All this happens at a speed of 7 times per second, so it is barely noticeable to the driver, who simply notices a vibration or pulsation on the brake handle or pedal.

Decisions on whether or not to operate the system (this is known as the "ABS Event") are made by the ECU on the basis of programmed values, compared to data from wheel-turning sensors.

Benefits and limitations of ABS
With this complex and effective system the driver has the possibility to stop the motorcycle in the shortest possible space, without having to worry about whether the wheels are locked and skated; at the same time by not losing traction we can maintain balance and direction.
Therefore where it will be most noticed its effectiveness will be on slippery surfaces (gravel, ice, pavement in bad condition...) and when it is operated by drivers with little experience. It should be stressed that all studies show that even professional drivers get a shorter brake with the ABS system.
This means that in a situation of emergency brake the ABS significantly increases safety and effectiveness.
It is necessary to keep in mind that the ABS is not suitable for all driving situations, since while we turn the handlebar sharply or while we lie on a curve its effectiveness is minimal, so we must continue to maintain the usual braking and driving precautions.
In case of emergency braking you have to put the motor upright and straight (this is fundamental) and brake firmly with both brakes, without lowering the pressure. The ABS will do the rest of the work for us.

ABS failures
Many users maintain some skepticism about electronic control systems, especially those that affect safety, as they may fail due to vibrations, humidity, bad contacts, etc.
In the case of the ABS we can say that it is a totally safe system, since the ECU monitors the state of the sensors and components continuously, and in case of detecting any anomaly the system is "disconnected," turning on a fault warning light on the dashboard.

In no case will we run out of brakes, since when the ABS stops working we simply have a traditional braking system, without anti-lock.
TECH TIP: in some models the ECU compares the sensor readings of the front and rear wheel, so if we make a "little horse" with the front wheel or a "burnout" with the long rear we can create a false ABS error.
One last recommendation: do not wait for a compromised situation to test your ABS, practice in a safe environment emergency brakes to familiarize yourself with the pulses of the controls and the ability to brake, in this way the driving will be more intuitive, fun and safe.

Frank Burguera

#mecanicaharley