abs for ebikes

Anti-lock Braking System: ABS for ebikes

A German university is designing an ABS for ebikes, so that the potentially dangerous lock of the front-wheel does not happen, even in sudden emergency brakes. With an update on a similar system presented by Volkswagen and Break Force One.

Ebikes with powerful motor, which helps them reach speeds of up to 45 km/h, are more and more widespread. They are starting to be used especially in those countries where they are considered legal (the so called speed-ebike category), such as Germany, the Netherlands or Switzerland.

Ebikes with high power and speed must have an adequate braking system. This is why speed-ebikes are often delivered with hydraulic disc brakes, with wide-diameter rotors, in order to guarantee a great braking force. We have noticed that for instance in our test of the Stromer ST2, a high-quality Swiss speed-ebike.

All of this means that nowadays even those who are not expert cyclists can have access to bikes with powerful braking systems. Until a few years ago this kind of brakes was only available on downhill mountain bikes, designed to be used by expert bikers who want to reach high speeds when going downhill; of course, anybody could walk into a mtb store and buy a downhill mountain bike, but that was a rare thing, as these are very specialized bikes.

Nowadays anybody can (more or less legally) walk into a regular ebike store and buy a regular-looking speed-ebike to use in town. The idea that you need to practice a bit before using a speed-ebike is not as widely shared as we would like: these bikes are quite different from “normal” bicycles. Cycling at 45 km/h in car traffic with a bike weighing 28 kg is not a banal experience, and it’s important to be able to deal with emergencies such as a sudden brake. These may not be motorbikes, but they ain’t granny bikes either.

A sudden brake can paradoxically be more dangerous at low-to-medium speeds than at higher speeds, at least for what concerns the probability of locking the front wheel. When you ride at 45 km/h the momentum of the bike makes it hard to lock the front wheel. It’s when the speed goes down to 15-20 km/h that a sudden brake can lead to locking the front wheel, if a non-expert cyclist, scared by the situation, pulls the brakes with all his strength. There comes into play the braking system: a “normal” city ebike would have v-brakes, or simple mechanical disc brakes, designed to be used at these relatively low speeds: even if you pull the lever very hard, this won’t lead to a locking of the front wheel (the rear wheel may lock, but that is much less of a problem). A speed-ebike, on the contrary, would have hydraulic disc brakes with maybe 180-200 mm rotors, designed to slow the bike down from a speed of 45 km/h, and overpowered for slower speeds. If a non-expert cyclist pulls hard these brakes at a speed of 15 km/h, it’s very easy for the front wheel to lock, and the cyclist risks vaulting over the handlebars. The problem gets worse in case of wet and slippery asphalt. An ABS for ebikes would get into play in this case, releasing the pressure on the brake system, so that the front wheel keeps rolling regularly. However, applying an ABS on ebikes is not simple.

For this reason a team of researchers at the German university of Pforzheim is designing an ABS system for ebikes. The project is financed by the German federal government, and is part of a wider project called “Bikesafe”. First of all the researchers have collected a wide range of data to better understand how and when the front wheel locks: a test bike has been loaded with a wide array of sensors. In order not to risk anyone’s limbs, a puppet has been used, just like in cars’ crash-tests. Because it would have been hard and expensive to have the puppet actually pedal on the bike, the motor was modified so that it would work even when the pedals were not moving. At a certain speed the motor was deactivated and the brakes were automatically activated, in various different ways (different levels of intensity mainly): the results were observed and noted, to understand why and how the front wheel locks and the puppet flies over the handlebars.

The second phase was that of developing an ABS for the front wheel; this was done in cooperation with a few firms working in the field (mainly Bosch and Magura). Ebikes have the advantage of already being fitted with an Electronic Control Unit and a source of energy (the battery) which can be exploited to manage also the ABS for ebikes, reducing the number and the weight of components to add to the bike. There are however many problems to solve. First of all there is the technical problem of actually making this system work. Then there are the problems of aesthetics, of weight, and of room: the ABS must not worsen these aspects of the bike. Finally there is the economic problem: the final price of an ebike with ABS must not be too much higher than the average price of a normal ebike.

At the moment the researchers are still working on this system, and there aren’t any more details. For more information, you can consult this report by the University of Pforzheim (pdf, in German) whence came all the pictures in this article.

Please remember that we think that ebikes in general are safer than normal bikes, for at least 5 reasons.

Update: the Break Force One ABS for ebikes

The idea of adding an ABS to ebikes is so promising that there are various teams working on it. At the moment the team that has the more advanced prototype seems to be Break Force One, a German firm specialized in the production of high-quality disc brakes for mountain bikes. Their system has just been presented at Eurobike 2016.

abs for ebikes
The Break Force One system

The main challenge is that of keeping the weight and the dimensions acceptable, so that they are compatible with usage on an ebike. The Break Force One system is made mainly of a 75mm long tube, with a 32mm diameter and 280 grams of weight. One needs such a tube for each brake that you want to apply the ABS system to. WIthin this tube there are all the electronic and mechanical components necessary for the working of the system. This tube must be positioned along the cable of a hydraulic disc brake system, anywhere you prefer between the lever and the disc; the system is not compatible with mechanical disc brakes, and neither with V-brakes; it’s also necessary to connect to the battery and to the ECU of the ebike. According to Break Force One, their system can “understand” when the front wheel is about to block (and/or when the rear wheel is consequently about to raise above the ground) due to an excessive brake pressure; at this time (even before the wheel actually locks, then) the control system within this tube takes charge, stops the connection between the lever and the brake, and determines the pressure to be applied on the oil, diminishing the intensity of the brake to eliminate the risk of locking the wheel.

These are the data available on the Break Force One website. However, we can’t help wondering how the system actually works, and especially how it can “understand” when to intervene. Even if the ABS system can access all the data inside the ebike’s ECU, we don’t think it could use this data to have such precise information on how the wheels are turning; ebikes ECU normally have mainly information on the transmission… what comes closer to a sensor which could be useful to an ABS system is the speed sensor based on a magnet on the rear wheel; however, this is surely not precise enough, and it doesn’t update fast enough for an ABS system. It’s clear that the Break Force One must be able to access other data from other sensors. We don’t believe that these sensors are on the tube we have talked about, because its designers say that it can be placed anywhere along the cable from the lever to the disc. There must be some accelerometres or other sensors which transmit data wirelessly to this tube. What do you think?

 

Anti-lock Braking System: ABS for ebikes last modified: 2016-10-19T16:27:44+00:00 by Paolo

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