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Precision bearings make electric bikes more reliable and energy efficient

Precision bearings make electric bikes more reliable and energy efficient Whilst most of the debate on how to reduce harmful emissions to the environment is focused on all-electric passenger vehicles, the pedal cycle industry is also now a significant growth market for new all-electric drive train technologies.

Rolling bearings are an integral part of bicycle drive trains. The Schaeffler Group's experience in developing bearing solutions for bicycles spans more than a century. Ever since Friedrich Fischer developed the industrial ball bearing more than 125 years ago, which laid the foundations for modern rolling bearing technology, Schaeffler's rolling bearings have been the preferred option in bicycles for their smoother operation, higher load carrying capacity and longer rating life.

More recently, Schaeffler has introduced a variety of energy efficient bearing solutions for pedal cycles, including seat pillars, headsets, saddle wing mountings, free wheel hubs, internal gear hubs and bottom brackets.

The BB29 FAG bottom bracket for example is designed for city and touring bicycles, providing smoother running and ensuring that the rider uses significantly less energy whilst pedaling.

The bottom bracket is the main bearing position on a bicycle. The BB29 FAG bottom bracket unit is unique in that it provides perfectly smooth operation due to its optimised bearing design. Unlike conventional bottom brackets, the bearings do not need to be braced in the frame.

The shaft of the BB29 unit is coated with a special corrosion protection agent, which provides corrosion resistance in salt-spray tests of more than 200 hours. Conventional bottom brackets are normally zinc-plated, offering only limited corrosion protection.

In addition, the two ball bearings on the BB29 are sealed on both sides and lubricated for life. This ensures maximum reliability and zero maintenance for the entire service life of the bearings.

The glass fibre reinforced plastic housing and dual-fix design ensure easier installation with available tools. The profile of the housing is suitable for holding both FAG tools (external) and Shimano tools (internal). The much reduced diameter in the centre of the bearing unit creates sufficient space for inserting cables for lights or other electrical connections on the cycle.

The emergence of the e-bike

Building on the foundations of the BB29 bottom bracket, Schaeffler has since developed a new bottom bracket bearing specifically for electric bicycles (e-bikes).

With e-bikes, the drive only becomes active when the rider is pedaling at a certain force (torque). The power rating and maximum speed of the bike are limited and so these bikes can normally be ridden without the need for an official licence. However, the drive system must be controlled and regulated. The data required to do this (i.e. the speed, direction and angle of rotation, torque) is ideally measured directly on the bottom bracket itself.
 
Based on the BB29 bottom bracket, Schaeffler's new compact speed sensor bottom bracket bearing, the BB RS, determines the speed, direction of rotation and angle of rotation using a non-contact measurement method.

The system has a much higher resolution than alternative designs, generating 16 pulses per shaft revolution. This enables more precise control via shorter response times in activating and deactivating the drive system. As a result, the drive can respond with much greater sensitivity to the individual riding characteristics, providing optimum assistance to the cyclist. The system is also capable of distinguishing between forwards and reverse pedaling and can include this information in the output signal.
 
In contrast to traditional speed sensor bottom bracket designs that are normally based on a magnetic disc with a Hall Effect sensor - which are openly accessible and therefore sensitive to external influences and foreign matter - the BB RS sensor bottom bracket bearing is a completely encapsulated system that can be accommodated in the design envelope of a conventional bottom bracket bearing. This means that the sensor is optimally protected, secure from disruptive influences and completely maintenance-free. Once the system is fitted, it is ready for operation without the need for further adjustment. The twin core cabling is located within the frame, giving optimum protection. The supply voltage is between 5 and 18 volts (rated voltage 12V) and so is compatible with all conventional control systems.
 

Easy-to-fit

Mounting is particularly easy due to the connection preventing reversed polarity and the dual fix design. The housing profile is suitable for the use of FAG tools (externally) and Shimano tools (internally). Since the diameter at the centre of the bearing unit is significantly reduced, this allows space for light cables and other connections. The plastic housing with glass fibre reinforcement compensates small mounting tolerances and makes mounting easier.
 
The new FAG sensor inner bearing BB RS was presented to the public for the first time at the Eurobike trade exhibition in September 2010, held in Friedrichshafen, Germany. Schaeffler also unveiled its new torque and speed sensor bottom bracket. A world first, the FAG torque sensor bottom bracket is able to determine the total torque from the sum of the force from the left and right pedals. Bosch is already using the device in its new high-performance drive.
 
With e-bikes, being able to correctly determine the rider's requirements for assistance from the motor as riding conditions change and the corresponding control of the power output, are critical factors in ensuring that the ride has a positive feel. As well as measuring the direction of rotation and speed, being able to measure the precise torque produced by the rider during pedaling, is a prerequisite for determining the exact additional power requirements.

The additional drive power provided by the electric motor is controlled principally by the torque sensor system in the bottom bracket. This means that the rider no longer needs to provide additional 'pedal power'.
 

Increased comfort, improved range

The new FAG torque sensor bottom bracket is characterised by the high resolution of the speed signal and by the accuracy of the torque sensor system. These characteristics dictate the quality of the output signal and the speed of response of the motor control system. The rider is therefore provided with optimum assistance in all riding conditions. This not only results in increased comfort, but also maximum energy efficiency. The drive characteristics of the new Bosch drive can be programmed and matched to the type of bicycle in up to four levels - eco, tour, sport and speed. A degree of assistance up to 250 per cent (speed) is available depending on the mode and assistance level.
 
Two alternative non-contact measurement methods are used in the compact bottom bracket unit. The speed and direction of rotation are measured by a Hall Effect sensor, while torque measurement is carried out by means of the magneto-elastic method. The measurement range is between 0 and 90Nm with an accuracy of up to one per cent. Up to 300Nm is optionally available in professional applications, for example, for performance measurement on racing bikes.
 

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