Bearings Increase Efficiency of Electric Bikes
The bearings do not need to be braced in the frame. The shaft of the BB29 unit is coated with a corrosion-protection agent, which provides corrosion resistance in salt-spray tests of more than 200 hours. In addition, the two ball bearings on the BB29 are sealed on both sides and lubricated for life, ensuring maximum reliability and zero maintenance. 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 FAG tools (external) and Shimano tools (internal).
The reduced diameter in the centre of the bearing unit creates sufficient space for inserting cables for lights or other electrical connections on the cycle. Building on the foundations of the BB29 bottom bracket, Schaeffler has since developed a bottom bracket bearing 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 (the speed, direction and angle of rotation, and torque) is ideally measured directly on the bottom bracket itself. Based on the BB29 bottom bracket, Schaeffler's 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. 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 18V (rated voltage 12V) and so is compatible with all conventional control systems. Mounting is said to be 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 FAG torque sensor bottom bracket is able to determine the total torque from the sum of the force from the left and right pedals. 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'. The 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 results in increased comfort and 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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