Precision bearing manufacturer Schaeffler has developed a variety of bearings, bottom brackets and other components for electric bicycles (e-bikes). These maintenance-free components offer longer operating life and smooth, lower friction operation, resulting in high efficiency and dynamics, as well as improved rider comfort.
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 the drive system must be controlled and regulated. The data required to do this (i.e. the speed, direction/angle of rotation and torque) is ideally measured directly on the bottom bracket itself.
Schaeffler’s torque sensor bottom brackets have quickly established themselves in the market as high performance units that ensure maximum comfort for the rider. In particular, the BBRTTS torque sensor bottom bracket provides torque measurement on both sides of the pedal, offering maximum rider comfort, higher efficiency and a longer range. The BBRTTS determines the total torque from the sum of the pedal forces from the left and right pedals. Depending on the riding conditions, the BBRTTS detects the rider’s requirements for assistance from the motor and controls the output accordingly. This offers the fastest possible reaction times from the control system, with up to 72 speed impulses per rotation of the crank. This means that the rider only has to cover very short distances (approx. 10cm) before the motor provides the required assistance.
Conventional torque sensor bottom brackets supply a maximum of 36 speed impulses per rotation of the crank, which means that a distance of approximately 40 to 100cm has to be covered before the assistance takes effect.
Other bottom bracket variants
Schaeffler’s range of bottom brackets for e-bikes also includes the BBRTS sensor bottom bracket. Rather than determining the total torque from the sum of the pedal forces from the left and right pedals, the BBRTS sensor bottom bracket enables non-contact measurement of speed, direction of rotation and torque from the left pedal only. With up to 72 speed impulses per revolution of the crank, this unit still offers very high resolution speed signals for precise, comfortable rider assistance, for example, in the smart e-bike manufactured by Daimler.
Deep groove ball bearings and Seals
Deep groove ball bearings from Schaeffler are used in the front wheels, rear wheels and the central drive of e-bikes. The improved surface geometry of the bearing raceways and balls reduces noise generation by up to 50 per cent compared to conventional deep groove ball bearings. These improvements, combined with improved surface quality, reduce friction by up to 35 per cent. The lower frictional torque and reduced heat generation enable the bearings to operate at high speeds.
Seals also play a key role in terms of reliability and energy efficiency, particularly in dusty or wet riding conditions. Schaeffler’s new efficient lip seal (ELS) offers an unbeatable combination of reliability and energy efficiency. At increasing bike speeds, this significantly reduces the frictional torque, and therefore the power loss of the wheel bearings. With its improved sealing, the ELS provides better protection for the bearing and smoother running.
Other bearing positions
At the connecting point between the handlebar stem and the fork, angular contact ball bearings from Schaeffler are fitted as headset bearings, which ensure the required precision and safety. During riding, the forces acting on the stanchions of the suspension forks are supported and transmitted by ELGOGLIDE plain bearings from Schaeffler.
In addition, drawn cup roller clutches from Schaeffler are used as one-way clutches in the drive of the electric motor. These transmit high torque forces in one direction. The bottom bracket spindle connects the pedals and sensor unit in the drive. Various designs of bottom bracket spindle are available as options. In addition, components can also be coated with Schaeffler’s Corrotect coating, which is resistant to neutral, organic fluids such as oil, brake fluid, petrol and aqueous salt solutions.