VS - Electrical Systems From Stop-Start to Hybridization

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Belt drive designs

Alternator

Whatever their type and technologies, modern belt drives must comply with the following requirements: For more performance ●● Automatic and constant tensioning ●● Compensation of the belt drive tolerances ●● Maximized torque transfer ●● Limitation of slippage For higher lifetime ●● Limitation of peak dynamic forces in the drive ●● Limitation of belt wear ●● Compensation of belt elongation (notably in heat conditions) Belt drive are governed by power needs, rotational speeds, torque transmission, efforts, dynamics and resonant phenomenons that makes them quite complex to design. Pulleys diameters are defined according to components working conditions for some strategic rpm ranges as: ●● engine idle ●● cranking ●● maximum engine rpm Torque transmission is done by friction of the belt on the pulleys, to secure this, a certain portion of the pulley must be wrapped by the belt, this critical parameter is called the wrap angle. The crankshaft pulley is at the heart of the belt drive, in belt driven hybridized architectures it is a torque source during electrical charge or recovery sequences and a torque consumer in torque assist or boost events. As a torque hub the crankshaft pulley has a large wrap angle. For more comfort ●● Limitation of noise

Idler

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A/C compressor

Crankshaft

The basics of a belt drive

The wrap angle The wrap angle is the angle of contact between the belt and a pulley, it is defined according to numerous parameters as: ●● Engine front end layout and constraints ●● Components positions ●● Torque to be transmitted per pulley ●● Belt type The wrap angle have a huge impact on the belt drive complexity, requiring in some cases to add multiple idlers to properly wrap the belt on more sensitive pulleys notably for BSG machines where the pulley diameter limits the belt contact surface. In static conditions (no rotation) the pulley is submitted to a load that is imposed by the belt tension (T0) on both sides of the wrap angle.

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