Enhancing comfort & safety in cars, trucks, & buses driven by combustion engines require more installed electric power on board. As of now, the claw-pole-rotor generator is the only category of automotive generator used in industry, with whole powers per unit up to 5 kW and speeds up to 18,000 rpm
A solid rotor claw-pole structure possessing ring-shaped single direct current (DC) excitation coil, though supplied via slip-rings & brushes from the battery on board, has proven to be simple & reliable, with low cost, low volume and low excitation power loss. In common, the claw-pole-rotor generator is a 3-phase generator with 3 or 6 slots per pole & with 12, 14, 16, 18 poles, & a diode full power rectifier.
Its major demerit is the rather large losses (due to low efficiency), around just 50% when operating at full power & high speed. Generating electricity on board with such high losses is no longer acceptable as the electric power requirements per vehicle increase. Enhancements to the claw-pole-rotor (or Lundell) generator design for better efficiency at higher powers per unit are currently under insistent investigation by both industry & academia, & encouraging results were recently published. A cross-section of a typical industrial claw-pole-rotor generator is shown in diagram 6.1. It includes the following main components:
1. Uniformly slotted laminated stator iron core
2. Three-phase alternating current (AC) winding: typically one layer with q = 1, 2 slots per pole per phase, star or delta connection of phases
3. Claw-pole rotor made of solid iron parts that surround the ring-shaped DC-fed excitation (single) coil
4. Copper slip-rings with low voltage drop brushes to transfer power to the DC excitation coil on the rotor
5. Bearings & an end frame made of 2 sides - the slip-ring side & the drive-end side; the generator is driven by the internal combustion engine (ICE) by means of a belt transmission The Lundell generator AC output is rectified through a 3- or 4-leg diode rectifier & connected dc batteries are used, but 42 Vdc batteries are now used as a new standard for automotive application loads. The diodes D1 to D6 (D8) serve the full-power output rectification & are designed for the maximum power of the generator. For huge units (for trucks, etc.), 3 elementary diodes in parallel are mounted on radiator semi-legs to fulfill the requirement of rather high current levels involved (28 Vdc batteries are representative for large vehicles).
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