Motor Vehicle Fan Blade Pseudo-Random Offset Noise Reduction
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Solution Overview
Problem
Alternator and alternator-starter fans in motor vehicles produce aeraulic noise, specifically a siren noise, due to their harmonic frequencies related to the number of blades, which existing noise reduction methods fail to effectively attenuate, thereby limiting cooling performance and imposing design constraints.
Innovation Solution
A fan design featuring a pseudo-random binary sequence for angular offsets of its fins, generated using an initial binary sequence and an exclusive OR operator, distributes fins with angular offsets of at least 4°, creating a random pattern that eliminates the harmonic noise associated with the number of blades and spreads sound energy across frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If fan blade size is constrained to reduce aerodynamic noise, then noise level is reduced, but cooling performance deteriorates
Solution Approach 1:
The patent applies asymmetry by distributing fan blades according to a pseudo-random binary sequence rather than equidistant spacing. This creates an asymmetric blade arrangement where angular offsets between successive blades follow a pseudo-random pattern (using XOR operation on binary sequences), eliminating the regular harmonic frequencies that cause aerodynamic noise while maintaining effective cooling surface area.
Solution Approach 2:
The patent changes the angular position parameter of each blade from a fixed equidistant value to variable values determined by a pseudo-random binary sequence. By varying the angular offsets according to the sequence (with minimum difference of 4° between offset values), the system transforms the regular periodic noise into spread spectrum noise, reducing peak noise levels while preserving cooling effectiveness.
2Ease of manufacture
If fan blades are arranged equidistantly, then manufacturing is simple, but characteristic noise emerges at rotational frequency harmonics
Solution Approach 1:
The patent replaces the symmetric equidistant blade arrangement with an asymmetric pseudo-random arrangement. Each blade's angular position is determined by cumulative XOR operations on binary sequences, creating irregular spacing that breaks the periodicity responsible for harmonic noise while remaining manufacturable through standardized angular offset application.
Solution Approach 2:
The patent converts the harmful periodic noise pattern into a beneficial spread spectrum noise distribution. By using pseudo-random binary sequences to determine blade positions, the concentrated harmonic energy at specific frequencies is dispersed across a broader frequency range, transforming a harmful concentrated noise source into a less problematic distributed noise profile.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the acoustic noise associated with the fan's rotation, allowing for optimal cooling performance without excessive design constraints, ensuring the noise blends with the engine noise, thus enhancing the overall vehicle's acoustic profile.
Implementation Method 1
the sequence of the fins exhibits a random character, through a phenomenon similar to scrambling, as described by the mathematical method known as the 'additive scrambler' method. Thus, the harmonic related to the number of fins is largely, if not completely, eliminated, and no other sound volume peaks are created at any particular frequency.
Data Source
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AI summary
Fan for a motor vehicle rotary electric machine comprising a succession of blades distributed about an axis of rotation, each of said blades being arranged angularly about said axis with respect to a position it would occupy if all the blades were spaced equidistantly, with a respective angular offset, the angular offset being adopted, for the successive blades, according to a pseudorandom binary sequence, from two predefined values for the fan, characterized in that the pseudorandom binary sequence is generated from an initial binary sequence and from a logic combination using an "exclusive OR" operator of bundles of two successive binary elements of said sequence.