What is Transfer Path Analysis (TPA)?

Definition

Transfer Path Analysis (TPA) is a signal processing method which aims at quantifying the contribution of different sound and vibration transfer paths from a set of excitation sources (e.g. electric motor magnetic forces, tyre/road friction forces, wind aerodynamic forces) to a set of receivers (e.g. sound pressure level, vibration level) through a complex structure (e.g. car body including chassis and windows). TPA method also allows the impact of transfer paths modifications at receiver points.

Air-borne and structure-borne transmission in EV

Application to e-NVH

E-motor TPA

Electric motors contain several excitations (aerodynamic, mechanical, magnetic). Different natures of excitations can also be distinguished in electromagnetic excitations such as winding harmonics, magnet harmonics, slotting harmonics and PWM harmonics.

In several applications, sound and vibration levels are receiver points can mix both air-borne and structure-borne contributions.

TPA is therefore an efficient method to analyze the physical origin of different sound and vibration harmonics and prioritize noise mitigation actions.

Test campaign TPA

A typical TPA test campaign includes the following steps:
- identification and instrumentation of the source/receiver connection points by means of accelerometers,
- identification of one or several target positions in the receiving structure and instrumentation by means of accelerometers or microphones,
- measurement of the transfer function matrix from each connection point to all other points,
- measurement of the transfer functions from each connection point to the receiver target position,
- measurement of the vibrations at the connection points while the source is operating.

TPA name includes a wide range of measurements and post-processing techniques (e.g. OTPA, ATPA).

EOMYS testing services include Advanced Transfer Path Analysis to solve noise and vibration issues coming from electric motor excitations.

Application to MANATEE - numerical TPA

The principle of TPA can also be applied in numerical models during virtual prototyping of electric motors, this is called Numerical Transfer Path Analysis (NTPA). MANATEE software specialized in electromagnetic and vibroacoustic simulation of electrical machines can separate air-borne and structure-borne noise sources. Load case contribution also allows to differentiate noise due to rotor excitations from noise due to stator excitations, noise and vibration due to Unbalanced Magnetic Pull or torque ripple.

See also

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