Abstract
The development process of a tyre usually involves a combination of simulation and testing techniques focused on characterizing acoustic/aerodynamic and vibrational phenomena. One of the acoustic phenomenon of interest is the absorption of the tyre, which affects the sound radiated. This properties is mainly related to local resonant effects, which can be changed by modifying the geometry of the tyre tread. A procedure is presented to determine the attenuation achieved due to a change in tyre tread configuration. The acoustic transfer path is measured from sound produced at one side of the tyre pavement contact area to the other. A miniature microphone and a small monopole with a known output have been developed to allow measurements inside the tyre grooves. Tyre sections with a circumferential groove only, as well as sections with additional side branches, have been evaluated.
Monopole
A monopole loudspeaker is used consisting of a tube that is open on one end and connected to a loudspeaker inside an enclosure at the other. The volume velocity of the sound radiated is measured with a particle velocity sensor. The particle velocity is linearly related to the radiated volume velocity 𝑄; 𝑄 = 𝑢𝑚𝑜𝑛𝑜𝑝𝑜𝑙𝑒𝐴, where 𝐴 is the tube’s opening area. The sensor is positioned 10mm from the centre of the monopole to avoid very high velocity levels. Sound pressure 𝑝, and particle velocity 𝑢 at a distance 𝑟 from the centre of a monopole given by:
𝑝 𝑟 = 𝑖 𝜌𝑓2𝑟 𝑄𝑒−𝑖𝑘𝑟 u 𝑟 = 4𝜋𝑄 𝑖𝑘𝑟+1𝑟3 𝑒−𝑖𝑘𝑟 where 𝜌 is the air density and 𝑓 is frequency.
TRANSFER PATH BASED TYRE ABSORPTION TESTS
E. Tijs
1
, B. Makwana
2
, O. Peksel
1
, S. Amarnath
2
, D. Bekke
2
1
Microflown Technologies, Tivolilaan 205, 6824 BV, Arnhem, the Netherlands
2Apollo Tyres, Colosseum 2, 7521 PT, Enschede, the Netherlands
e-mail: tijs@microflown.com
Loudspeaker in an enclosure
Open end of a tube with inner diameter of 15 mm
Mid-high frequency monopole
inner tube diameter 3mm particle
velocity sensor
Monopole extension piece and
miniature reference sensor
monopole microphone 22 cm top plate monopole top plate circumferential groove
Measurement set-up. Left: Schematic overview. Right: right side view.
Results of transfer path tests
The figures below show the absolute part of the transfer function of sound pressure, as measured by the microphone, to the volume velocity, as measured by the reference sensor of monopole loudspeaker. The right figure shows the differences between the sections with side branches relative to the section without side branch. It can be seen that damping is achieved by the additional side branches. The frequency where this occurs depends mainly on the length of the side branch. Attenuation is achieved in the band around 1kHz, depending on the configuration. For the section with two side branches there is additional damping for frequencies around 2.3kHz. These frequencies are close to the ones expected for quarter lambda resonators of this geometry.
Conclusions
A procedure is presented to determine the attenuation of the side branches of a tyre groove. The transfer path from one side of the flattened surface of a loaded tyre to the other side is measured, and the degree to which the amplitude and phase of sound waves are changed is captured. To enable such tests, a miniature monopole and a microphone have been developed that are small enough to fit in a tyre groove. Depending on the number of side branches and their orientation, damping was achieved at certain frequencies. The frequencies where this occurred were similar to those expected from theory.
Description of transfer path tests
I II III IV
74mm 74mm
74mm 37mm
Four tyre sections have been tested. One has a circumferential groove only, the other sections have additional side branches.
600 1000 2000 3000 6000 -8 -6 -4 -2 0 Frequency (Hz) p /Q ( P a s /m 3 ) d B
One straight side branch One oblique side branch Two oblique side branches Pipe (no side branch)
Left: absolute part of the transfer function. Right: discrepancies compared to the pipe without side branches.
600 1000 2000 3000 6000 106 107 Frequency (Hz) p /Q ( P a s /m 3 )
A flat pavement section is pressed onto the tyre. To determine the acoustic transfer path, the monopole extension piece is placed at one side of the flat tyre-pavement contact surface in the circumferential groove and a miniature ø3mm microphone is positioned at the other.
