21-06-2013, 04:04 PM
AN EXPERIMENTAL INVESTIGATION INTO NOISE AND VIBRATION OF AN
AUTOMOTIVE WIPER
ABSTRACT
As modern passenger cars become increasingly quieter, wiper operation vibration and noise become
more noticeable. As a result of the market information survey, most complaints about the wiper concern
operation noise. Wiper vibration and noise is classified into three main categories namely, squeal noise,
chattering, and reversal noise. Squeal noise is a high-frequency vibration of about 1000 Hz. Chattering
noise is a low-frequency vibration of 100Hz or less and reversal noise is an impact sound with a
frequency of 500 Hz or less produced when the wiper reverses. In this paper, we experimentally
investigate vibration and noise of a passenger car’s wiper. First, we determine natural frequencies of a
wiper using modal testing. Later, noise and vibration characteristics are observed during wiper operation
at the dry and wet conditions. Wiper noise and vibration is also examined at three different speeds, i.e.,
slow, moderate and fast.
INTRODUCTION
Windscreen wipers are indispensable components to the maintenance of a safe and comfortable field of
vision when driving on rainy days. A conventional wiper system as shown in Figure 1 comprises an
electric motor and a linkage mechanism which converts the rotational movement of the motor into the
back and forth motion of the wiper arms. The mechanical structure of the wiper blades is attached to the
arm tips, holds the rubber blade, which drains the water off the windscreen or to smooth the water on
the surface of the windscreen in order to create a thin film that allows light to pass through it without
refracting or bending as shown in Figure 2.
MODAL TESTING
The experimental study of structural vibration has made significant contributions for better
understanding in vibration phenomenon and for providing countermeasures in controlling such
phenomenon in practice. Typically, experimental observations are always to reach two-fold objectives
(Ewins, 1984):
• Determining the nature and vibration response levels
• Verifying theoretical models and predictions
The first measurement objective is referred to as a test where vibration forces or responses are measured
during structure normal service environmental operation while the second is a test where the structure or
component is vibrated with a known excitation. The second test is much more closely carried out under
control conditions and this type of test is nowadays known as modal testing or experimental modal
analysis (EMA). In this paper, modal analysis is performed at free-free boundary condition for the blade
and the primary yoke whilst at fixed boundary condition for the windscreen. The hammer test method is
used to determine natural frequencies of those components. In doing so, a Kistler Type 9722A500
impact hammer is used to produce the excitation force while a Kistler Type 8636C50 uni-axial
accelerometer is fix-mounted onto the tested components. Figure 4 shows overall set-up of the
experimental modal analysis.
CONCLUSIONS
The wiper produces a low frequency vibration and noise called chatter, with a frequency below 100Hz,
depending on environmental conditions and operating speeds. It is found that, regardless of wet or dry
conditions and different wiper speeds, the chattering noise is generated before and after the wiper
turnover. However, it seems that the wiper has steady motion in the middle of rotating stroke for the dry
condition compared to the wet condition, which non-uniform water films on the windscreen may disturb
contact between the rubber blade and the windscreen interfaces that lead to vibration. There is no single
squeal noise appears in current investigation and it suggests that closest natural frequencies between
wiper components do not guarantee for squeal generation. It is also observed that the windscreen is
experiencing streaking visual deterioration effect.