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Effect of Vibration Frequency on Mechanical Behavior of Automotive Sensor
International Journal of Mechatronics and Applied Mechanics, 2018, Issue 3 55
EFFECT OF VIBRATION FREQUENCY ON MECHANICAL BEHAVIOR OF AUTOMOTIVE SENSOR
Rochdi El Abdi1, Julien Labbé2, Florence Le Strat3, Erwann Carvou4
1, 2, 4Université de Rennes1- CNRS, Institut de Physique de Rennes- UMR 6251 Campus de Beaulieu, 35042 Rennes Cedex, France
3 Campus de Beaulieu, 35042 Rennes Cedex, France Entreprise Renault, DEA-TCM, 78084 Guyancourt, France
E-mail: [email protected]
Abstract: Due to repetitive micro-displacements, the fretting phenomenon was defined as an electrical and mechanical degradation of the electrical contact interface in automotive sensors. Commonly, the electrical degradation was quantified by the increase of contact resistance deduced from the contact voltage. This work aims to address the analysis of relative displacements according to three space directions between sensor components in contact for different vibration frequencies for a Top Dead Center sensor. Particular attention was paid to measurements of displacements near crimping zones. Keywords: Fretting corrosion, automotive sensors, relative displacements, vibration frequency.
1. Introduction
In the automotive fields, the vehicle vibrations
induce relative movements for hundreds of sensors
which were located near the engine, inside the seat
and in many other electronically components. The
vibrations could induce a displacement between two
sensor components in contact i.e. the male part and
the female part (the pin and the clip) and could
generate an electrical failure due to the well-known
fretting-corrosion phenomenon [1, 2]. A relative
displacement of 5μm was enough to produce
remains at the interface between the pin and the clip
and set an intermittent failure at the interface [3].
This phenomenon represents 60 % of electrical
failure within cars [4]. Electrical contacts were
generally made of a substrate of copper alloy plated
with a thin protective layer of non-noble metals. Tin
was usually used as a protective layer of the
substrate in order to combine a good conductivity,
good reliability and a low cost. A pure tin was
malleable and reacts with the oxygen to give hard
and brittle remains which cause high surface
damages. The substrate could be reach and it
generates copper oxide remains at the contact
surface [5].
In the electrical contact field, the fretting-
corrosion was an irreversible degradation which
avoids a good current conduction.
Several analyses were performed to understand
this phenomenon and how the current was
conducting through the interface for static and
dynamic contacts [6, 7]. Due to the many mechanical
parameters (forces, materials used, type of
vibration...), the numerical simulations provide
interesting results but cannot predict the real life
time of a sensor submitted to a fretting-corrosion
phenomenon [8].
The aim of this work was to understand the
influence of the vibration frequency on the
mechanical wear for different sensor parts in contact
and to study the relative displacements in three
directions for a sensor submitted to a real vibratory
profile used in automotive applications.
2. Sensor Used
In automotive applications, the TDC sensor (Top
Dead Center), also known as the "speed sensor", is
an electrical component whose purpose is to inform
the engine management system about the position of
the engine piston at the neutral point, as well as the
rotation speed of the crankshaft. It’s an inductive
andan "active" sensor because it creates its electrical
signal independently of any outside power source.
The TDC sensor was submitted to vertical and
horizontal vibration (Fig. 1).
Effect of Vibration Frequency on Mechanical Behavior of Automotive Sensor
International Journal of Mechatronics and Applied Mechanics, 2018, Issue 3 56
Figure: 1Schematic representation of TDC sensor in vertical (a) and horizontal (b) position and zoom
(c) of clip/pin contact zone
3. Applied Vibratory Profile
The sensor was subjected to vibrations transmitted by the engine and the passenger compartment of the car. When mounted near the car engine, the sensor was submitted to an acceleration and displacement profile given in Fig. 2. This profile will be applied during the tests for studied sensors in our laboratory. The sensor was submitted to displacements between a few micrometers and a few millimeters (Fig. 2).
On the other hand, the relationship between the frequency f, the displacement amplitude d (peak-to-peak) and the acceleration γ of a system subjected to vibrations like a shaker system are represented by the following equation:
2
(4. . )
d
f
(1)
Thus, the connectors were submitted to amplitude of vibrations which depended on the frequency and on the shaker acceleration.
Figure: 2 Vibratory profile used on shaker
4. Benches Used
The experimental set-up used consists of a shaker
(LDS V555 with a maximum force of 939N,
maximum acceleration of 100 g (g = 9.81 m/s2))
which can apply sinusoidal vibrations and to use the
vibratory profile of Fig. 2. A sinusoidal and vertical
vibration was applied on the lower part of the sensor
which will be positioned horizontally and vertically
(Fig. 3).
A LDV (Laser Doppler Vibrometer) was used to
obtain the displacement of target points on the
sensors’ surface (red points) (Fig. 3). The laser beam
from the LDV was directed at the surface of interest,
and the vibration amplitude and frequency were
extracted from the Doppler shift of the reflected
laser beam frequency due to the motion of the
surface (Fig. 4). The output of an LDV was generally
a continuous analog voltage that was directly
proportional to the target velocity component along
the direction of the laser beam.
The test aim was to measure for different
frequencies the relative displacements between the
different sensor parts, especially near crimping
zones (contact between wire and sensor
components) and at the contact interface between
the male part (pin) and the female part (clip) of the
sensor (Fig. 1).
(c)
Clip Clip
support
Shaker
Pin
Wire
Shaker
Support of
sensor
Sensor
Pin Wire
Clip
Dis
pla
cem
en
t
dir
ecti
on
Winding
Clip
support
(a) D
ispla
cem
en
t
dir
ecti
on
Shaker
Support of sensor
Sensor
Wire
Winding
Pin
Clip
Clip
support
(b)
Frequency (Hz)
Dis
pla
cem
ent
(m
)
Acc
eler
atio
n (
m/s
2 )
Effect of Vibration Frequency on Mechanical Behavior of Automotive Sensor
International Journal of Mechatronics and Applied Mechanics, 2018, Issue 3 57
Figure: 3 Shaker used and TDC sensor in vertical (a) and horizontal (b) position.
The six red points are targets for laser beam to obtain displacement measurements
Figure: 4 Laser Doppler Vibrometer used for
displacement measurements
5. Discussion and Results
(a) Displacements of sensor in vertical position Sensor was positioned in vertical position and
submitted to vertical shaker vibration (Fig. 3a). From 240 Hz to 440 Hz, the displacements along X-axis of the clip-support, the clip and the wire are similar (Fig. 5a). These displacements decrease according to the frequency and increase for a frequency higher than 600 Hz. The clip-support always has a greater displacement range than the clip and the sensor. The movements of the free wire influence the displacements of the connector as a whole. Note that the clip holder is attached to the sensor by a nut and this causes multidirectional movements.
All the displacements (except for the wire) along Y axis were similar (Fig. 5b), with low amplitude always less than 0.35 μm. Between 200 Hz and 740 Hz, the displacement ranges were less than 1 μm. The wire with one end free causes much higher displacement amplitudes.
When analyzing vibrations along Z axis (Fig. 5c), until 200 Hz there were few differences between the different displacement amplitudes, but these differences become more and more important when the frequency increases. The maximum value of the relative displacement between the wire and the sensor was less than 7 μm.
(b) Displacements of sensor in horizontal
position The sensor was horizontally placed on the shaker
(Fig. 3 b). From 120 Hz to 800 Hz, the displacements along X axis (Fig. 6a) become high and reach a maximum value when the frequency reaches 680 Hz. These displacements were smaller than those obtained for Z axis where all displacements are similar (Fig. 6c).
Along Y axis (Fig. 6b), the curves are similar, but with a phase shift and the differences between different displacements were always less than 1.3 μm except for the wire with high displacement amplitude at 800 Hz.
Figure: 5 Displacements of sensor in vertical position along X, Y and Z axes
Dir
ecti
on
of
vib
rati
on
Dir
ecti
on
of
vib
rati
on
Shaker
Wire
Support of
sensor
Sensor
(a) (b) Clip-support
Laser
Doppler
vibrometer
Sensor
Shaker
Frequency (Hz)
Displacement along X-axis
Dis
pla
cem
ent
ran
ge
(m
)
Frequency (Hz) Frequency (Hz)
Displacement along Y-axis Displacement along Z-axis
Dis
pla
cem
ent
ran
ge
(m
)
Dis
pla
cem
ent
ran
ge
(m
)
Sensor
Clip
Clip-support
Wire
Sensor
Clip
Clip-support
Wire
Sensor
Clip
Sensor
Clip
Clip-support
Wire
Sensor
Clip
Clip-support
Wire
(a) (b) (c)
Effect of Vibration Frequency on Mechanical Behavior of Automotive Sensor
International Journal of Mechatronics and Applied Mechanics, 2018, Issue 3 58
Figure: 6 Displacements of sensor in horizontal position along X, Y and Z axes
(c) Relative displacements between clip-
support and sensor An interest was placed on the analysis of the
relative displacements between the clip support and the sensor and between the clip and the pin (Fig. 1).
On the other hand, for a sensor horizontal
position (Fig. 7 b), the relative displacement along Z
axis exceeds 20 μm for the frequency of 200 Hz. This
leads to a sudden increase of the sensor electrical
voltage.
This frequency should therefore be avoided. The
same conclusions for the relative displacements
between the clip and the pine were obtained (Fig. 8).
Figure: 7 Relative displacements between clip support and sensor along X, Y and Z axes for sensor in vertical
(a) and horizontal (b) position
Figure: 8 Relative displacements between clip and pin along X, Y and Z axes for sensor in vertical
(a) and horizontal (b) position
The damaged area of the contact zone has 300 μm and 500 μm, (Fig. 9))
and the copper appears. At the left of this area, much debris were ejected.
In the middle of the contact surface, the tin layer no longer exists and thus the copper will oxidize and lead to the sensor dysfunction.
Sensor
Clip
Clip-support
Wire
Frequency (Hz) Frequency (Hz) Frequency (Hz)
Displacement along X-axis Displacement along Y-axis Displacement along Z-axis
Dis
pla
cem
ent
ran
ge
(m
)
Dis
pla
cem
ent
ran
ge
(m
)
Dis
pla
cem
ent
ran
ge
(m
)
Sensor
Clip
Clip-support
Wire
Sensor
Clip
Clip-support
Wire
(a) (b) (c)
Frequency (Hz)
Dis
pla
cem
ent
ran
ge (
m)
X axis
Y axis
Z axis
Relative displacement (clip support/sensor)
Dis
pla
cem
ent
ran
ge (
m)
X axis
Y axis
Z axis
Relative displacement (clip support/sensor)
Frequency (Hz)
(a) (b)
Frequency (Hz)
Dis
pla
cem
ent
ran
ge (
m)
X axis
Y axis
Z axis
Relative displacement (clip/pin)
X axis
Y axis
Z axis
Relative displacement (clip/pin)
Frequency (Hz)
Dis
pla
cem
ent
ran
ge (
m)
(a) (b)
Effect of Vibration Frequency on Mechanical Behavior of Automotive Sensor
International Journal of Mechatronics and Applied Mechanics, 2018, Issue 3 59
Figure: 9 SEM analysis and material percentages
along contact zone between clip and pin
6. Conclusion
The use of a laser Doppler vibrometer with non-
contact vibration measurements allowed defining
the type of relative movements between different
components of sensor used for automotive
applications. This has made it possible in particular
to emphasize non-intuitive vibratory behaviors such
as multiaxial movement directions.
The displacement amplitudes of the clip-support
generally were greater than those of the other
components of the sensor subject to the shaker
vibratory. Indeed, the clip-support was not
perfectlyfixed to the sensor. Moreover, the results
showed the clip-support vibrating were
tridimensional even if the shaker vibration was
unidirectional. Therefore, it was necessary to
characterize the vibrational behavior of each
component in three directions.
On the other hand, the vibratory behavior of the
clip-support slightly influences the clip movement
inside the sensor.
Finally, a sensor subjected to vibration excitations will have a multiaxial vibratory behavior which depends on the imposed vibrations and on the sensor type. Indeed, the vibratory behavior of the each sensor component depends on those of the other external components. However, they may be different. Therefore, analyzing the vibrational behavior of a connector was complex and requires a complete analysis.
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% % Tin
% Copper
Wear of
the contact zone
