ride-comfort of an automobile equipped with colloidal...

Ride-comfort of an automobile equipped with colloidal dampers at its frontal suspensions

C.V. Suciu Fukuoka Institute of Technology, Department of Intelligent Mechanical Engineering 3-30-1 Wajiro-Higashi, Higashi-ku, Fukuoka 811-0295, Kyushu, Japan email: [email protected]

Abstract Usual car suspensions employ oil dampers (ODs) mounted in parallel with compression helical springs (CHSs), the latter providing necessary restoring force to bring back the suspension to its initial position after a complete cycle of compression-extension. The energy of shock and vibration is mainly stored by the spring during compression and then, it is transferred to, and dissipated by the OD during extension. On the other hand, in the case of a colloidal damper (CD), since the liquid naturally exudes from the nanopores of lyophobic silica during decompression, the restoring force is intrinsically achieved, and the CHS can be omitted. Thus, the CD provides for a dual function, of absorber and spring, this allowing a compact and light design of the car suspension. Additionally, since dissipation is produced during the compression part of the working cycle, the suspension’s efficiency can be improved. In this work, four types of suspensions are considered: used and unused (100,000 and 0 km travel distance) ODs coupled with springs, and unused CDs with and without attached springs. Firstly, all absorbers were dynamically tested on a fatigue machine and the damping coefficients were found. Then, all suspensions were mounted on a real car and travel tests on normal road with an asphalt step were performed. Car’s ride-comfort and the vibration transmissibility from road to car’s drive-shaft were experimentally evaluated.

1 Introduction

Colloidal damper (CD) is a hydraulic absorber with high dissipative performances [1, 2], on order of 1-10 J/g, that employs the same cylinder-piston structure as the well-known oil damper (OD), but there are no orifices on the piston head, and the oil is replaced by an ecological mixture of lyophobic nanoporous silica and water. Energy of shock and vibration is dissipated mainly by the contact angle hysteresis that occurs at repetitive forced penetration (during compression) followed by natural exudation (during decompression) of water in/from the silica nanopores. Dissipated energy occurs as the relatively small difference between the surface energy of silica wall at compression and decompression (1-10 mJ/m2), multiplied by a large working surface, on order of 100-1000 m2/g. Such dissipative mechanism was called “nano-damping” as well as “surface dissipation”. Eroshenko et al. proposed the CD concept [1, 2], reported some fundamental research on it [3], and recently, extended their investigations towards applicative research for car suspensions [4]. On the other hand, Suciu, Iwatsubo et al. reported fundamental research on CDs in order to clarify the mechanism of energy dissipation [5], to evaluate the static [6] and dynamic [7] performances of CDs, and to find the optimum architecture [8] of the nanoporous silicas and their liquid-repellent coatings. In order to achieve a CD effective for both loading directions (e.g., left-right, or upward-downward) two compression-decompression chambers oppositely placed relative to the movement line of the piston were used [9]. As alternative, a single chamber can be employed, in which case the piston is linked to the loading line via a connecting-rod mechanism [8], able to transform the sinusoidal alternative excitation into a piston pulsation of double frequency. From an applicative perspective, by introducing silica into a tank, separated from the main cylinder by a filter permeable to water, it was possible to extend the CD’s life to accommodate real applications [10].

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Although some applicative studies were reported on the eventual usage of CDs for vehicle suspensions, many uncovered aspects remain open to investigation. Therefore, in this work, starting from the structural and functional analysis of the car’s frontal suspension, a simplified, compact and light design is proposed, by omitting the compression helical spring (CHS). Thus, actual car suspension employs an OD mounted in parallel with a CHS, the latter providing necessary restoring force to bring back the suspension to its initial position after a complete cycle of compression-extension (Fig. 1). The energy of shock and vibration is mainly stored by the spring during compression, and then, it is transferred to, and dissipated by the OD during extension. However, in the case of a CD (Fig. 2), since the liquid naturally exudes from the nanopores of lyophobic silica during decompression, the restoring force is intrinsically achieved, and the CHS can be omitted. Thus, the CD provides for a dual function, of absorber and spring, this allowing a simplified, compact and light design of the car suspension. In this view, here four types of suspensions are considered for experimental investigations: used and unused (100,000 and 0 km travel distance) ODs coupled with springs, and unused CDs with and without attached springs. Firstly, all absorbers are dynamically tested on a fatigue machine and the damping coefficients are found. Then, all suspensions are mounted on a real car and travel tests on normal road with an asphalt step are performed. Car’s ride-comfort and the vibration transmissibility from the rough road to the car’s drive-shaft are evaluated.

Figure 1: Actual car suspension Figure 2: Proposed car suspensions (OD with CHS) (CDs with and without CHS)

2 Excitation tests

Figure 3 illustrates the fatigue test machine and the measurement equipment used during excitation tests. Details concerning the measurement technique are given elsewhere [5-10]. By numerical calculus of the hysteresis area on the graph illustrating the variation of the damping force versus the piston stroke (Figs. 4 and 5) one estimates the dissipated energy and then the damping coefficient sc (Fig. 6).

Figure 7 compares the hysteresis obtained at 1 Hz frequency for unused CD, used and unused ODs. One observes that the OD’s hysteresis is larger for positive (extension) loads, and the CD’s hysteresis is larger for negative (compressive) loads. This proves that the energy of shock and vibration is dissipated by the OD mainly during extension, i.e., the secondary part of the working cycle. Oppositely, in the case of CD,

Oil Orifice (≅ 0.1 mm)

Oil damper (OD)

Compression helical spring (CHS)

Micro-filter (2μm) Water

Lyophobic nanoporous (7nm) micro-grain (20μm) of silica

Colloidal damper (CD) with and without compression helical spring (CHS)

WaterOil Orifice (≅ 0.1 mm)

Oil damper (OD)

Compression helical spring (CHS)

Micro-filter (2μm) Water

Lyophobic nanoporous (7nm) micro-grain (20μm) of silica

Colloidal damper (CD) with and without compression helical spring (CHS)

Water

4234 PROCEEDINGS OF ISMA2010 INCLUDING USD2010

the mechanical energy is directly dissipated during compression, i.e., the primary part of the working cycle.

Figure 3: Fatigue test machine and the measurement equipment used during excitation tests

Figure 4: Hysteresis change versus frequency Figure 5: Hysteresis change versus frequency (Unused OD) (Unused CD)

Figure 6: Damping change versus frequency Figure 7: Hysteresis shape at 1 Hz frequency (Unused CD, used and unused ODs) (Unused CD, used and unused ODs)

Fatigue test machine

Damper

Fatiguetest

machine

ControllerComputer

INPUTSinusoidal excitation

Pressuregauge

Load cellDamper

PressureOUTPUT

Stroke Damping force

Displacementsensor

CDOnly


Damper


Damper

Fatiguetest

machine

ControllerComputer


Pressuregauge

Load cellDamper

PressureOUTPUT


Displacementsensor

CDOnly

Fatiguetest

machine

ControllerComputer


Pressuregauge

Load cellDamper

PressureOUTPUT


Displacementsensor

CDOnly

800

Dam

ping

forc

e [N

]

1 Hz2 Hz

3 Hz4 Hz5 Hz

Piston stroke [mm]

600400

200

0-200-400

0 5-5 10 15-10-15

1[Hz]2[Hz]

3[Hz]

4[Hz]5[Hz]

1 Hz2 Hz

3 Hz

4 Hz5 Hz500

Dam

ping

forc

e [N

]

0

-500

-1000

-1500

-20000 10-10 20-20

Piston stroke [mm]

Unused OD Unused CD800

Dam

ping

forc

e [N

]

1 Hz2 Hz

3 Hz4 Hz5 Hz

Piston stroke [mm]

600400

200

0-200-400

0 5-5 10 15-10-15

1[Hz]2[Hz]

3[Hz]

4[Hz]5[Hz]

1 Hz2 Hz

3 Hz

4 Hz5 Hz500

Dam

ping

forc

e [N

]

0

-500

-1000

-1500

-20000 10-10 20-20

Piston stroke [mm]

800

Dam

ping

forc

e [N

]

1 Hz2 Hz

3 Hz4 Hz5 Hz

Piston stroke [mm]

600400

200

0-200-400

0 5-5 10 15-10-15

800

Dam

ping

forc

e [N

]

1 Hz2 Hz

3 Hz4 Hz5 Hz

Piston stroke [mm]

600400

200

0-200-400

0 5-5 10 15-10-15

1[Hz]2[Hz]

3[Hz]

4[Hz]5[Hz]

1 Hz2 Hz

3 Hz

4 Hz5 Hz500

Dam

ping

forc

e [N

]

0

-500

-1000

-1500

-20000 10-10 20-20

Piston stroke [mm]

1[Hz]2[Hz]

3[Hz]

4[Hz]5[Hz]

1 Hz2 Hz

3 Hz

4 Hz5 Hz500

Dam

ping

forc

e [N

]

0

-500

-1000

-1500

-20000 10-10 20-20

Piston stroke [mm]

Unused OD Unused CD

Dam

ping

coe

ffic

ient

, cs

[Ns/

m]

0Frequency, f [Hz]

Unused OD

Used OD

Unused CD

1 20

3 4 5 6

2000

4000

6000

8000

10000

Unused CD

Used OD

Unused OD

500

0

-500

-1000

-1500-2000

1000

Dam

ping

forc

e [N

]

0Piston stroke [mm]

5 10 15 20 25-25 -20 -15 -10 -5

f = 1Hz

Dam

ping

coe

ffic

ient

, cs

[Ns/

m]

0Frequency, f [Hz]

Unused OD

Used OD

Unused CD

1 20

3 4 5 6

2000

4000

6000

8000

10000

Dam

ping

coe

ffic

ient

, cs

[Ns/

m]

0Frequency, f [Hz]

Unused OD

Used OD

Unused CD

1 20

3 4 5 6

2000

4000

6000

8000

10000

Unused CD

Used OD

Unused OD

500

0

-500

-1000

-1500-2000

1000

Dam

ping

forc

e [N

]

0Piston stroke [mm]

5 10 15 20 25-25 -20 -15 -10 -5

f = 1Hz

Unused CD

Used OD

Unused OD

500

0

-500

-1000

-1500-2000

1000

Dam

ping

forc

e [N

]

0Piston stroke [mm]

5 10 15 20 25-25 -20 -15 -10 -5

f = 1Hz

VEHICLE DYNAMICS 4235

One observes that, at the same stroke variation, the hysteresis area of the unused CD (blue line in Fig. 7) is considerably larger than that obtained for the unused OD (green line in Fig. 7), this proving, in agreement with Ref. [2] that the CD has indeed higher dissipative performances. Hysteresis obtained for used OD is larger, both as stroke and damping force variation, than that of unused OD, and this can be explained by the obstruction of orifices by gums, deposed as a result of the oil aging. Since the test rig’s maximum working speed is limited, the maximum allowable piston stroke reduces when the frequency is increased. Consequently, all absorbers show decreased damping performances at frequency augmentation (Figs. 4 and 5), but the highest reduction rate is observed for CD, followed by the used and unused ODs (Fig. 6).

3 Travel tests

3.1 Car’s ride-comfort

Major sources of excitation in motor cars [11-13] are the engine, transmission system, air-conditioning system, road and aerodynamic excitations. On the other hand, the major sources of structural resonances and their frequency ranges are: rigid body vibrations of bouncing, pitching and rolling on suspension systems and wheels (0.5-2 Hz), forced vibrations of the vehicle body due to the engine shake (11-17) Hz, bending and torsional vibration of the body as a whole (25-40 Hz), as well as ring mode vibration of the passenger compartment and bending vibration of the driveline (50-150 Hz). Thus, structural resonances of various systems in a motor car are in the range of 0.5-150 Hz, but the resonances connected to suspension systems and wheels are in the domain of 0.5-2 Hz. Road excitation frequency increases with the vehicle speed and decreases with the wavelength of the road roughness; excitation frequencies from 0.1 to 0.5 Hz are important for evaluation of the motion sickness, and the domain of 0.5-80 Hz is recommended for evaluation of the health, perception and comfort [11, 12]. Since the perception of the car’s ride-comfort is different from one passenger to another, depending on its taste and physical constitution, in this work, in agreement with the ISO 2631-1 standard [11], the ride-comfort factor K is defined as [12]:

∑ Δ⋅=i

iiii ffRfHfGK ])()()([20 22 . (1)

Discrete values of the frequency if and frequency intervals ifΔ are given in Table 1, after Ref. [11]. The first succession of values from 1.0=f Hz ( 045.0=Δf Hz) to 8.0=f Hz ( 370.0=Δf Hz) should be multiplied by 10 and 100 to obtain the whole sequence up to 80 Hz (Table 1).

if [Hz] 0.100 0.125 0.160 0.200 0.250 0.315 0.400 0.500 0.630 0.800ifΔ [Hz] 0.045 0.060 0.075 0.090 0.115 0.150 0.185 0.230 0.300 0.370Table 1: Discrete values of the frequency and frequency intervals, after Ref. [11]

In order to estimate the transfer function )( ifH of vibration from the rough road to the car’s body, an adequate model should be adopted. In general, a vehicle with four wheels can be modeled as a system with 6 degrees of freedom (full-vehicle model). However, when the frequency of vertical vibration of the car’s body is below 2 Hz, it becomes possible to neglect the rolling and to assume that the left and right parts of the car are identical (half-vehicle model). Moreover, experience has proved that even the pitching movement is neglected (quarter-vehicle model), the excitation, ride-comfort and the fatigue lifetime of the commercial vehicles, moving on rough roads, can be predicted quite accurately [11-13]. Accordingly, in this work a quarter-vehicle model with two degrees of freedom moving on a rough road (Fig. 8.a) is used,


where sm is the vehicle sprung mass, tm is the unsprung mass, sk is the suspension spring constant, tk is the tire spring constant, sc is the suspension damping coefficient, and tc is the tire damping coefficient. Such model is based on the following assumptions: constant travel speed, no frontal-rear and/or axial rolling of the rigid-body vehicle, linear suspension and tire characteristics, linear contact between the tire and the road, and small pitch angles. Such model with two degrees of freedom can be further simplified to a quarter-vehicle model with one degree of freedom (Fig. 8.b), by defining the equivalent mass m of the vehicle, the equivalent spring constant k and the equivalent damping coefficient c as follows:

⎩⎨⎧

≅+=+=+= stss

stts cccc

mm

kkkmmm ;111; . (2)

Usually the tire damping coefficient can be neglected relative to the suspension damping coefficient, and consequently, scc ≅ . Irregular road roughness can be modeled as a spatial sinusoidal wave of amplitude Y and wavelength λ that produces a displacement excitation of the car, as follows (Figs. 8.a and 8.b):

ffRYvfftYy Δ=== )(2;/;2sin λπ . (3)

Excitation frequency f depends directly proportional on the vehicle speed v and inversely proportional on the road wavelength. Amplitude Y as well as the ride-comfort factor K depends on the power spectral density )( fR which can be written as:

W

vfS

vfR −= )2(1)( 0 π . (4)

Here, 0S is the reference power spectral density estimated at the reference wavelength, πλ 2= ; for normal road conditions, it can be taken as 6

0 10120 −⋅=S m3/cycle [12].

Figure 8.a: 2-degrees of freedom model Figure 8.b: 1-degree of freedom simplified model

Figure 8: Quarter models for vehicle suspension The exponent W can be taken as 2 for high frequencies and as 1.5 for low frequencies. Denominating as x the vehicle response, the relative displacement )2sin( φπ −=−= ftZyxz equals the absorber’s piston stroke (Fig. 8.b). Ratio of the acceleration amplitude of the relative motion to the excitation amplitude

YZ /&& is important to evaluate the vehicle ride-comfort and the ratio of the displacement amplitude of the

Rough road

sm

tm

sk sc

tctk

ftYy π2sin=Excitation:

Yλ

Travel speed, v

Rough road

ts mmm +=

mm

kkks

st

111+=

ts ccc +=k


Yλ

Travel speed, v

x)2sin( φπ −=−= ftZyxz

Relative displacement (piston stroke)

λvf =Rough road

sm

tm

sk sc

tctk


Yλ

Travel speed, v

Rough road

sm

tm

sk sc

tctk


Yλ

Travel speed, v

Rough road

ts mmm +=

mm

kkks

st

111+=

ts ccc +=k


Yλ

Travel speed, v



λvf =Rough road

ts mmm +=

mm

kkks

st

111+=

ts ccc +=k


Yλ

Travel speed, v



λvf =


relative motion to the excitation amplitude YZ / is important to design properly the absorber. Thus, Fig. 9 illustrates on double logarithmic scale the variation of the excitation amplitude Y (Fig. 9.a) and the piston amplitude Z (Fig. 9.b) versus frequency f for different values of the travel speed =v 10-120 km/h, in the case of normal road conditions, by assuming that the suspension’s natural frequency is

== π//5.0 mkfn 1 Hz and the dimensionless damping coefficient is == kmc /5.0ς 0.15.

Figure 9.a: Variation of excitation amplitude Figure 9.b: Variation of piston amplitude Figure 9: Variation of the excitation and piston amplitudes vs. frequency for normal road conditions One observes that on the double logarithmic scale, the excitation amplitude linearly decreases versus frequency. While the maximum excitation amplitude maxY is reached at the lowest frequency (0.1 Hz), the maximum piston amplitude maxZ is reached at resonance ( == nff 1 Hz). Values of both maxY and maxZ increase versus the travel speed. Based on the model shown in Fig. 8.b, the transfer function can be written as:

2222

2222

)/(4])/(1[)/(414)(

nini

niii ffff

ffffHς

ςπ+−

+= . (5)

Concerning the vibration perception, one introduces the transfer function )( ifG that expresses the extent in which the rider perceives vibration as agreeable. For vibration in horizontal direction the transfer gain is high in the range of 1-2 Hz, and for vibration in vertical direction, it has a peak in the range of 4-8 Hz. In this work one considers only the vibration in vertical direction, for which the function )( ifG becomes [12]:

⎪⎩

⎪⎨

⎧

≥+−∈−∈−

=8;375.0

]8,4[;3]4,0[;153

)(

ii

i

ii

i

fff

fffG [Hz]. (6)

Substituting equations (4-6) into equation (1), one calculates the ride-comfort factor and based on it, evaluates the efficiency of a given suspension. Such evaluation should take into account that the vibrations are not perceived for 1.0<K , are slightly perceived for 4.01.0 <≤ K , are agreeably perceived for 6.14.0 <≤ K , are strongly perceived for 3.66.1 <≤ K , and are very strongly perceived for 3.6≥K [11-12]. Moreover, as Fig. 10 illustrates after Ref. [12], one should consider also the variation of the car’s ride-comfort versus the travel time when evaluates the influence on the passenger sickness, concentration and health. An ideal suspension should lead to a ride-comfort factor in the range 0.4-1.6, since regardless the travel interval, the vibrations are agreeably perceived.

10-1

100

101

1021

5

10152025

Frequency, f [Hz]

Exci

tatio

n am

plitu

de, Y

[mm

]

Road condition:Normal

v = 80 km/h

v = 120 km/h

v = 10 km/h

10-1

100

101

1020.01

0.1

1

1025

Pisto

n am

plitu

de, Z

[mm

] Frequency, f [Hz]

v = 80 km/h


v = 120 km/h

v = 10 km/h

10-1

100

101

1021

5

10152025

Frequency, f [Hz]

Exci

tatio

n am

plitu

de, Y

[mm

]


v = 80 km/h

v = 120 km/h

v = 10 km/h

10-1

100

101

1021

5

10152025

Frequency, f [Hz]

Exci

tatio

n am

plitu

de, Y

[mm

]


v = 80 km/h

v = 120 km/h

v = 10 km/h

10-1

100

101

1020.01

0.1

1

1025

Pisto

n am

plitu

de, Z

[mm

] Frequency, f [Hz]

v = 80 km/h


v = 120 km/h

v = 10 km/h

10-1

100

101

1020.01

0.1

1

1025

Pisto

n am

plitu

de, Z

[mm

] Frequency, f [Hz]

v = 80 km/h


v = 120 km/h

v = 10 km/h


Figure 10: Variation of the car ride-comfort versus the travel time and influence on the passenger sickness, concentration and health, after Ref. [12]

3.2 Experimental procedure

Travel experiments are performed by using a Toyota Corolla II Super Windy car, with a total mass of 910 kg. Including the mass of the passengers (driver and experimenter) and the mass of the measurement equipment (Fig. 13), the sprung and unsprung masses, used in the quarter model of the vehicle suspension (Fig. 8.a), become =sm 300 kg and =tm 25 kg. As already discussed, the actual frontal suspension consists of an OD mounted in parallel with a CHS (Fig. 1). Spring coefficient of the CHS is =sk 21.6 N/mm, and the tire’s spring coefficient tk varies in the range 196-235 N/mm when the tire’s air pressure

0p is modified in the interval 1.5-2.5 bar. As previously stressed, the tire’s damping coefficient can be neglected, and the suspension’s damping coefficient can be taken from Fig. 6. In this work, four types of suspensions are considered: used and unused (100,000 and 0 km travel distance) ODs coupled with CHS, and unused CDs with and without attached CHS. All these four types of suspensions were successively mounted at the frontal wheels on the test car (Fig. 11), and travel tests on a normal road were performed. During all the experiments carried-out, the original rear suspensions (used ODs mounted in parallel with CHSs) were employed. An impulse-like excitation was obtained when the car passed over a semi-sinusoidal asphalt step (Fig. 12). Using the equipment shown in Fig. 13, the car vibrations were measured and recorded for the following values of the tire’s air pressure =0p 1.5, 1.75, 2, 2.25, 2.5 bar and travel speeds =v 5, 7.5, 10, 12.5, 15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, 35, 37.5, 40 km/h. Since a precise travel speed should be measured in the exact moment the car passes over the step, to accurately determine the ride-comfort factor, a GPS speedometer with an absolute error of ± 0.1 km/h was used. Acceleration was measured at three distinct points, i.e., at the upper part of suspension (body), at the lower part of suspension (damper) and at the driver seat. Using thermocouples and digital thermometers, one measures the temperature on the damper’s external surface and also the environmental temperature (Fig. 13). Recorded data is automatically processed by MATLAB and the ride-comfort factor is computed. Concerning the designed CD, inside the left part of its cylinder (Fig. 2) one introduces 8 g of silica powder, consisted from nanoporous micro-grains with a mean particle diameter of 20 μm, and a mean pore diameter of about 7 nm. The whole (inner and outer) surface of silica particles is coated with alkyl chains (C8H17) to become water-repellent. A filter [10], with a diameter of the orifices of 2 μm, is used to prevent the leakage of silica particles and, consequently, to extend the CD’s life until 1-10 millions cycles (Fig. 2).

0.1

1

10

100

1000

0.01 0.1 1 10

Travel time [h]

Rid

e-co

mfo

rt fa

ctor

, K[-

] 1：Influence on sickness

3：Influence on health2：Influence on concentration

1

2

3

Very strong perception

Strong perception

Agreeable sensation

0.1

1

10

100

1000

0.01 0.1 1 10

Travel time [h]

Rid

e-co

mfo

rt fa

ctor

, K[-

] 1：Influence on sickness

3：Influence on health2：Influence on concentration

1

2

3

Very strong perception

Strong perception

Agreeable sensation


Concerning the target of the present work, relative to compacting and lightening of the proposed suspension, Table 2 compares the size and the mass of the actual suspension (OD mounted in parallel with CHS) and the proposed suspensions (CD with and without attached CHS). One observes that simply replacing the OD by CD, the suspension remains almost unmodified concerning its outer diameter and mass. However, by omitting the CHS, not only a simplified design, but also a compact (60% reduction of the outer diameter) and light design (25% weight reduction) of the proposed suspension is achieved.

CHS Actual suspension (OD with CHS)

Proposed suspension(CD with CHS)

Proposed suspension(CD without CHS)

Outer diameter [mm] 130 135 135 55 (60% reduction) Mass [kg] 1.6 5.9 6.2 (5 % increase) 4.4 (25% reduction)

Table 2: Comparison of the size and mass of the actual and proposed suspensions

Figure 11: Actual and proposed frontal suspensions Figure 12: Semi-sinusoidal asphalt step

Figure 13: Measurement equipment attached to the car during travel tests

Car

OD with CHS

CD without

CHS

0.037 m

0.405 m

Car

OD with CHS

CD without

CHS

Car

OD with CHS

CD without

CHS

0.037 m

0.405 m

0.037 m

0.405 m

Amplifier ①

GPS speedometer

PC

Mobile recorder

Seat

Accelerometer ③

ThermometerBody

(Upper part)

Damper(Lowerpart)

Accelerometer ②

Accelerometer ①

Amplifier ②

Amplifier ③

Amplifier ①

GPS speedometer

PC

Mobile recorder

Seat

Accelerometer ③

ThermometerBody

(Upper part)

Damper(Lowerpart)

Accelerometer ②

Accelerometer ①

Amplifier ②

Amplifier ③


3.3 Experimental results

Variation of the ride-comfort factor against the car’s travel speed is given in Fig. 14 for the case of used OD mounted in parallel with a CHS, in Fig. 15 for the case of unused OD coupled with a CHS, in Fig. 16 for unused CD with attached CHS, and in Fig. 17 for unused CD without attached CHS. From Figs. 14-17 one observes that the tire’s air pressure has insignificant influence on the ride-comfort factor. On the other hand, the ride-comfort factor increases at augmentation of the travel speed, and such results are in agreement with the previously reported theoretical and experimental findings.

Figure 14: Variation of the ride-comfort factor Figure 15: Variation of the ride-comfort factor vs. car travel speed for used OD with CHS vs. car travel speed for unused OD with CHS

Figure 16: Variation of the ride-comfort factor Figure 17: Variation of the ride-comfort factor vs. car travel speed for unused CD with CHS vs. car travel speed for unused CD without CHS

Figure 18 illustrates the variation of the ride-comfort factor at the driver seat, obtained for =0p 2bar on normal road with an asphalt step, for all four different types of tested suspensions. The best ride-comfort is obtained in the case of unused OD with CHS; on the second place is the used OD with CHS; on the third place is the unused CD with CHS; and, the worst ride-comfort is found for unused CD without CHS. Aging of the OD, i.e., the leakage of the nitrogen gas and the obstruction of orifices due to the deposition of gums, explains the worsening of the car’s ride-comfort. Since the CD performances are worst than those of the aged OD, one might conclude that the obtained experimental results are not very encouraging. However, on one hand, for a relatively inexpensive car, as that employed in this work, all suspensions considered, including the best one designed by the car maker

5 10 15 20 25 30 35 40Car travel speed, v [km/h]

Rid

e-co

mfo

rt fa

ctor

, K[-

]

10-1

100

102

103

101

Driver seatNormal road & stepUsed OD with CHS

p0 = 1.50, 1.75, 2.00, 2.25, 2.50bar


10-1

100

102

103

101

Rid

e-co

mfo

rt fa

ctor

, K[-

] p0 = 1.50, 1.75, 2.00, 2.25, 2.50bar

Driver seatNormal road & step

Unused OD with CHS


Rid

e-co

mfo

rt fa

ctor

, K[-

]

10-1

100

102

103

101


p0 = 1.50, 1.75, 2.00, 2.25, 2.50bar


Rid

e-co

mfo

rt fa

ctor

, K[-

]

10-1

100

102

103

101

10-1

100

102

103

101


p0 = 1.50, 1.75, 2.00, 2.25, 2.50bar


10-1

100

102

103

101

Rid

e-co

mfo

rt fa

ctor

, K[-

] p0 = 1.50, 1.75, 2.00, 2.25, 2.50bar


Unused OD with CHS


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(new OD with CHS), produced a ride-comfort factor in the range 10-1000, i.e., considerably worst than ideal suspension ( 6.14.0 −=K ). However, such severe travel conditions, i.e., passage past asphalt steps, are relatively rarely encountered during the real ride of the car. Although not graphically illustrated here, in the case of travel tests on a normal road without asphalt step, all the suspensions tested produced ride-comfort factors in the range 1-10. Consequently, as shown in Fig. 10, even during a long period of riding, bad effects on the passenger sickness and concentration are not to be expected.

Figure 18: Comparative evaluation of the tested suspensions concerning the variation of the car’s ride-comfort factor versus the travel speed

On the other hand, one observes that the difference in performances of various suspensions investigated here reduces as the travel speed increases. It seems that, at the augmentation of the car velocity, when the vehicle passes over step, the impact energy transmitted increases, and consequently, the pressure inside the CD cylinder attains the necessary level to induce efficient penetration of the water inside the silica matrix. As another reason one might consider that, as the car travel speed v increases, the piston stroke reduces to values on order of 1 mm (see Fig. 9.b in the field of high frequencies, λ/vf = ). Thus, it seems that all types of absorbers become “equally ineffective” at high travel speeds. Although not encouraging from the ride-comfort standpoint, results obtained for CD without CHS prove that water natural exudation from silica matrix at the CD’s extension is able to provide the necessary restoration force; hence, simplification of the car suspension can be achieved by omitting the CHS. On the other hand, softening of the colloidal suspension by using silica with larger mean pore diameter might improve the car’s ride-comfort. This aspect will be addressed into our future work. In order to evaluate the transmissibility of vibrations from the rough road to the car’s drive-shaft, the FFT transformation of acceleration measured at the lower part of suspension versus the frequency is shown in Fig. 19.a for =v 20 km/h and in Fig. 19.b for =v 40 km/h, when the air pressure was set to =0p 2bar. Such graphs allow the identification of the main excitation frequencies in the vibration spectrum and hence, the identification of their possible sources. For all the considered travel speeds, vibration transmissibility from the rough road to the car’s drive-shaft (downward part of suspension) is the lowest for the unused CD without CHS; on the second place is the unused CD with CHS; and, the highest transmissibility is found for the unused OD without CHS. This can be explained by the fact that OD dissipates the impact energy during extension (the secondary part of the working cycle), and, on the contrary, CD directly dissipates the impact energy during compression (the primary part of the working cycle). In other words, it seems that, through a direct dissipation mechanism, the efficiency of car suspension can be improved, relative to the aspect of vibration transmissibility. When the CHS is mounted in parallel with the CD, a part of the shock energy is accumulated by the spring, diminishing the energy available for dissipation, and hence, reducing the efficiency of colloidal suspension.


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Figure 19.a: Results at 20 km/h travel speed Figure 19.b: Results at 40 km/h travel speed Figure 19: FFT transformation of the acceleration measured at the lower part of suspension

4 Conclusions

In this work, four types of car’s frontal suspensions were investigated as follows: used and unused (100,000 and 0 km travel distance) oil dampers (ODs) coupled with compression helical springs (CHSs), and unused colloidal dampers (CDs) with and without attached CHS. Firstly, all absorbers were dynamically tested on a fatigue machine and the damping coefficients were found. Then, all suspensions were mounted on a real car and travel tests on normal road with an asphalt step were performed. Car’s ride comfort and the vibration transmissibility from road to the car’s drive-shaft were experimentally evaluated. The main conclusions can be summarized as follows.

1. Aging of the OD produced on one hand, a larger hysteresis due to the obstruction of orifices by deposed gums, and, on the other hand, the worsening of the car’s ride-comfort, due to the leakage of the nitrogen gas.

2. OD dissipates the impact energy during extension, i.e., the secondary part of the working cycle, and, on the contrary, CD directly dissipates the impact energy during compression, i.e., the primary part of the working cycle. For this reason, the vibration transmitted from the rough road to the car’s drive-shaft is lower for suspensions employing CDs.

3. OD has to be mounted in parallel with a CHS, the latter providing necessary restoring force, to bring back the suspension to its initial position after a complete cycle of compression-extension. However, in the case of a CD, since the liquid naturally exudes from the nanopores of lyophobic silica during decompression, the restoring force is intrinsically achieved, and the CHS can be omitted. Thus, the CD provides for a dual function, of absorber and spring, this allowing a simplified design of the car suspension. Moreover, in this work by omitting the CHS, not only a simplified design, but also a compact (60% reduction of the outer diameter) and light design (25% weight reduction) of the proposed suspension was achieved.

4. Tire’s air pressure, varying in the range 1.5-2.5 bar, had insignificant influence on the car’s ride-comfort. On the other hand, the ride-comfort factor increased at augmentation of the travel speed, and such results were in agreement with the previously reported theoretical and experimental findings.

5. For a relatively inexpensive car, as that employed in this work, all the suspensions considered, including the best one designed by the car maker (new OD with CHS), produced a ride-comfort factor in the range 10-1000, i.e., considerably worst than ideal suspension

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( 6.14.0 −=K ) that provides agreeable perception of vibrations. However, such severe travel conditions, i.e., passage past asphalt steps, are relatively rarely encountered during the real ride of the car. In the case of travel tests on a normal road without asphalt step, all the suspensions tested produced ride-comfort factors in the range 1-10, consequently, even during a long period of riding, bad effects on the passenger sickness, concentration and health are not to be expected.

6. Although, as found for silica used in this work, the ride-comfort of a car equipped with CDs without CHSs is worst than that obtained for aged ODs with CHSs, softening of the colloidal suspension, by using silica with larger mean pore diameter, might improve the car’s ride-comfort. This aspect will be addressed into our future work.

Acknowledgements

This research was supported by the Japanese Ministry of Education, Grant-in-aid for scientific fundamental research, Project C-18560146. Technical support provided by Mr. H. NISHIZAWA @ Riken Enterprise Co. Ltd., Mr. H. YASUNAGA @ YASUNAGA Gear Tech. Co. Ltd., and Mr. Y. NAGATA @ NAGATA Metal-Sheet Co. Ltd. during the manufacturing of the proposed CD is acknowledged. Support provided by Messrs. H. IZAKI, T. FUJIMOTO, S. TANI, D. MORISAKI, and T. NONAKA from Fukuoka Institute of Technology, in the frame of their graduation research, during the car travel tests is also acknowledged.

References

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[2] A.V. Erochenko, Damper with High Dissipating Power, International Patent WO 01/55616 A1 (2001).

[3] A.V. Erochenko, A new paradigm of mechanical energy dissipation; Part 1: theoretical aspects and practical solutions, Proc. Inst. Mech. Eng., Part D, Journal of Automobile Eng., Vol. 221 (2007), pp. 285-300.

[4] A.V. Erochenko, I. Piatiletov, L. Coiffard, V. Stoudenets, A new paradigm of mechanical energy dissipation; Part 2: experimental investigation and effectiveness of a novel car damper, Proc. Inst. Mech. Eng., Part D, Journal of Automobile Eng., Vol. 221 (2007), pp. 301-312.

[5] C.V. Suciu, T. Iwatsubo, S. Deki, Investigation of a colloidal damper, Journal of Colloid and Interface Science, Vol. 259, Academic Press (2003), pp. 62-80.

[6] C.V. Suciu, T. Iwatsubo, S. Deki, Novel principle of mechanical energy dissipation; Part 1: static performances of colloidal damper, JSME International Journal, Vol. C47 (2004), pp. 180-188.

[7] C.V. Suciu, T. Iwatsubo, Novel principle of mechanical energy dissipation; Part 2: dynamic performances of colloidal damper, JSME International Journal, Vol. C47 (2004), pp. 189-198.

[8] C.V. Suciu, T. Iwatsubo, K. Yaguchi, M. Ikenaga, Novel and global approach of the complex and interconnected phenomena related to the contact line movement past a solid surface from hydrophobized silica gel, Journal of Colloid and Interface Science, Vol. 283, Academic Press (2005), pp. 196-214.

[9] T. Iwatsubo, C.V. Suciu, M. Ikenaga, K. Yaguchi, Dynamic characteristics of a new damping element based on surface extension principle in nanopores, Journal of Sound and Vibration, Vol. 308, Academic Press (2007), pp. 579-590.

[10] C.V. Suciu, K. Yaguchi, Endurance tests on a colloidal damper destined to vehicle suspension, Experimental Mechanics, Vol. 49, Springer (2009), pp. 383-393.


[11] Mechanical Vibration and Shock – Evaluation of Human Exposure to Whole-Body Vibration; Part 1: General Requirements, International Organization for Standardization, ISO 2631-1 (1997).

[12] S. Komamura, Automotive Suspension, Kayaba Tech. Publisher, Tokyo (2005). (in Japanese) [13] S.K. Jha, Characteristics and sources of noise and vibration and their control in motor cars, Journal

of Sound and Vibration, Vol. 47, Academic Press (1976), pp. 543-558.


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