chapter 4 vehicle testing - virginia tech
TRANSCRIPT
37
Chapter 4
Vehicle Testing
The purpose of this chapter is to describe the field testing of the controllable dampers on a Volvo
VN heavy truck. The first part of this chapter describes the test vehicle used in the damper field
testing. The second part provides a background on how the dampers were mounted on the test
vehicle. Next, the configuration of sensors used to control the dampers and acquire the test data,
as well as the data acquisition system are described. Finally, this chapter describes the field tests
that were performed along with an analysis of the results.
4.1 Test Vehicle Description
The test vehicle used in this study was a Volvo VN series, heavy truck with L4 cab, as shown in
Figure 4.1.
Figure 4.1. Volvo VN Heavy Truck, Model 770 with the Test Trailer
The test truck includes a 48 ft box trailer that was unladen for our tests. The tractor weighs
44,000 pounds and the legal limit on the gross vehicle weight for this vehicle is 80,000 pounds.
38
4.2 Damper Installation on Test Vehicle
The Volvo VN heavy truck has six dampers at the primary suspension, as shown in Figure 4.2.
Figure 4.2. Location of Primary Suspension Dampers on Test Vehicle
Of the six dampers, four were replaced with controllable MR Dampers, as shown in Figure 4.3.
Figure 4.3. Location of MR Dampers on Test Vehicle
We selected to place four dampers on the truck, because we did not have enough dampers for all
six locations, and our past experience had shown that we can get most of the benefits of
39
semiactive dampers by placing them on only two of the four locations at the drive axle. The four
MR dampers are shown installed on the front and rear axles in Figures 4.4 and 4.5, respectively.
fron
t
driver passenger
Figure 4.4. MR Dampers Installed on the Front Axle
rear
passengerdriver
Figure 4.5. MR Dampers Installed on the Rear Axle
The four MR dampers were wired to the system controller, which was located in the sleeper cab
of the test vehicle. The wiring between the controller MR dampers was installed such that they
can be used for repeated tests, while the MR dampers were installed for quick exchange with the
truck’s stock dampers.
40
4.3 Sensors and Data Acquisition System
In order to control the dampers according to the skyhook policy described in section 2.1.4, it is
necessary to sense the velocities at each end of the controllable dampers. The accelerometers
used for this, shown in Figure 4.6, were manufactured by PCB Piezotronics, and had a sensitivity
of 100 mV/g and were used in conjunction with a PCB 584 series 16 channel signal conditioner.
Figure 4.6. PCB Accelerometers Used for Field Testing
Eight accelerometers, one at each end of each damper, were used to capture the data needed to
control the four dampers, as shown in Figure 4.7. Four of the accelerometers were mounted on
the truck’s frame rail, near the top of each of the four MR dampers and four were located on the
front and rear axles, approximately below the accelerometers on the frame rail.
frame rail mountedaccelerometer
axle mountedaccelerometer
Figure 4.7. Rear Passenger-Side Accelerometers
41
Additionly, three accelerometers were used to capture data for evaluating vehicle ride quality.
These accelerometers were arranged in a triax configuration, as shown in Figure 4.8.
Figure 4.8. Accelerometer Triax
The accelerometer triax was located at the B-post, directly behind the driver, 35 inches above the
cab floor, as shown in Figure 4.9, in order to measure the vibration transmissions to the cab in
the vertical, lateral, and fore and aft directions.
Figure 4.9. Accelerometer Triax Location
The signals from the eight accelerometers located on the frame and axles of the truck were
multiplexed to allow the signal to be simultaneously recorded and used in the control of the
dampers. The acceleration signals were integrated by the controller to find the velocity at each
42
end of the dampers. Based on the sign of the relative velocity across each damper, the controller
supplies either a zero or a three amp current to the damper, according to the on-off skyhook
control policy that was discussed earlier.
All eleven channels of accelerometer data were sampled at 6000 Hz and recorded for the
duration of the test using a sixteen channel SONY DAT recorder model PC216Ax, shown in
Figure 4.10.
Figure 4.10. SONY DAT recorder
All channels of the DAT recorder were tested with known waveforms before and after the tests,
to ensure proper functioning of the recorder channels.
4.4 Field Testing
The effect of the dampers was investigated with respect to both transient and steady state
dynamics. In the transient dynamic tests, the truck was driven over the speed bump shown in
figure 4.11 at 6-7 mph.
Figure 4.11. Speed Bump Test
43
Driving over the speed bump induced large amplitude oscillations in the test vehicle, which were
then damped out by the suspension system. This test was performed repeatedly to increase the
accuracy of the data, which was collected for four cases:
1. The MR dampers on the truck, operated according to the on-off skyhook control policy
outlined previously.
2. The MR dampers on the truck, continuously operated in their off (zero current) state.
3. The MR dampers on the truck, continuously operated in their on (three amp current)
state.
4. The original passive dampers in place (i.e., stock dampers).
The above represent one semiactive case and three passive cases. The three passive cases
represent hard damping (MR dampers in their on state), soft damping (MR dampers in their off
state), and medium damping (stock dampers).
The steady state portion of the test consisted of driving the test vehicle along a straight,
level road at a sustained highway speed of 55 mph. In this case, the input to the suspensions is
the road input at the tires. The steady state tests were conducted for cases 1, 2, and 4 of the
transient tests. Case 3 was not performed with a steady state input as the expected performance
can be extrapolated from the measured performance of cases 2 and 4.
The data resulting from the field tests of the dampers consists of ten-second segments of
eleven channels of data sampled at 6000 Hz, resulting in approximately 660,000 data points for
each data segment. Each data set needed to be heavily processed in order to extract the
necessary information. Each of the data points in the data set is a voltage, which from the
sensitivity of the accelerometers and the gains of the signal conditioner, can be converted into
acceleration. Each data channel maps to an accelerometer in one of the eleven positions
previously outlined.
In order to discuss the separate accelerometers, it is necessary to label each of the
accelerometer positions. To facilitate this, each wheel of the truck was given a letter as shown in
Figure 4.12.
44
Figure 4.12. Accelerometer Position Convention
As shown in Table 4.1, accelerometers are then referred to by pair of letters referring first to the
wheel letter shown above, and second to either T of B corresponding to either frame-mounted or
axle-mounted accelerometers, respectively. The triax accelerometers are referred to by the
direction in which they are measuring.
Table 4.1. Accelerometer- Channel Assignments for Field Testing
Channel Position Measurement1 AT driver side front, frame accelerometer2 AB driver side front, axle accelerometer3 BT passenger side front, frame accelerometer4 BB passenger side front, axle accelerometer5 ET driver side rear, frame accelerometer6 EB driver side rear, axle accelerometer7 FT passenger side rear, frame accelerometer8 FB passenger side rear, axle accelerometer9 Y B-post roll
10 Z B-post heave11 X B-post pitch
4.5 Transient Data Analysis
The transient or speed bump data was looked at in both the time and frequency domains, but the
main analysis was carried out in the frequency domain. In each ten-second data set, the truck
hits the speed bump with the front wheels at about two seconds into the set. The ten second data
set is long enough for the vehicle oscillations to damp out by the end of the data set.
45
4.5.1 Time Domain Analysis of the Transient Data
The time domain analysis of the transient data was performed with respect to both acceleration
and displacement, with the first steps of the data processing being the same for both. The first
steps included decimating the data by first passing it through a lowpass filter, and then
resampling it at a lower frequency. The low pass filter used for the decimation was a 30 point
finite impulse response (FIR) filter, shown in Figure 4.13.
Figure 4.13. Frequency Response for 30 Point FIR Filter Used in Decimation
This filter was chosen because of its low pass-band ripple, and steep attenuation at higher
frequencies. The data was then resampled with a decimation factor of 60 (i.e., every 60th point
was used), moving the new Nyquist frequency to 50 Hz. The next step was to apply a digital
filter to the decimated data in order to eliminate both high frequency noise and low frequency
drift. A Chebyshev bandpass filter was created with a bandpass of 1 to 15 Hz, steep attenuation
on either side of the passband, and unity magnitude within the passband. The low end of the
bandpass was chosen to be 1 Hz to match the low end of the useful range of the accelerometers.
Figure 4.14 shows the ideal filter in red and the actual filter used in blue.
46
0 5 10 15 20 25 30 35 40 45 500
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
frequency (Hz)
mag
nitu
de
Figure 4.14. Frequency Response for Chebyshev Filter Used
The filter was applied to the data in first the forward direction and then the data reversed and the
filter reapplied. This eliminated phase distortion and modified the magnitude by the square of
the filter magnitude. The passband magnitude of the filter used is unity with small ripples to
eliminate the effect of the filter magnitude. This filtering was accomplished using the MATLAB
.m file “filtfilt”.
The effect of applying this type of filter was experimentally verified by testing a known
signal. The known test signal, shown in Figure 4.15, was a decaying 4 Hz sine wave.
0 1 2 3 4 5 6 7 8 9 10-2
-1.5
-1
-0.5
0
0.5
1
1.5
24 Hz test signal
time
sign
al
Figure 4.15. Test Signal Used for Validating Filters
47
The test signal was “hidden” by combining it with both a decaying 20 Hz sine wave and a
decaying 0.8 Hz sine wave, as shown in Figure 4.16.
0 1 2 3 4 5 6 7 8 9 10-2.5
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5test signal "hidden" with 0.8 and 20 Hz signals
time
sign
al
Figure 4.16. Test Signal “Hidden”
The combination of these three waves was put through the filter shown in Figure 4.14, using both
standard filter techniques and the zero-phase forward and reverse filtering that filtfilt applies.
The results of putting the “hidden” test signal through the filter in Figure 4.14 using both
standard filtering and zero-phase forward and reverse filtering are shown in Figure 4.17. The
MATLAB .m file for this purpose is included in Appendix 1b.
48
Figure 4.17. Effect of Applied Filters to a Known Signal
Though the zero phase forward and reverse filtering induces greater discrepancies at the start of
the data set than standard filtering, it is more effective at preserving the transient character of the
data. At this point the data processing differs depending on whether it is acceleration or
displacement that is of interest.
4.5.1.1 Acceleration Data Analysis
The acceleration data was mean-zeroed and plotted versus time to obtain the summary
information. The summary information consists of:
• the global acceleration maximum during the ten second data block
• the local acceleration maximum immediately following the global maximum
• the corresponding times of the two acceleration maximums
• the slope of the decay between the first and second acceleration maximums
• the RMS acceleration for the time period of one second before the first acceleration
maximum to two seconds after.
49
The MATLAB .m file that was used to compute this information is included in Appendix 1c. A
sample plot of the acceleration data for channel 10 (cab acceleration in the vertical direction) is
shown in Figure 4.18 with a line connecting the first and second peaks used in the summary
information.
0 1 2 3 4 5 6 7 8 9 10-5
-4
-3
-2
-1
0
1
2
3
4filtered acceleration of channel 10
acce
lera
tion
(m/s
2)
t ime (sec)
Figure 4.18. Sample Plot of Acceleration Data for Channel 10
Plots of this for the all channels tested in each of the four test scenarios (MR dampers with
skyhook control, MR continuously on, MR continuously off, and original dampers) are included
in Appendix 2. Values of both the maximum and RMS acceleration were averaged across like
data sets for each channel. There were nine data sets taken in which the test truck, equipped with
MR dampers and skyhook control, was driven over the same speed bump. The average peak
acceleration amplitude and average RMS acceleration for each of these nine sets of data were
averaged together. The results of this are shown in Figures 4.19 and 20.
50
Average Peak Acceleration Amplitude
0
2
4
6
8
10
12
14
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Acc
eler
atio
n
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e fro n t , f r a m e
B B p a s s e n g e r s i d e fro n t , a x le
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l l
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.19. Acceleration Results: Average Peak Acceleration Amplitude for the Test Vehicle
w/MR Dampers and Skyhook Control Policy
Average RMS Acceleration
0
0.5
1
1.5
2
2.5
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
RM
S A
ccel
erat
ion
P o s i t io n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m eA B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t , f r a m eB B p a s s e n g e r s i d e f r o n t , a x l eE T d r i v e r s i d e r e a r , f r a m eE B d r i v e r s i d e r e a r , a x leF T p a s s e n g e r s i d e r e a r , f r a m eF B p a s s e n g e r s i d e r e a r , a x l eY B -p o s t ro llZ B -p o s t h e a v eX B -p o s t p i t ch
Figure 4.20. Acceleration Results: Average RMS Acceleration for the Test Vehicle w/ MR
Dampers and Skyhook Control Policy
The test in which the truck with the MR dampers being operated continuously in the on or three
amp state was driven over the speed bump was repeated five times. The peak acceleration
amplitude and RMS acceleration from each of these five data sets were averaged together. Since
the quantities to be compared from one test case to another are averaged across data sets, the
51
number of data sets from test to test does not need to be the same. The results for the five data
sets are shown in Figures 4.21 and 22.
Average Peak Acceleration Amplitude
0
2
4
6
8
10
12
14
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Acc
eler
atio
n
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e fro n t , f r a m eB B p a s s e n g e r s i d e fro n t , a x l e
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l l
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.21. Acceleration Results: Average Peak Acceleration Amplitude for the Test Vehicle
w/MR Dampers Operated in the On State
Average RMS Acceleration
0
0.5
1
1.5
2
2.5
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
RM
S A
ccel
erat
ion
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e fro n t , f r a m eB B p a s s e n g e r s i d e fro n t , a x l e
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l l
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.22. Acceleration Results: Average RMS Acceleration for the Test Vehicle w/MR
Dampers Operated in the On State
There were four data sets in which the test vehicle was driven over the same speed bump with
the MR dampers on the truck and being operated continuously in the off or zero amp state. The
results for the four data sets are shown in Figures 4.23 and 24.
52
Average Peak Accelerat ion Ampl i tude
0
1
2
3
4
5
6
7
8
9
10
AT AB BT BB ET EB F T FB Y Z X
Accelerometer Posit ion
Acc
eler
atio
n
P o s i t io n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t, fra m e
B B p a s s e n g e r s i d e f r o n t, a x leE T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l eF T p a s s e n g e r s i d e r e a r , f ra m e
F B p a s s e n g e r s i d e r e a r , a x leY B - p o s t ro ll
Z B - p o s t h e a v eX B - p o s t p i t c h
Figure 4.23. Acceleration Results: Average Peak Acceleration Amplitude for the Test Vehicle
w/MR Dampers Operated in the Off State
Average RMS Accelerat ion
0
0.5
1
1.5
2
2.5
AT AB BT BB ET EB F T FB Y Z X
Accelerometer Posit ion
RM
S A
ccel
erat
ion
P o s i t io n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t, fra m e
B B p a s s e n g e r s i d e f r o n t, a x leE T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l eF T p a s s e n g e r s i d e r e a r , f ra m e
F B p a s s e n g e r s i d e r e a r , a x leY B - p o s t ro ll
Z B - p o s t h e a v eX B - p o s t p i t c h
Figure 4.24. Acceleration Results: Average RMS Acceleration for the Test Vehicle w/MR
Dampers Operated in the Off State
There were six data sets in which the test vehicle was driven over the same speed bump with the
truck’s original dampers in place. These data sets serve as a baseline with which to judge the
53
effectiveness of the MR dampers. The averaged maximum acceleration and averaged RMS
acceleration are shown in Figures 4.25 and 26.
Average Peak Acceleration
0
1
2
3
4
5
6
7
8
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Acc
eler
atio
n
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e fro n t , f r a m e
B B p a s s e n g e r s i d e fro n t , a x le
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l l
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.25. Acceleration Results: Average Peak Acceleration Amplitude for the Test Vehicle
with Original Dampers in Place
Average RMS Acceleration
0
0.5
1
1.5
2
2.5
AT AB BT BB ET EB FT FB Y Z X
Channel
RM
S A
ccel
erat
ion
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e fro n t , f r a m e
B B p a s s e n g e r s i d e fro n t , a x le
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l l
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.26. Acceleration Results: Average RMS Acceleration for the Test Vehicle with
Original Dampers in Place
54
4.5.1.2 Displacement Data Analysis
After the data was decimated and filtered, there were transients at the start and end of the data
that existed as artifacts of the digital filtering. This effect can be seen looking at the filter test
signal shown earlier in Figure 4.16. While the data was being analyzed in terms of acceleration,
this effect was unimportant, however since looking at the data in terms of displacement requires
the data to be integrated twice which amplifies these errors, corrections must be made. In order
to correct for this error, the value of the acceleration of the first and last one second of data was
set to zero, and then the data was again mean zeroed. To integrate the data, each set was put
through a 1/s integrator block (corresponding to multiplying each frequency component by 1/jw)
using the MATLAB command LSIM. The data, which is now velocity, was re-filtered using the
filter shown in Figure 4.13, and again mean zeroed. Finally, the data was again integrated using
an integrator block.
The data, which is now displacement, was plotted and summary information extracted. The
summary information consists of:
• the global displacement maximum during the eight second data block
• the local displacement maximum immediately following the global maximum
• the corresponding times of the two displacement maximums
• the slope of the decay between the first and second displacement maximums
• the RMS displacement for the time period going from one second before the first
displacement maximum to two seconds after.
The MATLAB .m file that was used to do this is included in Appendix 1d. Figures 4.27-33 are
sample plots for seven of the eleven measurement positions showing displacement versus time.
These plots show a trend that the MR dampers operated continuously in their off state allow the
highest levels of displacement, and the MR dampers operated continuously in their on state allow
the lowest levels of displacement. Both the MR semiactive and original damper displacements
tend to be between these two extremes.
55
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger frame displacement
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger frame displacement
time (sec)
MR dampersoperated withskyhook control
Originalpassivedampers
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger frame displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (pitch direction)
time (sec)
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.27. Front Passenger-Side Frame Displacement Sample Plots
56
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger axle displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger axle displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger axle displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front passenger axle displacement
time (sec)
MR dampersoperated withskyhook control
Originalpassivedampers
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.28. Front Passenger-Side Axle Displacement Sample Plots
57
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver frame displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver frame displacement
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver frame displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver frame displacement
time (sec)
MR dampersoperated withskyhook control
Originalpassivedampers
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.29. Rear Driver-Side Frame Displacement Sample Plots
58
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver axle displacement
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver axle displacement
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver axle displacement
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03front driver axle displacement
time (sec)
MR dampersoperated withskyhook control
Originalpassivedampers
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.30. Rear Driver-Side Axle Displacement Sample Plots
59
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (roll direction)
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (roll direction)
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (roll direction)
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (roll direction)
time (sec)
MR dampersoperated withskyhook control
Originalpassivedampers
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.31. B-Post Roll Displacement Sample Plots
60
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (heave direction)
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (heave direction)
time (sec)
(m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (heave direction)
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (heave direction)
time (sec)
disp
lace
men
t (m
)
MR dampersoperated withskyhook control
Originalpassivedampers
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.30. B-Post Heave Displacement Sample Plots
61
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (pitch direction)
time (sec)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (pitch direction)
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (pitch direction)
time (sec)
disp
lace
men
t (m
)
0 1 2 3 4 5 6 7 8-0.03
-0.02
-0.01
0
0.01
0.02
0.03body displacement (pitch direction)
time (sec)
disp
lace
men
t (m
)
MR dampersoperated withskyhook control
Originalpassivedampers
MR damperscontinuouslyoff (soft)
MR damperscontinuouslyon (hard)
Figure 4.33. B-Post Pitch Displacement Sample Plots
62
Plots of this for the all channels in each of the four test scenarios (MR dampers with skyhook
control, MR continuously on, MR continuously off, and original dampers) are included in
Appendix 3. Values of both the maximum and RMS displacement were averaged across like
data sets for each channel. There averaged maximum peak and RMS displacement for the nine
sets of data where the MR dampers were being controlled with the skyhook policy are shown in
Figures 4.34 and 35.
Average Peak Displacement Amplitude
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Dis
plac
emen
t
P o s i t io n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m eA B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t , f r a m eB B p a s s e n g e r s i d e f r o n t , a x l eE T d r i v e r s i d e r e a r , f r a m eE B d r i v e r s i d e r e a r , a x leF T p a s s e n g e r s i d e r e a r , f r a m eF B p a s s e n g e r s i d e r e a r , a x l eY B -p o s t ro llZ B -p o s t h e a v eX B -p o s t p i t ch
Figure 4.34. Displacement Results: Average Peak Displacement Amplitude for the Test Vehicle
w/MR Dampers and Skyhook Control Policy
63
Average RMS Displacement
0
0.002
0.004
0.006
0.008
0.01
0.012
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
RM
S D
ispl
acem
ent
P o s i t i o n M e a s u r e m e nt
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e f r o n t , f ra m e
B B p a s s e n g e r s i d e f r o n t , a xle
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o ll
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.35. Displacement Results: Average RMS Displacement for the Test Vehicle w/MR
Dampers and Skyhook Control Policy
The result of averaging the peak and RMS displacement for the five data sets where the test
vehicle was operated with the MR dampers continuously on are shown in Figures 4.36 and 37.
Average Peak Displacement Amplitude
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Dis
plac
emen
t
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t , f r a m e
B B p a s s e n g e r s i d e f r o n t , a x leE T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l eF T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x leY B - p o s t r o ll
Z B - p o s t h e a v eX B - p o s t p i t c h
Figure 4.36. Displacement Results: Average Peak Displacement Amplitude for the Test Vehicle
w/MR Dampers Operated in the On State
64
Average RMS Displacement
0
0.002
0.004
0.006
0.008
0.01
0.012
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
RM
S D
ispl
acem
ent
P o s i t io n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e f r o n t , f r a m e
B B p a s s e n g e r s i d e f r o n t , a x le
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B -p o s t ro ll
Z B -p o s t h e a v e
X B -p o s t p i tc h
Figure 4.37. Displacement Results: Average RMS Displacement for the Test Vehicle w/MR
Dampers Operated in the On State
The result of averaging the peak and RMS displacement for the four data sets where the test
vehicle was operated with the MR dampers continuously off are shown in Figures 4.38 and 39.
Average Peak Displacement Amplitude
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Dis
plac
emen
t
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e f r o n t , f ra m e
B B p a s s e n g e r s i d e f r o n t , a x le
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f ra m e
F B p a s s e n g e r s i d e r e a r , a xle
Y B -p o s t ro l l
Z B -p o s t h e a v e
X B -p o s t p i tc h
Figure 4.38. Displacement Results: Average Peak Displacement Amplitude for the Test Vehicle
w/MR Dampers Operated in the Off State
65
Average RMS Displacement
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
AT AB BT BB ET EB FT FB Y Z X
Channel
RM
S D
ispl
acem
ent
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e f r o n t , f ra m e
B B p a s s e n g e r s i d e f r o n t , a x le
E T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f ra m e
F B p a s s e n g e r s i d e r e a r , a xle
Y B -p o s t ro l l
Z B -p o s t h e a v e
X B -p o s t p i tc h
Figure 4.39. Displacement Results: Average RMS Displacement for the Test Vehicle w/MR
Dampers Operated in the Off State
The result of averaging the peak and RMS displacement for the six data sets where the test
vehicle was operated with the original dampers in place are shown in Figures 4.40 and 41.
Average Peak Displacement
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Dis
plac
emen
t
P o s i t io n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m eA B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t , f r a m eB B p a s s e n g e r s i d e f r o n t , a x l eE T d r i v e r s i d e r e a r , f r a m eE B d r i v e r s i d e r e a r , a x leF T p a s s e n g e r s i d e r e a r , f r a m eF B p a s s e n g e r s i d e r e a r , a x l eY B -p o s t ro llZ B -p o s t h e a v eX B -p o s t p i t ch
Figure 4.40. Displacement Results: Average Peak Displacement for the Test Vehicle with
Original Dampers in Place
66
Average RMS Displacement
0
0.002
0.004
0.006
0.008
0.01
0.012
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Posit ion
RM
S D
ispl
acem
ent
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m e
A B d r i v e r s i d e f r o n t , a x l e
B T p a s s e n g e r s i d e fro n t , f r a m e
B B p a s s e n g e r s i d e fro n t , a x l eE T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l e
F T p a s s e n g e r s i d e r e a r , f r a m e
F B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l l
Z B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.41. Displacement Results: Average Peak Displacement for the Test Vehicle with
Original Dampers in Place
4.5.1.3 Results of Time Domain Analysis of Transient Tests
There are two parts of the time domain analysis of the transient tests. The first part of the
discussion will deal with the acceleration data and the second part will look at the results derived
from the displacement data.
A comparison of the average peak accelerations as measured at the eleven measurement
points while the test vehicle is driven over the speed bump is shown in Figure 4.42.
67
Average Peak Acceleration Amplitude
0
2
4
6
8
10
12
14
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR ActiveMR 3AMR 0AOriginal
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.42. Average Peak Acceleration Comparison
A comparison of the four test cases shows that the MR dampers controlled with the skyhook
control policy exhibit equal or greater levels of average peak acceleration than the original
dampers on all channels. The levels of average peak acceleration were significantly higher for
the MR active case than the original dampers for accelerometer positions AB, BB, EB, and FB.
As these positions all represent to measurements being taken on the axles of the truck, this result
was not unexpected, as the MR dampers can be softer than the stock dampers. For the
measurement positions measuring frame acceleration (AT, BT, ET, and FT), the levels of
average peak acceleration were similar for the MR active case and the original dampers, with the
original damper case exhibiting slightly better performance (lower acceleration). The results of
the tests where the MR dampers were controlled with either zero (continuously off) or three
amps (continuously on) of current tend to envelope the average peak acceleration values of the
MR active case at positions measuring frame acceleration. The results of measurements made at
the B-post in the y, z, and x directions (corresponding to roll, heave, and pitch respectively) show
that the MR active case accentuates the acceleration seen by the cab of the vehicle.
A comparison of the average RMS accelerations as measured at the eleven measurement
points while the test vehicle is driven over the speed bump is shown in Figure 4.43.
68
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average RMS Acceleration
0
0.5
1
1.5
2
2.5
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR ActiveMR 3AMR 0AOriginal
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.43. Average RMS Acceleration Comparison
The comparison of the four test cases show that the MR dampers controlled with the skyhook
control policy exhibit greater levels of RMS acceleration than the case with the original dampers
on all channels measured on the axles of the truck. This was also found to be true for channels
measured on the frame in the front of the truck. However, the levels of RMS acceleration at the
frame in the rear of the truck (ET and FT) showed the MR active case to be better (lower levels
of RMS acceleration) than the original case. The MR active case is shown to transmit less RMS
acceleration to the frame of the truck than the cases where the MR dampers were either
continuously on or continuously off. The results of measurements taken at the B-post in the y, z,
and x directions (roll, heave, and pitch) show that the MR active case accentuates the
acceleration seen by the cab of the vehicle versus the original dampers.
A comparison of the average peak displacement as measured at the eleven measurement
points while the test vehicle is driven over the speed bump is shown in Figure 4.44.
69
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Displacement Amplitude
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR ActiveMR 3AMR 0AOriginal
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.44. Average Peak Displacement Comparison
The comparison shows that the use of the MR dampers with the skyhook control policy
increased the vertical displacement of both the axle and the frame in the front of the test vehicle
(AT, AB, BT, and BB) as compared to the stock dampers. In the rear of the truck, the
application of the MR dampers with the skyhook control policy had little effect on the vertical
displacement of either the axle or frame compared to the original dampers. Measurements taken
at the B-post in the y, z, and x directions (roll, heave and pitch of the cab of the truck) show
increased motion with the MR dampers and skyhook control policy when compared to the
original dampers.
A comparison of the average RMS displacement as measured at the eleven measurement
points while the test vehicle is driven over the speed bump is shown in Figure 4.45.
70
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average RMS Displacement
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR ActiveMR 3AMR 0AOriginal
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.45. Average RMS Displacement Comparison
The comparison shows that even though the MR dampers with the skyhook control policy had
higher levels of peak vertical displacement of the frame, the RMS displacement of the frame was
not increased. This points to higher levels of initial frame displacement as the truck passes over
the speed bump, but quicker dampening of the vibration in the MR dampers and the skyhook
control policy. The RMS displacement of the front axle was higher for the MR skyhook control
case than it was for the original dampers. The RMS displacements of the rear of the truck, both
axle and frame, were reduced in the MR damper skyhook control case.
4.5.2 Frequency Domain Analysis of the Transient Data
The transient data was investigated in the frequency domain as well. The first step in this
investigation mean zeroed the data. The next step involved creating an averaged fft of the
acceleration data for each data set. This was done by decimating each data set twenty times. In
each of the twenty sets the decimation started three elements later than the last set. This created
twenty ffts of the same data, which were then averaged together frequency by frequency. The
MATLAB m file that did this is included in Appendix 1-e. These averaged ffts were then again
averaged, this time across like data sets. The data sets included:
71
• Eight sets of data with the MR dampers were in place and controlled according to the sky
hook control policy
• Four data sets with the MR dampers were in place and powered continuously at three
amps
• Four data sets with the MR dampers were in place and not powered
• Five data sets with the stock dampers on the truck
A set of data (eleven measurement positions) for each of these four test cases is included as
Appendix 3.
In order to facilitate comparison between the four different test cases, the results of the
frequency domain analysis were looked at in terms of average peak intensity in four frequency
bands. The four frequency bands that were chosen for analysis are:
• 1-4 Hz
• 4-9 Hz
• 9-14 Hz
• 14-19 Hz.
These bands were chosen based on a study by M. Ahmadian [13], who correlates these bands to
different aspects of the truck dynamics. These correlations are summarized in Table 4.2.
Table 4.2. Summary of Frequency/Truck Dynamics Correlations
Frequency Band Truck Dynamics1-4 Hz rigid body modes of the truck frame (heave and pitch)4-9 Hz first bending mode of the truck frame
9-14 Hz wheel hop frequencies of the three tractor axles14-19 Hz second bending mode of the truck frame
For each of the four test cases, the average peak intensity was calculated for each of the for
frequency bands. The average peak intensity was defined as the sum over the frequency band of
the product of the magnitude of the acceleration at each frequency times the frequency width.
The MATLAB .m file used to calculate this information is included in Appendix 1f. This was
performed for each of the eleven channels of acceleration data captured. The average
acceleration peak intensity results in the 1-4 Hz frequency band, corresponding to the rigid body
modes of the truck frame, is shown in Figure 4.46 for the four cases tested.
72
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for Frequency Band 1-4 Hz
0.0000
0.0050
0.0100
0.0150
0.0200
0.0250
0.0300
0.0350
0.0400
0.0450
0.0500
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Ave
rage
Pea
k In
tens
ity (
m/s
^2-H
z)
MR Active
MR 3A
MR 0A
Original
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.46. Average Peak Intensity in the 1-4 Hz Frequency Band
The average acceleration peak intensity results in the 4-9 Hz frequency band, corresponding to
the first bending mode of the truck frame is shown in Figure 4.47 for the four cases tested.
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for Frequency Band 4-9 Hz
0.0000
0.0010
0.0020
0.0030
0.0040
0.0050
0.0060
0.0070
0.0080
0.0090
0.0100
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR Active
MR 3A
MR 0A
Original
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.47. Average Peak Intensity in the 4-9 Hz Frequency Band
The average acceleration peak intensity results in the 9-14 Hz frequency band, corresponding to
the wheel hop frequencies of the three tractor axles is shown in Figure 4.48 for the four cases
tested.
73
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for Frequency Band 9-14 Hz
0.0000
0.0010
0.0020
0.0030
0.0040
0.0050
0.0060
0.0070
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR Active
MR 3A
MR 0A
Original
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.48. Average Peak Intensity in the 9-14 Hz Frequency Band
The average acceleration peak intensity results in the 14-19 Hz frequency band, corresponding to
the second bending mode of the truck frame is shown in Figure 4.49 for the four cases tested.
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for Frequency Band 14-19 Hz
0.0000
0.0005
0.0010
0.0015
0.0020
0.0025
0.0030
0.0035
0.0040
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Ave
rage
Pea
k In
tens
ity (
m/s
^2-H
z)
MR Active
MR 3A
MR 0A
Original
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.49. Average Peak Intensity in the 14-19 Hz Frequency Band
The frequency domain analysis points to the effectiveness of the MR dampers and the skyhook
control policy. The average peak intensity of the measured acceleration is broken down into four
frequency bands. When these results are shown in terms of percent increase versus the case
where the truck was equipped with the original dampers, it is evident that there is a positive
74
effect of using the MR dampers with the skyhook control policy. A decrease in the average peak
intensity is shown by a negative percent increase. The results in the four frequency bands are
shown in Figure 4.50.
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity of MR Active Case vs. Original Case (Transient)
-60.0000
-40.0000
-20.0000
0.0000
20.0000
40.0000
60.0000
80.0000
100.0000
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Per
cent
Incr
ease
1-4 Hz4-9 Hz9-14 Hz14-19 Hz
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.50. Percent Increase of Average Peak Intensity: MR Active vs. Original (Transient)
In the front of the truck (AT, AB, BT, and BB) the use of the MR dampers with the skyhook
control policy significantly increased the average peak intensity of the acceleration of the axle in
both the 1-4 Hz and 14-19 Hz bands. The 4-9 Hz and 9-14 Hz bands showed a decrease in the
average peak intensity at these same positions. The rear of the truck (ET, EB, FT, and FB)
showed a significant reduction in the average peak intensity of the acceleration as measured on
both the axle and the frame of the truck. The acceleration measured in the cab of the roll, pith
and heave directions showed significant decreases in the average peak intensity in the frequency
bands 1-4 Hz, 4-9 Hz, and 14-19 Hz. The 4-9 Hz results in particular point to increased operator
comfort as the human body resonance typically falls in a 5-7 Hz range [12].
75
4.6 Steady State Data Analysis
The steady state data, like the transient data, was examined in both the time and frequency
domains. The time domain analysis of the transient data consisted of calculating the RMS
acceleration for three cases. The first of the three cases that was investigated was the truck
equipped with the MR dampers, and controlled according to the sky hook control policy. The
second of the three cases was the truck equipped with the MR dampers and operated with the
dampers continuously in the on or three amp state. The third case was the truck operated with
the original dampers in place. In each of the cases, the full ten second data block was used in the
RMS acceleration calculation. The result of this analysis is shown in Figure 4.51.
Position MeasurementAT driver side front,
frameAB driver side front,axleBT passenger side front,
frameBB passenger side front,axleET driver side rear, frame
RMS Acceleration for Steady State Data
0.0000
0.5000
1.0000
1.5000
2.0000
2.5000
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
RM
S A
ccel
erat
ion
MR Active
MR 3A
OriginalEB driver side rear, axleFT passenger side rear,
frameFB passenger side rear,axleY B-post roll
Z B-post heaveX B-post pitch
Figure 4.51. RMS Acceleration Results for Steady State Data
The steady state data was analyzed in the frequency domain in the same manner as the transient
data, with the exception that only three cases were investigated, the three cases being MR active,
MR 3A, and original dampers respectively. Another difference between the frequency domain
analysis carried out for the steady state and transient data is that in the steady state analysis
multiple data sets representing the same operating condition were not investigated as was the
case in the transient data analysis. A set of data (eleven measurement positions) for each of three
cases (MR active, MR 3A, and original) is included as Appendix 4. The average acceleration
76
peak intensity results in the 1-4 Hz frequency band, corresponding to the rigid body modes of the
truck frame, is shown in Figure 4.52 for the three cases tested.
Average Peak Intensity for Frequency Band 1-4 Hz
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR ActiveMR 3AOriginal
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.52. Average Peak Intensity in the 1-4 Hz Frequency Band
The average acceleration peak intensity results in the 4-9 Hz frequency band, corresponding to
the first bending mode of the truck frame is shown in Figure 4.53 for the three cases tested.
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for Frequency Band 4-9 Hz
0.00E+00
1.00E-03
2.00E-03
3.00E-03
4.00E-03
5.00E-03
6.00E-03
7.00E-03
8.00E-03
9.00E-03
1.00E-02
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Ave
rage
Pea
k In
tens
ity (
m/s
^2-H
z)
MR ActiveMR 3AOriginal
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.53. Average Peak Intensity in the 4-9 Hz Frequency Band
77
The average acceleration peak intensity results in the 9-14 Hz frequency band, corresponding to
the wheel hop frequencies of the three tractor axles is shown in Figure 4.54 for the three cases
tested.
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for frequency Band 9-14 Hz
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR Active
MR 3A
Original
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.54. Average Peak Intensity in the 9-14 Hz Frequency Band
The average acceleration peak intensity results in the 14-19 Hz frequency band, corresponding to
the second bending mode of the truck frame is shown in Figure 4.55 for the three cases tested.
78
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frame
Average Peak Intensity for Frequency Band 14-19 Hz
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
1.40E-02
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
MR Active
MR 3A
Original
EB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
Figure 4.55. Average Peak Intensity in the 14-19 Hz Frequency Band
4.6.1 Results of Time Domain Analysis of Steady State Tests
In order to clearly show the effect that the MR dampers had with the skyhook control policy as
compared to the original dampers, the percent increase in RMS acceleration is plotted in Figure
4.56. Since this is a percent increase, a negative number represents a decrease in the RMS value
of the measured acceleration.
Position MeasurementAT driver side front, frameAB driver side front, axleBT passenger side front, frameBB passenger side front, axleET driver side rear, frameEB driver side rear, axleFT passenger side rear, frameFB passenger side rear, axleY B-post rollZ B-post heaveX B-post pitch
RMS Acceleration of MR Active Case vs. Original Case
-60.0
-50.0
-40.0
-30.0
-20.0
-10.0
0.0
10.0
20.0
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Per
cent
Incr
ease
Figure 4.56. Percent Increase of RMS Acceleration: MR Active vs. Original (Steady State)
Channels 1 and 2, corresponding to the frame of the truck in the front show that the use of the
MR dampers with the skyhook control policy has reduced the RMS acceleration at these
positions by close to 50% on both sides of the truck. Channels 6 and 8 show that the RMS value
79
of the acceleration as measured on the rear axle was also significantly reduced. Further,
channels 9,10, and 11 show that the use of the MR dampers with the skyhook control policy on
the primary suspension was effective at reducing the RMS value of the acceleration seen by the
cab of the truck.
4.6.2 Results of Frequency Domain Analysis of Steady State Tests
In order to show the effectiveness of the MR dampers with the skyhook control policy versus the
original dampers, the percent increase in the average peak intensity was plotted. This is shown
in Figure 4.57.
Average Peak Intensit of MR Active Case vs. Original Case (Steady State)
-100.0000
-50.0000
0.0000
50.0000
100.0000
150.0000
200.0000
AT AB BT BB ET EB FT FB Y Z X
Accelerometer Position
Per
cent
Incr
ease
1-4 Hz4-9 Hz9-14 Hz14-19 Hz
P o s i t i o n M e a s u r e m e n t
A T d r i v e r s i d e f r o n t , f r a m eA B d r i v e r s i d e f r o n t , a x l eB T p a s s e n g e r s i d e f r o n t , f r a m eB B p a s s e n g e r s i d e f r o n t , a x l eE T d r i v e r s i d e r e a r , f r a m e
E B d r i v e r s i d e r e a r , a x l eF T p a s s e n g e r s i d e r e a r , f r a m eF B p a s s e n g e r s i d e r e a r , a x le
Y B - p o s t r o l lZ B - p o s t h e a v e
X B - p o s t p i t c h
Figure 4.57. Percent Increase of Average Peak Intensity: MR Active vs. Original (Steady State)
At most of the measurement locations, the MR dampers with the skyhook control policy showed
an increase in the average peak intensity of the measured acceleration. This points to larger
amplitude accelerations with shorter duration than with the original dampers.