1 DYNATUNE-XL SIMULATION TOOL SUITE 10 “EASY” STEPS TO HAPPY VEHICLE DYNAMICS A Vehicle Dynamics Tuning Guide Click image to follow link The following 10 Step Recipe is describing our Standard Approach & Recommendation for Creating a DYNATUNE-XL Vehicle Dynamics Model with subsequent Tuning & Optimizing for maximum Performance. All Analysis will be executed in the “EXPERT” Version of the DYNATUNE-XL RIDE & HANDLING MODULE using the standard included data set of a typical Formula Car.
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1
DYNATUNE-XL SIMULATION TOOL SUITE
10 “EASY” STEPS TO HAPPY VEHICLE DYNAMICS
A Vehicle Dynamics Tuning Guide
Click image to follow link
The following 10 Step Recipe is describing our Standard Approach & Recommendation for Creating a
DYNATUNE-XL Vehicle Dynamics Model with subsequent Tuning & Optimizing for maximum
Performance. All Analysis will be executed in the “EXPERT” Version of the DYNATUNE-XL RIDE &
HANDLING MODULE using the standard included data set of a typical Formula Car.
• STEP 7: LINEAR UNDERSTEER GRADIENT & SIDE SLIP ANGLE GRADIENT
• STEP 8: TIRE CHARACTERISTICS
• STEP 9: VEHICLE DYNAMICS OPTIMIZATION
• STEP 10: DAMPER OPTIMIZATION
This document will be referring frequently to the DYNATUNE-XL FAQ webpage for customers: http://www.dynatune-xl.com/support-rh.html
STEP 1: MASS PROPORTIES, DIMENSIONS & AERODYNAMICS
• The first essential step is to define Vehicle Mass & Vehicle Inertia. Whilst the mass data weight
and weight distribution are usually not difficult to obtain, it can be more complicated to define
the Yaw & Pitch Inertia data of the Vehicle on the VEHICLE DATA Sheet.
In such case we do recommend one of the following options:
1) Do use the Empirical Formula as indicated on the DYNATUNE-XL FAQ webpage.
2) Or use the Vehicle Passenger & Luggage Mass points feature as a “substitute” calculator by
replacing passengers with large vehicle components like for instance Motor, Gearbox and their
geometric location. This should give one - in combination with the already available unsprung
mass information - a good first indication of the total Inertia of the big solid parts. Finally, one
must define / estimate the Inertia for the Body in White to finalize the estimation.
Plan View
Plan View: Masses & Inertias
Fr. Right Pass. 0.0 kg Pass. 0.0 kg Pass. 0.0 kg
Pay-Load
36.0 kg 570.0 kg 0.0 kg 44.0 kg 0.0 kg
Z X 380.0 kgm² Pass.
Y
Driver 0.0 kg Pass. 0.0 kg Pass. 0.0 kg
0.0 mm 1765.0 mm 3040.0 mm
730.0 mm 0.0 mm 715.0 mm
Front H-Point 2nd Row H-Point 3rd Row H-Pt Pay-Load Mass Location
X Coordinate 1100.0 mm 1800.0 mm 2750.0 mm 3000.0 mm
Y Coordinate 400.0 mm 370.0 mm 230.0 mm 0.0 mm
650.0 kg 3040.0 mm 233.1 mm 605.3 kgm²CoG Z-Height
Fr. Unsprung Axle Mass
CURB Sprung Mass
CURB Sprung Yaw Inertia
Wheel Base
Fr. Wheel Center
X Coordinate
Y Coordinate
CURB Sprung Mass
Rr. Unsprung Axle Mass
Rr. Wheel Center
X Coordinate
Y Coordinate
Total Yaw Inertia
X Coordinate
Y Coordinate
Total Mass
All Model MASS and INERTIA Data refer to REFERENCE HEIGHT "0" which is defined according to CURB - UNLADEN - Weight Condition. Additional "DELTA" Front & Rear Ride Heights can be added to the REFERENCE Plane. This will affect the final CoG- Height, Suspension Roll Centre Heights and Aerodynamic Operating Points. Aerodynamic Loads will be imposed on top of the CURB Condition for the imposed Reference Speed.
• Finally, after having optimized the Lateral-G Performance of the vehicle, it is considered good
practice to check the transient stability of the vehicle. As a matter of fact, these stability checks
should already be performed at the first START/INITIALISE Calculations in order to avoid
potentially unpleasant surprises later. The most commonly used simulation procedures for
Vehicle Stabiltiy Analysis are the FREQUENCY STEER TEST and the STEP STEER TEST.
At this point some important notes are to be made:
▪ FREQUENCY STEER & STEP STEER EVENTS are only available in the “EXPERT”
Version of DYNATUNE-XL R&H MODULE.
▪ FREQUENCY STEER & STEP STEER EVENTS are typical OEM Road Car Test &
Simulation Procedures and less often applied on Racing Cars.
▪ FREQUENCY STEER & STEP STEER EVENTS do only make sense on vehicles with
an UG > 0. In fact, it is not possible to use these tests on inherently instable vehicles.
The fact that many Race & Rallye cars come with an (almost) inherently instable setup
is one of the contributors to not frequently using this kind of analysis.
▪ The interpretation of the FREQUENCY STEER & STEP STEER EVENTS is rather
complex for the novice and even a seasoned race engineer can struggle with that.
▪ It is very strongly recommended to consult all results on the FREQUENCY STEER &
STEP STEER sheets. If unfamiliar with the topic do consult the DYNATUNE-XL FAQ
webpage and/or collect more information on the internet.
1) The FREQUENCY STEER Test is a method to analyse the vehicle STABILITY behaviour in
the Frequency Domain. It basically describes how quick and how much the vehicle does
respond when excited with a certain amount of STEERING WHEEL ANGLE input at a certain
frequency. Any peaks in the graph indicate the natural frequency of the vehicle for parameters
like Yaw Velocity or Lateral Acceleration. The graphical representations of the results are
typically shown in a HALF logarithmic scale (X-Axis only).
Although this type of analysis does require a certain amount of elevated understanding of
vehicle dynamics principles it is not impossible to give some general “rule of thumb” tuning
guide lines:
- One should aim (on the horizontal axis) for the peaks to occur at the highest possible frequency.
By doing so the vehicle provides sufficient responsiveness up to very quick steering inputs.
- One should aim (on the vertical axis) for the peak overshoots to be as low as possible. By doing
so the vehicle response – when excited at that natural frequency – is still moderate and
controllable for the driver.
- When looking at Phase Shift Angles (as they are displayed on the FREQUENCY STEER Sheet)
one should aim to keep them as low as possible. The lesser the shift in phase, the quicker the
reaction of the vehicle to the input.
Frequency @ Peak Hz Hz 4.00 Hz 4.60 Hz
Static Gain @ 0 Hz 1/s g/° 0.449 °/g 16.863 °/s/g
Dyn. Overshoot @ Peak % % 36.11% % 89.96% %
Delay Time @ 1 Hz ms ms 77.7 ms -22.5 ms
Yaw / G-LatG-Lat / SWAVeh. Slip Angle / SWA
GENERIC FREQUENCY STEER RESPONSE DATA @ G-Long = 0g
Yaw Velocity / SWA Veh. Slip Angle / G-Lat
0.00
0.050
0.00%
45.7ms
Hz
-
%
1.00
0.849
0.33%
23.3
0.00
0.023
0.00%
123.4
0.000
0.005
0.010
0.015
0.020
0.025
0 1 10
Gain
[-]
Frequency [Hz]
GAIN Vehicle Slip Angle / SWA
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0 1 10
Gain
[g
/°]
Frequency [Hz]
GAIN G-Lat / SWA
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 1 10
Gain
[°/
g]
Frequency [Hz]
GAIN Vehicle Slip Angle / G-Lat
0
5
10
15
20
25
30
35
0 1 10
Gain
[°/
s/g
]
Frequency [Hz]
GAIN Yaw Velocity / G-Lat
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
0 1 10
Gain
[1/s
]
Frequency [Hz]
GAIN Yaw Velocity / SWA
15
- Aerodynamics can affect the results quite significantly (ref. aerodynamic high-speed instability)
and as such it is recommended to check the results for a range of velocities by using the
specially developed routine on the FREQUENCY STEER Sheet.
- The presented Metrics are the most commonly used metrics to evaluate the results of this test.
It is recommended to use those for evaluation in addition to the graphic representation.
2) The STEP STEER Test is a method to analyse the vehicle STABILITY behaviour in the Time
Domain. It basically describes how quick and how much the vehicle does respond when excited
with a certain amount of STEERING WHEEL ANGLE input. Maximum Amplitude/Overshoots
& Decay over time of the induced (lateral) oscillation of the vehicle are the most important
evaluation metrics.
- Like the previous test procedure also this specific type of analysis does require a certain amount
of understanding of vehicle dynamics principles. However, also in this case is it possible to
give some general “rule of thumb” tuning guide lines:
- One should aim (on the horizontal axis) for the peaks to occur as quickly as possible. By doing
so the vehicle demonstrates good responsiveness on a steering input.
- One should aim (on the vertical axis) for the peak overshoots to be as low as possible. By doing
so the vehicle response – when excited at that input – is moderate and the induced oscillation
will decay quicker resulting in earlier return of the vehicle into a stable trajectory.
- Aerodynamics can affect the results quite significantly (ref. aerodynamic high-speed instability)
and as such it is recommended to check the results for a range of velocities by using the
specially developed routine on the STEP STEER Sheet.
- The presented Metrics are the most commonly used metrics to evaluate the results of this test.
It is recommended to use those for evaluation in addition to the graphic representation.
STEP 10 DAMPER OPTIMIZATION
• In the last and final step the dampers will have to defined and optimized. As the “Handling”
section of the DYNATUNE-XL RIDE & HANDLING MODULE is functioning with a quasi-static
solving algorithm, damper forces do not affect the results. Hence ending up last on this list.
1) The first step in the damper optimization exercise is to set targets/analyse the numbers/charts
for Damping-Ratio – which is also known as Percentage Critical Damping on the DAMPER
TUNING sheet. In field of Damper Tuning, one should know and understand 2 particular values:
- 100%. A Damping-Ratio of 100% does mean that the vehicle is critically damped, which
does mean that it will not perform an oscillation after a vertical input but will move
(slowly) to its final position without any overshoot.
90% Response Time 44.0 ms 172.0 ms 140.0 ms
Peak Value 1.5 1/s 0.1 - 0.2 g/°
Time to reach Peak Value 108.0 ms 352.0 ms 316.0 ms
Dynamic Overshoot @ Peak 12.93% % 0.19% % 0.21% %
GENERIC STEP STEER RESPONSE DATA @ G-Long = 0g
Yaw Velocity Gain [1/s] Slip Angle Gain [-] G-Lat Gain [g/°]
-0.010
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Sli
p A
ng
le G
ain
[-]
Time [s]
Vehicle Slip Angle / SWA
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
0.180
0.0 0.5 1.0 1.5
G-L
at
Gain
[g
/°]
Time [s]
G-Lat / SWA
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Yaw
Velo
cit
y G
ain
[1/s
]
Time [s]
Yaw Velocity / SWA
16
- 70%. A Damping Ratio of 70% will allow the vehicle to do 1 positive overshoot and 1
negative undershoot (half-) oscillation relative to its final position after a vertical input.
2) The README section and DYNATUNE-XL FAQ webpage do provide a lot of information and
suggestions for Target Values for Damping Ratio and Typical Shapes of the above shown
curves. As a general rule of thumb, one can say that the range between 0 mm/s and 100 mm/s
vertical wheel speed does affect primarily the Body Control and the range above those speeds
affect does primarily affect Wheel Control.
• Next to the Classical Damping Ratio Charts, DYNATUNE-XL R&H MODULE does also offer an elementary transient (Linear Damping) RIDE FREQUENCY TEST and RIDE STEP TEST.
At this point corresponding notes to the ones in the handling section have to be made:
▪ RIDE FREQUENCY & RIDE STEP EVENTS are only available in the “EXPERT”
Version of DYNATUNE-XL R&H MODULE.
▪ RIDE FREQUENCY & RIDE STEP EVENTS are typically applied on 4-Poster
Hydraulic Rigs and are as Test & Simulation Procedures actually quite well known in
the world of Racing Cars.
▪ The interpretation of the RIDE FREQUENCY & RIDE STEP EVENTS is rather complex
for the novice and even a seasoned race engineer can struggle with the interpretation
of the charts.
▪ As the Ride Frequency operating range - with a range from 0 Hz to 30Hz – is
significantly larger than the Handling operating range, many additional Metrics have
been developed by the industry with a “somewhat more or less” empirical basis.
▪ It is very strongly recommended to consult all information on the README section and
on the DYNATUNE-XL FAQ webpage and/or collect more information on the internet
on the topic.
1) The RIDE FREQUENCY Test is a method to analyse the Vertical RIDE behaviour in the
Frequency Domain. It basically describes how quick and how much the vehicle does respond
when excited with a certain vertical ROAD input at a certain frequency. Any peaks in the graph
– which is called Transfer Function – does indicate the location natural frequency of the front
and rear Sprung Masses and/or Unspung Masses. Exciting modes are typically Bounce and
Pitch. The graphical representations of the results are typically shown in a FULL logarithmic
scale (X-Axis & Y-Axis).
17
As a general tuning recommendation, one can say that the peaks at the natural frequencies of
sprung & unsprung masses should be as low as possible and the transfer functions of especially
the unsprung masses should be as closely as possible to “1” over the whole operating range.
For vehicles with high aerodynamic loads (which are typically very sensitive to pitch angles) the
tuning usually is solely focused on optimizing the body transfer function.
2) The RIDE STEP Test is a method to analyse the Vertical RIDE behaviour in the Time Domain.
It basically describes how quick and how much the vehicle does respond when excited with a
certain vertical ROAD input. Maximum Amplitudes/Overshoots & Decay over time of the
induced (lateral) oscillation of the vehicle are the most important evaluation metrics.
Again, as a general recommendation one should aim for minimizing the Overshoots and reduce
the number of oscillations in the decaying phase. The indicated metrics on the picture are
commonly used in the world of ride development and provide goog tuning directions as such.
3) The special Ride Features in the DYNATUNE-XL R&H MODULE have been limited to Linear
Dampers. Especially for those who do want to deep dive into Damper Tuning DYNATUNE-XL
has specifically developed the SUSPENSION TUNING MODULE, which does also come with
a unique automatic damper creation and optimizing tool.
Click on picture to follow link to website
Body Dynamic Overshoot @ Peak Freq. 11.65 - Body Dynamic Overshoot @ Peak Freq. 3.71 -