UWE Bristol Engineering showcase 2015

Joseph Driscoll
BEng Mechanical Engineering
Project Supervisor
Dr. Benjamin Drew
Steering Control For Tilting Vehicles
Justification For Tilting Vehicles
In order for a conventional car to roll over, the
moment applied about the outer wheel by the
inertial forces must be higher than the moment
caused by weight acting at the centre of the
vehicle. Conventional vehicles generally have a
track width that will cause the vehicle to lose grip
and slide, before roll over is possible. Described
by: tt
2h > 1 Non-tilting vehicle free body diagram
Model Development
The simulation model was produced in Simulink.
The model was based on equations of motion
derived from the combination of a “bicycle model”
for the lateral characteristics of the vehicle, and an
inverted pendulum model to represent the tilting
degree of freedom of the model. The transfer
function from steering angle to tilt angle was then
found as:
φφ
(ss) = − mm tth UUUUUU+UU 2
ββ ff ll
II 1 +mm tt h 2 ss 2 −mm tt ggh
Simulations
A number of simulations were carried out, with
the primary objective of testing the control system
model under conditions that may occur in every
day driving situations. The simulation scenarios
included roundabouts at various speeds, a
motorway lane change, and the ISO 3888-2
obstacle avoidance test.
30
20
Desired
Actual
Project summary
Due to several factors such as rising congestion and
fuel prices, the need has arisen for a vehicle that
combines the fuel efficiency, manoeuvrability and
space saving attributes of a motorcycle, with the
safety and driveability of a conventional car; this
need has made way for a class of narrow track tilting
vehicles. An investigation was carried out into the
viability of steering tilt control (STC) in narrow track
tilting vehicles for road use.
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When the centre of mass is tilted into a curve, risk
of rolling over is reduced. If the vehicle is able to
tilt by angle φφ, and moments are taken about the
tilt axis (assuming system is in equilibrium and
assuming that the tilt axis is located at
approximately ground level), the relationship can
be found: UU = RRRR tttttttt. This relationship shows
that with a tilting degree of freedom, the
maximum allowable forward velocity for the
vehicle to remain in equilibrium is limited only by
the maximum achievable tilt angle of the vehicle.
Subsystems were added to the model in order to
plot global displacement of the vehicle model.
Global displacement conversion subsystem
A subsystem was also added to more adequately
simulate a realistic driver steering input, consisting
of a series of rate limiters to smooth the steering
input.
Steering angle smoothing subsystem
The final Simulink model was then produced,
ready to carry out various simulation scenarios to
test the viability of the control system.
0
-10
-20
-30
-40
0 10 20 30 40 50 60 70
Displacement (m)
Roundabout third exit simulation
Roundabout tests highlighted issues with the
Simulink model .
Motorway lane change simulation
The control system performed well in the high
speed, low steering angle manoeuvres
Displacement (m)
Displacement (m)
4
3.5
3
2.5
2
1.5
1
0.5
4
3
2
1
0
Displacement (m)
Desired
Actual
-1
20 40 60 80 100 120 140
Displacement (m)
Desired
Actual
Boundary
Boundary
Project Objectives
The main objective of the investigation was to
determine the viability of STC in tilting road vehicles.
In order to achieve the main objective it was
necessary to develop a vehicle model and control
system using Matlab and Simulink that would
mathematically simulate the behaviour of a vehicle
utilising STC.
Project Conclusion
It was concluded that although the theoretical vehicle
in the STC model was able to negotiate all of the test
manoeuvres successfully, the path deviation caused
by the required counter steer of the steering system
could be dangerous under real world conditions.
Therefore it is proposed that further research be
conducted into a system where STC would be assisted
by direct tilt control (DTC) in order to reduce path
deviations.
0
-0.5
-1
0 10 20 30 40 50 60
Displacement (m)
Tilting Vehicle free body diagram
Final Simulink model
ISO 3888-2 simulation
In emergency obstacle avoidance manoeuvres the
control system would produce a significant course
deviation at changes in vehicle heading.