UWE Bristol Engineering showcase 2015

Richard Thompson
Motorsport Engineering
Project Supervisor
Dr Benjamin Drew
Improving the stability of three wheeled vehicles
Preventing a three-wheeler from rolling over is very different to conventional cars. Unlike conventional cars where braking will make the system more stable,
the nature of the geometry means it will actually be more likely to overturn. With this in mind, developing an ESP system for a three wheeler like a Reliant
Robin needs to focused around torque vector control.
Axis Title
30
25
20
15
10
5
0
0
8.1
Three Wheel Rollover Under Acceleration (0.25g)
11.4
13.9
16.1
18
19.7
0 20 40 60 80 100 120
Axis Title
21.3
22.7
24.1
25.4
Accelerating through the corner is actually
favourable for a delta three wheeler with regards
to stability, the acceleration that can occur as a
consequence of torque vectoring is beneficial.
Three Wheel rollover under acceleration (0.5g)
Project summary
This study consists of an investigation into the
rollover stability of three-wheeled vehicles with a
single front wheel, and if the implementation of an
electronic stability program could improve it.
Project Objectives
• To research and understand rollover of three
wheeled vehicles
• To develop a mathematical model for three wheel
rollover .
• Research into the functionality behind ESP
systems.
• To devise a method for increasing the rollover
threshold of the vehicle.
30
This graph results from an input acceleration of
0.5g. The additional longitudinal acceleration
stabilises the vehicle round the corner compared
to the graph above with a lesser value of a. This
illustrates a small element of how controlling
torques can stabilise a three-wheeler
Image below is of a differential capable of
supplying different torques to each wheel.
Axis Title
25
20
15
10
5
0
26.6
25.2
23.8
22.2
20.6
18.8
16.8
14.6
11.9
8.4
0
0 20 40 60 80 100 120
Axis Title
Understeer gradiant
0.05
0.04
0.03
0.02
0.01
0
-0.01
-0.02
Understeer gradiant vs length L1 and L2
length L1/L2 (m)
0 0.5 1 1.5 2 2.5
Project Conclusion
This study had success in discovering that by creating
a longitudinal inertia force through short bursts of
acceleration; the rollover threshold for a delta threewheeler
could be increased resulting in a more stable
system. This study also yielded useful data as to why
differential braking as an option for a stability
program did not suit the geometry of the problem
and in fact had a detrimental effect on the cornering
stability by reducing the rollover threshold.
understeer gradiant vs L1
Understeer gradiant vs L2
The graph above maps the steady state cornering of the
three wheeler assuming no roller, neutral steer occurs
where the lines cross the x-axis. From table 7, neutral steer
occurs when L1 = 1.439333 = 2L/3. So the neutral steer point
occurs when the centre of gravity is closer to the rear axle
then the front. A useful design recommendation to assist
rollover mitigation would be to move the centre of mass
back towards the rear axle towards the neutral steer point.