Division of Information Technology, Engineering and the Environment
Agricultural Machinery Research Design Centre
Agricultural Machinery Research Design Centre
Computer Integrated Steering-Drive Systems
The objectives of this project are:
to integrate the two basic steering steering systems of a two wheel drive vehicle using a computer
demonstrate improved performance
This research studied the tractive performance of
integrated steering-drive systems by investigating a two-wheel-drive
vehicle having two independent rear drive wheels and non-driven
steerable front wheels. The feasibility of integrating the steering and
drive systems and the performance advantages that may be obtained was
investigates. In order to demonstrate the feasibility of the concept,
the steering system and the drive system of a test vehicle were
integrated using a computer with a specially-developed control program.
The software algorithm developed for the control program used the
mathematical relationship between the rear drive wheel speeds and the
steer handles of the non-driven front wheels to set the steer angles.
A test bed vehicle was fitted with control instrumentation to implement
the computer-integrated system. The circuitry of the hydraulic lines of
the hydraulically-driven test vehicle was modified to allow changes in
drive configuration. The test vehicle could be configures for the
following steering-drive configurations: open differential rear drive
with steerable front wheels, independent rear drive wheels with front
castors, locked differential rear driver with steerable front wheels and
the computer-integrated steering-drive system developed. The sensors on
the vehicle allowed data collection for characterising the vehicle and
wheels.
Computer models were developed for the various steering-drive
configurations from the force-relationships, longitudinal slip
relationships, vehicle geometry and turning geometry. Characteristics of
the test vehicles wheels for use in the models were measured
experimentally. The models were used to simulate the behaviour and
calculate the tractive performance, of the four steering-drive
configurations in various situations but actual tests were not able to
be conducted with the available resources. Unlike previous models, the
models of this research used force and longitudinal slip information
rather than power input and power output to produce values for drawbar
efficiency.
A theoretical analysis was conducted into the optimal slip conditions
for maximum track efficiency. The analysis was conducted using a more
rigorous mathematical analysis than previous researchers and used a
thorough graphical analysis to substantiate the mathematical analysis.
Previous studies concluded that under all traction conditions the
efficiency of slip will be a maximum when the slip of each wheel is
equal. This research revealed that, contrary to the previous literature,
efficiency of slip will not be a maximum when the slip of each wheel is
equal under non-uniform traction conditions. The simulations were
focussed on turning situations, non-uniform traction conditions and
traversing sloped. The optimal slip conditions and steer angles for
turning situations were also investigated and analysed. The
computer-integrated steering-drive system achieved a drawbar pull 50%
higher than that for a conventional open differential when undertaking a
10m radius turn with non-uniform traction conditions. Under these
conditions, the drawbar efficiency of the computer-integrated
steering-drive system was 5% greater than that for the open differential
at the lower drawbar pull.
It was concluded that it is feasible and beneficial to use a
computer-integrated steering system. Vehicles using such a system would
operate more effectively and efficiently when turning under load, moving
across slopes and in non-uniform traction conditions. More effectiveness
was provided through greater drawbar pull and higher drawbar efficiency.
