Comprehensive lumped parameter and multibody approach for the dynamic simulation of agricultural tractors with tyre–soil interaction

Modern agricultural tractors are complex systems,in which multiple physical(and technological)domains interact to reach a wide set of competing goals,including work operational performance and energy efficiency.This complexity translates to the dynamic,multi‐domain simulation models implemented to serve as digital twins,for rapid prototyping and effective pre‐tuning,prior to bench and on‐field testing.Consequently,a suitable simulation framework should have the capability to focus both on the vehicle as a whole and on individual subsystems.For each of the latter,multiple options should be available,with different levels of detail,to properly address the relevant phenomena,depending on the specific focus,for an optimal balance between accuracy and computation time.The methodology proposed here by the authors is based on the lumped parameter approach and integrates the models for the following subsystems in a modular context:internal combustion engine,hydromechanical transmission,vehicle body,and tyre–soil interaction.The model is completed by a load cycle module that generates stimulus time histories to reproduce the work load under real operating conditions.Traction capability is affected by vertical load on the wheels,which is even more relevant if the vehicle is travelling on an uncompacted soil and subject to a variable drawbar pull force as it is when ploughing.The vertical load is,in turn,heavily affected by vehicle dynamics,which can be accurately modelled via a full multibody implementation.The presented lumped parameter model is intended as a powerful simulation tool to evaluate tractor performance,both in terms of fuel consumption and traction dynamics,by considering the cascade phenomena from the wheel–ground interaction to the engine,passing through the dynamics of vehicle bodies and their mass transfer.Its capabilities and numerical results are presented for the simulation of a realistic ploughing operation.

A Newly Developed Differential Steering Rubber-tracked Agriculture Tractor

This paper introduces a newly developed ag tractor.The differential steering system and rubber tracks are described in detail.

Design of obstacle avoidance controller for agricultural tractor based on ROS

The obstacle avoidance controller is a key autonomous component which involves the control of tractor system dynamics,such as the yaw lateral dynamics,the longitudinal dynamics,and nonlinear constraints including the speed and steering angles limits during the path-tracking process.To achieve the obstacle avoidance ability of control accuracy,an independent path re-planning controller is proposed based on ROS(Robot Operating System)nonlinear model prediction in this paper.In the design process,the obstacle avoidance function and an objective function are introduced.Based on these functions,the obstacle avoidance maneuvering performance is transformed into a nonlinear quadratic optimization problem with vehicle dynamic constraints.Moreover,the tractor dynamics maneuvering performance can be effectively adjusted through the proposed objective function.To validate the proposed algorithm,a ROS based tractor dynamics model and the SLAM(Simultaneous Localization and Mapping)are established for numerical simulations under different speed.The maximum obstacle avoidance deviation in the simulation is 0.242 m at 10 m/s,and 0.416 m at 30 m/s.The front-wheel rotation angle and lateral velocity are within the constraint range during the whole tracking process.The numerical results show that the designed controller can achieve the tractor obstacle avoidance ability with good accuracy under different conditions.

Measurement and evaluation of whole body vibration of agricultural tractor operator

Exposure of whole body vibration(WBV)influences performance,comfort,and long term health risks of tractor operator.Therefore,measurement and evaluation of WBV parameters should be carried out to find probable effects on the health of tractor operators.In this study,a system was designed to measure the WBV of agricultural tractor operators and evaluated the hazard risks on operator’s body according to the ISO standards,and implementation of the WBV test in the official testing station was also suggested.A tri-axial accelerometer was employed to measure vibrations transmitted to the seated operator body as a whole through the supporting surface of the buttock on four typical farm roads under different speeds.The vector sum A(8)exposures on the rough tracks(earthen and grassland roads)exceeded the action limits of 0.5 m/s2 at a 10.9 km/h forward speed and reached to the action limit value at a 16.0 km/h forward speed on the concrete road.The vector sum of VDV(8)exposures did not exceed the action limits of 9.1 m/s1.75 and was greater on the grassland road.The vector sum Sed(8)exposures values exceeded the moderate probability of an adverse health limit of 0.5 MPa on all farm roads at high forward speeds and exceeded the high probability of an adverse health limit of 0.8 MPa on asphalt,concrete,and grassland roads which should be lower than the exposure limit values as suggested by the ISO and EC standards.The WBV evaluation procedure should be considered for implementation at the official tractor test station,which would response to domestic and international tractor test regulations and improve the market competitiveness.