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Trailers with an electrically powered support axle
von Patrick Seiniger, Maxim Bierbach, Oliver Batels und Jost GailThis project report describes an investigation into the influence powered trailers may have
on the driving dynamics of vehicle combinations compared with non-powered trailers.
Theoretical reasoning suggests that a destabilizing effect on the towing vehicle around the yaw axis may result in particular from shear forces and longitudinal forces with a pushing effect, which are transferred from the trailer to the coupling while, in contrast, longitudinal forces with a pulling effect are generally expected to have a stabilizing effect. Due to the application of the same driving force to the wheels on both sides of the trailer as long as there is always a resulting tractive force, the drive system is not expected to influence the shear force at the trailer coupling.
Bearing this in mind, trailers with a symmetrical driving force that is lower than the driving resistance force of the trailer do not have a significant negative impact on the dynamics of the vehicle combination.
As the required tractive effort of the towing vehicle is lower when the trailer is powered, the driveability of the vehicle combination is expected to improve. To verify these two assumptions, the stability at high speeds and the swerving behaviour were identified as decisive criteria and were assessed by performing a standard defined steering impulse test and a standard double lane change manoeuvre respectively. In addition, the expected lateral forces were quantified by means of simple equations for trailers with and without active drive.
The theoretical considerations were confirmed in driving tests. A slightly reduced sway control and characteristic speed were found in one of the two trailers when an axle was powered; no relevant differences were found in the other trailer. Driveability was not found to be worse for either of the trailers with active drive compared to the same trailers without active drive; in one trailer, driveability was found to have improved significantly when the drive was active. The simple equations to quantify the lateral forces were confirmed by measurements.
Based on the results, vehicle safety is not considered to be compromised if powered trailers are designed so that the driving forces are distributed evenly between both wheels and the trailers do not push the towing vehicle.
Uneven distribution of the driving forces could be used for active stabilization; however, as torque vectoring was not available in the vehicles, no such assumptions could be established and tested.
Theoretical reasoning suggests that a destabilizing effect on the towing vehicle around the yaw axis may result in particular from shear forces and longitudinal forces with a pushing effect, which are transferred from the trailer to the coupling while, in contrast, longitudinal forces with a pulling effect are generally expected to have a stabilizing effect. Due to the application of the same driving force to the wheels on both sides of the trailer as long as there is always a resulting tractive force, the drive system is not expected to influence the shear force at the trailer coupling.
Bearing this in mind, trailers with a symmetrical driving force that is lower than the driving resistance force of the trailer do not have a significant negative impact on the dynamics of the vehicle combination.
As the required tractive effort of the towing vehicle is lower when the trailer is powered, the driveability of the vehicle combination is expected to improve. To verify these two assumptions, the stability at high speeds and the swerving behaviour were identified as decisive criteria and were assessed by performing a standard defined steering impulse test and a standard double lane change manoeuvre respectively. In addition, the expected lateral forces were quantified by means of simple equations for trailers with and without active drive.
The theoretical considerations were confirmed in driving tests. A slightly reduced sway control and characteristic speed were found in one of the two trailers when an axle was powered; no relevant differences were found in the other trailer. Driveability was not found to be worse for either of the trailers with active drive compared to the same trailers without active drive; in one trailer, driveability was found to have improved significantly when the drive was active. The simple equations to quantify the lateral forces were confirmed by measurements.
Based on the results, vehicle safety is not considered to be compromised if powered trailers are designed so that the driving forces are distributed evenly between both wheels and the trailers do not push the towing vehicle.
Uneven distribution of the driving forces could be used for active stabilization; however, as torque vectoring was not available in the vehicles, no such assumptions could be established and tested.