Abstract
The article is dedicated to the methodology of designing component-in-the-loop (CiL) testing systems for automotive powertrains featuring several drivelines, including variants with individually driven axles or wheels. The methodical part begins with descriptions of operating and control loops of CiL systems having various simulating functionality—from a “lumped” vehicle for driving cycle tests to vehicles with independently rotating drivelines for simulating dynamic maneuvers. The sequel contains an analysis that eliminates a lack of clarity observed in the existing literature regarding the principles of building a “virtual inertia” and synchronization of loading regimes between individual drivelines of the tested powertrain. In addition, a contribution to the CiL methodology is offered by analyzing the options of simulating tire slip taking into account a limited accuracy of measurement equipment and a limited performance of actuating devices. The methodical part concludes with two examples of mathematical models that can be employed in CiL systems to simulate vehicle dynamics. The first one describes linear motion of a “lumped” vehicle, while the second one simulates vehicle’s trajectory motion taking into account tire slip in both the longitudinal and lateral directions. The practical part of the article presents a case study showing an implementation of the CiL design principles in a laboratory testing facility intended for an all-wheel-drive hybrid powertrain of a heavy-duty vehicle. The CiL system description is followed by the test results simulating the hybrid powertrain operation in a driving cycle and in trajectory maneuvering. The results prove the validity of the proposed methodical principles, as well as their suitability for practical implementations.
Highlights
Automotive powertrains, especially those with multiple driving axles or individually driven wheels, besides propelling the vehicle, can deliver several functions including control of traction and braking forces [1,2,3] and the yaw stability control called torque vectoring [1,4,5]
A typical example of a testing task requiring a more detailed model is simulation of trajectory maneuvers taking into account the limited tire-road adhesion. Such driving modes could be used to assess the powertrain performance in such tasks as traction control and torque vectoring. This requires taking into account the tire slip in both the longitudinal and lateral directions that entails modeling the vehicle trajectory motion and the wheel angular motion as independent dynamic processes linked by kinematic relations
When considering all-wheel-drive powertrains having functions that deal with vehicle active safety and dynamics, the CiL system is supposed to simulate vehicle maneuvers at road surfaces with a limited tire adhesion
Summary
Automotive powertrains, especially those with multiple driving axles or individually driven wheels, besides propelling the vehicle, can deliver several functions including control of traction and braking forces [1,2,3] and the yaw stability control called torque vectoring [1,4,5]. Johnson et al [25] describe a testing system that includes a virtual model of vehicle dynamics interacting with models of tires The latter are calculated using a backward approach resulting in approximate wheel slip estimates, which are taken into account in defining the reference shaft speeds of the tested powertrain units. Let us begin with the basic CiL concept of simulating an inertia equivalent to the mass of the considered vehicle to use that “virtual inertia” as an operating load for the tested powertrain (along with the velocity-dependent resistance forces) This technique implies using a simple virtual model that makes its description methodically vivid. When the sideslip is to be considered, the lateral and yaw vehicle dynamics are simulated, and the wheel’s center velocity is calculated using the yaw rate and the sideslip angle (a detailed description can be found, for example, in [30])
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