Modern heavy-duty vehicles are equipped with compression braking mechanisms that augment their braking capability and reduce wear of the conventional friction brakes. In this paper we consider a heavy-duty vehicle equipped with a continuously variable compression braking mechanism. The variability of the compression braking torque is achieved through controlling a secondary opening of the exhaust valve of the vehicle’s turbocharged diesel engine using a variable valve timing actuator. A model reference adaptive controller is designed to ensure good vehicle speed tracking performance in brake-by-wire driving scenarios in presence of large payload and road grade variations. The adaptive controller is integrated with backstepping procedure to account for compression braking actuator dynamics, with observers for various unmeasured quantities and with compensation schemes for actuator saturation. In addition to speed tracking, the vehicle mass and road grade are simultaneously estimated if persistence of excitation-type conditions hold. The final version of the controller is successfully evaluated on a high order crank angle model of a vehicle with a six-cylinder engine.
This paper considers a longitudinal speed control problem for heavy-duty vehicles equipped with variable compression brake. The use of compression brake reduces the wear of the conventional friction brakes, and it is, thus, a preferred way of controlling the vehicle speed during a steady descent or noncritical braking maneuvers. To perform more aggressive (critical) braking maneuvers or control vehicle speed during large changes in the grade, the compression brake must be coordinated with gear ratio adjustments and friction brakes. In this paper we develop nonlinear controllers that accomplish both noncritical and critical maneuvers. We also show how distance constraints from other vehicles in traffic may be included. The design technique is based on the speed-gradient (SG) approach, whereby the control action is chosen in the maximum descent direction for a scalar goal function. The nominal goal function is selected to address the speed regulation objective and, then, it is appropriately modified by barrier functions to handle the critical maneuver requirements. Two ways to handle the uncertainty in the road grade are discussed: through the use of an integral action of the SG controller for constant (but unknown) grades, and through the use of an added differential action for varying grades.
A uni®ed engine torque actuator for heavy-duty vehicles is developed in this paper. Based on averaging and identi®cation of the instantaneous torque response for changes in brake valve timing and fuel¯ow, we derive a control oriented engine model of a six cylinder, 350 Hp turbocharged diesel engine, equipped with a compression brake. This work bridges the gap between the detailed compression crank angle based models developed in the engine design community, and the ®rst order lag representation of diesel engine torque response used in the vehicle dynamics community. Moreover, we integrate the compression brake actuator with the service brakes and design a PI-controller that emulates the driver's actions during long descends on grades. The controller simply uses the engine speed measurement to activate the service brakes only when needed.
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