Longitudinal Control of Commercial Heavy Vehicles Equipped with Variable Compression Brake
In this report, we extend our previous work within MOU 372 on modeling and longitudinal speed control design for heavy commercial vehicles equipped with variable compression braking mechanisms. Previously, we developed a detailed crankangle based simulation model for a six cylinder, 350 hp diesel engine with a continuously varying compression brake that is capable of describing the intrinsic interactions between individual cylinder intake and exhaust processes, turbocharger dynamics during combustion and braking modes, and the transition between those modes. Moreover, for control design and analysis purposes we derived a low-order approximation of that model. In this report we present our new results on developing longitudinal control algorithms that coordinate the variable compression brake with conventional service brakes and gear selection. Specifically, we integrate the compression brake actuator with the service brakes and design a PI-controller that emulates the driver's actions on long grades. The controller uses the engine speed measurement to activate the service brakes only when retarding power of the compression brake is insufficient. We also employ robust linear control technique using the concept of structured singular values to design a controller that is robust to parameter variations and model uncertainty in the CHV. Finally, we compare the performance of this robust controller with the performance of an adaptive control scheme that we have derived within MOU 393. The performance of all the controllers is demonstrated through extensive simulations on the 24th order nonlinear vehicle model developed in our previous work within MOU 372.