Jeffrey M. Pfeiffer

Estimation Algorithms for Low Pressure Cooled EGR in Spark-Ignition Engines

Low-pressure, Cooled Exhaust Gas Recirculation (LPC EGR) brings significant fuel economy , NOx reduction and knock suppression benefits to a modern, boosted, downsized Spark Ignition (SI) engine. As a prerequisite to design an engine control system for LPC EGR, this paper presents development of a set of estimation algorithms to accurately estimate the flow rate, pressure states and thermal states of the LPC EGR-related components.

A Verification Study for Cam Phaser Position Control using Robust Engineering Techniques

This paper describes the verification and comparison of position control algorithms for a continuously-variable cam phaser. Robust Engineering techniques are used. Two non-linear PID control algorithms are designed to control cam phaser position. The first algorithm is a more complex control strategy while the second is a thrifted approach that seeks to reduce throughput requirements. An L18 orthogonal array is established with noise factors that affect the quality of cam phaser control. Using the orthogonal array, the number of experiment test points required to characterize the control algorithm response is reduced from 8,748 to thirty-six. The test points of the orthogonal array are investigated experimentally on a motored engine outfitted with cam phaser hardware. The desired and actual cam position data are compared and analyzed for all points in the orthogonal array. Both control algorithms result in similar signal to noise ratios for the bench testing, showing the thrifted control algorithm to perform similarly overall. A final verification of the control algorithms is performed on a vehicle with a complete engine management system. The more complex control algorithm is shown to yield superior performance in the vehicle-level evaluation. INTRODUCTION One of the most significant areas of development in engine hardware and engine management systems today is in the area of valvetrain actuation. Automakers and many suppliers have developed and are still designing systems to optimize the manipulation of the valves over the entire engine operating range. These strategies range from discrete camshaft phasing to full electronic control of the valves. Many of the technologies at the simpler end of the spectrum, such as cam phasing and multi-step valve lifters are already in production vehicles. Cam phasing is the shifting of the valve events in the crank angle (or cam angle) domain. Typically, a mechanical device is attached to the end of the camshaft(s) that allows super-imposed angular movement of the camshaft while it is being driven from the crankshaft. The cam phaser typically has between fifty and sixty crank angle degrees of phasing authority. For an automotive systems supplier, an essential aspect of development effort for any engine hardware is the associated management of that hardware by the engine management system. It is possible that the engine management system development effort can exceed that required by hardware development. The EMS engineer must consider the effect of the new component on an already-complex underhood compartment. The engineer’s design must satisfy these performance requirements while also meeting the strict budgetary limitations of the engine control computer. In EMS development, simplicity is a crucial characteristic for engine management algorithms. This paper describes a methodology for achieving this paradoxical tradeoff between performance and simplicity. Robust Engineering techniques are used to compare two position control algorithms for a continuously-variable cam phaser. The objective is to assess whether a simplified approach to cam phaser control can meet the performance requirements as suitably as a more throughput-costly algorithm which performs well. The paper describes the cam phaser hardware and software and the Robust Engineering strategy. The verification of the strategy is described through a 2001-01-0777 summary of the experimental implementation and results. OVERVIEW OF CAM PHASER HARDWARE This section describes the hardware system for cam phasing. In addition to the cam phaser and control valve hardware, general physical system characteristics such as oil properties, measurement and actuation are discussed. CONTINOUSLY-VARIABLE CAM PHASER The cam phaser used in this experiment is a helical type phaser. It is essentially an oil-actuated gear train. The central piece in the cam phaser is a piston which slides on a helical gear. The piston is pushed back and forth by means of engine oil pressure. A cut-away view of the cam phaser with a portion of the camshaft is shown in Figure 1. The authority of the phaser is fifty crank angle degrees. Figure 1: Continuously-variable cam phaser The response of the cam phaser is mostly dependent on oil pressure, but also depends heavily on oil temperature and the torque reactions from the camshaft. The phaser contains a return spring which pushes the piston back to its original position when commanded toward zero degrees. The presence of the spring makes the movement of the phaser very different depending on the direction of phasing (advance or retard). The position control strategy must have some method for dealing with this variation. CONTROL VALVE The cam phaser control valve is a four-way spool valve which directs the flow of engine oil toward the front or rear of the piston in the cam phaser. The valve is actuated by a PWM signal from the engine control unit. The response of the valve is dependent on system voltage, oil pressure and oil temperature. A side-view of the valve is shown in Figure 2. Vent1 Rear Supply Front