Downloaded from SAE International by Brought To You Michigan State Univ, Thursday, April 02, 2015 SAE TECHNICAL PAPER SERIES 2004-01-2977 IC Engine Retard Ignition Timing Limit Detection and Control using In-Cylinder Ionization Signal Ibrahim Haskara, Guoming G. Zhu and Jim Winkelman Visteon Corporation Reprinted From: SI Engine Experiment and Modeling (SP-1901) Powertrain & Fluid Systems Conference and Exhibition Tampa, Florida USA October 25-28, 2004 400 Commonwealth Drive, Warrendale, PA 15096-0001 U.S.A. Tel: (724) 776-4841 Fax: (724) 776-5760 Web: www.sae.org Downloaded from SAE International by Brought To You Michigan State Univ, Thursday, April 02, 2015 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. 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Printed in USA Downloaded from SAE International by Brought To You Michigan State Univ, Thursday, April 02, 2015 2004-01-2977 IC Engine Retard Ignition Timing Limit Detection and Control using In-Cylinder Ionization Signal Ibrahim Haskara, Guoming G. Zhu and Jim Winkelman Visteon Corporation Copyright © 2004 SAE International ABSTRACT through in-cylinder combustion information in order to optimally adjust the operational boundaries. Internal combustion engines are designed to maximize power subject to meeting exhaust emission The use of in-cylinder sensors for combustion control is requirements and minimizing fuel consumption. a promising way of improving the fuel economy, power However, the usable range of ignition timing is often output and emissions of production vehicles (see limited by knock in the advance direction and by 4,5,6,7,8 and the references cited therein among combustion instability (partial burn and misfire) in the others). In this paper, in-cylinder ionization signals are retard direction. This paper details a retard limit studied to determine a combustion stability metric for management system utilizing ionization signals in order ignition retard limit. Spark sweeps are conducted at to maintain the desired combustion quality and prevent different operating points. Stochastic properties (mean, the occurrence of misfire without using fixed limits. In- variance and probability distribution functions) of peak cylinder ionization signals are processed to derive a ionization location and the ionization energy content metric for combustion quality and closeness of distribution are correlated to the combustion quality combustion to partial burn/misfire limit, which is used to (COVariance of Indicated Mean Effective Pressure provide a limiting value for the baseline ignition timing in IMEP) and combustion type (normal, late but complete, the retard direction. For normal operations, this assures incomplete and misfire). A feedback parameter is that the combustion variability is kept within an derived from the ionization signal as an indicator of the acceptable range. During start-up operations, the retard closeness to the retard limit. Pressure measurements limit management can be used as a rapid catalyst light- are used to confirm information for these correlations. off strategy by maximally delaying the combustion as The data is then used to generate stochastic relations long as misfire and partial-burn are avoided. This from ignition timing to the processed ionization improved start-up strategy reduces cold-start HC parameter at different operating conditions. emissions by reducing the time required to increase the catalysts temperature to its light-off level. The closed A stochastic ignition retard limit control utilizing the loop nature of the system provides maximum usage of derived retard limit ionization parameter is also proposed the possible ignition timing range in the retard direction in the paper. Experimental data from dynamometer tests at any given operating condition. is included to demonstrate that the controller can limit and correct the ignition timing to keep the combustion INTRODUCTION quality/stability from exceeding a user-specified level. It is further shown that the control system is able to In a conventional spark-ignition (SI) engine, combustion operate the engine at its retard limit despite the cycle-to- is initiated at the spark plug by an electrical discharge. cycle combustion variability and inherent ionization Recent advances in the powertrain electronic controls signal variations owing to that stochastic nature. make it possible to employ online spark adjustment to optimize the engine operation in terms of power, fuel RETARD LIMIT MANAGEMENT economy and emissions. However, the range of ignition timing one would like to use is often limited by knock in )RUDFORVHGORRSLJQLWLRQFRQWUROV\VWHPWKHEHQHILWRI the advance direction and by combustion instability D FRPEXVWLRQ UHWDUG LQGLFDWRU LV WZRIROG 'XULQJQRUPDO (partial burn and misfire) in the retard direction. Since RSHUDWLQJ FRQGLWLRQV LI WKH EDVHOLQH LJQLWLRQ VWUDWHJ\ the feasible ignition timing range depends on the engine WHQGV WR SXVK WKH LJQLWLRQ WLPLQJ WR D OHYHO ZKHUH WKH operating conditions, it is beneficial to extract this online FRPEXVWLRQ YDULDELOLW\ LV QRW DFFHSWDEOH LJQLWLRQWLPLQJ Downloaded from SAE International by Brought To You Michigan State Univ, Thursday, April 02, 2015 FDQ EH OLPLWHG LQ WKH UHWDUG GLUHFWLRQ 6HFRQGO\ VLQFH ignition timing is too early (advanced), useful combustion WKLVUHWDUGOLPLWLVFRQWLQXDOO\DGMXVWHGE\PRQLWRULQJWKH work is wasted during the compression stroke. On the FRPEXVWLRQ WKURXJK WKH LQF\OLQGHU LRQL]DWLRQ VLJQDOV other hand, if the combustion process starts too late GLIIHUHQW FULWHULD FDQ VWLOO EH LQFOXGHG DQG RSWLPL]HG (retard), the peak pressure occurs later in the expansion RQOLQH WR GHWHUPLQH WKH ILQDO WLPLQJ LQVWHDG RI XVLQJ D stroke and its resulting torque diminishes. The optimum RQHILWVDOOOLPLWYDOXHRUPDS spark, for which the maximum brake torque is obtained in the presence of these opposing trends, is called MBT During engine warm-up, the retard limit management timing. Maximum brake power and minimum brake can seek the maximum retard possible while assuring specific fuel consumption are also achieved with MBT that misfire is avoided with the objective of increasing timing. A typical cylinder pressure behavior during a the catalyst temperature rapidly. Delaying the spark sweep is shown in Figure 2. This data was combustion through high values of ignition retard can gathered from a 3L, 6-cylinder engine operated in an shorten the time that it takes the catalyst to reach its engine dyno. Spark timing was swept from 37 oBTDC to light-off temperature. Therefore, the conventional three- 25 oATDC at 1500 RPM and 2.5 bar BMEP for MBT way catalyst becomes effective much sooner in reducing spark. For each spark, the plotted pressure signal is the tail-pipe emissions (1, 2, 3). However, if the ignition average of 300 consecutive cycles. retard is too much, engine-out HC emissions become excessive due to incomplete combustion as well as misfire. An open loop retard calibration needs to provide enough margins to avoid misfire at all conditions and with all types of fuels. It therefore is inherently conservative. On the other hand, a real time retard limit indicator as part of a closed loop strategy alleviates this conservatism by further being able to push the timing in the retard direction if things are favorable. That way, the catalyst light-off time is minimized and the tail-pipe emissions can be reduced. The architecture of a stochastic retard limit management system is shown in Figure 1. ,RQL]DWLRQGHWHFWLRQ ,RQ 3&0 5HWDUG/LPLW LJQLWLRQFRLOV 6LJQDOV 6LJQDO 0HWULF &RQGLWLRQLQJ &DOFXODWLRQ )LJXUH&\OLQGHUSUHVVXUHVGXULQJVSDUNVZHHS 'ZHOO ,JQLWLRQ 6WRFKDVWLF 3&0,JQLWLRQ &0' &RQWURO 5HWDUG/LPLW &RQWURO 6LJQDO &RQWURO As shown in Figure 3, the combustion torque peaks at a 6WUDWHJ\ *HQHUDWLRQ spark around 29 oBTDC (indicating the MBT timing for this operating point) and starts falling when the spark is further retarded. )LJXUH&ORVHGORRSUHWDUGOLPLWFRQWUROV\VWHP The covariance of IMEP is also included in Figure 4 as a DUFKLWHFWXUH measure of combustion quality. As a practical The ignition coil in this system is both a sensor and an convention, a covariance value around 3% is regarded actuator. As a sensor, it has one ionization output signal. as an indication of good quality combustion. For this As an actuator it has one dwell control input signal for operating point, ignition timing should be kept before 17 ignition. The ionization feedback signals of all cylinders oBTDC in order to maintain the covariance