Ignition timing control system for internal combustion engine

Details Ignition timing control system for internal combustion engine Ignition timing control system for internal combustion engine

2003-06-10

2004-05-04

Kwon, John (Department: 3747)

Internal-combustion engines

Spark ignition timing control

Electronic control

C123S568210, C701S108000

Reexamination Certificate

active

06729301

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an ignition timing control system for controlling the ignition timing of an internal combustion engine with EGR system.
2. Related Art
Exhaust gas recirculation (EGR) for recirculating engine exhaust gas through the engine's intake side into cylinders is widely practiced for reduction of combustion temperature in combustion chamber, whereby NOx emissions are reduced. In addition to NOx reduction, the EGR achieves another advantage that, given the same engine torque, the pressure in intake pipe increases greater than that attained by non-EGR operation, thus making it possible to reduce throttle loss. For this reason, fuel consumption can be improved by the EGR with a proper ignition timing which is set to provide the minimum advance for the best torque (MBT).
On the other hand, the EGR may cause slow combustion. For the countermeasure to relieve slow combustion, the ignition timing is advanced in accordance with the EGR rate in combustion chamber (hereinafter referred to as in-cylinder EGR rate). The in-cylinder EGR rate is represented, by way of example, by the ratio of an amount of EGR gas to an amount of fresh air that are introduced into the combustion chamber, and the determined EGR rate is provided for ignition timing control.
An engine with an EGR system generally operates to adjust the opening of an EGR valve for adjustment of an amount of EGR gas, the EGR valve being provided in an EGR passage that connects the engine's exhaust side to the intake side thereof. Since the engine intake system has a pressure storage effect, the in-cylinder EGR rate requires time to reach the intended EGR rate equivalent to the opening of the EGR valve which is opened or closed. In other words, there is a delay in changing the in-cylinder EGR rate with respect to the change in EGR valve opening.
This delay makes it difficult to calculate the in-cylinder EGR rate with accuracy. The calculation difficulty increases especially in a transition state, caused by a transition between EGR operation and non-EGR operation or by accelerated or decelerated vehicle running, where the in-cylinder EGR rate varies. As a consequence, it is quite difficult to control the ignition timing in a manner following the varying EGR rate so as to attain an optimal ignition timing that provides the MBT for improvement of fuel consumption.
In this regard, JP-A-2001-254659 discloses ignition timing control, wherein an amount of ignition timing advance for EGR operation and that for non-EGR operation are set beforehand in the form of map, respectively, as a function of engine rotation speed and intake air amount (amount of fresh air), whereas the in-cylinder EGR rate in the transition state is estimated. Then, amounts of ignition timing advance for EGR and non-EGR are subject to linear interpolation based on the estimated in-cylinder EGR rate, whereby an amount of ignition timing advance for the transition state is determined, which amount is used to correct a basic ignition timing to produce an optimum ignition timing to which the ignition timing is controlled. For the estimation of in-cylinder EGR rate, a steady-state EGR rate corresponding to engine rotation speed and intake air amount is determined from a map, and an EGR rate in a surge tank is determined from the steady-state EGR rate, etc. The estimation of in-cylinder EGR rate in the transition state is made based on the amounts of ignition timing advance for EGR and non-EGR operations, the steady-state EGR rate, and the EGR rate in surge tank of eight strokes past.
The ignition timing control using the linear interpolation of maps is based on the assumption that the ignition timing changes proportionally to the change in EGR rate. In actual, however, the change in EGR rate in a transition state is not in proportion to the change in ignition timing. The present inventors confirmed by experiments that, in a transition state, the ignition timing control based on linear interpolation causes the ignition timing to lead a proper ignition timing that provides the MBT.
Thus, the ignition timing control disclosed in JP-A-2001-254659 can cause knocking due to excessively advanced ignition timing during the transition state, and as a result, fuel consumption and drivability may be deteriorated.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ignition timing control system for an internal combustion engine for properly controlling the ignition timing even in a transition state where the EGR rate varies, to suppress occurrences of knocking due to excessively advanced ignition timing, thereby preventing deteriorated fuel consumption and drivability caused by knocking.
According to the present invention, there is provided an ignition timing control system for an internal combustion engine which comprises: EGR controlling means for controlling a valve opening of an EGR valve in accordance with a target EGR rate varying depending on an operating state of the internal combustion engine, the EGR valve being provided in an EGR passage that connects an exhaust system of the internal combustion engine to an intake system thereof; EGR rate estimating means for estimating an EGR rate of the internal combustion engine in accordance with the operating state thereof; target ignition timing setting means for setting a target ignition timing, corresponding to the EGR rate estimated by the EGR rate estimating means, based on an ignition timing for EGR operation and an ignition timing for non-EGR operation that are individually determined from first and second maps set in advance; retard amount setting means for setting a retard amount based on a ratio between the estimated EGR rate and the target EGR rate; ignition timing correcting means for correcting the target ignition timing, set by the target ignition timing setting means, in accordance with the retard amount set by the retard amount setting means; and ignition timing controlling means for controlling the ignition timing of the internal combustion engine in accordance with the target ignition timing corrected by the ignition timing correcting means.
According to the present invention, the EGR valve opening is controlled based on the target EGR rate that varies in dependence on the engine operating state. Depending on the EGR valve opening, exhaust gas serving as EGR gas is recirculated from the exhaust system of the engine to the intake system thereof, whereby the EGR rate of the internal combustion engine is adjusted to the target EGR rate. The EGR rate of the engine is estimated based on the engine operating state, whereas ignition timings for EGR and non-EGR operations are determined from the maps that are set beforehand. Based on these ignition timings, a target ignition timing is set, which corresponds to the estimated EGR rate.
When the target EGR rate varies with the changing engine operating state, the EGR valve opening is controlled by the EGR controlling means in such a manner that actual EGR rate follows the target EGR rate. However, due to the pressure storage effect of the intake system, the actual EGR rate changes with a delay with respect to the change in target EGR rate. In a transition state, e.g., during a transition between EGR and non-EGR operations, the target EGR rate changes, without delay, between the target EGR rate for the EGR operation and that (=0) for the non-EGR operation, and accordingly, the ratio between the target EGR rate and the estimated EGR rate (corresponding to the actual EGR rate) estimated by the EGR rate estimating means varies within a range from 0 to 1.0.
More specifically, just after the start of transition from non-EGR operation to EGR operation, the target EGR rate changes, without delay, from a value (=0) used prior to the start of transition (i.e., used for the non-EGR operation) to a larger value used even after completion of transition (i.e., used for the EGR operation), whereas the estimated EGR rate remains at a value (=0) used prior to the sta

Affiliated with

Also associated with

Rating

Ignition timing control system for internal combustion engine does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ignition timing control system for internal combustion engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ignition timing control system for internal combustion engine will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3263137