Torque control scheme for low emission lean burn vehicle

Details Torque control scheme for low emission lean burn vehicle Torque control scheme for low emission lean burn vehicle

2000-03-06

2001-07-03

Solis, Erick (Department: 3747)

Power plants

Internal combustion engine with treatment or handling of...

By means producing a chemical reaction of a component of the...

C123S295000, C123S681000, C701S109000

Reexamination Certificate

active

06253546

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to control systems for internal combustion engines and, more particularly, to a torque control strategy for gasoline direct injection stratified charge (DISC) and lean burn engines.
BACKGROUND OF THE INVENTION
Precious metal oxidation catalysts are generally used as a means for removing emissions from the exhaust gas of an internal combustion engine. These oxidation catalysts remove CO, HC, and NOx, simultaneously from engine exhaust gases when the air-fuel ratio of the exhaust gas is at a stoichiometric air-fuel ratio.
Exhaust after-treatment systems have included a second three-way catalyst downstream of the first three-way catalyst which is sometimes referred to as a lean NOx, trap (LNT) . Presently, however, the LNT is only a trapping device for NOx during the lean operation. The LNT must be periodically purged in order to maintain its level of efficiency. To meet the purge requirement, the DISC or lean burn engine must periodically operate at an air-fuel ratio rich of stoichiometry. In addition, the LNT has a very narrow operating temperature range beyond which the LNT trapping capacity and efficiency is greatly reduced.
For a DISC engine operating in a stratified mode, the LNT is typically purged by running the engine rich of stoichiometry for two-three seconds every 50 seconds. The engine control system must manage this purge cycle without causing noticeable torque disturbance to the vehicle. Prior art approaches to this problem involve the use of an electronic throttle, or other electrical supplemental torque devices, for example, a combined alternator-starter or continuously variable transmission (CVT). Such schemes, however, require actuators, in addition to the standard sensor set available on a DISC engine.
SUMMARY OF THE INVENTION
It is an object of the present invention to improve engine performance as well as fuel economy and emissions levels. It is another object of the present invention to provide a control strategy to optimize fuel consumption during the steady state operation of the engine and to minimize drivetrain disturbance during transient operation.
According to the present invention, the foregoing and other objects and advantages are attained by a method of minimizing torque disturbances in an internal combustion engine for a vehicle having a lean NOx trap that is periodically purged. The method includes the steps of generating feedforward values of first engine characteristics as a function of desired engine torque and generating feedback values of second engine characteristics as a function of intake manifold pressure. Target values are then calculated for predetermined engine variables based on the first and second engine characteristics. Engine variables are then set to the target values to compensate for torque disturbances resulting from the lean NOx trap purge cycle. According to the disclosed method, the feedforward path schedules the throttle, fuel rate and spark timing based on an engine model to produce a demanded engine torque. The feedback path then uses the values of fuel rate and spark timing to compensate for torque variations. This is accomplished by determining an error term as a function of a reference trajectory intake manifold pressure and measured intake manifold pressure.
One advantage of the present invention is that it reduces emissions and improves fuel economy. Another advantage is that it maintains constant, desired torque to the wheels for improved drivetrain performance during trap purge transient operation. Other features and advantages of the present invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.


REFERENCES:
patent: 5727385 (1998-03-01), Hepburn
patent: 5778666 (1998-07-01), Cullen et al.
patent: 6079204 (2000-06-01), Sun et al.
patent: 6082100 (2000-07-01), Boegner et al.
patent: 6164065 (2000-12-01), Denari et al.

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