Torque control strategy for engines with continuously...

Details Torque control strategy for engines with continuously... Torque control strategy for engines with continuously...

1999-06-01

2001-02-13

Nguyen, Tan (Department: 3661)

Data processing: vehicles, navigation, and relative location

Vehicle control, guidance, operation, or indication

Transmission control

C701S056000, C477S043000, C477S100000

Reexamination Certificate

active

06188944

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to engines having continuously variable transmission, and more particularly to a torque control strategy for gasoline direct injection stratified charge and lean burn port-fuel injected engines with continuously variable transmission.
BACKGROUND OF THE INVENTION
Precious metal oxidation catalysts are generally used as a means for removing pollutants from the exhaust gas of an internal combustion engine. These oxidation catalysts remove CO, HC, and NO
x
simultaneously from engine exhaust gases when the air-fuel ratio of the exhaust gas is at a stoichiometric air-fuel ratio. The ability of oxidation catalysts to remove NO
x
in the exhaust gas falls rapidly, however, when the air-fuel ratio of the exhaust gas becomes leaner. Therefore, in engines operating in a lean air-fuel ratio environment, such as a direct injection stratified charge engine (DISC) or other lean-burn engine technologies, it is difficult to remove NO
x
from the exhaust gas using a conventional oxidation catalyst.
Accordingly, to achieve NO
x
control, exhaust after-treatment systems have included a lean NO
x
trap (LNT). Presently, however, the LNT is only a trapping device during the lean operation. The LNT must be purged periodically in order to maintain its level of efficiency. To meet the purge requirement, the DISC or lean burn engine has to run at an air-to-fuel ratio rich of stoichiometry periodically during lean operation. 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 running in a stratified mode, the LNT is typically purged by running the engine rich of stoichiometry for 2-3 seconds every 50 seconds. The engine control system has to 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.
SUMMARY OF THE INVENTION
It is an object of the present invention to actively enhance engine performance and improve fuel economy and emissions. It is another object of the present invention to use continuously variable transmission (CVT) to mitigate the effects of torque disturbances due to the LNT purge cycle.
It is a further object of the present invention to provide a control strategy that combines the CVT with other engine control variables to optimize fuel consumption during the steady state operation of the engine and to minimize drivetrain disturbance during transient operation.
The foregoing and other objects and advantages are achieved through using the CVT as an additional actuator for torque and temperature management during the LNT purge cycle to mitigate torque disturbances from DISC engines. By adjusting the gear ratio and thus managing the engine load in response to the engine torque variation, the CVT can isolate the engine torque disturbance and prevent it from being transmitted to the vehicle drivetrain. Other engine control variables, such as the throttle, spark and fuel, are coordinated with the CVT gear actuation to keep the engine and transmission operating near the optimal regime where fuel consumption and emissions are minimized.
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 transients.
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.


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