1. Field of the Invention
The present invention relates to a vehicle exhaust gas recirculation system.
2. Description of the Background Art
The biggest challenge to current engine and vehicle manufactures is the increasing need for improved vehicle emissions. This continues to grow in criticality as the sheer number of vehicles continue to climb. Even small improvements in emissions levels in an engine gains large importance when multiplied across thousands or millions of vehicles.
In response, emissions requirements and regulations have tended to grow more and more stringent. However, this is in opposition to performance. It is no secret that strict emissions controls tend to adversely impact driveability, with engines having low emissions having reduced acceleration capabilities and slower throttle responses. This makes clean emission engines less desirable from a driveability point of view.
One way in which emissions levels may be reduced is through the use of exhaust gas recirculation (EGR). Commonly, in a related art EGR system an EGR conduit connects an exhaust manifold to an intake manifold. An EGR valve may be opened to allow exhaust gas from the exhaust manifold to be directed into the intake manifold, wherein the exhaust gas is reburned in the engine. In this manner, partially burned components of the exhaust gas are reburned, lowering emissions levels.
Typical related art EGR systems have remained relatively simple. A related art EGR valve or controller opens under predetermined conditions, such as in response to engine timing or in response to feedback from sensors.
Such related art EGR systems are desirable in terms of cost and simplicity, but suffer from drawbacks both in emissions levels and in driveability. An EGR system that operates strictly on sensor feedback or that generates fixed, predetermined outputs based on inputs is too rigid and cannot take into account the complex variables within an internal combustion engine. For example, a related art EGR system may not control exhaust gas flow based on an engine load, a rate of change in throttle position, ambient operating conditions, or multiple internal engine conditions. In addition, related art EGR systems do not take into account changes in an engine over time due to wear, dirt, ambient operating conditions or changes therein, etc.
What is needed, therefore, are improvements in EGR systems for internal combustion engines.
An exhaust gas recirculation apparatus adapted for use on an internal combustion engine is provided according to a first aspect of the invention. The apparatus comprises an engine operational model, with the engine operational model capable of outputting at least one engine operational characteristic, a feedback controller portion, the feedback controller portion receiving an emissions level feedback and generating a feedback control signal based on a difference between a predetermined EGR level and the emissions level feedback, a feedforward controller portion receiving a plurality of engine sensor inputs and using the plurality of engine sensor inputs in conjunction with the engine operational model to generate a feedforward control signal, the feedforward control signal capable of changing an EGR exhaust gas flow before the plurality of engine sensor inputs show a deviation from a predetermined emissions level, and a controller receiving the feedback control signal, the feedforward control signal, and accessing the engine operational model, the controller regulating an EGR exhaust gas flow in response to the feedback control signal, the feedforward control signal, and the engine operational model.
An exhaust gas recirculation apparatus adapted for use on an internal combustion engine is provided according to a second aspect of the invention. The apparatus comprises at least one EGR valve positioned in a conduit between an exhaust and an intake of the engine, an engine operational model, with the engine operational model capable of outputting at least one engine operational characteristic, a feedback controller portion, the feedback controller portion receiving an emissions level feedback and generating a feedback control signal based on a difference between a predetermined EGR level and the emissions level feedback, a feedforward controller portion receiving a plurality of engine sensor inputs and using the plurality of engine sensor inputs in conjunction with the engine operational model to generate a feedforward control signal, the feedforward control signal capable of changing an EGR exhaust gas flow before the plurality of engine sensor inputs show a deviation from a predetermined emissions level, and a controller receiving the feedback control signal, the feedforward control signal, and accessing the engine operational model, the controller regulating an EGR exhaust gas flow in response to the feedback control signal, the feedforward control signal, and the engine operational model.
A exhaust gas recirculation method adapted for use on an internal combustion engine is provided according to a third aspect of the invention. The method comprises the steps of generating an EGR engine model factor from an engine model constructed of engine operational characteristics, generating an EGR feedback factor from a plurality of engine sensor inputs, generating an EGR feedforward factor from the plurality of engine sensor inputs and the engine model, and controlling an EGR exhaust gas flow based on the EGR engine model factor, the EGR feedback factor, and the EGR feedforward factor.
The above and other features and advantages of the present invention will be further understood from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.