Catalytic converter early light off using cylinder deactivation

A vehicle includes an engine that has a plurality of cylinders and that generates exhaust gas. A catalytic converter reduces harmful emissions from the exhaust gas after achieving a light off temperature. A controller is connected to the engine and the catalytic converter. The controller deactivates the cylinder(s) of the engine before the catalytic converter achieves the light off temperature if the engine is operating at idle or low load. The controller waits a first period before deactivating the cylinder(s). The controller optimizes engine operating parameters to reduce a second period that is required to achieve the light off temperature. A temperature sensor is connected to the controller and senses ambient temperature. The controller does not deactivate the cylinders if the ambient temperature is below a first predetermined temperature. The controller activates all of the cylinders if the engine is operating at high load.

TECHNICAL FIELD

The present invention relates to engine control systems, and more particularly to engine control systems that deactivate one or more cylinders to promote the transition from rich to stoichiometric air-fuel ratios during startup and early light off of a catalytic converter.

BACKGROUND OF THE INVENTION

In order to reduce emissions, modern car engines carefully control the amount of fuel that is burned. The engines control the air-fuel ratio to achieve an optimum stoichiometric ratio. At the optimum stoichiometric ratio, all of the fuel is burned using all of the oxygen in the air. For gasoline, the stoichiometric ratio is about 14.7:1. In other words, for each pound of gasoline, 14.7 pounds of air is burned. The air-fuel ratio varies from the optimum stoichiometric ratio during driving. Sometimes the air-fuel ratio is lean (an air-to-fuel ratio higher than 14.7) and other times the air-fuel ratio is rich (an air-to-fuel ratio lower than 14.7).

The primary emissions of a car engine are nitrogen, carbon dioxide and water vapor. Air is approximately 78 percent nitrogen (N2) gas. Most of the nitrogen passes through the car engine. Carbon dioxide (CO2) is produced when carbon in the fuel bonds with the oxygen in the air. Water vapor (H2O) is produced when hydrogen in the fuel bonds with the oxygen in the air.

Because the combustion process is never perfect, some additional harmful emissions are also produced by car engines. Carbon monoxide (CO), a poisonous gas that is colorless and odorless, is produced. Hydrocarbons or volatile organic compounds (VOCs), resulting from unburned fuel that evaporates, are produced. Sunlight breaks these emission down to form oxidants that react with oxides of nitrogen to cause ground level ozone (O3), a major component of smog. Oxides of nitrogen (NO and NO2, together called NOx) contribute to smog and acid rain and cause irritation to human mucus membranes. Catalytic converters are designed to reduce these three harmful emissions.

Most modern cars are equipped with three-way catalytic converters. “Three-way” refers to the three harmful emissions that catalytic converters help to reduce—carbon monoxide, VOCs and NOx. The catalytic converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. Both types include a ceramic structure that is coated with a metal catalyst, usually platinum, rhodium and/or palladium. The catalytic converter exposes the catalyst to the exhaust stream while minimizing the amount of catalyst that is required due to the high cost of the catalyst materials.

There are two main types of structures that are used in catalytic converters—honeycomb and ceramic beads. Most cars today use a honeycomb structure. The reduction catalyst is the first stage of the catalytic converter that typically uses platinum and rhodium to help reduce the NOx emissions. When the NOx molecules contact the catalyst, the catalyst separates the nitrogen from the molecule, holds on to the nitrogen and frees the oxygen in the form of O2. The nitrogen bond with other nitrogen that are also held by the catalyst, forming N2. For example:
2NO=>N2+O2or 2NO2=>N2+2O2

The oxidation catalyst is the second stage of the catalytic converter that reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. The oxidation catalyst reacts the CO and hydrocarbons with the remaining oxygen in the exhaust gas. For example:

The third stage is a control system that monitors the exhaust stream and uses the information to control the fuel injection system. Typically an oxygen sensor is mounted between the engine and the catalytic converter. The oxygen sensor senses oxygen in the exhaust. An engine control system increases or decreases the amount of oxygen in the exhaust by adjusting the air-fuel ratio. The engine control system makes sure that the engine is running at close to the optimum stoichiometric ratio and that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and CO.

While the catalytic converter reduces pollution, the catalytic converter can still be improved substantially. The catalytic converter only works at a fairly high temperature. When a car is started, the catalytic converter does not reduce the pollution in the exhaust until the catalytic converter reaches a predetermined temperature that is also called the light off temperature.

One conventional solution to the problem is to move the catalytic converter closer to the engine. The hot exhaust gases reach the catalytic converter more quickly and heats it up faster. This approach tends to reduce the life of the catalytic converter by exposing it to extremely high temperatures. Most carmakers position the catalytic converter under the front passenger seat, far enough from the engine to keep the temperature down to levels that will not harm it.

Preheating the catalytic converter is another conventional way to reduce emissions. The easiest way to preheat the converter is to use electric resistance heaters. Unfortunately, the 12-volt electrical systems on most cars do not provide enough energy to heat the catalytic converter fast enough. Most drivers will not wait several minutes for the catalytic converter to heat up before starting their car.

SUMMARY OF THE INVENTION

A vehicle control system according to the invention controls an engine that includes a plurality of cylinders and that generates exhaust gas. A catalytic converter reduces harmful emissions from the exhaust gas after reaching a light off temperature. A controller is connected to the engine and the catalytic converter. The controller deactivates at least one of the cylinders of the engine before the catalytic converter achieves the light off temperature.

In other features of the invention, the controller waits a first period before deactivating the cylinder(s). The controller optimizes engine operating parameters while the cylinder(s) are deactivated to reduce a second period that is required to achieve the light off temperature.

In yet other features, a temperature sensor is connected to the controller and senses ambient temperature. The controller does not deactivate the cylinder(s) if the ambient temperature is below a first predetermined temperature.

In still other features, the controller only deactivates the cylinder(s) if the engine is operating at idle or low load. The controller does not deactivate the cylinder(s) if the engine is operating at high load.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG. 1, a vehicle10includes an engine12with a plurality of cylinders14-1,14-2, . . . ,14-n. The engine12is connected to a transmission16that drives front wheels17and/or rear wheels18of the vehicle10. The engine12is also connected to an exhaust manifold19. The exhaust manifold19directs exhaust gas20from the engine12to a catalytic converter22. An oxygen sensor24is typically located between the engine12and the catalytic converter22. As can be appreciated, the oxygen sensor24can be located in other positions and/or omitted. A muffler28is also located downstream from the catalytic converter22.

A controller32is connected to the catalytic converter22, the engine12, and to one or more engine operating sensors and/or environmental sensors, such as an ambient temperature sensor36. As will be described more fully below, the controller32deactivates one or more of the cylinders14of the engine12during idle or low load conditions as soon as possible after the engine12starts up. Cylinder deactivation methods are disclosed in U.S. Pat. No. 4,249,488 to Siegla and U.S. Pat. No. 4,230,076 to Mueller, which are hereby incorporated by reference. Other methods are disclosed in “Cadillac Sedan DeVille, Hold on for dear life with the world's first variable-displacement engine”,Car and Driver(April 1981); “New Mercedes revives V-8 cylinder deactivation”, Peter Robinson,Ward's Engine and Vehicle Technology Update(Oct. 1, 1998); and “Reduced Fuel Consumption and Emissions Through Cylinder Deactivation”, Malcolm H. Sanford et al (Oct. 7, 1998), which are hereby incorporated by reference. The working cylinders14are at a higher load with faster flame heads and more stable combustion (as compared to when all cylinders are operating). The controller32quickly transitions from rich to stoichiometric air fuel mixtures while simultaneously allowing spark angle retard for increased exhaust gas temperatures and quicker light off of the catalytic converter22. The idle speed of the engine12is also optimized as necessary during the warmup period of the catalytic converter22.

Once light off of the catalytic converter22is achieved, the engine12is switched back to default operation, which may or may not include operation using all of the cylinders14depending upon other factors. At very cold temperatures (such as −40° C. to 20° C.), full operation of the engine12(e.g., all cylinders) is performed.

Cylinder deactivation involves turning off one or more of the cylinders of the engine12during idle and light load operating conditions. Full engine operation is automatically restored when necessary for acceleration or for hauling heavy loads. During idle and light load operating conditions, the (fewer) working cylinders operate at higher load. During idle and light load operating conditions, the engine12has higher combustion stability and fuel efficiency due to better thermal, volumetric, and mechanical efficiency.

Referring now toFIG. 2, the controller32is illustrated in further detail. The controller32includes a processor34, memory37, and an input/output interface40. A cylinder actuation control module44controls activation and deactivation of the cylinders14of the engine12. The cylinder actuation control module44can be implemented as a software module or as a dedicated circuit. The memory37includes read-only memory (ROM), random access memory (RAM), flash memory, or other suitable electronic storage. The controller32can also be implemented as an application specific integrated circuit (ASIC).

Referring now toFIG. 3, steps performed by the controller32and the cylinder actuation control module44are shown in further detail and are generally designated50. Control begins with step52. In step54, the controller32determines whether the engine12is started. If not, control loops back to step54. Otherwise, the controller32continues with step58where all of the cylinders14are initially actuated. In step60, the controller32determines whether the temperature is less than a predetermined temperature such as 20° C. If it is, the cylinder actuation control module44ends in step64. If not, the controller32continues with step68and starts a timer. In step69, the controller32determines whether the catalytic converter22is at the light off temperature. If the catalytic converter22is not at the light off temperature, control continues with step72.

In step72, the controller32determines whether the engine12is on and is operating at idle or low load. If it is, the controller32continues with step76and determines whether the timer is up. Typically, the timer is preferably set for a first period that is equal to five to ten seconds after the engine12starts up. If the timer is not up, control continues with step69. Otherwise, control continues with step80where one or more of the cylinders14are deactivated and the engine12is optimized for light off of the catalytic converter22. Control continues from step80to step69.

If the conditions of step72are not met, control continues with step90where the controller32determines whether the engine12is on and at high load. If it is, the controller32continues with step94where all of the cylinders14are actuated. Control continues from step94to step69. When the catalytic converter22reaches its light off temperature as determined in step69, the controller32continues with step96where default operation of the engine12is performed, which may include activation of some or all of the cylinders14.