Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-10-18
2001-04-03
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C123S295000
Reexamination Certificate
active
06209526
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to mode transition control of a direct injection spark ignition engine.
BACKGROUND OF THE INVENTION
In direct injection spark ignition engines, the engine operates with stratified air/fuel operation in which the combustion chamber contains stratified layers of different air/fuel mixtures. The strata closest to the spark plug contains a stoichiometric mixture or a mixture slightly rich of stoichiometry, and subsequent strata contain progressively leaner mixtures.
The engine may also operate in a homogeneous mode of operation with a homogeneous mixture of air and fuel generated in the combustion chamber by early injection of fuel into the combustion chamber during the intake stroke. Homogeneous operation may be either lean of stoichiometry, at stoichiometry, or rich of stoichiometry.
Direct injection engines are also coupled to conventional three-way catalytic converters to reduce CO, HC, and NOx. When operating at air/fuel mixtures lean of stoichiometry, a NOx trap or catalyst is typically coupled downstream of the three-way catalytic converter to further reduce NOx.
The stratified mode of operation is typically utilized when the engine is operating in light to medium loads. The homogeneous mode of operation is typically used from medium to heavy load operating conditions. In certain conditions, it is necessary to transition from one engine mode of operation to the other. During these mode transitions, it is desired to deliver the requested engine output torque to provide good drive feel. However, in some circumstances, the range of acceptable lean air/fuel ratios of stratified operation do not overlap with the acceptable air/fuel ratios of homogeneous operation. Therefore, during the mode transition, a torque shock occurs because of the step change in engine air/fuel ratio.
One method of preventing the engine torque disturbance during mode transition is to change the injection mode one cylinder at a time according to the required amount of fuel to be injected. This reduces a large torque disturbance to several smaller torque disturbances. Such a method is described in U.S. Pat. No. 5,170,759.
The inventors herein have recognized a disadvantage with the above approach. Even though the large torque jump during mode transition is avoided, there are still several smaller torque jumps experienced. In other words, a single, large torque disturbance is substituted with multiple smaller torque disturbances which are still noticeable by the vehicle driver.
SUMMARY OF THE INVENTION
An object of the invention herein is to control an engine during mode transitions to provide a smooth torque output.
The above object is achieved and disadvantages of prior approaches overcome by a method for controlling an engine during a cylinder air/fuel ratio change from a first cylinder air/fuel ratio to a second cylinder air/fuel ratio. The method comprises the steps of changing the cylinder air/fuel ratio, and in response to said step of changing said cylinder air/fuel ratio, changing a number of cylinders carrying out combustion in the engine so that abrupt changes in an engine torque of the engine will be avoided during the cylinder air/fuel ratio change.
By using cylinder deactivation as an additional degree of freedom, abrupt changes in average engine torque can be avoided even during air/fuel ratio changes. Thus, during a mode transition where engine air/fuel ratio is constrained to change due to, for example, combustion limits, abrupt changes in average engine torque can be avoided by changing a number of active cylinders.
An advantage of the above aspect of the invention is that abrupt changes in engine output torque can be avoided during mode transitions.
Another advantage of the above aspect of the invention is that the range of stratified operation can be extended since the range of available transitions is increased.
Yet another advantage of the above aspect of the invention is that emissions can be reduced since the engine can be operated farther from air/fuel ratio combustion limits.
In another aspect of the invention, the above object is achieved by a control method for a spark ignited engine having multiple combustion chambers capable of operating in a stratified mode where fuel is injected during a compression stroke of the engine, wherein the engine is further capable of operating in a homogeneous mode of operation where fuel is injected during an intake stroke of the engine. The method comprises transitioning from said stratified mode to said homogeneous mode based on an operating condition; in response to said transition, disabling a number of cylinders by discontinuing fuel injection into disabled cylinders; and in response to said transition, changing an injection timing from compression stroke injection to intake stroke injection and changing a fuel injection amount to a remaining set of activated cylinders.
In yet another aspect of the invention, the above object is achieved by a control method for a spark ignited engine having multiple combustion chambers capable of operating in a stratified mode where fuel is injected during a compression stroke of the engine, wherein the engine is further capable of operating in a homogeneous mode of operation where fuel is injected during an intake stroke of the engine. The method comprises transitioning from said homogeneous mode to said stratified mode based on an operating condition; in response to said transition, enabling a number of cylinders by starting fuel injection into disabled cylinders; and in response to said transition, changing an injection timing from intake stroke injection to compression stroke injection and changing a fuel injection amount to an already enabled set of activated cylinders.
Therefore, when transitioning, for example, from stratified to homogenous mode, where cylinder air/fuel ratio discontinuities are unavoidable, abrupt changes in average engine torque can be avoided by compensating for increased torque in individual cylinders by deactivating fuel injection into a predetermined number of cylinders. Similarly, when transitioning from homogenous to stratified mode, abrupt changes in average engine torque can be avoided by compensating for decreased power in individual cylinders by reactivating fuel injection into a predetermined number of cylinders.
An advantage of the above aspect of the invention is that abrupt changes in engine output torque can be avoided during mode transitions.
Another advantage of the above aspect of the invention is that the range of stratified operation can be extended since the range of available transitions is increased.
Yet another advantage of the above aspect of the invention is that emissions can be reduced since the engine can be operated farther from air/fuel ratio combustion limits.
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Grizzle Jessy W.
Sun Jing
Ford Global Technologies Inc.
Gimie Mahmoud M
Russell John D.
Voutyras Julia
Yuen Henry C.
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