Internal-combustion engines – Charge forming device – Fuel injection system
Patent
1995-09-28
1998-07-14
Dolinar, Andrew M.
Internal-combustion engines
Charge forming device
Fuel injection system
123480, 123585, F02D 4104, F02D 4304
Patent
active
057788561
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a control device and control method for a lean-burn engine.
BACKGROUND ART
In order to improve the fuel consumption or exhaust gas characteristic of an internal combustion engine, it is well known to control the air-fuel ratio of a mixture supplied to the engine to an air-fuel ratio on the fuel-lean side with respect to the theoretical air-fuel ratio, to effect the lean driving (lean-burn driving) of the engine. In the air-fuel ratio control of this type, to prevent the engine output from becoming insufficient in the acceleration driving region and the like, the air-fuel ratio is controlled to a value near the theoretical air-fuel ratio in the acceleration driving region and the like, so as to effect the stoichiometric driving (in a broad sense, rich driving) of the engine. Therefore, for example, if the step-on operation of the accelerator pedal is released so that the driving state departs from the acceleration driving region during the running of a vehicle on which an engine controlled in the above described manner is mounted, only the amount of fuel is reduced to allow switching from the rich driving to the lean driving. In this case, the engine output is rapidly lowered to cause a shock, thus degrading the drivability of the vehicle.
To obviate this, an air-fuel ratio control device which changes only the intake air amount, without changing the supply amount of fuel to the engine, so as to keep the engine output constant at the time of switching from the rich driving to the lean driving is proposed in Japanese Patent Application KOKAI Publication No. H5-187295.
The proposed device, which carries out the rich driving in a particular driving state of the engine and which effects the lean driving in the other state, includes two bypass passages bypassing the throttle valve. An idling speed control (ISC) valve is provided in one of the bypass passages, and a vacuum-sensitive valve is provided in the other bypass passage. In the lean driving, a bypass valve provided in a control pressure passage which connects a throttle-valve-mounting-portion of the intake passage to the control chamber of the vacuum-sensitive valve is opened, so that bypass air of an amount suitable for the negative pressure in the intake passage and hence suitable for the engine driving state will be supplied to the engine via the bypass passage disposed on the vacuum-sensitive valve side. Further, a target amount of intake air for attaining the air-fuel ratio on the fuel-lean side is calculated according to the opening degree of the throttle valve, and the opening degree of the ISC valve is controlled according to a deviation between the target intake air amount and an actual intake air amount, so that the target intake air amount can be supplied to the engine.
According to the proposed device, a fluctuation in the engine output torque at the time of switching between the rich driving and the lean driving can be suppressed to a relatively small degree. However, since the intake air amount control of the proposed device is based on the control of the opening degree of the vacuum-sensitive valve according to the intake negative pressure in the throttle-valve-mounting-portion of the intake pipe, there is a limitation in optimizing the intake air amount control or in suppressing a fluctuation in the torque during the switching of driving modes.
That is, when the switching to the lean driving is made in an air-fuel ratio region where the fuel consumption is small and a generation amount of nitrogen oxide is small, the bypass air amount may become insufficient to lower the torque, or the bypass air may become excessive to accelerate the engine. To obviate this, if the air-fuel ratio is set near the theoretical air-fuel ratio to cope with the lowering in the torque, the generation amount of nitrogen oxide increases and the fuel consumption becomes large.
As shown in FIG. 1, a required amount of bypass air can be derived from volumetric efficiency and engine rotation speed, for example. According t
REFERENCES:
patent: 4434768 (1984-03-01), Ninomiya et al.
patent: 4616621 (1986-10-01), Kuroiwa et al.
patent: 5381768 (1995-01-01), Togai et al.
patent: 5413078 (1995-05-01), Mitsunaga et al.
Ishida Masaji
Okada Kojiro
Togai Kazuhide
Dolinar Andrew M.
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
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