Control device and control method for lean-burn engine

• US 5,813,386 A
• Filed: 03/28/1997
• Issued: 09/29/1998
• Est. Priority Date: 12/28/1993
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Original Assignee: Mitsubishi Jidosha Kogyo Kabushiki Kaisha
• Inventors: Okada, Kojiro, Togai, Kazuhide, Ishida, Masaji
• Primary Examiner(s): Dolinar, Andrew M.
• Application Number:
  US08/825,335
• Time in Patent Office: 550 Days
• Field of Search: 123/327, 123/406, 123/417, 123/339.23, 123/329, 123/339.14
• US Class Current: 123/339.14
• CPC Class Codes: F02D 37/02 one of the functions being ignition
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• CPC Class Codes: F02D 41/1475 Regulating the air fuel ratio at a value other than stoichiometry
• CPC Class Codes: F02D 41/3011 according to or using specific or several modes of combustion
• CPC Class Codes: F02D 41/307 to avoid torque shocks

Abstract

A control device of a lean-burn engine has an electronic control unit. Upon start of switching from stoichiometric driving to lean driving, the control unit (10) derives, from a map, a target pressure (P0) and a basic opening degree (D0) of an idling speed control valve, serving as an air bypass valve, based on the throttle opening degree (TPS) and the engine rotation speed (Ne) at the start of the switching. The control unit supplies driving pulses (N) of a number corresponding to the basic opening degree (D0) to a stepper motor (32) of the idling speed control valve. Then, the control unit supplies the stepper motor with driving pulses of a number corresponding to an opening degree correction amount (D1) which in turn corresponds to a deviation between the target intake pressure (P0) and an actual intake pressure (PB), to thereby suppress a change in the torque at the time of switching between the rich driving, including the stoichiometric driving, and the lean driving of the lean-burn engine.

Claims

1. A control device for a lean-burn engine, comprising:

load state detecting means for detecting a load state of the engine;

intake air amount adjusting means for adjusting an amount of intake air supplied to the engine; and

control means for controlling said intake air amount adjusting means according to the engine load state detected by said load state detecting means, so as to cause that change in the load state which permits a difference between output torques of the engine before and after switching to be reduced or canceled, when the switching is made from driving with a first air-fuel ratio which is set equal to a theoretical air-fuel ratio or on a fuel-rich side with respect thereto to driving with a second air-fuel ratio which is set on a fuel-lean side with respect to the theoretical air-fuel ratio, wherein

said intake air amount adjusting means includes an intake flow rate control valve provided in an intake passage for introducing the intake air into a combustion chamber of the engine, and

said control means controls the intake air amount of the engine towards an increasing side and temporarily delays ignition timing of the engine so as to be adapted for increase of the intake air amount, and then controls the ignition timing towards an advance side and controls air-fuel ratio towards a lean side.

2. The control device for a lean-burn engine according to claim 1, wherein the first air-fuel ratio is set to a first value which is substantially constant, and the second air-fuel ratio is set to a second value which is larger than the first value and which is substantially constant.

3. A control device for a lean-burn engine according to claim 2, wherein the first air-fuel ratio is set to the theoretical air-fuel ratio.

4. The control device for a lean-burn engine according to claim 1, wherein the first air-fuel ratio is set to a first value which is substantially constant, and the second air-fuel ratio is set according to the engine load state detected by said load state detecting means.

5. A control device for a lean-burn engine according to claim 4, wherein the first air-fuel ratio is set to the theoretical air-fuel ratio.

6. The control device for a lean-burn engine according to claim 1, further including:

rotation speed detecting means for detecting a rotation speed of the engine;

wherein the first air-fuel ratio is set to a substantially constant value, the second air-fuel ratio is set according to at least the engine rotation speed detected by said rotation speed detecting means, and said control means controls said intake air amount adjusting means according to the engine rotation speed detected by said rotation speed detecting means and the engine load state detected by said load state detecting means.

7. The control device for a lean-burn engine according to claim 1, wherein the first air-fuel ratio is set to the theoretical air-fuel ratio.

8. The control device for a lean-burn engine according to claim 1, wherein said intake air flow rate control valve includes a bypass valve provided in a throttle bypass passage.

9. The control device for a lean-burn engine according to claim 8, further including:

rotation speed detecting means for detecting a rotation speed of the engine;

wherein said control means controls drive of said bypass valve according to that controlled amount of an opening degree which is set based on the engine rotation speed detected by said rotation speed detecting means and the engine load state detected by said load state detecting means, so as to increase the air amount by a quantity which is set based on the load state detected by said load state detecting means.

10. The control device for a lean-burn engine according to claim 9, wherein said load detecting means includes a throttle opening degree sensor.

11. The A control device for a lean-burn engine according to claim 9, wherein said load detecting means includes a pressure sensor for detecting a negative pressure on a downstream side of a throttle valve.

12. The control device for a lean-burn engine according to claim 9, wherein said load detecting means includes an air flow sensor, and is operable to detect intake air amount information for one intake stroke in the engine based on an output of said air flow sensor.

13. The control device for a lean-burn engine according to claim 8, wherein said control means adjusts an opening degree of said bypass valve such that an idling speed is controlled to a desired rotation speed at a time of idle driving of the engine.

14. The control device for a lean-burn engine according to claim 1, wherein said control means delays ignition timing of the engine so as to be adapted for a change in the actual intake air amount towards an increasing side caused by said air amount adjusting means, and then controls the ignition timing towards an advance side and sets air-fuel ratio to the advancement of the ignition timing to thereby control the air-fuel ratio to a lean side.

15. The control device for a lean-burn engine according to claim 14, wherein said control means delays the ignition timing of the engine to follow a change in an actual intake air amount towards an increasing side caused by said air amount adjusting means, and then controls the ignition timing towards the advance side and sets air-fuel ratio to follow the advancement of the ignition timing to thereby control the air-fuel ratio to the lean side.

16. A control method for a lean-burn engine, comprising the steps of:

(a) detecting a load state of the engine; and

(b) controlling an amount of intake air supplied to the engine according to the detected engine load state, so as to cause that change in the load state which permits a difference between output torques of the engine before and after switching to be reduced or canceled, when the switching is made from driving with a first air-fuel ratio which is set equal to a theoretical air-fuel ratio or on a fuel-rich side with respect thereto to driving with a second air-fuel ratio which is set on a fuel-lean side with respect to the theoretical air-fuel ratio, wherein

said step (b) includes the sub-steps of;

controlling an amount of intake air of the engine towards an increasing side and temporarily delaying ignition timing of the engine so as to be adapted for increase of the intake air amount; and

controlling the ignition timing towards an advance side and controlling air-fuel ratio towards a lean side, after execution of said sub-step of controlling the intake air amount.

17. The control method for a lean-burn engine according to claim 16, wherein said step (b) includes the sub-steps of:

detecting a rotation speed of the engine;

setting a quantity by which an air amount is to be increased based on the load state detected in said step (a);

setting a controlled amount of an opening degree based on the detected engine load state and the detected engine rotation speed; and

controlling drive of a bypass valve, disposed in a bypass passage provided to bypass a throttle valve in an intake passage of the engine, according to the set controlled amount of the opening degree so as to permit the air amount to increase by the set quantity.

18. A control method for a lean-burn engine according to claim 16, wherein said step (b) includes the sub-steps of:

delaying ignition timing of the engine according to a change in an actual intake air amount towards an increasing side;

controlling the ignition timing towards an advance side and setting air-fuel ratio to increase of the ignition timing and controlling the air-fuel ratio towards a lean side, after execution of said sub-step of delaying the ignition timing.