JP2007285279A - Torque variation preventing and controlling system for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for suppressing a torque step which is caused by a backflow of a portion of secondary air into a cylinder. <P>SOLUTION: The torque variation preventing and controlling system prevents a sudden torque variation for an internal combustion with a secondary air supply unit, in which air is supplied upstream of a catalytic unit provided in an exhaust passage, thereby enhancing early activation of the catalytic unit. The torque variation preventing and controlling system includes: a backflow air volume calculating unit (S103) for calculating a backflow air volume which flows back to a combustion chamber out of the total volume of air supplied from the secondary air supply unit, according to engine operating conditions; and a torque variation suppressing means (S105) for suppressing a sudden torque variation caused by the backflow air. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a torque fluctuation prevention control device for an internal combustion engine.

2. Description of the Related Art Conventionally, an engine having a secondary air supply device that supplies secondary air to an exhaust passage during a cold start to promote early activation of a catalyst device is known. When secondary air is supplied to the exhaust passage, a portion of the secondary air may flow back into the cylinder due to exhaust pulsation. This affects the air-fuel ratio in the cylinder and the exhaust. Therefore, in an engine equipped with such a secondary air supply device, even when a portion of the secondary air flows back into the cylinder, the fuel is set so that the air-fuel ratio in the cylinder and the exhaust becomes the target air-fuel ratio. A technique for controlling the injection amount and the secondary air supply amount is known (see, for example, Patent Document 1).
JP-A-2005-90352

  By the way, when the secondary air supply device is used, the target air-fuel ratio in the cylinder is set smaller than the stoichiometric air-fuel ratio. Therefore, when a portion of the secondary air flows back into the cylinder, the output increases because the air-fuel ratio in the cylinder shifts to the theoretical air-fuel ratio side. If it does so, there existed a problem that a torque level | step difference generate | occur | produced and driveability deteriorated.

  The present invention has been made paying attention to such a problem, and an object of the present invention is to provide means for suppressing a torque step generated by a part of secondary air flowing back into a cylinder.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention provides an internal combustion engine provided with a secondary air supply device (10) for supplying air upstream of a catalyst device (32) provided in an exhaust passage (30) to achieve early activation of the catalyst device (32). A torque fluctuation prevention control device for preventing sudden fluctuations in the torque of the engine (1), wherein the amount of blowback air that flows back to the combustion chamber (5) out of the air supplied by the secondary air supply device (10), Blow-back air amount calculation means (step S103) for calculating according to the engine operating state, and torque fluctuation suppression means (steps S105, S204) for suppressing sudden fluctuations in torque generated by the blow-back air. Features.

  The present invention also includes a secondary air supply device (10) for supplying air upstream of the catalyst device (32) provided in the exhaust passage (30) so that the catalyst device (32) can be activated early. A torque fluctuation prevention control method for preventing sudden fluctuations in torque of the internal combustion engine (1), wherein the amount of blowback air that flows back to the combustion chamber (5) out of the air supplied by the secondary air supply device (10) Are calculated according to the engine operating state (step S103), and a torque fluctuation suppressing step (steps S105 and S204) for suppressing sudden fluctuations in torque generated by the blowback air. It is characterized by that.

  In the present invention, it is possible to suppress sudden fluctuations in torque generated when secondary air supply is started and stopped by blowing back the secondary air.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram showing a configuration of an engine 1 having a secondary air supply device 10 according to the present invention. The engine 1 includes a cylinder block 2 and a cylinder head 3 that covers the top of the cylinder block 2.

  The cylinder block 2 is formed with a plurality of cylinders 2a. In FIG. 1, one cylinder 2a is shown in order to prevent the drawing from being complicated and to facilitate understanding of the invention. A piston 4 is slidably fitted into the cylinder 2a. The cylinder block 2, the cylinder head 3, and the piston 4 define a pent roof type combustion chamber 5. A spark plug 6 is disposed at the center of the top wall of the combustion chamber 5.

  The cylinder head 3 is formed with an intake passage 20 and an exhaust passage 30 that open to the top wall of the combustion chamber 5. The intake valve 21 opens and closes the opening of the intake passage 20, and the exhaust valve 31 opens and closes the opening of the exhaust passage 30.

  In the intake passage 20, an airflow sensor 21, a throttle valve 22, and a fuel injection valve 23 are arranged in order from the upstream. A controller 50 described later detects the amount of fresh air taken in by the airflow sensor 21, and adjusts the fuel injection amount of the fuel injection valve 23 according to the detected amount. The opening degree of the throttle valve 22 is detected by a throttle sensor 24.

  An air-fuel ratio sensor 31 and a three-way catalyst 32 are arranged in the exhaust passage 30 in order from the upstream. The three-way catalyst 32 purifies the harmful three components of hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx) contained in the exhaust gas by oxidizing and reducing them. The air-fuel ratio sensor 31 is disposed at the inlet of the three-way catalyst 32 and detects the exhaust air-fuel ratio based on the oxygen concentration in the exhaust.

  The three-way catalyst 32 exhibits the purification performance of harmful three components of hydrocarbons, carbon monoxide, and nitrogen oxides only after reaching a predetermined temperature (hereinafter referred to as “activation start temperature”, about 300 ° C.). However, the exhaust temperature is low immediately after the engine is started. For this reason, the three-way catalyst 32 takes time to reach the activation start temperature. Then, the three-way catalyst 32 can hardly purify these harmful components until the activation start temperature is reached, and discharges a relatively large amount of harmful components into the atmosphere.

  In this manner, the three-way catalyst 32 discharges harmful components without purification until the activation start temperature is reached immediately after the engine is started. Therefore, in the present invention, the secondary air supply device 10 is provided in order to reduce such harmful components discharged without purification. The secondary air supply device 10 includes a secondary air supply passage 11, an air pump 12, and a cut valve 13.

  The secondary air supply passage 11 communicates with the exhaust passage 30. The secondary air supply passage 11 is connected upstream of the three-way catalyst 21 provided in the exhaust passage 30. An air pump 12 and a cut valve 13 are disposed in the secondary air supply passage 11.

  The air pump 12 is driven by a motor or an engine, and sends secondary air into the exhaust passage 30 via the secondary air supply passage 11.

  The cut valve 13 opens and closes the secondary air supply passage 11. The cut valve 13 is opened when the secondary air is supplied, and supplies the secondary air sent from the air pump 12 to the exhaust passage 30. On the other hand, the cut valve 13 is closed when the secondary air is not supplied to stop the supply of the secondary air to the exhaust passage 30 and prevent the backflow of the exhaust gas to the secondary air supply passage 11.

  The controller 50 optimally controls the fuel injection amount, ignition timing, and the like based on detection signals from various sensors such as the throttle sensor 24 and the air-fuel ratio sensor 31 described above. Further, the controller 50 controls the supply of secondary air by controlling the air pump 12 and the cut valve 13 based on the detection signal of the water temperature sensor 7 that detects the engine water temperature. The controller 50 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface).

  The secondary air supply device 10 is configured in this way, and supplies secondary air to the exhaust passage 30 when the temperature of the three-way catalyst 21 is not sufficiently raised as in the cold start. At the same time, the controller 50 increases the fuel injection amount in accordance with the supply of the secondary air. That is, when the secondary air is supplied, the in-cylinder air-fuel ratio is made richer than the stoichiometric air-fuel ratio, and rich combustion is performed. The exhaust gas after rich combustion is an exhaust gas in which hydrocarbons and carbon monoxide that are unburned fuel remain. The secondary air supply device 10 supplies secondary air to the exhaust gas, thereby promoting the oxidation (secondary combustion) of hydrocarbons and carbon monoxide in the exhaust gas to purify the exhaust gas. At the same time, the exhaust gas whose temperature has been raised by the secondary combustion is introduced into the three-way catalyst 32. Therefore, the time until the activation of the three-way catalyst 32 is promoted to reach the activation start temperature is shortened. The three-way catalyst 32 efficiently purifies the harmful three components of hydrocarbon, carbon monoxide, and nitrogen oxide at the same time when the exhaust air-fuel ratio is near the stoichiometric air-fuel ratio. Therefore, the increase in the fuel injection amount is set so that the exhaust air-fuel ratio at the inlet of the three-way catalyst 32 becomes the stoichiometric air-fuel ratio.

  By the way, when the secondary air is supplied to the exhaust passage 30, a part of the supplied secondary air may flow back to the combustion chamber 5 due to exhaust pulsation or the like (hereinafter referred to as “blowback”). As a result, the in-cylinder air-fuel ratio that is set rich is shifted to the stoichiometric air-fuel ratio side, so that the shaft torque increases. FIG. 2 shows how torque changes due to such blowback.

  FIG. 2 is a diagram showing the variation of the shaft torque with respect to the secondary air supply amount, and the line graph represents the shaft torque and the bar graph represents the secondary air supply amount. As shown in FIG. 2, the shaft torque indicated by the line graph is increased by blowing back when the secondary air is supplied compared to when the supply of the secondary air is stopped. Then, as indicated by an arrow, a torque step (abrupt fluctuations in torque) occurs at the start of the supply of secondary air, which causes discomfort to the driver.

  Therefore, in the present invention, the ignition timing is retarded so as to suppress the torque step generated at the start and stop of the supply of the secondary air and prevent the deterioration of the operation performance by such blowback. FIG. 3 is a diagram in which the shaft torque when the ignition timing is retarded is added to the diagram showing the variation of the shaft torque with respect to the secondary air supply amount of FIG. The solid line graph represents the shaft torque when the ignition timing is retarded. As shown in FIG. 3, according to the present invention, by retarding the ignition timing, an increase in shaft torque at the start of the supply of secondary air is suppressed, and the output is maintained at the shaft torque immediately before the start of supply. As a result, it is possible to suppress a torque step that occurs when the secondary air supply is started and stopped.

  Hereinafter, the suppression control of the torque step at the time of the secondary air supply by 1st Embodiment of this invention is demonstrated. FIG. 4 is a flowchart showing the suppression control executed by the controller 50 according to the first embodiment. When the ignition key is turned on and the engine is started, the controller 50 repeatedly executes this process every predetermined unit time.

  In step S101, the controller 50 determines whether the secondary air supply condition is satisfied. In the present embodiment, it is determined that the condition is satisfied if the engine water temperature is equal to or lower than a predetermined value.

  In step S101, when the secondary air supply condition is not satisfied, that is, when the engine water temperature is higher than the predetermined value, the controller 50 proceeds to step S106.

  On the other hand, when the secondary air supply condition is satisfied in step S101, that is, when the engine water temperature is lower than the predetermined value, the controller 50 proceeds to step S102.

  In step S <b> 102, the controller 50 drives the air pump 12 and opens the cut valve 13 to supply secondary air to the exhaust passage 30.

  In step S103, the controller 50 calculates a reverse flow rate (hereinafter referred to as “blow-back air amount”) of the secondary air to the combustion chamber 5 in accordance with the engine operating state.

  The ratio of blowback is substantially constant according to the engine operating state regardless of the supply amount of the secondary air. Therefore, the blowback air amount may be determined based on this characteristic, for example, by storing a map of the ratio of secondary air blowback according to the engine operating state set in advance through experiments in the ROM. An example of the map is shown in FIG. In the present invention, the ratio of secondary air blowing back is determined from the engine speed and engine load. However, the present invention is not limited to this, and the secondary air blowing is determined based on various parameters such as exhaust pulsation that affects the blowing back. The return ratio may be determined.

  In step S104, the controller 50 calculates the ignition timing retard amount from the ignition timing setting table for the blowback air amount calculated in step S103. FIG. 6 is a setting table of ignition timing with respect to the blowback air amount. As shown in this figure, the greater the amount of blowback air, the greater the torque step, and the greater the retard amount of the ignition timing. The retard amount of the ignition timing is set by this setting table to a value that can maintain the shaft torque immediately before the start of the supply of secondary air, as described above with reference to FIG.

  Note that the retard amount of the ignition timing may be set in consideration of combustion stability. FIG. 7 is a characteristic diagram showing a region of stable combustion. When the combustion stability is taken into consideration, the retard amount of the ignition timing is set to a value within the stable combustion region (combustion stability limit) shown in FIG. Depending on the amount of retard at the ignition timing, such as when the amount of blowback air is large, the engine may go out of the stable combustion region, that is, exceed the limit of combustion stability. In such a case, the fuel injection amount can be controlled at the same time so as to enter the stable combustion region. For example, if the retard amount is still insufficient after retarding from point A to point B in FIG. 7, the air-fuel ratio is simultaneously changed and controlled to point C.

  In step S105, the controller 50 retards the ignition timing of the spark plug 6 from the normal value based on the retard amount calculated in step S104. Thereby, the torque level difference which occurs at the time of starting and stopping the supply of secondary air by blowing back is suppressed.

  In step S <b> 106, the controller 50 stops driving the air pump 12 and closes the cut valve 13 to stop the supply of secondary air to the exhaust passage 30.

  In step S107, the controller 50 returns the ignition timing to the normal value and shifts the processing from the suppression control to the normal engine control.

  FIG. 8 is a time chart of the suppression control executed by the controller 50 according to the first embodiment. In addition, in order to clarify the correspondence with the flowchart, description will be made with the step number of the flowchart.

When the ignition key is turned on, the engine at time t ₁ is started, the controller 50 starts the control. First, the controller 50 determines whether or not the engine water temperature is equal to or lower than a predetermined temperature (S101). If the temperature is equal to or lower than the predetermined temperature (FIG. 8A), the controller 50 drives the air pump 12 and opens the cut valve 13 to supply secondary air (t _{1 in} FIG. 7B; S102). At this time, the controller 50 increases the fuel injection amount so that the exhaust air-fuel ratio at the inlet of the three-way catalyst 32 becomes the stoichiometric air-fuel ratio (FIG. 8C) (FIG. 8D).

  At this time, the controller 50 calculates the blow-back air amount of the secondary air (S103), and retards the ignition timing so as not to generate a torque step (FIG. 8E) (FIG. 8F; S105). ).

When the engine water temperature reaches a predetermined temperature at time t ₂ (FIG. 8A; NO in S101), the controller 50 stops driving the air pump 12 and closes the cut valve 13 to stop the supply of secondary air. (T _{2 in} FIG. 8A; S106). Thereafter, the controller 50 ends the suppression control (S107) and shifts to normal engine control.

  In the present embodiment described above, the torque step generated when the secondary air is started and stopped by blowing back the secondary air can be suppressed by controlling the ignition timing. Therefore, it is possible to eliminate the uncomfortable feeling felt by the driver due to the torque step and to improve the driving performance.

  Further, even when the cut valve 13 breaks down and the secondary air flows back into the exhaust passage 30, the torque step can be suppressed by the above-described suppression control, and deterioration of the driving performance can be prevented.

(Second Embodiment)
Next, torque step suppression control during secondary air supply according to a second embodiment of the present invention will be described. The second embodiment of the present invention is different from the first embodiment in that a torque step generated by blowing back secondary air is controlled by controlling the intake air amount and the fuel injection amount. Hereinafter, the difference will be described. In each of the following embodiments, the same reference numerals are used for portions that perform the same functions as those of the first embodiment described above, and repeated descriptions are omitted as appropriate.

  FIG. 9 is a flowchart showing the suppression control executed by the controller 50 according to the second embodiment.

  In step S204, the controller 50 reduces the amount of intake air corresponding to the amount of secondary air blow-back air calculated in step S203. Thereby, the torque level difference which occurs at the time of starting and stopping the supply of secondary air by blowing back is suppressed. The torque step is generated when the in-cylinder air-fuel ratio, which is set rich by secondary air blowing back, is shifted to the theoretical air-fuel ratio side and the shaft torque increases. Therefore, by reducing the amount of intake air corresponding to the amount of blowback air, an increase in shaft torque is suppressed and a torque step is suppressed.

  The secondary air used for the secondary combustion is reduced by the amount of blowback air. Therefore, the fuel injection amount increases with respect to the secondary air supply amount, and the exhaust air-fuel ratio at the inlet of the three-way catalyst 21 becomes rich. Therefore, in order to prevent this, the controller 50 reduces the intake air amount and suppresses the increase in the fuel injection amount by the blowback air amount.

  In step S206, the controller 50 returns the intake air amount and the fuel injection amount to the normal values, and shifts the processing from the suppression control to the normal engine control.

  FIG. 10 is a time chart of the suppression control executed by the controller 50 according to the second embodiment.

When the ignition key is turned on, the engine at time t ₁ is started, the controller 50 starts suppression control. When the engine water temperature is equal to or lower than the predetermined temperature (FIG. 10A), the controller 50 drives the air pump 12 and opens the cut valve 13 to supply secondary air (t _{1 in} FIG. 10B); S202). Then, the controller 50 decreases the intake air amount in accordance with the blowback air amount (FIG. 10 (G); S204). As a result, the occurrence of a torque step due to the secondary air blowing back is prevented (FIG. 10E).

When the supply of secondary air to the exhaust passage 30 is started at t ₁ , the controller 50 causes the exhaust air / fuel ratio at the inlet of the three-way catalyst 32 to become the stoichiometric air / fuel ratio (FIG. 10C). The fuel injection amount is increased (FIG. 8D). In this embodiment, the controller 50 reduces the amount of fuel for the amount of blowback air compared to the first embodiment in order to reduce the amount of intake air for the amount of blowback air (FIG. 10 (D); S204).

When the engine water temperature reaches a predetermined temperature at time t ₂ (FIG. 10A), the controller 50 stops driving the air pump 12 and closes the cut valve 13 to stop the supply of secondary air (FIG. 10). t ₂ of (a); S205). Thereafter, the controller 50 ends the suppression control (S206), and shifts the processing to normal engine control.

  According to the present embodiment described above, the torque step generated when secondary air supply is started and stopped by blowing back the secondary air can be suppressed by controlling the intake air amount and the fuel injection amount. Therefore, it is possible to eliminate the uncomfortable feeling felt by the driver due to the torque step and to improve the driving performance.

  Further, even when the cut valve 13 breaks down and the secondary air is flowing back into the exhaust passage 30, the torque step can be suppressed by the above-described suppression control, and deterioration of the driving performance can be prevented.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea. For example, in the first embodiment, the retard amount at the ignition timing is made constant, but the retard amount may be gradually reduced after suppressing the torque step at the time of supplying the secondary air. Although the secondary air supply stop condition is determined by the engine water temperature, the supply stop may be determined by determining the active state from parameters such as the amount of heat and the amount of air given to the three-way catalyst 21.

It is the schematic which shows the structure of the engine which has a secondary air supply apparatus. It is a figure showing the fluctuation | variation of the shaft torque with respect to secondary air supply amount. It is a figure showing the fluctuation | variation of the shaft torque with respect to secondary air supply amount. It is a flowchart which shows suppression control of the torque level difference at the time of secondary air supply by 1st Embodiment. It is a map of the ratio of secondary air blowing back. It is a setting table of the ignition timing with respect to the amount of blowback air. It is the characteristic view which showed the area | region of stable combustion. It is a time chart of suppression control by a 1st embodiment. It is a flowchart which shows suppression control of the torque level difference at the time of secondary air supply by 2nd Embodiment. It is a time chart of suppression control by a 2nd embodiment.

Explanation of symbols

1 engine (internal combustion engine)
10 Secondary air supply device 30 Exhaust passage 32 Three-way catalyst (catalyst device)
S103 Blowback air amount calculation means S105 Torque fluctuation suppression means

Claims (8)

A torque fluctuation prevention control device for preventing sudden fluctuations in torque of an internal combustion engine provided with a secondary air supply device that supplies air upstream of a catalyst device provided in an exhaust passage and promotes early activation of the catalyst device. And
Blow-back air amount calculating means for calculating the amount of blow-back air that flows back to the combustion chamber out of the air supplied by the secondary air supply device according to the engine operating state;
Torque fluctuation suppressing means for suppressing sudden fluctuations in torque generated by the blow-back air;
A torque fluctuation prevention control device for an internal combustion engine, comprising: The torque fluctuation preventing control apparatus for an internal combustion engine according to claim 1, wherein the torque fluctuation suppressing means adjusts an ignition timing in accordance with the blow-back air amount. 2. The torque fluctuation preventing control apparatus for an internal combustion engine according to claim 1, wherein the torque fluctuation suppressing means retards the ignition timing as the amount of blowback air increases. The torque fluctuation preventing control apparatus for an internal combustion engine according to claim 2 or 3, wherein the torque fluctuation suppressing means adjusts the ignition timing so as to be within a combustion stability limit. 2. The torque fluctuation preventing control apparatus for an internal combustion engine according to claim 1, wherein the torque fluctuation suppressing means reduces an intake air quantity corresponding to the blowback air quantity. The torque fluctuation suppression means maintains the exhaust air / fuel ratio at a stoichiometric air / fuel ratio by reducing the fuel injection amount from a normal increase value at the time of supplying secondary air in accordance with the blowback air amount. The torque fluctuation prevention control device for an internal combustion engine according to claim 5. The torque fluctuation prevention control device for an internal combustion engine according to any one of claims 1 to 6, wherein the blowback air amount calculation means is calculated from a load and a rotation speed of the internal combustion engine. This is a torque fluctuation prevention control method for preventing sudden fluctuations in torque of an internal combustion engine having a secondary air supply device that supplies air upstream of a catalyst device provided in an exhaust passage and promotes early activation of the catalyst device. And
A blowback air amount calculation step of calculating an air amount of blowback air that flows back to the combustion chamber out of the air supplied by the secondary air supply device, according to the engine operating state;
A torque fluctuation suppressing step for suppressing a sudden fluctuation in torque generated by the blow-back air;
A torque fluctuation preventing control method for an internal combustion engine, comprising: