JP2006257977A - Air-fuel ratio control device in gear shift - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a NO<SB>X</SB>emission amount when a rotary synchronization control of an engine is performed in down-shift. <P>SOLUTION: A control for synchronizing rotational speed with a transmission input side rotational speed after gear shift is started, by increasing engine output during depression of a clutch pedal in gear shift of a manual transmission. A fuel injection amount is corrected to be increased depending on oxygen storage amounts in an exhaust cleaning catalyst which is increased by fuel cut before the gear shift, while increase in throttle opening is limited by an upper limiter. Therefore, the oxygen storage amount is quickly decreased to make the inside of the catalyst be an atmosphere near a stoichiometric air-fuel ratio, and thereby the NO<SB>X</SB>emission amount is decreased. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to air-fuel ratio control when increasing engine output during downshifting, and more particularly to a technique for improving exhaust purification performance.

Patent Document 1 discloses a technique for avoiding a shift shock by performing rotation synchronous control for increasing the engine output during downshift and bringing the engine rotation speed close to the transmission input-side rotation speed after shifting. .
JP-A-5-229368

In the engine rotation synchronous control described in Patent Document 1, the throttle is opened by the target torque corresponding to the difference between the target rotation speed and the actual rotation speed. As a result, the transient intake air flow rate change is too large, and the air-fuel ratio control is not performed in time, and the engine is leaned.
In addition, as with the normal control, the fuel injection amount is only set according to the intake air flow rate. Therefore, when the fuel is cut during deceleration, a large amount of oxygen is stored in the exhaust purification catalyst, and the downshift operation performs the above-described operation. When the rotation synchronization control is performed, there is a problem that the air-fuel ratio at the time of resumption of fuel supply becomes excessively lean and the NOx emission amount further increases.

  The present invention has been made paying attention to such a conventional problem, and provides an engine air-fuel ratio control system at the time of gear shifting that can maintain good exhaust purification performance during engine output increase control during downshifting. The purpose is to do.

  For this reason, the present invention increases the fuel supply amount to make the air-fuel ratio richer than the stoichiometric air-fuel ratio in accordance with the oxygen storage amount of the exhaust purification catalyst attached to the exhaust system during engine output increase control performed during downshifting. It was set as the structure controlled.

  According to the configuration of the present invention, engine output increase control is performed at the time of downshift after deceleration when fuel cut is performed, and when a large amount of oxygen is stored in the exhaust purification catalyst, the air-fuel ratio is controlled to be rich. By doing so, the oxygen stored using the surplus fuel (HC) as a reducing agent can be quickly consumed and reduced to an appropriate storage amount during normal operation.

  As a result, the atmosphere in the catalyst quickly becomes about the stoichiometric air-fuel ratio, and the NOx emission amount during engine output increase control (rotation synchronization control) can be satisfactorily reduced.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of a vehicle showing an embodiment of the present invention.
The vehicle is equipped with an engine (internal combustion engine) 1 and a manual transmission 3 connected to the engine 1 via a clutch 2.
A throttle valve 13 driven by a throttle actuator 12 is provided in the intake passage 11 of the engine 1, and a fuel injection valve 14 is provided in an intake port for each cylinder.

The intake passage 11 upstream of the throttle valve 12 is provided with an air flow meter 15 for detecting the intake air flow rate Qa, and a throttle sensor 16 for detecting the opening (throttle opening) TVO of the throttle valve 13 is provided. ing.
An exhaust purification catalyst 18 such as a three-way catalyst that purifies by oxidizing and reducing exhaust pollutants is mounted in the exhaust passage 17 of the engine 1, and upstream of the exhaust purification catalyst 18 due to the oxygen concentration in the exhaust, etc. An air-fuel ratio sensor 19 for detecting the air-fuel ratio is provided.

Further, a clutch switch 20 for detecting depression of the clutch pedal is provided, and at the time of shifting, the clutch pedal is depressed, so that a shifting operation is detected.
Further, an accelerator opening sensor 21 that detects an accelerator pedal depression amount (accelerator opening) APO, a rotation speed sensor 22 that detects an engine rotation speed Ne, a shift position sensor 23 that detects a shift lever position SP of the transmission 3, A vehicle speed sensor 24 for detecting the vehicle speed VSP is provided.

Detection signals from the various sensors are input to an engine control unit (referred to as ECU in the figure) 25.
The engine control unit 25 executes rotation synchronization control that synchronizes the rotation speed of the engine 1 with the transmission input side rotation speed after the shift by the shift at the time of the shift. In particular, at the time of downshifting, the output of the engine 1 is increased to perform the rotation synchronous control. At that time, the air-fuel ratio rich control according to the present invention is executed.

FIG. 2 shows a block diagram of the downshift control.
(A) shows an intake air flow rate control unit, and (B) shows a fuel injection amount control unit.
The intake air flow rate control unit includes a rotation synchronization control part and a throttle opening restriction part.
In the rotation synchronization control part, the shift control determination unit A1 determines whether or not to perform shift control (rotation synchronization control) based on the signal of the clutch switch 16.

The target gear position setting unit A2 sets the gear position after the shift as the target gear position Gpt based on the shift lever position detected by the shift position sensor 19.
The target rotational speed calculation unit A3 calculates a target rotational speed Net at the time of shifting based on the vehicle speed VSP detected by the vehicle speed sensor 20 and the target gear position Gpt set by the target gear position setting unit A2. . Specifically, the transmission input side rotational speed when the gear position is the target gear position Gpt in the current operation state is calculated as the target rotational speed Net that synchronizes the engine rotational speed.

The rotational speed feedback control unit A4 receives the target rotational speed calculated by the target rotational speed calculation unit A3 and the rotational speed sensor 8 when the determination result that the shift control is performed is input from the shift control determination unit A1. Based on the difference from the actual rotational speed detected by the above, the feedback control amount of the engine torque in the rotation synchronous control is calculated.
The target throttle opening calculation unit A5 is based on the determination result from the shift control determination unit A1, and at non-shifting, based on the accelerator opening APO detected by the accelerator opening sensor 5, the target torque Tet. The target throttle opening TVOt corresponding to is calculated, and at the time of shifting, the target throttle opening TVOt corresponding to the feedback control amount in the rotation synchronous control is calculated.

The throttle opening limit portion outputs a throttle opening control signal to the throttle actuator based on the determination result from the shift control determination unit A1.
Specifically, the output signal switching unit A6 outputs the throttle opening control signal corresponding to the target throttle opening TVOt calculated corresponding to the accelerator opening APO at the time of non-shift.

On the other hand, at the time of shifting, the output signal switching unit A6 outputs a throttle opening degree control signal obtained by limiting the target throttle opening degree TVOt calculated by the rotation synchronization control by the upper limiter A7.
Next, the fuel injection amount control unit will be described.
The OSC (oxygen storage amount) calculation unit B1 estimates the oxygen storage amount (accumulated oxygen amount) OSC in the exhaust purification catalyst 18 based on detection signals such as the intake air flow rate Qa detected by the air flow meter 15. .

  As the estimation of the oxygen storage amount OSC, for example, the oxygen amount FO2 flowing into the exhaust purification catalyst is calculated from the lean amount with respect to the theoretical air-fuel ratio and the intake air flow rate Qa during the lean air-fuel ratio operation, and the oxygen amount FO2 A method is known in which a value obtained by multiplying the value by the oxygen storage rate K of the catalyst is integrated and calculated. The oxygen storage rate K decreases as the sequential oxygen storage amount OSC in the catalyst increases, and at an OSC or higher, K becomes substantially zero and the oxygen storage amount OSC is saturated.

However, as in this embodiment, when the fuel is cut by the immediately preceding deceleration operation at the time of shifting, the amount stored during the fuel cut is dominant, so the amount of oxygen in the intake air during this time is determined by the amount of oxygen in the catalyst. It can be estimated as an integrated value obtained by multiplying the storage rate K.
In addition, it can be simply estimated based on the average intake air flow rate during the fuel cut period and the fuel cut time.

The fuel increase calculation unit B2 calculates the fuel increase based on the oxygen storage amount OSC (and the intake air flow rate Qa) estimated as described above with reference to the fuel increase map.
The fuel increase map is set so that the fuel increase becomes larger as the oxygen storage amount OSC increases so as to obtain a predetermined equivalence ratio. The fuel increase may be set by an increase coefficient that is multiplied by the basic fuel injection amount set in the normal operation (theoretical air-fuel ratio operation) instead of the absolute amount.

  The fuel injection amount switching unit B3 normally outputs the fuel injection amount Ti set according to the air-fuel ratio (theoretical air-fuel ratio) in the normal operation with respect to the intake air flow rate Qa detected by the air flow meter 14 as it is. When the fuel supply is resumed (re-injection) in the rotation synchronous control from the fuel cut after the shift, the fuel injection amount Ti corrected by increasing the fuel injection amount by adding the fuel increase amount to the fuel injection amount in the normal operation is output by the adding unit B4. .

FIG. 3 shows changes in various state quantities due to the rotation synchronization control during the downshift as compared with the case where the rich control according to the present invention is not performed.
During the fuel cut before the shift, the oxygen storage amount in the exhaust purification catalyst 18 is saturated. When the downshift operation is performed in this state and the rotation synchronization control is started, the target rotation speed and the actual rotation speed are started. The throttle opening is increased in accordance with the difference between the two and the intake air flow rate is increased, but the increase in the throttle opening is restricted by the upper limiter, and the increase in the intake air flow rate is restricted.

On the other hand, the basic fuel injection amount Tp set corresponding to the theoretical air-fuel ratio according to the intake air flow rate Qa controlled as described above is set according to the oxygen storage amount OSC (and intake air flow rate Qa). The increment is added.
As a result, as the oxygen storage amount OSC increases, the air-fuel ratio becomes richer and the oxygen storage amount OSC that has been in the saturation state decreases to approximately zero due to the enrichment.

When the actual rotational speed Ne of the engine converges to the target rotational speed TNe, the throttle valve 13 is closed and the increase control of the intake air flow rate Qa is stopped while the increase control of the fuel injection amount Ti is stopped. The amount is controlled to Tp.
When the clutch pedal is released and the shift is completed, the rotation synchronization control is stopped, and until the driver performs the accelerator operation (acceleration operation), the throttle valve 13 is fully closed and the fuel cut is performed again.

In detail, when the actual rotational speed increases from the target rotational speed due to overshoot during rotational synchronization control, the throttle valve may be closed and a fuel cut may be performed. It is.
In this way, when the engine output is increased for rotational synchronization control during downshifting, even if the oxygen storage amount OSC in the exhaust purification catalyst 18 is increased due to fuel cut, the oxygen storage amount OSC is large. As the fuel injection amount increase correction amount is increased as occasion demands, the oxygen stored by the increased fuel (HC) can be quickly reduced and reduced, so that the NOx emission amount can be effectively reduced. Can do.

Also, at this time, by using the control for limiting the intake air flow rate with the upper limit limiter, it is possible to increase the rich degree due to the increase in the fuel injection amount while suppressing an excessive increase in the intake air flow rate, and to reduce the NOx. Increase.
FIG. 4 shows the effect of this embodiment.
In the figure, as in the conventional rotation synchronous control, the increase in the throttle opening is not limited, but is fully opened and the increase in the throttle opening is limited as compared with the case where the increase in the fuel injection amount is not performed. If the fuel injection amount is not increased only by opening from 8 to 4/8), a slight effect can be obtained in reducing NOx by reducing the lean degree, but increasing the fuel injection amount by fully opening the throttle ( It is clear that the NOx emission can be greatly reduced when enrichment is performed.

In the most basic embodiment, the throttle opening (intake air flow rate) is not limited as described above, and the enrichment may be performed only by increasing the fuel injection amount.
Also, as in this embodiment, when the equivalence ratio is increased by increasing the fuel injection amount while restricting the increase in throttle opening, the equivalent ratio is increased without restricting the increase in throttle opening Compared to the above, the effect margin is large, and restriction of the throttle opening when the equivalence ratio is increased is particularly effective.

Note that even if the restriction on the throttle opening (intake air flow rate) is increased to some extent (for example, from 4/8 opening to 2/8 opening), the effect of reducing the NOx emission amount may not be further enhanced. It is shown.
This is presumably because the rotation synchronization control time is prolonged if the intake air flow rate is excessively reduced. Therefore, it is preferable to set a more effective limit amount by conducting experiments and the like.

Note that in normal (conventional) rotation-synchronized control during downshifting, there is a possibility that fuel increase may be performed by entering the fuel increase region due to an increase in the intake air flow rate. If the oxygen storage amount is saturated due to fuel cut or the like, the NOx emission reduction effect is poor.
Note that when the intake air flow rate is limited by the throttle opening as in the present embodiment, the probability of entering the fuel increase region as described above is low, but if it does enter, avoiding excessive enrichment. Therefore, the setting of the fuel increase in the fuel increase region is canceled, and only the fuel increase setting according to the oxygen storage amount according to the present invention is performed.

Further, in the above embodiment, since the clutch is disengaged at the time of shifting because it is applied to the one equipped with the manual transmission, the maximum enrichment can be performed without considering the operability to the occupant by the engine rotation synchronization control. .
On the other hand, when the rotation synchronous control according to the present invention is applied to the automatic transmission, the transmission of the engine driving force is not completely disconnected, but the torque converter can absorb a certain amount of torque fluctuation, and particularly the intake air flow rate is reduced. By limiting, it is possible to increase the richness while suppressing a rapid increase in torque increase, and thus it is possible to execute this control while suppressing the influence of drivability on the occupant.

  When applied to a vehicle equipped with an automatic transmission, in the control block diagram of FIG. 2, the rotation synchronization control request signal at the time of downshift in the shift control of the automatic transmission is input to the shift control determination unit A1, and the target gear position setting The part A2 may be omitted, and the post-shift gear position at the time of a shift request in the shift control of the automatic transmission may be input to the target rotational speed calculation unit A3 as the target gear position.

1 is a schematic configuration diagram of a vehicle showing an embodiment of the present invention. It is a block diagram of engine rotation synchronous control at the time of downshift of the embodiment same as the above. It is a time chart which shows the change of the various state quantities at the time of rotation synchronous control same as the above. It is a graph which shows the effect in rotation control same as the above.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Clutch, 3 ... Transmission, 12 ... Throttle valve, 13 ... Throttle actuator, 14 ... Fuel injection valve, 15 ... Air flow meter, 16 ... Throttle sensor, 18 ... Exhaust gas purification catalyst, 19 ... Air-fuel ratio sensor , 20 ... clutch switch, 21 ... accelerator opening sensor, 22 ... rotational speed sensor, 23 ... shift position sensor, 24 ... vehicle speed sensor, 25 ... engine control unit

Claims (8)

  When increasing the engine output at the time of downshift, the fuel supply amount is increased according to the oxygen storage amount of the exhaust purification catalyst mounted in the exhaust system, and the air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio. An air-fuel ratio control device for engine speed change.   2. The engine air-fuel ratio control system for shifting an engine according to claim 1, wherein the intake air flow rate is limited by an upper limiter during the rich control of the air-fuel ratio.   The engine speed air-fuel ratio control apparatus according to claim 1 or 2, wherein the fuel injection amount is set according to an oxygen storage amount of the exhaust purification catalyst during the rich control of the air-fuel ratio.   The engine speed air-fuel ratio control apparatus according to any one of claims 1 to 3, wherein an oxygen storage amount of the exhaust purification catalyst is estimated based on an operating state.   5. The engine speed air-fuel ratio control apparatus for engine according to claim 4, wherein the oxygen storage amount of the exhaust purification catalyst is estimated based on a fuel cut state before a gear shift operation.   The fuel injection amount is set by releasing the restriction of the upper limiter of the fuel injection amount during the rich control of the air-fuel ratio when shifting is performed with the transmission of the engine driving force disconnected. 6. The air-fuel ratio control device for engine speed change according to claim 5.   7. The engine according to claim 1, wherein the engine output increase control is control for synchronizing the engine rotation speed with a transmission input-side rotation speed after downshift. Air-fuel ratio control device for shifting.   The air-fuel ratio rich control is performed when the downshift is detected and the engine output is controlled to increase in a vehicle in which a manual transmission is connected to the engine via a clutch. The engine speed change air-fuel ratio control apparatus according to any one of claims 1 to 7.

Images