JP3349250B2 - Engine air-fuel ratio control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an engine air-fuel ratio which makes the air-fuel ratio A / F leaner than the stoichiometric air-fuel ratio (λ = 1) when the engine load is smaller than a predetermined lean region determination load. The present invention relates to a fuel ratio control device.

[0002]

2. Description of the Related Art Conventionally, as an air-fuel ratio control apparatus for an engine of the above-mentioned example, there is an apparatus disclosed in Japanese Patent Publication No. 4-48932.

That is, when the engine load is smaller than a predetermined lean region determination load, the air-fuel ratio is made lean with respect to the stoichiometric air-fuel ratio (A / F = 14.7).
The above-described lean region determination load is changed according to the vehicle speed (absolute value of the load), and when the vehicle speed is higher than, for example, 45 km / h, the above-described lean region determination load is increased to extend the lean burn region. This is an air-fuel ratio control device for an engine.

However, this conventional apparatus has the following problems. In other words, when the air-fuel ratio is switched from rich to lean at a high vehicle speed where the load for switching the air-fuel ratio is large (even when the amount of change in the air-fuel ratio at the time of the switching is the same), the change in torque due to the air-fuel ratio is Even when the ratio is the same as at the low vehicle speed, the absolute amount of torque is large at such a high vehicle speed. Therefore, the driver feels discomfort due to a large torque difference (large torque drop) and eliminates this. However, when the driver steps on the accelerator, there is a problem in that the accelerator operation again causes so-called hunting in which the operation is switched from lean to rich again.

[0005]

According to the first aspect of the present invention, the lean region determination load is changed in accordance with the absolute value of the load, that is, the vehicle speed, and the higher the vehicle speed, the higher the lean region determination load. Then, while increasing the lean burn area, the above-mentioned lean area determination load has a larger hysteresis at a higher vehicle speed (here, the hysteresis means that the engine load is higher from the lower load side with respect to the lean area determination load. Hysteresis in which the air-fuel ratio switching line when changing to the load side and the air-fuel ratio switching line when the engine load changes from the high load side to the low load side is set differently. At high vehicle speeds where the fuel ratio switching load is large,
At low vehicle speeds, while increasing the hysteresis, it is possible to prevent hunting from switching from lean to rich again by the driver's accelerator operation due to the large torque difference when switching the air-fuel ratio from rich to lean. The object of the present invention is to provide an air-fuel ratio control device for an engine that can reduce the hysteresis, thereby promptly performing a lean transition and improving fuel efficiency, because the torque difference when the air-fuel ratio is switched is small.

According to a second aspect of the present invention, in addition to the object of the first aspect, the differential pressure between the upstream and downstream of the throttle valve (before and after the throttle valve) is reduced from a bypass passage that bypasses the throttle valve during lean operation. It is an object of the present invention to provide an air-fuel ratio control device for an engine capable of preventing a torque reduction during lean operation by increasing an intake air amount by utilizing the same.

[0007]

According to a first aspect of the present invention, there is provided an engine load detecting means for detecting an engine load, and a lean area determination in which the engine load detected by the engine load detecting means is set in advance. Lean determining means for determining whether the load is smaller than the load, and lean burn for making the air-fuel ratio lean with respect to the stoichiometric air-fuel ratio when the engine load is smaller than the lean region determining load based on the determination result of the lean determining means. An air-fuel ratio control device for an engine, comprising: a lean burn means for performing the lean region determination load, wherein the lean region determination load is set larger at a high vehicle speed than at a low vehicle speed, and the engine load is increased with respect to the lean region determination load. Line when the load changes from low load to high load, and air-fuel ratio when engine load changes from high load to low load Hysteresis and switching line is set differently provided, the hysteresis is characterized by an air-fuel ratio control system for an engine which is set as small when low vehicle speed increases at high speed.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, an air control valve is provided in a bypass passage that bypasses the throttle valve.
An air-fuel ratio control device for an engine provided with intake air increasing means for increasing the intake air amount by opening the air control valve when the lean burn means operates.

[0009]

According to the first aspect of the present invention, as shown in the claim correspondence diagram of FIG. 11, the above-mentioned lean determining means P1 has the engine load CE smaller than the preset lean region determining load. The lean burn means P2 determines whether the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (λ = 1) when the engine load is smaller than the lean area determination load based on the determination result of the lean determination means P1. The lean burn is performed in order to make the vehicle lean, but the lean region determination load is changed in accordance with the absolute value of the load, that is, the vehicle speed, and the lean region determination load is set to increase as the vehicle speed increases. Widen the lean zone on the side,
In addition, the air-fuel ratio switching line when the engine load changes from the low load side to the high load side and the air-fuel ratio switching when the engine load changes from the high load side to the low load side with respect to the lean region determination load. A hysteresis set differently from the line is provided, and this hysteresis is set to be small at a low vehicle speed and large at a high vehicle speed, so that the following effects are obtained.

That is, when the air-fuel ratio switching load is large and the vehicle speed is high, the torque drop when switching the air-fuel ratio from rich to lean becomes large, and the driver (driver) feels discomfort. Although the hunting tends to be switched from lean to rich again by the depressing operation, the above-mentioned hunting can be prevented since the hysteresis for the lean region determination load is set to be larger at higher vehicle speeds. There is an effect that can be done.

Further, at low vehicle speeds, the torque drop when the air-fuel ratio is switched from rich to lean is small. Therefore, by making the hysteresis small, the transition to lean can be performed promptly, and as a result, the fuel efficiency is improved. There is an effect that can be. According to a second aspect of the present invention, in addition to the effect of the first aspect, the above-described intake air amount increasing means opens the air control valve of the bypass passage when the lean burn means is operated, thereby increasing the throttle valve. Since the intake air amount is increased by the differential pressure on the downstream side, there is an effect that it is possible to prevent a torque reduction during lean operation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings. The drawing shows an air-fuel ratio control device for an engine, and FIG.
, An air flow sensor 1 is connected to the rear of an air cleaner that purifies intake air, and the air flow sensor 1 is configured to detect the intake air amount Q.

A throttle body 2 is connected to the rear of the above-mentioned airflow sensor 1, and a throttle valve 3 for controlling the amount of intake air is provided in a throttle chamber 3 in the throttle body 2. And this throttle valve 4
A surge tank 5 as an expansion chamber having a predetermined volume is connected to the downstream intake passage, and an intake manifold 7 communicating with an intake port 6 is connected downstream of the surge tank 5, and an injector 8 is connected to the intake manifold 7. Is arranged.

On the other hand, the above-described intake port 6 and exhaust port 11 which are appropriately connected to the combustion chamber 10 of the engine 9 are provided with an intake valve 12 and an exhaust valve 13 which are opened and closed by a valve operating mechanism (not shown), respectively. Mounting and cylinder head 1
4 is provided with an ignition plug 15 having a spark gap facing the above-described combustion chamber 10.

An exhaust manifold 16 is connected to the above-described exhaust port 11, and the exhaust manifold 16 is connected to the exhaust manifold 16.
An air-fuel ratio sensor 18 is disposed in an exhaust passage 17 communicating with the exhaust passage 17, and a catalyst converter 19, a so-called catalyst, for detoxifying harmful gas is connected to the rear of the exhaust passage 17.

A first bypass passage 20 for bypassing the above-described throttle valve 4 is provided, and the first bypass passage 20 has an ISC (idle speed control).
While an ISC valve 21 as a mechanism is interposed, a second bypass passage 22 that bypasses the above-described throttle valve 4 is provided, and an air control valve 23 (so-called ACV) that is controlled to open during lean operation is provided in the second bypass passage 22. The throttle body 2 is provided with a throttle sensor 24, and the water jacket 25 is provided with a water temperature sensor 26.

FIG. 2 shows a control circuit of the air-fuel ratio control device of the engine. The CPU 30 controls the intake air amount Q from the air flow sensor 1, the engine speed Ne from the distributor 27, and the throttle opening T from the throttle sensor 24.
VO, ON / OFF signals from an idle switch 28 provided integrally with the throttle sensor 24, the water temperature t of the engine cooling water from the water temperature sensor 26, the vehicle speed V from the vehicle speed sensor 29, and the air-fuel ratio from the air-fuel ratio sensor 18. The injector 8 and the air control valve 23 are driven and controlled according to a program stored in the ROM 31 based on various necessary signal inputs such as an A / F, and the RAM 32 stores necessary tables, maps, data, and the like.

Here, the above-described CPU 30 determines in advance the engine load detecting means for detecting the engine load (see the first step 51 in the flowchart shown in FIG. 6) and the current engine load CE detected by the engine load detecting means. The lean determination means (see steps 52 and 54 in the flowchart shown in FIG. 6) for determining whether or not the load is smaller than the set lean region determination load CEdL (see FIG. 3), and the determination result of the lean determination means. Engine load CE
Is lean lean means for performing lean burn to make the air-fuel ratio A / F lean with respect to the stoichiometric air-fuel ratio (λ = 1) when is smaller than the lean region determination load CEdL (the fifth step 55 in the flowchart shown in FIG. 6). ) And the air control valve 2 when the lean burn means operates.
3 is opened to increase the intake air amount (FIG. 5).
(See the third step 43 of the flowchart shown in FIG. 3).

In addition, the above-described lean region determination load CEd
As shown in FIG. 3, L is set to be larger at a high vehicle speed than at a low vehicle speed, and the air-fuel ratio is switched when the engine load changes from a low load side to a high load side with respect to the lean region determination load CEdL. A hysteresis (hys) set so that the line and the air-fuel ratio switching line when the engine load changes from the high load side to the low load side is provided, and the width of this hysteresis (hys) is small at low vehicle speed. It is set to increase at high vehicle speeds. Here, when the engine load CE changes from the low load side to the high load side, the value of the solid line in FIG.
(TGmax) to switch from the lean zone to λ = 1 zone. Conversely, when the engine load CE changes from the high load side to the low load side, the λ = 1 zone leans from the λ = 1 zone by the dotted line value (TGmin) in FIG. Switch to the zone.

FIG. 4 is a characteristic diagram showing the relationship between the throttle opening TVO and the torque. When the air-fuel ratio is changed from λ = 1 to lean, when the throttle opening TVO is large, the amount of torque drop becomes large, When the opening TVO is small, the amount of torque drop is small, and the magnitude of the hysteresis (hys) in FIG. 3 corresponds to the magnitude of the torque drop in FIG.

The operation of the air-fuel ratio control device for an engine thus configured will be described in detail below with reference to the flowcharts shown in FIGS. First, referring to FIG. 5, a flowchart showing the opening / closing control of the air control valve 23 will be described. In a first step 41, the CPU 30 determines the intake air amount Q from the airflow sensor 1, the distributor 2
7, the throttle opening TVO from the throttle sensor 24, the ON / OFF signal from the idle switch 28, the reading of various signals such as the water temperature t from the water temperature sensor 26, and CE = Q
The engine load CE is determined by the formula of / Ne.

Next, in a second step 42, the CPU 30 determines whether or not a lean burn is to be executed. This determination is made based on the determination logic shown in FIG. That is, when the water temperature t is 7
0 ° C. or more, engine speed Ne is 3000 rpm or less, all conditions that the idle switch 28 is OFF are satisfied, and the current engine load CE is not more than the enrichment judgment load or the throttle opening TVO is 1/2 or less. Is satisfied, the lean burn is determined to be executed.

In the above-described second step 42, when a YES determination of lean burn execution is made, the next third step 4
The process proceeds to step S3, and when a NO determination is made, another fourth
Move to step 44.

In the above-described third step 43, the CPU 30 sets the air control valve 2
3 is opened (open), while the fourth step 4 described above is performed.
At 4, the CPU 30 closes the air control valve 23. If the air control valve 23 is opened in response to the lean operation in the third step 43, the intake air is supplied from the second bypass passage 22 by the differential pressure across the throttle valve 4, so that the amount of intake air By increasing the amount, it is possible to prevent the torque from decreasing during lean operation.

Next, referring to FIG. 6, a flowchart showing the air-fuel ratio control will be described.
The PU 30 has an intake air amount Q from the air flow sensor 1, an engine speed Ne from the distributor 27, a throttle opening TVO from the throttle sensor 24, an ON / OFF signal from the idle switch 28, a water temperature sensor 26.
Necessary signals such as a water temperature t from the vehicle and a vehicle speed V from the vehicle speed sensor 29 are read, and CE = Q / Ne.
The engine load CE is calculated by the following equation.

Next, in a second step 52, the CPU 30 determines whether or not the lean burn is to be executed based on the determination logic shown in FIG. 7. When the determination is YES, the process proceeds to the next third step 53. The CPU 30 executes a stoichiometric air-fuel ratio operation in which the air-fuel ratio A / F is set to λ = 1 in the sixth step 56.

In the above-described third step 53, the CPU 30 determines whether the transmission is MT (manual transmission) or AT (automatic transmission). The transmission type signal is input to the CPU 30 in advance. Then, the process skips to a fifth step 55 at the time of MT determination, and shifts to the next fourth step 54 at the time of AT determination.

In the fourth step 54, the CPU 30 determines whether the determination value XCE is "1" or "0". As shown in FIGS. 8 and 3, when the current engine load CE changes from the high load side to the low load side, when the current engine load CE reaches the value (TGmin) from the value (TGmax), it is determined to be “1”. However, when the current engine load CE changes from the low load side to the high load side,
When it reaches the value (TGmax) from (TGmin), it is determined to be “0”. Here, the vehicle speed V is between the above values (TGmax) and (TGmin).
Corresponding to the hysteresis (hys) that changes in response to

In the above-described fourth step 54, XCE =
When it is determined to be 1, the process proceeds to the next fifth step 55,
When it is determined that XCE = 0, the process proceeds to another sixth step 56.

In the above-mentioned fifth step 55, the CPU 30 executes the lean burn operation so as to make the air-fuel ratio A / F lean with respect to the stoichiometric air-fuel ratio (λ = 1).
In step 56, the CPU 30 executes λ = 1 operation by, for example, air-fuel ratio feedback control so that the air-fuel ratio A / F is set to the stoichiometric air-fuel ratio A / F = 14.7.

In short, the lean determination means (see steps 52 and 54 in FIG. 6) determines whether the current engine load CE is smaller than a preset lean region determination load CEdL (see FIG. 3). The lean burn means (refer to the fifth step 55 in FIG. 6) performs the air-fuel ratio A / F when the current engine load CE is smaller than the lean area determination load CEdL based on the determination result of the lean determination means.
Is made lean with respect to the stoichiometric air-fuel ratio (A / F = 14.7). The lean region determination load CEdL is changed according to the absolute value of the load, that is, the vehicle speed V, and the lean burn is performed. The region determination CEdL is set to increase as the vehicle speed V increases, and the lean zone on the high vehicle speed side is widened as shown in FIG. 3, and the engine load is lower than the lean region determination load CEdL. The hysteresis (hysteresis) is set so that the air-fuel ratio switching line when the load changes from the load side to the high load side is different from the air-fuel ratio switching line when the engine load changes from the high load side to the low load side.
s), and this hysteresis (hys) is set to be small at low vehicle speeds and large at high vehicle speeds as shown in FIG.

That is, at a high vehicle speed at which the load for switching the air-fuel ratio is large, the torque drop when switching the air-fuel ratio from rich to lean becomes large, and the driver feels a sense of discomfort. Hunting such as switching from lean to rich is likely to occur, but the hysteresis (hys) for the lean region determination load CEdL is set to be greater at higher vehicle speeds. There is an effect that hunting can be prevented.

At low vehicle speeds, the torque drop when the air-fuel ratio is switched from rich to lean is small, so that the hysteresis
By reducing (hys), lean transition can be performed quickly, and as a result, there is an effect that fuel efficiency can be improved.

In addition, the aforementioned intake increasing means (third in FIG. 5)
(See step 43).
By opening the air control valve 23 of the bypass passage 22 and increasing the intake air amount by the differential pressure between the upstream and downstream of the throttle valve 4, there is an effect that a torque reduction during lean operation can be prevented.

FIG. 9 is a control circuit diagram showing another embodiment of the air-fuel ratio control device for the engine, in which the CPU 30 determines the amount of intake air Q from the airflow sensor 1 and the distributor 2
7, the throttle opening TVO from the throttle sensor 24, ON from an idle switch 28 provided integrally with the throttle sensor 24,
OFF signal, water temperature t of engine cooling water from water temperature sensor 26, vehicle speed V from vehicle speed sensor 29, air-fuel ratio sensor 18
A / F from air conditioner, O from air conditioner switch 61
N, OFF signal, boost sensor 6 for detecting intake negative pressure
2 and the air control valve 23 (so-called A) in accordance with a program stored in the ROM 31 based on various necessary signal inputs such as boost B from
The RAM 63 controls the drive of the CV, and the RAM 63 varies the lean region determination load CEdL in accordance with the vehicle speed V, and changes the value (T
A map (see FIG. 10) for changing the hysteresis of Gmax) (TGmin) according to the vehicle speed V and necessary data are stored.

In the above-mentioned map (see FIG. 10), the horizontal axis represents the vehicle speed V, and the vertical axis represents the intake negative pressure B [mmHg] and the lean region determination load CEdL (however, the percentage is shown assuming 100% at full load). ) Is a setting means for setting the above-described lean region determination load CEdL and the hysteresis between the values (TGmax) and (TGmin) corresponding to the vehicle speed V and the intake negative pressure B (or the engine load CE).

For example, when the vehicle speed V is in a range of 0 km / h to about 5 km / h, the hysteresis is set to 2%, and the vehicle speed V is about 5 km / h.
The hysteresis is set to 3% in a range from about 15 km / h to about 15 km / h, and the hysteresis is set to 4% (corresponding to about 30 mmHg of the intake negative pressure) when the vehicle speed V is higher than about 15 km / h. The lean region determination load CEdL is set so that the value increases as the vehicle speed V increases, as is clear from FIG.

Further, an air conditioner (air conditioner)
Is turned on, the engine load increases, so a value (TGmax A) corresponding to this is also set.

The CPU 30 determines the vehicle speed V from the vehicle speed sensor 29, the ON state from the air conditioner switch 61,
OFF signal and boost B from boost sensor 62
By reading various necessary signals such as the above, and executing the air-fuel ratio control based on the map of FIG. 10, the above-mentioned hunting is prevented by increasing the hysteresis at a high vehicle speed, and the hysteresis is reduced at a low vehicle speed. There is an effect that the control for promptly shifting to the lean state can be executed more finely and the air-fuel ratio control corresponding to the air conditioner ON can be executed.

In the correspondence between the configuration of the present invention and the above-described embodiment, the lean determining means of the present invention uses the CP of the embodiment.
Corresponding to each of the steps 52 and 54 by the U30 control, the engine load detecting means similarly performs the first step 51
(See FIG. 6), the lean burn means is provided by the CPU 3
0 control, the bypass passage corresponds to the second bypass passage 22, and the intake increasing means includes:
Although this corresponds to the third step 43 controlled by the CPU 30,
The present invention is not limited only to the configuration of the above embodiment.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an engine air-fuel ratio control device of the present invention.

FIG. 2 is a block diagram of a control circuit.

FIG. 3 is an explanatory diagram showing a state of a lean region determination load with respect to a vehicle speed.

FIG. 4 is a characteristic diagram showing a change state of a torque with respect to a throttle opening.

FIG. 5 is a flowchart showing opening / closing control of an air control valve.

FIG. 6 is a flowchart showing air-fuel ratio control.

FIG. 7 is a logic explanatory diagram of a lean burn execution condition.

FIG. 8 is an explanatory diagram of a determination process.

FIG. 9 is a control circuit block diagram showing another embodiment of the engine air-fuel ratio control device of the present invention.

FIG. 10 is an explanatory diagram of a map stored in a RAM.

FIG. 11 is a diagram corresponding to claims.

[Explanation of symbols]

 4 Throttle valve 22 Second bus path passage 23 Air control valve 43 Intake increasing means 51 Engine load detecting means 52, 54 Lean determining means 55 Lean burn means

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 301 F02D 45/00 301G (56) References JP-A-1-163435 (JP, A) JP-A-58-48754 (JP, A) JP-A-1-163432 (JP, A) JP-A-62-218632 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 29/00-45 / 00

Claims (2)

(57) [Claims] An engine load detecting means for detecting an engine load; a lean determining means for determining whether an engine load detected by the engine load detecting means is smaller than a predetermined lean area determining load; An air-fuel ratio control device for an engine, comprising: lean burn means for performing lean burn to make the air-fuel ratio lean with respect to the stoichiometric air-fuel ratio when the engine load is smaller than the lean region determination load based on the determination result of the lean determination means. The lean region determination load is set to be larger at a high vehicle speed than at a low vehicle speed, and the air-fuel ratio when the engine load changes from a low load side to a high load side with respect to the lean region determination load. Hysteresis set so that the switching line and the air-fuel ratio switching line when the engine load changes from the high load side to the low load side are different The provided, the hysteresis is smaller at low vehicle speed, air-fuel ratio control system for an engine which is set to be larger at a high vehicle speed. 2. An air control valve is provided in a bypass passage which bypasses a throttle valve, and intake air increasing means is provided for opening the air control valve and increasing an intake air amount when the lean burn means is operated. Item 2. An air-fuel ratio control device for an engine according to Item 1.