JP2932838B2 - Secondary air control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary air control device for an internal combustion engine having an exhaust system having first and second catalysts.

[0002]

_2. Description of the Related Art There is conventionally known a technique in which an O ₂ sensor for detecting an exhaust air-fuel ratio is provided in an exhaust system of an internal combustion engine, and the engine air-fuel ratio is feedback-controlled based on the output of the O ₂ sensor. By controlling the engine air-fuel ratio to be the stoichiometric air-fuel ratio based on the output of the O ₂ sensor, the purifying ability of the three-way catalyst provided in the exhaust system can be effectively exhibited, and the emission characteristics can be improved.

Usually, the above O_TwoSensors improve control responsiveness
It is provided on the upstream side of the catalyst in order to raise it. But most
Near the first O provided on the upstream side_TwoSensor (upstream O_TwoC
Sensor to accurately compensate for changes over time in the characteristics of the
In the exhaust system on the downstream side of the medium, the second O _TwoSet the sensor (downstream side)
So-called double O used for feedback control_TwoSen
Subsystems are also used.

The three-way catalyst provided in the exhaust system is also divided into an upstream side and a downstream side, and secondary air is introduced between the upstream (first) catalyst and the downstream (second) catalyst. There is known a device in which the purification efficiency of the HC and CO components of the second catalyst is improved. An example of such an apparatus is disclosed in JP-A-63-454.
No. 49 is disclosed. The device disclosed in this publication has a configuration in which a first O ₂ sensor, a first catalyst, a secondary air inlet, a second O ₂ sensor, and a second catalyst are arranged in the exhaust pipe in order from the upstream side. In the device of this publication, during normal operation without introducing secondary air, both the first and second O ₂
The air-fuel ratio feedback control is performed using the sensor. When the secondary air is introduced during deceleration operation or the like, the air-fuel ratio feedback control is performed only by the first (upstream) O ₂ sensor. I have.

When the secondary air is introduced, the output of the second (downstream) O ₂ sensor becomes lean.
_{2 When} feedback control is performed with the sensor output, the air-fuel ratio of the exhaust gas flowing into the first catalyst becomes significantly richer,
This is to prevent the efficiency of purifying HC, CO, etc., from decreasing.

[0006]

However, in the above prior art, since the control of the amount of secondary air supplied to the catalyst is not performed, the catalyst is not controlled when the air-fuel ratio feedback control during the fuel increase during cold operation is not performed. The air-fuel ratio at the inlet may not be the optimum value, which may cause a delay in catalyst warm-up and deterioration of emission. That is, during the fuel increase control such as when the engine is cold start air-fuel ratio feedback control is performed without the engine exhaust air-fuel ratio according to O ₂ sensor output shifts to the rich side. For this reason, the first catalyst and the second catalyst are deficient in oxygen, so HC,
In some cases, the CO purification rate decreases, and the emission deteriorates. Further, since the oxidation reaction in the catalyst is reduced, the reaction heat required for warming up the catalyst cannot be obtained, and in particular, there may be a problem that the warming up of the catalyst is delayed on the side of the second catalyst having a large volume.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a secondary air control device for an internal combustion engine which prevents deterioration of emission and delay of catalyst warm-up due to a fuel increase operation at a cold start of the engine.

[0008]

According to the present invention, an exhaust system includes a first O ₂ sensor, a first catalyst, and a second catalyst, which are arranged in order from the upstream side. A secondary air control device for an internal combustion engine, wherein a secondary air inlet is provided in an exhaust system between the second catalyst and a second O ₂ sensor at least downstream of the secondary air inlet. When increasing the amount of fuel during cold engine, controlling the amount of secondary air introduced from the secondary air inlet so that the output of the second O ₂ sensor becomes leaner than the stoichiometric air-fuel ratio. And a secondary air control device for an internal combustion engine.

[0009]

The secondary air amount is controlled so that the air-fuel ratio at the second catalyst inlet is leaner than the stoichiometric air-fuel ratio during the fuel increase operation at the time of cold start of the engine. For this reason, HC,
The oxidation reaction of CO is promoted, so that emission is reduced and catalyst warm-up is promoted. Since the introduction of the secondary air is performed downstream of the first catalyst, the air-fuel ratio at the first catalyst inlet remains on the rich side even if the secondary air is introduced during the fuel increase, Since the first catalyst has a relatively small volume, it can be quickly warmed up by the heat of the engine exhaust even if no oxidation reaction occurs in the catalyst.

Although the air-fuel ratio at the inlet of the second catalyst is maintained on the lean side, there is no problem that the emission of NOx increases because the generation of NOx components is small during the increase in fuel.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration of an embodiment of an engine to which the present invention is applied. In the figure, 1 is an engine body,
11 is an engine intake pipe, 12 is a throttle valve which is opened and closed by a driver's operation of an accelerator pedal, and 13 is an air flow meter provided at the intake pipe entrance. Also the intake pipe 11
A fuel injection valve 15 is provided at the engine inlet.

An exhaust pipe 2 of the engine 1 has a first catalyst 3 near the engine outlet and a second catalyst 4 downstream of the first catalyst 3.
Are provided. The first catalyst 3 has a relatively small volume so that the catalyst reaches the activation temperature in a short period of time after starting the engine, that is, the catalyst warm-up is completed in a short time. For example, the first catalyst 3 is installed in an engine room. You. The second catalyst 4 has a relatively large capacity so as to exhibit a sufficient purification ability, and is installed at a lower portion of a vehicle body floor. Further, on the upstream side of the first catalyst 3 is first O ₂ sensor 6 is provided in the exhaust passage, the second catalyst 4 inlet of the first catalyst 3 downstream, second O ₂ sensor 7 Are arranged respectively. A secondary air introduction pipe 8 is connected to an exhaust pipe downstream of the first catalyst 3 and upstream of the second O ₂ sensor 7. The secondary air introduction pipe is connected to a secondary air supply system such as an air pump (not shown) through an electromagnetic valve 9, and controls the opening and closing of the electromagnetic valve 9 to adjust the amount of secondary air supplied to the exhaust pipe 2. can do.

FIG. 1 shows an engine control unit (ECU) 10 for performing secondary air control according to the present invention. The ECU 10 is configured as, for example, a microcomputer system of a known type, performs the secondary air control of the present invention, and further includes a throttle valve 12 opening degree, an air flow meter 13
The air-fuel ratio control for adjusting the fuel injection amount from the fuel injection valve 15 is performed based on the output and the outputs of the first and second O ₂ sensors 6 and 7.

For these controls, the ECU 10 receives the throttle valve opening from a throttle opening sensor 12a provided on the throttle valve 12, the engine intake air amount from a flow meter 13, and inputs the engine intake air to a distributor 18 of the engine. An engine speed pulse is input from an engine speed sensor 16 provided, and an engine coolant temperature is input from a coolant temperature sensor 17 provided in the engine coolant passage. In addition, the first O ₂ sensor 6
And the outlet of the second O ₂ sensor 7 are also input to the ECU 10.

Similarly, for the above control, the output signal of the ECU 10 is supplied to the fuel injection valve 15 to control the fuel injection amount, and is also supplied to the solenoid valve 9 of the secondary air introduction pipe 8.
The amount of secondary air introduced into the exhaust pipe 2 is controlled. Next, FIG.
The secondary air control operation of the present invention by the ECU 10 will be described with reference to FIG.

This routine is executed by interruption processing, for example, every 50 milliseconds. When the routine is started in the figure, in step 101, the engine intake air amount Q, the engine speed N, and the engine coolant temperature THW are respectively obtained from the air flow meter 13, the engine speed sensor 16, the coolant temperature sensor 17, and the first and second engine speeds. The exhaust air-fuel ratios on the upstream side of the catalysts 3 and 4 are first and second O ₂ sensors 6 and 7, respectively.
Read from. Next, in step 102, step 1
It is determined from the operating parameters read in 01 whether or not the fuel increase during cold is being executed.

The fuel increase in the cold state is performed, for example, when the engine cooling water temperature is equal to or lower than a predetermined temperature and the engine load (represented by the intake air amount Q / N per one engine revolution) is equal to or lower than a predetermined value. If it is determined in step 102 that the fuel increase during cold operation has not been performed, the process proceeds to step 104, where the flag FB1 is set (= “1”), and
At 05, the secondary air introduction solenoid valve 9 is fully closed to stop the secondary air supply. Flag FB1 is a flag indicating whether to execute the air-fuel ratio feedback control based on the output first O ₂ sensor 6, air based on the first O ₂ sensor 6 output by a routine separately executed the flag FB1 is set Fuel ratio feedback control is executed. Since this feedback control is conventionally known, the description thereof is omitted here.

On the other hand, if it is determined in step 102 that the fuel increase during cold operation is being performed, the routine proceeds to step 103, where the flag FB1 is reset (= "0"). Flag F
When B1 is reset, the air-fuel ratio feedback control based on the output of the first O ₂ sensor 6 is stopped. Next, in steps 106 to 108, the secondary air amount is adjusted by adjusting the opening of the solenoid valve 9 based on the output of the second O ₂ sensor 7.

That is, in step 106, the second O
_{2 It} is determined whether or not the output of the sensor 7 is lean. If the output is lean, the opening of the solenoid valve 9 is set to α in step 107.
Only to reduce the secondary air supply. If the output of the O ₂ sensor 7 is rich in step 106, the opening of the solenoid valve 9 is increased by β in step 108 to increase the secondary air supply amount. The opening control amounts α and β of the solenoid valve 9 in steps 107 and 108 are set so that α <β. That is, the secondary air supply amount (corresponding to the control amount α) that is reduced by one execution of the routine is 1
It is set smaller than the secondary air supply amount (corresponding to the control amount β) which increases with the execution of the routine. Accordingly, by executing steps 106 to 108, the secondary air supply amount is easily controlled in the increasing direction, and the output of the second O ₂ sensor 7, that is, the air-fuel ratio at the inlet of the second catalyst 4, is controlled to the lean side. .

As described above, the air-fuel ratio at the inlet of the second catalyst 4 is maintained on the lean side even when the fuel is being increased when the engine is cold, and a sufficient amount of oxygen is supplied to the second catalyst. ,
The HC and CO components in the exhaust gas, which have been increased by the increase in fuel, can be satisfactorily purified by the second catalyst by the second catalyst, and the emission does not deteriorate. In addition, since the heat generated by the oxidation reaction of HC and CO is sufficiently obtained, the warm-up of the second catalyst is completed in a short time, so that an overall good purification ability can be obtained.

In the above embodiment, an example of an in-line multi-cylinder engine is described, but the present invention is also applicable to a V-type engine. That is, in the V-type engine, exhaust pipes are connected to both banks, respectively, the first catalyst is provided for each of these exhaust pipes, and the second catalyst is provided on the downstream side where both exhaust pipes join. Are provided in common. Also in this case, a similar effect can be obtained by providing a second O ₂ sensor downstream of the exhaust pipe junction and performing feedback control of the amount of secondary air introduced downstream of the first catalyst based on the output of the second O ₂ sensor.

In the above embodiment, the second O ₂ sensor is provided on the inlet side of the second catalyst. However, the same applies to the case where the second O ₂ sensor is provided on the outlet side of the second catalyst. Can be controlled.

[0023]

According to the present invention, it is possible to prevent the deterioration of the exhaust emission during the fuel increase operation when the engine is cold and to shorten the catalyst warm-up time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an internal combustion engine to which a secondary air control device according to the present invention is applied.

FIG. 2 is a flowchart showing the operation of the secondary air control device of the present invention.

[Explanation of symbols]

1 ... engine 2 ... exhaust pipe 3 ... first catalyst 4 ... second catalyst 6 ... first O ₂ sensor 7 ... second O ₂ sensor 8 ... secondary air induction pipe 9 ... solenoid valves 10 ... ECU 11 ... intake pipe 12 ... throttle valve 12a ... throttle opening degree sensor 13 ... air flow meter 15 ... fuel injection valve 16 ... engine speed sensor 17 ... cooling water temperature sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 3/22 301 F01N 3/22 321

Claims (1)

(57) [Claims] 1. An exhaust system comprising a first O ₂ sensor, a first catalyst, and a second catalyst arranged in order from an upstream side, wherein an exhaust gas between the first catalyst and the second catalyst is provided. A secondary air control device for an internal combustion engine in which a secondary air inlet is provided in a system and a second O ₂ sensor is arranged at least downstream of the secondary air inlet, and the fuel is increased when the engine is cold. Controlling the amount of secondary air introduced from the secondary air inlet so that the output of the second O ₂ sensor becomes leaner than the stoichiometric air-fuel ratio. apparatus.