JP3014525B2 - Engine secondary air control device - 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 engine.

[0002]

2. Description of the Related Art Generally, a secondary air control device for an engine supplies secondary air to an exhaust passage of the engine to oxidize carbon monoxide (CO) and hydrocarbons (HC) in exhaust gas and oxidize a catalyst. A device for accelerating the reduction reaction and purifying exhaust gas thereby, and from the viewpoint of preventing exhaust gas pollution, it is required to finely control the secondary air flow rate according to the operating state of the engine.

Conventionally, this type of secondary air control device has been designed so that the discharge amount of an electric air pump provided in a secondary air supply passage of an engine has a value stored in advance in accordance with the operating state of the engine. A device for controlling the number of revolutions of a drive motor of the air pump is known (Japanese Patent Laid-Open No. Sho 59-13).
No. 8714). According to this device, the primary purpose of finely controlling the secondary air flow rate in accordance with the operating state of the engine without increasing the driving loss of the air pump is achieved.

[0004]

However, in the case of the above-described conventional device for controlling the motor rotation speed, the flow rate change with respect to the rotation speed is very sensitive in a region where the motor rotation speed is low.
It turned out that the flow control accuracy was poor. That is, the relationship between the motor rotation speed N of the air pump and the secondary air flow rate (discharge flow rate) Q discharged from the air pump can be understood from the NQ characteristic curve shown as an example in FIG. Does not always maintain a moderate proportionality of the gradient over the entire region. In the region A where the motor rotation speed N is low, the gradient of the NQ characteristic curve is steep, and the slight motor rotation speed N Even if it changes, the discharge flow rate Q greatly changes, and a so-called hunting phenomenon is likely to occur. Therefore, there is a problem that the flow control accuracy is poor in the low rotation speed region A of the motor, and desired fine flow control cannot be performed unless the motor rotation speed N is increased to some extent.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to perform a desired fine control even in a low rotation speed region of a motor, and thus to maintain a secondary control of an engine capable of maintaining control accuracy over a wide discharge flow rate range. It is an object to provide an air control device.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention controls an electric air pump of a turbo blower type so that an appropriate amount of secondary air according to the operating state of the engine is obtained. In the control device, a characteristic curve of a motor applied voltage for obtaining an appropriate secondary air supply amount according to the operating state of the engine is selected from a map stored in a memory in advance, and a control signal is placed on the selected characteristic curve. Upon receiving the control signal to be output and the actual rotation speed fed back from the control signal and the rotation speed detection unit provided on the pump, the rotation value of the DC motor of the air pump is adjusted to the secondary air supply amount of the control signal. And a drive unit that drives the control cycle of the feedback control shorter as the secondary air supply amount is smaller than when the secondary air supply amount is larger. It is obtained by a configuration having a function of (claim 1).

In the secondary air control device according to the present invention, the drive section has a function of increasing the control gain of the feedback control as the secondary air supply amount is smaller than when the secondary air supply amount is larger. (Claim 2).

[0008]

According to the present invention, the control section stores a relationship between the operating state of the engine and the voltage applied to the motor to obtain an appropriate secondary air supply amount in accordance with the operating state from a memory in advance as a map. A curve is selected and a control signal is output on the curve. The drive unit receives the control signal and the actual rotation speed fed back, and drives the motor so that the motor rotation value of the air pump becomes the secondary air supply amount indicated by the control signal. At this time, the driving unit shortens the control cycle of the feedback control as the secondary air supply amount is smaller than when the secondary air supply amount is large. For this reason, especially in a region where the flow rate change with respect to the rotation speed is extremely sensitive and the flow control accuracy is poor, the frequency of correction of the secondary air supply amount increases in a low motor rotation speed range, the control accuracy is improved, and the hunting of the discharge flow rate is improved. The phenomenon can be suppressed small (claim 1).

Further, if the drive unit is provided with a function of increasing the control gain of the feedback control as the secondary air supply amount is smaller as compared with the case where the secondary air supply amount is larger, the flow rate control accuracy In a region where the motor rotation speed is poor, not only the frequency of correction of the secondary air supply amount but also the correction amount increases, so that the hunting phenomenon of the discharge flow rate is further reduced (claim 2).

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to one embodiment shown in the drawings.

In FIG. 1, an intake passage 2 for introducing mixed air to the engine 1 is connected to the engine 1. An air cleaner 3 is provided upstream of the intake passage 2 and a surge tank 4 is provided downstream of the air cleaner. Installed.
Further, a catalyst device (catalyst) 7 composed of a three-way catalyst is interposed in an exhaust passage 6 for discharging exhaust gas of the engine 1 to the outside.

A supply passage 9 constituting a secondary air supply device 8 is communicated upstream of the catalyst device 7 in the exhaust passage 6, and an upstream end thereof is connected to the air cleaner 3.
An electric air pump 10 including a centrifugal air pump 11 and a DC motor 12 is provided in the middle of the supply passage 9, and the DC motor 12 is rotationally controlled by a secondary air control device 13. Note that a reed valve 14 is further provided in the supply passage 9 downstream of the electric air pump 10.

As shown in FIG. 2, the secondary air control device 13 includes an EGI unit 15 as a control unit and an A / P
(Air pump) A / P drive unit 16 as drive unit
It is composed of The EGI unit 15 has an arithmetic function for determining the operating state of the engine based on input data such as a water temperature from a water temperature sensor (not shown), an engine speed from a crank angle sensor, and an engine load from an airflow sensor. . Also, the EGI unit 15
The relationship between the operating state of the engine divided into a plurality of regions and the voltage value to be applied to the motor 12 in order to obtain an appropriate amount of secondary air supply in each region, that is, the number of rotations of the motor, was previously obtained by an experiment. It has a memory that stores a map as a group of known characteristic curves. Then, according to the determined operating state of the engine, a control signal 17 of an appropriate operating voltage command is output on one of the characteristic curves in the map. The A / P drive unit 16 receives the control signal 17 and drives a corresponding control current by flowing the corresponding control current to the DC motor 12 of the centrifugal air pump 11. The actual number of revolutions N is monitored, and the current I of the motor is increased or decreased so that the difference from the target number of revolutions becomes zero.

As described above, basically, in the low-load, low-speed range, the secondary air amount is also increased in response to the increase in the exhaust amount, and the exhaust gas is effectively purified by the catalyst device 7. In the high-load and high-speed range, the heating of the catalyst device 7 is suppressed, and the durability of the catalyst device is improved. However, if the current air supply amount is grasped by using the rotation speed N of the motor 12 according to the control signal 17 as a guideline, as described above, there is a problem that the flow rate control accuracy deteriorates in a region where the motor rotation speed is low. .

Therefore, the A / P drive unit 16 has a function of shortening the control cycle of the feedback control as compared with when the secondary air supply amount is large, as the secondary air supply amount is small, and It has a function of increasing the control gain of the feedback control as compared with when the secondary air supply amount is large as the supply amount is small. That is, it has a function of changing the monitoring timing cycle for increasing or decreasing the current amount I given to the motor 12 and the increase or decrease amount when the discharge amount (air supply amount) Q of the pump is low or high.
Specifically, with respect to the current increase / decrease cycle (monitoring timing cycle) T applied to the motor 12 and the current increase / decrease gain G according to the difference between the target rotation speed and the pump discharge amount Q, As shown in FIGS. 4 (a) and 5 (a), when the current increase / decrease cycle T is long and the gradient θ of the current increase / decrease gain G is small, and when the discharge amount Q of the pump is low, FIG. 4
(B), as shown in FIG. 5 (b), the current increase / decrease cycle T is changed to be shorter and the current increase / decrease gain G is increased.

FIG. 6 shows the characteristics of the electric air pump 10 of the turbo blower type. FIG. 6A shows the discharge pressure P (mmHg) and the discharge flow rate Q (l / m) of the centrifugal air pump 11.
(b) shows the relationship between the discharge pressure P and the DC motor 1
2 shows the relationship with the rotation speed N (rpm). As can be seen from FIG. 6B, when the rotation speed N is a control parameter,
In particular, the discharge pressure P fluctuates greatly at low rotation speed fluctuations,
Therefore, the discharge flow rate Q also changes very sensitively from the characteristics shown in FIG. Here, looking at the PQ characteristics in FIG. 6A, a curve is plotted in a region where the discharge flow rate Q is larger than about 150 l / min (corresponding to the B area in FIG. 3). You can see that he is sleeping. Therefore, this discharge flow rate Q
Is associated with a region where the current is smaller than approximately 150 l / min and a region where the current is larger than 150 l / min.
Make changes.

In this configuration, a determination unit for determining the magnitude relationship of the number of revolutions N fed back is provided in the A / P drive unit 16 so as to correspond to about 150 l / min which is the boundary of the secondary air supply amount Q. In the region where the rotation value is smaller than this (the low flow region where the discharge flow rate Q is small), the current increase / decrease cycle T is shortened and the current increase / decrease gain G is increased. In a region where the rotational speed is equal to or greater than the above-mentioned rotation value (a high flow region where the discharge flow rate Q is large), the current increasing / decreasing cycle T is longer and the gradient of the current increasing / decreasing amount gain G
To make it smaller.

By performing such control, the hunting phenomenon of the secondary air flow rate (discharge rate) is converged within an extremely narrow width. Therefore, it is possible to prevent a reduction in purification efficiency due to an excessive secondary air flow rate and the cooling of the catalyst device 7, a reduction in NOx purification rate, and a waste of power consumption, and a purification of CH components due to an insufficient secondary air flow rate. Eliminate the decline,
Thus, appropriate purification of exhaust gas can be achieved.

In the above embodiment, the whole area of the secondary air supply amount is divided into two areas, a high discharge area Q and a low discharge area Q, and the change control of the current increase / decrease cycle T and the increase / decrease amount gain G is performed. Although performed, the present invention is not limited to this. In short, the smaller the secondary air supply amount, the shorter the control cycle of the feedback control as compared with the case where the secondary air supply amount is large. Therefore, the entire region of the secondary air supply amount is set to three or more. It may be performed by dividing into regions.

The A / P drive unit has a function of shortening the control cycle of the feedback control as compared with when the secondary air supply amount is large, as the secondary air supply amount is small. As the amount is smaller, only one of the functions for shortening the control gain of the feedback control as compared with the case where the secondary air supply amount is larger may be provided.

[0021]

As described above, according to the present invention, the following excellent effects can be obtained.

(1) In the configuration of the first aspect, the control cycle of the feedback control is shorter as the secondary air supply amount is smaller than when the secondary air supply amount is larger. In a region where the change is very sensitive and the motor speed is low where the flow rate control accuracy is poor, the frequency of correcting the secondary air supply amount increases, the control accuracy improves, and the hunting phenomenon of the discharge flow rate is suppressed to a small level. Therefore, control accuracy can be improved over the entire region of the secondary air supply amount, and stable control can be performed.

(2) In the configuration of claim 2, since the control gain of the feedback control is increased as the secondary air supply amount is smaller than when the secondary air supply amount is large, the flow rate control accuracy is poor. In the region where the motor rotation speed is low, the correction amount of the secondary air supply amount also increases, and the hunting phenomenon of the discharge flow rate can be further reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a block diagram of a secondary air control device in FIG.

FIG. 3 is a characteristic diagram showing a relationship between a rotation speed N of an electric air pump and a discharge flow rate Q.

FIG. 4 is an explanatory diagram showing a control cycle of feedback control in the drive unit of FIG. 2 for a high flow rate and a low flow rate of a discharge amount.

FIG. 5 is an explanatory diagram showing the control gain of the feedback control in the drive unit of FIG. 2 separately for a high flow rate and a low flow rate of the discharge amount.

FIG. 6 illustrates characteristics of an electric air pump.
(A) is a diagram showing the relationship between the discharge pressure P and the discharge flow rate Q, and (b) is a diagram showing the relationship between the discharge pressure P and the motor speed N.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 3 Air cleaner 4 Surge tank 5 Actuator 6 Exhaust passage 7 Catalyst device 8 Secondary air supply device 9 Supply passage 10 Electric air pump 11 Air pump 12 DC motor 13 Secondary air control device 14 Reed valve 15 EGI as control part Unit 16 A / P drive unit as drive unit 17 Control signal 18 Revolution detection unit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-138714 (JP, A) JP-A-4-362213 (JP, A) JP-A-49-129908 (JP, A) 87912 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/00-3/38 F01N 9/00

Claims (2)

(57) [Claims] 1. A control device for controlling an electric air pump of a turbo blower type to supply an appropriate amount of secondary air to an exhaust system of an engine in accordance with an operation state of an engine, from a map stored in a memory in advance. A control unit for selecting a characteristic curve of a motor applied voltage for obtaining an appropriate secondary air supply amount according to the operation state of the engine, and outputting a control signal based on the selected characteristic curve; A driving unit that receives the actual rotation speed fed back from the detection unit and drives the DC motor of the air pump so that the rotation value of the motor is the secondary air supply amount of the control signal, and the driving unit includes: The secondary air of an engine having a function of shortening the control cycle of the feedback control as compared with when the secondary air supply amount is large as the secondary air supply amount is small. Control device. 2. The drive unit according to claim 1, wherein the drive unit has a function of increasing the control gain of the feedback control as the secondary air supply amount is smaller than when the secondary air supply amount is large. 2. The secondary air control device for an engine according to claim 1.