JPS6138341B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an exhaust gas recirculation system for an engine.

Conventionally, in engine exhaust gas recirculation systems, in order to ensure the optimal amount of exhaust gas recirculation for each operating condition, a preset target value for the amount of exhaust gas recirculation is compared with the current value of the amount of exhaust gas recirculation. A system has been put into practical use that performs feedback control of the reflux control valve so that the current value matches the target value.

In this case, if the current detected state value is significantly different from a preset target value that represents the operating state of the recirculation flow control valve corresponding to the optimal exhaust gas recirculation amount in a certain operating state, In order to output a signal to the reflux control valve so that the target value is reached quickly, the control gain is changed according to the magnitude of the deviation value between the target state value and the detected state value. Control with good responsiveness is performed by increasing the control gain. Also, when the detected state value is close to the target state value, the reflux control valve is held in that state to prevent surging of the reflux amount due to excessive control and stabilize the control. It's on.

By the way, as a recirculation amount control valve that controls the amount of exhaust gas recirculation, one that changes the opening amount depending on the pressure inside the diaphragm chamber is known. A negative pressure introduction passage that introduces the negative pressure of It is known that the valve opening amount is changed by changing the valve opening amount.

In this type of reflux control valve, the solenoid valves that open and close each negative pressure and atmospheric passage are constantly magnetically excited and operated every time a signal is input, so their durability is a major issue. Ta.

Therefore, as in the exhaust gas recirculation system disclosed in Japanese Patent Application Laid-Open No. 53-107526, a target value corresponding to the operating condition is compared with a value indicating the actual valve position of the EGR control valve, and the target value is In a device that performs feedback control to the value and deactivates the valve when the deviation of the above value is within a predetermined value (dead band), the operation of the solenoid valve is limited within the above predetermined value, so its durability is limited. Although it is useful for improving durability, the predetermined value is always maintained constant even when the operating condition changes, so it cannot be expected to sufficiently improve durability.

The present invention has been made in response to the above-mentioned problems, and an object of the present invention is to improve the durability of a solenoid valve as much as possible.

Therefore, the present invention provides a negative pressure introduction passage for introducing the negative pressure of the intake system and an atmosphere introduction passage for introducing the atmosphere into the diaphragm chamber, and a first passage for opening and closing both the passages.
2. A recirculation flow control valve is provided in the middle of the exhaust gas recirculation passage by interposing a solenoid valve to change the opening amount according to the pressure in the diaphragm chamber, and a detected state value representing the operating state of the recirculation flow control valve; The first and second electromagnetic valves are set so that the detected state value matches the target state value by comparing the target state value representing the operating state of the recirculation amount control valve corresponding to the optimal exhaust gas recirculation amount in various operating states of the engine. In a device that performs feedback control of the reflux control valve by controlling the valve opening time, when the deviation value between the target state value and the detected state value is below a predetermined value, the first and second solenoid valves are made inoperable. This feature is characterized in that the recirculation flow control valve is maintained at its current state, and this predetermined value is increased when the engine load is high.
During high-load operation, the amount of intake air taken into the engine is larger than when the engine is running at low load, and the proportion of the exhaust gas recirculation amount to the total gas amount (intake air amount + exhaust gas recirculation amount) is small. The first and second solenoid valves that open and close each negative pressure introduction passage and atmospheric air introduction passage are inactivated to maintain a wide area (dead zone area) in which the pressure in the diaphragm chamber is maintained and the return flow control valve is maintained at its current state. As a result, the durability of the solenoid valve can be improved as much as possible without impeding drivability.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the exhaust gas recirculation device for an engine opens an exhaust gas recirculation passage 3 downstream of a throttle valve 2 in an intake passage 1 to recirculate part of the exhaust gas from the exhaust passage. A reflux control valve 4 is interposed in the middle of the reflux passage 3.

The recirculation amount control valve 4 is supported by a diaphragm 5 via a rod 6, and includes a valve body 7 for controlling opening and closing of the passage area of the exhaust gas recirculation passage 3, and also includes a negative pressure chamber partitioned by the diaphragm 5. (diaphragm chamber) 8 and an atmospheric chamber 9, negative pressure chamber 8
is connected to a negative pressure outlet 12 immediately downstream of the throttle valve 2 via a negative pressure introduction passage 11 having a negative pressure solenoid valve (first solenoid valve) 10, and an atmospheric solenoid valve (second solenoid valve).
The negative pressure chamber 8 is connected to the atmosphere through an atmosphere introduction passage 14 having a spring 15.
The diaphragm 5 is compressed by the spring 1 by the composite negative pressure formed by the intake pipe negative pressure and the atmospheric pressure.
5 to control the opening degree of the valve body 7 and increase the effective passage area of the exhaust gas recirculation passage 3 as the negative pressure in the negative pressure chamber 8 increases. There is.

On the other hand, the control device 16 includes an intake negative pressure sensor 1
7 detection signal S ₁ and engine speed sensor 1
8 detection signal S ₂ and the valve body 7 of the recirculation amount control valve 4.
lift amount detection sensor 19 that detects the lift amount of
Detection signal Ps and a storage signal in the storage device 20 are input, and the negative pressure solenoid valve 10 and the atmospheric solenoid valve 13 are controlled to open and close using a control signal output from the control device 16.

As shown in FIG. 2, the control device 16 includes a central processing unit 21, memories 22A and 22B, an input interface circuit 23 for inputting the detection signal of the engine rotation speed sensor 18, a negative pressure solenoid valve 10, and the atmosphere. An output interface circuit 24 for outputting a control signal to the solenoid valve 13, and an analog multiplexer 2 for inputting the outputs of the intake negative pressure sensor 17 and lift amount detection sensor 19.
5. AD the output of the analog multiplexer 25
An AD converter 26 that converts, a counter 27 that counts signal pulses from the engine rotation speed sensor 18 and detects the engine rotation speed, and each of the above devices 21 and 2.
Address/data bus 28 for exchanging address signals and data between 2A, 22B, 23, 24, 26, 27, and each of the above devices 21, 22
A, 22B, 23, 24, 25, 26, 27 and a control bus 29 for exchanging control signals.

The storage device 20 includes a storage device as shown in FIG. 3a.
Map1 is stored, and Map1 corresponds to the optimal exhaust gas recirculation amount determined from the current engine speed detected by the engine speed sensor 18 and the current negative pressure detected by the intake negative pressure sensor 17. A target value Pr of the lift amount of the recirculation amount control valve 4 is incorporated.

The memory 22B stores a Map 2 as shown in FIG. 3b, and the Map 2 includes a deviation value P (P= Pr-Ps) and the intake negative pressure of the engine, the control gain value is set to be higher as the deviation value P is larger, and the dead band region is set to be larger as the load is higher. In other words, curve A
And straight lines B and C are curves and straight lines formed by connecting the V ₀ , V ₁ , and V ₂ values among the values given in Map 2, respectively, and the values in Map 2 below curve A are all V ₀ This range is the dead band region, i.e. the region where the reflux control valve is maintained at its current state, and the values in the region between straight line B and curve A are greater than the V ₀ value and smaller than the V ₁ value; Similarly, the value between straight line C and straight line B is greater than V ₁ and smaller than V ₂ , and the range above straight line C is greater than V ₂ value. Straight lines B and C correspond to control gain values for controlling the recirculation amount control valve 4 to a target value, respectively, and are set so that the gain value of straight line C is higher than that of straight line B.

The action of the exhaust gas recirculation device configured as above is as follows.
This will be explained with reference to the flowchart shown in FIG.

(1) The current engine speed and intake negative pressure are read from the detection signals S ₂ and S ₁ of the engine speed sensor 18 and the intake negative pressure sensor 17, and are stored in the memories M ₁ and M ₂ of the memory 22A, respectively.

(2) From Map1 of the storage device 20, memory M ₁ ,
The target value Pr of the lift amount is determined by interpolation using the current engine speed and intake negative pressure stored in _M2 , and is stored in memory _M3 .

(3) The current lift amount detection value (detection signal) Ps is detected by the lift amount detection sensor 19 of the reflux control valve 4.
Read and put it into memory _M4 .

(4) Target value Pr stored in memories M ₃ and M ₄
The deviation value P between and the detected value Ps is calculated, and the deviation value P is stored in the memory _M5 .

(5) From Map2 of memory 22B, memory
A value V given by the absolute value of the deviation value P stored in M ₂ and M ₅ and the engine intake negative pressure is determined by interpolation.

(6) First, the value V is smaller than the value V ₀ , that is, Map
2, if it is in the region below characteristic curve A,
The negative pressure solenoid valve 10 is closed, and the atmospheric solenoid valve 13 is closed. This state continues for the time set by the timer T, and is then reset to the start.

That is, in this case, the pressure in the negative pressure chamber 8 of the reflux control valve 4 is maintained at the same pressure value.

In other words, when the detected value Ps is close to the target value Pr, the reflux control valve 4 is held in that state,
Efforts are being made to stabilize control. Here, this dead zone region is, as shown in FIG. 3b,
It becomes wider as the engine load increases. In other words, the absolute value |P| of the deviation value P existing in the dead zone region is larger under high load than under low load. This is for each solenoid valve (negative pressure solenoid valve 10, atmospheric solenoid valve 13)
This is due to the fact that in order to make the inoperable region (dead zone) as wide as possible in terms of durability, this dead zone is ensured as wide as possible in a high load range that does not significantly adversely affect drivability. In other words, when the engine is operating at low load, the amount of intake air taken into the engine is small, so the amount of exhaust gas recirculation accounts for a large amount of the total gas amount (amount of intake air + exhaust gas recirculation). Control must be performed with high precision. Therefore, widening the dead zone region greatly impairs drivability. On the other hand, during high-load operation, the amount of intake air is large, so accuracy is not required as much as when the load is low. Therefore, a wide area is secured in which the solenoid valves (negative pressure solenoid valve 10, atmospheric solenoid valve 13) are kept inactive (each passage 11, 14 is closed) during high loads that do not adversely affect drivability. , the durability of the solenoid valve can be improved.

(7) Next, if V≦V ₀ , it is compared with the value V ₁ , and if V≦V ₁ , it is determined whether the deviation value P is positive or negative, and if it is positive, the negative pressure solenoid valve 10 is activated. time
The atmospheric solenoid valve 13 is kept open by _t1 , and the atmospheric solenoid valve 13 is kept closed. If negative, the negative pressure solenoid valve 10 is closed, and the atmospheric solenoid valve 13 is closed.
is operated open for a time t ₁ .

When the deviation value P is positive, the current lift value of the recirculation amount control valve 4 is low (recirculation amount is small), so the valve body 7 is raised by the intake negative pressure introduced by the opening operation of the negative pressure solenoid valve 10. , the reflux amount increases.

When the deviation value P is negative, the current lift value of the reflux control valve 4 is high (the reflux amount is large), so the valve body 7 is lowered by the introduction of atmospheric air by the atmospheric solenoid valve 13, and the reflux amount is reduced.

Next, if the value V is greater than V ₁ and V≦V ₂ , then
If the deviation value P is positive, the negative pressure solenoid valve 10 is opened for a time _t2 , which is slightly longer than _t1 , and the atmospheric solenoid valve 13 is kept closed.
Therefore, in the case of V≦V ₂ , by opening the negative pressure solenoid valve 10 for a time (t ₂ ) longer than the opening operation time t ₁ when V≦V ₁ , that is, the negative pressure introduction passage 11 is lengthened. Time open, negative pressure chamber 8
By introducing a large negative pressure into the reflux amount control valve 4 in a short period of time, the recirculation amount control valve 4 can be quickly operated to the target position. Conversely, if the deviation value P is negative, the atmospheric solenoid valve 13 is opened by _t2 .

Furthermore, if the value V is greater than _V2 , the negative pressure solenoid valve 10 or the atmospheric solenoid valve 13
The opening operation time _t3 is set to be longer than _t2 , and in this embodiment, it is made to match the time specified by the timer T, and when the value V is larger than _V2 and is far apart from the target value, , by keeping the negative pressure solenoid valve 10 open (when the deviation value P is positive), or by keeping the atmospheric solenoid valve 13 open (when the deviation value P is negative); Control is performed to quickly reach the target value.

The time t for opening each solenoid valve in this way
The control gain value is changed by changing {(t ₁ ), (t ₂ ), (t ₃ )}.

In the above embodiment, the lift amount of the reflux control valve 4 is detected and the lift amount is controlled as the target value Pr, but this target state value representing the operating state of the reflux control valve 4 is In addition, the pressure in the negative pressure chamber of the diaphragm control valve, the pressure downstream of the orifice in the recirculation passage 3, the amount of exhaust gas recirculation flowing in the recirculation passage 3 (amount directly measured by a flow rate sensor), etc. can be adopted. .

Further, although Map 1 is designed to give the target value Pr using the engine rotation speed and intake negative pressure, the target value Pr is not limited to this, and may be the intake air amount and the engine rotation speed.

In Map 2, the load is replaced with the intake negative pressure in this example, but it may also be the intake air amount. In this case, when the intake air amount is small, the load is low, and the intake air amount increases. The load increases accordingly.

As is clear from the above explanation, the present invention
It is possible to improve the durability of the solenoid valves that control the opening and closing of the negative pressure introduction passage and the atmospheric air introduction passage provided in the diaphragm chamber of the return flow control valve without adversely affecting operability, making it possible to maintain effective operation for a long time. It is possible to achieve exhaust gas recirculation.

[Brief explanation of the drawing]

Figure 1 is a system diagram of the exhaust gas recirculation device, Figure 2 is a circuit diagram of the control device, Figure 3a is a graph of Map 1,
FIG. 3b is a graph of Map 2, and FIG. 4 is a flowchart showing the operation sequence. 3...Exhaust gas recirculation passage, 4...Return amount control valve, 8...Negative pressure chamber (diaphragm chamber), 9...Atmospheric chamber, 10...Negative pressure solenoid valve (first electromagnetic valve), 13... Atmospheric solenoid valve (second solenoid valve),
16...control device, 17...intake negative pressure sensor,
18... Engine speed sensor, 19... Lift amount detection sensor, Pr... Target value, Ps... Detected value, P... Deviation value.

Claims (1)

[Scope of Claims] 1. A negative pressure introduction passage for introducing the negative pressure of the intake system and an atmosphere introduction passage for introducing the atmosphere are provided in the diaphragm chamber, and first and second solenoid valves are interposed to open and close both passages. , a recirculation flow control valve that changes the amount of opening according to the pressure in the diaphragm chamber is provided in the middle of the exhaust gas recirculation passage, and a detected state value representing the operating state of the recirculation flow control valve and an optimum value for various operating conditions of the engine are provided. The valve opening times of the first and second electromagnetic valves are compared so that the detected state value matches the target state value by comparing the operating state of the recirculation amount control valve corresponding to the amount of exhaust gas recirculation. in which the return flow control valve is feedback-controlled by controlling the return flow rate control valve, when the deviation value between the target state value and the detected state value is below a predetermined value, the first and second electromagnetic valves are deactivated and the return flow is returned. While keeping the flow control valve in its current state,
An exhaust gas recirculation device for an engine, characterized in that the predetermined value is increased when the engine load is high.