JP3580558B2 - EGR device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an EGR device (exhaust gas recirculation control device) for an engine.
[0002]
[Prior art]
It is well known that a part of exhaust gas is recirculated to an intake pipe for the purpose of reducing NOx and the like. This EGR amount has an appropriate amount according to the operating conditions.
[0003]
Therefore, it is desirable to accurately detect the actual EGR amount and perform feedback control in comparison with the target EGR amount. However, a sensor for directly detecting the EGR amount in the intake pipe has not been realized so far.
[0004]
Therefore, conventionally, as disclosed in Japanese Patent Application Laid-Open No. Hei 1-216065, for example, an oxygen sensor is installed in the intake pipe, and the EGR rate is measured from the oxygen concentration in the intake pipe.
As disclosed in Japanese Patent Laying-Open No. 57-148048, a newly supplied air flow rate is detected by an air flow meter installed upstream of an opening of an exhaust gas recirculation conduit of an intake pipe. Also, a pressure detector for the intake pipe pressure is provided downstream to detect the total gas amount (the sum of the intake air amount and the exhaust gas recirculation amount) passing through the intake pipe from this pressure value, and determine the EGR amount from the difference between these detected values. Have been proposed.
[0005]
[Problems to be solved by the invention]
By the way, in addition to the exhaust gas being guided to the intake system through the EGR conduit, there is also a recirculation amount (so-called internal EGR) due to backflow from the combustion chamber to the intake pipe generated at the beginning of the intake stroke of the engine. Among them, when the EGR rate is measured from the oxygen concentration as in the former, it is difficult to detect the internal EGR, and particularly when the opening timing of the intake and exhaust valves changes, the control accuracy may decrease.
[0006]
Also, in the engine intake system, when the throttle valve opening changes, a pressure change occurs in the downstream volume of the throttle valve, and a substantial change in air occurs due to a change in air density. However, no consideration has been given to this in the EGR control.
[0007]
The present invention has been made in view of the above points, and an object of the present invention is to realize high-accuracy EGR control in consideration of a change in air density due to a change in pressure of an internal EGR and a downstream volume of a throttle valve in an intake pipe. .
[0008]
[Means for Solving the Problems]
The present invention proposes the following problem solving means to achieve the above object.
One is an EGR device that recirculates a part of the exhaust gas of an engine to an intake pipe, an air flow meter for obtaining an air flow rate (Go) passing through a throttle valve of the intake pipe, and a pressure (Pm) downstream of the throttle valve in the intake pipe. ), Means for detecting the engine speed (N), and a map for storing the volumetric efficiency (η) of the cylinder in relation to the pressure downstream of the throttle valve and the engine speed. throttle valve downstream pressure (Pm) and the engine rotational speed in the intake pipe reads volumetric efficiency of the cylinder stored in the map (N) (η), throttle valve downstream pressure (Pm) and the cylinder volumetric efficiency (eta) Means for calculating the cylinder inflow air amount (Gc) from the product of the above, and the pressure downstream of the throttle valve in the intake pipe detected by the pressure detector to differentiate the air density change due to the pressure change in the throttle valve downstream volume in the intake pipe. Accompanying Means for calculating and means for obtaining the air decrease amount (k · dPm / dt), wherein Go, Gc, than k · dPm / dt, EGR amount according to the following equation (exhaust gas recirculation) amount (Ge),
[Equation 4] Ge = Gc + k · dPm / dt−Go (1)
Means for feedback-controlling the EGR based on a deviation between the calculated EGR amount and a target EGR amount set in accordance with operating conditions,
And set to change the opening and closing timing of the intake valve of the engine in accordance with the operating conditions ,
Further, when the operation region becomes an operation region where the EGR control is not performed, the automatic rewriting mode for the volume efficiency (η) is entered, and the throttle valve passage air flow rate (Gc) obtained based on the above equation (1) when the EGR amount is zero is calculated. The volume efficiency (η) can be rewritten from the relationship with the pressure (Pm) downstream of the throttle valve .
[0009]
The other is an EGR device, an air flow meter for obtaining a throttle valve passing air flow rate (Go), a pressure detector for detecting a pressure (Pm) downstream of a throttle valve in an intake pipe, and an engine rotation speed. Means for detecting the number (N), a map for storing the volumetric efficiency (η) of the cylinder in relation to the pressure downstream of the throttle valve and the engine speed , means for determining the amount of air flowing into the cylinder (Gc), Means for calculating an amount (k · dPm / dt), means for calculating an EGR amount (exhaust gas recirculation) amount (Ge), and means for feedback controlling the EGR,
In addition, the opening and closing timing of the exhaust valve of the engine is set to be changed in accordance with the operating conditions. Further, the volume efficiency (η) of the cylinder is rewritten as in the first invention.
Further, in the EGR device, an air flow meter for obtaining a throttle valve passing air flow rate (Go), a pressure detector for detecting a pressure (Pm) downstream of a throttle valve in an intake pipe, and an engine , as in the above invention , Means for detecting the number of revolutions (N), a map for storing the volumetric efficiency (η) of the cylinder in relation to the pressure downstream of the throttle valve and the number of engine revolutions , means for determining the amount of air flowing into the cylinder (Gc), Means for calculating an increase / decrease amount (k · dPm / dt), means for calculating an EGR amount (exhaust gas recirculation) amount (Ge), and means for feedback-controlling the EGR,
Further, the volume efficiency (η) of the cylinder is rewritten as in the first invention.
[0010]
[Action]
The cylinder inflow air flow rate Gc includes, in addition to the throttle valve passage air flow rate Go, the exhaust gas guided through the EGR conduit. Further, when the pressure Pm in the intake pipe changes suddenly, the air substantially increases or decreases with a change in the air density in the intake pipe. Therefore, the true EGR with respect to the air flow rate can be obtained by considering the difference between the cylinder inflow air flow rate Gc and the throttle valve passing air flow rate Go with the air increase / decrease amount k · dPm / dt accompanying the change in the air density.
[0011]
Then, the EGR amount is appropriately corrected based on the difference between the EGR and the target EGR, and highly accurate EGR control is performed by feedback control involving the correction.
[0012]
【Example】
An embodiment of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a configuration diagram of an EGR device according to one embodiment of the present invention, and FIG. 2 is a flowchart showing an operation of EGR control.
[0014]
In FIG. 1, an air flow meter 5 is arranged in an intake pipe 1 of an engine upstream of a throttle valve 6. Downstream of the throttle valve 6, an outlet opening 10 b of the conduit 10 of the EGR control system is provided, and an inlet opening 10 a of the conduit 10 is opened to the exhaust pipe 2. 3 is an exhaust catalyst. Downstream from the throttle valve 6 and the EGR conduit outlet 10b in the intake pipe 1, a pressure detector 9 for detecting the pressure in this downstream region is arranged.
[0015]
Each detection signal of the air flow meter 5 and the pressure detector 9 is input to the control circuit 4. The control circuit 4 is for performing EGR control and comprises a microcomputer. The air flow meter 5 serves as a means for determining the flow rate Go of air passing through the throttle valve.
[0016]
The pressure detector 9 and a part of the arithmetic function of the control circuit 4 serve as a means for determining the cylinder air flow rate Gc. That is, the microcomputer serving as the control circuit 4 receives the pressure detection value Pm from the pressure detector 9 and multiplies this by the cylinder volume efficiency η to calculate the cylinder air inflow Gc. The arithmetic function of the pressure detector 9 and a part of the control circuit 4 is based on a change in air density due to a pressure change in the downstream volume of the throttle valve 6 in the intake pipe 1 (this pressure change is caused by a change in the throttle valve opening). This is a means for determining the amount of increase or decrease. That is, the control circuit 4 differentiates the detection value Pm from the pressure detector 9 to calculate the air increase / decrease amount k · dPm / dt in the volume downstream of the throttle valve 6.
[0017]
Further, the control circuit 4 calculates an EGR amount Ge from each of the above values based on the equation (1), and calculates an appropriate target EGR amount corresponding to the operating conditions as described later. A corrected EGR amount is obtained based on a deviation between the EGR amount and the actual EGR amount, and forms the center of a feedback control system that controls the EGR valve 8 provided in the conduit 10.
[0018]
Here, the EGR amount Ge is
[0019]
## EQU3 ## Ge = Gc + kdPm / dt-Go (1)
Pm: Intake pipe pressure k: Constant t: Expressed as time. Therefore, Ge can be calculated by calculating Go, Gc, and k · dPm / dt. As described above, Go can be measured by the air flow meter 5, and Gc is
[0020]
(Equation 4)
Gc = ηPm (2)
η: expressed by volumetric efficiency. Since η is determined by the engine shape and operating state, Pm may be measured.
[0021]
The EGR valve 8 of the present embodiment is a negative pressure responsive diaphragm valve, and its opening is controlled by applying a negative pressure adjusted by the actuator 7 to the diaphragm working chamber 8a. The actuator 7 has its pressure regulating chamber 7a communicating with the atmosphere via a pipe 11, communicating with the negative pressure downstream of the throttle valve 6 via a pipe 12, and controlling the pressure regulating valve 7b on / off by an EGR control signal (duty control signal). To adjust the negative pressure.
[0022]
Here, the EGR control will be described with reference to the flowchart of FIG.
[0023]
In step 101, the engine speed N, the cylinder air flow rate Go, and the intake pipe pressure Pm are measured. In step 102, a pressure change dPm in the intake pipe is obtained from the difference between the intake pipe pressure Pm and the intake pipe pressure Pmo taken in before that. In step 103, k · dPm / dt is calculated. In step 104, η stored in the map is read as a function of N and Pm, and Gc is calculated in step 105, and Ge is calculated in step 106.
[0024]
At step 107, the EGR rate GE (here, GE = Ge / total gas amount flowing into the cylinder of the intake system) stored in the map is read as a function of N and Go, and at step 108, the target value Geo of the EGR amount is calculated. I do. In step 109, a deviation ΔGe between the target value Geo and the actual measurement value Ge is calculated, and in step 110, a control signal of the EGR valve 8 proportional to ΔGe is output. In step 111, Pm is set to Pmo, and the processing ends.
[0025]
FIG. 3 shows an example of the relationship between the engine speed N and the charging efficiency (volume efficiency) η when the throttle valve is fully opened. In this example, Pm is approximately atmospheric pressure. When the throttle valve 6 is closed, Pm decreases, but η decreases in proportion thereto. Since the relationship between η and N differs depending on the length of the intake pipe and the opening and closing timings of the intake and exhaust valves, it is necessary to measure each time the specification is replaced with an engine.
[0026]
FIG. 4 shows an example of the relationship between the engine speed N and the EGR rate GE based on the throttle valve passing air amount Go. As Go increases, GE also increases. However, when Go becomes larger, GE is set to 0 to stop EGR again. In this embodiment, the operating conditions of the engine are represented by N and Go. However, instead of Go, the basic fuel injection amount Tp, the intake pipe pressure Pm, the throttle valve opening and the like can be substituted.
[0027]
The EGR control according to the present embodiment is applicable to an engine that changes the opening characteristics of intake and exhaust valves when the engine is running at low speed and at high speed. FIG. 5 shows low-speed and high-speed valve lift characteristics having such valve opening characteristics. The low-speed valve has a small lift, a late opening timing, and a fast closing timing. On the other hand, in the case of the high speed type, the lift is large and the valve opening timing is early and the valve closing timing is late. FIG. 6 shows the relationship between the engine speed N and the volumetric efficiency η in such a case. η is large where N is small and where N is large. In order to increase η in this manner, it is possible to change the valve lift characteristic continuously instead of changing it stepwise.
[0028]
Also, there is a variable stroke engine that changes the stroke of a piston to the amount of air intake of the engine. In this case as well, η changes depending on both the engine speed and the piston stroke, but the EGR control can be applied to this variable stroke engine.
[0029]
In the above embodiment, an analog EGR valve is used, but a digital EGR valve may be used instead. FIG. 7 shows a digital EGR valve, FIG. 8 shows its opening degree characteristics, and FIG. 9 shows an EGR device according to a second embodiment of the present invention to which the digital EGR valve is applied.
[0030]
In FIG. 7, the EGR valve 20 is constituted by solenoid valves 20a, 20b and 20c, and the orifices 21a, 21b and 21c are opened and closed by the solenoid valves. The opening ratio of this orifice is 1: 2: 4, and the upstream passage 22 of each orifice 21a, 21b, 21c is connected to the exhaust pipe 2 via the conduit 10-1 shown in FIG. The intake pipe 1 is connected to the downstream of the throttle valve 6 via the passages 23a and 23b.
[0031]
Each of the solenoid valves 20a, 20b, 20c of the EGR valve 20 is controlled to open and close by a signal from the control circuit 4.
[0032]
The opening characteristics of the digital EGR valve 20 will be described with reference to FIG. When an opening signal is input only to the solenoid valve 20a, the orifice diameter 21a having the minimum opening ratio of 1 opens. Next, when an opening signal is input only to the solenoid valve 20b, the orifice diameter 21b of the opening ratio 2 opens. Next, when an opening signal is input to the solenoid valves 20a and 20b, the orifice diameters 21a and 21b of the opening ratio 1 and the opening ratio 2 are opened, and the opening ratio becomes 3. Next, when an opening signal is input only to the solenoid valve 20c, the orifice diameter 21c having the opening ratio of 4 opens, and thereafter, by combining these opening signals, the opening ratio gradually increases to 5, 6, and 7. The maximum opening ratio becomes 7. That is, eight types of opening ratios are obtained in combination with the opening ratio 0 (fully closed).
[0033]
FIG. 10 shows an example of another analog type EGR valve. In the analog EGR valve 30, when a valve opening signal is input to an input terminal, a magnetic force is generated in the solenoid 35, the armature 33 moves, and the pair of valve bodies 31a, 31b open. This magnetic force balances the reaction force of the spring 34, so that a stroke proportional to the input signal is obtained. The exhaust gas flows in from the Ex side of the passage 36, flows out from the In side, and is sent to the intake pipe. The analog valve has an advantage that the valve opening of the EGR valve is continuously changed.
[0034]
FIG. 11 shows an analog EGR valve 40 according to another embodiment. In the EGR valve 40 of FIG. 11, an analog solenoid valve 41 is combined with a digital solenoid valve 20a, 20b, 20c as shown in FIG. 7, and the orifice 42 of the analog solenoid valve 41 is the minimum of the digital valve. And the same diameter as the orifice diameter 21a. The analog valve 40, when combined with a digital valve, enables continuous EGR amount control over a wide range as shown in FIG. 12 while minimizing the orifice diameter 42 of the analog solenoid valve 41.
[0035]
FIG. 13 shows a flowchart of another example of the EGR control according to the present invention.
[0036]
The EGR control in this example is the same as that in FIG. In step 121, the EGR rate GE is read from the engine speed N and the throttle valve passing air flow rate Go.
[0037]
At step 122, GE = 0 is determined. In the case of Yes, the automatic rewriting mode of the cylinder volume efficiency η is entered, Gc is calculated by Go and k · dPm / dt in step 130, η is calculated from Gc and Pm in step 131, and η is rewritten in step 132 do. On the other hand, when GE = 0 is NO, η is read in step 123, Gc is calculated in step 124, Ge is calculated in step 125, Geo is calculated in step 126, ΔGe is calculated in step 127, and the EGR valve is controlled in step 128. Step 129 is reached (these steps 123 to 129 correspond to steps 104 to 111 in FIG. 2). In the present embodiment, there is an advantage that the accuracy of the EGR control is further improved by automatically correcting η in the operation region where the EGR control is not performed by using steps 130 to 132.
[0038]
【The invention's effect】
As described above, according to the present invention, the difference between the air flow rate passing through the throttle valve and the air flow rate flowing into the cylinder and the air density of the downstream volume of the throttle valve due to a change in the throttle opening (a change in the intake pipe pressure in the downstream area of the throttle valve). In order to perform the EGR control in consideration of the change, it is possible to realize the EGR control with high accuracy by enabling the EGR control with the correction in consideration of the internal EGR of the engine and the increase and decrease of the air due to the change in the air density.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an EGR device according to an embodiment of the present invention.
FIG. 2 is a flowchart of EGR control in the embodiment.
FIG. 3 is an explanatory diagram showing a relationship between an engine speed N and a cylinder volume efficiency η stored as a map in a control unit of the EGR device.
FIG. 4 is an explanatory diagram showing a relationship among an engine speed N, a throttle valve passage air flow rate Go, and an EGR rate GE stored as a map in a control unit of the EGR device.
FIG. 5 is a lift characteristic diagram in a case where the intake and exhaust valves of the engine are provided with low-speed and high-speed valve lift characteristics as an application target of the embodiment.
FIG. 6 is a characteristic diagram showing the relationship between N and η in the low-speed and high-speed valve lift switching methods.
FIG. 7 is a sectional view showing an example of a digital EGR valve.
FIG. 8 is an explanatory diagram showing an opening degree characteristic of the digital EGR valve.
FIG. 9 is a configuration diagram of an EGR device using the digital EGR valve.
FIG. 10 is a sectional view showing an example of an analog type EGR valve.
FIG. 11 is a sectional view showing another example of the analog EGR valve.
FIG. 12 is an explanatory diagram showing the opening degree characteristics of the analog EGR valve of FIG. 11;
FIG. 13 is a flowchart showing another example of the EGR control according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... intake pipe, 2 ... exhaust pipe, 4 ... control circuit, 5 ... air flow meter, 6 ... throttle valve, 7 ... actuator for driving EGR valve, 8 ... EGR valve, 9 ... intake pipe pressure detector, 20 ... digital EGR valves, 30, 40: Analog EGR valves.

Claims (3)

In an EGR device that recirculates a part of the exhaust gas of an engine to an intake pipe, an air flow meter for obtaining an air flow rate (Go) passing through a throttle valve of the intake pipe and a pressure (Pm) downstream of the throttle valve in the intake pipe are detected. A pressure detector, means for detecting the engine speed (N), a map for storing the volumetric efficiency (η) of the cylinder in relation to the pressure downstream of the throttle valve and the engine speed, and a detected throttle in the intake pipe The cylinder volume efficiency (η) stored in the map is read from the pressure (Pm) downstream of the valve and the engine speed (N ), and the product of the pressure ( Pm ) downstream of the throttle valve and the cylinder volume efficiency (η) is read out. Means for determining the amount of air flowing into the cylinder (Gc), and differentiation of the pressure downstream of the throttle valve in the intake pipe detected by the pressure detector to increase the air increase due to a change in air density due to a pressure change in the downstream volume of the throttle valve in the intake pipe. Means for determining the amount (k · dPm / dt), wherein Go, Gc, than k · dPm / dt, and means for calculating the EGR amount in accordance with the following equation (exhaust gas recirculation) amount (Ge),
[Equation 1] Ge = Gc + k · dPm / dt−Go (1)
Means for feedback-controlling the EGR based on a deviation between the calculated EGR amount and a target EGR amount set in accordance with operating conditions,
And set to change the opening and closing timing of the intake valve of the engine in accordance with the operating conditions ,
Further, when the operation region becomes an operation region where the EGR control is not performed, the automatic rewriting mode for the volume efficiency (η) is entered, and the throttle valve passage air flow rate (Gc) obtained based on the above equation (1) when the EGR amount is zero is calculated. An EGR device characterized in that the volume efficiency (η) can be rewritten from the relationship with the pressure (Pm) downstream of the throttle valve . In an EGR device that recirculates a part of the exhaust gas of an engine to an intake pipe, an air flow meter for obtaining an air flow rate (Go) passing through a throttle valve of the intake pipe and a pressure (Pm) downstream of the throttle valve in the intake pipe are detected. A pressure detector, means for detecting the engine speed (N), a map for storing the volumetric efficiency (η) of the cylinder in relation to the pressure downstream of the throttle valve and the engine speed, and a detected throttle in the intake pipe The cylinder volume efficiency (η) stored in the map is read from the pressure (Pm) downstream of the valve and the engine speed (N ), and the product of the pressure ( Pm ) downstream of the throttle valve and the cylinder volume efficiency (η) is read out. Means for determining the amount of air flowing into the cylinder (Gc); and differentiation of the pressure downstream of the throttle valve in the intake pipe detected by the pressure detector to increase the air increase due to a change in air density due to a pressure change in the downstream volume of the throttle valve in the intake pipe. Means for determining the amount (k · dPm / dt), wherein Go, Gc, than k · dPm / dt, and means for calculating the EGR amount in accordance with the following equation (exhaust gas recirculation) amount (Ge),
[Equation 2] Ge = Gc + kdPm / dt-Go (1)
Means for feedback-controlling the EGR based on a deviation between the calculated EGR amount and a target EGR amount set in accordance with operating conditions,
And set to change the opening and closing timing of the exhaust valve of the engine in accordance with the operating conditions ,
Further, when the operation region becomes an operation region where the EGR control is not performed, the automatic rewriting mode for the volume efficiency (η) is entered, and the throttle valve passage air flow rate (Gc) obtained based on the above equation (1) when the EGR amount is zero is calculated. An EGR device characterized in that the volume efficiency (η) can be rewritten from the relationship with the pressure (Pm) downstream of the throttle valve . In an EGR device that recirculates a part of the exhaust gas of an engine to an intake pipe, an air flow meter for obtaining an air flow rate (Go) passing through a throttle valve of the intake pipe and a pressure (Pm) downstream of the throttle valve in the intake pipe are detected. A pressure detector, means for detecting the engine speed (N), a map for storing the volumetric efficiency (η) of the cylinder in relation to the pressure downstream of the throttle valve and the engine speed, and a detected throttle in the intake pipe The cylinder volume efficiency (η) stored in the map is read from the pressure (Pm) downstream of the valve and the engine speed (N ), and the product of the pressure ( Pm ) downstream of the throttle valve and the cylinder volume efficiency (η) is read out. Means for determining the amount of air flowing into the cylinder (Gc); and differentiation of the pressure downstream of the throttle valve in the intake pipe detected by the pressure detector to increase the air increase due to a change in air density due to a pressure change in the downstream volume of the throttle valve in the intake pipe. Means for determining the amount (k · dPm / dt), wherein Go, Gc, than k · dPm / dt, and means for calculating the EGR amount in accordance with the following equation (exhaust gas recirculation) amount (Ge),
[Equation 3] Ge = Gc + kdPm / dt-Go (1)
Means for feedback-controlling the EGR based on a deviation between the calculated EGR amount and a target EGR amount set in accordance with operating conditions,
Further, when the operation region becomes an operation region where the EGR control is not performed, the automatic rewriting mode for the volume efficiency (η) is entered, and the throttle valve passage air flow rate (Gc) obtained based on the above equation (1) when the EGR amount is zero is calculated. An EGR device characterized in that the volume efficiency (η) can be rewritten from the relationship with the pressure (Pm) downstream of the throttle valve .

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