JPH11257164A - Egr device of multiple cylinder engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR device of a multiple cylinder engine having a simple system, capable of precisely supplying EGR gas by the EGR amount to be stepwise determined, so that the exhaust gas amount for EGR(exhaust gas recirculation) may coincide with the target EGR amount to be determined according to the operating state of the engine. SOLUTION: In a multiple cylinder engine 1, an EGR exhaust passage 4B provided by separating an exhaust system passage of at least one cylinder from an exhaust gas system passage 4A of the other cylinder is branched into a plurality of branch exhaust passages 20i (20a, 20b and 20c), respective branch exhaust passages 20i and an EGR passage 6 joined to an intake system passage 3 are connected to one another by EGR branch passages 22i (22a, 22b and 22c), and a three-way valves 21i (21a, 21b and 21c) for switching EGR gas Gpe of the branch exhaust passage 201 to the EGR branch passage 21i and the downstream side of the branch exhaust passage 20i is provided on the connecting part for the branch exhaust passage 20i and the EGR branch passage 22i.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-cylinder engine such as a diesel engine, in which a part of exhaust gas is recirculated to an intake side to reduce the amount of NOx emission, and the flow rate of the recirculated gas can be adjusted. The present invention relates to an EGR device for a multi-cylinder engine.

[0002]

2. Description of the Related Art In exhaust gas countermeasures for diesel engines and the like, a part of exhaust gas, that is, EGR gas is returned to an intake system in order to reduce the amount of NOx (nitrogen oxide) in the exhaust gas. Keeping the combustion temperature low, N
EGR (exhaust gas recirculation, exhaust gas recirculation) that suppresses generation of Ox
Is known to be effective, and is widely used.

In this EGR device, as shown in FIG. 2, an intake passage 3 leading to an intake manifold 2 of an engine 1 and an exhaust manifold 4 and an exhaust passage 5 are connected by an EGR passage 6, and exhaust gas is exhausted from an exhaust system. The EGR gas Ge, which is a part of the gas Gt, is supplied to the fresh air A in the intake passage 3 via the EGR passage 6.
And is recirculated to the intake manifold 2 to perform EGR. The EGR passage 6 is provided with an EGR valve 7 for adjusting the flow rate of the EGR gas Ge in order to set the EGR rate according to the operating state of the engine 1.

However, in the simple ON / OFF control of either EGR or not,
When the EGR valve 7 provided in the EGR passage 6 is opened, the exhaust gas Ge enters the fresh air A through the EGR valve 7. In this case, the flow rate of the EGR gas Ge is determined by the pressure difference (Pe−Pb) between the exhaust extraction unit 5a and the intake mixing unit 3a, and the EGR amount is fixed, so that the rotation speed Ne of the engine 1, the load Lo, and the like are fixed. Cannot be controlled so as to obtain an optimal EGR amount according to the operating state of the vehicle.

[0005] Therefore, the EGR passage 6 is controlled by the controller 8 in accordance with the operating state of the engine 1.
EG that can adjust the flow rate of EGR gas Ge according to the R rate
An R valve 7 is provided. By controlling the opening degree of the EGR valve 7 by the controller 8, the flow rate of the EGR gas Ge passing through the EGR passage 6 is adjusted to an appropriate amount, and the NOx is reduced while the combustion state of the engine 1 is kept good. doing.

However, when EGR is performed, NOx decreases, but exhaust smoke tends to increase.
The control of the GR amount is important, and the EGR device in FIG. 2 has a simple mechanism and simple control, but cannot control the EGR amount. Therefore, it is necessary to set the EGR amount with a margin. Therefore, the maximum EGR amount can be set only by an EGR amount that is lower by this margin, and there is a problem that NOx cannot be reduced to just before the limit of the increase in exhaust smoke.

[0007] Since this limit of the EGR amount varies depending on the operating condition of the engine, in order to reduce NOx to the maximum at a barely permissible limit of exhaust smoke, EGR is required.
It is necessary to finely control the flow rate of the gas Ge. Therefore, in the EGR device as shown in FIG. 3, the exhaust pressure regulating valve 9 is provided in the exhaust passage 5 downstream of the branch point 5 a of the EGR passage 6, and the exhaust pressure Pe is controlled by the exhaust pressure regulating valve 9. Thus, the flow rate of the EGR gas Ge is adjusted.

Then, the EGR amount and intake air (a mixed gas (A + G) of fresh air A and EGR gas Ge in the intake manifold 2)
e)) because there is a correlation with the O2 concentration,
The concentration is detected by an O2 sensor 10 provided in the intake manifold 2, an EGR amount is estimated from the detected value, and a predetermined target E
A controller (control device) 8 called an engine control unit (ECU) that controls the operation of the entire engine by controlling the valve opening of the exhaust pressure regulating valve 9 so that the GR amount is obtained.
Is adjusted.

That is, when performing EGR, the EGR valve 7 is opened and the controller 8 controls the rotation speed Ne,
A load Lo and the like are input, a target EGR amount is read from a previously input EGR data map, and the O2 concentration of intake air (A + Ge) is detected by the O2 sensor 10, and the current EGR amount is determined from the O2 concentration. To estimate the target EG
The EGR is performed while adjusting the valve opening degree of the exhaust pressure adjusting valve 9, that is, the exhaust pressure Pe, while detecting a difference from the R amount and performing feedback control so as to be a target EGR amount.

By using an EGR device as shown in FIG. 3, the rotation speed Ne of the engine 1, the load Lo, O2
From the data of the sensor 10 and the like, the EG value is set so that the target EGR amount is at a level at which exhaust smoke and NOx can be reduced to the maximum.
The flow rate of the EGR gas Ge passing through the R passage 6 can be controlled.

[0011]

However, in actual use, the target EG is controlled by controlling the exhaust pressure regulating valve 9.
Although the control is performed so as to approach the R amount, since the exhaust pressure Pe is not constant and has a pulsation, it is difficult to control the exhaust pressure control valve 9, and the error of the actual EGR amount with respect to the target EGR amount is large. This error amount also fluctuates greatly, and the target EGR
There is a problem that EGR cannot be performed with an accurate EGR amount corresponding to the amount.

In other words, controlling the flow rate by the pressure difference requires complicated control, and generally, the flow rate flowing through the valve mainly includes the pressure difference before and after the valve, the pressure value before the valve, and the temperature before the valve. Further, at the time of pulsation, since it is determined by factors such as a pulsating pressure waveform, in order to pass only the target gas amount, the four points are accurately measured, and the valve opening is calculated based on these measured values. By making the determination, the amount of passing gas can be set to the target amount for the first time, and setting the amount of passing gas to the target amount is actually too complicated to be practical.

Further, in the EGR device shown in FIG.
An expensive sensor such as an O2 sensor 10 for detecting the GR amount, and a complicated and expensive controller 8 and complicated control for controlling the exhaust pressure Pe in accordance with the operating state of the engine 1 are required. Therefore, there is a problem that cost increase cannot be avoided. Also, as another device, the exhaust gas recirculation path is branched into a plurality of paths, and some of them are turned on / off in parallel.
A control EGR rate metering valve is arranged, and a common volume chamber is arranged on the inlet side or the outlet side of the valve,
EG is determined by the number of EGR rate adjusting valves
An exhaust gas recirculation device for controlling the amount of R is disclosed in Japanese Unexamined Patent Publication No. 7-247.
No. 911.

[0014] However, in this apparatus, a common volume chamber is provided to absorb pressure fluctuations.
Since the pressure upstream of the EGR rate adjusting valve changes due to the change in the number of the EGR rate adjusting valves, the distribution of the exhaust gas amount to the EGR passage side and the exhaust passage side changes.
The quantity is not proportional to the number of valves opened. Further, since the magnitude of the pressure is determined by an operating state such as a turbo state, it is difficult to control the EGR amount accurately.

In addition, various EGR devices have been proposed, but the error of the actual EGR amount with respect to the target EGR amount is still large, and if the error is to be reduced, the device and control become complicated, resulting in a high EGR amount. There is a problem of cost. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to reduce the EGR amount so that the EGR exhaust gas amount matches a target EGR amount determined by the operating state of the engine. EG of a multi-cylinder engine, which can be controlled to a fixed amount, can supply an accurate EGR amount with high accuracy, and is a simple system.
R device.

[0016]

An EGR device for a multi-cylinder engine for achieving the above object is to separate an exhaust passage of at least one cylinder from an exhaust passage of another cylinder in a multi-cylinder engine. And an EGR exhaust passage is provided, the EGR exhaust passage is branched into a plurality of branch exhaust passages, and each of the branch exhaust passages and the intake passage are joined.
A GR passage is provided and connected with an EGR branch passage, and EGR gas in the branch exhaust passage is supplied to a connecting portion between the branch exhaust passage and the EGR branch passage through the EGR branch passage and the branch exhaust passage. A three-way valve for switching to the downstream side is provided.

According to the above configuration, since the EGR gas is limited to only the gas exhausted from a specific cylinder, the total amount Gp of the EGR gas is always a constant ratio to the total exhaust gas amount Gt. Then, since this EGR gas is distributed to a plurality (for example, N) of branch exhaust passages, the EGR gas G
p is distributed at a fixed rate (for example, 1 / N). Further, the EGR gas Gpi distributed at a constant rate flowing through the branch exhaust passage is discharged to the atmosphere release side downstream of the EGR passage or the branch exhaust passage in each branch exhaust passage in accordance with the switching operation of the three-way valve. Flows selectively.

In this case, since the difference between the atmospheric pressure on the downstream side of the branch exhaust passage and the intake pressure (boost pressure) on the intake side is small, the change in exhaust pressure on the upstream side of the three-way valve caused by switching of the three-way valve is small. The flow rate of the exhaust gas passing through the three-way valve becomes small, and the change in the flow rate of the exhaust gas is small, and the amount of the distributed EGR gas (for example, Gp / N) flows to the intake side or the exhaust side. That is, according to the switching operation of each three-way valve, the distributed amount (for example, Gp / N) of the branched exhaust gas enters the intake side as EGR gas by the number (for example, n) of switching the three-way valve to the EGR passage side. As a whole, a certain amount (for example, nx
Gp / N) is supplied stably to the intake side.

Accordingly, the flow rate of the EGR gas can be adjusted stepwise with a relatively simple device having only a three-way valve for controlling the branch exhaust passage, the EGR branch passage, and ON / OFF switching and a simple control. And adjust the flow rate to E
The GR gas can flow with high accuracy.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an EGR device for a multi-cylinder engine according to the present invention will be described below with reference to the drawings. As shown in FIG. 1, the EGR device includes an exhaust manifold 4A which is an exhaust passage of a cylinder of the multi-cylinder engine 1.
And at least one cylinder is separated from the EG
An R exhaust passage 4B is provided. This EGR exhaust passage 4B
A plurality of (three in FIG. 1) branch exhaust passages 20a
Branches to 20b and 20c (hereinafter referred to as 20i).

Then, each of the branch exhaust passages 20i and the EGR passage 6 which merges with the intake system passage 3 such as the intake manifold 2 and the intake passage 3 are connected to the EGR branch passages 22a, 22b, 22.
c (hereinafter referred to as 22i) for connection. A three-way valve is provided at the connection between the branch exhaust passage 20i and the EGR branch passage 22i.
21a, 21b, and 21c (hereinafter, referred to as 21i) are provided, and by switching the three-way valve 21i, a branch exhaust passage is formed.
The EGR gas Gpe flowing through the EGR branch passage 22i
To supply the air to the intake system passage 3 or 2 via the EGR passage 6 and mix it into the fresh air A, or to discharge the air to the downstream side of the branch exhaust passage 20i, that is, to the atmosphere. To be configured.

The switching control of the three-way valve 21i is configured to be performed by a controller 8 called an engine control unit (ECU) that controls the entire operation of the engine 1. The controller 8 detects the operating state of the engine 1 by inputting data such as the rotation speed Ne and the load Lo of the engine 1 from various sensors (not shown), and detects the operating state according to a previously input EGR data map or program. Target EG according to
By calculating the R amount, the EGR amount passing through the EGR passage 6 becomes
Each three-way valve 21i is set to a value close to the target EGR amount.
Is output to each of the three-way valves 21i to perform switching control of each of the three-way valves 21i.

The control of the EGR amount in this EGR device is performed as follows. In FIG. 1, one cylinder is separated in a six-cylinder engine, and three branch exhaust passages 20i are provided. However, for general description, m cylinders are separated in an M-cylinder engine. A case in which N branch exhaust passages 20i are provided will be described.

In this EGR device, the exhaust gas Gp for EGR is limited to only the gas exhausted from the m cylinders, and is at most a fixed amount of m of the total exhaust gas amount (Gt = G + Gp). Gp = (m / M) × Gt. Next, the EGR exhaust gas Gp is distributed to the N branch exhaust passages 20i. First, the case of equal distribution will be described. The distribution exhaust gas Gp1, Gp2,
Gp3: hereinafter referred to as Gpi) is expressed as Gpi = (1 / N) × G
p = (m × Gt) / (M × N).

In each of the branch exhaust passages 20i, the distribution exhaust gas Gpi flowing through the branch exhaust passage 20i can be switched and flown to the EGR passage 6 or the downstream side of the branch exhaust passage 20i by the three-way valve 21i. By switching the three-way valves 21i to flow to the EGR passage 6, the exhaust gas can be supplied from the n branch exhaust passages 20i to the intake system passages 2 and 3 as the EGR gas Ge. The flow rate of Ge is expressed as Ge = n × Gpi = (n ×
m × Gt) / (M × N).

Therefore, of the M cylinders, the number m of cylinders separated for EGR, the number N of branch exhaust passages 20i branching off the exhaust passage 4B, and the number n of switching of the three-way valve 21i determine the exhaust gas Gt. (N × m) / (M × N) times can be supplied to the intake system passage 3 side with high accuracy and stability as the EGR gas Ge. For example, as shown in FIG.
Assuming that 6, m = 1 and N = 3, n = 0, 1, 2, and 3, so that the EGR gas amount Ge is a fixed ratio of the total exhaust gas amount, that is, 0, 1 of the total exhaust gas amount Gt. / 18, 1 /
The air can be supplied to the intake system passages 2 and 3 in four steps of 9 and 1/6.

In the above description, each branch exhaust passage 20
Although the exhaust gas Gpi in i is described as being distributed in the same amount, the number of stages and the number of each stage can be further improved by making the exhaust gas Gpi different without depending on the pipe diameter of each branch exhaust passage 20i, the shape of the branch portion, and the like. Can vary.
For example, if the distribution ratio of the exhaust gas Gp in the three branch exhaust passages 20i is 1: 2: 3, the combination of the branch exhaust passages 20i causes 0, 1/36, and 2/3 of the total exhaust gas amount Gt.
It can be supplied to the intake side in seven steps of 6, 3/36, 4/36, 5/36 and 6/36.

Next, the operation and effect of the configuration of the switching passage using the three-way valve 21i will be described. When a three-way valve for switching the passage is used, the difference ΔP1 between the pressure Pe on the upstream side of the three-way valve 21i and the atmospheric pressure Pa on the downstream side of the branch exhaust passage 20i =
The difference ΔP3 = Pb−Pa between the atmospheric pressure Pa and the boost pressure Pb is smaller than Pe−Pa or the difference ΔP2 = Pe−Pb between the pressure Pe and the boost pressure Pb on the intake side of the intake passages 2 and 3. Since the influence on the flow rate is larger in ΔP1 and ΔP2 and is hardly affected by ΔP3, the three-way valve 21
The change in the flow rate of the exhaust gas Gpi passing through the three-way valve 21i due to the switching of the passage i is small.

That is, since the pressure change ΔP3 generated by the switching of the three-way valve 21i is small, the change in the pressure Pe on the upstream side of the three-way valve 21i due to the influence of ΔP3 is small. The change in the ratio of the flow rate Gpi during this period is very small. In other words, the pressure difference ΔP1, ΔP2 before and after the three-way valve 21i,
Since the pressure value Pe before the valve, the temperature before the valve, and the pulsating pressure waveform conditions are almost the same during pulsation, the flow direction of the exhaust gas Gpi flowing through the three-way valve 21i is remarkably changed only by switching the flow direction with the three-way valve. Become smaller.

Therefore, the distributed EGR gas amount Gpi can be reliably and stably flowed to the intake side or the exhaust side. Therefore, according to the above configuration, the normal exhaust passage 4
A is provided with an EGR exhaust passage 4B dedicated to EGR separated from A, and only the exhaust gas Gp of the EGR exhaust passage 4B is branched and distributed to a plurality of branch exhaust passages 20i, and the distributed exhaust gas Gpi is selectively provided. Through the three-way valve 21i to the EGR passage 6 or the atmosphere open side.

Therefore, by changing the number m of the cylinders to be separated, the number N of the branch exhaust passages 20i, and the distribution ratio between the branch exhaust passages 20i, the stepwise EGR amount is changed in accordance with the operating state of the engine. E close to the set target EGR amount
The GR amount is selected and the EG amount is accurately and stably determined based on the EGR amount.
R can be. Moreover, setting the EGR amount stepwise and reliably performing the predetermined amount of EGR is more difficult than the conventional EGR apparatus that performs proportionally stepless control.
Since the range of fluctuation of the error with the GR amount can be reduced, more precise EGR control can be performed.

In addition, the EGR device has a branch exhaust passage.
20i, EGR branch passage 22i, three-way valve 21i and three-way valve 21
Since the system configuration is relatively simple with only the ON / OFF switching control means for the i, an expensive O2 sensor for detecting the EGR amount and a complicated feedback for proportionally controlling the EGR amount in an analog manner are provided. No control is required, resulting in a low-cost and simple device.

[0033]

As described above, according to the EGR system for a multi-cylinder engine of the present invention, the EGR exhaust passage dedicated to the EGR is provided separately from the normal exhaust passage.
Only the exhaust gas in the R exhaust passage is branched and distributed, and the distributed exhaust gas can be selectively circulated through the three-way valve to the EGR passage or the atmosphere opening side. By changing the number of passages and the distribution ratio between the branch exhaust passages, the EGR amount can be set stepwise, and the EGR amount close to the required target EGR amount can be set.
By selecting the flow rate of the GR gas, the EGR gas amount can be reliably recirculated to the intake side with high accuracy.

In addition, the EGR device includes a branch exhaust passage, an EGR branch passage, a three-way valve, and ON / OFF of a three-way valve.
A relatively simple system configuration only with the installation of the switching control means for the O2.
The sensor also does not require complicated feedback control for controlling the EGR amount in an analog or proportional manner.
A low-cost device can be provided.

Therefore, a simple system for performing a simple control, the target EGR determined by the operating state of the engine
Since the optimal amount of the EGR amount can be selected and supplied stably with respect to the amount, the EGR control with high accuracy can be performed.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an EGR device for a multi-cylinder engine according to the present invention.

FIG. 2 is a system configuration diagram of an EGR device of a conventional multi-cylinder engine.

FIG. 3 is a system configuration diagram of an EGR device of another conventional multi-cylinder engine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine main body 2 Intake manifold 3 Intake passage 4 Exhaust manifold 5 Exhaust passage 6 EGR passage 7 EGR valve 8 Controller 20a, 20b, 20c, 20i Branch exhaust passage 21a, 21b, 21c, 21i Three-way valve 22a, 22b, 22c, 22i EGR Branch passage A Fresh air G Exhaust gas Gp Branched exhaust gas Gt Total exhaust gas Ge EGR gas

Claims (1)

[Claims] In a multi-cylinder engine, an EGR exhaust passage is provided by separating an exhaust passage of at least one cylinder from an exhaust passage of another cylinder, and the EGR exhaust passage is branched into a plurality of branch exhaust passages. At the same time, each of the branch exhaust passages and an EGR passage that merges with the intake system passage are provided and connected with an EGR branch passage, and a connecting portion between the branch exhaust passage and the EGR branch passage is provided with a branch exhaust passage. An EGR device for a multi-cylinder engine, comprising a three-way valve for switching EGR gas between the EGR branch passage and a downstream side of the branch exhaust passage.