JPH04342862A - Exhaust gas rotary flow device of diesel engine with supercharger - Google Patents

Abstract

PURPOSE:To enhance the exhaust gas purifying performance by circulating much more exhaust gas at the time of supercharging when smoke is hard to be generated, and to prevent the generation of smoke due to a delay in rising of supercharging. CONSTITUTION:The rate of circulation of exhaust gas of a Diezel engine 21 having a turbocharger 24 can be controlled by stages depending on the full open and half-open of an exhaust gas rotary flow control valve 28 and the opening and closing of a throttle valve 38. A control unit 42 decides a target exhaust gas circulation rate, with a rotating speed and a throttle lever opening as a parameter according to a designated table, and at the time of acceleration, after the elapse of designated time, and it is switched to a table for supercharging.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to an exhaust gas recirculation device for a diesel engine that recirculates a portion of exhaust gas to the intake system in order to reduce NOx, and more particularly to an exhaust gas recirculation device for a turbocharged diesel engine equipped with a supercharger. .

0002

[Prior Art] Exhaust recirculation devices that recirculate part of the exhaust gas, which is an inert gas, back to the intake system in order to reduce NOx in the exhaust gas have been widely used in diesel engines. In the case of this diesel engine, the ratio of the amount of exhaust recirculation to fresh air, that is, the upper limit of the exhaust recirculation rate, is limited by the generation of smoke. That is, as the exhaust gas recirculation rate is increased, smoke in the exhaust gas increases accordingly, and therefore exhaust gas recirculation cannot be performed beyond a certain limit. Since this smoke is more likely to occur in high-load regions, the target exhaust recirculation rate is generally changed depending on the engine operating conditions, and control is performed to maximize exhaust recirculation within a range that does not cause excessive smoke. There is.

For example, Japanese Patent Laid-Open No. 62-271940 discloses that the optimum exhaust gas recirculation rate is determined based on a map using the engine speed and the throttle lever opening (accelerator operation amount) of the fuel injection pump as parameters. However, an exhaust gas recirculation device for a diesel engine is disclosed in which the amount of exhaust gas recirculation is controlled in accordance with this target value. Incidentally, the above publication exemplifies a configuration including a turbo supercharger.

0004

By the way, in a diesel engine equipped with a supercharger such as a turbo supercharger, more air is sent into the cylinder due to supercharging, so smoke is less likely to occur. Therefore, the exhaust gas recirculation rate, which is restricted by this smoke, can be increased compared to the case without a supercharger.

However, if the target exhaust recirculation rate corresponding to the engine speed and throttle lever opening is simply set high in the supercharging range, the actual supercharging pressure will increase after the throttle lever opening changes. During a transient period such as when the exhaust gas recirculation rate increases, there is a risk that the exhaust gas recirculation rate may exceed the smoke generation limit and generate a large amount of smoke. Therefore, in reality,
Even with a turbocharged diesel engine, the target exhaust recirculation rate could not be set that high, and there was room for improvement in exhaust purification performance.

[0006]

[Means for Solving the Problems] As shown in FIG. 1, an exhaust gas recirculation system for a diesel engine with a supercharger according to the present invention includes a diesel engine 1 equipped with a supercharger, and an exhaust passage of the diesel engine 1. an exhaust gas recirculation control valve 5 interposed in an exhaust gas recirculation passage 4 that communicates between the engine 2 and the intake passage 3; a rotation speed detection means 6 for detecting the rotation speed of the engine 1; and a rotation speed detection means 6 for detecting the throttle lever opening of the fuel injection pump. A lever opening detection means 7 that detects the lever opening, a plurality of types of target exhaust recirculation rate tables 8 that are set to different characteristics depending on the boost pressure, and a lever opening detection means 7 that detects the Table selection means 9 for selecting a target exhaust gas recirculation rate table 8; and a target exhaust system for determining a target exhaust gas recirculation rate by comparing the detected rotation speed and lever opening with the characteristics of the selected target exhaust gas recirculation rate table 8. The exhaust gas recirculation control means 11 includes a recirculation rate setting means 10 and an exhaust recirculation control means 11 that controls the amount of exhaust gas recirculation in accordance with the target exhaust recirculation rate.

[0007]

[Operation] The target exhaust gas recirculation rate setting means 10 determines the target exhaust gas recirculation rate by comparing the rotational speed of the engine 1 and the throttle lever opening with the target exhaust gas recirculation rate characteristics shown in table 8. The target exhaust gas recirculation rate characteristics are generally set such that the exhaust gas recirculation rate becomes lower in the high speed and high load region. Then, the exhaust gas recirculation control means 11 controls the amount of exhaust gas recirculation in accordance with this target exhaust gas recirculation rate, for example, by controlling the opening of the exhaust gas recirculation control valve 5 or controlling the pressure difference between the intake passage 3 and the exhaust passage 2. .

[0008] In the operating region of the engine 1, which is the supercharging region, the target exhaust gas recirculation rate table 8 is switched based on the elapsed time after the throttle lever opening reaches a predetermined opening. In other words, until the boost pressure actually increases during acceleration, characteristics suitable for a non-supercharged state are given, and from the point when the boost pressure actually increases, characteristics suitable for a supercharged state are given. Become.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a configuration explanatory diagram showing one embodiment of the exhaust gas recirculation system according to the present invention, in which 21 is, for example, a swirl chamber type diesel engine, 22 is an exhaust passage of this diesel engine 21, and 23 is an intake air passage. A passage 24 indicates a turbocharger in which an exhaust turbine 25 and a compressor 26 are coaxially connected.

The exhaust gas recirculation passage 27 connects the exhaust passage 22 upstream of the exhaust turbine 25 and the intake passage 23 upstream of the compressor 26.
It communicates with the downstream side, and an exhaust gas recirculation control valve 28 made of a negative pressure diaphragm valve is interposed in the passage. This exhaust gas recirculation control valve 28 is connected to a return spring 3 in two stages via an intermediate retainer with respect to a diaphragm 29.
0 and 31 are provided, so that a fully open state and a half open state can be stably obtained depending on the negative pressure.

The negative pressure introduced into the exhaust recirculation control valve 28 uses a vacuum pump 32 as a negative pressure source, and is appropriately diluted with the atmosphere by a first solenoid valve 33 and a second solenoid valve 34 to a predetermined pressure. is controlled. The first solenoid valve 33 and the second solenoid valve 34 are both three-way solenoid valves,
The first ports 33a, 34a to which the negative pressure passage 35 leading to the exhaust gas recirculation control valve 28 is connected are connected to the second ports 33b, 34b.
Alternatively, it is configured to selectively communicate with the third ports 33c and 34c. As shown by the arrows in the figure, a state in which the flow path communicates with the second ports 33b and 34b is shown as a flow path α, and a state in which it communicates with the third ports 33c and 34c is shown as a flow path β. The second port 33b of the first solenoid valve 33 and the second solenoid valve 34
, 34b are all exposed to the atmosphere via an air cleaner (not shown). Also, the third port 33 of the first solenoid valve 33
c is in communication with the vacuum pump 32 which serves as a negative pressure source, and the third port 34c of the second solenoid valve 34 is sealed. In addition, each of the first ports 33a, 34a and the negative pressure passage 3
5, an orifice 37 is interposed between each of them.

[0013] Also, the intake passage 2 on the upstream side of the compressor 26
3 is provided with a throttle valve 38 for generating negative pressure within the intake passage 23. This throttle valve 38
is driven to open and close by a negative pressure diaphragm actuator 39, and a third solenoid valve 41, which is also a three-way solenoid valve, is installed in the negative pressure passage 40 leading to the actuator 39.
is interposed. The third electromagnetic valve 41 includes a negative pressure passage 4
0 is connected to the second port 41b or the third port 41c selectively, the second port 41b is open to the atmosphere, and the third port 41c is connected to a negative pressure source. Vacuum pump 3
Connected to 2. Note that this third solenoid valve 41 also has a state in which it communicates with the second port 41b side through the flow path α and the third solenoid valve 41.
The state in which it communicates with the port 41c side is shown as a flow path β.

The throttle valve 38 has the function of increasing the negative pressure in the intake passage 23 by closing it, increasing the pressure difference across the exhaust gas recirculation control valve 28, and increasing the amount of exhaust gas recirculation. That is, in this embodiment, the exhaust recirculation control means is constituted by the first and second electromagnetic valves 33, 34, etc., which directly control the opening degree of the exhaust recirculation control valve 28, and the throttle valve 38, etc., which controls the pressure difference. has been done.

Each of the electromagnetic valves 33, 34, and 41 is ON/OFF controlled by an engine control unit 42 using a microcomputer system. 43
Reference numeral 44 detects the rotational speed of the engine 1 and includes a pulse generator, for example. Reference numeral 44 indicates a lever opening sensor such as a potentiometer that detects the throttle lever opening of a fuel injection pump (not shown). Reference numeral 45 detects the cooling water temperature. The detection signals of these water temperature sensors are input to the control unit 42.

Next, the operation of the above embodiment will be explained.

In the exhaust gas recirculation system configured as described above, the target exhaust gas recirculation rate is basically selected from a predetermined target exhaust gas recirculation rate table based on the rotational speed of the engine 21 and the throttle lever opening of the fuel injection pump. In this example,
A first target exhaust gas recirculation rate table based on the non-supercharged state and a second target exhaust gas recirculation rate table based on the supercharged state are provided in the memory of the control unit 42. FIG. 3 illustrates the characteristics of the first target exhaust recirculation rate table. From the low speed, low load side to the high speed, high load side, the exhaust recirculation becomes 0 from region A where the exhaust recirculation rate is highest. Areas up to area D are set in stages. FIG. 4 illustrates the characteristics of the latter second target exhaust recirculation rate table, in which regions A to D are set in stages, but the boundaries of each region are the same as the first target exhaust recirculation rate table. Compared to the reflux rate table, it is expanded to the high speed and high load side. For each region A to D, the electromagnetic valves 33, 34, 41, exhaust recirculation rate control valve 28, and throttle valve 38 are controlled as shown in Table 1 below.

[0018]

[Table 1]

That is, in region A, the exhaust recirculation control valve 2
8 is fully opened, and the throttle valve 38 is closed to provide a high exhaust gas recirculation rate. The target exhaust gas recirculation rate at this time is, for example, 40%. In region B, the exhaust gas recirculation control valve 28 is fully open and the throttle valve 38 is open, providing an intermediate exhaust gas recirculation rate. The target exhaust gas recirculation rate at this time is, for example, 20%. Further, in region C, the exhaust gas recirculation control valve 28 is in a half-open state, and a low exhaust gas recirculation rate is provided. The target exhaust recirculation rate at this time is, for example, 10%.
It is. Further, in region D, the exhaust gas recirculation control valve 28 is fully closed, and the exhaust gas recirculation rate becomes zero.

The flowchart shown in FIG. 5 shows a specific process flow using the above two types of tables.
This will be explained below. First, in step 1, the engine cooling water temperature TW at that time is compared with a predetermined value TW0. When the temperature is lower than TW0, exhaust gas recirculation is not performed regardless of the lever opening degree, etc., and the process proceeds to step 21 where area D is
Select.

[0021] When the water temperature TW is TW0 or higher, the engine speed R is read (step 2), and based on this, the lever opening L1, which is the boundary between area A and area B, is determined from the first target exhaust recirculation rate table. (Step 3) This is obtained as shown in the explanatory diagram of FIG. Then, the actual lever opening degree L at that time is compared with the above-mentioned boundary value L1 (step 4), and if the lever opening degree L is less than the boundary value L1, the process proceeds to step 5 and area A is selected.

Further, when the lever opening degree L is larger than the boundary value L1 of the first target exhaust gas recirculation rate table, the elapsed time T1 after the lever opening degree L exceeds the boundary value L1 is measured, and this is set as a predetermined time TS1. (Step 6). Until this elapsed time T1 reaches the predetermined time TS1, the actual supercharging pressure may be low, so step 6 to step 9
Proceed to the following. On the other hand, if T1≧TS1, it is considered that the supercharging pressure is actually increasing, so the lever opening L1, which is the boundary between region A and region B, is determined based on the second target exhaust recirculation rate table. ' is determined as shown in Figure 6 (Step 7
), and compare the actual lever opening L with this (step 8
). If the lever opening degree L is less than or equal to L1', the process advances to step 5 and area A is selected. In other words, a high target exhaust gas recirculation rate is provided in a manner suitable for the supercharging state. Also, lever opening L
If exceeds L1', proceed to step 9.

Next, in step 9, the lever opening degree L2, which is the boundary between region B and region C, is determined from the first target exhaust gas recirculation rate table, and in step 10, it is compared with the actual lever opening degree L. If L≦L2, region B is selected regardless of the supercharging state (step 11). If L>L2, measure the elapsed time T2 after the lever opening degree L exceeds the boundary value L2, and compare this with a predetermined time TS2 (step 12).
. Until this elapsed time T2 reaches the predetermined time TS2,
Proceed to step 15 and subsequent steps. On the other hand, if T2≧TS2, area B is determined based on the second target exhaust gas recirculation rate table.
The lever opening degree L2', which is the boundary between the area C and the area C, is determined as shown in FIG. 6 (step 13), and the actual lever opening degree L is compared with this (step 14). If the lever opening degree L is less than or equal to L2', the process advances to step 11 and region B is selected. If the lever opening degree L exceeds L2', the process proceeds to step 15.

[0024] After step 15, discrimination between area C and area D is performed in the same way. That is, in step 15,
The lever opening degree L3, which is the boundary between the area C and the area D, is determined from the first target exhaust gas recirculation rate table, and is compared with the actual lever opening degree L in step 16. If L≦L3, region C is selected regardless of the supercharging state (step 17). L>L3
In this case, the elapsed time T3 after the lever opening L exceeds the boundary value L3 is measured and compared with a predetermined time TS3 (step 18). This elapsed time T3 is a predetermined time TS
3, the process proceeds to step 21 and selects region D, which is the exhaust gas recirculation stop region. On the other hand, T3≧TS
3, the lever opening degree L3', which is the boundary between area C and area D, is determined based on the second target exhaust gas recirculation rate table as shown in FIG. 6 (step 19), and the actual lever opening degree L is determined from this. (step 20). Lever opening degree L is L3'
If it is below, proceed to step 17 and select area C. If the lever opening degree L exceeds L3', the process proceeds to step 21 and selects a region D where the exhaust gas recirculation is stopped.

Note that each elapsed time TS1 to TS3, which is a reference for switching between the first target exhaust recirculation rate table and the second target exhaust recirculation rate table, corresponds to the predetermined boost pressure when each lever opening degree L1 to L3 is maintained. This roughly corresponds to the time required to rise to TS1 and TS2, as shown in Figure 7.
>It has something to do with TS3. In other words, the larger the lever opening degree L is, the faster the actual boost pressure rises, so that the characteristics of the second target exhaust recirculation rate table can be switched to earlier.

As described above, in the above embodiment, during high supercharging when smoke is less likely to occur, a relatively high exhaust recirculation rate is provided compared to when no supercharging is performed, and even better exhaust purification performance is achieved. can get. Immediately after the lever opening increases, the exhaust recirculation rate is temporarily suppressed to the standard value when no supercharging occurs, reliably preventing smoke from occurring due to a delay in the rise of supercharging pressure. . Furthermore, since there is no need to detect actual boost pressure, there is no need to provide a boost pressure sensor.

In the above embodiment, the exhaust recirculation control valve 28
The opening/closing control of the throttle valve 38 is performed in conjunction with the opening control of the exhaust recirculation control valve 28, and the exhaust gas recirculation amount is controlled in stages. It is also possible to perform exhaust gas recirculation control corresponding to each region only by controlling the duty ratio of .

[0028]

[Effects of the Invention] As is clear from the above explanation, according to the exhaust gas recirculation device for a supercharged diesel engine according to the present invention, the exhaust gas recirculation is increased according to the boost pressure during supercharging where smoke is less likely to occur. Since the ratio is given, the exhaust purification performance can be further improved compared to the conventional one. Since the target exhaust recirculation rate table is not switched immediately after the lever opening changes, it is possible to reliably prevent smoke from occurring even if the rise of supercharging is delayed during a transition.

[Brief explanation of the drawing]

FIG. 1 is a claim correspondence diagram showing the configuration of the present invention.

FIG. 2 is a configuration explanatory diagram showing an embodiment of the present invention.

FIG. 3 is a characteristic diagram of a first target exhaust gas recirculation rate table based on a non-supercharging state.

FIG. 4 is a characteristic diagram of a second target exhaust gas recirculation rate table based on the supercharging state.

FIG. 5 is a flowchart showing the flow of processing when selecting each area.

FIG. 6 is an explanatory diagram when determining each boundary value of the lever opening degree based on the rotation speed.

FIG. 7 is a characteristic diagram showing the rise characteristics of supercharging pressure at each lever opening degree.

[Explanation of symbols]

1...Diesel engine 5...Exhaust recirculation control valve 6...Rotation speed detection means 7... Lever opening detection means 8...Target exhaust recirculation rate table 9...Table selection means 10...Target exhaust gas recirculation rate setting means 11...Exhaust gas recirculation control means

Claims (1)

[Claims] Claim 1: A diesel engine equipped with a supercharger, an exhaust recirculation control valve interposed in an exhaust recirculation passage that communicates an exhaust passage and an intake passage of the diesel engine, and a rotation valve for detecting the engine rotation speed. lever opening detection means for detecting the throttle lever opening of the fuel injection pump; multiple types of target exhaust recirculation rate tables set to different characteristics depending on the boost pressure; table selection means for selecting the target exhaust recirculation rate table based on the elapsed time after reaching a predetermined opening; and comparing the detected rotational speed and lever opening with the characteristics of the selected target exhaust recirculation rate table; 1. An exhaust recirculation device for a diesel engine with a supercharger, comprising: a target exhaust recirculation rate setting means for determining a target exhaust recirculation rate; and an exhaust recirculation control means for controlling an amount of exhaust recirculation in accordance with the target exhaust recirculation rate.