JPH04334750A - Exhaust circulation device of diesel engine with supercharger - Google Patents

Abstract

PURPOSE:To prevent generation of smoke due to delay of building up of supercharging as well as heightening exhaust purification performance by circulating rather more smoke at the time of supercharging when smoke is hard to generate. CONSTITUTION:An exhaust circulation rate of a diesel engine 21 with a turbo supercharger 24 can be gradually controlled by full opening and half opening of an exhaust circulation control valve 28 and opening-closing of a throttle valve 38. A control unit 42 corrects a control territory, which makes number of rotation and throttle lever opening as its parameter, on the basis of a detection signal of a supercharging pressure sensor 46.

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. The lever opening degree detection means 7 compares the detected rotation speed and lever opening degree with a plurality of target exhaust gas recirculation rate regions set in stages.
A target exhaust recirculation rate setting means 8 for selecting a target exhaust recirculation rate, an exhaust recirculation control means 9 for controlling the amount of exhaust recirculation in accordance with the target exhaust recirculation rate, and detecting the supercharging pressure of the engine 1 by the above-mentioned supercharger. and a correction means 11 that corrects the target exhaust gas recirculation rate range so that it becomes large at the time of high supercharging in accordance with the detected supercharging pressure.

[0007]

[Operation] The target exhaust gas recirculation rate setting means 8 determines the target exhaust gas recirculation rate by comparing the rotational speed of the engine 1 and the throttle lever opening with a predetermined target exhaust gas recirculation rate range. The target exhaust gas recirculation rate range is set in stages such that the higher the speed and the higher the load, the lower the exhaust gas recirculation rate. and,
The exhaust gas recirculation control means 9, in accordance with this target exhaust gas recirculation rate,
For example, the opening degree control of the exhaust recirculation control valve 5 or the intake passage 3
The amount of exhaust gas recirculated is controlled by controlling the pressure difference between the exhaust gas passage 2 and the exhaust passage 2.

[0008] Here, in the supercharging region of the engine 1,
Based on the actual boost pressure detected by the boost pressure detection means 10, the target exhaust gas recirculation rate region is expanded and corrected. In other words, when the boost pressure is high, a high target exhaust recirculation rate is given at higher speeds and higher loads.

[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. In addition, in the intake passage 23 downstream of the compressor 26, a boost pressure sensor 46 consisting of, for example, a semiconductor pressure sensor, etc.
is provided, and its detection signal is 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 control map based on the rotational speed of the engine 21 and the throttle lever opening degree of the fuel injection pump. Figure 3 shows a basic control map that determines the target exhaust recirculation rate during non-supercharging. Exhaust recirculation starts from region A with the highest exhaust recirculation rate from the low speed, low load side to the high speed, high load side. The range up to region D where is 0 is set in stages. 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.

On the other hand, in response to changes in supercharging pressure, the size of each region A to C where exhaust gas recirculation is performed is corrected according to the supercharging pressure, and the higher the supercharging, the more the region is on the high-speed, high-load side. Expanding. Specifically, a three-stage control map M1 is created depending on the boost pressure.
, M2, and M3 are set in advance as shown in FIG. 4, and correction according to the boost pressure is performed by performing interpolation calculations based on these control maps. In addition, each control map M1
, M2, and M3 themselves are actually tables having about 8×8 grid points, and interpolation calculations are performed between the grid points.

The flowchart shown in FIG. 5 shows a specific process flow for the correction according to the boost pressure, which will be explained below. First, in step 1, the engine cooling water temperature TW at that time is compared with a predetermined value T1. T
When the temperature is below 1, exhaust gas recirculation is not performed regardless of the lever opening degree, etc., and the process proceeds to step 13, where region D is selected.

If the water temperature TW is higher than T1, read the engine speed R and boost pressure P (steps 2 and 3),
Based on these, the lever opening degree L1, which is the boundary between area A and area B, is determined (step 4). As shown in the explanatory diagram of FIG. 6, this is the three-stage control map M1 described above.
, M2, M3 by interpolation calculation. Then, the actual lever opening degree L at that time is compared with the above-mentioned boundary value L1 (step 5), and if the lever opening degree L is less than the boundary value L1, the process proceeds to step 6 and area A is selected.

If the lever opening degree L is larger than the boundary value L1, the next lever opening degree L2, which is the boundary between area B and area C, is determined by similar interpolation calculation (step 7).
, and this is compared with the lever opening degree L (step 8). Here, if the lever opening degree L is less than or equal to the boundary value L2, the process proceeds to step 9 and area B is selected. If it is larger than the boundary value L2, the lever opening degree L3, which is the boundary between the next area C and area D, is determined by similar interpolation calculation (step 10).
, and this is compared with the lever opening degree L (step 11). Here, if the lever opening degree L is less than or equal to the boundary value L3, the process proceeds to step 12 and selects area C, and if it is greater than the boundary value L3, the process proceeds to step 13 and selects area D, which is the exhaust gas recirculation stop area. .

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. In particular, it detects the actual boost pressure,
Since the exhaust recirculation rate is corrected based on the boost pressure,
Even during transient times such as during acceleration, the exhaust gas recirculation rate is maintained at an appropriate rate, and smoke generation is reliably prevented.

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 .

[0026]

[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. Furthermore, since the actual supercharging pressure is detected and the exhaust gas recirculation rate is corrected based on this, it is possible to reliably prevent the occurrence of smoke even if the rise of supercharging is delayed during a transient period.

[Brief explanation of drawings]

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 control map showing a target exhaust recirculation rate region during no supercharging.

FIG. 4 is an explanatory diagram showing a three-stage control map according to boost pressure.

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

[Figure 6] Boundary values L1 to L of lever opening according to boost pressure
3 is an explanatory diagram for determining.

[Explanation of symbols]

1...Diesel engine 5...Exhaust recirculation control valve 6...Rotation speed detection means 7... Lever opening detection means 8...Target exhaust gas recirculation rate setting means 9...Exhaust recirculation control means 10...Supercharging pressure detection means 11...Correction 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. a lever opening detection means for detecting a throttle lever opening of the fuel injection pump, and a lever opening detection means that detects a throttle lever opening of the fuel injection pump, and compares the detected rotational speed and lever opening with a plurality of target exhaust recirculation ratio regions set in stages. , a target exhaust recirculation rate setting means for selecting a target exhaust recirculation rate; an exhaust recirculation control means for controlling the amount of exhaust recirculation in accordance with the target exhaust recirculation rate; An exhaust gas recirculation device for a diesel engine with a supercharger, comprising a boost pressure detection means and a correction means for correcting the above-mentioned target exhaust recirculation rate range in accordance with the detected boost pressure so that it increases at the time of high supercharging. .