JP2936673B2 - Exhaust gas recirculation control system for direct injection diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in an exhaust gas recirculation control device for a direct injection type diesel engine.

As with gasoline engines in (prior art) diesel engine, in order to suppress the occurrence of detrimental components in the exhaust NO _X, exhaust gas recirculation (hereinafter which is adapted to recirculate exhaust inert to the combustion chamber , EGR). Many control devices have been proposed, for example, in Japanese Patent Application Laid-Open No. 57-26252.

In these devices, EGR is used to connect the exhaust pipe and the intake pipe.
An EGR valve is installed in the passage, and the EGR valve is opened and closed by selectively introducing a constant negative pressure or a standby pressure to the working chamber of the EGR valve, and a throttle valve is provided in the intake pipe. Either a constant negative pressure or an atmospheric pressure is guided to the diaphragm device to open and close the intake throttle valve.

By controlling these EGR valve and intake throttle valve stepwise according to the three load ranges as shown in the table above, in the high load range where the EGR is cut, the output decreases when EGR is performed and a large amount of smoke is generated. In the middle load range where a small amount of EGR is performed and in the low load range where a relatively large amount of EGR is performed, the generation of NO _X Can be suppressed.

(Problems to be Solved by the Invention) Meanwhile, in order to reduce the combustion ignition delay and realize smooth combustion, a fuel injection control device that performs the combustion injection stepwise has an operation range (where the injection ends only with the initial lift). For example, the required EGR amount is different between an idling operation and a very low load operation) and an operation range in which injection is also performed by the main lift following the initial lift.

Nevertheless, when a large amount of EGR is performed uniformly in a low load region including these two operation regions in the conventional device, only a small injection amount is supplied, so that the operation region in which the injection is completed only by the initial lift is reduced. The amount of EGR is too large, and smoke, particulates, HC, etc. increase.

Therefore, the present invention appropriately controls the EGR amount in a low load region in accordance with an actual injection state such as whether injection is performed only by the initial lift or whether injection is also performed by the main lift, thereby improving exhaust characteristic. It is an object of the present invention to provide a fuel injection device for a diesel engine that has been improved.

(Means for Solving the Problems) As shown in FIG. 1, the present invention provides a fuel injection pump 51 driven by a cam rotating in synchronization with an engine to pump high-pressure fuel, and a needle corresponding to the pressure of the pumped fuel. In an exhaust gas recirculation control device for a direct injection diesel engine comprising an injection nozzle 52 that lifts stepwise in an initial stage and a main stage and injects fuel in multiple stages, and a device 53 that varies an EGR amount, a needle of the injection nozzle 52 is provided. Sensor 54 for detecting the lift amount of
Means 55 for determining whether the injection in the low load region is based on the initial lift only or based on the main lift based on the detected value, and based on the determination result only the initial lift A means 56 for setting the EGR amount to be small when the injection is performed, and increasing the EGR amount when the injection by the main lift is also performed; and the E so that the set EGR amount is obtained.
Means 57 for controlling the GR amount varying device 53 is provided.

If that is done also injected by the main lift (action) injection nozzle 52, the fuel gas temperature is the increasing NO _X increased, EGR amount is set larger by setting means 56, a large amount of EGR is When performed, the generation of NO _X is suppressed.

On the other hand, due to the characteristics of the multi-stage injection nozzle 52, when the injection ends only with the initial lift, only a small injection amount is supplied.

Also in this case, if a large amount of EGR is performed, smoke, particulates, HC, etc. increase, but in this case, when only a small injection amount is supplied, the setting means 56 By setting the EGR amount to a small value, it is possible to prevent an increase in smoke or the like and improve the exhaust characteristics.

(Embodiment) First, FIG. 2 shows an example of a fuel injection pump 1 which is a so-called row type fuel injection pump (see Japanese Patent Application Laid-Open No. 61-218769). Then, the fuel in the pressurizing chamber 13 is pumped to the fuel injection nozzle 20 through the fuel valve 14.

A control sleeve 15 is mounted around the plunger 12,
The start time of the fuel pumping is determined by the position of the sleeve 15. The sleeve 15 has a fuel chamber 16 into which fuel is fed and a pressurizing chamber
When the opening of the passage 17 is closed by the lower end of the sleeve 15 in the process of opening and closing the opening of the passage 17 provided in the plunger 12 communicating with the opening 13 toward the fuel chamber, and the plunger 12 rises, the fuel chamber The communication with the pressure chamber 16 is interrupted, and the pressure in the pressure chamber 13 starts to increase.

Further, when the port 17a branched from the passage 17 communicates with the communication port 15a provided in the middle of the sleeve 15 due to the rise of the plunger 12, the pressurizing chamber 13 communicates with the fuel chamber 16 again, and the fuel pumping ends. .

By moving the position of the sleeve 15 up and down by the position control mechanism 18, it is possible to advance or delay the fuel pumping start timing.

Further, since the branch port 17a is opened as an inclined groove around the plunger, by changing the rotation position of the plunger 12 around the axis by the rotation control mechanism 19,
The timing of communication with the passage 15a changes, and the timing of ending fuel pumping, that is, the fuel injection amount, can be changed.

Next, FIG. 3 shows an example of a fuel injection nozzle (disposed vertically in the center of the cylinder) 20 (see Japanese Patent Application Laid-Open No. Hei 1-1190460). A needle 22 is disposed inside a nozzle holder 21. The needle 22 has first and second springs.
The seat portion 25 is seated by 23 and 24.

When the pressure applied to the needle 22 is increased to a predetermined value or more by the fuel pressure from the fuel injection pump 10 introduced into the fuel pressure chamber 27, the first spring
While compressing 23, the needle 22 is lifted upward by a certain value (initial lift amount).

This is the initial injection and the fuel pressure is
This state is maintained until the set pressure of 24 is exceeded. Then, while compressing the second spring 24 via the spring seat 28, the needle 22 lifts greatly, and the main injection for supplying a large amount of fuel starts.

In this way, a gradual fuel injection is performed in which a small amount of fuel is injected during the initial lift (initial injection) period, and then a large amount of fuel is injected during the main lift (main injection) period.

To measure the actual lift amount of the needle 22, a needle lift sensor 29 is mounted on the upper part of the nozzle holder 21. For example, a magnetostrictive sensor or the like is used as the lift sensor 29. The lift sensor 29 is generated inside the magnetic material when the push rod 26 made of a magnetic material interlocked with the needle 22 approaches the magnetic field generated by the high-frequency coil of the measurement unit. The lift amount of the needle 22 is detected from a change in the inductance of the high-frequency coil that occurs according to a change in the eddy current or the magnetic permeability.

Next, an example of the EGR device is shown in FIG. 4. An EGR valve 34 is attached to an EGR passage 33 that communicates the exhaust pipe 31 and the intake pipe 32, and the valve 34 is connected to the vacuum pump 39 via a three-way valve 35. It is opened when a constant negative pressure is selectively introduced.

A butterfly type throttle valve 36 is mounted on the intake pipe 32 upstream of the EGR passage 33, and the duty control valve 38 controls the intake throttle valve in accordance with a control negative pressure guided to a diaphragm device 37 for driving the intake throttle valve. 36 is closed. That is,
The EGR amount increases as the closing angle of the intake throttle valve 36 increases, and the EGR amount can be changed steplessly by controlling the duty value to the control valve 38.

And, as a large amount of EGR is performed in the low load area,
By controlled by a controller 45 shown in FIG. 5, although reducing the NO _X lowers the combustion gas temperature,
Even in the low load range, such as when idling or very low load,
Since only a small amount of fuel is injected into the operation range where the injection is completed only by the initial lift, the EGR amount in that case is too large.

Therefore, in the present invention, when the injection is terminated only by the initial lift, the EGR amount is reduced in correspondence with the minute injection amount.

The controller 45 includes a CPU as an arithmetic unit, a ROM and a RAM as storage units, and a microcomputer including an I / O as an input / output unit.

In addition to the detection signal from the needle lift sensor 29, detection signals from an engine speed sensor 41, an accelerator opening sensor (engine load sensor) 42, and the like are input to the controller 45. A drive signal is output to a position control mechanism 18 of the sleeve 15 and a rotation control mechanism (injection amount adjustment mechanism) 19 of the plunger 12 so as to appropriately control the EGR amount, and the three-way valve 35 is turned ON and OFF.
And a duty signal to the control valve.

Here, the EGR control operation in the controller 45 will be described with reference to the flowchart of FIG.

First, in step 1, the engine speed Ne and the accelerator opening Ac
c, Read the needle lift data.

In step 2, it is checked whether the needle lift amount is larger than the initial lift amount (a predetermined value and a constant value). If it is larger, the injection by the main lift is performed (see FIG. 7 (A)). If the injection is completed only by the initial lift (see FIG. 7 (B))
Judgment is performed, and the EGR amount is set as follows according to the judgment result (steps 3 and 4).

As shown in FIG. 8, the EGR amount when the injection by the main lift is also performed is determined by the engine speed Ne and the accelerator opening.
Based on Acc, it is determined in four stages, and in the high load range, by cutting the EGR, it is possible to prevent the output reduction and the generation of a large amount of smoke when the EGR is performed, while on the other hand, in the low load range By increasing the amount of EGR, it is possible to reduce the combustion temperature while suppressing the
_X generation can be suppressed.

On the other hand, when the injection is terminated only by the initial lift, the EGR amount is set to a small value on the assumption that only a small injection amount is supplied (step 4). When the operating range in which the small value is set is superimposed on the mac of FIG. 8, as shown in FIG. 9, the low load range in which the EGR amount is large includes a region in which the EGR amount is small (shaded line). Part) is newly generated.

In other words, in the hatched portion, only a small injection amount is supplied due to the characteristics of the multi-stage injection nozzle.Therefore, since the combustion gas temperature does not rise, only a small amount of NO _X is generated, and the required EGR amount is small. Is enough.

In this way, the actual fuel injection state (whether the injection is performed only by the initial lift or the injection by the main lift is also performed) and the EGR amount is finely adjusted according to the injection state (combustion state). , It is possible to prevent the increase in smoke, particulates, HC, and the like caused by performing a large amount of EGR for a small injection amount, thereby improving the exhaust characteristics.

In step 5, the set EGR amount is stored at a predetermined address, and a series of routines ends.

In the above-described needle lift sensor, if a piezoelectric element is provided below the spring seat 28 in FIG. 3, the spring sheet 28 is separated from the piezoelectric element by the main lift, and is urged against the piezoelectric element. Since the spring force disappears, the output voltage from the piezoelectric element changes. Whether or not the main lift is also performed may be determined from this voltage change.

(Effects of the Invention) In the present invention, it is determined whether the injection is performed only by the initial lift of the fuel injection nozzle or the injection is also performed by the main lift. In addition, when the injection by the main lift is also performed, the configuration is to increase the EGR amount, so that it is possible to prevent the mismatch between the injection state and the EGR amount at idle or at a very low load, etc., and improve the exhaust characteristics Can be.

[Brief description of the drawings]

FIG. 1 is a view corresponding to claims of the present invention, FIG. 2 is a sectional view of a fuel injection pump showing one embodiment, FIG. 3 is a sectional view of a fuel injection nozzle, FIG. FIG. 6 is a block diagram of the controller, FIG. 6 is a flowchart of the same control operation, FIGS. 7 (A) and 7 (B) are output characteristic diagrams of the lift sensor, FIG. 8 is a map characteristic diagram of the EGR amount, 9
The figure is a characteristic diagram for explaining the operation of the embodiment. 10 ... fuel injection pump, 18 ... sleeve position control mechanism,
19 …… Plunger rotation control mechanism (injection amount adjustment mechanism), 20
…… Fuel injection nozzle, 29 …… Needle lift sensor, 31
... exhaust pipe, 32 ... intake pipe, 33 ... EGR passage, 34 ... EGR
Valve, 35 ... three-way valve, 36 ... intake throttle valve, 37 ... diaphragm device, 38 ... duty control valve, 41 ... engine speed sensor, 42 ... accelerator opening sensor (engine load sensor), 45 ……controller.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 25/07 550 F02M 25/07 550K 550R 570 570G

Claims (1)

(57) [Claims] 1. A fuel injection pump driven by a cam which rotates synchronously with an engine to pump high-pressure fuel, and an injection in which a needle is lifted stepwise in an initial stage and a main stage according to the pressure of the pumped fuel to inject fuel in multiple stages. In an exhaust gas recirculation control device for a direct injection diesel engine including a nozzle and a device that varies an EGR amount, a sensor that detects a lift amount of a needle of the injection nozzle, and a sensor in a low load range based on the detected value. Means for determining whether the injection is due to the initial lift alone or to the main lift.If the determination is based on the result of the initial lift only, the EGR amount is reduced. Means for setting each of the EGR amounts to a large value when injection by a lift is also performed; and the EGR amount variable device so as to achieve the set EGR amount. Exhaust gas recirculation control apparatus for a direct injection diesel engine, characterized in that a means for controlling.