JP2002097985A - Control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of white fumes caused by the increase of the injection for controlling idling speed when the combustion is unstable just after the cold start. SOLUTION: When the rotational frequency Ne exceeds the start judging rotational frequency Nstart (Step 2) and if the opening of an accelerator Acc is smaller than the judging opening of the accelerator Acc0 (Step 3), the quantity of correction of the injection ΔQ is calculated based on the deviation ΔN between a target frequency of idling rotation Nidle and the actual rotational frequency Ne and the idling speed is controlled by increasing/decreasing the injection quantity (Steps 8 and 9). Within a prescribed period of time TMW (Step 10), the maximum value of the correction quantity Dqmax is calculated according to the engine water temperature, and restrictions are placed so that larger correction should not be made (Steps 12-14). Therefore, the increase of unburned HC due to the increase of excessive injection as well as the deterioration of white fumes can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a diesel engine control device that maintains a predetermined idle speed by correcting increase or decrease of a fuel injection amount during idling.

[0002]

2. Description of the Related Art In general, in a diesel engine control device, a start mode is defined as a period from cranking by a starter motor to an engine speed reaching a predetermined value. The target fuel injection amount is set using a map corresponding to the engine temperature and the engine temperature (water temperature). When the engine speed reaches a predetermined value after the engine is started, it is determined that the engine is in the normal operation mode, and it is further determined whether or not the engine is in the idle operation mode according to the accelerator opening and the like. ing. Then, when in the idle operation mode, the target idle speed is set from the engine temperature, the battery voltage, and the like,
The fuel injection amount is feedback-controlled so that the engine speed detected by the engine speed sensor matches the target idle speed.

[0003] When the engine is started in a state where the engine temperature is extremely low, immediately after shifting from the start mode to the idle operation mode, the combustion is unstable due to the low combustion chamber temperature and the lubricating oil temperature is low. Therefore, since the friction is large, various problems are likely to occur. Therefore, various inventions have been made regarding control of the fuel injection amount, the injection timing, and the like during this period.

[0004] As one of them, in recent years, as a fuel injection mode of a diesel engine, pilot injection for injecting a small amount of fuel prior to main injection has been generally performed. This is to improve the ignitability and improve the combustion by performing the main injection with a small amount of the fuel of the pilot injection burned under conditions where the ignitability of the fuel is low, such as at low engine load and low temperature. Things. Further, recently, a so-called multi-stage pilot injection mode in which the pilot injection is divided into two or more stages has been proposed.

As a method of switching between several fuel injection modes according to the engine operating state, for example, Japanese Patent Application Laid-Open No. 2000-97077 discloses a method of switching the injection mode according to the fuel injection amount in the idle operation mode. Proposed. This focuses on the fact that when the friction torque decreases as the warm-up progresses, the fuel injection amount required to maintain the target idle speed decreases. This will be described below with reference to FIG. explain.

FIG. 1 schematically shows changes in the engine speed, fuel injection amount, and white smoke concentration when the engine is started from a low temperature state. At this low temperature, the engine is operated in a multistage pilot injection mode. Is started. After the fuel injection amount is shifted to the idle control mode, feedback control is performed so that the engine speed matches the target idle speed. Accompanying it, it gradually decreases. Therefore, in the idle control mode, when the fuel injection amount becomes lower than the predetermined reference value 1, it is considered that the warm-up is completed, and the mode is switched from the multi-stage pilot injection mode to the normal pilot injection mode. If the injection mode is switched too early, combustion may become unstable after the switching, but in this case, the fuel injection amount required to maintain the target idle speed increases, When the amount exceeds the reference value 2, it is determined that the combustion state has deteriorated, and the mode is switched again from the pilot injection mode to the multi-stage pilot injection mode. As a result, an attempt is made to set an optimal fuel injection mode according to the friction and combustion state of the engine.

[0007]

For example, for the period A in FIG.
In this case, the actual engine speed is lower than the target idle speed, and the fuel injection amount is increased and corrected by feedback control. However, when the combustion state is unstable immediately after the start, as in period D in FIG.
When the fuel injection amount is increased with a decrease in the engine speed, the unburned HC also increases.
There is a problem that white smoke is emitted.

Further, in the above-mentioned conventional technique, the period B shown in FIG.
The normal pilot injection mode, which is less ignitable than the multi-stage pilot injection mode, is continued until the fuel injection amount once falls below the reference value 1 and then starts increasing again and exceeds the reference value 2. Therefore, there is a problem that when the fuel injection amount increases, the emission of white smoke is more likely to occur due to an increase in unburned fuel.

[0009]

According to a first aspect of the present invention, there is provided a diesel engine control device for idling-time injection amount correction means for increasing or decreasing the fuel injection amount so that the engine speed becomes a predetermined idle speed during idling. A warm-up state determining means for determining a warm-up state of the engine; and an increase in the fuel injection amount by the idle-time injection amount correcting means when the warm-up state determining means determines that the engine is being warmed up. And correction suppression means for suppressing the above.

According to a second aspect of the present invention, the correction suppressing means limits the increase amount of the fuel injection amount for each cycle to a predetermined upper limit value or less. I have.

In the invention according to claim 3, the idle injection amount correction means performs feedback control of the fuel injection amount by a plurality of control elements including an integral element.
The correction suppressing means limits the correction amount in the idling injection amount correcting means to only the integral element.

That is, when the engine is being warmed up, when it becomes necessary to increase the fuel injection amount to maintain the target idle speed due to some disturbance or the like, the increase amount becomes relatively small. Is suppressed. As a result, an increase in unburned HC and an increase in white smoke are avoided. Note that, for example, even if the increase in the fuel injection amount is suppressed in the period B in FIG. 1, the state in which the engine speed is lower than the target idle speed continues for a while, but the target idle speed is reduced due to a decrease in engine friction. Since the fuel injection amount required to maintain the fuel pressure decreases, the fuel injection amount gradually converges to the target idle speed.

According to the second aspect of the present invention, the amount of increase in each cycle, that is, the rate of increase of the fuel injection amount, is regulated to a certain value or less.

According to a third aspect of the present invention, PI control or PDI control including an integral element as a control element is premised. When the engine is being warmed up, feedback control is performed with a correction amount of only the integral element. Therefore, the fuel injection amount changes slowly.

According to a fourth aspect of the present invention, there is provided a diesel engine control device, wherein the pilot injection means for separately injecting fuel into a main injection and a pilot injection preceding the main injection, and the warm-up state judging means determine that the engine is in a warm-up operation. And a pilot injection amount correcting means for relatively increasing the injection amount of the pilot injection when it is determined that there is a pilot injection amount.

When the pilot injection is performed as described above, generally, the total injection amount of the pilot injection and the main injection is increased / decreased for idle speed control. However, only the injection amount of the main injection is increased / decreased. Is also possible.
When the engine is warming up, the increase is limited by the correction suppressing means so that the increase is relatively small. Particularly, in the present invention, the injection amount of the pilot injection, which is a part of the total injection amount, is relatively increased. As a result, the ratio of the injection amount of the main injection to the total injection amount decreases. Since the pilot injection enhances the ignitability of the fuel of the main injection to be subsequently injected and contributes to prevention of white smoke, even if the injection amount of the pilot injection increases during the warm-up operation, White smoke does not increase. In particular, a state in which the engine speed is lower than the target idle speed irrespective of the auxiliary equipment load or the like (for example, period A in FIG. 1) is a state in which combustion generally deteriorates and a required engine torque is not obtained. By increasing the pilot injection amount, an effect of activating the combustion of the main injection can be obtained, and the engine speed can be made to follow the target idle speed without inducing the emission of white smoke due to the increase of the excess fuel.

The invention according to a fifth aspect of the present invention is characterized in that the number of pilot injections is increased to a large number as the pilot injection amount increases. For example, when the injection amount of the pilot injection is small, the pilot injection is performed once, and as the injection amount of the pilot injection increases, the pilot injection is performed in two or three times in multiple stages. By dividing the pilot injection into a large number of times, the ignitability at low temperatures is further improved.

According to the sixth aspect of the invention, the fuel injection amount is suppressed from increasing by the correction suppressing means until the predetermined time elapses after the engine is shifted from the start control state to the idle control state. I have. That is, while the combustion is relatively unstable, an excessive increase in the fuel injection amount is avoided.

In the invention according to claim 7, the increase of the fuel injection amount is suppressed by the correction suppressing means on condition that the fuel injection amount is equal to or more than a predetermined value. If the fuel injection amount itself is small, white smoke does not increase even if the fuel injection amount is increased to some extent.

[0020]

According to the present invention, when the engine temperature is low, emission of white smoke due to excessive fuel injection accompanying idle speed control can be suppressed.

In particular, according to the third aspect of the present invention, the feedback correction of the fuel injection amount is performed by limiting only the integral element, so that the fuel injection amount largely changes by the idle speed control immediately after starting. As a result, it is not necessary to increase the fuel injection amount more than necessary, so that the emission of white smoke can be suppressed.

According to the invention of claim 4, when the combustion is unstable, the injection amount of the pilot injection is increased,
Combustion of the main injection can be activated, and the engine speed can be made to follow the target idle speed without causing the emission of white smoke due to an increase in excess fuel.
Further, by using multi-stage pilot injection as in the invention of claim 5, unburned HC that causes white smoke is further suppressed.

According to the sixth aspect of the present invention, the control can be effectively performed immediately after the start, during a period in which the combustion chamber temperature is not sufficiently increased and the combustion is likely to be unstable.

According to the seventh aspect of the present invention, the control can be effectively performed until the engine friction decreases.

[0025]

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows a mechanical configuration of a control device of the diesel engine 1 according to the present invention. The engine 1 includes a common rail type fuel injection system, and includes a high pressure supply pump 2 and a high pressure supply pump 2. The fuel injection is turned ON-O by the common rail, that is, the pressure accumulation chamber 3 and the internal solenoid valve.
And an injector 4 for each cylinder for FF. Further, a crank angle sensor 6 using a toothed disk 5 is provided to detect the rotation speed and the crank angle of the engine 1. The fuel pressure in the accumulator 3 is determined by a pressure sensor 7
And is controlled via the pressure regulator 8 to a target value corresponding to the operating condition determined by the control unit 20. Signals of the crank angle sensor 6, an accelerator opening sensor 21 that outputs a signal corresponding to the accelerator opening, and a water temperature sensor 22 that detects an engine cooling water temperature are input to the control unit 20. The target injection amount is calculated based on the target injection amount. Further, the control unit 20
The valve opening time of the solenoid valve of the injector 4 is calculated according to the target injection amount and the pressure of the accumulator, and fuel injection is performed at a predetermined timing. The engine 1 includes a turbocharger 13, and an EGR tube 11 that communicates the intake passage 9 and the exhaust passage 10 is provided with an EGR valve 12 that controls an exhaust gas recirculation amount.

Next, the control flow in the first embodiment will be described with reference to the flowchart shown in FIG.

First, in step 1, the engine speed Ne, the accelerator opening Acc, and the engine coolant temperature Tw are read based on the detection signals of the respective sensors.

In step 2, the engine speed Ne is compared with a predetermined start determination speed Nstart. If the engine speed Ne is equal to or lower than the start determination rotation speed Nstart, it is determined that the engine is in the start mode, and the target injection amount for starting is set in step S4. This starting injection amount is
Usually, it is obtained from the engine speed Ne and the water temperature Tw.

The engine rotation speed Ne is equal to the start determination rotation speed Ns.
If it is greater than start, it is determined that the start has been completed, and the routine proceeds to step 5, where the accelerator opening Acc is compared with a predetermined idling determination opening Acc0.

The accelerator opening Acc is the idling opening A
If it is equal to or greater than cc0, it is determined that the engine is not idling, and the routine proceeds to step 6, where the engine speed Ne and the accelerator opening Ac are set.
The target injection amount is set according to c. That is, in the non-idle state, the fuel injection amount is basically controlled according to the load.

On the other hand, when the accelerator opening Acc is smaller than the idling determination opening Acc0, it is determined that the engine is idling, and idle speed control is performed by increasing or decreasing the fuel injection amount. Specifically, the process proceeds to step 7, and the engine target water temperature Tw is used to set the target idle speed Nidle from the table in FIG. 4 and the elapsed time threshold T from the table in FIG.
The MW and the injection amount threshold value QW are obtained from the table of FIG.

Next, at step 8, the deviation ΔN between the target idle speed Nidle and the actual engine speed Ne is calculated.
(ΔN = Nidle−Ne) is obtained, and in the next step 9, the correction amount ΔQ of the fuel injection amount is obtained from the characteristic map shown in FIG. 8 according to the deviation ΔN.

Next, in step 10, it is determined whether or not the elapsed time TMR at that time has reached the elapsed time threshold value TMW. The elapsed time TMR indicates the elapsed time after the shift from the start mode to the idle operation mode, as described later. In step 11, it is determined whether or not the fuel injection amount Qold of the previous cycle is equal to or more than the injection amount threshold value QW. The elapsed time TMR is equal to the elapsed time threshold TMW
And the fuel injection amount Qold is less than the injection amount threshold Q
If it is equal to or more than W, the process proceeds to step 12, and the injection amount correction amount upper limit value DQma is calculated from the table of FIG.
Find x. Then, in step 13, the injection amount correction amount ΔQ is limited by the upper limit value DQmax. Specifically, the smaller one of the correction amount ΔQ and the upper limit DQmax obtained from the map of FIG. 8 is set as the correction amount ΔQ.

On the other hand, when the elapsed time TMR is equal to or greater than the elapsed time threshold value TMW, or when the fuel injection amount Qold is less than the injection amount threshold amount QW, the process proceeds to step 14 without limiting the correction amount ΔQ. move on.

In step 14, a new fuel injection amount Qnew is set by adding the injection amount correction amount ΔQ to the fuel injection amount Qold in the previous cycle. This fuel injection amount Qnew
, The fuel injection is executed by another routine (not shown).

Finally, at step 15, the time interval ΔT for executing this control cycle is added to the value of the elapsed time TMR.

As described above, according to the first embodiment, under the condition that the combustion room temperature does not rise immediately after the engine is started and the engine friction is high, the correction for increasing the injection amount by the idle control is limited to a constant amount. Therefore, emission of white smoke due to injection of excess fuel can be suppressed.

Next, a second embodiment to which PID control is applied will be described with reference to the flowchart shown in FIG. Note that the system configuration of the second embodiment is not particularly different from the first embodiment of FIG. Hereinafter, the control flow will be described based on the flowchart of FIG.

Steps 1 to 8 in FIG.
The description is omitted because it is common to each step of the first embodiment in FIG.

In the second embodiment, the process proceeds from step 8 to step 20, and based on the PID control according to the rotational speed deviation ΔN, the proportional element Qp and the integral element Q
i and the differential element Qd are obtained.

FIG. 10 is a block diagram of the PID control shown as a discrete system.
It is obtained by multiplying N by a proportional gain Pgain. The integral element Qi is given as an integrated value obtained by multiplying the deviation ΔN by the integral gain Igain. The differential element Qd has a deviation Δ
It is obtained by multiplying the differential value of N by the differential gain Dgain. Note that “Z ⁻¹ ” in the figure is the previous calculated value. The above-mentioned proportional gain Pgain, integral gain Igain, and differential gain Dgain may be set to fixed constants, respectively, or may be set according to the rotational speed deviation ΔN or the engine water temperature. In PID control, the sum of these three is given as a correction amount.

Steps 10 and 11 following step 20 are the same as in the first embodiment, and the elapsed time TM
It is determined whether R has not reached the elapsed time threshold value TMW and whether the fuel injection amount Qold of the previous cycle is equal to or greater than the injection amount threshold value QW. When the elapsed time TMR is less than the elapsed time threshold value TMW and the fuel injection amount Qold is equal to or more than the injection amount threshold amount QW,
Proceeding to step 21, the proportional element Qp and the differential element Qd
Is set to 0.

On the other hand, when the elapsed time TMR is equal to or greater than the elapsed time threshold value TMW, or when the fuel injection amount Qold is less than the injection amount threshold amount QW, the proportional element Qp and the differential element Qd are not limited. Proceed to step 22.

Then, in step 22, the fuel injection amount Qnew is changed by the correction amount, ie, the proportional element Qp and the integral element Qp.
It is determined from the sum of i and the differential element Qd. Finally step 1
At 5, the elapsed time TMR is updated as described above.

According to the second embodiment, immediately after the start of the engine, under the condition that the combustion room temperature does not rise and the engine friction is high, the increase / decrease of the fuel injection amount for controlling the idling speed is determined only by the integral element. Since the operation is performed slowly, it is possible to suppress the emission of white smoke caused by an excessive increase or decrease in the fuel injection amount, as in the first embodiment.

Next, a third embodiment in which pilot injection is applied will be described with reference to the flowcharts of FIGS. The system configuration of the third embodiment is the same as that of the first embodiment shown in FIG.

The control of the third embodiment is the same as the control of the first embodiment shown in FIG. 3 except for the portion relating to the setting of the injection amount of the pilot injection. Therefore, only the different portions will be described below. I do. The steps having the same numbers as the respective steps in the first embodiment basically perform the same processing.

Steps 1 to 7 are the same as those in the first embodiment, except that in step 30 following step 7, the pilot injection is performed from the map shown in FIG. 13 using the engine speed Ne and the engine coolant temperature Tw. Set the amount.

Further, subsequent to step 13, the process of increasing the pilot injection amount shown in FIG. 12 is performed. That is,
Proceeding from step 13 to step 31, it is determined whether the engine speed Ne is lower than the target idle speed Nidle. If the engine speed Ne is lower than the target idle speed Nidle, in the next step 32, the speed deviation ΔN and the water temperature Tw are calculated. Is used to calculate the pilot injection amount increase value from the map of FIG. 14 and added to the pilot injection amount obtained in step 30. At the same time, the number of pilot injections is set based on the map of FIG. In FIG. 15, the number of divisions is two at the maximum. However, the number of divisions may be larger than the number of times. Can be prevented from deteriorating.

From step 32, step 1 in FIG.
4, the injection amount Qnew is obtained as described above.

Here, the new injection amount Qnew, the injection amount Qold of the previous cycle, and the injection amount threshold value QW are all treated as the total injection amount including both the pilot injection amount and the main injection amount. Although the correction amount ΔQ of the total injection amount is limited by the upper limit value DQmax, these values are treated as corresponding to only the injection amount of the main injection not including the pilot injection, and the main injection May be increased or decreased by the correction amount ΔQ, and the maximum value of the correction amount ΔQ may be limited by the upper limit value DQmax.

As described above, according to the third embodiment, when the engine speed falls below the target idle speed due to deterioration of combustion immediately after the engine is started and the combustion room temperature does not rise, excessive injection of the main injection is performed. At the same time, the pilot injection amount is increased, and this pilot injection is divided into a large number of times as necessary, so that ignitability is improved and combustion is improved, while suppressing an increase in white smoke. The engine speed can be increased toward the target idle speed.

The pilot injection control described in the third embodiment can be used in combination with the PID control in the second embodiment.

[Brief description of the drawings]

FIG. 1 is a time chart schematically showing a change in an engine speed or the like at the time of a low-temperature start according to a conventional technique.

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

FIG. 3 is a flowchart showing control contents of the first embodiment.

FIG. 4 is a characteristic diagram showing a relationship between an engine water temperature and a target idle speed.

FIG. 5 is a characteristic diagram showing a relationship between an engine water temperature and an elapsed time threshold.

FIG. 6 is a characteristic diagram showing a relationship between an engine water temperature and an injection amount threshold value.

FIG. 7 is a characteristic diagram showing a relationship between an engine water temperature and an injection amount correction amount upper limit value.

FIG. 8 is a characteristic diagram showing a relationship between a rotational speed deviation and an injection amount correction amount.

FIG. 9 is a flowchart showing control contents of a second embodiment.

FIG. 10 is a block diagram of PID control.

FIG. 11 is a flowchart showing control contents of a third embodiment.

FIG. 12 is a flowchart illustrating a part of a routine according to a third embodiment.

FIG. 13 is a characteristic diagram illustrating a relationship between a pilot injection amount with respect to an engine water temperature and an engine speed.

FIG. 14 is a characteristic diagram showing a relationship between a pilot injection amount increase value with respect to an engine water temperature and a rotation speed deviation.

FIG. 15 is a characteristic diagram showing the number of pilot injections.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 6 ... Crank angle sensor 20 ... Control unit 21 ... Accelerator opening sensor 22 ... Water temperature sensor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) PE08Z PF03Z

Claims (7)

[Claims] 1. An idling injection amount correcting means for increasing or decreasing a fuel injection amount so that an engine rotational speed becomes a predetermined idle rotational speed during idling; a warm-up state determining means for determining a warm-up state of the engine; Correction suppression means for suppressing an increase in the fuel injection amount by the idling injection amount correction means when the warm-up state determination means determines that the engine is being warmed up. Control unit for diesel engine. 2. The control device for a diesel engine according to claim 1, wherein the correction suppressing means limits an increase amount of the fuel injection amount in each cycle to a predetermined upper limit value or less. 3. The idling-time injection amount correction means performs feedback control of a fuel injection amount by a plurality of control elements including an integral element. The correction suppression means includes a correction amount in the idling-time injection amount correction means. 2. The control device for a diesel engine according to claim 1, wherein is limited to only the integral element. 4. A pilot injection means for separately injecting fuel into a main injection and a pilot injection preceding the main injection, and when the warm-up state determination means determines that the engine is being warmed up, the pilot injection The control device for a diesel engine according to any one of claims 1 to 3, further comprising: a pilot injection amount correction unit that relatively increases the injection amount. 5. The system according to claim 4, wherein the number of pilot injections is increased in accordance with an increase in the pilot injection amount.
2. The control device for a diesel engine according to claim 1. 6. The fuel injection amount is suppressed by the correction suppression means until a predetermined time elapses after a transition from an engine start control state to an idle control state. 6. The control device for a diesel engine according to any one of 5. 7. The diesel engine according to claim 1, wherein an increase in the fuel injection amount is suppressed by the correction suppressing means on condition that the fuel injection amount is equal to or more than a predetermined value. Control device.