JP2002195081A - Pressure-reducing control method of common rail pressure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent pressure undershoot, when an engine speed sinks to idle speed. SOLUTION: This pressure reduction control method of common rail pressure is a method of controlling the common rail pressure, by making a feedback process by adding at least an integral term to basic common rail pressure, and controlling so as to reduce the common rail pressure according to reduction in the engine speed. When a prescribed condition is realized, when the engine speed reduces to the vicinity of an idle speed Nei, another idle integral term different from normal times is used, and a value of the idle integral term is set to a value smaller to a side more negative than the value of the normal time integral term. The prescribed condition is desirable, when the engine speed becomes a prescribed idle determining engine speed Neij, and the difference between actual common rail pressure and target common rail pressure becomes a prescribed value ΔPj or larger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail pressure reduction control method, and more particularly to a common rail pressure reduction control method capable of improving idle characteristics of a common rail type diesel engine.

[0002]

2. Description of the Related Art Common rail type diesel engines usually perform feedback control of common rail pressure. In this case, at each predetermined control timing, a proportional term (hereinafter also referred to as P term) and an integral term (hereinafter also referred to as I term) are added to the basic common rail pressure to calculate the next common rail pressure, and the actual common rail pressure is sequentially calculated. While correcting the pressure, it approaches the target common rail pressure.

[0003]

When the engine speed drops to the idle speed, the target common rail pressure also decreases, but control cannot keep up with a certain speed, and the actual common rail pressure exceeds the target common rail pressure. Become like The I term also takes a negative value in order to follow this, and controls so as to decrease the actual common rail pressure steadily.

However, when the engine speed reaches the idle speed, the value of the term I is too small, and it is difficult to return the actual common rail pressure to the target common rail pressure corresponding to the idle speed. There is a problem that undershoot occurs. In this case, the fuel injection is affected, and a problem occurs that the engine speed does not easily settle to the idle speed.

[0005]

SUMMARY OF THE INVENTION A common rail pressure reduction control method according to the present invention feedback-controls a common rail pressure by adding at least an integral term to a basic common rail pressure, and controls a common rail pressure in response to a decrease in engine speed. In the method of controlling the pressure reduction, when the engine speed falls near the idle speed, if a predetermined condition is satisfied, another idle integral term different from the normal time is used, and the value of the idle integral term is set to the normal value. This is a value that is smaller on the negative side than the value of the integral term at the time.

Here, the predetermined condition is that the engine speed is equal to or lower than a predetermined idle determination engine speed, and a difference between an actual common rail pressure and a target common rail pressure is equal to or higher than a predetermined value. Is preferred.

After the idle integral term is used, it is preferable to use the normal integral term when another predetermined condition is satisfied.

It is preferable that the another predetermined condition is that a difference between the actual common rail pressure and the target common rail pressure is continuously lower than a predetermined value for a predetermined number of control times.

[0009]

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

The engine in this embodiment is a well-known common rail type diesel engine. The configuration is shown in FIG.
Shown in In the engine 1, fuel is injected from the injector 2 for each cylinder, and the fuel is stored in the common rail 3 under high pressure. Fuel is pumped from the supply pump 4 to the common rail 3, and the pressure control valve 5 is appropriately switched between a pressure feed side and a leak side by an electronic control unit (hereinafter referred to as an ECU) 6 to control the common rail pressure. The common rail pressure is detected by a common rail pressure sensor 7 and feedback-controlled to an optimum value by the ECU 6. The ECU 6 controls fuel injection, and controls the fuel injection amount and the like by controlling the energization time of the injector 2 and the like. The ECU 6 includes a common rail pressure sensor 7
Accelerator opening sensor other than the engine rotation sensor 8 and
Various information relating to the operating state is detected through various sensors such as a water temperature sensor and an atmospheric temperature sensor.

Here, in this fuel injection control device, means for positively reducing the common rail pressure is not particularly provided. The supply pump 4 is driven in synchronism with the engine 1 to perform only the pumping of fuel, and the pumping amount is merely changed by switching the pressure control valve 5. In other words,
The time during which the pressure control valve 5 is switched to the pumping side is EC
Feedback control is performed by U6, and the common rail pressure is increased by an amount corresponding to this time. The control target of the common rail pressure feedback control is the pressure control valve 5.

Therefore, when viewed from the common rail 3 side, only pressure is applied by the supply pump 4 and the pressure control valve 5. Therefore, the reduction of the common rail pressure depends exclusively on the fuel injection from the injector 2 and the fuel leak. In the present embodiment, the supply pump 4 is synchronously driven at half the engine speed.

Now, a common rail pressure feedback control method will be described below. FIG. 4 shows a calculation map of the basic common rail pressure P0. As shown, the map is provided in the form of a three-dimensional map, and is stored in the ECU 6 in advance. With this map, the basic common rail pressure P0 is uniquely determined from the engine speed Ne and the fuel injection amount Q. The lower the engine speed Ne and the lower the fuel injection amount Q, the lower the basic common rail pressure P0 in many cases.
The value of the basic common rail pressure P0 becomes the value of the target common rail pressure Pt as it is. Since both the engine speed Ne and the fuel injection amount Q are low in the idling region, the basic common rail pressure P0 often takes the lowest value (about 30 MPa). The engine idle speed Nei
Is 440 rpm in the present embodiment, and the fuel injection amount is uniquely determined mainly from the engine speed and the accelerator opening according to another map.

In practice, the actual common rail pressure PN is changed to the target common rail pressure P
Often does not match t. Therefore, the proportional term (P term) PP and the integral term (I term) PI are added to the basic common rail pressure P0, and the common rail pressure is corrected so that the actual common rail pressure PN approaches the target common rail pressure Pt. The feedback control is performed at every predetermined control timing, and based on the current value, the common rail pressure Pn as the final value to be controlled next time is calculated by Pn = P0 + PP + PI. In the present embodiment, feedback control is performed for each predetermined engine crank phase (ex. 120 ° CA).

The P term is a value stored in the ECU 6 as shown in FIG.
Obtained from the dimensional map. That is, the value PP of the P term is uniquely determined based on the difference between the actual common rail pressure PN and the target common rail pressure Pt, more precisely, the difference ΔP when the target common rail pressure Pt is subtracted from the actual common rail pressure PN. Determined. PP is 0 when ΔP is around 0,
From here, the value decreases as ΔP increases (that is, increases to the minus side), and conversely, the value increases as ΔP decreases (that is, increases to the plus side). The P term PP has a role to change the inclination of the increase and decrease of the common rail pressure, and takes a new value every control timing.

The term I is a value stored in the ECU 6 as shown in FIG.
Obtained from the dimensional map. Note that FIG. 3 shows two types of maps together, and here, only the same conventional maps indicated by solid lines will be described for convenience. Similarly to the P term, the value PI of the I term is uniquely determined based on ΔP. PI is a so-called zero cross, and is 0 only when ΔP is 0.
From here, the value decreases as ΔP increases (that is, increases to the minus side), and conversely, the value increases as ΔP decreases (that is, increases to the plus side).

The I term PI serves to converge the actual common rail pressure PN to the target common rail pressure Pt when the actual common rail pressure PN reaches the target common rail pressure Pt. This will be described later. Then, a new value is obtained for each control timing, but is added each time.

FIG. 1 shows how the common rail pressure P changes when the engine speed falls to the idle speed Nei. For example, when the engine speed drops to the idle speed Nei in an idle (free accelerator) or the like, the target common rail pressure Pt (shown by a broken line) drops accordingly. Then, the actual common rail pressure PN falls so as to follow this.

Conventionally, as shown by the solid line, even if the actual common rail pressure PN reaches the target common rail pressure Pti at the time of the idling rotation speed Nei, the value goes too far,
As shown by x1, a noticeable undershoot occurred. The reason is as follows.

That is, for example, when the engine speed falls to the idling speed relatively suddenly, as in the case of an idle blow, the manner in which the target common rail pressure drops sharply. Therefore, the actual common rail pressure must be sharply reduced. On the other hand, since the control is performed for each predetermined engine crank phase, the lower the rotation, the longer the control time interval becomes, and the control cannot keep up. Further, as described above, there is no positive means for lowering the common rail pressure, and it is necessary to rely exclusively on the fuel consumption by the injector 2. However, as the rotation decreases, the fuel injection amount decreases, and the common rail pressure hardly decreases. Therefore, in the control, the pressure difference ΔP increases more and more toward the positive side, and the value of the I term PI increases more and more toward the negative side as shown by the solid line in FIG. In other words, the control is in a direction to reduce the amount of pressure feed from the supply pump 4 side.

On the other hand, at the moment when the actual common rail pressure PN reaches the idling target common rail pressure Pti, it must be controlled so as to maintain the same value. However, at this time, since the value of the I term PI has already become a large negative value, it cannot easily return to 0 or a positive value, and the actual common rail pressure PN falls below the idling target common rail pressure Pti. For this reason, a large undershoot occurs.

As described above, since the actual common rail pressure PN is much lower than the target value, the pressure difference ΔP becomes large on the minus side, and the value of the I term PI takes a large plus value as shown by the solid line in FIG. Therefore, the control immediately returns to the idling-time target common rail pressure Pti, and excessively goes to the pressure plus side as indicated by x2. In this way, pressure hunting will occur.

[0023] Such undershoot and hunting of the common rail pressure also affects the fuel injection, causing the amount of fuel injection to vary, and causing undershoot and hunting of engine rotation.

Therefore, the present invention employs the following pressure reduction control method. That is, when the engine speed is the idle speed Ne
When the value falls to i, if a predetermined condition is satisfied, another idle integration term different from the normal time is used, and the value of the idle integration term is set to a value smaller on the minus side than the value of the integration term in the normal time.

This is specifically described as follows.
First, the predetermined condition is that, as shown in FIG. 1, the engine speed is equal to or lower than a predetermined idle determination engine speed Neij and the pressure difference ΔP between the actual common rail pressure and the target common rail pressure is equal to or higher than a predetermined value ΔPj. It is becoming. In the present embodiment, Neij = 1500 rpm and ΔPj = 9 MPa.

Next, the idle integral term (idle I term) is substantially the value shown by the dashed line in FIG. 3, and here is a negative value close to zero. That is, in FIG. 3, in addition to the normal I term indicated by the solid line, an idle I term used under the above-mentioned predetermined condition is also shown. The idle I term is Δ
The same value as in the normal state when P ≦ 0, and 0 when ΔP> 0
It is a negative value close to. However, when ΔP> 0, a larger value may be taken on the minus side as shown by the broken line.
As shown in the drawing, when ΔP> 0, the idle I term takes a smaller value on the minus side than the normal I term. However, depending on the situation, it is possible to take a positive value. The normal term I and the idle I term are stored in the ECU 6 in separate maps.

Of the idle I term, the portion having ΔP> 0 is substantially meaningful. This is because ΔP> before the engine speed reaches the idle speed Nei (particularly immediately before).
Because it is 0.

According to this, as shown in FIG. 1, at time 1 when the predetermined condition is satisfied, the map of the I term is switched, and the idle I term is selected. Then, the value of the term I decreases to the negative side, so that the value of the final common rail pressure Pn at each control timing becomes larger than in the past, and the way the actual common rail pressure PN drops becomes slower as shown by the dashed line in the figure.

However, the actual common rail pressure P
When N reaches the target common rail pressure Pti, the I term P
The value of I is not so negative. Therefore, whether the undershoot can be kept small as shown
Alternatively, it can be substantially zero, and can immediately return to or maintain the target pressure Pti.

Further, even if an undershoot occurs, the value of the idle I term takes a large value on the plus side as in the conventional case when ΔP ≦ 0, so that it is possible to immediately return to the target pressure Pti. Also, since ΔP returns from a small negative value, there is almost no excess to the positive pressure side, and pressure hunting is prevented.

As described above, since undershoot or hunting of the common rail pressure does not occur, variation in the fuel injection amount is also prevented, and the engine speed can be immediately settled at the idle speed Nei without undershoot or hunting.

Here, if the value of the idle I term is kept low, normal control may be hindered. Therefore, it is necessary to return to the normal term I. The condition at this time is that the pressure difference ΔP has become equal to or less than a predetermined value continuously for a predetermined number of times of control. In the present embodiment, the condition is that the pressure difference ΔP is equal to or less than 4 MPa continuously for 40 control times.

According to an actual machine test conducted by the inventor, the pressure undershoot was 8 MPa in the past, but was improved to 2 MPa in the present embodiment. Thereby, the effect of the present invention was confirmed.

It is to be noted that a so-called idle control is known as a prior art. In this method, the injector is instantaneously energized without lifting the needle valve within the range of elastic deformation of the needle valve of the injector, causing a fuel leak, thereby positively reducing the common rail pressure. But,
According to the test of the inventor, even under this control, the pressure reduction could not catch up, and a pressure undershoot occurred. There is also a method of separately providing a pressure reduction control valve, but a maximum of 120 Mpa
Since it must be able to withstand the above high pressure,
It is too expensive and cannot be adopted. The present invention can be dealt with only by changing the control software without causing such an increase in cost.

The embodiments of the present invention are not limited to those described above. For example, the present invention can be applied to a system that does not use the P term in the calculation of the final common rail pressure. Also, the present invention is applicable not only when the engine speed falls to the idle speed,
The present invention is also applicable to a case where the rotation speed drops to a low rotation speed in the vicinity.

[0036]

In summary, according to the present invention, the following excellent effects are exhibited. (1) It is possible to prevent undershoot of the common rail pressure when the engine speed falls to the idle speed. (2) As a result, variation in the fuel injection amount can be prevented, and the engine speed can be quickly settled at the idle speed.

[Brief description of the drawings]

FIG. 1 is a time chart showing a pressure reduction control method according to the present invention.

FIG. 2 is a calculation map of a P term.

FIG. 3 shows two types of maps in the calculation map of item I.

FIG. 4 is a calculation map of a basic common rail pressure.

FIG. 5 is a configuration diagram showing an engine of the embodiment.

[Explanation of symbols]

 1 engine 3 common rail 6 electronic control unit (ECU) Ne engine rotation speed Nei idle rotation speed Neij idle determination rotation speed P0 basic common rail pressure PI integral term (I term) PN actual common rail pressure Pt target common rail pressure Pti idle target common rail pressure ΔP Pressure difference ΔPj Predetermined value

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 55/02 350 F02M 55/02 350E F-term (Reference) 3G066 AA07 AB02 AC01 AC09 AD12 BA19 BA21 CB07U CB15 CD26 CE21 DA01 DA06 DC04 DC09 DC13 DC14 DC18 3G301 HA02 HA06 JA03 JA12 KA18 LB06 LB11 LC01 MA11 MA28 NA03 NA04 ND05 ND07 PA10Z PB03A PB03Z PB08A PB08Z PE01Z PE08Z PF03Z

Claims (4)

[Claims] 1. A method for feedback-controlling a common rail pressure by adding at least an integral term to a basic common rail pressure and for reducing a common rail pressure in response to a decrease in an engine speed, wherein the engine speed is an idle speed. When falling near the number, when a predetermined condition is satisfied, another idle integration term different from the normal time is used, and the value of the idle integration term is set to a value smaller on the minus side than the value of the normal integration term. Characteristic reduction method of common rail pressure. 2. The predetermined condition is that the engine speed is equal to or lower than a predetermined idle determination speed and a difference between an actual common rail pressure and a target common rail pressure is equal to or higher than a predetermined value. Item 4. The method for controlling pressure reduction of a common rail pressure according to Item 1. 3. The common rail pressure reduction control method according to claim 1, wherein the normal integration term is used when another predetermined condition is satisfied after using the idle integration term. 4. The common rail pressure reduction according to claim 3, wherein said another predetermined condition is that a difference between an actual common rail pressure and a target common rail pressure is continuously lower than a predetermined value for a predetermined number of control times. Control method.