JP2002371940A - Common rail type fuel injection control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the follow-up capability of a target common rail pressure to an actual common rail pressure in transition of a common rail pressure. SOLUTION: This common rail type fuel injection control device comprises a pressure reducing valve 9 connected to a common rail and reducing the common rail pressure by leaking fuel in the common rail. The pressure reducing valve 9 is operated when the actual common rail pressure is increased by a specified value or more over the target common rail pressure. Thus an overshoot caused when the pressure rises excessively can be prevented, and a pressure difference and an undershoot caused when a transient pressure lowers can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail type fuel injection control device applied to a diesel engine,
In particular, the present invention relates to a device with improved transient characteristics in common rail pressure control.

[0002]

2. Description of the Related Art Common rail type diesel engines usually perform feedback control of common rail pressure, especially PI control. In this case, at each predetermined control timing, a proportional term (hereinafter also referred to as a P term) and an integral term (hereinafter also referred to as an I term) with respect to a target common rail pressure (hereinafter also referred to as a target pressure).
Are calculated to determine the next common rail pressure, and the actual common rail pressure (hereinafter also referred to as actual pressure) is approached to the target common rail pressure while being sequentially corrected.

[0003]

However, during the transient pressure control, the same control constants (proportional term and integral term) as in the normal state are used, so that a difference between the target pressure and the actual pressure may occur during the transient pressure control. However, there is a problem that remarkable overshoot and undershoot occur.

That is, the target pressure is increased or decreased according to the engine operating state, for example, the accelerator opening. On the other hand, as shown in FIG. 7, when the accelerator opening is rapidly increased (I) after the accelerator opening becomes 0% and the target pressure is reduced (I), and thereafter the accelerator is kept constant (II), a relatively large overshoot is obtained. b occurs. If the accelerator opening is then sharply reduced thereafter (III), the decrease in the actual pressure cannot catch up with the decrease in the target pressure (actual pressure-target pressure> 0), causing a relatively large pressure difference c. After that, even if the accelerator opening is kept constant (IV), a relatively large undershoot d occurs. Due to the pressure difference c, the overshoot b, and the undershoot d, when the common rail pressure changes transiently, such as at the time of upshifting or at the time of a free accelerator (blanket), an unpleasant sensation or noise may occur. was there.

More specifically, for example, at the time of a transient pressure drop (III), since the actual pressure gradually exceeds the target pressure, the value of the term I also increases to the negative side, and the actual pressure decreases steadily. Control to be performed.

However, when the accelerator opening becomes steady (IV), the value of the term I has been cumulatively increased to a large negative value. It is difficult to return the actual pressure to the appropriate target pressure, and as a result, an undershoot d of the pressure occurs. For the same reason, overshoot b also occurs in the steady state (II) after the pressure transient rise (I).

However, the actual increase of the common rail pressure can be relatively easily performed by the supply pump, and the pressure difference during the transient pressure rise (I) and the overshoot b thereafter (II) need to be relatively small. . However, there is no means for positively reducing the actual common rail pressure, and the pressure reduction depends exclusively on fuel consumption by fuel injection from the injector and so-called idling control (switching leakage of a control valve without fuel injection) in the injector. I was However, there is a limit in fuel consumption due to fuel injection, and there is a problem in idling control that durability is reduced due to an increase in the number of times of operation of the injector control valve, an EDU burden is increased, and restrictions are associated therewith. Therefore, conventionally, it was difficult to reduce the actual common rail pressure to the target common rail pressure, and it was particularly difficult to eliminate the overshoot b and the pressure difference c.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to improve the followability of an actual common rail pressure to a target common rail pressure during a transition of the common rail pressure.

[0009]

A common rail type fuel injection control device according to the present invention is provided with a pressure reducing valve connected to the common rail and for reducing the common rail pressure by leaking fuel in the common rail.

[0010] Also, a common rail pressure detecting means for detecting an actual common rail pressure, a target common rail pressure determining means for determining a target common rail pressure based on an engine operating condition, and an actual common rail pressure corresponding to the target common rail pressure. It is preferable to further include common rail pressure control means for feedback-controlling the actual common rail pressure so as to approach, and pressure reducing valve control means for operating the pressure reducing valve when the actual common rail pressure becomes higher than the target common rail pressure by a predetermined value or more.

Further, the target common rail pressure determining means determines a target common rail pressure based on an engine speed and a fuel injection amount, and the common rail pressure controlling means determines an actual common rail pressure, a target common rail pressure and an actual common rail pressure. Preferably, a proportional term and an integral term are determined on the basis of the difference between the two, and the proportional term and the integral term are added to the target common rail pressure to obtain an actual common rail pressure to be controlled next time.

[0012]

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

FIG. 6 shows the overall configuration of a common rail fuel injection control device according to this embodiment. In the diesel engine 1, fuel is injected from the injector 2 for each cylinder, and the fuel is stored in the common rail 3 in a high pressure state. Fuel is pumped from the supply pump 4 to the common rail 3, and the pressure control valve 5 is appropriately switched between a pumping side and a leak side by an electronic control unit (hereinafter referred to as an ECU) 6 to control the fuel pressure supplied to the common rail 3. Is done. The actual common rail pressure is detected by a common rail pressure sensor 7 provided on the common rail 3 and is feedback-controlled 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 detects various types of information related to the operating state through various sensors such as a water temperature sensor and an atmospheric temperature sensor, in addition to the illustrated common rail pressure sensor 7, the engine rotation sensor 8, and the accelerator opening sensor 11.

The supply pump 4 is driven synchronously with the engine 1 at a rotation ratio of 1/2 to perform only fuel pumping. The supply pressure of the pumping fuel is controlled by a pressure control valve 5. The time during which the pressure control valve 5 is switched to the pressure feeding side is determined by the ECU 6.
, 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. From the common rail 3 side, only the pressure is applied by the supply pump 4 and the pressure control valve 5.

However, in this embodiment, the pressure reducing valve 9 is provided as a means for positively reducing the actual common rail pressure. The pressure reducing valve 9 is connected to the common rail 3,
During operation (open), the fuel in the common rail 3 is leaked directly to the fuel tank 10 to reduce the common rail pressure. As a matter of course, the leak from the common rail 3 is not performed when not operating (closed). The operation and non-operation of the pressure reducing valve 9 are switched by the ECU 6.

Next, a feedback control method of the common rail pressure will be described. 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. In many cases, the higher the engine speed Ne and the higher the fuel injection amount Q, the higher the basic common rail pressure P0. The value of the basic common rail pressure P0 becomes the value of the target common rail pressure Pt as it is. The fuel injection amount Q is uniquely determined mainly from the engine speed and the accelerator opening according to another map. Therefore, the target common rail pressure Pt is also a function of the accelerator opening.

In practice, the actual common rail pressure PN is reduced 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 target (basic) common rail pressure Pt (P0), and the actual common rail pressure PN is corrected to approach the target common rail pressure Pt. Such correction is the essential content of feedback control.
The feedback control is performed at every predetermined control timing,
Based on the current value, a common rail pressure Pn as a final value to be controlled next time is calculated by the equation Pn = P0 + PP + PI. In this embodiment, a 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 the value stored in the ECU 6 as shown in FIG.
Obtained from the dimensional map. The value PI of the I term is the same as the P term,
It is uniquely determined based on ΔP. PI is a so-called zero cross, and is 0 only when ΔP is 0. From this, there is a tendency that as ΔP increases, the value decreases (that is, increases toward the minus side), and conversely, as ΔP decreases, the value increases (that is, increases toward the plus side).

The I term PI functions 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. Then, a new value is obtained for each control timing, but is added each time.

Next, a method of controlling the pressure reducing valve 9 will be described with reference to a flowchart of FIG. 1 and a time chart of FIG.
The flow of FIG. 1 is repeatedly executed by the ECU 6 at each control timing. As in the case of FIG. 7, in the time chart of FIG. 5, for example, in the case of a free accelerator, the accelerator opening is rapidly increased from a low value (for example, 0 = idle) (I), and thereafter, is set to a constant value (II). This is an example of a case where the common rail pressure is lowered (III) and set to a constant value after the lowering (IV), that is, a case where the common rail pressure is raised and lowered transiently.

In the flow of FIG. 1, the first step 1
In step 01, the value of the actual common rail pressure PN detected by the common rail pressure sensor 7 is captured, and the value of the basic common rail pressure P0, that is, the value of the target common rail pressure Pt is captured according to the map shown in FIG. Next, the routine proceeds to step 102, where a pressure difference Pfd = PN-Pt between the actual common rail pressure PN and the target common rail pressure Pt is calculated. Next, in step 103, it is determined whether or not the pressure difference Pfd is equal to or greater than the pressure reducing valve operation upper threshold value Pdu. Here, the upper threshold value Pdu and the lower threshold value Pdd shown in step 106 are set in advance as the operation threshold value. Pdu> Pdd, and these two types of values are set to provide hysteresis.

When the pressure difference Pfd is equal to or larger than the threshold value Pdu,
Proceeding to step 104, the pressure reducing valve 9 is operated. This immediately reduces the common rail pressure. Thereafter, in step 105, the pressure reducing valve operation flag Flug is set (= 1), and the flow ends.

On the other hand, if the pressure difference Pfd is less than the threshold value Pdu in step 103, the routine proceeds to step 106, where it is determined whether or not the pressure difference Pfd is equal to or less than the pressure reducing valve operation lower threshold value Pdd. Step 108 if the pressure difference Pfd is equal to or less than the threshold value Pdd.
To deactivate the pressure reducing valve 9 and to operate the pressure reducing valve operation flag
Is reset (= 0), and this flow ends. Note that the initial value of this flag is 0.

In step 106, if the pressure difference Pfd is larger than the lower threshold value Pdd, the routine proceeds to step 107, where it is determined whether or not the pressure reducing valve operation flag Flug is 1. If it is 1, the process proceeds to step 104, and if it is 0, the process proceeds to step 108.

According to this, as shown in FIG. 5, when the pressure shifts from the transient rise (I) to the steady state (II), an overshoot occurs. Since the actual pressure is delayed with respect to the target pressure during the transient rise, the I term PI is cumulatively increased to the positive side (see FIG. 2). Therefore, even if the target pressure shifts to the steady state during the steady state, the actual pressure cannot immediately follow. Because. However, during the transient rise, the supply pump 4 can replenish the common rail pressure with high response, so that the delay of the actual pressure PN with respect to the target pressure Pt is small and the accumulation of the I term PI is small. Therefore, the degree of overshoot is small.

Here, the pressure difference P due to overshoot
When fd reaches the upper threshold value Pdu, the pressure reducing valve 9 is operated (steps 103 and 104), and the actual common rail pressure is immediately reduced. Thus, overshoot can be minimized.

Next, at the time of the pressure transient drop (III), the actual pressure PN has been greatly delayed with respect to the drop of the target pressure Pt in the past, but in the present embodiment, when the pressure difference Pfd reaches the upper threshold value Pdu. Immediately, the pressure reducing valve 9 is operated (step 103,
104), the actual pressure PN is immediately reduced, and can follow the decrease in the target pressure Pt. Since the followability of the actual pressure PN is excellent as described above, the accumulation of the I term PI decreases,
After that, even if the operation shifts to the steady state (IV), the occurrence of undershoot can be avoided or reduced.

The hysteresis of the flow shown in FIG. 1 will now be described. Once the pressure difference Pfd reaches the upper threshold value Pdu (Yes in step 103) and the pressure reducing valve is activated (step 104), the flag Flug becomes 1 (step 104). 10
5) Thereafter, even if the pressure difference Pfd falls to a value satisfying Pdd <Pfd <Pdu (No in step 106), the flag Flug remains 1, so that the result is Yes in step 107 and the pressure reducing valve continues to operate (step 104). After this, the pressure difference P
If fd falls to a value that satisfies Pfd ≦ Pdd (step 1
06, Yes), the pressure reducing valve is deactivated (step 10).
8) The flag Flug becomes 0 (step 109). Thereafter, even if the pressure difference Pfd rises to a value that satisfies Pdd <Pfd <Pdu (No in step 106), since the flag Flug is 0 (No in step 107), the pressure reducing valve remains inactive (step 108). ). Thereafter, the pressure reducing valve operates when Pdu ≦ Pfd is satisfied (at step 103).
Yes).

As described above, according to the present embodiment, the followability of the actual common rail pressure to the target common rail pressure can be improved during the transition of the common rail pressure, and the pressure difference, overshoot, and undershoot can be prevented. Therefore, the transient characteristics of the common rail pressure control are improved, and unnaturalness and noise are eliminated at the time of upshifting, free acceleration, and the like, and variations in the engine speed are minimized.

The embodiments of the present invention are not limited to those described above, and various modifications are possible.

[0032]

In summary, according to the present invention, the following excellent effects are exhibited. (1) The followability of the actual common rail pressure to the target common rail pressure can be improved during the transition of the common rail pressure. (2) It is possible to prevent a pressure difference, an overshoot, and an undershoot at the time of pressure transition, and it is possible to prevent a feeling of strangeness and an abnormal sound.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a pressure reducing valve control method according to an embodiment.

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

FIG. 3 is a calculation map of an I term.

FIG. 4 is a map for calculating a basic (target) common rail pressure.

FIG. 5 is a time chart showing a pressure transient characteristic and an operation method of a pressure reducing valve according to the embodiment.

FIG. 6 is a configuration diagram illustrating a common rail fuel injection control device according to the present embodiment.

FIG. 7 is a time chart showing a conventional pressure transient characteristic.

[Explanation of symbols]

 Reference Signs List 1 engine 3 common rail 6 electronic control unit (ECU) 7 common rail pressure sensor 8 engine rotation sensor 9 pressure reducing valve 11 accelerator opening sensor Ne engine speed Q fuel injection amount P0 basic common rail pressure PP proportional term (P term) PI integral term ( Item I) PN Actual common rail pressure Pt Target common rail pressure Pfd Pressure difference Pdu Pressure reducing valve operation upper threshold value Pdd Pressure reducing valve operation lower threshold value

 ──────────────────────────────────────────────────続 き Continued from the front page F term (reference) 3G066 AA07 AB02 AC09 BA19 BA22 BA51 CB07U CB15 CE21 DA06 DB16 DB17 DC04 DC09 DC11 DC14 DC18 3G301 HA02 JA03 JA07 JA37 KA11 KA22 LB06 LB11 LC01 MA11 NA03 NA04 NC02 ND01 NE17 NE19 PA09 PE01Z PE08Z PF03Z

Claims (3)

[Claims] 1. A common rail fuel injection control device, comprising: a pressure reducing valve connected to the common rail for reducing fuel in the common rail to reduce the common rail pressure. 2. A common rail pressure detecting means for detecting an actual common rail pressure; a target common rail pressure determining means for determining a target common rail pressure based on an engine operating state; 2. The pressure control apparatus according to claim 1, further comprising: common rail pressure control means for feedback-controlling the actual common rail pressure so as to approach, and pressure reducing valve control means for operating the pressure reducing valve when the actual common rail pressure becomes higher than a target common rail pressure by a predetermined value or more. Common rail fuel injection control device. 3. The target common rail pressure determining means determines a target common rail pressure based on an engine speed and a fuel injection amount, and the common rail pressure controlling means determines an actual common rail pressure, a target common rail pressure, and a target common rail pressure. 3. The common rail fuel according to claim 2, wherein a proportional term and an integral term are determined based on a difference between the two, and the proportional term and the integral term are added to the target common rail pressure to obtain an actual common rail pressure to be controlled next time. Injection control device.