JPH08177594A - Accumulator fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE: To stabilize the combustion state of a diesel engine and suppress the periodical fluctuation of engine speed satisfactorily. CONSTITUTION: When a foot is separated from an accelerator, the accelerator opening is gradually reduced to 0% from A%, and the engine speed is also engine accordingly. Then the fuel injection quantity changes a→b→c→d. While the fuel injection quantity changes a→b→c, the target fuel injection pressure of a common rail also changes α→β→γ in the same way. The fuel injection time is therefore stabilized, and the output characteristic and the like of an engine are improved. When the engine speed becomes less than Ne1 and the gradient of a curve L0 becomes large, the target fuel injection pressure is held to the fixed value Px (γ→δ). Accordingly, even if the engine speed periodically fluctuates in this area, the actual fuel injection pressure of the common rail follows the target fuel injection pressure well, so that the stability of the engine is secured, and the periodical fluctuation of engine speed is converged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-accumulation type fuel injection device for a diesel engine, which supplies a pressure-accumulated fuel to a pressure accumulation chamber by injecting the fuel.

[0002]

2. Description of the Related Art Conventionally, as this type of device, for example,
As described in JP-A-62-258160, a pressure accumulating chamber that stores fuel to be supplied to a diesel engine in a high pressure state, fuel pressure feeding means that pressure-feeds fuel to the pressure accumulating chamber, and fuel pressure in the pressure accumulating chamber is detected. Based on the operating state detected by the operating state detection means for detecting the operating state of the diesel engine including at least the engine speed, and the fuel injection amount to the diesel engine And a fuel injection amount calculation means for calculating the fuel injection amount, and a high-pressure fuel stored in the pressure accumulator is opened by a diesel valve for a time period corresponding to the calculated fuel injection amount and the fuel pressure detected by the fuel pressure detection means. Fuel injection means for injecting into the engine; target fuel pressure calculating means for calculating a target fuel pressure in the pressure accumulating chamber based on the operating state detected by the operating state detecting means; As the issued target fuel pressure and the fuel pressure detected by the fuel pressure detecting means is matched,
A pressure-accumulation type fuel injection device of a diesel engine including a pressure-feeding control unit that drives and controls the fuel pressure-feeding unit is considered. In the pressure-accumulation fuel injection device configured in this way,
The fuel injection amount to the diesel engine and the fuel pressure in the pressure accumulator can be controlled according to the operating state of the diesel engine.

Further, in a diesel engine, it is desirable to shorten the fuel injection time by the fuel injection means in order to stabilize the combustion state of the fuel. Further, the higher the fuel pressure in the pressure accumulating chamber, the shorter the fuel injection time for the same fuel injection amount. Therefore, in this type of pressure accumulating fuel injection device, it is considered to control the fuel pressure in the pressure accumulating chamber so as to change substantially similarly to the fuel injection amount calculated according to the operating state.

[0004]

However, the fuel pressure feeding means is constituted by a hydraulic system such as a pump, and the fuel pressure in the pressure accumulating chamber controlled via these means has sufficient followability to the target fuel pressure. Not. On the other hand, there are cases where the fuel injection amount has to be changed significantly in response to changes in the engine speed. For example, when the accelerator opening is 0% and the engine speed is low, the gradient of the fuel injection amount with respect to the change in the engine speed becomes relatively large. Therefore, even in such a case, if the target fuel pressure is changed like the fuel injection amount, the following problems occur.

The engine speed may periodically fluctuate as shown in FIG. 5 due to twisting of the power transmission system. In this case, the fuel injection amount also changes periodically according to the engine speed. However, when the target fuel pressure is periodically varied according to the engine speed as shown by the solid line in the figure, the actual fuel pressure in the accumulator (actual fuel pressure) is Due to the delay caused by the arithmetic processing,
In some cases, the target fuel pressure cannot be tracked as illustrated by the broken line. Then, the fluctuation of the fuel injection time is returned and promoted, so that the combustion state becomes unstable, and the fluctuation of the engine speed may be difficult to converge or may diverge.

Therefore, an object of the present invention is to provide a pressure-accumulation fuel injection device for a diesel engine, which can stabilize the combustion state of the diesel engine and can effectively suppress the periodic fluctuation of the engine speed. Made

[0007]

In order to attain the above object, the invention according to claim 1 is, as illustrated in FIG. 6, a pressure accumulating chamber for accumulating fuel to be supplied to a diesel engine in a high pressure state, and the pressure accumulating chamber. Fuel pumping means for pumping fuel to the chamber,
Fuel pressure detecting means for detecting the fuel pressure in the pressure accumulating chamber, operating state detecting means for detecting the operating state of the diesel engine including at least the engine speed, based on the operating state detected by the operating state detecting means, Fuel injection amount calculation means for calculating the fuel injection amount to the diesel engine, the calculated fuel injection amount, and a valve opening for a time corresponding to the fuel pressure detected by the fuel pressure detection means, the accumulated pressure Fuel injection means for injecting high-pressure fuel stored in the chamber to the diesel engine, and a target fuel pressure calculating means for calculating a target fuel pressure in the pressure accumulating chamber based on the operating state detected by the operating state detecting means, Pressure feeding control means for driving and controlling the fuel pressure feeding means so that the calculated target fuel pressure and the fuel pressure detected by the fuel pressure detecting means coincide with each other. In the accumulator fuel injection device for a diesel engine, when the target fuel pressure calculating means has a gradient of the fuel injection amount calculated by the fuel injection amount calculating means with respect to a change in the engine speed is less than a predetermined value, the fuel injection amount is A target fuel pressure that changes is calculated almost in the same manner as above, and when the gradient is equal to or higher than the predetermined value, the target fuel pressure is calculated so that the gradient with respect to the change in the engine speed becomes equal to or lower than a predetermined upper limit value. The gist is the accumulator type fuel injection device for diesel engines.

According to a second aspect of the present invention, the target fuel pressure calculating means sets an operating state in which the gradient of the fuel injection amount calculated by the fuel injection amount calculating means with respect to the change of the engine speed is the predetermined value or more. When the operating state detected by the storage means previously stored and the operating state detecting means does not correspond to the operating state stored in the storing means, a target fuel pressure that changes substantially similarly to the fuel injection amount is calculated, When the operating state detected by the operating state detecting means corresponds to the operating state stored in the storage means, the target fuel pressure is calculated so that the gradient with respect to the change in the engine speed becomes equal to or less than a predetermined upper limit value. The gist of the pressure-accumulation fuel injection device for a diesel engine according to claim 1 is provided with: a calculating means.

According to a third aspect of the present invention, the operating condition stored in advance in the storage means is that the accelerator opening is 0 and the engine speed is equal to or lower than a predetermined speed. The gist is the pressure-accumulation fuel injection device of the diesel engine described.

[0010]

In the invention according to claim 1 configured as described above, the fuel injection amount calculation means calculates the fuel injection amount to the diesel engine based on the operating state detected by the operating state detecting means. Then, the fuel injection means opens the valve for a period of time corresponding to the calculated fuel injection amount and the fuel pressure detected by the fuel pressure detection means, and injects the high-pressure fuel stored in the pressure accumulator into the diesel engine.

Further, the target fuel pressure calculating means calculates the target fuel pressure in the pressure accumulating chamber based on the operating state detected by the operating state detecting means, and the pumping control means calculates the target fuel pressure and the fuel pressure. The fuel pressure feeding means is drive-controlled so that the fuel pressure detected by the detection means matches.

Here, the target fuel pressure calculation means changes the fuel injection quantity substantially in the same manner as the fuel injection quantity when the gradient of the fuel injection quantity calculated by the fuel injection quantity calculation means with respect to the change in the engine speed is less than a predetermined value. Calculate fuel pressure. Therefore, the fuel injection time can be stabilized, which in turn can stabilize the combustion state of the diesel engine. Further, since the gradient of the fuel injection amount with respect to the change of the engine speed is less than the predetermined value, the gradient of the target fuel pressure with respect to the change of the engine speed becomes gentle. Therefore, even if the engine speed changes periodically, the actual fuel pressure in the accumulator (actual fuel pressure) can follow the change in the target fuel pressure, and the periodic change in engine speed can be improved. Can be converged.

Further, the target fuel pressure calculating means has a predetermined upper limit of the gradient with respect to the change in the engine speed when the gradient with respect to the change in the engine speed of the fuel injection amount calculated by the fuel injection amount calculating means is equal to or more than the predetermined value. The target fuel pressure is calculated so as to be equal to or less than the value. Therefore, also in this case, the actual fuel pressure can follow the change in the target fuel pressure even if the engine speed fluctuates periodically, and the periodic fluctuation of the engine speed can be favorably converged.

Therefore, according to the present invention, the combustion state of the diesel engine can be stabilized and the periodic fluctuation of the engine speed can be suppressed well. In the invention according to claim 2, the target fuel pressure calculating means stores in advance in the storage means an operating state in which the gradient with respect to the change in the engine speed of the fuel injection amount calculated by the fuel injection amount calculating means becomes the predetermined value or more. Therefore, when the operating state detected by the operating state detecting means does not correspond to the operating state stored in the storage means, the target fuel pressure that changes in substantially the same manner as the fuel injection amount described above, and when it corresponds, the engine speed The target fuel pressure at which the gradient with respect to the change in the number becomes equal to or less than the upper limit value is calculated by the calculation means. Therefore, in addition to the action and effect of the invention described in claim 1, the following action and effect can be obtained.

That is, the target fuel pressure calculating means detects by the operating state detecting means whether or not the gradient of the fuel injection amount calculated by the fuel injection amount calculating means with respect to the change of the engine speed becomes equal to or more than the predetermined value. It can be judged directly from the driving condition. Therefore, the processing by the target fuel pressure calculation means can be further simplified and speeded up.

According to a third aspect of the present invention, in the second aspect of the present invention, the operating condition stored in advance in the storage means is that the accelerator opening is 0 and the engine speed is equal to or lower than a predetermined speed. Is characterized by. Under such operating conditions, in general, the gradient of the fuel injection amount calculated by the fuel injection amount calculation means with respect to the change in the engine speed becomes steep. That is, the target fuel pressure calculating means can determine whether or not the gradient becomes equal to or more than the predetermined value, based on only the values of the accelerator opening degree and the engine speed at that time.
Therefore, in addition to the effect of the invention described in claim 2, the following action / effect can be obtained.

That is, the processing by the target fuel pressure calculating means can be further simplified and speeded up. Further, under such operating conditions, the power transmission system is likely to be twisted and the engine speed is likely to be periodically varied. Therefore, the periodic fluctuation of the engine speed can be suppressed more effectively.

[0018]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a fuel injection device for a diesel engine of an embodiment. As shown in FIG. 1, a diesel engine (hereinafter, simply referred to as an engine) 1 is provided with an injector 3 for each cylinder, and each injector 3 has a high pressure common to each cylinder via an electromagnetic valve 5 for fuel injection control. It is connected to a pressure accumulating pipe, a so-called common rail 7. Each solenoid valve 5 is controlled to open and close by a drive signal from an ECU (electronic control circuit) 9, and fuel in the common rail 7 is injected from the injector 3 to the engine 1 while the solenoid valve 5 is open.

The common rail 7 is connected to a high pressure supply pump 15 via a supply pipe 11 and a check valve 13. The high-pressure supply pump 15 boosts the fuel sucked from the fuel tank 17 via the well-known low-pressure supply pump 19 to a predetermined high pressure by a plunger (not shown) that reciprocates in synchronization with the rotation of the engine 1, and the common rail 7 receives the fuel. To supply. Further, the high-pressure supply pump 15 includes a discharge amount control device 21 for always maintaining the common rail 7 at a predetermined high pressure. Therefore, a high predetermined pressure corresponding to the fuel injection pressure is continuously accumulated in the common rail 7.

In addition to the solenoid valve 5 described above, the ECU 9 outputs a drive signal to the discharge amount control device 21 to control its operation. In addition, the ECU 9 includes a rotation speed sensor 23 that detects the rotation speed of the engine 1 (engine rotation speed), an accelerator opening sensor 25 that detects a depression amount (accelerator opening) of an accelerator (not shown), and a fuel pressure in the common rail 7. Detection signals from various sensors such as the pressure sensor 27 that detects (actual fuel injection pressure) are input.

The ECU 9 is a CPU for executing arithmetic processing,
R for temporarily storing the detection data of the sensors 23 to 27
ROM for storing AM and control programs described later
This is a well-known microcomputer having (not shown) as a main part, and determines the operating state of the engine 1 based on the input signals of the various sensors 23 to 27, and optimizes the electromagnetic valve 5 and the discharge amount control device 21. By outputting various driving signals, the fuel injection amount, the fuel injection timing, and the fuel injection pressure are independently controlled.

Next, the control executed by the ECU 9 will be described with reference to FIGS. First, the ECU 9 executes known processing for calculating the fuel injection amount based on the map illustrated in FIG. In the map of FIG. 2, the fuel injection amount is determined according to the engine speed detected by the speed sensor 23 and the accelerator opening detected by the accelerator opening sensor 25. Further, the map of FIG. 2 is set so that the fuel injection amount increases as the accelerator opening increases and the engine speed decreases, and further, the curves L0, L1, L2 corresponding to the accelerator opening, In most of the ..., As the engine speed increases, the gradient (absolute value) of the fuel injection amount with respect to the change in the engine speed increases.

The ECU 9 calculates an appropriate fuel injection amount from this map, and then calculates the fuel injection amount and the pressure sensor 27.
The corresponding fuel injection time is calculated on the basis of the actual fuel injection pressure detected in step 1, and the solenoid valve 5 is opened during the above fuel injection time at an appropriate timing according to the operating state of the engine 1 to perform the fuel injection. A well-known process for executing is performed.

As described above, the actual fuel injection pressure affects the fuel injection time, and eventually the combustion state of the engine 1. Therefore, the ECU 9 calculates the target fuel injection pressure that is the target value of the actual fuel injection pressure by the target fuel injection pressure calculation process shown in FIG. 3, and the actual fuel injection pressure is changed to the target fuel injection pressure by another routine not shown. The ejection amount control device 21 is drive-controlled so as to match with. Next, this target material injection pressure calculation processing will be described. It should be noted that the ECU 9 repeatedly executes this processing at a predetermined cycle while the engine 1 is operating.

When the processing is started, the ECU 9 determines in step 101 whether the accelerator opening is 0%. When the accelerator opening is 0%, the process proceeds to step 103, and when it is not 0%, the process proceeds to step 105. In step 103, it is determined whether the engine speed is less than or equal to the predetermined value Ne1. When the engine speed is less than or equal to the predetermined value Ne1, the process goes to step 107
When it is larger than 1, the process proceeds to step 105. That is, when the accelerator opening is 0% and the engine speed is equal to or less than the predetermined value Ne1 (steps 101, 10).
3: YES), the process proceeds to step 107, and otherwise the process proceeds to step 105.

At step 105, the target fuel injection pressure is calculated from the map similar to that shown in FIG. 2, and the processing is once terminated. On the other hand, in step 107, the target fuel injection pressure is set to a constant value Px and the processing is once performed. That is, as described below, when the accelerator opening is 0% and the engine speed is equal to or less than the predetermined value Ne1, the gradient of the fuel injection amount with respect to the change of the engine speed becomes large. Therefore, if the target fuel injection pressure is calculated using the map similar to FIG. 2, there is a possibility that the actual fuel injection pressure may not follow the target fuel injection pressure no matter how the discharge amount control device 21 is driven. Therefore, the target fuel injection pressure is set to the constant value Px. In other cases, the actual fuel injection pressure can sufficiently follow even if the target fuel injection pressure is calculated using the map similar to FIG. Then, when the actual fuel injection pressure is controlled according to the map similar to FIG. 2, the fuel injection time can be made substantially constant and extremely short. Then
The combustion state of each cylinder of the engine 1 is improved, and the output characteristics (fuel consumption, NOx emission amount, etc.) of the engine 1 can be improved satisfactorily.

Next, regarding the operation and effect of this embodiment,
A description will be given based on the specific example of FIG. FIG. 4 shows the fuel injection amount until the vehicle is stopped with the foot released from the accelerator while the vehicle equipped with the engine 1 of the embodiment is traveling at the accelerator opening A%.
It is explanatory drawing which showed the specific example of a target fuel injection pressure and the change of an accelerator opening.

When the foot is released from the accelerator, the accelerator opening gradually decreases from A% to 0%, and the engine speed also decreases accordingly. Then, the fuel injection amount decreases from the value corresponding to the point a to the value corresponding to the point b. After that, the fuel injection amount changes along the curve L0 corresponding to the accelerator opening = 0%, and increases as b → c → d as the rotational speed decreases. The point c is a point corresponding to the engine speed = Ne1.

Therefore, while the fuel injection amount changes from a → b → c, the target fuel injection pressure also changes in the same manner as α → β → γ by the processing of step 105. Therefore, as described above, the combustibility of each cylinder of the engine 1 and the output characteristic of the engine 1 can be improved. Further, when the engine speed falls below Ne1, the target fuel injection pressure is held at the constant value Px (the value corresponding to the point γ) by the processing of step 107 until γ → δ → ... reaches a predetermined idle speed. Change.

Here, even if the engine speed falls below Ne1, if γ → δ ′ changes similarly to the fuel injection amount, the following problems occur. That is, when the engine speed falls below Ne1, the slope of the curve L0 becomes extremely large. Therefore, when the power transmission system of the engine 1 is twisted in this region and the engine speed periodically changes (see FIG. 5), the target fuel injection pressure periodically changes with a relatively large amplitude. On the other hand, due to a mechanical transmission delay of the hydraulic system from the high-pressure supply pump 15 to the common rail 7, a delay due to the processing cycle of the target fuel injection pressure calculation processing of FIG. I can't quite follow. Then, as described above with reference to FIG. 5, the fluctuation of the fuel injection time is returned and promoted, so that the combustion state becomes unstable, and the fluctuation of the engine speed becomes difficult to converge or diverges. there's a possibility that.

Therefore, in this embodiment, the engine speed is Ne.
When it is less than 1, the target fuel injection pressure is fixed to a constant value Px (γ → δ → ...). Therefore, the actual fuel injection pressure can sufficiently follow the target fuel injection pressure. Therefore, the fluctuation of the fuel injection time is relatively small, and the periodic fluctuation of the engine speed can be favorably converged.

In the above embodiment, the common rail 7 serves as the pressure accumulating chamber, the high pressure supply pump 15 serves as the fuel pressure feeding means,
The pressure sensor 27 serves as the fuel pressure detecting means, and the rotation speed sensor 23
And the accelerator opening sensor 25 serves as the operating state detecting means,
The injector 3 and the solenoid valve 5 correspond to fuel injection means, respectively, and of the processing executed by the ECU 9, the processing for calculating the fuel injection amount based on the map of FIG. 2 is performed by the fuel injection amount calculation means, and the target fuel of FIG. The injection pressure calculation processing corresponds to the target fuel pressure calculation means, and the processing for driving and controlling the discharge amount control device 21 so that the actual fuel injection pressure matches the target fuel injection pressure corresponds to the pressure feed control means.

Further, the present invention is not limited to the above embodiments, and can be implemented in various modes without departing from the gist of the present invention. For example, in the above embodiment, the throttle opening is 0% and the engine speed is Ne.
Although the target fuel injection pressure is fixed to the constant value Px when it is 1 or less, the constant value Px may be further corrected by the cooling water temperature of the engine 1 or the like. In this case, it is possible to calculate the target fuel injection pressure more suited to the operating state of the engine 1. Further, since the cooling water temperature changes gently, the actual fuel injection pressure can follow well even if this correction is applied to the target fuel injection pressure. Furthermore, the throttle opening is 0%
Even when the engine speed is equal to or lower than Ne1, the target fuel injection pressure may be gently changed according to the change of the engine speed. Also in this case, it is possible to calculate the target fuel injection pressure more suited to the operating state of the engine 1 without impairing the followability of the actual fuel injection pressure. However, holding the target fuel injection pressure at the constant value Px as in the above embodiment can simplify and speed up the process of calculating the target fuel injection pressure.

Further, in the above embodiment, the magnitude of the gradient of the fuel injection amount is judged based on the throttle opening and the engine speed. The magnitude of the gradient may be determined to determine whether to change the target fuel injection pressure in the same manner as the fuel injection amount. For example, the magnitude of the gradient may be determined by partially differentiating the change in the fuel injection amount with the engine speed. In this case, it is possible to prevent periodic fluctuations in the engine speed under various operating conditions.

However, as in the above embodiment, it is better to judge whether or not the target fuel injection pressure is changed in the same manner as the fuel injection amount, depending on whether or not the preset operating condition is met. The calculation process of the injection pressure can be further simplified and speeded up. In particular, under the conditions of the accelerator opening = 0% and the engine speed ≦ Ne1 used in the above embodiment, the power transmission system is likely to be twisted and the engine speed is likely to be periodically varied. Therefore, in the above-described embodiment, the periodic fluctuation of the engine speed can be suppressed more effectively.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a fuel injection device for a diesel engine of an embodiment.

FIG. 2 is an explanatory diagram illustrating the configuration of a fuel injection amount calculation map according to the embodiment.

FIG. 3 is a flowchart showing a target fuel injection pressure calculation process of the embodiment.

FIG. 4 is an explanatory diagram showing a specific example of changes in fuel injection amount, target fuel injection pressure, and accelerator opening degree in the embodiment.

FIG. 5 is an explanatory diagram illustrating changes in conventional engine speed and fuel pressure.

FIG. 6 is a structural example of the present invention.

[Explanation of symbols]

1 ... Diesel engine 3 ... Injector
5 ... Solenoid valve 7 ... Common rail 9 ... ECU
15 ... High-pressure supply pump 17 ... Fuel tank 19 ... Low-pressure supply pump
21 ... Discharge amount control device 23 ... Rotation speed sensor 25 ... Accelerator opening sensor
27 ... Pressure sensor

Claims (3)

[Claims] 1. A pressure accumulating chamber for storing fuel to be supplied to a diesel engine in a high pressure state, fuel pressure feeding means for feeding fuel to the pressure accumulating chamber, fuel pressure detecting means for detecting a fuel pressure in the pressure accumulating chamber, and at least an engine. An operating state detecting means for detecting an operating state of the diesel engine including a rotation speed; and a fuel injection amount calculating means for calculating a fuel injection amount to the diesel engine based on the operating state detected by the operating state detecting means. Fuel injection means for injecting the high-pressure fuel stored in the pressure accumulating chamber to a diesel engine by opening the valve for a time corresponding to the calculated fuel injection amount and the fuel pressure detected by the fuel pressure detecting means And a target fuel pressure calculating means for calculating a target fuel pressure in the pressure accumulating chamber based on the operating state detected by the operating state detecting means, and the calculated target fuel pressure. In a pressure-accumulation fuel injection device for a diesel engine, comprising: a pressure-feeding control means for driving and controlling the fuel pressure-feeding means so that the fuel pressure detected by the fuel pressure detecting means matches, the target fuel pressure calculating means is When the gradient of the fuel injection amount calculated by the fuel injection amount calculation means with respect to the change of the engine speed is less than a predetermined value, a target fuel pressure that changes substantially similarly to the fuel injection amount is calculated, and the gradient is A pressure-accumulation fuel injection device for a diesel engine, wherein a target fuel pressure is calculated so that a gradient with respect to a change in the engine speed becomes equal to or less than a predetermined upper limit when the predetermined value or more. 2. The storage means for storing the operating condition in which the target fuel pressure calculating means stores in advance an operating state in which the gradient of the fuel injection amount calculated by the fuel injection amount calculating means with respect to the change of the engine speed is equal to or more than the predetermined value. When the operating state detected by the operating state detecting means does not correspond to the operating state stored in the storage means, a target fuel pressure that changes substantially similarly to the fuel injection amount is calculated,
When the operating state detected by the operating state detecting means corresponds to the operating state stored in the storage means, the target fuel pressure is calculated so that the gradient with respect to the change in the engine speed becomes equal to or less than a predetermined upper limit value. The pressure-accumulation fuel injection device for a diesel engine according to claim 1, further comprising: a calculating unit. 3. The accumulated pressure of the diesel engine according to claim 2, wherein the operating condition stored in advance in the storage means is that the accelerator opening is 0 and the engine speed is equal to or lower than a predetermined speed. Fuel injector.