JP2020090915A - Fuel injection system - Google Patents

Abstract

To provide a fuel injection system capable of improving accuracy in controlling a pressure of an internal fuel of a pressure accumulation vessel.SOLUTION: A fuel injection system 10 includes a common rail 11 as a pressure accumulation vessel, and a plurality of fuel injection valves 20 for injecting a high-pressure fuel. The fuel injection system 10 includes a decompression control unit executing decompression drive control to decompress the internal fuel of the pressure accumulation vessel without injecting the fuel from injection holes 34 of the fuel injection valves 20 as energization objects by opening a second opening/closing valve 52 by energizing one or more fuel injection valves 20 among the plurality of fuel injection valves 20 when the decompression request for decompressing the internal fuel of the pressure accumulation container is made, and a decompression number determination unit for determining the number of fuel injection valves 20 to which the execution of the decompression drive control is instructed, among the plurality of fuel injection valves 20 in accompany with the decompression request. The decompression control unit controls an energization time of the fuel injection valve 20 as execution objects of the decompression drive control on the basis of the number of the fuel injection valves 20 determined by the decompression number determination unit.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fuel injection system.

A fuel injection system is known in which a common rail as a pressure accumulator for accumulating high-pressure fuel is arranged in the middle of a fuel path connecting a fuel tank and a fuel injection valve, and high-pressure fuel in the common rail is injected from the fuel injection valve. (For example, see Patent Document 1). In the fuel injection system described in Patent Document 1, a pressure reducing valve is provided in the common rail, and the pressure reducing valve is opened at the time of deceleration or the like to rapidly reduce the fuel pressure in the common rail to the target pressure. Further, in the one described in Patent Document 1, the flow rate characteristic of the pressure reducing valve is learned by detecting the amount of decrease in fuel pressure in the common rail with respect to the energization time of the pressure reducing valve, and the learning result is used to energize the pressure reducing valve. Control is performed to correct the time.

JP, 2008-128163, A

In a multi-cylinder internal combustion engine, when the fuel injection valve is used as a pressure reducing valve to reduce the fuel pressure in the common rail, the number of fuel injection valves used as the pressure reducing valve may be limited depending on the operating state of the internal combustion engine. is there. In such a situation, if the fuel pressure in the common rail is reduced by the same control as when the number of fuel injection valves used as pressure reducing valves is not limited, the common rail cannot be depressurized rapidly and the fuel inside the common rail cannot be reduced. There is a concern that the accuracy of pressure control will decrease.

The present invention has been made in view of the above problems, and a main object of the present invention is to provide a fuel injection system capable of improving the accuracy of pressure control of internal fuel in a pressure accumulator.

In order to solve the above problems, the following means are adopted.

The present invention relates to a fuel including a pressure accumulator (11) for storing fuel in a high pressure state, and a fuel injection valve (20) provided for each cylinder for a plurality of cylinders of an internal combustion engine and injecting high pressure fuel in the accumulator. Regarding the injection system. In the invention according to claim 1, the fuel injection valve includes: a control chamber (36, 46) to which the high-pressure fuel from the accumulator is supplied through a high-pressure fuel passage (13, 14); and an interior of the control chamber. Needle valve (31) for injecting fuel from the injection hole (34) by moving in the axial direction according to the fuel pressure of the valve, and pressure adjustment for opening the valve with the energization to adjust the fuel pressure inside the control chamber. A valve (52), and when a decompression request for decompressing the internal fuel of the pressure accumulator is made, one or more of the fuel injection valves among the plurality of fuel injection valves are energized and the By opening the pressure regulating valve, a pressure reducing control unit for performing pressure reducing drive control for reducing the pressure of the internal fuel of the pressure accumulating container without injecting fuel from the injection hole of the fuel injection valve to be energized. And a pressure reduction number setting unit that sets the number of the fuel injection valves that command execution of the pressure reduction drive control in accordance with the pressure reduction request, and the pressure reduction control unit is set by the pressure reduction number setting unit. Based on the number of fuel injection valves, the energization time of the fuel injection valves for performing the pressure reduction drive control is controlled.

According to the above configuration, the energization time of the fuel injection valve to be implemented is controlled according to the number of fuel injection valves to be subjected to the pressure reduction drive control. In a situation where the number of fuel injection valves used for depressurizing the pressure accumulator is limited, if the fuel injection valves are controlled by the same energization time as when the limit is not imposed, the fuel flow rate discharged from the accumulator May be too small. In such a case, there is a concern that the internal fuel in the pressure accumulator cannot be quickly depressurized. On the other hand, according to the above configuration, the energization time of the fuel injection valve is variably controlled according to the number of fuel injection valves to which the internal fuel of the pressure accumulator is depressurized. Even when the number of fuel injection valves to be set is limited, an appropriate energization time can be set according to the number. As a result, the pressure of the internal fuel of the pressure accumulator can be quickly reduced to the target pressure, and the accuracy of the pressure control of the internal fuel of the pressure accumulator can be improved.

The figure which shows schematic structure of a fuel injection system. The figure which shows an example of the injection rate pattern of a fuel injection valve. The figure showing the fuel injection valve at the time of valve closing. The figure explaining operation|movement of the fuel injection valve of a high speed valve opening mode. The figure explaining operation|movement of a fuel injection valve at the time of shifting to a high speed valve closing mode from a high speed valve opening mode. The figure explaining operation|movement of the fuel injection valve in high-speed valve closing mode. The figure explaining operation|movement of the fuel injection valve of low speed valve opening mode. The figure explaining operation|movement of a fuel injection valve at the time of shifting to a low speed valve closing mode from a low speed valve opening mode. The figure explaining operation|movement of the fuel injection valve in low speed valve closing mode. The figure which shows the pressure reduction operation by a 2nd on-off valve. The time chart showing pressure reduction drive control of a fuel injection valve. 6 is a time chart showing a specific mode of drive control of the fuel injection valve when a rail pressure reduction request is generated. The figure explaining the energization time correction at the time of pressure reduction drive. The flowchart which shows the process sequence of pressure reduction drive control of a fuel injection valve. The figure which shows the map for setting of the pressure reduction drive number. The figure which shows a pressure reduction flow rate characteristic map.

Hereinafter, embodiments will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings, and the description of the portions having the same reference numerals is cited.

The present embodiment is embodied in a fuel injection system applied to a vehicle-mounted multi-cylinder diesel engine which is an internal combustion engine. In this fuel injection system, an electronic control unit (hereinafter, referred to as "ECU") is the center for controlling the fuel injection of the engine. As shown in FIG. 1, the fuel injection system 10 includes a common rail 11, a fuel injection valve 20, and an ECU 90.

In FIG. 1, the common rail 11 is connected to a downstream side of a high-pressure pump (not shown), and fuel (hereinafter referred to as “high-pressure fuel”) whose pressure is increased by the high-pressure pump is supplied. Inside the common rail 11, the high-pressure fuel pumped from the high-pressure pump is held in a high pressure state. The common rail 11 is not provided with a pressure reducing valve that lowers the fuel pressure inside the common rail 11 (hereinafter referred to as “rail pressure”).

A fuel injection valve 20 is connected to the common rail 11 via a high pressure pipe 12. The fuel injection valve 20 is a direct injection type that directly injects fuel into the combustion chamber of the engine 70, and one fuel injection valve is attached to each of a plurality of cylinders (four cylinders in this embodiment). It should be noted that FIG. 1 shows only the fuel injection valve 20 of one cylinder, and the description of the fuel injection valve 20 is omitted for the remaining cylinders.

The ECU 90 is a microcomputer including a CPU, a ROM, a RAM, a drive circuit, an input/output interface and the like. Detection signals are sequentially input to the ECU 90 from various sensors such as a crank angle sensor that detects a rotation speed of the engine 70 and an accelerator sensor that detects an accelerator operation amount. The ECU 90 calculates an optimum fuel injection amount and injection timing based on engine operation information such as engine rotation speed and accelerator operation amount, and outputs a corresponding energization pulse (injection signal) to the fuel injection valve 20. As a result, fuel injection by the fuel injection valve 20 is controlled in each cylinder.

Next, the configuration of the fuel injection valve 20 will be described in detail. The fuel injection valve 20 includes first to fourth main body portions 21 to 24, and the first to fourth main body portions 21 to 24 are integrated to form an injection valve main body. The first to fourth body portions 21 to 24 are arranged in this order in the axial direction of the fuel injection valve 20, and the fuel supplied from the common rail 11 to the first body portion 21 is provided in the fourth body portion 24. It injects from the injection hole 34. In the following description, the axial direction of the fuel injection valve 20 will be referred to as “vertical direction”, the first body portion 21 side of the fuel injection valve 20 will be referred to as “upward direction”, and the fourth body portion 24 side will be referred to as “downward direction”. ..

The first main body portion 21 is provided with a first high pressure passage 13 and a low pressure chamber 57. The first high-pressure passage 13 is formed across the first main body portion 21, the second main body portion 22, and the third main body portion 23, and penetrates the first to third main body portions 21 to 23. The first high-pressure passage 13 is connected to the high-pressure pipe 12 at the end opposite to the second main body 22 side. As a result, the high-pressure fuel from the common rail 11 is supplied to the first high-pressure passage 13 via the high-pressure pipe 12. A fuel pressure sensor 73 that detects the pressure of the fuel in the first high pressure passage 13 is attached to the first high pressure passage 13. The detection signal of the fuel pressure sensor 73 is input to the ECU 90.

The low-pressure chamber 57 is formed in the boundary portion with the second main body portion 22 in the first main body portion 21 by denting the surface facing the second main body portion 22 upward. The high-pressure fuel in the first high-pressure passage 13 passes through the second main body portion 22, the third main body portion 23, and the fourth main body portion 24, and the low-pressure chamber 57 stores the fuel whose pressure has been reduced. The low pressure chamber 57 is connected to the return pipe 65 via the low pressure passage 58, and further connected to the fuel tank 61. As a result, part of the high pressure fuel supplied to the fuel injection valve 20 is returned from the low pressure chamber 57 to the fuel tank 61 through the return pipe 65. An opening/closing valve 50 that controls the fuel injection state of the fuel injection valve 20 is provided inside the low pressure chamber 57. The on-off valve 50 is of an electromagnetic drive type, and the opening and closing of the valve is controlled by the ECU 90.

The second main body 22 is provided with a second high pressure passage 14, an intermediate chamber 26, a first passage 25, and a second passage 27. The second high-pressure passage 14 is a branch passage that branches from the first high-pressure passage 13, and is a fuel passage to which the high-pressure fuel from the common rail 11 is supplied. The second high pressure passage 14 is provided with a pressure rising orifice 14a. The boost orifice 14a limits the flow rate of the fuel flowing through the second high pressure passage 14. In the second high pressure passage 14, an annular chamber 14b is formed at the end portion on the side opposite to the first high pressure passage 13. The annular chamber 14b is a fuel passage portion formed in an annular shape in the boundary portion of the second main body portion 22 with the third main body portion 23. The high pressure fuel from the first high pressure passage 13 is introduced into the annular chamber 14b through the second high pressure passage 14.

The intermediate chamber 26 is a cylindrical chamber and is formed at the boundary between the second main body 22 and the third main body 23. The first passage 25 extends in the axial direction (vertical direction) of the fuel injection valve 20 inside the second main body portion 22 and penetrates the second main body portion 22. The first passage 25 has one end communicating with the low pressure chamber 57 and the other end communicating with the intermediate chamber 26. As a result, the intermediate chamber 26 communicates with the low pressure chamber 57 via the first passage 25.

The second passage 27 is formed inside the second main body portion 22 and extends in the same direction (vertical direction) as the first passage 25. The second passage 27 penetrates through the second main body 22, one end of which communicates with the low-pressure chamber 57, and the other end of which communicates with the first control chamber 46 of the third main body 23. .. A decompression orifice 27 a is provided in the second passage 27 at a position close to the first main body portion 21. The pressure reducing orifice 27a limits the flow rate of the fuel flowing through the second passage 27. The second passage 27 corresponds to the "second fuel passage", and the pressure reducing orifice 27a corresponds to the "second orifice".

The third main body 23 is provided with a first control chamber 46 and a connection passage 47. The first control chamber 46 is a chamber formed inside the injection valve body by denting the surface facing the second body portion 22 downward, and is in communication with the annular chamber 14b. The high pressure fuel from the first high pressure passage 13 is supplied to the first control chamber 46 via the second high pressure passage 14.

A driven valve 41 that is displaceable in the axial direction (vertical direction) of the fuel injection valve 20 is disposed inside the first control chamber 46. The driven valve 41 has a cylindrical shape, and has a third passage 42 formed in the center thereof so as to penetrate therethrough in the axial direction. The third passage 42 has an opening on the side of the second main body 22 that is open to the intermediate chamber 26, and an opening on the side of the fourth main body 24 that is open to the inside of the first control chamber 46. The third passage 42 is provided with a decompression orifice 42a. The flow rate of the fuel flowing through the third passage 42 is limited by the pressure reducing orifice 42a. The fuel flow rate on the outlet side of the pressure reducing orifice 27a included in the second passage 27 is set to be smaller than the fuel flow rate on the outlet side of the pressure reducing orifice 42a. The first passage 25 and the third passage 42 form a “first fuel passage”. The decompression orifice 42a corresponds to the "first orifice".

The driven valve 41 is provided with a spring 45 that biases the driven valve 41 in the direction toward the second main body portion 22 (upward). The driven valve 41 is in contact with the lower surface of the second main body portion 22 by the upward force due to the fuel pressure inside the first control chamber 46 and the biasing force of the spring 45. In this contact state, the driven valve 41 blocks the communication between the annular chamber 14b and the first control chamber 46, while the intermediate chamber 26 communicates with the first control chamber 46 through the third passage 42. Become. In this state, the fuel in the first control chamber 46 can flow into the low pressure chamber 57 via the third passage 42, the intermediate chamber 26 and the first passage 25.

In the state where the driven valve 41 is in contact with the lower surface of the second body portion 22, the fuel pressure inside the first control chamber 46 decreases, and the upward force due to the fuel pressure inside the first control chamber 46 and When the biasing force of the spring 45 falls below the downward force due to the fuel pressure inside the annular chamber 14b and the intermediate chamber 26, the driven valve 41 is displaced in the direction away from the lower surface of the second main body portion 22. As a result, the intermediate chamber 26 communicates with the first control chamber 46 without passing through the third passage 42, and the annular chamber 14b communicates with the first control chamber 46.

The second passage 27 directly connects the low pressure chamber 57 and the first control chamber 46. That is, the first control chamber 46 communicates with the low pressure chamber 57 via the second passage 27 regardless of the position (lifted state) of the driven valve 41. Further, a connection passage 47 extending from the first control chamber 46 to the fourth body portion 24 is formed in the third body portion 23. The connection passage 47 is provided with an orifice 47a, and the orifice 47a limits the flow rate of the fuel flowing through the connection passage 47.

The fourth body 24 is provided with a cylinder 35, a needle valve 31, a high pressure chamber 33, and a second control chamber 36. A plurality of injection holes 34 for injecting fuel toward the outside are formed at the tip of the cylinder 35. The needle valve 31 is housed inside the cylinder 35 so as to be capable of reciprocating in the vertical direction. A spring 32 that biases the needle valve 31 downward is attached to the upper surface of the needle valve 31.

The high pressure chamber 33 is provided in the middle of a passage that connects the first high pressure passage 13 and the injection hole 34. Inside the high pressure chamber 33, the tip of the needle valve 31 is arranged. The second control chamber 36 is provided inside the cylinder 35 on the side opposite to the injection hole 34 (above the needle valve 31). The second control chamber 36 communicates with the first control chamber 46 via a connection passage 47. As a result, the high-pressure fuel from the first high-pressure passage 13 is supplied to the second control chamber 36 via the first control chamber 46 and the connection passage 47. The fuel pressure inside the second control chamber 36 and the urging force of the spring 32 attached to the needle valve 31 act on the needle valve 31, so that the needle valve 31 closes the injection hole 34 (downward). It is displaced and the fuel injection valve 20 is closed.

When the fuel pressure inside the high pressure chamber 33 becomes larger than the total force of the fuel pressure inside the second control chamber 36 and the urging force of the spring 32, the needle valve 31 opens the injection hole 34 (upward direction). ), the fuel injection valve 20 is opened. When the fuel injection valve 20 is opened, the high pressure fuel in the high pressure chamber 33 is injected from the injection hole 34.

Next, the structure of the on-off valve 50 will be described. The on-off valve 50 is arranged inside the low pressure chamber 57 in the fuel passage that connects the first control chamber 46 and the low pressure chamber 57. The on-off valve 50 regulates the fuel pressure inside the first control chamber 46 by allowing and blocking the outflow of fuel from the first control chamber 46 to the low pressure chamber 57 under drive control by the ECU 90.

The opening/closing valve 50 has a first opening/closing valve 51 and a second opening/closing valve 52. The first opening/closing valve 51 is arranged on the first passage 25, and the open/close state thereof is controlled to switch between communication and cutoff between the low pressure chamber 57 and the first passage 25. The second opening/closing valve 52 is arranged on the second passage 27, and the open/close state of the second opening/closing valve 52 is controlled to switch the communication between the low pressure chamber 57 and the second passage 27 and the disconnection thereof. The ECU 90 independently controls the open/closed state of the first open/close valve 51 and the open/closed state of the second open/close valve 52 by electrically driving the first solenoid 53 and the second solenoid 54 independently of each other.

Specifically, when the first solenoid 53 is not energized, the first opening/closing valve 51 is in contact with the second body portion 22 by the urging force of the first spring 55. In this abutting state, the first on-off valve 51 blocks the communication between the low pressure chamber 57 and the first passage 25 (valve closed state). When the first solenoid 53 is energized while the first opening/closing valve 51 is closed, the first opening/closing valve 51 moves upward against the biasing force of the first spring 55 and is separated from the second main body portion 22. To do. In this state, the low pressure chamber 57 and the first passage 25 are in communication with each other (valve open state), and the fuel is allowed to flow from the first passage 25 into the low pressure chamber 57.

Further, when the second solenoid 54 is not energized, the second opening/closing valve 52 is in contact with the second body portion 22 by the urging force of the second spring 56. In this abutting state, the communication between the low pressure chamber 57 and the second passage 27 is blocked by the second opening/closing valve 52 (valve closed state). Further, when the second solenoid 54 is energized in the closed state of the second opening/closing valve 52, the second opening/closing valve 52 moves upward against the biasing force of the second spring 56 and is separated from the second main body portion 22. To do. In this state, the low pressure chamber 57 and the second passage 27 are communicated with each other (valve open state), and the inflow of fuel from the second passage 27 into the low pressure chamber 57 is allowed.

In the fuel injection control, the ECU 90 moves the needle valve 31 to the valve opening position and the valve closing position by switching between the opening and closing of the first opening/closing valve 51. As a result, the injection operation in which fuel is injected from the injection hole 34 and the injection stop operation in which fuel injection is stopped are switched. Further, the ECU 90 switches the opening/closing of the second opening/closing valve 52 in accordance with the drive control of the first opening/closing valve 51, so that the movement when the needle valve 31 moves to the opening position and the closing position. Control the speed. That is, the ECU 90 independently controls the opening/closing of the first opening/closing valve 51 and the second opening/closing valve 52 to determine the slope of the fuel injection rate, more specifically, the rising speed and the falling speed of the injection rate. Control each.

FIG. 2 shows an example of the injection rate pattern of the fuel injection valve 20. In any of the injection rate patterns, the first opening/closing valve 51 is opened at the start of fuel injection by the fuel injection valve 20, and the first opening/closing valve 51 is closed at the end of fuel injection. The second opening/closing valve 52 is controlled to open and close according to the rising speed and the falling speed of the injection rate.

Specifically, in the high-speed valve opening mode (injection start (H) mode) in which the rising rate of the injection rate at the start of fuel injection is made steep, the second opening/closing valve 52 is opened (Fig. 2(a) and (See (c)) In the low-speed valve opening mode (injection start (L) mode) in which the rising rate of the injection rate is slow, the second opening/closing valve 52 is closed (see FIGS. 2B and 2D). .. Further, in the high-speed valve closing mode (injection end (H) mode) in which the fall rate of the injection rate at the end of fuel injection is made steep, the second opening/closing valve 52 is closed (FIGS. 2A and 2B). )), the second on-off valve 52 is opened in the low-speed valve closing mode (injection end (L) mode) in which the falling rate of the injection rate is slowed (see FIGS. 2C and 2D). Further, the rising speed and the falling speed of the injection rate may be changed midway. According to the fuel injection valve 20, for example, as shown in FIG. 2E, an injection rate pattern (injection end (H→L) mode) for changing from the high speed valve closing mode to the low speed valve closing mode is realized, As shown in 2(f), it is also possible to realize an injection rate pattern (injection start (L→H) mode) for changing from the low speed valve opening mode to the high speed valve opening mode.

The relationship between the open/closed states of the first opening/closing valve 51 and the second opening/closing valve 52 and the operation of the fuel injection valve 20 will be described with reference to FIGS. Before the injection is started, the first solenoid 53 and the second solenoid 54 are de-energized, so that the first opening/closing valve 51 and the second opening/closing valve 52 are both closed, as shown in FIG. The communication between the high pressure chamber 33 and the injection hole 34 is blocked.

The case of the injection pattern in the high speed valve opening mode and the high speed valve closing mode (see FIG. 2A) will be described with reference to FIGS. Before the start of injection, when the first on-off valve 51 and the second on-off valve 52 are closed, the high-pressure fuel is introduced from the first high-pressure passage 13 to the second to fourth main body portions 22 to 24. The formed fuel storage portion (annular chamber 14b, intermediate chamber 26, first control chamber 46, second control chamber 36, high pressure chamber 33) and fuel passage (first passage 25, second passage 27, third passage 42, The connection passage 47) is maintained at a high pressure state equivalent to the fuel pressure in the first high pressure passage 13 (see FIG. 3).

When the first opening/closing valve 51 and the second opening/closing valve 52 are both closed by energizing the first solenoid 53 and the second solenoid 54 in the state where the first opening/closing valve 51 and the second opening/closing valve 52 are closed, as shown in FIG. As shown in, the first control chamber 46 communicates with the low pressure chamber 57 via the first passage 25, the third passage 42, and the second passage 27. As a result, the fuel inside the first control chamber 46 and the second control chamber 36 passes through two routes, a route passing through the first passage 25 and the third passage 42 and a route passing through the second passage 27. Flow into the low pressure chamber 57. Therefore, the fuel pressure inside the first control chamber 46 and the second control chamber 36 decreases at high speed, and the needle valve 31 is displaced at high speed in the valve opening direction (upward direction). As a result, fuel is injected from the injection hole 34. In this case, the injection rate rises at high speed as shown in FIG.

A differential pressure is generated before and after the decompression orifice 42a, and the sum of the upward force due to the fuel pressure inside the first control chamber 46 and the biasing force of the spring 45 is the inside of the intermediate chamber 26 and the annular chamber 14b. It is higher than the downward force due to fuel pressure. Therefore, the driven valve 41 is kept in contact with the second main body portion 22 when both the first opening/closing valve 51 and the second opening/closing valve 52 are open (see FIG. 4 ).

When the first opening/closing valve 51 is closed after the injection rate reaches the maximum, the fuel in the first control chamber 46 flows into the intermediate chamber 26 via the third passage 42, so that the inside of the intermediate chamber 26 The fuel pressure rises (see FIG. 5). Further, by closing the second opening/closing valve 52, the communication between the low pressure chamber 57 and the first control chamber 46 is cut off. In this case, the downward force due to the fuel pressure inside the intermediate chamber 26 and the annular chamber 14b becomes larger than the total of the upward force due to the fuel pressure inside the first control chamber 46 and the biasing force of the spring 45. As a result, the driven valve 41 moves downward (see FIG. 6). The downward movement of the driven valve 41 causes the high-pressure fuel in the first high-pressure passage 13 to flow into the first control chamber 46.

At this time, since the first opening/closing valve 51 and the second opening/closing valve 52 are both closed, the fuel pressure inside the first control chamber 46 rises at a high speed. When the fuel flows from the first control chamber 46 into the second control chamber 36 through the connection passage 47 and the fuel pressure inside the second control chamber 36 becomes higher than a predetermined pressure, the needle valve 31 starts to descend and closes. The operation shifts (see FIG. 6). In this case, as shown in FIG. 2A, the injection rate falls at a high speed. After that, the injection hole 34 is closed by the needle valve 31, so that the fuel injection by the fuel injection valve 20 is stopped.

Next, the case of the injection pattern in the low speed valve opening mode and the high speed valve closing mode (see FIG. 2B) will be described. Before the start of injection, in the state where the first opening/closing valve 51 and the second opening/closing valve 52 are closed (see FIG. 3 ), the second opening/closing valve 52 is maintained in the closed state as shown in FIG. When the on-off valve 51 is opened, the fuel inside the first control chamber 46 flows into the intermediate chamber 26 via the third passage 42 and the first passage 25. At this time, a differential pressure is generated before and after the decompression orifice 42a, and the sum of the upward force due to the fuel pressure inside the first control chamber 46 and the urging force of the spring 45 is the intermediate chamber 26 and the annular chamber 14b. It is higher than the downward force due to the internal fuel pressure. Therefore, the driven valve 41 is maintained in a state of being in contact with the second main body portion 22.

When the second on-off valve 52 is closed, fuel is not allowed to flow through the second passage 27, so that the fuel pressure inside the first control chamber 46 decreases at a low speed, and the needle valve 31 moves at a low speed. Displaces in the valve opening direction. In this case, as shown in FIG. 2B, the injection rate rises at a low speed. That is, the rate of increase (inclination) of the injection rate when the first opening/closing valve 51 is open and the second opening/closing valve 52 is closed is the injection rate when the first opening/closing valve 51 and the second opening/closing valve 52 are both open. Is smaller than the rising speed (slope) of. After the injection rate reaches the maximum, the operation is the same as the operation at the time of high speed fall shown in FIG.

Next, a case of the injection pattern in the high speed valve opening mode and the low speed valve closing mode (see FIG. 2C) will be described. First, the operation at high speed startup is similar to the operation at high speed startup shown in FIG. After the injection rate reaches the maximum, as shown in FIG. 8, when the second opening/closing valve 52 is maintained in the open state and the first opening/closing valve 51 is closed, the fuel in the first control chamber 46 passes through the third passage. It flows into the intermediate chamber 26 via 42, and the fuel pressure inside the intermediate chamber 26 rises. Further, since the second opening/closing valve 52 is in the open state, the fuel inside the first control chamber 46 flows into the low pressure chamber 57 via the second passage 27. The fuel pressure inside the intermediate chamber 26 increases, and the downward force due to the fuel pressure inside the intermediate chamber 26 and the annular chamber 14b causes the upward force due to the fuel pressure inside the first control chamber 46 and the spring 45. When it becomes larger than the total of the urging forces, the driven valve 41 moves downward (see FIG. 9). The downward movement of the driven valve 41 causes the high-pressure fuel in the first high-pressure passage 13 to flow into the first control chamber 46.

At this time, since the second opening/closing valve 52 is maintained in the open state, the fuel pressure inside the first control chamber 46 rises at a low speed. When fuel flows from the first control chamber 46 into the second control chamber 36 via the connection passage 47 and the fuel pressure inside the second control chamber 36 becomes higher than a predetermined pressure, the needle valve 31 starts to descend and closes. The operation shifts (see FIG. 9). In this case, as shown in FIG. 2C, the injection rate falls at a low speed. That is, the rate of decrease (gradient) of the injection rate in the state where the first opening/closing valve 51 is closed and the second opening/closing valve 52 is open is the injection rate in the state where both the first opening/closing valve 51 and the second opening/closing valve 52 are closed. Is smaller than the decreasing speed (slope) of. After that, the injection hole 34 is closed by the needle valve 31, so that the fuel is not injected from the injection hole 34.

FIG. 10 is a diagram showing an operation in the pressure reducing valve mode in which the second on-off valve 52 reduces the fuel pressure in the common rail 11 without injecting fuel from the fuel injection valve 20.

As described above, when both the first on-off valve 51 and the second on-off valve 52 are closed, the fuel pressure inside the second control chamber 36, the first control chamber 46, and the intermediate chamber 26 is equal to that of the first high-pressure passage 13. The fuel pressure is equal to the internal fuel pressure, and the driven valve 41 is in contact with the second body portion 22 (see FIG. 3 ). In the pressure reducing operation, the second opening/closing valve 52 is opened from this state. As a result, as shown in FIG. 10, the fuel in the first control chamber 46 is discharged to the low pressure chamber 57 via the second passage 27, and the driven valve 41 is lowered as the pressure inside the first control chamber 46 decreases. Move in the direction.

In the fuel injection valve 20, in the state where the first opening/closing valve 51 is closed and the second opening/closing valve 52 is opened, the flow rate of fuel through the pressure increasing orifice 14a is larger than the flow rate of fuel through the pressure reducing orifice 27a. It is set. Therefore, when the first opening/closing valve 51 is closed and the second opening/closing valve 52 is opened, the pressure loss of the fuel discharged from the inside of the first control chamber 46 through the second passage 27 in the second passage 27 is reduced. In this case, the pressure loss of the fuel flowing from the second high pressure passage 14 into the first control chamber 46 becomes larger than the pressure loss in the second high pressure passage 14. Accordingly, in the state where the first opening/closing valve 51 is closed and the second opening/closing valve 52 is opened, the needle valve 31 blocks the high pressure chamber 33 from the injection hole 34, that is, the fuel is injected from the injection hole 34. The state that is not done is maintained.

In addition, fuel flows from the common rail 11 into the first control chamber 46 via the first high pressure passage 13 and the second high pressure passage 14, and the inflow fuel is discharged from the first control chamber 46 to the low pressure chamber 57 to inject fuel. By returning to the upstream side (low pressure side) of the system, the fuel pressure inside the common rail 11 decreases. That is, the fuel pressure in the common rail 11 is reduced in a state where fuel is not injected from the fuel injection valve 20. Therefore, the fuel injection valve 20 has a function as a pressure reducing valve that reduces the fuel pressure in the common rail 11.

In the fuel injection valve 20, when the first passage 25 and the low pressure chamber 57 communicate with each other by the first opening/closing valve 51, the driven valve 41 blocks communication between the annular chamber 14b and the first control chamber 46. As described above, the flow passage area of the decompression orifice 42a, the opening area of the intermediate chamber 26 on the side of the third main body portion 23 (first control chamber 46), and the side of the third main body portion 23 (first control chamber 46) of the annular chamber 14b. The opening area and the biasing force of the spring 45 are set. That is, when the first passage 25 and the low pressure chamber 57 are communicated with each other by the first opening/closing valve 51, the first control chamber 46 and the intermediate chamber 26 are communicated with each other by the driven valve 41 via the third passage 42. This is achieved by limiting the fuel flow rate by the decompression orifice 42a, the exposed area of the driven valve 41 to the intermediate chamber 26, the exposed area of the driven valve 41 to the first high pressure passage 13, and the biasing force set by the spring 45. ing.

FIG. 11 is a time chart showing the pressure reduction drive control of the fuel injection valve 20. For example, when the vehicle is decelerated, if there is a pressure reduction request for reducing the rail pressure to the target pressure in a state where both the first opening/closing valve 51 and the second opening/closing valve 52 are closed, the second solenoid 54 is sent along with the pressure reduction request. Energization is started (time t11). At this time, the first solenoid 53 is not energized. With the start of energization of the second solenoid 54, the second opening/closing valve 52 starts to move in the axial direction after a predetermined valve opening delay time Td(i) has elapsed (time t12). As a result, the second opening/closing valve 52 is opened while the first opening/closing valve 51 is closed. By opening the second opening/closing valve 52, high-pressure fuel is discharged from the inside of the common rail 11, and the rail pressure starts to decrease (time t13). Then, when the depressurizing energization time TmF has elapsed from the start of energization, the energization of the second solenoid 54 is stopped (time t14), and the second opening/closing valve 52 is closed. Such a depressurizing operation causes a decrease in the rail pressure of the depressurized amount Pa.

Here, during operation of the engine 70, it may be necessary to reduce the rail pressure to the target pressure while continuing combustion in the engine 70, that is, while injecting fuel from the fuel injection valve 20. In such a case, in this system, some of the plurality of cylinders are set as injection command cylinders that command fuel injection, and fuel injection is continued using the fuel injection valve 20 provided in the injection command cylinders. On the other hand, for the remaining cylinders, fuel injection from the fuel injection valve 20 is not performed, and the rail pressure is reduced by using the fuel injection valve 20 as a pressure reducing valve. As a result, the continuous operation of the engine 70 and the reduction of the rail pressure to the target pressure are both achieved.

By the way, when the fuel injection valve 20 is used as a pressure reducing valve, the rail pressure reduction amount depends on the number of the fuel injection valves 20 that are driven to reduce the rail pressure (hereinafter, also referred to as “pressure reduction driving”). Be different. Specifically, when the energization time to each fuel injection valve 20 is the same, the rail pressure is reduced as the number of fuel injection valves 20 to be pressure-reduced (hereinafter, also referred to as “pressure-reduction driving number Nd”) increases. The amount becomes large, and conversely, the smaller the number Nd of pressure reduction driving, the smaller the pressure reduction amount of the rail pressure. Therefore, in a situation where the number of fuel injection valves 20 that can be pressure-reduced is limited, as in the case where the rail pressure is reduced to the target pressure while continuing the operation of the engine 70, the rail pressure is reduced to the target pressure. There is a concern that it may take a long time.

Therefore, in the present embodiment, when a pressure reduction request for reducing the rail pressure to the target pressure occurs, the energization time for the fuel injection valve 20 performing the pressure reduction operation of the rail pressure is changed according to the pressure reduction driving number Nd of the fuel injection valve 20. It is supposed to be controlled.

A specific mode of drive control of the fuel injection valve 20 when a rail pressure reduction request occurs during operation of the engine 70 will be described with reference to the time charts of FIGS. 12 and 13. 12 and 13 assume that the driver is decelerating the vehicle by performing an accelerator operation. FIG. 13 shows energization pulses to the second on-off valve 52 at the timing A and the timing B in FIG. 12 with respect to the fuel injection valve 20 instructing the pressure reduction drive.

In FIG. 12, consider a case where the accelerator operation is canceled and the accelerator opening becomes zero from the state where the accelerator opening is the first opening θ1. During the period in which the accelerator opening is set to the first opening θ1 (before time t21), the actual rail pressure is controlled by the target pressure PTrg (broken line in FIG. 12), and the pressure reduction request for the common rail 11 is not generated. .. In this case, normal fuel injection control is performed, that is, fuel injection control is performed by using the fuel injection valves 20 of all cylinders (four cylinders in this embodiment) as injection command cylinders that instruct fuel injection. When the number of cylinders of the engine 70 is N, the number of fuel injection valves 20 (hereinafter, also referred to as “injection number Na”) for which fuel injection is instructed is “N”, and the pressure reduction drive number Nd is “0”.

Consider a case in which the engine load decreases as the driver releases the accelerator operation at time t21, the target rail pressure PTrg is changed from P1 to P2 (P1>P2) on the low pressure side, and a pressure reduction request occurs. .. In this case, in order to match the actual rail pressure with the target pressure PTrg, the fuel injection valves 20 of at least some of the cylinders are depressurized in the period after time t21. When the rail pressure reduction request is issued at time t21, the accelerator opening is zero, and no injection command is issued to any of the fuel injection valves 20. In this case, in order to quickly reduce the actual rail pressure to the target pressure PTrg, the maximum value "4" is set as the pressure reduction driving number Nd.

Thereafter, at time t22, the driver operates the accelerator to change the accelerator opening to the second opening θ2 (θ2<θ1), and when the engine load increases, the number Na of injections increases according to the accelerator opening. As the injection number Na increases, the pressure reduction driving number Nd decreases. In FIG. 12, at time t22, “1” is set as the injection number Na and “3” is set as the pressure reduction driving number Nd. As a result, one cylinder (for example, the fourth cylinder) out of all cylinders is instructed to perform fuel injection at a predetermined injection timing, and the remaining cylinders (first cylinder to third cylinder) are supplied with predetermined drive timing. Decompression drive is commanded. The injection timing and the drive timing are calculated based on the engine operating state (engine rotation speed and engine load), respectively.

By reducing the pressure of the fuel injection valves 20 of some of the cylinders (three cylinders in FIG. 12), the actual rail pressure gradually decreases. Eventually, when the actual rail pressure matches the target pressure PTrg, the pressure reduction drive is terminated for the fuel injection valve 20 that is instructed to perform the pressure reduction drive, and normal fuel injection control is performed (time t23 and thereafter).

Here, when the number Nd of pressure reduction driving is simply reduced as the engine load increases, the amount of rail pressure reduction becomes smaller than when the rail pressure is reduced using all the fuel injection valves 20. In this case, it may take time to match the rail pressure with the target pressure PTrg (see the alternate long and short dash line in FIG. 12). In consideration of such a point, in the present embodiment, the energization time of the fuel injection valve 20 is variably controlled according to the number Nd of pressure-reduction driving. Specifically, the smaller the number Nd of pressure reduction drives, the longer the energization time of each fuel injection valve 20 to be pressure-reduced.

In FIG. 13, (a) shows the energization pulse output to the fuel injection valve 20 at the timing A in FIG. 12, and (b) shows the energization pulse output to the fuel injection valve 20 at the timing B in FIG. The pulse is shown. The pressure reduction driving number Nd at the time A is “4”, and the pressure reduction driving number Nd at the time B is “3”.

The length of the energizing pulse (energizing time) is calculated based on the difference between the actual rail pressure and the target pressure PTrg (hereinafter referred to as “pressure deviation ΔP”). Specifically, the larger the pressure deviation ΔP, the longer the energization time is set. At the timing A, the pressure deviation ΔP is as large as ΔP1, and a relatively long time TmFA is set as the energization time of the fuel injection valve 20. In each fuel injection valve 20, the time TmFA is set as the command value of the energization time, and each fuel injection valve 20 is depressurized based on the set command value. Here, the rail pressure is reduced using the fuel injection valves 20 of all the cylinders (first cylinder to fourth cylinder).

On the other hand, at the timing B, the pressure deviation ΔP is as small as ΔP2 (ΔP2<ΔP1). In this case, a time TmFB shorter than the time TmFA is set as the energization time of the fuel injection valve 20 calculated based on the pressure deviation ΔP (see the alternate long and short dash line in FIG. 13B). However, at the time B, it is necessary to secure the output as the engine load increases, and the pressure reduction driving number Nd is limited to "3". In this case, if the fuel injection valve 20 is pressure-reduced for the time TmFB calculated based on the pressure deviation ΔP, it takes time for the rail pressure to decrease to the target pressure PTrg. Therefore, after the time t22, the energization time of the fuel injection valve 20 during the pressure reducing drive is corrected to be longer because the number Nd of the pressure reducing drive is smaller. In FIG. 13, the basic energization time TmFB calculated based on the pressure deviation ΔP is corrected to be longer according to the pressure reduction driving number Nd, and the fuel injection valve 20 is instructed to perform the pressure reduction driving at the corrected time TmFk. Thus, the rail pressure is controlled so as to quickly converge to the target pressure PTrg.

Next, the processing procedure of the pressure reduction drive control of the fuel injection valve 20 will be described using the flowchart of FIG. This processing is executed by the microcomputer of the ECU 90 every predetermined cycle (for example, every 180°C).

In FIG. 14, in step S101, the target pressure PTrg is calculated. Here, the engine speed detected by the crank angle sensor and the accelerator operation amount detected by the accelerator sensor are input, and the target pressure PTrg is calculated using the sensor detection values. The target pressure PTrg is set to a value on the high pressure side as the engine speed increases or the accelerator operation amount increases.

In the following step S102, the actual rail pressure P detected by the fuel pressure sensor 73 is acquired. In step S103, the basic depressurization flow rate QmB of the common rail 11 is calculated based on the difference (pressure deviation ΔP) between the actual rail pressure P and the target pressure PTrg. Here, the basic reduced pressure flow rate QmB is calculated by the following equation (1). In the following formula (1), V represents the volume of the common rail 11, and K represents the bulk elastic coefficient.
QmB=ΔP×V÷K (1)
Instead of using the above equation (1), the basic depressurization flow rate QmB may be calculated using a two-dimensional map of the pressure deviation ΔP and the actual rail pressure P.

In step S104, the feedback correction amount QmFB stored in the RAM or the like of the ECU 90 is acquired, and the reduced pressure flow amount Qm of the common rail 11 is calculated using the basic reduced pressure flow amount QmB and the feedback correction amount QmFB. In this embodiment, the reduced pressure flow rate Qm is calculated by the following equation (2).
Qm=QmB+QmFB (2)

In a succeeding step S105, the pressure reduction driving number Nd is calculated. In the present embodiment, the pressure reduction driving number Nd is calculated based on the engine operating state (engine load and engine rotation speed). At this time, as the engine load is higher or the engine rotation speed is higher, a larger value is set as the injection number Na and a smaller value is set as the pressure reduction driving number Nd. FIG. 15 shows an example of a map for setting the number Nd of pressure reduction drives. According to the map of FIG. 15, the pressure reduction driving number Nd is set to “4” in the engine low rotation/low load region, and the pressure reduction driving number Nd decreases as the engine 70 increases in rotation/high load. The total number of the reduced pressure drive number Nd and the injection number Na is equal to or less than the total number of the fuel injection valves 20 mounted on the engine 70.

In the following step S106, the effective flow coefficient k(i) of each cylinder (where i represents the cylinder number, the same applies hereinafter) is calculated. The effective flow rate coefficient k(i) is a coefficient representing the pressure reducing performance of each fuel injection valve 20 in the current engine operating state, and is the actual rail pressure P and the pressure reducing flow rate per fuel injection valve (=Qm/Nd). Is calculated for each fuel injection valve 20 based on In the present engine operating state, when there is no error between the theoretical value and the actual value of the depressurized flow rate of each fuel injection valve 20, "1" is set as the effective flow rate coefficient k(i), and there is an error. In this case, a value less than 1 is set. Therefore, 0<k(i)≦1 in a cylinder that drives the fuel injection valve 20 to reduce pressure (hereinafter, also referred to as “pressure reduction drive cylinder”), and k(i)= in other cylinders (that is, injection command cylinders). It becomes 0.
Pressure-reduced cylinder: k(i)=f(P, Qm/Nd)
Injection command cylinder: k(i)=0

In step S107, the effective depressurization flow rate QmF is calculated by performing a guard process using the maximum depressurization flow rate set based on the depressurization performance of each fuel injection valve 20. Here, the maximum depressurization flow rate is calculated using the engine speed, the actual rail pressure P, and the integrated value Σk(i) of the effective flow coefficient k(i) of each cylinder, and the maximum depressurization flow rate and the depressurization flow rate Qm are calculated. The smaller value is set as the effective depressurization flow rate QmF.
QmF=min(Qm,f(Ne,P)*Σk(i))

In the following step S108, the effective depressurization flow rate QmF and the effective flow rate coefficient k(i) are used to calculate the depressurization flow rate QmI per one in the fuel injection valve 20 of the depressurization drive cylinder by the following equation (3).
QmI=QmF/(Σk(i)) (3)
In step S109, the reduced pressure flow rate QmI is converted into time to calculate the reduced pressure basic energization time Tm per fuel injection valve of the reduced pressure drive cylinder.
Tm=f (P, QmI)

In step S110, the pressure reduction start delay correction of the pressure reduction basic energization time Tm is performed. The time from the start of energization of the second solenoid 54 of the pressure-reduction driven cylinder to the actual opening of the second opening/closing valve 52 (hereinafter, referred to as "valve opening delay time Td(i)") is individual difference. There is. In addition, the time from the start of energization of the second solenoid 54 of the pressure-reduction driven cylinder until the rail pressure actually starts to decrease, that is, the pressure-reduction start delay time Ty(i), also differs for each fuel injection valve 20. In consideration of this point, in the present process, the depressurization flow rate characteristic of each fuel injection valve 20 is stored in the memory of the ECU 90 as a map or the like, and the depressurization drive characteristic corresponding to the fuel injection valve 20 of the depressurization drive cylinder is stored in the memory. The basic depressurization energization time Tm is corrected in accordance with the depressurized flow rate characteristics of each fuel injection valve 20 by reading from.

FIG. 16 shows an example of the reduced pressure flow rate characteristic map. In the depressurized flow rate characteristic map of FIG. 16, the relationship between the depressurized energization time and the depressurized flow rate of the common rail 11 is determined for each fuel injection valve 20 according to the rail pressure. The period from the depressurization energizing time 0 to the elapse of a predetermined time is a dead zone in which the rail pressure does not change even when the second solenoid 54 is energized, and the depressurization start delay time Ty(i) is set for each fuel injection valve 20. It is stored in advance. In the present embodiment, the pressure reduction start delay times Ty(1), Ty(2), Ty(4) of the first cylinder #1, the second cylinder #2, and the fourth cylinder #4 are the time TyA, and the third cylinder The pressure reduction start delay time Ty(3) of #3 is a time TyB that is longer than the time TyA. According to this reduced pressure flow rate characteristic map, it is possible to acquire the reduced pressure start delay time Ty(i) and the reduced pressure flow rate when the fuel injection valve 20 is driven to reduce the pressure independently. The microcomputer of the ECU 90 reads out the decompression start delay time Ty(i) of each fuel injection valve 20 with reference to the decompression flow rate characteristic map, and corrects the decompression basic energization time Tm by the following formula (4) to drive the decompression. The pressure reducing energization time TmF(i) for instructing the fuel injection valve 20 of the cylinder is calculated for each fuel injection valve 20.
TmF(i)=Tm+Ty(i) (4)

Returning to the description of FIG. 14, in step S111, a drive command corresponding to the pressure-reducing energization time TmF(i) is issued to the pressure-reducing cylinder, and pressure-reducing energization for reducing the rail pressure is executed. Note that which cylinder is to be the pressure-reduction driven cylinder is determined according to, for example, a predetermined selection order. Specifically, when the selection order is determined to be the first cylinder #1, the second cylinder #2, the third cylinder #3, and the fourth cylinder #4, when there are three pressure-reduction driven cylinders, the first cylinder is selected. ~ The third cylinder is set as the pressure-reduction driven cylinder. The injection command for the injection command cylinder is executed by another routine (not shown).

In subsequent step S112, the actual rail pressure (post-energization rail pressure Pb) is acquired after the power supply to the fuel injection valve 20 of the pressure-reduction driven cylinder is completed. In step S113, the feedback correction amount QmFB is calculated according to the difference between the actual rail pressure P before the start of the current energization and the post-energization rail pressure Pb, and stored in the memory. Here, the feedback correction amount QmFB is calculated by the following equation (5). In the formula (5), V represents the volume of the common rail 11, and K represents the bulk elastic coefficient.
QmFB=QmF−(P−Pb)×V÷K (5)

When the actual rail pressure P converges to the target pressure PTrg by repeatedly executing such a series of controls at a constant cycle, the pressure deviation ΔP between the target pressure PTrg and the actual rail pressure P becomes 0, and the fuel injection valve 20 is used. The pressure reduction drive is ended.

According to this embodiment described in detail above, the following excellent effects can be obtained.

The energization time of the fuel injection valves 20 to be pressure-reduced is controlled according to the number of the fuel injection valves 20 to be pressure-reduced. In a situation where the number of fuel injection valves 20 used for reducing the rail pressure is limited, the opening of the second opening/closing valve 52 is controlled by the same energization time as when the limitation is not imposed. It is feared that the rail pressure cannot be quickly reduced due to the low flow rate of reduced pressure. In this regard, in the above configuration, the energization time for pressure reduction drive to the fuel injection valves 20 is variably controlled according to the number of fuel injection valves 20 to be pressure-reduced, so that the number of fuel injection valves 20 to be pressure-reduced is limited. In this case, an appropriate energizing time can be set according to the number. As a result, the rail pressure can be quickly reduced to the target pressure RTrg, and the accuracy of rail pressure control can be improved.

Specifically, the depressurization energization time TmF is set such that the energization time of the second solenoid 54 becomes longer as the depressurization driving number Nd is smaller. As a result, even in a situation where the number of fuel injection valves 20 that can be pressure-reduced is limited, by increasing the pressure reduction flow rate per fuel injection valve 20, it is possible to cover the reduced pressure flow rate for the number reduction. ..

Further, in the fuel injection system that variably controls the injection rate of the fuel injection valve 20 by using the fuel injection valve 20 including the first opening/closing valve 51 and the second opening/closing valve 52, the pressure reducing function of the fuel injection valve 20 is used. Since the pressure reducing control is performed, even if the pressure reducing valve is not provided in the common rail 11 or if the pressure reducing valve fails in a system in which the common rail 11 is provided with the pressure reducing valve, the rail pressure can be accurately measured. Can be controlled by.

A structure in which the relationship between the energization time of the second solenoid 54 and the depressurized flow rate is stored in advance as depressurized flow rate characteristics for each fuel injection valve, and the depressurized basic energization time Tm is calculated using the stored depressurized flow rate characteristics. And There is an individual difference in the time from the start of energization of the second solenoid 54 to the time when the rail pressure actually decreases, and it is conceivable that the depressurization characteristics differ for each fuel injection valve 20 due to the individual difference. Therefore, with the above configuration, rail pressure control can be performed with higher accuracy.

Further, in the present embodiment, the reduced pressure flow characteristic map is stored in advance, and the reduced pressure basic energization time Tm is corrected using the reduced pressure start delay time Ty(i) read from the reduced pressure flow characteristic map. With this configuration, it is possible to accurately grasp the depressurized flow rate characteristic of each fuel injection valve 20, and to improve the rail pressure control accuracy.

Among the plurality of fuel injection valves 20, the number of fuel injection valves 20 included in the engine 70 (that is, the number of cylinders) is subtracted from the number Na of injections to be equal to or less than the number Nd of pressure reduction drive. In this case, the fuel injection valve 20 instructed to inject fuel and the fuel injection valve 20 instructed to reduce the rail pressure can be separated from each other, and both combustion of the engine 70 and reduction of the rail pressure can be achieved at the same time. it can.

In the fuel injection valve 20 that is driven to reduce pressure, by opening and closing the second opening/closing valve 52, pressure pulsation is likely to occur in the first high pressure passage 13 and the second high pressure passage 14. Therefore, when the fuel is injected from the fuel injection valve 20 used for the pressure reduction drive, the injection pressure is not stable, and the amount of fuel injected into the cylinder may become unstable. On the other hand, when the fuel injection valve 20 instructed to inject fuel and the fuel injection valve 20 instructed to drive the pressure reduction are separated from each other, when combustion of the engine 70 is continued in parallel with pressure reduction of the rail pressure, The fuel injection control can be accurately performed.

(Other embodiments)
The present invention is not limited to the above embodiment and may be implemented as follows, for example.

In the above embodiment, the pressure reduction driving number Nd is calculated based on the engine load and the engine rotation speed to calculate the pressure reduction driving number Nd based on the engine operating state. However, the pressure reduction driving number Nd is calculated based on the engine operating state. The configuration to be performed is not limited to this. For example, the number Nd of the pressure-reducing driving is performed depending on whether or not the fuel injection by the fuel injection valve 20 is performed in one or more cylinders of the first cylinder to the fourth cylinder, that is, whether or not there is an injection request. May be calculated. Specifically, when no fuel injection command is issued to any of the fuel injection valves 20 (when the accelerator opening is zero, etc.), the fuel injection valves mounted on the engine 70 are set as the pressure reduction driving number Nd. A total number of 20 (“4” in the fuel injection system of FIG. 1) is set. On the other hand, when at least one of the fuel injection valves 20 is instructed to inject fuel to burn the engine 70 (when the accelerator opening is greater than zero, etc.), a predetermined number (d) as the pressure reducing drive number Nd ( For example, "3") is set.

The pressure reduction driving number Nd may be calculated by setting the injection number Na based on the engine operating state and subtracting the injection number Na from the total number Nt of the fuel injection valves 20 mounted on the engine 70. At this time, the difference between the total number Nt and the injection number Na may be the pressure reduction driving number Nd, or the number smaller than the difference between the total number Nt and the injection number Na may be the pressure reduction driving number Nd.

-Instead of the configuration using the pressure reduction flow rate characteristic map stored in advance, the relationship between the pressure reduction energization time of the fuel injection valve 20 and the rail pressure reduction flow rate is learned and learned as the pressure reduction flow rate characteristic for each fuel injection valve 20. It is also possible to use the depressurized flow rate characteristic of each fuel injection valve 20 to calculate the energization time of the fuel injection valve 20 to be depressurized. According to this configuration, since the depressurized flow rate characteristic is acquired by learning, even when the depressurized flow rate characteristic changes from the initial state due to aged deterioration or the like, the energization time can be calculated corresponding to the change. The learning is performed, for example, by acquiring the reduced pressure flow rate of the rail pressure with respect to the command value during a period in which fuel injection is not performed from any of the fuel injection valves 20.

In the above embodiment, the decompression start delay time Ty(i) is used to correct the decompression basic energization time Tm, but the valve opening delay time Td(i) is used instead of the decompression start delay time Ty(i). It may be configured to correct the basic energizing time Tm for pressure reduction. In this case, the pressure reducing energization time TmF(i) for instructing the fuel injection valve 20 of the pressure reducing cylinder is calculated by the following equation (6).
TmF(i)=Tm+Td(i) (6)

There is a correlation between the valve opening delay time Td(i) and the pressure reduction start delay time Ty(i). Therefore, the decompression start delay time Ty(i) is calculated using the valve opening delay time Td(i), and the decompression energization time TmF(i) is calculated using the calculated decompression start delay time Ty(i). It may be configured. Also in this case, the depressurizing energization time TmF(i) can be accurately calculated according to the depressurized flow rate characteristics of each fuel injection valve 20. Specifically, in the case of performing fuel injection from the fuel injection valve 20 into the cylinder, it is the time from the start of energization of the fuel injection valve 20 to the actual start of fuel injection from the injection hole 34. A certain valve opening delay time Td(i) is learned. Then, the depressurization start delay time Ty(i) is calculated using the learned valve opening delay time Td(i), and the depressurization energization time TmF(i) is calculated by the above equation (4).

In the above-described embodiment, a part of all the cylinders is the pressure-reduction driven cylinder and the rest are the injection command cylinders, so that the fuel injection valve 20 for the pressure reduction drive and the fuel injection valve 20 for the injection command are separated from each other. The rail pressure may be reduced by reducing the pressure of the fuel injection valve 20 that issues an injection command. In this case, the fuel injection valve 20 is depressurized during the period when fuel injection is not performed.

The fuel pressure sensor 73 in the above embodiment is attached to the first high pressure passage 13 and detects the pressure of the high pressure fuel supplied to the fuel injection valve 20, but the fuel pressure sensor is attached to the first high pressure passage 13. It is not limited to what is present. For example, a fuel pressure sensor may be mounted on the common rail 11 to detect the pressure of the high pressure fuel supplied to the fuel injection valve 20. Alternatively, the fuel pressure sensor mounted on the fuel injection valve 20 may be used to detect the pressure inside the injection valve as the pressure of the high-pressure fuel, or the fuel discharge sensor mounted on the high-pressure pump may be used to detect the pump discharge pressure. It may be detected as the pressure of the high-pressure fuel.

The configuration of the fuel injection valve 20 is not limited to the configuration shown in FIG. For example, in the fuel injection valve 20 of FIG. 1, when the driven valve 41 blocks the first high pressure passage 13 and the first control chamber 46, the second passage 27 is formed inside the driven valve 41 and the third passage 27 is formed. It may be configured to communicate with the first control chamber 46 via a passage different from the passage 42. Alternatively, when the second passage 27 communicates with the intermediate chamber 26 and the driven valve 41 blocks the first high pressure passage 13 and the first control chamber 46, the second passage 27 connects the intermediate chamber 26 and the third passage 42. It may be configured to communicate with the first control chamber 46 via the.

Further, in the fuel injection valve 20 of FIG. 1, two or more opening/closing valves are provided as the second opening/closing valve 52 for adjusting the moving speed of the needle valve 31, and opening/closing of these two or more opening/closing valves are individually controlled. Therefore, the moving speed of the needle valve 31 may be adjusted with higher accuracy. In this case, the flow rate of fuel through the pressure increasing orifice 14a is set to be larger than the total flow rate of fuel through the pressure reducing orifices provided in the fuel passages of the two or more on-off valves.

In the above embodiment, the case where the invention is applied to the fuel injection system in which the common rail 11 is not provided with the pressure reducing valve has been described, but in the fuel injection system in which the common rail 11 is provided with the pressure reducing valve, the fuel injection valve 20 is replaced with the pressure reducing valve. You may make it function as.

The control unit and the method described in the present disclosure are provided by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied by a computer program, May be realized. Alternatively, the control unit and the method thereof described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method thereof described in the present disclosure are based on a combination of a processor and a memory programmed to execute one or a plurality of functions and a processor configured by one or more hardware logic circuits. It may be implemented by one or more dedicated computers configured. Further, the computer program may be stored in a computer-readable non-transition tangible recording medium as an instruction executed by a computer.

10... Fuel injection system, 11... Common rail (accumulation container), 13... First high pressure passage, 20... Fuel injection valve, 25... First passage, 27... Second passage, 31... Needle valve, 34... Injection hole, 36 ...Second control chamber, 46...first control chamber, 51...first opening/closing valve, 52...second opening/closing valve (pressure adjusting valve), 57...low pressure chamber, 70...engine (internal combustion engine), 73...fuel pressure sensor ( Fuel pressure detection unit), 90... ECU (pressure reduction control unit, pressure reduction number setting unit, basic time calculation unit, characteristic storage unit, characteristic learning unit, injection number setting unit, injection control unit).

Claims (9)

A fuel injection system comprising a pressure accumulator (11) for accumulating fuel in a high pressure state, and a fuel injection valve (20) provided for each cylinder for a plurality of cylinders of an internal combustion engine and injecting high pressure fuel in the accumulator. hand,
The fuel injection valve,
A control chamber (36, 46) to which the high-pressure fuel from the pressure accumulator is supplied through a high-pressure fuel passage (13, 14);
A needle valve (31) for injecting fuel from an injection hole (34) by moving in the axial direction according to the fuel pressure inside the control chamber;
A pressure adjusting valve (52) which opens with the energization to adjust the fuel pressure inside the control chamber;
Has
When a decompression request for decompressing the internal fuel of the pressure accumulator is made, by energizing one or more of the plurality of fuel injection valves to open the pressure regulating valve, the energization is performed. A pressure reducing control unit for performing a pressure reducing drive control for reducing the pressure of the internal fuel of the pressure accumulating container without injecting fuel from the injection hole of the target fuel injection valve of
A pressure reduction number setting unit that sets the number of the fuel injection valves that command execution of the pressure reduction drive control in accordance with the pressure reduction request,
Equipped with
The pressure reduction control unit is a fuel injection system that controls the energization time of the fuel injection valve that performs the pressure reduction drive control based on the number of the fuel injection valves set by the pressure reduction number setting unit. A fuel pressure detector (73) for detecting the fuel pressure of the high-pressure fuel,
A basic time calculation unit that calculates a basic drive time as an energization time of the fuel injection valve for the pressure reduction drive control based on a deviation between the fuel pressure detected by the fuel pressure detection unit and the target pressure of the high-pressure fuel. When,
Equipped with
The said pressure reduction control part correct|amends the said basic drive time so that the valve opening time of the said pressure control valve may become long, so that the number of the fuel injection valves which command execution of the said pressure reduction drive control decreases. Fuel injection system. A characteristic storage unit that stores the relationship between the energization time of the fuel injection valve and the reduced pressure flow rate of the internal fuel of the accumulator as a reduced pressure flow rate characteristic for each of the plurality of fuel injection valves,
The fuel injection system according to claim 1, wherein the decompression control unit calculates the energization time of the fuel injection valve using the decompression flow rate characteristic of each fuel injection valve stored in the characteristic storage unit. A characteristic learning unit that learns the relationship between the energization time of the fuel injection valve and the reduced pressure flow rate of the internal fuel of the pressure accumulator as a reduced pressure flow rate characteristic for each of the plurality of fuel injection valves,
The fuel injection system according to claim 1 or 2, wherein the decompression control unit calculates the energization time of the fuel injection valve by using the decompression flow rate characteristic of each of the fuel injection valves learned by the characteristic learning unit. The fuel injection according to any one of claims 1 to 4, wherein the pressure reduction number setting unit sets the number of fuel injection valves that command execution of the pressure reduction drive control based on an operating state of the internal combustion engine. system. An injection number setting unit that sets the number of fuel injection valves that command fuel injection among the plurality of fuel injection valves,
The pressure reduction number setting unit instructs the execution of the pressure reduction drive control to be equal to or less than the difference between the total number of the fuel injection valves included in the internal combustion engine and the number of the fuel injection valves that command the fuel injection. The fuel injection system according to claim 1, wherein the fuel injection system is set as the number of valves. When an injection request for injecting fuel from the fuel injection valve and the pressure reduction request occur, a part of the plurality of fuel injection valves is used as a fuel injection valve for instructing the fuel injection, and the rest is the pressure reduction. The fuel injection system according to any one of claims 1 to 6, which is a fuel injection valve that commands execution of drive control. The fuel injection valve,
A first on-off valve (51) connected to the control chamber and arranged in a first fuel passage (25, 42) having a first orifice (42a);
A second on-off valve (52) connected to the control chamber and arranged in a second fuel passage (27) having a second orifice (27a) for restricting the flow rate of fuel by a flow passage area smaller than the first orifice; ,
Have
The pressure regulating valve is the second opening/closing valve,
The injection control unit that variably controls the injection rate of the fuel injection valve by controlling the opening and closing of the first on-off valve and the second on-off valve. Fuel injection system. The decompression control unit injects fuel from the injection hole of the fuel injection valve for which execution of the decompression drive control is instructed by opening the second opening/closing valve while closing the first opening/closing valve. The fuel injection system according to claim 8, wherein the internal fuel of the pressure accumulating container is depressurized without being caused.

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