JP6772913B2 - Fuel injection control device - Google Patents

Description

The present invention relates to a fuel injection control device that controls the amount of fuel injected into an engine by using a piezo injector.

As a fuel injection control device that controls the amount of fuel injected into an engine by using a piezo injector, for example, the device described in Patent Document 1 is known. The device of Patent Document 1 has a first charge control pattern for main injection and a second charge control pattern for minute injection other than main injection as charge control patterns for charging the piezo element laminate in the piezo injector. are doing.

In the second charge control pattern, the rate of increase in the charge voltage of the piezo element laminate is made slower than that of the first charge control pattern in the first half of the charge period. On the other hand, in the latter half of the charging period, the rate of increase in the charging voltage of the piezo element laminate is made faster than that of the first charging control pattern. As a result, while keeping the charging completion arrival timing of the first charge control pattern and the second charge control pattern constant, the time when the charge voltage according to the second charge control pattern reaches the valve opening start value is charged by the first charge control pattern. The voltage is set to be later than the time when the valve opening start value is reached. As a result, it is possible to reduce the actual injection amount even if the command value of the injection period cannot be set to be equal to or less than the charging period of the piezo element laminate at the time of minute fuel injection.

Japanese Unexamined Patent Publication No. 2016-84748

In Patent Document 1 described above, when a plurality of injections are performed, after calculating the injection start time and injection period of each injection, for example, in the case of main injection, the first charge control pattern is adopted, and other than the main injection. In the case of minute injection (pre-injection, pilot injection, after-injection, post-injection), the second charge control pattern is adopted to charge the piezo element laminate. As described above, in Patent Document 1, the amount of fuel in each injection is controlled by the injection period.

Here, the fuel pressure injected from the piezo injector tends to be increased more and more in order to improve the fuel efficiency performance and the purifying property of the exhaust gas. When the fuel pressure inside the piezo injector is increased, if the injection amount is controlled by the injection period as in Patent Document 1, it is necessary to shorten the injection period corresponding to the minute injection. However, the injection command period for controlling this injection period is limited by the computing power of the fuel injection control device and the like, and there is a limit to its shortening.

The present invention has been made in view of the above points, and provides a fuel injection control device capable of injecting a minute amount of fuel with high accuracy even when the fuel pressure is increased. The purpose is.

In order to achieve the above object, in the fuel injection control device according to the present invention, the nozzle valve (32) opens when the piezo element (57) expands due to the input of energy, and the nozzle valve opens when the piezo element contracts due to the release of energy. The piezo injector (24) that closes the valve is used to control the amount of fuel injected into the engine (23).
Injection amount calculation units (S110, S120) that calculate the target fuel injection amount based on the operating state of the engine,
If the target fuel injection amount calculated by the injection amount calculation unit is less than the predetermined reference fuel injection amount, the target fuel injection amount is smaller than the reference total energy amount input to the piezo element when the reference fuel injection amount is injected. Total energy amount calculation unit (S210) that calculates the total energy amount corresponding to
It is provided with input energy amount control units (S220, S230) that control the amount of energy input to the piezo element so that the total energy amount is calculated by the total energy amount calculation unit.

The amount of elongation of the piezo element has a correlation with the total amount of energy input to the piezo element. In the present invention, a minute fuel injection amount is controlled by utilizing this relationship. Therefore, when the calculated target fuel injection amount is less than the predetermined reference fuel injection amount, the total energy amount calculation unit is smaller than the reference total energy amount input to the piezo element when injecting the reference fuel injection amount. Calculate the total energy amount corresponding to the target fuel injection amount. By inputting the calculated total energy amount into the piezo element, the extension amount of the piezo element corresponds to the target fuel injection amount. As a result, according to the present invention, it is possible to inject a desired minute amount of fuel with high accuracy without being restricted by the minimum injection command period.

The reference numbers in parentheses are merely examples of the correspondence with the specific configuration in the embodiment described later in order to facilitate the understanding of the present invention, and limit the scope of the present invention. Not intended.

In addition to the above-mentioned features, the technical features described in each claim of the claims will be clarified from the description of the embodiment and the attached drawings described later.

It is a block diagram which shows the whole structure of the fuel injection control system to which the fuel injection control device by Embodiment is applied. It is the schematic sectional drawing for demonstrating the structure of a piezo injector. It is a circuit diagram which showed the drive circuit of the piezo injector included in the fuel injection control device, and the ECU for controlling this drive circuit. It is a flowchart which showed the process executed by the fuel injection control device. It is a graph which showed that the injection period control is executed when the injection amount is equal to or more than the injection amount Qb corresponding to the minimum injection command period, and the input energy control is executed when it is less than the injection amount Qb. It is a flowchart which shows the processing content of input energy control. It is a graph which shows an example of the relationship between the injection amount less than Qb corresponding to the minimum injection command period, and the total energy amount. 6 is a timing chart showing an example of injection period control executed when the injection amount to be injected is equal to or more than the injection amount Qb corresponding to the minimum injection command period. 6 is a timing chart showing an example of injection period control executed when the injection amount to be injected is the injection amount Qb corresponding to the minimum injection command period. 6 is a timing chart showing an example of input energy control executed to inject an injection amount less than the injection amount Qb corresponding to the minimum injection command period. It is a graph for demonstrating a modification.

Hereinafter, embodiments of the fuel injection control device according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram showing an overall configuration of a fuel injection control system to which the fuel injection control device according to the present embodiment is applied.

As shown in FIG. 1, the fuel in the fuel tank 20 is pumped by the fuel pump 21 through a fuel filter (not shown). The fuel pump 21 includes a fuel metering valve, and discharges a fuel amount in response to an instruction signal from the fuel injection control device 1.

The fuel discharged from the fuel pump 21 is pressurized and supplied (pumped) to the common rail 22. The common rail 22 stores the fuel pumped from the fuel pump 21 in a high-pressure state, and supplies the fuel to the piezo injector 24 provided in each cylinder of the diesel engine 23 (4 cylinders are illustrated in FIG. 1) via the high-pressure fuel passage. To do. The piezo injector 24 is connected to a low-pressure fuel passage (not shown) that reaches the fuel tank 20, and is configured to be able to return fuel to the fuel tank 20 through the low-pressure fuel passage (not shown).

The structure of the piezo injector 24 will be described with reference to FIG. As shown in FIG. 2, a columnar needle accommodating portion 31 is provided at the tip of the body 30 of the piezo injector 24. The needle accommodating portion 31 has a two-stage configuration of a large diameter portion and a small diameter portion. The needle accommodating portion 31 accommodates a nozzle needle 32 that can be displaced in the axial direction thereof. Then, the high-pressure fuel from the high-pressure fuel passage is supplied to the needle accommodating portion 31 via the supply path 33 formed in the body 30.

The nozzle needle 32 is seated on the needle seat portion 34 formed at the tip of the small diameter portion of the needle accommodating portion 31 to shut off the needle accommodating portion 31 from the combustion chamber of the diesel engine 23 (nozzle needle valve closed state). On the other hand, the nozzle needle 32 communicates with the needle accommodating portion 31 and the combustion chamber of the diesel engine 23 by separating from the needle seat portion 34, and high-pressure fuel is supplied from the injection hole 35 connected to the needle accommodating portion 31 to the combustion chamber. (Nozzle needle valve open state).

In the needle accommodating portion 31, a nozzle cylinder 36 is provided on the back surface side of the nozzle needle 32 (the side opposite to the side seated on the needle seat portion 34). The nozzle cylinder 36 forms a control chamber 38 together with the rear end surface of the nozzle needle 32 and the inner surface of the body 30. Further, a return spring 39 is provided between the nozzle cylinder 36 and the flange of the nozzle needle 32, and the nozzle needle 32 is pressed by the return spring 39 in the direction of being seated on the needle seat portion 34.

The control plate 40 is housed in the control chamber 38. A through hole 41 including an orifice is formed in the center of the control plate 40. The control chamber 38 communicates with the intermediate valve chamber 46 via a communication passage 45 formed in the body 30. When the intermediate valve 47 provided in the intermediate valve chamber 46 is closed, high-pressure fuel is introduced from the needle accommodating portion 31 through the communication passage 44 including the orifice. Therefore, when the intermediate valve 47 is closed, the high-pressure fuel in the intermediate valve chamber 46 is introduced into the control chamber 38 via the communication passage 45, and the inside of the control chamber 38 is filled with the high-pressure fuel. The back pressure of the high-pressure fuel in the control chamber 38 presses the nozzle needle 32 in the direction of being seated on the needle seat portion 34.

Further, in the control chamber 38, a control chamber spring 42 is provided between the back end surface of the nozzle needle 32 and the control plate 40. The control chamber spring 42 presses the control plate 40 upward in the control chamber 38 (in the direction away from the nozzle needle 32) and abuts on the inner surface of the body 30. The control plate 40 in contact with the inner surface of the body 30 is placed on the upper surface of the control plate 40 via the supply passage 43 including the communication passage 45 and the orifice when the intermediate valve 47 is switched from the valve open state to the valve closed state. The high-pressure fuel applied pushes the body 30 away from the inner surface and downward (in the direction approaching the nozzle needle 32). Then, when the high-pressure fuel is introduced into the space between the control plate 40 and the nozzle needle 32 through the through hole 41 and the pressure difference applied to the upper and lower surfaces of the control plate 40 becomes smaller, the control plate 40 is moved. The pressing force of the control chamber spring 42 returns to the state of being in contact with the inner surface of the body 30.

The intermediate valve 47 provided in the intermediate valve chamber 46 receives a pressing force in the valve closing direction by the spring 48. By this pressing force, the intermediate valve 47 is seated on the valve seat portion 49, which is a corner portion of the opening formed on the upper surface of the intermediate valve chamber 46, so that the opening of the intermediate valve chamber 46 to the discharge passage 50 is opened. Is closed, and the communication between the intermediate valve chamber 46 and the discharge passage 50 connected to the low-pressure fuel passage is cut off (intermediate valve closed state).

On the other hand, the intermediate valve 47 is in contact with the pressure pin of the small diameter piston 51 displaceable in the piston cylinder 53. When the intermediate valve 47 is pushed downward by the pressure pin of the small diameter piston 51, the intermediate valve 47 is separated from the valve seat portion 49, the opening of the communication passage 44 in the intermediate valve chamber 46 is closed, and the intermediate valve chamber is closed. The 46 and the discharge passage 50 are communicated with each other (intermediate valve open state). As a result, the high-pressure fuel in the intermediate valve chamber 46 flows out to the low-pressure fuel passage through the discharge passage 50, so that the fuel pressure in the intermediate valve chamber 46 decreases.

The small-diameter piston 51 receives a pressing force in the direction of the intermediate valve 47 by a spring 52 provided between the small-diameter piston 51 and the piston cylinder 53. Due to this pressing force, the tip of the pressure pin of the small diameter piston 51 comes into contact with the intermediate valve 47. However, the pressing force of the spring 48 in the intermediate valve chamber 46 is higher than the pressing force of the spring 52, and due to the pressure of the high pressure fuel introduced in the intermediate valve chamber 46, the large diameter piston 55 causes the small diameter piston 51 to move. The intermediate valve 47 remains closed unless moved downward.

The upper surface of the small-diameter piston 51 opposite to the side on which the pressure pin is provided faces the lower surface of the large-diameter piston 55 via the oil-tight chamber 54. The upper surface of the large-diameter piston 55 is connected to the piezo element 57. Further, in the large-diameter piston 55, a pressing force is applied by the spring 56 in a direction away from the small-diameter piston 51. The piezo element 57 is fixed to the body 30 on the opposite side to the side connected to the large-diameter piston 55.

The piezo element 57 includes a laminated body in which a plurality of piezoelectric elements are laminated, and the piezo element 57 functions as an actuator by expanding and contracting due to the inverse piezoelectric effect. Specifically, the piezo element 57 is a capacitive load, which expands when electric energy is input and charged, and contracts when electric energy is released by electric discharge.

The operation of the piezo injector 24 having the above-described configuration will be described.

When electrical energy is applied to the piezo element 57 and the piezo element 57 expands, the large-diameter piston 55 moves in a direction approaching the small-diameter piston 51. Then, the movement of the large-diameter piston 55 is expanded and transmitted to the small-diameter piston 51 through the oil-tight chamber 54, and the small-diameter piston 51 moves larger than the large-diameter piston 55 in the direction of the intermediate valve 47. As a result, the intermediate valve 47 is pushed down and separated from the valve seat portion 49 to open the valve. At this time, the intermediate valve 47 closes the opening in the intermediate valve chamber 46 of the communication passage 44 that communicates the intermediate valve chamber 46 and the needle accommodating portion 31, and also communicates the intermediate valve chamber 46 with the discharge path 50. Therefore, the high-pressure fuel in the intermediate valve chamber 46 is discharged to the low-pressure fuel passage, and the fuel pressure in the intermediate valve chamber 46 decreases. As the fuel pressure in the intermediate valve chamber 46 decreases, the high-pressure fuel in the control chamber 38 flows out to the intermediate valve chamber 46 through the through hole 41 including the orifice and the communication passage 45. As a result, the fuel pressure in the control chamber 38, that is, the back pressure of the nozzle needle 32 decreases, so that the nozzle needle 32 moves in the direction of the control chamber 38 to open the valve.

When the electric energy input to the piezo element 57 is released by electric discharge and the piezo element 57 contracts, the large-diameter piston 55 and the small-diameter piston 51 move in a direction away from the intermediate valve chamber 46. Then, due to the pressing force of the spring 48, the intermediate valve 47 is seated on the valve seat portion 49 and is closed. As a result, the communication between the intermediate valve chamber 46 and the discharge passage 50 (low-pressure fuel passage) is cut off, and the opening of the communication passage 44 in the intermediate valve chamber 46 of the communication passage 44 is opened. Therefore, high-pressure fuel is introduced into the intermediate valve chamber 46 through the communication passage 44 including the orifice, and the fuel pressure gradually increases. The high-pressure fuel introduced into the intermediate valve chamber 46 is applied to the upper surface of the control plate 40. Further, high-pressure fuel from the supply path 43 including the orifice is also applied to the upper surface of the control plate 40.

The high-pressure fuel applied to the upper surface of the control plate 40 is also introduced into the control chamber 38 through the through hole 41 including the orifice. However, due to the presence of the orifice, there is a time delay for the fuel pressure in the control chamber 38 to become the same pressure as the high pressure fuel on the upper surface side of the control plate 40. Therefore, the control plate 40 moves in the direction approaching the nozzle needle 32 due to the differential pressure of the fuel pressure applied to the upper and lower surfaces. Then, the displacement of the control plate 40 is transmitted to the nozzle needle 32 via the control chamber spring 42, and the nozzle needle 32 is displaced so as to be seated on the needle seat portion 34. After that, when the pressure difference applied to the upper and lower surfaces of the control plate 40 becomes smaller, the control plate 40 returns to the state of being in contact with the inner surface of the body 30 due to the pressing force of the control chamber spring 42.

The fuel injection control system shown in FIG. 1 above detects the accelerator opening sensor that detects the opening degree of the accelerator pedal, the rotation sensor that detects the crank position and the rotation speed of the diesel engine 23, and the fuel pressure in the common rail 22. It is equipped with various sensors such as a fuel pressure sensor that detect the operating state of the diesel engine 23. The detection results of these various sensors are taken into the fuel injection control device 1. Then, the fuel injection control device 1 executes a process for operating various actuators of the diesel engine 23 such as the piezo injector 24 and the fuel pump 21 based on the detection result. Among the processes performed by the fuel injection control device 1, the configuration and processing for operating the piezo injector 24 will be described in detail below.

As shown in FIG. 3, the fuel injection control device 1 is a drive circuit for inputting (charging) electrical energy to the piezo element 57 of the piezo injector 24 and discharging (discharging) electrical energy from the piezo element 57. A 10 and an ECU 19 for controlling the drive circuit 10 are provided. Although only one piezo element 57 is shown in FIG. 3, the drive circuit 10 charges and discharges all the piezo elements 57 by switching the piezo element 57 to be processed by a changeover switch (not shown). To execute. However, the piezo element 57 may be divided into several groups, and a plurality of drive circuits 10 corresponding to the number of the groups may be provided.

The drive circuit 10 includes a DC-DC converter 12 as shown. The DC-DC converter 12 boosts the voltage of the battery 11 (for example, "12V") to a high voltage (for example, "150 to 300V") for charging the piezo element 57. The boosted voltage of the DC-DC converter 12 is applied to the capacitor 13. As a result, the capacitor 13 is charged to the boosted voltage. It is desirable that the capacitor 13 has a capacitance whose voltage hardly changes by one charging process of the piezo element 57.

The high-potential side terminal of the capacitor 13 is connected to the high-potential terminal side of the piezo element 57 via a series circuit of the charging switch 14 and the charge / discharge coil 16. A freewheel diode 14a is connected in parallel to the charging switch 14. The low potential terminal side of the piezo element 57 is grounded via the resistor 18.

The connection line 12b is branched from the connection line 12a between the charging switch 14 and the charge / discharge coil 16, and the branched connection line 12b is connected to the ground potential via the discharge switch 15. A freewheel diode 15a is connected in parallel to the discharge switch 15.

In the drive circuit 10 configured as described above, when the charging switch 14 is turned on, an gradually increasing current flows from the capacitor 13 to the piezo element 57 via the charging switch 14 and the charging / discharging coil 16. When the charge switch 14 is turned off from this state, the induced electromotive force generated in the charge / discharge coil 16 becomes a forward bias with respect to the free wheel diode 15a, and is composed of the charge / discharge coil 16, the piezo element 57, and the free wheel diode 15a. A gradually decreasing current flows through the closed circuit. That is, by turning the charging switch 14 on and off, as shown in FIG. 8 and the like, a piezo current for charging the piezo element 57 flows through the piezo element 57.

On the other hand, when the discharge switch 15 is turned on, a gradually increasing current flows from the piezo element 57 to the ground via the charge / discharge coil 16 and the discharge switch 15. When the discharge switch 15 is turned off from this state, the induced electromotive force generated in the charge / discharge coil 16 becomes a forward bias with respect to the freewheel diode 14a, and the piezo element 57, the charge / discharge coil 16, the freewheel diode 14a, and the capacitor A gradually decreasing current flows through a closed circuit consisting of 13. That is, by turning the discharge switch 15 on and off, as shown in FIG. 8 and the like, a piezo current for discharging the piezo element 57 flows through the piezo element 57.

The ECU 19 has a microcomputer (so-called microcomputer) configured to include a CPU, a ROM, a RAM, a register, an I / O port, and the like. In the ECU 19, the CPU of the microcomputer uses the temporary storage function of the RAM or the register, and the charging switch of the drive circuit 10 described above is based on a control program stored in advance in the ROM, various data acquired via the bus, and the like. A control signal for turning on / off the 14 and the discharge switch 15 is generated and output.

Here, in a diesel engine, in addition to the main injection, minute injections such as pre-injection, pilot injection, after-injection, and post-injection are performed in order to reduce engine noise and vibration, improve exhaust gas purification performance, and the like. Has become common. When such minute injection is performed, when the fuel pressure introduced inside the piezo injector 24 is further increased, the fuel injection control device is a type that controls the injection amount according to the injection period as in the conventional case. There is a possibility that sufficient accuracy cannot be obtained with respect to the minute injection due to the limit of the calculation speed or the like in 1.

Therefore, in the fuel injection control device 1 according to the present embodiment, when performing minute injection, the injection amount is controlled not by the injection period but by the electric energy input to the piezo element 57.

The electrical energy input to the piezo element 57 when the piezo element 57 is charged is determined by the product of the terminal voltage of the piezo element 57 and the piezo current flowing through the piezo element 57. The terminal voltage of the piezo element 57 increases as the piezo current is energized. As shown in FIG. 8 and the like, the piezo current gradually increases with the passage of time during the on period of the charging switch 14, and gradually decreases from the time when the charging switch 14 is turned off. The length of this on period determines the magnitude of the current value of the piezo current. Therefore, the electric energy input to the piezo element 57 can be controlled by the on period of the charging switch 14.

Then, as shown in FIG. 8, the piezo injector 24 repeatedly turns the charging switch 14 on and off, and when the total amount of electric energy input to the piezo element 57 reaches a predetermined valve opening required energy, the piezo injector 24 is operated. Due to the displacement of the small-diameter piston 51 due to the extension amount of the piezo element 57, the intermediate valve 47 begins to separate from the valve seat portion 49, and the intermediate valve 47 starts opening.

As described above, the extension amount of the piezo element 57 has a correlation with the total amount of electric energy input to the piezo element 57. In the fuel injection control device 1 according to the present embodiment, by utilizing this relationship, it is possible to control a minute fuel injection amount with high accuracy. Hereinafter, the process executed by the fuel injection control device 1 will be described with reference to the flowchart of FIG.

First, in the first step S100, the detection results of various sensors necessary for calculating the required injection amount, the number of injections, and the injection timing are acquired. For example, the fuel injection control device 1 acquires detection results from an accelerator opening sensor, a rotation sensor, a common rail fuel pressure sensor, a water temperature sensor, and the like. Then, in step S110, the required injection amount is calculated based on the acquired detection result. For example, based on the amount of operation of the accelerator pedal (accelerator opening) detected by the accelerator opening sensor and the engine rotation speed obtained from the detection result of the rotation sensor, the engine torque required according to the accelerator opening is calculated. The injection amount to be generated is calculated as the required injection amount.

In step S120, it is determined whether or not to perform divided injection in one combustion cycle of each cylinder of the engine based on the required injection amount calculated in step S110, the engine rotation speed, and the like. At this time, if it is determined that the split injection is performed, the number of times the split injection is performed, the injection timing of each injection, and the injection amount at each injection are further calculated based on the operating state of the diesel engine. On the other hand, when it is determined that the divided injection is not performed, the injection timing of one injection is calculated.

In step S130, it is determined whether or not the injection amount of the injection is equal to or more than the reference amount for the injection whose injection time comes earliest. Here, the reference amount can be set to a value corresponding to the injection amount injected from the piezo injector 24 when the injection period of the piezo injector 24 is set to the minimum injection command period. In this determination process, if it is determined that the injection amount is equal to or more than the reference amount, the process proceeds to step S140, and if it is determined to be less than the reference amount, the process proceeds to step S150.

In step S140, the injection amount to be injected is equal to or more than the reference amount, and it is possible to set the injection command period equal to or longer than the minimum injection command period for the injection of the injection amount to be injected. , The injection period control that controls the injection amount according to the injection period is executed. That is, in the present embodiment, as shown in FIG. 5, when the injection amount to be injected is Qa and is equal to or more than the injection amount Qb corresponding to the minimum injection command period, the injection period control is executed and the injection is performed. The injection amount is controlled according to the period.

An example of injection period control when the injection amount to be injected is Qa is shown in the timing chart of FIG. In this case, the injection command period corresponding to the required injection amount Qa is set by a map or the like according to the fuel pressure on the common rail 22. When the injection command period starts, as described above, the charging switch 14 is started on and off, and electric energy is input to the piezo element 57. When the total amount of the input electric energy reaches the required energy for opening the valve, the intermediate valve 47 starts opening the valve.

In FIG. 8, the reason why the peak value of the piezo current for charging is lower than the peak value of the piezo current for subsequent charging at the beginning of the injection period is that the intermediate valve 47 is suddenly displaced. This is to prevent the generation of noise and the like. However, the peak value of the piezo current for charging may be constant during the injection command period.

The nozzle needle 32 of the piezo injector 24 starts to open when the intermediate valve 47 is started to open and the back pressure in the control chamber 38 decreases. Therefore, there is a time lag between the start of opening the intermediate valve 47 and the start of opening the nozzle needle 32. Fuel injection is started when the nozzle needle 32 starts valve opening, and as shown in FIG. 8, the fuel injection rate gradually increases until the nozzle needle 32 reaches the fully open position.

Then, when the injection command period ends, the discharge switch 15 is started on and off, and the electric energy stored in the piezo element 57 is released. When the electric energy of the piezo element 57 decreases due to the release of the electric energy, the intermediate valve 47 starts to be displaced toward the closed position at a certain timing. Then, when the electric energy of the piezo element 57 is reduced to the energy required to open the valve, the intermediate valve 47 is closed.

With the displacement of the intermediate valve 47 in the valve closing direction, a differential pressure is generated in the fuel pressure applied to the upper and lower surfaces of the control plate 40, and the differential pressure causes the control plate 40 to be displaced toward the nozzle needle 32. start. As a result, the valve position of the nozzle needle 32 approaches the valve closing position. As a result, the fuel injection rate gradually decreases, and the fuel injection is stopped when the nozzle needle 32 reaches the valve closing position.

In the injection period control, in this way, the total amount of fuel injected from the piezo injector 24 from the start to the stop of fuel injection is controlled so as to correspond to the injection period.

An example of injection period control when the injection amount to be injected is the injection amount Qb corresponding to the minimum injection command period is shown in the timing chart of FIG. The total amount of electrical energy input to the piezo element 57 is the same as in the case of the injection amount Qa if the fuel pressure introduced into the piezo injector 24 is the same, but the injection command period is longer than in the case of the injection amount Qa. Is also getting shorter. However, the minimum injection command period is restricted by the calculation capacity, calculation cycle, time for charging process, and the like in the fuel injection control device 1. Therefore, there is a limit to shortening the minimum injection command period.

In step S150, the injection amount to be injected is less than the reference amount, and the target injection amount cannot be accurately injected depending on the injection period control. Therefore, the injection amount is controlled by the amount of energy input to the piezo element 57. Perform input energy control. In this input energy control, as shown in FIG. 5, the injection command period is set to the minimum injection command period, and the total amount of electric energy input to the piezo element 57 is the total amount of electric energy required to obtain the injection amount Qb. Control less than.

This input energy control will be described with reference to FIGS. 6, 7, 10, and the like. FIG. 6 is a flowchart showing the processing contents of the input energy control. FIG. 7 is a graph showing an example of the relationship between the injection amount less than the injection amount Qb corresponding to the minimum injection command period and the total energy amount. FIG. 10 is a timing chart showing an example of input energy control for injecting an injection amount Qc less than the injection amount Qb corresponding to the minimum injection command period. In the timing chart of FIG. 10, the state at the time of injecting the injection amount Qb corresponding to the minimum injection command period is shown by a dotted line.

In the input energy control, first, in step S210 of the flowchart of FIG. 6, the total amount of electric energy corresponding to the injection amount to be injected is obtained. For example, as shown in FIG. 7, when the injection amount to be injected is an injection amount Qc less than the injection amount Qb, the electric energy corresponding to the injection amount Qb is according to the relationship between the injection amount and the electric energy shown in FIG. The total amount of electric energy corresponding to the injection amount Qc is obtained by subtracting the injection amount energy sensitivity β (Pc0, Qb, Qc) based on the total amount Eb of.

The relationship between the injection amount and the total amount of electrical energy shown in FIG. 7 is experimentally measured in advance and stored in a memory such as a ROM of the ECU 19. However, the relationship between the injection amount and the total amount of electrical energy is measured and stored at various fuel pressures introduced into the piezo injector 24. This is because when the fuel pressure changes, the valve opening required energy of the intermediate valve 47 also changes, and as a result, the relationship between the injection amount and the total amount of electrical energy also changes. The relationship between the injection amount and the total amount of electrical energy shown in FIG. 7 may be saved as a function or as a map. In particular, when stored as a function, the relationship between the injection amount and the total amount of electrical energy may be approximated in linear form.

When the total amount of electric energy corresponding to the injection amount less than the reference amount is obtained as described above, then, in step S220 of the flowchart of FIG. 6, it is determined in advance based on the size of the reference electric energy with respect to the total amount Eb. According to the memorized relationship, the energization pattern in which the on period for turning on the charging switch 14 is shortened is set. The relationship used to shorten the on period is determined by the charging voltage of the capacitor 13 of the drive circuit 10, the inductance of the charge / discharge coil 16, the capacitance of the piezo element 57, the resistance value of the resistor 18, and the like, and the ROM of the ECU 19 and the like. Saved in memory.

For example, when the injection amount to be injected is Qc, as shown in the timing chart of FIG. 10, the on-periods of all the charging switches 14 are shortened from the on-periods of the charging switches 14 when the injection amount is Qb. Is also good. As a result, as shown in FIG. 10, the rate of energy input to the piezo element 57 is reduced, and the total amount of electrical energy input to the piezo element 57 is injected more than the total amount of electrical energy Eb corresponding to the injection amount Qb. It can be reduced by the amount energy sensitivity β (Pc0, Qb, Qc). As a result, as shown in FIG. 10, the valve opening start of the nozzle needle 32 can be delayed and the valve closing end of the nozzle needle 32 can be accelerated, and the total injection amount is controlled to the injection amount Qc smaller than the injection amount Qb. Will be done.

In order to make the total amount of electric energy input to the piezo element 57 smaller than the reference total amount of electric energy Eb, the on period of all the charging switches 14 is not shortened, but at least one on period. May be shortened. Alternatively, for example, by omitting at least one of the energy input due to the energization of the piezo current shown by the dotted line in FIG. 10, that is, by reducing the number of energy input, the total amount of electrical energy input to the piezo element 57 can be obtained. It can also be reduced.

Then, in step S230, the total amount of electrical energy input to the piezo element 57 is controlled to the target total amount of energy by turning the charging switch 14 on and off according to the set energization pattern.

The explanation will be continued by returning to the flowchart of FIG. 4 again. When the input energy control is executed in step S150 described above, the fuel injection amount actually injected from the piezo injector 24 is calculated and stored in the subsequent step S160. This actual fuel injection amount is determined by, for example, providing a pressure sensor in the piezo injector 24 for measuring the fuel pressure, and measuring the fuel pressure in the piezo injector 24 when the nozzle needle 32 is opened, which is measured by the pressure sensor. It can be calculated from the degree of decrease.

In step S170, it is determined whether or not all the injections calculated in step S120 have been completed. If it is determined that all the injections have not been completed, the process returns to the process of step S130. On the other hand, if it is determined that all the injections have been completed, the process proceeds to step S180.

In step S180, it is determined whether or not a verification request has occurred. The verification request means a request for confirming whether or not the total amount of electric energy input to the piezo element 57 corresponds to the actual injection amount so as to correspond to the target injection amount. This verification request is generated by the fuel injection control device 1, for example, when the vehicle starts traveling or every time a predetermined time elapses. If it is determined that the verification request has occurred, the process proceeds to step S190, and if it is determined that the test request has not occurred, the process shown in the flowchart of FIG. 4 ends.

In step S190, the difference in injection amount between the injection amount of each divided injection calculated in step S120 and the actual injection amount calculated and stored in step S160 is compared. At this time, when the minute injections smaller than the reference amount are performed a plurality of times, the average of the injection amount differences in the plurality of injections may be obtained.

In the following step S200, when the difference in injection amount exceeds the permissible range, the relationship between the injection amount and the total amount of electrical energy shown in FIG. 6 is corrected. As a result, even if the relationship between the injection amount and the total amount of electrical energy changes due to deterioration or wear of each part of the piezo injector 24, the target injection amount is injected from the piezo injector 24 regardless of such a change. Can be made to.

Although the preferred embodiment according to the present invention has been described above, the present invention can be variously modified and implemented without being limited to the above-described embodiment without departing from the gist of the present invention. ..

For example, in the above-described embodiment, the injection amount Qb corresponding to the minimum injection command period is set as the reference amount, and if the injection amount to be injected is equal to or more than the reference amount, the injection period control is executed, and if it is less than the reference amount, the injection period control is executed. It was intended to perform input energy control.

However, an injection amount other than the injection amount Qb corresponding to the minimum injection command period may be used as a reference amount. For example, as shown in FIG. 11, the injection amount Qa corresponding to the injection command period longer than the minimum injection command period may be used as the reference amount. Also in this case, if the injection amount to be injected is equal to or more than the reference amount, the injection period control is executed, and if it is less than the reference amount, the input energy control is executed. However, in the input energy control, as shown in FIG. 11, the injection command period is shortened as the injection amount to be injected decreases from the injection command period of the injection amount Qa to the minimum injection command period. Alternatively, as the injection command period, the same injection command period as the injection command period of the injection amount Qa may be used.

Further, in the above-described embodiment, a pressure sensor for measuring the fuel pressure is provided in the piezo injector 24, and the degree of decrease in the fuel pressure in the piezo injector 24 when the nozzle needle 32 is opened, which is measured by the pressure sensor. Therefore, it was explained that the actual fuel injection amount is calculated. In addition to this configuration, a property sensor for detecting the properties of the fuel may be further provided, and the fuel injection amount may be calculated in consideration of the properties of the fuel. For example, in a diesel engine, the properties of fuel for cold regions are different from those of fuel for non-cold regions. Since these fuels have different fuel densities, the calculation accuracy can be improved by detecting the properties of the fuel and reflecting it in the calculation of the fuel injection amount.

1: Fuel injection controller, 10: Drive circuit, 11: Battery, 12: DC-DC converter, 12a: Connection line, 12b: Connection line, 13: Capacitor, 14: Charging switch, 14a: Free wheel diode, 15: Discharge switch, 15a: Free wheel diode, 16: Charge / discharge coil, 18: Resistance, 19: ECU, 20: Fuel tank, 21: Fuel pump, 22: Common rail, 23: Diesel engine, 24: Piezo injector

Claims (10)

The nozzle valve (32) opens when the piezo element (57) expands due to the input of energy, and the nozzle valve (32) closes when the piezo element (57) contracts due to the release of energy. Is a fuel injection control device that controls the amount of fuel injected into the engine (23) by using the above.
Injection amount calculation units (S110, S120) that calculate the target fuel injection amount based on the operating state of the engine, and
When the target fuel injection amount calculated by the injection amount calculation unit is less than a predetermined reference fuel injection amount, it is smaller than the reference total energy amount to be input to the piezo element when the reference fuel injection amount is injected. The total energy amount calculation unit (S210) that calculates the total energy amount corresponding to the target fuel injection amount, and
A fuel injection control device including input energy amount control units (S220, S230) that control the amount of energy input to the piezo element so that the total energy amount is calculated by the total energy amount calculation unit. The piezo injector
A back pressure chamber (38) in which high-pressure fuel is introduced to generate back pressure of the nozzle valve, and
A valve chamber (46) provided between the back pressure chamber and the low-pressure passage and into which the high-pressure fuel is introduced through the introduction port,
A valve body (arranged in the valve chamber, driven in the valve opening direction according to the extension of the piezo element, closes the introduction port of the high-pressure fuel, and communicates the back pressure chamber and the low-pressure passage. 47) and
The fuel injection control device according to claim 1, wherein the total energy amount calculation unit calculates a total energy amount corresponding to the target fuel injection amount in consideration of the pressure of the high-pressure fuel. The fuel injection according to claim 1 or 2, wherein the amount of fuel (Qb) injected from the piezo injector is used as the reference fuel injection amount when the injection command period of the piezo injector is set to the minimum injection command period. Control device. The injection command period for injecting the target fuel injection amount is set to the same length as the injection command period for injecting the reference fuel injection amount, and the input energy amount control unit is within the injection command period. The fuel injection control device according to claim 3, wherein the energy corresponding to the total energy amount calculated by the total energy amount calculation unit is input to the piezo element. The invention according to claim 1 or 2, wherein when the injection command period of the piezo injector is set to an injection command period longer than the minimum injection command period, the amount of fuel injected from the piezo injector is used as the reference fuel injection amount. Fuel injection control device. The injection command period for injecting the target fuel injection amount is shorter than the injection command period corresponding to the reference fuel injection amount and is the minimum injection according to the ratio of the target fuel injection amount to the reference fuel injection amount. The injection command period is set to be longer than the command period, and the input energy amount control unit generates energy corresponding to the total energy amount calculated by the total energy amount calculation unit within the set injection command period. The fuel injection control device according to claim 5, which is charged into the fuel injection control device. The input energy amount control unit inputs energy to the piezo element in a plurality of times, and reduces the amount of energy input at least once to reduce the energy input rate. The fuel injection control device according to any one of claims 1 to 6, wherein a total energy amount smaller than the total energy amount when injecting the reference fuel injection amount is input to the piezo element. The input energy amount control unit inputs energy to the piezo element in a plurality of times, and reduces the number of times of energy input as compared with the case of injecting the reference fuel injection amount. The fuel injection control device according to any one of claims 1 to 6, wherein a total energy amount smaller than the total energy amount when injecting the reference fuel injection amount is input to the piezo element. When the target fuel injection amount calculated by the injection amount calculation unit is equal to or greater than the reference fuel injection amount, an injection period setting means (S140) for setting an injection command period according to the target fuel injection amount is provided.
When the target fuel injection amount is equal to or greater than the reference fuel injection amount, the fuel amount injected from the piezo injector is any one of claims 1 to 8 controlled by an injection command period set by the injection period setting means. The fuel injection control device according to. The actual injection amount estimation unit (S160) for estimating the actual fuel injection amount injected from the piezo injector is provided.
When the actual fuel injection amount estimated by the actual injection amount estimation unit and the target fuel injection amount are different, the total energy amount calculation unit calculates the total energy amount corrected according to the difference. The fuel injection control device according to any one of 1 to 9.

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