JPH04308338A - Fuel injection controller for diesel engine - Google Patents

Abstract

PURPOSE:To always drive (extend) a piezo actuator with accuracy even if a Diesel engine varies in the rotation in a fuel injection controlling device for extending the piezo actuator through a fly-back circuit. CONSTITUTION:A piezo actuator driving circuit 90 is provided with a current limiting circuit consisting of a comparator COM for generating a low level signal when the voltage of a resistor R2 exceeds desired voltage VPO and an AND circuit AND for turning on a transistor TR to supply current to a primary winding L1 when both charge controlling signal SP1 and comparator output reach high level. Current for shutting off current supply to the primary winding L1 to determine the extending amount of the piezo actuator 73 is controlled to desired current.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a fuel injection control device for a diesel engine that uses a piezo actuator to control the fuel injection amount, fuel injection timing, fuel injection rate, etc. from a fuel injection device that injects fuel into a diesel engine. More specifically, the present invention relates to a fuel injection control device for a diesel engine that controls fuel injection by passing a current through an inductor and driving a piezo actuator using a high voltage generated in the inductor when the current is interrupted.

0002

2. Description of the Related Art Conventionally, as one of the fuel injection control devices for diesel engines, there has been known a device that controls fuel injection by increasing or decreasing the fuel pressure in a high pressure chamber of a fuel injection device using a piezo actuator ( For example, JP-A-2-4
9953).

This type of fuel injection control device uses a highly responsive piezo actuator to realize pilot injection (fuel injection performed prior to main fuel injection) to improve fuel combustion efficiency in a diesel engine. The drive circuit for the piezo actuator includes a flyback circuit that charges and extends the piezo actuator using the high voltage generated in the inductor when the inductor is energized and the energization is cut off. is often used.

Furthermore, in such a flyback circuit, the charging voltage that determines the amount of extension of the piezo actuator is determined by the value of the current flowing through the inductor when the inductor is energized, and this current flow varies depending on the energization time of the inductor. Therefore, in a conventional fuel injection control device that uses a flyback circuit to drive a piezo actuator, the timing of charging the piezo actuator
By reducing the inductor energization time required to extend the piezo actuator by a predetermined amount, the time to start energizing the inductor is determined, and by energizing the inductor from this energization start time until the piezo actuator charging time, the amount of elongation of the piezo actuator can be determined. is under control.

That is, in order to accurately control the fuel pressure in the high pressure chamber of the fuel injection device, it is necessary to accurately control the amount of extension of the piezo actuator. Conventionally, it is necessary to start energizing the inductor before a predetermined time corresponding to the amount of extension of the piezo actuator.
By subtracting the energization time of the inductor from the piezo actuator charging time determined according to the rotation of the diesel engine, the energization start time corresponding to the rotation angle of the diesel engine is determined and the energization of the inductor is started. It is.

[0006]

[Problems to be Solved by the Invention] However, with such conventional fuel injection control devices, when the rotation of the diesel engine is stable, it is possible to accurately control the energization time of the inductor. When rotational fluctuations occur in the engine, the energization time of the inductor changes accordingly, making it impossible to accurately control the amount of extension of the piezo actuator, resulting in a problem in which fuel injection control accuracy deteriorates. .

The present invention was developed in view of these problems, and is capable of always accurately driving the piezo actuator even when rotational fluctuations occur in the diesel engine in a device that extends the piezo actuator using a flyback circuit to control fuel injection. (extension).

[0008]

[Means for Solving the Problems] That is, the present invention, which has been made to achieve the above object, expands and contracts by charging and discharging electric charges to increase and decrease the fuel pressure in the high pressure chamber of the fuel injection device, as illustrated in FIG. a piezo actuator for controlling the fuel injection discharged from the high pressure chamber; a energizing means for energizing the inductor; a charging means for charging the piezo actuator with a high voltage generated in the inductor when the energizing means interrupts the energization; a discharging means for discharging the charge accumulated in the piezo actuator due to charging; a calculating means for calculating charging and discharging timing of the piezo actuator based on the rotational speed and load of the diesel engine; and a calculating means for calculating charging and discharging timing of the piezo actuator based on the calculated charging timing. A diesel engine comprising: determining means for determining when to start energizing the inductor; and driving means for driving the energizing means from the energizing start time to the charging time, and driving the discharging means at the discharging time. In the fuel injection control device, a current detecting means for detecting a current flowing when the inductor is energized; and a current controlling the current flowing through the inductor so that the maximum current detected by the current detecting means becomes a predetermined target current. The present invention is characterized in that it is provided with a control means.

[0009]

[Operation] In the fuel control device for a diesel engine of the present invention configured as described above, the calculation means calculates the timing of charging and discharging the piezo actuator based on the rotational speed and load of the diesel engine, and the determining means calculates the timing of charging and discharging the piezo actuator. , the timing to start energizing the inductor is determined based on the calculated charging timing. Then, the driving means drives the energizing means from the determined energization start time to the charging time, and drives the discharging means at the discharge time. Further, in the present invention, the current detecting means detects the current flowing through the inductor, and the current controlling means controls the current flowing through the inductor so that the detected maximum current becomes a predetermined target current.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings. First, FIG. 2 is a schematic diagram of a fuel injection device 1 according to an embodiment of the present invention.

As shown in the figure, the fuel injection device 1 of this embodiment
A drive shaft 5, which rotates in synchronization with the rotation of a diesel engine (not shown), is rotatably inserted and supported in the housing 3 via a bush 7. Also, at one end of the housing 3 (on the right side in the figure), a distribution head 9 is provided.
is fixed, and a cylinder 11 is fixed to the distribution head 9. Further, a distribution rotor 13 is integrally formed at the tip of the drive shaft 5 (on the right side in the figure), and the distribution rotor 13 is rotatably housed within the cylinder 11.

On the other hand, a fuel supply pump 15 for supplying fuel to the fuel injection device 1 is provided at the outer end of the distribution head 9 (on the right side in the figure). This fuel supply pump 15 includes a casing 17 attached to the cylinder 11.
and a pump rotor 19 connected to the distribution rotor 13, and a plurality of vanes 21 are fitted into the pump rotor 19 so as to be retractable. When the pump rotor 19 rotates due to the rotation of the distribution rotor 13, the fuel in the fuel tank 23 is sucked up from the suction port 27 via the suction passage 25.
The fuel is discharged from the discharge port 29 into the discharge passage 31. Note that the pressure of the fuel discharged into the discharge passage 31 is regulated to a predetermined pressure by a pressure regulating valve 33, and then sent to an annular gallery 35 formed in the distribution head 9.

Next, the cylinder 11 is formed with a plurality of intake passages 37 communicating with the gallery 35, a plurality of distribution passages 39 for supplying fuel to each cylinder of the diesel engine, and a spill passage 41. Each distribution passage 39 communicates via a distribution passage 43 provided in the distribution head 9 with a delivery valve 45 for supplying fuel to each cylinder of the engine. Note that the delivery valve 45 is connected to a fuel injection valve (not shown) installed in each cylinder of the diesel engine.

Next, the distribution rotor 13 has a fuel passage 47.
is formed, and a plurality of suction passages 49, distribution passages 51, and spill passages 53 communicating with this fuel passage 47 are formed. Further, the distribution rotor 13 has a cylindrical hole 57 that slidably accommodates a pair of plungers 55 in an oil-tight state.
A fuel passage 4 is formed between both plungers 55.
A pressure generating chamber 58 communicating with 7 is formed.

A shoe 59 is provided at the radially outer end of each plunger 55, and a roller 61 is rotatably held in the shoe 59. Also, on the outer surface of this roller 61, there is an inner cam ring 6 having a plurality of cam ridges on the inner surface.
3 are arranged. Therefore, when the roller 61 slides on the cam surface of the inner cam ring 63 due to the rotation of the distribution rotor 13, the roller 61 reciprocates along the cam surface in the radial direction of the inner cam ring 63, and this reciprocating motion causes the shoe 5
9 to the plunger 55.

That is, in the fuel injection device 1 of this embodiment, the plunger 55 reciprocates in the radial direction of the distribution rotor 13 in accordance with the rotation of the distribution rotor 13. When moving outward in the direction (suction stroke), the suction passage 49 of the distribution rotor 13 and the suction passage 37 of the cylinder 11 communicate with each other, and the gallery 3
5 into the fuel passage 47, and conversely, when the plunger 55 moves inward in the radial direction of the distribution rotor 13 (pumping stroke), the suction passage 49 closes and the distribution passage 5
1, 39, and 43 communicate with each other to increase the pressure of fuel in the pressure generating chamber 58 and forcefully send the fuel to the delivery valve 45.

Next, the spill passage 53 of the distribution rotor 13 is
It communicates with the spill passage 41 of the cylinder 11 during the pressure feeding stroke. A spill passage 65 is formed at the end of the spill passage 41 and communicates with the gallery 35.
A spill valve 67 that can open and close the spill passage 65 is provided in the middle of the spill passage 65. That is, by opening and closing the spill passage 65 by the spill valve 67 during the pressure feeding stroke, the fuel pressure fed to the delivery valve 45 can be adjusted, and the fuel injection rate from the fuel injection device 1 can be controlled. There is.

The spill valve 67 is composed of a piston 71 that is slidably provided in an oil-tight state in a housing 69, and a number of laminated piezo elements that expand and contract as electric charges are charged and discharged to cause the piston 71 to slide. a piezo actuator 73, a cylinder 77 communicating with the inside of the housing 69 through a small hole 75 formed in the bottom of the housing 69, a valve body 79 slidably inserted into the cylinder 77, and a valve body 79. When the piezo actuator 73 expands and the piston 71 moves toward the cylinder 77,
Oil-tight chamber 8 formed by housing 69 and piston 71
The fuel pressure within 2 increases, and this fuel pressure causes the valve body 79 to move downward in the figure against the biasing force of the spring 81, thereby causing the valve body 79 to close the spill passage 65.

Next, a check valve 8 is installed in the gallery 35.
3 is provided, and this check valve 83 and fuel passage 8
5, the overflow fuel from the gallery 35 is guided to the cooling chamber 87 formed around the piezo actuator 73 in the housing 69 constituting the spill valve 67,
Further, overflow fuel from the cooling chamber 87 is discharged into the fuel tank 23 via a fuel passage 89. In other words, the piezo actuator 73 is cooled by the overflow fuel from the gallery 35.

The piezo actuator 73 is connected to the drive circuit 9
The drive is controlled by an electronic control circuit (ECU) 92 via 0 and 91. That is, the ECU 92 includes the CPU, ROM
A rotation angle sensor 93 that generates a pulse signal at each predetermined rotation angle of the diesel engine, and an accelerator sensor that detects the accelerator operation amount (accelerator opening degree) by the driver. 94 etc. detects the operating state of the diesel engine, and according to the detected operating state, the piezo actuator 73
The drive timing of the piezo actuator 73 (that is, the charging and discharging timing) is determined, and a control signal for expanding and contracting the piezo actuator 73 at the determined drive timing is outputted to the drive circuits 90 and 91, thereby controlling the drive of the piezo actuator 73. Note that this control (namely, fuel injection control) will be described later.

Next, drive circuits 90 and 91 which actually expand and contract the piezo actuator 73 in response to a control signal from the ECU 92 are each constructed as shown in FIG. Although the drive circuits 90 and 91 have the same configuration, in this embodiment, the drive circuit 90 is used for pilot injection, and the other drive circuit 91 is used for main injection.
0 is operated by pilot injection control signals SP1 and SP2 output from the ECU 92, and the drive circuit 91 is operated by the EC
Main injection control signals SM1 and SM output from U92
It operates according to 2.

As shown in FIG. 3, the drive circuit 90 of this embodiment
(91) is the transformer T as an inductor and the ECU9
The primary winding L of the transformer T is turned on by the charge control signal SP1 (SM1) output from the power supply switch SW, and the power supply voltage from the DC power supply B input via the power switch SW causes the primary winding L of the transformer T to be turned on.
a transistor TR as a current-carrying means for passing a current through the
Charging means that charges the piezo actuator 73 by causing current to flow to the piezo actuator 73 side using the high voltage generated in the secondary winding L2 of the transformer T when the transistor TR turns off and cuts off power to the primary winding L1. The diode D1 is turned on by the discharge control signal SP2 (SM2) output from the ECU 92, and the electric charge charged in the piezo actuator 73 is transferred through the secondary winding L2 of the transformer T and the current limiting resistor R1. A DC power source is generated by the MOS type field effect transistor FET as a discharging means and the high voltage generated in the primary winding L1 of the transformer T when the field effect transistor FET is turned off and the discharge of the piezo actuator 73 is completed. It is configured as a well-known flyback type drive circuit including a regeneration diode D2 that charges the DC power supply B by flowing current to the B side.

The drive circuit 90 (91) also includes a resistor R2 as a current detecting means for detecting the current i when the transistor TR is in the on state and the primary winding L1 of the transformer T is energized. The ECU 9 is provided with a voltage across the resistor R2 as a detection signal VP (VM) of the current i.
It is configured to output to 2.

Furthermore, a zener is installed between the drain and gate of the field effect transistor FET in order to prevent overvoltage from being applied to the piezo actuator 73 due to an abnormality in the control signal from the EUC 92, and damaging the piezo actuator 73 and each element. A diode D3 is provided to block the reverse current of the diode ZD1 and the Zener diode ZD1, and when the voltage applied to the piezo actuator 73 exceeds the Zener voltage, the field effect transistor FET is turned on to reduce the voltage. It is made possible. A Zener diode ZD2 is also provided between the collector and base of the transistor TR to turn on the transistor TR and protect the transistor TR when an overvoltage is applied to the transistor TR.

Note that in this embodiment, the transistor TR
A power transistor with a withstand voltage of 400 V or more and a maximum current of about 15 A is used for the FET, and a power MOSFET with a withstand voltage of 1 kV and a maximum current of about 7 A is used for the MOS field effect transistor FET.
However, the transformer T is a transformer with a turns ratio of 1:2 between the primary winding L1 and the secondary winding L2, and the Zener diode ZD1 is a Zener diode with a Zener voltage of 850 V (set by the withstand voltage of the piezo actuator 73). However, the Zener diode ZD2 is a Zener diode with a Zener voltage of 400V, the diode D1 is a diode with a withstand voltage of 1 kV or more and a maximum current of about 3 A, and the diode D2 is a diode with a withstand voltage of 400 V.
00V or more, diodes with a maximum current of about 5A, respectively.
It is used.

The drive circuit 90 (91
), as shown in FIG. 4, when the charging control signal SP1 (SM1) is input from the ECU 92,
1 turns on the transistor TR. Then, a current iP (iM) begins to flow through the primary winding L1 of the transformer T, and the current iP (iM) increases as time passes.

Next, when the input of the charging control signal S1 from the ECU 92 is stopped, at the time t2, the transistor TR
is turned off, and power supply to the primary winding L1 is cut off. At this time, the transformer T stores magnetic energy corresponding to the current (energization cutoff current) iPmax (iMmax) flowing in the primary winding L1, so this causes the secondary winding L2 of the transformer T to Current cutoff current iPmax (iM
max) is generated, and the piezo actuator 73 is charged and expanded by this high voltage. As a result, in the fuel injection device 1, the spill passage 65 is closed, the fuel pressure in the fuel passage 47 increases, and pilot injection (main injection) is started.

Next, the ECU 92 outputs the discharge control signal SP2 (
When SM2) is input, the field effect transistor FET is turned on at time t3, and the electric charge charged in the piezo actuator 73 starts to be discharged via the secondary winding L2 and resistor R1, and the discharge control signal SP2 ( At time t4 when SM2) is no longer input, the field effect transistor FET is turned off and the discharge is completed. This discharge causes the piezo actuator 73 to contract, so in the fuel injection device,
The spill passage 65 opens, the fuel pressure in the fuel passage 47 decreases, and the pilot injection (main injection) ends.

In this way, each drive circuit 90, 91 has an EC
The piezo actuator 73 is activated by charging control signals SP1, SM1 and discharge control signals SP2, SM2 from U92.
expand and contract. Therefore, next, each of these drive circuits 90, 91
charge control signals SP1, SM1 and discharge control signal SP2.
, SM2 will be described with reference to the flowchart shown in FIG. 5.

This fuel injection control process is a process that is executed in synchronization with the fuel injection to each cylinder of the diesel engine. When the process is started, first, in step 100, the information from the rotation angle sensor 93 and the accelerator sensor 94 is Based on the detection signal, the rotational speed NE of the diesel engine and the accelerator opening θACC representing the load on the diesel engine are calculated, and in the subsequent step 110, the rotational speed NE and the accelerator opening θAC are calculated.
Based on C, a pilot injection amount QP and a main injection amount QM of fuel are calculated.

Next, in step 120, as shown in FIG. 6, the piezo actuator 73 is expanded and contracted during the pressure stroke of the fuel injection device 1, so that the fuel injection device 1 is injected with the pilot injection amount QP and the main injection amount QM calculated above. Drive timings TP1, TP2, TM1, and piezo actuator 73 for pilot injection P and main injection M of fuel
A process as a calculation means for calculating TM2 is executed.

Note that each drive timing TP1, TP2, T
As is clear from FIG. 6, M1 and TM2 are the elapsed times from the input timing ts of the reference pulse output from the rotation angle sensor 93 at every predetermined rotation angle of the diesel engine, and TP1 is the time elapsed since the pilot injection is started. The extension timing (charging timing) of the piezo actuator 73, TP
2 is the contraction timing (discharge timing) of the piezo actuator 73 to end the pilot injection, TM1 is the extension timing (charging timing) of the piezo actuator 73 to start the main injection, and TM2 is the piezo actuator 73 to end the main injection. Each shows the contraction timing (discharge timing) of the actuator 73.

Next, in step 130, the current cutoff currents iPmax, iMmax that flowed through the primary winding L1 of each drive circuit 90 during the previous fuel injection are calculated. This calculation is
The detection signal VP output from each drive circuit 90, 91 during the previous fuel injection is determined by the cutoff voltage detection process shown in FIG.
Maximum values VPmax and VMmax of VM and each drive circuit 9
When the transistor TR of 0.91 is on, the transistor T
Bias current iPBE flowing between the base and emitter of R
, iMBE (constant value), and the resistance value r of each resistor R2,
It is executed based on the following equations (1) and (2) with as parameters.

[0034] iPmax=(VPmax/r)-iPBE...(
1) iMmax=(VMmax/r)-iMBE
(2) In other words, in the cutoff voltage detection process in FIG. 7, it is determined whether the detection signals VP and VM output from each drive circuit 90 and 91 exceed the maximum values VPmax and VMmax (steps 210 and 230), The detection signals VP and VM are at the maximum value V
If Pmax and VMmax are exceeded, the maximum value VPm
By changing ax, VMmax to the values of the detection signals VP, VM (steps 220, 240), the maximum value VPmax, VMmax of the voltage generated across the resistor R2 of each drive circuit 90, 91 during fuel injection Therefore, in step 150, the values VPmax,
Divide VMmax by the resistance value r of resistor R2 to find the current flowing through resistor R2 in each drive circuit 90, 91,
From this current, the bias current iP of the transistor TR is
By reducing BE and iMBE, each drive circuit 90,
The maximum current flowing through the primary winding L1 of 91, that is, the current cutoff currents iPmax and iMmax are calculated.

When the actual current cutoff currents iPmax and iMmax in each of the drive circuits 90 and 91 are calculated in this way, the initial value 0 is set to the maximum values VPmax and VMmax in step 140 for the next fuel injection. After setting, in the subsequent step 150, the deviation between the actual energization cutoff currents iPmax, iMmax obtained above and the preset target currents iPO, iMO, that is, the energization cutoff currents iP, i
The control errors ΔiP and ΔiM of M are calculated as shown in the following equations (3) and (4).

△iP=iPmax−iPO (3)
△iM=iMmax−iMO…(4)
In step 160, the obtained control errors △iP and △iM are used to determine the primary order of each drive circuit 90, 91 necessary to extend the piezo actuator 73 by a predetermined amount when the primary winding L1 is cut off. The energization times TdP and TdM to the winding L1 are corrected as shown in the following equations (5) and (6), and TdP=TdP-α・△iP...(5)T
dM=TdM-α・ΔiM (6) In the next step 170, the above-mentioned energization times TdP and TdM are subtracted from the extension timings TP1 and TM1 of the piezo actuator 73 calculated in step 120, so that the extension timings TP1 and TM1 are set. Then, processing as a determining means is executed to calculate timings TP0 and TM0 for starting energization to the primary winding L1 of each drive circuit 90 and 91 necessary to extend the piezo actuator 73 by a predetermined amount.

That is, the amount of expansion of the piezo actuator 73 is determined by the current-carrying current iPmax, iMmax of the primary winding L1 in each drive circuit 90, 91, and the current-carrying current iPmax, iMmax is determined by the current-carrying time of the primary winding L1. In this step 170, the energization time TdP, TdM is subtracted from the extension timing TP1, TM1 of the piezo actuator 73 to determine the energization start timing TP0, TdM to the primary winding L1 of each drive circuit 90, 91. It calculates TM0.

Once the energization start timings TP0 and TM0 of the primary windings L1 of each drive circuit 90 and 91 are determined in this way, the process moves to the following step 180, and the contraction timing of the piezo actuator 73 calculated in step 120 is determined. By adding a predetermined time required to discharge the piezo actuator 73 to 0V to TP2 and TM2, the discharge end timings TP3 and TM3 are calculated. Then, in the subsequent step 190, the charging control signals SP1, SP2 and the discharging control signals SP2, SM2 are set based on the input timing ts of the reference pulse from the rotation angle sensor 93.
The above calculated energization start timings TPO, TMO, extension timings TP1, TM1, contraction timings TP2, TM
By setting the discharge end timings TP3 and TM3, the timer device executes control signal output processing to output control signals SP1, SP2, SM1, and SM2 at each of these timings, and temporarily ends the processing. do.

Note that the process of step 190 corresponds to the above-mentioned driving means, and by this process, the timer device starts measuring time at the time ts when the reference pulse is input from the rotation angle sensor 93, and the timer device starts measuring time at the time ts when the reference pulse is input from the rotation angle sensor 93. As shown in FIG. 2, the output of the charging control signals SP1, SP2 is started at the time t1 when the measured time coincides with the energization start timings TPO, TMO, and the output of the charging control signals SP1, SP2 is started at the time t2 when the measured time coincides with the extension timing TP1, TM1. The output of the discharge control signals SP2 and SM2 is started at the time t3 when the clock time coincides with the contraction timings TP2 and TM2, and the output of the discharge control signals SP2 and SM2 is started at the time t4 when the clock time coincides with the discharge end timings TP3 and TM3. Stop the output of SP2 and SM2. As a result, the piezo actuator 73 operates at a drive timing TP1 corresponding to the operating state of the diesel engine, as shown in FIG.
, TP2, TM1, and TM2.

As explained above, in this embodiment,
Based on the maximum voltages VPmax and VMmax of the resistor R2 detected by the cutoff voltage detection process in FIG.
x and iMmax are calculated (step 130), and this current cutoff current iPmax, iMmax and target current iPO,i
The control errors △iP and △iM of the energization cutoff current are calculated from MO (step 140), and this energization cutoff current iPmax
, iMmax is larger than the target currents iPO, iMO, the energization time T of the primary winding L1 of each drive circuit 90, 91
dP, TdM are short, and on the other hand, the current cutoff current iPmax,i
When Mmax is smaller than the target currents iPO, iMO, the energization time TdP of the primary winding L1 of each drive circuit 90, 91
, TdM is corrected to become longer (step 160).
, the energization start timings TP0 and TP1 are determined (
step 170).

Therefore, according to this embodiment, even if rotational fluctuations occur in the diesel engine, the energization time to the primary winding L1 changes, and the energization cut-off current deviates from the target current, the current will be reduced at the time of the next fuel injection. By quickly correcting this deviation, it becomes possible to control the energization cutoff current to the target current, and it becomes possible to extend the piezo actuator 73 by a predetermined amount of extension.

Note that in this embodiment, each detection circuit 90
, 91 to determine the maximum voltages VPmax and VMmax of the resistor R2 based on the detection signals VP and VM from 91, and steps 130 to 130 to correct the energization times TdP and TdM of the primary winding L1 based on the detection results. The process 170 corresponds to the current control means.

[0043] In the above embodiment, the target value (target current) of the current cutoff current of the primary winding L1 has been described as being set in advance. However, in reality, even if the energization/cutoff current is constant, the voltage applied to the piezo actuator 73 increases as the capacitance of the piezo actuator 73 becomes smaller. If the capacitance is low and the capacitance is very small, the voltage applied to the piezo actuator 73 may become excessive and the piezo actuator 73 may be damaged. When the temperature of the piezo actuator 73 becomes high during operation, etc., and its capacitance becomes extremely large, the voltage applied to the piezo actuator 73 becomes too low, which impairs the drive of the piezo actuator 73 and, by extension, fuel injection control. may occur.

Therefore, in the apparatus of the above embodiment, the temperature of the piezo actuator 73 is directly detected by a temperature sensor, or the temperature of the engine oil, cooling water, fuel temperature,
The temperature of the piezo actuator 73 is estimated based on the operating state of the diesel engine such as the rotation speed, and based on this temperature, each drive circuit 90, 91 is adjusted using a map as shown in FIG.
By setting the target currents iPO and iMO of the primary winding L1 in , it becomes possible to further improve the control accuracy of fuel injection control.

Further, in the above embodiment, the energization cutoff current is controlled to the target current by correcting the energization time of the primary winding L1 based on the error of the energization cutoff current from the target current. As shown in 9, each drive circuit 9
0 and 91, respectively, the voltage of resistor R2 is the target voltage VPO
, VMO, and outputs a low level signal when the voltage of resistor R2 exceeds the target voltages VPO and VMO.
M, output signal from comparator COM and ECU92
A current limiting circuit as a current control means is provided as a current control means consisting of an AND circuit AND which turns on the transistor TR when charging control signals SP1 and SP2 from the comparator COM and the AND circuit AND are both at High level.
The energization/cutoff current of the primary winding L1 may be directly controlled to the target current by the operation.

In this case, if the target voltages VPO and VMO input to the comparator COM are set according to the target currents iPO and iMO obtained from the map shown in FIG. It becomes possible to control the cut-off current optimally according to the temperature of the piezo actuator 73 without delay in response.

The fuel injection control process when performing fuel injection control in this manner will be described below with reference to the flowchart shown in FIG. Note that in FIG. 10, step 30
The processes at steps 0, 310, 320, and 370 are the same as the processes at steps 100, 110, 120, and 190 in FIG. 5, so a detailed explanation will be omitted.

As shown in the figure, in this fuel injection control process, the drive timings of the piezo actuator 73 for pilot injection and main injection of fuel, that is, the extension timings TP1, TM1, and contraction timing TP2, TM
After calculating 2, in step 330, the preset energization time Td is subtracted from the extension timing TP1, TM1 to calculate the energization start timing TP0, TM0 of the primary winding L1, and at the same time, the energization start timing TP0, TM0 is calculated in advance at the contraction timing TP2, TM2. Discharge end timings TP3 and TM3 are calculated by adding the set discharge times. Note that the energization time Td in this case is set to a sufficiently long time such that even if rotational fluctuation occurs in the diesel engine, the energization current of the primary winding L1 can be controlled to be higher than the target current.

In the next step 340, using the map shown in FIG. 8, target values (target currents) iPO, iMO of the energization cutoff currents iPmax, iMmax corresponding to the temperature of the piezo actuator 73 are calculated, and the following step 3
In step 50, the following equation is calculated using the obtained target currents iPO, iMO, the resistance value r of the resistor R2, and the bias currents iPBE, iMBE flowing between the base and emitter of the transistor TR when the transistor TR is turned on as parameters. (7
), (8) to set the target current iPO,
Voltage VPO,V generated in resistor R2 when iMO flows
Calculate MO.

VPO=r(iPO+iPBE)...(7)V
MO=r(iMO+iMBE)...(8) Then, in the following step 360, this calculated voltage value VPO
, VMO are outputted as target voltages to the comparators COM of each drive circuit 90, 91, and after executing control signal output processing in the subsequent step 370, the processing is once terminated.

As described above, in the fuel injection control process of FIG. 10, the map of FIG. 8 is used to control the piezo actuator 7.
The target currents iPO and iMO corresponding to the temperature of No. 3 are determined (step 340), and the primary winding L1 of each drive circuit 90, 91 is
Target voltage VPO for flowing target current iPO, iMO to
, VMO is determined (step 350) and output to the comparator COM of each drive circuit 90, 91 shown in FIG.
Step 360).

Therefore, in the drive circuits 90 and 91 of FIG. 9, as shown in FIG. 11, when the charge control signal SP1 is input and the currents iP and iM flowing through the primary winding L1 reach the target currents iPO and iPM, The output of the comparator COM, and by extension the output of the AND circuit AND, changes from High to Low.
w, the transistor TR is turned off, and by turning off the transistor TR, the current flowing through the primary winding L1 iP,
When iM becomes lower than the target currents iPO, iPM, the transistor TR is turned on again, and thus the transistor TR repeats the on/off state to ensure that the current cutoff currents iPmax, iMmax of the primary winding L1 are set to the target currents. It becomes possible to control iPO and iMO.

Here, in step 330, the primary winding L
If the energization time Td for calculating the energization start timings TP0 and TM0 of 1 is set to a large value that takes into account the control error due to rotational fluctuations as described above, the energization cutoff current can be controlled to the target current. However, the current control time (ΔT shown in FIG. 11) after the current flowing through the primary winding L1 reaches the target current becomes longer as this error margin becomes larger, and the amount of heat generated by the transistor TR increases depending on this current control. Time △T
The size increases accordingly. For this reason, for example, the energization time Td is longer in the low-speed range of a diesel engine where rotational fluctuations are likely to occur, and the energization time Td is shortened in the high-speed range of a diesel engine where rotational fluctuations are less likely to occur. By using
This makes it possible to prevent overheating.

[0054]

[Effects of the Invention] As described in detail above, according to the fuel injection control device for a diesel engine of the present invention, in order to control the maximum conduction current (conduction current) of the inductor to the target current,
Even if the energization time of the inductor changes due to fluctuations in the rotation of the diesel engine, it is possible to extend the piezo actuator by a predetermined amount when the energization is interrupted, thereby ensuring fuel injection control accuracy.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating the configuration of the present invention.

FIG. 2 is a schematic configuration diagram showing the overall configuration of the fuel injection device of the embodiment.

FIG. 3 is an electric circuit diagram showing a drive circuit of the piezo actuator of the embodiment.

4 is a time chart illustrating the operation of the drive circuit of FIG. 3. FIG.

FIG. 5 is a flowchart showing fuel injection control processing executed by the ECU.

6 is a time chart illustrating the operation of the piezo actuator under the fuel injection control shown in FIG. 5. FIG.

FIG. 7 is a flowchart showing a cutoff voltage detection process executed by the ECU.

FIG. 8 is a diagram showing a map used when setting a target current based on the temperature of the piezo actuator.

FIG. 9 is an electric circuit diagram showing another configuration example of a piezo actuator drive circuit.

FIG. 10 is a flowchart showing another example of fuel injection control processing.

11 is a time chart illustrating the operation of the drive circuit of FIG. 9. FIG.

FIG. 12 is a diagram showing a map used when setting the energization time based on the rotation speed of the diesel engine.

[Explanation of symbols]

1...Fuel injection device 73...Piezo actuator
90, 91... Drive circuit 92... Electronic control circuit (ECU) 93... Rotation angle sensor 94... Accelerator sensor T... Transformer L1... Primary winding L2... Secondary winding
TR...Transistor FET...(MOS type) field effect transistor R1,
R2...Resistor D1, D2, D3...Diode ZD1, ZD2...Zener diode B...DC power supply COM...Comparator AND...AND circuit

Claims (1)

[Claims] 1. A piezo actuator that expands and contracts by charging and discharging electric charge to increase or decrease fuel pressure in a high pressure chamber of a fuel injection device to control fuel injection discharged from the high pressure chamber; and energizing means that energizes an inductor. a charging means for charging the piezo actuator with a high voltage generated in the inductor when the current supply is cut off by the current supply means; a discharging means for discharging the electric charge accumulated in the piezo actuator through the charging; ,
a calculating means for calculating charging and discharging timings of the piezo actuator; a determining means for determining a timing to start energizing the inductor based on the calculated charging timing; and a energizing means for driving the energizing means from the energizing start timing to the charging timing. and a driving means for driving the discharging means at the discharging timing, a current detecting means for detecting a current flowing when the inductor is energized, and a current detecting means detecting the current flowing through the inductor. 1. A fuel injection control device for a diesel engine, comprising: current control means for controlling the current flowing through the inductor so that the maximum current flowing through the inductor becomes a predetermined target current.