JP3777871B2 - Injector drive device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an injector driving device applied to a common rail type diesel engine or the like.
[0002]
[Prior art]
In a direct-injection diesel engine, a direct-injection gasoline engine, or the like, a common rail fuel injection device that can perform high-pressure injection and is advantageous for atomization of spray is used. In particular, spray atomization has a method of reducing the diameter of the nozzle hole, but the injection pressure tends to increase more and more because there is a limit in processing. In this sense, the common rail system has attracted more attention in recent years.
[0003]
Generally, in a common rail type fuel injection device, fuel pressurized by a high pressure pump is temporarily stored in a common rail (accumulation chamber), and this is injected into each cylinder by a predetermined amount at a predetermined timing from an injector.
[0004]
The injector opens and closes a nozzle hole provided at the lower end or the tip of the injector by raising and lowering a needle (needle valve) to execute fuel injection. In particular, there is an injector called a pressure balance type. This raises and lowers the needle by controlling the pressure in the pressure control chamber (balance chamber) on the rear end side of the needle.
[0005]
[Problems to be solved by the invention]
By the way, in the case of diesel combustion, initial combustion starts after a predetermined ignition delay period from the start of fuel injection. If rapid combustion is performed during this initial combustion, the in-cylinder temperature rises rapidly, and the amount of NOx generated increases. Therefore, there is a demand to connect the subsequent main combustion while performing the initial combustion relatively slowly.
[0006]
Usually, in a common rail injector, there is a tendency that a large amount of pressurized fuel that has been waiting in the injector at the same time as the needle rises is injected at once. If this is the case, the initial injection rate increases, the initial combustion becomes abrupt, and the previous request is not met. Therefore, various pressure balance type injectors that can suppress the initial injection rate have been proposed (Japanese Patent Laid-Open No. 11-22584).
[0007]
In general, a pressure balanced injector includes a pressure control chamber to which high-pressure fuel is constantly supplied. By selectively leaking the indoor fuel, the pressure inside the chamber is lowered and the needle rise is started. The fuel leak is controlled by an electromagnetic valve. The solenoid valve includes an on-off valve that opens and closes a leak hole in the pressure control chamber, a valve spring that urges the on-off valve in the closing direction, and an electromagnetic solenoid that drives the on-off valve in the opening direction against the spring force. Become.
[0008]
2. Description of the Related Art Conventionally, there is an injector that opens and closes an on-off valve in two stages, slows down an initial fuel leak rate, and raises a needle in two stages to suppress an initial injection rate.
[0009]
However, this used a method of providing two valve springs. If this is the case, the number of valve springs will naturally increase, resulting in an increase in cost due to an increase in the number of parts. Further, since the injection characteristics are determined based on the difference between the spring constants of the valve springs, there is a possibility that the injection characteristics may be affected by changes over time such as valve spring sag.
[0010]
[Means for Solving the Problems]
An injector drive device according to the present invention is an injector drive device that switches an initial fuel injection rate between a low initial injection rate and a high initial injection rate in accordance with an engine operating state, and the injector is driven in accordance with an applied voltage. An electromagnetic solenoid for opening operation, a battery connected to the electromagnetic solenoid, for applying a battery voltage to the electromagnetic solenoid, and connected to the electromagnetic solenoid, and a capacitor voltage higher than the battery voltage is applied to the electromagnetic solenoid When switching the initial injection rate to a low initial injection rate, the battery is connected to the electromagnetic solenoid, while when switching the initial injection rate to a high initial injection rate, the capacitor is And a driver unit connected to the electromagnetic solenoid .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0012]
FIG. 4 shows a common rail fuel injection device of a direct injection diesel engine to which the present invention is applied. An injector 1 is provided for each cylinder of the engine, and high pressure fuel having a common rail pressure (several tens to several hundreds of MPa) stored in the common rail 72 is constantly supplied to each injector 1 through a high pressure pipe 73. The fuel pumping to the common rail 72 is mainly performed by the high pressure pump 78. That is, the fuel at the normal pressure in the fuel tank 74 is sucked into the feed pump 76 through the fuel filter 75, and the fuel is sent to the high pressure pump 78 through the feed pipe 77. Here, the fuel is pressurized to a high pressure and sent to the common rail 72 through the high pressure pipe 79. The injector 1 is the pressure balance type common rail injector described above. Therefore, the fuel leaked from the pressure control chamber in the injector 1 is returned to the fuel tank 74 through the leak pipe 81. Further, since the high pressure pump 78 has a pressure control unit for controlling the outlet pressure, the fuel discharged from the high pressure pump 78 is returned to the fuel tank 74 through the return pipe 80.
[0013]
The fuel injection amount and injection timing of the injector 1 are controlled by an electronic control unit (hereinafter referred to as ECM) 82 and a driver unit 84 . E CM 82, the engine operating state from the sensors (not shown) (speed, load, etc.) senses, and determines the target injection quantity and target injection timing commensurate to the small voltage pulses corresponding to these drivers Send to unit 84. In response to this, the driver unit 84 applies a relatively large drive voltage to the electromagnetic solenoid 85 to open the injector 1. Further, the ECM 82 performs feedback control of the common rail pressure according to the engine operating state. That is, a common rail pressure sensor 83 is provided on the common rail 2, and the outlet pressure of the high pressure pump 78 is controlled based on this value.
[0014]
Next, the operation principle of the pressure balanced common rail injector used here will be described. As shown in FIG. 5, in the injector 1, a needle 53 is accommodated in a hole 52 in the nozzle body 51 so as to be able to move up and down, and high-pressure fuel having a common rail pressure Pc is supplied to the injection hole 55 through a gap between the hole 52 and the needle 53. Led. The fuel inlet is indicated at 56. A pressure control chamber 57 is provided on the rear end side of the needle 53, and is partitioned in communication with the fuel passage 61 on the injection hole 55 side with the throttle 58 as a boundary. The pressure control chamber 57 is provided with a leak hole 59, and the outlet of the leak hole 59 is opened and closed by an on-off valve 60. The on-off valve 60 is driven up and down by the cooperative action of the electromagnetic solenoid and the valve spring. The needle 53 is constantly urged in the injector valve closing direction (downward) by a spring (not shown) having a relatively low spring constant.
[0015]
In the nozzle hole closed state shown in FIG. 5, the leak hole 59 is closed, and the needle 53 is seated on the lower seat portion 62. At this time, the needle 53 receives a downward fuel pressure F ₁ , a downward spring force F _3, and an upward fuel pressure F ₂ . If the downward direction is positive, the force F received by the needle 53 is F ₁ + F ₃ −F ₂ . Here, when the common rail pressure is Pc, the needle cross-sectional area is A ₁ , and the seat cross-sectional area is A ₂ ,
F ₁ = Pc × A ₁
F ₂ = Pc × (A ₁ −A ₂ )
Therefore, F = F ₁ + F ₃ −F ₂ = F ₃ + Pc × A _2. Once the injection hole 55 is closed, the valve is theoretically maintained even if there is no spring force F ₃ . However, the presence of the spring force F ₃ completes the seating of the needle 53, that is, the valve closing.
[0016]
A ₂ is very small, and Pc × A ₂ is also a small value. Therefore, if there is no spring force F ₃ , the needle 53 is close to the state of floating because it is balanced by the fuel pressure. By breaking this balance state, the needle 53 rises and fuel injection is executed.
[0017]
FIG. 6 shows the fuel injection being executed or the nozzle hole being opened. At this time, the leak hole 59 is opened and the fuel in the pressure control chamber 57 is leaked. Since the throttle 58 is provided, the fuel supply to the pressure control chamber 57 cannot catch up with the leak, and the pressure in the pressure control chamber 57 becomes Pl lower than the common rail pressure Pc. As a result, the pressure balance is lost, the needle 53 is raised, and fuel injection is executed. During this execution, F ₁ = P1 × A ₁
F ₂ = Pc × A ₁
F = F ₁ + F ₃ −F ₂ = (P1−Pc) × A ₁ + F ₃
Then, F <0, that is, the needle 53 is raised.
[0018]
When the leak hole 59 is closed from this state, the pressure control chamber 57 returns to the common rail pressure Pc. Then, although the needle 53 is perfectly balanced depending on the fuel pressure, it is lowered due to the spring force F ₃ . That is, the spring force F ₃ is mainly required for lowering the needle. However, since the value itself can be small, a spring having a low spring constant can be used. Thus, when F changes from a negative value to a positive value, the needle 53 starts to descend. When the needle 53 is seated on the seat portion 62, fuel injection is stopped.
[0019]
A specific embodiment of an injector based on this principle is shown in FIG. The injector 1 accommodates the needle 4 in a hole 3a in the nozzle body 3 so as to be movable up and down. The injector 1 introduces fuel having a common rail pressure from the fuel inlet 2 communicating with the previous high-pressure pipe 73, and guides the high-pressure fuel to the lower injection hole 16 through the gap between the hole 3 a and the needle 4. In the hole 3a, as described above, the needle 4 is immersed in the high-pressure fuel and is in a floating state. The needle 4 is always urged downward by the spring 8, that is, in the injector valve closing direction. The spring 8 is a coil spring, and is sandwiched between the spring receiver 5 fixed to the needle 4 and the lower surface of the step portion 6 of the hole 3a in a compressed state.
[0020]
The top surface 9 of the needle 4 faces a small volume pressure control chamber 10, and high pressure fuel is always guided to the pressure control chamber 10 through the inlet passage 7 and the throttle passage 14 branched from the fuel inlet 2. Near the top surface 9, there is almost no gap between the needle 4 and the hole 3a, and fuel is not supplied to the pressure control chamber 10 from below through the gap. Therefore, a separate system inlet passage 7 and throttle passage 14 are provided, from which fuel is supplied to the pressure control chamber 10. Therefore, here, the throttle passage 14 forms the throttle 58.
[0021]
The fuel in the pressure control chamber 10 is selectively leaked from the leak hole 12 by raising and lowering the on-off valve 11. The on-off valve 11 is always urged downward (in the valve closing direction) by a valve spring 11a and normally closes the leak hole 12. As a result, the pressure control chamber 10 becomes a common rail pressure, the needle 4 is seated on the seat portion, the injection hole 16 is closed, and the injection is stopped. When the electromagnetic solenoid 85 is excited, the on-off valve 11 is driven upward (in the valve opening direction) against the spring force of the valve spring 11a to open the leak hole 12. As a result, fuel in the pressure control chamber 10 leaks, the pressure control chamber 10 becomes low pressure, the needle 4 rises and leaves the seat portion, the nozzle hole 16 opens, and fuel injection is executed. The leaked fuel reaches the previous leak pipe 81 through the leak passage 17.
[0022]
The on-off valve 11, the valve spring 11a, and the electromagnetic solenoid 85 constitute the electromagnetic valve 20 of the injector 1. The on-off valve 11 is a so-called flat seat valve that is formed in a circular flat plate shape and also serves as an armature for the electromagnetic valve 20. There is a minute gap above the on-off valve 11 so that the on-off valve 11 can be raised and lowered by a minute stroke (about 0.1 to 0.2 mm). The leak hole 12 is formed in the center of the valve seat member 21 inserted and fixed in the hole 3a. The valve seat member 21 has a central protrusion 22 that defines a leak hole outlet, and an outer peripheral protrusion 23 that is positioned at the outer peripheral edge. The upper surfaces of the projections 22 and 23 are flat at the same height and are formed flat. As a result, the on-off valve 11 is uniformly seated on the upper surfaces of the protrusions 22 and 23. By doing so, the on-off valve 11 is not pressed only against the central protrusion 22, and the on-off valve 11 is prevented from being bent or recessed.
[0023]
Next, an injector driving device according to the present invention will be described with reference to FIG. As shown in the figure, the driving device includes an ECM 82, a driver unit 84, an electromagnetic solenoid 85, and a battery 25. A battery voltage V _B (12 V in this case) generated by the battery 25 is applied and supplied to the electromagnetic solenoid 85 via the diode 26. The electromagnetic solenoid 85 is selectively supplied with the voltage V _C (here, 100 V) stored in the capacitor 27 via the transistor 28. V _B <V _C.
[0024]
The transistor 29 is also provided on the low potential side (ground side) of the electromagnetic solenoid 85. This is a main switch for the electromagnetic solenoid 85 and is turned ON only when a command pulse is sent from the ECM 82 .
[0025]
A capacitor charging circuit 30 is provided between the battery 25 and the capacitor 27. This includes an LR circuit 31 comprising a coil L and a resistor R, a transistor 32 as a switch provided on the low potential side of the LR circuit 31, a diode 33 provided in the middle of the circuit extending from this to the capacitor 27, and a transistor 32 And a clock 34 for generating an ON / OFF signal. The clock 34 is supplied with a small voltage (about 5 V in this case) that is constantly generated from the ECM 82, and generates a voltage pulse at very short time intervals. By the cooperative action of this and the LR circuit 31, the capacitor 27 is given a chopping current by a high voltage (here, 100V or more), and the capacitor 27 is charged.
[0026]
On the other hand, an AND element 35 is provided between the ECM 82 and the transistor 28, and the transistor 28 is turned ON / OFF according to the output of the AND element 35 .
[0027]
The ECM 82 sends a command pulse corresponding to the aforementioned target injection amount and target injection timing to the AND element 35 and the transistor 29. The ECM 82 selectively sends a high voltage request pulse to the AND element 35 based on the engine operating state. The AND element 35 outputs a current only when both of these pulses are input, and turns on the transistor 28. If any one of the pulses (especially the command pulse) is input, no current is output and the transistor 28 is turned off. The battery 25 side circuit and the capacitor 27 side circuit on the high potential side with respect to the electromagnetic solenoid 85 are in parallel with each other.
[0028]
An injector driving method by this driving apparatus will be described with reference to FIG. The figure shows a command pulse, a request pulse, an applied voltage to the electromagnetic solenoid 85, and a fuel injection rate from the top. The left side shows the case where there is a high voltage request, and the right side shows the case where there is no high voltage. In particular, the situation on the left is the same as that of the conventional injector driving method (see Japanese Patent Laid-Open No. 10-18888). Whether or not there is a high voltage request is determined by the ECM 82 based on the current engine operating state. This will be described later.
[0029]
First, the case where there is a high voltage requirement will be described. When the target injection start timing comes, the ECM 82 generates a rectangular command pulse having a length of time corresponding to the target injection amount. At the same time, a high voltage request pulse having a predetermined time length is generated to realize quick initial injection. Note that the voltage values of the command pulse and the high voltage request pulse are small voltages lower than the battery voltage V _B (here, about 5 V).
[0030]
Referring also to FIG. 1, the transistor 29 is turned on by the generation of the command pulse. Further, the transistor 28 is turned ON by the generation of the command pulse and the high voltage request pulse. As a result, the battery voltage V _B and the capacitor voltage V _C are simultaneously applied to the electromagnetic solenoid 85. Since V _B <V _C , the capacitor voltage V _C is applied at the beginning of conduction, but since the high voltage request pulse is turned off after a predetermined time for quick needle lift, only the battery voltage V _B is applied. Will come to be.
[0031]
Referring also to FIG. 3, when the capacitor voltage V _C, which is a high voltage, is applied, the electromagnetic force of the electromagnetic solenoid 85 rises all at once, so that the on-off valve 11 rises all at once and the fuel leak in the pressure control chamber 10 starts rapidly. To do. As a result, the needle 4 also rises rapidly, and fuel injection is performed at a high injection rate from the beginning of injection. Thereafter, the rise of the on-off valve 11 is maintained only by the battery voltage V _B , and the high injection rate injection is continued.
[0032]
When the command pulse and the high voltage request pulse disappear simultaneously, the transistors 28 and 29 are turned off, the electromagnetic solenoid 85 is demagnetized, and the on-off valve 11 of the electromagnetic valve 20 is closed. As a result, the fuel leak is stopped, the needle 4 is lowered, and the fuel injection is stopped. The capacitor 27 is charged until the next injection.
[0033]
Next, a case where there is no high voltage request will be described. As shown in FIGS. 1 to 3, at this time, only the command pulse is generated and the high voltage request pulse is not generated. Therefore, only the transistor 29 is turned on, and the transistor 28 remains off. As a result, only the battery voltage V _B is applied to the electromagnetic solenoid 85. Since this is a low voltage, the electromagnetic force of the electromagnetic solenoid 85 rises slowly. For this reason, the on-off valve 11 rises slowly, the amount of fuel leak continues to increase gradually, the needle rising speed also decreases, and the fuel injection rate rises gently. Thereby, the initial injection rate is suppressed.
[0034]
Thus, since a low voltage can be applied to the electromagnetic solenoid 85 at the initial stage of injection, the needle ascent rate can be slowed down and the initial injection rate can be suppressed. In addition, since a high voltage can be applied to the electromagnetic solenoid 85 at the initial stage of injection, the initial injection rate can be increased as usual. Furthermore, since the low initial injection rate and the high initial injection rate can be switched according to the engine operating state, it is possible to execute the injection rate control according to the actual engine operating state.
[0035]
That is, when it is determined that the ECM 82 is in the low / medium speed rotation / load operation which is the normal operation, the ECM 82 stops the generation of the high voltage request pulse and sets the low initial injection rate. This enables low emission operation with low NOx. On the other hand, when the ECM 82 determines that the high-speed rotation / load operation is being performed, the ECM 82 generates a high voltage request pulse to obtain a high initial injection rate.
[0036]
Originally, the initial injection rate is decreased to reduce the injection amount during the ignition delay period, but if this is done at high rotation and load, the injection time becomes excessively long and the entire injection amount is injected within the allowable time. There is a possibility of not being able to understand. This tendency is conspicuous because the allowable time becomes shorter as the rotation speed becomes higher. For these reasons, a high initial injection rate is set at high rotation and load.
[0037]
In any case, the switching conditions and switching points are preferably determined by an actual machine test or the like, and the switching points may be mapped according to the rotation and load.
[0038]
Thus, in the present invention, a low initial injection rate can be achieved by a simple circuit change. For this reason, it is advantageous in terms of the number of parts and cost compared to the conventional method of adding a valve spring of a solenoid valve. In addition, there is little influence on the injection characteristics due to the aging of the valve spring, and desired performance can be obtained stably for a long period of time.
[0039]
In addition, when there is a high voltage requirement, the high voltage is first applied, and then the low voltage is applied, because the on-off valve 11 in the stationary state is suddenly raised first. This is because only the valve 11 is held, so that a low voltage is sufficient.
[0040]
As mentioned above, this invention can take various embodiment besides the above.
[0041]
【The invention's effect】
According to the present invention, the following excellent effects are exhibited.
[0042]
(1) When suppressing the initial injection rate, it is possible to prevent an increase in the number of parts and cost.
[0043]
(2) The influence on the injection characteristics due to the aging of the valve spring can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an injector driving device according to the present invention.
FIG. 2 is a time chart showing an aspect of fuel injection by the drive device.
FIG. 3 is a longitudinal sectional view showing the whole injector.
FIG. 4 is a system diagram of a common rail fuel injection device.
FIG. 5 shows the operating principle of the pressure balance type injector according to the embodiment, and shows the injector valve closed state.
FIG. 6 is the valve open state.
[Explanation of symbols]
1 Injector 25 Battery 27 Capacitor
84 Driver unit 85 Electromagnetic solenoid V _B Battery voltage V _C Capacitor voltage

Claims (1)

An injector driving device configured to switch a fuel initial injection rate between a low initial injection rate and a high initial injection rate according to an engine operating state, and an electromagnetic solenoid for opening the injector according to an applied voltage; A battery connected to the electromagnetic solenoid for applying a battery voltage to the electromagnetic solenoid, a capacitor connected to the electromagnetic solenoid for applying a capacitor voltage higher than the battery voltage to the electromagnetic solenoid, and the initial injection When switching the rate to a low initial injection rate, the battery is connected to the electromagnetic solenoid, and when switching the initial injection rate to a high initial injection rate, a driver unit is connected to the electromagnetic solenoid. injector driving apparatus characterized by comprising a.

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