JP3391564B2 - Fuel pressure control system for high pressure injection engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel pressure control device for a high-pressure injection engine which can surely reduce the fuel pressure after the engine stops to atmospheric pressure. 2. Description of the Related Art Generally, in a high-pressure injection engine in which fuel is directly injected into a combustion chamber, it is necessary to inject the fuel at a pressure that can withstand the pressure in the combustion chamber (so-called in-cylinder pressure).
As described above, as a system for injecting fuel in a high pressure state, there is a so-called line pressure holding type high pressure injection system. [0003] This line pressure holding type high pressure injection system is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 4-339143. The line pressure holding type high pressure injection system holds a fuel line pressure at a predetermined high pressure state according to an engine operating state. The timing is controlled by ON / OFF timing of an electromagnetic solenoid or the like provided in the injector. More specifically, a high-pressure fuel pump is interposed on the upstream side of the fuel line, a high-pressure pressure regulator is interposed on the downstream side, and the injector is communicated between the two. The fuel pressure between the high-pressure pressure regulator and the high-pressure pressure regulator is maintained at a predetermined high-pressure state, high-pressure fuel is injected from the injector into the combustion chamber, and the fuel pressure is controlled by the relief amount of the high-pressure pressure regulator. are doing. Accordingly, the pressure of the relief fuel from the high pressure regulator is rapidly reduced from a high pressure state to a state close to the atmospheric pressure. When a fuel containing a relatively large amount of low boiling components such as gasoline is rapidly reduced in pressure from a high pressure state, vapor and cavitation are likely to occur. When vapor and cavitation occur in the relief fuel from the high-pressure pressure regulator,
The fuel pressure control performance of the high-pressure pressure regulator becomes unstable. Therefore, conventionally, a low-pressure pressure regulator is interposed downstream of the high-pressure pressure regulator, and the pressure of the return fuel discharged from the high-pressure pressure regulator is reduced in a stepwise manner. Cavitation was prevented from occurring. However, as a low-pressure pressure regulator interposed downstream of a high-pressure pressure regulator, a mechanical system using a relatively inexpensive diaphragm or the like is generally used in many cases. Since this so-called mechanical pressure regulator cannot actively control the fuel pressure, the fuel pressure cannot be released immediately even when the engine is stopped. Therefore, even if the high-pressure regulator is released when the engine is stopped, the high pressure of the fuel pressure in the fuel line is maintained for a while. On the other hand, when the engine is stopped, the in-cylinder pressure decreases and the fuel pressure relatively increases. Therefore, if the high-pressure state of the fuel pressure continues for a while after the engine is stopped, fuel leakage from the injector or the like is likely to occur. For example, if fuel is leaked from the injector, the fuel becomes over-rich at the time of restart, so that not only good starting performance cannot be obtained but also misfire or abnormal combustion. Further, the oil leaked by the leaked fuel may cause poor lubrication and various other adverse effects. The present invention has been made in view of the above circumstances, and it is possible to control the high pressure state of a fuel line in a stable state without generation of vapor or the like during engine operation, and to control the high pressure state of the fuel line after engine stop. An object of the present invention is to provide a fuel pressure control device for a high-pressure injection engine that can surely reduce the pressure of a fuel line to a value close to the atmospheric pressure. [0010] In order to achieve the above object, a fuel pressure control device for a high-pressure injection engine according to the present invention includes a high-pressure fuel pump provided in a fuel line and a high-pressure fuel pump. A high-pressure pressure regulator is disposed downstream of the high-pressure fuel pump, and a high-pressure line is provided between the high-pressure fuel pump and the high-pressure pressure regulator.
A high-pressure delivery line is provided from the fuel tank to the high-pressure fuel pump upstream, a low-pressure return line is provided from the high-pressure pressure regulator downstream to the fuel tank, and a high-pressure line is connected to an injector for directly injecting fuel into a combustion chamber. In the injection engine, the high-pressure pressure regulator is a normally-open type in which the high-pressure pressure regulator is opened when the engine is stopped, and a low-pressure return line downstream of the high-pressure pressure regulator is mechanically closed. Open switching valves are interposed in parallel. In the fuel pressure control device for a high-pressure injection engine according to the present invention, the high-pressure fuel pump is operated during the operation of the engine, and the high-pressure pressure regulator provided on the fuel line downstream of the high-pressure fuel pump. The fuel pressure is regulated by controlling the fuel pressure in the direction in which the pressure is reduced, and the fuel pressure in the high-pressure line between the high-pressure fuel pump and the normally open high-pressure pressure regulator is maintained at a high pressure. A normally-open switching valve connected in parallel to a mechanical low-pressure pressure regulator interposed in a low-pressure return line connecting the downstream of the high-pressure pressure regulator and the fuel tank is closed during engine operation. Since the valve state is maintained, the relief fuel from the high-pressure pressure regulator is regulated by the mechanical low-pressure pressure regulator, and is returned to the fuel tank while the fuel pressure is reduced stepwise without being rapidly reduced. Is done. On the other hand, when the engine is stopped by turning off the ignition switch, the normally-open high-pressure pressure regulator is opened, and the normally-open switching valve is opened. As a result, the fuel pressure in the high-pressure line is released from the normally-open high-pressure pressure regulator to the fuel tank via the normally-open switching valve. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a general outline of a high-pressure injection engine centering on a fuel line. A high-pressure injection engine (hereinafter, simply referred to as an "engine") 1 shown in this embodiment is a two-cycle direct injection four-cylinder gasoline engine, and includes a cylinder head 2, a cylinder block 3, and a piston 4 of the engine 1. The ignition plug 7 connected to the secondary side of the ignition coil 6a and the injector 8 for in-cylinder fuel injection face the combustion chamber 5 formed by the above. An igniter 6b is provided on the primary side of the ignition coil 6a. It is connected. A scavenging port 3a and an exhaust port 3b are formed in the cylinder block 3, and a coolant temperature sensor 9 is provided in a cooling water passage 3c formed in the cylinder block 3.
Is coming. The scavenging port 3a has an air supply pipe 10
An air cleaner 11 is attached to the air supply pipe 10 on the upstream side, and a scavenging pump 12 driven by rotation of the crankshaft 1a is interposed in the middle of the air supply pipe 10, and the scavenging pump 12 5
And the inside of the combustion chamber 5 is scavenged. A throttle valve 15a interlocked with an accelerator pedal 14 is provided downstream of the air cleaner 11 of the air supply pipe 10 and upstream of the scavenging pump 12. Further, an accelerator opening sensor 16 is connected to the accelerator pedal 14. On the other hand, a bypass control valve 15b for controlling the scavenging pressure of the scavenging pump 12 is provided in a bypass passage 13 for bypassing the scavenging pump 12. The exhaust port 3b is provided with an exhaust rotary valve 17 which opens and closes in synchronization with the rotation of the crankshaft 1a. An exhaust pipe 18 is connected through the exhaust rotary valve 17. Further, the exhaust pipe 18
Is provided with a catalytic converter 19, and a muffler 20 is connected to a downstream end. A crank rotor 21 is mounted on the crankshaft 1a. A crank angle sensor 22 such as an electromagnetic pickup is provided on the outer periphery of the crank rotor 21. On the other hand, reference numeral 23 denotes a fuel line, and a high-pressure fuel pump 28 is interposed in the fuel line 23,
Further, a high-pressure electromagnetic pressure regulator 33 is interposed downstream of the high-pressure fuel pump 28. Further, the upstream side of the high-pressure fuel pump 28 of the fuel line 23 constitutes a low-pressure delivery line 23a for delivering fuel from the fuel tank 24.
Pressure regulator and the high pressure electromagnetic pressure regulator 3
3 constitutes a high-pressure line 23b which boosts the fuel from the low-pressure delivery line 23a and supplies it to the injector 8, and further comprises a low-pressure return line 23c downstream from the high-pressure electromagnetic pressure regulator 33. I have. The high-pressure electromagnetic pressure regulator 33 is a normally-open type, and when the ON duty DUTY increases, the valve opening is controlled in the direction of narrowing, and the ON duty D
Fully closed at UTY = 100%. Note that as the valve opening of the high-pressure electromagnetic pressure regulator 33 is reduced, the fuel pressure in the high-pressure line 23b gradually increases. The low-pressure delivery line 23a and the low-pressure return line 23c are connected to the fuel bypass passage 23.
d, and the fuel bypass passage 23d
A first low-pressure pressure regulator 27a that regulates the fuel pressure of the low-pressure return line 23a using mechanical means such as a diaphragm is interposed, while a junction of the fuel bypass passage 23d of the low-pressure return line 23c. A second low-pressure pressure regulator 27b and a normally-open solenoid-operated directional control valve 35 are interposed in parallel on the upstream side. The second low pressure regulator 27b is a high pressure electromagnetic pressure regulator 33.
The pressure regulator regulates the downstream fuel pressure and has the same structure as the first low-pressure pressure regulator 27a. The set pressure P2 is set to the first low-pressure pressure regulator 27a.
a is set lower than the set pressure P1 (P2 <P
1) and the first pressure regulator 27a
Is set lower than the minimum set pressure P3 of the high-pressure electromagnetic pressure regulator 33 (P2 <P1 <P3). Therefore, for an atmospheric pressure of 1 atm,
1atm <P2 <P1 <P3. When the ignition switch 50 (see FIG. 2) is turned on, the solenoid coil SOL. Is excited to close the normally-open electromagnetic switching valve 35. In the low-pressure delivery line 23a, the fuel in the fuel tank 24 is sent out by a feed pump 25, passes through a fuel filter 26, and is regulated by the first low-pressure pressure regulator 27a. Supply to pump 28. In the high-pressure line 23b, the fuel supplied from the low-pressure delivery line 23a is pressurized by the high-pressure fuel pump 28, and a predetermined high-pressure fuel regulated by the high-pressure electromagnetic pressure regulator 33 is supplied to the high-pressure fuel. Filter 30, accumulator 3 for buffering pulsating pressure
1. The fuel is supplied to the injector 8 of each cylinder via a fuel supply path provided with a fuel pressure sensor 32 for detecting the fuel pressure.
This constitutes a so-called line pressure holding type high pressure injection system. The high-pressure fuel pump 28 is, for example, an engine-driven plunger pump, and is provided with a check valve at each of an intake port and a discharge port. When the engine is stopped, fuel from the low-pressure delivery line 23a can pass through. become. FIG. 2 shows a control device 40. The control device 40 includes a CPU 41, a ROM 42, an R
The AM 43, the backup RAM 44, and the I / O interface 45 are mainly configured by a microcomputer connected to each other via a bus line 46. The control device 40 includes a constant voltage circuit 4
The constant voltage circuit 47 is connected to a battery 49 via a relay contact of an ECU relay 48, and a relay coil of the ECU relay 48 is connected to the battery 49 via an ignition switch 50. I have. When the ignition switch 50 is turned on and the contact of the ECU relay 48 is closed, the constant voltage circuit 47 stabilizes the voltage of the battery 49 and supplies the voltage to each part of the control device 40. In addition, the backup R
A battery 49 is directly connected to the AM 44 via the constant voltage circuit 47, and a backup power supply is constantly supplied regardless of whether the ignition switch 50 is ON or OFF. A feed pump 25 is connected to the battery 49 via a relay contact of a feed pump relay 54. A battery 49 is connected to the input port of the I / O interface 45 to monitor the battery voltage.
The accelerator opening sensor 16, the water temperature sensor 9, and the fuel pressure sensor 32 are connected. On the other hand, an igniter 6b for driving the ignition coil 6a is connected to an output port of the I / O interface 45, and a feed pump relay to which power is supplied from the battery 49 via a drive circuit 55. 54, a relay coil RYFE, an injector 8, a high-pressure electromagnetic pressure regulator 33, and a solenoid coil SOL. Of a normally-open electromagnetic switching valve 35 (see FIG. 1). Next, a fuel supply system control routine by the controller 40 will be described with reference to the flowcharts of FIGS. The ignition switch 50 is ON
Then, when the power is supplied to the control device 40, the system is initialized (each flag is cleared). This flowchart is executed at predetermined time intervals after system initialization. In the first routine after the system is initialized, first, in step S1, the value of the normal control transition flag F2 is referred to. The initial value of the normal control transition flag F2 is 0, and therefore, the process proceeds from step S1 to step S2 to refer to the value of the initialization completion flag F1. Since the initial value of the initialization completion flag F1 is also 0, this step S2
Then, the process proceeds to step S3. Then, in step S3 and subsequent steps, an initialization routine is executed. That is, in step S3, the feed coil 25 is driven by turning on the feed pump relay 54 by energizing the relay coil RYFE of the feed pump relay 54. This feed pump 25
Is driven, fuel supply to the high-pressure fuel pump 28 is started. If the high-pressure fuel pump 28 is an engine-driven type, the pumping is started by starting the engine. Next, in step S4, the solenoid coil SOL. Of the normally-open electromagnetic switching valve 35 is energized to close the normally-open electromagnetic switching valve 35. The normally open electromagnetic switching valve 35 is provided with a high pressure electromagnetic pressure regulator 33.
The low-pressure return line 23c communicating downstream of the valve is interposed in parallel with the second low-pressure pressure regulator 27b. When the normally-open electromagnetic switching valve 35 is closed, the discharge from the high-pressure electromagnetic pressure regulator 33 is performed. The pressure of the relief fuel is regulated by the second low pressure regulator 27b within a range lower than the fuel pressure of the high pressure line 23b and higher than the atmospheric pressure. As a result, the relief fuel discharged from the high-pressure electromagnetic pressure regulator 33 is stepwise reduced in pressure upstream and downstream of the second low-pressure pressure regulator 27b and returned to the fuel tank 24. Therefore, generation of vapor and cavitation due to sudden pressure reduction is prevented. Thereafter, in step S5, the ON duty DUTY for the high-pressure electromagnetic pressure regulator 33 is set to FFH (100%), and in step S6
Then, this value is converted to the high pressure electromagnetic pressure regulator 33.
After setting as the output value of the I / O port for, the process proceeds to step S7, sets the initialization completion flag F1 indicating that the initialization has been completed, and exits the routine. In step S6, the ON duty DUTY for the high-pressure electromagnetic pressure regulator 33 is determined.
Is set to FFH, the high-pressure electromagnetic pressure regulator 33 is temporarily closed. Then, this initial setting routine ends,
Since the initialization completion flag F1 is set in step S7, in the second and subsequent routines, when the processing proceeds from step S1 to step S2, the initialization completion flag F1 is set to F1.
= 1, the flow branches to step S8, and the high-pressure line 23
b and the preset pressure PH (for example,
9.8 × 103 KPa) to determine whether the fuel pressure PF in the high pressure line 23b has reached the set pressure PH. If PF ≦ PH in step S8, the routine exits and the fuel pressure PF becomes equal to the set pressure P
Repeat this routine until H is reached. When the fuel pressure PF reaches the set pressure PH (PF> PH)
), The process proceeds from step S8 to step S9, the normal control transition flag F2 is set, and the routine exits. When the normal control transition flag F2 is set and the routine is thereafter executed, the flow branches from step S1 to step S11, and the routine shifts to a fuel pressure normal control routine for performing feedback control of the fuel pressure. In the fuel pressure normal control routine, first, in step S11, a target fuel pressure PFS is set from a target fuel pressure table using the engine speed N as a parameter. The target fuel pressure PFS is a control target value for setting the fuel pressure PF of the high-pressure line 23b to inject a substantially constant amount of fuel from the injector 8 to the combustion chamber 5 per unit time of injector valve opening. The optimum fuel pressure for the engine speed N is determined by the engine characteristics,
The fuel pressure is obtained for each operation region by an experiment or the like in consideration of the fuel pump noise and the like. As shown in step S11, the fuel pressure which is low at a low rotation speed and higher at a higher rotation speed is tabulated. These are stored in a series of addresses in the ROM 42. Next, steps S11 to S
In step S13, a basic control amount for the high-pressure electromagnetic pressure regulator 33, that is, a basic duty DB is set from a preset basic control amount table or a function formula using the target fuel pressure PFS as a parameter. A deviation ΔP between the target fuel pressure PFS and the fuel pressure PF is calculated (ΔP ← PFS−PF), and step S1 is performed.
Proceed to 4. In step S14, a proportional feedback value P is calculated by multiplying the proportional constant KP in the proportional integral control by the deviation ΔP (P ← KP × ΔP). further,
In step S15, the integral constant KI in the proportional integral control
Is added to the previous integral feedback value IOLD read from the RAM 43 to calculate a new integral feedback value I (I ← IOLD + KI
× ΔP). Then, when the operation proceeds to step S16, the RAM
43, the last integrated feedback value I stored in
OLD is updated with the current integrated feedback value I calculated in step S15, and in step S17, the proportional feedback value P and the integrated feedback value I are added to the basic duty DB to add the high-pressure electromagnetic pressure regulator. An ON duty DUTY, which is a feedback control amount with respect to 33, is set (DUTY ← DB
+ P + I), in step S18, this ON duty D
Set UTY and exit the routine. As a result, the high-pressure electromagnetic pressure regulator 33 regulates the fuel pressure PF of the high-pressure line 23b so as to follow the target fuel pressure PFS. From the injector 8, the fuel pressure to the combustion chamber 5 is almost constant per unit time of injector valve opening. Is injected. On the other hand, when the ignition switch 50 is turned off, the ON duty DUTY for the high-pressure electromagnetic pressure regulator 33 becomes 0 (%), and the solenoid coil of the normally-open electromagnetic switching valve 35 is turned off.
Power supply to SOL. Is stopped. The high-pressure electromagnetic pressure regulator 33 and the normally-open electromagnetic switching valve 35
Are normally open, both are open, and the fuel pressure PF in the high pressure line 23b is discharged to the fuel tank 24 through the high pressure electromagnetic pressure regulator 33 and the normally open electromagnetic switching valve 35. Is done. If the high-pressure fuel pump 28 is of an engine driven type, the fuel pumping to the high-pressure line 23b is stopped by stopping the engine. As a result, the fuel pressure in the high-pressure line 23b surely decreases to a value substantially close to the atmospheric pressure. As described above, in the present embodiment, the second low-pressure pressure regulator 27b is interposed downstream of the high-pressure electromagnetic pressure regulator 33, so that the high-pressure electromagnetic pressure regulator
Since the relief fuel discharged from the fuel tank 3 is gradually reduced in pressure, the occurrence of vapor and cavitation due to the rapid decrease in fuel pressure is prevented beforehand, and the high-pressure electromagnetic pressure regulator 33 stably controls the fuel pressure. can do. On the other hand, when the ignition switch 50 is
When FF is applied, the second pressure regulator 27b
The normally open electromagnetic switching valve 35 and the high pressure electromagnetic pressure regulator 33 connected in parallel with each other are returned to the open state, so that the fuel pressure PF in the high pressure line 23b is reliably reduced to a value close to the atmospheric pressure. As a result, fuel leakage from the injector 8 and the like communicating with the high-pressure line 23b is effectively prevented. The present invention is not limited to the above embodiment. For example, one or two other pressure regulators may be provided downstream of the second pressure regulator 27b in the low-pressure return line 23c. Interposed,
Moreover, the pressure of the relief fuel may be gradually reduced by setting the set pressure of each pressure regulator lower than the set pressure of the pressure regulator interposed immediately upstream. The present invention is naturally applicable not only to a two-cycle direct injection engine but also to a four-cycle direct injection engine. As described above, according to the present invention,
A low pressure return line downstream of the high pressure pressure regulator is equipped with a mechanical low pressure pressure regulator. The accompanying generation of paver and cavitation is prevented beforehand. As a result, the fuel pressure by the high-pressure pressure regulator can be controlled in a stable state. Also, since the low pressure regulator is of a mechanical type, it is inexpensive and has excellent durability.
Not only can the cost of the entire apparatus be reduced, but also high reliability can be obtained. Further, since the normally open type pressure regulator is adopted as the high pressure regulator, the normally open type switching valve which is closed during engine operation is connected in parallel to the low pressure regulator. The pressure regulator for pressure and the switching valve are opened, the fuel pressure in the high pressure line can be reliably reduced to a value close to the atmospheric pressure, fuel leakage in the high pressure line is prevented, and the reliability of the entire apparatus is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall schematic diagram focusing on a fuel line of a high-pressure injection engine. FIG. 2 is a circuit diagram of a control device. FIG. 3 is a flowchart showing a fuel supply system control routine. Flowchart showing fuel supply system control routine (continued) [Description of symbols] 1 High pressure injection type engine 5 Combustion chamber 8 Injector 23 Fuel line 23a Low pressure delivery line 23b High pressure line 23c Low pressure return line 24 Fuel tank 27b Mechanical pressure regulator for low pressure 28 High-pressure fuel pump 33 High-pressure electromagnetic pressure regulator 35 Normally-open solenoid valve

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁷ identification code FI F02M 63/00 F02M 63/00 ER (58) Field surveyed (Int.Cl. ⁷ , DB name) F02M 37/00 F02D 41 / 04 395 F02M 55/02 350 F02M 63/00

Claims (1)

(57) [Claim 1] A high-pressure fuel pump is disposed in a fuel line, and a high-pressure pressure regulator is disposed downstream of the high-pressure fuel pump. A high-pressure line between the fuel tank and the high-pressure pressure regulator; a low-pressure delivery line from the fuel tank to the high-pressure fuel pump upstream; a low-pressure return line from the downstream of the high-pressure pressure regulator to the fuel tank; In a high pressure injection type engine in which an injector for directly injecting fuel into the combustion chamber is connected, a normally open type in which the high pressure pressure regulator is opened when the engine is stopped, and a low pressure return line downstream of the high pressure pressure regulator, Mechanical pressure regulator for low pressure and engine operation Fuel pressure control apparatus for a high-pressure injection type engine, characterized in that the interposed normally open switching valve is closed in parallel.