JPH1030512A - Fuel pressure controller of cylinder fuel injection engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain short starting time by improving erection of a fuel pressure at the start of engine and enhancing the fuel injection characteristic of an injector without burdening a high pressure fuel pump driven by an engine with any share of load. SOLUTION: A high pressure fuel pump 7 driven by an engine 1 and an electric motor-driven auxiliary fuel pump 12 are provided in parallel in a fuel line 3, and at the start of the engine, the electric motor-driven auxiliary pump 12 is driven so as to erect the fuel pressure in a high pressure line 3b for improving the spray characteristic of fuel injected in the combustion chamber 1a of each cylinder. And when the fuel pressure in a high pressure line 3b is more than a set pressure and an engine number of revolution reaches more than the perfect combustion number of revolution, the electric motor-driven auxiliary fuel pump 12 is stopped so as to pressurize and supply fuel only from the high pressure fuel pump 7 to the high pressure line 3b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel pressure control device for a direct injection engine, in which an electric auxiliary fuel pump is driven at the time of starting to raise the fuel pressure early.

[0002]

2. Description of the Related Art As is well known, in a direct injection engine of this type, in which fuel is directly injected into a combustion chamber, it is necessary to inject fuel at a pressure that can withstand the pressure in the combustion chamber (so-called in-cylinder pressure). As a high-pressure fuel pump that generates the fuel pressure, an engine-driven high-pressure fuel pump that uses the output of an engine as a driving source is widely used.

However, the engine-driven high-pressure fuel pump has a small discharge rate when the engine speed is low, such as at the time of starting, and cannot sufficiently increase the fuel pressure in a high-pressure line communicating with the injector. As a result, the fuel spray characteristics of the injector deteriorate, and good starting performance cannot be obtained, and the time required for starting increases.

[0004] In particular, at extremely low temperatures (for example, -25 ° C or less)
When the engine is started, the battery voltage drops and the oil viscosity increases, so the cranking speed is 80 rpm.
The fuel pressure and the fuel flow rate of the high-pressure fuel pump are both insufficient, and the starting performance is more significantly reduced.

For example, Japanese Patent Application Laid-Open No. 60-237158 discloses a feed pump for supplying fuel to an engine-driven high-pressure fuel pump through a high-pressure line via a check valve as means for securing a fuel flow rate at the time of starting. When the discharge pressure of the feed pump is higher than the fuel pressure of the high-pressure line at the time of starting or the like, a technique of directly supplying the discharge fuel from the feed pump to the high-pressure line via a check valve is disclosed. .

[0006]

However, in the above-mentioned prior art, the fuel supplied from the ordinary feed pump is merely led to the high pressure line bypassing the engine driven high pressure fuel pump. Although the fuel flow to the line can be ensured, the fuel pressure cannot be sufficiently increased. That is, in the cylinder injection engine, the fuel pressure of the high pressure line is required to be about 3 to 15 MPa in order to inject fuel from the injector against the cylinder pressure, but the feed pressure of the feed pump is 0.3 MPa.
The feed pressure from this feed pump cannot increase the fuel pressure in the high pressure line until sufficient spray characteristics are obtained, and eventually the engine-driven high-pressure fuel pump Until the fuel pressure of the high pressure line increases due to an increase in the amount of fuel discharged from the fuel cell, good starting performance cannot be obtained, and the fuel pressure of the high pressure line cannot be increased in a short time at the time of starting.

As means for increasing the fuel pressure in the high-pressure line in a short time at the time of starting or the like, the capacity of the feed pump is increased in the above-mentioned prior art, and the capacity of the engine-driven high-pressure fuel pump is increased in the conventional system. It is sufficient to increase the pump capacity, but if the pump capacity is increased beyond necessity, not only the drive loss increases, the engine load during normal operation increases, but also the cost rises, which is not feasible.

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a fuel pressure control system for an in-cylinder injection engine capable of increasing the fuel pressure at the time of starting in a short time without increasing the engine load, and obtaining good starting performance. It is intended to provide a device.

[0009]

In order to achieve the above object, the present invention provides an engine-driven high-pressure fuel pump in a fuel line and a high-pressure pressure regulator downstream of the engine-driven high-pressure fuel pump. A high-pressure line between the engine-driven high-pressure fuel pump and the high-pressure pressure regulator; a low-pressure delivery line from the fuel tank to the engine-driven high-pressure fuel pump upstream; and a low-pressure delivery line from the high-pressure pressure regulator downstream to the fuel tank. A low-pressure return line, a feed pump is interposed in the low-pressure delivery line, and an in-cylinder injection engine in which an injector for directly injecting fuel into the combustion chamber is connected to the high-pressure line, wherein the high-pressure line and the low-pressure delivery line Connect the downstream of the feed pump with the auxiliary line The auxiliary line is provided with an electric auxiliary fuel pump which is driven at the time of start-up and is stopped at least in one state when the engine is completely exploded or when the fuel pressure of the high pressure line is equal to or higher than a set value. And

That is, according to the present invention, when the engine is started,
The electric auxiliary fuel pump is driven, and the fuel supplied from the feed pump is supplied to the high pressure line under pressure by the electric auxiliary fuel pump to increase the fuel pressure in the high pressure line. Then, when the engine is completely exploded or the fuel pressure of the high pressure line is at least one of the set values or more, the drive of the electric auxiliary fuel pump is stopped, and the fuel is pressurized and sent to the high pressure line only from the engine driven fuel pump. Pay.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an overall outline of a direct injection engine centering on a fuel line. In FIG. 1, reference numeral 1 denotes an engine. An in-cylinder injector 2 faces a combustion chamber 1a of each cylinder of the engine 1.

Reference numeral 3 denotes a fuel line for supplying fuel to the injector 2. An electric feed pump 5 is interposed on the fuel tank 4 side of the fuel line 3, and a fuel filter 6 is provided downstream thereof. The high pressure fuel pump 7 is interposed. The high-pressure fuel pump 7 is connected to a crankshaft 1b, which is an output shaft of the engine 1, via a belt 8, and is driven to rotate by the output of the engine 1. or,
The discharge side of the high-pressure fuel pump 7 communicates with a common rail 9, and the injector 2 disposed for each cylinder communicates with the common rail 9. Furthermore, the common rail 9
Is connected to the fuel tank 4 via a high-pressure pressure regulator 10 and a low-pressure pressure regulator 11.

The fuel line 3 includes a low-pressure delivery line 3a extending from the fuel tank 4 to the upstream of the high-pressure fuel pump 7.
A portion from the downstream of the high-pressure fuel pump 7 to the high-pressure pressure regulator 10 via the common rail 9 constitutes a high-pressure line 3b, and a portion from the downstream of the high-pressure pressure regulator 10 to the fuel tank 4 constitutes a low-pressure return line 3c.

Further, the downstream of the fuel filter 6 of the low-pressure delivery line 3a and the common rail 9 are communicated via an auxiliary line 3d. An electric auxiliary fuel pump 12 is interposed in the auxiliary line 3d. A check valve 13 for preventing fuel from flowing backward from the common rail 9 to the fuel pumps 7 and 12 downstream of the fuel pumps 7 and 12.
a, 13b, and both fuel pumps 7, 12
A fuel relief line 3 e for discharging the surplus of fuel supplied to the low pressure return line 3 c is communicated between the high pressure regulator 10 and the low pressure regulator 11 of the low pressure return line 3 c.

The electric auxiliary fuel pump 12 is turned on / off in accordance with a control signal from an electronic control unit (ECU) 14 mainly composed of a known microcomputer. The input terminal of the electronic control unit 14 is exposed to a rotation speed sensor 15 for detecting the engine rotation speed NE from the rotation of the crankshaft 1b and the high pressure line 3b such as the common rail 9, and the fuel pressure of the high pressure line 3b. A fuel pressure sensor 16 for detecting PFU, a starter switch 17 and the like are connected, and the drive of the electric auxiliary fuel pump 12 based on the detection signals of these sensors 15 and 16 and the ON / OFF signal of the starter switch 17, or Control the stop.

The control operation of the electric auxiliary fuel pump (hereinafter, abbreviated as auxiliary fuel pump) 12 executed by the electronic control unit 14 will be described below with reference to the flowchart shown in FIG.

Turn on an ignition switch (not shown)
Then, the electric feed pump 5 is turned on to supply the fuel in the fuel tank 4 to the fuel line 3 and turn on the power to the electronic control unit 14. In the electronic control unit 14, first, after the system is initialized (the value of the flag is cleared), the auxiliary fuel pump control routine shown in FIG. 2 is executed. Then, in step S1, it is checked whether or not the starter switch 17 is ON. Since the starter switch 17 immediately after turning on the ignition switch is in the OFF state, the process proceeds to step S2, and the value of the starter switch determination flag Flag1 is referred to. Since the initial value of the starter switch determination flag Flag1 is 0, the routine exits from the routine.

When the starter switch 17 is turned on to start the engine, the process proceeds from step S1 to step S3, where the starter switch discrimination flag Fla
g1 is set (Flag1 ← 1), the routine proceeds to step S4, the auxiliary fuel pump 12 is turned on, and the routine is exited.

When the auxiliary fuel pump 12 is turned on, the fuel supplied from the electric feed pump 5 is pressurized by the auxiliary fuel pump 12 provided in the auxiliary line 3d, and the high pressure fuel pump 7 is turned on. Bypass high pressure line 3
b and rapidly increases the fuel pressure PFU in the high pressure line 3b.

When the starter switch 17 is turned off after the engine has been operated independently, the process branches from step S1 to step S2, and the starter switch determination flag Fl
Since the value of ag1 is referred to and Flag1 = 1, the process proceeds to step S5. In steps S5 and S6, the stop timing of the auxiliary fuel pump 12 is determined based on the fuel pressure PFU and the engine speed NE. And the fuel pressure PFU
If is less than the set pressure PFUO (for example, 3 MPa) or the engine speed NE is less than the complete explosion speed NEO, the routine proceeds to step S4, where the ON operation of the auxiliary fuel pump 12 is maintained, and the routine exits.

The fuel pressure PFU is equal to the set pressure PFU.
O and the engine speed NE is equal to the complete explosion speed NEO
When this is the case, the process proceeds to step S7, the auxiliary fuel pump 12 is turned off, and the routine exits.

When the auxiliary fuel pump 12 is turned off, the fuel pressure PFU of the high-pressure line 3b is sufficiently raised to the set pressure PFUO, and the engine speed NE is increased to the complete explosion speed NEO or more. Therefore, the fuel sufficiently pressurized by the high-pressure fuel pump 7 driven by the engine 1 is supplied to the high-pressure line 3b. Therefore, even when the fuel pressure PFU of the high-pressure line 3b is low at the time of starting or the like, before the engine speed increases and the pressure of the fuel supplied from the high-pressure fuel pump 7 is sufficiently increased, the auxiliary The fuel pressure P of the high-pressure line 3b by the fuel pump 12
Since the FU is rapidly increased, fuel having good spray characteristics is injected from the injector 2 at the time of starting, and the starting time can be shortened.

Therefore, the capacity of the high-pressure fuel pump 7 may be set in accordance with the required flow from idling to the maximum output, and the capacity of the high-pressure fuel pump 7 can be relatively reduced. By reducing the size and weight of the high-pressure fuel pump 7, not only the manufacturing cost can be reduced, but also the drive loss during normal operation can be reduced, and the outfitting in the engine chamber is improved, and the freedom of design can be secured. it can.
Further, it is possible to set the rising characteristic of the fuel pressure of the high-pressure fuel pump 7 at the time of starting the engine loosely,
To that extent, the clearance of the sliding portion in the pump can be sufficiently ensured, and the manufacturing cost can be reduced and the durability can be improved. On the other hand, the rising characteristic of the fuel pressure PFU of the high-pressure line 3b at the time of starting can be set separately from the high-pressure fuel pump 7 by the auxiliary fuel pump 12. It can be set relatively freely according to the engine to which the pump is mounted.

[0024]

As described above, according to the present invention,
The upstream and downstream of the engine-driven high-pressure fuel pump is bypassed via an auxiliary line, and an electric auxiliary fuel pump is interposed in this auxiliary line. The engine is driven until the fuel pressure of at least one of the states is equal to or higher than a set value, and is stopped when the engine completes explosion or when the fuel pressure of the high pressure line is at least one of the states equal to or higher than the set value. At the time of low engine rotation, such as at the time of startup when the fuel supply amount of the high-pressure fuel pump is small, the fuel pressure of the high-pressure line can be quickly increased by the electric auxiliary fuel pump, and the spray characteristics of the injector at the time of startup are improved. Good starting performance is obtained.

Since the rise in fuel pressure at the time of starting is compensated by the electric auxiliary fuel pump, the capacity of the engine-driven high-pressure fuel pump may be set according to the required flow from idling to maximum output. As a result, the pump capacity becomes relatively small, so that the engine-driven high-pressure fuel pump can be reduced in size and weight, so that the outfitting inside the engine chamber is improved and the degree of freedom in design is increased. In addition, the reduction in size and weight of the engine-driven high-pressure fuel pump not only can reduce drive loss during normal operation, but also reduce manufacturing costs.

Further, since the rising characteristic of the fuel pressure at the start can be set by the electric auxiliary fuel pump, it is not necessary to consider the rising characteristic of the fuel pressure in the engine-driven high-pressure fuel pump. The clearance of the sliding portion can be sufficiently ensured, and not only can the manufacturing be facilitated, but also the durability can be improved.

Further, since the rise characteristic of the fuel pressure at the start can be set by an electric auxiliary fuel pump separately from the engine-driven high-pressure fuel pump, the rise characteristic of the fuel pressure at the start is provided. It can be set relatively freely according to the engine being used.

[Brief description of the drawings]

FIG. 1 is an overall schematic view centering on a fuel line of a direct injection engine.

FIG. 2 is a flowchart showing an electric auxiliary fuel pump control routine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 1a ... Combustion chamber 1b ... Output shaft (crankshaft) 2 ... Injector 3 ... Fuel line 3a ... Low pressure delivery line 3b ... High pressure line 3c ... Low pressure return line 3d ... Auxiliary line 4 ... Fuel tank 5 ... Feed pump 7 ... Engine driven high pressure fuel pump 10 ... High pressure regulator 12 ... Electric auxiliary fuel pump

Claims (1)

[Claims] An engine-driven high-pressure fuel pump is provided in a fuel line, and a high-pressure pressure regulator is provided downstream of the engine-driven high-pressure fuel pump. The engine-driven high-pressure fuel pump and the high-pressure pressure regulator A high pressure line, a low pressure delivery line from the fuel tank to the upstream of the engine driven high pressure fuel pump, a low pressure return line from the downstream of the high pressure pressure regulator to the fuel tank, and a feed pump to the low pressure delivery line. An in-cylinder injection engine in which an injector for directly injecting fuel into a combustion chamber is connected to the high-pressure line, wherein the high-pressure line and the low-pressure delivery line downstream of the feed pump communicate with each other via an auxiliary line, Drive to this auxiliary line at the start, A fuel pressure control device for a direct injection engine, comprising an electric auxiliary fuel pump which stops in at least one state after a complete engine explosion or when the fuel pressure of the high pressure line is equal to or higher than a set value.