JP3531896B2 - Common rail fuel injector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail type fuel injection device for a diesel engine which injects fuel through an accumulator. 2. Description of the Related Art As shown in FIG. 5, for example, an electric pump 2 having a pre-filter 2a provided in a fuel tank 1 is shown in FIG.
Is connected to a high-pressure pump 4 having a pressure control valve via a fuel filter 3 interposed in a fuel circuit f1, and the output side of the high-pressure pump 4 is connected by a fuel circuit f2 to a pipe-shaped accumulator 5 ( Hereinafter, the common rail is connected to a common rail 5, and fuel is injected to each cylinder by an electric signal from a control device 8 through a fuel injection nozzle 7 (the illustrated example shows six cylinders) connected to the common rail 5. 2. Description of the Related Art Fuel injectors are known. here,
Reference numeral 5a denotes a rail pressure sensor, 5b denotes a flow limiter, 5
c indicates a pressure limiter valve, and f3 and f4 indicate fuel return circuits, respectively. [0003] However, in the above technique, since the volume of the common rail is constant, the volume affects the function of the injection system, that is, the stability and responsiveness of the operation of the engine. It is important to match the volume to the injection system. In general, the volume of the common rail or accumulator is closely related to the pressure in the accumulator,
The larger the volume, the better the pressure stability, and the smaller the volume, the better the pressure response. Accordingly, it is difficult for a pressure accumulator having a constant volume to achieve both the pressure stability required for high-speed or high-load operation and the pressure response required for low-speed light-load operation, that is, stable operation at low speed. In particular, when operating conditions change to a high range, such as in a vehicle engine, it has been extremely difficult to reach a compromise with a constant volume. Also, the technique disclosed in Japanese Patent Application Laid-Open No. 2-112662 is disclosed, but relates to the improvement of the injection amount characteristic of the fuel injection nozzle in the accumulator type fuel injection device, and does not relate to the problem of the present application. Accordingly, it is an object of the present invention to provide a common rail type fuel injection device which achieves both pressure stability and pressure increasing performance. According to the present invention, in a common rail type fuel injection device for a diesel engine for injecting fuel through an accumulator, a piston is provided inside a pipe-shaped accumulator. A first part of the pressure accumulator, which is slidably provided and separated by a piston, is connected to the fuel injection nozzle by a high-pressure pump and a fuel injection pipe, and a second part of the pressure accumulator separated by the piston is A spring is provided for biasing the piston in a first partial direction, and is connected to the first and second on-off valves, the first on-off valve is connected to the high-pressure pump, and the second on-off valve is a fuel tank. The on-off valves are connected to a control device for controlling the engine. [0007] Since it is configured as described above,
The present invention has the following excellent effects. In other words, when the pressure pulsation in the common rail is large, the volume in the common rail can be increased during high rotation or high load to stabilize the pressure, and when the pumping capacity is low, the internal volume of the rail can be restored to the original volume. High pressure response can be maintained. [0008] Therefore, it is possible to sufficiently smoothly cope with a wide range of operating conditions from high speed and high load to idling, such as a vehicle engine. Embodiments of the present invention will be described below with reference to the drawings. In the drawings, members having the same functions as those of the related art are denoted by the same reference numerals, and redundant description will be omitted. FIG. 1 is a block diagram of a common rail fuel injection device according to the present invention. A fuel tank 1 is connected to an inlet side 4a of a high pressure pump 4 by a fuel circuit f1 in which a fuel filter 3 is interposed. The outlet side 4b of 4 is connected by a fuel circuit f2 to one end 5d of a main common rail 5, which is a first accumulator. The other end 5g of the main common rail 5 is connected to a sub-common rail 10 as a second accumulator via a high-pressure on-off valve 11, and the high-pressure on-off valve 11 is connected to an engine control device 8 by an electric circuit. ing. The pressure control valve 9 connected to the main common rail 5 is connected to the fuel tank 1 by a fuel return circuit f4, and the pressure control valve 9 is connected to the control device 8 by an electric circuit and attached to the main common rail 5. The pressure sensor 5a is connected to the control device 8 by an electric circuit. Further, the control device 8 is connected to an engine rotation sensor (not shown), a water temperature sensor, an air flow sensor, and the like by an electric circuit, and supplies a required amount of fuel to each cylinder via a nozzle according to a signal from these sensors as described below. It is configured to supply (inject). That is, during normal operation, the control device 8 calculates the pressure with respect to the volume of the common rail 5 based on signals from a rotation sensor, an air flow sensor and the like, determines the opening of the pressure control valve 9, and drives the pressure control valve 9. Thus, the pressure in the common rail 5 is maintained. In this state, when the load of the engine is suddenly applied, for example, when the vehicle is accelerating, signals from the rotation sensor, the common rail pressure sensor 5a and the like are input with reference to FIG. 3 (step S1). Then, it is determined whether or not the volume of the main common rail 5 is to be increased, that is, whether or not the stability needs to be improved (step S2). If YES, the on-off valve 11 is opened (Step S3), and if NO, the on-off valve 11 is closed (Step S4), control is performed to improve responsiveness, and the routine returns. Therefore, in high-speed, high-load and low-speed or idle operation, both efficient and smooth operation can be realized. FIG. 2 shows another embodiment of the present invention. A piston 21 is slidably provided inside a common rail 20, and a return spring 22 for urging the piston in a direction to reduce the volume of the common rail 20 is provided. The stopper 20a of the piston 21 is provided inside the common rail 20 for attachment, and the left side of the piston in the drawing is the volume of the common rail. A pressure sensor 5a provided on the left side of the piston 21 is connected to a control device by an electric circuit.
Through a return spring 22 of the common rail 21 via an on-off valve 24.
4 is connected. Therefore, in a normal operating state, the first
The on-off valve 23 is closed, and the on-off valve 2
The pressure control valve 9 is operated while the pressure control valve 9 is open. Then, for example, when the load of the engine is suddenly applied such as when accelerating the vehicle, referring to FIG.
A signal from the common rail pressure sensor 5a or the like is input (step S1), and it is determined whether or not the capacity of the common rail 20 is to be increased, that is, whether or not the stability needs to be improved (step S2). If YES, open / close valve 23
Is closed and the on-off valve 24 is opened (step S3). In the case of NO, the on-off valve 23 is opened and the on-off valve 24 is closed (step S3).
4), control is performed to improve the response, and the process returns. Therefore, there is an advantage that the best common rail volume can be set in accordance with the operation state, and finer control can be performed than in the first embodiment. The present invention is configured as described above,
The following excellent effects can be obtained. (1) The pressure inside the common rail can be stabilized by increasing the inner volume of the rail during high rotation or high load when pressure pulsation in the common rail is large. (2) When the pump pumping capacity is low and the rotation is low, the inner volume of the rail is returned to the original state, so that high pressure responsiveness can be maintained. (3) In the case of a variable volume using a piston, a rail internal volume suitable for the engine condition can be set. (4) Accordingly, it is possible to sufficiently cope with a wide range of operating conditions such as a vehicle engine, and it is possible to smoothly drive.

[Brief description of the drawings] FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing another embodiment of the present invention. FIG. 3 is a flowchart of the control in FIG. 1; FIG. 4 is a flowchart of the control in FIG. 2; FIG. 5 is an overall configuration diagram showing an example of a conventional technique. [Explanation of symbols] 1 ... fuel tank 2 ... Electric pump 3 ... Fuel filter 4 High pressure pump 5, 20, ... common rail 6. Fuel injection tube 7. Fuel injection nozzle 8 ... Control device 9 ... Pressure control valve 10 ... Sub common rail 11, 23, 24 ... on-off valve 21 ... Piston 22 ・ ・ ・ Return spring

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Claims (1)

(57) [Claim 1] In a diesel engine common rail type fuel injection device for injecting fuel via an accumulator, a piston is slidably inserted inside a pressure accumulator formed in a pipe shape. A first portion of the accumulator, separated by a piston, is connected to the fuel injection nozzle by a high-pressure pump and a fuel injection pipe, and a second portion of the accumulator separated by the piston.
Is provided with a spring for biasing the piston in the first partial direction, is connected to the first and second on-off valves, the first on-off valve is connected to the high-pressure pump, and the second on-off valve Is connected to a return circuit to a fuel tank, and their on-off valves are connected to a control device for controlling an engine.