Safety valve for fuel injection apparatus

Abstract

 A safety valve (3) provided in a fuel injection apparatus including an accumulator (1) in which fuel is accumulated, comprises: a housing (30) having an inside passage (31) for introducing the high-pressure fuel of the accumulator (1) into the inside of the housing (30) and a seat face (32) formed at a portion of the inside passage (31); a valve element (36) provided movably within the housing (30) and including a valve body (37) to open/close the seat face (32); an elastic member (38) for pressing and biasing the valve element (36) in a closing direction; and a fuel chamber (39) defined between the inner surface of the housing (30) and the valve element (36) so as to maintain a pressure for pressing the valve element (36) in a valve-opening direction, wherein the high-pressure fuel from the inside passage (31) is introduced into the fuel chamber (39) when the valve body (37) of the valve element (36) is separated from the seat face (32). With this safety valve (3), the high-pressure fuel of the accumulator (1) is introduced into the fuel chamber (39) in order to press the valve element (36) in the valve-opening direction so that the valve element (36) will be rapidly opened, with the result that the fuel pressure in the accumulator (1) can recover a predetermined value instantaneously.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a safety valve of an accumulator in a fuel injection apparatus of a diesel engine for injecting high-pressure fuel accumulated in the accumulator by means of an injector of an electronic control type provided in each cylinder.

Description of the Prior Art

[0002] There has been conventionally known a fuel injection apparatus, as disclosed in Japanese Patent Unexamined Publication No. 59-165858, which is arranged in such a manner that high-pressure fuel is accumulated in an accumulator called a common rail by a high-pressure supply pump, and the high-pressure fuel of the accumulator is injected by an injector of an electronic control type provided in each cylinder.

[0003] This fuel injection apparatus is provided with a safety valve which is opened for releasing the fuel when a pressure in the accumulator exceeds a predetermined value.

[0004] As shown in Fig. 5, the structure of the conventional safety valve is such that a tapered seat face 32 which is an opening portion of a passage 31 in communication with the accumulator is opened/closed by a ball valve 37, and that when the fuel pressure in the accumulator exceeds a biasing force of a spring 38 which presses and biases the ball valve 37 in a valve-closing direction, the ball valve 37 is opened to release the fuel of the accumulator to the low pressure side, thereby suppressing an increase of pressure in the accumulator.

[0005] With this structure, however, an area of an opening after the ball valve 37 is opened is insufficient. Consequently, even after the fuel has been once released through the opened valve, there is a risk that the pressure in the accumulator is increased to exceed a valve-opening pressure of the ball valve 37 when the fuel is pressurized and delivered again. Particularly when the fuel of a maximum flow rate Q_max is pressurized and delivered from the high-pressure supply pump to the accumulator, there is a risk, as shown in Fig. 6, that the fuel pressure is increased to exceed not only the valve-opening pressure Po but also a critical internal pressure P_E of an accumulation piping.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to provide a fuel injection apparatus capable of preventing an abnormal increase of a fuel pressure.

[0007] Therefore, the present invention is intended to provide a safety valve of a fuel injection apparatus which can obtain a property of a large flow rate after the valve is opened and which can constantly maintain the pressure in an accumulator to be not higher than a critical pressure.

[0008] It is a further object of the invention to provide a safety valve which enables the fail-safe system to function favorably at the time of a trouble by regulating a clearance between the inner peripheral surface of a small-diameter section and the outer peripheral surface of a valve element so as to set the increased fuel pressure in the accumulator to a predetermined value.

[0009] Another object of the invention is to provide a safety valve which enables the fuel pressure in the accumulator to recover a predetermined value instantaneously by opening the valve rapidly once it reaches a valve-opening pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 

Figs. 1 to 4 relate to one embodiment of a safety valve according to the present invention:

Fig. 1 is a cross-sectional view showing the whole structure of the safety valve;

Fig. 2 is a schematic view showing the entire system of a fuel injection apparatus including the safety valve applied to the present embodiment;

Fig. 3 is an enlarged fragmentary view of a portion enclosed by a circle line III in Fig. 1; and

Fig. 4 is an operational characteristic graph of the safety valve.

Figs. 5 and 6 relate to a prior art concerning the present invention:

Fig. 5 is a cross-sectional view showing the whole structure of the conventional safety valve; and

Fig. 6 is an operational characteristic graph of the safety valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0011] One embodiment of the present invention will be hereinafter described with reference to the attached drawings.

[0012] Referring to Fig. 2, fuel supplied from a fuel tank (not shown) is pressurized and delivered through a conduit via a delivery valve by means of a high-pressure supply pump 2 such as a priming pump, and accumulated in an accumulation chamber of an accumulator 1 which is called a common rail.

[0013] The high-pressure fuel accumulated in the accumulation chamber of the accumulator 1 is injected into an internal combustion engine through an opened nozzle hole when a nozzle needle having a distal-end portion to open/close the nozzle hole is biased in a valve-opening direction by a pressure of the fuel supplied through a check valve and a passage in an injector of an electronic control type (not shown) provided in each cylinder.

[0014] At an end portion of the accumulator 1, there is provided a safety valve 3 for controlling the fuel pressure in the accumulator 1 so as to prevent it from exceeding a critical value.

[0015] As shown in Figs. 1 and 3, the safety valve 3 comprises: a housing 30 which includes an inside passage 31 in communication with the accumulator 1, a tapered seat face 32 formed at an opening portion of the inside passage 31, a small-diameter section 33, a spring chamber 34 and a low-pressure passage 35 in communication with a fuel tank 4 on the low pressure side of the safety valve; a valve element 36 provided movably within the housing 30, with a ball valve 37 to open/close the seat face 32 being fixed on this valve element; and a spring 38 which presses and biases the valve element 36 in a valve-closing direction. The valve element 36 is closely fitted in the small-diameter section 33 of the housing 30, and a fuel chamber 39 which maintains a pressure for pressing the valve element 36 in the valve-opening direction is defined between the valve element 36 and the end surface of the small-diameter section 33.

[0016] The safety valve 3 of the above-described structure is operated in the following manner.

[0017] When the fuel pressure in the accumulator 1 is not higher than a valve-opening pressure of the ball valve 37 which is predetermined by the spring 38, the ball valve 37 is contacted with the seat face 32. With the ball valve 37 in this state, when the fuel pressure in the accumulator 1 is increased, the fuel introduced from the inside passage 31 causes the ball valve 37 to be opened against a biasing force of the spring 38. Consequently, the fuel introduced from the inside passage 31 flows into the fuel chamber 39 and presses the valve element 36 in the valve-opening direction. As a result, the valve element 36 is rapidly opened to allow the fuel introduced from the inside passage 31 to flow to the low pressure side of the safety valve at once so that the accumulator 1 will recover a predetermined pressure in an instant.

[0018] Fig. 4 illustrates a change of the fuel pressure in the accumulator 1 from the opening to the closing of the safety valve. When the ball valve 37 is opened at a valve-opening pressure Po, the fuel pressure is decreased to a pressure P_R instantaneously, and eventually reaches a valve-closing pressure P_c of the ball valve 37.

[0019] The pressure P_R can be set to a predetermined value by regulating a clearance a between the valve element 36 and the small-diameter section 33, and when the pressure P_R is set to a minimum value which the pressure in the accumulator 1 is required to have for operating the engine, the fail-safe and limp-home system can be functioned favorably at the time of a trouble.

[0020] According to the present invention, as described heretofore, when the valve body of the valve element is separated from the seat face, the high-pressure fuel introduced from the inside passage flows into the fuel chamber, and the pressure in this fuel chamber presses the valve element in the valve-opening direction so that the valve element will be rapidly opened, with the result that the fuel pressure in the accumulator can recover a predetermined value instantaneously.

[0021] A safety valve provided in a fuel injection apparatus including an accumulator in which fuel is accumulated, comprises: a housing having an inside passage for introducing the high-pressure fuel of the accumulator into the inside of the housing and a seat face formed at a portion of the inside passage; a valve element provided movably within the housing and including a valve body to open/close the seat face; an elastic member for pressing and biasing the valve element in a closing direction; and a fuel chamber defined between the inner surface of the housing and the valve element so as to maintain a pressure for pressing the valve element in a valve-opening direction, wherein the high-pressure fuel from the inside passage is introduced into the fuel chamber when the valve body of the valve element is separated from the seat face. With this safety valve, the high-pressure fuel of the accumulator is introduced into the fuel chamber in order to press the valve element in the valve-opening direction so that the valve element will be rapidly opened, with the result that the fuel pressure in the accumulator can recover a predetermined value instantaneously.

Claims

1. A safety valve provided in a fuel injection apparatus including an accumulator in which fuel is accumulated,
said safety valve for the fuel injection apparatus comprises:

a housing having an inside passage for introducing the high-pressure fuel of the accumulator into the inside of the housing and a seat face formed at a portion of said inside passage;

a valve element provided movably within said housing and including a valve body to open/close said seat face;

an elastic member for pressing and biasing said valve element in a closing direction; and

a fuel chamber defined between the inner surface of said housing and said valve element so as to maintain a pressure for pressing said valve element in a valve-opening direction,

the high-pressure fuel from said inside passage being introduced into said fuel chamber when the valve body of said valve element is separated from said seat face.

2. A safety valve for a fuel injection apparatus according to Claim 1, wherein said housing includes a small-diameter section in communication with said inside passage and a spring chamber whose diameter is larger than that of said small-diameter section, said valve element being closely fitted in said small-diameter section.

3. A safety valve for a fuel injection apparatus according to Claim 1 or 2, wherein the valve body of said valve element is a ball valve which is fixed to be pressed against said seat face, said fuel chamber being defined between an end portion of said valve element on which said ball valve is fixed and an end surface of said small-diameter section.

4. A safety valve for a fuel injection apparatus according to Claim 2, wherein the increased fuel pressure in said accumulator can be set to a predetermined value by regulating a clearance between the inner peripheral surface of said small-diameter section and the outer peripheral surface of said valve element.

Drawing