PRESSURE ACCUMULATION TYPE FUEL JETTING DEVICE

Abstract: Reliability of a system, in which fuel pressurized by a high pressure supply pump is accumulated in a common rail, is affected a great deal when piping connected to the common rail is broken or pulsation of fuel injection occurs, because of high pressure of the fuel. This invention is to improve reliability of the system by incorporating a mechanism to prevent outflow of fuel from the common rail even when the piping is broken or a mechanism to attenuate the pulsation of pressurized fuel into pipings around the common rail.

Description: The present invention relates to an accumulator type of fuel injection device used for diesel engines. For example, one of the accumulator type of fuel injection devices used for diesel engines is disclosed in the official gazette of Japanese Patent Application Laid Open No. 165858-1984. In the aforementioned fuel injection device, fuel of high pressure sent from a high pressure fuel pump is stored in a kind of surge tank referred to as a common rail, and the stored fuel is injected into an engine when an injection valve is opened. A fuel injection device of this kind is disclosed in the official gazette of Japanese Patent Application Laid Open No. 159366-1985 corresponding to EP-A-0 150 138 in which a safety device is provided to an injection valve, and when not less than a predetermined amount of fuel is supplied to the injection valve, the fuel supply passage is closed. However, very high pressure (for example, 150 Mpa) generated by a high pressure pump having a cam mechanism is stored in an accumulator pipe referred to as a common rail, so that there is a possibility that a portion of the ultra-high pressure fuel passage provided from the high pressure fuel pump to the injection valve through the common rail, is damaged and the high pressure fuel leaks outside, and further there is a possibility that reflection pressure waves generated by an injection valve of one cylinder are transmitted to other cylinders through the common rail, so that the opening and closing timing of the cylinder is affected and its injection amount and timing are fluctuated. US-A-4,539,959 discloses a fuel injection system according to the preamble of claim 1. There, a fuel rail is connected to injectors by means of fuel flow limiting valve assemblies which shut-off fuel flow to the respective injector in the event of a malfunction resulting in fuel flow to the injector which exceeds the maximum time required for an injection event or the maximum quantity of fuel desired for an injection event. JP-A-62-258160 discloses a fuel injection device wherein a common rail is connected to injectors by means of injection controlling solenoid valves. A high pressure fuel feed pump is connected to the common rail via a feeding piping and a check valve. It is a primary object of the present invention to improve the reliability of a fuel injection system by providing a mechanism which maintains high pressure fuel in a common rail even when a high pressure fuel passage around the common rail, for example, an injection pipe between the common rail and the injection valve, or a supply pipe between the high pressure supply pump and the common rail, is damaged, or by providing a mechanism which prevents the occurrence of pulsations of high pressure fuel. In order to attain the object of the invention, the fuel injection device of the invention comprises the features defined in claim 1. The fuel injection device may comprise a mechanism which prevents a back flow from the common rail to a high pressure pump, or which prevents a back flow from the injector to the common rail. Fig. 1 is a schematic illustration showing the entire structure of an example; Fig. 2 is a sectional view of an injector; Fig. 3 is a sectional view of a check valve; Fig. 4 is a sectional view showing the operation of the check valve; Fig. 5 is a sectional view of a safety device; and Fig. 6 is a schematic illustration showing the entire structure of another example. With reference to the attached drawings, an example of the present invention will be explained as follows. Fig. 1 shows the entire structure of a fuel injection device for use in a diesel engine of the example. Fig. 2 shows an injector 36 provided in each of the combustion chambers of a diesel engine. In Fig. 2, a lower casing member 1 comprises a lower body 2, a connecting portion 3 and a nozzle body 4, and the members 2, 3 and 4 are integrated into one unit by a retaining nut 5. In the nozzle body 4, a valve body sliding hole 6 and a fuel reserving chamber 7 are formed, and a nozzle hole 8 communicating with the fuel reserving chamber 7 is formed at the top of the nozzle body 4. A large diameter portion 10 of a nozzle needle 9 is slidably engaged in the valve body sliding hole 6. A connecting portion 11 is provided to the large diameter portion 10 of the nozzle needle 9, and a small diameter portion 12 and a valve body portion 13 are provided to the lower end portion of the nozzle needle 9. When seat portion X is opened or closed by the valve body portion 13, fuel injection from the nozzle hole 8 is turned on and off. A flange 14 and a piston pin 15 are integrally connected with the tip of the connecting portion 11 of the needle 9, and a piston 16 is disposed at the end of the piston pin 15. The nozzle needle 9 is pushed by a spring 17 in a closing direction. The piston 16 is slidably engaged in a cylinder 18 formed in the body lower 2, and in the cylinder 18, is formed a compression control chamber 19 into which the tip of the piston 16 is extended. A plate valve 20 having an orifice is provided in the upper portion of the pressure control chamber 19, and a spring 21 to push the plate valve 20 is also provided in the pressure control chamber 19. An upper casing member 23 having a three-way control valve (an electromagnetic valve) 22 is closely attached onto the body lower 2. That is, a cylindrical upper body 24 is screwed to the lower body 2. A three-way valve body 25 is located in an inside hole of the upper body 24, and a retaining nut 26 is screwed into the inside hole of the body upper 24. An outer valve 27 is slidably engaged in the three-way valve body 25, and an inner valve 28 is disposed in the inside hole of the outer valve 27. When a coil 29 is not energized, the outer valve 27 is located in a lower position due to the force of a spring 30, so that a high pressure side passage 31 and the pressure control chamber 19 are communicated with each other through an oil passage 32. When the coil 29 is energized, the outer valve 27 is moved upward, so that the pressure control chamber 19 and a drain passage (a low pressure side passage) 33 are communicated with each other through the oil passage 32. A fuel supply passage 34 is formed in the lower casing member 1, and one end of the fuel supply passage 34 is exposed onto the surface of the casing member (the lower body 2) 1, and the other end is communicated with the fuel reserving chamber 7 and the high pressure side passage 31 of the upper casing member 23. Further, an inlet 35 is screwed onto the surface of the lower casing member (the lower body 2) 1 so that the inlet 35 is communicated with the fuel supply passage 34. High pressure fuel in an accumulator pipe (a common rail) 38 described later, is supplied to the fuel reserving chamber 7 through the inlet 35 and the fuel supply passage 34, and at the same time the fuel is supplied to the three-way control valve 22. Fuel in the drain passage 33 can be removed to a drain tank. Consequently, when high pressure fuel is supplied to the pressure control chamber 19, a valve closing force generated by the aforementioned high pressure fuel in the direction from the piston 16 to the needle 9, is higher than a valve opening force generated by the fuel in the fuel reserving chamber 7, so that the needle 9 closes the nozzle hole 8. Under the aforementioned condition, the three-way valve 22 is controlled, so that the pressure control chamber 19 is communicated with the drain passage 33 on the low pressure side, and the fuel in the pressure control chamber 19 flows out to the low pressure side. Accordingly, the nozzle needle 9 is moved in an opening direction so that it can be opened and fuel can be injected. At this time, the hydraulic pressure is gradually decreased by the action of an orifice of the brake valve 20. As shown in Fig. 1, each injector 36 is connected with the high pressure accumulator pipe 38 which is common among the cylinders, though the injection pipe 37. The accumulator pipe 38 is connected with a high pressure supply pump 41 through a supply pipe 39 and a check valve 40. This high pressure supply pump 41 boosts the pressure of the fuel which has been sucked from a fuel tank 42 by a low pressure fuel pump 43, to a predetermined high pressure so that the pressure can be controlled. That is, the high pressure supply pump 41 is operated in this manner: a cam 45 is rotated synchronously with the rotation of an engine 44; a piston in a cylinder 46 is reciprocated; and then the fuel sent from the low pressure supply pump 43 is boosted and supplied to the accumulator pipe 38. In order to control the pressure of fuel in the accumulator pipe 38, that is, in order to control an amount of fuel to be injected which is supplied to the accumulator pipe 38, the high pressure supply pump 41 is provided with an electromagnetic valve 48 for controlling the delivery amount, wherein the electromagnetic valve 48 is closed at a predetermined timing while the fuel is being sent out by the high pressure pump 41. Information about the rotation and load of the engine is inputted into an electronic control unit (referred to as ECU, hereinafter) 49 by a cylinder discriminating sensor 50, a crank angle sensor 51 and a load sensor 52. Then, the ECU 49 outputs a control signal to the three-way control valve 22 so that the most appropriate injection timing and injection amount (injection time) can be provided in accordance with the state of the engine which is judged by the aforementioned information. Further, a pressure sensor 53 to detect the pressure in the accumulator pipe 38 is disposed in the accumulator pipe 38, and the ECU 49 controls the delivery amount so that the signal obtained by the pressure sensor 53 can be the most optimum value which has been previously set in accordance with the load and engine speed. That is, negative feedback control of pressure is carried out so that a more accurate pressure setting is conducted. The delivery amount is increased when delivery timing TF of the high pressure supply pump 41 is advanced. A check valve 82 is provided in the middle of the injection pipe 37. As shown in Fig. 3, a fuel passage 84, a valve body accommodation chamber 85 and a fuel passage 86 are provided in a housing 83 of the check valve 82. A ball valve 87 is disposed in the valve body accommodation chamber 85, and a spring 89 for pushing the ball valve 87 against a valve seat 88 is also disposed in the chamber 85. A fuel passage 84 is connected with an injection pipe 37a which is communicated with the injection valve 36. A fuel passage 86 is connected with an injection pipe 37b which is communicated with the accumulator pipe 38. The setting load of the spring 89 of the check valve 82 is determined in such a manner that the setting load is lower than the product (= P min ·A1) of the minimum pressure P min in the common rail and the pressure receiving area Al of the ball valve. The ball valve 87 is lifted by the inner pressure of the accumulator pipe 38 so that fuel passes through the check valve. The maximum load of the spring 89 is set at a value higher than the product (= P max ·A1) of the maximum pressure P max in the accumulator pipe and the pressure receiving area A1 of the ball valve. Accordingly, even when the pressure is increased to P max , the ball valve 87 does not block the upper fuel passage 84. When a reflection pressure wave is generated in the injection pipe 37 after the completion of fuel injection conducted by the injector 36, wherein the reflection wave is directed from the injector 36 to the accumulator pipe 38, the ball valve 87 is closed so that transmission of the reflection pressure wave into the accumulator pipe 38 can be prevented. Due to the foregoing, interference (pressure change in the accumulator pipe) between the cylinders which causes the fluctuation of injection timing and injection amount, can be prevented. As shown in Fig. 5, a safety device (a flow limiter) 54 is provided between the accumulator pipe 38 and the injection pipe 37. In the example shown in Fig. 5, when an amount of fuel which flows in the safety device 54 temporarily exceeds an allowed value, fuel supply to the injector 36 is temporarily stopped, and when the amount of fuel continuously exceeds the allowed value, the fuel supply to the injector 36 is permanently stopped. That is, as shown in Fig. 5, a seat member 168 having a seat portion 167 on which a ball 157 is seated and also having a passage 169, is movably disposed in a housing 158, and the seat member 168 is pushed by a return spring 165. The diameter of a press-fitting hole 164 is larger than the outer diameter of the ball 157, and smaller than the outer diameter of a piston 159. Springs 161 and 165 are held by a spacer 172 provided with a fuel passage 166. In this example, in the case where an amount of fuel which flows in safety device 54 temporarily exceeds an allowed value, the piston 159 and the ball 157 are moved, and the ball is seated on the seat portion 167 of the seat member 168 so that the fuel supply to the injector 36 is temporarily stopped. When the amount of fuel which flows in the safety device 54 returns into an allowable range, the piston 159 and the ball 157 are returned by the spring 161, so that the fuel sent from the accumulator pipe 38 is supplied to the injector 36 again through the safety device 54. In the case where an abnormality has occurred in the injector 36 or the injection pipe 37 has been damaged so that an amount of fuel which flows in the safety device 54 exceeds the allowable range continuously, the piston 159 and the ball 157 are moved, and the piston 159 is press-fitted into the press-fitting hole 164. Therefore, the movement of the ball 57 is perfectly restricted, and the fuel supply to the injector 22 is permanently stopped. In the examples shown in Figs. 1 and 5, a safety device 54 is disposed between the common rail 38 and the injection pipe 37. When the same safety device is disposed in the connecting portion between the supply pipe 39 and the common rail 38, leakage of high pressure fuel from the common rail 38 can be prevented even when a pipe between the high pressure supply pump 41 and the common rail 38 is damaged. In this case, the check valves 421 and 423 shown in Fig. 6 may be used for the safety device. These check valves 421, 423 allow the fuel supply from the high pressure pump side to the common rail side, and restricts the fuel passage from the common rail side to the high pressure pump side. On the other hand, when the fuel supply pipe 39 is damaged, the high pressure fuel in the common rail 38 is restricted by the check valves 421, 423 so that it can not pass to the fuel supply 39 side. Therefore, the high pressure fuel does not return to the high pressure pump side. Accordingly, when the fuel supply pipe 39 is damaged, leakage of fuel from the common rail side can be prevented. In the case of damage of the fuel supply pipe 39, the amount of fuel to be supplied from the high pressure pump 48 to the common rail 38 is reduced. Accordingly, in order to control the common rail pressure to a predetermined value, fuel delivery timing TF (an amount of fuel delivery) is set to be early (small). Therefore, when TF becomes smaller than a predetermined value TO, the ECU49 assumes that the fuel supply pipe 39 has been damaged, and stops driving the high pressure pump 48 and injecting fuel. As described above, in this example, the check valves 421, 423 are disposed in the end portion of the fuel supply pipe 39 on the common rail 38 side to allow fuel supply from the high pressure pump 48 to the common rail 38 and to restrict fuel passage from the common rail 38 to the high pressure pump 48. As a result, even when the fuel supply pipe 39 is damaged, fuel passage from the common rail 38 to the fuel supply pipe 39 is restricted by the check valves 421, 423, so that leakage of high pressure fuel can be prevented. Next, a system will be explained which has a means to work in such a manner that fuel is supplied only by one fuel supply system even when the other fuel supply system has been damaged, wherein in a normal condition, fuel is supplied from the high pressure pump 48 to the common rail 38 by two fuel supply systems. As shown by a one-dotted chain line in Fig. 6, pressure sensors 433 and 434 are provided in fuel supply pipes 39, so that the fuel pressure detected by the pressure sensors 433, 434 can be taken into the ECU 49. When the fuel supply pressure detected by the pressure sensors 433, 434 is decreased to a value not more than a predetermined value, the ECU49 judges that one of the fuel supply pipes, the pressure of which is decreased, has been damaged. Then, the ECU49 controls an electromagnetic valve for controlling the delivery quantity so that fuel supply to the damaged fuel supply pipe can be stopped and fuel supply to the other fuel supply pipe can be increased. As described above, in this example, the ECU49 judges which fuel supply pipe is damaged, from the signals sent from the pressure sensors 433, 434, and in the case where one of the fuel supply pipes is damaged, fuel supply to the common rail 38 is continued by the other fuel supply pipe. Therefore, when the diesel engine is mounted on a vehicle, the vehicle can be moved to a safe place even when one of the fuel supply pipes is damaged. As explained above, according to the present invention, leakage and pulsation of high pressure fuel caused when the high pressure fuel passage around the common rail has been damaged, can be prevented with a simple mechanism, and reliability of the system can be improved.

Claims: An accumulator type of fuel injection device comprising an accumulator pipe (38) which accumulates high pressure fuel, a fuel pipe which guides out the high pressure fuel from said accumulator pipe (38), an injector (36) provided to each cylinder, said injector receiving the fuel from said fuel pipe (37) and injecting it into an engine (44) being electrically controlled, and a safety device (54) provided between said accumulator pipe (38) and said fuel pipe (37), said safety device (54) comprising a first movable element (159) permanently stopping the fuel flow when the amount of fuel supplied from said accumulator pipe (38) to said fuel pipe (37) continuously exceeds a predetermined value, characterized in that the safety device (54) comprises a further movable element (157) for temporarily stopping the fuel flow when the amount of fuel supplied from said accumulator pipe (38) to said fuel pipe temporarily exceeds a predetermined value, said further movable element (157) being moved back, after a temporary shut-off of the fuel flow, to a position allowing further fuel flow when the fuel flow has returned into an allowable range. Fuel injection device according to claim 1, wherein the further movable element (157) is a ball (157). Fuel injection device according to claim 1 or 2, wherein the first movable element (159) is a piston being in contact with the further movable element (157). Fuel injection device according to claim 1, 2 or 3, comprising a press-fitting hole (164) having a diameter which is larger than the outer diameter of the further movable element (157), and is smaller than the outer diameter of the first movable element (159), wherein the first movable element (159) is press-fitted into the press-fitting hole (164) in case of a permanent shut-off. Fuel injection device according to any one of the preceding claims, comprising a seat member (168) adapted for receiving the further movable element (157) in case of a temporary shut-off of the fuel flow, the seat member (168) being pushed by a return spring (165).

Inventors: BAN MITSURU, IWANAGA TAKASHI, KARIYA YASUHIRO, KAWAGUCHI TAKAYOSHI, MAGARIO KENJI, SHIMA NOBUHIKO, BAN, MITSURU, IWANAGA, TAKASHI, KARIYA, YASUHIRO, KAWAGUCHI, TAKAYOSHI, MAGARIO, KENJI, SHIMA, NOBUHIKO, BAN, Mitsuru Nippondenso Co., Ltd., IWANAGA, Takashi Nippondenso Co., Ltd., KARIYA, Yasuhiro Nippondenso Co., Ltd., KAWAGUCHI, Takayoshi Nippondenso Co., Ltd., MAGARIO, Kenji Nippondenso Co., Ltd., SHIMA, Nobuhiko Nippondenso Co., Ltd.
Applicants: NIPPON DENSO CO, NIPPONDENSO CO., LTD.
Application year: 1992
Main classification: F02M55
IPC codes: F02M63, F02M59, F02D41, F02M47, F02M61, F02M55, F02B3