Safety valve

Abstract

To provide a low-cost safety valve which does not necessarily require high processing accuracy.SOLUTION: A safety valve disposed in a common rail type fuel injection device includes a piston valve and a housing including a piston housing surface housing the piston valve. The piston valve includes: a valve outer peripheral surface slidably engaging the piston housing surface; a plurality of slits each of which extends on the valve outer peripheral surface along a flow direction of fuel in the housing, which are arranged at intervals in a peripheral direction of the valve outer peripheral surface, and define slit flow paths for the fuel to flow between themselves and the piston housing surface; and a circumferential groove extending in a circumferential direction so that it is connected to the respective plurality of slits.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a safety valve for reducing the pressure in an accumulator chamber of a common rail fuel injection device. [Background technology]

[0002] Conventionally, safety valves for reducing the pressure in the accumulator chamber of a common rail fuel injection system have been known. For example, the safety valve disclosed in Patent Document 1 is installed in a common rail, which is an example of a common rail fuel injection system. The safety valve includes a housing and a piston housed in the housing. The housing is formed therein with a valve hole, a small diameter hole connected to the valve hole, and a damper chamber, which is a large diameter hole connected to the small diameter hole. The piston includes a ball valve for opening and closing the valve hole, a small diameter portion that fits into the small diameter hole, and a large diameter portion that fits into the damper chamber. Two notches (slits) are formed in the small diameter portion.

[0003] When the piston moves downstream as the safety valve operates, fuel in the accumulator flows from the valve hole into each of the two notches. As the piston moves further, the two notches reach the damper chamber. The fuel flows from the notches into the damper chamber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-031015 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned safety valve, if the piston is misaligned axially between the two notches, one of the two notches will reach the damper chamber first. In this case, fuel will enter the damper chamber through only one notch. As a result, the pressure balance between the two notches will be disrupted, potentially causing the piston to tilt. This can lead to poor sliding between the piston and the housing, and the piston may become stuck to the housing with the ball valve opening its valve hole. Therefore, high-precision machining is required during the piston manufacturing process to form the two notches so that they reach the damper chamber at the same time. This can result in increased safety valve costs.

[0006] An object of the present disclosure is to provide a low-cost safety valve that does not require high machining precision. [Means for solving the problem]

[0007] A safety valve according to at least one embodiment of the present disclosure comprises: A safety valve disposed in a common rail that stores fuel pressure, A piston valve; a housing including a piston receiving surface that receives the piston valve; Equipped with The piston valve is a valve outer peripheral surface that is slidably fitted onto the piston housing surface; a plurality of slits each extending in the valve outer peripheral surface along the fuel flow direction in the housing, the slits being spaced apart in the circumferential direction of the valve outer peripheral surface and defining a slit flow path through which the fuel flows between the valve outer peripheral surface and the piston accommodating surface; a circumferential groove extending in the circumferential direction so as to connect to each of the plurality of slits; Includes. [Effects of the Invention]

[0008] According to the present disclosure, a low-cost safety valve can be provided that does not require high machining precision. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram of a common rail system according to an embodiment; [Figure 2] 1 is a schematic enlarged view of a safety valve according to an embodiment; [Figure 3] 2 is a schematic cross-sectional view of the piston valve as viewed in the direction of the arrow AA. FIG. [Figure 4] 5 is a schematic cross-sectional view of the piston valve as viewed in the direction of the arrow BB. FIG. [Figure 5] 10A-10C are schematic diagrams illustrating the movement of a piston valve according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, several embodiments of the present disclosure will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the present disclosure. For example, expressions expressing relative or absolute arrangement such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" not only express such an arrangement exactly, but also express a state in which there is a relative displacement with a tolerance or an angle or distance to the extent that the same function is obtained. For example, expressions such as "identical," "equal," and "homogeneous" that indicate that something is in an equal state not only indicate a state of strict equality, but also indicate a state in which there is a tolerance or a difference to the extent that the same function is obtained. For example, expressions representing shapes such as a square shape or a cylindrical shape not only represent shapes such as a square shape or a cylindrical shape in the strict geometric sense, but also represent shapes including uneven portions, chamfered portions, etc., to the extent that the same effect can be obtained. On the other hand, the expressions "comprise," "include," or "have" one element are not exclusive expressions that exclude the presence of other elements. Note that the same components will be denoted by the same reference numerals and the description thereof will be omitted.

[0011] 1 is a schematic diagram of a common rail system 1 according to one embodiment of the present disclosure. The common rail system 1 includes a fuel tank 12 that stores fuel for a diesel engine, a high-pressure fuel pump 15 that pressurizes fuel from the fuel tank 12, a common rail 7 in which an accumulator chamber 8 is formed that accumulates the fuel pressurized by the high-pressure fuel pump 15, and a plurality of fuel injection devices (not shown) to which the fuel accumulated in the accumulator chamber 8 is supplied. Each of the plurality of fuel injection devices injects fuel from the accumulator chamber 8 into a combustion chamber (not shown) of the diesel engine.

[0012] The common rail system 1 further includes a safety valve 10 disposed in a common rail 7, which is an example of a common rail fuel injection device, and a return line 11 connected to the safety valve 10 and a fuel tank 12. The safety valve 10 is configured to discharge fuel in the accumulator chamber 8 into the return line 11 when the common rail pressure, which is the pressure in the accumulator chamber 8, exceeds an allowable upper limit value. The operating principle of the safety valve 10 will be described later. The return line 11 is configured to return the fuel discharged from the safety valve 10 to the fuel tank 12.

[0013] The safety valve 10 includes a housing 2 attached to the common rail 7. The housing 2 includes an inlet 23 communicating with the accumulator chamber 8, an outlet 28 communicating with the return line 11, and a housing flow path surface 25 extending between the inlet 23 and the outlet 28. Fuel passing through the inlet 23 flows to the outlet 28 via the housing flow path surface 25. The housing 2 is a substantially cylindrical member. Therefore, when viewed along the axial direction of the housing 2, the inlet 23, the outlet 28, and the housing flow path surface 25 are all circular. In the following description, the direction of fuel flow inside the housing 2 may be simply referred to as the "flow direction." The flow direction is a direction that substantially coincides with the axial direction of the housing 2.

[0014] 2 is a schematic enlarged view of a safety valve 10 according to an embodiment of the present disclosure. A piston valve 4 for opening and closing the inlet 23 and a spring 9 for biasing the piston valve 4 toward the inlet 23 are housed inside the housing flow path surface 25. The piston valve 4 includes a valve body 43, an abutment portion 49 that abuts against the spring 9, and a cylindrical sliding portion 44 that extends between the valve body 43 and the abutment portion 49. In this example, the abutment portion 49 abuts against the spring 9 via a valve opening pressure adjustment shim 3.

[0015] The housing flow path surface 25 includes a valve seat surface 26 on which the valve body 43 is seated, a piston accommodating surface 21 extending downstream in the flow direction from the valve seat surface 26, a tapered surface 24 connected to an accommodating surface downstream end 22 which is the downstream end of the piston accommodating surface 21, and a large-diameter flow path surface 29 arranged downstream of the tapered surface 24.

[0016] The valve seat surface 26 is a tapered surface that increases in diameter toward the downstream side in the flow direction and faces downstream. The piston accommodating surface 21 abuts against the sliding portion 44. The tapered surface 24 increases in diameter toward the downstream side. A tapered flow path Ct is formed inside the tapered surface 24. The large-diameter flow path surface 29 is a flow path surface having an inner diameter larger than the inner diameter of the piston accommodating surface 21. In other words, the piston accommodating surface 21 is understood to be a small-diameter flow path surface having an inner diameter smaller than that of the large-diameter flow path surface 29. A large-diameter flow path Cb through which the fuel flows is formed inside the large-diameter flow path surface 29, and in this example, the above-mentioned spring 9 is arranged in the large-diameter flow path Cb.

[0017] The sliding portion 44 of the piston valve 4 will be described with reference to FIGS. 2 to 4. As shown in FIGS. 2 and 3, the sliding portion 44 includes a valve outer peripheral surface 41 that slidably fits onto the piston housing surface 21, and a plurality of slits 42 that each extend linearly along the flow direction on the valve outer peripheral surface 41. The plurality of slits 42 are arranged at intervals in the circumferential direction of the valve outer peripheral surface 41. A slit flow path Cs (see FIG. 3) for fuel flow is defined between each slit 42 and the piston housing surface 21. In the example of FIG. 3, the number of slits 42 is three. In other examples, the number of slits 42 may be, for example, two or four or more. The plurality of slits 42 are preferably arranged at equal intervals in the circumferential direction.

[0018] Each slit 42 has a slit downstream end 46, which is the end on the downstream side in the flow direction, and a slit upstream end 47, which is opposite the slit downstream end 46. Although this is merely an example, the end of the sliding portion 44 on the valve disc 43 side is a tapered portion 44a that decreases in diameter toward the valve disc 43, and the slit upstream end 47 is formed as the tapered portion 44a. Therefore, the circumferential length of the slit upstream end 47 increases toward the downstream side in the flow direction. This reduces pressure loss of the fuel flow at the slit upstream end 47.

[0019] As shown in FIGS. 2 and 4, the piston valve 4 further includes a circumferential groove 48 extending circumferentially so as to connect to the plurality of slits 42. In this example, the circumferential groove 48 is an annular groove formed over the entire circumferential length of the piston valve 4. In addition, the circumferential groove 48 in this example connects to the downstream end portions 46 of each of the plurality of slits 42. When the valve body 43 of the piston valve 4 is seated on the valve seat surface 26, the circumferential groove 48 is located upstream of the downstream end portion 22 of the housing surface. A groove flow path Cg (see FIG. 4) into which fuel can flow is defined between the circumferential groove 48 and the piston housing surface 21. The groove flow path Cg extends circumferentially.

[0020] The operating principle of the safety valve 10 will be explained with reference to Figures 2 and 5. When the common rail pressure exceeds the allowable upper limit, the spring 9 compresses, causing the piston valve 4 to move downstream in the flow direction. This activates the safety valve 10. Fuel flows into each of the multiple slit channels Cs from the inlet 23, and the groove channels Cg are also filled with fuel. The piston valve 4 then moves further downstream, and at least a portion of the circumferential groove 48 moves downstream beyond the downstream end 22 of the housing surface (see Figure 5). Each slit channel Cs becomes connected to the large-diameter channel Cb via the groove channels Cg and the tapered channels Ct. The fuel in the slit channels Cs and the channels in the groove channels Cg flow into the large-diameter channel Cb via the tapered channels Ct. The fuel flowing through the large-diameter channel Cb flows out of the outlet 28 (see Figure 1) into the return line 11. After the pressure in the accumulator chamber 8 is reduced, the piston valve 4 returns to its original position due to the biasing force of the spring 9 (see Figure 2). When the valve element 43 is seated on the valve seat surface 26, the operation of the safety valve 10 ends.

[0021] Here, during manufacturing of the piston valve 4, misalignment in the flow direction (axial direction of the piston valve 4) may occur between the multiple slits 42 due to machining errors. In this regard, according to the above-described configuration, the circumferential groove 48 connects the multiple slits 42, so that two adjacent slits 42 communicate with each other. Therefore, when the safety valve 10 is activated, the multiple slit flow paths Cs can communicate with the large-diameter flow path Cb almost simultaneously via the groove flow paths Cg and the tapered flow paths Ct. This makes it possible to prevent fuel from accumulating in any particular slit flow path Cs among the multiple slit flow paths Cs. Therefore, during manufacturing of the piston valve 4, machining precision for strictly aligning the multiple slits 42 in the axial direction of the piston valve 4 is not essential. Therefore, a low-cost safety valve 10 that does not require high machining precision can be realized.

[0022] Furthermore, since the circumferential groove 48 is an annular groove formed over the entire circumferential length of the piston valve 4, any two circumferentially adjacent slits 42 communicate with each other. This makes it possible to more reliably prevent fuel from accumulating in a specific slit flow path Cs.

[0023] In a comparative example in which the circumferential groove 48 is disposed in the center of the slit 42 in the flow direction, fuel flowing through one of the slit channels Cs flows along the groove channels Cg of the circumferential groove 48 and into the adjacent slit channel Cs. In this case, fuel flowing through the groove channels Cg merges with fuel flowing through the slit channels Cs toward the center, causing pressure loss in the slit channels Cs. In this regard, with the present configuration in which the circumferential grooves 48 are connected to the downstream end portions 46 of the respective slits, fuel can flow circumferentially through the groove channels Cg toward the large-diameter channels Cb, thereby reducing pressure loss due to fuel merging. Therefore, the safety valve 10 can reduce the pressure in the accumulator chamber 8 in a short time. Note that the present disclosure does not exclude the comparative example described above.

[0024] Furthermore, when the piston valve 4 is seated on the valve seat surface 26, the circumferential groove 48 is located upstream of the downstream end 22 of the housing surface in the flow direction. According to the above configuration, when the piston valve 4 starts to move downstream to open the inlet 23, the circumferential groove 48 is filled with fuel as the circumferential groove 48 moves downstream of the downstream end 22 of the housing surface. As a result, a force that attempts to open the piston valve 4, which is derived from the pressure in the accumulator chamber 8, acts in the axial direction of the piston valve 4 from the valve body 43 to the circumferential groove 48. Therefore, even if the pressure in the accumulator chamber 8 drops slightly after the piston valve 4 leaves the valve seat surface 26, the piston valve 4 continues to move downstream. Since the piston valve 4 can be prevented from repeatedly moving upstream and downstream even when only a slight pressure fluctuation in the accumulator chamber 8 occurs, the inlet 23 is stably opened after the piston valve 4 starts to move.

[0025] Furthermore, when the piston valve 4 moves downstream, at least a portion of the circumferential groove 48 moves downstream of the downstream end 22 of the accommodating surface, so that each of the multiple slit flow paths Cs can more reliably communicate with the large-diameter flow path Cb via the groove flow path Cg and the tapered flow path Ct.

[0026] After the pressure accumulator 8 is depressurized, the piston valve 4 moves toward its original position. At this time, if the axis of the piston valve 4 is misaligned with the axis of the housing 2, the circumferential groove 48 may get caught on the downstream end 22 of the accommodating surface, preventing the piston valve 4 from returning to its original position. In this regard, if the housing 2 is configured to include the tapered surface 24, the axis of the piston valve 4 can be aligned with the axis of the housing 2 as the tapered surface 24 guides the piston valve 4 toward the upstream side. This prevents the circumferential groove 48 from getting caught, allowing the piston valve 4 to smoothly return to its original position after the pressure accumulator 8 is depressurized.

[0027] <Modification> The circumferential groove 48 does not have to be formed over the entire circumferential length of the piston valve 4. For example, the multiple slits 42 may include a first slit and a second slit on one circumferential side of the first slit, and the circumferential groove 48 may extend from the first slit toward the other side to the second slit. In this case, the circumferential groove 48 is not disposed on one side of the first slit or the other side of the second slit. In this embodiment, the housing 2 may not include the tapered surface 24, and the piston accommodating surface 21 may be directly connected to the large-diameter flow path surface 29.

[0028] The above-described safety valve 10 is a mechanical safety valve in which the spring 9 compresses when the common rail pressure reaches an upper limit of allowable pressure, but the present disclosure is not limited to this. The safety valve 10 may also be a solenoid safety valve that can independently move the piston valve 4. Furthermore, the outlet 28 does not have to be located at the other end of the housing 2. For example, it may be located in a side wall portion of the housing 2.

[0029] The common rail fuel injection system in which the safety valve 10 is disposed is not limited to the common rail 7. The common rail fuel injection system may be the high-pressure fuel pump 15 shown in FIG. 1. In other words, the safety valve 10 may be provided in the pump accumulator of the high-pressure fuel pump 15. Whether the safety valve 10 is disposed in the common rail 7 or the high-pressure fuel pump 15, the operating principle of the safety valve 10 remains the same.

[0030] <Summary> The contents of the above-described embodiments can be understood, for example, as follows.

[0031] 1) At least one embodiment of the safety valve (10) of the present disclosure comprises: A safety valve disposed in a common rail fuel injection system (common rail 7, high-pressure fuel pump 15) that stores fuel under pressure, a piston valve (4); a housing (2) including a piston receiving surface (21) for receiving the piston valve; Equipped with The piston valve is a valve outer peripheral surface (41) that is slidably fitted onto the piston accommodating surface; a plurality of slits (42) each extending in the valve outer peripheral surface along the fuel flow direction in the housing, the slits (42) being spaced apart in the circumferential direction of the valve outer peripheral surface and defining a slit flow path (Cs) through which the fuel flows between the valve outer peripheral surface and the piston accommodating surface; a circumferential groove (48) extending in the circumferential direction so as to connect to each of the plurality of slits; Includes.

[0032] When the pressure in the accumulator chamber in the common rail exceeds the allowable upper limit, the piston valve moves downstream in the flow direction, activating the safety valve. At this time, fuel flows from the accumulator chamber into each of the multiple slit passages. The piston valve then moves further, and each slit passage becomes connected to the large-diameter passage (Cb) formed downstream of the piston housing surface. The fuel in the slit passages flows into the large-diameter passage, reducing the pressure in the common rail. During the manufacturing of the piston valve, misalignment in the flow direction between the multiple slits can occur due to machining errors. In this regard, with the configuration 1) above, the circumferential grooves connect to each of the multiple slits, so that adjacent two slits communicate with each other. Therefore, when the piston valve moves downstream, the multiple slit passages can communicate with the large-diameter passage almost simultaneously through the groove passages (Cg) of the circumferential groove, preventing fuel from accumulating in a specific slit passage. This eliminates the need for high machining precision during the manufacturing of the piston valve to precisely align the multiple slits in the flow direction. Therefore, a low-cost safety valve that does not require high machining precision can be realized.

[0033] 2) In some embodiments, the safety valve described in 1) above, The circumferential groove is an annular groove formed over the entire circumferential length of the piston valve.

[0034] According to the above configuration 2), any two circumferentially adjacent slit passages can communicate with each other, which makes it possible to more reliably prevent fuel from accumulating in a particular slit passage.

[0035] 3) In some embodiments, the safety valve according to 1) or 2) above, The circumferential groove connects to a downstream slit end portion (46) of each of the plurality of slits, the downstream end portion in the flow direction of each of the slits.

[0036] In a comparative example in which a circumferential groove is disposed in the center of the slit in the flow direction, fuel flowing through the first slit passage flows along the groove passage of the circumferential groove into the second slit passage. In this case, fuel flowing through the groove passage and fuel flowing through the second slit passage toward the center merge, causing pressure loss in the second slit passage. In contrast, according to the configuration of 3) above, the circumferential groove is connected to the downstream end of each slit, so fuel can flow circumferentially through the groove passage toward the large-diameter passage, reducing pressure loss due to fuel merging. Therefore, the safety valve can reduce the pressure in the accumulator chamber in a short time.

[0037] 4) In some embodiments, the safety valve according to 3) above, When the piston valve is seated on the valve seat surface (26) of the housing, the circumferential groove is located upstream in the flow direction of the downstream end (22) of the piston accommodating surface, which is the downstream end of the piston accommodating surface.

[0038] According to the configuration of 4) above, when the piston valve starts to move downstream in the flow direction, the circumferential groove is filled with fuel as the circumferential groove moves downstream of the downstream end of the housing surface. A force that attempts to open the piston valve, which is derived from the pressure in the accumulator, acts on the piston valve in the axial direction. Therefore, even if the pressure in the accumulator drops slightly, the piston valve continues to move downstream. Since the piston valve can be prevented from repeatedly moving upstream and downstream even when only a slight pressure fluctuation occurs in the accumulator, the inlet is stably opened after the piston valve starts to move downstream.

[0039] 5) In some embodiments, the safety valve according to 3) or 4) above, When the piston valve moves downstream in the flow direction, at least a portion of the circumferential groove moves downstream of the downstream end (22) of the piston accommodating surface, which is the downstream end of the piston accommodating surface.

[0040] According to the above configuration 5), when the piston valve moves downstream, each of the plurality of slit flow paths can more reliably communicate with the large diameter flow path via the circumferential groove.

[0041] 6) In some embodiments, the safety valve described in 5) above, The housing further includes a tapered surface (24) that is connected to the downstream end of the accommodating surface and that increases in diameter toward the downstream side.

[0042] After the pressure in the accumulator chamber is reduced, the piston valve moves toward its original position. If the axis of the piston valve is misaligned with the axis of the housing at this time, the circumferential groove may get caught on the piston accommodating surface, preventing the piston valve from returning to its original position. In this regard, according to the configuration of 6) above, the axis of the piston valve can be aligned with the axis of the housing as the tapered surface guides the piston valve toward the upstream side. Because the circumferential groove is prevented from getting caught, the piston valve can smoothly return to its original position after the pressure in the accumulator chamber is reduced. [Explanation of symbols]

[0043] 1: Common rail system 2: Housing 3: Opening pressure adjustment shim 4: Piston valve 7: Common rail 8:Accumulation chamber 9: Spring 10: Safety valve 11: Return line 12: Fuel tank 15: High-pressure fuel pump 21: Piston housing surface 22: Downstream end of the storage surface 23: Entrance 24: Tapered surface 25: Housing flow path surface 26: Valve seat surface 28: Exit 29: Large diameter flow path surface 41: Valve outer circumferential surface 42: Slit 43: Valve body 44: Sliding part 44a: Tapered section 46: Downstream end of slit 47: Upstream end of slit 48: Circumferential groove 49: Contact part Cb: Large diameter flow path Cg: Groove channel Cs: Slit flow channel Ct: Tapered flow path

Claims

1. A safety valve disposed in a common rail fuel injection system, A piston valve; a housing including a piston receiving surface that receives the piston valve; Equipped with The piston valve is a valve outer peripheral surface that is slidably fitted onto the piston housing surface; a plurality of slits each extending in the valve outer peripheral surface along the fuel flow direction in the housing, the slits being spaced apart in the circumferential direction of the valve outer peripheral surface and defining a slit flow path through which the fuel flows between the valve outer peripheral surface and the piston accommodating surface; a circumferential groove extending in the circumferential direction so as to connect to each of the plurality of slits; Contains safety valve.

2. The circumferential groove is an annular groove formed over the entire circumferential length of the piston valve. The safety valve of claim 1.

3. The circumferential groove is connected to a downstream end of each of the plurality of slits, which is a downstream end in the flow direction. The safety valve according to claim 1 or 2.

4. When the piston valve is seated on the valve seat surface of the housing, the circumferential groove is located upstream in the flow direction of a downstream end of the piston accommodating surface, which is the downstream end of the piston accommodating surface. The safety valve according to claim 3.

5. When the piston valve moves downstream in the flow direction, at least a portion of the circumferential groove moves downstream of a downstream end of the piston accommodating surface, which is the downstream end of the piston accommodating surface. The safety valve according to claim 3.

6. The housing further includes a tapered surface that is connected to a downstream end of the accommodating surface and that increases in diameter toward the downstream side.

6. The safety valve of claim 5.

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