Safety valve

Abstract

This safety valve disposed in a common-rail fuel injection device comprises: a piston valve; and a piston-valve accommodating housing that includes a piston-receiving surface. The piston valve includes: a valve outer peripheral surface that fits in slidably against the piston-receiving surface; a plurality of slits each extending in the valve outer peripheral surface along the direction of fuel flow in the housing, the plurality of slits being disposed spaced apart circumferentially around the valve outer peripheral surface and also defining slit flow paths for the fuel to flow between the valve outer peripheral surface and the piston-receiving surface; and a circumferential groove extending circumferentially so as to connect to each of the plurality of slits.

Description

safety valve

[0001] This disclosure relates to a safety valve for reducing the pressure in an accumulator chamber of a common rail fuel injection system. This application claims priority to Japanese Patent Application No. 2024-080343, filed on May 16, 2024, with the Japan Patent Office, the contents of which are incorporated herein by reference.

[0002] Conventionally, safety valves for decompressing 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 within the housing. The housing is formed 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.

[0004] Japanese Patent Application Laid-Open No. 2002-031015

[0005] In the above-described 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 the 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 simultaneously. This can result in increased costs for the safety valve.

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

[0007] A safety valve according to at least one embodiment of the present disclosure is a safety valve arranged in a common rail that accumulates fuel under pressure, comprising: a piston valve; and a housing including a piston accommodating surface that accommodates the piston valve, wherein the piston valve includes: a valve outer peripheral surface that slidably fits onto the piston accommodating surface; a plurality of slits that each extend on the valve outer peripheral surface along the direction of fuel flow in the housing, the slits being spaced apart circumferentially around the valve outer peripheral surface and defining slit flow paths for the fuel to flow between the valve outer peripheral surface and the piston accommodating surface; and a circumferential groove that extends in the circumferential direction so as to connect to each of the plurality of slits.

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

[0009] Fig. 1 is a schematic diagram of a common rail system according to an embodiment; Fig. 2 is a schematic enlarged view of a safety valve according to an embodiment; Fig. 3 is a schematic cross-sectional view of a piston valve as viewed in the direction of the arrows A-A; Fig. 4 is a schematic cross-sectional view of a piston valve as viewed in the direction of the arrows B-B; Fig. 5 is a schematic diagram showing the movement of a piston valve according to an embodiment;

[0010] Several embodiments of the present disclosure will be described below 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 not intended to limit the scope of the present disclosure and are merely illustrative examples. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," or "have" one component are not exclusive expressions that exclude the existence of other components. Note that similar components may be assigned the same reference numerals and descriptions thereof may be omitted.

[0011] 1 is a schematic diagram of a common rail system 1 according to an 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 that forms an accumulator chamber 8 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 8 into the return line 11 when the common rail pressure, which is the pressure in the accumulator 8, exceeds an allowable upper limit. 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 fuel flows is formed inside the large-diameter flow path surface 29, and in this example, the above-mentioned spring 9 is disposed 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 spaced apart 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 shown in 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 spaced apart 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 narrows in diameter toward the valve disc 43, and the slit upstream end 47 is also formed as a 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 passage 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 passage Cg extends circumferentially.

[0020] The operating principle of the safety valve 10 will be described with reference to FIGS. 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 channel Cg is 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 FIG. 5). Each slit channel Cs becomes connected to the large-diameter channel Cb via the groove channel Cg and the tapered channel Ct. The fuel in the slit channel Cs and the channel in the groove channel Cg flow into the large-diameter channel Cb via the tapered channel Ct. The fuel flowing through the large-diameter channel Cb flows into the return line 11 from the outlet 28 (see FIG. 1). 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 FIG. 2). When the valve body 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, with 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 prevents 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 channel Cg of the circumferential groove 48 and into the adjacent slit channel Cs. In this case, fuel flowing through the groove channel Cg merges with fuel flowing through the slit channel Cs toward the center, resulting in pressure loss in the slit channel 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 channel Cg toward the large-diameter channel 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 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 during the process in which 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] <Modifications> 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 does not need to 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 allowable upper limit, 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 described in the above-described embodiments can be understood, for example, as follows.

[0031] 1) A safety valve (10) according to at least one embodiment of the present disclosure is a safety valve arranged in a common rail fuel injection device (common rail 7, high-pressure fuel pump 15) that accumulates fuel pressure, and comprises: a piston valve (4); and a housing (2) including a piston accommodating surface (21) that accommodates the piston valve, wherein the piston valve includes: a valve outer peripheral surface (41) that slidably fits onto the piston accommodating surface; a plurality of slits (42) that each extend on the valve outer peripheral surface along the direction of fuel flow in the housing, the slits being arranged at intervals circumferentially on the valve outer peripheral surface and defining slit flow paths (Cs) through which the fuel flows between the valve outer peripheral surface and the piston accommodating surface; and a circumferential groove (48) that extends in the circumferential direction so as to connect to each of the plurality of slits.

[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, according to the configuration 1) above, the circumferential grooves are connected 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, in the safety valve according to 1) above, the circumferential groove is an annular groove formed over the entire length of the piston valve in the circumferential direction.

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

[0035] 3) In some embodiments, in the safety valve described in 1) or 2) above, the circumferential groove is connected to a slit downstream end (46) that is a downstream end in the flow direction of each of the plurality of 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, with the configuration of 3) above, the circumferential groove is connected to the downstream end of each slit, allowing fuel to 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, in the safety valve described in 3) above, the circumferential groove is located upstream in the flow direction of a downstream end (22) of the piston accommodating surface, which is the downstream end of the piston accommodating surface, when the piston valve is seated on the valve seat surface (26) of the housing.

[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 a slight pressure fluctuation in the accumulator occurs, the inlet is stably opened after the piston valve starts to move downstream.

[0039] 5) In some embodiments, in 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 a 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 passages can more reliably communicate with the large diameter flow passage via the circumferential groove.

[0041] 6) In some embodiments, in 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 accumulator chamber is depressurized, the piston valve moves toward its original position. At this time, if the axis of the piston valve is misaligned with the axis of the housing, 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 accumulator chamber is depressurized.

[0043] 1: Common rail system 2: Housing 3: Valve opening pressure adjusting shim 4: Piston valve 7: Common rail 8: Accumulator chamber 9: Spring 10: Safety valve 11: Return line 12: Fuel tank 15: High-pressure fuel pump 21: Piston accommodation surface 22: Accommodation surface downstream end 23: Inlet 24: Tapered surface 25: Housing flow path surface 26: Valve seat surface 28: Outlet 29: Large diameter flow path surface 41: Valve outer peripheral surface 42: Slit 43: Valve body 44: Sliding portion 44a: Tapered portion 46: Slit downstream end 47: Slit upstream end 48: Circumferential groove 49: Contact portion Cb: Large diameter flow path Cg: Groove flow path Cs: Slit flow path Ct: Tapered flow path

Claims

1. A safety valve to be disposed in a common rail fuel injection device, comprising: a piston valve; and a housing including a piston accommodating surface that accommodates the piston valve, wherein the piston valve includes: a valve outer peripheral surface that slidably fits onto the piston accommodating surface; a plurality of slits that each extend on the valve outer peripheral surface along the direction of fuel flow in the housing, the slits being spaced apart circumferentially around the valve outer peripheral surface and defining slit flow paths for the fuel to flow between the valve outer peripheral surface and the piston accommodating surface; and a circumferential groove that extends in the circumferential direction so as to connect to each of the plurality of slits.

2. A safety valve as set forth in claim 1, wherein the circumferential groove is an annular groove formed over the entire circumferential length of the piston valve.

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

4. A safety valve as set forth in claim 3, wherein the circumferential groove is located upstream in the flow direction of the downstream end of the piston accommodating surface, which is the downstream end of the accommodating surface, when the piston valve is seated on the valve seat surface of the housing.

5. A safety valve as described in claim 3, wherein when the piston valve moves downstream in the flow direction, at least a portion of the circumferential groove moves downstream of the downstream end of the piston accommodating surface, which is the downstream end of the accommodating surface.

6. A safety valve as set forth in claim 5, wherein the housing is connected to the downstream end of the accommodating surface and further includes a tapered surface whose diameter increases toward the downstream side.

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