EGR valve

Abstract

An EGR valve 1 comprises: a housing 2 that has a flow passage 3; a valve seat 4 that is provided to the flow passage 3; a valve element 5 that can be seated on the valve seat 4; a valve stem 6 that causes the valve element 5 to move to the valve seat 4; an actuator 8 that causes the valve stem 6 to perform a stroke motion together with the valve element 5; bearings 10, 11 that support the valve stem 6 so as to be capable of stroke motion; and a deposit-preventing plug 16 for preventing deposits between the housing 2 and the valve stem 6. A diaphragm 18 is provided between the housing 2 and the valve stem 6, and occludes the space between the bearing 11 and the deposit-preventing plug 16. A central portion 18a of the diaphragm 18 is fastened to the valve stem 6, and an outer peripheral portion 18b is interposed between the housing 2 and the deposit-preventing plug 16.

Description

EGR valve

[0001] The technology disclosed in the present specification relates to an EGR valve that is provided in an EGR passage of an exhaust gas recirculation device (EGR device) and driven by an actuator.

[0002] Conventionally, as this type of technology, for example, the "EGR valve" described in the following Patent Document 1 is known. This EGR valve includes a housing having a flow passage. A valve seat is provided in the flow passage, and a valve body is provided to be seatable on the valve seat. Further, the valve body is integrally provided on a valve shaft to move the valve body relative to the valve seat. The housing is provided with a bearing that supports the valve shaft so as to enable stroke movement. A seal member is provided adjacent to the bearing between the housing and the valve shaft. Further, a deposit guard member is provided adjacent to the seal member between the housing and the valve shaft. A distance from one end of the bearing adjacent to the seal member to the tip of the seal member is defined as a first distance. A distance from the other end of the deposit guard member facing the flow passage to the tip of the seal member is defined as a second distance. The first distance and the second distance are set to be larger than the maximum stroke in the stroke movement of the valve shaft. With the above configuration, sealing failure caused by entrainment of foreign matter and deposits in the seal member provided on the valve shaft is prevented.

[0003] Japanese Patent Laid-Open No. 2013-7266

[0004] However, in the EGR valve described in Patent Document 1, when the valve is fully closed, the valve body may receive pressure in the EGR passage and a load may be applied in the valve opening direction. When this pressure load becomes larger than the biasing force of the spring that biases the valve body in the valve closing direction, the valve body lifts off the valve seat, a gap is formed between the valve body and the valve seat, and there is a risk that sealing leakage of EGR gas may occur.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an EGR valve capable of suppressing lifting of a valve body from a valve seat and preventing sealing leakage of EGR gas even when a pressure load in a valve opening direction is applied to the valve body in a fully closed state where the valve body is seated on the valve seat.

[0006] One embodiment of the present disclosure made to solve the above problems is an EGR valve comprising a housing having a flow path for EGR gas, a valve seat provided in the flow path, a valve body provided so as to be seatable on the valve seat, a valve stem provided integrally with the valve body to move the valve body relative to the valve seat, a driving means for axially stroking the valve stem together with the valve body, a bearing provided between the housing and the valve stem to support the valve stem so as to be able to stroke, and a deposit guard member provided between the housing and the valve stem to guard the space between the housing and the valve stem from deposits, wherein the flow path is divided into an upstream flow path closer to the deposit guard member and a downstream flow path further away from the deposit guard member, with the valve body positioned so as to be seatable on the valve seat in the upstream flow path, wherein a diaphragm is provided between the housing and the valve stem to shield the space between the bearing and the deposit guard member, the diaphragm includes a central part and an outer part, the central part is fastened to the valve stem and the outer part is sandwiched between the housing and the deposit guard member.

[0007] In this embodiment, when fully closed, the valve body seats on the valve seat in the upstream passage. In this state, if the pressure in the downstream passage becomes higher than the pressure in the upstream passage, a load acts on the valve body that lifts it away from the valve seat. At this time, the pressure on the downstream passage acts on the diaphragm through the gap between the deposit guard member and the valve stem, pushing the diaphragm away from the deposit guard member. This pressing force pushes the valve stem in the same direction, pushing the valve body in the direction that it seats on the valve seat. In other words, the load that lifts the valve body away from the valve seat is offset by the pressure on the diaphragm.

[0008] According to the EGR valve of this disclosure, even when the valve body is seated on the valve seat in the fully closed position, if a pressure load in the opening direction is applied to the valve body, the lifting of the valve body from the valve seat can be suppressed, thereby preventing leakage of the sealed EGR gas.

[0009] A cross-sectional view showing the EGR valve in the fully closed position according to one embodiment. An enlarged cross-sectional view showing the main part enclosed by the dashed rectangle in Figure 1, according to one embodiment.

[0010] Below, one embodiment of the GR valve will be described in detail with reference to the drawings.

[0011] [About the configuration of the EGR valve] Figure 1 shows a cross-sectional view of the EGR valve 1 when it is fully closed. Figure 2 shows an enlarged cross-sectional view of the main part enclosed by the dashed rectangle S1 in Figure 1. The EGR valve 1 is installed in the EGR passage that recirculates a portion of the exhaust gas (EGR gas) discharged from the engine to the intake passage, and is used to adjust the EGR gas flow rate.

[0012] The EGR valve 1 in this embodiment comprises a housing 2, an EGR gas passage 3 formed in the housing 2, a valve seat 4 provided in the passage 3, a valve body 5 provided so as to be seatable on the valve seat 4, a valve shaft 6 provided integrally with the valve body 5 to move the valve body 5 relative to the valve seat 4, and an actuator 8 that rotates an output shaft 7 to cause the valve shaft 6 to reciprocate (stroke) in the axial direction together with the valve body 5. The actuator 8 corresponds to an example of the "driving means" in this disclosed technology.

[0013] The flow path 3 formed in the housing 2 has an inlet 3a for introducing EGR gas and an outlet 3b for discharging EGR gas at both ends. The valve seat 4 is provided in the middle of the flow path 3 and has a valve hole 4a that communicates with the flow path 3.

[0014] The valve stem 6 is provided between the actuator 8 and the valve body 5, and in Figure 1, it is positioned to penetrate the housing 2 vertically. The valve body 5 is fixed to the lower end of the valve stem 6. The valve body 5 has a substantially conical shape, and its outer circumferential surface is in contact with or separated from the valve seat 4. A spring receiver 9 is integrally provided at the upper end of the valve stem 6. Between the housing 2 and the valve stem 6, a first thrust bearing 10 and a second thrust bearing 11 are provided, arranged in series to support the valve stem 6 so that it can move through a stroke. Each thrust bearing 10, 11 has a substantially cylindrical shape and is fitted and fixed into an assembly hole 2a formed in the center of the housing 2.

[0015] The actuator 8 includes a stator 22 containing a coil 21, a magnet rotor 23 provided inside the stator 22, and an output shaft 7 provided at the center of the magnet rotor 23. These components 7, 21-23, etc., are molded and covered by a resin casing 24. A connector 25 protruding laterally is integrally formed on the casing 24. Terminals 26 extending from the coil 21 are provided on the connector 25.

[0016] The output shaft 7 has a male thread 7a on its outer circumference. The lower end of the output shaft 7 is connected to a spring receiver 9 provided on the upper end of the valve shaft 6. The magnet rotor 23 includes a rotor body 27 and a cylindrical plastic magnet 28 integrally provided on the outer circumference of the rotor body 27. A first radial bearing 29 is provided between the upper end of the rotor body 27 and the casing 24. A second radial bearing 30 is provided between the lower end of the plastic magnet 28 and the first thrust bearing 10. These upper and lower radial bearings 29 and 30 support the magnet rotor 23 so that it can rotate inside the stator 22. A female thread 27a is formed in the center of the rotor body 27, which screws into the male thread 7a of the output shaft 7. A first compression spring 31 is provided between the magnet rotor 23 and the lower second radial bearing 30. A second compression spring 32 is provided between the spring receiver 9 at the upper end of the valve stem 6 and the second radial bearing 30, biasing the valve stem 6 toward the magnet rotor 23.

[0017] As shown in Figure 1, in the fully closed state with the valve body 5 seated on the valve seat 4, the magnetic rotor 23 rotates in one direction. Due to the screw-to-screw relationship between the male thread 7a of the output shaft 7 and the female thread 27a of the rotor body 27, the output shaft 7 rotates in one direction and strokes downward in the thrust direction (Figure 1) against the biasing force of the second compression spring 32. This stroke motion of the output shaft 7 causes the valve body 5 to stroke downward in Figure 1 together with the valve stem 6, causing the valve body 5 to separate from the valve seat 4 and open the valve.

[0018] On the other hand, in the fully open state where the valve body 5 is maximally separated from the valve seat 4, the magnetic rotor 23 rotates in the opposite direction. Due to the screw-to-screw relationship between the male thread 7a of the output shaft 7 and the female thread 27a of the rotor body 27, and the biasing force of the second compression spring 32, the output shaft 7 rotates in the opposite direction while stroking upward in the thrust direction shown in Figure 1. This stroking motion of the output shaft 7 causes the valve body 5 to stroke upward in Figure 1 together with the valve stem 6, and the valve body 5 seats on the valve seat 4, closing the valve.

[0019] As shown in Figures 1 and 2, a deposit guard plug 16 is provided between the housing 2 and the valve stem 6, spaced apart from the second thrust bearing 11, to protect the space between the housing 2 and the valve stem 6 from deposits. This deposit guard plug 16 is substantially cylindrical and has one end 16a and the other end 16b in the axial direction. The side of the deposit guard plug 16 facing the flow path 3, the other end 16b, is formed to be convex with respect to the flow path 3, and the valve stem 6 passes through its center. The deposit guard plug 16 corresponds to an example of a "deposit guard member" in this disclosed technology.

[0020] In this embodiment, the flow path 3 is divided by the valve seat 4 into a downstream flow path 3B closer to the deposit guard plug 16 and an upstream flow path 3A further from the deposit guard plug 16. The valve body 5 is positioned so as to be able to seat on the valve seat 4 in the upstream flow path 3A.

[0021] As shown in Figures 1 and 2, a diaphragm 18 is provided between the housing 2 and the valve stem 6 to shield the assembly hole 2a between the second thrust bearing 11 and the deposit guard plug 16. This diaphragm 18 includes a central part 18a and an outer peripheral part 18b. The central part 18a is fastened to the valve stem 6, and the outer peripheral part 18b is sandwiched between the housing 2 and one end 16a of the deposit guard plug 16.

[0022] [Operation and Effects of the EGR Valve] According to the EGR valve 1 of this embodiment described above, when fully closed, the valve body 5 seats on the valve seat 4 in the upstream passage 3A. In this fully closed state, when the pressure acting on the downstream passage 3B (for example, exhaust pressure) becomes higher than the pressure acting on the upstream passage 3A (intake pressure), a load acts on the valve body 5 that lifts it away from the valve seat 4. At this time, the pressure acting on the downstream passage 3B acts on the diaphragm 18 through the gap between the deposit guard plug 16 and the valve stem 6, pushing the diaphragm 18 away from the deposit guard plug 16. This pressing force pushes the valve stem 6 in the same direction, pushing the valve body 5 in the direction that it seats on the valve seat 4. In other words, the load that lifts the valve body 5 away from the valve seat 4 is offset by the pressure acting on the diaphragm 18. Therefore, even when the valve body 5 is seated on the valve seat 4 in the fully closed position, if a pressure load in the opening direction is applied to the valve body 5, the lifting of the valve body 5 from the valve seat 4 can be suppressed, and leakage of EGR gas can be prevented.

[0023] In this embodiment, the assembly hole 2a between the second thrust bearing 11 and the deposit guard plug 16 is shielded by the diaphragm 18. Therefore, even if foreign matter or condensed water enters the inside of the deposit guard plug 16 from the downstream flow path 3B through the gap between the deposit guard plug 16 and the valve stem 6, the diaphragm 18 prevents further intrusion of condensed water, etc. For this reason, there is no need to provide a sealing member between the deposit guard plug 16 and the second thrust bearing 11. In other words, conventionally, a sealing member such as a lip seal was provided at this position, but this sealing member can be omitted.

[0024] Furthermore, this disclosed technology is not limited to the embodiments described above, and it can be implemented by appropriately modifying a part of the configuration without departing from the spirit of the disclosed technology.

[0025] This disclosed technology can be used, for example, in EGR valves used in EGR systems for automobile engines.

[0026] 1 EGR valve 2 Housing 3 Flow path 3A Upstream flow path 3B Downstream flow path 4 Valve seat 5 Valve body 6 Valve stem 8 Actuator (driving means) 11 Second thrust bearing 16 Depot guard plug (depot guard member) 18 Diaphragm 18a Center 18b Outer circumference

Claims

1. An EGR valve comprising: a housing having a passage for EGR gas; a valve seat provided in the passage; a valve body provided so as to be seatable on the valve seat; a valve shaft provided integrally with the valve body for moving the valve body relative to the valve seat; a driving means for axially stroking the valve shaft together with the valve body; a bearing provided between the housing and the valve shaft for supporting the valve shaft so as to be able to stroke; and a deposit guard member provided between the housing and the valve shaft for guarding the space between the housing and the valve shaft from deposits, wherein the passage is divided into a downstream passage closer to the deposit guard member and an upstream passage further away from the deposit guard member, with the valve seat as the boundary, and the valve body is arranged so as to be seatable on the valve seat in the upstream passage, wherein a diaphragm is provided between the housing and the valve shaft to shield the space between the bearing and the deposit guard member. The EGR valve is characterized in that the diaphragm includes a central part and an outer part, the central part is fastened to the valve stem, and the outer part is sandwiched between the housing and the deposit guard member.

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