EGR valve

Abstract

In an EGR valve with male threads configured with unequal pitch, the load-bearing capacity of the thread engagement between the male and female threads is improved in the areas with short thread pitches, thereby improving the resolution of the stroke motion of the valve body relative to the valve seat. [Solution] The EGR valve 1 includes a valve seat, a valve body, a valve stem provided on one end of the valve body and having a male thread 11 on the other end, and a rotor body 27 having a female thread 12 that engages with the male thread 11, and a stepper motor that rotates the rotor body 27 to cause the valve stem to move in an axial stroke together with the valve body. The male thread 11 includes male threads 11a and male thread grooves 11b, and the male threads 11a are configured with an unequal pitch. The cross-section of the male threads 11a in the width direction is trapezoidal, and in the part with a short thread pitch P2, the male thread 11 and the female thread 12 are in surface contact, and in the part with a long thread pitch P1, the male thread 11 and the female thread 12 are in line contact.

Description

Technical Field

[0001] The technology disclosed in this specification relates to an EGR valve that regulates the EGR gas flow rate in an EGR passage.

Background Art

[0002] Conventionally, as this type of technology, a "needle valve" described in Patent Document 1 below is known. This valve converts the rotational torque generated by a drive source into linear motion via a lead screw to operate a needle (valve body). In this valve, an unequal thread pitch is provided on the male thread of the lead screw so that the lift amount of the valve body with respect to the valve seat per unit rotation speed increases stepwise or gradually.

[0003] The lead screw includes a rotating member (female thread) and a male thread slidably inserted into the inner circumference of the female thread. The male thread is provided on a columnar portion coaxial with the valve body. A steel ball is fixed to the inner circumferential surface of the female thread in a state where it is half-embedded. A thread groove having an arcuate cross-section in the width direction is formed on the outer circumference of the male thread. A part of the steel ball engages slidably with the thread groove. When the female thread rotates, the steel ball moves along the thread groove, and the male thread, valve shaft, and valve body move integrally in a stroke motion, and the valve body moves with respect to the valve seat.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the needle valve described in Patent Document 1, the male thread has a columnar shape and engages with the mating female thread through point support via a steel ball. Therefore, the thread engagement margin between the male thread and the female thread is narrow, and the load-bearing capacity of the thread engagement is insufficient.

[0006] This disclosed technology has been made in view of the above circumstances, and its purpose is to improve the load-bearing capacity of the thread engagement between the male and female threads in the portion with the short thread pitch, and to improve the resolution of the stroke motion of the valve body relative to the valve seat, in an EGR valve in which the thread pitch of the male thread is configured to be unequal. [Means for solving the problem]

[0007] To achieve the above objective, the technology described in claim 1 comprises a valve seat, a valve body seatable on the valve seat and constituting a metering section for EGR gas between itself and the valve seat, a valve stem with a male thread on one end of the valve body and a male thread on the other end, and a step motor including a rotor with a female thread that engages with the male thread, which rotates the rotor to cause the valve stem to move in an axial stroke together with the valve body, wherein the male thread includes male threads and male thread grooves, and the screw pitch of the male threads is configured to be unequal pitch, the male threads having a trapezoidal cross-section in the width direction, the male threads and female threads making surface contact in the short screw pitch area, and the male threads and female threads making line contact in the long screw pitch area.

[0008] According to the above technology configuration, in areas with a short screw pitch, the male thread moves a short distance relative to the female thread with more rotations as the rotor rotates. Also, since the cross-section in the width direction of the male thread is trapezoidal and the male and female threads make surface contact, the thread engagement depth between the male and female threads is widened. On the other hand, in areas with a long screw pitch, the male thread moves a long distance relative to the female thread with fewer rotations as the rotor rotates. Also, since the male and female threads make line contact, the thread engagement depth between the male and female threads is narrowed.

[0009] To achieve the above objective, the technology described in claim 2 is characterized in that, in the technology described in claim 1, the female screw includes female threads, the female threads are formed with one turn or less in the circumferential direction, and the cross-section in the width direction is trapezoidal.

[0010] According to the configuration of the above technology, in addition to the effects of the technology described in claim 1, the female thread is formed with one turn or less in the circumferential direction, so that the thread engagement is maintained without strong interference between the male and female threads regardless of changes in the thread pitch. Furthermore, since the cross-section of the female thread in the width direction is trapezoidal, the contact area between the male and female threads increases in areas with short thread pitches, and the amount of thread engagement between the male and female threads increases. [Effects of the Invention]

[0011] According to the technology described in claim 1, in an EGR valve in which the thread pitch of the male thread is configured to be unequal, the load-bearing capacity of the thread engagement between the male and female threads can be improved in the portion with a short thread pitch, and the resolution of the stroke movement of the valve body relative to the valve seat can be improved. Furthermore, in the portion with a long thread pitch, the male thread can move smoothly relative to the female thread, and the responsiveness of the stroke movement of the valve body relative to the valve seat can be improved.

[0012] According to the technology described in claim 2, in addition to the effects of the technology described in claim 1, a wide thread engagement area between the male and female threads can be secured in areas with a short thread pitch. [Brief explanation of the drawing]

[0013] [Figure 1] A cross-sectional view showing the closed state of an EGR valve according to one embodiment. [Figure 2] A cross-sectional view schematically showing the configuration of a male screw provided on the valve stem and a female screw provided on the rotor body, according to one embodiment. [Figure 3] A graph showing the relationship between the stroke of the valve stem (valve body) and the number of steps of a stepper motor, according to one embodiment. [Figure 4] A cross-sectional view similar to Figure 2, illustrating the proportional relationship between male and female threads. [Figure 5] This graph shows the relationship between the stroke of the valve stem (valve body) and the number of steps in a stepper motor, illustrating the proportional relationship. [Modes for carrying out the invention]

[0014] Below, one embodiment of the EGR valve will be described with reference to the drawings.

[0015] [Regarding the configuration of the EGR valve] Figure 1 shows a cross-sectional view of the closed state of the EGR valve 1 of this embodiment. As shown in Figure 1, the EGR valve 1 comprises a housing 3 having a flow path 2, a valve seat 4 provided in the flow path 2, a valve body 5 provided so as to be seatable on the valve seat 4 and constituting a metering section for EGR gas between itself and the valve seat 4, a valve stem 6 provided on one end of the valve body 5 and having a male screw 11 on the other end, and a stepper motor 7 that causes the valve stem 6 to reciprocate (stroke) in its axial direction.

[0016] The stepper motor 7 includes a rotor 23 with a female thread 12 that engages with a male thread 11. The stepper motor 7 rotates the rotor 23 to cause the valve stem 6 to move in an axial stroke. This EGR valve 1 has a poppet valve structure in which the valve body 5 moves perpendicular to the seat surface of the corresponding valve seat 4. In Figure 1, the male thread 11 and female thread 12 are shown in a simplified manner. The configuration of the male thread 11 and female thread 12 will be described later.

[0017] The valve stem 6 is positioned to penetrate the housing 3 vertically. A spring retainer 14 is provided on the lower side of the valve stem 6 adjacent to the male screw 11. The housing 3 has an inlet 2a and an outlet 2b at both ends of the flow path 2. The housing 3 is provided with a thrust bearing 15 that supports the valve stem 6 so that it can move axially. The rotation of the valve stem 6 is restricted and the stroke motion is guided by the cross-sectional shape of the valve stem 6 and the thrust bearing 15.

[0018] The stepper motor 7 includes a stator 22 having two-phase coils 21 and a rotor 23 provided inside the stator 22. These components 21-23 are molded and covered by a resin casing 24.

[0019] The rotor 23 includes a rotor main body 27 and a cylindrical magnet 28 integrally provided outside the rotor main body 27. A first radial bearing 29 is provided between the outer peripheral edge of the upper end portion of the rotor main body 27 and the casing 24. A second radial bearing 30 is provided between the inner peripheral edge of the lower end portion of the magnet 28 and the thrust bearing 15. By these radial bearings 29 and 30, the rotor 23 is rotatably supported inside the stator 22. At the center of the rotor main body 27, an internal thread 12 that engages with the external thread 11 of the valve shaft 6 is provided.

[0020] Between the spring receiver 14 of the valve shaft 6 and the lower second radial bearing 30, that is, between the spring receiver 14 and the housing 3, a valve body spring 32 for biasing the valve body 5 together with the valve shaft 6 in the direction approaching the step motor 7 (upward in FIG. 1) is provided. Also, between the rotor 23 and the second radial bearing 30, a rotor spring 33 for biasing the rotor 23 in the direction away from the valve seat 4 is provided.

[0021] Between the housing 3 and the valve shaft 6, a lip seal 34 having a substantially cylindrical shape for sealing between the housing 3 and the valve shaft 6 is provided adjacent to the thrust bearing 15.

[0022] [Configuration of external and internal threads] FIG. 2 schematically shows in a cross-sectional view the configuration of the external thread 11 provided on the valve shaft 6 and the internal thread 1​​​As shown in Figure 2, the female screw 12 includes female threads 12a. The female threads 12a are formed in a spiral shape with one or fewer turns in the circumferential direction, and the cross-section in the width direction is trapezoidal.

[0024] Figure 3 shows a graph illustrating the relationship between the stroke of the valve stem 6 (valve body 5) and the number of steps of the stepper motor 7 in this embodiment. As shown in Figure 3, the stroke is such that, between the number of steps "0 to S1", i.e., in the section with a long screw pitch P1, the male screw 11 moves a long distance with fewer rotations (number of steps) relative to the female screw 12 as the rotor 23 rotates, and in the section with a short screw pitch P2, the male screw 11 moves a short distance with more rotations (number of steps) relative to the female screw 12 as the rotor 23 rotates.

[0025] Here, the portion with a short screw pitch P2 can correspond to the region where the valve body 5 is close to the valve seat 4 (a region close to fully closed), and the portion with a long screw pitch P1 can correspond to the region where the valve body 5 is far from the valve seat 4 (a region close to fully open). In this case, when the valve body 5 approaches the valve seat 4, the resolution of the EGR gas flow rate can be improved. Also, when the valve body 5 moves away from the valve seat 4 and becomes fully open, the time required to open the valve to the point of full opening can be shortened, and the responsiveness of the fully open state can be improved.

[0026] [Regarding proportionality] Figure 4 shows a schematic diagram of the configuration of the male thread 11 and female thread 12 in relation to proportionality, using a cross-sectional view similar to that in Figure 2. As shown in Figure 4, in this proportionality, the configuration of the male thread 11 and female thread 12 is the same as in this embodiment, except for the setting of the thread pitch P3 of the male thread 11a. That is, the thread pitch P3 of the male thread 11a in this proportionality is set uniformly throughout the entire axial range of the male thread 11.

[0027] Figure 5 shows a graph illustrating the relationship between the stroke of the valve stem (valve body) and the number of steps in a stepper motor, in relation to the proportional relationship. As shown in Figure 5, in this proportional relationship, the stroke increases steadily as the number of steps increases.

[0028] [Regarding the operation and effects of the EGR valve] According to the configuration of this embodiment described above, in the section with a short screw pitch P2, the male screw 11 moves a short distance with many rotations relative to the female screw 12 as the rotor 23 rotates. Also, since the cross-section in the width direction of the male screw thread 11a is trapezoidal, and the male screw 11 and the female screw 12 are in surface contact, the thread engagement between the male screw 11 and the female screw 12 becomes wider. On the other hand, in the section with a long screw pitch P1, the male screw 11 moves a long distance with fewer rotations relative to the female screw 12 as the rotor 23 rotates. Also, since the male screw 11 and the female screw 12 are in line contact, the thread engagement between the male screw 11 and the female screw 12 becomes narrower. For this reason, in the EGR valve 1 in which the screw pitches P1 and P2 of the male screw thread 11a are configured to be unequal pitches, the load-bearing capacity of the thread engagement between the male screw 11 and the female screw 12 can be improved in the section with a short screw pitch P2, and the resolution of the stroke movement of the valve body 5 relative to the valve seat 4 can be improved. Furthermore, in areas with a long screw pitch P1, the male screw 11 can move smoothly relative to the female screw 12, improving the responsiveness of the stroke movement of the valve body 5 relative to the valve seat 4.

[0029] According to the configuration of this embodiment, since the female thread 12a is formed with one turn or less in the circumferential direction, the male thread 11 and the female thread 12 maintain thread engagement without strong interference regardless of changes in the thread pitch P1, P2 of the male thread 11a. Furthermore, since the cross-section of the female thread 12a in the width direction is trapezoidal, the contact area between the male thread 11 and the female thread 12 increases in areas with a short thread pitch P2, and the amount of thread engagement between the male thread 11 and the female thread 12 increases. For this reason, a wide amount of thread engagement between the male thread 11 and the female thread 12 can be secured in areas with a short thread pitch P2.

[0030] 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. [Industrial applicability]

[0031] This disclosed technology can be applied to EGR (Exhaust Gas Recirculation) devices. [Explanation of Symbols]

[0032] 1 EGR valve 4 valve seats 5 valve bodies, 6 Valve stem 7-step motor 11 Male screw 11a Male thread 11b Male thread groove 12 female threads 12a Female thread 23 Rotors P1 thread pitch P2 thread pitch

Claims

1. The valve seat, A valve body is provided so as to be seatable on the valve seat and, between itself and the valve seat, constitutes a metering unit for EGR gas. The valve stem has a valve body provided at one end and a male screw at the other end, A step motor includes a rotor having a female thread that engages with the male thread, and rotates the rotor to cause the valve shaft to move in an axial direction together with the valve body. An EGR valve comprising a male screw including a male thread and a male thread groove, wherein the thread pitch of the male thread is configured to be unequal pitch, The male thread has a trapezoidal cross-section in the width direction, and in areas with a short thread pitch, the male thread and the female thread make surface contact, while in areas with a long thread pitch, the male thread and the female thread make line contact. An EGR valve characterized by the following features.

2. In the EGR valve according to claim 1, The female thread includes female threads, and the female threads are formed with one turn or less in the circumferential direction, and the cross-section in the width direction is trapezoidal. An EGR valve characterized by the following features.

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