EGR valve

Abstract

Provided is an EGR valve comprising: a valve seat; a valve body; a valve shaft in which the valve body is provided on one end side and a male screw is provided on the other end side; and a step motor that includes a rotor body provided with a female screw engaged with the male screw and that rotates the rotor body to make the valve shaft stroke in the axial direction together with the valve body. The male screw includes a male screw thread and a male screw groove. The male screw thread is formed with an unequal pitch, and the male screw thread has a trapezoidal cross section in the width direction. The male screw and the female screw are in surface contact with each other at a portion having a short screw pitch, and the male screw and the female screw are in line contact with each other at a portion having a long screw pitch.

Description

EGR valve

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

[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 element). 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 element with respect to the valve seat per unit rotation speed increases stepwise or gradually.

[0003] The above 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 element. 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 element move integrally in a stroke motion, and the valve element moves with respect to the valve seat.

[0004] Japanese Patent Application Laid-Open No. 10-160034

[0005] However, in the needle valve described in Patent Document 1, the male thread is columnar and engages with the mating female thread through a 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 object is to improve the load-bearing capacity of the thread engagement between the male thread and the female thread at the portion with a short thread pitch and improve the resolution of the stroke motion of the valve element with respect to the valve seat in an EGR valve in which the thread pitch of the male thread is configured as an unequal pitch.

[0007] (1) In order to achieve the above objective, one aspect of the present disclosure provides an EGR valve comprising: 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 on which the valve body is provided at one end and which has a male thread at the other end; and a step motor including a rotor with a female thread that engages with the male thread, wherein the rotor is rotated to cause the valve stem to move in an axial direction together with the valve body, the male thread including a male thread and a male thread groove, and the screw pitch of the male thread being configured as an unequal pitch, wherein the cross-section in the width direction of the male thread is trapezoidal, and in the portion with a short screw pitch, the male thread and the female thread are in surface contact, and in the portion with a long screw pitch, the male thread and the female thread are in line contact.

[0008] In this embodiment, in areas with a short screw pitch, the male thread moves a short distance relative to the female thread with many 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 between the male and female threads becomes wider. 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 between the male and female threads becomes narrower.

[0009] The technology described in (2) is intended to be such that, in the embodiment of (1) above, 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] In this embodiment, since the female thread is formed with one turn or less in the circumferential direction, 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.

[0011] According to the technology described in (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 parts 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 parts 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 (2), a wide thread engagement area between the male and female threads can be secured in areas with a short thread pitch.

[0013] A cross-sectional view showing the closed state of an EGR valve according to one embodiment. 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. 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. A cross-sectional view similar to Figure 2, schematically showing the configuration of the male and female screws according to proportionality. 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 proportionality.

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

[0015] [About 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 setting of the cross-sectional shapes 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 body 27 and a cylindrical magnet 28 integrally provided on the outside of the rotor body 27. A first radial bearing 29 is provided between the rotor body 27 and the casing 24 on the outer circumference of the upper end. A second radial bearing 30 is provided between the magnet 28 and the thrust bearing 15 on the inner circumference of the lower end. These radial bearings 29 and 30 support the rotor 23 so that it can rotate inside the stator 22. A female thread 12 is provided at the center of the rotor body 27, which engages with the male thread 11 of the valve stem 6.

[0020] Between the spring receiver 14 of the valve stem 6 and the lower second radial bearing 30, that is, between the spring receiver 14 and the housing 3, a valve body spring 32 is provided to bias the valve body 5 toward the stepper motor 7 together with the valve stem 6 (upward in Figure 1). In addition, a rotor spring 33 is provided between the rotor 23 and the second radial bearing 30 to bias the rotor 23 toward away from the valve seat 4.

[0021] Between the housing 3 and the valve stem 6, a substantially cylindrical lip seal 34 is provided adjacent to the thrust bearing 15 to seal the space between the housing 3 and the valve stem 6.

[0022] [About the configuration of the male and female threads] Figure 2 shows a schematic cross-sectional view of the configuration of the male thread 11 provided on the valve stem 6 and the female thread 12 provided on the rotor body 27. As shown in Figure 2, the male thread 11 includes male threads 11a and male thread grooves 11b. The thread pitches P1, P1 of the male threads 11a are configured as unequal pitches. The male thread 11 has unequal thread pitches P1, P2 formed by changing the width of the male thread grooves 11b. The thread pitches P1, P2 include a short thread pitch P2 and a long thread pitch P1. The male threads 11a are formed in a helical shape, and the cross-section in the width direction is trapezoidal. In the area with the short thread pitch P2, the male thread 11 and the female thread 12 are in surface contact (shown as enclosed by a dashed ellipse C1 in Figure 2). In the area with the long thread pitch P1, the male thread 11 and the female thread 12 are in line contact (shown as point C2 in Figure 2).

[0023] 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 full open can be shortened, and the responsiveness of the fully open state can be improved.

[0026] [Regarding proportionality] Figure 4 shows a schematic cross-sectional view of the configuration of the male thread 11 and female thread 12 in relation to proportionality, similar to that of 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 over 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 portion 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 portion 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 portion 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 the section 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 and 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.

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

[0032] 1 EGR valve 4 Valve seat 5 Valve body 6 Valve stem 7 Stepper motor 11 Male thread 11a Male thread 11b Male thread groove 12 Female thread 12a Female thread 23 Rotor P1 Thread pitch P2 Thread pitch

Claims

1. An EGR valve comprising: 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 shaft provided on one end of the valve body and having a male thread on the other end; and a step motor including a rotor having a female thread that engages with the male thread, which rotates the rotor to cause the valve shaft to move in an axial direction together with the valve body, wherein the male thread includes a male thread and a male thread groove, and the thread pitch of the male thread is configured to be unequal, characterized in that the cross-section in the width direction of the male thread is trapezoidal, and in the portion with a short thread pitch, the male thread and the female thread are in surface contact, and in the portion with a long thread pitch, the male thread and the female thread are in line contact.

2. An EGR valve according to claim 1, wherein the female thread 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.

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