Hydraulic PWM control valve

Abstract

To provide a rotary spool type hydraulic PWM control valve that enables PWM control with a simple configuration.SOLUTION: A hydraulic PWM control valve comprises a cylindrical sleeve 100 fixedly housed inside a valve body, a rotary spool 200 that is housed inside the sleeve 100 and rotatable at a predetermined rotational speed, and a control spool 300 that is housed inside the rotary spool 200 and rotatable within a predetermined range around a central axis O. Within the predetermined range, the control spool can be rotated between (1) a fully closed outlet position in which the entire circumferential formation range of a sleeve outlet port 107 is included in the circumferential formation range of a convex portion 304, and (2) a fully open outlet position in which the circumferential formation range of the sleeve outlet port 107 and the circumferential formation range of a communicating recess 303 overlap to the greatest extent.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a hydraulic PWM (Pulse Width Modulation) control valve. [Background technology]

[0002] Hydraulic flow control techniques involve controlling the average flow rate per unit time by using PWM control of the valve's open / close time rate. When applying PWM control to general hydraulic equipment, it is desirable to operate PWM at as high a speed (high frequency) as possible to attenuate the vibration and noise that accompanies valve opening and closing and to control the fluid volume as a continuous flow. For this hydraulic PWM control, a solenoid valve with a poppet valve drive by an electromagnetic solenoid is generally used as the control valve that performs the ON / OFF switching operation. However, because the moving part of a solenoid valve is driven by electromagnetic force, if the mass of the moving part of the valve increases, the operating frequency of the opening / closing duty ratio cannot be increased, resulting in issues with responsiveness. Furthermore, due to limitations on the electromagnetic solenoid's driving force, it is difficult to achieve PWM control of large flow rates. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Fujikoshi Technical Report Vol.53 No.1 1997 "Electro-hydraulic control using high-speed solenoid valves, proportional valves, and proportional seat valves" by Hirohisa Tanaka Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned Non-Patent Document 1 discloses controlling the opening of a seat valve serving as a main valve by PWM control of a solenoid valve serving as a pilot valve. In the control valve disclosed in Non-Patent Document 1, only the solenoid valve serving as a pilot valve is directly controlled by PWM control, and the flow rate is controlled by controlling the opening of the seat valve serving as the main valve using this pilot valve. As such, hydraulic control valves using solenoid valves capable of PWM control are limited to applications requiring small flow rates, such as pilot valves, due to the constraints of the driving force of the electromagnetic solenoid, and it is difficult to control large flow rates, such as with main valves. Furthermore, Non-Patent Document 1 does not disclose a rotary spool type hydraulic control valve. The inventors conducted extensive research to achieve PWM control of a rotary spool type hydraulic control valve with a simple configuration, and have achieved the hydraulic PWM control valve disclosed herein.

[0005] An object of the present disclosure is to provide a rotary spool type hydraulic PWM control valve that enables PWM control with a simple configuration. [Means for solving the problem]

[0006] The hydraulic PWM control valve according to the present disclosure includes a valve body, a cylindrical sleeve fixedly accommodated within the valve body, a cylindrical rotary spool accommodated within the sleeve, and a columnar control spool accommodated within the rotary spool. The valve body has a body inlet port through which liquid is introduced into the hydraulic PWM control valve and a body outlet port through which the liquid is discharged from the hydraulic PWM control valve. The rotary spool is supported by the sleeve via a first fluid bearing provided on its outer circumferential surface so as to be rotatable about a central axis at a predetermined rotational speed. The control spool is supported by the rotary spool via a second fluid bearing provided on its outer circumferential surface so as to be rotatable within a predetermined range about the central axis. The sleeve is formed with a sleeve inlet port that constantly communicates the body inlet port with the interior of the sleeve, and a sleeve outlet port that constantly communicates the body outlet port with the interior of the sleeve. A first annular chamber constantly communicating with the sleeve inlet port is formed adjacent to the first fluid bearing portion between the sleeve and the rotating spool. A spool inlet port constantly communicating between the first annular chamber and the interior of the rotating spool is formed on the rotating spool. A second annular chamber constantly communicating with the spool inlet port is formed adjacent to the second fluid bearing portion between the rotating spool and the control spool. At an axially corresponding position corresponding to the sleeve outlet port of the sleeve in the direction of the central axis, communicating recesses communicating with the second annular chamber and protrusions in sliding contact with the inner peripheral surface of the rotating spool are alternately formed in the circumferential direction of the control spool. At the axially corresponding position, a spool outlet port capable of communicating between the communicating recess and the sleeve outlet port is formed on the rotating spool. Within the specified range, the control spool is rotatable between (1) a fully closed outlet position in which the entire circumferential formation range of the sleeve outlet port is included in the circumferential formation range of the convex portion, and (2) a fully open outlet position in which the circumferential formation range of the sleeve outlet port and the circumferential formation range of the communicating recess overlap to the greatest extent.

[0007] A plurality of first hydrostatic pockets may be formed at regular intervals in the circumferential direction on the outer peripheral surface of the first hydrodynamic bearing portion. When a boundary between the first hydrodynamic bearing portion and the first annular chamber is defined as a first inner boundary and a boundary of the first hydrodynamic bearing portion opposite the first inner boundary is defined as a first outer boundary, a first inner distance between each of the plurality of first hydrostatic pockets and the first inner boundary may be shorter than a first outer distance between each of the plurality of first hydrostatic pockets and the first outer boundary. The regular interval between the plurality of first hydrostatic pockets on the outer peripheral surface may be longer than the first outer distance.

[0008] A plurality of second hydrostatic pockets may be formed at regular intervals in the circumferential direction on the outer peripheral surface of the second hydrostatic bearing portion. When a boundary between the second hydrostatic bearing portion and the second annular chamber is defined as a second inner boundary and a boundary of the second hydrostatic bearing portion opposite the second inner boundary is defined as a second outer boundary, a second inner distance between each of the plurality of second hydrostatic pockets and the second inner boundary may be shorter than a second outer distance between each of the plurality of second hydrostatic pockets and the second outer boundary. The regular interval between the plurality of second hydrostatic pockets on the outer peripheral surface may be longer than the second outer distance. [Effects of the Invention]

[0009] According to the hydraulic PWM control valve of the present disclosure, a rotary spool valve capable of PWM control can be realized with a simple configuration. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an overall perspective view of a hydraulic PWM control valve according to an embodiment; [Figure 2] FIG. 2 is a perspective view showing a sleeve of the hydraulic PWM control valve together with a rotary spool and a control spool. [Figure 3] FIG. 2 is a perspective view showing the rotary spool. [Figure 4] FIG. 2 is a perspective view showing the control spool. [Figure 5] FIG. 3 is a cross-sectional view for explaining PWM control in the embodiment. [Figure 6]4 is an enlarged cross-sectional view of a first or second fluid bearing portion for explaining the centering action in the hydraulic PWM control valve. FIG. [Figure 7] FIG. 10 is a perspective view showing a control spool in a modified example of the embodiment. [Figure 8] FIG. 10 is a cross-sectional view illustrating PWM control in the modified example. DETAILED DESCRIPTION OF THE INVENTION

[0011] A hydraulic PWM control valve 1 according to an embodiment will be described below with reference to the drawings. As shown in Fig. 1, the hydraulic PWM control valve 1 includes a valve body 2, a cylindrical sleeve 100, a cylindrical rotary spool 200, and a columnar control spool 300. The sleeve 100 is fixedly housed inside the valve body 2. The rotary spool 200 is housed inside the sleeve 100. The control spool 300 is housed inside the rotary spool 200.

[0012] The valve body 2 has a pair of body inlet ports 3 that introduce fluid into the hydraulic PWM control valve 1, and a body outlet port (not shown) that discharges the introduced fluid from the hydraulic PWM control valve 1. One outlet port is formed on the surface of the valve body 2 opposite to the surface on which the body inlet ports 3 are formed. Working fluid is pressure-fed to the body inlet port 3 by an external pump or the like, and high-pressure working fluid is introduced into the hydraulic PWM control valve 1. Note that hereinafter, the working fluid will be simply referred to as "liquid," and this liquid also functions as a lubricating oil.

[0013] Furthermore, a first fluid bearing 201 that rotatably supports the rotating spool 200 is formed between the sleeve 100 and the rotating spool 200. Furthermore, a second fluid bearing 301 (see FIG. 4) that rotatably supports the control spool 300 is formed between the rotating spool 200 and the control spool 300. The first fluid bearing 201 and the second fluid bearing 301 are supplied with liquid introduced into the hydraulic PWM control valve 1 as lubricating oil. However, some of the liquid that serves as lubricating oil is discharged through the first fluid bearing 201 and the second fluid bearing 301. The valve body 2 also has a drain port (not shown) for this discharged liquid.

[0014] As shown in FIG. 1, the sleeve 100, rotary spool 200, and control spool 300 are all housed in a valve body 2, and their movement in the direction of a central axis O (see FIG. 2) is restricted by a pair of end caps 4 of the valve body 2. Hereinafter, the direction of the central axis O will be referred to simply as the axial direction. The sleeve 100 is fixed by the pair of end caps 4 so as not to rotate around the central axis O. The rotary spool 200 is supported by the sleeve 100 via a first fluid bearing 201 provided on its outer circumferential surface so as to be rotatable around the central axis O at a predetermined rotational speed. A rotary motor 5 for rotating the rotary spool 200 is fixed to the valve body 2 via the end caps 4. The rotary motor 5 is a servo motor that drives the rotary spool 200 at a constant speed. The control spool 300 is supported by the rotary spool 200 via a second fluid bearing 301 (see FIG. 3) provided on its outer circumferential surface so as to be rotatable around the central axis O within a predetermined range. In this embodiment, this predetermined range is 60 degrees. A rotary motor 6 for rotating the control spool 300 is fixed to the valve body 2 via the end cap 4. The rotary motor 6 is a servo motor that can rotate the control spool 300 to a predetermined rotation position.

[0015] As shown in FIGS. 1 and 2 , annular inlet chambers 102 communicating with each body inlet port 3 are formed between the valve body 2 and the sleeve 100. Therefore, a pair of annular inlet chambers 102 is formed corresponding to a pair of body inlet ports 3. Each annular inlet chamber 102 is formed by an inner circumferential inlet groove 7 formed on the inner circumferential surface of the valve body 2 and an outer circumferential inlet groove 103 formed on the outer circumferential surface of the sleeve 100. In this embodiment, the first fluid bearing portion 201 and the second fluid bearing portion 301 are located at the same position in the axial direction, and the annular inlet chamber 102 is disposed axially inward of the first fluid bearing portion 201 and the second fluid bearing portion 301. A total of eight sleeve inlet ports 104 are formed at equal intervals in the circumferential direction at the bottom of the outer circumferential inlet groove 103 of the sleeve 100. That is, the sleeve 100 is formed with sleeve inlet ports 104 that constantly communicate between the body inlet ports 3 and the interior of the sleeve 100. Each sleeve inlet port 104 has a circular flow passage cross-section.

[0016] Between the valve body 2 and the sleeve 100, there is also formed an outlet annular chamber 105 that communicates with the body outlet port. The inlet annular chamber 102 and the outlet annular chamber 105 are not in communication. The outlet annular chamber 105 is formed by an outlet inner circumferential groove 8 formed on the inner circumferential surface of the valve body 2 and an outlet outer circumferential groove 106 formed on the outer circumferential surface of the sleeve 100. The outlet annular chamber 105 is located in the center of the pair of inlet annular chambers 102. A total of three sleeve outlet ports 107 are formed at equal intervals in the circumferential direction at the bottom of the outlet outer circumferential groove 106 of the sleeve 100. That is, the sleeve 100 is formed with sleeve outlet ports 107 that constantly communicate between the body outlet port and the interior of the sleeve 100. Each sleeve outlet port 107 has a rectangular flow path cross section.

[0017] As shown in FIGS. 1 and 3 , a first annular chamber 202 communicating with each of the introduction annular chambers 102 is formed between the sleeve 100 and the rotating spool 200. Therefore, a pair of first annular chambers 202 is formed corresponding to each pair of introduction annular chambers 102. The introduction annular chambers 102 and the first annular chambers 202 are constantly in communication with each other via sleeve introduction ports 104. Each first annular chamber 202 is formed by an outer circumferential groove formed on the outer circumferential surface of the rotating spool 200. Alternatively, the first annular chamber 202 may be formed by an outer circumferential groove formed on the outer circumferential surface of the rotating spool 200 and an inner circumferential groove formed on the inner circumferential surface of the sleeve 100, as in the introduction annular chamber 102 described above. The first annular chamber 202 is disposed axially adjacent to and axially inside the first fluid bearing portion 201. A total of eight spool introduction ports 203 are formed at the bottom of the first annular chamber 202 at equal intervals in the circumferential direction. That is, the rotary spool 200 is formed with spool introduction ports 203 that constantly communicate between the first annular chamber 202 and the interior of the rotary spool 200. Each spool introduction port 203 has a circular flow passage cross section.

[0018] A valve land 204 is formed between the pair of first annular chambers 202, and is in sliding contact with the inner peripheral surface of the sleeve 100. One end of the rotary spool 200 is connected to the output shaft 9 of the rotary motor 5, and the rotary spool 200 is rotated at a predetermined rotational speed. At this time, the outer peripheral surface of the valve land 204 is in sliding contact with the inner peripheral surface of the sleeve 100. Three spool outlet ports 205 are formed in the valve land 204 at equal intervals in the circumferential direction. Each spool outlet port 205 has an elliptical flow passage cross section that is elongated in the axial direction. The axial width of the valve land 204 is larger than the axial opening width of the sleeve outlet port 107. The axial opening length of the spool outlet port 205 is approximately equal to the axial opening width of the sleeve outlet port 107. However, the circumferential opening length of the sleeve outlet port 107 is sufficiently larger than the circumferential opening width of the spool outlet port 205.

[0019] The first hydrodynamic bearing portions 201 located at both ends of the rotating spool 200 function as hydrostatic bearings when supplied with high-pressure liquid introduced into the first annular chamber 202 through the body inlet port 3, the inlet annular chamber 102, etc. This high-pressure liquid is supplied to the first hydrodynamic bearing portion 201 through a minute gap between the outer circumferential surface of the first hydrodynamic bearing portion 201 of the rotating spool 200 and the inner circumferential surface of the sleeve 100. First hydrostatic pockets 206 for retaining the supplied high-pressure liquid are formed on the first hydrodynamic bearing portion 201 at regular intervals LD1 in the circumferential direction. Each first hydrostatic pocket 206 is a recess in the outer circumferential surface of the first hydrostatic bearing portion 201, and may have any shape that can retain a certain amount of high-pressure liquid as lubricant. In this embodiment, the first hydrostatic pocket 206 has a bottom surface that is flat and parallel to the central axis O, making it easy to machine. The first hydrostatic pocket 206 not only retains high-pressure liquid as lubricating oil required for the hydrostatic bearing, but also functions to align the rotating spool 200 with respect to the sleeve 100. The aligning function will be described in detail later with reference to FIG.

[0020] As shown in Fig. 4, a second annular chamber 302 communicating with each of the first annular chambers 202 is formed between the rotary spool 200 and the control spool 300. Accordingly, a pair of second annular chambers 302 is formed corresponding to the pair of first annular chambers 202. Although the control spool 300 has been described as having a cylindrical shape, it may have an internal space, and the "cylindrical shape" of the control spool 300 referred to here also includes a cylindrical shape. One end of the control spool 300 is connected to the output shaft 10 of the rotary motor 6, and the control spool 300 is rotated within the predetermined range described above, i.e., within a range of 60 degrees around the central axis O in this embodiment.

[0021] The first annular chamber 202 and the second annular chamber 302 are constantly in communication with each other via the spool inlet port 203. That is, the control spool 300 is formed with a second annular chamber 302 that is constantly in communication with the spool inlet port 203. Each second annular chamber 302 is formed by an outer circumferential groove formed on the outer circumferential surface of the control spool 300. Note that, like the inlet annular chamber 102 described above, the second annular chamber 302 may be formed by an outer circumferential groove formed on the outer circumferential surface of the control spool 300 and an inner circumferential groove formed on the inner circumferential surface of the rotating spool 200. The second annular chamber 302 is disposed adjacent to and axially inside the second fluid bearing portion 301 in the axial direction.

[0022] At an axially corresponding position corresponding to the sleeve outlet port 107 in the axial direction, i.e., exactly at the center of the first fluid bearing portion 201 or the second fluid bearing portion 301 in this embodiment, the control spool 300 has communicating recesses 303 and protruding portions 304 alternately formed in the circumferential direction. Hereinafter, this position will be simply referred to as the axially corresponding position. The number of communicating recesses 303 is three, corresponding to the sleeve outlet port 107 and the spool outlet port 205, and the communicating recesses 303 are arranged at equal intervals in the circumferential direction. Accordingly, the number of protruding portions 304 is also three, and the protruding portions 304 are also arranged at equal intervals in the circumferential direction. Each communicating recess 303 communicates with the second annular chamber 302 in the axial direction. Meanwhile, the outer peripheral surface of the protruding portion 304 is in sliding contact with the inner peripheral surface of the rotating spool 200 as it rotates. It can be said that the spool outlet port 205 and valve land 204 described above are also formed in the rotating spool 200 at these corresponding positions.

[0023] The spool outlet port 205 of the rotating spool 200 described above can communicate between the communicating recess 303 and the sleeve outlet port 107 when in the axially corresponding position described above. Whether the communicating recess 303 and the sleeve outlet port 107 are communicated with each other depends on the rotational position of the control spool 300, i.e., the rotational position of the convex portion 304. Whether the communicating recess 303 and the sleeve outlet port 107 are communicated with each other depends on the rotational position of the control spool 300 within the predetermined range described above, i.e., within a range of 60 degrees. Here, the rotational position of the control spool 300 where the entire circumferential range of the sleeve outlet port 107 is included in the circumferential range of the convex portion 304 is referred to as the outlet fully closed position (see FIG. 5(a)). In this embodiment, when the control spool 300 is in the outlet fully closed position, the circumferential range of the sleeve outlet port 107 and the circumferential range of the convex portion 304 coincide with each other at a central angle of 60 degrees. The rotational position of the control spool 300 at which the circumferential range of the sleeve outlet port 107 and the circumferential range of the communicating recess 303 overlap most extensively is called the outlet fully open position (see FIG. 5(c)). In this embodiment, when the control spool 300 is in the outlet fully open position, the circumferential range of the sleeve outlet port 107 and the circumferential range of the communicating recess 303 coincide with each other at a central angle of 60 degrees.

[0024] The control spool 300 is rotatable between the fully open output position and the fully open output position within a rotation range of 60 degrees. Therefore, the control spool 300 can also be positioned at an intermediate output position (see, for example, FIG. 5(b)) between the fully closed output position and the fully open output position. The opening / closing duty ratio of the hydraulic PWM control valve 1 under PWM control is variably controlled depending on the rotation positions of the control spool 300. The relationship between the rotation position of the control spool 300 and the duty ratio of PWM control will be described in detail later with reference to FIG. 5.

[0025] The second hydrodynamic bearing portions 301 located at both ends of the control spool 300 function as hydrostatic bearings when supplied with high-pressure liquid introduced into the second annular chamber 302 through the body inlet port 3, the inlet annular chamber 102, etc. This high-pressure liquid is supplied to the second hydrodynamic bearing portions 301 through a minute gap between the outer circumferential surface of the second hydrodynamic bearing portion 301 of the control spool 300 and the inner circumferential surface of the rotating spool 200. Similar to the first hydrostatic pockets 206 of the rotating spool 200, second hydrostatic pockets 305 for retaining the supplied high-pressure liquid are formed on the second hydrostatic bearing portion 301 at regular intervals LD2 in the circumferential direction. Each second hydrostatic pocket 305 is a recess in the outer circumferential surface of the second hydrostatic bearing portion 301 and may have any shape capable of retaining a certain amount of high-pressure liquid as lubricant. In this embodiment, the second hydrostatic pockets 305 have a bottom surface that is flat and parallel to the central axis O, making them easy to machine. Like the first hydrostatic pocket 206, the second hydrostatic pocket 305 not only retains high-pressure liquid as lubricating oil required for the hydrostatic bearing, but also functions to align the control spool 300 with the rotating spool 200. This aligning function will also be described in detail later with reference to FIG. 6.

[0026] The relationship between the rotational position of the control spool 300 and the duty ratio of PWM control will be described with reference to FIG. 5. FIGS. 5(a) to 5(c) show cross-sectional views perpendicular to the central axis O. In this embodiment, the sleeve outlet ports 107, the communicating recesses 303, and the protruding portions 304 are each arranged at equal intervals in the circumferential direction by three. The communicating recesses 303 and the protruding portions 304 are alternately formed in the circumferential direction. As shown in these cross-sectional views, in this embodiment, the circumferential formation ranges of the sleeve outlet ports 107 of the sleeve 100 and the communicating recesses 303 and the protruding portions 304 of the control spool 300 all lie within a range that forms a central angle of 60 degrees around the central axis O.

[0027] FIG. 5A is a cross-sectional view of the control spool 300 when it is in the fully closed position. At the fully closed position, the circumferential area of ​​the sleeve outlet port 107 is included in the circumferential area of ​​the protrusion 304, and in this embodiment, the two areas coincide with each other. Therefore, regardless of the rotational position of the rotating spool 200, which rotates at a predetermined rotational speed, the sleeve outlet port 107 of the sleeve 100 and the communicating recess 303 of the control spool 300 are not connected to each other through the spool outlet port 205 of the rotating spool 200. That is, at the fully closed position, the duty ratio of the PWM control is 0%, and the hydraulic PWM control valve 1 is fully closed. At this time, fluid introduced into the hydraulic PWM control valve 1 from the body inlet port 3 is discharged from the drain port without being discharged from the body outlet port.

[0028] FIG. 5(c) is a cross-sectional view of the control spool 300 when it is in the fully open position. In the fully open position, the circumferential area of ​​the sleeve outlet port 107 overlaps with the circumferential area of ​​the communication recess 303 over the widest range, and in this embodiment, the two areas coincide with each other. When the control spool 300 is rotated 60 degrees in the rotational direction of the rotating spool 200 from the fully closed position shown in FIG. 5(a), the control spool 300 is positioned at the fully open position. While the spool outlet port 205 of the rotating spool 200 is positioned between the sleeve outlet port 107 and the communication recess 303, the sleeve outlet port 107 and the communication recess 303 are in communication with each other via the spool outlet port 205. Only while the sleeve outlet port 107 and the communicating recess 303 are in communication with each other through the rotating and moving spool outlet port 205, does the liquid supplied from the body inlet port 3 to the inside of the hydraulic PWM control valve 1 flow to the body outlet port. At the outlet fully open position, the duty ratio of the PWM control takes on the largest value possible for the hydraulic PWM control valve 1, and the hydraulic PWM control valve 1 is in a fully open state.

[0029] In this embodiment, the rotating spool 200 has three spool outlet ports 205 evenly spaced circumferentially. In other words, the spool outlet ports 205 are formed on the valve land 204 at intervals of 120 degrees. Therefore, each sleeve outlet port 107 is opened and closed by the valve land 204 and the spool outlet port 205, with one cycle being 120 degrees. In this embodiment, when the control spool 300 is in the fully open position, it is opened for 60 degrees of the 120 degrees, resulting in a PWM control duty cycle of approximately 50%. The inclined portion in the opening / closing timing diagram shown below the cross-sectional view indicates a state in which the spool outlet port 205 is partially in communication with the sleeve outlet port 107 or the communicating recess 303. Figure 5(c) shows a state in which the spool outlet port 205 is just about to begin communicating the sleeve outlet port 107 and the communicating recess 303.

[0030] FIG. 5(b) is a cross-sectional view of the control spool 300 in the intermediate position described above, which is located exactly midway between the fully closed and fully open positions. When the control spool 300 is rotated 30 degrees in the rotational direction of the rotating spool 200 from the fully closed position shown in FIG. 5(a), the control spool 300 reaches the intermediate position shown in FIG. 5(b). In this case, the sleeve outlet port 107 and the communication recess 303 are connected to each other only for 30 degrees out of 120 degrees by the spool outlet port 205. Therefore, the duty cycle of the PWM control is approximately 25%. FIG. 5(b) also shows the state in which the spool outlet port 205 is just about to connect the sleeve outlet port 107 and the communication recess 303.

[0031] In this manner, in this embodiment, the duty ratio can be continuously controlled between 0 and approximately 50%. For example, when the rotational speed of the rotary spool 200 is 3000 rpm, the rotary spool 200 rotates 50 times per second. Since the rotary spool 200 can open and close every 120 degrees, it can open and close three times per rotation. Therefore, the operating frequency of the PWM control is 150 Hz, which is a sufficiently high operating frequency. Furthermore, the hydraulic PWM control valve 1 uses the annular chamber and ports, and opens and closes the valve using the spool outlet port 205 at the above-mentioned shaft-corresponding position, thereby reducing internal pressure loss.

[0032] Next, the alignment function of the first fluid bearing portion 201 and the second fluid bearing portion 301 will be described with reference to FIG. 6 . The alignment principle is the same for both the first fluid bearing portion 201 and the second fluid bearing portion 301, so the first fluid bearing portion 201 will be used as an example. For the second fluid bearing portion 301, relevant reference numerals are enclosed in parentheses in FIG. 6 , and redundant explanations will be omitted. FIG. 6 is an enlarged cross-sectional view of the first fluid bearing portion 201, taken along a cross section including the central axis O. The central axis O is not shown in FIG. 6 . The right side of FIG. 6 is the first annular chamber 202 into which high-pressure liquid is introduced, and a first hydrostatic pocket 206 is formed on the first fluid bearing portion 201. Here, the boundary between the first fluid bearing portion 201 and the first annular chamber 202 is referred to as a first inner boundary BI1. Similarly, the boundary of the first fluid bearing portion 201 opposite the first inner boundary BI1 is referred to as a first outer boundary BO1. In order to provide a centering function, a first inner distance LI1 between the first inner boundary BI1 of the first hydrostatic pocket 206 and the first outer boundary BO1 is set shorter than a first outer distance LO1 between the first inner boundary BI1 and the first outer boundary BO1.

[0033] As described above, high-pressure liquid as lubricant is supplied from the first annular chamber 202 to the minute gap of the first fluid bearing portion 201, including the first hydrostatic pocket 206. The lubricant supplied to the first fluid bearing portion 201 lubricates the gap between the outer peripheral surface of the first fluid bearing portion 201 and the inner peripheral surface of the sleeve 100. As the lubricant is supplied from the first annular chamber 202, it is gradually discharged from the first fluid bearing portion 201 on the opposite side of the first annular chamber 202, and is further discharged from the hydraulic PWM control valve 1 through the drain port described above. At this time, the lubricant cools the first fluid bearing portion 201 and aligns the rotating spool 200 with respect to the sleeve 100. The position of the first fluid bearing portion 201 with respect to the sleeve 100 is adjusted by the lubricant so that the central axis of the sleeve 100 and the rotational axis of the rotating spool 200 coincide with the central axis O described above.

[0034] The lubricating oil is supplied to the first hydrodynamic bearing 201 from the left side in FIG. 6 and remains in the first hydrostatic pocket 206 to some extent for lubrication and cooling purposes, before being gradually discharged from the first hydrodynamic bearing 201 to the right side. The pressure loss, i.e., flow resistance, is indicated in the figure by E11 to E22 and F1 to F2. E11 to E22 indicate the pressure loss at the gap abrupt change area. E11 is the pressure loss when the lubricating oil flows from the first annular chamber 202 into the minute gap in the first hydrodynamic bearing 201, and E12 is the pressure loss when the lubricating oil flows from the minute gap to the first hydrostatic pocket 206. The pressure losses of E11 and E12 are considered to be equivalent to the pressure loss caused by an orifice. F1 is the pressure loss when the lubricating oil passes through the minute gap. The pressure loss between the first annular chamber 202 and the first hydrostatic pocket 206 can be considered a combination of the three pressure losses, E11, E12, and F1. Similarly, the pressure loss on the outflow side from the first hydrostatic pocket 206 can be considered to be a combination of three pressure losses, E21, E22, and F2, as shown in Fig. 6. However, the axial length LI1 of the minute gap that generates F1 is set shorter than the axial length LO1 of the minute gap that generates F2.

[0035] When the rotating spool 200 is eccentric with respect to the sleeve 100, the micro-gap becomes narrow on the eccentric side, and becomes wide on the reverse eccentric side, which is 180 degrees opposite to the central axis O. Here, each pressure loss at the gap abrupt change portion of E11 to E22 is proportional to the gap variation, that is, the square of the eccentricity. On the other hand, each pressure loss of the micro-gaps of F1 and F2 is proportional to the gap variation, that is, the cube of the eccentricity. Therefore, on the eccentric side where the micro-gap becomes narrow, the pressure loss variation due to the micro-gaps of F1 and F2 dominantly acts. Focusing on the eccentric side where the micro-gap becomes narrow, the increase in the pressure loss of the micro-gaps of F1 and F2 dominantly acts, but in the present embodiment, LI1 < LO1 in FIG. 6. For this reason, the pressure loss when the lubricating oil flows from the first annular chamber 202 to the first static pressure pocket 206 is smaller than the pressure loss when the lubricating oil flows out from the first static pressure pocket 206. As a result, the lubricating oil stays longer inside the first static pressure pocket 206 formed in the middle thereof, and the internal pressure of the first static pressure pocket 206 is increased to act so as to widen the micro-gap.

[0036] At this time, on the reverse eccentric side, the micro-gap is wider than on the eccentric side, and the lubricating oil flows more easily from the inflow side to the outflow side than on the eccentric side. Also, on the reverse eccentric side where the micro-gap widens due to eccentricity, the decrease in the pressure loss at the gap abrupt change portion of E11 to E22 dominantly acts, but there is no difference between the variation due to E11 and E12 on the inflow side and the variation due to E21 and E22 on the outflow side. Therefore, the effect of keeping the lubricating oil in the first static pressure pocket 206 does not occur or is smaller than on the eccentric side. Therefore, by the first fluid bearing portion 201 in which the first static pressure pocket 206 is arranged closer to the first annular chamber 202 on the inflow side, a centering force acts on the eccentric side of the rotating spool 200 toward the reverse eccentric side, and no force that obstructs this acts on the reverse eccentric side. Or, even if it acts, it does not become large enough to obstruct the centering force on the centering side. It can also be said that this centering force always acts to prevent eccentricity rather than acting to return the eccentric rotating spool 200.

[0037] Furthermore, in this embodiment, the constant distance LD1 (see FIG. 3) on the outer peripheral surface of the first hydrostatic pressure pocket 206 is set longer than the first outer distance LO1. If the constant distance LD1 were less than the first outer distance LO1, the lubricating oil in the first hydrostatic pressure pocket 206 on the eccentric side would be more likely to escape circumferentially to the opposite eccentric side. If the lubricating oil in the first hydrostatic pressure pocket 206 on the eccentric side escapes circumferentially, an effective centering force would no longer act on the eccentric side. Therefore, the constant distance LD1 is set longer than the first outer distance LO1 so that the lubricating oil flows axially without escaping circumferentially.

[0038] The axial width L1 of the first fluid bearing portion 201 is preferably long to reduce the amount of fluid leaking to the drain. However, the viscosity of the liquid in the first fluid bearing portion 201 acts as a load torque on the rotary motor 5. The longer the width L1, the greater the load torque. Therefore, the width L1 is determined taking into consideration the operating torque and allowable load torque of the rotary motor 5, as well as the amount of fluid leaking to the drain. Furthermore, the first inner distance LI1 must be sufficiently larger than the minute gap so that the pressure loss characteristics of F1 due to the minute gap are manifested. The centering function has been described above, but as mentioned above, the same applies to the second fluid bearing portion 301. The following correspondence exists between the first fluid bearing portion 201 and the second fluid bearing portion 301: first hydrostatic pockets 206 and their fixed distance LD1 - second hydrostatic pockets 305 and their fixed distance LD2. first inner boundary BI1 and first outer boundary BO1 - second inner boundary BI2 and second outer boundary BO2. First inner distance LI1 and first outer distance LO1 - second inner distance LI2 and second outer distance LO2.

[0039] FIG. 7 shows a rotary spool 200X according to a modification of the embodiment described above. This modification is identical to the embodiment described above in all respects except for the rotary spool 200X. The rotary spool 200X according to this modification has six spool outlet ports 205 formed at equal intervals in the circumferential direction. A diagram equivalent to FIG. 5 is shown in FIG. 8. FIG. 8(a) shows the fully closed position, FIG. 8(b) shows the intermediate position, and FIG. 8(c) shows the fully open position. Because six spool outlet ports 205 are formed, the spool can be opened and closed at a central angle of 60 degrees. In other words, six openings and closings occur per rotation of the rotary spool 200X. Furthermore, as shown in FIG. 8(c), a duty ratio of approximately 100% can be achieved at the fully open position. Thus, according to this modification, the duty ratio can be continuously controlled between 0 and approximately 100%, providing a wider control range than the embodiment described above. Furthermore, when the rotation speed of the rotating spool 200X is 3000 rpm, the operating frequency of the PWM control increases to 300 Hz.

[0040] The hydraulic PWM control valve 1 according to the above embodiment, including the above-described modified examples, includes a valve body 2, a cylindrical sleeve 100, a cylindrical rotary spool 200, and a columnar control spool 300. The valve body 2 has a body inlet port 3 through which liquid is introduced into the hydraulic PWM control valve 1 and a body outlet port (not shown) through which the introduced liquid is discharged from the hydraulic PWM control valve 1. The sleeve 100 is fixedly housed inside the valve body 2. The rotary spool 200 is housed inside the sleeve 100. The rotary spool 200 is supported by the sleeve 100 via a first fluid bearing portion 201 provided on its outer circumferential surface so as to be rotatable around the central axis O at a predetermined rotational speed. The control spool 300 is housed inside the rotary spool 200. The control spool 300 is supported by the rotary spool 200 via a second fluid bearing portion 301 provided on its outer circumferential surface so as to be rotatable around the central axis O within a predetermined range. It can also be considered that the control spool 300 supports the rotating spool 200 from the radially inner side.

[0041] A sleeve inlet port 104, which constantly communicates between the body inlet port 103 and the interior of the sleeve 100, and a sleeve outlet port 107, which constantly communicates between a body outlet port (not shown) and the interior of the sleeve 100, are formed in the sleeve 100. A first annular chamber 202, which constantly communicates with the sleeve inlet port 104, is formed adjacent to the first fluid bearing portion 201 and between the sleeve 100 and the rotary spool 200. A spool inlet port 203, which constantly communicates between the first annular chamber 202 and the interior of the rotary spool 200, is formed in the rotary spool 200. A second annular chamber 302, which constantly communicates with the spool inlet port 203, is formed adjacent to the second fluid bearing portion 301 and between the rotary spool 200 and the control spool 300. At an axially corresponding position in the direction of the central axis O corresponding to the sleeve outlet port 107, a communicating recess 303 communicating with the second annular chamber 302 and a protrusion 304 in sliding contact with the inner peripheral surface of the rotary spool 200 are alternately formed in the circumferential direction of the control spool 300. At the axially corresponding position, a spool outlet port 205 that can communicate between the communicating recess 303 and the sleeve outlet port 107 is formed in the rotary spool 200. The control spool 300 is rotatable within a predetermined range around the central axis O between the above-mentioned outlet fully closed position and the above-mentioned outlet fully open position.

[0042] Therefore, the hydraulic PWM control valve 1 can realize a rotary spool-type control valve capable of PWM control with a simple configuration in which the valve body 2, sleeve 100, rotary spool 200, and control spool 300 are housed in this order. PWM control requires the rotary spool 200 to rotate at a predetermined rotational speed, but the duty ratio is controlled by simply rotating the control spool 300 around the central axis O within a predetermined range, resulting in a simple structure and high operational reliability. Furthermore, since the valve is opened and closed using the spool outlet port 205 at the axially corresponding position using an annular chamber and ports, the liquid flow path configuration is simple and internal pressure loss is reduced. Furthermore, the rotary spool 200, which rotates at a predetermined rotational speed, is supported by the sleeve 100 from the radially outer side via the first fluid bearing 201 and by the control spool 300 from the radially inner side via the second fluid bearing 301, providing stable support for high-speed rotation. Because the rotary spool 200 can be rotated at high speed, the operating frequency of the PWM control can be increased, providing excellent response for the hydraulic PWM control valve 1. This operating frequency can also be controlled simply by changing the rotation speed of the rotary spool 200.

[0043] Furthermore, because the first fluid bearing portion 201 can be supplied with liquid lubricant from the adjacent first annular chamber 202, there is no need to form a supply path for lubricant to the first fluid bearing portion 201 inside a component such as the rotating spool 200, making it possible to realize the simple structure described above. Similarly, the second fluid bearing portion 301 can be supplied with liquid lubricant from the adjacent second annular chamber 302, making it possible to realize the simple structure described above. Furthermore, the first fluid bearing portion 201 and the second fluid bearing portion 301 can also be cooled using this liquid lubricant.

[0044] Furthermore, according to the above embodiment including the above modified example, a plurality of first hydrostatic pockets 206 are formed at regular intervals LD1 in the circumferential direction on the outer peripheral surface of the first hydrodynamic bearing portion 201. Therefore, the first hydrostatic pockets 206 can retain liquid as lubricant in the first hydrodynamic bearing portion 201, and the lubricity of the first hydrodynamic bearing portion 201 can be reliably achieved and maintained. Furthermore, the liquid as lubricant removes heat from the first hydrodynamic bearing portion 201 to cool it, and the first hydrostatic pockets 206 increase the amount of liquid retained in the first hydrodynamic bearing portion 201, thereby improving cooling performance.

[0045] Furthermore, in the above embodiment including the above modification, when the first inner boundary BI1 and the first outer boundary BO1 are defined as described above, the first inner distance LI1 between each first hydrostatic pocket 206 and the first inner boundary BI1 is set shorter than the first outer distance LO1 between each first hydrostatic pocket 206 and the first outer boundary BO1. Therefore, the centering action described with reference to Fig. 6 can be exerted, and the rotary spool 200 can be aligned with respect to the sleeve 100. Rotation of the rotary spool 200 is important in PWM control, and the centering function of the rotary spool 200 with respect to the sleeve 100 improves the reliability of PWM control.

[0046] Furthermore, the constant interval LD1 on the outer peripheral surface of the plurality of first hydrostatic pressure pockets 206 is set longer than the first outer distance LO1. This reliably prevents liquid from escaping in the circumferential direction from the first hydrostatic pressure pockets 206, and more reliably demonstrates the centering function. As a result, the reliability of PWM control can be further improved.

[0047] Furthermore, according to the above embodiment including the above modified example, a plurality of second hydrostatic pockets 305 are formed at regular intervals LD2 in the circumferential direction on the outer peripheral surface of the second hydrostatic bearing portion 301. Therefore, the second hydrostatic pockets 305 can retain liquid as lubricant in the second hydrostatic bearing portion 301, and the lubricity of the second hydrostatic bearing portion 301 can be reliably achieved and maintained. Furthermore, the liquid as lubricant removes heat from the second hydrostatic bearing portion 301 to cool it, and the amount of liquid retained in the second hydrostatic bearing portion 301 by the second hydrostatic pockets 305 increases, thereby improving cooling performance.

[0048] Furthermore, in the above embodiment including the above modification, when the second inner boundary BI2 and the second outer boundary BO2 are defined as described above, the second inner distance LI2 between each second hydrostatic pocket 305 and the second inner boundary BI2 is shorter than the second outer distance LO2 between each second hydrostatic pocket 305 and the second outer boundary BO2. Therefore, the centering action described with reference to FIG. 6 can be exerted, and the control spool 300 can be centered with respect to the rotary spool 200. This can also be said to center the rotary spool 200 with respect to the control spool 300. Rotation of the rotary spool 200 is important in PWM control, and the centering function of the rotary spool 200 with respect to the control spool 300 improves the reliability of PWM control.

[0049] Furthermore, the constant distance LD2 on the outer circumferential surface of the plurality of second hydrostatic pressure pockets 305 is set longer than the second outer distance LO2. This reliably prevents liquid from escaping in the circumferential direction from the second hydrostatic pressure pockets 305, and more reliably demonstrates the centering function. As a result, the reliability of PWM control can be further improved.

[0050] Although the above-described embodiments have been described with variations, modifications or variations of the above-described embodiments can be made based on the above disclosure. All components of the above-described embodiments and all features described in the claims may be individually extracted and combined, as long as they are not mutually inconsistent. For example, in the above-described embodiment, the rotating spool 200 is provided with the first fluid bearing portion 201 and the first annular chamber 202 on both sides of the spool outlet port 205. This arrangement provides a good balance and is preferable for preventing axial movement of the rotating spool 200. This arrangement is also preferable for maintaining the constantly rotating rotating spool 200 in a balanced manner. However, the first fluid bearing portion 201 and the first annular chamber 202 may be provided on only one side of the spool outlet port 205. The same applies to the control spool 300.

[0051] In the above embodiment, three sleeve outlet ports 107 are provided evenly spaced in the circumferential direction. However, one, two, four or more sleeve outlet ports 107 may be provided in the circumferential direction. However, if the number is small, the pressure received from the high-pressure liquid is likely to be uneven, which may increase the likelihood of eccentricity of the rotating spool 200 and the control spool 300. On the other hand, if the number is large, the flow path cross-sectional area may become narrower, which may increase internal pressure loss. [Explanation of symbols]

[0052] 1 Hydraulic PWM control valve 2 Valve body 3 Body Introduction Port 5 rotation motor 6 Rotating Motor 100 sleeves 104 Sleeve introduction port 107 Sleeve outlet port 200,200X rotating spool 201 1st fluid bearing section 202 First annular chamber 203 Spool introduction port 205 Spool outlet port 206 First static pressure pocket 300 Control Spool 301 2nd fluid bearing section 302 Second annular chamber 303 Connecting recess 304 Convex part 305 Second static pressure pocket BI1 First medial boundary BO1 1st outer boundary BI2 2nd inner boundary BO2 2nd outer boundary LD1 (first hydrostatic pocket 206) fixed distance LI1 First inner distance LO1 1st outer distance LD2 (second hydrostatic pocket 305) fixed interval LI2 2nd inner distance LO2 2nd outer distance O Central axis

Claims

1. A hydraulic PWM control valve, a valve body having a body inlet port for introducing a fluid into the hydraulic PWM control valve and a body outlet port for discharging the fluid from the hydraulic PWM control valve; a cylindrical sleeve fixedly housed inside the valve body; a cylindrical rotary spool housed inside the sleeve and supported by the sleeve via a first fluid bearing portion provided on an outer peripheral surface of the rotary spool so as to be rotatable about a central axis at a predetermined rotational speed; a cylindrical control spool that is housed inside the rotary spool and supported by the rotary spool via a second fluid bearing portion provided on the outer circumferential surface of the control spool so as to be rotatable within a predetermined range around the central axis, a sleeve introduction port that constantly communicates the body introduction port with the interior of the sleeve, and a sleeve outlet port that constantly communicates the body outlet port with the interior of the sleeve, are formed in the sleeve; a first annular chamber constantly communicating with the sleeve introduction port, the first annular chamber being formed adjacent to the first fluid bearing portion between the sleeve and the rotary spool; a spool inlet port is formed in the rotating spool to provide constant communication between the first annular chamber and the interior of the rotating spool; a second annular chamber constantly communicating with the spool inlet port, the second annular chamber being formed adjacent to the second fluid bearing portion between the rotary spool and the control spool; a communicating recess communicating with the second annular chamber and a protruding portion in sliding contact with an inner peripheral surface of the rotary spool are alternately formed in a circumferential direction of the control spool at axially corresponding positions in the direction of the central axis corresponding to the sleeve outlet port of the sleeve, a spool outlet port that can communicate between the communication recess and the sleeve outlet port at the shaft corresponding position is formed in the rotary spool; a hydraulic PWM control valve in which the control spool is rotatable within the predetermined range between: (1) a fully closed outlet position in which the entire circumferential formation range of the sleeve outlet port is included in the circumferential formation range of the convex portion; and (2) a fully open outlet position in which the circumferential formation range of the sleeve outlet port and the circumferential formation range of the communicating recess overlap over the widest range.

2. 2. The hydraulic PWM control valve according to claim 1, a hydraulic PWM control valve, wherein a plurality of first hydrostatic pockets are formed at regular intervals in the circumferential direction on the outer peripheral surface of the first fluid bearing portion;

3. 3. The hydraulic PWM control valve according to claim 2, a hydraulic PWM control valve, wherein when a boundary between the first fluid bearing portion and the first annular chamber is defined as a first inner boundary, and a boundary of the first fluid bearing portion opposite the first inner boundary is defined as a first outer boundary, a first inner distance between each of the plurality of first hydrostatic pockets and the first inner boundary is shorter than a first outer distance between each of the plurality of first hydrostatic pockets and the first outer boundary.

4. 4. The hydraulic PWM control valve according to claim 3, The hydraulic PWM control valve, wherein the constant spacing on the outer peripheral surface of the first plurality of hydrostatic pockets is longer than the first outer distance.

5. The hydraulic PWM control valve according to any one of claims 1 to 4, a hydraulic PWM control valve, wherein a plurality of second hydrostatic pockets are formed at regular intervals in the circumferential direction on the outer peripheral surface of the second fluid bearing portion;

6. 6. The hydraulic PWM control valve according to claim 5, a hydraulic PWM control valve, wherein when a boundary between the second fluid bearing portion and the second annular chamber is defined as a second inner boundary and a boundary of the second fluid bearing portion opposite the second inner boundary is defined as a second outer boundary, a second inner distance between each of the plurality of second hydrostatic pockets and the second inner boundary is shorter than a second outer distance between each of the plurality of second hydrostatic pockets and the second outer boundary.

7. 7. The hydraulic PWM control valve according to claim 6, The hydraulic PWM control valve, wherein the constant spacing on the outer peripheral surface of the plurality of second hydrostatic pockets is longer than the second outer distance.

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