Cross-Reference to Related Application(s)

This application is being filed on July 20, 2022, as a PCT International Patent application and claims the benefit of and priority to U.S. Provisional patent application Serial No. 63/223,765, filed July 20, 2021, the entire disclosure of which is incorporated by reference herein in its entirety.

Background

In axial piston pumps, the pumping chambers are required to connect and disconnect from the suction and discharge ports of the pump at the appropriate times to provide flow of the fluid. There is typically a relatively large difference in pressure between these ports. Metering grooves, orifices, or slots are often used to provide a small amount of flow to the oncoming piston to aid in the transition of pressure. During this transition of pressure, there can be very large differences in pressure which result in very high fluid velocities. When the fluid velocities are high, the static pressure drops and the dynamic pressure increases per Bernoulli's equation. Typical hydraulic fluids will have dissolved gasses that can come out of solution, or can be vaporized at sufficiently low pressures. When the gas comes out of solution, or the fluid is vaporized, the voids can be collapsed when subject to high pressures, leading to erosion damage of the valve plate, barrel, and pistons.

Summary

Aspects of the present disclosure relate to a metering feature used in the valve plate of an axial piston device such as an axial piston pump or an axial piston motor. Certain aspects are adapted for reducing the fluid velocity through a port in the valve plate as a piston chamber of a piston chamber block of a rotating group transitions from a first pressure to a second pressure (e.g., from inlet pressure to outlet pressure or from outlet pressure to inlet pressure) as the piston chamber block rotates relative to the valve plate. In one example, separate flow restrictions in series are provided to reduce the fluid velocity flowing through the valve port and to keep the static pressure higher in the restrictions when there are large differences in pressure between the pressure in the valve port and the pressure in the piston chamber as the piston chamber transitions from inlet pressure to outlet pressure or from outlet pressure to inlet pressure during rotation of the rotating group of the axial piston device. The fluid velocity can be reduced by dropping the pressure in multiple stages using the restrictions in series. The differential pressure across each restriction is lower so the velocity through each restriction is lower. Reducing the fluid velocity helps to avoid the creation of voids and the resulting cavitation damage to the pump.

Another aspect of the present disclosure relates to an axial piston device having a high-pressure side and a low-pressure side. The axial piston device includes a pressure transition passage that transitions the pressure in piston chambers of the axial piston device as the piston chambers transition from one of the low and high pressure sides of the axial piston device to the other of the low and high pressure sides of the axial piston device. The pressure transition passage includes first and second restrictions separated by a pressure recovery chamber.

A variety of additional aspects will be set forth in the description that follows. The aspects can relate to individual features and to combinations of features.

It is to be understood that both the forgoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the broad inventive concepts upon which the examples described herein are based.

Brief Description of the Drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate aspects of the present disclosure and together with the description, serve to explain the principles of the disclosure. A brief description of the drawings is as follows:

FIG. 1 is an exploded view of a hydraulic pump in accordance with the principles of the present disclosure.

FIG. 2 is a cross-sectional view of the hydraulic pump of FIG. 1.

FIG. 3 is an end view of a valve plate of the hydraulic pump of FIGS. 1 and 2.

FIG. 4 shows the valve plate of FIG. 3 mounted adjacent to and end cover of the hydraulic pump of FIGS. 1 and 2.

FIG. 5 is an end view of the end cover of the hydraulic pump of FIGS. 1 and 2. FIG. 6 is an enlarged view showing a portion of the end cover of FIG. 5 depicting a portion of a pressure transition passage defined in part by the end cover.

FIG. 7 is a cross-sectional view cut through the portion of the pressure transition passage defined by the end cover. FIG. 8 is a cross-sectional view cut through the end plate and the valve plate of the hydraulic pump of FIGS. 1 and 2, the cross-sectional view depicts the pressure transition passage of the hydraulic pump which is defined in part by the end cover and in part by the valve plate of the hydraulic pump.

FIG. 9 is a cross-sectional view depicting an alternative configuration for a pressure transition passage in accordance with the principles of the present disclosure.

Detailed Description

Aspects of the present disclosure relate to an axial displacement device (e.g., a hydraulic pump or hydraulic motor) that uses a multi-step pressure drop to reduce the velocity of the fluid entering the piston chambers of the rotating group during initiation of pressure transitions between low and high pressure sides of the device. This is accomplished by taking advantage of the fact that the velocity through an orifice can be described by the pressure differential exclusive of the area as shown in Eq. (1)

Placing multiple restrictions in series separated by a pressure recovery chamber divides the pressure loss between the restrictions respective to their relative resistance to flow. If the restrictions have equivalent resistance to flow the pressure drop through each resistance stage can be described by the total pressure drop divided by the number of resistances.

The pressure is preferably recovered between each stage for the resistances to function appropriately. This requires that the fluid kinetic energy represented by the velocity is largely converted into potential energy represented by the pressure. This is accomplished by reducing the velocity of the fluid after the restriction to a minimal value.

Reducing the velocity of the fluid through each restriction provides multiple benefits. A series of restrictions of a given size will flow the equivalent amount of a smaller singular restriction without the manufacturing difficulties or sensitivity to contaminants in the fluid. Another benefit of the series of restrictions is that the static pressure in the fluid stream passing through the restriction remains higher due to the lower velocity. Keeping the static pressure of the fluid flowing through the restriction higher reduces the amount of cavitation that occurs in the fluid stream. Avoiding the creation of entrained gas in the fluid helps to reduce the cavitation erosion damage that may occur on the nearby surfaces within the pump.

During operation the volume(s) between the restrictions is expected to drop to a fraction of the pressure difference. If the pressure in this volume remains substantially high, the effect of the restrictions will not be present as the potential energy in the chamber will be sufficient to raise the piston pressure without a significant drop. The various figures included in this disclosure depict an axial piston pump having a pressure transition feature for reducing the velocity of flow into the piston chambers of the axial piston pump during pressure transitions in accordance with the principles of the present disclosure. In the depicted example, the pressure transition feature is at the location where the piston chambers of the axial piston pump transition from a low-pressure side of the pump to a high-pressure side of the pump. It will be appreciated that pressure transition features in accordance with the principles of the present disclosure can also be used to reduce the velocity of flow out of the piston chambers as the axial piston pump transitions from a high-pressure side to a low pressure side of the axial piston pump. Additionally, pressure transition passages in accordance with the principles of the present disclosure are applicable to both hydraulic pumps and hydraulic motors.

FIGS. 1 and 2 depict an axial piston device in the form of a hydraulic pump 20 in accordance with the principles of the present disclosure. The hydraulic pump 20 includes a pump housing 22 including a main housing body 24 having a first end 26 and a second end 28. The pump housing 22 also includes an end cover 30 that mounts at the second end 28 of the main housing body 24. The pump housing 22 defines a high-pressure port (e.g., an outlet/discharge port) and a low-pressure port (e.g., an inlet/suction port). The end cover 30 defines a high-pressure passage 36 (see FIG. 5) in fluid communication with the high-pressure port and a low-pressure passage 38 (see FIG. 5) in fluid communication with the low-pressure port. The main housing body 24 defines an internal cavity 40 having an open end 42 covered by the end cover 30.

The hydraulic pump 20 also includes a drive shaft 44 that extends through the internal cavity 40. The drive shaft 44 is rotatable relative to the pump housing 22 about an axis of rotation 46. The drive shaft 44 has an end portion 48 that projects outwardly from the pump housing 22. The end portion 48 is accessible at the first end 26 of the main housing body 24 and is adapted for connection to a source of torque for driving rotation of the drive shaft 44 about the axis of rotation 46 to power pumping of the hydraulic pump 20.

The hydraulic pump 20 also includes a swash plate 50 and a rotating group 52 that mount within the pump housing 22. The rotating group 52 includes a piston chamber block 54 that mounts within the internal cavity 40 on the drive shaft 44 such that the piston chamber block 54 rotates in concert with the drive shaft 44 relative to the pump housing 22 about the axis of rotation 46. The piston chamber block 54 has a first end 56 that faces toward the swash plate 50 and an opposite second end 58 that faces toward the end cover 30. The piston chamber block 54 defines a plurality of axial piston chambers 60 circumferentially spaced about the axis of rotation 46. The rotating group 52 also includes a plurality of pistons 62 reciprocally mounted within the axial piston chambers 60. When the piston chamber block 54 rotates with the drive shaft 44 about the axis of rotation 46, the pistons 62 interact with the swash plate 50 causing the pistons 62 to reciprocate within the piston chambers 60. In certain examples, an angle of the swash plate 50 can be adjusted relative to the axis of rotation 46 to modify the stroke length of the pistons 62 to change the displacement of the hydraulic pump 20. It will be appreciated that the pistons 62 can include shoes 64 that engage an end face of the swash plate 50 and slide on the end face along a circular path that extends about the axis of rotation 46.

Referring to FIGS. 1 and 2, the hydraulic pump 20 also includes a valve plate 66 that mounts between the end cover 30 and the second end 58 of the piston chamber block 54. As shown at FIG. 3, the valve plate 66 defines a low-pressure opening 68 in the form of a curved slot that extends above the axis of rotation 46. In alternative examples, a plurality of low-pressure openings can be provided instead of one continuous curved slot. The valve plate 66 also includes a plurality of high-pressure openings 70 depicted as a plurality of openings positioned about the axis of rotation 46. In alternative examples, a single continuous curved slot could be used instead of the plurality of openings 70. The low-pressure opening 68 provides fluid communication between the low-pressure passage 38 of the end cover 30 and the piston chambers 60. The high-pressure openings 70 provide fluid communication between the high-pressure passage 36 of the end cover 30 and the piston chambers 60. The low-pressure opening is arranged along a first circumferential region 72 that extends about the axis of rotation 46, and the high-pressure openings 70 are arranged along a second circumferential region 74 that extends about the axis of rotation 46. The low-pressure opening 68 and the high-pressure openings 70 are defined through the valve plate 66 (e.g., axially through the valve plate 66) and have ends located at an axial end face 76 of the valve plate 66 that opposes the second end 58 of the piston chamber block 54. The first circumferential region 72 corresponds to a low-pressure side of the hydraulic pump and the second circumferential region 74 corresponds to a high-pressure side of the hydraulic pump.

The low-pressure opening 68 includes a timing notch 80 at one end of the low-pressure opening 68. Similarly, the high-pressure openings 70 include a timing notch 82 at one end of the plurality of high-pressure openings 70. The low-pressure opening 68 includes a leading end 68 A and a trailing end 68B. The timing notch 80 is located at the leading end 68A of the low-pressure opening 68 such that during rotation of the piston chamber block 54 about the axis of rotation 46 in a direction indicated by arrow 84 (see FIG. 4), the piston chambers 60 initially make fluid communication with the timing notch 80 before reaching a main portion of the low-pressure opening 68. The plurality of high-pressure openings 70 includes a leading end 70A and a trailing end 70B. The timing notch 82 is located at the leading end 70A of the plurality of high- pressure openings 70 such that during rotation of the piston chamber block 54 about the axis of rotation 46 in the direction 84, the piston chambers 60 initially make fluid communication with the timing notch 82 before reaching a main portion of the first high-pressure opening 70. As indicted above, arrow 84 represents a direction of rotation of the piston chamber block 54 about the axis of rotation 46.

The hydraulic pump 20 also defines a pressure transition passage 78 that provides fluid communication between the high-pressure passage 36 and the piston chambers 60 as the piston chamber block 54 rotates about the axis of rotation 46. The pressure transition passage 78 is depicted as a pre-pressurization passage for pre pressurizing the piston chambers 60 as the piston chambers transition from the low- pressure side to the high-pressure side of the hydraulic pump 20 during rotation of the piston chamber block 54 in the direction 84 about the axis of rotation 46. The pressure transition passage 78 includes a first end 86 at the high-pressure passage 36. The pressure transition passage 78 also has a second end 88 at the axial end face 76 of the valve plate 66 at a location between the trailing end 68B of the low-pressure opening 68 and the leading end 70A of the plurality of high-pressure openings 70. In the depicted example, the second end 88 is positioned between the trailing end 68B of the low pressure opening 68 and the timing notch 82 of the plurality of high-pressure openings 70.

The pressure transition passage 78 includes first and second flow restrictions 90, 92 separated by a pressure recovery chamber 94. The pressure transition passage 78 pre-pressurizes the piston chambers 60 as the piston chambers 60 transition from the first circumferential region 72 to the second circumferential region 74 (i.e., from the low-pressure side to the high-pressure side) of the hydraulic pump 20 during rotation of the piston chamber block 54 in the direction 84 about the axis of rotation 46. The pressure recovery chamber 94 is sized to reduce the velocity of hydraulic fluid flowing through the first and second flow restrictions 90, 92 when the pressure transition passage 78 is in communication with one of the piston chambers 60 during rotation of the piston chamber block 54 by converting kinetic energy into potential energy represented by pressure in the pressure recovery chamber 94. In certain examples, the flow restrictions can also be referred to as orifices. The first flow restriction 90, the recovery chamber 94, and the second flow restriction 92 are positioned in series.

In the depicted example, the first flow restriction 90 and the pressure recovery chamber 94 are defined by recesses in the end cover 30 and are defined between the end cover 30 and the valve plate 66. In the depicted example, the second flow restriction 92 is defined by the valve plate 66. In one example, the second flow restriction 92 can be a hole drilled through the valve plate 66, and the recesses in the end cover 30 which form the first flow restriction 90 and the recovery chamber 94 can be machined into an axial and face of the end cover 30. In other examples, the recesses corresponding to the recovery chamber 94 and the first flow restriction 90 can be defined (e.g., machined) in the valve plate 66. The pressure recovery chamber 94 provides a separation between the flow restrictions 90, 92 and a volume for pressure recovery downstream of the first flow restriction 90.

In one example, the pressure recovery chamber 94 has a cross-sectional area that is from 1.5 times to 4.0 times as large as a cross-sectional area of each of the flow restrictions 90, 92. In another example, the pressure recovery chamber 94 has a cross-sectional area that is from 2.0 times to 3.5 times as large as a cross-sectional area of each of the flow restrictions 90, 92. In still another example, the pressure recovery chamber 94 has a cross-sectional area that is from 2.0 times to 3.0 times as large as a cross-sectional area of each of the flow restrictions 90, 92. In one example, the pressure recovery chamber 94 has a cross-sectional area that no more than 4.0 times as large as a cross-sectional area of each of the flow restrictions 90, 92 In one example, the pressure recovery chamber 94 has a volume that is no greater than 2.0% of a volume of fluid within a given one of the piston chambers 60 during initiation of a pressure transition by the pressure transition passage 78. In another example, the pressure recovery chamber 94 has a volume that is no greater than 1.0% of a volume of fluid within a given one of the piston chambers during initiation of a pressure transition by the pressure transition passage 78. In still another example, the pressure recovery chamber 94 has a volume that is no greater than 0.5% of a volume of fluid within a given one of the piston chamber 60 during initiation of a pressure transition by the pressure transition passage 78. In a further example, the pressure recovery chamber 94 has a volume that is no greater than 0.25% of a volume of fluid within a given one of the piston chambers 60 during initiation of a pressure transition by the pressure transition passage 78. In certain examples, the intent of the pressure recovery chamber is to provide a relatively small volume between restrictions that serves as a mechanism to reduce the velocity through the restriction before entering the next. The intent of this solution is not to store appreciable energy in the volume, but to convert the kinetic energy of the fluid stream into potential energy before the following restriction.

In one example, the hydraulic pump has a volumetric displacement of 39-42 cm ³ for each rotation of the pump, the cross-sectional restriction area for each of the flow restrictions 90, 92 is in the range of 1.5-1.9 mm ² , the cross-sectional area of the pressure recovery chamber 94 is in the range of 4.6-5.0 mm ² , the volume of the pressure recovery chamber 94 is in the range of 0.01-0.02 cm ³ , and the volume within each piston chamber at the time pressure a pressure transition is initiated by the pressure transition passage 78 is in the range of 8.0-10.0 cm ³ . Of course, the above values are examples and other sizes can be used as well without departing from the scope of the present disclosure.

In other examples, more than two flow restrictions can be provided in series along the pressure transition passage 78. The flow restrictions can be separated by pressure recovery chambers. FIG. 9 shows an example pressure transition passage 178 having a first flow restriction 190, a second flow restriction 192, and third flow restriction 193. The third flow restriction 193 is defined by an opening through the valve plate 66. The first and second flow restrictions 190, 192 are respectively defined by inserts 195, 197 mounted (e.g., threaded) within an opening formed in the end cover 30. The insertl95 defines a first pressure recovery chamber 194 located between the first flow restriction 190 and the second flow restriction 192, and the insert 197 defines a second pressure recovery chamber 198 located between the second flow restriction 192 and the third flow restriction 193. As used herein, high-pressure and low-pressure are relative terms meaning that the high-pressure is a higher pressure than the low-pressure and are not limited to any particular magnitude of pressure.

The various examples described above are provided by way of illustration only and should not be construed to limit the scope of the present disclosure. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example examples and applications illustrated and described herein, and without departing from the true spirit and scope of the present disclosure.