Axial hydraulic piston pump

An axial piston pump including a housing, a cylinder block, and a swash block. The cylinder block is rotatable within the housing about a vertical axis and includes an array of openings in the cylinder block distributed about the vertical axis and an array of pistons reciprocatably movable within the respective openings. The swash block is rotatable about an axis of rotation that is transverse to the vertical axis, and the degree of rotation is configured to control the extent of reciprocation of the pistons as the cylinder block rotates. The swash block has arc shape conical bearing surfaces tilted relative to the axis of rotation that are configured to guide movement of the swash block rotationally about the axis of rotation and prevent movement of the swash block axially along the axis of rotation.

FIELD OF INVENTION

The present invention relates generally to axial hydraulic pistons pumps, and more particularly to swash block assemblies for use in axial hydraulic piston pumps.

BACKGROUND

Axial hydraulic piston pumps are used in a variety of applications, whether as a stand alone pump or as part of, for example, a hydraulic transmission. The components of an axial hydraulic piston pump typically include a cylinder block, a group of pistons vertically movable within openings in the cylinder block, a swash block the underside of which the pistons bear against, and a pair of arch bushings seated within recesses having axially spaced walls on the upper surface of the swash block. The cylinder block rotates the group of pistons about a vertical axis. A control arm rotates the swash block about an axis of rotation. During rotation, the swash block slides relative to the bushings, causing the bottom of the swash block to tilt upward on one side of the rotation axis and downward on the opposite side of the rotation axis. As the cylinder block rotates, each piston moves vertically downward on the downward tilted side and vertically upward on the upward tilted side in sliding relation in the openings into and out of the cylinder block, which, in turn, causes fluid to be transferred. The dual swash block bushings are formed in a matching arch to guide the swash block about its axis of rotation in a single plane when actuated by for example the control arm input. The matching arch bushings provide a vertical force to the swash block to counter the forces produced by the piston rotating group.

Some existing swash block assemblies have various shortcomings, drawbacks, and disadvantages relative to certain applications. For example, the swash block bushings formed in matching arches along the axis of rotation do not supply any guidance for the swash block in the lateral or rotational (yaw) directions. Typically, the movement of the swash block in the lateral and yaw directions is limited by mechanical surfaces or edges that are not coated to reduce friction, for example the walls of the recesses in the swash block and/or walls of the housing in which the swash block is mounted. In turn, the contact with these surfaces under high force creates significant drag which translates to the amount of force needed to actuate the swash block through the control input by the operator.FIG. 22shows contact stresses on the swash block in the form of different shades. The highest contact stresses, which are identified by the reference numeral700inFIG. 22, are at the walls where the sides of the arch bushings contact due to lateral movement of the swash block along the axis of rotation and/or yaw movement about the vertical axis.

The lack of guidance in the yaw direction also allows the swash block to move within that direction due to clearance between the edges of the bushings and the afore mentioned mechanical surfaces or edges such as walls of the swash block and/or housing. This movement is introduced by the actuation of the swash block by the control arm and is most significant when the actuation of the control arm is changed from one direction to the other. This freedom of movement of the swash block in the yaw direction allows for movement of the control arm input without a corresponding change in displacement of the pump until the contact with the mechanical surface or edge, for example walls, is made. This causes what is known as dead band, an undesirable effect in which there is an inaction or lag in action between the input of the control function and the corresponding change in what is being controlled.

Accordingly, there remains a need for further contributions in this area of technology.

SUMMARY OF INVENTION

The present invention provides, among other things, a swash block assembly that provides surfaces that are tilted relative to an axis of rotation of the swash block and that are configured to guide movement of the swash block rotationally about the axis of rotation and prevent movement of the swash block axially along the axis of rotation and rotatably about the vertical axis, which improves responsiveness between control input and the swash block and prevents or reduces dead band.

According to one aspect of the invention, an axial piston pump includes a housing, a cylinder block rotatable within the housing about a vertical axis and including an array of openings in the cylinder block distributed about the vertical axis and an array of pistons reciprocatably movable within the respective openings, a swash block rotatable about an axis of rotation that is transverse to the vertical axis, wherein the degree of rotation is configured to control the extent of reciprocation of the pistons as the cylinder block rotates, and arc shape conical bushings interposed between the swash block and an interior surface of the housing, wherein the arc shape conical bushings have surfaces tilted relative to the axis of rotation that are configured to guide movement of the swash block rotationally about the axis of rotation and prevent movement of the swash block axially along the axis of rotation.

Embodiments of the invention may include one or more of the following additional features separately or in combination.

The tilted surfaces of the arc shape conical bushings may be configured to prevent rotational movement of the swash block about a yaw axis that is transverse to the axis of rotation.

According to another aspect of the invention, an axial piston pump includes a housing, a cylinder block rotatable within the housing about a vertical axis and including an array of openings in the cylinder block distributed about the vertical axis and an array of pistons reciprocatably movable within the respective openings, and a swash block rotatable about an axis of rotation that is transverse to the vertical axis, wherein the degree of rotation is configured to control the extent of reciprocation of the pistons as the cylinder block rotates, wherein the swash block has arc shape conical bearing surfaces tilted relative to the axis of rotation that are configured to guide movement of the swash block rotationally about the axis of rotation and prevent movement of the swash block axially along the axis of rotation.

Embodiments of the invention may include one or more of the following additional features separately or in combination.

The arc shape conical bearing surfaces may include a pair of opposed arc shape conical bearing surfaces axially spaced apart along the axis of rotation.

The angle of tilt of one of the pair of arc shape conical bearing surfaces may be the same as the angle of tilt of the other of the pair of arc shape conical bearing surfaces.

The pair of opposed arc shape conical bearing surfaces may taper away from one another along the axis of rotation.

The axial piston pump may further include arc shape conical bushings interposed between the swash block and an interior surface of the housing, and the arc shape conical bushings may have surfaces tilted relative to the axis of rotation that cradle the swash block at the respective arc shape conical bearing surfaces.

The arc shape conical bushings may be tapered along the axis of rotation from one edge to an axially opposite edge.

An interior wall of the housing may define arc shape conical bearing surfaces tilted relative to the axis of rotation that cradle the swash block at the respective arc shape conical bearing surfaces of the swash block.

The axial piston pump may further include arc shape conical roller bearings interposed between the swash block and an interior surface of the housing, and the arc shape conical roller bearings may provide a plane of rollers tilted relative to the axis of rotation that cradle the swash block at the respective arc shape conical bearing surfaces of the swash block.

The arc shape conical roller bearings may be tapered along the axis of rotation from one edge to an axially opposite edge.

According to another aspect of the invention, a hydrostatic transmission may include an axial piston pump according to the invention, wherein rotation of the cylinder block controls the flow of hydraulic fluid from the pump to a hydraulic motor, and vice versa, to drive the hydraulic motor.

According to another aspect of the invention, a vehicle includes a hydrostatic transmission according to the invention, an engine for driving the cylinder block of the axial piston pump, and a drivetrain driven by the hydraulic motor.

According to another aspect of the invention, a swash block assembly includes a swash block having an axis of rotation and an opening that extends through the swash block along an axis transverse to the axis of rotation, the swash block including a bottom bearing portion that is configured to interface with a piston rotating group and a top portion that has arc shape bearing surfaces disposed angularly about the axis of rotation and axially on opposite sides of the opening that guide the swash block about the axis of rotation, wherein the arc shape bearing surfaces have conical shapes about the axis of rotation.

Embodiments of the invention may include one or more of the following additional features separately or in combination.

The arc shape bearing surfaces may be at opposing angles relative to the axis of rotation.

The arc shape bearing surfaces may include dual conical shape opposing surfaces.

The arc shape bearing surface may include one of a pair of arc shape conical bushings, a pair of arc shape conical roller bearings, or a pair of arc shape conical coated surfaces made of a low friction surface material.

The angles of the conical shapes of the arc shape bearing surfaces relative to the axis of rotation may be the same.

According to another aspect of the invention, an axial piston pump includes a housing, a cylinder block rotatable within the housing about a vertical axis and including an array of openings in the cylinder block distributed about the vertical axis and an array of pistons reciprocatably movable within the respective openings, a swash block rotatable about an axis of rotation that is transverse to the vertical axis, wherein the degree of rotation is configured to control the extent of reciprocation of the pistons as the cylinder block rotates, and at least one link coupled to a front portion of the swash block and actuatable to push and pull the front portion of the swash block about its axis of rotation in a manner that tilts the swash block relative to horizontal.

Embodiments of the invention may include one or more of the following additional features separately or in combination.

The at least one link may be a pair of links pivotably connected to the swash block at axially opposite ends thereof, or a single link pivotably connected to a center portion thereof.

The following description and the annexed drawings set forth certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features according to aspects of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

DETAILED DESCRIPTION

Referring now in detail to the drawings and initially toFIGS. 1-11, an exemplary axial hydraulic piston pump10according to the invention is indicated generally by reference numeral10. The pump10is shown on board a vehicle such as a zero-turn riding mower, represented by the broken line4inFIG. 1, for driving a hydraulic motor of a hydrostatic transmission of the vehicle. The engine of the vehicle drives an input shaft28of the pump10, which in turn hydraulically drives the motor via hydraulic fluid passages36,38. The motor in turn drives a drivetrain or other driven component of the vehicle. Although the axial piston pump10and associated system and method are herein described in relation to driving a hydraulic motor of a hydrostatic transmission, it will be appreciated by those skilled in the art that the pump10, system, and method may have other applications, including for example, a standalone pump for multiple different applications. Applications may include machine tools, agricultural and construction equipment, marine and offshore auxiliary power, metal forming and stamping equipment, plastics processing machinery, to name a few.

The axial piston pump10includes an upper housing portion6, a lower housing portion8, a cylinder block12, an array14of pistons16reciprocatably movable within openings18in the cylinder block12, and a tiltable swash block20. The pistons16are reciprocatably movable within the openings18in the cylinder block12along a vertical axis28, and the swash block20is configured to tilt about an axis of rotation34that is transverse to, in the illustrative embodiment perpendicular to, the vertical axis28. When the cylinder block12rotates the array of pistons16with the swash block20in a tilted position, the pistons16reciprocate within the openings18to draw and expel hydraulic fluid respectively through the pair of hydraulic fluid passages, or work ports36,38, in the lower housing portion8, which in turn drive the hydraulic motor or other application. A pair of arc shape grooves40,41in the upper housing portion6and a pair of arc shape conical bushings42,43seated in the grooves40,41cradle the swash block20. As will be described in greater detail below, the swash block20has a pair of arc shape conical bearing surfaces44,45that guide movement of the swash block20rotationally about the axis of rotation34and prevent movement of the swash block20axially along the axis of rotation34and rotatably about the vertical axis28, which improves responsiveness between control input and the swash block20and prevents or reduces dead band.

FIGS. 2-8show the exemplary axial hydraulic piston pump10in greater detail. A plurality of pistons16, five in the illustrative embodiment, are arranged in a circular array about the vertical axis28. The pistons16are slidably received within the openings18, in the form of cylinders in the illustrative embodiment, in the cylinder block12. In the illustrative embodiment, the axis of vertical movement of the pistons16is parallel to the vertical axis28, although other configurations may be possible. An input shaft46rotatably supported at its opposite ends in the upper and lower housing portions6,8, is coupled to the cylinder block12, for example by a spline connection, to rotate the cylinder block12about the vertical axis28. The bottom surface48of the cylinder block12slides against an upper surface50of a manifold plate54that forms part of the lower housing portion8. The bottom surface48of the cylinder block12has a plurality of arcuate slots58, five in the illustrative embodiment, that are in fluid communication with the respective openings18that slidably receive the pistons16. The upper surface50of the manifold plate54has a pair of arcuate slots36,38that serve as the respective work ports36,38of the pump10. The arcuate slots58of the cylinder block12and the arcuate slots36,38of the manifold plate54are disposed along a common radial distance from the vertical axis28. As will be appreciated, as the input shaft46drives and rotates the cylinder block12, the arcuate slots58slide over the work ports36,38to direct hydraulic fluid to the work port36and from the work port38, or vice versa to the work port38and from the work port36, depending on the tilt of the swash block20.

The pistons16protrude from the top of the cylinder block12and are biased toward the upward position. Any suitable biasing means may be used for biasing the pistons16upward. In the illustrative embodiment, each of the pistons16has a downward facing hollow62that receives a compression spring66. The compression spring66sits on a ledge disposed near the bottom of the opening18and abuts the underside of the top70of the piston16. The tops70of the pistons16bear against the underside82of the swash block20. In some applications, a thrust bearing may be seated within a recess in the underside82of the swash block20, with the tops70of the pistons16bearing against the underside of the thrust bearing, and the thrust bearing in turn bearing against an upper wall on the interior of the recess of the swash block20. As the cylinder block12rotates, the springs66urge the tops70of the pistons16to impart a vertical force against the swash block20. The swash block20functions as a cam to adjust the stroke or extent of reciprocation of the pistons16. Thus, as the cylinder block12rotates, the tilt orientation of the swash block20provides a cam action that effects piston16reciprocation and thus pumping of hydraulic fluid. Thus, the amount of hydraulic fluid pumped per shaft46revolution, or the displacement of the pump10, is based in part on the angle of tilt of the swash block20. As will be appreciated, the interface between the pistons16and the swash block20need not be limited to the as-shown configuration and other embodiments are contemplated. For example, the tops70of the pistons16may bear against the underside82of the swash block20directly, or be pivotably mounted to low friction pads via spherical ball joints, wherein the pads, in turn, bear against the underside82of the swash block20.

A control device30is configured to rotate the swash block20about its axis of rotation34to thereby tilt the swash block20relative to horizontal. The horizontal is a plane transverse to, in the illustrative embodiment perpendicular to, the vertical axis28. The control device30shown inFIGS. 2-5is in the form of a side-mounted control arm30rotatably supported in a side wall of the upper housing portion6. The control arm30is coupled to a link86and slider block90that slides within a slot94in the side98of the swash block20. The link86and slider block90allow the swash block20to be rotated about its axis of rotation34without the axis of rotation34passing through the structure of the swash block20. The slider block90also enables the axis of rotation of the control arm30to be vertically offset from the axis of rotation34of the swash block20, whether due to tolerance stackup, or by design for example due to space constraints within the pump housing. Rotation of the control arm30turns the link86, which causes the slider block90to abut either side of the slot94to urge the swash block20about its axis of rotation34. As the control device30rotates the swash block20for example counterclockwise inFIG. 2, the slider block90tilts the front102of the swash block20downward relative to horizontal, and the rear106of the swash black20upward relative to horizontal. Similarly, as the control device30rotates the swash block20clockwise inFIG. 2, the slider block90tilts the front102of the swash block20upward relative to horizontal, and the rear106of the swash block20downward relative to horizontal. Of course, other types of control devices30may be used to effect the tilting movement of the swash block20. For example, in one form, a side mounted lever or side mounted plunger may be configured upon actuation to tilt the swash block20. In another form, the swash block20may be connected at its opposite sides to opposing dowels or shafts supported by the sides of the housing. Further control devices30constructed in accordance with the invention will be described in greater detail below.

During counterclockwise tilting of the swash block20about its rotation axis34, the bottom82of the swash block20tilts upward on one side of the axis34, for example at the rear106of the swash block20, and downward on the opposite side of the axis34, for example at the front102of the swash block20. Similarly, during clockwise tilting of the swash block20about its rotation axis34, the bottom82of the swash block20tilts downward on one side of the axis34, for example at the rear106of the swash block20, and upward on the opposite side of the axis34, for example at the front102of the swash block20. This causes the pistons16on the upward tilted side of the swash block20to move upward owing to the spring bias of the pistons16toward the upward position, and urges the pistons16on the downward tilted side of the swash block20downward, that is, against the bias exerted by the springs66. As the cylinder block12rotates, the tops70of the pistons16follow the cam underside82of the swash block20(or the cam underside of a thrust bearing if present), and in so doing impart vertical and horizontal forces against the swash block20. The pistons16reciprocate axially within their respective openings18as the cylinder block12rotates the array14of pistons16about the vertical axis28. More particularly, as the cylinder block12rotates, each piston16moves vertically downward on the downward tilted side of the swash block20and vertically upward on the upward tilted side of the swash block20as the tops70of the pistons16slide under and bear against the underside82of the swash block20; or in applications with a thrust bearing interposed between the pistons16and swash block20, as the tops70of the pistons16slide under and bear against the underside of the thrust bearing, and the thrust bearing in turn bears against the underside82of the swash block20.

In operation, the control device30is operable to direct hydraulic fluid through the work ports36,38of the manifold plate54in either direction. For example, when the control device30tilts the front102of the swash block20downward relative to horizontal and the rear106of the swash block20upward relative to horizontal, the pistons16will move downward at the front102of the swash block20and upward at the rear106of the swash block20. Thus, as the cylinder block12rotates clockwise about the vertical axis28, a piston16will be carried about the axis28, moving axially downward as it is urged against the cam underside82from the upward tilted rear106of the swash block20to the downward tilted front102of the swash block20, and then thereafter axially upward as it is urged against the cam underside82from the downward tilted front102of the swash block20to the upward tilted rear106of the swash block20. This completes one revolution of the cylinder block12and one reciprocation of the piston16. Each additional rotation of the cylinder block12results in an additional reciprocation cycle of the piston16. As the piston16moves downward the piston16expels hydraulic fluid through the work port36, and as the piston16moves upward the piston16draws hydraulic fluid through the work port38. The other four pistons16of the array14function in a similar manner, resulting in continuous discharge of hydraulic fluid through the work port36and continuous drawing of hydraulic fluid through the work port38.

To reverse the flow of hydraulic fluid through the work ports36,38, the control device30tilts the swash block20clockwise inFIG. 2, so that the front102of the swash block20is tilted upward relative to horizontal, and the rear106of the swash block20is tilted downward relative to horizontal. As such, the pistons16move upward at the front102of the swash block20and downward at the rear106of the swash block20. Continuous rotation of the cylinder block12and the array14of pistons16results in continuous discharge of hydraulic fluid through the work port38and continuous drawing of hydraulic fluid through the work port36.

To cease flow through the work ports36,38, the control device30rotates the swash block20to a position at which its underside82is not tilted relative to horizontal, that is, so that there is no tilt in the front102or the rear106of the swash block20. As the cylinder block12rotates, the pistons16do not reciprocate, and instead remain axially fixed within their respective openings18and axially fixed relative to one another. As such, hydraulic fluid is neither expelled from nor drawn through the work ports36,38.

Referring now more closely toFIGS. 2-5, details of the swash block20and upper housing portion6interface will be described. The swash block20is slidably mounted within the upper housing portion6of the pump10for radially and axially guided tilting movement between the afore described upward and downward tilted positions. As shown inFIGS. 2-5, the upper housing portion6has a pair of arc shape grooves40,41defined at their edges by axially spaced walls109depending from the interior wall of the upper housing portion6. A pair of arc shape conical bushings42,43are interposed between the grooves40,41and the upper surface of the swash block20. In the illustrative embodiment, the grooves40,41receive the pair of arc shape conical bushings42,43which, in turn, cradle respective arc shape conical bearing surfaces44,45of the swash block20. The bushings42,43can be made of any suitable bearing materials, such as steel with a bronze coating. Each pair of grooves40,41, bushings42,43, and bearing surfaces44,45is axially spaced in the direction of the rotation axis34, and openings110,114extend therebetween through the upper housing portion6and the swash block20along the vertical axis28to accommodate passage therethrough of the input shaft46. Thus, the bushings42,43are disposed on axially opposite sides of the swash block opening114or otherwise straddle the swash block opening114. Protrusions118depend from the interior wall of the upper housing portion6that fit into holes122in the bushings42,43to aid in locating and holding the bushings42,43in place relative to the upper housing portion6. The bushings42,43seat within recesses122on the upper surface of the swash block20. Axially spaced walls126adjacent to the recesses122fit between inner axially spaced walls109of the upper housing portion6.

The spring-biased pistons16maintain an upward biasing force against the swash block20, the bushings42,43, and the upper housing portion6. During tilting of the swash block20about the axis34, the arc shape conical bearing surfaces44,45of the swash block20bear against, and slide relative to, the arc shape conical bushings42,43. The sliding movement of the swash block20along the arc shape conical bushings42,43causes the bottom82of the swash block20to tilt upward relative to horizontal on one side of the rotation axis34and downward relative to horizontal on the opposite side of the rotation axis34, to thereby induce the change in angle of the piston rotating group14that causes hydraulic fluid to be transferred through the work ports36,38, as described above.

Referring now more closely toFIG. 9-11, shown in greater detail are the configurations and mating surfaces of the components of the swash block20and the arc shape conical bushings42,43. The arc shape conical bearing surfaces44,45of the swash block20have opposing conical shapes130,131about the axis of rotation34of the swash block20. Likewise, the arc shape conical bushings42,43have opposing conical shapes130,131about the axis of rotation34of the swash block20. One way for the arc shape conical bushings42,43to realize the opposing conical shapes130,131, as shown for example inFIG. 10, is for the arc shape conical bushings42,43themselves to be tapered along the axis of rotation34from one edge E1, the inner edge in theFIG. 10embodiment, to an axially opposite edge E2, the outer edge in theFIG. 10embodiment. In the illustrative embodiment, there are two arc shape conical bushings42,43axially spaced apart along the axis of rotation34and disposed on axially opposite sides of the opening114passing through the swash block20. The angle of tilt A of the opposing conical shapes130,131relative to horizontal, which is relative to the axis of rotation34in the illustrative embodiment, is the same for the opposing conical shapes130,131, and is shown to be about five (5) degrees. The opposing conical shapes130,131taper in opposite directions, inFIG. 10away from one another along the axis of rotation34, i.e. in the direction away from the center of the swash block20or the opening114in the swash block20. As shown inFIG. 11, the opposing conical shapes130,131are disposed angularly about the axis of rotation34of the swash block20to have an arc shape B of about 90 degrees.

Those skilled in the art will appreciate that the opposing conical surfaces need not be configured as shown inFIGS. 9-11, and other embodiments are contemplated. For example, another way for the arc shape conical bushings42,43to realize the opposing conical shapes130,131, is for the bushings42,43to have similar thickness from edge E1to edge E2, and for the interior surface wall of the upper housing portion6to instead be tapered. The angle of tilt A of the opposing conical shapes130,131may be different for the opposing conical shapes130,131, and the angle of tilt A may be less than or greater than five degrees, depending on the application and configuration of the axial piston pump10. Thus, the conical shape130may have an angle of tilt A relative to horizontal that is larger (or smaller) than the angle of tilt A of the conical shape131. Further, the opposing conical shapes130,131may have tapers that approach one another along the axis of rotation34, i.e. in the direction toward from the center of the swash block20or the opening114in the swash block20. The opposing conical shapes130,131may be disposed angularly about the axis of rotation34to have an arc shape other than 90 degrees, again depending on the application and configuration of the axial piston pump10, for example, based on the desired interaction between the array14of pistons16and the underside82of the swash block20.

In operation, the opposing conical shapes130,131introduce radial alignment forces (vertical alignment forces in the illustrative embodiment) and axial alignment forces (horizontal alignment forces in the direction of the axis of rotation34in the illustrative embodiment), for example as shown at arrows138,139inFIG. 10, due to the vertical and horizontal force vectors created by each cone angle130,131. The vertical force vector138imparted on the conical bearing surfaces44,45of the swash block20counters, for example, the vertical forces produced by the piston rotating group14, e.g. the upward biasing force exerted by the spring-biased pistons16against the underside82of the swash block20, as well as the vertical component of the force exerted by the rotating cylinder block12through the pistons16.

The horizontal force vector139imparted on the conical bearing surfaces44,45of the swash block20counters, for example, the horizontal forces produced by the control device30on the swash block20, as well as other horizontal forces such as those produced by the piston rotating group14or the cylinder block12through the pistons16. As will be appreciated, when the control device30rotates the swash block20about its axis of rotation34, the swash block20will have a tendency to move laterally along the axis34and a tendency to rotate about the vertical axis28, also known as yaw movement. The axial, or thrust, component139imparted on the conical bearing surfaces44,45provides guidance for the swash block20about its axis of rotation34while also providing guidance to prevent lateral movement of the swash block20along the axis34and prevent rotational movement about the vertical axis28. As such, the conical bearing surfaces44,45prevent misalignment of the swash block20relative to its axis of rotation34. By preventing misalignment of the swash block20, the conical bearing surfaces44,45maintain clearances and thus prevent contact between the swash block20and mechanical surfaces or edges that are not coated to reduce friction, for example, contact between the edges of the arc shape conical bushings42,43and the walls109depending from the interior wall of the upper housing portion6, and/or contact between the walls109and the walls126of the swash block20. As such, drag caused by the contact between these surfaces is eliminated or significantly reduced, and the amount of force needed to actuate the swash block20through the control device30by an operator is significantly reduced. Of particular significance, the horizontal alignment force139created by the opposing cone angles130,131eliminates or significantly reduces dead band caused by movement of the swash block20in the yaw direction, or a change in actuation of the control device30from one direction to the other. The elimination or reduction of dead band provides the operator with an improved control feel and predictability of input to output or response of the axial piston pump10.

Reference is now made toFIGS. 12-15, which show views of an axial hydraulic piston pump210according to another embodiment of the invention. The axial piston pump210ofFIGS. 12-15is in many respects substantially the same as the above-referenced axial piston pump210ofFIGS. 2-11, and consequently the same reference numerals are used to denote structures corresponding to similar structures in the axial piston pump10ofFIGS. 2-11. In addition, the foregoing description of the axial piston pump10ofFIGS. 2-11is equally applicable to the axial piston pump210ofFIGS. 12-15, except as may be noted herein. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the axial piston pumps10,210may be substituted for one another or used in conjunction with one another where applicable.

The swash block20is slidably mounted within the upper housing portion6of the pump210for radially and axially guided tilting movement between the afore described upward and downward tilted positions. The upper housing portion6of the axial piston pump210includes a pair of arc shape conical bearing surfaces240,241that depend from the interior surface of the upper housing portion6and into the recesses122in the upper surface of the swash block20. The arc shape conical bearing surfaces240,241cradle the respective arc shape conical bearing surfaces44,45of the swash block20. The arc shape bearing surfaces44,45of the swash block20may be coated with a low friction surface material such as PTFE or the like to aid in the sliding action between the surfaces44,45and surfaces240,241. The axially spaced walls126adjacent to the recesses122fit between inner axially spaced walls109of the upper housing portion6.

As shown inFIG. 15, the arc shape conical bearing surfaces240,241formed by the housing interior have opposing conical shapes130,131about the axis of rotation34of the swash block20. As is also shown inFIG. 15, the arc shape conical bearing surfaces44,45of the swash block20likewise have opposing conical shapes130,131about the axis of rotation34of the swash block20.

In operation, the opposing conical shapes130,131introduce radial alignment forces (vertical alignment forces in the illustrative embodiment) and axial alignment forces (horizontal alignment forces in the direction of the axis of rotation34in the illustrative embodiment), for example as shown at arrows138,139inFIG. 15, due to the vertical and horizontal force vectors created by each cone angle130,131. The vertical and horizontal force vectors138,139imparted on the conical bearing surfaces44,45of the swash block20in many respects yield similar benefits as described above with respect to the embodiment ofFIGS. 2-11. Thus, the axial, or thrust, component139imparted on the conical bearing surfaces44,45provides guidance for the swash block20about its axis of rotation34while also providing guidance to prevent lateral movement of the swash block20along the axis34and prevent rotational movement about the vertical axis28. As such, the conical bearing surfaces44,45prevent misalignment of the swash block20relative to its axis of rotation34. By preventing misalignment of the swash block20, the conical bearing surfaces44,45maintain clearances and thus prevent contact between the swash block20and mechanical surfaces or edges that are not coated to reduce friction, for example, contact between the walls109depending from the interior wall of the upper housing portion6and the walls126of the swash block20. As such, drag caused by the contact between these surfaces is eliminated or significantly reduced, and the amount of force needed to actuate the swash block20through the control device30by an operator is significantly reduced. Of particular significance, the horizontal alignment force139created by the opposing cone angles130,131eliminates or significantly reduces dead band caused by movement of the swash block20in the yaw direction, or a change in actuation of the control device30from one direction to the other. The elimination or reduction of dead band provides the operator with an improved control feel and predictability of input to output or response of the axial piston pump210.

Reference is now made toFIGS. 16-19, which show views of an axial hydraulic piston pump410according to another embodiment of the invention. The axial piston pump410ofFIGS. 16-19is in many respects substantially the same as the above-referenced axial piston pumps10,210ofFIGS. 2-11andFIGS. 12-15, and consequently the same reference numerals are used to denote structures corresponding to similar structures in the axial piston pumps10,210ofFIGS. 2-11andFIGS. 12-15. In addition, the foregoing description of the axial piston pumps10,210ofFIGS. 2-11andFIGS. 12-15is equally applicable to the axial piston pump410ofFIGS. 16-19, except as may be noted herein. Moreover, it will be appreciated upon reading and understanding the specification that aspects of the axial piston pumps10,210,410may be substituted for one another or used in conjunction with one another where applicable.

The swash block20is slidably mounted within the upper housing portion6of the pump410for radially and axially guided tilting movement between the afore described upward and downward tilted positions. As shown inFIGS. 16-19, the arc shape grooves40,41of the upper housing portion6are defined at their edges by the axially spaced walls109depending from the interior wall of the upper housing portion6. A pair of arc shape conical roller bearings442,443are interposed between the grooves40,41and the upper surface of the swash block20. As will be appreciated, the arc shape conical roller bearings442,443may comprise any suitable conical roller bearing that reduces friction between the swash block20and upper housing portion6while transferring radial loads (vertical loads in the illustrative embodiment) and axial loads (horizontal loads in the direction of the axis of rotation34in the illustrative embodiment) from the swash block20to the upper housing portion6, including for example tapered roller bearings, needle roller bearings, among others. In the illustrative embodiment, the grooves40,41receive the pair of arc shape conical roller bearings442,443which, in turn, cradle the respective arc shape conical bearing surfaces of the swash block20. The bearings442,443seat within recesses122on the upper surface of the swash block20. Axially spaced walls126adjacent to the recesses122fit between inner axially spaced walls109of the upper housing portion6.

As shown inFIG. 19, the arc shape conical bearing surfaces44,45of the swash block20have opposing conical shapes130,131about the axis of rotation34of the swash block20. As is also shown inFIG. 19, the arc shape conical roller bearings442,443likewise have opposing conical shapes130,131about the axis of rotation34of the swash block20. One way for the arc shape conical roller bearings442,443to realize the opposing conical shapes130,131, as shown for example inFIG. 19, is for the arc shape conical roller bearings442,443themselves to be tapered along the axis of rotation34from one edge E1, the inner edge in theFIG. 19embodiment, to an axially opposite edge E2, the outer edge in theFIG. 19embodiment. It will be appreciated that each opposing conical shape130,131of the arc shape conical roller bearings442,443is defined by a conical plane that is tangent to the linear contact patches of the surfaces of each of the rollers445of the bearings442,443. Thus, the arc shape conical roller bearings442,443each provide a plane of rollers445tilted relative to the axis of rotation34that cradle the swash block20at the respective arc shape conical bearing surfaces44,45of the swash block20.

In operation, the opposing conical shapes130,131introduce radial alignment forces (vertical alignment forces in the illustrative embodiment) and axial alignment forces (horizontal alignment forces in the direction of the axis of rotation34in the illustrative embodiment), for example as shown at arrows138,139inFIG. 19, due to the vertical and horizontal force vectors created by each cone angle130,131. The vertical and horizontal force vectors138,139imparted on the conical bearing surfaces44,45of the swash block20in many respects yield similar benefits as described above with respect to the embodiment ofFIGS. 2-11and the embodiment ofFIGS. 12-15. Thus, the axial, or thrust, component139imparted on the conical bearing surfaces44,45provides guidance for the swash block20about its axis of rotation34while also providing guidance to prevent lateral movement of the swash block20along the axis34and prevent rotational movement about the vertical axis28. As such, the conical bearing surfaces44,45prevent misalignment of the swash block20relative to its axis of rotation34. By preventing misalignment of the swash block20, the conical bearing surfaces44,45maintain clearances and thus prevent contact between the swash block20and mechanical surfaces or edges that are not coated to reduce friction, for example, contact between the edges of the conical roller bearings442,443and the walls109depending from the interior wall of the upper housing portion6, and/or contact between the walls109and the walls126of the swash block20. As such, drag caused by the contact between these surfaces is eliminated or significantly reduced, and the amount of force needed to actuate the swash block20through the control device30by an operator is significantly reduced. Of particular significance, the horizontal alignment force139created by the opposing cone angles130,131eliminates or significantly reduces dead band caused by movement of the swash block20in the yaw direction, or a change in actuation of the control device30from one direction to the other. The elimination or reduction of dead band provides the operator with an improved control feel and predictability of input to output or response of the axial piston pump410.

Turning now toFIG. 20, there is shown a swash block assembly520and control device530according to the invention. As noted above, the axial hydraulic piston pumps10,210,410need not be limited to a side input control arm type control device30, and other actuation devices are contemplated. The control device530ofFIG. 20includes a double pin pull mechanism formed by a pair of links532pivotably connected at one end to a front portion of the swash block assembly520and at the other end to a control arm534. As shown inFIG. 20, the links532are pivotably connected to the swash block520at axially opposite ends thereof. The control arm534can be actuated by any suitable rotational control input, as would occur to those skilled in the art. Actuation of the control arm534pushes and pulls the pair of links532which in turn respectively push and pull the front portion of the swash block520about its axis of rotation34in a manner that tilts the swash block520relative to the horizontal, either with the front below horizontal and the rear above horizontal, or with the rear below horizontal and the front above horizontal. It has been found that the control device530ofFIG. 20results in improved stability in control of the swash block530, for all of the axial hydraulic piston pumps10,210,410described herein. It will be appreciated that the control device530could alternatively be connected to the rear of the swash block520depending on the application, or a pair of control devices530could be connected to the front and rear of the swash block520depending on the application.

FIG. 21shows a swash block assembly620and control device630according to another embodiment of the invention. The control device630ofFIG. 21includes a single pull mechanism formed by a link632pivotably connected at one end to a front portion of the swash block assembly620and at the other end to a control arm634. The control arm634can be actuated by any suitable rotational control input, as would occur to those skilled in the art. Actuation of the control arm634pushes and pulls the link632which in turn respectively pushes and pulls the front portion of the swash block620about its axis of rotation34in a manner that tilts the swash block620relative to the horizontal, either with the front below horizontal and the rear above horizontal, or with the rear below horizontal and the front above horizontal. It has been found that the control device630ofFIG. 21results in improved stability in control of the swash block630, for all of the axial hydraulic piston pumps10,210,410described herein. It will be appreciated that the control device630could alternatively be connected to the rear of the swash block620depending on the application, or a pair of control devices630could be connected to the front and rear of the swash block620depending on the application.