WO2017078852A1

WO2017078852A1 - Pump displacement control assembly

Info

Publication number: WO2017078852A1
Application number: PCT/US2016/052592
Authority: WO
Inventors: Matthew Herman Simon; Bruce DeWitt LARKIN; Dennis Allen; Randall THOMPSON; Bernard STREHLOW
Original assignee: Parker-Hannifin Corporation
Priority date: 2015-11-04
Filing date: 2016-09-20
Publication date: 2017-05-11

Abstract

A hydraulic pump includes a displaceable swash plate, a piston rotating group having a plurality of reciprocating pistons that interact against the swash plate to pump hydraulic fluid, a control piston that acts on the swash plate to control a displacement angle of the swash plate, and a displacement control assembly configured to provide mechanical feedback control of positioning of the control piston. The displacement control assembly is positioned non-coaxially relative to the control piston. The displacement control assembly includes a feedback piston, a feedback spring having a spring force that changes proportionally with the movement of the feedback piston, a moveable control spool, and a control actuator. A positioning of the control spool is determined based on a balance between the spring force and the actuator force, which controls a flow of hydraulic fluid to the control piston to provide feedback control of positioning of the control piston.

Description

Title: PUMP DISPLACEMENT CONTROL ASSEMBLY

Related Applications This application claims the benefit of U.S. Provisional Application No.

62/250,753 filed November 4, 2015, which is incorporated herein by reference.

Field of Invention

The present invention relates generally to hydraulic pumps, and more particularly to control mechanisms for variable displacement hydraulic pumps.

Background

Hydraulic fluid power systems are utilized to control motion in a variety of industries. Mining and drilling equipment, construction equipment, motor vehicle transmission systems, and various other industrial applications employ such hydraulic systems. In hydraulic control systems, a hydraulic pump converts mechanical power from a prime mover such as an internal combustion engine or electrical motor into hydraulic power which is supplied via fluid conduits to actuators which are used to control motion. The actuators may create rotary motion (e.g. hydraulic motor) or linear motion (e.g. hydraulic cylinder).

A common configuration of the hydraulic pump component of the system is a piston-type pump including a plurality of reciprocating pistons, which are in fluid communication through hydraulic porting with the hydraulic system. Rotation of the hydraulic pump rotating group against a moveable swash plate creates an axial motion of the pump pistons that forces hydraulic fluid through the hydraulic porting to the downstream components of the system. Accordingly, swash plate pumps achieve variable displacement by proper positioning the swash plate, which typically is performed using one or more control actuators such as a control piston. Other types of control actuators such as vanes may also be utilized, although a control piston presents a relatively simple design as compared to other control actuator mechanisms and therefore is the most common method of swash plate actuation. In designs using a control piston type of actuator, a control piston pushes on a swash plate, and the swash plate is tilted about a pivot axis from a maximum displacement angle generally on the order of 15 to 20 degrees, to a minimum displacement angle that is generally zero degrees. At zero degrees, there is no reciprocation of the pumping pistons in their respective bores, and therefore no output flow is produced.

It will be appreciated, therefore, that precise control of the positioning of the control piston is imperative so as to properly orient the swash plate with the desired displacement angle. Complex electronic control or comparable feedback systems have been employed for positioning of the control piston, which can be expensive.

Summary of Invention

The present invention provides an enhanced electro-hydraulic pump displacement control assembly that is particularly suitable for providing mechanical feedback control of positioning of a control piston that controls displacement of a swash plate to a precise swash plate displacement angle. The displacement or positioning of the swash plate is directly proportional to a force applied by a control actuator provided in a distinct displacement control assembly that is positioned adjacent to and non-coaxially with the control piston, while utilizing mechanical force feedback to ensure control repeatability and accuracy of the positioning of the control piston. In exemplary embodiments, the control actuator in the displacement control assembly is configured as an electrical linear actuator, i.e., a solenoid actuator, which shifts a valve spool to increase or decrease pressure behind the control piston and provide the proportional force.

A displacement control assembly includes the control actuator such as a solenoid, a control spool, a feedback spring, and a feedback follower piston all positioned and housed coaxially. Additionally, a biasing spring may be positioned coaxially outside the feedback spring to help maintain contact between the follower piston and the swash plate at low displacement angles and during rapid changes in the swash plate angle. The control bore and referenced components housed therein are positioned adjacently to a control piston bore that includes the control piston. In exemplary embodiments, the control piston and feedback follower piston may both act on the swash plate via a flatted pin. The solenoid produces a linear force that is proportional to the amperage applied, and the solenoid force acts on one end of the control spool. The opposite end of the spool is acted upon by the spring force of the feedback spring, which varies in proportion to swash plate angle. The follower feedback piston is utilized to transfer rotary or angular displacement of the swash plate into linear motion on the feedback spring, which alters the feedback spring force.

The control spool meters flow to and from the control piston via a control port that may be placed in fluid communication with either a pressurized supply port or a low case pressure drain port. As the control spool moves in a first direction due to the feedback spring force being greater than the solenoid force (also referred to as an error signal in controls engineering), the control spool will begin metering flow from the supply port to the control port, which feeds flow to the control piston until the control piston moves sufficiently to reduce the swash plate angle such that the feedback spring balances the solenoid force. At such position, the error becomes zero and the flow path is shut by the control spool that is now balanced at its neutral or closed position.

Conversely, as the control spool moves in a second direction opposite to the first direction due to the feedback spring force being less than the solenoid force, the connection from the supply port to the control port is blocked, and the control port is instead connected to the drain port connected to a drain tank or similar low case pressure. This essentially connects the control piston to the low case pressure, and when the control piston is connected to the low case pressure, the control piston will move oppositely due to the stroke-increasing moment created on the swash plate by the pumping pistons, or a biasing piston or other biasing device which increases the swash plate angle. When the swash plate angle increases sufficiently to cause the feedback spring force to equal the solenoid force, the error becomes zero, and the control spool shuts off the connection from the control port to the drain port (low case pressure). In this manner, a mechanical feedback is employed to provide for precise positioning of the control piston, and in turn precise angular displacement of the swash plate.

If power is removed from the solenoid, a third spool state may be utilized whereby the supply port is blocked from the control port, and the control port is vented to the low case pressure via a small flow path or orifice that opens up to the drain port (low case pressure). In such case, the control spool travels to its biased position under the feedback spring force, and the swash plate moves to maximum displacement. This configuration is used for applications requiring the pump to default to maximum displacement in the event of an electrical failure. An aspect of the invention, therefore, is a hydraulic pump. In exemplary embodiments, the hydraulic pump includes a displaceable swash plate that is configured to displace within a displacement angle range, a piston rotating group comprising a plurality of reciprocating pistons configured to interact against the swash plate to pump hydraulic fluid, a control piston configured to act on the swash plate to control a displacement angle of the swash plate within the displacement angle range, and a displacement control assembly configured to provide mechanical feedback control of positioning of the control piston. The displacement control assembly is positioned non-coaxially relative to the control piston.

In exemplary embodiments of the hydraulic pump, the displacement control assembly includes in essentially a coaxial configuration a feedback piston that is moveable within a cylinder adjacent to the control piston and acts as a follower piston relative to the control piston, a feedback spring having a spring force that changes proportionally with the movement of the feedback piston, a control spool that is moveable proportionally between a first position and a second position, and a control actuator. The feedback spring is configured to exert the spring force against a first end of the control spool, and the control actuator is configured to exert an actuator force against a second end of the control spool opposite the first end. A positioning of the control spool between the first position and the second position is determined based on a balance between the spring force and the actuator force acting on the control spool. The positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid to the control piston to provide positioning of the control piston.

These and further features of the present invention will be apparent with reference to the following description and attached drawings. In the description and drawings, particular embodiments of the invention have been disclosed in detail as being indicative of some of the ways in which the principles of the invention may be employed, but it is understood that the invention is not limited correspondingly in scope. Rather, the invention includes all changes, modifications and equivalents coming within the spirit and terms of the claims appended hereto. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

Brief Description of the Drawings

Fig. 1 is a drawing depicting a perspective view of an exemplary hydraulic pump in accordance with embodiments of the present invention, with the housing removed from the view. Fig. 2 is a drawing depicting a second perspective view of the exemplary hydraulic pump of Fig. 1 , with control piston and feedback piston cylinder components removed from the view.

Fig. 3 is a drawing depicting a top view of the exemplary hydraulic pump of

Fig. 1 .

Fig. 4 is a drawing depicting a side view of the exemplary hydraulic pump of

Fig. 1 , viewing on the displacement control assembly side.

Fig. 5 is a drawing depicting a side view of the exemplary hydraulic pump of Fig. 1 , viewing on the control piston side.

Fig. 6 is a drawing depicting a cross-sectional view through the displacement control assembly of the exemplary hydraulic pump of Fig 1 , with the swash plate at maximum displacement.

Fig. 7 is a drawing depicting a close-up view of the displacement control assembly portion of the hydraulic pump of Fig. 6.

Fig. 8 is a drawing depicting a close-up view of the displacement control assembly portion of the hydraulic pump of Fig. 6, being a view rotated 90° relative to Fig. 7.

Fig. 9 is a drawing depicting a cross-sectional view through the displacement control assembly of the exemplary hydraulic pump of Fig 1 , with the swash plate at minimum displacement. Fig. 10 is a drawing depicting a close-up view of the displacement control assembly portion of the hydraulic pump of Fig. 9.

Fig. 1 1 is a drawing depicting a close-up view of the displacement control assembly portion of the hydraulic pump of Fig. 9, being a view rotated 90° relative to Fig. 10.

Fig. 12 is a drawing depicting a cross-sectional view through the displacement control assembly of the exemplary hydraulic pump of Fig 1 , with the swash plate at maximum displacement during a failsafe mode of operation.

Fig. 13 is a drawing depicting a close-up view of the displacement control assembly portion of the hydraulic pump of Fig. 12.

Fig. 14 is a drawing depicting a close-up view of the displacement control assembly portion of the hydraulic pump of Fig. 12, being a view rotated 90° relative to Fig. 13.

Fig. 15 is a drawing depicting a close-up view of the portion of the

displacement control assembly as indicated by the indicator 15 in Fig. 14.

Detailed Description

Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale.

Figs. 1 -5 depict various views of an exemplary hydraulic pump 10 in accordance with embodiments of the present invention. Specifically, Fig. 1 is a drawing depicting a perspective view of the exemplary hydraulic pump 10 with the housing removed from the view. Fig. 2 is a drawing depicting a second perspective view of the exemplary hydraulic pump 10 of Fig. 1 , with control piston and feedback piston components removed from the view. Fig. 3 is a drawing depicting a top view of the exemplary hydraulic pump 10 of Fig. 1 . Fig. 4 is a drawing depicting a side view of the exemplary hydraulic pump 10 of Fig. 1 , viewing on the displacement control assembly side. Fig. 5 is a drawing depicting a side view of the exemplary hydraulic pump of Fig. 1 , viewing on the control piston side.

In exemplary embodiments, the hydraulic pump 10 is configured as an axial piston-type pump including a piston rotating group having a pump barrel and a plurality of reciprocating pistons housed within the pump barrel that interact against a displaceable swash plate. In particular, the hydraulic pump 10 may include a manifold 12 and a valve plate 13 against which a piston rotating group including a pump barrel 14 can rotate. The pump barrel 14 may house a rotating group of a plurality of pistons 16 that interact against a displaceable swash plate 18 that is configured to displace within a particular displacement angle range. As the piston rotating group rotates, the interaction of the pistons 16 against the swash plate 18 creates an axial motion of the pistons that forces hydraulic fluid through hydraulic porting to the downstream components of the system. For example, the manifold 12 may include porting and physical connection structures 20 for connecting fluid conduits such as hydraulic hose or tubing (not shown). An input shaft 22, which is driven by a prime mover, drives the rotation of the pump barrel 14 to pump the hydraulic fluid as described. As referenced above, the swash plate 18 may be tilted about a pivot axis within a displacement angle range, from between a maximum displacement angle generally on the order of 15 to 20 degrees for maximum flow, to a minimum displacement angle that is generally zero degrees. At zero degrees, there is no reciprocation of the pumping pistons in their respective bores, and therefore no output flow is produced. Figs. 1 -2 illustrate the swash plate in a displaced position of maximum displacement. A control piston 44 is configured to act on the swash plate 18 to control a displacement angle of the swash plate 18 within the displacement angle. Precise control of the positioning of the control piston is imperative so as to properly orient the swash plate to provide the desired flow rate. Accordingly, a displacement control assembly 26 is provided, which employs a mechanical feedback mechanism (described in more detail below) to precisely control the positioning of the control piston. In general, the displacement control assembly is configured to provide mechanical feedback control of positioning of the control piston, and the displacement control assembly is positioned non-coaxially relative to the control piston.

The displacement control assembly 26 includes a feedback cylinder 28 that houses a feedback piston that is located in a control bore and is configured to interact with the swash plate 18 cooperatively with the control piston. In other words, both the feedback piston and the control piston are configured to act on the swash plate. As further detailed below, the feedback piston acts as a follower piston relative to the control piston, and the feedback piston is located adjacent to the control piston. In the specific view of Fig. 2, the outer housing also is removed from the view.

In exemplary embodiments, the control piston and follower piston may both act on the swash plate 18 via a flatted pin 32, which may have a flatted face 34 and a rounded face 36 opposite to the flatted face. The feedback piston and the control piston are configured to act on the swash plate by acting on the flatted face of the flatted pin. Action of the pistons against the flatted face 34 causes the swash plate to pivot within the swashplate bearings 18a. As the swashplate pivots, the flatted pin rotates within slot 38, thereby maintaining surface contact between control piston/follower piston and flatted face 34 of pin 32. This minimizes contact pressure and wear, and minimizes side loading on the control and follower pistons. It will be appreciated that other mechanical means of transferring force to and from the swash plate may be utilized, but the flatted pin 32 is particularly suitable for use with the configuration of the displacement control assembly of the present invention.

Figs. 3-5 show the hydraulic pump including an additional outer housing 40. The outer housing 40 houses the pump barrel with the piston rotating group, and the swash plate and associated components. In addition, the housing 40 further houses components of the displacement control assembly.

Figs. 6-8 depict the hydraulic pump 10 in various cross-sectional views so as to illustrate the internal components, including the specific components of the displacement control assembly 26. Accordingly, like reference numerals are used to describe like components in Figs. 6-8 as in Figs. 1 -5. Fig. 6 is a drawing depicting a cross-sectional view through the displacement control of the exemplary hydraulic pump 10 of Fig 1 , with the swash plate at maximum displacement under a normal mode of operation. Fig. 7 is a drawing depicting a close-up view of the displacement control assembly 26 portion of the hydraulic pump 10 of Fig. 6. Fig. 8 is a drawing depicting a close-up view of the displacement control assembly 26 portion of the hydraulic pump of Fig. 6, being a view rotated 90° relative to Fig. 7.

As described above and reiterated with respect to the cross-sectional views, the hydraulic pump 10 may include a manifold 12 that includes the valve plate 13 against which the pump barrel 14 can rotate. The pump barrel 14 may include a rotating group of pistons 16 that interact against the displaceable swash plate 18 as described above. As the pump barrel 14 rotates, the interaction of the pistons 16 against the swash plate 18 creates an axial motion of the pistons that forces hydraulic fluid through hydraulic porting to the downstream components of the system. The input shaft 22 drives the rotation of the pump barrel 14 to pump the hydraulic fluid as described. Figs. 6-8 illustrate the swash plate in a displaced position of maximum displacement during a normal mode of operation. A control cylinder bore 24 machined into the housing 40 is best seen in the view shown in Fig. 8. The control cylinder bore houses the control piston 44 for controlling the displacement angle of the swash plate 18. The control piston 44 acts on the swash plate via the flatted pin 32, also shown in Figs. 7 and 8.

The details of the displacement control assembly 26 will now be described, which most readily are seen in the close-up views of Figs. 7 and 8. The

displacement control assembly 26 includes a control bore 50 and cross-drillings or ports machined into the housing 40, which houses in essentially a coaxial proximity a feedback piston 52, a feedback spring 54, a positioning spring 56, a control spool 58, and a control actuator 60. The displacement control assembly 26 is not coaxial with the control cylinder 24 including the control piston 44, but rather the displacement control assembly 26 is positioned adjacent to the control cylinder bore 24. The feedback piston 52 is moveable within control bore 50 machined into the housing 40 adjacent to the control cylinder bore 24, and the feedback piston is configured to act as a follower piston relative to the displacement of the control piston 44. In cooperation with the control piston 44, the feedback piston acts on the flatted face 34 of the flatted pin 32, with the flatted pin being configured to rotate via the rounded face 36 to effect the displacement of the swash plate (see particularly Fig. 7).

A sleeve 30 defines a bore for the movement of the control spool 58. The sleeve 30 may be configured as a stepped sleeve having a stepped outer diameter including a plurality of steps 31 , with the steps increasing in outward diameter from an end of the sleeve adjacent to the feedback piston 52 toward the control actuator 60. Sealing elements 33, such as o-ring or similar type annular seals, may be provided between adjacent steps of the sleeve 30 and the corresponding steps of the outer housing 40.

As referenced above, precise control of the positioning of the control piston is imperative so as to properly orient the swash plate. Accordingly, the displacement control assembly 26 employs a mechanical feedback mechanism to precisely control the positioning of the control piston. The feedback control is achieved by the positioning of control spool 58, which controls the flow of hydraulic fluid through porting to achieve a resultant fluid pressure associated with the positioning of the swash plate. The porting includes a supply port P in fluid communication with a supply of hydraulic fluid, a control port A that can provide a flow path of hydraulic fluid to and from the control piston, and a drain port A that can provide a drain of the hydraulic fluid to a tank or comparable low case pressure component. The P, A, and A' ports are labeled in the two close-up views of Figs. 7 and 8.

The control spool 58 is proportionally moveable between a first position and a second position corresponding to one or the other of increasing or decreasing the displacement angle of the swash plate. Accordingly, in exemplary embodiments the first position of the control spool corresponds to an increasing displacement of the swash plate, and the second position of the control spool corresponds to a

decreasing displacement of the swash plate. Figs. 6-8 depict the configuration of the displacement control assembly 26 with the control spool in the first position corresponding to increasing swash plate displacement. In normal operation, an end 61 of the control actuator moves the control spool 58 off of a seat 63.

The positioning of the control spool 58 is controlled by the counter-action of two opposing forces. The feedback spring 54 has a spring force that changes proportionally with the movement of the feedback piston. The first force thus is the spring force generated by the feedback spring 54, which tends to move the control spool in a first direction from the first position toward the second position (toward the right in Figs. 6-8). As the feedback spring force changes proportionally with the movement of the feedback piston, the spring force of the feedback spring 54 in turn is proportional to the displacement of the swash plate, as the swash plate

displacement angle ultimately is determinative of the degree of compression of the feedback spring. The second force is the opposing force generated by the control actuator 60, which tends to move the control spool in a second direction from the second position toward the first position (toward the left in Figs. 6-8). Accordingly, the feedback spring is configured to exert the spring force against a first end of the control spool, and the control actuator is configured to exert an actuator force against a second end of the control spool opposite the first end. A positioning of the control spool between the first position and the second position is determined based on a balance between the spring force and the actuator force acting on the control spool. The positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid to the control piston to provide mechanical feedback control of positioning of the control piston.

In exemplary embodiments, the control actuator 60 is a linear actuator, and more particularly a solenoid type linear actuator as depicted in the figures, the actuator force of which is proportional to the applied amperage. Alternatively, other means of providing a variable force such as a pressure supply acting on a piston could be utilized.

The second positioning spring 56 circumscribes the feedback spring 54, and the positioning spring 56 controls movement of the feedback piston 52 in response to abrupt changes in the position of the swash plate. In other words, the positioning spring 56 is configured as a biasing spring positioned coaxially outside of the feedback spring 54, which helps maintain contact between the feedback piston 52 and the swash plate at low displacement angles and during rapid changes of the swash plate displacement angle.

Figs. 9-1 1 are comparable to Figs. 6-8, except that Figs. 9-1 1 depict the hydraulic pump 10 with the swash plate at minimum (typically zero) displacement, which corresponds to the control spool being in the second position. Specifically, Fig. 9 is a drawing depicting a cross-sectional view of the exemplary hydraulic pump 10 of Fig 1 , with the swash plate at minimum displacement. Fig. 10 is a drawing depicting a close-up view of the displacement control assembly 26 portion of the hydraulic pump 10 of Fig. 9. Fig. 1 1 is a drawing depicting a close-up view of the displacement control assembly 26 portion of the hydraulic pump of Fig. 9, being a view rotated 90° relative to Fig. 10. Accordingly, the structures are essentially the same in Figs. 9-1 1 as in Figs. 6-8, with the positional configurations of the various components differing as corresponding to minimum displacement of the swash plate. The mechanical feedback control for precise positioning of the control piston is performed as follows. Generally, the positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid between the supply port P, the control port A, and the drain port A' to control the flow of hydraulic fluid to the control piston to provide positioning of the swash plate and therefore control of pump displacement. The control spool 58 meters flow to and from the control piston 44 via the control port A that may be placed in fluid communication with either the pressurized supply port P or the low case pressure or drain port A'. A user (or automated control mechanism) initiates a control signal as is conventional to energize the solenoid to achieve positioning of the control piston 44 to cause a corresponding resultant displacement of the swash plate as desired for a particular flow of hydraulic fluid through the pump. Depending on the change in displacement angle of the swash plate, the feedback piston acts as a follower piston that moves in response to movement of the control piston, which converts the angular

displacement or rotary motion of the swash plate to a linear motion of the feedback spring 54. This changes the amount of compression and thereby the spring force generated by the feedback spring 54, which in turn will change the positioning of the control spool 58. The resultant change in the positioning of the control spool 58 constitutes an error signal that initiates a feedback response based on the balance between the opposing feedback spring force and the solenoid force. In particular, the control spool 58 positioning alters flow of hydraulic fluid to the control piston 44 until the error is corrected, thereby achieving precise feedback control of the positioning of the control piston.

For example, as the control spool 58 moves in a first direction from the first position toward the second position (to the right in the figures) due to the feedback spring force of the feedback spring 54 being greater than the actuator force of the solenoid 60, the control spool 58 will begin metering flow from the pressurized supply port P to the control port A. This porting state with P-A in fluid communication feeds flow of hydraulic fluid to the control piston until the control piston moves sufficiently (to the left in the figures) to reduce the swash plate angle to balance the solenoid actuator force and the feedback spring force. At such position, the error becomes zero and the flow path P-A is shut by the control spool which is now balanced at its neutral or closed position. Conversely, as the control spool moves in a second direction opposite to the first direction from the second position toward the first position (to the left in the figures) due to the feedback spring force being less than the solenoid actuator force, the connection from the supply port P to the control port A is blocked, and the control port A is instead connected to the drain port A connected to a drain tank or similar low case pressure. This porting state with A-A' in fluid communication essentially connects the control piston 44 to the low case pressure, and when the control piston is connected to the low case pressure, the control piston will move oppositely (to the right in the figures) due to the stroke-increasing moment created on the swash plate by the pumping pistons of the piston rotating group, or bias piston or other biasing device, which increases the swash plate displacement angle. When the swash plate displacement angle increases sufficiently to cause the feedback spring force to equal the solenoid force, the error again becomes zero, and the control spool shuts off the flow path A-A from the control port to the drain port (low case pressure). In this manner, a mechanical feedback is employed to provide for precise positioning of the control piston 44, and in turn precise angular displacement of the swash plate.

To prevent loss of hydraulic power in the event of an electrical failure, it is often desirable for the default position of the swash plate to be at maximum

displacement. A third spool position is provided corresponding to a failsafe mode of operation. To prevent loss of hydraulic power in the event of an electrical failure, it is often desirable for the default position of the swash plate to be at maximum

displacement. This may occur, for example, in the case of an electrical failure in which power to the solenoid 60 fails. The displacement control assembly, therefore, is configured to operate in a third failsafe state in the event power is removed from the solenoid.

The failsafe mode of operation associated with the third spool position is depicted in Figs. 12-14. The configuration of Figs 12-14 has a significant difference as compared to the maximum displacement under normal operation depicted in Figs. 6-8. In the failsafe mode of operation of Figs. 12-14, the end 61 of the control actuator is fully retracted within the space defined by the seat 63. With such configuration, the end 59 of the spool 58 now presses directly against the seat 63.

Fig. 15 is a drawing depicting a close-up view of the portion of the

displacement control assembly as indicated by the indicator 15 in Fig. 14. If power is removed from the solenoid, a third spool state is utilized whereby the supply port P again is blocked from the control port A, and the control port is vented to the low case pressure via a small flow path or orifice 62 (see Fig. 15) that opens up to provide a drain of hydraulic fluid to the drain port A' (low case pressure) when the control actuator is deactuated. In such case, the control spool 58 travels to its biased position under the feedback spring force, and which moves the swash plate 18 to maximum displacement. This configuration is used for applications requiring the hydraulic pump 10 to default to maximum displacement in the event of an electrical failure. In this mode, a check valve (not shown) allows for pressure behind the control piston 44 to be controlled by external flow to and from an external maximum pressure compensator valve 42.

The configuration of the present invention has significant advantages over conventional configurations. The control spool 58 being balanced by low case pressure on both ends reduces the sensitivity and increases repeatability of the control over a control spool that is balanced by a variable pressure such as control pressure. The stepped control sleeve design reduces seal complexity and likelihood of seals being cut during installation of the sleeve into the housing. Both ends of the control spool are acted on by case pressure and not control pressure, which allows for a less costly solenoid tube to be utilized. Positioning the displacement control assembly adjacent to the control piston also enables a more robust control piston/housing interface that is less sensitive to wear and excess leakage due to its relatively longer length of engagement. In addition, the mechanical feedback control provides a simple and cost-effective control mechanism as compared to more complex direct electronic feedback control mechanisms. An aspect of the invention, therefore, is a hydraulic pump. In exemplary embodiments, the hydraulic pumps includes a displaceable swash plate that is configured to displace within a displacement angle range, a piston rotating group comprising a plurality of reciprocating pistons configured to interact against the swash plate to pump hydraulic fluid, a control piston configured to act on the swash plate to control a displacement angle of the swash plate within the displacement angle range, and a displacement control assembly configured to provide mechanical feedback control of positioning of the control piston, wherein the displacement control assembly is positioned non-coaxially relative to the control piston. The hydraulic pump may include one or more of the following features, either individually or in combination.

In an exemplary embodiment of the hydraulic pump, the displacement control assembly includes a feedback piston configured to act as a follower piston relative to the control piston, and the feedback piston is located adjacent to the control piston.

In an exemplary embodiment of the hydraulic pump, the feedback piston and the control piston both are configured to act on the swash plate.

In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes a flatted pin which has a flatted face and a rounded face opposite the flatted face. The feedback piston and the control piston are configured to act on the swash plate by acting against the flatted face of the flatted pin, the flatted pin rotates within a slot by the action of the control piston and the feedback piston, and the rotation of the flatted pin is converted into displacement of the swash plate.

In an exemplary embodiment of the hydraulic pump, the displacement control assembly includes a feedback piston that is moveable within a cylinder adjacent to the control piston and acts as a follower piston relative to the control piston, a feedback spring having a spring force that changes proportionally with the movement of the feedback piston, a control spool that is moveable between a first position and a second position, and a control actuator. The feedback spring is configured to exert the spring force against a first end of the control spool, and the control actuator is configured to exert an actuator force against a second end of the control spool opposite the first end. A positioning of the control spool between the first position and the second position is determined based on a balance between the spring force and the actuator force acting on the control spool. The positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid to the control piston to provide the mechanical feedback control of positioning of the control piston.

In an exemplary embodiment of the hydraulic pump, the control spool is in fluid communication with a supply port that is in fluid communication with a supply of hydraulic fluid, with a control port that is configured to provide a flow path of hydraulic fluid to the control piston, and with a drain port that is in fluid

communication with a low case pressure. The positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid among the supply port, the control port, and the drain port to control the flow of hydraulic fluid to the control piston to provide the mechanical feedback control of the positioning of the control piston. In an exemplary embodiment of the hydraulic pump, the displacement control assembly is configured to perform the mechanical feedback control of the positioning of the control piston. When the spring force of the feedback spring is greater than the actuator force of the control actuator, the control spool moves in a first direction from the first position toward the second position, thereby generating an error signal. The control spool begins metering flow from the supply port to the control port. The supply port in fluid communication with the control port feeds flow of hydraulic fluid to the control piston until the control piston moves sufficiently to change the swash plate angle to balance the actuator force and the feedback spring force. At a position of the control spool corresponding to the balance between the actuator force and the feedback spring force, the error becomes zero and the flow path from the supply port to the control port is shut by the control spool.

In an exemplary embodiment of the hydraulic pump, the displacement control assembly is configured to perform the mechanical feedback control of the positioning of the control piston further as follows. When the spring force of the feedback spring is less than the actuator force of the control actuator, the control spool moves in a second direction from the second position toward the first position, thereby generating an error signal. The control spool begins metering flow from the control port to the drain port. The control port in fluid communication with the drain port connects the control piston to the low case pressure until the control piston moves sufficiently to change the swash plate angle to balance the actuator force and the feedback spring force. At a position of the control spool corresponding to the balance between the actuator force and the feedback spring force, the error becomes zero and the flow path from the control port to the drain port is shut by the control spool. In an exemplary embodiment of the hydraulic pump, the first position corresponds to the swash plate being at a maximum displacement angle, and the moving of the control spool in the first direction results in the control piston acting to reduce the swash plate angle. In an exemplary embodiment of the hydraulic pump, the second position corresponds to the swash plate being at a minimum displacement angle, and the moving of the control spool in the second direction results in the control piston acting to increase the swash plate angle. In an exemplary embodiment of the hydraulic pump, the positioning of the control spool is balanced by case pressure.

In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes a flatted pin which has a flatted face and a rounded face opposite the flatted face. The feedback piston and the control piston are configured to act on the swash plate by acting against the flatted face of the flatted pin, the flatted pin rotates within a slot by the action of the control piston and the feedback piston, and the rotation of the flatted pin is converted to displacement of the swash plate. In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes a sleeve, and the control spool is housed coaxially within a bore defined by the sleeve.

In an exemplary embodiment of the hydraulic pump, the sleeve has a stepped outer diameter including a plurality of steps. In an exemplary embodiment of the hydraulic pump, the steps increase in outward diameter from an end of the sleeve adjacent to the feedback piston toward the control actuator.

In an exemplary embodiment of the hydraulic pump, sealing elements are provided between adjacent steps of the sleeve and an outer housing of the hydraulic pump.

In an exemplary embodiment of the hydraulic pump, the control actuator is a linear actuator.

In an exemplary embodiment of the hydraulic pump, the control actuator is a solenoid actuator. In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes a positioning spring configured as a biasing spring for the movement of the feedback piston.

In an exemplary embodiment of the hydraulic pump, the positioning spring is positioned coaxially around the feedback spring.

In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes an orifice that is configured to open to a low case pressure when the control actuator is de-actuated. The orifice provides a drain of hydraulic fluid, and the spring force of the feedback spring is biased to move the swash plate to maximum displacement when the orifice is open.

In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes a manifold including a pump running face against which the piston rotating group rotates, and including porting configured to communicate hydraulic fluid through the hydraulic pump. In an exemplary embodiment of the hydraulic pump, the hydraulic pump further includes an input shaft configured to drive rotation of the piston rotating group to pump the hydraulic fluid.

Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and

understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

Claims What is claimed is:

1 . A hydraulic pump comprising:

a displaceable swash plate that is configured to displace within a

displacement angle range;

a piston rotating group comprising a plurality of reciprocating pistons configured to interact against the swash plate to pump hydraulic fluid;

a control piston configured to act on the swash plate to control a displacement angle of the swash plate within the displacement angle range; and

a displacement control assembly configured to provide mechanical feedback control of positioning of the control piston, wherein the displacement control assembly is positioned non-coaxially relative to the control piston.

2. The hydraulic pump of claim 1 , wherein the displacement control assembly includes a feedback piston configured to act as a follower piston relative to the control piston, and the feedback piston is located adjacent to the control piston.

3. The hydraulic pump of claim 2, wherein the feedback piston and the control piston both are configured to act on the swash plate.

4. The hydraulic pump of claim 3, further comprising a flatted pin which has a flatted face and a rounded face opposite the flatted face; wherein:

the feedback piston and the control piston are configured to act on the swash plate by acting against the flatted face of the flatted pin;

the flatted pin rotates within a slot by the action of the control piston and the feedback piston; and

the rotation of the flatted pin is converted into displacement of the swash plate.

5. The hydraulic pump of claim 1 , wherein the displacement control assembly comprises:

a feedback piston that is moveable within a cylinder adjacent to the control piston and acts as a follower piston relative to the control piston; a feedback spring having a spring force that changes proportionally with the movement of the feedback piston;

a control spool that is moveable between a first position and a second position; and

a control actuator;

wherein:

the feedback spring is configured to exert the spring force against a first end of the control spool, and the control actuator is configured to exert an actuator force against a second end of the control spool opposite the first end;

a positioning of the control spool between the first position and the second position is determined based on a balance between the spring force and the actuator force acting on the control spool; and

the positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid to the control piston to provide the

mechanical feedback control of positioning of the control piston.

6. The hydraulic pump of claim 5, wherein:

the control spool is in fluid communication with a supply port that is in fluid communication with a supply of hydraulic fluid, with a control port that is configured to provide a flow path of hydraulic fluid to the control piston, and with a drain port that is in fluid communication with a low case pressure; and

the positioning of the control spool between the first position and the second position controls a flow of hydraulic fluid among the supply port, the control port, and the drain port to control the flow of hydraulic fluid to the control piston to provide the mechanical feedback control of the positioning of the control piston.

7. The hydraulic pump of claim 6, wherein the displacement control assembly is configured to perform the mechanical feedback control of the positioning of the control piston comprising:

when the spring force of the feedback spring is greater than the actuator force of the control actuator, the control spool moves in a first direction from the first position toward the second position, thereby generating an error signal;

the control spool begins metering flow from the supply port to the control port; the supply port in fluid communication with the control port feeds flow of hydraulic fluid to the control piston until the control piston moves sufficiently to change the swash plate angle to balance the actuator force and the feedback spring force; and

at a position of the control spool corresponding to the balance between the actuator force and the feedback spring force, the error becomes zero and the flow path from the supply port to the control port is shut by the control spool.

8. The hydraulic pump of claim 7, wherein the displacement control assembly is configured to perform the mechanical feedback control of the positioning of the control piston further comprising:

when the spring force of the feedback spring is less than the actuator force of the control actuator, the control spool moves in a second direction from the second position toward the first position, thereby generating an error signal;

the control spool begins metering flow from the control port to the drain port; the control port in fluid communication with the drain port connects the control piston to the low case pressure until the control piston moves sufficiently to change the swash plate angle to balance the actuator force and the feedback spring force; and

at a position of the control spool corresponding to the balance between the actuator force and the feedback spring force, the error becomes zero and the flow path from the control port to the drain port is shut by the control spool.

9. The hydraulic pump of claim 8, wherein the first position corresponds to the swash plate being at a maximum displacement angle, and the moving of the control spool in the first direction results in the control piston acting to reduce the swash plate angle.

10. The hydraulic pump of claim 9, wherein the second position

corresponds to the swash plate being at a minimum displacement angle, and the moving of the control spool in the second direction results in the control piston acting to increase the swash plate angle.

1 1 . The hydraulic pump of any of claims 5-10, wherein the positioning of the control spool is balanced by case pressure.

12. The hydraulic pump of any of claims 5-1 1 , wherein the feedback piston and the control piston both are configured to act on the swash plate.

13. The hydraulic pump of claim 12, further comprising a flatted pin which has a flatted face and a rounded face opposite the flatted face; wherein:

the rotation of the flatted pin is converted to displacement of the swash plate.

14. The hydraulic pump of any of claims 5-13, further comprising a sleeve, and the control spool is housed coaxially within a bore defined by the sleeve.

15. The hydraulic pump of claim 14, wherein the sleeve has a stepped outer diameter including a plurality of steps.

16. The hydraulic pump of claim 15, wherein the steps increase in outward diameter from an end of the sleeve adjacent to the feedback piston toward the control actuator.

17. The hydraulic pump of any of claims 15-16, wherein sealing elements are provided between adjacent steps of the sleeve and an outer housing of the hydraulic pump.

18. The hydraulic pump of any of claims 5-17, wherein the control actuator is a linear actuator.

19. The hydraulic pump of any of claims 5-18, wherein the control actuator is a solenoid actuator.

20. The hydraulic pump of any of claims 5-19, further comprising a positioning spring configured as a biasing spring for the movement of the feedback piston.

21 . The hydraulic pump of claim 20, wherein the positioning spring is positioned coaxially around the feedback spring.

22. The hydraulic pump of any of claims 5-21 , further comprising an orifice that is configured to open to a low case pressure when the control actuator is de- actuated;

wherein the orifice provides a drain of hydraulic fluid, and the spring force of the feedback spring is biased to move the swash plate to maximum displacement when the orifice is open.

23. The hydraulic pump of any of claims 1 -22, further comprising a manifold including a valve plate against which the piston rotating group rotates, and including porting configured to communicate hydraulic fluid through the hydraulic pump.

24. The hydraulic pump of any of claim 1 -23, further comprising an input shaft configured to drive rotation of the piston rotating group to pump the hydraulic fluid.