Patent Application
20120048105
The present invention generally relates to axial piston pumps, and more particularly relates to an auxiliary cam plate and auxiliary cam retainer that are configured to induce lubrication of the auxiliary cam plate-to-auxiliary cam retainer interface.
Axial piston pumps are used in myriad systems and environments. An axial piston pump generally includes a housing, a rotor, a port plate, a hanger (or swash plate), and an auxiliary cam assembly. The rotor is rotationally mounted within the housing, and has a number of piston bores formed therein. A piston is movably inserted into each one of the piston bores. The port plate is non-rotationally mounted within the housing adjacent one end of the rotor, and includes a low-pressure side and a high-pressure side. The hanger is also non-rotationally mounted in the housing but may be allowed to pivot about a central axis ninety degrees from the rotor axis. The hanger is disposed at an opposite end of the rotor and at an angle relative to the rotational axis of the rotor. The auxiliary cam assembly is coupled to the angularly disposed hanger and to each of the pistons.
With the above-described configuration, when the rotor is rotated the auxiliary cam assembly successively pulls the pistons from, while the hanger pushes the pistons back into, the piston bores. More specifically, pump is configured so that the pistons are pulled from the piston bores on the low pressure side of the port plate, thereby drawing fluid into the bores, and are pushed into the piston bores on the high pressure side of the port plate, thereby forcing fluid out of the piston bores.
The auxiliary cam assembly includes an auxiliary cam plate and an auxiliary cam retainer. The auxiliary cam plate is mounted on, and rotates with, the shaft, and includes a plurality of piston openings into which an end of each piston is inserted. The ends of each piston are retained via piston shoes that are inserted, one each, into a piston opening. The back flange of each piston shoe reacts its load on the auxiliary cam plate when its associated piston is being pulled from the piston bore. The rotating auxiliary cam plate reacts this load and that of the other pistons onto the auxiliary cam retainer. The auxiliary cam retainer is non-rotationally mounted within the housing or the hanger, and engages the auxiliary cam plate near its periphery.
The interface of the auxiliary cam plate and the auxiliary cam retainer can wear and significantly impact overall pump reliability. Hence, it is desirable to lubricate this interface. The fluid surrounding the interface is at relatively low case pressure. Simply relying on leakage of fluid into the interface is insufficient to provide adequate lubrication at operating conditions. Presently, known means of providing adequate lubrication involve the undesirable use of extensive channeling and/or galleries.
Hence, there is a need for providing a way to adequately lubricate the interface of the auxiliary cam plate and auxiliary cam retainer in an axial piston pump that does not rely on extensive channeling and/or galleries. The present invention addresses at least this need.
In one embodiment, an auxiliary cam assembly for an axial piston pump includes an auxiliary cam plate and an auxiliary cam retainer. The auxiliary cam plate is configured to be coupled to a rotatable shaft and includes a main body having a first side, a second side, and an outer peripheral surface. A central shaft opening extends between the first side and the second side for receiving the rotatable shaft. A plurality of piston openings surround the central opening and extend between the first side and the second side. Each piston opening is for receiving at least a portion of a piston. A circumferential cut is formed in and extends around the outer peripheral surface of the auxiliary cam plate. The auxiliary cam retainer has an engagement side, a non-engagement side, an inner peripheral surface, and an outer peripheral surface. At least a portion of the engagement side contacts the auxiliary cam plate first side. A plurality of ramps are formed in the engagement side. Each ramp slopes upwardly from a first end to a second end. A plurality of substantially flat pads are integrally formed on the engagement side and are disposed between each of the ramps. Each substantially flat pad extends between the first end of one ramp and the second end of another ramp.
In another embodiment, an axial piston pump includes a pump housing, a rotor, a plurality of pistons, a hanger, an auxiliary cam plate, and an auxiliary cam retainer. The rotor is rotationally mounted within the pump housing, and includes a shaft and a plurality of axial piston bores. The rotor is configured, upon receipt of an input torque on the shaft, to rotate about a rotational axis. Each piston is movably disposed within, and extends from, one of the plurality of axial piston bores. The hanger is non-rotationally mounted within the pump housing and has a opening through which the shaft extends. The hanger is disposed at an angle relative to the rotational axis. The auxiliary cam plate is disposed adjacent the hanger, and is coupled to the shaft and configured to rotate therewith. The auxiliary cam plate includes a main body having a first side, a second side, and an outer peripheral surface. A central opening extends between the first side and the second side, and the shaft extends through the central opening. A plurality of piston openings surround the central opening and extend between the first side and the second side. Each piston extends at least partially into one of the piston openings. A circumferential cut is formed in and extends around the outer peripheral surface of the auxiliary cam plate. The auxiliary cam retainer is coupled to the hanger and has an engagement side, a non-engagement side, an inner peripheral surface, and an outer peripheral surface. At least a portion of the engagement side contacts the auxiliary cam plate first side. A plurality of ramps are formed in the engagement side, and each ramp slopes upwardly from a first end to a second end. A plurality of substantially flat pads are integrally formed on the engagement side and are disposed between each of the ramps. Each substantially flat pad extends between the first end of one ramp and the second end of another ramp.
Furthermore, other desirable features and characteristics of the axial piston pump and auxiliary cam assembly will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.
Referring first to
The rotor 104 is rotationally mounted within the pump housing 102 via a rotor bearing 112, and includes a shaft 114 and a plurality of axial piston bores 116. It will be appreciated that the shaft 114 may be formed integrally with the rotor 104, or formed separate from the rotor 104 and subsequently coupled thereto. In either case, it is seen that the shaft 114 is also preferably rotationally supported in the pump housing 102 via a thrust bearing 118. The shaft 114 is adapted to receive an input torque from a suitable torque source, such as a motor or engine. The rotor 104 is configured, upon receipt of the input torque on the shaft 114, to rotate about a rotational axis 122.
The axial piston bores 116 each include a fluid port 124 through which fluid ingresses and egresses during operation of the pump 100. The fluid that ingresses and egresses the fluid ports 124 does so via the port plate 106, which includes a fluid inlet port 126 and a fluid outlet port 128. The fluid inlet port 126 and fluid outlet port 128 are in fluid communication with a fluid inlet passage 132 and a fluid outlet passage 134, respectively, formed in the lower section 101 of the pump housing 102.
The pistons 108 are each movably disposed in, and extend partially from, one of the axial piston bores 116. Each piston 108 includes a first end 136, a second end 138, and an internal fluid passage 142 that extends between the first and second ends 136, 138. The internal fluid passage 142, as will be described further below, allows a portion of the fluid that is drawn into and discharged from the axial piston bores 116 to flow out the piston second end 138 and act as a lubricant.
The second end 138 of each piston 108 is coupled to the hanger assembly 110, which has an opening 144 through which the shaft 114 extends. As
The hanger assembly 110 includes a hanger 202 and an auxiliary cam assembly 204. The hanger 202 is non-rotationally mounted within the pump housing 102. As is generally known, the angle at which the hanger 202 (and concomitantly the auxiliary cam assembly 204) is disposed, determines the overall stroke of the pistons 108 and thus the flow rate of the pump 100. In the embodiment depicted in
The auxiliary cam assembly 204, at least in the depicted embodiment, includes a cam plate 208, an auxiliary cam plate 212, and an auxiliary cam retainer 214. The cam plate 208 is fixedly coupled within the recess 206, and provides a surface 216 that piston shoes 218 movably engage. The piston shoes 218 (for clarity, only one depicted in
The auxiliary cam plate 212 is mounted on, and rotates with, the shaft 114. More specifically, and as shown more clearly in
The auxiliary cam retainer 214 is coupled to the hanger 202 and thus, like the hanger 202, is non-rotationally mounted within the pump housing 102. With reference to
During operation of the pump 100, as each piston 108 is being pulled from its associated piston bore 116, the load on each associated piston shoe 218 is reacted onto the rotating auxiliary cam plate 212. This load, and that of the other pistons 108, is in turn reacted onto the auxiliary cam retainer engagement side 602. As will now be described in more detail, the auxiliary cam plate 212 and auxiliary cam retainer 214 are configured such that the fluid within the pump housing 102, which is at a relatively low pressure, lubricates the interface of the auxiliary cam plate 212 and auxiliary cam retainer 214.
The auxiliary cam retainer 214, and more specifically the engagement side 602 of the auxiliary cam retainer 214, has a plurality of ramps 614 formed therein, and a plurality of substantially flat pads 616 integrally formed thereon. As shown more clearly in
The ramps 614 are also preferably formed to slope upwardly from the first end 802 to the second end 804 at a predetermined, fixed angle (θ). This predetermined, fixed angle may vary, but is preferably in the range of 8 to 20 arc minutes, with 7-10 arc minutes being more preferred, and 10 arc minutes being most preferred. It is further noted that the ramps 614 preferably slope upwardly in the direction of rotation of the auxiliary cam plate 212. Thus, as
Returning once again to
It is on the top of each of the substantially flat pad 616 where the resulting hydrodynamic fluid film supports the load of the rotating auxiliary cam plate 212 during operation. Each pad 616 is preferably formed with an equal, predetermined circumferential width (Wc) (see
The above-described ramps 614 and pads 616 that are formed in the auxiliary cam retainer 214 facilitate fluid induction and the formation of a hydrodynamic layer between the auxiliary cam plate 212 and auxiliary cam retainer 214. However, the auxiliary cam plate 212 and auxiliary cam retainer 214 are asymmetrically loaded during pump operation. As a result, the fluid that could form the hydrodynamic fluid film is bled off, thereby eliminating the effectiveness of the ramps 614 and pads 616. To alleviate this effect, the compliance of auxiliary cam plate 212 is controlled.
More specifically, and with reference to
No matter the specific configuration of the circumferential cut 404, it is noted that the predetermined depth (D) may vary, and is selected to provide the desired compliance. It is additionally selected so that the circumferential cut 404 does not penetrate into the piston openings 312, and at least overhangs the inner peripheral surface 604 of the auxiliary cam retainer 214. Though not depicted, in some embodiments, circumferential cut 404 may be scalloped between piston openings 312 to enhance compliance control. It will nonetheless be appreciated that the specific configuration and dimensions of the circumferential cut 404 may be determined on a case-by-case basis to achieve the desired compliance, and thereby assure that the auxiliary cam plate 212 and auxiliary cam retainer 214 are maintained sufficiently parallel to allow the pads 616 to create a load carrying hydrodynamic fluid film.
The auxiliary cam plate 212 and auxiliary cam retainer 214 described herein together provide a means to adequately lubricate the interface of these components that does not rely on extensive channeling and/or galleries. The specific configuration and dimensions of these components may be varied to attain the desired lubricity using lubricating fluids of varying viscosity.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
