Patent Application
20130152779
The present disclosure relates to pump assemblies and, more particularly, to a shaft arrangement for axial piston pump assemblies to withstand axial and radial loads.
Axial piston pumps are known to be used in hydraulically-actuated fuel injection systems. One exemplary axial piston pump is a hydraulic electronic unit injector (HEUI) pump assembly. The efficient operation of such pumps is significant to the overall operation of the engine. Moreover, the ability of such pumps to operate free of maintenance is important to reduce downtime of the system. While efficient operation is an important design criteria, issues such as weight, size, cost, and ease of assembly influence the overall design of such pump.
U.S. Pat. No. 6,035,828 to Anderson et al., which is incorporated herein by reference in its entirety, describes a fixed displacement, variable delivery axial piston pump for a hydraulically-actuated fuel injection system. In the system, a high pressure common rail supplies hydraulic fluid to a plurality of hydraulically-actuated fuel injectors mounted in a diesel engine. The hydraulic fluid received in the common rail is pressurized by the fixed displacement axial piston pump that is driven directly by the engine. The pump includes a plurality of pistons disposed in parallel about the central longitudinal axis of the pump. An angled camming surface or swash plate is fixed to the drive shaft and is biased against a proximal end of the pistons. Low pressure actuation fluid (e.g., lubricating oil) flows through windows in the radial outer surface of a swash plate and travels radially inward to the pistons in order to be pressurized. Reciprocation of the pistons is achieved by the rotation of the swash plate. Displacement of the pump is varied by a control valve that selectively varies the amount of pressurized fluid supplied to the pump outlet during the discharge stroke of each piston. FIG. 2 of Anderson et al. illustrates two opposed tapered roller bearing arrangements for receiving axial forces created during pump operation.
In another example, U.S. Pat. No. 6,896,491 to Trubnikov et al., which is incorporated herein by reference in its entirety, describes a fixed displacement, variable delivery axial piston pump for a hydraulically-actuated fuel injection system. Here, the fixed angle swash plate can include a cylindrical elongated portion. The elongated portion can be press-fitted over the center pump drive shaft for a secure fit. The end of the elongated portion can be a tapered end. The tapered end can frictionally engage a conical recess of gear drive mechanism such that the rotation of the center pump drive shaft is directly proportionally to the drive shaft of the engine.
While the aforementioned axial piston pump assemblies operate adequately, there is a need for an improved shaft arrangement to sufficiently withstand the rotational gear loads and the axial thrust loads. The present application is directed at overcoming one or more of the problems associated with axial piston pump assemblies of the prior art.
In one embodiment, a pump assembly is described herein for coupling to a rotatable member, such as, e.g., a gear to couple to an external drive shaft. A center shaft can extend at least partially through a housing chamber of a pump housing and is rotatable about a longitudinal axis. A plurality of reciprocating pistons can be disposed within the housing chamber radially about the center shaft. A cam unit can include a cam body and a central bore extending through the cam body about the longitudinal axis to receive a portion of the center shaft. A distal end of the cam unit can have a camming surface that extends radially outward from the cam body to engage each of the reciprocating pistons. One or more bearing assemblies can be disposed along the cam body between the distal and proximal ends of the cam unit. An adapter has a central opening extending therethrough about the longitudinal axis to engage the proximal end of the cam unit. A distally facing surface of the adapter can abut the most proximate bearing assembly. The distally facing surface may be spaced from a proximally facing surface of a shoulder portion of the cam unit. An outer radial surface of the adapter can engage the rotatable member. A clamping device is insertable through the central opening of the adapter and the central bore of the cam unit to fixedly attach to the center shaft.
In another embodiment, a method of connecting a rotatable member such as, e.g., a gear, to a pump assembly. An adapter can be coupled to the rotatable member via a conical friction interface. A bearing assembly can be coupled to the adapter such that a distal surface of the adapter is in an abutting relationship with the bearing assembly. The adapter can be fitted over a proximal end of a cam unit such that a gap is formed between the distal surface of the adapter and a confronting proximal surface of the cam unit. A distal end of the cam unit can include an angled camming surface in engagement with a plurality of pistons contained within the pump assembly.
Reference will now be made in detail to the exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Referring now to
As is well known in the art, the desired pressure in the common rail 12 is generally a function of the engine's operating condition. For instance, at high speeds and loads the rail pressure is generally desired to be significantly higher than the desired rail pressure when the engine is operating at an idle condition. One or more engine operating condition sensors 23 may be coupled to the engine at various locations to provide an electronic control module 15 with data through communication lines 24. Sensor(s) 23 may detect one or more engine parameters including, for example, engine speed, engine crankshaft position, engine coolant temperature, engine exhaust back pressure, air intake manifold pressure, throttle position, or any combination thereof. In addition, a pressure sensor 21 may provide the electronic control module 15 with a measure of the fluid pressure in the high pressure common rail 12 via a communication line 22. The electronic control module 15 may be designed to compare a desired rail pressure, which is a function of the engine operating condition, with the actual rail pressure as measured by the pressure sensor 21.
If the desired and measured rail pressures are different, the electronic control module 15 may command movement of a fluid delivery control assembly 17, such as a control valve, via a communication line 18. The position of the control assembly 17 facilitates in determining the amount of working fluid that leaves the pump 16 via the high pressure supply line 19 and goes to the common rail 12. Both of the control assembly 17 and the pump 16 may be contained in a single stationary pump housing 30. Further, the electronic control module 15 may be coupled to each fuel injector 13 via a communication line (not shown) to provide control signals to the working fluid valves of each fuel injector 13 to control the timing and duration of each fuel injection.
Referring now to
The pump housing 30 may also include a shaft opening 40 at its proximal gear end 42 and an outlet passage (not shown) at its distal end 46. The shaft opening 40 may communicate with the housing chamber 32 and receive a portion or an extension of the center shaft 34 therethrough. The outlet passage may communicate with the high pressure supply conduit 19 (
A cam unit 50 can be coupled to the center shaft 34 and is operable to cause a plurality of pistons 60 to reciprocate with relative movement between the cam unit and the pistons. The cam unit 50 can include a cam body 52 and a central bore 54 extending therethrough about the longitudinal axis LA. The central bore 54 is sized to receive a portion of the center shaft 34. The central bore 54 may include a counterbore arrangement. For example, in
The cam unit 50 can include a camming surface 56 at its first, distal end 50A to engage with each of the pistons 60. The camming surface 56 can extend radially outward relative to a cylindrical portion of the cam body, and may be positioned about the distal portion 54A of the central bore 54. The camming surface 56 may be shaped to have a fixed angle relative to the longitudinal axis LA. Relative rotation between the camming surface 56 of the cam unit 50 and the pistons 60 can cause the pistons 60 to reciprocate from left to right (when viewing the pistons as illustrated in
In
Referring back to
In one example, the pistons 60 can engage the camming surface 56 via a coupling configuration to allow for angular movement between the piston 60 and the camming surface 56, but not relative axial movement between the piston and the camming surface. In one example, the axial engaging end 61 of the pistons 60 may be coupled to a piston shoe 64, as shown in
A biasing plate 66 can be disposed about the shoes 64 to facilitate maintaining the shoes 64 in contact with the camming surface 56. In one example, the distal end 65 of the shoe 64 may include a recess or groove thereon to receive the biasing plate 66. The biasing plate 66 may include a plurality of shoe holes 67 formed therein spaced, such as, e.g., equally spaced, about a center hole 68 of the biasing plate 66 that is sized for receiving the center shaft 34. The shoe holes 67 of the biasing plate 66 may be configured to allow the shoes 64 to extend therethrough for the length of recess or groove of the shoe 64. The center hole 68 of the biasing plate 66 may be shaped, such as, e.g., to include a rounded portion, for receiving a similarly shaped rounded protrusion 34A of the center shaft 34. The rounded portion of the center hole 68 may be located on a more distal side of the biasing plate 66. A shaft compression spring (not shown) may extend between a portion of the pump housing 30 and a portion of the center shaft 34 to bias the rounded protrusion 34A of the center shaft 34 into the rounded portion of the center hole 68 of the biasing plate 66 and against the biasing plate. This, in turn, can urge the biasing plate 66 and the shoes 64 against the pump housing 30. Any other suitable arrangement of elements may be used to bias the pistons and the shoes against the pump housing.
The biasing force of the return spring 62 of the piston 60 can maintain the coupling between the shoes 64 and the respective proximal ends 61 of the pistons 60 to maintain contact with the camming surface 56 in a conventional manner. Because the camming surface 56 may have a fixed angle relative to the longitudinal axis LA, the pistons 60 can reciprocate through a fixed reciprocation distance with each cycle of rotation of the center shaft 34. Thus, the pump 16 can be thought of as a fixed displacement pump. However, the control valve 17 is configured to determine whether the fluid displaced by the pump 16 is either pushed into a high pressure area 75 (shown in dashed lines) within the pump housing in communication with the high pressure supply conduit 19 past a check valve (not shown) or spilled or leaked back into a low pressure area 76 via a spill port 77. The low pressure area 76 can be a portion of the housing chamber 32 containing a source of low pressure fluid 14. The low pressure fluid, which can be, e.g., the engine's lubricating oil sump, can be in fluid communication with the low pressure supply conduit 20.
In
In
The aforesaid connection of elements can provide for movement of the control sleeves 90 to cover or uncover the radial spill ports 77 formed in the pistons 60 based on movement of the sleeve actuator in a proximal or distal direction. To this end, the pressure within the piston bore 82 can only build when the shoe bore 84 is covered by the camming surface 56 and the spill ports 77 are covered by the sleeve 90. Thus, when the sleeve 90 covers the respective spill ports 77, fluid displaced by movement of the piston 90 can be pushed past the check valve, into the high pressure area 75 and eventually out of the outlet to the high pressure common rail 12.
In
The gear adapter body 100 may include a distal surface 110 to capture one or more bearing assemblies (shown as a pair of bearing assemblies 120A, 120B) between the distal surface 110 and a proximal surface 112 of the distal end 50A of the cam unit 50 disposed opposite to the distally facing camming surface 56. In one example, the pair of surfaces 110, 112 extend substantially perpendicular relative to the longitudinal axis in a confronting relationship with one another.
With reference to
The bearing assembly is coupled within the housing chamber 32 and is operable to support the rotation of the center shaft 34. The illustrated first bearing assembly 120A can be a tapered roller bearing assembly that includes an inner race or cone 122 for engagement with the center shaft 34, an outer race or cup 124 for engagement with the housing 30, and a plurality of rollers 126 disposed between the inner race 122 and the outer race 124. When employed, the second bearing assembly 120B may be similarly configured having an inner race 130, outer race 132, and rollers 134 therebetween. However, each of bearing assemblies may be embodied as any conventional bearing structure, and may be the same or different bearing configurations. A single bearing assembly or more than one bearing assemblies can support the center shaft 34 for rotation within and relative to the pump housing 30.
In one example, the first bearing assembly 120A and the second bearing assembly 120B may be tapered in the opposite direction to form two opposing tapered roller bearing assemblies. In another example, an inner race spacer 140 may be disposed in an abutting relationship between the respective inner races 122, 130 of the first and second bearing assemblies 120A, 120B. The inner race spacer 140 has a ring shape sized to fit over the cam unit 50 and an axial width sized for the desirable separation between the respective inner races. An outer race spacer 142 may be disposed in an abutting relationship between the respective outer races 124, 132 of the first and second bearing assemblies 120A, 120B. The outer race spacer 142 has a ring shape sized to fit over the cam unit 50 spaced radially from the inner race spacer 140 and an axial width sized for the desirable separation between the respective outer races 124, 132. The respective spacers 140, 142 can facilitate preloading of the bearing during assembling, which can be set by the desired separation width between the bearing assemblies. The distal surface 110 of the gear adapter 70 and the proximal surface 112 of the distal end 50A of the cam unit 50 are positioned to restrain any axial movement of the one or more bearing assemblies. The first bearing assembly 120A may be sized to withstand a greater axial load than the second bearing assembly 120B, while the second bearing assembly 120B may be sized to withstand a greater radial load than the first bearing assembly 120A.
A proximal end 111 of the gear adapter body 100 opposite the distal surface 110 can interface with the gear assembly 35. In one example, the outer surface of the proximal end 111 can be chamfered to form a conical surface. A gear of the gear assembly 35 may have a bore 150 formed therein with a tapered recess 152 to form a conical shape having the same degree of taper as the chamfered proximal end 111. The gear adapter 70 can be coupled to such gear such that the axial surface of the proximal end 111 of the adapter is spaced from the internal axial surface 35A of the gear by a gap 151. Consequently with such gap 151, the load path can be directed through the frictional interface between the chamfered proximal end 111 of the gear adapter 70 and the tapered recess 152 of the gear in order to form a gear-drive shaft fuse. Such fuse coupling is configured to allow the gear to spin loose during operation when the torque input is greater than the friction torque at the conical interface.
A shaft seal 153 can be included within the pump housing 30 to inhibit leakage of any internal fluid. The shaft seal 153 can have a ring shape to sealably engage over the cylindrical portion 100A of the gear adapter body 100 to form a substantially sealed surface between the inner surface of the shaft seal 109 and the outer surface of the gear adapter 70. In one example, the shaft seal 153 may be disposed along the cylindrical portion 100A of the gear adapter body 100 between the chamfered proximal end 111 and the radial flange 114 of the gear adapter 70. The shaft seal 153 may be captured between the pump housing and the radial flange of the adapter.
A clamping device 155 can be used to provide a desired clamping load to the shaft arrangement. The clamping device 155 can be fixedly secured to the center shaft 34. In one example, the clamping device 155 includes a proximal end 156 and a distal end 158. The proximal end 156 can be sized larger than the gear bore 150 and can be disposed in an abutting relationship with the gear. The distal end 158 can be elongated to extend from the proximal end 156 about the longitudinal axis LA, and sized to be inserted through the gear bore 150 to be coupled to the center shaft 34. The length of the elongated distal end 158 can be sized to extend through the gear bore 150, the gear adapter central opening 72, and at least partially through the cam unit central bore 54 beyond the internal shoulder 55. The distal end 156 can be securely fixed with the center shaft 34, such as, e.g., the distal end 156 can be threadably engaged with the center shaft 34. In one example, the distal end 156 may have threaded portion along its outer surface for threadable engagement with an internally threaded bore 159 formed in the proximal end 57 of the center shaft 34, as shown in
The shaft arrangement may be assembled as described in the following. It is recognized that the various components may be assembled by other means, and that this description is merely an exemplary method of assembling the shaft arrangement. With reference to
The second subassembly can be inserted through the respective bores of the first assembly such that the central opening 72 of the gear adapter 70 receives the proximal end 50B of the cam unit 50. The proximal end of the bearing assembly is positioned proximally beyond the proximal end of the confronting surface 115 of the cam unit 50 such that the gap 113 is formed between the confronting surface 115 and the distal surface 110. A rotatable member such as a gear can be fitted over the proximal end 111 of the gear adapter 70. The clamping device 155 can be inserted from the proximal end through the bores of the gear, the gear adapter 70, and the cam unit 50 to be securely engaged with the center shaft 34. To this end, the secure engagement can provide a desired clamping axial force and torque between the components. In this assembly, the bearing assemblies need not be press-fitted over the cam unit and are thus loose fitted over the cam unit.
However, the inner races may be press-fitted over the cam unit body by various means. For example, the inner races may be heated for expansion, while the cam unit is cooled for contraction before being inserted within the heated inner races. After the temperatures equalize, the inner races can be fitted tightly over the cam unit with a friction fit. It is recognized that other attachment mechanisms between the bearing assemblies and the cam unit can be under taken for a loose fit or a friction fit.
With reference to
In operation, rotation of the drive shaft of engine 9 causes rotation of the center shaft 34 of the pump 16 via the gear assembly 35. The rotation of the center shaft 34 may act to rotate the cam unit 50 relative to the pistons 60 and the pump housing 30. A biasing force may urge the center shaft 34 against the biasing plate 66 to maintain the shoes 64 and the pistons 60 against the angled camming surface 50. Accordingly, rotation of the camming surface 50 of the cam unit 50 causes pistons 60 to reciprocate in accordance with the axial rise and fall of the angled camming surface 50. During a suction stroke of a piston 60 (associated with movement of the piston from its top-dead-center, distal-most, position to its bottom-dead-center, proximal-most position), low pressure fluid is drawn from the low pressure supply conduit 20 into the housing chamber 30, in through the inlet passage 80, through the shoe bore 84, and into the axial bore 82 of the piston 60 and the pump chamber of the piston. During a discharge stroke of a piston (associated with movement of the piston from its bottom-dead-center, proximal-most, position to its top-dead-center, distal-most, position), the piston 60 is out of alignment with the inlet passage 80 due to rotation of the cam unit 50 so that movement of the piston in a distal direction reduces the size of the pump chamber to pressurize the fluid within the axial bore 82 and the pump chamber of the piston 60. Some of the pressurized fluid is then expelled through the outlet passage (not shown), beyond a check valve (not shown), into the high pressure area 75, into the outlet passage of the pump housing 30, and through the high pressure supply conduit 19 to the common rail 12.
As discussed above, if a desired fluid pressure in the rail is different than the actual pressure in the rail, the amount of high pressure fluid leaving the pump 16 may be varied by the control assembly 17. The control assembly 17 may include the sleeve actuator, a control lever, the idler annulus and the sleeves 90. If the electric control module 15 determines that the pump 16 is supplying excess fluid through the high pressure supply conduit 19 to the common rail 12, a signal may be sent along the communication line 18 to the control assembly 17 to move the respective actuator, control lever, idler annulus, and control sleeves 90 so that the radial spill ports 77 of the piston 60 are uncovered at some point during the piston's discharge stroke. Once the radial spill ports 77 are uncovered, pressurized fluid within the pump chamber and the axial bore 82 of the piston 60 is expelled to the low pressure area 76 of the housing chamber 30, rather than through the outlet passage. Thus, the position of the control sleeve 77 on the piston 60 controls the amount of fluid in the pump chamber that is pressurized and forced through the high pressure outlet passage.
The shaft arrangement described herein can inhibit axial movement of the bearing assembly, such as, e.g., at least two bearing assemblies 120A, 120B, while maintaining a fuseable joint between the rotatable member and the center shaft 34, and a seal between the pump housing 30 and the center shaft 34. For example, the proximal end of the adapter 70 is configured to maintain a frictional interface (e.g., the conical interface) between the center shaft 34 via the cam unit 50 and the rotatable member such as the gear assembly 35 to permit the rotatable member from spinning loose from the center shaft 34 during high torque applications. The distal end of the adapter 70 can be in an abutting relationship with the proximal-most bearing assembly, while leaving a small gap 113 (e.g., about 0.75 mm) between the distal end of the adapter 70 and the center shaft 34 via the cam unit 50. This arrangement directs substantially all of the clamping load axially though the bearing assemblies 120A, 120B, rather than directly through the center shaft 34 via the cam unit 50. The attachment between the clamping device 155 and the center shaft 34 permits a desired clamping force to be transmitted between the rotatable member, the adapter, the bearing assemblies and spacers, the center shaft, and the cam unit, as shown, e.g., in
The above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. For instance, other types of control valves could be substituted for the example illustrated control valve without departing from the intended scope of the present invention. Thus, those skilled in the art will appreciate that various modifications can be made to the illustrated embodiment without departing from the spirit and scope of the present invention, which is defined in terms of the claims set forth below.
