TW201619511A - Modular hydraulic power pack - Google Patents

Abstract

A gear train assembly for use in a modular hydraulic power pack includes a gear train, a housing, and a plurality of supports disposed between the gear train and the housing to radially and axially restrain the gear train relative to the housing. The gear train couples a drive assembly to a pump assembly. The drive assembly is coupled to an input gear of the gear train, and the pump assembly is coupled to an output gear of the gear train. The output gear has a female spline that permits the pump assembly to be removable from the gear train assembly.

Description

Modular hydraulic power unit

The present invention generally relates to a gear train assembly, and more particularly to a gear train assembly for facilitating a modular hydraulic power pack.

The hydraulic power pack produces a pressurized working fluid to be used in a hydraulic system and/or hydraulic power equipment. Generally speaking, a hydraulic power pack includes a pump that supplies one of a working fluid and a motor that drives the pump at a specified pressure and flow rate. The pump and motor are selected to meet the specific operational requirements of the power pack (ie, the desired flow rate and pressure of the working fluid). Supplemental components such as pressure regulators, pressure relief valves, recirculation lines, and the like can be incorporated into the hydraulic power pack to facilitate the satisfaction of operational requirements.

Thus, the components of each hydraulic power pack are adjusted to one of the power pack specific applications or over-segmented to operate under a maximum operating condition and less stringent operating conditions. Adjusting the power pack to a particular application requires the operator to have several power packs, with different components in the power pack increasing maintenance costs while making the power pack too large, resulting in increased operating costs when the power pack is operating below the maximum operating conditions. In addition, hydraulic power pack components (especially pumps and motors) require regular maintenance to ensure the operational performance of the power pack. Periodic maintenance includes, inter alia, disassembly of components, replacement of worn components, reassembly of components, and verification of power pack performance through testing. The time and tools required to perform maintenance tasks such as these also increase the cost of operating the hydraulic power unit.

Therefore, there is a need for one of the modular hydraulic power units that can be easily customized into an application and maintained by replacing the modules of the power pack.

In one embodiment, a gear train assembly for use in a modular hydraulic power pack includes a gear train, a housing, and is disposed between the gear train and the housing for radial and axial relative to the housing A plurality of supports of the gear train are constrained. The gear train assembly is configured to couple a drive assembly to a pump assembly. The drive assembly is coupled to an input gear of the gear train and the pump assembly is coupled to an output gear of the gear train. The output gear has a pin slot that allows the pump assembly to be removed from the gear train assembly.

In another embodiment, a modular hydraulic power pack includes a drive assembly, a pump assembly, and a drive assembly that couples the drive assembly to the pump assembly. The drive assembly includes: a motor enclosed within a housing; and a first shaft member having a drive pinion at one of the ends of the first shaft member. The pump assembly includes: a screw; a pump housing enclosing the screw; and a thrust bearing that constrains the screw relative to the pump housing in a direction substantially parallel to one of the rotational axes of the screw. The screw extends from a first end to a second end, wherein the first end has an outer pin slot. The gear train assembly includes: a gear train housing enclosing the gear train assembly; an input gear engaged with the drive pinion; and an output gear having engagement with the outer bolt slot of the screw A slot in one of the inner diameters of the output gear. The gear train assembly further includes a second stage pinion axially adjacent to the input gear and a gear shaft member extending along a common rotational axis of the input gear and the second stage pinion. The gear shaft member rotatably couples the input gear to the second stage pinion gear that meshes with the output gear. The pump assembly is removably attached to the gear train assembly.

10‧‧‧Hydraulic power unit

12‧‧‧ Gear train assembly

14‧‧‧Drive assembly

16‧‧‧ pump assembly

18‧‧‧Management block

20‧‧‧Export

22‧‧‧ Entrance

24‧‧‧storage tank

26‧‧‧ cabinet

28‧‧‧ Cover

30‧‧‧Fluid indicator

32‧‧‧ pipe connection

34‧‧‧ pressure gauge

36‧‧‧Relief valve

38‧‧‧fasteners

40‧‧‧fasteners

42‧‧‧Brushless motor

44‧‧‧ shaft parts

46‧‧‧ bearing

48‧‧‧ bearing

50‧‧‧ Shell

52‧‧‧End board

54‧‧‧inside/inside

56‧‧‧ drive pinion

58‧‧‧Axis

60‧‧‧fan

62‧‧‧Outside

64‧‧‧ catheter

66‧‧‧ Gear Train

68‧‧‧ input gear

70‧‧‧Secondary pinion

72‧‧‧ Output gear

74‧‧‧ shaft parts

76‧‧‧Common rotation axis

78‧‧‧Axis

80‧‧‧ inner bolt slot

82‧‧‧ Shell

84‧‧‧ bearing

86‧‧‧ bearing

88‧‧‧ bushing

90‧‧‧ bushing

92‧‧·wheels

94‧‧‧ bearing

96‧‧‧ bearing

98‧‧‧ bushing

100‧‧‧ bushing

102‧‧‧ screws

104‧‧‧Shell

106‧‧‧Free end

108‧‧‧Axis extension

108a‧‧‧outer slot

108b‧‧‧ guiding surface

110‧‧‧ Activity nut

112‧‧‧buffer

114‧‧‧ Coupler

116‧‧‧cylinder

118‧‧‧Shell end plate

120‧‧‧ pole

122‧‧‧ nuts

124‧‧‧Washers

126‧‧‧cylinder

127‧‧‧ hydraulic cylinder

128‧‧‧ thrust bearing assembly

130‧‧‧ convex ring

130a‧‧‧Flange

132‧‧‧ convex ring

132a‧‧‧Flange

134‧‧‧ bearing

136‧‧‧ thrust flange

138‧‧‧Flange section

2-2‧‧‧ line

Figure 1 is an isometric view of a hydraulic power pack having a modular drive, pump and gear train assembly.

Figure 2 is a cross-sectional view of one of the hydraulic power units taken along line 2-2 of Figure 1.

1 is an isometric view of a hydraulic power pack 10 that includes, in addition to the other components discussed below, a gear train assembly 12 that couples the drive assembly 14 to the pump assembly 16. The drive assembly 14 supplies mechanical power to the pump assembly 16 through the gear train assembly 12. The pump assembly 16 provides hydraulic power to the manifold block 18 via a pump fluid 16 containing a working fluid (not shown in FIG. 1).

The manifold block 18 is equipped with at least one outlet 20 and at least one inlet 22 to supply and retrieve working fluid from the hydraulic drive assembly or system attached to the power pack 10, respectively. A plurality of inlets 22 and outlets 20 can be attached to the manifold block 18 for operating a plurality of hydraulic drive assemblies. For example, the manifold block 18 can have four inlets 22 and four outlets 20 for operating up to four hydraulic drive assemblies or systems as shown in FIG. Each inlet 22 and outlet 20 are adapted to be mechanically attached to a tube and/or hose (not shown in Figure 1) to facilitate circulation of the working fluid to the hydraulic drive assembly or system. Preferably, each inlet 22 and outlet 20 is one of the techniques known in the art to quickly open the hydraulic connection.

The sump 24 contains a large amount of supplemental working fluid to supplement the fluid that is leaking or otherwise automatically force group 10 or connected to the components of the power pack 10. The sump 24 includes a tank 26, a lid 28, and a fluid indicator 30. The housing 26 has a generally cylindrical body that is equipped with one of the generally hemispherical ends that are oriented toward the manifold block 18. The threaded end of one of the boxes 26 with respect to the hemispherical end engages the mating threads of the cover 28. When attached, the case 26 and cover 28 are formed to be fluidly coupled to one of the manifold blocks 18 at the tube connection 32. As the working fluid within the sump 24 is exhausted, the fluid indicator 30 allows an operator to determine the volume of working fluid within the sump 24.

Pressure gauge 34 and pressure relief valve 36 are fluidly coupled to manifold block 18. The gauge 34 is configured to determine the pressure of the working fluid within the manifold block 18 and the pressure relief valve 36 is discharged from the manifold block 18 when the pressure of one of the working fluids within the manifold block 18 exceeds a pressure set point. Working fluid. Meter 34 and valve 36 are each suitable for any meter or valve known in the art for performing such functions.

The gear train assembly 12 and the drive assembly 14 form a first module, and the pump assembly 16 is formed A second module. The first and second modules are independent such that the easily disassemblable pump assembly 16 is used for maintenance, module replacement, and customization of the output pressure and flow of one of the working fluids within the power pack 10. In some embodiments, the gear train assembly 12 is coupled to the drive assembly 14 using a plurality of fasteners 38 and coupled to the pump assembly 16 using a plurality of fasteners 40 (see FIG. 2), but may be mechanically attached. Any other suitable component. When fasteners 38 and 40 are used, hand tools (e.g., a wrench) can be used to disassemble and assemble assemblies 12, 14 and 16, thereby eliminating the need for one of the specialized tools and expertise.

2 is a cross-sectional view of the hydraulic power pack 10 taken along line 2-2 of FIG. 1 showing the drive assembly 14 coupled to the gear train assembly 12 of the pump assembly 16. As will be described in further detail below, the gear assembly 12 and drive assembly 14 are formed separately from the pump assembly 16 by removing the fasteners 40 extending through the pump assembly 16 into the gear train assembly 12. Module. The fastener 40 can be fabricated from any suitable material known in the art and can be any suitable bolt-type configuration fastener 40 required to support the pump assembly 16 from the gear train assembly 12. Although only one fastener 40 is shown in FIG. 2, it should be understood that one of the fasteners 40 extending through one of the portions of the pump assembly 16 to attach the pump assembly 16 to the gear train assembly 12 is symmetric. kind.

The drive assembly 14 provides mechanical power to the power pack 10. In the embodiment shown in FIG. 2, the drive assembly 14 includes a brushless motor 42 as is known in the art. Motor 42 has a shaft member 44 that extends between bearing 46 and bearing 48. Motor 42 is disposed within housing 50 of enclosure motor 42. In particular, the bearing 46 is disposed between the shaft member 44 and the outer casing 50 to radially constrain the motor 42 relative to the outer casing 50. Similarly, a bearing 48 is disposed between the shaft member 44 and the end plate 52 to radially constrain the motor 42 relative to the outer casing 50 that engages the inner side 54 of the drive assembly 14. To interface with the gear train assembly 12, the motor 42 has a drive pinion 56 disposed at an inboard end 54 of the shaft member 44. The brushless motor 42 receives a three-phase alternating current at a specified voltage to cause the motor 42 to rotate about a shaft 58 that extends through one of the geometric centers of the motor 42. Rotation of the motor 42 causes the drive pinion 56 to provide mechanical power to the gear train assembly 12.

Motor 42 includes a fan 60 disposed at an outer side end 62 of drive assembly 14 as appropriate. Fan 60 drives cooling air from the surrounding environment into housing 50 where cooling is provided to motor 42. After cooling the motor 42, the cooling air is exhausted from the outer casing 50 at any suitable location. In some embodiments, the cooling air is exhausted through a conduit 64 surrounding the fan 60 at the outer end 62 of the drive assembly 14.

Although the drive assembly 14 is described with reference to the brushless motor 42, other types of motors can be used to drive the gear train assembly 12. For example, the motor 42 can be replaced with another type of electric motor (eg, a permanent magnet motor) or a pneumatic motor or other suitable motor known in the art.

Gear train assembly 12 includes a gear train 66 to transfer mechanical power from drive assembly 14 to pump assembly 16. Gear train 66 includes an input gear 68, a secondary pinion 70, and an output gear 72. Gear 68 meshes with drive pinion 56 of drive assembly 14 to transmit mechanical power generated by drive assembly 14 to gear train assembly 12. The secondary pinion 70 is adjacent the gear 68 along a shaft 74 that extends through a common axis of rotation 76 of the gears 68 and 70. Gears 68 and 70 can be attached to shaft member 74 or integrally formed with shaft member 74. Preferably, the secondary pinion 70 is integral with the shaft member 74 and the gear 68 is attached to the shaft member 74, as shown in FIG. The output gear 72 meshes with the secondary pinion 70 and thus rotates about a shaft 78 that is offset from the shaft 74. The output gear 72 includes an inner slot 80 positioned along an inner diameter of one of the output gears 72. The inner pin slot 80 is configured to permit bi-directional displacement of a mating component along the shaft 78. Preferably, the inner pin groove 80 is formed by a plurality of grooves extending substantially parallel to the axis 78 along the inner diameter of the output gear 72 to form an inner half of the parallel key pin groove.

Gears 56, 68, 70 and 72 each have gear teeth extending from an outer diameter surface. The pitch circle diameter and the number of teeth contained on each gear are used to determine an effective gear ratio of one of the gear trains 66. The particular gear ratio of the gear train 66 is related to the rotational speed of the motor 42 and the desired rotational speed of the pump assembly 16. In general, the gear ratio between the two mating gears is determined by dividing the number of teeth of the driven gear by the number of teeth of the drive gear. When the driven gear has more teeth than the driving gear (ie, one gear ratio greater than 1.0), the driven gear rotates more than the driving gear Slower. This configuration is considered to be a reduction gear set. In some embodiments, multiple deceleration sets can be used. In the embodiment shown in FIG. 2, the gear 68 has more teeth than the drive pinion 56, and the output gear 72 has more teeth than the secondary pinion 70. Thus, the gear train 66 is in some embodiments a two-stage reduction gear set.

Gear train 66 is enclosed and supported by outer casing 82 and end plate 52. As will be discussed below, using one of the bearing and bushing configurations, the gear train 66 is supported within the gear train assembly 12 such that the assembly 12 and the drive assembly 14 are independent. Because the gear train 66 is independent and the inner pin groove 80 allows axial displacement of the pump assembly 16, the pump assembly 16 can be removed from the hydraulic power pack 10 without obstructing the gear train assembly 12 and the drive assembly 14.

Gears 68 and 70 and shaft member 74 are supported within gear train assembly 12 by bearings 84 and 86 disposed at opposite ends of shaft member 74. A bearing 84 is positioned between the shaft member 74 and the end plate 52 to radially constrain the shaft member 74 relative to the end plate 52, and the bearing 86 is positioned between the shaft member 74 and the outer casing 82 to radially constrain the shaft member 74 relative to the outer casing 82. . Bushings 88 and 90 axially constrain gears 68 and 70 within gear train assembly 12. In particular, the bushing 88 is adjacent the bearing 84 and disposed between the gear 68 and the end plate 52 to prevent the gear 68 from moving along the shaft 76 toward the bearing 84. Likewise, the bushing 90 is adjacent the bearing 86 and disposed between the gear 70 and the outer casing 82 to prevent the gear 70 from translating along the shaft 76 toward the bearing 86.

Output gear 72 is constrained within gear train assembly 12 in a manner similar to one of gears 68 and 70. Output gear 72 includes a hub 92. The hub 92 extends axially from the opposite face of the output gear 72 relative to the shaft 78. Output gear 72 is radially constrained within gear train assembly 12 by bearings 94 and 96 and axially constrained within gear train assembly 12 by bushings 98 and 100. Bearing 94 is disposed between hub 92 and end plate 52 and bearing 96 is disposed between hub 92 and outer casing 82. Bushing 98 is positioned between output gear 72 and end 52 to limit displacement of output gear 72 toward bearing 94, and bushing 100 is positioned between output gear 72 and outer casing 82 to limit displacement of output gear 72 toward bearing 96. Bearings 84, 86, 94 and 96 can be any suitable bearing known in the art, such as a needle bearing. Similarly, bushings 88, 90, 98, and 100 can be any of those known in the art. Suitable for bushings.

The pump assembly 16 converts mechanical power from the gear train assembly 12 into hydraulic power for operating a hydraulically operated machine or system. The pump assembly 16 includes a screw 102 enclosed within a pump housing 104. The screw 102 extends from the output gear 72 of the gear train assembly 12 along the shaft 78 to the free end 106. In some embodiments, the screw 102 has a shaft extension 108 having an outer bolt groove 108a. The shaft extension 108 has an internal thread that engages an external thread at one end of the screw 102. Additionally, the shaft extension 108 includes a guide surface 108b. The guide surface 108b has a diameter that forms a positioning fit with the radially innermost portion of the inner pin groove 80. In other embodiments, the shaft extension 108 is integral with the screw 102. The outer pin slot 108a is configured to engage the inner slot 80 of the output gear 72. Preferably, the outer pin groove 108a is formed by a plurality of projections extending from an outer surface of one of the screws 102 to engage an equal number of corresponding grooves on the pin groove 80 to form one of the outer portions of the parallel key pin grooves. Thus, the outer pin groove 108a and the inner pin groove 80 allow for bidirectional displacement of the screw 102 along the shaft 78 while coupling the output gear 72 to the screw 102 in a circumferential and radial direction relative to the shaft 78.

The movable nut 110 has an internal thread that is threaded outside the engagement screw 102 along one of its inner diameters. Preferably, the movable nut 110 has internal threads that cooperate with the external threads of the screw 102 to form a portion of a closed loop track (not shown in Figure 2). The closed loop track is configured to receive a ball bearing (not shown in Figure 2) that reduces the friction between the screw 102 and the nut 110. When utilizing this configuration, the screw 102 is a ball screw and the nut 110 is a ball nut as is known in the art.

When the drive assembly 14 and the gear train assembly 12 cause the screw 102 to rotate about the shaft 78, the movable nut 110 translates axially along one of the outer surfaces of the screw 102. The bumper 112 is concentrically configured with the screw 102 to relieve vibration from the movable nut 110 and prevent the nut 110 from colliding with one of the elastomeric materials of the thrust bearing assembly 128 (discussed in detail below). The coupler 114 engages a circumferentially extending groove in the movable nut 110 to transmit axial displacement of the nut 110 to the cylinder 116. In some embodiments, the coupler 114 is integral with the cylinder 116. Concentrically placing the cylinder 116 with the screw 102 allows The free end 106 is guided along an inner surface of one of the cylinders 116. As the movable nut 110 linearly translates along the screw 102, the cylinder 116 is directed through one of the apertures in the outer casing end plate 118. The cylinder 116 has a rod 120 that is inserted into the free end of one of the cylinders 116 outside of the pump housing 104. The nut 122 engages the external thread of the rod 120. Nut 122 and washer 124 attach plate 126 to one end of cylinder 116. The cylinder 116 extends perpendicular to the screw 102 and couples the cylinder 116 to an adjacent hydraulic cylinder 127 disposed on the opposite side of the plate 126. Thus, the rotational motion generated by the drive assembly 14 and transmitted by the gear train assembly 12 is converted by the screw 102 and the movable nut 110 into a linear motion within the pump assembly 16. This linear motion is converted to hydraulic power by actuation of one or more hydraulic cylinders coupled to the cylinder 116 by the plate 126. Hydraulic cylinder 127 supplies working fluid through outlet 20 and receives fluid through inlet 22 to operate a hydraulic power assembly or system that is attached to power pack 10.

The screw 102 is axially constrained within the pump housing 104 by a thrust bearing assembly 128. The thrust bearing assembly 128 includes collars 130 and 132 that engage an unthreaded outer surface of one of the screws 102 formed between the steps within the screw 102. The collars 130 and 132 have flanges 130a and 132a for axially constraining the bearing 134 within the thrust bearing assembly 128, respectively. A thrust flange 136 that engages the pump housing 104 is disposed between the bearings 134. Accordingly, the thrust bearing assembly 128 transmits axial forces from the translational movable nut 110 to the pump housing 104. The pump housing 104 has a flange portion 138 that engages an end plate 52 of the gear train assembly 12. The pump housing 104 is attached to the gear train assembly 12 by fasteners 40.

The respective configurations of gear train assembly 12, drive assembly 14 and pump assembly 16 allow for easy removal of pump assembly 16 for maintenance and/or customization of hydraulic power pack 10. To remove the pump assembly 16, an operator removes the fastener 40 and disengages the inner pin slot 80 by translating the pump assembly 16 along the shaft 78. Thereafter, maintenance can be performed on the pump assembly 16 prior to reinstalling the pump assembly 16 onto the hydraulic power pack 10. Additionally, the pump assembly 16 can be replaced with a different pump assembly equipped with one of the hydraulic cylinders having a configuration different from one of the pump assemblies 16, thus varying the pressure and flow rate of the working fluid delivered by the hydraulic power pack 10.

Although the invention has been described with reference to the preferred embodiments, those skilled in the art will recognize Changes in form and detail may be made without departing from the spirit and scope of the invention.

10‧‧‧Hydraulic power unit

12‧‧‧ Gear train assembly

14‧‧‧Drive assembly

16‧‧‧ pump assembly

40‧‧‧fasteners

42‧‧‧Brushless motor

44‧‧‧ shaft parts

46‧‧‧ bearing

48‧‧‧ bearing

50‧‧‧ Shell

52‧‧‧End board

54‧‧‧inside/inside

56‧‧‧ drive pinion

58‧‧‧Axis

60‧‧‧fan

62‧‧‧Outside

64‧‧‧ catheter

66‧‧‧ Gear Train

68‧‧‧ input gear

70‧‧‧Secondary pinion

72‧‧‧ Output gear

74‧‧‧ shaft parts

76‧‧‧Common rotation axis

78‧‧‧Axis

80‧‧‧ inner bolt slot

82‧‧‧ Shell

84‧‧‧ bearing

86‧‧‧ bearing

88‧‧‧ bushing

90‧‧‧ bushing

92‧‧·wheels

94‧‧‧ bearing

96‧‧‧ bearing

98‧‧‧ bushing

100‧‧‧ bushing

102‧‧‧ screws

104‧‧‧Shell

106‧‧‧Free end

108‧‧‧Axis extension

108a‧‧‧outer slot

108b‧‧‧ guiding surface

110‧‧‧ Activity nut

112‧‧‧buffer

114‧‧‧ Coupler

116‧‧‧cylinder

118‧‧‧Shell end plate

120‧‧‧ pole

122‧‧‧ nuts

124‧‧‧Washers

126‧‧‧cylinder

127‧‧‧ hydraulic cylinder

128‧‧‧ thrust bearing assembly

130‧‧‧ convex ring

130a‧‧‧Flange

132‧‧‧ convex ring

132a‧‧‧Flange

134‧‧‧ bearing

136‧‧‧ thrust flange

138‧‧‧Flange section

Claims (14)

A gear train assembly for use in a modular hydraulic power pack to couple a drive assembly to a pump assembly, the gear train assembly including: a gear train including: an input gear, Configuring to couple to the drive assembly; and an output gear having a slot configured to engage one of the outer pin slots of the pump assembly at one of the inner diameters of the output gear; Enclosing the gear train; and a plurality of support members disposed between the gear train and the outer casing configured to constrain the gear train radially and axially relative to the outer casing; wherein the plurality of support members And the inner pin groove allows the pump assembly to be disconnected from the gear train assembly and removed as a unit from the modular hydraulic power pack. The gear train assembly of claim 1, wherein the inner pin slot is configured to prevent transmission from being substantially parallel to a rotational axis of the output gear. A gear train assembly according to claim 2, wherein the inner bolt groove forms a portion of a parallel key pin groove. The gear train assembly of claim 1, wherein the input gear has a first plurality of teeth extending from an outer diameter of one of the input gears, and the output gear has a second plurality extending from an outer diameter of one of the output gears a tooth, and wherein the ratio of the second plurality of teeth divided by the first plurality of teeth is greater than 1.0. The gear train assembly of claim 4, the gear train further comprising: a shaft member extending along a rotational axis of the input gear; and an intermediate gear coupled to the shaft member adjacent to the input gear, wherein the gear The intermediate gear meshes with the output gear. The gear train assembly of claim 5, wherein the gear train is a two-stage reduction gear train. The gear train assembly of claim 1, and further comprising: a first plurality of fasteners configured to couple the outer casing to a drive assembly; and a second plurality of fasteners State to couple the outer casing to the pump assembly. The gear train assembly of claim 5, the plurality of supports comprising: a first plurality of bearings disposed between the shaft member and the outer casing to radially constrain the shaft member relative to the outer casing; a plurality of bearings disposed axially extending relative to the output gear and radially constraining the output gear relative to the housing relative to the housing; a first plurality of bushings, such as relative to the housing shaft The input gear, the intermediate gear and the shaft member are constrained; and a second plurality of bushings axially constrain the output gear relative to the outer casing. A modular hydraulic power unit comprising: a drive assembly comprising: a motor; a motor housing enclosing the motor; and a first shaft member having a position disposed at one end thereof a drive pinion; a pump assembly comprising: a screw having an outer pin groove at one end thereof; a pump housing enclosing the screw; and a thrust bearing relative to the The pump housing constrains the ball screw in a direction substantially parallel to one of the rotational axes of the ball screw; and a gear train assembly coupling the drive assembly to the pump assembly, the gear train assembly comprising: a gear train housing enclosing the gear train assembly; an input gear that meshes with the drive pinion; and an output gear including: an inner bolt groove at an inner diameter of the output gear The outer bolt groove of the screw is engaged; and a hub extending from the opposite side of the output gear; a second stage pinion gear axially adjacent to the input gear and meshing with the output gear; a gear shaft member along the Extending about a rotational axis of the input gear and the second stage pinion, the gear shaft rotatably coupling the input gear to the second stage pinion; wherein the pump assembly is removably attached to the gear Department assembly. The hydraulic power pack of claim 9, and further comprising: a first plurality of bearings disposed between the gear shaft member and the outer casing to radially constrain the gear shaft member relative to the outer casing; and second A plurality of bearings are disposed between the hub and the outer casing to radially constrain the output gear relative to the outer casing. The hydraulic power pack of claim 10, and further comprising: a first plurality of bushings axially constraining the input gear, the second stage pinion gear and the gear shaft member relative to the outer casing; and the second plurality A bushing that axially constrains the output gear relative to the outer casing. The hydraulic power pack of claim 9, wherein the inner bolt slot and the outer bolt slot allow the ball screw to be displaced relative to the output gear in an axial direction substantially parallel to one of the rotational axes of the output gear and constrained The ball screw rotates relative to the output gear. The hydraulic power unit of claim 9, wherein the gear train assembly is a two-stage reduction gear system. The hydraulic power pack of claim 9, and further comprising: a first plurality of fasteners that couple the gear train assembly to the drive assembly; and a second plurality of fasteners that wait for the gear housing Coupled to the pump housing.