WO2008076451A1

WO2008076451A1 - Ptm transfer case utilizing hydraulic power to perform range/mode shift and on-demand active clutch actuation

Info

Publication number: WO2008076451A1
Application number: PCT/US2007/025965
Authority: WO
Inventors: Larry A. Pritchard; Tsunlock A. Yu; Philip J. Francis
Original assignee: BorgWarner Inc
Current assignee: BorgWarner Inc
Priority date: 2006-12-21
Filing date: 2007-12-19
Publication date: 2008-06-26
Anticipated expiration: 2009-06-21

Abstract

A transfer case having an input shaft, a gear assembly operably associated with the input shaft, a primary output shaft, a range selector operably associated with the gear assembly for selectively connecting the input shaft to the primary output shaft. The present invention also includes a secondary output shaft, and clutch assembly operably associated with the secondary output shaft, for selectively transferring rotational force from the primary output shaft to the secondary output shaft, as well as an actuator which is operably associated with at least one valve. The actuator directs fluid through the valve to the range selector for the purpose of changing the rotational speed of the primary output shaft in relation to the input shaft. The range selector is also used to direct fluid to the clutch assembly to transfer rotational force from the primary output shaft to the secondary output shaft.

Description

PTM TRANSFER CASE UTILIZING HYDRAULIC POWER TO PERFORM RANGE/MODE SHIFT AND ON-DEMAND ACTIVE CLUTCH ACTUATION

CROSS-REFERENCE TO RELATED APPLICATIONS

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

60/876,264, filed December 21 , 2006.

FIELD OF THE INVENTION The present invention relates to a transfer case having a single actuator to perform range and shift functions, as well as torque-on-demand functions which may be equipped to have pre-emptive engagement.

BACKGROUND OF THE INVENTION Transfer cases are generally known for having the ability to selectively transfer power to a primary set of wheels, as well as a primary set of wheels and a secondary set of wheels at the same time. These types of transfer cases also typically have the ability to operate at a direct gear ratio where the ratio from input to output is 1 :1 , as well as a reduced gear ratio where the ratio of input to output ranges from 2.5:1 to 4:1. The reduced gear ratio is usually achieved by using a planetary gear set having a sun gear, a set of planetary gears, and a carrier. The transfer case typically has an input shaft connected to a transmission, where the input shaft can be directly engaged with an output shaft, or the input shaft can transfer rotational force through the planetary gearset to the output shaft, producing a reduced amount of speed and an increased amount of torque. Changing from the reduced gear ratio to the direct gear ratio, and vice versa, is often accomplished with the use of some type of actuator, which is usually a range selector having the ability to engage the input shaft to the output shaft directly, as well as engage the input shaft to the output shaft by using the planetary gearset.

Additionally, transfer cases also have what is commonly known as "torque-on-demand" capability. One way of achieving torque-on-demand capability is through the use of a clutch assembly having an apply piston which can selectively engage a clutch pack. The clutch pack is typically contained within a housing where the housing is connected to a sprocket, and the sprocket is circumscribed by a chain. The chain circumscribes another sprocket which is mounted on a secondary output shaft. As the clutch is engaged and disengaged, the power will be transferred from the output shaft through the clutch assembly, the sprocket, the chain, and then the sprocket mounted on the secondary output shaft. The secondary output shaft is typically connected to a drive shaft which is used to deliver power to a secondary set of wheels. This allows power to be transferred to a secondary set of wheels on an as-needed basis. The clutch also has an actuator, used for engaging and disengaging the clutch assembly, which can either be an electromagnetic actuator or a hydraulic actuator.

Having an actuator for the range selector as well as an actuator for the clutch assembly is not always conducive to meeting various packaging requirements, or operating system requirements.

Accordingly, there exists a need for a transfer case having a single actuator with the capability to change the ratio of input to output, as well as perform the torque-on-demand functions.

SUMMARY OF THE INVENTION

A transfer case having an input shaft, a gear assembly operably associated with the input shaft, a primary output shaft, a range selector operably associated with the gear assembly for selectively connecting the input shaft to the primary output shaft. The present invention also includes a secondary output shaft, and clutch assembly operably associated with the secondary output shaft, for selectively transferring rotational force from the primary output shaft to the secondary output shaft, as well as an actuator which is operably associated with at least one valve.

The actuator directs fluid through the valve to the range selector for the purpose of changing the rotational speed of the primary output shaft in relation to the input shaft. The range selector is also used to direct fluid to the clutch assembly to transfer rotational force from the primary output shaft to the secondary output shaft. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

The figure is a schematic representation of a transfer case having a single actuator, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

A transfer case according to the present invention is shown in Figure 1 , generally at 10. The transfer case 10 has an input shaft 12 connected to a gear assembly, shown generally at 14. The gear assembly in this embodiment is a planetary gearset 14 having a sun gear 16 connected to the input shaft 12, a set of planetary gears 18 in mesh with the sun gear 16, as well as a ring gear 20. The ring gear 20 is fastened to a housing 22, and does not rotate relative to the housing 22. The planetary gears 18 are mounted on, and free to rotate with respect to, a carrier 24. The carrier 24 has a first set of splines 26 which are selectively engagable with a set of corresponding splines 28 on a range selector, generally shown at 30. The corresponding splines 28 of the range selector 30 are also selectively engagable with a second set of splines 32 connected to the sun gear 16.

The corresponding splines 26 on the range selector 30 are connected to a shift sleeve 34 slidably disposed on a primary output shaft 36 through a spline connection 38. Although the shift sleeve 34 is allowed to slide along the primary output shaft 36, the shift sleeve 34 rotates in unison with the primary output shaft 36 because of the spline connection 38.

The shift sleeve 34 includes a shift collar 40 which is received by an extension 42. The extension 42, formed as a portion of a shift fork 44, and the shift fork 44 is mounted on a shift rail 46. The shift rail 46 is supported by a sleeve 48, and connected to a piston 50. The piston 50 is disposed in a cylinder 52 and is biased in one direction by a spring 54. The spring 54 biases the piston 50 in a direction outward from the cylinder 52, the function of which will be described later. The position of the piston 50 is detected by a first range shift position sensor 56 and a second range shift position sensor 58.

In addition to the shift sleeve 34, the primary output shaft 36 is also used with a clutch assembly, generally shown at 60. The clutch assembly 60 includes a clutch pack, generally shown at 62, having a hub 64 splined to the primary output shaft 36, and a first series of clutch plates 66 which are slidably disposed along the hub 64 through a typical spline connection. The first series of clutch plates 66 are interleaved with a second series of clutch plates 68. The second series of clutch plates 68 are connected to a clutch housing 70, also through a typical spline connection. The clutch assembly 60 also includes a pressure plate 72 for applying a force to the clutch pack 62. The pressure plate 72 receives force from a thrust bearing 74, which allows the pressure plate 72 to rotate with the first set of clutch plates 66. The thrust bearing 74 receives force from a clutch piston 76 disposed within a clutch cylinder 78. Also connected to the clutch housing 70 is a sprocket 80 which is partially circumscribed by a chain 82.

Fluid is delivered to the range selector 30 and the clutch assembly 60 by a single actuator, generally shown at 84. The actuator 84 is connected to a main fluid conduit 86 which splits into a first fluid conduit 88 and a second fluid conduit 90. The first fluid conduit 88 delivers fluid to the cylinder 52 of the range selector 30, and the second fluid conduit 90 delivers fluid to the clutch cylinder 78. The actuator 84 in this embodiment is a typical ball screw assembly having a motor/brake 92 connected to a gear reduction set 94. The gear reduction set 94 is connected to a ball screw 96 which has threads that are used with corresponding threads in a threaded nut 98. The threaded nut 98 is connected to a sleeve 100, which is connected to an annular piston 102. The threaded nut 98, sleeve 100, and annular piston 102 all move together when the ball screw 96 rotates. The gear reduction set 94 is used for multiplying the amount of torque transferred from the motor/brake 92 to the ball screw 96. However, the motor/brake 92 could also be connected directly to the ball screw 96 if desired. The annular piston 102 is slidably disposed within an elongated cylinder 104. Connected to the elongated cylinder 104 is a fluid delivery conduit 106. The fluid delivery conduit 106 includes a filter 108 for removing debris from the fluid as it is delivered from a sump 110 into the elongated cylinder 104. The elongated cylinder 104 is connected to the main fluid conduit 86.

Disposed in the first fluid conduit 88 is a first solenoid 112, the first solenoid 112 is used for selectively closing off fluid flow to the first fluid conduit 88, preventing fluid from being delivered to the range selector 30. Disposed in the second fluid conduit 90 is a second solenoid 114 for selectively closing off the second fluid conduit 90, and preventing fluid from being delivered to the clutch assembly 60, as well as a pressure sensor 116 for detecting the amount of fluid pressure in the clutch cylinder 78. In operation, a control unit (not shown) will perform the activation of the actuator 84, the first solenoid 112 and the second solenoid 114. The actuator 84 is used to operate both the range selector 30 and the clutch assembly 60 based on input from the first range shift position sensor 56, the second range shift position sensor 58, and the pressure sensor 114. The motor 92 can rotate the gear reduction set 94 in two directions, one for translating the annular piston 102 toward the main fluid conduit 86, and one for translating the annular piston 102 away from the main fluid conduit 86. As the gear reduction set 94 is rotated in a first direction, the ball screw 96 will rotate and the threads on both the ball screw 96 and threaded nut 98 will cause the threaded nut 98 to translate along the ball screw 96, and also cause the sleeve 100 to move the piston 102 away from the main fluid conduit 86, drawing fluid into the elongated cylinder 104 from the fluid delivery conduit 106. Once the elongated cylinder 102 is filled with fluid, the motor 92 will cause the gear reduction set 94 to rotate in a second direction, and the ball screw 96 will rotate in the opposite direction causing the threaded nut 98 to translate along the ball screw 96 in the opposite direction compared to when the gear reduction set 94 is rotated in the first direction. This causes the threaded nut 98, the sleeve 100, and the piston 102, to move toward the main fluid conduit 86, the fluid will be forced into both the first fluid conduit 88 and the second fluid conduit 90, and then to the range selector 30 or the clutch assembly 60, depending upon whether the first solenoid 112 or the second solenoid 114 is open or closed. If the first solenoid 112 is open, the second solenoid 114 will be closed, and vice versa.

If the first solenoid 112 is open, the fluid will be delivered into the cylinder 52. Normally the first position, or default position, for the range selector 30 is where the corresponding splines 28 are engaged with the second set of splines 32 located on the sun gear 16. When the range selector 30 is configured in this manner, the input shaft 12 and the primary output shaft 36 will rotate in unison, providing a direct ratio, or 1 :1 ratio between the input shaft 12 and the primary output shaft 36. The range selector 30 is placed in this default or first position by the spring 54 applying force to the piston 50 in the cylinder 52. The force received by the piston 50 forces the shift rail 46, along with the shift fork 44, the extension 42, and the shift sleeve 34 to move in the direction of the sun gear 16, and the corresponding splines 28 to be engaged with the second set of splines 32.

As the fluid is forced into the cylinder 52, fluid pressure builds against the piston 50, and the piston 50, the shift rail 46, the shift fork 44, and the extension 42 along with the shift sleeve 34 will move away from the sun gear 16. The force applied to the piston 50 will build fluid pressure against the piston 50 on the opposite side of the spring 54, overcoming the force of the spring 54. As this occurs, the splines 28 will engage with the first set of splines 26 on the carrier 24. Once the splines 28 are engaged with the first set of splines 26 on the carrier 24, the range selector 30 will be in a second position, where the planetary gearset 14 will operate at a reduced gear ratio. The power from the input shaft 12 will travel through the sun gear 16, and cause the planetary gears 18 to rotate as well. The planetary gears 18 are in mesh with both the sun gear 12 and the ring gear 20.

As the planetary gears 18 rotate, the carrier 24, and therefore the primary output shaft 36, will rotate at a reduced speed compared to the input shaft 12 because of the planetary gears 18. In addition to reducing the speed, the amount of torque output will increase. The ratio of speed reduction and torque increase will depend upon the number of teeth on the sun gear 12, the planetary gears 18, and the ring gear 20. Typically, the planetary gearsets 14 can have a range from 2.5:1 to 4:1 , but it is within the scope of the invention that other ratio ranges may be selected, depending upon the particular application.

The range selector 30 can be placed into a third position, or neutral position, where the splines 28 are not in contact with either the first set of splines 26 or the second set of splines 32. Placing the range selector 30 in this third position is accomplished by forcing enough fluid into the cylinder 52 to overcome the force of the spring 54 and cause the piston 50, the shift rail 46, the shift fork 44, the extension 42, and the shift sleeve 34 to move away from the sun gear 16 such that the splines 28 are no longer in contact with the second set of splines 32. However, the fluid pressure applied is not so great so as to move the shift rail 46, the shift fork 44, and the extension 42 to cause the splines 28 to engage with the first set of splines 26. Once the splines 28 are no longer in contact with the second set of splines 32, and not in contact with the first set of splines 26, the range selector 30 will be in the third position, or neutral configuration, and no power is transferred from the input shaft 12 to the primary output shaft 36. The range selector 30 can remain in this condition if so desired by the operator.

Because the position of the piston 50 is detected by the first range shift position sensor 56 and the second range shift position sensor 58, the control unit will be able to command the actuator 84 to deliver the proper amount of fluid into the cylinder 52, depending on whether it is desired for the range selector to be in the first position, second position or third position. The actuator 84 is also used for operating the clutch assembly 60. To actuate the clutch assembly 60, the first solenoid 112 is closed, and the second solenoid 114 is opened, allowing fluid to flow through the second fluid conduit 90 and into the clutch cylinder 78. As the fluid continues to flow into the clutch cylinder 78, fluid pressure will build behind the clutch piston 76. The fluid pressure will then cause the clutch piston 76 to move in the clutch cylinder 78 toward the thrust bearing 74, and apply a force to the thrust bearing 74. The force from the piston 76 is transferred through the thrust bearing 74 to the pressure plate 72, compressing the clutch pack 62. Compressing the clutch pack 62 with enough force from the clutch piston 76 will cause the primary output shaft 36 and the clutch housing 70 to rotate in unison. When clutch pack 62 is compressed in this manner, any rotational force in the primary output shaft 36 will be transferred from the primary output shaft 36 through the hub 64, the clutch pack 62, the clutch housing 70, the sprocket 80 and the chain 82.

However, it should be noted that if desired, a reduced amount of fluid can be introduced into the clutch cylinder 78 to build a reduced amount pressure behind the clutch piston 76. This will allow for relative rotation between the first series of clutch plates 66, and the second series of clutch plates 68, but the first series of clutch plates 66 will still be in frictional contact with the second series of clutch plates 68, thereby causing the clutch pack 62 to transfer a reduced amount rotational force from the primary output shaft 36 through the hub 64, the clutch pack 62, the clutch housing 70, the sprocket 80 and the chain 82. The amount of pressure applied to the clutch pack 62 can be varied from having the clutch pack 62 completely released, to having the clutch pack fully compressed, or any variation therebetween.

The primary output shaft 36 is typically connected to a drive shaft (not shown) for providing power to a primary set of wheels (also not shown), used for propelling a vehicle. The chain 82 can be connected to another sprocket (not shown) for selectively providing power to a secondary output shaft (also not shown) connected to a secondary set of wheels. Power can be provided to the secondary set of wheels when the vehicle has encountered driving conditions where the primary set of wheels has reduced traction. The actuator 84 used in the transfer case 10 of the present invention is not limited to delivering fluid to the range selector 30 and the clutch assembly 60. The actuator 84, in combination with the first solenoid 112 and the second solenoid 114, can also be used to hold the clutch assembly 60 in an engaged or disengaged position, while operating the range selector 30. Conversely the actuator 84 and solenoids 112, 114 can also be used to hold the range selector 30 in the direct ratio, neutral, or reduced gear ratio configurations, while operating the clutch assembly 60.

For instance, the splines 28 of the range selector 30 can remain engaged to either first set of splines 26 or the second set of splines 32, or disengaged from both the first set of splines 26 as well as the second set of splines 32, by simply using the actuator 84 to force the proper amount of fluid through the first fluid conduit 88 and closing the first solenoid 112, allowing the actuator 84 to selectively engage and disengage the clutch assembly 60 as necessary.

Conversely, the clutch assembly 60 can be held in an engaged or disengaged position, depending upon the mode of operation desired, by simply using the actuator 84 to force the proper amount of fluid through the second fluid conduit 90, and closing the second solenoid 114, and the actuator 84 can then be used solely to operate the range selector 30, selecting between neutral, the direct ratio, or the reduced gear ratio.

It is also within the scope of the invention to have a single solenoid located at the intersection of the main fluid conduit 86, the first fluid conduit 88, and the second fluid conduit 90, which can replace the first solenoid 112 and the second solenoid 114. Having a single solenoid located at the at the intersection of the main fluid conduit 86, the first fluid conduit 88, and the second fluid conduit 90 would allow a single solenoid to be used along with the actuator 84 for directing fluid into the first fluid conduit 88 and the second fluid conduit 90 in the same manner as the first solenoid 112 and second solenoid 114. The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Claims

CLAIMSWhat is claimed is:

1. A transfer case, comprising: an input shaft; a gear assembly operably associated with said input shaft; a primary output shaft; a range selector operably associated with said gear assembly for selectively connecting said input shaft to said primary output shaft; a secondary output shaft; a clutch assembly operably associated with said secondary output shaft, for selectively transferring rotational force from said primary output shaft to said secondary output shaft; and an actuator operably associated with at least one valve, and said actuator directs fluid through said at least one valve, causing said at least one valve to direct fluid to either said range selector to change the rotational speed of said primary output shaft in relation to said input shaft, or to said clutch assembly to transfer rotational force from said primary output shaft to said secondary output shaft.

2. The transfer case of claim 1 , wherein said gear assembly is a planetary gearset comprising: a sun gear mounted on said input shaft; at least one planetary gear in mesh with said sun gear, said at least one planetary gear mounted on a carrier; and

a ring gear circumscribing said sun gear and said at least one planetary gear, and in mesh with said at least one planetary gear, and said range selector is moved to a first position to place said range selector in direct connection with said sun gear to cause said input shaft and said primary output shaft to rotate in unison, said range selector is moved to a second position where said range selector is in direct connection with said carrier, providing a reduced gear ratio between said input shaft and said primary output shaft, and said range selector is moved to a third position where said input shaft is disconnected from said primary output shaft.

3. The transfer case of claim 1, said range selector further comprising: a shift sleeve slidably disposed on said primary output shaft, said shift sleeve having a set of splines for engaging said gear assembly; a shift fork connected to said shift sleeve; a shift rail connected to said shift fork, said shift rail also connected to a shaft having a piston, and said piston and at least a portion of said shaft are disposed in a cylinder; and a spring disposed in said cylinder on the opposite side of said piston in relation to said shaft, and said spring applies force to said piston to bias said shift fork to a first position, and when fluid is selectively delivered into said cylinder from said at least one valve by said actuator, pressure will build on said piston, causing said piston to move said shift fork to either a second position or a third position.

4. The transfer case of claim 1 , said actuator further comprising: a motor; a ball screw connected to said motor, said ball screw disposed within an elongated cylinder, said ball screw operably associated with a sleeve; and a piston connected to said sleeve, said motor is actuated in a first direction to cause said ball screw to also rotate in said first direction, causing said sleeve to translate along said ball screw, and said piston to move in said elongated cylinder, delivering fluid to said at least one valve, and said motor is actuated in a second direction to cause said ball screw to also rotate in said second direction, causing said sleeve to translate along said ball screw and said piston to move in said elongated cylinder, drawing fluid into said elongated cylinder.

5. The transfer case of claim 4, further comprising a gear reduction assembly connected to said motor and said ball screw, wherein said gear reduction assembly will transfer an increased amount of rotational force to said ball screw when said motor is actuated in said first direction or said second direction.

6. The transfer case of claim 1 , said clutch assembly further comprising: a clutch pack having a first series of clutch plates slidably disposed on a hub, said hub connected to said primary output shaft, and a second series of clutch plates interleaved with said first series of clutch plates and slidably disposed within a clutch housing; a sprocket connected to said housing, said sprocket at least partially circumscribed by a chain, said chain operably associated with said secondary output shaft; a clutch piston partially disposed within a clutch cylinder, said clutch cylinder in fluid communication with said actuator and said at least one valve; and a pressure plate operably associated with said clutch piston and said clutch pack, such that said actuator selectively delivers fluid to said clutch cylinder through said at least one valve, building fluid pressure in said clutch cylinder to move said pressure plate in said clutch cylinder, causing said clutch piston to apply force to said pressure plate, compressing said clutch pack and causing said primary output shaft to transfer rotational force to said secondary output shaft.

7. The transfer case of claim 1 , further comprising: a main fluid conduit connected to said actuator; a first fluid conduit for placing said main fluid conduit in fluid connection with said range selector; a second fluid conduit for placing said main fluid conduit in fluid communication with said clutch assembly; and said at least one valve is further comprised of a first solenoid valve disposed within said first fluid conduit, and a second solenoid valve disposed within said second fluid conduit, and said first solenoid valve is closed and said second solenoid valve is open to allow said actuator to direct fluid through said second fluid conduit, actuating said clutch assembly, and said first solenoid valve is open and said second solenoid valve is closed to allow said actuator to direct fluid through said first fluid conduit to actuate said range selector.

8. A transfer case having a single actuator, comprising: an actuator connected to a main fluid conduit, said main fluid conduit connected to a first fluid conduit and a second fluid conduit; a range selector operably associated with said first fluid conduit, and a planetary gearset; a clutch assembly in fluid communication with said second fluid conduit; a first solenoid valve disposed within said first fluid conduit; and a second solenoid valve disposed within said second fluid conduit, such that said first solenoid valve is open and said second solenoid valve is closed allowing fluid to be selectively delivered by said actuator through said main fluid conduit and through said first fluid conduit to said range selector to change said range selector from a first position to either a second position or a third position, and said first solenoid valve is closed and said second solenoid valve is open allowing fluid to be selectively delivered by said actuator through said main fluid conduit and through said second fluid conduit, engaging said clutch assembly.

9. The transfer case having a single actuator of claim 8, further comprising: said planetary gearset having a sun gear connected to an input shaft, a series of planetary gears in mesh with said sun gear and mounted on a carrier, a ring gear circumscribing and in mesh with said series of planetary gears, a first set of splines connected to said carrier, and a second set of splines connected to said sun gear; a primary output shaft, slidably supporting said shift sleeve by way of a spline connection; said range selector further comprising a cylinder for receiving fluid from said first fluid conduit, a piston connected to a shift rail, said piston disposed within said cylinder, a spring disposed within said cylinder for applying force to said piston on the opposite side of said piston in relation to said shift rail, a shift fork connected to said shift rail, said shift rail operably associated with a shift sleeve having a set of splines such that said spring biases said piston, said shift rail, said shift fork and said shift sleeve toward said first position, and fluid is received in said cylinder to cause fluid pressure to build behind said piston on the opposite side of said piston as said spring, thereby causing said piston, said shift rail, said shift fork, and said shift sleeve to selectively move said shift sleeve toward either of said second position or said third position.

10. The transfer case having a single actuator of claim 9, said first position of said range selector further comprising said splines of said shift sleeve engaged with said second set of splines, said second position of said range selector further comprising said splines of said shift sleeve engaged with said first set of splines, and said third position at said range selector further comprising said splines of said shift sleeve to be engaged with neither said first set of splines or said second set of splines.

11. The transfer case having a single actuator of claim 8, said clutch assembly comprising: a first series of clutch plates slidably disposed thereon and supported by a hub; a second series of clutch plates slidably disposed within a clutch housing, said second series of clutch plates interleaved with said first series of clutch plates; said first series of clutch plates and said second series of clutch plates forming a clutch pack; a pressure plate operably associated with said clutch pack; a clutch cylinder having a clutch piston, said clutch cylinder for receiving fluid from said second fluid conduit; and a thrust bearing disposed between said clutch piston and said pressure plate, said thrust bearing allowing said pressure plate to rotate relative to said clutch piston, and fluid is received in said clutch cylinder from said second fluid conduit, building pressure to said clutch piston, causing said clutch piston to apply force to said thrust bearing, said thrust bearing to apply force to said pressure plate, compressing said clutch pack.

12. The transfer case having a single actuator of claim 8, said actuator comprising: a motor operably associated with a gear reduction set; a ball screw connected to said gear reduction set, said ball screw operably associated with a threaded nut, said threaded nut connected to a sleeve, and said sleeve connected to an annular piston; an elongated cylinder for receiving said annular piston, said elongated cylinder in fluid communication with said main fluid conduit; and a sump connected to said elongated cylinder through a fluid delivery conduit, and said motor is actuated in a first direction to cause said gear reduction set to rotate said ball screw in said first direction, causing threaded nut to translate along said ball screw such that said sleeve moves said piston away from said main fluid conduit, drawing fluid into said elongated cylinder from said sump, and said motor is actuated in a second direction, said gear reduction set will rotate said ball screw in said second direction, causing said threaded nut to translate along said ball screw such that said sleeve moves said piston toward said main fluid conduit, forcing fluid into said main fluid conduit.

13. A transfer case having a single actuator, comprising: a range selector operably associated with a planetary gear set; a first fluid conduit having a first solenoid valve, said first fluid conduit for placing said range selector in fluid communication with an actuator; a second fluid conduit; a clutch assembly having a clutch pack connected to said second fluid conduit, said second fluid conduit for placing said clutch assembly in fluid communication with said actuator; and a main fluid conduit connected to said actuator, said main fluid conduit connected to said first fluid conduit and said second fluid conduit, and said first solenoid valve is open and said second solenoid valve is closed such that said actuator directs fluid through said first fluid conduit to said range selector causing said range selector to move from a first position to either a second position or a third position, and said first solenoid valve is closed and said second solenoid valve is open such that said actuator directs fluid through said second fluid conduit to said clutch assembly, causing said clutch pack to become compressed.

14. The transfer case according to claim 13, said planetary gear set further comprising: an input shaft having a sun gear; at least one planetary gear circumscribing and in mesh with said sun gear; a ring gear connected to a housing, said ring gear in mesh with said at least one planetary gear; a carrier connected to said at least one planetary gear; a first set of splines connected to said carrier; and a second set of splines connected to said sun gear, and said splines of said range selector are engaged with said first set of splines located on said carrier to cause said planetary gear set to operate at a reduced gear ratio, and said splines of said range selector are engaged with said second set of splines to cause said planetary gear set to operate at a direct gear ratio.

15. The transfer case according to claim 14, said range selector further comprising: a cylinder connected to said first fluid conduit; a piston connected to a shift rail, said piston slideably disposed within said cylinder, and said shift rail partially disposed within said cylinder; a spring disposed within said cylinder on the opposite side of said piston in relation to said shift rail; a shift fork connected to said shift rail; and

a shift sleeve operably associated with said shift fork, said shift sleeve slideably disposed on a primary output shaft, and said shift sleeve including a set of splines operably associated with said first set of splines and said second set of splines, and fluid is fed into said cylinder from said first fluid conduit, causing fluid pressure to build against said piston overcoming the force of said spring causing said shift rail, said shift fork, and said shift sleeve to move said shift sleeve from a first position where said set of splines on said shift sleeve are engaged with said second set of splines, to a second position where said set of splines on said shift sleeve are engaged with said first set of splines, or a third position where said set of splines on said shift sleeve are not engaged with either of said first set of spines or said second set of splines, and said shift sleeve is biased to said first position by said spring.

16. The transfer case according to claim 13, said clutch assembly further comprising: a hub disposed on and rotatable with a primary output shaft, said hub slideably supporting a first series of clutch plates; a second series of clutch plates slidably disposed within and rotatable with a clutch housing, said second series of clutch plates interleaved with said first series of clutch plates; a pressure plate operably associated with said first series of clutch plates; a thrust bearing for applying force to said pressure plate; a clutch cylinder for receiving fluid from said second fluid conduit; and a clutch piston disposed within said clutch cylinder, operably associated with said thrust bearing, and fluid is fed through said second fluid conduit into said clutch cylinder causing fluid pressure to build behind said clutch piston, thereby causing said clutch piston to apply a force to said thrust bearing, said thrust bearing to apply a force to said pressure plate, said pressure plate to apply force to said first series of clutch plates and said second series of clutch plates, engaging said clutch assembly.

17. The transfer case according to claim 13, said actuator assembly further comprising: a motor operably associated with a gear reduction set; a ball screw connected to said gear reduction set; a threaded nut threadably connected to said ball screw; a sleeve, slideably disposed within an elongated cylinder, connected to said ball screw; and a piston connected to said sleeve, and said motor is actuated in a first direction to cause said gear reduction set to rotate said ball screw in said first direction, causing said threaded nut to translate along said ball screw and said sleeve and said piston to translate within said elongated cylinder, and said motor is actuated in a second direction to cause said gear reduction set to rotate said ball screw in said second direction causing said threaded nut to translate along said ball screw in the opposite direction compared to when said ball screw is rotated in said first direction, also causing said sleeve and said piston to translate within said elongated cylinder.