CONTROL SYSTEM AND SHIFT STRATEGY FOR A THREE MODE DUAL RANGE DISCONNECT AXLE SYSTEM

CLAIM OF PRIORITY

The present application claims the benefit of priority to U.S. Provisional Application No. 62/204,266 filed on August 12, 2015, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to tandem drive axle systems and more specifically to control systems and shifting strategies for tandem drive axle systems.

BACKGROUND OF THE INVENTION

Vehicles incorporating tandem drive axles benefit in many ways over vehicles having a single driven axle; Inter-axle differentials in such vehicles may be configured to distribute torque proportionately or disproportionately between the axles. Additionally, shift mechanisms may be provided to such vehicles to permit the disengagement of one of the driven axles or to transition from single axle operation to tandem axle operation, among other benefits. However, such shift mechanisms are subject to wear, especially in the case of repeated shifting. As a result, such shift mechanisms can overheat, causing damage and excessive wear.

Operation of shifting mechanisms that permit the disengagement of one of the driven axles may be affected by temperature variations. When a portion of a tandem drive axle is disengaged, the disengaged portion quickly adjusts to a temperature of an environment the tandem drive axle is operated in. In low temperature environments, lubricants used with the disengaged portion will greatly increase in viscosity. At higher operating speeds, when one of the driven axles is typically disengaged to increase driveline efficiency, such a condition can rapidly occur. The condition is a result of the higher operating speeds, which results in increased airflow around the tandem drive axle. In such a situation, the disengaged portion must be carefully "spooled" up to allow for reengagement of the shifting mechanism without causing damage thereto. Such a process may delay a down shift of the tandem drive axle to a point where an ability to disengage a portion of a tandem drive axle becomes counterproductive.

It would be advantageous to develop a control system and method of shifting a tandem drive axle system that facilitates quick shifting between operating modes and provides enhanced control over a shifting mechanism. SUMMARY OF THE INVENTION

Presently provided by the invention, a control system and method of shifting a tandem drive axle system that facilitates quick shifting between operating modes and provides enhanced control over a shifting mechanism, has surprisingly been discovered.

In a first embodiment, the present invention is directed to a control system for a tandem drive axle system. The control system comprises a first actuator, a second actuator, and a controller. The first actuator is in driving engagement with a first clutching device of the tandem drive axle system. The first clutching device is for shifting operating modes of the tandem drive axle system. The second actuator is in driving engagement with a second clutching device. The second clutching device is for disengaging an axle of the tandem drive axle system. The controller actuates the first actuator. In response to actuation of the first actuator by the controller, movement of the first actuator facilitates actuation of the second actuator.

In another embodiment, the present invention is directed to a method of shifting a tandem drive axle system. The method comprises the steps of providing a tandem drive axle system including a first clutching device, a second clutching device, a first actuator, a second actuator, and a first valve, the tandem drive axle system in a 6x4 mode of operation; communicating with the second actuator through the first valve; actuating _, the first actuator to adjust an operational mode of the tandem drive axle system to a 6x2 mode of operation; actuating the first valve using movement of the first actuator, stopping communication with the second actuator through the first valve; and actuating the second actuator in response to stopping communication with the second actuator through the first valve, wherein actuating the second actuator disengages an axle of the tandem drive axle system.

In yet another embodiment, the present invention is directed to a method of shifting a tandem drive axle system. The method comprises the steps of providing a tandem drive axle system including a first clutching device, a second clutching device, a first actuator, a second actuator, and a valve, the tandem drive axle system in a 6x2 mode of operation; actuating the first actuator to adjust an operational mode of the tandem drive axle system to a 6x4 mode of operation; actuating the valve using movement of the first actuator; communicating with the second actuator through the valve; and actuating the second actuator in response to the communication through the valve, wherein actuating the second actuator engages an axle of the tandem drive axle system.

Various aspects of this invention will become apparent to those skilled- in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a schematic diagram of a drive axle system including control system according to an embodiment of the invention, the drive axle system in a 6x2 mode of operation;

FIG. 1 B is a table indicating a position of components of the drive axle system shown in FIG. 1A when the drive axle system is in the 6x2 mode of operation;

FIG. 2A is a schematic diagram of components of the drive axle system shown in FIG. 1A, the components shown in a 6x4 mode of operation;

FIG. 2B is a table indicating a position of components of the drive axle system shown in FIG. 1 A when the drive axle system is in the 6x4 mode of operation;

FIG. 3A is a schematic diagram of components of the drive axle system shown in FIG. 1A, the components shown in a third mode of operation; FIG. 3B is a table indicating a position of components of the drive axle system shown in FIG. 1A when the drive axle system is in the third mode of operation;

FIG. 4A is a schematic diagram of components of the drive axle system shown in FIG. 1A, the components shown in the 6x4 mode of operation, where an axle assembly of the drive axle system is in the process of being engaged;

FIG. 4B is a table indicating a position of components of the drive axle system shown in FIG. 1A when the drive axle system is in the 6x4 mode of operation, where an axle assembly of the drive axle system is in the process of being engaged; and

FIG. 5 is a table which provides a context for a method of shifting the drive axle system shown in FIG. 1A, where an engagement status of

components of the drive axle system is shown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts of the present invention. Hence, specific dimensions, directions, orientations or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated-otherwise.

FIG. 1 A illustrates a drive axle system 10 for a vehicle having a power source 11. The drive axle system 10 preferably includes a power distribution unit 12, a first axle assembly 14, and a second axle assembly 16. The drive axle system 10 is drivingly engaged with a power source 1 . As shown, the drive axle system 10 includes the three assemblies 12, 14, 16, but it is understood the drive axle system 10 may include fewer or more assemblies or components.

The power source 11 is drivingly engaged with an input shaft 18 of the power distribution unit 12, and applies power thereto. The power source 1 is, for example, an internal combustion engine; however, it is understood that the power source 11 may include an electric motor or another source of rotational output. It is understood that the power source 11 may be a hybrid power source including both an internal combustion engine and an electric motor. Further, it is understood that the power source 11 may be a hybrid power source including a kinetic energy source or that the power source 11 be another type of hybrid power source. Further, it is understood that the power source 11 may include a transmission (not shown) as known in the art.

Further, it is understood that the power source 11 may include a clutch (not shown) as known in the art, for one of reducing and interrupting a rotational force transferred to the power distribution unit 12.

The power distribution unit 12 includes an input shaft 18, an inter-axle differential 19, a first output gear 20, a plurality of driving pinions 21 , a transfer shaft 22, a second output gear 24, and a clutch 28. As shown, power distribution unit 12 includes the seven components 18, 19, 20, 21 , 22, 24, 28 disposed in a housing 30 buf it is understood the power distribution unit 12 may include fewer or more components.

The input shaft 18 is at least partially disposed in the housing 30.

Preferably, the input shaft 18 is an elongate member; however the Input shaft 18 may be any other shape. Bearings 32 disposed between the input shaft 18 and the housing 30 permit the input shaft 18 to rotate about an axis of the input shaft 18. Tlie input shaft 18 has a first end portion 33, a middle portion 34, and a second end portion 35.

The first end portion 33 is in driving engagement with the power source 1 . The first end portion 33 is a rotatably mounted shaft drivingly coupled to the input shaft 18. Alternately, the first end portion 33 may be integrally formed with the input shaft 18.

The middle portion 34 has a diameter greater than a diameter of the first end portion 33. The middle portion 34 is a substantially disc shaped body drivingly coupled to the input shaft 18. Alternately, the middle portion 34 may be integrally ^" formed with the input shaft 18.

The second end portion 35 is a substantially hollow body having a diameter greater than a diameter of the first end portion 33. The second end portion 35 is drivingly coupled to the middle portion 34. Alternately, the second end portion 35 may be integrally formed with the middle portion 34. The second end portion 35 has a pinion carrier 36, a first set of clutch teeth 37, and an engagement portion 38 formed thereon.

The pinion carrier 36 is a substantially disc shaped body drivingly coupled to the second end portion 35 of the input shaft 18. The pinion carrier 36 includes a plurality of pinion supports 39 protruding from a first side of the pinion carrier 36. The engagement portion 38 is formed on a second side of the pinion carrier 36. As is known In the art, the pinion carrier 36 is also known as a planet carrier.

The engagement portion 38 is a conical surface oblique to the input shaft 18; however, the engagement portion 38 may have any other shape. The first set of clutch teeth 37 are formed on the pinion carrier 36 radially inward from the engagement portion 38.

The inter-axle differential 19 includes the pinion carrier 36, the plurality of driving pinions 21 , the first output gear 20, and the transfer shaft 22. The inter-axle differential 19 is a planetary differential as known in the art; however, it is understood that the inter-axle differential 19 may be a bevel gear differential or any other type of differential.

The plurality of driving pinions 21 is rotatably disposed on the pinion supports 39 of the pinion carrier 36. Each of the driving pinions 21 have gear teeth formed on an outer surface thereof. As is known in the art, each of the driving pinions 21 is also known as a planet gear. Preferably, bearings are disposed between each of the driving pinions 21 and the pinion supports 39, however, the driving pinions 21 may be directly mounted on the pinion supports 39,

The first output gear- 20 is a gear concentrically disposed within the second end . ortion 35 of the input shaft 18. The first output gear 20 is a substantially- cup shaped body having an inner surface having gear teeth 40 formed on. As is known in the art, the first output gear 20 is known as a ring gear. The gear teeth 40- are engaged with the gear teeth formed on the outer surface of each of the driving pinions 21.

The first output gear 20 includes an output shaft 41 drivingly coupled thereto. Alternately, the first output gear 20 may be integrally formed with the output shaft 41. The first output gear 20 is drivingly engaged with the first axle assembly 14 through the output shaft 41 . The output shaft 41 is collinear with the input shaft 18. Bearings 32 disposed between the output shaft 41 and the housing 30 support the output shaft 41 and permit the output shaft 41 to rotate about an axis of the output shaft 41.

A bevel gear pinion 42 is drivingly coupled to the output shaft 41 opposite the first output gear 20. Alternately, the bevel gear pinion 42 may be integrally formed with the output shaft 41. As is known in the art, the bevel gear pinion 42 has gear teeth formed on an outer surface thereof. The bevel gear pinion 42 may be one of a hypoid gear, a spiral bevel gear, a straight bevel gear, or any other gear known to those skilled in the art.

The transfer shaft 22 is a hollow shaft rotatably disposed in the housing 30 and having an axis of rotation concurrent with the axis of rotation of the input shaft 18. Preferably, the transfer shaft 22 is a hollow elongate cylindrical member; however the transfer shaft 22 may be any other shape. Bearings may be disposed between the transfer shaft 22 and pinion carrier 36 or a portion of the first output gear 20 to permit the transfer shaft 22 to rotate about an axis of the transfer shaft 22. The transfer shaft 22 has a first end portion 43 having a first set of clutch teeth 44 formed on an outer surface thereof, and a second end portion 45, having a second set of gear teeth 46 formed on an outer surface thereof.

The first end portion 43 and the second end portion 45 are integrally formed with the transfer shaft 22, however, it is understood that the first end portion 43 and the second end portion 45 may be formed separate from a remaining portion of the transfer shaft 22 and coupled thereto in any

conventional manner. The first set of clutch teeth 44 and the second set of gear teeth 46 are formed in the transfer shaft 22. Alternately, the first end portion 43 and the second end portion 45 may be formed separate from and drivingly oupled to the transfer shaft 22. As is known in the art, the second end portion 45 having the gear teeth 46 is known as a sun gear. The second set of gear teeth 46 are engaged with the plurality of driving pinions 21 and the first set of clutch teeth 44 are disposed adjacent the first set of clutch teeth 37 of the pinion carrier 36. The first portion 43 of the transfer shaft 22 may be selectively engaged with the second output gear 24 or the second end portion 35 of the input shaft 18.

The second output gear 24 is a gear concentrically disposed about a portion of the transfer shaft 22. The second output gear 24 has a central perforation having a diameter greater than a diameter of the transfer shaft 22. The second output gear 24 is a substantially disc shaped body having a first end portion 47, a second end portion 48 defining an outer diameter of the second output gear 24, and an engagement portion 49. Bearings 32 disposed between the second output gear 24 and the housing 30 or the output shaft 41 permit the second output gear 24 to rotate about an axis of the second output gear 24. The axis of the second output gear 24 is concurrent with the axis of the input shaft 18. A first set of clutch teeth 50 are formed on the first end portion 47 adjacent the first set of clutch teeth 44 of the transfer shaft 22. A second set of gear teeth 51 are formed on the second end portion 48. The second output gear 24 is drivingly engaged with the second axle assembly 16.

The engagement portion 49 is formed in the second output gear 24 intermediate the first end portion 47 and the second end portion 48. As shown, the engagement portion 49 is a conical surface oblique to the input shaft 18; however, the engagement portion 49 may have any other shape.

The clutch 28- is a shift collar concentrically disposed about the transfer shaft 22. The clutch 28 includes a set of inner clutch collar teeth 52 formed on an inner surface thereof, a first synchronizer 53, and a second synchronizer 54. The set of inner clutch collar teeth 52 are engaged with the first set of clutch teeth 44 of the transfer shaft 22. The clutch 28 can be slidably moved along the-axis of the input shaft 18 as directed automatically by a controller 55 while maintaining engagement of the inner clutch collar teeth 52 and the first set of clutch teeth 44. A shift fork ^" 56 disposed in an annular recess formed in the clutch 28 moves the clutch 28 along the axis of the input shaft 18 into a first position, a second position, or a third position. -A first actuator 57, which is drivingly engaged with the shift fork 56, is engaged to-position the shift fork 56 as directed by the controller 55. Consequently, the shift fork 56 positions the clutch 28 into the first position, the second position, or the third position. In the first position, the inner clutch collar teeth 52 of the clutch 28 are drivingly engaged with the first set of clutch teeth 44 of the transfer shaft 22 and the first set of clutch teeth 37 of the pinion carrier 36. When the power distribution unit 12 is placed in the first position, the inter-axle differential 19 is placed in a "locked out" condition and only the first axle assembly 14 is driven through the output shaft 41. This mode of operation for the drive axle system 10 may be referred to as a 6x2 mode of operation, and Is suitable for operating the vehicle at higher speeds and lower torque.

In the second position, inner clutch collar teeth 52 of clutch 28 are drivingly engaged with the first set of clutch teeth 44 of the transfer shaft 22 and the first set of clutch teeth 50 of the second output gear 24. When the power distribution unit 12 is placed in the second position, torque applied by the input shaft 18 is distributed through the inter-axle differential 19 and both the first axle assembly 14 and the second axle assembly 16 are driven through the output shaft 41 and the second output gear 24. This mode of operation for the drive axle system 10 may be referred to as a 6x4 mode of operation, and is suitable for operating the vehicle at lower speeds and higher torque.

In the third position, the inner clutch collarteeth 52 of the clutch 28 are only drivingly engaged with the first set of clutch teeth 44 of the transfer shaft 22. It is understood the clutch 28, the clutch teeth 37, 44, 5Ό, 52, the

synchronizers 53, 54, and the engagement portions 38, 49 may be substituted with any ciutching device that permits selective engagement of a driving and a driven part.

A portion of the first actuator 57 is in driving engagement with a mechanically operated valve 72. In response to movement of the first actuator 57, the mechanically operated valve 72 is engaged and disengaged.

Alternately, it is understood that the mechanically operated vatve 72 may be an operated in another manner in response to a command from, the controller 55.

The first synchronizer 53 is an annular oody coupled to the clutch 28 adjacent the engagement portion. 3&of the pinion carrier 36. The first synchronizer 53 has a first conical engagement surface 58. Alternately, the first synchronizer 53 may have an engagement surface having any other shape. When the clutch 28 is moved from the third position towards the first position, the first conical engagement surface 58 contacts the engagement portion 38 of the pinion carrier 36, causing the clutch 28 to act upon the pinion carrier 36. When the clutch 28 is moved further towards the first set of clutch teeth 37 of the input shaft 18, the clutch 28 continues to act upon the pinion carrier 36 as the inner clutch collar teeth 52 become drivingly engaged with the first set of clutch teeth 44 of the transfer shaft 22 and the first set of clutch teeth 37 of the pinion carrier 36.

The second synchronizer 54 is an annular body coupled to the clutch 28 adjacent the first end portion 47 of the second output gear 24. The second synchronizer 54 has a second conical engagement surface 59. Alternately, the second synchronizer 54 may have an engagement surface having any other shape. When the clutch 28 is moved from the third position into the second position, the second conical engagement surface 59 contacts the engagement portion 49 of the second output gear 24, causing the clutch 28 to act upon the second output gear 24. When the clutch 28 is moved further towards the first set of clutch teeth 50 of the second output gear 24, the clutch 28 continues to act upon the second output gear 24 as the inner clutch collar teeth 52 become drivingly engaged with the first set of clutch teeth 44 of the transfer shaft 22 and the first set of clutch teeth 50 of the second output gear 24.

The first axle assembly 14 includes the bevel gear pinio 42, a first driving gear 60, a first wheel differential 61 , and a first pair of output axle shafts 62. As shown, the first axle assembly 14 includes the four components 42, 60, 61 , 62 disposed in a first axle housing 63 but it is understood the first axle assembly 14 may include fewer or more components.

The first driving gear 60 is coupled to a nousing of the first wheel differential -61 by a plurality of fasteners or a weld and is rotatable about an axis of the first pair of output axle shafts 62 within tne first axle housing 63.

Alternately, the first driving gear 60 may be integrally formed with the first wheel differential 61. As is known in the art, the first driving gear 60 has gear teeth formed on an outer surface thereof. The first driving gear 60 may be one of a hypoid gear, a spiral bevel gear, a straight bevel gear, or any other gear known to those skilled in the art. The first driving gear 60 is drivingly engaged with the bevel gear pinion 42 and has a first gear ratio. As a non-limiting example, the first gear ratio may be a 2.26:1 ratio, but it is understood that other ratios may be used. The output shaft 41 is drivingly engaged with the first driving gear 60 of the first axle assembly 14 through a single gear mesh.

The first wheel differential 61 is a bevel gear style differential as is known in the art having a plurality of driving pinions and a pair of side gears drivingly engaged with the first pair of output axle shafts 62. The first wheel differential 61 is rotatably disposed within the first axle housing 63 about the axis of the first pair of output axle shafts 62. Alternately, other styles of differentials may be used in place of the first wheel differential 61.

The first pair of output axle shafts 62 are elongate members having a common axis rotatably mounted within the first axle housing 63. Bearings 32 disposed between the first pair of output axle shafts 62 and the first axle housing 63 permit the first pair of output axle shafts 62 to rotate therein. The side gears of the first wheel differential 61 are disposed on first ends of each of the first output axle shafts 62 and wheels (not shown) are disposed on second ends of each of the first output axle shafts 62.

The second axle assembly 16 includes an inter-axle shaft 64, a second driving gear 65, a second wheel differential 66, a second pair of output axle shafts 67, and an axle clutch 68. As shown, the second axle assembly 16 includes the five components 64, 65, 66, 67, 68 disposed in a second axle housing 69 but it is understood the second axle assembly 16 may include fewer or more components.

The inter-axle shaft 64 comprises at least one elongate member drivingly engaged with the second output gear 24 through a driven gear 70 coupled to the inter-axle shaft 64. As illustrated^ the inter-axle shaft 64 comprises a plurality of elongate members connectedly joints. Bearings 32 disposed between the inter-axle shaft 64 and the housings- 30, 69 permit the inter-axle shaft 64 to rotate therein.

A bevel gear pinion 71 is drivingly coupled to the inter-axle shaft 64 opposite the driven gear 70. As is known in the art, the bevel gear pinion 71 has gear teeth formed on an outer surface thereof. The bevel gear pinion 71 may be one of a hypoid gear, a spiral bevel gear, a straight bevel gear, or any other gear known to those skilled in the art. The second driving gear 65 is a ring style bevel gear as is known in the art having a set of gear teeth engaged with the gear teeth formed on the bevel gear pinion 71. The second driving gear 65 is coupled to a housing of the second wheel differential 66 by a plurality of fasteners or a weld and is rotatable about an axis of the second pair of output axle shafts 67 within the second axle housing 69. Alternately, the second driving gear 65 may be integrally formed with the second wheel differential 66. The second driving gear 65 is drivingly engaged with the bevel gear pinion 71 and has a second gear ratio. As a non-limiting example, the second gear ratio may be a 4.88:1 ratio, which is a lower gear ratio than the first gear ratio, but it is understood that other ratios or a ratio equal to the first gear ratio may be used.

The second wheel differential 66 is a bevel gear style differential as is known in the art having a plurality of driving pinions and a pair of side gears drivingly engaged with the second pair of output axle shafts 67. The second wheel differential 66 is rotatabiy disposed within the second axle housing 69 about the axis of the second pair of output axle shafts 67. Alternately; other styles of differentials may be used in place of the second wheel differential 66.

The second pair of output axle shafts 67 are elongate members having a common axis rotatabiy mounted within the second axle housing 69. Bearings 32 disposed between the pair of second output axle shafts 67 and the second axle housing 69 perirut the second pair of output axle shafts 67 to rotate therein. The side gears of the second wheel differential 66 are disposed on first ends of each of the second output axle shafts 67 and wheels (not shown) are disposed on second ends of each of the second output axle shafts 67.

The axle clutch 68 is a dog style clutch that divides one of the second output axle shafts 67 into first and second portions _^ Alternately, the ^~ axle clutch 68 may be a component of the second wheel differential 66 which engages a- side gear of the second wheel differential 66 and one of the second output axle shafts 67 or any other clutching device as known in the art. The axle clutch 68 may also be a plate style clutch or any other style of clutch. The axle clutch 68 has a plurality of teeth formed thereon for selectively engaging corresponding teeth formed on the first portion and the second portion of the second output axle shafts 67. The axle clutch 68 is urged into an engaged position or a disengaged position by a shift fork 73. A second actuator 74, which is drivingly engaged with the shift fork 73, is engaged to position the shift fork 73, and thus the axle clutch 68, as directed by the controller 55. When the axle clutch 68 is in the engaged position, the first portion of one of the second output axle shafts 67 is drivingly engaged with the second portion of one of the second output axle shafts 67.

The controller 55 is in communication with the power source 11 , the first actuator 57, the second actuator 74, at least one sensor 75, a pair of primary solenoid valves 76, 77, and a secondary solenoid valve 78. Preferably, the controller 55 is in electrical communication with the power source 11 , the first actuator 57, the second actuator 74, the at least one sensor 75, and the solenoid valves 76, 77, 78. The controller 55 may be in communication with the power source 11 , the first actuator 57, the second actuator 74, the at least one sensor 75, and the solenoid valves 76, 77, 78 using electrical conductors, pneumatics, hydraulics, a wireless communication medium, or another type of communication. The controller 55, in co-operation with the valves 72, 76, 77, 78, the actuators 57, 74, and the at least one sensor 75 form a control system for the drive axle system 10. The controller 55 implements a method of shifting the drive axle system 10 that reduces wear on the clutches 28, 68 and facilitates quick shifting between the 6x2 mode of operation and the 6x4 mode of operation.

The controller 55 is configured to accept an input containing information regarding at least one of an operating condition of the power source 11 , a temperature of the second axle assembly 16, a speed of a portion of the transfer- shaft 22, a speed of the second output gear 24, a speed of a portion of the second axle assembly 16, an amount ©f the rotational force transferred to the power distribution unit 12, a position of the clutch 28, and a position of tfie axle clutch 68. The controller 55 uses the input to adjust the at least one of the operating condition of the power source 11 , the position of the clutch 28, the position of the axle clutch 68, a duration between successive positions of the clutch 28, and an engagement of the valves 72, 76, 77, 78. The controller 55 performs the adjustment to the operating condition of the power source 1 , the position of the clutch 28, the position of the axle clutch 68, the duration between successive positions of the clutch 28, and the engagement of the valves 72, 76, 77, 78 based on at least one of the operating condition of the power source 1 , the temperature of the second axle assembly 16, the speed of the second output gear 24, the speed of a portion of the second axle assembly 16, the amount of the rotational force transferred to the power distribution unit 12, the position of the clutch 28, the position of the axle clutch 68, and the engagement of the valves 72, 76, 77, 78. The controller 55 references at least one of a series of instructions and conditions, an operator input, at least one data table, and at least one algorithm to determine the adjustment made to the operating condition of the power source 1 1 , the position of the clutch 28, the position of the axle clutch 68, the duration between successive positions of the clutch 28, and the engagement of the valves 72, 76, 77, 78.

The at least one sensor 75 may be disposed within the housing 30, the first axle housing 63, and the second axle housing 69. Further, it is understood that the at least one sensor 75 may be disposed on an outer surface of one of the housings 30, 63, 69 or mounted elsewhere on the vehicle. The at least one sensor 75 is configured as known in the art to monitor at least one of the operating condition of the power source 11 , the temperature of the second axle assembly 16, the speed of a portion of the transfer shaft 22, the speed of the second output gear 24, the speed of a portion of the second axle assembly 16, the amount of a rotational force transferred to the power distribution unit 12, the position of the clutch 28, and the position of the axie clutch 68. The operating condition of the power source 11 may be at least one of an indication that the power source 11 is operating, a rotational speed of the power source 11 , a state of a transmission forming a portion of the power source! 1 , and a speed of the vehicle. Further, it is understood that the at least onesensor may be configured to indicate an engagement of the valves 72, 76, 77, 78.

The solenoid valve 76 is a three way electrically actuated solenoid valve having a normally closed position; however, it is understood that the solenoid valve 76 may be another type of valve. The solenoid valve 76 is in fluid communication with an air supply (not shown), a portion of the first actuator 57, and an exhaust conduit (not shown). Further, the solenoid valve 76 is in electrical communication with the controller 55. When the solenoid valve 76 is in the normally closed position, a first chamber 79 of the first actuator 57 is in fluid communication with the exhaust conduit via a first conduit 80, allowing a piston 81 of the first actuator 57 to displace air from the first chamber 79 of the first actuator 57 to the exhaust conduit through the first conduit 80. In response to a signal from the controller 55, the solenoid valve 76 may be placed in an open position. In the open position, the first chamber 79 of the first actuator 57 is in fluid communication with the air supply through the first conduit 80, pressurizing the first chamber 79 and displacing the piston 81 within the first actuator 57. Further, when the solenoid valve 76 is in the open position, neither the first chamber 79 nor the air supply is in fluid communication with the exhaust conduit.

The solenoid valve 77 is a three way electrically actuated solenoid valve having a normally closed position; however, it is understood that the solenoid valve 77 may be another type of valve. The solenoid valve 77 is in fluid communication with the air supply, a portion of the first actuator 57, and the exhaust conduit. Further, the solenoid valve 77 is in electrical communication with the controller 55. When the solenoid valve 77 is in the normally closed position, a second chamber 82 of the first actuator 57 is in fluid communication with the exhaust conduit via a second conduit 83, allowing the piston 81 of the first actuator 57 to displace air from the second chamber 82 of the first actuator 57 to the exhaust conduit through the second conduit 83. In response to a signal from the controller 55, the solenoid valve 77 may be placed in an open position. In the open position, the second chamber 82 of the first actuator 57 is in fluid communication with the air supply through the second conduit 83, pressurizing the second chamber 82 and displacing the piston 81 within-theflrst actuator 57. Further, when the solenoid valve 77 is in the open position _T neither the second chamber 82 nor the air supply is in fluid communication with the exhaust conduit,

The solenoid valve 78 is a three way electrically actuated solenoid valve having a normally closed position; however, it is understood that the solenoid valve 78 may be another type of valve. The solenoid valve 78 is in fluid communication with the air supply, a portion of the second actuator 74, and the exhaust conduit. Further, the solenoid valve 78 is in electrical communication with the controller 55. When the solenoid valve 78 is in the normally closed position, a first chamber 84 of the second actuator 74 is in fluid communication with the exhaust conduit via a third conduit 85, allowing a piston 86 of the second actuator 74 to displace air from the first chamber 84 of the second actuator 74 to the exhaust conduit through the third conduit 85. In response to a signal from the controller 55, the solenoid valve 78 may be placed in an open position. In the open position, the first chamber 84 of the second actuator 74 is in fluid communication with the air supply through the third conduit 85, pressurizing the first chamber 84 and displacing the piston 86 within the second actuator 74. Further, when the solenoid valve 78 is in the open position, neither the first chamber 84 nor the air supply is in fluid communication with the exhaust conduit.

The mechanically operated valve 72 is a three way valve having a normally closed position; however, it is understood that the mechanically operated valve 72 may be another type of valve. The mechanically operated valve 72 is actuated by a movement of the piston 81 of the first actuator 57. When the clutch 28 is placed in the second position, an actuation member 87 of the first actuator 57 engages the valve 72 to place the valve 72 in an open position. When the clutch 28 is placed in the first position, the actuation member 87 of the first actuator 57 disengages from the valve 72, allowing the valve 72 to return to the normally closed position. As shown in FIG. 1A, the actuation member 87 is a cylindrical portion of the first actuator 57 In driving engagement with the piston 81. The actuation member 87 is a linear cam which engages the valve 72 in response to a position of the piston 81.

The valve 72 is in fluid communication with the first conduit 80, a fourth conduit 88, and the exhaust conduit. Further, the solenoid valve 78 may be in electrical communication with the controller 55 to communicate a position of the valve 72. When the valve 72 is in the normally closed position, a second chamber 89 of the second actuator 74 is in fluid communication with the exhaust conduit via the fourth conduit 88, allowing a piston 86 of the second actuator 74 to displace air from the second chamber 89 of the second actuator 74 to the exhaust conduit through the fourth conduit 88. In response to movement of the actuation member 87, the valve 72 may be placed in an open position. In the open position, the second chamber 89 of the second actuator 74 is in fluid communication with the air supply through the first conduit 80, the valve 72, and the fourth conduit 88, pressurizing the second chamber 89 and displacing the piston 86 within the second actuator 74. Further, when the valve 72 is in the open position, neither the second chamber 89 nor the air supply is in fluid communication with the exhaust conduit.

In use, the controller 55 implements a method of shifting the drive axle system 10 that facilitates quick shifting between the 6x2 mode of operation and the 6x4 mode of operation and provides enhanced control over a shifting mechanism of the drive axle system 10. FIG. 1A illustrates the drive axle system 10 in the 6x2 mode of operation, where the axle assembly 16 is drivingly disengaged and the clutch 28 is placed into the first position. FIG. 1 B is a table indicating a position of each of the solenoid valves 76, 77, 78, the mechanically operated valve 72, and the clutches 28, 68 when the drive axle system 10 is in the 6x2 mode of operation.

The clutches 28, 68, especially the synchronizers 53, 54 of the clutch 28, are wear items, sensitive to both high shift density and gear drag of the driving gears 60, 65. Repeated shifting due to hunting can overheat the synchronizers 53, 54 or other components of the clutch 28 and cause excessive wear and damage. Excessive drag of the driving gears 60, 65 can also produce excessive wear and damage to the synchronizers 53, 54 or other components of the clutch 28 by prolonging shifts and as a result of high thermal loading. In addition to these problems, excessive drag due to a low lubricant temperature can prolong a downshift (from the 6x2 mode of operation to the 6x4 mode of operation) to the point that such a down shift is counter-productive. Because the drive axle system 10 allows the second pair of output axle shafts 67 to be drivingly disengaged, excessive drag due to th& fow lubricant temperature is a greater concern because a temperature of the second axle assembly 16 may be similar to an ambient temperature the drive axle system 10 is operated in. Such a problem may be exaggerated when a vehicle incorporating the drive axle system 10 is traveling at higher speeds, where the axle lubricant cools more rapidly and the downshift normally occurs. To solve such a problem, the controller 55 implements a method of shifting the drive axle system 10 that improves durability and performance by adding a third mode of operation. The third mode is a "high range", or 4x2 mode of operation, where the vehicle operated at higher speeds and lower torque, but with the driving gear 65 of the second axle assembly 16 remaining in driving engagement with the second pair of output axle shafts 67, and thus a surface the vehicle is operating on.

Normal operation of the drive axle system 10 at lower vehicle speeds remains low range, in the 6x4 mode of operation, with both axle assemblies 14, †6 drivingly engaged. A drive ratio for the 6x4 mode of operation may be a blend of the drive axle ratios used with the axle assemblies 14, 16.

Normal operation of the drive axle system 10 at higher vehicle speeds remains the 6x2 mode of operation with a fast axle ratio, where the inter-axle shaft 64 is drivingly disengaged from the clutch 28 and the driving gear 65 is disconnected from the second pair of output axle shafts 67. In the 6x2 mode of operation, the driving gear 65 is Tn an idle state.

The third mode of operation, the 4x2 mode, is the 6x2 mode of operation with the fast axle ratio, but with the driving gear 65 of the axle assembly 16 drivingly engaged with the second pair of output axle shafts 67, and thus the -surface the. vehicle is operating on. The driving gear 65 and the second pair of output axle shafts 67 remain synchronized with the surface the vehicle is operating on, which is typically a road.

The advantage of the third mode of operation is that it allows for fast shifts between the two axle ratios (the 6x2 mode of operation and the 6x4 mode of operation) without having to re-synchronize the driving gear in an idle condition. With the third mode of operation, the two available axle ratios of the drive axie system 1Θ mayi>e used to create an additional transmission gear function, for example a "top " gear function, which has less wear on the synchronizers 53, 54 of the clutch 28.

Ivlany shift strategies may be used to take advantage of the third mode of operation of the drive axle system 10. A first non-limiting example of a shift strategy used with the drive axle system 0 is that whenever the vehicle speed is considered to be stabilized in a high axle ratio, the second pair of output axle shafts 67 may be disconnected. Alternatively, when a shift density of the drive axle system 10 is high, the driving gear 65 of the axle assembly 16 may be kept engaged.

Another problem which may be addressed by the third mode of operation is cold weather performance. When the temperature of air, which generally reflects the temperature of a lubricant used in axle assembly 16 is low, such as in conditions of snow, ice, or frigid ambient temperatures, the driving gear 65 may kept drivingly engaged. With the driving gear 65 engaged, a full range of transmission and axle ratios is still available for selection by an operator or the controller 55, but transitions between the operating modes of the drive axle system 10 may be made more quickly. The third mode of operation allows the controller 55 to improve a hardware life of the clutch 28 and its components and make a fast downshift from the 6x2 mode of operation (high range) to the 6x4 mode of operation (low range). The third mode of operation may find particular usefulness in cold weather transient scenarios where traction of the vehicle the drive axle system 10 is incorporated in is an issue.

An additional benefit of the drive axle system 10 including the third mode of operation is delayed engagement of the second actuator 74 when required by high differential speeds between the transfer shaft 22 and the second output gear 24, requiring a longer synchronization period. The drive axle system 10 including the third mode of operation allows the air logic utilized with the mechanically operated valve 72, the second actuator 74, and the secondary solenoid valve 78 to be mitigated or even overridden until the driving gear 65 (and thus the second output gear 24) is synchronized with the transfer shaft 22 when downshifting from the ^3x2 mode of operation to the 6x4 mode of operation.

FIGS. 2-4 illustrate the drive axle system 10 in states of operation other than the 6x2 mode of operation described hereinabove.

FIG.2A illustrates components of the drive axle system 10 in the 6x4 mode of operation, where the axle assembly 16 is drivingly engaged and the clutch 28 is placed into the second position. FIG. 2B is a table indicating a position of each of the solenoid valves 76, 77, 78, the mechanically operated valve 72, and the clutches 28, 68 when the drive axle system 10 is in the 6x4 mode of operation. As shown in FIG. 2A, air flow from the valve 76 is ported through the valve 72 so that the driving gear 65 (shown in FIG. 1A) will be engaged if two conditions are met. Those conditions are that the valve 76 must be energized and the clutch 18 must also be placed in the second position (engaged in low range).

FIG. 3A illustrates components of the drive axle system 10 in the 6x2 mode of operation with the clutch 68 engaged, described above as the third mode of operation, where the axle assembly 16 is drivingly engaged and the clutch 28 isr placed into the first position. FIG. 3Bis a table indicating a position of each of the solenoid valves 76, 77, 78, the mechanically operated valve 72, and the clutches 28, 68 when the drive axle system 10 is in the 6x2 mode of operation with the clutch 68 engaged.

FIG. 4A illustrates components of the drive axle system 10 in the 6x4 mode of operation, where the axle assembly 16 is in the process of being engaged and the clutch 28 is placed into the second position. FIG. 4B is a table indicating a position of each of the solenoid valves 76, 77, 78, the mechanically operated valve 72, and the clutches 28, 68 when the drive axle system 10 is in the 6x4 mode of operation where the axle assembly 16 is in the process of being engaged.

FIG. 5 is a table which provides a context for the method of shifting the drive axle system 10 that facilitates quick shifting between the 6x2 mode of operation and the 6x4 mode of operation and provides enhanced control over the drive axle system 10. As shown in FIG. 5, which is a non-limiting example, there are four stages of gearing in play: a front gearbox, an auxiliary gearbox (high and low range), the ranges provided by the drive axle system 10 (the 6x2 and 6x4 modes of operation), and the engagement of the driving gear 65 of the second- pair of output axle shafts 67 as actuated by the second actuator 74. It should be noted that in this example, there are three stable states associated with the highest geared transmission ratio, 10th gear. These states may be referred to as 10th gear with a low axle ratio (10.1), 10th gear with a high axle ratio (10.2) and 10th gear with a high axle ratio and with the ring gear disconnected (10.3). In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiments, however, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its scope or spirit.