(12) United States Patent 

Morscheck et a1. 

US008523738B2 

US 8,523,738 B2 

Sep. 3, 2013 

(10) Patent N0.: 

(45) Date of Patent: 

(54) 

(75) 

(73) 

(21) 

(22) 

(65) 

(60) 

(51) 

(52) 

(58) 

METHOD OF SHIFTINGA TANDEM DRIVE 

AXLE HAVING AN INTER-AXLE 

DIFFERENTIAL 

Inventors: Timothy J. Morscheck, Portage, MI 

(US); Kenneth E. Cooper, Toledo, OH 

(US); James F. Ziech, Kalamazoo, MI 

(US); Richard A. Nellums, Maumee, 

OH (US); Steven J. WesoloWski, 

Waterville, OH (US); Donald J. 

Remboski, AnnArbor, MI (US) 

Assignee: Dana Heavy Vehicle Systems Group, 

LLC, Maumee, OH (US) 

Notice: Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 

U.S.C. 154(b) by 55 days. 

Appl. N0.: 13/353,944 

Filed: Jan. 19, 2012 

Prior Publication Data 

US 2013/0017927 A1 Jan. 17,2013 

Related U.S. Application Data 

Provisional application No. 61/435,007, ?led on Jan. 

21, 2011. 

Int. Cl. 

B60W10/00 (2006.01) 

U.S. Cl. 

USPC ............. .. 477/77; 477/36; 477/110; 475/221; 

475/332 

Field of Classi?cation Search 

USPC ............. .. 477/35, 36, 77, 107, 110; 475/221, 

475/223, 332, 343 

See application ?le for complete search history. 

(56) References Cited 

U.S. PATENT DOCUMENTS 

2,166,099 A 12/1937 Quartullo 

2,291,174 A 3/1939 Stewart 

2,290,089 A 7/1942 Bock 

2,574,986 A 10/1947 Schou 

2,936,036 A 5/1960 Norelius 

3,146,842 A 9/1964 Nelson et a1. 

3,221,832 A 12/1965 Holmstrom 

3,324,965 A 6/1967 Koch et :11. 

3,388,760 A 6/1968 Christie 

3,577,804 A 5/1971 Ohno 

3,657,935 A 4/1972 O’Brien 

3,706,350 A 12/1972 Bokovoy 

3,792,628 A 2/1974 Stieg 

3,827,520 A 8/1974 Mueller 

(Continued) 

FOREIGN PATENT DOCUMENTS 

CN 201346995 Y 1/2009 

EP 1 527 938 A2 5/2005 

(Continued) 

Primary Examiner * Justin Holmes 

(74) Attorney, Agent, or Firm * Marshall & Melhom LLC 

(57) ABSTRACT 

A method of shifting a poWer distribution unit for a vehicle 

from a ?rst operating state to a second operating state is 

provided. The method includes the step of adjusting a rota 

tional speed of a portion of a second axle assembly using a 

clutching device to impart energy to a lubricant Within the 

second axle assembly. A controller in communication With a 

poWer source of the vehicle adjusts an operating condition of 

the poWer source to facilitate moving the clutching device. 

The poWer distribution unit includes an inter-axle differential 

capable being placed in a locked condition by the clutching 

device and of accommodating a rotational difference betWeen 

a ?rst output gear and a second output gear With the inter-axle 

differential. 

44 Claims, 4 Drawing Sheets 
US 8,523,738 B2 

Page 2 

References Cited 6,840,880 B2 1/2005 Glassner 

6,863,634 B2 3/2005 Holman et al. 

6,877,573 B2 4/2005 Hasegawa U'S' PATENT DOCUMENTS 6,918,851 B2 7/2005 Ziech et al. 

3,915,032 A 10/1975 Ottemann 6,926,634 B2 8/2005 Haka 

3,916,728 A 11/1975 Behar et al. 6,932,734 B2* 8/2005 HWa et a1. ................... .. 475/221 

3,976,154 A 8/1976 Clark et a1. 6,953,411 B2 10/2005 Burns et al. 

4,046,210 A 9/1977 Nelson 6,964,310 B2 11/2005 Hasegawa 

4,050,534 A 9/1977 Nelson et al. 7,044,880 B2* 5/2006 Bowen ........................ .. 475/205 

4,194,586 A 3/1980 Hicks 7,093,681 B2 8/2006 Strain 

4,263,824 A 4/1981 Mueller 7,096,990 B2 8/2006 Borgen etal. 

4,432,431 A 2/1984 Russell 7,163,483 B2 1/2007 Haka 

4,462,271 A 7/1984 Stieg 7,195,579 B2 3/2007 Claussen et a1. 

4,560,018 A 12/1985 Satzler 7,291,083 B2 11/2007 Almaguer 

4,677,873 A 7/1987 Eastman er :11 7,306,536 B2 12/2007 Ziech 

4,754,847 A 7/1988 GlaZe et 61. 7,399,251 B2 7/2008 Mueller et al. 

4,779,699 A 10/1988 Hatano ....................... .. 180/248 7,410,440 B2 8/2008 Garcia et a1. 

4,887,487 A 12/1989 May?eld 7,491,145 B2 2/2009 Mizon et al. 

5,176,590 A 1/1993 HaydOCk 7,611,414 B2 11/2009 Mueller et al. 

5,267,489 A 12/1993 Ziech 7,686,728 B2 3/2010 Imbert 

5,370,018 A 12/1994 Kwasniewski 2006/0172852 A1* 8/2006 Claussen et a1. .............. .. 477/35 

5,435,790 A 7/1995 Kota et al. 2006/0272866 A1 12/2006 Ziech 

5,641,044 A 6/1997 Morscheck 2008/0210508 A1 9/2008 Heisey et al. 

5,651,748 A 7/1997 Adarn et a1. 2010/0206654 A1 8/2010 Cimattiet al. 

5,711,389 A 1/1998 Schlosser 2010/0248888 A1 9/2010 Hamperlet al. 

5,860,889 A 1/1999 Schlosser et al. 

5,876,301 A 3/1999 Tabata et a1. ................ .. 477/109 FOREIGN PATENT DOCUMENTS 

5,950,750 A 9/1999 Dong et a1. _ 

6,085,853 6,154,700 A 11/2000 7Wernick Jones JP 58337125 2 A12/1996 

6,258,009 B1 7/2001 Thomas et al. KR 20030000505 A H2003 

6,327,935 B1 12/2001 Joslin et al. W0 WO 2008019779 A2 2/200g 

6,517,462 B2 2/2003 Borgan eta1~ W0 WO 2008113484 A1 9/2008 

6,530,861 B1 3/2003 Nakashima 

6,659,249 B2 12/2003 Borgen et al. * cited by examiner 

US. Patent 

ROTATIONAL SPEED

TIME 

Sep. 3, 2013 Sheet 2 of4 US 8,523,738 B2 

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(‘,5 / / Power Source 

g / _- --Transfer Shaft 

.% / —------Second Output Gear E II/ | I | g): / l ------F|rst Drrvrng Gear 

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,/ // ‘r -_ -Power Source 

/' - - - -Transfer Shaft 

/ ---—--—Second Output Gear 

/' ------First Dn'ving Gear 

__\_\__ \ / 

\ 

A B D E [Fig-3 
US. Patent Sep. 3, 2013 Sheet 3 of4 US 8,523,738 B2 

__--Power Source 

_ - - -Transfer Shaft 

_--_---Second Output Gear 

-___--First Driving Gear 

It 

TIME 

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US 8,523,738 B2 

1 

METHOD OF SHIFTING A TANDEM DRIVE 

AXLE HAVING AN INTER-AXLE 

DIFFERENTIAL 

CLAIM OF PRIORITY 

The present application claims priority to and incorporates 

by reference US. Provisional Application No. 61/435,007 

?led Jan. 21, 2011, entitled “TWo Speed Tandem Drive Axle 

Having an Inter-Axle Differential.” 

FIELD OF THE INVENTION 

The present invention relates to a vehicle drive train and to 

a method of shifting a tandem drive axle for the vehicle drive 

train having an inter-axle differential from a ?rst operating 

state to a second operating state. 

BACKGROUND OF THE INVENTION 

Vehicles incorporating tandem drive axles bene?t in many 

Ways over vehicles having a single driven axle. Inter-axle 

differentials in such vehicles may be con?gured 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 bene?ts. HoWever, such 

versatility typically requires the incorporation of additional 

drive train components into the vehicle at added expense and 

Weight. Such added Weight results in a decreased fuel e?i 

ciency of the vehicle. 

Components of the tandem drive axle may also be selected 

based on a gear reduction ratio present in an axle. Axle ratios 

may be of a tWo-speed con?guration to permit the vehicle to 

operate in a loW speed and high torque manner or in a high 

speed and loW torque manner. It is preferred to drive both 

axles When the loW speed and high torque manner of opera 

tion is desired (to distribute the higher torque amongst a 

greater number of Wheels) and it is advantageous to operate a 

single axle When the high speed and loW torque manner of 

operation is desired (to decrease Windage and frictional losses 

When torque distribution is of loWer concern). HoWever, 

incorporation of both the tWo-speed con?guration, an axle 

disconnect function, and the inter axle differential may be 

prohibitive With respect to cost and Weight. Such added 

Weight, Windage losses, and frictional losses result in a 

decreased fuel e?iciency of the vehicle. 

Additionally, When components are provided to permit the 

disengagement of one of the driven axles or to transition from 

the vehicle from single axle operation to tandem axle opera 

tion, a complexity of the tandem drive axle is increased. 

Typically, such operations may require manual engagement 

by an operator When speci?c conditions are present or may 

require the operator to stop the vehicle to engage speci?c 

components. Such features, While providing additional func 

tionality to the vehicle, may not be properly implemented by 

the operator or may not be used at all by the operator. When 

such features are not properly implemented, a shift from one 

operating state to another may result in damage to the tandem 

drive axle or a rough shift, either of Which typically result in 

a dissatisfaction of the operator. 

It Would be advantageous to develop a method of shifting a 

tandem drive axle system from a loW speed and high torque 

tandem axle manner of operation to a high speed and loW 

torque single axle manner of operation that reduces Windage 

and frictional losses and facilitates improved shifting from 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

2 one operating state to another Without excessively increasing 

a cost and a Weight of the tandem drive axle. 

SUMMARY OF THE INVENTION 

Presently provided by the invention, a method of shifting a 

tandem drive axle system from a loW speed and high torque 

tandem axle manner of operation to a high speed and loW 

torque single axle manner of operation that reduces Windage 

and frictional losses and facilitates improved shifting from 

one operating state to another Without excessively increasing 

a cost and a Weight of the tandem drive axle, has surprisingly 

been discovered. 

In one embodiment, the present invention is directed to a 

method of shifting a poWer distribution unit for a vehicle from 

a ?rst operating state to a second operating state. The method 

includes the steps of drivingly engaging a ?rst axle assembly 

With a ?rst output of the poWer distribution unit and drivingly 

engaging a second axle assembly With a second output of the 

poWer distribution unit. Next, the method includes the step of 

drivingly engaging an input of the poWer distribution unit 

With an output of a poWer source, the poWer distribution unit 

including an inter-axle differential, the ?rst output, the second 

output, and a ?rst clutching device having a ?rst position and 

a second position, the ?rst clutching device in the ?rst posi 

tion locking the inter-axle differential, engaging the ?rst out 

put With the input of the poWer distribution unit, and disen 

gaging the second output from the inter-axle differential, the 

?rst clutching device in the second position unlocking the 

inter-axle differential and engaging the ?rst output and the 

second output With the inter-axle differential. Next, the 

method includes the steps of placing the ?rst clutching device 

in one of the ?rst position and the second position and apply 

ing a rotational force to the input of the poWer distribution 

unit. Next, the method includes the steps of adjusting the 

rotational force transferred to the poWer distribution unit to 

facilitate moving the ?rst clutching device and moving the 

?rst clutching device from one of the ?rst position and the 

second position to a third position, the ?rst clutching device in 

the third position neither locking the inter-axle differential 

nor engaging the second output With the inter-axle differen 

tial. Lastly, the method includes the steps of adjusting a rota 

tional speed of the input of the poWer distribution unit to 

facilitate moving the ?rst clutching device from the third 

position, moving the ?rst clutching device from the third 

position to one of the ?rst and second positions, and adjusting 

the rotational force transferred to the poWer distribution unit. 

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 accom 

panying draWings. 

BRIEF DESCRIPTION OF THE DRAWINGS 

The above, as Well as other advantages of the present 

invention, Will become readily apparent to those skilled in the 

art from the folloWing detailed description When considered 

in the light of the accompanying draWings in Which: 

FIG. 1 is a schematic vieW of a tandem drive axle system 

including a poWer distribution unit according to an embodi 

ment of the present invention; 

FIG. 2 is a chart illustrating a ?rst example of shifting the 

poWer distribution unit from a ?rst operating state to a second 

operating state; 

FIG. 3 is a chart illustrating a second example of shifting 

the poWer distribution unit from the ?rst operating state to the 

second operating state; 
US 8,523,738 B2 

3 

FIG. 4 is a chart illustrating a third example of shifting the 

power distribution unit from the ?rst operating state to the 

second operating state; 

FIG. 5 is a chart illustrating a ?rst example of shifting the 

poWer distribution unit from the second operating state to the 

?rst operating state; and 

FIG. 6 is a schematic vieW of a tandem drive axle system 

including a poWer distribution unit according to another 

embodiment of the present invention. 

DETAILED DESCRIPTION OF THE INVENTION 

It is to be understood that the invention may assume various 

alternative orientations and step sequences, except Where 

expressly speci?ed to the contrary. It is also to be understood 

that the speci?c devices and processes illustrated in the 

attached draWings, and described in the folloWing speci?ca 

tion are simply exemplary embodiments of the inventive con 

cepts de?ned in the appended claims. Hence, speci?c dimen 

sions, directions or other physical characteristics relating to 

the embodiments disclosed are not to be considered as limit 

ing, unless the claims expressly state otherWise. 

FIG. 1 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 ?rst axle assembly 14, 

and a second axle assembly 16. The drive axle system 10 is 

drivingly engaged With a poWer source 11. 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 11 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 under 

stood 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 ?rst output gear 20, a plurality 

of driving pinions 21, a transfer shaft 22, a second output gear 

24, and a clutch 28. Preferably, the components 18, 19, 20, 21, 

22, 24, 28 are formed from a hardened steel, hoWever the 

components 18, 19, 20, 21, 22, 24, 28 may be formed from 

any other rigid material. As shoWn, poWer distribution unit 12 

includes the seven components 18, 19, 20, 21, 22, 24, 28 

disposed in a housing 30 but 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. The input shaft 18 has a ?rst endportion 33, 

a middle portion 34, and a second end portion 35. 

The middle portion 34 has a diameter greater than a diam 

eter of the ?rst end portion 33. The middle portion 34 is a 

substantially disc shaped body drivingly coupled to the input 

shaft 18. Altemately, 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 ?rst end 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

4 

portion 33 and the middle portion 34. 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 

input shaft 18 and the middle portion 34. The second end 

portion 35 has a pinion carrier 36, a ?rst 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 ?rst side of the pinion carrier 

36 into the second end portion 35 of the input shaft 18. 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 ?rst 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 3 6, 

the plurality of driving pinions 21, the ?rst output gear 20, and 

the transfer shaft 22. The inter-axle differential 19 is a plan 

etary differential as knoWn in the art; hoWever, it is under 

stood that the inter-axle differential 19 may be a bevel gear 

differential or any other type of differential. 

The plurality of driving pinions 21 are 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 dis 

posed 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 ?rst output gear 20 is a gear concentrically disposed 

Within the second end portion 35 of the input shaft 18. The 

?rst 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 ?rst 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 ?rst output gear 20 includes an output shaft 41 driv 

ingly coupled thereto. Altemately, the ?rst output gear 20 may 

be integrally formed With the output shaft 41. The ?rst output 

gear 20 is drivingly engaged With the ?rst 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 ?rst output gear 20. Altemately, 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. Bear 

ings may be disposedbetWeen the transfer shaft 22 andpinion 

carrier 36 to permit the transfer shaft 22 to rotate about an axis 

of the transfer shaft 22. The transfer shaft 22 has a ?rst end 

portion 43 having a ?rst set of clutch teeth 44 formed on an 
US 8,523,738 B2 

5 

outer surface thereof, and a second end portion 45, having a 

second set of gear teeth 46 formed on an outer surface thereof. 

The ?rst end portion 43 and the second end portion 45 are 

integrally formed With the transfer shaft 22. The ?rst set of 

clutch teeth 44 and the second set of gear teeth 46 are formed 

in the transfer shaft 22. Altemately, the ?rst end portion 43 

and the second end portion 45 may be formed separate from 

and drivingly coupled 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 ?rst 

set of clutch teeth 44 are disposed adjacent the ?rst set of 

clutch teeth 37 of the pinion carrier 36. The ?rst portion 43 of 

the transfer shaft 22 may be selectively engaged With the 

second output gear 24 or the pinion carrier 36 

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 ?rst end 

portion 47, a second end portion 48 de?ning 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 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 ?rst set of clutch teeth 50 are formed on the ?rst 

end portion 47 adjacent the ?rst 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 ?rst 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 

?rst synchroniZer 53, and a second synchroniZer 54. The set 

of inner clutch collar teeth 52 are engaged With the ?rst 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 engage 

ment of the inner clutch collar teeth 52 and the ?rst 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 ?rst position, a second position, or a 

third position. A ?rst 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 ?rst position, the second 

position, or the third position. In the ?rst position, the inner 

clutch collar teeth 52 of the clutch 28 are drivingly engaged 

With the ?rst set of clutch teeth 44 of the transfer shaft 22 and 

the ?rst set of clutch teeth 37 of the pinion carrier 36. In the 

second position, inner clutch collar teeth 52 of clutch 28 are 

drivingly engaged With the ?rst set of clutch teeth 44 of the 

transfer shaft 22 and the ?rst set of clutch teeth 50 of the 

second output gear 24. In the third position, the inner clutch 

collar teeth 52 of the clutch 28 are only drivingly engaged 

With the ?rst set of clutch teeth 44 of the transfer shaft 22. It 

is understood the clutch 28, the clutch teeth 37, 44, 50, 52, the 

synchroniZers 53, 54, and the engagement portions 38, 49 

may be substituted With any clutching device that permits 

selective engagement of a driving and a driven part. 

5 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

6 

The ?rst synchroniZer 53 is an annular body coupled to the 

clutch 28 adjacent the engagement portion 38 of the pinion 

carrier 36. The ?rst synchroniZer 53 has a ?rst conical engage 

ment surface 58. Altemately, the ?rst synchroniZer 53 may 

have an engagement surface having any other shape. When 

the clutch 28 is moved from the third position toWards the ?rst 

position, the ?rst conical engagement surface 58 contacts the 

engagement portion 38 of the pinion carrier 36, causing the 

clutch 28 to act upon the pinion carrier 3 6. When the clutch 28 

is moved further toWards the ?rst set of clutch teeth 37 of the 

input shaft 18, the clutch continues to act upon the pinion 

carrier 36 as the inner clutch collar teeth 52 become drivingly 

engaged With the ?rst set of clutch teeth 44 of the transfer 

shaft 22 and the ?rst 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 ?rst end portion 47 of the second 

output gear 24. The second synchroniZer 54 has a second 

conical engagement surface 59. Alternately, the second syn 

chroniZer 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 engage 

ment 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 ?rst 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 ?rst set of clutch teeth 44 of the transfer 

shaft 22 and the ?rst set of clutch teeth 50 of the second output 

gear 24. 

The ?rst axle assembly 14 includes the bevel gear pinion 

42, a ?rst driving gear 60, a ?rst Wheel differential 61, and a 

?rst pair of output axle shafts 62. Preferably, the components 

42, 60, 61, 62 are formed from a hardened steel, hoWever the 

components 42, 60, 61, 62 may be formed from any other 

rigid material. As shoWn, the ?rst axle assembly 14 includes 

the four components 42, 60, 61, 62 disposed in a ?rst axle 

housing 63 but it is understood the ?rst axle assembly 14 may 

include feWer or more components. 

The ?rst driving gear 60 is coupled to a housing of the ?rst 

Wheel differential 61 by a plurality of fasteners or a Weld and 

is rotatable about an axis of the ?rst pair of output axle shafts 

62 Within the ?rst axle housing 63. Alternately, the ?rst driv 

ing gear 60 may be integrally formed With the ?rst Wheel 

differential 61 . As is knoWn in the art, the ?rst driving gear 60 

has gear teeth formed on an outer surface thereof. The ?rst 

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 ?rst driving gear 60 is drivingly engaged 

With the bevel gear pinion 42 and has a ?rst gear ratio. As a 

non-limiting example, the ?rst 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 ?rst driving gear 

60 of the ?rst axle assembly 14 through a single gear mesh. 

The ?rst Wheel differential 61 is a bevel gear style differ 

ential as is knoWn in the art having a plurality of driving 

pinions and a pair of side gears drivingly engaged With the 

?rst pair of output axle shafts 62. The ?rst Wheel differential 

61 is rotatably disposed Within the ?rst axle housing 63 about 

the axis of the ?rst pair of output axle shafts 62. Alternately, 

other styles of differentials may be used in place of the ?rst 

Wheel differential 61. 

The ?rst pair of output axle shafts 62 are elongate cylin 

drical members having a common axis rotatably mounted 

Within the ?rst axle housing 63. Bearings 32 disposed 

betWeen the ?rst pair of output axle shafts 62 and the ?rst axle 
US 8,523,738 B2 

7 

housing 63 permit the ?rst pair of output axle shafts 62 to 

rotate therein. The side gears of the ?rst Wheel differential 61 

are disposed on ?rst ends of each of the ?rst output axle shafts 

62 and Wheels (not shoWn) are disposed on second ends of 

each of the ?rst 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. 

Preferably, the components 64, 65, 66, 67, 68 are formed from 

a hardened steel, hoWever the components 64, 65, 66, 67, 68 

may be formed from any other rigid material. As shoWn, the 

second axle assembly 16 includes the ?ve components 64, 65, 

66, 67, 68 disposed in a second axle housing 69 but it is 

understoodthe second axle assembly 16 may include feWer or 

more components. 

The inter-axle shaft 64 comprises at least one elongate 

cylindrical 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 cylindrical members connected by 

joints. Bearings 32 disposed betWeen the inter-axle shaft 64 

and the housing 30 permit the inter-axle shaft 64 to rotate 

therein. 

Abevel gearpinion 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 gearpinion 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 ?rst gear 

ratio, but it is understood that other ratios or a ratio equal to 

the ?rst 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 dif 

ferential 66 is rotatably disposed Within the second axle hous 

ing 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 cylin 

drical members having a common axis rotatably 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 permit the second pair of output axle 

shafts 67 to rotate therein. The side gears of the second Wheel 

differential 66 are disposed on ?rst 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 ?rst and secondportions. 

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 

20 

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35 

40 

45 

50 

55 

60 

65 

8 

other style of clutch. The axle clutch 68 has a plurality of teeth 

formed thereon for selectively engaging corresponding teeth 

formed on the ?rst 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 ?rst portion of 

one of the second output axle shafts 67 is drivingly engaged 

With the secondportion of one of the second output axle shafts 

67 . 

The controller 55 is in communication With the poWer 

source 11, the ?rst actuator 57, the second actuator 74, and at 

least one sensor 75. Preferably, the controller 55 is in electri 

cal communication With the poWer source 11, the ?rst actua 

tor 57, the second actuator 74, and the at least one sensor 75. 

Alternately, the controller 55 may be in communication With 

the poWer source 11, the ?rst actuator 57, the second actuator 

74, and the at least one sensor 75 using pneumatics, hydrau 

lics, or a Wireless communication medium. 

The controller 55 is con?gured to accept an input contain 

ing information regarding at least one of an operating condi 

tion 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 of the rotational force 

transferred to the poWer distribution unit 12, a position of the 

clutch 28, and a position of the 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, and a duration betWeen 

successive positions of the clutch 28. The controller 55 per 

forms the adjustment to the operating condition of the poWer 

source 11, the position of the clutch 28, the position of the 

axle clutch 68, and the duration betWeen successive positions 

of the clutch 28 based on at least one of the operating condi 

tion of the poWer source 11, 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, and the position of the 

axle clutch 68. 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 11, the position of the clutch 28, the position of the 

axle clutch 68, and the duration betWeen successive positions 

of the clutch 28. 

The at least one sensor 75 may be disposed Within the 

housing 30, the ?rst 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 con?gured 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 axle 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 11, and a speed of the vehicle. 
US 8,523,738 B2 

In use, a method for use With the drive axle system 10 

facilitates shifting the power distribution unit 12 from a ?rst 

operating state to a second operating state. 

When the poWer distribution unit 12 is placed in the ?rst 

operating state, only the ?rst axle assembly 14 is driven in a 

high speed and loW torque manner of operation. The ?rst 

operating state is employed When the vehicle reaches a “cruis 

ing” speed, Which typically requires a reduced amount of 

torque to maintain the “cruising” speed. In the ?rst operating 

state, the clutch 28 is placed in a ?rst position. In the ?rst 

position, the inter-axle differential 19 is locked and the ?rst 

output gear 20 is drivingly engaged With the input shaft 18 

through the inter-axle differential 19 in the locked condition. 

When the inter-axle differential 19 is locked, the pinion car 

rier 36, the plurality of driving pinions 21, the ?rst output gear 

20, and the transfer shaft 22 rotate concurrently because inner 

clutch collar teeth 52 of the clutch 28 are drivingly engaged 

With the ?rst set of clutch teeth 37 of the pinion carrier 36 and 

the ?rst set of clutch teeth 44 of the transfer shaft 22. Further, 

in the ?rst position, the second output gear 24 is disengaged 

from the clutch 28 and the transfer shaft 22, and thus the 

inter-axle differential 19 and the input shaft 18. When the 

poWer distribution unit 12 is placed in the ?rst operating state, 

the axle clutch 68 may be disengaged, permitting the second 

output gear 24, the driven gear 70, the inter-axle shaft 64, the 

second driving gear 65, and the second Wheel differential 66 

to coast to an idle condition. 

When the poWer distribution unit 12 is placed in the second 

operating state, the ?rst axle assembly 14 and the second axle 

assembly 16 are simultaneously driven in a loW speed and 

high torque manner of operation. The second operating state 

is employed When the vehicle is operated at loWer speeds or 

When the vehicle is accelerating. When the vehicle is operated 

at loWer speeds or When the vehicle is accelerating, an 

increased amount of torque is typically required. In the sec 

ond operating state, the clutch 28 is placed in a second posi 

tion. In the second position, the inter-axle differential 19 is 

unlocked and the output shaft 41 of the ?rst output gear 20 and 

the second output gear 24 are drivingly engaged With the 

input shaft 18 through the inter-axle differential 19. The pin 

ion carrier 36 simultaneously drives the ?rst output gear 20 

and the transfer shaft 22 through the plurality of driving 

pinions 21. When the inter-axle differential 19 is unlocked, 

the pinion carrier 36, the plurality of driving pinions 21, the 

?rst output gear 20, and the transfer shaft 22 are free to rotate 

With respect to one another. Further, in the second position, 

the ?rst set of clutch teeth 50 of the second output gear 24 and 

the ?rst set of clutch teeth 44 of the transfer shaft 22 are 

engaged With the inner clutch collar teeth 52 of the clutch 28. 

When the poWer distribution unit 12 is placed in the second 

operating state, the axle clutch 68 is engaged, permitting the 

second output gear 24 to drive the second pair of output axle 

shafts 67 through the driven gear 70, the inter-axle shaft 64, 

the second driving gear 65, and the second Wheel differential 

66. 

FIGS. 2-4 are three charts illustrating three non-limiting 

examples of shifting the poWer distribution unit 12 from a ?rst 

operating state to a second operating state. 

The shifting procedure as illustrated in FIG. 2 is employed 

by the controller 55 When the temperature of the second axle 

assembly 16 is above the predetermined value prior to initia 

tion of the shifting procedure. Further, it is understood that the 

example illustrated in FIG. 2 may be selected by the control 

ler 55 on the basis that the shifting procedure illustrated in 

FIG. 2 is advantageous When the temperature of the second 

axle assembly 16 is Within a predetermined temperature 

range. A horiZontal axis shoWn in FIG. 2 indicates a duration 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

10 

of time from a ?rst chronological reference point, A, to a 

fourth chronological reference point, D. Chronological refer 

ence points B and C respectively occur betWeen points A and 

D. 

A vertical axis shoWn in FIG. 2 indicates a rotational speed 

of the ?rst output gear 20, the transfer shaft 22, the second 

output gear 24, and the poWer source 11. The vertical axis 

begins at a rotational speed of Zero and increases as the 

vertical axis extends aWay from the horiZontal axis. A rota 

tional speed of the poWer source 11 depicted in FIG. 2 is 

merely for purposes of example, and the shifting procedure is 

not limited to the depicted speeds. 

Point A indicates a starting time of the shifting procedure. 

At point A, the poWer distribution unit 12 is in the ?rst oper 

ating state. In the ?rst operating state, the clutch 28 is in the 

?rst position. When directed by the controller 55 or by an 

operator of the vehicle, the shifting procedure is initiated by 

verifying disengagement of the axle clutch 68 and by adjust 

ing the rotational force transferred to the poWer distribution 

unit 12. 

The step of adjusting the rotational force transferred to the 

poWer distribution unit 12 may be performed by one of adjust 

ing an operating condition of the poWer source 11 and at least 

partially disengaging a clutch (not shoWn) forming a portion 

of the poWer source 11. When the step of adjusting the rota 

tional force transferred to the poWer distribution unit 12 is 

performed by adjusting the operating condition of the poWer source 1 1, the operating condition of the poWer source 11 may 

be adjusted by one of increasing or decreasing a fuel supplied 

to the poWer source 11. When the rotational force is a positive 

rotational force (meaning the poWer source 11 is applying a 

rotational force to the poWer distribution unit 12) the fuel 

supplied to the poWer source 11 is decreased to reduce the 

rotational force. When the rotational force is a negative rota 

tional force (meaning the poWer distribution unit 12 is apply 

ing a rotational force to the poWer source 11) the fuel supplied 

to the poWer source 11 is increased to increase the rotational 

force. When the step of one of reducing and interrupting the 

rotational force transferred to the poWer distribution unit 12 is 

performed by at least partially disengaging a clutch or other 

device (neither are shoWn) associated With the poWer source 

11, an amount of engagement of the clutch or other device 

(neither are shoWn) associated With the poWer source 11 is 

decreased to reduce the rotational force. Adjusting the rota 

tional force transferred to the poWer distribution unit 12 as 

mentioned hereinabove is performed until the rotational force 

transferred to the poWer distribution unit 12 is about equal to 

an amount of rotational force applied by the poWer distribu 

tion unit 12 to the poWer source 11. 

When the rotational force transferred to the poWer distri 

bution unit 12 is about equal to an amount of rotational force 

applied by the poWer distribution unit 12, the controller 55 

engages the ?rst actuator 57 to move the clutch 28 from the 

?rst position to the third position. Point B of FIG. 2 indicates 

a time in the shifting procedure When the clutch 28 is placed 

in the third position. As mentioned hereinabove, When the 

clutch 28 is placed in the third position, the inter-axle differ 

ential 19 is unlocked and the second output gear 24 is disen 

gaged from the transfer shaft 22, and thus the inter-axle dif 

ferential 19. Once the clutch 28 is placed in the third position, 

the controller 55 further engages the ?rst actuator 57 to move 

the clutch 28 from the third position to the second position 

While simultaneously adjusting the rotational speed of the 

poWer source 11. 

As shoWn in FIG. 2, the duration of time betWeen points B 

and C represents a duration of time Where the clutch 28, Which 

is drivingly engaged With the transfer shaft 22, is acting upon 
US 8,523,738 B2 

11 

the second output gear 24 but before the inner clutch collar 

teeth 52 engage the ?rst set of clutch teeth 50 of the second 

output gear 24. When the clutch 28 acts upon the second 

output gear 24, a rotational force is applied to the second 

output gear 24. The rotational force applied to the second 

output gear 24 causes the second output gear 24, the driven 

gear 70, the inter-axle shaft 64, the second driving gear 65, 

and the second Wheel differential 66 to adjust the rotational 

speed from the idle condition to one of a predetermined speed 

and a target speed. 

The predetermined speed is obtained by the controller 55 

by referencing information stored in the at least one data 

table. The target speed is calculated by the controller 55 using 

the at least one algorithm and a speed of the vehicle. To 

facilitate adjusting the rotational speed to one of the prede 

termined speed and the target speed, the rotational speed of 

the poWer source 11 is adjusted. As a non-limiting example, 

the rotational speed of the poWer source 11 may be adjusted 

by one of increasing or decreasing a fuel supplied to the 

poWer source 11. A shoWn in FIG. 2, the rotational speed of 

the poWer source 11 is increased betWeen points B and C. A 

near constant rotational speed of the ?rst pair of output axle 

shafts 62 (as the vehicle coasts during the shifting procedure) 

backdrives the ?rst output gear 20. The ?rst output gear 20, 

backdriven at the near constant rotational speed, permits 

increases in the rotational speed of the poWer source 11 to be 

directly re?ected in the rotational speed of the transfer shaft 

22 through the inter-axle differential 19. The concurrent rota 

tion of the pinion carrier 36 (as driven by the input shaft 18) 

and the ?rst output gear 20 drives the transfer shaft 22 through 

the plurality of driving pinions 21 to adjust the rotational 

speed of the second output gear 24, the driven gear 70, the 

inter-axle shaft 64, the second driving gear 65, and the second 

Wheel differential 66 through the clutch 28. 

A shoWn in FIG. 2, the one of the predetermined speed and 

the target speed are obtained When the rotational speed of the 

transfer shaft 22 and the second output gear 24 are about 

equal. Further, the one of the predetermined speed and the 

target speed permits a meshing engagement betWeen the sec 

ond output gear 24 and the transfer shaft 22 With the clutch 28. 

When the one of the predetermined speed and the target 

speed are obtained, the controller 55 further engages the ?rst 

actuator 57 to move the clutch 28 from the third position to the 

second position. Point C of FIG. 2 indicates a time in the 

shifting procedure When the clutch 28 is placed in the second 

position. As mentioned hereinabove, When the clutch 28 is 

placed in the second position, the inter-axle differential 19 is 

unlocked and the second output gear 24 is engaged With the 

transfer shaft 22, and thus the inter-axle differential 19. 

When the one of the predetermined speed and the target 

speed are obtained, the controller 55 commands the second 

actuator 74 to move the axle clutch 68 to an engaged position. 

Point C of FIG. 2 indicates the time of the shifting procedure 

When the controller 55 commands the second actuator 74 to 

move the axle clutch 68 to an engaged position. Point D of 

FIG. 2 indicates the time of the shifting procedure When the 

axle clutch 68 is engaged. As shoWn in FIG. 2, the duration of 

time betWeen points C and D represents a duration of time 

after the controller 55 commands the second actuator 74 to 

engage the axle clutch 68 but before the axle clutch 68 is 

engaged. The axle clutch 68 may not immediately engage due 

to a misalignment betWeen the ?rst portion and the second 

portion of one of the second pair of output axle shafts, a 

slipping condition of one of the Wheels (not shoWn) coupled 

to the second pair of output axle shafts 67, or due to both 

conditions. As shoWn in FIG. 2, once the one of the predeter 

mined speed and the target speed are obtained, a substantially 

20 

25 

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35 

40 

45 

50 

55 

60 

65 

12 

constant rotational speed of the poWer source 11 is main 

tained by the controller 55. When the axle clutch 68 is 

engaged, the second pair of output axle shafts 67 is drivingly 

engaged With the second output gear 24 through the driven 

gear 70, the inter-axle shaft 64, the second driving gear 65, 

and the second Wheel differential 66. 

Following point D, the step of one of increasing and resum 

ing the rotational force transferred to the poWer distribution 

unit 12 may be performed by one of adjusting an operating 

condition of the poWer source 11 and by engaging the clutch 

(not shoWn) forming a portion of the poWer source 11. When 

the step of increasing the rotational force transferred to the 

poWer distribution unit 12 is performed by adjusting the oper 

ating condition of the poWer source 11, the operating condi 

tion of the poWer source 11 may be adjusted by increasing the 

fuel supplied to the poWer source 11. When the step of 

increasing and resuming the rotational force transferred to the 

poWer distribution unit 12 is performed by engaging the 

clutch (not shoWn), the amount of engagement of the clutch 

(not shoWn) associated With the poWer source 11 is increased 

to increase the rotational force. Adjusting the rotational force 

transferred to the poWer distribution unit 12 as mentioned 

hereinabove completes the shifting procedure as illustrated in 

FIG. 2, and the controller 55 returns control of one of the 

operating conditions of the poWer source 11 and the clutch 

(not shoWn) to the operator. 

Once the drive axle system 10 is placed in the second 

operating state, the rotational force applied to the poWer dis 

tribution unit 12 by the poWer source 11 is distributed 

betWeen the ?rst output gear 20 and the second output gear 24 

through the inter-axle differential 19. A rotational difference 

of the ?rst output gear 20 and the second output gear 24 

caused by a difference betWeen the ?rst gear ratio and the 

second gear ratio is accommodated by the inter-axle differ 

ential 19. Because the inter-axle differential 19 accommo 

dates the rotational difference betWeen the ?rst gear ratio and 

the second gear ratio, a cumulative gear ratio is provided. The 

cumulative gear ratio is intermediate the ?rst gear ratio and 

the second gear ratio. 

The shifting procedure as illustrated in FIG. 3 is employed 

by the controller 55 When the temperature of the second axle 

assembly 16 is beloW the predetermined value prior to initia 

tion of the shifting procedure. Further, it is understood that the 

example illustrated in FIG. 3 may be selected by the control 

ler 55 on the basis that the shifting procedure illustrated in 

FIG. 3 is advantageous When the temperature of the second 

axle assembly 16 is Within a predetermined temperature 

range. The shifting procedure illustrated in FIG. 3 may be 

selected When the temperature of the second axle assembly 16 

is loW enough to substantially reduce an effectiveness of the 

synchroniZer 54 of the clutch 28 in acting upon the second 

output gear 24 due to an increase in viscosity of the lubricant 

disposed in the second axle assembly 16. A horiZontal axis 

shoWn in FIG. 3 indicates a duration of time from a ?rst 

chronological reference point, A, to a ?fth chronological ref 

erence point, E. Chronological reference points B, C, and D 

respectively occur betWeen points A and E. 

A vertical axis shoWn in FIG. 3 indicates the rotational 

speed of the ?rst output gear 20, the transfer shaft 22, the 

second output gear 24, and the poWer source 11. The vertical 

axis begins at a rotational speed of Zero and increases as the 

vertical axis extends aWay from the horizontal axis. The rota 

tional speed of the poWer source 11 depicted in FIG. 3 is 

merely for purposes of example, and the shifting procedure is 

not limited to the depicted speeds. 

Point A indicates a starting time of the shifting procedure. 

At point A, the poWer distribution unit 12 is in the ?rst oper 
US 8,523,738 B2 

13 

ating state. In the ?rst operating state, the clutch 28 is in the 

?rst position. When directed by the controller 55 or by an 

operator of the vehicle, the shifting procedure is initiated by 

verifying disengagement of the axle clutch 68 and by adjust 

ing the rotational force transferred to the poWer distribution 

unit 12. 

The step of adjusting the rotational force transferred to the 

poWer distribution unit 12 may be performed by one of adjust 

ing an operating condition of the poWer source 11 and at least 

partially disengaging a clutch (not shoWn) forming a portion 

of the poWer source 11. When the step of adjusting the rota 

tional force transferred to the poWer distribution unit 12 is 

performed by adjusting the operating condition of the poWer source 11, the operating condition of the poWer source 11 may 

be adjusted by one of increasing or decreasing a fuel supplied 

to the poWer source 11. When the rotational force is a positive 

rotational force (meaning the poWer source 11 is applying a 

rotational force to the poWer distribution unit 12) the fuel 

supplied to the poWer source 11 is decreased to reduce the 

rotational force. When the rotational force is a negative rota 

tional force (meaning the poWer distribution unit 12 is apply 

ing a rotational force to the poWer source 11) the fuel supplied 

to the poWer source 11 is increased to increase the rotational 

force. When the step of one of reducing and interrupting the 

rotational force transferred to the poWer distribution unit 12 is 

performed by at least partially disengaging a clutch or other 

device (neither are shoWn) associated With the poWer source 

11, an amount of engagement of the clutch or other device 

(neither are shoWn) associated With the poWer source 11 is 

decreased to reduce the rotational force. Adjusting the rota 

tional force transferred to the poWer distribution unit 12 as 

mentioned hereinabove is performed until the rotational force 

transferred to the poWer distribution unit 12 is about equal to 

an amount of rotational force applied by the poWer distribu 

tion unit 12 to the poWer source 11. 

When the rotational force transferred to the poWer distri 

bution unit 12 is about equal to an amount of rotational force 

applied by the poWer distribution unit 12, the controller 55 

engages the ?rst actuator 57 to move the clutch 28 from the 

?rst position to the third position. Point B of FIG. 3 indicates 

a time in the shifting procedure When the clutch 28 is placed 

in the third position. As mentioned hereinabove, When the 

clutch 28 is placed in the third position, the inter-axle differ 

ential 19 is unlocked and the second output gear 24 is disen 

gaged from the transfer shaft 22, and thus the inter-axle dif 

ferential 19. 

Once the clutch 28 is placed in the third position, the 

controller 55 decreases a rotational speed of the poWer source 

11. As a non-limiting example, the rotational speed of the 

poWer source 11 may be decreased by decreasing a fuel 

supplied to the poWer source 11. A shoWn in FIG. 3, the 

rotational speed of the poWer source 11 is decreased betWeen 

points B and C. A near constant rotational speed of the ?rst 

pair of output axle shafts 62 (as the vehicle coasts during the 

shifting procedure) backdrives the ?rst output gear 20. The 

?rst output gear 20, backdriven at the near constant rotational 

speed, permits decreases in the rotational speed of the poWer 

source 11 to be directly re?ected in the rotational speed of the 

transfer shaft 22 through the inter-axle differential 19. The 

concurrent rotation of the pinion carrier 36 (as driven by the 

input shaft 18) and the ?rst output gear 20 retards the transfer 

shaft 22 through the plurality of driving pinions 21 to adjust 

the rotational speed of the transfer shaft 22. The rotational 

speed of the transfer shaft 22 is adjusted to facilitate a smooth 

engagement of the clutch 28 With the second output gear 24 

When the clutch 28 is moved from the third position to the 

second position. As a non-limiting example, the rotational 

5 

10 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

14 

speed of the poWer source 11 may be decreased betWeen 

points B and C to decrease the rotational speed of the transfer 

shaft 22 to about Zero. Point C of FIG. 3 indicates a time in the 

shifting procedure When the clutch 28 is placed in the second 

position. 

When the rotational speed of the transfer shaft 22 is 

adjusted to facilitate a smooth engagement of the clutch 28 

With the second output gear 24, the controller 55 further 

engages the ?rst actuator 57 to move the clutch 28 from the 

third position to the second position While simultaneously 

adjusting a rotational speed of the poWer source 11. 

As shoWn in FIG. 3, the duration of time betWeen points C 

and D represents a duration of time Where the inner clutch 

collar teeth 52 are drivingly engaged With the clutch teeth 44 

of the transfer shaft 22 and the clutch teeth 50 of the second 

output gear 24 but before the controller 55 commands the 

second actuator 74 to move the axle clutch 68 to an engaged 

position. 

When the clutch 28 is engaged With the second output gear 

24, the second output gear 24 is drivingly engaged With the 

transfer shaft 22. When the second output gear 24 is drivingly 

engaged With the transfer shaft 22, the rotational speed of the 

second output gear 24, the driven gear 70, the inter-axle shaft 

64, the second driving gear 65, and the second Wheel differ 

ential 66 may be adjusted to one of a predetermined speed and 

a target speed. 

Further, When the second output gear 24 is drivingly 

engaged With the transfer shaft 22, the second driving gear 65 

and the second Wheel differential 66 imparts energy to the 

lubricant disposed Within the second axle assembly 16. The 

duration of time betWeen points C and D may be determined 

by the controller based on the temperature of the second axle 

assembly 16 as indicated by the sensor 75. The controller 55 

may increase or decrease the duration of time betWeen points 

C and D until the temperature of the second axle assembly 16 

is above the predetermined value. As a non-limiting example, 

the predetermined value may be about 200 Fahrenheit. 

The predetermined speed is obtained by the controller 55 

by referencing information stored in the at least one data 

table. The target speed is calculated by the controller 55 using 

the at least one algorithm and a speed of the vehicle. To 

facilitate adjusting the rotational speed to one of the prede 

termined speed and the target speed, the rotational speed of 

the poWer source 11 is adjusted. As a non-limiting example, 

the rotational speed of the poWer source 11 may be adjusted 

by one of increasing or decreasing a fuel supplied to the 

poWer source 11. A shoWn in FIG. 3, the rotational speed of 

the poWer source 11 is increased betWeen points C and D. A 

near constant rotational speed of the ?rst pair of output axle 

shafts 62 (as the vehicle coasts during the shifting procedure) 

backdrives the ?rst output gear 20. The ?rst output gear 20, 

backdriven at the near constant rotational speed, permits 

increases in the rotational speed of the poWer source 11 to be 

directly re?ected in the rotational speed of the transfer shaft 

22 through the inter-axle differential 19. The concurrent rota 

tion of the pinion carrier 36 (as driven by the input shaft 18) 

and the ?rst output gear 20 drives the transfer shaft 22 through 

the plurality of driving pinions 21 to adjust the rotational 

speed of the second output gear 24, the driven gear 70, the 

inter-axle shaft 64, the second driving gear 65, and the second 

Wheel differential 66 through the clutch 28 placed in the 

second position. 

A shoWn in FIG. 3, the one of the predetermined speed and 

the target speed are obtained When the rotational speed of the 

second output gear 24, the driven gear 70, the inter-axle shaft 

64, the second driving gear 65, and the second Wheel differ 

ential 66 permits a meshing engagement betWeen the ?rst 
US 8,523,738 B2 

15 

portion of one of the second pair of output axle shafts 67 and 

the second portion of one the second pair of output axle shafts 

67 With the axle clutch 68. 

When the one of the predetermined speed and the target 

speed are obtained, the controller 55 commands the second 

actuator 74 to move the axle clutch 68 to the engagedposition. 

Point D of FIG. 3 indicates the time of the shifting procedure 

When the controller 55 commands the second actuator 74 to 

move the axle clutch 68 to the engaged position. Point E of 

FIG. 3 indicates the time of the shifting procedure When the 

axle clutch 68 is engaged. As shoWn in FIG. 3, the duration of 

time betWeen points D and E represents a duration of time 

after the controller 55 commands the second actuator 74 to 

engage the axle clutch 68 but before the axle clutch 68 is 

engaged. The axle clutch 68 may not immediately engage due 

to a misalignment betWeen the ?rst portion and the second 

portion of one of the second pair of output axle shafts, a 

slipping condition of one of the Wheels (not shoWn) coupled 

to the second pair of output axle shafts 67, or due to both 

conditions. As shoWn in FIG. 3, once the one of the predeter 

mined speed and the target speed are obtained, a substantially 

constant rotational speed of the poWer source 11 is main 

tained by the controller 55. When the axle clutch 68 is 

engaged, the second pair of output axle shafts 67 is drivingly 

engaged With the second output gear 24 through the driven 

gear 70, the inter-axle shaft 64, the second driving gear 65, 

and the second Wheel differential 66. 

Following point E, the step of one of increasing and resum 

ing the rotational force transferred to the poWer distribution 

unit 12 may be performed by one of adjusting an operating 

condition of the poWer source 11 and by engaging the clutch 

(not shown) forming a portion of the poWer source 11. When 

the step of increasing the rotational force transferred to the 

poWer distribution unit 12 is performed by adjusting the oper 

ating condition of the poWer source 11, the operating condi 

tion of the poWer source 11 may be adjusted by increasing the 

fuel supplied to the poWer source 11. When the step of 

increasing and resuming the rotational force transferred to the 

poWer distribution unit 12 is performed by engaging the 

clutch (not shoWn), the amount of engagement of the clutch 

(not shoWn) associated With the poWer source 11 is increased 

to increase the rotational force. Adjusting the rotational force 

transferred to the poWer distribution unit 12 as mentioned 

hereinabove completes the shifting procedure as illustrated in 

FIG. 3, and the controller 55 returns control of one of the 

operating conditions of the poWer source 11 and the clutch 

(not shoWn) to the operator. 

Once the drive axle system 10 is placed in the second 

operating state, the rotational force applied to the poWer dis 

tribution unit 12 by the poWer source 11 is distributed 

betWeen the ?rst output gear 20 and the second output gear 24 

through the inter-axle differential 19. A rotational difference 

of the ?rst output gear 20 and the second output gear 24 

caused by a difference betWeen the ?rst gear ratio and the 

second gear ratio is accommodated by the inter-axle differ 

ential 19. Because the inter-axle differential 19 accommo 

dates the rotational difference betWeen the ?rst gear ratio and 

the second gear ratio, a cumulative gear ratio is provided. The 

cumulative gear ratio is intermediate the ?rst gear ratio and 

the second gear ratio. 

The shifting procedure as illustrated in FIG. 4 is employed 

by the controller 55 When the temperature of the second axle 

assembly 16 is beloW the predetermined value prior to initia 

tion of the shifting procedure. Further, it is understood that the 

example illustrated in FIG. 4 may be selected by the control 

ler 55 on the basis that the shifting procedure illustrated in 

FIG. 4 is advantageous When the temperature of the second 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

16 

axle assembly 16 is Within a predetermined temperature 

range. The shifting procedure illustrated in FIG. 3 may be 

selected When the temperature of the second axle assembly 16 

is loW enough to reduce an effectiveness of the synchroniZer 

54 of the clutch 28 in acting upon the second output gear 24 

due to an increase in viscosity of the lubricant disposed in the 

second axle assembly 16. A horizontal axis shoWn in FIG. 4 

indicates a duration of time from a ?rst chronological refer 

ence point, A, to a ?fth chronological reference point, E. 

Chronological reference points B, C, and D respectively occur betWeen points A and E. 

A vertical axis shoWn in FIG. 4 indicates a rotational speed 

of the ?rst output gear 20, the transfer shaft 22, the second 

output gear 24, and the poWer source 11. The vertical axis 

begins at a rotational speed of Zero and increases as the 

vertical axis extends aWay from the horiZontal axis. The rota 

tional speed of the poWer source 11 depicted in FIG. 4 is 

merely for purposes of example, and the shifting procedure is 

not limited to the depicted speeds. 

Point A indicates a starting time of the shifting procedure. 

At point A, the poWer distribution unit 12 is in the ?rst oper 

ating state. In the ?rst operating state, the clutch 28 is in the 

?rst position. When directed by the controller 55 or by an 

operator of the vehicle, the shifting procedure is initiated by 

verifying disengagement of the axle clutch 68 and by adjust 

ing the rotational force transferred to the poWer distribution 

unit 12. 

The step of adjusting the rotational force transferred to the 

poWer distribution unit 12 may be performed by one of adjust 

ing an operating condition of the poWer source 11 and at least 

partially disengaging a clutch (not shoWn) forming a portion 

of the poWer source 11. When the step of adjusting the rota 

tional force transferred to the poWer distribution unit 12 is 

performed by adjusting the operating condition of the poWer source 1 1, the operating condition of the poWer source 11 may 

be adjusted by one of increasing or decreasing a fuel supplied 

to the poWer source 11. When the rotational force is a positive 

rotational force (meaning the poWer source 11 is applying a 

rotational force to the poWer distribution unit 12) the fuel 

supplied to the poWer source 11 is decreased to reduce the 

rotational force. When the rotational force is a negative rota 

tional force (meaning the poWer distribution unit 12 is apply 

ing a rotational force to the poWer source 11) the fuel supplied 

to the poWer source 11 is increased to increase the rotational 

force. When the step of one of reducing and interrupting the 

rotational force transferred to the poWer distribution unit 12 is 

performed by at least partially disengaging a clutch or other 

device (neither are shoWn) associated With the poWer source 

11, an amount of engagement of the clutch or other device 

(neither are shoWn) associated With the poWer source 11 is 

decreased to reduce the rotational force. Adjusting the rota 

tional force transferred to the poWer distribution unit 12 as 

mentioned hereinabove is performed until the rotational force 

transferred to the poWer distribution unit 12 is about equal to 

an amount of rotational force applied by the poWer distribu 

tion unit 12 to the poWer source 11. 

When the rotational force transferred to the poWer distri 

bution unit 12 is about equal to an amount of rotational force 

applied by the poWer distribution unit 12, the controller 55 

engages the ?rst actuator 57 to move the clutch 28 from the 

?rst position to the third position. Point B of FIG. 4 indicates 

a time in the shifting procedure When the clutch 28 is placed 

in the third position. As mentioned hereinabove, When the 

clutch 28 is placed in the third position, the inter-axle differ 

ential 19 is unlocked and the second output gear 24 is disen 

gaged from the transfer shaft 22, and thus the inter-axle dif 

ferential 19. 
US 8,523,738 B2 

1 7 

Once the clutch 28 is placed in the third position, the 

controller 55 further engages the ?rst actuator 57 to move the 

clutch 28 from the third position to the second position While 

simultaneously adjusting a rotational speed of the poWer 

source 11. As shoWn in FIG. 4, the rotational speed of the 

poWer source 11 is decreased betWeen points B and C as the 

second synchroniZer 54 of the clutch 28 acts upon the second 

output gear 24 but before the clutch 28 is placed in the second 

position. 

As a non-limiting example, the rotational speed of the 

poWer source 11 may be decreased by decreasing a fuel 

supplied to the poWer source 11. A shoWn in FIG. 4, the 

rotational speed of the poWer source 11 is decreased betWeen 

points B and C. A near constant rotational speed of the ?rst 

pair of output axle shafts 62 (as the vehicle coasts during the 

shifting procedure) backdrives the ?rst output gear 20. The 

?rst output gear 20, backdriven at the near constant rotational 

speed, permits decreases in the rotational speed of the poWer 

source 11 to be directly re?ected in the rotational speed of the 

transfer shaft 22 through the inter-axle differential 19. The 

concurrent rotation of the pinion carrier 36 (as driven by the 

input shaft 18) and the ?rst output gear 20 retards the transfer 

shaft 22 through the plurality of driving pinions 21 to adjust 

the rotational speed of the transfer shaft 22. The rotational 

speed of the transfer shaft 22 is adjusted to facilitate a smooth 

engagement of the clutch 28 With the second output gear 24 

When the clutch 28 is moved from the third position to the 

second position. Point C indicates a time in the shifting pro 

cedure When the clutch 28 is placed in the second position. 

When one of the rotational speed of the poWer source 11 

and the rotational speed of the transfer shaft 22 are adjusted to 

facilitate a smooth engagement of the clutch 28 With the 

second output gear 24, the controller 55 further engages the 

?rst actuator 57 to engage the clutch 28 With the second 

output gear 24 then increasing a rotational speed of the poWer 

source 11. BetWeen points C and D, When the clutch 28 is 

placed in the second position, the rotational speed of the 

poWer source 11 is increased. 

As shoWn in FIG. 4, the duration of time betWeen points C 

and D represents a duration of time Where the inner clutch 

collar teeth 52 are drivingly engaged With the clutch teeth 44 

of the transfer shaft 22 and the clutch teeth 50 of the second 

output gear 24 but before the controller commands the second 

actuator 74 to move the axle clutch 68 to an engaged position. 

When the clutch 28 is engaged With the second output gear 

24, the second output gear 24 is drivingly engaged With the 

transfer shaft 22. When the second output gear 24 is drivingly 

engaged With the transfer shaft 22, the rotational speed of the 

second output gear 24, the driven gear 70, the inter-axle shaft 

64, the second driving gear 65, and the second Wheel differ 

ential 66 may be adjusted to one of a predetermined speed and 

a target speed. 

Further, When the second output gear 24 is drivingly 

engaged With the transfer shaft 22, the second driving gear 65 

and the second Wheel differential 66 imparts energy to the 

lubricant disposed Within the second axle assembly 16. The 

duration of time betWeen points C and D may be determined 

by the controller based on the temperature of the second axle 

assembly 16 as indicated by the sensor 75. The controller 55 

may increase or decrease the duration of time betWeen points 

C and D until the temperature of the second axle assembly 16 

is above the predetermined value. As a non-limiting example, 

the predetermined value may be about 200 Fahrenheit. 

The predetermined speed is obtained by the controller 55 

by referencing information stored in the at least one data 

table. The target speed is calculated by the controller 55 using 

the at least one algorithm and a speed of the vehicle. To 

20 

25 

30 

35 

40 

50 

55 

60 

65 

18 

facilitate adjusting the rotational speed to one of the prede 

termined speed and the target speed, the rotational speed of 

the poWer source 11 is adjusted. The rotational speed of the 

poWer source 11 is adjusted by adjusting the rotational speed 

of the poWer source 11. As a non-limiting example, the rota 

tional speed of the poWer source 11 may be adjusted by 

increasing a fuel supplied to the poWer source 11. A shoWn in 

FIG. 4, the rotational speed of the poWer source 11 is 

increased betWeen points C and D. A near constant rotational 

speed of the ?rst pair of output axle shafts 62 (as the vehicle 

coasts during the shifting procedure) backdrives the ?rst out 

put gear 20. The ?rst output gear 20, backdriven at the near 

constant rotational speed, permits increases in the rotational 

speed of the poWer source 11 to be directly re?ected in the 

rotational speed of the transfer shaft 22 through the inter-axle 

differential 19. The concurrent rotation of the pinion carrier 

36 (as driven by the input shaft 18) and the ?rst output gear 20 

drives the transfer shaft 22 through the plurality of driving 

pinions 21 to adjust the rotational speed of the second output 

gear 24, the driven gear 70, the inter-axle shaft 64, the second 

driving gear 65, and the second Wheel differential 66 through 

the clutch 28 placed in the second position. 

A shoWn in FIG. 4, the one of the predetermined speed and 

the target speed are obtained When the rotational speed of the 

second output gear 24, the driven gear 70, the inter-axle shaft 

64, the second driving gear 65, and the second Wheel differ 

ential 66 permits a meshing engagement betWeen the ?rst 

portion of one of the second pair of output axle shafts 67 and 

the second portion of one the second pair of output axle shafts 

67 With the axle clutch 68. 

When the one of the predetermined speed and the target 

speed are obtained, the controller 55 commands the second 

actuator 74 to move the axle clutch 68 to the engaged position. 

Point D of FIG. 4 indicates the time in the shifting procedure 

When the controller 55 commands the second actuator 74 to 

move the axle clutch 68 to the engaged position. Point E of 

FIG. 4 indicates the time of the shifting procedure When the 

axle clutch 68 is engaged. As shoWn in FIG. 4, the duration of 

time betWeen points D and E represents a duration of time 

after the controller 55 commands the second actuator 74 to 

engage the axle clutch 68 but before the axle clutch 68 is 

engaged. The axle clutch 68 may not immediately engage due 

to a misalignment betWeen the ?rst portion and the second 

portion of one of the second pair of output axle shafts, a 

slipping condition of one of the Wheels (not shoWn) coupled 

to the second pair of output axle shafts 67, or due to both 

conditions. As shoWn in FIG. 4, once the one of the predeter 

mined speed and the target speed are obtained, a substantially 

constant rotational speed of the poWer source 11 is main 

tained by the controller 55. When the axle clutch 68 is 

engaged, the second pair of output axle shafts 67 is drivingly 

engaged With the second output gear 24 through the driven 

gear 70, the inter-axle shaft 64, the second driving gear 65, 

and the second Wheel differential 66. 

FolloWing point E, the step of one of increasing and resum 

ing the rotational force transferred to the poWer distribution 

unit 12 may be performed by one of adjusting an operating 

condition of the poWer source 11 and by engaging the clutch 

(not shoWn) forming a portion of the poWer source 11. When 

the step of increasing the rotational force transferred to the 

poWer distribution unit 12 is performed by adjusting the oper 

ating condition of the poWer source 11, the operating condi 

tion of the poWer source 11 may be adjusted by increasing the 

fuel supplied to the poWer source 11. When the step of 

increasing and resuming the rotational force transferred to the 

poWer distribution unit 12 is performed by engaging the 

clutch (not shoWn), the amount of engagement of the clutch 
US 8,523,738 B2 

19 

(not shown) associated With the power source 11 is increased 

to increase the rotational force. Adjusting the rotational force 

transferred to the poWer distribution unit 12 as mentioned 

hereinabove completes the shifting procedure as illustrated in 

FIG. 4, and the controller 55 returns control of one of the 

operating conditions of the poWer source 11 and the clutch 

(not shoWn) to the operator. 

Once the drive axle system 10 is placed in the second 

operating state, the rotational force applied to the poWer dis 

tribution unit 12 by the poWer source 11 is distributed 

betWeen the ?rst output gear 20 and the second output gear 24 

through the inter-axle differential 19. A rotational difference 

of the ?rst output gear 20 and the second output gear 24 

caused by a difference betWeen the ?rst gear ratio and the 

second gear ratio is accommodated by the inter-axle differ 

ential 19. Because the inter-axle differential 19 accommo 

dates the rotational difference betWeen the ?rst gear ratio and 

the second gear ratio, a cumulative gear ratio is provided. The 

cumulative gear ratio is intermediate the ?rst gear ratio and 

the second gear ratio. 

FIG. 5 is a chart illustrating an example of shifting the 

poWer distribution unit 12 from a second operating state to a 

?rst operating state. FIG. 5 illustrates a non-limiting example 

of shifting the poWer distribution unit 12 from the second 

operating state to the ?rst operating state. 

A horiZontal axis shoWn in FIG. 5 indicates a duration of 

time from a ?rst chronological reference point, A, to a third 

chronological reference point, C. Chronological reference 

point B occurs betWeen points A and C. 

A vertical axis shoWn in FIG. 5 indicates a rotational speed 

of the ?rst output gear 20, the transfer shaft 22, the second 

output gear 24, and the poWer source 11. The vertical axis 

begins at a rotational speed of Zero and increases as the 

vertical axis extends aWay from the horiZontal axis. The rota 

tional speed of the poWer source 11 depicted in FIG. 5 is 

merely for purposes of example, and the shifting procedure is 

not limited to the depicted speeds. 

Point A indicates a starting time of the shifting procedure. 

At point A, the poWer distribution unit 12 is in the second 

operating state. In the second operating state, the clutch 28 is 

in the second position. When directed by the controller 55 or 

by an operator of the vehicle, the shifting procedure is initi 

ated by disengaging the axle clutch 68 and by adjusting the 

rotational force transferred to the poWer distribution unit 12. 

Point A of FIG. 5 indicates the time of the shifting proce 

dure When the controller 55 commands the second actuator 74 

to move the axle clutch 68 to a disengaged position. Point B 

of FIG. 5 indicates the time of the shifting procedure When the 

axle clutch 68 is disengaged. As shoWn in FIG. 5, the duration 

of time betWeen points A and B represents a duration of time 

after the controller 55 commands the second actuator 74 to 

disengage the axle clutch 68 but before the axle clutch 68 is 

disengaged. The axle clutch 68 may not immediately disen 

gage due to a slipping condition of one of the Wheels (not 

shoWn) coupled to the second pair of output axle shafts 67. As 

shoWn in FIG. 5, to facilitate disengagement of the axle clutch 

68, a substantially constant rotational speed of the poWer 

source 11 is maintained by the controller 55. When the axle 

clutch 68 is disengaged, the second pair of output axle shafts 

67 is drivingly disengaged from the second output gear 24. 

The step of adjusting the rotational force transferred to the 

poWer distribution unit 12 may be performed by one of adjust 

ing an operating condition of the poWer source 11 and at least 

partially disengaging a clutch (not shoWn) forming a portion 

of the poWer source 11. When the step of adjusting the rota 

tional force transferred to the poWer distribution unit 12 is 

performed by adjusting the operating condition of the poWer 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

20 source 1 1, the operating condition of the poWer source 11 may 

be adjusted by one of increasing or decreasing a fuel supplied 

to the poWer source 11. When the rotational force is a positive 

rotational force (meaning the poWer source 11 is applying a 

rotational force to the poWer distribution unit 12) the fuel 

supplied to the poWer source 11 is decreased to reduce the 

rotational force. When the rotational force is a negative rota 

tional force (meaning the poWer distribution unit 12 is apply 

ing a rotational force to the poWer source 11) the fuel supplied 

to the poWer source 11 is increased to increase the rotational 

force. When the step of one of reducing and interrupting the 

rotational force transferred to the poWer distribution unit 12 is 

performed by at least partially disengaging a clutch or other 

device (neither are shoWn) associated With the poWer source 

11, an amount of engagement of the clutch or other device 

(neither are shoWn) associated With the poWer source 11 is 

decreased to reduce the rotational force. Adjusting the rota 

tional force transferred to the poWer distribution unit 12 as 

mentioned hereinabove is performed until the rotational force 

transferred to the poWer distribution unit 12 is about equal to 

an amount of rotational force applied by the poWer distribu 

tion unit 12 to the poWer source 11. 

When the rotational force transferred to the poWer distri 

bution unit 12 is about equal to an amount of rotational force 

applied by the poWer distribution unit 12, the controller 55 

engages the ?rst actuator 57 to move the clutch 28 from the 

second position to the third position. Point B of FIG. 5 indi 

cates a time in the shifting procedure When the clutch 28 is 

placed in the third position. As mentioned hereinabove, When 

the clutch 28 is placed in the third position, the inter-axle 

differential 19 is unlocked and the second output gear 24 is 

disengaged from the transfer shaft 22, and thus the inter-axle 

differential 19. As shoWn in FIG. 5, betWeen points B and C, 

When the clutch 28 is moved to the third position and the axle 

clutch 68 is disengaged, the second output gear 24, the driven 

gear 70, the inter-axle shaft 64, the bevel gear pinion 72, the 

second driving gear 65, and the second Wheel differential 66 

coast to the idle condition. 

Once the clutch 28 is placed in the third position, the 

controller 55 further engages the ?rst actuator 57 to move the 

clutch 28 from the third position to the ?rst position While 

simultaneously adjusting a rotational speed of the poWer 

source 11. As shoWn in FIG. 5, the rotational speed of the 

poWer source 11 is decreased as the ?rst synchroniZer 53 of 

the clutch 28 acts upon the pinion carrier 36 but before the 

clutch 28 is placed in the ?rst position. 

As a non-limiting example, the rotational speed of the 

poWer source 11 may be decreased by decreasing a fuel 

supplied to the poWer source 11. A shoWn in FIG. 5, the 

rotational speed of the poWer source 11 is decreased betWeen 

points B and C. A near constant rotational speed of the ?rst 

pair of output axle shafts 62 (as the vehicle coasts during the 

shifting procedure) backdrives the ?rst output gear 20. The 

?rst output gear 20, backdriven at the near constant rotational 

speed, permits decreases in the rotational speed of the poWer 

source 11 to be directly re?ected in the rotational speed of the 

transfer shaft 22 through the inter-axle differential 19. The 

concurrent rotation of the pinion carrier 36 (as driven by the 

input shaft 18) and the ?rst output gear 20 retards the transfer 

shaft 22 through the plurality of driving pinions 21 to adjust 

the rotational speed of the transfer shaft 22. The rotational 

speed of the transfer shaft 22 is adjusted to facilitate a smooth 

engagement of the clutch 28 With the ?rst output gear 20 When 

the clutch 28 is moved from the third position to the ?rst 

position. 

When one of the rotational speed of the poWer source 11 

and the rotational speed of the transfer shaft 22 are adjusted to 
US 8,523,738 B2 

21 

facilitate a smooth engagement of the clutch 28 With the ?rst 

output gear 20, the controller 55 further engages the ?rst 

actuator 57 to move the clutch 28 from the third position to the 

?rst position. Point C of FIG. 5 indicates a time in the shifting 

procedure When the clutch 28 is placed in the ?rst position. As 

mentioned hereinabove, When the clutch 28 is placed in the 

?rst position, the inter-axle differential 19 is locked and the 

?rst output gear 20 is engaged With the input shaft 18 through 

the inter-axle differential 19 in the locked condition. 

FolloWing point C, the step of one of increasing and resum 

ing the rotational force transferred to the poWer distribution 

unit 12 may be performed by one of adjusting an operating 

condition of the poWer source 11 and by engaging the clutch 

(not shoWn) forming a portion of the poWer source 11. When 

the step of increasing the rotational force transferred to the 

poWer distribution unit 12 is performed by adjusting the oper 

ating condition of the poWer source 11, the operating condi 

tion of the poWer source 11 may be adjusted by increasing the 

fuel supplied to the poWer source 11. When the step of 

increasing and resuming the rotational force transferred to the 

poWer distribution unit 12 is performed by engaging the 

clutch (not shoWn), the amount of engagement of the clutch 

(not shoWn) associated With the poWer source 11 is increased 

to increase the rotational force. Adjusting the rotational force 

transferred to the poWer distribution unit 12 as mentioned 

hereinabove completes the shifting procedure as illustrated in 

FIG. 5, and the controller 55 returns control of one of the 

operating conditions of the poWer source 11 and the clutch 

(not shoWn) to the operator. 

FIG. 6 depicts yet another embodiment of the present 

invention. The embodiment shoWn in FIG. 6 is similar to the 

embodiment shoWn in FIG. 1. Similar features of the embodi 

ment shoWn in FIG. 6 are numbered similarly in series, With 

the exception of the features described beloW. 

FIG. 6 illustrates a drive axle system 10' for a vehicle 

having a poWer source 11'. The drive axle system 10' prefer 

ably includes a poWer distribution unit 612, a ?rst axle assem 

bly 14', and a second axle assembly 16'. The drive axle system 

10' is drivingly engaged With a poWer source 11'. As shoWn, 

the drive axle system 10' includes the three assemblies 612, 

14', 16', but it is understood the drive axle system 10' may 

include feWer or more assemblies or components. 

The poWer distribution unit 612 includes an input shaft 

618, an inter-axle differential 619, a ?rst output gear 620, a 

plurality of driving pinions 621, a transfer shaft 622, a second 

output gear 624, and a clutch 628. As shoWn, poWer distribu 

tion unit 612 includes the seven components 618, 619, 620, 

621, 622, 624, 628 disposed in a housing 30' but it is under 

stood the poWer distribution unit 612 may include feWer or 

more components. 

The tandem drive axle system 10' includes the input shaft 

618 at least partially disposed in the housing 30'. Preferably, 

the input shaft 618 is an elongate cylindrical member, hoW 

ever the input shaft 618 may be any other shape. Bearings 32' 

disposed betWeen the input shaft 618' and the housing 30' and 

the input shaft 618 and the transfer shaft 622 permit the input 

shaft 618 to rotate about an axis of the input shaft 618. The 

input shaft 618 has a ?rst end portion 633, having a ?rst set of 

clutch teeth 637 formed thereon, a middle portion 634, and a 

second end portion 635, having a pinion carrier 636 disposed 

thereon. 

The ?rst end portion 633 has a diameter greater than a 

diameter of the middle portion 634. The ?rst end portion 633 

is a substantially disc shaped body drivingly coupled to the 

input shaft 618. Altemately, the ?rst end portion 633 may be 

integrally formed With the input shaft 618. The ?rst end 

portion 633 includes an engagement portion 638 formed 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

22 

therein adjacent an outer peripheral edge thereof. As shoWn, 

the engagement portion 638 is a conical surface oblique to the 

input shaft 618, hoWever, the engagement portion 638 may 

have any other shape. The ?rst set of clutch teeth 637 are 

formed on the ?rst end portion 633 intermediate the input 

shaft 618 and the engagement portion 638. 

The pinion carrier 636 is a substantially disc shaped body 

having a plurality of pinion supports 639 protruding there 

from adjacent a peripheral edge of the pinion carrier 636, 

hoWever, the pinion carrier 636 may be any other rounded 

shape and may have a plurality of recesses or perforations 

formed therein. As is knoWn in the art, the pinion carrier 636 

is also knoWn as a planet carrier. 

The plurality of driving pinions 621 are rotatably coupled 

to the pinion supports 639. Each of the driving pinions 621 

have gear teeth formed on an outer surface thereof. As is 

knoWn in the art, each of the driving pinions 621 is also knoWn 

as a planet gear. Preferably, bearings are disposed betWeen 

each of the driving pinions 621 and the pinion supports 639, 

hoWever, the driving pinions 621 may be directly mounted on 

the pinion supports 639. 

The transfer shaft 622 is a holloW shaft concentrically 

disposed about the input shaft 618. Preferably, the transfer 

shaft 622 is a holloW elongate cylindrical member, hoWever 

the transfer shaft 622 may be any other shape. Bearings 32' 

disposed betWeen the transfer shaft 622 and the housing 30' 

and the input shaft 618 and the transfer shaft 622 permit the 

transfer shaft 622 to rotate about an axis of the transfer shaft 

622. The axis of the transfer shaft 622 is concurrent With the 

axis of the input shaft 618. The transfer shaft 622 has a ?rst 

end portion 643, having a ?rst set of clutch teeth 644 formed 

on an outer surface thereof, and a second end portion 645, 

having a second set of gear teeth 646 formed on an outer 

surface thereof. 

The ?rst end portion 643 and the second end portion 645 

are substantially disc shaped bodies having an outer diameter 

greater than a diameter of the transfer shaft 622. The ?rst end 

portion 643 and the second end portion 645 are drivingly 

coupled to the transfer shaft 622. Altemately, the ?rst end 

portion 643 and the second end portion 645 may be integrally 

formed With the transfer shaft 622 and may have a diameter 

substantially equal to the transfer shaft 622. Similarly, the ?rst 

set of clutch teeth 644 and the second set of clutch teeth 646 

may be formed directly in the transfer shaft 622. As is knoWn 

in the art, the second end portion 645 having the clutch teeth 

646 is knoWn as a sun gear. The second set of clutch teeth 646 

are engaged With the plurality of driving pinions 621 and the 

?rst set of clutch teeth 644 are disposed adjacent the ?rst set 

of clutch teeth 637 of the input shaft 618. 

The second output gear 624 is a gear concentrically dis 

posed about the input shaft 618 and the transfer shaft 622. The 

second output gear 624 has a central perforation having a 

diameter greater than a diameter of the transfer shaft 622. The 

second output gear 624 is a substantially disc shaped body 

having a ?rst end portion 647, a second end portion 648 

de?ning an outer diameter of the second output gear 624, and 

an engagement portion 649. Bearings (not shoWn) disposed 

betWeen the transfer shaft 622 and the second output gear 624 

permit the second output gear 624 to rotate about an axis of 

the second output gear 624. The axis of the second output gear 

624 is concurrent With the axis of the input shaft 618. A ?rst 

set of clutch teeth 650 are formed on the ?rst end portion 647 

adjacent the ?rst set of clutch teeth 644 of the transfer shaft 

622. A second set of gear teeth 651 are formed on the second 

end portion 648. 

The engagement portion 649 is formed in the second out 

put gear 624 intermediate the ?rst end portion 647 and the 
US 8,523,738 B2 

23 

second end portion 648. As shown, the engagement portion 

649 is a conical surface oblique to the input shaft 618; hoW 

ever, the engagement portion 649 may have any other shape. 

The clutch 628 is a shift collar concentrically disposed 

about the input shaft 618 and the transfer shaft 622. The clutch 

628 includes a set of inner clutch collar teeth 652 formed on 

an inner surface thereof, a ?rst synchroniZer 653, and a sec 

ond synchroniZer 654. The set of inner clutch collar teeth 652 

are engaged With the ?rst set of clutch teeth 644 of the transfer 

shaft 622. The clutch 628 can be slidably moved along the 

axis of the input shaft 618 as directed automatically by the 

controller 55' While maintaining engagement of the inner 

clutch collar teeth 652 and the ?rst set of clutch teeth 644. A 

shift fork 56' disposed in an annular recess formed in the 

clutch 628 moves the clutch 628 along the axis of the input 

shaft 618 into a ?rst position, a second position, or a third 

position. The ?rst actuator 57', Which is drivingly engaged 

With the shift fork 56', is engaged to position the shift fork 56' 

as directed manually by the controller 55'. Consequently, the 

shift fork 56' positions the clutch 628 into the ?rst position, 

the second position, or the third position. In the ?rst position, 

the clutch 628 is drivingly engaged With the ?rst set of clutch 

teeth 644 of the transfer shaft 622 and the ?rst set of clutch 

teeth 637 of the input shaft 618. In the second position, the 

clutch 628 is drivingly engaged With the ?rst set of clutch 

teeth 644 of the transfer shaft 622 and the ?rst set of clutch 

teeth 650 of the second output gear 624. In the third position, 

the inner clutch collar teeth 652 of the clutch 628 are only 

drivingly engaged With the ?rst set of clutch teeth 644 of the 

transfer shaft 622. It is understood the clutch 628, the clutch 

teeth 637, 644, 650, 652, the synchroniZers 653, 654, and the 

engagement portions 638, 649 may be substituted With any 

clutching device that permits selective engagement of a driv 

ing and a driven part. 

The ?rst synchroniZer 653 is an annular body coupled to 

the clutch 628 adjacent the ?rst end portion 633 of the input 

shaft 618. The ?rst synchroniZer 653 has a ?rst conical 

engagement surface 658. Alternately, the ?rst synchroniZer 

653 may have an engagement surface having any other shape. 

When the clutch 628 is moved from the third position toWards 

the ?rst position, the ?rst conical engagement surface 658 

contacts the engagement portion 638 of the ?rst end portion 

633 of the input shaft 618, causing the clutch 628 to act upon 

the input shaft 618. When the clutch 628 is moved toWards the 

?rst set of clutch teeth 637 of the input shaft 618, the clutch 

628 continues to act upon the input shaft 618 as the inner 

clutch collar teeth 652 become drivingly engaged With the 

?rst set of clutch teeth 644 of the transfer shaft 622 and the 

?rst set of clutch teeth 637 of the input shaft 618. 

The second synchroniZer 654 is an annular body coupled to 

the clutch 628 adjacent the ?rst end portion 647 of the second 

output gear 624. The second synchroniZer 654 has a second 

conical engagement surface 659. Alternately, the second syn 

chroniZer 654 may have an engagement surface having any 

other shape. When the clutch 628 is moved from the third 

position into the second position, the second conical engage 

ment surface 659 contacts the engagement portion 649 of the 

?rst end portion 647 of the second output gear 624. When the 

clutch 628 is moved further toWards the ?rst set of clutch teeth 

650 of the second output gear 624, the clutch 628 continues to 

act upon the second output gear 624 as the inner clutch collar 

teeth 652 become drivingly engaged With the ?rst set of clutch 

teeth 644 of the transfer shaft 622 and the ?rst set of clutch 

teeth 650 of the second output gear 24. 

The ?rst output gear 620 is a gear concentrically disposed 

about the input shaft 618 and the pinion carrier 636. The ?rst 

output gear 620 has a central recess having a diameter greater 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

24 

than an outer diameter of the pinion carrier 636. The ?rst 

output gear 620 is a substantially cup shaped body having an 

inner surface having gear teeth 640 formed on. As is knoWn in 

the art, the ?rst output gear 620 is knoWn as a ring gear. The 

gear teeth 640 are engaged With the gear teeth formed on the 

outer surface of each of the driving pinions 621. 

The ?rst output gear 620 includes an output shaft 641 

drivingly coupled thereto. Alternately, the ?rst output gear 

620 may be integrally formed With the output shaft 641. The 

output shaft 641 is collinear With the input shaft 618. Bearings 

32' disposed betWeen the output shaft 641 and the housing 30' 

support the ?rst output gear 620 and permit the output shaft 

641 to rotate about an axis of the output shaft 641. 

An axle clutch 668 is a shift collar having a conical engage 

ment surface that divides one of the second output axle shafts 

67' into ?rst and second portions. Alternately, the axle clutch 

668 may be a plate style clutch or any other style of friction 

clutch. The axle clutch 668 has a plurality of teeth formed 

thereon for selectively engaging corresponding teeth formed 

on the ?rst portion and the second portion of the second 

output axle shafts 67'. The axle clutch 668 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 668, as directed by the controller 55'. When the 

axle clutch 668 is in the engaged position, the ?rst portion of 

one of the second output axle shafts 67' is drivingly engaged 

With the secondportion of one of the second output axle shafts 

67'. 

The axle clutch 668 may be selectively engaged to impart 

energy to a lubricant disposed Within the second axle housing 

69'. Preferably, When the axle clutch 668 is used to impart 

energy to the lubricant disposed Within the second axle hous 

ing 69', the axle clutch 668 is a clutch capable of acting upon 

on a connecting component in a variable manner, such as a 

shift collar having a conical engagement surface. When the 

axle clutch 668 is used to impart energy to the lubricant 

disposed Within the second axle housing 69', the controller 55' 

one of engages and partially engages the axle clutch 668 until 

a temperature of the second axle assembly 16' is above a 

predetermined value. As a non-limiting example, the prede 

termined value may be about 200 Fahrenheit. 

The axle clutch 668 and the clutch 628 may be simulta 

neously used to impart energy to the lubricant disposed Within 

the second axle housing 69'. When the axle clutch 668 and the 

clutch 628 are simultaneously used to impart energy to the 

lubricant disposed Within the second axle housing, the axle 

clutch 668 cooperates With the clutch 628 to adjust the rota 

tional speed of the second output gear 624, the driven gear 70', 

the inter-axle shaft 64', the second driving gear 65', and the 

second Wheel differential 66' to one of the predetermined 

speed and a target speed. 

In use, the method for use of the drive axle system 10' 

facilitates shifting from the ?rst operating state to the second 

operating state. Similarly, the shifting procedures described 

above for use With the drive axle system 10, may be used With 

the drive axle system 10', accommodating for the differences 

of the embodiment shoWn in FIG. 6 as described hereinabove. 

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 

speci?cally illustrated and described Without departing from 

its spirit or scope. 
US 8,523,738 B2 

25 

What is claimed is: 

1. A method of shifting a power distribution unit for a 

vehicle from a ?rst operating state to a second operating state, 

the method comprising the steps of: 

drivingly engaging a ?rst axle assembly With a ?rst output 

of the poWer distribution unit; 

drivingly engaging a second axle assembly With a second 

output of the poWer distribution unit; 

drivingly engaging an input of the poWer distribution unit 

With an output of a poWer source, the poWer distribution 

unit including an inter-axle differential, the ?rst output, 

the second output, and a ?rst clutching device having a 

?rst position and a second position, the ?rst clutching 

device in the ?rst position locking the inter-axle differ 

ential, engaging the ?rst output With the input of the 

poWer distribution unit, and disengaging the second out 

put from the inter-axle differential, the ?rst clutching 

device in the second position unlocking the inter-axle 

differential and engaging the ?rst output and the second 

output With the inter-axle differential; 

placing the ?rst clutching device in one of the ?rst position 

and the second position; 

applying a rotational force to the input of the poWer distri 

bution unit; 

adjusting the rotational force transferred to the poWer dis 

tribution unit to facilitate moving the ?rst clutching 

device; 

moving the ?rst clutching device from one of the ?rst 

position and the second position to a third position, the 

?rst clutching device in the third position neither locking 

the inter-axle differential nor engaging the second out 

put With the inter-axle differential; 

adjusting a rotational speed of the input of the poWer dis 

tribution unit to facilitate moving the ?rst clutching 

device from the third position; 

moving the ?rst clutching device from the third position to 

one of the ?rst and second positions; and 

adjusting the rotational force transferred to the poWer dis 

tribution unit. 

2. The method according to claim 1, Wherein the inter-axle 

differential is a planetary differential comprising a carrier 

drivingly engaged With the input of the poWer distribution 

unit, a plurality of driving pinions rotatably disposed on the 

carrier, a ring gear drivingly engaged With the ?rst output of 

the poWer distribution unit, and a sun gear selectively driv 

ingly engaged With the second output of the poWer distribu 

tion unit. 

3. The method according to claim 2, Wherein the ?rst 

clutching device comprises a shift collar in splined engage 

ment With a portion of the sun gear, a ?rst synchroniZer, and 

a second synchroniZer, the ?rst synchroniZer acting upon the 

carrier as the ?rst clutching device is moved toWards the ?rst 

position and the second synchroniZer acting upon the second 

output as the ?rst clutching device is moved toWards the 

second position. 

4. The method according to claim 2, Wherein the ?rst 

clutching device comprises a shift collar in splined engage 

ment With a portion of the sun gear and a synchroniZer, the 

synchroniZer acting upon the second output as the ?rst clutch 

ing device is moved toWards the second position. 

5. The method according to claim 2, further comprising the 

step of providing a controller in communication With a ?rst 

clutching device actuator and at least one sensor, the at least 

one sensor for monitoring at least one of an operating condi 

tion of the poWer source, a temperature of the second axle 

assembly, a speed of the sun gear, a speed of the second output 

gear, a speed of a portion of the second axle assembly, an 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

26 

amount of the rotational force transferred to the poWer distri 

bution unit, a position of a second clutching device for selec 

tively disengaging a ?rst portion of the second axle assembly 

from a second portion of the second axle assembly, and a 

position of the ?rst clutching device to adjust at least one of 

the operating condition of the poWer source, the position of 

the ?rst clutching device and the second clutching device, and 

a duration betWeen successive positions of the ?rst clutching 

device based on at least one of the operating condition of the 

poWer source, the temperature of the second axle assembly, 

the speed of the sun gear, a speed of the second output gear, a 

speed of a portion of the second axle assembly, the amount of 

the rotational force transferred to the poWer distribution unit, 

and the position of the ?rst clutching device and the second 

clutching device. 

6. The method according to claim 1, Wherein the step of one 

of adjusting the rotational force transferred to the poWer 

distribution unit may be performed by adjusting an operating 

condition of the poWer source. 

7. The method according to claim 1, Wherein folloWing the 

step of moving the ?rst clutching device from one of the ?rst 

position and the second position, the step of adjusting the 

rotational speed of the input of the poWer source is performed 

by adjusting an operating condition of the poWer source is 

adjusted. 

8. The method according to claim 1, Wherein the ?rst 

output is a ?rst output gear and the second output is a second 

output gear. 

9. The method according to claim 1, Wherein the ?rst 

clutching device is selectively engaged to adjust a rotational 

speed of a portion of the second axle assembly. 

10. The method according to claim 1, further comprising 

the step of moving the ?rst clutching device from the third 

position to the second position When a temperature of the 

second axle assembly is above a predetermined value. 

11. The method according to claim 1, Wherein folloWing 

the step of moving the ?rst clutching device to the third 

position, the step of adjusting the rotational speed of the input 

of the poWer distribution unit is performed by adjusting a 

rotational speed of the poWer source. 

12. The method according to claim 11, further comprising 

the step of maintaining a substantially constant rotational 

speed of the poWer source once one of a predetermined speed 

and a target speed is obtained and moving the ?rst clutching 

device from the third position to one of the ?rst and second 

positions. 

13. The method according to claim 12, Wherein one of the 

predetermined speed and the target speed of the poWer source 

causes a sun gear forming a portion of the inter-axle differ 

ential and the second output to rotate at speeds permitting 

meshing engagement therebetWeen With the ?rst clutching 

device. 

14. The method according to claim 1, Wherein the second 

axle assembly further includes a second clutching device, the 

second clutching device selectively disengaging a ?rst por 

tion of the second axle assembly from a second portion of the 

second axle assembly. 

15. The method according to claim 14, Wherein the step of 

moving the ?rst clutching device from the third position to the 

second position partially engages the second output and the 

?rst portion of the second axle assembly to adjust a rotational 

speed of the second output and the ?rst portion of the second 

axle assembly to one of a target speed and an idle condition, 

the target speed facilitating engagement betWeen the ?rst 

portion of the second axle assembly and the second portion of 

the second axle assembly With the second clutching device. 
US 8,523,738 B2 

27 

16. The method according to claim 14, wherein the second 

clutching device is selectively engaged to impart energy to a 

lubricant disposed Within the second axle assembly. 

17. The method according to claim 16, further comprising 

the step of engaging the second clutching device When a 

temperature of the second axle assembly is above a predeter 

mined value. 

18. The method according to claim 14, Wherein the ?rst 

clutching device and the second clutching device are simul 

taneously engaged to adjust a rotational speed of a portion of 

the second axle assembly. 

19. A method of shifting a poWer distribution unit for a 

vehicle from a ?rst operating state to a second operating state, 

the method comprising the steps of: 

drivingly engaging a ?rst axle assembly With a ?rst output 

of the poWer distribution unit; 

drivingly engaging a second axle assembly With a second 

output of the poWer distribution unit; 

drivingly engaging an input of the poWer distribution unit 

With an output of a poWer source, the poWer distribution 

unit including an inter-axle differential, the ?rst output, 

the second output, and a ?rst clutching device having a 

?rst position and a second position, the ?rst clutching 

device in the ?rst position locking the inter-axle differ 

ential, engaging the ?rst output With the input of the 

poWer distribution unit, and disengaging the second out 

put from the inter-axle differential, the ?rst clutching 

device in the second position unlocking the inter-axle 

differential and engaging the ?rst output and the second 

output With the inter-axle differential; 

placing the ?rst clutching device in the ?rst position; 

applying a rotational force to the input of the poWer distri 

bution unit; one of reducing and interrupting the rotational force trans 

ferred to the poWer distribution unit; 

moving the ?rst clutching device from the ?rst position to 

a third position, the ?rst clutching device in the third 

position unlocking the inter-axle differential; 

adjusting a rotational speed of the input of the poWer dis 

tribution unit to facilitate moving the ?rst clutching 

device from the third position; 

adjusting a rotational speed of a ?rst portion of the second 

axle assembly to a target speed, the target speed facili 

tating engagement betWeen the ?rst portion of the sec 

ond axle assembly and a second portion of the second 

axle assembly; 

moving the ?rst clutching device from the third position to 

the second position; and 

one of increasing and resuming the rotational force trans 

ferred to the poWer distribution unit. 

20. The method according to claim 19, Wherein the inter 

axle differential is a planetary differential comprising a car 

rier drivingly engaged With the input of the poWer distribution 

unit, a plurality of driving pinions rotatably disposed on the 

carrier, a ring gear drivingly engaged With the ?rst output of 

the poWer distribution unit, and a sun gear selectively driv 

ingly engaged With the second output of the poWer distribu 

tion unit. 

21. The method according to claim 20, Wherein the ?rst 

clutching device comprises a shift collar in splined engage 

ment With a portion of the sun gear, a ?rst synchroniZer, and 

a second synchroniZer, the ?rst synchroniZer acting upon the 

carrier as the ?rst clutching device is moved toWards the ?rst 

position and the second synchroniZer acting upon the second 

output as the ?rst clutching device is moved toWards the 

second position. 

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35 

40 

45 

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55 

60 

65 

28 

22. The method according to claim 20, Wherein the ?rst 

clutching device comprises a shift collar in splined engage 

ment With a portion of the sun gear and a synchroniZer, the 

synchroniZer acting upon the second output as the ?rst clutch 

ing device is moved toWards the second position. 

23. The method according to claim 20, further comprising 

the step of providing a controller in communication With a 

?rst clutching device actuator and at least one sensor, the at 

least one sensor for monitoring at least one of an operating 

condition of the poWer source, a temperature of the second 

axle assembly, a speed of the sun gear, a speed of the second 

output gear, a speed of a portion of the second axle assembly, 

an amount of the rotational force transferred to the poWer 

distribution unit, a position of a second clutching device for 

selectively disengaging the ?rst portion of the second axle 

assembly from the second portion of the second axle assem 

bly, and a position of the ?rst clutching device to adjust at 

least one of the operating condition of the poWer source, the 

position of the ?rst clutching device and the second clutching 

device, and a duration betWeen successive positions of the 

?rst clutching device based on at least one of the operating 

condition of the poWer source, the temperature of the second 

axle assembly, the speed of the sun gear, a speed of the second 

output gear, a speed of a portion of the second axle assembly, 

the amount of the rotational force transferred to the poWer 

distribution unit, and the position of the ?rst clutching device 

and the second clutching device. 

24. The method according to claim 19, Wherein the step of 

one of reducing and interrupting the rotational force trans 

ferred to the poWer distribution unit may be performed by 

adjusting an operating condition of the poWer source. 

25. The method according to claim 19, Wherein folloWing 

the step of moving the ?rst clutching device from the ?rst 

position to the third position, the step of adjusting the rota 

tional speed of the input of the poWer distribution unit is 

performed by adjusting an operating condition of the poWer source. 

26. The method according to claim 19, Wherein the ?rst 

output is a ?rst output gear and the second output is a second 

output gear. 

27. The method according to claim 19, Wherein the step of 

adjusting a rotational speed of a ?rst portion of the second 

axle assembly is performed by selectively engaging the ?rst 

clutching device. 

28. The method according to claim 19, further comprising 

the step of moving the ?rst clutching device from the third 

position to the second position When a temperature of the 

second axle assembly is above a predetermined value. 

29. The method according to claim 19, Wherein folloWing 

the step of moving the ?rst clutching device to the third 

position, the step of adjusting the rotational speed of the input 

of the poWer distribution unit is performed by adjusting a 

rotational speed of the poWer source. 

30. The method according to claim 29, further comprising 

the step of maintaining a substantially constant rotational 

speed of the poWer source once one of a predetermined speed 

and a target speed is obtained and moving the ?rst clutching 

device from the third position to the second position. 

31. The method according to claim 30, Wherein one of the 

predetermined speed and the target speed of the poWer source 

causes a sun gear forming a portion of the inter-axle differ 

ential and the second output to rotate at speeds permitting 

meshing engagement therebetWeen With the ?rst clutching 

device. 

32. The method according to claim 19, Wherein the second 

axle assembly further includes a second clutching device, the