# (12) United States Patent Ziech et a1. US008911321B2



# US 8,911,321 B2 Dec. 16, 2014 (10) Patent N0.: 

## (45) Date of Patent:

(54) (71)

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(51) TANDEMAXLE SYSTEM 

### Applicant: Dana HeavyVehicle Systems Group, LLC, Maumee, OH (US)

Inventors: James F. Ziech, Kalamazoo, MI (US); Donald J. Remboski, AnnArbor, MI 

### (US); RichardA. Nellums, Maumee, 

### OH (US); Benjamin J. Passino, Maumee, OH (US); Stephen C. 

### Cochran, Sylvania, OH (US); Stephen A. Edelen, Battle Creek, MI (US) 

### Assignee: Dana HeavyVehicle Systems Group, LLC, Maumee, OH (US)

Notice: Subject to any disclaimer, the term ofthis patent is extended or adjusted under 35 

### U.S.C. 154(b) by 0 days. Appl. No.: 13/973,166
Filed: Aug. 22, 2013

Prior Publication Data
US 2014/0057752A1 Feb. 27, 2014



### Related U.S.Application Data 

### Provisional applicationNo. 61/692,292, ?led onAug. 

### 23, 2012.

Int. Cl. 

### F16H 48/06 (2006.01) B60K 17/16 (2006.01) B60K 17/36 (2006.01) (52) U.S. Cl.

CPC

............... .. B60K17/16 (2013.01); B60K17/36 

## (2013.01)

USPC

........................................................ .. 475/221 

### (58) Field ofClassi?cation Search None 

### See application ?le for complete searchhistory.
(56) References Cited

U.S. PATENT DOCUMENTS

180/2409

. 74/606 R

..... .. 475/222 475/221 475/221

.. 475/221 RE25,269 E * 10/1962 Christie

.. 5,267,489 A * 12/1993 Ziech

.... .. 6,514,169 3 Turner et al. 7,258,644 8/2007 et a1. 7,306,536 B2* 12/2007 Ziech

....... ..

8,398,520 B1* 3/2013 Bassi et a1.

........... .. . 8,523,738 B2 * 9/2013 Morscheck et a1. 477/77 8,651,994 B2 * 2/2014 Bassi et a1.

.................. .. 475/221 2006/0272866 A1 2010/0248888 A1 12/2006 Ziech 9/2010 Hamperlet a1.

FOREIGN PATENT DOCUMENTS

WO 2008019779 A2 WO 2008113484 A1 2/2008 9/2008
* cited by examiner
Primary Examiner * Dirk Wright (74) Attorney, Agent, or Firm * Marshall & Melhorn, LLC 

### (57) ABSTRACT

A tandem axle system has a forward axle system and a rear axle system. A method of selectively driving one or both of 

### the axle systems is described.


### 50 Claims, 7 Drawing Sheets

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## US 8,911,321 B2 1
TANDEMAXLE SYSTEM

RELATEDAPPLICATIONS


### This application claims bene?t ofandpriority to US. Pro 

### visional Application Ser. No. 61/692,292 ?led on Aug. 23, 

### 2012 which is fully incorporatedby reference herein.

BACKGROUND OF THE INVENTION

The typical NorthAmerican class 8 truckrear tandem axle is a full time 6><4 drivelinewith an inter-axle differential lock 

### and optional wheel differential lock(s). This system offers good traction in most conditions, but suffers from spin loss and gear mesh inef?ciencies. Alternate 6><2 drive-line sys 

### tems can improve the spin loss and gear loss ef?ciency, but these systems are limited on tractive effort due to the single drive axle. The 6><2 system can utilize a wheel differential lock and to shift weight to the drive axle under low traction 

### conditions to improve tractive effort, but cannot equal the performance ofthe 6x4 system traction. What is needed is a tandem axle system that has the ef?ciency of a 6x2 tandem 

### with the tractive effort ofthe 6x4 system.

SUMMARY OF THE INVENTION



### Methods for driving tandem axle systems are described. 

### Generally, themethods compriseproviding a rotational input into the tandem axle system, which comprises a forwardaxle system and a rear axle system. The rotational input may be continuously provided to the forward axle system or the rear 

### axle system. When the rotational input is provided continu ously to the forward axle system, the rear axle system is 

### selectively engaged and disengaged to control churning losses and increase the ef?ciency ofthe tandem axle system. 

### When rotational input is provided continuously to the rear 

### axle system, the forward axle system is selectively engaged and disengaged to control churning losses and increase the 

### ef?ciency of the tandem axle system. Various embodiments oftandem axle systems areprovidedutiliZing components to engage and disengage the forward or rear axle systems.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic depiction ofone embodiment ofthe 

### tandem axle system;

FIG. 2 is a schematic depiction ofa second embodiment of 

### the tandem axle system;

FIG. 3 is a schematic depiction of a third embodiment of 

### the tandem axle system;

FIG. 4 is schematic depiction of a fourth embodiment of 

### the tandem axle system;

FIG. 5 is a schematic depictionofa ?fth embodimentofthe 

### tandem axle system;

FIG. 6 is a schematic depiction of a sixth embodiment of 

### the tandem axle system;

FIG. 7A is a schematic depiction ofa seventh embodiment 

### ofthe tandem axle system; and

FIG. 7B is a partial view of the tandem axle system depicted in FIG. 7A but with a modi?cation to two shift mechanisms.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Turning now to FIG. 1, one embodiment ofa tandem axle 

### system 10 is schematically depicted. The system 10 com prises ofa forward axle system 12 and a rear axle system 14. 20

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## 2 Rotational energy isprovidedto the tandemaxle system 10 through an input shaft 16 that is rotated by an internal com 

### bustion engine (not shown).

A gerotor pump 18 is rotated by the input shaft 16. The gerotor pump 18 pumps lubricant to rotating parts in the 

### forward axle system 12 regardless ofthe operating condition of the forward axle system 12, which can be selectively 

### engaged anddisengaged.

The input shaft 16 is connected to an interaxle differential (IAD) 20. The IAD 20 comprises at least two side gears 22 and at least two pinion gears 24, with the side gears 22 and 

### pinion gears 24 being in driving engagement with one another. The side gears 22 and pinion gears 24 are located within an IAD carrier 26. The IAD 20 provides differential action between the forward axle system 12 and the rear axle 

### system 14.

An output shaft 28 connected to one ofthe IAD side gears 22 is connected to a ?rst end of a propeller shaft 30. The 

### propeller shaft 30 extends between the forward axle system 12 andthe rear axle system 14. A second end ofthepropeller shaft 30 is connected to a rearpinion gear 32. The rearpinion gear 32 is drivingly connected to a rearring gear 34. The rear ring gear 34 is connected to a rear differential 36.

Thereardifferential 36 comprises at leasttwo side gears 38 andat least two piniongears 40 to permit differential rotation between the wheels (not shown) on a ?rst axle shaft 42 and a second axle shaft 44 connected to the side gears 38.



### A ?rst concentric shaft 46 isprovided about the input shaft 16. The ?rst concentric shaft 46 is connected to one of the IAD side gears 22. The ?rst concentric shaft 46 also carries a 

### dog clutch gear 48.

A synchronizer system 50 is concentric with the ?rst con centric shaft 46. The synchronizer system 50 comprises a cone assembly 52. The cone assembly 52 may be selectively moved inthe axial direction into and out ofengagement with


### aplate assembly 54 aportionofwhichis angledtoreceivethe

cone assembly 52.

The cone assembly 52 is rotatable andvia the axial move 

### ment, it may be brought into selective engagement with the plate assembly 54. The rotation of the cone assembly 52 is 

### imparted to the plate assembly 54, which causes the plate assembly 54 torotate.As thecone assembly 52 isbrought into 

### additional engagementwith the plate assembly 54, theplate assembly 54 is matched or substantially matched to the same 

### rotational speed ofthe cone assembly 52.

Atapredeterminedtime, suchaswhentherotational speed oftheplate assembly 54 andcone assembly 52 arematchedor 

### substantiallymatchedvia substantial engagementoftheplate and cone assemblies 52, 54, a shift fork 56moves adog clutch ring 58 on the dog clutch gear 48 also to a synchronizer gear 

### 60. Thedog clutchring 58 rotationally connects the synchro nizer gear 60 and the dog clutch gear 48.



### While a synchronizer system is described above, dog clutches, friction plate clutches or an over-running clutches 

### may be used instead ofthe synchronizer system.



### The synchronizer system 50 is selectively connected to, and thus selectivelyrotates, a drop gear set 62. The drop gear set 62 is connected to an input shaft 64 of the forward axle 

### system 12. The input shaft 64 is providedwith, or connected to, apinion shaft 66. Thepinion shaft 66 has apiniongear 68. Thepiniongear 68 is connected to a differential ring gear 70. The ring gear 70 is connected to a differential carrier 72. At least two pinion gears 74 and at least two side gears 76 are located within the differential carrier 72.

Shafts extend into the differential carrier 72 and connect with the side gears 76. The shafts extend outboard the differ 

### ential carrier 72. The shafts may be full length shafts or they

## US 8,911,321 B2 3
may be stub shafts. First and second stub shafts 78, 80 are 

### shown extending from the carrier 72.

A clutch 82, such as a dog-type clutch, may be located on the second stub shaft 80. The clutch 82 may selectivelymove 

### along the stub shaft 80 for connecting and disconnecting the stub shaft 80 with an axle shaft 84 rotationally supporting at 

### least one wheel and tire (not shown).

The clutch 82 may comprise a ?rst set of splines or gears 82Athatare selectively connectedwitha secondsetofsplines

or gears 82B via a clutch ring 82C. The clutch ring 82C 

### selectively connects the gears 82A, 82B when moved by a shift fork 82D.



### A selectively engagable clutch 86 may be provided at the interaxle differential 20 for locking the output shaft 28 to the 

### input shaft 16. In the depicted embodiment, the ?rst concen tric shaft 46 is selectively connected to the TAD carrier 26 with the clutch 86. The lAD carrier 26 is provided with a set of teeth, a gear, or splines; teeth 88 will be used in the fol 

### lowing description. The clutch 86, such as a dog-type clutch, 

### is designedto selectively engageanddisengagewiththe TAD 

### housing teeth 88. The clutch 86 selectively joins the TAD carrier teeth 88 with a gear 90 on the concentric shaft 46.

Based on the foregoing, it can be appreciated that the tandem axle system 10 can be operated in different modes. 

### Typically, therearaxle system 14 is engaged inthe drive-line 

### full time and the forward axle system 12 is engaged for only intermittent use, such as for startup and low speed traction 

### conditions. The forward axle system 12 is disengaged and allowed to idle most ofthe time.



### The tandem has three modes ofoperation: ?rst, 6x2 with 

### the forward axle system 12 disconnected; second, 6><4 with the TAD open with the forward and rear axle systems 12, 14 

### providing drive; and third, 6x4 with the TAD locked and the forward and rear axle systems 12, 14 providing drive.



### In the ?rstmode ofoperation, the synchronizer system 50 is not engaged so rotational power transfers from the engine to the rear axle system 14 through the locked lAD 20; no rotational poweris transmittedto the forwardaxle system 12. Also, the clutch 86betweenthe stub shaft 80 andaxle shaft 84 is unlocked so that the forward axle system 12 is not rotating, 

### thus reducing, orpreventing, oil churning losses.

In the secondmode ofoperation, the synchronizer system 50 is engaged thus connecting both the forward and the rear 

### axle systems 12, 14 to the engine. The lAD 20 is unlocked. In other words, the differential carrier 26 is not locked to the concentric shaft 46 with the interaxle differential clutch 86. Further, the fork 82D moves the ring 82C to connect the stub shaft 80 and the axle shaft 84 so that they rotate together.

In the third mode of operation, the clutches 82, 86 on the concentric shaft 46 and the stub shaft 80 ofthe axle shaft 84 

### ofthe forwardaxle system 12 are engaged. Thus, the forward axle system 12 provides rotational power to the forward wheels andtires. The lAD 20 is locked so thatthe forwardand

rearaxle systems 12, 14 are driven at the same speed. Inother words, the differential carrier 26 is locked to the concentric 

### shaft 46 with the interaxle differential clutch 86. Further, the fork 82D moves the ring 82C to connect the stub shaft 80 and the axle shaft 84 so that they are rotate together.

Turning now to FIG. 2, a second embodiment ofa tandem 

### axle system 92 is depicted. The system 92 comprises a for ward axle system 94 and arear axle system 96.An input shaft 

### 98 is provided and rotatedby an internal combustion engine (not shown). The shaft 98 is connectedto an inter-axle differ 

### ential (IAD) 100. The lAD 100 is comprised ofat least two side gears 102 and at least two pinion gears 104. The side gears 102 andpinion gears 104 aremeshedwith one another. 20

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## 4

An output shaft 106 is connected to one set of side gears 102. The output shaft 106 extends to a synchronizer system 108. The output shaft 106, or a gear 110 on the shaft 106, 

### rotates the synchronizer system 108. The synchronizer sys tem 108 comprises a cone assembly 112. The cone assembly 

### 112, may be selectivelymoved in the axial direction into and out of engagement with a plate assembly 114 a portion of which is angled to receive the cone assembly 112.

The cone assembly 112 is rotatableby gear 110 andviathe 

### axialmovement, itmaybebrought into selective engagement with the angledplate assembly 114. The rotation ofthe cone 

### assembly 112 is imparted to the angledplate assembly 114, which causes the angledplate assembly 114 to rotate.As the


### cone assembly 112 is brought into additional engagement 

### with the plate assembly 114, the plate assembly 114 is matched to the same rotational speed as the cone assembly 112.

At a predetermined time, such as when the rotational 

### speeds oftheplate andconeassemblies 112, 114arematched,

or substantiallymatched, a shift fork 116 moves a dog clutch ring 118 on the gear 110 also to a synchronizer gear 120.



### Thedogclutchring 118 thenrotationally connects the gear 110 and the synchronizer gear 120.

While a synchronizer system is described above, it can be 

### appreciated that dog clutches, friction plate clutches or an 

### over-running clutches may be used instead of the synchro 

### nizer system.

The plate assembly 114 is connected to a propeller shaft 122. The propeller shaft 122 extends to the rear axle system 96. The rear axle system 96 has a pinion shaft 124 rotatedby 

### the propeller shaft 122. The pinion shaft 124 rotationally drives a ring gear 126 mounted to a rear differential carrier 128. The rear differential carrier 128 houses at least two pinion gears 130 and at least two side gears 132.

Shafts extend into the rear differential carrier 128 and connect with the side gears 132. The shafts extend outboard the reardifferential carrier 128. The shaftsmaybe full length shafts or theymaybe stub shafts. First and second stub shafts 134, 136 are shown extending from the carrier 128.

A clutch 138, such as a dog-type clutch, maybe located on 

### the second stub shaft 136. The clutch 138 may selectively


### move along the second stub shaft 136 for connecting and disconnectingthe second stub shaft 136withanaxle shaft 140 

### rotationally supporting at least one wheel and tire (not 

## shown).

The clutch 138 may comprise a ?rst set ofsplines or gears 138A that are selectively connected with a second set of splines or gears 1386 via a clutch ring 138C. The clutch ring 

### 138C selectively connects thegears 138A, 1388 whenmoved by a shift fork 138D.



### A shaft 142 concentric withthe input shaft 98 is connected to one ofthe side gears 102 in the TAD 100. A drop gear set 144 is mounted on the concentric shaft 142.

The drop gear set 144 is connected to an input shaft 146 of 

### the forward axle system 94. The input shaft 146 is provided with, orconnectedto, apinion shaft 148. Thepinion shaft 148 has a pinion gear 150. The pinion gear 150 is connected to a differential ring gear 152. The ring gear 152 is connectedto a differential carrier 154. At least two pinion gears 156 and at least two side gears 158 are located within the differential carrier 154.



### Firstand second shafts 160, 162 extendinto thedifferential carrier 154 and connect with the side gears 158. The shafts 160, 162 extend outboard the differential carrier 154. The 

### shafts 160, 162 may be full length shafts or theymay be stub shafts. Regardless, at least onewheel andtire (not shown) are mounted on the shafts 160, 162.

## US 8,911,321 B2 5
A clutch 164 selectively connects the concentric shaft 142 to the input shaft 98. The clutch 164 may be such as a dog 

### type clutch, but other types ofclutches are permissible. The clutch 164 selectively connects a gear 166 on the input shaft 98 with a gear 168, or splines, on the concentric shaft 142.



### The clutch 164 comprises a clutchring 164A that is selec 

### tively moved to join the gears 166, 168 by a shift fork 164B.

Based on the foregoing, it can be appreciated that the tandem axle system 92 can be operated in different modes. 

### Typically, the forwardaxle system 94 is engagedinthedrive line full time and the rear axle system 96 is engaged for only intermittent use, such as for startup and low speed traction conditions. The rear axle system 96 is disengaged and allowed to idle most ofthe time.



### The tandem axle system 92 has three modes ofoperation: ?rst, 6x2 with the rear axle system 96 disconnected; second, 6x4 with the IAD 100 open with the front and rear axle 

### systems 94, 96 connected; and third, 6x4 with the IAD 100 locked and the front and rear axle systems 94, 96 connected.



### Inthe ?rstmodeofoperation, the synchronizer system 108 is not engaged. Rotational power is therefore not transmitted 

### to the rear axle system 96; only the forward axle system 94 receives rotational power.Also, the clutch 138 is unlocked so 

### that the rear axle system 96 is not rotating, thus reducing oil 

### churning losses. Clutch ring 164A connects the input shaft gear 166 with the concentric shaft 142 so that they rotate 

## together.

In the secondmode ofoperation, the synchronizer system 108 is engaged and rotational power is provided to both the forward axle system 94 and the rear axle system 96. The clutch 164 on the concentric shaft 142 is engaged with the 

### input shaft 98 so that the stub shaft 136 rotates with the axle shaft 140.



### In the third mode of operation, the synchronizer system 108 is engaged as described above.And the clutch 164 on the concentric shaft 142 is axially shifted so that it is lockedwith 

### the input shaft 98 so that theyrotate together, thus locking the IAD 100. Further, the clutch 164 on the rear axle stub shaft 136 is locked so that the stub shaft 136 andthe outboard shaft 140 are connected.

Turning now to FIG. 3, a third embodiment of a tandem 

### axle system 170 is depicted. The system 170 comprises a forward axle system 172 and a rear axle system 174. An 

### internal combustion engine (not shown) is connected to an input shaft 176 to impart rotational energy to the shaft 176. The shaft 176 is connected to an inter-axle differential (IAD) 178. The IAD 178 has at least two pinion 180 gears and at least two side gears 182 in engagementwith one another. One set ofside gears 182 is connected to an output shaft 184. The other set of side gears 182 is connected to a shaft 186 that is 

### concentric with the output shaft 184.

The concentric shaft 186 is connected to a drop gear set 188. The drop gear set 188 connects the IAD 178 with the 

### forward axle system 172. Moreparticularly, the drop gear set 188 drives a pinion shaft 190. The pinion shaft 190 is driv 

### ingly connected to a ring gear 192. The ring gear is mounted to a differential carrier 194 and rotates the carrier 194. The differential carrier 194 houses at least two pinion gears 196 and at least two side gears 198.

First and second axle shafts 200, 202 are connected to the sidegears 198 forrotationtherewith. The axle shafts 200, 202 

### rotate the wheels and tires (not shown) located opposite the side gears to move the vehicle over the ground.

The IAD output shaft 184 is connected to a synchronizer 

### system 204. The output shaft 184 rotates the synchronizer system 204. The synchronizer system 204 comprises a cone 

### assembly 206. The cone assembly 206 may be selectively 20

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## 6 moved inthe axial direction into and out ofengagement with

aplate assembly 208 that is angledto receive the cone assem 

### bly 206.

The rotation ofthe cone assembly 206 is imparted to the 

### angled plate assembly 208, which causes the angled plate assembly 208 to rotate.As the cone assembly 206 is brought 

### into additional engagementwith the plate assembly 208, the plate assembly 208 rotates at the same rate as the cone assem 

### bly 206.

Atapredeterminedtime, suchaswhentherotational speed 

### oftheplate assembly 208 andcone assembly 206 arematched

or substantiallymatched, a shift fork 210 moves a dog clutch ring 212 on an output shaft gear 214 also to a synchronizer 

### gear 216. The dog clutch ring 212 rotationally connects the gear 214 and the synchronizer gear 216.

While a synchronizer system 204 has been described 

### above, it can be appreciated that dog clutches, friction plate clutches or an over-running clutches may be used instead of 

### the synchronizer system 204.

The plate assembly 208 is connected to a propeller shaft 218. The propeller shaft 218 extends to the rear axle system 174. The rear axle system 174 has a pinion shaft 220 rotated 

### by the propeller shaft 218. The pinion shaft 220 rotationally drives a ring gear 222 mounted to a rear differential carrier 224. The rear differential carrier 224 houses at least two pinion gears 226 and at least two side gears 228.



### Firstand second shafts 230, 232 extendinto thedifferential carrier 224 and connect with the side gears 228. The shafts 

### extend outboard the differential carrier 224. The shafts 230, 232 may be full length shafts or they may be stub shafts. A stub shaft is shown for shaft 232.

A clutch 234, suchas a dog-type clutch, maybe located on the stub shaft 232. The clutch 234 comprises a shift fork 236 

### and a dog clutch ring 238. The dog clutch ring 238 may selectively connect the stub shaft 232 and an axle 237 rota 

### tionally supporting at least one wheel and tire.



### Another clutch 240, whichmay be a dog-type clutch, may selectively connect the differential carrier 194 and the con centric shaft 186. The clutch 240 comprises a shift fork 242 

### and adog clutchring 244. The dog clutchring 244 is adapted to move ina ?rst axial directionto lockthe carrier 194 andthe 

### concentric shaft 186 together and ina second axial direction,

so that the carrier 194 and shaft 186 are not locked together and able to move independently from one another.

Based on the foregoing, it can be appreciated that the tandem axle system 170 can be operated in different modes.



### Inthepresent embodiment, the forwardaxle system 172 is engaged in the drive-line full time and the rear axle system 

### 174 is engaged for only intermittent use, such as for startup and low speedtractionconditions. Therearaxle system 174 is disengaged and allowed to idle most ofthe time.



### The tandemaxle system 170has threemodes ofoperation: ?rst, 6x2withtherearaxle system 174 disconnected; second, 6x4 with the inter-axle differential 178 open with the front 

### andrearaxle systems 172, 174 connected; andthird, 6x4with the inter-axle differential 178 locked and the front and rear 

### axle systems 172, 174 connected.



### Inthe ?rstmodeofoperation, the synchronizer system 204 is open and rotational energy is directed exclusively to the 

### forward axle system 172. No rotational energy is provided to 

### therearaxle system 174,particularlywhenthedog clutch 234 is disengaged. Moreparticularly, the shift fork 236moves the collar 238 so that the stub shaft 232 is not engaged with the 

### axle shaft 237. Thus, lubricant churning losses intherearaxle system 174 areminimized orprevented. Clutch ring 244 has 

### engaged the differential carrier of the inter-axle differential 178 and the concentric shaft 186 so that they rotate together.

## US 8,911,321 B2 7 In the secondmode ofoperation, the synchronizer system 

### 204 is engaged and rotational energy is passed through the synchronizer system 204 to the rear axle system 174; rota 

### tional energy is alsoprovidedto the forwardaxle system 172. 

### The clutch ring 244 has not engaged the differential carrier 178 with the concentric shaft 186 so they do not rotate together. The dog clutch 234 on the rear axle system 174 connects the stub shaft 232 with the axle shaft 237.



### In the third mode of operation, the synchronizer system 204 is engaged and, in addition, the clutch 240 on the differ ential carrier 194 andtheconcentric shaft 186 ismoved so that the differential carrierofthe interaxledifferential 178 andthe concentric shaft 186 are locked together and rotate together. The dog clutch 234 on the rear axle system 174 connects the stub shaft 232 with the axle shaft 237.

Turning now to FIG. 4, another embodiment of a tandem 

### axle system 246 is depicted. The system 246 comprises a forward axle system 248 and a rear axle system 250. The 

### system 246 also comprises an input shaft 252 rotationally 

### driven by an internal combustion engine (not shown). The input shaft 252 is connectedto aninter-axledifferential (IAD) 254. The IAD 254 has at least two pinion gears 256 and at least two side gears 258. One set of side gears 258 is con nected to a shaft 260 that is concentric with the input shaft 252.

A drop gear set 262 is connected to the concentric shaft 260. The drop gear set 262 is connected to a pinion shaft 264 ofthe forward axle system 248. The pinion shaft 264 has a pinion gear 266. The pinion gear 266 is connected to a dif ferential ring gear 268. The ring gear 268 is connected to a differential carrier 270. At least two pinion gears 256 and at least two side gears 258 are located within the differential carrier 270.

Shafts 272 extend into the differential carrier 270 and con nect with the side gears 258. The shafts 272 extend outboard 

### the differential carrier 270. The shafts 272 may be full length shafts or they may be stub shafts.

The other set ofIAD side gears 258 is connected an output shaft 274. The output shaft 274 is connected to a propeller shaft 276. The propeller shaft 276 extends to the rear axle system 250. The rear axle system 250 has a pinion shaft 278 

### rotatedby thepropeller shaft 276. The pinion shaft 278 rota tionally drives a ring gear 280 mounted to a rear differential carrier 282. The rear differential carrier 282 houses at least two pinion gears 282A and at least two side gears 282B.



### Firstand second shafts 284, 286 extendinto thedifferential carrier 282 and connect with the side gears 258. The shafts 284, 286 extend outboard the differential carrier 282. The 

### shafts 284, 286 may be full length shafts ortheymay be stub shafts.A stub shaft 286 is depictedas extending from one side ofthe carrier 282.



### A synchronizer system 288 is connected to the stub shaft 286. The stub shaft 286 rotates the synchronizer system 288. 

### Moreparticularly,the system 288 comprises aplateassembly 290 connected to the stub shaft 286; the plate assembly 290 rotates with the shaft 286.

The synchronizer system 288 also comprises a coneassem 

### bly 292. The cone assembly 292maybe selectivelymoved in the axial direction into and out ofengagementwith an angled 

### plate 294 ofthe plate assembly 290 that is angled to receive the cone assembly 292.



### The cone assembly 292 may be brought into selective 

### engagement with the angled plate 294. The rotation of the


### cone assembly 292 is impartedto the angledplate 294, which

causes the angled plate 294 to rotate. As the cone assembly 

### 292 isbrought into additional engagementwiththeplate 294, the two begin to rotate at the same rotational rate. 20

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## 8 The coneassembly 292 is connectedto a shaft 296 adjacent 

### to the stub shaft 286. When the synchronizer system 288 is 

### engaged the shaft 296 adjacent the stub shaft 286 is rotated.

Atapredeterminedtime, suchaswhentherotational speed ofthe plate 294 and cone assembly 292 are matched or sub stantially matched, a shift fork 298 moves a dog clutch ring 300 on an axle shaft gear 302 also to a synchronizergear 304. 

### The dog clutch ring 300 rotationally connects the axle shaft gear 302 and the dog clutch gear 304. Outboard ends ofthe 

### shaft or stub shaft supportthewheels andtires (not shown) for the rear axle system 250.



### Another clutch 306, whichmay be a dog-type clutch, may selectively connect the concentric shaft 260 anda gear 308 on the input shaft 252. The clutch 306 is adaptedtomove ina ?rst axial direction to lock the concentric shaft 260 and the gear 308 together and in a second axial direction, which does not 

### lock the concentric shaft 260 and gear 308 together. A shift fork 310 selectivelymoves a clutchring 312betweenthe shaft 260 and the gear 308.

Another clutch 314, which also maybe such as a dog-type 

### clutch, may selectively connect the IAD output shaft 274 and the propeller shaft 276. This clutch 314 is also adapted to
move in a ?rst axial direction to lock the output shaft 274 and 

### propeller shaft 276 together and in a second axial direction that does not lock the two shafts 274, 276 together. A shift fork 316 selectively moves a clutch ring 318 between the 

### output shaft 274 and the propeller shaft 276.

Based on the foregoing, it can be appreciated that the tandem axle system 246 can be operated in different modes.



### Inthepresent embodiment, the forwardaxle system 248 is engaged in the drive-line full time and the rear axle system 

### 250 is engaged for only intermittent use, such as for startup and low speedtractionconditions. Therearaxle system 250 is disengaged and allowed to idle most ofthe time to reduce, or 

### prevent, lubricant churning losses.

The tandem has three modes ofoperation: ?rst, 6x2 with therearaxle systems 250 disconnected; second, 6x4 withthe IAD 254 open with the forward and rear axle systems 248, 

### 250 connected; and third, 6x4 with the IAD locked and the forward and rear axle systems 248, 250 connected.



### In the ?rst mode ofoperation, the clutch 314 between the 

### IAD 274 output shaft and thepropeller shaft 276 is open and rotational energy is directed exclusively to the forward axle system 248. The synchronizer system 288 at the rear axle system 250 is openthusnorotational energyisprovidedtothe

rear axle system 250. The rear axle system 250 is not rotated and lubricant churning losses are prevented or minimized. Moreparticularly, the fork 298hasmovedthering 300 so that it does not engage both the axle shaft 296 and synchronizer 

### system 288. Clutchring 312has engagedboth the concentric shaft 260 and the input shaft 252.

In the second mode of operation, the clutch 314 between 

### the IAD output shaft 274 andthepropeller shaft 276 ismoved in the axial directionto close the connectionbetween the two. 

### Thus,rotational energy ispassedthroughthe clutch 314tothe
rearaxle system 250, androtational energy is alsoprovidedto 

### the forwardaxle system 248. The fork 298hasmovedthering 300 so that it engages both the axle shaft 296 and synchro 

### nizer system 288 and the two rotate together. The clutchring 312 is not engaged with the concentric shaft 260.

The third mode of operation is the same as the second, 

### exceptthatthe clutch 314 betweenthe input shaft 252 andthe concentric shaft 260 is closed so that the IAD 254 is locked. Further, the fork 298hasmovedthering 300 so that it engages 

### both the axle shaft 296 and synchronizer system 288 and the 

### two rotate together. The clutch ring 312 is engaged with the concentric shaft 260.

## US 8,911,321 B2

FIG. 5 depicts another embodiment ofa tandem axle sys tem 320. The system 320 comprises a forward axle system 322 and a rear axle system 324. An input shaft 326 is con nected to receive rotational energy from a prime mover (not shown). The input shaft 326 rotates an inter-axle differential 

### (IAD) 328. The IAD 328 comprises at least two pinion gears 330 andat leasttwo side gears 332housedinsidea differential carrier 334. The side gears 332 are meshed with the pinion
gears 330.

One side gear 332 is connected to a shaft 336 concentric aboutthe input shaft 326. The concentric shaft 336has a setof teeth, splines or a gear located on an outside surface; the depicted embodimenthas a gear 338. In addition, the concen tric shaft 336 has a drop gear set 340 connected thereto.

The drop gear set 340 connects the concentric shaft 336 to
a synchronizer shaft 342. The synchronizer shaft 342 rotates

a synchronizer system 344. A gear 346 is located on the 

### synchronizer shaft 342.A dog clutchring 348 is mounted on the gear 346 for rotation therewith.



### The synchronizer system 344 comprises a cone assembly 350. The cone assembly 350may be selectivelymoved in the axial direction into andoutofengagementwithaplateassem 

### bly 352 that is angled to receive the cone assembly 350.

The rotation ofthe cone assembly 350 is imparted to the 

### plate assembly 352, which causes the plate assembly 352 to rotate. The plate assembly 352 has an angled surface 354 complimentary to the shape ofthe cone assembly 350.As the


### cone isbroughtinto additional engagementwiththeplate, the two begin to rotate at the same rotational rate.

Atapredeterminedtime, suchaswhentherotational speed 

### oftheplateassembly 352andconeassembly 350 arematched

or substantially matched, a shift fork 356 moves the dog clutch ring 348 on the synchronizer shaft gear 346 to a syn 

### chronizer gear 358. The dog clutch ring 348 rotationally connects the synchronizer shaft gear 346 and the synchro nizer gear 358.

While a synchronizer system 344 is describedabove, it can 

### be appreciated that dog clutches, friction plate clutches or over-running clutches may be used instead of the synchro nizer system 344.

The plate assembly 352 is connected to a propeller shaft 360. The propeller shaft 360 extends to the rear axle system 324. The rear axle system 324 has a pinion shaft 362 rotated 

### by the propeller shaft 360. The pinion shaft 362 rotationally drives a ring gear 364 mounted to a rear differential carrier 366. The rear differential carrier 366 houses at least two pinion gears 368 and at least two side gears 370.

Shafts extend into the differential carrier 366 and connect with the side gears 370. The shafts extend outboard the dif ferential carrier 366. The shafts may be full length shafts or 

### theymaybe stub shafts. The shafts comprise ?rst and second shafts 372, 374.

A clutch 376, such as a dog-type clutch, may be connected to the second shaft 374. The clutch 376 may comprise a ?rst set ofsplines or gears 376 that are selectively connectedwith

a second set ofsplines or gears 380 via a clutchring 382. The 

### clutchring 382 selectively connects the gears 378, 380 when movedby a shift fork 384. Thus, the clutch 376 can rotation ally connect the stub shaft 374 with an outboard axle 386 that 

### supports at least one wheel and tire (not shown) thereon.

Another side gear 332 is connected to an output shaft 388 ofthe IAD 328. The output shaft 388 may be a pinion shaft with a pinion gear 390 thereon. The pinion gear 390 is in 

### driving engagementwitharing gear 392. Theringgear 392 is mounted to a differential carrier 394 of the forward axle 

### system 322 and imparts rotation thereto. 20

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## 10
The carrier 394 houses at least one side gear 396 and at least one pinion gear 398. The side gear 396 andpinion gear 398 are meshed with one another. Axle shafts 400 are con nected to each side gear 396 for rotation therewith.

Another clutch 402, also such as a dog type clutch, may be 

### designed to move axially along the input shaft 326. More speci?cally, the clutch 402 selectively engages with an input shaftgear 404 andthe concentric shaftgear 338.Aclutchring 

### 406 is selectivelymovedbetweenthegears 404, 338bya shift fork 408 to connect or disconnect them.

Based on the foregoing, it can be appreciated that the tandem axle system 320 can be operated in different modes.



### Inthepresent embodiment, the forwardaxle system 322 is engaged in the drive-line full time and the rear axle system 

### 324 is engaged for only intermittent use, such as for startup and low speedtractionconditions. Therearaxle system 324 is 

### disengagedandpermittedtoremainidleexceptforexemplary conditions as noted above to improve ef?ciency and reduce 

### drive-line and churning losses.

The tandemaxle system 320has threemodes ofoperation: ?rst, 6x2withtherearaxle system 324 disconnected; second, 6x4 withthe inter-axle differential 328 openwiththe forward 

### axleandrearaxle systems 322, 324 connected; andthird, 6x4 with the inter-axle differential locked and the forward and

rear axle systems 322, 324 connected.



### Inthe ?rstmodeofoperation, the synchronizer system 344 is not engaged andno rotational energy isprovidedto therear 

### axle system 324. Thus, fromtheplate assembly 352 rearward is idle; drive-line energy is not used to rotate it and lubricant 

### churning losses arenotexperienced. Instead, all therotational energy isprovidedto the forwardaxle system 322. The clutch 402 may be engaged. The clutch 376 on the rear axle system is not engaged, thus churning losses from the rear wheels in the rear axle system 324 are prevented or reduced.



### In the secondmode ofoperation, the synchronizer system 344 is engagedandrotational energy fromthe input shaft 326 isprovidedto boththe forward andtherearaxle systems 322, 324. The IAD 328 is open and the clutch 376 on the rear axle system 324 is engagedto rotate the axle shaft 386. The clutch 

### 402 is engaged so that the input shaft 326 and the concentric 

### shaft 336 rotate together.

The third mode of operation is the same as the second, 

### exceptthatthe clutch 402 betweenthe input shaft 326 andthe concentric shaft 336 is closed so that the IAD 328 is locked. The clutch 376 is engaged so that the stub shaft 375 is rota 

### tionally connected to the axle shaft.

Turning now to FIG. 6, another embodiment of a tandem 

### axle system 410 is schematically depicted. The system 410 comprises a forward axle system 412 and a rear axle system 

### 414. Rotational energy isprovidedby an internal combustion 

### engine (not shown) to an input shaft 416.Agerotorpump 418 is drivenby the input shaft 416 and is used to pump lubricant to themoving parts ofa forward axle system 412. The pump 

### provides lubricant to the forward axle system 412 when the forward axle system 412 is not engaged, or when splash lubricant is not suf?cient.

The input shaft 416 extends to an inter-axle differential 

### (IAD) carrier420toprovidethecarrier 420withrotation. The carrierhouses an IAD 422 comprisedofat leasttwo sidegears 424 and at least two pinion gears 426. The gears 424, 426 are drivingly connected to one another.



### A concentric shaft 428 is located about the input shaft 416. The concentric shaft 428 is connected to one ofthe side gears 424.

The concentric shaft 428 provides rotation to a synchro 

### nizer system 430. The synchronizer system 430 comprises a
cone assembly 432. The cone assembly 432 may be selec

## US 8,911,321 B2 11 tivelymovedintheaxial directioninto andoutofengagement withaplate assembly 434.Axialmovement is impartedto the

cone assembly 432 by a shift fork 436 that engages a clutch 

### ring 438.

The cone assembly 432 may be brought into selective 

### engagementwith the plate assembly 434. The rotation ofthe


### cone assembly 432 is imparted to the plate assembly 434, which causes the plate assembly 434 to rotate. As the cone 

### assembly 432 isbrought into additional engagementwith the 

### plate assembly 434, the plate assembly 434 is brought up to the same rotation as the cone assembly 432.

Atapredeterminedtime, suchaswhentherotational speed 

### oftheplate assembly 434 andconeassembly 432 arematched


### or substantially matched, the clutch ring 438 engages gears 440, 442 so that they are locked together.



### While a synchronization system 430 is described above, 

### dog clutches, frictionplate clutches or over-running clutches may be used instead ofthe synchronizer system 430.

Theplate assembly 434 is connected to a set ofdrop gears 446. The drop gears 446 connect with a pinion shaft 448 for 

### the forwardaxle system 412. Thepinion shaft 448haspinion gear 450 meshed with a ring gear 452. The ring gear 452 is mounted to a differential carrier 454 to impart rotation to the carrier 454. The differential carrier 454 houses at least two pinion gears 456 and at least two side gears 458.

Axle shafts are connectedto the side gears 458. The shafts, 

### whichmaybe stub shafts, extend from the differential carrier 454.

One stub shaft 460 is selectively connected to an adjacent shaft 462by a clutch 464, suchas adog clutch. Theclutch 464 may comprise a ?rst set of splines, or gear 466, that are selectively connected with a second set of splines or a gear 

### 468 via a clutch ring 470. The clutch ring 470 selectively connects the gears 466, 468 whenmovedby a shift fork 472. Thus, the clutch 464 can rotationally connect the stub shaft 460with the axle 462 that supports at least onewheel andtire 

### (not shown) thereon.

The other IAD sidegear is 424 connectedto anoutput shaft 474. The output shaft 474 is connected to a propeller shaft 476. Thepropeller shaft 476 spans between the IAD 422 and the rear axle system 414.

Therearaxle system 414 comprises apinion shaft 478with
apiniongear480thereon. Thepiniongear 480 ismeshedwith

a ring gear 482 attached to a differential carrier 484. The differential carrier 484 houses at least two pinion gears 486 and at least two side gears 488.Axle shafts 490 are connected to the side gears 488 forrotation therewith. Wheels and asso ciated tires (not shown) are connected to the axle shafts 490 outboard ofthe side gears 488.

Based on the foregoing, it can be appreciated that the tandem axle system 410 can be operated in different modes.

In the present embodiment, the rear axle system 414 is 

### engaged in the drive-line full time and the forward axle sys tem 412 is engaged for only intermittent use, such as for 

### startup and low speed traction conditions. The front axle system 412 is disengagedandallowedto idlemost ofthetime to increasedriveline ef?ciency andto reduce orprevent lubri 

### cant churning losses.

The tandemaxle system 410has threemodes ofoperation: 

### ?rst, 6x2 with the forward axle system 412 disconnected; second, 6x4 withthe inter-axle differential open 422 withthe 

### forward andrearaxle systems 412, 414 connected; andthird, 6x4 with the inter-axle differential 422 locked and the for ward and the rear axle systems 412, 414 connected.



### Inthe ?rstmodeofoperation, the synchronizer system 430 is not engaged and no rotational energy is provided to the 

### forward axle system 412. Instead, all the rotational energy is 20

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65 

## 12 provided to the rear axle system 414. The clutch on the for 

### ward axle system 412 is open thus the forward axle system 412 isprovidedwithno rotationtoreduce orprevent lubricant 

### churning losses in the forward axle system 412. The clutch 

### 430 is engaged so that the input shaft 416 is rotationally connected to the concentric shaft 428.



### In the secondmode ofoperation, the synchronizer system 430 is engagedandrotational energy fromthe input shaft 416 is provided to both the front and the rear axle systems 412, 414. The IAD 422 is open and the clutch on the forward axle 

### system 412 is engaged. The clutch ring 438 is moved to unlock the input shaft 416 from the concentric shaft 428.

The third mode of operation is the same as the second, 

### except that the synchronizer system 430 is engagedbetween the IAD 422 and the input shaft 416, thus locking the IAD 422. The clutchring 438 is moved to lockthe input shaft 416 to the concentric shaft 428.

Turning now to FIG. 7A, yet another embodiment of a 

### tandem axle system 492 is depicted. The system 492 com prises a forward axle system 494 and a rear axle system 496. An input shaft 498 is connected to receive rotational energy 

### from aprimemover (not shown). The input shaft 498 rotates
adifferential carrier500.At least twodifferentialpiniongears 502 and at least two side gears 504 are meshed with one anotherandarehousedwithinthedifferential carrier500. The 

### carrier 500, the differential pinion gears 502 and side gears 504 comprise an inter-axle differential 517.

One side gear 504 is connected to a pinion shaft 506. The 

### pinion shaft 506 has a pinion gear 508 thereon. The pinion gear 508 is meshed with a ring gear 510 on the forward axle system 494. The ring gear 510 is connected to a forward differential carrier 512. The carrier 512 houses at least one differentialpiniongear 514 andat least one side gear516. The pinion gear 514 and side gear 516 are meshed with one another. Inthedepicted embodiment, there are two sidegears 516.

Each side gear 516 is drivingly connected to an axle shaft 

### 518. Theaxle shafts 518 supportwheels andtires (not shown) thereon.



### A concentric shaft 520 is located about the input shaft 498. The concentric shaft 520 is connected to one ofthe side gears 504. A gear 522, or splines, is provided on the shaft 520 

### opposite the connectionwith the side gear 504.

The concentric shaft 520 provides rotation to a synchro 

### nizer system 524. The synchronizer system 524 comprises a
cone assembly 526. The cone assembly 526 may be selec 

### tivelymovedintheaxial directioninto andoutofengagement withaplate assembly 528.Axialmovement is impartedto the

cone assembly 526 by a shift fork 530 that engages a clutch 

### ring 532.

The cone assembly 526 may be brought into selective 

### engagementwith the plate assembly 528. The rotation ofthe


### cone assembly 526 is imparted to the plate assembly 528, which causes the plate assembly 528 to rotate. As the cone 

### assembly 526 isbrought into additional engagementwiththe 

### plate assembly 528, the plate assembly 528 is brought up to the same rotation as the cone assembly 526.

Atapredeterminedtime, suchaswhentherotational speed 

### oftheplate assembly 528 andcone assembly 526 arematched


### or substantially matched, the clutch ring 532 engages the concentric shaftgear522 andagear534 ontheplateassembly 528 so that they are locked together.



### While a synchronization system 524 is described above, 

### dog clutches, frictionplate clutches or over-running clutches may be used instead ofthe synchronizer system 524.

Theplate assembly 528 is connectedto a drop gear assem bly 536. The assembly 536 comprises a gear 538 onanoutput

## US 8,911,321 B2 13 shaft 540. The rotation ofthe drop gear assembly 536 rotates the output shaft gear 538. The output shaft gear 538 is rota 

### tionally connected to a propeller shaft 542. The propeller shaft 542 is rotationally connected to a rearpinion shaft 544.

The rear pinion shaft 544 has a pinion gear 546 meshed with a rear differential ring gear 548. The ring gear 548 is mounted on a differential carrier 550. The carrier 550 houses 

### atleasttwopiniongears 552, connectedtothe carrier550, and two side gears 554 meshed with the pinion gears 552.

Shafts extend into the differential carrier 550 and connect with the side gears 554. The shafts extend outboard the dif ferential carrier 550. The shafts may be full length shafts or 

### theymaybe stub shafts. First and second stub shafts 556, 558

are shown extending from the carrier 550.

A clutch 560, such as a dog-type clutch, maybe located on 

### the second stub shaft 558. The clutch 560 may selectively


### movealong the stub shaft 558 forconnecting anddisconnect ing the stub shaft 558 with an axle shaft 562 rotationally 

### supporting at least one wheel and tire (not shown).

The clutch 560 may comprise a ?rst set ofsplines 564, or a gear, that are selectively connected with a second set of splines 566, or a gear, via a clutch ring 568. The clutch ring 

### 568 selectively connects the splines 564, 566whenmovedby

a shift fork 570.



### The input shaft 498 has a gear 572 mounted thereon adja cent the concentric shaft gear 522. A clutch 574, such as a 

### dog-type clutch, is provided to selectively connect the input shaft gear 572 and the concentric shaft gear 522.



### The clutch 574 comprises a clutch ring 576 with internal teeth or splines.A shift fork 578 selectively moves the clutch 

### ring 576 fromthe input shaftgear 572 aloneto the input shaft gear 522 andthe concentric shaft gearto rotationally connect 

### them together.

Turning now to FIG. 7B, it can be appreciated that shift forks 578 and 530 canbe combined into a single shiftmecha 

### nism 580. The single shift mechanism 580 comprises shift collars 532 and 576 moved in concert with one another. The movement ofthe collars 532, 576 canbeby a single shift fork that is connectedto both collars 532, 576, or it canbe by two shift forks that are connectedtogether, as shown inthe ?gure.



### The tandemaxle system 492has threemodes ofoperation: ?rst, 6x2withtherearaxle system 496 disconnected; second, 6x4 withthe inter-axledifferential 517 openwiththe forward 

### andrearaxle systems 494, 496 connected; andthird, 6x4with the inter-axle differential 517 locked and the forward and the
rear axle systems 494, 496 connected.



### Inthe ?rstmodeofoperation, the synchronizer system 524 is not engaged andno rotational energy isprovidedto therear 

### axle system 496. Instead, all therotational energy isprovided to the forward axle system 494. The clutch 560 on the rear 

### axle system 496 is open thus the forward axle system 494 is provided with no rotation to reduce or prevent lubricant churning losses in the rear axle system 496. The shift collar 576 does not connect the input shaft 498 to the concentric shaft 520.



### In the secondmode ofoperation, the synchronizer system 524 is engagedandrotational energy fromthe input shaft 498 isprovidedto boththe forward andthe rearaxle systems 494, 496. The IAD 517 is open and the clutch 560 on the rear axle 

### system 496 is engaged. The clutch ring 568 is engaged with the stub shaft 558 and the axle shaft 562 so that they rotate 

### together. The shift collar 576 is moved so that the input shaft 498 is not connected with the concentric shaft 520.

The thirdmodeofoperationis the same as the secondmode 

### ofoperation and the clutch 574 between the input shaft 498 and the concentric shaft 570 is closed. 20

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## 14 What is claimed is: 

### 1.Amethod ofdriving a tandem axle system, comprising: providing rotation to an input shaft for said tandem axle 

### system, said input shaft rotation being continuously transmitted to a rear axle system of said tandem axle 

### system andbeing selectivelyprovided to a forward axle system of said tandem axle system, 

### said input shaft driving an inter-axle differential having

differentialpinion gears and ?rst and second side gears, wherein said ?rst side gear is connected to a shaft con 

### centric with said input shaft, and said second side gear drives a rear pinion gear that provides rotation to said

rear axle system comprising a rear differential and rear axles connected to said rear differential, wherein said concentric shaft drives a cone assembly of a 

### synchronizer system, said cone assembly is selectively 

### engagable with a plate assembly of said synchronizer system to rotate saidplate assembly, wherein saidplate assembly rotationally drives a forward

pinion gear for providing rotation to said forward axle 

### system comprising a forward differential, said forward differential driving at least one stub shaft selectively connected to an axle shaft by a forward axle system clutch. 2. The method of claim 1, wherein said cone assembly is 

### selectivelymoved into engagementwith saidplate assembly by a ?rst shift forkmoving a ?rst clutchring slidable on a ?rst gear on said concentric shaft to saidplate assembly.

3. The method of claim 1, wherein a second shift fork selectively moves, a second clutch ring from a second con centric shaft gear into engagement with a differential carrier ofsaid interaxledifferential to lock saiddifferential carrierto said concentric shaft.

4. The method ofclaim 3, wherein a third shift fork selec tivelymoves a third clutchring to connect said stub shaft and 

### said axle shaft so that they rotate together.



### 5. The method ofclaim 1, wherein said plate assembly is drivingly engaged with a drop gear set to drive said forward 

### pinion gear.

6. Themethod ofclaim 1, wherein ina ?rst operationmode of said tandem axle system, said cone assembly is not 

### engaged with said plate assembly, and said forward axle system clutch is open and a differential carrier and said con centric shaft are locked and a third shift fork selectively

moves a thirdclutchring to disconnect said stub shaftand said axle shaft so that they do not rotate together.

7. The method of claim 1, wherein in a second mode of 

### operation of said tandem axle system, said cone assembly is 

### engagedwith saidplate assembly and a differential carrier is not locked to said concentric shaftwith an interaxle differen tial clutch and a third shift fork selectively moves a third clutch ring to connect said stub shaft and said axle shaft so 

### that they rotate together.

8. The method of claim 1, wherein in a third mode of 

### operation of said tandem axle system, said cone assembly is 

### engagedwith saidplate assembly and a differential carrier is locked to said concentric shaft with an interaxle differential clutch and a third shift fork selectively moves a third clutch ring to connect said stub shaft and said axle shaft so that they 

### rotate together.

9.Amethod ofdriving a tandem axle system, comprising: providing rotation to an input shaft for said tandem axle 

### system, said input shaft rotation being continuously transmittedto a forwardaxle system ofsaid tandem axle 

### system and being selectively provided to a rear axle 

### system of said tandem axle system,

## US 8,911,321 B2 15 said input shaft driving an inter-axle differential having

differentialpinion gears and ?rst and second side gears, wherein said ?rst side gear is connected to a shaft con 

### centric with said input shaft, and said second side gear 

### providing rotational input to a synchronizer system, wherein said concentric shaft has a drop gear set mounted



### forrotationthereon, saiddrop gear set drivinga forward pinion gear connected to a forward differential of said forward axle system, wherein forward axles are con nectedto saidforwarddifferential forrotationtherewith, wherein said synchronizer systemcomprises a coneassem



### bly selectively engageable with a plate assembly to rotate saidplate assembly, wherein said plate assembly provides rotation to a rear

differential ofsaidrearaxle system, saidreardifferential driving at least one stub shaft selectively connectedto an axle shaft by a rear axle system clutch. 10. The method ofclaim 9, wherein a ?rst shift fork selec tively moves a ?rst clutch ring to connect an input shaft gear with a concentric shaft gear so that they rotate together. 11. The method of claim 9, wherein a second shift fork selectively moves a second clutch ring to connect an inter axle differential output shaft with said cone assembly so that 

### they rotate together.

12. The method of claim 9, wherein a third shift fork selectivelymoves a thirdclutchring to connect said stub shaft and said axle shaft so that they rotate together.

13. The method of claim 10, wherein in a ?rst mode of 

### operation ofsaid tandem axle system, said cone assembly is 

### not engaged with said plate assembly so rotation is only 

### provided to said forward axle system, said ?rst clutch ring
connects an input shaft gear with a concentric shaft gear so 

### that they rotate together and a third shift fork selectively

moves a thirdclutchring to disconnect said stub shaftand said axle shaft so that they do not rotate together.

14. The method of claim 9, wherein in a second mode of 

### operation ofsaid tandem axle system, said cone assembly is 

### engagedwith saidplate assembly to transfer rotation to said

rear axle system and said ?rst clutch ring does not connect saidinput shaftgearwith saidconcentric shaftgearandathird shift fork selectivelymoves a third clutchring to connect said stub shaft and said axle shaft so that they rotate together.

15. The method of claim 9, wherein in a third mode of 

### operation ofsaid tandem axle system, said cone assembly is 

### engagedwith saidplate assembly to transfer rotation to said
rearaxle system and said ?rst clutchring connects said input shaft gear with said concentric shaft gear so that they rotate together and a third shift fork selectivelymoves a third clutch ring to connect said stub shaft and said axle shaft so that they 

### rotate together.

16. A method for driving a tandem axle system, compris 

## ing:

providing rotation to an input shaft for said tandem axle



### system, said input shaft rotation being continuously transmittedto a forwardaxle system ofsaidtandem axle 

### system and being selectively provided to a rear axle 

### system of said tandem axle system, wherein said input shaft rotationally drives a differential

carrier ofan inter-axle differential, said differential car rierhousing adifferentialpinion and a ?rst and a second side gear, wherein said ?rst side gear drives an output shaft and said

second side gear provides rotational input to a shaft 

### concentric with said output shaft, wherein said concentric shaft drives a pinion shaft for a



### forward differential of said forward axle system, 10

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## 16 wherein forward axles are connected to said forward 

### differential for rotation therewith, wherein said output shaft drives a synchronizer system



### comprisinga coneassembly selectivelyengageablewith
a plate assembly to rotate saidplate assembly, wherein said plate assembly provides rotation to a rear

differential ofsaidrearaxle system, saidreardifferential driving at least one stub shaft selectively connectedto an axle shaft by a rear axle system clutch. 17. The method of claim 16, wherein a ?rst shift fork selectivelymoves a ?rst clutch ring between said differential carrier and said concentric shaft so that they rotate together.

18. The method of claim 16, wherein a second shift fork selectively moves a second clutch ring between said output 

### shaft and saidplate assembly so that they rotate together.

19. The method of claim 16, wherein a third shift fork of said rear axle system clutch selectively moves a third clutch 

### ring between said stub shaft and said axle shaft so that they 

### rotate together.

20. The method of claim 16, wherein in a ?rst mode of 

### operation ofsaid tandem axle system, said synchronizer sys tem is open, said rear axle system clutch is open and rotation 

### isprovided only to said forwardaxle system anda ?rst clutch 

### ringhas engaged said differential carrier and said concentric shaft so that they rotate together and a third shift fork selec tively moves a third clutch ring to disconnect said stub shaft and said axle shaft so that they do not rotate together.

21. The method ofclaim 16, wherein in a second mode of 

### operation ofsaid tandem axle system, said synchronizer sys tem is closed and a ?rst clutch ring has not engaged said 

### differential carrier and said concentric shaft so that they do not rotate together and a third shift fork selectively moves a third clutch ring to connect said stub shaft and said axle shaft


### so that they rotate together.

22. The method of claim 16, wherein in a third mode of 

### operation ofsaid tandem axle system, said synchronizer sys tem is closed and said ?rst clutch ring engages both said differential carrierand saidconcentric shaft so thattheyrotate together and a third shift fork selectivelymoves a third clutch ring to connect said stub shaft and said axle shaft so that they 

### rotate together.

23. A method for driving a tandem axle system, compris 

## ing:

providing rotation to an input shaft for said tandem axle 

### system, said input shaft rotation being continuously transmittedto a forwardaxle system ofsaid tandem axle 

### system and being selectively provided to a rear axle 

### system of said tandem axle system, wherein said input shaft rotationally drives an inter-axle

differential comprising a differential pinion and a ?rst and a second side gear, wherein said ?rst side gear drives a shaft concentric with

said input shaft and said second side gear drives an 

### inter-axle differential output shaft, wherein said concentric shaft drives a pinion shaft for a



### forward differential of said forward axle system, wherein forward axles are connected to said forward 

### differential for rotation therewith, wherein said inter-axle differential output shaft drives a



### reardifferentialpinion shaft, saidreardifferentialpinion shaft providing rotation to a rear differential housing a differential pinion gear and two side gears, wherein one ofsaid side gears drives a stub shaft connected to aplate 

### assembly of a synchronizer system, said synchronizer system also comprising a cone assembly selectively 

### engageablewith saidplate assembly.

## US 8,911,321 B2 17 24. The method of claim 23, wherein a ?rst shift fork selectively moves a ?rst clutch ring to engage both an input shaft gear and said concentric shaft so that they rotate 

## together.

25. The method of claim 22, wherein a second shift fork selectively moves a second clutch ring to engage both said inter-axle differential output shaft and said rear differential 

### pinion shaft so that they rotate together.

26. The method of claim 22, wherein a third shift fork selectivelymoves a third clutchring engage said cone assem 

### bly with saidplate assembly so that they rotate together.

27. The method of claim 23, wherein in a ?rst mode of 

### operation of said tandem axle system, a ?rst clutch ring is 

### engaged with said concentric shaft and said synchronizer system is open and rotation is only provided to said forward axle system and a second shift fork selectively moves a sec 

### ondclutchringto disconnect saidoutput shaftand saidpinion shaft so that they do not rotate together.

28. The method ofclaim 23, wherein in a second mode of 

### operation ofsaid tandemaxle system, a ?rst clutchring isnot 

### engaged with said concentric shaft, a second clutch ring engages both the inter-axle differential output shaft and a propellershafttoprovidedriveto thereartandemaxle system and a third shift fork selectively moves a third clutch ring to connect said stub shaft and said axle shaft so that they rotate 

## together.

29. The method of claim 23, wherein in a third mode of 

### operation of said tandem axle system, a ?rst clutch ring is 

### engaged with said concentric shaft, a second clutch ring engages both the inter-axle differential output shaft and a propeller shaft to provide drive to the rear axle system and a third shift fork selectivelymoves a thirdclutchringto connect said stub shaft and said axle shaft so that they rotate together.



### 30. A method for driving a tandem axle system, compris 

## ing:

providing rotation to an input shaft for said tandem axle



### system, said input shaft rotation being continuously transmittedto a forwardaxle system ofsaidtandem axle 

### system and being selectively provided to a rear axle 

### system of said tandem axle system, wherein said input shaft rotationally drives an inter-axle

differential, said inter-axledifferential comprising adif ferential pinion and a ?rst and a second side gear, wherein said ?rst side gear drives a shaft concentric with



### said input shaft and said second sidegeardrives an input 

### pinion gear for a forward differential, wherein said concentric shaft drives a synchronizer shaft



### for a synchronizer system comprising a plate assembly and a cone assembly connected to said synchronizer 

### shaft, saidcone assembly is selectively engageablewith 

### saidplate assembly, wherein said plate assembly provides rotation to a rear



### differential pinion shaft, said rear differential pinion shaft providing rotation to a rear differential housing a differential pinion gear and two side gears. 31. The method of claim 30, wherein a stub shaft is con nected to one of said rear differential side gears for rotation therewith, said stub shaft having a gear thereon, and a ?rst shift fork selectively moves a ?rst clutch ring to engage both said stub shaft gear and an axle so that they rotate together.

32. The method of claim 30, wherein a second shift fork selectivelymoves a secondclutchringto engagebothaninput shaft gear and said concentric shaft so that they rotate 

## together. 20

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65 

## 18 33. The method of claim 30, wherein a third shift fork selectively moves a third clutch ring to engage both said 

### synchronizer shaft and saidplate assembly so that theyrotate 

## together.

34. The method of claim 30, wherein in a ?rst mode of 

### operation ofthe tandem axle system, a second clutch ring is 

### engaged with the input shaft gear and said concentric shaft, said synchronizer system is open and said ?rst clutch ring is not engaged with said stub shaft gear and said axle.

35. The method ofclaim 30, wherein in a second mode of 

### operation of the tandem axle system, a third clutch ring 

### engages said synchronizer shaft and saidplate assembly and

a ?rstclutchring engages the stub shaft gearand saidaxle and

a second shift fork selectively moves a second clutch ring to disconnect said input shaft and said concentric shaft so that 

### they do not rotate together.

36. The method of claim 30, wherein in a third mode of 

### operation of the tandem axle system, a third clutch ring 

### engages said synchronizer shaft and said plate assembly, a ?rst clutchring engages said stub shaft gearand saidaxle and

a second clutch ring engages both said input shaft gear and said concentric shaft.



### 37. A method for driving a tandem axle system, compris mg:

providing rotation to an input shaft for said tandem axle 

### system, said input shaft rotation being continuously transmitted to a rear axle system of said tandem axle 

### system andbeing selectivelyprovided to a forward axle system of said tandem axle system, wherein said input shaft rotationally drives an inter-axle



### differential, said inter-axledifferential comprising adif ferential pinion and a ?rst and a second side gear, wherein said ?rst side gear drives a shaft concentric with



### said input shaft and said second sidegeardrives an input pinion gear for a rear differential of said rear axle sys 

### tem, wherein said concentric shaft drives a cone assembly of a 

### synchronizer system, said synchronizer system also comprising aplate assembly, wherein saidplateassemblyis connectedto aninputpinion

gear of said forward axle system, said forward axle 

### system also comprising a differential having a pair of side gears and differential pinion gears. 38. The method of claim 37, wherein a stub shaft is con nected to one of said forward differential side gears for rota tiontherewith, saidstub shafthavingagearthereon, anda ?rst shift fork selectively moves a ?rst clutch ring to engage both said stub shaft gear and an axle so that they rotate together.

39. The method of claim 37, wherein a second shift fork selectivelymoves a second clutch ring into engagement with


### a concentric shaftgear, saidplate assembly andan input shaft 

### gear and selectively moves said synchronizer system into 

### engagement.

40. The method of claim 37, wherein in a ?rst mode of 

### operation ofsaid tandem axle system, said synchronizer sys tem is not engaged and a ?rst clutch ring is not engaged with

a stub shaftgearandanaxle anda second shift fork selectively
moves a second shift clutch ring to lock the input shaft to the concentric shaft.

41. The method ofclaim 37, wherein in a second mode of 

### operation of said tandem axle system, said cone assembly is engagedwith saidplate assembly so thatbothassemblies are 

### rotating together and a ?rst clutch ring is engagedwith both said stub shaft gear and an axle and a second shift fork selectively moves a second shift clutch ring to unlock the 

### input shaftwith respect to the concentric shaft.

## US 8,911,321 B2 19 42. The method of claim 37, wherein in a third mode of 

### operation ofsaid tandem axle system, said cone assembly is engagedwith saidplate assembly so thatboth assemblies are 

### rotating togetheranda ?rst clutchring is engagedwithbotha stub shaft gear and an axle and the inter-axle differential is locked and a second shift fork selectively moves a second 

### shift clutchring to lockthe input shaftto the concentric shaft.



### 43. A method for driving a tandem axle system, compris 

## ing:

providing rotation to an input shaft for said tandem axle



### system, said input shaft rotation being continuously transmittedto a forwardaxle system ofsaidtandem axle 

### system and being selectively provided to a rear axle 

### system of said tandem axle system, wherein said input shaft rotationally drives an inter-axle

differential, said inter-axledifferential comprising adif ferential pinion and a ?rst and a second side gear, wherein said ?rst side gear drives a shaft concentric with



### said input shaft and said second sidegeardrives an input pinion gear for a forward differential of said forward 

### axle system, wherein said concentric shaft drives a cone assembly ofa



### synchronizer system, said synchronizer system also comprising aplate assembly, wherein saidplateassemblyis connectedtoaninputpinion

gear of said rear axle system, said rear axle system also 

### comprising a differential having apair ofside gears and 

### differential pinion gears. 44. The method of claim 43, wherein a stub shaft is con nected to one of said rear differential side gears for rotation therewith, said stub shaft having a gear thereon, and a ?rst 

### shift fork selectivelymoves a ?rst clutch ring to engage both said stub shaft gear and an axle so that they rotate together.

45. The method of claim 41, wherein a second shift fork selectivelymoves a second clutch ring into engagement with

a concentric shaft gear and an input shaft gear so that they 

### rotate together. 20

25

30

35 

## 20 46. The method of claim 43, wherein a third shift fork selectively moves a third clutch ring into engagement with 

### saidconcentric shaftgearand saidplateassembly so thatthey 

### rotate together.

47. The method of claim 43, wherein in a ?rst mode of 

### operation ofsaid tandem axle system, said synchronizer sys tem is not engaged and a ?rst clutch ring is not engaged with

a stub shaftgearandanaxle anda second shift fork selectively

moves a second clutch ring to connect said concentric shaft 

### and said input shaft so that they rotate together.

48. The method ofclaim 43, wherein in a second mode of 

### operation of said tandem axle system, said cone assembly is engagedwith saidplate assembly so thatbothassemblies are 

### rotating togetheranda ?rst clutchring is engagedwithbotha stub shaft gear and an axle so that they rotate together and a second shift fork selectively moves a second clutch ring to disconnect said input shaft and said concentric shaft so that 

### they do not rotate together.

49. The method of claim 43, wherein in a third mode of 

### operation of said tandem axle system, said cone assembly is engagedwith saidplate assembly so thatbothassemblies are 

### rotating togetheranda ?rst clutchring is engagedwithbotha stub shaft gear and an axle so that they rotate togetherandthe inter-axle differential is locked and a second shift fork selec tively moves a second clutch ring to connect said input shaft and said concentric shaft so that they rotate together.

50. The method of 43, wherein a second clutch ring and thirdclutchring are connectedto a single shiftmechanism for 

### moving saidclutchrings inconcertwithoneanother,wherein said single shift mechanism selectively moves said second clutch ring into engagement with a concentric shaft gear and


### an input shaft gear so that theyrotate together and said single 

### shiftmechanism selectivelymoves said third clutchring into 

### engagement with said concentric shaft gear and said plate 

### assembly so that they rotate together.

* * * * *