(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) 

(72) 

(73) 

(*) 

(21) 

(22) 

(65) 

(60) 

(51) 

TANDEM AXLE SYSTEM 

Applicant: Dana Heavy Vehicle Systems Group, 

LLC, Maumee, OH (US) 

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

Donald J. Remboski, AnnArbor, MI 

(US); Richard A. 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 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 0 days. 

Appl. No.: 13/973,166 

Filed: Aug. 22, 2013 

Prior Publication Data 

US 2014/0057752 A1 Feb. 27, 2014 

Related U.S. Application Data 

Provisional application No. 61/692,292, ?led on Aug. 

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 of Classi?cation Search 

None 

See application ?le for complete search history. 

(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 .... .. 

7,306,536 7,258,644 6,514,169 B2* 12/20073 8/2007Ziech Turner et ....... et a1.al. .. 

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 
US. Patent Dec. 16, 2014 Sheet 1 0f 7 US 8,911,321 B2 
US. Patent Dec. 16, 2014 Sheet 2 0f 7 US 8,911,321 B2 

N .OE
US. Patent Dec. 16, 2014 Sheet 3 0f 7 US 8,911,321 B2 

Kw 

@211 

1.. 8 EN 

i i _..“www A

w 

xi at; 4%: > x- 

\+ 2N 

X 

H A3mm NV 
US. Patent Dec. 16, 2014 Sheet 4 0f 7 US 8,911,321 B2 

w .UE
US. Patent Dec. 16, 2014 Sheet 5 0f 7 US 8,911,321 B2 
US. Patent Dec. 16, 2014 Sheet 6 0f7 US 8,911,321 B2 
US. Patent Dec. 16, 2014 Sheet 7 0f 7 US 8,911,321 B2 
US 8,911,321 B2 

1 

TANDEM AXLE SYSTEM 

RELATED APPLICATIONS 

This application claims bene?t of and priority to US. Pro 

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

2012 which is fully incorporated by reference herein. 

BACKGROUND OF THE INVENTION 

The typical North American class 8 truck rear tandem axle 

is a full time 6><4 driveline with 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 of the 6x4 system traction. What is needed is a 

tandem axle system that has the ef?ciency of a 6x2 tandem 

with the tractive effort of the 6x4 system. 

SUMMARY OF THE INVENTION 

Methods for driving tandem axle systems are described. 

Generally, the methods comprise providing a rotational input 

into the tandem axle system, which comprises a forward axle 

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 of the 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 

of tandem axle systems are provided utiliZing components to 

engage and disengage the forward or rear axle systems. 

BRIEF DESCRIPTION OF THE FIGURES 

FIG. 1 is a schematic depiction of one embodiment of the 

tandem axle system; 

FIG. 2 is a schematic depiction of a 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 depiction of a ?fth embodiment of the 

tandem axle system; 

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

the tandem axle system; 

FIG. 7A is a schematic depiction of a seventh embodiment 

of the 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 of a tandem axle 

system 10 is schematically depicted. The system 10 com 

prises of a forward axle system 12 and a rear axle system 14. 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

2 

Rotational energy is provided to the tandem axle 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 of the operating condition 

of the forward axle system 12, which can be selectively 

engaged and disengaged. 

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 of the 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 and the rear axle system 14. A second end of the propeller 

shaft 30 is connected to a rear pinion gear 32. The rear pinion 

gear 32 is drivingly connected to a rear ring gear 34. The rear 

ring gear 34 is connected to a rear differential 36. 

The rear differential 36 comprises at least two side gears 38 

and at least two pinion gears 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 is provided 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 in the axial direction into and out of engagement with 

a plate assembly 54 a portion of which is angled to receive the 

cone assembly 52. 

The cone assembly 52 is rotatable and via 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 to rotate. As the cone assembly 52 is brought into 

additional engagement with the plate assembly 54, the plate 

assembly 54 is matched or substantially matched to the same 

rotational speed of the cone assembly 52. 

At a predetermined time, such as when the rotational speed 

of the plate assembly 54 and cone assembly 52 are matched or 

substantially matched via substantial engagement of the plate 

and cone assemblies 52, 54, a shift fork 56 moves a dog clutch 

ring 58 on the dog clutch gear 48 also to a synchronizer gear 

60. The dog clutch ring 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 of the synchronizer system. 

The synchronizer system 50 is selectively connected to, 

and thus selectively rotates, 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 provided with, or connected 

to, a pinion shaft 66. The pinion shaft 66 has a pinion gear 68. 

The pinion gear 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 selectively move 

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 

82A that are selectively connected with a second set of splines 

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 designed to selectively engage and disengage with the 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, the rear axle system 14 is engaged in the 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 of the time. 

The tandem has three modes of operation: ?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 ?rst mode of operation, 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 power is transmitted to the forward axle system 12. 

Also, the clutch 86 between the stub shaft 80 and axle shaft 84 

is unlocked so that the forward axle system 12 is not rotating, 

thus reducing, or preventing, oil churning losses. 

In the second mode of operation, 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 of the axle shaft 84 

of the forward axle system 12 are engaged. Thus, the forward 

axle system 12 provides rotational power to the forward 

wheels and tires. The lAD 20 is locked so that the forward and 

rear axle systems 12, 14 are driven at the same speed. In other 

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 of a tandem 

axle system 92 is depicted. The system 92 comprises a for 

ward axle system 94 and a rear axle system 96. An input shaft 

98 is provided and rotated by an internal combustion engine 

(not shown). The shaft 98 is connected to an inter-axle differ 

ential (IAD) 100. The lAD 100 is comprised of at least two 

side gears 102 and at least two pinion gears 104. The side 

gears 102 and pinion gears 104 are meshed with one another. 

20 

25 

30 

35 

40 

50 

55 

60 

65 

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 selectively moved 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 rotatable by gear 110 and via the 

axial movement, it may be brought into selective engagement 

with the angled plate assembly 114. The rotation of the cone 

assembly 112 is imparted to the angled plate assembly 114, 

which causes the angled plate 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 of the plate and cone assemblies 112, 114 are matched, 

or substantially matched, a shift fork 116 moves a dog clutch 

ring 118 on the gear 110 also to a synchronizer gear 120. 

The dog clutch ring 118 then rotationally 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 rotated by 

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 rear differential carrier 128. The shafts may be full length 

shafts or they may be 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, may be located on 

the second stub shaft 136. The clutch 138 may selectively 

move along the second stub shaft 136 for connecting and 

disconnecting the second stub shaft 136 with an axle shaft 140 

rotationally supporting at least one wheel and tire (not 

shown). 

The clutch 138 may comprise a ?rst set of splines 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 the gears 138A, 1388 when moved 

by a shift fork 138D. 

A shaft 142 concentric with the input shaft 98 is connected 

to one of the 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, or connected to, a pinion shaft 148. The pinion shaft 148 

has a pinion gear 150. The pinion gear 150 is connected to a 

differential ring gear 152. The ring gear 152 is connected to a 

differential carrier 154. At least two pinion gears 156 and at 

least two side gears 158 are located within the differential 

carrier 154. 

First and second shafts 160, 162 extend into the differential 

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 they may be stub 

shafts. Regardless, at least one wheel and tire (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 of clutches 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 clutch ring 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 forward axle system 94 is engaged in the drive 

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 of the time. 

The tandem axle system 92 has three modes of operation: 

?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. 

In the ?rst mode of operation, 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 second mode of operation, 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 locked with 

the input shaft 98 so that they rotate 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 and the 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 engagement with one another. One 

set of side 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. More particularly, 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 

side gears 198 for rotation therewith. 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 

25 

30 

35 

40 

45 

50 

55 

60 

65 

6 

moved in the axial direction into and out of engagement with 

a plate assembly 208 that is angled to receive the cone assem 

bly 206. 

The rotation of the 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 engagement with the plate assembly 208, the 

plate assembly 208 rotates at the same rate as the cone assem 

bly 206. 

At a predetermined time, such as when the rotational speed 

of the plate assembly 208 and cone assembly 206 are matched 

or substantially matched, 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. 

First and second shafts 230, 232 extend into the differential 

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, such as a dog-type clutch, may be 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, which may 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 a dog clutch ring 244. The dog clutch ring 244 is adapted 

to move in a ?rst axial direction to lock the carrier 194 and the 

concentric shaft 186 together and in a 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. 

In the present embodiment, the forward axle 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 speed traction conditions. The rear axle system 174 is 

disengaged and allowed to idle most of the time. 

The tandem axle system 170 has three modes of operation: 

?rst, 6x2 with the rear axle system 174 disconnected; second, 

6x4 with the inter-axle differential 178 open with the front 

and rear axle systems 172, 174 connected; and third, 6x4 with 

the inter-axle differential 178 locked and the front and rear 

axle systems 172, 174 connected. 

In the ?rst mode of operation, the synchronizer system 204 

is open and rotational energy is directed exclusively to the 

forward axle system 172. No rotational energy is provided to 

the rear axle system 174, particularly when the dog clutch 234 

is disengaged. More particularly, the shift fork 236 moves the 

collar 238 so that the stub shaft 232 is not engaged with the 

axle shaft 237. Thus, lubricant churning losses in the rear axle 

system 174 are minimized or prevented. 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 second mode of operation, 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 also provided to the forward axle 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 and the concentric shaft 186 is moved so that 

the differential carrier of the interaxle differential 178 and the 

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 connected to an inter-axle differential (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 

of the 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 of IAD 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 

rotated by the propeller 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. 

First and second shafts 284, 286 extend into the differential 

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 or they may be stub 

shafts. A stub shaft 286 is depicted as extending from one side 

of the carrier 282. 

A synchronizer system 288 is connected to the stub shaft 

286. The stub shaft 286 rotates the synchronizer system 288. 

More particularly, the system 288 comprises a plate assembly 

290 connected to the stub shaft 286; the plate assembly 290 

rotates with the shaft 286. 

The synchronizer system 288 also comprises a cone assem 

bly 292. The cone assembly 292 may be selectively moved in 

the axial direction into and out of engagement with an angled 

plate 294 of the 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 imparted to the angled plate 294, which 

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

292 is brought into additional engagement with the plate 294, 

the two begin to rotate at the same rotational rate. 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

8 

The cone assembly 292 is connected to 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. 

At a predetermined time, such as when the rotational speed 

of the 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 synchronizer gear 304. 

The dog clutch ring 300 rotationally connects the axle shaft 

gear 302 and the dog clutch gear 304. Outboard ends of the 

shaft or stub shaft support the wheels and tires (not shown) for 

the rear axle system 250. 

Another clutch 306, which may be a dog-type clutch, may 

selectively connect the concentric shaft 260 and a gear 308 on 

the input shaft 252. The clutch 306 is adapted to move in a ?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 selectively moves a clutch ring 312 between the shaft 

260 and the gear 308. 

Another clutch 314, which also may be 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. 

In the present embodiment, the forward axle 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 speed traction conditions. The rear axle system 250 is 

disengaged and allowed to idle most of the time to reduce, or 

prevent, lubricant churning losses. 

The tandem has three modes of operation: ?rst, 6x2 with 

the rear axle systems 250 disconnected; second, 6x4 with the 

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 of operation, the clutch 314 between the 

IAD 274 output shaft and the propeller 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 open thus no rotational energy is provided to the 

rear axle system 250. The rear axle system 250 is not rotated 

and lubricant churning losses are prevented or minimized. 

More particularly, the fork 298 has moved the ring 300 so that 

it does not engage both the axle shaft 296 and synchronizer 

system 288. Clutch ring 312 has engaged both the concentric 

shaft 260 and the input shaft 252. 

In the second mode of operation, the clutch 314 between 

the IAD output shaft 274 and the propeller shaft 276 is moved 

in the axial direction to close the connection between the two. 

Thus, rotational energy is passed through the clutch 3 14 to the 

rear axle system 250, and rotational energy is also provided to 

the forward axle system 248. The fork 298 has moved the ring 

300 so that it engages both the axle shaft 296 and synchro 

nizer system 288 and the two rotate together. The clutch ring 

312 is not engaged with the concentric shaft 260. 

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

except that the clutch 314 between the input shaft 252 and the 

concentric shaft 260 is closed so that the IAD 254 is locked. 

Further, the fork 298 has moved the ring 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 of a 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 and at least two side gears 332 housed inside a 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 

about the input shaft 326. The concentric shaft 336 has a set of 

teeth, splines or a gear located on an outside surface; the 

depicted embodiment has 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 clutch ring 348 is mounted on 

the gear 346 for rotation therewith. 

The synchronizer system 344 comprises a cone assembly 

350. The cone assembly 350 may be selectively moved in the 

axial direction into and out of engagement with a plate assem 

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

The rotation of the 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 of the cone assembly 350. As the 

cone is brought into additional engagement with the plate, the 

two begin to rotate at the same rotational rate. 

At a predetermined time, such as when the rotational speed 

of the plate assembly 352 and cone assembly 350 are matched 

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 described above, 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 

they may be 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 of splines or gears 376 that are selectively connected with 

a second set of splines or gears 380 via a clutch ring 382. The 

clutch ring 382 selectively connects the gears 378, 380 when 

moved by 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 

of the IAD 328. The output shaft 388 may be a pinion shaft 

with a pinion gear 390 thereon. The pinion gear 390 is in 

driving engagement with a ring gear 392. The ring gear 392 is 

mounted to a differential carrier 394 of the forward axle 

system 322 and imparts rotation thereto. 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

10 

The carrier 394 houses at least one side gear 396 and at 

least one pinion gear 398. The side gear 396 and pinion 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 

shaft gear 404 and the concentric shaft gear 338. A clutch ring 

406 is selectively movedbetween the gears 404, 338 by a 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. 

In the present embodiment, the forward axle 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 speed traction conditions. The rear axle system 324 is 

disengaged and permitted to remain idle except for exemplary 

conditions as noted above to improve ef?ciency and reduce 

drive-line and churning losses. 

The tandem axle system 320 has three modes of operation: 

?rst, 6x2 with the rear axle system 324 disconnected; second, 

6x4 with the inter-axle differential 328 open with the forward 

axle and rear axle systems 322, 324 connected; and third, 6x4 

with the inter-axle differential locked and the forward and 

rear axle systems 322, 324 connected. 

In the ?rst mode of operation, the synchronizer system 344 

is not engaged and no rotational energy is provided to the rear 

axle system 324. Thus, from the plate assembly 352 rearward 

is idle; drive-line energy is not used to rotate it and lubricant 

churning losses are not experienced. Instead, all the rotational 

energy is provided to the forward axle 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 second mode of operation, the synchronizer system 

344 is engaged and rotational energy from the input shaft 326 

is provided to both the forward and the rear axle systems 322, 

324. The IAD 328 is open and the clutch 376 on the rear axle 

system 324 is engaged to 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, 

except that the clutch 402 between the input shaft 326 and the 

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 is provided by an internal combustion 

engine (not shown) to an input shaft 416. A gerotor pump 418 

is driven by the input shaft 416 and is used to pump lubricant 

to the moving parts of a 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) carrier 420 to provide the carrier 420 with rotation. The 

carrier houses an IAD 422 comprised of at least two side gears 

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 of the 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 

tively moved in the axial direction into and out of engagement 

with a plate assembly 434. Axial movement is imparted to the 

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

ring 438. 

The cone assembly 432 may be brought into selective 

engagement with the plate assembly 434. The rotation of the 

cone assembly 432 is imparted to the plate assembly 434, 

which causes the plate assembly 434 to rotate. As the cone 

assembly 432 is brought into additional engagement with the 

plate assembly 434, the plate assembly 434 is brought up to 

the same rotation as the cone assembly 432. 

At a predetermined time, such as when the rotational speed 

of the plate assembly 434 and cone assembly 432 are matched 

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, friction plate clutches or over-running clutches 

may be used instead of the synchronizer system 430. 

The plate assembly 434 is connected to a set of drop gears 

446. The drop gears 446 connect with a pinion shaft 448 for 

the forward axle system 412. The pinion shaft 448 has pinion 

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 connected to the side gears 458. The shafts, 

which may be stub shafts, extend from the differential carrier 

454. 

One stub shaft 460 is selectively connected to an adjacent 

shaft 462 by a clutch 464, such as a dog clutch. The clutch 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 when moved by a shift fork 472. 

Thus, the clutch 464 can rotationally connect the stub shaft 

460 with the axle 462 that supports at least one wheel and tire 

(not shown) thereon. 

The other IAD side gear is 424 connected to an output shaft 

474. The output shaft 474 is connected to a propeller shaft 

476. The propeller shaft 476 spans between the IAD 422 and 

the rear axle system 414. 

The rear axle system 414 comprises a pinion shaft 478 with 

a pinion gear 480 thereon. The pinion gear 480 is meshed with 

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 for rotation therewith. Wheels and asso 

ciated tires (not shown) are connected to the axle shafts 490 

outboard of the 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 disengaged and allowed to idle most of the time 

to increase driveline ef?ciency and to reduce or prevent lubri 

cant churning losses. 

The tandem axle system 410 has three modes of operation: 

?rst, 6x2 with the forward axle system 412 disconnected; 

second, 6x4 with the inter-axle differential open 422 with the 

forward and rear axle systems 412, 414 connected; and third, 

6x4 with the inter-axle differential 422 locked and the for 

ward and the rear axle systems 412, 414 connected. 

In the ?rst mode of operation, 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 

25 

30 

35 

40 

45 

50 

55 

60 

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 is provided with no rotation to reduce or prevent 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 second mode of operation, the synchronizer system 

430 is engaged and rotational energy from the 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 engaged between 

the IAD 422 and the input shaft 416, thus locking the IAD 

422. The clutch ring 438 is moved to lock the 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 a prime mover (not shown). The input shaft 498 rotates 

a differential carrier 500. At least two differential pinion gears 

502 and at least two side gears 504 are meshed with one 

another and are housed within the differential carrier 500. 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 

differential pinion gear 514 and at least one side gear 516. The 

pinion gear 514 and side gear 516 are meshed with one 

another. In the depicted embodiment, there are two side gears 

516. 

Each side gear 516 is drivingly connected to an axle shaft 

518. The axle shafts 518 support wheels and tires (not shown) 

thereon. 

A concentric shaft 520 is located about the input shaft 498. 

The concentric shaft 520 is connected to one of the side gears 

504. A gear 522, or splines, is provided on the shaft 520 

opposite the connection with 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 

tively moved in the axial direction into and out of engagement 

with a plate assembly 528. Axial movement is imparted to the 

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

ring 532. 

The cone assembly 526 may be brought into selective 

engagement with the plate assembly 528. The rotation of the 

cone assembly 526 is imparted to the plate assembly 528, 

which causes the plate assembly 528 to rotate. As the cone 

assembly 526 is brought into additional engagement with the 

plate assembly 528, the plate assembly 528 is brought up to 

the same rotation as the cone assembly 526. 

At a predetermined time, such as when the rotational speed 

of the plate assembly 528 and cone assembly 526 are matched 

or substantially matched, the clutch ring 532 engages the 

concentric shaft gear 522 and a gear 534 on the plate assembly 

528 so that they are locked together. 

While a synchronization system 524 is described above, 

dog clutches, friction plate clutches or over-running clutches 

may be used instead of the synchronizer system 524. 

The plate assembly 528 is connected to a drop gear assem 

bly 536. The assembly 536 comprises a gear 538 on an output 
US 8,911,321 B2 

13 

shaft 540. The rotation of the 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 rear pinion 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 

at least two pinion gears 552, connected to the carrier 550, 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 

they may be 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, may be located on 

the second stub shaft 558. The clutch 560 may selectively 

move along the stub shaft 558 for connecting and disconnect 

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 of splines 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, 566 when moved by 

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 from the input shaft gear 572 alone to the input shaft 

gear 522 and the concentric shaft gear to rotationally connect 

them together. 

Turning now to FIG. 7B, it can be appreciated that shift 

forks 578 and 530 can be combined into a single shift mecha 

nism 580. The single shift mechanism 580 comprises shift 

collars 532 and 576 moved in concert with one another. The 

movement of the collars 532, 576 can be by a single shift fork 

that is connected to both collars 532, 576, or it can be by two 

shift forks that are connected together, as shown in the ?gure. 

The tandem axle system 492 has three modes of operation: 

?rst, 6x2 with the rear axle system 496 disconnected; second, 

6x4 with the inter-axle differential 517 open with the forward 

and rear axle systems 494, 496 connected; and third, 6x4 with 

the inter-axle differential 517 locked and the forward and the 

rear axle systems 494, 496 connected. 

In the ?rst mode of operation, the synchronizer system 524 

is not engaged and no rotational energy is provided to the rear 

axle system 496. Instead, all the rotational energy is provided 

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 second mode of operation, the synchronizer system 

524 is engaged and rotational energy from the input shaft 498 

is provided to both the forward and the rear axle 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 third mode of operation is the same as the second mode 

of operation and the clutch 574 between the input shaft 498 

and the concentric shaft 570 is closed. 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

14 

What is claimed is: 

1. A method of driving 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 and being selectively provided to a forward axle 

system of said tandem axle system, 

said input shaft driving an inter-axle differential having 

differential pinion 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 said plate assembly, 

wherein said plate 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 

selectively moved into engagement with said plate assembly 

by a ?rst shift fork moving a ?rst clutch ring slidable on a ?rst 

gear on said concentric shaft to said plate 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 

of said inter axle differential to lock said differential carrier to 

said concentric shaft. 

4. The method of claim 3, wherein a third shift fork selec 

tively moves a third clutch ring to connect said stub shaft and 

said axle shaft so that they rotate together. 

5. The method of claim 1, wherein said plate assembly is 

drivingly engaged with a drop gear set to drive said forward 

pinion gear. 

6. The method of claim 1, wherein in a ?rst operation mode 

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 third clutch ring to disconnect said stub shaft and 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 

engaged with said plate assembly and a differential carrier is 

not locked to said concentric shaft with 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 

engaged with said plate 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. A method of driving 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 forward axle system of said 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 

differential pinion 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 

for rotation thereon, said drop gear set driving a forward 

pinion gear connected to a forward differential of said 

forward axle system, wherein forward axles are con 

nected to said forward differential for rotation therewith, 

wherein said synchronizer system comprises a cone assem 

bly selectively engageable with a plate assembly to 

rotate said plate assembly, 

wherein said plate assembly provides rotation to a rear 

differential of said rear axle system, said rear differential 

driving at least one stub shaft selectively connected to an 

axle shaft by a rear axle system clutch. 

10. The method of claim 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 

selectively moves a third clutch ring 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 of said 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 third clutch ring to disconnect said stub shaft and said 

axle shaft so that they do not rotate together. 

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

operation of said tandem axle system, said cone assembly is 

engaged with said plate assembly to transfer rotation to said 

rear axle system and said ?rst clutch ring does not connect 

said input shaft gear with said concentric shaft gear 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. 

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

operation of said tandem axle system, said cone assembly is 

engaged with said plate assembly to transfer rotation to said 

rear axle system and said ?rst clutch ring connects said input 

shaft gear with said concentric shaft gear so that they 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. 

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 

transmitted to a forward axle system of said tandem 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 of an inter-axle differential, said differential car 

rier housing a differential pinion 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 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

16 

wherein forward axles are connected to said forward 

differential for rotation therewith, 

wherein said output shaft drives a synchronizer system 

comprising a cone assembly selectively engageable with 

a plate assembly to rotate said plate assembly, 

wherein said plate assembly provides rotation to a rear 

differential of said rear axle system, said rear differential 

driving at least one stub shaft selectively connected to an 

axle shaft by a rear axle system clutch. 

17. The method of claim 16, wherein a ?rst shift fork 

selectively moves 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 said plate 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 of said tandem axle system, said synchronizer sys 

tem is open, said rear axle system clutch is open and rotation 

is provided only to said forward axle system and a ?rst clutch 

ring has 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 of claim 16, wherein in a second mode of 

operation of said 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 of said tandem axle system, said synchronizer sys 

tem is closed and said ?rst clutch ring engages both said 

differential carrier and said concentric shaft so that they 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. 

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 

transmitted to a forward axle system of said 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 

rear differential pinion shaft, said rear differential pinion 

shaft providing rotation to a rear differential housing a 

differential pinion gear and two side gears, wherein one 

of said side gears drives a stub shaft connected to a plate 

assembly of a synchronizer system, said synchronizer 

system also comprising a cone assembly selectively 

engageable with said plate 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 

selectively moves a third clutch ring engage said cone assem 

bly with said plate 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 

ond clutch ring to disconnect said output shaft and said pinion 

shaft so that they do not rotate together. 

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

operation of said tandem axle system, a ?rst clutch ring is not 

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 tandem axle 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 selectively moves a third clutch ring to 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 

transmitted to a forward axle system of said 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, said inter-axle differential comprising a dif 

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 side gear drives 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, said cone assembly is selectively engageable with 

said plate 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 

selectively moves a second clutch ring to engage both an input 

shaft gear and said concentric shaft so that they rotate 

together. 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

1 8 

33. The method of claim 30, wherein a third shift fork 

selectively moves a third clutch ring to engage both said 

synchronizer shaft and said plate assembly so that they rotate 

together. 

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

operation of the 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 of claim 30, wherein in a second mode of 

operation of the tandem axle system, a third clutch ring 

engages said synchronizer shaft and said plate assembly and 

a ?rst clutch ring engages the stub shaft gear and said axle 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 clutch ring engages said stub shaft gear and said axle 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 and being selectively provided to a forward axle 

system of said tandem axle system, 

wherein said input shaft rotationally drives an inter-axle 

differential, said inter-axle differential comprising a dif 

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 side gear drives 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 a plate assembly, 

wherein said plate assembly is connected to an input pinion 

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 

tion 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. 

39. The method of claim 37, wherein a second shift fork 

selectively moves a second clutch ring into engagement with 

a concentric shaft gear, said plate assembly and an input shaft 

gear and selectively moves said synchronizer system into 

engagement. 

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

operation of said tandem axle system, said synchronizer sys 

tem is not engaged and a ?rst clutch ring is not engaged with 

a stub shaft gear and an axle and a second shift fork selectively 

moves a second shift clutch ring to lock the input shaft to the 

concentric shaft. 

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

operation of said tandem axle system, said cone assembly is 

engaged with said plate assembly so that both assemblies are 

rotating together and a ?rst clutch ring is engaged with both 

said stub shaft gear and an axle and a second shift fork 

selectively moves a second shift clutch ring to unlock the 

input shaft with respect to the concentric shaft. 
US 8,911,321 B2 

19 

42. The method of claim 37, wherein in a third mode of 

operation of said tandem axle system, said cone assembly is 

engaged with said plate assembly so that both assemblies are 

rotating together and a ?rst clutch ring is engaged with both a 

stub shaft gear and an axle and the inter-axle differential is 

locked and a second shift fork selectively moves a second 

shift clutch ring to lock the input shaft to 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 

transmitted to a forward axle system of said 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, said inter-axle differential comprising a dif 

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 side gear drives an input 

pinion gear for a forward differential of said forward 

axle system, 

wherein said concentric shaft drives a cone assembly of a 

synchronizer system, said synchronizer system also 

comprising a plate assembly, 

wherein saidplate assembly is connected to an input pinion 

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

comprising a differential having a pair of side 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 selectively moves 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 

selectively moves 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 

said concentric shaft gear and said plate assembly so that they 

rotate together. 

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

operation of said tandem axle system, said synchronizer sys 

tem is not engaged and a ?rst clutch ring is not engaged with 

a stub shaft gear and an axle and a 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 of claim 43, wherein in a second mode of 

operation of said tandem axle system, said cone assembly is 

engaged with said plate assembly so that both assemblies are 

rotating together and a ?rst clutch ring is engaged with both a 

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 

engaged with said plate assembly so that both assemblies are 

rotating together and a ?rst clutch ring is engaged with both a 

stub shaft gear and an axle so that they rotate together and the 

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 

third clutch ring are connected to a single shift mechanism for 

moving said clutch rings in concert with one another, 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 they rotate together and said single 

shift mechanism selectively moves said third clutch ring into 

engagement with said concentric shaft gear and said plate 

assembly so that they rotate together. 

* * * * *