WO2016205480A1

WO2016205480A1 - Disconnectable 6x4 tandem axle and method of operation

Info

Publication number: WO2016205480A1
Application number: PCT/US2016/037820
Authority: WO
Inventors: Harry W. TROST
Original assignee: Dana Heavy Vehicle Systems Group, Llc
Priority date: 2015-06-16
Filing date: 2016-06-16
Publication date: 2016-12-22

Abstract

A disconnectable axle for a tandem axle vehicle which allows a user to selectively switch between 6x2 and 6x4 axle driving mode. The forward tandem axle system has a forward tandem axle housing with a through shaft (112) extending through a housing cover (104). The through shaft is then connected to a tubular coupling device (178) that is slidably engagable with a coupling shaft (144) by extending or retracting a piston (218). The piston moves a shift shaft (228) that is connected to a shifting fork which in turn moves the tubular coupling device (178) to either engage or disengage the coupling shaft (144). A first inter axle differential side gear (168) is then attached to the opposite end of the coupling shaft. The tandem axle vehicle further includes a rear tandem axle system that may include one or more sliding clutches. The forward tandem axle system may further include a synchronous shifting device that engages the through shaft.

Description

TITLE

DISCONNECTABLE 6X4 TANDEM AXLE

AND METHOD OF OPERATION

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit to U.S. Provisional Patent Application No. 62/180,244 filed on June 16, 2015, which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a disconnectable axle for use in a tandem axle vehicle.

BACKGROUND OF THE DISCLOSURE

Vehicles incorporating multiple drive axles benefit in many ways over vehicles that are driven by only a single drive axle. For example, vehicles utilizing multiple drive axle systems may be configured to distribute torque either proportionally or disproportionately between the axles. However, vehicles utilizing multiple drive axle systems typically have a lower fuel efficiency than vehicles utilizing a single drive axle system. Various connect and disconnect mechanisms can be utilized in such vehicles to permit the engagement and disengagement of one or more of the drive axles to allow a user to transition from single axle operation to multiple axle operation.

However, this typically requires the incorporation of additional drive train components into the vehicle which add extra weight and expense.

Many conventional axle connect and disconnect mechanisms require the disconnectable axle to be moved in and out of place in order to disengage the axle and transition between 6x4 and 6x2 axle driving mode. One of the disadvantages of this type of axle connect and disconnect system is the amount of time, additional components and cost necessary to transition between 6x2 and 6x4 axle driving mode. It would therefore be advantageous to develop an axle connect and disconnect system that would allow the user to selectively switch between 6x2 and 6x4 axle driving modes on the fly without having to stop the vehicle. It would therefore also be advantageous develop a connectable and disconnectable tandem axle system that does not require the entire axle to be moved in and out of place in order to transition between 6x2 and 6x4 axle driving mode.

It would also be advantageous to develop a connectable and

disconnectable tandem axle system that can be easily engineered without excessively increasing either the weight or the cost of the drive axle system while still receiving the benefits of both single and multiple drive axle operation.

SUMMARY OF THE DISCLOSURE

A vehicle tandem axle system which allows a user to selectively switch between 6x2 and 6x4 driving mode. The vehicle tandem axle system includes a forward tandem axle system and a rear tandem axle system. The forward tandem axle system includes a forward tandem axle housing cover having an opening therein. A through shaft extends through the opening in the forward tandem axle cover. The through shaft is then rotatably connected to one end of a coupling shaft. A first inter axle differential side gear is then drivingly connected to the opposite end of the coupling shaft from the through shaft. A tubular coupling device is then connected to the outer surface of the through shaft via a plurality of splines on an outer surface of the through shaft and a plurality of splines on an inner surface of the tubular coupling device that are complementary to the plurality of splines on the outer surface of the through shaft. Rotatively connected to an outer surface of the tubular coupling device is one end of a shift fork. A piston is then connected to a shift shaft which is then connected to an end of the shift fork opposite the tubular coupling device.

When the piston is activated it moves the shift shaft which moves the shift fork which in turn moves the tubular coupling device to facilitate the selective engagement or disengagement of the coupling shaft from the through shaft. BRIEF DESCRIPTION OF THE DRAWINGS The above, as well as other advantages of the present disclosure, will become readily apparent to those skilled in the art from the following detailed description when considered in light of the accompanying drawings in which:

Fig. 1 is a schematic top-plan view of a vehicle having a tandem rear axle assembly according to this invention;

Fig. 2 is a partial cut-away side view of a forward tandem axle system according to one embodiment wherein a tubular coupling device is in a second position;

Fig. 3 is a cut-away end view of the forward tandem axle system illustrated in Fig. 2;

Fig. 4 is a perspective view of the forward tandem axle system illustrated in Fig. 2;

Fig. 5 is a partial cut-away view from the opposite side of the forward tandem axle system illustrated in Fig. 2 wherein the tubular coupling device is in a first position and not engaging the coupling shaft;

Fig. 6 is a schematic cut-away top view of a rear tandem axle system; Fig. 7 is a partial cut-away top view of a rear tandem axle system according to an alternative embodiment;

Fig. 8 is a schematic cut-away top view of a rear tandem axle system according to yet another alternative embodiment;

Fig. 9 is a schematic cut-away side view of a forward tandem axle system according to yet another alternative embodiment; and

Fig. 10 is a schematic cut-away side view of a forward tandem axle system according to yet another alternative embodiment.

DETAILED DESCRIPTION OF THE DISCLOSURE

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

Fig. 1 schematically illustrates a vehicle having a tandem rear axle assembly according to this invention. The vehicle 10 has an engine 12 which is drivingly connected to a transmission 14. A transmission output shaft 16 is then drivingly connected to the end of the transmission 14 opposite the engine 12. The transmission 14 is a power management system which provides controlled application of the rotational power provided by the engine 12 by means of a gearbox.

A first propeller shaft 18 extends from the transmission output shaft 16 and drivingly connects to a forward tandem axle system 20. The rotational power is transmitted through the forward tandem axle system 20 as described in more detail below.

The front tandem axle system 20 further includes a first forward tandem axle half shaft 22 and a second forward tandem axle half shaft 24. A first end 26 of the first forward tandem axle half shaft 22 is drivingly connected to a first forward tandem axle wheel assembly 28. A second end 30 of the first forward tandem axle half shaft 22 is drivingly connected to the forward tandem axle system 20. Drivingly connected to the side of the forward tandem axle system 20 opposite the first forward tandem axle half shaft 22 is a second end 32 of the second forward tandem axle half shaft 24. A first end 34 of the second forward tandem axle half shaft 24 is then drivingly connected to a second forward tandem axle wheel assembly 36.

As schematically illustrated in Fig.1 , a forward tandem axle system output shaft 38 then extends from the forward tandem axle system 20 to a rear tandem axle system 40. The rear tandem axle system 40 is drivingly

connected to the forward tandem axle output shaft 38, such as through a second propeller shaft, which provides rotational power from the front tandem axle system 20 to the rear tandem axle system 40. The rotational power is then transmitted through the rear tandem axle system 40 as described in more detail below. The rear tandem axle system 40 further includes a first rear tandem axle half shaft 42 and a second rear tandem axle half shaft 44. A first end 46 of the first rear tandem axle half shaft 42 is drivingly connected to a first rear tandem axle wheel assembly 48. A second end 50 of the first rear tandem axle half shaft 42 is drivingly connected to the rear tandem axle system 40. Drivingly connected to the side of the rear tandem axle system 40 opposite the first rear tandem axle half shaft 42 is the second end 52 of the second rear tandem axle half shaft 42. A first end 54 of the second rear tandem axle half shaft 42 is drivingly connected to a second rear tandem axle wheel assembly 56.

The tandem axle system of the present invention includes a

disconnectable forward tandem axle system 100 as illustrated in Figs. 2, 3, 4 and 5. The forward tandem axle system 100 includes a forward tandem axle housing 102 and a forward tandem axle housing cover 104. The forward tandem axle housing cover 104 has an inner surface 106 and an outer surface 108. Extending from the outer surface 108 to the inner surface of the forward tandem axle housing cover 104 is an opening 110.

The forward tandem axle system 100 further includes a though shaft 112 having a first end portion 114, a second end portion 116, a middle portion 118 and an outer surface 120. The first end portion 114 of the through shaft 112 extends outside the forward tandem axle housing cover 104 and is drivingly connected to a source of rotational energy. As a non-limiting example, the source of rotational energy may be an engine, a propeller shaft, a transmission, a differential, a drive shaft, a power transfer unit, a forward tandem axle output shaft or a transfer case. The second end portion 116 of the through shaft 112 then extends through the opening 110 in the forward tandem axle housing cover 104 and into the forward tandem axle housing 102. The second end portion 116 of the through shaft 112 further includes an inner surface 122 and an outer surface 124 defining a hollow portion 126. Circumferentially extending from the outer surface 124 of the second end portion 116 of the through shaft 112 is a plurality of splines 128.

Extending axially outboard from the outer surface 108 of the forward tandem axle housing cover 104 and adjacent to the opening 110 in the forward tandem axle housing cover 104, is a through shaft bearing housing 130 having a first end 132, second end 134, an inner surface 136 and an outer surface 138. Additionally, the through shaft bearing housing 130 is co-axial with the though shaft 112. At least a portion of the first end portion 114 of the through shaft 112 extends outside the though shaft bearing housing 130. The inner surface 136 and the outer surface 138 of the through shaft bearing housing 130 defines a hollow portion 140 therein. The second end 134 of the through shaft bearing housing is integrally connected to the outer surface 108 of the forward tandem axle housing cover 104.

Within the hollow portion 140 of the through shaft bearing housing 130 is at least one through shaft bearing 142 that is disposed between the outer surface 120 of the through shaft 112 and the inner surface 136 of the through shaft bearing housing 130. The through shaft beating 142 rotatably supports the through shaft 112 within the through shaft bearing housing 130.

As illustrated in Figs. 2 and 5, the second end portion 116 of the through shaft 112 is rotatively connected to a coupling shaft 144 that extends co-axially with the through shaft 112. The coupling shaft 144 has a first end portion 146, a second end portion 148, a middle portion 150 and an outer surface 152. The first end portion 146 of the coupling shaft 144 has a reduced diameter portion 154 that is located in a bearing 156 within the hollow portion 140 in the second end portion 134 of the through shaft 112. As a non-limiting example, the bearing 156 located in the hollow portion 140 in the second end portion 34 of the through shaft 112 is a pilot bearing or a bushing. Circumferentiaily extending from the outer surface 152 of the first end portion 146 of the coupling shaft 144 and axially inboard from the reduced diameter portion 54 of the first end portion 146 of the coupling shaft 144, is a plurality of splines 158.

Additionally, the outer surface 152 of the second end portion 148 of the coupling shaft 144 also includes a plurality of splines 160 circumferentiaily extending from the outer surface 152 of the second end portion 148 of the coupling shaft 144. The second end portion 148 of the coupling shaft 144 is then drivingly connected to one end of an inter axle differential 162 as described in more detail below. In an alternative embodiment (not shown), based on the disclosure of Figs. 2, 5, 9 and 10, it is understood that the first end portion 146 of the coupling shaft 144 may include an inner surface and an outer surface defining a hollow portion therein instead of a reduced diameter portion 154.

Additionally, the second end portion 116 of the through shaft 112 may further include a reduced diameter portion instead of the hollow portion 126 previously described. The plurality of splines 128 on the outer surface 120 of the second end portion 116 of the through shaft 112 would then be located axially inboard from the reduced diameter portion on the second end portion 116 of the through shaft 112. In accordance with this alternative embodiment, the reduced diameter portion on the second end portion 116 of the through shaft 112 is located in a bearing within the hollow portion of the first end portion 146 of the coupling shaft 144. As a non-limiting example, the bearing located in the hollow portion in the first end portion 146 of the coupling shaft 144 is a pilot bearing or a bushing.

As illustrated in Figs. 2 and 5, the through shaft 112 and the coupling shaft 144 extend co-axially above a front tandem axle half shaft 161. More particularly the through shaft 112 and the coupling shaft 114 are located radially transversely above the front tandem axle half shaft 161.

Drivingly connected to the second end portion 148 of the coupling shaft

144 is the inter axle differential 162. The inter axle differential 162 has two pinion gears 164 and 166, a first inter axle differential side gear 168 and a second inter axle differential side gear (not shown). The first inter axle differential side gear 164 of the inter axle differential 162 extends axially outboard from the inter axle differential 162 and has an inner surface 170 and an outer surface 172 defining a hollow portion 174 therein. The first inter axle differential side gear 164 extends co-axially with the coupling shaft 144.

Circumferentially extending from the inner surface 170 of the first inter axle differential side gear 164 is a plurality of splines 176. The plurality of splines 176 on the inner surface 170 of the first inter axle differential side gear 164 are complementary to and mesh with the plurality of splines 160 extending from the outer surface 152 of the second end portion 148 of the coupling shaft 144. In order for the user to selectively switch between a 6x2 axle driving mode and a 6x4 axle driving mode a tubular coupling device 178 is used. The tubular coupling device 178 has an inner surface 180 and an outer surface 182 defining a hollow portion 184 therein. Circumferentially extending from the inner surface 180 of the tubular coupling device 178 is a plurality of splines 186. The plurality of splines 186 extending from the inner surface 180 of the tubular coupling device 178 are complementary to the plurality of splines 128 extending from the outer surface 120 of the second end portion 116 of the though shaft 112. Additionally, the plurality of splines 186 extending from the inner surface 180 of the tubular coupling device 178 are complementary to and selectively engagable and disengagable with the plurality of splines 160 extending from the outer surface 152 of the first end portion 146 of the coupling shaft 144. According to this embodiment, the plurality of splines 186 on the inner surface 180 of the tubular coupling device 178 remain engaged with the plurality of splines 128 on the outer surface 120 of the second end portion 116 of the through shaft 112 at all times.

In a preferred embodiment, as illustrated in Figs. 2 and 5, the outer surface 182 of the tubular coupling device 178 further includes a channel 188 that is co-axial with the tubular coupling device 178 and extends

circumferentially along the outer surface 182 of the tubular coupling device 178.

Disposed radially outboard from the through shaft 112 is a shift shaft housing 190 having a first end portion 192, a second end portion 194, a top portion 196, a bottom portion 198, an inner surface 200 and an outer surface 202. At least a portion of the outer surface 202 of the second end portion 194 of the shift shaft housing 190 is integrally connected to the outer surface 108 of the forward tandem axle housing cover 104.

In an alternative embodiment, at least a portion of the outer surface 202 of the bottom portion 198 of the shift shaft housing 190 is integrally connected to the outer surface 138 of the through shaft bearing housing 130. It is within the scope of this invention that the outer surface 202 of the shift shaft housing 190 may be integrally connected to the outer surface 108 of the forward tandem axle housing cover 104 and the outer surface 138 of the through shaft bearing housing 130.

The inner surface 200 and the outer surface 202 of the shift shaft housing 190 defines a hollow portion 204 therein. Extending from the inner surface 200 to the outer surface 202 of the bottom portion 198 of the shift shaft housing 190 is an opening 206. The second end portion 194 of the shift shaft housing 190 has a recess 205 extending from said inner surface 200 of said shift shaft housing 190 toward said outer surface 202 of said shift shaft housing 190.

According to an alternative embodiment, the shift shaft housing 190 further includes a piston cover 208 having an inner surface 210 and an outer surface 212. The inner surface 210 of the piston cover 208 is then integrally connected to the first end portion 194 of the shift shaft housing 190.

Fig. 3 is a cut-away end view of the forward tandem axle system illustrated in Fig. 2. The disconnectable forward tandem axle system 100, as shown in Fig. 3, illustrates the through shaft 112, the through shaft bearing housing 130, the shift shaft housing 190, the forward tandem axle housing cover 104 and the piston cover 208. As it can be seen by referencing Fig. 3, the through shaft bearing housing 130 having the inner surface 136 and the outer surface 138. The shift shaft housing 190 has a top portion 196 and a bottom portion 198 wherein the bottom portion 198 of the shift shaft housing 190 is integrally connected to the outer surface 138 of the through shaft bearing housing 130.

Fig 4. is a perspective view of the forward tandem axle system illustrated in Fig. 2. The disconnectable forward tandem axle system 100, as shown in Fig. 4, illustrates the through shaft 112, the through shaft bearing 142, the through shaft bearing housing 130, the shift shaft housing 190, the piston cover 208 and the forward tandem axle housing cover 104. As illustrated in Fig. 4 the through shaft 112 is located within the at least one through shaft bearing 142 within the hollow portion 140 of the through shaft bearing housing 130.

Additionally, as shown in Fig. 4, the outer surface 202 of the second end 194 of the shift shaft housing 190 and the outer surface 138 of the second end 134 of the through shaft bearing housing 130 are integrally connected to the outer surface 108 of the forward tandem axle housing cover 104.

In order to move the tubular coupling device 178 from a first position 214 (Fig. 5) to a second position 216 (Fig. 2) a piston 218 having a first end 220 and a second end 222 is utilized. The piston 218 is disposed radially outboard from the through shaft 112 and has an axis that is parallel to the through shaft 112. At least a portion of the first end 220 of the piston 218 is integrally connected to the inner surface 200 of the first end portion 192, the top portion 196 and/or the bottom portion 198 of the shift shaft housing 190. Additionally, drivingly connected to the first end 220 of the piston 218 is a piston activating device (not shown) which provides the energy necessary to move the piston 218 from a first position 224 (Fig. 5) to a second position 226 (Fig. 2). In an alternative embodiment, the piston 218 is replaced with a motor (not shown) to move the tubular coupling device 178 from the first position 214 to the second position 216.

Extending co-axially with the piston 218 is a shift shaft 228 having a first end 230, a second end 232 and an outer surface 234. Integrally connected to the first end 230 of the shift shaft 228 is the second end 220 of the piston 218. The outer surface 234 of the shift shaft 228 includes an annulet 236 that circumferentially extends from the outer surface 234 of the shift shaft 228. At least a portion of the second end 232 of the shift shaft 218 extends into the recess 205 in the second end portion 194 of the shift shaft housing 190.

In an alternative embodiment as illustrated in Fig. 2, the shift shaft 228 may further include a spring 238 that is co-axial with the shift shaft 228. The spring 238 has a first end 240, a second end 242, an inner diameter 244 and an outer diameter 246. The inner diameter 244 and the outer diameter 246 of the spring 238 defines a hollow portion 248 therein. Disposed radially outboard from the outer surface 234 of the shift shaft 228 is the inner diameter 244 of the spring 238 such that at least a portion of the shift shaft 228 is disposed within the hollow portion 248 of the spring 238. The second end 242 of the spring 238 is adjacent to and axially inboard from the second end 232 of the shift shaft 228. Disposed axially inboard from the annulet 236 is the first end 240 of the spring 238. When the piston 218 moves from its first position 224 to its second position 226 it compresses the spring 238 thereby loading it with energy. The energy loaded in the spring 238 is then released when the piston 218 moves from its second position 226 to its first position 224. The energy released from the spring 238 provides an additional force which helps aid the piston 218 in moving from its second position 226 to its first position 224.

In order to translate the power generated by the piston 218 to the tubular coupling device 178, as illustrated in Figs. 2 and 5, a shift fork 250 having a first end 252 and a second end 254 is utilized. The first end 252 of the shift fork 250 is integrally connected to the outer surface 234 of the shift shaft 228. In a preferred embodiment, the first end 252 of the shift fork 250 is integrally connected to the annulet 236 on the outer surface 234 of the shift shaft 228. In an alternative embodiment, the first end 252 of the shift fork 250 has an opening 256 extending from a first side 258 to a second side 260 of the shift fork 250. The opening 256 in the first end 252 of the shift fork 250 is

complementary to the shape of the outer surface 234 of the shift shaft 228 such that at least a portion of an axial wall of the opening 256 is integrally connected to the outer surface 234 of the shift shaft 228. The shift fork 250 then extends through the opening 256 in the bottom portion 198 of the shift shaft housing 190 and into the forward tandem housing 100 until the second end 254 of the shift fork 250 is rotatively connected to the outer surface 182 of the tubular coupling device 178.

In the embodiment disclosed in Figs. 2 and 5, where the tubular coupling device 178 includes the channel 188 on the outer surface 182 of the tubular coupling device 178, the shift fork 250 extends until at least a portion of the second end 254 of the shift fork 250 ia disposed within the channel 188. When in the channel 188 the tubular coupling device 178 will be able to freely rotate while the shift fork 250 remains in place.

The shift fork 250 according to the present disclosure may take any shape that till facilitate the translation of the force from the piston 218 to the tubular coupling device 178. In a non-limiting example, the shift fork 250 may be either straight or s-shaped as illustrated in Figs. 2, 5 and 9. Fig. 5 is a partial cut-away view from the opposite side of the forward tandem axle system illustrated in Fig. 2. This figure illustrates the piston 218 in its first position 224 and the tubular coupling device 178 in its first position 214. As it can be seen by referencing Fig. 5, when the piston 218 is in its first position 224 the piston 218 is retracted. When the tubular coupling device 178 is in its first position 224 the plurality of splines on the inner surface 180 of the tubular coupling device 178 are not meshing or engaging with the plurality of splines 158 on the outer surface 152 of the first end portion 146 of the coupling shaft 144. By retracting or extending the piston 218 it moves the shift shaft 228 which moves the shift fork 250 which in turn moves the tubular coupling device 178 from the first position 214 illustrated in Fig. 5 to the second position 216 illustrated in Fig. 2. This action allows the user of the to selectively engage or disengage the coupling shaft 144 thereby facilitating the switching between a 6x2 axle driving mode to a 6x4 axle driving mode.

As illustrated in Fig. 6, the tandem axle system further includes a rear tandem axle system 264 having a rear differential 266 which includes a ring gear 268, two pinion gears 270 and 272, a first rear differential side gear 274 and a second rear differential side gear 276. Drivingly connected to one end of the rear tandem axle system 264 is a rear axle input shaft 278 having a first end (not shown) and a second end 280. The first end (not shown) of the rear axle input shaft is drivingly connected to a source of rotational energy. As a non-limiting example, the source of rotational energy may be a propeller shaft, a differential, a drive shaft, a power transfer unit, a forward tandem axle output shaft or a transfer case. The second end 280 of the rear axle input shaft 278 is drivingly connected to the ring gear 268.

In an alternative embodiment as illustrated in Fig. 6, the rear tandem axle system 264 includes a first rear axle half shaft 282 having a first end 284 and a second end 286. The first end 284 of the first rear axle half shaft 282 is drivingly connected to a first rear tandem axle wheel assembly (not shown). In accordance with this embodiment, the rear tandem axle system 264 further includes a first rear axle coupling shaft 290 having a first end 292 and a second end 294. The first end 292 of the first rear axle coupling shaft 290 is rotatively connected to the second end 286 of the first rear axle half shaft 282. The second end 294 of the first rear axle coupling shaft 290 is drivingly connected to the first rear differential side gear 274. A first rear axle sliding clutch 296 is then used to selectively engage and disengage the first rear axle half shaft 282 from the first rear axle coupling shaft 290.

As illustrated in Fig. 6, the first rear axle sliding clutch 296 has a first position 304 and a second position 306. The embodiment illustrated in Fig. 6 shows the first rear axle sliding clutch 296 in a first position 304 (top) and a second position 306 (bottom). In the first position 304 the first rear axle sliding clutch 296 is not engaged with the first rear axle coupling shaft 290. When the first rear axle sliding clutch 296 is in the second position 306, the first rear axle sliding clutch 296 is engaged with the first rear axle coupling shaft 290.

In accordance with the embodiment illustrated in Fig. 6, a second rear axle half shaft 298 having a first end 300 and a second end 302 is drivingly connected to the second rear differential side gear 276. As discussed in the previous embodiment, the first end 300 of the second rear axle half shaft 298 is drivingly connected to the second rear differential side gear 276. The second end 302 of the second rear axle half shaft 298 is then drivingly connected to a second rear tandem axle wheel assembl (not shown).

In yet another embodiment as illustrated in Fig. 7, a rear tandem axle system 1264 having a rear differential 1266 which includes a ring gear 1268, two pinion gears 1270 and 1272, a first rear differential side gear 1274 and a second rear differential side gear 1276. Drivingly connected to one end of the rear tandem axle system 1264 is a rear axle input shaft 1278 having a first end (not shown) and a second end 1280. The first end (not shown) of the rear axle input shaft is drivingly connected to a source of rotational energy. As a non- limiting example, the source of rotational energy may be a propeller shaft, a differential, a drive shaft, a power transfer unit, a forward tandem axle output shaft or a transfer case. The second end 1280 of the rear axle input shaft 1278 is drivingly connected to the ring gear 1268.

According to the embodiment illustrated in Fig. 7, the rear tandem axle system 1264 includes a first rear axle half shaft 1282 having a first end 1284 and a second end 1286. The first end 1284 of the first rear axle half shaft 1282 is drivingly connected to a first rear tandem axle wheel assembly (not shown). In accordance with this embodiment, the rear tandem axle system 1264 further includes a first rear axle coupling shaft 1290 having a first end 1292 and a second end 1294. The first end 1292 of the first rear axle coupling shaft 1290 is rotatively connected to the second end 1286 of the first rear axle half shaft 1282. The second end 1294 of the first rear axle coupling shaft 1290 is drivingly connected to the first rear differential side gear 1274. A first rear axle sliding clutch 1296 is then used to selectively engage and disengage the first rear axle half shaft 1282 from the first rear axle coupling shaft 1290.

As illustrated in Fig. 7, the first rear axle sliding clutch 1296 has a first position 1303 and a second position 1305. The embodiment illustrated in Fig. 7 shows the first rear axle sliding clutch 1296 in a first position 1303 (top) and a second position 1305 (bottom). In the first position 1303 the first rear axle sliding clutch 1296 is not engaged with the first rear axle coupling shaft 1290. When the first rear axle sliding clutch 1296 is in the second position 1305, the first rear axle sliding clutch 1296 is engaged with the first rear axle coupling shaft 1290.

In accordance with the embodiment illustrated in Fig. 7, a second rear axle half shaft 1298 having a first end 1300 and a second end 1302 is drivingly connected to the second rear differential side gear 1276. As discussed in the previous embodiment, the first end 1300 of the second rear axle half shaft 1298 is drivingly connected to the second rear differential side gear 1276. The second end 1302 of the second rear axle half shaft 1298 is then drivingly connected to a second rear tandem axle wheel assembly (not shown).

As illustrated in Fig. 7, the rear tandem axle system 1264 further includes the use of a second rear axle sliding clutch 1306. In accordance^{^} with this embodiment, the rear tandem axle system 1264 includes a second rear axle half shaft 1308 having a first end 13 0 and a second end 312. The second end 1312 of the second rear axle half shaft 1308 is drivingly connected to a second rear tandem axle wheel assembly (not shown). The rear tandem axle system 1264 further includes the use of a second rear axle coupling shaft 1316 having a first end 1318 and a second end 1320. The second end 1320 of the second rear axle coupling shaft 1316 is rotatively connected to the first end 1310 of the second rear axle half shaft 1308. The first end 1318 of the second rear axle coupling shaft 1316 is then drivingly connected to the second rear differential side gear 1276. The second rear differential sliding clutch 1306 is used to selectively engage and disengage the second rear axle half shaft 1308 from the second rear axle coupling shaft 1316.

As illustrated in Fig. 7, the second rear axle sliding clutch 1306 has a first position 1313 and a second position 1315. The embodiment illustrated in Fig. 7 shows the second rear axle sliding clutch 1306 in a first position 1313

(top) and a second position 1315 (bottom). In the first position 1313 the second rear axle sliding clutch 1306 is not engaged with the second rear axle coupling shaft 1316. When the second rear axle sliding clutch 1306 is in the second position 1315, the second rear axle sliding clutch 1306 is engaged with the second rear axle coupling shaft 1316.

As illustrated in Fig. 8, the tandem axle system further includes a rear tandem axle system 2264 having a rear differential 2266 which includes a ring gear 2268, two pinion gears 2270 and 2272, a first rear differential side gear 2274 and a second rear differential side gear 2276. Drivingly connected to one end of the rear tandem axle system 2264 is a rear axle input shaft 2278 having a first end (not shown) and a second end 2280. The first end (not shown) of the rear axle input shaft is drivingly connected to a source of rotational energy. As a non-limiting example, the source of rotational energy may be a propeller shaft, a differential, a drive shaft, a power transfer unit, a forward tandem axle output shaft or a transfer case. The second end 2280 of the rear axle input shaft 2278 is drivingly connected to the ring gear 2268.

Drivingly connected to the first Fear differential side gear 2274, as illustrated in Fig. 8, is a first rear axle half shaft 2282 having a first end 2284 and a second end 2286. The first end 2284 of the first rear axle half shaft 2282 is drivingly connected to a first rear tandem axle wheel assembly (not shown). The second end 2286 of the first rear axle half shaft 2282 is drivingly connected to the first rear differential side gear 2274. As illustrated in Fig. 8, the second rear differential side gear 2276 is drivingly connected a second rear axle half shaft 2230 having a first end 2232 and a second end 2234. The first end 2232 of the second rear axle half shaft 2230 is drivingly connected to the second rear differential side gear 2276. The second end 2234 of the second rear axle half shaft 2230 is drivingly connected to a second rear tandem axle wheel assembly (not shown).

Fig. 9 is a partial cut-away side view of a forward tandem axle system 3000 according to an alternative embodiment. According to this embodiment, the tandem axle system described functions and includes the same

components as described above, however the tubular coupling device 178, as illustrated in Figs. 2 and 5, is replaced with a sliding clutch 3002. According to this embodiment, the forward tandem axle system 3000 includes a forward tandem axle housing cover 3004 having an inner surface 3006 and an outer surface 3008. Extending from the inner surface 3006 to the outer surface 3008 of the forward tandem axle housing cover 3004 is an opening 3010.

The forward tandem axle system 3000 according to the embodiment illustrated in Fig. 9, includes a through shaft 3012 having a first end portion 3014, a second end portion 3016, a middle portion 3017, and an outer surface 3018. The first end portion 3014 of the through shaft 3012 is drivingly connected to a source of rotational energy (not shown). Circumferentially extending from the outer surface 3018 of the second end portion 3016 of the through shaft is a plurality of splines 3020.

Rotatively connected to the second end portion 3016 of the through shaft 3012 is a coupling shaft 3022 that extends co-axially with the though shaft 3012. The coupling shaft 3022 has a first end portion 3024, a second end portion 3026 and an outer surface 3028. The first end portion 3024 of the coupling shaft 3022 is rotatively connected to the second end portion 3016 of the through shaft 3012. Circumferentially extending from the outer surface 3028 of the first end portion 3024 of the coupling shaft 3022 is a plurality of clutch teeth 3030. In a non-limiting example, the plurality of clutch teeth 3030 on the outer surface 3028 of the first end portion 3024 of the coupling shaft 3022 is a plurality of face clutch teeth, a plurality of dog clutch teeth or a friction clutch. Circumferentially extending from the outer surface 3028 of the second end portion 3026 of the coupling shaft 3022 is a plurality of splines 3032.

As illustrated in Fig. 9, the through shaft 3012 and the coupling shaft 3022 extends co-axially above a front tandem axle half shaft 3034. More particularly the through shaft 3012 and the coupling shaft 3022 are located radially transversely above the front tandem axle half shaft 3034.

In accordance with the embodiment illustrated in Fig. 9, the forward tandem axle system 3000 further includes the sliding clutch 3002 extending co- axially with the through shaft 3012 and having a first end portion 3036, a second end portion 3038, an inner surface 3040 and an outer surface 3042. The inner surface 3040 and the outer surface 3042 of the sliding clutch 3002 defines a hollow portion 3044 therein. Circumferentially extending from the inner surface 3040 of the sliding clutch 3002 is a plurality of splines 3046 that are complementary to and meshingly engaged with the plurality of splines 3020 on the outer surface 3018 of the second end portion 3016 of the through shaft 3012. The second end portion 3038 of the sliding clutch 3002 has a plurality of clutch teeth 3048 circumferentially extending from the outer surface 3042 of the second end 3038 of the sliding clutch 3002. The plurality of clutch teeth 3048 on the outer surface 3042 of the sliding clutch 3002 are selectively engagable with the plurality of clutch teeth 3030 on the outer surface 3028 of the first end portion 3024 of the coupling shaft 3022.

In the alternative embodiment illustrated in Fig. 9, the outer surface 3042 of the sliding clutch 3002 further includes a channel 3050 that is co-axial with the sliding clutch 3002 and extends circumferentially along the. outer surface 3042 of the sliding clutch 3002.

In order to move the sliding clutch 3002 to selectively engage the plurality of clutch teeth on the outer surface 3028 of the first end portion 3024 of the coupling shaft 3022 a piston 3052 is utilized. The piston 3052 is integrally connected to a shift shaft 3054 which is integrally connected to one end of a shift fork 3056. Rotatively connected to the end of the shift fork 3056 opposite the shift shaft 3054 is the sliding clutch 3002. When the piston 3052 extends or retracts it moves the shift shaft 3054 which moves the shift fork 3056 which in turn moves the sliding clutch 3002 from a first position 3058 to a second position 3060. In the first position 3058 the plurality of clutch teeth 3020 on the outer surface 3018 of the sliding clutch 3002 are not meshingly engaged with the plurality of clutch teeth 3030 on the outer surface 3028 of the coupling shaft 3022 defining a gap 3062 therebetween. In the second position 3060 the plurality of clutch teeth 3020 on the outer surface 30 8 of the sliding clutch 3002 are meshingly engaged with the plurality of clutch teeth 3030 on the outer surface 3028 of the coupling shaft 3022. The embodiment illustrated in Fig. 9 shows the sliding clutch 3002 in the first position 3058 (top) and the second position 3060 (bottom).

In an alternative embodiment, the shift shaft 3054 further includes a spring 3064 as illustrated in Fig. 9 that is co-axial with the shift shaft 3054. The spring 3064 has a first end 3066, a second end 3067, an inner diameter 3068 and an outer diameter 3070. The inner diameter 3068 and the outer diameter 3070 of the spring 3064 defines a hollow portion 3072 therein. The shift shaft 3054 has a first end 3074, a second end 3076 and an outer surface 3078. The outer surface 3078 of the shift shaft 3054 includes an annulet 3080 that circumferentially extends from the outer surface 3078 of the shift shaft 3054. Disposed radially outboard from the outer surface 3078 of the shift shaft 3054 is the inner diameter 3068 of the spring 3064 such that at least a portion of the shift shaft 3054 is disposed within the hollow portion 3072 of the spring 3064. The second end 3066 of the spring 3064 is adjacent to and axially inboard from the second end 3076 of the shift shaft 3054. Disposed axially inboard from the annulet 3080 is the first end 3066 of the spring 3064. When the piston 3052 moves from a first position (not shown) to its second position 3082 it

compresses the spring 3064 thereby loading it with energy. The energy loaded in the spring 3064 is then released when the piston 3052 moves from its second position (not shown) to its first position 3080. The energy released from the spring 3064 provides an additional force which helps aid the piston 3052 in moving from its second position (not shown) to its first position 3082. As previously described, the tandem axle system according to the embodiment illustrated in Fig. 9 may further include the rear tandem axle system 2264 illustrated in Fig. 8 as previously described. The tandem axle system according to the embodiment illustrated in Fig. 9 may further include the first rear axle sliding clutch 296 illustrated in Fig. 6 as previously described.

Additionally, the tandem axle system according to the embodiment illustrated in Fig. 9 may further include the first rear axle sliding clutch 1296 and the second rear axle sliding clutch 1306 illustrated in Fig. 7 as previously described. In the same way as previously described, the first rear sliding clutch 296 or 1296 selectively engages and disengages said first rear axle half shaft 282 or 1282 from said first rear axle coupling shaft 290 or 1290. Similarly, as previously discussed, the second rear axle sliding clutch 1306 selectively engages and disengages the second rear axle half shaft 1308 from the second rear axle coupling shaft 1316.

As illustrated in Fig. 10, the forward tandem axle system 4000 may further include a synchronous shifting device 4002. According to this embodiment the forward tandem axle system 4000 includes a through shaft 4004 having a first end portion 4006, a second end portion 4008 and an outer surface 4010. The second end portion 4008 of the through shaft 4004 is rotatively connected to a coupling shaft 4012. Attached to the outer surface

4010 of the first end portion 4006 of the through shaft 4004 at a point outside a forward tandem axle housing cover 4014 is the synchronous shifting device 4002. According to a non-limiting example, the synchronous shifting device 4002 may be an inline motor that is connected to the outer surface 4010 of the first end portion 4006 of the through shaft 4004.

The synchronous shifting device 4002 includes a synchronous shifting device housincj 4016, a stator 4018 and a rotor 4020. The synchronous shifting device housing 4016 has a first end 4022, a second end 4024, an inner surface 4026 and an outer surface 4028 defining a hollow portion 4030 therein. The second end 4024 of the synchronous shifting device housing 4016 is integrally connected to a through shaft bearing housing 4032 and/or a shift shaft housing 4034. According to an alternative embodiment, the synchronous shifting device housing 4016 is part of an extended through shaft bearing housing (not shown), an extended shift shaft housing (not shown) and/or an electric motor support (not shown).

As illustrated in Fig. 10, the stator 4018 has an inner surface 4036 and an outer surface 4038 defining a hollow portion 4040 therein. The stator 4018 is co-axial with the through shaft 40004 and the through shaft 4004 extends through the hollow portion 4040 of the stator 4018. The outer surface 4038 of the stator 4018 is connected to the inner surface 4026 of the synchronous shifting device housing 4016.

Radially inboard from the stator 4018 and the synchronous shifting device housing 4016 is the rotor 4020 having an inner surface 4042 and an outer surface 4044. The outer surface 4044 of the rotor 4020 is connected to the inner surface 4036 of the stator 4018 and the inner surface 4042 of the rotor 4020 is drivingly connected to the outer surface 4010 of the through shaft 4004. The rotor 4020 then rotates the through shaft 4004 thereby increasing the angular velocity of the through shaft 4004 to match angular velocity of the coupling shaft 4012. This allows the user to switch between 6x2 and 6x4 axle driving mode on the fly without stopping and without gnashing the clutch teeth or the splines.

In accordance with the provisions of the patent statutes, the present invention has been described to represent what is considered to represent the preferred embodiments. However, it should be noted that this invention can be practiced in other ways than those specifically illustrated and described without departing from the spirit or scope of this invention.

Claims

What is claimed is:

1. A tandem axle system, comprising:

a forward tandem axle system, comprising;

a forward tandem axle housing having a cover with an inner surface and an outer surface;

wherein said cover of said forward tandem axle housing has an opening extending from said inner surface to said outer surface of said forward tandem axle housing cover; a through shaft having a first end portion, a second end portion, a middle portion and an outer surface;

wherein said first end portion of said through shaft extends outside said forward tandem axle housing;

wherein said middle portion of said through shaft extends through said opening in said forward tandem axle housing cover; wherein said outer surface of said second end portion of said through shaft has a plurality of splines circumferentially extending from said outer surface of said second end portion of said through shaft;

a coupling shaft having a first end portion, a second end portion, a middle portion and an outer surface;

wherein said coupling shaft extends co-axially with said through shaft;

wherein said first end portion of said coupling shaft is rotatably connected to said second end portion of said through shaft;

wherein said first end portion of said coupling shaft further comprises a plurality of splines circumferentially extending from said outer surface of said first end portion of said coupling shaft; wherein said outer surface of second end portion of said coupling shaft has a plurality of splines circumferentially extending from said outer surface of said second end portion of said coupling shaft;

an inter axle differential having two pinion gears, a first inter axle differential side gear and second inter axle differential side gear;

wherein said first inter axle differential side gear extends axially outboard from said inter axle differential and co-axially with said coupling shaft;

wherein said first inter axle differential side gear has an inner surface and an outer surface defining a hollow portion therein;

wherein said inner surface of said first inter axle differential side gear has a plurality of splines circumferentially extending from said inner surface of said first inter axle differential side gear complementary to said plurality of splines circumferentially extending from said outer surface of second end portion of said coupling shaft;

a tubular coupling device having an inner surface and an outer surface defining a hollow portion therein;

wherein said tubular coupling device is co-axial with said through shaft;

wherein said inner surface of said tubular coupling device has a plurality of splines circumferentially extending from said inner surface complementary to said plurality of splines

circumferentially extending from said outer surface of second end portion of said through shaft and said plurality of splines circumferentially extending from said outer surface of said first end portion of said coupling shaft;

wherein said tubular coupling device selectively engages said plurality of splines on said outer surface of first end portion of said coupling shaft; a shift shaft housing having a first end portion, a second end portion, a top portion, a bottom portion, an inner surface and an outer surface;

wherein said shift shaft housing is disposed radially outboard from said though shaft;

wherein at least a portion of said outer surface of said second end portion of said shift shaft housing is integrally connected to said outer surface of said forward tandem axle housing cover;

wherein said second end portion of said shift shaft housing has a recess extending from said inner surface of said shift shaft housing;

wherein said inner surface and said outer surface of said shift shaft housing defines a hollow portion therein;

wherein said bottom portion of said shift shaft housing has an opening extending from said inner surface to said outer surface of said bottom portion of said shift shaft housing;

a piston having a first end, a second end and an outer surface; wherein said piston is disposed radially outboard from said through shaft and has an axis parallel to said through shaft;

wherein at least a portion of said first end of said piston is integrally connected to said inner surface of said first end portion of said shift shaft housing;

a shift shaft having a first end, a second end and an outer surface;

wherein said shift shaft is co-axial with said piston;

wherein said first end of said shift shaft is internally connected to said second end of said piston;

wherein said second end of said shift shaft extends into the recess in said second end portion of said shift shaft housing; a shift fork having a first end and a second end; wherein said first end of said shift fork is integrally connected to said outer surface of said shift shaft;

wherein said second end of said shift fork extends through said opening in said bottom portion of said shift shaft housing; wherein said second end of said shift fork is integrally connected to said outer surface of said tubular coupling device; a rear tandem axle system, comprising;

a rear differential having a ring gear, two pinion gears, a first rear differential side gear and a second rear axle differential side gear;

a rear axle input shaft having a first end and a second end;

wherein said first end of said rear axle input shaft is drivingly connected to a source of rotational energy;

wherein said second end of said rear axle input shaft is drivingly connected to said rear differential ring gear;

a first rear axle half shaft having a first end and a second end; wherein said first end of said first rear axle half shaft is drivingly connected to a first rear tandem axle wheel assembly; wherein said second end of said first rear axle half shaft is drivingly connected to said first rear differential side gear;

a second rear axle half shaft having a first end and a second end; wherein said first end of said second rear axle half shaft is drivingly connected to said second rear differential side gear; and wherein said second end of said second rear axle half shaft is drivingly connected to a second rear tandem axle wheel assembly.

2. The tandem axle system of claim 1 , wherein said tubular coupling has a first position and a second position;

wherein at said first position said plurality of splines on said inner surface of said tubular coupling device mesh only with said plurality of splines on said outer surface of said second end portion of said through shaft; and wherein at said second position said plurality of splines on said inner surface of said tubular coupling device mesh with said plurality of splines on said outer surface of said second end portion of said through shaft and said plurality of splines on said outer surface of said first end portion of said coupling shaft.

3. The tandem axle system of claim 1 , wherein said shift fork is s-shaped.

4. The tandem axle system of claim 1 , further comprises:

a through shaft bearing housing having a first end, a second end, an inner surface and an outer surface;

wherein said inner surface and said outer surface of said through shaft bearing housing defines a hollow portion therein; wherein said through shaft bearing housing is co-axial with said through shaft;

wherein said through shaft bearing housing extends axially outboard from said outer surface of said forward tandem axle housing cover;

wherein said second end of said through shaft bearing housing is integrally connected to said outer surface of said forward tandem axle housing cover;

at least one through shaft bearing is disposed within said hollow portion of said through shaft bearing housing; wherein said at least one through shaft bearing is disposed between said outer surface of said through shaft and said inner surface of said through shaft bearing housing;

wherein said at least one through shaft bearing rotatably supports said through shaft within said through shaft bearing housing; and

wherein said at least a portion of the first end portion of said through shaft extends outside said through shaft bearing housing.

5. The tandem axle system of claim 1 , wherein said tubular coupling device further comprises a channel on said outer surface of said tubular coupling device;

wherein said channel on said outer surface of said tubular coupling device is co-axial with said tubular coupling device;

wherein said channel on said outer surface of said tubular coupling device extends circumferentially along said outer surface of said tubular coupling device; and

wherein at least a portion of said second end portion of said shift work extends into said channel on said outer surface of said tubular coupling device.

6. The tandem axle system of claim 1 , further comprising a spring having a first end, a second end, an inner diameter and an outer diameter;

wherein said spring is co-axial with said shift shaft; wherein said inner diameter and said outer diameter of said spring defines a hollow portion therein;

wherein said inner diameter of said spring is disposed radially outboard from said outer surface of said shift shaft; and

wherein said second end of said spring extends into said recess in said second end portion of said shift shaft housing.

7. The tandem axle system of claim 1 , wherein said through shaft and said coupling shaft are radially transversally above said front tandem axle half shafts.

8. The tandem axle system of claim 1 , further comprising a synchronous shifting device that is integrally connected to the outer surface of the first end portion of the through shaft.

9. A tandem axle system, comprising:

a forward tandem axle system, comprising;

wherein said cover of said forward tandem axle housing has an opening extending from said inner surface to said outer surface of said forward tandem axle housing cover;

a through shaft having a first end portion, a second end portion, a middle portion and an outer surface;

wherein said coupling shaft extends co-axially with said through shaft;

wherein said first end portion of said coupling shaft further comprises a plurality of splines circumferentially extending from said outer surface of said first end portion of said coupling shaft; wherein said outer surface of second end portion of said coupling shaft has a plurality of splines circumferentially extending from said outer surface of said second end portion of said coupling shaft; an inter axle differential having two pinion gears, a first inter axle differential side gear and second inter axle differential side gear;

wherein said tubular coupling device is co-axial with said through shaft;

wherein said tubular coupling device selectively engages said plurality of splines on said outer surface of first end portion of said coupling shaft;

a shift shaft housing having a first end portion, a second end portion, a top portion, a bottom portion, an inner surface and an outer surface; wherein said shift shaft housing is disposed radially outboard from said though shaft;

a shift shaft having a first end, a second end and an outer surface;

wherein said shift shaft is co-axial with said piston;

wherein said second end of said shift shaft extends into the recess In said second end portion of said shift shaft housing; a shift fork having a first end and a second end;

wherein said first end of said shift fork is integrally connected to said outer surface of said shift shaft;

a rear axle input shaft having a first end and a second end; wherein said first end of said rear axle input shaft is drivingly connected to a source of rotational energy;

a first rear axle coupling shaft having a first end and a second end;

wherein said first rear axle coupling shaft is transverse to said rear axle input shaft;

wherein said second end of said first rear axle coupling shaft is drivingly connected to said first rear differential side gear;

a first rear axle half shaft having a first end and a second end;

wherein said first rear axle half shaft is co-axial with said first rear axle coupling shaft;

wherein said first end of said first rear axle half shaft is drivingly connected to a first rear tandem axle wheel assembly;

wherein said second end of said first rear axle half shaft is rotatably connected to said first end of said first rear axle coupling shaft; and

a first rear axle sliding clutch whereirr said first rear axle sliding clutch selectively engages and disengages said first rear axle half shaft from said first rear axle coupling shaft.

10. The tandem axle system of claim 9, wherein said tubular coupling device has a first position and a second position;

wherein at said first position said plurality of splines on said inner surface of said tubular coupling device mesh only with said plurality of splines on said outer surface of said second end portion of said through shaft; and

wherein in said second position said plurality of splines on said inner surface of said tubular coupling device mesh with said plurality of splines on said outer surface of said second end portion of said through shaft and said plurality of splines on said outer surface of said first end portion of said coupling shaft.

11. The tandem axle system of claim 9, wherein said shift fork is s-shaped.

12. The tandem axle system of claim 9, further comprises:

wherein said through shaft bearing housing extends axially outboard from said- outer surface of said forward tandem axle housing cover;

The tandem axle system of claim 9, further comprises:

a second rear axle coupling shaft having a first end and a second wherein said second rear axle coupling shaft is transverse to said rear axle input shaft;

wherein said first end of said second rear axle coupling shaft is drivingly connected to said second rear axle side gear; a second rear axle half shaft having a first end and a second end; wherein said second rear axle half shaft is co-axle with said second rear axle coupling shaft;

wherein said first end of said second rear axle half shaft is rotatably connected to said second end of said second rear axle coupling shaft;

wherein said second end of said second rear axle half shaft is drivingly connected to a second rear tandem axle wheel assembly; and

wherein a second rear axle sliding clutch selectively engages and disengages said second rear axle half shaft from said second rear axle coupling shaft.

14. The tandem axle system of claim 9, wherein said tubular coupling device further comprises a channel on said outer surface of said tubular coupling device;

15. The tandem axle system of claim 9, further comprising a spring having a first end, a second end, an inner diameter and an outer diameter;

16. The tandem axle system of claim 9, wherein said through shaft and said coupling shaft are radially transversally above said front tandem axle half shafts.

17. The tandem axle system of claim 9, further comprising a synchronous shifting device that is integrally connected to the outer surface of the first end portion of the through shaft.

A tandem axle system, comprising:

a forward tandem axle system, comprising;

wherein said middle portion of said through shaft extends through said opening in said forward tandem axle housing cover;

wherein said outer surface of said second end portion of said through shaft has a plurality of splines circumferentially extending from said outer surface of said second end portion of said through shaft;

a coupling shaft having a first end portion, a second end portion, a middle portion, and an outer surface;

wherein said coupling shaft extends co-axially with said through shaft;

wherein said outer surface of said first end portion of said coupling shaft further comprises a plurality of clutch teeth circumferentially extending from said outer surface of said first end portion of said coupling shaft;

wherein said outer surface of said second end portion of said coupling shaft has a plurality of splines circumferentially extending from said outer surface of said second end portion of said coupling shaft;

an inter axle differential having two pinion gears, a first inter axle differential side gear and a second inter axle side gear;

wherein said inner surface of said first inter axle differential side gear has a plurality of splines

circumferentially extending from said inner surface of said first inter axle differential side gear complementary to said plurality of splines circumferentially extending from said outer surface of said second end portion of said coupling shaft;

a sliding clutch having a first end portion, a second end portion, an inner surface and an outer surface;

wherein said sliding clutch is co-axial with said through shaft;

wherein said inner surface and said outer surface of said sliding clutch defines a hollow portion therein;

wherein said inner surface of said sliding clutch has a plurality of splines circumferentially extending from said inner surface of said sliding clutch complementary to said plurality of splines circumferentially extending from said outer surface of said second end portion of said through shaft; wherein said outer surface of said second end portion of said sliding clutch further comprises a plurality of clutch teeth circumferentially extending from said outer surface of said second end portion of said sliding clutch; wherein said plurality of clutch teeth

circumferentially extending from said outer surface of said second end portion of said sliding clutch are selectively engagable with said plurality of clutch teeth

circumferentially extending from said outer surface of said first end portion of said coupling shaft;

a shift shaft housing having a first end portion, a second end portion, a top portion, a bottom portion, an inner surface and an outer surface;

wherein said shift shaft housing is disposed radially outboard from said through shaft;

wherein said inner surface and said outer surface of said shift shaft housing defines a hollow portion therein; wherein at least a portion of said outer surface of said second end portion of said shift shaft housing is integrally connected to said outer surface of said forward tandem axle housing cover;

wherein said second in portion of said shift shaft housing has a recess extending from said inner surface of said shift shaft housing;

wherein said bottom portion of said shift shaft housing has an opening extending from said inner surface to said outer surface of said bottom portion of said shift shaft housing

wherein at least a portion of said first end portion of said piston is integrally connected to said inner surface of said first end portion of said shift shaft housing;

a shift shaft having a first end, a second end and an outer surface;

wherein said shift shaft is co-axial with piston;

wherein said first end portion of said shift shaft is integrally connected to second end of said piston;

wherein said second end of said shift shaft extends into said recess in said second end portion of said shift shaft housing;

a shift fork having a first end and a second end;

wherein said second end of said shift fork extends through said opening in said bottom portion of said shift shaft housing;

wherein said second end portion of said shift fork is integrally connected to said outer surface of said sliding clutch;

a rear tandem axle system, comprising;

a rear axle input shaft having a first end and a second end; wherein said first end of said rear axle input shaft is drivingly connected to a source of rotational energy; wherein said second end of said rear axle input shaft is drivingly connected to said rear differential ring gear;

a first rear axle coupling shaft having a first end and a second end;

a first rear axle half shaft having a first end and a second end;

a first rear axle sliding clutch wherein said first rear axle sliding clutch selectively engages and disengages said first rear axle half shaft from said first rear axle coupling shaft.

19. The tandem axle system of claim 18, wherein said sliding clutch has a first position and a second position;

wherein at said first position said plurality of clutch teeth on said outer surface of said second end portion of said sliding clutch are not meshingly engaged with said plurality of clutch teeth on said outer surface of said first end portion of said coupling shaft defining a gap there between; and wherein at said second position said plurality of teeth on said outer surface of said second end of said sliding clutch are meshingly engaged with said plurality of clutch teeth on said outer surface of said first end portion of said coupling shaft.

20. The tandem axle system of claim 18, wherein said shift fork is s-shaped.

21. The tandem axle system of claim 18, further comprises:

a through shaft bearing housing having a first end, a second end, inner surface and an outer surface;

at least one through shaft bearing is disposed within said hollow portion of said through shaft bearing housing;

wherein said at least one through shaft bearing is disposed between said outer surface of said through shaft and said inner surface of said through shaft bearing housing;

22. The tandem axle system of claim 18, further comprises:

a second rear axle coupling shaft having a first end and a second end;

wherein said second rear axle coupling shaft is transverse to said rear axle input shaft;

23. The tandem axle system of claim 18, wherein said tubular coupling device further comprises a channel on said outer surface of said tubular coupling device;

24. The tandem axle system of claim 18, further comprising a spring having a first end, a second end, an inner diameter and an outer diameter;

25. The tandem axle system of claim 18, wherein said through shaft and said coupling shaft are radially transversally above said front tandem axle half shafts.

26. The tandem axle system of claim 18, further comprising a synchronous shifting device that is integrally connected to the outer surface of the first end portion of the through shaft.