Tandem axle system

A tandem axle system for vehicle having an optimized inter-axle driveline is depicted and described. The system has a forward drive axle system having a forward pinion gear drivingly connected to a drive side of a forward portion of a forward ring gear. The system also has a rear drive axle system having a rear pinion gear drivingly connected to a drive side of a rear portion of a rear ring gear. An inter-axle driveline connects the forward drive axle system with the rear drive axle system.

FIELD OF THE INVENTION

The present invention relates to a tandem axle system for vehicles. More particularly, the present invention relates to a tandem axle system for vehicles having an optimized inter-axle driveline between a forward drive axle system and a rear drive axle system.

BACKGROUND OF THE INVENTION

Those skilled in the art know that drive is provided for a vehicle such as a class 8 truck from a forward rear drive axle to a rear rear drive axle of tandem axles through an inter-axle driveline. Typical tandem axles have high inter-axle driveline cardan joint angles due to the high position of the forward axle output shaft joint and the low position of the rear axle input joint. High inter-axle driveline cardan joint angles in typical tandem axles can also be attributed to the short distance between the forward axle output joint and the rear tandem axle input joint. Those skilled in the art know that high inter-axle driveline carden joint angles are generally undesirable since the noise and vibration of the joints increase as the angles increase. The low position of the rear axle input joint also undesirably reduces the ground clearance of the inter-axle driveline.

Based on the above, it can be appreciated that a long inter-axle driveline is desirable since such a driveline will reduce the angles. Therefore, if the standout dimension, which is the distance between the centerline of the axle shaft and the front of the rear axle input shaft, can be reduced, a longer inter-axle driveline can be accommodated in the tandem axle system.

Various prior art inventions have tried to address these disadvantages of tandem axles. For example, U.S. Pat. No. 1,856,748 (hereinafter “the '748 patent”) provides for a driving mechanism designed to eliminate excessive angles in the universal joints of vehicles under normal driving conditions. FIG. 2 of the '748 patent depicts a propeller shaft e driving a universal joint f. Joint f is connected to a first differential mechanism f1. The joint f supplies power to f1 which apportions that power between axles b1 and c1. A hyperbolical spiral hypoid driving pinion f2 supplies a portion of the power to the ring gear b4 while a second similar driving hypoid pinion f3 supplies the remaining power to the ring gear c4. It should be noted that both the f2 and f3 driving hypoid pinions are operating on the coast side of the respective b4 and c4 ring gears which is known to be the undesirable weak side of the gear tooth in the '748 patent.

A shaft g connects the differential housings b3 and c3. To align the shaft g with propeller shaft e, the axis of the forward driving pinion f2 falls above the axis of the shaft b1 while the axis of pinion f3 is below the axis of shaft c1. It should be noted that the rear axle input is below center and as such does not provide good ground clearance for the rear of inter-axle driveline g.

According to the '748 patent, this design aligns the axis of pinions f2 and f3 with one another and with the shafts e and g. The pinion f3 drives from the rear side of the ring gear c4 and the forward pinion f2 drives from the forward side of the ring gear b4.

U.S. Pat. No. 1,791,138 (hereinafter “the '138 patent”) provides for a dual axle drive having ring gears f1 and f3 mounted on opposite sides of the transmission shaft x, as best seen inFIG. 6. The hypoid pinion f meshes with the ring gear f1 rearward from the live axle a3 while the hypoid pinion f2 meshes with the ring gear f3 forward of the live axle b3.

FIG. 3 of the '138 patent depicts the forward pinion on the rear side of the forward ring gear and the rear pinion on the forward side of the rear ring gear. The '138 patent also teaches that the rear pinion is located above the center of the rear ring gear. The forward pinion is also above the center of the front ring gear. It should be noted that the forward drive hypoid pinion f is operating on the desirable stronger side of ring gear f1 but the rear drive hypoid pinion f2 is operating on the undesirable weak coast side of ring gear f3. Additionally, the placement of the inter-axle power divider differential d1, d2, d3 components and the forward axle pinion f to the rear of the forward axle results in an undesirably short inter-axle driveline.

Despite trying to address some of the problems with tandem axles, the representative prior art discussed above can be improved. Specifically, it would be advantageous to optimize the inter-axle driveline by minimizing the cardan joint angles and improving the inter-axle driveline ground clearance.

SUMMARY OF THE INVENTION

The present invention is a tandem axle system having a forward drive axle system having a forward hypoid gear set comprising a forward pinion gear drivingly connected to a drive side of a forward portion of a forward ring gear. The system also has a rear drive axle system having a rear hypoid gear set comprising a rear pinion gear drivingly connected to a drive side of a rear portion of a rear ring gear. An inter-axle driveline connects the forward drive axle system with the rear drive axle system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 1, a vehicle10having an engine12drivingly connected to a change speed transmission14is depicted. A shaft16is connected to the output portion of the transmission14, such as by a single cardan universal joint yoke18as known to those skilled in the art, and is drivingly connected to an input, such as by a single cardan U-joint yoke20, also as known to those skilled in the art, of a forward drive axle assembly22of tandem axles24.

As described in more detail below, drive is transmitted from the yoke20to a first forward drive axle26and a second forward drive axle28of a forward drive axle assembly22. The first forward drive axle26provides drive to at least one wheel30and associated tire (not shown) and the second forward drive axle provides drive to at least one wheel32and associated tire (not shown), as known to those skilled in the art.

A through shaft, numbered generically with reference number34, extends through the forward drive axle system22and is drivingly connected to an inter-axle driveline36. The inter-axle driveline36connects the forward drive axles26,28with a first rear drive axle38and a second rear drive axle40. More specifically, the inter-axle driveline36transmits drive from a single cardan U-joint yoke98output to an input, such as a single cardan U-joint yoke42, as known to those skilled in the art, for the rear drive axles38,40. The rear drive axles38,40are part of a rear drive axle assembly44. The first rear drive axle38provides drive to at least one wheel46and associated tire (not shown) and the second rear drive axle40provides drive to at least one wheel48and associated tire (not shown), as known to those skilled in the art.

Referring now toFIGS. 2 and 3, a portion of yoke20is depicted as being connected to an input shaft50of the forward drive axle assembly22. Those skilled in the art will appreciate that the forward drive axle assembly22is located within a forward drive axle assembly housing52, shown only inFIG. 3. The input shaft50is mounted for rotation with respect to the forward drive axle assembly housing52on at least one bearing54.

As seen in bothFIGS. 2 and 3, a helical side gear56is secured to and rotates with the input shaft50. The helical side gear56is in mesh with a pinion helical gear58. The pinion helical gear58is attached to the pinion shaft60of a forward pinion gear62. The pinion shaft60is mounted for rotation with respect to the forward drive axle housing52with at least one bearing64. The forward pinion gear62is also supported for rotation with a bearing66. The bearing66may be supported by a bolt-on bearing cage68.

The forward pinion gear62is part of a forward hypoid gear set70also comprising a forward ring gear72. As shown inFIGS. 2 and 3, the forward pinion gear62is preferably in mesh with a drive side74of the forward ring gear72. Those skilled in the art will appreciate that the drive side74of the forward ring gear72comprises convex ring gear teeth75. Only a representative sample of the convex ring gear teeth75are depicted inFIG. 2. Meshing the forward pinion gear62with the convex ring gear teeth75on the drive side74of the forward ring gear72is a much stronger mesh than if the pinion gear62was meshed with the coast side of the gear72. It is also preferred that the forward pinion gear62is meshed with a forward portion76of the forward ring gear72and that an axis of rotation78of the forward pinion gear62is located below an axis of rotation80of the ring gear72.

The forward ring gear72is connected to the first and second forward drive axles26,28with a wheel differential82, which is partially shown inFIG. 3, for providing rotational drive to the axles26,28.

Referring toFIGS. 2 and 3, the helical side gear56is depicted as being in mesh with one side84of an inter-axle differential86. The inter-axle differential86is mounted for rotation with the input shaft50. At least one output side gear88is in mesh with the other side90of the inter-axle differential86. At least one bearing92is located between the output side gear88and the forward drive axle system housing52to permit the output side gear88to rotate with respect to the housing52.

The output side gear88is connected to rear output shaft34. The rear output shaft34extends rearwardly toward the back of the housing52above the rotational axis80of the forward ring gear72. At least one bearing96supports the rear output shaft34for rotation with respect to the housing52. A yoke98connects the rear output shaft34with the inter-axle driveline36, as shown inFIG. 2.

The forward drive axle assembly22may also comprise an inter-axle differential lockout clutch100, as shown inFIG. 3. The lockout clutch100comprises an axially moveable clutch gear102attached to the input shaft50with a plurality of splines104. The helical side gear56has a complementary clutch gear106to the axially moveable clutch gear102. The axially moveable clutch gear102is connected to a shift fork108that moves clutch gear102into and out of engagement with clutch gear106on the helical side gear56. The inter-axle differential lock out clutch100selectively allows the forward drive axle assembly22and the rear drive axle assembly44to be drivingly locked together.

The inter-axle driveline36is connected to an input shaft110for the rear drive axle assembly44with yoke42, as seen inFIGS. 2 and 4. A forward portion112of the input shaft110is supported for rotation with respect to a rear drive axle assembly housing114with at least one bearing116, as seen inFIG. 4.

Referring to bothFIGS. 2 and 4, a rear pinion gear118is connected to a rearward portion120of the input shaft110. Preferably, the rear pinion gear118is concentrically located about the input shaft110for rotation therewith. The rear pinion gear118is part of a rear hypoid gear set122also comprising a rear ring gear124. The rear pinion gear118is drivingly connected to the rear ring gear124. In the preferred embodiment best seen inFIG. 2, the rear pinion gear118is engaged with a drive side126of an upper, rear portion128of the ring gear124. More specifically, an axis of rotation130of the rear pinion gear118is located above an axis of rotation132of the rear ring gear124.

Those skilled in the art will appreciate that the drive side126of the rear ring gear124comprises convex ring gear teeth129. Only a representative sample of convex ring gear teeth129are depicted inFIG. 2. Meshing the rear ring gear124with the convex ring gear teeth129on the drive side126of the rear ring gear124is a much stronger mesh than if the pinion gear118was meshed with the coast side of the gear118.

As seen inFIG. 4, the rear pinion gear118and input shaft110are mounted for rotation with respect to the rear drive axle assembly housing114with a bearing134.

The rear ring gear124is connected to a rear wheel differential136as shown inFIG. 4. The rear wheel differential136provides drive to the first and second rear drive axles38,40, as known by those skilled in the art.

The rear wheel differential136is preferably offset to one side of the input shaft110to allow the input shaft110to clear the rear wheel differential136and connect with the rear pinion gear118.

FIG. 5depicts an alternative embodiment of the present invention wherein the rear pinion gear118and the input shaft110are supported for rotation with respect to the rear drive axle assembly housing114with two bearings134. Like reference numbers have been used inFIG. 5for similar or identical components depicted inFIG. 4and described above.

Regardless of the number of bearings used to support the rear pinion gear118, and/or the input shaft110, it is preferred that the rear output shaft34of the forward drive axle assembly22, the inter-axle driveline36and the input shaft110of the rear drive axle assembly44substantially share a common, substantially straight, axis of rotation138. In the preferred embodiment, an angle140between the rear output shaft34, the inter-axle driveline36and the input shaft110is between zero degrees and ±three degrees. In a most preferred embodiment, the angle140is zero degrees.

The rear drive axle assemblies44depicted inFIGS. 4or5also advantageously have a reduced standout dimension142,142′ as compared to other known designs. Note thatFIG. 5may have a slightly different standout dimension142′ than the dimension142depicted inFIG. 4. Those skilled in the art know that the standout dimension is typically defined as the distance between a front portion144of the input shaft110and a centerline146of the axle shaft38or40. Based on the capacity requirements for the rear drive axle assembly44, standout dimensions will vary between assemblies. For example, the larger the capacity of the assembly, the larger the standout dimension. Note that for a prior art rear drive axle assembly of a particular capacity, a rear drive axle assembly44of the design of the present invention having the same capacity will have a smaller standout dimension.

For example, the standout dimension for a prior art rear drive axle assembly might be between approximately 85% to 95% of the of the ring gear diameter148,148′. The standout dimension142,142′ for a rear drive axle assembly44of the present invention, however, is between approximately 70% to 80% of the ring gear diameter148,148′. Preferably, the standout dimension142,142′ for a rear drive axle assembly44of the present invention, is approximately 72% to 75% of the ring gear diameter148,148′.

The inter-axle driveline36is thus optimized to reduce or eliminate the vertical distance between the yoke98shared by the through shaft34of the forward drive axle assembly22and the inter-axle driveline36and the yoke42shared by the input shaft110of the rear drive axle assembly44and the inter-axle driveline36. Additionally, the yoke42shared by the input shaft110of the rear drive axle assembly44and the inter-axle driveline36is higher than those of the prior art thus advantageously providing a high ground clearance.