Patent Description:
An axle assembly having an interaxle differential unit is disclosed in <CIT>.

According to the invention a method of making an interaxle differential unit is provided as set out in claim <NUM>.

The axle assembly <NUM> may be provided with a vehicle of any suitable type, such as a truck, bus, farm equipment, military transport or weaponry vehicle, or cargo loading equipment for land, air, or marine vessels.

The axle assembly <NUM> may be part of a vehicle drivetrain that may include multiple axle assemblies that may be connected in series. For instance, the axle assembly <NUM> may be part of a tandem axle configuration that may include two axle assemblies connected in series. The axle assembly <NUM> that is operatively connected to at least one torque source, such as an electric motor or an internal combustion engine, may be referred to as a first axle assembly. The axle assembly that receives propulsion torque from the torque source by way of the first axle assembly may be referred to as a second axle assembly. In <FIG>, the axle assembly <NUM> is depicted as being a first axle assembly.

The axle assembly <NUM> may provide torque to its associated wheel assemblies and may provide torque to the second axle assembly. As best shown with reference to <FIG> and <FIG>, the axle assembly <NUM> may include a housing <NUM>, an input yoke <NUM>, an input shaft <NUM>, a first gear <NUM>, a clutch collar <NUM>, a driven gear <NUM>, a drive pinion <NUM>, a differential assembly <NUM>, at least one axle shaft <NUM>, an interaxle differential unit <NUM>, an output shaft <NUM>, an output yoke <NUM>, or combinations thereof. These components are shown to facilitate an abbreviated discussion of the operation of the axle assembly <NUM>.

Referring to <FIG>, the housing <NUM> may receive various components of the axle assembly <NUM>. In addition, the housing <NUM> may facilitate mounting of the axle assembly <NUM> to the vehicle.

The input yoke <NUM> may facilitate coupling of the axle assembly <NUM> to a torque source. The input yoke <NUM> may be operatively connected to the input shaft <NUM>. It is contemplated that the input yoke <NUM> may be omitted, such as when a torque source like an electric motor is integrated with the axle assembly <NUM>.

Referring to <FIG> and <FIG>, an example of an input shaft <NUM> is shown. The input shaft <NUM> may extend along and may be configured to rotate about an axis <NUM>. For example, the input shaft <NUM> may be rotatably supported by one or more bearings that may be disposed on the housing <NUM>. The input shaft <NUM> may be operatively connected to the interaxle differential unit <NUM>. In at least one configuration, the input shaft <NUM> may include a first spline <NUM> that may engage the clutch collar <NUM>.

Referring to <FIG> and <FIG>, the first gear <NUM>, which may also be referred to as a drive gear, may be part of an interaxle differential unit gear nest of the interaxle differential unit <NUM> as will be discussed in more detail below. The first gear <NUM> may be rotatable about the axis <NUM>. In addition, the first gear <NUM> may be selectively coupled to the input shaft <NUM> with the clutch collar <NUM>. For instance, the first gear <NUM> may be rotatable about the axis <NUM> with the input shaft <NUM> when the clutch collar <NUM> couples the first gear <NUM> to the input shaft <NUM> and the first gear <NUM> may be rotatable about the axis <NUM> with respect to the input shaft <NUM> when the clutch collar <NUM> does not couple the first gear <NUM> to the input shaft <NUM>. In at least one configuration, the first gear <NUM> may have a center bore that may receive the input shaft <NUM> and optionally a bearing that may rotatably support the first gear <NUM> on the input shaft <NUM>. In at least one configuration, the first gear <NUM> may include outer gear teeth <NUM>, face gear teeth <NUM>, and side gear teeth <NUM>.

The outer gear teeth <NUM> may engage and may mesh with teeth on the driven gear <NUM>. The outer gear teeth <NUM> may extend away from the axis <NUM> and may be arranged around an outside diameter of the first gear <NUM>.

The face gear teeth <NUM> may include a set of teeth that may be arranged on a side or face of the first gear <NUM> that may face away from the interaxle differential unit <NUM> and toward the clutch collar <NUM>. The face gear teeth <NUM> may selectively engage teeth on the clutch collar <NUM>, such as when the clutch collar <NUM> couples the first gear <NUM> to the input shaft <NUM>.

Referring to <FIG>, the side gear teeth <NUM> may be disposed on an opposite side of the first gear <NUM> from the face gear teeth <NUM>. The side gear teeth <NUM> may be arranged around the axis <NUM> and that may face toward gears that may be disposed inside the interaxle differential unit <NUM>.

Referring to <FIG> and <FIG>, the clutch collar <NUM>, if provided, may be moveable along the axis <NUM> to engage or disengage the first gear <NUM>. In at least one configuration, the clutch collar <NUM> may be generally ring-shaped and may define a clutch collar hole <NUM>, a clutch collar spline <NUM>, a clutch collar face gear <NUM>, and an annular groove <NUM>.

Referring to <FIG>, the clutch collar hole <NUM> may extend around the axis <NUM>. The clutch collar hole <NUM> may receive the input shaft <NUM>.

Referring to <FIG> and <FIG>, the clutch collar spline <NUM> may be disposed in the clutch collar hole <NUM>. The clutch collar spline <NUM> may include a plurality of spline teeth that may extend toward the axis <NUM> and that may mate or mesh with the teeth of the first spline <NUM> of the input shaft <NUM>. As such, the clutch collar <NUM> may be rotatable about the axis <NUM> with the input shaft <NUM> and may be moveable along the axis <NUM> or moveable in an axial direction with respect to the input shaft <NUM>.

The clutch collar face gear <NUM> may include a set of teeth that may be arranged around the axis <NUM> and that may face toward and extend toward the face gear teeth <NUM> of the first gear <NUM>. The teeth of the clutch collar face gear <NUM> may selectively engage the teeth of the face gear teeth <NUM> of the first gear <NUM>.

The annular groove <NUM> may receive a linkage, such as a fork, that may operatively connect the clutch collar <NUM> to an actuator that may position the clutch collar <NUM> along the axis <NUM>.

Referring to <FIG>, the driven gear <NUM> may be rotatable about a second axis <NUM>. For example, the drive pinion <NUM> may be received in a center bore of the driven gear <NUM> and the driven gear <NUM> may be fixedly disposed on the drive pinion <NUM> or may be couplable to the drive pinion <NUM> such that the driven gear <NUM> and the drive pinion <NUM> may rotate together about the second axis <NUM>. The driven gear <NUM> may include a plurality of teeth that may be generally arranged about an outside diameter of the driven gear <NUM> and that may mate or mesh with the teeth of the outer gear teeth <NUM> of the first gear <NUM>. Only a portion of the driven gear <NUM> disposed above the second axis <NUM> is shown in <FIG>. The second axis <NUM> may be disposed substantially parallel to the axis <NUM>. The term "substantially parallel" as used herein means the same as or very close to parallel and includes features or axes that are within ±<NUM>° of being parallel each other.

The drive pinion <NUM> may operatively connect the torque source to the differential assembly <NUM>. The drive pinion <NUM> may be spaced apart from the input shaft <NUM> and may be configured to rotate about an axis, such as a second axis <NUM>. The drive pinion <NUM> may rotate with the driven gear <NUM>. It is also contemplated that the drive pinion <NUM> may rotate about the axis <NUM> in other configurations, such as when the first gear <NUM> and the driven gear <NUM> are omitted or when the output shaft <NUM> extends through the drive pinion <NUM>. A gear portion may be disposed at an end of the drive pinion <NUM>.

The differential assembly <NUM> may be at least partially received in the housing <NUM>. Only a portion of the differential assembly <NUM> is shown. The differential assembly <NUM> may be rotatable about an axis, such as a differential axis that may be disposed substantially perpendicular to the second axis <NUM>. The term "substantially perpendicular" is used herein to designate features or axes that are the same as or very close to perpendicular and includes features that are within ±<NUM>° of being perpendicular each other. The differential assembly <NUM> may transmit torque to the axle shafts <NUM> and wheels. For example, the differential assembly <NUM> may be operatively connected to the axle shafts <NUM> and may permit the axle shafts <NUM> to rotate at different rotational speeds in a manner known by those skilled in the art. The differential assembly <NUM> may have a ring gear <NUM> that may have teeth that may mate or mesh with the teeth of the gear portion of the drive pinion <NUM>. Accordingly, the differential assembly <NUM> may receive torque from the drive pinion <NUM> via the ring gear <NUM> and transmit torque to the axle shafts <NUM>.

Referring to <FIG>, the axle shafts <NUM> may transmit torque from the differential assembly <NUM> to corresponding wheel hubs and wheels. The axle shafts <NUM> may extend along and may be rotatable about a third axis <NUM>, which may be the differential axis. Each axle shaft <NUM> may have a first end and a second end. The first end may be operatively connected to the differential assembly <NUM>. The second end may be disposed opposite the first end and may be operatively connected to a wheel.

Referring to <FIG> and <FIG>, an example of an interaxle differential unit <NUM> is shown. The interaxle differential unit <NUM> may accommodate or compensate for rotational speed differences between different drive axle assemblies, such as speed differences between the axle assembly <NUM> and a second axle assembly that is connected in series with the axle assembly <NUM>. The interaxle differential unit <NUM> may be provided in various locations. In <FIG>, the interaxle differential unit <NUM> is disposed inside the housing <NUM> on the input shaft <NUM>; however, it is contemplated that the interaxle differential unit <NUM> may be provided in other locations, such as closer to the output yoke <NUM> or with the second axle assembly. It is also contemplated that interaxle differential unit <NUM> may be disposed on a shaft other than the input shaft <NUM>. In at least one configuration, the interaxle differential unit <NUM> may include an interaxle differential unit gear nest <NUM> and an annular case <NUM>.

The interaxle differential unit gear nest <NUM> may include a plurality of gears that may operatively connect the input shaft <NUM> to the output shaft <NUM>. In at least one configuration, the interaxle differential unit gear nest <NUM> may include a second gear <NUM>, a spider <NUM>, and a plurality of pinion gears <NUM>. The interaxle differential unit gear nest <NUM> may also include the first gear <NUM>.

The second gear <NUM> may be disposed proximate the input shaft <NUM>. For example, the second gear <NUM> may extend along the axis <NUM> and may have a center bore that may receive and/or support an end of the input shaft <NUM>. A bearing may be provided in the center bore between the input shaft <NUM> and second gear <NUM> to facilitate alignment and relative rotation. The center bore may also include a spline or splined portion that may be spaced apart from the input shaft <NUM> and that may receive and engage a corresponding spline on another shaft, such as the output shaft <NUM>. As such, the second gear <NUM> may not rotate about the axis <NUM> with respect to the output shaft <NUM>.

Referring to <FIG> and <FIG>, the spider <NUM> may be fixedly disposed on the input shaft <NUM>. For instance, the spider <NUM> may include a center bore that may include splines that may mate with corresponding splines on the input shaft <NUM> to help align and secure the spider <NUM> to the input shaft <NUM>. As such, the spider <NUM> may rotate about the axis <NUM> with the input shaft <NUM>. The spider <NUM> may also include one or more pins <NUM> that may extend away from the center bore of the spider <NUM>.

One or more pinion gears <NUM> may be rotatable with respect to the spider <NUM>. A pinion gear <NUM> may be rotatably disposed on a pin <NUM>. The pinion gear <NUM> may include teeth that may mesh or mate with the side gear teeth <NUM> of the first gear <NUM> and may mesh or mate with teeth of the second gear <NUM>.

The annular case <NUM> may receive the interaxle differential unit gear nest <NUM>. The annular case <NUM> may be a continuous seamless ring that may be made from a single piece of material and may not be an assembly of multiple parts. As such, the annular case <NUM> may not have free ends that meet each other and may be free of welds or joining seams. In addition, the cross-sectional profile of the annular case <NUM> around the axis <NUM> may be constant or symmetrical as is best shown in <FIG>. In at least one configuration and as is best shown with reference to <FIG> and <FIG>, the annular case <NUM> may have a first end surface <NUM>, a second end surface <NUM>, a first opening <NUM>, a second opening <NUM>, and may define an annular case cavity <NUM>. The annular case <NUM> may also include a first enlarged lip <NUM>, a second enlarged lip <NUM>, a center portion <NUM>, an annular groove <NUM>, or combinations thereof.

The first end surface <NUM> may be disposed at a first end of the annular case <NUM>. For instance, the first end surface <NUM> may face toward the first gear <NUM>. The first end surface <NUM> may extend around the axis <NUM> and may encircle the first opening <NUM>. In addition, the first end surface <NUM> may be disposed substantially perpendicular to the axis <NUM>.

The second end surface <NUM> may be disposed at an opposite end of the annular case <NUM> from the first end surface <NUM>. As such, the second end surface <NUM> may face away from the first gear <NUM>. The second end surface <NUM> may extend around the axis <NUM> and may encircle the second opening <NUM>. In addition, the second end surface <NUM> may be disposed substantially perpendicular to the axis <NUM>.

Referring to <FIG>, the first opening <NUM> may extend around the axis <NUM>. The first opening <NUM> may be encircled by the first end surface <NUM>. In at least one configuration, the first opening <NUM> may have a larger diameter than the second opening <NUM>.

The second opening <NUM> may be disposed at an opposite end of the annular case <NUM> from the first opening <NUM>. The second opening <NUM> may extend around the axis <NUM>. The second opening <NUM> may be encircled by the second end surface <NUM>. In at least one configuration, the first opening <NUM> and the second opening <NUM> may be the only holes or openings in the annular case <NUM>. As such, no other through holes or blind holes may be provided in or defined by the annular case <NUM>.

The first enlarged lip <NUM> may extend from the first end surface <NUM>. The first enlarged lip <NUM> may have a greater wall thickness than the center portion <NUM>. In at least one configuration, the first enlarged lip <NUM> may extend in an axial direction between the first end surface <NUM> and the center portion <NUM> and may extend radially from a curved interior surface that may face toward the axis <NUM> to an exterior surface that may extend substantially parallel to the axis <NUM>.

The second enlarged lip <NUM> may extend from the second end surface <NUM>. The second enlarged lip <NUM> may have a greater axial length than the first enlarged lip <NUM>. In at least one configuration and as is best shown in <FIG>, the second enlarged lip <NUM> may have an inner lip surface <NUM> and an outer lip surface <NUM>. The inner lip surface <NUM> may encircle the axis <NUM> and may extend substantially parallel to the axis <NUM>. The outer lip surface <NUM> may be disposed in a nonparallel relationship with the inner lip surface <NUM>. For example, the outer lip surface <NUM> may extend at an angle with respect to the axis <NUM> such that the outer lip surface <NUM> extends further from the axis <NUM> as the distance from the second end surface <NUM> increases.

The center portion <NUM> may be axially positioned between the first enlarged lip <NUM> and the second enlarged lip <NUM>. The center portion <NUM> may have a part-spherical surface <NUM> that may face toward the axis <NUM>. The part-spherical surface <NUM> may extend continuously around the axis <NUM> and may be disposed at a substantially constant radial distance from a center point <NUM> that may be positioned along the axis <NUM>. For instance, the part-spherical surface <NUM> may resemble a portion of a sphere and may extend around a spherical segment, which may be a portion of a sphere that may be disposed between two substantially parallel planes that may be disposed substantially perpendicular to the axis <NUM>.

Referring primarily to <FIG>, the annular groove <NUM> may be axially positioned between the first enlarged lip <NUM> and the part-spherical surface <NUM> of the center portion <NUM>. The annular groove <NUM> may face toward the axis <NUM> and may extend outward or away from the axis <NUM> with respect to the part-spherical surface <NUM> and may extend from an end of the part-spherical surface <NUM>. The annular groove <NUM> may also be disposed further from the axis <NUM> than the inner lip surface <NUM>.

Referring to <FIG>, the output shaft <NUM> may extend along and may be configured to rotate about the axis <NUM>. For instance, the output shaft <NUM> may be supported by one or more bearings that may be disposed on the housing <NUM>. The output shaft <NUM> may be coupled to the interaxle differential unit <NUM>. For example, the output shaft <NUM> may be fixedly coupled to the second gear <NUM>.

Referring to <FIG>, the output yoke <NUM> may facilitate coupling of the axle assembly <NUM> to another axle assembly. For instance, the output yoke <NUM> may be fixedly coupled to the output shaft <NUM> and may be operatively connected to a second axle assembly in any suitable manner, such as via a prop shaft.

Referring to <FIG>, a flowchart of a method of making an interaxle differential unit is shown. Many steps of the method are associated with making the annular case <NUM>. Pictorial representations of some of these steps are shown in <FIG>.

At block <NUM>, a workpiece may be provided. An example of a workpiece <NUM> is shown in <FIG>. The workpiece <NUM> is single piece of material that may be made of ASTM <NUM> bearing steel. The workpiece <NUM> may be a piece of bar stock that may be cut to a predetermined length. The workpiece <NUM> may have any suitable cross-sectional shape. For instance, the workpiece <NUM> may have a cylindrical cross section.

At block <NUM>, the workpiece <NUM> may be heated to soften the material and facilitate forming. For example, the workpiece <NUM> may be heated in a furnace in a manner known by those skilled in the art.

At block <NUM>, the workpiece <NUM> may be flattened. An example of a flattened workpiece <NUM> is shown in <FIG>. The workpiece <NUM> may be flattened after the workpiece <NUM> is heated. The workpiece <NUM> may be flattened to form a generally cylindrical solid disc that may have an increased diameter and a reduced height as compared to <FIG>. The workpiece <NUM> may be flattened in any suitable manner, such as with rollers, a forging press, or the like.

At block <NUM>, the workpiece <NUM> is pierced. An example of a pierced workpiece <NUM> is shown in <FIG>. Piercing the workpiece <NUM> creates a through hole <NUM> at or near the center of the workpiece <NUM>. The through hole <NUM> may be disposed along a center axis <NUM>. The workpiece <NUM> may be pierced after the workpiece <NUM> has been heated and flattened. The workpiece <NUM> may be pierced in any suitable manner, such as with a tool like a piercing die that may be inserted from the top side <NUM> to the bottom side <NUM> of the workpiece <NUM>. The workpiece <NUM> may be a seamless ring that may have a generally rectilinear cross-section after piercing and may include an inner side <NUM> that may face toward the center axis <NUM> and an outer side <NUM> that may be disposed opposite the inner side <NUM> and that may face away from the center axis <NUM>.

At block <NUM>, the workpiece <NUM> is ring roll forged to form the annular case. Ring roll forging may occur after the workpiece <NUM> has been heated and pierced and may include a sequence of ring roll forging steps.

For instance, a first ring roll forging step may reduce the wall thickness W of the workpiece <NUM>, may increase the inside diameter of the workpiece <NUM> or diameter of the through hole <NUM>, and may increase the outside diameter of the workpiece <NUM> as shown in <FIG>. The workpiece <NUM> may have a different rectilinear cross-section after the first ring roll forging step as compared to the cross-section of the workpiece <NUM> after piercing. The ring roll forging steps may be accomplished using a plurality of rollers in a manner known by those skilled in the art. For example, an axial roller may roll along the top side <NUM>, the bottom side <NUM>, or both. An idler roller and a drive roller may roll along the inner side <NUM> and the outer side <NUM>, respectively, and may move away from the center axis <NUM> of the through hole <NUM> during ring roll forging to increase the inside diameter and the outside diameter of the workpiece <NUM> and to help reduce the wall thickness W of the workpiece <NUM>. The inner side <NUM> may be disposed substantially parallel to the outer side <NUM> during the first ring roll forging step. The workpiece <NUM> may be rotated about the center axis <NUM> during ring roll forging.

The workpiece <NUM> may undergo one or more additional ring roll forging steps to change the rectilinear cross-section to a non-rectilinear cross-section. For instance, one or more additional ring roll forging steps may contour the inner side <NUM> and the outer side <NUM> and alter the wall thickness W therebetween to provide a desired cross-sectional shape, such as that shown in <FIG>. Such steps may also be accomplished using a plurality of rollers in a manner known by those skilled in the art. For instance, a sequence of rollers may roll along the inner side <NUM> and the outer side <NUM> to progressively form the inner side <NUM> and the outer side <NUM> to a desired cross sectional profile such as is shown in <FIG>. The workpiece <NUM> may be referred to as an annular case after ring roll forging is complete. An example of the workpiece <NUM> after ring roll forging is shown in <FIG>. The top side <NUM> or a portion thereof may become or may be referred to as a first end surface <NUM> of the annular case that is shown in <FIG> after ring roll forging is complete. Similarly, the bottom side <NUM> or a portion thereof may become or may be referred to as a second end surface <NUM> of the annular case after ring roll forging is complete.

In the cross sectional profile shown in <FIG>, the majority of the inner side <NUM> may not be disposed parallel to the outer side <NUM> in contrast to the generally parallel positioning that may be associated with the first ring roll forging step as shown in <FIG>. For instance forming the cross sectional profile may include increasing the inside diameter of the inner side <NUM> between the first end surface <NUM> and the second end surface <NUM>, such as at the part-spherical surface <NUM> such that at least a portion of the inner side <NUM> may have a larger diameter than the first end surface <NUM> and the second end surface <NUM>. As such, the first opening <NUM> and the second opening <NUM> may have smaller diameters than a portion of the inner side <NUM> that is axially positioned between them.

The workpiece <NUM> may be annealed after ring roll forging is complete to strengthen the workpiece <NUM> and to facilitate material handling.

At block <NUM>, the workpiece <NUM> may be machined. Machining may remove material from predetermined locations of the workpiece <NUM>. For instance, material may be removed from the first end surface <NUM>, the second end surface <NUM>, or both, after ring roll forging and before heat treating. Any suitable material removal process may be used. For example, material may be removed with a cutting tool in a manner but known by those skilled in the art.

At block <NUM>, the workpiece <NUM> is heat treated to harden the workpiece <NUM>. Heat treating may include martempering the entire workpiece <NUM> and thus the entire annular case. For example, the workpiece <NUM> may be heated above the upper critical point of the material from which it is made. For instance, the workpiece <NUM> may be heated to a temperature of <NUM> to <NUM> to austenitize the workpiece in a neutral atmosphere to prevent decarbonization of the workpiece. The workpiece may be held at this temperature until the temperature becomes uniform throughout the cross section of the workpiece <NUM>. Then, the workpiece <NUM> may then be quenched in a salt, oil, or lead bath having a temperature of <NUM> to <NUM> below the martensite start temperature of the material from which the workpiece <NUM> is made. The workpiece <NUM> may be quenched for a predetermined period of time, such as approximately <NUM>-<NUM> minutes. Then, the workpiece <NUM> may be allowed to air cool to room temperature or ambient temperature. The workpiece <NUM> may have a surface hardness and an internal hardness or core through hardness of at least HRC <NUM> after heat treating. The workpiece <NUM> may then be tempered after quenching. For instance, the workpiece <NUM> may be tempered at a temperature of <NUM> to <NUM> for approximately <NUM> to <NUM> minutes within one hour of quenching.

At block <NUM>, the grinding of the workpiece <NUM> may occur. Grinding may remove material from predetermined locations of the workpiece <NUM>. For example, the first end surface <NUM>, the second end surface <NUM>, or both, may undergo grinding after heat treating to provide a desired surface finish that may facilitate operation of the interaxle differential unit when in use.

At block <NUM>, the interaxle differential unit is assembled. The interaxle differential unit is assembled by installing the interaxle unit differential gear nest <NUM> inside the annular case <NUM>. For instance, one or more pinion gears <NUM> may be mounted on the spider <NUM>, the spider <NUM> and pinion gears <NUM> may be inserted through an opening of the annular case <NUM>, such as the first opening <NUM>, and into the annular case <NUM>, and gears such as the first gear <NUM> and the second gear <NUM> may be brought into engagement with the pinion gears <NUM> by inserting them into the first opening <NUM> and the second opening <NUM>, respectively.

The present invention may allow an interaxle differential unit to be provided with a one-piece annular case that may be manufactured more efficiently and may require fewer assembly steps than multi piece case designs. In addition, an annular case and an interaxle differential unit may be provided with less weight, which may help reduce material usage and vehicle energy consumption. The annular case may have improved durability as compared to multi case designs or interaxle differential unit cases that may be made of heat treat cast iron. For instance, the inner side of the annular case may better withstand friction associated with rotating pinion gears, which may rotate at high speeds during spinout conditions in which the rotational speed of one axle assembly greatly differs from another that is connected in series. As a result, wear or damage to the annular case caused by spinning pinion gears may be reduced or avoided, thereby increasing the durability and potential life of the interaxle differential unit.

Claim 1:
A method of making an interaxle differential unit (<NUM>), the method comprising:
piercing a workpiece (<NUM>) to form a through hole (<NUM>);
ring roll forging the workpiece (<NUM>) to form an annular case (<NUM>) that is a seamless ring;
heat treating the annular case (<NUM>); and
installing an interaxle differential unit gear nest (<NUM>) inside the annular case (<NUM>).