METHOD OF MAKING AN INTERAXLE DIFFERENTIAL UNIT AND AN ANNULAR CASE

A method of making an interaxle differential unit. The method may include piercing a workpiece and then ring roll forging the workpiece to form an annular case that is a seamless ring. The annular case may be heat treated before installing an interaxle differential unit gear nest inside the annular case.

TECHNICAL FIELD

This relates to a method of making an interaxle differential unit and an annular case of the interaxle differential unit.

BACKGROUND

An axle assembly having an interaxle differential unit is disclosed in U.S. Pat. No. 9,816,603.

SUMMARY

In at least one embodiment a method of making an interaxle differential unit is provided. The method may include piercing a workpiece to form a through hole. The workpiece may be roll forged to form an annular case that is a seamless ring. The annular case may be heat treated after ring roll forging. An interaxle differential unit gear nest may be subsequently installed inside the annular case.

DETAILED DESCRIPTION

Referring toFIG. 1, an example of an axle assembly10is shown. The axle assembly10may 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 assembly10may be part of a vehicle drivetrain that may include multiple axle assemblies that may be connected in series. For instance, the axle assembly10may be part of a tandem axle configuration that may include two axle assemblies connected in series. The axle assembly10that 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. InFIG. 1, the axle assembly10is depicted as being a first axle assembly.

The axle assembly10may provide torque to its associated wheel assemblies and may provide torque to the second axle assembly. In at least one embodiment and as is best shown with reference toFIGS. 1 and 2, the axle assembly10may include a housing20, an input yoke22, an input shaft24, a first gear26, a clutch collar28, a driven gear30, a drive pinion32, a differential assembly34, at least one axle shaft36, an interaxle differential unit38, an output shaft40, an output yoke42, or combinations thereof. These components are shown to facilitate an abbreviated discussion of the operation of the axle assembly10.

Referring toFIG. 1, the housing20may receive various components of the axle assembly10. In addition, the housing20may facilitate mounting of the axle assembly10to the vehicle.

The input yoke22may facilitate coupling of the axle assembly10to a torque source. The input yoke22may be operatively connected to the input shaft24. It is contemplated that the input yoke22may be omitted, such as when a torque source like an electric motor is integrated with the axle assembly10.

Referring toFIGS. 2 and 3, an example of an input shaft24is shown. The input shaft24may extend along and may be configured to rotate about an axis50. For example, the input shaft24may be rotatably supported by one or more bearings that may be disposed on the housing20. The input shaft24may be operatively connected to the interaxle differential unit38. In at least one configuration, the input shaft24may include a first spline60that may engage the clutch collar28.

Referring toFIGS. 2 and 3, the first gear26, which may also be referred to as a drive gear, may be part of an interaxle differential unit gear nest of the interaxle differential unit38as will be discussed in more detail below. The first gear26may be rotatable about the axis50. In addition, the first gear26may be selectively coupled to the input shaft24with the clutch collar28. For instance, the first gear26may be rotatable about the axis50with the input shaft24when the clutch collar28couples the first gear26to the input shaft24and the first gear26may be rotatable about the axis50with respect to the input shaft24when the clutch collar28does not couple the first gear26to the input shaft24. In at least one configuration, the first gear26may have a center bore that may receive the input shaft24and optionally a bearing that may rotatably support the first gear26on the input shaft24. In at least one configuration, the first gear26may include outer gear teeth70, face gear teeth72, and side gear teeth74.

The outer gear teeth70may engage and may mesh with teeth on the driven gear30. The outer gear teeth70may extend away from the axis50and may be arranged around an outside diameter of the first gear26.

The face gear teeth72may include a set of teeth that may be arranged on a side or face of the first gear26that may face away from the interaxle differential unit38and toward the clutch collar28. The face gear teeth72may selectively engage teeth on the clutch collar28, such as when the clutch collar28couples the first gear26to the input shaft24.

Referring toFIG. 3, the side gear teeth74may be disposed on an opposite side of the first gear26from the face gear teeth72. The side gear teeth74may be arranged around the axis50and that may face toward gears that may be disposed inside the interaxle differential unit38.

Referring toFIGS. 2 and 3, the clutch collar28, if provided, may be moveable along the axis50to engage or disengage the first gear26. In at least one configuration, the clutch collar28may be generally ring-shaped and may define a clutch collar hole80, a clutch collar spline82, a clutch collar face gear84, and an annular groove86.

Referring toFIG. 3, the clutch collar hole80may extend around the axis50. The clutch collar hole80may receive the input shaft24.

Referring toFIGS. 2 and 3, the clutch collar spline82may be disposed in the clutch collar hole80. The clutch collar spline82may include a plurality of spline teeth that may extend toward the axis50and that may mate or mesh with the teeth of the first spline60of the input shaft24. As such, the clutch collar28may be rotatable about the axis50with the input shaft24and may be moveable along the axis50or moveable in an axial direction with respect to the input shaft24.

The clutch collar face gear84may include a set of teeth that may be arranged around the axis50and that may face toward and extend toward the face gear teeth72of the first gear26. The teeth of the clutch collar face gear84may selectively engage the teeth of the face gear teeth72of the first gear26.

The annular groove86may receive a linkage, such as a fork, that may operatively connect the clutch collar28to an actuator that may position the clutch collar28along the axis50.

Referring toFIG. 2, the driven gear30may be rotatable about a second axis90. For example, the drive pinion32may be received in a center bore of the driven gear30and the driven gear30may be fixedly disposed on the drive pinion32or may be couplable to the drive pinion32such that the driven gear30and the drive pinion32may rotate together about the second axis90. The driven gear30may include a plurality of teeth that may be generally arranged about an outside diameter of the driven gear30and that may mate or mesh with the teeth of the outer gear teeth70of the first gear26. Only a portion of the driven gear30disposed above the second axis90is shown inFIG. 2. The second axis90may be disposed substantially parallel to the axis50. The term “substantially parallel” as used herein means the same as or very close to parallel and includes features or axes that are within ±2° of being parallel each other.

The drive pinion32may operatively connect the torque source to the differential assembly34. The drive pinion32may be spaced apart from the input shaft24and may be configured to rotate about an axis, such as a second axis90. The drive pinion32may rotate with the driven gear30. It is also contemplated that the drive pinion32may rotate about the axis50in other configurations, such as when the first gear26and the driven gear30are omitted or when the output shaft40extends through the drive pinion32. A gear portion may be disposed at an end of the drive pinion32.

The differential assembly34may be at least partially received in the housing20. Only a portion of the differential assembly34is shown. The differential assembly34may be rotatable about an axis, such as a differential axis that may be disposed substantially perpendicular to the second axis90. 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 ±2° of being perpendicular each other. The differential assembly34may transmit torque to the axle shafts36and wheels. For example, the differential assembly34may be operatively connected to the axle shafts36and may permit the axle shafts36to rotate at different rotational speeds in a manner known by those skilled in the art. The differential assembly34may have a ring gear100that may have teeth that may mate or mesh with the teeth of the gear portion of the drive pinion32. Accordingly, the differential assembly34may receive torque from the drive pinion32via the ring gear100and transmit torque to the axle shafts36.

Referring toFIG. 1, the axle shafts36may transmit torque from the differential assembly34to corresponding wheel hubs and wheels. The axle shafts36may extend along and may be rotatable about a third axis102, which may be the differential axis. Each axle shaft36may have a first end and a second end. The first end may be operatively connected to the differential assembly34. The second end may be disposed opposite the first end and may be operatively connected to a wheel.

Referring toFIGS. 2 and 3, an example of an interaxle differential unit38is shown. The interaxle differential unit38may accommodate or compensate for rotational speed differences between different drive axle assemblies, such as speed differences between the axle assembly10and a second axle assembly that is connected in series with the axle assembly10. The interaxle differential unit38may be provided in various locations. InFIG. 3, the interaxle differential unit38is disposed inside the housing20on the input shaft24; however, it is contemplated that the interaxle differential unit38may be provided in other locations, such as closer to the output yoke42or with the second axle assembly. It is also contemplated that interaxle differential unit38may be disposed on a shaft other than the input shaft24. In at least one configuration, the interaxle differential unit38may include an interaxle differential unit gear nest110and an annular case112.

The interaxle differential unit gear nest110may include a plurality of gears that may operatively connect the input shaft24to the output shaft40. In at least one configuration, the interaxle differential unit gear nest110may include a second gear120, a spider122, and a plurality of pinion gears124. The interaxle differential unit gear nest110may also include the first gear26.

The second gear120may be disposed proximate the input shaft24. For example, the second gear120may extend along the axis50and may have a center bore that may receive and/or support an end of the input shaft24. A bearing may be provided in the center bore between the input shaft24and second gear120to facilitate alignment and relative rotation. The center bore may also include a spline or splined portion that may be spaced apart from the input shaft24and that may receive and engage a corresponding spline on another shaft, such as the output shaft40. As such, the second gear120may not rotate about the axis50with respect to the output shaft40.

Referring toFIGS. 2 and 3, the spider122may be fixedly disposed on the input shaft24. For instance, the spider122may include a center bore that may include splines that may mate with corresponding splines on the input shaft24to help align and secure the spider122to the input shaft24. As such, the spider122may rotate about the axis50with the input shaft24. The spider122may also include one or more pins130that may extend away from the center bore of the spider122.

One or more pinion gears124may be rotatable with respect to the spider122. A pinion gear124may be rotatably disposed on a pin130. The pinion gear124may include teeth that may mesh or mate with the side gear teeth74of the first gear26and may mesh or mate with teeth of the second gear120.

The annular case112may receive the interaxle differential unit gear nest110. The annular case112may 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 case112may 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 case112around the axis50may be constant or symmetrical as is best shown inFIG. 4. In at least one configuration and as is best shown with reference toFIGS. 3 and 4, the annular case112may have a first end surface140, a second end surface142, a first opening144, a second opening146, and may define an annular case cavity148. The annular case112may also include a first enlarged lip150, a second enlarged lip152, a center portion154, an annular groove156, or combinations thereof.

The first end surface140may be disposed at a first end of the annular case112. For instance, the first end surface140may face toward the first gear26. The first end surface140may extend around the axis50and may encircle the first opening144. In addition, the first end surface140may be disposed substantially perpendicular to the axis50.

The second end surface142may be disposed at an opposite end of the annular case112from the first end surface140. As such, the second end surface142may face away from the first gear26. The second end surface142may extend around the axis50and may encircle the second opening146. In addition, the second end surface142may be disposed substantially perpendicular to the axis50.

Referring toFIG. 4, the first opening144may extend around the axis50. The first opening144may be encircled by the first end surface140. In at least one configuration, the first opening144may have a larger diameter than the second opening146.

The second opening146may be disposed at an opposite end of the annular case112from the first opening144. The second opening146may extend around the axis50. The second opening146may be encircled by the second end surface142. In at least one configuration, the first opening144and the second opening146may be the only holes or openings in the annular case112. As such, no other through holes or blind holes may be provided in or defined by the annular case112.

The first enlarged lip150may extend from the first end surface140. The first enlarged lip150may have a greater wall thickness than the center portion154. In at least one configuration, the first enlarged lip150may extend in an axial direction between the first end surface140and the center portion154and may extend radially from a curved interior surface that may face toward the axis50to an exterior surface that may extend substantially parallel to the axis50.

The second enlarged lip152may extend from the second end surface142. The second enlarged lip152may have a greater axial length than the first enlarged lip150. In at least one configuration and as is best shown inFIG. 5, the second enlarged lip152may have an inner lip surface160and an outer lip surface162. The inner lip surface160may encircle the axis50and may extend substantially parallel to the axis50. The outer lip surface162may be disposed in a nonparallel relationship with the inner lip surface160. For example, the outer lip surface162may extend at an angle with respect to the axis50such that the outer lip surface162extends further from the axis50as the distance from the second end surface142increases.

The center portion154may be axially positioned between the first enlarged lip150and the second enlarged lip152. The center portion154may have a part-spherical surface170that may face toward the axis50. The part-spherical surface170may extend continuously around the axis50and may be disposed at a substantially constant radial distance from a center point250that may be positioned along the axis50. For instance, the part-spherical surface170may 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 axis50.

Referring primarily toFIG. 5, the annular groove156may be axially positioned between the first enlarged lip150and the part-spherical surface170of the center portion154. The annular groove156may face toward the axis50and may extend outward or away from the axis50with respect to the part-spherical surface170and may extend from an end of the part-spherical surface170. The annular groove156may also be disposed further from the axis50than the inner lip surface160.

Referring toFIG. 2, the output shaft40may extend along and may be configured to rotate about the axis50. For instance, the output shaft40may be supported by one or more bearings that may be disposed on the housing20. The output shaft40may be coupled to the interaxle differential unit38. For example, the output shaft40may be fixedly coupled to the second gear120.

Referring toFIG. 1, the output yoke42may facilitate coupling of the axle assembly10to another axle assembly. For instance, the output yoke42may be fixedly coupled to the output shaft40and may be operatively connected to a second axle assembly in any suitable manner, such as via a prop shaft.

Referring toFIG. 6, a flowchart of a method of making an interaxle differential unit is shown. Many steps of the method are associated with making the annular case112. Pictorial representations of some of these steps are shown inFIGS. 7-11.

At block200, a workpiece may be provided. An example of a workpiece220is shown inFIG. 7. The workpiece220a single piece of material that may be made of ASTM 52100 bearing steel. The workpiece220may be a piece of bar stock that may be cut to a predetermined length. The workpiece220may have any suitable cross-sectional shape. For instance, the workpiece220may have a cylindrical cross section.

At block202, the workpiece220may be heated to soften the material and facilitate forming. For example, the workpiece220may be heated in a furnace in a manner known by those skilled in the art.

At block204, the workpiece220may be flattened. An example of a flattened workpiece220is shown inFIG. 8. The workpiece220may be flattened after the workpiece220is heated. The workpiece220may be flattened to form a generally cylindrical solid disc that may have an increased diameter and a reduced height as compared toFIG. 7. The workpiece220may be flattened in any suitable manner, such as with rollers, a forging press, or the like.

At block206, the workpiece220may be pierced. An example of a pierced workpiece220is shown inFIG. 9. Piercing the workpiece220may create a through hole222at or near the center of the workpiece220. The through hole222may be disposed along a center axis230. The workpiece220may be pierced after the workpiece220has been heated and flattened. The workpiece220may be pierced in any suitable manner, such as with a tool like a piercing die that may be inserted from the top side224to the bottom side226of the workpiece220. The workpiece220may be a seamless ring that may have a generally rectilinear cross-section after piercing and may include an inner side240that may face toward the center axis230and an outer side242that may be disposed opposite the inner side240and that may face away from the center axis230.

At block208, the workpiece220may be ring roll forged to form the annular case. Ring roll forging may occur after the workpiece220has 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 workpiece220, may increase the inside diameter of the workpiece220or diameter of the through hole222, and may increase the outside diameter of the workpiece220as shown inFIG. 10. The workpiece220may have a different rectilinear cross-section after the first ring roll forging step as compared to the cross-section of the workpiece220after 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 side224, the bottom side226, or both. An idler roller and a drive roller may roll along the inner side240and the outer side242, respectively, and may move away from the center axis230of the through hole222during ring roll forging to increase the inside diameter and the outside diameter of the workpiece220and to help reduce the wall thickness W of the workpiece220. The inner side240may be disposed substantially parallel to the outer side242during the first ring roll forging step. The workpiece220may be rotated about the center axis230during ring roll forging.

The workpiece220may 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 side240and the outer side242and alter the wall thickness W therebetween to provide a desired cross-sectional shape, such as that shown inFIG. 4. 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 side240and the outer side242to progressively form the inner side240and the outer side242to a desired cross sectional profile such as is shown inFIG. 4. The workpiece220may be referred to as an annular case after ring roll forging is complete. An example of the workpiece220after ring roll forging is shown inFIG. 11. The top side224or a portion thereof may become or may be referred to as a first end surface140of the annular case that is shown inFIG. 4after ring roll forging is complete. Similarly, the bottom side226or a portion thereof may become or may be referred to as a second end surface142of the annular case after ring roll forging is complete.

In the cross sectional profile shown inFIG. 4, the majority of the inner side240may not be disposed parallel to the outer side242in contrast to the generally parallel positioning that may be associated with the first ring roll forging step as shown inFIG. 10. For instance forming the cross sectional profile may include increasing the inside diameter of the inner side240between the first end surface140and the second end surface142, such as at the part-spherical surface170such that at least a portion of the inner side240may have a larger diameter than the first end surface140and the second end surface142. As such, the first opening144and the second opening146may have smaller diameters than a portion of the inner side240that is axially positioned between them.

The workpiece220may be annealed after ring roll forging is complete to strengthen the workpiece220and to facilitate material handling.

At block210, the workpiece220may be machined. Machining may remove material from predetermined locations of the workpiece220. For instance, material may be removed from the first end surface140, the second end surface142, 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 block212, the workpiece220may be heat treated to harden the workpiece220. Heat treating may include martempering the entire workpiece220and thus the entire annular case. For example, the workpiece220may be heated above the upper critical point of the material from which it is made. For instance, the workpiece220may be heated to a temperature of 830° C. to 845° C. 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 workpiece220. Then, the workpiece220may then be quenched in a salt, oil, or lead bath having a temperature of 5° C. to 15° C. below the martensite start temperature of the material from which the workpiece220is made. The workpiece220may be quenched for a predetermined period of time, such as approximately 4-5 minutes. Then, the workpiece220may be allowed to air cool to room temperature or ambient temperature. The workpiece220may have a surface hardness and an internal hardness or core through hardness of at least HRC 60 after heat treating. The workpiece220may then be tempered after quenching. For instance, the workpiece220may be tempered at a temperature of 175° C. to 185° C. for approximately 250 to 260 minutes within one hour of quenching.

At block214, the grinding of the workpiece220may occur. Grinding may remove material from predetermined locations of the workpiece220. For example, the first end surface140, the second end surface142, 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 block216, the interaxle differential unit may be assembled. The interaxle differential unit may be assembled by installing the interaxle unit differential gear nest110inside the annular case112. For instance, one or more pinion gears124may be mounted on the spider122, the spider122and pinion gears124may be inserted through an opening of the annular case112, such as the first opening144, and into the annular case112, and gears such as the first gear26and the second gear120may be brought into engagement with the pinion gears124by inserting them into the first opening144and the second opening146, 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.