Patent Application
20150159699
1. Field of the Invention
The present invention pertains to the art of assembling driveline components for motor vehicles, and, more particularly, to the rotation of driveline components during assembly in order to ensure proper alignment of the components.
2. Background of the Invention
In a typical four-wheel drive vehicle, an engine delivers torque to a transmission, which in turn delivers the torque to a transfer case. The transfer case divides the torque between a primary driveshaft and a secondary driveshaft (e.g., rear and front driveshafts), thereby selectively rotating the primary and secondary driveshafts. The transfer case operates in several different drive modes that determine the manner in which the transfer case delivers torque to the primary and secondary driveshafts. These modes typically include a two-wheel drive operating mode, in which all of the torque from the input shaft is delivered to the primary or rear driveshaft, and one or more four-wheel drive operating modes (e.g., four-wheel drive high and low modes), in which the transfer case provides torque to all four wheels.
Four-wheel drive vehicles also typically include mechanisms that enable the front wheels to be selectively connected and disconnected from the vehicle's front or secondary driveline. These mechanisms are activated as the vehicle is shifted from a two-wheel drive mode to a four-wheel drive mode, thereby allowing the torque from the front driveshaft to be communicated to the front wheels. Oftentimes, the mechanisms are automatically actuated by use of a controller or control system. In one arrangement, the connection and disconnection of the front wheels is accomplished by moving a splined ring gear back and forth via a shift fork. In the two-wheel drive mode, the splines of the ring gear mesh only with the splines of a front half shaft. In the four-wheel drive mode, the splines of the ring gear mesh with both the splines of the front half shaft and splines formed on a portion of a front hub bearing assembly. When in four-wheel drive mode, rotation of the front half shaft will cause rotation of the front hub bearing assembly. As a result, the front wheel coupled to the front hub bearing assembly will also rotate.
During assembly of a vehicle having such a system, it is important that all driveline components are properly aligned. For example, it is important that the splines of the front half shafts are properly aligned with the splines of the front hub bearing assemblies when each front hub assembly is attached to the vehicle and secured with a fastener. Conventionally, as an operator assembles the components, each front hub assembly is slid onto the half shaft such that one end of the half shaft is inserted into the hub bearing assembly. Upon initial insertion, the half shaft and hub bearing assembly splines may not be aligned properly. Additionally, even if the half shaft is aligned with the hub bearing assembly, it is possible for the two components to move back out of alignment. For example, this could occur if the operator, or some other object, bumps one of the components. Regardless, if the splines are not aligned, then the operator will not be able to fully insert the half shaft. At this point, the operator will need to rotate the half shaft relative to the hub bearing assembly until the splines of each are aligned. When this occurs, the half shaft can be moved so as to become fully inserted into the hub bearing assembly. However, in some cases, the operator does not initially notice that the components are misaligned during insertion, and, therefore, does not perform the required rotation.
If the components are not aligned during a run down and tightening of the fastener that couples them together, either because they were never aligned or because they were aligned but became misaligned, then the shift fork will be deflected and can fracture. This will lead to noise, vibration and harshness concerns for a driver of the vehicle. Specifically, the noise, vibration and harshness are caused by the ring gear, which moves freely when not held in place by the shift fork. Even more importantly, if the shift fork fails totally as a result of misalignment during assembly, then the vehicle will be unable to shift into the four-wheel drive mode.
Based on the above, there exists a need in the art for a way to ensure that proper alignment is maintained between driveline components during the assembly process.
The present invention is directed to assembling driveline components for motor vehicles wherein one driveline component is rotated relative to another driveline component until the driveline components are properly aligned. This rotation is accomplished through the use of a fastener, preferably the same fastener used to secure the driveline components to one another. The fastener is preferably a lock nut, and, more specifically, a prevailing torque nut. In a preferred embodiment, the fastener requires at least 20 Nm of force in order to be run down on one of the driveline components. Running down and tightening the fastener occurs during an assembly step of the driveline components relative to one another. The alignment of the driveline components preferably takes place between splines of one driveline component and splines of the other driveline component. In the preferred embodiment, the driveline components are a half shaft and a hub bearing assembly, with the half shaft being rotated relative to the hub bearing assembly.
Additional objects, features and advantages of the present invention will become more readily apparent from the following detail description of preferred embodiments when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.
With initial reference to
Front half shafts 114, 115 are coupled to and receive torque from secondary driveshaft 112 through a front differential assembly 116. Rear half shafts 118, 119 are coupled to and receive torque from primary driveshaft 110 through a rear differential assembly 120. Front wheels 122, 123 are coupled to hub bearing assemblies 124, 125, which are in turn coupled to front half shafts 114, 115, while rear wheels 126, 127 are coupled to rear half shafts 118, 119. In a two-wheel drive mode, hub bearing assemblies 124, 125 are uncoupled from front half shafts 114, 115 so that hub bearing assemblies 124, 125 do not receive torque from secondary driveshaft 112. Preferably, in the two-wheel drive mode, transfer case 104 does not provide torque to secondary driveshaft 112. In a four-wheel drive mode, hub bearing assemblies 124, 125 are coupled to front half shafts 114, 115 so that hub bearing assemblies 124, 125 do receive torque from secondary driveshaft 112. Because front wheels 122, 123 are coupled to hub bearing assemblies 124, 125, front wheels 122, 123 only receive torque from secondary driveshaft 112 when hub bearing assemblies 124, 125 are driven.
Hub bearing assembly 124 is installed in steering knuckle 204 that, during a later assembly step not discussed herein, would itself be coupled to a suspension (not shown) of vehicle 100. Steering knuckle 204 pivots to enable vehicle 100 to be steered.
Fastener 202 is provided in order to securely couple half shaft 114 to hub bearing assembly 124. In a preferred embodiment, fastener 202 is a prevailing torque nut, although fastener 202 can comprise any such fastener that causes half shaft 114 to rotate relative to hub bearing assembly 124 when fastener 202 is run down, as discussed below. For example, fastener 202 can comprise any suitable type of lock nut, of which a prevailing torque nut is one type.
With reference to
Inner member 302 and outer member 304 of hub bearing assembly 124 define a raceway 310 therebetween. Generally, raceway 310 includes roller elements 312 that allow inner member 302 to rotate relative to outer member 304. A plurality of wheel studs 314 extend from wheel hub portion 308, which is formed as a portion of inner member 302. Wheel studs 314 are configured to engage and support wheel 122. As a result, when half shaft 114 causes inner member 302 to rotate, as described below, wheel 122 will also be caused to rotate. Bearings 316, 317 are provided on half shaft 114 in order to facilitate rotation of inner member 302 with half shaft 114. Bearings 316, 317 may also serve as seals, which prevent contaminants, such as dirt, water or salt, from entering hub bearing assembly 124. Half shaft 114 has a threaded portion 318, at its distal end, on which fastener 202 will be run down and tightened.
A wheel end actuator 320 is coupled to steering knuckle 204 by at least one fastener 322, which may be a bolt, for example. Wheel end actuator 320 includes a shift fork 324, a diaphragm 326 and a vacuum line 328. When a vacuum is applied to vacuum line 328, diaphragm 326 causes shift fork 324 to move toward the proximal end of half shaft 114 (i.e., to the left in
During the assembly process, it is important that half shaft splines 334 and bearing splines 336 are properly aligned. If splines 334, 336 are not aligned, then, as half shaft 114 is inserted into hub bearing assembly 124, half shaft splines 334 will not mesh with ring gear splines 332 and ring gear 330 will be forced toward the distal end of half shaft 114 (i.e., to the right, as shown in
In contrast, when half shaft splines 334 are aligned with bearing splines 336, then, as half shaft 114 is inserted into hub bearing assembly 124, half shaft splines 334 will appropriately mesh with ring gear splines 332 and ring gear 330 will remain in place, as shown in
In order to more clearly explain the meshing of the various splines, reference will first be made to
In general,
In a situation where half shaft 114 is located within ring gear 330 with splines 332 and splines 334 properly meshed, as shown in
With reference to
The method of aligning half shaft splines 334 and bearing splines 336 during assembly will now be described. Wheel end actuator 320, which holds ring gear 330 in place through shift fork 324, resists the movement of ring gear 330 to a position closer to the distal end of half shaft 114 (i.e., to the right in
This rotation of half shaft 114 relative to hub bearing assembly 124 is effected through the use of fastener 202. As discussed above, fastener 202 is preferably a prevailing torque nut, but can be another type of lock nut or any other fastener that, when run down, will cause half shaft 114 to rotate relative to hub bearing assembly 124. Specifically, half shaft 114 is caused to rotate because fastener 202 has a high installation torque. In other words, a relatively large amount of torque is required to run down fastener 202. This torque is sufficiently large such that half shaft 114 is also rotated. In one embodiment, at least 20 Nm, and preferably approximately 25 Nm, of torque is required to run down fastener 202, which is also sufficient to rotate half shaft 114. In contrast, a typical fastener might require 10 Nm or less to be run down. In such a case, the fastener would be run down, but half shaft 114 would remain stationary.
Generally speaking, a lock nut is a threaded nut that resists loosening due to vibrations or torque. Prevailing torque nuts are a particular type of lock nut wherein some portion of the nut deforms elastically to provide a locking action. A standard nut has threads that are designed to easily mate with threads on a corresponding male portion. As a result, a relatively smaller amount of torque is required in order to run down a standard nut. In accordance with one embodiment of the present invention, the threads of a nut are altered or deformed so that a relatively large amount of force is required to run down the nut. One way to accomplish this is to change a pitch of the threads so that the pitch does not match a pitch of the threads on the corresponding male portion. Of course, other suitable methods of deforming or altering the threads can also be employed. Additionally, in another embodiment, instead of modifying the threads of the nut, the threads of the corresponding male portion are modified, which, in the embodiments described above, is represented by threaded portion 318 of half shaft 114. Although a standard nylon lock nut may be appropriate for some applications, experimentation with such nuts showed that the nylon simply melted when used in accordance with the embodiments described herein. In other words, various types of lock nuts may be used, but the lock nuts must have a sufficiently high installation torque so that half shaft 114 is rotated during rundown.
An arrangement wherein the alignment of splines occurs during a rundown of a fastener, as described above, is especially advantageous because it ensures that alignment occurs during the final assembly step (i.e., at the last possible moment). If the alignment were to occur prior to the rundown of the fastener, as is conventional, then it is possible that the rundown itself, or some other intermediate event, could move the splines back out of alignment. It is important that the splines are in alignment during the rundown because it is the forces applied at this time that can lead to a fractured shift fork.
The rundown of fastener 202 is accomplished through the use of a torque gun 900, which is shown in
Once fastener 202 has been tightened, ring gear splines 332, half shaft splines 334 and bearing splines 336 will remain meshed until a vacuum is applied by vacuum line 328 during operation of vehicle 100. As discussed above, this vacuum will cause ring gear 330 to move to the position shown in
Although described with reference to preferred embodiments of the invention, it should be readily understood that various changes or modifications could be made to the invention without departing from the spirit thereof. For instance, the front driveshaft could be the primary driveshaft while the rear driveshaft is the secondary driveshaft. In addition, although reference is made to a half shaft and a hub bearing assembly, other driveline components could be used in connection with the present invention. For example, a single driveshaft could be used rather than two half shafts. In general, the invention is only intended to be limited by the scope of the following claims.
