Shaft balancing system and methods

A shaft assembly has a shaft body, a first universal joint coupled to a first end of the shaft body, and a second universal joint coupled to a second end of the shaft body. A method for dynamically balancing the shaft assembly includes rotating the shaft assembly at a predetermined speed, determining a level of imbalance of the shaft assembly while rotating the shaft assembly at the predetermined speed, iteratively adjusting the position of the shaft body with respect to the first and second universal joints in response to the level of imbalance to determine an optimal level of imbalance while rotating the shaft assembly, and securely positioning the first and second universal joints with respect to the shaft body.

TECHNICAL FIELD

The present invention generally relates to the testing and design of shaft assemblies, and more particularly relates to methods and systems for dynamically balancing such assemblies.

BACKGROUND

Shaft assemblies, such as “propshafts” and the like, are often used in automotive and aeronautical applications, and typically include a shaft body having universal joints coupled at both ends. Given the high speeds of such shafts during operation, it is desirable that any dynamic imbalances inherent in the shaft assembly be minimized, thereby reducing vibration and improving the lifetime of any powerplant components to which the shaft assembly is coupled.

Currently known methods for balancing shaft assemblies are unsatisfactory in a number of respects. For example, conventional methods generally focus on adding weights to the exterior of the shaft body in order to counteract any sensed imbalances. Such weights increase the overall weight of the assembly, and may detach during handling or operation. Furthermore, welding weights to the shaft can reduce tubing strength of the shaft body, and can also result in imprecise weight placement due to operator error, available space, inexact correction weights, or a change in the dynamic state caused by heat absorbed by the shaft. Because of such imprecision, a “verification spin” of the finished assembly is almost always necessary, greatly increasing manufacturing time and expense.

Another common method for shaft balancing, one that does not require adding individual weights, involves designing the shaft body with extra material—generally in the form circular features—and then removing material from these features to counteract any dynamic imbalance. Such methods also result in producing an unnecessarily heavy shaft, and consequently have a deleterious effect on performance and fuel economy.

Accordingly, it is desirable to provide improved systems and methods for dynamically balancing shaft assemblies. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.

BRIEF SUMMARY

In accordance with one embodiment of the present invention a shaft assembly to be balanced has a shaft body, a first universal joint coupled to a first end of the shaft body, and a second universal joint coupled to a second end of the shaft body. A method for dynamically balancing the shaft assembly includes rotating the shaft assembly at a predetermined speed, determining a level of imbalance of the shaft assembly while rotating the shaft assembly, iteratively adjusting the position of the shaft body with respect to the first and second universal joints in response to the level of imbalance to determine a minimum level of imbalance while rotating the shaft assembly, and securely positioning the first and second universal joints with respect to the shaft body.

An apparatus for balancing a shaft assembly in accordance with one embodiment includes: a first balancing head including a first set of actuatable pins configured to adjustably grasp the universal joint bearing cups at the first end of the shaft assembly and adjustably position the shaft body with respect to the first universal joint; a second balancing head including a second set of actuatable pins configured to adjustably grasp the universal joint bearing cups at the second end of the shaft assembly and adjustably position the shaft body with respect to the second universal joint; a shaft-spinning subsystem configured to cause rotation of the shaft assembly; a sensor subsystem configured to determine a level of imbalance of the shaft assembly during the rotation of the shaft-spinning subsystem; a controller coupled to the sensor subsystem and the first and second sets of actuatable pins, the controller configured to iteratively adjust the first and second sets of actuatable pins in response to the level of imbalance to determine an optimal (minimal) level of imbalance during the rotation of the shaft-spinning subsystem; and a plurality of retention components configured to securely position the first and second universal joints with respect to the shaft body.

DETAILED DESCRIPTION

The following discussion generally relates to methods and apparatus for dynamically balancing shaft assemblies by iteratively adjusting its components during spin testing. In that regard, the following detailed description is merely illustrative in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. For the purposes of conciseness, conventional techniques and principles related to shaft design, automated testing, dynamic balancing systems, and the like need not be described in detail herein.

Referring to the conceptual block diagram shown inFIG. 1, a balancing apparatus100in accordance with the present invention is configured to accept, secure, and balance a shaft assembly102. Shaft assembly102, as is known in the art, includes a shaft body103having a pair of universal joints104coupled to opposite ends. In this regard,FIG. 2is an overview of a typical shaft assembly102balanced in the traditional manner, i.e., by the addition of compensating weights204. In this illustration, a slip yoke202is coupled to the leftmost universal joint104, and the rightmost universal joint is intended to couple to the driven axle. Shaft body103may be a single-piece or multi-piece type (which typically requires additional articulating joints) This invention is applicable to any and all universal joints in any type of propshaft, and may be used in connection with propshafts without slip yokes, propshafts with an inboard slip mechanism, and propshafts with flanges.

Referring again toFIG. 1, balancing apparatus100includes actuatable pins110slideably controlled by respective actuators120. One set of actuatable pins110is configured to adjustably grasp the leftmost universal joint104at the end of shaft assembly102and adjustably position shaft body102with respect to the respective universal joint104. A second set of actuatable pins110configured to adjustably grasp the rightmost universal joint104at the end of shaft assembly102and adjustably position shaft body103with respect to the rightmost universal joint104.

A shaft-spinning subsystem135is configured to cause rotation of shaft assembly102relative to the assembly structure or housing. Shaft-spinning subsystem135may include any suitable conventional motor and control system capable of rotating at a predetermined speed, as is known in the art.

A sensor subsystem130is configured to determine a level of imbalance of shaft assembly102during rotation and communicate imbalance information to a balancing module152within a controller150(e.g., a general purpose computer, a microcontroller, or any other suitable combination of hardware, software, and/or firmware). Such sensor subsystems130generally sense forces along a plurality of axes as assembly102is rotated, and are well known in the art.

Controller150is coupled to sensor subsystem130and the first and second sets of actuatable pins110via any convenient wired or wireless communication channel (e.g., standard Ethernet, WiFi, Bluetooth, ZigBee, etc.). Controller150, via balancing module152, is configured to iteratively adjust the first and second sets of actuatable pins110in response to the level of imbalance (received from subsystem130) to determine a minimum level of imbalance during actual rotation. After the optimal (most balanced) configuration is determined, a number of retention components are configured to securely position the first and second universal joints104with respect to shaft body103, as described in further detail below.

FIG. 3shows an overview of a balancing apparatus100in accordance with one embodiment. As shown, one end of shaft assembly102is connected (via actuatable pins110) to a fixed balancing head302, and the opposite end of shaft assembly102is likewise connected to adjustable (slideable) balancing head304. That is, balancing head304may slide with respect to base or housing306in order to accommodate a variety of shaft lengths.

Referring now to the close-ups shown inFIGS. 4A and 4B, a universal joint104generally includes an internal cross-shaped component408rotatably coupled to a pair of yokes404via bearing structures having respective bearing cups402. In one embodiment, the actuatable pins110are configured to apply a compressive force on bearing cups402during the balancing process, allowing component408to be adjusted along two perpendicular axes with respect to yokes404.

In one embodiment, retention components410are in situ formed polymeric retainers (FIG. 4A). That is, the retaining components are formed (for example, by injecting and curing a liquid thermoplastic compound between the relevant components) while assembly102is still secured within the testing apparatus. In one embodiment, for example, retainers410are formed from a nylon-based material injected into the resulting gap, then suitably cured. A number of other standard methods can be used to secure the universal joints104using various metal forming operations—i.e., “staking operations”. This latter embodiment is shown inFIG. 4B, where deformed sections411are used to secure the components.

FIG. 5is a flowchart generally illustrating a method for balancing a shaft assembly in accordance with one embodiment. As shown, the shaft assembly undergoes initial setup within the test assembly (502). This might typically include initial positioning of the shaft, universal joints, actuatable pins, etc.

Next, the test assembly is activated to cause rotation of the shaft assembly at a predetermined speed (504). The test speed may be selected depending upon the nature of the application. In one embodiment, for example, the shaft assembly is rotated at approximately 3500 rpm.

Next, the system (via controller150, balancing module152, and sensing subsystem130) determines a level of imbalance of shaft assembly102during rotation (506). As mentioned above, the nature of such sensors and the acquisition of force data are well known in the art, and need not be described herein.

Balancing module152then iteratively adjusts the position of the shaft body with respect to the first and second universal joints (e.g., via signals sent to actuatable pins110) in response to the level of imbalance to determine an optimal level of imbalance while rotating the shaft assembly (508,510). The optimization may be performed in accordance with a variety of known algorithms, including steepest descent, and the like. Since the positioning pins110have mass, and therefore contribute to the total rotating imbalance, the balancing optimization algorithm takes their positioning into account to determine the resultant dynamic balance state of the rotating shaft.

After optimization is complete, the rotation is ceased, and before removing assembly102from test apparatus100the first and second universal joints are secured in place relative to shaft body103using a retention scheme as described above (512).

While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient and edifying road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention and the legal equivalents thereof.