Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2001-05-18
2002-04-30
Chapman, John E. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S660000
Reexamination Certificate
active
06378374
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to testing apparatuses and methods and, more particularly, to an apparatus for testing a constant velocity (“CV”) joint and a method thereof.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, a bell-type CV Rzeppa joint
5
is illustrated. The joint
5
is made up of a spherical housing, also referred to as the outer race
6
, an inner race
7
containing six longitudinally oriented grooves in which ball bearings travel, six ball bearings
8
, and a cage
9
that holds the balls in place. The outer and inner races
6
and
7
are grooved to guide the ball bearings
8
along a spherical path that is oriented in the axial direction. The spherical path of the grooves allows an articulation angle between the inner and outer races
6
and
7
to occur while torque is transmitted through the ball bearings
8
.
An input shaft
11
is typically attached to either the outer race
6
or the inner race
7
, and an output shaft
13
is attached to the remaining outer race
6
or inner race
7
which is not connected to the input shaft
11
and which is also connected to the load. When input torque is applied at constant velocity, the CV joint
5
transmits an output torque at a constant velocity over a range of angles between the input and output shafts
11
and
13
.
CV joints are frequently used in automotive applications, particularly in front-wheel drive cars. In an automotive application, one CV joint is typically mounted to each end of an axle, forming a “CV joint-axle-CV joint” combination commonly called the “half shaft.” One end of the half shaft mounts to the transmission output flange and the opposite end mounts to the wheel axle. This assembly allows the wheel to move up and down through its range of suspension travel and also allows a steering angle to be applied, all while the wheel is being driven.
For a variety of different reasons, such as wear or accidents, a CV joint may need to be replaced by either a new or a remanufactured CV joint. Since the cost of a remanufactured CV joint can be about {fraction (1/10)} the cost of a new CV joint, there is a large demand for these remanufactured units. Currently, the industry has no effective mechanism for evaluating remanfactured CV joints. As a result, defective remanufactured CV joints are sometimes distributed and sold.
Typically, the damage associated with CV joints is a scoring or failure of the ball bearing surface or the race. This failure mode results in a nonsmooth bearing surface which causes vibration-induced noise to occur when the CV joint is operated. This noise is an indication of the high stresses and heat that are generated in the bearing which eventually leads to a catastrophic failure of the joint. Noise is also a reliable indication of CV joint health as disclosed in R. Dunn, “A Study of Signature Analysis Regarding A Rzeppa Type Constant Velocity Joint” Master Thesis, Rochester Institute of Technology, 2000 which is herein incorporated by reference. Therefore, detection of CV joint noise is tantamount to detecting CV joint damage.
To test a CV joint, prior testing devices require a rotation and movement of the CV joint similar to the action it would see when installed in a vehicle. Unfortunately, one of the problems with these prior testing devices is that some energy dissipative device must be incorporated to apply a torque. This leads to high power consumption in the drive system and the generation of mechanical and electrical noise that can interfere with detecting signals used to evaluate the CV joint. Additionally, the high torque loads used by these prior testing devices are not easy to accurately control, compounding the difficulty of obtaining clean data about the CV joint. Further, the rotation of the CV joint makes it difficult to place sensors on the CV joint requiring the use of non-contacting, telemetry or slip rings to detect failures which also complicates obtaining data about the CV joint.
One prior design for a device for testing CV-joints consisted of a motor driving a torque brake with the CV joint mounted as a link in the drivetrain, as disclosed in Dunn, R., Masters Thesis, “A Study of Signature Analysis Regarding A Rzeppa Type Constant Velocity Joint,” Rochester Institute of Technology, 2000 which has already been incorporated in by reference. By mounting the torque brake (a magnetic particle brake in this case) on a pivot, a range of operating angles could be induced in the CV joint. Torque levels were limited by the power of the motor and energy dissipation capacity of the brake. The CV-joint condition was determined by monitoring acoustic emissions from a rotating and articulated CV joint using as audio sensor (microphone). In this particular design, the microphone was not an effective diagnostic tool because of the considerable background noise that needed to be filtered out. This prior design also had two qualities that made it prohibitive as a commercial product. First, it is time consuming to place the CV joint in the testing device and second, the size and operating cost of the motor and dynamometer threatens to outweigh the benefits of the machine in a commercial environment.
SUMMARY OF THE INVENTION
An apparatus for testing at least one joint in accordance with one embodiment of the present invention includes an articulation device and a defect detection system. A first joint being tested has an inner race rotatably mounted within an outer race, a driving shaft connected to either the inner race or outer race, and a load bearing shaft connected to the other one of the inner race or outer race. The articulation device connects to the driving shaft and articulates the driving shaft to articulate the first outer race with respect to the first inner race without rotating the driving and load bearing shafts. The defect detection system detects first signals from the first joint during the articulation of the first outer race with respect to the first inner race and determines if there is a defect in the first joint based on the detected first signals.
A method for testing at least one joint in accordance with another embodiment of the present invention includes a few steps. The joint has a first inner race rotatably mounted within a first outer race, a first driving shaft connected to one of the first inner and outer races, and a load bearing shaft connected to the other one of the first inner and outer races. The first outer race is articulated with respect to the first inner race without rotating the driving and load bearing shafts. First signals from the joint are detected during the articulation of the first outer race with respect to the first inner race. The detected first signals are used to determine if there is a defect in the joint.
The present invention provides a testing apparatus and method that can effectively quantify the condition of a CV-joint to determine if it is salvageable, scrap, or within operating specifications. The present invention can also be used to test new or remanufactured CV-joints to failure to gain a greater understanding of failure mechanisms.
One of the features of the present invention is the articulation of the CV joint through its full range of motion without any rotation of the shafts connected to the CV joint. By eliminating the rotation, the detection instrumentation or sensors may be placed directly on the CV joint. This enables the sensors to more accurately capture signals used to evaluate the condition of the CV joint. The elimination of the rotation of the shafts also eliminates the background noise associated with this motion which further enhances the ability of the detection instrumentation or sensors to pick up the signals of interest. Further, the power requirements are reduced because power is only needed to articulate, not rotate the shafts connected to the CV joint.
Another feature of the present invention is more accurate torque control. The present invention applies torque while articulating CV-joints in a controlled environment. This capability, when coupled wi
Nixon & Peabody LLP
Rochester Institute of Technology
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