Patent Application
20080168823
The invention relates to a device for testing a range of finished cylindrical roller elements in rolling contact fatigue and has the flexibility of being reconfigured to also test a range of tappets. More particularly, the invention relates to a device having the aforementioned capability afforded by the utilization of three equally-spaced load cylinders configured alternatively (a) with means comprising cylindrical shaped idler rollers to apply a line contract load to three locations on a rotating cylindrical element undergoing testing: (b) with means of holding tappets or similar assemblies and loading them into a single driving idler roller; or (c) with means of holding a roller and axle assembly and loading them against a single driving roller and measuring the torque exerted on the axle.
Known prior art test devices of this kind, for example, those disclosed in the Patent to Minter, U.S. Pat. No. 4,452,065 and the patent to Bacigalupo, et al., U.S. Pat. No. 5,837,882 are generally designed to evaluate material performance and require that a sample to be tested be prepared of predefined dimensions so as to fit the test apparatus and as such is limited to evaluating a sample of the material and not the actual finished product. The known prior art also utilizes a plurality of spherical bearings to apply the load to the test element which yields a less significant near circular contact shape as compared to an elliptical contact shape with a width much greater than its length when the load is applied using cylindrically shaped idler rollers.
The invention accordingly fulfills a need that exists in the known prior art for a more versatile and more realistic test assembly, i.e., for a machine whereby the actual production specimen of manufactured parts may be evaluated.
The invention provides a fatigue test machine useful in performing accelerated rolling contact fatigue endurance tests on the bearing rollers used in roller finger followers and tappets and allows verification of the performance of production parts and permits valid comparisons with new material roller designs.
The machine of the invention affords the capability for evaluating roller materials and roller crown geometry because it accurately simulates the cam-roller contact geometry using an actual bearing roller as the test specimen. It also provides the capability of evaluating the effects on the rollers of cam finish, of cam profile, of oil condition, and of alignment relative to a cam. In a first of three alternative embodiments of the invention, three idler roller assembles with the outer diameter ground to simulate the actual cam profile and surface finish are comprised by means of hydraulic cylinders into the outside diameter of the bearing roller under test as it rotates, thereby essentially duplicating the rolling action of a cam lobe. Because the bearing roller under test is loaded evenly between the three idler roller assemblies, it experiences three stress cycles per revolution, accelerating the generation of fatigue spalling damage on the outer diameter. Load and speed are regulated using a closed loop control program of a standard commercial computer. Ease of replacing baring rollers under test and servicing the idler roller assemblies is an attractive feature of the machine of the invention.
Lubrication for the bearing roller and the idler roller assemblies is supplied by a recirculating oil system with oil temperature regulated as needed, either by heating or cooling, using a closed loop control, to monitor the viscosity of the oil in the bearing roller-idler roller interface. The oil may be brought up to the specified temperature before the motor is started and the load is applied to the test part. Failure of a test specimen or one of the idler roller assemblies is determined by the increase in signal output from an accelerometer located to detect the changes in the vibration level that occur when a spall develops in the surface of a roller. The controls for the machine comprise a commercially available computer that is programmed to permit continuous operation of the machine with automated shut off for test specimen failure or upon reaching a predetermined number of revolutions of the test specimen.
The invention is devised with the capability of testing a finished production part simulating a commercial customer application of the part and is adaptable to a range of outre diameters, inner diameters and widths of a cylindrically shaped test specimen. The configuration of the machine of the invention comprises three cylindrically shaped rollers that apply a load to the cylindrical specimen mounted on the spindle as distinguished from other means such as spherical rolling elements described in the prior art. Consequently, the invention creates an elliptical contact shape between the idler rollers and the test specimen whose width along the axis of rotation is much greater than its length in the cylindrical direction and is often referred to as a “line” contact. This contact shape is significantly different from the near circular contact ellipse that exists between the prior art's spherical rolling elements and the test specimen. Another significant difference in the nature of the contact feature provided by the apparatus of the invention involves the adjustment of the “line” contact between the cylindrical bodies. The invention includes provisions to align the axes of rotation of the test specimen and the idler rollers to ensure that the axis of rotation of each idler roller lies in a plane with the axis of the test specimen. This alignment directions is often called “skew.” The other alignment concern is within the common plane of the test specimen and each idler roller. The angle between the two axes of rotation—i.e., the angle between the test specimen and an individual idler roller within the plane is referred to as “tilt.” The invention contains provisions to align the idler rollers in theses two directions. A description summary of the fatigue test apparatus of the invention is presented at page 29 of the May 2006 issue of TEST & MEASUREMENT WORLD, which is incorporated in its entirety herein by reference.
The “skew” and “tilt” adjustments of the invention also enable a testing method, which examines the interactions of the test specimen and idler roller surfaces. Different surface finishes can be tested with different amounts of skew and tilt to examine the effects of these parameters on either the surface or sub-surface initiated failure modes.
In a second alternative embodiment of the invention can be reconfigured to test a range of tappet assemblies, which consist of a cylindrical roller with an inner diameter, a pin or axle about which the roller rotates and tappet body into which the pin or axle is secured. This second configuration enables the evaluation of three test specimens simultaneously by mounting the tappet assemblies in mounting fixtures attached to the machine in place of the three idler roller assemblies. By means of a hydraulic cylinder, the machine compresses the tappet assembles into a cylindrical driving roller mounted on the motor spindle. In this configuration the invention permits the assessment of the durability of a bearing roller and axle combination. Different axle materials, bearing roller inner diameter conditions, or geometric clearances can be evaluated in this configuration. In addition, utilizing the “skew” and “tilt” adjustments of the invention enable the evaluation of the wear and durability performance of the tappet assemblies under misaligned conditions.
A third embodiment, the machine of the invention is similar to the second embodiment with the exception that the pin or axle is fitted with a torque transducer. The configuration enables the measurement of the bearing torque under a variety of load, alignment, and temperature conditions, which can be used to evaluate the performance of roller inner diameter conditions, or geometric clearances can be evaluated in this configuration using torque as the measurement parameter.
In the first embodiment of the testing machine of the invention as shown in
A control station 32 shown in
In preparation for a test the operator adjusts the load assemblies 13 to the desired alignment of “tilt” and “skew.” The idler roller rings 23 can be manufactured from a desired material to represent the conditions that may exist in the actual application of the bearing roller 29 and, for example, manufactured using a process which can create a surface geometry profile and finish that represents conditions that may exist in the actual application of a piece to be tested, e.g., the bearing roller 29. Various commercially available lubricants can be used in the invention to change the elastohydrodynamic lubrication characteristics that exist in the contact area between the idler roller ring 23 and bearing roller 29. Nozzle 30 position and lubrication flow can be adjusted to desired conditions with the oil flow control valve 31.
Prior to starting a test, the machine of the invention can be operated in a manual mode whereby an operator has full control of the applicable operating parameters. In the manual mode the operator can establish the test parameters for load, speed and lubricant temperature before recording data relating to test signals on actual specimens derived from the accelerometer 27 that are processed with FFT by the control station 32. The operator can then set-up warning and “stop test” vibration amplitudes for a multitude of arbitrary frequency bands at the control station 32 by referencing a previously recorded accelerometer signal FFT. Means are provided for measuring the amplitude in multiple selected frequency bands of the vibration generated by the rolling contact between the idler bearings and the specimen under test. In addition, the operator can define the maximum number of revolutions for the test specimen.
Once these test parameters have been established, the operator starts a test in an automatic mode whereby the computer program in the control station 32 will signal warnings when test parameters fall outside prescribed limits or when vibration acceleration amplitudes within any of the multitude of arbitrary frequency bands have reached a warning limit. Control station 32 programming is device to stop a test if any of the safety switches are activated, when vibration acceleration amplitudes have reached the “stop test” limit in any of the multitude of arbitrary frequency bands or when the bearing roller 29 has reach the maximum number of revolutions limit defined for the test by the operator.
In an alternative embodiment of the invention as shown in
In a further alternative embodiment as illustrated by reference to
The test machine of the invention is designed to evaluate surface initiated failure modes, such as microspalling and also subsurface failure modes such as fatigue spalling that occur on bearings rollers 29 in highly loaded elastohydrodynamic rolling contact regimes. In the embodiments referred to in
It will be understood that the invention has been described in an illustrative manner and that minor modifications obvious to one skilled in the art are contemplated in the light of the above description. Accordingly, various modifications may be made without departing from the scope of the invention as defined in the claims which follow.
