Apparatus for testing lubricating and material properties

In an apparatus for testing lubricating or material properties, two clamping assemblies are pressed together. Each clamping assembly has a clamping surface facing the clamping surface on the other assembly. The first clamping surface has two annular roller paths with the axes of the paths spaced apart. The second clamping surface has one annular roller path intersecting the roller paths on the first clamping surface. Four balls roll in the roller path of the second clamping surface with two of the balls rolling in one of the roller paths of the first clamping surface and the other two balls rolling in the other roller path of the first clamping surface. The clamping assembly with the second clamping surface oscillates back and forth relative to the clamping assembly with the first clamping surface. The pulling force developed by the movement of the balls is measured as an indication of the properties of a lubricant filled into the roller paths or of the materials of the balls and the roller paths.

SUMMARY OF THE INVENTION 
The present invention is directed to a testing apparatus for checking the 
lubricating properties of lubricants and the rolling and sliding 
properties of materials. The apparatus is formed of a first and a second 
clamping assembly each with a clamping surface facing toward the other. A 
drive mechanism oscillates one of the clamping assemblies relative to the 
other with the oscillation taking place perpendicular to the direction in 
which the two clamping assemblies are pressed together. A measuring unit 
is provided for determining the pulling force developed during the 
oscillating movement. 
Such a testing apparatus is known from the brochure "Optimol-SRV." In the 
known apparatus, the clamping surfaces are two plane surfaces disposed 
parallel to one another and roller bodies, such as balls or cylinder 
shaped rollers, are positioned between them so that they roll on the 
clamping surfaces. Alternatively, it is also possible to clamp sliding 
pieces between the clamping surfaces to determine the properties of 
lubricants and materials under sliding friction. 
By and large the known device has proven to be excellent. It has been 
found, however, that it would be desirable to perform tests on lubricants 
and other materials in the presence of both rolling and sliding motion. 
Therefore, it is the primary object of the present invention to provide a 
testing apparatus of the type described above employing simple means, 
possibly using elements of known testing instruments, so that the 
properties of lubricants and materials can be checked while there is 
simultaneous rolling and sliding motion. 
In accordance with the present invention, one of the clamping surfaces of 
the clamping assemblies is provided with two annular roller paths with the 
axes of the roller paths in spaced relation and the other clamping 
assembly is provided with a single roller path. A tangent plane to the 
bottom of the roller paths in one clamping surface is parallel to the 
tangent plane to the bottom of the roller path in the other clamping 
surface. The rolling or sliding elements are provided by four balls 
arranged to roll in the roller path of the other clamping surface with two 
balls in each of the roller paths in the one clamping surface. 
It is especially possible with the testing apparatus of the present 
invention to simulate approximately the conditions which occur in 
so-called homokinetic drives such as used particularly for power 
transmission from vehicle gear assemblies to the vehicle wheels in the 
automotive industry. 
In the following text where the examination of material properties is 
mentioned such materials involves the material forming the clamping 
surfaces as well as the materials forming the sliding or rolling elements. 
When the testing apparatus embodying the present invention is used, the 
balls used as the rolling or sliding elements have a tendency to rise 
along the slopes of the synclinal surfaces of annular roller paths, that 
is opposite surfaces forming the roller path inclined inwardly toward one 
another and meeting in the base or invert of the roller paths. This 
tendency is counteracted by the contact pressure which is effective 
between the two clamping assemblies so that the prevention of the movement 
out of the roller paths corresponds to a sliding friction which is 
superimposed on the rolling friction which takes place along the bottom 
line or invert of the annular roller paths. Such conditions are 
particularly comparable to the conditions experienced in homokinetic 
drives. The conditions can be varied to a great extent by geometric 
changes in the annular roller paths and in the balls or rolling elements. 
For instance, the dimensioning of the annular roller paths in the 
different clamping surfaces relative to one another is a possible way of 
influencing the conditions, and another way is to adjust the ball radius 
to the radius of curvature of the annular roller paths. Further, there 
are, of course, the usual adjustment parameters as well as the contact 
pressure between the two clamping assemblies and the frequency and 
amplitude of the relative movement between the two clamping assemblies. 
It is particularly interesting to note that the above conditions can be 
produced when an oscillation drive with a linear drive direction is 
available in conventional testing instruments. 
Optimum results were achieved in a test run when the direction of the 
oscillating drive was set essentially parallel to the connecting line of 
the spaced apart axes of the first annular roller paths. Optimum practical 
results were also achieved in those cases where the first annular roller 
paths and, if necessary, the second annular roller path have the same 
diameter with the first annular roller paths almost touching one another 
along their radially outer peripheries and with the axial spacing of the 
first annular roller paths dimensioned so that in the center position of 
the second annular roller path between the centers or axes of the first 
annular roller paths, the four balls providing the rolling elements are 
located approximately in positions defining the corners of a square. 
By changing the relation of the ball radius and the radius of curvature of 
the roller paths, it is particularly useful for varying the extent of 
superimposed sliding friction. Due to the wear of the annular roller paths 
and in view of the desire to use different materials, it is recommended to 
construct the annular roller paths as replaceable roller plates which can 
be inserted into and removed from the clamping surfaces of the clamping 
assemblies. 
Since the roller plates can be produced in a simple manner on conventional 
machine tools, particularly on rotary machines, it is recommended that the 
roller plates be constructed in an annular form so that they can be 
detachably inserted into annular recesses in the clamping surfaces of the 
clamping assemblies. The annular roller plates forming the first annular 
roller paths may have polished sections along adjacent peripheral areas 
where they are in contact with one another. These polished sections afford 
greater freedom in the location of the first annular roller paths relative 
to one another and it also permits the annular plates containing the 
roller paths to be fixed relative to one another so that they do not 
rotate. 
As is known in the present state of the art, the carriers for the first 
and/or second annular roller paths can be supported with respect to the 
associated clamping assembly by a pressure meter which forms a part of the 
measuring device. In particular, a piezoelectric pressure meter is 
suitable and has the advantage of supplying an electric signal and, 
therefore, easily processed measured variable. 
The oscillation drive mechanism can be formed in a known manner using an 
electromagnetic oscillator. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be made to the accompanying drawings and descriptive matter in 
which there are illustrated and described preferred embodiments of the 
invention.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 the testing apparatus of the present invention includes a first 
or lower clamping assembly 10 and a second or upper clamping assembly 12. 
The lower clamping assembly 10 includes a foundation 14 with a two-plate 
carrier 16 formed of an upper plate 16a slidable with respect to a lower 
plate 16b in the direction of the double headed arrow 18. Upper carrier 
plate 16a is supported relative to the lower carrier plate 16b by a 
piezoelectric pressure meter as it moves in the direction of the arrow 18. 
The piezoelectric meter is located in a testing circuit with schematically 
illustrated connections 20. A clamping table 22 is firmly secured to the 
upper carrier plate 16a, that is, it is positioned on the upper surface of 
the upper carrier plate. Clamping table 22 has a clamping surface 
containing two annular grooves 22a, 22b with the axes of these grooves 
disposed in spaced apart relation. As can be seen in FIGS. 1 and 2 the 
annular grooves 22a, 22b are arranged in side-by-side relation. Annular 
roller plates 24a, 24b are inserted into the annular grooves 22a, 22b. 
Each of the annular roller plates 24a, 24b has an annular roller path 26a, 
26b with the path in transverse section having synclinal surfaces as can 
be seen in FIG. 1a. The synclinal surfaces are inclined downwardly toward 
one another from the opening of the roller path and meet along the bottom 
line or invert of the roller path. The annular roller plates 24a, 24b are 
ground linearly along the peripheral surfaces facing one another and these 
surfaces are in contact along a line 28 so that the roller plates are held 
against rotation in the annular grooves 22a, 22b. The grinding of the 
adjacent surfaces provides a polished surface on each of the roller plates 
disposed in contact with one another. 
Upper clamping assembly 12 includes a support 30 aligned above the clamping 
table 22 of the lower clamping assembly. Support 30 has an additional 
annular roller plate 32 facing downwardly toward the roller plates 24a, 
24b. Roller plate 32 has an annular roller path 34 in its downwardly 
facing surface and the roller path also has synclinal surfaces. In the 
illustrated example, all of the annular roller paths have the same inside 
diameter, outside diameter and radius of curvature of the groove-like 
roller path. As a consequence, each of the roller paths has the same 
diameter of the invert or bottom lines of the path. The axis of the 
annular roller plate 32 extends through the imaginary line connecting the 
spaced apart axes of the annular roller plates 22a, 22b. 
Upper clamping assembly 12 is moved back and forth in the direction of the 
arrows 36a, 36b by an electromagnetic oscillation drive, not shown, so 
that the upper clamping assembly moves linearly parallel to the imaginary 
line connecting the axes of the annular roller plates 24a, 24b. The 
surfaces of annular roller plates 24a, 24b and 34 which face one another 
are disposed in parallel relation. As a consequence, the tangential planes 
or surfaces containing the inverts or bottom lines of the annular roller 
paths 26a, 26b on the lower clamping assembly and of the annular roller 
path 34 of the upper clamping assembly are in parallel relation. The upper 
clamping assembly can be pressed downwardly in the direction of the arrow 
P by a pressing device, not shown. 
Four roller elements or balls 38a, 38b, 38c and 38d are inserted into the 
annular roller path 34 in the clamping surface of the upper clamping 
assembly, however, in the clamping surface of the lower clamping assembly 
two balls 38a, 38c are located in the annular roller path 26a while the 
other two balls 38b, 38d are positioned in the annular roller path 26b. In 
other words, all four balls are located in the annular roller path 34 
while each the other two roller paths 26a, 26b only hold two of the balls. 
In the schematic showing in FIG. 3, the annular roller paths 26a, 26b are 
shown in full lines while the annular roller path 34 is shown in two 
different positions in broken lines. As viewed in FIG. 3, the left-hand 
showing of the annular roller path 34 is in the centered position of the 
upper clamping assembly 12 relative to the lower clamping assembly 10 and 
the right-hand showing of the annular roller path 34 displays the extreme 
right-hand position of the clamping assembly 12 when it is oscillated 
relative to the clamping assembly 10. In FIG. 3, the left-hand showing of 
the annular roller path 34 illustrates the position of the balls 38a, 38b, 
38c and 38d by solid black circles forming the centered position of the 
upper annular roller path 34 relative to the lower annular roller paths 
26a, 26b. In the right-hand showing of the annular roller path 34, 
displaying the extreme rightward position of the upper clamping assembly 
12 when it is oscillated relative to the lower clamping assembly 10, the 
balls are shown as circles in the positions in which they move in the 
lower annular roller paths 26a, 26b during the oscillating movement. 
The synclinally shaped surfaces of the annular roller paths may be filled 
with a lubricant, for instance one having a fatty consistency. If a 
continuous lubrication is to be afforded, either the entire testing 
apparatus or the space limited to the clamping table 22 and the annular 
roller plate 32 can be enclosed. 
When the second or upper clamping assembly 12 undergoes the oscillatory 
movement in the direction of the arrows 36a, 36b, then the balls 36a-36d 
move from the centered position illustrated by the solid black circles 
into the position illustrated by the open circles. During the oscillating 
movement the balls will move to the left and the right of the centered 
position shown by the solid black circles. During this back and forth 
oscillating movement, where the upper clamping assembly 12 effects a 
linear movement relative to the lower clamping assembly 10, the balls 
38a-38d undergo a rolling movement along the annular roller paths 26a, 26b 
and 34, and at the same time they tend to ride upwardly or downwardly on 
the synclinal surface 40 of the roller paths. Such movement is prevented 
by the contact pressure exerted on the two clamping assemblies 10, 12. By 
preventing the tendency of the balls to ride upwardly on the synclinal 
surfaces, a sliding friction is superimposed on the rolling friction along 
the annular roller paths. 
During the motion of the upper clamping assembly 12 in the direction of the 
arrows 36a, 36b, a pulling force is transferred to the annular roller 
plates 24a, 24b in the direction of the double headed arrow 18 by the 
annular roller path 34, the balls 38a-38d, and the annular roller paths 
26a, 26b. This pulling force is absorbed by the piezoelectric pressure 
transmission element between the carrier plates 16a, 16b so that an 
electric signal, corresponding to the magnitude of the force, is provided 
which is then converted and measured in an electric conversion and 
measuring unit, not shown. This measured result affords a function of the 
contact pressure P and also a function of rolling and sliding friction 
and, as a result, an indication of the lubrication properties and/or the 
material properties of the balls 38a-38d as well as of the materials 
forming the roller paths 26a, 26b and 34. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.