Testing apparatus

Details Testing apparatus Testing apparatus

1998-08-20

2001-01-02

Raevis, Robert (Department: 2856)

Measuring and testing

Frictional resistance, coefficient or characteristics

Utility Patent

active

06167745

ABSTRACT:

TECHNICAL FIELD
This invention relates to testing apparatus and, in particular, to apparatus for testing rolling traction and/or friction forces. Typical applications include fuel economy modelling of automotive engine oils, boundary additive evaluation and friction measurements for traction fluids.
BACKGROUND OF THE INVENTION
A number of forms of apparatus have been proposed, in the past, for testing friction and/or traction forces. However, accurate measurement is difficult to achieve as known forms of testing apparatus have in-built resistances, such as internal friction, which can influence the total force the apparatus is attempting to measure.
By way of example, traction in rolling/sliding contacts is usually determined by measuring torque applied to one of the rotating specimens or by measuring the reaction force felt by a body supporting one of the rotating specimens.
If measuring the torque applied, it is normally necessary to position the torque transducer behind bearings supporting the specimen drive shaft. This means that the transducer is also measuring the torque applied to overcome frictional resistance in the bearings and/or oil seal and is thus not giving an accurate measurement of the applied torque alone.
If measuring the reaction force, this is normally measured by a force transducer which constrains the body supporting one of the rotating specimens from moving in the direction of the traction force. Because of the applied load, the body is, normally, supported by additional means. In order to maximise the accuracy of the traction measurement, the additional means of support needs to have extremely low resistance to motion in the direction of the traction force. This is typically achieved by using rolling element bearings or air bearings within the additional support. However, whilst such bearings have very low frictional resistance, they have sufficient resistance to reduce the accuracy of the traction measurement. Also, such frictional resistance as they do have will normally vary with variations in magnitude of the applied load.
For practical purposes it may not be possible to entirely eliminate extraneous forces. What is therefore required is a form of apparatus in which any extraneous forces are predictable and which can thus be eliminated by a calibration process.
It is an object of this invention to provide traction and/or friction testing apparatus in which any extraneous force inherent in the apparatus is predictable such that any measurement of traction or friction force will be directly proportional to the actual force.
SUMMARY OF THE INVENTION
Accordingly, in one aspect, the invention comprises traction or friction testing apparatus, said apparatus comprising:
a first traction surface;
a second traction surface constructed and arranged to, in use, contact said first traction surface, said first and second traction surfaces being arranged for rotational engagement therebetween;
a support structure constructed and arranged to support said first and second traction surfaces with respect to one another whilst allowing rotational movement therebetween;
drive means operable to effect differential rotation between said first and second traction surfaces and thereby to generate a traction or friction force therebetween; and
force measuring means associated with at least said first and second traction surfaces to provide a measure arising from said traction or friction force,
said apparatus being characterised in that any force arising between said first and said second traction surfaces due to traction or friction therebetween is resisted solely by elastic deformation of said support structure and/or said force measuring means.
The subject invention is constructed and arranged to measure rolling traction and/or friction. To that end, the first traction surface is conveniently planar in form whilst the second traction surface has a circular component to allow rotating motion thereof with respect to the first surface. More preferably, the second traction surface is provided by the surface of a spherical ball.
In a particularly preferred form, the first traction surface comprises a planar disc adapted to be mounted for rotation about its central axis.
The support structure preferably includes first support means constructed and arranged to rotatably mount said first traction surface; and second support means constructed and arranged to rotatably support said second traction surface, said first and second support means being relatively displaceable to allow said first and second traction surfaces to be moved into contact with their respective axes of rotation lying in a substantially common plane.
Conveniently, the first support means mounts said first traction surface for rotation about a substantially vertical axis. The second support means is mounted for pivotal movement about a substantially horizontal axis to permit said second traction surface to be displaced into contact with said first traction surface.
Preferably said second support means further includes elastic flexure means constructed and arranged to permit elastic movement of said second traction surface with respect to said first traction surface in the direction of the resulting traction or friction force, yet resist movement of said second traction surface in orthogonal directions.
The drive means may include a first drive motor to rotate said first traction surface; and a second drive motor to rotate said second traction surface. The drive means may further include displacement means to variably displace said second traction surface into contact with said first traction surface in a direction normal to said first traction surface. This displacement means is conveniently provided, in part, by a stepper motor.
The force measuring means preferably comprises a linear force transducer mounted to detect movement of said second traction surface due to a traction or friction force being generated between said first and second traction surfaces.
Many variations in the way the invention may be performed will present themselves to those skilled in the art. The only limitations on the scope of the invention should be imposed by the appended claims and not by the description of one preferred embodiment which follows.


REFERENCES:
patent: 4023402 (1977-05-01), Watanabe
patent: 5115664 (1992-05-01), Hegde et al.
patent: 5377525 (1995-01-01), Hutchinson et al.
patent: 5679883 (1997-10-01), Wedeven
patent: 1105319 (1968-03-01), None
patent: WO 94/05449 (1994-03-01), None

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