Patent Description:
The present invention relates to a torsiometer, and particularly to a torsiometer for torsional measurements on components of automotive transmission systems such as, for example, tensioners for belt transmission systems.

As is known, tensioners for belt transmission systems basically comprise a base designed to be fastened to the engine, an arm rotatable on a pin carried by the base and a pulley carried by the arm at one end thereof and designed to cooperate with the belt to transmit a tensioning force thereto.

For this purpose, the tensioner comprises a spring having an end constrained to the base and an end constrained to the arm, so as to transmit a tensioning torque to the arm.

In order to check the performance of the tensioners, a torsiometer is normally used in which rotation angles of the arm are set with respect to the base and the tensioning torque is measured.

Known torsiometers normally comprise a motor unit constituted by an electric motor equipped with a spindle on which the base of the tensioner is mounted and a torsiometric unit comprising a torsiometric cell facing the spindle and coaxial thereto. The torsiometric cell is interposed between a fixed support, the position of which relative to the spindle is adjustable by a slide, and a reaction member on which the arm discharges its force in response to the rotation of the base. The angle of rotation of the base is measured by an encoder associated with the spindle.

Torsiometers of the previously described type suffer from a certain number of causes of error.

A first cause of error is linked to the fact that transducers of the torsiometric cell, no matter how opportunely oriented, also "sense" a flexural component of the deformation, in addition to the torsional one. The resulting error is proportional to the torque.

A second cause of error is linked to the fact that the tensioner generates radial forces that tend to misalign the spindle and the torsiometric cell; the shift grows with wear and causes systematic errors, the influence of which increases as the length of the tensioner's arm decreases.

Another cause of error is the flexure of the spindle, proportional to the torque.

Finally, another cause of error is constituted by the fact that the encoder detects angles not exactly corresponding to the actual rotation, as part of the stress that should cause pure torsional deformation of the spring, in reality produces flexural deformations.

From the combined foregoing considerations, the need emerges for producing a torsiometer that reduces measurement uncertainty.

<CIT> discloses a test stand for an internal combustion engine including a drive and/or load system, a force transmission device for connecting the internal combustion engine with the drive and/or load system, and a sensor and evaluation system for automatically collecting and evaluating measurement variables, wherein the force transmission device comprises a system for detecting torque and rotation angle, which system is coupled to the internal combustion engine in a torsionally stiff manner.

The aforementioned object is achieved by a torsiometer according to claim <NUM>, wherein the torsiometric cell is interposed between the motor unit and the spindle, coaxially with the latter, and is connected to at least one of the spindle and the motor unit by a joint configured to absorb bending loads.

In this way, the above described causes of error are eliminated.

According to the invention, the joint is a multi-stage universal joint. Moreover, said joint is configured to absorb the bending loads and comprising a plurality of elements constrained to each other in a rotatable manner about mutually orthogonal axes. Preferably, said elements are telescopically mounted one inside the other.

For a better understanding of the present invention, a preferred embodiment is described hereinafter, by way of non-limitative example and with reference to the accompanying drawings, in which:.

With reference to <FIG> and <FIG>, reference numeral <NUM> indicates, as a whole, a torsiometer for testing tensioners for belt transmission systems.

The torsiometer <NUM> essentially comprises:.

More specifically, the motor unit <NUM> comprises an electric motor <NUM> and a reduction gear <NUM>, not described in detail as it does not form part of the present invention. The reduction gear <NUM> comprises an outer casing <NUM> fixed to the vertical wall <NUM> in a cantilever fashion on the opposite side of the table <NUM>, and a hollow shaft <NUM> lying on axis A, extending through an opening <NUM> in the vertical wall <NUM> and terminating with a flange <NUM> (<FIG>). The hollow shaft <NUM> receives the motion from an output member of the reduction gear <NUM>, not shown, through a tongue <NUM> (<FIG> and <FIG>).

A sleeve lying on axis A, constituting the output member <NUM> of the motor unit <NUM> and therefore referred to hereinafter as "sleeve <NUM>" for brevity, is fixed to the flange <NUM>.

The sleeve <NUM> extends over the table <NUM> and is supported, in proximity of its opposite end <NUM>, by an adjustable support <NUM> fixed to the table <NUM> by a radial bearing <NUM>.

The end <NUM> of the sleeve <NUM> is connected to the load cell <NUM> by a multi-stage universal joint <NUM>, shown in detail in <FIG>.

With reference to these figures, the universal joint <NUM> basically comprises three rings <NUM>, <NUM>, <NUM> and an output flange <NUM>, telescopically mounted one inside the other.

The outer ring <NUM> is constrained to the sleeve <NUM> with rotational freedom about an axis B orthogonal to the axis A and incident therewith. This constraint is implemented by means of a pair of diametrically opposite brackets <NUM>, radially fixed in an outwardly cantilever fashion on the end <NUM> of the sleeve <NUM>, and a pair of radial pins <NUM> lying on axis B, engaging respective holes <NUM> of the brackets <NUM> in an angularly free manner and embedded in respective diametrically opposite radial holes <NUM> of the outer ring <NUM> (<FIG> and <FIG>).

The intermediate ring <NUM> is constrained to the outer ring <NUM> with rotational freedom about an axis C orthogonal to the axis B. This constraint is implemented by means of a pair of radial pins <NUM> lying on axis C, engaging respective holes <NUM> of the outer ring <NUM> in an angularly free manner and embedded in respective diametrically opposite radial holes <NUM> of the intermediate ring <NUM>.

In an entirely similar manner, the inner ring <NUM> is constrained to the intermediate ring <NUM> with rotational freedom about an axis D perpendicular to the axis C. This constraint is implemented by means of a pair of radial pins <NUM> lying on axis D, engaging respective holes <NUM> of the intermediate ring <NUM> in an angularly free manner and embedded in respective diametrically opposite radial holes <NUM> of the inner ring <NUM>.

Finally, the output flange <NUM>, this also having an annular shape, is constrained to the inner ring <NUM> with rotational freedom about an axis E perpendicular to the axis D. This constraint is implemented by means of a pair of radial pins <NUM> lying on axis E, engaging respective holes <NUM> of the inner ring <NUM> in an angularly free manner and embedded in respective diametrically opposite radial holes <NUM> of the output flange <NUM>.

The flange <NUM> is connected to the spindle <NUM> by the torsiometric cell <NUM>.

More specifically, the spindle <NUM> comprises a shaft <NUM> lying on axis A, which is radially supported by a bearing <NUM> housed in the end <NUM> of the sleeve <NUM> and extends passing through the universal joint <NUM>, and an end flange <NUM> facing the flange <NUM> of the joint. The torsiometric cell <NUM>, having an annular shape, is housed coaxially with the shaft <NUM> between the flange <NUM> and the flange <NUM> of the spindle <NUM>, and has respective end flanges <NUM>, <NUM>, which are respectively fixed to the flange <NUM> and the flange <NUM> of the spindle <NUM> by respective pluralities of axial screws. In <FIG> and <FIG>, only the screws <NUM> for connection to the output flange <NUM> are shown.

The spindle <NUM> is integrally connected to an elongated shaft <NUM> housed inside the hollow shaft <NUM>. For this purpose, the spindle <NUM> comprises a spacer <NUM> lying on axis A, arranged inside the sleeve <NUM> and connected to the shaft <NUM> and to the shaft <NUM> by respective threaded connections <NUM>, <NUM>. The spacer <NUM> is radially supported with respect to the sleeve <NUM> by a bearing <NUM> at its end <NUM> opposite to the shaft <NUM>, into which the shaft <NUM> screws. It is important to note that the bearings <NUM>, <NUM> support the spindle <NUM> radially, but in an axially free manner, so as to avoid undesired exchanges of forces.

The axial positioning of the spindle <NUM> is defined by a constraint system <NUM> configured so as to avoid the transmission of forces or torque between the spindle <NUM> and the sleeve <NUM> (except for the axial constraint reaction).

This constraint system <NUM> preferably comprises a punctiform axial support produced as described below.

The sleeve <NUM> (<FIG>) is equipped with a pair of diametric through slots <NUM>, parallel to each other, which have an elongated section in the axial direction and are aligned with each other in this direction.

In turn, the spacer <NUM> is provided with a pair of corresponding diametric through slots <NUM>, parallel to each other, which have an elongated section in the axial direction and are aligned with each other in this direction.

The slots <NUM> and <NUM> house respective elongated bars <NUM> with axial clearance. The bars <NUM> are housed with transversal clearance in the slots <NUM> of the spacer <NUM>, and instead housed in a sliding manner, but without transversal clearance, in the slots <NUM>.

The bars <NUM> are provided with respective slots <NUM>, elongated in the axial direction, which are engaged in a sliding manner by respective pins <NUM> carried by the sleeve <NUM>, so as to create a purely radial (longitudinal) constraint for the bars <NUM>.

The bars <NUM> rest centrally, with their axial ends facing each other, on axial pins <NUM> lying on axis A and carried by the spacer <NUM>.

The punctiform axial support ensures that no torque is exchanged between the sleeve <NUM> and the spindle <NUM>, except for the axial constraint reaction.

The bars <NUM> are also axially constrained to the sleeve <NUM> by respective pairs of grub screws <NUM> housed in respective axial holes <NUM> of the sleeve <NUM> and acting axially on the opposite ends of the bars <NUM>, on the side opposite to pins <NUM>.

The shaft <NUM> is connected, in a known manner that is not shown, to the mobile unit of the encoder <NUM>, the casing <NUM> of which is fixed to the outer casing <NUM> of the reduction gear <NUM> by a bracket <NUM>.

The reaction unit <NUM> (<FIG> and <FIG>) basically comprises a first slide <NUM> sliding in a direction parallel to the axis A on guides <NUM> arranged on the table <NUM>. The first slide <NUM> carries a vertical support <NUM> for a second slide <NUM>, sliding with respect thereto in a horizontal direction perpendicular to the axis A. The second slide <NUM> carries a reaction pin <NUM> extending in a cantilever fashion in a direction parallel to the axis A (<FIG> and <FIG>).

The torsiometric cell <NUM>, the encoder <NUM> and the electric motor <NUM> are connected to an electronic control unit, which is designed to control the electric motor to perform the measurement cycles and record torque data as a function of the angle of rotation, in a manner which is in itself known.

The operation of the torsiometer <NUM> is as follows.

<FIG> schematically shows a tensioner <NUM> for which it is wished to determine the torsiometric characteristic.

The tensioner <NUM> comprises, in a known manner, a base <NUM>, an arm <NUM> rotatable on the base <NUM> against the action of a spring <NUM> interposed between them in a known manner, and an idler pulley <NUM> mounted on an end of the arm <NUM>.

The base <NUM> of the tensioner is fixed on the flange <NUM> of the spindle <NUM> so that the axis of rotation of the arm <NUM> with respect to the base <NUM> coincides with the axis A.

The slides <NUM>, <NUM> of the reaction unit <NUM> are configured and locked so as to arrange the reaction pin <NUM> in a position for interacting with the arm <NUM> of the tensioner <NUM> mounted on the spindle <NUM>.

The measurement cycle comprises a first step of approach in which the electric motor <NUM>, via the reduction gear <NUM>, the hollow shaft <NUM>, the sleeve <NUM>, the universal joint and the torsiometric cell <NUM>, makes the spindle <NUM> and the tensioner <NUM> rotate about the axis A, until the arm <NUM> comes into contact with the reaction pin <NUM> (<FIG>).

From this moment, a further rotation of the spindle <NUM> produces a deformation of the spring of the tensioner <NUM>, as the arm <NUM> is locked by contact with the reaction pin <NUM>, and the torsiometric cell <NUM> reads the torque transmitted in a manner in itself known; the angle of rotation of the spindle <NUM> is transmitted through the spacer <NUM> and shaft <NUM> to the encoder <NUM> and measured by the latter.

Since the torsiometric cell <NUM> is connected directly to the spindle <NUM> and is integral therewith, all error components related to parasitic eccentricities that might occur in known torsiometers, in which, as has been said, the torsiometric cell is usually arranged in the reaction unit, are eliminated.

Furthermore, due to the multi-stage universal joint <NUM>, subjecting the torsiometric cell <NUM> to flexural stresses is avoided, therefore ensuring that the cell reads the pure torsion torque.

Finally, the punctiform axial support between the sleeve <NUM> and the spindle <NUM> ensures that, even in the presence of parasitic load components, albeit avoided due to the configuration of the constraints, there can be no torque transmitted between the sleeve <NUM> and the spindle <NUM>.

Finally, it is clear that modifications and variants can be made to the described torsiometer <NUM> without departing from the scope defined in the claims.

For example, the joint <NUM> could be interposed between the load cell and the spindle <NUM>, instead of between the sleeve <NUM> and the load cell <NUM>.

Furthermore, the joint <NUM> and the constraint system <NUM> could be made in a different manner, as long as they are functionally equivalent.

Claim 1:
A torsiometer for determining a torsiometric characteristic of a component (<NUM>) of an automotive transmission system, said component (<NUM>) comprising at least a first member (<NUM>) and a second member (<NUM>) rotationally coupled together by at least one elastic member (<NUM>) interposed therebetween, the torsiometer (<NUM>) comprising:
a spindle (<NUM>) having a rotation axis (A) and configured to receive the first member (<NUM>) of said component (<NUM>);
a motor unit (<NUM>) connected to the spindle (<NUM>) and designed to drive said spindle (<NUM>) to rotate about said axis (A);
a reaction unit (<NUM>) facing the spindle (<NUM>) and provided with a reaction member (<NUM>) for the second member (<NUM>) of said component (<NUM>);
an encoder (<NUM>) configured to measure the rotation angles of the spindle (<NUM>); and
a torsiometric cell (<NUM>) configured to measure the torque transmitted to the component (<NUM>), the torsiometric cell (<NUM>) being interposed between the motor unit (<NUM>) and the spindle (<NUM>), coaxially with the latter;
the torsiometer characterised in that the torsiometric cell (<NUM>) is connected to at least one of the spindle (<NUM>) and the motor unit (<NUM>) through a multi-stage universal joint (<NUM>) configured to absorb the bending loads and comprises a plurality of elements (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) constrained to each other in a rotatable manner about mutually orthogonal axes (B, C, D, E) .