GB2170915A - Dynamometers - Google Patents

Abstract

An electric or hydraulic dynamometer has a stator 1 provided with an arm 3 acting on a force sensor 4, the stator being pivoted to a base 9 at an axis 6 which does not coincide with the axis of the rotor shaft 2. Elastic supports for damping vibration may be provided between supporting arms 5 and the pivot 6 or between support members 8 and the base 9. <IMAGE>

Description

SPECIFICATION Electric or hydraulic dynamometer whose oscillation axis does not coincide with the rotation axis of the drive shaft The invention pertains to an electric or hydraulic dynamometer whose oscillation axis does not coincide with the rotation axis of the drive shaft.

It is known that the essential quality required to measure machines and equipments such as dynamometers is the greatest precision.

An electric or hydraulic dynamometer of the known type for measuring a motor power usually consists of a rotor and a stator that are coaxial. The stator is free to oscillate with respect to a support base and is provided with an arm acting by means of its free end on a dynamometer measure member. The rotor shaft is connected usually through a joint, to the motor shaft the power of which is wished to be measured. In order to carry out the desired measurement the rotor is suitably braked for example by means of water jets in the case of hydraulic dynamometers or by means of magnetic fields in the case of electric dynamometers or by the use Qf other suitable means.

As a result the stator is subjected to a rotation torque so that its arm exerts a certain force on the- dynamometer measure member.

As the distance between the point of application of the measure member and the axis of the rotor shaft is known, it is sufficinet to multiply this distance by the force detected by the dynamometer measure member in order to obtain the value of the torque-exerted by the motor being tested.

The precision degree attainted by this dynamometer measure member is very high so that also the - precision degree of the dynamometer depending upon the latter is remarkable.

In order to achieve a free oscillation of the stator, -the latter has to be provided on both sides with two coaxial hubs through which the rotor shaft passes. Said hubs are supported by journal bearings which, owing to the sizes of the hubs above all when high power dynamometers are concerned, have big sizes too; preferably they have swinging balls or rollers and cannot be very precise as to their sizes.

However the precision in size is very important as the dynamometer measure member must be in a position to detect also very small load variations on the stator arm.

As the dynamometer weight is considerable and it always has very small oscillations the bearing balls tend to dig housings in their containing rings, which housings adversely affect the precision of the dynamometer measure member.

In order to avoid that it is necessary to slightly rotate the bearings periodically so that the creation of said housings may be prevented or at least restricted. However this solution is only an expedient as the bearings can be progressively rotated only through the distance existing between two subsequent balls and in any case their lifetime is reduced.

The object of the present invention is therefore to eliminate the above mentioned drawbacks. The invention, as defined in the appended claims, provides an electric or hydraulic dynamometer which is very precise and capable of maintaining such a precision in the course of time.

The advantages achieved by the present invention essentially consist in that in a dynamometer of this type it is possible to use bearings which, while having the sufficient load capacities, haye much smaller sizes with respect to the known ones and hence are much more precise.

A further advantage of the invention is that, by virtue of the reduced sizes of the journal bearings, it is also possible to use other kinds of bearings,, more precise in size and with less plays.

Yet another advantage of the invention, resulting from the reduced sizes of the journal bearings, resides in that the servicing of the latter can take place more readily than with the bearings hitherto and in that they last longer.

A still further advantage of the invention resides in that the use of journal bearings of reduced sizes causes a remarkable reduction in the hysteresis of the same and consequently in the passive resistance of the whole dynamometer.

The invention will be described in more detail hereafter with reference to the accompanying drawings showing one embodiment thereof.

In the drawings: Figure 1 is a side view of the dynamometer of the invention; Figure 2 is a rear view of the dynamometer seen in Fig. 1; Figure 3 is a part sectional view taken along the rotor axis, of a detail of the dynamometer; Figure 4 is a sectional view of an alternative embodiment of the detail seen in Fig. 3.

As shown in figs. 1 and 2, a dynamometer consists of a stator 1, supported by a base 9, and a rotor (not shown), in a coaxial relation.

The rotor is connected to a shaft 2 which projects from the stator and to which the shaft of a motor of which it is wished to measure the power is also integrally and coaxially connected by a joint (not shown).

The stator 1 is provided on both sides with two coaxial hubs 12 crossing the rotor shaft 2, and radially with an arm 3, acting by its free end on a dynamometer measure member 4 for example a weight transducer, supported by the base 9.

In accordance with the invention (Fig. 3) each hub 12 of the stator 1 is surrounded by a respective collar 13 held therein by a lock ing member 14, for example a ring nut, and enabled to rotate relative to its corresponding hub 12 by one or more reference members such has pegs 15. Each collar 13 is provided with a supporting arm 5 radially crossed at its free end by a pivot 6 supported through jour nal bearings 7 by a support member 8 fas tened to the base 9.

According to the preferred embodiment shown in the figures, the supporting arms 5 are substantially vertically aligned below the rotor shaft 2. The pivots 6 are of the kind having a head at one end and a threaded por tion at the other end.

Spacers 17 are provided between each sup porting arm 5 and the inner rings of the corre sponding journal bearings 7. The locking of the inner rings of the journal bearings 7, of spacers 17 and of the corresponding support ing arm 5 on each pivot 6 takes piace by means of the head 16 of the pivot 6 itself and by a ring nut 18 screwed on the threaded end portion of the same pivot 6. By locking the ring nuts 18 it is possible to rotate the pivots 6 in order to periodicaily modify the position of the rotating members of the jour nal bearings 7. In this way a sector of the journal bearings 7 that had not been previ ously load stressed is brought into the region of maximum work.

Each pivot 6 may be freely coupled with its housing to its respective supporting arm 5 and that preferably when small power dyna mometers are concerned in order to limit the starting frictions. Otherwise (see Fig. 3) each supporting arm 5 may be provided, at its free end, with a cut coplanar with the axis of its respective pivot 6 and be crossed by a screw 19 at right angles to the latter for locking the same.

As shown in Fig. 4 the journal bearings 7 of one of the two supporting arms 5 are free to move axially in their outer housing 20 obtained in the respective support member 8 in order to allow the absorption of axial expan sions mainly due to heat.

in order to reduce the effects of the vibrations transmitted to the dynamometer by the motor the insertion of spring supports 10 between the support members 8 and the base 9 is envisaged (see Fig. 3).

On the contrary, in the embodiment shown in Fig. 4 the effect of said vibrations is reduced by introducing an elastic support ring 11 between each supporting arm 5 and the respective pivot 6.

Obviously at the time of its practical accomplishment the dynamometer might be provided with further known elements which are not considered to be within the purview of the invention; for example covers might be added to the housings 20 of the support members 8, in order to restrict the factors that adversely affect the precision of the dynamometer itself.

It should also be understood that various modifications and variations may be made to the details of construction of the elements disclosed herein without departing from the spirit and scope of this invention; for example the supporting arms 5 can be directly obtained from the hubs 6. Furthermore all details may be replaced by technically equivalent elements.

Claims (11)

1. An electric or hydraulic dynamometer consisting of a stator free to oscillate with respect to a base and provided with an arm acting on a dynamometer measure member, and of a rotor fitted on the drive shaft and coaxial with the stator, characterized in that its oscillation axis is disposed so that it does not coincide with the axis of the drive shaft.

2. The dynamometer according to claim 1, characterized in that the oscillation axis is disposed parallel to the axis of the drive shaft.

3.-'The dynamometer according to claim 1, characterized in that the oscillation axis is substantially disposed on its vertical centre-ofgravity axis.

4. The dynamometer according to claim 3, characterized in that the oscillation axis is disposed below the axis of the drive shaft.

5. The dynamometer according to claim 1, characterized in that said stator is provided with two parallel supporting arms crossed by a pivot parallel to the drive shaft and supported, so that it can freely oscillate, by journal bearings housed in support members fastened to said base.

6. The dynamometer according to claim 5, characterized in that each supporting arm is crossed by a respective pivot and each pivot is supported by a pair of journal bearings disposed on the two sides of the corresponding supporting arm.

7. The dynamometer according to claim 6, characterized in that the two journal bearings of at least one of the supporting arms are mounted on the respective support member so that they can slide axially.

8. The dynamometer according to claim 5, characterized in that a spring support suitable for damping vibrations is inserted between the support members and the base.

9. The dynamometer according to claim 6, characterized in that an elastic support ring suitable for damping vibrations is inserted between each supporting arm and the respective pivot.

10. The dynamometer according to claim 5, characterized in that said supporting arms are freely rotatable about their respective pivot in order to limit the starting frictions.

11. An electric or hydraulic dynamometer, substantially as hereinbefore described with reference to the accompanying drawings.