Electric dynamometer

Details Electric dynamometer Electric dynamometer

1983-02-25

1985-04-09

Ruehl, Charles A.

Measuring and testing

Dynamometers

Responsive to torque

G01L 322

Patent

active

045093741

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION



TECHNICAL FIELD

This invention relates to an eddy current type electric dynamometer for measuring a torque of a motor vehicle or the like.


BACKGROUND ART

FIG. 1(a) and FIG. 2(a ) are views illustrating respective constructions of conventional eddy current type electric dynamometers, and FIG. 1(b) and FIG. 2(b) are sectional views of the respective constructions illustrated in FIG. 1(a) and FIG. 2(a). The construction illustrated in FIG. 1(a) and FIG. 1(b) is the so-called drum type eddy current dynamometer while the construction illustrated in FIG. 2(a) and FIG. 2(b) is the so-called disc type eddy current dynamometer.
In FIG. 1(a), FIG. 1(b), FIG. 2(a), and FIG. 2(b), reference numeral 1 designates a shaft, and a rotor 2 (an inductor) is mounted to the shaft 1 with the rotor 2 and the shaft arranged to be integrally rotated. In the case of FIGS. 1(a) and (b), a loss drum 3 is mounted to a yoke 4 to face the rotor 2. An exciting coil 5 is wound inside the yoke 4, and the loss drum 3 and the rotor 2 are arranged to have a gap 6 therebetween.
In the construction of FIGS. 2(a) and 2(b), said rotor 2 extends into a notch on the yoke 4 and this yoke 4 and the notch are arranged to form a gap 6 therebetween. An exciting coil 5 is wound inside the yoke 4.
A path for a magnetic flux is designated by the phantom line arrow in FIG. 1(a) and FIG. 2(a).
The operation of a conventional electric dynamometer of the drum type illustrated in FIGS. 1(a) and 1(b) is quite the same in principle as that of the disc type illustrated in FIGS. 2(a) and 2(b), and will be described with references to FIGS. 1(a) and 1(b). When a constant current flows through the exciting coil 5, the direction of the magnetic flux caused thereby will depend on the direction of the current. Upon rotating the shaft 1 with respect to the outer yoke 4, the rotor 2 is also rotated. Referring to one point on the surface of the loss drum 3 or the yoke 4, the rotation of the rotor 2 is accompanied by a change in radial width of the gap 6 with time. This is because the rotor 2 is provided with alternating concave and convex portions as shown in FIG. 1(b). Accordingly, a change in magnitude of the magnetic flux results. In short, the high and low density portions of the magnetix flux are moved along with the rotation of the rotor 2.
If the density of the magnetic flux penetrating through a conductor is temporally changed then the so-called eddy current is generated there. As a result, a force acts across the rotor 2 and the yoke 4 in a direction to stop the rotation while electrical energy is converted to thermal energy by means of the electric resistance of the loss drum 3 during the conduction of eddy current through the loss drum.
According to the principles of the operation as described above, the eddy current dynamometer can absorb input rotational energy to the shaft 1 in the form of thermal energy.
It is generally constructed so that a torque applied to the yoke 4 can be read by a torque meter (not shown). The yoke 4 in the eddy current dynamometer is produced so as to be slightly rotatable for the purpose of measuring the torque but the same is impossible to continue to be rotated about the shaft 1. The yoke 4 is, on the whole, in a substantially stationary state with respect to the ground.
Further it is described for caution's sake that the function of the loss drum 3 is not essential and is to improve the efficiency of the energy conversion.
The loss drum is normally made from a material identical in reluctance to and higher in electric resistance than the rotor 2 or the yoke 4 so as to cause the greater part of the generation of heat therein.
The eddy current dynamometer has the advantage that the structure thereof as described above is cheap and small-sized as compared to other electric dynamometers, for example, a DC generator type dynamometer or an exchange generator type dynamometer.
FIG. 3 illustrates one example of the characteristics of the eddy current type dynamometers illustrated in FIG. 1(a) and FIG. 2(

REFERENCES:
patent: 2389572 (1945-11-01), Winther

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