Electricity: measuring and testing – Electrical speed measuring – Including motor current or voltage sensor
Patent
1995-04-10
1997-02-11
O'Shea, Sandra L.
Electricity: measuring and testing
Electrical speed measuring
Including motor current or voltage sensor
324166, 322 28, G01P 346
Patent
active
056024703
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a circuit arrangement for measuring the rotational speed of a generator. More particularly, it relates to a circuit arrangement for a starting detection of a three-phase generator.
In motor vehicles, three-phase generators which excite themselves after the motor driving them has started up are usually used to generate the electrical energy. So that this self-excitation occurs reliably and safely, measures which improve the self-excitation are usually initiated directly after the motor vehicle engine starts.
One customary method consists in using the charge monitoring lamp to pre-excite the generator. For this purpose, during starting, energy is fed to the exciter winding from the battery via the charge monitoring lamp. Another method consists in providing an additional lead between the battery and the exciter winding of the generator and conducting an additional exciter current via this connection during the starting process.
The aforesaid measures are disclosed, for example, in the German Offenlegungsschrift 38 43 161 and the corresponding U.S. Pat. No. 5,107,198. In the known solutions, additional means for detecting the start of the engine are required.
However, in generator voltage controller systems, it is also known to use the rotational-speed-dependent alternating voltage in a phase winding of the three-phase generator in order to detect starting. In such a case, a voltage measurement is carried out in the voltage controller, during which voltage measurement the voltage is measured between the phase and earth and, when a threshold value is exceeded, it is detected that the engine is starting and thus the three-phase generator is beginning to rotate.
This type of starting detection has the disadvantage that, if the switch-on threshold is too high, the cut-in speed of the generator is too high and, if the threshold is too low, the signal-to-noise ratio becomes too small, so that starting may be detected erroneously.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a circuit arrangement of the above mentioned general type, which avoids the disadvantages of the prior art.
More particularly, it is an object of the present invention to provide a circuit arrangement of the above mentioned type, which has the advantage that either the threshold voltage can be increased when the cut-in speed is the same, as a result of which the signal-to-noise ratio is improved, or that the cut-in speed can be lowered. The threshold voltage here is the voltage which, when exceeded, permits the start of rotation of the generator to be detected.
This advantage is achieved in that the voltage between one phase and earth is evaluated in a generator with star-connected phase windings, while a different phase winding is connected to earth via a further resistor. By means of this measure, a voltage divider is obtained which consists of the input resistor of the voltage meter and the additional resistor, this voltage divider being connected to the phase-to-phase voltage between the two phase windings. This phase-to-phase voltage is higher than the phase voltage by a factor .sqroot.3.
Furthermore, it is advantageous that the threshold voltage which, when exceeded, permits the start of rotation of the generator to be detected, can be set easily by suitable selection or variation of the further resistor.
The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. FIG. 1 shows a circuit arrangement according to the invention, and in FIG. 2 an equivalent circuit diagram is illustrated which permits the relationships to be more easily recognized.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
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REFERENCES:
patent: 4079306 (1978-03-01), Mori et al.
patent: 5107198 (1992-04-01), Meyer et al.
Autoelektrik Autoelektronik Manual, Bosch, 1987, pp. 24-29 1987.
Hoeber Matthias
Kohl Walter
Mittag Rainer
O'Shea Sandra L.
Patidar Jay M.
Robert & Bosch GmbH
Striker Michael J.
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