Electricity: measuring and testing – Internal-combustion engine ignition system or device
Reexamination Certificate
2001-06-26
2004-08-17
Le, N. (Department: 2858)
Electricity: measuring and testing
Internal-combustion engine ignition system or device
Reexamination Certificate
active
06777941
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to testing alternators, and more specifically, to an alternator testing method and system controlling the coupling of a load to the alternator during the test.
BACKGROUND OF THE INVENTION
An alternator converts mechanical motions into alternating current (AC) by electromagnetic induction. The alternating current is then passed through a rectifier assembly, such as a full-wave rectifier bridge comprising diodes, to convert the AC into DC to power other electrical systems. For example, an alternator in an automotive vehicle is driven by the engine to power the vehicle's electrical system, such as for charging the battery, powering headlights, and the like. The alternator output, however, is not perfectly smooth. The waveform of an alternator output is similar to a low-magnitude ripple riding on a DC component.
Alternator tests are conducted when alternators are under load, i.e., a load is coupled to the output terminals of the alternator to draw current therefrom. Alternator testers often have a set of probes or wires to couple to the output terminals of the alternator for detecting parameters of the alternator output, such as the output voltage, the ripple amplitude, the average current of the output, and so on. Usually, handheld alternator testers for testing vehicle alternators use a load capable of drawing up to 10 amperes of current. For alternators used in an automotive vehicle, the test of alternator under load may be conducted by turning on electrical accessories powered by the alternator, such as the head lights, radio, air conditioner, and the like.
Several problems may occur when testing alternators. First, since the ripple component of the alternator output is a small signal, the ripple waveform is subject to noise interference and may be difficult to observe. Second, when the load is coupled to the alternator, the alternator output waveform may not respond to, or does not always respond to the change of load immediately. Accordingly, the alternator output is unstable until a certain period of time has elapsed. If the tester determines alternator operation based on parameters collected from the unstable waveform, error in test results will occur. Third, using electrical accessories on a vehicle as a load draws inconsistent currents from the alternator. The alternator output level therefore tends to fluctuate, which makes precise test difficult. In addition, the load used in alternator tests generates a lot of heat, which causes safety concerns.
SUMMARY OF THE INVENTION
Accordingly, there exists a need for accurately determining the health of an alternator. There is another need to provide a stable load for use in alternator tests. Still another exists for evaluating the health of an alternator based on a stable alternator output. An additional need exists for providing high resolution signals for testing an alternator. There is still another need for dissipating heat generated by the load during the alternator test.
These and other needs are addressed by the present invention. The invention is an alternator testing method and system that provides high resolution signals and stable loads during alternator tests. According to one aspect of the invention, evaluation of the alternator operation is based on parameters collected after the load is coupled to the alternator for a predetermined period of time, so that the parameters reflect a stable alternator output. In another aspect, the load is coupled to the alternator for a very short period of time to reduce the heat generated during the test. In still another aspect, the load is housed in a handheld housing and capable of drawing large currents, for example, 50 amperes, from the alternator in order to produce better signal resolution.
The method according to the present invention comprises the steps of: coupling a load to the alternator, evaluating the operation of the alternator based on parameters collected after the load has been coupled to the alternator for a first predetermined period of time.
In one aspect of the invention, the alternator may be driven by a motor, such as an engine powered by fossil fuels. According to one embodiment of the invention, the method further includes a step of detecting motor speed or alternator speed. The load is applied to the alternator only after the motor speed or alternator speed reaches a predetermined level. In another aspect of the invention, the load is decoupled from the alternator after the load has been coupled to the alternator for a predetermined period of time.
The system of the present invention comprises a load, and a terminal for receiving an alternator output signal representative of an alternator characteristic, and a switch device for selectively coupling the load to the alternator. A controller is configured for determining the characteristics of the alternator output signal and for generating a first switch operation signal to control the switch device to couple the load to the alternator. The controller determines the characteristics of the alternator output signal based on parameters collected after the load has been coupled to the alternator for a predetermined period of time.
According to one aspect of the invention, the system is contained in a housing having a size suitable to be held in one's hand. The system may further include a cooling device, such as a fan, for dissipating the heat generated by the load. The controller generates a second switch operation signal to control the switch device to decouple the load from the alternator after the load has been coupled to the alternator for a predetermined period of time.
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Brott Alejandro P.
Faehnrich Richard J.
Goctzelmann Alan D.
Thibedeau Dennis G.
Willems Paul A.
He Amy
Le N.
McDermott Will & Emery LLP
Snap-On Incorporated
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