The present invention relates to a control device for a generator wherein the control device uses a conductor, such as a wire, embedded in the generator to control the output power of the generator. The control device monitors an electrical potential across the conductor in determining the total generator output current. The control device is configured to limit and/or cease the generator output power when the electrical potential is within a predetermined range and/or above a predetermined value. Where temperature variation of the conductor is substantial, the control device may be configured to measure the temperature of the conductor to compensate for the temperature variation. A sensor can be positioned within the generator in specific locations to measure either directly, indirectly, or by inference, the conductor temperature. Where the generator uses a field coil whose electrical current is supplied by the generator, the control device may further be configured to measure the field current and subtract it from the total generator output current. The control device can be further configured to monitor other parameters, as will be discussed below, to improve the generator functionality.
The present invention further relates to a generator incorporating process-controlled conductors which may be utilized to determine the total generator output current. The generator comprises one or more such conductors which carry a portion or all of the total electrical current generated by the generator. The conductors are made of a specific shape during the manufacture of the generator, allowing accurate determination of the total generator output current without the need for additional sensors. Specifically, the length and/or diameter of the conductors are kept within a specific tolerance range. The control device may be used with a generator incorporating either an ordinary or a process-controlled conductor for its operation.
Modern vehicles incorporate complex electronics and electrical equipment in their construction. Such electrical equipment include generators and energy storage devices such as batteries. A generator is used to power the vehicle's electrical system and to recharge the battery. The battery is used to power the electrical system when the vehicle engine is not operating or when the generator can not produce sufficient electrical power. Ordinarily, the generator includes a voltage regulator that maintains the generator voltage at a regulation voltage. Modern generators include a control device that, in addition to regulating the generator voltage, operates to monitor the generator performance in relation with the vehicle electrical and mechanical system. See, for instance, Becker et al., U.S. Pat. No. 6,184,661, incorporated herein in its entirety, where the control device operates to limit the generator output power in order to protect the engine from excessive generator torque, and Jabaji, U.S. Pat. No. 5,907,233, incorporated herein in its entirety, where the control device monitors the AC signal generated by the stator windings and, in the absence of the AC signal, removes the field coil current in order to protect the battery from excessive drain. Because the generator is an essential if not the only source of electrical power within the vehicle electrical system, a control device that purports to control the generator operation in relation to the vehicle's electrical and mechanical system must be able to sense the generator output current.
Generator output current can be obtained by different methods. Two widely used sensors for current measurement, known to skilled artisans, are the current shunt resistor and Hall Effect sensor. The former is typically used to measure currents in the order of 10's of Amperes while the latter is preferred when the current is in the order of 100's of Amperes due to the need to minimize power dissipation in the measurement device. The simpler more economic method is the current shunt resistor method which involves placing the shunt in the path of the output current and measuring the voltage across the shunt. The shunt must be sufficiently low in resistance to avoid significant alteration of the output current it is to measure. Additionally, temperature variation of the shunt must be taken into consideration when measuring the voltage across the shunt. This is because the shunt resistance varies with temperature. Such temperature variations are caused either by the ambient temperature variations or heat generated by resistive loss as current passes through the shunt.
Current shunt resistors are made up of different materials, depending on the application. They typically have two leads which are made up of copper or copper alloys, and an encapsulation which is made up of ceramic or silicon compounds. A current shunt resistor, incorporated in a generator in a vehicle, is exposed to high levels of shock and vibration which may cause the shunt to fail. Due to the brittle nature of the materials used in the construction of the shunt resistor, they are prone to fatigue failures. In particular, shunt resistors may develop cracks due to the shock and vibration. When a crack develops, the shunt resistor may become either completely severed or, alternatively, its resistance may become extremely high. In either event the shunt fails and generator output may cease.
A shunt resistor further introduces an external element to the generator assembly. Shunt resistors that can withstand high currents that are in the order of 100's of amperes are typically large in size. This is because any shunt resistor used in a generator must have a very low voltage drop to minimize the resistive power loss. Incorporating a large shunt resistor within a generator assembly makes the generator larger and heavier than it would otherwise be, which is undesirable as vehicle manufacturers seek lighter and smaller accessories.
An internal conductor inherent in the generator assembly and capable of carrying electrical current substantially proportional to the total generator output current may be advantageously utilized as a shunt resistor provided that the conductor shape is well controlled during the manufacturing process. This is because the resistance of the conductor is proportional to its shape. A typical generator comprises stator windings that produce the generator output current via a varying magnetic field. Multi-phase generators have multiple stator windings that are connected via Δ (delta) or Y arrangement, known to skilled artisans. Each phase carries a proportional amount of the total generator output current. For instance in a 3-phase generator, each phase carries approximately ⅓ of the total generator output current, assuming the phase windings are identical. In the manufacture of a typical generator, a conductor, such as a wire, is used to connect a phase to an output terminal. For DC generators, each phase is coupled to a pair of rectifying diodes to convert the AC output to a DC output. The conductor may be positioned between the phase and the output terminal for an AC generator, and between either, the phase winding and the corresponding diode pair, or between the diode pair and the output terminal for DC generators.
The conductor shape, i.e. cross section and length, are determined according to the generator output current rating and design. Most manufacturers designate a particular cross section or wire gage to be used for the generator wiring. The length of the conductor is designated by design, but may be trimmed during assembly. The trimming occurs because during assembly of a multi-component generator the conductor routing is not controlled with a high precision. However, if such routing is controlled, there will be no need to trim the conductor during assembly and the conductor length in the generator may be controlled with a high level of accuracy. Since, as mentioned before, the resistance of the conductor is directly proportional to its length, the conductor can serve as a shunt resistor whose electrical potential can be measured with a high level of precision. Furthermore, since such conductors are made up of stranded wires, they are extremely flexible and resistant to shock and vibration. Therefore, incorporating one or more such conductors in a generator makes accurate measurement of the total generator output current possible without the need for a conventional shunt or Hall effect device.
As mentioned above, generators produce electrical power via their phase windings. In a multi-phase generator, the total electrical power generated by the generator is the sum of the electrical power generated by the individual phase windings. Thus, the total generator output current may be measured by measuring the electrical potential across individual conductors and summing the result. However, as will be demonstrated below in the detailed description of the preferred embodiments, only one conductor coupled with a phase winding may be used to measure the total generator output current. This is possible by calibrating the conductor's electrical potential at various generator output current and correlating the result to the total generator output current.
Accurate measurement of the total generator electrical power must take into account the conductor's temperature variation. A direct measurement of the conductor temperature is possible by placing a temperature sensor in close proximity to the conductor. Where direct measurement of the conductor temperature is impractical, an indirect measurement can be achieved by measuring the temperature of certain other components and correlating between the components' temperatures and that of the conductor's. For instance, the temperature of the conductor can be accurately estimated by measuring the temperature of the generator's control device/voltage-regulator or the generator's field coil. In the latter case, a sensor capable of measuring the resistance variation of the field coil can be used to infer the temperature of the conductor.
A generator in a vehicle electrical system converts the vehicle's engine's mechanical power into electrical power. The generator provides the electrical power to electrical loads and batteries in the vehicle. A control device manages the electrical power distribution to the loads and batteries. The control device's primary task is to control the output power of the generator. This can be achieved by controlling the generator output current and voltage. Conventional generators, however, do not control the output power. They control the output voltage by simply maintaining it at a regulation voltage, hence their names, voltage regulators. For these generators, the output current is a function of the electrical current demand by the electrical loads and/or the batteries without any limitation other than the maximum available current at the corresponding rotational speed (RPM). Modern generators, such as those disclosed in Becker et al., control the output current in relation to other components in the vehicle, such as certain vehicle operating conditions or engine drive limitations. To control the output current or electric power, the control device must directly or indirectly measure the output current. A generator equipped with one or more conductors provides the generator's control device a simple, economical, and efficient way to directly measure the generator's output current without the need for additional sensors.
A generator's control of the output current can be a function of the generator's performance and those of other components within the vehicle electrical and mechanical system. For instance, a generator's output current may be limited or ceased based on the temperature of the generator's output terminal. An excessive temperature of the output terminal may be an indication of a loose cable connecting the generator to the battery. Other parameters, as discussed more thoroughly below, may be important in controlling the output voltage and/or output current. Such parameters include battery temperature, battery type, battery voltage, and the ratio between the RPMs of the engine and generator.
Modern vehicles monitor the electronics and electrical equipment in the vehicle electrical system to improve system performance. For instance, a vehicle electrical engine control device may monitor the vehicle engine operating conditions and manipulate the generator output power in relation to the operating conditions. A generator equipped with a control device that is capable of acquiring system information can complement such vehicle's electrical system and improve the vehicle's performance. For instance, a generator control device that can gather data from other components whose performance affect the generator itself can exchange the acquired data with the vehicle electrical system including the vehicle's computer network for a more efficient control. Additionally, a generator control device that can alter the generator's performance as a function of the acquired data can further assist the other components in the vehicle to perform their tasks more efficiently.
Although various systems have been proposed which touch upon some aspects of the above problems, they do not provide solutions to the existing limitations in providing a simple, economical, and efficient means to measure the total output current of a generator, and to control its output current in relation to other components in the electrical system. In all the various systems, an external sensor is used to measure the generator output current and in none of the proposed systems is the output current control as comprehensive as the present invention.
For example, the Antone patent, U.S. Pat. No. 5,724,932, discloses an alternating current control apparatus and method for glow plugs that controls the output current of an alternator, in relation to the current demand by the glow plugs, to improve the glow plugs longevity. The apparatus uses an external current sensor to measure the alternator output current. In Clark et al., U.S. Pat. No. 5,670,070, the disclosure describes a method and system for controlling the output current of a three-phase alternator used in a welding apparatus. The alternator output current is controlled in response to a desired fixed slope operating current/voltage characteristic curve. This invention involves utilizing an external shunt resistor to measure the alternator's output current. In Judge et al., U.S. Pat. No. 5,216,350, a method and system for controlling an alternator is disclosed. The control system includes an alternator, battery, and various electrical loads. The output current of the alternator is controlled when there is excessive current demand by the electrical loads. The control system uses an external current sensor to measure the alternator output current. The MacFarlane patent, U.S. Pat. No. 4,839,575, discloses a voltage regulator for an alternator that monitors and limits the alternator's output current. The output current is measured via a current level sensor, an external element with the disadvantages as discussed above. In all of these systems, the generator's output current is sensed via an external sensor whereas the generator of the present invention includes a process-controlled conductor that is part of conventional internal generator wiring and may be implemented in the ordinary course of manufacturing the generator. In addition, the control device of the present invention controls the generator output current in response to a comprehensive group of system components affecting the system performance.
Generators convert mechanical power into electrical power for use by electrical loads. For instance, in a vehicle electrical system a generator supplies electrical power to the vehicle electrical loads as well as the battery. Control of the electrical power generated by the generator is essential in the electrical system to ensure proper system performance. Accurate determination of the electrical power involves accurate determination of both the electrical current and voltage. Therefore, it is desirable to construct a generator, utilizing process-controlled conductors, that is capable of providing a means for measuring its total output current in a simple, economical, and efficient manner. It is further desirable to include a control device that is capable of measuring the total generator output current and limiting and/or ceasing the generator output power in response to the measured output current as well as a host of other parameters associated with the components within the electrical system.
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