FIELD OF THE INVENTION Methods and apparatus of the present invention are related to arc protection in relays for driving motors, and in particular to arc protection in wiper motor relay switches.

BACKGROUND OF THE INVENTION In some industrial applications, mechanical relays or switches are used for switching power to a motor to drive the motor (e.g., on or off). In such technology, the motor is typically supplied with a direct current to power the motor, and a mechanical switch is used to implement the switching. A mechanical switch may be used, for example, because typical semiconductor switches may be more expensive than mechanical switches when used to handle the current levels needed for the motor. One area of such technology is in the field of automotive applications, such as wiper systems for cars or other automotive vehicles. A known drawback of conventional motor systems, such as wiper motors, is that an arc (e.g., a Townsend arc) can occur when the mechanical relay is switched from one state to another while the switch is in an open state. Such arcs can create damage on the relay contacts and can undesirably affect the operation of other electrical systems. For example, the arc can be audibly heard over a car's radio system when it is sparked during the switching of the relay. Thus, it is desired to provide improved circuitry that minimizes or avoids some or all of these drawbacks.

SUMMARY OF THE INVENTION In accordance with the principles of the present invention, methods and apparatus are provided to prevent or minimizing the occurrence or the magnitude of unwanted arcs that may occur when a mechanical arm of a switch moves away from a contact. The switch can be arranged in a circuit to supply power to a motor by connecting the motor to a power supply such as a battery. For example, circuitry can be added to, across, or in conjunction with the switch in a circuit to provide such arc protection. A capacitor, transient voltage suppressor, diodes, and resistors can be components of such circuitry. The capacitor and transient voltage suppressor can be configured in parallel and connected across the arm and a contact (e.g., the "live" contact) of the switch. The capacitor and suppressor can also be configured to be in series with the motor. A resistor and diode arranged in parallel can also be configured in series with the motor and the suppressor. In operation, the circuitry can be configured based on the inductance of the wiring and any components between the switch and a power source, the inductance of the wiring and any components leading to the motor, and the characteristics of the transient voltage suppresser to drop the current flow through the motor when the switch arm is moved away from a "live" contact that connected the motor to a power supply. The current flow drops at rate that permits the current flowing through the switch to drop to zero before the switch is closed or shortly thereafter. The circuitry is also configured to provide a current path away from the switch when a switch arm moves away from a "live" contact.

BRIEF DESCRIPTION OF THE DRAWINGS Further features of the invention, its nature, and various advantages will be more apparent from the following detailed description, taken in conjunction with the accompanying drawings in which like reference characters refer to like parts throughout, and in which: FIG. 1 is a circuit diagram of an illustrative circuit that provides mechanical relay arc protection in accordance with one embodiment of the present invention; and FIG. 2 is a circuit diagram of an illustrative circuit that provide arc protection against for a mechanical relay that drives three motors in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Apparatus and methods can be provided that protect against the sparking of arcs by minimizing or avoiding such arcs when a relay is switching from one state to another. The protection can be provided while minimizing or avoiding undesirable levels of electromagnetic emission or radiation. Circuitry can be configured to provide for such protection and to provide other optional but preferred advantages, such to allow electromagnetic braking of the motor in the circuit when the relay is in an off-state. Circuitry such as a resistor-capacitor-diode network may be used to provide such advantages. One example of a circuit that includes such arc protection according to one embodiment of the invention is illustrated in FIG. 1. In FIG. 1, battery power source 10 (e.g., a car battery) is the power supply for a wiper motor (e.g., a wiper motor of a car wiper system). In the circuitry, Vm 20 is representative of the wiper motor and Lm 22 is representative of system inductance in the path to the motor 20. Inductor L is representative of the system inductance (e.g., the inductance in the path between power source 10 and relay 14. The circuitry also includes relay 14, capacitor 16, transient voltage suppressor ("TVS") 18, resistor 24, diode 26 and diode 28. In operation, when relay 14 is in the RUN position, power is supplied to the wiper motor Vm 20 to, for example, run the wiper blades of a car. When a control signal received to turn off the motor, relay 14 is activated to switch to the PARK position. In conventional relay systems, arcs can occur between the relay and the relay contacts when the relay arm is in between the two contacts during switching. Arcs can be eliminated or minimized with the use of, e.g., capacitor 16, TVS 28, resistor 24, diode 26 and diode 28. During the period in which relay 14 is "open" (i.e., in between the RUN and PARK states), capacitor 16 can draw current from the path of inductor 12. The charging of capacitor 16 may be of a very short duration, such as on the order of 1 μs. The charging of capacitor 16 reduces or eliminates the flow of current in the path to relay 14 when relay 14 is opened, which in turn minimizes or prevents an arc from forming. TVS 18 is arranged in parallel with capacitor 16. TVS 18 is configured to minimize, or preferably suppress, voltage levels below a specified level (e.g., 60 Volts, 100 Volts, etc.) across capacitor 16. TVS 18 can inhibit or prevent the voltage across capacitor 16 from reaching above dielectric breakdown. In this illustrated embodiment, during the period in which relay 14 is open, capacitor 16 can be charged followed by TVS 18 being charged. Once TVS 18 is charged to a configured level, such as to build a sufficiently high voltage, TVS 18 starts to conduct when the configured level is reached. In that state, TVS 18 will have the characteristic of a voltage source having a polarity opposite to power source 10. Thus, TVS 18 will cause a negative current slope and thus, cause the current through the motor path to drop. The characteristic of TVS 18 can be selected to control the drop off rate of the current flowing through motor 20. As such, capacitor 16 and TVS 18 can be used to protect against (i.e., inhibit or prevent) arcs and to drop the current flowing to motor 20 to zero or substantially to zero. Typically, the duration of charging of charging capacitor 16 will be much shorter than the activation of TVS 18 to conduct a current in the negative direction. In comparison, mechanical relay will typically take longer to change states than TVS 18 to conduct. This is not, however, always the case. The current drop off rate directly relates to the electromagnetic characteristics of the circuitry. For example, if the circuitry is configured to have a motor current fall time of 1 μs, the circuitry could for example generate radiation in the 1 Mega Hertz range, which would likely be unsatisfactory. If the rate was set to 100 μs, however, the generated radiation could for example be about 10 kilo Hertz, which can be considered to be an insignificant increase in electromagnetic radiation in accordance with one embodiment of the invention. In implementing this feature, inductor 22 and TVS 18 are used in determining the rate of drop off and in turn, to assist in filtering radiation that could be generated from a rapid current drop. If relay 14 reaches the closed state after the current flowing to motor 20 drops to zero, the connection of relay 14 and the voltage across diode 28 will cause a short across motor 20. This will allow electromagnetic braking to occur to dissipate motor energy generated from the spinning of the mechanical motor (e.g., a motor that includes components such as a wiper arm). If the current flowing to motor 20 does not drop to zero by the time that relay 14 is closed, diode 28 will not start to conduct (because of a negative bias on diode 28) until the motor current falls to zero. In that situation, when the current flowing to motor 20 drops to zero through the use of TVS 18, diode 28 will start to conduct and draw current through that path (through the diode). At that time, electromagnetic braking starts. Accordingly, the function of diode 28 is to provide motor 20 and TVS 18 enough time to discharge inductance of inductor 22. When relay 14 is returned to the RUN position, resistor 24 can be configured to function to discharge capacitor 16. The capacitor is discharged through resistor 24 so that the capacitor 16 starts at zero voltage or substantially zero voltage when relay 14 is opened again. Examples of circuit component characteristics are as follows: resistor 24 can have a resistance in the range of about 100 to a few kilo-Ohms, capacitor 16 can have a capacitance in the range of about 0.1 μF to 1 μF, TVS 18 may be a 60 Volt - 1 Watt TVS. Other characteristics may also be implemented in accordance with the invention described herein. FIG. 2 illustrates another example of an embodiment that provides circuit protection that includes simplified circuitry for use with multiple motors. As shown, the circuitry includes a resistor-diode pair for each motor in the circuit, which is a similar structure to the circuit of FIG. 1. In FIG 2., a single capacitor and a single TVS is implemented. The circuit in FIG. 2 operates with respect to arc protection or minimization in the same way as the circuit of FIG. 1 with some exceptions. When relay 34 is in the RUN position, capacitor 30 is not discharged to a zero charge as in the circuit of FIG. 1. When relay 34 is opened, capacitor 30 will be able to protect against an arc or voltage spike that rises above the existing charge of capacitor 30, which will likely be the voltage level of power source 36. Thus, the circuitry provides protection against some arcs by minimizing or avoiding the arcs. If desired, the circuit of FIG. 1 may also be modified to be implemented in this way. Thus, arc protection can be provided that minimizes, inhibits, or prevents one or more arcs from being generated when a mechanical relay is switching from an ON state to another state. The protection can be particularly suitable for inhibiting or preventing arcs in systems in which motors (e.g., car motor wipers) are driven by a mechanical switch. Other advantages can also be provided by such circuitry, systems, methods, apparatus, as noted herein. One advantage of the present invention is that motor current fall time can be limited by the voltage across TVS 18 and the total inductance of L 12 and Lm 22: (VWs/(L12 + Lm22) = Δlm/Δt). With this arrangement and appropriate configuration of values of the given equation to control the rate of the current fall time, the conductive emission spectrum of this circuitry can be configured to be at a frequency at or below about 1OkHz. Such a low emissions solution can allow for the circuitry to easily comply with EMC requirements below 150kHz (typical automotive radiated emission requirement). In FIGS. 1 and 2, specific circuit components, types of circuit components, and circuit arrangements are shown. Embodiments of the present invention are not limited to these specific circuit components, types of circuit components, or circuit arrangement. Components, types of circuit components, or circuits arrangements that provide the same or substantially the same functionality may also be implemented in accordance with the principles of the present invention. The term "about," as used herein, should generally be understood to refer to both numbers in a range of numerals. Moreover, all numerical ranges herein should be understood to include each whole integer within the range. It should be understood that the terms "capacitor," "transient voltage suppressor," and "diode," for example, each include a single electronic device or an arrangement of multiple devices that together provide the intended effect of a capacitor, voltage suppressor, or diode, respectively. Although preferred embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description of the Preferred Embodiments, it will be understood that the invention is not limited to the embodiments disclosed but is capable of numerous rearrangements and modifications of parts and elements without departing from the spirit of the invention. It will be understood that the details of every design and embodiment may be slightly different or modified by one of ordinary skill in the art without departing from the systems, apparatus, and methods taught by the present invention.