Abstract:
Motors and method of operation thereof operable in a running mode wherein the motor operates at a constant speed, and operable in a park mode wherein the motor is dynamically parked. The motor is housed within a housing and includes a rotating park disk configured to cause the motor to dynamically park. A park wire electrically couples the park disk to a switch configured to selectively switch the motor between the running mode and the park mode, and a power wire electrically couples the park disk to a power source. The park disk is electrically isolated from the power source during operation of the motor in the running mode and the park wire is electrically connected to the power source through the park disk and the power wire during operation of the motor in the park mode.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part patent application of co-pending U.S. patent application Ser. No. 14/511,534, filed Oct. 10, 2014, which claims the benefit of U.S. Provisional Application No. 61/986,745, filed Nov. 19, 2013. The contents of these prior applications are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention generally relates to electric motors. More particularly, this invention relates to electric motors of types that are adapted to drive windshield wipers and incorporate a dynamic park capability. 
         [0003]    The motor vehicle industry utilizes electric motors to drive windshield wipers. In general, a windshield wiper system having a dynamic park function comprises a motor, a rotary-to-linear motion converter mechanism, windshield wipers, a switch for controlling the motor, and a park disk. An exemplary 24 volt direct current (DC) windshield wiper motor  10  as known in the art is represented in  FIG. 1 . 
         [0004]    As conventional in the art, the motor  10  may be controlled, for example, with a manual selector switch  17  ( FIGS. 10-12 ), to be operable in any one of three possible modes of operation: park, high speed, and low speed. The motor  10  incorporates a park disk  12  for what is known and referred to as dynamic parking which is a process of returning the windshield wipers to their original starting or ‘park’ positions when the motor  10  is turned off with the switch  17 . The park disk  12  is rotatably mounted within a gear head  13 , rotates as a result of engaging a worm gear  15  driven by a rotor (not shown) within an electric motor housing  11  of the motor  10 , and drives a rotary-to-linear motion converter mechanism functionally coupled to a windshield wiper (not shown). The park disk  12  is a circular disk-shaped component that includes a ground tab  14 , park section  16 , and battery positive section  18 .  FIG. 2  represents an interior portion of a gear housing plate  20  that is configured to be assembled to the gear head  13  for interaction with the park disk  12  of  FIG. 1 . The gear housing plate  20  has ground, park, and battery positive contacts  22 ,  24  and  26 , respectively, which interact with the ground tab  14 , park section  16 , and battery positive section  18 , respectively, of the park disk  12  as the park disk  12  rotates.  FIG. 3A  represents a diagram of the park disk  12  as assembled with three armatures corresponding to the ground, park, and battery positive contacts  22 ,  24  and  26 .  FIG. 10  is a wiring diagram representing a system and method of wiring the park disk  12  to the switch  17  and a battery  13 . As represented, a positive terminal (‘+’) of the battery  13  is connected to the switch  17  and a negative terminal (‘−’) of the battery  13  is connected directly to a contact  21  on the motor  10 . The high input wire  52 , low input wire  50 , and park wire  54  connect the switch  17  to contacts  21  on the motor  10 . The switch  17  is connected by a battery positive wire  52  to the battery positive contact  26  at the park disk  12 . In  FIG. 10 , the switch  17  is set to the park position (‘off’) thereby electrically connecting the park wire  54  to the low input wire  50 . In the figures, the position of the switch  17  is depicted by a solid arrow. The motor  10  is represented as being turned off and the park disk  12  is located in the park position. 
         [0005]    During operation, when the manual selector switch  17  (motor switch) is set to a low or high position (‘low’ or ‘high’), the motor  10  operates in low or high speed mode, respectively. Operation of the motor  10  consequently rotates the park disk  12  and, through the rotary-to-linear motion converter mechanism, moves the windshield wipers back and forth across the windshield both at low or high speed depending on the mode of operation of the motor  10 . While the motor  10  is running in low or high speed modes, the park disk  12  continuously rotates, with each full rotation corresponding to one complete swipe (across the windshield and back to the park position) of the windshield wipers. 
         [0006]      FIG. 11  represents the wiring diagram of  FIG. 10  when the switch  17  is set to the low position (‘low’) thereby connecting the low input wire  50  to the positive terminal on the battery  13 , and the motor  10  is operating in low speed mode. Current flows from a positive terminal on a battery  13  to the switch  17 , through the switch  17  to a low input wire  50 , through the low input wire  50  to the motor  10  (via contact  21 ), through the motor  10  to a battery negative wire  56  (via contact  21 ), and through the battery negative wire  56  to the negative terminal on the battery  13  (or ground). During this time, the high input wire  52  and the park wire  54  are open at the switch. The park disk  12  is represented as being in an exemplary transient operating position. It should be understood that the system operates in substantially the same manner when in high speed mode rather than low speed mode. When the switch  17  is set to the high position (‘high’), the high input wire  52  is connected to the positive terminal on the battery  13 , and the low input wire  50  and park wire  54  remain open. 
         [0007]    If the switch is moved to the park position (‘off’) while the motor  10  is operating in low or high speed mode, the park disk  12  enters the park mode and continues to rotate, for example, through the transient position shown in  FIG. 3A , until it reaches a predetermined park position, represented in  FIG. 3B .  FIG. 12  represents the wiring diagram of  FIG. 11  when the switch is set from the low position (‘low’) to the park position (‘off’) and the motor  10  is operating in park mode. The switch  17  connects the park wire  54  and the low input wire  50  such that current flows from the positive terminal on the battery  13  to the switch  17 , through the switch  17  to a battery positive wire  58 , through the battery positive wire  58  to the park disk  12  (via the contact  21  and the battery positive contact  26 ), through the park disk  12  to a park wire  54  (via the park contact  24 ), through the park wire  54  to the switch  17 , through the switch  17  to the low input wire  50 , through the low input wire  50  to the motor  10  (via contact  21 ), through the motor  10  to the battery negative wire  56  (via contact  21 ), and through the battery negative wire  56  to the negative terminal on the battery  13  (or ground). During this time, the low input wire  50  and the high input wire  52  are not directly connected to the positive terminal of the battery  13  within the switch  17 , rather power is provided through the park wire  54 . If the park disk  12  is in a transient operating position, as represented in  FIG. 12 , the motor will continue to operate at low speed and until the park disk rotates to the park position, represented in  FIGS. 3B and 10 . 
         [0008]    As represented in  FIG. 3B , the park position of the motor  10  is reached when the battery positive contact  26  is suspended over an opening  19  in the park disk  12  and therefore is not electrically connected to the battery positive section  18 , the park contact  24  is electrically connected to the park section  16 , and the ground contact  22  is electrically connected to the ground tab  14 . Once the park disk  12  reaches the park position, the circuit represented in  FIG. 12  is opened as a result of the battery positive contact  26  no longer being in contact with the battery positive section  18  and the motor  10  functions as a load generator developing a torque that rapidly stops the motor  10  and thereby stops the windshield wipers in their park position. The dynamic park function ensures that the windshield wipers will always return to their park position regardless of their current position when the switch  17  is turned to ‘off.’ 
         [0009]    In normal operation of the motor  10  in either high or low speed modes, the park disk  12  continuously rotates and makes contact to both +24 volts (i.e., battery positive contact  26  electrically connected battery positive section  18 ) and ground (i.e., ground contact  22  electrically connected to ground tab  14 ) once during each revolution of the park disk  12  thereby sequentially creating a negative pulse and a positive pulse of conducted and radiated electromagnetic emissions. On dynamic park motors such as the windshield wiper motor  10  of  FIG. 1 , these pulses occur when the voltage goes from +24 volts to ground (0 volts) and then back to +24 volts. For example,  FIG. 4A  represents a measurement of pulses taken from a conventional dynamic park motor, such as the motor  10  of  FIG. 1 , as the park disk  12  rotates. These pulses may travel through wires exiting the motor  10 , for example, high input wire  52 , low input wire  50 , park wire  54 , battery positive wire  58 , and battery negative wire  56 , and radiate therefrom causing electro-magnetic interference (EMI) during each revolution of the park disk  12 . 
         [0010]    Increasingly, electronic devices are installed in or used around motor vehicles which are sensitive to the EMI generated by electric motors. In certain cases, EMI can pose a security risk. For example, the EMI generated by the windshield wiper motor  10  of  FIG. 1  can be detected and traced to a military vehicle in which the motor  10  is installed, indicated by a repeating signal on radar which reveals the location and direction of the vehicle. Such military vehicles must meet strict government EMI control regulations, such as U.S. military standard MIL-STD-461F. Consequently, there is a need for systems and methods suitable for reducing or eliminating this pulse of electromagnetic emissions. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0011]    The present invention provides electrical motors and methods of operation thereof suitable for reducing or eliminating a pulse of electromagnetic emissions produced by the electric motors. 
         [0012]    According to a first aspect of the invention, an electrical motor is operable in at least one running mode wherein the electrical motor operates at a constant speed, and is operable in a park mode wherein the electrical motor is dynamically parked. The electrical motor is housed within a housing and includes a rotating park disk configured to cause the electrical motor to dynamically park. A park wire electrically couples the park disk to a motor switch. The motor switch is configured to selectively switch the electrical motor between the at least one running mode and the park mode, and a power wire electrically couples the park disk to a power source. Portions of the park wire and the power wire exit the housing of the electrical motor so as to be disposed externally of the housing. The park disk is electrically isolated from the power source during operation of the electrical motor in the at least one running mode and the park wire is electrically connected to the power source through the park disk and the power wire during operation of the electrical motor in the park mode. The park wire provides power to the electrical motor in the park mode such that the electrical motor dynamically parks. 
         [0013]    According to a second aspect of the invention, an electrical motor is operable in at least one running mode wherein the electrical motor operates at a constant speed, and is operable in a park mode wherein the electrical motor is dynamically parked. The electrical motor is housed within a housing and includes a rotating park disk functionally coupled to a ground contact, a park contact, and a battery positive contact. The park disk is configured to cause the electrical motor to dynamically park by operating the electrical motor in the at least one running mode until the park disk rotates to a park position such that the park disk is electrically coupled to the ground contact and the park contact and not electrically coupled to the battery positive contact. A park wire electrically couples the park contact to a motor switch configured to selectively switch the electrical motor between the at least one running mode and the park mode, and a battery positive wire electrically couples the battery positive contact to a positive terminal on a battery. Portions of the park wire and the battery positive wire exit the housing of the electrical motor so as to be disposed externally of the housing. The park disk is electrically isolated from the power source during operation of the electrical motor in the at least one running mode and the park wire is electrically connected to the power source through the park disk and the battery positive wire during operation of the electrical motor in the park mode until the park disk rotates to a park position, the park wire providing power to the electrical motor in the park mode such that the electrical motor dynamically parks. 
         [0014]    According to a third aspect of the invention, a method of operating an electrical motor that is operable in at least one running mode wherein the electrical motor operates at a constant speed and that is operable in a park mode wherein the electrical motor is dynamically parked. The electrical motor is housed in a housing and includes a rotating park disk configured to cause the electrical motor to dynamically park. A park wire electrically couples the park disk to a motor switch configured to selectively switch the electrical motor between the at least one running mode and the park mode, and a power wire electrically couples the park disk to a power source. Portions of the park wire and the power wire exit the housing of the electrical motor so as to be disposed externally of the housing. The method includes electrically isolating the park disk from the power source during operation of the electrical motor in the at least one running mode, and electrically connecting the park wire to the power source through the park disk and the power wire during operation of the electrical motor in the park mode. 
         [0015]    A technical effect of the invention is the ability to greatly reduce or eliminate EMI produced by electric motors, for example, an electric motor operating to drive windshield wipers having a park disk. Specifically, by electrically isolating the power wire from the park disk during operation of the motor in a running mode, electromagnetic emissions may be, and preferably are, reduced, captured, and suppressed before the emissions can conduct through and radiate from wires which are exposed to an exterior of the motor. Electromagnet emissions can potentially be reduced to an extent capable of protecting electronic devices that might otherwise be sensitive to EMI, and/or avoid detection and tracing of the motor or a vehicle in which the motor is installed. 
         [0016]    Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  represents a windshield wiper motor of a type known in the art wherein the motor is shown partially disassembled to expose a park disk for illustrative purposes. 
           [0018]      FIG. 2  represents an interior portion of a gear housing plate having ground, park, and battery positive contacts adapted for interaction with the park disk of  FIG. 1 . 
           [0019]      FIGS. 3A and 3B  are diagrams representing a park disk of an electric motor and corresponding ground, park, and battery positive contacts of the types depicted in  FIGS. 1 and 2 , wherein  FIG. 3A  represents the park disk in a transient operating position, and  FIG. 3B  represents the park disk in a park position. 
           [0020]      FIGS. 4A and 4B  are graphs representing measurements of electromagnetic emissions from, respectively, a conventional electrical motor of a type known in the art and an electrical motor in accordance with an aspect of the invention. 
           [0021]      FIG. 5  represents a printed circuit board having components thereon suitable for suppressing EMI produced from an electrical motor in accordance with an aspect of the invention. 
           [0022]      FIG. 6  represents an exterior portion of a gear housing plate of an electrical motor of a type known in the art. 
           [0023]      FIG. 7  represents the printed circuit board of  FIG. 5  as installed on the exterior portion of the gear housing plate of  FIG. 6  in accordance with an aspect of the invention. 
           [0024]      FIGS. 8 and 9  are wiring diagrams representing circuits suitable for suppressing the EMI of an electric motor in accordance with aspects of the invention. 
           [0025]      FIGS. 10 through 12  are exemplary wiring diagrams of a windshield wiper system comprising a windshield wiper motor of the types depicted in  FIGS. 1 and 2 .  FIG. 10  represents the switch in the park position and the park disk in the park position.  FIG. 11  represents the switch in the low position and the motor operating in low speed mode.  FIG. 12  represents the switch in the park position and the motor operating in park mode. 
           [0026]      FIGS. 13 through 15  are wiring diagrams of a windshield wiper system in accordance with certain aspects of the present invention.  FIG. 13  represents the switch in the park position and the park disk in the park position.  FIG. 14  represents the switch in the low position and the motor operating in low speed mode.  FIG. 15  represents the switch in the park position and the motor operating in park mode. 
           [0027]      FIG. 16  is a wiring diagram of a windshield wiper system comprising the circuit of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The present invention relates to systems and methods suitable for reducing or eliminating electromagnetic emissions produced by an electric motor, particular but nonlimiting examples of which include dynamic park electric motors used for driving windshield wipers on motor vehicles. The systems described hereinafter reduce the electromagnetic emissions produced by the electric motors during operation in a running mode by isolating a power wire from the park disk with a relay or a functional equivalent thereof. The emissions are captured and suppressed before they can conduct through and radiate from the wires to the motor switch and the surrounding environment, as represented in  FIG. 4B . These systems may be installed during manufacture of the motors or may be installed on motors after manufacture, and provide reduced electromagnetic emissions within industry standards, such as the U.S. military standard MIL-STD-461F. The systems can suppress the emissions with a circuit of components wired directly into a motor&#39;s electrical system, and preferably (though not required) installed externally to the motor without altering or changing any physical characteristics of the motor. This promotes a cost effective solution on electric motors where EMI suppression is needed, a notable but nonlimiting example of which is military vehicles. In the drawings, identical reference numerals denote the same or functionally equivalent elements throughout the various views. 
         [0029]      FIG. 5  represents a system including a printed circuit board  30  having components thereon suitable for suppressing electromagnetic emissions produced from an electric motor, such as the motor  10  of  FIG. 1 , in accordance with an aspect of the invention.  FIG. 6  represents an exterior portion of the gear housing plate  20  of  FIG. 2 , which as previously discussed is adapted for assembly with the +24 volt DC electric motor  10  of  FIG. 1 .  FIG. 7  represents the printed circuit board  30  of  FIG. 5  installed on the exterior portion of the gear housing plate  20  of  FIG. 6  in accordance with an aspect of the invention. The printed circuit board  30  has located thereon bypass capacitors  32 , an RC filter  34  (comprising a resistor and capacitor in parallel), an isolation relay  36 , inductors  38 , a Faraday cage  40 , an EMI filter PC board  42  including EMI filter caps  44 , and at least one filter capacitor  46 . The bypass capacitors  32 , RC filter  34 , isolation relay  36 , and inductors  38  are preferably electrically connected according to the wiring diagram represented in  FIG. 8 . It should be understood that the components and wiring of the system disclosed in  FIGS. 5 and 8  represent a single embodiment of the invention as directed towards the motor  10 , and that other functionally equivalent components and wiring may be used for the motor  10  or other motors. For example, the number and size of the bypass capacitors  32  used in the system may vary depending on the specific motor to which the system is coupled or the application for which it is being used. 
         [0030]    As previously stated, during operation of the motor  10  at least one pulse of conducted and radiated electromagnetic emissions may be produced with every complete rotation of the park disk  12 . Such pulses may travel through wires that are exposed to an exterior of the motor  10  (for example, low and high input wires  50  and  52 ) that connect the motor switch (“SWITCH” in  FIG. 8 ) to the motor  10 , and may then radiate from the wires and potentially cause EMI.  FIG. 8  represents the high input wire  52  and the low input wire  50  traveling from the motor  10  through the optional Faraday cage  40 , through a ferrite bead  48 , through the inductors  38 , and on to the motor switch. Preferably, the system includes the Faraday cage  40 , EMI filter PC board  42 , EMI filter caps  44 , and filter capacitor  46 . If included, the high input wire  52  and the low input wire  50  first travel into the Faraday cage  40  that houses the filter capacitors  46  and through the capacitors  46 . The Faraday cage  40 , capacitors  46 , and any other components within the cage  40  act to suppress electromagnetic emissions traveling on the high and low input wires  52  and  50  during operation of the motor  10 . The high and low input wires  52  and  50  may then travel out of the Faraday cage  40  and through the EMI filter PC board  42  having EMI filter caps  44  before continuing on to the ferrite bead  48  represented in  FIG. 8 . These components preferably capture, reduce, and/or eliminate emissions before they can conduct through and radiate from the wires  50  and  52 . 
         [0031]    Conventionally, the park disk  12  would be connected to power at any point in its rotation when the battery positive contact  26  is electrically connected battery positive section  18  during operation of the motor  10 , for example, when the park disk  12  is in the position depicted in  FIG. 3A . According to an aspect of the present invention, in order to prevent electromagnetic emissions from occurring and subsequently traveling through wires exposed to the exterior of the motor  10  while the motor  10  is operating, the park disk  12  is entirely electrically isolated from the power (battery positive wire  58 ) during operation of the motor  10  in high and low speed modes with the isolation relay  36 , which may be, for example, an electromechanical relay or an equivalent thereof. The isolation relay  36  is configured to be normally open during operation of the motor  10  in high and low speed modes thereby electrically isolating the park disk  12  from power. Since the park disk  12  is isolated from power during operation in high and low speed modes, park disk  12  will not repeatedly transition from +24 volts to ground (0 volts) and then back to +24 volts as it otherwise would with every rotation if power was connected, and therefore electromagnetic pulses will not occur. When the motor switch is moved to the park position (‘off’), the isolation relay  36  is energized, providing power to the park disk  12  allowing the motor to operate in park mode and dynamically park.  FIG. 13  is a wiring diagram representing a nonlimiting system and method of wiring the park disk  12 , the switch  17 , and the battery  13  in accordance with certain aspects of the invention.  FIG. 13  is similar to the wiring diagram of  FIG. 10 ; however, the isolation relay  36  has been located on the battery positive wire  58  to electrically isolate the park disk  12  from the positive terminal of the battery  13  during operation of the motor  12  in a running mode (e.g., high or low). In  FIG. 13 , the switch  17  is set to the park position (‘off’) thereby electrically connecting the park wire  54  to the low input wire  50 . The motor  10  is represented as being turned off and the park disk  12  is located in the park position. 
         [0032]    In view of the above, the motor  10  functionally coupled to the system operates as follows. When the motor  10  is off and the motor switch is set to the park position (‘off’), the park disk  12  is in the dynamic park position, that is, the ground contact  22  is in contact with the ground tab  14  of the park disk  12  (for example, as represented in  FIG. 3B ). When the motor switch is set to either the low or high position (‘low’ or ‘high’), the motor  10  begins running in low or high speed mode, respectively. While the motor  10  is running in low speed mode, the high input wire is open. Conversely, when the motor  10  is running in high speed mode, the low input wire is open. Regardless, when operating in either low or high speed modes, electrical current flows between the switch  17  and the motor  10  through the corresponding high or low input wire  52  or  50 . For example,  FIG. 14  represents the system of  FIG. 13  when the switch is set to the low position (‘low’) thereby electrically connecting the positive terminal of the battery  13  to the low input wire  50 , and the motor  10  is operating in low speed mode. As represented, current flows from a positive terminal on the battery  13  to the switch  17 , through the switch  17  to the low input wire  50 , through the low input wire  50  to the motor  10  (via contact  21 ), through the motor  10  to the battery negative wire  56  (via contact  21 ), and through the battery negative wire  56  to the negative terminal on the battery  13  (or ground). During this time, the high input wire  52  and the park wire  54  are open at the switch, and the isolation relay  36  is open. The park disk  12  is represented as being in an exemplary transient operating position. It should be understood that the system operates in substantially the same manner when in high speed mode rather than low speed mode. When the switch  17  is set to the high position (‘high’), the high input wire  52  is connected to the positive terminal of the battery  13 , and the low input wire  50  and park wire  54  remain open. 
         [0033]    When the motor switch  17  is set back to the park position (‘off’) from either the high position (‘high’) or the low position (‘low’), the high input wire  52  is open and the low input wire  50  is electrically connected to the park wire  54  on the motor switch. At this point, the isolation relay  36  is energized and thereby connects the battery positive wire  58  to the park disk  12  through the common and normally open contacts of the isolation relay  36 , causing the motor  10  to continue to operate in park mode at low speed. For example,  FIG. 15  represents the system of  FIG. 13  when the switch  17  is set from the low position (‘low’) to the park position (‘off’) thereby electrically connecting the positive terminal of the battery  13  to the low input wire  50 , and the motor  10  is operating in park mode. The isolation relay  36  is energized, closes, and connects the battery positive wire  58  to the park disk  12 . Since the park disk  12  is depicted as being in a transient operating position, the motor  10  continues to operate at low speed until the park disk  12  rotates to the park position. While operating in park mode, current flows from the positive terminal on the battery  13  to the switch  17 , through the switch  17  to the battery positive wire  58 , through the battery positive wire  58  to the park disk  12  (via the battery positive contact  26 ), through the park disk  12  to the park wire  54  (via the park contact  24 ), through the park wire  54  to the switch  17 , through the switch  17  to the low input wire  50 , through the low input wire  50  to the motor  10  (via contact  21 ), through the motor  10  to the battery negative wire  56  (via contact  21 ), and through the battery negative wire  56  to the negative terminal on the battery  13  (or ground). Once the park disk  12  rotates to the park position, the circuit represented in  FIG. 15  is opened (battery positive contact  26  is over the opening  19 ) and the isolation relay  36  is de-energized, thereby removing power from the park disk  12  and causing the motor  10  to cease operation. 
         [0034]      FIG. 16  is a wiring diagram representing another nonlimiting system and method of wiring the park disk  12 , the switch  17 , and the battery  13  in accordance with certain aspects of the invention, and includes the circuit represented in  FIG. 8 . Despite having additional components for emission reduction, the isolation relay  36  is still located on the battery positive wire  58  to electrically isolate the park disk  12  from the positive terminal of the battery  13  during operation of the motor  12  in a running mode. As such, the system of  FIG. 16  operates in substantially the same manner as the system of  FIGS. 13 through 15  in regards to the dynamic parking function and therefore will not be discussed further herein. In  FIG. 16 , the switch  17  is set to the park position (‘off’) thereby electrically connecting the park wire  54  to the low input wire  50 . The motor  10  is represented as being turned off and the park disk  12  is located in the park position. 
         [0035]    According to another aspect of the invention, the isolation relay  36  of  FIGS. 8 through 16  may be replaced with a solid-state relay (switch)  60 , for example, as represented in a wiring diagram of  FIG. 9 . The solid-state relay  60  is represented as an optocoupled solid-state relay comprising an optocoupler (opto-isolated triac)  62 .  FIG. 9  shows RC filters  34  that correspond to the RC filters  34  of  FIGS. 5, 7 and 8 , and therefore each comprise a resistor and capacitor in parallel with each other. It may be beneficial to also include a metal oxide varistor (MOV) as a surge protector as represented in  FIG. 9 .  FIG. 9  further shows current limiting resistors  66  that limit a trigger current at the output of the optocoupler  62  and gate (TRIAC)  68  of the solid-state relay  60 . When the motor  10  is operating in either low or high speed mode, only a nominal current, for example, less than five milliamperes, will be flowing through the resistors in the RC filters  34 . During this time, there is no current flow through the rest of the solid-state relay  60 . 
         [0036]    When the switch  17  is set from either the high or low position to the park position (‘off’), the park wire  54  is electrically connected to the low input wire  50  at the switch  17 . This provides power to the input of the optocoupler  62 , coupling the TRIAC output of the optocoupler  62  (signal driver) and turning the solid-state relay  60  on. Electrical current then flows from power at the switch  17  through the battery positive wire  58  to the park disk  12  of the motor  10 . During this time, there is a nominal current, for example, less than five milliamperes, flowing in the resistors in the RC filters  34 , and there is no current flow through the rest of the solid-state relay  60 . 
         [0037]    Windshield wiper systems as described herein produce significantly reduced levels of electromagnetic emissions relative to dynamic parking motors which have power connected to the park disk  12  during operation. Investigation leading to the present invention determined that by electrically isolating park disk  12  from the power during operation of the motor  10  in running modes (e.g., high and low speed modes), emissions of the motor  10  can be near or below industry standards, such as the U.S. military standard MIL-STD-461F. Notably, windshield wiper systems that are wired in the manner represented in  FIGS. 13 through 16  will continue to produce an electromagnetic pulse when the motor  10  dynamically parks, that is, when the isolation relay  36  is energized and the power is connected to the park disk  12  and then subsequently disconnected when the park disk  12  reaches to the park position. However, in the example of military vehicle safety, it is believed that this would still reduce the likelihood of a military vehicle being tracked by the EMI generated by the motor  10 . In particular, the emission could only be detected as a single pulse rather than a repeating signal and therefore only provide a momentary location without indicating a direction of the vehicle. 
         [0038]    While the invention has been described in terms of specific embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical location of the components on the printed circuit board  30  could differ from that shown, functionally equivalent components other than those noted could be used, and the number and size of components used could differ. Therefore, the scope of the invention is to be limited only by the following claims.