Abstract:
A time delay relay includes a coil having a longitudinal axis therethrough and an armature proximate an end of the coil. The armature is movable between an energized position and a de-energized position. A tube is positioned within the coil. The tube has a longitudinal axis that is substantially coincident with the axis of the coil. A metallic core is disposed within the tube. The core is movable along the longitudinal axis of the tube in response to a magnetic field in the coil to induce movement of the armature to the energized position. A time delay occurs between the onset of the presence of the magnetic field and the movement of the armature to the energized position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. application Ser. No. 11/454,217, filed Jun. 17, 2006, and entitled “Time Delay Relay”, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates generally to electromagnetic relays, and more specifically, to a relay having a time delay in the actuation of the relay.  
         [0003]     A typical electromagnetic relay includes a contact mounted on an armature that is held in an open position by a spring. A coil wound core attracts the armature to the core when sufficient current is passed through the coil to energize the core to overcome the spring and attract the armature to the core.  
         [0004]     In some applications, it may be desirable to have a time delay in the actuation of a relay. For instance, in the case of an electric motor, such as in a hand held power tool, it may be advantageous to have a time delay before full power is applied to the motor. As an example, a time delay relay may be used in parallel with a current limiting resistor. The current limiting resistor limits the current to a motor when the motor is switched on providing a soft start. After a time delay, the relay shorts out the resistor making full power available to the motor.  
         [0005]     In a typical time delay relay, the time delay is achieved electronically, such as through the addition of capacitor delay circuitry, a time delay integrated circuit, or the like. Such relays, however, have various shortcomings. The electronics added to provide the time delay function increases both the cost and complexity of the relay. In addition, the size of the relay may also be increased.  
         [0006]     A need remains for a time delay relay that is simply constructed and that can be economically produced. Further, a need remains for a time delay relay that will fit in the packages of current relays that do not include a time delay.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0007]     In one aspect, a time delay relay is provided. The relay includes a coil having a longitudinal axis therethrough and an armature proximate an end of the coil. The armature is movable between an energized position and a de-energized position. A tube is positioned within the coil. The tube has a longitudinal axis that is substantially coincident with the axis of the coil. A metallic core is disposed within the tube. The core is movable along the longitudinal axis of the tube in response to a magnetic field in the coil to induce movement of the armature to the energized position. A time delay occurs between the onset of the presence of the magnetic field and the movement of the armature to the energized position.  
         [0008]     Optionally, the delay relay also includes a yoke and a biasing member between the yoke and the armature. The biasing member biases the armature toward the de-energized position. A movable contact is mounted on the biasing member, and the coil is wound about a bobbin having a fixed contact mounted thereon. The core is movable within the tube between an energized position and a de-energized position. The tube includes a biasing element that biases the core toward the de-energized position. The tube is closed and is filled with a hydraulic fluid.  
         [0009]     In another aspect, a time delay relay is provided that includes a coil having a longitudinal axis therethrough and an armature proximate an end of the coil. The armature is movable between an energized position and a de-energized position. A tube is positioned within the coil. The tube has a longitudinal axis that is substantially coincident with the axis of the coil. A metallic core is disposed within the tube. The core is movable along the longitudinal axis of the tube in response to a magnetic field in the coil to induce movement of the armature to the energized position after a time delay. The time delay is mechanically determined by the time required for the core to move from a de-energized position wherein the core is not centered within the coil to an energized position wherein the core is substantially centered within the coil. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a cross-sectional view of a known electromagnetic relay.  
         [0011]      FIG. 2  is a perspective view of a time delay relay formed in accordance with an exemplary embodiment of the present invention.  
         [0012]      FIG. 3  is a cross-sectional view of the relay shown in  FIG. 2  taken along the line  3 - 3  shown in a de-energized state.  
         [0013]      FIG. 4  is a cross-sectional view of the relay shown in  FIG. 2  taken along the line  3 - 3  and shown in an energized state.  
         [0014]      FIG. 5  is a cross-sectional view of a relay formed in accordance with an alternative embodiment of the present invention.  
         [0015]      FIG. 6  is a cross-sectional view of the relay shown in  FIG. 5  in an energized state. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  is a cross-sectional view of a known electromagnetic relay  100  having no actuation time delay. Relay  100  includes a yoke  102 , a coil  104  that surrounds a core  106 , and a movable armature  108 . Relay  100  includes a stationary contact  110  and a movable contact  112  that is attached to a spring  114 . The spring  114  biases the armature  108  away from the core  106  so that the contacts  110  and  112  are normally open. When sufficient current is present in the coil  104 , the relay  100  is energized and the armature  108  is magnetically attracted to the core  106  moving the armature  108  toward the core  106  and moving the movable contact  112  into engagement with the stationary contact  110 .  
         [0017]      FIG. 2  illustrates a perspective view of a time delay relay  200  formed in accordance with an exemplary embodiment of the present invention. The relay  200  includes a coil  202  and an armature  204 . A biasing member  206 , which in some embodiments is a flat spring, biases the armature  204  away from a core  260  (see  FIG. 3 ) and also carries a movable contact  210 . A source or power connection is made to the relay  200  through a tab  212  that is also electrically connected to the armature  204 , the biasing member  206 , and the contact  210 . A second tab  214  is electrically connected to a fixed contact  238  (see  FIG. 3 ). Pins  220  and  222  are provided for coil connections and also for printed circuit board connections or other outside connections to the coil  202 . A cylinder or tube  230  extends beyond the coil  202 .  
         [0018]      FIG. 3  illustrates a cross sectional view of the relay  200  in a de-energized state.  FIG. 4  illustrates a cross sectional view of the relay  200  in an energized state. The coil  202  is wound about a bobbin  234  and has a longitudinal axis  236 . The bobbin  234  is molded from a dielectric material. In the illustrated embodiment, a fixed contact  238  is mounted on the bobbin  234 . A conductive strip  239  provides a conductive path from the fixed contact  238  to the tab  214  ( FIG. 2 ). The fixed contact  238  is aligned for engagement with the movable contact  210  when the relay  200  is energized. The armature  204  pivots about an end  240  of a yoke  242  between a de-energized position, as shown in  FIG. 3 , and an energized position wherein the movable contact  210  engages the fixed contact  238  as depicted in  FIG. 4 . The biasing member  206  has an end  244  attached to the armature  204  and a second end  246  that is attached to the yoke  242  such that the biasing member  206  biases the armature toward the de-energized position.  
         [0019]     The tube  230  extends beyond the coil  202 , bobbin  234  and a bottom end  248  of the yoke  242 . The tube  230  has a longitudinal axis  250  that substantially coincides with the longitudinal axis  236  of the coil  202 . The tube  230  contains a core  260  that is movable between a de-energized position, as shown in  FIG. 3 , and an energized position, as shown in  FIG. 4 . A biasing element  262  is provided to bias the core  260  toward the de-energized position. The core  260  may include a cavity  264  that receives an end of the biasing element  262 . The tube  230  is fabricated from a non-magnetic material. In an exemplary embodiment, tube  230  is of brass construction. The tube  230  is closed and is filled with a hydraulic fluid  266 . With reference to  FIG. 4 , the core  260  has an outside diameter  270  and the tube  230  has an internal diameter  274 . A clearance gap  276  is provided inside the tube  230  that is determined by the difference in the tube internal diameter  274  and the core outer diameter  270 . In an exemplary embodiment, the core outer diameter is about 0.1485 inches, the tube inner diameter is about 0.156 inches, and the clearance gap is about 0.004 inches. A seal  280  and a core cap  282  are installed at the open end of the tube  230  to close the tube  230 . The tube  230  is oriented such that the core cap  282  is proximate the armature  204 . In one embodiment, a lip  284  on the tube  230  is crimped over the core cap  282  to retain the core cap  282  and seal  280 .  
         [0020]     In operation, a current is applied to the coil  202  to energize the relay  200 . In the de-energized position, the core  260  is partially within and partially outside the coil&#39;s magnetic field. The magnetic field in the coil  202  induces the core  260  to move toward the core cap  282  to center itself in the coil&#39;s magnetic field. The core  260  is sized such that when centered in the magnetic field, the core  260  engages the core cap  282 . The armature  204  is then pulled from its de-energized position toward the core cap  282  to an energized position closing the contacts  210  and  238 . The time between the onset of the magnetic field in the coil  202  and the movement of the armature  204  to its energized position closing the contacts  210  and  238  represents the time delay that is provided by the relay  200 . Thus, the time delay is mechanically determined and results from the time required for the core  260  to move from a de-energized position wherein the core  260  is not centered within the coil  202  to an energized position wherein the core  260  is substantially centered within the coil  202 . When the core  260  is substantially centered, it also engages the core cap  282  to initiate actuation of the armature  204 .  
         [0021]     When current flow through the coil  202  is turned off so that the magnetic field is no longer present, biasing element  262  returns the core  260  to its de-energized position. Simultaneously, the biasing member  206  returns the armature  204  to its de-energized position opening the contacts  210  and  238 . The hydraulic fluid  266  is displaced by flowing through the clearance gap  276  as the core  260  moves through the hydraulic fluid  266 . The time delay in the relay  200  is influenced by the viscosity of the hydraulic fluid  266  as well the dimensions of the tube  230  and the core  260 . As an example, at the tube  230  and core  260  diameters previously mentioned, a hydraulic fluid viscosity of about 25 centistokes yields a time delay of about 600 milliseconds. It should be noted that the  FIGS. 2-4  represent enlarged views of the time delay relay  200 . For proper perspective, about eight drops of hydraulic fluid fills the tube  230  when the core  260  and biasing element  262  are installed.  
         [0022]      FIG. 5  illustrates a cross-sectional view of a relay  300  formed in accordance with an alternative embodiment of the present invention. In  FIG. 5 , the relay  300  is shown in a de-energized state.  FIG. 6  illustrates a cross-sectional view of the relay  300  in an energized state. The relay  300  includes both normally open contacts and normally closed contacts as will be described. In other respects, the relay  300  is similar to the relay  200  previously described, and like reference numbering is generally used in describing like components.  
         [0023]     The relay  300  includes a coil  302  and an armature  304 . A spring  306  carries a movable contact  310 . A normally closed fixed contact  324  electrically engages the movable contact  310  when the relay  300  is de-energized. A normally open fixed contact  326  electrically engages the movable contact  310  when the relay  300  is energized. A tube  330  extends beyond the coil  302 . The coil  302  is wound about a bobbin  334  and has a longitudinal axis  336 . The normally open fixed contact  326  is mounted on the bobbin  334  and is aligned for engagement with the movable contact  310  when the relay  300  is energized. The armature  304  pivots about an end  340  of a yoke  342  between a de-energized position, as shown in  FIG. 5 , and an energized position, as depicted in  FIG. 6 . The biasing member  306  has an end  344  attached to the armature  304  and a second end  346  that is attached to the yoke  342  such that the biasing member  306  biases the armature toward the de-energized position wherein the movable contact  310  engages the normally closed fixed contact  324 .  
         [0024]     The tube  330  extends beyond the coil  302 , bobbin  334  and a bottom end  348  of the yoke  342 . The tube  330  has a longitudinal axis  350  that substantially coincides with the longitudinal axis  336  of the coil  302 . The tube  330  contains a core  360  that is movable between a de-energized position ( FIG. 5 ) and an energized position ( FIG. 6 ). The spring  306  biases the armature away from the core  360 . A biasing element  362  is provided to bias the core  360  toward the de-energized position. The core  360  may include a cavity  364  that receives an end of the biasing element  362 . The tube  330  is fabricated from a non-magnetic material. In an exemplary embodiment, tube  330  is of brass construction. The tube  330  is closed and is filled with a hydraulic fluid  366 . A seal  380  and a core cap  382  are installed at the open end of the tube  330  to close the tube  330 . The tube  330  is oriented such that the core cap  382  is proximate the armature  304 . In one embodiment, a lip  384  on the tube  330  is crimped over the core cap  382  to retain the core cap  382  and seal  380 .  
         [0025]     In operation, when a current is applied to the coil  302  to energize the relay  300 , the magnetic field in the coil  302  induces the core  360  to move toward the core cap  382  to center itself in the coil&#39;s magnetic field. The core  360  is sized such that when centered in the magnetic field, the core  360  engages the core cap  382 . The armature  304  is then pulled from its de-energized position toward the core cap  382  to an energized position, opening the connection between the movable contact  310  and the normally closed fixed contact  324  and establishing an electrical connection between the movable contact  310  and the normally open fixed contact  326 . The time between the onset of the magnetic field in the coil  302  and the movement of the armature  304  to its energized position represents the time delay that is provided by the relay  300 . Thus, the time delay is mechanically determined and results from the time required for the core  360  to move from a de-energized position wherein the core  360  is not centered within the coil  302  to an energized position wherein the core  360  is substantially centered within the coil  302 . When the core  360  is substantially centered, it also engages the core cap  382  to initiate actuation of the armature  304 .  
         [0026]     When current flow through the coil  302  is turned off so that the magnetic field is no longer present, biasing element  362  returns the core  360  to its de-energized position. Simultaneously, the biasing member  306  returns the armature  304  to its de-energized position opening the connection between the movable contact  310  and the normally open fixed contact  326  and re-establishing the connection between the movable contact  310  and the normally closed fixed contact  324 .  
         [0027]     The embodiments thus described provide a simple, compact, and low cost time delay relay. The time delay is mechanically produced by replacing the steel core of a standard relay with a tube or cylinder containing a movable core in a hydraulic fluid to provide a predetermined delay. Thus, the cost of additional electronics is avoided. In addition, other than the slight extension of the hydraulic tube, the size of the relay package is not appreciably increased.  
         [0028]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.