Patent Publication Number: US-3969597-A

Title: Key operated electric ground switch

Description:
BACKGROUND OF THE INVENTION 
     Electric grounding switches are frequently used on small internal combustion engines to short the ignition system and prevent the engine from running when the switch is turned to its off position. Such switches are applied to chain saws, power lawn mowers, and similar equipment. 
     Generally, such switches are of a toggle or slide type and do not include an integral locking feature to prevent unauthorized starting of the engine. As a safety feature, it is desirable to provide a locking switch which prevents the engine from being started by an unauthorized user. This is an important safety feature for equipment such as power lawnmowers, which possibly could be accidentally started by children who are unaware of the attendant dangers of operating such equipment. 
     Accordingly, it is desirable to provide for a grounding switch for internal combustion engines which is simple and economical to manufacture and which includes an integral locking feature to prevent unauthorized operation of the equipment with which such a switch is used. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of this invention to provide an improved electric switch. 
     It is another object of this invention to provide an improved key-operated electric switch. 
     It is a further object of this invention to provide an improved key-operated electric grounding switch. 
     It is yet another object of this invention to provide a key-operated electric switch of simple and economical construction. 
     It is still another object of this invention to construct a grounding switch with a two-part body portion, one of the parts made of insulating material and the other part made of conductive material, employing a spring to interconnect a movable contact with a conductive terminal mounted in the nonconductive portion of the housing, with a provision for insertion of an operating key into the conductive portion of the housing to engage the contact and to move it out of engagement with the conductive portion of the housing as the key is rotated. 
     In accordance with a preferred embodiment of this invention, an electric switch comprises a housing having an elongated hollow housing portion with a closed end and an open end, and a hollow conductive housing portion having a first end with an aperture in it, for accommodating a rotatable key, and a second open end for receiving and engaging the open end of the insulating housing portion in an assembled relationship. A terminal is mounted in the closed end of the insulating housing portion and extends outwardly from it. A conductive contact is movably located in the switch housing and is electrically connected to the terminal by a conductive compression spring which biases the contact into electrical conductive contact with a shoulder in the first end of the conductive housing portion of the switch housing. A cam surface on the inner surface of the first end of the conducting housing portion engages a projection or lobe on a key inserted into the aperture to cause the key to bias the conductive contact away from electrical contact with the conductive housing portion when the key is rotated from a first position to a second position within the conductive housing portion of the switch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 show a top view and a cut-away side view, respectively of a preferred embodiment of the invention with a key located in its insertion and removal position within the switch; 
     FIGS. 3 and 4 show top and partially cut-away side views, respectively, of the embodiment of FIGS. 1 and 2 with the key rotated 90°; 
     FIGS. 5 and 6 show top and partially cut-away side views, respectively, of a modification of the embodiment shown in FIGS. 1, 2, 3 and 4; 
     FIG. 7 shows additional details of a portion of the embodiment illustrated in FIGS. 5 and 6; 
     FIG. 8 shows cross-sectional view of the conductive cap portion of the embodiment illustrated in FIGS. 1, 2, 3 and 4; 
     FIG. 9 shows an alternative embodiment of a key which may be used in conjunction with the apparatus illustrated in FIGS. 1 through 6; and 
     FIG. 10 shows a ground terminal lock washer which can be used in conjunction with the devices illustrated in FIGS. 1 through 6. 
     DETAILED DESCRIPTION 
     Referring now to the drawings wherein like reference numerals are used throughout the several figures to indicate the same or similar components, there are illustrated two different embodiments of a key operated grounding switch of a type suitable for use with internal combustion engines and the like for shorting out the ignition and preventing operation of the engine until a key is inserted into the switch and rotated to the &#34;on&#34; position of the switch. 
     In FIGS. 1 and 2, there is shown a key operated electric grounding switch in which the switch body is in two portions. One of these portions comprises a cylindrically-shaped plastic insulating housing 10 having a closed lower end to which a conductive terminal 11 is attached by a rivet 13 extending through the closed bottom end of the plastic housing 10 into the interior. The rivet 13 may be made of copper or some other suitable electrically conductive material. 
     A second portion of the switch housing is made of electrically conductive metal, preferably die cast zinc, in the form of a cylindrical cap 14 for the plastic housing portion 10. The metal cap has a shoulder 16 on it which engages a flange 18, integrally formed as part of the plastic housing portion 10, so that the metal cap 14 receives the plastic housing 10 which also abuts against an upper shoulder 19 formed on the inside surface of the upper end of the cap 14. The upper portion of the cap 14 is exteriorly threaded to facilitate mounting of the switch into the metal frame or shroud of an engine with which it is to be used. A cylindrical hole 21 is formed in the center of the otherwise closed upper end of the cap 14, and a slot 22 extends to one side of the hole 21 to accommodate a lobe on a removable key 24 which is to be inserted into the switch housing to operate the switch. 
     The plastic and metal portions 10 and 14 of the switch housing are secured together by bending an extension 15 on the metal housing 14 over the flange 18 on the plastic housing portion 10 to clamp the flange 18 between the shoulder 16 and the bent over extension 15; thereby locking the two parts of the housing together. 
     Electrical contact between the terminal 11 and the conductive cap 14, which constitutes the second terminal of the switch, is effected through the rivet 13 which also is attached to a conductive compression spring 26 (preferably made of spring steel), which in turn engages a cup-shaped eyelet contact 28 having an outwardly flared upper portion 30 biased into electrical contact with the shoulder 19 of the cap 14 by the spring 26. 
     As shown in FIG. 2, when the key 24 is inserted into the switch a cylindrical shank 31 on the key fits into the contact eyelet 28, and a key lobe 33 is passed downwardly through the slot 22 in the top of the cap 14. When the key 24 then is rotated 90°, as shown in FIGS. 3 and 4, the cam surface of the lobe 33 engages a mating cam surface including detent 35 which cam surface is similiar to that shown in FIG. 7 formed on the inner surface of the upper portion of the cap 14 to cam the key 24 downwardly, as shown in FIG. 4. This presses the eyelet 28 out of engagement with the shoulder 19 of the cap 14 against the compression force of the spring 26. As a result the electrical contact which previously was made between the terminal 11 and the cap 14 through the spring 26 and the eyelet contact 28 is broken. 
     In the version shown in FIGS. 1, 2, 3 and 4, the switch in a two-position switch having an &#34;on&#34; position and an &#34;off&#34; position, shown respectively in FIGS. 1, 2 and 3, 4. The key 24 cannot be rotated any farther than 90°, because the lobe 33 on the key engages an abutment formed at the end of the cam surface 35 (shown most clearly in FIG. 2) to prevent further rotation of the key. When the key 24 once again is rotated to the position shown in FIGS. 1 and 2, the grounding switch is closed, making electrical contact between the terminal 11 and the cap 14; and the key may be removed to lock the switch in this position. 
     FIG. 8 shows the upper metal cap or housing portion in cross-sectional view, without the key 24 in it to more clearly illustrate the cylindrical hole 21 and slot 22 for accommodating the key. Also in Fig. 8, the cap 14 is shown prior to the bending over of the extensions 15 to secure the cap to the flange 18 on the plastic housing portion 10. 
     FIGS. 5, 6 and 7 illustrate an alternative embodiment of the invention accommodating three-positions of rotation of a key 24. This is effected by shaping the cam surface 35&#39;, formed on the inner surface of the upper end of the cap 14, to continue past the position shown in FIG. 4 to a hollowed out position 180° from the position illustrated in FIGS. 1 and 2. This permits the key 24 to rise within the cap 14 sufficiently high to permit the conductive eyelet 28 to once again engage the shoulder 19 to make electrical contact with it. Since there is no slot, however, about the lobe 33 of the key 25 when it is rotated to the position shown in FIGS. 5 and 6, the key is held in place in the switch. The remainder of the parts of the switch, however, are in the same conductive connected position as in FIGS. 1 and 2 when the key may be removed to place the switch in its lock position. 
     FIG. 7 illustrates the general shape of the cam surface 35&#39; for the version of the switch shown in FIGS. 5 and 6. In FIG. 7 the second key position, corresponding to the position of the key in the switch shown in FIG. 4, is illustrated in solid lines; and the dotted line illustrations show the positions of the key and the eyelet conductor for each of the other two positions of the key 24. 
     FIG. 9 illustrates an alternative embodiment of a key 50 which includes a coil spring 38 fastened to the shank of the key around the shaft 31. When a key such as the key 50 shown in FIG. 9 is inserted into any of the switch configurations shown in FIGS. 1 through 8, it must be inserted with sufficient force to compress the spring 38 which engages the outer surface of the upper side of the cap 14. The key 50 then may be inserted and rotated in the manner illustrated for the key 24 in FIGS. 1 through 6. When the key 50 is rotated to the lock position of the switch, as illustrated in FIGS. 1 and 2, the spring 38 operates to push the key upwardly out of the switch. 
     FIG. 10 illustrates a lock washer ground terminal 40 having a terminal projection 41 and including a thread engaging inner diameter 42. This lock washer is illustrated threaded into operating position onto the cap 14 of the switch in FIG. 4, and may be used in conjunction with the switch where the switch is used with engines which are mounted to plastic housings or the like. In such a mounting, the extension 41 accommodates a grounding connection to a suitable point. 
     As an alternative to the use of a plastic or non-conductive key 24, it is possible to use a metal key if the shaft 31 and lobe 33 are made of plastic or are coated with a suitable insulating material, such as nylon or the like.