Engine Ignition Grounding Switch

The present invention relates to internal combustion engines and, more particularly, to an engine ignition grounding switch by means of which the engine may be stopped.

Objects of the present invention are to provide an improved ignition grounding switch particularly adapted for use in combination with low-horsepower internal combustion engines of the type widely used to power lawn mowers or the like and which is economical to manufacture and assemble, and which is reliable in operation. More specifically, it is an object of the invention to provide an improved ignition grounding switch of the described type having fixed and movable contact members in which spring-bias forces in the fixed contact member are utilized in such a manner that electrical connection between the fixed and movable members is facilitated when the two come into mechanical contact despite an accumulation of dirt, grease or grime, etc. on one or both of the members.

The novel features which are considered to be characteristic of the present invention are set forth in particular in the appended claims. The invention itself, however, together with additional objects, features and advantages thereof, will be best understood from the following description when read in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a presently preferred embodiment of the engine ignition grounding switch provided by the present invention carried on a carburetor control bracket of an internal combustion engine;

FIG. 2 is an elevational sectional view longitudinally bisecting the engine ignition grounding switch shown in FIG. 1;

FIGS. 3 and 4 are sectional views respectively taken along the lines 3--3 and 4--4 of FIG. 2; and

FIG. 5 is an elevational view of a shorting terminal of the switch shown by itself in its free state condition.

Referring to FIG. 1, a throttle control lever 26 and a coaxial control follower 28 are conventionally mounted for corotation on a carburetor control bracket 24 which is fixedly carried on an engine adjacent the carburetor (not shown). Follower 28 is connected to the carburetor throttle valve (not shown) by a link 30, and control lever 26 is connected to a suitable operator-responsive control mechanism (not shown) by a Bowden cable 32. Control lever 26 is connected via bracket 24 to engine electrical ground, i.e., the engine block. Follower 28 is biased by a carburetor valve return spring (not shown) into abutment with the usual idle adjustment screw 34 carried by lever 26. It is conventional in construction of low-horsepower internal combustion engines adapted for use on lawn mowers or the like to locate throttle control lever 26, control follower 28 and screw 34 below rather than above mounting plate 24 in assembly, to thereby protect the control lever and follower from unwanted contact and damage, and to help protect against an accumulation of dust and dirt, etc. on the control mechanism. Hence, the lever and follower are mounted to the underside of bracket 24, the composite assembly shown in FIG. 1 being thus viewed upwardly from beneath the control bracket.

Referring to FIGS. 1-4, the engine ignition grounding switch provided by the present invention includes an elongated block 10, preferably injection molded from suitable plastic material having good electrical insulation properties, into which a blind T-shaped aperture or channel 12 is axially cored. Channel 12 is fully open at the front end of block 10 but only the wings or head of the "T" break through the rear block wall 14 to form a terminal-receiving slot 16, the base or leg of the T-channel stopping short of and terminating at the inside surface of wall 14. Block 10 has two relieved tapered projections 18,20 extending from a lateral wall 22 thereof adjacent the head of the T-channel, which projections serve as mounting lugs to snap-fasten block 10 to control bracket 24 with the open front end of channel 12 facing toward lever 26. A shorting terminal 36 having respective inner and outer ends 37,38 is received into the leg of T-shaped channel 12. Inner terminal end 37 is bent or kinked, as at 40, with the innermost end of bend 40 being turned upon itself to form a hairpin-shaped portion 42. The free state geometries of bend 40 and hairpin 42 are shown in FIG. 5 and differ from their configurations in assembly, best seen in FIG. 2, due to the terminal end 37 being compressed as it is pushed endwise into clip channel 12 until hairpin 42 abuts the inside surface of rear wall 14. Thus, in its assembled condition, terminal end 37 develops spring tension to bear at two points against the opposing inside face of lower block wall 22, i.e., at the ends 44,46 of bend 40, and at one point against the opposing roof 48 of channel 12, i.e., at the free end 52 of hairpin 42. Free end 52 is oriented relative to channel roof 48 so as to be slightly angulated or inclined with respect thereto as shown in FIG. 2, and is adapted to dig into roof 48 and to thus resist any forces tending to remove or withdraw terminal 36 from block 10. Outer terminal end 38 is formed into another hairpin-shaped portion having two ramp portions; a first portion 60 extending axially from bend end 44 through the open end of aperture 12 toward lever 26 and parallel to the plane of travel thereof, and a second portion 62 inclined with respect to portion 60 at an angle generally acute to said plane of travel or direction of motion of control lever 26.

The switch provided by the present invention, comprising insulator block 10 and terminal 36 described above, is adapted to receive a conventional spade terminal 54 in the rear end of the insulator block via slot 16. Spade terminal 54 is connected to the engine magneto (not shown) via conductor 55, and has an oval detent hole 56, at its center which, when the spade is inserted into slot 16, rides beneath the curved portion of hairpin 42 at bend terminus 46 until a portion of terminus 46 registers with hole 56 in the spade terminal, whereupon the bend is forced into the hole by the spring bias of the terminal wire. Spade terminal 54 is thus releasably locked to the grounding switch within insulator block 10 by this spring-detent feature of the invention. Bottom wall 22 extends outwardly of rear wall 14 to form a ledge 57 under which terminal 54 is positioned, thereby preventing terminal 54 from becoming bent or stressed into contact with bracket 24 and forming an insulation barrier between the terminal and bracket to protect against undesirable ignition grounding caused by moisture or corrosion, etc.

In operation, grounded control lever 26, as it is moved toward its engine shut-off position, is adapted to make electrical contact with terminal 36, and to thus electrically connect the magneto, via terminal 54 and conductor 55, to electrical ground, whereby generation of the engine ignition spark is prevented. Terminal 36 is first struck along end portion 62 by control lever 26 as the latter is moved toward the full-off throttle position. In FIG. 2, lever 26 and outer terminal end 38 are shown in solid lines at respective positions in which contact therebetween is imminent, and in phantom lines at the full-off throttle position. Thus, it will be noted that terminal end 38 is cammed upwardly and rides along an adjacent opposing relatively sharp edge 63 of control lever 26 as the latter is moved from initial to full engagement. Edge 63 is preferably a right angle edge of the type customarily imparted during die blanking or stamping of lever 26, and thus ordinarily is already available without requiring special machining of this part.

During movement of the control lever, terminal 36 is further stressed within clip channel 12 in a direction additive to the above-mentioned stresses imparted to the terminal in assembly, so that loading stresses caused by lever 26 are carried back into the portion of the terminal enclosed within the insulator block. Due to this mode of engagement, and due to the use of a small diameter spring wire for the grounding terminal, preferably on the order of 0.031 inch in diameter (No. 13 Gauge), the deflection imparted to the wire by control lever 26 as the latter moves to its full-off position develops a relatively high unit contact pressure in making grounding contact to the throttle lever. With this structure, terminal 36 is able to cut through and make electrical contact with control lever 26 despite the fact that the lever and/or spring wire may be covered by oil, dirt, grease, ice or corrosion, etc., thereby insuring positive grounding of the engine ignition system despite such adverse environmental conditions.