Abstract:
A safety throttle is provided for a hand held pneumatic tool in which a pivotable intermediate member must be manually moved, by a prior secondary movement, into a slotted throttle lever before the later primary movement of the throttle lever will allow the intermediate member to activate a throttle valve to actuate the pneumatic tool.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a portable hand held power tool and more particularly to a safety throttle for use on pneumatic tools to prevent inadvertent actuation of the tool. 
     2. Description of the Prior Art 
     Prior art devices use a &#34;lock-off&#34; throttle where unintentional throttle valve actuation is avoided by preventing the motion of, or &#34;locking&#34; the throttle lever. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention a simple and rugged pneumatic hand tool is provided with a safety throttle in which the throttle contact is not in position to move until a safety lock is released or moved. The safety throttle of the present design is not easily bypassed by the operator or accidental movement of the tool. 
     The principle object of this invention is a throttle mechanism so constructed that the throttle lever cannot actuate the throttle valve from a rest condition without the proper positioning of an intermediate member, which requires a separate and distinct motion prior to normal depression of the throttle lever. 
     To elaborate, means are provided whereby the primary throttle manipulation is ineffective until a functionally necessary intermediate element is repositioned by a prior or preliminary secondary physical motion which then permits the primary throttle manipulation. 
     Further objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and the accompanying drawings in which: 
     FIG. 1 is a cross sectional view of a prior art throttle when the actuating lever or trigger is in the OFF position. 
     FIG. 2 is a cross sectional view of the prior art apparatus of FIG. 1 showing the throttle lever in the full ON position. 
     FIG. 3 is a cross sectional view of the apparatus of the present invention with the safety throttle in the OFF position. 
     FIG. 4 is a cross sectional view of the apparatus of the present invention showing the intermediate member moved toward a position to permit actuation of the throttle. 
     FIG. 5 is a further cross sectional view of the present invention showing the safety throttle in the full ON position. 
     FIG. 6 is a partial top view of the present invention showing the throttle lever slotted to receive the intermediate member. 
     FIG. 7 is a cross-sectional view of an alternative embodiment of the invention showing a one-piece construction of the throttle valve. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the drawings, FIGS. 1 and 2 show a cross sectional view of a prior art hand held pneumatic tool 10 having a body member 11 and in which air, from a source not shown, flows from tool inlet 12 to air passage 14 under control of an intermediate valve arrangement. 
     The intermediate valve arrangement of FIG. 1 shows the throttle lever 16 pivotable around the throttle lever pivot pin 18. As the throttle lever 16 is depressed or moved from right to left in FIG. 1, the throttle lever 16 pivots around throttle lever pin 18 to depress the throttle valve push pin or rod 20, which in turn unseats and opens throttle valve 22, as shown in FIG. 2. This allows air to flow from the tool inlet 12 through holes 24 in the valve tube 26, then through the annular space 28 between the valve push pin 20 and tube 26, and on through handle passage 14 to a piston cycling valve (not shown) which automatically directs the air to reciprocate the impacting piston of the tool 10. 
     Upon release of the throttle lever 16 valve spring 30 returns all parts to the rest position as shown in FIG. 1 and tool operation ceases. As may be seen in FIGS. 1 and 2 the triangular projection 32 on throttle lever 16 is always in a position to depress push pin 20 if lever 16 is moved forward from the rest position shown in FIG. 1. 
     It should be noted that accidental movement of the throttle lever 16 will permit air flow to air passage 14 accidentally. This invention is directed to preventing that, without locking the throttle valve lever 16 or push pin 20. 
     The safety valve of the present invention will now be described with reference to FIGS. 3 to 7. The basic operation of the invention may be understood from a description of the cross-sectional FIGS. 3, 4 and 5. FIG. 3 illustrates the safety valve in the OFF position, FIG. 5 in the ON position and FIG. 4 in an intermediate position between those of FIGS. 3 and 5. 
     Referring to FIGS. 3, 4 and 5, the hand held tool 34 of the present invention has a body member 35 and includes the tool air inlet 12 and air passage 14 to the piston (not shown) as in the prior art device of FIGS. 1 and 2. Also, the throttle valve 22 and members 24, 26, 28 and 30 remain the same as the prior art device of FIGS. 1 and 2, for purposes of the first embodiment of the invention. 
     Throttle lever 36 of the present invention, pivotable around pin 37, no longer has the triangular projection 32 and has been slotted 38, as shown in FIG. 6 to accept the intermediate member 40. In this embodiment the intermediate member 40 has a shallow &#34;v&#34; shape with unequal length legs, and it pivots relative to throttle lever 36 on pin 42. A coil spring 44 constantly urges intermediate member 40 toward a rest position relative to throttle lever 36. In this position the upper leg portion of intermediate member 40 is pushed away from the throttle lever 36 while the lower leg of intermediate member 40 is urged against the throttle lever 36. The spring 44 is confined within lever 36 and acts against lever 36 and intermediate safety member 40. 
     Also shown in FIGS. 3, 4 and 5 are a spring 46 and a cross pin 48. The spring 46 is very light compared to valve spring 30 and serves only to retain push pin 50 and keep it in contact with throttle valve 22. 
     It should be noted that spring 46 and cross pin 48 would be unnecessary if the throttle 22 and push pin 50 were made in one piece. This alternative embodiment is illustrated in FIG. 7 wherein the valve/pin member 52 represents the &#34;one-piece&#34; alternative to the arrangement illustrated in FIGS. 3, 4 and 5. 
     Returning now to FIG. 3, if throttle lever 36 is pressed forward toward the body 35 of the tool 10 the lower short leg 54 of intermediate member 40 will butt against the side of push pin 50 and cannot depress pin 50 to open the throttle valve 22. This acts as a safety arrangement to prevent accidental activation of the throttle valve 22. 
     In order for throttle lever 36 to cause the opening of the valve 22 the upper longer leg of intermediate safety member 40 must be pulled back toward and into the slot 38 in lever 36, with lever 36 also being pulled back from the tool 34 far enough to allow the end of the short leg 54 of intermediate member 40 to move to clear the top edge of push pin 50, and engage the top end of the push pin 50 when the throttle lever 36 is pressed forward toward the body 35 of the tool 34. 
     If these conditions are met, the short leg 54 of the intermediate member 40 becomes analagous to the triangular projection 32 on the standard lever 16 of prior art FIGS. 1 and 2, and throttle lever 36 of FIGS. 3, 4 and 5 affords complete control of the throttle valve 22 position from OFF, FIG. 3 to full ON, FIG. 5. When the throttle lever 36 is allowed to come back beyond the OFF position far enough to allow spring 44 to snap the end of the short leg 54 of intermediate member 40 off the top of push pin 50 the intermediate member 40 returns to the rest position as shown in FIG. 3. In the position shown in FIG. 3 the throttle lever 36 is incapable of actuating the throttle mechanism until intermediate member 40 and throttle lever 36 are reset as indicated above. 
     It is thus seen that the primary function of the throttle lever 36 being moved to open the throttle valve 22 depends on a prior secondary physical motion to reposition the intermediate safety element member 40 so as to allow the throttle lever to open the throttle. 
     It should be understood that variations and modifications of the described apparatus may be envisioned without departing from the spirit of the invention and scope of the claims.