Restoring device for an adjusting element
BACKGROUND OF THE INVENTION 
     The invention is based on a restoring device for an adjusting element, in particular for a throttle device of an internal combustion engine. A restoring device is already known in which a return spring subjected to bending engages an actuation member in the restoring direction. An embodiment of such a spring has the disadvantage that if the spring subjected to bending should break, no further restoring force is exerted upon the actuation member and hence this member is no longer returned automatically to its initial position. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The restoring device according to the invention has the advantage over the prior art that a second spring subject to bending is provided, which has no influence on the restoration of the actuation member so long as the first such spring is capable of functioning; however, if the first spring subject to bending should be defective the second spring comes into use and urges the actuation member in the restoring direction. 
     By means of the characterics recited herein advantageous further developments of and improvements to the restoring device are attainable. It is particularly advantageous for the first and second springs subject to bending to be disposed one inside the other, so that the device can be accommodated in a small space. 
    
    
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment taken in conjunction with the drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a restoring device according to the invention for an adjusting element in plan view; 
     FIG. 2 is a section taken along the line II--II of FIG. 1; and 
     FIG. 3 is a section taken along the line III--III of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The restoring device for an adjusting element shown in FIGS. 1, 2 and 3 serves for example to restore a throttle valve 1, acting as the adjusting element, of an internal combustion engine not otherwise shown. The throttle valve 1 is connected in a rotationally fixed manner with a shaft 2 and to a variable extent controls the quantity of air flowing through an intake tube 4 embodied in a throttle valve fitting 3. The shaft 2 is rotatably supported in a sleeve bearing 6 of the throttle valve fitting 3 by way of example and has one end 7 that protrudes out of the throttle valve fitting 3. A snap ring 9 is disposed in an annular groove 8 of the shaft 2, on which snap ring 9 is secured between an annular disc 10, oriented toward the slide bearing, and an annular disc 11 on the other side, and disposed on the shaft 2. Resting against the annular disc 11, a bushing 13 is rotatably supported on the shaft 2, its axial movement being limited on the outer end by a lever 14 acting as an actuation member. The lever 14 has a through opening 15, with which it can be pushed onto the end 7 of shaft 2, which has flattened areas 16, of the shaft 2 and then fastened in place by a threaded nut 18 with an interposed shim 17 between the lever 14 and the nut. Coaxially with the shaft 2, a bearing bushing 20 is disposed on and surrounds a portion of the throttle valve fitting 3. This bushing 20 guides a first coiled return spring 21 subjected to a bending restoring force, which extends coaxially with the shaft 2 and is embodied in helical form. The end 22 of the coil spring oriented toward the bearing bushing 20 is bent in the shape of a hook and suspended from a protrusion 23 of the throttle valve fitting 3, while the other end 24 of this first spring 21 subject to bending engages the bushing 13. The end 24 of the spring is bent in the form of a hook, and engages a step 25 of the bushing 13 in such a manner that the step 25 comes to rest on an edge of the lever 14 and urges it in the restoring direction; that is, it tends to rotate it in the closing direction of the throttle valve 1. The actuation of the throttle valve 1, in an internal combustion engine, is effected by a so-called gas pedal, not shown, which via a lever linkage 26 engages the lever 14 and by way of which the throttle valve 1 is rotatable into the opening position counter to the force of the first spring 21 subject to a bending restoring force. 
     In accordance with the invention, a helically embodied second coil spring 29 subject to a bending restoring force is disposed in an annular groove 28 of the bushing 13, extending coaxially with the shaft 2. One end 30 of this spring 29 protrudes out of the annular groove 28 and engages the lever 14, while the other end 31 is bent and protrudes for example into a longitudinal groove 32 of the bushing 13. Oriented toward the throttle valve fitting 3, a stop step 33 is embodied on the bushing 13, protruding into a recess 34 of the throttle valve fitting 3. The second spring 29 subject to a bending restoring force is designed such that its spring force is less than that of the first spring 21 subject to bending. As a result, with its step 25, the bushing 13 is rotated so far by the first spring 21 subject to bending, counter to the force of the second spring 29 subject to bending, that the step 25 comes to rest on the lever 14 and the stop step 33, upon a rotational movement of the shaft 2, freely executes this same rotational movement as well within the recess 34. The second spring 29 subject to bending accordingly has no influence on the throttle valve 1 in the restoring direction. However, if the action of the first spring 21 subject to bending should be absent, for instance because of breakage, then the second spring 29 subject to bending comes into action and rotates the bushing 13, and hence the stop step 33, in the recess 34 until such time as the stop step 33 comes to rest on a stop face 35 of the throttle valve fitting 3--that is, until such time as this step 33 is no longer spaced apart from the stop face 35--and the second spring 29 subject to bending now acts, instead of the first spring 21, upon the shaft 2 of the throttle valve 1 in the restoring direction. The device is small in size as a result of the disposition of the second spring 29 subject to bending inside the first such spring 21. The disposition of the second spring 29 subject to bending assures the proper functioning of the throttle valve 1 if the first spring 21 should fail. 
     The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.