Patent Publication Number: US-2002011679-A1

Title: Carburetor with a starting device

Description:
DESCRIPTION  
       [0001] For starting an internal combustion engine which is in a tool, a starting device is necessary in the carburetor, usually in form of a choke valve. The choke valve is characterized among other things in that it can take up at least two operating states, preferably the states “ON” and “OFF”. The change of the operating state can be caused by turning or pivoting the rotatably arranged choke valve about a defined angle, whereby both operating states are respectively at the beginning or at the end of the rotation angle area. The rotatable arrangement is usually guaranteed by a spindle fixedly connected with the choke valve which runs through a bore hole in the carburetor. An adjusting lever which is actively connected with an adjusting element to be actuated by the tool operator is also fixedly connected with the spindle. In order to guarantee a safe actuation, the adjusting element and the adjusting lever are usually connected with each other in at least one axis.  
       [0002] During the operation of such a tool, the carburetor and the housing surrounding it among other elements are excited to movements by vibrations. If a decoupling of the carburetor from the housing takes place due to appropriate damping elements, both components carry out different movements when excited. There results herefrom the problem of the assignment of the adjusting element to be actuated by the operator. If the adjusting element is assigned to the housing, the adjusting lever connected with the carburetor carries out, when excited, a movement with an amplitude and a frequency which differ from that of the adjusting element fixedly connected with it in at least one axis. Thus, the interface between the adjusting lever and the adjusting element is highly stressed during the operation of the tool and could fail.  
       [0003] An assignment of the adjusting element to the carburetor, i.e. to the adjusting lever, could remove this problem. However, when the operator actuates the adjusting element, the adjusting element itself and the carburetor assigned thereto is moved in its elastic damping elements used for the vibration decoupling. Thereby, additionally to the switching movement, the adjusting element carries out, when actuated, an undefined movement which is often felt by the operator as being unpleasant. Moreover, for an assignment of the adjusting element to the carburetor, the adjusting element itself and the housing carry out different movements by vibration excitation due to the operation of the tool. Since the adjusting element must be in any case guided through the housing, the leadthrough about the adjusting element must be selected so big as to exclude a damage of the differently vibrating parts. With this arrangement, a closed housing around the carburetor can hardly be realized because of certain requirements, for example in a motor saw.  
       [0004] Therefore, the aim of the invention is to create a choke actuation which does not show the described disadvantages and which in particular allows that the adjusting lever on the carburetor and the adjusting element to be actuated by the operator have no contact with each other during the operation of the tool and thus a damage of the adjusting lever or of the adjusting element is avoided in case of a different vibration excitation. Furthermore, it should be possible to assign the adjusting element to the housing surrounding the carburetor and to guide it through this housing almost without gap. In particular, for this assignment, when actuated the adjusting element should carry out only the actual switching movement.  
       [0005] The aim is achieved by the totality of the characteristic features of claim  1 . The heart of the invention consists in configuring the adjusting lever of the choke spindle in such a way that, for a movement of the adjusting lever beyond a dead centre, the choke valve can compulsorily only take up the end positions “ON” and “OFF”.  
       [0006] A preferred configuration of the carburetor according to the invention is characterized in that the choke valve is placed on a spindle which is rotatably positioned in the carburetor body and which extends through the carburetor body to the outside, that the adjusting lever is fixed on the spindle, that a tension lever which extends transversaly to the spindle in a first direction is fixed on the spindle and that a tension spring is applied on the tension lever, this spring exerting a force directed opposite to the first direction. The dead centre results in this case when the axis of the spindle goes through a line which connects the working point of the tension spring and the fixing point of the other end of the tension spring with each other.  
       [0007] Preferably, for actuating the adjusting lever, a separate adjusting element is provided for which is in gear with the adjusting lever for pivoting the adjusting lever beyond the dead centre. In particular, the carburetor is placed in a housing, the adjusting element is guided through the housing to the outside and can be actuated from outside and the adjusting element is placed swivelling on the housing, the carburetor being arranged elastically in the housing and the adjusting lever and the adjusting element being disengaged when the adjusting lever takes up one of the two end positions. 
     
    
    
     [0008] The invention will be explained in detail below by means of an embodiment with reference to the attached drawings.  
     [0009]FIG. 1 is a perspective representation of a carburetor according to a preferred embodiment of the invention.  
     [0010]FIG. 2 shows the elastic suspension of the carburetor of FIG. 1 in a housing with an adjusting element fixed on the housing.  
     [0011]FIG. 3 a - c  are three partial figures which show both end positions (FIG. 3 a  and  3   c ) and the intermediary dead centre of the adjusting lever for the carburetor of FIG. 1. 
    
    
     [0012]FIG. 1 is a perspective representation of a carburetor according to a preferred embodiment of the invention. The carburetor  10  comprises a carburetor body  11  through which a conduit runs. In this conduit, a choke valve  12  is placed rotatably or swivelling on a spindle  13 . The spindle  13  is positioned in a bore hole in the carburetor body  11  and extends at least one one side through the carburetor body  11  to the outside. Two levers connected with each other, namely an adjusting lever  14  and a tension lever  20 , are fixed on the end of the spindle  13  which is situated outside the carburetor body  11 —and for example formed out of a punched and bent sheet steel part. By swivelling the adjusting lever  14 , the spindle  13  can be rotated and thus the choke valve  12  can be rotated and/or swivelled. The choke valve  12  preferably takes up two positions which are situated respectively at the end of the rotation angle area. In the one position, which is represented in FIG. 1, the choke valve  12  is in the “ON” position, i.e. it is approximately parallel to the axis of the intake duct. In the other position which is twisted about approximately 90°, the choke valve  12  is in the “OFF” position, i.e. it closes the duct. Corresponding end positions of the adjusting lever  14  are assigned to both positions of the choke valve  12 .  
     [0013] According to the invention, there is now a dead centre between these two end positions of the adjusting lever  14 , dead centre beyond which the adjusting lever  14  must be moved when it should be brought from the one end position to the other end position. Beyond the dead centre it moves automatically into the corresponding end position. According to FIG. 2, an adjusting element  16  is provided for actuating the adjusting lever  14 . The adjusting element  16  is positioned swivellable by means of a drag bearing  10  in a housing  17  which surrounds the carburetor  10 . The adjusting element  16  extends through the housing  17  and can be operated from outside. According to FIG. 3, it can be brought in gear with the adjusting lever  14  over two V-shaped widened actuating levers  21  and  22  in order to swivel the adjusting lever  14  into one of the two directions.  
     [0014] In the represented embodiment, the concrete embodiment of the dead centre consists in that a tension spring  15  is connected with the adjusting lever  14  as well as with the carburetor body  11  over the tension lever  20 . If both suspension points OP and UP of the tension spring  15  on the tension lever  20  and on the carburetor body are in a line with the pivot of the adjusting lever  14  or of the choke spindle  13 , this is the dead centre position (FIG. 3 b ). The distance between the two spring suspension points OP and UP is the biggest at this position and thus also the spring power. If the adjusting lever  14  is now moved further by a few degrees into one the two possible rotating directions, the distance of the spring suspension points OP and UP is reduced, the tension of the tension spring  15  is released and the adjusting lever  14  as well as the choke valve  12  connected herewith tilt into a defined operating state (“ON” according to FIG. 1 and/or  3   c  or “OFF” according to FIG. 3 a ). The movement of the adjusting lever  14  beyond the dead centre is obtained by the adjusting element  16  actuated by the tool operator. The adjusting lever  14  and the adjusting element  16  are constructed in such a way that they have contact with each other only when they are guided beyond the dead centre, while they are without any contact and/or disengaged in the two operating states “ON” and “OFF” of the choke valve  12 . Thus, a relative movement of the two components to each other, caused by different vibration excitation during the operation of the tool, can be admitted.  
     [0015] Thus, an elastic suspension of the carburetor  10 , its vibration being decoupled from the housing  17 , is possible by means of corresponding elastic elements  18  (FIG. 2), while the adjusting element  16  to be operated by the operator can be assigned to the housing  17 . For this assignment, the leadthrough of the adjusting element  16  through the housing  17  can be sealed. The adjusting element  16  carries out the switching movement alone when actuated since it is movably coordinated with the housing  17  in only one axis.  
     [0016] Because of the fact that the adjusting lever  14  must be guided beyond the dead centre and that it then automatically guides the choke valve  12  into one of its two operating positions by means of the spring tension of the tension spring  15 , the whole system “actuation of a starting device” is not susceptible to tolerances. An elastic carburetor suspension as well as bigger tolerances for the fabrication of the adjusting lever  14  and of the adjusting element  16  are possible.  
     LIST OF REFERENCE NUMERALS  
     [0017] 10  Carburetor  
     [0018] 11  Carburetor body  
     [0019] 12  Choke valve  
     [0020] 13  Spindle  
     [0021] 14  Adjusting lever  
     [0022] 15  Tension spring  
     [0023] 16  Adjusting element  
     [0024] 17  Housing  
     [0025] 18  Elastic element  
     [0026] 19  Drag bearing  
     [0027] 20  Adjusting lever  
     [0028] 21 ,  22  Actuating lever  
     [0029] OP Upper suspension point (tension spring)  
     [0030] UP Lower suspension point (tension spring)