Patent Publication Number: US-7717974-B2

Title: Air filter arrangement for an internal combustion engine

Description:
The instant application should be granted the priority date of Mar. 24, 2006 the filing date of the corresponding German patent application 10 2006 013 602.0. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an air filter arrangement for an internal combustion engine, in particular for the two cycle engine of a manually guided implement such as a power saw, a cut-off machine, or the like. 
     U.S. Pat. No. 6,328,288 B1 discloses a carburetor having an air filter, with a mixture channel and an air channel opening out at the base of the air filter. U.S. Pat. No. 5,503,649 A furthermore discloses disposing shield elements between the inlet opening of the mixture channel and the filter element for retaining fuel that pulses back out of the mixture channel, thus preventing contamination of the air filter. 
     With air filter arrangements where an air channel and a mixture channel communicate with the clean chamber of the air filter, the channels are customarily disposed on the air filter in such a way that no fuel can pass into the air channel from the mixture channel. 
     It has been shown that at low speeds, a considerable portion of the fuel passes back into the air filter from the mixture channel due to the pulsations in the mixture channel. This fuel is not available for the combustion, and thereby results in a leaner mixture in the combustion chamber of the internal combustion engine. This impairs the operating behavior of the internal combustion engine. 
     It is an object of the present invention to provide an air filter arrangement for an internal combustion engine that also at low speeds enables a good operating behavior. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This object, and other objects and advantages of the present invention, will appear more clearly from the following specification in conjunction with the accompanying schematic drawings, in which: 
         FIG. 1  is a side view of one exemplary embodiment of an air filter arrangement; 
         FIG. 2  is a plan view of the air filter arrangement of  FIG. 1 ; 
         FIG. 3  is a perspective illustration of the air filter arrangement of  FIG. 1 ; 
         FIG. 4  is a cross-sectional view taken along the line IV-IV in  FIG. 1 ; 
         FIG. 5  is a perspective illustration of the air filter arrangement without the filter element; 
         FIG. 6  is a perspective illustration of the air filter arrangement with a partially cut-away air filter element; and 
         FIG. 7  is an exploded view of the air filter arrangement. 
     
    
    
     SUMMARY OF THE INVENTION 
     The air filter arrangement of the present application comprises an air filter element that delimits a first clean chamber, with an inlet opening being provided for an air channel and an inlet opening being provided for a mixture channel; a shield is provided for shielding the air filter element relative to the mixture channel, wherein the inlet opening of the air channel is in communication with the inlet opening of the mixture channel via the shield. 
     Instead of providing as good a separation of the air channel and the mixture channel as possible, as has been previously provided, and also preventing fuel in the air filter from passing into the air channel, it is proposed pursuant to the present invention that the inlet openings of the air channel and of the mixture channel be deliberately connected to one another via the shield. By means of this connection or communication, it is possible, in particular at low speeds, in other words when relatively large quantities of fuel pass into the air filter, for the fuel from the air filter to also pass into the air channel. Thus, at low speeds fuel is supplied not only via the air channel but also via the mixture channel. Consequently, a significant leaning of the mixture in the combustion chamber of the internal combustion engine is avoided at low speeds. At high speeds, the pulsations are less strong in the mixture channel, so that here essentially no fuel passes into the air filter. At high speeds, largely fuel-free air is thereby supplied via the air channel, whereby this fuel-free air can serve for scavenging where provided for. As a result, low emission values are achieved at high speeds. The shield simultaneously prevents contamination of the air filter from fuel that has passed out of the mixture channel into the air mixture. 
     The shield delimits a second clean chamber that is connected with the first clean chamber by means of at least one communication opening, wherein the inlet openings of the air channel and the mixture channel respectively open into the second clean chamber. Due to the fact that the inlet openings of both channels open into a second clean chamber, it is possible for the fuel that passes back into the air filter to pass nearly entirely to the internal combustion engine, whereby no fuel can pass into the first clean chamber and to the air filter. 
     The shield advantageously extends the mixture channel and the air channel up to the communication opening. At low speeds, often insufficient fuel and combustion air can be supplied to the internal combustion engine. It has been shown that for an adequate filling of the air channel and of the mixture channel, the channel lengths that are available are critical. An extension of these channels effects an improvement of the filling, whereby in particular resonance characteristics of the channels should also be taken into account. Due to the fact that the mixture channel and the air channel are extended by the shield, it is possible to achieve extended channel lengths in a simple manner where the installation space is small. By the provision of the communication opening in the shield, it is possible to achieve a coordination of the channel lengths. As a result, it is also possible to adapt an air filter arrangement to an internal combustion engine simply by exchanging the shield. It is also possible in a straightforward manner to achieve a good degree of filling of the channels, and an adequate supply of the internal combust ion engine with fuel and combustion air. 
     The shield advantageously has a bulged portion that extends over the inlet opening of the mixture channel. Fuel that has passed over out of the mixture channel can collect in the bulged portion, and from there can again be guided back into the mixture channel via the combustion air that is drawn in. The shield advantageously has a channel-like connecting portion that extends from the inlet opening of the mixture channel to the inlet opening of the air channel, and by means of which the air channel and the mixture channel are interconnected. The connecting portion ensures that at low speeds fuel can also pass out of the mixture channel into the air channel. The fuel supplied via the air channel prevents an excessive leaning of the fuel/air mixture in the combustion chamber. In addition, the fuel in the air channel effects a cleaning of a throttle element, for example an air valve or choke, that is disposed in the air channel. Thus, an ability of the throttle element in the air channel to be able to close well can also be ensured over long periods of operation. By adapting the length of the connecting portion, the ratio of the lengths of the channels to one another can be altered. In this way, it is possible to coordinate the resonances of the channel lengths. The channel-like connecting portion expediently adjoins the bulged portion. 
     The shield can have a transverse portion that adjoins the channel-like connecting portion and extends transverse thereto. The transverse portion advantageously extends at least partially over the inlet opening of the air channel. The transverse portion expediently has a top portion in which is disposed at least one communication opening. The fuel that has passed into the air filter collects at the top portion, thereby extensively avoiding passage of the fuel into the first clean chamber. The top portion is advantageously disposed on that side of the transverse portion that faces away from the connecting portion. As a result, a relatively large spacing is achieved between the communication opening and the inlet opening of the mixture channel. At least one communication opening is advantageously disposed on that side of the inlet opening of the air channel that faces away from the inlet opening of the mixture channel. Also thereby is it possible to largely prevent passage of fuel into the first clean chamber. 
     At least one guide surface can be disposed on the shield adjacent to the inlet opening of the air channel; this guide surface conveys retained fuel to the inlet opening of the mixture channel. The inlet opening of the air channel, relative to the effective direction of the force of gravity, is advantageously, in a customary installation position of the air filter arrangement, disposed above the inlet opening of the mixture channel. As a result, the force of gravity contributes to prevent fuel from being able to pass out of the second clean chamber into the first clean chamber. The air filter element in particular extends over the shield in a dome-like manner. 
     Further specific features of the present application will be described in detail subsequently. 
     DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Referring now to the drawings in detail,  FIGS. 1 to 3  show an air filter arrangement  1  for an internal combustion engine, especially for a two-cycle engine in a manually guided implement such as a power saw, a cut-off machine a brushcutter, or the like. The air filter arrangement  1  comprises an air filter  2  having an air filter frame  3  on which is disposed a filter element  4 . The filter element  4  spans the flat air filter frame  3  in a dome-like manner, and is supported on struts  23 , which form a lattice, the lattice openings of which are covered by the filter element  4 . 
     Disposed on the air filter frame  3  is a grip element  20  that cooperates with snap-fit connectors  22  on the air filter housing  21 . On the opposite side of the frame  3  tabs  24  are provided on the frame  3  that extend into receiving means  25  formed on the air filter housing  21 . The air filter  2  is fixed on the air filter housing  21  by means of the tabs  24  and the grip element  20 . By releasing the latching or engagement by raising the grip element  20 , the air filter  2  can be removed from the air filter housing  21 , for example for cleaning purposes. 
     The receiving means  25  are formed on support members  38  that extend on that side of the air filter housing  21  that faces away from the grip element  20 . Disposed on each support member  38  is a respective anti-vibration element  6  by means of which the air filter housing  21  is supported against a housing member of the manually-guided implement. 
     In a customary installed position of the air filter arrangement  1 , the grip element  20 , as shown in  FIG. 1 , is disposed at the top relative to the effective direction  50  of the force of gravity, while the anti-vibration elements  6  extend below the air filter  2 . 
       FIG. 4  shows a cross-sectional view through the air filter arrangement  1 . The air filter housing  21  has an air filter base  5  to which is secured a carburetor  7 . A portion of a mixture channel  9  is formed in the carburetor  7 . Disposed in the mixture channel  9  is a butterfly valve  13 , and upstream thereof a choke valve  14 . Opening into the mixture channel  9  is a fuel opening  39  that supplies fuel to the mixture channel  9  as a function of the underpressure or vacuum in the mixture channel. The mixture channel  9  opens into the air filter  2  at an inlet opening  10  that is formed in the air filter base  5 . 
     Supported on the carburetor  7  is an air channel portion  8  in which an air channel  11  is guided. Pivotably mounted in the air channel  11  is a choke or air valve  15 . The air channel portion  8  is held on a connector  16  on the air filter base  5 . The air channel  11  opens into the air filter  2  via an inlet opening  12  that is formed in the air filter base  5 . The mixture channel  9  has a longitudinal axis  29 , and the air channel  11  has a longitudinal axis  31 . 
     The air filter  2  delimits a clean chamber  18 . The air filter frame  3  has a sealing rim  30  via which it rests upon the air filter housing  21  and thus seals the clean chamber  18  relative to the atmosphere. Disposed in the clean chamber  18  is a shield  17  that extends over the inlet openings  10  and  12  of the mixture channel  9  and the air channel  11  respectively, and delimits a second clean chamber  28  that is disposed in the interior of the first clean chamber  18 . In the direction of the longitudinal axis  29  of the mixture channel  9 , the shield  17  is disposed between the inlet opening  10  of the mixture channel and the air filter element  4 , and in the direction of the longitudinal axis  31  of the air channel  11 , the shield  17  is disposed between the inlet opening  12  of the air channel and the air filter element  4 . 
     As shown in  FIG. 4  and in the perspective illustration of  FIG. 5 , the shield  17  has a bulged portion  32  that extends over the inlet opening  10  of the mixture channel  9 , and that on that side that is remote from the inlet opening  12  of the air channel  11  adjoins the air filter base  5 . As shown in  FIG. 5 , the bulged portion  32  also extends along the lateral regions of the inlet opening  10 , so that the bulged portion  32  is open only in the direction toward the inlet opening  12  of the air channel  11 . At the longitudinal sides of the inlet opening  10 , the shield  17  is secured to the air filter base  5  via securement nuts  27 . 
     Adjoining the bulged portion  32  is a channel-like connecting portion  33  that extends between the inlet opening  10  of the mixture channel  9  and the inlet opening  12  of the air channel  11 ; the connecting portion  33  extends over that region disposed between the two inlet openings  10 ,  12  in a tunnel-like manner. A transverse portion  34  adjoins the connecting portion  33  approximately at the level of the longitudinal axis  31  of the air channel  11 . The bulged portion  32 , the connecting portion  33 , and the transverse portion  34  form a T-shape, whereby the transverse portion  34  forms the crosspieces of the T. 
     On that side facing the connecting portion  33 , the transverse portion  34  is provided with guide surfaces  35  that are inclined toward the connecting portion  33 . On that side remote from the connecting portion  33 , the transverse portion  34  is provided with a top portion  19 . Formed in the top portion  19 , opposite to the guide surfaces  35 , are communication openings  26  that connect the first clean chamber  18  with the second clean chamber  28  that is formed in the shield  17 . The communication openings  26  are disposed beyond the extension of the connecting portion  33 . 
     As shown in  FIG. 4 , the rear wall  36  of the bulged portion  32  is inclined relative to the longitudinal axis  29  of the mixture channel  9  by an angle β that is less than 90°. The rear wall  37  of the connecting portion  33  is inclined relative to the longitudinal axis  29  of the mixture channel  9  by an angle α of greater than 90°. As shown in  FIG. 4 , the top  19  rises toward the inlet opening  12  of the air channel  11 . The top  19 , the rear wall  37 , and the rear wall  36  of the shield  17  thereby conduct condensed or deposited fuel back to the mixture channel  9 . 
     During operation, combustion air is drawn in through the filter element  4  into the first clean chamber  18 , from there via the communication openings  26  into the second clean chamber  28 , and into the air channel  11  and the mixture channel  9 . At low speeds, strong pulsations occur in the mixture channel  9 . In particular at high load, in other words when the butterfly valve  13 , the choke valve  14  and the air valve  15  are completely opened, relatively large quantities of fuel are flung out of the mixture channel  9  into the bulged portion  32  of the shield  17 . There, the fuel is partially deposited or condensed on the walls of the shield  17  and is conveyed back into the mixture channel  9  by the bulged portion  32 . A portion of the fuel passes into the air channel  11 , in which the fuel effects a cleaning of the air valve. At low speeds fuel is supplied to the internal combustion engine not only via the air channel  11  but also via the mixture channel  9 . Further fuel can be deposited on the shield  17  and is conveyed back into the mixture channel  9 . 
     At high speeds the pulsations in the intake channel are relatively low. As a result, at most small quantities of fuel pass into the shield  17 . The fuel is deposited essentially in the bulged portion  32 , and passes back into the mixture channel  9 . At high speeds, no fuel, or at most very small quantities of fuel, are supplied via the air channel  11 . As a result, a two-cycle engine having scavenging that is operated by the air filter arrangement  1  can achieve low emission values at high speeds. 
     The shield  17  extends the mixture channel  9  to the communication openings  26 . The air channel  11  is also extended by the flow length between the inlet opening  10  and the communication openings  26 . In this connection, the communication openings  26  are disposed in such a way that the overall lengths of the mixture channel and the air channel are coordinated with one another, so that during operation resonance results that leads to a good filling of the channels. As a result, in particular at low speeds, it is possible to achieve an increase of the torque of the internal combustion engine. 
     To ensure that at high speeds no fuel passes out of the bulged portion  32  and into the air channel  11 , the inlet opening  12  of the air channel  11 , relative to the effective direction  50  of the force of gravity, is disposed above the inlet opening  10  of the mixture channel  9  and above the bulged portion  32 . Due to the force of gravity, the fuel is supplied to the mixture channel  9  and not to the air channel  11 . In this connection, the customary installed position of the air filter arrangement  1  relates to the position that results from the customary position during operation. With power saws and cut-off machines, this position corresponds approximately to the position when the implement is set on the ground. 
     As shown in the exploded view of  FIG. 7 , the shield  17  is secured to the air filter base  5  via the securement nuts  27 . The shield  17  has no contact with other components. The filter element  4  extends over, and is spaced from, the shield  17 . To adapt the lengths of the mixture channel  9  and the air channel  11 , for example in order to use the air filter arrangement  1  with a different internal combustion engine, the shield  17  can be exchanged. The communication openings  26  can be arranged on the shield  17  in such a way that a good coordination or adaptation of the lengths of the channels results. It is also possible to lengthen the connecting portion  33  for adaptation of the channel lengths, for example by providing the connecting portion  33  with a bend. Additional guide elements could also be provided for altering the channel lengths and/or in order to guide the fuel in a precisely controlled manner. 
     The air channel and the mixture channel could also be guided in a common channel tube, at least over a portion of their length, and can be separated from one another by a partition. 
     The specification incorporates by reference the disclosure of German priority document 10 2006 013 602.0 filed Mar. 24, 2006. 
     The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.