FR2878564A1 - EXHAUST SYSTEM OF A WORKING APPARATUS DRIVEN BY A THERMAL ENGINE - Google Patents

Abstract

The invention relates to an exhaust system of a work device driven by a heat engine (1), in particular a hedge trimmer or a similar type of work device. The exhaust system comprises an exhaust pipe (2) for a flow of exhaust gas (3), where the exhaust pipe (2) opens to the open air through an exhaust end (4) . A condensate conductive member (6), which rotates and narrows the flow section, is provided on an inner wall (5) of the exhaust pipe (2).

Description

The invention relates to an exhaust system of a working apparatus

guided manually

  thermal, in an apparatus comprising an exhaust gas, wherein the exhaust pipe opens into the air by an end of exhaust.

  Hand-operated work equipment such as hedge trimmers, brushcutters, chain saws or similar type of work equipment are driven by heat engines which, in usual designs, include lost oil lubrication. In particular, in the case of two-cycle engine type models, the mixture of air and fuel introduced into the engine contains a small proportion of lubricating oil which, after passing through the engine, is evacuated to free air, in the form of fine fog, with the flow of exhaust gas occurring. In addition to said oil mist, combustion residues, moisture contained in the air or similar substances can also lead to fogging which is to be observed also in the case of four-stroke engines.

  It has been found that the above mentioned substances have a tendency in the flow of exhaust gas to form a condensation film on interior surfaces of the exhaust system. With regard to specific forms of construction, it is to be observed that, driven by a particular motor of a hedge trimmers or working of similar type, exhaust pipe for a flow, the condensation film is transported in the direction of the flow of gas exhaust. In the area of the end of the tailpipe exhaust, a build-up of condensation may form that drips at the end of the exhaust, or even passes back to the outside of the exhaust pipe. exhaust, towards the engine. This leads to unpleasant fouling which necessitates frequent cleaning of the working apparatus.

  The object of the invention is to improve an exhaust system of the type initially described, so that a fouling effect is avoided.

  The object is achieved by providing an exhaust system of a working apparatus driven by a heat engine, characterized in that a condensate conductive element, which rotates and narrows the flow section, is disposed on a wall inside the exhaust pipe. The arrangement of the conductive conductive element, rotating in the circumferential direction, has the effect of preventing the movement of the condensation film towards the flow of exhaust gas.

  The condensate conductive member extends inward radially from the inner wall of the exhaust pipe. The condensation accumulated or deposited on the walls of the exhaust pipe accumulates in this area and is directed inwards radially. At the same time, the rotating conductive conductive element causes, due to its inward radial extent, a narrowing of the free flow section. The speed of the exhaust gas flow is here locally increased. From the increased flow velocity accumulated and inwardly directed condensation is caused by the flow of exhaust gas and transported to the open air. It prevents a flow, drop by drop, of the condensation coming out of the exhaust pipe.

  In an advantageous development, the exhaust pipe is mounted downstream of an exhaust silencer, where the conductive conductive element is in a portion of the exhaust pipe placed outside the exhaust silencer. The part of the exhaust pipe outside is not bathed in hot exhaust gases. The comparatively cool environment favors the formation of condensation. In this area, the arrangement of the condensate conductive element results in a new entrainment of the condensed material in the exhaust stream almost directly at the location of the condensation formation. The formation of larger condensation accumulations and the inherent risk of drop formation are reliably avoided.

  The condensate conductive element is advantageously disposed in the immediate vicinity upstream of the end of the exhaust. A new condensation or deposition of the condensed material passing through the exhaust stream is prevented from occurring.

  In a preferred embodiment, the condensate conducting element forms, in its section, a point of separation for the flow of exhaust gas. The concept chosen here, concerning the point of separation, is not limited to an angular edge shape. It encompasses any aerodynamic shape that narrows the exhaust pipe flow section and, unlike a Venturi-like configuration, produces a flow detachment, with respect to the surface, with a formation of vortices. producing then. The detachment of the flow, with respect to the condensate conductive element, and the subsequent formation of vortices, promote the effect of driving the exhaust gas stream on the condensation film deposited on the sides of the walls.

  Whirlpool - shaped condensation droplets are transported into the inner - near - axis area of the exhaust stream, making it difficult to re - deposit the next pipe walls.

  In a suitable improvement, the conductive conductive member extends spiral-shaped along the inner wall of the exhaust pipe. The axially extending spiral shape allows, to a limited extent, axial movement of the wall-side condensed film and thus a distribution over the axial extent of the condensate conductive member. The condensation being distributed over the length of the conductive condensate element, it can, with greater efficiency, to iron in the flow of exhaust gas, the deposited condensation. To obtain a sufficient deflection effect, in the case of a reduced volume of construction, a number of turns, in the range between two turns and six turns, and, in particular, concerning an embodiment with about four turns, s' is revealed to be appropriate.

  In an advantageous embodiment, the condensate conducting element is, by its end placed downstream, guided in the region of a central axis of the exhaust pipe. Residual condensation which, over the length of construction of the condensate conducting element, is not redirected in the flow of exhaust gas, passes, in the direction of flow of the exhaust gas, in front of the element condensate conductor up to its downstream end. Thus, the residual condensation is guided in the region of the central axis where, in an improved manner, it can be absorbed and evacuated by the flow of exhaust gas. The formation of residual amounts of condensation is avoided.

  In a suitable embodiment, the conductive conductive member is designed as a spiral wire spring. The circular shape of the section of the wire has proved to be effective, both for the absorption of the deposited condensation flow, and for the flow guidance, with the formation of vortices of the exhaust gas flow. These advantageous effects go hand in hand with a simple and inexpensive construction method.

  The wire spring is preferably curved radially inwards at its upstream end. The end of the inward bent wire can be used simply as a mounting aid. At the same time, the end of the wire penetrating the flow section contributes to vortex formation and, therefore, to improved new absorption of condensation.

  In an advantageous embodiment, the metal wire is maintained in the exhaust pipe, being prestressed in the radial direction. Radial preload has the effect, in addition to a reliable fixation in position, a radial compressive force applying between the spring and the inner wall. In this zone, a sealing effect is observed. The condensation film can not pass between the wire spring and the pipe wall. Further, the condensation film is radially inwardly directed around the section of the spring wire, where the conditions for further entrainment into the exhaust stream are optimal.

  Exemplary embodiments of the invention are described in detail, in drawings.

  The overall figure, manually afterwards, way more using drawings. In these 1 shows, in a representation a guided work apparatus such as an exemplary trimmer and including an exhaust system indicated as a block diagram; FIG. 2 shows a view, in transparency and in perspective, of the exhaust pipe of the arrangement according to FIG. 1, comprising details with respect to the conductive conducting element disposed inside said exhaust pipe; Figure 3 shows, in an enlarged diagrammatic view and sectional view, the flow conditions in the sectional area of the wire of the condensate conductive member with respect to the arrangement according to Figure 2; FIG. 4 shows a perspective view of an insulated part of the condensate conductive element according to FIG. 2, in the form of a wire spring; FIG. 5 shows a variant of the wire spring according to FIG. 4, comprising one end of the wire taken in the region of the central axis.

  FIG. 1 shows, in a perspective view, a manually guided work apparatus such as, for example, a hedge trimmer which is driven by a heat engine 1. In place of a hedge trimmer, it can be provided also a brush cutter, a chainsaw, a chain saw or a similar type of work machine.

  The heat engine 1, not shown in greater detail, is held in a casing 17 and covered almost completely by the casing 17. From the heat engine 1, it is seen in the illustration shown here only one candle lug. ignition 20 and a start handle 19 for starting the engine 1.

  For guiding the hedge trimmer, there is provided a front handle 15 and a rear handle 16, whereby a cutting blade 18 driven by the heat engine 1 can be guided along the vegetation to be cut.

  In the embodiment shown, the heat engine 1 is a two-stroke, lost-oil lubrication engine, a two-stroke engine for the operation of which a proportion of lubricating oil is mixed with the fuel. But it can also be provided a separate lubrication comprising a separate lubricating oil reservoir and a lubrication at least almost without loss, for example in the case of a four-stroke engine.

  The exhaust gases occurring during operation of the heat engine 1 are directed through an exhaust system and discharged into the open air, said exhaust system being covered by the casing 17 and indicated in the drawings as being a schematic functional representation. The exhaust system comprises, for this purpose, an exhaust silencer 7 and an exhaust pipe 2 mounted downstream in the direction of flow. An exhaust gas flow indicated by an arrow 3 first passes through the exhaust silencer 7 and then the exhaust pipe 2, until it passes into the open air at the end of the engine. Exhaust pipe 4 free exhaust 2. To achieve the connection guiding the flow, the exhaust pipe 2 enters the exhaust muffler 7, through an inner portion 9 of the exhaust pipe. A portion 8 of the exhaust pipe 2, located downstream of this inner portion, extends outside the exhaust silencer casing 7. In the immediate vicinity of the exhaust end 4, a conductive element 6 of the condensation, described below in more detail, is disposed upstream of this exhaust end, in the pipe portion 8 placed outside.

  The exhaust pipe 2 according to Figure 1 is shown in Figure 2, in a view shown in transparency and in an enlarged manner. The exhaust pipe 2 is designed having a circular section and extends along a central axis 12. At the end of the exhaust 4 is disposed a conductive element 6 of the condensation which, in the example shown embodiment, is designed as a spiral wire spring 14. The wire spring 14 in the form of a spiral or, likewise, a helical spring, is introduced, under the effect of a radial prestressing, into the free end of the exhaust pipe 2, of the radial prestressing exhaust, the metallic is secured in position, by close friction 4. Under the effect of the end spring force wire and by safety of form, interior, in the shape of one of the exhaust pipe 2.

  and fits, inner wall side 5 For axial attachment, in position, of the wire spring 14, the exhaust pipe 2 is further provided, at the end of the exhaust 4, a fixing axial indicated by reference 21.

  The exhaust pipe 2, upstream of the conductive element 6 of the condensation, provides the flow of exhaust gas 3, a flow section of circular shape and unobstructed. This flow section is narrowed by the wire spring 14 rotating several times in the circumferential direction of the exhaust pipe 2 and protruding radially inwards with respect to the inner wall 5.

  The flow conditions at the conductive element 6 of the condensation are shown schematically and enlarged in FIG. 3. The circular section of a wire 22 of the spring 14 (FIG. 2) is compressed. against the inner wall 5 of the exhaust pipe 2. The flow of the exhaust stream 3 may be represented by flow lines of which, for the sake of clarity, only two flow lines 27 are represented. of the wall. Upstream of the wire 22, a condensation film 23 is deposited on the inner wall 5. The condensation film 23, due to the interaction with the exhaust gas stream 3 and, where appropriate, under the effect of the force of gravity, seeks to migrate towards the exhaust end 4 (FIG. 2), towards the flow of exhaust gas 3. According to the representation according to FIG. 3, it can be seen that the film condensing 23, following the above, accumulates upstream of the wire 22 and is directed by the conductive element 6 of the condensation, away from the inner wall 5 in the direction of the central axis 12 ( Figure 2).

  The chosen aerodynamic shape of the circular section of the wire 22 causes an interruption of the laminar flow of the exhaust gas stream 3. Downstream of the existing maximum wall gap with respect to the inner wall 5 is formed a point detachment 26 behind which detaches the flow, with respect to the surface of the conductive element 6 of the condensation and with respect to the next part of the inner wall 5. Vortices are formed indicated by the reference 25. point of separation 26, with respect to the section of the wire 22, is represented, along the length of the material of the wire, as a detachment line rotating around the central axis 12 (FIG. 2), depending on what, at least a considerable part of the exhaust gas stream 3 close to the wall is raised in vortices, downstream of the conducting element 6 of the condensation. In place of the circular section of the wire 22, which has been shown, other sectional shapes, for example angular, may also be appropriate, with the formation of an aerodynamic detachment point 26.

  The narrowing of the free flow section, by the conducting element 6 of the condensation, causes a local acceleration of the flow of exhaust gas 3, which acceleration is shown in the drawings by a gap falling between the lines 27, and which reaches its largest value, approximately in the region of the maximum radial projection of the conductive element 6 of the condensation, with respect to the inner wall 5. The gas flow of Exhaust 3 and / or the weight force causes (s) the condensation film 23 around the section of the wire 22, into the area mentioned above. In this zone, the high flow velocity, in association with the detached vortices 25, causes dissolution of the condensation film 23, in scattered drops indicated by the reference 24 and which are driven by the flow of exhaust gas 3, without being able to be deposited again on the inner wall 5. The detachment point 26 and the drops 24 have a radial distance, with respect to the inner wall 5, which helps to avoid a new fixation.

  FIG. 4 shows, in a perspective view of an individual part, the wire spring 14 according to FIG. 2. The wire spring 14 suitably comprises from two to six turns approximately rotating helically. . In the exemplary embodiment shown, a winding profile slightly greater than four turns 10 is provided. The wire spring 14 is furthermore, at its end 13 placed upstream, curved inwards in the radial direction, according to what the end 13 penetrates inside the flow section of the exhaust gas stream 3 (Figure 2).

  A variant of the wire spring 14 according to FIG. 4 is shown in FIG. 5, according to which the end 11 of the spring, placed downstream with respect to the direction of flow of the exhaust gas flow 3 ( 2), is guided from circumferentially circumferentially extending turns radially inward to a longitudinal axis 28 of the wire spring 14. At this location, the end 11 in the downstream state is bent extending towards the longitudinal axis 28. In the mounted state, the turns 10, as in the embodiment according to Figures 2 and 4, extending in shape spiral, apply against the inner wall 5 of the exhaust pipe 2.

  The longitudinal axis 28 coincides here with the median axis 12 of the exhaust pipe 2 (Figure 2).

  The end 11 of the wire spring 14, located downstream, is therefore at least almost on the median axis 12 of the exhaust pipe 2 or in the middle of the flow section. the example 5 coincides with the exhaust gas examples 3.

  characteristics and of realization according to that of figure 4.

  Other embodiments shown here, the conductive element 6 of the condensation is designed as a spiral wire spring 14. But it may also be advantageous to use a sheet metal strip, an embossing of the contours of the circumferential wall of the exhaust pipe 2 or comparable embodiments. Instead of a spiral-shaped profile, an annular ring-like configuration, in the form of a hole-shaped diaphragm, may also be appropriate, where, also, several circular disks may be cascaded, one behind the other .

Claims (10)

R E V E N D I C A T IO N S   An exhaust system of a working apparatus driven by a heat engine (1), in particular a hedge trimmer or similar type of working apparatus, comprising an exhaust pipe (2) for an exhaust stream (3), where the exhaust pipe (2) opens into the open air through an exhaust end (4), characterized in that a conductive element (6) of the condensation , which rotates and reduces the flow section, is disposed on an inner wall (5) of the exhaust pipe (2).   2. Exhaust system according to claim 1, characterized in that the exhaust pipe (2) is mounted downstream of an exhaust silencer (7), where the conductive element (6) of the condensation is in a pipe section (8) placed outside the exhaust silencer (7).   3. Exhaust system according to claim 1 or 2, characterized in that the conductive element (6) of the condensation is disposed in the immediate vicinity, upstream of the exhaust end (4).   4. Exhaust system according to one   any of claims 1 to 3,   characterized in that the conducting element (6) of the condensation forms, in its section, a detachment point (26) for the exhaust gas flow (3).   2878564 16 5. Exhaust system according to one   any of claims 1 to 4,   characterized in that the condensing conductive element (6) extends spirally along the inner wall (5) of the exhaust pipe (2).   6. Exhaust system according to claim 5, characterized in that the conductive element (6) of the condensation has between two and six turns approximately and, in particular, about four turns (10).   7. Exhaust system according to claim 5 or 6, characterized in that the conductive element (6) of the condensation is guided by its end (11) downstream in the region of a central axis (12). ) of the exhaust pipe (2).   8. Exhaust system according to any one of claims 5 to 7, characterized in that the conductive element (6) of the condensation is designed as a spiral-shaped wire spring (14).   Exhaust system according to claim 8, characterized in that the wire spring (14) at its upstream end (13) is curved inwards in the radial direction.   10. Exhaust system according to claim 8 or 9, characterized in that the wire spring (14) is held in the exhaust pipe (2), being prestressed in the radial direction. 30