Handheld Work Apparatus, and Exhaust Gas After-Treatment Unit for a Handheld Work Apparatus, and Exhaust Muffler

This application is a continuation application of United States patent application having application Ser. No. 19/112,527 filed Mar. 17, 2025 which is a 371 national stage application of international patent application PCT/EP2023/075239, filed Sep. 14, 2023, designating the United States and claiming priority from German applications 10 2022 123 838.5, filed Sep. 16, 2022, 10 2022 123 839.3, filed Sep. 16, 2022, 10 2022 123 840.7, filed Sep. 16, 2022, and European application 22196226.9, filed Sep. 16, 2022, and the entire content of the above applications is incorporated herein by reference.

Known from JP 2009-156158 A is a handheld work apparatus having an exhaust muffler which has a catalytic converter. The catalytic converter can be made of wire and is coated with a catalytic material such as platinum.

Combustion engine-powered handheld work apparatuses such as, for example, chain saws, angle grinders, brushcutters, blowers, lawnmowers or the like are subjected to increasingly tougher statutory requirements with regard to the composition of the exhaust gases. In order to meet these requirements, it is also known in the case of small engines of this type to use catalytic converters for the exhaust gas after-treatment. The parameters for catalytic converters of this type in handheld work apparatuses differ in many ways from the parameters in the automotive sector, for example. Due to the limited available installation space, exhaust mufflers in handheld work apparatuses of this type have to be configured to be comparatively small. At the same time, contact between the operator and hot parts of the work apparatus has to be avoided. Therefore, strict requirements also apply in terms of the exhaust gas temperatures. The combustion engines used are often mixture-lubricated engines. Owing to the fact that the fuel in mixture-lubricated engines is at least partially supplied to the crankcase of the combustion engine, precise metering of the fuel per cycle is not possible. Therefore, the composition of the exhaust gas in small engines of this type fluctuates significantly more than in the automotive sector, for example, where precise controlling of the quantity of fuel injected directly into the combustion chamber per cycle takes place.

In terms of temperature and weight, as well as in terms of fluctuating exhaust gas compositions, other requirements therefore have to be set for exhaust mufflers for handheld work apparatuses of this type than for exhaust mufflers as used in the automotive sector, or for diesel engines or for four-cycle engines with dedicated lubrication, so that solutions from the latter sector cannot simply be transferred to exhaust mufflers for handheld work apparatuses.

It is an object of the disclosure to provide a handheld work apparatus which is of a simple and robust construction. An additional object of the disclosure lies in specifying an exhaust gas after-treatment unit for the exhaust muffler of a handheld work apparatus.

In terms of the handheld work apparatus, the above object is achieved by a work apparatus according to various embodiments of the disclosure.

In terms of the exhaust gas after-treatment unit, the above object is achieved by an exhaust gas after-treatment unit according to various embodiments of the disclosure.

It is provided according to the disclosure that the exhaust gas after-treatment unit does not have a catalytically effective coating. A catalytically effective coating herein is a coating which acts as a catalytic converter, thus reduces the activation energy for the chemical conversion of the exhaust gases, and as a result increases the response rate. A catalytically effective coating is in particular a coating containing precious metal. The catalytically effective coating is in particular a coating which serves largely for converting hydrocarbons and/or nitrogen oxides.

Owing to the fact that the exhaust gas after-treatment unit does not have a catalytically effective coating, the exhaust gases are significantly less heated in the exhaust muffler than in the case of an exhaust gas after-treatment unit having a catalytically effective coating. As a result, a smaller installation space of the exhaust muffler is possible because a shorter cooling section for exhaust gases is required in the muffler. Owing to the fact that the exhaust gas after-treatment unit does not have a catalytically effective coating, raw materials, in particular precious metals of the catalytically effective coating, are saved and the cost for the production of the exhaust gas after-treatment unit are reduced. It has been surprisingly demonstrated that a sufficient treatment of the exhaust gases, in particular in terms of the conversion of particles, is possible in the exhaust gas after-treatment unit in combustion engines in handheld work apparatuses even without a catalytically effective coating of the exhaust gas after-treatment unit. In particular, the through-flow unit, preferably a wire element of the through-flow unit, does not have a catalytically effective coating.

The through-flow unit must have a minimum thickness in order to achieve a sufficient dwell time of the exhaust gases in the through-flow unit, so that sufficient converting of exhaust gases can take place. A through-flow unit which serves to convert particles has a thickness of at least 10 mm in the region passed through by exhaust gas. The through-flow unit may have a smaller thickness in peripheral regions. For example, the through-flow unit can be radiused or have a bevel in peripheral regions. The stated thickness of at least 10 mm is provided at least across 70% of the largest cross section, in particular across at least 80% of the largest cross section.

A high stability of the through-flow unit results by virtue of the comparatively large thickness of the through-flow unit. The cross sections herein lie perpendicularly to a main flow direction through the exhaust gas after-treatment unit. The largest cross section is the largest cross section of the through-flow unit perpendicular to the main flow direction. The thickness is advantageously measured parallel to the main flow direction. The thickness is preferably perpendicular to the first upstream end face of the through-flow unit.

The thickness of the through-flow unit in the region of the through-flow unit passed through by the flow of exhaust gas is preferably at least 15 mm, particular preferably at least 20 mm, across at least 70% of the largest cross section. The thickness of the through-flow unit in the region of the through-flow unit passed through by the flow of exhaust gas is preferably at least 10 mm, in particular at least 15 mm, across the entire largest cross section.

Advantageously, all through-flow units of exhaust gas after-treatment units of the exhaust muffler in the region of the through-flow units passed through by the flow of exhaust gas have a thickness of at least 10 mm across at least 70% of the largest cross section.

The at least one through-flow unit is advantageously at least partially, in particular completely, coated with a washcoat. A washcoat is presently a coating that increases the surface without reducing the activation energy for the chemical conversion. For example, the washcoat can be of aluminum oxide. The washcoat has the effect of improving the particle-converting effect. Advantageously, the through-flow unit includes at least one wire element of metal. Owing to the fact that the through-flow unit includes at least one wire element of metal, the through-flow unit acts as a particle converter. Oil droplets in the flow of exhaust gas are converted at sufficiently high temperatures in the wire element, resulting in the reduction of particles.

It has been demonstrated that a coating with a washcoat is advantageous in particular for a wire element in order to achieve positive results during particle conversion.

A wire element herein is understood to be a dimensionally stable element which is formed from at least one wire of metal. A wire herein is a thin, elongate, flexible metal part. The wire preferably has a round cross section. An angular cross section or any other suitable cross-sectional shape may also be advantageous. The cross section of the wire over its length is advantageously constant within the scope of the usual manufacturing tolerances. The wire is preferably produced by drawing.

In an alternative embodiment, the through-flow unit can also have a through-flow unit of a different construction instead of a wire element.

The wire cross section of the at least one wire element, in particular of all wire elements, of the exhaust gas after-treatment unit is advantageously at least 0.07 mm2. If the wire has a round wire cross section, the diameter of the wire is advantageously at least 0.3 mm. A sufficient stability of the wire element is achieved as a result. At the same time, a large surface of the wire element is achieved so that a positive particle reduction is achieved. The wire cross section of the wire element is advantageously not more than 0.8 mm2. The diameter of the wire in the case of a round wire cross section is advantageously not more than 1 mm.

The wire of the wire element advantageously consists at least partially, in particular completely, of a nickel alloy or of stainless steel. Stainless steel is presently in particular stainless steel according to DIN EN 10 088.

The density of at least one wire element, at least in the region passed through by the flow of exhaust gas, is advantageously 0.6 g/cm3 to 2.0 g/cm3. The density of all the wire elements of the exhaust gas after-treatment unit, at least in the region passed through by the flow of exhaust gas, is preferably 0.6 g/cm3 to 2.0 g/cm3. It has been demonstrated that a positive particle reduction can be achieved by way of a density of the wire element in the stated range. The density of the wire element is closely associated with the proportion of the cavities of the wire element to the entire volume of the wire element. As a result, the density of the wire element influences the flow resistance and the dwell time of the exhaust gases in the wire element. If the density is in the stated range, favorable values in terms of the flow resistance and the dwell time can be achieved.

It has been demonstrated that the volume of the wire elements is relevant to a positive particle reduction. The sum of the volumes of the regions passed through by the flow of all wire elements of the through-flow unit is advantageously at least 0.6 times the cubic capacity of the combustion engine.

The wire element is preferably formed from a knitted metal mesh. The wire element is preferably helically wound. The wire element is particularly preferably a helically wound knitted metal mesh mat. In an advantageous design embodiment, the wire element is disposed in the exhaust muffler in such a way that the winding axis extends through the upstream end face and the downstream end face of the wire element. In the case of an approximately cylindrical shape of the wire element, a constant thickness of the wire element, within the scope of the usual manufacturing tolerances, across a large part of the cross section, in particular across the entire cross section, can thus be simply achieved. The winding axis advantageously extends perpendicularly to the upstream end face and/or to the downstream end face of the wire element.

The smallest cross section of the through-flow unit in the region of the through-flow unit passed through by the flow of exhaust gas is advantageously at least 8 mm2, in particular at least 12 mm2, per cubic centimeter of cubic capacity of the combustion engine.

It is advantageously provided that the exhaust muffler has an exhaust inlet into the exhaust muffler and an exhaust outlet from the exhaust muffler. At least one through-flow unit, in particular at least one wire element of the exhaust gas after-treatment unit, is advantageously disposed in each flow path from the exhaust inlet to the exhaust outlet. Accordingly, the exhaust muffler in an embodiment does not have a bypass in relation to the at least one wire element. Accordingly, exhaust gas must forcibly flow through at least one through-flow unit, in particular through at least one wire element of the exhaust gas after-treatment unit. A positive particle reduction is ensured as a result. There is advantageously no flow path from the exhaust inlet to the exhaust outlet that does not lead through at least one through-flow unit. A flow path is presently understood to be a fluidic connection from the exhaust inlet to the exhaust outlet of the exhaust muffler. A multiplicity of flow paths from the exhaust inlet to the exhaust outlet can be formed in the exhaust muffler.

In order to ensure that exhaust gases that flow out of the exhaust gas after-treatment unit can be sufficiently cooled in the exhaust muffler, it is advantageously provided that the second muffler chamber has a volume which is at least 80% of the cubic capacity of the combustion engine.

The combustion engine is in particular a mixture-lubricated combustion engine. The combustion engine is particularly preferably a two-stroke engine. In mixture-lubricated combustion engines, the exhaust gas contains oil droplets which can be converted in the wire element. The work apparatus is advantageously configured in such a manner that the temperature of the exhaust gas flow on an upstream side of the exhaust gas after-treatment unit after at least 2 minutes of operating time of the combustion engine under full load is 450° C. to 750° C. This temperature can be achieved, for example, by a suitable basic design of the combustion engine and/or a suitable arrangement of the exhaust gas after-treatment unit. Temperatures of this type are in particular achieved in mixture-lubricated combustion engines in handheld work apparatuses, in particular in the case of two-stroke engines. It has been demonstrated that sufficient temperatures for a positive particle reduction are present at temperatures in this temperature range on the upstream side of the exhaust gas after-treatment unit. Therefore, any additional heating of the exhaust gas after-treatment unit, for example by a heating element or by a catalytic reaction of a catalytically effective coating of parts of the exhaust gas after-treatment unit, is therefore not mandatory. This results in a simple construction of the work apparatus.

For an exhaust gas after-treatment unit for a handheld work apparatus it is advantageously provided that the exhaust gas after-treatment unit includes at least one through-flow unit, in particular at least one through-flow unit having at least one wire element of metal. The exhaust gas after-treatment unit does not have a catalytically effective coating. Accordingly, the wire element of metal is not coated with a catalytic material. The wire element does not have a coating, or the coating of the wire element does not have a catalytic effect. A coating of the wire element in particular does not include any precious metal. This results in a simple cost-effective construction, and the exhaust gases leaving the wire element have a comparatively low temperature.

The disclosure furthermore relates to an exhaust muffler and to a combustion engine having an exhaust muffler.

A ceramic catalytic converter element for an exhaust muffler is disclosed in US 2002/0042344. The catalytic converter element has in one embodiment a central region which has a higher quantity of catalytic coating per volumetric unit than a peripheral region. Due to the arrangement of the central region in the projection surface of the gas inlet, a higher proportion of the exhaust gas flow is to be purified when idling as compared to an operation under full load.

It has been demonstrated that exhaust mufflers can overheat during operation when an excessive sub-flow of the exhaust gas is subjected to catalytic after-treatment.

It is a further object to provide an exhaust muffler which has a simple construction and enables the temperatures occurring during operation to be set.

This object is, for example, achieved by an exhaust muffler according to various embodiments of the disclosure.

An additional object of the disclosure lies in specifying a combustion engine having an exhaust muffler. This object is achieved by a combustion engine according to various embodiments of the disclosure.

It is provided that the exhaust muffler has a first through-flow unit and a second through-flow unit for exhaust gas after-treatment. The through-flow units have different quantities of catalytically effective coating. The quantity of catalytic coating herein relates to the mass of the catalytic coating. As a result, the through-flow units are differently heated during operation. A plurality of flow paths for exhaust gas are formed in the exhaust muffler, wherein a first flow path leads only through the first through-flow unit, and a second flow path leads only through the second through flow-unit. Owing to a suitable basic configuration of the flow paths, the quantity of exhaust gas that flows through the first flow path and that is guided through the second flow path can be structurally predefined. The flow cross sections of the flow paths are structurally predefined and invariable. This results in a simple construction of the exhaust muffler. In particular, mechanical means, such as flaps, slides or the like, for controlling and varying the flow path are not provided.

In order to enable a positive setting of the quantities of the exhaust gas that flow through the first flow unit and of the quantities of exhaust gas that flow through the second flow unit, the present disclosure provides that the first through-flow unit and the second through-flow unit are disposed so as to be spatially separated from one another. The spatially separated arrangement has the effect that an exhaust gas sub-flow flows either through the first through-flow unit or through the second through-flow unit. A cross flow between the through-flow units is precluded by virtue of the spatially separate arrangement. As a result, defined flow conditions, which are in particular set as a function of the rotating speed, are achieved in the exhaust muffler. Owing to the spatial separation, it can be predefined better than in the prior art which exhaust gas proportions flow through which of the through-flow units at which overall exhaust gas flows.

The setting can be performed in such a way, for example, that a larger proportion of exhaust gas flows through the second through-flow unit, which has the higher quantity of catalytic effective coating, at low rotating speeds than at high rotating speeds. As a result, rapid heating of the exhaust muffler can be achieved at low rotating speeds, so that the exhaust gas after-treatment becomes completely effective quickly upon starting, and overheating of the exhaust muffler at high rotating speeds can be prevented.

The spatial separation is advantageously configured in such a manner that a cross flow between the through-flow units is impossible. The spatial separation is advantageously provided in such a manner that an exhaust gas sub-flow flows either only through the first through-flow unit or only through the second through-flow unit. Additionally, one or a plurality of additional through-flow units can be provided. For example, a third through-flow unit, through which a third flow path is formed, can be provided, and an additional exhaust gas sub-flow flows only through the third through-flow unit and bypasses the first through-flow unit and the second through-flow unit.

It has been demonstrated that overheating of exhaust mufflers having a catalytic coating can take place in particular when a combustion engine on which the exhaust muffler is disposed operates at high load during stationary operation. In this operation, there is the highest mass flow through the combustion engine because throttle elements in the intake port of the combustion engine are completely opened. The spatial separation according to the disclosure of the first through-flow unit and of the second through-flow unit, which have different quantities of catalytically effective coating, makes it possible to size, position and/or form the through-flow units in such a way that, in particular at high exhaust gas mass flows through the exhaust muffler, this results in a smaller sub-flow through the second through-flow unit than at lower exhaust gas mass flows. As a result, overheating of the exhaust muffler can be prevented in particular at a high load during stationary operation.

The at least one through-flow unit, thus in particular the first through-flow unit and/or the second through-flow unit, is advantageously coated with a washcoat and/or with a catalytic coating. Advantageously, each through-flow unit is provided with a washcoat and/or with a catalytic coating. However, it can also be provided that at least one through-flow unit has neither a washcoat nor a catalytic coating. A through-flow unit which is provided with neither a washcoat nor a catalytic coating serves largely to reduce particles. Lubricating oil in the form of droplets, which is converted by the through-flow unit, is contained in exhaust gases of mixture-lubricated combustion engines. Oil droplets are converted by the first through-flow unit as soon as the temperatures required therefor have been reached. The particles are reduced as a result. The second through-flow unit, which is coated with a catalytically effective coating, in particular with precious metal, serves largely to convert hydrocarbons and/or nitrogen oxides.

A catalytically effective coating is presently understood to be a coating which acts as a catalytic converter, thus reduces the activation energy for the chemical conversion of the exhaust gases, and increases the response rate as a result. A washcoat is presently not considered to be a catalytic coating. A washcoat is regarded as a coating which enlarges the surface of a substrate, for example of the first through-flow unit and/or of the second through-flow unit, without reducing the activation energy for the chemical conversion. The first through-flow unit does not have to have a catalytically effective coating, but may have a washcoat.

The first through-flow unit and the second through-flow unit advantageously have a mutual spacing. Owing to this fact, a spatial separation of the through-flow units can be easily achieved, and a cross flow from the first into the second through-flow unit, or from the second into the first through-flow unit, can be avoided in particular.

A simple configuration embodiment results when the first through-flow unit and the second through-flow unit are disposed in a partition wall of the exhaust muffler, between a first muffler chamber and a second muffler chamber. The first through-flow unit and the second through-flow unit have a mutual spacing in particular in the partition wall.

In an advantageous variant of embodiment it is provided that the first muffler chamber at least partially surrounds the second muffler chamber. The first muffler chamber is advantageously separated from the second muffler chamber by a divider in which the first through-flow unit and the second through-flow unit are disposed. The divider can be configured to be tubular, for example. The divider can be formed by a tube or by one or a plurality of partition walls, for example. The divider is preferably configured as a tube which is closed on one side and into which the exhaust gases from the first muffler chamber flow either by way of the first through-flow unit or by way of the second through-flow unit. The exhaust gases preferably flow out of the second muffler chamber by way of the open end of the tubular divider.

In an advantageous alternative embodiment it is provided that the exhaust muffler has a third muffler chamber. The first through-flow unit is advantageously disposed in a first partition wall which separates the first muffler chamber and the second muffler chamber from one another. The second through-flow unit is advantageously disposed in a second partition wall which separates a third muffler chamber from the second muffler chamber. The third muffler chamber is advantageously disposed in the second flow path in the flow direction between the first muffler chamber and the second muffler chamber. When a third muffler chamber is provided, exhaust gases from the first muffler chamber can accordingly flow either through the first through-flow unit into the second muffler chamber, or from the first muffler chamber first into the third muffler chamber and from there through the second through-flow unit into the second muffler chamber.

A passage through the first partition wall and the second partition wall, which leads from the first muffler chamber into the third muffler chamber, is advantageously provided. The throttling of the second flow path can be set by way of the arrangement and the dimensions of the passage. In this way, the splitting of the exhaust gas flows between the first and the second flow path can be easily set. Advantageously, the volumes of the first muffler chamber and of the third muffler chamber are of different sizes. It can be provided here that the first muffler chamber is larger than the third muffler chamber. However, it can also be advantageous for the third muffler chamber to be larger than the first muffler chamber. In an advantageous alternative configuration embodiment, the first muffler chamber and the third muffler chamber can be of approximately identical size.

In a particularly advantageous configuration embodiment, the outflow direction from the first through-flow unit and the outflow direction from the second through-flow unit oppose one another. The sub-flows of the exhaust gas that flow through the first and the second through-flow unit mutually influence one another due to the opposing outflow directions in the second muffler chamber. The magnitude of the influence herein is a function of the volumetric flow of the exhaust gas. As a result, different splits of the sub-flows among the flow paths can be easily achieved for different rotating speeds of a combustion engine.

The outflow surface from the first through-flow unit and the outflow surface from the second through-flow unit are advantageously at least partially congruent in the outflow direction from the first through-flow unit. The mutually opposing flows from the through-flow units throttle one another as a function of the overall exhaust gas mass flow and of the exhaust gas mass sub-flows through the through-flow units. The mutual influence can be set by a suitable choice of the degree of congruence and of the spacing of the outflow surfaces. Influencing the mass flows by the flow paths so that the exhaust gases are split differently among the flow paths as a function of the rotating speed can easily be achieved. At the same time, a compact construction is achieved as a result. Exhaust gas exiting the first through-flow unit advantageously throttles the exhaust gas flow flowing through the second through-flow unit. As a result, the exhaust gas flow flowing through the second through-flow unit is reduced as the overall exhaust gas mass flow through the exhaust muffler increases.

It has proven advantageous when the spacing between the outflow surfaces of the first through-flow unit and of the second through-flow unit in the second muffler chamber is less than 3 cm, in particular less than 2 cm.

A simple construction of the exhaust muffler is achieved when at least one through-flow unit includes at least one wire element. It is known to use coated wire elements as catalytic converters in particular for handheld work apparatuses such as chainsaws, angle grinders, brushcutters or the like. Wire elements of this type are very robust and easy to produce, and therefore well suited for use in work apparatuses of this type. The wire element is particularly preferably formed from metal wire pressed into shape. Each through-flow unit herein can include one or a plurality of wire elements. The individual wire elements of one through-flow unit can be in mutual contact, or be mutually spaced apart. The through-flow elements of one through-flow unit can advantageously be disposed in a common housing which is held in a partition wall or a divider, for example. The housing herein can at least be partially formed integrally with a partition wall or a divider, or be formed separately from the partition wall or the divider, or be fixedly connected thereto.

Each flow path advantageously leads through the exhaust muffler through one through-flow unit. Accordingly, no exhaust gas that has not passed through at least one through-flow unit leaves the exhaust muffler. An effective exhaust gas after-treatment can easily be ensured as a result.