Two-stroke engine with an exhaust gas system and use thereof

Abstract

The invention relates to an exhaust gas system (6) comprising a two-stroke engine (16), wherein the exhaust gas system (6) has an exhaust gas line (13) and at least two catalyst support bodies (2, 3), the exhaust gas line (13) forms a concentric region (10) with an inner central channel (15) and with a concentrically outer circumferential channel (5), a first catalyst support body (2) is situated in the inner central channel (15) and a second catalyst support body (3) is situated in the concentrically outer circumferential channel (5), and the exhaust gas system (6) and the catalyst support bodies (2, 3) are configured such that exhaust gas coming from the two-stroke engine (16) at a flow speed flows through the at least two catalyst support bodies (2, 3) one after the other as the dwell time increases.

Description

[0001] Exhaust system with a two-stroke engine and its use

[0002] The invention relates to an exhaust system. In particular, an exhaust system for a motorcycle with a two-stroke engine is proposed, wherein the exhaust system comprises an exhaust pipe and (catalytic) devices for cleaning the exhaust gas.

[0003] Exhaust systems for two-stroke engines, such as those found in motorcycles, differ from those of cars primarily in that they offer less installation space and therefore less room for exhaust-cleaning components. However, increasingly stringent emission limits are being imposed on motorcycles as well, due to emissions standards. This results in increased efforts, particularly for motorcycles with two-stroke engines. Because of a different combustion mixture and the addition of oil to the combustion chamber, two-stroke engines produce significantly higher emissions than four-stroke engines.

[0004] In particular, an increased hydrocarbon concentration in the exhaust gas necessitates greater efforts in the design of exhaust systems. Coupled with the limited space required for motorcycles, this necessitates new approaches to providing exhaust gas purification systems. Specifically, the use of conventional exhaust systems, such as those employed on four-stroke motorcycles, can lead to temperatures within the exhaust aftertreatment components of two-stroke motorcycles that could damage them. In particular, catalytic coatings and their carriers can be damaged and their function impaired. Consequently, comprehensive exhaust gas purification cannot be guaranteed, and compliance with emission limits cannot be achieved.

[0005] Based on this, the object of the invention is to at least partially solve the problems described with reference to the prior art. In particular, it aims to create a means of efficient exhaust gas purification for motorcycles, especially those with two-stroke engines, in very confined / compact installation space in / on the frame and / or under high thermal loads.

[0006] This problem is solved by the features of the independent claims. Further advantageous embodiments of the invention are specified in the dependent claims. It should be noted that features listed individually in the claims can be combined with one another in any technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, which also presents further preferred embodiments of the invention.

[0007] To solve this problem, an exhaust system with a two-stroke engine is used, comprising an exhaust pipe and at least two catalyst carriers. The exhaust system and the catalyst carriers are designed such that the exhaust gas from the two-stroke engine flows through the catalyst carriers sequentially with increasing residence time.

[0008] The exhaust pipe, which in particular defines or limits the flow path for the exhaust gas, forms a concentric section with an inner central channel and a concentric outer circumferential channel. A first catalyst support body is arranged in the inner central channel, and a second catalyst support body is arranged in the concentric outer circumferential channel.

[0009] The exhaust system of a motorcycle can begin at the two-stroke engine and end at a muffler. It is possible that the exhaust system runs partially within or alongside the motorcycle's frame. It is also possible that the exhaust system extends into an area outside the frame. Preferably, the exhaust system is designed so that it does not obstruct or endanger the rider of the motorcycle. The exhaust system is also preferably arranged so that it is protected from damage when the motorcycle is being operated.

[0010] The exhaust system has an exhaust pipe in which several separate catalyst carriers are arranged. The exhaust pipe may consist of several pipe sections. These pipe sections may be bent or curved to ensure the exhaust system is as compact as possible on the motorcycle. The exhaust pipe may also include a (separate) housing for a catalyst carrier. If the exhaust system consists of multiple pipe sections, housings, etc., these components are joined together in a gas-tight manner, for example, by welding.

[0011] It is possible for the catalyst support bodies to be arranged and secured within the pipe sections. It is also possible for at least one catalyst support body to be arranged in a housing, and for the housing to be attached to the pipe sections, allowing exhaust gases to pass through and making the catalyst support bodies and housing part of the exhaust system. The catalyst support body can, in particular, be designed with a honeycomb structure comprising a plurality of approximately parallel adjacent channels. The honeycomb structure can be formed, for example, with one or more smooth / corrugated metal foils that are stacked, wound, and / or twisted and permanently attached within the pipe section and / or the housing. The metal foils can be soldered together (at least partially or partially). The honeycomb structure can provide a surface within / on the channels to which a suitable, catalytically active coating is applied.The catalyst support bodies of the exhaust system may differ, particularly with regard to at least one element of the following group: dimension(s), volume, material, channel density, coating, flow resistance, etc.

[0012] The exhaust system and / or the catalyst support bodies are designed such that exhaust gas from the two-stroke engine flows through the catalyst support bodies (or all of them) sequentially with increasing residence time. "Residence time" is defined in particular as the time it takes for an exhaust gas stream to travel from an inlet to an outlet of a catalyst support body. A longer residence time can lead to increased cleaning performance and / or reduced temperature stress on the catalyst support body. With a shorter residence time, the cleaning performance and / or temperature stress decrease during operation of the exhaust system. In particular, the catalyst support bodies are designed so that the exhaust gases are treated stepwise or successively within the catalyst support bodies. This preferably prevents individual catalyst support bodies from overheating due to excessive treatment load.The higher the cleaning efficiency of a catalyst support, the greater the temperature rise. The residence time can be achieved or adjusted, in particular, by varying the channel density of the catalyst support and / or by using different dimensions of the catalyst support. Preferably, the residence time can be adjusted by varying the length and / or diameter of the catalyst support. Thus, the residence time in the catalyst support increases when it is longer and / or wider. With a longer residence time, more exhaust gases are processed or treated.

[0013] The concentric section can form part of the exhaust system. Preferably, the concentric section is formed or bounded by (at least) one housing for a catalyst support body. The concentric section is configured with an inner central channel and a concentric outer circumferential channel. Preferably, the exhaust system has an inlet connection to the concentric section that opens (gas-tight to the environment) into / onto the inner central channel. Preferably, the exhaust system has an outlet connection that is (gas-tight to the environment) connected to the outer circumferential section. Preferably, the exhaust gases can be directed through the exhaust system so that they can enter the concentric section via the inlet connection into the inner central channel. It is possible for the exhaust gases to exit the concentric section again from the concentric outer circumferential channel via the outlet connection.

[0014] A first catalyst support body is arranged in the inner central channel, and a second catalyst support body is arranged separately in the concentric outer circumferential channel. The exhaust gases can thus be routed first through the first catalyst support body and then through the second catalyst support body (spaced along the flow path). A deflection of approximately 180° can be formed between the two catalyst support bodies. The concentric arrangement of the catalyst support bodies allows for the adjustment of mutual temperature influence through direct or indirect heat conduction, thereby enabling more efficient exhaust gas purification. In particular, a larger quantity of exhaust gases can be purified in a smaller space within the concentric area than if the two catalyst support bodies were arranged one behind the other. Furthermore, this arrangement results in a very compact exhaust system design.

[0015] The first and second catalyst support bodies can be arranged in the concentric region such that they radially overlap. The first catalyst support body can be (partially) enclosed radially by the second catalyst support body. It is possible that the first and second catalyst support bodies are separated from each other (only) by a single (tubular) housing. Preferably, the first catalyst support body is longer than the second catalyst support body. Preferably, the first catalyst support body extends over the entire length of the concentric region or up to 85% of its length. It is possible that the first catalyst support body extends beyond the length of the concentric region (on one side or even both sides), for example, having a body length of up to 150% of the length of the concentric region.Preferably, the first catalyst support body extends over up to 40% of the diameter of the concentric region. Preferably, the second catalyst support body extends over up to 65% of the length of the concentric region. Preferably, the second catalyst support body extends over up to 60% of the diameter of the concentric region.

[0016] It is possible for the exhaust system to have a pretreatment section between the two-stroke engine and the concentric section, which may be designed as a joined pipe section, e.g., in the form of a manifold. A third catalyst support body may be arranged in this pretreatment section. It is possible for the exhaust gas, flowing at a certain velocity, to pass through the at least three catalyst support bodies with increasing residence time. It is possible for the exhaust gas to first pass through the third catalyst support body before entering the concentric section. It is possible for only pretreated exhaust gas to enter the concentric section, where it can undergo further treatment. It is possible for the pretreatment section to connect directly to the two-stroke engine or to be connected to the two-stroke engine via a manifold or pipe system. Preferably, the pretreatment section is located close to the engine.Preferably, the exhaust pipe from a connection to the two-stroke engine to a connection from the pretreatment area to the concentric area is not longer than 30 cm.

[0017] The exhaust system may have an aftertreatment section, which may optionally be designed as a joined pipe section, e.g., in the manner of an exhaust pipe, whereby this aftertreatment section preferably does not include a silencer unit. Preferably, the aftertreatment section is a connection from the concentric section to a rearward-terminating section of the exhaust system at the rear of the motorcycle, in particular to a silencer section. The aftertreatment section may connect to the concentric section and have a maximum length of 50 cm.

[0018] A fourth catalyst support body can be arranged in the aftertreatment section. Preferably, the fourth catalyst support body is arranged as close as possible to an outlet of the concentric section. It is possible for the exhaust gas, flowing at a certain velocity, to pass through the at least three catalyst support bodies with increasing residence time. Preferably, the exhaust gas line has a length of less than 10 cm from the end of the concentric section to the beginning of the fourth catalyst support body in the aftertreatment section.

[0019] The concentric section can have a (separate, optionally joined / welded) deflector cap. The deflector cap can connect the inner central channel with the concentric outer circumferential channel. Preferably, exhaust gases can be diverted by the deflector cap so that they flow from the inner central channel to the concentric outer circumferential channel. Preferably, the exhaust gases can thus be diverted within the concentric section. In this way, the exhaust gases can be introduced into the concentric section and, before exiting to the aftertreatment section, flow through the first catalyst support body and the second catalyst support body.

[0020] The deflection cap can be located at the lowest point of the exhaust system when it is fixed or installed on the motorcycle. It is possible that the concentric section with connections to the pre-treatment and post-treatment sections is positioned at the top, with the deflection cap forming the lower end of this concentric section. The deflection cap may also be a reinforced component (e.g., with thicker walls, ribs, etc.) to protect it from damage should it come into contact with the ground.

[0021] The deflector cap can have at least one flow-guiding element oriented towards or extending to the inner central channel. Exhaust gases from the inner central channel may impinge upon the flow-guiding element and be diverted (radially) to the concentric outer circumferential channel (preferably in a laminar or low-turbulence manner). Preferably, the flow-guiding element is a projection, particularly a rounded one, extending into the deflector cap. The exhaust gas flow from the inner central channel may be divided and distributed by the flow-guiding element.

[0022] The concentric area can include an (outer) double jacket with a (closed, circumferential) air gap. The double jacket may provide insulation for the concentric area. It may also reduce the risk of burns from the casing of the concentric area.

[0023] A multitude of catalyst carriers can be arranged in series from the two-stroke engine up to a section of the muffler. Exhaust gas from the two-stroke engine, flowing at a certain velocity, can pass through the catalyst carriers sequentially with increasing residence time.

[0024] In particular, a motorcycle with a two-stroke engine is proposed, featuring an exhaust system according to the configuration proposed here.

[0025] The solution to the problem is also provided by the use of an exhaust system in a motorcycle with a two-stroke engine, wherein the exhaust system and the catalyst support bodies are arranged in such a way that exhaust gas coming from the two-stroke engine at a flow velocity flows through the catalyst support bodies one after the other with increasing residence time.

[0026] The exhaust system offers particular advantages and provides relief with regard to the problems mentioned at the outset. The specific advantages and design features described for the exhaust system are applicable and transferable to the described use of the exhaust system, and vice versa.

[0027] The invention and its technical context are explained in more detail below with reference to five figures. The illustrations are schematic and not intended to demonstrate scale relationships. The explanations given with reference to individual details of the figures can be extracted and freely combined with information from the preceding description, unless a person skilled in the art would necessarily conclude otherwise, or such a combination is explicitly excluded. The figures schematically depict:

[0028] Fig. 1: a schematic sectional view of an exhaust system,

[0029] Fig. 2: a schematic sectional view of a concentric region in a first orientation,

[0030] Fig. 3: a three-dimensional representation of the exhaust system, and

[0031] Fig. 4: a schematic sectional view of the concentric area in a second orientation.

[0032] Fig. 1 shows a schematic sectional view of the exhaust system 6. Arrows indicate the flow path of exhaust gas through the exhaust system 6, starting at a two-stroke engine 16 and ending at a silencer section 17. The exhaust gas is first passed through a third catalyst support body 1 and from there into a first catalyst support body 2 in the concentric region 10. The first catalyst support body 2 is arranged in an inner central channel 15 of the concentric region 10. After passing through the first catalyst support body 2, the exhaust gas enters a deflector cap 14. There, it is diverted into a second catalyst support body 3, which is arranged in an outer circumferential channel 5. The outer circumferential channel 5 is arranged around the inner central channel 15. Thus, the outer circumferential channel 5 forms an annular region in which the second catalyst support body 3 extends.After passing through the second catalyst support body 3, the exhaust gas enters a fourth catalyst support body 4.

[0033] Fig. 2 shows a schematic sectional view of the concentric region 10 in a first orientation. It can be seen that the first catalyst support body 2 in the inner central channel 15 is surrounded in an annular fashion by the second catalyst support body 3 in the outer circumferential channel 5. Fig. 3 shows a three-dimensional representation of the exhaust system 6. It can be seen how an exhaust pipe 13 of the exhaust system 6 is designed so that exhaust gas can flow through it. It can be seen how the third catalyst support body 1 is arranged in the pretreatment region 9. Furthermore, it can be seen that the pretreatment region 9 is connected to the concentric region 10 in such a way that the exhaust gas can pass directly from the third catalyst support body 1 to the first catalyst support body 2 in the inner central channel 15.It can also be seen how the deflector cap 14, as part of the exhaust gas line 13, directs the exhaust gas from the inner central channel 15 to the outer circumferential channel 5, allowing it to flow from the first catalyst support body 2 to the second catalyst support body 3. A flow-guiding element 7 is also arranged in the deflector cap 14, which can redirect the exhaust gas with minimal flow restrictions. From the inner central channel 15, the exhaust gas can be directed out of the concentric area 10 into the aftertreatment area 11 to the fourth catalyst support body 4. An exhaust gas probe 12 is arranged in the aftertreatment area 11 to measure the exhaust gas flowing through it.

[0034] Fig. 4 shows a schematic sectional view of the concentric region 10 from Fig. 5 in a second orientation. It can be seen that the first catalyst support body 2 is longer than the second catalyst support body 3. It can also be seen that the first catalyst support body 2 and the second catalyst support body 3 terminate at the same height towards the deflecting cap 14.

[0035] The solution proposed here can at least partially alleviate the problems described with reference to the state of the art. In particular, solutions have been presented that enable an exhaust system for a motorcycle, especially one with a two-stroke engine, to efficiently clean exhaust gases. Reference numeral

[0036] 1 third catalyst support body

[0037] 2 first catalyst support body

[0038] 3 second catalyst support body

[0039] 4 fourth catalyst support body

[0040] 5 external circumferential channel

[0041] 6 Exhaust system

[0042] 7 flow-conducting element

[0043] 8 Double jacket

[0044] 9 Pretreatment area

[0045] 10 concentric areas

[0046] 11 Post-treatment area

[0047] 12 Exhaust gas probe

[0048] 13 Exhaust pipe

[0049] 14 Deflection cap

[0050] 15 internal central channel

[0051] 16 two-stroke engine

[0052] 17 Silencer section

Claims

Claims 1. Exhaust system (6) with a two-stroke engine (16), wherein the exhaust system (6) has an exhaust pipe (13) and at least two catalyst support bodies (2, 3), wherein the exhaust pipe (13) forms a concentric region (10) with an inner central channel (15) and with a concentric outer circumferential channel (5), wherein a first catalyst support body (2) is arranged in the inner central channel (15) and a second catalyst support body (3) is arranged in the concentric outer circumferential channel (5), wherein the exhaust system (6) and the catalyst support bodies (2, 3) are arranged such that exhaust gas coming from the two-stroke engine (16) at a flow velocity flows through the at least two catalyst support bodies (2, 3) successively with increasing residence time.

2. Exhaust system (6) according to claim 1, wherein the first catalyst support body (2) and the second catalyst support body (3) are arranged radially overlapping.

3. Exhaust system (6) according to one of the preceding claims, wherein the exhaust pipe (13) has a pretreatment area (9) between the two-stroke engine (16) and the concentric area (10), and wherein a third catalyst support body (1) is arranged in this pretreatment area (9), and wherein the exhaust gas coming from the two-stroke engine (16) at a flow velocity flows through the at least three catalyst support bodies (1, 2, 3) successively with increasing residence time.

4. Exhaust system (6) according to one of the preceding claims, wherein the exhaust pipe (13) has an aftertreatment section (11) adjoining the concentric section (10) and having a maximum length of 50 cm, and wherein a fourth catalyst support body (4) is arranged in this aftertreatment section (11), and wherein the exhaust gas coming from the two-stroke engine (16) at a flow velocity at least three catalyst support bodies (2,3,4) are successively flowed through with increasing residence time.

5. Exhaust system (6) according to one of the preceding claims, wherein the concentric region (10) has a deflecting cap (14), wherein the deflecting cap (14) connects the inner central channel (15) with the concentric outer circumferential channel (5).

6. Exhaust system (6) according to claim 5, wherein the deflector cap (14) is arranged at a lowest point of the exhaust system (6).

7. Exhaust system (6) according to one of claims 5 and 6, wherein the deflecting cap (14) has at least one flow-guiding element (7) oriented towards the inner central channel (15).

8. Exhaust system (6) according to one of the preceding claims, wherein the concentric region (10) comprises a double jacket (8) with an air gap.

9. Exhaust system (6) according to one of the preceding claims, wherein a plurality of catalyst carrier bodies (1, 2, 3, 4) are arranged in series from the two-stroke engine (16) to a silencer section (17), wherein exhaust gas coming from the two-stroke engine (16) at a flow velocity flows through all these catalyst carrier bodies (1, 2, 3, 4) successively with increasing residence time.

10. Motorcycle with a two-stroke engine (16), comprising an exhaust system (6) according to one of the preceding claims.

11. Use of an exhaust system (6) in a motorcycle with a two-stroke engine (16), wherein the exhaust system (6) and the catalyst carrier bodies (1, 2, 3, 4) are arranged such that exhaust gas coming from the two-stroke engine (16) at a flow velocity flows through the catalyst carrier bodies (1, 2, 3, 4) successively with increasing residence time.

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