GB2229224A

GB2229224A - I.c. engine exhaust system

Info

Publication number: GB2229224A
Application number: GB8922139A
Authority: GB
Inventors: Gunter Karl; Hansjorg Pohler; Bernd Noack; Gunter Dunewald
Original assignee: ZSCHOPAU MOTORRAD VEB
Current assignee: ZSCHOPAU MOTORRAD VEB
Priority date: 1989-03-15
Filing date: 1989-10-02
Publication date: 1990-09-19
Also published as: JPH02248612A; DE3926921A1; GB8922139D0; FR2644510A1; DD286727A7

Description

- 1 F.MAUST SYSTEM FOR AN INTERNAL COMBUSTION ENGINE An exhaust system is

known whose basic structure comprises an output- governing section and a silencer section. The output-governing section comprises. in sequence, the following components namely an exhaust duct,, an exhaust tube, a diffuser, a cylindrical section. a reflex orifice and an end tube. The output section of the exhaust system determines, to a decisive extent. the utilisation of the exhaust-gas pressure oscillations.

With this design,, every component has a specific function contributing, within a large speed range,, to the achievement of optimal pressure conditions at the outlet. Bearing in mind the components, the desired pressure chracteristic is achieved as follows: The gases issuing from the outlet under high pressure flow through the exhaust tube and enter the diffuser, where, owing to the sudden enlargement in cross-section, negative reflections are brought about. The negative-pressure waves generated flow back towards the outlet. thus contributing to the charge cycle in the cylinder. However, the exhaust pressure wave is only partly reflected in the diffuser. The other part of the pressure wave passes on to the reflex orifice, where the pressure wave is positively reflected as a result of which an excess pressure wave returns to the outlet. This pressure wave has the function of restoring fresh charge lost into the cylinder in order to bring about a dynastic follow-on charge.

The pressure waves in the exhaust system are propagated at the speed of sound. The total length of the output-governing section is normally designed in such a way that the positive pressure wave reflected at the component reaches the cylinder again a short time before the,outlet closing". With the known technical solutions, the sections of the exhaust system are arranged in sequence in the direction in which the exhaust gases flow, which, in particular with low rotary turning speeds, gives rise to long exhaust systems. With two-wheeled vehicles this causes, in part, difficulties to find sufficient space for them and results in the exhaust system having a large sound-emitting surface.

W 41 The present invention is intended to reduce, by rational design and arrangement of the output-governing section. the constructional length of the exhaust system and to achieve a pressure characteristic at the outlet of the internal-combustion engine that will support the charge cycle in optimal manner.

In the present invention,, the components of the output governing section are not only arranged in sequence in the direction of exhaust gas flow but they are also nested in one another and, accordingly, arranged above one another, as a result of which the advancing exhaust pressure wave is caused, by an even number 2n of negative reflections and n position reflections, to change the signs of its direction (2n + 1) times, while, with a view to ensuring proper operation in the discharge space. Preferably no separate reflex orifice is provided in the direction of the exhaust gas flow. So as to achieve repeated reversal of the direction in which the advancing exhaust gas pressure wave travels, the counter-cone is arranged, at the front end of the cylindrical section, in the direction opposite to the exhaust silencer and linked with the diffuser or exhaust tube, with the diffuser protruding through the counter-cone and partly into the cylindrical section, whereby the diameter at the diffuser outlet is smaller than the diameter of the cylindrical section so that an annular gap is formed.

In another embodiment, the cylindrical section into which the diffuser protrudes, forming an annular gap with the cylindrical section at the diffuser outlet, is open at its front end and partly surrounded by a second cylindrical section, the diameter of which is larger, as a result of which a second annular gap is formed between the two cylindrical sections and the second cylindrical section is connected, in the direction of the exhaust silencer, by means of a counter-cone with the first cylindrical section. and at the front end by means of a component,, preferably a counter-cone, with the diffuser or exhaust tube, respectively. By way of counter-cones, orifices with graduated diameters or a reflection wall can be provided in the cylindrical section or in the diffuser zone. The diameter ratio between the diffuser outlet and the cylindrical section is within the range 0.85 to 0.65. The diffuser maybe provided at the diffuser outlet with a curvature advantageous to flow. By way of support,, a support t - 5 plate with a flow-through opening can be provided between the diffuser and the cylindrical section. The distance between the diffuser outlet in the cylindrical section and the start of the exhaust silencer is not less than 0.5 of the diameter of the cylindrical section.

Within the output governing section of the exhaust system according to the invention, the advancing exhaust pressure wave changes the sign of the direction in which it travels by an odd number of times, i.e. (2n +1) times before the reflected exhaust pressure wave again reaches the outlet device and contributes to the improvement of the charge cycle. With a view to changing the direction of travel, an even number 2n, of negative reflections takes place and n of positive reflections. As a result, it is possible for the positive reflection at the constricted cross-section not to take place in the direction of the exhaust gas flow. The repeated change of the direction in which the pressure wave travels is essential for a major reduction of the construction length of the output-governing section and also for achieving a high degree of efficiency.

- 6 A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an exhaust system for a two-stroke internal combustion engine and a graph illustrating the optimum pressure characteristic at the outlet, Figure 2 shows an exhaust system with orifices of graduated diameters, Figure 3 shows a further embodiment of an exhaust system for an internal combustion engine in which the pressure wave changes direction five times, and a graph illustrating the optimum pressure characteristics at the outlet is Figure 4 shows an exhaust system in which the diffuser outlet is designed in a manner advantageous to flowt Figure 5 shows an exhaust system with a support ring, Figure 6 shows a support system for a four-stroke internal combustion engine and a graph illustrating the optimum pressure characteristic at the outlet.

Referring to Figure 1, it can be seen that the output governing section of an exhaust system comprises an outlet tube 3, a diffuser 4. a cylindrical section 5 is and a counter-cone 6 arranged at the front end 10 of the cylindrical section 5, facing in the direction opposite to exhaust silencer 12. The counter-cone 6 is connected with diffuser 4 or exhaust tube 3, respectively, so that it is closed. Diffuser 4 protrudes through the counter-cone 6 as far as location 8 of discharge space 11 of the cylindrical section 5. At location 8. the diameter dD of the diffuser 4 is smaller than diameter dZ of the cylindrical section 5.

The ratio between the two diameters dD and dZ is between 0.85 and 0.65. Since the diameter of the diffuser 4 is smaller, an annular gap 7 exists at location 8 between the diffuser 4 and the cylindrical section 5.

In the Figure 1 embodiment, the reflection length corresponds to the formula LR=LA + LK + LD + LG/2. In the Figure 2 e mbo diment, orifices 13 with graduated diameters are provided, in place of the counter-cone 6. in the cylindrical section within the zone of the diffuser 4, said orifices being firmly connected to the diffuser 4 or the cylindrical section 5. Figure 3 shows an exhaust system in which the component of the output governing section has been designed with a view - 8 to repeated nesting. In this embodiment, the cylindrical section 5 into which the diffuser 4 protrudes to form an annular gap 7 at the diffuser outlet with the cylindrical section 5, is open at its front end 10 and partly surrounded by a second cylindrical section 14 of larger diameter. As a result, a second annular gap 17 is formed at section 16 between the two cylindrical sections 5,, 14. The cylindrical section 14 is, in the direction of exhaust silencer 12, connected, by means of a counter-cone 6, with the cylindrical section 5. and at front end 18, by means of counter-cone 15, with diffuser 4 or exhaust tube 3, respectively. By means of the counter-cone 15, it is also possible to provide a straight wall.

According to Figure 3, the reflection length results from the following formula:

IR = LA+ LK+ ID + PAi 1 + Wi2 where K = 2 Figure 3 also shows the characteristic of the main reflection and indicates the five directional changes of the pressure wave.

1 - 9 The diffuser 4 in Figure 4 is provided at its outlet with a curvature 19 advantageous to flow.

In Figure 5,, an orifice in the form of a support plate 20 with flowthrough openings 21 is provided between the diffuser 4 and the cylindrical section 5. This ensures, on the one hand, that the diffuser 4 is supported against the cylindrical section 5 while, on the other hand, fixing the area of flow through the openings 21 makes it possible to influence, with one and the same exhaust configurations, the torque or output characteristics, respectively. With this embodiment the distance of the support plate 20 from location 8 must be selected in accordance with the required characteristic. With the embodiment shown in Figures 1 to 5, also other reflection points occur, among the above components causing the main reflection. With all embodiments, for instance, additional reflections are to be expected at the junction between 20 the output governing section and the exhaust silencer. With the embodiment of Figure 5, yet an additional reflection occurs at the counter-cone 6.

- 10 For this reason the distance between location 8 and the start of the exhaust silencer 12 as well as the distance between location 16 in Figure 3 and attachment point 9 of the counter-cone 15 must be such as to ensure that these reflection phenomena exert an additional positive influence on the pressure characteristic achieved at the outlet.

Figure 6 shows an embodiment for a four stroke internal combustion engine. The basic design is as described with respect to Figure 1. With this embodiment,, however, it is of interest that. during the exhaust phase, the pressure characteristic is not negatively affected by the reflection to be expected owing to the attached exhaust silencer 12. The pressure wave reflected by the exhaust silencer 12 should therefore arrive at the discharge valve only after,outlet closing". The distance between point 8 and the exhaust silencer 12 must be selected accordingly, The sequence during the exhaust process in the Figure 1 embodiment is as follows: The pre-exhaust pressure wave travels through the exhaust duct 2 and the exhaust tube 3 and then through the diffuser 4. Since the - 11 cross-section of the diffuser 4 increases steadily,, negative pressure waves (returning share of wave) go back to the outlet 1, effectively supporting the cylinder purging process. At location 8, the advancing pressure wave encounters an abrupt increase in cross section, as a result of which a pronounced negative reflection takes place which, on the one hand, generates a negative pressure wave returning to the outlet 1, and on the other hand, an advancing negative pressure wave travelling in the direction of the counter cone 6. This causes the direction of travel of the pressure wave to change. At the counter-cone 6. the negative pressure wave is, as a result of the narrowing cross section, reflected in equipolar manner, which again causes the pressure wave to change its direction of travel. As it arrives at location 8, the negative pressure wave encounters an abrupt increase in cross section, which causes the polarity of the pressure wave to change. As a result, an excess pressure wave travels in the direction of the outlet 1 i.e. the direction of the pressure wave has changed again. With correct tuning. this pressure wave permits recharging of the cylinder prior to the end of the exhaust process. The illustrated characteristic of the reflections in the output governing section constitutes only a simplified presentation. In addition to the process as described, a multitude of other reflections also occur. For instance,'Xeflections occur as the pressure waves return into the diffuser 4, since they are then in the presence of a continuously diminishing cross section, or there is the possibility of reflections of the pressure wave portions travelling into the discharge space 11 of the cylindrical section 5. In order to enable the above sequence of pressure wave reflections to be achieved with high efficiency, it is necessary to omptimise the diameter ratio at location 8 of the diffuser 4 and the cylindrical section 5. In order to ensure that the exhaust is pressure wave reflected by the counter-cone 6 arrives at the outlet 1 shortly before,outlet closing",, the.

reflection length LR needed for the required rotary tuning speed range must be determined.

With four-stroke internal combustion engines tht above design has, in particular, the advantage that the required pressure characteristic at the discharge valve can be achieved without impeding the free discharge of 9 exhaust gases by devices installed in their direction of discharge.. - 1 1 t - 14

Claims

1. An exhaust system for an internal combustion engine comprising an output governing section including an exhaust tube, a diffuser, a cylindrical section and a counter-cone and an exhaust silencer all arranged in sequence in the direction of exhaust gas flow, the system including a component operable to cause positive reflection of the advancing pressure wave arranged at a distance from the exhaust duct so that the excess pressure wave generated contributes to recharging of the engine cylinder, the components of the output-governing section not only being arranged in, sequence in the direction of exhaust gas flow but also nested In one another and,, as a result, arranged above one another,, whereby,, in use, the advancing exhaust pressure wave changes, owing to an even number 2n of negative reflections and n positive reflections,, the sign of its direction of travel (2n + 1) times.

is

2. An exhaust system according to claim 1 wherein no - is - separate reflex orifice is provided in order to ensure proper operation in the discharge space in the direction of exhaust gas flow.

3. An exhaust system according to claim 1 or claim 2 wherein the countercone at the front end of cylindrical section is arranged opposite the exhaust silencer and connected with the diffuser or exhaust tube respectively to cause the direction in which the advancing exhaust gas pressure wave travels to change its direction repeatedly, the diffuser protruding through the counter cone and partly into the cylindrical section, whereby the diameter of the diffuser outlet is smaller than the diameter of the is cylindrical section to provide an annular gap therebetween.

4. An exhaust system according to any of claims 1-3 wherein the cylindrical section into which the diffuser protrudes forms, at the diffuser outlet. an annular gap with the cylindrical section, said cylindrical section is being open at its front end and partly surrounded by a second cylindrical section of larger diameter so that a second annular gap is formed between the two cylindrical sections, the second cylindrical section being connected, in the direction of the exhaust silencer, by means of the counter-cone with the cylindrical section and, at its front end, with the diffuser or the exhaust tube respectively, by a component, preferably a second counter-cone.

5. An exhaust system according to any of the preceding claims, wherein orifices with graduated diameters or a reflection wall are provided as the counter-cone in,the cylindrical section or in the zone of the diffuser.

6. Exhaust system according to any of the preceding claims wherein the diameter ratio (dD/dZ) between the diffuser and the cylindrical section is in the range 0.85 to 0.65.

7. An exhaust system according to any one of the preceding claims wherein the diffuser is provided, at the diffuser outlet, with a curvature advantageous to flow.

is

8. An exhaust system according to any one of the preceding claims wherein a support plate with flow through openings is provided between the diffuser and the cylindrical section.

9. An exhaust system according to any one of the preceding claims wherein the distance between the outlet of the diffuser and the start of the exhaust silencer amounts to at least 0.5 of the diameter of the cylindrical section.

10. An exhaust system substantially as herein described with reference to the accompanying drawings.

Published 1990 at The Patent Mice, State House. 6E 71 High Holborn. LondonWC1R4TP. Further copies niaybeobtLined from The Patent Office Sales Branch, St Mary Cray. Orphigton, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1,187 t