GB2321498A

GB2321498A - Two-stroke i.c. engine exhaust system with active control of effective tuned le

Info

Publication number: GB2321498A
Application number: GB9701258A
Authority: GB
Inventors: John Stephen Roberts
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-01-22
Filing date: 1997-01-22
Publication date: 1998-07-29
Also published as: GB9701258D0

Abstract

Located within the rear section 2 of the expansion chamber is conical baffle 3 attached to an axial stinger 4 which is slidable in a guide 5. The baffle 3 is pre-loaded towards the engine by a spring 13 inside a bellows 19. The shape and position of the baffle 3 is designed to reflect sonic pulses generated by the exhaust port so as to maximise engine efficiency. The invention allows the baffle 3 to be moved along the length of the expansion chamber in response to dynamic engine parameters, eg engine speed. The optimum baffle position is determined by design or experiment and the relationship between baffle position and the control parameter is encoded in the position control system 17. A servo positioned 18 then moves the stinger 4 eg via cables (14, fig.3). Instead of being hollow, the stinger may be solid with a side exhaust gas exit being provided (fig.2).

Description

EXHAUST SYSTEMS FOR INTERNAL COMBUSTION ENGINES This invention relates to exhaust systems for internal combustion engines and in particular to exhaust systems of variable tuned length.

This invention provides a practical means by which the effective tuned length of an exhaust system (expansion chamber) for two stroke internal combustion engines may be varied by an active electronic servo control system to optimise the effective length while the engine is operating.

A typical expansion chamber exhaust system design allows the exhaust gases to pass though three sections; the diffuser; the baffle ; and the stinger. The shupe and position of the baffle is designed to reflect the sonic pulses generated by the opening and closing of the exhaust port so as to maximise engine efficiency. This invention allows the exhaust system designer to design a baffle shape which can be moved along the length of the expansion chamber in response to dynamic engine parameters (e.g.

engine speed).

Functional Description A specific example of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows a sectional view of an example exhaust system showing the moving baffle and an axially mounted stinger.

Figure 2 shows an alternative sectional view of an example exhaust system showing a moveable baffle with a side exit stinger.

Figure 3 shows an example of an actuation system attached to a movable baffle via a sliding stinger or push rod..

Figure 4 shows the exhaust system control loop.

A conical baffle 3 is attached to the end of an axial stinger pipe 4. The assembly is located within the rear section 2 of the expansion camber by sliding the axial stinger 4 (or solid push rod 16 if an independent side gas exit 15 as shown in Figure 2 is used) through an outer stinger guide 5. The axial stinger 4 (or push rod 16) is now able to slide axially inside the rear section 2. A spring 13 pre-loads the baffle 3 towards the engine.

A bellows 19 is mounted axially, over spring 13, so as to provide a seal aginst exhaust gas leakage and provide a means of keeping the sliding surfaces of the axial stinger 4 (or push rod 16) and stinger guide 5 clean.

The axial stinger 4 (or push rod) protrudes beyond the stinger guide 5. This enables a crank linkage 8 to be attached between the axial stinger 4 (or push rod 16) and the stinger guide 5. In this example a pulley 9 is arranged to connect the moveable baffle 3 and axial stinger 4 (or push rod) to a remote servo control system via the actuation cables 14.

The linkage system is mounted on a stinger guide 6. This is clamped to the stinger guide 5 and secured by bolts 11. The linkage 8 is clamped to the axial stinger 4 (or push rod 16) by an axial stinger clamp 7 and secured by bolts 12. At the end of the - 3 stinger guide 6 is a flange 10 which is used to attach a silencer.

The stinger guide 6 is designed so as to enables the axial stinger clamp 7 to move without rotating about the stinger axis.

The diffuser 1 is attached to the rear section 2 by a sliding joint and clamp 16.

The proposed system may be dismantled by removing the diffuser 1 section then loosening the stinger guide bolts 11 and the axial stinger clamp bolts 7. The baffle 3 and axial stinger 4 (or push rod 16) may now be extracted from the outer stinger 5 and rear section 2.

Electronic Control System The controlled position of exhaust baffle 3 is determined by the active electronic position control system 17. This controller processes an engine parameter signal (taken directly from an engine transducer or from the engine management system) and uses closed loop control techniques to maintain the optimum baffle 3 position.

Optimum baffle position is determined either by design or experiment. The relationship between baffle position and the control parameter is encode within the controller. This data may be stored in tabular form or encoded as an equation. Figure 5 shows a graph of data typical of the relationship between engine speed and the baffle 3. The controller uses a remote servo positioner 18 to control the actuator (and so the baffle 3) directly via control cables 14.

The control parameter in this case is engine speed which may be detected via a hall effect switch which senses a passing magnet mounted on the crank shaft.

Claims

1. An exhaust system for an internal combustion engine, the tuned length of the exhaust being variable by an actuation unit under the control of an electronic control means which receives signals indicative of dynamic operating parameters of the associated engine and the current tuned length of the exhaust system and issues signals to the actuation unit to vary the tuned length of the system in accordance with a predetermined relationship between dynamic parameter value and tuned length.

2. A system according to claim 1 in which the tuned length is varied by movement of a baffle within an expansion chamber of the system.

3. A system according to claim 2 in which the baffle is attached to stinger or push rod on which the actuation unit operates to vary the position of the baffle.

4. A system according to claim 3 in which the stinger is hollow and exhaust gases leave the system via The stingen

5. A system according to any one of the claims 2 to 4 in which the baffle is spring loaded towards the engine so as to equalise the force created by exhaust gases as they pass through the system.

6. A system according to claims 2 to 5 in which an exhaust gas seal is provided between the stinger (or push rod) and a stinge (or push rod guide) guide by means of a bellows.

7. A system according to any one of claims 3 to 6 in which the actuation unit is connected with the stinger or push rod via a guided sliding block which is clamped to the stinger or push rod.

8. A system according to any one of claims 2 to 7 in which the actuation unit includes a rotary servo motor connected to the baffle via a crank mechanism to convert the rotary motor movement into linear baffle movement

9. A system according to claim 8 in which the servo motor is located remote from the expansion chamber and is connected, via cables or other mechanical connection including the crank, to the baffle.

10. An exhaust system for an internal combustion engines constructed and arranged substantially as herein before described with reference to and as shown in the accompanying drawings.