GB2258496A

GB2258496A - A combined noise reduction and torque enhancement system for an i.c. engine

Info

Publication number: GB2258496A
Application number: GB9116548A
Authority: GB
Inventors: Stephen Mark Hutchins; Ian Stothers; Neil Malcolm Mcdougall
Original assignee: Lotus Cars Ltd
Current assignee: Lotus Cars Ltd
Priority date: 1991-07-31
Filing date: 1991-07-31
Publication date: 1993-02-10
Also published as: GB9116548D0

Abstract

A plug 4 which may take various forms (Figs. 4 to 6) affects inlet or exhaust flow. The plug 4 is kept stationary or is oscillated by a mechanical engine drive or by a controller 6 in response to a signal from a microphone 10 in order to achieve torque increase and silencing. <IMAGE>

Description

A COMBINED NOISE REDUCTION AND TOROUE ENHANCEMENT SYSTEM FOR AN INTERNAL COMBUSTION ENGINE The present invention relates to a combined noise reduction and torque enhancement system for an internal combustion engine.

Internal combustion engines produce a large amount of noise in the inlet and exhaust system. A significant amount of work has been done in cancelling exhaust noise.

Conventionally, in the exhaust system, passive sound absorbing material and irregular flow paths are used in silencers to reduce the transmission of noise. More recently, active noise attenuation systems have also been utilised which either produce sound in anti-phase with the noise to cancel it or constrict the exhaust pipe at a frequency of the noise to be attenuated. The latter system is disclosed in EP 0307639 and this can significantly reduce the noise produced by opening of the exhaust valves. However, such a system does not provide for both noise reduction and torque enhancement.

The present invention provides a combined noise reduction and torque enhancement system for an internal combustion engine comprising constriction means for constricting the exhaust and/or inlet of said internal combustion engine, and control means for oscillating said constriction means to periodically constrict or occlude said exhaust and/or inlet at at least one frequency related to the rotation frequency of said internal combustion engine.

In one aspect of the present invention a reference means is provided to provide a reference signal indicative of the rotation frequency of the internal combustion engine and the control means is responsive to the reference signal to oscillate the constriction means at at least one frequency related to the frequency of the reference signal.

In another aspect of the present invention the control means is mechancially coupled to the internal combustion engine to oscillate the constriction means at a frequency related to the rotation frequency of the internal combustion engine.

In a preferred embodiment of the present invention the constriction means comprises a plug member arranged to be oscillated in an aperture along the axis of flow of gas in said exhaust and/or inlet. Preferably the control means is adapted to vary the mean position and/or amplitude of oscillation of the plug member dependent on the rotation frequency of the internal combustion engine.

In one aspect of the present invention the plug member has a paraboloidal surface for periodic co-operation with the wall defining said aperture to constrict or occlude said exhaust and/or inlet.

In another aspect of the present invention the plug member comprises a first and second conical portion, said conical portions being joined at bases thereof, said system further including a frustoconical portion defining said aperture and said plug member being arranged such that the conical surface of said first conical portion co-operates with the frustoconical surface of said frustoconical portion to constrict or occlude said exhaust and/or inlet.

To provide an increased torque at higher rpm, in one embodiment of the present invention the aperture has a larger mean cross-sectional area than said exhaust and/or inlet and is situated in an enlarged portion of said exhaust and/or inlet.

In another aspect of the present invention a noise measuring means is provided adjacent the exhaust outlet and/or engine inlet to measure the resultant noise. The control means is then responsive to said measured noise to adapt the oscillations of the constriction means to reduce the resultant noise.

The present invention also provides a method for reducing noise and enhancing torque produced from an internal combustion engine comprising the steps of oscillating a constriction means to periodically constrict or occlude the exhaust and/or inlet of said internal combustion engine at at least one frequency related to the rotation frequency of said internal combustion engine.

In one aspect of the present invention a reference signal indicative of the rotation frequency of the internal combustion engine is provided and the constriction means is oscillated at at least one frequency related to the frequency of said reference signal.

In another aspect of the present invention the constriction means is mechanically coupled to the internal combustion engine, and the constriction means is oscillated in response to a force transmitted by said mechanical coupling.

Preferably, the exhaust and/or inlet is constricted or occluded by the action of a plug means which is oscillated along the axis of flow of gas in an aperture in said exhaust and/or inlet and the mean positon and/or amplitude of oscillation of the plug member is varied in response to changes in the rotation frequency of the internal combustion engine.

In a further aspect of the present invention the resultant noise emitted by the exhaust and/or inlet is measured and used to adapt the oscillations of the constriction means to reduce the resultant noise.

Preferably, the noise is reduced and torque enhanced for a four stroke internal combustion engine.

The present invention also provides a combined noise reduction and torque enhancement device for an internal combustion engine comprising a member to deflect the flow of gas in the exhaust and/or inlet of said internal combustion engine, said flow being deflected off the axis and substantially symmetrically about the axis.

In one aspect of the present invention the member has a paraboloided surface arranged in the direction of flow of said gas.

In another aspect of the present invention the member comprises a first and second conical portion, the conical portions being joined at bases thereof, the device further including a frustoconical aperture formed in the exhaust and/or inlet, the member being arranged in the frustoconical aperture such that the conical surface of the first conical portion is parallel to and spaced from the surface of the frustoconical aperture.

To provide an increased torque at higher rpm, in one embodiment of the present invention the device includes an enlarged portion of said exhaust and/or inlet having an enlarged cross-sectional area, and said member is arranged in said enlarged portion.

Examples of the present invention will now be described with reference to the drawings, in which: Figure 1 illustrates a schematic diagram of a combined noise reduction and torque enhancement system according to one embodiment of the present invention; Figure 2 illustrates the noise reduction achieved with the arrangement of Figure 1 from a four stroke internal combustion engine under full load at 1800 rpm; Figure 3 illustrates the noise reduction achieved in the arrangement of Figure 1 from a four stroke internal combustion engine under full load at 2700 rpm; Figure 4 illustrates the plug member according to one embodiment of the present invention; Figure 5 illustrates the plug member according to a further embodiment of the present invention; Figure 6 illustrates a plug member according to a still further embodiment of the present invention.

Referring now to Figure 1, a schematic diagram of a combined noise reduction and torque enhancement system is illustrated in which exhaust gases from an engine 1 flow down an exhaust pipe 2 which can have the usual conventional silencers 3 to an outlet at which a plug 4 is arranged to be oscillated by a shaker 5. The shaker 5 is driven by a controller 6 through an amplifier 7. The controller 6 receives a signal indicative of the engine rotation rate on line 8 through a filter 9. The signal can conveniently be the tachometer signal of the engine 1. The filter 9 is provided to manipulate the signal by for example removing higher harmonics of the reference signal such that the controller 6 receives a single frequency signal, the frequency of which is related to the rotation frequency of the engine 1. Alternatively, more than one frequency related to the rotation frequency of the engine may be received by the controller 6, to oscillate the plug 4 at more than one frequency. The controller 6 also receives a signal from a microphone 10 which is situated very close to the outlet of the exhaust and the plug 4.

The error signal to the controller 6 allows for adaptive control of the oscillation of the plug 4 in order to provide a better cancellation of the noise.

The system of Figure 1 can be used with either two or four stroke internal combustion engines (Diesel or petrol engines).

The arrangement in Figure 1 is operated as follows.

When the engine 1 is running, exhaust noise is transmitted down the exhaust pipe 2 to the outlet. The shaker 5 oscillates the plug 4 at the frequencies of the pulses of pressure resulting from the opening of the exhaust valves of the engine 1. This frequency in normal four cylinder engines is twice the roation frequency of the crankshaft.

The plug 4 shown in Figure 1 has a paraboloidal surface which co-ooperate with the wall of the exhaust pipe to constrict or occlude the exhaust pipe when a pressure pulse resulting from the opening of an exhaust valve is received. The controller 6 not only controls the frequency (or frequencies) of oscillation of the plug,- but also the amplitude and/or mean positions of the plug 4. Thus at higher engine speeds, the mean position and/or amplitude of oscillation of the plug 4 can be changed to compensate for the increased flow and avoid the predominance of viscosity effects. In the arrangement of Figure 1 the mean position of the plug 4 was varied between 3-lOmm.

The microphone 10 can provide an indication of the success of cancellation of the noise to enable the controller 6 to adaptively control the shaker 5 in order to provide a better cancellation of the noise.

Figures 2 and 3 show the degree of success in cancelling noise for a four cylinder four stroke engine under full load at 1800 and 2700 rpm respectively. These 0 results were taken at 1 metre and 45 from the outlet of the exhaust pipe. The plot A illustrates the noise emitted by the exhaust system as standard. Plot B illustrates the noise with the plug 4 in place but stationary. Plot C illustrates the noise with the plug 4 being oscillated under the control of the controller 6.

As can be seen from Figures 2 and 3, there is a significant reduction in noise with the plug 4 merely being placed in a stationary position in the flow of exhaust gas. The noise reduction is further increased when the plug 4 is oscillated at a frequency related to the rotation frequency of the engine 1.

Table 1 illustrates the enhancement of torque produced by utilising the plug 4 in Figure 1. As shown in Table 1, the torque is increased by 0.6% at 1800 rpm when the plug 4 is stationary. When the plug 4 is oscillated the torque is increased by 1.9%.

Clearly therefore there is more than one effect causing the reduction and noise and enhancement of torque produced by the engine 1. When the plug 4 is stationary, as shown in Figure 4, the gas flowing down the exhaust pipe 2 is deflected off axis and symmetrically about the axis to flow around and over the paraboloidal surface of the plug 4. When the gas is deflected off axis the centripetal force results in there being a lower pressure near the axis. This is the Coanda effect. This lower pressure tends to pull the plug 4 towards the aperture in the exhaust pipe 2. If the plug 4 is held stationary then clearly there is an equal and opposite force tending to improve the flow of exhaust gases down the exhaust pipe 2.

Also, the gas is deflected into a constricted region between the plug 4 and the wall of the exhaust pipe 2. In this constriction the Bernoulli effect causes an increased flow and reduced pressure.

When the plug is oscillated the phase of the reflected waves at the exhaust outlet is controlled. This phase can be adjusted to aid exhaust scavenging.

Table 1 also illustrates the effect on torque of using the plug 4 at a higher engine speed of 2700 rpm.

When the plug 4 is both stationary and oscillating, there is a decrease in torque of 2.2%. This decrease in torque is due to constriction on the flow of gases due to obstruction by the plug 4. This can be overcome by increasing the cross-sectional area of the exhaust pipe and' also the plug 4 to reduce any viscous effects. Such an arrangement is shown in both Figures 5 and 6.

Thus the arrangement shown in Figure 1 in which the plug 4 is oscillated along the axis of flow of exhaust gas can decrease the noise at all engine speeds whilst increasing the torque at lower engine speeds and decreasing the torque at higher engine speeds. Such an effect on the torque provided from an engine is quite desirable since generally engines will give lower torque at lower rpm than at higher rpm. Therefore such an effect on the torque produced by an engine can be quite desirable since it tends to equalise the torque provided by an engine over the engine speed range. If no reduction in torque at higher rpm is desirable then the arrangements shown in Figures 5 and 6 can be preferentially used. In these arrangements the cross-sectional area in which the plug 4 operates is increased to maintain the throughput and reduce viscous effects.

To maximise the Coanda effect, the plug 4 shown in Figure 5 can be used, which comprises a first conical portion and a second conical portion, both of which are joined at bases thereof to form the plug 4. A gas flowing in a duct is deflected off axis over the surface. The gas then flows over the surface towards the rear of the plug 4. At the rear of plug 4 a vortex is set up which provides a pressure drop thus improving the flow through the exhaust pipe 2. The conical portion of the plug 4 is arranged to be sited within a frustoconical portion 20 of the exhaust pipe 2 such that the surface of the conical portion of the plug 4 lies parallel to and spaced from the surface of the frustoconical portion 20. The cross-sectional area of the exhaust pipe 2 is equal to the cross-sectional area provided by the channel between the conical portion of the plug 4 and the frustoconical portion 20.This ensures that there is no restriction on flow.

The arrangement shown in Figure 1 is limited to receiving an electrical signal indicative of the rotation frequency of the engine 1. It is also considered that the plug 4 could be mechanically coupled to the engine 1 such that by, for example, the use of cams, the rotational force of the engine is transmitted to drive the oscillation of the plug 4.

The arrangement shown in Figure 1 illustrates the use of the plug 4 at the outlet of the exhaust 2. However, for practical applications this arrangement is not particularly useful. Figures 4, 5 and 6 illustrate arrangements which can practically be applied to an exhaust system of an internal combustion engine.

Referring to Figure 4, an enlarged portion of the exhaust pipe forming a silencer box 21 is provided in which the plug 4 is situated in an aperture defined by the wall of the exhaust pipe 2 at its interface with the silencer box 21. The plug 4 is provided with a driving rod 22 which couples the plug 4 to the shaker 25. The driving rod 22 passes through the silencer box 21 and is carefully sealed at this point to ensure no leakage of the exhaust gases.

Exhaust gases exit through the exhaust port 23. This arrangement allows for the shaker 25 to be situated out of the flow of the hot and corrosive exhaust gases. The silencer box 21 can also contain conventional muffler material and irregular pathways to reduce flow noise. Thus this arrangement provides for a combined conventional muffler with an oscillating plug arrangement according to one embodiment of the present invention.

Figure 5 illustrates an alternative plug 4 which comprises a first and second conical portion connected at bases thereof. This plug 4 is arranged in a frustoconical portion 20 of the exhaust pipe 2 such that the surface of the first conical portion lies parallel to and spaced from the surface of the frustoconical portion 20. When the plug 4 is oscillated, the surfaces of the conical portion of the plug 4 and the frustoconical portion 20 can approach and meet to constrict or occlude the exhaust pipe 2.

In Figure 6 the same shape actuator as shown in Figure 4 is used. The plug 4 has a paraboloidal surface and is larger than the plug shown in Figure 4. The exhaust pipe 2 has a larger cross-section at the point in which the plug 4 is situated. This ensures that the cross-sectional area of the exhaust pipe is not constricted by the presence of the plug 4 when the plug is in its mean position.

In all of the arrangements shown in Figures 1, 4, 5 and 6, the plug 4 can either be oscillated or can merely be kept stationary in order to provide a reduction in noise and enhancement in torque output from the internal combustion engine 1. Thus, the arrangement shown in Figure 1 can provide a far greater increase in torque at low rpm as well as a greater noise reduction, than can be achieved by merely placing a plug 4 in the flow of exhaust gases.

However, the arrangement shown in Figure 1 is far more complex than merely providing a plug 4 in an exhaust pipe 2. Thus, for applications where a larger increase in torque and greater reduction in noise is required, an active system such as that . shown in Figure 1 should be employed. Where a lower reduction in noise and smaller increase in torque at low rpm is adequate, simply providing a plug 4 in the flow of exhaust gases down an exhaust pipe 2 provides for some torque enhancement and noise reduction.

Although the examples of the present invention hereinbefore described have been considered in relation to an exhaust pipe of an internal combustion engine, the present invention is equally applicable to the inlet of an internal combustion engine.

TABLE 1 INFLUENCE ON TOROUE FIGURES (Nm)

Engine Speed (rpm) 1800 2700 Standard Exhaust (Nm) Plug in place (stationary)(Nm) 698 + 2 917 + 8 (+0.6%) (-2.2%) Plug in place (cancelling)(Nm) 707 + 2 917 + 8 (+1.9) (-2.2%)

Claims

CLAIMS 1. A combined noise reduction and torque enhancement system for an internal combustion engine, comprising constriction means for constricting the exhaust and/or inlet of said internal combustion engine, and control means for oscillating said constriction means to periodically constrict or occlude said exhaust and/or inlet at at least one frequency related to the rotation frequency of said internal combustion engine.
2. A combined noise reduction and torque enhancement system as claimed in Claim 1, further including a reference means providing a reference signal indicative of the rotation frequency of said internal combustion engine, and wherein said control means is responsive to said reference signal to oscillate said constriction means at at least one frequency related to the frequency of said reference signal.
3. A combined noise reduction and torque. enhancement system as claimed in Claim 1, wherein said control means is mechanically coupled to said internal combustion engine to oscillate said constriction means at a frequency related to the rotation frequency of said internal combustion engine.
4. A combined noise reduction and torque enhancement system as claimed in any preceding claim, wherein said constriction means comprises a plug member arranged to be oscillated along the axis of flow of gas and in an aperture in said exhaust and/or inlet.
5. A combined noise reduction and torque enhancement system as claimed in Claim 4, wherein said control means is adapted to vary the mean positon and/or amplitude of oscillation of said plug member dependent on the rotation frequency of said internal combustion engine.
6. A combined noise reduction and torque enhancement system as claimed in Claim 4 or Claim 5, wherein said plug member has a paraboloidal surface for periodic co-operation with the wall defining said aperture to constrict or occlude said exhaust and/or inlet.
7. A combined noise reduction and torque enhancement system as claimed in Claim 4 or Claim 5, wherein said plug member comprises a first and second conical portion, said conical portions being joined at bases thereof, said system further including a frustoconical portion defining said aperture and said plug member being arranged such that the conical surface of said first conical portion co-operates with the frustoconical surface of said frustoconical portion to constrict or occlude said exhaust and/or inlet.
8. A combined noise reduction and torque enhancement system as claimed in any of Claims 4 to 7, wherein said aperture has a larger mean cross-sectional area than said exhaust and/or inlet and is situated in an enlarged portion of said exhaust and/or inlet.
9. A combined noise reduction and torque enhancement system as claimed in any preceding claim further including a noise measuring means positioned adjacent the exhaust outlet and/or inlet to measure the resultant noise, wherein said control means is responsive to said measured noise to adapt the oscillations of said constriction means to reduce the resultant noise.
10. A method for reducing noise and enhancing torque produced from an internal combustion engine, comprising the steps of oscillating a constriction means to periodically constricting or occluding the exhaust and/or inlet of said internal combustion engine at at least one frequency related to the rotation frequency of said internal combustion engine.
11. A method as claimed in Claim 10 further including the step of providing a reference signal indicative of the rotation frequency of said internal combustion engine, wherein said constriction means is oscillated at at least one frequency related to the frequency of said reference signal.
12. A method as claimed in Claim 10, wherein said constriction means is mechanically coupled to said internal combustion engine and said constriction means is oscillated in response to a force transmitted by said mechanical coupling.
13. A method as claimed in any of Claims 10 to 12, wherein said exhaust and/or inlet is constricted or occluded by the action of a plug means which is oscillated along the axis of flow of gas in an aperture in said exhaust and/or inlet.
14. A method as claimed in Claim 13, wherein the mean 'position and/or amplitude of oscillation of said plug member is varied in response to changes in the rotation frequency of said internal combustion engine.
15. A method as claimed in any Claims 11 to 14, wherein the resultant noise emitted by said exhaust and/or inlet is measured and used to adapt the oscillation of said constriction means to reduce said resultant noise.
16. A method as claimed in any of Claims 11 to 15, wherein the noise is reduced and torque enhanced for a four stroke internal combustion engine.
17. A combined noise reduction and torque enhancement device for an internal combustion engine, comprising a member to deflect the flow of gas in the exhaust and/or inlet of said internal combustion engine, said flow being deflected off the axis and substantially symmetrically about the axis.
18. A combined noise reduction and torque enhancement device as claimed in Claim 17, wherein said member has a paraboloidal surface arranged in the direction of flow of said gas.
19. A combined noise reduction and torque enhancement device as claimed in Claim 17, wherein said member comprises first and second conical portions, said conical portions being joined at bases thereof, said device further including a frustoconical aperture formed in said exhaust and/or inlet, said member being arranged in said frustoconical aperture such that the conical surface of said first conical portion is parallel to and spaced from the surface of said frustoconical aperture.
20. A combined noise reduction and torque enhancement device as claimed in any of Claims 17 to 19, wherein said device includes an enlarged portion of said exhaust and/or inlet having an enlarged cross-section and said member is arranged in said enlarged portion.
21. A combined noise reduction and torque enhancement system as hereinbefore described with reference to any of the drawings.