GB2114657A - Heated and unheated air intake system of an I.C. engine air cleaner - Google Patents

Abstract

An air cleaner 1 has a duct 3 connected by way of a temperature controller 6 with a gate 7 to a heated air duct 4 and an ambient air duct 5. At least one of the ducts 4 and 5 is provided with at least one calibrated hole 8 or 9 positioned at a location to reduce sound propagation. Specific hole dimensions and spacings from the open ends of the ducts together with relative duct cross-sections are disclosed. <IMAGE>

Description

SPECiFICATION Air intake system of internal combustion engine This invention relates to mechanical engineering, particularly to engine construction, and more specifically to air intake systems of internal combustion engines.

The invention can find application in air intake systems of most motor vehicle type internal combustion engines, particularly automobile, marine and locomotive engines and the like, as well as stationary engines, such as those used for driving generators and compressors, when it is necessary to reduce the noise level emitted by air intake systems.

It is an object of the present invention to improve the noise performance of an air intake system.

Another object is to improve the reliability and operational stability of an internal combustion engine during acceleration at low ambient temperatures.

The objects are attained by that in an air intake system of an internal combustion engine comprising an air cleaner with an inlet port having connected thereto a mixed air duct, heated and ambient air ducts having open ends on the sides thereof opposite to the one that connect them to the mixed air duct through a temperature controller with a gate to proportion the flow of air, according to the invention, at least one of the heated and ambient air ducts is provided with at least one calibrated hole positioned at a location where the sound pressure is most pronounced.

Such a construction of the air intake system allows to reduce the amount of air intake noise associated with resonance oscillations and thereby bring down the overall level of noise produced by a motor vehicie. Also, this obviates the need for a pneumatic drive to block the heated air duct during engine acceleration which, firstly, improves the engine operating stability at low ambient temperatures and, secondly, reduces the overall manufacturing costs of air intake system.

Preferably, at least one calibrated hole is positioned in the heated air duct at a distance 0.2 to 0.5 the total length of the heated and mixed air ducts as measured from the open end of the heated air duct to the inlet port of the air cleaner, the ratio between the total flow area of the calibrated holes and the cross-sectional area of the heated air duct ranging between 0.1 and 0.08.

Advisably, at least one calibrated hole is provided in the ambient air duct, this calibrated hole being positioned relative to the open end of the ambient air duct at a distance of 0.2 to 0.5 the total length of the ambient and mixed air ducts as measured from the open end of the ambient air duct to the inlet port of the air cleaner, the ratio between the total flow area of the calibrated holes and the cross-sectional area of the ambient air duct ranging between 0.01 and 0.08.

This arrangement of the air intake system enables to improve the reliability and stability of noise reduction.

Preferably, at least one of the heated or ambient air ducts is of a composite construction with parts thereof being interconnected by means of a sleeve having provided therein calibrated holes.

The ducts constructed in such a manner make it possible to reduce the size of the air intake system, whereas the provision of the holes in the rigid sleeve in conjunction with the flexible ducts provides high geometrical accuracy of the holes and improves the reliability of the system regardless of the bent or curved shape of the ducts.

Advisably, the heated air duct is flexible, the air inlet thereof having an air intake sleeve provided with a plurality of radially disposed holes.

This allows to reduce the temperature of a joint between the flexible duct and the hot intake sleeve thereby preventing scorching of the duct and improving the reliability of the air intake system of an internal combustion engine.

Desirably, the minimum hydraulic diameter of the heated air duct is 0.8 to 1.2 the minimum hydraulic diameter of the ambient air duct.

The above ratio between the minimum hydraulic diameters of the air ducts makes it possible to effectively reduce air intake noise with minimum losses of the engine power.

The invention wiil now be described in greater detail with reference to preferred embodiments thereof taken in conjunction with the accompanying drawings, in which: Fig. 1 shows an air intake system of an internal combustion engine according to the invention; Fig. 2 illustrates schematically distribution of pressures during resonance oscillations in the air intake system without holes in heated and ambient air ducts; Fig. 3 shows another modification of the air intake system embodying the present invention; Fig. 4 shows a modified form of a composite air duct; and Fig. 5 shows a modified form of the inlet end of a flexible heated air duct provided with an air intake sleeve.

An air intake system of internal combustion engine according to the invention comprises an air cleaner 1 having an inlet port 2 to which there is connected a mixed air duct 3. Ducts of heated and ambient air 4 and 5, respectively, have open ends and are connected by other ends thereof to the duct 3 of mixed air through a temperature controller 6 provided with a gate 7 that proportions the intake flows of heated and ambient air. The heated air duct has calibrated holes 8 (alternatively, one such hole may be provided), whereas the ambient air duct 5 has calibrated holes 9.

With reference to Fig. 1, the air intake system operates as follows.

In the intermediate position of the gate 7 of the temperature controller 6 air is sucked into the air cleaner 1 both through the open ends of the heated and ambient air ducts 4 and 5 and through the holes 8 and 9. The volumetric variable of the air sucked in, which is determined by variations in the cylinder displacements at open inlet valves of the engine, is much weakened in the air cleaner, whereafter it is radiated through the open ends of the ducts 4 and 5 and the calibrated holes 8 and 9.At frequencies f1 and f2 determined by the equations: c c f2=k k---- and f1=k 212 211 where 11 and 12 are the lengths of the ducts 4 and 5 measured from their open ends to the air cleaner 1 including the mixed air duct 3; c is the sound velocity; and K is 1, 2 3... series of natural numbers, resonance oscillations in the ducts 3, 4 and 5 occur.

Analyses and tests have shown that in an air intake system with one duct, such as with the ambient air duct 5, these oscillations are not dangerous, because at high load operating conditions with the throttle fully open they are largely suppressed by churning losses at the open end when the velocity of gas passing through is high. The problem becomes more complicated in a system with two air intake ducts. In a position of the gate 7 short of completely blocking one of the ducts, usually the heated air duct 4, the velocity of gas flowing through this duct 4 is low, damping is weak, whiie the resonance oscillations are heavy.

The holes 8 (or 9) wherethrough air is additionally forced into the system to cause additional damping are arranged in locations of the maximum sound pressure on the ducts 4 (or 5) to suppress the above two types of oscillations.

Distribution of pressures in the first type of resonance oscillations in the heated and ambient air ducts 4 and 5 without calibrated holes is illustrated in Fig. 2. Zones of zero pressure are located at the ends of the ducts 4 and 5 and in the zone of the inlet port 2.

For a more efficient suppression of resonance oscillations of the first type it is advisable to position the holes 8 (Fig. 1) at a distance of 0.20 to 0.5 the total length of the heated and mixed air ducts 4 and 3, respectively, as measured from the open end of the duct 4 to the inlet port 2 of the air cleaner 1. The calibrated holes 9 are preferably to be positioned at a distance of 0.20 to 0.5 the total length of the ambient and mixed air ducts 5 and 3, respectively as measured from the open end of the duct 5 to the inlet port 2 of the air cleaner 1.

Locating the holes 8 and 9 at distances greater than 0.5 11 (or 0.5 12) impedes the suppression of the low frequency noise due to increased resonance frequency of the mass of air in the ducts (as a mass on a spring of equivalent compliance to the flow of air in the air cleaner 1).

Conversely, locating the holes at a distance less than 0.20 it (or 0.20 12) shifts the holes to zones where pressure is too low and hampers the efficiency of suppression of the first type of resonance oscillations.

Further, undersize diameters of the calibrated holes 8 and 9 result in insufficient noise suppression.

On the other hand, too large diameters of the holes affect the efficiency of the open end portions of the ducts 4 or 5 to result in a reduced dampening of the low frequency noise.

Engine tests have shown that the optimum ratio is: F1=(0.01 +0.08) F2 where F1 is the flow area of the holes; and F2 is the cross-sectional area of the duct.

The provision of the holes 8 and 9 and positioning thereof in the manner shown in Fig. 1 is advantageous in that it reliably reduces the noise produced by the air intake system and enables to obviate the need for an overly complicated mechanism of a pneumatic drive.

This gives sizable economic benefits during mass production thanks to reduced production costs of the temperature controller 6 due to a greatly simplified construction thereof. Another beneficial effect is attained by stabilizing the temperature of inflowing air at the inlet to the carburetor at all operating conditions including full load operating conditions, which improves performance stability of the engine and reduces toxicity of exhaust.

Alternatively, the heated air duct may not be of integral construction. Illustrated in Figs. 3 and 4 is a modified form of the air intake system of an internal combustion engine embodying the present invention featuring a composite heated air duct 10. Parts 11 and 12 of the heated air duct 10 are joined together by a sleeve 13 having radially disposed calibrated holes 14 iocated and sized substantially as the calibrated hole 8 with reference to Fig. 1.

Such an arrangement affords to make the air intake system of an internal combustion engine less bulky, whereas the provision of the radial calibrated holes 14 (Figs. 3 and 4) in the rigid sleeve 13 with the parts 11 and 12 of the heated air duct 10 being flexible affords highly accurate geometry of the holes 14 to improve the reliability of the system.

Ambient air ducts may also be fashioned in the manner just described.

For reasons of manufacturing efficiency the parts 11 and 12 of the heated air duct 10 are fabricated from corrugated paper reinforced by metal foil to add flexibility to the duct 10 and simplify its accommodation on the engine. During operation the inlet end of the duct 10 (Fig. 5) is heated by heat radiated from an exhaust manifold pipe 15. As a result, this end may become scorched to loosen the connection thereof with an inlet sleeve 1 6 and result in a failure of the system.This is undesirable and may be avoided by supplying to the interior of the sleeve 1 6 by means of which the part 1 2 of the duct 10 is connected to a shroud 1 7 a flow of relatively cool air in the amount proportioned so as to have the heat entering the intake system be sufficient for normal performance of the engine at all operating conditions. Thanks to such cooling, the durability of the connection is extended. For this purpose, a plurality of radial holes 18 are provided on the side surface of the sleeve- 16, the total flow area of these holes being between 0.01 and 0.08 the cross-sectional area of the sleeve 16. As the engine warms up, the air which embraces the exhaust manifold pipe 1 5 becomes heated to a sufficient degree.Heat is further transferred to the shroud 17, sleeve 1 6 and the heated air duct 10.

During a suction stroke of the engine an increased velocity of air being sucked in causes a sudden decrease in static pressure in the feed system, as well as in the ducts 5 and 10, whereby a portion of cool ambient air enters the interior of the sleeve 16 through the holes 1 8. This reduces the thermal effect exerted on elements susceptible to heating, including the connection area of the inlet end of the part 12 of the heated air duct 10. However, this is permissible only within certain limits. For this very reason the holes 18 are calibrated and their total flow area must be 0.01 to 0.08 the cross-sectional area of the sleeve 1 6. An increase in the flow area of the holes 1 8 affects the temperature control of air entering the carburetor, i.e., no sufficient heating of the incoming air is ensured.Conversely, reduced flow area of the holes leads to insufficient cooling action bringing down the efficiency of the system. One important aspect of the invention associated with the manner the elements of the system are cooled is the proper positioning of the holes 1 8 lengthwise of the sleeve 1 6. It has been found most preferable to locate the holes at a distance of from 0.8 to 3.0 the diameter of the sleeve 1 6 from the shroud 17. In this case, a stream of cool ambient air flows around the connection between the sleeve 1 6 and the duct 10 thereby effectively cooling the fitting portion of the latter.When the holes 1 8 are spaced relative to the shroud a distance less than 0.8 the diameter of the sleeve 1 6, the flow of ambient air will tend to run towards the geometrical axis of the sleeve 1 6 rather than towards the walls thereof due to the distribution of the static pressure lengthwise of the sleeve 16, thereby failing to provide a sufficient cooling action. A further increase in the distance between the holes 1 8 and the shroud 17, specifically to a value of 3.0 the diameter of the sleeve 16 is not advisable for purely structural considerations; in addition, such an increase in the distance may result in that the elements of the connection may be affected but negligibly by heat.

The provision of the calibrated radial holes 1 8 in the sleeve 1 6 gives another advantageous effect, particularly it reduces vortex noises generated at the edge of the shroud 1 7 at the place of connection thereof to the sleeve 1 6, especially when the connection radius selected exclusively to simplify the manufacture is small, such as less than 0.25 the radius of the inlet sleeve. This is dictated by the following. Disruption of the flow of heated air being sucked into the sleeve 1 6 from a clearance formed by the surface of the exhaust manifold pipe 15 and the shroud 1 7 during an exhaust stroke of the engine is inevitable. Eddies thus formed tend to generate pressure oscillations emitted outside in the form of noise.The holes 1 8 in the sleeve 1 6 act to suppress vortex formation therein, which in turn reduces the amount of noise emitted by the edges of the shroud 1 7.

The foregoing approach to the problem makes it possible to improve the durability of the connection of the part 12 of the flexible heated air duct 10 in a simple and reliable manner which is easy to execute without increasing the amount of metal to be consumed.

Yet another important feature with respect to reducing the level of air intake noise produced at full load operating conditions of the engine without affecting the power performance thereof is the selection of the most optimum geometry of the heated and ambient air ducts 4 and 5 (Fig, 1).

It has been found most advantageous that the minimum hydraulic diameter of the heated air duct 4 must be 0.8 to 1.2 the minimum hydraulic diameter of the ambient air duct 5. In the intermediate position of the gate 7 of the temperature controller 6 air is sucked into the air cleaner 1 through both the heated and ambient air -ducts 4 and 5, and through the holes 8 and 9 provided in the ducts 4 and 5. The variable component of the volumetric consumption of air determined by variations in the engine cylinder displacements at the inlet valves open becomes less pronounced in the air cleaner 1 and in a weakened form is emitted through the open ends of the ducts 4 and 5 and the holes 8 and 9.

Analyses and tests have shown that in a two-duct air intake system in a position of the temperature controller gate 6 short of blocking one of the ducts, normally the heated air duct 4, the velocity of gas in this duct is low, noise suppression is insufficient while resonance oscillations are quite pronounced. A reduction in the cross-sectional area of the heated air duct 4 acts to increase the induced drag and lower the natural frequency of the system, whereby the range of noise suppression is shifted toward the lower frequencies to result in an increase in both the frequency range of noise suppression and the efficiency of such a suppression. In addition, the provision of the heated air duct 4 with a minimum hydraulic diameter of 0.8 to 1.2 the minimum hydraulic diameter of the ambient air duct 5 results in a reduced cross-sectional area of the duct (emitter) and increases the amount of acoustic loads exerted on the chamber of the air cleaner 1 in the high frequency range. Reduction of the hydraulic diameters leads to more hydraulic losses, which results in reduced volumetric efficiency of breathing of the engine cylinders and, as a consequence, in the loss of the engine power. High values of these diameters entail increased noise level. Therefore, a series of tests have shown that the use of the heated air duct 4 having the hydraulic diameter within a range of between 0.8 and 1.2 the value of the hydraulic diameter of the ambient air duct 5 affords at certain operating conditions of the engine to bring down the level of sound pressure to 7 dB and the total noise level to as low as 5 dBA. Therewith, acoustic efficiency was quite pronounced in the low, medium and high frequency range.

The objects and advantages of the present invention are accomplished in the manner described heretofore.

Claims (8)

1. An air intake system of an internal combustion engine comprising an air cleaner with an inlet port having connected thereto a mixed air duct; connected to the mixed air duct by way of a temperature controller with a gate to proportion the flows of air are heated and ambient air ducts having open ends on the sides thereof opposite to the one that connect them to the mixed air duct; at least one of the heated and ambient air ducts is provided with at least one calibrated hole positioned at a location where the sound pressure level is most pronounced.

2. An air intake system of an internal combustion engine according to claim 1 wherein at least one calibrated hole is positioned in the heated air duct at a distance of from 0.2 to 0.5 the total length of the heated and mixed air ducts as measured from the open end of the heated air duct to the inlet port of the air cleaner, the ratio between the total flow area of the calibrated holes and the cross-sectional area of the heated air duct ranging between 0.01 and 0.08.

3. An air intake system of an internal combustion engine according to claim 1 wherein at least one calibrated hole is provided in the ambient air duct, this calibrated hole being positioned relative to the open end of the ambient air duct at a distance of 0.2 to 0.5 the total length of the ambient and mixed air ducts as measured from the open end of the ambient air duct to the inlet port of the air cleaner, the ratio between the total flow area of the calibrated holes and the cross-sectional area of the ambient air duct ranging from 0.01 to 0.08.

4. An air intake system of an internal combustion engine according to claim 1 wherein each of the heated and ambient air ducts has at least one calibrated hole, the calibrated hole of the heated air duct being positioned relative to the open end thereof at a distance of 0.2 to 0.5 the total length of the heated and mixed air ducts as measured from the open end of the heated air duct to the inlet portion of the air cleaner, the ratio between the total flow area of the calibrated holes and the cross-sectional area of the heated air duct ranging between 0.01 and 0.08, whereas the calibrated hole of the ambient air duct is positioned relative to the open end thereof at a distance of 0.2 to 0.5 the total length of the ambient and mixed ducts as measured from the open end of the ambient air duct to the inlet port of the air cleaner, the ratio between the total flow area of the calibrated holes and the crosssectional area of the ambient air duct ranging between 0.01 and 0.08.

5. An air intake system of an internal combustion engine according to any of claims 1 to 4 wherein at least one of the heated or ambient air ducts is of a composite construction with parts thereof being interconnected by means of a sleeve having arranged therein calibrated holes.

6. An air intake system of an internal combustion engine according to any of the claims 1 to 5, wherein the heated air duct is flexible, the air inlet end thereof having an air intake sleeve provided with radially disposed holes.

7. An air intake system of an internal combustion engine according to any of the claims 1 to 6 wherein the minimum hydraulic diameter of the heated air duct is 0.8 to 1.2 the minimum hydraulic diameter of the ambient air duct.

8. An air intake system of an internal combustion engine substantially as heretofore described with reference to the accompanying drawings.