GB2121875A - Multi-cylinder internal combustion engine with a combination turbocharger and inertia supercharger - Google Patents

Abstract

An inertia supercharger includes a pair of first collection passages (33A, 33B) connected respectively to the intake manifolds (32A, 32B) and a single second collection passage (34) connected to the first collection passages (33A, 33B). A turbocharger (35) includes a turbine (37) coupled to the exhaust manifold (38) and a compressor (36) coupled to the second collection passage (34). The inertia supercharger and the turbocharger (35) have different ranges of engine RPM in which the volumetric efficiency of the engine (31) is improved. The first collection passages (33A, 33B) each have an inside diameter D and a joined by a wall having a radius R, the radius R and the diameter D having the relationship R/D / 0.05. The opening and closing of the valve (40) in the passage (39) connecting the first collection passages (33A, 33B) provide different ranges of engine RPM over which the volumetric efficiency is improved. <IMAGE>

Description

SPECIFICATION Multicylinder internal combustion engine with a combination turbocharger and inertia supercharger The present invention relates to a multicylinder internal combustion engine having a combination turbocharger and inertia supercharger.

It is well known in the art to equip multicylinder diesel engines with a blower or supercharger to increase the volumetric efficiency of the engine.

Known superchargers that have found wide use include turbochargers and inertia superchargers.

In ordinary applications, either the turbocharger or the inertia supercharger singly is associated with diesel engines.

Turbochargers use some of the waste heat energy in the exhaust gases to force air into the engine cylinders at a pressure higher than atmospheric pressure. The turbochargers are disadvantageous in that they fail to increase the volumetric efficiency effectively throughout a full range of engine RPM. For example, efforts to obtain a maximum increase in the volumetric efficiency at high engine RPM result in a lower volumetric efficiency at low engine RPM than wouid be when air would be drawn in normally.

The same problem is experienced with inertia superchargers in that a greatest volumetric efficiency increase at low engine RPM is accompanied by a reduced volumetric efficiency at high engine RPM.

Therefore, the turbochargers and inertia superchargers can attain a maximum volumetric efficiency only in a certain range of engine RPM, and a poorer volumetric efficiency results outside that range. To cope with this deficiency, it is customary practice to design turbochargers and inertia superchargers such that the volumetric efficiency will be maximized in the range of RPM in which the engine operates frequently or high engine power is required.

The range of engine RPM in which the engine is supercharged for the maximum volumetric efficiency will be hereinafter referred to as a "matching range".

Many attempts have been made to eliminate the problems with the turbocharger and the inertia supercharger. One such known arrangement is disclosed in Japanese Patent Publication No.

57-2892, in which different matching ranges are set up by a turbocharger and an inertia supercharger, respectively, and the common collection tube of an intake manifold is short.

Another prior proposal is for inertia supercharging only, with engine cylinders divided into two groups having intake strokes that are not overlapped and coupled to respective intake manifolds each having first collection tubes coupled to a single second collection tube for increasing the volumetric efficiency. The second collection tube serves as a damping chamber to enable the intake manifolds to effect independent inertia supercharging. According to a modification of this arrangement, the first collection tubes are coupled arcuately to the second collection tube, and the second collection tube and the manifolds serve as respective damping chambers for selecting two matching ranges due to inertia supercharging.The above prior art arrangements however fail to provide an analysis of the desired shape for the coupling between the first and second collection tubes which gives a sufficient engine performance.

Accordingly, it is an object of the present invention to provide a multicylinder internal combustion engine having a combination turbocharger and an inertia supercharger which includes an air intake tubing providing increased volumetric efficiency due to inertia supercharging.

According to the present invention, a multicylinder internal combustion engine has a plurality of engine cylinders divided into two groups in which intake strokes are not overlapped, a pair of intake manifolds connected respectively to the two groups of engine cylinders, and an exhaust manifold connected to the engine cylinders. An inertia supercharger includes a pair of first collection passages connected respectively to the intake manifolds and a single second collection passage connected to the first collection passages. A turbpcharger includes a turbine coupled to the exhaust manifold and a compressor coupled to the second collection passage. The inertia supercharger and the turbocharger have their own different ranges of engine RPM in which the volumetric efficiency of the engine is improved.The first collection passages where they are joined to the second collection passage are of a curved configuration having an inner wall with a radius of curvature R, and each has an inside diameter D along the curved configuration. The radius of curvature R and the inside diameter D are defined in accordance with the relationship R/D > = 0.05.

The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

Figure 1 is a plain view of an internal combustion engine equipped with a conventional inertia supercharger; Figure 2 is a plan view of an internal combustion engine equipped with another prior inertia supercharger; Figure 3 is a plan view of an internal combustion engine having a conventional combination turbocharger and inertia supercharger; Figure 4 is a plan view of an internal combustion engine with a combination turbocharger and inertia supercharger according to the present invention; Figure 5 is a graph showing characteristic curves which represent the relationships between the volumetric efficiency and the engine RPM of the internal combustion engine illustrated in Figure 4; Figure 6 is a fragmentary plan view of a tube coupling in the engine of Figure 4; and Figure 7 is a graph illustrative of a characteristic curve representing the relationship between the ratio of a diameter to a radius of the tube coupling of Figure 6 and the volumetric efficiency.

The present invention will be described as being incorporated in diesel engines. However, a combination turbocharger and inertia supercharger of the present invention is equally applicable to gasoline engines.

Turbochargers comprise a turbine rotatable by an exhaust gas and a compressor drivable by the turbine to force air into the engine cylinders at a pressure higher than atmospheric pressure. The turbocharger alone fails to increase the volumetric efficiency sufficiently as the latter tends to be lowered outside the matching range provided by the turbocharger. On the other hand, inertia supercharging is roughly classified into two groups. According to one type of inertia supercharging, an air intake pulsation is utilized to propagate a positive pressure wave into an engine cylinder immediately prior to the closing of the intake valve. With the other type of inertia supercharging, the inertia of a mass of air in the intake manifold is used to produce an inertia effect for forcing the air into an engine cylinder.Such an inertia effect is nothing but a pressure wave acting in the vicinity of an air intake port, and can be regarded as the vibration of a column of air in the air intake tube.

One conventional inertia supercharger is constructed as shown in Figure 1. A six-cylinder internal combustion engine 1 has cylinders grouped into two divisions in which their air intake strokes are not overlapped, and a pair of intake manifolds 2A, 2B leading to the two cylinder groups, respectively. The intake manifolds 2A, 2B are connected to a damping chamber 3 which is joined to a single collection tube 4. With this prior arrangement, a mass of air in each of the intake manifolds 2A, 2B vibrates, and the damping chamber 3 serves as an open end for both of the intake manifolds 2A, 2B, the damping chamber 3 having a large volume. Since the damping chamber 3 is heavy and takes up a large space, there has been a need for an inertia supercharger with no such damping chamber.

To meet such a need, there has been proposed an arrangement as shown in Figure 2 which is composed of two intake manifolds 1 2A, 1 2B having ends extending parallel to each other and joined to a single tube 13 having a cross-sectional area which is substantially the same as the total cross-sectional area of the intake manifolds 1 2A, 12B. The tube 13 is considered to act as a damping chamber as shown at 3 in Figure 1 for providing a sufficient damping effect.

With the known arrangements shown in Figures 1 and 2, columns of air in the manifolds 2A, 2B, 1 2A, 12B are accelerated repeatedly on opening of intake valves and hence vibrated, each air column having its own natural frequency. A maximum amount of air can be drawn into the engine cylinders when the natural frequency is in conformity with the frequency of openings of the intake valves which depends on the engine RPM.

Consequently, the volumetric efficiency is at its maximum when the engine RPM reaches a certain value, and becomes poorer at other engine RPM.

Figure 3 shows still another known apparatus as disclosed in Japanese Patent Publication No.

57-2892. The disclosed apparatus has resonant tubes 21 and resonant tanks 22, the arrangement being that air pressure in the resonant tanks 22 is increased to force an increased amount of air into engine cylinders 23. According to the description of Publication No. 57-2892, columns of air in the resonant tubes 21 vibrate and have a single natural frequency as the resonant tanks 22 are of a relatively large volume, and pressure waves return to the resonant tanks 22 at all times at engine RPM higher than the matching range, with the result that the volumetric efficiency will be prevented from becoming lower than would be with air drawn in normally though the inertia effect is more or less reduced.The apparatus of Figure 3 utilizes inertia supercharging at low engine RPM and a turbocharger at high engine RPM, a combination inertia supercharger and turbocharger which is most desirable. However, the resonant tanks 22 and a required vessel 24 make the overall system heavy and large in size, taking up a large space. This places a limitation on the layout of an engine compartment.

With the prior problems in view, the present inventors have developed an inertia supercharger associated with a turbocharger as shown in Figure 4.

In Figure 4, an internal combustion engine 31 has six cylinders divided into two groups in which the air intake strokes are not overlapped. The cylinder groups are coupled respectively to two manifolds 32A, 32B which have collection tubes 33A, 33B, respectively, that are joined to a single collection tube 34. The collection tube 34 is connected via an inter-cooler 41 to a compressor 36 of a turbocharger 35 having a turbine 37 to which the exhaust gas is supplied from an exhaust manifold 38.

The collection tubes 33A, 33B are also interconnected by a bypass tube 39 which can be opened and closed by a valve 40 disposed therein.

The internal combustion engine 31 has supercharging effects as follows: When the engine 31 rotates at high RPM, the turbocharger 35 becomes effective in its operation to force air into the engine cylinders. When the engine 31 rotates at low and medium RPM, the inertia supercharging then becomes effective to force air into the engine cylinders. More specifically, when the valve 40 is closed, the inertia supercharging works at low engine RPM as the frequency of vibrations of the tube system downstream of the collection tube 34 is small. When the valve 40 is open, the tube system downstream of the bypass tube 39 vibrates, resulting in a higher natural frequency which allows the inertia supercharging to be effective at medium engine RPM. The intercooler 41 serves to lower the temperature of intake air which has been pressurized by the compressor 36 for an increased volumetric efficiency.However, the intercooler 41 may be dispensed with.

Figure 5 is illustrative of characteristic curves indicating the foregoing engine operation, the graph having a vertical axis indicating volumetric efficiency liv and a horizontal axis indicating engine RPM. The curve A indicates an engine operation in which the turbocharger 35 is actuated, the curve B an engine operation in which the valve 40 in the bypass tube 39 is open, and the curve C an engine operation in which the valve 40 is closed.

The arrangement of Figure 4 is advantageous in that there is no large-volume chamber in the intake air tube system so that the overall construction is relatively lightweight and takes up a relatively small space. The bypass tube 39 with the valve 40 therein permits the intake tubing to selectively have two different natural frequencies for an improved volumetric efficiency of the engine.

The inertia supercharger normally requires an analysis of the vibrations of the tube system and corrects them through experiments. No reliable and complete tube construction could be achieved only by computations.

On designing the coupling between the collection tubes 33A, 33B and the collection tube 34 in the arrangement of Figure 4, the following characteristics have been found: As shown in Figure 6, the ends of the parallel collection tubes 33A, 33B are joined to the end of the parallel collection tube 34 by means of a tubular coupling 42. This coupling 42 is of a C-shaped arcuate configuration having the legs thereof joined to the collection tubes 33A, 33B, whereas the collection tube 34 is joined to the midpoint of the bight of the C-shaped coupling tube 42. This tube 42 is of the same diameter D as the collection tubes 33A and 33B. The inner curved wall of the coupling 35 is defined by a radius of curvature R. It has been found that as the radius of curvature R is varied, the volumetric efficiency is improved.The volumetric efficiency is increased in the range in which the inertia supercharging is effected, and aimost no increase in the volumetric efficiency results in the matching range in which the turbocharger operates. Stated otherwise, the radius of curvature R has a certain effect on the inertia supercharging effect, but has substantially no effect on the performance of the turbocharger.

Figure 7 is a graph showing a characteristic curve E with a vertical axis indicating the volumetric efficiency 77v and a horizontal axis indicating the ratio R/D where R is the radius of curvature of an inner wall of the curved configuration where the collection tubes are joined and D is the inside diameter of each of the collection tubes 33A, 33B along the curved configuration. The characteristic curve E rises steeply from R/D = 0, becomes less steep at R/D = 0.05, and begins to become flat at R/D = 0.1. The volumetric efficiency liv remains substantially unchanged at the ratio R/D which is greater than 0.1.

The reason why the above characteristic can be achieved will now be considered.

The inertia supercharging is closely related to the natural frequency of the intake tube system, and varies dependent on how far the tubing can be regarded as mass air. For R/D = 0.05 or more, the collection tubes 33A, 33B become joined to each other into a single tube system, whereby the volume of air introduced into one of the collection tubes 33A or 33B is the total of the volumes of air supplied from the collection tube 34 and the other of the collection tubes 33A and 33B. For example, the air introduced into tube 33A is supplied from tubes 33B and 34, and similarly the air introduced into tube 33B is supplied from tubes 33A and 34.

Thus, in the present invention, a greater volume of air is introduced than in the prior art systems, namely a greater mass of air is introduced whereby a higher volumetric efficiency is attained.

Factors for increasing the effect of the inertia supercharging will be considered on the basis of assumptions from experimental results, but a theoretical analysis therefor still remains to be effected.

Those factors which affect the inertia supercharging in relation to the air intake tubing include the length (L) of the air intake tubing, the cross-sectional area (f) of the air intake tubing, and the resistance (y) to air flow of the air intake tubing.

Assuming that the coupling construction between the collection tubes 33A, 338 and the collection tube 34 has an effect on the inertia effect, the resistance (,unto air flow of the air intake tubing is considered to be the governing factor, and varies with the ratio R/D and governs the volumetric efficiency. The flow resistance (y) serves to increase the volumetric efficiency throughout the full range of engine RPM. In general, the smaller the rate of air flow the smaller the flow resistance.

The advantageous effect through selection of the ratio R/D according to the present invention is considered to result from the two resonant points, the small flow resistance, and other unknown causes.

The present invention is therefore constructed on the basis of experimental results, and its theoretical analysis remains to be perfected.

With the present invention, as described above, the inertia supercharger and the turbocharger are combined, and the inertia supercharging is rendered effective in two or more matching ranges, thereby increasing the volumetric efficiency as a whole, an arrangement which is quite advantageous.

With the turbocharger operating in a high engine RPM range and the inertia supercharger operating in a low engine RPM range, the exhaust gas and the inertia effect can effectively be utilized.

For R/D = 0.1 or higher, the volumetric efficiency remains substantially unchanged, and hence can freely be determined to meet a particular design requirement.

Claims (7)

1. A multicylinder internal combustion engine, comprising: a plurality of engine cylinders divided into two groups in which intake strokes are not overlapped; a pair of intake manifolds connected respectively to said two groups of engine cylinders; an inertia supercharger including a pair of first collection passages connected respectively to said intake manifolds and a single second collection passage connected to said first collection passages; an exhaust manifold connected to said engine cylinders; a turbocharger including a turbine coupled to said exhaust manifold and a compressor coupled to said second collection passage, said inertia supercharger and said turbocharger having different ranges, respectively, of engine RPM in which a volumetric efficiency of the engine is improved; and said first collection passages where they are joined to said second collection passage being curved along an arcuate configuration having an inner wall of a radius of curvature R, and each having an inside diameter D along said arcuate configuration, said radius of curvature R and said inside diameter D meeting the relationship R/D > 0.05.

2. A multicylinder internal combustion engine according to claim 1, including a bypass passage interconnecting said first collection passages and having a valve therein.

3. A multicylinder internal combustion engine, comprising: a plurality of engine cylinders divided into two groups in which the intake strokes are not overlapped; an exhaust manifold connected to said cylinders; a pair of intake manifolds connected respectively to said two groups of cylinders; an inertia supercharger connected to said intake manifolds for improving the volumetric efficiency of the engine over a first range of engine RPM, said supercharger including a pair of first collection passages each connected respectively to one of said intake manifolds and a single second collection passage connected to said pair of first collection passages;; said inertia supercharger including a tubular coupling for connecting said first collection passages to said second collection passage, said tubular coupling comprising a tubular member of inside diameter D, said tubular member being curved into a C-shaped arcuate configuration having the legs thereof respectively joined to the ends of said first collection passages, said second collection passage being joined to the bight of said C-shaped tubular member substantially at the midpoint thereof, and said C-shaped tubular member having an inner curved wall which extends between said pair of first collection passages and is defined by a radius of curvature R; and a turbocharger connected to said second collection passage for improving the volumetric efficiency of the engine over a second range of engine RPM which is different from said first range, said turbocharger including a turbine coupled to said exhaust manifold and a compressor coupled to said second collection passage.

4. An engine as claimed in claim 3, wherein said radius R and said inside diameter D are defined in accordance with the relationship R/D being greater than or equal to 0.05.

5. An engine according to claim 3 or 4, wherein the ends of said first collection passages where they connect to said coupling are substantially parallel and are spaced apart by a distance substantially equal to twice said radius of curvature, said first collection passages also being of inside diameter D, and said second collection passage being connected to the bight of said coupling adjacent the radially outer curved wall thereof.

6. An engine according to claim 3, 4 or 5, including a bypass passage connected between said pair of first collection passages at a location downstream of said coupling, and openable and closable valve means associated with said bypass passage.

7. A multicylinder internal combustion engine substantially as described with reference to, and as illustrated in, Fig. 4 of the accompanying drawings.