Abstract:
A suction system for supplying an internal combustion engine with combustion air, especially in an automobile. The suction system includes at least one separate air collector from which individual suction pipes each lead to the air inlets of the respective cylinders of the internal combustion engine. The suction pipes are configured as ram tubes for the top speed areas of the internal combustion engine. At least one compensation flap is located in the air collector. When closed, the compensation flap divides the air collector to provide a long pre-suction section and when open, instead of a long pre-suction section provides an air collector with an increased volume.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an induction system for supplying an internal combustion engine with combustion air, in particular for a motor vehicle, having at least one separate air manifold, from which in each case cylinder-specific induction pipes lead to air intakes of cylinders of the internal combustion engine. 
     2. Discussion of the Prior Art 
     It is known from Asia-Pacific Automotive Report, volume 234, May 4, 1996, to use two switchable valves to switch a tuned pipe long or short and thus to change a corresponding tuned length as desired. However, this system only switches between two different tuned states, ensuring optimum cylinder filling only over a limited speed range. For this reason, a third switchable valve is provided, which in the open state increases a cross section of flow for combustion air accordingly, so that at high revs a high mass flow is ensured. However, this completely destroys any tuned effect in the induction system for the combustion air and does not provide any kind of assistance for-filling the cylinders. 
     SUMMARY OF THE INVENTION 
     The present invention is therefore based on the object of providing an induction system of the above type in which the above drawbacks are overcome and of achieving optimum cylinder filling with combustion air over the maximum possible speed range of the internal combustion engine. 
     To this end, according to the invention the induction pipes are designed as ram pipes for upper speed ranges of the internal combustion engine and at least one balancing valve is arranged in the air manifold, which valve optionally, in the closed position, divides the air manifold to form a long preintake length or, in the open position, instead of a long preintake length provides an air manifold with an increased volume. 
     This has the advantage that, in a structurally simple, space-optimized manner, it is optionally possible to achieve a tuned-intake charging for low speed ranges of the internal combustion engine, by closing the balancing valves, or to achieve a ram-type charging for high speed ranges of the internal combustion engine, by opening the balancing valves. 
     For internal combustion engines with cylinders which are arranged on separate cylinder banks, for example in the case of an 8-cylinder engine in a V or double-V arrangement or VR arrangement, it is particularly advantageous to provide two separate air manifolds. 
     An additional tuned state for a middle speed range of the internal combustion engine is achieved by the fact that in each case two air manifolds are connected to one another via a tuned pipe, the tuned pipe having a tuned valve for optionally opening or closing the pipe in such a manner that the respective air manifolds are optionally connected or not connected to one another via the tuned pipe. 
     In a preferred embodiment, the internal combustion engine has a crankshaft with a 180° crank angle and n cylinders, in which, to ensure that there is no disruption to the induction processes, the cylinders 1 to n/2 are connected to a first air manifold via respective induction pipes and the cylinders (n/2+1) to n are connected to a second air manifold via respective induction pipes. 
     Preferably, n=4 or 8. In the latter case, an ignition sequence for the cylinders 1 to 8 is, for example, as follows: 1-5-2-6-4-8-3-7. 
     A particularly small space requirement as the result of a compact design is achieved by the fact that the cylinders are distributed, for example, over at least two cylinder banks, in particular over two double cylinder banks, each air manifold supplying cylinders of one cylinder bank or one double cylinder bank with combustion air, and the induction pipes of the first air manifold crossing those of the second air manifold. 
     In this case, the balancing valve and the induction pipes of an air manifold are expediently arranged in such a manner that, when the balancing valve is closed, there is an increasing induction length for the cylinders which are supplied in each case via the induction pipes as the cylinder number increases. 
     In another preferred embodiment, the internal combustion engine has a crankshaft with a 90° crank angle and n cylinders, in each case n/2 or (n−1)/2 of the cylinders being connected to a first air manifold via respective induction pipes and the other n/2 or (n+1)/2 cylinders being connected to a second air manifold via respective induction pipes. 
     Expediently, n=4 or 8. In the latter case, an ignition sequence of the cylinders 1 to 8 is, for example, as follows: 1-5-7-4-8-3-2-6. 
     In this case, to ensure that there is no disruption to the induction processes, the cylinders 1, 2, 7, 8 are preferably connected to the first air manifold and the cylinders 5, 6, 3, 4 are preferably connected to the second air manifold. 
     A particularly small space requirement as a result of a compact design is achieved by the fact that the cylinders are distributed over at least two cylinder banks, in particular over two double cylinder banks, the air manifolds being arranged in each case adjacent to one cylinder bank or double cylinder bank and opposite to the other cylinder bank or double cylinder bank, in which arrangement some of the induction pipes of one air manifold lead to the opposite cylinder bank or double cylinder bank, crossing over the induction pipes of the other air manifold, and some of these induction pipes lead to the adjacent cylinder bank or double cylinder bank in an overhead arrangement. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Further features, advantages and advantageous configurations of the invention are given in the following description of the invention with reference to the appended drawings, in which: 
     FIGS. 1 and 2 show a first preferred embodiment of an induction system according to the invention, in a partially sectional plan view, in each case in different switching states; 
     FIG. 3 shows a second preferred embodiment of an induction system according to the invention, in partially sectional plan view; 
     FIG. 4 shows the second preferred embodiment of an induction system according to the invention from FIG. 3, in a cross-sectional illustration; 
     FIG. 5 shows a third preferred embodiment of an induction system according to the invention, in a partially sectional plan view; 
     FIG. 6 shows the third preferred embodiment of an induction system according to the invention from FIG. 5, in section on line A—A from FIG. 5; 
     FIG. 7 shows the third preferred embodiment of an induction system according to the invention from FIG. 5, in section on line B—B from FIG. 5; 
     FIGS. 8 to  10  show the second preferred embodiment of an induction system according to the invention from FIG. 3 in partially sectional plan view, in each case in different switching states. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The first preferred embodiment of an induction system according to the invention which is illustrated in FIGS. 1 and 2 comprises, as seen in the direction of flow, an air filter  10 , a preintake length  12 , an air manifold  14  and cylinder-specific induction pipes  16  which lead to air intakes (not shown) for cylinders of an internal combustion engine  18 . A balancing valve  20  is arranged rotatably in the air manifold  14 , in such a manner that, in the closed position, as shown in FIG. 1, it divides the air manifold  14  into two parts. A chamber  22  of the air manifold  14  which is on the air filter side in this case additionally acts as a preintake length, while a chamber  24  which is on the induction pipe side acts as an air manifold of reduced volume. In this switching position shown in FIG. 1, combustion air which is drawn in by the internal combustion engine  18  flows in the direction of the arrows  26  along an extended preintake length, and the dimensions of the components are selected in such a manner that tuned-intake charging results for a lower speed range of the internal combustion engine  18 , since reflection of pressure waves at the air filter system  10  and in the preintake length controls the fluid dynamics. 
     In the second switching position illustrated in FIG. 2, the balancing valve has been rotated through 90 degrees by a drive  28 , such as for example an electric motor, resulting in an air manifold  14  of increased volume comprising the sum of chambers  22  and  24  and, furthermore, reducing the preintake length  12 . The induction pipes  16 , which are expediently designed and dimensioned as ram pipes for the internal combustion engine  18  in an upper speed range, now control the flow of the combustion air which is drawn in by the internal combustion engine, resulting in ram-pipe charging. In this switching position, therefore, the reflection of the pressure waves at the air manifold  14  determines the system performance. 
     The balancing valve  20  does not necessarily have to be arranged in a single piece in the air manifold  14 . Rather, it is also possible for the balancing valve to be divided into two or more sections which are rotated together or separately and are mounted separately. This has the advantage that the tendency of large balancing valves  20  to flutter is effectively reduced. Furthermore, in an advantageous refinement of the invention, it is also possible to provide a plurality of balancing valves  20  one behind the other, in such a manner that the air manifold volume and therefore also the length of the preintake section can be increased and reduced in a number of steps. 
     The particular advantage of the induction system according to the invention resides in the combination of the ram pipe and tuned principle. Depending on the position of the balancing valves  20 , a single induction system is deliberately used to produce either tuned-intake charging or ram-pipe charging. However, there is no need for a plurality of differently dimensioned ram pipes or air manifolds. 
     In the illustration shown in FIGS. 1 and 2, the induction system according to the invention is designed, by way of example, for a 4-cylinder engine. However, a corresponding inventive design for engines with any desired number of cylinders is also possible. Therefore, further exemplary embodiments for internal combustion engines  18  with eight cylinders are described below, although this too is to be understood purely as an example providing a better explanation of the principle of the invention. 
     The induction system according to the invention is also suitable, as mentioned above, for 8-cylinder engines, as shown in FIGS. 3 to  7 . In this case, the cylinders of the internal combustion engine  18  are in a double-V arrangement, i.e. in the form of a so-called VR engine. Two air manifolds  14  and  15  are provided, in each case one air manifold  14  being connected to specified cylinders of the internal combustion engine  18  and the other air manifold  15  being connected to the remaining cylinders of the internal combustion engine  18 , supplying the cylinders with combustion air via air intakes  29 . The preintake length  12  supplies the air manifolds  14  and  15  with combustion air. A balancing valve  20 , which is mounted so that it can rotate about a pin  30 , is arranged in each of the two air manifolds  14 ,  15 . In addition, in a type of parallel connection in terms of the induction pipes  16 , a tuned pipe  32  which connects the two air manifolds  14  and  15  is provided. In the tuned pipe  32  there is a tuned valve  36  which is mounted so that it can rotate about a pin  34  and which optionally, depending on its position, does or does not produce fluid communication between the air manifolds  14  and  15  via the tuned pipe  32 . The balancing valves  20  and the tuned valve  36  can be actuated by the drive  28 , for example dedicated electric motors, in such a manner the valves  20  and  36  are in either an open or a closed position. Suitably combining the open and closed positions of the valves  20  and  36  results essentially in three different switching states which are described in more detail below with reference to FIGS. 8 to  10 . 
     The essential difference between the two embodiments shown in FIGS. 3 and 4, on the one hand, and FIGS. 5 to  7 , on the other hand, is that FIGS. 3 and 4 show an embodiment for an internal combustion engine  18  with a so-called 180° crank angle, while FIGS. 5 to  7  show an embodiment for an internal combustion engine  18  with a so-called 90° crank angle. 
     This induction pipe design according to the invention shown in FIGS. 3 to  7  is also a combined ram-pipe/tuned-intake system in which the volumes of the manifolds  14  and  15  and the lengths of the corresponding preintake pipes  12  can be switched. The system allows a high delivery level over a wide speed spectrum. To optimize the space required, it can be of very shallow design. 
     To produce unimpeded induction processes, in the embodiment shown in FIGS. 3 and 4 in each case cylinders with a 180° crank angle spark gap are connected to each of the manifolds  14 ,  15 . For an ignition sequence 1-5-2-6-4-8-3-7 (“180° crankshaft”), the cylinders 1, 2, 3 and 4 and 5, 6, 7 and 8 are each connected to a common manifold  14  or  15  (FIG.  3 ). This results, for example, in a crossed induction pipe arrangement which is outlined in section in FIG. 4 for all eight cylinders. The air manifold  14  is arranged above a cylinder bank  38  and the corresponding induction pipes  16  run to an opposite cylinder bank  40 , above which the other air manifold  15  is arranged. The induction pipes  16  of the latter manifold  15  are in turn connected, in a similar way, to the cylinder bank  38  which lies opposite the air manifold  15 . 
     For the ignition sequence 1-5-7-4-8-3-2-6 (“90° comfort crankshaft”) in accordance with the embodiment shown in FIGS. 5 to  7 , to ensure that there is no disruption to the induction processes, the cylinders 1, 2, 7 and 8 and the cylinders 3, 4, 5 and 6 have to be supplied from in each case one common air manifold  14 ,  15  (FIG.  5 ). For this purpose, by way of example, the induction pipes  16  of the cylinders 1, 2, 5 and 6 are arranged “overhead”, as illustrated in FIG. 7, and the induction pipes  16  of the cylinders 3, 4, 7 and 8 are arranged “crossed”, as illustrated in FIG.  6 . 
     The switchable change in volume of the air manifolds  14  and  15  using the balancing valves  20  adapts the system oscillation in particular in the lower speed range. For this purpose, by switching, the air manifold volume which is capable of oscillation, in conjunction with the geometry of the preintake length  12  between air manifolds  14 ,  15  and air filter (not shown in FIGS. 3 to  7 ), is switched to a tuned system which is capable of oscillation. 
     The air manifold volume can be reduced by suitably switching the balancing valves  20 , and part of the air manifold volume can be used as a pipe-like extension  22  of the preintake length  12  (FIG.  8 ). This results in a natural frequency of the oscillation system which is adapted to the lower speeds and is used for tuned-intake charging. 
     This switchable transverse connection between the two air manifolds  14  and  15  by means of the tuned pipe  32  allows tuned vibration between the two air manifolds  14  and  15 . By configuring the tuned pipe length and tuned pipe diameter, the tuned-intake system is adapted to the appropriate engine system. This tuned-intake system is used in particular in the middle speed range in order to optimize the induction pipe oscillation. 
     When the tuned valve  36  in the tuned pipe  32 , which is also referred to as the transverse pipe, is closed, ram-pipe charging is produced by the induction pipes  16  and the air manifold volume. The system is adapted using the induction pipe diameter and induction pipe length and air manifold volume  22 ,  24  in conjunction with the induction brought about by the cylinders. 
     Differences in the oscillation lengths of the induction pipes  16  caused by different duct lengths in cylinder heads are balanced by the passage of the induction pipes between the cylinder head and main manifold (not shown in the figures). In engines with a variable camshaft, this status is additionally taken into account, for example by using different intake cam contours. Furthermore, defined pressure losses from the individual induction pipes  16  can be used as a compensating measure. 
     The operating principle of the induction system according to the invention is explained below with reference to FIGS. 8 to  10 . FIGS. 8 to  10  show, purely by way of example, partially sectional plan views of the embodiment shown in FIG. 3, but these explanations apply to all embodiments or, where they relate to the additional switching of the tuned valve  36 , to all embodiments with at least two air manifolds  14  and  15 . 
     The operating principle of the switching operations which is explained below with reference to the example of the 180° crankshaft (FIG. 3) applies mutatis mutandis to the 90° crankshaft (FIG.  5 ), in which case the changed passage of the induction pipes (induction pipes of cylinders 1, 2, 7 and 8 and 3, 4, 5 and 6 running to in each case one manifold) are to be taken into account for the ignition sequence of the physical crankshaft. 
     Switching step  1  (FIG. 8) is used to fill the cylinders in the lower speed range. For this purpose, the manifold volumes are reduced by closing the balancing valves  20 , and the filter air intake lengths  12  are extended by the separate air manifold regions  22  and  24 . The tuned valve  36  between the air manifolds  14  and  15  remains closed. In engines with a variable camshaft, the intake camshafts are preferably switched to the moment position (early opening times). In this switching position, the reflection of the pressure waves at the air filter system and in the preintake length  12  becomes significant. As a result, a tuned-intake charging is produced in the lower speed range. The part-pipes of the transverse pipe or tuned pipe  32  which is closed by the tuned valve are used as λ/4 pipes to assist the system oscillation of the air manifold  14 ,  15 . 
     In switching step  2  (FIG.  9 ), the manifold volumes are increased by opening the balancing valves  20 . The tuned valve  36  is closed. In the case of engines with a variable camshaft, the intake camshafts are preferably in the early position. In this switching position, the reflection of the pressure waves at the air manifold  14 ,  15  determines the performance of the system. The induction system according to the invention operates using the principle of ram-pipe charging. 
     In switching step  3  (FIG.  10 ), the balancing valves  20  and the tuned valve  36  are open. In the case of engines with a variable camshaft, the intake camshafts are preferably in the early position. By opening the tuned valve  36 , mass transfer between the air manifolds  14  and  15  becomes possible and tuned oscillation between the two manifolds  14  and  15  is generated. This tuned oscillation is used to increase the cylinder filling in the middle speed range. 
     In the case of engines with a variable camshaft, it is additionally possible to produce a switching step  4  which, in terms of the position of balancing valves  20  and tuned valve  36 , is similar to switching step  2  which is explained above. The entire volume of the air manifolds is available as a result of the balancing valves  20  being opened. Because the tuned valve  36  is closed, direct exchange of pressure between the two air manifolds  14  and  15  is prevented. In addition, however, a late position of the intake camshafts adapts the ram-pipe charging system to upper speed ranges. 
     By adapting pipe lengths and pipe diameters in the induction system, in combination with the reduction in the volume of the air manifolds and a possible adjustment of intake camshafts, the induction system is adapted to the particular engine configuration. 
     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.