The present invention relates generally to a fuel intake system for an automobile internal combustion engine and, more particularly, to a supercharger used in the fuel intake system.
For boosting the power output of the automobile internal combustion engine, the use of a supercharger has long been well known. In particular, the supercharger of a type comprising a compressor and a turbine connected together with the compressor and adapted to be driven by exhaust gases emitted from the engine is generally referred to as a turbo supercharger or a turbo-charger.
With the supercharger utilizing the exhaust-gas turbine, i.e., the turbocharger, it has often been experienced, and it is quite natural that, even though the engine is operating under a condition requiring the supply of the supercharged air or air-fuel mixture, the latter tends to be short of the required amount particularly when the engine operates at a low speed with the flow of the exhaust gases consequently retarded.
In order to obviate the above described problem, a solution is disclosed in any one of the Japanese Laid-open Pat. Publications No. 55-137314 and No. 55-156226, laid open to public inspection on Oct. 27, 1980 and Dec. 5, 1980, respectively, and U.S. Pat. No. 4,315,488 and No. 4,315,489, both patented Feb. 16, 1982.
All of these publications discloses a fuel intake system which comprises a primary intake system and an auxiliary intake system including a supercharger in the form of a displacement air pump driven by a drive unit, for example, the automobile engine. These prior art fuel intake systems are generally so designed that, when and so long as the load imposed on the engine is smaller than a predetermined value, only the primary intake system is brought into operation to supply a combustible air-fuel mixture into the engine through an associated primary intake port, but when and so long as the load on the engine is larger than the predetermined value and at least during the period in which the engine undergoes the compression stroke, the auxiliary intake system is brought into operation together with the primary intake system to allow a supercharged air from the supercharger to be supplied into the engine through an associated auxiliary intake port in parallel with the supply of the air-fuel mixture. These prior art systems appear advantageous in that, since the supercharger is comprised of the displacement air pump driven by the engine, the supply of the supercharged air into the engine would not be caused to be short of the required amount even at a low speed engine operating condition during which the flow of the exhaust gases through the exhaust manifold tends to be retarded.
Any one of the above discussed publications discloses the use of a primary throttle valve disposed in a primary intake passage of the primary intake system for regulating the flow of air prior to being mixed with fuel or an air-fuel mixture, an auxiliary throttle or timing valve disposed in an auxiliary intake passage of the auxiliary intake system downstream of the supercharger or displacement air pump with respect to the direction of flow of the supercharged air towards the engine, and a relief passage having a relief valve for relieving the supercharged air in part or in whole to the atmosphere or back to the suction side of the supercharger.
However, the auxiliary throttle or timing valve employed in the last two of the above mentioned Japanese publications as well as both of the U.S. patents is so positioned and so designed as to allow the supercharged air to flow therethrough to the engine in correspondence with change in load on the engine, for example, during the high load engine operating condition. On the other hand, the auxiliary throttle or timing valve employed in the first mentioned Japanese publication is so positioned and so designed as to allow the supercharged air to flow therethrough to the engine each time the engine is brought into the compression stroke.
Specifically, the fuel intake system in any one of the first three publications is disclosed as applied to the piston engine whereas that in any one of the last two publications is disclosed as applied to the rotary piston engine or Wankel engine. In particular, the first mentioned Japanese publication is directed to the use of the fuel intake system in a multi-cylinder internal combustion engine comprising, for example, two engine cylinders.
In any event, the use of the displacement air pump involves the following problem. Any fluid displacement device including, for example, the displacement air pump now under discussion, is of a design wherein suction and delivery ports thereof open and close alternately, and the delivery characteristic thereof exhibits a substantially pulsating flow of fluid during the continued operation of such device. Because of the above described design characteristic of the fluid displacement device, the supply of the supercharged air to the engine fluctuates for a given engine speed in such a manner that the engine receives the supercharged air at a time, but does not receive it at a different time, unless the displacement air pump is synchronized in operation with the engine, i.e., unless care is taken to render the timing at which the air pump delivers the supercharged air to match with the timing at which the engine requires the supercharged air (at least during the period in which the engine undergoes the compression stroke). Once this happens, the purpose for which the supercharger is utilized cannot be fulfilled to the maximum available extent.
In addition, the last mentioned Japanese publication, that is, Laid-open Pat. Publication No. 55-156226 also discloses the use of a secondary air supply system for supplying to an engine exhaust system a secondary air necessary to substantially purify the exhaust gases emitted from the engine. This secondary air supply system includes a secondary air supply passage extending between the delivery side of the supercharger and the exhaust manifold and having a flow regulator for controlling the effective cross sectional area of the secondary air supply passage according to the load on the engine. The flow regulator is in the form of a three-way rotary valve having three ports communicated respectively to the delivery side of the supercharger, the exhaust manifold and the suction side of the supercharger, the passage between the flow regulator and the suction side of the supercharger being used to relieve a portion of the supercharged air back to the suction side of the supercharger. In this arrangement, since the flow regulator is required separately of the supercharger, the fuel intake system for the engine tends to be complicated in construction and expensive to manufacture.
Moreover, when it comes to a multi-cylinder internal combustion engine, as the number of the engine cylinders increases, the supercharger as well as the timing valve necessary to distribute the supercharged air selectively into the engine cylinders must be driven at the increased speed to enable the supply of the supercharged air to be synchronized with the firing sequence in these engine cylinders. For example, assuming that the supercharger is driven at a given speed for the two-cylinder engine, the four-cylinder or six-cylinder engine will require the supercharger to be driven at a speed twice or three times the given speed because a longer time is required to complete the firing of all of the engine cylinders than in the two-cylinder engine. Accordingly, driving the supercharger at the increased speed may result in the overheating of the supercharger to such an extent as to result in the reduction in service life of the supercharger. Although this problem may be obviated if plural superchargers are employed in operatively coupled relation to each other, this obviously renders the system expensive in cost and complicated in structure and, yet, not reliable in operation.