Abstract:
A multiple cylinder engine controls an air/fuel ratio accurately by improved detection of the fluctuations in a vacuum due to a change in the openings of throttle valves. The multiple cylinder engine includes a plurality of intake passages that independently feed intake air to cylinders; fuel injectors; throttle valves; a pressure sensor; and a fuel controller that controls fuel injection of each cylinder using the detected pressure. The multiple cylinder engine may further include a vacuum inlet passage having an inlet port opened into intake passages that introduces the pressure of the intake passages into the pressure sensor. The vacuum inlet passage preferably includes a throttle portion having a passage area of no more than one ninth that of the inlet port.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a multiple cylinder engine such as a V-type 2-cylinder engine and, more particularly, to a multiple cylinder engine capable of controlling an air/fuel ratio accurately. 
     2. Description of Related Art 
     In a small general-purpose engine to be used in an agricultural machine, a small-sized power generator or the like, a carburetor is generally employed in an intake system of the engine. In case there is considered the response of the engine at its acceleration/deceleration, the countermeasures against exhaust emissions of recent years and the homogeneous distribution of mixtures, however, it is thought that a fuel injection device (especially, an electronic control type fuel injection system) for injecting fuel directly into the intake pipe is advantageous over the carburetor. From this background, the fuel injection device is being adopted at present. 
     Here will be briefly described the construction of the fuel injection device by exemplifying a fuel injection type V-type engine for adjusting a fuel injection quantity by measuring an intake pipe vacuum downstream of a throttle valve and by converting the measured vacuum into an intake air flow. This fuel injection device is constituted, as shown in  FIG. 9 , to include a fuel injection valve  81 , a fuel pressure adjustor  82  and a pressure sensor  83  shared by individual cylinders  80  and  80 . An intake passage  84 , as shared by the individual cylinders  80  and  80 , and the fuel pressure adjustor  82  are connected by conduit  86 . The intake passage  84  and the pressure sensor  83  are connected by conduit  85 . The pressure sensor  83  has a vacuum inlet port  85   a , which is opened into the intake passage  84  downstream of a throttle valve  87 . 
     In the case of this constitution, the intake pressure is averaged conveniently for the fuel pressure adjustor  82 , even if it is introduced from the intake passage  84  shared by the two cylinders into the single fuel pressure adjustor  82 . As the peaks of the intake pressure of the intake pipe are excessive close on the time axis, however, they are unclear for the pressure sensor  83  to detect, so that the accuracy of the injection quantity control is deteriorated. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a multiple cylinder engine capable of controlling an air/fuel ratio accurately by accurately detecting the fluctuations of a vacuum in an inlet passage of the engine, due to a change in the openings of throttle valves. 
     According to the first aspect of the present invention, a multiple cylinder engine comprises: a plurality of cylinders; a plurality of intake passages for feeding intake air to the individual cylinders independently of each other; a fuel injector provided for each intake passage; a throttle valve provided for each intake passage; a pressure sensor for detecting the pressure of one of the intake passages; and fuel control means for controlling the injection quantity of the fuel injector of each cylinder by using the detected pressure. 
     According to aspects of the present invention, the pressure sensor detects the vacuum from one of the intake passages provided independently for each cylinder. With this the detection is not influenced by another cylinder so that it can detect the vacuum accurately. Therefore, the detection accuracy of the intake air flow based on the vacuum is improved, which increases the accuracy of the fuel control by the fuel control means on the basis of the vacuum. Here, an intake air flow of the intake passage, in which the vacuum is not detected, can be obtained from the vacuum in the intake passage, in which the vacuum is detected. The intake air flow of the intake passage, in which the vacuum is not detected, is obtained by predetermining its ratio to the intake air flow of the intake passage, in which the vacuum is detected, and by storing the determined data in the fuel control means. 
     Preferably, the multiple cylinder engine further comprises a vacuum inlet passage having an inlet port opened in the intake passage for introducing the pressure of the intake passage into the pressure sensor, and the vacuum inlet passage includes a throttle portion having a passage area of one ninth or less as large as that of the inlet port. 
     Thus, if a dynamic pressure is detected at the time of detecting the vacuum value, the peak values and the bottom values of the waveforms of the pressure fluctuations become unclear so that the fluctuations of the vacuum in the air intake passage due to the small change in the openings of the throttle valves are hard to detect. As a result, it is difficult to control the air/fuel ratio accurately. However, with the above structure, the vacuum inlet passage is provided with the throttle portion so that the waveforms of the pressure fluctuations, as might otherwise be made unstable by the influence of the dynamic pressure, are stabilized to clarify the peak values and the bottom values of the waveforms obtained thereby to improve the accuracy of the vacuum detection by the pressure sensor. As a result, it is possible to control the air/fuel ratio accurately. Moreover, the passage area of the throttle portion is set to one ninth or less of that of the inlet port so that the fluctuations of the vacuum due to the small change of the throttle valve opening can be tolerated to detect the vacuum accurately. 
     Preferably, a throttle body forming a section of the intake passage and having the throttle valve and an intake port of the cylinders is connected by an intake manifold, and the vacuum inlet passage is formed in the throttle body and a outlet portion of the vacuum inlet passage is formed in the mating face of the throttle body with the intake manifold. 
     Thus, the vacuum inlet passage leading to the pressure sensor and the section of the intake passage communicating with the vacuum inlet passage are formed in the throttle body so that a separate member for forming the vacuum inlet passage and mounting parts such as bolts can be eliminated to reduce the number of parts and to facilitate the assembly. Moreover, a outlet portion of the vacuum inlet passage is positioned in a mating face in the throttle body with the intake manifold so that this portion can be easily formed. 
     Preferably, the multiple cylinder engine further comprises a fuel pressure adjustor for adjusting the pressure of the fuel to be fed to the fuel injectors. A pressure introduction passage is formed in the throttle body or in the intake manifold for introducing the pressure of the each intake passage into the fuel pressure adjustor. The pressure introduction passage has its leading end portion positioned in the mating face between the throttle body and the intake manifold. 
     Thus, the pressure introduction passage is formed in the throttle body or in the intake manifold, and its leading end portion is positioned in the mating face between the throttle body and the intake manifold so that separate members for forming those passages and mounting parts such as bolts can be eliminated to reduce the number of parts and to facilitate the assembly. Moreover, the pressure introduction passage has its leading end portion positioned in the mating face between the throttle body and the intake manifold so that it can be easily formed. 
     Preferably, the leading end portion includes an expansion chamber and an introduction port for connecting the expansion chamber to the each intake passage. The introduction port has a passage area set smaller than a maximum passage area of the expansion chamber. 
     Thus, air introduced from the intake passages into the introduction port is averaged gently in its pressure by the expansion chamber. When the air is introduced from the expansion chamber into the fuel pressure adjustor, therefore, the fuel pressure can be adjusted to the optimum by the fuel pressure adjustor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional front elevation showing a V-type 2-cylinder engine according to an embodiment of the present invention; 
         FIG. 2  is a front elevation showing an essential portion of the V-type 2-cylinder engine according to the same embodiment, and shows an arrangement of a throttle body, a fuel pressure adjustor, a fuel introduction pipe and so on; 
         FIG. 3  is a longitudinal section of an essential portion of the V-type 2-cylinder engine according to the same embodiment, and shows an intake passage, a fuel passage and so on; 
         FIG. 4  is a sectional view of line IV—IV of  FIG. 1 ; 
         FIG. 5  is a top plan view showing an essential portion of the V-type 2-cylinder engine according to the embodiment of the present invention; 
         FIG. 6  is a sectional view taken along line VI—VI of  FIG. 2 , to which an intake manifold is added; 
         FIG. 7  is a sectional view taken along line VII—VII of  FIG. 2 , to which the intake manifold is added; 
       FIGS.  8 (A) and  8 (B) are diagrams illustrating relationships between a vacuum value on pressure fluctuations and the time with and without a throttle portion in a vacuum outlet passage; and 
         FIG. 9  is a sectional view showing a fuel injection device of the conventional industrial engine. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A V-type 2-cylinder engine according to an embodiment of the present invention will be described with reference to  FIG. 1  to FIG.  5 . In  FIG. 1 , the V-type 2-cylinder engine  1  is a general-purpose engine to be used in an industrial machine, an agricultural machine or the like. The V-type 2-cylinder engine  1  includes: cylinders  2  and  3  arranged in the V-shape at different angle (e.g., 90 degrees) positions around a crank axis CT; a throttle body  4  (although only its front end flange portion is shown) arranged in the V-shaped space (or the bank space) between those cylinders  2  and  3 ; and an intake manifold  5  interposed between the throttle body  4  and the intake ports  2   a  and  3   a  of the two cylinders  2  and  3 . The throttle body  4  is connected, as shown in  FIG. 3 , to an upper air cleaner D through an intake duct member  15  which is mounted on a front end flange face  4   e . On the bottom portion of the air cleaner D, there is mounted an intake temperature sensor A for detecting the temperature of the cleaned air in the air cleaner D. 
     The individual cylinders  2  and  3  shown in  FIG. 1  are provided with cylinder bodies  2   b  and  3   b , in which pistons P are slidably fitted, and cylinder heads  2   c  and  3   c . These cylinder heads  2   c  and  3   c  are provided with ignition plugs  2   d  and  3   d  and intake valves  2   e  and  3   e . The reciprocal motions of the pistons P are transmitted as rotational motions through a connecting rod R to a crankshaft K. 
     Between the individual cylinders  2  and  3 , moreover, there are mounted fuel injectors  6  and  7 , which are inclined and have their leading end nozzles  10   a  and  10   b  oriented obliquely downward to the outer side. These fuel injectors  6  and  7  are individually mounted in mounting holes  8   a  and  8   b , which are formed at symmetrical positions in the intake manifold  5 , through ring-shaped rubber seals  9   a  and  9   b  with the leading end nozzles  10   a  and  10   b  being directed toward the intake ports  2   a  and  3   a  of the individual cylinders  2  and  3 . 
     In the V-type 2-cylinder engine  1 , moreover, there are formed two intake passages  11   a  and  11   b  for feeding the intake air independently to the individual cylinders  2  and  3 . The throttle body  4  is provided with two intake passages  4   a  and  4   b  forming sections of the intake passages  11   a  and  11   b . As shown in  FIG. 3 , the intake passages  4   a  and  4   b  are individually provided therein with throttle valves  4   c . In the intake duct member  15 , too, there are formed two intake passages  15   a  and  15   b  which communicate with the intake passages  4   a  and  4   b  to form sections of the intake passages  11   a  and  11   b.    
     On the upper side of the throttle body  4 , there is disposed an injection fuel introduction portion  12   a  of a fuel passage  12 . Two fuel introduction pipes  13  for feeding the fuel from the injection fuel introduction portion  12   a  to the fuel injectors  6  and  7  ( FIG. 1 ) are fitted and supported between the throttle body  4  and the intake manifold  5  respectively. The fuel introduction pipes  13  are supported in such a manner that protrusions  13   a  formed at one-side end of the fuel introduction pipe  13  is inserted into a positioning hole  5   a  formed in the intake manifold  5 , and a leading end portion of the fuel introduction pipe  13  is inserted into a fuel introduction pipe mounting hole  12   b  formed in the fuel introduction portion  12   a  through O-rings  12   c , as shown in FIG.  4 . As a result, the fuel introduction pipes  13  are supported between the throttle body  4  and the intake manifold  5 . Moreover, the throttle body  4  and the intake manifold  5  are fixed by bolts  21   b  which are fastened in threaded holes  17  of the intake manifold  5  shown in FIG.  3 . 
     In the upper portion of the throttle body  4 , moreover, there is formed a vacuum inlet passage  18  of  FIG. 6  for extracting the intake pressure of the intake passage  11   a  downstream of the throttle valve  4   c , and the leading end of the vacuum inlet passage  18  is connected to a pressure sensor C ( FIG. 7 ) so that the intake pressure in one intake passage  11   a  (or the other intake passage  11   b ) can be detected by the pressure sensor C. This pressure sensor C is mounted on the back portion of the intake manifold  5  through a bracket  19 , as shown in FIG.  5 . The pressure value detected by the pressure sensor C is sent as a detection signal to a computer  20  of  FIG. 1  or fuel control means. With a map programmed in advance in the computer  20 , the fuel injection rates of the fuel injectors  6  and  7  of the individual cylinders  2  and  3  are determined from the relationship between the pressure value and the engine speed rpm. In this determination of the fuel injection rates, the detection data of the intake temperature sensor A and a water thermometer B inserted in a cooling water passage  22  shown in  FIG. 3  are also inputted to the computer  20  so that the injection rates of the fuel are corrected. 
     On the other hand, the fuel injectors  6  and  7  shown in  FIG. 1  are inserted between the fuel introduction pipes  13  and the intake manifold  5  and supported in a sealed state such that their leading end nozzles  10   a  and  10   b  are supported through the rubber seals  9   a  and  9   b  in the mounting holes  8   a  and  8   b  of the intake manifold  5  and such that their root end sides are inserted into the fuel injector inserting holes  13   a  of the fuel introduction pipes  13  through shock absorbing dampers  6   a  and O-rings  6   b , as described by representing the case of the fuel injector  6  in FIG.  4 . Here, the injection fuel introduction portion  12   a  is desirably formed integrally with the throttle body  4 , but may also be constructed by making it as a separate member and by mounting it on the throttle body  4  by mounting means such as fasteners. 
     Between and slightly over the fuel injectors  6  and  7 , as shown in  FIG. 2 , there is mounted a common fuel pressure adjustor  14  for adjusting the pressure of the fuel to be fed to the fuel injectors  6  and  7 . This fuel pressure adjustor  14  is connected in a sealed state, as shown in  FIG. 3 , by mounting a bypass pipe portion  14   a  extended from its front portion (as located on the right side of  FIG. 3 ) through an O-ring  14   b  in a fuel pressure adjustor mounting hole  4   d  formed in the throttle body  4 , and is mounted on the throttle body  4  by means of not-shown bolts. 
     Moreover, the fuel pressure adjustor  14  is arranged, as shown in a top plan view in  FIG. 5 , on one side (or the front side) across the fuel injectors  6  and  7  in the longitudinal direction along the rotation axis CT of the engine. On the other side (or the rear side), there is arranged the pressure sensor C for detecting the pressure in the intake passages  11   a  and  11   b . As shown in  FIG. 5 , the fuel in the fuel tank (although not shown) is introduced through the injection fuel introduction portion  12   a  into the fuel introduction pipes  13  of  FIG. 3  by attaching the fuel pipe from the fuel tank to a fuel connection pipe  16  which is connected to the injection fuel introduction portion  12   a  in the throttle body  4 . As shown in  FIG. 3 , the fuel introduced into the injection fuel introduction portion  12   a  flows, as indicated by a solid arrow a, from the fuel introduction pipes  13  into the fuel injectors  6  and  7  (FIG.  2 ), whereas the excess fuel is returned, as indicated by a dotted arrow b, from the fuel pressure adjustor  14  via a return passage  28  to the fuel tank. With this arrangement, the fuel injection type V-type 2-cylinder engine can be easily reconstructed by replacing the carburetor of the general carburetor type V-type 2-cylinder engine and the manifold for the carburetor, by the throttle body  4  and the intake manifold  5 . In accordance with the needs, therefore, the specifications can be quickly changed from the carburetor type to the fuel injection device type of the invention. 
     At an intake stroke of the V-type 2-cylinder engine thus constructed, as the intake valves  2   e  and  3   e  shown in  FIG. 1  are opened and the pistons P go down, the pressures in the cylinders  2  and  3  drop so that the air is sucked from the intake passages  11   a  and  11   b  formed in the throttle body  4  and the intake manifold  5 . At this time, the intake vacuum of the sucked air is detected in a high accuracy by the pressure sensor C (FIG.  5 ), and the detected value obtained is inputted together with the engine speed to the computer  20  or the fuel control means so that the fuel injection rate is determined. At this time, the detected data of the intake temperature sensor A and the water thermometer B ( FIG. 3 ) are also inputted to the computer  20  to correct the injection rates determined. On the basis of the instructions of the computer  20 , moreover, the injection rates by the fuel injectors  6  and  7  are controlled, and the fuels in the controlled injection rates are injected from the fuel injectors  6  and  7  into the intake passages  11   a  and  11   b  of the intake manifold  5  so that the optimum mixtures are homogeneously distributed and fed to the cylinders  2  and  3 . 
     Here, the fuel injectors  6  and  7  are individually provided for each cylinder  2  and  3  in the V-space of the engine so that the mixtures can be homogeneously distributed. Moreover, not only the fuel injectors  6  and  7  but also the accompanying fuel pressure adjustor  14  is arranged in the V-space, and the intake passages  11   a  and  11   b  and the fuel passage  12  are integrally formed in the throttle body  4  and the intake manifold  5 , so that the pipes to be employed can be reduced to the necessary minimum to make a compact structure as a whole. Moreover, the fuel injectors  6  and  7  and the fuel introduction pipes  13  are mounted on the throttle body  4  and the intake manifold  5  by not fastening but inserting them, so that their mountability and assembling performance are improved. 
     FIG.  6  and  FIG. 7  describe the detail of the vacuum extracting portions of the intake passages. In order to make the details of the vacuum inlet passage  18  especially understandable, however, the fuel injectors  6  and  7  and the fuel pressure adjustor  14  are omitted in FIG.  6  and  FIG. 7  for convenience. 
     In  FIG. 6 , the vacuum inlet passage  18  is formed by extending it normal to a flange face  4   f  of a mating face with the intake manifold  5  in the throttle body  4 . The vacuum inlet passage  18  is provided at its one end with an inlet port  18   a  opened into one intake passage  4   a  (or  11   a ) and at its other end with a thin groove  18 c of  FIG. 2  (outlet portion of the vacuum inlet passage) opened in the flange face  4   f . One end portion of the groove  18   c  is connected, as shown in  FIG. 7 , to the pressure sensor C through a communication passage  23  formed in the intake manifold  5  and through a connection pipe  24 . In the vacuum inlet passage  18 , as shown in  FIG. 6 , there is formed a throttle portion  18   b  which has a passage area set to about one ninth or less as large as the passage area of the inlet port  18   a . If the passage area of the throttle portion  18   b  exceeds about one ninth of that of the inlet port  18   a , the vacuum value to be detected by the pressure sensor C ( FIG. 7 ) may be made unstable by the influences of a dynamic pressure. 
     As a passage for detecting a controlling vacuum to control the fuel pressure adjustor  14  of  FIG. 7 , on the other hand, there is formed in the throttle body  4  a pressure introduction passage  25  for introducing the pressure in the intake passages  11   a  and  11   b  into the fuel pressure adjustor  14 . This pressure introduction passage  25  is positioned at its portion or leading end portion at a mating face  5   f  with the throttle body  4  in the intake manifold  5 . The leading end portion is opened in the flange face  4   f  of the throttle body  4 . This leading end portion is provided, as shown in  FIG. 2 , with an expansion chamber  25   a , and introduction ports  25   b  and  25   c  for connecting the expansion chamber  25   a  and the intake passages  4   a  and  4   b . The passage area of the introduction ports  25   b  and  25   c  is set smaller than the maximum passage area of the expansion chamber  25   a . Here, the passage area of the expansion chamber  25   a  is a sectional area normal to the air flow in the expansion chamber  25   a . Moreover, the introduction ports  25   b  and  25   c  are formed to have small sections, and the expansion chamber  25   a  is desired to have a passage area of at least five times that of the introduction ports  25   b  and  25   c.    
     Both the vacuum inlet passage  18  of FIG.  6  and the expansion chamber  25   a  of  FIG. 7  are formed in the direction normal to the flange faces  4   f  and  5   f  of the mating face between the throttle body  4  and the intake manifold  5 , so that they can be easily machined. 
     A detection path of the control vacuum for controlling the fuel pressure adjustor  14  is formed in the throttle body  4 , but a pressure introduction passage  25 ′ may be formed in the intake manifold  5 , as indicated by phantom lines of FIG.  7 . Moreover, the detection path may be formed over the intake manifold  5  and the throttle body  4  by forming, for example, only the introduction ports  25   b  and  25   c  in the intake manifold  5  and by forming the remaining portion in the throttle body  4 . 
     According to the vacuum detecting means thus constructed, the pressure detected by the pressure sensor C of  FIG. 7  is the vacuum from one intake passage  4   a  (or  11   a ) but not the vacuums from a plurality of intake passages, and the vacuum is not averaged so that it can be accurately detected. 
     Therefore, the detection accuracy of the intake air flow based on the vacuum is improved to increase the accuracy of the fuel control by the computer  20  ( FIG. 1 ) on the basis of the vacuum. Here, the intake air flow of the intake passage  11   b , the vacuum of which is not detected, can be easily obtained from the vacuum, i.e., the intake air flow of the intake passage  11   a , the vacuum of which is detected, by predetermining the ratio of the intake air flow of the intake passage  11   a  and the intake passage  11   b  and by storing the ratio data in the computer  20 . 
     Concerning the pressure sensor C of  FIG. 7 , moreover, the detected vacuum value is so stabilized in the waveform of the pressure fluctuations by the existence of the throttle portion  18   b  disposed in the vacuum inlet passage  18  that the peak value and the bottom value become clear, as illustrated in FIG.  8 (A). Therefore, the fuel injection rate can be adjusted to establish a desired air/fuel ratio. Without the throttle portion, as illustrated in FIG.  8 (B), the pressure fluctuations are made unstable by the influences of the dynamic pressure so that the peak value and the bottom value become unclear, resulting in failure to establish the desired air/fuel ratio. 
     Here, the embodiment thus far described has been exemplified especially by the V-type 2-cylinder engine, but the present invention can be similarly applied to all other multiple cylinder engines. 
     Numerous modifications and alternative embodiments of the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode carrying out the invention. The detail of the structure and/or function may be varied substantially without departing from the spirit of the invention and all modification which come within the scope of the appended claims are reserved.