Abstract:
An intake passage of an internal combustion engine is divided into two intake passages downstream of a throttle valve. A tumble generating valve is disposed in one of these two intake passages. When the engine is stopped, the tumble generating valve is fully closed once and then opens by a specified opening angle. While the engine is inoperative, the tumble generating valve is held at that angle until the engine is started again.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an air intake system of an engine and more particularly to an air intake system of an engine having a tumble generating valve for generating tumble stream in a combustion chamber of the engine. 
     2. Discussion of Related Arts 
     It is well known that the combustion condition of an internal combustion engine enhances when a tumble stream is generated in a combustion chamber of the engine. When the combustion condition enhances, miscellaneous advantages such as an improvement of startability of an engine, an improvement of exhaust emissions by making a lean mixture condition and the like, are provided. 
     Japanese Patent Application Laid-open No. Toku-Kai-Hei 5-209582 discloses an air intake system in which an intake port is divided into two parts, a light load port and a heavy load port, by a partition and a tumble generating valve is provided on the heavy load port side. A fuel injector is disposed opposite to the partition such that injected fuel collides against the partition directly and a part of the partition against which fuel collides is shaped in convex and concave so as to enhance atomization of fuel. 
     The tumble generating valve (hereinafter referred to as TGV) is closed at starting. That is, at starting, in order to enhance startability or to make lean air-fuel mixture, air-fuel mixture is supplied only from the light load port side with the TGV closed so as to generate a tumble stream in the combustion chamber. Further, from the view point of reducing cranking time, it is desirable that the TGV has been closed before the ignition switch is turned on in order to delete time lag necessary for closing the TGV when the ignition switch is turned on. Hence, the TGV is closed when the engine stops and is maintained in a closed condition until the engine is started again. 
     However, when the TGV is left closed while the engine is in standstill, the engine is cooled down and as a result the TGV is apt to be stained with oil, residues and the like. Further, when temperature is low, the TGV might be frozen by water. As a result, there is a problem that the TGV is stuck due to stains or frozen water. 
     One solution of this problem is that the TGV is left open when the engine is in standstill. However, since it is necessary to close the TGV once when the engine is started, the starting time is elongated by an operation time (0.5 to 1.0 second) of the TGV from an open to closed condition. This elongation of starting time provides a driver with a bad operational feeling and spoils a customer&#39;s satisfaction. Accordingly, the structure of the TGV remaining open can not introduced easily. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an air intake system having a tumble generating valve (TGV) capable of preventing a faulty operation without spoiling startability of an engine. 
     To attain the object, an air intake system of an internal combustion engine having an intake passage divided into a first passage and a second passage downstream of a throttle valve and a control valve provided in the first passage for controlling a flow of air comprises an electronic control unit provided to open and hold the control valve at a specified opening angle while the engine is inoperative after the engine is stopped. Also, the electronic control unit of the air intake system is adopted to fully close the control valve before opening the control valve at the specified angle. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic sectional view showing an air intake system of an engine according to an embodiment of the present invention; 
     FIG. 2 is a flowchart showing a control strategy of a TGV of the air intake system of FIG. 1 when an engine is stopped; and 
     FIG. 3 is a flowchart showing a control strategy of a TGV of the air intake system of FIG. 1 when an engine is stopped. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, reference numeral  1  denotes a cylinder block of an engine and reference numeral  2  denotes a cylinder head in which an intake port  3  and an exhaust port  4  are formed. The intake port  3  and exhaust port  4  are provided with an intake valve (not shown) and an exhaust valve (not shown) respectively. The cylinder block  1  includes a cylinder bore  5  in which a piston  6  is slidably disposed. Further, a combustion chamber  7  is formed by an inner wall of the cylinder bore  5 , a top surface of the piston  6  and an undersurface of the cylinder head  2 . Further, the intake port  3  is connected at the upstream side thereof with an air intake system  10 . 
     The air intake system  10  has an intake manifold  11  communicating with the intake port  3  and a throttle valve  12  on he upstream side thereof. As shown in FIG. 1, a partition  8  is provided at and part close to the intake port  3  of the intake manifold  11  so as to separate an air intake passage  9  into two passages. That is, a main passage (first passage)  13  and a tumble passage (second passage)  14  are formed in the intake manifold  11 . 
     There is provided a tumble generating valve (TGV)  15  in the main passage  13 . The TGV  15  has a valve  16  and a shaft  17  and is controlled by an electronic control unit (ECU)  18 . When an opening angle of the TGV is controlled at 0 degree, the main passage  13  is in a closed condition. 
     The shaft  17  is actuated by a DC motor (not shown). The DC motor is controlled by the ECU  18  which outputs control signals based on an ON-OFF signal of the ignition switch, an engine speed and the like. The shaft  17  is shared with TGVs of other cylinders so as to actuate other TGVs simultaneously when the shaft  17  is driven. Further, the shaft  17  is connected with the DC motor through gears and the like so that the reduced number of rotation of the motor is transmitted to the shaft  17 . 
     On the other hand, the tumble passage  14  is provided with a fuel injector  19 . When the TGV  15  is closed and intake air is delivered to the intake port  3  only through the tumble passage  14 , a tumble stream is generated in the combustion chamber  7  as shown by a broken line of FIG.  1 . 
     Next, how to control the TGV  15  of thus constituted air intake system  10  will be described by reference to FIG.  2 . First, when the engine is in standstill, the TGV  15  is not completely closed but the valve  16  is held slightly open. That is, when the engine is started, the valve  16  is transferred from a slightly open condition to a fully closed condition. 
     At a step S 1 , it is checked whether the ignition switch is turned on or off. Then, in case where the ignition switch is turned on, the program goes to a step S 2  where it is checked whether or not the engine is operative. In case where the engine is operative, the program goes to a step S 3  where the TGV  15  is normally controlled. Then, the program goes to a step S 4  where a flag F 1  is set and the program leaves the routine. 
     On the other hand, in case where it is judged at the step S 2  that the engine is not operative, that is, the engine is in standstill, the program goes to a step S 5  where the flag F 1  is checked. When the engine stalls, since the flag F 1  is set, the program goes from the step S 5  to a step S 6 . 
     At the step S 6 , the TGV  15  (drive motor) is energized for 1.5 seconds for example to be rendered fully closed once. At this moment, the ECU  18  recognizes this position as 0 degree. Then, the program goes to a step S 7  where the TGV  15  is energized in an opening direction for 0.3 seconds for example to be rendered open by 10 degrees. After the TGV  15  is set in a slightly open condition, the program goes to S 8  where the flag F 1  is cleared. Then, the program goes to a step S 9  where a flag F 2  which will be described hereinafter is checked. 
     Since this is not a case where the ignition switch is suddenly turned off while the engine is operative, the flag F 1  has not yet set and the program goes from the step S 9  directly to RETURN. 
     After that, at a next routine, when the ignition switch is left on, the program steps from S 1  to S 2 . Since the engine is already stopped and the flag F 1  is cleared, the program leaves the routine through the step S 5 . On the other hand, the ignition switch is turned OFF, the program goes from the step S 1  to a step S 12 . Since the flag F 1  has been already cleared, the program goes to a step S 11  where the power source of the ECU  18  is shut-off and an execution of the routine is stopped. 
     In case where the ignition switch is turned off while the engine is operative, there is a very short instant that the engine is in standstill with the ignition switch turned on. Hence, in order to do a series of operation S 1 , S 2 , S 5 , S 6  and S 7  until the TGV is in the slightly open condition, a very fast processing is needed. 
     However, it is difficult to require such fast processing from the ECU  18  which must do miscellaneous engine controls. Accordingly, in case where the ignition switch is suddenly turned off, the flag F 2  is set after this condition is recognized and the TGV  15  is controlled from a fully closed condition to a slightly open condition while some leeway time is given to the shutting-off of the power source of the ECU  18 . 
     Since the ignition switch is turned off, the program goes from the step S 1  to the step S 12  where the flag F 1  is checked. In this case, since the engine was operative immediately before, the flag F 1  which has been set at the step S 4  is still remained. On the other hand, in case where the ignition switch has been turned off after the program passed steps S 1 , S 2 , S 5 , S 6 , S 7  and S 8 , the flag F 1  has been cleared. That is, it can be judged by confirming the existence of the flag F 1  at the step S 12  whether or not the ignition switch has been suddenly turned OFF while the engine is operated. 
     As a result of confirmation at the step S 12 , in case where the flag F 1  is set, it is judged that the ignition switch is turned off and the program goes to a step S 13  where the flag F 2  is set. After the flag F 2  is set, the program goes to S 6  where the TGV  15  is fully closed. Then, the program goes to the step S 7  in which the TGV  15  is slightly open and goes to the step S 8 . 
     At the step S 8 , the flag F 1  is cleared and the program steps to a step S 9 . 
     At the step S 9 , the flag F 2  is checked. In this case, since the flag F 2  is set, the program goes to a step S 10  where the flag F 2  is cleared. Further, the program goes to a step S 11  where the power source of the ECU  18  is shut off and then the program leaves the routine. In this case, since the ignition switch is turned off and also the power source of the ECU  18  is shut off, the present routine is finished here. 
     According to the air intake system  10  of the present invention, the TGV  15  is set to a slightly open condition (opening angle is 10 degrees in this embodiment) and is held in this condition until the engine is started next again. While the engine is in standstill, a small clearance is made between the valve  16  of the TGV  15  and the inner wall of the main passage  13 . This small clearance prevents the valve  16  from being stuck or inappropriately operated due to stains and frozen water adhered to surroundings of the valve  16 . Accordingly, a faulty operation of the TGV  15  due to stains or frozen water can be prevented without particularly using new devices or members. 
     Next, how to control the TGV  15  at when the engine is started will be described by reference to FIG.  3 . As shown in FIG. 3, when the ignition switch is turned on, at a step S 21  it is checked whether or not the engine is started. Unless the engine is started, the program goes to a step S 22  where the TGV  15  is fully closed and leaves the routine. 
     That is, the ECU  18  energizes the TGV  15  in a closing direction for 0.5 seconds to fully close the TGV  15  which has been slightly opened by the control when the engine stops previously. At this moment, time needed for fully closing the TGV  15  is very short, about 0.1 to 0.3 seconds. Accordingly, the air intake system  10  using this type TGV can prevents the TGV  15  from being stuck without spoiling startability. 
     Further, when the TGV  15  is fully closed, the main passage  13  is closed and as a result air is supplied to the intake port  3  only through the tumble passage  14 . As a result, a tumble stream is formed in the combustion chamber  7  and startability can be enhanced. On the other hand, when the engine starting is confirmed at the step  21 , the program goes to s step S 23  where the TGV  15  is controlled in an ordinary manner and leaves the routine. 
     According to the aforesaid embodiment, the TGV is designed so as to be fully closed once when the engine stops but it is possible to directly place the valve in a slightly open condition. 
     Further, time energizing the TGV  15  and an valve opening angle in a slightly open condition are not restricted to examples described before. For example, the valve opening angle in a slightly open condition can be established arbitrarily within the scope of not affecting the extension of starting time. However, considering the closing time of the valve, the valve opening angle is preferably less than 15 degrees. 
     Further, in this embodiment the air intake system incorporating a tumble generating valve (TGV) is described but the present invention may be applied to an air intake system having a swirl control valve (SCV) for generating a swirl stream in the combustion chamber. 
     While the presently preferred embodiment of the present invention has been shown and described, it is to be understood that this disclosure is for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.