Control apparatus for internal combustion engine provided with permanent magnet type starting motor
BACKGROUND OF THE INVENTION 
     The present invention generally relates to a control apparatus for an internal combustion engine of a vehicle, in which an operating state of a starting motor for starting the internal combustion engine is detected so as to actuate an internal combustion engine start control device to operate in starting of the engine, and particularly relates to an internal combustion engine control apparatus of the type described above provided with a starting motor having a permanent magnet as a field magnet. 
     In an internal combustion engine control apparatus provided with a permanent magnet type starting motor, which is known, for example, in Japanese Patent Unexamined Publication No. 55-46064, a start control device (for example, a starting fuel increasing device, or the like) actuated to operate in starting or cranking of the internal combustion engine is arranged to be actuated upon detection of a voltage applied to a solenoid coil of a magnet switch provided for driving/stopping the starting motor. 
     In such a case as described above where the magnetic field of the starting motor is provided by a permanent magnet, however, there has been a problem that an induced voltage generated in the starting motor even after turning-off of a key switch, may be applied to the solenoid coil of the magnet switch and this voltage applied to the coil of the magnet switch is detected as if the starting motor is operating. 
     This erroneous detection may actuate the start control device to operate at an undesired time. For example, in a start control device provided with fuel increasing means for increasing fuel in starting of the internal combustion engine, the fuel increasing operation is continued even after the starting motor has been stopped, resulting in such a problem that a failure in firing of the fuel may be caused or an exhaust gas becomes dirty too much because of the excessive fuel supply. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to solve the foregoing problems in the prior art. 
     It is another object of the present invention to provide an apparatus for controlling an internal combustion engine provided with a starting motor having a permanent magnet, as a field magnet, for starting the engine, which is capable of preventing the operating condition of the motor from being erroneously judged by a voltage induced in the motor after deenergizing the motor, thereby preventing a start control device from erroneously operating at an undesired time. 
     In order to attain the above objects, an apparatus of the present invention is provided with means for comparing a voltage at a junction point of three parts, that is, a key switch and series and shunt coils of a magnet switch, with a battery voltage and means for determining whether the motor is in a predetermined operating condition or not, or whether the motor is energized for starting the engine or not, based on an output of the comparator means, thereby preventing the operating condition of the motor from being erroneously judged by a voltage induced in the motor when the motor is still rotating by its inertia after deenergized. 
     In such an arrangement as described above, when the key switch is opened, the comparing means never produce its output signal even if the starting motor is rotated by inertia, and therefore the start control device is not actuated to operate. 
     The present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the whole arrangement of an engine starting system to which a control apparatus according to the present invention is applied; 
     FIG. 2 is a block diagram showing an embodiment of a device for detecting the operation of the starting motor according to the present invention; and 
     FIG. 3 is a diagram showing time-variation of an induced voltage generated in the permanent magnet type starting motor when rotating by inertia after the key switch is opened at different numbers of revolutions per minute of the same. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, an embodiment according to the present invention will be described in detail. 
     When a key switch 3 is closed, a current is allowed to pass through a series coil R C  of a solenoid coil 2b of a magnet switch MS and a starting motor 2a from a battery 1. Then, a normally open contact 2c of the magnet switch MS is closed by magnetomotive force generated in the series coil R C , so that the starting motor 2a is energized by an electric power from the battery 1 through the contact 2c. When the starting motor 2a starts to drive an engine (not shown) and the key switch 3 is opened, the contact 2c of the magnet switch MS is still held at its closed state by magnetomotive force of a shunt coil R P  of the coil 2b energized by an induced voltage of the motor which is still rotating by inertia. 
     A control circuit 4 has an input terminal B to which a voltage V B  of the battery 1 is applied and another input terminal S to which a voltage V S  at a junction a between the key switch 3 and the coil 2b is applied. 
     In FIG. 2 showing the control circuit 4 in detail, there are provided a comparator 6 and a series circuit of resistors R 1  and R 2  connected between the input terminal B and the earth. The voltage V S  received at the input terminal S is applied to a positive terminal of the comparator 6 through a resistor R 3 , while the voltage V B  applied to the input terminal B is divided by the series connection of the resistors R 1  and R 2  to obtain a reference voltage V ST  which is applied to a negative terminal of the comparator 6 through a resistor R 4 . 
     The output of the comparator 6 is applied, after divided by a series connection of resistors R 5  and R 6 , to a microcomputer 7. 
     The microcomputer 7 makes a judgement as to whether the starting motor 2a is actively driven for rotation or rotated by inertia on the basis of the output of the comparator 6, or whether the engine is in its cranking state or not. If it is decided that the engine is in its cranking state, a controlling output is generated at an output terminal b of the microcomputer 7, and applied to the base of a transistor 8 after divided by a series connection of resistors R 7  and R 8 . So long as the output of the microcomputer 7 is generated at its output terminal b, the transistor 8 is kept conductive so as to supply a current to a solenoid 5 for opening a valve (not shown) used to increase fuel. In brief, the valve for increasing fuel is opened by the solenoid 5 so as to increase the fuel supply to the engine while the engine is in its cranking state. 
     Now, description will be made of the way how to detect the state of operation of the starting motor 2a. 
     The input voltage V S  applied to the input terminal S after the key switch 3 has been opened is obtained by the following expression: ##EQU1## where R.sub.γP represents a resistance value of the shunt coil R P  ; R.sub.γC represents a resistance value of the series coil R C  ; and V a  represents an induced voltage which is generated in the starting motor 2a due to rotation-by-inertia thereof after the motor is deenergized. The induced voltage decreases at a certain rate which varies depending on the number of revolutions per minute N1-N3 at which the motor 2a was driven just before deenergized, as shown in FIG. 3. 
     Here, the induced voltage V a  is not larger than the voltage V B  (that is, V a  ≦V B ), and therefore the voltage V S  is necessarily smaller than V B  (that is, V S  &lt;V B ). 
     On the other hand, when the key switch 3 is in its closed state, the input voltage V S  is equal to or substantially equal to V B , and therefore when the starting motor 2a is in its operating state, the input voltage V S  takes a value substantially equal to the voltage V B . 
     On the other hand, the reference voltage V ST  applied to the negative input of the comparator 6 can be expressed as follows: ##EQU2## Accordingly, if the respective resistance values R 1 , R 2 , R.sub.γP, and R.sub.γC are selected to satisfy the following relationships (3), ##EQU3## the input voltages V S  and V ST  applied to the comparator 6 satisfies the relationship 
     
         V.sub.S ≃V.sub.B &gt;V.sub.ST 
    
     when the key switch 3 is in its closed state and the motor 2a is therefore energized for rotation, so that the output of the comparator 6 becomes high in its level. 
     When the key switch 3 is opened, on the contrary, even if the induced voltage V a  is generated by the inertia-rotation of the motor 2a, the input voltage V S  is necessarily smaller than the voltage V ST  so as to make the output of the comparator low because ##EQU4## 
     Accordingly, if the output level of the comparator 6 is supervised by the microcomputer 7, the judgement can be clearly made as to whether the permanent magnet type starting motor 2a is being rotated owing to the turning-on of the key switch 3 or not, that is, as to whether the engine is in its cranking state or not. In addition to the embodiment as described above, the start control device may include a suction air increasing device, an ignition timing control device, etc.