Abstract:
An apparatus for controlling an ignition timing of an engine is capable of reducing or preventing occurrences of backfires. The apparatus includes a no-load deceleration state detector for detecting that an engine is in a no-load deceleration state. An engine speed detector detects an engine speed. An advanced timing setting unit sets an advanced ignition timing (retard amount) in situations where the occurrence of backfires are likely, such as during the no-load deceleration state. A converter  105  determines an ignition angle θ ig  on the basis of an output pulse of a pulse generator and an advance amount provided by the advanced ignition timing setting unit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an apparatus for controlling an ignition timing of an engine. More particularly, the present invention relates to an apparatus for controlling an ignition timing of an engine, which is capable of reducing the likelihood of backfires.  
           [0003]    2. Description of the Relevant Art  
           [0004]    When engine speed is decreased sharply, the ratio of fresh air to the volume of a cylinder is lowered. Hence, a charging efficiency decreases, so that the air/fuel ratio in the cylinder becomes lean. As a result, the possibility of backfires increases, such that a flame propagating speed becomes slow and flame spreads into an intake path.  
           [0005]    Systems are known in the background art to decrease the likelihood of backfiring. For example, Japanese Patent Bulletin No. 2,646,216 discloses an ignition timing control system. In the background art, when sudden deceleration occurs, the ignition timing control advances the ignition timing (relative to a normal ignition timing) until a throttle is fully closed.  
           [0006]    According to the background art, the ignition timing is advanced (relative to the normal ignition timing) until the throttle is fully closed, when sudden deceleration occurs. After the throttle is fully closed, the ignition timing is reset to the standard or normal ignition timing. In other words, the ignition timing is no longer advanced.  
           [0007]    According to experiments conducted by the inventors, backfires occur most often in a sudden deceleration state. Backfires particularly occur when the throttle is suddenly opened from a no-load deceleration state.  
           [0008]    Based upon the inventor&#39;s experiments, it can be seen that the system of the background art has drawbacks. In the system of the background art, the ignition timing is reset from the advanced state to the normal state at the time when the throttle is fully closed. However, if the throttle is suddenly opened during a no-load deceleration state, backfires are likely to occur.  
           [0009]    On the other hand, if the ignition timing is advanced after the throttle opening operation is detected at the time of sudden deceleration, the flame propagation speed just before the opening operation cannot be improved. When the ignition timing is advanced only on condition that the throttle is fully closed, poor engine performance results, particularly a “knocking” problem occurs.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to solve one or more of the drawbacks associated with the systems and techniques of the background art.  
           [0011]    It is an object of the present invention to provide an apparatus for controlling ignition timing of an engine, capable of effectively preventing backfires by a simple configuration.  
           [0012]    These and other objects are accomplished by an apparatus for variably controlling an ignition timing of an engine in accordance with operating conditions of the engine, said apparatus comprising: a no-load deceleration state detector for detecting that an engine is in a no-load deceleration state; an engine speed detector for detecting an engine speed; and a controller advancing an ignition timing when said no-load deceleration state detector detects the no-load deceleration state and said engine speed detector detects the engine speed to be in a speed range.  
           [0013]    Further, these and other objects are accomplished by an apparatus for variably controlling an ignition timing of an engine in accordance with operating conditions of the engine, said apparatus comprising: a standard ignition timing setting unit for providing standard ignition timing control signals during normal engine operating conditions; an advanced ignition timing setting unit for providing advanced ignition timing control signals during engine operating conditions prone to backfiring; a pulse generator sensing an angular position of a crankshaft, and outputting pulse signals; a converter for receiving the pulse signals from said pulse generator; a switch to selectively connect one of said standard ignition timing setting unit and said advanced ignition timing setting unit to said converter; and a no-load deceleration state determining unit controlling the operation of said switch, said no-load deceleration state determining unit causing said switch to connect said advanced ignition timing setting unit to said converter during engine operating conditions prone to backfiring and causing said switch to connect said standard ignition timing setting unit to said converter at other times, wherein the engine operating conditions prone to backfiring include a speed of the engine being within a predetermined speed range.  
           [0014]    Moreover, these and other objects are accomplished by a method of controlling an ignition timing of an engine comprising the steps of: sensing if a throttle is fully closed; if the throttle is fully closed, determining an engine speed; if the engine speed is with a predetermined speed range, comparing a drop rate in the engine speed to a threshold value; and if the drop rate meets or exceeds the threshold value, advancing an ignition timing.  
           [0015]    According to the present invention, the ignition timing is advanced at the time of sudden opening of the throttle from the no-load deceleration state, which is the time when backfires occur the most. As a result, combustion can be finished in a cylinder before an exhaust port is opened, so that the occurrence of backfires can be reduced or prevented, without deteriorating the operation of the engine, such as avoiding knocking.  
           [0016]    According to the present invention, whether or not the engine is in the no-load deceleration state is determined on the basis of throttle angle and engine speed. Thus, a detector for detecting that the engine and the output shaft are disengaged from each other is unnecessary.  
           [0017]    Alternatively, according to the present invention, by using the fact that the drop rate of the engine speed, at the time of no-load deceleration, is peculiar to each engine, whether or not the engine is in the no-load deceleration state can be determined on the basis of only the engine speed. Thus, a detector for detecting a throttle angle is also unnecessary.  
           [0018]    Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein:  
         [0020]    [0020]FIG. 1 is a block diagram showing a configuration of main components of an ignition timing control apparatus, in accordance with the present invention;  
         [0021]    [0021]FIG. 2 is a flowchart for explaining operations of the apparatus of FIG. 1; and  
         [0022]    [0022]FIG. 3 is a timing chart for further explaining the operations of the apparatus of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    In FIG. 1, a coolant temperature sensor  21  senses temperature T eng  of cooling water of the engine. A Ne sensor  22  senses an engine speed or RPM (Ne). A throttle position sensor  23  senses a throttle angle θth. A pulse generator  24  generates a pulse signal representing a crank angle of a crankshaft of the engine.  
         [0024]    An ignition control unit  10  calculates an ignition timing on the basis of the cooling water temperature T eng , engine speed Ne, throttle angle θth, and pulse generation timing of the pulse generator  24 . The ignition control unit  10  supplies arc energy to an ignition plug  26 , via an ignition coil  25 .  
         [0025]    The ignition control unit  10  includes several sub-components. A standard ignition timing setting unit  101  sets a standard ignition timing (advance amount or retard amount) on the basis of the cooling water temperature T eng , engine speed Ne, and throttle angle θth. An advance angle timing setting unit  102  sets an advance ignition timing (retard angle). The advance ignition timing (retard angle) is set in environments where the occurrence probability of backfires is high (e.g. a no-load deceleration state). The advance timing (retard angle) is set on the basis of the cooling water temperature T eng , engine speed Ne, and throttle angle θth. The advance amount is set to be larger than the advance amount selected by the standard ignition timing setting unit  101 , in the case where the engine is not in the no-load deceleration state.  
         [0026]    A ΔN detecting unit  103  detects a rate of change (ΔN) in engine speed. A no-load deceleration state determining unit  104  determines whether or not the engine is in the no-load deceleration state. In the no-load deceleration state, the engine and the output shaft are disengaged from each other. In other words, the no-load deceleration state determining unit  104  determines whether or not a clutch is disengaged or a gear position is neutral and whether or not the throttle is closed, on the basis of the engine speed Ne, throttle angle θth, and rate of change ΔN in engine speed.  
         [0027]    When the engine is in the no-load deceleration state, a switching unit  106  is controlled to connect the advanced ignition timing setting unit  102  to a converter  105 . When the engine is not in the no-load deceleration state, the switching unit  106  is controlled to connect the standard ignition timing setting unit  101  to the converter  105 .  
         [0028]    The converter  105  determines an ignition angle θ ig  on the basis of output pulses of the pulse generator  24  and the advance amount or retard amount provided by the standard ignition timing setting unit  101  or the advanced ignition timing setting unit  102 . The arc energy supplied to the ignition coil  25  is interrupted at the ignition angle θ ig , thereby allowing the ignition plug  26  to ignite at an optimum timing.  
         [0029]    With reference to the flowchart of FIG. 2 and the timing chart of FIG. 3, operations of the ignition control unit  10  will be described. The flowchart of FIG. 2 focuses on the processes in the no-load deceleration state determining unit  104 .  
         [0030]    In step S 10 , it is determined, based upon an output signal of the throttle position sensor  23 , whether or not the throttle is in a fully closed state. When the throttle is not in the fully closed state, like at time t 0  in FIG. 3, it is determined that the engine is not in the no-load deceleration state. When the engine is not in the no-load deceleration state, backfires are not prone to occur, and the program advances to step S 13 .  
         [0031]    In step S 13 , the switching unit  106  is controlled so that the standard ignition timing setting unit  101  is connected to the converter  105 . As a result, in the ignition control unit  10 , the ignition angle θ ig  is calculated on the basis of the standard ignition timing set by the standard ignition timing setting unit  101  and a detection timing of the pulse signals of the pulse generator  24 . Therefore, normal ignition, allowing the plug  26  to make ignition at the ignition angle θ ig , is executed.  
         [0032]    When the throttle is fully closed (at time t 1  in FIG. 3), the fully closed state is detected in step S 10 . Processing then proceeds to step S 11 . In step S 11 , it is determined whether or not the engine speed Ne detected by the Ne sensor  22  is within a predetermined control execution range. As an example, the control execution range may be set to a low speed range from an idle speed (about 1000 rpm) to 3000 rpm. Consequently, for example, at time t 2 , when the engine speed Ne enters the control execution range, the program advances to step S 12 .  
         [0033]    In step S 12 , it is determined whether or not a drop rate ΔN of the engine speed Ne, obtained by the ΔN detecting unit  103 , is equal to or higher than a predetermined reference drop rate ΔN ref . For example, the reference drop rate ΔN ref  may be set to 200 rpm/100 msec. When the drop rate ΔN of the engine speed Ne exceeds the reference drop rate ΔN ref  (see time t 3  in FIG. 3), processing proceeds to step S 14 . In step S 14 , the switching unit  106  is controlled so that the advanced ignition timing setting unit  102  is connected to the converter  105 .  
         [0034]    By the control method illustrated in FIG. 2, the ignition control unit  10  controls the ignition of the plug  26  to make ignition at a desirable ignition angle θ ig . The ignition angle θ ig  is calculated on the basis of the advance amount, set in the advance ignition timing setting unit  102 , and the detection timing of the pulse signal, provided by the pulse generator  24 .  
         [0035]    As previously mentioned, backfires are most prone to occur during the no-load deceleration state. When the no-load deceleration state (expressed by a dotted line portion of line θ ig  in FIG. 3), is detected and the engine speed is in the low speed range, the ignition timing is advanced (relative to a normal ignition timing). Therefore, even when the throttle is suddenly opened from the no-load deceleration state at time t 4 , backfires are not prone to occur.  
         [0036]    Whether or not the engine is in the no-load deceleration state is determined on the basis of the throttle angle and the engine speed. According to the present invention, it is not required to detect whether or not the engine and the output shaft are disengaged from each other. Consequently, a sensor for sensing that a gear is in the neutral position, a sensor for sensing that the clutch is disengaged, or similar sensors are unnecessary.  
         [0037]    According to the results of experiments conducted by the inventors, the drop rate of the engine speed at the time of the no-load deceleration is peculiar to each engine. Whether or not the engine is in the no-load deceleration state can therefore be determined on the basis of only the drop rate of the engine speed. With such a configuration, the throttle position sensor also becomes unnecessary and may be eliminated.  
         [0038]    The ignition control  10  has many advantages over the background art:  
         [0039]    Since the no-load deceleration state, where backfires are most prone to occur, is detected and the ignition timing is advanced, even when the throttle is suddenly opened after that, occurrence of backfires can be effectively reduced or prevented.  
         [0040]    Whether the engine is in the no-load deceleration state or not is determined on the basis of the throttle angle and the engine speed. By this arrangement, a sensor for sensing that the engine and the output shaft are disengaged from each other, such as a sensor for sensing that the clutch is disengaged or a gear is in the neutral position, is unnecessary.  
         [0041]    The present invention appreciates the fact that the drop rate of the engine speed at the time of the no-load deceleration is peculiar to each engine. Whether or not the engine is in the no-load deceleration state may be determined on the basis of only the engine speed. Thus, a throttle position sensor can also be rendered unnecessary.  
         [0042]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.