Ignition timing control apparatus for an internal combustion engine

Abstract

There are provided a first ignition timing table for high-octane fuel and a second ignition timing table for low-octane fuel. When the second table is switched over to the first table, there is at first the difference in between basic ignition timings according to the first and second tables, and then the difference is reduced with time at a constant rate. An actual ignition timing during the switchover of an ignition timing table is determined by subtracting the reducing difference from the basic ignition timing according to the first table. The actual ignition timing when knocking is detected is compared with a predetermined threshold. If the former exceeds the latter, the second table is switched over to the first table, and otherwise the second table is maintained, whereby the actual ignition timing can be changed smoothly even during the switchover of an ignition timing table.

We claim: 
     
       1. An ignition timing control apparatus for an internal combustion engine, comprising: ignition unit means for supplying an ignition signal to the engine at a predetermined ignition timing;   knocking sensor means, attached to the engine, for detecting the vibration of the engine and producing a knocking detection signal indicating the degree of occurring knocking;   control unit means including a processor, which has plural tables for providing basic ignition timings and is programmed so as to execute the following steps:   selecting one of the plural tables on the basis of the knocking detection signal; and   determining, in accordance with the selected ignition timing table; an actual ignition timing to be supplied for said ignition unit as the predetermined ignition timing, characterized in that     the plural ignition tables includes a first ignition timing table providing a basic ignition timing for high-octane fuel and a second ignition timing table providing a basic ignition timing for low-octane fuel, and   when one of the first and second ignition timing tables is switched over to the other ignition timing table, the processor included in said control unit means further executes the processing of the following steps:   setting the other ignition timing table;   obtaining a difference between the basic ignition timings according to the first and second ignition timing tables;   reducing the difference with time at a predetermined constant rate;   correcting the basic ignition timing according to the one ignition timing table by the reducing difference so that when the reducing difference becomes zero, the actual ignition timing becomes equal to the basic ignition timing according to the other ignition timing table;   comparing the reducing difference with a certain threshold provided in advance; and   determining whether the one ignition timing table is to be maintained or switched over to the other ignition timing table in accordance with the comparison result of the preceding step.   
     
     
       2. An ignition timing control apparatus according to claim 1, characterized in that if the occurrence of knocking is detected until the reducing difference does not reach zero, a predetermined amount is added the present value of the reducing difference.   
     
     
       3. An ignition timing control apparatus according to claim 1, characterized in that the engine starts under the ignition timing control according to the second table.   
     
     
       4. An ignition timing control apparatus according to claim 3, characterized in that before said setting step, the processing executed by the processor further includes step of discriminating whether or not an operating state of the engine is of a predetermined operational condition.   
     
     
       5. An ignition timing control apparatus according to claim 4, characterized in that the predetermined operational condition is discriminated to be satisfied when the temperature of the engine is kept stably at a certain value.   
     
     
       6. An ignition timing control apparatus according to claim 5, characterized in that the predetermined operational condition is discriminated to be satisfied when a time duration elapsing from the start of the engine exceeds a predetermined value.   
     
     
       7. An ignition timing control apparatus according to claim 6, characterized in that the time duration is an accumulation of time durations, in which the output of the engine exceeds a predetermined level. .Iadd.   
     
     
       8.  An ignition timing control apparatus for controlling an ignition unit of an internal combustion engine, comprising: a knocking sensor, to be attached to the engine, for detecting vibration of the engine and for producing a knocking detection signal indicating the occurrence of knocking; and   a control unit for generating an ignition timing signal to control said ignition unit on the basis of selected basic ignition timing values, including a processor having means for storing at least a first ignition timing table of basic ignition timing values for high-octane fuel and a second ignition timing table of basic ignition timing values for low-octane fuel, said processor being programmed to execute the following steps: (a) at the time of starting of the engine, selecting said second ignition timing table to provide basic ignition timing values for generating said ignition timing signal;   (b) detecting a predetermined operational condition of the engine after the starting of the engine;   (c) automatically switching from said second ignition timing table to said first ignition timing table to provide basic ignition timing values for generating said ignition timing signal upon detecting said predetermined operational condition; and   (d) determining whether to continue to generate said ignition timing signal on the basis of basic ignition timing values from said first ignition timing table or to switch back to said second ignition timing table in accordance with the receipt of a knocking detecting signal..Iaddend. .Iadd.     
     
     
       9.  An ignition timing control apparatus according to claim 8, wherein said step (c) comprises: (c1) obtaining a basic ignition timing value from said first ignition timing table;   (c2) correcting said basic ignition timing value obtained in substep (c1) by a correction amount;   (c3) reducing said correction amount with time at a predetermined rate;   (c4) repeating said substeps (c2) and (c3) until said correction amount is reduced to zero..Iaddend. .Iadd.10. An ignition timing control apparatus according to claim 9, wherein said correction amount is determined from the difference between basic ignition timing values in said first and second ignition timing tables..Iaddend. .Iadd.11. An ignition timing control apparatus according to claim 9, wherein said step (d) comprises:   (d1) detecting receipt of a knocking detection signal during substeps (c2) to (c4);   (d2) comparing the value of said correction amount to a predetermined threshold value; and   (d3) switching back to said second ignition table when the value of said correction amount does not exceed said predetermined threshold value when said knocking detection signal is received..Iaddend. .Iadd.12. An ignition timing control apparatus according to claim 8, wherein said step (b) comprises:   (b1) detecting when the temperature of the engine reaches and remains   
     
     
        stably at a predetermined temperature..Iaddend. .Iadd.13.  An ignition timing control apparatus according to claim 8, wherein said step (b) comprises: (b2) detecting when a predetermined time duration has elapsed from the time of starting of the engine..Iaddend. .Iadd.14. An ignition timing control apparatus according to claim 13, wherein said time duration is an accumulation of time durations during which the output of the engine exceeds a predetermined level..Iaddend. .Iadd.15. An ignition timing control apparatus for controlling an ignition unit of an internal combustion engine, comprising:   a knocking sensor, to be attached to the engine, for detecting vibration of the engine and for producing a knocking detection signal indicating the occurrence of knocking; and   a control unit for generating an ignition timing signal to control said ignition unit on the basis of selected basic ignition timing values, including a processor having means for storing at least a first ignition timing table of basic ignition timing values for high-octane fuel and a second ignition timing table of basic ignition timing values for low-octane fuel, said processor being programmed too execute the following steps:   (a) determining from one of said first and second ignition timing tables a basic ignition timing value to be used in generating said ignition timing signal; and   (b) switching over from said one of said first and second ignition timing tables to the other of said first and second ignition timing tables to obtain basic ignition timing values for generating said ignition timing signal, including:   (b1) obtaining a basic ignition timing value from said other of said first and second ignition timing tables;   (b2) correcting said basic ignition timing value obtained in substep (b1) by a correction amount;   (b3) reducing said correction amount with time at a predetermined rate;   (b4) repeating said substeps (b2) and (b3) until said correction amount is   
     
     
        reduced to zero..Iaddend. .Iadd.16.  An ignition timing control apparatus according to claim 15, wherein said processor is programmed to execute the following additional step: (c) during the switching over performed in step (b), determining whether to continue to generate said ignition timing signal on the basis of basic ignition timing values from said other of said first and second ignition timing tables or to switch back to said one of said first and second ignition timing tables in accordance with receipt of a knocking detection signal..Iaddend. .Iadd.17. An ignition timing control apparatus according to claim 16, wherein said step (c) comprises:   (c1) detecting receipt of a knocking detection signal during substeps (b2) to (b4);   (c2) comparing the value of said correction amount to a predetermined threshold value; and   (c3) switching back to said one of said first and second ignition tables when the value of said correction amount has a predetermined relationship to said threshold value when said knocking detection signal is   
     
     
        received..Iaddend. .Iadd.18.  An ignition timing control apparatus according to claim 15, wherein said correction amount is determined from the difference between basic ignition timing values in said first and second ignition timing tables..Iaddend.