Preignition detecting system and method

Abstract: A preignition detecting system capable of detecting a preigniting condition (PI) at an early time. It is detected that in an abnormal vibration determining step the occurrence of vibration larger than a predetermined threshold level after the passage of a first predetermined period of time from the ignition has been detected and that said abnormal vibration determining step has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a second predetermined period of time longer than said first predetermined period of time from the ignition. In a preignition determining step it is than determinined that preignition is occurring when it is determined at said abnormal vibration detecting step that abnormal vibration is occurring.

Description: 1. Field of the invention This invention relates to a preignition detecting system and method in an internal combustion engine and, more particularly, to a preignition detecting system and method capable of detecting a preigniting condition quickly. 2. Description of the Related Art In an internal combustion engine, preignition is a phenomenon in which residual heat possessed by a spark plug or a deposit in a cylinder creates a hot spot causing the air-fuel mixture to be spontaneously ignited during the compression stroke. Preignition causes not only a sharp decrease in the engine output or a change in the engine revolution but also, in extreme cases, damage to the internal combustion engine. Therefore, there has been proposed several devices and methods for determination and controlling preignition. f. i. by comparing the output of different time windows, which are specific for particular frequency components and ruled by crankshaft position signals (EP-A-0 454 486) or by comparing two time intervals whereby one is lying before the total dead center (TDC) and the other is lying after the TDC (US A-4 750 103, US-A-5 083 278). In the Unexamined Japanese Utility Model Publication (Kokai) No. 1-88042 has been proposed a device for controlling an internal combustion engine which so determines that preignition has occurred when vibration larger than a predetermined level is detected before ignition in each cylinder, and cuts off the supply of fuel to the cylinder. According to the above-mentioned device for controlling the internal combustion engine which detects the occurrence of preignition when vibration larger than a predetermined level is detected before the ignition, however, it is only after the preignition has proceeded to a considerable degree that the occurrence of preignition can be detected. By that time, it is no longer possible to avoid the probability of causing damage to the internal combustion engine and, besides, drivability is deteriorated due to cut-off of the fuel supply. SUMMARY OF THE INVENTION The present invention was accomplished in view of the above-mentioned circumstances, and its object is to provide a preignition detecting system and method capable of detecting a preigniting condition quickly. According to an aspect of the present invention, there is provided a preignition detecting system comprising: ignition timing control means for determining an ignition timing depending upon the conditions in which an internal combustion engine is operating; abnormal vibration determining means for determining that abnormal vibration is occurring, said abnormal vibration timing detecting means comprises: first abnormal vibration detecting means which detects that said abnormal vibration determining means has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a first predetermined period of time from the ignition effected by said ignition timing control means; second abnormal vibration detecting means which detects that said abnormal vibration determining means has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a second predetermined period of time longer than said first predetermined period of time from the ignition affected by said ignition timing control means; and preignition determining means for determining that preignition is occurring when it is determined by said first abnormal vibration detecting means that abnormal vibration is occurring. According to another aspect of the present invention, there is provided a preignition detecting method comprising: an ignition timing control step; an abnormal vibration determining step; an abnormal vibration timing detecting step, said abnormal vibration timing detecting step comprises: a first abnormal vibration detecting step which detects that said abnormal vibration determining step has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a first predetermined period of time from the ignition effected at said ignition timing control step; a second abnormal vibration detecting step which detects that said abnormal vibration determining step has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a second predetermined period of time longer than said first predetermined period of time from the ignition effected at said ignition timing control step; and a preignition determining step, said preignition determining step determines that preignition is occurring when it is determined at said first abnormal vibration detecting step that abnormal vibration is occurring. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating the constitution of a preignition detecting system; Fig. 2 is a flow chart of a routine for detecting the crank angle; Fig. 3 is a flow chart of a routine for controlling the ignition timing; Fig, 4 is a flow chart of a processing for detecting the preignition; Fig. 5 is a flow chart of another processing for detecting the preignition; Fig. 6 is a graph showing a change in the ignition timing with the passage of time; Fig. 7 is a graph showing a change in the vibration level with the passage of time; Fig. 8 is a diagram illustrating the constitution of an embodiment according to the invention; Fig. 9 is a flow chart of a routine for controlling the gate; Fig. 10 is a flow chart of a second routine for controlling the ignition timing; and Fig. 11 is a timing diagram. The embodiment of Figs. 1 to 7 are shown for illustrative purpose only. DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 is a diagram illustrating the constitution of a preignition detecting system, wherein an internal combustion engine 10 has a piston 103 which moves up and down in a cylinder 102 formed in a cylinder block 101. - In an upper part of the cylinder 102 are arranged an intake valve 104, an exhaust valve 105 and an ignition plug 106. The air-fuel mixture supplied through the intake valve 104 is compressed and is ignited by the ignition plug 106, so that the piston 103 is pushed down to produce a driving force. The up and down motions of the piston 103 are converted into a rotational force by a crank shaft (not shown). A timing rotor 107 is attached to the front end of the crank shaft. The timing rotor 107 has teeth maintaining an angle of 30 degrees (a total of twelve teeth), and a crank position sensor 111 installed adjacent to the timing rotor 107 outputs an electric pulse every time when a tooth passes. Therefore, the crank position sensor 111 can detect the crank shaft angle every 30 degrees. A projection is formed on an intake cam shaft (not shown) which drives the intake valve 104, and a cam shaft sensor 112 positioned adjacent to the intake cam shaft outputs an electric pulse every time when the projection passes. Thus, the cam shaft sensor 112 makes it possible to detect one turn of the cam shaft, i.e., to detect one cycle of the internal combustion engine. Moreover, a vibration sensor 113 is attached to the cylinder block 101 to detect vibration produced by the internal combustion engine. Outputs of the crank position sensor 111, cam shaft sensor 112 and vibration sensor 113 are passed to a controller 12. The controller 12 is constituted by a microcomputer comprising a CPU 122, a memory 123, an input interface 124 and an output interface 125 with a data bus 121 at the center. Outputs of the sensors are passed to the CPU 122 through the input interface 124. An ignition command signal is output from the output interface 125 of the controller 12, and is supplied to the ignition plug 106 through an igniter 131 and an ignition coil 132. Figure 2 is a flow chart of a routine for detecting the crank angle executed by the CPU 122, and is executed as an interrupt process every time a pulse is output from the crank position sensor 111. At a step 21, an index i which represents the crank angle is increased and at a step 22, it is determined whether the index i has reached 12 or not. When the determination at step 22 is affirmative, i.e., when the index i is 12 (i = 12), the index i is then reset at a step 23 and the control proceeds to a step 24. When the determination at the step 22 is negative, the control proceeds directly to the step 24. At the step 24, the time TF fetched from a free-run timer when the routine was executed in the previous time is stored in TB and at a step 25, the time TF of the free-run timer is fetched to terminate the routine. Figure 3 is a flow chart of a routine for controlling the ignition timing executed by the CPU 122 every after a predetermined time interval. At a step 31, a vibration level R of the internal combustion engine detected by the vibration sensor 113 is fetched and at a step 32, a vibration level K is determined as a function of the vibration level R, i.e., K = K(R). As this function, a moving average of the vibration level R can be used. At a step 33, it is determined whether the vibration level K is larger than a predetermined threshold level ε or not. In the above-mentioned case, whether abnormal vibration is occurring or not is determined depending upon the magnitude of the vibration level K. However, the occurrence of abnormal vibration can be also determined relying upon the frequency of the vibration level K that exceeds a predetermined second threshold value η within a predetermined period of time TP. Here, the second threshold value η may be smaller than the threshold value ε. When the determination at the step 33 is negative, i.e., when it is so determined that no abnormal vibration is occurring, the control proceeds to a step 34 where a process is executed for advancing the ignition timing. That is, at the step 34, the ignition timing TI' is advanced by subtracting a predetermined advancing angle ΔT L from a reference ignition timing TI. As is well known, the reference ignition timing TI is determined as a function of the engine speed Ne and the intake air flow GN, i.e., TI = TI(Ne, GN) At a step 35, the ignition timing TI' is limited by a maximum advancing timing T L , and the routine is terminated. When the determination at the step 33 is affirmative, i.e., when it is judged that abnormal vibration is occurring, the control proceeds to a step 36 where the ignition timing TI' is delayed by adding a predetermined delaying angle ΔT D to the reference ignition timing TI. Here, the predetermined delaying angle ΔT D is larger than the predetermined advancing angle ΔT L so that abnormal vibration can be quickly suppressed. At a step 37, the ignition timing TI' is limited by a maximum delaying timing T D . The control then proceeds to a step 38 where a processing is executed to detect the preignition, and the routine is terminated. Figure 4 is a flowchart of a process for detecting the preignition which is executed at the step 38 in the routine for controlling the ignition timing of Figure 3. At a step 41, a time TN, when abnormal vibration is detected, is read out from a free-run timer. When a condition, in which the vibration level K exceeds the predetermined second threshold value η more than a predetermined number of times within a predetermined period of time, is used as a basis for determining the occurrence of abnormal vibration, the time TN at which abnormal vibration larger than the second threshold value η is detected first within the predetermined period of time TP, is read out from the free-running timer. Here, the time TN at which the vibration is detected may not be the one at which vibration larger than the second threshold value η is detected first within the predetermined period of time TP, but may be the one at which vibration is detected after the preceding vibrations have been detected a plural number of times, e.g., may be the one at which vibration is detected in the second time or the third time. A step 42 calculates the time TK at which abnormal vibration is detected in compliance with the following equation, TK = it + (TN - TB)/(TF - TB) where "it" is a previous time when a pulse from the crank position sensor 111 is detected. That is, based on a pulse output from the crank position sensor 111, the time is corrected by a ratio of the time up to detecting abnormal vibration to the time between the pulses. At a step 43, it is determined whether or not a difference between the time TK of detecting abnormal vibration and the time converted from ignition timing TI' using the present engine speed Ne is smaller than the predetermined threshold value δ. The threshold value δ is determined as a positive value. The step 43 may detect a change in the time TK at which abnormal vibration is detected, i.e., may detect whether abnormal vibration is occurring frequently. When the determination at the step 43 is affirmative, i.e., when the difference between the time TK of detecting abnormal vibration and the reference ignition timing TI is smaller than the predetermined threshold value δ, it is so determined that the preignition has occurred and an alarm is generated at a step 44. At a step 45, the operation is carried out to avoid preignition, and the routine is then terminated. The following operations can be carried out to avoid the preignition. 1. Set the ignition timing at a maximum delaying timing T D . 2. Increase the amount of fuel injection to bring the air/fuel ratio to be smaller than or equal to a lower limit of the combustible range. 3. Decrease the amount of fuel injection to bring the air/fuel ratio to be higher than or equal to an upper limit of the combustible range. 4. Close the throttle valve. That is, according to the case in which it is determined that the preignition is occurring when the time TK of detecting abnormal vibration is close to the present ignition timing TI, it is allowed to detect the occurrence of preignition at an early time. The preignition, however, may not be detected at sufficiently high precision depending upon a threshold value with which abnormal vibration is determined or a threshold value of a difference between the time of detecting abnormal vibration and the present ignition timing. According to another embodiment is determined that preignition is occurring when the vibration continues to increase despite the ignition timing being delayed to cope with the occurrence of abnormal vibration, in order to enhance the precision of detection. Figure 5 is a flow chart of a process for detecting preignition, wherein a rate of change in the ignition timing dT/dt is calculated at a step 51. The rate of change in the ignition timing dT/dt can be calculated using, for example, the equation dT/dt = F (TI - TIB) where TIB is the ignition timing of when the routine was executed in the previous time and the function F is a moving average of (TI - TIB). At a step 52, it is determined whether the rate of change in the ignition timing dT/dt is larger than a predetermined threshold value C 0 or not, i.e., whether the ignition timing is being delayed continuously or not. Figure 6 is a graph showing a change in the ignition timing with the passage of time, wherein the abscissa represents the time and the ordinate represents the ignition timing. The ignition timing is delayed as the ordinate goes up. Here, in practice, the threshold value C 0 exhibits a hysteresis characteristic of some width. When the determination at the step 52 is affirmative, i.e., when it is determined that the ignition timing is being delayed continuously, the control proceeds to a step 53 where a rate of change in the engine vibration level dK/dt is calculated in compliance with, for example, the equation dK/dt = G(K- KB) where KB is the vibration level of the internal combustion engine of when the routine was executed in the previous time, and the function G is a moving average of (K - KB). At a step 54, it is determined whether the rate of change in the vibration level dK/dt is larger than a predetermined threshold value C 1 or not, i.e. , whether the vibration of the internal combustion engine is continuing to increase or not. Figure 7 is a graph showing a change in the vibration of the internal combustion engine, wherein the abscissa represents the time and the ordinate represents the vibration level. Here, in practice, the threshold value C 1 exhibits hysteresis of some width. When the determination at the step 54 is affirmative, i.e., when the vibration of the internal combustion engine continues to increase, it is determined that the preignition is occurring and an alarm is generated at a step 55. At a step 56, the operation is carried out to avoid the occurrence of the above-mentioned preignition, and the routine is terminated. That is, it is determined that the preignition is occurring when the rate of change in the ignition timing and vibration becomes greater than the predetermined threshold value despite the operation is carried out to suppress abnormal vibration. It is thus made possible to detect the occurrence of preignition at an early time and reliably. According to the above, the vibration level R must be fetched at very short time intervals to maintain the precision of detection inevitably causing the CPU 122 to bear a considerably large burden. A possibility to decrease the burden born by the CPU 122 according to an embodiment of the present invention will be explained below. Figure 8 is a diagram illustrating the respective constitution according to the invention. Here, a vibration sensor 113 is connected to an input interface 124 which comprises a gate 81a, a peak holder 82a and an A/D converter 83a that are connected in series, and a gate 81b, a peak holder 82b and an A/D converter 83b that are connected in series. The gates 81a and 81b are controlled by two gate control signals Ga and Gb output from the output interface 125. Figure 9 is a flow chart of a gate control routine, wherein it is determined at a step 91 whether a first predetermined period of time T 1 has passed from the ignition timing TI. Here, the first predetermined period of time T 1 (e.g., time until the top dead center is reached after the ignition timing TI) is set to be shorter than a time by which it is expected that the so-called knocking (abnormal vibration of an internal combustion engine which is not preignition) may occur in the internal combustion engine after the ignition timing TI. When the determination at step 91 is affirmative, the control proceeds to a step 92 where it is determined whether a second predetermined period of time T 2 has passed from the ignition timing TI. The second predetermined period of time T 2 is set to be longer than a time by which it is expected that the so-called knocking may occur in the internal combustion engine after the ignition timing TI. When the determination at the step 92 is negative, the control proceeds to a step 93 where a gate opening command is output to the first gate 81a. The control then proceeds to a step 96. When the determination at the step 92 is affirmative, a step 94 outputs a gate closing command to the first gate 81a and a step 95 outputs a gate opening command to the second gate 81b. The control then proceeds to a step 96. At the step 96, it is determined whether a third predetermined period of time T 3 has passed from the ignition timing TI. The third predetermined period of time T 3 is set to be longer than the second predetermined period of time T 2 . When the determination at the step 96 is affirmative, a step 97 outputs a gate closing command to the second gate 81b and the routine is terminated. When the determination at the step 91 or at the step 96 is negative, the routine is readily terminated. According to this gate control routine, a vibration peak P 1 detected by the vibration sensor 113 from the first predetermined period of time T 1 after the ignition timing TT to the second predetermined period of time T 2 , is stored in the first peak holder 82a, and a vibration peak P 2 detected by the vibration sensor 113 from the second predetermined period of time T 2 to the third predetermined period of time T 3 is stored in the second peak holder 82b. Figure 10 is a flow chart of a second routine for controlling the ignition timing, wherein the first vibration peak P 1 stored in the first peak holder 82a and the second vibration peak P 2 stored in the second peak holder 82b are fetched at a step 101. At a step 102, it is determined whether the first vibration peak P 1 is higher than a first predetermined level α. When the determination at the step 102 is affirmative, it is regarded that the preignition is occurring and an alarm is generated at a step 103. Then, at a step 104, the operation is carried out to avoid the occurrence of preignition, and the routine is terminated. When the determination at the step 102 is negative, the control proceeds to a step 105 where it is determined whether the second vibration peak P 2 is higher than a predetermined second level β. When the termination at the step 105 is affirmative, it is regarded that the so-called knocking is occurring, and the control proceeds to a step 106 where the predetermined delay angle ΔT D is added to the reference ignition timing TI to get a delayed ignition timing TI'. At a step 107, the delayed ignition timing TI' is limited by the maximum delaying time T D' and the routine is terminated. When the determination at the step 105 is negative, it is regarded that abnormal vibration (preignition and knocking) is not occurring, and the control proceeds to a step 108 where a predetermined advance angle ΔT L is subtracted from the reference ignition timing TI to get an advanced ignition timing. At a step 109, the advanced ignition timing TI is limited by the maximum advancing timing T L and the routine is finished. It is desired that the first predetermined level α is set to be higher than the second predetermined level β, i.e., α > β. This is because the intensity of vibration due to the preignition is larger than the intensity of vibration due to knocking. Figure 11 is a timing diagram, wherein the abscissa represents the time and the ordinate represents, downward in the order mentioned, output of the vibration sensor, output of the first gate Ga, output of the first peak holder, output of the second gate Gb and output of the second peak holder. That is, Figure 10 shows a case where the preignition is occurring in the #3 cylinder. According to the above construction according to the invention, a decreased amount of load is born by the CPU since the vibration peak may be fetched after the top dead center is reached in a given cylinder until the top dead center is reached in the next cylinder. In order to detect the condition where preignition may occur in the internal combustion engine, the engine may often be provided with a cylinder pressure sensor or an ion sensor for detecting flame relying upon the presence of ions for each of the cylinders. However, providing the sensors for each of the cylinders is disadvantageous in economy and in mounting technique. Besides, ion sensors can detect hot spots only that exist near the sensors. The preignition detecting system of the present invention, however, is capable of quickly detecting the preignition without requiring any additional sensors. According to the preignition detecting system of the invention, the CPU bears a decreased burden, since the peak of vibration needs to be fetched after the top dead center in a given cylinder until the top dead center in the next cylinder.

Claims: A preignition detecting system comprising: ignition timing control means for determining an ignition timing depending upon the conditions in which an internal combustion engine is operating; abnormal vibration determining means for determining that abnormal vibration is occurring, said abnormal vibration timing detecting means comprises: first abnormal vibration detecting means which detects that said abnormal vibration determining means has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a first predetermined period of time from the ignition effected by said ignition timing control means; second abnormal vibration detecting means which detects that said abnormal vibration determining means has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a second predetermined period of time longer than said first predetermined period of time from the ignition affected by said ignition timing control means; and preignition determining means for determining that preignition is occurring when it is determined by said first abnormal vibration detecting means that abnormal vibration is occurring. Preignition detecting system according to claim 1, wherein said first abnormal vibration detecting means determines that abnormal vibration is occurring when vibration larger than a predetermined first threshold level is being generated, and said second abnormal vibration detecting means determines that abnormal vibration is occurring when vibration larger than a predetermined second threshold level which is lower than said first threshold level is being generated. A preignition detecting method comprising: an ignition timing control step; an abnormal vibration determining step; an abnormal vibration timing detecting step, said abnormal vibration timing detecting step comprises: a first abnormal vibration detecting step which detects that said abnormal vibration determining step has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a first predetermined period of time from the ignition effected at said ignition timing control step; a second abnormal vibration detecting step which detects that said abnormal vibration determining step has determined the occurrence of vibration larger than a predetermined threshold level after the passage of a second predetermined period of time longer than said first predetermined period of time from the ignition effected at said ignition timing control step; and a preignition determining step, said preignition determining step determines that preignition is occurring when it is determined at said first abnormal vibration detecting step that abnormal vibration is occurring. Preignition detecting method according to claim 3, wherein said first abnormal vibration detecting step determines that abnormal vibration is occurring when vibration larger than a predetermined first threshold level is being generated, and said second abnormal vibration detecting step determines that abnormal vibration is occurring when vibration larger than a predetermined second threshold level which is lower than said first threshold level is being generated.

Inventors: HASHIZUME KATSUSHI, MOGI KAZUHISA, HASHIZUME, KATSUSHI, MOGI, KAZUHISA
Applicants: TOYOTA MOTOR CO LTD, TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1996
Main classification: G01L23
IPC codes: G01M15, G01L23