Preignition detecting system

Abstract: A preignition detecting system capable of detecting a preigniting condition (PI) at an early time. Vibration of an internal combustion engine is detected by a vibration sensor 113, and is fetched by a controller 12. The crank angle is detected by a crank angle sensor 111. It is so determined that PI has occurred when a difference between the ignition timing and the crank angle at which the vibration level exceeds a predetermined level becomes smaller than a predetermined value. It is further determined that the PI is occurring when the vibration level continues to increase despite the ignition timing being delayed continuously, enabling the occurrence of PI to be detected quickly and reliably. Furthermore, the constitution is simplified by installing a first gate that opens after the passage of a short period of time from the ignition timing and a second gate that opens thereafter.

Description: This invention relates to a preignition detecting system and detecting method in an internal combustion engine and, more particularly, to a preignition detecting system and method capable of detecting a preigniting condition quickly. 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. From US-A-5,347,846 a knocking detecting device is known, wherein the time in which knocking may occur is subdivided into a plurality of time intervals, the intervals being determined by the position of the crankshaft angle. It is determined in which time window there is the highest signal amplitude. A somewhat broader window centred around the above window is used for knock detection. US-A-4,643,846 discloses a vibration testing apparatus for detecting (excess) vibrations in a rotating internal combustion engine. Time windows triggered by the real firing of the cylinders are generated in order to separate events which are related to the different cylinders. DE-A-31 02 299 shows an ignition system having knocking measurement means. The time window for signal analysis is triggered by the true ignition signal and not by some crankshaft sensor signal. There is however no vibration sensor, but ion current measurement. Japanese Utility Model Publication (Kokai) No. 1-88042 proposes 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. However, in this known 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, 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. The present invention was accomplished in view of the above-mentioned circumstances, and its object is to provide a preignition detecting system and preignition detecting method, respectively, capable of detecting a preigniting condition quickly. Solution of this object is achieved by what is claimed in claims 1 or 2, respectively. Thus, according to one 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 when a vibration component within a predetermined frequency range as a result of detecting vibration of the internal combustion engine is larger than a predetermined level or when vibration within a predetermined frequency range occurs more often than a predetermined frequency after the ignition is effected by said ignition timing control means; abnormal vibration timing detecting means for detecting a timing at which it is determined by said abnormal vibration determining means that abnormal vibration is occurring; and a preignition determining means for determining that preignition is occurring depending upon a time difference between the ignition timing determined by said ignition timing control means and the timing of abnormal vibration detected by said abnormal vibration timing detecting means. According to a further aspect of the present invention there is provided a preignition detecting method comprising: an ignition timing control step for determining an ignition timing depending upon the conditions in which an internal combustion engine is operating; an abnormal vibration determining step for determining that abnormal vibration is occurring when a vibration component within a predetermined frequency range as a result of detecting vibration of the internal combustion engine is larger than a predetermined level or when vibration within a predetermined frequency range occurs more often than a predetermined frequency after the ignition is effected at said ignition timing control step; an abnormal vibration timing detecting step for detecting a timing at which it is determined at said abnormal vibration determining step that abnormal vibration is occurring; and a preignition determining step for determining that preignition is occurring depending upon a time difference between the ignition timing determined at said ignition timing control step and the timing of abnormal vibration detected at said abnormal vibration timing detecting step. The preignition detecting system and method thus determines whether the preignition is occurring or not based upon a difference between the timing at which abnormal vibration is occurring and the ignition timing. The following is a more detailed description of preferred embodiments of the present invention, which is to be seen in conjunction with the accompanying drawings, in which: 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; and Fig. 4 is a flow chart of a first processing for detecting the preignition. Figure 1 is a diagram illustrating the constitution of a preignition detecting system according to the present invention, 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 the step 22 is affirmative, i.e., when the index i is 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 embodiment, 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 first 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 6, 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 present invention it is determined that the preignition is occurring when the time TK of detecting abnormal vibration is close to the present ignition timing TI, so that 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 the preignition detecting system of the present invention, it is so determined that the preignition is occurring when a difference between the knocking timing and the ignition timing becomes smaller than a predetermined value. Therefore, the preignition is reliably detected without using any additional sensors.

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 (10) is operating; abnormal vibration determining means for determining that abnormal vibration is occurring when a vibration component within a predetermined frequency range as a result of detecting vibration of the internal combustion engine (10) is larger than a predetermined level or when vibration within a predetermined frequency range occurs more often than a predetermined frequency after the ignition is effected by said ignition timing control means; abnormal vibration timing detecting means for detecting a timing at which it is determined by said abnormal vibration determining means that abnormal vibration is occurring; and a preignition determining means for determining that preignition is occurring depending upon a time difference between the ignition timing determined by said ignition timing control means and the timing of abnormal vibration detected by said abnormal vibration timing detecting means. A preignition detecting method comprising: an ignition timing control step for determining an ignition timing depending upon the conditions in which an internal combustion engine (10) is operating; an abnormal vibration determining step for determining that abnormal vibration is occurring when a vibration component within a predetermined frequency range as a result of detecting vibration of the internal combustion engine (10) is larger than a predetermined level or when vibration within a predetermined frequency range occurs more often than a predetermined frequency after the ignition is effected at said ignition timing control step; an abnormal vibration timing detecting step for detecting a timing at which it is determined at said abnormal vibration determining step that abnormal vibration is occurring; and a preignition determining step for determining that preignition is occurring depending upon a time difference between the ignition timing determined at said ignition timing control step and the timing of abnormal vibration detected at said abnormal vibration timing detecting step.

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: F02D45, F02P5, G01M15, G01L23