Crank angle detecting apparatus and reference angular position detection method for internal combustion engine

A rotor is provided such that the rotor rotates with a crank shaft of an engine. A plurality of detection sections are formed on a rotor periphery at equal angle intervals. A particular detection section is used for detection of a reference crank angle. A pickup is provided near the rotor periphery. A crank angle detecting apparatus receives pulse signals from the pickup, and sequentially detects a detection section time. The detection section time is a time interval from the front end to the rear end of the detection section. The crank angle detecting apparatus also sequentially detects a time between each two adjacent detection sections (detection section distance time), which is a time from the rear end of one detection section to the front end of the next detection section. A reference angle detection signal, which indicates detection of the detection section dedicated for the reference angle, is generated when at least two ratio conditions are met. These ratio conditions are decided based on the detection section time and the detection section distance time.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a crank angle detecting apparatus and a reference angular position detection method for determining that the crank shaft of an internal combustion engine reaches a reference angular position.

2. Description of the Related Art

When controlling the timing of fuel injection for feeding fuel to an internal combustion engine by using an injector, or when controlling the ignition timing for causing the spark plug to perform spark discharge, a rotation angular position (i.e., crank angle) of the crank shaft of the engine is detected (determined) based on the reference angular position, and then these timings are set.

A typical crank angle detecting apparatus for detecting a rotational angle of the crank shaft of the engine includes a disc-shaped rotor, which rotates with the crank shaft, and an electromagnetic pickup, which is disposed in the vicinity of the outer periphery of the rotor. A plurality of convex sections or concave sections as detection sections are provided on the outer periphery of the rotor. The convex or concave sections are made of a magnetic material, and spaced from each other at a predetermined angle. When the rotor rotates with the crank shaft, a pulse is generated from the electromagnetic pickup upon passing of the detection section in the vicinity of the electromagnetic pickup. A certain detection section is omitted at a location which corresponds to the reference angle of the crank shaft so that a special pulse is generated at the reference crank angle while the rotor rotates 360 degrees. Alternatively, a longer detection section is provided at a location which corresponds to the reference angle of the crank shaft so that a special pulse is generated. The special pulse has a different shape than other ordinary pulses. For example, the special pulse includes a relatively long no-peak period. A time point at which the crank shaft is on the reference angular position is detected, and pulses are counted on the basis of this detected time point. Then, the fuel injection timing and the ignition timing are set. Such apparatuses are disclosed in, for example, Japanese Patent Application Laid-Open (Kokai) No. S59-31406, Japanese Patent Application Laid-Open No. S59-173562, and Japanese Patent Application Laid-Open No. H6-17735.

In order to improve the accuracy of the timing setting, it is required to increase the number of detection sections on the rotor. In order to detect a time point for every fifteen degrees of the crank angle, for example, twenty four detection sections are required to be disposed at regular intervals on the outer periphery of the rotor. If the number of detection sections increases, the distance between each two detection sections becomes narrower. When the longer detection section which is elongated in the direction of rotation of the rotor should be provided on the rotor to detect the reference angular position, it is difficult in reality to form a sufficiently long detection section on the rotor surface. As a result, the accuracy of detection of the elongated detection section drops.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a crank angle detecting apparatus which can detect, with a high degree of accuracy, that the crank shaft reaches the reference angular position even when the number of detection sections on the rotor is increased.

Another object of the present invention is to provide a reference angular position detection method which can detect, with a high degree of accuracy, that the crank shaft reaches the reference angular position even when the number of detection sections on the rotor is large.

According to a first aspect of the present invention, there is provided a crank angle detecting apparatus that includes a rotor which rotates in conjunction with a crank shaft of an internal combustion engine. The rotor has a plurality of detection sections provided at equiangular intervals on the outer periphery thereof. One of the detection sections is used in detection of a reference crank angle, and is longer than other detection sections in a circumferential direction of the rotor. The crank angle detecting apparatus also includes a pickup disposed in the vicinity of the outer periphery of the rotor for generating a pulse signal every time the pickup detects a front end of each detection section and for generating another pulse signal every time the pickup detects a rear end of each detection section. The crank angle detecting apparatus also includes a time detector for sequentially detecting, in response to the pulse signals generated from the pickup, a detection section time, which is a time interval between detection of the front end of one detection section and detection of the rear end of the same detection section. The detection section time represents the length of the detection section. The time detector also detects a detection section distance time, which is a time interval between detection of the rear end of one detection section and detection of the front end of a next detection section. The detection section distance time represents the distance between the detection sections. The crank angle detecting apparatus also includes a reference angle determination circuit for generating a reference angle detection signal which indicates detection of the detection section used in detection of the reference angle, when at least two ratio conditions obtained from the detection section time and the detection section distance time which are obtained from the time detection circuit are satisfied.

According to a second aspect of the present invention, there is provided another crank angle detecting apparatus. This crank angle detecting apparatus includes a rotor which rotates in conjunction with a crank shaft of an internal combustion engine. The rotor has a plurality of detection sections provided on the outer periphery of the rotor. An angular distance between front ends of each two adjacent detection sections is the same for all the detection sections, or an angular distance between rear ends of each two adjacent detection sections is the same for all the detection sections. One of the detection sections is used in detection of a reference crank angle, and is longer than other detection sections in the circumferential direction of the rotor. The crank angle detecting apparatus also includes a pickup disposed in the vicinity of the outer periphery of the rotor for generating a pulse signal every time when detecting a front end and a rear end of each detection section separately. The crank angle detecting apparatus also includes a time detection circuit for sequentially detecting, in response to the pulse signals from the pickup, a first time interval between the rear ends of each two adjacent detection sections if the angular distance between the front ends of each two adjacent detection sections is the same for all the detection sections, or a second time interval between the front ends of each two adjacent detection sections if the angular distance between the rear ends of the detection sections is the same for all the detection sections. The crank angle detecting apparatus also includes a reference angle determination circuit for generating a reference angle detection signal which indicates detection of the detection section used in detection of the reference angle, when a ratio condition obtained from the first or second time interval which is detected by the time detection circuit is satisfied.

According to a third aspect of the present invention, there is provided another crank angle detecting apparatus. This crank angle detecting apparatus includes a rotor which rotates in conjunction with a crank shaft of an internal combustion engine. The rotor has a plurality of detection sections provided on the outer periphery thereof. An angular distance between front ends of each two adjacent detection sections is the same for all the detection sections, or an angular distance between rear ends of each two adjacent detection sections is the same for all the detection sections. One of the detection sections is used in detection of a reference crank angle, and is longer than other detection sections in a circumferential direction of the rotor. The crank angle detecting apparatus also includes a pickup disposed in the vicinity of the outer periphery of the rotor for generating a pulse signal every time when detecting a front end and a rear end of each detection section separately. The crank angle detecting apparatus also includes a first time detection circuit for sequentially detecting, in response to the pulse signals from the pickup, a detection section time between detection of the front end and rear end of each detection section, and a detection section distance time between detection of the rear end of one detection section and detection of the front end of a next detection section. The crank angle detecting apparatus includes a second time detection circuit for sequentially detecting, in response to the pulse signals from the pickup, a first time interval between the rear ends of each two adjacent detection sections if the angular distance between the front ends of the detection sections is the same for all the detection sections, or a second time interval between the front ends of each two adjacent detection sections if the angular distance between the rear ends of the detection sections is the same for all the detection sections. The crank angle detecting apparatus includes a reference angle determination circuit for generating a reference angle detection signal which indicates detection of the detection section used in detection of a reference angle, when at least two ratio conditions obtained from the detection section time and the detection section distance time which are detected by the first time detection circuit are satisfied, or when another ratio condition obtained from the first or second time interval which is detected by the second time detection circuit is satisfied.

According to a fourth aspect of the present invention, there is provided a reference angular position detection method for a crank shaft of an internal combustion engine. This detection method is used in a crank angle detecting apparatus. The crank angle detecting apparatus includes a rotor which rotates in conjunction with the crank shaft of the internal combustion engine and has a plurality of detection sections provided at equiangular intervals on the outer periphery thereof. One of the detection sections is used in detection of a reference crank angle and is longer than other detection sections in a circumferential direction of the rotor. The crank angle detecting apparatus also includes a pickup disposed in the vicinity of the outer periphery of the rotor for generating a pulse signal every time when detecting a front end and a rear end of each detection section separately. The reference angular position detection method includes the step of sequentially detecting, in response to the pulse signals from the pickup, a detection section time, which is a time interval between detection of the front end of each detection section and detection of the rear end of the same detection section, and a detection section distance time, which is a time interval between detection of the rear end of one detection section and detection of the front end of a next detection section. The reference angular position detection method also includes the step of generating a reference angle detection signal which indicates detection of the detection section used in detection of the reference crank angle, when at least two ratio conditions obtained from the detection section time and the detection section distance time are satisfied.

According to a fifth aspect of the present invention, there is provided another reference angular position detection method for a crank shaft of an internal combustion engine. This detection method is used in a crank angle detecting apparatus. The crank angle detecting apparatus includes a rotor which rotates in conjunction with the crank shaft and has a plurality of detection sections. The detection sections are provided on the outer periphery of the rotor. An angular distance between front ends of each two adjacent detection sections is the same for all the detection sections, or an angular distance between rear ends of each two adjacent detection sections is the same for all the detection sections. One of the detection sections is used in detection of a reference crank angle, and is longer than other detection sections in a circumferential direction of the rotor. The crank angle detecting apparatus includes a pickup disposed in the vicinity of the outer periphery of the rotor for generating a pulse signal every time when detecting a front end and a rear end of each detection section separately. The reference angular position detection method includes the step of sequentially detecting, in response to the pulse signals from the pickup, a first time interval between the rear ends of each two adjacent detection sections if the angular distance between the front ends of each two adjacent detection sections is the same for all the detection sections, or a second time interval between the front ends of each two adjacent detection sections if the angular distance between the rear ends of each two adjacent detection sections is the same for all the detection sections. The reference angular position detection method also includes the step of generating a reference angle detection signal which indicates detection of the detection section dedicated for the reference angle detection, when a ratio condition obtained from the first or second time interval is satisfied.

According to a sixth aspect of the present invention, there is provided another reference angular position detection method for a crank shaft of an internal combustion engine. This detection method is used in a crank angle detecting apparatus. The crank angle detecting apparatus includes a rotor which rotates in conjunction with the crank shaft and has a plurality of detection sections. The detection sections are provided on the outer periphery of the rotor. An angular distance between front ends of each two adjacent detection sections is the same for all the detection sections, or an angular distance between rear ends of each two adjacent detection sections is the same for all the detection sections. One of the detection sections is used in detection of a reference crank angle, and is longer than other detection sections in a circumferential direction of the rotor. The crank angle detecting apparatus also includes a pickup disposed in the vicinity of the outer periphery of the rotor for generating a pulse signal every time when detecting a front end and a rear end of each detection section separately. The reference angular position detection method includes the step of sequentially detecting, in response to the pulse signals from the pickup, a detection section time between detection of the front end of one detection section and detection of the rear end of the same detection section, and a detection section distance time between detection of the rear end of one detection section and detection of the front end of a next detection section. The reference angular position detection method also includes the step of sequentially detecting, in response to the pulse signals from the pickup, a first time interval between the rear ends of each two adjacent detection sections if the angular distance between the front ends of each two adjacent detection sections is the same for all the detection sections, or a second time interval between the front ends of each two adjacent detection sections if the angular distance between the rear ends of each two adjacent detection sections is the same for all the detection sections. The reference angular position detection method also includes the step of generating a reference angle detection signal which indicates detection of the detection section dedicated for detection of the reference angle, when at least two ratio conditions based on the detection section time and the detection section distance time are satisfied, or when another ratio condition based on the first or second time interval is satisfied.

These and other objects, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and the appended claims when read and understood in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring toFIG. 1, an engine control apparatus to which the crank angle detecting apparatus of the present embodiment is applied will be described. This engine control apparatus includes the crank angle detecting apparatus1, an ECU (Electric Control Unit)2, a sensor group3, an injector4, and an ignition device5.

The crank angle detecting apparatus1has a disc-shaped rotor11provided on a crank shaft10of a four-cycle internal combustion engine. The rotor11rotates in conjunction with a rotation of the crank shaft10. The outer peripheral surface of the rotor11is provided with twenty-four convex sections12at fifteen-degree interval. These convex sections12are made of a magnetic material, and serve as detection sections. An electromagnetic pickup13is disposed in the vicinity of the outer periphery of the rotor11. When the rotor11rotates, a pair of positive and negative pulses are generated from the electromagnetic pickup13when the convex section12passes the vicinity of the electromagnetic pickup13. These positive and negative pulses are crank angle pulse signals. The rotor11rotates in the direction of the arrow A inFIG. 1.

The fifteen-degree interval between each two convex sections12is measured from the rear end of one detection section12to the rear end of a next detection section12in the rotation direction (or circumferential direction) of the rotor11. One of the twenty-four convex sections12, which is a convex section12a, is a convex section indicating a reference crank angle. The reference angle is the crank angle at the rear end of the convex section12ain the rotation direction of the rotor11, which is a position of −7 degrees from the TDC (top dead center) of a piston in the 360 degrees of the rotor11. The convex section12ais longer than other convex sections12in the rotation direction of the rotor11. In other words, the length between the rear end and the front end of the elongated convex section12ais larger than the length of other convex section. Thus, the timing for detecting the front end of the convex section12aperformed by the electromagnetic pickup13is earlier than the timing for detecting the front end of other convex sections12. The length between the front end and the rear end of the convex section12ais, for example, twice the distance between the front end of the convex section12aand the rear end of a neighboring convex section12c. The length between the front end and the rear end of the convex section12ais, for example, twice the length between the front end and the rear end of other convex sections12.

When the rotor11rotates in the rotation direction A, the rear end of the convex section12b, which is detected after the convex section12a, is positioned within a range of 0 through 10 degrees from the TDC. In this embodiment, it is positioned at eight degrees from the TDC. A crank angle pulse signal obtained from the elongated convex section12ais a reference pulse signal.

The ECU2is connected to the output of the electromagnetic pickup13. The ECU2has a filter circuit21, a comparison circuit22, an edge detection circuit23, a CPU24, a RAM25, a ROM26, output interface circuits27,28, and an A/D converter29.

The filter circuit21has a resistance21aand capacitors21b,21c. The filter circuit21eliminates a high-frequency noise components in the pulse signals generated from the electromagnetic pickup13, and produces a pair of positive and negative pulses.

The comparison circuit22has a comparator22a, a reference voltage source22b, and resistances22cthrough22f. The comparison circuit22has a hysteresis function. The comparison circuit22generates a low-level output signal when an output signal from the filter circuit21becomes a predetermined voltage Vth or higher, and generates a high-level output signal when the output signal from the filter circuit21is a predetermined voltage −Vth or less. The high-level output period corresponds to the period of the convex sections12including the convex section12aof the rotor11, and the low-level output period corresponds to a period between the convex sections12(i.e., a period of the flat sections of the rotor11). An output signal from the comparison circuit22is supplied as a crank angle signal to the CPU24.

The edge detection circuit23detects a rising edge and falling edge of the signal output from the comparison circuit22.

The CPU24counts the low-level period and high-level period separately in response to the edge detection performed by the edge detection circuit23, and finds the elongated convex section12aindicating the reference crank angle on the basis of a result of the counting. The CPU24repeatedly executes a crank synchronous process, which will be described later, and detects a reference crank angle and a crank stage of the crank angle to perform control of the ignition timing and fuel injection based on the detection results. The CPU24, RAM25, ROM26, output interface circuits27,28, and A/D converter29are connected to a bus.

The output interface circuit27drives the injector4in response to an injector drive command from the CPU24. The injector4is provided in the vicinity of an intake port of an intake pipe of the internal combustion engine, and injects fuel. The output interface circuit28activates the ignitor5in response to an energization start command and an ignition start command from the CPU24. Specifically, energization of an ignition coil (not shown) of the ignitor5is started in response to the energization start command, and the energization is stopped in response to the ignition start command, whereby an ignition plug (not shown) is caused to perform spark discharge. The ignitor5is, for example, a full-transistor ignitor, which supplies the electricity to the ignition coil, generates high voltage by means of accumulated charges of the ignition coil, and applies the high voltage to the ignition plug.

The A/D converter29converts an analog signal sent from the sensor group3, which detects engine operating parameters such as the intake pipe pressure PB, coolant temperature TW, throttle opening θth, and oxygen concentration O2in the exhaust gas, to a digital signal. These engine operating parameters are used for the engine control.

In the engine control apparatus, an output signal from the electromagnetic pickup13passes through the filter circuit21, and becomes a negative pulse in the form of an inverted triangle with respect to the front end of each convex section12(including12a) of the rotor11, and a positive pulse in the form of a triangle with respect to the rear end of each convex section12, as shown inFIG. 2. In the comparison circuit22, an output signal of the filter circuit21is compared with the predetermined voltage −Vthwhen the output signal decreases, and is compared with the predetermined voltage Vthwhen the output signal increases. Therefore, the crank angle signal supplied from the comparison circuit22to the edge detection circuit23becomes high level for the convex sections12of the rotor11and low level for the concave sections (flat sections) between the convex sections12, as shown inFIG. 2.

The edge detection circuit23detects a rising edge and falling edge of the crank angle signal and supplies a signal indicating the time point of each detection to the CPU24. The CPU24measures the time period between the rising edges and falling edges detected by the edge detection circuit23. The rising edges correspond to the front ends of the convex sections12and the falling edges correspond to the rear ends of the convex sections12. The time period corresponding to the convex section12of the rotor11from a rising edge to a falling edge is detected as a convex section time TA (detection section time). The time period corresponding to a concave section between the convex sections12of the rotor11from a falling edge of one convex section to a rising edge of a next convex section is detected as a convex section time TB (time between detection sections or detection section distance time).

The CPU24performs the crank synchronous process, as shown inFIG. 3andFIG. 4. The CPU24first determines whether a rising edge of an output signal from the comparison circuit22is detected or not, in response to an output signal from the edge detection circuit23(Step S1). When a rising edge is detected, measurement of the concave section time TB is ended (Step S2). Then, the previous concave section time TBi−1 is taken as the previous-before-previous concave section time TBi−2, and the current concave section time TBi is taken as the previous concave section time TBi−1 (Step S3). Subsequently, the newly obtained concave section time TB is taken as the current concave section time TBi (Step S4), and measurement of a convex section time TA is started (Step S5). It should be noted that i indicates the current value for each of the convex section time TA and concave section time TB, i−1 indicates the previous value and i−2 indicates the previous-before-previous value.

When a rising edge is not detected, it is determined whether a falling edge of the output signal of the comparison circuit22is detected (Step S6). When a falling edge is detected, the measurement of the convex section time TA is ended (Step S7). Then, the previous convex section time TAi−1 is taken as the previous-before-previous convex section time TAi−2, the current convex section time TAi is taken as the previous convex section time TAi−1 (Step S8), and the newly obtained convex section time TA is taken as the current convex section time TAi (Step S9). Subsequently, measurement of the concave section time TB is started (Step S10). The CPU24also increases the crank stage TCSTG by 1 (Step S11). The crank stage TCSTG indicates any one of stages1through24corresponding to the equiangular intervals defined by the convex sections12, as shown inFIG. 6. Each crank stage TCSTG is 24-degree wide. As understood fromFIG. 6, the angular distance between the rear ends of each two adjacent detection sections12is the same for all the detection sections12in this embodiment.

The CPU24computes the ratio TAi−1/TBi−1 from the previous convex section time TAi−1 and the previous concave section time TBi−1, and determines whether the ratio TAi−1/TBi−1 is at least a first predetermined value MA (for example, 2) (Step S12). TAi−1/TBi−1≧MA is a first ratio condition. If this first ratio condition is satisfied, the CPU24computes the ratio TAi−1/TAi between the previous convex section time TAi−1 and the current convex section time TAi, and determines whether the ratio TAi−1/TAi is at least a second predetermined value MB (for example, 2) (Step S13). TAi−1/TAi≧MB is a second ratio condition. If this second ratio condition is satisfied, a reference angle detection flag F is set as the reference angle detection signal since the convex section time TAi−1 corresponds to the convex section12aindicating the reference angle (Step S14), and the crank stage TCSTG is set to 1 (Step S15). InFIG. 2, the reference angle detection flag F is set to 1 at the time t.

When the first ratio condition, TAi−1/TBi−1≧MA, is satisfied, it is assumed that the TAi−1 corresponding to the elongated convex section12ais detected. When the second ratio condition, TAi−1/TAi≧MB, is satisfied, it can be judged that the current TAi−1 corresponds to the elongated convex section12a.

When TAi−1/TBi−1<MA or TAi−1/TAi<MB is established, the CPU24takes the current time between falling edges TCi as TBi+TAi, and takes the previous time between falling edges TCi−1 as TBi−1+TAi−1 (Step S17). The current time between rising edges TDi is taken as TBi+TAi−1, and the previous time between rising edges TDi−1 is taken as TBi−1+TAi−2 (Step S18).

The CPU24also computes the ratio TCi−1/TCi between the previous time between falling edges TCi−1 and the current time between falling edges TCi, and determines whether the ratio TCi−1/TCi is within a predetermined range 1−MC through 1+MC (MC is a fourth predetermined value and 0.102, for example) (Step S19). 1−MC≦TCi−1/TCi≦1+MC is a fourth ratio condition. When the fourth ratio condition is satisfied, the CPU24computes the ratio TDi/TDi−1 between the current time between rising edges TDi and the previous time between rising edges TDi−1, and determines whether the ratio TDi/TDi−1 is at least a third predetermined value MD (for example, 2) (Step S20). TDi/TDi−1≧MD is a third ratio condition. When the third ratio condition is satisfied, a flag F is set since the convex section time TAi−1 corresponds to the elongated convex section12aindicating the reference angle (Step S14).FIG. 5shows an example in which the flag F is 1 when 1−MC≦TCi−1/TCi≦1+MC and TDi/Tdi−1≧MD are established at the time t.

When the fourth ratio condition 1−MC≦TCi−1/TCi≦1+MC is satisfied, it means that the angular velocity is stable. If the third ratio condition TDi/Tdi−1≧MD is satisfied, it can be judged that the current TDi contains TAi−1 corresponding to the convex section12a.

On the other hand, if 1−MC>TCi−1/TCi and TCi−1/TCi>1+MC (Step S19), the stable condition of the angular velocity is not satisfied. Thus, the reference angle detection flag F is reset (Step S21). When TDi/TDi−1<MD is established even if the stable condition of the angular velocity is satisfied (Step S20), the process proceeds to Step S21to reset the reference angle detection flag F, since the convex section time TAi−1 does not correspond to the convex section12aindicating the reference angle.

In this manner, the CPU24detects the reference crank angle position, and sets the crank stages TCSTG for the respective convex sections12on the basis of the detected reference angular position. The energization timing for the ignition coil of the ignitor5, the timing of starting ignition of the ignition plug of the ignitor5, and the timing of fuel injection performed by the injector4are set on the basis of the crank stages TCSTG.

It should be noted that this embodiment performs first determination for the convex section12ain Steps S12and S13, and second determination for the convex section12ain Steps S19and20, but either one of the first and second determinations may be omitted.

Although the first determination is executed earlier than the second determination in the illustrated embodiment, the second determination may be executed earlier than the first determination.

It should also be noted that when TAi−1/TBi-1<MA or TAi−1/TAi<MB of the first determination is established, the reference angle detection flag F may be reset immediately.

In the above described embodiment, the ratio TAi−1/TBi−1 between the previous value of the detection section time and the previous value of the detection section distance time, and the ratio TAi−1/TAi between the previous value of the detection section time and the current value of the detection section time are used as at least two ratios decided based on the detection section time and the detection section distance time. However, the present invention is not limited in this regard. For example, the ratio TAi/TBi and the ratio TAi/TAi−1 may be used, or the ratio TAi/TAi−2 and the ratio TAi−1/TAi may be used, or a combination of three ratios may be used.

As the ratio based on the time between the front ends of the detection sections, the ratio TDi/TDi−1 between the current value and the previous value of the time between front ends is used in the above described embodiment. However, the present invention is not limited in this regard.

In the above described embodiment, the angle distance between the rear ends of each two adjacent convex sections12on the rotor11is the same for all the convex sections12. Alternatively, the angle distance between the front ends of the convex sections12may be made the same. In this case, the ratio TCi/TCi−1 between the current value and the previous value of the time between rear ends of each two adjacent convex sections12is used to detect the convex section12a.

In the above described embodiment, the protrusions12are formed as the detection sections along the outer periphery of the rotor11, but recesses may be formed as the detection sections along the outer periphery of the rotor11.

Instead of the convex sections12formed along the outer periphery of the rotor11, certain elements may be buried in the outer periphery of the rotor as the detection sections, or suitable marks may be provided on the outer periphery of the rotor as the detection sections.

Although the detection sections12are detected by the electromagnetic pickup13in the illustrated embodiment, the detection sections12may be detected by a suitable optical device.

Although the above described embodiment deals with a case in which the present invention is applied to a four-cycle internal combustion engine of a single cylinder type, the present invention can also be applied to a four-cycle internal combustion engine of a multi-cylinder type or a two-cycle internal combustion engine.

As understood from the foregoing description, the present invention generates the reference angle detection signal, which indicates the detection of the particular detection section12a, when at least two ratio conditions are met. Therefore, it is possible to detect at high accuracy a fact that the crank angle reaches the reference angle position, even when the number of detection sections on the rotor is large.

This application is based on Japanese Patent Application No. 2005-227834 filed on Aug. 5, 2005 and the entire disclosure thereof is incorporated herein by reference.