Rotational speed detection device

Abstract

A rotational speed detection device (1) is provided with a signal plate (2) and a crank angle sensor (3). The signal plate (2) has a protrusion (5) that protrudes from an outer circumferential surface (4). The crank angle sensor (3) has a first sensor element (6) and a second sensor element (7) separated along the circumferential direction of the signal plate (2), and can detect passage of the protrusion (5) by using a differential waveform (W3) between a first output waveform (W1) of the first sensor element (6) and a second output waveform (W2) of the second sensor element (7). In the crank angle sensor (3), the relationship between the distance from the first sensor element (6) to the second sensor element (7) and the length of the protrusion (5) along the circumferential direction of the signal plate (2) is set so as to maximize the absolute value of the slope of a section (S) between a peak and a trough of the differential waveform (W3).

Description

Rotational speed detector

[0001] The present invention relates to a rotation speed detection device.

[0002] For example, Patent Document 1 discloses a semiconductor magnetic sensor disposed to face the crank rotor, which has a first sensor unit that outputs a first pulse signal when a detection tooth formed at an equal angular pitch on the outer periphery of the crank rotor passes by, and a second sensor unit that outputs a second pulse signal when the detection tooth passes by.

[0003] The semiconductor magnetic sensor disclosed in Patent Document 1 functions as a so-called differential sensor that utilizes the phase difference that exists between the first pulse signal and the second pulse signal, and is capable of determining whether the crankshaft is rotating forward or backward.

[0004] However, in Patent Document 1, no consideration is given to the variation characteristics of sensing by the semiconductor magnetic sensor. In other words, in Patent Document 1, if the variation in sensing by the semiconductor magnetic sensor when detecting that any target tooth of the crank rotor has passed multiple times is large, there is a risk that this will be recognized as a rotation variation of the internal combustion engine.

[0005] Therefore, in Patent Document 1, when an internal combustion engine is controlled using the output signal from the semiconductor magnetic sensor, there is a risk that the internal combustion engine will be controlled by recognizing the sensing variation of the semiconductor magnetic sensor as a rotation variation of the internal combustion engine.

[0006] Therefore, there is room for further improvement in reducing the sensing variation of the differential sensor.

[0007] Japanese Patent Application Publication No. 9-32620

[0008] The rotation speed detection device of the present invention comprises a disk-shaped rotating member and a rotation detection sensor arranged to face the outer peripheral surface of the rotating member, wherein the rotating member has a protrusion protruding from the outer peripheral surface in the radial direction of the rotating member, and the rotation detection sensor has a first sensor element and a second sensor element spaced apart along the circumferential direction of the rotating member, and is capable of detecting the passage of the protrusion using a differential waveform between a first output waveform output from the first sensor element and a second output waveform output from the second sensor element, and the relationship between the distance from the first sensor element to the second sensor element and the length of the protrusion along the circumferential direction of the rotating member is set so as to maximize the absolute value of the slope between the peaks and valleys of the differential waveform.

[0009] According to the present invention, the rotation speed detection device improves the sensing variation characteristics of the rotation detection sensor, and improves the rotation detection accuracy of the rotation detection sensor.

[0010] 1 is a diagram illustrating the detection principle of a crank angle sensor, in which (a) is a diagram schematically illustrating the positional relationship between the crank angle sensor and a protrusion of a signal plate, (b) is a diagram illustrating an example of a first output waveform detected by a first sensor element of the crank angle sensor and an example of a second output waveform detected by a second sensor element of the crank angle sensor, (c) is a diagram illustrating an example of a differential waveform determined from the first output waveform and the second output waveform, and (d) is a diagram illustrating an example of a signal output from the crank angle sensor.

[0023] FIG. 1 is a diagram illustrating repeatability.

[0024] FIG. 2 is a diagram illustrating changes in the first output waveform and the second output waveform when the length of the protrusion is changed.

[0025] FIG. 3 is a diagram illustrating changes in repeatability when the length of the protrusion is changed.

[0026] FIG. 4 is a diagram illustrating changes in repeatability when the distance between the sensor elements is changed.

[0011] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0012] FIG. 1 is an explanatory diagram illustrating the detection principle of a crank angle sensor 3 used in a rotation speed detection device 1 according to the present invention. FIG. 1(a) is an explanatory diagram schematically illustrating the positional relationship between the crank angle sensor 3 and a protrusion 5 formed on the outer periphery of a signal plate 2. FIG. 1(b) is an explanatory diagram illustrating an example of a first output waveform W1 detected by a first sensor element 6 of the crank angle sensor 3 and an example of a second output waveform W2 detected by a second sensor element 7 of the crank angle sensor 3. FIG. 1(c) is an explanatory diagram illustrating an example of a differential waveform W3 determined from the first output waveform W1 and the second output waveform W2. FIG. 1(d) is an explanatory diagram illustrating an example of a signal output (output signal) finally output from the crank angle sensor 3.

[0013] The rotation speed detection device 1 is capable of detecting the rotation speed of a crankshaft (not shown) of an internal combustion engine (not shown), and includes a signal plate 2 as a rotating member and a crank angle sensor 3 as a rotation detection sensor.

[0014] The signal plate 2 has a disk shape and is attached to the crankshaft, for example, with its center of gravity positioned on the rotation axis along its axial direction. The crankshaft corresponds to a rotatable shaft member.

[0015] The signal plate 2 has a plurality of protrusions 5 that protrude from the outer peripheral surface 4 in the radial direction of the signal plate 2. The outer peripheral surface 4 is a curved surface that is continuous in an annular shape along the circumferential direction (rotational direction) of the signal plate 2. The protrusions 5 are formed to protrude at equal intervals along the circumferential direction of the signal plate 2. The protrusions 5 are formed to have a predetermined length along the circumferential direction of the signal plate 2. The protrusions 5 are formed, for example, so that their lengths along the circumferential direction of the signal plate 2 are the same.

[0016] The crank angle sensor 3 is disposed to face the outer peripheral surface 4 of the signal plate 2. The crank angle sensor 3 has a first sensor element 6 and a second sensor element 7 that are spaced apart from each other. The crank angle sensor 3 is disposed such that the first sensor element 6 and the second sensor element 7 are spaced apart from each other along the circumferential direction of the signal plate 2. The first sensor element 6 and the second sensor element 7 are formed, for example, by a Hall element or the like.

[0017] The crank angle sensor 3 can detect the passage of the protrusion 5 using a differential waveform W3 between a first output waveform (first magnetic flux waveform) W1 formed by connecting first sensor element output signals output from the first sensor element 6 in time series and a second output waveform (second magnetic flux waveform) W2 formed by connecting second sensor element output signals output from the second sensor element 7 in time series. In other words, the crank angle sensor 3 can detect the passage of the protrusion 5 using a differential signal between the first sensor element output signal and the second sensor element output signal. The differential waveform W3 is a waveform formed by connecting differential signals, which are the difference between the first sensor element output signal and the second sensor element output signal, in time series, as shown in Figure 1(c) .

[0018] As shown in Fig. 1(b), the first sensor element output signal and the second sensor element output signal are so-called analog signals whose magnitude (output) changes continuously depending on the distance from the protrusion 5, and represent the magnetic flux strength (magnetic flux density). As shown in Fig. 1(b), the first output waveform W1, the second output waveform W2, and the differential waveform W3 are so-called analog waveforms whose values ​​change continuously, and represent the continuous change in the magnetic flux strength (magnetic flux density).

[0019] The crank angle sensor 3 detects the timing when the value on the differential waveform W3 becomes equal to or less than a predetermined internal criterion T as the timing when the protrusion 5 has passed. The crank angle sensor 3 detects the timing when the protrusion 5 has passed and outputs the detected timing as an output signal to the outside. As shown in FIG. 1D , for example, the crank angle sensor 3 outputs the voltage supplied to the crank angle sensor 3 as an output signal when the value of the differential signal, which is the value on the differential waveform W3, becomes equal to or less than the predetermined internal criterion T, and then changes the voltage of the output signal to "0" after a predetermined time has elapsed. In other words, when the value readable from the differential waveform W3 becomes equal to or less than the predetermined internal criterion T, the crank angle sensor 3 determines that the protrusion 5 has passed in front of the crank angle sensor 3 and changes the value of the signal output. More specifically, the crank angle sensor 3 changes its signal output when the signal plate 2 rotates and the protrusion 5 passes in front of it.

[0020] The crank angle sensor 3 has improved robustness against variations in the timing at which the differential waveform W3 crosses (steps over) the internal criterion T, and therefore has improved repeatability, as the slope of the differential waveform W3 increases when the differential waveform W3 crosses (steps over) the internal criterion T. The slope of the differential waveform W3 refers to the slope of the section S between the peaks and valleys of the differential waveform W3. In other words, the crank angle sensor 3 has improved robustness against variations in the timing at which the differential signal falls below the internal criterion T, and therefore has improved repeatability, as the rate of change of the value (output value) of the differential signal when the differential signal falls below the internal criterion T increases. The rate of change of the value (output value) of the differential signal refers to the slope of the section S between the peaks and valleys of the differential waveform W3.

[0021] In this specification, repeatability refers to the sensing variation characteristic (amount of variation) of the crank angle sensor 3 that occurs when detecting multiple rotations (multiple passes) of an arbitrary protrusion 5, as shown in FIG. 2, for example. If the repeatability is high (poor), it may be recognized as a rotation variation of the signal plate 2. Therefore, in the case of the signal plate 2 attached to the crankshaft, improving the repeatability is important for controlling the fuel injection, ignition timing, etc. of the internal combustion engine. FIG. 2 is an explanatory diagram of repeatability.

[0022] The slope between the peaks and valleys of the differential waveform W3 increases as the first output waveform W1 intersects with the second output waveform W2 at points where the absolute value of the slope between the peaks and valleys is large. As shown in FIG. 3 , the earlier the first output waveform W1 and the second output waveform W2 intersect, the more likely they are to intersect at a point where the slope between their peaks and valleys is large. However, as shown in FIG. 3 , the earlier the first output waveform W1 and the second output waveform W2 intersect, the smaller their amplitudes become, and the smaller the slope between their peaks and valleys become. The shorter the length of the protrusion 5 along the circumferential direction of the signal plate 2, the smaller the slope between their peaks and valleys become. FIG. 3 is an explanatory diagram showing how the first output waveform W1 and the second output waveform W2 change when the length of the protrusion 5 along the circumferential direction of the signal plate 2 is changed.

[0023] Here, the inventors of the present application have found that the magnitude of the slope between the peaks and valleys of the differential waveform W3 depends on the length of the protrusions 5 along the circumferential direction of the signal plate 2. Specifically, they have found that the repeatability takes an extreme value when the length of the protrusions 5 along the circumferential direction of the signal plate 2 is the sensor element distance D, which is the center-to-center distance between the first sensor element 6 and the second sensor element 7, as shown in Figure 4. Figure 4 is an explanatory diagram that schematically shows the change in repeatability when the sensor element distance D is fixed and the length of the protrusions 5 along the circumferential direction of the signal plate 2 is changed.

[0024] Therefore, the rotation speed detection device 1 sets the relationship between the sensor element distance D and the length of the protrusion 5 along the circumferential direction of the signal plate 2 so as to maximize the absolute value of the slope between the peak and the valley of the differential waveform W3 before and after the protrusion 5 passes the crank angle sensor 3. In other words, the rotation speed detection device 1 sets the relationship between the sensor element distance D and the length of the protrusion 5 along the circumferential direction of the signal plate 2 so as to maximize the absolute value of the rate of change of the differential signal before and after the protrusion 5 passes the crank angle sensor 3.

[0025] More specifically, the rotation speed detection device 1 sets the distance D between the sensor elements to be the same as the length of the protrusion 5 along the circumferential direction of the signal plate 2 .

[0026] As a result, in the rotation speed detection device 1, the sensing variation characteristics of the crank angle sensor 3 are improved, and the rotation detection accuracy by the crank angle sensor 3 is improved.

[0027] Therefore, according to the present invention, the internal combustion engine can perform combustion control (fuel injection control, ignition timing control, etc.) with higher accuracy.

[0028] The inventors of the present application have also found that repeatability depends on the length of the protrusions 5 along the circumferential direction of the signal plate 2, and therefore on the distance D between the sensor elements. Specifically, they have found that the repeatability takes an extreme value when the distance D between the sensor elements is equal to the length of the protrusions 5 along the circumferential direction of the signal plate 2, as shown in Figure 5. Figure 5 is an explanatory diagram that schematically shows the change in repeatability when the distance D between the sensor elements is changed while the length of the protrusions 5 along the circumferential direction of the signal plate 2 is fixed.

[0029] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

Claims

1. A rotational speed detection device comprising: a disc-shaped rotating member attached to a rotatable shaft member; and a rotation detection sensor disposed to face an outer peripheral surface of the rotating member, wherein the rotating member has a protrusion protruding in a radial direction of the rotating member from the outer peripheral surface, the rotation detection sensor has a first sensor element and a second sensor element spaced apart along a circumferential direction of the rotating member, and is capable of detecting that the protrusion has passed by using a differential waveform between a first output waveform output from the first sensor element and a second output waveform output from the second sensor element, and a relationship between a sensor element distance, which is a distance between the first sensor element and the second sensor element, and a length of the protrusion along the circumferential direction of the rotating member is set so as to maximize an absolute value of an inclination between a peak and a valley of the differential waveform.

2. The rotational speed detection device according to claim 1, wherein the sensor element distance is set to be the same as the length of the protrusion along the circumferential direction of the rotating member.

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