WO2006137142A1

WO2006137142A1 - Engine rpm measuring method and device thereof

Info

Publication number: WO2006137142A1
Application number: PCT/JP2005/011553
Authority: WO
Inventors: Kiyokatsu Iwahashi; Masaharu Ohya; Yasutaka Nakajima
Original assignee: Rion Co., Ltd.
Priority date: 2005-06-23
Filing date: 2005-06-23
Publication date: 2006-12-28
Also published as: JPWO2006137142A1; JP4651667B2

Abstract

[PROBLEMS] To provide an engine rpm measuring device capable of accurately measuring engine rpm from engine exhaust sound. [MEANS FOR SOLVING PROBLEMS] There is provided a device for measuring an engine rpm by converting an engine exhaust sound into a digital signal. The device includes: an FFT analysis unit (3) for detecting a primary frequency from frequency characteristic of an idling state; a band pass filter (6) following a change of the primary frequency and processing the engine exhaust sound changing from the idling state; a zero cross waveform generation unit (7) excluding an amplitude component from the data outputted from the band pass filter (6); ΔF-V conversion unit (8) for outputting a value in accordance with a frequency of the data outputted from the zero cross waveform generation unit (7); a frequency modulation unit (5) for updating the sampling frequency of data inputted to the band pass filter (6) according to the value outputted from the ΔF-V conversion unit (8); and an engine rpm calculation unit (9) for calculating the engine rpm according to the value outputted from the frequency modulation unit (5).

Description

Specification

Engine speed measurement method and apparatus

Technical field

TECHNICAL FIELD [0001] The present invention relates to an engine speed measurement method and apparatus for measuring the engine speed as well as engine exhaust sound power.

Background art

[0002] Exhaust noise from a muffler emitted from an automobile is called proximity exhaust noise, and its measurement method is standardized by JIS and ISO. In recent years, proximity exhaust noise measurement has been applied in Japan to detect poorly maintained vehicles such as modified mufflers.

In proximity exhaust noise measurement, it is necessary to measure the maximum noise level from when the engine speed is maintained for several seconds in a stopped state (idle blowing) to when the accelerator is rapidly turned off and the engine is idling. Therefore, in addition to the sound level meter, a device that detects the engine speed is required.

[0003] Conventionally, apart from the sound level meter, it is detected by using electromagnetic waves of high tension cord force at the time of plug spark for detecting the engine speed, or due to the movement of the engine block or the engine piston around it. A tachometer has been used which detects and uses a magnet attachment type vibration sensor to detect the vibration.

Exhaust noise is noise that has pulsation sound associated with explosion in the cylinder that causes the engine to rotate, and detecting the pulsation frequency of this pulsation sound is equivalent to detecting the engine speed. . Therefore, a method is known in which the frequency of exhaust noise is analyzed, the maximum peak frequency is regarded as the primary frequency component of the pulsation frequency, and the engine speed is detected.

Disclosure of the invention

Problems to be solved by the invention

[0004] However, due to recent developments in automobile technology, there are an increasing number of cars and engine blocks that do not have high-tension cords and aluminum blocks (including motorcycles) that do not have high-tension cords. The technology we are using has become unusable. Even if technology that uses electromagnetic waves or vibrations can be used to detect the number of revolutions, the revised ISO that is currently being considered attempts to regulate that the engine room is closed by a hood.

It is assumed that it will be difficult to install the sensor in the engine room and pull the sensor cable out of the engine room.

[0005] In addition, even in the exhaust sound frequency analysis method using FFT (Fast Fourier Transform) analysis, even if the primary frequency component is larger than other low-order or high-order frequency components, the engine is highly accurate. Force that can detect the rotational speed The lower-order or higher-order frequency component is larger than the primary frequency component. In some cases, the engine speed cannot be detected accurately. Therefore, this method cannot always accurately detect the engine speed that changes every moment.

[0006] Furthermore, in order to control a poorly maintained vehicle such as a modified muffler vehicle, the noise greatly depends on the rotational speed, so there are cases where the current proximity exhaust noise measurement method cannot cope. In other words, the noise value exceeding the proximity exhaust noise value determined by the automobile manufacturer based on the proximity exhaust noise measurement method exceeds the predetermined engine speed required by the proximity exhaust noise measurement method. In order to clarify such an event, it is necessary to accurately correlate changes in engine speed with changes in exhaust noise, and monitor engine speed changes and noise levels sequentially.

[0007] The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to accurately measure the engine exhaust sound power and the engine speed. It is an object of the present invention to provide an engine speed measurement method and apparatus capable of performing the same. Means for solving the problem

[0008] In order to solve the above-mentioned problem, the invention according to claim 1 determines the idling state frequency characteristic force primary frequency by using a method of measuring engine speed by converting engine exhaust sound into a digital signal. The first step, the second step of processing the engine exhaust sound changing idling state force with a bandpass filter that follows the change of the primary frequency, and the step of removing amplitude fluctuations from the data output from the second step The third step, the third step, the fourth step for outputting a value corresponding to the frequency of the output data, and the input to the band pass filter of the second step according to the value output from the fourth step Data sump A fifth step of updating the ring frequency and a sixth step of calculating the engine speed according to the output value of the fourth step are provided.

[0009] The invention according to claim 2 is an apparatus for measuring engine speed by converting engine exhaust sound into a digital signal, a frequency detection unit for detecting a primary frequency from frequency characteristics in an idling state, and the primary frequency A band-pass filter that processes engine exhaust sound that changes from an idling state following a change in the power level, a zero-cross processing unit that removes fluctuations in the data force amplitude output from the band-pass filter, and a output from the zero-cross processing unit AF-V converter that outputs a value corresponding to the frequency of the data to be transmitted, and frequency modulation that updates the sampling frequency of the data input to the bandpass filter according to the value output from the AF-V converter And an engine speed calculator for calculating the engine speed according to the value output from the frequency modulator.

[0010] The invention according to claim 3 is the engine speed measurement device according to claim 2, wherein the frequency modulation unit is a thinning interval determination unit that determines a thinning interval of sampling data of engine exhaust sound; The AF-V conversion unit includes a low-pass filter that outputs a change in frequency as a change in amplitude, and a low-pass filter that thins out the sampling data according to the thinning-out interval determined by the thinning interval determination unit. It also becomes the effective power calculation unit that converts the effective value output by to a value equivalent to the frequency.

The invention's effect

[0011] According to the present invention, there is a lower order than the primary frequency component of the pulsation sound included in the exhaust sound! / ヽ is non-contact and closes the hood even if the higher order frequency component is large. It is possible to easily and accurately measure the engine speed, which changes from moment to moment in a state of being hot.

Brief Description of Drawings

FIG. 1 is a block diagram of an engine speed measuring device according to the present invention.

[Figure 2] Flow chart showing the measurement procedure in the idling state

[Figure 3] Flow chart showing the measurement procedure when the engine speed changes

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Here, Fig. 1 is a block diagram of the engine speed measuring device according to the present invention, and Fig. 2 is in an idling state. FIG. 3 is a flowchart showing the measurement procedure when the engine speed changes.

[0014] The present invention is in principle equivalent to detecting the primary frequency component of the pulse-like sound included in the exhaust sound, but does not directly detect the primary frequency component by direct frequency analysis. By using the digital frequency relationship and changing the sampling frequency for digitizing the exhaust sound signal based on the information of the pulsation sound itself contained in the exhaust sound, the changed sampling frequency has a fixed relationship. It has a feature that it expresses the engine speed!

First, the digital filter and digital frequency used in the present invention will be outlined. Using an IIR (cyclic) digital bandpass filter with fc [H z] as the center frequency of the analog real frequency f as an example, the sampling frequency fs [Hz], the center frequency fc [Hz] of the analog real frequency f, and The nature of the digital filter will be described.

The frequency characteristic H (z) of an IIR (cyclic) digital bandpass filter is expressed by the following equation (1).

[0016] [Equation 1]

N-1

H (z) = "g—— (1)

2 Dm "Z

Here, z = e ^{j2 it i / is} , and N and M are integers and satisfy the condition of N ≦ M. an and bm are coefficients that determine the frequency characteristics of the digital filter.

[0018] In equation (1), it is assumed that coefficients an and bm of a digital bandpass filter having fc [Hz] as the center frequency of the analog real frequency f are determined under the condition of the sampling frequency fs [Hz]. When the coefficients an and bm are fixed and the sampling frequency fs is increased by k times, this digital filter shifts the center frequency to k times fc.

[0019] Because in z = e ^{j2 it i / is} , if fd = f / fs and fdc = fc / fs, (k'fc) Z (k'f s) is also fdc, This is the same as the digital filter frequency characteristic H (z) expressed by equation (1). Hereafter, fd is unitless but called digital frequency. In other words, the digital filter When the numbers an and bm are fixed, the characteristic H (z) is uniquely determined by the digital frequency fd, which is the ratio of the analog real frequency f and the sampling frequency fs.

[0020] As shown in Fig. 1, an engine speed measurement device according to the present invention includes a microphone 1, an AZD conversion unit 2, and an FFT (Fast Fourier Transform) analysis unit that convert engine exhaust sound into an analog electrical signal. 3, low-pass filter (LPF) 4, frequency modulation unit 5, band-pass filter (BPF) 6, zero-cross waveform generation unit 7, AF-V (frequency voltage) conversion unit 8, engine rotation A number calculation unit 9 is provided.

Instead of the FFT analysis unit 3 as a frequency detection unit, a frequency analysis unit having the same function as the FFT analysis unit 3 may be used. If the engine exhaust sound is digital data stored on a memory card or the like, it is not necessary to provide the microphone 1 and the AZD converter 2.

[0021] The AZD converter 2 converts the exhaust sound collected by the microphone 1 into a digital signal at a sampling frequency fp [Hz]. Sampling frequency fp is determined by the condition expressed by the following equation (2), where D is the maximum decimation interval of the decimation unit, which will be described later, and R [rpm] is the maximum measurable rotational speed.

[0022] [Equation 2]

-¾ ^--R- c <f _P (2)

60

[0023] Here, c is a coefficient determined by engine specifications, and is generally 3 in a 6-cylinder 4-cycle engine. The data generated here is used as sampling data.

[0024] The FFT analysis unit 3 is provided only for determining the primary frequency component MHz of the pulsation sound in the exhaust sound when the engine of the vehicle to be measured is idling. The primary frequency component fc is determined as a frequency having a peak value near the frequency using the engine specifications (idling speed, engine type, etc.).

[0025] The low-pass filter 4 is provided so that the aliasing phenomenon due to the sampling theorem does not occur when the sampling data is thinned out by the thinning-out device connected to the subsequent stage. The cutoff frequency fac [Hz] of the Rhonos filter 4 is set within the range indicated by the following equation (3) using the maximum thinning interval 0, the maximum rotation speed R, and the coefficient c in equation (2). [0026] [Equation 3]

-^ ■ R- c <f _ac <^. ^ (3)

[0027] The bandpass filter 6 has, as a center frequency, the ratio of the primary frequency component fc determined by the FFT analyzer 3 and the sampling frequency fs (= fpZD), fdc (equation (1)). This is fixed until the detection of the engine speed of the vehicle to be measured is completed. The band-pass filter 6 is the same as described above if the thinning-out device 11 in the preceding stage accurately inputs the sampling data で), which is the input of the band-pass filter 6 in proportion to the engine speed change, at the interval I. Due to the nature of the digital filter, as a result, it follows the primary frequency component of the pulsation sound in the exhaust sound, and functions to selectively extract the primary frequency component while suppressing other components.

[0028] The zero-cross waveform generation unit 7 converts the output waveform into a rectangular wave having an amplitude of 1 or -1 depending on whether the output waveform (close to a sine wave) of the bandpass filter 6 is larger or smaller than zero. The Depending on the engine speed, the amplitude of the primary frequency component of the pulsation noise in the exhaust sound may fluctuate. This fluctuation is detected by the low-pass filter 13 and the effective power calculator 14 (described later). As a result, the amplitude variation is eliminated by using a zero-cross waveform. As a result, the change in the output amplitude of the preceding bandpass filter 6 can be absorbed.

[0029] The A-F-V conversion unit 8 includes a low-pass filter (LPF) 13, an effective power calculation unit 14, and a gate unit 15, and outputs a change in frequency as a voltage. The low-pass filter 13 is provided to detect a change in the primary frequency component of the pulsation sound in the exhaust sound accompanying a change in the engine speed. The following equation (4) is the output amplitude vf based on the general frequency amplitude characteristic of the nth-order butter-throw bus filter having the cutoff frequency flp [Hz].

[0030] [Equation 4]

[0031] When a signal having a frequency f in the gradient frequency range (f> flp) of the amplitude characteristic of the low-pass filter 13 is input, the output amplitude vf of the low-pass filter 13 changes when the input frequency changes. In other words, the change width of the input frequency can be known by capturing this change width. The cut-off frequency flp [Hz] of the low-pass filter 13 needs to be smaller than the primary frequency component fc so that the primary frequency component fc [Hz] corresponds to the slope frequency region of the low-pass filter 13.

The effective power calculation unit 14 is provided to calculate a value equivalent to the output amplitude vf shown in the output signal force equation (4) of the low-pass filter 13. The gate unit 15 is a switch that connects the output of the effective power calculation unit 14 to the subsequent thinning interval determination unit 12 at regular intervals. This interval is determined by the response time of the bandpass filter 6 and the response time of the effective power calculation unit 14. Empirically, the switch is turned on at intervals of 5 to 10 cycles of the signal input to the effective power calculation unit 14, and the output value of the effective power calculation unit 14 at that time is output.

[0033] The frequency modulation unit 5 includes a decimation unit 11 that decimates sampling data ΧΦ according to a decimation interval d (i), and a decimation interval determination unit 12 that gives the decimation interval d (i) to the decimation unit 11. The sampling frequency is modulated according to the pressure level.

The decimation interval determination unit 12 uses the output value vfc of the effective power calculation unit 14 in the idling state, the output value vKi of the gate unit 15 at the i time point, and the decimation interval d (i) at the i time point to i + 1 The decimation interval d (i + l) is calculated using the following equation (5).

[0034] [Equation 5]

Here, INT [·] is an operator that rounds [·] to an integer. The initial value d0 is the maximum thinning interval D.

[0036] The engine speed calculation unit 9 also calculates the engine speed Ri using the following equation (6) for the thinning interval di force calculated at the time point i by the thinning interval determination unit 12.

[0037] [Equation 6]

[0038] Here, R0 is the number of revolutions during idling, AVG [·] is the operator that performs the average operation of the tom force and the i + m interval, and m is an arbitrary integer.

[0039] The operation of the engine speed measuring device according to the present invention configured as described above and the engine speed measuring method will be described.

First, the engine speed measurement operation when the engine is idling is performed according to the flowchart shown in FIG. In step SP1, microphone 1 converts the exhaust sound during idling to an analog electrical signal. Next, in step SP2, the AZD conversion unit 2 converts the exhaust sound collected by the microphone 1 into a digital signal at the sampling frequency fp [Hz]. Then, in step SP3, the primary frequency component (fundamental frequency) fc [Hz] of the pulsation sound in the exhaust sound when the engine is idling is determined (first step).

[0040] Next, the engine speed measurement operation for the engine exhaust sound that also changes the idling state force is performed according to the flowchart shown in FIG. In step SP11, the engine exhaust sound is converted into an analog electric signal by the microphone 1. In step SP12, the AZD conversion unit 2 digitally inputs the exhaust sound collected by the microphone 1 at the sampling frequency fp [Hz].

[0041] Next, in step SP13, the low-pass filter 4 having a cutoff frequency fac [Hz] is passed through to prevent the aliasing phenomenon caused by the sampling theorem from occurring in the AZD-converted digital signal.

In step SP14, the output signal (sampling data Χφ) of the low-pass filter 4 is thinned out according to the interval I (interval) d (i) (i time point) determined by the thinning interval determination unit 12 in step SP18. The digital frequency fd, which is the ratio of the analog actual frequency f to the sampling frequency fs, is made constant (fifth step).

[0042] In step SP15, the sampling data Xft) is interleaved with the interspace I and the interval di, so that the bandpass filter 6 with the center frequency fdc (= fcZfs) is excluded from the nature of the digital frequency. The primary frequency component is selectively extracted while following the primary frequency component of the pulsating sound in the aerial sound and suppressing the other components (second step). Note that the primary frequency component fc [Hz] obtained in step SP3 is used as the initial setting parameter, and the coefficients an and bm of the bandpass filter 6 are determined.

[0043] Next, in step SP16, in order to remove the amplitude change of the primary frequency component from the output waveform of the bandpass filter 6 (close to a sine wave), the output waveform is subjected to an amplitude force depending on whether the output waveform is larger or smaller than zero. Convert to ^ or 1 square wave (3rd step).

[0044] In step SP17, when the sampled signal force having the frequency f is input using the gradient frequency region (f> flp) of the amplitude characteristic of the low-pass filter 13 having the cutoff frequency force ¾p [Hz], When the input frequency changes, the output amplitude _V i¾ of the low-pass filter 13 changes. Therefore, the effective power is calculated, and a voltage whose magnitude changes according to the change of the input frequency is output from the gate unit 15 (fourth step ).

[0045] Next, in step SP18, the output signal of the AF-V conversion unit 8 is input to the decimation interval determination unit 12 of the frequency modulation unit 5, and the decimation interval d (i + l) is calculated by equation (5). Is done. The thinning interval d (i + l) is sent to step SP19 (sixth process) and to step SP14 (fifth process).

On the other hand, in step SP19, the engine speed R (i + 1) is calculated from the thinning interval d (i + 1) calculated by the thinning interval determination unit 12 using equation (6) (sixth step).

Thus, by changing the sampling frequency, it is possible to construct the bandpass filter 6 that dynamically tracks the primary frequency component proportional to the engine speed. Assuming that the engine speed in the idling state is 500 rpm to lOOOOrpm and that the primary frequency component is the largest frequency component in that frequency range, there is no practical problem. Since it dynamically follows changes in the engine speed based on the frequency at that time, it is more accurate than a method that simply considers the peak frequency of the FFT result as the engine speed, as in the prior art. In addition, since zero cross processing is performed, it is not affected by the amplitude fluctuation of the primary frequency component.

Industrial applicability

[0047] Compared to the primary frequency component of the pulsation sound included in the exhaust sound, the low-order or high-order frequency component Even if the minutes are large, the engine speed can be measured with high accuracy in a non-contact state and with the hood closed, so that the application range can be expanded.

Claims

The scope of the claims

[1] The method of measuring engine speed by converting engine exhaust sound into a digital signal, the first step of determining the frequency characteristic force primary frequency in the idling state, and the engine exhaust sound that also changes the idling state force The second step of processing by the band pass filter that follows the change of the primary frequency, the third step of removing the fluctuation of the data force amplitude output from the second step, and the frequency of the data output from the third step A fourth step of outputting a corresponding value, a fifth step of updating a sampling frequency of data input to the bandpass filter of the second step according to a value output from the fourth step, and a fourth step of An engine speed measurement method comprising a sixth step of calculating an engine speed according to an output value.

[2] A device for measuring engine speed by converting engine exhaust sound into a digital signal, a frequency characteristic force in an idling state, and a frequency detector for detecting a primary frequency, and following the change in the primary frequency Idle state force A band-pass filter that processes engine exhaust sound that changes, a zero-cross processing unit that removes amplitude fluctuations from the data output from this band-pass filter, and the frequency of the data output from this zero-cross processing unit An AF-V converter that outputs a corresponding value, a frequency modulator that updates a sampling frequency of data input to the bandpass filter according to a value output from the AF-V converter, and the frequency modulation An engine speed characterized by comprising an engine speed calculation unit for calculating the engine speed according to a value output from the unit Number measuring device.

[3] The frequency modulation unit also serves as a decimation interval determination unit that determines the sampling interval of engine exhaust sound sampling data, and a decimation unit that decimates the sampling data according to the decimation interval determined by the decimation interval determination unit. 3. The AF-V conversion unit includes: a low-pass filter that outputs a change in frequency as an amplitude change; and an effective power calculation unit that converts an effective value output from the low-pass filter into a value equivalent to a frequency. The engine speed measuring device described.