SUCTION AIR MEASURING DEVICE

Abstract: A suction air measuring device comprises vortex detection means (3-10) for detecting Karman vortex signal of vortex in a suction conduit (1) of an engine as a digital signal and sorting it in a storage means at a predetermined time period and binarizing means (11) for binarizing an output of the vortex detection means (3-10) to obtain a Karman vortex pulse signal, setting or resetting the Karman vortex pulse signal when an output of the vortex detection means (3-10) increases from a lower extreme thereof resetting or setting the Karman vortex signal when the output of the vortex detection means (3-10) decreases from an upper extreme thereof by a predetermined value.

Description: The present invention relates to a suction air measuring device for use in an electronic controlled fuel injection device of an automobile engine. A method is known, for example from Japanese Utility Model Application Laid-Open No. 41665/1979, in which a vortex generating member is provided in a conduit and the flow rate of fluid passing therethrough is measured on the basis of occurrence frequency of Karman vortices generated downstream of the vortex generating member. This method utilizes the fact that ultrasonic signal waves transmitted or received through the conduit are phase-modulated by Karman vortices generated in the fluid. By demodulating the signal, the vortex-modulated signal is detected as an analog electric signal. The analog electric signal is usually binarized by comparing it with a predetermined voltage by a voltage comparator and outputted as a Karman vortex pulse signal having a frequency equal to the occurrence frequency of the vortex. Use of such Karman vortex flow rate sensor as a suction air sensor of an automobile engine gives rise to the problem that, when the throttle valve of the engine is opened substantially, air pulsation due to the suction operation of the engine is produced in the suction conduit and the output level of the electric signal is greatly changed according to the pulsation of suction air. When such output signal is binarized according to the known method, pulse drop problem occurs. In order to solve this problem, Japanese Utility Model Application Laid-Open No. 72119/1982 proposes removing fluctuations of the analog electric signal due to pulsation of the suction air by passing it through a differentiation circuit. In this solution, however, the signal level is lowered when the frequency thereof is low. In order to remove the latter problem, in 72119/1982, the input characteristic of the differentiation circuit is changed according to the output of the pulse circuit, i.e. according to the pulse frequency of Karman vortices generated by the measuring device itself. Therefore, once such pulse drop occurs, the pulse drop situation continues. An object of the present invention is to provide a suction air measuring device for an automobile engine capable of providing Karman vortex pulse signal substantially corresponding to the amount of suction air regardless of pulsation of suction air due to engine operation. According to the invention, there is provided a suction air flow measuring device for an engine comprising a vortex generating member inserted into a suction conduit of said engine, vortex detection means comprising sensor means responsive to a periodic wave transmitted through the air flow and providing a periodic sensor signal, shaping means to convert said sensor signal into a square wave signal and means to convert said square wave signal into a digital electrical signal indicative of phase displacement of said periodic wave caused by Karman vortices generated downstream of said vortex generating member and to store said digital electrical signal in a memory means at instants corresponding to the leading edges of pulses in said square wave signal, and a processing means arranged to cause binarizing of said digital electrical signal by setting a first signal level when said digital electrical signal starts to increase from a lower extreme thereof by a predetermined value, and setting a second signal level when said digital electrical signal decreases from an upper extreme thereof by a predetermined value, to provide a Karman pulse signal representative of said air flow. Preferably, said processing means comprises a microprocessor arranged to execute a predetermined program in synchronism with the storing of said digital electrical signal in said memory means. Expediently, said processing means is arranged to set and reset a flip-flop whose output provides said first and second signal levels. EP-A-0 277 240 (published 10.08.88) discloses a similar device to the invention, using a binarizing technique which is different, being based on comparison of filter outputs. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 is a block circuit diagram showing an embodiment of a suction air measuring device according to the present invention; Figs. 2A to 2D and 3A and 3B are timing charts of signals at various points in Fig. 1; Fig. 4 is a flow chart showing a sequence of signal processing in the embodiment in Fig. 1; and Fig. 5 is a timing chart showing the signal processing in the embodiment in Fig. 1. In Fig. 1 which is a block diagram of an embodiment of a suction air measuring device according to the present invention, a vortex generating member 2 is disposed in a predetermined position in a suction conduit of an engine and an ultrasonic receiving vibrator 4 detects the Karman vortex generated downstream of the generating member 2. The ultrasonic vibrator 4 has a resonance frequency around 40 KHz and is disposed in the suction conduit 1 together with an ultrasonic transmitting vibrator 3 opposing thereto. The transmitting vibrator 3 has a resonance frequency around 40 KHz and is excited to transmit an ultrasonic wave to the receiving vibrator 4. A resonance detection circuit 5 detects a vibration of the ultrasonic transmitting vibrator 3 at its resonance frequency and provides a detection output to a voltage controlled oscillator 6. The voltage controlled oscillator 6 responds to the output of the resonance detection circuit 5 to produce a pulse signal having a frequency around 20 MHz The pulses of the pulse signal are counted by a counter 7 of 9 bits so that the frequency thereof is divided by 512. A drive circuit 8 drives the ultrasonic transmitting vibrator 3 with the pulse signal whose frequency is divided by 512. The sinusoidal output signal of the ultrasonic receiving vibrator 4 is wave-shaped by a wave-shaper 9 to obtain a pulse signal. A nine bit latch circuit 10 reads the content of the counter 7 at a timing corresponding to a leading pulse edge of the output pulse signal of the wave-shaper 9. The output of the latch circuit 10, i.e., a change of the phase-demodulated signal, is judged by a micro processor 11, and according to the judgement made, a flip-flop (FF) circuit 12 is set or reset. The output of the FF 12 is a Karman vortex pulse. Operation of the device constructed as above will be described with reference to Figs. 2A to 2D, in which Fig. 2A shows the output a of the voltage controlled oscillator 6, i.e., a clock input of the counter 7, Fig. 2B shows a count value b of the counter 7, Fig. 2C shows the most significant bit of the counter 7, i.e., the drive pulse of the ultrasonic transmitting vibrator 3, and Fig. 2D shows the output d of the wave-shaper 9. The content e of the latch circuit 10 is also shown in Fig. 2B. As shown in Fig. 2B, the counter 7 of 9 bits counts the output a of the voltage controlled oscillator 6 from 0 to 511 reciprocally. Therefore, the most significant bit thereof becomes the drive pulse c whose frequency is the oscillator output a divided by 512. The ultrasonic transmitting vibrator 3 is driven by the drive pulse c through the drive circuit 8. The voltage controlled oscillator 6 is feedback-controlled by the resonance detection circuit 5 such that the frequency of the pulse c coincides with the resonance frequency of the ultrasonic transmitting vibrator 3. Since the resonance frequency of the vibrator 3 is about 40 KHz, the oscillation frequency of the voltage controlled oscillator 6 is controlled to about 20 MHz ( 512 x 40 KHz resonance frequency ). The ultrasonic wave from the ultrasonic transmitting vibrator 3 is phase-modulated by Karmen vortices in the suction conduit 1 and received by the ultrasonic receiving vibrator 4. An output waveform of the ultrasonic receiving vibrator 4 is substantially a sinusoidal wave whose frequency is about 40 KHz. This is wave-shaped by the wave-shaper 9, resulting in the phase-modulated received pulse d as shown in Fig. 2D. By picking-up the content of the counter 7 into the latch circuit 10 at the timing corresponding to the leading edge of the pulse d, the output e of the latch circuit 10 becomes the phase-demodulated signal. That is, since the counter 7 serves as a frequency divider as well as a phase counter for dividing one period corresponding to 360° of the transmitting wave c by 512, the content of the counter 7 latched at the timing of leading edge of the received pulse d becomes the phase-demodulated signal. The Karman vortex signal is detected as a digital electric signal ( phase-demodulated signal ) e, in this manner. The frequency of this phase-demodulated signal e, i.e., the Karman vortex frequency is practically from about 10 Hz to about 2500 Hz. An amplitude of the phase-demodulated signal e is detected by the micro processor 11 to obtain the Karman vortex pulse. This will be described with reference to Figs. 3A and 3B in which Fig. 3A shows the phase-demodulated signal e and Fig. 3B shows the Karman vortex pulse f. As shown in Fig. 3A, the micro processor 11 sets the FF 12 when the signal e increases by 2 steps or more after it starts to increase and resets the FF 12 when the signal e decreases by 2 steps or more after it starts to decrease. The amount of "2" steps corresponds to the content of the latch circuit 10, that is, "2" when 360° of one period of the drive pulse signal c for the vibrator is counted as 512. The processing to be performed by the micro processor 11 will be described with reference to a flow chart shown in Fig. 4. In step S1 in Fig. 4, the micro processor 11 is put in a ready state for operation until the received pulse d start to rise. Upon occurence of the leading edge of the pulse d at which the latch circuit 10 latches the phase-demodulated signal e, the micro processor 11 reads the latched data and stores it in a memory M1, as shown in step S2. Then, in step S3, extremes of the amplitude of the phase-demodulated signal are judged. That is, it is judged whether the signal e starts to increase from a lower extreme or to decrease from an upper extreme. When such extreme is detected, the preceding content of the memory M1, i.e., the value of the phase demodulated signal e at the time of extreme detection, is transferred to another memory M2 and stored therein, in step S4. Therefore, the memory M2 stores the lower extreme value D1 ( Fig. 3B ) of the phase-demodulated signal e when it increases and the upper extreme value D2 ( Fig. 3B ) when it decreases. In steps S5 and S6, it is determined whether not the content stored in the memory M1 is larger than that in the memory M2 by 2 steps. If yes, the FF 12 is set. When it is determined that the content of the memory M1 is smaller than that in the memory M2 by 2 steps in steps S7 and S8, the FF 12 is reset. The above processing is repeated in synchronism with leading edges of the received pulse signal d. Fig. 5 shows a timing relation between the leading edge of the received pulse d and the processing of the micro processor 11. The processing to be performed by the micro processor 11 must be synchronized with the received pulse d, otherwise, an erroneous data read may occur when a leading edge of the received pulse occurs during a readout operation of the phase-demodulated signal e from the latch circuit 10 in the step S2. As described, the Karman vortex signal is obtained by binarizing the phase-demodulated signal e by means of the detection of the extremes of the signal e by the micro processor 11. Therefore, the present device has no dependency on the signal level thereof and hence the pulsation of suction air. Further, due to the use of the micro processor 11, there is no dependency on frequency of the demodulated signal. The suction air measuring device described comprises vortex detection means for detecting Karman vortex signal of vortex generated behind a vortex generating member inserted into a suction conduit of an engine as a digital signal and storing it in a storage means at a predetermined time period and binarizing means for binarizing an output of the vortex detection means to obtain a Karman vortex pulse signal and setting or resetting the Karman vortex pulse signal when a variation of the output of the vortex detection means exceeds a predetermined value. When the output of the vortex detection means decreases, after a termination of increase, to a predetermined value or smaller, the Karman vortex pulse signal is reset or set.

Claims: A suction air flow measuring device for an engine comprising a vortex generating member (2) inserted into a suction conduit (1) of said engine, vortex detection means (3-10) comprising sensor means responsive to a periodic wave transmitted through the air flow and providing a periodic sensor signal, shaping means (9) to convert said sensor signal into a square wave signal (d) and means to convert said square wave signal (d) into a digital electrical signal (e) indicative of phase displacement of said periodic wave caused by Karman vortices generated downstream of said vortex generating member (2) and to store said digital electrical signal (e) in a memory means (M1) at instants corresponding to the leading edges of pulses in said square wave signal (d), and a processing means (11) arranged to cause binarizing of said digital electrical signal (e) by setting a first signal level when said digital electrical signal (e) increases from a lower extreme thereof by a predetermined value, and setting a second signal level when said digital electrical signal decreases from an upper extreme thereof by a predetermined value, to provide a Karman pulse signal (f) representative of said air flow. The suction air measuring device as claimed in claim 1, wherein said processing means (11) comprises a microprocessor (11) arranged to execute a predetermined program in synchronism with the storing of said digital electrical signal in said memory means (M1). The suction air measuring device as claimed in claim 1 or 2 wherein said processing means (11) is arranged to set and reset a flip-flop (12) whose output provides said first and second signal levels.

Inventors: TUTUMI, KAZUMICHI C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1988
Main classification: G01F1
IPC codes: G01F1, G01D7