GB2029027A

GB2029027A - A suction air flow detector for an internal combustion engine

Info

Publication number: GB2029027A
Application number: GB7927846A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1978-08-10
Filing date: 1979-08-10
Publication date: 1980-03-12
Also published as: FR2433107A1; GB2029027B; JPS5525509A; DE2932366A1; FR2433107B1

Abstract

A suction air flow detector for an internal combustion engine comprises first pulse generating means (1, 2, 3, 4) for generating pulse signals corresponding to rotating angles of the engine, second pulse generating means (5, 6) for generating pulse signals having frequencies corresponding to suction air flows, and counter means (7) for counting pulse numbers of the pulse signals during a determined period of time of the pulse signals from the first pulse generating means to generate signals, thereby producing digital signals corresponding to suction air flow per unit rotating angles of the internal combustion engine. In this manner, the flow detector according to the invention directly detects the suction air flow per unit rotation of the engine, so that the range of the signal variation is limited to 4-5 times of the minimum signal to facilitate the arithmetic processing of the signal by means of a microcomputer of a small capacity. <IMAGE>

Description

SPECIFICATION A suction air flow detector for an internal combustion engine The present invention relates to a suction air flow detector for use in a fuel injection system for an internal combustion engine.

In conventional electronically controlled fuel injection systems for internal combustion engines, suction air flows (air flows per unit time) are generally detected for example by the use of an air flow sensor.

The air flow sensor usually produces analog voltage signals corresponding to suction air flows.

In digital signal processing, after the analog voltage signal is converted into a digital signal, it is divided by a rotating speed of an engine to obtain a value corresponding to a suction air flow per unit rotation of the engine, thereby, according to the obtained value, determining a fuel amount (in practice a pulse width of a fuel injection pulse) to be supplied to the engine.

With engines for vehicles, the suction air flow at the maximum output of the engines becomes as much as 40 times of that in idling of the engine.

Therefore, the maximum output of the air flow sensor becomes 40 times of the minimum output.

For the purpose of digitally processing such wide range outputs, an arithmetic unit having a capacity of more than 11 bits would be needed in consideration of arithmetic processing accuracies.

In controlling the fuel supply for an engine based on such digitally processed outputs, however, the capacity of the microcomputer to be used for the fuel supply control is usually in the order of 4--8 bits. When the outputs corresponding to the 11 bit capacity are inputted in the 8 bit microcomputer for the arithmetic processing, the arithmetic system would be unavoidably very complicated.

Therefore the arithmetic process not only for analog-digital converting but also for fuel supply control for an engine as above described is effected by a microcomputer, a total arithmetic system would become more complicated.

Furthermore, when an arithmetic circuit which carries out the arithmetic process for the above digital process in place of the microcomputer, the circuit would also become complicated.

It is an object of the invention to provide an improved suction air flow detector which overcomes the above disadvantages in the prior art.

It is another object of the invention to provide a suction air flow detector which comprises means for producing signals having frequencies proportional to suction air flow and which by counting the signals generates digital signals proportional to the suction air flows per unit revolutions of an engine.

The suction air flow detector for an internal combustion engine according to the invention comprises first pulse generating means for generating pulse signals corresponding to rotating angles of the engine, second pulse generating means for generating pulse signals having frequencies corresponding to a suction air flows, and counter means for counting pulse numbers of the pulse signals delivered from the second pulse generating means during a determined period of said pulse signals from said first pulse generating means so as to generate signals, thereby producing digital signals corresponding to suction air flows per unit rotating angles of the internal combustion engine.

The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.

Fig. lisa block diagram of one embodiment of the detector according to the invention; Fig. 2 shows wave forms of signals generated in the circuit in Fig. 1; and Fig. 3 is a block diagram of an application of the detector according to the invention.

Referring to Fig. 1 illustrating a block diagram of one embodiment of the suction air flow detector according to the invention, the detector comprises an engine rotating angle sensor 1 for detecting rotated crank angles of an engine, which generates a signal per each crank angle 1200 (6 cylinders), 180 (4 cylinders) or 3600, a wave form shaping circuit 2 for shaping the wave form of the signal to obtain a pulse signal a, a monostable multivibrator 3 adapted to be triggered at the trailing edge of the pulse signal a to produce a pulse signal b, and a monostable multivibrator 4 adapted to be triggered at the trailing edge of the pulse signal b to produce a pulse signal c.

On the other hand, the detector includes a Karman vortices flow meter 5 generating signals having frequencies proportional to suction air flows and a wave form shaping circuit 6 to which is fed the signal from the flow meter 5 to obtain a pulse signal d.

A counter 7 counts the pulse signals d and is reset every time the pulse signal c is fed thereto. A latch circuit 8 functions to read out the contents of the counter 7 to produce an output signal S1 every time the pulse signal b is given to the latch circuit 8.

As can be seen from Fig. 2, the pulse signal b is produced immediately before the pulse signal c, so that the latch circuit 8 stores the contents in the counter 7 immediately before it is reset and produces the output signal S1. The output signal S1 from the latch circuit 8 is a digital signal proportional to the pulse number of the pulse signals d per a unit rotation of an engine (the period T1 in Fig. 2) and therefore proportional to the suction air flow per the unit rotation.

In the circuit shown in Fig. 1, the suction air flow per unit rotation can be directly detected.

Accordingly, the range of the variation in signal S is at most within 4-5 times of the minimum, so that this suction air flow detector ensures a great simplification of an arithmetic unit for the fuel injection system.

Fig. 3 is a block diagram of one example of a fuel injection system using the detector according to the invention. The system comprises a suction air flow detector 9 as shown in Fig. 1, a central processing unit 1 0 for a microcompuzer, an accumulator 11 adapted to be actuated in transferring data, arithmetic processing or the like, an input/output interface 12, a ROM (read only memory) 13, a RAM (random access memory) 14, an input/output interface 15, an injection valve 16 and a data bus 1 7.

The central processing unit 10 serves to read out the output signals Sr from the suction air flow detector 9 through the inpufoutput interface 12 according to the program stored in the ROM 13 and also read out signals S2 fed to the input/output interface 15 from sensors (not shown) for detecting various engine operation parameters such as cooling water, atmospheric and exhaust gas temperatures or the like so as to calculate an injection pulse width from the reference injection flow determined by the signal S, and added with a correction value determined by the signal S, An injection pulse 83 having the calculated pulse width is produced from the input/output interface 1 5. The injection pulse S3 drives the injection valve 16 to effect a fuel injection. The RAM 14 temporariiy stores intermediate values during the calculation.

The detector according to the invention may be used not only for a fuel injection system but also for an ignition advance control device and an exhaust gas recirculation system.

In place of the Karman vortices flow meter as shown in Fig. 1, a turbine flow meter may be used for the purpose. In short, any ones producing signals having frequencies proportional to suction airflows may be used.

As can be seen from the above description, the detector according to the invention directly calculates the suction air flow per unit rotation of an engine, so that the range of signal variation is within 4-5 times which can be easily arithmetically processed by an 8 bit microcomputer. As a dividing circuit is not necessary, the time required for processing a signal becomes shorter so that the fuel injection system can be simplified.

Claims

1. A suction air flow detector for an internal combustion engine comprising first pulse generating means for generating pulse signals corresponding to rotating angles of the engine, second pulse generating means for generating pulse signals having frequencies corresponding to a suction air flows, and counter means for counting pulse numbers of the pulse signals delivered from the second pulse generating means during a determined period of said pulse signals from said first pulse generating means so as to generate signals, thereby producing digital signals corresponding to suction air flows per unit rotating angles of the internal combustion engine.

2. A detector as set forth in claim 1, wherein said first pulse generating means comprises an engine rotating angle sensor for detecting rotated crank angles of the engine to generate a signal per each crank angle, a wave form shaping circuit for shaping a wave form of the signal from the engine rotating angle sensor to obtain a first pulse signal, a first monostable multivibrator triggered at a trailing edge of the first pulse signal to produce a second pulse signal and a second monostable multivibrator triggered art a trailing edge of the second pulse signal to produce a third pulse signal, said second pulse generating means comprises a flow meter for generating signals having frequencies proportional to suction air flows and a second wave form shaping circuit to which is fed the signal from the flow meter to obtain a pulse signal, and said counter means comprises a counter for counting the pulse signals from said second wave form shaping circuit, said counter being reset every time the pulse signal is fed thereto from said second monostable multivibrator and a latch circuit reading out contents of said counter to produce an output signal every time the pulse signal from the first monostable multivibrator is given to the latch circuit.

3. A detector as set forth in claim 2, wherein said flow meter is a Karman vortices flow meter.

4. A detector as set forth in claim 2, wherein said flow meter is a turbine flow meter.

5. A detector as set forth in claim 1 , wherein further comprises injection valve control means for receiving said digital signals from said detector and producing pulses corresponding to values determined by engine operation parameters and an injection valve controlled by the pulses delivered from the injection valve control means.

6. A detector as set forth in claim 5, wherein said injection valve control means comprises a central processing unit for a microcomputer, an accumulator actuated in transferring data and arithmetic processing, first input/output interface, a read only memory, a random access memory, second input/output interface and a data bus connecting these components.

7. A suction air flow detector substantially as described with reference to, and as illustrated in, the accompanying drawings.