GB2049992A

GB2049992A - Automatic control of fuel supply in i.c. engines

Info

Publication number: GB2049992A
Application number: GB8012850A
Authority: GB
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1979-04-21
Filing date: 1980-04-18
Publication date: 1980-12-31
Also published as: DE3015240A1; FR2454527A1; GB2049992B

Abstract

A carburettor 10 is disclosed for supplying fuel to an internal combustion engine. The carburettor comprises an induction passage 12 in communication with the engine, fuel delivery means 30 for supplying a controlled amount of fuel into said induction passage in accordance with the rate of air flow through the induction passage. An auxiliary fuel delivery means 34 is provided for supplying compensating fuel to the induction passage and is associated with fuel controlling means 50 for controlling the rate of fuel flow therethrough. The operation of the fuel controlling means is controlled by a computer in accordance with the amount of air flowing through the induction passage and the rate of change thereof. Additionally compensation may be made for engine temperature, exhaust gas composition, starting and the like. <IMAGE>

Description

SPECIFICATION Electronic controlled carburetor 1. Field of the Invention This invention relates to a carburetor having auxiliary fuel supply means for supplying a controlled amount of compensating fuel to the carburetor induction passage.

2. Description of the Prior Art With conventional simple carburetors, an insufficient amount of fuel is supplied into the carburetor induction passage particularly at idling and low output power conditions where the throttle angle (the opening degree of the throttle valve) and venturi vacuum is very small. In order to avoid the problem, means such as a slow system has been provided to compensate the lack of fuel flow into the carburetor induction passage. The same problem occurs when the throttle valve is rapidly opened for engine acceleration and it has been overcome by the use of an acceleration pump. However, such conventional measures result in complex carburetors.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a simple carburetor which can supply a proper air-fuel mixture over the wide range of engine operating conditions.

Another object of the present invention is to provide an electronic controlled carburetor which includes a microcomputer for controlling the amount of compensating fuel in accordance with various engine operating conditions.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be described in greater detail by reference to the following description taken in connection with the accompanying drawings, in which: Fig. 1 is a schematic view showing one embodiment of a carburetor made in accordance with the present invention; Fig. 2 is a graph showing the relationship between the correction factor K1 and the sensed engine temperature ET; Fig. 3 is a graph showing the relationship between the correction factor B and the sensed rate of change in throttle angle or venturi vacuum P; Fig. 4 is a graph showing the relationship between the correction factor C and the sensed valve drive voltage V; Fig. 5 (comprising two figures, 5A and 5B) shows a flow chart of a computer program executed at a constant interval of time;; Figure 6 shows a flow chart of a computer program executed every time the engine rotates a turn; Fig. 7 is a graph showing the relationship between the basic pulse width A, and the sensed engine temperature ET; Fig. 8 is a graph showing the relationship between the correction factor K2 and the sensed engine speed N; Fig. 9 is a graph showing the relationship between the correction factor K3 and the time T at which the starter motor switch is first turned on; Fig.10 shows a flow chart of a computer program executed with the starter motor switch being turned on; and Fig. 11 shows a flow chart of a computer program executed at a constant interval of time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greater detail to the drawings, Fig. 1 illustrates a carburetor assembly 10 including an induction passage 12. The induction passage 12 has an inlet end ieading from an air cleaner (not shown) and an outlet end leading to the intake passage 14 of an intake manifold of an associated internal combustion engine 1 6. A stationary ring 22 is secured to the inner wall of the induction passage 12 near its inlet end to form a fixed venturi therein. A variable positionable throttle valve 24 is situated within the induction passage 12 near its outlet end and effective for controlling the flow of a combustible mixture from the induction passage 12 into the intake passage 14 of the engine manifold.

The carburetor assembly 10 also comprises a main fuel conduit 26 with its one end being in communication with a float chamber (not shown).

The other end of the conduit 26 leads to an air bleed 28 and hence to a main fuel nozzle 30 which opens into the fixed venturi of the intake passage 12. The air bleed 28 is effective to admix air with fuel flowing to the nozzle 30 so as to improve fuel vaporizing characteristics and suppress production of an over-rich mixture at medium and high engine output conditions. It is preferable to provide an orifice within the main fuel conduit 26 for restriction of the fuel flow so as to achieve a somewhat lean mixture.

At a position downstream of the fixed venturi and upstream of the throttle valve 24, an auxiliary fuel conduit 32 opens into the induction passage 12. The other end of the fuel conduit 32 is in communication with the float chamber. The auxiliary fuel conduit 32 is provided with a solenoid valve 34 for controlling the fuel flow through the fuel conduit 32.

The position of the throttle valve 24 is monitored by a throttle angle sensor 40. The output of the throttle angle sensor 40 is utilized to determine the rate of air flow in the induction passage 12 along with measurement of engine speed made by an engine speed sensor 42 disposed at the rotary shaft 18 of the engine 1 6. It is to be noted that the throttle angle sensor 40 may be replaced with another suitable sensor for measuring intake-manifold vacuum which is utilized to infer intake air flow or engine load. A temperature sensor 44 is inserted into the coolant jacket 20 within the cylinder block of the engine 1 6 for measuring cylinder-head coolant temperature.

The output of these sensors 40, 42 and 44 are applied to a control circuit 50 which comprises a microcomputer. The control ciruit 50 is responsive to the engine operating condition indicative signals from the sensors 40, 42 and 44 for controlling the degree of opening of the solenoid valve 34 so that a controlled amount of fuel can be supplied into the induction passage 1 2 and mixed with the somewhat lean mixture from the venturi to provide a proper air-fuel mixture. For example, the control circuit 50 may be designed to provide a train of drive pulses of a constant frequency and pulse width varying in accordance with the sensed engine operating conditions so as to control the average opening degree of the solenoid valve 34.The control circuit 50 comprises a micro-processor 52, a read only memory (ROM) 54, a random access memory (RAM) 56, and an inpulloutput control unit 58.

The operation of the control circuit 50 is as follows: First of all, the control circuit 50 reads venturi vacuum or throttle angle P sensed by the throttle angle sensor 40 and engine rotational speed N sensed by the speed sensor 42 and then calculates a basic drive pulse width A from the read values P and N. The basic drive pulse width A may be obtained by looking up a two-dimensional table based upon the read values P and N.

The basic drive pulse width A is corrected in accordance with various correction factors including a correction factor K, varying according to engine temperature as shown in Fig. 2, a correction factor B varying with the rate of change in throttle angle or venturi vacuum as shown in Fig. 3, a correction factor C varying as a function of solenoid valve drive voltage as shown in Fig. 4, and a correction factor a determined by the feedback signal from an air/fuel ratio sensor 46 which is provided in the exhaust system of an engine.

The control circuit 50 reads engine temperature ET as inferred from measurement of engine coolant temperature made by the temperature sensor 44 and calculates the correction factor K7 from the read value ET. The correction factor K1 may be obtained by looking up a one-dimensional table based upon the read value ET.

The control circuit 50 reads throttle angle or venturi vacuum P and calculates the difference AP between the previous and present values to obtain the rate of change in throttle angle or venturi vacuum P from which the correction factor B is obtained. The control circuit 50 also determines the correction factors C and a in a suitable manner. The basic pulse width A of the drive pulses to be applied to the solenoid valve 34 is corrected to an optimum value Y in accordance with these corrections factors K1, B, C and a.For example, the control circuit 50 may be designed to calculate the optimum pulse width Y from the following equation: Y=(AK1 + B) + C With an assumption that the basic pulse width A and the correction factor K, are obtained by looking up tables and the correction factors B, C and a are obtained by calculations, the operation of the control circuit 50 will be further described with reference to Figs. 5A, 5B and 6 which are flow diagrams of the computer program stored in the ROM 54. In this case, clock pulses applied to the microcomputer are used as interrupt signals and the computer program is started every time a clock pulse is applied thereto, for example, every 10 microseconds.

The computer program is entered at point 102 each time a clock pulse is applied to the microprocessor 52. The computer reads engine rotational speed N sensed by the speed sensor 42 at the point 104 and stores the value N in the first address of the RAM 56 at the point 106. At the point 108 in the program, the content of the second address of the RAM 56 which stored throttle angle or venturi vacuum in the previous program execution is read into registor 1 of the microprocessor 52.

Following this, throttle angle or venturi vacuum is read into registor 2 of the microprocessor 52 at the point 110 and stored in the second address of the RAM 56 at the point 112. At the point 114 in the program, the computer subtracts the content of registor 1 from that of registor 2 to obtain a difference AP and stores the difference AP in the third address of the RAM 56. Then, the computer reads engine temperature ET sensed by the temperature sensor 44 and stores it in the fourth address of the RAM 56 at the point 116. At the following point 11 8, the computer reads the contents of the first and second addresses of the RAM 56 and looks up a basic pulse width A which is stored in the fifth address of the RAM 56 at the point 120.At the point 122 the computer reads the content of the fourth address of the RAM 56 and looks up the correction factor K1 which is stored in the sixth address of the RAM 56 at the point 124.

At the point 126 in the program, the computer reads the content AP from the third address of the RAM 56 into a registor of the microprocessor 52, subtracts a constant 1.0 from the read value AP, and multiplies the resulting difference by a constant 2.0 to obtain the correction factor B = (AP - 1.0) x 2.0. Relative to the calculation of the correction factor B, a decision is made at the point 128 whether or not the correction factor B is negative. If at the point 128 it is found that the correction factor B is negative, the program proceeds to a point 130 at which the correction factor B is rendered zero. At the point 132, the computer reads the content D (correction factor for the acceleration of the engine) of the seventh address of the RAM 56.

The program then proceeds from the point 1 32 to a point 134 of Fig. 5B at which a decision is made relative to the correction factor B. If the correction factor B is equal to or larger than the content D, the program is transferred along the YES program branch to a point 136 at which the correction factor B is stored in the seventh address instead of the content D.

At the point 138 in the program, the computer reads solenoid valve drive voltage V and calculates a correction factor C corresponding to the value V.

The calculated correction factor C is stored in the eight address of the RAM 56. At the point 140, the computer calculates the correction factor a based on the signal from the air/fuel ratio sensor 46 and stores it in the ninth address of RAM 56.

At the point 142 in the program, the computer calculates an optimum pulse width Y in accordance with the following equation Y=Ax K1 x a+D+C The content D of the seventh address of the RAM 56 is tested at every rotation of the engine.

This will be described with reference to the flow diagram of Fig. 6. The computer program is entered at the point 202 each time the engine rotates a turn. At the following point 204, the computer subtracts a constant 3.0 from the content D of the seventh address of the RAM 56.

The program then proceeds to a point 206 at which a decision is made relative to the resulting difference. If the difference is negative, it is rendered zero. Otherwise, the difference is stored in the seventh address of the RAM 56.

According to such computer program execution, the solenoid valve 34 controls the amount of fuel through the auxiliary fuel conduit 32 so that the carburetor 10 can supply a proper air-fuel mixture to the engine so as to ensure good engine operating stability at idling or low output conditions where the throttle angle is relatively small and can supply a somewhat rich mixture to the engine so as to ensure sufficient acceleration performance during acceleration where the rate of change in throttle angle or venturi vacuum is very large.

The control circuit 50 may be designed to excecute another computer program during engine starting conditions so as to improve the stability of engine starting operation. For this purpose, the control circuit 50 is associated with a starter motor switch 48 which is turned on when the start motor is in operation and is turned off when the start motor is out of operation.

The control circuit 50 makes a decision relative to the state of the starter motor switch. This decision is whether the starter motor switch is turned on or off. If the starter motor switch is OFF, the first described computer program is executed to control the solenoid valve 34 in accordance with various engine conditions. If the starter motor switch is ON: that is, during engine starting conditions, the control circuit 50 reads engine temperature ET such as coolant temperature and calculates a basic pulse width At from the read value ET. The basic pulse width A, may be obtained by looking up a table based upon the read value ET. The basic pulse width A1 varies as a function of engine temperature ET as shown in Fig. 7.

The basic drive pulse width A, is corrected in accordance with various correction factors including a correction factor K2 generally decreasing with increase in engine speed N as shown in Fig. 8 and a correction factor K3 generally decreasing with time lapse T after the starter switch is turned on as shown in Fig. 9. The control circuit 50 reads engine speed N and calculates the correction factor K2 from the read value N. The correction factor K2 may be obtained by looking up a table based upon the read value N.

The control circuit 50 then reads the time laps T after the starter motor switch is first turned on and calculates the correction factor K3 from the read value T. The correction factor K3 may be obtained by looking up a table based upon the read value T.

Following this, the control circuit 50 multiplies the values A1, K2 and K3 to determine the corrected pulse width A2 = A, x K2 x K3 of the drive pulses to be applied to the solenoid valve 34 during engine starting conditions.

On the other hand, the control unit 50 determines the basic pulse width A3 of the drive pulses to be applied to the solenoid valve 34 when the engine is not under starting conditions by looking up a table based upon engine speed N and throttle angle P (or venturi vacuum). The basic pulse width A3 is corrected in accordance with a correction factor K4 varying as a function of engine temperature ET and a constant correction factor K5. The correction factor K4 is obtained by looking up a table based upon engine temperature ET. The control circuit 50 multiplies the values A3, K4 and K5 to determine the corrected pulse width A4 = A3 x K4 x K5.

The control circuit 50 then compares the pulse width value A2 with the pulse width value A4. If the value A2 is larger than the value A4, the value A2 is determined as the pulse width of the drive pulses to be applied to the solenoid valve 34. Otherwise, the value A4 is determined as the pulse width thereof. That is, the value A2 is determined as the drive pulse width during engine starting conditions and the value A4 is determined as the drive pulse width when the engine becomes not under starting conditions. The reason for this is that the air/fuel ratio of a mixture supplied to the engine is required to be over-rich in the beginning of engine starting operation and gradually rendered lean with time lapse.Although the value A2 is larger than the value A4 in the beginning of engine starting operation, it gradually falls and eventually becomes lower than the value A4. In other words, the carburetor 10 supplies a over-rich mixture to the engine due to the pulse width A2 of the drive pulses applied to the solenoid valve 34 just after the engine is started. the mixture to the engine becomes lean with time lapse due to the characteristics of the pulse width value A2 decreasing with time lapse. At the end of engine starting operation, an optimum air/fuel ratio, e.g.

the stoichiometric air/fuel ratio is maintained due to the pulse width A4 of the drive pulses applied to the solenoid valve 34.

With an assumption that the basic pulse width values A1 and A3 and the correction factor K4 are obtained by looking up tables and the correction factors K2 and K3 and the corrected basic pulse width values A2 and A4 are obtained by calculations, the operation of the control circuit 50 will be further described with reference to the flow chart of Fig. 10.

At the block 302 in the computer program, a decision is made relative to the state of the starter motor switch. If the starter motor switch is OFF, at a point 303 control is transferred to another routine used when the engine is not under starting conditions. If the starter motor switch is ON, the program proceeds to a point 304 at which engine temperature ET is read. At the point 306 in the program, the computer looks up a basic pulse width value A, in accordance with the read value ET.

The computer then reads engine speed N at the point 308 and determines the correction factor K2 in accordance with the read value N at the point 310. The determination of the correction factor K2 is made in such a manner as to adopt (1.0) if the read value N is smaller than 200 rpm, (-0.0025N + 1.45) if the read value N is between 200 rpm and 600 rpm, and (0.1) if the read value N is larger than 600 rpm.

The computer then reads the value T of the timer which is included in the computer 50 at the point 312 and determines the correction factor K3 in accordance with the read value T at the point 314. The determination of the correction factor K3 is made in such a manner as to adopt (1.0) if the read value T is smaller than 7 seconds, ,(-0.2T + 2.4) if the read value T is between 7 seconds and 12 seconds, and (0.0) if the read value T is larger than 12 seconds. At the point 31 6 in the program, the computer multiplies values A1, K2 and K3 to determine the corrected pulse width A2=A, x K2 x K3.

Following this, the computer reads throttle angle or venturi vacuum P at the point 31 8 and looks up a basic pulse width value A3 in accordance with the read values N and P at the point 320. At the point 322 in the program, the computer looks up a correction factor value K4 in accordance with the read value ET. The computer then multiplies the read values A3, K4 and K5 (= 1.3) to determine the corrected pulse width A4 at the point 324. At the point 326, a decision is made whether or not the value A2 is larger than the value A4. If the value A2 is equal to or larger than the value A4, the value A2 is selected at the point 328 as the pulse width of the drive pulses applied to the solenoid valve 34. Otherwise, the value A4 is selected at the point 330 as the pulse width thereof.

According to such computer program execution, the solenoid valve 34 controls the amount of fuel through the auxiliary fuel conduit 32 so that the carburetor 10 can supply a mixture with an optimum air/fuel ratio during engine starting operation.

There has been provided, in accordance with the present invention, a simple carburetor which including a microcomputer for controlling the amount of compensating fuel in accordance with various engine operating conditions so that the carburetor can supply a proper air-fuel mixture over the wide range of engine operating conditions.

While this invention has been described in connection with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all alternatives, modifications and variations that fall within the spirit and broad scope of the appended

Claims

claims. CLAIMS

1. A carburetor for supplying fuel to an internal combustion engine, comprising: (a) An induction passage formed for communicating with said engine; (b) a venturi suited within said induction passage; (c) A throttle valve suited within said induction passage downstream of said venturi; (d) fuel reservoir means for containing fuel; (e) fuel delivery means for communicating between said fuel reservoir means and said induction passage a said venturi, said fuel delivery means being effective to meter the rate of fuel flow from said fuel reservoir means into said induction passage in accordance with the rate of air flow through said induction passage; (f) auxiliary fuel delivery means communicating between said fuel reservoir means and said induction passage for supplying compensating fuel to said induction passage downstream of said venturi;; (g) fuel controlling means associated with said auxiliary fuel delivery means for controlling the rate of fuel flow through said auxiliary fuel delivery means; (h) first sensor means for generating an electrical signal indicative of the amount of air flowing through said induction passage; and (i) a microcomputer responsive to said first sensor means for determining the rate of change of the amount of air flowing through said induction passage, said computer controlling the operation of said fuel controlling means in accordance with amount of air flowing through said induction passage and the rate of change thereof.

2. A carburetor according to claim 1, which further comprises second sensor means for generating an electrical signal indicative of engine temperature, in which said computer is adapted to control the operation of said fuel controlling means in accordance with the amount of air flowing through said induction passage, the rate of change thereof, and the engine temperature.

3. A carburetor according to claim 2, in which -said engine has in its exhaust passage air/fuel ratio sensor means for providing a feedback signal indicative of the air/fuel ratio at which said engine is operating, and in which said computer is adapted to control the operation of said fuel controlling means in accordance with the amount of air flowing through said induction passage, the rate of change thereof, the engine temperature, and the air/fuel ratio.

4. A carburetor according to claim 1, in which said first sensor means is adapted to monitor the degree of opening of said throttle valve and engine speed.

5. A carburetor according to claim 1, in which said first sensor means is adapted to monitor the vacuum appearing in said venturi and engine speed.

6. A carburetor according to claim 1, which further comprises third sensor means for detecting said engine being under starting conditions, and in which said computer is adapted to be responsive to said third sensor means for controlling the operation of said fuel metering means in accordance with engine starting conditions.

7. A carburetor according to claim 6, in which said third sensor means is adapted to sense starter motor actuation, engine temperature and engine speed.

8. A carburetor according to claim 6, in which said third sensor means is in the form of a throttle angle sensor for detecting the angle of opening degree of said throttle valve.

9. A carburetor according to claim 6, in which said third sensor means is in the form of a timer for detecting the time lapse after said engine starts.