GB2294130A

GB2294130A - Diesel engine fuel cut-off control system

Info

Publication number: GB2294130A
Application number: GB9520973A
Authority: GB
Inventors: Motor Company Limited Nissan; Hirotada Muraki; Masayuki Ohki; Kazuhiro Ishigami
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1994-10-13
Filing date: 1995-10-13
Publication date: 1996-04-17
Anticipated expiration: 2015-10-13
Also published as: GB2294130B; GB9520973D0; JP3324297B2; JPH08109847A

Abstract

For controlling a diesel engine having a fuel cut valve 29 in a supply line to a fuel injection pump, a dual-CPU type system is used which comprises a main-CPU 51 for controlling the quantity of fuel injected by the pump in accordance with an operation condition of the engine and a sub-CPU 52 for controlling the valve 29. The sub-CPU has a plurality of output ports P1 -P3. A first circuit of the Sub-CPU issues a request for stopping fuel supply to the pump when at least the fuel injection quantity control carried out by the main-CPU is found to be abnormal. A second circuit of the sub-CPU feeds each of the output ports P1 -P with an instruction signal representing present/absence of the request. A logic circuit 54, 55 which is operatively interposed between the output ports of the sub-CPU and the valve 29 operates the valve 29 in a manner to stop the fuel supply to the pump only when all of the instruction signals from the output ports P1 -P3 represent presence of the request. Fuel supply can also be cut off when the engine key is switched to the off position or when the sub-CPU diagnoses any abnormal condition of the engine. Unnecessary engine shut downs, eg when the sub-CPU malfunctions, are avoided. <IMAGE>

Description

The present invention relates in general to control systems for controlling diesel engines, and more particularly, to the control systems of a type applied to a diesel engine which is equipped, at a fuel inlet passage led to the pumping chamber of a fuel injection pump, with a fuel cut valve (FCV). More specifically, the present invention is concerned with a control system of a diesel engine, which comprises a microcomputer including a main-central processing unit (main-CPU) which processes control of the fuel injection pump and a sub-central processing unit (sub-CPU) which processes control of the fuel cut valve.

In control systems of diesel engines, there is a type having an electronic governor by which a fuel injection pump of the engine is controlled in accordance with an engine operation condition, such as engine rotation speed, throttle valve angle and the like. The fuel injection pump is equipped, at a fuel inlet passage led to the pumping chamber thereof, with an electromagnetic type fuel cut valve. The fuel cut valve assumes an opened position when energized and a closed position when deenergized. When the fuel cut valve is turned to the closed position, the fuel supply to the pumping chamber is suppressed, thereby stopping the engine enforcedly. When an engine key switch assumes ON position, the fuel cut valve is energized to assume the opened position.When the engine key switch is turned to OFF position, the fuel cut valve is deenergized to assume the closed position and thus the engine is stopped.

Japanese Patent First Provisional Publication 57-18433 shows a diagnostic system incorporated with such engine control system for diagnosing the fuel injection control. That is, when the diagnostic system finds an abnormal condition of the fuel injection control, the fuel cut valve is turned to the closed position to stop the engine.

For reliably carrying out both the abovementioned fuel injection quantity control and the fuel cut control, there has been proposed usage of a so-called "dual-CPU type microcomputer" as a main element of the control system. That is, in this control system, the quantity of fuel injected by the fuel injection pump (that is, operation of the electronic governor) is controlled by a main-CPU and the fuel cut effected by the fuel cut valve is controlled by a sub-CPU.

However, hitherto, the work sharing between the main-CPU and the sub-CPU has not been given satisfactory thought. In fact, when the sub-CPU fails to operate normally, it tends to occur that due to absence of stable outputs to the fuel cut valve from the sub-CPU, the fuel cut valve is turned to the closed position. In this case, the engine is forced to stop even though the main-CPU is kept in a condition satisfied for controlling the engine.

It would therefore be desirable to be able to provide a dual-CPU type microcomputer installed control system for a diesel engine, which is free of the abovementioned drawback.

According to the present invention, there is provided a dual-CPU type microcomputer installed control system for a diesel engine, which, in addition to the normal fuel cut control processed by the sub-CPU, can keep the fuel cut valve in its opened position when the sub-CPU fails to operate normally. With this, the above-mentioned undesired engine stop is suppressed.

In accordance with a first aspect of the present invention, there is provided a control system for controlling a diesel engine which has a fuel cut valve in a fuel supply line led to a fuel injection pump. The control system comprises a main-CPU for controlling the quantity of fuel injected by the fuel injection pump in accordance with an operation condition of the diesel engine; a sub-CPU for controlling the fuel cut valve, the sub-CPU having a plurality of output ports; first means possessed by the sub CPU, the first means issuing a request for stopping fuel supply to the fuel injection pump when at least the fuel injection quantity control carried out by the main-CPU is found to be abnormal; second means possessed by the sub-CPU, the second means feeding each of the plurality of output ports of the sub-CPU with an instruction signal representing presence/absence of the request; and a logic circuit operatively interposed between the output ports of the sub CPU and the fuel cut valve, the logic circuit operating the fuel cut valve in a manner to stop the fuel supply to the fuel injection pump from the fuel cut valve only when all of the instruction signals fed thereto from the plurality of output ports of the sub-CPU represent presence of the request.

In accordance with a second aspect of the present invention, there is provided a control system for controlling a diesel engine which has an electrically actuated fuel cut valve in a fuel supply line led to a distributor injection pump.

The control system comprises a main-CPU for controlling the quantity of fuel injected by the injection pump in accordance with an operation condition of the diesel engine; a sub-CPU for controlling the fuel cut valve, the sub-CPU having three output ports; first means possessed by the sub-CPU, the first means issuing a request for stopping fuel supply to the injection pump when an engine key switch is turned to OFF position, or when the fuel injection quantity control made by the main-CPU is found to be abnormal or when any diagnosis processed by the sub-CPU finds any abnormal condition of the engine; second means possessed by the sub-CPU, the second means feeding the three output ports of the sub-CPU with respective instruction signals which represent presence/absence of the request; and a logic circuit operatively disposed between the output ports of the sub-CPU and an electric actuator of the fuel cut valve, the logic circuit operating the fuel cut valve in a manner to stop the fuel supply to the distributor injection pump from the fuel cut valve only when all of the injection signals fed thereto from the three output ports represent presence of the request.

Preferred features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view of a diesel engine to which a control system accw'dThg to the present invention is practically applied; Fig. 2 is a sectional view of a distributor injection pump which is controlled by the control system; Fig. 3 is a graph showing a fuel injection characteristic of the distributor injection pump with respect to engine rotation speed and throttle valve angle; Fig. 4 is a schematically illustrated control circuit of the control system; Fig. 5 is a flowchart of programmed operation steps of 4ms-job, which are processed by a sub CPU installed in the control circuit of Fig. 4; ; Fig. 6 is a flowchart of programmed operation steps of 10ms-job, which are also processed by the sub-CPU; and Fig. 7 is a flowchart of programmed operation steps of background-job, which are also processed by the sub-CPU.

Referring to Fig. 1 of the drawings, there is shown a diesel engine 1 to which the present invention is practically applied.

A distributor injection pump 4 is driven by a crankshaft 2 of the engine 1 through a timing pulley-and-belt mechanism 3. Four high-pressure pipes 5 extend from the pump 4 to four fuel injection nozzles 6 whose tips are exposed to respective combustion chambers of the engine 1.

Referring to Fig. 2, there is shown the detailed of the distributor injection pump 4. A drive shaft 10 driven by the engine 1 drives a feed pump 11 to introduce fuel into a pump housing 12 from a fuel tank (not shown).

Coaxially connected to the drive shaft 10 is an axially movable plunger 14 which has a cam disc 13 coaxially disposed on one end portion thereof. The other end portion of the plunger 14 is slidably received in a cylinder 15 to bring about a high pressure pumping action, in such a manner as will become apparent hereinafter. The cam disc 13 is formed on its front surface with a plurality of equally spaced cams. Concentrically and spacedly disposed about the junction portion between the drive shaft 10 and the plunger 14 is a roller holder 17 which holds a plurality of rollers which contact with the cam-provided front surface of the cam disc 13. The angular position of the roller holder 17 can be adjusted by a timer piston 16. The number of the rollers corresponds to the number of the cylinders of the associated engine 1.Thus, when, due to rotation of the drive shaft 10, the cam disc 13 rotates together with plunger 14, the cams of the cam disc 13 ride over the rollers one after another thereby inducing reciprocating movements of the plunger 14 in the cylinder 15. That is, when the drive disc 10 makes one turn, the plunger 14 is reciprocated by the number of the cams of the cam disc 13 while making one turn about its axis When, upon intake stroke, the plunger 14 is moved leftward in Fig. 2, the fuel in the pump housing 12 is led into a pumping chamber 20 of the cylinder 15 through an intake port 18 of the cylinder 15 and an intake groove 19 of the plunger 14.When thereafter, upon compression stroke, the plunger 14 is moved rightward, the fuel in the pumping chamber 20 is compressed and led to one of the high pressure pipes 5 and to the associated fuel injection nozzle 6 through a distribution groove 21 of the plunger 14, one of outlet ports 22 of the cylinder 15, and a delivery valve 23.

Slidably disposed about a middle portion of the plunger 14 is a control sleeve 24. When cutoff ports 25 of the plunger 14, which communicate with the pumping chamber 20, are drawn from the control sleeve 24, the fuel in the pumping chamber 20 is drained through the cut-off ports 25, thereby to induce termination of fuel injection. Thus, by changing the position of the control sleeve 24 with work of an electronic governor 26, the termination of the fuel injection, that is, the quantity of fuel injection, can be controlled.

The electronic governor 26 is of a step motor type. An output rod 27 of the step motor has at its leading end an eccentric projection 28 which is pivotally engaged with a groove formed on an outer surface of the control sleeve 24. Thus, when the output rod 27 is rotated about its axis, the control sleeve 24 is slid axially on the plunger 14, thereby changing its position relative to the plunger 14.

In the intake port 18, there is installed a fuel cut valve (FCV) 29 of electromagnetic type.

When energized, the valve 29 opens the intake port 18, and when deenergized, the valve 29 closes the intake port 18. Thus, when the fuel cut valve 29 is deenergized, the fuel supply to the pumping chamber 20 is suppressed and thus the engine is stopped enforcedly.

Now, it is to be noted that the electronic governor 26 and the fuel cut valve 29 are controlled by a control unit 30 as is shown in Fig. 1.

The electronic governor 26 is controlled in accordance with both engine rotation speed "NE" detected by an engine rotation speed sensor 31 and throttle valve angle "ACC" detected by a throttle valve angle sensor 32. More specifically, based on the detected engine rotation speed "NE" and the detected throttle valve angle "ACC", the position of the control sleeve 24 is adjusted by the electronic governor 26 so that the injection pump 4 can exhibit such a fuel injection characteristic as depicted by the graph of Fig. 3. A servo-control is used for adjusting the position of the control sleeve 24.

Thus, for detecting the existing position of the control sleeve 24, a position sensor 33 is employed which issues a signal (CSP) representative of the position of the control sleeve 24.

When an engine key switch is turned to ON position, the fuel cut valve 29 is energized to open the fuel intake port 18 of the injection pump 4. When the engine key switch is turned to OFF position, the fuel cut valve 29 is deenergized to close the intake port 18.

Furthermore, as will become apparent hereinafter, when a diagnostic system finds an abnormal condition of the fuel injection quantity control effected by the electronic governor 26, the fuel cut valve 29 is deenergized to stop fuel supply to the pumping chamber 20 of the injection pump 4.

Fig. 4 shows the detail of the control unit 30. The control unit 30 comprises a main-CPU 51 and a sub-CPU 52 which are connected through a communication line 53 to obtain a serial communication. Although not shown in the drawing, the main-CPU 51 and the sub-CPU 52 are each equipped with a runaway monitoring circuit.

The runaway monitoring circuit monitors the program-run signal and resets the CPU 51 or 52 when a runaway occurs.

The main-CPU 51 has a certain software incorporated therewith for controlling the quantity of fuel injected from the injection pump 4 in accordance with the operation condition of the engine 1. That is, in accordance with the engine rotation speed "NE", the throttle valve angle "ACC", the control sleeve position "CSP" and the like, the electronic governor 26 is controlled to adjust the position of the control sleeve 24, that is, to adjust the quantity of fuel injected from the injection pump 4.

In addition to the above-mentioned software, a software for diagnosing the engine rotation speed sensor 31, a software for diagnosing the throttle valve angle sensor 32, and a software for diagnosing the sub-CPU 52 are incorporated with the main-CPU 51.

The sub-CPU 52 has a certain software incorporated therewith for controlling the fuel cut valve 29 in an after-mentioned manner.

Furthermore, a software for diagnosing the servocontrol of the electronic governor 26, a software for diagnosing the control sleeve position sensor 33, and a software for diagnosing the main CPU 51 are incorporated with the sub-CPU 52.

As is understood from the circuit of Fig. 4, the sub-CPU 52 is formed with first, second, and third output ports P1, P2, and P3 for controlling the fuel cut valve 29.

As is seen from the drawing, signals from the first, second,and third output ports P1, P2,and P3 are fed to a NAND circuit 55, which is a logic circuit. An inverter 54 (viz., NOT circuit) is interposed between the second output port P2 and the NAND circuit 55. The first and third output ports P1 and P3 are earthed through respective pull-down resistors R1 and R3, and the second output port P2 is connected to a constant voltage power source "Vcc" through a pull-up resistor R2.

An output terminal of the NAND circuit 55 is connected to a base terminal of anNPN transistor Trl. A collector terminal of the transistor Trl is connected to a base terminal of a PNP transistor T2r. An emitter terminal of the NPN transistor Trl is earthed.

An emitter terminal of the PNP transistor Tr2 is connected through a resistor R4 to a battery power source "VB", and a collector terminal of the PNP transistor Tr2 is connected to one end of a solenoid of the fuel cut valve 29. The other end of the solenoid is earthed. Although not shown in the drawing, a shutter circuit is employed which shuts off the power source "VB" when the engine key switch is turned to OFF position.

Accordingly, only when the first, second, and third output ports P1, P2,and P3 of the sub-CPU 52 assume respectively H-level, L-level and H- level, the output of the NAND circuit 55 assumes L-level causing OFF condition of the NPN transistor Trl and OFF condition of the PNP transistor Tr2. It is to be noted that, due to provision of the inverter 54, the L-level signal from the second output port P2 is converted to Hlevel signal before being fed to the NAND circuit 55. Thus, the fuel cut valve 29 is deenergized to assume the closed position, thereby effecting a fuel cut, and thus the engine 1 is stopped.

Figs. 5, 6,and 7 show respective flowcharts of programmed operation steps of 4ms-job, lOmsjob, and background-job which are carried out by the sub-CPU 52.

The 4ms-job will be described in detail with reference to the flowchart of Fig. 5.

At step S11, a predetermined diagnosis is carried out. That is, one of the above-mentioned three diagnoses (that is, the diagnosis for the servo-control of the electronic governor 16, the diagnosis for the control sleeve position sensor 33, or the diagnosis for the main-CPU 51) is carried out by the sub-CPU 52 as the 4ms-job. In fact, the three diagnoses are suitably shared to the 4ms/job, the 10ms-job,and the background-job.

For example, in case for diagnosing the electronic governor 26, a difference between a target position of the control sleeve 24 and an existing position of the same, detected by the control sleeve position sensor 33, is monitored.

When the monitored difference is kept great for a certain time, an"NG" flag is set and stored in a memory judging that the electronic governor 26 has made an abnormal operation. While, in case for diagnosing the control sleeve position sensor 33, the voltage value of a signal issued from the sensor 33 is monitored. When the monitored voltage value becomes beyond a predetermined range, an"NG" flag is set and stored in a memory judging that the sensor 33 has made an abnormal operation. While, in case for diagnosing the main-CPU 51, the condition of a reset signal output terminal of the runaway monitoring circuit of the main-CPU 51 is monitored. When the reset signal is issued, an"NG" flag is set and stored in a memory judging that the main-CPU 51 has made an abnormal operation.

For ease of understanding, let us suppose that step S11 carries out the diagnosis for the servo-control of the electronic governor 16.

Thus, if, as a result of the diagnosis, an abnormal operation of the electronic governor 16 is found, anNG-flag is set and stored in a memory.

At step S12 of the flowchart of Fig. 5, a judgment is carried out as to whether a request for energizing the fuel cut valve 29 (which will be referred to as "FCV-ON request" hereinafter) has been issued or not in the lOms-job (step S25 or S26) of the flowchart of Fig. 6. It is to be noted that a request for deenergizing the fuel cut valve 29 (which will be referred to as "FCV OFF request hereinafter) corresponds to a request for fuel cut (which will be referred to as fuel cut request" hereinafter).

If the FCV-ON request has been issued in the 10ms-job, the operation flow goes to step S13 to cause the first output port P1 to assume L-level.

While, if the FCV-ON request has not been issued, that is, if the FCV-OFF request has been issued in the 10ms-job, the operation flow goes to step S14 to cause the first output port P1 to assume H-level.

The 10ms-job will be described in detail with reference to the flowchart of Fig. 6.

At step S21, one of the above-mentioned three diagnoses is carried out. For ease of understanding, let us suppose that step S21 carries out the diagnosis for the control sleeve position sensor 33. If, as a result of the diagnosis, an abnormal operation of the sensor 33 is found, anNG-flag is set and stored in a memory.

At step S22, a judgment is carried out as to whether an engine key switch takes OFF position or not. It YES, that is, when the engine key switch takes OFF position, the operation flow goes to step S25 to issue FCV-OFF request (that is, fuel cut request). If NO at step S22, that is, when the engine key switch keeps ON position, the operation flow goes to step S23. At this step, a judgment is carried out as to whether or not FCV-OFF request is issued by the main-CPU 51 as a result of diagnosing the rotation speed sensor 31 and the throttle valve angle sensor 32.

If YES, that is, when FCV-OFF request is issued by the main-CPU 51, the operation flow goes to step S25 for issuing the fuel cut request. If NO at step S23, that is, when FCV-OFF request is not issued by the main-CPU 51, the operation flow goes to step S24. At this step, a judgment is carried out as to whether or not any NG flag has been set and stored in either one of the 4ms-job of Fig. 5 (at step S11), the lOms-job of Fig. 6 (at step S21), and the background-job of Fig. 7 (at step S31). If YES, that is, when any NG flag is found in any one of the memories of the three jobs, the operation flow goes to step S25 for issuing the fuel cut request. If NO at step S24, that is, when no NG flag is not found, the operation flow goes to step S26 to issue FCV-ON request (that is, fuel supply request). At step S27, a judgment is carried out as to whether FCV ON request (that is, fuel supply request) has been issued or not. If YES, that is, when the FCV-ON request (viz., fuel supply request) has been issued1 the operation flow goes to step S28 to cause the second output port P2 to assume Hlevel. While, if NO at step S27, that is, when FCV-OFF request (viz., fuel cut request) has been issued, the operation flow goes to step S29 to cause the second output port P2 to assume Llevel.

The background-job of Fig. 7 will be described in detail with reference to the flowchart of Fig. 7.

At step S31, one of the above-mentioned three diagnoses is carried out. For ease of understanding, let us suppose that the step S31 carries out the diagnosis for the main-CPU 51.

Thus, if, as a result of the diagnosis, an abnormal operation of the main-CPU 51 is found, an NG-flag is set and stored in a memory.

At step S32, a judgment is carried out as to whether FCV-ON request (viz., fuel supply request) has been issued or not at step S25 or S26 of the 10ms-job of Fig. 6. If YES, that is, when the FCV-ON request has been issued in the 10ms-job, the operation flow goes to step S33 to cause the third output port P3 to assume L-level.

While if NO, that is, when FCV-OFF request (viz., fuel cut request) has been issued in the lOms- job, the operation flow goes to step S34 to cause the third output port P3 to assume H-level.

When the engine 1 is under normal condition, FCV-ON request (viz., fuel supply request) is issued at step S26 of the 10ms-job of Fig. 6.

In this case, at step S13 of the 4ms-job of Fig. 5, the first output port P1 of the sub-CPU 52 is forced to assume L-level, and at step S28 of the lOms-job of Fig. 6, the second output port P2 is forced to assume H-level, and at step S33 of the background-job of Fig. 7, the third output port P3 is forced to assume L-level.

Accordingly, the output of the NAND circuit 55 of the control circuit of Fig. 4 assumes Hlevel. Thus, the NPN transistor Trl assumes ON condition and thus also the PNP transistor Tr2 assumes ON condition. With this, the fuel cut valve 29 is energized to assume the opened position, so that the engine 1 continues the normal operation.

However if the engine key switch is turned OFF, or if fuel cut request has been requested by the main-CPU 51 as a result of diagnosing the rotation speed sensor 31 and the throttle valve angle sensor 32, or if anNG flag has been set in either one of the 4ms-job, the lOms-job, and the background-job, FCV-OFF request (viz., fuel cut request) is issued at step S25 of the 10ms-job of Fig. 6. This means that FCV-ON request (viz., fuel supply request) is not issued in the lOms- job of Fig. 6.

In this case, at step S14 of the 4ms-job of Fig. 5, the first output port P1 of the sub-CPU 52 is forced to assume H-level, and at step S29 of the 10ms-job of Fig. 6, the second output port P2 is forced to assume L-level, and at step S34 of the background-job of fig. 7, the third output port P3 is forced to assume H-level.

Accordingly, the output of the NAND circuit 55 of the control circuit of Fig. 4 assumes Llevel. Thus, both the NPN transistor Trl and the PNP transistor Tr2 assume OFF condition, so that the fuel cut valve 29 is deenergized to assume the closed position. Thus, fuel cut is effected and thus the engine 1 is enforcedly stopped.

If the sub-CPU 52 fails to operate normally, the output levels of the first, second, and third output ports P1, P2, and P3 become unstable.

However, since, due to the nature of the NAND circuit 55, the output of the same does not assume L-level so long as the first, second, and third output ports P1, P2, and P3 of the sub-CPU 52 do not assume H-level, L-level,and H-level respectively, the fuel cut valve 29 keeps the opened position. That is, L-level of the output of the NAND circuit 55, which induces the fuel cut, is established only when the first, second, and third output ports P1, P2, and P3 assume the H-, L-, and H-levels respectively. More specifically, the output of the NAND circuit 55 almost always establishes H-level when the sub CPU 52 fails to operate normally. With H-level assumed by the output of the NAND circuit 55, the NPN transistor Trl and the PNP transistor Tr2 assume ON condition. Thus, even under such an abnormal condition of the sub-CPU 52, the engine 1 can operate without stopping under control of the main-CPU 51.

When the sub-CPU 52 is subjected to a reset, the first, second, and third output ports P1, P2, and P3 assume a high impedance condition.

In this case, the output of the NAND circuit 55 shows H-level due to presence of the three resistors R1, R2, and R3 associated with the first, second,and third output ports P1, P2,and P3. That is, in such case, due to the pull-down resistors R1 and R3 and the pull-up resistor R2, all signals fed to the three input ports of the NAND circuit 55 are forced to assume L-level, and thus the output of the NAND circuit 55 shows Hlevel. Thus, even if the sub-CPU 52 is subjected to a reset, the engine can operate without stopping under control of the main-CPU 51.

Claims

Claims:

1. A control system tor a diesel engine having a fuel cut valve in a fuel supply line to a fuel injection pump, the control system comprising: a main-CPU for controlling the quantity of fuel injected by said fuel injection pump in accordance with an operation condition of said diesel engine; a sub-CPU for controlling the fuel cut valve, said sub-CPU having a plurality of output ports; first means possessed by said sub-CPU, said first means issuing a request for stopping fuel supply to said fuel injection pump when at least the fuel injection quantity control carried out by said main-CPU is found to be abnormal; second means possessed by said sub-CPU, said second means feeding each of the plurality of output ports of said sub-CPU with an instruction signal representing presence/absence of said request; and a logic circuit operatively interposed between said output ports of said sub-CPU and said fuel cut valve, said logic circuit operating said fuel cut valve in a manner to stop the fuel supply to said fuel injection pump from said fuel cut valve only when all of the instruction signals fed thereto from the plurality of output ports of said sub-CPU represent presence of said request.

2. A control system as claimed in Claim 1, in which the instruction signals fed by said second means to the plurality of output ports of said sub-CPU are produced by respective programmed jobs having different execution timings.

3. A control system as claimed in Claim t or 2, in which at least one of the instruction signals fed to said plurality of output ports by said second means has a characteristic, on presence/absence of said request, opposite to that of the remaining instruction signals.

4. A control system as claimed in Claim 3, further comprising an inverter which converts the characteristic of the selected instruction signal to that of the remaining instruction signals before the selected instruction signal is fed to said logic circuit.

5. A control system as claimed in any preceding claim, in which the number of the output ports of said sub CPU is three.

6. A control system as claimed in any preceding claim, in which said first means issues said request when an engine key switch is turned to OFF position and/or when any diagnosis controlled by said sub CPU finds any abnormal condition of the engine.

7. A control system as claimed in any preceding claim, in which said fuel injection quantity control processed by said main-CPU is based on engine rotation speed, throttle valve angle, and position of a control sleeve installed in the fuel injection pump.

8. A control system as claimed in Claim 7, in which said main-CPU further processes a diagnosis for diagnosing an engine rotation speed sensor, a diagnosis for diagnosing a throttle valve angle sensor, and a diagnosis for diagnosing the operation of said sub-CPU.

9. A control system as claimed in Claim 8, in which said sub-CPU further processes a diagnosis for diagnosing a servo-control of an electronic governor included in said fuel injection pump, a diagnosis for diagnosing a sensor for sensing the position of said control sleeve, and a diagnosis for diagnosing the operation of said main-CPU.

10. A control system for a diesel engine having an electrically actuated fuel cut valve in a fuel supply line to a distributor injection plump, the control system comprising: a main-CPU for controlling the quantity of fuel injected by said injection pump in accordance with an operation condition of said diesel engine; a sub-CPU for controlling the fuel cut valve, said sub-CPU having three output ports; first means possessed by said sub-CPU, said first means issuing a request for stopping fuel supply to said injection pump when an engine key switch is turned to OFF position, or when the fuel injection quantity control made by said main-CPU is found to be abnormal, or when any diagnosis processed by said sub-CPU finds any abnormal condition of the engine;; second means possessed by said sub-CPU, said second means feeding the three output ports of said sub-CPU with respective instruction signals which represent presence/absence of said request; and a logic circuit operatively disposed between said output ports of said sub-CPU and an electric actuator of said fuel cut valve, said logic circuit operating said fuel cut valve in a manner to stop the fuel supply to said distributor injection pump from said fuel cut valve only when all of the injection signals fed thereto from said three output ports represent presence of said request.

11. A control system as claimed in Claim 10, further comprising an inverter which is interposed between one of said three output ports of said sub-CPU and one of three input ports possessed by said logic circuit.

12. A control system substantially as described with reference to, and as shown in, the accompanying drawings.