GB2293897A

GB2293897A - Fuel injection control system

Info

Publication number: GB2293897A
Application number: GB9520532A
Authority: GB
Inventors: Hirotada Muraki; Masayuki Ohki; Kazuhiro Ishigami
Original assignee: Nissan Motor Co Ltd
Current assignee: Nissan Motor Co Ltd
Priority date: 1994-10-06
Filing date: 1995-10-04
Publication date: 1996-04-10
Anticipated expiration: 2015-10-04
Also published as: GB2293897B; GB9520532D0; JPH08105349A

Abstract

In a diesel engine fuel injection quantity control system having redundant engine speed sensors 31, 33, a first engine revolution speed sensor 31 is installed at the crankshaft side, to detect a first speed value N1, and a second engine revolution speed signal 33 is installed at the injection pump side to detect a second speed value N2. If the ratio of N2 to N1 falls outside a predetermined range, one of the sensors 31, 33 is determined as malfunctioning. In this event, the speed value N1 or N2 which is larger is deemed to indicate the correct engine revolution speed and is used to calculate the fuel injection quantity. The method of detecting sensor malfunction is disclosed in detail (See Figures 4 and 5). <IMAGE>

Description

FUEL INJECTION QUANTITY CONTROLLING APPARATUS AND METHOD FOR DIESEL ENGINE WITH FAIL-SAFE STRUCTURE The present invention relates to a fuel injection quantity controlling apparatus and method for a Diesel engine, having a fail-safe structure against a failure in an engine revolution speed sensor.

Japanese Patent Application First Publication (unexamined) No. Showa 57-18433 (published on January 30, 1992) exemplifies a previously proposed engine control apparatus in which using an engine revolution speed sensor (so-called, crank angle sensor) which outputs a pulse train signal whenever an engine crankshaft has revolved through a predetermined angle.

specifically, an engine revolution speed sensor of an electromagnetic pickup type which is disposed so as to face against gear tooth-shaped circular plate which is revolved in synchronization with a revolution of the engine crankshaft is used, the engine revolution speed is determined according to the pulse train signal output from the engine revolution speed sensor, and various types of engine controls such as a fuel injection quantity control are carried out on the basis of the determined engine revolution speed. Hence, if the engine revolution speed sensor fails, it becomes difficult to perform an appropriate control of the fuel injection quantity. Then, such a fail-safe structure as described below is adopted.That is to say, for example, in a case where a detected value of the engine revolution speed is out of a predetermined range at a time wherein a lubricating oil temperature of the engine or a fuel temperature within a fuel injection pump has reached to a predetermined value, the failure in the engine revolution speed sensor is determined to occur. During the occurrence of failure in the engine revolution speed, the engine has stopped.

However, the above-described fail-safe structure is concentrated into a countermeasure against a perfect failure of the engine revolution speed sensor such as a line breakage in the engine revolution speed sensor. The above-described fail-safe structure cannot detect and cannot cope with an intermittent failure in the engine revolution speed sensor. The intermittent failure is, specifically, defined as a jump of reading any one of the gear tooth of the circular disc described above so that the pulse train signal has a defect in a pulse (or pulses) (since the engine revolution speed is detected according to a number of pulses per unit of time in the pulse train signal).

In addition, if the engine is stopped whenever the failure in the engine revolution speed sensor occurs, the vehicle in which the above-described engine is mounted cannot run to reach to some repairing site.

Although, to cope with the failure of the engine revolution speed sensor, at least two of such an engine revolution speed sensor as described above are adopted as a dual system. In the dual system, one of the engine revolution speed sensors has failed perfectly due to its line breakage, the perfect failure is detected and the control of the engine is continued on the basis of a signal derived from the other of the engine revolution speed sensors. However, in such a dual system as described above, in a case where the intermittent failure of either one of the engine revolution speed sensors occurs, output signals from both of the engine revolution speed sensors are simply compared with each other.

However, this simple comparison cannot determine (identify) which of the engine revolution sensors has intermittently failed. In the last analysis, there is no remedy except to stop the engine.

It would therefore be desirable to be able to provide a fuel injection quantity controlling apparatus and method for a Diesel engine in which such an intermittent failure in an engine revolution speed sensor as described ~~~~~~~~~~~~~~~~~~~~~ above can be detected and a vehicle in which the Diesel engine to which the present invention is applicable is mounted can continue to run within a safe range.

According to one aspect of the present invention, there is provided a fuel injection quantity controlling apparatus for a Diesel engine, comprising: a) a first engine revolution speed sensor which is so arranged and constructed as to detect a first engine revolution speed of the Diesel engine and as to generate and output a first engine revolution speed signal indicative of the engine revolution speed; b) a second engine revolution speed sensor which is so arranged and constructed as to detect a second engine revolution speed of the Diesel engine and as to generate and output a second engine revolution speed signal indicative of the engine revolution speed. said second engine revolution speed sensor being separately and independently arranged from said first engine revolution speed sensor; c) abnormality determining means for comparing both of the detected first and second engine revolution speed signals with each other and determining a presence or absence in a malfunction of at least either one of said first and second revolution speed signals on the basis of a result of comparison thereof; d) engine revolution speed signal selecting means for estimating either one of the first or second engine revolution speed signals which indicates a value higher than that of the other as being functioning properly and estimating the other of the first or second engine revolution speed signals which indicates a value lower than that of the one of either the first or second engine revolution speed signal as malfunctioning improperly when said abnormality determining means determines that the presence in malfunction of at least either one of the first or second revolution speed signal; and e) fuel injection quantity determining means for determining a fuel injection quantity supplied to the Diesel engine on the basis of either one of the first or second engine revolution speed signal which is estimated to function properly by said engine revolution speed signal selecting means.

According to another aspect of the present invention, there is provided a fuel injection quantity controlling method for a Diesel engine, comprising the steps of: a) generating and outputting a first engine revolution speed signal indicative of the Diesel engine revolution speed from a first engine revolution speed sensor; b) generating and outputting a second engine revolution speed signal indicative of the Diesel engine revolution speed from a second engine revolution speed sensor substantially at the same time as the step a). said second engine revolution speed sensor being separately and independently arranged from said first engine revolution speed sensor; c) comparing both of the detected first and second engine revolution speed signals with each other and determining a presence or absence in a malfunction of at least either one of said first and second revolution speed signals on the basis of a result of comparison at said step c); d) estimating either one of the first or second engine revolution speed signals which indicates a value higher than that of the other as being functioning properly and estimating the other of the first or second engine revolution speed signals which indicates a value lower than that of the one of either the first or second engine revolution speed signal as malfunctioning improperly when the presence in malfunction of at least either one of the first or second revolution speed signal is determined at said step c); e) detecting an opening angle of an engine accelerator; and f) calculating a fuel injection quantity supplied to the Diesel engine on the basis of the engine accelerator opening angle detected at said step e) and either one of the first or second engine revolution speed signal which is estimated to function properly at said step d).

BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1A is a circuit block diagram of a preferred embodiment of a fuel injection quantity controlling apparatus for a Diesel engine according to the present invention.

Fig. 1B is an internal circuit block diagram of a control unit 29 shown in Fig. 1A.

Fig. 2 is a cross sectional view of a fuel injection pump 4 of the Diesel engine shown in Fig. 1A.

Fig. 3 is a control characteristic graph of a fuel injection quantity with respect to an opening angle of an accelerator and engine revolution speed used in the preferred embodiment shown in Figs. 1A and 1B.

Fig. 4 and Fig. 5 are integrally an operational flowchart for determining a failure in either of engine revolution speed sensors shown in Fig. 1A executed in the control unit shown in Figs. 1A and 1B.

Fig. 6 is an operational flowchart for calculating a fuel injection quantity executed in the control unit shown in Figs. 1A and 1B.

Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention.

Fig. 1 shows a system configuration of a preferred embodiment of a fuel injection quantity controlling apparatus for a Diesel engine according to the present invention.

A distribution-type fuel injection pump 4 is installed which is driven by means of a crankshaft 3 of a Diesel engine 1 via a timing pulley/belt mechanism 3. A highly pressurized fuel is distributed under a pressure into a fuel injection nozzle 6 of each cylinder via an inner highly pressurized pipe 5.

Fig. 2 shows an expanded cross-sectional view of the distribution-type fuel injection pump 4 shown in Fig. 1A.

A rotating axle 10 driven (hereinafter, referred to as a driven axle) by means of the engine 1 drives a feed pump 11 so that fuel is sucked into a pump housing 12 from a fuel tank (not shown).

A plunger 14 having a cam disc 13 is disposed in the pump housing 12 so as to be coaxial with the driven axle 10, the cam disc 13 being linked to the driven axle 10 so as to be enabled to move relatively to the driven axle 10 in its axial direction and the plunger 14 being reciprocated within a cylinder 15 so as to carry out a high pressure pumping action.

A plurality of cams whose number corresponds to a number of engine cylinders are formed on a flange surface of the cam disc 13 having equally spatial distances with one another thereon. The plurality of cams are contacted with a roller held by means of a roller holder 17, the roller position being adjustable by means of a timer piston 16. Whenever the cams ride over the roller due to the revolution of the cam disc 13, the plunger 14 is axially moved. Hence, the plunger 14 is revolving coaxially with the driven axle 10, reciprocating by the number of cams per unit of revolution.

As shown in Fig. 2, in a case where the plunger 14 is in a suck phase moved in a left-handed direction as viewed from Fig. 2, the fuel within the pump housing 12 is sucked into a pumping chamber 20 from a suction port 18 at the cylinder 15 via a suction groove 19. When the plunger 14 is transferred to a pressurized feed phase (the plunger 14 is moved in a right-handed direction as viewed from Fig. 2), the fuel within the pumping chamber 20 is compressed so as to be introduced into one of a plurality of drain ports 22 at the cylinder 15 from a distribution groove 21 of the plunger 14. Then, the fuel is pressurized and supplied to the fuel injection nozzle 6 from a supply valve 23 via the inner highly pressurized distribution pipe 5.

A control sleeve 24 is slidably fitted into a part of the plunger 14 which is outside of the cylinder 15. When a cut-off port 25 of the plunger 14 is exposed externally from an inner peripheral surface of the control sleeve 24, the fuel within the pumping chamber 20 is leaked from the cut-off port 25 so that the fuel injection is ended. An electronic governor 26 permits a positional adjustment of the control sleeve 24 to control the end of fuel injection, namely, the fuel injection quantity.

The electronic governor 26 shown in Fig. 2 is a stepping motor type, an engagement projection 28 formed eccentrically on a tip of an output rod 27 being engaged with an engagement groove located on an outer periphery of the control sleeve 24. The governor 26 controls the pivotal position of the output rod 27 so that the axial position of the control sleeve 24 can be controlled.

The electronic governor 26 is electrically controlled according to a signal derived from a control unit 29 (refer to Figs. 1A and 1B). The governor 26 controls the position of the control sleeve 24 according to the engine revolution speed of the Diesel engine 1 and accelerator opening angle so as to obtain a fuel injection quantity characteristic as shown in Fig. 3.

In the embodiment, a signal disc plate 30 is attached around an outer peripheral surface of the crankshaft 2, as shown in Fig. 1A, in order to detect the engine revolution speed. The signal plate 30 has its outer peripheral end on which a plurality of teeth are inscribed so as to produce a pulse train signal. A first engine revolution speed sensor 31 of an electromagnetic pickup type is installed so as to face against the tooth portion of the outer peripheral surface of the signal plate 30. Hence, the first revolution speed sensor 31 produces the pulse train signal whose pulse is output whenever the engine crankshaft 2 is revolved through a predetermined angle (predetermined crank angle) so that the engine revolution speed can be detected according to a period of the pulse train signal (or the number of pulses per predetermined period of time).

In addition, as appreciated from Figs. 1A and 2, another signal plate 32 having the same structure as the signal plate 30 is attached around an outer peripheral surface of the driven axle 10 of the fuel injection pump 4. A second revolution speed sensor 33 of the same electromagnetic type is disposed so as to face against the signal plate 30. Hence, a pulse signal is generated from the second engine revolution speed sensor 33 whenever the driven axle 10 of the fuel injection pump 4 so that the engine revolution speed can be detected according to the period of the pulse signal (or the number of pulses per predetermined time).

The pulse signals derived from both of the first and second engine revolution speed sensors 31 and 33 are received by a control unit 29 together with a signal derived from an accelerator opening angle sensor 34 indicating an opening angle of an accelerator of the Diesel engine. It is noted that an accelerator to which the accelerator opening angle sensor 34 is usually linked to the electronic governor 26.

The control unit 29, as shown in Fig. 1B, includes a microcomputer having an output interface, a memory, a CPU, an input interface, and a common bus.

The control unit 29 detects the engine revolution speed on the basis of the pulse signals from both of the first and second engine revolution speed sensors 31 and 33 as will be described later, detects the accelerator opening angle from the signal from the accelerator opening angle sensor 34, and performs the control over the electronic governor 26 on the basis of the detected engine revolution speed and opening angle of the accelerator.

An engine check (warning) lamp 35 is connected to the control unit 29 to inform a vehicular driver (operator of the Diesel engine) of an abnormal condition in the Diesel engine as will be described later.

A fuel cut-off valve 36 used to stop the engine 1 is installed in a suction port 18 so as to close the port 18 to halt the fuel supply to the engine 1.

Figs. 4 and 5 are, integrally,aflowchart of detecting a malfunction of the signals from the engine revolution speed sensors 31 and 33 and fail-safe operation of the Diesel engine. Fig. 6 is a flowchart for explaining a calculation of the fuel injection quantity when either of the signals of the engine revolution speed sensors 31 and 33 has malfunctioned.

Figs. 4 and 5 are integrally a flowchart indicating an abnormality determination routine for either of the output pulse train signals from the first or second engine revolution speed sensor 31 and 33.

The routine shown in Figs. 4 and 5 is executed for each predetermined time interval (aT milliseconds).

At a step S1, the microcomputer (control unit 29, hereinafter simply referred to as the CPU) detects (determines) the first engine revolution speed N1 on the basis of the pulse train signal from the first engine revolution speed sensor 31 (located at the engine side,i.e., crankshaft side).

At a step 52, the CPU detects (determines) the second engine revolution speed N2 on the basis of the pulse train signal from the second engine revolution speed sensor 33 (located at the engine driven side, i.e., fuel injection pump side).

At a step S3, the CPU determines whether either of a first flag Nl, indicating N1 is abnormal. i.e., that the value of the N1 is false due to the malfunction of the first engine revolution speed signal,or a second flag N2,indicating N2 is abnormal, i.e., that the value of the N2 is false due to the malfunction of the second engine revolution speed signal, is set or reset.

if neither the first nor second flag is set (NO) at the step S3, the routine goes to a step S4.

At the step S4, the CPU calculates a ratio between the value of the first engine revolution speed Nl derived from the first engine revolution speed sensor 31 and that of the second engine revolution speed N2 derived from the second engine revolution speed sensor 33 as N2/N1 and compares the ratio N2/N1 with both of a predetermined abnormality determination (ratio) lower limit value RMIN (for example, 0.5) and a predetermined abnormality determination (ratio) upper limit value RMAX (for example, 1.5) so as to determine whether the ratio N2/N1 falls within a range between these upper and lower limit values RMAx and RUIN.

In a case where the condition such that RMIN s N2/N1 s R pX is satisfied (YES) at the step S4, the CPU determines that both values of the engine revolution speed values N1 and N2 are normal and the routine goes to a step S6. At the step S6, a timer TNG is cleared to zero and the routine is ended.

However, if such the condition as RMIN 5 N2/N1 s R MAX is not satisfied (NO) at the step S4, the routine goes to a step S5.

At the step S5, the CPU determines whether the value of the first engine revolution speed N1 is equal to or above a predetermined abnormality enabling revolution speed NMIN (for example, 500 R.P.M.) or whether the value of the second engine revolution speed N2 is equal to or above the predetermined abnormality enabling revolution speed NMIN (for example, 500 R.P.M.).

At the step S5, if N1 < NMIN and N2 < NMIN (NO), the routine goes to the step S6 in which the timer TNG is cleared to zero and the routine is ended since the determination of the failure in the sensor 31 or 33 is not carried out.

However, if N1 a N MIN or N2 a N MIN at the step S5 (YES), the routine goes to a step S7 in which the timer TNG value is substituted for the present timer value plus the predetermined time interval of the routine LT (T NG = TNG + hT).

At the next step S8, the CPU determines whether a value of the timer TNG is equal to or above a predetermined determination delay time STNG (for example, 500 milliseconds) (TNG a ST NAG). If the value of the timer TNG is below STNG (NO), the routine is ended. On the other hand, if the timer value TNG is equal to or above the predetermined delay time STNG at the step S8 (YES), the CPU determines either of which sensor 31 or 33 occurs failure and the routine goes to a step S9.

In detail , in the embodiment, the control unit 29 determines that either the first or second engine revolution speed sensor 31 or 33 must be abnormal according to the following three conditions: (1) An equation of RMIN s N2/N1 s R MAX is not satisfied; (2) N1 2 N MIN or N2 2 N MIN; and (3) A state in which both conditions of (1) and (2) are satisfied is continued for a period of time denoted by STNG as the predetermined determination delay time.

Next, at a step S9, the CPU compares the values of both of the first and second engine revolution speed N1 and N2 derived from the first and second engine revolution speed sensors 31 and 33 with each other.

If N1 < N2 (NO) at the step S9, the routine goes to a step S10 in which the CPU deems that the first engine revolution speed sensor 31 has failed which outputs the first engine revolution speed pulse train signal whose value is lower (smaller) than that of the second engine revolution speed pulse train signal from the second engine revolution speed sensor 33 and sets the first flag N1 ( - 1 If N2 > N1 (YES) at the step S9, the routine goes to a step S11 in which the CPU deems that the second engine revolution speed sensor 33 has failed which outputs the second engine revolution speed pulse train signal whose value is lower (smaller) than that of the first engine revolution speed pulse train signal from the first engine revolution speed sensor 33 and sets, in turn, the second flag N2.

Thereafter, the routine goes to a step S12 in which the engine check (warning) lamp 35 is turned on to inform the driver (operator of the Diesel engine) of the failure in either the sensor 31 or 33. Alternatively, the warning lamp 35 may serve to identify which of the two sensors 31 or 33 has failed.

It is noted that after the setting of either the first or second flag N1 or N2, the next routine goes from the step S3 to a step S13.

Referring to Fig. 5, the CPU calculates the ratio of N2/N1 between the first engine revolution speed N1 detected at the step S1 and the second revolution speed N2 detected at the step S2 and compares the ratio N2/N1 with both of the predetermined determination enabling lower limit RMIN (for example, 0.5) and of the predetermined upper limit RMAX (for example, 1.5) so as to determine whether the ratio falls within the range between the upper and lower limits RMAX and RMIN.

If (NO), namely, the condition of RMIN # N2/N1 c R MAX is not satisfied. either sensor 31 or 33 has continued to malfunction so that the routine goes to a step S15 in which a value of a timer TOK is cleared to zero and the present routine is ended.

On the other hand, if the condition of RMIN s N2/N1 < R MAX (YES) at the step S13, the routine goes to a step S14.

At the step S14, the CPU determines whether the first engine revolution speed N1 detected from the first engine revolution speed sensor 31 is equal to or above the predetermined determination enabling revolution speed NMIN (for example, 500 R.P.M.) and whether the second engine revolution speed N2 detected from the second engine revolution speed sensor 33 is equal to or above the predetermined determination enabling revolution speed NMIN (for example, 500 R.P.M.).

If, at the step S14, N1 < NMIN or N2 < NMIN (NO), the routine goes to the step S15 and the present routine is ended.

If N1 2 N MIN and N2 a N MIN at the step S14 (YES), the routine goes to a step S16.

At the step S16, the value of the other timer TOK is incremented by the #T (TOK = TOK + #T).

Then. the routine goes to a step S17.

At the step S17, the CPU determines whether the timer value TOK is equal to or above another predetermined determination delay time STOK (for example, one second). If TOK < STOK, the routine is ended.

If the timer value TOK is equal to or above the other predetermined determination delay time STOK (YES) at the step S17, the CPU determines that both of the first and second engine revolution speed sensors 31 and 33 have recovered to function normally and the routine goes to a step S18. At the step S18, both first and second flags N1 and N2 are reset (to " 0 That is to say, in the embodiment, after the determination that either the first or second revolution speed sensor 31 or 33 has failed, the CPU determines that both of the first and second revolution speed sensors have normally outputted the first and second engine revolution speed pulse train signals according to the following three conditions:: (1A) The equation of RMIN s N2/N1 s R MAX is satisfied; (2A) N1 a N MIN and N2 2 N MIN; and (3A) A state in which the above two conditions (1A) and (2A) are satisfied is continued for the time duration equal to or above the other predetermined determination delay time STOK.

Next, Fig. 6 shows a flowchart indicating a fuel injection quantity calculation routine with the engine revolution speed set for the control over the fuel injection pump.

At a step S21, the CPU determines whether the first flag N1 is set.

If YES at the step S21, since the first engine revolution speed sensor 31 malfunctions and the second engine revolution speed sensor 33 operates normally, the routine goes to a step S22.

At the step S22, the CPU determines that the second engine revolution speed value N2 is deemed to be the engine revolution speed N for the engine control.

On the other hand, if NO at the step S21, the routine goes to a step S23 in which the first engine revolution speed N1 detected from the first engine revolution speed sensor 31 is deemed to be the engine revolution speed N although such a case that the second flag N2 is set or not set (reset) is present.

In detail , when the first flag N1 indicates that the first engine revolution speed signal N1 is false (indicates abnormal. i.e., the first engine revolution sensor 31 malfunctions), the second engine revolution speed value N2 is used as the engine revolution speed value N since, at this time, the second engine revolution speed sensor 33 functions normally. If neither the first flag N1 nor second flag N2 is set, since both of the first and second engine revolution speed sensors 31 and 33 are normal (function normally), the first engine revolution speed value N1 derived from the first engine revolution speed sensor 31 located at the crankshaft side is used as the engine revolution speed N.

Thereafter, the routine goes to a step S24.

At the step S24, the CPU calculates the fuel injection quantity (Q) in accordance with the fuel injection characteristic shown in Fig. 3 on the basis of the engine revolution speed value N determined at either of the steps S22 or S23 and the accelerator opening angle determined from the signal from the accelerator opening angle sensor 34.

The control unit 29 outputs the control signal to the electronic governor 26 according to the determined fuel injection quantity at the step S24 so that the position of the control sleeve 24 shown in Fig. 2 is controlled so as to provide the determined fuel injection quantity.

Claims

Claims:

1. A fuel injection quantity controlling apparatus for a Diesel engine, comprising: a) a first engine revolution speed sensor which is so arranged and constructed as to detect a first engine revolution speed of the Diesel engine and as to generate and output a first engine revolution speed signal indicative of the engine revolution speed; b) a second engine revolution speed sensor which is so arranged and constructed as to detect a second engine revolution speed of the Diesel engine and as to generate and output a second engine revolution speed signal indicative of the engine revolution speed, the first and second engine revolution speed sensors being mutually separate and independent;; c) abnormality determining means for comparing the detected first and second engine revolution speed signals with each other and determining presence or absence of a malfunction of at least one of the said first and second signals on the basis of the comparison; d) engine revolution speed signal selecting means for estimating that the one of the first and second engine revolution speed signals which indicates a value higher than that indicated by the other signal is functioning properly and estimating that the other signal which indicates a value lower than that of the one signal is malfunctioning, when the abnormality determining means determines the presence of a malfunction of at least one of the said first and second signals; and e) fuel injection quantity determining means for determining a fuel injection quantity to be supplied to the Diesel engine on the basis of that one of the first and second signals which is estimated to function properly by the engine revolution speed signal selecting means.

2. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 1, which further comprises an accelerator opening angle sensor which is so arranged and constructed as to detect an opening angle of an engine accelerator, and wherein the fuel injection quantity determining means determines the fuel injection quantity on the basis of an output signal of the accelerator opening angle sensor indicating the detected accelerator opening angle and that one of the first and second engine revolution speed signals which is estimated to function properly.

3. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 1 or 2, wherein the abnormality determining means comprises: calculating means for calculating a ratio N2/N1 between the values of the first and second engine revolution signals; first comparing means for comparing the calculated ratio N2/N1 with a predetermined abnormality determination lower limit RMIN and with a predetermined abncrmality determination upper limit RMAX so as to determine whether the calculated ratio falls within a range limited by the predetermined lower and upper limits (RMIN S N2/N1 { R second comparing means for comparing both of the values of the first and second engine revolution speeds N1,2 with a predetermined abnormality determination enabling engine revolution speed threshold value NMIN so as to determine whether either one of the first and second engine revolution speed values Nl or N2 is equal to or greater than the predetermined abnormality determination enabling engine revolution speed threshold value NMIN (N1 2 N MIN or N2rN MIN) when said first comparing means determines that the ratio N2/N1 < RMIN or N2/N1 > RMAX ; and time measuring means for counting a time duration during which said second comparing means determines that N1 a N MIN or N2 2 N MINt said first comparing means determining that the ratio N2/N1 does not fall within the range, and for determining whether the counted time duration exceeds a predetermined time duration STNG

4.A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 3, wherein said abnormality determining means determines that at least one of said first and second engine revolution speed signals malfunctions when said time measuring means determines that the time duration exceeds the predetermined time duration STNG

5.A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 4, wherein said engine revolution speed signal selecting means comprises third comparing means for comparing the values of the first and second engine revolution speed signals (N1, N2), estimating that the second engine revolution speed signal malfunctions improperly when the value of the first engine revolution speed signal indicates greater than that of the second engine revolution speed signal, and estimating that the first engine revolution speed signal malfunctions improperly when the value of the first engine revolution speed signal indicates smaller than that of the second engine revolution speed signal.

6. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in any preceding claim, including warning means for outputting a warning signal to a warning lamp to turn on the warning lamp to inform an operator of the Diesel engine of malfunction of either one of the first and second engine revolution speed sensors in response to the estimation by said engine revolution speed signal selecting means that either one of the first and second engine revolution speed signals malfunctions improperly.

7. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in any preced t clairs, wherein said first engine revolution speed sensor is attached onto a first position of the Diesel engine at which a revolution speed of a crankshaft of the Diesel engine is measured and said second engine revolution speed sensor is attached onto a second position of the Diesel engine at which a revolution speed of a fuel injection pump driven by said Diesel engine is measured.

8. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 7, wherein both of the first and second revolution speed sensors are constituted by electromagnetic pickups.

9. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in either claim 7 or claim 8, which further comprises first flag means which is set to - 1 - when said engine revolution speed signal selecting means estimates that the first engine revolution speed signal malfunctions and second flag means which is set to 1 when said engine revolution speed signal selecting means estimates that the second engine revolution speed signal malfunctions.

10. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 9, which further comprises properly functioning return determining means for determining whether either one of the first and second engine revolution speed signals functions properly on the basis of whether predetermined conditions are all satisfied when either of said first and second flag means is set to - 1 -

11.A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 10, wherein said predetermined conditions are: 1) a condition that a relationship- > RMIN 5 N2/N1 s R MAX is satisfied; 2) a coodition that Ni? NMIN and N2 2 N MIN are satisfied; and 3) a state in which said condition of the relationship RMIN s N2/N1 S R MAX is satisfied and the other condition of N1 a N MIN and N2 2 N MIN is satisfied is continued for another predetermined time duration STOK

12. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 11, wherein said properly functioning return determining means resets said set flag means to 0 - when the predetermined conditions are all satisfied and outputs a warning release signal to turn off the warning lamp.

13. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 9, wherein said fuel injection quantity calculating means calculates the fuel injection quantity from the first engine revolution speed signal output from said first engine revolution speed sensor as the engine revolution speed indicative signal (N) and an accelerator opening angle (ACC) detected by an accelerator opening angle sensor so that, as the engine revolution speed is increased, the fuel injection quantity becomes reduced when said abnormality determining means determines that neither the first nor second engine revolution speed signal malfunctions improperly.

14. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 13, wherein said fuel injection quantity calculating means calculates the fuel injection quantity from either of the first and second engine revolution speed signals,depending on which flag means is set to " 1 " as the engine revolution speed signal (N = N1, or N = N2), and the accelerator opening angle (ACC) detected by said accelerator opening angle sensor, so that as the engine revolution speed is increased, the fuel injection quantity becomes reduced.

15. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in claim 3 or any claim dependent thereon , wherein the predetermined abnormality determination lower limit value RMIN is 0.5, the predetermined abnormality determination upper limit value RMAX is 1.5, the predetermined abnormality determination enabling threshold value NMIN is 500 R.P.M., and the predetermined time durations STNG and STOK are 500 milliseconds and one second respectively.

16. A fuel injection quantity controlling apparatus for a Diesel engine as claimed in any one of the preceding claimsl through 15, which further comprises an electronic governor which controls a position of a control sleeve so that the calculated fuel injection quantity is supplied to the Diesel engine.

17. A fuel injection controlling apparatus for a Diesel engine, substantially as described with reference to, and as shown in, the accompanying drawings.

18. A fuel injection quantity controlling method for a Diesel engine, comprising the steps of: a) generating and outputting a first engine revolution speed signal indicative of the Diesel engine revolution speed from a first engine revolution speed sensor; b) generating and outputting a second engine revolution speed signal indicative of the Diesel engine revolution speed from a second engine revolution speed sensor substantially at the same time as the step a).

said second engine revolution speed sensor being separately and independently arranged from said first engine revolution speed sensor; c) comparing both of the detected first and second engine revolution speed signals with each other and determining presence or absence of a malfunction of at least either one of said first and second revolution speed signals on the basis of a result of comparison at said step c);; d) estimating either one of the first and second engine revolution speed signals which indicates a value higher than that of the other as being functioning properly and estimating the other of the first or second engine revolution speed signals which indicates a value lower than that of the said one of the first and second engine revolution speed signal as malfunctioning improperly when the presence of malfunction of at least either one of the first and second revolution speed signals is determined at said step c); e) detecting an opening angle of an engine accelerator; and f) calculating a fuel injection quantity supplied to the Diesel engine on the basis of the engine accelerator opening angle detected at said step e) and either one of the first and second engine revolution speed signal which is estimated to function properly at said step d).

19. A fuel injection controlling method for a Diesel engine, substantially as described with reference to, and as shown in, the accompanying drawings.