Abstract:
In a Diesel engine with a Bosch-type fuel pump or the like having a control lever which determines the fuel injection quantity, idling speed is controlled by a movable stopper which abuts the control lever to place a lower limit on fuel injection quantity during idling. A control unit derives a target idling speed value according to engine temperature, electrical load, etc. and controls the pneumatic actuator of the stopper in accordance with the difference between actual engine speed during idling and the target idling speed. When the engine is not idling, the pneumatic actuator may be controlled to act as a dashpot, damping the return of the control lever to its idling position. Electromagnetically controlled valves respond to the control unit by providing atmospheric pressure or negative pressure to the pneumatic actuator. An auxiliary valve is provided for bypassing a defective atmospheric pressure supplying valve.

Description:
BACKGROUND OF THE INVENTION 
     FIELD OF THE INVENTION 
     The present invention relates generally to an idling speed control method and its system for a Diesel engine which prevents excessively low engine idling speed, unstable engine operation, and engine stalling when auxiliary vehicle equipment associated with a load on the engine such as an air conditioner is operated during engine idling and when the engine is started when the engine cooling water temperature is below a predetermined value, i.e., during cold engine start-up. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide method and system for controlling an idling speed for a Diesel engine wherein the system adjusts an angular position of a control member for controlling an amount of fuel supplied to the engine according to the angular position so that an actual idling speed achieves a target idling speed, the target idling speed being determined depending on whether the auxiliary equipment is operated and whether the engine cooling water temperature is below a predetermined value. 
     It is another object of the present invention to provide the idling speed control method and system for a Diesel engine which prevents excessive increases in the actual engine idling speed caused by continuous increases in rotational angles of the control member so as to continuously increase the quantity of fuel to the engine due to a failure in a component of the system. 
     It is still another object of the present invention to provide a cost effective idling speed control system for a Diesel engine. 
     These objects can be achieved by providing a Diesel engine idling speed control system which comprises a pressure-responsive actuator having a stopper which can engage a control member, the angular position of which controls the amount of fuel injected into the Diesel engine, within a movable range of the control member, a negative pressure source which supplies a negative pressure to the actuator, a first normally-closed electromagnetic valve disposed within a negative-pressure passage connecting the negative pressure source and the actuator, a second electromagnetic valve disposed within a passage branching from the negative pressure passage and normally open to expose the negative pressure passage to atmosphere, a first sensor which detects the engine speed, a second sensor which detects an engine load, a detector which detects an additional engine operating condition, and means for selectively opening or closing of the first and second electromagnetic valves such that the engine idling speed approaches a target idling speed according to an idling operating condition when detection signals from the first and second sensors and the detector are received and the second sensor detects the idling state and for controlling the operations of the first and second electromagnetic valves such that the stopper is moved in the direction of the control member in which the amount of injected fuel increases when the engine is operating well outside of the idling range. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention may be obtained from the following description in conjunction with the attached drawings in which like reference numerals designate corresponding elements and in which: 
     FIG. 1 is a simplified block diagram of a first preferred embodiment according to the present invention wherein portions of the fuel injection pump are omitted; 
     FIG. 2 is a timing chart of an operating control parameter in the case of an engine operating in the idling state to which the first preferred embodiment shown in FIG. 1 is applied; 
     FIG. 3 is an operational flowchart of a control unit in the first preferred embodiment when the engine is operating in the idling state; 
     FIG. 4 is a timing chart of a control parameter of engine operation when the engine is operating in a state other than the idling state; 
     FIG. 5 is an operational flowchart of the control unit in the first preferred embodiment when the engine is operating in a state other than the idling state; 
     FIG. 6 is a simplified block diaphragm of a second preferred embodiment according to the present invention, portions of the fuel injection pump being omitted; and 
     FIG. 7 is a timing chart of a control parameter of engine operation for the second preferred embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will hereinafter be made to the drawings in order to facilitate understanding of the present invention. 
     FIG. 1 shows a first preferred embodiment according to the present invention. 
     A fuel injection pump 1 is not fully shown in FIG. 1. However, the fuel injection pump 1 and a control lever 2 extending ouside the housing of the pump 1 are detailed in Japanese Patent Publication No. 54-30315 and Japanese Patent Publication No. 55-54639, the disclosures of both of which are hereby incorporated by reference. 
     As shown in FIG. 1, a pressure-responsive actuator 4 is divided by means of a diaphragm 4a into two chambers, a pressure-responsive chamber 4b and atmospheric-pressure chamber 4c, the pressure-responsive chamber 4b having a spring 4d seating between a side wall and the diaphragm 4a and the atmospheric-pressure chamber 4c being exposed to the air. 
     The fuel injection pump 1 is provided with the control lever 2 extending therefrom and constituting a control member of the fuel injection pump 1 for controlling the amount of fuel to be injected into the engine. As shown schematically in FIG. 1, a swing arm 3 is pivotably attached to the fuel pump housing 1 and its upper tip is free to abut the free end of control lever 2. The upper tip of arm 3 lies on the low side of the control lever 2, i.e. if the arm 3 and lever 2 are in contact, then if the lever 2 is actuated externally to increase the fuel supply to the engine, the control lever 2 will separate from the tip of swing arm 3. 
     A stopper 5 having a profile as shown in FIG. 1 extends from the diaphragm 4a of the actuator 4 through the atmospheric chamber 4c into the range of movement of the lower tip of the above-described swing arm 3. The stopper 5 serves to limit the minimum amount of injected fuel mediated by the control lever 2 when the stopper 5 abuts the swing arm 3. Vacuum pressure generated by a negative-pressure generator 6 is conducted to the pressure-responsive chamber 4b of the actuator 4 via a negative-pressure passage 8. 
     Also shown in FIG. 1, a negative-pressure control valve 15 disposed within the negative-pressure passage 8 normally closes the negative-pressure passage 8 when not energized and open same when energized by a control unit 18. An atmospheric-pressure inlet passage 16 connected to an air cleaner (not shown) merges with the negative-pressure passage 8, and an atmospheric-pressure inlet valve 17 disposed within the atmospheric-pressure inlet passage 16 is normally held open to expose the negative-pressure passage 8 to the atmosphere. 
     It should be noted the above-mentioned negative-pressure control valve and atmospheric-pressure inlet valve 15 and 17 are capable of being controlled not to open or close continuously or through a plurality of steps but rather open and close strictly between fully on and off positions selectively on the basis of an electromagnetic switching action. 
     The control unit 18 comprises a microcomputer having an input/output interface, memory, and a Central Processing Unit (CPU). The individual circuit blocks are not shown. The input/output interface of the control unit 18 receives various signals: an ON/OFF signal S 1  sent from an ignition switch IG; an engine speed-indicative signal S2 from an engine speed sensor 11 which detects the current engine speed n, e.g., from crankshaft rotation or ignition timing; an auxiliary equipment operation-indicative signal S3 derived from an accessory equipment switch 12 capable of detecting the operational state of accessories such as an air conditioner or torque converter associated with the engine; an accelerator pedal depression angle-indicative signal S4 from an acceleration sensor 13 which detects a depression angle of an accelerator pedal; and a water temperature-indicative signal S5 from a cooling water temperature sensor 10 which detects the cooling water temperature of the engine. 
     The load on the engine is detected by the acceleration sensor 13, or alternatively is detected from the rotational angle of the control lever 2 or the displacement of a control member except the control lever 2 which controls the amount of fuel injected by the fuel injection pump 1. 
     It should be noted that the acceleration sensor 13 detects the idling state on the basis of the depression angle of the accelerator pedal (not shown). The control unit 18 determines that the engine is idling depending on whether the depression angle of the accelerator pedal detected by the acceleration sensor 13 coincides with a predetermined angle assumed by the accelerator pedal during idling. 
     A target idling speed n e  previously set on the basis of the water temperature-indicative signal S5 from the cooling water temperature sensor 10 and the accessory equipment operation-indicative signal S3 from the accessory equipment switch 12, which is stored in the memory of the control unit 18. 
     When the engine is detected to be operating in the idling state on the basis of the signal S 4  from the acceleration sensor 13, the control unit 18 compares the actual idling speed n obtained from the engine speed-indicative signal S2 from the sensor 11 with the target idling speed n e  fetched from the memory thereof, and selectively controls the negative-pressure control valve 15 and the atmospheric-pressure inlet valve 17 so as to adjust the actual idling speed n to match the target idling speed n e  if they do not agree with each other. 
     On the other hand, when the engine is detected to be changing from the idling state to a normal running state, the control unit 18 does not actuate the pressure control valve 15 and atmospheric-pressure inlet valve 17 (i.e., the pressure control valve 15 is closed and atmospheric-pressure inlet valve 17 is open) for a predetermined period of time t 1  so that the negative-pressure passage 8 is exposed to atmosphere to displace the stopper 5 rightward as viewed in FIG. 1 (Under this condition, the control lever 2 will mediate the minimal limit value of fuel injection quantity if the swing arm 3 is forced by the control lever 2 to abut the stopper 5). The predetermined period of time t 1  is determined to allow for the time required for the controlled negative pressure within the negative-pressure passage 8 to settle to atmospheric pressure. 
     Thereafter, the control unit 18 actuates both valves 15 and 17, i.e., the atmospheric pressure inlet valve 17 is closed and the negative-pressure control valve 15 is opened for a predetermined period of time td so as to introduce the negative pressure into the negative-pressure passage 8 and the pressure-responsive chamber 4b, thereby moving the stopper 5 slightly leftward as viewed in FIG. 1. (Under this condition, the stopper 5 is shifted to a position at which the control lever 2 will mediate a fuel injection quantity corresponding to an idling speed higher than the target idling speed n e  if the swing arm 3 is forced by the control lever 2 to abut the stopper 5). The predetermined period of time td is previously set according to one of the accelerator depression angle, the idling speed, or the cooling water temperature at the instantaneous time when the engine operating condition changes from the idling state to another running state. 
     The operation of the idling control system of the first preferred embodiment during idling will be described in detail with reference to the timing chart of FIG. 2 and the flowchart of FIG. 3. 
     The control unit 18 derives the actual idling speed n from the engine speed signal S2 received from the engine speed sensor 11 whenever a predetermined period of time t 1  has passed and compares the actual idling speed n with the target idling speed n e  previously set on the basis of the accessory equipment operation signal S3 from the auxiliary switch 12 and the water temperature signal S5 from the water temperature sensor 10. Since the target idling speed n e  actually represents an engine speed band X having a predetermined width 2α (the region indicated by oblique lines between the lines ne 1  and ne 2  in FIG. 2 and a represents |ne-ne 2  | and |ne-ne 1  |), the control unit 18 at each time of t 1  determines whether the actual idling speed n is within the engine idling speed band X by solving the following inequality: |n-n e  |≦X/2 as seen in FIG. 3. 
     In the case where the actually measured idling speed n is lower than the target idling speed n e  i.e., the answer of |n-n e  |≦X/2 is NO and subsequent answer of inequality ne&gt;n is YES as shown in FIG. 3, the control unit 18 actuates the atmospheric-pressure inlet valve 17 to close while actuating the negative-pressure control valve 15 to open for a predetermined period of time tv to intensify the controlled negative pressure in the actuator 4, i.e., in the pressure-responsive chamber 4b and thus to shift the stopper 5 and the swing arm 3 such that the control lever 2 is pivoted via the swing arm 3 to increase the amount of injected fuel to the engine. Consequently, the idling speed n is increased toward the target idling speed n e . 
     In the case when the actual idling speed n is higher than the target idling speed n e  i.e., the answer of |n-n e  |≦X/2 is NO and subsequent answer of inequality ne&gt;n is NO, the control unit 18 de-activates, i.e. closes the negative pressure control valve 15 while deactivating, i.e. opening the atmospheric-pressure inlet valve 17 for a predetermined period of time ta, thus reducing the controlled negative pressure within the pressure-responsive chamber 4b by admixture of atmospheric pressure. The stopper 5 is thus shifted in the opposite direction in which the amount of injected fuel to the engine is decreased. Consequently, the idling speed n is decreased toward the target idling speed n e . 
     When the actual idling speed n is detected to be within the target idling speed band X i.e., the answer of |n-n e  |≦X/2 is YES, the position of the stopper 5 need not be adjusted, so both the negative-pressure control valve 15 and the atmospheric-pressure inlet valve 17 remain closed, i.e., only the atmospheric-pressure inlet valve 17 is actuated by the control unit 18. 
     In more detail, the predetermined period of time tv for which the control unit 18 closes the atmospheric-pressure inlet valve 17 while opening the negative pressure control valve 15 in order to increase the idling speed n, and the time ta for which the control unit 18 closes the negative-pressure control valve 15 while opening the atmospheric pressure inlet valve 17 in order to decrease the idling speed n, are necessary to allow the controlled negative pressure applied to the actuator 4 to settle to a stable level. The actual idling speed n may fluctuate until the times tv, ta have passed. 
     Therefore, if the operation of the negative-pressure control valve 15 and atmospheric-pressure inlet valve 17 take all of the predetermined period of time t 1 , the idling speed n measured immediately after the end of these operations would only reflect transient phenomena. Thus, stable control would not be achieved if the idling speed n measured during the transient time were compared with the target idling speed n e . 
     The time tv, ta are, therefore, set so as to satisfy the respective inequalities tv&lt;t 1  and ta&lt;t 1 . The controlled negative pressure (in other words, the actually measured idling speed n) can easily settle within the remaining times ti-tv, ti-ta after the end of operation of the negative-pressure control valve 15 and atmospheric-pressure inlet valve 17 by the control unit 18. In this way, the actual idling speed n measured after each prdetermined period of time t 1  will be stable when compared with the target idling speed n e . 
     Next, the case in which the engine changes to the idling state after engine deceleration will be described below with reference to the timing chart of FIG. 4 and the flowchart of FIG. 5. 
     FIG. 4 illustrates the progress of selected parameters as a driver depresses the accelerator pedal from point A until point B to accelerate the engine, holds the engine at a constant speed until point C with the depression force of he accelerator pedal remaining unchanged, and finally releases the depression force from the accelerator pedal to decelerate the engine, thus allowing the engine to return to the idling state. 
     Depression forces, i.e., angular position changes of the accelerator pedal are directly transmitted to the control lever 2 via a link mechanism (not shown) during the period between points A and B. Since the control lever 2 is pivotted by the accelerator pedal in the direction in which the fuel quantity increases according to the increase in the depression angle of the accelerator pedal, the engine speed increases with high responsiveness. In this case, the control lever 2 separates from the swing arm 3 while the lower tip of the latter remains in contact with the stopper 5. The idling control passes to a halt routine until after point C is reached. 
     FIG. 5 is an operational flowchart of the control unit 18 during the halt routine. 
     If the accelerator pedal is depressed through less than a predetermined angular limit θ 1  at an initial program step, a flag FLG 1 is set to &#34;1&#34;, allowing the previously described idling control program to be executed. Otherwise, FLG 1 is checked at the next step, and since FLG 1 will be &#34;1&#34; when this routine is first executed, control will pass to a path 102 rather than a null path 110. In the path 102, first the two valves 15 and 17 are once de-energized, i.e., the negative-pressure control valve 15 is closed and atmospheric-pressure inlet valve 17 is opened for the predetermined period of time t 1 . Thus the negative-pressure passage 8 is exposed to atmosphere, until its pressure reaches a stable value at atmospheric pressure. 
     After the predetermined period of time t 1  has elapsed, the atmospheric-pressure inlet valve 17 is closed and negative pressure control valve 15 is opened for a predetermined time td. Negative pressure is thus introduced into the negative-pressure passage 8. The predetermined period of time td for which the negative-pressure control valve 15 is open is previously set according to one of the accelerator pedal depression angle θ, the idling speed n, or the cooling water temperature at the time when the engine is out of idling. The stopper 5 is moved slightly left as viewed in FIG. 1 during the predetermined period of time td. Due to the characteristics of the pressure-responsive actuator 4, the stopper 5 moves as shown by a curve E in FIG. 4 with a response delay from point G at which the introduction of the negative pressure into the negative-pressure passage 8 begins. The stopper 5 stops moving at a position at which the rotational angle of the control lever 2 would be increased by α in the idling state. (The position of the stopper 5 is shown by a dash-and-dot line of FIG. 4). When a predetermined period of time td has passed, the negative pressure control valve 15 is closed and flag 1 is reset to &#34;0&#34;. When this routine is repeated thereafter, control passes through the paths 100, 101 and 110, so that the above-described state remains unchanged. 
     Next, when the depression force of the accelerator pedal is released at point C, the signal S4 from the acceleration sensor 13 is used to determine that the engine is changing to the idling state. At this time, the negative-pressure valve 15 and atmospheric-pressure valve 17 are selectively opened or closed so that the engine speed n reaches the target idling speed n e  appropriate for the idling state as described above. However, as described above, due to the response delay of the pressure-responsive actuator 4 from the time when the control unit 18 recognizes that the depression force of the accelerator pedal is released, the response of the stopper 5 to the actuator 4 takes time later than the response of the swing arm 3 contacted with the control lever 2 to the release of the accelerator pedal. Due to the net response delay (F-D), the swing arm 3 abuts the stopper 5 at point D before the stopper 5 reaches the target idling speed. Thereafter, due to the balance between the response delay of the actuator 4 and stopper 5 and the biasing force of a spring linked to the rotational axle of the control lever 2 (not shown) acting on the accelerator pedal and control lever 2, the displacement speed of the control lever 2 is damped so that the control lever 2 moves towards its target idling speed position at a slow, decelerating rate without hunting as indicated by the curve H in FIG. 4. 
     That is to say, in the case where the engine changes from a decelerating state to an idling state and the control unit 18 begins to control the idling speed, the initial negative-pressure value of the pressure responsive chamber 4b, in other words, the initial value of the idling speed, depends on the predetermined period of time td described before. If the predetermined period of time td is set longer, the controlled negative pressure of the actuator 4 is increased, so that the initial value of the idling speed will be higher. If the predetermined period of time td is set shorter, the initial value of the idling speed will be lowered. 
     Therefore, the idling speed control system according to the present invention introduces a negative pressure only for the predetermined period of time td. 
     In addition, if the wiring to either of the negative-pressure control valve 15 or the atmospheric-pressure inlet valve 17 should break, the negative pressure passage 8 will be opened to the air with the negative-pressure control valve 15 closed and atmospheric pressure inlet valve 17 open. Consequently, the stopper 5 would return to the position at which the control lever 2 mediates the minimum limit value of the fuel injection quantity. Therefore, even if the driver releases the accelerator pedal, the stopper 5 will limit the movement of the swing arm 3. Consequently, the stopper 5 will not return to the idling speed increase position, so the engine speed will not continue to increase. 
     It should be noted that electromagnetic control valves employed in the present invention are less expensive and have better responsiveness than those which can open and close continuously. 
     FIG. 6 is a simplified block diagram of a second preferred embodiment according to the present invention. 
     As shown in FIG. 6, an auxiliary atmospheric-pressure inlet passage 19 is additionally provided between the atmospheric-pressure inlet passage 16 and the air cleaner, and an auxiliary valve 20 is disposed within the auxiliary atmospheric-pressure inlet passage 19. 
     It should be noted that all three of the negative-pressure control valve 15, the atmospheric-pressure inlet valve 17, and the auxiliary valve 20 are electromagnetic valves which open or close only between fully-open and fully-closed positions on the basis of the electromagnetic switching action. 
     Since the control unit 18 comprises the same elements as in the first preferred embodiment, detailed description thereof will be omitted. 
     In a case where the idling speed n is lower than the target idling speed n e  after a predetermined period of time t 2  has passed, the control unit 18 recognizes that the wiring to the normally open atmospheric-pressure inlet valve 17 is broken, stops electrical power supply to the atmospheric-pressure inlet valve 17, and opens or closes the normally-closed auxiliary valve 20 in place of the atmospheric-pressure inlet valve 17 the negative pressure control valve 15 so that the idling speed n reaches the target idling speed n e . 
     Thus, if the actually measured idling speed converges asymptotically toward the target idling speed during the predetermined period of time t 2 , more detailed description will be omitted since the operation is the same as in the first preferred embodiment. 
     In a case where the actually measured idling speed is higher than the target idling speed n e  during the predetermined period of time t 2  and does not converge toward the target idling speed, the control unit 18 recognizes that a passage around the atmospheric-pressure inlet valve 17 linked with the atmospheric-pressure inlet passage 16 is clogged, stops the electrical power supply to the atmospheric-pressure inlet valve 17, and sends electrical power to the auxiliary valve 20 to open the auxiliary valve 20 (while the negative-pressure control valve remains closed), thus reducing the negative pressure in the negative-pressure passage in order to decrease the idling speed. 
     Therefore, in cases where the atmospheric-pressure inlet valve 17 is not capable of opening, the control unit 18 activates the auxiliary valve 20 to open after the predetermined period of time t 2  has passed and thus the stopper 5 returns to the position corresponding to the lowest limit value that the control lever 2 provides. 
     Consequently, the control lever 2 is limited by  the stopper 5 via the swing arm 3 even after the driver releases the accelerator pedal so that the danger of the stopper failing to return to the idling speed position due to the continuous supply of vacuum pressure to the pressure-responsive chamber 4b via the negative-pressure passage 8, thus allowing the engine speed to continue to increase, can be avoided. 
     Furthermore, after the predetermined period of time t 2  has passed, the auxiliary valve 20 starts to act as the atmospheric-pressure inlet valve 17 and operates in conjunction with the negative pressure control valve 15 to match the idling speed to the target idling speed. 
     In summary, the auxiliary valve 20 is actuated in place of the atmospheric-pressure inlet valve 17 after the predetermined period of time t 2  has elasped when the actually measured idling speed is higher or lower than the target idling speed and does not converge toward the target idling speed, with the atmospheric-pressure inlet valve 17 held closed due to its failure. Eventually, the actual idling speed settles to within the idling speed band X as shown in FIG. 7. It should be noted that the auxiliary valve 20 has the same flow cross-section as the atmospheric-pressure inlet valve 17 and the opening period of the auxiliary valve 20 is set to be the same as that (ta) of the atmospheric-pressure inlet valve 17. 
     In the second preferred embodiment, the idling speed control system comprises an auxiliary atmospheric-pressure inlet passage 19 branching from the negative-pressure passage 8, an auxiliary valve 20 disposed within the auxiliary atmospheric-pressure inlet passage 19 which is normally closed and opens upon energization, and means for actuating the auxiliary valve to serve as the atmospheric-pressure inlet valve in a case where the idling speed is higher or lower than the target idling speed continuously for longer than a certain period of time. This has the advantageous result of a fail safe function preventing excessive increase of the idling speed in case of clogging in the atmospheric-pressure inlet valve 17. 
     In the above-described first and second preferred embodiments, when the engine changes from idling to normal running, the stopper 5 is eventually moved left as viewed from FIG. 3 or FIG. 6 to increase the idling engine speed when the negative pressure control valve 15 is opened for a predetermined period of time. Consequently, the actuator 4 has a dashpot effect. 
     In addition, if the duration tv for which the negative pressure control valve 15 is opened in response to an energizing signal from the control unit 14 is the same as that (ta) for which the atmospheric-pressure inlet valve 17 is opened in response to a deenergizing signal from the control unit 14, the range of increase in the engine speed caused by the negative-pressure control valve 15 in response to the energizing signal coincides with the range of decrease in the engine speed caused by the atmospheric-pressure inlet valve 17 in response to the deenergizing signal, thereby resulting in hunting across the target idling speed. Therefore, the control system is more efficient if the durations for which each of the negative-pressure control valve 15 and the atmospheric-pressure inlet valve 17 is opened in response to the signal from the control unit 14 (ta and tv shown in FIG. 4) are not the same and are not related by a simple integral ratio such as 2:1, 3:1, or 4:1. 
     It will be fully understood by those skilled in the art that the foregoing description is in terms of preferred embodiments of the present invention wherein various changes and modifications may be made without departing from the spirit and scope of the present invention, which is to be defined by the appended claims.