Control apparatus of rotational speed of engine
This is a continuation of Application Ser. No. 07/520,481 filed May 8, 1990, abandoned Jan. 6, 1992. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     Conventionally, there have been apparatuses for adjusting the specific volume of intake air of an automobile engine to control the engine speed to a desired value. The prior art apparatuses suffer from the problem that a sudden change in electrical load on a generator, which is driven by the engine, causes a change in torque load on the engine, resulting in a decrease in engine speed due to a time delay of the speed controlling operation. 
     Japanese Patent Preliminary Publication No. 59-83600 and U.S. Pat. No. 4,459,489 disclose apparatuses in which the output current of the generator slowly increases in response to the sudden increase in electrical load on the generator. 
     FIG. 4 illustrates the operation of one such prior art apparatus when a feedback control of the engine speed is being performed. A load signal M denotes the presence and absence of an electrical load on the generator. As soon as the generator is applied with an electrical load, the output voltage V of the generator drops and then slowly increases to the value before the load is applied; thus the output current i slowly increases. A feedback correction signal I denotes a feedback correction amount for bringing the difference between an actual speed and a desired speed of the engine, and is used to increase the specific volume of intake air in accordance with the increase in load on the generator such that the engine speed is maintained at the desired value. In this manner, when a large load is applied on the generator while the feedback control is being performed, the engine speed N can be maintained generally at a desirable condition though it undergoes little change. 
     The dotted lines in FIG. 4 show the responses of the output current i of the generator, the feedback control amount I, and the speed N which results if the output voltage of the generator is maintained constant rather than dropping as depicted by the solid line when the large load is applied. The sudden increase in the output current i as shown in the dotted line causes an increase of torque load on the engine which in turn causes the abrupt drop of the engine speed N. Meanwhile, the feedback correction amount I is applied with some delay time, therefore the engine speed N returns through a damped oscillation to the value before the large electrical load is applied. As mentioned above, in the prior art apparatus, too large a change in engine speed can be prevented when the electrical load is applied while the feedback control of the engine speed is being performed. 
     However, it should be noted that an automobile engine will encounter the following phenomenon. In FIG. 5, a signal S represents engine conditions, being L when the engine is idle and H when the engine is loaded. During the loaded condition, the feedback control of the engine speed is not carried out; therefore the feedback amount I is zero. At this time, if the electrical load M is applied to the generator, then the output current i of the generator slowly increases responding to the change in load and does not affect the engine speed since the engine output is inherently large at this time. As soon as the engine goes into the idling condition (i.e., S=L), the feedback control of the engine speed is begun but the engine speed N is no longer maintained constant, dropping rapidly as depicted in the solid line since the output current i being drawn from the generator is large enough to impose a heavy load on the engine. The feedback correction amount I slowly increases to cause an increase in the specific volume of intake air of the engine such that the decrease in the engine speed N may be recovered. Due to the delay time in feedback correction, the engine speed N approaches a target value through a damped oscillation. 
     As mentioned above, in the prior art speed control apparatus, the change in the engine speed N can be retarded when the electrical load is applied to the generator while the feedback control of the engine speed is being carried out, but the engine speed will change greatly if the feedback control of the engine speed is begun while the electrical load is being applied. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a rotational speed control apparatus in which the rotational speed of an engine can be maintained even when the engine goes into the idling condition while an electrical load is being applied to a generator. 
     When the engine goes to the idling condition from the loaded condition, a predetermined amount of I1 much larger than the predetermined incremental amount ΔI is added to the feedback correction amount I to provide the drive signal of a much larger value than in the normal idling condition; thus the engine can be operated without too large a drop in engine speed. For example, as shown in FIG. 3, when the engine is in the idling condition (YES at steps 1004, 1005), the rotational speed signal N is compared with the target speed Nt to decide which one is greater than the other (steps 1009). Then, the predetermined amount of ΔI is subtracted from or added to the feedback correction amount I (steps 1010, 1012, 1011), depending on which is greater N or Nt. The feedback correction amount I=I±ΔI, thus calculated, is then added to the basic control amount Cb to produce the drive signal C by which the bypass valve 5 then controls its opening to control the engine speed. The above-mentioned procedure is recursively performed upon a pulse sized from rotational speed detector 42 to adjust the engine speed so that the actual speed N becomes equal to the target speed Nt. 
     When the engine goes to the loaded condition from the idling condition, the value of the feedback correction amount I used during the idling condition is stored to provide for the next possible change from the loaded condition to the idling condition. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Features and other objects of the invention will be more apparent from the detailed description of the preferred embodiments with reference to the accompanying drawings in which: 
     FIG. 1 is a diagram showing a general arrangement of control apparatus of the rotational speed of an engine according to the present invention; 
     FIG. 2 is a block diagram showing the detail of the control apparatus in FIG. 1; 
     FIG. 3 is a flowchart showing the operation of a first embodiment of the control apparatus in FIG. 1; 
     FIG. 4 is a diagram showing waveforms of various parameters of the engine conditions when the engine is in the idle condition; 
     FIG. 5 is a diagram showing waveforms at various parameters of the engine when the engine goes from the loaded condition to the idle condition, dotted lines representing the present invention; and 
     FIG. 6 is a flowchart showing the operation of a second embodiment of the control apparatus in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First embodiment 
     FIG. 1 is a diagram showing a general arrangement of a control apparatus of the rotational speed of an engine according to the present invention. Air is supplied to an engine 1 through an inlet pipe 2 in which an inlet valve 3 is located to adjust the flow rate of air. A bypass tube 22 is connected at one end thereof to the upstream of the valve 3 in the inlet pipe 2 and at the other end thereof to the input side of a bypass control valve 5. A bypass tube 21 is connected at one end thereof to the downstream of the valve 3 in the inlet pipe 2 and at the other end thereof to the output side of the bypass control valve 5. The bypass control valve 5 controls the amount of air therethrough in accordance with a drive signal C from a speed controller 10. An idle switch 11 is operated, in interlocked relation with the valve 3, to close when the engine is in the idle condition. A pulley 40 is attached to an output shaft 1a of the engine 1 and drives a generator 6 by means of a belt 43. The generator 6 having a regulating apparatus is of the same type as disclosed by Japanese Patent Preliminary Publication No. 59-83600, in which the output current of the generator slowly increases in response to the sudden increase in electrical loads on the generator. 
     The output current of the generator 6 responds with some delay to the increase in electrical load. A gear 41 is magnetized at its teeth each of which activates a rotational-speed detector 42 to detect the engine speed when each one of the teeth passes by the rotational speed detector 42. Each one of the output pulses of rotational speed detector 42 triggers the control program of a speed controller 10, which will be described later. The battery 7 is connected in parallel with the generator 6. A series circuit of an electrical motor 9 and a switch 8 is connected in parallel with the battery 7. A temperature sensor 12 detects the temperature of cooling water of the engine. The speed controller 10 receives a rotational speed signal N from the rotational-speed detector 42, a signal S from the idle switch 11, and a water temperature signal W from the temperature sensor 12 to thereby manipulate these signals to output the drive signal C to the bypass control valve 5. 
     FIG. 2 shows an arrangement of the speed controller 10. An input interface 101 receives a rotational speed signal N from the rotational speed detector 42, a signal S from the idle switch 11, and the water temperature signal W from the temperature sensor 12. CPU 102 transmits and receives various data between a memory 103, as well as receives the signals through the interface 101 and performs arithmetic and logic operation to provide the drive signal C. The drive signal C is then power-amplified to a power level required for driving the bypass control valve 5 which is of a pulse-driven type. An output interface 104 amplifies the signal outputted from CPU 102 and outputs the drive signal C for driving a bypass control valve 5. 
     FIG. 3 is a flowchart, illustrating the operation of a first embodiment of a rotational speed control apparatus of an engine according to the present invention. The program in FIG. 3 is triggered by each one of the output pulses from the rotational speed detector 42. The rotational speed control program is stored in the memory 103 and is executed by CPU 102. Upon a pulse input from the detector 42, the program is started. At step 1001, the water temperature signal W representative of the temperature of the engine cooling water is read in. At step 1002, CPU reads out from the memory 103 a basic control amount Cb and a target speed Nt for each value of the water temperature signal W. At step 1003, the actual speed N is read. At step 1004, CPU detects the condition of the idle switch 11 by reading the signal S to make a decision based on whether or not the engine 1 is in the idling condition. If the engine is in the idling condition, then, at step 1005 the feedback correction amount I is read. The value of I may be zero, resulted from the last normal idling operation. At step 1006, a decision is made based on whether or not the engine was previously in the idling condition. If the engine is still in the idling condition at step 1006, then the program proceeds to step 1009 to compare the actual speed N with the target speed Nt to decide which is greater than the other. If N-Nt=0, the feedback correction amount I is held at the previous value at step 1012; if N&gt;Nt, the feedback correction amount I is updated by the feedback correction amount I minus an incremental amount ΔI; if N&lt;Nt, the feedback correction amount I is updated by the feedback correction amount I plus the incremental amount ΔI. The correction amount ΔI is a predetermined experimental value. 
     Meanwhile, if the engine is not previously in the idling condition at step 1006, then the program proceeds to step 1007 where the feedback correction amount I is updated by the present value I plus the predetermined amount I1, thereafter proceeds to step 1008 where the control signal C=Cb+I is calculated. Then, the drive signal C is outputted to the valve 5. It should be noted that the magnitude of I1 is much greater than that of ΔI. This large value of I=I+I1 is used as an initial value for the feedback control, which prevents the drop of the engine speed as shown in FIG. 5 shortly after the engine goes into the idling condition, ensuring the stable speed of the engine. 
     If the engine is not in the idling condition at step 1004, the program proceeds to step 1013 to hold a current feedback correction amount I. The program then waits for the next trigger pulse from the rotational speed detector 42 to start again. 
     While the values of ΔI at steps 1010 and 1011 have been described as being of the same value, these values may be different depending on the difference in sensitivity between when the engine speed is increased and when the engine speed is decreased. Selecting the value of ΔI in accordance with the magnitude of N-Nt permits the smooth and rapid settlement of the feedback action. Further, setting a proper value of I1, in accordance with the initial values of the engine speed and the engine temperature or cooling water temperature allows an optimum control. 
     Operation of the first embodiment 
     When the engine goes to the idling condition from the loaded condition (YES at steps 1004 and 1005, NO at step 1006), the predetermined value of I1 much larger than the predetermined value ΔI is added to the feedback correction amount I to provide the drive signal much larger than in the steady idling condition. Thus, the engine can be operated without too large a drop in its speed. It should be noted the program does not directly make a decision based on whether or not the electrical load is on. However, the presence of the electrical load during idling period of the engine causes the drop in engine speed; therefore the speed-drop actually indicates the presence of the electrical load. When the engine is normally in the idling condition (YES at steps 1004, 1005), the rotational speed signal N is compared with the target speed Nt to decide which one is greater than the other (steps 1009.) Then the predetermined value of ΔI is subtracted from or added to the value of the feedback correction amount I (steps 1010, 1012, 1011.) The feedback correction amount I&#39;=I±ΔI, thus calculated, is then added to Cb to produce the drive signal C which is fed to the bypass valve 5. The bypass valve 5 then controls its opening to control the engine speed. The above-mentioned procedure is repeated to adjust the engine speed so that the actual speed N approaches and then approximates the target speed Nt. 
     When the engine goes to the loaded condition from the idling condition, the value of the feedback correction amount I is stored to provide for the next possible change from loaded condition to idling condition. 
     Second embodiment 
     FIG. 6 is a flowchart of the speed control program, illustrating the operation of a second embodiment of a rotational speed control apparatus of an engine according to the invention. The flowchart is triggered by each one of the output pulses from the rotational speed detector 42. The rotational speed control program is stored in the memory 103 and is executed by CPU 102. Upon a pulse input from the rotational speed detector 42, the program is started. 
     At step 1001, the water temperature signal W representative of the temperature of the engine cooling water is read in. At step 1002, CPU reads out from the memory 103 a basic control amount Cbo and a target speed Nt which has been stored in advance in the memory 103 for each value of the water temperature signal W, and at step 1003 the actual speed N is read in. At step 1005, CPU detects the condition of the idle switch 11 by reading the signal S to make a decision based on whether or not the engine 1 is in the idling condition. The value of I may be zero, resulting from the last normal idling operation. Then, at step 1006, a decision is made based on whether or not the engine was previously in the idling condition. If not, then the program proceeds to step 1007 to produce the basic control amount Cb by adding the present value Cbo to a predetermined amount Cb1, thereafter proceeds to step 1008. 
     Meanwhile, if the engine is still in the idling condition at step 1006, then the program proceeds to step 1009 to compare the actual speed N with the target speed Nt to decide which is greater than the other. If N-Nt=0, the feedback correction amount I is held at the previous value at step 1012; if N&gt;Nt, the feedback correction amount I is updated by the feedback correction amount I minus an incremental amount ΔI at step 1010; if N&lt;Nt, the feedback correction amount I is updated by the feedback correction amount I plus the incremental amount ΔI at step 1011. Then, at step 1013, a decision is made based on whether or not Cb≦Cbo. If Cb≦Cbo, then step 1008 is entered; if not Cb≦Cbo, then step 1014 is entered where Cb is updated by Cb minus ΔCb. Then, the program proceeds to step 1008 to calculate the drive signal C=Cb+I, which is outputted to the valve 5. 
     Thereafter, the program waits for the next trigger pulse from the rotational speed detector 42 to start again. 
     Operation of the second embodiment 
     When the engine goes to the idling condition from the loaded condition (YES at steps 1004 and 1005, NO at step 1006), the predetermined value of Cb1 is added to the first basic control amount Cbo to provide a second basic control amount Cb so that a drive signal C is much larger than in the idling condition. It should be noted that the program does not directly make a decision based on whether or not the electrical load is on. However, the presence of the electrical load during the idling period of the engine causes the drop in engine speed, therefore the speed-drop indicates the presence of the electrical load. 
     When the engine is normally in the idling condition (YES at steps 1004, 1005), the rotational speed signal N is compared with the target speed Nt to decide which one is greater than the other (steps 1009.) Then the predetermined incremental amount of ΔI is subtracted from or added to the value of the feedback correction amount I (steps 1010, 1011, 1012.) The relation between Cb1, ΔCb and ΔI is Cb1&gt;ΔCb&gt;ΔI. The second basic control amount Cb is subtracted by a predetermined decremental amount ΔCb if Cb is not Cb≦Cbo. Then, the feedback correction amount (calculated at steps 1010, 1011, 1012) is added to Cb to produce the drive signal C which in turn is fed to the bypass valve 5 (step 1008.) The bypass valve 5 then controls its opening to control the engine speed. The above-mentioned procedure is repeated to adjust upon a pulse signal from the rotational speed detector 42, the engine speed so that the actual speed N approaches and then approximates the target speed Nt. The subtraction of the predetermined amount ΔCb is carried out for every cycle of the above-mentioned procedure until Cb is equal to Cbo. 
     Thus, the engine can be operated without too large a drop in engine speed. 
     When the engine goes to the loaded condition from the idling condition, the value of the feedback correction amount I is stored to provide for the next possible change from loaded condition to idling condition.