Abstract:
A method and apparatus for controlling a control parameter of a controlled device, such as the idle speed of an internal combustion engine, permits the setting of the control parameter in a tamper-proof manner. A control unit receives an adjustment value in the form of a compensation signal from an adjusting device, such as a potentiometer, during an adjustment mode and calculates a control value to control the parameter of the controlled device. When adjustment of the control parameter is complete, a normal mode is entered in which the calculated control value is stored in a non-volatile memory for use in controlling the controlled device, and the control unit ignores further signals received from the adjusting device.

Description:
This application is a continuation of application Ser. No. 103,292, filed Oct. 1, 1987, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an engine control system for internal combustion engines, or more in particular, to an engine control system having the functions of fine adjustment of control values including idle engine speed and mixture ratio. 
     Conventional engine control systems have a mechanism for fine adjustment of such values as a control target. An example of adjustment of idle engine speed is disclosed, for example, in &#34;Automotive Engineering&#34; No. 7, 1986, p. 83 to p. 84. 
     In the aforementioned prior art system, the idle set engine speed is finely adjusted in such a manner that a constant voltage is applied across a variable resistor provided for an engine control system, and the neutral potential thereof is read by an A/D converter thereby to change the set engine speed in accordance with the potential. 
     In this conventional system, however, the fact that the set value is easy to change by operation of the variable resistor adversely affects the tamperproofness, and that, a movable part provided therein poses the problem of a deviation of the set value due to vibration or damage to the movable part by improper operation. 
     SUMMARY OF THE INVENTION 
     Accordingly, the object of the present invention is to provide a tamper-proof, highly reliable engine control system which has no movable part for fine adjustment. 
     According to the present invention, there is provided an engine control system, wherein a movable adjustment unit which has been mounted with the conventional control system is provided separately from a control unit and is adapted for electrical connection therewith, which control unit includes a memory for storing a compensation value for operation in connection with the adjustment unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing a configuration of an embodiment of the present invention. 
     FIG. 2 shows a configuration of a conventional control system. 
     FIG. 3 shows an actual appearance of the prior art. 
     FIG. 4 is a diagram showing a compensation value of a target idle engine speed. 
     FIG. 5 is a flowchart showing the operation of an embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described below. FIG. 2 is a diagram showing a conventional system of idle engine speed control, in which the opening of an air path 16 bypassing a throttle valve 15 is controlled by a proportional solenoid valve 14 driven by a duty factor signal. In this case, the idle engine speed is set to a preprogrammed target value, such as 700 rpm, by feedback control through a control unit 1 of an engine 3. The method of this control, which will not be described in detail herein, is well known. This target value is set initially at a central value which is considered optimum. Nevertheless, it may be desired to make some fine adjustment depending on engine quality variations or secular variations. 
     For this purpose, according to the prior art, a fine adjustment mechanism 4 such as shown in FIG. 2 is added to the control unit 1. The fine adjustment mechanism 4 is a potentiometer of the rotary type, and is adapted to be rotated by a screw driver from the side of a case of the control system 1 in the manner shown in FIG. 3. The control unit 1 reads the neutral voltage V R  of the potentiometer 4 through an A/D converter 7, and according to the value thus read, searches a table having characteristics shown in FIG. 4 to determine a compensation value ΔN SET  of the target engine speed. This compensation value is added to a central value N SET φ of target engine speed set in advance thereby, thus calculating the final target engine speed N SET . 
     Specifically, 
     
         N.sub.SET =N.sub.SETφ +ΔN.sub.SET 
    
     where 
     
         ΔN.sub.SET =f (V.sub.R) 
    
     Then, in a manner to attain the target engine speed N SET , feedback control is effected. The control unit 1 includes a CPU 9 for a computation operation, a memory (ROM 10, RAM 11) for storing a program and control constants, and an I/O circuit 8 for input and output control, as is well known. 
     In this system having a fine adjustment mechanism 4 which is easy to operate, as mentioned above, the tamper-proofness is adversely affected. Also, the fact that the control system 1 has a movable adjustment mechanism results in the disadvantage that the setting is liable to deviate under vibrations, or the system is subject to damage by faulty operation. According to the present invention, these disadvantages are obviated by a configuration shown in FIG. 1. 
     The potentiometer 4 shown in FIG. 1 is mounted on an adjustment unit 2 separate from the control system 1. The adjustment unit 2 also has a circuit 12 for producing a mode switch signal and a circuit 13 for producing a compensation amount memory command signal. According to the embodiment under consideration, these circuits are all realized by an on/off switch. The adjustment unit 2 is adapted for electrical connection to the control unit 1 through a connector. In the embodiment under consideration, such a connection is established by five signal wires including a power wire S1 for the potentiometer 4, an earth wire S2, a neutral voltage signal wire (compensation signal wire) S3 for the potentiometer 4, a mode switch signal wire S4 and a compensation amount command signal wire S5. Now, the signals of the wires S1, S2, S3, S4 and S5 are designated as S1&#39;, S2&#39;, S3&#39;, S4&#39; and S5&#39; respectively hereafter. 
     On the control unit 1 side, the power wire S1 is supplied with a constant voltage of +5 V from a constant voltage source 5, the wire S2 is connected to the earth of the control unit 1, the wire S3 is connected to the A/D converter 7, and the wires S4 and S5 are pulled up to the power of +5V of the constant-voltage source through a resistor on one hand and are connected to the I/0 8 on the other hand. As a result, voltage levels of the wires S4 and S5 are read as &#34;low&#34; (hereinafter referred to as &#34;L&#34;) when switches 12, 13 are on and as &#34;high&#34; (hereinafter referred to as &#34;H&#34;) when the switches 12, 13 are off. 
     The S4&#39; is read as &#34;H&#34; when the adjustment unit 2 is not connected to the control unit 1 or when the switches 12, 13 are off even if the adjustment unit 2 is connected to the unit 1. In this case, the control unit 1 operates in a normal mode, and the input signals of the wires S3 and S5 have no meaning (are ignored). 
     When the adjustment unit 2 is connected to the control unit 1 and the switch 12 is turned on with the S4&#39; being read as &#34;L&#34;, on the other hand, the control unit 1 shifts to the adjustment mode, thereby making the signals on the wires S3 and S5 valid. In the adjustment mode, the signal S3 is read through the A/D converter, and then the following calculation is made in a manner similar to the prior art: 
     
         N.sub.SET =N.sub.SETφ +ΔN.sub.SET 
    
     In the process, the switch 13 is off (that is, S5&#39;=&#34;H&#34;), and as long as the signal S5&#39; is &#34;H&#34;, the value ΔN SET  is updated successively with the change in the S3&#39; signal, and the resulting value is stored temporarily in RAM 11. The engine speed is monitored by operating the potentiometer 4, and when the desired engine speed is reached, the switch 13 is turned on to reduce the signal S5&#39; to &#34;L&#34;. Then, the control unit 1 writes the value ΔN SET  stored in the RAM 11 into a non-volatile memory 6 such as EEPROM or RAM backed up with a battery. In this embodiment, the circuit is configured in such a way that when the S5&#39; is &#34;L&#34; the wire S3 becomes invalid, and therefore, if the value of ΔN SET  written in the memory 6 is to be rewritten, the condition of S5&#39;=&#34;H&#34; is required to be restored (with the switch 13 off) to repeat the aforementioned process. Once the desired value of ΔN SET  is written in the memory 6 in this way, the switch 12 is turned off and further the adjustment unit 2 is disconnected from the connector, thus cutting the connection between the control unit 1 and the adjustment unit 2, whereby the signal S4&#39; is made &#34;H&#34; for operation in the normal mode. In the normal mode, the control unit 1 reads out the value of ΔN SET  written in the memory 6, and by use of this value, computes the value N SET  =N SET φ +ΔN SET , so that control is effected with the resulting N SET  as a target engine speed. A flowchart of the aforementioned operation is shown in FIG. 5. 
     Step 20 decides whether the mode switch signal S4&#39; is &#34;H&#34; or &#34;L&#34;, and if it is &#34;L&#34;, the adjustment mode is decided. The next step 21 decides whether the compensation amount memory command signal S5&#39; is &#34;H&#34; or &#34;L&#34;, and if it is &#34;H&#34;, the compensation value ΔN SET  is changed. Step 22 reads the neutral voltage V R  of the potentiometer 4, followed by step 24 where a binary data of ΔN SET  proportional to the neutral voltage is stored in the RAM 11. The next step 25 adds the target engine speed central value N SET φ and the compensation value N SET  so that the final target engine speed N SET  is determined to decide whether the desired target engine speed has been reached or not. If the desired engine speed is not yet reached, the neutral point potential is changed by the potentiometer 4, followed by repeating the operation of the steps 22, 24 and 25. 
     When the desired engine speed is reached, by contrast, in step 21, the switch 13 is turned on which reduces the signal S5&#39; to &#34;L&#34;, followed by step 23 where the value ΔN SET  is shifted from the RAM 11 to the memory in the form of a RAM or an EEPROM backed up. 
     In the case where the signal S4&#39; is &#34;H&#34; at step 20, a normal control mode prevails, and step 26 determines the final target engine speed N SET  from the value ΔN SET   stored in the memory 6 and the value N SET φ stored in the ROM 10. 
     An embodiment of the present invention has been explained above as an adjustment of a target value of idle engine speed. It is evident, however, that a similar configuration is applicable also to various controls such as compensation of the air-fuel ratio. 
     Unlike the embodiment described above, a control output (such as a duty factor of the an ISC valve drive signal), but not a control target value, may be adjusted, in which case the feedback control is suspended, but the output is fixed to a predetermined value in adjustment mode. 
     Further, instead of using an independent digital or analog signal as S3&#39;, S4&#39; or S5&#39; as in the present embodiment, a common signal wire may be used by serial communication. 
     Furthermore, in the normal control mode, it is also possible to correct the value written in the memory 6 in the adjustment mode sequentially for compensation of secular variations, etc. by what is called the learning programming. 
     According to the present invention, the adjustment is impossible without an exclusive adjustment unit, and therefore, the tamper-proofness is not adversely affected, while at the same time improving the reliability with movable parts being eliminated.