Patent Publication Number: US-4317364-A

Title: Self-testing control system for an internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a self-testing control system for an internal combustion engine, and more particularly to a control system, preprogrammed memory unit having a program for testing the microcomputer so it executes necessary decisions and processes. 
     2. Description of the Prior Art 
     Recently, various control systems using a microcomputer have been developed to control operating values of an internal combustion engine; typical controlled operating values are fuel injection rate, ignition timing, exhaust gas recirculation, catalyst temperature, etc. A conventional analog or digital circuit for controlling an internal combustion engine operating value, is usually be tested by supplying a particular input signal to an actuator that affects the operating value. An output value obtained in response to the actuator being driven by the input signal is compared with a predetermined reference value. In this case, since a conventional circuit is relatively simple in structure, it is comparatively easy to test the circuit. On the other hand, in a control system using a microcomputer having a central processing unit (CPU), it is not possible readily to extract the necessary data from the CPU and to decide whether the control system is operating normally since all the arithmetic operations are executed in the CPU in time sharing mode. Even if such testing were possible, it would be complicated and expensive to realize a test program for testing such a control system using a microcomputer. 
     In addition, it is very difficult to decide whether the microcomputer is out of order, or whether the actuators and sensors for controlling the above-mentioned operating values, such as fuel injection rate, ignition timing, and exhaust gas recirculation, are not operating, or whether other electrical circuits, than the microcomputer, or mechanical parts are damaged. Therefore, when repairing the system in a repair shop it is necessary to test the system by removing the microcomputer completely even if the microcomputer is in fact operating normally. 
     In addition, the microcomputer is generally installed in the control system at a position where it is relatively difficult to remove, from the standpoint of protection from vibration; accordingly it is more difficult to conduct a test of the microcomputer provided for a control system with the microcomputer installed in position. 
     SUMMARY OF THE INVENTION 
     With the above problem in mind, therefore, it is the primary object of the present invention to provide a new and improved self-testing control system for an internal combustion engine, wherein the control system includes a memory unit preprogrammed with a test program for testing the microcomputer without any special apparatus, and without removing the microcomputer from the vehicle. 
     It is another object of the present invention to provide a self-testing control system for an internal combustion engine in which timing signals to start the test are responsive to a power signal generated when a power supply is turned on, a start signal generated when the engine is being cranked, and a revolution indicating signal generated when the engine is rotating. 
     It is a further object of the present invention to provide a self-testing control system for an internal combustion engine in which the time interval between an instant in power signal and the beginning of a start signal, between an instant in a power signal and the end of a start signal, or between the beginning of a start signal and the end of a start signal, and so on are used for testing the system. 
     It is still a further object of the present invention is to provide a self-testing control system for an internal combustion engine in which engine operating values, such as catalyst temperature, fuel injection rate, ignition advance angle, and exhaust gas recirculation, rate are controlled. 
     It is still a further object of the present invention to provide a self-testing control system for an internal combustion engine in which are displayed both the states of the starting signals and the actually detected states of engine operating values. 
     With the above and other objects in view, the present invention provides a self-testing control system for an internal combustion engine. The system comprises a memory unit pre-programmed with a test program for testing a computer which controls operating values of the internal combustion engine. By using this system, it is possible to decide whether the computer is operating normally when a predetermined checking procedure is carried out in accordance with the test program for the microcomputer. 
     The above and other related objects and features of the invention will be apparent from the following description of the disclosure illustrated in the accompanying drawings and the novelty thereof pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and advantages of the self-testing control system for an internal combustion engine according to the present invention over a prior-art control system will be more apparent from the following description of the preferred embodiments of the invention taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic block diagram showing an example of the self-testing control system of the present invention; 
     FIG. 2 consists of three flowcharts showing an example of the test procedure of the present invention; 
     FIG. 3 is a flowchart showing another example of the test procedure of the present invention; and 
     FIG. 4 is a graph showing an example of relationship between catalyst temperature and catalyst sensor output value. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIGS. 1 and 2 is illustrated a first preferred embodiment of the present invention. In this case, self-testing control system 10 is so configured as to control catalyst temperature and to provide an alarm function. 
     In the self-testing control system 10 of FIG. 1, an input/output interface 12 receives an engine revolution signal S 1  indicating that the engine is rotating, an engine start signal S 2  indicating that the engine is being started (in cranking condition), and a catalyst temperature signal S 3  indicating the temperature of a catalytic apparatus for purifying exhaust gas, converts these signals S 1 , S 2 , and S 3  from analog to digital if necessary, and supplies these signals to a microcomputer 14 (including a central processing unit and a memory unit). When the catalyst temperature t exceeds a predetermined danger temperature t d , the microcomputer 14 supplies a signal S 4  to an indicator lamp driver 16 to turn on an indicator lamp 18, thus indicating that the catalyst temperature is abnormally high. Also, a reset circuit 20 can reset the input/output interface 12, the microcomputer 14, and the indicator lamp river 16, when the power supply 22 is turned on with a power switch 24. 
     In FIG. 1, although other control devices are necessary in order to control the catalyst temperature, only the alarm function is illustrated since the other devices are not directly related to the main subject of the present invention. 
     In the memory unit of microcomputer 14 is pre-programmed a test program for testing system 10 and the microcomputer. 
     By operating the control system shown in FIG. 1 in accordance with programs shown as flowcharts in FIG. 2, it is possible to test all functions and to control catalyst temperatures of an internal combustion engine. 
     In this system, first, when the power switch 24 is turned on, i.e. closed, power from D.C. source 22 is supplied to the system 10. Consequently, a reset signal S 5  derived from the reset circuit 20 initializes the internal conditions of the microcomputer 14. That is, the reset signal S 5  resets the indicator lamp driver 16 to make the indicator lamp 18 go off (block 211 in FIG. 2(a)) 
     Under these conditions, microcomputer 14 begins to operate in accordance with the program shown in FIG. 2(a). 
     First, the catalyst temperature t in the computer 14 is initialized to a predetermined temperature t 1  which is higher than a danger temperature t d  (block 212) before an actual detected catalyst temperature t a  is read into the memory of microcomputer 14. 
     Next, the process shown in FIG. 2(b) is repeatedly executed by returning to block 221 from block 226 at fixed time intervals in accordance with interrupt signals; for example, signals are derived whenever arithmetic operations to convert an analog catalyst temperature signal S 3  to a digital signal are completed. 
     In the flowchart of FIG. 2(b), the first engine operating condition check is whether the engine is rotating or not (block 222). If the engine is rotating, the program proceeds to, block 223 to check as to whether the engine is being cranked. If the engine is rotating and is not being cranked, that is, if the engine is in normal operation, signal S 3  indicative of actual detected catalyst temperature t a  supplied to the memory in microcomputer 14 via interface 12 to replace t 1  (&gt;td) (block 225; Lamp: OFF). On the other hand, if the engine is rotating and is being cranked or if the engine is not rotating and is being cranked; that is, if the engine is being cranked regardless of whether the engine is rotating or not, the detected catalyst temperature t a  is not written into the memory and the initialized temperature t 1  stored in the memory is not changed (block 244; Lamp: oN). In summary, the engine operating condition is checked using revolution signal S 1  and a start signal S 2 . 
     Finally, the arithmetic operations shown in FIG. 2(c) are excecuted. In this flowchart, if the engine is rotating (block 232) and the catalyst temperature t a  is higher than the danger temperature t d  (block 233), the indicator lamp 18 is turned on (block 234). If t a  is lower than t d , the lamp 18 goes off (block 235). In addition, if the engine is not rotating, no comparison of catalyst temperature t a  is made, and control returns directly from RETURN (block 236) to START (block 231). 
     Accordingly, the following operation can be expected in accordance with the flowcharts in FIG. 2, when engine operation and the microcomputer are normal: 
     (1) When the power switch 24 is closed, the indicator lamp 18 goes off, since a reset signal S 5  initializes the internal conditions of the microcomputer 14 (block 211). After the system is reset, the catalyst temperature t is initialized to a predetermined temperature t 1  higher than the danger temperature t d  (block 212). 
     (2) While the engine is cranked even if the engine is rotating, the indicator lamp 18 comes on, since the actually detected catalyst temperature t a  is not written in the memory, and the stored valve of t 1  (&gt;t d ) is unchanged. (block 224). 
     (3) After the engine has been cranked, that is, when the engine is running, the indicator lamp 18 goes off since the detected catalyst temperature t a  is written in to memory to replace the stored value of t 1  (&gt;t d ) (block 225) and the catalyst temperature is normal (block 235). 
     However, in the case where the catalyst temperature is abnormal when the engine is running (that is, the temperature t a  is above t d ), as a matter of course, the indicator lamp 18 comes on to indicate an abnormal condition. 
     As described above, by checking that the indicator lamp 18 comes on only during cranking operation, it is possible to decide that the microcomputer is normal. 
     Furthermore, if the program is changed so that the indicator lamp is turned on by the reset signal S 5  and the catalyst temperature is initialized to t 2  which is less than the danger temperature t d , it is also possible to make the indicator lamp 18 come on from the time when the power switch 24 is turned on to the time when the engine is cranked, and to make the indicator lamp 18 go off while the engine is being cranked (since t 2  &lt;t d ). In this case, if the catalyst temperature is normal, the indicator lamp 18 goes off while the engine is rotating, since actual catalytic temperatures are written into memory and are normally lower than the danger temperature t d . 
     As described above, according to the flowchart shown in FIG. 2, it is determined that the mirocomputer 14 is normal when the indicator lamp 18 comes on only while the engine is being cranked, or from the time when the power is turned on to the time when the engine is cranked. 
     FIG. 3 is a flowchart of a second embodiment of the present invention. In this case, the test is made by using only the start signal S 2 . Therefore, the indicator lamp 18 comes on while the engine is being cranked regardless of other conditions. If the engine is not being cranked, the indicator lamp 18 comes on only when the catalyst temperature t a  exceeds the danger temperature t d . 
     The operation of this embodiment is now described in detail with reference to FIG. 3: 
     First, the engine operating condition is checked as to whether or not the engine is being cranked (block 302). If the engine is being cranked, the indicator lamp 18 comes on (block 307). If the engine is not being cranked, the detected catalyst temperature t a  is written into the memory to replace the previous value thereof (block 303). 
     Next, the temperature t a  is compared with the danger temperature t d  (block 304). If t a  is lower than t d , the indicator lamp 18 goes off (block 305). 
     Accordingly, if the indicator lamp comes on only while the engine is being cranked (that is, while the starter motor is rotating) and goes off immediately after the engine begins to rotate, the system is considered as operating normally. 
     The following advantages of the present invention will be seen from a consideration of the embodiments described above. 
     The testing procedure is reset simply by generating a reset signal S 5  again (turn the power switch off and on again). 
     If a sensor such as a thermistor is used for detecting the catalyst temperature t, the sensor output values are inversely proportional to the detected temperature (see FIG. 4). Therefore, the values handled internally by the microcomputer vary in the opposite way to the temperature values which they represent. Thus, the signs of the various relations involved may in practical implementation appear to be reversed; however, the above description is in terms of the underlying represented temperature value, the algorithm is the same. In FIG. 4, even if the catalyst temperature t 1  is higher than the danger temperature t d  and t 2  is lower than t d , the senor output value A corresponding to t 1  is smaller than the danger output value B corresponding to t d , and the sensor output value C corresponding to t 2  is greater than output value B. 
     In addition, although a signal indicator lamp is used for displaying the conditions of both the catalyst temperature and the computer system in the above embodiments, it is possible to use two separate indicator lamps or other alarm means, such as light emitting diodes, or alternatively, audible warning devices such as buzzers. 
     In addition, in the above embodiments, the actually detected operating parameter is the catalyst temperature. However, other engine operating parameters such as revolution speed, intake air rate, and engine cooling water temperature can be detected for controlling engine operating values. Also, the predetermined engine operating value is catalyst temperature, but other values such as fuel injection rate, ignition advance angle, and exhaust gas recirculation rate are also controllable by a system of this type. 
     As stated above, according to the present invention, it is possible to readily test the computer only by changing the program. As a result, it is possible to readily repair the control system for an internal combustion engine without removing the microcomputer from the vehicle or without spending much time to diagnose parts other than the computer. 
     Although it is impossible to locate the failure location in the microcomputer, it is possible to decide with ease whether or not the microcomputer is operating normally whenever the engine is started. 
     If is further to be 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 invention, which is to be defined by the appended claims.