Abstract:
There is provided a control device for an engine including an automatic stop and start function, wherein detected data taken prior to an engine stop or results of an operation carried out based on the detected data are retained in executing an engine automatic stop control. In particular, in a case where the technology is applied to an engine including a thermostat proper operation determination function, a thermostat proper operation determination process is constructed so as to continue to be executed in executing an engine automatic stop control.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a control device for an engine having an automatic stop and start function. 
     2. Description of the Related Art 
     Known in JP-A-4-246252 or the like is a vehicle having an engine automatic stop and start function in which the engine is automatically stopped when it goes into predetermined engine stopping conditions, and it is also automatically started when it goes into predetermined engine re-starting conditions. This technology has been developed to further promote the reduction of exhaust gas emissions and conservation of energy. 
     On the other hand, a thermostat is provided on a water-cooled engine which has a function to maintain the temperature of water in a water jacket within a predetermined range, and an abnormal operation of the thermostat invites a reduction of combustion efficiency attributed to improper engine temperatures, worse exhaust gas properties and fuel economy thereby resulting. Due to this, recently it is one of significant subjects in the field of engine control to find an abnormal state of the thermostat at an earlier stage. 
     Proposed as a means for finding an abnormal state of a thermostat at an earlier stage in, for example, JP-A-11-141337 is a system in which the quantity of intake air which is directly related to the total heat release value of an engine is accumulated since the engine is started and in which, when the accumulated value of the quantity of intake air has reached a predetermined value, an estimated cooling water temperature calculated based on a total heat release value of the engine estimated from the accumulated value on condition that the thermostat is in normal operation is compared with an actually measured cooling water temperature actually measured by a cooling water temperature sensor, whereby the thermostat is determined to be in an abnormal state when a deviation between the estimated cooling water temperature and the actually measured cooling water temperature exceeds a predetermined value. 
     In recent years, however, the combustion control of an engine which is related to the ignition timing or the quantity of injected fuel is generally controlled in an electronic fashion, and on suitable occasions data in a CPU installed in an electronic control unit (ECU) needs to be initialized and a self-diagnostic process also needs to be performed on the CPU on such occasions. Conventionally, it is common practice to execute the initialization of data and self-diagnostic process at the time of cranking. 
     However, in a case where an engine automatic stop and start function is applied to a vehicle equipped with the aforesaid thermostat proper operation determination function, since the CPU is initialized when the engine is re-started after it has been automatically stopped, there may be a risk of interrupting the thermostat proper operation determination based on an accumulated value of the quantity of intake air since the engine is initially started. 
     SUMMARY OF THE INVENTION 
     The present invention was made with a view to solving such a problem inherent in the related art, and an main object thereof is to provided a control device improved such that even if an automatic stop and start function is added to a vehicle, there is caused no risk of a thermostat proper operation determination device malfunctioning to make a wrong judgement 
     With a view to attaining the above object, according to aspects of the invention, there is provided a control device for an engine includeng an automatic stop and start function, wherein detected data taken prior to an engine stop or results of an operation carried out based on the detected data are retained in executing an engine automatic stop control. In particular, in a case where the technology is applied to an engine including a thermostat proper operation determination function, a thermostat proper operation determination process is constructed so as to continue to be executed during an engine automatic stop control. 
     According to the constructions, since the processes are jumped to be performed when the engine is initially started, the accumulated data for use in determining whether the thermostat is in proper operation does not have to be initialized. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a typical diagram showing an engine cooling system to which the invention is applied; 
     FIG. 2 is a schematic flowchart of a thermostat monitor execution permission routine; 
     FIG. 3 is a schematic flowchart of a thermostat monitor routine; 
     FIG. 4 is a graph showing cooling water temperature increase properties lines related to determination on the failure of a thermostat; and 
     FIG. 5 is a schematic flowchart of an engine load accumulation routine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, the invention will be described in detail below. 
     FIG. 1 is a typical diagram showing an engine cooling system to which the invention is applied. In FIG. 1, a water jacket  2  formed within a cylinder block of an engine  1  is connected at one end to a bottom side of a radiator  5  via a cooling water supply passage  3  and a water pump  4  and at the other end to a top side of the radiator  5  via a cooling water discharge passage  6  and a thermostat  7 . The cooling water discharge passage  6  communicates with an upstream side of the water pump  4  via a bypass passage  8  which is branched off before the thermostat  7 . 
     Cooling water discharged from the water pump  4  returns to the water pump  4  via the water jacket  2  and the bypass passage  8  when the thermostat  7  is closed, whereas when the thermostat  7  is open, the cooling water so discharged flows into the radiator  5  from the water jacket  2  via the cooling water discharge passage  6 . 
     A fan  10  is additionally provided on the radiator  5  which is adapted to be driven by an electric motor  9 . The fan  10  is constructed so as to be driven intermittently when the voltage of a battery B is applied thereto via a temperature switch  11  provided on the bottom side of the radiator  5 . Therefore, the temperature of the cooling water within the water jacket  2  or the temperature of the engine is maintained within a predetermined range by operating the thermostat  7  so as to be opened or closed while allowing heat to be dissipated from the radiator  5 . 
     Note that a heater  12  for heating the passenger compartment is connected between the water jacket  2  and the cooling water supply passage  3 , and the part of cooling water heated by the engine  1  is constructed so as to be used as a source of heating. 
     The electric motor  9  for driving the fan  10  is connected to an electronic control unit  18  for controlling the engine  1  based on detected values from a cooling water temperature sensor  13  for detecting the temperature of cooling water on a downstream side of the radiator  5 , an engine speed sensor for detecting the engine speed of the engine  1 , a manifold air pressure sensor  15  for detecting the load of the engine  1 , a vehicle speed sensor  16  for detecting the running speed of the vehicle and a temperature sensor  17  for detecting the atmospheric temperature. 
     The engine  1  is constructed so as to automatically be stopped when the stop of the vehicle is confirmed or predetermined conditions for predicting the stop of the engine are met. In executing the automatic stop control, a flag is set in a control program which indicates that an automatic stop control is being executed. 
     An abnormal operation of the thermostat  7  induces a reduction in combustion efficiency attributed to improper engine temperatures and causes deterioration in exhaust emissions properties and fuel economy. To cope with this, a monitor system for monitoring the operating state of the thermostat  7  is incorporated in the electronic control unit  18  of the engine to which the invention is applied. 
     Referring to FIG. 2, a thermostat monitor execution permission routine will be described next. First, whether or not the engine is currently under automatic stop control is determined (Step A 1 ). In the event that the automatic stop control is being executed in this step, whether or not initial values of both the temperature and the cooling water temperature fall within a predetermined environmental range (for example, −6.7 to 45 degrees C.) is determined, and also whether or not a value resulting when the atmospheric temperature is subtracted from the cooling water temperature when the engine is initially started falls, within a predetermined value (for example, 6 degrees C.) is determined (Step A 2 ). In the event that the engine goes into these conditions, the monitor execution permission flag is set to 1 (Step A 3 ), whereas the engine does not go into those conditions, the monitor execution permission flag is set to 0 (Step A 4 ). 
     In the event that the engine is not currently being under automatic stop control in Step A 1 , whether or not the engine is in a starting mode or whether or not the ignition key has been operated so as to put the engine in an idling state is determined (Step A 5 ), and in the event that the engine is determined not to be in the starting mode here, then the flow advances to Step A 2 , whereas in the event that the engine is determined to be in the starting mode, data related to the atmospheric temperature and the cooling water temperature both of which constitute a basis for the cooling loss calculation is initialized (Step A 6 ). 
     Next, a thermostat monitor routine will be described with reference to FIG.  3 . First, whether or not the engine is being under automatic stop control is determined (Step B 1 ), and in the event that the engine is determined to be under automatic stop control,jumping a starting mode determination step B 2  and checking on the thermostat monitor permission flag whether or not the execution of the monitoring of the thermostat is permitted is determined (Step B 3 ). Here, in the event that the execution of the monitoring of the thermostat is determined to be permitted (flag is set to 1), there after a cooling loss accumulated value is calculated (Step B 4 ) from a heat dissipation value through usage of the heater, a heat dissipation value through running wind and the atmospheric temperature. And, an estimated cooling temperature when it is predicted that the thermostat operates properly is calculated from the cooling loss accumulating valve and an engine load accumulated value obtained separately from the cooling loss accumulated value (Step B 5 ). Then, whether or not the thermostat operates properly is determined by comparing the estimated cooling temperature and an actually measured cooling water temperature (Step B 6 ). 
     Here, the determination whether or not the thermostat operates properly will briefly be described. As shown in FIG. 4, when the estimated cooling water temperature reaches a failure determination value (for example, 75 degrees C.) before the actually measured cooling water temperature reaches a proper operation determination value (for example, 70 degrees C.), then it is determined that the thermostat is in failure (see arrow {circle around ( 1 )} of FIG.  4 ). Additionally, in the event the actually measured cooling temperature is lower a predetermined value (for example, 15 degrees C.) than the estimated cooling temperature before the actually measured cooling water has reached the proper operation determination value and before the estimated cooling temperature has reached the failure determination value, then it is determined that the thermostat is in failure (see arrow {circle around ( 2 )} of FIG.  4 ). 
     In the event that an average vehicle speed when the actually measured cooling temperature has reached the proper operation determination value is equal to or greater than a predetermined value (for example, 30 km/h), the thermostat is determined to operate properly even if the actually measured cooling temperature is higher than the estimated cooling temperature (see arrow {circle around ( 3 )} of FIG.  4 ). Additionally, even if an average vehicle speed when the actually measured cooling water temperature has reached the proper operation determination value is equal to or smaller than the predetermined value, the thermostat is determined to operate properly if the estimated temperature is a predetermined value (for example, 60 degrees C.) or less (see arrow {circle around ( 4 )} of FIG.  4 ). 
     In the event that the engine is determined not to be under automatic stop control in Step B 1 , then in Step B 2 , whether or not the engine is in the starting mode is determined, and in the event that the engine is determined to be in the starting mode here, remaining steps onward are jumped without condition. In contrast, in the event that the engine is here determined not to be in the starting mode, in Step B 3 , the thermostat monitor permission flag is checked to determine whether or not a monitor permission has been granted. In the event that the monitor permission flag is set at 1, then the flow advances to the aforesaid thermostat proper operation determination process, and on the contrary, in the event that the monitor permission flag is set at 0, steps onward are jumped. 
     Note that as shown in FIG. 5, the engine load accumulation is performed in Step C 4  on conditions that the engine is not under automatic stop control (determined in Step C 1 ), that the engine is not in the starting mode (determined in Step C 2 ), and that the monitor permission is granted (determined in Step C 3 ). In the event that the engine is under automatic stop control, remaining steps onward are jumped, and in the event that the engine is in the starting mode or that no monitor permission is granted (flag is set at 0), then the data related to the engine load accumulation is initialized (Step C 5 ). 
     The engine load accumulation is obtained by correcting the fuel injection time with a function of the engine speed and manifold air pressure. 
     While only certain embodiments of the invention have been specifically described herein, it will apparent that numerous modifications may be made thereto without departing from the spirit and scope of the invention. 
     Thus, according to the invention, when the engine is re-started after it has automatically been stopped, since processing steps that are to be performed when the engine is initially started are jumped, accumulated data for use in determining whether or not the thermostat operates properly does not have to be initialized. Consequently, the invention is remarkably advantageous in preventing the thermostat from malfunctioning to make a wrong decision on whether or not the thermostat properly operates when the engine automatic stop and start function is added to the vehicle.