Abstract:
This invention relates to a method of cooling an engine for an automobile. The method operates using a predictive, feed-forward element combined with a fuzzy logic feedback controller to achieve accurate control over engine temperature. The fuzzy logic feedback is only utilized in the event that the predictive control results in a cylinder head temperature outside a predetermined range.

Description:
BACKGROUND 
     1. Field of the Invention 
     This invention relates to a method of cooling an engine for an automobile. 
     2. Related Technology 
     In a typical motor vehicle cooling circuit, coolant passes through a jacket surrounding the vehicle engine and its temperature rises. It then passes through the radiator, entering the radiator through a manifold and then passing through cooling tubes where air flows over the tubes to remove heat from and to reduce the temperature of the coolant before the coolant is re-circulated via a second manifold to the vehicle engine. 
     Cooling systems generally have a coolant pump for pumping coolant through the engine coolant circuit. A valve is conventionally provided to prevent coolant circulating through the radiator while the engine is warming up. The cooling system usually includes a fan for blowing air over the radiator in the event that the coolant becomes too hot in situations where the speed of the automobile does not provide the necessary cooling air flow over the radiator. 
     Known methods of cooling engines usually include controls based on output of a thermostatic device for opening and closing the valve and for switching the fan on and off. The speed of the water pump is generally operated in dependence upon the engine speed. 
     Such known systems use feedback from sensors in order to control the valve, the fan and the water pump. The emission levels and fuel economy achieved by an engine is known to be directly related to the operating temperature of the engine. An optimum temperature can be identified for any given engine; running the engine at this temperature for prolonged periods of time will result in reduced emissions and improved fuel economy. 
     However, due to the interactive nature of the individual system components it is possible to reject a given quantity of heat in a number of different ways. Ideally the components would controlled to optimize power consumption as well as emissions and fuel consumption. 
     The problem with known systems is that it is difficult to operate the engine at an optimum temperature in order to optimize emissions, while also optimizing fuel consumption and power consumption. Furthermore, traditional controllers such as proportional-integral-derivative (PID) controllers are based on comparing a measured value with a desired value (an error based approach) and calculates proportion, integrals and/or derivatives of the error in order to provide an adjusted input value. This approach requires large amounts of processor power and memory. Furthermore it assumes that the system being modeled is linear, or behaves as a monotonic function. 
     A simpler controller is sought which uses less system resources. 
     SUMMARY 
     This invention seeks to alleviate the aforementioned problems, and the proposed system operates using a predictive, feed-forward element combined with a fuzzy logic feedback controller to achieve accurate control over engine temperature with minimal controller effort and dynamic instability. 
     The controller of this invention utilizes a fuzzy logic controller to effectively control the feedback element of the strategy. A fuzzy logic controller operates using a number of logic based rules (IF X AND Y THEN Z, for example) rather than attempting to model a system mathematically. These are used in combination with a set of output membership functions used to define the system responses based on the value of the desired inputs. For example, rather than dealing with temperature control in terms such as “SP=500 F”, “T&lt;1000 F”, or “210 C &lt;TEMP &lt;220 C”, terms such as “IF (process is too cool) AND (process is getting colder) THEN (add heat to the process)” or “IF (process is too hot) AND (process is heating rapidly) THEN (cool the process quickly)” are used. These terms are imprecise and yet very descriptive of what must actually happen. 
     Due to the discrete nature of a fuzzy logic system, the system memory usage (both storage (read only memory) and processing (random access memory)) levels are considerably reduced when compared to a conventional PID controller. 
     Typically fuzzy logic controllers are used as predictive feed-forward controllers. 
     According to the invention there is provided a method of regulating the temperature of an engine for an automobile having a radiator, a coolant pump, a coolant fan and a coolant flow regulating valve, the method comprising the steps of: 
     a) determining a required radiator heat rejection; 
     b) determining a required engine cylinder head temperature; 
     c) determining a first pump speed, a first fan speed and a first valve position in dependence upon the required heat rejection and a radiator simulation model; 
     d) determining a cylinder head temperature error in dependence on a measured cylinder head temperature and the required cylinder head temperature; in the event that the error is outside a predetermined range 
     e) determining a pump speed modifier, a fan speed modifier and a valve position modifier in dependence upon fuzzy logic rules; 
     f) setting the fan speed in dependence upon the first fan speed and the fan speed modifier; 
     g) setting the pump speed in dependence upon the first pump speed and the pump speed modifier; and 
     h) setting the valve position in dependence upon the first valve position and the valve position modifier; and in the event that the error is within the predetermined range 
     i) setting the fan speed in dependence upon the first fan speed; 
     j) setting the pump speed in dependence upon the first pump speed; and 
     k) setting the valve position in dependence upon the first valve position. 
     Preferably the determining step c) comprises the sub-steps of: in the event that the valve is set at a predetermined maximum opening position, determining the first pump speed and first fan speed according to data stored in a first database; in the event that the valve is not set at the predetermined maximum opening position determining the first pump speed and the first valve position according to data stored in a second database. 
     In a preferred embodiment the data in the first database and in the second database is predetermined using a radiator performance model. 
     Preferably, the required radiator heat rejection is generated at step a) in dependence upon the heat generated by the engine less the heat dissipated by heat sinks. 
     In one embodiment the heat sinks are auxiliary heaters, an exhaust gas recirculation unit, an oil cooler and/or a cabin heater. 
     The data in the first database may be generated by repeating the steps: choosing a fan speed; determining the required coolant flow according to the radiator performance model; and determining the corresponding pump speed; until an optimum fan and pump speed have been found. 
     The data in the second database may be generated by the steps of determining the required coolant flow according to the radiator performance model; and repeating the step of choosing a valve position and determining the corresponding pump speed until an optimum valve position and pump speed have been found. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a flow chart illustrating initial steps in a method of regulating the temperature of an automobile; 
         FIG. 2  is a flow chart illustrating steps used to determine pump speed, fan speed and valve position according to the present invention; 
         FIGS. 2   a  and  2   b  are flow charts illustrating generation of a lookup tables; 
         FIG. 3  is a flowchart illustrating steps used to determined modified pump speed, fan speed and valve position, in the event that temperature remains outside acceptable limits after the steps illustrated in  FIG. 2 ; and 
         FIG. 4  is a flow chart illustrating the steps performed after the engine is switched off. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring firstly to  FIG. 1 , at step  102  the values of various external inputs are read for use by the method. Various inputs are read from an engine control unit (ECU) for example the following values may be provided by the ECU: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Description 
                 Value Range 
               
               
                   
                   
               
             
             
               
                   
                 Engine Speed 
                 0-6500 rpm 
               
               
                   
                 Throttle Position 
                 0-100% 
               
               
                   
                 Cylinder Head Temperature (CHT) 
                 −40-320° C. 
               
               
                   
                 Vehicle Speed 
                 0-255.99 km/hr 
               
               
                   
                 Fuel Demand 
                 0-225 mg/stroke 
               
               
                   
                 Ignition State 
                 0/1/2 (Off/Run/Crank) 
               
               
                   
                 AC Required 
                 0-1 (On/Off) 
               
               
                   
                 Ambient Air Temperature (AAT) 
                 −40-320° C. 
               
               
                   
                 Manifold Air Pressure (MAP) 
                 0-1500 kpa 
               
               
                   
                 Charge Air Temperature (ACT) 
                 −40-250° C. 
               
               
                   
                 Exhaust Gas Recirculation (EGR) Valve 
                 0-10.0 mm valve lift 
               
               
                   
                 Position 
               
               
                   
                 Idle Speed Fuel Demand 
                 0-255.99 mg/stroke 
               
               
                   
                 Intake Mass Air Flow (MAF) 
                 0-20 kg/second 
               
               
                   
                   
               
             
          
         
       
     
     Some input variables are taken directly from analogue sensors located throughout the vehicle, for example: 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Description 
                 Value Range 
               
               
                   
                   
               
             
             
               
                   
                 Heater/Ventilation/Air Conditioning 
                 Cold/warm/hot 
               
               
                   
                 (HVAC) Setting 
               
             
          
           
               
                   
                 Heater/Air Con Blower Speed 
                 0-100% 
                   
               
               
                   
                 Engine Inlet Coolant Temperature (EIT): 
                 −40-150° 
                 C. 
               
               
                   
                 Coolant Control Valve Inlet Coolant 
                 −40-150° 
                 C. 
               
               
                   
                 Temperature (VIT): 
               
               
                   
                 Engine Sump Oil Temperature (SOT): 
                 −40-150° 
                 C. 
               
               
                   
                 Coolant Control Valve Positional 
                 0-200° 
               
               
                   
                 Feedback (VPFB) 
               
               
                   
                   
               
             
          
         
       
     
     Some of the input variables are subjected to low pass filtering in order to remove transient spikes and noise. 
     At step  104  the required heat rejection is calculated. All cooling system heat sources and sinks are evaluated, therefore establishing the level of residual heat left within the coolant system. The sum of all sources and sinks determines the required radiator heat rejection. 
     The heat generated by the engine, Q eng , is determined using the relationship:
 
 Q   eng   =K ×Engine Speed A ×Engine Load B 
 
Engine Load=f{Engine Speed, Throttle Position, Fuel Demand}
 
     Where constants A, B and K are derived using experimental data for a given engine. 
     The heat used by auxiliary heaters, Q aux , is dependent upon the Cylinder Head Temperature (CHT) and the Ambient Air Temperature (AAT):
 
Q aux =f{CHT, AAT}.
 
     The exhaust gas recirculation (EGR) cooler contributes to heat rejection by an amount Q EGR  in dependence upon the exhaust gas flow and the coolant flow and upon the difference between the exhaust gas temperature and the valve inlet temperature:
 
 Q   EGR /ETD EGR   =K ×gas_flow A ×coolant_flow B 
 
ETD EGR   =T _exhaust−VIT
 
     Where “Gas_flow” is dependent upon the EGR valve position, “Coolant_flow” is dependent upon Engine Speed and VPFB, “T_exhaust” is dependent upon engine load, engine speed and AAT, and “ETD” stands for Extreme Temperature Difference. 
     Again constants A, B and K (which are different from those constants mentioned above) are determined using experimental data. 
     The oil cooler contributes to heat rejection by an amount Q OC , in dependence upon the rate of coolant flow and the rate of oil flow, and upon the difference between the engine sump oil temperature (SOT) and the engine inlet coolant temperature (EIT):
 
 Q   OC /ETD OC   =K ×oil_flow A ×cool_flow B 
 
Oil_flow=f{Engine Speed}
 
ETD OC=SOT−EIT 
 
     The heater cabin contributes to heat rejection by an amount Q HC  in dependence upon the air flow across the heater and the difference between the coolant control valve inlet coolant temperature (VIT) and the ambient air temperature (AAT).
 
 Q   HC /ETD HC   =K ×air_flow A ×cool_flow B 
 
ETD HC =VIT−AAT
 
     Air_flow is heatercore air flow and is dependent upon the Heater/Air Con blower speed. 
     Again constants A, B and K (different from those above) are determined using experimental data. 
     At step  106  the required cylinder head temperature (CHT) is determined as a function of engine speed and engine load. 
     At step  108  the limits of operation of the fan, pump and valve are calculated. 
     The minimum speed of the fan is set in dependence upon the air conditioning requirement. If air conditioning is required, then the fan speed minimum is set to stationary air-conditioning requirements. If the vehicle speed exceeds the required fan speed, then the fan is deactivated, i.e. the maximum speed is set to 0 RPM. 
     The pump range is dependent upon a predefined maximum engine temperature, CHT and engine inlet temperature. The pump speed minimum is set to allow a minimum “coolant_flow” in dependence upon Q eng  and the predefined maximum engine temperature 
     The HVAC setting is used to determine a minimum and maximum heater flow to avoid over pressurizing the heater core. Current data suggests that satisfactory heater performance can be obtained using 15-30 liters/min heater flow. 
     The valve range (degrees rotation) is dependent upon heater flow, oil flow and minimum coolant flow. These are used determine valve min/max angular positions. 
     If the measured CHT is more than 5° below the required CHT at step  110  then the engine is in warm up mode. In this case at step  112  the pump speed, fan speed and valve opening are all set to the minimum values determined at step  108  until the difference between the required CHT and the measured CHT (CHR error) is less than 5°. Once the CHT is within this range the engine is in normal operating mode, and the open loop controller illustrated by  FIG. 2  is initiated. 
     Referring now to  FIG. 2 , a first pump speed, first fan speed and first valve position are determined. 
     At step  202  the valve positional feedback is used to compare the current valve position to the maximum valve position determined at step  108 . If the valve is not already at its maximum opening position then a first pump speed and first valve position are determined at step  204  by reference to lookup table  214 . The first fan speed is set to be equal to the minimum level determined at step  108 . 
     If the valve position is already at its maximum opening position at step  202  then at step  206  a first pump speed and first fan speed are determined which reject the required amount of heat while using the least amount of electrical power by reference to lookup table  216 . The first valve position is set to be equal to the maximum opening position determined at step  108 . 
     The lookup tables  214 ,  216  are generated offline using an engine simulator and an optimization routine as illustrated in  FIG. 2   a  and  FIG. 2   b.    
     Referring now to  FIG. 2   a , the optimizer routine for generating the lookup table  214  for use by step  204  will now be described. 
     A radiator performance model is used to determine the required coolant flow to achieve the required heat rejection using the following relationships.
 
 q   cool =( Q   rad /(ETD RAD   ×K×q   air   A )) 1/B 
 
ETD RAD =VIT−AAT
 
 Q   rad   =Q   eng   −Q   aux   −Q   EGR   −Q   OC   −Q   HC .
 
q air   =f {Fan speed, Radiator cross sectional Area, Ambient Air Temperature}
 
     Constants A B and K are determined by results of a radiator simulation. 
     At step  222  a required coolant flow is determined using the above equations. 
     A valve position is chosen at step  224  and at step  226  the pump speed required to obtain the required coolant flow at the chosen valve position is determined using a lookup table. 
     Steps  224  and  226  are repeated until an optimum position using minimum power is found at step  228 . 
     The valve position chosen at step  224  is increased and decreased by a step size which is determined by an algorithm which increases the step size if the valve position and pump speed are a long way from an optimum point and which decreases the step size when the valve position and pump speed are close to an optimum. 
     At step  230  the required radiator heat rejection is written to the lookup table  214  along with the associated optimum valve position and pump speed. 
     The optimizer routine for generating the lookup table  216  for use by step  206  will now be described with reference to  FIG. 2   b.    
     At step  232  a fan speed is chosen, and at step  234  a required coolant mass flow is determined using the radiator simulator model described above. 
     At step  226  the pump speed required to obtain the required coolant mass flow at the chosen valve position is determined using a lookup table. 
     Steps  234 , 236  and  238  are repeated until an optimum point is found at step  238 . An optimum is determined based on the total power requirement of the pump and the fan. 
     The fan speed chosen at step  232  is increased and decreased by a step size which is determined by an algorithm which increases the step size if the fan speed and pump speed are a long way from an optimum point and which decreases the step size when the fan speed and pump speed are close to an optimum. 
     At step  240  the required radiator heat rejection is written to the lookup table  214  along with the associated optimum fan speed and pump speed. 
     Referring back not to  FIG. 2 , once the fan speed, pump speed and valve position have been determined and set, the CHT error is measured. If the CHT error is not within acceptable predetermined limits then a closed loop controller using fuzzy logic rules is initiated at step  212 . 
     Referring now to  FIG. 4 , at step  302  the required CHT and the CHT error are used from previous steps  106  and  208  and at step  305  the change in CHT error is determined. 
     At step  306  a pump speed modifier, a fan speed modifier and a valve position modifier are calculated using the following fuzzy logic rules: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                   
                 Change in CHT 
                 Valve position 
                 Pump speed 
                 Fan speed 
               
               
                 CHT error 
                 error 
                 modifier 
                 modifier 
                 modifier 
               
               
                   
               
             
             
               
                 H+ 
                 H− 
                 0 
                 0 
                 0 
               
               
                 L+ 
                 H− 
                 H− 
                 H− 
                 H− 
               
               
                 H− 
                 H− 
                 H− 
                 H− 
                 H− 
               
               
                 L− 
                 H− 
                 H− 
                 H− 
                 H− 
               
               
                 H+ 
                 H+ 
                 H+ 
                 H+ 
                 H+ 
               
               
                 L+ 
                 H+ 
                 L+ 
                 L+ 
                 L+ 
               
               
                 H− 
                 H+ 
                 0 
                 0 
                 0 
               
               
                 L− 
                 H+ 
                 L+ 
                 L+ 
                 L+ 
               
               
                 H+ 
                 L− 
                 L+ 
                 L+ 
                 L+ 
               
               
                 L+ 
                 L− 
                 0 
                 0 
                 0 
               
               
                 H− 
                 L− 
                 H− 
                 H− 
                 H− 
               
               
                 L− 
                 L− 
                 H− 
                 H− 
                 H− 
               
               
                 H+ 
                 L+ 
                 H+ 
                 H+ 
                 H+ 
               
               
                 L+ 
                 L+ 
                 L+ 
                 L+ 
                 L+ 
               
               
                 H− 
                 L+ 
                 H+ 
                 H+ 
                 H+ 
               
               
                 L− 
                 L+ 
                 0 
                 0 
                 0 
               
               
                   
               
               
                 H = large change 
               
               
                 L = small change 
               
               
                 + = increase 
               
               
                 − = decrease 
               
             
          
         
       
     
     For example the first row indicates that for a large hot CHT error and a large decrease in CHT error, all the modifiers will be set to 0. 
     Once the modifiers have been determined using the fuzzy logic rules, the modifiers are applied to the first fan speed, first pump speed and first valve position calculated at step  204  or  206 . 
     Referring now to  FIG. 4 , whether or not the fuzzy logic closed loop controller is initiated by the decision at step  210 , at step  402  the ignition signal and engine rpm is used to determine whether the engine is still running. If so, then the process resumes at step  102  ( FIG. 1 ). If not, then a desired run on time is determined at step  406  in dependence upon ETD RAD  (defined above as VIT−AAT). The pump and fan speed are then set at a predetermined value for the desired run on time at step  408 . 
     It is to be recognized that various alterations, modifications, and/or additions may be introduced into the constructions and arrangements of parts described above without departing from the scope of the present invention as defined in the following claims.