Patent Publication Number: US-6213061-B1

Title: Control system for minimizing electricity consumption in a cooling system of an internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a control system for the cooling system of the internal combustion engine of a motor vehicle. 
     More specifically, the subject of the invention is a control system for a cooling system which comprises a liquid-based cooling circuit including a radiator with an associated electrically-powered fan assembly and at least one electric pump operable to cause the coolant liquid to flow through the radiator and the internal combustion engine. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a control system for a cooling system of this type, operable to reduce to the minimum the electric power required to extract the desired amount of heat from the internal combustion engine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the invention will become apparent from the detailed description which follows, provided purely by way of non-limitative example, with reference to the appended drawings, in which: 
     FIG. 1 is a block diagram of a cooling system for an internal combustion engine with a control system according to the invention; 
     FIG. 2 is an exemplary graph, which illustrates the qualitative relationship between the electric power to be supplied to an electric pump and to an electric fan respectively in a cooling system for an internal combustion engine, in dependence on the heat to be extracted from the engine; and 
     FIG. 3 is a block diagram illustrating the structure of a part of the control system of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, an internal combustion engine for a motor vehicle is generally indicated E, A circulating-liquid cooling system associated with the said engine is generally indicated  1 . 
     The cooling system  1  comprises a liquid-based cooling circuit including a radiator  2  connected to the engine E by pipes  3  and  4 . An electric fan  5  for drawing a flow of air through the radiator  2  is connected to this radiator by known means. 
     The liquid cooling circuit also includes at least one electric pump, indicated  6 , for circulating the liquid. 
     The electric fan  5  and the electric pump  6  are controlled by an electronic control unit ECU in dependence on signals received by the said unit from a plurality of sensors. 
     In particular, the control unit ECU is connected with (for example) a sensor S 1  operable to supply electric signals indicating the temperature of the engine E, a sensor S 2  operable to transmit signals indicating the speed of the vehicle and a sensor S 3  supplying signals indicating the temperature of the ambient air, that is of the air outside the motor vehicle. 
     As will be seen more clearly later, the control unit ECU is set to control the electric fan  5  and the electric pump  6  so as to optimize the reduction in the overall electric power to be supplied to the said fan  5  and pump  6  in order to cool the internal combustion engine E as required. 
     The modus operandi of the control unit ECU is based on the considerations explained hereinafter with reference to FIG.  2 . 
     In the graph of FIG. 2 the electric power P FANM  supplied to the electric fan  5  is plotted on the abscissa, while the electric power P PMP  supplied to the electric pump  6  is plotted on the ordinate. In the graph, the curves indicated P T1 , P T2  P T3  correspond to constant values of beat energy P extracted from the engine E by the cooling system described above. The given curves correspond to three different heat energy values, where P T1 &lt;P T2 &lt;P T3 . 
     The significance of the curves shown in FIG. 2 is as follows. With reference, for example, to the curve P T1 , this curve defines the pair of values P PMP , P FANM  which enable heat energy to the value P T1  to be extracted from the internal combustion engine E. The heat energy P T1  can thus be extracted from the engine by supplying the pump  6  with electric power to the value P PMPA  while simultaneously supplying the electric fan  5  with electric power to the value P FANMA  (point A on the curve P T1 ) or (for example) by supplying the pump  6  with electric power P PMPB  and simultaneously supplying the fan  5  with electric power P FANMB  (point B). The working point indicated A in FIG. 2 corresponds to a total electricity consumption equal to the sum of the electric power values P PMPA  and P FANMA . In the same way, the working point B corresponds to a total electricity consumption equal to the sum of the electric power value P PMPB  and the electric power value P FANMB . 
     For a given value P T1  (for example) of the heat energy to be removed from the engine E, there is an optimum working point, indicated Q 1  in FIG. 2, which corresponds to a minimum total electricity consumption. In other words, the point Q 1  is the working point on the curve P T1  where the sum of the electric power values supplied to the electric fan and the electric pump is a minimum. 
     Similar optimum working points, corresponding to minimum electricity consumption, exist along each of the curves P T =constant: in FIG. 2 the working point corresponding to minimum electricity consumption for the curves P T2  and P T3  are indicated Q 2  and Q 3  respectively. 
     In the graph of FIG. 2, the optimum working points Q 1  form a curve indicated Q. This curve represents the locus of the working points of minimum total electricity consumption. Each operating condition of the vehicle can be computed by means of the value of the air temperature outside the vehicle and the instantaneous speed thereof. 
     With reference to FIG. 3, the control unit ECU includes a processing and control stage ST with an associated memory M. 
     The processing stage ST receives the signals transmitted by the sensors S 1  to S 3  and is connected to a memory M storing values representing the corresponding curves Q defined above for a plurality of different operating conditions of the vehicle. 
     The stage ST is operable to control activation of the electric pump  6  and the electric fan  5 , in particular to control the electric power supplied to each respectively. 
     In operation, the processor stage ST receives signals from the sensors S 2  and S 3  which identify the instantaneous operating condition of the motor vehicle, and the signal from the sensor S 1  which indicates the temperature of the engine E. 
     On the basis of the signals supplied by the sensors S 2  and S 3 , the processor stage ST selects from the memory M the values of a corresponding predetermined function expressing the curve Q which represents the locus of the working point of minimum total electricity consumption for that particular operating condition. 
     Once the said curve Q has been identified, at the start of the control operation, the stage ST supplies the electric pump  6  (or the electric fan  5 ) with a predetermined, relatively low, value of electric power and supplies the electric fan (or the electric pump) with the value of electric power that corresponds to the power supplied to the electric pump  6  (electric fan  5 ) according to the curve Q relating to that instantaneous operating condition. The stage ST then checks the temperature of the engine E (reported by the sensor S 1 ) and if this should be higher (lower) than a predetermined reference value, initiates an increase (decrease) in the electric power supplied to the pump  6  and the fan  5 , moving their working point along the previously determined curve Q. 
     The curve Q which is used to obtain feedback to control the temperature of the engine E can be changed when the signals supplied to the stage ST from the sensors S 2  and S 3  indicate that a noticeable change has taken place in at least one of the two parameters identifying the operating condition of the vehicle: that is the speed thereof and the outside air temperature. 
     The values of electric power that must be supplied at any one time to the electric fan and to the electric pump can be controlled, for example by means of modulation of the duty cycle of the voltage supplied to this equipment. 
     The control system described above enables the cooling system to work at optimum efficiency, thus ensuring that electricity consumption is kept to a minimum for every operating condition. 
     Naturally, the principle of the invention remaining the same, embodiments and manufacturing details can be varied widely from those described and illustrated here purely by way of non-limitative example, without departing thereby from the scope of the present invention, as claimed in the appended claims. 
     In particular, the scope of the invention covers a system in which two electric fans, or one electric fan unit with two fans operated by the same electric motor, are associated with the radiator.