Abstract:
A method of conserving energy during a heating event wherein a coolant is heated in a cooling system is disclosed. The method includes establishing a first set point temperature for a first point in the cooling system and establishing a second set point temperature lower than the first set point temperature for a second point in the cooling system. Normally, the coolant is maintained at the second set point temperature at the second set point in the cooling system. During the heating event, the second set point temperature is raised to substantially match the first set point temperature to reduce necessary heating of the coolant at the first point.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/622,650, filed Oct. 27, 2004. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to coolant systems for vehicles. More particularly, the present invention relates to a coolant temperature control method which utilizes matching of a valve temperature set point, which controls the temperature of a coolant flowing into a propulsion system, and a heater set point, which controls the temperature of a coolant flowing into a heater core, in heating situations and reversion of the valve temperature set point back to a value which is optimal for efficient operation of the propulsion system in non-heating situations. 
     BACKGROUND OF THE INVENTION 
     In an automotive cooling system, an electronically controlled valve or other flow control device may control the temperature of a coolant at one point in the system, such as at the entry point of the coolant into the propulsion system of a vehicle, for example. The temperature of the coolant at this point in the system, known as the valve temperature, can be measured by a temperature sensor. The valve or other flow control device may control the valve temperature of the coolant at this point, according to a target temperature or valve set point temperature, by varying the ratio of the quantity of coolant flowing through a radiator or other heat exchanger to the quantity of coolant bypassing the radiator or heat exchanger and flowing into the propulsion system of the vehicle. 
     Under certain operating conditions, there may be situations, which call for additional temperature requirements at another point in the cooling system. These situations could include, for example, situations in which cabin heating and/or windshield defrosting is/are required. One of these additional temperature requirements could be that of the coolant entering a heater core, which provides heated air to the vehicle cabin, for example. At this point in the system, a heater temperature of the coolant would be measured by a different temperature sensor than that used to measure the valve temperature. The heater temperature requirement at that point in the system, corresponding to a heater set point temperature, may be different from the valve temperature requirement. Furthermore, the cooling system may include a coolant heater, which can be operated to augment the heater temperature of the coolant in order to achieve the heater set point temperature requirement at this point in the system. 
     In heating situations, the coolant heater typically consumes energy in order to heat the coolant. In meeting heater set point temperature requirements, it is therefore desirable to minimize the quantity of energy consumed by the coolant heater in order to maximize vehicular energy efficiency. For various reasons, the valve set point temperature may be lower than the heater set point temperature. The situation can therefore arise in which the heater set point temperature calls for the addition of heat from the coolant heater whereas the valve set point temperature simultaneously calls for the dissipation of heat from the radiator. This can lead to reduced vehicular energy efficiency because the coolant heater is consuming energy to add heat to the coolant while the valve is distributing the coolant through the radiator in order to draw the heat back out of the coolant. 
     Therefore, a control strategy is needed in which the valve set point temperature changes to more closely match the heater set point temperature when a heating situation arises and reverts to a value, which is optimal for cooling of the propulsion system when a heating situation does not exist. Such a strategy would facilitate optimum energy efficiency throughout all operating conditions. 
     SUMMARY OF THE INVENTION 
     The present invention is generally directed to a novel method of conserving fuel during a heating event in a cooling system such as a vehicle cooling system. The method is suitable for use in an automotive coolant system having a propulsion system, such as an internal combustion engine or fuel cell stack, for example, and a coolant line, which distributes coolant into and out of the propulsion system. A coolant heater is provided in the coolant line for heating the coolant prior to distribution of the coolant into a heater core during a heating event. A valve is provided in the coolant line for selectively distributing the coolant through either a radiator, radiator bypass line that bypasses the radiator, or both. 
     According to the method of the invention, a heater set point temperature is initially established. The heater set point temperature is used to control the operation of the heater so as to raise the coolant temperature to the heater set point temperature during a heating event. A valve set point temperature is also established. The valve set point temperature determines whether the valve will distribute the coolant through the radiator to dissipate heat from the coolant, shunt the coolant through the radiator bypass line to retain heat in the coolant, or a combination of both. 
     In the absence of a heating event, the coolant system is normally operated according to the valve set point temperature. Therefore, the valve distributes the coolant through the radiator as needed, which dissipates excess heat from the coolant to subsequently facilitate absorption of heat by the coolant from the propulsion system to facilitate optimum energy efficiency and/or performance of the propulsion system. During a heating situation, the coolant heater is operated to heat the coolant prior to distribution of the coolant into the heater core. Accordingly, at the onset of the heating situation, the valve set point temperature is elevated to substantially match the heater set point temperature. Therefore, the valve shunts the coolant through the radiator bypass line such that heat is retained in the coolant. Consequently, the coolant heater consumes less vehicle energy than would have been the case had the elevation of the valve set point not occurred since the temperature of the coolant subsequently flowing into the coolant heater is now substantially the same as the heater set point temperature. When the heating situation no longer exists, the valve set point temperature returns to the original value to facilitate optimal energy efficiency and/or performance of the propulsion system efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a vehicle coolant system in implementation of the present invention; and 
         FIG. 2  is a flow diagram, which summarizes operational steps carried out according to the method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIG. 1 , a schematic diagram of a coolant system in implementation of the present invention is generally indicated by reference numeral  10 . The coolant system  10  may be a vehicle coolant system, which is designed to absorb heat from a propulsion system  12 , such as an internal combustion engine or a fuel cell stack, for example, which propels a vehicle. The propulsion system  12  is disposed in fluid communication with a coolant inlet line  28 , which distributes a liquid coolant into the propulsion system  12 , and a coolant outlet line  30 , which distributes the coolant from the propulsion system  12 . As used herein, the term “downstream” refers to the direction of coolant flow through the coolant inlet line  28  or coolant outlet line  30  of the vehicle coolant system  10 . 
     A coolant heater  14  is typically provided in the coolant outlet line  30 , downstream of the propulsion system  12 . A heater core  18  is provided in the coolant outlet line  30 , downstream of the coolant heater  14 . A heater temperature sensor  16  is typically provided in the coolant outlet line  30 , between the coolant heater  14  and the heater core  18 . The heater core  18  provides for the thermal exchange of heat from coolant flowing through the coolant outlet line  30  to air which flows into the cabin of the vehicle, as is known by those skilled in the art. In operation of the vehicle coolant system  10 , the heater temperature sensor  16  senses the temperature of the coolant in the coolant outlet line  30  prior to entry of the coolant into the heater core  18 . 
     The inlet port of a three-way valve  20  is provided in fluid communication with the coolant outlet line  30 , downstream of the heater core  18 . The coolant outlet line  30  extends from one outlet port of the valve  20 , whereas a radiator bypass line  24  extends from the other outlet port of the valve  20 . The inlet of a radiator  22  or other heat exchanger is disposed in fluid communication with the coolant outlet line  30 , downstream of the valve  20 . 
     The coolant inlet line  28  is disposed in fluid communication with the outlet of the radiator  22  and with the coolant inlet of the propulsion system  12 . The radiator bypass line  24  is confluently connected to the coolant inlet line  28 , between the radiator  22  and the propulsion system  12 . A valve temperature sensor  26  is provided in the coolant inlet line  28 , typically between the radiator bypass line  24  and the propulsion system  12 . In operation of the vehicle coolant system  10 , the valve temperature sensor  26  measures the temperature of coolant flowing through the coolant inlet line  28  prior to entry of the coolant into the propulsion system  12 . 
     In operation of the vehicle coolant system  10 , coolant (not shown) is pumped from the coolant inlet line  28 , through the propulsion system  12  and into the coolant outlet line  30 , respectively, to absorb heat from the propulsion system  12  as the propulsion system  12  propels the vehicle. Under many circumstances, the heater  14  is not operated as the coolant flows through the heater  14  and the heater core  18 , respectively. However, under circumstances in which a “heating situation” arises, as will be hereinafter described, the heater  14  is operated to augment heating of the coolant prior to distribution of the coolant into the heater core  18 . A “heating situation” includes circumstances in which heated air is required for the cabin interior or for windshield defrosting purposes, for example. Accordingly, in a heating situation, the coolant heater  14  initiates heating of the coolant in the event that the heater temperature sensor  16  determines that the temperature of the coolant, referred to herein as the heater temperature, falls below a threshold value, referred to herein as the heater set point temperature. 
     Depending on the position of the valve  20 , coolant flowing from the heater core  18  is distributed either through the radiator  22 , in which case heat is dissipated from the coolant, or through the radiator bypass line  24 , in which case heat is retained by the coolant, or a combination of the two. In the event that the temperature of the coolant as measured by the valve temperature sensor  26 , referred to herein as the valve temperature, meets or exceeds a threshold value, referred to herein as the valve set point temperature, the valve  20  distributes some or all of the coolant through the radiator  22 . On the other hand, in the event that the valve temperature falls below the valve set point temperature, the valve  20  distributes the coolant through the radiator bypass line  24 , such that heat is retained by the coolant. The coolant then enters the propulsion system  12  to absorb heat from the propulsion system  12 . 
     Under many operating circumstances, the valve temperature of the coolant at the valve temperature sensor  26  exceeds the valve set point temperature. Consequently, the valve  20  distributes some or all of the coolant through the radiator  22 , thereby ensuring that the temperature of the coolant as it enters the propulsion system  12  is sufficiently low to facilitate absorption of heat from the propulsion system  12 . This, in turn, may facilitate optimum energy efficiency and/or performance of the propulsion system  12 . 
     In certain vehicle coolant system  10  operating conditions, the heater set point temperature, which controls operation of the coolant heater  14 , is set higher than the valve set point temperature, which controls operation of the valve  20 . Therefore, during a heating situation, the coolant heater  14  heats the coolant to such a degree that the heater temperature of the coolant, as measured by the heater temperature sensor  16 , rises to the level of the heater set point temperature. This ensures that sufficient thermal exchange is conducted in the heater core  18  between the coolant and air to meet the heated air demands of the vehicle cabin. 
     Because the heater set point temperature is higher than the valve set point temperature, however, the valve temperature sensor  26  causes the valve  20  to distribute the coolant through the radiator  22  in order to dissipate heat from the coolant and lower the temperature of the coolant down to the valve set point temperature. Therefore, the valve temperature of the coolant, as measured by the valve temperature sensor  26 , is less than the heater temperature of the coolant as previously measured by the heater temperature sensor  16 . As the coolant emerges from the propulsion system  12 , the actual temperature of the coolant is typically still below the heater set point temperature. Consequently, the heater  14  is required to consume energy in order to subsequently raise the temperature of the coolant distributed from the propulsion system  12  back up to the heater set point temperature prior to distribution of the coolant through the heater core  18 . 
     Referring next to  FIG. 1 , in conjunction with the flow diagram of  FIG. 2 , the method of the present invention is carried out by initially establishing a heater set point temperature for operation of the coolant heater  14 , as indicated in step  1  of  FIG. 2 . Throughout operation of the vehicle, the heater set point temperature may change depending on the need for heated air inside the vehicle cabin for example. A valve set point temperature is also established for operation of the valve  20 , as indicated in step  2 . In step  3 , in the absence of a heating situation, the vehicle coolant system  10  is operated according to the valve set point temperature. Accordingly, the valve  20  normally distributes the coolant through the radiator  22  to dissipate heat from the coolant. Therefore, the valve temperature of the coolant, as measured by the valve temperature sensor  26 , drops and approaches or meets the valve set point temperature prior to distribution of the coolant into the propulsion system  12 . In the event that the valve temperature of the coolant falls below the valve set point temperature, the valve  20  shunts the coolant through the radiator bypass line  24  to maintain the valve temperature of the coolant as close as possible to the valve set point temperature. 
     In the propulsion system  12 , the coolant absorbs heat and then is distributed through the coolant outlet line  30 . The valve set point temperature ensures that the valve temperature of the coolant flowing into the propulsion system  12  is such that absorption of heat from the propulsion system  12  by the coolant is sufficient to facilitate optimal energy consumption and/or performance from the propulsion system  12 . In the absence of a heating situation, the coolant heater  14  is typically not operated to facilitate heated air demands inside the vehicle cabin. Therefore, in the absence of a heating situation, vehicle energy is typically not consumed by the coolant heater  14 . 
     At the onset of a heating situation, however, the heater set point temperature requirements must now be met to facilitate the increased demand for heated air inside the vehicle cabin. Accordingly, the coolant heater  14  is operated to realize the heater set point temperature, which is typically higher than the valve set point temperature, as indicated in step  4  of  FIG. 2 . Accordingly, the coolant heater  14  augments the temperature of the coolant such that the heater temperature of the coolant rises and approaches or meets the raised or modified heater set point temperature. This heating of the coolant by the coolant heater  14  ensures that thermal exchange between the heated coolant and air in the heater core  18  is sufficient to meet the increased heated air demands inside the vehicle cabin. 
     As indicated in step  5 , at the onset of the heating situation, the valve set point temperature is raised to establish a modified valve set point temperature, which substantially matches the heater set point temperature. Consequently, the valve  20  distributes the coolant substantially through the radiator bypass line  24  rather than substantially through the radiator  22 . As a result, the valve temperature of the coolant remains at an elevated level as the coolant is distributed through the propulsion system  12 , coolant outlet line  30  and coolant heater  14 , respectively. Therefore, the heater temperature of the coolant, as measured by the heater temperature sensor  16 , substantially meets the heater threshold temperature. Consequently, the coolant heater  14  either need not be operated at all, operated at a significantly reduced power, or only intermittently in order to maintain the heater temperature at or close to the heater set point temperature. This substantially reduces the consumption of vehicle energy by the coolant heater  14  throughout the heating situation. 
     When the heating situation is over, the heater set point temperature is no longer used to control the coolant temperature entering the heater core. Therefore, the coolant heater  14  is typically no longer operated to heat the coolant. As indicated in step  6  of  FIG. 2 , the valve set point temperature returns to the original value. Consequently, the valve  20  again distributes the coolant through the radiator  22  to dissipate excess heat from the coolant prior to distribution of the coolant into the propulsion system  12 . This again facilitates optimum absorption of heat from the propulsion system  12  by the coolant, contributing to optimum energy consumption and/or performance of the propulsion system  12 . 
     It is to be understood that the invention is not limited to the exact construction and method which has been previously delineated, but that various changes and modifications may be made without departing from the spirit and scope of the invention as delineated in the following claims.