Patent Application
20170106721
This disclosure relates generally to vehicle heating, ventilation, and air conditioning (HVAC) system operation. More particularly, the disclosure relates to energy-efficient systems and methods for vehicle window defogging and for prevention of window refreezing.
During motor vehicle operation, often external and internal climate conditions combine to lead to window fogging and/or re-freezing. That is, after an initial warm-up phase of operation of the vehicle during which typically the vehicle windscreen, side windows, etc. are defogged and/or de-iced, in part by use of the vehicle heating, ventilation, and air-conditioning (HVAC) system. However, during vehicle operation conditions may be conducive to window fogging and/or re-freezing. For example, exterior ambient temperatures may be sufficiently cold and passenger cabin conditions may be sufficiently warm and humid to promote condensation on one or more of the windows, leading to windscreen fogging and/or re-freezing.
A conventional solution to this problem is to continuously divert a portion of a conditioned airflow from the HVAC system to one or more of the windows to prevent window fogging/re-freezing during vehicle operation. While substantially effective, such constant airflow bleed from the HVAC system can have negative consequences, including additional undesired noise, vibration, etc. from airflow and increased HVAC blower load, undesirably increased temperatures in an upper portion of the vehicle passenger cabin, passenger “dry eye” from constant air flow, and others.
Moreover, the HVAC system is a critical element of the modern motor vehicle for other reasons than defogging/de-icing. Efficient HVAC performance is required in all environments for vehicle occupant comfort and for all weather visibility issues. In turn, efficient HVAC performance is increasingly a concern for overall vehicle energy management which also affects fuel economy in combustion engine-driven vehicles and hybrid vehicles, and range and electrical power budget in electric vehicles and hybrids. Continuously directing airflow to a window during vehicle operation can impose a significant and potentially excessive energy usage which may undesirably impact the vehicle's overall energy budget.
To solve this and other problems, the present disclosure relates at a high level to energy-efficient systems and methods for vehicle window defogging and for prevention of window refreezing. Advantageously, the described systems and methods incorporate consideration of various inputs relevant to conditions conducive to window fogging/re-freezing. According to those inputs, sufficient levels of conditioned air are directed to the window. By the described systems/methods, diversion of conditioned airflow to the vehicle window is substantially restricted to periods of vehicle operation when interior/exterior conditions are deemed conducive to window fogging/re-freezing rather than simply directing a continuous stream of conditioned air to a window to prevent fogging/re-freezing with the attendant disadvantages described above.
In accordance with the purposes and benefits described herein, in one aspect a method for prevention of fogging or re-freezing of a vehicle windscreen is described that includes, by one or more controllers, calculating a windscreen interior surface dew point temperature value and/or a probability value of a windscreen interior surface fogging and/or exterior surface re-freezing. Then only a sufficient conditioned airflow is provided to the windscreen to prevent the calculated fogging and/or re-freezing probability value from exceeding a predetermined fogging and/or re-freezing risk threshold value. In embodiments, this occurs after an initial passenger cabin warm-up period and during operation of the vehicle HVAC system in a floor mode.
In an embodiment, only a sufficient conditioned airflow is provided to cause a windscreen interior surface temperature value to exceed the windscreen interior surface dew point temperature value or to cause a windscreen exterior surface temperature value to exceed a windscreen exterior surface freezing temperature. The windscreen interior surface dew point temperature value or windscreen exterior surface temperature value may be adjusted by a variety of inputs, including exterior and interior climate-related inputs, vehicle occupant inputs, remote inputs, and others.
In another aspect, a system is provided for prevention of fogging or re-freezing of a vehicle windscreen according to the above described methods, including one or more controllers and a vehicle heating, ventilation, and cooling (HVAC) system including at least one actuator operatively connected to the one or more controllers and to at least one door associated with at least one windscreen defrost duct. The one or more controllers are configured to calculate a windscreen interior surface dew point temperature value and/or a probability value of a windscreen interior surface fogging and/or exterior surface re-freezing, and to cause the HVAC system to provide only a sufficient conditioned airflow to the windscreen to prevent the calculated fogging and/or re-freezing probability value from exceeding a predetermined fogging and/or re-freezing risk threshold value. The one or more controllers are further configured to translate the door between a closed configuration, a fully open configuration, and at least one intermediate configuration to regulate airflow volume to the windscreen.
In embodiments, a variety of devices are provided in the system for providing or receiving the exterior and interior climate-related inputs, vehicle occupant inputs, remote inputs, and others. These include without intending any limitation various sensors such as sun load/direction sensors, rain sensors, passenger cabin relative humidity sensors, windscreen relative humidity sensors, windscreen interior surface temperature sensors, windscreen exterior surface temperature sensors, passenger cabin temperature sensors, vehicle occupant sensors, vehicle speed sensors, wind speed/direction sensors, vehicle-associated exterior ambient temperature sensors, and others. Other contemplated devices include an HVAC system control panel, an electronic automatic temperature control (EATC) module, receivers for remote temperature data, receivers for remote humidity data, receivers for crowd-sourced data, and others.
In the following description, there are shown and described embodiments of the disclosed energy-efficient systems and methods for vehicle window defogging and for prevention of window refreezing. As it should be realized, the systems/methods are capable of other, different embodiments and its several details are capable of modification in various, obvious aspects all without departing from the devices and methods as set forth and described in the following claims. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not as restrictive.
The accompanying drawing figures incorporated herein and forming a part of the specification, illustrate several aspects of the disclosed energy-efficient systems and methods for vehicle window defogging and for prevention of window refreezing, and together with the description serve to explain certain principles thereof. In the drawings:
Reference will now be made in detail to embodiments of the disclosed systems and methods for vehicle window defogging and for prevention of window refreezing, examples of which are illustrated in the accompanying drawing figures wherein like reference numerals identify like features.
Reference is now made to
Air passing through the HVAC system 100 also typically passes through an evaporator core 110 for cooling/dehumidifying if the vehicle air-conditioning system is activated. Certain HVAC systems activate the air-conditioning system to dehumidify air passing through the system even if the air is to be subsequently warmed. An evaporator drain 112 may be included to allow discharge of condensate generated during the process of dehumidifying air passing through the HVAC system. A heater core 114 is provided to increase the temperature of the air passing through the HVAC system 100 if the vehicle heating system is activated, and as is known is substantially a small radiator in design and effect.
An HVAC system 100 also usually includes at least ducts 116a, 116b, 116c leading respectively to one or more defrost vents (not shown), one or more passenger cabin main upper vents (not shown), and one or more passenger cabin floor vents (not shown). Actuable mode doors 118a, 118b control the direction of airflow through the HVAC system 100, i.e. whether conditioned air is directed to the defrost vents (defrost mode), to the floor vents (floor mode), to the main upper vents, or combinations. A blend door 120 controls the amount of airflow passing through the heater core 114. As is known, this in turn determines the warmth of the air reaching the various vehicle vents. Actuators 122 control the translation of mode doors 118a, 118b and blend door 120 from an open configuration to a closed configuration. Various actuator designs are known in the art, including cable style actuators, vacuum-driven actuators, electronic stepper motors, and others.
Representative settings provided by the mode doors 118a, 118b and blend door 120 include full heat (the blend door 120 diverts all airflow through the heater core 114), economy mode (blend door 120 diverts all airflow past the heater core 114 but the vehicle air-conditioning system is not activated), and max air-conditioning (blend door 120 diverts all airflow past the heater core 114 and the vehicle air-conditioning system is activated).
Other devices may be incorporated into or operatively connected to the HVAC system 100, including passenger cabin air temperature sensors (not shown) and vent/outlet temperature sensors (not shown) for providing accurate passenger cabin and air temperature values, allowing fine-tuned control of the HVAC elements described above for precise passenger cabin temperature/humidity control. In turn, it is known to provide dual zone/quad zone HVAC systems including divided mode doors and separate plenums, to allow providing different temperature settings to different portions of the vehicle passenger cabin.
With the foregoing as background, as summarized above the present disclosure is directed to methods for preventing fogging and/or re-freezing of a vehicle window such as a windscreen or others, and to systems for implementing the methods. At a high level, the methods comprise, after an initial vehicle passenger cabin warm-up, determining whether a risk of windscreen fogging/re-freezing requires providing a sufficient conditioned airflow to the windscreen to prevent/reduce the risk of such fogging/re-freezing. As will be appreciated, as used herein “conditioned” refers to adjusting a temperature and/or a humidity of air passing through the vehicle HVAC system as required according to ambient and/or passenger cabin conditions of temperature, humidity, etc. As will also be appreciated, as used herein the term “sufficient” refers to an airflow speed, air temperature, air humidity, or combinations thereof necessary to negate the determined risk of fogging/re-freezing. In one embodiment, on determining a risk of windscreen fogging/re-freezing, according to the described method a determination is made of whether a full air bleed, i.e. full airflow, to the windscreen is required, whether a reduced air bleed is satisfactory, or whether no air bleed to the windscreen is required.
In determining the risk of fogging/re-freezing, according to the described methods a variety of inputs that may influence or increase the risk of windscreen fogging/re-freezing may be considered. Without intending any limitation, these inputs may include sun load/direction, rain, passenger cabin relative humidity, windscreen interior or exterior relative humidity, windscreen interior surface temperature, windscreen exterior surface temperature, passenger cabin temperature, number of vehicle occupants, vehicle speed/rate of travel, wind speed/direction, exterior ambient temperature, data/input provided by a vehicle occupant, remotely generated temperature information, remotely generated relative humidity information, and crowd-sourced data. By these and other inputs a determination may be provided of a risk of windscreen fogging/re-freezing, allowing an informed decision as to whether a conditioned airflow should be provided to the vehicle windscreen, if so for how long, and even potentially of specific parameters (temperature, relative humidity, etc.) of the conditioned air so provided. By this expedient, energy usage is conserved compared to simply providing a constant flow of conditioned air to the windscreen as is common in conventional strategies for reducing risk of windscreen fogging/re-freezing.
In more detail, the described methods comprise use of various inputs as summarized above in calculating one or more of a windscreen fogging probability, a windscreen direct dew point, and a windscreen and/or windscreen wiper freezing risk value or probability value. That probability value is then compared against a suitable benchmark or threshold value, and from that comparison a determination is made of whether a full air bleed, a partial air bleed, or no air bleed from an HVAC airflow is required to reduce the determined fogging/re-freezing risk value to an acceptable level.
A defrost flow control door 218 (see the discussion above of
Without intending any limitation, examples of sensors 222 contemplated for inclusion in the present system 200 include sun load/direction sensors, rain sensors, passenger cabin relative humidity sensors, windscreen relative humidity sensors, windscreen interior surface temperature sensors, windscreen exterior surface temperature sensors, passenger cabin temperature sensors, vehicle occupant sensors, vehicle speed sensors, wind speed/direction sensors, vehicle-associated exterior ambient temperature sensors, and others. It will be appreciated that a number of designs for each of the above-described sensors are known in the art, and inclusion of any such suitable sensor is contemplated herein. As non-limiting examples, rain sensors based on a principle of total internal reflection of an infrared light beam are well known for detecting rainfall, and are often used in conjunction with a controller 224 to automatically actuate vehicle 202 wiper blades. Likewise, a variety of temperature and relative humidity sensors are known in the art. Still more, various passenger or vehicle occupant sensors are known, including pressure sensors associated with passenger seat 217, sensors associated with vehicle seat belt buckles, camera systems connected to controllers including logic for detecting vehicle occupants, etc.
Inputs gathered by the described sensors 222a . . . 222n, as well as potentially other inputs provided to controller 224 including vehicle occupant input such as manual actuation or programming of HVAC system 212, manual or automatic wiper blade actuation, remote temperature data, remote relative humidity data, etc., are provided to controller 224, which in turn utilizes those inputs to accomplish the methods of the present disclosure.
In an embodiment of a method according to the disclosure, a suitable windscreen fogging benchmark or threshold value is a windscreen dew point temperature (TDEWPOINT), i.e. the temperature and/or relative humidity at which moisture begins to condense on the vehicle windscreen. A determination is made of the amount of conditioned air (if any) required to raise an interior temperature of the windscreen (TGLASSint) to above the threshold TDEWPOINT.
In more detail and with reference to
If TGLASSint>TDEWPOINT, at step 310 after a predetermined time period a determination is made whether TGLASSint<TDEWPOINT. If so, a current defrost flow is maintained (step 312) to continue to increase TGLASSint. If at step 312 TGLASSint>TDEWPOINT, this indicates that the risk of fogging is reduced and that the defrost flow may be safely reduced (step 314), such as (with reference to
As will be appreciated and as will be discussed further below, the fogging threshold value TDEWPOINT may be adjusted as necessary according to other inputs influencing TDEWPOINT, in non-limiting examples including sun load/direction, rain, passenger cabin relative humidity, windscreen interior or exterior relative humidity, windscreen interior surface temperature, windscreen exterior surface temperature, passenger cabin temperature, number of vehicle occupants, vehicle speed/rate of travel, wind speed/direction, exterior ambient temperature, and others.
In an embodiment wherein TDEWPOINT is established as the fogging benchmark or threshold value, the described method contemplates adjusting that threshold value according to measured vehicle speed (VSPEED), measured exterior ambient temperature (TEXT), and defroster flow rate (DEF FLOW), and defroster temperature (TDEF) according to a formula:
T
GLASSint=[(VSPEED)·(TEXT)]+[(DEF FLOW)·(TDEF)]/(VSPEED)+(DEF FLOW) (1)
As will be appreciated, this accounts for the fact that as vehicle speed increases, the interior glass temperature begins to approach the exterior ambient temperature, whereby TENT could potentially fall below TDEWPOINT. To adjust for this, according to the method the system could do one or both of increasing the defroster flow rate and increasing the defroster temperature. TGLASSint could be estimated analytically, measured directly such as by an infrared camera or other suitable means, or estimated by taking a limited number of on-glass sensor readings and interpolating TGLASSint by calculation or by calibration data.
Of course, TDEWPOINT could be perfectly calculated if temperature and humidity could be exactly determined at every point in the vehicle passenger cabin 204. However, in actuality a vehicle usually includes a limited number of sensors, for example one temperature and one humidity sensor by cluster. Thus, typically TDEWPOINT is estimated. In an embodiment, TDEWPOINT may be estimated according one or more of the formulae:
T
DEWPOINT
=T
DEWPOINT(Temperature, percent relative humidity)interior+C1 (number of vehicle occupants (2); or
T
DEWPOINT
=T
DEWPOINT (Temperature, percent relative humidity)interior+C1 (number of vehicle occupants+C2(VSPEED) (3); or
(2) or (3)+C3 (rain sensor signal) (4).
Of course, still other factors could be considered as described above including without intending any limitation Cx (sunload sensor data), Cx1 (total drive time), Cx2 [externally supplied (e.g. cloud-sourced) weather data], and others.
In other embodiments, a suitable windscreen re-freezing benchmark or threshold value is provided by a predetermined windscreen temperature at which re-freezing is likely (TREFREEZE), and a determination is made of the amount of conditioned air (if any) required to raise an exterior temperature of the windscreen (TGLASSext) to above TREFREEZE. TREFREEZE may be set at a predetermined ambient temperature threshold or benchmark whereby windscreen re-freezing is possible or likely, such as 0° F.
With reference to
If TGLASSext>TREFREEZE, at step 410 after a predetermined time period a subsequent determination is made whether TGLASSext<TDEWPOINT. If so, a current defrost flow is maintained (step 312) to continue to increase TGLASSext. If at step 412 TGLASSext>TREFREEZE, this indicates that the risk of re-freezing is averted and that the defrost flow may be safely reduced (step 414), such as (with reference to
As set forth above in the discussion of the fogging threshold value, the re-freezing threshold value may be adjusted as necessary according to other inputs influencing TREFREEZE as will be discussed. As will appreciated, TREFREEZE occurs when TGLASSext<0° C. In use, the described system controls for TGLASSext to keep that value higher than TREFREEZE plus a safety factor. In embodiments, TREFREEZE may be expressed as a function F of various relevant inputs, including exterior/ambient temperature, vehicle speed, defrost airflow velocity, and defrost airflow temperature. Other potential inputs relevant to TREFREEZE include sun load/direction, rainfall, wiper settings, and others.
Ideally, TGLASSext could be accurately measured at all points across the vehicle windshield, such as by infrared camera technology. In practice, however, vehicle manufacturers can include only limited numbers of sensors for gauging factors that may contribute to (TGLASSint, TEXT, etc.) and uncertainty is introduced into the calculations. In embodiments wherein TREFREEZE is used as the windscreen re-freezing benchmark or threshold value, the described method contemplates adjusting that threshold value according to measured vehicle speed (VSPEED), measured exterior ambient temperature (TEXT), and defroster flow rate (DEF FLOW), and defroster temperature (TDEF) according to a formula:
T
GLASSext≈[(DEF FLOW)·(TDEF)]−[(VSPEED)·(TDEF)]/(TEXT)]/(DEF FLOW)+[(VSPEED) (6)
In embodiments, TREFREEZE (a minimum target for TGLASSext) is estimated:
T
REFREEZE
=T
EXT
+C
2(VSPEED)+C4[(DEF FLOW)·(TDEF)] (7); or
T
REFREEZE
=T
EXT
+C
2(VSPEED)+C4[(DEF FLOW)·(TDEF)]+C3 (rain sensor signal) (8).
Of course, other factors could be considered and included as described above including Cx (sunload sensor data), Cx1 (total drive time), Cx2 [externally supplied (e.g. cloud-sourced) weather data], and others.
Thus, it will be appreciated that by the above teachings systems and methods are provided for vehicle windscreen defogging/re-freezing prevention which advantageously provide energy savings compared to conventional systems/methods. The described systems and methods allow window defogging/re-freezing prevention during vehicle operation, yet obviate any need for a constant, consistently increased defrost airflow and attendant energy costs and other disadvantages. Obvious modifications and variations are possible in light of the above teachings. All such modifications and variations are within the scope of the appended claims when interpreted in accordance with the breadth to which they are fairly, legally and equitably entitled.
