Abstract:
A method for determining ambient air temperature outside of a vehicle with a sensor mounted on the vehicle, includes the steps of determining a road speed of the vehicle, comparing the determined road speed to a reference road speed value, if the determined road speed is below the reference road speed value, activating a device to move ambient air across the sensor, the ambient air being drawn from a location outside the vehicle, taking a temperature reading with the sensor, and, if the temperature reading is lower than a stored temperature value, storing the lower temperature reading as the ambient air temperature.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/301,749, filed Feb. 5, 2010. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    Conventional systems in a vehicle for measuring ambient air temperature include a sensor placed on the vehicle in a location exposed to ambient air. Any location on the vehicle, however, is subject to heat generated by the vehicle engine, exhaust, transmission, etc., which could influence a temperature measurement. When the vehicle is stationary or moving slowly, for example, a boundary layer of hot air exists around the engine compartment and exhaust components, and ambient air temperature measurement is influenced by the heat in this boundary layer. 
         [0003]    Various methods for reducing or correcting for the effect of vehicle-generated heat are known. U.S. Pat. No. 5,813,765 to Peel et al. includes placing the temperature sensor on the radio antenna to locate it as far as possible from vehicle heat sources. U.S. Pat. No. 7,387,437 to Brown et al. discloses using multiple sensors placed at different locations on the vehicle, comparing the readings from the multiple sensors, and applying a correction factor generated according to vehicle speed and other factors. U.S. Pat. No. 4,770,543 to Burghoff et al. discloses a method including monitoring vehicle speed and using a temperature measured when speed exceeds a threshold, and, when speed drops below the threshold, storing and using a last temperature measurement before the speed dropped below the threshold. 
         [0004]    The invention improves on the art in proposing a method and system for measuring ambient air outside a vehicle that overcomes deficiencies in the art. According to the invention, a temperature sensor is mounted in a flow path of an air blowing or moving device, such as the engine radiator fan. A controller is configured to monitor at least one vehicle parameter, compare the vehicle parameter to a reference parameter, and responsive to the comparison, control the air blowing device and make an ambient air temperature reading. 
         [0005]    According to the invention, the vehicle parameter may be a vehicle speed value, and the air blowing device is controlled to be activated to move ambient air across the sensor if the vehicle speed value is below a road speed reference value stored in a controller memory. 
         [0006]    According to another aspect of the invention, the method includes the steps of monitoring the vehicle speed for a measured interval after taking the temperature reading, and, if the determined road speed remains below the road speed reference value during the interval, further including activating the device to move ambient air across the sensor, taking a temperature reading with the sensor, and holding the temperature reading as the current ambient air temperature if the temperature reading is lower than the stored temperature value. 
         [0007]    According to another aspect of the invention, the sensor is mounted in an air flow path of a vehicle radiator fan, and the step of controlling the device to move ambient air across the sensor comprises activating the radiator fan. 
         [0008]    Alternatively, an air blowing device to move air across the sensor may be provided if locating the sensor in the radiator fan flow path is not convenient or desired. 
         [0009]    According to another aspect of the invention, the method includes applying a correction to the temperature reading and storing the corrected temperature reading as the ambient air temperature. The correction may compensate for the effect of heat not removed by the activated fan, and may constitute a subtraction of 2 degrees Celsius. 
         [0010]    The method also includes the step of communicating the current ambient air temperature to vehicle components, for example, by broadcasting a temperature signal on the CAN bus. The Engine Management System and other controllers can then make use of the temperature information to perform various functions. 
         [0011]    According to the invention, the method includes taking a plurality of temperature readings during a predetermined time duration while the fan is activated and storing a lowest temperature reading as the current ambient air temperature. 
         [0012]    According to another aspect of the invention, if the determined road speed is above the road speed reference value, for example 50 kph, for at least a predetermined time duration, the method includes continuously taking temperature readings as the ambient air temperature. The predetermined time duration may be set at 90 seconds to allow sufficient air flow over the temperature sensor to remove enough engine heat for an accurate ambient air temperature reading. 
         [0013]    According to yet another aspect of the invention, if the determined road speed is above a second road speed reference value, for example 80 kph, which is higher than the first road speed reference value, the method includes immediately continuously taking temperature readings and storing a lowest value as the ambient air temperature. 
         [0014]    According to another aspect of the invention, the method includes monitoring the engine temperature, and upon determining that the engine temperature is below a reference temperature, for example, 50 degrees Celsius, which indicates a cold engine start, taking a temperature reading with the sensor, and, holding the temperature reading as the current ambient air temperature. 
         [0015]    According to yet another aspect of the invention, the method includes monitoring the engine temperature and if the engine temperature is above the reference temperature, for example, 50 degrees Celsius, which indicates a warm engine or may indicate a warm engine start, holding the last held temperature reading as the current ambient air temperature for a measured interval, activating the device to move ambient air across the sensor after the measured interval, taking a temperature reading with the sensor and, holding the temperature reading as the current ambient air temperature if the temperature reading is lower than the held temperature value. The measured interval for holding the last held temperature may be 60 minutes, for example. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0016]      FIG. 1  is a schematic representation of an embodiment of a system according to the invention; 
           [0017]      FIG. 2  is a schematic representation of a controller arrangement in accordance with the invention; 
           [0018]      FIG. 3  is a functional diagram of a portion of an embodiment of a method according to the invention; and 
           [0019]      FIG. 4  is a diagram of another portion of the method of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    An exemplary embodiment of a system for determining ambient temperature according to the invention is illustrated schematically in  FIG. 1 . The system includes a temperature sensor  10  mounted on the vehicle (not illustrated) in an air flow path  12  of an air blowing device or fan  14 . The fan  14  may conveniently be the vehicle radiator fan. Alternatively, a dedicated fan may be provided if mounting the temperature sensor near the radiator is not desired. The fan  14  or air blowing device is arranged to draw air from outside the vehicle, i.e., ambient air, and move it across the temperature sensor. 
         [0021]    A controller  20  is connected to receive temperature readings from the temperature sensor  10 . The sensor  10  may be connected to an instrument cluster module (See,  FIG. 2 ) which receives the temperature reading and passes it to a Vehicle Electronic Control Unit (ECU). The controller  20  is also connected to the fan  14  to control operation of the fan, and is connected to receive signals from a vehicle speed sensor  22  and engine temperature sensor  24 . The controller may be implemented as a single device, which in this described embodiment is the Vehicle ECU. 
         [0022]    The controller  20  broadcasts the ambient air temperature value onto the vehicle data network  26 , for example, a J1939 CAN link to communicate the value to other systems on the vehicle that make use of the temperature value. This may include, for example, the instrument cluster, which displays the temperature value to the driver, and the Engine Management System. The Engine Management System may use the ambient air temperature in performing certain functions, for example, in exhaust aftertreatment systems temperature models, in mass flow calculations and condensation protection, and controlling exhaust gas recirculation cooler cleaning, among others. 
         [0023]    Alternatively, the controller  20  may comprise several devices interconnected for communication by the vehicle data bus, each performing one or more of the control functions, as illustrated in  FIG. 2 . For example, the controller  20  may be implemented as and comprise an Engine Management unit  32  controlling the fan and reading engine temperature, an Instrument Cluster unit  34  reading ambient temperature, and a Vehicle ECU  30  reading vehicle speed and performing other logic. In this arrangement, the Instrument Cluster  34  provides the temperature sensor reading to the VECU  30  and to a Climate Control unit  36 . The VECU  30  logic, as explained below, includes correcting the temperature sensor reading to produce an ambient temperature signal for the EMS  32 . Other configurations are also possible. 
         [0024]    The controller  20  contains control logic and processes the ambient air temperature signal. According to the invention, the temperature sensor value may be processed by applying a correction factor. According to the invention, the correction factor may be a subtraction of 2 degrees C. to compensate for the effects of heat that cannot be removed by the activation of the fan. 
         [0025]    An exemplary embodiment of a method according to the invention is shown in the functional diagrams of  FIGS. 3 and 4 . The method as shown should not be understood as requiring certain steps to be performed in a particular sequence; rather, the figures show relationships between and among functions, and, as described below, it should be understood that certain functions may be performed continuously or performed simultaneously in parallel, and depending on the result of a function, subsequent functions may then be performed. 
         [0026]    The controller  20  determines the ambient air temperature according to the method described below, and holds and communicates the ambient air temperature to other vehicle components, which may be as described above. The terms “held” or “hold” here means storing the value in memory and using that stored value when communicating the ambient air temperature. According to the invention, when the engine is shut off, the controller will hold the currently held temperature value until a new value is held. 
         [0027]    Referring now to  FIG. 3 , the controller  20  will access various vehicle systems or sensors to monitor vehicle parameters  40 , including engine temperature (e.g., engine oil or coolant temperature), vehicle speed, and key position. Monitoring vehicle parameters continues as other functions are performed, as certain values for vehicle parameters will determine that functions are performed, overriding other functions, as will be understood. The value for engine temperature is compared to a reference temperature. The value for vehicle speed is compared to a reference first speed and a reference second speed, which is higher than the first speed. 
         [0028]    If the controller  20  determines that the engine temperature is below an engine temperature reference value  42 , for example a coolant temperature of 50 degrees Celsius, which may indicate a cold engine start, the ambient temperature sensor  10  is read continuously and the value broadcast continuously  44 . The controller  20  continues to monitor vehicle parameters. 
         [0029]    Similarly, if the controller  20  determines that the vehicle speed has been above the first reference vehicle speed for more than a predetermined time interval  42 , the ambient temperature sensor  10  is read continuously and the value broadcast continuously. The first reference vehicle speed is high enough that an air flow over the sensor is sufficient to give an accurate temperature reading, which hi this embodiment is 50 kph. The predetermined time interval is sufficiently long to provide an ambient air flow to remove from the sensor and its environs heat that may be present if the vehicle had been stopped or moving slowly. In this embodiment, the predetermined time interval is 90 seconds. The controller continues to monitor the vehicle parameters  40 . 
         [0030]    Also, if the controller  20  determines that the vehicle speed is above the second reference vehicle speed, which in this embodiment is 80 kph, the ambient temperature sensor  10  is read continuously and the value broadcast continuously  44 . This second, higher speed reference is sufficiently high, and will involve a sufficiently long acceleration time, that the temperature sensor  10  reading is considered accurate. The controller  20  continues to monitor vehicle parameters. 
         [0031]    If the controller determines that the vehicle speed is below the first reference speed or the engine temperature is above the engine reference temperature value, the last valid temperature sensor reading is held  48 . A 60 minute delay timer is started  50 . Note that the vehicle parameters continue to be monitored. After 60 minutes, if the vehicle parameters have not changed (i.e., the speed remains below the reference vehicle speed and/or the engine temperature remains above the reference engine temperature), the fan is requested  52 . 
         [0032]    Turning to  FIG. 4 , the fan request results in the fan being activated  60 . A maximum fan run time is calculated  62  based on vehicle parameters related to heat generation and vehicle speed when power take-off equipment is in use. For example, the maximum fan run time may be calculated as follows: if the vehicle is moving at less than a PTO speed (in a speed range within which power take off equipment may operate, in this embodiment 8 kph) and the engine torque is greater than a PTO torque (here, 50% of maximum engine torque) and the coolant temperature is above a PTO coolant temperature (here, 80 degrees C.), the maximum fan run time is set at 5 minutes. Otherwise, the maximum fan run time is set at 150 seconds. The fan run times are calculated to provide a sufficient flow of air to the sensor to remove enough engine heat to allow an accurate ambient air temperature reading. 
         [0033]    Once the fan starts, the controller reads the temperature sensor immediately and repeats reading at read intervals  64 . The read interval may be set at a duration appropriate to detect changes in the temperature sensor reading induced by the active fan, for example 60 seconds. 
         [0034]    The controller monitors vehicle parameters for conditions related to determining a valid temperature reading  66 . The controller monitors the fan run time to determine if the maximum fan run time has been reached  72  or that the vehicle speed has been above the first vehicle reference speed for more than 90 seconds  74  or that the vehicle speed is above the second vehicle reference speed  76  or that the engine temperature is below the reference engine temperature  78 . If any of those parameters is met, the fan is stopped  70 . An override may be provided to protect the fan clutch by keeping the fan on for a minimum fan run period, for example, 30 seconds. 
         [0035]    If none of the parameters of fan run time  72 , vehicle speed  74 ,  76 , or engine temperature  78  is met, the controller continues to read the temperature sensor at the read intervals, and continues to monitor the fan run time, vehicle speed, and engine temperature. Again, if any of the vehicle parameters is met, as described above, the fan is stopped  70 . 
         [0036]    Alternatively, the controller may monitor for minimum fan run time, and at the end of the minimum run time, the controller will compares read temperature values to determine if the values are changing or stable. If the values are not changing or are changing within a minimum range, that is the readings differ by no more than a minimal amount, for example 1 degree C., the controller may determine that a valid temperature reading has been taken and stop the fan. If the temperature readings are not within the minimum range, the controller would continue to monitor the parameters or fan run time, vehicle speed, and engine temperature as described above. 
         [0037]    Once the fan is stopped, the lowest read temperature sensor value is held and broadcast as the ambient temperature  48  and the hold timer is again run for 60 minutes  50 , returning to the function as described in connection with  FIG. 3 . Also, as described above, the controller continues to monitor vehicle parameters of vehicle speed and engine temperature, which can trigger an interruption of the timer. 
         [0038]    Referring to  FIG. 3  and to step  48 , when the controller holds the last valid ambient temperature value, it continues to monitor the temperature sensor and compare the readings to the held value  54 . If a read value is lower than the held value, the lower value is held as the ambient air temperature  56 . 
         [0039]    If the controller determines that the key position is “off”, indicating that the vehicle has been shut down  80 , the last valid temperatures sensor reading is held as the ambient air temperature  82  and the hold timer continues to run. If the vehicle is started within the hold timer run time, the controller will determine ambient temperature according to the function described in connection to the hold timer (refer to step  50 ) or until the system detects a change in vehicle parameters calling for a new temperature sensor reading. 
         [0040]    The invention has been described in terms of preferred principles, embodiments, components, and steps, but those of skill in the art will recognize that substitutions may be made without departing from the scope of the invention as defined in the following claims.