Abstract:
Barometric pressure is determined in a hybrid electric vehicle from manifold absolute pressure. During engine operation, wide open throttle is commanded and output torque disturbances are offset by the electric machine. Barometric pressure is estimated based on sensed intake manifold pressure and engine speed dependent pressure offsets. During engine shut down, barometric pressure may be determined from manifold pressure without any offset adjustments.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a method and system for estimating barometric pressure and, more particularly, to a method and system for estimating barometric pressure in a hybrid vehicle. 
       BACKGROUND OF THE INVENTION 
       [0002]    Barometric pressure varies with weather conditions and altitude. IN a motor vehicle, an accurate determination of barometric pressure is essential for various engine control functions. For instance, precise metering of the amount of air and fuel delivered to the engine is necessary to achieve the desired combustion as well as acceptable vehicle emissions. When the barometric pressure drops, typically the timing needs to be retarded and the fuel mixture richened. In addition, the barometric pressure may also be used to control idle bypass airflow, check for limp-in conditions and other diagnostic functions. 
         [0003]    Barometric pressure can be measured in a variety of ways. Currently, in automotive applications, the barometric pressure can be measured using a barometric pressure sensor mountable on any suitable place on the vehicle where it sees true atmospheric pressure. Such a sensor generates an output signal indicative of the atmospheric pressure. The barometric pressure reading is then used for the various engine control functions. However, barometric pressure sensors can be costly and it is always desirable, particularly in automotive applications, to minimize costs. 
         [0004]    Consequently, methods have been developed for estimating barometric pressure without the use of a separate or dedicated barometric pressure sensor. It is know, for example, that barometric pressure can be estimated when the vehicle&#39;s throttle is wide open (i.e., WOT) and, in some cases, when the vehicle&#39;s throttle is at some part throttle positions using an existing manifold absolute pressure sensor. However, there is typically a lower throttle position threshold below which barometric pressure cannot be estimated reliably. IN a hybrid vehicle, the accelerator pedal is not typically coupled to the throttle. Since the operator doesn&#39;t directly control the throttle, operation at WOT may not occur when needed or prolonged operation at or below the lower throttle position threshold is quite possible, thereby resulting in unreliable barometric pressure estimates. 
         [0005]    Thus, it is desirable to have a reliable method for determining barometric pressure in a hybrid vehicle without the need for a barometric pressure sensor. 
       SUMMARY OF THE INVENTION 
       [0006]    An engine in a hybrid electric vehicle includes a manifold absolute pressure sensor and a controller. The pressure sensor senses a pressure of the intake manifold. The controller determines if the engine is running, determines a first barometric pressure as the intake manifold pressure if the engine is not running, and determines a second barometric pressure if the engine is running. 
         [0007]    A method for continuously estimating barometric pressure values in a hybrid vehicle having an engine, an electric machine and an intake manifold includes sensing a pressure of the intake manifold, determining if the engine is running, determining a first barometric pressure as the intake manifold pressure if the engine is not running, and determining a second barometric pressure if the engine is running. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic of a hybrid electric vehicle incorporating the method of the present invention; and 
           [0009]      FIG. 2  is a flowchart of a method for estimating barometric pressure according to the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]    Referring to  FIG. 1 , a schematic of a hybrid electric vehicle  10  is shown. The hybrid electric vehicle  10  includes an engine  12 , a power source  14 , an electrical machine  16 , and at least one control module  18 . The hybrid electric vehicle  10  may have any suitable drive train configuration, such as a series hybrid drive, a parallel hybrid drive, or a split hybrid drive as is known by those skilled in the art. The engine  12  is of the internal combustion type having a rotating crankshaft, the rotations of which are sensed by a speed sensor  20 . Speed sensor  20  may be any appropriate sensor of the type adapted to generate a signal indicative of the rotational speed of the crankshaft. An example of such a sensor is a magnetic pickup adjacent to a toothed flywheel (now shown) of the engine  12  coupled to a counter that counts pulses for unit time and supplies such counts on a regular basis. 
         [0011]    The engine  12  is also supplied with an air delivery system of the type wherein the intake air flows from the atmosphere at barometric pressure through an air filter  22  and past a throttle plate  24  which controls the regulation and flow of air into the intake manifold  26 . Associated with the intake manifold  26  is a pressure sensor  28  for measuring manifold absolute pressure (MAP). MAP sensor  28  generates a signal indicative of the absolute pressure within the intake manifold  26  downstream of the throttle plate  24 . 
         [0012]    The power source  14  may be of any suitable type. For example, an electrical power source  14  such as a battery, a battery pack having a plurality of electrically interconnected cells, a capacitor, or a fuel cell may be employed. Alternatively, a non-electrical power source, such as a hydraulic power source could be employed. For simplicity, the description below will primarily refer to an embodiment of the present invention that incorporates an electrical power source. 
         [0013]    The electrical machine  16  may be of any suitable type, such as a motor, motor-generator, or starter-alternator. In  FIG. 1 , the electrical machine  16  is connected to the engine  12  and the power source  14 . More specifically, the electrical machine  16  may be powered by the power source  14  and may be adapted to drive the engine  12  or one or more vehicle traction wheels  30 . In addition, power may flow through the electrical machine  16  in the opposite direction to charge the power source or drive the engine  12 . In the embodiment shown in  FIG. 1 , the electrical machine  16  is connected to a differential  32  that is connected to a pair of axles  34  that are each connected to a vehicle traction wheel  30 . 
         [0014]    The control module  18  is used to monitor and control various aspects of the hybrid vehicle  10 . For example, the control module  18  may be connected to the engine  12 , the power source  14 , and electrical machine  16  to monitor and control their operation and performance. In addition, the control module  18  also processes inputs from the various sensors for controlling the engine  12  and electrical machine  16 . 
         [0015]    With a hybrid vehicle, since there is both an engine  12  and an electrical machine  16  for driving the vehicle  10 , there will be times in which the engine  12  is not turning, or running, and times when it is. When the engine  12  is not running, the intake manifold  26  will fill with atmospheric air and, thus, the barometric pressure can be estimated to equal the pressure measured by MAP  28  since there is little or not air flow. Preferably, this estimate is taken after a precalibrated amount of time has elapsed since the engine stopped running in order to allow the intake manifold  26  sufficient time to fill with the atmospheric air, for example, five (5) seconds. 
         [0016]    In situations in which the engine  12  is running, barometric pressure needs to be estimated based on other information. The most accurate estimation of barometric pressure is possible when the throttle plate  24  is at WOT since pressure drop across the throttle valve will be minimized and predictable, control module  18  commands the throttle plate  24  to WOT when the engine  12  is in a running condition. This can be done without the driver noticing by counter-balancing the extra torque created by the engine  12  operating at WOT via the control module commanding a reciprocal decrease in current to the electrical machine  16  to result in minimal net torque difference at the powertrain output. 
         [0017]    Prior to operating the engine  12  at WOT, however, it is preferable to check for faults, such as faults associated with the throttle plate  24  or the engine speed sensor  20 . A throttle plate  24  fault would be a fault in any sensor measured throttle position, a fault with the throttle motor control such that the throttle plate  24  cannot be controlled, or a detection of too high an airflow compared to what the airflow estimated from the throttle position should be, which cold be indicative of the throttle plate  24  having fallen off, bent, having a hole therein or otherwise failed open. The MAP sensor  28  is checked to determine that it is operating in a standard range, i.e. below an upper limit and above a lower limit. Also engine speed faults may be present if the engine speed sensor  20  is missing or erratic. 
         [0018]    If there are not faults, the barometric pressure update may be performed by controlling the engine to operate at the WOT condition. During WOT, a pressure drop between the atmosphere and the intake manifold  26 , also termed an offset value, is obtained from a lookup table stored in a memory (such as a read only memory, not shown) in control module  18  that is a function of the air flow rate, or engine speed. The offset value, or pressure drop, is added to an air pressure value as measured by MAP  28 . After the air pressure is measured, the throttle plate  24  is returned to the position it was in before being forced to WOT. 
         [0019]    Barometric pressure updates, for the engine running scenario, are preferably performed periodically, either after a predetermined amount of time has elapsed or after the vehicle has traveled a predetermined distance. In the preferred embodiment, barometric pressure is updated after the vehicle has traveled a predetermined distance, since driving a vehicle on an incline could result in errors in an engine management system due to a lack of barometer update. In vehicle testing, it was discovered that driving a vehicle up or down a typical grade over 10 km resulted in errors in the engine management system. Therefore, the barometric pressure can be scheduled to be updated every 10 km when the engine is running. Thus, once the barometric pressure estimate has been performed, a distance counter, e.g., Distance Since Last Baro Pressure Update, ” is reset to zero. 
         [0020]    Turning now to  FIG. 2 , a flow chart outlining the steps associated with the method of the present invention will be described. As will be appreciated by one of ordinary skill in the art, the flowchart represents control logic which may be implemented using hardware, software, or combination of hardware and software. For example, the various functions may be performed using a programmed microprocessor. 
         [0021]    The control logic may be implemented using any of a number of known programming or processing techniques or strategies and is not limited to the order or sequence illustrated. For instance, interrupt or event-driven processing is typically employed in real-time control applications, such as control of an engine or vehicle subssystem, rather than a purely sequential strategy as illustrated. Like wise, pair processing, multitasking, or multi-threaded systems and methods may be used to accomplish the objectives, features, and advantages of the present invention. 
         [0022]    This invention is independent of the particular programming language, operating system processor, or circuitry used to develop and/or implement the control logic illustrated. Likewise, depending upon the particular programming language and processing strategy, various functions may be performed in the sequence illustrated at substantially the same time or in a different sequence while accomplishing the features and advantages of the present invention. The illustrated functions may be modified or in some cases omitted without departing from the spirit or scope of the present invention. 
         [0023]    The method begins at  100  by determining if the engine  12  is running or not. If the engine  12  is not running, the method proceeds to step  110  where a check is made to determine if a predetermined amount of time has elapsed since the engine stopped running. If so, the barometric pressure is updated with a value equivalent to the air pressure as sensed by MAP sensor  28 , step  112 . If the predetermined amount of time has not elapsed, the method returns to the beginning of the sequence. 
         [0024]    After the barometric pressure is updated, step  112 , a counter is reset to zero, step  114 , for use in determine the barometric pressure during the engine running condition. 
         [0025]    Returning to step  100 , if the engine is running, the method proceeds to step  116  to determine if the vehicle  10  has traveled a predetermined distance since the previous barometric pressure update was performed. If not, the method returns to the beginning of the sequence. If the vehicle has traveled the predetermined distance, a check is made to determine if there are any faults, step  118 . 
         [0026]    If there are not faults, the method proceeds to step  120  wherein the engine  12  is controlled to operate at the WOT condition long enough to estimate the barometric pressure and determine the offset value. Simultaneously, the electric machine  16  is controlled to operate at a decreased current so as to counter balance the excess torque resulting from operating the engine  12  at WOT. Depending upon the powertrain configuration, the electric machine torque (and hence the electric machine current) may actually be increased or decreased in order to counteract the increased engine torque output. 
         [0027]    After the barometric pressure is updated at step  120 , the method proceeds to step  122  where the counter is reset to zero for use in determining when the next barometric pressure update is performed when the engine  12  is running. 
         [0028]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.