Abstract:
A control system ( 10 ) and method for controlling an operational position of a throttle valve in an engine. The system includes a position sensor ( 16 ) operably connected to the throttle valve that generates a first signal. A controller is operably connected to the position sensor. The controller ( 18 ) is configured to determine a current position of the throttle valve using a transfer function defining a curve with no breakpoints and the signal from the position sensor. The controller ( 18 ) is further configured to change the operational position of the throttle valve based on the current position and a desired position of the throttle valve.

Description:
TECHNICAL FIELD 
     The present invention relates generally to a control system for an engine of an automotive vehicle, and more particularly to a method and apparatus for controlling an operational position of a throttle valve in the engine. 
     BACKGROUND OF THE INVENTION 
     Electronic engine controllers have used position sensors for closed loop control of throttle valves. A desired resolution for the position sensor depends on the specific application of the sensor. Also for a particular application the desired resolution may vary throughout a desired position sensing range. For example, the preferred resolution for the throttle position sensor may be higher at lower position angles (near a closed position) versus higher position angles. Typically, a position sensor has an output signal defined by a transfer function with different slopes is preferred for sensor fault detection. 
     Traditionally, throttle positions sensors have output signals defined by linear transfer functions. An engine controller uses the linear transfer function characteristic to determine an operational position of a throttle valve based on the output signal. Unfortunately, the position sensors, having a single sloped linear transfer function, have a relatively equivalent resolution over the entire range of operation which may be undesirable for throttle valve applications. 
     Further, some electronic controllers utilize multiple slope linear transfer functions to map a throttle position sensor voltage to a throttle position. The multiple slope linear transfer functions allow for a varying position resolution over the position sensing range that may be desired for throttle valve applications. However, each of these multiple slope linear transfer functions have a breakpoint which is a point where two line segments with different slopes meet. As a result, position measurement of throttle valve near these breakpoints may result in position measurement errors. 
     The inventors herein have recognized that it would be desirable to have a position control system with increased resolution in important operational regions of interest that is simpler to implement and more accurate than known methods. 
     SUMMARY OF THE INVENTION 
     The foregoing and advantages thereof are provided by a method and apparatus for controlling an operational position of a throttle valve in an engine. The system includes a position sensor operably connected to the throttle valve that generates a first signal. A controller is operably connected to the position sensor. The controller is configured to determine a current position of the throttle valve using a transfer function defining a curve with no breakpoints and the signal from the position sensor. The controller is further configured to change the operational position of the throttle valve based on the current position and a desired position of the throttle valve. 
     One of several advantages of the present invention is that it provides an improved method of determining a position of a device, with increased accuracy, due to increased resolution in a range where more resolution is desired. 
     Additionally, the present invention provides increased resolution in a control system that has manufacturing and interpreting ease equal to or better than traditional control systems. 
     Furthermore, the present invention provides several alternatives that have different varying slope conversion characteristics as to satisfy various different applications. 
     The present invention itself, together with attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a more complete understanding of this invention reference should now be had to the embodiments illustrated in greater detail in the accompanying figures and described below by way of examples of the invention wherein: 
     FIG. 1 is a block diagrammatic view of a control system in accordance with an embodiment of the present invention; 
     FIG. 2 is a plot illustrating an example of an output position signal defined by a logarithmic-type transfer function according to an embodiment of the present invention; 
     FIG. 3 is a plot illustrating an example of an output position signal defined by a square-type transfer function according to an embodiment of the present invention; 
     FIG. 4 a  is a divider-type electrical schematic for an output position signal defined by a divider-type transfer function according to an embodiment of the present invention; 
     FIG. 4 b  is an equivalent electrical schematic of the schematic of FIG. 4 a  according to an embodiment of the present invention; 
     FIG. 5 is a plot illustrating an example of an output position signal defined by a divider-type transfer function according to an embodiment of the present invention; 
     FIG. 6 is an example of two redundant position sensor transfer functions, used simultaneously, according to an embodiment of the present invention; 
     FIG. 7 is a logic flow diagram illustrating a method of performing an action within an automotive vehicle in accordance with an embodiment of the present invention; and 
     FIG. 8 is a logic flow diagram illustrating a method of controlling a position of a device within an automotive vehicle in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following description, various operating parameters and components are described for one constructed embodiment. These specific parameters and components are included as examples and are not meant to be limiting. 
     Also in the following description, the term “position” does not refer to a location in a vehicle. Position refers to an operational for a throttle valve. For example, an operational position of a throttle valve may vary from zero degrees (closed position) to ninety degrees (full open position). 
     Referring now to FIG. 1, a block diagrammatic view of a control system  10  in accordance with an embodiment of the present invention is shown. The control system  10  is located within a vehicle  12 . The control system  10  includes a device  14 . A first position sensor  16  generates a first position sensor output signal corresponding to the position of the device  14 . A controller  18  converts the position output signal into a first actual position signal. The controller  18  compares the first actual position signal to a desired signal and generates a position modification signal. The position modification signal is coupled to an actuator  20  to adjust the position of the device  14 . A redundant position sensor  22  may be used to confirm the first position sensor output signal. 
     Controller  18  may be a microprocessor-based controller such as a computer having a central processing unit, memory (RAM and/or ROM), and associated inputs and outputs operating in cooperation with a communications bus. Controller  18  may be a portion of a main control unit, such as a powertrain control module or a main vehicle controller, or it may be a stand-alone controller. 
     The controller  18  utilizes a non-linear transfer function in converting the first position sensor output signal into the first actual position signal. The controller  18  may use one of the following non-linear transfer functions: a logarithmic-type, a square-type, or a divider-type as further described below, or other type having a continuous varying slope portion. Note the logarithmic-type, square-type, and divider-type transfer functions have continuously varying slopes, but other non-linear transfer functions having a continuous varying slope portion may be used. In other word, the transfer functions do not have break points. The non-linear transfer functions may be performed using solid state logic devices or computer software. 
     Referring now to FIG. 2, a plot illustrating an example of a logarithmic-type transfer function  30  according to an embodiment of the present invention is shown. Transfer function  30  corresponds to the following logarithmic-type transfer function equation: 
     
       
           deg=− 15*[log(1−(volts−0.5)/4] 
       
     
     where deg corresponds to the actual position of the device  14  in degrees and volts is the first position sensor output signal voltage. For the transfer functions mentioned in this application the controller  18  may set a predetermined low fault threshold and a high fault threshold, to limit the maximum and minimum values of a position sensor operating range. The low fault threshold is represented by line  32 . The high fault threshold is represented by line  34 . The logarithmic-type transfer function  30  is applicable in systems that have a controller with logarithmic conversion capabilities. For less sophisticated systems the following square-type transfer function and divider-type transfer function may be used. The non-linear transfer function  30 , as with other non-linear transfer functions, may have a high-resolution range A, a medium-resolution range B, and a low-resolution range C. When the device  14  is a throttle, having three resolution ranges is preferred so as to have high resolution at lower position angles and lower resolution at higher position angles. The varying resolution in turn provides greater sensitivity at lower position angles. 
     Referring now to FIG. 3, a plot illustrating an example of a square-type transfer function  40  according to an embodiment of the present invention is shown. Transfer function  40  corresponds to the following square-type transfer function equation: 
      deg=83*[(volts−0.5)/4] 2   
     where deg corresponds to the actual position of the device  14 , volts is the first position sensor output signal voltage, and the number  83  is the maximum position of the device  14 . The square-type transfer function  40  is the simplest to implement, as compared with the logarithmic-type and the square-type transfer functions, in that a non-sophisticated controller with only minimum mathematical calculation capability is able to use the square-type transfer function  40  with out the need for a look-up table. 
     Referring now to FIGS. 4A,  4 B, and  5 , of a divider-type electrical schematic  50 , an equivalent electrical schematic  52 , and a plot illustrating an example of a divider-type transfer function  54  according to an embodiment of the present invention. The wiper  51  corresponds to the variable or moving portion of the sensor. Wiper  51  travels between a maximum position and a minimum position and has a voltage output corresponding to the position. 
     where: Rh=position sensor resistor value above the maximum wiper position 
     Rsw=position sensor resistor value that wiper is able to travel 
     R 1 =position sensor resistor value below minimum wiper position 
     Rup=pull up resistor value 
     R 1 eq=[(Rh+Rsw−(deg/ 83 )*Rsw)*Rup]/[Rh+Rsw−(deg/ 83 )*Rsw+Rup] 
     R 2 eq=R 1 +Rsw*deg/ 83   
     Transfer function  54  corresponds to the following transfer function equation in conjunction with a look-up table  24 : 
     
       
         volts=[5/( R   1 eq+ R   2 eq)]* R   2 eq 
       
     
     Similarly, a pull down resistor may be used to get the desired low end resolution improvement with a negative sloping sensor. The judicious selections of pull up or pull down, or a combination thereof, can be used to provide the desired position resolution characteristics. The first position sensor output signal is converted into an equivalent first position sensor output signal, which is then converted into the first actual position signal through the use of the look-up table  24 . The transfer function  54  also requires minimum mathematical calculation capability, but as stated requires the use of the look-up table  24 , which is not required for the transfer functions  30  and  40 . 
     Referring now to FIGS. 1 and 6, an example of two redundant position sensor transfer functions, used simultaneously, according to an embodiment of the present invention is shown. The above-described transfer functions may be used with redundant position sensors. For example, when the transfer function  40  and the redundant position sensor  22  are used, a first transfer function  40  corresponding to the first position sensor  16 , may be the inverse of a redundant transfer function  40 ′ corresponding to a redundant position sensor. The transfer functions  40  and  40 ′ are diverse such that they are mirror images of each other across a centerline  50 . In so doing, the resulting signals from the first transfer function  40  and the redundant transfer function  40 ′ may be added together at any point in time and result in the same constant value. When the constant value does not equal a set value the controller  18  may than determine that a fault exists on one or more of the position sensors  16  and  22 . Also, when using a redundant position sensor in order to prevent common fault modes, whereby each position sensor is generating the same output signal, a traditional linear transfer function may be used in conjunction with a diverse related non-linear transfer function of the present invention. The combination of a linear transfer function and a non-linear transfer function reduces the potential for the two position sensors  40  and  40 ′ to produce the same output value at any point in time, thereby, further preventing undetected faults. 
     Of the above-described transfer functions  30 ,  40 , and  54 , no transfer function is necessarily better than the other. The transfer function to use depends on the application and system capabilities. Also the values in the above non-linear transfer function equation are meant to be for example purposes. Other values may be used to adjust the shape of the transfer functions depending upon the application. 
     Referring now to FIG. 7, a logic flow diagram illustrating a method of performing an action within the automotive vehicle  12  in accordance with an embodiment of the present invention is shown. 
     In step  60 , the position sensor  16  generates a position sensor output signal corresponding to a position of the device  14 . 
     In step  62 , the controller  18  converts the position sensor output signal into an actual position signal utilizing a non-linear transfer function, as described above. 
     In step  64 , controller  18  performs an action in response to the actual position signal. An action may include any of the following: adjusting the position of a device, recording a value, modifying the performance of a system, or other action that may be performed by a controller. 
     Referring now to FIG. 8, a logic flow diagram illustrating a method of controlling a position of the device  14  within the automotive vehicle  12  in accordance with an embodiment of the present invention is shown. 
     In step  70 , the controller  18  converts the position sensor output signal into an actual position signal utilizing a non-linear transfer function, as in step  62  above. 
     In step  72 , the controller  18  determines a desired position of the device  14 . The desired position of the device  14  may be a predetermined value stored in the controller memory or may be calculated using various formulas and parameters depending upon the resulting action to be performed. 
     In step  74 , the controller  18  compares the actual position to the desired position and generates a position modification signal. 
     In step  76 , the controller  18  transfers the position modification signal to the actuator  20  so as to adjust the actual position of the device  14 . 
     The present invention by utilizing a nonlinear transfer function having a continuous varying slope portion, to determine a position of a device, provides increased resolution in a range where increased resolution is more desired over other ranges where a lower amount of resolution is sufficient. Also by providing several possible easy to manufacture and convert transfer function options allows the present invention to be versatile in that it may be applied in various related and unrelated applications. 
     The above-described method, to one skilled in the art, is capable of being adapted for various purposes and is not limited to the following applications: automotive vehicles, control systems, sensor systems, or other applications containing position sensors. The above-described invention may also be varied without deviating from the true scope of the invention.