Abstract:
A method for synchronizing a plurality of pedal position sensors in a motor vehicle. A series of voltages are accumulated from each of a plurality of pedal position sensors. Representative voltages are determined from the series of voltages. The representative voltages are assigned to linear relationships from which an offset is determined.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to synchronizing the voltage of position sensors, and more particularly to a method for synchronizing the zero position of a plurality of pedal position sensors in the automotive industry. 
     2. Background of the Invention 
     Position sensors are used to allow an electrical circuit to gain information about an event or a continuously varying condition. A type of position sensor is a potentiometric sensor. Potentiometric sensors are widely used as position sensors in various automotive applications. In particular, potentiometric sensors are used to obtain throttle and accelerator pedal position measurements. 
     With the introduction of electronically controlled engines, electronically controlled transmissions and electronic throttle control devices, a rotary potentiometer sensor is one type of sensor used for detecting the angular position or movement of the accelerator pedal. 
     Potentiometric sensors are used as voltage dividers, A voltage is applied across two extreme ends of a resistor. An intermediate tap is provided between the two extremes of the resistor. The tap is mechanically linked to the device which is to be sensed, and the position of the device is determined by the voltage at the intermediate tap. 
     The accelerator pedal position sensors detect the actual accelerator pedal position and outputs an accelerator pedal position signal to the electronic engine control unit (ECU) and the electronic automatic transmission controller (EATX), respectively. The ECU determines a target throttle position in response to the actual accelerator pedal position and other parameters representing engine driving conditions. The EATX translates the actual accelerator pedal position into the throttle angle in a similar way as the ECU does. 
     When an accelerator pedal position is requested by the driver, the ECU calculates the target throttle according to the request and sends the throttle related information to the EATX. 
     A common problem when applications include a plurality of sensors (pedal position sensors) is that the voltage may vary from sensor (pedal position sensor) to sensor (pedal position sensor) due to production variation even for a fixed pedal position. In the intended application, absence of synchronizing the zero position of the pedal position sensors, the EATX and the ECU would interpret a pedal angle request differently, thus the performance of the vehicle is hindered. 
     Therefore, this invention provides a more accurate and reliable method of ensuring that each automotive electronic controller is obtaining synchronized interpretation, or establishing a common reference point of the voltage from the pedal position sensors at any given pedal position. 
     SUMMARY OF INVENTION 
     The present invention overcomes the aforementioned disadvantages as well as other disadvantages. In accordance with the teachings of the present invention, the present invention provides a more accurate and reliable method of ensuring that the automotive electronic controllers are obtaining synchronized interpretation of the voltages when a plurality of pedal position sensors are present. 
     In a vehicle with Electronic Throttle Control (ETC), the accelerator pedal controls pedal position sensors (PPS) and according to the voltage from the PPS, the ECU controls the throttle opening. In a vehicle with an Engine control unit (ECU) and an Automatic Transmission Controller (EATX), the EATX and ECU may have independent PPS responding to the accelerator pedal. The voltage for a same pedal position may vary from PPS to PPS due to production variation, and the controllers may obtain different pedal positions from their own PPS. This hinders the performance of the vehicle. 
     In the present application, the ECU uses a predefined threshold that does not change with different PPS. The EATX also uses a threshold. In order to compensate for PPS production variations, a method has been developed to adapt the EATX threshold to achieve synchronization with the ECU threshold. Since in this application the ECU and EATX are separate modules and they communicate through a communication BUS with significant latency, this method also identifies the ECU and EATX PPS voltage readings (or their interpretations) that correspond to the same steady pedal positions. 
     It is an object of the invention to provide a method which is capable of synchronizing a plurality of pedal position sensors, providing the equal pedal angle information to the automotive electronic controllers regardless of the rotation angle of the pedal. 
     The ECU reads its PPS voltage (PPS 1 ) and compares it against a threshold. When the voltage is below the threshold, the ECU assumes a zero pedal requested throttle. The ECU computes a throttle opening from the difference between the voltage and the threshold when the read voltage is above the threshold. The ECU then controls the ETC to achieve the desired throttle and controls the engine accordingly. 
     The EATX reads a voltage from a different PPS (PPS 3 ) and compares it against its threshold. When this voltage is below the threshold, the EATX assumes a zero throttle. The EATX also computes a throttle from the difference between the voltage and the threshold when the voltage is above the threshold. 
     To best control the transmission, the EATX needs to be synchronized with the ECU on PPS voltage interpretation, or in other words, the threshold voltages of the EATX and ECU should correspond to the same pedal position. Then, the EATX and ECU will both interpret a zero or non-zero throttle from the same pedal position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram representation of the pedal position sensors according to the present invention incorporated into a motor vehicle. 
     FIG. 2 shows the flow of the overall process steps to synchronize pedal positions sensors to zero position. 
     FIG. 3 is a graph representing the offset value required to synchronize the pedal position sensors. 
     FIG. 4 is a graph of pedal position percentage versus pedal position sensor voltage. 
     FIG. 5 is a graph of time traces of PVS and V pps3  at varying pedal angles showing two steady pedal angles. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With initial reference to FIG. 1, a general configuration including first and second pedal position sensors PPS 1  and PPS 3  incorporated in a motor vehicle  24  is shown and identified at reference  12  and  14  respectively. Pedal position sensors  12  and  14  operatively connect to ECU  16  and EATX  18  through conductors  32  and  34  respectively. The EATX  18  is further configured to receive processed pedal data including pedal position percentage (PVS) from BUS  22 . 
     With continued reference to FIG.  1  and further reference to FIG. 2, the overall process steps to synchronize pedal position sensors  12  (PPS 1 ) and  14  (PPS 3 ) will be described. At block  20  the EATX  18  reads and stores the current pedal position sensor voltage (V pps3 ) from its PPS 3    14 . The EATX  18  also reads the most recent engine PVS over the BUS  22 . The PVS is calculated by the ECU from the pedal position sensor (PPS 1 ) reading, as will be described in greater detail, and transferred over the BUS  22 . The ECU interprets a zero throttle (idle) for 0% PVS and interprets a non-zero throttle if PVS is greater than 0%. The EATX receives the PVS with the bus latency. 
     At decision block  30  it is determined if the PVS and V pps3  are stabilized in responding to a stabilized pedal angle. To identify steady pedal angles, it is assumed that the PVS and V PPS3  should be steady for a period of time with variation less than a predetermined tolerance. If so, then at block  50  an accumulation of values of both V pps3  and PVS take place. If not, the current V PPS3  and PVS are stored at block  40  as the initial point of the assumed stabilized zone and the old values are discarded, then, the program is exited at block  90 . 
     At decision block  60  it is determined if enough values have been accumulated for the current steady pedal angle. Sufficient accumulation is defined by a repetitive pattern of values within a predetermined tolerance. The accumulation defines a pair of averaged PVS and V pps3  to define a more representative steady pedal angle with less noise. If enough values have been accumulated, then at decision block  70  it is determined if an averaged pair of PVS and V pps3  have already been defined for a previous steady pedal angle. If enough values have not been accumulated, the program exists at block  90 . If the averaged pair of PVS and V pps3  have been defined for two steady pedal angles the routine proceeds to block  80 . It must then be determined at decision block  80  if there is adequate separation between the two steady pedal angle values in order to perform a valid computation. If so, then the offset value of c is calculated at block  100 . As such, c is the value at which the EATX threshold must adapt to achieve synchronization. A mathematical development used to determine c will later be described in detail. 
     If there is not adequate separation, one pair of the accumulated V pps3  and PVS (in the present application, the older pair) are cleared at block  110 , the program exits and the process begins at enter. Once the offset value of c is determined at block  100 , the oldest pair of values are cleared at block  110  and the program exists at block  90  and the entire process begins at enter. 
     Turning now to FIG. 3, voltage traces from the ECU and the EATX are shown. The horizontal axis represents pedal angle and the vertical axis represents voltage (V). Line  110  (V pps1 ) is the voltage the ECU reads from pedal position sensor  12 . Line  120  (V pps3 ) is the voltage the EATX reads from pedal position sensor  14 . Each voltage trace has a linear relation with the pedal angle. Idle angle is the pedal angle threshold used for interpreting non-zero throttle request. Any pedal angle less than the Idle angle is interpreted as a zero throttle request and any pedal angle greater than Idle angle is interpreted as a non-zero throttle request. The Idle angles are defined by V ECU0  and V EATX0  for the ECU and the EATX, respectively. 
     V ECU0  is the threshold that the ECU uses to interpret non-zero throttle request from the pedal. V EATX0  is the threshold that the EATX uses to interpret non-zero throttle request from the pedal. Any voltage value higher than its threshold voltage is interpreted as a non-zero throttle request by its controller, and any voltage values less than its threshold is interpreted as zero throttle request (idle). Due to production variation of the pedal position sensor assembly, the relation between the V EATX0  and V ECU0  is variable. If a fixed threshold value is used for either ECU or EATX (throughout this example, ECU is the fixed value), the other (EATX in this example) needs to identify its threshold such that the EATX and ECU read their respective threshold voltages at the same pedal angle (Idle angle). 
     The EATX interpretation of its pedal position sensor reading must be synchronized with engine pedal position percentage (PVS). In this regard, V EATX0  is the value of the voltage (V PPS3 ) the EATX read when the pedal is at the angle position that the value of the voltage (V PPS1 ) the ECU read is V ECU0 . PVS,  130  is a linear translation of the voltage (V PPS1 ) the ECU read from its pedal position sensor  14 . It is defined as 0% when the voltage is at or lower than the lower threshold (V ECU0 ) and is defined as 100% when the voltage is at or higher than a predefined upper threshold. The PVS,  130  vs. V PPS3 ,  120  also has a linear relation when PVS,  130  is larger than 0% and less than 100%. 
     FIG. 4 is a graph of the PVS vs. V pps3 . A and B are defined by the two pairs of the averaged PVS and V pps3  for two steady pedal angles. The linear model of PVS versus V pps3  is defined if A and B are obtained, provided PVS for both A and B is larger than 0% and less than 100%. V pps3  preferably range from 0.64 to 4.8 volts. To satisfy the adequate separation requirement of block  80  in FIG. 2, the PVS values, P VS1  and P VS2 , are preferably separated by at least 20%. Similarly, the V PPS3  values, V PPS31  and V PPS32 , are preferably separated by at least 1 volt. Then the V EATX0  can be calculated from the linear model by setting PVS=0% in the model throughout an accumulation of points to determine the offset value c. Those skilled in the art will recognize that the separation requirements described herein may be varied without departing from the scope of the invention. 
     FIG. 5 shows the time traces of PVS and V pps3  at varying pedal angles with two steady pedal angles. To identify the steady pedal angles, it is assumed that the PVS and V pps3  should be steady for a period of time with variation less than a predefined tolerance. For example, the preferred maximum tolerance depicted in FIG. 5 is 59 millivolts for V pps3  and 1.2% for PVS. Those skilled in the art will recognize that other tolerances may be employed while achieving similar results. A data pair (V pps3 , PVS) are stored as the initial point of an assumed stabilized period. Each time a new pair of PVS and V pps3  are received and are within a tolerance of the initial point, they are considered stabilized PVS and V pps3  corresponding to a steady pedal angle, and are accumulated. The accumulation process continues until an in-coming data pair is out of the tolerance with respect to the initial point, or a predefined number of data pairs have been accumulated. In the event that new data is out of tolerance, or enough data has been accumulated, the following new data will be saved as the new initial point again. 
     The following shows the detailed mathematical development of this invention. At the outset, the PPS voltages V PPS1 , V PPS2 , and V PPS3  are linearly related to pedal angle: 
     
       
           V   PPS1   =K 1(Π)+ b 1   (1)  
       
     
     
       
           V   PPS2   =K 2(Π)+ b 2   (2)  
       
     
       V   PPS3   =K 3(Π)+ b 3   (3) 
     Where Π=Pedal Angle, K1-K3=constants, b1b3=constants. The ECU reads V PPS1  and V PPS2  and performs the following calculation: 
     
       
           PVS=L* ( V   PPS1   −V   ECU0 ) for  V   PPS1   ≧V   ECU0    (4) 
       
     
     
       
         PVS=0% for V PPS1 &lt;V ECU0   
       
     
     
       
         Limit PVS≦100% 
       
     
     where V ECU0  is the ECU threshold for interpreting V pps1 . L is a constant defining pedal travel angle range to achieve 0% to 100% PVS. The EATX reads V PPS3 . As such, from equations (1) and (3), V pps3  is linearly related to V pps1 . Equation (4) also shows linear relation between PVS and V pps1 . The following linear relations are established. 
     
       
           PVS=a* ( V   pps   −C ) for 0 &lt;PVS&lt; 100   (5) 
       
     
     
       
           PVS= 0% with  V   PPS1   &lt;V   ECU0   
       
     
     In this regard, the linear model of Equation (5) defines the condition such that when Vpps3=c, PVS=0%. Thus, c should be the threshold the EATX uses to interpret Vpps3. If c is used as V EATX0  the ECU  16  and EATX  18  will interpret a zero or non-zero throttle at a same pedal angle. 
     Referring now to FIG. 4, two averaged data pairs of PVS and Vpps3 are used to compute the constants in equation (5). Assuming the two data pairs (PVS1, V pps31 ) and (PVS2, V pps32 ), the following equations are established. 
     
       
           PVS 1 =a* ( V   PPS31   −c )  
       
     
     
       
           PVS 2 =a* ( V   PPS32   −c )  
       
     
     Solving for a and c yields: 
     
       
           a= ( PVS 1 −PVS 2)/( V   PPS31   −V   PPS32 )   (6)  
       
     
     
       
           c=−PVS 1( V   PPS31   −V   PPS32 )/( PVS 1 −PVS 2)+ V   PPS31    (7)  
       
     
     Thus, with two averaged data pairs of PVS and Vpps3 obtained for two different steady pedal angles, c can be calculated. Considering noises in the V pps1  and V pps3  signal, c is calculated only when there is enough separation between the two steady pedal angles which can be described as: 
     
       
         | V   PPS31   −V   PPS32   |&gt;constant 1 and | PVS 1 −PVS 2|&gt; constant 2  
       
     
     constant1 and constant2 defines the minimum separation between the two steady pedal angles. To further reduce the noise effect on synchronization, V EATX0  is adapted to c with the following adaptive method 
     
       
           V   EATX0 =( V   EATX0   +C )/2  
       
     
     The method incorporated herein adapts V EATX0  to synchronize EATX interpretation of its PPS reading with V ECU0  as a defined constant. Accordingly, a similar approach can be developed to adapt V ECU0  with V EATX0  as a defined constant. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.