Abstract:
An electronic throttle control system is described where a throttle position sensor has multiple slopes depending on the operating region. At low throttle positions, a greater slope, and thus a greater sensitivity is provided, thereby increasing control resolution. At greater throttle positions, a lower slope, and thus lower sensitivity is provided. In this way, an output signal that varies across the entire operating region of the throttle is provided for monitoring and control, while improved performance at low throttle angles can be simultaneously achieved. A method of making the sensor is also described.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/184,946, filed Feb. 25, 2000, Attorney Docket Number 200-0308, titled “ELECTRONIC THROTTLE SYSTEM”. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The field of the invention relates to electronically controlled throttle units in vehicles having a drive unit.  
         BACKGROUND OF THE INVENTION  
         [0003]    In some engines, an electronically controlled throttle is used for improved performance. In such systems, position of the throttle is controlled via closed loop feedback control. Typically, to provide redundancy multiple throttle position sensors are provided.  
           [0004]    One method to provide two throttle position sensors uses sensors of different gradients, each linear over the entire operating range, another uses gradients of opposite sign. Still other methods use saturating sensors. These methods are described U.S. Pat. Nos. 5,136,880, 5,260,877, and 4,693,111, respectively.  
           [0005]    The inventors herein have recognized some disadvantages of the above approaches. In particular, when a high resolution saturating sensor and a low resolution sensor are used together, there is a saturated region where the saturating sensor provides less information than the unsaturated region. Alternatively, when different gradients are used, each linear over the entire region, the analog to digital converters are over-specified and under-utilized to accommodate the low resolution sensor. Another disadvantage with prior approaches is that multiple tracks, interconnections between the tracks, and wiper arms may be required to provide multiple outputs having different characteristics.  
         SUMMARY OF THE INVENTION  
         [0006]    An object of the present invention is to provide electronic throttle control systems and sensors.  
           [0007]    The above object is achieved and disadvantages of prior approaches overcome by a position sensor according to the present invention. In one aspect, the sensor comprises a substrate, and a track positioned on said substrate including at least two contiguous first and second segments, each of said segments having a different material property.  
           [0008]    By having a sensor with two operating regions, it is possible to obtain high resolution at low throttle angles, and thereby have better airflow control as well as to obtain information throughout the operating range without over-specifying and under-utilizing A/D converters.  
           [0009]    An advantage of the above aspect of the invention is improved monitoring.  
           [0010]    Another advantage of the above aspect of the invention is improved control.  
           [0011]    In another aspect of the present invention, the sensor further comprises a single movable wiper for sliding over said track to provide an electrical signal having an amplitude related to position of said wiper.  
           [0012]    An advantage of the above aspect of the present invention is that a simplified structure is provided with a single track having two segments, no interconnection between the segments, and only a single wiper arm moving across both segments.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The object and advantages of the invention claimed herein will be more readily understood by reading an example of an embodiment in which the invention is used to advantage with reference to the following drawings wherein:  
         [0014]    [0014]FIG. 1 is a block diagram of a vehicle illustrating various components related to the present invention;  
         [0015]    [0015]FIG. 2 a  is a schematic diagram of the position sensor;  
         [0016]    [0016]FIGS. 2 b  and  4  are graphs showing output characteristics of the sensor;  
         [0017]    [0017]FIGS. 3, 5, and  6  are block diagrams of embodiments in which the invention is used to advantage. 
     
    
     DESCRIPTION OF THE INVENTION  
       [0018]    Internal combustion engine  10 , comprising a plurality of cylinders, is controlled by electronic engine controller  12 . Engine  10  can be a port fuel injected engine, a directed injected engine, a gasoline engine, a diesel engine, or any other type of engine utilizing redundant position sensors. Engine  10  is coupled to intake  20  and exhaust  22 . A throttle  24  is positioned in intake  20 . Position sensor  30 , described later herein with particular reference to FIG. 2, is coupled to throttle  24 .  
         [0019]    Controller  12  is shown in FIG. 1 as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , an electronic storage medium for executable programs and calibration values shown as read only memory chip  106  in this particular example, random access memory  108 , keep alive memory  110 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors  40  coupled to engine  10 , in addition to signals from position sensor  30 . Controller  12  is also shown sending various signals to actuators  44  coupled to engine  10 . Additionally, an electric motor  46  is coupled to throttle  24  and receives a control signal from controller  12  to control position of throttle  44 , as well as engine torque, or vehicle acceleration.  
         [0020]    Referring now to FIG. 2, and in particular to FIG. 2 a , position sensor  30  is shown. In this particular depiction, position sensor  30  is shown as an unrolled version of a rotary (angular) sensor. Those skilled in the art will recognize, in view of this disclosure, that the present invention is applicable to angular position sensors for measuring angular deflection as will as displacement position sensors for measuring deflection in a uniform direction, i.e., along a line.  
         [0021]    Sensor  30  has substrate  200 , which supports tracks  210  and  212 . First track  210  and second track  212  are tracks of resistive material that are used to produce two potentiometer signals (S 1 , S 2 ). Additional tracks can be placed on substrate  200  without departing from the present invention. Second track  212  has two contiguous segments, first segment  220  and a second segment  222 . Track  212  is produced by applying the first track segment of a first resistivity on the substrate, and applying, contiguous to said first track segment, a second track segment having a second resistivity on the substrate. Conductive path  214  supplies a grounded, or low voltage signal to first segment  220  of track  212 . Conductive path  214  also supplies a grounded, or low voltage signal, to an opposite end of track  210  as that of track  212 . Conductive path  226  supplies a supply voltage signal to second segment  222  of track  212 , as well as, to an opposite end of track  210  as that of track  212 . Wipers  228  and  230  provide signals S 1  and S 2  to conductive paths  232  and  234  respectively. First and second segment of track  212  have different material properties. In particular, they provide different resistivities. In the embodiment depicted in FIG. 2 a , the different resistivities are provided by different track widths. Those skilled in the art will recognize, in view of this disclosure, various other methods of having two segments, each with different resistivities.  
         [0022]    Referring now to FIG. 2 b , a graph showing the output voltage characteristics of sensor  30  are shown versus wiper position. θk identifies the point where the two segments of track  212  transition. This region may be a sharp point, as illustrated in FIG. 2 b , or might have some curvature, and thus there would be a transition region, the size of which depends on the manufacturing process chosen to produce the two segments.  
         [0023]    Continuing with FIG. 2 b , opposite polarity of signals S 1  and S 2  is obtained by conductive paths  214  and  226  being connected to opposite ends of tracks  212  and  210 . Similarly, the two linear segments of signal S 2 , each having a different slope, are obtained by having two segements ( 220 ,  222 ) of track  212 , each having a different resistivity. Lines  240  and  242  represent the closed stop and open stop of throttle  24 .  
         [0024]    Referring now to FIG. 3, a routine is shown for determining whether output signals S 1  and S 2  of sensor  30  are in agreement. First, in step  310 , first throttle position (θ 1 ) is determined based on signal S 1  and the characteristics, or resistance, of track  210 . In particular, as described later herein, first throttle position is determined based on a slope and offset of signal S 1 . Next, in step  312 , second throttle position (θ 2 ) is measured and determined based on signal S 2 . In particular, the characteristics of track  212  are used. As described later herein, when measured voltage signal (S 1 ) is less than a predetermined value, a first slope and first offset are used to convert signal S 2  to θ 2 . When the voltage is greater than said level, a second slope and offset are used to convert signal S 2  to θ 2 . Next, in step  314 , a difference (e) is determined between first throttle position and second throttle position. In step  316 , a determination is made as to whether first throttle position is less than a predetermined value D 1 . In other words, a determination is made in step  316  as to whether the throttle is operating in the region of the first segment of track  212  or in the region of the second segment of track  212 . When the answer to step  316  is YES, a determination is made in step  318  as to whether the absolute value of the difference between the first and second throttle positions is greater than the threshold value E 1 . Otherwise, when the answer to step  316  is NO, a determination is made as to whether the absolute value of the difference is greater than threshold value E 2 . According to the present invention, different threshold levels are used depending on whether the throttle is operating in the first segment or second segment of track  212 . In other words, since the signals have different sensitivity and resolution, different threshold values are used to account for this. In this way, it is possible to obtain higher sensitivity to disagreement in regions of low throttle position where a small change in throttle position produces a large change in engine torque, and lesser resolution in regions a large change of throttle position produces only a small change in engine torque. When the answer to either step  318  or  320  is YES, disagreement is indicated in step  322 .  
         [0025]    Referring now to FIG. 4, a detailed graph showing the output characteristics of sensor  30  is shown. In particular, slope m 1  and offset o 1  are shown for the first segment of track  212 , second slope m 2  and second offset o 2  are shown for the second segment of track  212 . Also, slope {overscore (m)}, and offset {overscore (o)}, are shown for track  210 . Three regions (circled  1 ,  2 , and  3 ) are shown on the left-hand side of FIG. 4. Region  2  represents the region of the transition between the first and second segments of track  212 . Voltage levels VL 1  and VL 2  define region  2 . Voltage levels VL 1  and VL 2  are predetermined values that represent physically determined limits due to manufacturing tolerance between which the transition resides. In addition, vertical dash lines show the close stop and open stop positions.  
         [0026]    The following equations show how signals S 1  and S 2  are converted to throttle positions using the slopes and offsets.  
         For                 signal                 S                 1     ,       θ   1     =         S                 1     -     o   _         m   _                   For                 signal                 S                 2                 in                 the                 lower                 region     ,       θ   2     =         S                 2     -     o   1         m   1                   For                 signal                 S                 2                 in                 the                 upper                 region     ,       θ   2     =         S                 2     -     o   2         m   2                               
 
         [0027]    Referring now to FIG. 5, a routine is described for learning the region of the transition between first and second segments of track  212 . First, in step  510 , a determination is made as to whether first signal S 1  is varying. In other words, when learning both a slope and an offset from the given information, improved accuracy can be obtained if what is known as “persistence of excitation” to those skilled in the art is present. If only the offset is learned of signal S 2  in the upper region, step  510  can be deleted. When the answer to step  510  is YES, the routine continues to step  512  and calculates the current measurement at step i of first and second throttle positions (θ 1   i ,θ 2   i ). Next, in step  514 , the current value of the error signal (er i ) is calculated based on the measured throttle position as shown:  
           er   i =θ 1   i −θ 2   i    
         [0028]    Next, in step  516 , a determination is made as to whether first voltage signal S 1  is less than voltage limit VL 1 . When the answer to step  516  is YES, the routine continues to step  518  where the routine updates first slope and first offset (m 1 , o 1 ). The following equations describe the updating of learning of the slope and the offset of the first segment of track  212 :  
           m   1   i+1   =f ( er   i   ,m   1   i   ,o   1   i ,θ 1   i )  
           o   1   i+1   =g ( er   i   ,m   1   i   ,o   1   i ,θ 1   i )  
         [0029]    In a preferred embodiment, functions f,g represent a recursive least squares algorithm. However, those skilled in the art will recognize, in view of this disclosure, that various other algorithms can be used drive error signal (er) to zero or to a minimum by adjusting the slopes and offsets. For example, a learning algorithm, of the type described in U.S. Pat. No. 5,464,000, could be adapted to cooperate with the present invention.  
         [0030]    Otherwise, when the answer to step  516  is NO, a determination is made in step  520  as to whether first voltage signal S 1  is greater than voltage limit  2 . When the answer to step  520  is YES, the routine updates or learns the second slope and offset (m 2 , o 2 ), in step  522 :  
           m   2   i+1   =f ( er   i   ,m   2   i   ,o   2   i ,θ 1   i )  
           o   2   i+1   =g ( er   i   ,m   2   i   ,o   2   i ,θ 1   i )  
         [0031]    From either step  518  or  522 , the routine continues to step  524  and updates transition voltage Vk. Transition voltage Vk is calculated according to the following equation:  
         V   k     =         m   1              o   2     -     o   1           m   1     -     m   2           +     o   1                             
 
         [0032]    Thus, according to the present invention, it is possible to learn the region of the transition based on measurements of the first and second sensor. In this way, it is possible to use signal S 2  for feedback control with high accuracy, despite the presence of the transition as described in FIG. 6.  
         [0033]    Referring now to FIG. 6, a routine is described for controlling throttle  24 . First, in step  606 , a check for in-range signal readings is made. Then, in step  608 , a determination is made as to whether both signals S 1  and S 2  are in-range. When the answer to step  608  is YES, the routine continues to step  610 . Otherwise, the routine continues to step  609 , where the throttle is controlled based on whichever signal is in-range. Next, in step  610 , a check is made as to whether in-range disagreement is indicated in step  322 . When agreement is indicated in step  610 , the routine continues to step  611  where a determination is made as to whether signal S 2  is less that voltage Vk minus tolerance amount (γ). When the answer to step  611  is YES, the routine continues to step  612  and controls throttle position based on first throttle position (θ 1 ), which is based on signal S 1 . When the answer to step  612  is NO, the routine continues to step  613  and controls throttle position based on second throttle position (θ 2 ), which is based on signal S 2 . In this way, increased control resolution can be obtained by using the sensor with the greater absolute value of gradient. In an alternative embodiment, the downward sloping signal can be used, regardless of the determination in step  611 , as the default to provide closed loop feedback control of throttle position.  
         [0034]    When the answer to step  610  is NO, the routine continues to step  614 , where a determination is made as to whether signal S 2  is greater than learned voltage (Vk) plus a small tolerance value (δ). In particular, in step  610 , when sensors  1  and When the answer to step  614  is YES, it is determined that the throttle is operating in the first segment of track  212 , and in step  616 , second throttle position is calculated from first slope and first offset (m 1 ,o 1 ). Otherwise, when the answer to step  614  is NO, it is determined that the throttle is operating in the second segment of track  212  and second throttle position is calculated from the second slope and second offset (m 2 , o 2 ). Then, in step  620 , throttle position is controlled based on the greater of first throttle position and second throttle positions. In this way, a conservative approach is taken in that the greater of the throttle positions is selected so that feedback control will always tend to close the throttle in the event that one of the sensors indicates an incorrect value.  
         [0035]    Because measured throttle position from either track  210  or  212  can be used for feedback control, it is important to know the region of the transition of track  212 . In particular, since a system gain is changing, it is important that the correct slope and offset are used. This is also why a positive tolerance is used in step  614  so that the system errs on selecting the greater slope. In other words, if assumed sensor slope and actual sensor slope differ, then the actual system gain will be different than the actual. As described, the present invention selects a positive tolerance, thereby providing a conservative approach since the lower region of throttle position slope is greater than the upper region of throttle position slope. In other words, a tolerance range is given where the greater slope is selected, thereby giving lower system gain in the transition region, which is conservative.  
         [0036]    In an alternative embodiment, only offset o 2  is learned. In particular, due to the manufacturing process, the location of the transition will mostly affect offset o 2 . Thus, this parameter alone can be learned and used in the present invention.  
         [0037]    Although several examples of embodiments which practice the invention have been described herein, there are numerous other examples which could also be described. The invention is therefore to be defined only in accordance with the following claims.