Abstract:
A throttle miswire detection system including a powertrain control module (PCM) coupled to a throttle actuator and a pair of throttle plate position sensors. In detecting miswires, the PCM sets the throttle plate to a default position in which a default position value is measured by the position sensors. The PCM then sets the throttle plate to a closed position in which a closed position value is measured by the position sensors. After recording the receiving measurements, the PCM computes a negative slope sensor difference and a positive slope sensor difference. The PCM calculates a slope ratio consisting of the positive slope sensor difference divided by the negative slope sensor difference. If the slope values or slope ratio are not within prescribed limits, then the PCM deactivates the throttle actuator.

Description:
FIELD OF THE INVENTION 
     The present invention relates to motor vehicle electronic throttle control, and more particularly, to a system for detecting miswires that may adversely affect the performance of the electronic throttle. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     Previous motor vehicle throttle controls operate via a mechanical linkage between the accelerator pedal and the throttle body such that a throttle plate is rotated in concert with the movement of the accelerator cable. This method includes biasing for defaults the linkage to a default operating position consistent with regulations. Despite the simplicity and success of the mechanical throttle controls, the design was not adaptable to current automotive designs that emphasize reduced weight, responsiveness to varying travel conditions, and improved fuel economy. 
     Electronic throttle controls provide an alternative throttle control mechanism that improves the efficiency of air introduction into the cylinder. Generally, an electronic throttle includes a throttle plate, a throttle actuator, and a number of microprocessors and sensors for regulating the flow of air via the throttle valve. In particular, position sensors are utilized to determine the angle of the throttle plate, while a processor can cause the adjustment of the throttle plate angle in response to an increase or decrease in demand for air. In a typical throttle system, the electronic throttle is coupled to a powertrain control module (PCM). 
     Many PCM&#39;s employ various means to assure against any electronic malfunction or misread on the part of the electronic throttle. One method of assurance is to utilize redundant sensors, whereby more than one sensor responds to a particular condition so that the failure of a single sensor or an electronic component does not induce a throttle position greater than driver demand. More hardware, such as a redundant PCM, can be added to the throttle controls. However, the proliferation of components only increases the cost of throttle control, and by itself, cannot solve all the problems associated with throttle control. 
     Following the current trends in electronic throttle designs, a sensor malfunction would be overcome by utilizing a signal from its redundant counterpart. Redundancy thus allows the throttle control to operate. However, in the case of an electronic throttle control miswire, it is not desirable for the electronic throttle to continue operation. If there is a wiring error between the PCM and the electronic throttle control, the electronic throttle may perform, but it likely will not perform according to its design intent. That is, the PCM may be responsive to driver intent, but the electronic throttle would be incapable of receiving a command signal indicative of that intent. 
     Accordingly, the present invention includes a systematic method of detecting an electronic throttle control miswire and disabling the throttle control in response thereto. In particular, the present invention is an electronic throttle miswire detection system having as its main components an electronic throttle including a throttle plate, a throttle actuator, a first and second position sensor, and a PCM coupled to the throttle actuator and the respective sensors. The sensors, the throttle actuator, and the PCM cooperate to control the angular position of the throttle plate. 
     In detecting miswires, the PCM sets the throttle plate to a default position in which a default position value is measured by the position sensors. The PCM then sets the throttle plate to a closed position in which a closed position value is measured by the position sensors. After recording the receiving measurements, the PCM computes a negative slope sensor difference consisting of the default position value as measured by the first throttle position sensor less the closed position value as measured by the first throttle position sensor. The value of the negative slope sensor difference is then inverted, or multiplied by negative one. Similarly, the PCM computes a positive slope sensor difference consisting of the default position value as measured by the second throttle position sensor less the closed position value as measured by the second throttle position sensor. 
     If either the positive slope sensor difference or the negative slope sensor difference is less than zero, the PCM deactivates the throttle actuator. After normalizing the respective sensor difference values, the PCM calculates a slope ratio consisting of the positive slope sensor difference divided by the negative slope sensor difference. If the slope ratio falls within a prescribed safe harbor, then the PCM continues normal operation. If the slope ratio is either below or above the safe harbor, then the PCM deactivates the throttle actuator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of the electronic throttle miswire detection system of the present invention. 
     FIG. 2 a  is a schematic diagram showing a common electronic throttle miswire. 
     FIG. 2 b  is a schematic diagram showing a common electronic throttle miswire. 
     FIG. 2 c  is a schematic diagram showing a common electronic throttle miswire. 
     FIG. 2 d  is a schematic diagram showing a pair of common electronic throttle miswires. 
     FIG. 2 e  is a schematic diagram showing a second pair of common electronic throttle miswires. 
     FIG. 2 f  is a schematic diagram showing three concurrent electronic throttle miswires. 
     FIG. 2 g  is a schematic diagram showing a third pair of common electronic throttle miswires. 
     FIG. 2 h  is a schematic diagram showing a short circuit within the electronic throttle wiring. 
     FIG. 3 is a graphical representation of a symmetrical relationship between throttle plate angle and output voltage. 
     FIG. 4 is a graphical representation of an asymmetrical relationship between throttle plate angle and output voltage. 
     FIG. 5 is a flow chart depicting the miswire detection method according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention consists of a system for detecting an electronic throttle control miswire and disabling the throttle control is response thereto. In particular, the present invention is an electronic throttle miswire detection system  10  having as its main components an electronic throttle  11  coupled to a PCM  12 . The PCM  12  controls the operation of the electronic throttle  11 , thereby determining the mass rate of fresh air that is introduced into the combustion process. 
     As shown in FIG. 1, the electronic throttle  11  consists of a throttle actuator  14 , which is adapted to rotate of throttle plate  17  disposed within a throttle valve  16 . The throttle plate  17  is arranged such that it is rotatable over a range of 93°, preferably from a closed position determined to be 7° to a full-open position determined to be 100°. For purposes of the present invention, the throttle plate  17  may also be located at a default position, which is approximately 7.5° above the closed position, or approximately 14.5°. The angular position of the throttle plate  17  is measured by a dual throttle position sensor  18 , which consists of at least a first throttle position sensor and a second throttle position sensor. For purposes of this description, the first and second throttle position sensors are located within a single dual throttle position sensor  18 , although they may operate remotely in alternate embodiments. 
     The electronic throttle  11  is coupled to the PCM  12  via a set of wires  20 ,  22 ,  24 ,  26 ,  28 ,  30 . In a typical arrangement, there may be as many as 120 wires that transmit signals between the electronic throttle  11  and the PCM  12 . However, for purposes of this invention, the only six wires that are considered are those that are most likely to result in miswiring. In particular, the PCM  12  is coupled to the throttle actuator  14  via the “Motor−” wire  20  and “Motor+” wire  22 . The PCM  12  is coupled to the dual position sensor  18  via the TP 1 -NS wire  28  and the TP 2 -PS wire  26 . 
     The TP 1 -NS wire  28  transmits a signal indicative of the position of the throttle plate  17  as measured by the first throttle position sensor; and the TP 2 -PS wire  26  transmits a signal indicative of the position of the throttle plate  17  as measured by the second throttle position sensor. The respective outputs of the dual position sensor  18  are quantified with respect to a reference voltage, which is measured relative to the voltage supplied by the Vreference wire  30  and the ground wire  24 , also coupled to the dual position sensor  18 . Accordingly, for any angular position of the throttle plate  17 , each of the first and second throttle position sensors will register an output voltage as a percentage of the reference voltage, as discussed further herein. Properly wired, the PCM  12  and electronic throttle  11  will cooperatively regulate the position of the throttle plate  17  for efficient vehicle performance. 
     However, as shown in FIGS. 2 a ,  2   b ,  2   c ,  2   d ,  2   e ,  2   f ,  2   g  and  2   h , it is possible for miswires to occur that, while not rendering the PCM  12  or electronic throttle  11  inactive, might hamper the performance of the vehicle. For example, FIG. 2 a  schematically represents a “Motor−” wire  20  and “Motor+” wire  22  switch. FIG. 2 b  depicts a TP 2  wire  26  and TP 1  wire  28  switch. FIG. 2 c  shows a Vreference wire  30  and ground wire  24  switch. FIG. 2 f  depicts a triple-switch in which the “Motor−” wire  20  and “Motor+” wire  22 , the TP 2  wire  26  and TP 1  wire  28 , and the Vreference wire  30  and ground wire  24  are respectively switched. Collectively, the miswires depicted in FIGS. 2 a ,  2   b ,  2   c , and  2   f  may be referred to as asymmetrical miswires, the import of which is discussed further herein. 
     FIGS. 2 d ,  2   e , and  2   g  show a set of double-switch scenarios. In FIG. 2 d , the “Motor−” wire  20  and “Motor+” wire  22  are switched; and the TP 2  wire  26  and TP 1  wire  28  are switched. In FIG. 2 e , the “Motor−” wire  20  and “Motor+” wire  22  are switched and so are the Vreference wire  30  and ground wire  24 . In FIG. 2 g , the TP 2  wire  26  and TP 1  wire  28  and the Vreference wire  30  and ground wire  24  are respectively switched. The miswires depicted in the foregoing Figures may be referred to as symmetrical miswires, the import of which is discussed further herein. 
     FIG. 2 h  is a special case of a throttle miswire in which the TP 2  wire  26  and TP 1  wire  28  are shorted. 
     FIG. 3 is a graphical representation of a relationship between the throttle plate  17  angle and the output voltage recorded by the first and second sensors of the dual sensor  18 . The output of the first sensor is denoted TP 1 -NS, where the suffix NS refers to the negative slope of the graph. The output of the second sensor is denoted TP 2 -PS, where the suffix PS refers to the positive slope of the graph. 
     FIG. 4 is a graphical representation of an a second relationship between the throttle plate  17  angle and the output voltage recorded by the first and second sensors of the dual sensor  18 . Again, the output of the first sensor is denoted TP 1 -NS, where the suffix NS refers to the negative slope of the graph. The output of the second sensor is denoted TP 2 -PS, where the suffix PS refers to the positive slope of the graph. 
     The graphs shown in FIGS. 3 and 4 are representative of different ways of processing the outputs of the first and second sensors with respect to throttle plate  17  angle. The electronic throttle  11  may be determinative of whether the data is processed in accordance with FIG. 3 or FIG.  4 . As noted previously, the common miswirings occur in symmetrical and asymmetrical fashion, depending upon the number of sets of crossed wires. Accordingly, it is a feature of the present invention that both processes illustrated in FIGS. 3 and 4 are utilized in order to detect both types of miswirings. 
     FIG. 5 is a flowchart describing the method by which the PCM  12  detects miswirings. Upon initialization, step S 100 , the PCM  12  instructs the throttle actuator  14  to open or close the throttle plate  17  as shown in step S 102 . The PCM  12  then delays a prescribed time while the throttle actuator  14  attains a steady state or a default position, as shown in step S 104 . 
     Once the throttle actuator  14  is in a steady state, then the PCM  12  proceeds to step S 106  in which it records the output of the first position sensor in the default position, denoted TP 1 _default. In step S 108 , the PCM  12  records the output of the second position sensor in the default position, denoted TP 2 _default. In step S 110 , the PCM  12  instructs the throttle actuator  14  to close the throttle plate  17  until the throttle actuator  14  has attained a steady state as shown in step S 112 . Once the throttle actuator  14  is in a steady state, then the PCM  12  proceeds to step S 114  in which it records the output of the first position sensor in the closed position, denoted TP 1 _close_stop. In step S 116 , the PCM  12  records the output of the second position sensor in the closed position, denoted TP 2 _close_stop. 
     In steps S 118  and S 120 , the PCM  12  computes the quantities denoted the Positive Slope Sensor Difference (PSSD) and the Negative Slope Sensor Difference (NSSD), respectively. As shown, the PSSD is the change in voltage readings between the default and closed positions of the second position sensor, or PSSD=TP 2 _default−TP 2 _close_stop. Similarly, the NSSD is the change in voltage readings between the default and closed positions of the first position sensor, or NSSD=TP 1 _default−TP 1 _close_stop. In step S 121 , the PCM  12  inverts the value of the NSSD by multiplying the NSSD by negative one. Given both the PSSD and the NSSD calculated above, the PCM  12  can systematically check for any miswirings, of either the symmetrical or asymmetrical variety. 
     In step S 122 , the PCM  12  inquires as to whether either the PSSD or the NSSD is less than zero. As noted, in step S 121  the NSSD was inverted. As such, an NSSD value of less than zero in step S 122  implies that the NSSD as calculated in step S 120  was greater than zero, thereby indicating a fault in the throttle wiring. 
     A value of less than zero is indicative of an asymmetrical miswire, consisting generally of a type of miswiring shown in FIGS. 2 a ,  2   b ,  2   c , and  2   f . If either of the PSSD or the NSSD is negative, then the PCM  12  proceeds to step S 128 , which requests a 0.5 second delay to allow for the uncovering of ancillary faults which may render this test invalid. For example, faults such as a position sensor output out of range, an open throttle motor circuit, or a stuck throttle may be detected. Following the delay, the PCM  12  inquires as to whether any additional faults exist, as shown in step S 130 . If no other faults are detected, then in step S 132 , the PCM  12  deactivates the throttle actuator  14  such that the throttle plate  17  returns to the default position. Step S 134  represents the termination of the miswire detection system check. 
     Returning to step S 122 , if the PCM  12  does not calculate that one of the PSSD or the NSSD is less than zero, then the PCM  12  proceeds to step S 123  in which it normalizes the PSSD and the NSSD. As shown in FIG. 4, the TP 2 -PS slope is twice that of the TP 1 -NS slope. Therefore, in normalizing the PSSD and the NSSD, the PCM  12  either multiplies the NSSD by 2 or divides the PSSD by 2. 
     Following normalization, the PCM  12  in step S 124  computes the slope ratio of the sensor outputs, shown as: Slope_Ratio=PSSD/NSSD. In step S 126 , the PCM  12  inquires as to whether the slope ratio is within a prescribed safe harbor between 0.87 and 1.2. A value of the slope ratio outside the safe harbor is indicative of a symmetrical miswire of the type shown in FIGS. 2 d ,  2   e , and  2   g.    
     If the slope ratio is either less than 0.87 or greater than 1.2, then the PCM  12  proceeds to step S 128 . As before, the PCM  12  executes a 0.5 second delay to uncover any ancillary faults such as a position sensor output out of range, an open throttle motor circuit, or a stuck throttle. Thereafter, the PCM  12  inquires as to whether any additional faults exist, as shown in step S 130 . If another fault, such as a faulty throttle position sensor, is detected, then in step S 132 , the PCM  12  deactivates the throttle actuator  14  such that the throttle plate  17  returns to the default position. The PCM  12  then completes the system check at step S 134 . 
     If the slope ratio is within the safe harbor between 0.87 and 1.2, then the PCM  12  proceeds to step S 134 , and the system check is complete. 
     As noted, the PCM  12  is capable of processing the voltage readings from the first and second position sensors as shown in FIGS. 3 and 4. However, because the TP_ 1  and TP_ 2  sensor curves shown FIG. 3 are symmetrical in nature, they are not useful in detecting symmetrical miswirings of the type shown in FIGS. 2 d ,  2   e , and  2   g . That is, the NSSD and PSSD would have the same absolute differences in voltage irrespective of the direction of their respective slopes. Therefore, a double miswire, as shown in FIG. 2 d , would effectively cancel itself out such that both the NSSD and PSSD would have the same value as if the wiring were proper. 
     By way of comparison, the signal processing illustrated in FIG. 4 is capable of detecting both symmetrical and asymmetrical miswires, due to the asymmetrical nature of the TP_ 1  and TP_ 2  curves. Accordingly, the NSSD and the PSSD do not have the same absolute values independent of their respective orientation. As such, the signal processing shown in FIG. 4 enables the PCM  12  to detect symmetrical miswires. 
     In a preferred embodiment, the PCM  12  is adapted to utilize the signal processing method illustrated in FIG. 4 for detecting both symmetrical and asymmetrical miswires. Alternatively, the PCM  12  may utilize both types of signal processing to ensure redundant measurements of the NSSD and PSSD. 
     As described, the present invention consists of a system and associated method for detecting miswirings in a throttle control system. Advantageously, the present invention includes a mechanism for disabling the throttle actuator in the event of a miswire in order to ensure the efficiency and accuracy of the throttle control system.