METHOD FOR MONITORING A VECTOR-BASED POSITION SENSOR

Abstract

A method for monitoring a vector-based position sensor, the method comprising: detecting a position of a rotary shaft with the position sensor, wherein the detected position includes: a sine signal including a sine function of a detected angle of the rotary shaft and a cosine signal including a cosine function of the detected angle of the rotary shaft (120); calculating an absolute value of the sine signal and an absolute value of the cosine signal with a diagnostic controller (122, 124); and comparing at least one of the absolute value of the sine signal and the absolute value of the cosine signal with a minimum threshold (128) with the diagnostic controller to determine whether the absolute value of the sine signal and / or the absolute value of the cosine signal is less than the minimum threshold, or whether the absolute value of the sine signal and / or the absolute value of the cosine signal is equal to or greater than the minimum threshold; characterized by Calculating a minimum downtime period using the equation tf, min ≈ 2 arcsin (K low A 1) (30 (π) (n) (RPP)) (flr) ((n) (RPP) (ts) 30); where t f,min the minimum downtime period is K lowis an expected minimum signal amplitude modified by a scaling factor, A1 is the amplitude of the non-faulty signal, n is the shaft speed in revolutions per minute, RPP is a sensor scaling factor, flr is a rounding function that rounds down to the nearest integer, and t s the sampling time is wherein the diagnostic controller indicates a failure if at least one of the absolute value of the sine signal and the absolute value of the cosine signal is less than the minimum threshold value (142) for at least the duration of the minimum failure period.

Description

INTRODUCTION

[0001] This invention generally relates to a method for monitoring a vector-based position sensor according to the preamble of claim 1, as is essentially known from US 2014 / 0 375 241 A1. Regarding the further prior art, reference is made to US 2008 / 0 116 886 A1.

[0002] The rotational position of a rotating shaft, such as an electric motor shaft, is a key input used by control systems. Many rotation sensors generate an output comprising a sine signal in the form of S=Asin(θ) and a cosine signal in the form of C=Acos(θ), where A is a scaling factor and θ is the angle sensed by the rotation sensor. Control systems can use the sine and cosine signals to calculate the rotational position of the rotating shaft.

[0003] If the position sensor outputs an erroneous signal, either a sine signal or a cosine signal, the calculated position of the rotating shaft will be incorrect and the control system may not operate properly. Therefore, it is important to monitor the operation of the position sensor to detect an erroneous signal from the position sensor. SUMMARY

[0004] According to the invention, a method for monitoring a vector-based position sensor is proposed, which is characterized by the features of claim 1. The method includes detecting a position of the rotary shaft with the position sensor. The detected position of the rotary shaft includes a sine signal and a cosine signal. The sine signal includes a sine function of a detected angle of the rotary shaft. The cosine signal includes a cosine function of the detected angle of the rotary shaft. An absolute value of the sine signal and an absolute value of the cosine signal are calculated using a diagnostic controller. The diagnostic controller compares at least one of the absolute value of the sine signal and the absolute value of the cosine signal with a minimum threshold value.The absolute value of the sine signal or the cosine signal is compared to the minimum threshold to determine whether the absolute value of the sine signal and the absolute value of the cosine signal are less than the minimum threshold, or whether at least one of the absolute value of the sine signal and the absolute value of the cosine signal is equal to or greater than the minimum threshold. A diagnostic controller indicates a fault with the position sensor if at least one of the absolute value of the sine signal and the absolute value of the cosine signal is less than the minimum threshold.

[0005] In one embodiment of the method, the diagnostic controller compares the absolute value of the sine signal with the absolute value of the cosine signal to identify which of the absolute value of the sine signal and the absolute value of the cosine signal has a larger value. The one of the absolute value of the sine signal and the absolute value of the cosine signal that has the larger value is defined as a largest signal value. The step of comparing the at least one of the absolute value of the sine signal and the absolute value of the cosine signal with the threshold value includes comparing the largest signal value with the threshold value.

[0006] In one embodiment of the method, the diagnostic controller compares the largest signal value to the maximum threshold to determine whether the largest signal value is equal to or less than the maximum threshold, or whether the largest signal value is greater than the maximum threshold. The diagnostic controller may indicate a fault with the position sensor if the largest signal value is greater than the maximum threshold.

[0007] The method of monitoring the position sensor is an interactive process that is continuously repeated over a sampling period. Accordingly, one aspect of the method of monitoring the position sensor involves continuously acquiring the sine signal and the cosine signal over the sampling period.

[0008] One aspect of the method of monitoring the position sensor involves calculating a minimum failure time period as a function of a rotational speed of the shaft.

[0009] Another aspect of the position sensor monitoring method involves the diagnostic controller incrementing a failure timer when the maximum signal value is less than the minimum threshold. The diagnostic controller indicates a failure with the position sensor when the failure timer increments to a failure time limit. The failure time limit is less than the minimum failure time, which is a function of the rotating cell's speed.

[0010] In one embodiment of the method of monitoring the position sensor, the diagnostic controller extracts a value of the detected angle from the detected sine signal and the detected cosine signal. The diagnostic controller then calculates a sine function of the extracted value of the detected angle to define a sine of the extracted value and calculates a cosine function of the extracted value of the detected angle to define a cosine of the extracted value.

[0011] In one embodiment, the diagnostic controller extracts the sine of the extracted value to define a scaled sine of the extracted value and scales the cosine of the extracted value to define a scaled cosine of the extracted value. The diagnostic controller then calculates an absolute value of the scaled sine of the extracted value and an absolute value of the scaled cosine of the extracted value.

[0012] In one embodiment of the method, the diagnostic controller calculates a difference between the absolute value of the sine signal and the absolute value of the scaled sine of the extracted value to define a sine value difference. The diagnostic controller further calculates a difference between the absolute value of the cosine signal and the absolute value of the scaled cosine of the extracted value to define a cosine value difference.

[0013] In one embodiment of the method of monitoring the position sensor, the minimum threshold is defined as being equal to a value substantially equal to zero. The step of comparing the at least one absolute value of the sine signal and the absolute value of the cosine signal to the minimum threshold includes comparing a sine value difference to the minimum threshold to determine whether the sine value difference is less than the minimum threshold, or whether the sine value difference is equal to or greater than the minimum threshold. The step of comparing the at least one absolute value of the sine signal and the absolute value of the cosine signal to the minimum threshold includes comparing a cosine value difference to the minimum threshold to determine whether the cosine value difference is less than the minimum threshold, or whether the cosine value difference is equal to or greater than the minimum threshold.The diagnostic controller may also compare the sine value difference and the cosine value difference to a maximum threshold to determine whether the sine value difference and the cosine value difference are each greater than the maximum threshold, or whether the sine value difference and the cosine value difference are each not greater than the maximum threshold. The diagnostic controller may indicate a failure if either the sine value difference and / or the cosine value difference is less than the minimum threshold, or if the sine value difference and / or the cosine value difference is greater than the maximum threshold.

[0014] According to the invention, the minimum downtime is calculated using the following equation: tf,min≈2arcsin(KlowA1)(30(π)(n)(RPP))(flr)((n)(RPP)(ts)30); where t f,min the minimum downtime duration is K lowis an expected minimum signal amplitude modified by a scaling factor, A1 is the amplitude of the non-faulty signal, n is the shaft speed in revolutions per minute, RPP is a sensor scaling factor, flr is a floor function that rounds down to the nearest integer, and t s is the sampling time.

[0015] In another embodiment of the method for monitoring the position sensor, the minimum failure time is calculated using the following equation: tf,min=(Tf)(flr)(tsTcyc)+(flr(ts−(Tcyc)(floor(tsTcyc))Tcyc−Tf))((ts)−(Tcyc)(flr)(tsTcyc)−(Tcyc−Tf)), where t f,min the minimum downtime duration is t s is the sampling time, and flr is a floor function that is rounded to the nearest integer. T f is calculated from the equation: Tf=(Tcycπ)arccos(A12+A22−2KlowA12−A22) where K lowis the square of the expected minimum signal amplitude, A1 is the amplitude of the sine signal, and A2 is the amplitude of the cosine signal. T cyc is calculated from the equation: Tcyc=(30(n)(RPP)) where n is the shaft speed in revolutions per minute, and RPP is a sensor scaling factor.

[0016] Accordingly, the method for monitoring the position sensor provides a novel process for identifying a failure using one or both of the sine signal or the cosine signal from the position sensor. The method described herein provides an efficient process that produces a fast failure detection time while being computationally efficient and requiring little computational effort from the diagnostic controller.

[0017] As such, the method described herein is a new process that improves the operation of the diagnostic controller.

[0018] The foregoing features and advantages, as well as other features and advantages of the present teachings, can be readily derived from the following detailed description of the best modes for carrying out the teachings when considered in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flowchart illustrating a first embodiment of a method for monitoring a vector-based position sensor. Fig. 2 is a flowchart illustrating a second embodiment of the method for monitoring the vector-based position sensor. DETAILED DESCRIPTION

[0019] Those skilled in the art will recognize that terms such as "above," "below," "up," "down," "top," "bottom," etc., are used descriptively for the figures. Furthermore, the teachings herein may be described in terms of functional or logical block components or various processing steps, respectively. It should be noted that such block components may be constructed from any number of hardware, software, and / or firmware components configured to perform the specified functions.

[0020] Referring to FIGS., wherein like reference numerals designate like parts throughout the several views, a method for monitoring a position sensor is generally illustrated. The method described herein can be used to monitor the performance of a rotational position sensor. The position sensor can include any type of sensor that outputs a sine signal and a cosine signal for a sensed angle θ of the rotating shaft. The sine signal is a sine function of a sensed angle of the rotating shaft and can generally be described by the equation S=A sin(θ), where S is the sine signal, A is the scaling factor, and θ is the angle sensed by the rotation sensor. The cosine signal is a cosine function of the sensed angle of the rotating shaft and can generally be described by the equation C=A cos(θ), where C is the cosine signal, A is the scaling factor, and θ is the angle sensed by the rotation sensor.

[0021] The method described herein may be embodied as a sensor diagnostic algorithm operable on a diagnostic controller. The diagnostic controller may include a computer or processor and may include all software, hardware, memory, algorithms, connections, sensors, etc., necessary to manage and control the operation of the position sensor. The diagnostic controller may be a standalone device or may be integrated into another machine, such as another controller or another computer. The diagnostic controller may alternatively be referred to as a control module, a controller, a control unit, a computer, etc.It should be noted that diagnostic control may include any device capable of analyzing data from different sensors, comparing data, performing calculations, making the necessary decisions required to evaluate the operation of the position sensor, and performing the necessary tasks necessary to monitor the operation of the position sensor.

[0022] The diagnostic controller may be embodied by one or more digital or host computers, each having one or more processors, read-only memory (ROM), random access memory (RAM), electrically programmable read-only memory (EPROM), optical drives, magnetic drives, etc., a high-speed clock, analog / digital (A / D) circuits, digital / analog (D / A) circuits, and all necessary input / output (I / O) circuits, input / output devices and communication interfaces, as well as signal conditioning and buffer circuits.

[0023] Computer-readable storage may include any volatile / non-volatile medium that participates in the provision of data or computer-readable instructions. Storage may be non-volatile or volatile. Non-volatile media may include, for example, optical or magnetic disks and other persistent storage. Volatile media may include, for example, dynamic random access memory (DRAM) that forms main memory. Other examples of memory embodiments include a floppy disk, a flexible disk or hard disk, magnetic tape or other magnetic media, a CD-ROM, DVD, or other optical media, as well as other possible storage elements, such as flash memory.

[0024] The diagnostic controller includes tangible, non-volatile memory on which computer-executable instructions are recorded, including the sensor diagnostic algorithm. The diagnostic controller's processor is configured to execute the sensor diagnostic algorithm. The sensor diagnostic algorithm implements the method for monitoring the position sensor.

[0025] The method of monitoring the position sensor is an interactive process whose steps are performed multiple times within a sampling period. One iteration of the process is described in more detail herein. The iterative process is repeated, and the results of each iteration are used to monitor the performance of the position sensor, as described in more detail below.

[0026] Generally, the method of monitoring the position sensor involves detecting an angular position of the rotary shaft with the position sensor. The detected angular position of the rotary shaft includes the sine signal and the cosine signal. An absolute value for each of the sine signal and the cosine signal is calculated, and at least one of the absolute value of the sine signal and the absolute value of the cosine signal is compared with the minimum threshold value. The position sensor may be faulty if one of the absolute value of the sine signal and the absolute value of the cosine signal, which is compared with the minimum threshold value, is smaller than the minimum threshold value. However, when one of the sine signal and cosine signal approaches zero, the other of the sine signal and cosine signal approaches one due to the nature of the sine and cosine values.This natural fluctuation between the sine signal and the cosine signal makes it difficult to diagnose the position sensor from a single detected angle of the rotating shaft. Accordingly, the process is an iterative procedure in which the steps of the procedure are repeatedly executed to ensure that an erroneous sine signal or an erroneous cosine signal is detected as the sine value and that the cosine value fluctuates between zero and one of the different detected angles θ.

[0027] With reference to Fig. 1, a first embodiment of the method of the position sensor is described in more detail. The first embodiment of the method involves detecting a position of the rotary shaft with the position sensor. The detected position of the rotary shaft includes the sine signal and the cosine signal for a specific measured angle θ of the rotary shaft. As mentioned above, the sine signal includes a sine function of the detected angle θ of the rotary shaft, and the cosine signal includes a cosine function of the detected angle θ of the rotary shaft. The step of detecting the sine signal and the cosine signal, i.e., detecting the position of the rotary shaft, is generally represented by box 120 in Fig. 1 is specified.

[0028] An absolute value of the sine signal and an absolute value of the cosine signal are calculated. The step of calculating the absolute value of the sine signal is generally described by Box 122 in Fig. 1. The step of calculating the absolute value of the cosine signal is generally described by box 124 in Fig. 1. As used herein, the term "absolute value" may be interpreted as the magnitude of a real number without regard to its sign, or as the actual magnitude of a numerical value or measurement, regardless of its relationship to other values.

[0029] The absolute value of the sine signal is then compared with the absolute value of the cosine signal to identify which of the absolute values of the sine signal and the absolute value of the cosine signal has a larger value or a larger magnitude. The step of identifying which of the absolute values of the sine signal and the absolute value of the cosine signal has the largest value is generally represented by box 126 in Fig. 1. The larger of the absolute value of the sine signal and the absolute value of the cosine signal is defined as the largest signal value. For example, if the sine signal has an absolute value of 0.50 and the cosine signal has an absolute value of 0.86, then the cosine signal has the largest value, and the largest signal value is defined as equal to the absolute value of the cosine signal, i.e., 0.86.

[0030] A sample timer is incremented to track a cumulative amount of time while the position sensor is monitored. The step of incrementing the sample timer is generally described by box 127 in Fig. 1. The sampling timer may also include, among other things, a time tracking device of the diagnostic controller. The sampling timer is incremented for each iteration of the process by the amount of time sampled by the position sensor.

[0031] As generally described above, at least one absolute value of the sine signal and one absolute value of the cosine signal are compared to the minimum threshold. The first embodiment of the method of monitoring the position sensor defines the comparison of one of the absolute value of the sine signal and the absolute value of the cosine signal to the minimum threshold while comparing the largest signal value to the minimum threshold. The step of comparing the largest signal value to the minimum threshold is generally represented by box 128 in Fig. 1. Accordingly, for the first embodiment of the method described herein, the specific one of the absolute value of the sine signal and the absolute value of the cosine signal that is compared to the minimum threshold is the respective one of the absolute value of the sine signal and the absolute value of the cosine signal that has the largest value, which was previously defined as the largest signal value. The largest signal value is compared to the minimum threshold to determine whether the largest signal value is less than the minimum threshold, or whether the largest signal value is equal to or greater than the minimum threshold. The minimum threshold is a predefined value that indicates a lower limit for a proper signal from the position sensor, or a minimum expected value, depending on the specific sensor, signal conditioning circuit, etc.

[0032] The position sensor may be faulty if the largest signal value is less than the minimum threshold, which is generally specified at 130. If the position sensor is faulty, the largest signal value is less than the minimum threshold for a period of time within the sampling period. Accordingly, a failure timer is continuously incremented while at least one of the absolute value of the sine signal and the absolute value of the cosine signal, i.e., the largest signal value, is less than the minimum threshold within the sampling period. The step of incrementing the failure timer is generally specified by box 132 in Fig. 1. The failure timer tracks the cumulative amount of time that the largest signal value is less than the minimum threshold. The failure timer is a measurement of the amount of time that the position sensor generates a signal indicating a failure.

[0033] If the largest signal value is not less than the minimum threshold, i.e., if the largest signal value is equal to or greater than the minimum threshold, which is generally specified at 129, then the diagnostic controller compares the failure timer with the failure time limit to determine whether the failure timer is less than the failure time limit, or whether the failure timer is equal to or greater than the failure time limit. The step of comparing the failure timer with the failure time limit is generally specified by box 138 in Fig. 1 and is described in more detail below.

[0034] In addition, the largest signal value can be compared to the threshold to determine whether the largest signal value is equal to or less than the maximum threshold, or whether the largest signal value is greater than the maximum threshold. The step of comparing the largest signal value to the threshold is generally described in Box 134 in Fig. 1. The maximum threshold is a predefined value that specifies an upper limit for the proper signal from the position sensor or a maximum expected value, depending on the specific sensor, signal conditioning circuit, etc.

[0035] The position sensor may be faulty if the largest signal value is greater than the maximum threshold, which is generally specified at 136. If the position sensor is faulty, the largest signal value is greater than the maximum threshold for a period of time within the sampling period. Accordingly, the failure timer may be continuously incremented while at least one of the absolute value of the sine signal and the absolute value of the cosine signal, i.e., the largest signal value, is less than the maximum threshold within the sampling period. The step of incrementing the failure timer is generally specified by box 132 in Fig. 1. The failure timer tracks a cumulative amount of time during which the largest signal value is greater than the maximum threshold. It should be noted that the diagnostic controller may include separate failure timers to track the largest signal value relative to the maximum threshold and the minimum threshold, respectively.

[0036] If the largest signal value is not greater than the maximum threshold, i.e., if the largest signal value is equal to or less than the maximum threshold, which is generally specified at 135, then the diagnostic controller compares the failure timer with the failure time limit to determine whether the failure timer is less than the failure time limit, or whether the failure timer is equal to or greater than the failure time limit. The step of comparing the failure timer with the failure time limit is generally specified by box 138 in Fig. 1 and is described in more detail below.

[0037] As mentioned above, the process described herein is an interactive process in which each of the steps described above for the first embodiment of the method for monitoring the position sensor is repeatedly executed. The diagnostic controller indicates a failure with the position sensor when the failure timer is greater than the failure time limit, ie, when a value of the failure timer has been incremented to a predetermined value, ie, the failure time limit is less than a sampling time limit.

[0038] The downtime limit may be defined according to a calculation of the minimum downtime for a given set of conditions that constitutes a downtime according to previous determinations. Accordingly, the downtime timer is compared to the downtime limit if the downtime timer is less than the downtime limit or if the downtime timer is equal to or greater than the downtime limit. The step of comparing the downtime timer to the downtime limit is generally described by Box 138 in Fig. 1. If the failure timer has incremented to a value equal to or greater than the failure time limit in less than the sample time limit, which is generally specified at 140, then the indication of a failure with the position sensor takes place. The step of indicating a failure with the position sensor is generally indicated by box 142 in Fig. 1. The position sensor failure may be indicated in any suitable manner, including but not limited to setting a diagnostic code in the diagnostic control, illuminating a warning lamp, displaying a message, etc.

[0039] If the failure timer is less than the failure time limit, which is generally specified at 139, then the sample timer is compared to the sample time limit to determine whether the sample timer is equal to or greater than the sample time limit, or whether the sample timer is less than the sample time limit. The step of comparing the sample timer to the sample time limit is generally specified by box 144 in Fig. 1. The sample time limit can be defined to include any time period sufficient to detect a failure with the position sensor. It should be noted that the longer the sample time limit, the more likely a failure indication is to be received, and conversely, the shorter the failure time limit, the less likely a failure indication is to be received. The sample time limit should be defined to include a time period that is at least greater than a minimum failure time period, which will be described in more detail below. If the sample timer is less than the sample time limit, which is generally specified at 146, then nothing further is done and the process is repeated.If the sample timer is equal to or greater than the sample time limit, generally indicated at 148, and the failure timer has not been incremented to a value equal to or greater than the failure time limit, then the diagnostic controller indicates no failure with the position sensor. The step of indicating no failure with the position sensor is generally indicated by box 150 in FIG. Fig. 1 is specified.

[0040] As mentioned above, the process is repeatedly performed over a sampling period to determine whether the failure time limit counter increments within the sampling time limit. In other words, if the sampling period is less than the sampling time limit, then there is insufficient time to fully diagnose the position sensor, and the process is repeated until the sampling period, as measured by the sampling timer, is equal to or greater than the sampling time limit.

[0041] The sampling time limit can be defined based on a minimum failure period. The minimum failure period is a minimum period in which the failure is detectable during a sampling period for a given set of conditions. The minimum failure period is the guaranteed minimum failure time detected during a sampling period, i.e., the guaranteed time during which the diagnosed signal(s) is (are) below (above) the minimum (maximum) signal threshold. The minimum failure period provides an upper limit for setting a failure time limit at which a failure is indicated. The failure time limit must be set to a value or period equal to or less than the minimum failure period to ensure that a failure in the position sensor is detected.Accordingly, for a failure to be detected, the failure timer must be equal to or greater than the downtime limit, and the downtime limit must be less than the minimum downtime period.

[0042] The minimum failure period can be defined as a function of the rotational speed of the rotating shaft. For example, the minimum failure period for the first embodiment of the position sensor monitoring method can be calculated from Equation 1 below. rf,min≈2arcsin(KlowA1)(30(π)(n)(RPP))(flr)((n)(RPP)(ts)30)

[0043] Within equation 1, t f,min the minimum downtime period is K lowis an expected minimum signal amplitude modified by a scaling factor, A1 is the amplitude of the non-faulty signal, n is the shaft speed in revolutions per minute, RPP is a sensor scaling factor, flr is a floor function rounded to the nearest even number, and t s The sampling period. Calculating the minimum failure period for the first embodiment of the positioning sensor monitoring method is an approximation, since Equation 1 only considers full sampling windows and not partial sampling windows. Furthermore, calculating the minimum failure period using Equation 1 above depends on the sampling rate of the diagnostic controller. Equation 1 reflects a calculation of a minimum failure period based on an infinite sampling rate, i.e., continuous sampling. Slower sampling rates may affect the calculated minimum failure period.

[0044] With reference to Fig. 2, a second embodiment of the method is described in more detail. The second embodiment of the method for monitoring the position sensor includes detecting the position of the rotary shaft with the position sensor. The detected position of the rotary shaft includes the sine signal and the cosine signal for a specific measured angle θ of the rotary shaft. The step of detecting the sine signal and the cosine signal, i.e., detecting the position of the rotary shaft, is generally represented by box 220 in Fig. 2. As mentioned above, the sine signal includes a sine function of the detected angle θ of the rotating shaft and the cosine signal includes a cosine function of the detected angle θ of the rotating shaft.

[0045] An absolute value of the sine signal and an absolute value of the cosine signal are calculated. The step of calculating the absolute value of the sine signal is generally described by box 222 in Fig. 2. The step of calculating the absolute value of the cosine signal is generally described by box 224 in Fig. 2. As used herein, the term "absolute value" may be interpreted as the magnitude of a real number without regard to its sign, or as the actual magnitude of a numerical value or measurement, regardless of its relationship to other values.

[0046] A value of the detected angle θ is extracted from the detected sine signal and the detected cosine signal. The step of extracting the detected angle is generally described by box 226 in Fig. 2. The diagnostic controller can extract the sensed angle θ in any suitable manner. For example, the sine signal can be divided by the cosine signal to define a signal quotient, and the arctan of the signal quotient can be calculated to derive the sensed angle θ. Alternatively, a tracking loop can be used to extract the sensed angle θ from the sine signal and the cosine signal. It should be noted that the sensed angle θ can be extracted in a different manner not shown or described herein.

[0047] Once the detected angle θ has been extracted from the sine signal and the cosine signal, the diagnostic controller calculates the sine function of the extracted value of the detected angle θ to define a sine of the extracted value. The step of calculating the sine function of the extracted value of the detected angle is generally represented by box 228 in Fig. 2. In addition, the diagnostic controller calculates the cosine function of the extracted value of the detected angle θ to define a cosine of the extracted value. The step of calculating the cosine function of the extracted value of the detected angle θ is generally represented by box 230 in Fig. 2 is specified.

[0048] The sine of the extracted value can be scaled to define a scaled sine of the extracted value. The step of scaling the sine of the extracted value is generally described by Box 232 in Fig. 2. Similarly, the cosine of the extracted value can be scaled to define a scaled cosine of the extracted value. The step of scaling the cosine of the extracted value is generally described by Box 234 in Fig. 2. The sine of the extracted value and the cosine of the extracted value can be scaled by multiplying the sine of the extracted value and the cosine of the extracted value by a multiplier. The multiplier is the smallest expected amplitude of the sensor outputs.

[0049] An absolute value of the scaled sine of the extracted value is then calculated. The step of calculating the absolute value of the scaled sine of the extracted value is generally described by Box 236 in Fig. 2. Similarly, an absolute value of the scaled cosine of the extracted value is also calculated. The step of calculating the absolute value of the scaled cosine of the extracted value is generally described by Box 238 in Fig. 2. As mentioned above, the term “absolute value” can be interpreted as the magnitude of a real number regardless of its sign, or as the actual magnitude of a numerical value or measurement, regardless of its relationship to other values.

[0050] A difference between the absolute value sine signal and the absolute value of the scaled sine of the extracted value is then calculated, and the difference is defined as a sine value difference. The step of calculating the sine value difference is generally described by Box 240 in Fig. 2. A difference between the absolute value of the cosine signal and the absolute value of the scaled cosine of the extracted value is also calculated, and the difference is defined as a cosine value difference. The step of calculating the cosine value difference is generally described by Box 242 in Fig. 2 is specified.

[0051] A sample timer is incremented to track a cumulative amount of time while the position sensor is monitored. The step of incrementing the sample timer is generally described by box 243 in Fig. 2. The sampling timer may also include, among other things, a time tracking device of the diagnostic controller. The sampling timer is incremented for each iteration of the process by the amount of time sampled by the position sensor.

[0052] As mentioned above, at least one absolute value of the sine signal and one absolute value of the cosine signal are compared with the minimum threshold value. For the second embodiment of the method of monitoring the position sensor, the minimum threshold value is defined as a value that is substantially equal to zero or slightly above zero. Furthermore, comparing at least one of the absolute value of the sine signal and the absolute value of the cosine signal in the context of the second embodiment of the method of monitoring the position sensor is defined as comparing the sine value difference with the minimum threshold value, i.e. zero, to determine whether the sine value difference is smaller than the minimum threshold value, or equal to or greater than the minimum threshold value, and comparing the cosine value difference with the minimum threshold value, i.e.zero to determine whether the cosine difference is less than, equal to, or greater than the minimum threshold. Furthermore, the sine difference and the cosine difference may each be compared to a maximum threshold. The maximum threshold is a predefined value that indicates an upper limit for the proper signal from the position sensor or a maximum expected value, depending on the specific sensor, signal conditioning circuit, etc. The step of comparing the sine difference to the minimum threshold and the maximum threshold is generally represented by box 244 in FIG. Fig. 2. The step of comparing the cosine value difference with the minimum threshold and the maximum threshold is generally described by Box 246 in Fig. 2 is specified.

[0053] The position sensor may be faulty if the sine value difference is less than the minimum threshold, i.e., less than zero, or if the sine value difference is greater than the maximum threshold, generally specified at 252. Furthermore, the position sensor may be faulty if the sine value difference is less than the minimum threshold, e.g., less than zero, or greater than the threshold, generally specified at 254. A failure timer may be continuously implemented if both the sine value difference and the cosine value difference, or only one of them, is less than the minimum threshold within the exhaust period, or if both the sine value difference and the cosine value difference, or only one of them, is greater than the threshold within the sampling period. The step of incrementing the failure timer is generally specified by box 256 in Fig. 2. The failure timer tracks a cumulative period of time that the sine value difference and / or the cosine value difference is less than the minimum threshold.

[0054] If the sine value difference is not less than the minimum threshold, i.e., if the sine value difference is equal to or greater than the minimum threshold, and if the sine value difference is not greater than the maximum threshold, i.e., if the value difference is greater than, equal to, or less than the maximum threshold, which is generally specified at 248, then the diagnostic controller compares the value of the failure timer with the failure time limit to determine whether the value of the failure timer is less than the failure time limit, or whether the value of the failure timer is equal to or greater than the failure time limit. The step of comparing the value of the failure timer with the failure time limit is generally specified by box 258 in Fig. 2 and described in more detail below. Similarly, if the cosine value difference is not less than the minimum threshold, i.e., if the cosine value difference is not equal to or greater than the minimum threshold, and if the cosine value difference is not greater than the maximum threshold, i.e., if the cosine value difference is equal to or less than the maximum threshold, which is generally specified at 250, then the diagnostic controller compares the value of the failure timer with the failure time limit to determine whether the value of the failure timer is less than the failure time limit, or whether the value of the failure timer is equal to or greater than the failure time limit. The step of comparing the value of the failure timer with the failure time limit is generally specified by box 258 in Fig. 2 and described in more detail below.

[0055] As mentioned above, the process described herein is an interactive process in which each of the steps described above for the second embodiment of the method of monitoring the position sensor is repeatedly performed. The diagnostic controller indicates a failure with the position sensor when the failure timer increments the failure time limit in less than the sample time limit. The value of the failure timer is compared to the failure time limit to determine whether the value of the failure timer is less than the failure time limit, or whether the value of the failure timer is equal to or greater than the failure time limit. The step of comparing the value of the failure timer to the failure time limit is generally represented by box 258 in Fig. 2. If the failure timer is equal to or greater than the failure time limit, which is generally specified at 262, then the diagnostic controller indicates a failure with the position sensor. The step of indicating a failure with the position sensor is generally indicated by box 264 in Fig. 2. The position sensor failure may be indicated in any suitable manner, including but not limited to setting a diagnostic code in the diagnostic control, illuminating a warning lamp, displaying a message, etc.

[0056] If the failure timer is less than the failure time limit, which is generally specified at 260, then the sample timer is compared to the sample time limit to determine whether the sample timer is equal to or greater than the sample time limit, or whether the sample timer is less than the sample time limit. The step of comparing the sample timer to the sample time limit is generally specified by box 266 in Fig. 2. It should be noted that the sample timer is a measure of the cumulative sample time duration. If the sample timer is less than the sample time limit, generally specified at 268, then nothing further is done and the process is repeated. If the sample timer is equal to or greater than the sample time limit, generally specified at 270, and the failure timer has not been incremented to a value equal to or greater than the failure time limit, then the diagnostic controller indicates no failure with the position sensor. The step of indicating no failure with the position sensor is generally indicated by box 272 in Fig. 2 is specified.

[0057] As mentioned above, the process is repeatedly performed over a sampling period to determine whether the failure timer increments to the failure time limit within the sampling time limit. In other words, if the sampling timer is less than the sampling time limit, then there is insufficient time to properly diagnose the position sensor, and the process is repeated until the failure timer is equal to or greater than the failure time limit, or the sampling timer is equal to or greater than the sampling time limit.

[0058] The failure period can be defined based on a minimum failure period. The minimum failure period is a minimum period in which the failure is detectable during the sampling period for a given set of conditions. The minimum failure period provides an upper limit for setting a failure time limit at which a failure is indicated. The failure time limit must be set to a value or a period less than the minimum failure period to ensure that a failure in the position sensor is detected. Accordingly, for a failure to be detected, the failure timer must be equal to or greater than the failure time limit, and the failure time limit must be less than the minimum failure period.

[0059] The minimum failure period can be defined as a function of the rotational speed of the rotating shaft. For example, the minimum failure period for the second embodiment of the position sensor monitoring method can be calculated from Equation 2 below. tf,min=(Tf)(flr)(tsTcyc)+(flr(ts−(Tcyc)(floor)(tsTcyc)Tcyc−Tf))((ts)−(Tcyc)(flr)(tsTcyc)−(Tcyc−Tf))

[0060] Within equation 2, t f,min the minimum downtime duration is t s the sampling time, and is a floor function that is rounded to the nearest integer. T f is calculated from equation 3 below. Tf=(Tcycπ)arccos(A12+A22−2KlowA12−A22)

[0061] Within equation 3, K low is the square of the expected minimum signal amplitude, A1 is the amplitude of the sine signal, and A2 is the amplitude of the cosine signal. T cyc is calculated from equation 4 below. Tcyc=(30(n)(RPP))

[0062] Within Equation 3, n is the shaft speed in revolutions per minute, and RPP is a sensor scaling factor. Furthermore, the calculation of the minimum failure period using Equation 2 above depends on the diagnostic controller's sampling rate. Equation 2 reflects a calculation of a minimum failure period based on an infinite sampling rate, i.e., continuous sampling. Slower sampling rates may affect the calculated minimum failure period.

Claims

[1] A method for monitoring a vector-based position sensor, the method comprising: detecting a position of a rotary shaft with the position sensor, wherein the detected position includes: a sine signal including a sine function of a detected angle of the rotary shaft and a cosine signal including a cosine function of the detected angle of the rotary shaft (120); calculating an absolute value of the sine signal and an absolute value of the cosine signal with a diagnostic controller (122, 124); and comparing at least one of the absolute value of the sine signal and the absolute value of the cosine signal with a minimum threshold (128) with the diagnostic controller to determine whether the absolute value of the sine signal and / or the absolute value of the cosine signal is less than the minimum threshold, or whether the absolute value of the sine signal and / or the absolute value of the cosine signal is equal to or greater than the minimum threshold; characterized by Calculating a minimum downtime period using the equation tf,min≈2arcsin(KlowA1)(30(π)(n)(RPP))(flr)((n)(RPP)(ts)30); where t f,min the minimum downtime period is K lowis an expected minimum signal amplitude modified by a scaling factor, A1 is the amplitude of the non-faulty signal, n is the shaft speed in revolutions per minute, RPP is a sensor scaling factor, flr is a rounding function that rounds down to the nearest integer, and t s the sampling time is wherein the diagnostic controller indicates a failure if at least one of the absolute value of the sine signal and the absolute value of the cosine signal is less than the minimum threshold value (142) for at least the duration of the minimum failure period. [2] The method of claim 1, further comprising comparing, with the diagnostic controller, the absolute value of the sine signal with the absolute value of the cosine signal (126) to identify which of the absolute value of the sine signal and the absolute value of the cosine signal has a greater value, and defining one of the absolute value of the sine signal and the absolute value of the cosine signal that has a greater value as a largest signal value. [3] The method of claim 1, further comprising continuously detecting the sine signal and the cosine signal over a sampling period (120, 127). [4] The method of claim 2, wherein indicating the failure is incrementing a failure timer (132) with the diagnostic controller when the largest signal value is less than the minimum threshold value (128). [5] The method of claim 1, further comprising extracting a value of a detected angle from the detected sine signal and the detected cosine signal with the diagnostic controller (226). [6] The method of claim 5, further comprising calculating a sine function from the extracted value of the sensed angle with the diagnostic controller to define a sine of the extracted value (228) and calculating a cosine function of the extracted value of the sensed angle with the diagnostic controller to define a cosine of the extracted value (230). [7] The method of claim 6, further comprising scaling the sine of the extracted value to define a scaled sine of the extracted value (232), and scaling the cosine of the extracted value to define a scaled cosine of the extracted value (234). [8] The method of claim 7, further comprising calculating an absolute value of the scaled sine of the extracted value with the diagnostic controller (236) and calculating an absolute value of the scaled cosine of the extracted value of the diagnostic controller (238). [9] The method of claim 8, further comprising calculating a difference between the absolute value of the sine signal and the absolute value of the scaled sine of the extracted value to define a sine value difference with the diagnostic controller (240) and calculating a difference between the absolute value of the cosine signal and the absolute value of the scaled cosine of the extracted value to define a cosine value difference (242).

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