SYSTEMS AND METHODS TO MONITOR SEATS FOR DIAGNOSTICS, PROGNOSTICS AND DEGRADATION

A method is provided for detecting a fault in a gear system for repositioning a seat assembly in an automotive vehicle. The gear system includes a gear train operatively coupled to a motor. The method includes the steps of measuring a current drawn by the motor to reposition the seat assembly, recording the current over time as a current waveform, converting the current waveform into a frequency domain, determining a base frequency of the current waveform based on the converted current waveform, calculating a power spectrum density at the base frequency, calculating a total band power of the power spectrum density, and determining whether the total band power is greater than a predetermined total band power threshold.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seat assembly having a gear train. More particularly, the invention relates to methods of detecting faults within the gear train of the seat assembly.

2. Description of Related Art

Seat assemblies in automotive vehicles typically include systems to control the movement and positioning of the seat assemblies. Over time, performance of the systems degrades due to repetitive operation or aging effects, which may impede the smooth transition between the seat configurations, alter the positioning of the seat assembly, and/or diminish proper functioning of the seat assembly. In addition, expected and unexpected impacts can change various system components. There is a need for a system that can detect variations that occur over time so that the system may be repaired before the degradation becomes noticeable to the user and/or the system becomes non-operational.

SUMMARY OF THE INVENTION

According to one embodiment, there is provided a method for detecting a fault in a gear system for repositioning a seat assembly in an automotive vehicle. The gear system includes a gear train operatively coupled to a motor. The method comprises the steps of measuring a current drawn by the motor to reposition the seat assembly, recording the current over time as a current waveform, converting the current waveform into a frequency domain, determining a base frequency of the current waveform based on the converted current waveform, calculating a power spectrum density at the base frequency, calculating a total band power of the power spectrum density, and determining whether the total band power is greater than a predetermined total band power threshold.

According to another embodiment, there is provided a method for detecting a fault in a gear system for repositioning a seat assembly in an automotive vehicle. The gear system includes a gear train operatively coupled to a motor. The method comprises the steps of measuring a current drawn by the motor to reposition the seat assembly, recording the current over time as a current waveform, using a continuous wavelet transformation process to calculate a signature of the current waveform, and determining whether the signature is greater than a predetermined signature threshold.

According to another embodiment, there is provided a method for detecting a fault in a gear system for repositioning a seat assembly in an automotive vehicle. The gear system includes a gear train operatively coupled to a motor. The method comprises the steps of applying a voltage pulse to the motor, measuring a current drawn by the motor while the voltage pulse is applied to the motor, recording the current over time as a current waveform, determining a rise time in the current waveform for the current to reach a predetermined current amplitude, and determining whether the rise time is greater than a predetermined rise time threshold.

According to another embodiment, there is provided a method for detecting a fault in a gear system for repositioning a seat assembly in an automotive vehicle. The gear system includes a gear train operatively coupled to a motor having a drive shaft. The method comprises the steps of measuring a hall effect signal from the drive shaft indicating a rotational position and a rotational speed of the drive shaft over time, comparing the hall effect signal to an expected hall effect signal for the motor, and determining whether the hall effect signal is different from the expected hall effect signal.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention relates to systems and methods for detecting faults in the operation of seat assemblies10in automotive vehicles. Directional references employed or shown in the description, figures, or claims, such as top, bottom, upper, lower, upward, downward, lengthwise, widthwise, left, right, and the like, are relative terms employed for ease of description and are not intended to limit the scope of the invention in any respect. Referring to the Figures, like numerals indicate like or corresponding parts throughout the several views.

As depicted inFIG.1, the seat assembly10includes a seat back12, a seat cushion14, a seat base16, a pair of adjuster assemblies18, and a linkage assembly20. The seat back12is rotatably coupled to the seat cushion14. The linkage assembly20pivotably couples the seat cushion14to the seat base16. The seat base16is transposable fore and aft along the pair of adjuster assemblies18.

The seat assembly10also includes an electronic control unit (ECU)22and one or more gear systems24. Each gear system24includes a gear train26operatively coupled with one or more motors29. The ECU22controls the movement and positioning of the seat assembly10by controlling the motors29which drive the gear trains26. The ECU22not only controls the movement and positioning of the seat assembly10, but it also monitors these activities to ensure that they are working properly over time.

The exemplary gear train26shown inFIG.2includes a drive gear30, a plurality of driven gears31,32and a rack33. Each of the gears30,31,32and the rack33includes teeth30a,31a,32a,33athat meshingly engage with each other. The driven gears31,32are each coupled to a respective shaft34,35that is operatively coupled to other components of the seat assembly10, e.g., the linkage assembly20. The motor29includes a drive shaft36fixedly coupled to the drive gear30. The gear shafts34,35and the drive shaft36are rotationally supported by one or more bearings, thrust washers, and the like.

The gear train26is configured to generally lock in place when in non-operating conditions. Maintaining proper locking of the gears30-33avoids unexpected movement of the seat assembly10.

The seat assembly10includes a hall effect sensor38that is operatively connected to the drive shaft36. The hall effect sensor38outputs a hall effect signal42comprising a series of hall effect pulses44(seeFIG.8) indicative of the rotational position and the rotational speed of the drive shaft36. Because the rotational position of the drive shaft36is related to movement of the gear train26and the resulting movement of the seat assembly10, the ECU22can be configured to predict the resulting movement of the seat assembly10based in part on the hall effect signal42.

Over time, the components of the gear system24can degrade or become faulty. For example, the gear teeth30a,31a,32a,33a, bearings or shafts34,35,36may become worn or damaged or become misaligned. These defects can alter or impede the performance of the gear train26. For example, the gear system24may become inoperable or the gear train26may not lock properly. The defects also may increase the amount of noise or vibration in the seat assembly10or cause unexpected movements.

A gear system24that is operating as expected and is free of defects is generically described as a healthy gear system24. In contrast, a gear system24having defects is generically described as an unhealthy gear system24.

FIG.3shows the engagement of the gear teeth30a,31awhen the gears30,31are free of defects, whileFIG.4shows the engagement of the gear teeth30a,31awhen the gears30,31are worn or damaged. As shown inFIG.3, the gear teeth30a,31aare typically configured such that there is a predefined amount of backlash46between the teeth30a,31a. As shown inFIG.4, wear or damage to the gear teeth30a,31amay alter the spacing and increase the backlash46between the teeth30a,31a, which translates into loss motion between the gears30,31. Damaged gears30,31may slip under load or shift relative to each other so that the gears30,31may rotate relative to each other when in non-operating conditions. Movement of the gear train26during non-operating conditions is undesirable and is described as improper locking.

Each gear30,31has an operating pitch circle48,50. In a healthy gear train26, the operating pitch circles48,50are typically tangent to each other, as shown inFIG.3. Bearing wear and shaft34,35,36wear may cause the gears30,31to separate or shift relative to each other, forming a gap52between the operating pitch circles48,50of the gears30,31, as shown inFIG.4. In addition, damaged bearings can cause a “wobbly axis” where the drive shaft36or the gear shafts34,35wobble within the opening of the bearing around the longitudinal axis of the bearing.

The mechanical connections between the gears30,31,32and the respective mounting shafts36,34,35may loosen over time to cause a “loose axis” where a gear30-32will rotate relative to a mounting shaft36,34,35. A gear30-32that is loose on a mounting shaft36,34,35can result in improper locking in the gear train26and can result in damage to the gear teeth30a-33a. Further, the improper locking can cause unexpected movement of the seat assembly10during adverse conditions.

The ECU22is configured to monitor the current drawn by the motor29during operation of the gear train26. The ECU22also records the current over time, as reflected in the exemplary current waveform54shown inFIG.5. When the motor29initially receives power, the motor29begins to rotate the drive shaft36causing the drive gear30to rotate. The current drawn by the motor29rapidly increases as the motor29initiates rotation of the drive shaft36and all of the gears30-32and equipment tied to the gear train26, as reflected in portion A of the current waveform54inFIG.5. After the gear train26starts moving, less power is needed to drive the gear train26. Therefore, the current will begin to decrease after it reaches a peak,56, as reflected in portion B of the current waveform54. Portion C shows the current waveform54during steady state conditions. As shown, the steady state current forms ripples that reflect torsional vibrations in the gear system24. The gears30-32and motor29cause torsional vibrations in the gear system24that are related to a number of factors including the speed with which each gear30-32is rotating, the number of gear teeth30a-32ain each gear30-32, and the speed of rotation of the mounting shafts36,34,35. The torsional vibrations include vibrational components having base frequencies F29-F32, which reflect the operating frequencies of the motor29and the gears30-32during steady state conditions. The base frequency F29of the motor29is typically larger than the base frequencies F30-F32of the individual gears30-32of the gear train26. Thus, the ripples in the current waveform54include frequency components F29-F32of the motor29and gears30-32of the gear train26. Portion D ofFIG.5shows the current waveform54when the gear train26encounters an expected or unexpected impact.

FIG.6shows a graphical representation of an exemplary demanded torque58applied by the motor29during steady state conditions. The torque58forms torque ripples, which reflect the torsional vibrations in the gear system24. Similar to the ripples in the current waveform54, these torque ripples include frequency components F29-F32of the motor29and the gears30-32of the gear train26.

Defects in the gear system24are reflected in the current waveform54drawn by the motor29and the demanded torque58applied by the motor29during steady state conditions. For example,FIG.5illustrates some differences in the current waveform54when the gear system24is healthy versus the current waveform54′ when the gear system24is unhealthy. As shown, the maximum amplitude peak56of the current waveform54of the healthy gear system24is larger than the maximum amplitude peak56′ of the current waveform54′ of the unhealthy gear system24. In addition, the rise time dt1to reach a maximum amplitude peak56for the healthy gear system24is shorter than the rise time dt2to reach a maximum amplitude peak56′ for the unhealthy gear system24.

Further, during steady state conditions, as reflected in portion C ofFIG.5, the current waveform54′ driving the unhealthy gear system24is not as consistent as the current waveform54driving the healthy gear system24, and has a greater amplitude variation60than the amplitude variation62of the healthy current waveform54. It is to be appreciated that the actual current waveforms54,54′ drawn by the motor29during operation of the gear system24will vary based in part on the specific gear train26, the specific motor29, and factors such as specific defects present in the unhealthy gear system24.

Certain motors29are powered using a pulse width modulated (PWM) signal that can vary from 0% duty cycle (i.e., no signal is provided) to 100% duty cycle (i.e., full power is provided). The drive force provided to the motor29is related to the duty cycle of the PWM signal.FIG.7shows an exemplary transfer function64between the rotational speed of the drive shaft36in relation to the drive force provided to the motor29with a healthy gear system24. As depicted, the rotational speed of the drive shaft36increases as the PWM duty cycle increases, while the slope of the curve decreases with increasing PWM duty cycles. When the gear train26has one or more wobbly axes of shafts36,34,35, the resulting transfer function66is similar to the normal transfer function64, but includes oscillations. In contrast, when the gear train has one or more loose axes of shafts36,34,35, the transfer function68reflects a lower rotational speed of the drive shaft36with increasing drive force, and initially includes oscillations.

Referring toFIG.8, when the gear system24is healthy, exemplary hall effect pulses44have a consistent pulse period P (i.e., the amount of time between successive transitions from low voltage LV to high voltage HV). In contrast, the pulse period P in an unhealthy gear system24may fluctuate over time, as illustrated inFIG.10. Thus, variation in the pulse periods P under constant PWM power may be indicative of faults in gear system24, such as one or more loose or wobbly axes of shafts36,34,35, or unacceptable backlash46.

FIG.9illustrates exemplary hall effect pulses44when the drive shaft36stops rotating, such as when PWM power is terminated to the motor29or the seat assembly10impacts an expected or unexpected obstruction. When the power is terminated or the seat assembly10impacts an obstruction at time70, the hall effect pulses44will terminate shortly thereafter.

In contrast and as illustrated inFIG.11, with an unhealthy gear system24, the backlash46in the gear train26and/or defects such as one or more wobbly axes or loose axes of shafts36,34,35may cause additional oscillatory rotational movement of the drive shaft36in both forward and rearward rotational directions after the power is terminated or the seat assembly10impacts an obstruction, resulting in more hall effect pulses44appearing after time70compared to the number of hall effect pulses44appearing after time70with a healthy gear system24. A stop threshold76can be experimentally determined to identify unhealthy gear systems24when the amount of hall effect pulses44detected after impact70is greater than the stop threshold76.

Defects in the gear system24can be detected by analyzing the current waveform54using motor current signature analysis (MCSA) to isolate and evaluate changes in the frequency components F29-F32. A method for determining whether there are any faults in the gear system24according to a first embodiment of the present invention is shown inFIGS.5,6, and12through15. Referring toFIG.15, the ECU22initially provides power to the motor29(step88) and records the motor current waveform54,54′ (step90). The ECU22then filters noise from the steady state portion C of the current waveform54,54′ (step92), and converts the filtered current waveform54,54′ into the frequency domain94(step96).FIG.12shows a graphical representation of the current waveform54,54′ converted in the frequency domain94. The base frequencies F29-F32shown inFIG.12correspond to the base frequencies F29-F32in the torsional vibrations caused by the motor29and the gears30-32, respectively. Because the frequency components F29-F32are also included in the torque ripples, the ECU22alternatively may convert the demanded torque58into the frequency domain94rather than converting the current waveform54,54′ into the frequency domain94at step96.

The ECU22then calculates the power spectrum density98at the base frequencies F29-F32and at the harmonics of the base frequencies F29-F32(FIG.15, step100). Referring toFIG.13, the power spectrum density98is concentrated near the base frequencies F29-F32when the gear system24is healthy. In contrast, when the gear system24is unhealthy, the power spectrum density98′ will accumulate around the base frequencies F29-F32and around harmonics of the base frequencies F29-F32, as shown inFIG.14.

Referring back toFIG.15, the ECU22then calculates the total band power at the base frequencies F29-F32and the harmonics of the base frequencies F29-F32(step102), and compares the calculated total band power to a predetermined total band power threshold (step104). If the calculated total band power is less than or equal to the total band power threshold, then the gear system24is considered healthy and the ECU22continues operating the gear system24(step106). If the calculated total band power is greater than the total band power threshold, then the gear system24is considered unhealthy and the ECU22stores a corresponding fault code in memory (step108), and notifies the occupant that a fault has been detected (step110). The ECU22then continues operation of the gear system24(step106).

A method for determining whether there are any faults in the gear system24according to a second embodiment of the present invention is shown inFIG.16. In the second method, the ECU22initially provides power to the motor29(step114) and records the motor current waveform54,54′ (step116). The ECU22then filters noise from the current waveform54,54′ (step118) and transforms the filtered current waveform54,54′ using continuous wavelet transformation to produce a calculated signature (step120). Continuous wavelet transformation uses a small specifically designed wave (which is also stretchable) to convolute with the current waveform54,54′ being analyzed to extract hidden abnormal signatures embedded in transient and local data.

The ECU22compares the calculated signature with a predetermined signature threshold (step122). The signature threshold is determined by comparing the signatures of the healthy and unhealthy gear systems24. If the calculated signature is less than the signature threshold, then the gear system24is considered healthy and the ECU22continues operating the gear system24(step124). If the calculated signature is greater than the signature threshold, then the gear system24is considered unhealthy and the ECU22stores a corresponding fault code in memory (step126), and notifies the occupant that a fault has been detected (step128). The ECU22then continues operation of the gear system24(step124).

A method for determining whether there are any faults in the gear system24according to a third embodiment of the present invention is shown inFIGS.17through19. Referring toFIG.17, the ECU22initially provides a voltage pulse VP to the motor29(step132) while the gear train26is in a locked condition. The voltage pulse VP has a voltage amplitude VI and a time period TI that is insufficient to cause unexpected movement of the seat assembly10. In one embodiment, a controlled voltage pulse VP having a voltage amplitude VI of about 7 volts is provided by the ECU22across the terminals of the motor29for a time period TI of approximately 0.5 seconds, as shown inFIG.18.

Referring back toFIG.17, the ECU22records the resulting motor current waveform134,134′ (step136) and filters noise from the current waveform134,134′ (step138).FIG.19shows an exemplary current waveform134when the gear train26is properly locked, and an exemplary current waveform134′ when the gear train26is improperly locked. Referring toFIGS.17and19, the ECU22measures the rise time dt3, dt4between initialization of the controlled voltage pulse VP and the time that the current waveform134,134′ reaches a predetermined amplitude140(step142). The ECU22compares the measured rise time dt3, dt4to a rise time threshold RT (step144). The predetermined current amplitude140and the rise time threshold RT are selected based on experimental data comparing a healthy gear system24with an unhealthy gear system24. Alternatively, the current amplitude140and the rise time threshold RT can be determined based in part on a prior evaluation of the gear system24by the ECU22.

Referring toFIG.17, if the measured rise time dt3, dt4is less than or equal to the rise time threshold RT, then the gear system24is considered healthy and the ECU22continues operating the gear system24(step146). If the measured rise time dt3, dt4is greater than the rise time threshold RT, then the locking of the gear train26is not proper and the ECU22stores a corresponding fault code in memory (step148), and notifies the occupant that a fault has been detected (step150). The ECU22then continues operation of the gear system24(step146).

A method for determining whether there are any faults in the gear system24according to a fourth embodiment of the present invention is shown inFIGS.20A-B. In the fourth method, the ECU22initially provides power to the motor29(step152) and records the hall effect pulses44received from the hall effect sensor38in response to rotation of the drive shaft36(step154). Next, the ECU22evaluates the hall effect pulses44(step156). If the hall effect pulses44are irregular, then the gear system24is considered unhealthy, and the ECU22stores a corresponding fault code in memory (step158) and notifies the occupant that a fault has been detected (step160). After notifying the occupant about the fault, the ECU22continues to operate the gear system24(step162). The ECU22also continues to operate the gear system24if at step156it did not detect irregular hall effect pulses44.

While the ECU22operates the gear system24(step162), it monitors for impacts (step164) and waits until power to the motor29is terminated (step166). If the ECU22detects an impact, then the ECU22counts the hall effect pulses44received after the impact was detected (step168) and determines whether the counted hall effect pulses44exceeds a predetermined impact threshold (step170). If the counted hall effect pulses44is greater than the impact threshold, then the gear system24is considered unhealthy and the ECU22stores a corresponding fault code in memory (step172), and notifies the occupant that a fault has been detected (step174). If the counted hall effect pulses44is less than or equal to the impact threshold, then no further action is required by the ECU22(step176).

If the ECU22terminates power to the motor29(step166), then the ECU22counts the hall effect pulses44received after power was terminated to the motor29(step178), and determines whether the counted hall effect pulses44exceeds the predetermined stop threshold (step180). If the counted hall effect pulses44is greater than the stop threshold, then the gear system24is considered unhealthy and the ECU22stores a corresponding fault code in memory (step182), and notifies the occupant that a fault has been detected (step184). If the counted hall effect pulses44is less than or equal to the stop threshold, then no further action is required by the ECU22(step176).

Each of the methods for evaluating the condition of the gear system24disclosed above may be repeated at any desired interval without varying the scope of the invention. For example, an exemplary method for notifying occupants of the seat assemblies10when to bring the automotive vehicle into service is shown inFIGS.21A-B. Initially, all counters, including a counter for tracking the number of ignition cycles run between system maintenance and the counters used to track various defects in the seat assembly10, are reset to zero (step188). The ECU22waits for the start of a new ignition cycle (step190) before it increments the ignition cycle counter (step192). The ECU22then determines whether the ignition cycle counter exceeds a threshold (step194). If the ignition cycle counter exceeds the threshold, then the ECU22alerts the occupant that it is time to bring the automotive vehicle in for system maintenance (step196).

The ECU22then checks the gear system24for any faults (step198). For example, the ECU22may run one or more of the methods disclosed above. The ECU22determines if any faults were detected (step200). If any faults were detected, the ECU22identifies the fault type (step202) and increments the counter for that fault type (step204). The ECU22then checks if the counter for the fault type exceeds a threshold (step206). If the counter for the fault type exceeds the threshold, then the ECU22notifies the occupant that the fault was detected (step208) so that the occupant may bring the automotive vehicle in for service. The ECU22then waits for the next ignition cycle before running the process again.