Usage and failure monitoring of steering systems

Abstract

Steering system (40), comprising: an engine (46); a controller (16); and a monitoring system (200) comprising at least one memory device and a processor (205), the monitoring system being coupled to the controller (16), the monitoring system (200) being configured to determine in real time a useful life of the steering system (40), the determination of the useful life comprising: Tracking an attribute signal; based on the determination that the attribute signal (902) rises above an upper threshold (401, 601, 701, 801) and then falls below a lower threshold (402, 602, 702, 802): Selecting a subset of categories based on a frequency content of the attribute signal; Selecting a category from the subset of categories based on a peak load (415) occurring sequentially on the attribute signal via a secondary attribute signal; and Incrementing a counter for the selected category; and Calculate the useful life based on a ratio of the counter for the selected category and a predetermined count for that selected category.

Description

[0001] The invention relates to a steering system, a method for determining the service life of such a steering system in real time and a computer program product with a storage device in which computer-executable instructions are stored. background

[0002] An electric power steering (EPS) system typically includes components such as a steering wheel, a column, a rack-and-pinion gear box, an electric motor actuator, and more. The EPS assists the driver in steering a vehicle by providing the required assist torque. The assist torque is based on the torque applied by the operator. In steady-state conditions, the operator torque and the assist torque counteract the rack force generated by the tire-road interaction.

[0003] A typical steer-by-wire (SbW) system comprises a road wheel actuator (RWA) unit and a handwheel (or steering wheel) actuator (HWA) unit. Unlike EPS, the two units in SbW are mechanically separated and communicate via a CAN (Controlled Area Network) interface (or other similar digital communication protocols). The HWA unit receives a rack force signal from the RWA unit to generate a corresponding torque feel for the operator. Alternatively, the handwheel angle and vehicle speed can also be used to generate the desired torque feel for the operator. The angle from the HWA unit is sent to the RWA unit, which performs position control to control the rack movement.

[0004] DE 10 2004 017 660 A1 discloses a method and a device for stress analysis in electrical and / or electromechanical systems, wherein at least one system-specific load variable is detected, at least one characteristic parameter is determined using the system-specific load variable, a load level of at least one component of an electrical and / or electromechanical system is determined using the parameter, and the parameter is determined taking into account a load duration. DE 11 2016 000 953 T5 discloses a power steering device having a control unit equipped with an abnormality detection circuit.The abnormality detection circuit is configured to judge the occurrence of an abnormality in the power steering apparatus when a peak level of a frequency component of a steering torque that periodically changes in a frequency range becomes higher than a predetermined value. Summary

[0005] It is an object underlying the invention to provide an improved steering system for monitoring a service life of the steering system, a method for determining the service life of such a steering system and a corresponding computer program product.

[0006] The object is achieved according to the invention by a steering system having the features of claim 1, a method having the features of claim 9 and by a computer program product having the features of claim 15. Advantageous further developments emerge from the subclaims.

[0007] According to one or more embodiments, a steering system includes a motor, a controller, and a monitoring system, further comprising at least one memory unit and a processor. The monitoring system is coupled to the controller and determines, in real time, a useful life of the steering system. The determination of the useful life is performed using a method that includes tracking an attribute signal. The method further includes, based on determining that the attribute signal rises above an upper threshold and subsequently falls below a lower threshold, selecting a subset of categories based on a frequency content of the attribute signal. The method further includes selecting a category from the subset of categories based on a peak load sequentially occurring on the attribute signal via a secondary attribute signal.The method further includes incrementing a counter for the selected category. The method further includes calculating the usage time based on a ratio of the counter for the selected category and a predetermined count for that selected category.

[0008] According to one or more embodiments, a method for determining the useful life of a steering system in real time comprises tracking an attribute signal associated with the steering system. The method further comprises, based on determining that the attribute signal rises above an upper threshold and subsequently falls below a lower threshold, selecting a subset of categories based on a frequency content of the attribute signal. The method further comprises selecting a category from the subset of categories based on a peak load sequentially occurring on the attribute signal via a secondary attribute signal. The method further comprises incrementing a counter for the selected category. The method further comprises calculating the useful life based on a ratio of the counter for the selected category and a predetermined count for that selected category.

[0009] According to one or more embodiments, a computer program product includes a storage device having computer-executable instructions stored therein, wherein the computer-executable instructions, when executed by a processing unit, cause the processing unit to determine, in real time, a useful life of a steering system. Determining the useful life of the steering system comprises performing a method including tracking an attribute signal associated with the steering system. The method further comprises, based on determining that the attribute signal rises above an upper threshold and subsequently falls below a lower threshold, selecting a subset of categories based on a frequency content of the attribute signal.The method further comprises selecting a category from the subset of categories based on a peak load occurring sequentially at the attribute signal via a secondary attribute signal. The method further comprises incrementing a counter for the selected category. The method further comprises calculating the usage time based on a ratio of the counter for the selected category and a predetermined count for that selected category.

[0010] These and other advantages and features will become clearer from the following description taken in conjunction with the drawings. Brief description of the drawings

[0011] The specifics of the exclusive rights described herein are particularly pointed out and distinctly claimed in the claims at the end of the application. The foregoing and other features and advantages of embodiments of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 illustrates an EPS system according to one or more embodiments; Fig. 2 is an exemplary embodiment of a steer-by-wire steering system according to one or more embodiments; Fig. 3 shows an example system for monitoring the usage and failure of steering systems according to one or more embodiments; Fig. 4 shows an example of position-based cycle counting with torque monitoring according to one or more embodiments; Fig. 5 is a flowchart illustrating an example method for using position-based cycle counting to categorize usage according to one or more embodiments; Fig. 6 shows a count increment for a temperature gradient cycle according to one or more embodiments; Fig. 7 shows a categorization of vehicle usage according to distance versus speed monitoring according to one or more embodiments; Fig. 8 shows an exemplary categorization of the vehicle environment by the monitoring system according to one or more embodiments; and Fig. 9 shows a flowchart of an example method for real-time calculation of a useful life for the steering system according to one or more embodiments.

[0012] The diagrams shown here are for illustrative purposes only. Many variations of the diagram or the processes described therein may exist without departing from the scope of the invention. For example, the steps may be performed in a different order, or steps may be added, omitted, or modified. Also, the term "coupled" and variations thereof describe a communication path between two elements and do not imply a direct connection between the elements without intervening elements / connections between them. All such variations are considered part of the application. Detailed description

[0013] The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

[0014] As used herein, the terms module and submodule refer to one or more processing circuits, such as an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory executing one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality. It should be noted that the submodules described below may be combined and / or further subdivided.

[0015] The present application relates generally to steering systems and, more particularly, describes one or more techniques for tracking usage with sensor inputs and understanding the magnitude relative to design intent.

[0016] The steering system assists the driver in steering a vehicle by providing the necessary torque assistance. Today, a modern steering system typically includes components such as a steering wheel, column, rack and pinion, electric motor actuator, etc. The assist torque is based on the torque applied by the operator. In steady-state conditions, the operator torque and the assist torque counteract the rack force generated by the tire-road interaction.

[0017] With reference to the figures in which the technical solutions are described with reference to specific embodiments, without limiting them, Fig. 1 illustrates an exemplary embodiment of an electric power steering (EPS) system 40 suitable for implementing the disclosed embodiments. The steering mechanism 36 is a rack-and-pinion type system and includes a toothed rack (not shown) in the housing 50 and a pinion gear (also not shown) located beneath the gear housing 52. It should be noted that, although a rack-and-pinion type system is illustrated herein as an example, the technical solutions described herein are applicable to any type of EPS, such as rack-based, column-based, pinion-based, etc. When the operator input, hereinafter referred to as the steering wheel 26 (e.g., handwheel, and the like), is rotated, the upper steering shaft 29 and the lower steering shaft 51, which is connected to the upper steering shaft 29 via a universal joint 34, rotate the pinion gear.Rotation of the pinion moves the rack, which moves tie rods 38 (only one shown), which in turn moves steering knuckles 39 (only one shown), which rotate one or more steerable wheels or tires 44 (only one shown).

[0018] The electric power steering assistance is provided by the control device, generally designated by reference numeral 24, which includes the controller 16 and an electric machine 46, which may be a permanent magnet synchronous motor (PMSM) or a permanent magnet direct current (PMDC) motor, or any other type of motor, and is referred to hereinafter as motor 46. The controller 16 is powered by the vehicle power supply 10 through line 12. The controller 16 receives a vehicle speed signal 14 representative of the vehicle speed from a vehicle speed sensor 17. The steering angle is measured by the position sensor 32, which may be an optical encoder type sensor, a variable resistance type sensor, or any other suitable type of position sensor, and provides a position signal 20 to the controller 16.The motor speed can be measured with a tachometer or other device and transmitted to the controller 16 as a motor speed signal 21. A motor speed, known as ω. m can be measured, calculated, or a combination of these. For example, the motor speed ω m as the change in the motor position θ, as measured by a position sensor 32, over a prescribed time interval. For example, the motor speed ω m as a derivative of the motor position θ from the equation ω m = Δθ / Δt, where Δt is the sampling time and Δθ is the position change during the sampling interval. Alternatively, the motor speed can be derived from the motor position as the rate of position change over time. It should be noted that there are numerous known methods for performing the function of a derivative.

[0019] When the handwheel 26 is turned, the torque sensor 28 detects the torque applied to the handwheel 26 by the vehicle operator. The torque sensor 28 may include a torsion bar (not shown) and a variable resistance type sensor (also not shown) that outputs a variable torque signal 18 to the controller 16 in proportion to the degree of twisting of the torsion bar. Although this is one type of torque sensor, any other suitable torque measuring device used with known signal processing techniques will suffice. In response to the various inputs, the controller sends a command 22 to the electric motor 46, which, via worm 47 and worm gear 48, provides torque assist to the steering system, thereby providing torque assist for the vehicle's steering.

[0020] It should be noted that although the disclosed embodiments are described by reference to motor control for electric steering applications, it should be understood that these references are illustrative only and the disclosed embodiments may be applied to any motor control application using an electric motor, e.g., steering, valve control, and the like. Furthermore, the references and descriptions contained herein may apply to many forms of parameter sensors, including, but not limited to, torque, position, speed, and the like. It should be noted that reference is made herein to electric machines, including, but not limited to, motors, but for brevity and simplicity, reference will be made hereinafter only to motors without limitation.

[0021] In the illustrated control system 24, the controller 16 uses the torque, position, speed, and the like to calculate one or more commands to provide the required output. The controller 16 is arranged in communication with the various systems and sensors of the motor control system. The controller 16 receives signals from each of the system sensors, quantifies the received information, and in response, issues one or more output command signals, in this case, for example, to the motor 46. The controller 16 is configured to develop the appropriate voltage(s) from the inverter (not shown), which may optionally be incorporated into the controller 16 and is referred to herein as the controller 16, so that when applied to the motor 46, the desired torque or position is produced.In one or more examples, controller 16 operates in a feedback control mode as a current controller to generate command 22. Alternatively, in one or more examples, controller 16 operates in a feedforward control mode to generate command 22. Since these voltages are related to the position and speed of motor 46 and the desired torque, the position and / or speed of the rotor and the torque applied by an operator are determined. A position encoder is connected to steering shaft 51 to sense the angular position θ. The encoder may sense the rotational position based on optical sensing, magnetic field changes, or other methods. Typical position sensors include potentiometers, coordinate transducers, resolvers, encoders, and the like, as well as combinations including at least one of the foregoing components.The position encoder outputs a position signal 20 which indicates the angular position of the steering shaft 51 and thus that of the motor 46.

[0022] The desired torque may be determined by one or more torque sensors 28 transmitting torque signals 18 indicative of applied torque. One or more exemplary embodiments include such a torque sensor 28 and the torque signal(s) 18 therefrom responsive to a compliant torsion bar, T-bar, spring, or similar device (not shown) configured to provide a response indicative of the applied torque.

[0023] In one or more examples, a temperature sensor(s) 23 is / are disposed on the electric machine 46. Preferably, the temperature sensor 23 is configured to directly measure the temperature of the sensing portion of the motor 46. The temperature sensor 23 sends a temperature signal 25 to the controller 16 to facilitate the processing and compensation prescribed herein. Typical temperature sensors include thermocouples, thermistors, thermostats, and the like, as well as combinations of at least one of the foregoing sensors, which, when suitably arranged, provide a calibratable signal proportional to the respective temperature.

[0024] The position signal 20, the speed signal 21, and one or more torque signals 18 are applied to the controller 16, among others. The controller 16 processes all input signals to generate values corresponding to each of the signals, resulting in a rotor position value, a motor speed value, and a torque value that are available for processing in the algorithms described here. Measurement signals, such as those mentioned above, are also typically linearized, compensated, and filtered as desired to improve the properties or eliminate undesirable characteristics of the acquired signal. For example, the signals may be linearized to improve processing speed or to address a wide dynamic range of the signal. In addition, frequency- or time-based compensation and filtering may be used to eliminate noise or avoid undesirable spectral characteristics.

[0025] To perform the prescribed functions and the desired processing and corresponding calculations (e.g., identification of engine parameters, control algorithm(s), and the like), the controller 16 may include, among other things, one or more processors, computers, DSPs, memories, storage, registers, timing / clocking, interrupts, communication interface(s), and input / output signal interfaces, and the like, as well as combinations of at least one of the foregoing. For example, the controller 16 may include processing and filtering of input signals to enable accurate sampling and conversion or capture of such signals from communication interfaces. Additional features of the controller 16 and specific processes therein are discussed in detail later in this document.

[0026] Another type of steering system, in particular a steer-by-wire (SbW) system 40 in a vehicle 100 is shown in Fig. 2. It should be noted that the SbW system 40 shown and described can be deployed in an autonomous or semi-autonomous vehicle or in a more conventional vehicle. The SbW system 40 includes a handwheel actuator (HWA) 110 and a roadwheel actuator (RWA) 120.

[0027] The HWA 110 includes one or more mechanical components 112, such as a handwheel (steering wheel), a steering column, and a motor / inverter attached to the steering column via either a gear mechanism or a direct drive system. The HWA 110 further includes a microcontroller 114 that controls the operation of the mechanical components 112. The microcontroller 114 receives and / or generates torque via the one or more mechanical components 112.

[0028] The RWA includes one or more mechanical components 124, such as a steering rack and / or pinion, coupled to a motor / inverter via a ball nut / ball screw (gearbox). The rack is connected to the vehicle's road wheels / tires via tie rods. The RWA 120 includes a microcontroller 124 that controls the operation of the mechanical components 124. The microcontroller 122 receives and / or generates torque across the one or more mechanical components 124.

[0029] Microcontrollers 112 and 122 are coupled via electrical connections that enable the transmission / reception of signals. As mentioned herein, a controller may include a combination of HWA controller 112 and RWA controller 122, or one of the specific microcontrollers. Microcontrollers 112 and 122 may be the same as controller 16 described herein.

[0030] In one or more examples, controllers 112 and 122 and SbW system 40 communicate with each other via a CAN interface (or other similar digital communication protocols). Steering of the vehicle 100 equipped with SbW system 40 is accomplished via the steering gear with an input shaft rotated by the RWA 120, e.g., by a servo actuator. The RWA 120 receives an electronic communication signal via the operator's rotation of the steering wheel. An operator controls the steering wheel to steer the vehicle 100 in a direction-dependent manner. The angle from the HWA 110 is sent to the RWA 120, which performs position control to control the rack movement to guide the road wheel. However, due to the lack of a mechanical connection between the steering wheel and the road wheels, the operator does not receive a feel for the road without torque feedback (unlike an EPS, as described above).

[0031] In one or more examples, the HWA 110, coupled to the steering column and steering wheel, simulates the driver's on-road feel. The HWA 110 can apply tactile feedback in the form of torque to the steering wheel. The HWA unit receives a rack force signal from the RWA 120 to generate a corresponding torque feel for the operator. Alternatively, the handwheel angle and vehicle speed can also be used to generate the desired torque feel for the operator.

[0032] It should be noted that a steering system 40 may hereinafter refer to an EPS system or an SbW system as described herein, and that the technical solutions described herein are applicable to both types of steering systems.

[0033] With the increased use of electrical components and communication instead of mechanical connections in the steering system, the driver's input (either in direct mechanical connection (SbW) or control (ADA)) to the wheel is removed / replaced by an electrical communication connection. While such technology enables (but is not limited to): package freedom, new safety mechanisms, and flexibility, it also eliminates some of the driver perception that was previously transmitted to the driver through the mechanical connection.

[0034] Consider a mechanically based steering system that slowly degrades over time. As components wear beyond their validation lifespan, the manufacturer relies on the human driver's perception as a detection mechanism to prevent catastrophic failure modes that may occur after the perceptual warning. The development of play between threaded interfaces or wear of moving parts, creating increased friction levels, will eventually result in noise or a heavy feel detected by the operator and, in turn, prompting a service call. Consider the impeller actuator of an SbW System 40 or ADA system, where these failures are either rejected as a disturbance by the position control mechanism, masked by other under-the-hood running noise, or isolated by compliant mounting bushings.Accordingly, monitoring the various components of a steering system for their respective use and failure poses a technical challenge. It should be noted that such a technical challenge can also exist with mechanically based steering systems, even when the operator is unaware of component wear.

[0035] The technical solutions described here address such technical challenges by using a structure of cycle counters and event monitors to track the usage and operating environment of the steering system over time. The correlation between these counted cycles and those of a predefined validation plan is used to generate an active warning to the driver that an operating environment beyond the validation plan is about to occur (increased probability of failure). The event monitoring component can also be used to query returned material for failure modes that may be a function of a specific use case (e.g., sharp right turns) or environment (e.g., extremely cold weather). Event monitoring data can also be used to authenticate whether the counted cycles are valid based on vehicle usage.

[0036] Fig. 3 shows an example system for monitoring steering system usage and failure according to one or more embodiments. System 200 may be an electronic circuit including, among other things, a processor and memory, wherein the electronic circuit communicates with one or more processors and components of steering system 40. In one or more examples, system 200 may be a portable computing device capable of wireless or wired communication with the steering system.

[0037] The system 200 includes, among other things, a processor 205, a memory 210 coupled to a memory controller 215, and one or more input devices 245 and / or output devices 240, such as peripheral or control devices, communicatively coupled via a local I / O controller 235. These devices 240 and 245 may include, for example, battery sensors, position sensors (altimeter 40, accelerometer 42, GPS 44), indicator / identification lights, and the like. Input devices such as a conventional keyboard 250 and mouse 255 may be coupled to the I / O controller 235. The I / O controller 235 may, for example, be one or more buses or other wired or wireless connections as known in the art. The I / O controller 235 may include additional elements that have been omitted for simplicity, such as:Controllers, buffers (caches), drivers, repeaters and receivers to enable communications.

[0038] The I / O devices 240, 245 may further include devices that communicate both inputs and outputs, e.g., disk and tape storage, a network interface card (NIC) or modulator / demodulator (for accessing other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephony interface, a bridge, a router, and the like.

[0039] Processor 205 is a hardware device for executing hardware instructions or software, particularly those stored in memory 210. Processor 205 may be a custom-built or off-the-shelf processor, a central processing unit (CPU), an auxiliary processor comprising multiple processors associated with the system, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, or other instruction-executing device. Processor 205 includes a cache 270, which may include, among other things, an instruction cache for accelerating the retrieval of executable instructions, a data cache for accelerating the retrieval and storage of data, and a translation lookaside buffer (TLB) for accelerating the translation of virtual to physical addresses for both executable instructions and data. Cache 270 may be implemented as a hierarchy of further cache levels (L1, L2, etc.).) be organized).

[0040] Memory 210 may include one or more combinations of volatile memory elements (e.g., random access memory, RAM, such as DRAM, SRAM, SDRAM) and non-volatile memory elements (e.g., ROM, erasable programmable read-only memory (EPROM), electronically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), tape, compact disc read-only memory (CD-ROM), disk, floppy disk, cartridge, cassette, or the like). In addition, memory 210 may include electronic, magnetic, optical, or other types of storage media. It should be noted that memory 210 may have a distributed architecture in which various components are located remotely from one another but are accessible by processor 205.

[0041] The instructions in memory 210 may include one or more separate programs, each containing an ordered list of executable instructions for implementing logical functions. In the example of Fig. 2, the instructions in memory 210 include a suitable operating system (OS) 211. The operating system 211 can essentially control the execution of other computer programs and provides scheduling, input / output control, file and data management, memory management, and communication control and related services.

[0042] Additional data, including, for example, instructions for processor 205 or other retrievable information, may be stored in memory 220, which may be a storage device such as a hard disk or solid-state drive. The stored instructions in memory 210 or memory 220 may include instructions that enable the processor to perform one or more aspects of the systems and methods described herein.

[0043] System 200 may further include a display controller 225 coupled to a user interface or display 230. In some embodiments, display 230 may be an LCD screen. In other embodiments, display 230 may include a plurality of LED status lights. In some embodiments, system 200 may further include a network interface 260 for coupling to a network 265. Network 265 may be an IP-based network for communication between system 200 and an external server, client, and the like via a broadband connection. In one embodiment, network 265 may be a satellite network. Network 265 transmits and receives data between system 200 and external systems.In one embodiment, the external system may be another aerial drone or a drone docking system, where sending and receiving data allows system 200 to identify the other drone or docking system and determine when to transfer the payload to the other drone. In some embodiments, network 265 may be a managed IP network managed by a service provider. For example, network 265 may be implemented wirelessly using wireless protocols and technologies such as WiFi, WiMax, satellite, or others. Network 265 may also be a packet-switched network such as a local area network, a wide area network, a metropolitan area network, the Internet, or a similar type of network environment.The network 265 may be a fixed wireless network, a wireless local area network (LAN), a wireless wide area network (WAN), a personal area network (PAN), a controller area network (CAN), a virtual private network (VPN), an intranet, or other suitable network system, and may include equipment for receiving and transmitting signals.

[0044] The monitoring system 200 tracks the usage and useful life of the steering system 40 through position-related cycle counting within the steering system 40 by monitoring one or more parameters. As previously mentioned, the steering system 40 may be an EPS system or one or more actuators in the case of an ADAS EPS or SbW system 40. In one or more examples, the monitoring system 200 may monitor and track position cycles to account for varying levels of wear and tear. The monitoring system may distinguish between high- and low-frequency content in the position cycles. Furthermore, the monitoring system 200 may distinguish between high- and low-load situations based on engine torque and track the position cycles in association with the respective load.

[0045] In addition, the monitoring system 200 tracks motor torque (or handwheel torque) cycles to account for high-stress usage. The monitoring system 200 also tracks temperature gradient cycle counts to identify transient thermal events in the steering system 40. The monitored cycles can be differentiated between high (shock) and low gradient.

[0046] The monitoring system 200 also calculates an estimate of current usage based on a development validation cycle. The development validation cycle is a predetermined model for the use of one or more components of the steering system 40. The estimate is further based on the mechanical position and loading of the steering system 40. The monitoring system 200 also determines the temperature of the controller 16 and / or the motor 46 based on a temperature sensor. In one or more examples, the controller 16 may include a thermistor (not shown) for sensing the temperature.

[0047] Alternatively or additionally, the monitoring system 200 tracks usage and useful life of the steering system 40 using a distance-based cycle count calculated locally within the steering system 40, e.g., based on time and vehicle speed. The distance and speed monitoring is further used to categorize vehicle usage types such as city, residential, highway, and the like. Start-up / ignition temperature monitoring is also used to determine the vehicle's native environment, such as polar, temperate, tropical, and the like. In one or more examples, this information is used to validate the accuracy of the cycle count. For example, if the part has met the validation useful life but only registers as a standard temperature or moderate temperature operating classification, a conflict may occur.

[0048] During position-based tracking, the monitoring system 200 records, in one or more examples, the number of times the motor position in the steering system 40 exceeds an upper threshold (deg_upper) and falls below a lower threshold (deg_lower) relative to a trimmed center position (in both positive and negative polarity). In one or more examples, each index of the counter is considered half a count of a complete cycle when either threshold is exceeded.

[0049] Fig. Figure 4 shows an example of position-based cycle counting according to one or more embodiments. Motor position 405 is shown changing in a sine wave; however, it is understood that motor position 405 may vary in any other regular / irregular pattern. Each time motor position 405 exceeds upper threshold 401 or falls below lower threshold 402, an index of a counter is incremented. The increment may be a 1 / 2 count in one or more examples, as described above. Any other increment value is possible, e.g., 1, 2, and the like.

[0050] Position-based counting is divided into several usage types based on the frequency content (using a simple low-pass filter) and the peak load measured between the upper and lower position cycle thresholds (401, 402). Peak load is defined as the total system torque, corresponding to the motor and handwheel torque.

[0051] A structure of the peak load measurement strategy is shown below in Fig. 4. The peak load 415 is measured during the period 410, ie after the motor position 405 has exceeded the upper threshold 401 and the lower threshold 402 has not yet been undercut.

[0052] Fig. 5 shows a flowchart of an example method for using position-based cycle counting to categorize usage according to one or more embodiments. Here, the categorization is performed into four independent usage types. However, it should be understood that a different number and different usage types may be used for categorization in other examples. The method includes position tracking (505), which includes incrementing the position counter index each time the thresholds (401, 402) are exceeded by the change in motor position 405. It should be noted that, although Fig. 4 only represents the threshold crossing in the positive polarity, the position counter index is similarly incremented when the motor position 405 exceeds the thresholds in the negative cycle of the motor position 405.

[0053] The frequency of the motor position change is calculated based on the rate of change of the position counter index (510). The frequency content is also compared to predefined frequency thresholds (510). If the position counter index changes at least at the rate corresponding to the predefined frequency threshold, the frequency content can be designated as "high frequency"; otherwise, it can be designated as "low frequency." For example, two filter thresholds (510) are defined, and based on the frequency content of the position sensor, the classification is either high (high frequency) or low (low frequency).

[0054] In both cases, low frequency or high frequency, the peak load 415 on the steering system 40 during the duration 410 is also evaluated (515). If the peak load 415 is above a load threshold, the peak load 415 may be referred to as "high load" and otherwise as "low load." The peak load in this case may be the maximum value of the motor torque during the position count ( Fig. 4). Accordingly, in this case, based on the frequency content and peak load, the position tracking can be categorized into 4 categories (520), each represented by one of the categories low frequency - low load, low frequency - high load, high frequency - low load, and high frequency - high load.

[0055] Position-based cycle counting can be used to describe the various wear and fatigue-based tests used in validation test plans for mechanical system validation. During developmental testing (DV), threshold calibration values are established, and the actual cycle counts from the DV tests are recorded. The counts from each category (520) are used to normalize the current operating state of the steering system 40 (in counts) against the service life counts (from the completion of DV). This facilitates real-time service life estimation. Intermediate counts of each type are also available as output. DV cycles are typically correlated to a vehicle's service life in miles, providing more detail about the system in question.An example formula used for real-time estimation of useful life (vs. DV) is shown below in Equation 1, where N is the number of categories (N=4 in the example above). %Use time=∑1NType i countsType i counts per DVN×100

[0056] Alternatively, or in addition, torque-based cycle counting can be used in a similar way instead of position-based cycle counting. In this case, the total system torque from motor and handwheel torque is used as input instead of a position. In other words, the same operations described in the flowchart of Fig. 5 can be followed, but instead of incrementing the counter index based on a comparison of the motor position to the upper and lower thresholds (401, 402), a comparison of the handwheel torque to the thresholds is used. The system's peak load 415 is then measured and used in the same manner as described above. This output is used to evaluate high-output utilization systems versus low-output utilization systems. The utilization time calculation of Equation 1 can still be used. The DV counts are also based on the torque input at the handwheel.

[0057] According to one or more embodiments, a temperature gradient-based cycle count is used to determine the useful life of the steering system 40. The temperature gradient-based cycle count uses a local measurement of the ignition temperature when the vehicle 100 is started (turned on). Temperature sensors 23 are arranged to measure the ignition temperature and provide such a measurement to the monitoring system 200.

[0058] Temperature gradient-based cycle tracking uses a temperature rate of change [degC / s] rather than an absolute value (as was the case with position- and torque-based tracking). A high temperature rate of change (above a temperature rate threshold) may strain one or more components of the steering system 40, such as a circuit board, an electronic circuit, or another such component. The strain may be negative, particularly if there is a design oversight in the thermal expansion coefficient of materials.

[0059] Temperature gradient-based cycles are divided into two types based on the rate of change of temperature; each method uses a rate calibration as described above and two threshold calibrations [degC_upper, degC_lower] to define a count.

[0060] Fig. 6 shows a count increment for a temperature gradient cycle according to one or more embodiments. The ignition temperature measurement 605 is compared to an upper temperature threshold 601 and a lower temperature threshold 602. A slope of the curve is calculated during a duration 610, where the duration 610 represents the state when the ignition temperature 605 exceeds the upper threshold 601 and decreases again to reach the lower threshold 602. Depending on the slope of the curve, which corresponds to one or more slope calibration types 620, a temperature gradient type is selected and the corresponding counter is incremented. For example, the temperature gradients can be categorized into two cycles to distinguish between relatively extreme temperature shifts and mild temperature shifts over a certain period of time.The extreme temperature shift may be represented by a calibrated slope 620 for a particular temperature change per 10 minutes, while a mild temperature shift may be represented by a calibrated slope 620 for the particular change per 10 minutes or any other such duration. It should be understood that in other examples, more than two temperature gradient categories may be used using different slope calibration types 620.

[0061] Similar to position-dependent counting, electrical validation plans include tests to ensure immunity to thermal fatigue. Using techniques to normalize against the DV plan (similar to the position-based lifetime calculations described above), temperature-based cycle counting can be used to describe the real-time lifetime estimate (based on thermal cycling). In one or more examples, the real-time lifetime estimate against DV using thermal cycling is shown below in Equation 2, where M is the number of counts of each matching slope. %Useful life=∑1NSlope i countsSlope i counts per DVM×100

[0062] In addition, further lifetime utilization for automotive components is performed through the accumulation of mileage. Data acquisition test plans are often developed to validate vehicle systems (such as the steering system) based on an assumed lifetime of mileage. Distance monitoring allows the monitoring system 200 to calculate a real-time mileage measurement on-site, rather than relying on other vehicle subsystems.

[0063] Alternatively or additionally, monitoring system 200 uses an odometer calculation performed by steering system 40. Such odometer calculations are independent of other vehicle subsystems. The odometer calculation is performed using a vehicle speed input received via CAN 265. An example calculation is shown below in Equation 3. Distance traveled = vehicle speed × steering system activation time

[0064] Such parameter monitoring facilitates validation of the results of the position- and / or temperature-based service life calculations described above. If the correlation between vehicle service life counts and cycle counts does not match that of the validation plan, the service life estimate results become invalid.

[0065] Another indicator of the service life of automotive components is the creation of profiles for the vehicle's use case, where such profiling indicates how the vehicle is driven. In particular, in the case of the steering system 40, the vehicle 100 used in city traffic versus highway traffic may exhibit completely different wear profiles of the steering system 40 in significantly different ways.

[0066] For example, monitoring distance versus speed can categorize the use of vehicle 100 into 3 types: urban area, residential area, and highway. Fig. 7 shows a categorization of vehicle usage according to distance versus speed monitoring, in accordance with one or more embodiments. In the illustrated example, the upper thresholds 701 and the lower speed thresholds 702 [kph_upper, kph_lower] are used to establish threshold ranges. The high speed correlates with highway driving, the low speed with city driving, and the range in between with residential driving. In one or more examples, a predetermined amount of time is used to ensure that operation of the vehicle 100 remains in a particular category before usage in that range is counted. Accordingly, for example, only if the vehicle 100 is operating at a vehicle speed above the upper threshold 701 for at least the predetermined amount of time (e.g., 5 seconds, 10 seconds, 3 minutes, etc.)) is used, the vehicle's highway usage counter increments by 100 in this case. The counters for the other categories increment similarly.

[0067] Another important indicator of the service life of automotive components is the vehicle operating environment, i.e., the external conditions under which the vehicle is driven. For the steering system 40 in particular, operation in extremely cold weather and operation in arid climates can have completely different effects on thermal degradation and expected failure. Accordingly, the monitoring system 200 uses the start-up temperature to grasp / categorize the vehicle's operating environment.

[0068] Fig. Figure 8 shows an exemplary categorization of the vehicle environment by the monitoring system according to one or more embodiments. In the illustrated example, the vehicle environment is categorized into three types: Polar, Temperate, and Tropical, based on the initial temperature of the temperature sensor 23. Note that other categorizations are possible in other examples. Starting with the initial temperature ensures that the classification is valid and accurate.

[0069] The categorization (820) may be performed using an upper threshold 801 and a lower temperature threshold 802 (degC_upper, DegC_lower) to define threshold ranges. The high temperature threshold 801 may correlate with a tropical climate (820), the low temperature threshold 802 with a polar climate (820), and a range between the two thresholds correlates with a temperate climate (820). A predetermined constant time period is used to ensure that the initial temperature reading is that of a true startup and not that of an ignition cycle.For a true start-up, the initial temperature is expected to change toward a steady-state operating temperature; if this change is not observed within a certain calibratable time constant, it is assumed that an ignition cycle, not a start-up cycle, has occurred, and the count for a climate type is ignored.

[0070] Such additional information, such as the vehicle environment, which indicates the climate in which the vehicle 100 is used, the vehicle usage profile, which indicates the typical usage scenario of the vehicle 100, and the distance for which the steering system 40 has been used, can be used in conjunction with the counting cycle-based usage time calculation. The counting cycle-based usage time can be calculated using one or more attributes, such as engine position, temperature, and the like, as described herein. The additional information can be used, for example, to scale the calculated usage time. For example, the usage time is multiplied by a scaling factor corresponding to the vehicle environment, the usage profile, or both. Accordingly, a usage time (U) is adjusted to U*S, where S is the scaling factor.The scaling factor may increase or decrease the calculated usage time based on the vehicle environment and / or the usage profile. In one or more examples, multiple scaling factors are used, one for the vehicle environment and one for the usage profile.

[0071] Alternatively, the vehicle environment and / or usage profile may indicate a nonlinear calculation used to adjust the calculated usage time. Accordingly, the adjusted usage time (AU) can be represented as AU = f (U, vehicle environment, usage profile), where f is a nonlinear function.

[0072] Furthermore, in one or more examples, the vehicle environment and / or usage profile may be used to select a set of counts per DV used for calculating the usage time. For example, if the vehicle 100 is used in a tropical climate, the counts per DV used will be different than those used for the vehicle 100 in a polar climate. Similarly, the counts per DV may be different for a vehicle in city traffic than for a vehicle in highway traffic.

[0073] Fig.9 shows a flowchart of an example method for calculating a useful life for the steering system in real time, according to one or more embodiments. The method includes tracking an attribute signal associated with the steering system 40 (902). The attribute signal may be motor position, temperature, torque, and the like, as described herein. Furthermore, the method includes determining whether the attribute signal rises above an upper threshold and subsequently falls below a lower threshold (904). The method further includes selecting a subset of categories based on a frequency content of the attribute signal (906). Furthermore, the method includes selecting a category from the subset of categories based on a peak load (908).

[0074] For example, as described here with respect to motor position, among the four types of position-based categories, frequency content eliminates (or selects) two categories, and peak load facilitates the selection of one of the two categories from the chosen subset.

[0075] The method further includes incrementing a counter for the selected category (910). The method further includes calculating the useful life based on a ratio of the counter for the selected category and a predetermined count for that selected category (912). The predetermined count for the selected category includes the DV counts measured during testing of the components. In one or more examples, the predetermined count used is based on other categorization performed, such as the usage profile, the vehicle environment, and the like. As described herein, the useful life may be calculated using the counts thus determined for all categories.

[0076] The technical solutions described here accordingly facilitate the determination of an estimated service life of a steering system in real time by monitoring one or more attribute signals received from one or more sensors. The estimated service life can be adjusted based on the determination of a vehicle environment and a vehicle usage profile to improve the accuracy of the estimated service life. Furthermore, the determined service life can be validated using a distance measurement specific to the steering system, rather than an odometer reading on the vehicle itself. As already mentioned, the technical solutions described here can be used with any type of steering system, such as an EPS system, a SbW system, and the like.

[0077] While the technical solutions have been described in detail with only a limited number of embodiments, it is readily understood that the invention is not limited to such disclosed embodiments. Rather, the technical solutions may be modified to incorporate any number of variations, alterations, substitutions, or equivalent arrangements not previously described but which fall within the scope of the technical solutions. While various embodiments of the technical solutions have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the technical solutions are not to be considered limited by the foregoing description.

Claims

[1] Steering system (40), comprising: an engine (46); a controller (16); and a monitoring system (200) comprising at least one memory device and a processor (205), the monitoring system being coupled to the controller (16), the monitoring system (200) being configured to determine in real time a useful life of the steering system (40), the determination of the useful life comprising: Tracking an attribute signal; based on the determination that the attribute signal (902) rises above an upper threshold (401, 601, 701, 801) and then falls below a lower threshold (402, 602, 702, 802): Selecting a subset of categories based on a frequency content of the attribute signal; Selecting a category from the subset of categories based on a peak load (415) occurring sequentially on the attribute signal via a secondary attribute signal; and Incrementing a counter for the selected category; and Calculate the useful life based on a ratio of the counter for the selected category and a predetermined count for that selected category. [2] Steering system (40) according to claim 1, characterized by that the monitoring system (200) is further configured to notify an operator of the usage time calculated using the attribute signal. [3] Steering system (40) according to claim 1, characterized by that the calculation of the useful life is carried out using: %Useful life=∑1NType i countsPredetermined type i counts N, where N is the number of categories and type i counts are the number for category i and are a function of the intended service life of the steering system (40). [4] Steering system (40) according to claim 3, characterized by that the attribute signal is a motor position signal and the secondary attribute signal is a torque signal (18). [5] Steering system (40) according to claim 3, characterized by that the attribute signal is a torque signal (18). [6] Steering system (40) according to claim 3, characterized by that the monitoring system (200) is further configured to: determine an operating environment of the steering system (40) based on a start-up temperature. [7] Steering system (40) according to claim 3, characterized by that the monitoring system (200) is further configured to: determine an operating profile of the steering system (40) based on a classification of the vehicle speed. [8] Steering system (40) according to claim 1, characterized by in that the monitoring system (200) is further configured to validate the usage time calculated on the basis of a distance for which the steering system (40) has been used. [9] A method for determining the useful life of a steering system (40) in real time, the method comprising: Tracking an attribute signal associated with the steering system (40); based on determining that the attribute signal rises above an upper threshold (401, 601, 701, 801) and then falls below a lower threshold (402, 602, 702, 802): Selecting a subset of categories based on a frequency content of the attribute signal; Selecting a category from the subset of categories based on a peak load (415) occurring sequentially on the attribute signal via a secondary attribute signal; and Incrementing a counter for the selected category; and calculating the usage time based on a ratio of the counter for the selected category and a predetermined count for the selected category. [10] Method according to claim 9, characterized by that the calculation of the useful life is carried out using: %Useful life=∑1NType i countsPredetermined type i counts N, where N is the number of categories and type i counts are the number for category i and are a function of the intended service life of the steering system (40). [11] Method according to claim 10, characterized by that the attribute signal is a motor position signal and the secondary attribute signal is a torque signal. [12] Method according to claim 10, characterized by that the attribute signal is a torque signal (18). [13] Method according to claim 10, characterized by: determining an operating environment of the steering system (40) based on a starting temperature. [14] Method according to claim 10, characterized by : Determining an operating profile of the steering system (40) based on a classification of the vehicle speed. [15] A computer program product comprising a storage device in which computer-executable instructions are stored, the computer-executable instructions, when executed by a processing unit, causing the processing unit to determine in real time a useful life of a steering system (40), the determination of the useful life comprising: Tracking an attribute signal associated with the steering system (40); based on determining that the attribute signal rises above an upper threshold (401, 601, 701, 801) and then falls below a lower threshold (402, 602, 702, 802): Selecting a subset of categories based on a frequency content of the attribute signal; Selecting a category from the subset of categories based on a peak load (415) occurring sequentially on the attribute signal via a secondary attribute signal; and incrementing a counter for the selected category; and Calculate the useful life based on a ratio of the counter for the selected category and a predetermined count for that selected category. [16] Computer program product according to claim 15, characterized by that the calculation of the useful life is carried out using: %Useful life=∑1NType i countsPredetermined type i counts N, where N is the number of categories and type i counts are the number for category i and are a function of the intended service life of the steering system. [17] Computer program product according to claim 16, characterized by that the attribute signal is a motor position signal and the secondary attribute signal is a torque signal (18). [18] Computer program product according to claim 16, characterized by that the attribute signal is a torque signal (18). [19] Computer program product according to claim 16, characterized by : Determining an operating environment of the steering system (40) based on a starting temperature. [20] Computer program product according to claim 16, characterized by : Determining an operating profile of the steering system (40) based on a classification of the vehicle speed.

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