Low temperature friction compensation method and system for an electric power steering system

Abstract

A low-temperature friction compensation method and system of an electric power steering system, comprising: obtaining a PCB temperature-sensitive resistance voltage inside a controller of the electric power steering system when the vehicle is powered on; controlling a motor output detection signal of the electric power steering system, and collecting a starting current of the motor under the detection signal; determining an estimated initial temperature of a steering column of the electric power steering system based on the PCB temperature-sensitive resistance voltage, the starting current, and a preset offline three-dimensional mapping table, and then determining a basic compensation torque of the electric power steering system, and determining a real-time compensation torque of the electric power steering system in the running process, and performing torque compensation processing. The application accurately calculates the estimated initial temperature of the steering column through the PCB temperature-sensitive resistance voltage and the starting current of the motor under the detection signal, so that the low-temperature friction compensation is more accurate, and no additional hardware such as temperature sensors is needed, thereby avoiding the increase of hardware cost and assembly complexity.

Description

Technical Field

[0001] This application relates to the field of automotive electronic control technology, specifically to a low-temperature friction compensation method and system for an electric power steering system. Background Technology

[0002] In extremely low temperatures, the lubricating grease in the electric power steering (EPS) system's columns, gears, and other moving parts becomes viscous. Simultaneously, the slight thermal expansion and contraction of the metal materials can cause changes in the fit clearances. These combined effects significantly increase the static and dynamic friction of the system. This results in excessively heavy steering effort for the driver during cold starts, severely impacting driving experience and safety.

[0003] In related technologies, additional temperature sensors can be added to directly measure the tubing temperature, and then low-temperature friction compensation can be performed based on the directly measured tubing temperature. However, this approach leads to an increase in hardware costs and assembly complexity. Summary of the Invention

[0004] This application provides a method and system for low-temperature friction compensation in an electric power steering system, aiming to avoid increasing hardware costs and assembly complexity when performing low-temperature friction compensation.

[0005] Firstly, this application provides a low-temperature friction compensation method for an electric power steering system, the method comprising:

[0006] When the vehicle is powered on, the voltage of the PCB thermistor inside the controller of the electric power steering system is obtained;

[0007] Control the motor output detection signal of the electric power steering system, and collect the starting current of the motor under the detection signal;

[0008] Based on the PCB thermistor voltage, starting current, and a preset offline three-dimensional mapping table, the estimated initial temperature of the steering column of the electric power steering system is determined. The offline three-dimensional mapping table includes the correspondence between the PCB thermistor voltage, starting current, and the actual temperature of the steering column.

[0009] Based on the estimated initial temperature, the basic compensation torque of the electric power steering system is determined;

[0010] Based on the aforementioned basic compensation torque, the real-time compensation torque of the electric power steering system during operation is determined.

[0011] Torque compensation processing is performed according to the real-time compensation torque.

[0012] In the above embodiments, the estimated initial temperature of the steering column is accurately calculated by using the voltage of the PCB thermistor and the starting current of the motor under the detection signal, making low-temperature friction compensation more accurate, and eliminating the need for additional hardware such as temperature sensors, thereby avoiding increased hardware costs and assembly complexity.

[0013] In some embodiments, before determining the estimated initial temperature of the steering column of the electric power steering system based on the PCB thermistor voltage, starting current, and a preset offline three-dimensional mapping table, the method further includes:

[0014] In the cryogenic environment chamber, the ambient temperature is sequentially controlled at multiple preset low-temperature points;

[0015] At each of the aforementioned low-temperature points, record the voltage value of the PCB thermistor;

[0016] At each of the aforementioned low-temperature points, the peak current of the motor under preset starting conditions is measured;

[0017] The actual temperature of the steering column at each of the aforementioned low-temperature points was measured using a contact sensor;

[0018] The offline three-dimensional mapping table is obtained by generating the numerical value of the PCB thermistor voltage and the mapping relationship between the peak current and the actual temperature.

[0019] In the above embodiments, a high-precision correlation model between environmental thermal parameters, mechanical damping characteristics and real physical temperature was constructed through an offline calibration process. By using true value measurements in a laboratory environment, the difficult-to-quantify low-temperature friction characteristics were transformed into a data mapping table that can be characterized by electronic signals, providing a reliable data benchmark for temperature estimation in actual operation.

[0020] In some embodiments, determining the real-time compensation torque of the electric power steering system during operation based on the basic compensation torque includes:

[0021] Based on the PCB thermistor voltage and the motor operating current during the operation of the electric power steering system, the temperature rise of the steering column relative to the estimated initial temperature is determined.

[0022] Based on the temperature rise value, determine the friction compensation attenuation amount;

[0023] The real-time compensation torque is obtained by correcting the basic compensation torque using the friction compensation attenuation amount.

[0024] In the above embodiments, the friction compensation force is adaptively adjusted (attenuated) according to the temperature rise value, which realizes a smooth transition from the low temperature high damping state to the normal temperature state. This avoids the abnormal feel problem caused by long-term fixed compensation and ensures that the driver can obtain a stable, natural and linear steering feel throughout the entire warm-up process after the vehicle is cold-started.

[0025] In some embodiments, determining the friction compensation attenuation based on the temperature rise value includes:

[0026] Obtain the preset temperature rise attenuation coefficient;

[0027] The friction compensation attenuation amount is determined based on the product of the temperature rise value and the temperature rise attenuation coefficient.

[0028] In the above embodiments, a product algorithm based on linear coefficients is used to calculate the attenuation of friction compensation, so as to facilitate the exit of the low-temperature friction compensation mechanism.

[0029] In some embodiments, the torque compensation process according to the real-time compensation torque includes:

[0030] Acquire the hand force torque signal applied to the steering wheel;

[0031] Based on the hand force torque signal, the basic assist torque is determined;

[0032] A torque compensation command is triggered, comprising the sum of the base assist torque and the real-time compensation torque, to perform the torque compensation process.

[0033] In the above embodiments, the low-temperature friction compensation component is superimposed on the conventional EPS power steering control loop in a feedforward manner, realizing the decoupling and fusion of the normal temperature power steering logic and the low-temperature compensation logic, ensuring that the vehicle can provide the driver with consistent, accurate and smooth steering feel feedback regardless of whether it is starting in severe cold or driving in normal temperature conditions.

[0034] In some embodiments, before triggering the torque compensation command, which includes the sum of the base assist torque and the real-time compensation torque, to perform the torque compensation process, the method further includes:

[0035] The real-time compensation torque is determined to be greater than zero;

[0036] The low-temperature friction compensation method for the electric power steering system also includes:

[0037] If the real-time compensation torque is less than or equal to zero, a torque compensation command including the basic assist torque is triggered to perform the torque compensation process.

[0038] In the above embodiments, by introducing zero-value determination and amplitude limiting logic, a clear exit boundary is set for the low-temperature friction compensation strategy to ensure that the compensation torque always appears as a positive auxiliary force, and to ensure the unidirectionality and stability of the steering feel during the transition from the low-temperature high-friction state to the normal temperature state.

[0039] In some embodiments, after obtaining the voltage of the PCB thermistor inside the controller of the electric power steering system, the method further includes:

[0040] Determine whether the voltage of the PCB temperature sensor is lower than the preset low temperature threshold.

[0041] If the voltage of the PCB thermistor is less than the low temperature determination threshold, the step of controlling the motor output detection signal of the electric power steering system is executed.

[0042] In the above embodiments, by adding ambient temperature-based prediction logic before the active detection action, normal temperature conditions that do not require compensation can be effectively identified, and intelligent control is achieved to activate the compensation function only when needed under low temperature conditions.

[0043] In some embodiments, controlling the motor output detection signal of the electric power steering system and acquiring the starting current of the motor under the detection signal includes:

[0044] The motor is controlled to perform a steering drive process with a preset small angle of the steering column;

[0045] The instantaneous load current of the motor is obtained when it performs a steering drive process with a preset small angle of steering column.

[0046] The starting current is determined based on the instantaneous load current.

[0047] In the above embodiments, the motor is used as a sensor. Without changing the vehicle's driving state or interfering with the driver's feel, the current characteristic value reflecting the true damping state of the system is directly measured through a very small amplitude drive test. This allows the system to not only rely on temperature sensors but also combine actual mechanical load feedback to evaluate the impact of low temperature, ensuring the accuracy and robustness of the friction compensation strategy.

[0048] In some embodiments, determining the base compensation torque of the electric power steering system based on the estimated initial temperature includes:

[0049] Obtain a preset temperature-compensation torque correlation table, wherein the correlation table includes the reference value of compensation torque required to overcome static friction under different mechanical temperatures;

[0050] Based on the estimated initial temperature, the corresponding compensation torque benchmark value is found in the temperature-compensation torque correlation table and used as the basic compensation torque.

[0051] In the above embodiments, by establishing a pre-calibrated temperature-torque mapping mechanism, the complex low-temperature rheological physical properties are solidified into lookup table logic, which ensures the physical accuracy of the initial compensation torque while guaranteeing the real-time control.

[0052] Secondly, embodiments of this application provide a low-temperature friction compensation system for an electric power steering system, which is used to perform any of the low-temperature friction compensation methods for an electric power steering system.

[0053] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: by using the voltage of the PCB thermistor and the starting current of the motor under the detection signal, the estimated initial temperature of the steering column can be accurately calculated, making low-temperature friction compensation more accurate, and eliminating the need for additional hardware such as temperature sensors, thereby avoiding the increase in hardware costs and assembly complexity. Attached Figure Description

[0054] Figure 1 This is a flowchart illustrating a low-temperature friction compensation method for an electric power steering system in an embodiment of this application. Detailed Implementation

[0055] The terminology used in the following embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification of this application, the singular expressions “a,” “an,” “the,” “the,” and “this” are intended to include the plural expressions as well, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this application refers to any or all possible combinations including one or more of the listed items.

[0056] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as implying or suggesting relative importance or implicitly indicating the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature, and in the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more.

[0057] In a first aspect, embodiments of this application provide a low-temperature friction compensation method for an electric power steering system. This method is applied to a low-temperature friction compensation system (hereinafter referred to as the "system") for an electric power steering system, and the system can execute the steps of the low-temperature friction compensation method for the electric power steering system in any embodiment.

[0058] Reference Figure 1 A method for low-temperature friction compensation in an electric power steering system may include the following steps:

[0059] S101. When the vehicle is powered on, obtain the voltage of the PCB thermistor inside the controller of the electric power steering system.

[0060] In this embodiment, "vehicle power-on" refers to the vehicle's ignition switch being in the ON state or the Electric Power Steering (EPS) system being awakened from sleep mode and entering operating mode. "Controller interior" refers to the circuit environment integrated within the Electronic Control Unit (ECU) housing. "PCB (Printed Circuit Board) thermistor voltage" refers to the voltage signal across a thermistor (such as a negative temperature coefficient thermistor) mounted on the ECU mainboard. This voltage signal, after analog-to-digital conversion, serves as an electronic parameter reflecting the ambient temperature of the controller board.

[0061] S102, control the motor output detection signal of the electric power steering system, and collect the starting current of the motor under the detection signal.

[0062] In this embodiment, controlling the motor output detection signal refers to injecting a specific test command into the motor windings before the power steering motor officially outputs steering assist torque, or during the very short initialization period. This detection signal is configured to have a specific amplitude or frequency, and its purpose is not to drive the steering wheel to produce visible rotation, but to detect the load impedance state of the motor rotor. Acquiring the starting current refers to measuring the response current generated in the three-phase windings or busbar of the motor at the instant the detection signal is applied. Because the viscosity of the lubricating grease increases sharply at low temperatures, the static friction of the mechanical transmission system increases significantly. This change in physical characteristics is directly reflected in the current response characteristics of the motor when it attempts to overcome resistance.

[0063] In some embodiments of this application, the detection signal may be a high-frequency injection signal or a small step torque command, ensuring that the magnitude of the generated action is suppressed within a range imperceptible to the driver due to the existence of system inertia and friction, thereby achieving active detection of the system's mechanical damping state without affecting the driving experience.

[0064] S103. Based on the PCB thermistor voltage, starting current, and a preset offline three-dimensional mapping table, determine the estimated initial temperature of the steering column of the electric power steering system. The offline three-dimensional mapping table includes the correspondence between the PCB thermistor voltage, starting current, and the actual temperature of the steering column.

[0065] In this embodiment, the estimated initial temperature refers to the physical temperature value of the steering column (i.e., mechanical gear rack and bearing components) at the current moment, derived by an algorithm. The offline three-dimensional mapping table is a multi-dimensional data matrix pre-stored in the controller's non-volatile memory. This mapping table establishes a non-linear relationship between the electronic ambient temperature (characterized by PCB voltage), the mechanical damping state (characterized by starting current), and the actual core temperature of the mechanical components.

[0066] S104. Determine the basic compensation torque of the electric power steering system based on the estimated initial temperature.

[0067] In this embodiment, the base compensation torque refers to an initial feedforward torque value that the system needs to apply to counteract the increased static friction caused by lubricant solidification and material shrinkage at low temperatures. The determination of this torque value depends on the physical property model of the steering column.

[0068] In some embodiments of this application, the controller internally stores a "temperature-friction characteristic curve". Based on the estimated initial temperature, the system retrieves the theoretical compensation value required to maintain a good feel at the current temperature from the characteristic curve or the corresponding lookup table.

[0069] S105. Based on the basic compensation torque, determine the real-time compensation torque of the electric power steering system during operation.

[0070] In this embodiment, the operating process refers to the dynamic time period after the vehicle starts, during which the motor begins to assist steering and the system itself generates heat. Real-time compensation torque refers to the final compensation command after dynamically correcting the base compensation torque over time and changing operating conditions. Due to the Joule heat generated by the motor and the transfer of temperature from the engine compartment, the grease in the steering column and gearbox gradually softens, reducing friction. Therefore, the compensation torque cannot remain constant; otherwise, the steering feel will become too light or floaty after the engine warms up.

[0071] In some embodiments of this application, the system introduces a temperature rise decay model, which calculates the rate of temperature rise based on the real-time estimated motor power consumption or running time, and accordingly reduces the base compensation torque proportionally or non-linearly to generate a real-time compensation torque that can follow the changes in the system's thermal equilibrium state.

[0072] S106. Perform torque compensation processing according to the real-time compensation torque.

[0073] In this embodiment, torque compensation processing refers to adding the calculated real-time compensation torque to the final output command of the electric power steering system. The low-temperature friction compensation system of the electric power steering system vector-sums this real-time compensation torque with the base assist torque calculated based on the driver's hand force, and drives the inverter through technologies such as space vector pulse width modulation to control the motor to output the synthesized total torque. This step ensures that at the moment the driver turns the steering wheel, the motor can provide additional power to overcome the high viscous resistance at low temperatures, so that the hand force felt by the driver is consistent with that at normal temperature.

[0074] As can be seen, the embodiments of this application accurately calculate the estimated initial temperature of the steering column by using the voltage of the PCB thermistor and the starting current of the motor under the detection signal, making low-temperature friction compensation more accurate, and eliminating the need for additional hardware such as temperature sensors, thereby avoiding the increase in hardware costs and assembly complexity.

[0075] In some embodiments of this application, before determining the estimated initial temperature of the steering column of the electric power steering system based on the PCB thermistor voltage, starting current, and a preset offline three-dimensional mapping table, the following may also be included:

[0076] S201. In the cryogenic environment chamber, the ambient temperature is sequentially controlled at multiple preset cryogenic temperature points.

[0077] In this embodiment, the low-temperature environment chamber refers to a professional testing laboratory device capable of precisely regulating and maintaining internal temperature and humidity, with a volume sufficient to accommodate a complete vehicle or electric power steering system test bench. The preset low-temperature points refer to several discrete temperature values ​​selected within the system's designed operating range, such as -40℃, -30℃, -20℃, -10℃, and 0℃. Control encompasses both temperature regulation and constant temperature maintenance.

[0078] In some embodiments of this application, the low-temperature friction compensation system of the electric power steering system will execute a heat preservation program of a preset duration after adjusting the ambient temperature to each target temperature point. The duration is usually set to be sufficient for the metal structure of the steering column and the internal lubricating grease to reach a complete thermal equilibrium state, ensuring that the internal temperature of the mechanical components is consistent with the set temperature of the environmental chamber, thereby eliminating the interference of temperature gradient on calibration data.

[0079] S202. At each low temperature point, record the voltage value of the PCB thermistor.

[0080] In this embodiment, "recording" refers to reading the digital quantity converted by the analog-to-digital converter inside the controller using a data acquisition device or debugging tool. The temperature represented by the recorded PCB thermistor voltage is theoretically equivalent to the ambient chamber temperature and the steering column temperature.

[0081] S203. At each low temperature point, measure the peak current of the motor under preset starting conditions.

[0082] In this embodiment, the preset start-up condition refers to sending specific open-loop or closed-loop test commands to the motor controller, such as applying a voltage vector with a fixed slope or a position step command, to cause the motor to produce a small movement capable of overcoming static friction. Peak current refers to the electrical parameter at which the phase current or bus current reaches its maximum value at the instant the motor rotor begins to move (i.e., the moment of overcoming maximum static friction). This parameter is directly and physically related to the dynamic viscosity of the lubricating grease at the current temperature and the tightness of the mechanical fit clearance.

[0083] S204. Use a contact sensor to measure the actual temperature of the steering column at each low-temperature point.

[0084] In this embodiment, a contact sensor refers to a temperature-sensing element such as a thermocouple or resistance temperature detector (RTD) that can be directly attached to the surface of the object being measured and conduct heat. The actual temperature of the steering column at each low-temperature point is considered the true value during the calibration process.

[0085] S205. Generate the numerical value of the PCB thermistor voltage, the mapping relationship between the peak current and the actual temperature, and obtain an offline three-dimensional mapping table.

[0086] In this embodiment, the mapping relationship refers to a mathematical model or data set describing the corresponding logic between input and output variables. The generation process involves organizing, cleaning, and fitting a large number of discrete data points collected in the above steps. The offline three-dimensional mapping table is a structured data block stored in non-volatile memory, using the PCB thermistor voltage and peak current as row and column indices (or the X and Y axes as input), and the actual temperature of the steering column as the lookup value (or the Z axis).

[0087] In some embodiments of this application, the low-temperature friction compensation system of the electric power steering system establishes this relationship through polynomial surface fitting or neural network training, and discretizes it into a look-up table. The function of this table is that, during actual vehicle operation (non-thermal equilibrium state), the system can use the readily available PCB voltage and the starting current reflecting the resistance characteristics to deduce the actual temperature of the steering column, which is difficult to measure directly, thereby transforming the complex physical and thermodynamic problem into a lookup table operation through calibration data.

[0088] As can be seen, the embodiments of this application construct a high-precision correlation model between environmental thermal parameters, mechanical damping characteristics and real physical temperature through an offline calibration process, and use true value measurements in a laboratory environment to transform the difficult-to-quantify low-temperature friction characteristics into a data mapping table that can be characterized by electronic signals, providing a reliable data benchmark for temperature estimation in actual operation.

[0089] In some embodiments of this application, determining the real-time compensation torque of the electric power steering system during operation based on the base compensation torque may include:

[0090] S301. Based on the PCB thermistor voltage and motor operating current during the operation of the electric power steering system, determine the temperature rise of the steering column relative to the estimated initial temperature.

[0091] In this embodiment, the operation process refers to the duration from vehicle startup to the point where the EPS motor begins to respond to torque commands and perform assisted steering. During this process, the temperatures of the system components are no longer in static equilibrium but dynamically change with heat generation and dissipation. The PCB thermistor voltage continues to serve as the fundamental signal reflecting the thermal state of the controller and its surrounding environment. The motor's operating current refers to the real-time phase current flowing through the three-phase windings of the motor, the square of which (I0) 2 It is directly proportional to the Joule heat generated by the copper losses of the motor. The temperature rise (ΔT) refers to the increment of the calculated temperature of the steering column at the current moment relative to the estimated initial temperature (T_initial) determined during system power-on initialization.

[0092] S302. Determine the friction compensation attenuation amount based on the temperature rise value.

[0093] In this embodiment, the friction compensation attenuation amount refers to the torque value that needs to be deducted from the basic compensation torque. Since the viscosity of grease decreases non-linearly with increasing temperature (typically approximating an exponential decay relationship), this causes the inherent frictional resistance of the mechanical system to gradually decrease. To avoid applying excessive initial compensation torque at high temperatures, which could lead to a floaty feel or overshoot during self-centering, a correction amount must be introduced.

[0094] S303. The basic compensation torque is corrected by the friction compensation attenuation to obtain the real-time compensation torque.

[0095] In this embodiment, the correction is a mathematical operation, typically represented by subtraction. Obtaining the real-time compensation torque refers to calculating the friction compensation component that should ultimately be applied to the motor control command in the current control cycle. The specific calculation logic is: Real-time compensation torque = Basic compensation torque - Friction compensation attenuation.

[0096] As can be seen, the embodiments of this application adaptively adjust (attenuate) the friction compensation force according to the temperature rise value, realizing a smooth transition from the low temperature high damping state to the normal temperature state, avoiding the abnormal feel problem caused by long-term fixed compensation, and ensuring that the driver can obtain a stable, natural and linear steering feel throughout the entire warm-up process after the vehicle is cold-started.

[0097] In some embodiments of this application, determining the friction compensation attenuation based on the temperature rise value may include:

[0098] S401, Obtain the preset temperature rise attenuation coefficient.

[0099] In this embodiment, the temperature rise attenuation coefficient is a dimensionless or scalar parameter with specific physical units, used to quantify the rate at which the frictional resistance of the steering column decreases with increasing temperature. The default setting refers to the fact that this coefficient was calibrated during the system development phase through extensive temperature-induced frictional force testing in a climate chamber and stored in a non-volatile memory unit.

[0100] In some embodiments of this application, considering that the viscosity-temperature characteristics of lubricating grease are typically non-linear, using only a globally fixed coefficient may not be accurate enough. The low-temperature friction compensation system of the electric power steering system can look up a specific temperature rise attenuation coefficient matching the estimated initial temperature from a set of preset coefficient tables. For example, when the initial temperature is -40℃, a larger attenuation coefficient is selected due to the extremely rapid viscosity change; while when the initial temperature is -10℃, a relatively smaller attenuation coefficient is selected. This piecewise linearization approach retains the simplicity of the algorithm while ensuring the rationality of compensation termination at different low-temperature starting points.

[0101] S402. Determine the friction compensation attenuation amount based on the product of the temperature rise value and the temperature rise attenuation coefficient.

[0102] In this embodiment of the application, the calculation formula for determining the friction compensation attenuation amount is: friction compensation attenuation amount = temperature rise value × temperature rise attenuation coefficient, thereby obtaining the compensation torque value that should be reduced at the current moment.

[0103] As can be seen, the embodiments of this application use a product algorithm based on linear coefficients to calculate the attenuation of friction compensation, so as to facilitate the exit of the low-temperature friction compensation mechanism.

[0104] In some embodiments of this application, torque compensation processing based on real-time compensated torque may include:

[0105] S501, Obtain the hand torque signal applied to the steering wheel.

[0106] In this embodiment, the hand force torque signal refers to an electrical signal collected by a torque sensor mounted on the steering column, reflecting the magnitude and direction of the torque applied by the driver when operating the steering wheel. This signal is typically generated by detecting the torsion angle of the torsion bar connecting the steering wheel input shaft and the pinion output shaft.

[0107] S502. Determine the basic assist torque based on the hand force torque signal.

[0108] In this embodiment, the base assist torque refers to the main assist torque used to reduce the driver's steering load, calculated by referring to a table based on the preset assist characteristic curve of the electric power steering system. This torque is mainly used to overcome the self-centering torque between the tires and the ground, as well as the system's basic friction at room temperature.

[0109] S503, triggers a torque compensation command that includes the sum of the base assist torque and the real-time compensation torque, to perform torque compensation processing.

[0110] In this embodiment, the torque compensation command refers to the generated final target current command, which is sent to the motor drive circuit (such as the inverter arm). Torque compensation processing involves controlling the switching of the power transistors using pulse width modulation (PWM) technology to drive the motor and output the synthesized total torque. At this point, the total torque output by the motor includes two contributions: one part is used for normal steering assistance, and the other part is specifically used to overcome the increased viscous frictional resistance due to solidification at low temperatures, thereby physically offsetting the negative impact of low-temperature environments on the mechanical transmission efficiency of the steering system.

[0111] As can be seen, the embodiment of this application superimposes the low-temperature friction compensation component into the conventional EPS power steering control loop in a feedforward manner, thereby achieving the decoupling and fusion of the normal temperature power steering logic and the low-temperature compensation logic, ensuring that the vehicle can provide the driver with consistent, accurate and smooth steering feel feedback regardless of whether it is starting in severe cold or driving in normal temperature conditions.

[0112] In some embodiments of this application, before triggering a torque compensation command that includes the sum of the base assist torque and the real-time compensation torque to perform torque compensation processing, the following may also be included:

[0113] S601, confirm that the real-time compensation torque is greater than zero.

[0114] In this embodiment, a real-time compensation torque greater than zero means that the torque value after correction for friction compensation attenuation remains positive. Physically, this means that although the temperature of the steering column has increased relative to the initial moment, resulting in a decrease in the viscosity of the internal grease, the current mechanical friction resistance is still higher than the reference friction force at standard operating temperature. Therefore, the system still needs to provide additional positive auxiliary torque to offset this residual low-temperature resistance.

[0115] In some embodiments of this application, the low-temperature friction compensation method for the electric power steering system may further include:

[0116] S602. If the real-time compensation torque is less than or equal to zero, trigger a torque compensation command including the basic assist torque to perform torque compensation processing.

[0117] In this embodiment, a real-time compensation torque less than or equal to zero means that the frictional attenuation caused by temperature rise has completely offset or even exceeded the initially estimated low-temperature frictional increment. This situation typically occurs after the vehicle has been running for a period of time, when the internal temperature of the steering system has approached or reached the normal operating temperature range. Triggering a torque compensation command that includes the base assist torque means that the system automatically ignores the calculated negative or zero compensation values ​​and sends only the base assist torque as the final target command to the motor controller.

[0118] As can be seen, the embodiments of this application, by introducing zero-value determination and amplitude limiting logic, set a clear exit boundary for the low-temperature friction compensation strategy, so as to ensure that the compensation torque always appears as a positive auxiliary force, and to ensure the unidirectionality and stability of the steering feel during the transition from the low-temperature high-friction state to the normal temperature state.

[0119] In some embodiments of this application, after obtaining the voltage of the PCB thermistor inside the controller of the electric power steering system, the following may be included:

[0120] S701. Determine whether the voltage of the PCB temperature-sensitive resistor is lower than the preset low temperature judgment threshold.

[0121] In this embodiment, the PCB thermistor is configured in the circuit such that its output voltage signal is positively correlated with the ambient temperature; that is, the lower the temperature, the lower the voltage. The preset low temperature threshold refers to a pre-stored voltage limit value, which corresponds to a specific physical critical temperature (e.g., 0°C or -10°C).

[0122] S702. If the voltage of the PCB thermistor is less than the low temperature judgment threshold, execute the step of controlling the motor output detection signal of the electric power steering system.

[0123] In this embodiment, if the voltage of the PCB thermistor is less than the low-temperature threshold, it means that the controller determines that the current ambient temperature is low enough to potentially significantly increase the viscous friction of the mechanical system, thereby affecting the steering feel and return-to-center performance. The step of controlling the motor output detection signal of the electric power steering system refers to the system formally activating the active detection logic, allowing the current controller to inject a specific high-frequency or pulse detection current into the motor windings. Conversely, if the voltage is higher than the threshold, the system will skip the subsequent active detection and complex compensation calculations, directly adopting the default control strategy at room temperature.

[0124] As can be seen, the embodiments of this application effectively identify ambient temperature conditions that do not require compensation by adding a prediction logic based on ambient temperature before the active detection action, thereby realizing intelligent control that only activates the compensation function on demand under low temperature conditions.

[0125] In some embodiments of this application, controlling the motor output detection signal of the electric power steering system and collecting the motor's starting current under the detection signal may include:

[0126] S801 controls the motor to perform steering drive processing of the steering column at a preset small angle.

[0127] In this embodiment, the preset small angle refers to a pre-calibrated and stored threshold value for a tiny mechanical rotation angle (e.g., within ±3 degrees of the motor rotor angle, corresponding to a steering wheel angle typically less than 0.5 degrees). The physical significance of this angle setting is that, under static friction between the vehicle tires and the ground, the mechanical displacement within this angle range is insufficient to overcome the tire's self-centering torque, thus preventing actual wheel deflection. This ensures that the drive has no impact on the vehicle's trajectory, and the driver can hardly perceive it through touch. The steering column steering drive processing refers to the low-temperature friction compensation system of the electric power steering system applying a specific excitation vector to the motor via the inverter, controlling the motor rotor to perform one or more controlled tiny rotations near the current equilibrium position.

[0128] In some embodiments of this application, the system may inject a low-amplitude, short-duration sine or triangular wave position command into the motor, causing the mechanical structure to produce micro-motions within the allowable range of backlash or elastic deformation, thereby serving as an excitation source for physical detection.

[0129] S802. Obtain the instantaneous load current of the motor when it performs steering drive processing at a preset small angle.

[0130] In this embodiment, the instantaneous load current refers to the current component that is directly used to generate electromagnetic torque, which is collected in real time by a current sensor and processed by a microcontroller during the aforementioned micro-motion process. This current physically reflects the torque required for the motor to overcome the static friction between internal mechanical components (such as worm gears and bearings) and the viscous resistance generated by the solidification of grease at low temperatures when attempting to rotate the steering column.

[0131] S803. Determine the starting current based on the instantaneous load current.

[0132] In this embodiment of the application, determining the starting current refers to extracting features from a series of instantaneous load current data collected within the micro-motion time window to obtain a scalar value that can characterize the current maximum static friction resistance level of the mechanical system.

[0133] In some embodiments of this application, the low-temperature friction compensation system of the electric power steering system uses a peak detection algorithm to identify the peak value of the current waveform at the moment of micro-motion start-up, or to calculate the average current value of the micro-motion constant speed segment, and uses the processed value as the starting current.

[0134] As can be seen, the embodiments of this application utilize the motor as a sensor, and without changing the vehicle's driving state or interfering with the driver's feel, directly and physically measure the current characteristic value that reflects the true damping state of the system through a very small amplitude drive test. This allows the system to not only rely on the temperature sensor, but also combine actual mechanical load feedback to evaluate the impact of low temperature, ensuring the accuracy and robustness of the friction compensation strategy.

[0135] In some embodiments of this application, determining the basic compensation torque of the electric power steering system based on an estimated initial temperature may include:

[0136] S901. Obtain a preset temperature-compensation torque correlation table, wherein the correlation table includes the reference value of compensation torque required to overcome static friction under different mechanical temperatures.

[0137] In this embodiment, the preset temperature-compensated torque correlation table refers to a data array or map pre-stored in non-volatile memory. This correlation table quantifies the nonlinear relationship between the temperature and internal resistance torque of the mechanical structure of the steering system (including gears, racks, bearings, seals, etc.). The compensation torque reference value required to overcome static friction at different mechanical temperatures refers to the theoretical feedforward torque value required by the motor to overcome the static friction caused by the increased viscosity of lubricating grease due to low-temperature solidification and the tightening of material fits at specific low-temperature nodes (e.g., -40℃, -30℃, -20℃, etc.).

[0138] S902. Based on the estimated initial temperature, find the corresponding compensation torque reference value in the temperature-compensation torque correlation table and use it as the basic compensation torque.

[0139] In this embodiment of the application, looking up the corresponding compensation torque reference value in the temperature-compensation torque association table means that the controller's algorithm module reads the index value and searches for it in the stored data array.

[0140] As can be seen, the embodiments of this application establish a pre-calibrated temperature-torque mapping mechanism, which solidifies the complex low-temperature rheological physical properties into a lookup table logic, ensuring the physical accuracy of the initial compensation torque while guaranteeing the real-time control.

[0141] In some embodiments of this application, in the step of correcting the base compensation torque using the friction compensation attenuation to obtain the real-time compensation torque, a dynamic shear correction logic based on the thixotropic properties of the lubricating grease may also be introduced, specifically including:

[0142] S1001. Monitor the real-time shear rate parameters of the steering components of the electric power steering system.

[0143] In this embodiment, the steering component refers to the mechanical assembly in an electric power steering system that is filled with grease and undergoes relative motion, mainly including a worm gear reduction mechanism and a rack and pinion steering gear. The real-time shear rate parameter is a physical quantity that characterizes the relative motion velocity between the fluid layers within the grease. Since grease is a non-Newtonian fluid, its viscosity depends not only on temperature but also significantly on the shear rate (i.e., shear thinning).

[0144] In some embodiments of this application, the low-temperature friction compensation system of the electric power steering system uses the real-time mechanical angular velocity of the motor or the steering angular velocity of the steering wheel as a real-time shear rate parameter. The signal from the position sensor is differentiated to calculate the current absolute value of the angular velocity |Omega_t|. The larger this parameter, the faster the mechanical components move, and the stronger the shear force on the lubricating grease.

[0145] S1002. Update the shear history factor of the grease based on the real-time shear rate parameter.

[0146] In this embodiment, the shear history factor is a dimensionless state variable ranging from 0 to 1, used to simulate the destruction and recovery process of the grease's microstructure. When the shear history factor is 1, it represents that the grease is in a completely static recovery state, with an intact internal structure and the highest viscosity; when the factor approaches 0, it represents that the grease's structure is completely destroyed under violent agitation, and the viscosity drops to an extreme value.

[0147] In some embodiments of this application, the shear history factor can be updated using a discrete-time iterative approach. The sampling period is set to Delta_t, the factor at the previous time step is Lambda_prev, and the factor at the current time step is Lambda_curr. If |Omega_t| is detected to be greater than a preset shear threshold Omega_th (i.e., rapid steering is occurring), it can be determined that the grease has undergone "shear thinning," calculated using the following formula:

[0148] Lambda_curr=Lambda_prev-K_break×(|Omega_t|-Omega_th)×Delta_t

[0149] Where K_break is the structural failure rate constant.

[0150] If |Omega_t| is detected to be less than or equal to Omega_th (i.e., the steering wheel remains stationary or slowly creeps), it can be determined that the grease has undergone "thixotropic recovery," calculated according to the following formula:

[0151] Lambda_curr=Lambda_prev+K_recover×Delta_t

[0152] Where K_recover is the structural recovery rate constant.

[0153] After each iteration, Lambda_curr can be throttled to ensure that its value always remains between [Lambda_min, 1], where Lambda_min is the preset minimum value of the shear history factor.

[0154] The physical significance of this step lies in the fact that it not only considers how fast the rotation is at the current moment, but also "remembers" whether there was a sharp turn just now, thus accurately simulating the dynamic physical process of the lubricating grease changing from thick to thin and then statically recovering.

[0155] S1003. Calculate the dynamic shear correction coefficient based on the shear history factor.

[0156] In this embodiment, the dynamic shear correction coefficient is a proportional coefficient used to reduce the real-time compensation torque in real time. This coefficient is positively correlated with the shear history factor.

[0157] In some embodiments of this application, the system determines the dynamic shearing correction coefficient K_shear using the following linear mapping formula:

[0158] K_shear=C_offset+(1-C_offset)×Lambda_curr

[0159] C_offset is the minimum viscosity retention ratio (e.g., 0.3) used to prevent the compensation amount from being excessively reduced.

[0160] S1004. The real-time compensation torque is obtained by correcting the basic compensation torque using the dynamic shear correction coefficient and the friction compensation attenuation.

[0161] In this embodiment, the real-time compensation torque = (basic compensation torque - friction compensation attenuation) × dynamic shear correction coefficient.

[0162] Understandably, in low-temperature environments, although the initial viscosity of the grease is high, it will drop instantly if the driver makes an emergency lane change (high shear rate). If a large compensation torque is still output according to the high viscosity standard at this time, it will lead to excessive power steering, causing the steering wheel to drift or even overshooting the centering point. By introducing a dynamic shear correction coefficient, the compensation force can be automatically reduced during rapid steering and automatically restored after the driving becomes stable, achieving a true simulation of the physical properties of friction.

[0163] As can be seen, the embodiments of this application utilize shear history factors to dynamically track the destruction and recovery state of the microstructure of grease, effectively avoiding the floating driving feel or system instability caused by overcompensation under low temperature and high-speed steering conditions, and ensuring the control accuracy and feel consistency of the electric power steering system across the entire dynamic range.

[0164] Secondly, this application provides a low-temperature friction compensation system for an electric power steering system. The low-temperature friction compensation system for the electric power steering system is used to execute the low-temperature friction compensation method for the electric power steering system described in any embodiment. The specific technical content can be found in the corresponding content of the low-temperature friction compensation method for the electric power steering system, and will not be repeated here.

[0165] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for low-temperature friction compensation in an electric power steering system, characterized in that, The low-temperature friction compensation method for the electric power steering system includes: When the vehicle is powered on, the voltage of the PCB thermistor inside the controller of the electric power steering system is obtained; Control the motor output detection signal of the electric power steering system, and collect the starting current of the motor under the detection signal; Based on the PCB thermistor voltage, starting current, and a preset offline three-dimensional mapping table, the estimated initial temperature of the steering column of the electric power steering system is determined. The offline three-dimensional mapping table includes the correspondence between the PCB thermistor voltage, starting current, and the actual temperature of the steering column. Based on the estimated initial temperature, the basic compensation torque of the electric power steering system is determined; Based on the aforementioned basic compensation torque, the real-time compensation torque of the electric power steering system during operation is determined. Torque compensation processing is performed according to the real-time compensation torque.

2. The low-temperature friction compensation method for an electric power steering system as described in claim 1, characterized in that, Before determining the estimated initial temperature of the steering column of the electric power steering system based on the PCB thermistor voltage, starting current, and a preset offline three-dimensional mapping table, the method further includes: In the cryogenic environment chamber, the ambient temperature is sequentially controlled at multiple preset low-temperature points; At each of the aforementioned low-temperature points, record the voltage value of the PCB thermistor; At each of the aforementioned low-temperature points, the peak current of the motor under preset starting conditions is measured; The actual temperature of the steering column at each of the aforementioned low-temperature points was measured using a contact sensor; The offline three-dimensional mapping table is obtained by generating the numerical value of the PCB thermistor voltage and the mapping relationship between the peak current and the actual temperature.

3. The low-temperature friction compensation method for an electric power steering system as described in claim 1, characterized in that, The determination of the real-time compensation torque of the electric power steering system during operation, based on the aforementioned basic compensation torque, includes: Based on the PCB thermistor voltage and the motor operating current during the operation of the electric power steering system, the temperature rise of the steering column relative to the estimated initial temperature is determined. Based on the temperature rise value, determine the friction compensation attenuation amount; The real-time compensation torque is obtained by correcting the basic compensation torque using the friction compensation attenuation amount.

4. The low-temperature friction compensation method for an electric power steering system as described in claim 3, characterized in that, The determination of friction compensation attenuation based on the temperature rise value includes: Obtain the preset temperature rise attenuation coefficient; The friction compensation attenuation amount is determined based on the product of the temperature rise value and the temperature rise attenuation coefficient.

5. The low-temperature friction compensation method for an electric power steering system as described in claim 1, characterized in that, The torque compensation process according to the real-time compensated torque includes: Acquire the hand force torque signal applied to the steering wheel; Based on the hand force torque signal, the basic assist torque is determined; A torque compensation command is triggered, comprising the sum of the base assist torque and the real-time compensation torque, to perform the torque compensation process.

6. The low-temperature friction compensation method for an electric power steering system as described in claim 5, characterized in that, The triggering includes a torque compensation command comprising the sum of the base assist torque and the real-time compensation torque, and before performing the torque compensation process, it further includes: The real-time compensation torque is confirmed to be greater than zero; The low-temperature friction compensation method for the electric power steering system also includes: If the real-time compensation torque is less than or equal to zero, a torque compensation command including the basic assist torque is triggered to perform the torque compensation process.

7. The low-temperature friction compensation method for an electric power steering system as described in claim 1, characterized in that, After obtaining the voltage of the PCB thermistor inside the controller of the electric power steering system, the method further includes: Determine whether the voltage of the PCB temperature sensor is lower than the preset low temperature threshold. If the voltage of the PCB thermistor is less than the low temperature determination threshold, the step of controlling the motor output detection signal of the electric power steering system is executed.

8. The low-temperature friction compensation method for an electric power steering system as described in claim 1, characterized in that, The method of controlling the output detection signal of the motor of the electric power steering system and collecting the starting current of the motor under the detection signal includes: The motor is controlled to perform a steering drive process with a preset small angle of the steering column; The instantaneous load current of the motor is obtained when it performs a steering drive process with a preset small angle of steering column. The starting current is determined based on the instantaneous load current.

9. The low-temperature friction compensation method for an electric power steering system as described in claim 1, characterized in that, Determining the basic compensation torque of the electric power steering system based on the estimated initial temperature includes: Obtain a preset temperature-compensation torque correlation table, wherein the correlation table includes the reference value of compensation torque required to overcome static friction under different mechanical temperatures; Based on the estimated initial temperature, the corresponding compensation torque benchmark value is found in the temperature-compensation torque correlation table and used as the basic compensation torque.

10. A low-temperature friction compensation system for an electric power steering system, characterized in that, The low-temperature friction compensation system of the electric power steering system is used to perform the low-temperature friction compensation method of the electric power steering system according to any one of claims 1 to 9.

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