A method for improving the output performance of a low-temperature cold-start electric power steering system

Abstract

The application discloses a method for improving the output performance of a low-temperature cold-start electric power steering system, and belongs to the field of automobile power steering, and comprises the following steps: after a vehicle unlocking instruction is input, the state of a plurality of source sensors is read, and pre-heating is unlocked when a low-temperature condition is met; in a pre-heating standby state, an activation source is monitored, the intention of a driver is judged and the safety boundary of the vehicle is judged, and a heating instruction containing an expected mode is issued; the steering motor is controlled to be switched to a self-heating mode, the target current of the cross axis is set to zero, the target current of the direct axis is determined based on the motor temperature and the low-voltage bus voltage, closed-loop heating is realized by injecting high-frequency alternating current; a safety exit condition is polled in real time, and when the condition is triggered, the heating is stopped and the system is smoothly switched to a conventional torque control mode. According to the application, the motor temperature is raised to above the power limitation removal threshold before the driver shifts gears and starts, the power limitation caused by the low-temperature insulation embrittlement is eliminated, full power torque is provided under extremely cold working conditions, and the motor overheating and the excessive consumption of the storage battery are avoided.

Description

Technical Field

[0001] This application pertains to the automotive field, and particularly relates to electric power steering systems for pure electric vehicles and hybrid vehicles. Background Technology

[0002] With improvements in battery and electronic control capabilities, the market share of pure electric vehicles and hybrid vehicles is increasing year by year in high-latitude, low-temperature regions. However, the low-temperature adaptability issues of pure electric and hybrid vehicles are gradually becoming apparent. Pure electric vehicles, without an engine heat source, place higher demands on thermal management and electronic control strategies.

[0003] Most existing EPS (Electric Power Steering) systems use low-voltage DC motors. In low-temperature environments of -25℃ to -40℃, to prevent irreversible physical damage, the power is linearly reduced to zero. This is because insulation materials (such as winding enamel) harden and become brittle at low temperatures, and their shrinkage rate differs from that of metallic materials, potentially leading to insulation cracking or peeling, causing a short circuit risk. Aging of insulation materials may reduce insulation strength, and high current increases the risk of electrical faults. Upon initial start-up after cryogenic soaking, the EPS system reduces power to protect the motor, losing some steering assistance, causing the driver to feel a heavy hand position, requiring more than ten minutes of driving before returning to normal. Summary of the Invention

[0004] To address the aforementioned issues, this application provides a method for improving the output performance of an electric power steering system for cold starts in low temperatures. This method can quickly raise the operating temperature of the EPS motor, improve the power steering performance of EPS for cold starts in ultra-low temperatures, and not affect vehicle use.

[0005] In a first aspect, embodiments of the present invention provide a method for improving the output performance of a cold-start electric power steering system, comprising: Wake up the vehicle controller, read the status of multiple source sensors, and enter the preheating standby state when the low temperature environment and vehicle stationary conditions are met. In the preheating standby state, a heating command is sent to the steering controller after it is determined that the driver's intention and safety boundary conditions are met; After receiving the heating command, the electric power steering controller switches to self-heating mode, sets the quadrature axis current to zero, and dynamically calculates the direct axis target current based on temperature and voltage. It injects high-frequency alternating current using a soft-start strategy that combines space vector modulation technology with graded preheating, and adjusts the closed loop based on the temperature rise rate and power transistor junction temperature. During the heating process, the system polls for driver takeover intentions, gear and speed changes, low-voltage power supply abnormalities, or system malfunctions that force the system to exit. Once any of these conditions are met, the system immediately shuts off the entire axle arm to stop heating and smoothly switches to the conventional torque control mode that provides full steering assistance.

[0006] In a preferred embodiment of the present invention, the conditions for determining whether to enter the preheating standby state include: Compare ambient temperature with ambient temperature activation threshold, steering motor body temperature with power limit protection temperature limit, vehicle speed with maximum vehicle speed safety threshold, and low voltage bus voltage with minimum safe voltage threshold. If the ambient temperature is confirmed to be below the ambient temperature activation threshold, the steering motor body temperature is below the power limit protection temperature limit, the vehicle speed is below the maximum vehicle speed safety threshold, the gear is in parking or neutral, and the low voltage bus voltage is above the minimum safe voltage threshold, then the unlocking preheating conditions are determined to be met.

[0007] As a preferred embodiment of the present invention, determining whether the driver's intent and safety boundary conditions are met includes monitoring local activation sources and remote activation sources: The triggering conditions for the local activation source are: the driver's door changes from locked to open, the seat changes from unoccupied to occupied, and the steering wheel torque in the steering wheel angle torque is less than a preset rotation threshold. The triggering condition for the remote activation source is receiving a remote preprocessing instruction and the remaining power of the power battery being higher than the low power protection threshold.

[0008] In a preferred embodiment of the present invention, the step of determining the direct-axis target current includes: The corresponding temperature current limit value is obtained based on the current temperature of the steering motor body, and the steady-state hardware power limit value is obtained based on the maximum continuous power loss of the power switch and the phase resistance of the stator winding after temperature compensation correction. By comparing the temperature current limit value with the steady-state hardware power limit value, the smaller of the two values ​​is selected as the direct-axis target current.

[0009] As a preferred embodiment of the present invention, the closed-loop adjustment includes: Obtain the real-time temperature of the steering motor body in the current measurement and control cycle and the historical temperature of the steering motor body in the previous measurement and control cycle, and calculate the absolute temperature increment of the two. Divide the absolute temperature increment by a fixed calculation step size to obtain the transient temperature rise rate reference feedback; The transient temperature rise rate reference feedback is compared with the preset safe temperature rise rate range. When the temperature rise rate exceeds the upper limit, the amplitude of the direct-axis target current is reduced in the opposite direction by the proportional-integral regulator.

[0010] As a preferred embodiment of the present invention, the soft-start strategy includes a preheating stage and a rapid heating stage; During the preheating stage, the initial direct-axis target current is set to the first proportional value of the rated current of the steering motor, and a direct-axis high-frequency alternating current parallel to the rotor magnetic field direction is injected into the stator winding. During the rapid heating phase, when the temperature of the current steering motor body rises above a preset brittle transition temperature threshold, the direct shaft target current is increased to a second proportional value of the steering motor rated current, wherein the second proportional value is greater than the first proportional value.

[0011] As a preferred embodiment of the present invention, the forced exit conditions include: The driver's intention to take over is detected. The criteria for this are: the seat occupancy status changes to occupancy and the steering wheel torque in the steering wheel angle torque is greater than the preset takeover torque threshold, or the steering wheel angle change rate is greater than the preset angle change rate threshold. The system detects that the gear has been shifted to drive or reverse and the vehicle speed exceeds the starting threshold. The low-voltage bus voltage was detected to be below the power outage threshold and remained below the preset time for an extended period. Automatic parking activation or a system-level malfunction is detected, and a remote command is received to cancel it.

[0012] As a preferred embodiment of the present invention, the step of stopping heating and switching to the conventional torque control mode includes: Immediately set the direct-axis target current to zero, disconnect all power switching transistors to enter the full bridge arm off state, and record the current heating duration and highest temperature; Based on the steering wheel torque signal and the current vehicle speed, the basic assist reference value is calculated through the basic assist mapping table. Then, the basic assist reference value is adjusted proportionally using a low temperature compensation factor determined by the current steering motor body temperature, and a new cross-axis target current is output to drive the motor to generate steering assist.

[0013] As a preferred embodiment of the present invention, the step of calculating the basic assist reference value through the basic assist mapping table includes: locating adjacent calibration nodes surrounding the current input coordinates, and calculating the rated basic assist reference value for smooth transition using a bilinear interpolation algorithm.

[0014] Secondly, embodiments of the present invention provide a system for improving the output performance of a low-temperature cold-start electric power steering system, comprising: a system initialization and low-temperature determination module, used to wake up the vehicle controller to close the high-voltage relay and stabilize the low-voltage network, and read the status of multiple source sensors to calculate whether the current unlocking preheating conditions are met; a multi-source activation and safety access module, used to monitor local door and seat status changes or receive remote preprocessing instructions in the preheating standby state, determine the driver's behavioral intention and the safety boundary of the anti-tow vehicle, and issue a heating instruction containing the desired mode to the controller; a high-frequency direct-axis current closed-loop control module, used to set the quadrature-axis target current to zero, dynamically determine the direct-axis target current according to temperature and voltage, and inject high-frequency alternating current using a soft-start strategy combining space vector modulation technology and graded preheating; and a safety monitoring and active exit module, used to poll the driver's takeover intention, gear speed changes, low-voltage power supply abnormalities, and system fault exit conditions at fixed intervals, and execute full-axle arm shutdown to stop heating after triggering, record status data, and smoothly switch to the conventional torque control mode.

[0015] Compared with the prior art, this application has the following advantages: This invention utilizes the collaborative operation of the vehicle controller and the EPS controller to actively inject a direct-axis high-frequency alternating current parallel to the rotor magnetic field into the EPS motor during the low-temperature cold start phase (from when the driver unlocks the car until before shifting gears). Joule heating is generated using winding resistance and core losses. Simultaneously, based on multi-source signals such as seat pressure sensors, steering wheel torque angle sensors, vehicle speed, gear position, and battery voltage, the driver's intentions and safety boundaries are determined in real time. This enables graded power injection, closed-loop temperature rise rate regulation, and a multi-condition forced exit mechanism. Compared to existing technologies, this application can raise the EPS motor temperature above the power limit release threshold before the driver shifts gears, eliminating the power assist output limitation caused by insulation embrittlement at low temperatures. This allows the steering system to still provide full rated power assist torque in extremely cold environments, reducing driver effort while preventing motor overheating damage and excessive battery consumption, thus improving the functional safety and driving comfort of pure electric vehicles in cold regions.

[0016] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating a method for improving the output performance of an electric power steering system during cold starts at low temperatures is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Example 1 During the cold start phase of pure electric vehicles or hybrid vehicles, the insulation material of the EPS motor becomes brittle at extremely low temperatures. Traditional systems that directly output high torque can lead to excessive localized thermal stress. Current technologies typically employ a strategy of limiting motor output power to protect the motor, but this directly results in the driver losing some power steering assistance during the initial cold start, posing a significant safety hazard and affecting normal driving operation. Existing preheating solutions rely on external heating equipment, increasing costs or failing to provide seamless heating before the driver enters the vehicle, and their ability to handle extremely cold conditions remains insufficient.

[0021] To solve the above technical problems, such as Figure 1 As shown, Embodiment 1 of the present invention provides a method for improving the output performance of an electric power steering system for cold starts at low temperatures, applicable to pure electric vehicles or hybrid vehicles, specifically including: The system initialization and low temperature judgment module uses the underlying bus to read low voltage bus voltage, ambient temperature, EPS motor body temperature, vehicle speed, gear, seat occupancy status, and steering wheel angle torque multi-source sensor data to calculate whether the current conditions for unlocking the preheating gate, such as low temperature environment and vehicle stationary state, are met. The multi-source activation and security access module monitors local or remote activation sources, determines the driver's behavioral intentions and vehicle safety boundaries such as anti-towing, and sends heating enable commands containing the desired mode to the underlying controller. The high-frequency d-axis current closed-loop control module sets the quadrature axis target current to zero based on the field-oriented control algorithm, dynamically calculates the direct axis target current based on temperature and voltage, injects high-frequency alternating current using a soft-start strategy combining space vector modulation technology and graded preheating, and performs closed-loop adaptive adjustment based on the temperature rise rate and junction temperature. The safety monitoring and active exit module polls the driver's intention to take over, gear and speed changes, low-voltage power supply abnormalities, and system fault exit conditions at fixed intervals. Upon triggering, it shuts off the entire axle arm to stop heating, records status data, and smoothly switches to the normal torque control mode.

[0022] To better illustrate the technical solution of Embodiment 1 of the present invention, and in conjunction with the method for improving the output performance of the electric power steering system for cold starts in low temperatures, the overall vehicle strategy is explained in detail. Taking a pure electric passenger vehicle equipped with a keyless entry and start system, a 12V low-voltage power supply network, a CAN bus, and an EPS system (including a built-in temperature sensor and a TAS angle and torque sensor) as an example, the method includes the following steps: S1. Wake up the vehicle controller, close the high-voltage relay and stabilize the low-voltage network, read the status of multiple source sensors, calculate whether the current conditions for unlocking preheating, such as low temperature environment and vehicle stationary state, are met, and enter the preheating standby state after determining that the conditions are met. S2. In the preheating standby state, monitor the changes in the status of local doors and seats or receive remote preprocessing instructions, determine the driver's behavioral intentions and vehicle anti-towing safety boundaries, and send heating instructions containing the desired mode to the EPS controller. S3. After receiving the command, the EPS controller switches to self-heating mode, sets the quadrature axis current to zero, and dynamically calculates the direct axis target current based on temperature and voltage. It uses a soft-start strategy that combines space vector modulation technology with graded preheating to inject high-frequency alternating current, calculates the temperature rise rate and power transistor junction temperature, and performs closed-loop adaptive adjustment. S4. During the heating process, continuously poll the driver's intention to take over, changes in gear and vehicle speed, abnormal low-voltage power supply, or system failure conditions for forced exit. Once any condition is met, immediately shut down the entire axle arm to stop heating, record the status data, and smoothly switch to the conventional torque control mode that provides full steering assistance.

[0023] In this invention, the gating signal calculated in step S1 is a prerequisite for starting the self-heating process; the activation source determined in step S2 is the entry point for capturing the driver's intention and triggering the heating action; the high-frequency d-axis current injection executed in step S3 is the execution mechanism for realizing active heating of the motor rotor without torque; the real-time polling and safe exit in step S4 are the boundary defenses to ensure that normal driving is not disturbed and to prevent electrical overload; the above steps work together to construct a full-link closed loop from driver intention recognition, active self-heating closed-loop control to seamless exit and restoration of power assist, which can ensure that the heating process does not affect normal driving, does not damage the motor insulation, and does not cause the battery charge to be too low, and realizes the active release of the power limitation of the steering motor at low temperatures.

[0024] Furthermore, the method for improving the output performance of the electric power steering system during cold starts at low temperatures is described in detail, including the following:

[0025] First, step S1 includes system initialization and low temperature condition determination, which includes the following sub-steps.

[0026] S11. When the driver approaches the vehicle with the key and performs an unlocking operation or issues a remote pre-processing command via a mobile app, the Vehicle Control Unit (VCU) is activated, controlling the high-voltage relay to close and the DC-DC converter (DCDC) to start, converting the power battery energy into a stable 12V low-voltage output to charge the 12V battery. The EPS controller (EPS-ECU) performs a power-on self-test, reading the following status through the underlying bus: low-voltage bus voltage. It is sampled by an ADC with an accuracy of ±0.1V; ambient temperature Temperature from a standalone ambient temperature sensor or a temperature channel integrated into the VCU; EPS motor body temperature. The NTC thermistor pre-embedded inside the EPS controller is calibrated using a temperature model; current vehicle speed The speed is obtained from the wheel speed sensor via the CAN bus; the current gear. (P / R / N / D), from the gear shifter or VCU; driver's seat occupancy status. From the pressure sensor; steering wheel torque With corner , From TAS sensor, accuracy ±0.1Nm.

[0027] S12. The EPS controller calculates whether self-heating needs to be activated and executes the gate condition determination formula: ; where, in the formula This represents a Boolean signal for the preheating gate condition. This signal is set to true if and only if all state conditions on the right side of the expression are simultaneously met, and is used to control the system to enter the preheating standby state. This represents the current external ambient temperature of the vehicle. The two values ​​represent the calibrated ambient temperature activation threshold, and their comparison defines the baseline for initiating heating action in extremely cold environments. Typical calibration values ​​are -15℃ to -20℃. This represents the temperature of the EPS steering motor body, calibrated using the model. This represents the protection temperature limit that triggers the motor power limiting strategy. This condition is used to identify whether there is a risk of cold brittle fracture in the motor insulation material, and because EPS power limiting strategies typically reduce power linearly starting from -10°C, The typical calibration value is -10℃. This represents the vehicle's current actual speed. This represents the maximum safe vehicle speed at which self-heating is permitted, ensuring that high-frequency injection operations are performed only when the vehicle is stationary or crawling at extremely low speeds. The typical calibration value is 3 km / h. This indicates the vehicle's current gear position. This represents the set of safe gears consisting of Park (P) and Neutral (N). The above conditions, combined with the constraint heating strategy, activate only in non-driving gears to isolate the risk of unexpected vehicle towing or movement. This represents the low-voltage bus supply voltage sampled in real time. This represents the minimum safe voltage threshold for maintaining stable operation of the vehicle's low-voltage electrical network. This comparative calculation aims to prevent the low-voltage battery from being drained due to continuous heating power consumption. Typical calibration value is 10.8V, ensuring low-temperature start-up capability. (Symbol) Representing logical intersection operation, it indicates that five types of multi-source physical and state conditions, namely ambient temperature, motor temperature, vehicle speed, vehicle gear, and power supply voltage, must simultaneously reach the set benchmark before the system can output a valid enable command to enter the high-frequency alternating current closed-loop control loop.

[0028] If all of the above conditions are met. If the condition is true, the system enters a preheating standby state, awaiting further driver input or activation via remote command. If any condition is not met, the heating process is skipped, and the system directly enters the regular EPS power assist mode.

[0029] Furthermore, step S2 includes heating activation based on driver behavior and safety boundaries, comprising the following sub-steps: S21. In the preheating standby state, the system monitors the following two types of activation sources: Local activation source: The driver's door was detected to have changed from locked to open, and the seat pressure sensor signal was detected. The steering wheel torque changes from an unoccupied state to an occupied state. A reading of <0.5 Nm indicates that the driver has not actively turned the steering wheel. This activation point signifies that the driver is about to sit down but has not yet started driving, and is the trigger point for activating the heating system.

[0030] Remote activation source: When the vehicle is connected to the internet, the user sends a remote pre-processing command via a mobile app, and the power battery... ,in To prevent over-discharge of the high-voltage battery, a low-battery protection threshold is set. At this point, there's no need to wait for the door to open; the system can directly activate heating, but conditions must be met, including vehicle speed being zero, gear being in Park (P), and battery voltage being safe.

[0031] S22, when any activation source is valid and step S12 is complete... When true, the VCU sends a CAN message HeatingCmd=1 to the EPS controller, along with the desired heating mode, including standard mode or fast mode, with fast mode corresponding to a higher d-axis current.

[0032] S23. The system also sets mandatory prohibition conditions: if ADAS function is detected to be activated, such as APA automatic parking in progress, or the vehicle is in towing mode, the vehicle speed is >3km / h and the gear is not P, then the VCU will forcibly set HeatingCmd=0 and notify the EPS controller to cancel heating via the CAN bus.

[0033] Furthermore, step S3 includes closed-loop control of the active heating of the EPS motor, comprising the following sub-steps: S31. Upon receiving HeatingCmd=1, the EPS controller immediately switches from the normal torque assist mode to the self-heating mode. Its control algorithm is based on field-oriented control (FOC) and sets the quadrature-axis target current. To avoid generating any driving torque; S32, Direct-axis target current Based on the current motor temperature and low-voltage bus voltage Dynamic calculation: ; Where, in the formula, Representing the direct-axis target current, it is a control command used in the field-oriented control algorithm to generate stator high-frequency Joule heating and core eddy current losses without generating average quadrature-axis drive torque. This represents the minimum value function, used to select the smaller value between the dynamic temperature current limit and the steady-state hardware power limit to implement the most stringent underlying hardware protection mechanism. This represents a temperature-current limiting function. Based on the elongation at break and physical brittleness characteristics of polyesterimide enameled wire in different low-temperature ranges, this function outputs the maximum stator current allowed to pass under the current condition. This is used to prevent excessively rapid local transient temperature rise from causing thermal stress microcracks. For example, when... Take 0.4 when <-20℃. When -20℃≤ Take 0.6 when the temperature is below -10℃. ,when Temperature drops to 0 at ≥-10℃ (heating stops). This refers to the rated current of the EPS motor. The temperature of the EPS motor body, which is dynamically calibrated by the internal temperature model, is used as the input of the limiting function to form a closed-loop feedback. This parameter represents the maximum continuous power loss that the power switching transistors in the three-phase bridge drive circuit of the EPS controller can withstand. It sets the physical upper limit of heat dissipation at the inverter hardware level to prevent thermal breakdown caused by the accumulation of heat during high-frequency switching modulation, which could lead to excessive junction temperature of the power semiconductor devices. This represents the stator winding phase resistance after dynamic correction by a temperature compensation coefficient. This resistance value is updated in real time with changes in motor temperature, reflecting the transient physical impedance characteristics of the winding. , .constant The phase number coefficient represents the phase resistance of a three-phase motor with star or delta connection. The fundamental multiplier for determining the total heating power of the three-phase system is determined together. The formula extracts the system's highest power dissipation boundary and divides it by the total transient resistance of the three phases, performing a square root operation to ensure dimensional consistency. This completes the equivalent conversion from power and resistance dimensions to current dimensions, outputting the theoretically maximum allowable effective value of the phase current under the power dissipation limit. Through dual constraints of insulation material temperature-current limiting and inverter hardware thermal power boundary, this formula ensures that the heating alternating current injected into the motor windings remains within the physical safety domain.

[0034] S33. To avoid audible noise, the PWM switching frequency is set to... =20kHz, higher than the upper limit of human ear sensitivity of 15-18kHz, and uses space vector modulation (SVPWM) to improve DC bus utilization.

[0035] S34. Due to the sharp decrease in the elongation at break of the insulating material (polyesterimide enameled wire) at low temperatures, applying a full-amplitude current instantaneously may cause microcracks in the enamel film due to Joule thermal shock. Therefore, this embodiment adopts a soft-start strategy combining staged preheating with high-frequency d-axis current injection to avoid the quadrature-axis torque component caused by the rotation of the current vector space. Warm-up phase (first 15 seconds): Settings ,Keep The inverter injects a direct-axis high-frequency alternating current (20kHz) into the motor stator windings, which is completely parallel to the direction of the rotor magnetic field. Since the current vector is locked to the d-axis, the rotor does not experience any average electromagnetic torque, and the steering wheel remains stationary.

[0036] Rapid heating stage: when The temperature rises above the preset brittle transition temperature threshold. (For example, at -18℃) the system will Increased to 0.65 Continue to maintain At this point, the motor's copper losses and high-frequency core losses further increase, leading to a faster rate of temperature rise. To monitor winding hotspots, the EPS controller's built-in high-frequency current sampling module calculates the effective value of the three-phase current every 1ms. If the current in any phase exceeds 1.1 This indicates a local overcurrent, so immediately... Reduce by 10% and record any abnormal events.

[0037] Alternative Note: In some implementations, a square wave current with a frequency of several hundred Hz to several kHz can be injected into the d-axis. This also does not generate torque, but it can increase eddy current losses in the core. However, regardless of the waveform used, it is essential to maintain... This is to ensure that there is no additional torque output.

[0038] S35. The system calculates the temperature rise rate of the motor windings in real time: ; in, It represents the real-time temperature rise rate of the motor windings, reflecting the dynamic change gradient of heat accumulation inside the stator windings per unit time. Represents the system at the current moment The transient temperature of the motor body, calculated by the built-in thermistor and temperature calibration model, is used as the real-time temperature observation value for the current closed-loop control cycle. This indicates that the system was in the previous measurement and control cycle, i.e. The historical motor body temperature parameters, which are locked in the controller's memory at all times, form a discrete difference sequence in the time dimension with the current temperature variable. The time interval between two adjacent temperature samples and the fixed calculation step size of the temperature rise rate monitoring module define the time resolution for the system to perform discrete differential calculations. Numerator term Calculate the absolute temperature increment of the motor within a single measurement and control step, and divide it by the time denominator. It satisfies the principle of consistency of physical dimensions and outputs a transient temperature rise rate reference feedback quantity used to drive the proportional-integral regulator to dynamically correct the heating current and prevent the generation of Joule thermal shock microcracks in the insulated enameled wire.

[0039] S36. By comparing the actual temperature rise rate with the preset safe temperature rise rate range through the proportional-integral regulator, the direct-axis current command amplitude is automatically reduced in the reverse direction when the temperature rise rate exceeds the upper limit; the junction temperature of the power transistor is collected synchronously, and the switching frequency is temporarily reduced and the current is reduced proportionally when the junction temperature approaches the safe boundary, thus constructing a dual closed-loop adaptive adjustment defense line.

[0040] Specifically, for example: assume the maximum permissible temperature rise rate of the copper winding at low temperatures is calibrated to be 0.8℃ / s. If... If the temperature exceeds 1.0℃ / s, the PI controller will automatically reduce its speed. The goal is to maintain the temperature rise rate within the range of 0.5-0.8℃ / s. Conversely, if the temperature rise rate is below 0.2℃ / s and the heating time has exceeded 30 seconds, the rate should be gradually increased. (Increases by 5% each time, with a maximum of 0.8) In addition, the junction temperature of the power transistor (MOSFET) is obtained by the EPS controller through a built-in temperature sensor. .like If the temperature exceeds 105℃, temporarily reduce the PWM switching frequency to 16kHz to reduce switching losses and simultaneously reduce... 20%, until Temperatures have dropped below 95°C.

[0041] Furthermore, S4 includes mandatory exit based on human intervention and security boundaries, comprising the following sub-steps: S41. During the heating process, the EPS controller continuously polls the following conditions at a preset period (e.g., 10ms). Once any condition is met, heating is immediately stopped, and the control mode is switched back to the normal torque assist mode: Condition A - Driver takeover intention: Driver's seat pressure The change from an unoccupied state to an occupied state indicates that the driver is seated and the steering wheel torque is adjusted. (Calibration value 1.0 Nm), or the rate of change of rotation angle. >30° / s. This indicates that the driver has begun to actively operate the steering wheel and requires immediate assistance. To avoid false triggering of the seat pressure signal due to body movement, the system incorporates a 50ms de-jitter filter: it is only considered valid if the pressure signal remains stable for more than 100ms.

[0042] Condition B - Vehicle enters driving preparation state: Gear shifted from P / N to D or R, and vehicle speed... > The starting threshold (e.g., 0.5 km / h) indicates that the driver is about to start and the heating should be turned off immediately to ensure the steering assist response.

[0043] Condition C - Low-voltage power supply safety: Bus voltage The duration of the power failure threshold (e.g., 10.5V) exceeds 200ms. EPS is one of the main loads of the 12V system. If the voltage is too low, it may cause the vehicle controller or instrument panel to restart. Therefore, power preservation should be given priority.

[0044] Condition D - System-level interlock: Automatic parking is activated when the ADAS system detects an APA_Active=1 signal; internal fault flags in the EPS controller (such as overcurrent, overtemperature, or communication loss) are set; motor temperature... Exceeded (e.g., -5℃) indicates that no further heating is needed and the temperature has already exceeded the power limit release threshold.

[0045] Condition E - Remote command cancellation: HeatingCmd=0 is received from VCU.

[0046] S42. When any of the above conditions are triggered, the EPS controller performs the following operations: Immediately Set the transistors to zero and disconnect all power switches (both upper and lower bridge arms are off), thus entering the full bridge arm off state. This state does not provide any freewheeling path, and the residual energy in the motor windings will be naturally fed back to the bus capacitor through the anti-parallel diodes, without generating unexpected braking or driving torque.

[0047] As an alternative safety mode, in some systems requiring rapid braking energy release, all lower arm switches can be turned on when heating is discontinued to achieve active short circuit. This embodiment preferentially uses full arm shutdown.

[0048] Record the current heating time and highest temperature Stored in non-volatile memory.

[0049] S43. Send a status message HeatState=0 to the VCU, along with an exit reason code, such as 0x01 indicating driver takeover, 0x02 indicating low voltage, etc.

[0050] Switch to normal torque control mode, at this time From steering wheel torque signal and vehicle speed Determined by the basic helper mapping table: ; Where, in the formula, Representing the quadrature-axis target current, it is the control command component in the field-oriented control algorithm that directly determines the effective electromagnetic torque output by the motor. This represents the basic assist mapping table stored in the EPS controller's memory, used to calculate the baseline value of the basic assist requirement under rated thermodynamic conditions based on the input dynamic physical parameters. This represents the steering wheel torque signal collected in real time by the steering angle torque sensor, reflecting the magnitude and direction of the physical force exerted by the driver when operating the steering wheel, and constitutes the pre-input parameter of the basic power steering mapping; This represents the current actual vehicle speed obtained through the underlying bus, serving as another control dimension for power steering mapping, used to achieve dynamic adjustment of steering characteristics from low-speed high power steering to high-speed low power steering. This represents the system's internally set low-temperature compensation factor, a dimensionless proportionality coefficient responsible for performing protective safety limiting or derating corrections on the target drive current under extremely cold conditions. The formula analyzes the driver's steering intention, vehicle driving state, and motor thermodynamic boundaries to output the target current command used to drive the motor to generate steering assistance.

[0051] Among them, the basic assistance mapping table This is used to solidify the core steering feel characteristics of the EPS system, establishing a non-linear mapping relationship between steering wheel torque, vehicle speed, and target auxiliary current. The mapping table is based on vehicle speed. The dimension is divided into multiple discrete feature calibration nodes (e.g., 0km / h, 20km / h, 60km / h, 120km / h). Under low-speed conditions, a high assist gradient needs to be set to reduce the physical load on the driver when steering in place or at low speeds; under high-speed conditions, the assist gradient needs to be reduced and the center physical dead zone range expanded to maintain the stability of the vehicle during high-speed straight-line driving. At a single vehicle speed node, the steering wheel torque... The input variation is used to calibrate the assist curve. This curve is divided into a center dead zone (to suppress false assist caused by minor road disturbances and sensor drift), a linear transition zone (to provide smooth and predictable electromagnetic assist feedback), and a saturation zone (to limit the physical upper limit of motor torque output). Engineering calibration personnel collect objective steering load and subjective driving experience data through real-vehicle road tests. The continuous physical characteristic curve is discretized and transformed into a two-dimensional matrix array, which is then burned and stored as constant data in the non-volatile memory of the EPS controller. When the system is in the normal torque control mode or after reaching the safety boundary conditions and exiting the low-temperature active heating phase, the EPS controller dynamically executes the lookup table logic within the basic control cycle. The controller receives the real-time steering wheel torque output from the TAS sensor via internal hardwire. It also obtains the current vehicle speed broadcast by the wheel speed sensor via the CAN bus. Before entering the lookup table logic unit, the two dynamic physical parameters need to undergo low-pass filtering to eliminate signal abrupt changes caused by high-frequency mechanical vibration or electromagnetic crosstalk. Real-time coordinate points under actual operating conditions. It is difficult to accurately locate the fixed discrete matrix nodes. The controller runs an addressing algorithm to locate the four adjacent calibration nodes surrounding the current input coordinates, and uses a bilinear interpolation algorithm to calculate the rated base assist reference value for a smooth transition. The base assist reference value obtained by looking up the table is input to the subsequent multiplier unit, along with the low temperature compensation factor. Perform proportional calculations. Since the heating exit conditions have been met... The system is now in a safe physical operating region, the compensation factor has converged to a full proportional coefficient value of 1, and the system directly outputs the quadrature-axis target current. The bottom-level magnetic field orientation control module drives the motor to output full steering assist.

[0052] As an optional embodiment, when the seat pressure changes from an occupied state to an unoccupied state, but the steering wheel torque remains zero and the gear position remains unchanged, the system will not immediately disengage the heating, but will instead enter a state of maintaining heating but reducing power. (Reduce by 50%). If the driver does not return to their seat after 10 seconds, the heating will be completely deactivated to save energy.

[0053] As an optional embodiment, if a detection is made during the heating process... If the voltage drops below 10.5V but lasts for less than 100ms (e.g., due to other load surges), the system will not immediately shut down, but will instead... The voltage is temporarily limited to 20% of the rated value, and then gradually increased back up after the voltage recovers to above 11V. This function can prevent the power transistor from being overloaded by frequent start-stop cycles.

[0054] As an optional embodiment, in remote pre-processing mode, if the system detects the driver's approach (distance < 3 meters) via changes in the RSSI intensity of the Bluetooth key or the capacitive sensing of the door handle, and the seat pressure has not yet been triggered, the system switches the heating current from the fast mode to the standard mode, and simultaneously indicates that heating is in progress via exterior lights or a buzzer. Once the door is opened, the system immediately proceeds to step S4, driver takeover monitoring.

[0055] As an optional embodiment, if the EPS controller reads If the temperature exceeds a reasonable range (e.g., below -50℃ or above 150℃), or if five consecutive sampling values ​​show a change exceeding 20℃, the temperature sensor is considered faulty. In this case, the system will adopt a conservative heating strategy: setting the direct-axis target current. For a fixed conservative value (e.g., 0.2) This strategy maintains closed-loop control while imposing a total heating time limit (e.g., 60 seconds). This approach avoids motor overheating damage due to sensor failure without compromising the stability of the FOC closed-loop.

[0056] In the above embodiments, during the vehicle's low-temperature cold start phase (the time window from when the driver unlocks the vehicle to when they engage gear and drive), the vehicle control unit (VCU) and the EPS controller work together. Utilizing the existing three-phase bridge drive circuit of the EPS system, a controllable high-frequency alternating current is injected into the motor windings, causing the motor to actively heat up. Simultaneously, multi-source sensors monitor the driver's intentions and vehicle safety boundaries in real time, ensuring that the heating process does not affect normal driving, damage the motor insulation, or cause the battery charge to drop too low. Once the motor temperature reaches the threshold for releasing the power limit, the system automatically disengages the heating, allowing the driver to receive full power steering assistance, thus resolving the issue of the driver feeling excessive force during initial start-up.

[0057] 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; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for improving the output performance of a cold-start electric power steering system at low temperatures, characterized in that, include: Wake up the vehicle controller, read the status of multiple source sensors, and enter the preheating standby state when the conditions are met; In the preheating standby state, a heating command is sent to the steering controller after it is determined that the driver's intention and safety boundary conditions are met; After receiving the heating command, the electric power steering controller switches to self-heating mode, sets the quadrature axis current to zero, and dynamically calculates the direct axis target current based on temperature and voltage. It injects high-frequency alternating current using a soft-start strategy that combines space vector modulation technology with graded preheating, and adjusts the closed loop based on the temperature rise rate and power transistor junction temperature. During the heating process, the system polls for driver takeover intentions, gear and speed changes, low-voltage power supply abnormalities, or system malfunctions that force the system to exit. Once any of these conditions are met, the system immediately shuts off the entire axle arm to stop heating and smoothly switches to the conventional torque control mode that provides full steering assistance.

2. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 1, characterized in that, The conditions for determining whether to enter the preheating standby state include: Compare ambient temperature with ambient temperature activation threshold, steering motor body temperature with power limit protection temperature limit, vehicle speed with maximum vehicle speed safety threshold, and low voltage bus voltage with minimum safe voltage threshold. If the ambient temperature is confirmed to be below the ambient temperature activation threshold, the steering motor body temperature is below the power limit protection temperature limit, the vehicle speed is below the maximum vehicle speed safety threshold, the gear is in parking or neutral, and the low voltage bus voltage is above the minimum safe voltage threshold, then the unlocking preheating conditions are determined to be met.

3. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 1, characterized in that, Determining whether the driver's intent and safety boundary conditions are met includes monitoring both local and remote activation sources: The triggering conditions for the local activation source are: the driver's door changes from locked to open, the seat changes from unoccupied to occupied, and the steering wheel torque in the steering wheel angle torque is less than a preset rotation threshold. The triggering condition for the remote activation source is receiving a remote preprocessing instruction and the remaining power of the power battery being higher than the low power protection threshold.

4. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 1, characterized in that, The steps for determining the direct-axis target current include: The corresponding temperature current limit value is obtained based on the current temperature of the steering motor body, and the steady-state hardware power limit value is obtained based on the maximum continuous power loss of the power switch and the phase resistance of the stator winding after temperature compensation correction. By comparing the temperature current limit value with the steady-state hardware power limit value, the smaller of the two values ​​is selected as the direct-axis target current.

5. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 4, characterized in that, The closed-loop adjustment includes: Obtain the real-time temperature of the steering motor body in the current measurement and control cycle and the historical temperature of the steering motor body in the previous measurement and control cycle, and calculate the absolute temperature increment of the two. Divide the absolute temperature increment by a fixed calculation step size to obtain the transient temperature rise rate reference feedback; The transient temperature rise rate reference feedback is compared with the preset safe temperature rise rate range. When the temperature rise rate exceeds the upper limit, the amplitude of the direct-axis target current is reduced in the opposite direction by the proportional-integral regulator.

6. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 1, characterized in that, The soft-start strategy includes a preheating phase and a rapid heating phase; During the preheating stage, the initial direct-axis target current is set to the first proportional value of the rated current of the steering motor, and a direct-axis high-frequency alternating current parallel to the rotor magnetic field direction is injected into the stator winding. During the rapid heating phase, when the temperature of the current steering motor body rises above a preset brittle transition temperature threshold, the direct shaft target current is increased to a second proportional value of the steering motor rated current, wherein the second proportional value is greater than the first proportional value.

7. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 1, characterized in that, The forced exit conditions include: The driver's intention to take over is detected. The criteria for this are: the seat occupancy status changes to occupancy and the steering wheel torque in the steering wheel angle torque is greater than the preset takeover torque threshold, or the steering wheel angle change rate is greater than the preset angle change rate threshold. The system detects that the gear has been shifted to drive or reverse and the vehicle speed exceeds the starting threshold. The low-voltage bus voltage was detected to be below the power outage threshold and remained below the preset time. Automatic parking activation or a system-level fault is detected, and a remote command is received to cancel it.

8. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 7, characterized in that, The step of stopping heating and switching to the normal torque control mode includes: Immediately set the direct-axis target current to zero, disconnect all power switching transistors to enter the full bridge arm off state, and record the current heating duration and highest temperature; Based on the steering wheel torque signal and the current vehicle speed, the basic assist reference value is calculated through the basic assist mapping table. Then, the basic assist reference value is adjusted proportionally using a low temperature compensation factor determined by the current steering motor body temperature, and a new cross-axis target current is output to drive the motor to generate steering assist.

9. The method for improving the output performance of a low-temperature cold-start electric power steering system according to claim 8, characterized in that, The process of calculating the basic assist reference value through the basic assist mapping table includes: locating the adjacent calibration nodes surrounding the current input coordinates, and using a bilinear interpolation algorithm to calculate the rated basic assist reference value for smooth transition.

10. A system for improving the output performance of a cold-start electric power steering system, comprising the method described in any one of claims 1-9, characterized in that, include: The system initialization and low temperature determination module is used to wake up the vehicle controller to close the high voltage relay and stabilize the low voltage network, and read the status of multiple source sensors to calculate whether the current unlocking preheating conditions are met. The multi-source activation and safety access module is used to monitor changes in the status of local doors and seats or receive remote pre-processing instructions in the preheating standby state, determine the driver's behavioral intentions and the safety boundary of the trailer vehicle, and send heating instructions containing the desired mode to the controller. The high-frequency direct-axis current closed-loop control module is used to set the quadrature-axis target current to zero, dynamically determine the direct-axis target current based on temperature and voltage, and inject high-frequency alternating current using a soft-start strategy that combines space vector modulation technology with graded preheating. The safety monitoring and active exit module is used to poll the driver's intention to take over, gear and speed changes, low voltage power supply abnormalities and system fault exit conditions at fixed intervals, and execute the full axle arm shutdown to stop heating after triggering, record status data and smoothly switch to the normal torque control mode.

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