Auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation

Abstract

The application discloses an auxiliary winding type electric power steering motor capable of actively suppressing vibration and torque pulsation, which comprises a main three-phase winding for generating a steering assist torque, and an auxiliary three-phase winding arranged in the same stator slot as the main three-phase winding but electrically isolated from each other. The auxiliary three-phase winding is driven by an independently controlled inverter stage for injecting high-frequency harmonic cancellation current. By generating an anti-phase magnetic motive force (MMF) opposite to the torque pulsation, vibration component and road disturbance generated by the main three-phase winding, the application can effectively reduce the noise, vibration and harshness (NVH) of the steering column. When the main inverter fails, the auxiliary three-phase winding can also provide redundant torque capacity. The architecture does not require additional mechanical dampers and does not increase the computing load of the electronic control unit (ECU), and can improve the NVH performance of the EPS.

Description

Technical Field

[0001] This invention relates to the field of electric drive motors, and in particular to an auxiliary winding type electric power steering motor that actively suppresses vibration and torque pulsation. Background Technology

[0002] With the rapid development of vehicle electrification and intelligent driving, electric power steering (EPS) systems have been widely used in passenger cars and commercial vehicles. However, traditional EPS motors are prone to torque pulsation and cogging torque. Cogging torque originates from the interaction between the rotor permanent magnet and the stator slot magnetic permeability changes, producing periodic pulsations even under no-load conditions. Furthermore, inverter harmonics, winding distribution effects, and mechanical eccentricity can cause dynamic torque pulsations in the 20–400 Hz frequency band. These disturbances are transmitted to the steering column and steering wheel, resulting in noise, vibration, and acoustic harshness (NVH), reducing driving comfort and perceived vehicle quality.

[0003] Existing NVH (Noise, Vibration, and Harshness) reduction technologies for electric power steering (EPS) systems mainly fall into the following categories: 1. Software-based torque ripple suppression technology implemented in the motor controller. This type of technology requires the electric power steering electronic control unit (EPSECU) to allocate a large amount of computing resources and is difficult to tune parameters for varying driving conditions; 2. Solutions using mechanical dampers or vibration isolators. This solution increases the system's weight, complexity, and cost, and often degrades steering feel; 3. High-precision magnet shaping or stator skew design. While this design can reduce torque ripple, it increases manufacturing costs and reduces torque density.

[0004] Therefore, these solutions have the following problems: 1. Increased computational load on the electronic control unit (ECU). 2. Inability to completely counteract vibrations under varying road conditions and resonance conditions. 3. Requirement of additional mechanical components such as shock absorbers or isolators, leading to increased costs and complexity.

[0005] Therefore, there is an urgent need for an auxiliary winding type electric power steering motor that can actively suppress vibration and torque pulsation. This EPS motor can internally suppress vibration to reduce reliance on complex ECU algorithms and mechanical damping devices. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides an auxiliary winding type electric power steering motor that actively suppresses vibration and torque pulsation, solving the following technical problems: 1. Increased computational load on the electronic control unit (ECU). 2. Inability to completely eliminate vibration under varying road conditions and resonance conditions. 3. Requirement of additional mechanical components (such as dampers or vibration isolators), increasing cost and complexity.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: an auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation, comprising: a stator and a rotor, wherein the stator has multiple stator slots and the rotor is a surface-mounted permanent magnet rotor; a main three-phase winding, arranged in the stator slots, adopting a delta connection and electrically connected to the main inverter, for outputting steering assist torque; and an auxiliary three-phase winding, arranged in the same slot as the main three-phase winding and electrically isolated from the main three-phase winding by an insulating gasket, forming a two-layer coil structure with the inner layer being the main three-phase winding and the outer layer being the auxiliary three-phase winding, wherein the auxiliary three-phase winding adopts a star connection with an internal isolated neutral point, and the neutral point is not connected to the main inverter. The three-phase winding connection point or chassis connection; a dual inverter architecture, integrated on the same PCBA and controlled by the same MCU, includes a main inverter electrically connected to the main three-phase winding, and a low-power half-bridge auxiliary inverter controlled by an additional MOSFET / PWM channel and electrically connected to the auxiliary three-phase winding through an independent terminal; wherein, the auxiliary inverter is used to drive the auxiliary three-phase winding to inject a compensation current that is opposite in phase and frequency matched to the torque pulsation of the main three-phase winding, so as to reduce cogging torque, torque fluctuation, noise, vibration and acoustic roughness, and the auxiliary three-phase winding is used to provide emergency assistance in the event of failure of the main three-phase winding or the main inverter.

[0008] As a preferred embodiment of the present invention, the auxiliary three-phase winding is wound in the same direction as the main three-phase winding to maintain a uniform magnetic flux direction. It can be arranged above the main three-phase winding or separated by an isolation pad. The turns ratio of the two is 1:3. The ampere-turns of the auxiliary three-phase winding are limited to 10-15% of those of the main three-phase winding. The turns ratio makes the inductance of the auxiliary three-phase winding 1 / 9 that of the main three-phase winding, thereby achieving high-frequency compensation current injection of 20-400Hz.

[0009] As a preferred embodiment of the present invention, the auxiliary three-phase winding uses 0.6-0.8 mm enameled copper wire with 10-12 turns per slot, and the main three-phase winding uses 1.5 mm diameter enameled copper wire with 30 turns per slot.

[0010] As a preferred embodiment of the present invention, the neutral point of the auxiliary three-phase winding is set in isolation and is not connected to the connection point of the main three-phase winding or the chassis; the independent terminal of the auxiliary three-phase winding is soldered to a dedicated pad in the auxiliary inverter area of ​​the PCBA, and the output terminal of the auxiliary three-phase winding is connected to form an isolated neutral point.

[0011] As a preferred embodiment of the present invention, a steering torque sensor and a rotor position encoder are configured; the controller identifies torque fluctuations or steering column resonance frequencies in the 20–400Hz frequency band by real-time Fourier transform or adaptive notch filtering based on the signals collected by the steering torque sensor and rotor position encoder, and drives the auxiliary three-phase winding to inject a compensation current with the opposite phase to the fluctuation; the controller has a built-in frequency mapping function, which is used to store frequency calibration values ​​according to the vehicle platform and compensate for the target fluctuation frequency.

[0012] As a preferred technical solution of the present invention, the 20-400Hz frequency band corresponds to the steering column resonance and road surface excitation vibration. The compensation current injected into the auxiliary three-phase winding can realize the attenuation of road noise and the vibration filtering caused by lane change bumps. Moreover, the compensation current injection does not interfere with the main three-phase winding assist circuit.

[0013] As a preferred technical solution of the present invention, when the main three-phase winding or the main inverter fails, the controller can reconfigure the control parameters of the auxiliary inverter, switch the auxiliary three-phase winding from NVH suppression mode to emergency assist mode, and provide emergency assist torque of 10%-15% of the rated torque.

[0014] As a preferred embodiment of the present invention, the motor includes a stator back iron, and a mechanical stress control ring is provided on the outer periphery of the stator back iron. The mechanical stress control ring is installed on the outside of the stator back iron by interference fit. The outside of the mechanical stress control ring is the motor housing. The mechanical stress control ring is made of elastic metal material and is used to improve the circumferential stiffness of the stator and reduce structural vibration under radial electromagnetic force excitation. The mechanical stress control ring cooperates with the harmonic cancellation current control of the auxiliary three-phase winding to form a dual vibration suppression system of structural vibration suppression and magnetomotive force compensation, so as to improve the torque pulsation suppression efficiency.

[0015] As a preferred embodiment of the present invention, the mechanical stress control ring is made of a highly elastic metal material, and the thickness of the mechanical stress control ring is 0.3–0.8 mm.

[0016] This invention also provides a method for operating an auxiliary winding type electric power steering motor that actively suppresses vibration and torque pulsation, comprising: Under normal steering conditions, the main inverter drives the main three-phase winding to output steering assist torque. The controller identifies the target torque fluctuation component based on the signals collected by the steering torque sensor and rotor position encoder, and controls the auxiliary inverter to inject a compensation current that is opposite in phase and matches the frequency of the target torque fluctuation component into the auxiliary three-phase winding, which is co-slotted with and electrically isolated from the main three-phase winding. This causes the auxiliary three-phase winding to generate a reverse magnetomotive force on the same magnetic axis as the main three-phase winding, thereby reducing cogging torque, torque fluctuation, noise, vibration and acoustic roughness. Under fault conditions, the controller monitors the status of the main three-phase winding or the main inverter in real time. When a fault is detected, the control parameters of the auxiliary inverter are reconfigured, so that the auxiliary three-phase winding switches from the compensation mode to the emergency assist mode and outputs an emergency assist torque of 10%-15% of the rated torque.

[0017] Compared with the prior art, the beneficial effects that this invention can achieve are: 1. The main three-phase winding adopts a three-phase delta or star connection to generate torque and is connected to the main inverter stage; the auxiliary three-phase winding adopts a three-phase star connection with an independent neutral point to cancel harmonics and is connected to an independent auxiliary inverter stage. The auxiliary three-phase winding is completely isolated from the main three-phase winding to avoid cross-interference. 2. The auxiliary three-phase winding is concentrically wound in the same stator slot as the main three-phase winding, but has fewer turns and a thinner conductor wire diameter, resulting in lower inductance and smaller back electromotive force, thus enabling high-bandwidth current injection.

[0018] 3. During coordinated control, the main three-phase winding provides assist torque, while the auxiliary three-phase winding injects reverse magnetomotive force at frequencies corresponding to the cogging torque harmonics and NVH frequency bands, suppressing cogging torque and offsetting fluctuations, significantly reducing steering vibration and noise, and achieving smoother operation. 4. The auxiliary three-phase winding current is limited to within 15% of the main magnetomotive force to minimize copper loss and slot fill factor redundancy. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the main three-phase winding of the present invention; Figure 2 This is a schematic diagram of the main three-phase delta winding used for torque in an EPS motor. Figure 3 This is a schematic diagram of the auxiliary three-phase windings used for NVH suppression in an EPS motor. Figure 4 Schematic diagram of star-connected auxiliary three-phase winding configuration for NVH suppression in EPS motors; Figure 5 Flowchart of NVH suppression algorithm for auxiliary three-phase windings of EPS motor; Figure 6 This is a block diagram of the internal structure of a PCBA. Figure 7 A schematic diagram showing the distribution of the main three-phase windings and the auxiliary three-phase windings; in: 1. Stator back iron; 2. Mechanical stress control ring; 3. Shell; 4. Stator teeth; 5. Inner lining; 6. Main three-phase winding copper coils; 7. Outer padding; 8. Auxiliary three-phase winding copper coil; 9. Top tape; AuxU-in, auxiliary U-phase input; AuxU-out, auxiliary U-phase output; AuxV-in, auxiliary V-phase input; AuxV-out, auxiliary V-phase output; AuxW-in, auxiliary W-phase input; AuxW-out, auxiliary W-phase output; Aux-Nuetral, auxiliary neutral line; PCBA, printed circuit board assembly; MCU, microcontroller. Detailed Implementation

[0020] To make the technical means, creative features, objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments. However, the following embodiments are merely preferred embodiments of this invention and not all of them. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the protection scope of this invention.

[0021] Table 1. Configuration of the Main Three-Phase Delta Winding Structure in EPS Motors ; Table 2. NVH Suppression Auxiliary Three-Phase Winding Configuration Table for Electric Power Steering (EPS) Motors ; Example 1: Basic EPS Motor Structure In this embodiment, as Figures 1-2 As shown, the stator has 12 slots, and the rotor has an 8-pole structure. Each slot is wound with 30 turns of 1.5 mm diameter copper wire, and the windings are distributed in a three-phase delta configuration. The U, V, and W phases each occupy 4 slots, with an electrical angle interval of 120°. By aligning the magnetic polarity through alternating winding directions (clockwise / counterclockwise), the induced electromotive force of each coil is positively superimposed within each phase. The three phases are then connected in a delta configuration, outputting strong torque, suitable for EPS systems.

[0022] Basic EPS motor specifications (refer to Table 1) 1. Number of stator slots: 12 (S1–S12 arranged clockwise) 2. Number of rotor poles: 8 poles (surface-mounted permanent magnets) 3. Wire diameter: 1.5 mm enameled copper wire 4. Number of turns per slot: 30 turns 5. Connection method: Three-phase delta (U, V, W terminals) EPS motor main three-phase winding delta connection U-phase: S1 (U1+) → S4 (U1-) → S7 (U2+) → S10 (U2-) → U-terminal V phase: S3 (V1+) → S6 (V1-) → S9 (V2+) → S12 (V2-) → V terminal W phase: S5 (W1+) → S2 (W1-) → S11 (W2+) → S8 (W2-) → W terminal Delta connection: Connect the ends of the coils to form a closed delta circuit for phases U, V, and W. Each connection point serves as an output terminal. Each phase (U, V, W) contains two sets of coils (e.g., U1 and U2), wound in series—therefore, each phase has one start lead and one end lead.

[0023] Triangle closure connection method: Connect the U-phase end (S10) to the V-phase start end (S3). Connect the V phase end (S12) to the W phase start end (S5). Connect the W phase end (S8) to the U phase start end (S1). Terminal block designation: U = [S1 + S8], V = [S3 + S10], W = [S5 + S12] Example 2: Auxiliary three-phase windings for NVH suppression in EPS motors like Figures 1-5 As shown, the electric power steering (EPS) motor is equipped with a dual-winding stator, including both a primary three-phase winding for generating torque and an auxiliary three-phase winding for noise and vibration cancellation (NVH suppression). Figure 7 As shown, the EPS motor includes stator teeth 4 evenly distributed within the stator back iron 1. The outer side of the stator teeth 4 is wrapped with an inner layer pad 5. The outer side of the inner layer pad 5 is wound with the main three-phase winding copper coil 6. Then, an outer layer pad is wrapped around the main three-phase winding for insulation. After the insulation is completed, the auxiliary three-phase winding copper coil 8 is wound to form a complete EPS motor stator. Finally, a top tape 9 can be wrapped around the stator to provide mechanical fixation and additional insulation. like Figure 6As shown, the three main three-phase windings (U, V, W) and the three auxiliary three-phase windings (AuxU, AuxV, AuxW) can be connected via two inverters controlled by an MCU within the same PCBA. These two inverters then control the main and auxiliary three-phase windings respectively. Therefore, the auxiliary three-phase windings are electrically isolated within the same PCBA by using a separate low-power inverter. No additional PCBA is required; only additional MOSFET / PWM channels need to be added within the same main PCBA. A MOSFET is a metal-oxide-semiconductor field-effect transistor, a voltage-controlled element; PWM, or pulse width modulation, is a technique for adjusting the pulse width.

[0024] The auxiliary three-phase winding has the following characteristics (refer to Table 2): 1. Winding direction and connection method The auxiliary three-phase windings are wound in the same direction as the main coils in each slot (as shown in Table 2) to maintain a consistent magnetic flux direction. The auxiliary three-phase windings are connected in a star (Y) configuration, with the neutral point internally connected. The neutral point of the auxiliary three-phase windings is completely isolated from the star or delta connection of the main three-phase windings.

[0025] Three starting leads, AuxU (auxiliary U phase), AuxV (auxiliary V phase), and AuxW (auxiliary W phase), are individually led out and connected to a separate auxiliary inverter stage on the control printed circuit board. When the primary three-phase windings generate boost torque, cogging torque and inverter harmonics produce vibrational components. The auxiliary three-phase windings, driven by a small inverter, are injected with a controlled, counter-current of high frequency to generate a reverse magnetomotive force to counteract torque fluctuations. Because the auxiliary three-phase windings are low-inductance and isolated, they can track harmonics up to 200–400 Hz without interfering with the boost torque.

[0026] 2. Wires and number of turns Recommended conductor diameter: 0.6–0.8 mm enameled copper wire (≈ US wire gauge 22–20).

[0027] Recommended number of turns per slot: 10 turns (range 10–12 turns depending on slot fill rate).

[0028] This configuration achieves: a turns ratio of ≈10 / 30 = 1 / 3 (relative to the main three-phase windings). Inductance ratio ≈ (1 / 3) 2 =1 / 9 (relative to the main three-phase winding), enabling high-frequency current tracking up to approximately 400Hz.

[0029] 3. Electromagnetic properties Magnetomotive force margin: The auxiliary current is limited to about 0.3 times the main peak current. At this time, the magnetomotive force generated by the auxiliary three-phase winding is about 10% of that of the main three-phase winding, which is sufficient to offset the torque fluctuation harmonics and will not interfere with the assist torque.

[0030] Back EMF: approximately one-third of the main three-phase winding, ensuring that the auxiliary three-phase winding does not interfere with the main inverter during high-speed operation.

[0031] 4. Thermal and Electrical Limitations The continuous RMS current of the auxiliary three-phase winding is limited to 0.25–0.35 times the RMS current of the main three-phase winding, depending on the slot fill factor and cooling conditions. Due to the pulsed characteristics of NVH compensation, transient peak values ​​up to 0.5 times the main RMS current are allowed, with a duration of < 1 second, provided that the copper temperature rise is kept within a safe range.

[0032] 5. Alternative designs (space-constrained tanks) In structures with limited slot volume, the auxiliary three-phase windings can be replaced with 0.5–0.6 mm wire, with 8–10 turns per slot. In all cases, the ampere-turns of the auxiliary three-phase windings are limited to within 15% of the main three-phase windings to ensure that the power steering feel is not affected.

[0033] 6. Reasons for reducing the number of turns Using the same parameters as the main three-phase winding (1.5 mm wire, 30 turns) would result in: excessive inductance (approximately 9 times), making it impossible to achieve rapid harmonic injection at 200–400 Hz; over-torque, interfering with the tactile feedback; and wasted slot fill factor, increasing heat load. Therefore, the auxiliary three-phase winding is specifically designed with fewer turns and thinner wire specifications.

[0034] 7. Manufacturing and Debugging The main UVW coils are wound and connected in a standard delta configuration. The auxiliary coils are then wound, either placed above the main three-phase windings or separated from them using insulating spacers. The AuxU, AuxV, and AuxW terminals are soldered to dedicated pads in the auxiliary inverter area of ​​the PCB. The auxiliary neutral point is formed by connecting three return leads, with the connection insulated with heat-shrink tubing or epoxy resin.

[0035] 8. Debugging process: When the rotor is locked, inject a small-amplitude sinusoidal current (50–100Hz) into AuxU, while keeping AuxV and AuxW at zero current. Verify torque ripple using a force sensor. Perform a 20–400Hz frequency sweep test to verify cancellation performance. Configure current limiting and thermal protection parameters in the auxiliary inverter firmware.

[0036] Series path per phase: AuxU: S1 → S4 → S7 → S10 (AuxU-in = S1 start end, AuxU-out = S10 end end) AuxV: S3 → S6 → S9 → S12 (AuxV-in = S3 starting end, AuxV-out = S12 ending end) AuxW: S5 → S2 → S11 → S8 (AuxW-in = S5 starting end, AuxW-out = S8 ending end) Auxiliary three-phase winding (NVH) – 12-slot layout In this embodiment, the auxiliary three-phase windings are housed together with the main three-phase windings in a 12-slot, 8-pole stator. The auxiliary phases AuxU, AuxV, and AuxW occupy the same slots as the U, V, and W phases (slot distribution: AuxU = 1, 4, 7, 10; AuxV = 3, 6, 9, 12; AuxW = 5, 2, 11, 8), and are wound in the same direction. Each auxiliary slot contains 10 turns of 0.7 mm (±0.1 mm) diameter enameled copper wire, therefore the number of turns per slot is approximately one-third that of the main three-phase windings.

[0037] The auxiliary phases are connected in a star configuration with an independent neutral point and driven by a dedicated inverter, injecting a reverse micro-current in the 20–400Hz frequency band. The selection of turns and current limits ensures that the ampere-turns of the auxiliary three-phase windings do not exceed 10–15% of the main three-phase windings under any operating condition, thus providing vibration cancellation capability while ensuring that the boost torque and thermal margin remain unaffected. The reduced turns lower the inductance of the auxiliary three-phase windings to approximately one-ninth of that of the main three-phase windings, meeting the bandwidth requirements for NVH suppression.

[0038] The auxiliary three-phase windings share 12 stator slots with the main three-phase windings, and the winding directions are exactly the same. AuxU occupies slots 1, 4, 7, and 10; AuxV occupies slots 3, 6, 9, and 12; and AuxW occupies slots 5, 2, 11, and 8. Each auxiliary slot contains 10 turns of 0.7 mm enameled copper wire. The auxiliary phases form an independent neutral point by connecting AuxU-out (end of S10), AuxV-out (end of S12), and AuxW-out (end of S8), achieving a star connection. The other ends, AuxU-in (start of S1), AuxV-in (start of S3), and AuxW-in (start of S5), are connected to a dedicated three-phase auxiliary inverter on the controller's printed circuit board. The ampere-turns of the auxiliary three-phase windings are limited to within 15% of those of the main three-phase windings to achieve vibration cancellation in the 20–400 Hz frequency range without affecting the boost torque.

[0039] In a 12-slot, 8-pole concentrated winding EPS motor, the main fluctuations originate from the spatial order related to the interaction between the slots and poles. In practice, under typical operating conditions, a spectrum line that varies with the rotational speed can be observed, and it is concentrated in the 20–400 Hz frequency band.

[0040] Example 3: Active Vibration Suppression EPS Motor with Mechanical Stress Control Ring like Figure 3 As shown, this embodiment is based on the structure of embodiment 2. A mechanical stress control ring 2 is provided on the outer periphery of the stator back iron 1. The mechanical stress control ring 2 is a closed circular ring structure, which can be rolled from an elastic metal plate with a thickness of 0.3-0.8 mm. It is installed on the outside of the stator back iron 1 through an interference fit or a slot structure. The outside of the mechanical stress control ring 2 is the motor housing 3. The mechanical stress control ring 2 is made of elastic metal material and is used to improve the circumferential stiffness of the stator and reduce the structural vibration under radial electromagnetic force excitation. The mechanical stress control ring 2 cooperates with the harmonic cancellation current control of the auxiliary three-phase winding to improve the torque pulsation suppression efficiency. Because the mechanical stress control ring 2 provides additional circumferential stiffness, the structural vibration amplitude of the motor in the 200-600 Hz frequency band is reduced by approximately 15-25%. Combined with the anti-phase harmonic current injected into the auxiliary three-phase windings, this achieves a more significant reduction in torque ripple and NVH (noise, vibration, and harshness). Experiments show that adding the mechanical stress control ring 2 improves the harmonic cancellation efficiency of the auxiliary three-phase windings by approximately 12-18%.

[0041] By adding a mechanical stress control ring 2, this invention improves the circumferential stiffness of the stator at the structural end, significantly reducing the "breathing mode" vibration of the stator under radial electromagnetic force excitation, thus reducing NVH at its source. Compared with traditional solutions that rely solely on inverter algorithms or mechanical damping components, this invention uses a dual approach of "structure + magnetomotive force" to suppress vibration, resulting in higher anti-resonance capability and controllability.

[0042] In summary, the mechanical stress control ring 2 is used to improve the circumferential stiffness of the stator and suppress the "breathing mode" structural vibration of the stator under radial magnetic pull excitation. This structure not only reduces the noise of the motor body, but also makes the harmonic cancellation magnetomotive force generated by the auxiliary three-phase windings more effective, thereby improving the active vibration suppression performance.

[0043] Example 4 Vibration Detection and Control The controller receives signals from the torque sensor and rotor position sensor. It performs Fourier transform (FFT) analysis or employs an adaptive notch filter to identify the resonant frequency of the steering column. Once the resonant frequency is identified, the auxiliary three-phase windings are driven by injecting a dq-axis current that is out of phase with the detected vibration, generating a corrective micro-torque. The compensation amount is continuously adjusted to suppress the vibration amplitude.

[0044] Example 5 Thermal Insulation In one embodiment, the auxiliary three-phase winding is encased in a separate slot liner with higher thermal resistance. This reduces heat transfer from the primary three-phase winding, ensuring the auxiliary three-phase winding operates at lower temperatures and thus extending its service life.

[0045] Example 6: Failover Operation In another embodiment, when the primary three-phase winding or inverter fails, the auxiliary three-phase winding can be reconfigured to provide limited assist torque (10–15% of the rated torque). This ensures fault-tolerant operation and allows the vehicle to maintain steering capability in limp-home mode.

[0046] EPS control architecture 1. Sensing: Steering torque sensor + rotor position encoder.

[0047] 2. Vibration detection: Identify the resonant frequency of the steering column (20–400Hz) through real-time Fourier transform (FFT) analysis or adaptive notch filter.

[0048] 3. Auxiliary three-phase winding drive: The controller generates an anti-phase micro-torque command through dq axis current injection to counteract the detected vibration frequency.

[0049] 4. Failover Mode: If the primary three-phase winding inverter fails, the auxiliary three-phase winding inverter will be reconfigured to provide limp-home steering assistance.

[0050] Operating method 1. When turning, the main torque is applied through the main three-phase winding.

[0051] 2. Continuously monitor the vibration spectrum of the steering column.

[0052] 3. A correction micro-current is injected into the auxiliary three-phase winding to counteract the target frequency.

[0053] 4. Store the calibration values ​​at the frequency points on the vehicle platform.

[0054] 5. If necessary, switch the auxiliary three-phase winding to emergency boost mode.

[0055] Mathematical analysis of torque ripple suppression 1. Torque ripple model of the main three-phase winding For an EPS brushless DC (BLDC) motor, the electromagnetic torque of the main three-phase windings can be expressed as:

[0056] in: Average assist torque; Torque pulsation; : No. h The amplitude of the second harmonic; Angular frequency of a harmonic; The phase of a harmonic.

[0057] In EPS systems, harmonic frequencies affect NVH (noise, vibration, and harshness). It is typically in the 20–400 Hz frequency band (the resonance region of the steering column and rack).

[0058] 2. Magnetomotive force (MMF) and torque of auxiliary three-phase windings The auxiliary three-phase winding has: Number of turns per phase: ; Phase current: ; Magnetomotive force ( MMF ):

[0059] The torque of the auxiliary three-phase winding (for the main harmonic) can be expressed as:

[0060] in, The auxiliary torque constant (Nm / A) is proportional to the following:

[0061] ( =Magnetic flux per pole air gap) Since the auxiliary three-phase winding shares the same slots and magnetic shafts as the main three-phase winding, its torque acts on the exact same torque shaft, thus directly canceling out the pulsation of the main three-phase winding.

[0062] 3. Conditions for harmonic cancellation A major pulsating harmonic in the main torque:

[0063] Drive the auxiliary three-phase winding with a canceling current:

[0064] in: : Amplitude of the injected auxiliary current; 180° phase shift; Small phase error caused by delay / bandwidth The auxiliary torque is then:

[0065] The total torque becomes:

[0066] Using the standard phasor results, the synthesized pulsation amplitude is:

[0067] like = 0 and ,but → Perfectly offset.

[0068] In practice, and → Significant but imperfect suppression.

[0069] Therefore, this formula directly demonstrates the mathematical principle of pulsation suppression.

[0070] 4. Correlation between winding design (turns ratio and bandwidth) Number of turns per main three-phase winding: ; Number of turns per auxiliary three-phase winding: ; but:

[0071] Therefore, the auxiliary phase inductance is about one-ninth of the main phase inductance.

[0072] For a given available voltage angular frequency The current response of the lower harmonic command is approximately:

[0073] Therefore, under the same injection voltage and frequency:

[0074] In other words, under the same voltage limit, the harmonic current generated by the auxiliary three-phase winding is about 9 times that of the main three-phase winding.

[0075] 5. Quantitative Example (EPS Motor) Consider a specific implementation: Main three-phase winding: number of turns per slot =30; Inductance ≈1.8mH; Auxiliary three-phase winding: number of turns per slot =10; Inductance ≈0.2mH; Average torque: T 0 = 2.5 Nm; Main pulsating harmonics: f =120Hz (steering column resonance frequency band); The pulsation amplitude measured before calibration: A =0.41Nm (0.82Nm interpeak value) Select the auxiliary torque amplitude:

[0076] (approximately) A (80%), and set a small phase error, for example: =10°.

[0077] Substitute into the formula:

[0078]

[0079] Therefore, the pulsation amplitude decreases: A 0.41Nm→0.10Nm The interpeak pulsation becomes: 0.82Nm→0.20Nm The decrease was approximately 75%.

[0080] This is consistent with the degree of improvement described in the examples (e.g., from 0.82 Nm interpeak value to 0.14–0.20 Nm interpeak value).

[0081] Based on the above embodiments and formula verifications, this invention has the following advantages: it provides a built-in vibration cancellation function, improving NVH performance without the need for external dampers; it enhances safety by providing an auxiliary emergency assist mode; due to the adaptive nature of resonance cancellation, it reduces calibration costs for original equipment manufacturers (OEMs); it achieves a high-end steering feel, giving the motor greater value; it achieves vibration suppression directly within the motor body; it reduces reliance on external electronic control unit (ECU) algorithms and mechanical dampers; it improves driver comfort and NVH performance; it provides functional safety redundancy through the fault transfer function of the auxiliary three-phase winding; and it enables the motor to be positioned as a high-end EPS solution.

[0082] In the description of this invention, it should be understood that the terms "front", "rear", "left", "right", "up", "down", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0083] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. An auxiliary winding type electric power steering motor that actively suppresses vibration and torque pulsation, characterized in that: include: The stator and rotor, wherein the stator has multiple stator slots and the rotor is a surface-mounted permanent magnet rotor; The main three-phase windings are arranged in the stator slots, adopt a delta connection, and are electrically connected to the main inverter to output steering assist torque. The auxiliary three-phase winding is arranged in the same slot as the main three-phase winding and is electrically isolated from the main three-phase winding through an insulating pad, forming a two-layer coil structure with the inner layer being the main three-phase winding and the outer layer being the auxiliary three-phase winding. The auxiliary three-phase winding adopts a star connection with an internal isolated neutral point, and the neutral point is not connected to the connection point of the main three-phase winding or the chassis. The dual inverter architecture is integrated on the same PCBA and controlled by the same MCU. The dual inverter architecture includes a main inverter that is electrically connected to the main three-phase winding, and a low-power half-bridge auxiliary inverter that is controlled by an additional MOSFET / PWM channel and electrically connected to the auxiliary three-phase winding through an independent terminal. The auxiliary inverter is used to drive the auxiliary three-phase winding to inject a compensation current that is opposite in phase and matches the frequency of the torque pulsation of the main three-phase winding, so as to reduce cogging torque, torque fluctuation, noise, vibration and acoustic roughness. The auxiliary three-phase winding is used to provide emergency assistance when the main three-phase winding or the main inverter fails.

2. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 1, characterized in that: The auxiliary three-phase winding is wound in the same direction as the main three-phase winding to maintain a uniform magnetic flux direction. It can be arranged above the main three-phase winding or separated by an isolation pad. The turns ratio of the two is 1:

3. The ampere-turns of the auxiliary three-phase winding are limited to 10-15% of those of the main three-phase winding. The turns ratio makes the inductance of the auxiliary three-phase winding 1 / 9 of that of the main three-phase winding, thereby achieving high-frequency compensation current injection of 20-400Hz.

3. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 2, characterized in that: The auxiliary three-phase winding uses 0.6-0.8 mm diameter enameled copper wire with 10-12 turns per slot, while the main three-phase winding uses 1.5 mm diameter enameled copper wire with 30 turns per slot.

4. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 1, characterized in that: The neutral point of the auxiliary three-phase winding is set in isolation and is not connected to the connection point of the main three-phase winding or the chassis. The independent terminal of the auxiliary three-phase winding is soldered to a dedicated pad in the auxiliary inverter area of ​​the PCBA, and the output terminal of the auxiliary three-phase winding is connected to form an isolated neutral point.

5. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 1, characterized in that: The system is equipped with a steering torque sensor and a rotor position encoder. Based on the signals collected by the steering torque sensor and rotor position encoder, the controller identifies torque fluctuations or steering column resonance frequencies in the 20–400Hz frequency band through real-time Fourier transform or adaptive notch filtering, and drives the auxiliary three-phase winding to inject a compensation current with the opposite phase to the fluctuation. The controller has a built-in frequency mapping function, which is used to store frequency calibration values ​​according to the vehicle platform and compensate for the target fluctuation frequency.

6. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 5, characterized in that: The 20-400Hz frequency band corresponds to steering column resonance and road surface excitation vibration. The compensation current injected into the auxiliary three-phase winding can achieve road noise attenuation and vibration filtering caused by lane change bumps, and the compensation current injection does not interfere with the main three-phase winding assist circuit.

7. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 1, characterized in that: When the main three-phase winding or the main inverter fails, the controller can reconfigure the control parameters of the auxiliary inverter, switching the auxiliary three-phase winding from NVH suppression mode to emergency assist mode, providing 10%-15% of the rated torque as emergency assist torque.

8. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 1, characterized in that: The motor includes a stator back iron (1), and a mechanical stress control ring (2) is provided on the outer periphery of the stator back iron (1). The mechanical stress control ring (2) is installed on the outside of the stator back iron (1) by interference fit. The outside of the mechanical stress control ring (2) is the motor housing (3). The mechanical stress control ring (2) is made of elastic metal material and is used to improve the circumferential stiffness of the stator and reduce the structural vibration under radial electromagnetic force excitation. The mechanical stress control ring (2) cooperates with the harmonic cancellation current control of the auxiliary three-phase winding to form a dual vibration suppression system of structural vibration suppression and magnetomotive force compensation, so as to improve the torque pulsation suppression efficiency.

9. The auxiliary winding type electric power steering motor for actively suppressing vibration and torque pulsation according to claim 8, characterized in that: The mechanical stress control ring (2) is made of a highly elastic metal material and has a thickness of 0.3–0.8 mm.

10. A method for operating a motor according to any one of claims 1-9, characterized in that: include: Under normal steering conditions, the main inverter drives the main three-phase winding to output steering assist torque; The controller identifies the target torque fluctuation component based on the signals collected by the steering torque sensor and rotor position encoder, and controls the auxiliary inverter to inject a compensation current that is opposite in phase and matches the frequency of the target torque fluctuation component into the auxiliary three-phase winding, which is co-slotted with and electrically isolated from the main three-phase winding. This causes the auxiliary three-phase winding to generate a reverse magnetomotive force on the same magnetic axis as the main three-phase winding, thereby reducing cogging torque, torque fluctuation, noise, vibration and acoustic roughness. Under fault conditions, the controller monitors the status of the main three-phase winding or the main inverter in real time. When a fault is detected, the control parameters of the auxiliary inverter are reconfigured, so that the auxiliary three-phase winding switches from the compensation mode to the emergency assist mode and outputs an emergency assist torque of 10%-15% of the rated torque.

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