A method for controlling the maximum static friction torque of a permanent magnet brake

Abstract

The present invention relates to a method for controlling the maximum static friction torque of a permanent magnet brake; the method for controlling the maximum static friction torque of a permanent magnet brake of the present invention controls the maximum static friction torque that can be output by the permanent magnet brake by controlling the input voltage of the permanent magnet brake, and there is a quantitative relationship between the input voltage and the maximum static friction torque. The present invention controls the maximum static friction torque in real time through voltage control to achieve the purpose of locking the motor shaft with adjustable torque. Through the formula derivation process, it can be determined that the maximum static friction torque of the permanent magnet brake is directly related to the input voltage, and when the voltage is adjusted, the maximum static friction torque changes accordingly. The maximum static friction torque output by the permanent magnet brake is controllable, so the caliper can be allowed to stay at any desired target clamping force position and maintain it during the release process. This control method can reduce the workload of the motor, protect the motor and reduce energy consumption.

Description

Technical Field

[0001] The invention relates to vehicle braking technology, and in particular to a technology for achieving permanent magnet brake braking through dynamic adjustment. Background Art

[0002] In the electronic mechanical braking system, permanent magnet brakes are widely used as a brake that can effectively maintain the current state of the machine. Permanent magnet brakes can be used to lock the motor shaft, especially when the motor is out of control and cannot be braked, the permanent magnet brake can achieve the purpose of timely locking.

[0003] Depending on the usage scenario, the permanent magnet brake can be designed as a power-off brake type and a power-on brake type. The following uses the power-off brake type as an example to explain its function: When the power is off, the black iron inside the permanent magnet brake is attracted by the permanent magnet. At this time, the leaf spring connected to the black iron is stretched, and the black iron fits tightly against the friction plate. When the motor shaft tends to rotate, a static friction torque will be generated between the black iron and the friction plate to prevent the motor shaft from rotating to achieve a braking effect. When the power is turned on, the coil generates an electromagnetic field that cancels out the magnetic field of the permanent magnet. At this time, the black iron is pulled back by the leaf spring, and a gap is generated between it and the friction plate, and no friction is generated. The inner ring of the brake can rotate freely with the motor shaft.

[0004] However, the existing permanent magnet brake has only two functions for the locking principle of the motor shaft: fully open and fully closed, that is, the maximum static friction torque that the permanent magnet brake can output can only be selected between zero and the designed maximum value. This control method limits the use effect of the permanent magnet brake. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned technology, the present invention provides a technology for conveniently adjusting the maximum static friction torque of the permanent magnet brake on the motor shaft.

[0006] The present invention first provides a method for controlling the maximum static friction torque of a permanent magnet brake, which controls the maximum static friction torque that can be output by the permanent magnet brake by controlling the input voltage of the permanent magnet brake; there is a quantitative relationship between the input voltage and the maximum static friction torque.

[0007] Preferably, the relationship between the maximum static friction torque that the permanent magnet brake can output and the input voltage is:

[0008] ,

[0009] In the formula and are all constants; according to the above formula, by controlling the input voltage of the permanent magnet brake , so that the permanent magnet brake outputs a controllable maximum static friction torque 。

[0010] Preferably, the derivation process of the relationship between the maximum static friction torque and the input voltage is as follows:

[0011] The voltage equation of the energized coil inside the permanent magnet brake is:

[0012] ,

[0013] where U is the power supply voltage, I is the current intensity, R is the winding resistance, L is the inductance intensity, and t is a period of time;

[0014] The current of the coil inside the permanent magnet brake is:

[0015] ,

[0016] The suction force F of the electromagnet can be calculated by the following formula:

[0017] ,

[0018] where is the working air-gap magnetic flux, is the vacuum permeability, S is the cross-sectional area of the magnetic circuit, and B is the magnetic induction intensity;

[0019] The calculation formula for the magnetic induction intensity B is:

[0020] ,

[0021] where N is the number of turns of the coil, is the air-gap length;

[0022] It can be derived that the calculation formula for the suction force F of the electromagnet is:

[0023] ,

[0024] The suction force of the electromagnet is regarded as a repulsive force with a direction opposite to the suction force direction of the permanent magnet;

[0025] Let the suction force of the permanent magnet (specifically, it can be a permanent magnet) on the ferromagnetic iron be , and the repulsive force generated by the energized coil be , the elastic force of the plate spring be , and the supporting force received by the ferromagnetic iron when pressing on the friction plate be ; The supporting force received by the ferromagnetic iron is:

[0026] ,

[0027] The maximum static friction torque The calculation formula for is:

[0028] ,

[0029] In the formula is the static friction coefficient, is the equivalent distance from the static friction force to the center of the circle;

[0030] It can be deduced that the relationship between the maximum static friction torque that the permanent magnet brake can output and the input voltage is:

[0031] ,

[0032] Due to the attraction of the permanent magnet to the black iron is a constant. When the power is off, the compression of the friction plate by the black iron is very small, so the tension of the leaf spring is is regarded as a constant; the above formula is equivalent to: .

[0033] Preferably, the structure of the permanent magnet brake comprises a brake inner ring, a plate spring sheet, a black iron, a friction plate, a coil winding, a permanent magnet and a brake outer ring, wherein the brake inner ring is connected to the black iron through the plate spring sheet, a gap is provided between the black iron and the friction plate, and the friction plate, the coil winding, the permanent magnet and the brake outer ring are connected in sequence;

[0034] The inner ring of the brake is fixed on the motor shaft, and the contact between the black iron and the friction plate generates torque for braking the motor shaft.

[0035] Preferably, the permanent magnet brake is applied to the electronic mechanical brake. When the electronic mechanical brake is in the braking state, a wheel-end motor fails unexpectedly and becomes unavailable; the motor shaft is gradually released by adjusting and controlling the clamping force of the wheel end.

[0036] Preferably, the clamping force of the brake caliper at a certain wheel end on the automobile friction disc at a certain moment is At this time, the amount of compression of the brake caliper on the friction disc of the car is The elastic force on the brake caliper from the friction disc of the car is also The rebound force is transmitted to the permanent magnet brake and the torque of the motor shaft through the mechanical transmission mechanism. ; At this time, if the motor at the wheel end fails unexpectedly and becomes unavailable, the input voltage to control the permanent magnet brake is , so that its maximum static friction torque is To lock the motor shaft, prevent the brake caliper from rebounding by the car friction disc, so that the wheel end can maintain the clamping force ;

[0037] If the vehicle speed is detected to drop to a certain safety threshold, and the wheel end clamping force is expected to be reduced to , then by adjusting the input voltage of the permanent magnet brake to , at this time the maximum static friction torque output by the permanent magnet brake is , the motor shaft will drive the inner ring of the permanent magnet brake to overcome the friction force and rotate until the compression of the brake caliper on the friction disc of the car is reduced to At this time, the clamping force of the brake caliper on the friction disc of the car is , the torque transmitted to the motor shaft by the rebound force is , the motor shaft will be locked again, and the wheel end clamping force will remain .

[0038] Preferably, the permanent magnet brake is connected to the motor shaft of the electronic mechanical brake through a motor matching shaft; the permanent magnet brake is a power-off braking type or a power-on braking type.

[0039] Preferably, the permanent magnet brake is made to output a static friction torque greater than its set maximum static friction torque by reverse magnetization.

[0040] Preferably, a reverse voltage is connected to both ends of the electromagnet. At this time, the electromagnetic field generated by the coil will be superimposed on the magnetic field of the permanent magnet. At this time, the black iron will be attracted by the permanent magnet and the energized coil at the same time, and the supporting force it receives is:

[0041] ,

[0042] At this time, the maximum static friction torque that the permanent magnet brake can output is:

[0043] ,

[0044] Even if the permanent magnet brake output exceeds the set value Maximum static friction torque.

[0045] The beneficial effect of the present invention is that the maximum static friction torque is controlled in real time through voltage control to achieve the purpose of locking the motor shaft with adjustable torque.

[0046] The maximum static friction torque output by the permanent magnet brake is controllable, so the caliper can be stopped and maintained at any desired target clamping force position during the release process. This control method can reduce the motor's workload, protect the motor and reduce energy consumption.

[0047] Through the formula derivation process, it can be determined that the maximum static friction torque of the permanent magnet brake is directly related to the input voltage. When the voltage is adjusted, the maximum static friction torque changes accordingly.

[0048] When the motor shaft rotates, it drives the inner ring of the brake and the black iron to rotate. In the non-braking state, there is a gap between the black iron and the friction plate. When braking is required, the voltage of the coil winding is changed, the magnetic force changes, and the black iron contacts the friction plate to generate friction, thereby producing a braking effect or locking effect on the motor shaft.

[0049] In addition, in the preferred embodiment, a reverse voltage is applied to both ends of the permanent magnet brake to make it output a maximum static friction torque exceeding the design value, so that the clamping force maintained by the remaining wheel ends meets the parking requirement. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a simplified schematic diagram of the electromechanical brake structure.

[0051] Figure 2 Schematic diagram of the structure of a permanent magnet brake in an embodiment of the present invention.

[0052] Figure 3 4 is a control flow chart of the electronic mechanical braking system in an embodiment of the present invention.

[0053] Figure 4 It is a force analysis diagram of black iron in an embodiment of the present invention.

[0054] Figure 5 : is the input-output relationship curve of the permanent magnet brake in the embodiment of the present invention.

[0055] Description of reference numerals:

[0056] 1-permanent magnet brake; 2-motor matching shaft; 3-motor; 4-motor shaft; 5-mechanical transmission mechanism; 6-brake caliper; 7-automobile friction disc;

[0057] 11-brake inner ring; 12-plate spring leaf; 13-black iron; 14-friction plate; 15-coil winding; 16-permanent magnet; 17-brake outer ring. DETAILED DESCRIPTION

[0058] like Figure 1 The figure shows a schematic diagram of the structure of an existing electronic mechanical brake. It includes a permanent magnet brake 1, a motor matching shaft 2, a motor 3, a motor shaft 4, a mechanical transmission mechanism 5, a brake caliper 6 and a vehicle friction disc 7. The motor 3 outputs power through the motor shaft 4, and converts the force in the mechanical transmission mechanism 5, so that the brake caliper 6 presses and rubs the vehicle friction disc 7 to generate pressure for braking; the specific structure and braking method of the mechanical transmission mechanism 5, the brake caliper 6 and the vehicle friction disc 7 belong to the existing technology and will not be repeated here.

[0059] The motor mating shaft 2 is connected to the motor shaft 4, and when the motor mating shaft 2 is braked, the motor shaft 4 can be braked. The permanent magnet brake 1 locks or brakes the motor mating shaft 2. The braking principle of the permanent magnet brake 1 is as follows:

[0060] As Figure 2 shown in the figure is the structure of a permanent magnet brake according to this embodiment, which includes a brake inner ring 11, a plate spring 12, a black iron 13, a friction plate 14, a coil winding 15, a permanent magnet 16, and a brake outer ring 17;

[0061] Among them, the brake inner ring 11 is connected to the black iron 13 through the plate spring 12, there is a gap between the black iron 13 and the friction plate 14, and the friction plate 14, the coil winding 15, the permanent magnet 16, and the brake outer ring 17 are connected in sequence;

[0062] The brake inner ring 11 is fixed on the motor mating shaft 2 (or directly fixed on the motor shaft 4), and when the black iron 13 contacts the friction plate 14, a torque is generated to brake the rotation of the motor shaft 4.

[0063] When power is off, the black iron 13 inside the permanent magnet brake 1 is attracted by the permanent magnet 16. At this time, the plate spring 12 connected to the black iron 13 is stretched, and the black iron 13 is in close contact with the friction plate 14. When the motor shaft 4 has a tendency to rotate, a static friction torque will be generated between the black iron 13 and the friction plate 14 to prevent the motor shaft 4 from rotating, so as to achieve the braking effect. When power is on, the coil winding 15 generates an electromagnetic field, which cancels out the magnetic field of the permanent magnet 16. At this time, the black iron 13 is pulled back by the plate spring 12, a gap is generated between the black iron 13 and the friction plate 14, and no friction force is generated anymore. The brake inner ring 11 can rotate freely with the motor shaft 4.

[0064] As Figure 3 shown is the process diagram of the permanent magnet brake of this embodiment receiving signal control.

[0065] In the first implementation method on the left, when a braking signal is received, the motor shaft 4 rotates forward to drive the brake caliper 6 to clamp the vehicle friction disc 7, and the permanent magnet brake 1 cuts off power to lock the motor shaft 4, thus preventing the motor shaft 4 from rotating back.

[0066] In the second implementation method on the right, when a brake release signal is received, the permanent magnet brake 1 is powered on to release the motor shaft 4, and the motor shaft 4 rotates reversely to drive the brake caliper 6 to release the vehicle friction disc 7.

[0067] In the above two implementation methods, only a selection can be made between zero and the designed maximum value. This control method limits the use effect of the permanent magnet brake, and the adjustment control is achieved through the following method.

[0068] Embodiment 1:

[0069] This embodiment first provides a method for controlling the maximum static friction torque of a permanent magnet brake, which controls the maximum static friction torque that can be output by the permanent magnet brake by controlling the input voltage of the permanent magnet brake; there is a quantitative relationship between the input voltage and the maximum static friction torque.

[0070] Through voltage control, the maximum static friction torque is controlled in real time to achieve the purpose of motor shaft locking with adjustable torque.

[0071] Preferably, the relationship between the maximum static friction torque that the permanent magnet brake can output and the input voltage is:

[0072] ,

[0073] In the formula and are all constants; according to the above formula, by controlling the input voltage of the permanent magnet brake , so that the permanent magnet brake outputs a controllable maximum static friction torque .

[0074] Embodiment 2:

[0075] The relationship between the maximum static friction torque and the input voltage is derived as follows:

[0076] The voltage equation of the energized coil inside the permanent magnet brake is:

[0077] ,

[0078] Where U is the power supply voltage, I is the current intensity, R is the winding resistance, L is the inductance intensity, and t is a period of time;

[0079] The current of the internal coil of the permanent magnet brake is:

[0080] ,

[0081] The suction force F of the electromagnet can be calculated using the following formula:

[0082] ,

[0083] In the formula is the working air gap flux, is the vacuum magnetic permeability, S is the cross-sectional area of ​​the magnetic circuit, and B is the magnetic induction intensity;

[0084] The calculation formula of magnetic induction intensity B is:

[0085] ,

[0086] Where N is the number of coil turns, is the air gap length;

[0087] The calculation formula of the electromagnet's suction force F can be deduced as follows:

[0088] ,

[0089] The attraction of the electromagnet is considered as a repulsive force in the opposite direction to the attraction of the permanent magnet;

[0090] like Figure 4 As shown, the attraction of the permanent magnet on the black iron is , the repulsive force generated by the energized coil is , the elastic force of the leaf spring is The supporting force of the black iron when it is pressed on the friction plate is ; The support force on the black iron is:

[0091] ,

[0092] Maximum static friction torque The calculation formula is:

[0093] ,

[0094] In the formula is the static friction coefficient, is the equivalent distance from the static friction force to the center of the circle;

[0095] It can be deduced that the relationship between the maximum static friction torque that the permanent magnet brake can output and the input voltage is:

[0096] ,

[0097] Due to the attraction of the permanent magnet on the black iron is a constant. When the power is off, the compression of the friction plate by the black iron is very small, so the tension of the leaf spring is is regarded as a constant; the above formula is equivalent to: .

[0098] like Figure 5 As shown in the figure, it is a relationship diagram between input voltage and maximum static friction torque. When the input positive voltage increases gradually, the maximum static friction torque decreases accordingly. In this way, the required maximum static friction torque can be quickly given by controlling the input voltage as needed. Figure 5 In the figure, the voltage to the right of the zero point on the horizontal axis is positive, and the voltage to the left of the zero point is negative.

[0099] In a specific application, when the electronic mechanical brake is in a braking state, the brake caliper 6 clamps the automobile friction disc 7, and the automobile friction disc 7 is squeezed and elastically deformed. After receiving the brake release signal, the permanent magnet brake 1 will be energized to release the motor shaft 4, and the brake caliper 6 will be rebounded by the elastic force of the automobile friction disc 7. If the traditional control method is used to directly energize the permanent magnet brake 1 to a maximum static friction torque of zero, then the clamping force of the brake caliper 6 requires the output torque of the motor 3 to be maintained and adjusted. If the maximum static friction torque output by the permanent magnet brake 1 is controllable, then during the release process, the brake caliper 6 can be allowed to stay at any desired target clamping force position and maintain it. This control method can reduce the workload of the motor, protect the motor and reduce energy consumption.

[0100] Embodiment 3:

[0101] If a wheel-end motor fails unexpectedly and becomes unavailable when the electronic mechanical brake is in braking state, this control method can make the clamping force of the wheel end match the braking control algorithm of the whole vehicle; the clamping force can be gradually released instead of only maintaining the maximum and minimum values, which provides more operating space for the braking control algorithm of the whole vehicle and improves the safety of the electronic mechanical braking system.

[0102] Preferably, the clamping force of the brake caliper 6 on the friction disc 7 of the vehicle at a certain wheel end at a certain moment is At this time, the compression amount of the brake caliper 6 on the automobile friction disc 7 is The elastic force on the brake caliper 6 by the friction disc 7 of the automobile is also The rebound force is transmitted to the permanent magnet brake and the torque of the motor shaft 4 through the mechanical transmission mechanism. ; At this time, if the motor at the wheel end fails unexpectedly and becomes unavailable, the input voltage to control the permanent magnet brake is , so that its maximum static friction torque is To lock the motor shaft, prevent the brake caliper 6 from being rebounded by the vehicle friction disc 7, so that the wheel end can maintain the clamping force ;

[0103] If the vehicle speed is detected to drop to a certain safety threshold, and the wheel end clamping force is expected to be reduced to , then by adjusting the input voltage of the permanent magnet brake to , at this time the maximum static friction torque output by the permanent magnet brake is , the motor shaft will drive the inner ring of the permanent magnet brake to overcome the friction force and rotate until the compression of the brake caliper 6 on the automobile friction disc 7 is reduced to At this time, the clamping force of the brake caliper 6 on the automobile friction disc 7 is , the torque transmitted to the motor shaft 4 by the rebound force is , the motor shaft 4 will be locked again, and the clamping force at the wheel end will also be maintained as .

[0104] Preferably, the permanent magnet brake is a power-off braking type or a power-on braking type.

[0105] Embodiment 4:

[0106] Although the maximum value of the maximum static friction torque that the permanent magnet brake can output can be changed by adjusting the structure of the permanent magnet brake and selecting different materials, for each produced permanent magnet brake, this maximum value is a fixed value. Embodiment 4 can further achieve the adjustment of the maximum value, and the specific method is as follows:

[0107] In this embodiment, the permanent magnet brake is made to output a maximum static friction torque greater than its set value by the method of reverse magnetization enhancement.

[0108] Specifically, a reverse voltage is applied across the electromagnet. At this time, the electromagnetic field generated by the coil will be superimposed on the magnetic field of the permanent magnet. At this time, the yoke will be simultaneously subjected to the suction force of the permanent magnet and the suction force of the energized coil, and the supporting force it receives is:

[0109] ,

[0110] At this time, the maximum static friction torque that the permanent magnet brake can output is:

[0111] ,

[0112] Even if the permanent magnet brake outputs a maximum static friction torque exceeding the set value .

[0113] As Figure 5 shown, when the input voltage is a reverse voltage and the voltage gradually increases, the maximum static friction torque output by the permanent magnet brake gradually increases.

[0114] Let the maximum clamping force of the brake caliper on the vehicle friction disc be , and the clamping force required for parking is , and there is . Therefore, the permanent magnet brake selected in the electromechanical brake is such that the clamping force that can be maintained when it outputs the maximum static friction torque is , and there is . However, when one or more wheel-end motors fail and become unavailable, the clamping force that the remaining wheel ends can maintain through the permanent magnet brake will be less than the clamping force required for parking, and the vehicle will have a risk of rolling backward. At this time, a reverse voltage can be applied across the permanent magnet brake to make it output a maximum static friction torque exceeding the design value, so that the clamping force that the remaining wheel ends can maintain meets the parking requirements.

[0115] In this embodiment, the direction of the force is changed by setting the reverse voltage, thereby changing the maximum static friction torque that the permanent magnet brake can output; in actual applications, the direction of the voltage can be forward or reverse, and according to the braking requirements encountered during the braking process, it can be actively selected or alternately coordinated to achieve better braking requirements.

Claims

1. A method for controlling the maximum static friction torque of a permanent magnet brake, characterized in that: The structure of the permanent magnet brake includes a brake inner ring, a plate spring sheet, black iron, a friction plate, a coil winding, a permanent magnet and a brake outer ring; the brake inner ring is connected to the black iron through the plate spring sheet, and there is a gap between the black iron and the friction plate; the friction plate, the coil winding, the permanent magnet and the brake outer ring are connected in sequence; the brake inner ring is fixed on the motor shaft, and the contact between the black iron and the friction plate generates torque for braking the motor shaft; when the power is off, the black iron inside the permanent magnet brake is attracted by the permanent magnet, the plate spring sheet connected to the black iron is stretched, and the black iron is pulled apart. The iron fits tightly with the friction plate. When the motor shaft tends to rotate, static friction torque will be generated between the black iron and the friction plate to prevent the motor shaft from rotating, thereby achieving a braking effect. When power is turned on, the coil winding generates an electromagnetic field, which cancels out the magnetic field of the permanent magnet. At this time, the black iron is pulled back by the plate spring sheet, and a gap is generated between it and the friction plate. No more friction is generated, and the inner ring of the brake can rotate freely with the motor shaft. The maximum static friction torque that can be output by the permanent magnet brake is controlled by controlling the input voltage of the permanent magnet brake. There is a quantitative relationship between the input voltage and the maximum static friction torque. The relationship between the maximum static friction torque that the permanent magnet brake can output and the input voltage is: ， In the formula is the static friction coefficient, is the equivalent distance from the static friction force to the center of the circle, is the attraction of the permanent magnet on the black iron, It is the elastic force of leaf spring; is the vacuum permeability, is the cross-sectional area of ​​the magnetic circuit, is the number of coil turns, is the winding resistance, is the air gap length; the above formula is equivalent to: ， In the formula and are all constants; according to the above formula, by controlling the input voltage of the permanent magnet brake , so that the permanent magnet brake outputs a controllable maximum static friction torque .

2. The maximum static friction torque control method of a permanent magnet brake according to claim 1, characterized in that: The relationship between the maximum static friction torque and the input voltage is derived as follows: The voltage equation of the energized coil inside the permanent magnet brake is: ， In the formula is the power supply voltage, is the current intensity, is the winding resistance, is the inductance, t is a period of time; The current of the internal coil of the permanent magnet brake is: ， The suction force of the electromagnet is calculated using the following formula: ， In the formula is the working air gap flux, is the vacuum permeability, is the cross-sectional area of ​​the magnetic circuit, is the magnetic induction intensity; Magnetic induction intensity The calculation formula is: ， In the formula is the number of coil turns, is the air gap length; The calculation formula of the suction force of the electromagnet can be deduced as follows: ， The attraction of the electromagnet is considered as a repulsive force in the opposite direction to the attraction of the permanent magnet; Assume that the attraction of the permanent magnet on the black iron is , the repulsive force generated by the energized coil is , the elastic force of the leaf spring is The supporting force of the black iron when it is pressed on the friction plate is ; The support force on the black iron is: ， Maximum static friction torque The calculation formula is: ， In the formula is the static friction coefficient, is the equivalent distance from the static friction force to the center of the circle; It can be deduced that the relationship between the maximum static friction torque that the permanent magnet brake can output and the input voltage is: ， Due to the attraction of the permanent magnet on the black iron is a constant. When the power is off, the compression of the friction plate by the black iron is very small, so the tension of the leaf spring is is regarded as a constant; the above formula is equivalent to: .

3. The maximum static friction torque control method of a permanent magnet brake according to claim 1, characterized in that: The permanent magnet brake is applied to the electronic mechanical brake. When the electronic mechanical brake is in the braking state, a wheel-end motor fails unexpectedly and becomes unusable; the motor shaft is gradually released by adjusting and controlling the clamping force of the wheel end.

4. The maximum static friction torque control method of a permanent magnet brake according to claim 3, characterized in that: Assume that the clamping force of the brake caliper on the friction disc of the vehicle at a certain wheel end at a certain moment is At this time, the amount of compression of the brake caliper on the friction disc of the car is The elastic force on the brake caliper from the friction disc of the car is also The rebound force is transmitted to the permanent magnet brake and the torque of the motor shaft through the mechanical transmission mechanism. ; At this time, if the motor at the wheel end fails unexpectedly and becomes unavailable, the input voltage to control the permanent magnet brake is , so that its maximum static friction torque is To lock the motor shaft, prevent the brake caliper from rebounding by the car friction disc, so that the wheel end can maintain the clamping force .

5. The maximum static friction torque control method of a permanent magnet brake according to claim 4, characterized in that: If the vehicle speed is detected to drop to a certain safety threshold, and the wheel end clamping force is expected to be reduced to , then by adjusting the input voltage of the permanent magnet brake to , at this time the maximum static friction torque output by the permanent magnet brake is , the motor shaft will drive the inner ring of the permanent magnet brake to overcome the friction force and rotate until the compression of the brake caliper on the friction disc of the car is reduced to At this time, the clamping force of the brake caliper on the friction disc of the car is , the torque transmitted to the motor shaft by the rebound force is , the motor shaft will be locked again, and the wheel end clamping force will remain .

6. The maximum static friction torque control method of a permanent magnet brake according to claim 5, characterized in that: The permanent magnet brake is connected to the motor shaft of the electronic mechanical brake through the motor matching shaft; The permanent magnet brake is of the power-off braking type, or the permanent magnet brake is of the power-on braking type.

7. The maximum static friction torque control method of a permanent magnet brake according to claim 1, characterized in that: The permanent magnet brake outputs a torque greater than its set maximum static friction torque by reverse magnetization.

8. The maximum static friction torque control method of a permanent magnet brake according to claim 7, characterized in that: When the reverse voltage is connected, the electromagnetic field generated by the coil will be superimposed on the magnetic field of the permanent magnet. At this time, the black iron will be attracted by the permanent magnet and the energized coil at the same time, and the supporting force it receives is: ， At this time, the maximum static friction torque that the permanent magnet brake can output is: ， Even if the permanent magnet brake output exceeds the maximum static friction torque set value.

Images