A disc brake based on magnetostrictive material and control method thereof

Abstract

The present invention discloses a disc brake based on magnetostrictive material and a control method thereof. A new type of magnetostrictive intelligent material is used in the disc brake, which can undergo telescopic deformation under the influence of a magnetic field and generate sufficient thrust. The present invention uses it in the disc brake as a brake driver to replace the original hydraulic pump structure, and adopts a double hysteresis telescopic driver to drive two brake pistons of the fixed caliper disc brake respectively, while retaining the advantages of the disc brake, reducing the volume of the fixed caliper disc brake, so that it can be used on cars. In addition, the brake eliminates the hydraulic oil circuit, simplifies the system structure, and saves costs.

Description

Technical Field

[0001] The invention belongs to the technical field of automobile mechanical brakes, and specifically refers to a disc brake based on magnetostrictive materials and a control method thereof. Background Art

[0002] The rotating element in the friction pair of a disc brake is a metal disc that works on the end surface, called a brake disc; the friction element clamps the brake disc from both sides to produce braking. The fixed element has a variety of structural forms, and disc brakes can be roughly divided into two categories: caliper disc type and full disc type.

[0003] The existing disc brakes on the market are mainly hydraulic type, controlled by hydraulic pressure, and the main components are brake disc, wheel cylinder, brake caliper, oil pipe, brake pad, etc. Disc brakes have fast heat dissipation, light weight, simple structure and convenient adjustment. Especially under high load, they have good high temperature resistance, stable braking effect, and are not afraid of muddy water invasion, and can be used in winter and bad road conditions.

[0004] At present, a lot of achievements have been made in the research of disc brakes. For example, the Chinese invention patent application number is 201410785712.9, entitled “A disc brake with giant magnetostrictive boosting function and method thereof”, which uses the magnetostrictive phenomenon of magnetostrictive materials to propose a disc brake with magnetostrictive boosting function, which has the characteristics of simple and reliable structure, good compatibility with existing brake systems, and does not affect the normal operation of ABS; it can reduce the braking distance during emergency braking while improving driving safety; the Chinese invention patent application number is 201610902190.5, entitled “A hydraulic self-boosting disc brake”, which provides a hydraulic self-boosting disc brake that adds a boosting device on the basis of the existing floating caliper disc brake to achieve a two-way boosting effect during automobile braking and improve braking efficiency; the Chinese invention patent application number is 201811214157.9, entitled “A magnetic fluid disc brake”, which uses intelligent material magnetic fluid to provide a disc brake that is different from the traditional braking method, and combines hydraulic braking with magnetic fluid regulation braking to achieve a multi-stage braking method.

[0005] From the above research on disc brakes, although disc brakes have considerable advantages, their high cost, complex brake structure, complex hydraulic system layout and hydraulic hysteresis and other problems have not been solved.

[0006] Magnetostrictive materials are a type of new intelligent material that can expand and contract along the direction of magnetization when magnetized in a magnetic field, and the thrust generated by magnetostrictive strain is very large. If a powered coil is used as a magnetic field source, the change in the size of the magnetostrictive material can be controlled when the current passing through the coil changes or the distance from the magnet changes. Because they are controlled by the magnetic field with fast response time, good frequency characteristics, high energy density, large coupling coefficient, and have sensing and driving functions, they have broad application prospects in many fields. Summary of the invention

[0007] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a disc brake based on magnetostrictive material and a control method thereof, so as to solve the problems of high cost, complex brake structure, complex hydraulic system layout and hydraulic hysteresis of the disc brake in the prior art; the present invention utilizes the advantages of the new intelligent material magnetostrictive material, such as fast response time under magnetic field control, good frequency characteristics, high energy density, and large thrust generated when deformed, and controls the magnetic field change by controlling the current in the energized coil to achieve control of the expansion and contraction of the magnetostrictive material, and uses this as a brake driver to replace the original hydraulic drive, thereby improving the response speed of the brake and removing the hydraulic system, greatly simplifying the structure of the brake system and the brake, and saving costs.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A disc brake based on magnetostrictive material of the present invention comprises: a brake assembly, a left brake driver, a right brake driver and a force and displacement transmission module;

[0010] The brake assembly comprises: a brake caliper body, a guide pin, a left brake pad back plate, a left brake pad, a left piston, a right piston, a rubber ring, a right brake pad, a right brake pad back plate and a brake disc;

[0011] The brake caliper body is fixed on the steering knuckle of the front axle of the vehicle, and a left brake actuator and a right brake actuator are installed on the brake caliper body;

[0012] The brake disc is fixed to the wheel hub of the car and extends between the left brake pad and the right brake pad;

[0013] The left brake pad back plate and the right brake pad back plate are connected to the left piston and the right piston respectively, are suspended on the guide pin, and can move along the guide pin; the left brake pad and the right brake pad are fixed on the left brake pad back plate and the right brake pad back plate respectively;

[0014] Rubber rings are respectively embedded in the trapezoidal cross-section ring grooves on the inner walls of the holes of the left piston and the right piston, and the rubber rings are used to return the brakes to their original positions when braking ends;

[0015] The left brake driver and the right brake driver both comprise: a driver housing, a giant magnetostrictive rod, an excitation coil, a degaussing coil, a magnetic isolation pad and a magnetic isolation top cover;

[0016] The input end of the giant magnetostrictive rod is fixed to the bottom end inside the driver housing;

[0017] The excitation coil and the demagnetization coil are both wound on the giant magnetostrictive rod;

[0018] The magnetic isolation pad is closely attached to the inner side of the driver housing; the magnetic isolation top cover is screwed on the top of the left brake driver and the right brake driver, and together with the magnetic isolation pad, isolates the influence of the magnetic field on the outside;

[0019] The force and displacement transmission module is used to transmit the force and displacement output by the left brake driver and the right brake driver, and includes: a giant magnetostrictive rod, a transmission rod, a piston push rod and a support pin;

[0020] The support pins are fixed on both sides of the brake caliper body;

[0021] The middle part of the transmission rod is hinged on the support pin, the lower end is hinged to the input end of the piston push rod, and the upper end of the transmission rod is hinged to the output end of the giant magnetostrictive rod;

[0022] The output end of the piston push rod is fixedly connected to the piston.

[0023] Furthermore, slide grooves are respectively provided on the left and right sides of the brake caliper body for installing the left brake driver and the right brake driver.

[0024] Furthermore, the left brake actuator and the right brake actuator are fixed to the brake caliper body by fixing screws.

[0025] Furthermore, the brake also includes: an adjusting gasket, which is used in conjunction with the fixing screw to adjust the positions of the left brake actuator and the right brake actuator.

[0026] Furthermore, the giant magnetostrictive rod has a circular cross-section, a length greater than 5 cm, and a diameter greater than 10 mm.

[0027] Furthermore, the material used for the giant magnetostrictive rod should be a giant magnetostrictive material with a magnetostriction coefficient of not less than 2000 ppm.

[0028] Furthermore, the cross section of the driver housing is ⊥-shaped.

[0029] Furthermore, the two brake actuators have consistent internal layout structures and are symmetrically installed at the front and rear locations of the upper part of the brake caliper body.

[0030] Furthermore, the excitation coils in the two brake drivers use one wire, the wires in the excitation coils are arranged in a completely consistent manner, and after current is passed through, the currents in the two excitation coils are in the same direction relative to the brake driver.

[0031] Furthermore, the degaussing coils in the two brake actuators use one wire, the wires in the degaussing coils are arranged in a completely consistent manner, and after current is passed through, the currents in the two degaussing coils are in the same direction relative to the brake actuator.

[0032] The present invention also provides a control method for a disc brake based on a magnetostrictive material, comprising the following steps:

[0033] (1) When the brake pedal is pressed to brake, the vehicle status information and pedal information are collected and transmitted to the electronic control unit (ECU);

[0034] (2) The electronic control unit receives the vehicle status information and the pedal information, obtains the required target braking force after processing, calculates the current required for the excitation coil according to the required target braking force, and adjusts the current to the required current value and inputs it into the excitation coil;

[0035] (3) The electronic control unit adjusts the current in the excitation coil according to the working state of the brake pedal to change the magnetic field strength in the excitation coil, so that the giant magnetostrictive rods in the two brake actuators are deformed and output the required braking force;

[0036] (4) When braking ends, the electronic control unit controls the excitation coil to be powered off, and the demagnetization coils in the two brake actuators are fed with a current in the opposite direction (relative to the actuator structure) to the current previously fed into the excitation coils, thereby eliminating the magnetic field, causing the giant magnetostrictive rod to return to its original length, and braking ends.

[0037] Preferably, the vehicle status information includes: a vehicle speed signal and a wheel speed signal.

[0038] Preferably, the pedal information is a pedal displacement signal and a pedal speed signal.

[0039] Preferably, when calculating the current in the excitation coil in step (2), it is only necessary to calculate the current required in the excitation coil in a single brake driver based on half of the required target braking force, that is, the current required to be input.

[0040] Preferably, the force and displacement output by the two brake actuators during the braking process in step (3) should be completely consistent, being half of the required braking force and displacement respectively.

[0041] Preferably, the formula used in step (2) to calculate the braking force required to be output by the giant magnetostrictive rod in a single brake actuator is:

[0042]

[0043] The formula for calculating the deformation of the giant magnetostrictive rod required to output the required braking force is:

[0044]

[0045] The formula for calculating the required coil input current is:

[0046]

[0047] In the formula, F c F is the output force of the required single brake actuator giant magnetostrictive rod; z is the required braking force; ε is the required deformation of the giant magnetostrictive rod of a single brake actuator; E is the elastic modulus of the giant magnetostrictive rod; r is the radius of the giant magnetostrictive rod; π is the pi constant; I is the current in the required coil; L is the length of the part of the giant magnetostrictive rod wound with the coil; a is the characteristic constant (depending on the material properties); μ0 is the vacuum magnetic permeability; N is the number of coil turns.

[0048] Preferably, the step (3) further comprises: during the braking force adjustment process, if the braking force needs to be reduced, passing a current opposite to that of the excitation coil through the demagnetization coil to eliminate the influence of hysteresis on the braking force.

[0049] Beneficial effects of the present invention:

[0050] Compared with the existing disc brake, the present invention adopts a method of controlling the magnetostrictive deformation by controlling the current of the energized coil to realize braking drive, and uses the current as a signal transmission medium, so that the electrification of the automobile braking system is easier to realize.

[0051] Since the hydraulic oil circuit is eliminated, the designed disc brake retains the advantages of the traditional disc brake and greatly simplifies the brake system and the brake structure.

[0052] The core of the brake driver of the present invention is magnetostrictive material, so the high response rate of the material itself is also inherited by the brake, which greatly improves the response rate of the brake. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a front view of the disc brake based on magnetostrictive material of the present invention;

[0054] Figure 2 A top view of a disc brake based on magnetostrictive material according to the present invention;

[0055] Figure 3 A side view of a disc brake based on magnetostrictive material according to the present invention;

[0056] Figure 4 It is a schematic cross-sectional view of the driver AA of the present invention;

[0057] Figure 5 This is a flow chart of the disc brake control method of the present invention;

[0058] Figure 6 It is a structural schematic diagram of the present invention applied to a floating caliper disc brake;

[0059] In the figure, 1-brake caliper body, 2-guide pin, 3-left brake pad back plate, 4-left brake pad, 5-left piston, 6-rubber ring, 7-support pin, 8-right brake pad, 9-right brake pad back plate, 10-brake disc, 11-right piston, 12-driver housing, 13-magnetic isolation liner, 14-giant magnetostrictive rod, 15-magnetic isolation top cover, 16-transmission rod, 17-piston push rod, 18-adjusting gasket, 19-left brake driver, 20-fixing screw, 21-excitation coil, 22-demagnetization coil, 23-right brake driver, 24-slide. DETAILED DESCRIPTION

[0060] In order to facilitate the understanding of those skilled in the art, the present invention is further described below in conjunction with embodiments and drawings. The contents mentioned in the implementation modes are not intended to limit the present invention.

[0061] Reference Figures 1 to 4 As shown, a disc brake based on magnetostrictive material of the present invention comprises: a brake assembly, a left brake actuator 19, a right brake actuator 23 and a force and displacement transmission module;

[0062] The brake assembly comprises: a brake caliper body 1, a guide pin 2, a left brake pad back plate 3, a left brake pad 4, a left piston 5, a right piston 11, a rubber ring 6, a right brake pad 8, a right brake pad back plate 9 and a brake disc 10;

[0063] The brake caliper body 1 is fixed on the steering knuckle of the front axle of the vehicle, and a left brake actuator 19 and a right brake actuator 23 are installed thereon;

[0064] The brake disc 10 is fixed on the wheel hub of the vehicle and extends between the left brake pad 4 and the right brake pad 8;

[0065] The left brake pad back plate 3 and the right brake pad back plate 9 are connected to the left piston 5 and the right piston 11 respectively, and are suspended on the guide pin 2 and can move along the guide pin 2; the left brake pad 4 and the right brake pad 8 are fixed on the left brake pad back plate 3 and the right brake pad back plate 9 respectively;

[0066] Rubber rings 6 are respectively embedded in the trapezoidal cross-section annular grooves on the inner walls of the holes of the left piston 5 and the right piston 11, and the rubber rings 6 are used to return the brakes to their original positions when braking is completed;

[0067] The left brake driver 19 and the right brake driver 23 each include: a driver housing 12, a giant magnetostrictive rod 14, an excitation coil 21, a degaussing coil 22, a magnetic isolation pad 13 and a magnetic isolation top cover 15;

[0068] The input end of the giant magnetostrictive rod 14 is fixed to the bottom end inside the driver housing 12;

[0069] The excitation coil 21 and the demagnetization coil 22 are both wound around the giant magnetostrictive rod 14;

[0070] The magnetic isolation pad 13 is closely attached to the inner side of the driver housing 12; the magnetic isolation top cover 15 is screwed onto the top of the left brake driver 19 and the right brake driver 23, and together with the magnetic isolation pad 13 isolates the influence of the magnetic field on the outside;

[0071] The force and displacement transmission module is used to transmit the force and displacement output by the left brake driver 19 and the right brake driver 23, and includes: a giant magnetostrictive rod 14, a transmission rod 16, a piston push rod 17 and a support pin 7;

[0072] The support pins 7 are fixed on both sides of the brake caliper body 1;

[0073] The middle part of the transmission rod 16 is hinged on the support pin 7, the lower end is hinged to the input end of the piston push rod 17, and the upper end of the transmission rod 16 is hinged to the output end of the giant magnetostrictive rod 14;

[0074] The output end of the piston push rod 17 is fixedly connected to the piston.

[0075] The left and right sides of the brake caliper body 1 are respectively provided with sliding grooves 24 for installing the left brake actuator 19 and the right brake actuator 23 .

[0076] The left brake actuator 19 and the right brake actuator 23 are fixed to the brake caliper body 1 by means of fixing screws 20 .

[0077] The brake further comprises: an adjusting washer 18 , which is used in conjunction with a fixing screw 20 to adjust the positions of a left brake actuator 19 and a right brake actuator 23 .

[0078] The giant magnetostrictive rod 14 has a circular cross section, a length greater than 5 cm, and a diameter greater than 10 mm.

[0079] The material used for the giant magnetostrictive rod 14 should be a giant magnetostrictive material with a magnetostriction coefficient of not less than 2000 ppm.

[0080] The cross section of the driver housing 12 is ⊥-shaped.

[0081] The two brake actuators have consistent internal layout structures and are symmetrically installed at the front and rear positions of the upper part of the brake caliper body.

[0082] The excitation coils 21 in the two brake drivers use one wire, the arrangement of the wires in the excitation coils is completely consistent, and after the current is passed through, the currents of the two excitation coils are in the same direction relative to the brake driver.

[0083] The degaussing coils 22 in the two brake drivers use one wire, the wires in the degaussing coils are arranged in the same way, and after current is passed through, the currents in the two degaussing coils are in the same direction relative to the brake driver.

[0084] Reference Figure 5 This embodiment also provides a control method for the above-mentioned disc brake, based on the above-mentioned system, comprising the following steps:

[0085] (1) When the driver steps on the brake pedal to brake, the sensor collects the pedal displacement signal 26, the pedal speed signal 27, the vehicle speed signal 28, the wheel speed signal 29 and the braking force signal 25, and transmits the above collected information to the ECU 30;

[0086] (2) ECU30 (electronic control unit) receives pedal displacement signal 26, pedal speed signal 27, vehicle speed signal 28, and wheel speed signal 29, obtains the required target braking force after processing, and then calculates the current required for the excitation coil 21 based on the required target braking force; and adjusts the current to the required current value and inputs it into the excitation coil.

[0087] (3) According to the driver's operation on the brake pedal, the ECU adjusts the current in the excitation coil 21 to change the magnetic field strength in the excitation coil 21, so that the giant magnetostrictive rod 14 in the left brake driver 19 and the right brake driver 23 are deformed and output the required braking force. Then, the braking force output by the left brake driver 19 and the right brake driver 23 acts on the left and right pistons 5 and 11 through the transmission rod 16 and the piston push rod 17, so that the two pistons move toward the brake disc 10, and the left brake pad 4 and the right brake pad 8 are pressed against the brake disc 10 through the left brake pad back plate 3 and the right brake pad back plate 9, thereby completing the braking.

[0088] (4) When braking is finished, the ECU controls the excitation coil 21 to be powered off, and the demagnetization coils 22 in the two brake actuators are fed with a current in the opposite direction (relative to the brake actuator structure) to the current previously fed into the excitation coil 21, thereby eliminating the magnetic field and restoring the giant magnetostrictive rod 14 to its original length. At the same time, as the rubber ring 6 and the giant magnetostrictive rod 14 return to their original state, the left piston 5 and the right piston 11, together with the left brake pad back plate 3 and the right brake pad back plate 9 and the left brake pad 4 and the right brake pad 8, return to their original positions, and braking is finished.

[0089] The pedal information includes a pedal displacement signal 26 and a pedal speed signal 27 , and the vehicle status signal includes a vehicle speed signal 28 and a wheel speed signal 29 .

[0090] When calculating the current in the excitation coil 21, it is only necessary to calculate the current required in the excitation coil 21 in a single brake driver according to half of the required target braking force, which is the current required to be input;

[0091] Among them, during the braking process, the force and displacement output by the left brake actuator 19 and the right brake actuator 23 should be completely consistent, which are half of the required braking force and displacement respectively;

[0092] The formula used in step (2) to calculate the braking force required to be output by the giant magnetostrictive rod in a single brake actuator is:

[0093]

[0094] The formula for calculating the deformation of the giant magnetostrictive rod required to output the required braking force is:

[0095]

[0096] The formula for calculating the required coil input current is:

[0097]

[0098] In the formula, F c F is the output force of the giant magnetostrictive rod in the required single brake actuator; z is the required braking force; ε is the deformation of the giant magnetostrictive rod in the required single brake actuator; E is the elastic modulus of the giant magnetostrictive rod; r is the radius of the giant magnetostrictive rod; π is the pi constant; I is the current in the required coil; L is the length of the part of the giant magnetostrictive rod wound with the coil; a is the characteristic constant (depending on the material properties); μ0 is the vacuum magnetic permeability; N is the number of coil turns.

[0099] Wherein, the step (3) also includes: during the braking force adjustment process, if the braking force needs to be reduced, a current opposite to that of the excitation coil is passed through the demagnetization coil to eliminate the influence of hysteresis on the braking force.

[0100] like Figure 6 As shown, the present invention can be applied to floating caliper disc brakes in addition to fixed caliper disc brakes.

[0101] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A disc brake based on magnetostrictive material, characterized in that: include: Brake assembly, left brake actuator, right brake actuator and force and displacement transmission module; The brake assembly comprises: a brake caliper body, a guide pin, a left brake pad back plate, a left brake pad, a left piston, a right piston, a rubber ring, a right brake pad, a right brake pad back plate and a brake disc; The brake caliper body is fixed on the steering knuckle of the front axle of the vehicle, and a left brake actuator and a right brake actuator are installed on the brake caliper body; The brake disc is fixed to the wheel hub of the car and extends between the left brake pad and the right brake pad; The left brake pad back plate and the right brake pad back plate are connected to the left piston and the right piston respectively, are suspended on the guide pin, and can move along the guide pin; the left brake pad and the right brake pad are fixed on the left brake pad back plate and the right brake pad back plate respectively; Rubber rings are respectively embedded in the trapezoidal cross-section ring grooves on the inner walls of the holes of the left piston and the right piston, and the rubber rings are used to return the brakes to their original positions when braking ends; The left brake driver and the right brake driver both comprise: a driver housing, a giant magnetostrictive rod, an excitation coil, a degaussing coil, a magnetic isolation pad and a magnetic isolation top cover; The input end of the giant magnetostrictive rod is fixed to the bottom end inside the driver housing; The excitation coil and the demagnetization coil are both wound on the giant magnetostrictive rod; The magnetic isolation pad is closely attached to the inner side of the driver housing; the magnetic isolation top cover is screwed on the top of the left brake driver and the right brake driver, and together with the magnetic isolation pad, isolates the influence of the magnetic field on the outside; The force and displacement transmission module is used to transmit the force and displacement output by the left brake driver and the right brake driver, and includes: a giant magnetostrictive rod, a transmission rod, a piston push rod and a support pin; The support pins are fixed on both sides of the brake caliper body; The middle part of the transmission rod is hinged on the support pin, the lower end is hinged to the input end of the piston push rod, and the upper end of the transmission rod is hinged to the output end of the giant magnetostrictive rod; The output end of the piston push rod is fixedly connected to the piston; The left and right sides of the brake caliper body are respectively provided with sliding grooves for installing the left brake actuator and the right brake actuator; The left brake actuator and the right brake actuator are fixed on the brake caliper body by fixing screws.

2. The magnetostrictive material-based disc brake according to claim 1, characterized in that: The brake also includes an adjusting gasket, which is used in conjunction with the fixing screw to adjust the positions of the left brake actuator and the right brake actuator.

3. The magnetostrictive material-based disc brake according to claim 1, characterized in that: The excitation coils in the two brake drivers use one wire, the wire arrangement in the excitation coils is completely consistent, and after the current is passed through, the currents in the two excitation coils are in the same direction relative to the brake driver.

4. The magnetostrictive material-based disc brake according to claim 1, characterized in that: The degaussing coils in the two brake drivers use one wire, the wires in the degaussing coils are arranged in exactly the same way, and after current is passed through, the currents in the two degaussing coils are in the same direction relative to the brake driver.

5. A control method for a disc brake based on magnetostrictive material, based on the brake according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) When the brake pedal is pressed to brake, the vehicle status information and pedal information are collected and transmitted to the electronic control unit; (2) The electronic control unit receives the vehicle status information and the pedal information, obtains the required target braking force after processing, calculates the current required for the excitation coil according to the required target braking force, and adjusts the current to the required current value and inputs it into the excitation coil; (3) The electronic control unit adjusts the current in the excitation coil according to the working state of the brake pedal to change the magnetic field strength in the excitation coil, so that the giant magnetostrictive rods in the two brake actuators are deformed and output the required braking force; (4) When braking ends, the electronic control unit controls the excitation coil to be powered off, and the demagnetization coils in the two brake actuators are fed with a current in the opposite direction to the current previously fed into the excitation coils, thereby eliminating the magnetic field, causing the giant magnetostrictive rod to return to its original length, and braking ends.

6. The control method of a disc brake based on magnetostrictive material according to claim 5, characterized in that: When calculating the current in the excitation coil in step (2), it is only necessary to calculate the current required in the excitation coil in a single brake driver based on half of the required target braking force, that is, the current required to be input.

7. The control method of a disc brake based on magnetostrictive material according to claim 5, characterized in that: During the braking process in step (3), the force and displacement output by the two brake actuators should be completely consistent, being half of the required braking force and displacement respectively.

8. The control method of a disc brake based on magnetostrictive material according to claim 5, characterized in that: The formula used in step (2) to calculate the braking force required to be output by the giant magnetostrictive rod in a single brake actuator is: The formula for calculating the deformation of the giant magnetostrictive rod required to output the required braking force is: The formula for calculating the required coil input current is: In the formula, F c F is the output force of the required single brake actuator giant magnetostrictive rod; z is the required braking force; ε is the required deformation of the giant magnetostrictive rod of a single brake actuator; E is the elastic modulus of the giant magnetostrictive rod; r is the radius of the giant magnetostrictive rod; π is the pi constant; I is the current in the required coil; L is the length of the part of the giant magnetostrictive rod wound with the coil; a is the characteristic constant; μ0 is the magnetic permeability of vacuum; N is the number of turns of the coil.

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