A device and method for measuring the friction coefficient of a tire with a road surface

Abstract

The application provides a tire and road surface friction coefficient measuring device and a measuring method, the measuring device comprises a bearing body, a tire, a wheel shaft, a transmission part, a magnetic field generator and a wire frame, the bearing body is driven by an external force to move the tire through the wheel shaft, the wheel shaft is arranged on the bearing body, the transmission part is arranged on the bearing body, the magnetic field generator is arranged on the bearing body, the wire frame comprises a rotating part and a coil, the rotating part is in transmission connection with the wheel shaft through the transmission part, and the coil is located in a uniform magnetic field and is fixedly connected with the rotating part; the magnetic field generator and the wire frame are arranged, the coil is located in the uniform magnetic field generated by the magnetic field generator during testing, the coil is subjected to the action of an ampere force after being electrified, and the rotating part is hindered from rotating, when the rotating part stops rotating, a torque equation acting on the rotating part is established, and the friction coefficient between the tire and the road surface can be measured according to the current in the coil, so that the measured friction coefficient is accurate, and the measuring efficiency of the measuring device is improved.

Description

Technical Field

[0001] This invention relates to the field of friction coefficient measurement technology, and in particular to a measuring device and method for measuring the friction coefficient between a tire and a road surface. Background Technology

[0002] The coefficient of friction between the tire and the road surface is one of the important factors affecting tire braking performance, and is often referred to as the tire's adhesion coefficient. The higher the coefficient of friction between the tire and the road surface, the better the tire's braking performance. For automobiles or other moving vehicles that use tires as moving elements, the better the tire's braking performance, the better the vehicle's driving performance. Therefore, measuring the coefficient of friction between the tire and the road surface is of great significance.

[0003] Chinese patent CN206618673U discloses a low-speed adjustable slip ratio tire friction coefficient testing device for slippery road surfaces, including a slip support, a slip device, a transmission mechanism, a slip reducer, a power system, an experimental device, and a movable controller. The slip device is movably mounted on the slip support and has a friction wheel that can slide back and forth. The friction wheel is connected to the slip reducer through the transmission mechanism. The power system drives the slip device. The experimental device contacts the outer surface of the friction wheel. During testing, the slip device drives the friction wheel to rotate, and the slip reducer prevents the friction wheel from rotating through the transmission mechanism. When the friction wheel changes from a rolling state to a sliding state on the experimental device, the torque sensor in the power system feeds back torque information to the movable controller, which calculates the friction coefficient between the tire and the slippery road surface.

[0004] However, in actual testing, the above-mentioned testing device has the following technical problems: Since the tension of the power system acting on the sliding device is constantly changing, when the tension on the friction wheel is equal to the friction force, the friction wheel will not immediately change from a rolling state to a sliding state. Therefore, the torque information collected by the torque sensor will deviate from the torque information in the actual testing process, thereby reducing the accuracy of the testing device. In order to improve the accuracy of the friction coefficient test, the operators need to repeat the test work to reduce the test deviation of the friction coefficient, which makes the entire friction coefficient test process very cumbersome. Summary of the Invention

[0005] In view of this, the present invention proposes a measuring device and method for measuring the coefficient of friction between a tire and a road surface, which solves the technical problem in the prior art that the accuracy and testing efficiency of the testing device are reduced due to the deviation of the torque information collected by the torque sensor.

[0006] The technical solution of this invention is implemented as follows:

[0007] The present invention provides a measuring device for the coefficient of friction between a tire and a road surface, comprising a carrier, a tire, a wheel axle, and a transmission component. The carrier is located above the road surface and moves in a direction parallel to the road surface under the drive of an external force. The tire is located on one side of the carrier and is in contact with the road surface. The wheel axle is movably mounted on the carrier and fixedly connected to the tire. The transmission component is movably mounted on the carrier.

[0008] It also includes a magnetic field generator and a wire frame. The magnetic field generator is fixedly mounted on the support body and is used to generate a uniform magnetic field. The wire frame includes a rotating component and at least one set of coils. The rotating component is movably mounted on the support body. The rotating component is connected to the wheel axle through a transmission component and rotates circumferentially under the drive of the wheel axle. The coils are located in the uniform magnetic field and are fixedly connected to the rotating component. When the coils are energized, they resist the circumferential rotation of the rotating component under the action of Ampere force.

[0009] Based on the above technical solutions, preferably, the number of coils is two sets, and the two sets of coils are insulated from each other and arranged in a cross manner.

[0010] More preferably, the included angle between the two sets of coils is 90°.

[0011] Based on the above technical solutions, preferably, the coil has a symmetrical structure, and the axis of symmetry of the coil is the central axis of the rotating component.

[0012] Based on the above technical solutions, preferably, the transmission component includes a first bevel gear, a second bevel gear, a third bevel gear, and a transmission shaft. The first bevel gear is fixedly mounted on the wheel axle, the second bevel gear is fixedly mounted on one end of the transmission shaft, and the third bevel gear is fixedly mounted on the other end of the transmission shaft and on the rotating component. The transmission shaft is movably mounted on the carrier. The second bevel gear on the transmission shaft meshes with the first bevel gear on the wheel axle, and the third bevel gear on the transmission shaft meshes with the third bevel gear on the rotating component.

[0013] More preferably, when the number of drive shafts is greater than or equal to two, only one drive shaft is provided with a second bevel gear, and both ends of the remaining drive shafts are provided with a third bevel gear, and the third bevel gears on adjacent drive shafts mesh with each other.

[0014] Based on the above technical solutions, preferably, the magnetic field generator is a Helmholtz coil.

[0015] Based on the above technical solutions, preferably, it also includes electrode carriers, wherein there are two electrode carriers, and the two electrode carriers are electrically connected to the positive terminal and the negative terminal of the coil, respectively.

[0016] Based on the above technical solutions, preferably, a monitor is also included, which is installed on the carrier and used to monitor the movement state of the wheel axle.

[0017] The present invention also provides a method for measuring the coefficient of friction between a tire and a road surface, applied to the aforementioned device for measuring the coefficient of friction between a tire and a road surface, comprising the following steps:

[0018] S01: Weigh the measuring device and place it on the road surface. Calculate the pressure exerted by the tire on the road surface based on the pressure point between the measuring device and the road surface.

[0019] S02: Drive the load-bearing body to move in a direction parallel to the road surface. When the tire rolls on the road surface, calculate the friction force on the tire based on the pressure exerted by the tire on the road surface in S01, measure the radius of the tire, and calculate the torque of the friction force acting on the wheel axle.

[0020] S03: Measure the torque transmission ratio of the transmission components, and calculate the torque of the rotating components caused by friction in combination with the torque of the wheel axle caused by friction in S02.

[0021] S04: Turn on the magnetic field generator to generate a uniform magnetic field and calculate the magnetic induction intensity of the uniform magnetic field.

[0022] S05: Measure the size of the coil, pass current into the coil, calculate the Ampere force on the coil by combining the magnetic induction intensity of the uniform magnetic field in S04, and calculate the maximum torque of the Ampere force on the rotating part.

[0023] S06: Gradually increase the current flowing into the coil until the rotating part stops rotating. Based on the torque of the rotating part caused by friction in S03 and the maximum torque of the rotating part caused by Ampere force in S05, establish the torque equation. Calculate the coefficient of friction between the tire and the road surface based on the current in the coil when the rotating part stops rotating.

[0024] The measuring device and measuring method of the present invention have the following advantages over the prior art:

[0025] (1) Set up a magnetic field generator and a wire frame. During the test, the coil inside the wire frame is located in the uniform magnetic field generated by the magnetic field generator. After the coil is energized, it is subjected to the Ampere force, which hinders the rotation of the rotating part. When the maximum torque of the Ampere force on the rotating part is equal to the torque of the friction force on the rotating part, the rotating part immediately stops rotating, and the tire immediately changes from rolling to sliding on the road surface. At this time, establish the torque equation acting on the rotating part. The friction coefficient between the tire and the road surface can be measured according to the current in the coil. The friction coefficient measured in this way is more accurate and improves the accuracy of the measuring device.

[0026] (2) According to the Ampere force calculation formula, since the magnetic induction intensity and the coil remain unchanged in the uniform magnetic field, the Ampere force on the coil is proportional to the current flowing into the coil. Therefore, the operator can accurately control the change in Ampere force. When the rotating part stops rotating, the operator stops increasing the current in the coil. The tire always slides on the road surface. At this time, the operator can reduce the test deviation of the friction coefficient by fine-tuning the current. There is no need to repeat the measurement many times, which improves the measurement efficiency of the measuring device. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the measuring device of the present invention;

[0029] Figure 2 for Figure 1 Enlarged structural diagram of region A in the middle;

[0030] Figure 3 for Figure 1 A magnified structural diagram of region B in the middle;

[0031] Figure 4 for Figure 1 A magnified structural diagram of region C in the middle;

[0032] Figure 5 This is a schematic diagram of the coil structure of the present invention within a uniform magnetic field;

[0033] Figure 6 This is a schematic diagram of the forces acting on the coil when the torque applied to the rotating component by the Ampere force is at its maximum.

[0034] In the diagram: 1. Carrier; 2. Tire; 3. Wheel axle; 4. Transmission component; 41. First bevel gear; 42. Second bevel gear; 43. Third bevel gear; 44. Drive shaft; 5. Magnetic field generator; 6. Wire frame; 61. Rotating component; 62. Coil; 7. Electrode carrier plate; 8. Monitor. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] like Figures 1-6 As shown, a tire-road friction coefficient measuring device of the present invention includes a carrier 1, a tire 2, a wheel axle 3, a transmission component 4, a magnetic field generator 5, and a wire frame 6.

[0037] The carrier 1 serves as the main body of the measuring device. The carrier 1 is located above the road surface and moves in a direction parallel to the road surface under the drive of external force. Here, the operator can set a hook on the carrier 1. During the test, the carrier 1 is connected to the mobile device through the hook, so that the carrier 1 has the ability to move.

[0038] Tire 2 serves as the test piece. Tire 2 is located on one side of the carrier 1 and is in contact with the road surface. During the test, only tire 2 is in contact with the road surface on the measuring device. There are two states of motion of tire 2 on the road surface: one is that tire 2 rolls on the road surface, and the other is that tire 2 slides on the road surface.

[0039] The wheel axle 3 is movably mounted on the carrier 1 and fixedly connected to the tire 2. During the test, since the tire 2 is connected to the wheel axle 3, the wheel axle 3 has two working states on the carrier 1: when the tire 2 is in a rolling state, the wheel axle 3 rotates on the carrier 1; when the tire 2 is in a sliding state, the wheel axle 3 does not rotate on the carrier 1.

[0040] To ensure the stability of the carrier 1 during the test, specifically, there are two tires 2. The two tires 2 are symmetrically arranged on both sides of the carrier 1 along the direction of movement of the carrier 1, and the two tires 2 are fixedly connected to the two ends of the wheel axle 3 respectively.

[0041] The transmission component 4 is movably mounted on the carrier 1 and is used to drive the connection between the wheel axle 3 and the wire frame 6.

[0042] The magnetic field generator 5 is fixedly mounted on the support body 1 and is used to generate a uniform magnetic field.

[0043] The wire frame 6 includes a rotating component 61 and at least one set of coils 62. The rotating component 61 is movably mounted on the carrier 1. The rotating component 61 is connected to the wheel axle 3 via the transmission component 4 and rotates circumferentially under the drive of the wheel axle 3. The coils 62 are located in a uniform magnetic field and are fixedly connected to the rotating component 61. When the coils 62 are energized, they resist the circumferential rotation of the rotating component 61 under the action of the Ampere force.

[0044] During the test, the carrier 1 drives the tire 2 to roll on the road surface. The wheel axle 3 drives the rotating part 61 to rotate circumferentially through the transmission part 4. Since the rotating part 61 is fixedly connected to the coil 62, the coil 62 will also rotate counterclockwise. When the coil 62 is energized, the coil 62 will be subjected to the Ampere force in the uniform magnetic field, which will hinder the circumferential rotation of the rotating part 61.

[0045] In a preferred embodiment, in order to enhance the resistance of the coil 62 to the rotating part 61 after it is energized, there are two sets of coils 62. The two sets of coils 62 are insulated from each other and are arranged in a cross manner. Specifically, the included angle between the two sets of coils 62 is 90°. During the test, when the included angle between the two sets of coils 62 and the magnetic field lines in the uniform magnetic field is 45°, the resistance of the coil 62 to the rotating part 61 is the greatest.

[0046] As a preferred embodiment, considering that the coil 62 will be affected by circumferential force during rotation, in order to improve the rotational stability of the coil 62 and avoid the coil 62 causing the rotating part 61 to vibrate on the carrier 1, which would affect the accuracy of the friction coefficient measurement, the coil 62 is designed as a symmetrical structure, and the axis of symmetry of the coil 62 is the central axis of the rotating part 61. Specifically, the coil 62 is a square structure.

[0047] As a preferred embodiment, a technical structure of a transmission component 4 is provided here. The transmission component 4 includes a first bevel gear 41, a second bevel gear 42, a third bevel gear 43, and a transmission shaft 44. The first bevel gear 41 is fixedly mounted on the wheel axle 3, the second bevel gear 42 is fixedly mounted on one end of the transmission shaft 44, and the third bevel gear 43 is fixedly mounted on the other end of the transmission shaft 44 and on the rotating component 61. The transmission shaft 44 is movably mounted on the carrier 1. The second bevel gear 42 on the transmission shaft 44 meshes with the first bevel gear 41 on the wheel axle 3, and the third bevel gear 43 on the transmission shaft 44 meshes with the third bevel gear 43 on the rotating component 61. Here, the transmission component 4 adopts gear transmission. Compared with other transmissions, gear transmission has the technical characteristics of smooth transmission and precise transmission ratio. During testing, the torque transmission ratio of the transmission component 4 is equal to the ratio of the radius of the second bevel gear 42 to the radius of the first bevel gear 41.

[0048] In this embodiment, to facilitate the operator in calculating the torque transmission ratio of the transmission component 4, when the number of transmission shafts 44 is greater than or equal to two, only one transmission shaft 44 is provided with a second bevel gear 42, and both ends of the remaining transmission shafts 44 are provided with third bevel gears 43, and the third bevel gears 43 on adjacent transmission shafts 44 mesh with each other. When calculating the transmission ratio of the transmission component 4, since the third bevel gears 43 on adjacent transmission shafts 44 mesh with each other, in an ideal state, the torque transmission ratio between adjacent transmission shafts 44 is 1. Therefore, no matter how many transmission shafts 44 there are, the torque transmission ratio of the transmission component 4 is always equal to the ratio of the radius of the second bevel gear 42 to the radius of the first bevel gear 41.

[0049] Specifically, there are two drive shafts 44. One end of the first drive shaft 44 is equipped with a second bevel gear 42, and the other end of the first drive shaft 44 is equipped with a third bevel gear 43. Both ends of the second drive shaft 44 are equipped with third bevel gears 43. The connection relationship between the transmission component 4, the wheel axle 3, and the wire frame 6 is as follows: the second bevel gear 42 on the first drive shaft 44 meshes with the first bevel gear 41 on the wheel axle 3; the third bevel gear 43 on the first drive shaft 44 meshes with the third bevel gear 43 on the second drive shaft 44 near the end of the first drive shaft 44; and the third bevel gear 43 on the second drive shaft 44 near the end of the rotating component 61 meshes with the third bevel gear 43 on the rotating component 61.

[0050] As a preferred embodiment, the magnetic field generator 5 is a Helmholtz coil. A Helmholtz coil is an electromagnetic component that can generate a uniform magnetic field in a small area. During testing, the operator passes current into the Helmholtz coil to obtain a uniform magnetic field.

[0051] As a preferred embodiment, the tire-road friction coefficient measuring device of the present invention further includes an electrode carrier plate 7. There are two electrode carrier plates 7, and the two electrode carrier plates 7 are electrically connected to the positive terminal and the negative terminal of the coil 62, respectively. Here, the electrode carrier plate 7 serves as the receiving electrode of the coil 62. Specifically, the electrode carrier plate 7 is electrically connected to the electrode terminal of the coil 62 through a brush.

[0052] As a preferred embodiment, the tire-road friction coefficient measuring device of the present invention further includes a monitor 8, which is mounted on the carrier 1 and is used to monitor the motion state of the wheel axle 3. Specifically, the monitor 8 is a speed sensor, encoder, or other element with speed monitoring function. During the test, since the wheel axle 3 is connected to the rotating component 61 by transmission, the operator can monitor the motion state of the rotating component 61 by monitoring the motion state of the wheel axle 3.

[0053] The present invention also provides a method for measuring the coefficient of friction between a tire and a road surface, applied to the aforementioned device for measuring the coefficient of friction between a tire and a road surface, comprising the following steps:

[0054] S01: Weigh the measuring device and place it on the road surface. Calculate the pressure exerted by tire 2 on the road surface based on the pressure point between the measuring device and the road surface.

[0055] S02: Drive the carrier 1 to move in a direction parallel to the road surface. When the tire 2 rolls on the road surface, calculate the friction force on the tire 2 based on the pressure exerted by the tire 2 on the road surface in S01, measure the radius of the tire 2, and calculate the torque of the friction force acting on the wheel axle 3.

[0056] S03: Measure the torque transmission ratio of transmission component 4, and calculate the torque of friction force acting on rotating component 61 by combining the torque of friction force acting on wheel axle 3 in S02.

[0057] S04: Turn on magnetic field generator 5 to generate a uniform magnetic field and calculate the magnetic induction intensity of the uniform magnetic field.

[0058] S05: Measure the dimensions of coil 62, pass current through coil 62, calculate the Ampere force on coil 62 by combining the magnetic induction intensity of uniform magnetic field in S04, and calculate the maximum torque of Ampere force acting on rotating part 61.

[0059] S06: Gradually increase the current flowing into coil 62 until rotating part 61 stops rotating. Based on the torque of friction force on rotating part 61 in S03 and the maximum torque of Ampere force on rotating part 61 in S05, establish a torque equation. Calculate the coefficient of friction between tire 2 and road surface based on the current in coil 62 when rotating part 61 stops rotating.

[0060] Here, the measurement method is explained using formulas based on the optimal operating condition of the measuring device:

[0061] Without considering frictional losses in the measuring device, assuming the road surface is horizontal, the carrier 1 is connected to the moving trolley, the moving trolley has two wheels and can drive the carrier 1 to move horizontally, and there are two tires 2, which are symmetrically arranged on both sides of the carrier 1 along the direction of movement of the carrier 1, and the two tires 2 are respectively fixedly connected to both ends of the wheel axle 3, which is perpendicular to the direction of movement of the carrier 1. The transmission component 4 adopts the bevel gear transmission structure in the preferred embodiment above, and the magnetic field generator 5 adopts a Helmholtz coil. The rotating component 61 is horizontally positioned, and its central axis is perpendicular to the magnetic field lines of the magnetic field generator 5 on the horizontal plane. The coil 62 has a square structure, and its axis of symmetry is the central axis of the rotating component 61. During the rotation of the coil 62, its long side is parallel to the central axis of the rotating component 61 and cuts the magnetic field lines in the uniform magnetic field. Its wide side is perpendicular to the central axis of the rotating component 61 and rotates around the central axis of the rotating component 61. There are two sets of coils 62, which are insulated from each other and are arranged at a 90° angle.

[0062] S01: Weigh the measuring device (m) and place it on a horizontal surface. At this point, tire 2 is in contact with the surface. The operator connects the carrier 1 and the trolley using hooks or other connectors. Since the trolley has two wheels and the measuring device has two tires 2, there are four pressure points between the measuring device and the surface. The formula for calculating the pressure F1 exerted by a single tire 2 on the surface is as follows:

[0063]

[0064] in, denoted as , where is the pressure point between the measuring device and the road surface; m is the weight of the measuring device; and g is the acceleration due to gravity.

[0065] S02: The trolley drives the carrier 1 to move in a direction parallel to the road surface. Due to the frictional force f, the tire 2 rolls on the road surface. The frictional force f between the tire 2 and the road surface is calculated based on the pressure F1 in S01. The calculation formula is as follows:

[0066]

[0067] Where μ is the coefficient of friction between tire 2 and the road surface;

[0068] The formula for calculating the torque M1 exerted by the frictional force f on wheel axle 3 is as follows:

[0069]

[0070] Where R0 is the radius of tire 2.

[0071] S03: Measure the torque transmission ratio of transmission component 4. Here, transmission component 4 uses gear transmission. The torque transmission ratio of transmission component 4 is equal to the speed ratio of the internal gears of transmission component 4, that is, the torque transmission ratio of transmission component 4 is equal to the ratio of the radius of the second bevel gear 42 to the radius of the first bevel gear 41. Combined with the torque M1 in S02, calculate the torque M2 of the frictional force f acting on the rotating component 61. The calculation formula is as follows:

[0072]

[0073] Where R1 is the radius of the first bevel gear 41; and R2 is the radius of the second bevel gear 42.

[0074] S04: When a current I0 is passed through a Helmholtz coil, the Helmholtz coil generates a uniform magnetic field. Calculate the magnetic induction intensity B in the uniform magnetic field using the following formula:

[0075]

[0076] Where, μ0=4π×10 -7 H / m is a constant value; N0 is the number of turns in the Helmholtz coil; I0 is the current in the Helmholtz coil; R is the radius of the Helmholtz coil.

[0077] S05: Current I is passed into coil 62 e Based on the magnetic induction intensity B in S04 and the current I flowing through coil 62 e The Ampere force F2 on coil 62 is calculated using the following formula:

[0078]

[0079] Among them, I e L1 is the current inside coil 62, and L1 is the length of the long side of coil 62;

[0080] Since there are two sets of coils 62, which are insulated from each other and crossed, and the angle between the two sets of coils 62 is 90°, when the angle between the two sets of coils 62 and the magnetic field lines in the uniform magnetic field is 45°, the resistance of the coils 62 to the rotating part 61 is the greatest, and the torque M3 exerted by the Ampere force F2 on the rotating part 61 is the greatest. Therefore, the formula for calculating the maximum torque M3 exerted by the Ampere force F2 on the rotating part 61 is as follows:

[0081]

[0082] Where N1 is the number of turns in coil 62, and L2 is half the length of the wide side of coil 62;

[0083] Due to the effect of torque M3, coil 62 will hinder the circumferential rotation of rotating part 61, and the rotational speed of rotating part 61 will begin to decrease. At this time, M2 > M3.

[0084] S06: Gradually increase the current I flowing into coil 62 e Until the rotating part 61 stops rotating, the torque M2 exerted on the rotating part 61 by the frictional force f is equal to the maximum torque M3 exerted on the rotating part 61 by the Ampere force F2. The rotating part 61 reaches a torque balance state, and the torque equation M2 = M3 is established as follows:

[0085]

[0086] After simplification, the friction coefficient μ and the current I in coil 62 are obtained. e The relationship is as follows:

[0087]

[0088] Based on the above relationship, the current I in coil 62 when rotating component 61 stops rotating is... e The coefficient of friction μ between tire 2 and the road surface can then be calculated;

[0089] When the rotating part 61 stops rotating, the tire 2 immediately changes from a rolling state to a sliding state on the road surface.

[0090] Working principle: such as Figures 1-6 As shown, the carrier 1 drives the tire 2 to roll on the road surface. The wheel axle 3 drives the rotating part 61 to rotate circumferentially through the transmission part 4. Since the rotating part 61 is fixedly connected to the coil 62, the coil 62 will also rotate counterclockwise. When the coil 62 is energized, the coil 62 will be subjected to the Ampere force in the uniform magnetic field, which will hinder the circumferential rotation of the rotating part 61. When the torque of the friction force on the rotating part 61 is equal to the torque of the Ampere force on the rotating part 61, the rotating part 61 stops rotating. At this time, the wheel axle 3 stops rotating, and the tire 2 slides on the road surface. The operator can calculate the coefficient of friction between the tire 2 and the road surface based on the current in the coil 62 when the rotating part 61 stops rotating.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A tire and road surface friction coefficient measuring device, comprising a carrier body (1), a tire (2), a wheel shaft (3) and a transmission member (4), wherein, the carrier body (1) is located above the road surface and moves in the direction parallel to the road surface under the driving of external force; the tire (2) is located on one side of the carrier body (1) and is in contact with the road surface; the wheel shaft (3) is movably arranged on the carrier body (1) and is fixedly connected with the tire (2); the transmission member (4) is movably arranged on the carrier body (1); characterized in that it further comprises a magnetic field generator (5), a wire frame (6) and an electrode carrier plate (7), wherein, the magnetic field generator (5) is fixedly arranged on the carrier body (1) and is used to generate a uniform magnetic field, and the magnetic field generator (5) is a Helmholtz coil; the wire frame (6) comprises a rotating member (61) and at least one set of coils (62), wherein, the rotating member (61) is movably arranged on the carrier body (1), and the rotating member (61) is in transmission connection with the wheel shaft (3) through the transmission member (4) and rotates circumferentially under the driving of the wheel shaft (3); the coil (62) is located in the uniform magnetic field and is fixedly connected with the rotating member (61), and the coil (62) hinders the circumferential rotation of the rotating member (61) under the action of the Ampere force after being electrified; the number of the coil (62) is two sets, and the two sets of coils (62) are insulated from each other and arranged in cross or symmetry, and the included angle between the two sets of coils (62) arranged in cross is 90°; when the two sets of coils are arranged in symmetry, the symmetry axis of the coil (62) is the central axis of the rotating member (61); the number of the electrode carrier plate (7) is two, and the two electrode carrier plates (7) are electrically connected with the positive and negative electrode connectors of the coil (62) respectively; the transmission member (4) comprises a first bevel gear (41), a second bevel gear (42), a third bevel gear (43) and a transmission shaft (44), wherein, the first bevel gear (41) is fixedly arranged on the wheel shaft (3); the second bevel gear (42) is fixedly arranged on one end of the transmission shaft (44); the third bevel gear (43) is fixedly arranged on the other end of the transmission shaft (44) and the rotating member (61); the transmission shaft (44) is movably arranged on the carrier body (1), and the second bevel gear (42) on the transmission shaft (44) is engaged with the first bevel gear (41) on the wheel shaft (3), and the third bevel gear (43) on the transmission shaft (44) is engaged with the third bevel gear (43) on the rotating member (61).

2. A device for measuring the coefficient of friction between a tire and a road surface as set forth in claim 1, characterized in that: When the number of the transmission shaft (44) is greater than or equal to two, only one of the transmission shaft (44) is provided with the second bevel gear (42), and the other transmission shaft (44) is provided with the third bevel gear (43) on both ends, and the third bevel gears (43) on the adjacent two transmission shafts (44) are engaged.

3. A device for measuring the coefficient of friction between a tire and a road surface as set forth in claim 1, characterized in that: It further comprises a monitor (8) arranged on the carrier body (1) for monitoring the motion state of the wheel shaft (3).

4. A method of measuring the tire-to-road friction coefficient, characterized in that: The application is applied to the tire and road surface friction coefficient measuring device of any one of claims 1-3, comprising the following steps: S01: weigh the measuring device and place it on the road surface, and calculate the pressure exerted by the tire (2) on the road surface according to the pressure points between the measuring device and the road surface; S02: drive the carrier (1) to move in a direction parallel to the road surface, and calculate the frictional force acting on the tire (2) when the tire (2) rolls on the road surface according to the pressure exerted by the tire (2) on the road surface in S01, measure the radius of the tire (2), and calculate the torque acting on the wheel shaft (3) by the frictional force; S03: measure the torque transmission ratio of the transmission member (4), and calculate the torque acting on the rotating member (61) by the frictional force according to the torque acting on the wheel shaft (3) by the frictional force in S02; S04: turn on the magnetic field generator (5) to generate a uniform magnetic field, and calculate the magnetic induction intensity of the uniform magnetic field; S05: measure the size of the coil (62), pass current into the coil (62), and calculate the Ampere force acting on the coil (62) and the maximum torque acting on the rotating member (61) by the Ampere force according to the magnetic induction intensity of the uniform magnetic field in S04; S06: gradually increase the current passed into the coil (62) until the rotating member (61) stops rotating, establish a torque equation according to the torque acting on the rotating member (61) by the frictional force in S03 and the maximum torque acting on the rotating member (61) by the Ampere force in S05, and calculate the friction coefficient between the tire (2) and the road surface according to the current in the coil (62) when the rotating member (61) stops rotating.

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