CN213425879U

CN213425879U - Rotor core with stepped variable air gap pole wing and switched reluctance motor

Info

Publication number: CN213425879U
Application number: CN202022230656.6U
Authority: CN
Inventors: 顾志强; 李运忠; 刘正昂
Original assignee: Shenzhen Huayin Power Technology Co ltd
Current assignee: Shenzhen Huayin Power Technology Co ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2021-06-11
Anticipated expiration: 2030-09-29

Abstract

The utility model discloses a rotor core and switched reluctance motor with cascaded variable air gap utmost point wing belongs to the switched reluctance motor field. The utility model discloses an evenly be provided with a n rotor core salient pole on the rotor core, n is greater than or equal to 2, the rotor core salient pole all is provided with utmost point body and utmost point wing, end connection rotor core yoke portion in the radial of utmost point body, the utmost point wing is connected respectively on the left side and the right side of the radial outer tip of utmost point body, be the echelonment that utmost point body height utmost point wing is low between utmost point wing and the utmost point body, the utmost point wing extends to the outside of keeping away from utmost point body, the radial lateral surface of utmost point wing is the echelonment, and on the extending direction of utmost point wing, the radial lateral surface of utmost point wing and the distance at rotor. The phase number of the switched reluctance motor is q, q is more than or equal to 3, m salient poles are uniformly arranged on a stator core, and m/n is q. The utility model discloses a set up the radial lateral surface of utmost point wing into the echelonment, have more level and smooth salient pole air gap volume rate of change, therefore torque pulsation is lower.

Description

Rotor core with stepped variable air gap pole wing and switched reluctance motor

Technical Field

The utility model relates to a switched reluctance motor field especially relates to a rotor core and switched reluctance motor with cascaded variable air gap polar wing.

Background

The major drawback of switched reluctance motors is torque ripple and noise. Circular telegram salient pole magnetic attraction is cut to magnetic attraction and radial magnetic attraction, tangential magnetic attraction produces the torque, radial magnetic attraction does not produce the torque, at the inductance in-process that rises, also the in-process that the salient pole aligns, after the excitation is stable, radial magnetic attraction constantly increases, tangential magnetic attraction constantly reduces, when the salient pole aligns completely, radial magnetic attraction is the biggest, tangential magnetic attraction is zero, so radial magnetic attraction is the leading cause of switched reluctance motor torque pulsation and noise.

The switched reluctance motor has the advantages that high speed is easy to realize, but the influence of high switching frequency on the motor efficiency needs to be considered at high speed, the switching frequency is in direct proportion to the number of poles of a rotor core, the number of poles of a stator core is in direct proportion to the full rate of a winding slot, so that the design is ensured to have higher number of poles of the stator core and lower number of poles of the rotor core, namely, the number of poles of the stator core and the rotor core is as large as possible, the number of poles of the stator core and the rotor core of the traditional q-phase switched reluctance motor is m/n-q/(q-1), a theorem is established, and the number of poles of the stator core and the rotor core cannot be further increased by the design, for example, the number of poles of 3 phases is q/(q-1) is 1.5, and the number of poles of 4 phases. The switching frequency is directly proportional to the switching efficiency loss.

Therefore, how to solve the above contradiction and how to reduce the torque ripple, the switching frequency and the switching efficiency loss of the switched reluctance motor under the condition of the same phase number and the same salient pole number of the stator core is a technical problem to be solved by the conventional switched reluctance motor.

To this problem, the applicant has designed "a rotor core and switched reluctance motor with variable air gap pole wing", and has proposed the utility model patent application, this scheme is under the condition that keeps same phase number and stator core salient pole number with traditional switched reluctance motor, through setting up stator core number ratio for m/n ═ q, the rotor pole number has been reduced to increased the surplus angle of commutation (B-A), the outer tip both sides of salient pole increase the pole wing and reduce marginal air gap, the pole wing sets up gradual change air gap and produces gradual change inductance, and then reach the purpose that reduces switched reluctance motor torque ripple and reduce the switching efficiency loss. The outer side face of the wing of the rotor core is in a circular arc shape, but in the actual use process, the applicant finds a more optimized stepped variable air gap pole wing.

SUMMERY OF THE UTILITY MODEL

In order to improve the not enough of prior art, the utility model aims at providing a rotor core and switched reluctance motor with cascaded air gap utmost point wing sets up to the echelonment through the radial lateral surface with the utmost point wing to on the extending direction of utmost point wing, the radial lateral surface of utmost point wing and the distance at rotor core center are according to cascaded degressive change, can further improve the smooth nature of motor operation.

The utility model discloses a solve its technical problem and the technical scheme who adopts is:

a rotor core with a step-type variable air gap pole wing is characterized in that n rotor core salient poles are uniformly arranged on the rotor core, n is more than or equal to 2, the rotor core salient poles are respectively provided with a pole body and a pole wing, namely the middle part of the rotor core salient pole is defined as the pole body, the radial inner end part of the pole body is connected with a yoke part of the rotor core, the left side and the right side of the radial outer end part of the pole body are respectively connected with the pole wing, the pole wing and the pole body are in a step shape with the height of the pole body and the height of the pole wing, the pole wing extends towards the outer side far away from the pole body, the radial outer side surface of the pole wing is in a step shape, and in the extending direction of the pole wing, the distance between the; the mechanical angle of the pole body of the salient pole of the rotor core is C, the mechanical included angle of the outermost side edge of two pole wings on any salient pole of the rotor core is D, D is more than or equal to 2C and less than or equal to 5C, the number of steps on the left side and the right side of the pole body is x, and x is more than or equal to 2.

In the utility model, the mechanical angle occupied by the width of each preferred ladder is C1, C2, … and Cx, then Ci is not less than C/8 and not more than 3C/4, i is 1, 2, … and x.

In the utility model, D is preferably not less than 2.5C and not more than 4.5C.

In the utility model, preferably, Ci is not less than C/4 and not more than C/2.

The utility model discloses in, it is preferred adjacent two the step height difference is delta h, then 0.1mm is less than or equal to delta h is less than or equal to 1.5 mm.

The utility model discloses in, it is preferably same the structure of two utmost point wings on the rotor core salient pole is symmetrical about the axis of utmost point body.

The rotor core is applied to a switched reluctance motor, and the switched reluctance motor with the rotor core provided with the stepped variable air gap pole wing is obtained and comprises a stator core and a rotor core, wherein the phase number of the switched reluctance motor is q, q is more than or equal to 3, and m salient poles are uniformly arranged on the stator core; n rotor core salient poles are uniformly arranged on the rotor core, n is more than or equal to 2, and m/n is q/(q-1), or m/n is q; the rotor core salient poles are provided with pole bodies and pole wings, namely the middle parts of the rotor core salient poles are defined as the pole bodies, the radial inner ends of the pole bodies are connected with a yoke part of the rotor core, the left sides and the right sides of the radial outer ends of the pole bodies are respectively connected with the pole wings, the pole wings and the pole bodies are in a step shape with the height of the pole bodies and the height of the pole wings being low, the pole wings extend towards the outer sides far away from the pole bodies, the radial outer side surfaces of the pole wings are in the step shape, and in the extending direction of the pole wings, the distance between the radial outer side surfaces of the pole wings and the center of the rotor; the mechanical angle of the pole body of the salient pole of the rotor core is C, the mechanical included angle of the outermost edges of the two pole wings on any salient pole of the rotor core is D, 2C is larger than or equal to D and is smaller than or equal to 5C, the number of steps on each pole wing is x, x is larger than or equal to 2, the mechanical angle occupied by the width of each step is C1, C2, … and Cx, Ci is larger than or equal to C/8 and is smaller than or equal to 3C/4, and i is 1, 2, … and x.

In the above switched reluctance motor, further optimization of the rotor core refers to the aforementioned arrangement of the rotor core.

To the concrete setting of the air gap between ladder and stator core salient, establish the radial outer tip of rotor core utmost point body is s, adjacent two with the air gap between the stator core salient the difference of the air gap size between ladder and the stator core salient is the ss, then 0.1mm is less than or equal to s and is less than or equal to ss and is less than or equal to 1.5 mm.

Since the technical scheme is used, the beneficial effects of the utility model are that:

1. the utility model discloses a stator core, be the echelonment that the utmost point body height utmost point wing is low between utmost point wing and the utmost point body, the radial lateral surface of utmost point wing sets up to the echelonment to on the extending direction of utmost point wing, the radial lateral surface of utmost point wing and the distance at rotor core center are according to cascaded degressive change, because the process that the torque produced is the process that salient pole air gap volume reduces, torque and salient pole air gap volume rate of change are approximately proportional, the stairstepping utmost point wing is compared convex utmost point wing and is had more level and smooth salient pole air gap volume rate of change, therefore torque pulsation is lower. According to actual test measurement, under the condition of the same electromagnetic parameters, the ratio of the maximum torque to the minimum torque of the traditional switched reluctance motor without pole wings is about 5; the switched reluctance motor with the arc-shaped pole wing is arranged, and the ratio of the maximum torque to the minimum torque is about 3; set up the utility model discloses cascaded utmost point wing's switched reluctance motor, maximum torque is about 2 with the ratio of minimum torque.

2. The utility model discloses a switched reluctance motor is the m/n through setting up stator-rotor core number ratio and is q, for the condition of m/n q/(q-1), has reduced the rotor core number of poles, has increased the surplus angle of commutation, reduces marginal air gap through the outer tip both sides increase utmost point wing of salient pole, produces gradual change inductance through setting up gradual change air gap to the utmost point wing, and then reaches the purpose that reduces switched reluctance motor torque ripple.

Drawings

Fig. 1 is a schematic structural diagram of a rotor core having stepped variable air gap pole wings according to embodiment 1 of the present invention.

Fig. 2 is a schematic structural diagram of a stator and a rotor of a switched reluctance motor with a rotor core having a stepped variable air gap pole wing according to embodiment 2 of the present invention.

Fig. 3 is a schematic structural diagram of a stator and a rotor of a switched reluctance motor with a rotor core having a stepped variable air gap pole wing according to embodiment 3 of the present invention.

Fig. 4 is a schematic structural diagram of a stator and a rotor of a switched reluctance motor with a rotor core having a stepped variable air gap pole wing according to embodiment 4 of the present invention.

The meanings of the labels in the figures are: 10-stator core, 20-rotor core, 21-pole body, 22-pole wing and 23-rotor core yoke part.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail by the following embodiments with reference to the accompanying fig. 1-4. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The utility model provides a rotor core with cascaded variable air gap utmost point wing, as shown in fig. 1, evenly be provided with n rotor core salient poles on this rotor core 20, n is greater than or equal to 2, the rotor core salient pole all is provided with utmost point body 21 and utmost point wing 22, the middle part of rotor core salient pole is defined as utmost point body 21 promptly, the radial interior end connection rotor core yoke portion 23 of utmost point body 21, utmost point wing 22 is connected respectively to the left side and the right side of the radial outer tip of utmost point body 21, be the echelonment that utmost point body height utmost point wing is low between utmost point wing 22 and the utmost point body 21, utmost point wing 22 extends to the outside of keeping away from utmost point body 21, the radial lateral surface of utmost point wing 22 is the echelonment, and in the extending direction of utmost point wing 22, the radial lateral surface of utmost point wing 22 and the distance at rotor; if the mechanical angle of the pole body 21 of the salient pole of the rotor core is set to be C, and the mechanical included angle of the outermost side edge of the two pole wings 22 on any salient pole of the rotor core 20 is D, the utility model discloses preferably 2C is less than or equal to D and is less than or equal to 5C, more preferably 2.5C is less than or equal to D and is less than or equal to 4.5C, thereby the width of the salient pole wing is limited in a reasonable range, so as to reduce the edge air gap, thereby ensuring that the edge air gap is in a reasonable range. The number of the steps on the left side and the right side of the pole body is x respectively, x is more than or equal to 2, the mechanical angle occupied by the width of each step is C1, C2, … and Cx, preferably, Ci is more than or equal to C/8 and less than or equal to 3C/4, i is 1, 2, … and x, more preferably, C/4 is more than or equal to Ci and less than or equal to C/2; thereby limiting the width of each step on the pole wing 22 to a preferred range. By limiting parameters such as the width of the pole wing 22, the number of steps on the pole wing 22, the width of each step and the like, when the rotor core 20 is applied to a switched reluctance motor, a smoother volume change rate of a salient pole air gap can be obtained, so that torque pulsation is smoother, and the motor can run more smoothly. In this structure, it is preferable that the two pole pieces 22 on the same salient pole of the rotor core have a structure symmetrical with respect to the central axis of the pole body 21. In this structure, utmost point body 21 and utmost point wing 22 are the definition of a convenient description, and in actual production, utmost point body 21 and utmost point wing 22 can be split type, also can the integral type shaping as an organic whole, all fall within the utility model discloses a within the protection scope.

The utility model discloses rotor core 20 with above-mentioned structural feature can be applied to in the q phase switched reluctance motor that the stator core number of poles is m, and it can be applied to in the ordinary switched reluctance motor, in the switched reluctance motor of m/n ═ q/(q-1) promptly, more preferably be applied to in the switched reluctance motor that further improves than the stator core number of poles, promptly: the switched reluctance motor comprises a stator core 10 and a rotor core 20, wherein if the phase number of the motor is q, q is more than or equal to 3, m salient poles are uniformly arranged on the stator core 10, n rotor core salient poles are uniformly arranged on the rotor core 20, and n is more than or equal to 2, the number relation of the designed stator and rotor salient poles is m/n-q.

For the switched reluctance motor, handing-over commutation mechanical angle is A360 °/qn, and A stands for every looks circular telegram and only hands over the non-overlapping minimum commutation mechanical angle, and the inductance zone mechanical angle that rises is B180 °/n, and B stands for the biggest mechanical angle that every looks allowwed circular telegram, the utility model discloses the remaining angle of definition commutation is (B-A) ═ 180 °/q)/n, and the commutation surplus angle is bigger, and radial magnetic attraction is smaller during the commutation, and then torque ripple and noise are less. The utility model discloses owing to set up stator and rotor core number ratio for m/n ═ q, reduced rotor core 20 utmost point numbers, then obtained the remaining angle of bigger commutation, can reduce torque ripple and noise.

In some preferred embodiments, if the height difference between two adjacent steps is set to be Δ h, then Δ h is less than or equal to 0.1mm and less than or equal to 1.5 mm. The air gap between the stator and the rotor is changed by limiting the height difference of each step on the pole wing 22, so that a smoother volume change rate of the air gap of the salient pole is formed, pulsation in the operation process is reduced, and the motor further runs more smoothly. The utility model discloses in, the difference in height of ladder both includes the difference in height between utmost point body and the utmost point wing 22, also includes the difference in height of each ladder on the utmost point wing 22.

The height difference of the above steps, i.e. the design rule for limiting the air gap generated between the rotor core 20 and the stator core 10, corresponds to the switched reluctance motor, where s is the air gap between the radial outer end of the pole body 21 and the salient pole of the stator core 10, and ss is the difference in the size of the air gap between two adjacent steps and the salient pole of the stator core 10, then s is greater than or equal to 0.1mm and less than or equal to ss and less than or equal to 1.5 mm.

Example 1

A rotor core 20 with a stepped variable air gap pole wing shown in fig. 1, wherein 4 rotor core salient poles are uniformly arranged on the rotor core 20, each rotor core salient pole is provided with a pole body 21 and a pole wing 22, namely, the middle part of each rotor core salient pole is defined as the pole body 21, the radial inner end part of the pole body 21 is connected with a rotor core yoke part 23, the left side and the right side of the radial outer end part of the pole body 21 are respectively connected with the pole wings 22, a step shape with a high pole body and a low pole body is formed between the pole wings 22 and the pole body 21, the pole wings 22 extend towards the outer side far away from the pole body 21, the radial outer side surfaces of the pole wings 22 are step-shaped, and in the extending direction of the pole wings 22, the distance between the radial outer side surfaces of the pole wings 22 and; the structure of the two pole wings 22 on the same salient pole of the rotor core is symmetrical about the central axis of the pole body 21. The mechanical angle of the pole body 21 of the rotor core salient pole is C, which is 14 ° in this embodiment; the mechanical included angle of the outermost edges of the two pole wings 22 on any salient pole of the rotor core 20 is D, then D is greater than or equal to 28 degrees and less than or equal to 70 degrees, D is 62 degrees in the embodiment, the number of steps on the left side and the right side of the pole body is respectively 4, the mechanical angle occupied by the width of each step is C1, C2, … and C4, Ci is greater than or equal to 1.75 and less than or equal to 10.5, and i takes the value of 1, 2, 3 and 4; in this embodiment, C1 is 5 °, C2 is 6 °, C3 is 6 °, and C4 is 7 °.

The height difference between the pole body 21 and the pole wing 22 and the height difference of each step on the pole wing 22 are both delta h, and delta h is more than or equal to 0.1mm and less than or equal to 1.5 mm.

Example 2

Fig. 2 is a schematic diagram of a stator and rotor structure of a switched reluctance motor with a rotor core 20 having stepped variable air gap pole wings. The phase number of motor is 3 for q, evenly is provided with 12 salient poles on the stator core 10, evenly is provided with 4 rotor core salient poles on the rotor core 20, accords with the utility model discloses well m/n is the law of q. Other features of the rotor core 20 are the same as those of the rotor core 20 in embodiment 1.

After the stator core 10 and the rotor core 20 are mounted, if the air gap between the radial outer end portion of the rotor core body 21 and the salient pole of the stator core 10 is s, and the difference between the sizes of the air gaps between two adjacent steps and the salient pole of the stator core 10 is ss, the relationship that s is greater than or equal to 0.1mm and less than or equal to s and less than or equal to 1.5mm is satisfied, in the embodiment, s is 0.2mm, and ss is 0.4 mm.

Example 3

Fig. 3 is a schematic diagram of a stator and rotor structure of a switched reluctance motor with a rotor core having stepped variable air gap pole wings. The phase number of motor is 3 for q, evenly is provided with 6 salient poles on the stator core 10, evenly is provided with 4 rotor core salient poles on the rotor core 20, accords with the utility model discloses well m/n is the law of q/(q-1). Other features of the rotor core 20 are the same as those of the rotor core 20 in embodiment 1.

After the stator core 10 and the rotor core 20 are installed, if the air gap between the radial outer end portion of the rotor core body 21 and the salient pole of the stator core 10 is s, and the difference of the air gaps between two adjacent steps and the salient pole of the stator core 10 is ss, the relationship that s is greater than or equal to 0.1mm and less than or equal to ss and less than or equal to 1.5mm is satisfied. In this example, s is 0.2mm and ss is 0.4 mm. Compare ordinary pole number ratio and be 6/4 three-phase switch reluctance motor, owing to used the utility model discloses a cascaded air gap utmost point wing that becomes, the operation of motor is more in the same direction as smooth.

Example 4

Fig. 4 is a schematic diagram of a stator and rotor structure of a switched reluctance motor with a rotor core having stepped variable air gap pole wings. The phase number of motor is 4 for q, evenly is provided with 8 salient poles on the stator core 10, evenly is provided with 6 rotor core salient poles on the rotor core 20, accords with the utility model discloses well m/n is the law of q/(q-1). The rotor core 20 is uniformly provided with 6 rotor core salient poles, the rotor core salient poles are provided with pole bodies 21 and pole wings 22, namely the middle parts of the rotor core salient poles are defined as the pole bodies 21, the radial inner end parts of the pole bodies 21 are connected with a rotor core yoke part 23, the left sides and the right sides of the radial outer end parts of the pole bodies 21 are respectively connected with the pole wings 22, a step shape with high pole body and low pole wing is formed between the pole wings 22 and the pole bodies 21, the pole wings 22 extend towards the outer side far away from the pole bodies 21, the radial outer side surfaces of the pole wings 22 are step-shaped, and in the extending direction of the pole wings 22, the distance between the radial outer side surfaces of the pole wings 22 and the center of the rotor core; the structures of the two pole wings 22 on the same rotor core salient pole are symmetrical about the central axis of the pole body 21; the mechanical angle of the pole body 21 of the rotor core salient pole is C, which is 14 ° in this embodiment; the mechanical included angle of the outermost edges of the two pole wings 22 on any salient pole of the rotor core 20 is D, then D is greater than or equal to 28 degrees and less than or equal to 70 degrees, D is 38 degrees in the embodiment, the number of steps on the left side and the right side of the pole body is respectively 2, the mechanical angle occupied by the width of each step is C1 and C2, then Ci is greater than or equal to 1.75 and less than or equal to 10.5, and i takes the value of 1 and 2; in this embodiment, C1 is 6 ° and C2 is 6 °.

The height difference between the pole body 21 and the pole wing 22 and the height difference of each step on the pole wing 22 are both delta h, and delta h is more than or equal to 0.1mm and less than or equal to 1.5 mm. After the stator core 10 and the rotor core 20 are installed, if the air gap between the radial outer end of the pole body 21 and the salient pole of the stator core 10 is set to be s, and the difference of the air gaps between two adjacent steps and the salient pole of the stator core 10 is set to be ss, the relation that s is greater than or equal to 0.1mm and less than or equal to ss and less than or equal to 1.5mm is satisfied. In this example, s is 0.2mm and ss is 0.7 mm.

Compare ordinary pole number than the four-phase switch reluctance machine who is 8/6, owing to used the utility model discloses a cascaded variable air gap utmost point wing 22, the operation of motor is more in the same direction as smooth.

Any utility model creation is through the application and the combination to prior art in order to create new things, to the primary and secondary judgement of numerous technical problems, and to the application combination of numerous technical means, there is unlimited possibility, the above-mentioned only is the description of the preferred embodiment of the utility model, should point out because the limited of literal expression, and there is unlimited concrete structure objectively, to ordinary technical staff in this field, under the prerequisite that does not deviate from the principles of the utility model, can also make a plurality of improvements, these improvements should also regard as the scope of protection of the utility model.

Claims

1. A rotor core with stepped variable air gap pole wings is characterized in that: the rotor core is uniformly provided with n rotor core salient poles, n is more than or equal to 2, the rotor core salient poles are provided with pole bodies and pole wings, namely the middle parts of the rotor core salient poles are defined as the pole bodies, the radial inner end parts of the pole bodies are connected with yoke parts of the rotor core, the left sides and the right sides of the radial outer end parts of the pole bodies are respectively connected with the pole wings, the pole wings and the pole bodies are in a step shape with the height of the pole bodies and the height of the pole wings being low, the pole wings extend towards the outer sides far away from the pole bodies, the radial outer side surfaces of the pole wings are in the step shape, and in the extending direction of the pole wings, the distance between the radial outer side surfaces of the pole; the mechanical angle of the pole body of the salient pole of the rotor core is C, the mechanical included angle of the outermost side edge of two pole wings on any salient pole of the rotor core is D, D is more than or equal to 2C and less than or equal to 5C, the number of steps on the left side and the right side of the pole body is x, and x is more than or equal to 2.

2. The rotor core having stepped variable air gap wings of claim 1, wherein: the mechanical angle occupied by the width of each step is C1, C2, … and Cx, Ci is more than or equal to C/8 and less than or equal to 3C/4, and i is 1, 2, … and x.

3. The rotor core having stepped variable air gap wings of claim 1, wherein: d is more than or equal to 2.5C and less than or equal to 4.5C.

4. The rotor core having stepped variable air gap wings of claim 1, wherein: ci is more than or equal to C/4 and less than or equal to C/2.

5. The rotor core with stepped variable air gap pole wing of claim 1 or 2, wherein: the difference value of the heights of two adjacent steps is delta h, and the delta h is more than or equal to 0.1mm and less than or equal to 1.5 mm.

6. The rotor core having stepped variable air gap wings of claim 1, wherein: the structures of the two pole wings on the same salient pole of the rotor core are symmetrical about the central axis of the pole body.

7. A switched reluctance machine having a rotor core with stepped variable air gap pole wings comprising a stator core and a rotor core according to any one of claims 1 to 6, wherein: the phase number of the switched reluctance motor is q, q is more than or equal to 3, m salient poles are uniformly arranged on the stator core, and m/n is q.

8. A switched reluctance machine having a rotor core with stepped variable air gap pole wings comprising a stator core and a rotor core according to any one of claims 1 to 6, wherein: the phase number of the switched reluctance motor is q, q is more than or equal to 3, m salient poles are uniformly arranged on the stator core, and m/n is q/(q-1).

9. A switched reluctance motor having a rotor core with stepped variable air gap pole wings as claimed in claim 7 or 8, wherein: and the air gap between the radial outer end part of the rotor iron core body and the stator iron core salient is s, and the difference value of the sizes of the two adjacent stepped air gaps is ss, so that s is more than or equal to 0.1mm and less than or equal to ss and less than or equal to 1.5 mm.