Patent Description:
A tread brake is known as one type of braking system for a railway vehicle. A tread brake is a braking system which, by pressing a brake shoe against a tread of a wheel of a railway vehicle, generates a frictional force between the tread and the brake shoe, and applies a brake to the railway vehicle using the frictional force.

In the case of utilizing a tread brake to apply a brake to a railway vehicle, because frictional heat is produced between the tread and the brake shoe, the temperature of the wheel, particularly the temperature of a rim that forms an outer circumferential portion of the wheel rises. As a result, thermal expansion of the rim occurs, and thermal stress is generated in the rim. Various wheel shapes have conventionally been proposed in order to reduce such thermal stress.

For example, Patent Literature <NUM> proposes a wheel including a rim that forms an outer circumferential portion of the wheel, a boss that forms an inner circumferential portion of the wheel, and a web that has a substantially S-shaped cross section. In the wheel proposed in Patent Literature <NUM>, for the purpose of reducing thermal stress of the web and the rim, the amount of displacement of the rim with respect to the boss, and the amount of displacement of the web on the rim side are set to a predetermined value or more, respectively. The amount of displacement of the rim with respect to the boss is the distance between a perpendicular line extending from an end on the rim side of a curved plate-thickness center line of the web to an axial centerline of the wheel, and a perpendicular line extending from an end on the boss side of the plate-thickness center line to the axial centerline of the wheel. The amount of displacement of the web on the rim side is the distance between a perpendicular line extending from the end on the rim side of the plate-thickness center line to the axial centerline of the wheel, and a perpendicular line extending from the center of the rim in the axial direction of the wheel to the axial centerline of the wheel.

For example, Patent Literature <NUM> proposes a wheel in which a web is given a curved cross-sectional shape for the purpose of reducing thermal stress of the rim. In the wheel proposed in Patent Literature <NUM>, the web has a cross-sectional shape that is referred to as a "bell shape". Both ends of a curved plate-thickness center line of the web are arranged on the same side with respect to the central plane of the wheel (a plane perpendicular to the axial centerline of the wheel). On the other hand, the midpoint of the plate-thickness center line is arranged on the opposite side to both ends of the plate-thickness center line with respect to the center plane of the wheel.

Patent Literature <NUM> describes a railway vehicle wheel comprises a hub and a tire carrying a flange, which hub and tire are mutually connected by means of a disc or a number of spokes. The tire comprises a thin visco-elastic layer for dissipating vibrations originating from the contact of the railway vehicle wheel with a railway track. Said visco-elastic layer is circular and concentric to the tire. <CIT> shown an example of a wheel.

Usually, compressive residual stress is imparted to the rim of a wheel to be used in a railway vehicle by performing a heat treatment or the like during production. However, when a brake is applied to a railway vehicle by a tread brake and if high thermal stress is generated in the rim and plastic deformation occurs, the compressive residual stress of the rim may in some cases be reversed to tensile residual stress. Specifically, during braking of a railway vehicle, on one hand the temperature of the rim increases due to friction between the tread and the brake shoe and consequently the rim attempts to thermally expand, on the other hand the temperature increase on the inner circumferential side of the wheel is small. Therefore, the thermal expansion of the rim is inhibited, and in the rim, compressive stress is generated, in particular, in the circumferential direction of the wheel. If the compressive stress exceeds the yield point, plastic deformation of the rim occurs, and after the rim is cooled, the compressive stress reverses to tensile stress and acts as residual stress in the rim. It is considered that if a crack is generated in the tread in a state in which tensile residual stress has been generated in the rim, there is a possibility that the generated crack will propagate to the inside of the wheel. Hence, when a tread brake is used for applying a brake to a railway vehicle, it is necessary to reduce thermal stress that arises in the rim that is caused by the tread brake, and thereby suppress the generation of tensile residual stress in the rim.

The wheels disclosed in Patent Literatures <NUM> and <NUM> each have a web that has a curved shape. By this means, constraining thermal expansion of the rim from the web is relaxed. Hence, it is considered that, in the wheels disclosed in Patent Literatures <NUM> and <NUM>, thermal stress generated in the rim during braking of the railway vehicle is reduced, and it is less likely for tensile residual stress to be generated in the rim. However, in a case where the web is curved, there is a problem that the weight of the wheel increases.

An objective of the present invention is to provide a wheel with respect to which a reduction in weight and suppression of the generation of tensile residual stress in the rim can both be achieved.

A wheel according to the present invention is to be used in a railway vehicle. The wheel includes the features of claim <NUM>.

The angle α is defined as being <NUM>° in a case where the plate-thickness center line is parallel to the radial direction, and is defined as being less than <NUM>° in a case where the plate-thickness center line is inclined with respect to the radial direction by rotating to the opposite side to the flange around an inner end in the radial direction of the plate-thickness center line from a position of <NUM>°.

According to the present invention, a reduction in the weight of a wheel as well as suppression of the generation of tensile residual stress in the rim of the wheel can both be achieved.

A wheel according to the embodiment (first configuration) is to be used in a railway vehicle. The wheel includes a boss, a rim, and a web. The boss forms an inner circumferential portion of the wheel. An axle of the railway vehicle is to be inserted into the boss. The rim forms an outer circumferential portion of the wheel. The rim includes a tread and a flange. The tread is to come into contact with a top surface of a rail on which the railway vehicle travels. The flange protrudes from the tread outward in a radial direction of the wheel. The web has an annular shape and connects the rim and the boss. The center of the rim in an axial direction is disposed closer to the flange in the axial direction than the center of the boss in the axial direction is. The axial direction is a direction in which the central axis of the wheel extends. The web has a plate-thickness center line that has a linear shape when the wheel is viewed in a longitudinal section. When an angle that the plate-thickness center line forms with the axial direction is denoted by α, a distance in the axial direction from a side face on an opposite side to the flange among both side faces in the axial direction of the rim to an outer end in the radial direction of the plate-thickness center line is denoted by Pw, a length of the rim in the axial direction is denoted by Wr, and Pw/Wr is denoted by L, the wheel according to the first configuration satisfies the following Formula (<NUM>): <MAT> where, the angle α is <NUM>° or less. The angle α is defined as being <NUM>° in a case where the plate-thickness center line is parallel to the radial direction, and is defined as being less than <NUM>° in a case where the plate-thickness center line is inclined with respect to the radial direction by rotating to the opposite side to the flange around an inner end in the radial direction of the plate-thickness center line from a position of <NUM>°.

In the wheel according to the first configuration, the plate-thickness center line of the web is linear when the wheel is viewed in its longitudinal section and has no inflection point. In other words, the web connects the boss and the rim without substantially curving. Therefore, in comparison to a case where the web is curved, the weight of the web can be reduced. Hence, the wheel can be reduced in weight.

When a brake shoe of a tread brake is pressed against the tread of the rim of a wheel and thereby produces frictional heat, the rim undergoes thermal expansion. When the web constrains the thermal expansion of the rim, thermal stress is generated in the rim. If the thermal stress in the rim becomes excessive, the rim may be plastically deformed during braking of the railway vehicle, and after the rim is cooled, tensile residual stress may be generated in the circumferential direction of the wheel. On the other hand, the wheel according to the first configuration is formed in a shape such that a constraint imposed on the rim by the web is relaxed. More specifically, in the wheel according to the first configuration, on the premise that the center of the rim is located closer to the flange than the center of the boss is, the dimensions of each part are set so as to satisfy Formula (<NUM>) that takes into account both the angle of the plate-thickness center line of the web with respect to the axial direction of the wheel, and the position of the plate-thickness center line with respect to the rim. By this means, a constraint imposed on the rim by the web is effectively relaxed, and thermal expansion of the rim during braking can be allowed. Hence, thermal stress of the rim can be reduced, and plastic deformation of the rim can be suppressed. Therefore, the occurrence of a situation in which residual stress of the rim reverses to tensile when the rim is cooled after braking of the railway vehicle can be suppressed.

Thus, according to the wheel of the first configuration, a reduction in the weight of the wheel as well as suppression of the generation of tensile residual stress in the rim can both be achieved.

As mentioned above, in the wheel according to the first configuration, the plate-thickness center line of the web is linear when the wheel is viewed in its longitudinal section and has no inflection point. In this case, stress concentration is unlikely to occur in the web. It is therefore possible to reduce thermal stress of the web that is generated during braking of a railway vehicle.

According to the first configuration, the angle of the plate-thickness center line of the web with respect to the axial direction of the wheel is <NUM>° or less. Therefore, the web does not incline to the inner side of the track as it extends outward in the radial direction. Hence, the rigidity of the web can be secured against a load that the wheel receives in the axial direction thereof from a rail when passing through a curve, in other words, a load (lateral force) that the wheel receives from the inner side of the track. Therefore, stress generated in the web can be reduced.

An angle α that the plate-thickness center line forms with the axial direction is preferably <NUM>° or less (second configuration).

According to the second configuration, the angle of the plate-thickness center line of the web with respect to the axial direction of the wheel is <NUM>° or less. In this case, the web inclines to the outer side of the track as it extends outward in the radial direction. Hence, the rigidity of the web with respect to a lateral force can be improved, and stress generated in the web can be reduced more. Further, since the necessity to increase the plate thickness of the web in order to secure the rigidity of the web with respect to a lateral force decreases, the weight of the web and the wheel can be reduced more.

The web may have a plate thickness that decreases as the web extends outward in the radial direction until a point inward from the outer end of the plate-thickness center line and has a minimum plate thickness at the point (third configuration).

In the drawings, the same or equivalent components will be denoted by the same reference characters and repetitive description thereof will not be made.

<FIG> is a longitudinal sectional view of a wheel <NUM> according to the present embodiment. The longitudinal section refers to a cross section of the wheel <NUM> taken along a plane including a central axis X of the wheel <NUM>. The longitudinal section of the wheel <NUM> is symmetric about the central axis X, and thus <FIG> illustrates the wheel <NUM> on one side of the central axis X only. Hereinafter, a direction in which the central axis X of the wheel <NUM> extends will be referred to as an axial direction, and a radial direction and a circumferential direction of the wheel <NUM> will be simply referred to as radial direction and circumferential direction, respectively.

Referring to <FIG>, the wheel <NUM> is used in a railway vehicle. The wheel <NUM> includes a boss <NUM>, a rim <NUM>, and a web <NUM>.

The boss <NUM> forms an inner circumferential portion of the wheel <NUM>. The boss <NUM> has a substantially cylindrical shape the axial centerline of which is the central axis X. An axle of the railway vehicle (not illustrated) is to be inserted into the boss <NUM>.

The rim <NUM> forms an outer circumferential portion of the wheel <NUM>. The rim <NUM> is disposed outside the boss <NUM> in the radial direction. The rim <NUM> includes a tread <NUM> and a flange <NUM>. The tread <NUM> and the flange <NUM> are provided on the outer peripheral surface of the rim <NUM>.

The tread <NUM> faces outward in the radial direction. The tread <NUM> is to come into contact with a top surface of a rail on which the railway vehicle travels. Typically, the diameter of the tread <NUM> gradually increases toward the flange <NUM> side. For example, the tread <NUM> may be a conical tread or may be an arc tread.

The flange <NUM> is provided at one end of the rim <NUM> in the axial direction. The flange <NUM> protrudes from the tread <NUM> outward in the radial direction. When the railway vehicle travels on right and left rails, the flange <NUM> is positioned inward from the rails. Hereinafter, in the axial direction of the wheel <NUM>, a direction toward a side on which the flange <NUM> is disposed will be referred to as a flange direction, and the opposite direction will be referred to as a counter-flange direction.

The rim <NUM> further includes both side faces <NUM> and <NUM> in the axial direction. The side face <NUM> is a side face on a flange <NUM> side, and the side face <NUM> is a side face on the opposite side to the flange <NUM>. In other words, the side face <NUM> is disposed in the flange direction with respect to the side face <NUM>. The side face <NUM> is disposed in the counter-flange direction with respect to the side face <NUM> across the tread <NUM> and the flange <NUM>.

The rim <NUM> is disposed in the flange direction with respect to the boss <NUM>. More specifically, a center Cr of the rim <NUM> in the axial direction is disposed closer to the flange <NUM> in the axial direction than a center Cb of the boss <NUM> in the axial direction is. When the railway vehicle travels, the center Cr of the rim <NUM> is positioned on the inner side in the track width direction relative to the center Cb of the boss <NUM>.

The web <NUM> has an annular shape. The web <NUM> connects the boss <NUM> and the rim <NUM>. The web <NUM> has a plate thickness that is smaller as a whole than each of a boss width Wb and a rim width Wr. The plate thickness of the web <NUM> is large on its boss <NUM> side and small on its rim <NUM> side. The boss width Wb refers to the length of the boss <NUM> in the axial direction. The rim width Wr refers to the length of the rim <NUM> in the axial direction, and is the maximum distance from the side face <NUM> to the side face <NUM> of the rim <NUM> in the axial direction.

The web <NUM> includes both side faces <NUM> and <NUM> in the axial direction. The side face <NUM> is a side face on a flange <NUM> side, and the side face <NUM> is a side face on the opposite side to the flange <NUM>. In other words, the side face <NUM> is disposed in the flange direction with respect to the side face <NUM>. The side face <NUM> is disposed in the counter-flange direction with respect to the side face <NUM>. When the wheel <NUM> is viewed in its longitudinal section, the side faces <NUM> and <NUM> are preferably inclined with respect to the radial direction. The side faces <NUM> and <NUM> are connected to the rim <NUM> via connecting portions <NUM> and <NUM>, respectively. The side faces <NUM> and <NUM> are connected to the boss <NUM> via connecting portions <NUM> and <NUM>, respectively. Each of the connecting portions <NUM>, <NUM>, <NUM> and <NUM> has, for example, a substantially arcuate shape when the wheel <NUM> is viewed in its longitudinal section.

In the present embodiment, one of an end (R end) <NUM> of the connecting portion <NUM> on the web <NUM> side and an end (R end) <NUM> of the connecting portion <NUM> on the web <NUM> side that is positioned more inward than the other in the radial direction is defined to be an outer circumference end of the web <NUM>. In addition, one of an end (R end) <NUM> of the connecting portion <NUM> on the web <NUM> side and an end (R end) <NUM> of the connecting portion <NUM> on the web <NUM> side that is positioned more outward than the other in the radial direction is defined to be an inner circumference end of the web <NUM>. The outer circumference end of the web <NUM> can be regarded as a root of the web <NUM> with respect to the rim <NUM>. The inner circumference end of the web <NUM> can be regarded as a root of the web <NUM> with respect to the boss <NUM>. In the present embodiment, the end <NUM> of the connecting portion <NUM> and the end <NUM> of the connecting portion <NUM> are the outer circumference end and the inner circumference end of the web <NUM>, respectively.

The plate thickness of the web <NUM> decreases as the web <NUM> extends outward in the radial direction until a position inward from the outer circumference end <NUM> and is minimized at the position. The web <NUM> has its minimum plate thickness at a position that is inward from the outer circumference end <NUM> in the radial direction and is in the vicinity of the outer circumference end <NUM>. A position at which the plate thickness of the web <NUM> is minimized substantially coincides with a position at which a bending stress produced in the web <NUM> by a bending load received by the wheel <NUM> from a rail when the railway vehicle passes a curve is minimized. For example, the plate thickness of the web <NUM> can be minimized at a position that is <NUM> to <NUM> inward from the outer circumference end <NUM> in the radial direction.

The web <NUM> has a plate-thickness center line A. The plate-thickness center line A is a line that, when the wheel <NUM> is viewed in its longitudinal section, is formed by connecting the plate thickness centers of the web <NUM> extending from the boss <NUM> to the rim <NUM>. The plate-thickness center line A passes midpoints between the side faces <NUM> and <NUM> and extends from the boss <NUM> side to the rim <NUM> side. When the wheel <NUM> is viewed in its longitudinal section, the plate-thickness center line A has a linear shape. A linear shape herein includes not only a perfect straight line but also a very gentle arc having a curvature radius of, for example, <NUM> or more, or even a polygonal chain. In other words, the plate-thickness center line A is any line that can be recognized as a substantially straight line when the wheel <NUM> is viewed in its longitudinal section. Since the plate-thickness center line A has a linear shape when the wheel <NUM> is viewed in its longitudinal section, the web <NUM> has a substantially flat disk shape and is not substantially bent in the axial direction.

The plate-thickness center line A has an outer end Aa in the radial direction, and an inner end Ab in the radial direction. The outer end Aa is a point at which the plate-thickness center line A is connected to a straight line that passes the outer circumference end <NUM> of the web <NUM> and extends in the axial direction. The inner end Ab of the plate-thickness center line A is a point at which the plate-thickness center line A is connected to a straight line that passes the inner circumference end <NUM> of the web <NUM> and extends in the axial direction.

The position of the web <NUM> with respect to the rim <NUM> is determined by the position in the axial direction of the outer end Aa of the plate-thickness center line A. In the present embodiment, among the both side faces <NUM> and <NUM> of the rim <NUM>, the distance in the axial direction from the side face <NUM> in the counter-flange direction to the outer end Aa of the plate-thickness center line A is defined as a web position Pw. The smaller that a ratio L (L = Pw/Wr) of the web position Pw to the rim width Wr is, the farther that the outer circumference end <NUM> of the web <NUM> will be from the flange <NUM>, and the larger that the ratio L is, the closer that the outer circumference end <NUM> of the web <NUM> will be to the flange <NUM>.

The ratio L (L = Pw/Wr) of the web position Pw to the rim width Wr is determined by the relation with an angle α of the plate-thickness center line A. The ratio L of the web position Pw to the rim width Wr, and the angle α of the plate-thickness center line A are determined so as to satisfy the following Formula (<NUM>).

The angle α of the plate-thickness center line A is an angle that, when the wheel <NUM> is viewed in its longitudinal section, the plate-thickness center line A forms with the axial direction. In a case where the plate-thickness center line A is a very gentle curve, the angle α is determined to be an angle formed by a tangential line at a center of the plate-thickness center line A (midpoint between the outer end Aa and the inner end Ab) with the axial direction. In a case where the plate-thickness center line A is a polygonal chain, the angle α is determined to be an angle formed by the longest segment among segments included in the plate-thickness center line A with the axial direction. With regard to the angle α, the angle α is defined as being <NUM>° in a case where the plate-thickness center line A is parallel with the radial direction. Further, the angle α is defined as being less than <NUM>° in a case where the plate-thickness center line A is inclined with respect to the radial direction as a result of the plate-thickness center line A rotating to the opposite side to the flange <NUM> around the inner end Ab from the position of <NUM>°. In other words, in a case where the outer end Aa of the plate-thickness center line A is disposed in the counter-flange direction with reference to the position where the angle α is <NUM>°, the angle α is determined as being less than <NUM>°.

The angle α of the plate-thickness center line A is set to <NUM>° or less. The angle α is preferably <NUM>° or less, which however depends on specifications of a tread brake used for the wheel <NUM> or the like. As the angle α decreases and the inclination of the web <NUM> in the counter-flange direction increases, the more that a constraint imposed on the rim <NUM> by the web <NUM> is relaxed, and deformation of the rim <NUM> during braking of the railway vehicle is more easily allowed. From the viewpoint of the manufacturability of the wheel <NUM> and the like, the angle α is preferably <NUM>° or more.

On the other hand, as the ratio L of the web position Pw to the rim width Wr increases and the root of the web <NUM> with respect to the rim <NUM> comes closer to the flange <NUM>, the more that a constraint imposed on the rim <NUM> by the web <NUM> is relaxed, and deformation of the rim <NUM> during braking of the railway vehicle is more easily allowed. From the viewpoint of the manufacturability of the wheel <NUM> and the like, the ratio L is preferably set within a range of <NUM> or more to <NUM> or less.

In the wheel <NUM> according to the present embodiment, the angle α of the plate-thickness center line A, and the ratio L of the web position Pw with respect to the rim width Wr are both appropriately set so that a constraint imposed on the rim <NUM> by the web <NUM> is relaxed. Specifically, in the present embodiment, on the premise that the center Cr of the rim <NUM> is located closer to the flange <NUM> in comparison with the center Cb of the boss <NUM>, and the web <NUM> and the plate-thickness center line A thereof have a linear shape when the wheel <NUM> is viewed in its longitudinal section, the angle α of the plate-thickness center line A and the ratio L of the web position Pw to the rim width Wr are set so as to satisfy the relation in the aforementioned Formula (<NUM>). By this means, in the wheel <NUM> in which the center Cr of the rim <NUM> is located closer to the flange <NUM> in comparison with the center Cb of the boss <NUM>, and in which the web <NUM> and the plate-thickness center line A thereof have a linear shape, the degree of constraint imposed on the rim <NUM> by the web <NUM> can be effectively reduced. Therefore, when the brake shoe of a tread brake presses against the tread <NUM> of the rim <NUM> and frictional heat is generated, thermal expansion of the rim <NUM> is less likely to be inhibited. Hence, when using a tread brake to apply a brake to the railway vehicle, thermal stress of the rim <NUM> that occurs due to the tread brake can be reduced, and plastic deformation of the rim <NUM> can be suppressed. As a result, the occurrence of a situation in which residual stress of the rim <NUM> reverses to tensile after the rim <NUM> is cooled can be suppressed.

In the wheel <NUM> according to the present embodiment, when the wheel <NUM> is viewed in its longitudinal section, the plate-thickness center line A of the web <NUM> is linear and has no inflection point. In other words, the web <NUM> connects the boss <NUM> and the rim <NUM> without substantially curving. Therefore, in comparison to a case where the web <NUM> is curved, the weight of the web <NUM> can be reduced. Hence, a reduction in the weight of the wheel <NUM> can be realized.

Further, because the plate-thickness center line A has a linear shape and the web <NUM> substantially does not curve, stress concentration in the web <NUM> can be eased during application of a brake to the railway vehicle by a tread brake. Hence, thermal stress of the web <NUM> that is generated during braking of the railway vehicle can be reduced.

For example, in a case where the web <NUM> inclines in the flange direction (toward the inner side of the track) as it extends outward in the radial direction, the rigidity of the web <NUM> with respect to a load which the wheel <NUM> receives in the axial direction thereof from a rail when passing through a curve, that is, a load (lateral force) by which the wheel <NUM> is pushed in the flange direction by the rail will decrease. In contrast, in the present embodiment, since the angle α of the plate-thickness center line A is set to <NUM>° or less, the web <NUM> substantially does not incline in the flange direction as it extends outward in the radial direction. Thus, the rigidity of the web <NUM> with respect to a lateral force can be secured. Therefore, stress generated in the web <NUM> can be reduced.

In the wheel <NUM> according to the present embodiment, the angle α of the plate-thickness center line A is preferably <NUM>° or less. In this case, the web <NUM> will incline in the counter-flange direction (toward the outer side of the track) as it extends outward in the radial direction. By this means, the rigidity of the web <NUM> with respect to a lateral force can be improved, and stress generated in the web <NUM> can be further reduced.

In a case where, when the wheel <NUM> is viewed in its longitudinal section, the side faces <NUM> and <NUM> of the web <NUM> are parallel with the radial direction of the wheel <NUM> (a case where the side faces <NUM> and <NUM> are perpendicular to the central axis X of the wheel <NUM>), the rim <NUM> is liable to be constrained by the web <NUM>. Therefore, preferably the side faces <NUM> and <NUM> of the web <NUM> are inclined with respect to the radial direction of the wheel <NUM>. For example, the side faces <NUM> and <NUM> may each be inclined with respect to the radial direction so as to go in the counter-flange direction (toward the outer side of the track) as the side faces <NUM> and <NUM> approach the rim <NUM>. By causing the side faces <NUM> and <NUM> to incline in the radial direction, the constraint imposed on the rim <NUM> by the web <NUM> can be further relaxed.

In the present embodiment, the plate thickness of the web <NUM> decreases as the web <NUM> extends outward in the radial direction until a point inward from the outer end Aa of the plate-thickness center line A and is minimized at the point. More specifically, in the web <NUM>, the position at which the bending stress produced by a bending load received from a rail when the railway vehicle passes a curve is minimized is made to substantially coincide with the position at which the plate thickness is minimized. With this configuration, it is possible to prevent fatigue fracture of the web <NUM>, increasing the durability of the wheel <NUM>.

An embodiment according to the present disclosure is described above, but the present disclosure is not limited to the above embodiment, and various modifications may be made without departing the gist and scope of the present disclosure.

The present invention will be described below more in detail with reference to EXAMPLE. However, the present invention should not be construed to be limited to the EXAMPLE described below.

A numerical analysis by the finite element method (FEM analysis) was conducted in order to investigate wheel shapes which are capable of suppressing the generation of tensile residual stress in the rim. In the FEM analysis, an analytic model having the same shape as that of the wheel <NUM> according to the above-described embodiment (<FIG>) was created, and evaluation of the residual stress of the rim was performed while the angle (plate angle) α of the linear plate-thickness center line A, and the ratio L (L = Pw/Wr) of the web position Pw to the rim width Wr were changed. Further, evaluation of the residual stress of the rim was also performed with respect to an analytic model of a wheel having a web with an S-shaped cross section. <FIG> is a view that schematically illustrates a wheel having a web with an S-shaped cross section. The respective parameters α and conditions of L are shown in Table <NUM>.

The FEM analysis was conducted with general-purpose software (ABAQUS Ver. <NUM>, from Dassault Systemes SE). In the analysis, to simulate braking of a railway vehicle with a tread brake, heat flux was provided to a region of a tread of a wheel that is to come into contact with a brake shoe of the tread brake. Braking duration was set at <NUM> seconds, and an inner circumferential portion of a wheel was fully constrained.

The values for residual stress of the rim (rim residual stress) obtained by the FEM analysis are shown in Table <NUM>. In Table <NUM>, the rim residual stress shows the maximum circumferential stress of the rim after braking and cooling. If the rim residual stress is a negative value, it indicates that the residual stress of the rim was compressive after braking also, while if the rim residual stress is a positive value, it indicates that the residual stress of the rim changed to tensile after braking.

As shown in Table <NUM>, in each of Examples <NUM> to <NUM>, the rim residual stress was a negative value. In other words, in Examples <NUM> to <NUM>, because the thermal stress of the rim during braking was reduced, the residual stress of the rim could be kept compressive after braking also. On the other hand, in Comparative Examples <NUM> to <NUM>, the rim residual stress became a positive value. In other words, in Comparative Examples <NUM> to <NUM>, the result of the FEM analysis showed that the residual stress of the rim changed in tensile after braking. In Comparative Example <NUM>, the rim residual stress was a negative value, but because the web was curved, the weight of the wheel increased in comparison to Examples <NUM> to <NUM> and Comparatives Example <NUM> to <NUM> in which the web was not curved. Thus, in Example <NUM> to <NUM>, it was possible to suppress the generation of tensile residual stress in the rim without increasing the weight of the wheel.

Hereunder, the influence of the plate angle α and the ratio L of the web position Pw to the rim width Wr on the residual stress of the rim is discussed.

<FIG> is a graph showing the relation between the plate angle α and the rim residual stress with respect to Example <NUM>, Comparative Example <NUM>, and Comparative Example <NUM> in each of which the value of the ratio L of the web position Pw to the rim width Wr is the same. As illustrated in <FIG>, it is found that the value of the rim residual stress becomes larger as the plate angle α increases. Therefore, it can be said that as the plate angle α becomes smaller, the possibility that residual stress of the rim will change to tensile after braking of the railway vehicle decreases.

<FIG> is a graph showing the relation between the ratio L of the web position Pw to the rim width Wr and the rim residual stress with respect to Example <NUM>, Comparative Example <NUM>, and Comparative Example <NUM> in each of which the plate angle α is the same. As illustrated in <FIG>, it is found that as the ratio L of the web position Pw to the rim width Wr increases, the value of the rim residual stress decreases. Therefore, it can be said that as the ratio L becomes larger, the possibility that the residual stress of the rim will change to tensile after braking of the railway vehicle decreases.

Thus, the smaller that the plate angle α is, the more that the residual stress of the rim decreases, and furthermore, the larger that the ratio L of the web position Pw to the rim width Wr is, the more that the residual stress of the rim decreases. The reason for this will be described referring to <FIG> are diagrams exemplifying, in an exaggerated manner, a deformation which occurred in a wheel during braking in Example <NUM>, Example <NUM>, and Comparative Example <NUM>, respectively.

In Example <NUM> in which the plate angle α was a small value of <NUM>°, which is small, as illustrated in <FIG>, when the heat flux was applied to the tread <NUM>, the rim <NUM> moved by a large amount in the flange direction. In other words, in Example <NUM>, because the plate angle α was small, a constraint imposed by the web <NUM> with respect to movement of the rim <NUM> in the flange direction was reduced, and thermal expansion of the rim <NUM> could be allowed. Therefore, in Example <NUM>, thermal stress generated in the rim <NUM> during braking was reduced, and the residual stress of the rim <NUM> remained compressive after braking.

In Example <NUM> in which the ratio L of the web position Pw to the rim width Wr was a comparatively large value of <NUM>, as illustrated in <FIG>, when the heat flux was applied to the tread <NUM>, the rim <NUM> rotated in the flange direction. In other words, in Example <NUM>, since the ratio L was secured, a constraint imposed by the web <NUM> with respect to rotation of the rim <NUM> in the flange direction was reduced, and thermal expansion of the rim <NUM> could be allowed. Therefore, in Example <NUM>, thermal stress generated in the rim <NUM> during braking was reduced, and the residual stress of the rim <NUM> remained compressive after braking.

In contrast, in Comparative Example <NUM> in which the plate angle α was <NUM>° which was large compared to Example <NUM>, and the ratio L of the web position Pw to the rim width Wr was <NUM> which was small compared to Example <NUM>, as illustrated in <FIG>, almost no movement or rotation of the rim <NUM> occurred. In Comparative Example <NUM>, a constraint imposed by the web <NUM> with respect to movement and rotation of the rim <NUM> was large, and when the heat flux was applied to the tread <NUM>, thermal expansion of the rim <NUM> was inhibited. Therefore, in Comparative Example <NUM>, thermal stress generated in the rim <NUM> during braking was large, and the residual stress of the rim <NUM> changed to tensile after braking.

As described above, both the plate angle α and the ratio L of the web position Pw to the rim width Wr are involved in reversal of residual stress of a rim to tensile that occurs due to braking performed by a tread brake. Therefore, the relation between the plate angle α and the ratio L which can prevent residual stress of the rim from changing to tensile when a brake is applied to a railway vehicle by a tread brake was determined. <FIG> illustrates, in the relation between the plate angle α and the ratio L, a limit line at which residual stress of the rim does not reverse to tensile.

The plotted points in <FIG> represent results obtained by performing a similar FEM analysis as the FEM analysis described above, and represent the ratio L = web position Pw/rim width Wr when the rim residual stress was <NUM> with respect to respective plate angles α of <NUM>°, <NUM>°, <NUM>°, <NUM>°, and <NUM>°. A straight line in <FIG> was obtained by approximating these plotted points by the method of least squares, and is represented by L = <NUM>. 0223α-<NUM>. In the region on the upper side of the straight line, the rim residual stress becomes compressive. Hence, a case where residual stress of a rim can be substantially prevented from becoming tensile is a case where the plate angle α and the ratio L satisfy the following Formula (<NUM>). However, the plate angle α is to be <NUM>° or less. The following Formula (<NUM>) can be applied as long as the wheel is one in which the center of the rim is disposed closer to the flange than the center of the boss is, and the web and the plate-thickness center line thereof have a linear shape.

It was confirmed whether or not the respective Examples and respective Comparative Examples satisfied the above Formula (<NUM>). As shown in Table <NUM>, Examples <NUM> to <NUM> in which the rim residual stress was a negative value satisfied the above Formula (<NUM>). On the other hand, Comparative Examples <NUM> and <NUM> in which the rim residual stress was a positive value did not satisfy the above Formula (<NUM>). Thus, it can be said that in a wheel in which the center of the rim is disposed closer to the flange than the center of the boss is, and in which the web and a plate-thickness center line thereof have a linear shape, in a case where the plate angle α and the ratio L of the web position Pw to the rim width Wr are set so as to satisfy the above Formula (<NUM>), generation of tensile residual stress in the rim can be suppressed.

Claim 1:
A wheel (<NUM>) to be used in a railway vehicle, the wheel (<NUM>) comprising:
a boss (<NUM>) that forms an inner circumferential portion of the wheel (<NUM>) and into which an axle of the railway vehicle is to be inserted;
a rim (<NUM>) that forms an outer circumferential portion of the wheel (<NUM>) and includes a tread (<NUM>) to come into contact with a top surface of a rail on which the railway vehicle travels and a flange (<NUM>) protruding outward from the tread (<NUM>) in a radial direction of the wheel (<NUM>); and
a web (<NUM>) that has an annular shape and connects the boss (<NUM>) and the rim (<NUM>), wherein
a center (Cr) of the rim (<NUM>) in an axial direction that is a direction in which a central axis (X) of the wheel (<NUM>) extends is disposed closer to the flange (<NUM>) in the axial direction than a center (Cb) of the boss (<NUM>) in the axial direction is,
the web (<NUM>) has a plate-thickness center line (A) having a linear shape when the wheel (<NUM>) is viewed in a longitudinal section,
and characterized in that
when an angle that the plate-thickness center line (A) forms with the axial direction is denoted by α, the angle being defined as being <NUM>° in a case where the plate-thickness center line (A) is parallel to the radial direction, and as being less than <NUM>° in a case where the plate-thickness center line (A) is inclined with respect to the radial direction by rotating to an opposite side to the flange (<NUM>) around an inner end (Ab) in the radial direction of the plate-thickness center line (A) from a position of <NUM>°, and
when a distance in the axial direction from a side face (<NUM>) on an opposite side to the flange (<NUM>) among both side faces (<NUM>, <NUM>) in the axial direction of the rim (<NUM>) to an outer end (Aa) in the radial direction of the plate-thickness center line (A) is denoted by Pw, a length of the rim (<NUM>) in the axial direction is denoted by Wr, and Pw/Wr is denoted by L, the wheel satisfies Formula (<NUM>) below: <MAT>
where, the angle α is <NUM>° or less.