Caster

Abstract

To provide a caster capable of coping with the situation requiring the caster to get over a level difference or the like in spite of a relatively small size.SOLUTION: A caster includes: a fixed shaft attached to a vehicle body and having a plurality of inner ring raceway surfaces formed in an outer periphery thereof; an outer ring disposed around the fixed shaft and having a plurality of outer ring raceway surfaces formed in an inner periphery thereof so as to correspond to the inner ring raceway surfaces; balls rollably disposed along the plurality of inner ring raceway surfaces and the outer ring raceway surfaces; a fork portion coupled to the outer ring; a wheel shaft coupled to the fork portion; and a wheel rotatably held around the wheel shaft. Therein a center line of the fixed shaft and a center of the wheel shaft are offset to each other in a horizontal direction.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a caster.

Background Art

[0002] Conventionally, as one of the means of transportation for the elderly and the like, a silver car that can assist in walking while carrying luggage such as a bag is known. In addition, in order to compensate for the decline in motor functions of the elderly and the like, silver cars with assist functions and brake functions have also appeared, holding the potential for market expansion. With the improvement of the functions of silver cars, their weight also tends to increase.

[0003] In a general silver car, a caster including small-diameter wheels is attached to the vehicle body main body, and by rolling the wheels on the ground, the operator can push the silver car with a light force.

[0004] Here, if the direction of the wheels is fixed with respect to the vehicle body main body, a burden is generated when changing the direction of a silver car or the like. Therefore, some casters are provided with a wheel turning mechanism so that the direction of the wheels can be changed with respect to the vehicle body main body.

[0005] Patent Document 1 discloses a caster having a wheel turning mechanism including a support shaft pivotally supported on an object to be attached such as a vehicle body main body, a synthetic resin main body frame in which a radial bearing (deep groove ball bearing) for bearing the support shaft is insert-molded, and a wheel pivotally supported on the main body frame. According to this wheel turning mechanism, the main body frame is rotatably supported with respect to the support shaft with low friction by the deep groove ball bearing, so that the main body frame and the wheel can be turned around the support shaft.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In a silver car with four wheels, casters having a wheel turning mechanism are often provided at two locations on the driven wheel (front wheel) side. Here, when the distance between the axis of the support shaft and the perpendicular line dropped from the center of rotation of the wheel to the ground is defined as the offset amount, in order to enhance the drivability of the driven wheel and enable the caster to turn with a small force, it is desirable to increase the offset amount as much as possible. However, if this offset amount is too large, the amount of protrusion of the wheel from the vehicle body during turning becomes large, resulting in poor usability, so there is naturally a limit to the offset amount.

[0008] By the way, as another problem caused by increasing the offset amount, the distance from the support shaft to the wheel center may become long. When the distance from the support shaft to the wheel center becomes long, for example, when crossing a step, when an impact force is applied from the step to the wheel, a relatively large moment is generated between the support shaft and the body frame, so a countermeasure is required.

[0009] Providing a large deep groove ball bearing as a countermeasure against a large moment causes a problem of increasing the size and weight of the caster. On the other hand, as an option to reduce the diameter instead of a large deep groove ball bearing, there is a choice of using a needle bearing. However, although the needle bearing has the advantage of a relatively small outer diameter, since the caster turning bearing also receives an axial load generated by the load of the luggage and the vehicle body weight in addition to the radial load, when a needle bearing is provided in the caster, a separate thrust bearing is also required, resulting in an increase in the number of parts.

[0010] The present invention has been made in view of the above problems, and an object thereof is to provide a caster that is relatively small in size and can cope with situations such as crossing a step.

Means for Solving the Problems

[0011] The caster of the present invention is attached to the vehicle body main body, a fixed shaft having a plurality of inner ring raceway surfaces formed on the outer periphery, an outer ring disposed around the fixed shaft and having a plurality of outer ring raceway surfaces formed on the inner periphery corresponding to the inner ring raceway surfaces, balls rollably disposed along the plurality of inner ring raceway surfaces and the outer ring raceway surfaces, a fork portion connected to the outer ring, an axle connected to the fork portion, and a wheel rotatably held around the axle, and the center line of the fixed shaft and the center of the axle are horizontally offset. It is characterized by this.

Effect of the Invention

[0012] According to the present invention, it is possible to provide a caster that is relatively small in size and can cope with climbing over steps.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of the caster 10 according to the present embodiment. FIG. 2 is a cross-sectional view showing a state where the upper part of the caster 10 is cut along the axis.

[0015] The caster 10 includes a caster body 20, a wheel 30, and an axle 40 that rotatably supports the wheel 30 with respect to the caster body 20. The caster 10 of the present embodiment is preferably applied to driven wheels (two front wheels) such as a silver car, a baby carriage, a shopping cart, a wheelchair, and other carts.

[0016] The caster body 20 has an inverted U-shaped fork portion 21, a cylindrical outer ring 22 fixed to the upper end of the fork portion 21 and extending in the vertical direction, a fixed shaft 23 disposed radially inside the outer ring 22 and extending in the vertical direction, and a plurality of balls 24 arranged in two rows between the outer ring 22 and the fixed shaft 23, and these constitute a wheel turning mechanism.

[0017] The fork portion 21 is integrally formed from a pair of leg portions 21a, 21a that extend in parallel and a connecting portion 21b that connects the upper ends of the leg portions 21a, 21a. The lower ends of the leg portions 21a, 21a are connected by an axle 40 horizontally disposed near the lower ends of the leg portions 21a. The axle 40 passes through the central portion of the wheel 30 disposed between the leg portions 21a, 21a. The wheel 30 is rotatably held with respect to the axle 40 by a bearing (not shown) disposed at the central portion of the wheel 30.

[0018] In FIG. 2, a first outer ring raceway surface 22a and a second outer ring raceway surface 22b are formed in two rows on the inner periphery of the thin-walled cylindrical outer ring 22 having its lower end attached to the connecting portion 21b. The first outer ring raceway surface 22a is the upper row raceway surface, and the second outer ring raceway surface 22b is the lower row raceway surface.

[0019] The fixed shaft 23 is composed of a large-diameter portion 23a located on the upper side, a small-diameter portion 23b that is smaller in diameter than the large-diameter portion 23a and is continuous with the lower end portion of the large-diameter portion 23a. The upper end of the large-diameter portion 23a is fixed to a vehicle body main body (not shown). The small-diameter portion 23b is inserted through a circular opening 21c that penetrates the connecting portion 21b of the fork portion 21 with a clearance, and protrudes downward from the connecting portion 21b.

[0020] On the outer periphery of the large-diameter portion 23a of the fixed shaft 23, a first inner raceway surface 23c is formed corresponding to the first outer raceway surface 22a, and a second inner raceway surface 23d is formed corresponding to the second outer raceway surface 22b. Between the first outer raceway surface 22a and the first inner raceway surface 23c, and between the second outer raceway surface 22b and the second inner raceway surface 23d, a plurality of balls 24 held by a cage 25 are arranged so as to be rollable with respect to the raceway surfaces. The outer ring 22, the large-diameter portion 23a, the balls 24, and the cage 25 constitute a double-row ball bearing, and by this ball bearing, the outer ring 22 and the fork portion 21 can be swiveled accurately with low friction with respect to the fixed shaft 23.

[0021] The outer ring 22 is axially positioned with respect to the fixed shaft 23 via a plurality of balls 24. For this reason, the fixed shaft 23 is held in a state where there is a clearance with respect to the upper surface of the connecting portion 21b around the circular opening 21c at the step portion between the large-diameter portion 23a and the small-diameter portion 23b. A male thread 23e is formed on the outer periphery of the small-diameter portion 23b. By screwing a nut 28 onto the male thread 23e protruding downward from the circular opening 21c, the lower end of the outer ring 22 abuts against the upper surface of the fork portion 21, that is, the outer ring 22 is attached in a state where it does not separate from the connecting portion 21b. Therefore, it is not necessary to perform welding, adhesion, etc. between the outer ring 22 and the fork portion 21. By changing the tightening amount of the nut 28, the axial position of the outer ring 22 with respect to the fixed shaft 23 can be changed, and thereby the preload of the ball bearing can be adjusted.

[0022] Above the first outer raceway surface 22a and the first inner raceway surface 23c, an annular first seal 26 for sealing the outer ring 22 and the large-diameter portion 23a is disposed. Also, below the second outer raceway surface 22b and the second inner raceway surface 23d, an annular second seal 27 for sealing the outer ring 22 and the large-diameter portion 23a is disposed. The first seal 26 and the second seal 27 can suppress the entry of foreign matter from the outside into the raceway surface.

[0023] FIG. 3(a) is a schematic view of the caster 10 on a horizontal plane as viewed in the axial direction of the wheel axle 40, and FIG. 3(b) is an enlarged cross-sectional view showing IIIB indicated by the arrow in FIG. 3(a), but the illustration of the nut is omitted. FIG. 4(a) is a schematic view of the caster 10 when overcoming a step as viewed in the axial direction of the wheel axle 40, and FIG. 4(b) is an enlarged cross-sectional view showing the IVB portion indicated by the arrow in FIG. 4(a), but the nut is omitted. Here, referring to FIG. 3(a), the caster angle C refers to the angle formed by a straight line L connecting a point P1 where the center axis O (central axis) of the fixed shaft 23 serving as the turning axis intersects the upper surface of the fork portion 21 and the center P2 of the wheel axle 40 with the vertical line when the center axis O is set as O.

[0024] Here, the distance X between the center P2 of the wheel axle 40 and the center axis O is defined as the offset amount. The offset amount X is determined according to the caster angle C and is smaller than the radius R of the wheel 30 here. The caster angle C is preferably 15° or more and 30° or less, and the radius R of the wheel 30 is preferably 50 mm or more.

[0025] Assuming that the caster 10 is attached to a silver car (not shown), the vehicle weight borne by the caster 10 is transmitted to the wheel axle 40 via the wheel 30, and the reaction force F1 is applied vertically from the horizontal plane HP toward the wheel axle 40. Therefore, an axial load F1 acts on the outer ring 22 in the central axis direction of the fixed shaft 23 via the fork portion 21. The axial load F1 is shared and supported by the upper and lower rows of balls 24.

[0026] On the one hand, since the central axis (swivel axis) O of the fixed shaft 23 and the center of the wheel axle 40 are horizontally shifted by an offset amount X, a moment M1 = (F1·X) that attempts to tilt the outer ring 22 with respect to the fixed shaft 23 acts in the clockwise direction on the paper surface.

[0027] In the present embodiment, since the upper and lower rows of balls 24 are arranged at a distance Y apart along the central axis O, the moment M1 can be supported. When the moment M1 occurs, if the total horizontal force (radial load) applied to the ball 24 from the raceway surface is F3, then F3·Y = F1·X holds. From this, F3 = (F1·X) / Y.

[0028] On the other hand, as shown in Fig. 4(a), when the wheel 30 attempts to cross the step ST, it is assumed that a maximum horizontal reaction force F2 acts on the wheel. In such a case, a vertical reaction force F1 and a maximum horizontal reaction force F2 act on the wheel axle 40. Therefore, when the distance between the center of the wheel axle 40 and the center of the lower row of balls 24 is Z, a moment M2 = (F1·X)+(F2·Z) that attempts to tilt the outer ring 22 with respect to the fixed shaft 23 acts in the clockwise direction on the paper surface.

[0029] When the moment M2 occurs, if the total horizontal force (radial load) applied to the ball 24 from the raceway surface is F3’, then F3’·Y = (F1·X)+(F2·Z) holds. From this, F3’ = ((F1·X)+(F2·Z)) / Y, and F3’ > F3. According to the present embodiment, since the upper and lower rows of balls 24 are arranged at a distance Y apart along the central axis O, even a moment M2 larger than the moment M1 can be supported, and high support rigidity can be realized.

[0030] From the above, assuming that the wheel 30 crosses the step ST, the axial load F1 and the radial load F3’ are determined, and based on this, the life is calculated to determine the appropriate specification (diameter) of the ball 24.

[0031] Furthermore, according to the present embodiment, since the first inner ring raceway surface 23c and the second inner ring raceway surface 23d are formed on the outer periphery of the fixed shaft 23, the inner ring becomes unnecessary, and the outer diameter of the outer ring 22 can be reduced accordingly. In addition, the fixed shaft 23 that is screwed into the nut 28 also serves as the mounting bolt for the fork portion 21, and thus the number of components can be reduced by these means.

[0032] If the caster 10 is pre-assembled, the upper end of the fixed shaft 23 can be easily assembled into the caster 10 without using a special tool, for example, by pushing it into a circular hole formed at the bottom of the vehicle body main body, and the manufacturing man-hours can be reduced. At this time, in order to prevent the vehicle body main body from contacting the outer ring 22, a flange portion protruding radially outward may be provided on the outer periphery of the large-diameter portion 23a of the fixed shaft 23 while being spaced above the outer ring 22.

[0033] By designing the caster 10 in a compact manner in this way, the caster angle C can be freely set within a range where the offset amount X does not exceed the radius R of the wheel 30, the degree of freedom in design can be increased, and the turning performance and straight-ahead stability of the caster 10 can be improved. Further, a so-called back-to-back angular ball bearing may be constituted by the fixed shaft 23, the outer ring 22, and the balls 24 arranged in a double row. Since the angular ball bearing has a contact angle, it can support the radial load and the axial load simultaneously. By providing the contact angle, the moment rigidity is improved, and by applying preload, it becomes possible to support the load with the double-row balls 24, so that an improvement in quietness and stability is expected.

[0034] The present invention is not limited to the above-described embodiments, and it is also contemplated by the present invention that those skilled in the art can make changes and applications based on combining each configuration of the embodiments, the description in the specification, and well-known techniques, and such are included in the scope for which protection is sought.

Explanation of reference numerals

[0035] 10 Caster 20 Caster body 21 Fork part 22 Outer ring 23 Fixed shaft 24 Ball 25 Retainer 30 Wheel 40 Axle

Claims

1. A fixed shaft attached to the vehicle body main body and having a plurality of inner ring raceway surfaces formed on its outer periphery, An outer ring disposed around the fixed shaft and having a plurality of outer ring raceway surfaces formed on its inner periphery corresponding to the inner ring raceway surfaces, Balls arranged to be rollable along the plurality of inner ring raceway surfaces and the outer ring raceway surfaces, A fork portion connected to the outer ring, An axle connected to the fork portion, A wheel rotatably held around the axle, characterized by the center line of the fixed shaft and the center of the axle being horizontally offset. A caster characterized by the above.

2. The fork portion has a pair of legs to which the axle is attached and a connecting portion that connects one ends of the legs, The fixed shaft has a large-diameter portion that forms the outer ring raceway surface and a small-diameter portion that is smaller in diameter than the large-diameter portion, The small-diameter portion is inserted into an opening formed in the connecting portion, A male thread is formed on the small-diameter portion protruding from the opening, and a nut is screwed onto the male thread. The caster according to claim 1, characterized by the above.

3. One end of the outer ring abuts against the connecting portion, Separation between the outer ring and the connecting portion is prevented by screwing the male thread and the nut. The caster according to claim 2, characterized by the above.

4. By changing the amount of screwing of the nut with respect to the male thread, the axial position of the outer ring with respect to the fixed shaft can be changed. The caster according to claim 2, characterized by the above.

5. The end portion of the fixed shaft can be press-fitted into a circular hole of the vehicle body main body. The caster according to claim 1, characterized by the above.

6. The caster angle of the fork portion is 15° or more and 30° or less. The caster according to claim 1, characterized by the above.

7. The radius of the wheel is 50 mm or more. The caster according to claim 1, characterized by the above.

Images