SWING ARM LINKAGE FOR A MID-WHEEL DRIVE WHEELCHAIR

Abstract

The present disclosure relates to a swing arm linkage (1) for a mid-wheel drive wheelchair, comprising: a first swing arm (3) having a first swing arm pivot point (3a) and a linkage member first mounting point (3b), a second swing arm (5) having a second swing arm pivot point (5a) and a linkage member second mounting point (5b), a linkage member (7) configured to be connected to the linkage member first mounting point (3b) and to the linkage member second mounting point (5b), to enable force transfer between the second swing arm (5) and the first swing arm (3), wherein the linkage member (7) has an elongated shape defining a linkage axis (A) extending between the linkage member first mounting point (3b) and the linkage member second mounting point (5b), a first straight line being formed between the first swing arm pivot point (3a) and the linkage member first mounting point (3b), and a second straight line being formed between the second swing arm pivot point (5a) and the linkage member second mounting point (5b), wherein the linkage member first mounting point (3b) and the linkage member second mounting point (5b) are so arranged relative to each other that the sum of an angle α between the linkage axis and a line perpendicular to the first straight line and extending from the linkage member first mounting point and an angle β between the linkage axis and a line perpendicular to the second straight line and extending from the linkage member second mounting point is constant or increasing with increasing ditch angle.

Claims

1. A swing arm linkage for a mid-wheel drive wheelchair comprising a first caster wheel, a second caster wheel and a drive wheel, comprising: a first swing arm having a first swing arm pivot point and a linkage member first mounting point, a second swing arm having a second swing arm pivot point and a linkage member second mounting point, a linkage member configured to be connected to the linkage member first mounting point and to the linkage member second mounting point, to enable force transfer between the second swing arm and the first swing arm, wherein the linkage member has an elongated shape defining a linkage axis extending between the linkage member first mounting point and the linkage member second mounting point, a first straight line being formed between the first swing arm pivot point and the linkage member first mounting point, and a second straight line being formed between the second swing arm pivot point and the linkage member second mounting point, wherein the linkage member first mounting point and the linkage member second mounting point are so arranged relative to each other that the sum of an angle α between the linkage axis and a line perpendicular to the first straight line and extending from the linkage member first mounting point and an angle β between the linkage axis and a line perpendicular to the second straight line and extending from the linkage member second mounting point is constant or increasing with increasing ditch angle, the ditch angle being the acute angle between two planes of which a first plane is tangent to both a second caster wheel contact point to ground and a ground contact point of a drive wheel, and a second plane is tangent to a first caster wheel ground contact point and a drive wheel ground contact point.

2. The swing arm linkage of claim 1, wherein the sum of the angles α and β is less than 30 degrees at a ditch angle of 0 degrees.

3. The swing arm linkage of claim 1, wherein the sum of the angles α and β is less than 25 degrees at a ditch angle of 0 degrees.

4. The swing arm linkage of claim 1, wherein the sum of the angles α and β is less than 20 degrees at a ditch angle of 0 degrees.

5. The swing arm linkage of claim 1, wherein the sum of the angles α and β is less than 10 degrees at a ditch angle of 0 degrees.

6. The swing arm linkage of claim 1, wherein the ratio between the leverage arm of the second swing arm and the leverage arm of the first swing arm is constant with increasing ditch angle.

7. The swing arm linkage of claim 1, wherein the ratio between the leverage arm of the second swing arm and the leverage arm of the first swing arm is between 2 and 3 for any ditch angle between 0 and 25 degrees.

8. The swing arm linkage of claim 1, wherein the first swing arm is a rear swing arm and the second swing arm is a front swing arm.

9. The swing arm linkage of claim 1, wherein the line perpendicular to the first straight line intersects an extension of the second straight line and the line perpendicular to the second straight line intersects an extension of the first straight line.

10. A mid-wheel drive wheelchair comprising the swing arm linkage of claim 1.

11. The mid-wheel drive wheelchair of claim 10, comprising a chassis, wherein the first swing arm is pivotally connected to the chassis via the first swing arm pivot point and the second swing arm is pivotally connected to the chassis via the second swing arm pivot point.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The specific embodiments of the inventive concept will now be described, by way of example, with reference to the accompanying drawings, in which:

[0026] FIG. 1 is a schematic side view of an example of a swing arm linkage for a mid-wheel drive wheelchair;

[0027] FIG. 2 schematically illustrates the definition of the ditch angle;

[0028] FIG. 3 shows one aspect of the geometry of the swing arm linkage in FIG. 1, illustrating angles α and β;

[0029] FIG. 4 is a graph that shows the composite angle (the sum of angles α and β) as a function of the ditch angle for a number of swing arm linkage designs;

[0030] FIG. 5 shows another aspect of the geometry of the swing arm linkage in FIG. 1, illustrating leverage arms X and Y;

[0031] FIG. 6 is a graph that shows the front/rear leverage arm ratio as a function of the ditch angle for a number of swing arm linkage designs; and

[0032] FIG. 7 schematically shows a side view of a mid-wheel drive wheelchair comprising the swing arm linkage in FIG. 1.

DETAILED DESCRIPTION

[0033] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplifying embodiments are shown. The inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0034] The present disclosure relates to a swing arm linkage, or swing arm assembly, for a mid-wheel drive wheelchair. The swing arm linkage has a first swing arm, or first pivot arm, a second swing arm, or second pivot arm, and a linkage member which connects the first swing arm with the second swing arm, thereby allowing force transfer between the second swing arm and the first swing arm. In particular, the linkage member is configured to transfer a pivot motion of the second swing arm to a pivot motion of the first swing arm.

[0035] Hereto, the first swing arm has a linkage member first mounting point and the second swing arm has a linkage member second mounting point. The linkage member is configured to be connected to the linkage member first mounting point. The linkage member is furthermore configured to be connected to the linkage member second mounting point. A first straight line being formed between the first swing arm pivot point and the linkage member first mounting point, and a second straight line being formed between the second swing arm pivot point and the linkage member second mounting point. As mentioned earlier, these straight lines are imaginary lines merely introduced for the definition of certain angles. The linkage member first mounting point and the linkage member second mounting point are so arranged relative to each other that the sum of an angle α between the linkage axis and a line perpendicular to the first straight line and extending from the linkage member first mounting point and an angle β between the linkage axis and a line perpendicular to the second straight line and extending from the linkage member second mounting point is constant or increasing with increasing ditch angle. The sum of the angles α and β is in particular constant or increases as the ditch angle increases from 0 degrees to angles in the order of tens of degrees.

[0036] The linkage member has an elongated shape and extends between the linkage member first mounting point and the linkage member second mounting to point. The linkage member may comprise at least one rigid member or may comprise at least one resilient member or may comprise a combination of both rigid and resilient members. Using resilient members alone or in combination with rigid members may contribute to an increased ride comfort for the user. The length of the linkage member is dependent on the placement of the first and second mounting points.

[0037] Examples of a swing arm linkage will now be described with reference to FIGS. 1-6.

[0038] FIG. 1 depicts an example of a swing arm linkage 1 for a mid-wheel drive wheelchair. The swing arm linkage 1 comprises a first swing arm 3, a second swing arm 5 and a linkage member 7. According to the present example, the first swing arm 3 is a rear swing arm and the second swing arm 5 is a front swing arm, but it could alternatively be the other way around.

[0039] The first swing arm 3 has a first swing arm pivot point 3a. The first swing arm 3 is configured to be pivotally connected to a chassis 9 of a mid-wheel drive wheelchair, at the first swing arm pivot point 3a, which thus forms a pivot axis of the first swing arm 3.

[0040] The first swing arm 3 has a linkage member first mounting point 3b to which the linkage member 7 is configured to be connected. The first swing arm 3 has a portion 3c extending from the first swing arm pivot point 3a, configured to cause pivoting of the first swing arm 3 about the first swing arm pivot point 3a. The linkage member first mounting point 3b is provided on the portion 3c and the linkage member 7 is thus connected to this portion 3c.

[0041] The second swing arm 5 has a second swing arm pivot point 5a. The second swing arm 5 is configured to be pivotally connected to the chassis 9 at the second swing arm pivot point 5a, which thus forms a pivot axis of the second swing arm 5. The second swing arm 5 has a portion 5c extending from the second swing arm pivot point 5a. The linkage member second mounting point 5b is provided on the portion 5c and the linkage member 7 is thus connected to this portion sc.

[0042] The first swing arm 3 and the second swing arm 5 may furthermore have a respective caster wheel assembly 3d, 5d. Hereto, the first swing arm 3 may include a first caster wheel assembly 3d and the second swing arm 5 may include a second caster wheel assembly 5d.

[0043] To facilitate the understanding of where the swing arm linkage 1 is located on the chassis 9, relative to a drive wheel, a drive wheel hub 11 is also shown, to which a drive wheel is configured to be mounted. The drive wheel hub 11 is arranged between the rear caster wheel assembly 3d and the front caster wheel assembly 5d.

[0044] FIG. 2 shows a definition of the ditch angle γ. The ditch angle γ is the acute angle between the two planes P1 and P2 of which the first plane P1 is tangent to both the second caster wheel 25 contact point to the ground and a ground contact point of the drive wheel D, and the second plane P2 is tangent to the first caster wheel 27 ground contact point and a drive wheel D ground contact point.

[0045] FIG. 3 shows a diagram of one aspect of the geometry of the swing arm linkage 1. Hereto, only the first swing arm pivot point 3a, the linkage member first mounting point 3b, the second swing arm pivot point 5a and the linkage member second mounting point 5b, and their relative location is shown. The linkage member 7 has an elongated shape and defines a linkage axis A, extending between the linkage member first mounting point 3b and the linkage member second mounting point 5b. A first straight line 13 extending between the first swing arm pivot point 3a and the linkage member first mounting point 3b has been drawn in FIG. 3. Moreover, a line 17 perpendicular to the first straight line 13 and extending from the linkage member first mounting point 3b is shown, extending in the same plane as the first straight line 13 and the linkage axis A. Similarly, a second straight line 15 extending between the second swing arm pivot point 5a and the linkage member second mounting point 5b has been drawn. Moreover, a line 19 perpendicular to the second straight line 15 and extending from the linkage member second mounting point 5b is shown, extending in the same plane as the second straight line 15, the first straight line 13 and the linkage axis A. The linkage member first mounting point 3b and the linkage member second mounting point 5b are so arranged relative to each other that the sum of the angle α between the linkage axis A and the line 17 perpendicular to the first straight line 13 and the angle β between the linkage axis A and the line 19 perpendicular to the second straight line 15 is constant or increasing with increasing ditch angle. According to one variation, the sum is less than 30 degrees at zero ditch angle.

[0046] The sum of the absolute values of angles α and β, alternatively expressed as the composite angle of α and β, may according to one variation be less than 25 degrees at zero ditch angle, for example less than 20 degrees, or less than 15 degrees or less than to degrees. According to one variation, the composite angle of α and β may be 0 degrees at zero ditch angle.

[0047] As can be seen in FIG. 3, the line 17 perpendicular to the first straight line 13 intersects an extension of the second straight line 15. Similarly, the line 19 perpendicular to the second straight line 15 intersects an extension of the first straight line 13. It is to be noted that the extensions of the imaginary lines 13 and 15 are also imaginary.

[0048] FIG. 4 shows a plot of a number of tests performed by the inventors for mid-wheel drive wheelchairs having swing arm linkages with different geometries. One of the tests, described by curve C1, is an example of the swing arm linkage 1 disclosed herein, the others (curves C2 and C3) having the sum of angles α and β decreasing with increasing ditch angle and the sum has a value greater than 30 degrees at zero ditch angle. Here, the ditch angle is plotted for each of three cases until the drive wheels have lost traction with the underlying support.

[0049] As noted above, curve C1 describes the behaviour of a mid-wheel drive wheelchair having a swing arm linkage according to a variation of the swing arm linkage 1 where the sum of the angles α and β is less than 25 degrees for ditch angles up until the drive wheels lose traction with the underlying support. In the example, the composite angle of α and β is essentially 20 degrees at its maximum.

[0050] As can be seen in the plot, curves C2 and C3 which describe geometries having composite angles greater than 30 degrees in the specified range reduce their composite angle as the ditch angle increases, while for the example described by curve C1 the composite angle is slightly increased as the ditch angle is increased. It can furthermore be noted that the test where the composite angle is less than 25 for any ditch angle in the test range, i.e. curve C1, maintains traction with the underlying support for a greater ditch angle than the tests described by curves C2 and C3.

[0051] With reference to FIG. 5 another aspect of the geometry, according to one variation of the swing arm linkage 1, will now be described. According to the example shown in FIG. 5, a diagram of a geometry of one variation of the swing arm linkage 1 is shown, with the positions of the first swing arm pivot point 3a, the linkage member first mounting point 3b, the second swing arm pivot point 5a and the linkage member second mounting point 5b being depicted. The leverage arm X of the second swing arm 5 is also shown, as is the leverage arm Y of the first swing arm 3. According to one variation, the ratio between the leverage arm X of the second swing arm 5 and the leverage arm Y of the first swing arm 3 is constant with increasing ditch angle. According to a variation, the ratio is in the range between 2 and 3 for any ditch angle between 0 and 25 degrees. This ratio is preferably kept as constant as possible over the range of ditch angles, thereby ensuring that the force transfer for any given force will be the same or essentially the same for any ditch angle.

[0052] FIG. 6 shows a plot of a number of tests performed on mid-wheel drive wheelchairs having different geometries. Curve C4 shows an example of a geometry where the ratio between the leverage arm X of the second swing to arm 5 and the leverage arm Y of the first swing arm 3 is in the range between 2 and 3, for any ditch angle in the range 0 to 25 degrees. The geometry of the swing arm linkage described by curve C4 furthermore has the geometry previously described, with the composite angle being below 30 degrees for any ditch angle in the range 0 to 25 degrees. More specifically, the swing arm linkage used in the test shown in FIG. 5 described by curve C4 is the same swing arm linkage used in the test described by curve C1 in FIG. 4. It can again be observed that traction will be provided for greater ditch angles than for the other swing arm linkages used in the test.

[0053] FIG. 7 shows an example of a mid-wheel drive wheelchair 21, i.e. a wheelchair that is powered by means of a drive wheel arranged between front caster wheels and rear caster wheels. Hereto, the mid-wheel drive wheelchair 21 has a seating system 23, a chassis 9, and a swing arm linkage 1 mounted to the chassis 9 and provided with a front caster wheel 25 and rear caster wheel 27.

[0054] The inventive concept has mainly been described above with reference to a few examples. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims.