Suspension with means supporting a vehicle frame

TECHNICAL FIELD

The present invention relates to a suspension according to the preamble to claim 1. The invention can be related to the vehicle industry.

BACKGROUND OF THE INVENTION

There are today various types of vehicles adapted to climbing. For example the inventors of the present invention have previously disclosed a device where a linking arrangement is rotatable about a point of rotation to achieve a lifting moment for the vehicle for climbing. Such a device is described for example in WO 2007/094735 A1 published on 23 August 2007. This device has proved to function satisfactorily. However, it is now subject to further improvement.

It is desirable that a user should be able to maneuver the vehicle in a maximum user-friendly manner with as few hand movements as possible when negotiating obstacles. For example it is desirable that the user not be required to direct his attention away from the traffic or the most suitable path before negotiating an obstacle. If the vehicle is pushed by hand, it should not be necessary to remove one's hands from the vehicle frame when the user wishes to turn or change the direction of the vehicle.

It can be difficult for a user of limited physical capacity to steer a vehicle with all the wheels in contact with the supporting surface. It can also be difficult for him to determine the position an adjustable stop should have for optimum climbing ability.

SUMMARY OF THE INVENTION

The above-mentioned problems have been solved by the features disclosed in claim 1.

A user will not need to adjust the vehicle to increase maneuverability but can direct his attention to the traffic instead. Cost-effectiveness in manufacturing is increased as well, since fewer components are required while maintaining good maneuverability and climbing ability. Good climbing ability is obtained by the virtue of the fact that the front supporting means always meet the obstacle at a higher level, thus producing a greater lifting force and less of an opposing force. A user never needs to think of adjusting the suspension.

Preferably the forward supporting means is forced to an elevated position by means of an abutment fixed to the suspension.

A user can thus concentrate on the traffic instead of on adjusting the suspension prior to climbing.

The suspension suitably includes a linkage element to which the primary supporting means and the forward supporting means are arranged on either side of a pivot point permitting vertical rotation of the linkage element.

In this manner, the pivotability of the linkage element permits the suspension to follow the topography of the obstacle.

Alternatively, the fixed abutment is disposed on a fork element to stop the rotation of the linkage element.

Thus the fork element itself can be used as an abutment to elevate the forward supporting means. This is advantageous since the fork is thereby

pivotabie to pivoting the vehicle frame while the permanent abutment of the linkage element, such as a collar or a yoke, can follow the pivoting of the fork relative to the vehicle frame.

Preferably the fixed abutment is adapted to the vehicle frame to stop the rotation of the linkage element.

In this manner the vehicle frame itself can be used as an abutment for the linkage element, which is cost-effective, since fewer components need to be used.

Suitably the abutment is a damping element.

This will increase comfort when the vehicle frame rolls over an obstacle.

Alternatively the primary supporting means consist of a rear wheel and the forward supporting means consist of a front wheel.

In this manner the suspension can be used for a wheeled vehicle such as a rollator, cart, wagon or off-road vehicle.

Preferably the front wheel is arranged permanently elevated above the supporting surface at a distance corresponding to at least 2-25%, preferably 3-15% of the diameter of the front wheel.

It is thus possible when designing a vehicle and with a view to the desired application to set a permanent elevated height of the front wheel of the vehicle frame at a height where the optimum climbing effect is achieved and the diameter of the rear wheel selected so that the rear wheel will roll over the obstacle. The front wheel and the rear wheel can have the same diameter or different diameters depending on the application.

Suitably the primary supporting means and the front supporting means are aligned with the pivot point.

This makes it possible to use a straight linkage element, which is cost- effective for manufacturing.

Alternatively, the suspension is arranged non-pivoting in relation to the vehicle frame.

In this manner, the suspension can be used for a cargo vehicle with non- steerable wheels with good steerabiiity despite overlapping wheels at each suspension.

Preferably the vehicle frame is tippable in the forward driving direction so that both the primary supporting means and the front supporting means can be brought into contact with the supporting surface.

The suspension can thus be used with advantage in a trolley for example.

SHORT DESCRIPTION OF THE DRAWINGS

The present invention will be described in detail below with the aid of examples referring to the accompanying schematic drawings, of which: Figs. 1a, 1 b and 1c show a suspension according to a first embodiment in a side view,

Figs. 2a and 2b show a suspension according to a second embodiment in a side view,

Fig. 3 shows the principle for a lifting moment according to known technology,

Figs. 4a, 4b and 4c show a suspension with skis according to a third embodiment as seen from the side,

Fig. 5 shows a suspension with a rearwardly directed shorter linkage arm

(bakat?) which cooperates with a permanent abutment of a fork, Fig. 6 shows a suspension with symmetrically placed wheels about a pivot point,

Fig. 7 shows a suspension with wheels aligned with each other or with the wheel axles aligned with the pivot point,

Figs. 8a and 8b show a suspension where the primary supporting means consists of two wheels placed next to each other transversely to the direction of travel,

Fig. 9a and 9b show a suspension where the permanently elevated front supporting means consist of two wheels facing each other transversely to the direction of travel, Fig. 10a and 10b shows a forth embodiment of a suspension with a permanent abutment,

Figs. 11a, 11 b and 11c show a fifth embodiment according to the invention,

Figs. 12a, 12b and 12c show a non-pivoting suspension with a permanent abutment, Fig. 13 shows a sixth embodiment according to the invention,

Figs. 14a - 14c show a seventh embodiment according to the invention, and

Figs. 15a - 15d show the relationship between the height of the obstacle and the wheel radius of a permanently elevated wheel.

DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described as examples. For the sake of clarity, components having no importance for the invention have been left out of the drawing. The same components which are shown in a number of figures can in certain cases lack reference numerals, but correspond to those which have reference numerals. An even supporting surface means a

supporting surface which for the moment does not have any obstacles for the suspension to pass over and has a texture of less than 5 mm.

Fig. ia, 1b and 1c show a suspension 1 according to a first embodiment as seen from the side. The suspension 1 comprises a front fork 3', the upper end of which is disposed to pivot about a vertical axis S, and a rear permanently mounted fork 3". The suspension 1 is mounted on a vehicle frame 7, which is disposed, in its primary direction of travel D, to be able to climb over an obstacle 9. The suspension 1 comprises a primary supporting means 11, such as a front wheel 13" and a rear wheel 13", the wheels 13' and 13" supporting the vehicle frame 7, for contact with a supporting surface 15. The wheels 13', 13" are, as viewed in the direction of travel D, located behind a front supporting means 17, such as front wheel 19.The wheel 13" is rotatably securedly mounted at the lower end of the rear fork 3". The wheel 13' is rotatably securedly mounted to the lower rear end of the front fork 3', which is pivotable about the axis S. The front wheel 19 is permanently elevated above the supporting surface 15 and is rotatably securedly mounted to the front end of the fork 3', so that contact is avoided between the front wheel 19 and the supporting surface 15 when rolling over a smooth surface. The front wheel 19 is elevated permanently above the even surface 15 so much that, despite the elevated position, it can come in contact with said obstacle 9. The wheels 13', 13", 19 are all rotatably securedly mounted to the suspension 1 , so that no wheel 13', 13", 19, nor the suspension itself 1 is allowed to move vertically relative to the vehicle frame 7.

When propelling the vehicle over an even supporting surface 15, the vehicle frame 7 is borne by the wheels 13', 13". The wheel 19 has no contact with the even supporting surface 15 (see fig. 1a).

The wheel axle 21 of the wheel 13" serves as a pivot axis m, about which the suspension 1 when rolling over obstacles tends to rotate with a moment M

lifting up the vehicle frame 7, when the front wheel 19 striking the obstacle 9 is subjected to a force Fx in a direction substantially counter to a pushing force Gx in the direction of travel D (see fig. 1b).

The suspension 1 acts as a lever about the pivot axis m when the elevated position of the front wheel 19 causes the wheel 19 to strike the obstacle 9 at a higher position, with the result being that the radially acting force F acting on axle 23 of the wheel 19 has a sharp angle of attack, and in that way creates a clockwise positive moment M about the pivot axis m, and a force Ff lifting the vehicle frame 7 is achieved (see fig. 1 c).

Because of the fact that the forward wheel 19 is permanently elevated above the even supporting surface 15, there will be less friction against the even supporting surface 15, in comparison to the case where both wheels 13' 19 would be in contact with the supporting surface 15, and good tumability about the turning axis S is achieved, at the same time as the climbing ability is still good. At the same time, the tendency to twisting of the fork 3' around the turning axis S when climbing over an obstacle 9 is reduced, and a user (not shown) does not need to adjust the suspension 1 to the elevated position. The capacity of the suspension 1 to negotiate obstacles is improved as well by virtue of the fact that the spacing of the wheel 19 from the supporting surface 15 during manufacturing can be adjusted for optimum climbing ability for a commonly occurring obstacle height (see the explanation in connection with figs. 15a - 15d below). At the same time, the twisting torque for the suspension 1 (as seen in the direction of travel D) about the turning axis S of the fork 3' is reduced when the forwardmost wheel 13' in the direction of travel D strikes the obstacle 9, since the wheel 13' will strike the obstacle 9 at a higher position (see fig. 1c) and the force Ff lifting the vehicle frame 7 will thereby increase relative to the force Fx acting counter to the direction of travel D with the result that the suspension 1 will complete its climb over the obstacle 9 instead of being twisted and stopping the propulsion of the vehicle

frame 7. The suspension 1 is also very cost-effective in manufacture and requires fewer components than a suspension with a rotatable linkage arm and an adjustable abutment. Furthermore, a suspension is obtained with higher strength since it consists of fewer moving parts.

Figs. 2a and 2b show a suspension 1 according to a second embodiment of a view from the side. The suspension 1 comprises a fork 3, the upper end of which is arranged prvotable about a vertical axis S. A lower end of the fork 3 has a horizontal pivot point R about which a linkage arm 5 is pivoted at a pivot point R. The suspension 1 is mounted on a vehicle frame 7 which is disposed to be able to climb over an obstacle 9 in its primary direction of travel D. The suspension 1 comprises a primary supporting means 11 , such as a rear wheel 13, which supports the vehicle frame 7, for contact with a supporting surface 15. The rear wheel 13 is, relative to the direction of travel D, located behind a forward supporting means 17, such as a front wheel 19. The front wheel 19 and the rear wheel 13 are mounted rotatably at either end of the linkage arm 5 so that the front wheel 19 is mounted closer to the pivot point R than the rear wheel 13. The wheel axle 21 of the rear wheel 13 serves as a fulcrum m, about which the suspension 1 tends to rotate when negotiating an obstacle providing a lifting torque M to the vehicle frame 7 when a force Fx is applied to the forward wheel 19 in a direction substantially counter to the propelling force Gx in the direction of travel D. The linkage arm 5 acts as a lever by virtue of the fact that the pivot point R is located between an imaginary line through the wheel axles 21 , 23 of the rear wheel 13 and the forward wheel 19 in a plane transverse to the fulcrum m and the supporting surface. The forward wheel 19 is disposed permanently elevated over the supporting surface 15 so that contact is avoided between the forward wheel 19 and the supporting surface when traveling over an even surface. The forward wheel 19 is forced into an elevated position by means of an abutment 25 permanently mounted in the suspension 1. The forward wheel 19 is permanently elevated to such a degree above the even surface 15 so

that, despite the elevated position, it can come into contact with said obstacle 9.

The permanently mounted abutment means 25 comprises a permanent abutment 27, which achieves the permanently elevated position of the forward wheel 19 above the surface 15. The permanent abutment 27 is arranged on the fork 3 to stop the pivoting of the linkage arm 5 (anticlockwise in fig. 2a), so that the forward wheel 19 is prevented from contact with the even supporting surface 15. The permanent abutment 27 is disposed, when negotiating an obstacle, to permit pivoting of the linkage arm 5 which creates the lifting moment M (clockwise in fig. 2b). The permanent abutment 27 comprises an abutment arm 29 welded securedly to the fork 3. The abutment arm 29 is provided with a collar 31 which serves to receive the wheel axle 21 of the rear wheel 13. The abutment arm 29 is welded at its other end securedly to the side of the fork 3 which faces backwards in the direction of travel D. By virtue of the fact that the forward wheel 19 is permanently elevated above the even surface 15, there is reduced friction against the even surface 15 in comparison to the case where both wheels would be in contact with the surface, and at the same time, the climbing ability is improved (see the explanation in conjunction with figs. 15a - 15d below). At the same time, a user (not shown) does not need to adjust the suspension 1 to the elevated position. The construction of the permanent abutment means 25 is cost-effective in manufacture and requires fewer components than an adjustable abutment. A permanently elevated forward wheel 19 increases the turnability of the suspension 1 about a turning axis at the same time as a shorter distance a between the pivot point R and the front wheel axle 23 in comparison with the distance b between the pivot point R and the rear wheel axle 21 reduces the tendency to twist when climbing.

Fig. 3 shows the principle of the lifting moment M according to known technology. The forward wheel axle 23 and the rear wheel axle 21 are shown

schematically rotatably mounted to the linkage arm 5. The linkage arm 5 is rotatably mounted to the vehicle frame at pivot point R. A pushing force Gx is applied to the pivot point R to propel the vehicle frame forward. An encounter with an obstacle will apply a counterforce F to the front wheel axle 23. This force F can be divided into two components, i.e. a lifting force Fy and a counterforce Fx. The distance from the rear wheel axle 21 to the forward wheel 23 is defined as a+b. The lifting force Fy is multiplied by the distance a+b to give the lifting moment M for the linkage arm 5. A force Ff lifting the vehicle frame 7 is created, and this lifting force Ff is greater than Fy since the distance b between the pivot point R and the rear wheel axle 21 is shorter than the distance a+b between the front wheel axle 23 and the rear wheel axle 21. The linkage arm 5 thus serves as a lever lifting the vehicle frame 7 when negotiating an obstacle.

Figs. 4a, 4b and 4c show schematically a third embodiment of a suspension 1 comprising a forward ski 33 providing a forward permanently elevated supporting means 17 and a rear ski 35 providing a primary supporting means 11 , in accordance with a second embodiment. The skis 33, 36 are mounted vertically rotatable to a straight linkage arm 5 which is pivoted to a fork 3 about the pivot point R. A yoke 37 providing a permanent abutment 27 is screwed securedly with one end at the portion of the linkage arm 5 located between the forward ski 33 and the pivot point R. The other end of the yoke 37 is provided with a hook 39. When operating over an even supporting surface 15, the yoke 37 with the hook 39 will always hold the forward ski 33 above the even surface 15 by virtue of the fact that the hook 39 is in contact with the fork 3, thus preventing rotation counterclockwise of the linkage arm 5 (as seen in fig. 4a) and holding the forward ski 33 always elevated above the even supporting surface 15. Fig. 4b shows the suspension 1 encountering an obstacle 9. The forward ski 33 is always elevated by means of a permanent abutment 27 so that Fy when the forward ski 33 strikes the obstacle 9, is less than Fx. That is to say, by virtue of the fact that the forward ski 33 is

permanently elevated, Fy will be greater than if the forward ski had not been elevated. This larger force Fy generated will contribute to the fact that the force Ff lifting the vehicle frame 7 at the pivot point R will be greater by the lifting moment M.

Fig. 4c shows how the forward ski 33 is permitted to pivot further about the pivot point R with continued sliding over the obstacle. The hook 39 separates from the back surface of the fork 3 and the yoke 37 will be displaced beside the fork 3, preventing the linkage arm 5 to rotate clockwise (as seen in fig. 4c) so that the rear ski 35 can also begin to climb.

Fig. 5 shows the suspension 1 comprising a linkage arm 5 with a different ratio. The linkage arm 5 cooperates with the permanent abutment 27 on the fork 3. The suspension 1 is turnable about a vertical turning axis S. The pivot point R is below an imaginary line L going through the forward wheel axle 23 and the rear axle 21. The front distance between forward wheel axle 23 and the pivot point R is longer than the rear distance b between the rear wheel axle 21 and the pivot point R. The suspension 1 with the forward wheel 19 permanently elevated above the even surface 15 contributes together with the longer forward distance a to reducing the load when climbing on the forward wheel 19, so that it can more easily climb over the obstacle 9.

Fig. 6 shows a suspension 1 with symmetrically placed wheels 13, 19 about the pivot point R, i.e. distance a is equal to distance b.

Fig. 7 shows a suspension 1 with rear and forward wheels 13, 19 arranged in line with each other and with the rear and forward wheel axles 21 , 23 located in alignment with the pivot point R. The permanent abutment 27 extends in this case in the direction towards the rear axle 21 to permit rotation of the suspension clockwise (as seen in fig. 6) when climbing. That is to say that the rotation of the linkage arm 5 when climbing has a reverse rotation

direction to the rotation direction Rh of the rear wheel 13. The forward wheel 19 and rear wheel 13 are mounted on the linkage arm 5 in line with each other as seen in the direction of travel, i.e. they are not arranged overlapping in contrast to the suspension as shown in fig. 2a. The permanently elevated front wheel 19 increases the turnability about the turning axis S, as described above, at the same time as the rear and forward wheels 13, 19 arranged in line with each other eliminate the risk for twisting of the vehicle frame 7 when climbing over the obstacle 9.

Fig. 8a and 8b show a suspension 1 where the primary supporting means 11 consists of two rear wheels 13', 13" placed next to each other transversely to the direction of travel. The two rear wheels, 13' 13" relative to the forward wheel 19 can absorb more load. The centrally placed forward wheel 19 eliminates the risk of twisting of the vehicle frame 7 when climbing over the obstacle 9.

The figures 9a and 9b show a suspension 1 where the permanently elevated forward supporting means 17 consists of two forward wheels 19', 19" placed next to each other in a direction transverse to the direction of travel D. In this manner, greater forces can be taken up by the two forward wheels 19', 19" when hitting the obstacle 9 at the same time as the risk of twisting of the vehicle frame 7 is eliminating when climbing.

The figures 10a and 10b show a fourth embodiment of a suspension 1 with a permanent abutment 27. The linkage arm consists here of an m-shaped linkage element 6 with an upper web 41 having three flanges 43', 43", 43"' extending towards the supporting surface 15. The two outermost flanges 43',

43"' are provided at their lower ends with pivot pins 45 which are mounted on a fork 3 to achieve the pivot point R. The forward wheel 19 is mounted between the forward portion of one of the outer flanges 43' and the middle flange 43". The rear wheel 13 is mounted between the rear portions of the

other outer flange 43'" and the middle flange 43". The fork 3 is made with an upper base portion 47, from which two flanges 49', 49" (one of which is hidden in the figure) extend downwards toward the supporting surface 15. The base portion 47 comprises a fixed mounted stop pin 51 which constitutes the abutment means 25. The stop pin 51 extends through a central hole 53 which extends in the direction of travel D in the upper web 41 of the linkage element 6. The hole 53 is the form of a slot and has a rear abutment end 55 and a forward abutment end 56. The rear abutment end 55 of the hole 53 acts to prevent the counterclockwise rotation of the linkage element 6, i.e. it prevents the linkage element 6 from rotating in the same rotation direction Rh as the rear wheel 13 when moving over a supporting surface 15. In this manner, the forward wheel 19 is permanently elevated above the supporting surface 15 when moving over an even supporting surface but clockwise rotation is permitted when negotiating an obstacle in the same manner as in the previously described embodiment. The difference here is that the permanent abutment, the stop pin 51 , is disposed to also automatically prevent the continued rotation clockwise (opposite to the direction of rotation Rh of the rear wheel 13) when rolling over an obstacle due to the forward stop 56 of the hole 53. The stop pin 51 is blocked by the front abutment end 56 and thus prevents the wheel axles 21 , 23 from shifting position in the direction of travel D when negotiating an obstacle.

Figs. 11a, 11b and 11c show a fifth embodiment according to the invention. A permanent abutment 27 is fixed on top of the m-shaped linkage element 6. The permanent abutment 27 is provided with a rubber cushion 57 (or plastic cushion) to dampen the impact against the base portion 47 when the linkage element 6 rotates back after climbing over an obstacle (not shown). Fig. 11 b shows clearly that the wheel surfaces for contact with the supporting surface 15 are asymmetrical with the major wheel sides (those with the greatest radii) facing toward each other. This reduces the tendency for the suspension 1 to twist when climbing. This embodiment is turnable about the turning axis S

and is suitable for transport carts (not shown) for merchandise handling in a warehouse.

Figs. 12a, 12b and 12c show a non-turnable suspension 1 with a permanent abutment 27. The suspension 1 cannot be turned and the fork 3 is fixedly mounted in the vehicle frame 7. A vehicle (not shown) with this suspension 1 can be maneuvered by virtue of the fact that the forward wheel 19 is permanently elevated above the supporting surface 15 and only the rear wheel 13 needs to be displaced transversally to the direction of movement D over the supporting surface 15 when the vehicle makes a turn. The suspension 1 thus provides less friction against the supporting surface 15 and the maneuverability will be good despite the fact that the suspension 1 itself is not tumable. This embodiment is suitable for example for a cargo cage for truck transport.

Fig. 13 shows a sixth embodiment of the invention. According to this embodiment the permanent stop 27 is the vehicle frame 7 itself. The rear portion of the linkage arm 5 (as seen in the direction of travel D) is in contact with the vehicle frame 7 thus holding the forward wheel permanently elevated above the even surface 15. This embodiment can be suitable for a construction cart for example.

Figs. 14a - 14c show a seventh embodiment according to the invention. In this example, the suspension 1 is part of a hand truck 59 with levers with handles 61. The hand truck 59 is disposed to be able to climb over the obstacle 9 shown in fig. 14c in its primary direction of travel D. The suspension 1 comprises a rear wheel 13 supporting the frame 7 of the hand truck 59 for contact with the supporting surface 15. This rear wheel 13 is located behind a forward wheel 19. The rear wheel 13 serves as a fulcrum m (see fig. 14c), about which the suspension 1 , when negotiating an obstacle, tends to rotate with a moment M lifting the vehicle frame 7, when a force F

substantially counter to the direction of travel D is applied to the front wheel 19. This force F can be divided into components Fx (opposing) and Fy (lifting) (see also fig. 15a). The forward wheel 19 is arranged to be permanently elevated above the supporting surface 15 so that contact is avoided between the forward wheel 19 and the supporting surface 15 when moving in the direction of travel D over an even surface 15, but it is only elevated to such a degree that it can come into contact with the obstacle 9 during normal travel over the supporting surface 15. The permanent abutment 27 cooperates with a climbing abutment 63 which during climbing prevents the linkage arm from "folding over" in a rotation direction opposite to the rotation direction Rh of the rear wheel 13. Both the permanent abutment 27 and the climbing abutment 63 are integrated in the frame 7 of the hand truck 59. The hand truck 59 is tippable in the direction of the travel D so that both the primary supporting means 11 and the forward supporting means 17 can be brought into contact with the supporting surface 15, which facilitates parking and loading the hand truck 59.

Figs. 15a - 5d show schematically the relationship between a height h above the even supporting surface 15 which the forward wheel 19 must be permanently elevated to relative to the height H of an obstacle and the radius r of the forward wheel 19.

This relationship can be defined by the formula:

A [ H - h = r - r sin α ] where B [ 45° ≤ α < 90° ]

The designation H is the height of the obstacle and the designation h is the permanent elevation of the forward wheel 19 above an even supporting surface 15 without obstacle. The designation r is the wheel radius and α is

the angle between an imaginary straight line — passing through the striking point for the forward wheel 19 against the obstacle 9 and the forward wheel axle 23 - and an imaginary line which has its substantially horizontal orientation starting from the striking point in the direction opposite to the direction of travel D.

Fig. 15a shows an example where the lifting component Fy and the counteracting component Fx are of the same magnitude, i.e. the angle α is 45°. It is however desirable that Fy be greater than Fx to obtain the desired lifting moment and improve climbing ability. But for the sake of simplicity we will determine for this example that the angle α is 45°. Assume that thresholds in a building are 4.0 cm high. H will be set at 4.0. The cart will be provided with forward wheels 19 which have a wheel radius of 8.0 cm. We assume that such wheels are cost-effective to manufacture and are commercially available and are suitable for the application. It will now be of interest to determine the permanently elevated height h for the forward wheel 19 of the vehicle frame 7. According to equation A above, the permanent elevation h will be:

h = H - r + r sin α = 4 - 8 + 8 sin 45° = 1.7 cm

Now an example will be described (see fig. 15b), where it is desired to create a greater lifting moment by providing an Fy which is greater than Fx. We have as an example a cart (not shown) which is to be adapted for indoor use. The thresholds in the building have a height of 4.0 cm. H will thus be set at 4.0. The forward wheel 19 of the frame 7 has a wheel radius of 8.0 cm. The angle α is selected to be 60° since then the lifting component Fy will be greater than the counteracting component Fx.

According to the equation A above the permanent elevated height will then be:

h = H - r + r sin α = 4 - 8 + 8 sin 60° = 2.9 cm

Fig. 15c shows as an example a case where we wish to have a lifting moment which is the optimum, where Fy is quite a bit larger than Fx. We select the angle α to be 85°. The thresholds in the building are also in this case 4.0 cm high, making H 4.0. The forward wheel 19 of the frame 7 has a wheel radius of 8.0 cm.

According to the equation A above the permanent elevated height will then be:

h = H - r + r sin α = 4 - 8 + 8 sin 85° = 3.9 cm

That is to say that the ratio between the height of the obstacle H, the wheel diameter (two times the wheel radius r) and how high the abutment means 25 is disposed to permanently lift the forward wheel 19, can be defined with an upper limit where the forward wheel 19 strikes the obstacle 9 at such a height that the lifting component Fy of the normal force F will be greater (and apply a greater lifting force) than the counteracting component Fx. By holding the forward wheel 19 permanently elevated, it will thus be possible to keep the component Fy and its lifting force higher, which is advantageous for negotiating obstacles which are higher, and at the same time the user will not need to take his eyes from the traffic.

It is thus advantageous to arrange the forward wheel 19 permanently elevated above the even supporting surface 15 so that the angle α is greater than 45°. A user can thus also easily steer the vehicle over the supporting surface with only the rear wheel 13 in contact with the even supporting surface 15 at the same time as better climbing properties are provided and

the user does not need to adjust the forward wheel to an elevated position but rather can concentrate on steering the vehicle.

Fig. 15c illustrates as an example that it is possible to optimize the elevation of the forward wheel 19 in such a manner that the striking of the rear wheel

13 against the obstacle 9 will be to sharp, i.e. the counteracting force Fx acting on the rear wheel 13 will be greater than the force Gx applied to the suspension to push the vehicle frame 7 (the vehicle) over the obstacle 9.

Therefore, in this case according to fig. 15c the diameter of the rear wheel 13 should have the larger diameter DS so that the rear wheel 13 will overcome the obstacle 9. The forward wheel 19 and the rear wheel 13 thus do not need to have the same wheel diameter to achieve the desired climbing properties.

Fig. 15d shows an example where the angle α is substantially less than 45°. The permanently elevated height h will then be very small in relation to the obstacle height H and the wheel radius r. This example is intended to illustrate that the counteracting force Fx will then be much greater than the lifting component Fy, which can mean poor climbing characteristics.

The examples above according to figs. 15a - 15d make it clear that the angle α should be greater than 45° and less than 90°, preferably between 50° and 80°. In other words, the forward wheel is set elevated above the supporting surface a distance corresponding to at least 2 - 25%, preferably 3-15% of the diameter of the forward wheel.

As an example it can be said that a rollator wheel of 310 mm in diameter is suitably permanently elevated above the supporting surface by a height of 10 mm.

Thus, based on the desired application it is possible to during design of the vehicle to set the permanent elevated height of the forward wheel 19 of the

vehicle frame 7 to a height where optimum climbing effect is achieved and the diameter DS of the rear wheel 13 is selected so that the rear wheel 13 overcomes the obstacle 9. The forward wheel 19 and the rear wheel 13 can have the same diameter or different diameters depending of the application.

A permanent elevation corresponding to 2-25% of the diameter of the forward wheel is to be preferred. It should however be noted that in order to create a climbing effect for negotiating lower obstacles, a compromise between optimum climbing ability for a given obstacle height and a broader range as regards minimum-maximum climbing height can give better performances overall.

The present invention should not be seen as limited to the above-described embodiments. Rather, modifications and combinations thereof can occur within the scope of the invention. For example, more than three wheels can be used for the suspension. In addition to wheels and skis, other supporting means can be used as slats. The suspension can be used for a rollator, a golf caddy, baby carriage, a shopping cart, transport carts of different types, railed vehicles, cable-drawn vehicles etc.