WO2009011582A1

WO2009011582A1 - Rear wheel suspension for a vehicle and vehicle equipped with such a suspension

Info

Publication number: WO2009011582A1
Application number: PCT/NL2008/050487
Authority: WO
Inventors: Olaf Gert-Jan Moro; Henrikus Wilhelmus Ekelschot
Original assignee: Terberg Specials B.V.
Priority date: 2007-07-16
Filing date: 2008-07-16
Publication date: 2009-01-22
Also published as: NL2000753C2

Abstract

The present invention relates to a rear wheel suspension for a vehicle having at least two rear wheels and a chassis, wherein each of the two wheels is connected with a supporting arm that is pivotally connected with the chassis, and wherein at each of the two supporting arms a fluid spring element is provided, of which one end is associated with the supporting arm and the other end is associated with the chassis, wherein the fluid spring element via a connection that is open to the fluid is in communication with a fluid reservoir, which forms part of the supporting arm, wherein the supporting arm is at least partly embodied as a flat box having a bottom, side walls, and an upper surface, with the average width of the box being greater than an average height of the side walls. The invention also relates to a vehicle equipped with such a rear wheel suspension.

Description

Rear wheel suspension for a vehicle and vehicle equipped with such a suspension

The present invention relates to a rear wheel suspension for a vehicle having at least two rear wheels and a chassis, wherein each of the two wheels is connected with a supporting arm that is pivotally connected with the chassis, and wherein at each of the two supporting arms a fluid spring element is provided, of which one end is associated with the supporting arm and the other end is associated with the chassis, wherein the fluid spring element via a connection that is open to the fluid is in communication with a fluid reser- voir, which forms part of the supporting arm. The invention relates especially to a rear wheel suspension for an ambulance .

Rear wheel suspensions for wheels of vehicles exist in a wide variety of types, each with its own strong and less strong points.

Especially with respect to utility vehicles, there is a need for a large functional space such as the loading space of trucks and delivery vans. With respect to convenient handling such as loading and unloading of loads, but also to enable persons to enter the loading space more easily, the floor of the loading space is preferably low, without reducing the space between vehicle and ground too much. This means that a wheel suspension is needed requiring only a small vertical space. With a particular category of such utility vehicles including, for example, an ambulance, there is not only a need for a low loading floor but also the necessity of stable road-holding. Ambulances regularly encounter situations in which speed is important with not always the best road condi- tions. This leads almost inevitably to the choice of an independent wheel suspension. For the benefit of the load, in the case of an ambulance the patient or patients to be transported, the spring comfort of the vehicle must be of high quality. Although these requirements have been described with an ambulance in mind, they are in no way limited to this application. Likewise with regard to the transport of fragile goods that may be breakable such as for example glass, or may be otherwise sensitive to shocks, such as instruments or for example electronics, these properties are of importance. The prior art provides solutions to each of the above-mentioned requirements individually. However, to this day there is no wheel suspension that adequately combines the three above-mentioned desired properties, which are an independent wheel suspension, a low loading floor and high quality spring comfort.

The German document DE 39 09 916 C2 describes a wheel suspension according to the preamble of claim 1. It is an object of the present invention to provide a wheel suspension for a vehicle of the type mentioned in the introduction, having a modest overall height while affording good properties with regard to both road holding and vehicle spring comfort . This objective is achieved by a rear wheel suspension according to claim 1. The spring action of such a rear wheel suspension is produced not only by the movement of the fluid in the spring element, but also in the reservoir. In this way almost the entire deflection of the spring element can be utilized without an excessive increase of the spring stiffness. This makes it possible to use a relatively small spring element, so that the overall height is limited while maintaining the comfortable spring properties of a fluid spring. The overall height is further limited because the supporting arms, each of which forming a reservoir, are embodied as a flat box. This allows the good road holding properties of an independent rear wheel suspension to be combined with the comfort of for example a pneumatic suspension, and a modest overall height. According to claim 1 a flat box is then defined by the fact that the average length and width are greater than the average height of the side walls. This may be expressed, for example, numerically by referring to a flat box if the average height of the box is less than the cubic root of the volume of the box. However, a flat box may also be defined by the fact that the average height is less than both the average length and the average width.

In this situation, the flatter the box, the smaller the overall height. However, the height of the side walls of the box may not be reduced arbitrarily. The height of the supporting arm contributes considerably to the stiffness and the supporting capacity of the supporting arm. Moreover, a certain height is needed to give the reservoir volume and thereby its function as reservoir. A good balance between modest height and sufficient supporting capacity and volume of the supporting arm can be realized if the average width of the box is at least twice the maximum height of the side- walls. If the spring element rests on the bottom of the box, a minimum overall height may be realized in this assemblage by not adding the height of the box to the height of the spring element, but by allowing these to partly overlap. For the rear wheel suspension according to the in- vention to function properly, it is important that the fluid is able to move freely between the spring element and the reservoir. If between the spring element and the reservoir a communication port is provided, whose diameter is approximately the same as the inside diameter of the bellows, the fluid is ensured of unimpeded movement between the spring element and the reservoir.

An exceptionally favourable construction is obtained when the underside of the spring element is at its circumference connected via a seal with the top side of the reservoir, with the underside of the spring element resting on the floor of the reservoir, being connected thereto by means of at least three evenly distributed supporting elements . This allows the spring element to be placed very closely to the floor of the reservoir, while the fluid is able to flow be- tween the spring element and the reservoir.

If the fluid consists entirely of air, a relatively simple construction is generally possible, because many stan- dard components at relatively acceptable costs can be used for a pneumatic suspension.

Since the effective volume of the fluid is determined both by the spring element and the reservoir, a rela- tively simple spring element, such as a bellows, will suffice, making the total construction more economical.

A comfortably-sprung vehicle is obtained with a relatively soft suspension. This may be achieved, for example, by the spring element being in communication with a reservoir, so that the total volume of the fluid is larger than the volume of the spring element, producing a spring constant that does not vary too much with the compressive load. For this it is a requirement that the pressure in the spring element and in the reservoir is essentially the same. Not only in the static condition, but also during operation, in other words during compression and extension. Therefore, the smallest diameter of the open connection between the spring element and the fluid reservoir needs to be sufficiently large so as not to cause any significant damping. Notably experiments have shown this to be the case when the ratio of the smallest cross-section of the connection (11) to the volume of the spring element is at least 1.5%, and preferably at least 3.0%, with the cross-section being given in dm² and the volume in dm³. The characteristic of the suspension according to the invention is to a large extent determined by the relation between the volume of the spring element and the volume of the reservoir. A large spring element and a small reservoir provide a relatively stiff suspension as is desirable, for example, for sporty motoring. A large reservoir, on the other hand, provides a softer spring characteristic with a lower natural frequency. Good results can be obtained with a wheel suspension according to the invention when the ratio of the volume of the spring element to the volume of the reservoir ranges from 4:1 to 1:2. This range covers a fairly stiff and thus sporty suspension (ratio 4:1), nevertheless making use of the modest overall height and independent pneumatic suspension, as well as a suspension of a very soft spring char- acteristic (ratio 1:2), which is nevertheless able to take a considerable pressure increase and hence to absorb shocks in the spring system, so as to also in the practical sense covering a useful area of applicability. In a particularly pre- ferred embodiment of the invention, especially for application in an ambulance, the volume of the spring element (3) and the volume of the reservoir (5) are essentially the same.

For a comfortably-sprung vehicle, the dimensions of the spring element and the reservoir are advantageously such that a natural frequency of the spring element and the reservoir is lower than 1.5 Hz, preferably 1.2 Hz.

With a vehicle having a rear wheel suspension according to the invention a vehicle can be provided that has a loading floor with a height of less than 400 mm. Because of the modest height at the suspension, a loading floor of such a height makes it also still possible to realize a free space under the wheel suspension of at least 150 mm and a space under the floor of at least 250 mm. The invention will how be further elucidated by way of an exemplary embodiment, with reference to the appended drawings, in which:

Fig. 1 shows a schematic perspective illustration of an embodiment of a rear wheel suspension according to the invention; and Fig. 2 shows a cross section through the line II-II of fig. 1.

Fig. 1 is a schematic representation in perspective of an embodiment according to the invention of a rear wheel suspension for a wheel of a vehicle, generally indicated with reference numeral 1. The rear wheel suspension for the other wheel is not shown, but is a mirror image of the suspension illustrated. The rear wheel suspension comprises a supporting arm 2 and an air spring 3 in the form of a bellows . The supporting arm is provided with two fastening eyes 4, 4' for the pivotal connection of the supporting arm to the frame of the vehicle. Practically the entire supporting arm is embodied in the form of a box 5, having a bottom 6, side walls 7, and an upper surface 8. At its top side 9, the air spring 3 is fas- tened to the frame and at the lower side is associated by means of ring 12 with the upper surface 8 of the box 5, in a manner that will be described in more detail below. Through the opening 11, air is able to freely flow between air spring 3 and box 5. For the rest, the box 5 is closed and forms an air reservoir for a spring system that is comprised of an air spring 3 and a box 5.

In order to provide the supporting arm 2 with stiffness, the supporting arm 2 has to comprise at least one and preferably several flat parts in an orientation approximately at right angles to the bottom 6. In this embodiment of the invention, these stiffening elements are formed by the side- walls 7 of the box 5. In this way and without adding extra height to the supporting arm 2, a reservoir is created for air for the spring system. In addition, the air in the air spring 3 and the air in the reservoir are in open communication with each other and form an air volume that is compressed during the jounce travel and extended during the rebound travel. In contrast to traditional air springs, this avoids that the last part of the deflection of the air spring 3 very progressively increases in stiffness, as is the case with an air spring system according to the prior art, making that part of the air spring' s deflection ineffectual for a comfortable spring performance . Since during compression the increase in air pressure in the air spring 3 is also absorbed by the air in the box 5, the stiffness of the air spring 3 will at the end of its deflection not have increased unac- ceptably, so that the whole deflection of the air spring 3 is effective for a comfortable spring performance. In this way it is possible to obtain an air spring that exhibits a comfortable spring performance while at the same time the overall height required is modest.

To obtain a low natural frequency of the spring system, the air volume of the air spring 3 is approximately the same as the volume of the box 5. In order to allow the air to pass as freely as possible between the air spring 3 and the box 5, the air spring 3 is at its lower side provided with an opening 11 of which the cross section is practically the same as the cross section of the air spring 3.

With the aid of a ring 12, the air spring 3 is sealingly attached to the upper surface 8 of the box 5. Fig. 2 shows that at the position where the air spring 3 is fastened to the upper surface 8 by means of ring 12, the distance between the upper surface 8 and the lower surface 6 of box 5 is smaller. This further reduces the overall height of the wheel suspension 1. The air spring 3 is supported on the bottom side 6 of the box 5 by means of bushes 14, which at the ring 12 around opening 11 form an airtight connection between the top side 8 of the box 5. Through the bushes 14 pass bolts 13, which pass from the bottom side 6 of the box 5 through the bushes 14, keeping a ring 12 fastened to the upper surface 8. The bushes 14 with the bolts 13 passing there-through are distributed over the ring 12 at equal mutual distances. The number of bushes is chosen such that a good connection is maintained also during operation. The height of the bushes 14 and consequently the local internal height of box 5 is chosen to be as low as possible to ensure that the overall height for the wheel suspension 1 is as low as possible. Nevertheless, the height of the bushes 14 has to be adequate so as not to restrict the flow of air between the air spring 3 and the box 5 during the spring action. To this end the height of the bushes 14 will have to be at least 2 mm. The height further depends on any restriction of the orifice, which is caused by the number and the shape of the bushes 14.

A preferred embodiment comprises in addition to the bushes 14, or as part thereof, discharge openings to allow water to drain away through the box 5 from the recesses near the ring 12. These discharge openings are not shown in the drawing, but their shape and fastening are essentially the same as the bushes 14. In a typical exemplary embodiment of a wheel suspension according to the present invention that is, for example, suitable for an ambulance having an axle load of 2000 kg, the height of the side walls 7 of the box 5 is in general approximately 110 mm. The height of the air spring 3 is 170 mm. The diameter of opening 11 is approximately 120 mm and if there are eight bushes 14 distributed over the circumference of the ring 12, the height of the bushes 14 is ap- proximately 7 mm.

This provides an air-sprung independent wheel suspension with a natural frequency of approximately 1.2 Hz, which results in a particularly comfortable spring performance, while the spring has a maximum deflection of 100 mm. This means that an ambulance can be built with a free space under the wheel suspension of at least 150 mm and under the floor of at least 250 mm, while the height of the loading floor is less than 400 mm. The height of a standard fixed coachgate is 120 mm, which makes it possible to build a com- fortably sprung ambulance, having an independent wheel suspension according to the invention, a free space of more than 150 mm and a loading floor that is less than 400 mm high.

It will be obvious that the above-described embodiments of the invention can be modified in numerous ways, all within the scope of the invention as defined by the appended claims .

Claims

CIAIMS

1. A rear wheel suspension (1) for a vehicle having at least two rear wheels and a chassis, wherein each of the two wheels is connected with a supporting arm (2) that is pivotally (4, 4') connected with the chassis, and wherein at each of the two supporting arms (2) a fluid spring element (3) is provided, of which one end is associated with the supporting arm and the other end (9) is associated with the chassis, wherein the fluid spring element (3) via a connection (11) that is open to the fluid, is in communication with a fluid reservoir (5) that forms part of the supporting arm (2), characterised in that the supporting arm (2) is at least partly embodied as a flat box (5) forming the reservoir (5), having a bottom (6), side walls (7), and an upper surface (8), with the average length and width at the box being greater than the average height of the side walls.

2. A rear wheel suspension (1) according to claim 1, characterised in that the average length and width of the box is at least twice the average height of the sidewalls.

3. A rear wheel suspension (1) according to claim 1 or 2, characterised in that at the spring element (3) the upper surface (8) is locally recessed and the underside of the spring element (3) rests on the floor (6) of the Box (5) by means of at least three evenly distributed supporting elements .

4. A rear wheel suspension (1) according to one of the claims 1 to 3, characterised in that the fluid is air.

5. A rear wheel suspension (1) according to one of the claims 1 to 4, characterised in that the spring element (3) is a bellows.

6. A rear wheel suspension (1) according to one of the claims 1 to 5, characterised in that the spring element (3) and the reservoir (5) are in communication such that the pressure in the spring element and the pressure in the reservoir are essentially the same.

7. A rear wheel suspension (1) according to one of the claims 1 to 6, characterised in that when the cross- section is given in dm² and the volume in dm³, the ratio of the smallest cross section of the connection (11) to the volume of the spring element is at least 1.5%, and preferably at least 3.0%.

8. A rear wheel suspension (1) according to one of the claims 1 to 7, characterised in that the ratio of the volume of the spring element (3) to the volume of the reser- voir (5) ranges from 4:1 to 1:2.

9. A rear wheel suspension (1) according to one of the claims 1 to 8, characterised in that the volume of the spring element (3) and the volume of the reservoir (5) are essentially the same .

10. A rear wheel suspension (1) according to one of the claims 1 to 9, characterised in that the spring element (3) has a height between 100 and 200 mm.

11. A vehicle with a loading floor that extends over the rear wheel suspension, characterised in that the vehicle is provided with a rear wheel suspension (1) according to one of the claims 1 to 10 and the loading floor has a height of < 400 mm.

12. A vehicle according to claim 11, characterised in that the free space under the wheel suspension is least 150 mm.