TECHNICAL FIELD

The invention relates to a leaf spring suspension arrangement for providing suspension for a frame of a vehicle. The invention further relates to a method for assembling a leaf spring suspension arrangement, and to a vehicle comprising such a leaf spring suspension arrangement.

Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may accordingly also be used in other vehicles such as buses, vans, sport utility vehicles, and construction equipment, e.g. wheel loaders, excavators, articulated haulers, etc.

BACKGROUND

A leaf spring is a type of spring used for suspension in vehicles. A leaf spring comprises plurality of laminated or stacked arc-shaped steel/composite spring elements typically having rectangular cross-section. The stack of arc-shaped spring elements is attached to the chassis of the vehicle at the end-points of the stack. The centre part of the stack provides a mounting location for a vehicle axle. At least one stack is provided for each of the wheels of the vehicle. A leaf spring suspension may be provided as a single stack of spring elements but may also comprise more than one stack of spring elements. An exemplary leaf spring suspension is disclosed in US7520517.

Leaf springs often suffer from so-called“scissoring” which is when the stacked spring elements are misaligned due to a side-wise slip of the leaf springs caused by for example application of lateral load. Scissoring may be either between individual leaf spring elements, i.e. inter leaf scissoring, or between stacks of leaf spring elements, i.e. inter stack scissoring. The misalignment may for example be on the order of an angular deviation of about one degree between the leaves of the leaf spring. Depending on the type and size of the leaf spring suspension, scissoring may lead to a spatial separation at the end of the leaves of about 5 mm - 20 mm. Scissoring may often occur during assembly of a leaf spring suspension or during transportation of the leaf spring suspension prior to assembly, but also for example during a driving event such as cornering or changing of lane. However, scissoring is generally more likely to occur during transportation of the leaf spring suspension prior to assembly on a vehicle than during a driving event. Scissoring may lead to excessive wear on suspension parts and noisy operation in addition to assembly complications.

Accordingly, there is a need for an improved leaf spring suspension with reduced scissoring issues.

SUMMARY

An object of the invention is to provide a leaf spring suspension arrangement which at least alleviates the problem of scissoring. According to a first aspect of the invention, the object is achieved by a leaf spring suspension arrangement according to claim 1.

According to the first aspect of the invention, there is provided a leaf spring suspension arrangement for providing suspension for a frame of a vehicle, the frame being connectable to a wheel axle via the leaf spring suspension arrangement. The leaf spring suspension arrangement comprises: a first stack of arc-shaped leaf spring elements stacked in parallel in a stacking direction, a second stack of arc-shaped leaf spring elements stacked with the first stack of arc-shaped leaf spring elements in the stacking direction, two alignment bolts, each arranged through a respective through-hole extending through the first stack and through the second stack of arc-shaped leaf spring elements in the stacking direction, the alignment bolts being tightened with a respective nut, wherein the through-holes extend through each of the arc-shaped leaf spring elements of the first stack and through each of the arc-shaped leaf spring elements of the second stack, wherein the alignment bolts are arranged for preventing relative rotational motion between the arc-shaped leaf spring elements of the first stack and the second stack of arc-shaped leaf spring elements.

The present invention is based on the realization that by using two (or more) alignment bolts instead of one centre bolt a relative rotational rotation may be prevented between the stacks of leaf spring elements or between the individual leaf spring elements whereby scissoring may be prevented.

Accordingly, the two (or more) alignment bolts cooperate to restrict the relative rotational degree of freedom of the leaves. In prior art solutions, alignment clips surrounding one or more stacks of leaf spring elements may be used to attempt to reduce scissoring during assembly and transportation. However, with the invented leaf spring suspension arrangement as provided in the first aspect of the invention, such alignment clips may advantageously be omitted since the alignment bolts may be tightened through the stacks of leaf spring elements prior to transportation and/or assembly to at least alleviate the problem of scissoring.

The frame of the vehicle is the main supporting structure, to which vehicle components are attached and may be provided in the form of a chassis of the vehicle.

The wheel axle is the axle to which a wheel of the vehicle is attached and is held in position relative the other wheels of the vehicle as well as the frame of the vehicle.

The leaf spring elements may have a rectangular cross-section and be relatively elongated along a longitudinal direction. The stacking is made in the stacking direction which is substantially orthogonal to the longitudinal direction of the leaf spring elements. That the leaf spring elements are stacked in parallel means that the longitudinal direction of each of the leaf spring elements are substantially aligned with each other. The through-holes through the first stack of leaf spring elements and the second stack of leaf spring elements are made by individual holes in each of the leaf spring elements, the individual holes being aligned with each other in the stacks of leaf spring elements.

The first stack and the second stack of leaf spring elements may comprise different number of leaf spring elements, and/or differently shaped leaf spring elements. It is also possible that the first stack and the second stack of leaf spring elements comprise identical leaf spring elements but different number of leaf spring elements. The same number of leaf spring elements in the two stacks is of course also a possibility. One of the first stack and the second stack may be a“helper” stack and the other one may be a“main” stack of leaf spring elements. According to one embodiment, the through-holes that extend through the first stack and the second stack of arc-shaped leaf spring elements may be symmetrically located with respect to a centre axis through the first stack and the second stack of leaf spring elements. Hereby an advantage is provided in that the symmetric location of the through- holes and thereby also the alignment bolts ensures a uniform load on the leaf spring stacks from the alignment bolts when they are tightened with the nuts. A uniform load from the alignment bolts is preferable in order to not compromise the functionality of the suspension due to non-uniform suspension characteristics.

According to a further embodiment, at least one of the through-holes may be an oblong through-hole comprising an oblong cross-section in a plane orthogonal to the stacking direction. An oblong hole may be rectangular, oval, i.e. the length is greater than the width of the through-hole in the cross-section. By having at least one oblong through-hole assembly of even a relatively high stack of leaf spring elements is facilitated, i.e. there is room for the holes in the leaf spring element to be slightly misaligned before assembly of the leaf spring arrangement since the alignment bolt can anyhow be mounted through the oblong through-hole through the entire stacks and subsequently be tightened. In some embodiments, each of the through-holes may be an oblong through-hole which further facilitates assembly of the leaf spring suspension arrangement.

It may be important to have a relatively small clearance between the alignment bolts an inner wall of the corresponding through-hole. A smaller clearance advantageously further prevents scissoring. Accordingly, the clearance between each alignment bolt and an inner wall of the respective through-hole may be less than 1 mm, or preferably less than 0.5 mm.

According to yet a further embodiment, two U-bolts may be arranged two clamp together the arc-shaped leaf spring elements of the first stack and the second stack, wherein the through-holes are located in a span between the U-bolts. The U-bolts stretches around three sides of the leaf spring stacks, whereby the span is the distance between the centres of the two U-bolts. The U-bolts preferably clamps all the leaf spring elements. The U-bolts advantageously provides for a holding the stacks together once the leaf spring suspension arrangement is mounted on a vehicle. In order to further prevent scissoring, the through-holes should preferably be located as far as possible from each other but reach through all the leaf spring elements. Furthermore, the U-bolts should also be far from each other and still claim all the leaf spring elements together. Accordingly, and according to yet another embodiment, the through-holes may be located as far as possible from each other but within the span of the U-bolts.

According to another embodiment, a spring seat may be provided for mounting the first stacks and the second stack of leaf spring elements on the vehicle axle, the spring seat comprises one locating hole for each alignment bolt, whereby the locating holes in the spring seat are configured to receive a respective alignment bolt such that the rotational relative motion between the stacks of leaf spring elements and the vehicle axle is prevented in the plane of the locating holes. The spring seat is configured to be attached to the bottom stack of the first stack and the second stack, and is subsequently mounted to the vehicle axle. In other words, the spring seat is configured as an attachment adapter for mounting of the stacks of leaf spring elements on the vehicle axle. In order to improve the accuracy of the alignment of the leaf spring elements with an intended mounting direction, (most commonly in the front-rear direction of the vehicle, orthogonally to the vehicle axle), the spring seat is advantageously provided with locating holes in which the alignment bolts may be fitted.

The leaf spring suspension arrangement may be any one of a multi leaf suspension, a progressive leaf suspension, a multi stage leaf suspension, a bogie leaf suspension, or a parabolic leaf suspension.

There is further provided a vehicle comprising a leaf spring suspension arrangement according to anyone of the above discussed embodiments of the first aspect of the invention. The vehicle may be a heavy duty vehicle.

According to a second aspect of the invention, the object is achieved by a method according to claim 12.

According to the second aspect, there is provided a method for assembling a leaf spring suspension arrangement adapted for providing suspension for a frame of a vehicle, the frame being connectable to a wheel axle via the leaf spring suspension arrangement. The method comprises: arranging a first plurality of arc-shaped leaf spring elements in parallel in a first stack in a stacking direction; arranging a second plurality of arc-shaped leaf spring elements in a second stack in the stacking direction; arranging an alignment bolt through a first through-hole through the first stack and the second stack of leaf spring elements, arranging an alignment bolt through a second through-hole through the first stack and the second stack of leaf spring elements, tightening a nut to each of the alignment bolts for maintaining each alignment bolt in the respective through-hole.

The through-holes may be made by making an individual through-hole in each of the leaf spring elements and stacking the leaf spring elements with respect to each other such that the through-holes in the leaf spring elements are aligned.

Effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 is a descriptive illustration of a prior art leaf spring suspension in which scissoring has occurred;

Fig. 2 illustrates a vehicle comprising a leaf spring suspension arrangement according to embodiments of the invention; Fig. 3 conceptually illustrates a leaf spring suspension arrangement according to embodiments of the invention;

Fig. 4a is a schematic view of a leaf spring suspension arrangement according to embodiments of the invention

Fig. 4b is a cross-section of the leaf spring suspension arrangement shown in fig. 4a;

Fig. 5 conceptually illustrates a leaf spring suspension arrangement according to embodiments of the invention;

Fig. 6 conceptually illustrates a leaf spring suspension arrangement according to embodiments of the invention;

Fig. 7 is a cross-section of the leaf spring suspension arrangement shown in fig. 6, and Fig. 8 is a flow-chart of method steps according to embodiments of the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. For example, although the invention will mainly be described with reference to a truck, but may equally well be applicable to other vehicles such as buses, vans, sport utility vehicles, and construction equipment, e.g. wheel loaders, excavators, articulated haulers, etc.

FIG.1 illustrate a prior art leaf spring suspension 1 comprising a plurality of leaf spring elements 2 in two stacks 3, 4 which are stacked with each other. Alignment clips 5 (only one is numbered) are arranged to attempt to keep the leaf spring elements aligned with each other and U-bolts 6 are arranged to hold the stacks 3, 4 together. Furthermore, a single centre bolt 7 is arranged through the two stacks 3, 4 of leaf spring elements 2 to hold the leaf spring elements 2 closely packed. However, as is a common problem with prior art leaf spring suspensions 1 , the leaf spring elements 2 of the two stacks 3, 4 have been misaligned with each other, i.e.“scissoring” has occurred. As illustrated in fig. 1 an angle a has been formed between the stacks 3, 4 of leaf spring elements suffering from scissoring. This angle may be about 1 degree or even larger. Scissoring may lead to excessive wear on suspension parts and noisy operation in addition to assembly complications.

Fig. 2 illustrates a vehicle in the form of a truck 104. The truck 104 comprises a leaf spring suspension arrangement 100 which is adapted to provide suspension for a frame 102 of the truck 104. The leaf spring suspension arrangement 100 is therefore attached to the frame 102 and is also connected to a wheel axle 106 of the truck 104; in this particular example the wheel axle 106 is a rear wheel axle 106 of the truck 104. The wheel axle 106 is configured to maintain a relative location of the wheels 107 mounted on the axle 106.

The leaf spring suspension arrangement 100 comprises a first stack 108 of leaf spring elements and a second stack 1 12 of leaf spring elements. The leaf spring suspension arrangement 100 is here illustrated as a multi stage leaf spring suspension. However, the invention is applicable to various types of leaf spring suspension arrangements such as a progressive leaf suspension, a bogie leaf suspension, or a parabolic leaf suspension.

The wheel axle 106 is in here located at a central part of the second stack 1 12 of leaf spring elements 110. The first stack 108 and the second stack 1 12 are substantially symmetric.

Fig. 3 illustrates a leaf spring suspension arrangement 100. There is shown a first stack 108 and a second stack 1 12 of leaf spring elements 1 10. The leaf spring elements 1 10 in each stack 108, 1 12 are stacked in a stacking direction 1 11 which is substantially orthogonal to a longitudinal direction 1 13 along a leaf spring element 1 10. The leaf spring elements 1 10 are generally arc-shaped and elongated along the longitudinal direction 1 13. The leaf spring elements 1 10 are stacked in parallel, e.g. an axis in the longitudinal direction 113 for each leaf spring element are generally parallel.

Alignment bolts (not shown in fig. 3) are arranged in through-holes extending through the entire stacks 108, 1 12 of leaf spring elements 1 10. In fig. 3 only the nuts 120, 121 which are tightened onto the alignment bolts are shown and not the alignment bolts. The alignment bolts prevents relative rotational motion between the leaf spring elements 110. In fig. 3 there is further shown optional alignment clips 1 16 holding part of the leaf spring elements 1 10 together in the second stack 112. Furthermore, an attachment member for mounting of the leaf spring suspension arrangement on the vehicle frame are here also shown in the form of a bushing 1 19a which is pressed into a leaf spring eye 119b.

Fig. 4a illustrates a leaf spring suspension arrangement 100 according to embodiments of the invention. Fig. 4b is a cross-sectional view of the leaf spring suspension arrangement 100 in fig. 4a along the line A-A. Similar to the leaf spring suspension arrangement 100 shown in fig. 3, there is a first stack 108 of leaf spring elements 1 10 and a second stack 1 12 of leaf spring elements 1 10. The first stack 108 is place on the second stack 112 such that the leaf spring elements of both the stacks 108, 1 12 are stacked with each other in parallel. Alignment bolts 114, 115 are arranged in through-holes 117, 118 which extend all the way through the first stack 108 and the second stack of leaf spring elements 110. A nut 120, 121 is tightened on each bolt 1 14, 115 in order to firmly maintain the alignment bolt 114, 1 15 in the respective through-hole 117, 1 18. The nuts 120, 121 also ensure that a force is applied in the stacking direction 11 1 along the alignment bolts’ main axis, to thereby hold the first stack 108 and the second stack 1 12 of leaf spring elements tightly together in place. In particular, the rotational degree of freedom for the leaf spring elements 110 is restricted by the two alignment bolts 1 14, 1 15.

The clearance 125 between each alignment bolt 1 14, 1 15 and an inner wall of the respective through-hole 1 17, 1 18 may be less than 1 mm, or preferably less than 0.5 mm.

Although the embodiments herein illustrate leaf spring suspension arrangements with two alignment bolts it is understood that more than two alignment bolts may be used, such as 3, 4, 5, 6, etc. alignment bolts.

In the embodiment shown in fig. 4a, the two alignment bolts 1 14, 1 15 are arranged in through-holes 117, 1 18 that are symmetrically located with respect to the centre axis 123 which is orthogonal with the longitudinal direction 113, and parallel with the stacking direction 11 1. In other words, the virtual centre axis 123 lies through the centre of the first stack 108 and through the centre of the second stack 1 12 as seen in a plane orthogonal to the stacking direction 11 1. Now turning to fig. 5 which schematically illustrates an embodiment of the invention where one of the though-holes is an oblong through-hole 118. As mentioned above, the leaf spring elements 1 10 are generally arc-shaped before they are assembled to form a leaf spring suspension arrangement 100. When the alignment bolts 1 14, 1 15 with their respective nuts 120, 121 are tightened in the through-holes 1 17, 1 18 they cause the leaf spring elements 1 10 to at least partly flatten out. However, due to the arc-shape of the leaf spring elements 110, it may be difficult to properly align the through-holes of all the leaf spring elements 110 to form the through-hole through both the stacks 108, 112 of leaf spring elements 110 such that the alignment bolt can be fitted through the through-hole. This is particularity the case when one of the alignment bolts 114, 1 15 has been tightened in its through-hole 1 17, 118, and the second alignment bolt is going to be arranged in its respective through-hole 1 17, 118. The first alignment bolt then restricts the motion of the leaf spring elements such that it may be difficult to fit the second alignment bolt though its though-hole. Accordingly, it may be advantageous for at least one of the through-holes to have an oblong cross-section which allow for the alignment bolt to pass through the hole 1 14, 1 15 even if the leaf spring elements are not closely packed and at least partly flattened out.

Accordingly, in fig. 5 there is shown a leaf spring suspension arrangement 100 having one circular through-hole 1 18 and one oblong through-hole 1 18. The close-up shows the through-holes as seen from above the leaf spring suspension arrangement 100 and there is further shown a partial cross-section to conceptually illustrate the inside of the oblong through-hole 118. The oblong through-hole 1 18 is slot-shaped and thus has one side which is longer than another side a seen in the close-up viewed from above the leaf spring suspension arrangement 100. The leaf spring elements 110 (only one is numbered) are arc-shaped but due to the oblong shape of the through hole 118, the alignment bolt 1 14 may still be fitted through all the leaf spring elements 1 10 of both the stacks.

Fig. 6 conceptually illustrates a leaf spring suspension arrangement 100. Similar to the above described embodiments, this embodiment comprises the first stack 108 and the second stack 1 12 of leaf spring elements 1 10, and the alignment bolts 1 14, 1 15 being arranged in their respective through-hole 1 17, 1 18 and tightened with nuts 120, 121. In this embodiment, there is also included two U-bolts 126, 127. The U-bolts 126, 127 are arranged partly surrounding the stacks 108, 112 of leaf spring elements 1 10, and through a bottom plate 200. The bottom plate 200 is adapted to be arranged on one side of the vehicle axle 106 and a leaf spring seat 130 on the opposite side of the vehicle axle 106 from the bottom plate 200 (see fig. 2). The U-bolts are tightened on the bottom side of the bottom plate 200 such that the leaf spring seat 130 and the stacks 108, 1 12 of leaf spring elements 1 10 are pulled towards the vehicle axle 106 and held firmly in place on the vehicle axle 106.

The leaf spring elements 1 10 may have different length. As conceptually shown in e.g. fig. 6 or fig. 7, the bottom leaf spring element 1 10 of each stack 108, 1 12 is the shortest leaf spring element of the respective stack. Furthermore, the top leaf spring element is the longest leaf spring element of the respective stack. In order for the U-bolts 126, 127 to maintain pressure on the entire stacks, the U-bolts are arranged with a span 128 between each other shorter than or equal to the length of the shortest leaf spring element among the leaf spring elements 1 10 of both stacks. Furthermore, it is preferable that the alignment bolts 114, 115 pass through all the leaf spring elements 1 10 of both stacks 108, 1 12 (or all the stacks if there are more than two stacks). Consequently, the through-holes 1 17, 1 18 through which the alignment bolts 1 14, 115 are arranged are preferably located in the span 128 between the alignment bolts 114, 1 15.

Optionally, an alignment plate 134 having a planar central part 135 and corrugated edge portions 136 arranged on top of the first stack 108. The alignment bolts 114, 1 15 pass through through-holes in the planar central part 135 of the alignment plate 134. The corrugated edge portions 136 of the alignment plate 134 ensure that the U-bolts 126, 127 are held in place such that the span 128 is maintained.

Fig. 7 conceptually illustrates a cross-section of the embodiment in fig. 6, although not showing the bottom plate 200. The leaf spring seat 130 is adapted to be mounted in a predetermined orientation on the vehicle axle 106 such that the leaf spring suspension is correctly aligned with respect to the vehicle axle 106. The leaf spring suspension arrangement may for example be orthogonally arranged with respect to the vehicle axle 106, as is shown in fig. 2. The nuts 141 , 142 (not all nuts are shown, there are two nuts needed for each U-bolt) are used for tightening the U-bolts 126, 127 on the bottom side of the bottom plate 200 (see fig. 6). In order to facilitate the orientation of the leaf spring elements 1 10 with respect to the leaf spring seat 130, the two alignment holes 132, 133 in the leaf spring seat 130 are adapted to receive the alignment bolts 1 14, 1 15 that are mounted through their respective through- hole 117, 118. When the alignment bolts 114, 1 15 are arranged in the alignment holes 132, 133, the rotational movement of the leaf spring elements 110 with respect to the leaf seat is restricted, whereby the rotational movement of the leaf spring elements 1 10 with respect to the vehicle axle 106.

Fig. 8 is a flow-chart of method steps for assembling a leaf spring suspension arrangement according to an embodiment of the invention. In a first step S100 a first plurality of leaf spring elements are arranged in parallel in a first stack in a stacking direction. Subsequently (or simultaneously) S102, a second plurality of leaf spring elements are arranged in a second stack in the stacking direction, the first stack is stacked with the second stack. An alignment bolt is arranged (S104) through a first through-hole through the first stack and the second stack of leaf spring elements. Furthermore, another alignment bolt is arranged (S106) through a second through-hole through the first stack and the second stack of leaf spring elements. Subsequently (S108), a nut is tightened to each of the alignment bolts for maintaining each alignment bolt in the respective through-hole (1 17, 1 18).

The through-holes may be made by making an individual through-hole in each of the leaf spring elements and stacking the leaf spring elements with respect to each other such that the through-holes in the leaf spring elements are aligned. By making at least one of the though-holes an oblong through-hole facilitates to fit the corresponding alignment bolt in the through-hole.

Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Accordingly, it is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.