Patent Description:
The teachings of the present disclosure can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the present disclosure will focus on a heavy-duty vehicle, the general inventive concept is not restricted to this particular vehicle, but may also be used in other vehicles such as cars.

In vehicle suspensions where a rigid axle is located and controlled by leaf springs, many compromises have to be made. Such compromises can adversely reflect on the suspension performance under various loading conditions to which it is subjected during the operation of the vehicle. Examples of such loading condition is vehicle roll about the longitudinal roll centre which occurs when the vehicle is negotiating a bend or is subjected to forces induced by strong winds in the transverse direction. A further loading is termed "bump steer", which occurs when a wheel on one side of the vehicle is deflected upwards by an obstacle on the road surface.

Under such load conditions, the left and right wheel centres may become displaced relative to each other, resulting in large reaction forces between the leaf springs on the left side and the right side of the vehicle. In case of conventional U-shaped leaf springs, this will cause a twisting deformation of the axle and the leaf springs, and the deformation of the axle will displace the wheel centres in a way that reduces the desired understeer effect on the total steering.

<CIT> addresses the above problem by providing a vehicle suspension in which the leaf springs have a different configuration compared to the traditional U-shaped leaf springs. In <CIT> the leaf springs have convex portions extending towards the frame of the vehicle. Nevertheless, there is still room for improvement when it comes to handling characteristics.

The documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> disclose leaf springs for use in a vehicle. The document <CIT> disclose the preamble of claim <NUM>.

An object of the invention is to provide a leaf spring with improved handling characteristics. This and other objects, which will become apparent in the following discussion, are achieved by a leaf spring according to the accompanying independent claim. Some nonlimiting exemplary embodiments are presented in the dependent claims.

In vehicle suspensions, there is a term referred to as the "datum line". The datum line is an imaginary reference line between the front and rear leaf spring end eyes. A common design goal is to maximize the distance between the datum line and the intermediate portion of the leaf spring that is attached to the axle, since a large distance enables increased wheel motion, improved comfort and increased packaging space for an air spring.

However, the inventors have realized that with the prior art leaf springs the handling properties are compromised if said distance from the datum line is increased, because the wind-up centre will be at a too low level. The wind-up centre is the imaginary point on the leaf spring centre part standing relatively still during braking. The ball joint of the steering arm (attached to the steering knuckle) should desirable be located at the wind-up centre. However, if the wind-up centre is located at a too low level, then it is very difficult to find a steering arm that does not conflict with the axle. The inventors have unexpectedly realized that by providing a convex leaf spring portion on one side of the attachment to the axle and a concave leaf spring portion on the other side of the attachment to the axle, the wind-up centre can be provided at a high level (i.e. far from the ground) even though said distance to the datum line is increased compared to the distance that is practically possible in the prior art leaf springs. Hereby, improved handling characteristics are obtainable even with a large distance to the datum line.

According to a first aspect of the present disclosure, there is provided a leaf spring for use in a vehicle suspension, comprising:.

By having a first upwardly facing convex portion formed between the first end and the axle attachment portion, in combination with a second upwardly facing concave portion formed between the axle attachment portion and the second end, the wind-up centre can be higher when the leaf spring is mounted as part of a vehicle suspension, even though the distance to the datum line is increased compared to the prior art vehicle suspensions. This allows for improved handling characteristics.

The leaf spring is intended to be mounted to a vehicle such that the first end is closer to the front of the vehicle, while the second end of the leaf spring is closer to the rear of the vehicle. Thus, the first end of the leaf spring may also be referred to as a front end, and the second end of the leaf spring may also be referred to as a rear end. In addition, as understood from above, the leaf spring also has an intended orientation relative to the ground when properly mounted. The lower surface is intended to face the ground, while the upper surface is intended to face away from the ground, when the leaf spring is properly mounted to the vehicle as part of a vehicle suspension. Suitably, the lower surface of the leaf spring may be in contact with the axle when the leaf spring is in its mounted position. From the above, it should thus also be understood that directional terms such as downwardly, lower, below, etc. are terms relative to the ground on which a vehicle stands. Thus, downwardly is in a direction towards the ground, while upwardly is in a direction away from the ground. Similarly, if a first component is located at a lower level than a second component, then the first component is located closer to the ground.

According to at least one exemplary embodiment, the axle attachment portion is the thickest portion of the leaf spring. This reduces the risk of undesirable stress in the axle attachment portion when the leaf spring forms part of a vehicle suspension subjected to loads. In at least some exemplary embodiments, the lower surface of the axle attachment portion of the leaf spring is planar in order to match a corresponding planar portion of the axle. Suitably, the first upwardly facing convex portion is void of any planar subportion. Similarly, the second upwardly facing concave portion is suitably void of any planar subportion. Thus, in at least some exemplary embodiments, the first upwardly facing convex portion extends in a continuous curved path from the axle attachment portion to the first end. Similarly, in at least some exemplary embodiments, the second upwardly facing concave portion extends in a continuous curved path from the axle attachment portion the second end.

According to at least one non-claimed example, the second upwardly facing concave portion extends upwardly from the axle attachment portion to the second end. This is advantageous as it allows the wind-up centre to be positioned higher compared to a flat or an upwardly facing convex rear portion of prior art leaf springs.

According to the invention, the second upwardly facing concave portion is formed by:.

According to at least one exemplary embodiment, the second subportion has a steeper slope from said lowest point to the second end compared to the slope of the first subportion from the lowest point to the axel attachment portion.

Since the second subportion is configured to lean upwards in order for the leaf spring to get back to the datum line from said lowest point, it may advantageously be configured with a steep slope. By providing a steep slope of the second subportion a shorter offset is obtainable between the leaf spring end eye at the second end and the frame of the vehicle. This in turn allows a shackle, which is configured to engage the leaf spring eye, to be made smaller and therefore the bracket to which the shackle is attachable can be made lighter.

According to the invention, the extension of the second subportion forms a curved path from said lowest point to the second end, wherein the smallest radius of said curvature of the second subportion is smaller than any radius of curvature of the first subportion. This too provides the advantage of allowing for a smaller shackle and lighter bracket to be used in a vehicle suspension.

According to at least one exemplary embodiment, the first end comprises a first end eye and the second end comprises a second end eye, wherein the shortest distance between said first and second end eyes defines a geometrical datum line, wherein.

According to at least one exemplary embodiment, the relationship between said distance C, said predetermined first length A, and said predetermined second length B is:
C > (A+B)/X where X is <NUM>, suitably <NUM>, more suitably <NUM>.

By increasing the distance C, an increased wheel motion is enabled. Furthermore, driver comfort is improved and the packaging space for an optional air spring is increased. The above relationship may also be expressed as the distance (A+B) between the first and second eyes divided by said shortest distance (C) between the centre of the axle attachment portion and the datum line is less than <NUM>, suitably less than <NUM>, more suitably less than <NUM>.

According to at least one exemplary embodiment, a first straight imaginary geometrical line is drawable between the end points of the first upwardly facing convex portion, from the first end to the axle attachment portion, wherein perpendicularly to the first straight imaginary geometrical line the largest distance a between the first straight imaginary geometrical line and the first upwardly facing convex portion is defined as a > A/Y where Y is <NUM>, suitably <NUM>, more suitably <NUM>.

By configuring the first upwardly facing convex portion with a large distance a, positive handling characteristics are achievable. The distance a can be regarded as a measure of how much the first upwardly facing convex portion bulges upwardly.

According to at least one exemplary embodiment, a second straight imaginary geometrical line is drawable between the end points of the second upwardly facing concave portion, from the second end to the axle attachment portion, wherein perpendicularly to the second straight imaginary geometrical line the largest distance b between the second straight imaginary geometrical line and the second upwardly facing concave portion is defined as b > B/Z wherein Z is <NUM>, suitably <NUM>, more suitably <NUM>. By configuring the second upwardly facing concave portion with a large distance b, positive handling characteristics are achievable. The distance b can be regarded as a measure of how much the second upwardly facing concave portion bulges downwardly.

The above discussed distances a, b and C have been found to result in an advantageous leaf spring when in use in a vehicle suspension of a vehicle. In particular, such a leaf spring having the geometry with the above discussed distances a, b and C reduces the reaction forces that deform the axle and the leaf spring of prior art vehicle suspensions. The present leaf spring provides axle steer effects which give a desirable understeering behaviour. Because of this advantageous effects, when the present leaf spring is used in a vehicle suspension there is no need for a large rear spring anchorage with large offset, thus saving both weight and cost, and additionally providing ample space for an optional auxiliary spring.

According to a second aspect of the present disclosure, there is provided a vehicle suspension comprising a leaf spring according to the first aspect, including any embodiment thereof.

The advantages of the vehicle suspension of the second aspect are largely analogous to the advantages of the leaf spring of the first aspect, including any embodiment thereof.

According to at least one exemplary embodiment, the vehicle suspension comprises:.

wherein the first end of the leaf spring is connected to the first bracket and the second end of the leaf spring is connected to the shackle in order to compensate for length changes of the leaf spring under load conditions.

Suitably the first frame position and the second frame position are, relative to each other, a front frame position and a rear frame position, respectively. Thus, the first bracket may in such case be referred to as a front bracket and the second bracket may be referred to as a rear bracket.

According to at least one exemplary embodiment, said leaf spring is a first leaf spring, the vehicle suspension further comprising:.

The first and the second leaf springs may suitably have corresponding features.

It should be understood that the vehicle suspension may, in at least some exemplary, embodiments comprise a stack of first leaf springs at one end of the axle and a stack of second leaf springs at the other end of the axle, wherein the lowermost leaf spring in each stack is in contact with the axle.

According to a third aspect of the present disclosure, there is provided a vehicle comprising a leaf spring according to the first aspect (including any embodiment thereof) or a vehicle suspension according to the second aspect (including any embodiment thereof).

The advantages of the vehicle of the third aspect are largely analogous to the advantages of the leaf spring of the first aspect, including any embodiment thereof.

All references to "a/an/the portion, element, apparatus, component, arrangement, device, means, etc." are to be interpreted openly as referring to at least one instance of the portion, element, apparatus, component, arrangement, device, means, etc., unless explicitly stated otherwise. Further features of, and advantages with, the teachings of the present disclosure will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present disclosure may be combined to create embodiments other than those described in the following, without departing from the scope of the present disclosure.

The general inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain aspects are shown. The general inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments and aspects set forth herein; rather, the embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope to those skilled in the art. Accordingly, it is to be understood that the present general inventive concept is not limited to the embodiments described herein 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.

<FIG> illustrates a vehicle <NUM> according to at least one exemplary embodiment of the present disclosure. The exemplary illustration in <FIG> shows a heavy-duty vehicle <NUM>. More specifically <FIG> shows a vehicle in the form of a tractor unit for towing a trailer unit (not shown), which together may make up a semitrailer vehicle. However, the teachings of the present disclosure are applicable to other types of vehicles as well. For instance, the vehicle may be a different type of vehicle for cargo transport, such as a truck, or a truck with a dolly unit arranged to tow a trailer unit, etc. Other exemplary vehicles include buses, construction equipment, and even passenger cars. The vehicle <NUM> may be operated by a driver or it may be an autonomous vehicle.

The illustrated vehicle <NUM> is supported on wheels <NUM>, some of which are driven wheels. The front wheels <NUM> may suitably be steered wheels. The wheels <NUM>, such as the wheels at the front axle, may be associated with a vehicle suspension in accordance with the teachings of this disclosure. Such a vehicle suspension may in its turn comprise a leaf spring in accordance with the teachings of this disclosure. Such a leaf spring will now be discussed in connection with <FIG>.

<FIG> illustrates in a perspective view a vehicle suspension <NUM> comprising two leaf springs <NUM> in accordance with at least one exemplary embodiment. <FIG> schematically illustrates a side or cross-sectional view of a leaf spring <NUM> according to at least one exemplary embodiment, when mounted as part of a vehicle suspension <NUM>. The illustration in <FIG> may, for instance, show one of the leaf springs <NUM> in the vehicle suspension <NUM> of <FIG>.

With reference to both <FIG> and <FIG>, each leaf spring <NUM> has a first end <NUM> and a second end <NUM>. The first end <NUM> is connected to a first bracket <NUM> configured to be attached rigidly to a vehicle frame <NUM> at a first frame position (see <FIG>). More specifically, the first end <NUM> of the leaf spring <NUM> comprises a first end eye <NUM> for engaging with the first bracket <NUM>. The second end <NUM> of each leaf spring <NUM> is connected to a shackle <NUM>. More specifically, the second end <NUM> comprises a second end eye <NUM> for engaging with the shackle <NUM>. The shackle <NUM> is pivotally connected to a second bracket <NUM> configured to be attached rigidly to the vehicle frame <NUM> at a second frame position (see <FIG>). The connection between the second end <NUM> of the leaf spring <NUM> and the shackle <NUM> is made in order to compensate for length changes of the leaf spring <NUM> under load conditions. <FIG> also shows a drag link <NUM> which interconnects a pitman arm <NUM> with a steering arm <NUM> for controlling a steerable wheel (these components do not form part of the vehicle suspension <NUM> as such). It can therefore be understood that, in this example, the first end <NUM> is intended to be arranged forwardly of the second end <NUM>. The first end <NUM> of each leaf spring <NUM> may thus be regarded as a front end <NUM> of the leaf spring <NUM>, while the second end <NUM> may be regarded as a rear end of the leaf spring <NUM>.

The vehicle suspension <NUM> further comprises a rigid axle <NUM> extending transversely of the vehicle frame <NUM>, which axle <NUM> is mounted to the two leaf springs <NUM> at an axle attachment portion <NUM> of the respective leaf spring <NUM>. As shown in the example in <FIG>, each leaf spring <NUM> may suitably be fastened/clamped (at each axle attachment portion <NUM>) to the axle <NUM> by means of brackets or similar. For instance, a pair of U-shaped dowel pins <NUM> may be placed over the leaf spring <NUM> to hold down the leaf spring <NUM>, wherein the dowel pins <NUM> may further extend through bores in the axle <NUM> and be tightened.

With reference to <FIG> and <FIG>, the leaf spring <NUM> comprises a lower surface <NUM> configured to face downwardly towards the ground when used in a vehicle suspension. As illustrated, the lower surface <NUM> may face and be in contact with the axle <NUM>. The leaf spring <NUM> comprises an upper surface <NUM> which is located opposite to the lower surface <NUM> and which is configured to face upwardly when used in a vehicle suspension. As illustrated, the upper surface <NUM> may face away from the axle <NUM>. The upper surface <NUM> as well as the lower surface <NUM> extend longitudinally from the first end <NUM> to the second end <NUM> of the leaf spring <NUM>. The axle attachment portion <NUM> of the leaf spring <NUM> is located between the first end <NUM> and the second end <NUM>. The axle attachment portion <NUM> is configured to be attached to the axle <NUM> such that the longitudinal extension of the upper surface <NUM> and lower surface <NUM> of the leaf spring <NUM> is directed transversely to main direction of extension of the axle <NUM>.

In <FIG> a Cartesian coordinate system (x, y, z) is illustrated. The x-axis corresponds to the longitudinal direction of the vehicle. The x-axis may also be referred to as the roll axis. The longitudinal extensions of the leaf springs <NUM> in <FIG> are substantially parallel to the roll axis. The y-axis may also be referred to as the pitch axis. The longitudinal extension (i.e. the main direction of extension) of the axle <NUM> is substantially parallel with the pitch axis. The z-axis may also be referred to as the yaw axis. The upper surface <NUM> of the leaf spring <NUM> is thus intended to be separated from the lower surface <NUM> of the leaf spring <NUM> along the z-axis (more specifically along a direction parallel to the z-axis).

As best seen in <FIG>, the leaf spring <NUM> comprises a first upwardly facing convex portion <NUM> formed between the first end <NUM> of the leaf spring <NUM> and the axle attachment portion <NUM> of the leaf spring <NUM>. The first upwardly facing convex portion <NUM> can be seen to bulge upwardly (i.e. bulge upwardly in a direction parallel with the z-axis). The leaf spring <NUM> also comprises a second upwardly facing concave portion <NUM> formed between the axle attachment portion <NUM> and the second end <NUM>. This second upwardly facing concave portion <NUM> can be seen as a downwardly projecting bulge, i.e. bulging in the opposite direction compared to the first upwardly facing convex portion <NUM> in relation to the z-axis. As will later be discussed in connection with <FIG>, such a combination of a first upwardly facing convex portion <NUM> and a second upwardly facing concave portion <NUM> allows for the wind-up centre to be at a higher level (as seen in relation to the z-axis) compared to known leaf springs, even if the distance to the datum line is increased. This allows for improved handling properties.

From the previous discussion, as well as from the drawings, it can be understood that according to at least some exemplary embodiments, the longitudinal extension of the leaf spring <NUM> may follow an S-shaped path. In more general terms, in accordance with at least some exemplary embodiments, the leaf spring <NUM> is S-shaped.

Continuing with <FIG> and <FIG>, the axle attachment portion <NUM> may suitably be the thickest portion of the leaf spring <NUM>. Furthermore, at the axle attachment portion <NUM> the lower side <NUM> of the leaf spring <NUM> may suitably be substantially flat/planar in order to mate with a similarly flat/planar plate portion <NUM> (see <FIG>) of the axle <NUM>.

As shown in <FIG>, the second upwardly facing concave portion <NUM> is formed by a first subportion <NUM>, which extends downwardly from the axle attachment portion <NUM> to a lowest point <NUM> of the second upwardly facing concave portion <NUM>, and a second subportion <NUM> which extends upwardly from said lowest point <NUM> to the second end <NUM>. As can be seen in <FIG>, the lowest point <NUM> represents a global minimum of the leaf spring <NUM>. In contrast, there is a highest point <NUM>, i.e. a global maximum of the leaf spring <NUM>, formed by the first upwardly facing convex portion <NUM>.

As can be seen in <FIG>, the second subportion <NUM> has a steeper slope from said lowest point <NUM> to the second end <NUM> compared to the slope of the first subportion <NUM> from the lowest point <NUM> to the axle attachment portion <NUM>. Hereby, a shorter offset is obtainable between the second end eye <NUM> and the vehicle frame <NUM>. This in turn allows the shackle <NUM>, which is configured to engage the second end eye <NUM>, to be made smaller and therefore the second bracket <NUM> to which the shackle <NUM> is attachable can be made lighter. Furthermore, the extension of the second subportion <NUM> forms, according to the invention, a curved path from said lowest point <NUM> to the second end <NUM>, wherein the smallest radius of curvature of the second subportion <NUM> is smaller than any radius of curvature of the first subportion <NUM>.

As mentioned previously, the first end <NUM> comprises a first end eye <NUM> and the second end <NUM> comprises a second end eye <NUM>. The shortest distance between the first end eye <NUM> and the second end eye <NUM> defines a geometrical datum line D. The datum line D is thus understood to extend substantially in parallel with the x-axis (roll axis). An intermediate point on the datum line D is separated from the centre of the axle attachment portion by a distance C, which is the shortest distance between the centre of the axle attachment portion <NUM> and the datum line D. The first end eye <NUM> is separated from the intermediate point by a predetermined first length A along said datum line D. The second end eye <NUM> is separated from the intermediate point by a predetermined second length B along said datum line D. The relationship between said distance C, said predetermined first length A, and said predetermined second length B may suitably be C > (A+B)/X where X is <NUM>, suitably <NUM>, more suitably <NUM>.

In <FIG> there is indicated a first straight imaginary geometrical line E drawn between the end points of the first upwardly facing convex portion <NUM>, from the first end <NUM> to the axle attachment portion <NUM>. Perpendicularly to this first straight imaginary geometrical line E the largest distance a between the first straight imaginary geometrical line E and the first upwardly facing convex portion <NUM> may be defined as a > A/Y where Y is <NUM>, suitably <NUM>, more suitably <NUM>. The largest distance a extends to a point on the first upwardly facing convex portion <NUM> which may coincide with the previously mentioned highest point <NUM> (global maximum).

In <FIG> there is also indicated a second straight imaginary geometrical line F drawn between the end points of the second upwardly facing concave portion <NUM>, from the second end <NUM> to the axle attachment portion <NUM>. Perpendicularly to this second straight imaginary geometrical line F the largest distance b between the second straight imaginary geometrical line F and the second upwardly facing concave portion <NUM> may be defined as b > B/Z wherein Z is <NUM>, suitably <NUM>, more suitably <NUM>. The largest distance b extends to a point on the second upwardly facing concave portion <NUM> which may coincide with the previously mentioned lowest point <NUM> (global minimum).

<FIG> also indicates that the vehicle suspension <NUM> may optionally include an air spring <NUM>, such as an air bellow extending between the leaf spring <NUM> and the vehicle frame <NUM>. It should be understood that on the one hand, it may be desirable to reduce the spacing between the datum line D and the vehicle frame <NUM> as that will allow a reduction of the size, and thus the weight, of the first and second brackets <NUM>, <NUM> and reduce reaction forces in the vehicle frame <NUM>. On the one hand, to increase the packaging space for the air spring <NUM>, it may be desirable to increase the distance C. Increasing the distance C also allows for increased wheel motion and improved comfort.

<FIG> is a schematic comparison between the leaf spring <NUM> in <FIG> and a conventional leaf spring <NUM>. Thus, in <FIG>, the leaf spring <NUM> of <FIG> is shown in solid line. The extension of a conventional U-shaped leaf spring <NUM> is shown in dashed line.

<FIG> is a schematic diagram for the two leaf springs <NUM>, <NUM> in <FIG>, indicating the roll steer angle over axle roll angle for a vehicle subjected to vertical roll. Vertical roll implies that the vehicle is not subjected to a side force. This type of loading is caused by so-called "bump-steer" when one of the wheels on a rigid axle is deflected upwards by an obstacle such as a ridge or a rock on the road surface. The roll steer angle in the diagram is the average roll steer angle for the left and right wheels. As can be seen from the solid line, representing the roll steering when using a leaf spring <NUM> of an exemplary embodiment of the present disclosure (such as the one in <FIG>), even a relatively large axle roll angle will have a negligible effect on the roll steer angle. This can be compared to the roll steer behaviour of a conventional under-bent leaf spring <NUM>, as indicated by the dashed line in <FIG>. The diagram indicates that the leaf spring <NUM> according to the present disclosure will cause increased under-steer which gives an improved steering feel for the driver when driving across an uneven surface.

<FIG> is another schematic comparison between the leaf spring <NUM> in <FIG> and said conventional leaf spring <NUM>. Thus, <FIG> is based on <FIG>, showing a comparison between two leaf springs <NUM>, <NUM>, namely a leaf spring <NUM> in accordance with the teachings of the present disclosure (solid line) and a conventional U-shaped leaf spring <NUM> (dashed line).

<FIG> also indicates the respective wind-up centre, WC, for the two leaf springs <NUM>, <NUM>, and the respective Ross point, RP, for the two leaf springs <NUM>, <NUM>. The wind-up centre, WC, is an imaginary point standing relatively still during a braking manoeuvre. The Ross point, RP, is an imaginary point in space about which a leaf spring under vertical load will arc. The imaginary line between the Ross point and the wind-up centre is referred to as the Ross line. The angle between the Ross line and the datum line D is referred to as the Ross angle.

Good handling characteristics are generally reached when the drag link <NUM> is connected between the Ross point, RP, and the wind-up centre, WC, i.e. the Ross line should suitably match the extension of the drag link. It is therefore desirable to have the steering gear with the pitman arm at the Ross point, RP, and the steering arm at the wind-up centre, WC.

With the conventional U-shaped leaf blade <NUM> it is difficult to position the steering gear (close to the Ross point, RP) and the steering arm (close to the wind-up centre, WC) because of packing limitations. Even if you succeed in positioning the conventional U-shaped leaf blade <NUM> with respect to the Ross point, RP, and the wind-up centre, WC, the shorter Ross line and larger Ross angle (cf. indicated dashed drag link/Ross line <NUM>) will have negative impact on handling characteristics compared to the handling characteristics of the leaf spring <NUM> (solid line) of the present disclosure.

As can be seen in <FIG>, the shape of the leaf spring <NUM> of the present disclosure results in a longer Ross line and a smaller Ross angle, thereby making the steering support less sensitive (smaller angular motion during vertical spring travel). Furthermore, the position of the wind-up centre, WC, is close to the leaf spring centre which makes it possible to use the steering arm geometry with clearance to the axle. This makes it possible to reduce axle offset with good axle ground clearance (i.e. corresponding to the vertical distance G to the tire circle <NUM> indicated by the dash-dotted circle in <FIG>). The shape of the leaf spring <NUM> also creates good and stable understeering level together with reduced low level unwanted steering effects like bump and brake steer.

Furthermore, although only a conventional U-shaped leaf spring <NUM> has been indicated in <FIG>, some comments may also be made with respect to the previously mentioned leaf spring in <CIT>. That prior art leaf spring will not work satisfactorily if the distance C is made larger, which as explained above is desirable. The substantially S-shaped leaf spring <NUM> of the present disclosure will, however, give good handling properties even with a larger distance C, as its wind-up centre, WC, and Ross point, RP, will be in good design space positions. By combining an over-bent front (first upwardly facing convex portion) and an under-bent rear (second upwardly facing concave portion), the distance C can be allowed to be made larger than in the prior art leaf spring.

Claim 1:
A leaf spring (<NUM>, <NUM>) for use in a vehicle suspension (<NUM>), comprising:
- a lower surface (<NUM>) configured to face downwardly towards the ground when used in a vehicle suspension,
- an upper surface (<NUM>) which is located opposite to the lower surface and which is configured to face upwardly when used in a vehicle suspension,
- a first end (<NUM>) configured to be mounted closer to a front end of a vehicle,
- a second end (<NUM>) configured to be mounted closer to a rear end of the vehicle, wherein the upper surface and the lower surface extend longitudinally from the first end to the second end,
- an axle attachment portion (<NUM>) located between the first end and the second end, the axle attachment portion being configured to be attached to an axle (<NUM>) such that the longitudinal extension of the upper and lower surface of the leaf spring is directed transversely to the axle,
- a first upwardly facing convex portion (<NUM>) formed between the first end and the axle attachment portion, and
- a second upwardly facing concave portion (<NUM>) formed between the axle attachment portion and the second end,
wherein the second upwardly facing concave portion (<NUM>) is formed by:
- a first subportion (<NUM>), which extends downwardly from the axle attachment portion (<NUM>) to a lowest point (<NUM>) of the second upwardly facing concave portion, and
- a second subportion (<NUM>) which extends upwardly from said lowest point (<NUM>) to the second end (<NUM>),
wherein the extension of the second subportion (<NUM>) forms a curved path from said lowest point (<NUM>) to the second end (<NUM>), characterized in that the smallest radius of said curvature is smaller than any radius of curvature of the first subportion (<NUM>).