Patent Description:
Leaf spring arrangements are generally used as a suspension arrangement for vehicles. These leaf spring arrangements vary with the size of the vehicle to be suspended.

Within the leaf spring arrangement, individual leaf springs or a combination of leaf springs are deflected dependent on the load of the vehicle. Accordingly, different constructions have been created in order to collect data with respect to the acting vehicle load to be used in the vehicle control.

<CIT> discloses an apparatus and system to detect load applied to a vehicle suspension. An example apparatus includes a vehicle spring positioned between a first spring seat and a second spring seat. A cap is coupled to the first spring seat to define a cavity. A force sensor is positioned in the cavity adjacent surface of the first spring seat. The force sensor is made of a thin film transducer which is arranged on top of a stack of several leaf springs. The stack of leaf springs including the thin film transducer is fastened by means of several U-bolts to the axle of the vehicle. Such thin-film transducers used as a force sensor are very sensitive. If it is directly mounted within the stack of leaf springs, it is susceptible to damage and contamination leading to failure of the collected data.

<CIT> describes a multi-leaf spring arrangement including a load cell for measuring the vehicle load. The sensor is positioned on a bar-like arrangement. This bar like arrangement is mounted by a first pair of U-bolts to the multi-leaf spring stack. A second pair of U-bolts is used to fasten the sensor construction to the vehicle axle. The bar-like construction bearing the sensor is stiff with respect to acting bending forces. Consequently, the bar-like construction bearing the sensor does not easily follow the deflections of the adjacent leaf spring. As a consequence, the measured deflection is smaller compared to the deflection of the leaf spring leading to a distorted result.

<CIT> also describes a vehicle load measuring device including a sensing element for detecting a strain to measure the load of the vehicle. To this end, different constructions are disclosed which are combined with a multi-leaf spring arrangement. According to one alternative, a leveling plate is proposed, which is integrated in the stack of multiple leaf springs mounted on top of each other. This leveling plate is fixed to the stack of leaf springs and to the vehicle axis by means of a pair of U-bolts. Furthermore, the leveling plate has a rectangular shape being similar to a part of the leaf spring. The leveling plate having a shape of a thick rectangular plate includes a recess formed at its center. A sensing element of the strain gauge type is fitted into the recess. In order to hold the sensing element in position, it is adhered or welded to the thick rectangular plate. The leveling plate including the sensing element is interposed between the leaf spring and the axle case for mounting the whole arrangement to the vehicle axis.

<CIT> also discloses a beam-type transducer assembly adapted for insulation between the stack of leaf springs and an axle of vehicle such as a truck or a semi-trailer for measuring the load on the axle. To this end, an elastically bendable beam construction is proposed. The beam construction is mounted in the multi-leaf spring arrangement by means of at least eight fastening bolts extending through respective fastening openings. On opposed sides of the bendable beam, a pair of fulcrum pins is positioned to support the deflection of the beam construction during use. Based on this construction, the bendable beam is bend around the pair of fulcrum pins being arranged in a smaller distance to each other as compared to the second pair of fulcrum pins. A plurality of conventional strain gauge is adhered to the surfaces of the beam. As a consequence, on opposed sides of the beam, at least two strain gauges are adhered to detect the deflection of the bendable beam in combination with the stack of multi-leaf springs. Based on the number of strain gauges used and the sophisticated construction of the bendable beam, the proposed load measuring device is expensive and requires extensive control efforts.

A further electrical measuring device is described in <CIT>. The device for measuring the weight of a load comprises a plurality of electrical resistance strain gauge elements connected in electrical bridge form and bonded to one major face or both major faces of a resilient metal plate having a thickness as herein described, so that the resulting assembly forms a transducer which is adapted to be electrically connected to an indicator for indicating the electrical output from the transducer. The transducer being constructed in such a way as to be capable of being mounted on a leaf spring assembly interposed between the axle of a road vehicle and that part of the vehicle which carries the load, or in such a way that said resilient plate can form part of said assembly. The metal plate having resiliency characteristics substantially the same as or better than said spring assembly.

With respect to the variety of load measuring devices in combination with a multi-leaf spring arrangement, it is an object of the present invention to provide an alternative arrangement which is robust and resistant to withstand contamination. Furthermore, it is an object to provide a simple construction requiring less control efforts for low detection.

The above object is solved by a transducer plate adapted to be mounted in a multi-leaf spring arrangement according to independent claim <NUM>. Furthermore, the object is solved by a multi-leaf spring arrangement of a motor vehicle comprising a plurality of leaf springs in combination with the transducer plate according to independent claim <NUM>. Modifications and further developments result from the following description, the drawings as well as the appending claims.

The inventive transducer plate is adapted to be mounted in a multi-leaf spring arrangement so that a deflection of an adjacent leaf spring can be measured. Further, said transducer plate comprises the following features: at least two oppositely arranged clamping ridges which are spaced from each other by a bending section, at least two stiffening webs oppositely arranged to each other and each bridging a distance between the opposed clamping ridges wherein the at least two stiffening webs are spaced from each other by the bending section, and mechanically decoupled from the bending section by an intermediate separation segment formed as a recess or an opening, and a measuring sector centrally arranged in the bending section between the clamping ridges and the stiffening webs, respectively, wherein a wire strain gauge can be disposed on the measuring sector for deflection evaluation.

Based on an increasing need to evaluate vehicle data, like the weight or the loading status of a vehicle, suspension components of the vehicle are combined with sensor arrangements. These sensor arrangements evaluate a deflection of the suspension component to draw conclusions on the loading condition and/or the weight of the vehicle.

A widely used suspension component consists of a stack of several leaf springs combined in a known multi-leaf spring arrangement which is coupled to a vehicle axle. The individual leaf springs as well as the stack of leaf springs are deflected or deformed dependent on the vehicle weight and/or vehicle loading.

The transducer plate is formed like a multifunctional bending bar following the deflection of the multi-leaf spring arrangement. To this end, the transducer plate has preferably substantially a square shape. A bending section is arranged in the center of the transducer plate. The bending section is preferably framed and thereby mechanically shielded by the two opposed clamping ridges and the two opposed stiffening webs. The clamping ridges ensure a reliable fastening to the multi-leaf spring arrangement so that the transducer plate may follow the leaf deflection. The pair of stiffening webs preferably bridge the distance between the clamping ridges to reinforce the frame surrounding the bending section. Thus, the combination of the clamping ridges and the stiffening webs form the preferred frame in which the bending section may follow the leaf spring deflection. To increase the adaptability of the bending section to the leaf spring deflection, and in particular of the centrally arranged measuring sector, an intermediate recess or opening mechanically decouples the stiffening webs from the bending section. By means of the separation segments, the bending section and also the measuring sector are less bonded to the stiffening webs.

According to a preferred embodiment of the invention, only one strain gauge is mounted on the measuring sector. The strain gauge follows the deflections of the measuring sector and the leaf spring, to generate a corresponding electrical signal.

According to the invention, the at least two clamping ridges have two fastening openings, respectively, for mounting the transducer plate in a multi-leaf spring arrangement.

In a known manner, a multi-leaf spring arrangement is mounted by preferred U-bolts to a vehicle axle or a similar constructive element. The U-bolts are preferably used to fasten the transducer plate to the leaf spring arrangement. Since the legs of the U-bolts extend through the fastening openings of the transducer plate, the transducer plate becomes an additional stack element of the multi-leaf spring arrangement. Furthermore, the preferred combination of the U-bolts and the fastening openings guarantee a suitable orientation of the transducer plate to the leaf springs. Further preferred, the stiffening webs of the transducer plate according to the invention have a stiffening thickness which is at least <NUM> % smaller than a clamping thickness of the clamping ridges each measured perpendicularly to the transducer plate.

According to a preferred embodiment of the invention, the clamping thickness of the clamping ridges is larger than a stiffening thickness of the stiffening webs. The clamping ridges have to assure the stable fastening of the transducer plate to the leaf spring arrangement. The stiffening webs are preferably configured to meet a compromise between the stabilization of the transducer plate and an increased flexibility of the transducer plate parallel to the leaf spring orientation. An increased flexibility is achieved by having a reduced stiffening thickness as compared to the clamping thickness. Thereby, the transducer plate may more easily follow the deflection of the leaf springs.

According to a further preferred embodiment of the transducer plate, the bending section comprises symmetrically arranged recesses or gaps positioned between the stiffening ridge and the measuring sector, respectively.

The bending section is to follow the leaf springs deflection to support an accurate strain measurement at the measuring sector. To facilitate a measurable bending of the bending section and the measuring sector, recesses or gaps between each stiffening web and the bending section are arranged. The gaps or openings or recesses release or reduce a mechanical coupling between each stiffening web and the adjacent bending section. Thereby, the stabilizing frame-like construction of the transducer plate is retained. Within the frame-like construction, a bending flexibility of the bending section and the measuring sector is preferably enhanced. As a consequence, the fixing of the bending section by the stiffening webs is reduced by the recesses or gaps.

As a further preferred construction of the above-described transducer plate, the recesses have a remaining plate thickness smaller than the stiffening thickness of the stiffening ribs.

According to preferred embodiments of the present invention, the depth of the recess is varied in order to optimize the bending of the measuring sector.

The preferred recesses or gaps of the bending sections have a triangular form tapering in the direction of the measuring sector.

Further preferred, the triangular shape of the recesses or gaps has a certain orientation in the bending section. Preferably, one side of the triangular shape is parallel to the stiffening web to realize a mechanical decoupling between the stiffening web and the bending section. Furthermore, the at least two recesses or the at least two gaps are symmetrically arranged with respect to the measuring sector. The symmetric arrangement preferably guarantees that the measuring sector follows the leaf spring deflection with no lateral distortion within the bending section.

According to an additionally preferred embodiment of the present invention, the transducer plate comprises a measuring face and a supporting face wherein the measuring face includes the surface of the measuring sector onto which the at least one strain gauge can be mounted, and the supporting face has a depression for receiving a damping element.

The transducer plate preferably has a measuring face and a supporting face. With respect to a multi-leaf spring assembly mounted adjacent to a vehicle axle, the transducer plate preferably faces with the supporting face to the stack of leaf springs or the adjacent leaf spring. According to a preferred construction of the transducer plate, the clamping ridges extend beyond the measuring sector in a direction perpendicular to the transducer plate face. Based on this construction principle, it is also preferred to mount the transducer plate on the multi-leaf spring assembly facing with the measuring face to the adjacent leaf spring. The projecting clamping ridges realize a clearance between the measuring sector and the leaf spring or a mounting plate. Thereby, the at least one strain gauge positioned on the measuring sector is protected against unintentional contact.

According to a further preferred embodiment of the present invention, the transducer plate is integrated into a multi-leaf spring assembly having an additional bumper. A bumper serves for protecting a vehicle from greater mechanical loads, either abrupt loads, like shocks, or permanent loads due to a loading or an overloading of the vehicle. To detect mechanical vehicle loads absorbed by a bumper, the transducer plate preferably has a receiving bumper recess at the supporting face. Dependent on the loading condition, the vehicle bumper engages the bumper recess and introduces a mechanical loading into the transducer plate. The mechanical loading of the bumper recess results in a deflection of the measuring sector and the strain gauge mounted thereon. The corresponding electrical signal generated by the strain gauge represents a strength of the mechanical loading of the vehicle by means of the bumper. It is further preferred that the strain gauge data represents a combination of the bending of the transducer plate generated by the leaf spring or springs as well as the bumper impact.

Preferred according to the invention, the measuring sector bears at least one strain gauge and is encapsulated as a safeguard against contamination and damage.

Based on the construction of the transducer plate, preferably only one strain gauge is mounted on the measuring sector. The electrical signal produced by the only one strain gauge is sufficient for drawing conclusions regarding the loading condition of the vehicle. The electrical signals are submitted to a control unit of the vehicle for processing and interpretation.

In order to protect the strain gauge against damage and contamination, the measuring sector bearing the strain gauge is preferably encapsulated by a sealing mass, like resin or similar materials.

According to a further preferred embodiment of the present invention, the depression of the supporting face of the transducer plate is arranged on a lateral plate section which extends laterally of the clamping ridge and remote from the bending section.

According to different preferred embodiments of the transducer plate, the bumper recess or the bumper depression on the supporting face is arranged below the bending section between the oppositely arranged clamping ridges.

According to further preferred embodiment, the transducer plate has a lateral extension extending laterally beyond one of the clamping ridges. The laterally arranged bumper recess or depression is positioned laterally from, but not below the measuring sector. Nevertheless, a bumper engaging the lateral bumper depression deflects the transducer plate as well as the measuring sector resulting in a corresponding electrical signal from the strain gauge.

As further preferred according to the present invention, the transducer plate is made as a one-part unit.

According to a further preferred embodiment of the present invention, the transducer plate is a one-piece component. Preferably, it is manufactured from a steel plate or the like by a combination of the following: cutting, rolling, milling and drilling.

The present invention also provides a multi-leaf spring arrangement of a motor vehicle comprising a plurality of leaf springs arranged in a stack, a vehicle axle and a number of U-bolts encompassing the vehicle axle wherein the number of U-bolt retains the plurality of leaf springs between the vehicle axle and the transducer plate according to any of the preceding claims.

In the following, the present invention will be described in detail based on the drawings showing preferred embodiments of the present invention. In the drawings, the same reference signs denote the same elements and/or components.

<FIG> shows an exemplary illustration of a multi-leaf spring arrangement <NUM> used to suspend a connected vehicle axle <NUM>. A number of leaf springs <NUM> are fixed by U-bolts <NUM> to the vehicle axle <NUM>. To this end, the U-bolts <NUM> encompass the vehicle axle <NUM> and their threaded ends <NUM> are fixed by means of nuts <NUM> within the fastening openings <NUM> of a transducer plate <NUM>.

According to another preferred embodiment, the threaded ends <NUM> of the U-bolts <NUM> are fixed in respective openings of a retaining plate (not shown). The preferred transducer plate <NUM> can be positioned between two leaf springs <NUM> or on top of the stack of leaf springs <NUM> below the vehicle axle <NUM>.

The preferred transducer plate <NUM> is arranged to follow the deflection of an adjoining or neighboring leaf spring <NUM>. If the transducer plate <NUM> is positioned within the stack of these springs <NUM>, the legs of the U-bolts <NUM> extend through the fastening openings <NUM> and the threaded ends <NUM> are fixed remote from the transducer plate <NUM>.

According to a further preferred embodiment of the invention, the transducer plate <NUM> is made as a one-piece metal part by known manufacturing techniques.

A preferred embodiment of the transducer plate <NUM> in combination with an adjacent leaf spring <NUM> is depicted in <FIG>. The fastening openings <NUM> forming part of a pair of clamping ridges <NUM> are not occupied by the legs of the U-bolts <NUM> for illustrational reasons. The clamping ridges <NUM> are oppositely arranged to each other to guarantee a reliable fastening of the transducer plate <NUM> adjacent to a leaf spring <NUM>.

A distance between the opposed clamping ridges <NUM> is preferably bridged by a pair of stiffening webs <NUM>. According to a preferred embodiment of the invention, two stiffening webs <NUM> are oppositely arranged to each other bridging the clamping ridges <NUM> and border the transducer plate <NUM> to the outside. The pair of clamping ridges <NUM> and the pair of stiffening webs <NUM> commonly surround a bending section <NUM> of the transducer plate <NUM>.

The clamping ridges <NUM> realize a stable coupling and a defined position of the transducer plate <NUM> to/on the leaf spring <NUM> or the stack of leaf springs <NUM>. Their construction preferably prevents or reduces a bending of the transducer plate <NUM> resulting from a change of a curvature along the longitudinal axis of the clamping ridges <NUM>.

The stiffening webs <NUM> preferably assure the plate-like configuration of the transducer plate <NUM>, but also enable the transducer plate <NUM> to follow or adopt the deflection of the at least one adjacent leaf spring <NUM>. To this end, the stiffening webs <NUM> preferably have a stiffening thickness ts less than a clamping thickness tc of the clamping ridges <NUM>. The stiffening thickness ts and the clamping thickness tc are measured perpendicular to the transducer plate <NUM>. Different preferred configurations of the stiffening thickness ts and the clamping thickness tc are shown in <FIG>. Accordingly, the stiffening thickness ts can be smaller or equal to the clamping thickness tc. Preferably, the stiffening thickness ts is at least <NUM> % smaller than the clamping thickness tc.

The bending section <NUM> of the transducer plate <NUM> is preferably surrounded by the clamping ridges <NUM> and the stiffening webs <NUM>. To enhance the flexibility of the bending section <NUM> to follow the leaf spring deflection, an intermediate separation segment <NUM> is arranged between the stiffening web <NUM> and the bending section <NUM>, respectively. Preferably, a pair of intermediate segments <NUM> is symmetrically arranged with respect to a measuring sector <NUM>. The measuring sector <NUM> is centrally positioned within the bending section <NUM>.

The intermediate separation segment <NUM> is formed as a recess or an opening. The recess is preferably positioned at the measuring face fm or at the support face fs of the transducer plate <NUM>. Based on the configuration of the intermediate separation segment <NUM>, the bending section <NUM> and particularly the measuring sector <NUM> are mechanically decoupled from the stiffening webs <NUM>. As a consequence, the measuring sector <NUM> more easily follows the deflection of the leaf spring <NUM> since the mechanical stiffening influence of the stiffening webs <NUM> is reduced.

According to a preferred embodiment shown in <FIG>, the intermediate separation segment <NUM> is formed as an opening. Thereby, a connection between the stiffening web <NUM> and the adjacent bending section <NUM> is separated. According to the preferred embodiment of <FIG>, the intermediate separation segment <NUM> is realized like a recess.

The recesses or gaps realizing the intermediate separation segment <NUM> are preferably symmetrically arranged with respect to the measuring sector <NUM>. The symmetrical positioning of the intermediate separation segment <NUM> prevents distortions of the measuring sector <NUM> parallel to the longitudinal axis of the clamping ridges <NUM>. As a consequence, the imaginary halves of the transducer plate <NUM> formed by the line B-B follow the deflection of the spring <NUM> having the same deformation.

According to the preferred embodiment of the transducer plate <NUM> shown in <FIG>, the intermediate separation segments <NUM> have a triangular shape. The triangular shape is preferably oriented in such a way that one side extends parallel to the stiffening webs <NUM>. The remaining two sides extend in the direction of the measuring sector <NUM>. Preferably, the triangular shape of the intermediate separation segment <NUM> tapers in the direction of the measuring sector <NUM>.

It is further preferred that the shape of the intermediate separation segment <NUM> is triangular but does not have straight sides as shown in <FIG>.

In the embodiment of <FIG>, the intermediate separation segments <NUM> are formed like separation channels or openings extending parallel to the stiffening webs <NUM>. Preferably, the stiffening webs <NUM> and the bending section <NUM> have the same thickness being smaller than the clamping thickness tc.

In the preferred embodiment of <FIG>, the symmetrically arranged intermediate separation segments <NUM> form together a double T-shape, which can also be considered as a rotated H. Furthermore, the intermediate separation segments <NUM> each having a T-shape are formed as a recess, respectively. The T-shape is divided in a first cuboidal recess standing parallel to the stiffening web <NUM> and a second cuboidal recess extending perpendicularly to the stiffening web <NUM> so that both perpendicular recesses meet at the measurement sector <NUM>. The measurement sector <NUM> has a small thickness compared to the remaining transducer plate <NUM>.

According to a preferred embodiment of the present invention, only one strain gauge <NUM> is mounted on the surface section of measurement sector <NUM> forming part of the measuring face fm of the transducer plate <NUM>. The strain gauge <NUM> is preferably formed like a longitudinal strip or band which is oriented perpendicularly to the clamping ridges <NUM> or parallel to the stiffening webs <NUM>.

Further preferred, the strain gauge <NUM> is mounted centrally between the clamping ridges <NUM> and the stiffening webs <NUM>. Referring to <FIG>, the strain gauge <NUM> is arranged at the bottom of a recess formed by the intermediate separation segments <NUM>.

Independent of the configuration of the transducer plate <NUM>, the strain gauge <NUM> is preferably covered by a protecting material, like resin, plastic or the like. The protecting cover acts like a safeguard against contamination and/or damage from the surrounding. Furthermore, the protecting cover has preferably a sufficient elasticity not affecting the deformation of the transducer plate <NUM> following the deflection of the leaf spring <NUM>.

Referring to <FIG>, different sectional views along the line A-A of <FIG> are shown. The cross-sectional illustration shows a cut through the centrally arranged measurement sector <NUM>, the stiffening webs <NUM> and the intermediate separation segments <NUM>. The thickness of the measurement sector <NUM>, the clamping thickness tc and the stiffening thickness ts were varied and combined in different configurations of the transducer plate <NUM>. If the transducer plate <NUM> is bent during use in or on a multi-leaf spring arrangement <NUM>, a neutral state N exists within the bent transducer plate <NUM>. The bending moment M is indicated as a double arrow. It acts on the transducer plate <NUM> around axis y. The neutral state N indicated by the dashed line N in <FIG> emphasizes that along this line or within this plane, the material of the transducer plate <NUM> is not subject to mechanical tensions, neither compressive stresses nor tensile stresses. As a consequence, no strain occurs at the neutral state N deforming the material of the transducer plate <NUM> even if the transducer plate follows the deflection of the leaf spring <NUM>. In this context, it has to be guaranteed that the geometric configuration of the transducer plate <NUM> does not shift the neutral state N to the surface of the measurement sector <NUM> where the strain gauge <NUM> is mounted.

If the strain gauge <NUM> lies within the neutral state N, then no deflections of the leaf spring <NUM> could be measured. Such a disadvantageous situation results from the geometric configuration as shown in <FIG>.

According to a further preferred embodiment of the present invention, the multi-leaf spring arrangement <NUM> comprises a bumper <NUM>. The bumper <NUM> absorbs mechanical loads exposed to a vehicle (not shown). If a vehicle is loaded up to a certain level, the bumper <NUM> approaches and contacts the preferred transducer plate <NUM>. During contact, the transducer plate <NUM> supports the bumper <NUM>. To this end, the bumper tip <NUM> engages a depression <NUM> provided at the transducer plate <NUM>.

According to a preferred embodiment of the present invention, the depression <NUM> for receiving the bumper tip <NUM> is positioned at the supporting face fs of the transducer plate <NUM>. As shown in <FIG>, the depression <NUM> is positioned below the measuring sector <NUM> bearing the strain gauge <NUM>.

According to a further preferred embodiment of the transducer plate <NUM>, the depression <NUM> is arranged in a lateral extension <NUM> of the transducer plate <NUM> extending laterally of only one clamping ridge <NUM>, but not between two clamping ridges <NUM> (see <FIG>).

Referring to the embodiment having the lateral extension <NUM> of the transducer plate <NUM> with depression <NUM>, the depression <NUM> is arranged at the support face fs. It is further preferred to place the depression <NUM> at the measuring face fm in order to combine the transducer plate <NUM> in another orientation with the multi-leaf spring arrangement <NUM>.

The depression <NUM> receiving the bumper tip <NUM> is bent around the y-axis as follows from <FIG>. To facilitate a bending of the depression <NUM>, an elongated recess or notch <NUM> extends preferably parallel to the clamping ridges <NUM> through the center of the depression <NUM>.

Claim 1:
A transducer plate (<NUM>) adapted to be mounted in a multi-leaf spring arrangement (<NUM>) so that a deflection of an adjacent leaf spring (<NUM>) can be measured, said transducer plate (<NUM>) comprises the following features:
a) at least two oppositely arranged clamping ridges (<NUM>) which are spaced from each other by a bending section (<NUM>),
b) at least two stiffening webs (<NUM>) oppositely arranged to each other and each bridging a distance between the opposed clamping ridges (<NUM>) wherein the at least two stiffening webs (<NUM>) are
b1) spaced from each other by the bending section (<NUM>), and
b2) mechanically decoupled from the bending section (<NUM>) by an intermediate separation segment (<NUM>) formed as a recess or an opening, and the transducer plate (<NUM>) comprises further
c) a measuring sector (<NUM>) centrally arranged in the bending section (<NUM>) between the clamping ridges (<NUM>) and the stiffening webs (<NUM>), respectively, wherein a wire strain gauge can be disposed on the measuring sector (<NUM>) for deflection evaluation, characterized in that
d) the at least two clamping ridges (<NUM>) have two fastening openings (<NUM>), respectively, for mounting the transducer plate (<NUM>) in a multi-leaf arrangement (<NUM>).